Guidance on the application of the CLP criteria : guidance to Regulation (EC) No 1272/2008 on classification, labelling and packaging (CLP) of substances and mixtures.
Date: 2024-02-08
Institutions: European Chemicals Agency
Subjects: chemical industry, chemical product, classification, dangerous substance, environmental protection, labelling, packaging, public health, user guide

Guidance on the Application of the CLP Criteria 

Version 6.0 – Jan 2024 

1 

G U I D A N C E  

Guidance on the Application of the CLP 
Criteria 

Guidance to Regulation (EC) No 1272/2008 on classification, labelling 
and packaging (CLP) of substances and mixtures 

Version 6.0 
Jan 2024 

 
 
 
 
 
 
 
 
2 

LEGAL NOTICE 

Guidance on the Application of the CLP Criteria 

Version 6.0 – Jan 2024 

This document aims to assist users in complying with their obligations under the CLP Regulation. 
However,  users  are  reminded  that  the  text  of  the  CLP  Regulation  is  the  only  authentic  legal 
reference and that the information in this document does not constitute legal advice. Usage of 
the  information  remains  under  the  sole  responsibility  of  the  user.  The  European  Chemicals 
Agency does not accept any liability with regard to the use that may be made of the information 
contained in this document. 

Guidance on the Application of CLP Criteria 

Reference: 
Cat.Number:  
ISBN:  
DOI:   
Publ.date:  
Language:    

ECHA-24-G-01-EN 
ED-02-24-008-EN-N 
978-92-9468-343-4 
10.2823/74224 
Jan 2024 
EN 

© European Chemicals Agency, 2024 

If you have questions or comments in relation to this  document please send them (quote the 
reference and issue date) using the information request form. The information request form can 
be accessed via the Contact ECHA page at: 

http://echa.europa.eu/contact 

European Chemicals Agency 

P.O Box 400, FI-00121 Helsinki, Finland 

 
 
 
 
 
 
 
 
 
Guidance on the Application of the CLP Criteria 

Version 6.0 – Jan 2024 

3 

Date 

August 2009 

April 2011 

April 2012 

DOCUMENT HISTORY 

Version 

Comment 

n.a. 

n.a. 

First edition 

Please note that change between the version published in 
August 2009 and that of April 2011 are not recorded in this 
document history.  

Version 2.0  Revision of the Guidance addressing content in relation to the 
environmental criteria chapters and Annexes following the 2nd 
Adaptation to Technical Progress to the CLP Regulation 
(Commission Regulation (EU) No 286/2011). The ECHA 
Secretariat revised the Guidance Part 4 – Environmental 
hazards and Annexes of the guidance document referring to 
the revised criteria for the long-term aquatic hazard for 
substances and mixtures and added new Part 5 – Additional 
hazards referring to the hazard class ‘hazardous to the ozone 
layer’. As well, a number of examples have been included in 
the respective Parts and Annexes to illustrate the revisions 
performed. Further to this, a range of editorial corrections were 
proposed for Part 1 – General principles for classification and 
labelling. 

The update includes the following: 

•  Revision of Part 1, by eliminating and amending out of 
date information and restructuring the text in order to 
reflect the Guidance update.  

•  All green boxes in Part 4 that are impacted by the 2nd 
ATP were updated. As the CLP legal text uses commas 
instead of dots to define numbers smaller than 1, the 
green boxes now show commas as well. 

•  Revision of Part 4, by providing guidance on the 

application of the new long-term aquatic hazard criteria 
for substances and mixtures.  

•  Section 4.1.3 Classification of substances hazardous to 

the aquatic environment and section 4.1.4 Classification 
of mixtures hazardous to the aquatic environment were 
substantially revised, for example by addition of new 
references, as well as the new/revised examples to 
illustrate relevant topics in the Part 4. 

•  New Part 5 – Additional hazards was added (please note 

that Part 5: Labelling was deleted from the Guidance in 
previous non-recorded versions and covered via a new 
Guidance on Labelling and Packaging in accordance with 
Regulation (EC) No 1272/2008 published in April 2011). 

•  Most of the I.3 sub-sections in Annex I – Aquatic toxicity 

were revised. 

 
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Guidance on the Application of the CLP Criteria 

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• 

In Annex II – Rapid degradation the terminology was 
modified. 

•  Most of the Annex IV – Metals and Inorganic Metal 

Compounds was substantially modified and revised, as 
well as in sub-section IV.7 new examples were added. 

Version 3.0  Revision of Guidance Part 3 Health Hazards, relating to specific 

concentration limits (SCLs) for 4 hazard classes and the 
inclusion of a new Annex.  

November 
2012 

The update includes the following: 

•  Revision of Part 3, by providing guidance on the setting 
of lower and higher SCLs for 4 health hazard classes in 
section 3.2.2.5 Skin Corrosion/Irritation; section 3.3.2.5 
Serious Eye Damage/Eye Irritation; section 3.7.2.5 
Reproductive Toxicity and section 3.8.2.6 STOT-SE, in 
accordance with CLP Article 10(7); 

• 

Inclusion of a new Annex (Annex VI) providing guidance 
on setting SCLs for the reproductive toxicity hazard 
class based on potency considerations. 

Version 4.0 

(i) Revision of the CLP Guidance addressing content in relation 
to the Part 2: Physical hazards, Part 3: Health hazards and 
Annex VI following the 2nd and the 4th Adaptation to Technical 
Progress to the CLP Regulation (Commission Regulation (EU) 
No 286/2011 of 10 March 2011 and Commission Regulation 
(EU) No 487/2013 of 8 May 2013). 

November 
2013 

The revision includes: 

•  Numbering of chapters within CLP Guidance, Parts 2 & 3 

were synchronised with corresponding chapter 
numbering of CLP, Annex I. 

•  Changes in the legal text due the 2nd and 4th ATPs. 

•  Changes in the legal text due to the 4th ATP were 

highlighted in orange within all relevant green boxes. All 
changes are preceded by a note highlighting the 
changes. (To note: a corrigendum will change the colour 
of relative legal text boxes from orange to green when 
the 4th ATP applies). 

In addition, the revisions to Part 2: Physical hazards include 
the following: 

•  Chapters ‘Pyrophoric liquids and solids’ and ‘Oxidising 
liquids and solids’ were divided into four chapters: 
‘Pyrophoric liquids’, ‘Pyrophoric solids’, ‘Oxidising liquids’ 
and ‘Oxidising solids’ respectively. 

•  Based on the 4th ATP the CLP Guidance Chapter 2.2 

Flammable gases was extended to take into account the 
scope of CLP, Annex I, section 2.2 to include chemically 
unstable gases.  

•  Further, the 4th ATP amended the criteria in CLP Annex 
I, Section 2.3 Flammable aerosols and renamed it into 

 
 
Guidance on the Application of the CLP Criteria 

Version 6.0 – Jan 2024 

5 

2.3 Aerosols. Hence, the CLP Guidance was amended 
accordingly.  

•  All chapters were rechecked and redundant and/or 

outdated information were deleted, reorganised and/or 
revised. For example, ‘Introduction’ chapters were 
significantly shortened, however several “examples” 
sections (i.e. ‘Example for classification…’) were further 
elaborated. 

•  Where missing, a new sub-chapter ‘Relation to other 

physical hazards’ was added. 

•  Sub-chapter 2.0.4 ‘Physical state’ was extended with 
additional information about substance/mixture form 
and some examples.  

• 

• 

In sub-chapter 2.1.5.2 ‘Additional labelling provisions’ 
within chapter 2.1 ‘Explosives’ further guidance about 
hazard communication was provided. 

In sub-chapter 2.5.6.1 a new recommendation for shot 
hazard codes to identify the classification of gasses 
under pressure was added.  

•  Footnotes with references to endorsed or on-going 
revisions of the GHS which have not yet been 
implemented into the CLP via a respective ATP were 
included in relevant sub-chapters of this guidance for 
information only. 

In addition, the major revisions to Part 3: Health hazards 
include the following: 

•  All sections: revisions to legal text for the 4th ATP, 

including revisions to Precautionary Statements in the 
Tables with labelling information. 

•  Section 3.1: the introduction of new guidance for the 4th 

ATP in section 3.1.4.1. 

•  Sections 3.2.2.5 and 3.3.2.5: clarification to the 

recently published text (Version 3.0) for the setting of 
SCLs. 

•  Section 3.4 (sensitisation) has been significantly re-

organised to present all the information on respiratory 
sensitisation together, followed by the information on 
skin sensitisation. This is in line with how the sections 
are presented in the CLP Regulation and in GHS 
documents. 

•  Section 3.4: integration of subcategories for respiratory 
and skin sensitisation based on potency of a substance; 
clarification of semi-quantitative terms like ‘low to 
moderate sensitisation rate’ and ‘high or low exposure’; 
elaboration of evaluation of human data for skin 
sensitisation and the addition of new examples. 

•  Section 3.7: the introduction of new guidance for the 4th 

ATP in section3.7.4.1 and section 3.7.5.1. 

 
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Guidance on the Application of the CLP Criteria 

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(ii) Corrigendum of Part 1: General principles for classification 
and labelling and Part 4: Environmental hazards and its related 
Annexes I-V.    

The corrigendum includes the following: 

•  The list of abbreviations was updated. 

•  Update or deletion of outdated references to Guidance 
on information requirements and chemical safety 
assessment, Endpoint specific guidance (Chapter R.7a) 
within Annexes I-V. 

•  A footnote informing the reader that with effect from 1 
September 2013, Directive 98/8/EC had been repealed 
by Biocidal Products Regulation (EU) No 528/2012 was 
added. 

• 

In Part 1, Part 4 and Annexes modal verbs ‘shall’ were 
replaced with ‘must’ where appropriate.  

•  A footnote related to respiratory sensitisation and skin 

sensitisation in Table 1.1 was removed. 

•  A correction to Example D, sub-chapter 4.1.4.7.5 was 
applied, namely a reference to CLP, Annex I, point (b) 
(ii) of Table 4.1.0 was introduced. In addition, the result 
of a summation method calculation was corrected.   

Version 4.1  Corrigendum to take account of the end of the transition period 
of the 4th ATP (as foreseen in version 4.0 above): 

June 2015 

•  change the colour of relative legal text boxes from 

• 

• 

orange to green;  
in Part 2, to delete section 2.2.1 Flammable gases and 
section 2.3.1 Flammable Aerosols (outdated text) and 
renumber sections 2.2.2 Flammable gases (including 
chemically unstable gases) and 2.3.2 Aerosols 
accordingly; 
in Part 3, to delete the “outdated text” in sections 
3.7.4.1 and 3.7.5.1 in Reproductive Toxicity. 

In addition, minor editorial errors were corrected and minor 
reformatting was made. 

Version 5.0   Partial revision of the Guidance to update the content mainly 
following the 8th Adaptation to Technical Progress to the CLP 
Regulation (Commission Regulation (EU) No 286/2011). 
Revision of few specific additional topics. 

July 2017 

The update includes the following: 

(i) Throughout the document: 

•  Revision of legal references and legal text quotations. 

•  Renumbering of some sections. 

•  Deletion of sections regarding the reclassification of 
substances and mixtures previously classified in 
accordance with the DSD or DPD. 

 
 
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(ii) Revision of Part 1: 

•  Deletion of reference to pre-CLP legislation and 

transitional period. 

•  Addition of reference to read-across and grouping in the 

context of bioavailability. 

•  Removal of quotation of Article 31(3) of REACH. 

•  Clarification about applicability of additivity principle. 

•  Clarification about the application of mixture rules to 

substances with CMR constituents. 

•  Reduction of section 1.2.3.1 on physical hazards to 

avoid redundancy with section 2.0.4. 

•  Revision of section 1.7 and removal of unnecessary 

information. Table on additional information using 
transport classification moved to a new Annex VII. 

(iii) Revision of the following sections of Part 2: 

•  2.1 (Explosives): replacement of new figure 2.1.3; 

update of label elements; addition new note 2 to table 
2.1.2 on requirement for SDSs. 

•  2.3 (Aerosols): update of text on classification criteria; 

update of decision logic 2.3.1-a; update of section 2.3.6 
on the relation to transport classification. 

•  2.14 (Oxidising solids): addition of criteria using test 

0.3; update of labelling elements. 

(iv) Minor changes to the following sections in Part 2: 

•  2.8 (Self-reactive): update of label elements. 

•  2.12 (Emitting flammable gases): update of label 

elements. 

•  2.15 (Organic peroxides): update of decision 

logic.2.15.1; update of label elements. 

(v) Revision of following sections in Part 3: 

•  3.1 (Acute toxicity): Reference to new in-vitro test. 

Indication that harmonised ATE values will be included 
in Annex VI to CLP. Deletion of reference to the concept 
of relating the conditions of an acute inhalation test to 
real life. Indication that not-classified components may 
influence ATE and, in general, clarification about 
components to be considered for mixture classification 
according to the case. Indication to avoid under 
classification for oral toxicity. Additon of a new example 
(13) on the application of additivity methods for 
mixtures with components in different physical forms. 

•  3.2 (Skin corrosion): Subsection on non-testing 

methods updated and clarified the need to assess the 
relevance. Update of classification criteria. Inclusion of 
new figure illustrating the tiered evaluation approach. 
Inclusion of a new figure illustrating the relative weight 

 
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Guidance on the Application of the CLP Criteria 

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of different available pieces of information to be 
considered when weight of Evidence (WoE) is applied. 
Replacement of the decision logic chart with separate 
decision logics for substances and mixtures, based on 
the chart from GHS. Clarification about classification of 
mixture as Category 1 without subcategory. 

•  3.3 (Serious eye damage/irritation): Clarification of the 

need for further data when considerations about 
alkaline/acid reserve suggest no risk added. 
Interpretation of non-testing methods results enhanced. 
Mentioned the use of LVET data. Inclusion of new figure 
illustrating the tiered evaluation approach. Inclusion of 
reference to new figure on hierarchy of information 
added in section 3.2. Replacement of the decision logic 
chart with separate decision logics for substances and 
mixtures, based on the chart from GHS.  

•  3.4 (Respiratory or skin sensitisation): Deletion of the 
relationship between skin and respiratory sensitisation 
potential. Identification of non-human data brought in 
line with REACH guidance. Introduction of available non-
testing systems. Clarification of the test sample to be 
used in human diagnostic patch testing. 

•  3.5 (Germ cell mutagenicity): Reference to OECD TG 

488 added. New section on classification of substances 
containing CMR constituents, additives or impurities 
included.  

(iv) Minor changes to the following sections in Part 3: 

•  3.6 (Carcinogenicity): Removal of reference to 

supporting evidence for classification under DSD. 
Update of label elements. New section included on 
classification of substances containing CMR constituents, 
additives or impurities. 

•  3.7 (Reproductive toxicity): New section included on 

classification of substances containing CMR constituents, 
additives or impurities. 

•  3.8 (STOT-SE): Editorial corrections to the examples. 

(vi) Minor changes to Part 4 to update the terminology when 
referring to short-term (acute) and long-term (chronic) studies. 

Version 6.0  Part 4 has been updated to provide clarifications, correct errors, 
delete  information  considered  irrelevant,  and  add  text  on  new 
OECD TGs. The update includes the following: 

Jan 2024 

•  Section 4.1.3.3.1: The paragraph referring to the absence 
of  chronic  data  has  been  amended  to  reflect  general  data 
availability and established practice; 

•  Section 4.1.3.3.1; Additional text was added to clarify cases 
where  data  on  a  degradation  product  may  need  to  be 
considered; 

•  Section  4.1.3.3.1:  A  reference  to  a  topic  the  guidance 

 
 
 
Guidance on the Application of the CLP Criteria 

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annexes do not directly comment on was deleted; 

•  At  the  end  of  section  4.1.3.3.2:  Some  text  was  added  to 
further  define  instances  where  Category  Chronic  4  may 
apply; 

•  Section 4.1.3.3.3: Text was added on the fact that M-factors 

are considered part of the classification; 

•  Section 4.1.4.5: Clarification on deriving classification when 
using toxicity values calculated from the additivity formula 
was added; 

•  Section 4.1.4.7.5: Correction to Example D and explanation 

added; 

•  Section  4.1.7  was  deleted  as  any 
reclassification from DSD is out of date; 

reference 

to 

•  Annex I.2: General statements on most commonly occurring 
issues during aquatic toxicity testing have been added; 

•  Annex  I.2.1.1:  General  considerations  on  OECD  TG  236 

were added; 

•  Annex  I.2.1.2:  General  considerations  regarding  various 

relevant OECD TGs added; 

•  Annex  I.2.2.1:  A  more  recent  change  in  the  respective 

OECD TG (202) is reflected; 

•  Annex  I.2.2.1:  Clarifications  on  invertebrate  data  beyond 

Daphnia Magna were added; 

•  Annex  I.2.2.2:  A  more  recent  change  in  the  respective 

OECD TG protocol (202 part II) is reflected; 

•  Annex  I.2.2.2:  Clarifications  on  invertebrate  data  beyond 

Daphnia Magna were added; 

•  Annex  I.2.3.2:  Clarifications  on  aquatic  macrophyte  data 

were added;  

•  Annex I.2.3.2: CLP preference on algae as the preferred test 

species deleted; 

•  Annex I.3.2: Clarification on use of surrogate approach for 

chronic classification added; 

•  Annex  I.4:  Clarification  on  use  of  data  for  difficult  to  test 

substances added; 

•  Annex II.2: Two first sentences of the paragraph have been 
deleted  as  they  were  vague  and  did  not  offer  any  added 
value; 

•  Annex 

II.2.3.6:  An  additional  statement 

that  soil 
degradation  data  can  be  used  under  certain  conditions  in 
the absence of aquatic degradation data has been added;  

•  Annex  II.2.3.7:  Clarification  on  the  use  of  anaerobic 

degradation data has been added; 

•  Annex  II.3.1:  Clarification  on  the  general  guidance  for 
complex substances has been added (also change in I.4.5); 

•  Annex II.3.5: Clarification text on presence of both positive 
and negative ready biodegradability tests has been added; 

 
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Guidance on the Application of the CLP Criteria 

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•  Annex III.2.1: Footnote 29 has been deleted as it is out of 

date; 

•  Annex 

III.2.1.2:  Clarification 

text  on 

radio-labelled 

substances has been added; 

•  Annex III.2.2.2, Table III.1 has been deleted; 

•  Annex  III.2.2.2,  Guidance  on  (Q)SAR  BCFs  and  their  use 

has been added; 

•  Annex III.5: Text added to emphasise that a conclusion on 
bioaccumulation is required under CLP and that a conclusion 
as “inconclusive” is still possible, albeit not preferred; 

•  Annex III.5: More explicit wording added on the conclusion 

on bioaccumulation, based on the available data; 

•  Annex  IV.3:  Rapid  removal  footnote  amended  to  reflect 

CARACAL decision on rapid removal;  

•  Annex  IV.5.4:  Correction  of  error  regarding  loading  rates 

used to determine chronic M-factors; 

•  Annex IV.5.6: Correction of how alloys are considered under 
CLP  to  remove  reference  to  ‘special  preparations’  and 
accurately reflect CLP Art. 2(27); 

•  Table  IV.1:  Correction  of  criteria  error  on  determining  M-

factors for readily soluble metal compounds; 

Besides  these  changes,  typos,  spelling  errors  and  other 
formatting issues, such as homogenisation of referencing (both 
within  the  document  and  to  external  sources),  have  been 
addressed.  Note,  such  changes  are  not  substantial  and  do  not 
alter the content. 

 
 
 
 
 
 
Guidance on the Application of the CLP Criteria 

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PREFACE  

This  document  is  the  Guidance  on  the  Application  of  the  CLP  Criteria.  It  is  a  comprehensive 
technical  and  scientific  document  on  the  application  of  Regulation  (EC)  No  1272/2008  on  the 
classification,  labelling  and  packaging  of  substances  and  mixtures  (CLP),  which  replaced  the 
Dangerous  Substances  Directive  67/548/EEC  (DSD)  and  the  Dangerous  Preparations  Directive 
1999/45/EC  (DPD)  in  a  staggered  way.  CLP  is  based  on  the  Globally  Harmonised  System  of 
Classification and Labelling of Chemicals (GHS) and is implementing the provisions of the GHS 
within the EU. The objective of this document is to provide detailed guidance on the application 
of the CLP criteria for physical, health and environmental hazards. The guidance is developed to 
primarily assist manufacturers, importers and downstream users in applying the classification and 
labelling criteria, and it also includes practical examples. It is also assumed to be the guidance 
on classification and labelling for Competent Authorities in the Member States (MS CA), for the 
Commission services and the European Chemicals Agency (ECHA). 

In certain chapters, like for example the ones on carcinogenicity, mutagenicity and reproductive 
toxicity, the guidance includes to a larger  extent scientific advice on  how to interpret different 
data used for classification. This additional guidance is based on experience gained within the EU 
during the application of the classification criteria under Directive 67/548/EEC, and is written for 
the experts within the respective fields.  

This  guidance  document  was  developed  as  a  REACH  Implementation  Project  (RIP  3.6)  at  the 
Institute  for  Health  and  Consumer  Products  (IHCP)  of  the  Joint  Research  Centre  in  Ispra,  with 
support from working groups consisting of experts on classification and labelling from EU Member 
States and Industry. The project started in September 2007 and the different working groups had 
meetings and continuous discussions to discuss and develop the guidance text until spring 2009. 
Finally all texts were consolidated and edited at the IHCP. RIP 3.6 was financially supported with 
an administrative arrangement made with Directorate-General Enterprise and Industry (currently 
DG Growth). The guidance was handed over to ECHA in summer 2009. 

After  that  the  guidance  has  been  revised  twice  –  version  2.0  in  April  2012  on  the  long-term 
aquatic hazard and version 3.0 in November 2012 in relation to the guidance chapters on setting 
of specific concentration limits (SCLs) for health hazards.   

During 2012/2013, further drafting work was done in close collaboration with European experts, 
to take account of a range of guidance aspects (for example further guidance on the criteria for 
respiratory  and  skin  sensitisation,  and  other  health  related  points,  as  well  as  guidance  on  the 
criteria for chemically unstable gases and aerosols and other physical hazards related changes) 
following the 2nd and/or the 4th Adaptation to Technical Progress (ATP) to the CLP (Commission 
Regulation (EU) No 286/2011 and No 487/20131). This work resulted in publication of version 4.0 
in  November  2013  and  the  subsequent  corrigendum  version  4.1  June  2015  to  update  the  text 
following the transitional period for the 4th ATP. 

In  relation  to  labelling  and  packaging,  a  new  stand-alone  guidance  document  was  prepared 
(‘Guidance  on  Labelling  and  Packaging  in  accordance  with  Regulation  (EC)  No  1272/2008’), 
warranting the deletion of Part 5 and of Annex V of the Guidance on the Application of the CLP 
Criteria.  The  Guidance  on  Labelling  and  Packaging  in  accordance  with  Regulation  (EC)  No 
1272/2008 
under 
http://guidance.echa.europa.eu/guidance_en.htm. 

published 

guidance 

website, 

ECHA’s 

on 

is 

1 Commission Regulation (EU) No 286/2011 of 10 March 2011 and Commission Regulation (EU) No 
487/2013 of 8 May 2013 amending, for the purposes of its adaptation to technical and scientific progress, 
Regulation (EC) No 1272/2008 of the European Parliament and of the Council on classification, labelling 
and packaging of substances and mixtures. 

 
 
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Guidance on the Application of the CLP Criteria 

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Both guidance documents were further updated in 2016 to address the changes due to the 8th 
ATP  (e.g.  new  alternative  methods  to  classify  oxidising  solids,  changes  in  the  classification  for 
skin  corrosion/irritation,  serious  eye  damage/irritation  and  aerosols,  as  well  as  changes  in 
precautionary statements).  

Therefore,  the  current  version  of  the  Guidance  reflects  the  changes  made  by  the  8th  ATP 
(Regulation 2016/918) in Annex I to CLP. These changes apply from 1 February 2018.  

However: 

•  The 8th ATP may already be applied on a voluntary basis before that date. 

•  Substances  and  mixtures  placed  on  the  market  before  1  February  2018  shall  not  be 
required to be relabelled and repackaged in accordance with the 8th ATP during a period 
of two years, i.e. before 1 February 2020. 

Between 2019 and 2023, the part 4 of the guidance (hazards to the aquatic environment) and 
annexes I – IV were updated to provide guidance on new OECD TGs, provide clarity on a number 
of  areas,  and  correct  a  number  of  errors/typos.  More  substantial  matters  were  updated  by 
consulting  a  PEG  established  for  the  purpose,  RAC,  and  Member  States/COM  via  CARACAL. 
Matters  editorial  in  nature  (spelling  and  typos)  were  update  following  a  fast  track  procedure 
involving only CARACAL. This update represents the 6th update of the CLP guidance (v 6.0). 

 
 
 
Guidance on the Application of the CLP Criteria 

Version 6.0 – Jan 2024 

13 

Table of Contents 

1.  PART  1:  GENERAL  PRINCIPLES  FOR  CLASSIFICATION  AND 

LABELLING .................................................................................... 46 

1.1. 

INTRODUCTION ................................................................................... 46 
1.1.1.  The objective of the guidance document ............................................................ 46 
1.1.2.  Background ................................................................................................... 47 
1.1.3.  Hazard classification ....................................................................................... 47 
1.1.4.  Who is responsible for the hazard classification .................................................. 48 
1.1.5.  Which substances and mixtures should be classified ........................................... 48 
1.1.6.  What information is needed for classification ...................................................... 50 
Information for the classification of substances .......................................... 50 
Information relevant for the classification of mixtures ................................. 52 
1.1.7.  Data evaluation and reaching a decision on classification ..................................... 52 
Classification of substances ...................................................................... 52 
Influence  of 
classification of a substance ..................................................................... 53 
1.1.8.  Updating of hazard classifications ..................................................................... 53 
1.1.9.  The interface between hazard classification and hazard communication ................. 53 
1.1.10.  The interface between self-classification and harmonised classification, and the list 

individual  constituents  on  the 

impurities,  additives  or 

1.1.6.1. 
1.1.6.2. 

1.1.7.1. 
1.1.7.2. 

of harmonised classifications ............................................................................ 53 
1.1.11.  The Classification and Labelling Inventory (C&L Inventory) .................................. 55 
1.1.12.  Relation of classification to other EU legislation .................................................. 56 

1.1.12.1.  REACH 56 
1.1.12.2.  Plant Protection Products and Biocides ...................................................... 56 
1.1.12.3.  Transport legislation ............................................................................... 56 

1.2.  THE  SIGNIFICANCE  OF  THE  TERMS  ‘FORM  OR  PHYSICAL  STATE’  AND 
‘REASONABLY  EXPECTED  USE’  WITH  RESPECT  TO  CLASSIFICATION 
ACCORDING TO CLP ............................................................................. 57 
1.2.1. 
‘Form or physical state’ and ‘reasonably expected use’ ........................................ 57 
1.2.2.  The term ‘reasonably expected use’ in relation to hazard classification .................. 57 
1.2.3.  The term ‘form or physical state’ in relation to hazard classification ...................... 58 
1.2.3.1. 
Physical hazards ..................................................................................... 58 
1.2.3.2.  Human health hazards ............................................................................ 58 
Environmental hazards ............................................................................ 59 
1.2.3.3. 

1.3.  SPECIFIC  CASES  REQUIRING  FURTHER  EVALUATION  –  LACK  OF 

BIOAVAILABILITY ................................................................................. 59 
1.3.1.  Definition ...................................................................................................... 59 
1.3.2.  Bioavailability ................................................................................................ 60 
1.3.2.1.  Human health hazards ............................................................................ 60 
Environmental hazards ............................................................................ 61 
1.3.2.2. 

1.4.  USE OF SUBSTANCE CATEGORISATION (READ-ACROSS AND GROUPING) AND 

(Q)SARS FOR CLASSIFICATION AND LABELLING ....................................... 62 
1.4.1. 
(Q)SAR ......................................................................................................... 63 
1.4.2.  Grouping ....................................................................................................... 64 
1.4.3.  Read-across ................................................................................................... 64 

1.5.  SPECIFIC CONCENTRATION LIMITS AND M-FACTORS ................................ 64 
1.5.1.  Specific concentration limits ............................................................................. 64 

 
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1.5.2.  Multiplying factors (M-factors) .......................................................................... 66 
1.5.3.  Harmonised ATE values ................................................................................... 67 

1.6.3.1. 
1.6.3.2. 

1.6.  MIXTURES .......................................................................................... 67 
1.6.1.  How to classify a mixture ................................................................................ 67 
1.6.2.  Classification for physical hazards ..................................................................... 68 
1.6.3.  Health and environmental hazards .................................................................... 69 
Classification derived using data on the mixture itself ................................. 69 
Bridging principles .................................................................................. 70 
1.6.3.2.1.  Dilution ............................................................................................. 70 
1.6.3.2.2.  Batching ............................................................................................ 71 
1.6.3.2.3.  Concentration of highly hazardous mixtures ........................................... 71 
1.6.3.2.4.  Interpolation within one hazard category ............................................... 71 
1.6.3.2.5.  Substantially similar mixtures .............................................................. 72 
1.6.3.2.6.  Review of classification where the composition of a mixture has changed .. 73 
1.6.3.2.7.  Aerosols (some health hazards only) ..................................................... 74 
Classification based on calculation or concentration thresholds ..................... 74 
1.6.3.3.1.  Classification based on calculation ........................................................ 74 
1.6.3.3.2.  Classification based on concentration thresholds ..................................... 76 
1.6.3.3.3.  Additivity Vs. non additivity of hazards .................................................. 77 
1.6.4.  Classification of mixtures in mixtures ................................................................ 79 
Example: Classification of Mixture A .......................................................... 79 
Example: Classification of Mixture B .......................................................... 82 

1.6.4.1. 
1.6.4.2. 

1.6.3.3. 

1.7.  ANNEX VII TO CLP ............................................................................... 85 

2.  PART 2: PHYSICAL HAZARDS ......................................................... 88 

2.0. 

INTRODUCTION ................................................................................... 88 
2.0.1  General remarks about the prerequisites for classification and testing ................... 88 
Safety ........................................................................................................... 88 
2.0.2 
2.0.3  General conditions for testing .......................................................................... 88 
2.0.4 
Physical state ................................................................................................. 89 
2.0.5  Quality .......................................................................................................... 90 

2.1.4.1. 
2.1.4.2. 
2.1.4.3. 
2.1.4.4. 
2.1.4.5. 

2.1.  EXPLOSIVES ....................................................................................... 90 
2.1.1. 
Introduction ................................................................................................... 90 
2.1.2.  Definitions and general considerations for the classification of explosives .............. 91 
2.1.3.  Relation to other physical hazards .................................................................... 92 
2.1.4.  Classification of substances, mixtures or articles as explosives ............................. 92 
Identification of hazard information .......................................................... 92 
Screening procedures and waiving of testing .............................................. 92 
Classification criteria ............................................................................... 93 
Testing and evaluation of hazard information ............................................. 95 
Classification procedure and decision logics................................................ 95 
2.1.4.5.1.  Acceptance procedure ......................................................................... 96 
2.1.4.5.2.  Assignment procedure to a division ....................................................... 99 
2.1.5.  Hazard communication for explosives.............................................................. 105 
Pictograms, signal words, hazard statements and precautionary statements 105 
Additional labelling provisions ................................................................ 106 
2.1.5.2.1.  Packaging dependance ...................................................................... 106 
2.1.5.2.2.  Supplemental hazard information ....................................................... 107 
Further communication requirements ...................................................... 108 

2.1.5.1. 
2.1.5.2. 

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2.1.6.  Relation to transport classification .................................................................. 108 
2.1.7.  Examples of classification for explosives .......................................................... 109 
Example of substances and mixtures fulfilling the classification criteria ........ 109 
Example of substances and mixtures not fulfilling the classification criteria .. 110 

2.1.7.1. 
2.1.7.2. 

2.2.  FLAMMABLE GASES (INCLUDING CHEMICALLY UNSTABLE GASES) .............. 114 
Introduction ................................................................................................. 114 

2.2.1. 
2.2.2.  Definitions  and  general  considerations  for  the  classification  of  flammable  gases 

(including chemically unstable gases) ............................................................. 114 
2.2.3.  Relation to other physical hazards .................................................................. 114 
2.2.4.  Classification of substances and mixtures as flammable gases (including chemically 

unstable gases) ............................................................................................ 114 
Identification of hazard information ........................................................ 114 
2.2.4.1. 
Screening procedures and waiving of testing for gas mixtures .................... 115 
2.2.4.2. 
Classification criteria ............................................................................. 115 
2.2.4.3. 
2.2.4.4. 
Testing and evaluation of hazard information ........................................... 116 
2.2.4.5.  Decision logic ....................................................................................... 117 
2.2.4.5.1.  Decision logic for flammable gases ...................................................... 118 
2.2.4.5.2.  Decision logic for chemically unstable gases ......................................... 119 
2.2.5.  Hazard communication for flammable gases (including chemically unstable gases) 120 
Pictograms, signal words, hazard statements and precautionary statements 120 
2.2.6.  Relation to transport classification .................................................................. 121 
2.2.7.  Example of classification for flammable gases .................................................. 121 

2.2.5.1. 

2.3.  AEROSOLS ......................................................................................... 123 
2.3.1. 
Introduction ................................................................................................. 123 
2.3.2.  Definitions and general considerations for the classification of aerosols ............... 123 
2.3.3.  Relation to other physical hazards .................................................................. 123 
2.3.4.  Classification of aerosols ............................................................................... 124 
2.3.4.1. 
Classification criteria ............................................................................. 124 
Testing and evaluation of hazard information ........................................... 125 
2.3.4.2. 
2.3.4.3.  Decision logic ....................................................................................... 125 
2.3.4.3.1.  Decision logic for aerosols .................................................................. 126 
2.3.4.3.2.  Decision logic for spray aerosols ......................................................... 127 
2.3.4.3.3.  Decision logic for foam aerosols .......................................................... 128 
2.3.5.  Hazard communication for aerosols ................................................................ 129 
Pictograms, signal words, hazard statements and precautionary statements 129 
Additional labelling provisions ................................................................ 129 
2.3.6.  Relation to transport classification .................................................................. 130 
2.3.7.  Examples of classification for aerosols ............................................................. 130 
Examples of aerosols fulfilling the classification criteria ............................. 130 
Examples of aerosols not fulfilling the classification criteria ........................ 131 

2.3.7.1. 
2.3.7.2. 

2.3.5.1. 
2.3.5.2. 

2.4.  OXIDISING GASES .............................................................................. 132 
2.4.1. 
Introduction ................................................................................................. 132 
2.4.2.  Definitions and general considerations for the classification of oxidising gases ...... 132 
2.4.3.  Relation to other physical hazards .................................................................. 132 
2.4.4.  Classification of substances and mixtures as oxidising gases .............................. 132 
Identification of hazard information ........................................................ 132 
Screening procedures and waiving of testing ............................................ 132 
Classification criteria ............................................................................. 132 
Testing and evaluation of hazard information ........................................... 133 

2.4.4.1. 
2.4.4.2. 
2.4.4.3. 
2.4.4.4. 

 
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2.4.5.1. 

2.4.4.5.  Decision logic ....................................................................................... 133 
2.4.5.  Hazard communication for oxidising gases ....................................................... 134 
Pictograms, signal words, hazard statements and precautionary statements 134 
2.4.6.  Relation to transport classification .................................................................. 134 
2.4.7.  Example of classification for oxidising gases..................................................... 134 
Example of substances and mixtures not fulfilling the classification criteria .. 134 

2.4.7.1. 

2.5.  GASES UNDER PRESSURE .................................................................... 136 
Introduction ................................................................................................. 136 

2.5.1. 
2.5.2.  Definitions and general considerations for the classification of gases under pressure

 .................................................................................................................. 136 
2.5.2.1.  Definition of ‘gas’ .................................................................................. 136 
2.5.2.2.  Definition of gases under pressure .......................................................... 136 
2.5.3.  Relation to other physical hazards .................................................................. 136 
2.5.4.  Classification of substances and mixtures as gases under pressure ..................... 136 
Identification of hazard information ........................................................ 136 
2.5.4.1. 
Classification criteria ............................................................................. 137 
2.5.4.2. 
2.5.4.3. 
Testing and evaluation of hazard information ........................................... 137 
2.5.4.4.  Decision logic ....................................................................................... 138 
2.5.5.  Hazard communication for gases under pressure .............................................. 140 
Pictograms, signal words, hazard statements and precautionary statements 140 
2.5.6.  Relation to transport classification .................................................................. 141 
2.5.7.  Examples of classification for gases under pressure .......................................... 142 
Examples of substances and mixtures fulfilling the classification criteria ...... 142 
2.5.7.1.1.  Example mixture: 9 % (O2) + 16 % (N2O) + 75 % (N2) ........................ 142 

2.5.7.1. 

2.5.5.1. 

2.6.4.1. 
2.6.4.2. 

2.6.  FLAMMABLE LIQUIDS ........................................................................... 143 
2.6.1. 
Introduction ................................................................................................. 143 
2.6.2.  Definitions and general considerations for the classification of flammable liquids .. 143 
2.6.3.  Relation to other physical hazards .................................................................. 143 
2.6.4.  Classification of substances and mixtures as flammable liquids .......................... 143 
Identification of hazard information ........................................................ 143 
Screening procedures and waiving of testing ............................................ 143 
2.6.4.2.1.  Boiling point ..................................................................................... 143 
2.6.4.2.2.  Flash point ....................................................................................... 144 
Classification criteria ............................................................................. 144 
Testing and evaluation of hazard information ........................................... 144 
2.6.4.4.1.  Testing ............................................................................................ 145 
2.6.4.4.2.  Evaluation of hazard information ........................................................ 146 
2.6.4.5.  Decision logic ....................................................................................... 146 
2.6.5.  Hazard communication for flammable liquids ................................................... 148 
Pictograms, signal words, hazard statements and precautionary statements 148 
Additional labelling provisions for flammable liquids .................................. 148 

2.6.5.1. 
2.6.5.2. 

2.6.4.3. 
2.6.4.4. 

2.6.6.  Re-classification  of  substances  and  mixtures  classified  as  flammable  liquids 

2.6.6.1. 

2.6.7.1. 

according to DSD and DPD or already classified for transport ............................. 149 
Relation to transport classification .......................................................... 149 
2.6.7.  Examples of classification for flammable liquids ................................................ 149 
Examples of substances and mixtures fulfilling the classification criteria ...... 149 
2.6.7.1.1.  Example 1 ....................................................................................... 149 
2.6.7.1.2.  Example 2 ....................................................................................... 150 
Examples of substances and mixtures not fulfilling the classification criteria . 150 
2.6.7.2.1.  Example 3 ....................................................................................... 150 

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2.6.8.  References .................................................................................................. 150 

2.7.  FLAMMABLE SOLIDS ............................................................................ 151 
2.7.1. 
Introduction ................................................................................................. 151 
2.7.2.  Definitions and general considerations for the classification of flammable solids ... 151 
2.7.3.  Relation to other physical hazards .................................................................. 151 
2.7.4.  Classification of substances and mixtures as flammable solids ............................ 152 
2.7.4.1. 
Identification of hazard information ........................................................ 152 
2.7.4.2. 
Screening procedures and waiving of testing ............................................ 152 
2.7.4.3. 
Classification criteria ............................................................................. 152 
Testing and evaluation of hazard information ........................................... 153 
2.7.4.4. 
2.7.4.5.  Decision logic ....................................................................................... 153 
2.7.5.  Hazard communication for flammable solids .................................................... 155 
Pictograms, signal words, hazard statements and precautionary statements 155 
2.7.6.  Relation to transport classification .................................................................. 155 
2.7.7.  Examples of classification for flammable solids ................................................. 155 
Example of substances and mixtures fulfilling the classification criteria ........ 155 
Examples of substances and mixtures not fulfilling the classification criteria . 156 
2.7.8.  References .................................................................................................. 156 

2.7.7.1. 
2.7.7.2. 

2.7.5.1. 

2.8.4.1. 
2.8.4.2. 
2.8.4.3. 

2.8.  SELF-REACTIVE SUBSTANCES AND MIXTURES ......................................... 157 
2.8.1. 
Introduction ................................................................................................. 157 
2.8.2.  Definitions and general considerations for the classification of self-reactives ........ 157 
2.8.3.  Relation to other physical hazards .................................................................. 158 
2.8.4.  Classification of substances and mixtures as self-reactive .................................. 158 
Identification of hazard information ........................................................ 158 
Classification criteria ............................................................................. 158 
Testing and evaluation of hazard information ........................................... 160 
2.8.4.3.1.  Thermal stability tests and temperature control .................................... 160 
2.8.4.3.2.  Additional considerations and testing .................................................. 161 
2.8.4.3.3.  Additional classification considerations ................................................ 162 
2.8.4.4.  Decision logic ....................................................................................... 163 
2.8.5.  Hazard communication for self-reactives ......................................................... 165 
Pictograms, signal words, hazard statements and precautionary statements 165 

2.8.5.1. 

2.8.6.  Relation to transport classificationaccording to DSD and DPD or already classified 

for transport ................................................................................................ 166 
2.8.7.  Examples of classification for self-reactives ...................................................... 166 
Examples of substances and mixtures fulfilling the classification criteria ...... 166 

2.8.7.1. 

2.9.  PYROPHORIC LIQUIDS ......................................................................... 170 
2.9.1. 
Introduction ................................................................................................. 170 
2.9.2.  Definitions and general considerations for the classification pyrophoric liquids ...... 170 
2.9.3.  Relation to other physical hazards .................................................................. 170 
2.9.4.  Classification of substances and mixtures as pyrophoric liquids .......................... 171 
Identification of hazard information ........................................................ 171 
2.9.4.1. 
Screening procedures and waiving of testing ............................................ 171 
2.9.4.2. 
Classification criteria ............................................................................. 171 
2.9.4.3. 
2.9.4.4. 
Testing and evaluation of hazard information ........................................... 171 
2.9.4.5.  Decision logic ....................................................................................... 172 
2.9.4.5.1.  Decision logic for pyrophoric liquids .................................................... 172 
2.9.5.  Hazard communication for pyrophoric liquids ................................................... 173 
Pictograms, signal words, hazard statements and precautionary statements 173 

2.9.5.1. 

 
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2.9.7.1. 

2.9.6.  Relation to transport classification .................................................................. 173 
2.9.7.  Examples of classification for pyrophoric liquids ................................................ 174 
Examples of substances and mixtures fulfilling the classification criteria ...... 174 
2.9.7.1.1.  Example 1 ....................................................................................... 174 
2.9.7.1.2.  Example 2 ....................................................................................... 175 
Examples of substances and mixtures not fulfilling the classification criteria . 175 
2.9.7.2.1.  Example 3 ....................................................................................... 175 
2.9.8.  References .................................................................................................. 175 

2.9.7.2. 

2.10.  PYROPHORIC SOLIDS .......................................................................... 176 
2.10.1.  Introduction ................................................................................................. 176 
2.10.2.  Definitions and general considerations for the classification pyrophoric solids ....... 176 
2.10.3.  Relation to other physical hazards .................................................................. 177 
2.10.4.  Classification of substances and mixtures as pyrophoric solids ........................... 177 
2.10.4.1.  Identification of hazard information ........................................................ 177 
2.10.4.2.  Screening procedures and waiving of testing ............................................ 177 
2.10.4.3.  Classification criteria ............................................................................. 177 
2.10.4.4.  Testing and evaluation of hazard information ........................................... 178 
2.10.4.5.  Decision logic ....................................................................................... 178 
2.10.4.5.1. Decision logic for pyrophoric solids ..................................................... 178 
2.10.5.  Hazard communication for pyrophoric solids .................................................... 179 
2.10.5.1.  Pictograms, signal words, hazard statements and precautionary statements 179 
2.10.6.  Relation to transport classification .................................................................. 179 
2.10.7.  Examples of classification for pyrophoric solids ................................................. 180 
2.10.7.1.  Examples of substances and mixtures fulfilling the classification criteria ...... 180 
2.10.7.1.1. Example 1 ....................................................................................... 180 
2.10.7.1.2. Example 2 ....................................................................................... 180 
2.10.7.2.  Examples of substances and mixtures not fulfilling the classification criteria . 180 
2.10.7.2.1. Example 3 ....................................................................................... 180 
2.10.7.2.2. Example 4 ....................................................................................... 181 
2.10.8.  References .................................................................................................. 181 

2.11.  SELF-HEATING SUBSTANCES AND MIXTURES .......................................... 182 
2.11.1.  Introduction ................................................................................................. 182 
2.11.2.  Definitions  and  general  considerations  for  the  classification  of  self-heating 

substances and mixtures ............................................................................... 182 
2.11.3.  Relation to other physical hazards .................................................................. 182 
2.11.4.  Classification of self-heating substances and mixtures ....................................... 182 
2.11.4.1.  Identification of hazard information ........................................................ 182 
2.11.4.2.  Screening procedures and waiving of testing ............................................ 183 
2.11.4.3.  Classification criteria ............................................................................. 183 
2.11.4.4.  Testing and evaluation of hazard information ........................................... 184 
2.11.4.4.1. General remarks ............................................................................... 184 
2.11.4.4.2. Sample preparation .......................................................................... 184 
2.11.4.4.3. Criteria and evaluation ...................................................................... 184 
2.11.4.5.  Decision logic ....................................................................................... 185 
2.11.4.6.  Exemption ........................................................................................... 186 
2.11.5.  Hazard communication for self-heating substances and mixtures ........................ 188 
2.11.5.1.  Pictograms, signal words, hazard statements and precautionary statements 188 
2.11.6.  Relation to transport classification .................................................................. 188 
2.11.7.  Examples of classification for self-heating substances and mixtures .................... 189 
2.11.7.1.  Examples of substances and mixtures fulfilling the classification criteria ...... 189 

 
 
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2.11.7.2.  Examples of substances and mixtures not fulfilling the classification criteria . 189 
2.11.8.  References .................................................................................................. 190 

2.12.  SUBSTANCES  AND  MIXTURES  WHICH,  IN  CONTACT  WITH  WATER,  EMIT 

FLAMMABLE GASES ............................................................................. 191 
2.12.1.  Introduction ................................................................................................. 191 
2.12.2.  Definitions  and  general  considerations  for  the  classification  of  substances  and 

mixtures which, in contact with water, emit flammable gases ............................ 191 
2.12.3.  Relation to other physical hazards .................................................................. 191 
2.12.4.  Classification  of  substances  and  mixtures  which,  in  contact  with  water,  emit 

flammable gases .......................................................................................... 192 
2.12.4.1.  Identification of hazard information ........................................................ 192 
2.12.4.2.  Screening procedures and waiving of testing ............................................ 193 
2.12.4.3.  Classification criteria ............................................................................. 193 
2.12.4.4.  Testing and evaluation of hazard information ........................................... 193 
2.12.4.4.1. Testing procedure ............................................................................. 193 
2.12.4.4.2. Evaluation of hazard information ........................................................ 195 
2.12.4.5.  Decision logic ....................................................................................... 195 

2.12.5.  Hazard communication for substances and mixtures which, in contact with water, 

emit flammable gases ................................................................................... 197 

2.12.5.1.  Pictograms,  signal  words,  hazard  statements  and  precautionary  statements 

for substances and mixtures .................................................................. 197 
2.12.5.2.  Additional labelling provisions ................................................................ 197 
2.12.6.  Relation to transport classification .................................................................. 198 
2.12.7.  Examples of classification for substances and mixtures which, in contact with water, 

emit flammable gases ................................................................................... 198 
2.12.7.1.  Example of a substance fulfilling the classification criteria .......................... 198 
2.12.7.1.1. Example 1 ....................................................................................... 198 
2.12.7.2.  Example of a substance not fulfilling the classification criteria .................... 199 
2.12.7.2.1. Example 2 ....................................................................................... 199 
2.12.8.  References .................................................................................................. 199 

2.13.  OXIDISING LIQUIDS ........................................................................... 200 
2.13.1.  Introduction ................................................................................................. 200 
2.13.2.  Definitions and general considerations for the classification of oxidising liquids..... 200 
2.13.3.  Relation to other physical hazards .................................................................. 200 
2.13.4.  Classification of substances and mixtures as oxidising liquids ............................. 201 
2.13.4.1.  Identification of hazard information ........................................................ 201 
2.13.4.1.1. Screening procedures and waiving of testing ........................................ 201 
2.13.4.2.  Classification criteria ............................................................................. 202 
2.13.4.3.  Testing and evaluation of hazard information ........................................... 203 
2.13.4.4.  Decision logic ....................................................................................... 203 
2.13.4.5.  Hazard communication for oxidising liquids .............................................. 205 
2.13.4.5.1. Pictograms, signal words, hazard statements and precautionary statements

  205 

2.13.5.  Relation to transport classification .................................................................. 205 
2.13.6.  Examples of classification for oxidising liquids .................................................. 206 
2.13.6.1.  Examples of substances and mixtures fulfilling the classification criteria ...... 206 
2.13.6.2.  Examples of substances and mixtures not fulfilling the classification criteria . 206 
2.13.7.  Reference .................................................................................................... 206 

2.14.  OXIDISING SOLIDS ............................................................................. 207 
2.14.1.  Introduction ................................................................................................. 207 

 
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2.14.2.  Definitions and general considerations for the classification of oxidising solids ...... 207 
2.14.3.  Relation to other physical hazards .................................................................. 208 
2.14.4.  Classification of substances and mixtures as oxidising solids .............................. 208 
2.14.4.1.  Identification of hazard information ........................................................ 208 
2.14.4.1.1. Screening procedures and waiving of testing ........................................ 208 
2.14.4.2.  Classification criteria ............................................................................. 209 
2.14.4.3.  Testing and evaluation of hazard information ........................................... 211 
2.14.4.4.  Decision logic ....................................................................................... 211 
2.14.4.5.  Hazard communication for oxidising solids ............................................... 213 
2.14.4.5.1. Pictograms, signal words, hazard statements and precautionary statements

  213 

2.14.5.  Relation to transport classification .................................................................. 213 
2.14.6.  Examples of classification for oxidising solids ................................................... 214 
2.14.6.1.  Examples of substances and mixtures fulfilling the classification criteria ...... 214 
2.14.6.2.  Examples of substances and mixtures not fulfilling the classification criteria . 214 
2.14.7.  Reference .................................................................................................... 214 

2.15.  ORGANIC PEROXIDES .......................................................................... 215 
2.15.1.  Introduction ................................................................................................. 215 
2.15.2.  Definitions and general considerations for the classification of organic peroxides .. 215 
2.15.3.  Relation to other physical hazards .................................................................. 215 
2.15.4.  Classification of substances and mixtures as organic peroxides .......................... 216 
2.15.4.1.  Identification of hazard information ........................................................ 216 
2.15.4.2.  Classification criteria ............................................................................. 216 
2.15.4.3.  Testing and evaluation of hazard information ........................................... 218 
2.15.4.3.1. Thermal stability tests and temperature control .................................... 218 
2.15.4.3.2. Additional considerations and testing .................................................. 219 
2.15.4.3.3. Additional classification considerations ................................................ 219 
2.15.4.4.  Decision logic ....................................................................................... 220 
2.15.5.  Hazard communication for organic peroxides ................................................... 222 
2.15.5.1.  Pictograms, signal words, hazard statements and precautionary statements 222 
2.15.5.2.  Additional labelling provisions for organic peroxides .................................. 223 
2.15.6.  Relation to transport classification .................................................................. 223 
2.15.7.  Examples of classification for organic peroxides ................................................ 223 
2.15.7.1.  Examples of substances and mixtures fulfilling the classification criteria ...... 223 
2.15.7.2.  Additional remarks ................................................................................ 226 

2.16.  CORROSIVE TO METALS ....................................................................... 227 
2.16.1.  Introduction ................................................................................................. 227 
2.16.2.  Definitions  and  general  considerations  for  the  classification  of  substances  and 

mixtures corrosive to metals .......................................................................... 228 
2.16.3.  Relation to other physical hazards .................................................................. 228 
2.16.4.  Classification of substances and mixtures as corrosive to metals ........................ 228 
2.16.4.1.  Identification of hazard information ........................................................ 228 
2.16.4.2.  Screening procedures and waiving of testing ............................................ 229 
2.16.4.3.  Classification criteria ............................................................................. 229 
2.16.4.4.  Testing and evaluation of hazard information ........................................... 230 
2.16.4.4.1. General considerations ...................................................................... 230 
2.16.4.4.2. Additional notes on best practice for testing ......................................... 232 
2.16.4.5.  Decision logic ....................................................................................... 234 
2.16.5.  Hazard communication for substances and mixtures corrosive to metals ............. 235 
2.16.5.1.  Pictograms, signal words, hazard statements and precautionary statements 235 

 
 
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2.16.6.  Relation to transport classification .................................................................. 236 
2.16.7.  Examples of classification for substances and mixtures corrosive to metals .......... 236 
2.16.7.1.  Example of metal specimen plates after exposure to a corrosive mixture ..... 237 
2.16.8.  References .................................................................................................. 237 

3.  PART 3: HEALTH HAZARDS .......................................................... 238 

3.1.2.3. 

3.1.2.1. 

3.1.2.2. 

3.1.  ACUTE TOXICITY................................................................................. 238 
3.1.1.  Definitions and general considerations for acute toxicity .................................... 238 
3.1.2.  Classification of substances for acute toxicity ................................................... 238 
Identification of hazard information ........................................................ 238 
3.1.2.1.1.  Identification of human data .............................................................. 238 
3.1.2.1.2.  Identification of non-human data ........................................................ 239 
Classification criteria ............................................................................. 239 
3.1.2.2.1.  Harmonised ATE values ..................................................................... 241 
3.1.2.2.2.  Minimum classification ...................................................................... 241 
Evaluation of hazard information ............................................................ 241 
3.1.2.3.1.  Evaluation of human data .................................................................. 241 
3.1.2.3.2.  Evaluation of non-human data............................................................ 242 
3.1.2.3.3.  Weight of evidence ........................................................................... 245 
3.1.2.4.  Decision on classification ....................................................................... 245 
Setting of specific concentration limits ..................................................... 245 
3.1.2.5. 
3.1.2.6.  Decision logic for classification of substances ........................................... 245 
3.1.3.  Classification of mixtures for acute toxicity ...................................................... 247 
3.1.3.1.  General considerations for classification .................................................. 247 
Identification of hazard information ........................................................ 247 
3.1.3.2. 
Classification criteria ............................................................................. 247 
3.1.3.3. 
3.1.3.3.1.  When data are available for the complete mixture ................................ 247 
3.1.3.3.2.  When data are not available for the complete mixture: bridging principles248 
3.1.3.3.3.  When data are available for all ingredients ........................................... 248 
3.1.3.3.4.  Special case for acute inhalation toxicity .............................................. 249 
3.1.3.3.5.  When data are not available for all ingredients ..................................... 251 
3.1.3.3.6.  Ingredients  that  should  be  taken  into  account  for  the  purpose  of 

classification .................................................................................... 254 
3.1.3.3.7.  Non-classified components ................................................................. 254 

3.1.3.4.  Generic  concentration  limits  for  substances  triggering  classification  of 

3.1.4.1. 
3.1.4.2. 

mixtures .............................................................................................. 255 
3.1.3.5.  Decision on classification ....................................................................... 255 
3.1.3.6.  Decision logic for classification of mixtures............................................... 255 
3.1.4.  Hazard communication in the form of labelling for acute toxicity ........................ 257 
Pictograms, signal words, hazard statements and precautionary statements 257 
Additional labelling provisions ................................................................ 259 
3.1.5.  Examples of classification for acute toxicity ...................................................... 262 
Examples of substances fulfilling the criteria for classification ..................... 262 
3.1.5.1.1.  Example 1: Methanol ........................................................................ 262 
3.1.5.1.2.  Example 2: N,N-Dimethylaniline ......................................................... 262 
3.1.5.1.3.  Example 3 ....................................................................................... 263 
3.1.5.1.4.  Example 4 ....................................................................................... 264 
3.1.5.1.5.  Example 5 ....................................................................................... 264 
3.1.5.1.6.  Example 6 ....................................................................................... 264 
3.1.5.1.7.  Example 7: 2,3-Dichloropropene ........................................................ 265 

3.1.5.1. 

 
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3.1.5.3. 

3.1.5.1.8.  Example 8 ....................................................................................... 266 
3.1.5.1.9.  Example 9 ....................................................................................... 266 
Examples of substances not fulfilling the criteria for classification ............... 267 
3.1.5.2.1.  Example 10...................................................................................... 267 
Example of mixtures fulfilling the criteria for classification ......................... 268 
3.1.5.3.1.  Example 11...................................................................................... 268 
3.1.5.3.2.  Example 12a .................................................................................... 269 
Examples of mixtures not fulfilling the criteria for classification .................. 269 
3.1.5.4.1.  Example 12b .................................................................................... 269 

3.1.5.4. 

3.1.5.5. 

Example  of  the  application  of  the  additivity  method  for  mixtures  for  acute 
inhalation toxicity with ingredient substances in different physical forms (gas, 
vapour, mist or dust). ........................................................................... 270 
3.1.5.5.1.  Example 13...................................................................................... 270 
3.1.6.  References .................................................................................................. 272 

3.2.2.1. 

3.2.2.2. 
3.2.2.3. 

3.2.  SKIN CORROSION/IRRITATION ............................................................. 273 
3.2.1.  Definitions for classification for skin corrosion/irritation ..................................... 273 
3.2.2.  Classification of substances for skin corrosion/irritation ..................................... 273 
Identification of hazard information ........................................................ 273 
3.2.2.1.1.  Identification of human data .............................................................. 273 
3.2.2.1.2.  Identification of non human data ........................................................ 273 
3.2.2.1.2.1.  Consideration of physico-chemical properties ............................... 273 
3.2.2.1.2.2.  pH and acid/alkaline reserve ...................................................... 274 
3.2.2.1.2.3.  Non-testing methods: (Q)SARs and expert systems ...................... 274 
3.2.2.1.2.4.  Testing methods: in vitro methods .............................................. 275 
3.2.2.1.2.5.  Testing methods: In vivo data .................................................... 276 
Classification criteria ............................................................................. 277 
Evaluation of hazard information ............................................................ 278 
3.2.2.3.1.  Evaluation of human data .................................................................. 282 
3.2.2.3.2.  Evaluation of non human data ............................................................ 282 
3.2.2.3.2.1.  In vitro data ............................................................................. 282 
3.2.2.3.2.2.  In vivo data ............................................................................. 282 
3.2.2.3.3.  Weight of evidence ........................................................................... 284 
3.2.2.4.  Decision on classification ....................................................................... 286 
Setting of specific concentration limits ..................................................... 286 
3.2.2.5. 
3.2.2.6.  Decision logic for classification of substances ........................................... 288 
3.2.3.  Classification of mixtures for skin corrosion/irritation ........................................ 289 
Identification of hazard information ........................................................ 289 
Classification criteria for mixtures ........................................................... 290 
3.2.3.2.1.  When data are available for the complete mixture ................................ 290 
3.2.3.2.1.1.  Mixtures with extreme pH .......................................................... 290 
3.2.3.2.2.  When data are not available for the complete mixture: bridging principles292 
3.2.3.2.3.  When data are available for all ingredients or only for some ingredients .. 292 
3.2.3.2.3.1.  Ingredients  that  should  be  taken  into  account  for  the  purpose  of 

3.2.3.1. 
3.2.3.2. 

classification ............................................................................ 292 
3.2.3.2.3.2.  The additivity approach is applicable ........................................... 292 
3.2.3.2.3.3.  The additivity approach is not applicable ...................................... 293 

3.2.3.3.  Generic  concentration  limits  for  substances  triggering  classification  of 

mixtures .............................................................................................. 294 
3.2.3.3.1.  When the additivity approach is applicable ........................................... 294 
3.2.3.3.2.  When the additivity approach is not applicable ..................................... 295 
3.2.3.4.  Decision logic for classification of mixtures............................................... 295 

 
 
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3.2.4.1. 
3.2.4.2. 

3.2.4.  Hazard communication in form of labelling for skin corrosion/irritation ................ 298 
Pictograms, signal words, hazard statements and precautionary statements 298 
Additional labelling provisions ................................................................ 299 
3.2.5.  Examples of classification for skin corrosion/irritation ........................................ 299 
Examples of substances fulfilling the criteria for classification ..................... 299 
3.2.5.1.1.  Example 1: Standard test according to OECD TG 404 with three animals . 299 
3.2.5.1.2.  Example 2: Test carried out with one animal with a test substance which is 

3.2.5.1. 

3.2.5.2. 

suspected as corrosive ...................................................................... 300 
3.2.5.1.3.  Example 3: Test carried out with more than three animals ..................... 300 
Examples of mixtures fulfilling the criteria for classification ........................ 301 
3.2.5.2.1.  Example 4: Mixture without extreme pH, with ingredients with SCLs ....... 301 
3.2.5.2.2.  Example  5:  Mixture  without  extreme  pH,  and  non-applicability  of  the 

3.2.5.3. 

additivity approach ........................................................................... 301 
Examples of mixtures not fulfilling the criteria for classification .................. 302 
3.2.5.3.1.  Example 6: Mixture without extreme pH, with ingredients with SCLs ....... 302 
3.2.6.  References .................................................................................................. 303 

3.3.2.1. 

3.3.2.2. 
3.3.2.3. 

3.3.  SERIOUS EYE DAMAGE/EYE IRRITATION ................................................. 304 
3.3.1.  Definitions for classification for serious eye damage/eye irritation ...................... 304 
3.3.2.  Classification of substances for serious eye damage/eye irritation ....................... 304 
Identification of hazard information ........................................................ 304 
3.3.2.1.1.  Identification of human data .............................................................. 304 
3.3.2.1.2.  Identification of non human data ........................................................ 304 
3.3.2.1.3.  Consideration of physico-chemical properties ....................................... 304 
3.3.2.1.4.  pH and the acid/alkaline reserve ......................................................... 304 
3.3.2.1.5.  Non-testing methods: (Q)SARs and expert systems .............................. 305 
3.3.2.1.5.1.  Testing methods: in vitro methods .............................................. 305 
3.3.2.1.5.2.  Testing methods: In vivo methods .............................................. 306 
Classification criteria ............................................................................. 307 
Evaluation of hazard information ............................................................ 308 
3.3.2.3.1.  Evaluation of human data .................................................................. 311 
3.3.2.3.2.  Evaluation of non-human data............................................................ 311 
3.3.2.3.2.1.  Ex vivo/in vitro data .................................................................. 311 
3.3.2.3.2.2.  In vivo data ............................................................................. 312 
3.3.2.3.3.  Weight of evidence ........................................................................... 314 
3.3.2.4.  Decision on classification ....................................................................... 314 
3.3.2.5. 
Setting of specific concentration limits ..................................................... 314 
3.3.2.6.  Decision logic for classification of substances ........................................... 316 
3.3.3.  Classification of mixtures for serious eye damage/eye irritation .......................... 317 
Identification of hazard information ........................................................ 317 
Classification criteria for mixtures ........................................................... 318 
3.3.3.2.1.  When data are available for the complete mixture ................................ 318 
3.3.3.2.1.1.  Mixtures with extreme pH .......................................................... 319 
3.3.3.2.2.  When data are not available for the complete mixture: bridging principles320 
3.3.3.2.3.  When data are available for all ingredients or only for some ingredients of 

3.3.3.1. 
3.3.3.2. 

the mixture ...................................................................................... 320 

3.3.3.2.3.1.  Ingredients  that  should  be  taken  into  account  for  the  purpose  of 

classification ............................................................................ 320 
3.3.3.2.3.2.  The additivity approach is applicable ........................................... 320 
3.3.3.2.3.3.  The additivity approach is not applicable ...................................... 321 

3.3.3.3.  Generic  concentration  limits  for  substances  triggering  classification  of 

mixtures .............................................................................................. 322 

 
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3.3.3.3.1.  When the additivity approach is applicable ........................................... 322 
3.3.3.3.2.  When the additivity approach is not applicable ..................................... 323 
3.3.3.4.  Decision logic for classification of mixtures............................................... 323 
3.3.4.  Hazard communication in form of labelling for serious eye damage/eye irritation .. 325 
Pictograms, signal words, hazard statements and precautionary statements 325 
3.3.5.  Examples of classification for serious eye damage/eye irritation ......................... 326 
Examples of substances fulfilling the criteria for classification ..................... 326 
3.3.5.1.1.  Example 1: Standard test according to OECD TG 405 with three animals . 326 
3.3.5.1.2.  Example 2: Test carried out with more than 3 rabbits ........................... 328 
Examples of mixtures fulfilling the criteria for classification ........................ 330 

3.3.5.2. 

3.3.5.1. 

3.3.5.2.1.  Example 3: Application of the additivity approach for mixtures containing 

ingredients without SCLs ................................................................... 330 

3.3.5.2.2.  Example 4: Application of the additivity approach for mixtures containing 

ingredients which may have SCLs ....................................................... 331 

3.3.5.2.3.  Example 5: Application of the additivity approach for mixtures containing 

ingredients which may have SCLs ....................................................... 331 
3.3.6.  References .................................................................................................. 332 

3.4.2.1. 

3.4.  RESPIRATORY OR SKIN SENSITISATION ................................................. 333 
3.4.1.  Definitions and general considerations for respiratory or skin sensitisation ........... 333 
3.4.2.  Classification of substances for sensitisation .................................................... 333 
Classification of substances for respiratory sensitisation ............................ 333 
3.4.2.1.1.  Identification of hazard information..................................................... 333 
3.4.2.1.1.1.  Identification of human data ...................................................... 333 
3.4.2.1.1.2.  Identification of non human data ................................................ 334 
3.4.2.1.2.  Classification criteria for substances .................................................... 334 
3.4.2.1.3.  Evaluation of hazard information ........................................................ 335 
3.4.2.1.3.1.  Human data ............................................................................. 335 
3.4.2.1.3.2.  Non human data ....................................................................... 336 
3.4.2.1.4.  Decision on classification ................................................................... 336 
3.4.2.1.5.  Setting of specific concentration limits ................................................. 336 
3.4.2.1.6.  Decision logic for classification of substances ....................................... 337 
Classification of substances for skin sensitisation ...................................... 338 
3.4.2.2.1.  Identification of hazard information..................................................... 338 
3.4.2.2.1.1.  Identification of human data ...................................................... 338 
3.4.2.2.1.2.  Identification of non human data ................................................ 338 
3.4.2.2.2.  Classification criteria for substances .................................................... 338 
3.4.2.2.3.  Evaluation of hazard information ........................................................ 340 
3.4.2.2.3.1.  Human data ............................................................................. 340 
3.4.2.2.3.2.  Non human data ....................................................................... 343 
3.4.2.2.3.2.1. Mouse Local Lymph Node Assay .................................................. 345 
3.4.2.2.3.3.  Guinea Pig Maximisation Test (GPMT, OECD TG 406)..................... 345 
3.4.2.2.3.4.  Buehler assay (OECD TG 406) .................................................... 346 
3.4.2.2.3.5.  Non-guideline skin sensitisation tests .......................................... 346 
3.4.2.2.3.6.  Animal test methods conducted for purposes other than sensitisation

3.4.2.2. 

  346 

3.4.2.2.3.7.  Weight of evidence ................................................................... 346 
3.4.2.2.4.  Decision on classification ................................................................... 348 
3.4.2.2.5.  Setting of specific concentration limits ................................................. 348 
3.4.2.2.6.  Decision logic for classification of substances ....................................... 351 
3.4.3.  Classification of mixtures for respiratory or skin sensitisation ............................. 352 
Identification of hazard information for respiratory sensitisation ................. 352 
Identification of hazard information for skin sensitisation ........................... 352 

3.4.3.1. 
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3.4.3.3. 

Classification criteria for mixtures ........................................................... 352 
3.4.3.3.1.  When data are available for all ingredients or only for some ingredients .. 353 
3.4.3.3.2.  When data are available for the complete mixture ................................ 355 
3.4.3.3.3.  When data are not available for the complete mixture: Bridging Principles355 
3.4.3.4.  Decision logic for classification of mixtures............................................... 355 
3.4.3.4.1.  Decision logic for classification of mixtures for respiratory sensitisation ... 356 
3.4.4.  Hazard communication for respiratory or skin sensitisation ................................ 358 
Pictograms, signal words, hazard statements and precautionary statements 358 
Additional labelling provisions ................................................................ 359 
3.4.5.  Examples of classification for skin sensitisation ................................................ 359 

3.4.4.1. 
3.4.4.2. 

3.4.5.1. 

Example of substances and mixtures fulfilling the criteria for classification for 
skin sensitisation .................................................................................. 359 
3.4.5.1.1.  Example 1 ....................................................................................... 359 
3.4.5.1.2.  Example 2 ....................................................................................... 359 
3.4.5.1.3.  Example 3 ....................................................................................... 359 
3.4.5.1.4.  Example 4 ....................................................................................... 359 
3.4.5.1.5.  Example 5 ....................................................................................... 360 
3.4.5.1.6.  Example 6 ....................................................................................... 360 
3.4.5.1.7.  Example 7 ....................................................................................... 360 
3.4.5.1.8.  Example 8 ....................................................................................... 360 

3.4.5.2. 

Example of substances or mixtures not fulfilling the criteria for classification 
for skin sensitisation ............................................................................. 361 
3.4.5.2.1.  Example 9 ....................................................................................... 361 
3.4.5.2.2.  Example 10...................................................................................... 361 

3.4.5.3. 

Examples of substances fulfilling the criteria for classification for respiratory 
sensitisation ......................................................................................... 361 
3.4.5.3.1.  Example 11...................................................................................... 361 
3.4.5.3.2.  Example 12...................................................................................... 361 
3.4.6.  References .................................................................................................. 362 

3.5.2.1. 

3.5.2.2. 
3.5.2.3. 

3.5.  GERM CELL MUTAGENICITY .................................................................. 364 
3.5.1.  Definitions and general considerations for classification for germ cell mutagenicity 364 
3.5.2.  Classification of substances for germ cell mutagenicity ...................................... 365 
Identification of hazard information ........................................................ 365 
3.5.2.1.1.  Identification of human data .............................................................. 365 
3.5.2.1.2.  Identification of non human data ........................................................ 365 
Classification criteria for substances ........................................................ 366 
Evaluation of hazard information ............................................................ 367 
3.5.2.3.1.  Evaluation of human data .................................................................. 367 
3.5.2.3.2.  Evaluation of non human data ............................................................ 367 
3.5.2.4.  Decision on classification ....................................................................... 367 
3.5.2.5. 

Classification  of  substances  containing  CMR  constituents,  additives  or 
impurities ............................................................................................ 369 
3.5.2.6. 
Setting of specific concentration limits ..................................................... 370 
3.5.2.7.  Decision logic for classification of substances ........................................... 371 
3.5.3.  Classification of mixtures for germ cell mutagenicity ......................................... 372 
Classification criteria for mixtures ........................................................... 372 
3.5.3.1.1.  When data are available for the complete mixture ................................ 372 
3.5.3.1.2.  When data are not available for the complete mixture: bridging principles372 

3.5.3.1. 

3.5.3.2.  Generic  concentration  limits  for  substances  triggering  classification  of 

mixtures .............................................................................................. 372 

 
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3.5.3.3.  Decision logic for classification of mixtures............................................... 373 
3.5.4.  Hazard communication in form of labelling for germ cell mutagenicity ................. 376 
Pictograms, signal words, hazard statements and precautionary statements 376 
Additional labelling provisions ................................................................ 376 

3.5.4.1. 
3.5.4.2. 

3.6.2.1. 
3.6.2.2. 
3.6.2.3. 

3.6.  CARCINOGENICITY .............................................................................. 378 
3.6.1.  Definitions and general considerations for classification for carcinogenicity .......... 378 
3.6.2.  Classification of substances for carcinogenicity ................................................. 378 
Identification of hazard information ........................................................ 378 
Classification criteria for substances ........................................................ 378 
Evaluation of hazard information ............................................................ 380 
3.6.2.3.1.  Specific considerations for classification ............................................... 380 
3.6.2.3.2.  Additional considerations for classification ............................................ 382 
3.6.2.3.3.  Consideration of mutagenicity ............................................................ 389 
3.6.2.3.4.  Non testing data ............................................................................... 389 
3.6.2.4.  Decision on classification ....................................................................... 390 
Classification of substances containing CMR constituents ........................... 390 
3.6.2.5. 
3.6.2.6. 
Setting of specific concentration limits ..................................................... 391 
3.6.2.7.  Decision logic for classification of substances ........................................... 391 
3.6.3.  Classification of mixtures for carcinogenicity .................................................... 392 
Classification criteria for mixtures ........................................................... 392 
3.6.3.1.1.  When data are available for all ingredients or only for some ingredients .. 392 
3.6.3.1.2.  When data are available for the complete mixture ................................ 392 
3.6.3.1.3.  When data are not available for the complete mixture: bridging principles393 
3.6.3.2.  Decision logic for classification of mixtures............................................... 393 
3.6.4.  Hazard communication in form of labelling for carcinogenicity ............................ 395 
Pictograms, signal words, hazard statements and precautionary statements 395 
Additional labelling provisions ................................................................ 396 
Some additional considerations for re-classification ................................... 396 
3.6.5.  Examples of classification for carcinogenicity ................................................... 396 
3.6.6.  References .................................................................................................. 396 

3.6.4.1. 
3.6.4.2. 
3.6.4.3. 

3.6.3.1. 

3.7.2.1. 

3.7.1.1. 

3.7.2.2. 

3.7.  REPRODUCTIVE TOXICITY .................................................................... 400 
3.7.1.  Definitions and general considerations for reproductive toxicity .......................... 400 
Special considerations on effects on or via lactation .................................. 401 
3.7.2.  Classification of substances for reproductive toxicity ......................................... 401 
Identification of hazard information ........................................................ 401 
3.7.2.1.1.  Identification of human data .............................................................. 401 
3.7.2.1.2.  Identification of non human data ........................................................ 401 
Classification criteria ............................................................................. 401 
3.7.2.2.1.  Classification in the presence of parental toxicity .................................. 402 
3.7.2.2.1.1.  Effects to be considered in the presence of marked systemic effects 402 
3.7.2.2.1.2.  Relevance of specific effects in the parent .................................... 403 
3.7.2.2.2.  Substances causing effects on or via lactation ...................................... 405 
Evaluation of hazard information ............................................................ 406 
3.7.2.3.1.  Use of data from standard repeat dose tests ........................................ 406 
3.7.2.3.2.  Study design .................................................................................... 406 
3.7.2.3.3.  Evaluation of evidence relating to effects on or via lactation ................... 407 
3.7.2.4.  Decision on classification ....................................................................... 408 
Classification of substances containing CMR constituents ........................... 408 
3.7.2.5. 
Setting of specific concentration limits ..................................................... 409 
3.7.2.6. 
3.7.2.6.1.  Procedure ........................................................................................ 409 

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3.7.2.6.2.  Cases where potency evaluation is difficult or unfeasible ....................... 410 
3.7.2.6.3.  Determination of the ED10 value ......................................................... 410 
3.7.2.6.3.1.  Determination in practice ........................................................... 410 
3.7.2.6.3.2.  Quantal or non-parametric data .................................................. 411 
3.7.2.6.3.3.  Continuous or parametric data ................................................... 411 
3.7.2.6.3.4.  Data combining incidence and magnitude .................................... 412 
3.7.2.6.3.5.  Specific data types .................................................................... 412 
3.7.2.6.4.  Provisional evaluation of the potency classification ................................ 413 
3.7.2.6.5.  Modifying factors .............................................................................. 413 
3.7.2.6.5.1.  Type of effect / severity ............................................................. 414 
3.7.2.6.5.2.  Data availability ........................................................................ 414 
3.7.2.6.5.3.  Dose-response relationship ........................................................ 415 
3.7.2.6.5.4.  Mode or mechanism of action ..................................................... 415 
3.7.2.6.5.5.  Toxicokinetics ........................................................................... 415 
3.7.2.6.5.6.  Bio-accumulation of substances .................................................. 415 
3.7.2.6.6.  Assigning specific concentration limits (SCLs) ....................................... 416 
3.7.2.6.6.1.  Assigning two SCLs to a substance .............................................. 417 
3.7.2.7.  Decision logic for classification of substances ........................................... 418 
3.7.3.  Classification of mixtures for reproductive toxicity ............................................ 419 
Classification criteria for mixtures ........................................................... 419 
3.7.3.1.1.  When data are available for the individual ingredients ........................... 420 
3.7.3.1.2.  When data are available for the complete mixture ................................ 420 
3.7.3.1.3.  When data are not available for the complete mixture: bridging principles420 
3.7.3.2.  Decision logic for classification of mixtures............................................... 421 
3.7.4.  Hazard communication in form of labelling for reproductive toxicity .................... 424 
Pictograms, signal words, hazard statements and precautionary statements 424 
Additional labelling provisions ................................................................ 426 
3.7.5.  Examples .................................................................................................... 427 
Examples of the determination of SCLs ................................................... 427 
3.7.5.1.1.  Example 1 ....................................................................................... 427 
3.7.5.1.2.  Example 2 (developmental part only) .................................................. 428 
3.7.5.1.3.  Example 3 (limited to developmental toxicity) ...................................... 431 
3.7.5.1.4.  Example 4 ....................................................................................... 433 

3.7.4.1. 
3.7.4.2. 

3.7.3.1. 

3.7.5.1. 

3.8.2.1. 

3.8.2.2. 

3.8.  SPECIFIC TARGET ORGAN TOXICITY – SINGLE EXPOSURE (STOT-SE) ......... 435 
3.8.1.  Definitions and general considerations for STOT-SE .......................................... 435 
3.8.2.  Classification of substances for STOT-SE ......................................................... 436 
Identification of hazard information ........................................................ 436 
3.8.2.1.1.  Identification of human data .............................................................. 436 
3.8.2.1.2.  Identification of non human data ........................................................ 436 
Classification criteria for Categories 1 and 2 ............................................. 437 
3.8.2.2.1.  Guidance values ............................................................................... 439 
Classification criteria for Category 3: Transient target organ effects ............ 440 
Evaluation of hazard information on STOT-SE for substances ..................... 441 
3.8.2.4.1.  Evaluation of human data .................................................................. 441 
3.8.2.4.2.  Evaluation of non human data ............................................................ 443 
3.8.2.4.3.  Evaluation of non-testing and in vitro data ........................................... 445 
3.8.2.4.4.  Conversions ..................................................................................... 445 
3.8.2.4.5.  Weight of evidence ........................................................................... 445 
3.8.2.5.  Decision on classification of substances ................................................... 446 
3.8.2.6. 
Setting of specific concentration limits for STOT-SE .................................. 446 
3.8.2.7.  Decision logic for classification of substances ........................................... 448 

3.8.2.3. 
3.8.2.4. 

 
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3.8.3.1. 
3.8.3.2. 

3.8.3.  Classification of mixtures for STOT-SE ............................................................ 450 
Identification of hazard information ........................................................ 450 
Classification criteria for mixtures ........................................................... 450 
3.8.3.2.1.  When data are available for the complete mixture ................................ 450 
3.8.3.2.2.  When data are not available for the complete mixture: bridging principles451 
3.8.3.2.3.  When data are available for all ingredients or only for some ingredients of 

the mixture ...................................................................................... 451 

3.8.3.2.4.  Components of a mixture that should be taken into account for the purpose 

of classification ................................................................................. 451 

3.8.3.3.  Generic  concentration  limits  for  substances  triggering  classification  of 

3.8.5.1. 

3.8.4.1. 
3.8.4.2. 

mixtures for STOT-SE ........................................................................... 451 
3.8.3.4.  Decision logic for classification of mixtures............................................... 453 
3.8.4.  Hazard communication in form of labelling for STOT-SE .................................... 456 
Pictograms, signal words, hazard statements and precautionary statements 456 
Additional labelling provisions ................................................................ 457 
3.8.5.  Examples of classification for STOT-SE ............................................................ 457 
Examples of substances fulfilling the criteria for classification ..................... 457 
3.8.5.1.1.  Example 1: Methanol ........................................................................ 457 
3.8.5.1.2.  Example 2: Tricresyl phosphate .......................................................... 458 
3.8.5.1.3.  Example 3: Sulfur dioxide .................................................................. 458 
3.8.5.1.4.  Example 4: Toluene .......................................................................... 459 
Examples of substances not fulfilling the criteria for classification ............... 459 
3.8.5.2.1.  Example 5: ABC ............................................................................... 459 
3.8.5.2.2.  Example 6: N,N-Dimethylaniline ......................................................... 460 

3.8.5.2. 

3.9.2.1. 

3.9.2.2. 
3.9.2.3. 

3.9.  SPECIFIC TARGET ORGAN TOXICITY – REPEATED EXPOSURE (STOT-RE) ..... 461 
3.9.1.  Definitions and general considerations for STOT-RE .......................................... 461 
3.9.2.  Classification of substances for STOT-RE ......................................................... 462 
Identification of hazard information ........................................................ 462 
3.9.2.1.1.  Identification of human data .............................................................. 462 
3.9.2.1.2.  Identification of non human data ........................................................ 462 
Classification criteria for substances ........................................................ 463 
Evaluation of hazard information ............................................................ 466 
3.9.2.3.1.  Evaluation of human data .................................................................. 467 
3.9.2.3.2.  Evaluation of non human data ............................................................ 467 
3.9.2.3.3.  Conversions ..................................................................................... 469 
3.9.2.3.4.  Weight of evidence ........................................................................... 470 
3.9.2.4.  Decision on classification ....................................................................... 471 
Additional considerations ....................................................................... 472 
3.9.2.5. 
3.9.2.5.1.  Irritating/corrosive substances ........................................................... 472 
3.9.2.5.2.  Hematotoxicity ................................................................................. 472 
3.9.2.5.3.  Mechanisms not relevant to humans (CLP Annex I, 3.9.2.8.1. (e)) .......... 475 
3.9.2.5.4.  Adaptive responses (CLP Annex I, 3.9.2.8.1. (d)) ................................. 476 
3.9.2.5.5.  Post-observation periods in 28 day and 90 day studies .......................... 476 
Setting of specific concentration limits ..................................................... 476 
3.9.2.6. 
3.9.2.7.  Decision logic for classification of substances ........................................... 478 
3.9.3.  Classification of mixtures for STOT-RE ............................................................ 479 
Identification of hazard information ........................................................ 479 
3.9.3.1. 
Classification criteria for mixtures ........................................................... 479 
3.9.3.2. 
3.9.3.3.  When data are available for the complete mixture .................................... 479 
3.9.3.3.1.  When data are not available for the complete mixture: bridging principles479 

 
 
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3.9.3.3.2.  When data are available for all ingredients or only for some ingredients of 

the mixture ...................................................................................... 479 

3.9.3.3.3.  Components of a mixture that should be taken into account for the purpose 

of classification ................................................................................. 480 

3.9.3.4.  Generic  concentration  limits  for  substances  triggering  classification  of 

mixtures .............................................................................................. 480 
3.9.3.5.  Decision logic for classification of mixtures............................................... 480 
3.9.4.  Hazard communication in form of labelling for STOT-RE .................................... 482 
Pictograms, signal words, hazard statements and precautionary statements 482 
Additional labelling provisions ................................................................ 483 
3.9.5.  Examples of classification for STOT-RE ............................................................ 483 
Examples of substances fulfilling the criteria for classification ..................... 483 

3.9.4.1. 
3.9.4.2. 

3.9.5.1. 

3.9.5.1.1.  Example 1: Hydroxylamine / Hydroxylamonium salts (CAS no. 7803-49-8)

  483 

3.9.5.1.2.  Example 2: But-2-yn-1,4-diol (EC No 203-788-6; CAS No 110-65-6) ...... 485 
3.9.5.1.3.  Example 3: XYZ ................................................................................ 487 
Examples of substances not fulfilling the criteria for classification ............... 489 

3.9.5.2. 

3.9.5.2.1.  Example 4: MCCPs (Medium Chain Chlorinated Paraffins) = Alkanes, C14-17, 

3.9.5.3. 

Chloro- (EC No 287-477-0; CAS No 85535-85-9).................................. 489 
Examples of mixtures fulfilling the criteria for classification ........................ 491 
3.9.5.3.1.  Example 5 ....................................................................................... 491 
3.9.5.3.2.  Example 6 ....................................................................................... 491 
3.9.5.3.3.  Example 7 ....................................................................................... 491 
3.9.5.3.4.  Example 8 ....................................................................................... 492 
Example of mixtures not fulfilling the criteria for classification .................... 492 
3.9.5.4.1.  Example 9 ....................................................................................... 492 
3.9.6.  References .................................................................................................. 493 

3.9.5.4. 

4.  PART 4: ENVIRONMENTAL HAZARDS ........................................... 494 

4.1.  HAZARDOUS TO THE AQUATIC ENVIRONMENT ........................................ 494 
4.1.1. 
Introduction ................................................................................................. 494 
4.1.2.  Scope ......................................................................................................... 494 
4.1.3.  Classification of substances hazardous to the aquatic environment ..................... 495 

4.1.3.1. 

4.1.3.2. 

Information  applicable  for  classification  of  substances  hazardous  to  the 
aquatic environment ............................................................................. 495 
4.1.3.1.1.  Substance properties used for classification ......................................... 495 
4.1.3.1.2.  Information and data availability ........................................................ 495 
Evaluation of available information ......................................................... 496 
4.1.3.2.1.  General considerations ...................................................................... 496 
4.1.3.2.2.  Substances difficult to test ................................................................. 496 
4.1.3.2.3.  Interpretation of data for aquatic toxicity, degradation and bioaccumulation

  498 

4.1.3.2.3.1.  Aquatic toxicity ......................................................................... 498 
4.1.3.2.3.2.  Degradation ............................................................................. 499 
4.1.3.2.3.3.  Bioaccumulation ....................................................................... 502 
4.1.3.2.4.  Using weight of evidence in evaluations in the context of C&L ................ 503 
4.1.3.2.4.1.  General aspects of weight of evidence ......................................... 503 
4.1.3.2.4.2.  Guidance on WoE for data deficient substances ............................ 504 
4.1.3.2.4.3.  Guidance on WoE for substances for which more than one valid piece 

of data is available for a given data element ................................ 504 
4.1.3.2.4.4.  Outliers ................................................................................... 505 

 
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4.1.3.3. 

4.1.3.2.4.5.  Weight of evidence in degradation .............................................. 505 
4.1.3.2.4.6.  Weight of evidence in bioaccumulation ........................................ 505 
Classification categories and criteria........................................................ 506 
4.1.3.3.1.  Outline of the core classification system .............................................. 506 
4.1.3.3.2.  The ‘safety net’ ................................................................................ 510 
4.1.3.3.3.  Setting an M-factor for highly toxic substances ..................................... 511 
4.1.3.4.  Decision on classification: examples for substances .................................. 512 
4.1.3.4.1.  Example A: Hydrophilic substance, straightforward classification based on 

acute and chronic toxicity data ........................................................... 514 

4.1.3.4.2.  Example B: Hydrophilic substance, straightforward classification based on 

acute data, no chronic toxicity data available ....................................... 516 

4.1.3.4.3.  Example  C:  Moderately  water  soluble  substance,  straightforward 
classification  based  on  acute  data,  chronic  toxicity  data  available  for  two 
trophic levels only; combined set of (Q)SAR data and experimental data . 519 
4.1.3.4.4.  Example D: Substance with several toxicity data for a trophic level ......... 522 
4.1.3.4.5.  Example E: ‘Safety net’ classification category Chronic 4 ....................... 525 
4.1.3.4.6.  Example  F:  Substance  difficult  to  test,  toxicity  above  level  of  water 

solubility .......................................................................................... 527 
4.1.4.  Classification of mixtures hazardous to the aquatic environment ........................ 530 
4.1.4.1.  General considerations for classification of mixtures hazardous to the aquatic 

4.1.4.2. 
4.1.4.3. 

environment ........................................................................................ 530 
Information requirements ...................................................................... 531 
Classification  criteria  for  mixtures  hazardous  to  the  aquatic  environment 
based on test data on the mixture as a whole .......................................... 532 

4.1.4.4.  When  experimental  aquatic  toxicity  data  are  not  available  for  the  complete 

mixture: bridging principles ................................................................... 534 

4.1.4.5.  When hazard data (information on toxicity or classification) are available for 

all the components of the mixture .......................................................... 534 

4.1.4.6.  When hazard data (information on toxicity or classification) are available for 

only some components of the mixture ..................................................... 539 
4.1.4.7.  Decision on classification: examples for mixtures ...................................... 540 
4.1.4.7.1.  Example  A:  When  classification  data  are  available  for  some  or  all 
components  of  a  mixture:  straightforward  application  of  the  summation 
method ........................................................................................... 541 

4.1.4.7.2.  Example B1: When toxicity data on the mixture as a whole is available for 

all three trophic levels: classification based on test data for the mixture .. 543 

4.1.4.7.3.  Example B2: When information on the classification of the components is 
available and toxicity data on the mixture as a whole is available for some, 
but not all three trophic levels: use of the summation method ............... 545 

4.1.4.7.4.  Example C: When no data are available on the mixture as a whole and its 
components, but test data are available on a similar tested mixture: use of 
the bridging principles – dilution with water ......................................... 547 

4.1.4.7.5.  Example D: When test data are available for some, but not all components 
of the mixture: use of the additivity formula and of the summation method
  548 

4.1.5.  Metal and metal compounds .......................................................................... 552 
4.1.6.  Hazard communication for hazards to the aquatic environment .......................... 552 
4.1.7.  References .................................................................................................. 554 

5.  PART 5: ADDITIONAL HAZARDS ................................................... 555 

5.1.  HAZARDOUS TO THE OZONE LAYER ....................................................... 555 

 
 
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ANNEXES .......................................................................................... 556 

I.3 

I.2.3 

I.2.2 

I.2.1 

I.1 
I.2 

I.2.2.1 
I.2.2.2 

I.2.1.1 
I.2.1.2 

I.2.3.1 
I.2.3.2 

I  ANNEX I: AQUATIC TOXICITY ................................................................... 556 
Introduction ................................................................................................. 556 
Description of tests ....................................................................................... 556 
Fish tests ............................................................................................. 557 
Acute testing .................................................................................... 557 
Chronic testing ................................................................................. 558 
Tests with Aquatic Crustacea ................................................................. 559 
Acute testing .................................................................................... 559 
Chronic testing ................................................................................. 560 
Algae / other aquatic plant tests ............................................................. 560 
Tests with algae ............................................................................... 560 
Tests with aquatic macrophytes .......................................................... 561 
Aquatic toxicity concepts ............................................................................... 561 
Acute toxicity ....................................................................................... 561 
Chronic toxicity .................................................................................... 562 
Exposure regimes ................................................................................. 563 
Test media for algae and Lemna ............................................................. 563 
Use of substance categorisation (read-across and grouping) and (Q)SARs for 
classification and labelling ..................................................................... 563 
Substances which are difficult to test .............................................................. 563 
Unstable substances ............................................................................. 564 
Poorly soluble substances ...................................................................... 564 
Other factors contributing to concentration loss ........................................ 565 
Perturbation of the test media ................................................................ 565 
Complex substances ............................................................................. 566 
References .................................................................................................. 566 

I.4.1 
I.4.2 
I.4.3 
I.4.4 
I.4.5 

I.3.1 
I.3.2 
I.3.3 
I.3.4 
I.3.5 

I.4 

I.5 

II.2.1 

II.1 
II.2 

II.2.2 
II.2.3 

II.2.1.1 
II.2.1.2 

II  ANNEX II: RAPID DEGRADATION .............................................................. 568 
Introduction ................................................................................................. 568 
Interpretation of degradability data ................................................................ 568 
Ready biodegradability .......................................................................... 568 
Concentration of test substance .......................................................... 569 
Time window .................................................................................... 569 
BOD5/COD ........................................................................................... 570 
Other convincing scientific evidence ........................................................ 570 
Aquatic simulation tests .................................................................... 570 
II.2.3.1 
II.2.3.2 
Field investigations ........................................................................... 571 
II.2.3.3  Monitoring data ................................................................................ 571 
Inherent and Enhanced Ready Biodegradability tests ............................ 571 
II.2.3.4 
Sewage treatment plant simulation tests ............................................. 572 
II.2.3.5 
Soil and sediment degradation data .................................................... 572 
II.2.3.6 
Anaerobic degradation data ............................................................... 572 
II.2.3.7 
Hydrolysis ........................................................................................ 572 
II.2.3.8 
II.2.3.9 
Photochemical degradation ................................................................ 572 
II.2.3.10  Estimation of degradation .................................................................. 573 
II.2.3.11  Volatilisation .................................................................................... 573 
No degradation data available ................................................................ 573 
General interpretation problems ..................................................................... 573 
Complex substances ............................................................................. 573 

II.3.1 

II.2.4 

II.3 

 
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II.3.2 
II.3.3 
II.3.4 
II.3.5 
II.3.6 

Availability of the substance ................................................................... 574 
Test duration less than 28 days .............................................................. 574 
Primary biodegradation ......................................................................... 574 
Conflicting results from screening tests ................................................... 575 
Variation in simulation test data ............................................................. 575 
Decision scheme .......................................................................................... 576 
References .................................................................................................. 577 

II.4 
II.5 

III.3 

III.2.2 

III.2.1 

III.1 
III.2 

III  ANNEX III: BIOACCUMULATION ................................................................ 578 
Introduction ................................................................................................. 578 
Interpretation of bioconcentration data ........................................................... 578 
Bioconcentration factor (BCF) ................................................................. 579 
III.2.1.1  BCF in different test species ............................................................... 579 
III.2.1.2  Use of radio-labelled substances ......................................................... 580 
Octanol-water-partitioning coefficient (Kow) .............................................. 580 
III.2.2.1  Experimental determination of Kow ...................................................... 581 
III.2.2.2  Use of (Q)SARs for determination of log Kow and BCF............................. 581 
Chemical classes that need special attention with respect to BCF and Kow values .. 581 
Substances difficult to test ..................................................................... 581 
Poorly soluble and complex substances ................................................... 582 
High molecular weight substances .......................................................... 582 
Surface-active substances (surfactants) .................................................. 582 
III.3.4.1  Octanol-water-partition coefficient (Kow) .............................................. 583 
Conflicting data and lack of data..................................................................... 583 
Conflicting BCF data .............................................................................. 583 
Conflicting log Kow data ......................................................................... 583 
Expert judgement ................................................................................. 583 
Decision scheme .......................................................................................... 583 
References .................................................................................................. 585 

III.3.1 
III.3.2 
III.3.3 
III.3.4 

III.4.1 
III.4.2 
III.4.3 

III.5 
III.6 

III.4 

IV.2.2 

IV.2.1 

IV.1 
IV.2 

IV  ANNEX IV: METALS AND INORGANIC METAL COMPOUNDS ............................ 586 
Introduction ................................................................................................. 586 
Application of aquatic toxicity data and solubility data for classification ............... 588 
Interpretation of aquatic toxicity data ..................................................... 588 
IV.2.1.1  Metal complexation and speciation ...................................................... 590 
Interpretation of solubility data .............................................................. 590 
IV.2.2.1  Assessment of existing data ............................................................... 590 
IV.2.2.2  Screening T/D test for assessing solubility of metal compounds .............. 591 
Full T/D test for assessing solubility of metals and metal compounds ...... 591 
IV.2.2.3 
Comparison of aquatic toxicity data and solubility data .............................. 592 
Assessment of environmental transformation ................................................... 592 
Bioaccumulation ........................................................................................... 594 
Classification strategies for metals and metal compounds .................................. 595 
Introduction ......................................................................................... 595 
Classification strategies for metals .......................................................... 595 
IV.5.2.1  Classification strategy for determining acute aquatic hazard for metals ... 595 
IV.5.2.2  Classification strategy for determining long-term aquatic hazard for metals

IV.3 
IV.4 
IV.5 

IV.5.1 
IV.5.2 

IV.2.3 

  596 

IV.5.2.2.1  Approach based on available chronic toxicity reference data .................. 596 
IV.5.2.2.2  The surrogate approach ..................................................................... 597 
Classification strategies for metal compounds .......................................... 600 

IV.5.3 

 
 
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IV.5.3.1  Classification  strategies  for  determining  acute  aquatic  hazard  for  metal 

compounds ...................................................................................... 600 

IV.5.3.2  Classification strategy for determining long-term aquatic hazard for metal 

IV.5.4 
IV.5.5 
IV.5.6 

compounds ...................................................................................... 601 
IV.5.3.2.1  Approach based on available chronic toxicity reference data .................. 602 
IV.5.3.2.2  The surrogate approach ..................................................................... 603 
Setting M-factors for metals and inorganic metal compounds ..................... 606 
Particle size and surface area ................................................................. 607 
Classification of mixtures of metals and metal compounds ......................... 609 
IV.5.6.1  Classification of alloys and complex metal containing materials .............. 609 
References .................................................................................................. 610 
Decision on classification: examples for metals and metal compounds ................ 611 

IV.6 
IV.7 

IV.7.1 

IV.7.2 

IV.7.3 

IV.7.3.1 

Example A: Soluble metal compound with acute and chronic toxicity data and 
no evidence of rapid environmental transformation (Me2 (SO4)2). ............... 612 
Example  B:  Poorly  soluble  metal  compound  with  acute  and  chronic  toxicity 
data, transformation/dissolution data at 7 days (low loading rate) and at 28 
days  (only  low  and  medium  loading  rates)  and  no  evidence  of  rapid 
environmental transformation ................................................................ 615 
Example C: Metal in powder and massive form with acute and chronic toxicity 
data and Transformation/Dissolution data at 7  days (low, medium and high 
loading rates) and at 28 days (only the high loading rate) and no evidence of 
rapid environmental transformation ........................................................ 619 
Explanatory note to Example C - Critical Surface Area (CSA) approach .... 624 

IV.7.4 

Example  D:  Hazard  classification  of  a  soluble  metal  salt:  the  case  of  rapid 
environmental transformation  through speciation in the water column ....... 626 

V  ANNEX V: COLLECTION OF INTERNET LINKS FOR THE USERS OF THE GUIDANCE

 ........................................................................................................ 630 

VI  ANNEX  VI:  BACKGROUND  DOCUMENT  TO  THE  GUIDANCE  FOR  SETTING 
SPECIFIC  CONCENTRATION  LIMITS  FOR  SUBSTANCES  CLASSIFIED  FOR 
REPRODUCTIVE TOXICITY ACCORDING TO REGULATION (EC) NO 1272/2008631 
Executive summary ...................................................................................... 631 
Introduction ................................................................................................. 632 

VI.1 
VI.2 

VI.2.1 

VI.2.2 

VI.2.3 

VI.2.4 

VI.2.4.1 
VI.2.4.2 

General description of the classification system for reprotoxic substances and 
mixtures .............................................................................................. 632 
Description of the process for the development of a method to set SCLs for 
reproductive toxic substances ................................................................ 633 
Considering potency in setting specific concentration limits for various health 
hazards ............................................................................................... 634 
Parameters for potency for reproductive toxicity ....................................... 635 
Potency parameters for developmental toxicants (Muller et al, 2012) ...... 635 
Potency  parameters  for  substances  with  an  adverse  effect  on  sexual 
function and fertility (Muller et al, 2012).............................................. 637 
VI.2.4.3  Conclusions on the most appropriate parameter for potency .................. 639 
Modifying factors .......................................................................................... 640 
Boundaries of the potency groups ........................................................... 640 
Non-modifying factors ................................................................................... 641 
Species and strains ............................................................................... 641 
Systemic or maternal toxicity ................................................................. 641 
Mutagenicity ........................................................................................ 641 
Volatility .............................................................................................. 641 
Potency groups and specific concentration limits .............................................. 642 

VI.3.1 

VI.4.1 
VI.4.2 
VI.4.3 
VI.4.4 

VI.3 

VI.4 

VI.5 

 
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VI.5.1 

Justification  of  the  proposed  potency  boundaries  and  specific  concentration 
limits 642 

VI.5.1.1  General considerations on potency groups ........................................... 642 
VI.5.1.1.1  Legal requirements ........................................................................... 642 
VI.5.1.1.2  Scientific results of the database analysis ............................................ 642 
VI.5.1.1.3  Policy related considerations and proposed method ............................... 643 
VI.5.1.1.4  Other methods considered ................................................................. 643 
VI.5.1.2 
Justification of the boundaries between the three potency groups ........... 644 
VI.5.1.3  Concentration limits for Category 1 and Category 2 substances .............. 648 
Assigning SCLs ..................................................................................... 649 
References .................................................................................................. 649 

VI.5.2 

VI.6 

VII   ANNEX  VII:  RELATION  BETWEEN  TRANSPORT  AND  CLP  CLASSIFICATION 

REGARDING PHYSICAL HAZARDS .......................................................... 650 

 
 
 
 
 
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Table of Tables 

Table 1.1 

Table 1.2 
Table 1.3 
Table 1.4 
Table 1.5 
Table 1.6  

Table 2.1 

Table 2.2 

Table 2.3 

Table 2.4 

Table 3.1 
Table 3.2 
Table 3.3 
Table 3.4 
Table 3.5 
Table 3.6 
Table 3.7  
Table 3.8 
Table 3.9 

Table 3.10 
Table 3.11 
Table 3.12 
Table 3.13 
Table 3.14 
Table 3.15  

Table 3.16 
Table 3.17 
Table 3.18 
Table 3.19 
Table 4.1 

Table IV. 1 
Table IV. 2 
Table IV. 3 

Table VI. 1 

Possibilities for setting SCL for health hazards addressed in relevant 
sections of the guidance ..................................................................... 65 
Ingredients in Mixture A ..................................................................... 81 
Ingredient 'Fragrance mixture' ............................................................ 82 
Ingredients in Mixture B ..................................................................... 84 
Ingredients ‘base powder’ ................................................................... 85 
Hazard classes where the translation tables in Annex VII to CLP indicate 
that no direct translation was possible from DSD to CLP ......................... 86 
Examples of hazards, depending on the property of the emitted gas, when 
substances and mixtures are in contact with water ................................ 191 
Minimum mass loss of specimens after different exposure times 
(corresponding to the criterion of 6.25 mm/year) .................................. 231 
Minimum intrusion depths after exposure times (corresponding to the 
criterion of localized corrosion of 6.25 mm/year) ................................... 231 
Examples of classified and non classified substances and mixtures in Class 
2.16 ................................................................................................. 236 
Types of Human Studies ..................................................................... 341 
Relatively high or low frequency of occurrence of skin sensitisation* ........ 341 
Relatively high or low exposure * ........................................................ 342 
Sub-categorisation decision table ......................................................... 342 
Definition of significant skin sensitising effect ........................................ 344 
Skin Sensitisation Potency in the Mouse Local Lymph Node Assay ............ 348 
Potency on basis of the Guinea Pig Maximisation Test ............................ 349 
Potency on basis of the Buehler assay .................................................. 349 
Skin sensitising potency for substances and recommendations on 
concentration limits ........................................................................... 350 
Example of the calculation of the ED10 .................................................. 411 
Example on the calculation of the ED10 ................................................. 411 
Example on the calculation of the ED10 for testicular effects (N=10) ......... 412 
Boundaries of the potency groups. ....................................................... 413 
SCLs for substances in each potency group and classification category ..... 417 
Hazard statements for reproductive toxicity: H360 and H361, and their 
specifications .................................................................................... 425 
Equivalent guidance values for 28-day and 90-day studies...................... 466 
Food conversion ................................................................................ 469 
Conversion drinking water .................................................................. 469 
Inclusion of route of exposure in Hazard statement ................................ 472 
Hazard statement Codes relevant for the hazard class Hazardous to the 
Aquatic Environment .......................................................................... 554 

 M-factors for inorganic substances ...................................................... 606 
 Acute toxicity data deemed reliable for ‘Metal’ are presented as mg/L Me  628 
 Chronic toxicity data deemed reliable for ‘Metal’ are presented as mg/L 
Me ................................................................................................... 628 

 Average values (assuming log/normal distribution) (in mg/kg bw/day) 
and potency differences for parameters for all developmental toxicants of 
the database (Muller et al, 2012) ......................................................... 636 

 
 
 
36 

Table VI. 2 

Table VI. 3 

Table VI. 4 

Table VI. 5 
Table VI. 6 

Table VI. 7 

Table VI. 8 

Guidance on the Application of the CLP Criteria 

Version 6.0 – Jan 2024 

 Average values (assuming log/normal distribution) (in mg/kg bw/day) 
and potency differences for parameters for developmental toxicants 
(N=44) with all 6 parameters (Muller et al, 2012) .................................. 636 
 Average values (assuming log/normal distribution) (in mg/kg bw/day) 
and potency differences for parameters for all fertility toxicants of the 
database .......................................................................................... 637 
 Average values (assuming log/normal distribution) (in mg/kg bw/day) 
and potency differences for parameters for fertility toxicants (N=34) with 
all 6 parameters ................................................................................ 639 
 Boundaries of the potency groups ....................................................... 640 
 Percentages of substances in the three potency groups using the ED10 
and some of the modifying factors for different boundaries of the potency 
groups and considering the saturated vapour concentration of low potency 
substances ....................................................................................... 645 
 Percentages of substances in the three potency groups using the ED10 
and some of the modifying factors but not volatility for different borders 
of the potency groups ........................................................................ 647 
 SCLs for substances in each potency group and classification category .... 648 

Tabel VII. 1 

Relation between transport and CLP classifications regarding physical 
hazards ............................................................................................ 650 

Table of Figures 

Figure 1.1 
Figure 1.2  

Figure 1.3  

Figure 1.4  

Figure 2.1  
Figure 2.2  
Figure 2.3  

Figure 2.4  
Figure 2.5  
Figure 2.6  
Figure 2.7  
Figure 2.8  
Figure 2.9  
Figure 2.10  
Figure 2.11  

Figure 2.12  
Figure 2.13  
Figure 2.14  
Figure 2.15  

How to classify a mixture .................................................................... 68 
Application of the bridging principle: dilution for determining the acute 
toxicity classification of a mixture ........................................................ 71 
Application of the bridging principle: interpolation for determining the 
aquatic acute hazard classification of a mixture ..................................... 72 
Application of the bridging principle: substantially similar mixtures for 
determining the skin irritation classification of a mixture ........................ 73 
Decision logic for oxidising gases (Decision logic 2.4 of GHS) .................. 133 
Decision logic for gases under pressure (Decision logic 2.5 of GHS) ......... 139 
Amended GHS decision logic for flammable liquids to include derogations 
for gas oil, diesel, light heating, sustained combustibility and for phrases 
EUH018, EUH209 and EUH209A .......................................................... 147 
Decision logic for flammable solids (Decision logic 2.7 of GHS) ................ 154 
Decision logic 2.8 for self-reactive substances and mixtures .................... 164 
Decision logic for self-reactive substance example: NP, technically pure ... 169 
Decision logic for pyrophoric liquids (Decision logic 2.9 of GHS) ............... 172 
Decision logic for pyrophoric solids (Decision logic 2.10 of GHS) .............. 178 
Extrapolation towards large volumes .................................................... 187 
Volume dependency of the critical temperature for charcoal .................... 190 
Decision logic for substances and mixtures which, in contact with water, 
emit flammable gases (Decision logic 2.12 of GHS) ................................ 196 
Decision logic for oxidising liquids (Decision logic 2.13 of GHS) ............... 204 
Decision logic for oxidising solids (Decision logic 2.14 of GHS) ................ 212 
Decision logic 2.15 for organic peroxides .............................................. 221 
Potential pH (also called Pourbaix) diagram for iron in water at 25 °C, 
indicating stable form of the Fe element and implicitly, corrosion domains  227 

 
 
 
 
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Figure 2.16  

Figure 2.17  

Figure 2.18 

Figure 3.1  
Figure 3.2  
Figure 3.3  

Figure 3.4  
Figure 3.5  

Figure 3.6  
Figure 3.7  
Figure 3.8  

Figure IV. 1 
Figure IV. 2 

Figure IV. 3 

Figure IV. 4 

Figure IV. 5 

Figure IV. 6 

Example of testing equipment available on the market to perform UN Test 
C.1 .................................................................................................. 233 
Decision logic for substances and mixtures corrosive to metals (Decision 
logic 2.16 of GHS) ............................................................................. 234 
Example of corroded metal plates after testing according to UN Test C.1 
for a classified mixture ....................................................................... 237 
Tiered evaluation for skin corrosion/skin irritation .................................. 279 
Simplified illustration of the relative weight of the available information ... 285 
Mixture without human or animal data on skin corrosion/irritation or 
relevant data from similar tested mixtures, pH is  2 or  11.5 ................ 291 
Tiered evaluation for serious eye damage/eye irritation .......................... 309 
Mixture not classified as Skin Corr. 1 and without animal or human data 
on serious eye damage/eye irritation or relevant data from similar tested 
mixtures, pH is  2 or  11.5 ............................................................... 319 
Procedure for setting SCL for reproductive toxicity ................................. 409 
Comparison between the NOAEL and the ED versus the guidance values .. 444 
Comparison between the NOAEL and the ED versus the guidance values .. 468 

Classification strategy for determining acute aquatic hazard for metals .... 596 
Classification strategy for determining long-term aquatic hazard for 
metals .............................................................................................. 598 
Classification strategy for determining long-term aquatic hazard for 
metals in absence of appropriate chronic toxicity reference and/or T/Dp 
data ................................................................................................. 599 
Classification strategy for determining acute aquatic hazard for metal 
compounds ....................................................................................... 601 
Classification strategy for determining long-term aquatic hazard for metal 
compounds ....................................................................................... 604 
Classification strategy for determining long-term aquatic hazard for metal 
compounds in absence of appropriate chronic toxicity reference and/or 
T/Dp data ......................................................................................... 605 

 
 
 
 
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LIST OF ABBREVIATIONS 

Standard term / 
Abbreviation  

Explanation  

ADD 

ADN 

ADR 

ANE 

ASTM 

ATE 

ATP 

BAM 

BCF 

BCOP 

BfR 

Directive 75/324/EEC on aerosol dispensers2 

European Agreement concerning the International Carriage of 
Dangerous Goods by Inland Waterways (Accord européen relatif au 
transport international des marchandises dangereuses par voie de 
navigation intérieure)3 

European Agreement concerning the International Carriage of 
Dangerous Goods by Road (Accord européen relatif au transport 
international des marchandises dangereuses par route)4 

Ammonium Nitrate Emulsion 

American Society for the Testing of Materials 

Acute Toxicity Estimate 

Adaptation to Technical Progress (ATP) to the CLP Regulation 

Bundesanstalt für Materialforschung und -prüfung (Federal Institute 
for Materials Research and Testing) 

Bioconcentration Factor 

Bovine Corneal Opacity and Permeability test 

German Federal Institute for Risk Assessment 

BfR DSS 

Decision support system by the German Federal Institute for Risk 
Assessment 

BMF 

BOD 

BP 

bw 

Biomagnification factor  

Biological Oxygen Demand 

Boiling point 

Body weight 

2 Directive (75/324/EEC) of the Council on the approximation of the laws of the Member States relating to 
aerosol dispensers [OJ L 147, 9.6.1975, p.40]. Directive as last amended by Commission Directive 
2013/10/EU [ OJ L 77, 20.03.2013, p.20]. 

3 European Agreement concerning the International Carriage of Dangerous Goods by Inland Waterways, 
concluded at Geneva on 26 May 2000, as amended. 

4 European Agreement concerning the International Carriage of Dangerous Goods by Road, concluded at 
Geneva on 30 September 1957, as amended. 

 
 
 
 
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Standard term / 
Abbreviation  

Explanation  

C&L 

CA 

cATpE 

CLP 

CNS 

COD 

CSA 

CSR 

DIN 

DNA 

DOC 

DPD 

DSD 

EC3  

ECHA 

ECVAM 

Classification and Labelling 

Competent Authority 

Converted Acute Toxicity point Estimate 

Regulation (EC) No 1272/2008 on classification, labelling and 
packaging of substances and mixtures5 

Central Nervous System 

Chemical Oxygen Demand 

Chemical Safety Assessment 

Chemical Safety Report 

Deutsches Institut für Normung (German Institute for 
Standardisation)  

Deoxyribonucleic Acid 

Dissolved Organic Carbon 

Directive 1999/45/EC on the classification and labelling of 
Dangerous Preparations6 

Directive 67/548/EEC on the classification and labelling of 
Dangerous Substances7 

Effective Concentration inducting a stimulation index of 3 in the 
LLNA test 

European Chemicals Agency, Helsinki (https://echa.europa.eu/) 

European Centre for the Validation of Alternative Methods 
(http://ihcp.jrc.ec.europa.eu/our_labs/eurl-ecvam) 

ED 

Effective Dose  

5 Regulation (EC) No 1272/2008 of the European Parliament and Council of 16 December 2008 on 
classification, labelling and packaging of substances and mixtures, amending and repealing Directives 
67/548/EEC and 1999/45/EC and amending Regulation (EC) No 1907/2006 [OJ L 353, 31.12.2008, p. 1]. 

6 Directive 1999/45/EC of the European Parliament and of the Council of 31 May 1999 concerning the 
approximation of the laws, regulations and administrative provisions of the Member States relating to the 
classification, packaging and labelling of dangerous preparations [OJ L 200, 30.7.1999, p. 1]. 

7 Council Directive 67/548/EEC of 27 June 1967 on the approximation of laws, regulations and 
administrative provisions relating to the classification, packaging and labelling of dangerous substances 
[OJ 196, 16.8.1967, p. 1]. 

 
 
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Standard term / 
Abbreviation  

Explanation  

EN 

ERV 

ESAC 

EUH 

f/F 

FP 

GCL 

GHS 

GJIC 

GLP 

GnRH 

GPMT 

GV 

Hb 

A European Standard 

Ecotoxicity Reference Value 

ECVAM Scientific Advisory Committee  
(https://eurl-ecvam.jrc.ec.europa.eu/about-ecvam) 

The hazard statements carried through from DSD and DPD, which 
are not yet included in the GHS are codified as ‘EUH’ 

Female 

Flash point 

General Concentration Limits 

Globally Harmonised System of Classification and Labelling of 
Chemicals8 

Gap junction intercellular communication 

Good Laboratory Practice 

Gonadotropin-releasing hormone 

Guinea Pig Maximisation Test 

Guidance Value 

Haemoglobin 

HET-CAM 

Hen's Egg Test on Chorio-allantoic Membrane 

HS (or H 
statement) 

Hazard statement 

HSM 

Ht 

IARC 

Human skin model 

Hematocrit   

International Agency for Research on Cancer (http://www.iarc.fr/) 

IATA DGR 

International Air Transport Association , Dangerous Goods 
Regulations Manual 

IBC 

Intermediate Bulk Container 

8 Globally Harmonised System of Classification and Labelling of Chemicals (GHS), Fifth revised edition, 
United Nations, New York and Geneva, 2013. 

 
 
 
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Standard term / 
Abbreviation  

Explanation  

ICAO TI 

ICE 

IEC 

International Civil Aviation Organization (Technical Instructions for 
the Safe Transport of Dangerous Goods by Air) 

Isolated Chicken Eye 

International Electrotechnical Commission (http://www.iec.ch/) 

IMDG Code 

International Maritime Dangerous Goods Code 

IMO 

IPCS 

IR&CSA 

IRE 

ISO 

ITDG 

ITS 

Kow 

LEL 

International maritime Organisation 

International Programme on Chemical Safety (joint programme of 
WHO, ILO and UNEP) 

Guidance on Information Requirements and Chemical Safety 
Assessment, ECHA 
(http://guidance.echa.europa.eu/docs/guidance_document/informa
tion_requirements_en.htm) 

Isolated Rabbit Eye 

International Organisation for Standardization 

Directive 2008/68 on the Inland Transport of Dangerous Goods9 

Integrated Testing Strategy 

The n-octanol/water partition coefficient 

Lower Explosion Limit 

LD50/LC50 

Median (50%) lethal dose/concentration 

LFL 

LLNA 

Lower Flammability Limit 

Local Lymph Node Assay  

LO (A) EL/C 

Lowest Observed (Adverse) Effect Level/Concentration 

LVET 

m/M 

Low Volume Eye Test 

Male 

MetHB 

Methaemoglobinaemia 

9 Directive 2008/68/EC of the European Parliament and of the Council of 24 September 2008 on the inland 
transport of dangerous goods, implementing the European Agreement concerning the International 
Carriage of Dangerous Goods by Road (ADR), the Regulations concerning the International Carriage of 
Dangerous Goods by Rail (RID) and the European Agreement concerning the International Carriage of 
Dangerous Goods by Inland Waterways (ADN) [OJ L 260, 30.9.2008, p. 13]. 

 
 
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Standard term / 
Abbreviation  

Explanation  

MetHb 

Methaemoglobin 

M-factor 

Multiplying factor 

MP 

MSCA 

MTD 

MW 

n.a. 

NC 

NE 

Melting Point 

Member State Competent Authority 

Maximal Tolerated Dose 

Molecular weight 

Not available  

No Classification 

Narcotic effect(s) 

NO(A)EC 

No Observed  (Adverse) Effect Concentration 

NO(A)EL 

No Observed  (Adverse) Effect Level 

ODS 

ODP 

OECD 

Ozone Depleting Substances 

Ozone Depleting Potential 

Organisation for Economic Co-operation and Development 

OECD TG 

OECD Test Guideline 

All Test Guidelines are available at the OECD homepage: 
http://www.oecd.org/document/40/0,3343,en_2649_34377_37051
368_1_1_1_1,00.html 

OP  

Oxidising Power  

P statement  
(or PS) 

PB/PK 

PPARα 

PS (or P 
statement) 

Precautionary statement 

Physiologically-based pharmacokinetic 

Peroxisome proliferator-activated receptor-alpha 

Precautionary statement 

(Q)SAR 

(Quantitative) Structure Activity Relationship 

 
 
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Standard term / 
Abbreviation  

Explanation  

REACH 

RID 

RIP 

RTI 

Regulation (EC) No 1907/2006 of the European Parliament and of 
the Council concerning the Registration, Evaluation, Authorisation 
and Restriction of Chemicals10 

Règlement concernant le transport international ferroviaire de 
marchandises dangereuses (Regulations concerning the 
International Carriage of Dangerous Goods by Rail)11 

REACH Implementation Project 

Respiratory tract irritation 

SADT 

Self-Accelerating Decomposition Temperature 

SCL 

SDS 

SIFT 

SSD 

Specific Concentration Limit 

Safety Data Sheet 

Skin integrity function test 

Species Sensitivity Distribution 

STOT-SE 

Specific Target Organ Toxicity - Single Exposure 

STOT-RE 

Specific Target Organ Toxicity - Repeated Exposure 

SVC 

T25 

T95 

T/D 

T/Dp 

TER 

TG 

Saturated Vapour Concentration 

The daily dose (in mg/kg bodyweight/day) inducing a tumour 
incidence of 25 % upon lifetime exposure 

Inhalation chamber equilibrium (attained at the time t95) 

Transformation/Dissolution 

Transformation/Dissolution Protocol 

Transcutaneous electrical resistance 

Test Guideline 

10 Regulation (EC) No 1907/2006 of the European Parliament and of the Council of 18 December 2006 
concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), establishing 
a European Chemicals Agency, amending Directive 1999/45/EC and repealing Council Regulation (EEC) No 
793/93 and Commission Regulation (EC) No 1488/94 as well as Council Directive 76/769/EEC and 
omission of Directives 91/155/EEC, 93/67/EEC, 93/105/EC and 2000/21/EC. [OJ L 396, 30.12.2006 p.1.] 
[Corrigendum: OJ L 136, 29.5.2007 p.3]. 

11 Regulations concerning the International Carriage of Dangerous Goods by Rail, appearing as Appendix C 
to the Convention concerning International Carriage by Rail (COTIF) concluded at Vilnius on 3 June 1999, 
as amended. 

 
 
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Standard term / 
Abbreviation  

Explanation  

TGD 

TM 

Technical Guidance Document 

Test Method as listed in the Test Methods Regulation 

Test Methods 
Regulation 

Regulation (EC) No 440/2008 laying down test methods pursuant 
to the REACH Regulation12 

TOPKAT 

Mathematical (Q)SAR model for prediction of skin 
corrosion/irritation 

UDP 

UDPG 

UEL 

UFL 

UGT 

UN 

UN-MTC 

UN RTDG Model 
Regulations 

Uridine 5'-diphosphate 

Uridine diphosphate glucuronyl 

Upper Explosion Limit 

Upper Flammability Limit 

UDP-glucuronyltransferase 

United Nations 

The UN Manual of Tests and Criteria contains criteria, test methods 
and procedures to be used for classification of dangerous goods 
according to the provisions of Parts 2 and 3 of the United Nations 
Recommendations on the Transport of Dangerous Goods, Model 
Regulations, as well as of chemicals presenting physical hazards 
according to the Globally Harmonized System of Classification and 
Labelling of Chemicals (GHS). More information and the latest 
revision are available at: 
http://www.unece.org/trans/danger/publi/manual/manual_e.html. 

UN Recommendations on the Transport of Dangerous Goods - 
Model Regulations. It covers all modal transport regulations (ADR, 
RID, ADN, IMDG and ITDG). It is regularly updated and amended 
every two years.  

More information and the latest revision are available at: 
http://www.unece.org/trans/danger/publi/unrec/rev13/13nature_e.
html  

UNSCEGHS (or 
SCEGHS) 

United Nations SubCommittee of Experts on the Globally 
Harmonised System 
(http://www.unece.org/trans/danger/publi/ghs/ghs_welcome_e.ht
ml) 

12 Council Regulation (EC) No 440/2008 of 30 May 2008 laying down test methods pursuant to Regulation 
(EC) No 1907/2006 of the European Parliament and of the Council on the Registration, Evaluation, 
Authorisation and Restriction of Chemicals (REACH) [OJ L 142, 31.5.2008, p. 1] [Corrigendum: OJ L 143, 
3.6.2008, p. 55]. 

 
 
 
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Standard term / 
Abbreviation  

Explanation  

UNSCETDG (or 
SCETDG) 

United Nations SubCommittee of Experts on the Transport of 
Dangerous Goods 
(http://www.unece.org/trans/danger/danger.htm) 

US-FHSA 

UVCB 

VDI 

VP 

WAF 

WoE 

WSF 

United States Federal Hazardous Substance Act - 40 Code of 
Federal Regulations 1500.41 

Substances of unknown or variable composition, complex reaction 
products or biological materials 

Verein Deutscher Ingenieure (The Association of German 
Engineers) 

Vapour Pressure 

Water Accommodated Fraction 

Weight of Evidence 

Water soluble fraction 

NOTEs to the reader:  

In this document, text cited from Regulation (EC) No 1272/2008 is indicated in green 
boxes in italic font. 

  This symbol highlights text to be noted. 

 
 
 
 
 
 
 
 
 
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1.  PART 1: GENERAL PRINCIPLES FOR CLASSIFICATION AND 

LABELLING 

1.1.  INTRODUCTION 

1.1.1.  The objective of the guidance document 

This document is a comprehensive technical and scientific guidance on the application of 
Regulation (EC) No 1272/2008 on the classification, labelling and packaging of substances and 
mixtures13, hereafter referred to as CLP. 

CLP amended the Dangerous Substance Directive 67/548/EEC14 (DSD), the Dangerous 
Preparations Directive 1999/45/EC15 (DPD) and Regulation (EC) No 1907/200616 (REACH), and 
repealed DSD and DPD from 1 June 2015 (CLP Article 61). CLP was implemented based on the 
United Nations’ Globally Harmonised System of Classification and Labelling of Chemicals (UN 
GHS) without lowering the protection of human health and the environment, compared to the 
classification, labelling and packaging system in DSD and DPD. The implementation of GHS into 
CLP followed various declarations made by the Community to confirm its intention to contribute 
to GHS development and to implement GHS into EU law.  

A core principle of CLP is self-classification of a substance or mixture by the manufacturer, 
importer or downstream user (CLP Article 4(3) and Recital 17), which involves identification of 
the hazards of the substance or mixture followed by classification as a result of the comparison 
of the hazard information with the criteria in CLP. This guidance will enable industry to self-
classify chemicals and to provide appropriate hazard communication information to the target 
populations potentially handling the substance or mixture or exposed to it. For substances of 
particular concern (carcinogens, mutagens, substances toxic for reproduction (CMRs) and 
respiratory sensitisers) or for other substances where EU-wide action is needed, CLP sets out a 
system for formal harmonisation of classifications at EU level. 

Given that many provisions under REACH are linked to classification, the implementation of 
REACH and CLP is interlinked and should be planned and applied in tandem. General advice on 
the implementation of CLP is available in the ECHA’s Introductory Guidance on the CLP 
Regulation, available on the ECHA website (http://echa.europa.eu/web/guest/guidance-
documents/guidance-on-clp).  

The objective of this document is to provide detailed guidance on the application of the CLP 
criteria for physical, health and environmental hazards.  

13 Regulation (EC) No 1272/2008 of the European Parliament and of the Council on classification, labelling 
and packaging of substances and mixtures, amending and repealing Directives 67/548/EEC and 
1999/45/EC, and amending Regulation (EC) No 1907/2006 [OJ L 353, 31.12.2008, p. 1]. 

14 Council Directive 67/548/EEC relating to the classification, packaging and labelling of dangerous 
substances, as amended [OJ 196, 16.8.1967, p. 1]. 

15 Directive 1999/45/EC as of 30 July 2002 of the European Parliament and of the Council relating to the 
classification, packaging and labelling of dangerous preparation, as amended [OJ L 200, 30.7.1999, p.1]. 

16 Regulation (EC) No 1907/2006 of the European Parliament and of the Council concerning the 
Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), establishing a European 
Chemicals Agency, amending Directive 1999/45/EC and repealing Council Regulation (EEC) No 793/93 and 
Commission Regulation (EC) No 1488/94 as well as Council Directive 76/769/EEC and omission of 
Directives 91/155/EEC, 93/67/EEC, 93/105/EC and 2000/21/EC. [OJ L 396, 30.12.2006 p.1.]  
[Corrigendum: OJ L 136, 29.5.2007 p.3]. 

 
 
 
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1.1.2.  Background  

The aim of classification and labelling is to identify the hazardous properties of a substance or a 
mixture by applying specific classification criteria to the available hazard data, and then to 
provide appropriate hazard labelling and information on safety measures. 

The EU has had a comprehensive system for the classification and labelling of dangerous 
substances and mixtures for over 40 years, in the past mainly DSD and DPD. In addition, the 
Safety Data Sheet (SDS) Directive 91/155/EEC17 required suppliers to provide more detailed 
information for professional users. These directives contributed to a single market in chemicals 
in the EU, based on a high level of protection of human safety and health and the environment. 

The GHS was developed worldwide to minimise differences between systems of different 
jurisdictions for classification and labelling of substances and mixtures. The GHS aims to 
contribute towards global efforts to provide protection from hazardous effects of chemicals and 
to facilitate trade. 

The GHS criteria for classifying hazardous substances and mixtures were developed taking into 
account existing systems for hazard classification, such as the EU supply and use system, the 
Canadian and US Pesticide systems, GESAMP18 hazard evaluation procedure, IMO19 Scheme for 
Marine Pollutants, the UN Recommendations on the Transport of Dangerous Goods (UN/RTGD), 
and the US Land Transport. These systems include supply and subsequent use of chemicals, the 
sea transport of chemical substances as well as transport of chemical substances by road and 
rail. The harmonised criteria are therefore intended to identify hazardous chemicals in a 
common way for use throughout all these systems. 

The GHS provides a basis for an internationally uniform information system on hazardous 
substances and mixtures. It provides harmonised criteria for classification and hazard 
communication measures for different target audiences, including consumers, workers and 
emergency responders, and in transport. It follows a ‘building block’ approach to enable 
jurisdictions to adopt the system according to the needs of their law and the various target 
audiences. However, although the final aim of GHS is to have a fully harmonised classification 
and labelling system worldwide, it is recognised that differences may persist between sectors ( 
e.g. transport, supply and use), but should not occur within a sector globally (section 1.1.3.1.5, 
UNSCEGHS, 6th revision). 

The GHS was agreed by the UN Committee of Experts on the Transport of Dangerous Goods and 
the Globally Harmonized System of Classification and Labelling of Chemicals (CETDG/GHS).  It 
was formally approved by the UN Economic and Social Council (UN ECOSOC) in July 2003 and 
published further in 2003 after a decade of negotiations. It is updated biannually. The changes 
in GHS are not authomatically reflected in the CLP Regulation. The latter is adapted and 
updated by the Commission via Adaptations to Technical Progress (ATPs - see Article 53(1) of 
CLP).  

1.1.3.  Hazard classification 

Hazard classification is a process involving the identification of information on the physical, 
health, environmental or other hazards of a substace or a mixture as set out in Annex I to CLP. 
This is followed by the comparison of the hazard information (including the severity of hazard) 
with defined criteria, in order to determine the classification of the substance or mixture. Thus, 

17 Council Directive 91/155/EEC relating to defining and laying down the detailed arrangements for the 
system of specific information relating to dangerous preparations and dangerous substances, as amended 
[OJ L 076, 22.03.1991, p. 35], repealed and replaced by Regulation (EC) No 1907/2006 as of 1 June 2007. 

18 Group of Experts on the Scientific Aspects of Marine Environmental Protection. 

19 International Maritime Organisation. 

 
 
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under CLP, a manufacturer, importer or downstream user will apply the following steps to arrive 
at a self-classification of a substance or a mixture: 

• 

identification of relevant available information regarding the potential hazards (including 
severity of hazard) of a substance or mixture; 

•  examination of the information gathered to assess whether it is relevant, reliable and 

sufficient for classification purposes;  

•  evaluation of the information (data) by applying the classification criteria in Annex I, CLP 

for each hazard class and differentiation; and 

•  decision on whether the hazard information for the substance or mixture meets the 

criteria for one or more hazard classes or differentiations and therefore decision on the  
classification of the substance or mixture as hazardous in relation to these hazard 
classes or differentiations (assignment of hazard categories, SCL(s), M-factor(s) and 
hazard statement(s) according to the provisions in Annex I, CLP). 

Preliminary information on identification of relevant data is provided in section 1.1.6 of this 
guidance document, while guidance on available test methods is provided in Part B of the ECHA 
Guidance document on Information Requirements and Chemical Safety Assessment (Chapters 
R.2 to R.4, IR&CSA), available on the ECHA Website 
(http://echa.europa.eu/web/guest/guidance-documents/guidance-on-information-requirements-
and-chemical-safety-assessment). Chapters R.7a/b/c of the same Guidance provide more 
detailed information and endpoint-specific guidance. 

Classification according to CLP is based on intrinsic hazards, i.e. the basic properties of a 
substance or mixture as determined in standard tests or by other means designed to identify 
hazards. It should be noted that for some hazard classes the intrinsic properties of a substance 
or mixture are not always the only aspects relevant for classification, e.g. explosives or aerosols 
for which classification is also package dependent, or aspiration hazard which may not be 
relevant for certain package types. As CLP is hazard-based, it does not take exposure into 
consideration in arriving at a classification. It should further be noted that classification of 
substances and mixtures may be required even when placed on the market in forms that are 
not hazardous. E.g. metals in massive form, alloys, mixtures containing polymers or 
elastomers, should be classified according to the criteria for e.g. toxic effects by inhalation but 
may not need to be labelled. 

1.1.4.  Who is responsible for the hazard classification 

CLP and REACH place the responsibility for hazard classification and related provisions such as 
packaging, hazard communication and SDS on the suppliers of substances and mixtures. Both 
substances and mixtures must be classified, labelled and packaged in accordance with CLP 
before placing them on the market. 

1.1.5.  Which substances and mixtures should be classified 

Substances and mixtures placed on the market fall within the scope of classification under CLP 
and should be evaluated in order to reach a decision as to whether or not the criteria are met 
and therefore if they should be classified. Substances are also subject to classification where 
they are subject to registration or notification under REACH, even if they are not placed on the 
market. 

However, a number of substances and mixtures are exempted from the requirements of the CLP 
Regulation as a whole (CLP Article 1): 

 
 
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• 

• 

radioactive substances and mixtures (Directive 96/29/Euroatom20); 

substances and mixtures which are subject to customs supervision, provided that they 
do not undergo any treatment or processing, and which are in temporary storage, or in a 
free zone or free warehouse with a view to re-exportation, or in transit; 

•  non-isolated intermediates; 

• 

substances and mixtures used in scientific experimentation, analysis or chemical 
research, provided they are not placed on the market and they are used under controlled 
conditions in accordance with EU workplace and environmental legislation; 

•  waste, as defined in Directive 2006/12/EC21; and 

• 

certain substances or mixtures in the finished state, intended for the final user:  

•  medicinal products, as defined in Directive 2001/83/EC22,  

•  veterinary medicinal products, as defined in Directive 2001/82/EC23,  

• 

cosmetic products, as defined in Directive 76/768/EEC24,  

•  medical devices as defined in Directive 90/385/EEC25 (active implantable medical 
devices) and 93/42/EEC26 (medical devices in general), which are invasive or 
used in direct physical contact with the human body, and in vitro diagnostic 
medical devices (Directive 98/79/EC27), and 

• 

food or feeding stuffs as defined in Regulation 178/200228, including when they 
are used as food additives within the scope of Directive 89/107/EEC29, as a 
flavouring in foodstuffs within the scope of Directive 88/388/EEC and Decision 

20 Council Directive 96/29/Euratom of 13 May 1996 laying down basic safety standards for the protection 
of the health of workers and the general public against the dangers arising from ionizing radiation [OJ L 
159, 29.6.1996, p. 1]. 

21 Directive 2006/12/EC of the European Parliament and of the Council of 5 April 2006 on waste [OJ L 114, 
27.4.2006, p. 9]. 

22 Directive 2001/83/EC of the European Parliament and of the Council of 6 November 2001 on the 
Community code relating to medicinal products for human use [OJ L 311, 28.11.2001, p. 67]. 

23 Directive 2001/82/EC of the European Parliament and of the Council of 6 November 2001 on the 
Community code relating to veterinary medicinal products [OJ L 311, 28.11.2001, p. 1]. 

24 Council Directive 76/768/EEC of 27 July 1976 on the approximation of the laws of the Member States 
relating to cosmetic products [OJ L 262, 27.9.1976, p. 169]. 

25 Council Directive 90/385/EEC of 20 June 1990 on the approximation of the laws of the Member States 
relating to active implantable medical devices [OJ L 189, 20.7.1990, p. 17]. 

26 Council Directive 93/42/EEC of 14 June 1993 concerning medical devices [OJ L 169, 12.7.1993, p. 1]. 

27 Directive 98/79/EC of the European Parliament and of the Council of 27 October 1998 on in vitro 
diagnostic medical devices [OJ L 331, 7.12.1998, p. 1]. 

28 Regulation (EC) No 178/2002 of the European Parliament and of the Council of 28 January 2002 laying 
down the general principles and requirements of food law, establishing the European Food Safety Authority 
and laying down procedures in matters of food safety [OJ L 31, 1.2.2002, p. 1]. 

29 Council Directive 89/107/EEC of 21 December 1988 on the approximation of the laws of the Member 
States concerning food additives authorized for use in foodstuffs intended for human consumption [OJ L 
40, 11.2.1989, p. 27]. 

 
 
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1999/217/EC30, as an additive in feeding stuffs within the scope of Regulation 
(EC) 1831/200331, and in animal nutrition within the scope of Directive 
82/471/EEC32.  

In addition, Member States may exempt certain substances or mixtures in specific cases where 
necessary for the purpose of national defence. 

Although CLP does not apply to the transport of dangerous goods by air, sea, road, rail or inland 
waterways (CLP Article 1(6)), the criteria for classification are normally intended to be the same 
in the two systems. Thus, a substance or mixture classified in a hazard class which is common 
to both CLP and the transport legislation will normally be classified the same in both systems. 
However, the transport classifications do not include all of the GHS categories, so the absence 
of a transport classification does not mean the substance or mixture should not be classified 
under CLP. The relation between transport and CLP classification regarding physical hazards is 
detailed in Annex VII to this document.  

1.1.6.  What information is needed for classification 

1.1.6.1. 

Information for the classification of substances 

The classification of a substance is based on the relevant information available on its hazardous 
properties. This information can include experimental data generated in tests for physical 
hazards, toxicological and ecotoxicological tests, historical human data such as accident records 
or epidemiological studies, or information generated in in vitro tests, (Quantitative) Structure 
Activity Relationships ((Q)SAR), ‘read-across’, or grouping approaches. 

CLP does not require new testing for the purpose of classification for health or environmental 
hazards; testing for physical hazards is required unless adequate and reliable information is 
already available (CLP Article 8(2)). However, a substance placed on the market for research 
and development (R&D) purposes may have been manufactured or imported in quantities that 
are too small to perform physical hazard testing. In these cases it would not be proportionate to 
request the respective manufacturer, importer or downstream user to perform the tests 
required in Part 2 of Annex I to CLP.  

Although data may be provided through the application of REACH, it should be recognised that 
the data set required by REACH (particularly at lower tonnages) will not necessarily enable the 
comparison with the criteria for all hazard classes. Information may also be available from other 
EU legislation for which there are specific requirements for test data to be generated, such as 
legislation on plant protection products (Regulation (EC) No 1107/200933 and Directive 

30 1999/217/EC: Commission Decision of 23 February 1999 adopting a register of flavouring substances 
used in or on foodstuffs drawn up in application of Regulation (EC) No 2232/96 of the European Parliament 
and of the Council of 28 October 1996 [OJ L 84, 27.3.1999, p. 1]. 

31 Regulation (EC) No 1831/2003 of the European Parliament and of the Council of 22 September 2003 on 
additives for use in animal nutrition [OJ L 268, 18.10.2003, p. 29]. 

32 Council Directive 82/471/EEC of 30 June 1982 concerning certain products used in animal nutrition [OJ L 
213, 21.7.1982, p. 8]. 

33 Regulation (EC) No 1107/2009 of the European Parliament and of the Council of 21 October 2009 
concerning the placing of plant protection products on the market repeals Council Directives 79/117/EEC 
and 91/414/EEC with effect from 14 June 2011. However Article 80 of Regulation (EC) No 1107/2009 
specifies that directive 91/414/EEC shall continue to apply with respect to active substances included in 
Annex I to that Directive for certain transitional periods. 

 
 
 
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91/414/EEC34) and on biocidal products (Regulation (EU) No 528/201235 and Directive 
98/8/EC36), or from various non-EU programmes. Finally, the supplier may decide to conduct 
new testing in order to fill data gaps, provided that he has exhausted all other means of 
generating information. Testing on animals must be avoided wherever possible and alternative 
methods (including in vitro testing, the use of (Q)SARs, read-across and/or grouping 
approaches) must always be considered first, provided they are scientifically validated, 
sufficiently adequate and reliable.  

In the case of a substance containing impurities, additives or other constituents, the 
classification of the substance should, similar to mixtures, preferably be based on available 
information (including test data) on the substance except when classifying for CMR properties or 
when evaluating the bioaccumulation and degradation properties within the ‘hazardous to the 
aquatic environment’ hazard class (referred to in sections 4.1.3.3.2 and 4.1.2.9 of Annex I to 
CLP). In such cases it is strongly recommended that the classification of the substance, similar 
to mixtures (Articles 6(3), 6(4) and 10 of CLP), is based on information of known CMR 
constituent(s) as there is no toxicological difference between a mixture and a substance 
containing other constituent substances37. In exceptional cases, data on the substance itself 
might show relevant effects for classification for CMR and/or bioaccumulation or degradation 
properties which have not been identified from the information on the constituent substances. 
These data should then be used, if available. 

If, for the purpose of CLP, it is required or decided to generate new data, certain test methods 
and quality conditions must be met. Studies must be conducted in accordance with the EU test 
methods (Regulation (EC) 440/2008)38 or other international test methods validated according 
to international procedures such as those of the OECD. For physical hazards new tests must be 
carried out in compliance with a relevant recognised quality system or by laboratories 
complying with a relevant recognised standard, and for health and environmental hazards in 
compliance with the principles of Good Laboratory Practice (GLP39). Animal tests must comply 
with the Directive 86/609/EEC40. Tests on non-human primates are prohibited for the purposes 
of CLP. Tests on humans must not be performed for the purpose of CLP. However, existing data 
obtained from other sources, such as accident records and epidemiological and clinical studies, 
can be used. 

34 Council Directive 91/414/EEC of 15 July 1991 concerning the placing of plant protection products on the 
market, as amended [OJ L 230, 19.8.91, p. 1]. 

35 Regulation (EU) No 528/2012 of the European Parliament and of the Council of 22 May 2012 concerning 
the making available on the market and use of biocidal products. It should be noted that with effect from 1 
September 2013, Biocidal Products Regulation (EU) No 528/2012 repealed Directive 98/8/EC. 

36 Directive 98/8/EC of the European Parliament and of the Council of 16 February 1998 concerning the 
placing of biocidal products on the market, as amended [OJ L 123, 24.4.98, p. 1]. 

37 Please note that there is a case still pending before the Court of Justice on the classification of an UVCB 
substance based on information on its constituents: Case C-691/15 P. 

38 Council Regulation (EC) No 440/2008 laying down test methods pursuant to Regulation (EC) No 
1907/2006 of the European Parliament and of the Council concerning the Registration, Evaluation, 
Authorisation and Restriction of Chemicals (REACH)[OJ L 142, 31.5.2008, p. 1]. 

39 More information on the GLP principles and related requirements is available in the Q&As section on the 
ECHA website at https://www.echa.europa.eu/web/guest/support/qas-support/qas.  

40  Directive  86/609/EEC  regarding  the  protection  of  animals  used  for  experimental  and  other  scientific 
purposes, [OJ L 358, 18.12.1986, p. 1]. 

 
 
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1.1.6.2. 

Information relevant for the classification of mixtures 

For mixtures, classification for physical hazards should normally be based on the results of tests 
carried out on the mixtures themselves (unless, as for substances, a mixture placed on the 
market for R&D purposes has been manufactured or imported in quantities that are too small to 
perform physical hazard testing). New tests for physical hazards must be carried out in 
compliance with a relevant recognised quality system or by laboratories complying with a 
relevant recognised standard. 

When considering health and environmental hazards, the classification should preferably be 
based on information (including test data) on the mixture itself, if available, except when 
classifying for e.g. CMR effects or when evaluating the bioaccumulation and degradation 
properties within the ‘hazardous to the aquatic environment’ hazard class referred to in sections 
4.1.2.8 and 4.1.2.9 of Annex I to CLP. In these cases, classification of the mixtures must be 
based on the information on the substances. 

New tests for the purpose of classification and labelling for health or environmental hazards of 
substances and mixtures, may only be performed when the manufacturer, importer or 
downstream user has exhausted all other means of generating information according to Article 
8 of CLP. According to this article, this includes application of the general rules provided in 
section 1 of Annex XI to REACH which refers to possible alternative methods/approaches to 
animal testing of a substance when required in REACH, i.e. the use existing data, weight of 
evidence, (Q)SARs, in vitro, grouping of substances and read-across, provided they are 
considered adequate for the purpose of classification and labelling. In the case of mixtures (and 
multiconstituent substances), it has to be re-assured that the method is relevant and reliable 
for the mixture (see specific guidance for each hazard class).  

Thus, if no in vivo test data are available on a mixture, such data should normally not be 
generated; rather, all available information on the ingredients41 of the mixture should be used 
to derive a classification.  

Annex I to CLP specifies ‘bridging principles’ which enables suppliers to derive health or 
environmental classifications of their mixtures based on available data on similar tested 
mixtures and on the ingredient substances. Annex I also provides specific rules for the 
classification of mixtures based on the classification of the individual substances in the mixture. 

1.1.7.  Data evaluation and reaching a decision on classification 

1.1.7.1.  Classification of substances 

After the available information has been assembled, a systematic evaluation of this information 
is necessary in order to derive a classification. The information must be compared with the 
criteria for classification for each hazard class or differentiation within the hazard class. 
Differentiation is a distinction depending on the route of exposure or the nature of the effects. A 
decision should be made as to whether the substance meets the criteria for classification. When 
this is the case; the classifier should assign one or more hazard categories for each relevant 
hazard class or differentiation. The substance is then assigned the appropriate hazard 
communication elements. 

In some cases the classification decision may be straightforward, requiring only an evaluation of 
whether the substance gave a positive or negative result in a specific test that can be directly 
compared with the classification criteria. In other cases, scientific judgements must be made 
(e.g. on dose-response relationships, equivocal results and non-standardised tests) in a weight 
of evidence determination when applying the criteria. Expert judgement may therefore be 

41 Note that the term “ingredient” is used in this guidance with the same meaning of “component” to 
indicate a substance in amixture. 

 
 
 
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needed to decide whether the results of a particular test or the available information in a Weight 
of evidence assessment meet the criteria laid down in Annex I.  

1.1.7.2. 

Influence of impurities, additives or individual constituents on the 
classification of a substance  

Substances may contain impurities, additives, or other constituents while still meeting the 
substance definition in CLP. This applies to both mono-constituent, multi-constituent (e.g. 
reaction masses) and UVCB substances. The classification of such impurities, additives or 
individual constituents may influence the classification of the substance, in addition to the other 
hazardous properties. If data on the substance with its components are not available (or for 
CMRs, see section 1.1.6.1), in principle, the same classification and labelling rules as for 
mixtures should apply also for such substances42. 

1.1.8.  Updating of hazard classifications 

Updating of classifications may be necessary if, for example, new information is obtained or if 
the criteria in CLP are amended. When manufacturers, importers or downstream users become 
aware of new information or an amendment to CLP or when a change is introduced in a 
substance or mixture, they must reconsider the classification of the substance or mixture. Note 
that “new” here refers to information not previously considered (or even new interpretation of 
old data), not necessarily newly produced data. A downstream user may use the classification 
derived in accordance with the criteria by his supplier; this does not relieve the downstream 
user from the obligation to share new information with the supplier to allow him to meet the 
requirements. 

Please, see also Section 1.1.10 addressing changes in harmonised classifications. 

1.1.9.  The interface between hazard classification and hazard 

communication 

CLP provides an integrated system of hazard communication elements on the label including 
hazard pictograms, signal words, hazard statements and precautionary statements. Provision of 
this information to the end user is obligatory, irrespective of conditions of use and risk. While 
the Chemical Safety Assessment (CSA) on a particular substance performed for the purpose of 
REACH may indicate ‘safe use’, a situation resulting in unforeseen exposure may occur, such as 
in an accident. In such a situation, workers, managers and emergency personnel will need 
information on the hazard profile of the substance, which will be provided by the label and the 
SDS. These sources of information will also provide useful information to the worker on the safe 
handling of the chemical.  

It is recognised that the hazard communication needs of the various end users may differ. 
Consumers are primarily dependent on the label of a substance or a mixture as a source of 
hazard and precautionary information, while the requirement for provision of an SDS is 
primarily applicable to professional users. Thus, the label facilitates communication of key 
hazard information on a substance or a mixture and additional safety advice (precautionary 
statements) to consumers, as well as to workers. 

1.1.10.  The interface between self-classification and harmonised 

classification, and the list of harmonised classifications 

CLP places emphasis on self-classification by industry of the substances or mixtures they 
supply. In some cases, substances are subject to harmonised classification at EU level, while 

42 Please note that a case is still pending before the Court of Justice on the classification of a UVCB based 
on information on its constituents: Case C-691/15 P. 

 
 
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mixtures must always be self-classified, except for pesticidal and biocidal products where the 
Member State competent authorities (MSCAs) decide on the classification as part of the national 
authorisation scheme (CLP Article 36(2)). 

If a substance has a harmonised classification as provided in Annex VI to CLP, this classification 
must always be used by a manufacturer, importer or downstream user, except for the minimum 
classifications indicated with an asterisk (*) in Table 3.1. The use of the minimum classification 
is explained in section 1.2.1 of Annex VI. For such minimum classifications, when available data 
exists to justify a more stringent category than the given minimum, the more stringent 
category must be used. It should be noted that where some but not all hazard classes or 
differentiations within a hazard class have been harmonised, the remaining hazards must be 
evaluated and self-classified to complete the classification (according to CLP Article 4(3) and 
CLP Recital 17). Note that the presence of an impurity/additive/constituent which leads to 
classification in a more severe hazard classification than the harmonised classification of the 
substance (in Annex VI, CLP) should be taken into account in the classification of the substance. 
(As for substances in Annex VI, the name of the substance to be put on the label should include 
also the name of the impurity/additive/constituent (i.e. substance name followed by “containing 
≥x% name of impurity”) in cases where they contribute significantly to the classification of the 
substance as in the case above (see 1.1.1.4, Annex VI, CLP)). 

Under CLP, the harmonised classification and labelling of substances normally aims to cover  
properties of the highest concern (CMR and respiratory sensitisation) but CLP also allows 
harmonisation for other properties if there is a need for such an action at EU-level. Decisions on 
harmonised classification are taken by the European Commission through comitology (CLP 
Article 37(5)), following a proposal submitted to ECHA and an opinion developed by ECHA's Risk 
Assessment Committee (RAC) on the proposal (CLP Article 37(4)). Whenever a manufacturer, 
importer or downstream user has new information which may affect a harmonised classification, 
he must submit a proposal for a change to the member State Competent Authority where the 
substance is placed on the market. 

Substances regulated under the Biocidal Products Regulation (EU) No 528/2012 or under the 
Plant Protection Products Regulation (EC) No 1107/2009 will normally be subject to harmonised 
classification and labelling for all hazardous properties. These proposals for harmonised 
classification and labelling are prepared by MSCAs only (CLP Article 36(2)). However, in general 
proposals for harmonised classification for a particular substance to be added in Annex VI to 
CLP can be made by both MSCAs and by manufacturers, importers and downstream users (CLP 
Article 37). Only MSCAs can propose a revision of an existing harmonised classification and 
labelling to ECHA (CLP Article 37(6)). 

A new or revised harmonised classification of a substance set out in Annex VI to CLP must be 
applied from the date specified in the respective ATP, although suppliers may use this 
classification before that date. 

When a supplier decides not to apply the harmonised C&L of a substance before this date, they 
must identify and examine all available information for the self-classification. Thus they should 
take into consideration the opinion adopted by the ECHA Risk Assessment Committee (RAC) on 
the harmonised C&L for that substance. 

If the C&L of a substance is already harmonised in the same hazard class, compliance with the 
existing harmonised C&L is legally required until it is formally changed in an ATP to CLP. The 
new harmonised C&L may be voluntarily applied as soon as the respective ATP enters into force. 
At the date of applicability, as provided for in the respective ATP, the suppliers are obliged to 
comply with the new harmonised C&L. 

Harmonised classification and labelling of a substance provides for a high level of protection of 
human health and the environment, and provides legal clarity for different suppliers of the same 
substance of high concern (i.e. manufacturers of substances, importers of substances or 

 
 
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mixtures, producers of specific articles, downstream users (including manufacturers of 
mixtures) and distributors). 

Part 3 of Annex VI to CLP contains the list of harmonised classifications and labellings (except 
precautionary statements). All harmonised classifications previously adopted under DSD and 
listed in Annex I to DSD were translated to CLP classifications and carried over to the list of 
harmonised classifications in Annex VI to CLP also including the Notes assigned to the entries as 
referred to in the DSD. This was done to maintain the same level of protection under CLP as 
under DSD. The harmonisation of classification of substances is a continuous process building 
on all efforts already done within the EU so far to evaluate hazards of substances that caused 
concern. 

Annex VI contains a number of entries indicated with Note B. The note relates to substances 
(acids, bases, etc.) that are placed on the market in aqueous solutions. The required 
classification and labelling may be different at different concentrations. These entries have a 
general designation of the following type: ‘nitric acid … %’. These entries give the classification 
of the substance in a water solution above the GCL or SCL. The GCLs or SCLs are applied as 
usual in the classification of any mixture containing the substance. Thus, the concentration of 
the undiluted substance is compared with the GCL or SCL, as appropriate. For example, when 
diluted 75% phosphoric acid is added to a mixture to make up 10% of the mixture, the final 
concentration of phosphoric acid in the final mixture is 7.5%. As for this substance the SCL for 
skin and eye irritation is 10%, the final mixture does not require classification for these hazard 
classes based on phosphoric acid. The presence of Note B specifies that the supplier of an 
aqueous solution of such a substance must state the percentage concentration of the solution 
on the label. 

Note that the pure substance, i.e. not in water solution, may have different hazards. If there is 
no entry in Annex VI covering the anhydrous form, a classification would need to be derived 
based on available information. As the human body contains water, it is likely that the hazards 
of the aquatic solution still apply. Additional hazards may however occur, for example, hydrogen 
cyanide is Flam. liq.1 when it is pure but not in solution. 

1.1.11.  The Classification and Labelling Inventory (C&L Inventory) 

Manufacturers and importers are required to notify ECHA of the classification and labelling of 
hazardous substance(s) placed on the market as such or in a mixture (above a certain 
concentration leading to the classification of the mixture) and of substances subject to 
registration in accordance with the REACH Regulation. ECHA will then include the information in 
the classification and labelling inventory in the form of a database. Substances require 
notification within one month after their placing on the market. There is no need to notify the 
substance if the same information has already been submitted as part of a registration under 
REACH by the same actor, as the classification and labelling, when part of the registration 
package, will automatically be added to the C&L Inventory (CLP Article 40(1)). Further guidance 
on what should be included in a notification and how to do it is available on the ECHA website 
http://echa.europa.eu/web/guest/regulations/clp/cl-inventory/notification-to-the-cl-inventory. 

ECHA makes certain information from the C&L Inventory publicly available on its website, 
including the substance name, the classification, labelling and any relevant specific 
concentration limit or M-factor(s). It is indicated in the Inventory if there is a harmonised 
classification for the entry, or if it is an agreed entry between manufacturers or importers. 
Multiple notifications of the same substance can be submitted by different manufacturers or 
importers, with potential differences in the notified classifications. Notifiers and registrants are 
required to make every effort to come to an agreed entry. 

The information in the C&L Inventory comes from registrations and C&L notifications. This 
information has not been reviewed or verified by the Agency or any other authority. 

 
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1.1.12.  Relation of classification to other EU legislation 

A network of EU legislation relies on classification in one way or the other (see section 22 of the 
Introductory Guidance on the CLP Regulation for a detailed list of the laws concerned). This 
downstream legislation includes laws protecting consumers and workers, as well as rules on 
transport, biocides, pesticides, cosmetics and waste. Therefore, apart from the important 
hazard communication on the label and in the SDS, there are significant downstream 
consequences of classification in that it also has a direct effect on risk management measures 
under REACH and other legislation. 

1.1.12.1.  REACH  

Classification plays a key role in REACH; it must be included in the registration dossier for a 
substance and it triggers certain provisions such as the performance of an exposure assessment 
and risk characterisation as part of the CSA and the obligation to provide an SDS. Classification 
of a substance as mutagenic, carcinogenic or toxic to reproduction (CMR) may also lead to 
restrictions and the need to apply for authorisations ((EC) No 1907/2006). 

1.1.12.2.  Plant Protection Products and Biocides 

Active substances as well as any plant protection products or biocidal products containing them 
must be classified in accordance with the CLP Regulation.  

Regarding plant protection products, it should be noted that with effect from 14 June 2011, 
Directive 91/414/EEC has been repealed by Regulation (EC) 1107/2009, which concerns their 
placing on the market. This means that references to the repealed Directive must now be 
construed as references to the new Regulation. Nevertheless, Article 80 of the new Regulation 
specifies that Directive 91/414/EEC must continue to apply with respect to active substances 
included in Annex I to that Directive for certain transitional periods. 

Regarding biocidal products, it should be noted that with effect from 1 September 2013, 
Directive 98/8/EC has been repealed by Regulation (EU) 528/2012, which concerns ther making 
available on the market and use. This means that references to the repealed Directive must now 
be construed as references to the new Regulation. Nevertheless, Articles 89 – 95 of the new 
Regulation specifies the transitional measures which must continue to apply. 

In relation to classification, the new Regulations, bring about some changes, e.g. certain 
classifications (e.g. CMR, Cat. 1A and 1B) may now preclude approval of the respective 
substance as an active substance, safener, or synergist in plant protection products or biocidal 
products. 

1.1.12.3.  Transport legislation 

Many of the GHS criteria (by hazard class) are already implemented through the UN Model 
Regulations for Transport of Dangerous Goods and related legal instruments (ADR, RID, ADN, 
IMDG Code and ICAO TI). 

Available transport classifications can be a source of information for the classification and 
labelling of substances and mixtures under CLP, especially for physical hazards, see also Section 
2 of this document. 

 
 
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1.2.  THE SIGNIFICANCE OF THE TERMS ‘FORM OR PHYSICAL STATE’ 

AND ‘REASONABLY EXPECTED USE’ WITH RESPECT TO 
CLASSIFICATION ACCORDING TO CLP 

1.2.1. 

‘Form or physical state’ and ‘reasonably expected use’ 

CLP refers to the terms ‘form or physical state’ and ‘reasonably expected use’ in the following 
Articles:  

Article 5(1) Manufacturers, importers and downstream users of a substance shall identify the 
relevant available information for the purposes of determining whether the substance entails a 
physical, health or environmental hazard as set out in Annex I 

[….] 

The information shall relate to the forms or physical states in which the substance is placed on 
the market and in which it can reasonably be expected to be used. 

Article 6(1) The information shall relate to the forms or physical states in which the mixture 
is placed on the market and, when relevant, in which it can reasonably be expected to be 
used.  

Article 8(6) Tests that are carried out for the purposes of this Regulation shall be carried out 
on the substance or on the mixture in the form(s) or physical state(s) in which the substance 
or mixture is placed on the market and in which it can reasonably be expected to be used. 

Article 9(5) When evaluating the available information for the purposes of classification, the 
manufacturers, importers and downstream users shall consider the forms and physical states 
in which the substance or mixture is placedon the market and in which it can be reasonably be 
expected to be used. 

The objective of hazard classification is to identify the intrinsic physical, health and 
environmental hazards of substances and mixtures taking into account all uses that can be 
reasonably expected. 

In this context, the intention of the UN GHS should be kept in mind: 

The GHS (subsection 1.3.2.2.1) uses the term ‘hazard classification’ to indicate that only the 
intrinsic hazardous properties of substances or mixtures are considered. 

The following guidance is intended to clarify the references to 'reasonably expected use' and 
'form or physical state' in this context. 

1.2.2.  The term ‘reasonably expected use’ in relation to hazard classification 

Hazard classification is based on the intrinsic properties of a substance or mixture and does not 
take into account exposure. Reasonably expected use summarises all physical forms and states 
of a substance or mixture that may occur during intended use or reasonably foreseeable 
conditions of misuse. 

Reasonably expected use of a substance or mixture is as follows: 

•  Any process, including production, handling, maintenance, storage, transport or disposal.  

•  All technical operations/manufacturing activities like e.g. spraying, filing, and sawing.  

•  Any putative consumer contact through e.g. do-it-yourself or household chemicals. 

•  All professional and non-professional uses including reasonably foreseeable accidental 

exposure, but not abuse such as criminal or suicidal uses.  

 
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Reasonably expected use is also related to any consumer disposal or any work in which a 
substance or mixture is used, or intended to be used irrespective of its present limited use or 
use pattern. Thus, use should not be mixed up with usage category. 

1.2.3.  The term ‘form or physical state’ in relation to hazard classification 

Depending on different prerequisites, form or physical state is taken into account differently in 
the practice of testing and classification for physical, health, and environmental hazards which is 
described in the following paragraphs. 

It should be noted that in some cases a substance may autooxidise (in contact with air) or 
decompose to a more hazardous form. This may warrant classification of the substance even 
though it in itself is not or is less hazardous. A case-by-case evaluation should be done 
considering available hazard information on humans or animals and/or the rate and extent of 
autoxidation or decomposition. The case-by-case evaluation should also consider how the 
substance can be reasonably expected to be used. 

1.2.3.1.  Physical hazards 

Different forms or physical states of a substance or mixture may result in different physical 
properties and hazards with possible consequences for the hazard classification of a substance 
or mixture. Putative forms comprise properties such as crystal structure, particle size, 
homogeneity (e.g. emulsions) and texture (e.g. viscosity or tablet form). Examples of physical 
state factors are: surface treatment (e.g. coating), state of aggregation, moisture content, 
residual solvent, activation or stabilisation. 

The classification of a substance or mixture relates to the tested form and physical state. If the 
form and / or physical state is changed it has to be evaluated whether this might affect the 
classification and whether re-testing is necessary. For example, a hazardous phase separation 
may occur due to a temperature change under conditions of storage, or a solid substance may 
be molten to bring it into the liquid phase (e.g. for pumping). 

General considerations 

The test sample should be representative for the substance or mixture placed on the market. 
This is especially important in case of small 'batch' production. Mixtures might for example 
contain inert components which, if they are over-represented in the test sample, will lead to 
incorrect hazard classification. 

Specific requirements of certain test methods 

Some test methods for the classification of physical hazards have specific requirements 
regarding the form / particle size of the sample to be tested. In these cases, the specific 
requirements of the test methods prevail. Examples of tests which have specific requirements 
regarding the form/particle size of the sample to be tested include those used to determine the 
classification of explosives and of substances which in contact with water emit flammable gases. 

In other test methods, there are no specific requirements regarding the particle size but it is 
stated explicitly that the particle size may have a significant effect on the test result. Therefore, 
these properties should be mentioned in the test report (i.e. testing of oxidising solids).  

Section 2.0.4 provide further details about the relevance of the physical state for testing 
purposes. 

1.2.3.2.  Human health hazards 

Also for human health, different forms (e.g. particle sizes, coating) or physical states may result 
in different hazardous properties of a substance or mixture in use. However, due to test 
complexity, not every form or physical state can be tested for each health hazard. In general, 
testing should be performed on the smallest available particle size and the default approach is 

 
 
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to test for different routes of exposure (oral, dermal, inhalation). Again, due to test complexity, 
mostly the data for only one exposure route are available.  

In general, the assumption is made that the testing conditions of valid animal assays reflect the 
hazards to man and these data must be used for classification. Moreover, it is assumed that 
classification for human health hazards takes into account all the potential hazards which are 
likely to be faced for all forms or physical states in which the substance is placed on the market 
and can reasonably be expected to be used. It is assumed that it comprises putative accidental 
exposures. This approach generally, but not necessarily comprehensively, covers the whole 
range of intrinsic properties of a substance or mixture: in some cases, substances or mixtures 
have to be transformed into specific forms not mirroring ‘real-life’ exposures in order that an 
animal test can be performed. As a consequence, the results of such tests may have to be 
evaluated taking into account any limitations due to the fact that the specific form of the tested 
substance or mixture does not or not perfectly represent that to which human exposure may 
occur during intended, known, or reasonably expected use. Such evaluation has to be 
performed according to the state of the scientific and technical knowledge. The burden of proof 
is on the person placing a substance or mixture on the market. 

1.2.3.3.  Environmental hazards 

The environmental hazard classification is principally concerned with the aquatic environment 
and the basis of the identification of hazard is the aquatic toxicity of the substance or mixture, 
and information on the degradation and bioaccumulation behaviour. 

The system of classification is designed to ensure that a single classification applies to a 
substance. In general it takes no account of the specific form since this can vary and is not 
intrinsic to the substance. The form in which the substance is placed on the market is taken into 
account when deciding what label to apply and various derogations from labelling exist, e.g. for 
metals in the massive form. In the massive form the hazard may not be present and the 
substance need not be labelled. The SDS will, however, indicate the classification and intrinsic 
hazardous properties to warn the user that subsequent transformation of the substance may 
produce the hazardous form.  

For aquatic hazard classification, organic substances are generally tested in the dissolved form. 
Exceptions to this approach include complex, multi-component substances and metals and their 
compounds. Examples of alternative approaches include the use of Water Accommodated 
Fractions (WAF) for complex, multi-component substances where the toxicity cut-off is related 
to the loading, and a test strategy for metals and their compounds in which the specific form 
(i.e. particle size) used for testing is standardised and forms or physical states are not further 
taken into account.  

1.3.  SPECIFIC CASES REQUIRING FURTHER EVALUATION – LACK OF 

BIOAVAILABILITY 

1.3.1.  Definition 

Bioavailability is the rate and extent to which a substance can be taken up by an organism and 
is available for metabolism or interaction with biologically significant receptors. Bioavailability 
(biological availability) involves both release from a medium (if present) and absorption by an 
organism (IPCS 2004). 

 
 
 
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Article 12 

Specific cases requiring further evaluation 

Where, as a result of the evaluation carried out pursuant to Article 9, the following properties 
or effects are identified, manufacturers, importers and downstream users shall take them into 
account for the purposes of classification: 

[…] 

(b) conclusive scientific experimental data show that the substance or mixture is not 
biologically available and those data have been ascertained to be adequate and reliable; 

[…] 

In general, bioavailability is not explicitly evaluated in hazard classification – the observation of 
systemic toxicity implicitly demonstrates a degree of bioavailability. On the other hand, when no 
toxicity is demonstrated in a test, this may be a result of either lack of intrinsic toxicity of the 
substance or lack of bioavailability in the test system employed. Nevertheless, as indicated in 
Article 12 (b) of CLP there may be cases where a specific evaluation of bioavailability is 
warranted. Bioavalibility may also need to be considered for grouping and read-across. 

In general terms, for a substance or mixture to have an effect on a biological or environmental 
system, there must be some degree of bioavailability. Therefore, it follows that a substance or 
mixture need normally not be classified when it can be shown by conclusive experimental data 
from internationally acceptable test methods, e.g. from the Test Method Regulation (EC) No 
440/2008, that the substance or a substance in a mixture is not biologically available (UN GHS 
1.3.2.4.5.1). A non bioavailable substance may, however, react with e.g. other components in a 
mixture to transform to soluble available forms. The rate and extent at which this process, 
known as ‘transformation’ for the purposes of the classification guidance, takes place can vary 
extensively between different substances, and can be an important factor in determining the 
appropriate hazard category (see Annex IV, Section IV.1 of this document). Note that a 
substance which is inert and insoluble may still pose a hazard requiring classification, e.g. 
asbestos fibers. Further, it is important to note that bioavailability is not limited to systemic 
bioavailability but also includes local bioavailability for example for local effects like irritation 
and sensitisation. 

When considering the non-bioavailability of a substance or a mixture, the evaluation should be 
based on data for all relevant constituents of a substance or ingredients of the mixture. Further, 
one should consider potential interaction of the ingredients that could influence the 
bioavailability of the mixture as such or one of its components. 

Bioavailability considerations are only relevant with respect to classification for health and/or 
environmental hazards and not for physical hazards. 

1.3.2.1.  Human health hazards 

The assumption is that all substances and mixtures are considered to be bioavailable to some 
extent. However, there are a few specific cases in which bioavailability may have an influence 
on hazard classification. For instance in the case of some metals and polymers, the nature of 
the physical form (metals in solid form) and the molecular size (polymers are very large 
molecules), or their physico-chemical properties may limit absorption. Where a supplier 
proposes derogation from hazard classification on the basis of bioavailability, he has to provide 
adequate and robust data to support the conclusion of lack of bioavailability. It is possible that a 
substance is bioavailable by one route but not another (e.g. absorbed following inhalation but 
not absorbed through the skin). In such cases the lack of bioavailability may derogate 
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In general, a prediction of lower bioavailability must be supported by robust evidence and a 
weight of evidence determination using expert judgment must be applied. 

Information on bioavailability is usually obtained from adequate, reliable, and conclusive 
toxicokinetic studies for all relevant routes of exposure and all relevant forms or physical states 
where the substance and/or metabolite(s) of the substance have been quantified in body fluids 
and/or target organs. At present (2016), in vitro tests for release of moieties in biological fluids 
are being developed, but have not yet been agreed by OECD. It should be noted that concluding 
that there is lack of or reduced bioavailability has a high burden of evidence and needs to be 
supported by robust data and expert evaluation.  

Bioavailability of a substance or a substance in mixtures is normally assumed if there are in 
vitro studies available which show the solubility of a substance or mixture in body fluids or 
artificial simulated body fluids. Furthermore, conclusions on bioavailability of a substance or a 
mixture may be based on considerations of the physical properties of a substance or derived 
from Structural Activity Relationships (SAR). Note also that bioavailability is not limited to 
solubility, local bioavailability and the uptake of (nano)particles also has to be taken into 
account. Further, a substance or mixture can be transformed, e.g. by gastric fluid so that the 
substance absorbed may differ from the substance delivered. In certain exceptional 
circumstances it may be possible that a substance on its own or in a mixture can be considered 
to be non-bioavailable, based on either appropriate in vitro data, e.g. from skin absorption 
models, SAR considerations or consideration of the physical properties of the substance, if the 
respective requirements described above have been taken into account in an adequate analysis. 

1.3.2.2.  Environmental hazards 

The hazard classification for the aquatic environment is based on the three elements aquatic 
toxicity, bioaccumulation and degradation. The measurement of toxicity to aquatic organisms 
and its use within a hazard classification system introduces a number of compounding 
problems. The substance is not dosed directly into the organism but rather into water in which 
the organism lives. While this reflects more accurately the manner in which the organism will 
receive the dose in the environment, it does not allow the direct control of the dose which is an 
important part of much mammalian toxicity testing. The dose is limited by the bioavailability of 
the substance, the maximum dose being determined by the level of water solubility. 

It is usually assumed that toxic effects are only measured following exposure to the dissolved 
fraction, i.e. organisms are exposed to substances dissolved in water. It is assumed that the 
substances will either be absorbed by the organisms through passive diffusion or taken up 
actively by a specific mechanism. Bioavailability may, therefore, vary between different 
organisms. In the case of bioaccumulation, oral exposure could also be considered for 
substances with high Log Kow. Further guidance of the impact of bioavailability caused by the 
size of the molecule and how this is considered for aquatic hazard classification can be found in 
Annex III to this document. 

In general, there are no specific environmental test methods developed to measure biological 
availability of substances or mixtures. This aspect is built into the testing methodology for 
toxicity and if adverse effects are identified the substance should be classified accordingly. 
Substances which lack bioavailability would not be absorbed by the exposed organisms and 
therefore due to lack of toxic effects these substances would not be classified, unless they are 
known to degrade or transform to hazardous products. For example see the strategy for metals 
classification in Annex IV to this document. 

 
 
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1.4.  USE OF SUBSTANCE CATEGORISATION (READ-ACROSS AND 

GROUPING) AND (Q)SARS FOR CLASSIFICATION AND LABELLING 

Article 5(1) Manufacturers, importers and downstream users of a substance shall identify the 
relevant available information for the purposes of determining whether the substance entails a 
physical, health or environmental hazard as set out in Annex I, and, in particular, the 
following: 

[…] 

 (c) any other information generated in accordance with section 1 of Annex XI to Regulation 
(EC) No 1907/2006; 

Article 6(1) Manufacturers, importers and downstream users of a mixture shall identify the 
relevant available information on the mixture itself or the substances contained in it for the 
purposes of determining whether the mixture entails a physical, health or environmental 
hazard as set out in Annex I, and, in particular, the following: 

[…] 

 (c) any other information generated in accordance with section 1 of Annex XI to Regulation 
(EC) No 1907/2006 for the mixture itself or the substances contained in it; 

Article 9(1) Manufacturers, importers and downstream users of a substance or a mixture 
shall evaluate the information identified in accordance with Chapter 1 of this Title by applying 
to it the criteria for classification for each hazard class or differentiation in Parts 2 to 5 of 
Annex I, so as to ascertain the hazards associated with the substance or mixture  

Article 9(3) Where the criteria cannot be applied directly to available identified information, 
manufacturers, importers and downstream users shall carry out an evaluation by applying a 
weight of evidence determination using expert judgement in accordance with section 1.1.1 of 
Annex I to this Regulation, weighing all available information having a bearing on the 
determination of the hazards of the substance or the mixture, and in accordance with section 
1.2 of Annex XI to Regulation (EC) No 1907/2006. 

Article 13 If the evaluation undertaken pursuant to Article 9 and Article 12 shows that the 
hazards associated with the substance or mixture meet the criteria for classification in one or 
more hazard classes or differentiations in Parts 2 to 5 of Annex I, manufacturers, importers 
and downstream users shall classify the substance or mixture in relation to the relevant 
hazard class or classes or differentiations by assigning the following:  

(a) one or more hazard categories for each relevant hazard class or differentiation;  

(b) subject to Article 21, one or more hazard statements corresponding to each hazard 
category assigned in accordance with (a). 

Section 1 of Annex XI to REACH provides a list of data that can be used instead of testing when 
standard data are missing. This Annex specifies the conditions under which results of (Q)SARs, 
read-across and grouping may be used in order to fulfil the information requirements under 
REACH and refers to the adequacy of the information for the purpose of classification of 
substances. It states e.g. that results of (Q)SARs may be used instead of testing when the 
(Q)SAR models have been scientifically validated, ‘the substance falls within the applicability 
domain’, the ‘results are adequate for the purpose of classification and labelling’ and ‘adequate 
and reliable documentation of the applied method is provided’. Results generated by read-
across and grouping may, according to the same principles, be used for classification and 
labelling if they are ‘adequate for classification and labelling’, ‘have adequate and reliable 
coverage of the key parameters addressed in the corresponding test method’, ‘cover an 
exposure duration comparable to or longer than the corresponding test method’, and ‘adequate 
and reliable documentation of the applied method’ is provided. 

 
 
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According to CLP Article 9(3), a weight of evidence determination using expert judgement has 
to be applied where the criteria cannot be applied directly to the available data. This 
determination is further described in CLP Annex I, 1.1.1. 

It is important to note that most of the criteria for classification are directly related to specific 
test methods. Thus, the adequacy of results of (Q)SARs, read-across and grouping should be 
evaluated against the criteria taking into account that normally the individual method attempts 
to estimate the same hazard as the criterion. Nevertheless, when grouping, read-across and 
(Q)SARs are being used alone or as a part of the basis for classification, it is normally necessary 
to do so employing weight of evidence and expert judgement in order to be able to apply the 
criteria to the information leading to a decision on the classification when the criteria are met 
(Article 13, CLP). 

CLP Annex I, 1.1.1.3 refers to the consideration of any information that is relevant for the 
determination of a hazard including the category approach. The latter encompasses grouping 
and read-across to help in a weight of evidence determination which is needed when the 
application of the criteria is not straightforward and cannot be applied directly to the available 
information (Article 9(1)(3), recital (33)).  

Annex I: 1.1.1.3. A weight of evidence determination means that all available information 
bearing on the determination of hazard is considered together, such as the results of 
suitable in vitro tests, relevant animal data, information from the application of the category 
approach (grouping, read-across), (Q)SAR results, human experience such as occupational 
data and data from accident databases, epidemiological and clinical studies and well 
documented case reports and observations. The quality and consistency of the data shall be 
given appropriate weight. Information on substances or mixtures related to the substance or 
mixture being classified shall be considered as appropriate, as well as site of action and 
mechanism or mode of action study results. Both positive and negative results shall be 
assembled together in a single weight of evidence determination. 

IR&CSA, Chapter R.6 provides extensive advice on the use of (Q)SARs and grouping of 
substances including guidance on read-across, for developing the data set for hazard 
evaluation. Guidance on the use of (Q)SAR and grouping for specific hazard classes is given in 
IR&CSA, Chapter R.7. 

In general, read-across, grouping and use of (Q)SARs as the sole information elements to 
obtain data on basic physical-chemical properties is not recommended, since reliable data 
should normally be available or is easily obtainable through testing. However, there may 
occasionally be practical problems with testing of substances for physical-chemical properties, 
especially for UVCBs where the properties may be dependent on the variable composition. 
Therefore, the appropriateness of using read-across, categorisation and (Q)SARs for physical-
chemical assessment should be considered on a case by case basis. This should also be the case 
when such data are considered for the evaluation of health and environmental hazards in order 
to apply the criteria for classification. 

Given the availability of extensive guidance only a brief overview of each approach is presented 
below. For classification of mixtures see Section 1.6 of this document. 

1.4.1.  (Q)SAR 

Structure Activity Relationships and Quantitative Structure Activity Relationships, collectively 
referred to as (Q)SARs, are defined in IR&CSA, Chapter R.6.1.1 as theoretical models that can 
be used to predict in a qualitative or quantitative manner the physico-chemical, biological (e.g. 
toxicological) or environmental fate properties of compounds from knowledge of their chemical 
structure.  

 
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It should be noted that the use of (Q)SAR results requires the user to be sufficiently skilled to 
understand the applicability of the selected (Q)SAR and to interpret the results in terms of 
reliability and adequacy for the purpose of classification and labelling. 

Extensive guidance on the use of (Q)SAR for hazard identification is given in IR&CSA, Chapter 
R.6.1. Guidance on the use of (Q)SARs for classification and labelling is also given in IR&CSA, 
Chapter R.6.1.4.2. This guidance is directly applicable to CLP. It should be noted that the 
(Q)SAR approach is not directly applicable to inorganic substances. 

1.4.2.  Grouping 

Guidance on grouping of substances for the purpose of hazard evaluation is given in IR&CSA, 
Chapter R.6.2. Annex XI to REACH opens the possibility of evaluating substances not on a one-
by-one basis, but by grouping substances in categories. A substance category is a group of 
substances whose physico-chemical, human health, environmental and/or environmental fate 
properties are expected to be similar or to follow a regular pattern as a result of structural 
similarity. 

The use of grouping for hazard evaluation in the grouping approach means that not every 
substance needs to be tested for every hazard. Read-cross by interpolation can be used to fill 
data gaps, as well as trend analysis and (Q)SAR, and in addition the overall data for that 
category must prove adequate to support the hazard assessment.  

In some cases it is necessary to create sub-groups within a category of substances, e.g. when 
there is a consistent trend within a group with regard to the potency of an effect which may 
justify different classifications or setting of SCLs (see also IR&CSA, R.6.2.1.2).  

1.4.3.  Read-across 

Read-across is the use of hazard specific information for one substance (‘source’) to predict the 
same hazard for another substance (‘target’), which is considered to have similar physico-
chemical, human health, environmental fate and/or (eco)toxicological properties. This can be 
based on structural similarity with a parent substance or its transformation products, and their 
bioavailability, bioaccessiblity, or known physico-chemical properties such as water solubility. 
For certain substances without test data, the formation of common significant metabolites or 
information on metabolites of tested substances or information from precursors, may be 
valuable information (IR&CSA, Chapter R.6.2.5.2 and OECD 2004). For any hazard, read-across 
may be performed in a qualitative or quantitative manner. Extensive guidance on the use of 
read-across is given in IR&CSA, Chapter R.6.2.2.1.  

Specific guidance for certain types of substances such as reaction products and multi-
constituent substances, complex substances, isomers, metals and metal compounds and other 
inorganic compounds is given in IR&CSA, Chapter R.6.2.5. 

1.5.  SPECIFIC CONCENTRATION LIMITS AND M-FACTORS 

1.5.1.  Specific concentration limits  

Article 10(1) Specific concentration limits and generic concentration limits are limits 
assigned to a substance indicating a threshold at or above which the presence of that 
substance in another substance or in a mixture as an identified impurity, additive or individual 
constituent leads to the classification of the substance or mixture as hazardous. 

Specific concentration limits shall be set by the manufacturer, importer or downstream user 
where adequate and reliable scientific information shows that the hazard of a substance is 
evident when the substance is present at a level below the concentrations set for any hazard 

 
 
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class in Part 2 of Annex I or below the generic concentration limits set for any hazard class in 
Parts 3, 4 and 5 of Annex I. 

In exceptional circumstances specific concentration limits may be set by the manufacturer, 
importer or downstream user where he has adequate, reliable and conclusive scientific 
information that a hazard of a substance classified as hazardous is not evident at a level 
above the concentrations set for the relevant hazard class in Part 2 of Annex I or above the 
generic concentration limits set for the relevant hazard class in Parts 3, 4 and 5 of that Annex. 

Article 10(3) Notwithstanding paragraph 1, specific concentration limits shall not be set for 
harmonised hazard classes or differentiations for substances included in Part 3 of Annex VI. 

The specific concentration limit (SCL) concept allows a fine tuning of the contribution of certain 
hazardous substances to the classification of mixtures based on the potency of the substances, 
as well as a classification of other substances containing these substances as impurities, 
additives or individual constituents. The SCL concept is generally only applicable to health 
hazards. For physical hazards, classification must normally be established on the basis of test 
data for the respective mixture, where applicable. 

The procedure of derivation of SCLs is different for every health hazard class and therefore 
guidance on how to set SCLs is provided in the respective chapters of the different health 
hazard classes. A general overview on the applicability of SCLs and guidance availability for 
setting SCLs for health hazards is illustrated by Table 1.1 below.  

SCLs should take precedence over the generic concentration limits (GCLs) given in the relevant 
health hazard sections of Annex I to CLP. In case specific concentration limits have been set in 
Annex VI to CLP, these must be applied. Moreover, manufacturers, importers or downstream 
users may not set their own SCLs for hazards subject to harmonised classifications in Annex VI 
to CLP.  

However, if a hazard class is not included in Annex VI and adequate and reliable data exist 
showing a hazard below the GCL, SCLs must be set by a manufacturer, importer or downstream 
user in accordance with CLP and be available in the C&L Inventory. SCLs should be 
communicated via the SDS. 

Table 1.1  Possibilities for setting SCL for health hazards addressed in relevant sections of the 
guidance 

Hazard class  

Category 

Lower SCL 
than GCL 

Higher SCLs than 
GCL (in exceptional 
circumstances) 

Guidance 

Acute toxicity  

all 

not applicable 

not applicable 

not necessary 

Skin corrosion/  

irritation  

Serious eye 
damage/  

eye irritation  

Respiratory  

sensitisation  

all 

all 

yes 

yes 

yes 

available in Section 3.2 

yes 

available in Section 3.3 

all 

yes* 

yes* 

see Section 3.4 

*currently not available; 

 
 
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Hazard class  

Category 

Lower SCL 
than GCL 

Higher SCLs than 
GCL (in exceptional 
circumstances) 

Guidance 

Skin sensitisation  

all 

yes 

yes* 

Germ cell 
mutagenicity  

Carcinogenicity  

Reproductive 
toxicity  

STOT-SE  

STOT-RE  

Aspiration hazard  

all 

all 

all 

1 

2 

3 

1 

2 

1 

yes* 

yes* 

yes 

yes 

yes 

no 

yes 

yes 

no 

yes 

yes 

no 

no 

yes 

no 

no 

available  in  Section  3.4 
*currently not available 

see Section 3.5 

*currently not available 

available in Section 3.6 

available  in  Section  3.7 
and in Annex IV 

available in Section 3.8 

see Section 3.8 

available in Section 3.8 

available in Section 3.9 

see Section 3.9 

not 
appropriate 

not appropriate 

not necessary 

1.5.2.  Multiplying factors (M-factors)  

Article 10(2) M-factors for substances classified as hazardous for the aquatic environment, 
acute category 1 or chronic category 1, shall be established by manufacturers, importers and 
downstream users. 

Article 10(4) Notwithstanding paragraph 2, M-factors shall not be set for harmonised hazard 
classes or differentiations for substances included in Part 3 of Annex VI for which an M-factor 
is given in that Part. 

However, where an M-factor is not given in Part 3 of Annex VI for substances classified as 
hazardous to the aquatic environment, acute category 1 or chronic category 1, an M-factor 
based on available data for the substance shall be set by the manufacturer, importer or 
downstream user. When a mixture including the substance is classified by the manufacturer, 
importer or downstream user using the summation method, this M-factor shall be used. 

For the hazard class ‘Hazardous to the Aquatic Environment’, SCLs are not applicable. Instead 
the M-factors concept is used.  

The M-factors are used in the application of the summation method for classification of mixtures 
containing substances that are classified as very toxic. The concept of M-factors has been 
established to give an increased weight to very toxic substances when classifying mixtures. M-
factors are only applicable to the concentration of a substance classified as hazardous to the 
aquatic environment (categories Acute 1 and Chronic 1) and are used to derive by the 
summation method the classification of a mixture in which the substance is present. They are, 

 
 
 
 
 
 
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however, substance-specific and it is important that they are being established already when 
classifying substances. 

For further guidance on how to establish the M-factor see Section 4.1.3.3.3 of this document. 

M-factors should have been established in accordance with Article 10 of CLP and be available in 
the C&L Inventory.  

For the harmonised classifications in Annex VI to CLP, M-factors must be set by the 
manufacturer, importer or downstream user in case there is no M-factor provided, in accordance 
with CLP Article 10(4). 

1.5.3.  Harmonised ATE values 

From 2016 harmonised Acute Toxicity Estimates (ATE) may be included in annex VI of CLP. 
These values have to be used, just as any other harmonised item. ATEs are one way of 
expressing acute toxicity (see Annex I to CLP, 3.1.2.1). 

1.6.  MIXTURES 

1.6.1.  How to classify a mixture 

The classification of mixtures under CLP is for the same hazards as for substances. As a general 
rule and as is the case with substances, available relevant data on the mixture as a whole 
should primarily be used to determine classification where applicable, also considering the 
validity and suitability of the used test method, with regard to testing mixtures in general and 
the specific mixture of concern. Not all the test methods relevant for substances may be 
suitable for (all) mixtures and for this reason care has to be taken. Note that for skin 
sensitisation, care has to be taken so that the doses used do not render the results unreliable. If 
this cannot be done, further approaches to mixture classification may be applied. When 
evaluating CMR hazards and biodegradation and bioaccumulation properties, classification of the 
mixture should according to Article 6(3) and (4) always be based on the ingredient substances 
for these particular hazard classes. However, if data on a mixture show CMR properties even in 
absence of data on possible CMR ingredientes, the mixture has to be classified appropriately 
following Article 6(3). 

It is important to choose the most appropriate method to determine the classification for a 
mixture for each hazard class, differentiation or category. The method will depend on whether 
the mixture is being assessed for physical, health or environmental hazards and on the type and 
quality of information that is available (see also Section 1.2.3 of this document on form or 
physical state).   

It is important to get a clear picture on which substances and mixtures are contained in a 
mixture. Basic information on substances would include the substance identity, its classification 
and any assigned SCLs or M-factors, and concentration in the mixture and, where relevant, 
details of any impurities and additives including their identity, classification and concentration. 
Where an ingredient in a mixture is itself a mixture, it is necessary to get information on the 
ingredient substances of that mixture together with their concentrations, classifications and any 
applied SCLs or M-factors. 

Useful sources for such information are the SDS from the supplier of the substance or the 
mixture, and the C&L Inventory provided by ECHA, which also includes the harmonised 
classifications of substances listed in Annex VI to CLP. Also data from registration dossiers are a 
valuable source of information. 

It should be noted that an SDS should also be provided in some cases when the mixture does 
not meet the criteria for classification but certain specific criteria are met (see Article 31(3) of 
REACH). 

 
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Further dialogue with the supplier may be necessary to obtain additional information. For 
example on compositional information for the mixture supplied. 

The classification of mixtures follows the sequence displayed in Figure 1.1, for each hazard class 
independently (except for CMR and when evaluating biodegradation and bioaccumulation 
properties):  

Figure 1.1  How to classify a mixture 

There is a mixture to classify 

All available information should be gathered 

Are available test data for the 
mixture sufficient for classification?  

(CLP Article 9 (2)-(3)) 

(For physical hazards: consider 
whether new testing needs to be 
performed. Consult the criteria.)  

Yes 

No 

Classify  the  mixture  for  the 
relevant hazard 

Is there data available 
on similar tested 
mixtures and individual 
hazardous ingredients?  

Yes 

Is it possible to 
apply any of the 
bridging principles?  

Yes 

Classify the 
mixture for 
the relevant 
hazard 

No 

No 

Use the known or derived hazard data 
on the individual ingredients to classify 
the mixture for the relevant hazard, 
using the methods in each section of 
CLP Annex I, Part 3, Part 4 and Part 5 

Are hazard data available 
for all or some 
ingredients? 

Yes 

No 

Unable to classify the mixture – go back to 
ingredient suppliers to obtain additional 
information 

  Note: The principles for using expert judgement and weight of evidence determination (CLP 

Article 9(3) and (4)) and Annex I, section 1.1.1.) should be taken into account. 

1.6.2.  Classification for physical hazards 

The majority of the physical hazards of mixtures should be determined through testing based on 
the methods or standards referred to in CLP Annex I, Part 2. In a few cases, the classification of 
mixtures can also be derived through a calculation, if sufficient appropriate data are available 

 
 
 
 
  
 
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(see CLP Annex I 2.2.4.1 and ISO 10156 for flammable gases, CLP Annex I 2.4.4 and ISO 
10156 for oxidizing gases and CLP Annex I, 2.6.4.2 and 2.6.4.3 for flammable liquids). 

Test methods for physical hazards are referred to in each physical hazard class chapter of CLP. 
Most of these test methods can be found in the UN Manual of Tests and Criteria, see the website 
http://www.unece.org/trans/danger/publi/manual/manual_e.html. A few of these test methods 
are contained in standards which are also referred to in CLP (see particularly flammable gases, 
oxidizing gases and flammable liquids). When test result, based on other methods or standards 
(which are not referred to in CLP) are available, then these data may still be used, provided 
they are adequate for the purpose of hazard determination. Expert judgement is necessary to 
conclude whether there is sufficient documentation to assess the suitability of the test used, and 
whether the test was carried out using an acceptable level of quality assurance  and thus on the 
adequacy of such data for the purposes of classification according to CLP. 

Please note that in practice the physical hazards of a substance or mixture may differ from 
those shown by tests, e.g. in case of certain ammonium-nitrate-based compounds (explosive / 
oxidising properties) and certain halogenated hydrocarbons (flammable properties). Such 
experience must be taken into account for the purpose of classification (CLP Article 12(a)). 

The information available or generated must be checked to determine if it is directly comparable 
to the respective hazard criteria and if it is, then it can be used to derive the classification 
immediately. Where the criteria cannot be directly applied to the available data, expert 
judgement should be used for the evaluation of the available information in a weight of 
evidence determination (CLP Article 9(3) and CLP Annex I, 1.1.1.).   

1.6.3.  Health and environmental hazards 

For the purpose of classification for health or environmental hazards, for each hazard check 
whether or not there is information: 

•  on the mixture itself; 

•  on similar tested mixtures and ingredient substances; or 

•  on the classification of ingredient substances and their concentrations in the mixture.  

As pointed out in the introduction to this chapter, the supplier should be contacted if it is 
considered that the information on the substances or mixtures supplied is not sufficient for 
classification purposes. 

The information available on the hazard under consideration, will determine if the mixture 
should be classified using the approaches below in the following sequence (CLP Article 9): 

a.  Classification derived using data on the mixture itself (see Section 1.6.3.1 of this 

document), by applying the substance criteria of Annex I to CLP;  

b.  Classification based on the application of bridging principles (see Section 1.6.3.2 of this 
document), which make use of test data on similar tested mixtures and ingredient 
substances; and 

c.  Classification based on calculation or on concentration thresholds, including SCLs and M-

factors. 

1.6.3.1.  Classification derived using data on the mixture itself 

Classification derived using data on the mixture itself, by applying the substance criteria of 
Annex I to CLP, is applicable for all hazards, except: CMR hazards (see CLP Article 6(3)), 
bioaccumulation and biodegradation properties within the evaluation of the ‘hazardous to the 
aquatic environment’ hazard class referred to in sections 4.1.2.8 and 4.1.2.9 of Annex I to CLP 
(see CLP Article 6(4)). 

 
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Article 6(3) For the evaluation of mixtures pursuant to Chapter 2 of this Title in relation to 
the ‘germ cell mutagenicity’, ‘carcinogenicity’ and ‘reproductive toxicity’ hazard classes 
referred to in sections 3.5.3.1, 3.6.3.1 and 3.7.3.1 of Annex I, the manufacturer, importer or 
downstream user shall only use the relevant available information referred to in paragraph 1 
for the substances in the mixture. 

Further, in cases where the available test data on the mixture itself demonstrate germ cell 
mutagenic, carcinogenic or toxic to reproduction effects which have not been identified from 
the information on the individual substances, those data shall also be taken into account. 

Article 6(4) For the evaluation of mixtures pursuant to Chapter 2 of this Title in relation to 
the ‘biodegradation and bioaccumulation’ properties within the ‘hazardous to the aquatic 
environment’ hazard class referred to in sections 4.1.2.8 and 4.1.2.9 of Annex I, the 
manufacturer, importer or downstream user shall only use the relevant available information 
referred to in paragraph 1 for the substances in the mixture. 

Where the criteria cannot be directly applied to the available data, expert judgement should be 
used for the evaluation of the available information in a weight of evidence determination (CLP 
Article 9(3) and CLP Annex I, 1.1.1). Note that the test method used must be suitable for the 
mixture tested. If data from test methods other than those indicated in Article 8(3) are used, a 
comparison with the methods indicated in that article has to be made to verify the effect on the 
evaluation of the information. 

1.6.3.2.  Bridging principles 

In the case of a classification for health or environmental hazards, relevant information on the 
mixture itself may not always be available. However, where there are sufficient data on similar 
tested mixtures and individual hazardous ingredient substances, CLP allows bridging principles 
to be used to classify the mixture (CLP Annex I, 1.1.3).Only one bridging principle could be 
applied in the evaluation of a hazard class with the exception of Aerosols, where a mixture 
classified based on another bridging principle is used in an aerosol container. However, different 
bridging principles may apply to different hazard classes. 

To apply these bridging principles certain conditions should be considered for their application. 
The conditions are summarised below. 

It is necessary to consult Annex I of CLP, Part 3 for health hazards and Part 4 for environmental 
hazards, before undertaking any of these assessments. 

In case it is not possible to classify the mixture by applying bridging principles and a weight of 
evidence determination using expert judgement by applying the criteria in Annex I to test 
results of a mixture, then the mixture should be classified using the other methods described in 
CLP Annex I, Parts 3 and 4. 

1.6.3.2.1.  Dilution 

Where the tested mixture is diluted with a substance (diluent) that has an equivalent or lower 
hazard category than the least hazardous original ingredient substance, then it can be assumed 
that the respective hazard of the new mixture is equivalent to that of the original tested 
mixture. The application of dilution for determining the classification of a mixture is illustrated 
by Figure 1.2. 

 
 
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Figure 1.2  Application of the bridging principle: dilution for determining the acute toxicity 
classification of a mixture 

Diluent B 
(classification 
known) 

Mixture A 
(tested) 

Mixture C (A+B) 

(not tested) 

Example: Mixture A, which has been classified as acute toxic category 2 based on test data, is 
subsequently diluted with diluent B to form mixture C. If diluent B has an equivalent or lower 
acute toxicity classification than the least acutely toxic ingredient in mixture A and is not 
expected to affect the hazard classification of other ingredients, then mixture C may be also 
classified as acutely toxic category 2. However, this approach may over-classify mixture C, thus 
the supplier may choose to apply the additivity formula described in CLP Annex I, 3.1.3.6 (see 
Section 1.6.3.3.1 of this document). 

Note that also the diluent of the tested mixture is considered a relevant ingredient. 

Consider using this particular bridging principle also when, for example,  

•  diluting an irritant mixture with water, 

•  diluting an irritant mixture with a non-classified ingredient, or 

•  diluting a corrosive mixture with a non-classified or irritant ingredient. 

In case a mixture is diluted with another mixture, see Section 1.6.4.1 of this document. 

Within the ‘hazardous to the aquatic environment’ hazard class, if a mixture is formed by 
diluting another classified mixture or substance with water or other totally non-toxic material, 
the toxicity of the mixture can also be calculated from the original mixture or substance (see 
section 4.1.3.4.3 of Annex I to CLP and mixture example C in Section 4.1.4.7 of this document). 

1.6.3.2.2. 

Batching  

Where a batch of a tested mixture is produced under a controlled process, then it can be 
assumed that the hazards of each new batch are equivalent to those of previous batches. This 
method must not be used where there is reason to believe that the composition may vary 
significantly, affecting the hazard classification. 

1.6.3.2.3. 

Concentration of highly hazardous mixtures 

Where a tested mixture is already classified in the highest hazard category or sub-category, an 
untested mixture which contains a higher concentration of those ingredient substances that are 
in that category or sub-category should also be classified in the highest hazard category or sub-
category (CLP Annex I, 1.1.3.3). 

1.6.3.2.4. 

Interpolation within one hazard category   

Assume there are three mixtures (A, B and C) which contain identical hazardous components. If 
mixtures A and B have been tested and are in the same hazard category, and mixture C is not 

 
 
 
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tested and has concentrations of those hazardous components intermediate to the 
concentrations in mixtures A and B, then mixture C is assumed to be in the same hazard 
category as A and B. The application of interpolation for determining the classification of a 
mixture is illustrated by Figure 1.3 (CLP Annex I, 1.1.3.4). 

Figure 1.3  Application of the bridging principle: interpolation for determining the aquatic acute 
hazard classification of a mixture 

90% 

30% 

10% 

70% 

Mixture A 

(Aquatic Acute 1) 

Mixture B 

(Aquatic Acute 1) 

60% 

30% ≤ conc. ≤ 90% 

40% 

10% ≤ conc. ≤ 70% 

Mixture C 

(Interpolate as Aquatic Acute 1) 

1.6.3.2.5. 

Substantially similar mixtures   

Two mixtures contain an identical ingredient at the same concentration. Each of the two 
mixtures contains an additional ingredient which is not identical with each other; however they 
are present in equivalent concentrations and the hazard category of these two ingredients is the 
same and neither of them is expected to affect the hazard classification of the other ingredient. 
If one of the mixtures is classified based on test data it may be assumed that the hazard 
category of the other mixture is the same. The application of substantially similar mixtures for 
determining the classification of a mixture is illustrated by Figure 1.4 (CLP Annex I, 1.1.3.5). 

 
 
 
  
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Figure 1.4  Application of the bridging principle: substantially similar mixtures for determining 
the skin irritation classification of a mixture 

Ingredient A 

10% 

Ingredient B 

Ingredient B 

90%

Ingredient C 

10% 

Mixture P 
(tested) 

(Skin Irrit. 2) 

Mixture Q 

(not tested) 

Example: If the Ingredient C has the same hazard category and the same potency as Ingredient 
A, then Mixture Q can be classified as Skin Irrit. 2 like Mixture P. Potency may be expressed by, 
for example, differences in the specific concentration limits of Ingredients A and C. This method 
should not be applied where the irritancy of Ingredient C differs from that of Ingredient A.   

1.6.3.2.6. 

Review of classification where the composition of a mixture has changed 

Article 15(2) Where the manufacturer, importer or downstream user introduces a change to 
a mixture that has been classified as hazardous, that manufacturer, importer or downstream 
user shall carry out a new evaluation in accordance with this Chapter where the change is 
either of the following: 

(a) a change in the composition of the initial concentration of one or more of the hazardous 
constituents in concentrations at or above the limits in Table 1.2 of Part 1 of Annex I; 

(b) […] 

Annex I: 1.1.3.6 Review of classification where the composition of a mixture has changed 

The following variations in initial concentration are defined for the application of Article 15(2)(a): 

Bridging Principle for changes in the composition of a mixture 

Table 1.2 

Initial concentration range of the 
constituent 

Permitted variation in initial concentration of the 
constituent 

≤ 2,5 % 

2,5 < C ≤ 10 % 

10 < C ≤ 25 % 

25 < C ≤ 100 % 

± 30 % 

± 20 % 

± 10 % 

± 5 % 

  NOTE: The guidance below explaining Table 1.2 in the green box relates to a change in the 
composition of mixtures already classified as hazardous. A change in the composition of 
non-hazardous mixtures may result in concentration thresholds being reached and a need 

 
 
 
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to classify the changed mixture as hazardous. Where the manufacturer, importer or 
downstream user introduces a change to a mixture not classified for a specific hazard, that 
manufacturer, importer or downstream user must therefore always carry out a new 
evaluation for that hazard in accordance with Chapter 2 of Title II to CLP (see Article 15(1) 
of CLP).  

When a manufacturer, importer or downstream user introduces a change in the composition of 
the initial concentration of one or more of the hazardous constituents of a mixture classified as 
hazardous, that manufacturer, importer or downstream user must carry out a new evaluation, if 
the change in concentrations is at or above the limits in Table 1.2 of Part 1 of Annex I to CLP. 

However, where the variations of the initial concentrations of the constituents lie within the 
permitted variation, manufacturer, importer or downstream user does not need to carry out a 
new evaluation and may use the current classification of the mixture. 

The following example is to illustrate what is meant by the permitted variations in Table 1.2. 

Example: Mixture A is classified as hazardous based on the initial concentration of two 
hazardous constituents, substance A and substance B. The initial concentrations in the mixture 
of substance A and substance B are 2 % and 12 %, respectively. The permitted variation 
according to Table 1.2 is for substance A ± 30 % of the initial concentration and for substance B 
± 10 % of the initial concentration. This means that the concentration in the mixture may for 
substance A vary between 1.4 % and 2.6 % and for substance B between 10.8 % and 13.2 %, 
without having to carry out a new evaluation in accordance with Chapter 2 of Title II to CLP: 

Substance A:  2  ±0.3 = ±0.6   →  

1.4 – 2.6 

Substance B:  12  ±0.1 = ±1.2   →  

10.8 – 13.2 

1.6.3.2.7. 

Aerosols (some health hazards only) 

A mixture in aerosol form is considered to have the same classification as the non-aerosolised 
form of a mixture, provided that the propellant used does not affect these hazards upon 
spraying and data demonstrating that the aerosolised form is not more hazardous than the non-
aerosolised form is available (see CLP Annex I, 1.1.3.7.). 

1.6.3.3.  Classification based on calculation or concentration thresholds 

In most cases, test data on the mixture itself or similar mixtures will not be available, therefore 
bridging principles and weight of evidence determination using expert judgement for all of the 
necessary health and environmental hazard assessments may not be applied. In these cases, 
classification must be based on calculation or on concentration thresholds referring to the 
classified substances present in the mixture. 

In the case where one or more mixtures are added to another mixture, the same requirement 
applies: it is necessary to know all ingredient substances, their hazard classifications and their 
concentrations to be able to derive a correct hazard classification of the final mixture. For 
further details see Section 1.6.4 of this document.  

1.6.3.3.1. 

Classification based on calculation  

More detailed guidance on the selection of the most appropriate method is provided in the 
specific section for each hazard class. 

An example is the hazard class acute toxicity where a calculation formula is used which is based 
on acute toxicity estimates and concentrations, and a modified formula for determining the 
classification of a mixture containing substances of unknown acute toxicity. 

 
 
 
 
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Annex I: 3.1.3.6.1. 

[…] 

The ATE of the mixture is determined by calculation from the ATE values for all relevant 
ingredients according to the following formula for Oral, Dermal or Inhalation Toxicity: 

where: 
Ci = concentration of ingredient i ( % w/w or % v/v) 
i = the individual ingredient from 1 to n 
n = the number of ingredients 
ATEi = Acute Toxicity Estimate of ingredient i. 

Annex I: 3.1.3.6.2.3. If the total concentration of the ingredient(s) with unknown acute 
toxicity is ≤ 10 % then the formula presented in section 3.1.3.6.1 shall be used. If the total 
concentration of the ingredient(s) with unknown toxicity is > 10 %, the formula presented in 
section 3.1.3.6.1 shall be corrected to adjust for the total percentage of the unknown 
ingredient(s) as follows: 

For more information on the CLP calculation formulae for this hazard, please see Section 
3.1.3.3.3 of this document. 

Another example is provided by hazard class ‘hazardous to the aquatic environment’, namely 
the additivity formula: 

Annex I: 4.1.3.5.2. Mixtures can be made of a combination of both components that are 
classified (as Acute Category 1 and/or Chronic Category 1, 2, 3 or 4) and others for which 
adequate toxicity test data are available. When adequate toxicity data are available for more 
than one component in the mixture, the combined toxicity of those components is calculated 
using the following additivity formulas(a) and (b), depending on the nature of the toxicity 
data: 

(a) Based on acute aquatic toxicity: 

where: 
Ci = concentration of component i (weight percentage) 
L(E)C50i = (mg/l) LC50 or EC50 for component i 
η = number of components 
L(E)C50m = L(E)C50 of the part of the mixture with test data 

The calculated toxicity may be used to assign that portion of the mixture a short-term (acute) 
hazard category which is then subsequently used in applying the summation method;

(b) Based on chronic aquatic toxicity: 

=niimixATECATE100=−niimixunknownATECATE%)10if C(100=η50ii50miL(E)CCL(E)CC 
 
 
 
 
  
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Where: 
Ci = concentration of component i (weight percentage) covering the rapidly degradable 
components 
Cj = concentration of component i (weight percentage) covering the non-rapidly degradable 
components 
NOECi = NOEC (or other recognised measures for chronic toxicity) for component i covering 
the rapidly degradable components, in mg/l; 
NOECj = NOEC (or other recognised measures for chronic toxicity) for component i covering 
the non-rapidly degradable components, in mg/l; 
n = number of components, and I and j are running from 1 ton; 
EqNOECm = Equivalent NOEC of the part of the mixture with test data; 
[…] 

  NOTE: The full use of this approach requires access to the whole aquatic toxicity data set 

and the necessary knowledge to select the best and most appropriate data. CLP has limited 
the use of the additivity formulae to those circumstances where the substance hazard 
category is not known, although the acute and/or chronic toxicity data are available. With 
the aquatic toxicity data at hand the ingredient substance classification and M-factor(s) 
could easily be gained by a direct comparison with the substance criteria, which then could 
be fed straight into the summation method. It will therefore usually not be necessary to 
use the additivity formulae. 

For more information on the CLP calculation formulae for this hazard please see Section 4.1.4.3 
of this document. 

1.6.3.3.2. 

Classification based on concentration thresholds 

Generic concentration thresholds 

For most hazard classes or differentiations, classification based on concentration thresholds may 
be applicable. CLP distinguishes between two different kinds of generic concentration 
thresholds:  

•  Generic cut-off values: these values are the minimum concentrations for a substance to 
be taken into account for classification purposes. These substances are also referred to 
as relevant ingredients in some hazard classes (see Sections 3.1, 3.2 and 3.3). When a 
classified substance is present in a concentration above the generic cut-off value it 
contributes to the mixture classification even if it does not trigger classification of the 
mixture directly. The generic cut-off values are defined for some hazard classes and 
categories only and are listed in Table 1.1 of Annex I to CLP; 

•  Generic concentration limits (GCL): these values are the minimum concentrations for a 
substance which trigger the classification of a mixture if exceeded by the individual 
concentration or the sum of concentrations of relevant substances (where the individual 
substance concentrations can be ‘added’ to each other in a straight forward way); they 
are set out in parts 2-5 of Annex I for those hazard classes where they apply.  

Generic concentration thresholds are generic for a hazard class, differentiation or category. The 
difference between a generic cut-off value and a generic concentration limit is demonstrated 
through the example of the skin irritation hazard: while Table 1.1 of Annex I to CLP defines the 
generic cut-off value to be 1 % for a skin irritant substance which is present in a mixture, Table 
3.2.3 of Annex I to CLP shows that a GCL of the skin irritant substance above or equal to the 
concentration limit of 10% triggers classification of the mixture for skin irritation. However, at  
1 % and below 10 %, the substance may still contribute to the classification of the mixture as 
skin irritant. This because the concentration would be taken into account if other skin 

+=+njjniimjiNOEC x 0,1CNOECCNOEC EqCC 
 
 
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corrosive/irritant substances are present in the mixture below the relevant generic 
concentration limits. If additivity applies, classification as provided by the summation in CLP 
Annex I, Table 3.2.3 may be applicable, i.e.: 

(10  Skin Corrosive Categories 1A, 1B, 1C) + Skin Irritant Category 2 should be ≥ 10 % 

Specific concentration thresholds 

In contrast to generic thresholds, ‘Specific Concentration Limits’ (SCLs) and/or specific cut-off 
values may be established for individual substances:  

•  SCLs are described in section 1.5.1 of this document and where they have been 

established they are included in Table 3.1 of Annex VI to CLP43 and/or in the C&L 
Inventory (CLP Article 42). For ‘hazardous to the aquatic environment’ the Multiplying 
factors (M-factors) concept44 is used instead of SCLs, see section 1.5.2 of this guidance. 
SCLs and M-factors included in Tables 3.1 must be used where applicable and, for 
classifications not included in Annex VI, SCLs and M-factors notified to the C&L Inventory 
can be considered and used where applicable. 

•  Cut-off values that may be different from the generic values and that are to be used in 

specific cases are given in 1.1.2.2.2(a) and (b) of Annex I to CLP. For example 
concerning aquatic hazard, for a substance with an established M-factor, the cut-off 
value is always the generic cut-off value divided by the M-factor; hence, (0.1/M) % (see 
1.1.2.2.2(b) and 4.1.3.1 of Annex I to CLP).  

1.6.3.3.3. 

Additivity Vs. non additivity of hazards 

For some hazard classes additivity concepts are normally not applicable. In these cases, the 
general approach is that if a substance or mixture contains two substances each present at a 
concentration below the GCL defined for that hazard class or differentiation, even if the sum of 
the substances' concentrations is above this limit, the mixture will not be classified, as far as no 
lower SCL has been set.  

Additivity is normally not applied for the following hazard classes: 

a.  skin and respiratory sensitisation; 

b.  germ cell mutagenicity; 

c.  carcinogenicity;  

d.  reproductive toxicity;  

e.  specific target organ toxicity, single and repeated exposure, categories 1 and 2; 

f.  skin corrosion/irritation in certain cases (see CLP Annex I, 3.2.3.3.4); and 

g.  serious eye damage/eye irritation in certain cases (see CLP Annex I, 3.3.3.3.4). 

However, in certain cases for these hazard classes additivity may be scientifically justified. 
Expert judgement is needed.  

43 Please note that Table 3.2 of Annex VI to CLP is deleted from 1 June 2017 by Commission Regulation 
(EU) 2016/1179 (9th ATP) amending CLP.  

44 M-factors are used to derive, by means of the summation method, the classification of a mixture in 
which the substance is present for which the M-factor has been established. For further guidance on how 
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If the mode of action (MoA) of two substances is the same, additivity can reasonably be 
assumed. Examples of cases where additivity applies is reprotoxicity of anticoagulant 
rodenticides (a group of substances affecting the same enzyme in the same way), reprotoxicity 
of substances releasing boron ions, skin sensitisation by nickel substances and carcinogenicity 
and mutagenicity of formaldehyde releasers. For the latter group of substances there are 
notes45 in Annex VI stating that the levels of releasable formaldehyde from different 
components of a mixture must be added. This applies regardless whether the substances have a 
harmonised classification or not, whether the purpose of the substance is to act as a 
formaldehyde releaser or not and it includes formaldehyde itself. 

When the MoA is different, there may be some cases where it is deemed appropriate to assume 
additive or synergistic effects. In other cases, there may be no cause for additivity. 

For STOT SE-RE 1 and 2 additivity may be assumed for substances with the same target organ, 
especially if the MoAs are similar. Again, in other cases there may be no reason to assume 
additivity. 

Additivity is used for the following hazard classes or differentiations: 

a.  Acute toxicity (according to specific formula); 

b.  skin corrosion/irritation (besides the cases mentioned in CLP Annex I, 3.2.3.3.4); 

c.  serious eye damage/eye irritation (besides the cases mentioned in CLP Annex I, 

3.3.3.3.4); 

d.  specific target organ toxicity, single exposure Category 3 (respiratory tract irritation);  

h.  specific target organ toxicity, single exposure Category 3 (narcotic effects);  

e.  aspiration hazard (plus consideration of viscosity of the final mixture); 

f.  short-term (acute) and long-term (chronic) aquatic toxicity and 

g.  Hazardous for the ozone layer. 

In these cases, as well as in the specific cases described above when additivity may be 
scientifically justified, if the sum of the concentrations of one or several substances classified for 
the same hazard class/category in the mixture equals or exceeds the GCL set out for this hazard 
class/category, the mixture must be classified for that hazard. For substances that have an SCL 
or M-factor(s), these should be taken into account when applying the summation methods. The 
method described in section 3.2.3.2.3.2 can be used when one or more substances in a mixture 
have SCLs.  

If the sum of (ConcA / clA) + (ConcB / clB) + …. + (ConcZ / clZ) is   1 then the mixture needs 
to be classified for the hazard class in question. 

Where   ConcA = the concentration of substance A in the mixture; 

      clA = the concentration limit (either specific or generic) for substance A; 

            ConcB = the concentration of substance B in the mixture; 

45 The 10th ATP added the following notes in Annex I to CLP:  

“Note 8: The classification as a carcinogen need not apply if it can be shown that the maximum theoretical 
concentration of releasable formaldehyde, irrespective of the source, in the mixture as placed on the 
market is less than 0,1%.” 

“Note 9: The classification as a mutagen need not apply if it can be shown that the maximum theoretical 
concentration of releasable formaldehyde, irrespective of the source, in the mixture as placed on the 
market is less than 1%.” 

 
 
 
 
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      clB = the concentration limit (either specific or generic) for substance B; etc. 

An example is provided for the hazard class serious eye damage /eye irritation: in case there 
are only substances classified as eye irritation Category 2 present in a mixture, then their sum 
must be equal to or exceed the generic concentration limit of 10 % in order for the mixture to 
be classified in Category 2 as well. Note that only relevant substances (i.e. for eye irritants, 
above the generic cut-off value of 1%) should be summed up and contribute to mixture 
classification. Further guidance on the application of SCLs when using the summation method to 
derive conclusions on skin corrosion / irritation or serious eye damage/eye irritation hazards can 
be found in Sections 3.2 and 3.3 of this document.  

1.6.4.  Classification of mixtures in mixtures 

For physical hazards, an adequate hazard classification is generally derived by testing. To 
determine the classification of a mixture for health or environmental hazards using the 
additivity or summation methods, information on all the component substances, including their 
individual hazard classification and concentration, is generally required. In the case where one 
or more mixtures are added to another mixture, the same requirement applies: it is generally 
necessary to know all component substances, their hazard classifications and their 
concentrations to be able to derive a correct hazard classification of the final mixture. It is 
generally not possible to derive the correct hazard classification for the final mixture by using 
only the hazard classification(s) of the mixtures that were combined to make it. For example, a 
mixture containing 1% of a Carc. Cat. 1B substance would be classified as Carc. Cat. 1B. Taking 
1% of this mixture into another mixture would lead to a concentration of the ingredient causing 
the carcinogenic classification of 0.01%, i.e. below the GCL. The same situation may occur also 
for substances classified due to an impurity. 

However, there is one exception. If the acute toxicity estimate (ATE) of a mixture is known 
(either actual or derived), this value can be used to derive a correct classification for acute 
toxicity if this mixture is added to another mixture. 

Thus, it is very important that suppliers of mixtures communicate the necessary information 
listed above on component substances (including their individual hazard classification and 
concentration) down the supply chain, normally in the SDS, to enable a correct classification to 
be established by downstream users formulating new mixtures from their products. However, 
the information provided in the SDS may not be sufficient, for example where only a 
concentration range is quoted for a particular substance or where the mixture contains other 
substances classified as hazardous but which are present below the concentration which triggers 
the obligation to indicate the substance in the SDS. Thus further dialogue with the supplier of 
the mixture may be necessary to obtain additional information on the constituent substances to 
ensure correct classification and labelling of the new mixture. 

In situations, where tested mixtures are added to other tested or untested mixtures, an 
adequate hazard classification can only be derived by taking account of the test data as well as 
the knowledge on all ingredient substances, their hazard classifications, and their 
concentrations in these mixtures. Such an approach is a case-by-case analysis and requires 
expert judgement. 

1.6.4.1.  Example: Classification of Mixture A 

Note that the example only addresses health hazards. For compositional details see Table 1.2 
and Table 1.3 below. 

Mixture A is a water solution containing a surfactant, a thickening agend dye and a fragrance 
mixture. Classification of components and composition of the fragrance mixture are known. 

No test data are available on Mixture A and it is not possible to apply bridging principles due to 
lack of data on similar tested mixtures. Therefore it is necessary to identify the ingredients in 
Mixture A (including their % w/w and classification).  

 
 
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Mixture A does not contain any ingredients classified as a respiratory sensitiser, CMR, STOT or 
aspiration hazard. Therefore it is possible to conclude that Mixture A will not be classified as 
hazardous for these particular hazard classes. 

Acute toxicity 

As indicated in CLP Annex I, point 3.1.3.3(b), there are two options to calculate the acute 
toxicity of Mixture A: (i) treat the 'fragrance mixture' as an ingredient when calculating the ATE 
for Mixture A, or (ii) break the 'fragrance mixture' down into its component ingredients and only 
take over the relevant ingredients (CLP Annex I, 3.1.3.3(a) and 3.1.3.6.1) into the calculation 
for the ATE of Mixture A.   

Following option (i) it is first necessary to calculate ATEmix of the 'fragrance mixture' (see Table 
1.3) taking into account 'FM component 1' and 'FM component 2' (other components can be 
excluded as their LD50 values are > 2000 mg/kg): 

The ATEmix for the 'fragrance mixture' can then be included in the calculation of the ATEmix for 
Mixture A: 

Following option (ii) it is only necessary to include 'FM component 1' from the 'fragrance 
mixture' (present in Mixture A at 1.76 %), as 'FM component 2' is present in a concentration < 
1%). Calculation of the ATEmix for Mixture A according to option (ii): 

Both options indicate that the calculated ATEmix of Mixture A is > 2000 mg/kg thus mixture A is 
not classified as hazardous for acute toxicity by the oral route. 

  NOTE: If an acute oral toxicity test (i.e. an actual LD50 value) was available for the 

fragrance mixture, then this should be used in the calculation for the ATE of Mixture A. 

Skin corrosion/irritation 

Work out the actual levels of the 'fragrance mixture' ingredients in Mixture A and carry out the 
summation method (CLP Annex I, Table 3.2.3) using the relevant ingredients. 

mg/kg15975000.1712302.35100ATEATEC100ATEATECATE100mixniimixniimix=+=→=→=mg/kg1330015970.518000.8100ATEmix=+=mg/kg17200123076.118000.8100ATEmix=+= 
 
 
 
 
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Mixture A does not contain any ingredient classified as Skin Corr. 1A, B or C. Therefore Mixture 
A is not classified as Skin Corr. 1A, B or C. 

The 'fragrance mixture' contains ingredients classified as Skin Irrit. 2, but these are all present 
in Mixture A at concentrations < 1 % and can be disregarded (generic cut-off values to be taken 
into account, CLP Annex I, Table 1.1). Mixture A does also contain 8 % of the 'anionic 
surfactant' classified as Skin Irrit. 2, but as the concentration of the 'anionic surfactant' < 10 % 
(GCL, CLP Annex I, Table 3.2.3), Mixture A is not classified as Skin Irrit. 2. 

Serious eye damage/eye irritation 

Work out the actual levels of the 'fragrance mixture' ingredients in Mixture A and carry out the 
summation method (CLP Annex I, Table 3.3.3) using the relevant ingredients: 

Mixture A contains 8 % of an ingredient classified as Eye Dam. 1, thus Mixture A must also be 
classified as Eye Dam. 1 (i.e. the relevant ingredient is present in a concentration above the 
GCL of 3 %). The 'fragrance mixture' also contains an ingredient classified as Eye Dam. 1, but 
this is present in Mixture A at a concentration < 1 % and can disregarded. 

Skin sensitisation 

The 'fragrance mixture' contains four ingredients classified as skin sensitisers (cat 1) but their 
actual levels in Mixture A are belowthe GCL of 1 % thus Mixture A is not classified as a skin 
sensitiser. However, the four skin sensitiser ingredients are present above 0.1 %, thus 
additional labelling information EUH208 (CLP Annex II, 2.8) would be required on the label for 
Mixture A. 

In summary, mixture A is classified as Eye Dam.1 and additional labelling information is needed 
on the label. EUH208 — ‘Contains (name of sensitising substance). May produce an allergic 
reaction’. 

Table 1.2  Ingredients in Mixture A 

Ingredient 

% w/w  Oral LD50 (rat) 

Classification 

Anionic surfactant 

8.00 

1800 mg/kg 

Acute Tox. 4 (oral) 

Eye Dam. 1 

Skin Irrit. 2 

Thickening agent 

0.80 

> 5000 mg/kg 

Not classified 

Dye 

0.05 

> 5000 mg/kg 

Not classified 

Fragrance mixture  

5.00 

not tested 

Acute Tox. 4 (inhalation, oral) 

(see list of ingredients below) 

Water 

Total: 

86.15 

100.00 

Skin Sens. 1 

Eye Dam. 1 

Skin Irrit. 2 

Aquatic Chronic 2 

Not classified 

 
 
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Table 1.3  Ingredient 'Fragrance mixture'  

Ingredient 

% w/w  % in Mixture A 

Oral LD50 (rat) 

Classification 

FM component 1 

35.20 

1.76 

1230 mg/kg 

FM component 2 

17.00 

0.85 

not available 

(use cATpE 500) 

Acute Tox. 4 
(inhalation, oral) 

Acute Tox. 4 (oral) 
Skin Sens. 1 

FM component 3 

16.00 

0.8 

3600 mg/kg 

Skin Sens. 1 

Skin Irrit. 2 

FM component 4 

13.40 

FM component 5 

7.00 

0.67 

0.35 

3100 mg/kg 

Skin Sens. 1 

> 2000 mg/kg 

Eye Dam. 1 

Aquatic Chronic 2  

FM component 6 

6.00 

0.3 

4400 mg/kg 

Flam. Liq. 3  

Skin Sens. 1  

Skin Irrit. 2 

Aquatic Chronic 1 

FM component 7 

FM component 8 

2.80 

2.60 

0.14 

0.13 

> 5000 mg/kg 

Not classified 

> 5000 mg/kg 

Aquatic Chronic 1 

Total: 

100.00 

5.00 

1.6.4.2.  Example: Classification of Mixture B 

Note that the example only addresses health hazards.  

Mixture B is a powder form detergent containing a base powder, silicates, carbonate and 
inorganic processing aid. The compositional details including the %w/w and classification of the 
ingredients are provided in Table 1.4 and Table 1.5 below. 

No test data are available on Mixture B and it is not possible to apply bridging principles due to 
lack of data on similar tested mixtures.  

Mixture B does not contain any ingredients classified as a skin sensitiser, CMR or aspiration 
hazard. Therefore it is possible to conclude that Mixture A will not be classified as hazardous for 
these particular hazard classes. 

Acute toxicity 

As indicated in CLP Annex I, 3.1.3.3(b), there are two options to calculate acute toxicity of 
Mixture B: (i) treat the 'base powder' as an ingredient when calculating the ATE for Mixture B, 
or (ii) break the 'base powder' down into its component ingredients and only take over the 
relevant ingredients (CLP Annex I, 3.1.3.3(a) and 3.1.3.6.1) into the calculation for the ATE of 
Mixture B.   

Following option (i) it is first necessary to calculate the ATEmix of the 'base powder' taking into 
account the non-ionic surfactant (other components can be excluded as LD50 values are > 2000 
mg/kg): 

 
 
 
 
 
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The ATEmix for the 'base powder' can then be used for the calculation of the ATEmix for Mixture B: 

Following option (ii) it is only necessary to include the non-ionic surfactant from the 'base 
powder' (present in Mixture B at 3.6%). Other ingredients in the 'base powder' can be excluded 
as LD50 > 2000 mg/kg for all of them. The calculation of the ATEmix for Mixture B applying option 
(ii): 

Both options indicate that the calculated ATEmix of Mixture B is > 2000 mg/kg. Therefore Mixture 
B is not classified as hazardous for acute toxicity by the oral route. 

  NOTE:  If  an  acute  oral  toxicity  test  (i.e.  an  actual  LD50  value)  was  available  for  the  'base 

powder' then this should be used in the calculation for the ATE of Mixture B. 

Skin corrosion/irritation 

Additvity is considered to apply. Work out the actual levels of the 'base powder' ingredients in 
Mixture B and carry out the summation method (CLP Annex I, Table 3.2.3) using the relevant 
ingredients: 

Mixture B does not contain any ingredients classified as Skin Corr. 1A, B or C thus Mixture B is 
not classified as Skin Corr. 1A, B or C. 

Mixture B does however contain 23 % ingredients classified as Skin Irrit. 2 (11% silicates, 8% 
anionic surfactant and 4% anionic surfactant from the 'base powder'), as the content of 
classified ingredients are > 10% also Mixture B is classified as Skin Irrit. 2. 

mg/kg27785000.18100ATEATEC100ATEATECATE100mixniimixniimix==→=→=mg/kg286018000.87700.1827780.20100ATEmix=++=mg/kg286018000.87700.185006.3100ATEmix=++= 
 
 
 
 
 
 
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Serious eye damage/eye irritation 

Work out the actual levels of the 'base powder' ingredients in Mixture B and carry out the 
summation method (CLP Annex I, Table 3.3.3) using the relevant ingredients: 

Mixture B contains 40.6 % ingredients classified as Eye Dam.1 (18% substance X, 11% 
silicates, 8 % anionic surfactant and 3.6 % non-ionic surfactant), thus Mixture B is also 
classified as Eye Dam.1.  

Respiratory sensitisation 

Mixture B contains 0.7% of the ingredient 'enzymes' classified for respiratory sensitisation 
category 1. However this is below the concentration triggering classification (CLP Annex I, Table 
3.4.5) thus Mixture B is not classified as a respiratory sensitiser. However ingredient 'enzymes' 
trigger additional labelling information EUH208 (CLP Annex II, 2.8). 

STOT 

Mixture B does not contain any ingredients classified as STOT RE or STOT SE 1 or 2, but it 
contains 11% of an ingredient classified as STOT SE 3 (respiratory tract irritation). The generic 
concentration limit is 20 % for extrapolating the classification as STOT SE 3 from an ingredient 
to the mixture (CLP Annex I, 3.8.3.4.5.), thus Mixture B does not trigger classification as STOT 
SE 3 (respiratory tract irritation). 

In summary, mixture B is classified as Skin Irrit. 2, Eye Dam. 1 and additional labelling 
information is needed on the label. EUH208 — ‘Contains (name of sensitising substance). May 
produce an allergic reaction’. 

Table 1.4  Ingredients in Mixture B 

Ingredient 

% w/w  Oral LD50 (rat)  Classification 

Base powder  

(see list of ingredients below) 

20.00 

not tested 

Eye Dam.1 

Skin Irrit. 2 

Ox. Sol. 1  

Substance X 

18.00 

770 mg/kg 

Acute Tox. 4 (oral)  

Eye Dam. 1 

Eye Dam. 1 

Silicates 

11.00 

3400 mg/kg 

Skin Irrit. 2  

STOT SE 3 (respiratory tract irritation)  

Carbonate 

7.00 

4090 mg/kg 

Eye Irrit. 2 

Inorganic processing aid 

11.30 

> 5000 mg/kg  Not classified 

Builder 

16.00 

> 5000 mg/kg  Not classified 

Acute Tox. 4 (oral)  

Anionic surfactant 

8.00 

1800 mg/kg 

Eye Dam. 1 

Skin Irrit. 2  

Substance Y 

5.00 

> 5000 mg/kg  Not classified 

Enzymes  

0.70 

> 2000 mg/kg  Resp. Sens. 1 

 
 
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Ingredient 

% w/w  Oral LD50 (rat)  Classification 

Polycarboxylate 

3.00 

> 5000 mg/kg  Not classified 

Total: 

100.00 

Table 1.5  Ingredients ‘base powder’ 

Ingredient 

% w/w  % in Mixture B  Oral LD50 (rat) 

Classification 

Non-ionic surfactant 

18.00 

3.6 

500 mg/kg 

Eye Dam. 1 

Acute Tox. 4 (oral) 

Anionic surfactant 

20.00 

4.0 

> 2000 mg/kg 

Aquatic Acute 1 

Skin Irrit. 2 

Eye Irrit. 2 

Builder 

50.00 

10.0 

> 5000 mg/kg 

Not classified 

Carbonate 

8.00 

Inorganic processing aid 

4.00 

1.6 

0.8 

4090 mg/kg 

Eye Irrit. 2 

> 5000 mg/kg 

Not classified 

Total: 

100.00 

20.00 

1.7.  ANNEX VII TO CLP 

Article 61(5) Where a substance or mixture has been classified in accordance with 
Directive 67/548/EEC or 1999/45/EC before 1 December 2010 or 1 June 2015 respectively, 
manufacturers, importers and downstream users may amend the classification of the 
substance or mixture using the conversion table in Annex VII to this Regulation. 

  NOTE: Article 61 uses the term ‘conversion table’ and Annex VII uses the term 

‘translation table’. These terms have the same meaning i.e. the tables in Annex VII to 
CLP that relate classifications according to DSD or DPD to a classification according to 
CLP. 

The tables contained in Annex VII to CLP show how classifications in accordance with the DSD 
were converted into the corresponding classification under CLP and included in Table 3.1 of 
Annex VI to CLP46. The tables also aimed to support translation of existing self-classifications in 
accordance with DSD into classifications in accordance with CLP.  

Although conceptually similar, the coverage of CLP and the DSD or DPD is different. In some 
cases, the relationship between the category of danger and corresponding R-phrases and the 
hazard categories and corresponding hazard statements is clear, but in other cases, it is less 
well defined. Additionally, CLP introduced new hazard classes reflecting hazards that were not 
covered or were only partly covered by DSD and DPD.  

46 Note that the 8th ATP has corrected the Annex VII to CLP. The current Annex VII suggests R34 = Skin 
Corr. 1 whereas the original translation was to Skin Corr. 1B. 

 
 
 
 
 
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While the tables explicitly point out where no translation was possible or where minimum 
classification would be applied, they do not identify situations where CLP hazard classes or 
categories, not covered by the DSD and DPD, are required under CLP. In the particular case of 
‘no classification’ under the DPD, the table would not provide any indication for a reasonable 
translation to a CLP classification.   

As mentioned, the Annex VII (to CLP) translation tables did not always give a direct translation. 
For certain hazard classes, including acute toxicity and STOT repeated exposure, a translation 
from DSD to CLP according to Annex VII to CLP, resulted in a recommended minimum 
classification.  This minimum classification is also indicated as such in Table 3.1 in Annex VI, 
and should only be used if no additional hazard information is available (see also CLP Annex VI, 
1.2.1).  

It should be noted that whenever data for a substance or mixture is available for a hazard class, 
the substance or mixture must be classified in accordance with the CLP criteria and the Annex 
VII (to CLP) tables must no longer be used. 

Table 1.6 identifies where no direct translation was possible according to the Annex VII (to CLP) 
translation tables for substances and mixtures requiring classification under DSD or DPD. 

In addition to the differences indicated in Table 1.6, it should be noted that for some hazards, 
the generic concentration limits to be applied for mixtures, were lowered under CLP as 
compared to DPD. Lower generic concentration limits were set for skin corrosion (R34 and R35), 
severe eye damage and eye irritation (R41 and R36), skin irritancy (R38) and reproductive 
toxicity (R60, R61, R62 and R63). 

Table 1.6   Hazard classes where the translation tables in Annex VII to CLP indicate that no 
direct translation was possible from DSD to CLP 

Classifications 
under DSD or DPD 

Potential translation 
outcomes 

Comments 

E, R2 

E, R3 

1) Explosive.  

2) Organic peroxide 

3) Flammable solid 

4) Oxidising solid 

5) Self-reactive 

6) No classification 

O, R8 (liquid) 

Oxidising liquid 

O, R8 (solid) 

Oxidising solid 

F, R11 (solid) 

1) Flammable solid 

1a) Possibly self-heating 
in addition 

Change of classification criteria and method; case-
by-case considerations  

See Annex VII to this Guidance for additional  
information on transport classifications 

All liquid substances or mixtures classified O,R8 are 
classified as oxidising liquids under CLP. 

See Annex VII to this Guidance for additional  
information on transport classifications 

The test methods for oxidising solids in 67/548/EEC 
and CLP were different. Most solids classified O, R8 
are also classified as oxidising solids under CLP.  

See Annex VII to this Guidance for additional  
information on transport classifications 

Solid substances or mixtures classified F, R11 may 
be classified as flammable solids or self reactives 
under CLP. If classified as flammable solids, they 
may additionally be classified as self-heating. 

 
 
 
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Classifications 
under DSD or DPD 

Potential translation 
outcomes 

Comments 

2) Self-reactive 

See Annex VII to this Guidance for additional  
information on transport classifications 

F, R15 

Substance or mixture 
which, in contact with 
water, emit(s) 
flammable gas(es) 

See Annex VII to this Guidance for additional  
information on transport classifications 

 
 
 
 
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2.  PART 2: PHYSICAL HAZARDS 

2.0.  INTRODUCTION 

2.0.1  General remarks about the prerequisites for classification and testing 

The purpose of this chapter is to give some general guidance with respect to the classification of 
physical hazards, the generation of test data and their interpretation. The intention of CLP is to 
identify hazards of chemical substances and mixtures and to provide a systematic approach – 
using classification - to communicate them based on harmonized criteria. The classification 
process involves three steps: 

1.  gathering of relevant information regarding the hazards of a substance or mixture 

(Articles 5 – 8 of CLP); 

2.  evaluation of hazard information to ascertain the hazards associated with the substance 

or mixture (Article 9 of CLP); and 

3.  a decision on whether the substance or mixture will be classified as hazardous and the 
degree of hazard, where appropriate, by comparison of the data with agreed hazard 
classification criteria (Article 13 of CLP). 

Generally, for bothsubstances and mixtures, the tests required in Annex I of CLP must be 
performed unless there is adequate and reliable information already available. Testing is 
required to determine physical hazards including the physico-chemical properties necessary for 
the respective classification unless alternative methods are specifically permitted. Before 
undertaking testing of a substance or mixture, enquiries should be made to ascertain the 
availability of data, e.g. flash points, on the substance or mixture. 

2.0.2  Safety 

In most cases, the classification is based on data derived from testing. Special care is required 
when new or unknown substances or mixtures are tested. If possible, preliminary tests should 
be carried out before larger quantities are handled. Appendix 6 of the UN Recommendations on 
the transport of dangerous goods Manual of Tests and Criteria (UN-MTC) 'Screening procedures' 
allows gathering valuable information about physico-chemical properties based on small-scale 
tests. Further aspects of safety are given in the general introduction, Section 1.4 of the UN-MTC 
or within the individual test procedures. 

2.0.3  General conditions for testing 

Samples offered for testing must in all aspects be representative of the substance or mixture to 
be classified. Therefore, it is helpful to characterise or specify the sample for the purposes of 
documentation (i.e. batch number, production code, impurities etc.). Further characterisation 
(i.e. analysis) is highly recommended in cases where the presence of diluents, activators, 
stabilisers or moisture may influence the outcome of the test. 

In some cases, additional parameters like (e.g.) physical condition, particle size and shape, 
specific surface area, density, crystal structure, may influence the test result. Therefore, these 
properties should be mentioned in the test report.  

The tests must be performed on the substance or mixture in the appropriate physical form 
where changes in that form may influence the outcome of the test (see also Articles 5 and 6 of 
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2.0.4  Physical state 

The physical state determines which hazard classes should be considered for testing. As the CLP 
states47, hazard classification is based on intrinsic properties of the substance or mixture which 
are determined not only by its physical state but also its form. 

As mentioned in Chapter 1.2 of this guidance, the same solid substance or mixture may have 
different forms such as flakes, prills, or powder. Furthermore, e.g. a powder may contain 
particles of different size, and particles of the same size may have different shapes, crystallinity 
or allotropy etc. These differences may result in different intrinsic properties, and consequently, 
different physical hazards of the powder. Particle size is crucial for several classes such as 
explosives, flammable solids, self-reactive substances, pyrophoric solids, self-heating 
substances, solid organic peroxides and substances which, in contact with water, emit 
flammable gases. Therefore not only the physical appearance, but also other parameters should 
be considered when identifying the form, since they may trigger different classifications of the 
same substance or mixture. 

An example of different classification due to different intrinsic properties of forms is red 
phosphorus (flammable solid) and white phosphorus (pyrophoric solid) (different allotropes). It 
is therefore important to evaluate case by case whether available information on the physical 
properties of the substance and mixture placed on the market, is applicable to the examined 
form, and whether additional testing should be performed.  

The form of a substance or mixture as placed on the market might be such that it is not 
possible to test it in this form, e.g. if it is in the form of tablets or pellets. In such 
circumstances, the physical hazards of the substance or mixture must be considered for 
classification especially if they are friable and produce secondary effects due to abrasion or 
crushing during supply and use. If phase separation does occur, the hazardous properties of the 
most hazardous phase of the substance or mixture must be communicated. 

If further testing is required, the choice of the test method should be done after thorough 
evaluation of its suitability for the substance or mixture, as the properties of the form (e.g. for 
powders especially size and shape of the particle) may have a significant effect on the test 
results.  

The definitions for gases, liquids and solids are given in Annex I, Part 1 of CLP: 

Annex I: Part 1, 1.0.     Definitions 

Gas means a substance which:  

(i)  at 50 °C has a vapour pressure greater than 300 kPa (absolute); or  

(ii) is completely gaseous at 20 °C at a standard pressure of 101.3 kPa; 

Liquid means a substance or mixture which:  

(i)  at 50 °C has a vapour pressure of not more than 300 kPa (3 bar); 

(ii) is not completely gaseous at 20 °C and at a standard pressure of 101,3 kPa; and  

(iii) which has a melting point or initial melting point of 20 °C or less at a standard 

pressure of 101,3 kPa; 

Solid means a substance or mixture which does not meet the definitions of liquid or gas. 

In some cases (i.e. viscous substances or mixtures), a specific melting point cannot be 
determined. Such a substance or mixture must be regarded as a liquid if either the result of the 

47 CLP Article 5(1), 6(1) and 8(6). 

 
 
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ASTM D 4359-90 test as amended (standard test method for determining whether a material is 
a liquid or a solid) indicates ‘liquid’ or the result of the test for determining fluidity 
(penetrometer test) prescribed in Section 2.3.4 of Annex A of ADR indicates ‘not pasty’. 

2.0.5  Quality 

The determination of data must be based on the methods named in Annex I, Part 2 of CLP. For 
most hazard classes in Annex I, Part 2 of CLP there is reference made to the UN-MTC which 
gives very detailed descriptions of the test methods. For the classification of flammable gases, 
oxidising gases and for the determination of the flash point there are references to international 
standards in Annex I, Part 2 of CLP. Whenever possible, the laboratory should validate the 
performance of the methods used e.g. by participating in inter-laboratory testing or by using 
reference materials. Any deviation from the test procedure or standard should be documented 
and, if necessary, justified. 

The reliability of all test results used for the classification of hazardous substances and mixtures 
is important and therefore their transparency and comparability must be ensured. 

For these purposes, CLP requires in Article 8 the following:  

Article 8 (5) 

[…] 

Where new tests for physical hazards are carried out for the purposes of this Regulation, 
they shall be carried out, at the latest from 1 January 2014, in compliance with a relevant 
recognised quality system or by laboratories complying with a relevant recognised standard. 

[…] 

In general, the following alternative strategies can be pursued: 

1.  compliance with the principles of good laboratory practice (GLP) (as formerly required by 

the DSD); 

2.  application of EN ISO/IEC 17025 General requirements for the competence of testing and 

calibration laboratories as amended as a relevant recognised standard; 

3.  other internationally recognised standards of comparable scope. 

Any laboratory that carries out physical hazard tests for classification purposes can therefore 
choose how to fulfil the quality requirements of CLP. 

2.1.  EXPLOSIVES 

2.1.1.  Introduction 

The requirements in Chapter 2.1 ‘Explosives’ of Annex I of CLP are identical to those in Chapter 
2.1 of GHS. 

The classification of explosives according to the GHS is almost entirely adopted based on the UN 
Recommendations on the Transport of Dangerous Goods – Model Regulations (UN RTDG Model 
Regulations), which are appropriate for transport and also storage of packaged explosives.  

The classification of substances, mixtures and articles in the class of explosives and further 
allocation to a division is a very complex procedure. References to Part I of the UN-MTC and 
related expertise are necessary. 

 
 
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2.1.2.  Definitions and general considerations for the classification of 

explosives 

The following definition is given in CLP for the class of explosives. 

Annex I: 2.1.1.1.     The class of explosives comprises 

(a)  explosive substances and mixtures; 

(b)  explosive articles, except devices containing explosive substances or mixtures in such 
quantity or of such a character that their inadvertent or accidental ignition or initiation 
shall not cause any effect external to the device either by projection, fire, smoke, heat 
or loud noise; and 

(c) 

substances, mixtures and articles not mentioned in points (a) and (b) which are 
manufactured with a view to producing a practical, explosive or pyrotechnic effect. 

Additional remark related to the applicability of 2.1.1.1 (a) (see also UN RTDG Model 
Regulations, 2.1.1.1 (a)): 

•  a substance or mixture which is not itself an explosive but which can form an explosive 

atmosphere of gas, vapour or dust is not included in this class; 

•  explosive behaviour related to the thermal decomposition of organic peroxides and of 
self-reactive substances and mixtures is covered by those specific hazard classes and 
therefore not included in the hazard class explosives. 

In addition the following definitions apply for explosives:  

Annex I: 2.1.1.2.  

[…]  

An explosive substance or mixture is a solid or liquid substance or mixture of substances 
which is in itself capable by chemical reaction of producing gas at such a temperature and 
pressure and at such a speed as to cause damage to the surroundings. Pyrotechnic 
substances are included even when they do not evolve gases. 

A pyrotechnic substance or mixture is a substance or mixture of substances designed to 
produce an effect by heat, light, sound, gas or smoke or a combination of these as the result 
of non-detonative self-sustaining exothermic chemical reactions. 

An unstable explosive is an explosive which is thermally unstable and/or too sensitive for 
normal handling, transport and use. 

An explosive article is an article containing one or more explosive substances or mixtures. 

A pyrotechnic article is an article containing one or more pyrotechnic substances or mixtures. 

An intentional explosive is a substance, mixture or article which is manufactured with a view 
to produce a practical explosive or pyrotechnic effect. 

Certain physical hazards (due to explosive properties) are altered by dilution, as is the case for 
desensitized explosives, by inclusion in a mixture or article, packaging or other factors.  

Explosive substances and mixtures wetted with water or alcohols, or diluted with other 
substances to suppress their explosive properties, may be treated differently to their non-
wetted or non-diluted counterparts i.e. different hazard classes may apply, depending on the 
physical properties of the wetted/diluted substance or mixture. 

 
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2.1.3.  Relation to other physical hazards 

For safety reasons, substances, mixtures or articles which have already been classified as 
Explosives (Class 1 according to the UN RTDG Model Regulations) should not be considered for 
classification in any other physical hazard classes. Since the explosion hazard is more severe 
than other physical hazards there is no need to further perform classification tests for other 
potential physical hazards. 

When considering substances and mixtures for classification within the hazard class explosives, 
the following checks should be performed with respect to other hazard classes: 

Substances, mixtures and articles that have been manufactured with a view to producing a 
practical explosive or pyrotechnic effect, are classified as explosives by definition according to 
2.1.1.1(c) of Annex I of the CLP. It should be checked whether such a substance or mixture is 
an unstable explosive. 

Thermally unstable substances or mixtures that are not classified as explosives should be 
considered for classification as self-reactive substances and mixtures. 

Mixtures of oxidising substances and mixtures with combustible material that are not classified 
as explosives should be considered for classification as self-reactive substances and mixtures, 
oxidising liquids or oxidising solids. 

Due to the complexity of these issues, expert advice should always be sought when dealing with 
classification of substances and mixtures with potentially explosive properties.  

2.1.4.  Classification of substances, mixtures or articles as explosives 

2.1.4.1. 

Identification of hazard information 

Information on the following types of hazards is relevant for the evaluation of substances, 
mixtures and articles for the class of explosives: 

sensitivity to shock; 

thermal stability; 
sensitiveness to impact and friction; 

• 
•  effects of heating and ignition under confinement; 
• 
• 
•  mass explosion hazard; 
•  projection hazard; 
• 

fire and radiant heat hazard. 

2.1.4.2.  Screening procedures and waiving of testing 

The screening procedure is described in: 

CLP, Annex I, Part 2, paragraphs 2.1.4.2 and 2.1.4.3; Appendix 6 of the UN-MTC. 

The screening procedure may be used for new substances or mixtures which are suspected of 
having explosive properties. It should not be used for substances and mixtures manufactured 
with the intention of producing a practical explosive or pyrotechnic effect. 

Explosive properties are associated with the presence of certain chemical groups in a molecule 
which can react to produce very rapid increases in temperature and/or pressure. The screening 
procedure is aimed at identifying the presence of such reactive groups and the potential for 
rapid energy release.  

Examples of groups which may indicate explosive properties in organic materials are: 

•  C-C unsaturation (e.g. acetylenes, acetylides, 1, 2-dienes); 
•  C-Metal, N-Metal (e.g. Grignard reagents, organo-lithium compounds); 

 
 
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•  Contiguous nitrogen atoms (e.g. azides, aliphatic azo compounds, diazonium salts, 

hydrazines, sulphonylhydrazides); 

•  Contiguous oxygen atoms (e.g. peroxides, ozonides); 
•  N-O (e.g. hydroxyl amines, nitrates, nitro compounds, nitroso compounds, N-oxides, 

1,2-oxazoles); 

•  N-halogen (e.g. chloramines, fluoroamines); 
•  O-halogen (e.g. chlorates, perchlorates, iodosyl compounds). 

A substance or mixture is not classified as explosive: 

a.  when there are no chemical groups associated with explosive properties present in the 

molecule; 

or 

b.  when the substance or mixture contains chemical groups associated with explosive 

properties which include oxygen and the calculated oxygen balance is less than -200; 

The oxygen balance is calculated for the chemical reaction: 

 

Using the formula: 

Oxygen balance = 

or 

or 

c.  when the organic substance or a homogenous mixture of organic substances contains 

chemical groups associated with explosive properties but the exothermic decomposition 
energy is less than 500 J/g and the onset of exothermic decomposition is below 500 ºC. 
(The temperature limit is to prevent the procedure being applied to a large number of 
organic materials which are not explosive but which will decompose slowly above 500 ºC 
to release more than 500 J/g.) The exothermic decomposition energy may be 
determined using a suitable calorimetric technique; 

d.  for mixtures of inorganic oxidising substances with organic material(s), the concentration 

of the inorganic oxidising substance is: 

• 

• 

less than 15 % by mass, if the oxidising substance is assigned to Categories 1 or 2; 

less than 30 % by mass, if the oxidising substance is assigned to Category 3. 

If the screening procedure identifies the substance or mixture to be a potential explosive or if it 
is a mixture containing any known explosives, the classification (acceptance) procedure for the 
class of explosives (see Section 2.1.4.5.1) has to be applied. If the exothermic decomposition 
energy of organic materials is less than 800 J/g, a UN gap test is not required, neither according 
to Series 1 Type (a) nor according to Series 2 Type (a).  

2.1.4.3.  Classification criteria  

The criteria for the classification of explosives are given in the following tables. 

Annex I: 2.1.2.1. Substances, mixtures and articles of this class are classified as an unstable 
explosive on the basis of the flowchart in Figure 2.1.2. The test methods are described in 
Part I of the UN RTDG, Manual of Tests and Criteria. 

OOHC2zyx2z4yx−++OHCO222yx+()weightmolecular z2yx21600−+− 
 
 
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2.1.2.2. Substances, mixtures and articles of this class, which are not classified as an 
unstable explosive, shall be assigned to one of the following six divisions depending on the 
type of hazard they present: 

(a) Division 1.1 

Substances, mixtures and articles which have a mass explosion hazard 

(a mass explosion is one which affects almost the entire quantity present virtually 
instantaneously); 

(b) Division 1.2 

Substances, mixtures and articles which have a projection hazard but 

not a mass explosion hazard; 

(c) Division 1.3 

Substances, mixtures and articles which have a fire hazard and either a 

minor blast hazard or a minor projection hazard or both, but not a mass explosion 
hazard: 

(i)  combustion of which gives rise to considerable radiant heat; or 

(ii)  which burn one after another, producing minor blast or projection effects or 

both; 

(d) Division 1.4 

Substances, mixtures and articles which present no significant hazard: 

−  substances, mixtures and articles which present only a small hazard in the event of 

ignition or initiation. The effects are largely confined to the package and no projection 
of fragments of appreciable size or range is to be expected. An external fire shall not 
cause virtually instantaneous explosion of almost the entire contents of the package; 

(e) Division 1.5 

Very insensitive substances or mixtures which have a mass explosion 

hazard: 

−  substances and mixtures which have a mass explosion hazard but are so insensitive 

that there is very little probability of initiation or of transition from burning to 
detonation under normal conditions; 

(f) Division 1.6 

Extremely insensitive articles which do not have a mass explosion 

hazard: 

−  articles which contain only extremely insensitive substances or mixtures and which 

demonstrate a negligible probability of accidental initiation or propagation. 

2.1.2.3. Explosives, which are not classified as an unstable explosive, shall be classified in 
one of the six divisions referred to in section 2.1.2.2 based on Test Series 2 to 8 in Part I of 
the UN RTDG, Manual of Tests and Criteria according to the results of the tests laid down in 
Table 2.1.1: 

Table 2.1.1 

Criteria for explosives 

Category 

Criteria 

Unstable explosives or 
explosives of Divisions 1.1 
to 1.6 

For explosives of Divisions 1.1 to 1.6, the following are the core 
set of tests that need to be performed: 

Explosibility: according to UN Test Series 2 (section 12 of the UN 
RTDG, Manual of Tests and Criteria). Intentional explosives (¹) 
shall not be subject to UN Test Series 2. 

Sensitiveness: according to UN Test Series 3 (section 13 of the 
UN RTDG, Manual of Tests and Criteria). 

Thermal stability: according to UN Test 3(c) (sub-section 13.6.1 
of the UN RTDG, Manual of Tests and Criteria). 

 
 
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Further tests are necessary to allocate the correct Division. 

(¹) This comprises substances, mixtures and articles which are manufactured with a view to 
producing a practical, explosive or pyrotechnic effect. 

Where the test is conducted in the package form and the packaging is changed, a further test 
must be conducted where it is considered that the change in packaging will affect the outcome 
of the test. 

Classification tests must be performed on the substance or mixture as supplied. If the same 
chemical is to be presented in a physical form different from that which was tested and which is 
considered likely to materially alter its performance in a classification test, the substance or 
mixture must also be tested in the new form. 

2.1.4.4.  Testing and evaluation of hazard information  

Where test data are available, these must be evaluated against the set criteria for classification. 

When the screening procedure indicates that a substance or mixture may possess explosive 
properties, a cautious approach when performing the tests is necessary to ensure safe handling. 

For information on the test procedures see the following Section 2.1.4.5 where the individual 
test series are described in context with the respective decision logic. 

The test procedures for the classification of explosives are described in detail in the Part I of the 
UN-MTC. 

2.1.4.5.  Classification procedure and decision logics 

Any substance, mixture or article having, or suspected of having, explosives characteristics 
must be considered for classification in the hazard class of explosives. Substances, mixtures and 
articles classified in this hazard class must be assigned to the appropriate division or must be 
classified as unstable explosive. 

The classification process is divided into two stages, the acceptance procedure and the 
assignment procedure.  

In the acceptance procedure, intrinsic explosive properties of a substance, mixture or article are 
determined through tests of its sensitivity, stability and explosion effects. If the substance, 
mixture or article is not characterised as unstable explosive and is provisionally accepted into 
the class of explosives, it is then necessary to ascertain the correct division by applying the 
assignment procedure. The further subdivision into compatibility groups A to S is described in 
detail in the UN RTDG Model Regulations, Section 2.1.2. The compatibility groups and their 
recommended combination identify types of explosives which are deemed to be compatible, e.g. 
for combined storage or transportation and can therefore be used to distinguish technical 
requirements (especially) in these sectors. However, assignment of compatibility groups is not 
part of the classification system according to CLP. 

The tests for acceptance and the further tests to determine the correct division are grouped into 
eight test series. Classification procedures, test methods and criteria are described in detail in 
Part I of the UN-MTC. 

NOTE: The person responsible for the classification of explosives should be experienced in 
this field and be familiar with the criteria for classification. 

 
 
 
 
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2.1.4.5.1. 

Acceptance procedure 

The acceptance procedure is used to determine whether or not a substance, mixture or article is 
a candidate for the class of explosives or is an unstable explosive.  

The test methods used for deciding on provisional acceptance into the class of explosives are 
grouped into four series, numbered 1 to 4 (see CLP Annex I, Figure 2.1.2 reported below). 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Annex I: Figure 2.1.2 

Procedure for provisional acceptance of a substance, mixture or article in the class 
of explosives (Class 1 for transport) 

 
 
 
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The numbering of Test Series 1 to 4 relates to the sequence of assessing the results rather than 
the order in which the tests should be conducted. It may be important for the safety of test 
personnel that certain tests, using small amounts of material, be conducted first 
before proceeding to experiment with larger quantities.  

Starting the testing procedure with Test Series 3 is highly recommended, because these tests 
involve relatively small sample sizes, which reduces the risk to test personnel. 

Test Series 1 

Within Test Series 1 the question ‘Is it an explosive substance / mixture?’ is answered on the 
basis of the results of three types of tests to assess possible explosive effects. The question 
is answered ‘Yes’ if a ‘+’ is obtained in any of the three types of tests. If the answer is ‘No’, 
the substance / mixture is rejected from this class; it is not an explosive. Under certain 
conditions the test Type 1 (a) can be replaced by certain tests of Test Series F, see UN-MTC, 
Section 11.3.5.  

The three types of test used are (recommended test is indicated within brackets): 

Type 1 (a): 

a shock test with defined booster and confinement to determine the ability 
of the substance to propagate a detonation (UN Gap test, zero gap); 

Type 1 (b): 

a test to determine the effect of heating under confinement (Koenen test); 
and 

Type 1 (c): 

a test to determine the effect of ignition under confinement (time/pressure 
test). 

Test Series 2 

Series 2 tests are used to answer the question ‘Is the substance / mixture too insensitive for 
acceptance into this Class?’. In general, the basic apparatus and method used is the same as 
that for Test Series 1 but with less stringent criteria, e.g. in the case of gap tests, the gap 
used is greater than zero. The question is answered ‘No’ if a ‘+’ is obtained in any of the 
three types of test. If the answer is ‘Yes’, the substance / mixture is rejected from this class; 
it is not an explosive. Under certain conditions test Type 2 (a) can be replaced by certain 
tests of Test Series F, see UN-MTC, Section 12.3.4. 

The following three types of test are used (recommended test is indicated within brackets): 

Type 2 (a): 

a shock test with defined initiation system and confinement to determine 
sensitivity to shock (UN gap test) (with a defined gap e.g. 50 mm); 

Type 2 (b): 

a test to determine the effect of heating under confinement (Koenen test); 
and 

Type 2 (c): 

a test to determine the effect of ignition under confinement (Time/pressure 
test). 

If the substance or mixture is manufactured with a view to produce a practical explosive or 
pyrotechnic effect, it is unnecessary to conduct Test Series 1 and 2 for purposes of 
classification. 

Test Series 3 

As stated above it is recommended to carry out Test Series 3 before Test Series 1 and 2 for 
safety reasons due to the small sample amount needed. It is also recommended to carry out 
Test Series 3 even if negative results have been obtained in Test Series 1 and/or 2 because 
only Test Series 3 gives information about the thermal stability and the sensitivity to 
mechanical stimuli (impact and friction). 

Test Series 3 is used to answer the questions ‘Is the substance / mixture thermally 
stable?’ and ‘Is the substance / mixture too dangerous for transport in the form in which it 

 
 
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was tested?’ This involves tests for determining the sensitiveness of the substance or mixture 
to mechanical stimuli (impact and friction), and to heat and flame.  

The following four types of tests are used (recommended test is indicated within brackets): 

Type 3 (a): 

a falling weight test to determine sensitiveness to impact (BAM 
Fallhammer); 

Type 3 (b): 

a friction; or impacted friction test to determine sensitiveness to friction 
(BAM friction apparatus); 

Type 3 (c): 

an elevated temperature test to determine thermal stability (thermal 
stability test at 75 °C); and 

Type 3 (d): 

an ignition test to determine the response of a substance or mixture to fire 
(small scale burning test). 

The first question is answered ‘No’ if a ‘+’ is obtained in Test type 3(c). Then the substance / 
mixture is considered as thermally unstable and either classified as an unstable explosive or 
as a self-reactive substance or mixture.  

The second question is answered ‘Yes’ if a ‘+’ is obtained in any of the Test types 3(a), 3(b) 
or 3(d). If a ‘+’ is obtained, the substance / mixture may be encapsulated or packaged to 
reduce its sensitiveness to external stimuli or is classified as an unstable explosive. 
Furthermore, the explosive may be desensitized in order to suppress/reduce its explosive 
properties in which case the classification procedure has to be restarted.  

Test Series 4 

Series 4 tests are intended to answer the question ‘Is the article, packaged article or 
packaged substance or mixture too dangerous to be transported?’. Conditions which may 
occur during supply and use include high /low temperature and high relative humidity, 
vibration, bumping and dropping.  

The two types of test to be carried out are: 

Type 4 (a): 

a test of thermal stability for articles; and 

Type 4 (b): 

a test to determine the hazard from dropping. 

The question is answered ‘Yes’ if a ‘+’ is obtained in either Test type 4 (a) or 4 (b) and the 
substance or mixture or article is classified as an unstable explosive. 

It is important to note that a substance / mixture which fails Test Series 2 (i.e. it is sensitive 
enough for acceptance into the class of explosives) may still, if properly packaged, leave the 
class of explosives provided that it is not designed to have an explosive effect and does not 
exhibit any explosive hazard in Test Series 6 of the assignment procedure (see example for 
musk xylene). Such an exclusion from the class of explosives is restricted to the specific type 
and size of package tested. 

Especially for substances / mixtures, which have explosive properties according to Test Series 1 
and/or 2 but can leave the class of explosives after Test Series 6 due to proper packaging, it is 
necessary to communicate these properties in the Safety Data Sheet (SDS). Furthermore, the 
results from Test types 3 (a) and 3 (b) should be documented in the SDS when they meet the 
criteria of EU test method A.14 in Regulation (EC) No 440/2008 (these are substances with a 
sensitiveness to impact, determined by UN Test Series 3 (a) (ii) of 40 J or less and/or a 
sensitiveness to friction, determined by Test Series 3 (b) (i) of 360 N or less). 

2.1.4.5.2. 

Assignment procedure to a division 

The assignment procedure to one of six divisions, depending on the type of hazard they 
present, applies to all substances, mixtures and/or articles that are candidates for the class of 
explosives. A substance, mixture or article must be assigned to the division which corresponds 

 
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to the results of the tests to which the substance, mixture or article, as offered for supply and 
use, has been subjected. Other test results, and data gathered from accidents which have 
occurred, may also be taken into account.  

The test methods used for assignment to a division are grouped into three series – numbered 5 
to 7 – designed to provide the information necessary to answer the questions in Figure 2.1.3 in 
CLP. 

  NOTE: The person responsible for the classification of explosives should be experienced in 

this field and be familiar with the criteria for classification. 

 
 
 
 
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Annex I: Figure 2.1.3 

Procedure for assignment to a division in the class of explosives (Class 1 for 
transport) 

 
 
 
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Test Series 5 

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Test Series 5 is only carried out for explosive substances/mixtures which are very insensitive 
and therefore candidates for division 1.5. Typical substances/mixtures are blasting agents 
such as ANFO, slurries, and emulsion explosives. 

The results from three types of series 5 tests are used to answer the question ‘Is it a very 
insensitive explosive substance/mixture with a mass explosion hazard?’.  

The test types are (recommended test is indicated within brackets): 

Type 5 (a): a shock test to determine the sensitivity to intense mechanical stimulus (cap 
sensitivity test); 

Type 5 (b): thermal tests to determine the tendency of transition from deflagration to 
detonation (French or USA DDT test); and 

Type 5 (c): a test to determine if a substance, when in large quantities, explodes when 
subjected to a large fire. 

The question is answered ‘No’ if a ‘+’ is obtained in any of the three test types. A candidate 
for Division 1.5 should pass one test of each type. 

Test Series 6 

The results from four types of series 6 tests are used to determine which division, amongst 
Divisions 1.1, 1.2, 1.3 and 1.4, corresponds most closely to the behaviour of the substance, 
mixture or article to be classified if a load is involved in a fire resulting from internal or 
external sources or an explosion from internal sources. The results are also necessary to 
assess whether a substance, mixture or article can be assigned to Compatibility Group S of 
Division 1.4 and whether or not it should be excluded from this class. Test Series 6 should be 
applied to packages of substances, mixtures or articles in the condition and form in which 
they are offered for supply and use. 

The four test types are (recommended test is indicated within brackets): 

Type 6 (a): a test on a single package to determine if there is mass explosion of the contents 
(single package test); 

Type 6 (b): a test on packages of an explosive substance, mixture or explosive articles, or 
non-packaged explosive articles, to determine whether an explosion is propagated from one 
package to another or from a non-packaged article to another (stack test); and 

Type 6 (c): a test on packages of an explosive substance, mixture or explosive articles, or 
non-packaged explosive articles, to determine whether there is a mass explosion or a hazard 
from dangerous projections, radiant heat and/or violent burning or any other dangerous 
effect when involved in a fire (bonfire test); 

Type 6 (d): a test on an unconfined package of explosive articles to which special provision 
347 of Chapter 3.3 of the UN RTDG Model Regulations applies, to determine if there are 
hazardous effects outside the package arising from accidental ignition or initiation of the 
contents.  

Test types 6 (a), 6 (b), 6 (c) and 6 (d) are performed in alphabetical order. However, it is not 
always necessary to conduct tests of all types. Test type 6 (a) may be waived if explosive 
articles are carried without packaging or when the package contains only one article. Test 
type 6 (b) may be waived if in each type 6 (a) test: 

 
 
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the exterior of the package is undamaged by internal detonation and/or ignition; or 
the contents of the package fail to explode, or explode as feebly as would exclude 

• 
• 
propagation of the explosive effect from one package to another in test type 6(b). 

Test type 6(c) may be waived if, in a type 6(b) test, there is practically instantaneous 
explosion of virtually the total contents of the stack. In such cases the product is assigned to 
Division 1.1. 

Test type 6 (d) is a test used to determine whether a 1.4S classification is appropriate and is 
only used if Special Provision 347 of Chapter 3.3 of the UN RTDG Model Regulations applies. 
The results of test series 6 (c) and 6 (d) indicate if 1.4S is appropriate, otherwise the 
classification is 1.4 other than S. 

If a substance or mixture gives a ‘—‘ result (no propagation of detonation) in the Series 1 
type (a) test, the 6(a) test with a detonator may be waived.  

If a substance gives a ‘—‘ result (no or slow deflagration) in a Series 2 type (c) test, the 6 
(a) test with an igniter may be waived. 

Test Series 7 

Test Series 7 aims at military explosives (Extremely Insensitive Substance: EIS or article 
containing an EIS) and is generally not relevant for explosives for civil use. Therefore the 
individual tests are not described here. If needed, they can be found in the UN- MTC, Part I, 
Section 17. 

Test Series 8 

The question whether a candidate for ammonium nitrate emulsion or suspension or gel, 
intermediate for blasting explosives (ANE) is insensitive enough for classification as oxidising 
is answered by series 8 tests. The three test types are (recommended test is indicated within 
brackets): 

Type 8 (a): a test to determine the thermal stability (Thermal Stability Test for ANE); 

Type 8 (b): a shock test to determine sensitivity to intense shock (ANE gap test); and 

Type 8 (c): a test to determine the effect of heating under confinement (Koenen test). 

Test Series 8 is used to establish whether an ammonium nitrate emulsion or suspension or 
gel, intermediate for blasting explosives (ANE) may leave the class of explosives or not. 
Substances or mixtures failing any of the tests must be classified as explosives (Division 1.1. 
or 1.5) or as an unstable explosive in accordance with CLP Annex I, Figure 2.1.4. If they pass 
all three tests they are classified as an oxidising liquid or solid. 

 
 
 
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Annex I: Figure 2.1.4 

Procedure for the classification of ammonium nitrate emulsion, suspension or gel 
(ANE) 

 
 
 
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2.1.5.  Hazard communication for explosives 

2.1.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements48  

Annex I: Table 2.1.2 

Label elements for explosives 

Classificati
on 

Unstable 
Explosive 

Division 
1.1 

Division 
1.2 

Division 
1.3 

Division 
1.4 

Division 
1.5 

Division 
1.6 

GHS 
Pictogram
s 

Signal 
Word 

Danger 

Danger 

Danger 

Danger 

Warning 

Danger 

Hazard 
Statement 

H200: 
Unstable 
Explosive 

H201: 
Explosive; 
mass 
explosion 
hazard 

H202: 
Explosive; 
severe 
projection 
hazard 

H203: 
Explosive; 
fire, blast 
or 
projection 
hazard 

H204: Fire 
or 
projection 
hazard 

H205: May 
mass 
explode in 
fire 

Pre-
cautionary 
Statement 

Prevention 

P201 

P250 

P280 

P210 

P230 

P234 

P240 

P250 

P280 

P210 

P230 

P234 

P240 

P250 

P280 

P210 

P230 

P234 

P240 

P250 

P280 

Pre-
cautionary 
Statement 

Response 

P370 + 
P372 + 
P380+P3
73 

P370 + 
P372 + 
P380 + 
P373 

P370 + 
P372 + 
P380 + 
P373 

P370 + 
P372 + 
P380 + 
P373 

P210 

P234 

P240 

P250 

P280 

P370 + 
P372 + 
P380 + 
P373 

P370 + 
P380 + 
P375 

P210 

P230 

P234 

P240 

P250 

P280 

No signal 
word 

No hazard 
statement 

No pre-
cautionary 
statement 

P370 + 
P372 + 
P380 + 
P373 

No pre-
cautionary 
statement 

Pre-
cautionary 
Statement 

Storage 

P401 

P401 

P401 

P401 

P401 

P401 

No pre-
cautionary 
statement 

48 The combination statement P370+P372+P380+P373 applies to division 1.4 except for compatibility 
group S in transport packaging, whereas the combination statement P370+P380+P375 applies to division 
1.4 compatibility group S in transport packaging. 

 
 
 
 
 
 
 
 
 
 
 
 
 
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P501 

P501 

P501 

P501 

P501 

P501 

No pre-
cautionary 
statement 

106 

Pre-
cautionary 
Statement 

Disposal 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

The intrinsic explosive properties of substances and mixtures regarding their stability and 
sensitivity are only investigated within Test Series 1, 2 and 3 during the acceptance procedure. 
Subsequent tests for the assignment to the Divisions 1.1, 1.2, 1.3 and 1.4 (Test Series 6) are 
carried out with the packaged substances, mixtures or articles. The type of packaging may 
significantly influence the test outcome. 

Consequently, there are some deficiencies in the hazard communication of the GHS for 
unpacked or repacked explosive substances and mixtures, especially for substances and 
mixtures, which are provisionally accepted in the class of explosives but are later rejected from 
this class due to their packaging in the assignment procedure (see CLP Annex I, Figure 2.1.1 
and Figure 2.1.3 and Section 2.1.4.5.1 of this guidance). These substances and mixtures have 
explosive properties but there might be no hazard communication about these properties due to 
the subsequent classification in a hazard class other than the class of explosives. Musk xylene is 
an example which illustrates this issue (see Section 2.1.7.2). The results of Test Series 6 for 
musk xylene in the specified packaging lead to the exclusion of this substance from the hazard 
class of explosives. But musk xylene on its own (unpacked) shows explosive properties due to 
heating under confinement (Koenen test). Also repacking of the substance in a packaging other 
than the tested one can result in a completely different outcome of Test Series 6.  

This issue is not sufficiently clarified under GHS, but should be kept in mind by everyone 
applying the CLP criteria. 

2.1.5.2.  Additional labelling provisions  

2.1.5.2.1. 

Packaging dependance 

Explosives are normally classified in their transport packaging. The packaging itself may be 
crucial for the classification. This is clear from the Figure 2.1.3 in Section 2.1.4.5.2 especially 
when it comes to Test Series 6. The assignment of an explosive substance or mixture to a 
particular Division within the hazard class of explosives is thus only valid for the substance and 
mixture in the packaging in which it was tested, which is usually the transport packaging. 
Because of the package-dependence of the classification, paragraph 2.1.2.4 of the Annex I to 
the CLP prescribes: 

Annex I: 2.1.2.4. If explosives are unpackaged or repacked in packaging other than the 
original or similar packaging, they shall be retested. 

Further, according to NOTE 1 to Table 2.1.2 in Section 2.1.3 of Annex I to CLP, unpackaged 
explosives or explosives repacked in packaging other than the original or similar packaging 
must have the following label elements: 

Annex I: 2.1.3.     Hazard communication  

[…] 

NOTE 1: Unpackaged explosives or explosives repackaged in packaging other than the 
original or similar packaging shall include the following label elements: 

(a) 

the pictogram: exploding bomb; 

(b) 

the signal word: “Danger”; and 

 
 
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(c) 

the hazard statement: 'explosive; mass explosion hazard'  

Unless the hazard is shown to correspond to one of the hazard categories in Table 2.1.2, in 
which case the corresponding symbol, signal word and/or the hazard statement shall be 
assigned. 

Normally, if explosives are unpackaged or repacked in packaging other than the original or 
similar packaging the classification procedure needs to be performed again in order to 
determine which Division the explosive belongs to in the new packaging. The label elements 
prescribed in NOTE 1 to Table 2.1.2, as quoted above, are the same as those of Division 1.1 
and in practice this Division constitutes the most severe classification of a repackaged explosive. 
(Please note that Table 2.1.2 foresees also the hazard category ‘Unstable explosive’, which is 
assigned on the basis of the intrinsic properties of a substance or mixture via Test Series 3 and 
it is not package dependent). Therefore, the CLP allows labelling of a repackaged explosive with 
labelling corresponding to Division 1.1 instead of retesting. This, however, overestimates the 
hazardous properties unless the explosive in fact belongs to Division 1.1. 

Many explosives are supplied in inner packages which are placed together in an outer package 
and where the entity as a whole, i.e. the combination of inner and outer packages, constitutes 
the transport packaging. According to the UN RTDG Model Regulations and the modal transport 
regulations (ADR, RID, ADN and IMDG Code, ICAO TI) the classification tests are performed in 
the transport packaging. Under Article 33(1) of CLP where the hazard pictograms(s) required by 
CLP relate to the same hazard as in the rules for the transport of dangerous goods, the 
respective CLP hazard pictogram(s) do not need to appear on the outer packaging.  

The classification in accordance with rules on the transport of dangerous goods is almost 
entirely identical to the corresponding classification procedure used in CLP and hence the CLP 
classification will automatically be known for the transport packaging. However, the CLP 
classification for the inner package alone strictly speaking is not known to the manufacturer, 
importer or downstream user as this will not have been derived from the classification of the 
transport packaging. On the other hand, it is normally not practicable to perform the required 
tests on the inner packages. Therefore, normally the same classification as for the transport 
packaging may be assumed for the inner packages. The labelling requirements for the inner 
packages are those foreseen in Table 2.1.2 of Annex I to the CLP. However, the following 
exceptions apply: 

•  Transport packages in which the packaging is designed such that mass explosion is 

prevented by the packaging, e.g. by arranging the individual inner packages crosswise 
(so that they are not neighbouring each other) and by separating them with specified 
material. This is especially the case when packing instruction P101 according to section 
4.1.5 of the ADR applies. In this case the inner package should be labelled in accordance 
with Note 1 to Table 2.1.2 of Annex I to the CLP (i.e. as Division 1.1 unless tested 
otherwise). 

•  Packages in which explosives of different divisions are contained (for such cases see 

especially the mixed packing provisions MP 20 to MP 24 in section 4.1.10 of the ADR). 
•  Furthermore, they do not apply if the packaging is changed, as stated in Note 1 to Table 

2.1.2 of Annex I to the CLP. 

2.1.5.2.2. 

Supplemental hazard information 

Some R-phrases under DSD are not covered by hazard classes in the current GHS. They are 
included as supplemental hazard statements in Part 1 of Annex II to CLP. The following EU 
hazard statements are important in connection with explosive properties:  

 
 
 
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Annex II: 1.1.1.     EUH001 – ‘Explosive when dry’ 

For explosive substances and mixtures as referred to in chapter 2.1 of part 2 of Annex I, 
placed on the market wetted with water or alcohols or diluted with other substances to 
suppress their explosives properties. 

EUH001 must be assigned to explosives which are wetted, diluted, dissolved or suspended with 
a phlegmatizer in order to reduce or suppress their explosive properties (desensitized explosives 
in the sense of the foreseen new hazard class for desensitized explosives) and which do not 
meet the criteria of the hazard class of explosives. 

Annex II: 1.1.6.     EUH044 – ‘Risk of explosion if heated under confinement’ 

For substances and mixtures not in themselves classified as explosive in accordance with 
section 2.1 of part 2 of Annex I, but which may nevertheless display explosive properties in 
practice if heated under sufficient confinement. In particular, substances which decompose 
explosively if heated in a steel drum do not show this effect if heated in less-strong 
containers. 

Some substances and mixtures which may react explosively if heated under confinement are 
not covered adequately by the classification system. This may e.g. be the case for: 

• 

• 

substances or mixtures which are exempted from the class of explosives based on their 
packaging and according to results of the Test Series 6; 
substances or mixtures with a SADT of more than 75 °C for a 50 kg package which 
therefore cannot be classified as self-reactive. 

EUH044 must be assigned to such substances or mixtures, in order to make the user aware of 
these properties. 

2.1.5.3.  Further communication requirements 

According to Note 2 to Table 2.1.2, explosive properties of certain substances and mixtures 
which are exempted from classification as explosives must be communicated to the user via the 
SDS (when one is required). 

Annex I: 2.1.3.     Hazard communication  

[…] 

NOTE 2: Substances and mixtures, as supplied, with a positive result in Test Series 2 in Part 
I, Section 12, of the UN RTDG, Manual of Tests and Criteria, which are exempted from 
classification as explosives (based on a negative result in Test Series 6 in Part I, Section 16 
of the UN RTDG, Manual of Tests and Criteria,) still have explosive properties. The user shall 
be informed of these intrinsic explosive properties because they have to be considered for 
handling – especially if the substance or mixture is removed from its packaging or is 
repackaged – and for storage. For this reason, the explosive properties of the substance or 
mixture shall be communicated in Section 2 (Hazards identification) and Section 9 (Physical 
and chemical properties) of the Safety Data Sheet and other sections of the Safety Data 
Sheet, as appropriate 

2.1.6.  Relation to transport classification 

Division 1.1 – 1.6 within Class 1 of the UN RTDG Model Regulations covers explosive 
substances, mixtures and articles. Normally, the transport classification in accordance with the 
UN RTDG Model Regulations and the modal transport regulations (ADR, RID, ADN and IMDG 
Code, ICAO TI) can be used one-to-one when deriving the CLP classification for explosives, 

 
 
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which are packaged in authorised transport packaging. See Annex VII of this guidance for 
additional information on transport classification in relation to CLP classification. 

For the use of other packaging or for unpacked substances and mixtures the additional labelling 
provisions (see Section 2.1.5.2) have to be observed or re-testing is necessary.  

2.1.7.  Examples of classification for explosives 

Examples are given below for the classification of substances. Equivalent information would be 
needed for mixtures.  

2.1.7.1.  Example of substances and mixtures fulfilling the classification 

criteria 

a.  RESULTS FROM APPLICATION OF THE ACCEPTANCE PROCEDURE 

Step 

Test  

Conclusion 

Rationale 

0. General data: 

0.1 Name of the substance / 
mixture: Hexanitrostilbene 

1. Is the substance / mixture a 
candidate for ammonium nitrate 
emulsion, suspension or gel, 
intermediate for blasting explosive 
(ANE)? 

2. Is the substance / mixutre 
manufactured with the view to 
producing a practical explosive or 
pyrotechnic effect? 

3. Test Series 3 

3.1 Thermal stability: 

3.2 Impact sensitivity: 

No 

Yes 

75 °C / 48 hour 
test (test 3(c)) 

Result: ‘—‘, 
thermally stable 

BAM 
Fallhammer test 
(test 3(a)(ii)) 

Result: Limiting 
impact energy 5 J 

3.3 Friction sensitivity: 

BAM friction 
test (test 
3(b)(i)) 

Result: Limiting 
load > 240 N 

4. Is the substance / mixture 
thermally stable? 

5. Is the substance / mixture too 
dangerous in the form in which it was 
tested? 

6. Conclusion: 

Yes 

No 

PROVISIONALLY 
ACCEPT INTO 
THIS CLASS 

‘—‘, not too 
dangerous 
in form 
tested 

‘—‘, not too 
dangerous 
in form 
tested 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Step 

10.1 Exit: 

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Test  

Conclusion 

Rationale 

Apply the 
assignment 
procedure 

b.  RESULTS FROM APPLICATION OF THE ASSIGNMENT PROCEDURE 

Step 

Test 

Conclusion 

Rationale 

1. Is the substance a candidate 
for Division 1.5? 

2. Test Series 6 

No 

Result: Package the 
substance 

2.1 Effect of initiation in the 
package: 

Test 6(a) with detonator 

Result: detonation, 
crater 

2.2 Effect of propagation: 

Type 6(b) with detonator  Result: detonation of 

the whole stack of 
packages, crater 

2.4 Effect of fire engulfment: 

Test 6(c) may be waived 
because of the result of 
the 6(b) test. 

3. Is the result a mass explosion? 

Yes 

4. Conclusion: 

Assignment to 
Division 1.1 

2.1.7.2.  Example of substances and mixtures not fulfilling the classification 

criteria  

This example is taken from the UN-MTC, Part I, Section 10.5.2, Figure 10.5. 

c.  RESULTS FROM APPLICATION OF THE ACCEPTANCE PROCEDURE 

Step 

Test 

Conclusion 

Rationale 

0. General data: 

0.1 Name of the substance / 
mixture: 5-tert-butyl-2,4,6-
trinitro-m-xylene   (musk 
xylene) 

1. Is the substance / mixutre a 
candidate for ammonium nitrate 
emulsion, suspension or gel, 
intermediate for blasting explosive 
ANE? 

2. Is the substance / mixture 
manufactured with the view to 

No 

No 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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111 

Step 

Test 

Conclusion 

Rationale 

Fragmentation 
type ‘F’ ‘+’, 
shows some 
explosive effects 
on heating 
under 
confinement 

Fragmentation 
type ‘F’ ‘+’, 
violent effect on 
heating under 
confinement. 

producing a practical explosive or 
pyrotechnic effect? 

3. Test Series 1 

3.1 Propagation of Detonation:  

UN gap test 
(test 1(a)) 

Result:’+’, propagation 
of detonation 

3.2 Effect of heating under 
confinement:  

Koenen test 
(test 1(b)) 

Result: Limiting 
diameter 12.0 mm 

3.3 Effect of ignition under 
confinement:   

Time/pressure 
test (test 
1(c)(i)) 

Result: ‘—’, no effect on 
ignition under 
confinement 

4. Is it an explosive substance / 
mixture? 

Yes 

5.  Test Series 2 

5.1 Sensitivity to shock:  

UN gap test 
(test 2(a)) 

Result: ‘—’, not 
sensitive to shock 

5.2 Effect of heating under 
confinement:  

Koenen test 
(test 2(b)) 

Result: Limiting 
diameter 12.0 mm 

5.3 Effect of ignition under 
confinement:  

Time/pressure 
test (test 
2(c)(i)) 

Result: ‘—’, no effect on 
ignition under 
confinement 

6. Is the substance / mixture too 
insensitive for acceptance into this 
class? 

No 

Conclusion:  

7. Test Series 3 

Substance to be 
considered for this class 

7.1 Thermal stability: 

75 °C/48 hour 
test (test 3(c)) 

Result: ‘—’, thermally 
stable 

7.2 Impact sensitivity:  

BAM 
Fallhammer test 
(test 3(a)(ii)) 

Result: Limiting impact 
energy 25 J", not too 
dangerous in form 
tested. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Step 

Test 

Conclusion 

Rationale 

7.3 Friction sensitivity:  

BAM friction 
test (test 
3(b)(i)) 

Result: Limiting load > 
360 N 

‘—’, not too 
dangerous in 
form tested 

8. Is the substance / mixture 
thermally stable? 

9. Is the substance / mixture too 
dangerous in the form in which it was 
tested? 

Yes 

No 

10. Conclusion: 

10.1 Exit 

PROVISIONALLY 
ACCEPT INTO THIS 
CLASS 

Apply the assignment 
procedure 

The explosive 
properties shall be 
communicated in the 
safety data sheet in 
accordance with section 
2.1.5.3 above. 

 
 
 
 
 
 
 
 
 
 
 
 
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d.  RESULTS FROM APPLICATION OF THE ASSIGNMENT PROCEDURE 

Step 

Test 

Conclusion 

Rationale 

1. Is the substance a candidate for 
Division 1.5? 

No 

Result: Package the 
substance 

2. Test Series 6 

2.1 Effect of initiation in the 
package:  

Test 6(a) with 
detonator 

2.2 Effect of ignition in the 
package:  

Test 6(a) with 
igniter 

Result: Only localised 
decomposition around 
detonator 

No significant 
reaction 

Result: Only localised 
decomposition around 
igniter 

No significant 
reaction 

2.3 Effect of propagation:  

Type 6(b) test 
not required as 
no effect outside 
package between 
packages in 6(a) 
test 

2.4 Effect of fire engulfment:  

Test 6 

Result: Only slow 
burning with black 
smoke occurred.  

No effects which 
would hinder fire 
fighting 

3. Is the result a mass explosion? 

4. Is the major hazard that from 
dangerous projections? 

5. Is the major hazard radiant heat 
and/or violent burning but with no 
dangerous blast or projection hazard? 

6. Is there nevertheless a small 
hazard in the event of ignition or 
initiation? 

7. Is the substance manufactured 
with the view to producing a practical 
explosive or pyrotechnic effect? 

8. Conclusion:  

8.1 Exit  

No 

No 

No 

No 

No 

NOT AN EXPLOSIVE 

Consider for another 
class (e.g. flammable 
solid) 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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2.2.  FLAMMABLE GASES (INCLUDING CHEMICALLY UNSTABLE GASES) 

2.2.1.  Introduction 

The criteria for ‘Flammable gases (including chemically unstable gases)’ are found in Annex I, 
Section 2.2 of CLP and are identical to those in Chapter 2.2 of GHS.  

2.2.2.  Definitions and general considerations for the classification of 
flammable gases (including chemically unstable gases) 

Annex I: 2.2.1.     Definitions 

2.2.1.1 Flammable gas means a gas or gas mixture having a flammable range with air at 20 
°C and a standard pressure of 101.3 kPa. 

2.2.1.2. A chemically unstable gas means a flammable gas that is able to explode even in 
the absence of air or oxygen. 

The flammable range of a flammable gas is defined between the ‘lower flammability limit’ (LFL) 
in air and the ‘upper flammability limit’ (UFL) in air. In technical literature, the terms ‘lower 
explosion limit’ (LEL) and ‘upper explosion limit’ (UEL) are often used instead of the LFL and 
UFL, respectively. 

The hazard class of flammable gases also covers chemically unstable gases as defined above. 

2.2.3.  Relation to other physical hazards 

Annex I: 2.2.2.     Classification criteria 

[…] 

Note: Aerosols shall not be classified as flammable gases; see Section 2.3. 

For flammable gases that are packaged in aerosol dispensers see 2.3 Aerosols. If classified as 
aerosols, they do not have to be classified as flammable gases in addition. 

2.2.4.  Classification of substances and mixtures as flammable gases 

(including chemically unstable gases)  

2.2.4.1. 

Identification of hazard information  

Many gases are classified as flammable gases in Annex VI of CLP and more gases are classified 
as flammable gases in the UN RTDG Model Regulations.  

For gases that are not classified as flammable gases in Annex VI of CLP nor in the UN RTDG 
Model Regulations, there is ample scientific literature giving the flammability range for most 
gases (e.g. IEC 60079-20-1, Explosive atmospheres – Part 20-1: Material characteristics for gas 
and vapour classification – Test methods and data as amended).   

In the case a gas or gas mixture needs to be tested for flammability, a recognised international 
standard must be used such as the EN 1839, Determination of explosion limits of gases and 
vapours as amended or ISO 10156, Gases and gas mixtures – Determination of fire potential 
and oxidising ability for the selection of cylinder valves outlets as amended. 

Information on a number of chemically unstable gases can be found in the UN-MTC, Section 35. 
Tables 35.1 and 35.2 within UN-MTC, Section 35.3.2.1 contain information on a number of 
chemically unstable gases together with their classification and Category.  

 
 
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If information on other gases than the ones mentioned in the above tables is needed a test 
method for determination of chemical instability of gases and gas mixtures is described in UN-
MTC, Section 35. However, it should be noted that this test method is not applicable to liquefied 
gas mixtures. In case the gaseous phase above a liquefied gas mixture may become chemically 
unstable after withdrawal, this should be communicated via the SDS. 

2.2.4.2.  Screening procedures and waiving of testing for gas mixtures 

There are thousands of gas mixtures on the market and there are a limited number of test 
reports for the flammability of gas mixtures in the scientific literature. Tests to determine the 
flammability range are time consuming and expensive for gas mixtures which are often 
prepared on demand. In most of the cases, the formulator of the gas mixture will use a 
calculation method as described in ISO 10156 as amended (see Section 2.2.4.4) to determine if 
the mixture is flammable or not.  

If the calculations in accordance with ISO 10156 as amended show that a gas mixture is not 
flammable it is also not classified as chemically unstable and therefore it is not necessary to 
carry out the tests for determining chemical instability for classification purposes. 

Expert judgement should be applied to decide whether a flammable gas or gas mixture is a 
candidate for classification as chemically unstable in order to avoid unnecessary testing of gases 
where there is no doubt that they are stable. Functional groups indicating chemical instability in 
gases are triple bonds, adjacent or conjugated double-bonds, halogenated double-bonds and 
strained rings. 

Gas mixtures containing only one chemically unstable gas are not considered as chemically 
unstable and therefore do not have to be tested for classification purposes if the concentration 
of the chemically unstable gas is below the higher of the following generic concentration limits: 

a.  the lower explosion limit (LEL) of the chemically unstable gas; or 

b.  3 mole%. 

Furthermore, for some gases there are also specific concentration limits available and these are 
indicated in the tables 35.1 and 35.2 within UN-MTC, Section 35.3.2.1. 

2.2.4.3.  Classification criteria  

The criteria for the classification of flammable gases (including chemically unstable gases) are 
given in the following tables: 

 
 
 
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Annex I: 2.2.2. Table 2.2.1 

Criteria for flammable gases 

Category  Criteria 

1 

2 

Gases, which at 20 °C and a standard pressure of 101.3 kPa: 

(a) are ignitable when in a mixture of 13 % or less by volume in air; or 

(b) have a flammable range with air of at least 12 percentage points regardless of 

the lower flammable limit. 

Gases, other than those of Category 1, which, at 20 °C and a standard pressure of 
101.3 kPa, have a flammable range while mixed in air. 

Annex I: 2.2.2 Table 2.2.2 

Criteria for chemically unstable gases 

Category  Criteria 

A 

B 

Flammable gases which are chemically unstable at 20 °C and a pressure of 101.3 
kPa. 

Flammable gases which are chemically unstable at a temperature greater than 20 
°C and/or a pressure greater than 101.3 kPa. 

2.2.4.4.  Testing and evaluation of hazard information 

ISO 10156 as amended describes a test method and a calculation method for the classification 
of flammable gases. The test method may be used in all cases, but must be used when the 
calculation method cannot be applied. 

The calculation method applies to gas mixtures and can be applied when the TCi for all 
flammable components and the Kk for all inert components are available. These are listed for a 
number for gases in ISO 10156 as amended. In the absence of TCi value for a flammable gas, 
the value of the LFL can be used and ISO 10156 proposes the value of 1.5 where no Kk value is 
listed. The calculation method described in ISO 10156 as amended uses the criterion that a gas 
mixture is considered non-flammable in air if: 

Equation 2.2.4.4.a 

where: 

Equation 2.2.4.4.b 

and where: 

 is the equivalent content of the i:th flammable gas in the mixture, in % 

1'1=niiciTA==+=pkkkniiiiBKAAA11'iA' 
 
 
 
 
 
 
 
 
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 is the maximum content of flammable gas i which, when mixed with nitrogen, 

is not flammable in air, in % 

 is the molar fraction of the i:th flammable gas in the mixture, in % 

 is the molar fraction of the k:th inert gas in the mixture, in % 

 is the coefficient of equivalency of the inert gas k relative to nitrogen 

 is the number of flammable gases in the mixture 

 is the number of inert gases in the mixture 

The principle of the calculation method is the following:  

Where a gas mixture contains an inert diluent other than nitrogen, the volume of this diluent is 
adjusted to the equivalent volume of nitrogen using the equivalency coefficient for the inert gas

. From this the equivalent contents 

 are then derived through Equation 2.2.4.4.b, which 

should be viewed as the corresponding concentration of the flammable gases if nitrogen was the 
only inert gas present in the mixture. In Equation 2.2.4.4.a the equivalent contents are then 
, which have been experimentally found using nitrogen as the 
compared to the constants 

(only) inert gas. 

It should be noted that ISO 10156 uses molar fractions in some of its equations. For most gases 
under normal (i.e. non-extreme) conditions, however, the volume fraction can be assumed to 
be equal to the molar fraction, which is the same as assuming ideal gas behaviour for all gases 
in the mixture. Furthermore, although normally a fraction is a number ranging from 0 to 1, in 
this case it is easier to express it as percentage, i.e. the fraction multiplied by 100. 

The calculation method described in ISO 10156 as amended determines only if the mixture is 
flammable or not. It does not determine a flammability range and therefore the calculation 
method cannot determine if the mixture is flammable Category 1 or Category 2. Therefore, to 
be on the safe side, mixtures determined to be flammable according the calculation method are 
classified Flammable gas; Category 1. If, however, there is a need to distinguish between 
Category 1 and Category 2, the lower and the upper explosion limits have to be determined by 
using a suitable test method (e.g. EN 1839 or ISO 10156 as amended). 

For mixtures containing both flammable and oxidising components, special calculation methods 
are described in ISO 10156 as amended. 

Gases or compressed gas mixtures that are classified as flammable have to be considered for 
classification as chemically unstable in addition. If the screening procedures described in Section 
2.2.4.2 are not conclusive, the gas or gas mixture has to be tested. The test method is 
described in UN-MTC, Section 35. It uses the same equipment as the test method for oxidising 
gases according to ISO 10156 as amended and therefore could be applied by laboratories that 
also carry out the tests for oxidising gases. 

2.2.4.5.  Decision logic  

Classification of flammable gases is laid down in the following flow-charts which are applicable 
according to CLP. 

  NOTE: The person responsible for the classification of flammable gases (including 

chemically unstable gases) should be experienced in this field and be familiar with the 
criteria for classification.  

ciTiAkBkKnpkKiA'ciT 
 
 
 
 
 
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2.2.4.5.1.  Decision logic for flammable gases 

Annex I: Figure 2.2.1 

Flammable gases 

Gaseous substance or mixture of gases 

Does it have a flammable range with air at 
20 °C and a standard pressure of 101.3 kPa? 

NO 

Not classified 

YES 

At  20  °C  and  a  standard  pressure  of  101.3 
kPa, does it: 

a.

ignite  when  in  a  mixture  of  13 %  or 
less by volume in air?; or 

b. have a flammable range with air of at 
least 12 percentage points regardless 
of the lower flammable limit? 

YES 

Category 1 

Danger 

NO 

Category 2 

No pictogram 

Warning 

 
 
 
 
 
 
 
 
 
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2.2.4.5.2.  Decision logic for chemically unstable gases 

Annex I: Figure 2.2.2 

Chemically unstable gases 

Flammable gas or gas mixture 

Is it chemically unstable at 20 °C and a 
standard pressure of 101.3 kPa? 

YES 

NO 

Is it chemically unstable at a temperature 
greater than 20 °C and/or a pressure 
greater than 101.3 kPa? 

YES 

NO 

Not classified as 
chemically unstable 

Category A 

(chemically 
unstable gas) 

No additional 
pictogram 

No additional 
signal word 

Category B 

(chemically 
unstable gas) 

No additional 
pictogram 

No additional 
signal word 

 
 
 
 
 
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2.2.5.  Hazard communication for flammable gases (including chemically 

unstable gases) 

2.2.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

Annex I: 2.2.3. Table 2.2.3 

Label elements for flammable gases (including chemically unstable gases) 

Classification 

Flammable gas 

Chemically unstable gas 

Category 1 

Category 2 

Category A 

Category B 

GHS Pictogram 

No pictogram 

No additional 
pictogram 

No additional 
pictogram 

Signal Word 

Danger 

Warning 

Hazard 
Statement 

H220: Extremely 
flammable gas 

H221: Flammable 
gas 

No additional 
signal word 

No additional 
signal word 

Additional hazard 
statement H230: 
May react 
explosively even 
in the absence of 
air 

Additional hazard 
statement H231: 
May react 
explosively even 
in the absence of 
air at elevated 
pressure and/or 
temperature 

P210 

P210 

P202 

P202 

P377 
P381 

P377 
P381 

P403 

P403 

Precautionary 
Statement 
Prevention 

Precautionary 
Statement 
Response 

Precautionary 
Statement 
Storage 

Precautionary 
Statement 
Disposal 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

 
 
 
 
 
 
 
 
 
 
 
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2.2.6.  Relation to transport classification 

The criteria for flammable gases Category 1 correspond to the criteria that are in use for 
classifying flammable gases in the UN RTDG Model Regulations. Consequently all gases listed as 
flammable in the UN RTDG Model Regulations and in the modal transport regulations (ADR, RID, 
ADN and IMDG Code, ICAO TI) must be classified as Flam.Gas 1; H220. See Annex VII for 
additional information on transport classification in relation to CLP classification. 

2.2.7.  Example of classification for flammable gases 

EXAMPLE MIXTURE:  2 % (H2) + 6 % (CH4) + 27 % (AR) + 65 % (HE) 

Calculation steps: 

Step 1: Assign the gases and state their molar fractions, assuming the molar fractions are 
equal to the volume fractions (ideal gas behaviour for all gases). 

H2 is flammable gas 1, 

yielding  = 2 mole % 

CH4 is flammable gas 2, 

yielding  = 6 mole % 

Ar is inert gas 1, 

He is inert gas 2, 

yielding  = 27 mole % 

yielding  = 65 mole % 

=2  

=2  

since there are two flammable gases in the mixture 

since there are two inert gases in the mixture 

Step 2: Look up the values of 

 and 

 in ISO 10156 as amended. 

= 

= 

=  

= 

5.5 mole % 

8.7 mole % 

0.55 

0.9 

Step 3: Calculate the equivalent gas contents

 for the flammable gases according to 

Equation 2.2.4.4.b 

= 2.46 mole % 

 = 7.38 mole % 

Step 4: Calculate the flammability of the gas mixture according to Equation 2.2.4.4.a 

1A2A1B2BnpciTkK1cT2cT1K2KiA'()()659.02755.0622'1+++=A()()659.02755.0626'2+++=A 
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= 1.29 

Step 5: Compare the outcome to the criterion in Equation 2.2.4.4.a 

Since 1.29 > 1, this particular gas mixture is considered to be flammable. 

7.838.75.546.2'''221121+=+==cciciiTATATA 
 
 
 
 
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2.3.  AEROSOLS 

2.3.1.  Introduction 

Identical criteria related to the flammability of aerosols are found in Annex I, Section 2.3 of CLP, 
Chapter 2.3 of GHS as well as in the Aerosol Dispensers Directive (ADD) 75/324/EEC.  

2.3.2.  Definitions and general considerations for the classification of 

aerosols 

Annex I: 2.3.1. Aerosols, this means aerosol dispensers, are any non-refillable receptacles 
made of metal, glass or plastics and containing a gas compressed, liquefied or dissolved under 
pressure, with or without a liquid, paste or powder, and fitted with a release device allowing 
the contents to be ejected as solid or liquid particles in suspension in a gas, as a foam, paste 
or powder or in a liquid state or in a gaseous state. 

2.3.3.  Relation to other physical hazards 

There is no direct relation to other physical hazards. 

1.  Annex I, 2.3.2.1.  

[…] 

Note 2: 

Aerosols do not fall additionally within the scope of Sections 2.2 (flammable gases), 2.5 
(gases under pressure), 2.6 (flammable liquids) and 2.7 (flammable solids). Depending on 
their contents, aerosols may however fall within the scope of other hazard classes, including 
their labelling elements.  

 
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2.3.4.  Classification of aerosols 

2.3.4.1.  Classification criteria  

Annex I: 2.3.2.1. Aerosols shall be classified in one of the three categories of this hazard 
class, depending on their flammable properties and their heat of combustion. They shall be 
considered for classification in Category 1 or 2 if they contain more than 1% components (by 
mass) which are classified as flammable according to the following criteria set out in this Part: 

– Flammable gases (see Section 2.2); 

– Liquids with a flash point ≤ 93 °C, which includes Flammable Liquids according to section 
2.6; 

– Flammable solids (see Section 2.7); 

or their heat of combustion is at least 20kJ/g. 

Note 1: 

Flammable components do not cover pyrophoric, self-heating or water-reactive substances 
and mixtures because such components are never used as aerosol contents. 

[…] 

2.3.2.2. An aerosol shall be classified in one of the three categories for this Class on the basis 
of its components, of its chemical heat of combustion and, if applicable, of the results of the 
foam test (for foam aerosols) and of the ignition distance test and enclosed space test (for 
spray aerosols) in accordance with Figures 2.3.1(a) to 2.3.1(c) of this Annex and sub-sections 
31.4, 31.5 and 31.6 of Part III of the UN RTDG, Manual of Tests and Criteria. Aerosols which 
do not meet the criteria for inclusion in Category 1 or Category 2 shall be classified in 
Category 3. 

Note: 

Aerosols containing more than 1% flammable components or with a heat of combustion of at 
least 20 kJ/g, which are not submitted to the flammability classification procedures in this 
section shall be classified as aerosols, Category 1. 

Under the ADD and also in UN-MTC, Section 31, flammability classification for aerosols refers to 
‘extremely flammable’, ‘flammable’ and ‘non-flammable’. This respectively corresponds to the 
terms ‘Aerosol, Category 1’, ‘Aerosol, Category 2’ and ‘Aerosol, Category 3’ which are used in 
CLP. 

The following identical criteria can be found in both CLP and ADD: 

The aerosol is classified as ‘Aerosol, Category 3’ if it contains 1 % or less flammable 
components49 and the chemical heat of combustion is less than 20 kJ/g. 

The aerosol is classified as ‘Aerosol, Category 1’ if it contains 85 % or more flammable 
components and the chemical heat of combustion is 30 kJ/g or more. 

All other aerosols should be submitted to the appropriate flammability classification procedures 
in order to select the appropriate Category 1, 2 or 3. However, if these are not submitted to the 

49 Depending on their flash point value, also certain liquids not classified under CLP as Flam. Liq., Cat. 1, 2 
or 3, will be considered as flammable components in an aerosol. The CLP hazard class of Flammable liquids 
covers liquids of flash point ≤ 60 °C while a liquid component in an aerosol is considered flammable when 
its flash point is ≤ 93 °C. 

 
 
 
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flammability classification procedures they must be automatically classified as ‘Aerosol, 
Category 1’. 

The chemical heat of combustion is determined in accordance with CLP Annex I, 2.3.4.1 which 
is identical to point 1.10 of the Annex to ADD. 

2.3.4.2.  Testing and evaluation of hazard information 

Results from the ignition distance test, the enclosed space test and the foam flammability test 
may be used for classification related to the flammability of aerosols. These test methods are 
described under point 6.3 of the Annex to ADD and are therefore available in all EU languages. 
They are also described in the UN-MTC Section 31. 

After evaluation according to the appropriate criteria (see previous sections) the aerosol is 
classified in one of the three categories. 

2.3.4.3.  Decision logic  

The classification procedure is also laid down in the following flow-charts which are applicable 
according to CLP.  

  NOTE: The person responsible for the classification of aerosols should be experienced in this 

field and be familiar with the criteria for classification. 

 
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2.3.4.3.1.  Decision logic for aerosols 

Annex I: Figure 2.3.1 (a) 

for aerosols 

AEROSOL 

Does it contain ≤ 1% flammable 
components (by mass) and does it have a 
heat of combustion < 20 kJ/g? 

Does it contain ≥ 85% flammable 
components (by mass) and does it have a 
heat of combustion ≥ 30 kJ/g? 

' 

For spray aerosols, go to decision logic 
2.3.1(b) 

For foam aerosols, go to decision logic 
2.3.1(c)' 

Category 3 

No pictogram 

Warning 

Category 1 

Danger 

   YES  NO  YES  NO  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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2.3.4.3.2.  Decision logic for spray aerosols 

Annex I: Figure 2.3.1 (b) 

Spray aerosols 

SPRAY AEROSOL 

In the ignition distance test, does ignition occur 
at a distance ≥ 75 cm? 

YES 

NO 

Does it have a heat of combustion < 20 kJ/g? 

NO 

YES 

In the ignition distance test, does ignition occur 
at a distance ≥ 15 cm? 

NO 

In the enclosed space ignition test; is:  

(a) the time equivalent ≤ 300 s/m³or  

(b) the deflagration density ≤ 300 g/m³? 

YES 

YES 

NO 

Category 3 

No pictogram 

Warning 

Category 1 

Danger 

Category 2 

Warning 

Category 2 

Warning 

Category 2 

Warning 

 
 
 
 
 
 
 
 
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2.3.4.3.3.  Decision logic for foam aerosols 

Annex I: Figure 2.3.1 (c) 

Foam aerosols 

FOAM AEROSOL 

In the foam test, is:  

(a) the flame height ≥ 20 cm and the flame duration ≥ 2 s; or 
(b) the flame height ≥ 4 cm and the flame duration ≥ 7 s? 

YES 

NO 

In the foam test; is the flame height ≥ 4 cm and the flame 
duration ≥ 2 s? 

YES 

Category 1 

Danger 

Category 2 

Warning 

NO 

Category 3 

No pictogram 

Warning 

 
 
 
 
 
 
 
 
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2.3.5.  Hazard communication for aerosols 

2.3.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

Annex I: Table 2.3.1 

Label elements for aerosols 

Classification 

Category 1 

Category 2 

Category 3 

GHS Pictograms 

No pictogram 

Signal Word 

Danger 

Warning 

Warning 

H222: Extremely 
flammable aerosol 

H223: Flammable 
aerosol 

Hazard Statement 

H229: Pressurised 
container: May burst 
if heated. 

H229: Pressurised 
container: May burst 
if heated. 

H229: Pressurised 
container: May burst 
if heated. 

P210 

P211 

P251 

P210 

P211 

P251 

P210 

P251 

P410 + P412 

P410 + P412 

P410 + P412 

Precautionary 
Statement 
Prevention 

Precautionary 
Statement Response 

Precautionary 
Statement Storage 

Precautionary 
Statement Disposal 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

2.3.5.2.  Additional labelling provisions  

The ADD imposes additional labelling requirements on all aerosols, flammable or not. 

For example: 

Where an aerosol dispenser contains flammable components but is not classified as flammable 
(i.e. ‘Aerosol, Category 3’), the quantity of flammable material contained in the aerosol 
dispenser must be stated clearly on the label, in the form of the following legible and indelible 
wording: ‘X % by mass of the contents are flammable’. 

 
 
 
 
 
 
 
 
 
 
 
 
 
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2.3.6.  Relation to transport classification 

Aerosol dispensers (UN 1950) belong to Class 2 in the UN RTDG Model Regulations and in the 
modal transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI). Flammability 
classification criteria are harmonised between CLP and in the modal transport regulations (ADR, 
RID, ADN and IMDG Code, ICAO TI). 

Aerosols, Category 1 and 2 fall under Division 2.1 (sometimes referred to as Class 2.1 or Group 
F, FC, TF or TFC depending on their contents with hazardous properties). Aerosols, Category 3 
fall under Division 2.2 (sometimes referred to as Class 2.2 or Group A, O, T, C, CO, TC or TOC 
depending on their contents with hazardous properties). See Annex VII for additional 
information on transport classification in relation to CLP classification. 

2.3.7.  Examples of classification for aerosols 

For reasons of simplification the active materials chosen in the examples have been considered 
as non-combustible materials (Hc = 0 kJ/g). However this is not the case in practice. 

2.3.7.1.  Examples of aerosols fulfilling the classification criteria  

Deodorant: 

Composition: 

         Butane/propane:  

70 % (flammable components, Hc = 43.5 kJ/g) 

         Ethanol:   

25 % (flammable components, Hc = 24.7 kJ/g) 

         Others:   

5 % (non-flammable components, Hc = 0 kJ/g) 

This spray aerosol contains 95 % of flammable components, and its chemical heat of combustion 
equals 36.6 kJ/g (= 0.70 * 43.5 + 0.25 * 24.7). 

This aerosol is classified as Aerosol, Category 1. 

Air freshener (wet): 

Composition: 

         Butane/propane: 

30 % (flammable components, Hc = 43.5 kJ/g) 

         Others:   

70 % (non-flammable components, Hc = 0 kJ/g) 

This spray aerosol contains 30 % of flammable components and its chemical heat of combustion 
equals 13.1 kJ/g. 

In the ignition distance test, the ignition occurs at less than 75 cm but more than 15 cm. 

This aerosol is classified as Aerosol, Category 2. 

Shaving foam: 

Composition: 

         Butane/propane:  

4 % (flammable components, Hc = 43.5 kJ/g) 

         Others:   

96 % (non-flammable components, Hc = 0 kJ/g) 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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This foam aerosol contains 4 % of flammable components and its chemical heat of combustion 
equals 1.7 kJ/g. 

In the foam test, the flame height is less than 4 cm and the flame duration less than 2 s. 

This aerosol is classified as Aerosol, Category 3. 

However, according to the requirements of ADD, the quantity of flammable components must be 
stated clearly on the label: ‘4% by mass of the contents are flammable’. 

2.3.7.2.  Examples of aerosols not fulfilling the classification criteria  

By definition, all aerosol dispensers fall under one of the three categories for this hazard class. 

 
 
 
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2.4.  OXIDISING GASES 

2.4.1.  Introduction 

The requirements in Chapter 2.4 ‘Oxidising gases’ of Annex I of CLP are identical to those in 
chapter 2.4 of the GHS.  

2.4.2.  Definitions and general considerations for the classification of 

oxidising gases   

Annex I: 2.4.1. Oxidising gas means any gas or gas mixture which may, generally by 
providing oxygen, cause or contribute to the combustion of other material more than air 
does. 

2.4.3.  Relation to other physical hazards 

Oxidising gases do not need to be classified in any other hazard class apart from ‘Gases under 
pressure’ where appropriate. 

2.4.4.  Classification of substances and mixtures as oxidising gases   

2.4.4.1. 

Identification of hazard information  

There are not many pure gases that are oxidising. Most oxidising gases are identified as such in 
the UN RTDG Model Regulations and in ISO 10156 Gases and gas mixtures: Determination of 
fire potential and oxidizing ability for the selection of cylinder valve outlets as amended. 

2.4.4.2.  Screening procedures and waiving of testing 

There are thousands of gas mixtures containing oxidising gases on the market and there are 
very few test reports on oxidising potential of gas mixtures in the scientific literature. Tests 
according to ISO 10156 as amended in order to determine the oxidising potential are time 
consuming and expensive for gas mixtures which are often prepared on demand. In most of the 
cases, the formulator of the gas mixture will use a calculation method as described in ISO 
10156 as amended. 

2.4.4.3.  Classification criteria 

Annex I: 2.4.2. Table 2.4.1 

Criteria for oxidising gases 

Category  Criteria 

Any gas which may, generally by providing oxygen, cause or contribute to the 
combustion of other material more than air does. 

1 

Note: 

‘Gases which cause or contribute to the combustion of other material more than air does’ 
means pure gases or gas mixtures with an oxidising power greater than 23.5 % as 
determined by a method specified in ISO 10156 as amended. 

Please note that ISO 10156-2:2005 has been integrated into the revised version ISO 
10156:2010. ISO 10156:2010 supersedes EN 720-2:1996 and ISO 10156-2:2005. 

 
 
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2.4.4.4.  Testing and evaluation of hazard information   

ISO 10156 as amended describes a test method and a calculation method for the classification 
of oxidising gases. The test method may be used in all cases, but must be used when the 
calculation method cannot be applied. 

The calculation method applies to gas mixtures and can be applied only when the Ci for all 
oxidising components and the Kk for all inert components are available. These are listed for a 
number of gases in ISO 10156 as amended. For gas mixtures the calculation method described 
in ISO 10156 as amended uses the criterion that a gas mixture should be considered as more 
oxidising than air if the ‘Oxidising Power’ (OP) of the gas mixture is higher than 0.235 (23.5 %).  

The OP is calculated as follows: 

Equation 2.4.4.4.a 

Where: 

xi 

Ci 

Kk 

Bk 

is the molar fraction of the i:th oxidising gas in the mixture, in % 

is the coefficient of oxygen equivalency of the i:th oxidising gas in the mixture 

is the coefficient of equivalency of the inert gas k relative to nitrogen 

is the molar fraction of the k:th inert gas in the mixture, in % 

is the number of oxidising gases in the mixture 

is the number of inert gases in the mixture 

For mixtures containing both flammable and oxidising components, special calculation methods 
are described in ISO 10156 as amended. 

2.4.4.5.  Decision logic  

Classification of oxidising gases is done according to decision logic 2.4.4.1 as included in the 
GHS. 

  NOTE: The person responsible for the classification of oxidising gases should be 

experienced in this field and be familiar with the criteria for classification. 

Figure 2.1  Decision logic for oxidising gases (Decision logic 2.4 of GHS) 

Gaseous substance or mixture of gases 

Does the gas contribute to the combustion of 
other material more than air does? 

NO 

Not classified 

YES 

Category 1 

Danger 

===+=nipkkkiniiiBKxCxOP111np 
 
 
   
 
 
 
 
 
 
 
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2.4.5.  Hazard communication for oxidising gases 

2.4.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

Annex I: Table 2.4.2 

Label elements for oxidising gases 

Classification 

Category 1 

GHS Pictogram 

Signal word 

Danger 

Hazard statement 

H270: May cause or intensify fire; oxidiser 

Precautionary Statement Prevention 

P220 
P244 

Precautionary Statement Response 

P370 + P376 

Precautionary Statement Storage 

P403 

Precautionary Statement Disposal 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

2.4.6.  Relation to transport classification 

Most oxidising gases are classified as such with subsidiary risk 5.1 in the UN RTDG Model 
Regulations. Consequently all gases listed as oxidising in the UN RTDG Model Regulations and in 
the modal transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) must be classified as 
Ox. Gas 1. See Annex VII for additional information on transport classification in relation to CLP 
classification. 

2.4.7.  Example of classification for oxidising gases   

2.4.7.1.  Example of substances and mixtures not fulfilling the classification 

criteria  

EXAMPLE OF A CLASSIFICATION USING THE CALCULATION METHOD OF ISO 10156 AS 
AMENDED 

Example Mixture: 9 % (O2) + 16 % (N2O) + 75 % (N2) 

Calculation steps 

Step 1: Ascertain the coefficient of oxygen equivalency (Ci) for the oxidising gases in the mixture and 
the nitrogen equivalency factors (Kk) for the non-flammable, non-oxidising gases. 

 
 
 
 
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Ci (N2O) =  

0.6 (nitrous oxide) 

Ci (O) = 

1 (oxygen) 

Kk (N2) = 

1 (nitrogen) 

Step 2: Calculate the Oxidising Power (OP) of the gas mixture according to Equation 2.4.4.4.a 

0.186 < 0.235 (18.6 % < 23.5 %), therefore the mixture is not considered as an 
oxidising gas. 

186.0175.016.009.06.016.0109.0111=+++=+====nipkkkiniiiBKxCxOP 
 
 
 
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2.5.  GASES UNDER PRESSURE 

2.5.1.  Introduction 

The requirements in Chapter 2.5 ‘Gases under pressure’ of Annex I of CLP are identical to those 
in Chapter 2.5 of GHS. The hazard class ‘Gases under pressure’ corresponds to Class 2 ‘Gases’ 
in the UN RTDG Model Regulations.   

2.5.2.  Definitions and general considerations for the classification of gases 

under pressure 

2.5.2.1.  Definition of ‘gas’ 

Annex I: 1.0. Gas means a substance which (i) at 50 °C has a vapour pressure greater 
than 300 kPa (absolute); or (ii) is completely gaseous at 20 °C at a standard pressure of 
101.3 kPa; 

This definition means that substances and mixtures are considered as gases when their boiling 
point or initial boiling point (BP) is not higher than 20 °C. Substances and mixtures with a 
boiling point or initial boiling point higher than 20 °C are liquids except those few that develop a 
vapour pressure higher than 300 kPa at 50 °C; these substances and mixtures are considered 
as gases because of the pressure hazard when packaged. 

Hydrogen fluoride (HF) with a BP of 19.4 °C is a borderline line case that has always been 
classified as a liquid. 

2.5.2.2.  Definition of gases under pressure  

Annex I: 2.5.1.1. Gases under pressure are gases or gas mixtures which are contained in a 
receptacle at a pressure of 200 kPa (gauge) or more at 20 °C, or which are liquefied or 
liquefied and refrigerated. 

They comprise compressed gases, liquefied gases, dissolved gases and refrigerated liquefied 
gases. 

This definition means in practice that compressed gases or dissolved gases that are packaged at 
a pressure less than 200 kPa are not classified for this hazard. 

Dissolved gases packaged at a pressure less than 200 kPa (gauge) are liquids and should be 
classified as such if they have other hazardous properties, e.g. flammable liquids. 

Also, liquids packaged under a layer of inert gas (e.g. nitrogen or helium) remain to be 
classified as liquids and not as gases under pressure. 

2.5.3.  Relation to other physical hazards 

Gases under pressure may also need to be classified for the hazard classes flammable gases 
and oxidising gases where relevant. 

2.5.4.  Classification of substances and mixtures as gases under pressure  

2.5.4.1. 

Identification of hazard information  

Many gases are identified as such in the UN RTDG Model Regulations and many flammable 
gases and some oxidising gases are identified as gases in Annex VI of CLP. The UN RTDG Model 
Regulations identifies further if the gas can be packaged as a ‘compressed gas’, a ‘liquefied gas’, 
a ‘refrigerated liquefied gas’ and a ‘dissolved gas’. To determine whether a substance is a gas in 

 
 
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case it is not listed in the UN RTDG Model Regulations and in case of doubt, the following 
physical characteristics are necessary:  

• 

• 

the boiling point;  

the vapour pressure at 50 °C. 

See also IR & CSA, Chapter R.7a: Endpoint specific guidance, Section R.7.1.3 (Boiling point), 
R.7.1.5 (Vapour pressure). 

For those substances that meet the definition of a gas (see Section 2.5.2), the critical 
temperature is also necessary. For the classification of gas mixtures based on the pseudo-
critical temperature see Section 2.5.4.3.  

The references according to Section 2.6.8 provide good quality data on boiling points, vapour 
pressure and the critical temperature of substances. 

2.5.4.2.  Classification criteria  

Annex I: Table 2.5.1 

Criteria for gases under pressure 

Group 

Criteria 

Compressed 
gas 

A gas which when packaged under pressure is entirely gaseous at 
- 50 °C; including all gases with a critical temperature  - 50 °C. 

A gas which, when packaged under pressure, is partially liquid at 
temperatures above - 50 °C. A distinction is made between: 

Liquefied gas 

high pressure liquefied gas: a gas with a critical temperature between 

i) 
- 50 °C and + 65 °C; and 

low pressure liquefied gas: a gas with a critical temperature above + 

ii) 
65 °C. 

Refrigerated 
liquefied gas 

A gas which when packaged is made partially liquid because of its low 
temperature. 

Dissolved gas 

A gas which when packaged under pressure is dissolved in a liquid phase 
solvent. 

Note:  

Aerosols shall not be classified as gases under pressure. See Section 2.3. 

2.5.4.3.  Testing and evaluation of hazard information  

The critical temperature of pure gases is well defined and can be found in technical literature, 
e.g. EN 13096 Transportable gas cylinders — Conditions for filling gases into receptacles — 
Single component gases as amended. 

For gas mixtures, the classification is based on the ‘pseudo-critical temperature’ which can be 
estimated as the mole weighted average of the components’ critical temperatures. 

Pseudo-critical temperature =  

=niCritiix1T 
 
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where xi is the molar concentration of component i and T

 is the critical temperature (in °C 

or in K) of the component i.  

2.5.4.4.  Decision logic  

Classification of gases under pressure is done according to decision logic 2.5.4.1 as included in 
the GHS. 

  NOTE: The person responsible for the classification of gases under pressure should be 

experienced in this field and be familiar with the criteria for classification. 

iCrit 
 
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Figure 2.2  Decision logic for gases under pressure (Decision logic 2.5 of GHS)  

The substance or mixture is a gas 

Is the gas contained in a receptacle at a pressure of 200 kPa 
(gauge) or more at 20 °C, or is the gas liquefied or liquefied and 
refrigerated? 

No 

Not classified as a 
gas under 
pressure 

Yes 

Dissolved gas  

Yes 

Is the gas dissolved in a liquid phase solvent? 

No 

Warning 

Is the gas partially liquid because of its low temperature? 

No 

Is the gas partially liquid at temperatures above – 50 °C? 

No 

Warning 

Refrigerated 
liquefied gas  

Yes 

No 

Is its critical temperature above + 65 °C? 

No 

Is its critical temperature between – 50 °C + 65°C? 

Is the gas entirely in gaseous state at – 50 °C? 

(Low pressure) 
Liquefied gas  

Yes 

Warning 

(High pressure) 
Liquefied gas  

Yes 

Warning 

Compressed gas  

Yes 

Warning 

 
 
 
 
 
 
 
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2.5.5.  Hazard communication for gases under pressure 

2.5.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

Annex I: Table 2.5.2 

Label elements for gases under pressure 

Classification 

Compressed gas 

Liquefied gas 

Refrigerated 
liquefied gas 

Dissolved gas 

GHS Pictogram 

Signal Word 

Warning 

Warning 

Warning 

Warning 

Hazard 
Statement 

H280: Contains 
gas under 
pressure; may 
explode if heated 

H280: Contains 
gas under 
pressure; may 
explode if heated 

H281: Contains 
refrigerated 
gas; may cause 
cryogenic burns 
or injury 

H280: 
Contains gas 
under 
pressure; 
may explode 
if heated 

P282 

P336 + P315 

P410 + P403 

P410 + P403 

P403 

P410 + P403 

Precautionary 
Statements 
Prevention 

Precautionary 
Statements 
Response 

Precautionary 
Statements 
Storage 

Precautionary 
Statements 
Disposal 

Note:  

Pictogram GHS04 is not required for gases under pressure where pictogram GHS02 or 
pictogram GHS06 appears. 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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2.5.6.  Relation to transport classification 

Gases are listed in UN RTDG Model Regulations and in the transport regulations (ADR, RID, 
ADN)50 with an indication of the physical state in their name for compressed gases (e.g. Argon, 
compressed), for refrigerated liquefied gas (e.g.  Oxygen, refrigerated liquid) and for dissolved 
gas (e.g. Acetylene, dissolved). These indications of the physical state 
can  be  used  to  identify  the  group  of  gases  under  pressure according to CLP. The gas 
names without an indication of the physical state are ‘liquefied gases’ by default. See Annex VII 
for additional information on transport classification in relation to CLP classification. 

50 The classification codes according to the ADR, Sections 2.2.2.1.2 and 2.2.2.1.3 are: 1. Compressed gas; 
2. Liquefied gas; 3. Refrigerated liquefied gas; 4. Dissolved gas. A asphyxiant; O oxidizing; F flammable; T 
toxic; TF toxic, flammable; TC toxic, corrosive; TO toxic, oxidizing; TFC toxic, flammable, corrosive; TOC 
toxic, oxidizing, corrosive.  

 
 
 
 
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2.5.7.  Examples of classification for gases under pressure 

2.5.7.1.  Examples of substances and mixtures fulfilling the classification 

criteria 

2.5.7.1.1. 

Example mixture: 9 % (O2) + 16 % (N2O) + 75 % (N2) 

EXAMPLE MIXTURE: 9 % (O2) + 16 % (N2O) + 75 % (N2) 

Calculation steps: 

Step 1: Ascertain the critical temperatures in Kelvin for the gases in the mixture: 

Oxygen (O2):  

Nitrous Oxide (N2O):  

Nitrogen (N2):  

TCrit = -118.4 °C  (= 154.75 K) 

TCrit = +36.4 °C (= 309.55 K) 

TCrit = -147 °C (= 126.15 K) 

Step 2: Calculate the pseudo-critical temperature: 

0.09  154.75 K + 0.16  309.55 K + 0.75  126.15 K= 158.7 Kelvin = - 115.08 °C 

The pseudo-critical temperature is lower than -50 °C, therefore the mixture is a ‘compressed gas’. 

 
 
 
 
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2.6.  FLAMMABLE LIQUIDS 

2.6.1.  Introduction 

The criteria for ‘Flammable liquids’ are found in Annex I, Section 2.6 of CLP and are not 
identical to those of GHS as the respective GHS Chapter 2.6 contains additional classification 
criteria - Category 4 for flammable liquids.  

2.6.2.  Definitions and general considerations for the classification of 

flammable liquids  

Annex I: 2.6.1. Flammable liquid means a liquid having a flash point of not more than 60 °C.  

The flash point is the lowest temperature of the liquid, corrected to a barometric pressure of 
101.3 kPa, at which application of a test flame causes the vapour of the liquid to ignite 
momentarily and a flame to propagate across the surface of the liquid under the specified 
conditions of test. This means, the lower explosion limit is exceeded at the flash point. 

2.6.3.  Relation to other physical hazards 

For flammable liquids that are packaged in aerosol dispensers, see Section 2.3 on Aerosols. If 
classified as flammable aerosols, they must not be classified as flammable liquids in addition 
(see Section 2.3). 

2.6.4.  Classification of substances and mixtures as flammable liquids 

2.6.4.1. 

Identification of hazard information 

For the decision if a substance or mixture is a liquid see Section 2.0.4. 

For the classification of a substance or mixture as a flammable liquid, data on the flash point 
and on the boiling point (or the initial boiling point) are needed. For experimental determination 
of the flash point information on the viscosity of the liquid is needed, in order to select a 
suitable method. Furthermore, in order to make use of the derogation for classification in 
Category 3 according to Annex I Section 2.6.4.5 of CLP (see Section 2.6.4.3), information on 
sustained combustibility is necessary. 

Experimentally determined data or data taken from reliable data sources are to be preferred 
over calculated ones. See also IR & CSA, Chapter R.7a: Endpoint specific guidance, Section 
R.7.1.3 (Boiling point), R.7.1.9 (Flash point). 

The references in Section 2.6.8 provide good quality data on boiling points (all three references) 
and flash point (first reference) of substances.  

Special care is required when viscous substances or mixtures are tested or when halogenated 
compounds are present (see Section 2.6.4.4.1). 

2.6.4.2.  Screening procedures and waiving of testing 

2.6.4.2.1. 

Boiling point 

Normally calculation methods based on increments give satisfying results for substances and 
mixtures. With respect to the criterion for distinguishing between Category 1 and 2 (boiling 
point of 35 °C) only that method with a mean absolute error lower than 5 °C could be 
recommended for screening.  

 
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2.6.4.2.2. 

Flash point 

Calculation should work for pure liquids, neglecting impurities, if the vapour pressure curve and 
lower explosion limit are accurately known. For mixtures, calculation of the flash point is 
sometimes not reliable and at this time, it is not possible to predict what the accuracy of a 
calculated value is. Calculation can be used as a screening test for mixtures, and a flash point 
need not be determined experimentally if the calculated value using the method cited in CLP 
Annex I, 2.6.4.3 is 5 °C greater than the relevant classification criterion (23 °C and 60 °C, 
respectively). However, the restrictions outlined in the CLP Annex I, 2.6.4.2 must be taken 
account of.  

Calculation based on structural similarity or properties is often only applicable to a narrowly 
defined set of substances. For mixtures they are not yet applicable. 

Therefore for both flash point and boiling point experimental determination is recommended. 

2.6.4.3.  Classification criteria 

A flammable liquid has to be classified in one of the 3 categories of this class. 

Annex I: Table 2.6.1 

Label elements for flammable liquids 

Category 

Criteria 

1 

2 

3 

Flash point < 23 °C and initial boiling point ≤ 35 °C 

Flash point < 23 °C and initial boiling point > 35 °C 

Flash point ≥ 23 °C and ≤ 60 °C1 

(1) For the purpose of this Regulation gas oils, diesel and light heating oils having a flash 

point between > 55 °C and ≤ 75 °C may be regarded as Category 3. 

Note:  

Aerosols shall not be classified as flammable liquids; see section 2.3. 

Annex I: 2.6.4.5. Liquids with a flash point of more than 35 °C and not more than 60 °C 
need not be classified in Category 3 if negative results have been obtained in the sustained 
combustibility test L.2, Part III, section 32 of the UN RTDG, Manual of Tests and Criteria. 

Gas oils, diesel and light heating oils in the flash point range of 55 °C to 75 °C may be regarded 
as a whole. The reason is that these hydrocarbon mixtures have varying flash points in that 
range due to seasonal requirements (EN 590 Automotive fuels – Diesel- Requirements and Test 
Methods as amended). If they are regarded as a whole for CLP they have to be regarded as 
Category 3. This states however no preliminary decision with respect to downstream 
Regulations and legislation.   

2.6.4.4.  Testing and evaluation of hazard information  

The assignment to the respective hazard category will determine the technical means to be 
taken to avoid dangerous events. In combination with other safety characteristics like explosion 
limits or auto ignition temperature this can lead to clear restrictions in the conditions of use. 
The relevant data are to be communicated via the CSR and SDS (see IR&CSA Part F: Chemical 
Safety Report, Part G: Extending the SDS and Guidance on compilation of safety data sheets 
respectively). 

 
 
 
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2.6.4.4.1. 

Testing  

Suitable methods are listed in CLP Annex I, Table 2.6.3. 

In case of substances with a high decomposition potential, a method using small amounts of 
liquid (e.g. EN ISO 3679 Determination of flash point - Rapid equilibrium closed cup method as 
amended) is recommended to reduce the amount of substance under test. 

The method to be used has to be chosen taking into account the properties of the liquid 
(viscosity, halogenated compounds present) and the scope of the standard. 

For classification purposes it is recommended to use the mean of at least two test runs. One of 
these runs may be automated. In case of a deviation between manual and automated 
determination above the tolerance limits of the method, the lower value should be taken or the 
determination should be repeated with manual observation. If the experimentally determined 
flash point is found to be within ± 2 °C a threshold limit when using a non-equilibrium method, 
it is recommended to repeat the determination with an equilibrium method. 

If no flash point is found up to 60 °C and (partly) halogenated compounds are present or if 
there is the possibility of loss of volatile flammable or non-flammable components (i.e. the 
liquid is a candidate for the assignment of EUH018, EUH209 or EUH209A) or if in doubt, the 
explosion limits should be determined in order to decide whether labelling with EUH018, 
EUH209 or EUH209A is appropriate. Determination of explosion limits should be carried out 
according to EN 1839 Determination of explosion limits of gases and vapours as amended or 
ISO 10156 Gases and gas mixtures – Determination of fire potential and oxidising ability for the 
selection of cylinder valves outlets as amended or EN 15794 Determination of explosion points 
of flammable liquids as amended. 

Substances 

For non-halogenated substances, the flash point is usually found 80 °C to 130 °C below the 
boiling point. Special care has to be taken when a sample contains impurities with a lower 
boiling point than the main compound. Even if their concentration is below 0.5 %, especially if 
their boiling point is substantially lower, they may have a strong effect on the test result. 
Impurities with a higher boiling point will normally have no effect on the flash point. 

Within the respective scope, every standard is applicable. 

Mixtures 

The flash point may be lower than the lowest flash point of the components and non-volatile 
components may influence the flash point. 

Equilibrium methods are advised if the boiling points of the components of the mixture cover a 
wide range of temperatures or their concentrations are very different. They are also advised in 
case of viscous mixtures (alternatively: test methods with low heating rates (1 °C per min) 
using a stirrer). 

In case of viscous mixtures or if an inerting substance is present at low concentrations and this 
is a highly volatile compound, the ignitability of the mixture may depend on the temperature at 
which the tests are started. When an inerting substance is present temperature ranges may 
exist where the vapour phase is inerted and other temperature ranges where it is not. 

Halogenated compounds 

The difference between boiling point and flash point may be lower than with non-halogenated 
compounds.  

It is highly recommended to run the tests under careful control with manual observation.  

Test results may be very difficult to reproduce. In such cases, classification should be based on 
the lowest value found (flash or burning inside or outside the cup) or on the value obtained 

 
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during the screening run if in the main trial performed in accordance with the standard, no flash 
could be found. 

2.6.4.4.2. 

Evaluation of hazard information 

Flash points determined by testing or from the mentioned internationally recognised qualified 
literature are to be preferred over those derived by calculation because of the error of most of 
the QSAR methods and their limited application range. 

If in literature different flash points are found for the same substance the one found as 
evaluated or recommended has to be preferred. 

If in literature different flash points are found for the same substance where none is found as 
evaluated/recommended the lower one has to be preferred because of safety reasons or an 
experimental determination should be carried out. 

According to the criteria either Category 1, Category 2 or Category 3, including the relevant 
hazard statement and signal word, have to be assigned (see Section 2.6.5). In case the criteria 
for EUH018, EUH209 or EUH209A are met, the liquid has to be labelled with the respective 
supplemental hazard statement as well. In the majority of cases EUH018 covers EUH209 and 
EUH209A. 

2.6.4.5.  Decision logic 

Compared to the decision logic 2.6 for flammable liquids contained in the GHS chapter 2.6.4.1, 
this decision logic below is amended to include derogations for gas oil, diesel, light heating, 
sustained combustibility and for phrases EUH018, EUH209 and EUH209A. 

  NOTE: The person responsible for the classification of flammable liquids should be 

experienced in this field and be familiar with the criteria for classification. 

 
 
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Figure 2.3  Amended GHS decision logic for flammable liquids to include derogations for gas oil, 
diesel, light heating, sustained combustibility and for phrases EUH018, EUH209 and EUH209A 

The substance or mixture is a liquid 

Flash point ≤ 60 °C 

Yes 

No 

Gas oil, diesel, light 
heating oil with flash 
point up to 75 °C 

No 

Yes 

Halogenated 
substance, mixture 
containing 
halogenated, volatile 
or non volatile 
flammable 
substances  

No 

Yes 

Yes 

Flash point < 23 °C 

No 

No 

No 

Yes 

Explosive vapour/air 
mixture possible  
(EN 1839, EN 15794) 

 Category 3 

No 

Flash point > 35 °C 

Yes 

Warning 

Sustained combustibility 

Yes 

No 

  Category 2 

Not subject of 
hazard class 
‘flammable liquid  

EUH209, 
EUH209A, 
EUH018 

Boiling point ≤ 35 °C 

No 

Yes 

Danger 

No need to be classified as 
‘flammable liquid’  

  Category 1 

Danger 

 
 
 
 
 
 
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2.6.5.  Hazard communication for flammable liquids  

2.6.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

Annex I: 2.6.3. Table 2.6.2 

Label elements for flammable liquids 

Classification 

Category 1 

Category 2 

Category 3 

GHS Pictograms 

Signal Word 

Danger 

Danger 

Warning 

Hazard 
Statement 

Precautionary 
Statement 
Prevention 

Precautionary 
Statement 
Response 

Precautionary 
Statement 
Storage 

Precautionary 
Statement 
Disposal 

H224: Extremely 
flammable liquid and 
vapour 

H225: Highly 
flammable liquid and 
vapour 

H226: Flammable liquid 
and vapour 

P210 
P233 
P240 
P241 
P242 
P243 
P280 

P210 
P233 
P240 
P241 
P242 
P243 
P280 

P210 
P233 
P240 
P241 
P242 
P243 
P280 

P303 + P361 + P353 
P370 + P378 

P303 + P361 + P353 
P370 + P378 

P303 + P361 + P353 
P370 + P378 

P403 + P235 

P403 + P235 

P403 + P235 

P501 

P501 

P501 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

2.6.5.2.  Additional labelling provisions for flammable liquids 

Annex II: 1.1.4.     EUH018 – 'In use, may form flammable/explosive vapour-air 
mixture' 

For substances and mixtures not classified as flammable themselves, which may form 
flammable/explosive vapour-air mixtures. For substances this might be the case for 
halogenated hydrocarbons and for mixtures this might be the case due to a volatile 
flammable component or due to the loss of a volatile non-flammable component. 

 
 
 
 
 
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Substances or mixtures which do not show a flash point but do have an explosion range or may 
become flammable in use have to be labelled with EUH018. 

Annex II: 2.9. Liquid mixtures containing halogenated hydrocarbons 

For liquid mixtures which show no flashpoint or a flashpoint higher than 60 ˚C but not more 
than 93 ˚C and contain a halogenated hydrocarbon and more than 5 % highly flammable or 
flammable substances, the label on the packaging shall bear one of the following statements, 
depending on whether the substances referred to above are highly flammable or flammable: 

EUH209 — ‘Can become highly flammable in use’ or 

EUH209A — ‘Can become flammable in use’ 

  Note: EUH209 and EUH209A are limited to special types of mixtures whereas EUH018 
covers a wider range of mixtures. In the majority of cases EUH018 covers EUH209 and 
EUH209A. Information about testing can be found in Section 2.6.4.4.1 paragraph 5. 

2.6.6.  Re-classification of substances and mixtures classified as flammable 
liquids according to DSD and DPD or already classified for transport 

2.6.6.1.  Relation to transport classification 

Class 3 of the UN RTDG Model Regulations and the modal transport regulations (ADR, RID, ADN 
and IMDG Code, ICAO TI) cover flammable liquids based on the same criteria as the CLP hazard 
class flammable liquid. In general there is a correspondence between transport packing groups 
and CLP hazard categories. However, in many cases specific exceptions apply. Further, the UN 
RTDG Model Regulations cover substances and mixtures transported above their flash point and 
desensitized explosives. In practice the information on flash point and boiling point needed for 
classification is available and it is recommended to classify based on the data rather than use 
direct translation. See Annex VII for additional information on transport classification in relation 
to CLP classification. 

2.6.7.  Examples of classification for flammable liquids 

2.6.7.1.  Examples of substances and mixtures fulfilling the classification 

criteria  

2.6.7.1.1. 

Example 1 

MIXTURE OF: N-BUTYLACETATE + P-XYLENE + 1,3,5-TRIMETHYLBENZENE 

(7.9 MOL %     +     60.3 MOL %     +     31.7 MOL %) 

Initial boiling point (calculated): 

Flash point (calculated): 

140 °C 

26 °C 

calculated flash point is within 5 °C to the limiting value of 23 °C 

 flash point has to be measured. 

Dyn. Viscosity at 20 °C (DIN 53019): 

8 mPas 

Flash point (EN ISO 3679): 

30.0 °C 

 According to boiling point and measured flash point result: Flam.Liq. Category 3 

 
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2.6.7.1.2. 

Example 2 

HYDROCARBONS AND DICHLOROMETHANE (70 VOL %     +     30 VOL %) 

Initial Boiling point (calculated): 

52 °C 

Flash point: 

no flash point according to a standard 

 Because the hydrocarbon part of the mixture has a flash point by itself (- 12 °C) the question ‘Is 
an explosive vapour/air mixture possible’ (EN 1839 as amended, EN 15794 as amended) or ‘Can it 
become highly flammable / flammable during use?’ has to be answered. 

Answer: Yes an explosion range exists; yes it can become highly flammable during use. 

 According to the answer, the mixture has to be labelled with EUH018 or EUH209 

Note 1: In that case EUH018 covers EUH209 

Note 2: The EUH018 must only be assigned if the substance or mixture is classified as hazardous 
(Article 25 (1) of CLP)  

Cannot be classified as flammable liquid because the mixture has no flash point. 

2.6.7.2.  Examples of substances and mixtures not fulfilling the classification 

criteria 

2.6.7.2.1. 

Example 3 

AQUEOUS FORMULATION OF ALIPHATIC POLYURETHANE RESIN 

Boiling point (EC 440/2008, EU test method A.2): 

92 °C 

Dyn. Viscosity at 20 °C (DIN 53019 as amended): 

1938 mPas 

Sample is highly viscous, use low heating rate for flash point determination (1 °C /min). 

Flash point (EN ISO 13736 as amended): 

42.5 °C 

Sustained combustibility test (UN- MTC L.2) at 60.5 °C: 

combustion not sustained 

Sustained combustibility test (UN-MTC L.2)at 75 °C: 

combustion not sustained 

 According to the flash point result: Category 3 

However, does not necessarily have to be classified as flammable liquid Category 3 because it did 
not sustain combustion. 

2.6.8.  References 

Brandes, E. and Möller, W.: Safety Characteristic Data, Volume 1, Flammable gases and liquids, 
nw-Verlag, 2008 

William M. Haynes et al. (2012) CRC Handbook of Chemistry and Physics 93rd Edition. CRC 
Press, Taylor and Francis, Boca Raton, FL 

O'Neil, Maryadele J. et al. © (2016, 2012) The Merck Index - An Encyclopedia of Chemicals, 
Drugs, and Biologicals (14th Edition – Version 14.9). Merck Sharp & Dohme Corp., a subsidiary 
of Merck & Co., Inc. 

 
 
 
 
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2.7.  FLAMMABLE SOLIDS 

2.7.1.  Introduction 

The criteria for ‘Flammable solids’ are found in Annex I, Section 2.7 of CLP and are identical to 
those in Chapter 2.7 of GHS.  

2.7.2.  Definitions and general considerations for the classification of 

flammable solids 

Annex I: 2.7.1.1.  

A flammable solid means a solid which is readily combustible, or may cause or contribute to 
fire through friction. 

Readily combustible solids are powdered, granular, or pasty substances or mixtures which are 
dangerous if they can be easily ignited by brief contact with an ignition source, such as a 
burning match, and if the flame spreads rapidly. 

Special consideration on particle size 

Annex I: 2.7.2.3.  

[…] 

Note 1: 

The test shall be performed on the substance or mixture in its physical form as presented. If 
for example, for the purposes of supply or transport, the same chemical is to be presented in 
a physical form different from that which was tested and which is considered likely to 
materially alter its performance in a classification test, the substance shall also be tested in 
the new form. 

[…] 

The finer the particle size of a solid substance or mixture, the greater the area exposed to air 
will be, and since flammability is a reaction with the oxygen in air, the particle size will greatly 
influence the ability to ignite. Hence it is very important that flammable properties for solids are 
investigated on the substance or mixture as it is actually presented (including how it can 
reasonably be expected to be used, see Article 8 (6) of CLP). This is indicated by the Note cited 
in CLP Annex I, 2.7.2.3.For further information please see Section 1.2 within this Guidance.  

2.7.3.  Relation to other physical hazards 

Explosives, organic peroxides, self-reactive substances and mixtures as well as pyrophoric or 
oxidising solids should not be considered for classification as flammable solids since flammability 
is an intrinsic hazard in these classes. 

However, flammable solids can present other physical hazards at the same time, i.e. they might 
be self-heating or corrosive or emit flammable gases in contact with water. 

For flammable solids that are packaged in aerosol dispensers, see Section 2.3, Aerosols. If 
classified as flammable aerosols, they must not be classified as flammable solids in addition 
(see Section 2.7). 

 
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2.7.4.  Classification of substances and mixtures as flammable solids 

2.7.4.1. 

Identification of hazard information  

For the classification of a substance or mixture as a flammable solid data on the following 
properties are needed: 

•  melting point;  

• 

• 

information on water reactivity; 

information on flash point for solids containing flammable liquids. 

See also IR & CSA, Chapter R.7a: Endpoint specific guidance, Section R.7.1.2 (Melting/freezing 
point), R.7.1.9 (Flash point). 

Many organic solid substances or mixtures fulfil the criteria to be classified as flammable solids. 
For inorganic solids, the classification as flammable is rather rare.  

2.7.4.2.  Screening procedures and waiving of testing 

In general, a possible classification as a flammable solid should be considered for any solid 
organic substance or mixture containing such material. For inorganic material, testing may be 
waived in cases where the substance is commonly known to be not flammable (i.e. stable salts 
or metal oxides) or where a flammability hazard can be excluded by any other scientific 
reasoning. In many cases, a simple screening test (see Section 2.7.4.4) can be used to 
determine whether a solid should be classified as flammable. Solid substances and mixtures are 
classified as flammable according to their burning behaviour. 

The test method as described in Part III, Sub-section 33.2.1.4.3.1 in the UN-MTC should be 
applied for screening purposes. Alternatively, the burning index (referred to as ‘class number’ in 
VDI 2263) as obtained from the Burning Behaviour test (VDI 2263, part 1) may be used. If a 
burning index of 3 or less is found, the substance or mixture should not be classified as a 
flammable solid and no further testing is required. However, if smouldering or a flame is 
observed, the full test must be carried out. 

2.7.4.3.  Classification criteria  

The classification criteria are fully in accordance with the GHS system. 

Annex I: 2.7.2.1. Powdered, granular or pasty substances or mixtures (except powders of 
metals or metal alloys – see 2.7.2.2) shall be classified as readily combustible solids when 
the time of burning of one or more of the test runs, performed in accordance with the test 
method described in Part III, sub-section 33.2.1, of the UN RTDG, Manual of Tests and 
Criteria, is less than 45 seconds or the rate of burning is more than 2,2 mm/s. 

2.7.2.2. Powders of metals or metal alloys shall be classified as flammable solids when they 
can be ignited and the reaction spreads over the whole length of the sample in 10 minutes 
or less. 

2.7.2.3. A flammable solid shall be classified in one of the two categories for this class using 
Method N.1 as described in 33.2.1 of the UN RTDG, Manual of Tests and Criteria in 
accordance with Table 2.7.1; 

 
 
 
 
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Table 2.7.1 

Criteria for flammable solids 

Category  Criteria 

Burning rate test 

Substances and mixtures other than metal powders: 

(a) 

(b) 

wetted zone does not stop fire and 

burning time < 45 seconds or burning rate > 2,2 mm/s 

Metal powders: 

burning time  5 minutes 

Burning rate test 

Substances and mixtures other than metal powders: 

(a) 

(b) 

wetted zone stops the fire for at least 4 minutes and 

burning time < 45 seconds or burning rate > 2,2 mm/s 

Metal powders: 

burning time > 5 minutes and  10 minutes 

1 

2 

[…] 

Note 2:  

Aerosols shall not be classified as flammable solids; see section 2.3. 

2.7.4.4.  Testing and evaluation of hazard information  

For safety reasons, it is advisable to test for explosive and self-reactive properties first and to 
rule out pyrophoric behaviour before performing this test. The classification test is described in 
Part III, Sub-section 33.2.1.4.3.2 of the UN-MTC. The sample should be tested in its 
commercially relevant form. Special care has to be taken that the sample forms an unbroken 
strip or powder train in the test mould. Large pieces that do not fit into the mould should be 
gently crushed. For pasty or sticking substances it may be helpful to line the mould with a thin 
plastic foil which is withdrawn after having formed the train. Classification is based upon the 
fastest burning rate / shortest burning time obtained in six test runs, unless a positive result is 
observed earlier. For substances and mixtures other than metal powders, the category is 
assigned depending on whether the wetted zone is able to stop the flame. 

2.7.4.5.  Decision logic  

Classification of flammable solids is done according to decision logic 2.7.4 as included in the 
GHS. 

  NOTE: The person responsible for the classification of flammable solids should be 

experienced in this field and be familiar with the criteria for classification. 

 
 
 
 
 
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Figure 2.4  Decision logic for flammable solids (Decision logic 2.7 of GHS) 

The substance/mixture is a solid 

Screening test 

Negative 

Not classified 

Positive 

Burning rate test: 

a.

For substances or mixtures other than metal powders: 

No 

Burning time < 45 s or burning rate > 2.2 mm/s? 

b. Metal powders: Burning time  10 min? 

Not classified 

Yes 

a.

For substances or mixtures other than metal powders: 

No 

Does the wetted zone stop propagation of the flame? 

b. Metal powders: Burning time > 5 min? 

Yes 

Category 1 

Danger 

Category 2 

Warning 

 
 
 
 
 
 
 
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2.7.5.  Hazard communication for flammable solids 

2.7.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

Annex I: 2.7.3. Table 2.7.2 

Label elements for flammable solids 

Classification 

Category 1 

Category 2 

GHS Pictograms 

Signal Word 

Danger 

Warning 

Hazard Statement 

H228: Flammable Solid 

H228: Flammable Solid 

Precautionary Statement Prevention 

P210 
P240 
P241 
P280 

P210 
P240 
P241 
P280 

Precautionary Statement Response 

P370 + P378 

P370 + P378 

Precautionary Statement Storage 

Precautionary Statement Disposal 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

2.7.6.  Relation to transport classification 

Division 4.1 within Class 4 of the UN RTDG Model Regulations covers flammable substances, 
solid desensitized explosives and self-reactive liquids or solids. If a transport classification 
according to the modal transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) is 
available it should be kept in mind that transport classification is based on prioritisation of 
hazards (see UN RTDG Model Regulations, Section 2.0.3) and that flammable solids have a 
relatively low rank in the precedence of hazards. Therefore, the translation from transport 
classification to CLP should be only done if a transport classification for a flammable solid is 
explicitly available. The conclusion that a substance or mixture not classified as a flammable 
solid for transport should not be classified as a flammable solid according to CLP is, in general, 
not correct. See Annex VII for additional information on transport classification in relation to 
CLP classification. 

2.7.7.  Examples of classification for flammable solids 

2.7.7.1.  Example of substances and mixtures fulfilling the classification 

criteria 

The following example shows a classification based on test data: 

 
 
 
 
 
 
 
 
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TEST SUBSTANCE: ‘FLAMMALENE’ (ORGANIC MATERIAL, SOLID) 

Screening test (VDI 2263, part 1):  

burning index: 5 (burning with an open flame or 
emission of sparks)  

Conclusion: Substance is candidate for classification as a flammable solid, further testing 
required. 

UN Test N.1 (Test method for readily 
combustible solids): 

Burning times for a distance of 100 mm (6 runs): 44 
s; 40 s; 49 s; 45 s; 37 s; 41 s. 

Shortest burning time is less than 45 s; substance is 
a flammable solid. 

Wetted zone stops the fire, no reignition. 

Conclusion: Classify as flammable solid, Category 2. 

2.7.7.2.  Examples of substances and mixtures not fulfilling the classification 

criteria  

Many inorganic salts and oxides are not flammable such as NaCl, NaBr, KI, FeO, MnO etc. 

Urea or phthalic acid anhydride are examples of organic substances that would not be classified 
as flammable solids. 

2.7.8.  References 

VDI guideline 2263, part 1, 1990, Test methods for the Determination of the Safety 
Characteristics of Dusts 

 
 
 
 
 
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2.8.  SELF-REACTIVE SUBSTANCES AND MIXTURES 

2.8.1.  Introduction 

The criteria for ‘Self-reactive substances and mixtures’ are found in Annex I, Section 2.8 of CLP 
and are identical to those in Chapter 2.8 of GHS.  

In general, substances or mixtures classified as self-reactive substances and mixtures can 
decompose strongly exothermically when 50 kg are exposed to temperatures of 75 °C or lower 
depending on the Self-Accelerating Decomposition Temperature (SADT) of the substance or 
mixture. 

Self-reactive substances and mixtures display a very wide range of properties. The most 
hazardous type is TYPE A of self-reactive substances and mixtures that are too dangerous to 
transport commercially though they can be stored safely with appropriate precautions. At the 
other end of the scale this classification includes substances and mixtures that only decompose 
slowly at temperatures well above the normal storage and transport temperatures (e.g. 75 °C). 

The decomposition of self-reactive substances and mixtures can be initiated by heat, contact 
with catalytic impurities (e.g. acids, heavy-metal compounds, and bases), friction or impact. 
The rate of decomposition increases with temperature and varies with the substance or mixture. 
Decomposition, particularly if no ignition occurs, may result in the evolution of toxic gases or 
vapours. For certain self-reactive substances and mixtures, the temperature must be controlled 
during storage and handling. Some self-reactive substances and mixtures may decompose 
explosively, particularly if confined. This characteristic may be modified by the addition of 
diluents or by the use of appropriate packaging. Some self-reactive substances and mixtures 
burn vigorously. Self-reactive substances are, for example, some compounds of the types listed 
below: 

c.  Aliphatic azo compounds (-C-N=N-C-); 

d.  Organic azides (-C-N3); 

e.  Diazonium salts (-CN2

+Z-); 

f.  N-nitroso compounds (-N-N=O); and 

g.  Aromatic sulfohydrazides (-SO2-NH-NH2). 

This list is not exhaustive and substances with other reactive groups, combination of groups and 
some mixtures of substances may have similar properties. Additional guidance on substances, 
which may have self-reactive properties, is given in Appendix 6, Section 5.1 of the UN-MTC. 

Additional hazardous properties, resulting in subsidiary labelling, are indicated in the list of 
already classified self-reactive substances and mixtures included in the UN RTDG Model 
Regulations, Section 2.4.2.3.2.3. 

Commercial self-reactive substances and mixtures are commonly formulated by dilution with 
solid and liquid substances with which they are compatible.  

2.8.2.  Definitions and general considerations for the classification of self-

reactives  

In CLP the following definition is given for self-reactive substances and mixtures: 

Annex I: 2.8.1.1. Self-reactive substances or mixtures are thermally unstable liquid or solid 
substances or mixtures liable to undergo a strongly exothermic decomposition even without 
participation of oxygen (air). This definition excludes substances and mixtures classified 
according to this Part as explosives, organic peroxides or as oxidising. 

 
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2.8.1.2. A self-reactive substance or mixture is regarded as possessing explosive properties 
when in laboratory testing the formulation is liable to detonate, to deflagrate rapidly or to 
show a violent effect when heated under confinement. 

General considerations 

Annex I: 2.8.3.     Hazard communication 

Type G has no hazard communication elements assigned but shall be considered for 
properties belonging to other hazard classes. 

2.8.3.  Relation to other physical hazards 

Neither the burning properties nor the sensitivity to impact and friction form part of the 
classification procedure for self-reactive substances and mixtures in CLP. These properties may 
be of importance in safe handling of self-reactive substances and mixtures (see additional tests 
in Section 2.8.4.3.2). 

In addition, the following should be noted: 

Explosive properties 

The explosive properties do not have to be determined according to the CLP Annex I, Chapter 
2.1, because explosive properties are incorporated in the decision logic for self-reactive 
substances and mixtures. Note that substances and mixtures may have explosive properties 
when handled under higher confinement.   

2.8.4.  Classification of substances and mixtures as self-reactive  

2.8.4.1. 

Identification of hazard information 

The classification of a self-reactive substance or mixture in one of the seven categories ‘types A 
to G’ is dependent on its detonation, deflagration and thermal explosion properties, its response 
to heating under confinement, its explosive power and the concentration and the type of diluent 
added to desensitize the substance or mixture. Specifications of acceptable diluents that can be 
used safely are given in the UN RTDG Model Regulations, Section 2.4.2.3.5. 

The classification of a self-reactive substance or mixture as type A, B or C is also dependent on 
the type of packaging in which the substance or mixture is tested as it affects the degree of 
confinement to which the substance or mixture is subjected. This has to be considered when 
handling the substance or mixture; stronger packaging may result in more violent reactions 
when the substance or mixture decomposes. This is why it is important that storage and 
transport is done in packaging, allowed for the type of self-reactive substance and mixture, that 
conforms the requirements of the UN-packaging or IBC instruction (P520/IBC520) or tank 
instruction (T23). 

The traditional aspects of explosive properties, such as detonation, deflagration and thermal 
explosion, are incorporated in the decision logic Figure 2.8.1 of CLP (see Section 2.8.4.4). 
Consequently, the determination of explosive properties as prescribed in the hazard class 
explosives needs not to be conducted for self-reactive substances and mixtures. 

2.8.4.2.  Classification criteria 

According to CLP, substances and mixtures must be considered for classification in this hazard 
class as a self-reactive substance or mixture unless: 

Annex I: 2.8.2.1. […] 

 
 
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(a) they are explosives, according to the criteria given in 2.1; 

(b) they are oxidising liquids or solids, according to the criteria given in 2.13 or 2.14, except 
that mixtures of oxidising substances, which contain 5 % or more of combustible organic 
substances shall be classified as self-reactive substances according to the procedure defined 
in 2.8.2.2; 

(c) they are organic peroxides, according to the criteria given in 2.15; 

(d) their heat of decomposition is less than 300 J/g; or 

(e) their self-accelerating decomposition temperature (SADT) is greater than 75 °C for a 50 

kg package (See UN RTDG, Manual of Test and Criteria, sub-sections 28.1, 28.2, 28.3 and 
Table 28.3.) 

2.8.2.2. Mixtures of oxidising substances, meeting the criteria for classification as oxidising 
substances, which contain 5 % or more of combustible organic substances and which do not 
meet the criteria mentioned in (a), (c), (d) or (e) in 2.8.2.1, shall be subjected to the self-
reactive substances classification procedure;  

Such a mixture showing the properties of a self-reactive substance type B to F (see 2.8.2.3) 
shall be classified as a self-reactive substance. 

[…] 

In addition to the above, substances and mixtures must be considered for classification in this 
hazard class unless: 

Annex I: 2.8.4.2.  

[…] 

(a) There are no chemical groups present in the molecule associated with explosive or self-
reactive properties; examples of such groups are given in Tables A6.1 and A6.2 in 
Appendix 6 of the UN RTDG, Manual of Tests and Criteria. 

[…] 

In the CLP decision logic (see Section 2.8.4.4), classification of self-reactive substances or 
mixtures is based on performance based testing in both small scale tests and, where necessary, 
some larger scale tests with the substance or mixture in its packaging. The concept of ‘intrinsic 
properties’ is, therefore, not necessarily, applicable to this hazard class. 

Self-reactive substances or mixtures are classified in one of the seven categories of ‘types A to 
G’ according to the classification criteria given in Section 2.8.2.3 of Annex I, CLP. The 
classification principles are given in the decision logic in Figure 2.8.1 of CLP (see Section 
2.8.4.4) and the Test Series A to H, as described in the Part II of the UN-MTC, should be 
performed. 

 
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Annex I: 2.8.2.3. Self-reactive substances and mixtures shall be classified in one of the 
seven categories of ‘types A to G’ for this class, according to the following principles: 

(a) any self-reactive substance or mixture which can detonate or deflagrate rapidly, as 

packaged, shall be defined as self-reactive substance TYPE A; 

(b) any self-reactive substance or mixture possessing explosive properties and which, as 

packaged, neither detonates nor deflagrates rapidly, but is liable to undergo a thermal 
explosion in that package shall be defined as self-reactive substance TYPE B; 

(c) any self-reactive substance or mixture possessing explosive properties when the substance 

or mixture as packaged cannot detonate or deflagrate rapidly or undergo a thermal 
explosion shall be defined as self-reactive substance TYPE C; 

(d) any self-reactive substance or mixture which in laboratory testing: 

(i) detonates partially, does not deflagrate rapidly and shows no violent effect when 

heated under confinement; or 

(ii) does not detonate at all, deflagrates slowly and shows no violent effect when 

heated under confinement; or 

(iii) does not detonate or deflagrate at all and shows a medium effect when heated 

under confinement; 

shall be defined as self-reactive substance TYPE D; 

(e) any self-reactive substance or mixture which, in laboratory testing, neither detonates nor 
deflagrates at all and shows low or no effect when heated under confinement shall be 
defined as self-reactive substance TYPE E; 

(f) any self-reactive substance or mixture which, in laboratory testing, neither detonates in 
the cavitated state nor deflagrates at all and shows only a low or no effect when heated 
under confinement as well as low or no explosive power shall be defined as self-reactive 
substance TYPE F; 

(g) any self-reactive substance or mixture which, in laboratory testing, neither detonates in 

the cavitated state nor deflagrates at all and shows no effect when heated under 
confinement nor any explosive power, provided that it is thermally stable (SADT is 60 oC 
to 75 oC for a 50 kg package), and, for liquid mixtures, a diluent having a boiling point not 
less than 150 oC is used for desensitisation shall be defined as self-reactive substance 
TYPE G. If the mixture is not thermally stable or a diluent having a boiling point less than 
150 oC is used for desensitisation, the mixture shall be defined as self-reactive substance 
TYPE F. 

Where the test is conducted in the package form and the packaging is changed, a further test 
shall be conducted where it is considered that the change in packaging will affect the outcome 
of the test. 

A list of currently classified self-reactive substances and mixtures is included in the UN RTDG 
Model Regulations, Section 2.4.2.3.2.3. 

2.8.4.3.  Testing and evaluation of hazard information 

2.8.4.3.1. 

Thermal stability tests and temperature control 

In addition to the classification tests given in decision logic Figure 2.8.1 of CLP, the thermal 
stability of the self-reactive substances and mixtures has to be assessed in order to determine 
the SADT.  

The SADT is defined as the lowest temperature at which self-accelerating decomposition of a 
substance or mixture may occur in the packaging as used in transport, handling and storage. 

 
 
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The SADT is a measure of the combined effect of the ambient temperature, decomposition 
kinetics, package size and the heat transfer properties of the substance or mixture and its 
packaging. 

There is no relation between the SADT of a self-reactive substance and mixture and its 
classification in one of the seven categories ‘types A to G’. The SADT is used to derive safe 
handling, storage and transport temperatures (control temperature) and alarm temperature 
(emergency temperature).   

Depending on its SADT a self-reactive substance and mixture needs temperature control and 
the rules as given in CLP Annex I, 2.8.2.4, consist of the following two elements: 

1.  Criteria for temperature control: 

2.  Self-reactive substances and mixtures need to be subjected to temperature control when 

the SADT is ≤ 55 ° C. 

3.  Derivation of control and emergency temperatures: 

Type of receptacle  SADT* 

Control temperature 

Emergency temperature 

Single packagings 
and IBC’s 

20 °C or less 

20 °C below SADT 

10 °C below SADT 

over 20 °C to 35 °C 

15 °C below SADT 

10 °C below SADT 

over 35 °C 

10 °C below SADT 

5 °C below SADT 

Tanks 

< 50 °C 

10 °C below SADT 

5 °C below SADT 

*i.e. the SADT of the substance/mixture as packaged for transport, handling and storage. 

It should be emphasized that the SADT is dependent on the nature of the self-reactive 
substance or mixture itself, together with the volume and heat-loss characteristics of the 
packaging or vessel in which the substance or mixture is handled. The temperature at which 
self-accelerating decomposition occurs falls: 

•  as the size of the packaging or vessel increases; and 

•  with increasing efficiency of the insulation on the package or vessel.   

The SADT is only valid for the substance or mixture as tested and when handled properly. 
Mixing the self-reactive substances and mixtures with other chemicals, or contact with 
incompatible materials (including incompatible packaging or vessel material) may reduce the 
thermal stability due to catalytic decomposition, and lower the SADT. This may increase the risk 
of decomposition and has to be avoided. 

2.8.4.3.2. 

Additional considerations and testing 

Explosive properties 

The sensitivity of self-reactive substances and mixtures to impact (solids and liquids) and 
friction (solids only) may be of importance for the safe handling of the substances and mixtures, 
in the event that these substances and mixtures have pronounced explosive properties (e.g. 
rapid deflagration and/or violent heating under confinement). Test methods to determine these 
properties are described in Test Series 3 (a) (ii) and 3 (b) (i) of the UN-MTC. This information 
should be documented in the SDS. 

Burning properties  

Although there are currently no dedicated storage guidelines for self-reactive substances and 
mixtures (although in some countries under development), often the regulations for organic 
peroxides are referred to. For storage classification the burning rate is commonly used, see 
Section 2.15 on organic peroxides. 

 
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The flash point for liquid self-reactive substances or mixtures is only relevant in the 
temperature range where the product is thermally stable. Above the SADT of the self-reactive 
substance or mixture, flash point determination is not relevant because decomposition products 
are evolved. 

  NOTE: In case a flash point determination seems reasonable (expected flash point below 
the SADT) a test method using small amount of sample is recommended. In case the self-
reactive substance or mixture is diluted or dissolved, the diluent may determine the flash 
point. 

Auto-ignition temperature 

The determination of the auto ignition temperature is not relevant for self-reactive substances 
and mixtures, because the vapours decompose during the execution of the test. Available test 
methods are for non-decomposing vapour phases. Auto ignition of self-reactive substance and 
mixtures vapours when they decompose, can never be excluded. This information should be 
documented in the SDS. 

Self-ignition temperature 

Also self-ignition temperature determination (test applicable for solids) is not relevant. The 
thermal stability of self-reactive substances and mixtures is quantitatively given by the SADT 
test.  

Control and Emergency temperatures 

The Control and Emergency temperatures are based on the SADT as determined by UN Test 
H.4. The Dewar vessel used in the UN Test H.4 is supposed to be representative for the 
substance or mixture handled in packages. For handling of the substance or mixture in larger 
quantities (IBCs/tanks/vessels etc.) and/or in better (thermally) insulated containers under 
more thermal insulated conditions, the SADT has to be determined for that quantity with the 
given degree of insulation. From that SADT the Control and Emergency temperatures can be 
derived (see also Section 2.15.4.3) 

2.8.4.3.3. 

Additional classification considerations 

Currently, the following properties are not incorporated in the classification of self-reactives 
under the CLP: 

•  mechanical sensitivity i.e. impact and friction sensitivity (for handling purposes); 

•  burning properties (for storage purposes);  

• 

flash point for liquids; and 

•  burning rate for solids. 

In addition to the GHS criteria CLP mentions that:  

Annex I: 2.8.2.2  

[…] 

Where the test is conducted in the package form and the packaging is changed, a further 
test shall be conducted where it is considered that the change in packaging will affect the 
outcome of the test. 

Please note that polymerising substances do not fulfil the criteria for classification as self-
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2.8.4.4.  Decision logic 

Classification of self-reactive substances and mixtures is done according to decision logic 2.8 as 
included in the GHS. 

  NOTE: The person responsible for the classification of self-reactive substances and mixtures 

should be experienced in this field and be familiar with the criteria for classification. 

 
 
 
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Figure 2.5  Decision logic 2.8 for self-reactive substances and mixtures 

 
 
 
 
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2.8.5.  Hazard communication for self-reactives 

2.8.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements 

According to CLP the following label elements must be used for substances and mixtures 
meeting the criteria for this hazard class: 

Annex I:  Table 2.8.1 

Label elements for self-reactive substances and mixtures 

Classification 

Type A 

Type B 

Type C & D 

Type E & F 

Type G2 

GHS pictograms 

Signal Word 

Danger 

Danger 

Danger 

Warning 

Hazard Statement 

H240: 

H241: 

H242: 

Heating may 

Heating may 

Heating may 

cause an 

cause a fire or 

cause a fire 

explosion 

explosion 

H242: 
Heating 

may cause a 
fire 

Precautionary 
statement 

Prevention 

Precautionary 
statement 

Response 

Precautionary 
statement 

Storage 

Precautionary 
statement 

Disposal 

P210 

P234 

P235 

P240 

P280 

P370 + P372 
+ P380 + 
P373 

P403 

P411 

P420 

P501 

P210 

P234 

P235 

P240 

P280 

P210 

P234 

P235 

P240 

P280 

P210 

P234 

P235 

P240 

P280 

P370 + P380 

P370 + P378  P370 + P378 

+ P375 
[+P378]1 

P403 

P411 

P420 

P501 

P403 

P411 

P420 

P501 

P403 

P411 

P420 

P501 

There are 
no label 
elements 
allocated 
to this 
hazard 
category 

 
 
 
 
 
 
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1 See the introduction to Annex IV for details on the use of square brackets. 

2 Type G has no hazard communication elements assigned but should be considered for properties 
belonging to other hazard classes. 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

2.8.6.  Relation to transport classificationaccording to DSD and DPD or 

already classified for transport 

Division 4.1 within Class 4 of the UN RTDG Model Regulations covers flammable substances, 
solid desensitized explosives and self-reactive liquids or solids. A list of already classified self-
reactive substances is included in UN RTDG Model Regulations, Section 2.4.2.3.2.3. This table 
includes self-reactive substances of various types from type B to type F. See Annex VII for 
additional information on transport classification in relation to CLP classification. 

2.8.7.  Examples of classification for self-reactives 

2.8.7.1.  Examples of substances and mixtures fulfilling the classification 

criteria 

Substance to be classified: NP 

Molecular formula: n.a. 

According to CLP Annex I, Section 2.8.2.1, the substance has: 

•  an energy content of 1452 kJ/kg; and 

•  a SADT of 45 °C (in 50 kg package); 

and consequently it has to be considered for classification in the hazard class self-reactive 
substances and mixtures. 

Test results and classification according to CLP decision logic 2.8.1 for self-reactive substances 
and mixtures and the UN - MTC, Part II, is as follows: 

CLASSIFICATION TEST RESULTS 

1. Name of the self-reactive substance or mixture:  NP 

2. General data 

2.1. Composition 

2.2. Molecular formula 

2.3. Physical form 

2.4. Colour   

2.5. Density (apparent) 

3. Detonation (test series A) 

NP, technically pure 

n.a. 

solid, fine powder 

brown 

460 kg/m3 

Box 1 of the decision logic 

Does the substance propagate a detonation? 

3.1. Method  

3.2. Sample conditions 

3.3. Observations 

UN Test A.1: BAM 50/60 steel tube test 

technically pure substance 

fragmented part of the tube: 12, 18cm 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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CLASSIFICATION TEST RESULTS 

3.4. Result   

3.5. Exit 

4. Deflagration (test series C) 

No 

1.3 

Box 5 of the decision logic 

Does the substance propagate a deflagration? 

4.1. Method 1 

Time/pressure test (test C.1) 

4.1.1. 

Sample conditions 

ambient temperature 

4.1.2.  Observations 

498, 966, 3395 ms   

4.1.3. 

Result   

4.2. Method 2 

Yes, slowly 

Deflagration test (test C.2) 

4.2.1. 

Sample conditions 

temperature: 20 °C 

4.2.2.  Observations 

deflagration rate: 0.90, 0.87 mm/s 

4.2.3. 

Result   

4.3. Final result 

4.4. Exit 

Yes, slowly 

Yes, slowly 

5.2 

5. Heating under confinement (test series E) 

Box 8 of the decision logic: 

What is the effect of heating it under defined 
confinement? 

5.1. Method 1 

Koenen test (test E.1) 

5.1.1. 

Sample conditions 

5.1.2.  Observations 

5.1.3. 

Result   

5.2. Method 2 

5.2.1. 

Sample conditions 

5.2.2.  Observations 

5.2.3. 

Result   

5.3. Final result 

5.4. Exit 

Limiting diameter: < 1.0 mm 

fragmentation type ‘A’ 

Low 

Dutch pressure vessel test 

(test E.2) 

Limiting diameter: <1.0 mm (with 10 g), 1.0 mm 
(50 g) 

low 

low 

8.3 

6. Thermal stability (outside of the decision logic) 

6.1. Method  

Heat accumulation storage test (test H.4) 

6.2. Sample conditions 

: 

mass 232.5 g. Half life time of cooling of Dewar 
vessel with 

400 ml water: 10.0 hrs.(representing substance in 
package) 

6.3. Observations 

self-accelerating decomposition at 45 °C 

no self-accelerating decomposition at 40 °C 

6.4. Result   

SADT 45 °C (in 50 kg package) 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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CLASSIFICATION TEST RESULTS 

7. General remarks 

The decision logic is given in Figure 2.6 

8. Final classification 

Hazard / hazard class: 

Label 

Signal word   

Hazard statement 

Temperature control  

Control temperature* 

Emergency temperature* 

*See UN-MTC, table 28.2. 

Self-reactive substance, Type D, solid, temperature 
controlled 

Flame (GHS02) 

Danger 

H242: Heating may cause a fire 

Needed based on SADT (45 °C, in package) 

35 °C (in package) 

40 °C (in package) 

 
 
 
 
 
 
 
 
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Figure 2.6  Decision logic for self-reactive substance example: NP, technically pure 

 
 
 
 
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2.9.  PYROPHORIC LIQUIDS  

2.9.1.  Introduction 

The criteria for ‘Pyrophoric liquids’ are found in Annex I, Section 2.9 of CLP and are identical to 
those in Chapter 2.9 of GHS.  

Pyrophoricity, i.e. the ability to spontaneously ignite in air, is the result of a reaction of a 
substance or mixture with the oxygen in the air. The reaction is exothermic and has the 
particularity that it starts spontaneously, i.e. without the aid of a supplied spark, flame, heat or 
other energy source. Another way of saying this is that the auto-ignition temperature for a 
pyrophoric substance or mixture is lower than room (ambient) temperature. 

Organo-metals and organo-metalloids may be suspected of being pyrophores, as well as their 
derivatives. Also organo-phosphines and their derivatives, hydrides and their derivatives and 
haloacetylene derivatives may show pyrophoricity (Urben, 2007).  

There are also pyrophoric substances or mixtures that do not belong to the above mentioned 
groups of chemicals, i.e. the list above is not exhaustive. Since pyrophoric substances or 
mixtures ignite spontaneously in air, pyrophoricity is a very dangerous property. In case of 
doubt it should therefore be thoroughly investigated whether a given substance or mixture is 
pyrophoric. More information on pyrophoric substances can e.g. be found in Bretherick’s 
Handbook of Reactive Chemical Hazards (Urben, 2007). 

2.9.2.  Definitions and general considerations for the classification pyrophoric 

liquids 

The definition in CLP for pyrophoric liquids is as follows: 

Annex I: 2.9.1.     Definition  

Pyrophoric liquid means a liquid substance or mixture which, even in small quantities, is 
liable to ignite within five minutes after coming into contact with air. 

2.9.3.  Relation to other physical hazards  

Pyrophoric substances and mixtures will react spontaneously with air already in small amounts 
and more or less instantaneously (within minutes). This differentiates them from self-heating 
substances and mixtures, which also react spontaneously with air but only when in larger 
amounts and after an extended period of time (hours or days). While liquids in themselves 
generally do not exhibit self-heating properties due to the limited contact with air (which can 
occur only at the surface), liquids that are adsorbed onto solid particles should, in general, be 
considered for classification in the hazard class self-heating substances and mixtures, see 
Chapter 2.11 of this guidance. 

Pyrophoricity may be expected for certain reactive metals and some of their compounds (e.g. 
hydrides and other organo-metal compounds). Many of these substances and mixtures will also 
react vigorously with water under the production of flammable gases. Such substances and 
mixtures may thus be classified in the hazard class substances and mixtures which in contact 
with water emit flammable gases in addition, see Chapter 2.12 of this guidance. It should be 
noted in this context that water-reactive substances and mixtures may also to some extent 
react with the humidity in air, although such a reaction is seldom vigorous. A substance or 
mixture that spontaneously ignites in air in accordance with the test procedures is to be 
considered pyrophoric, regardless of the reaction mechanism. 

Liquids not classified as pyrophoric but that can burn may belong to the hazard class flammable 
liquids depending on their flash point and ability to sustain combustion, see Section 2.6 of this 
guidance. 

 
 
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2.9.4.  Classification of substances and mixtures as pyrophoric liquids 

2.9.4.1. 

Identification of hazard information  

Since the tests to determine pyrophoricity are simple and require no special equipment, see 
Section 2.9.4.4 below, there is in general no reason to go to data sources instead of performing 
tests. Furthermore, the possibilities of waiving tests are ample both for known pyrophores and 
for substances and mixtures known not to be pyrophoric, see Section 2.9.4.2 below. If 
information anyway is taken from literature or other data sources, it is of utmost importance 
that the correct physical form is considered, see Section 2.0.4. Naturally, all data sources 
should be carefully evaluated with regard to reliability and scientific validity. 

2.9.4.2.  Screening procedures and waiving of testing 

In case a liquid is known from practical handling to be pyrophoric no testing is necessary. Such 
liquids are classified as pyrophoric liquids without testing. This would also be the case if the 
liquid spontaneously ignites upon opening of the receptacle when trying to perform the tests for 
classification. 

According to the additional classification considerations in CLP Annex I, 2.9.4, the classification 
procedure for pyrophoric liquids need not be applied when experience in manufacture or 
handling shows that the liquid does not ignite spontaneously on coming into contact with air at 
normal temperatures (i.e. the liquid is known to be stable at room temperature for prolonged 
periods of time (days)). 

2.9.4.3.  Classification criteria  

Section 2.9.2.1 of Annex I of CLP specifies the classification criteria:  

Annex I: Table 2.9.1 

Criteria for pyrophoric liquids 

Category 

Criteria 

1 

The liquid ignites within 5 min when added to an inert carrier and exposed to 
air, or it ignites or chars a filter paper on contact with air within 5 min. 

2.9.4.4.  Testing and evaluation of hazard information  

In Section 2.9.2.1 of Annex I of CLP reference to the test-methods are made: 

Annex I: 2.9.2.1. A pyrophoric liquid shall be classified in a single category for this class 
using test N.3 in part III, sub-section 33.3.1.5 of the UN RTDG, Manual of Tests and Criteria 
according to Table 2.9.1: 

The UN Test N.3 for pyrophoricity is quite simple and sufficiently described in Part III, Section 
33 of the UN-MTC. No special equipment is needed. Essentially the substance or mixture is 
exposed to air to see if it ignites. For liquids which do not spontaneously ignite when poured, 
the surface in contact with air is increased using a filter paper. Ignition or charring of the filter 
paper is regarded as a positive response in the test, i.e. such a liquid is considered to be 
pyrophoric. 

It is important that samples for testing of pyrophoric properties are carefully packed and sealed. 
Furthermore, the material offered for testing should be freshly prepared, since the reactive 
properties may diminish due to aging or agglomeration. Whenever experiments are to be done 

 
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one should be careful – a pyrophoric substance or mixture may well ignite already upon opening 
the receptacle! 

It should be noted that the mechanism of oxidation is, in general, very complex, and that the 
humidity of air might influence the rate of reaction. Therefore a false negative may result when 
performing the tests in an extremely dry environment, and this condition must be avoided when 
performing the tests for classification for pyrophoricity. The filter paper test of UN Test N.3 for 
pyrophoric liquids should be carried out at 25 ± 2 °C and a relative humidity of 50 ± 5 % (see 
UN-MTC, Section 33.3.1.5). 

2.9.4.5.  Decision logic  

Classification of pyrophoric liquids is done according to decision logic 2.9.4.1 as included in the 
GHS. 

  NOTE: The person responsible for the classification of pyrophoric liquids should be 

experienced in this field and be familiar with the criteria for classification. 

2.9.4.5.1.  Decision logic for pyrophoric liquids  

Figure 2.7  Decision logic for pyrophoric liquids (Decision logic 2.9 of GHS) 

The substance/mixture is a liquid 

Does it ignite within 5 min when poured into a porcelain 
cup filled with diatomaceous earth or silica gel? 

Yes 

No 

Does it ignite or char a filter paper within 5 min? 

Yes 

No 

Category 1 

Danger 

Category 1 

Danger 

Not 
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2.9.5.  Hazard communication for pyrophoric liquids  

2.9.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

Annex I: 2.9.3 Table 2.9.2 

Label elements for pyrophoric liquids 

Classification 

GHS Pictogram 

Signal Word 

Hazard Statement 

Precautionary Statement Prevention 

Precautionary Statement Response 

Precautionary Statement Storage 

Precautionary Statement Disposal 

Category 1 

Danger 

H250: Catches fire spontaneously if 
exposed to air 

P210 
P222 

P231 + P232 

P233 
P280 

P302 + P334 
P370 + P378 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

2.9.6.  Relation to transport classification 

Division 4.2 within Class 4 of the UN RTDG Model Regulations covers pyrophoric solids, liquids 
and self-heating substances and mixtures. UN Test N.3 that is used for classification for 
pyrophoricity for liquids according to CLP is also used for classification in the subdivision 
pyrophoric substances and mixtures in Division 4.2: Substances liable to spontaneous 
combustion according to the UN RTDG Model Regulations. The criteria for Category 1 according 
to CLP (which is the only category for pyrophoric liquids) and for packing group I in Division 4.2 
according to the modal transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) are also 
exactly the same. Furthermore, all pyrophoric substances and mixtures are assigned to packing 
group I within Division 4.2, which is used exclusively for pyrophoric substances and mixtures. 

Therefore, any liquid assigned to Division 4.2, packing group I according to the modal transport 
regulations (ADR, RID, ADN and IMDG Code, ICAO TI) will be classified in Category 1 of the 
hazard class pyrophoric liquids according to CLP. See Annex VII for additional information on 
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2.9.7.  Examples of classification for pyrophoric liquids 

Please note that the substance and mixture names in this chapter are fictitious.  

2.9.7.1.  Examples of substances and mixtures fulfilling the classification 

criteria  

2.9.7.1.1. 

Example 1 

Name:  

Pyrpherdine 

Physical state: 

Liquid 

Pyrophoric properties: 

Unknown, therefore the UN Test N.3 of the UN-MTC was applied. 
However, when opening the receptacle in order to perform the test, 
Pyrpherdine self-ignited. 

Classification:  

Pyrophoric liquid, Category 1 

 
 
 
 
 
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2.9.7.1.2. 

Example 2 

Name:  

Qulipyr 

Physical state: 

Liquid 

Pyrophoric properties: 

Unknown, therefore the UN Test N.3 of the UN-MTC was applied. 

Test result:  

When poured according to the test procedure, nothing happened. The 
procedure was repeated six times, each time giving a negative result 
(i.e. no ignition). Therefore Qulipyr was supplied to a filter paper in 
accordance with the test method. In the second trial the filter paper 
was charred within five minutes. 

Classification:  

Pyrophoric liquid, Category 1 

2.9.7.2.  Examples of substances and mixtures not fulfilling the classification 

criteria  

2.9.7.2.1. 

Example 3 

Name:  

Notpyratal 

Physical state: 

Liquid 

Pyrophoric properties: 

Unknown, therefore UN Test N.3 of the UN-MTC was applied. 

Test result:  

When poured according to the test procedure nothing happened in 
either of six trials. Therefore Notpyratal was supplied to a filter paper 
in accordance with the test method, whereupon no ignition or charring 
occurred in either of three trials. 

Classification:  

Not a pyrophoric liquid 

2.9.8.  References 

Urben, Peter G. (2007). Bretherick's Handbook of Reactive Chemical Hazards, Volumes 1-2 (7th 
Edition). Elsevier. 

 
 
 
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2.10.  PYROPHORIC SOLIDS 

2.10.1.  Introduction 

The criteria for ‘Pyrophoric solids’ are found in Annex I, Section 2.10 of CLP and are identical to 
those in Chapter 2.10 of GHS.  

Pyrophoricity, i.e. the ability to spontaneously ignite in air, is the result of a reaction of a 
substance or mixture with the oxygen in the air. The reaction is exothermic and has the 
particularity that it starts spontaneously, i.e. without the aid of a supplied spark, flame, heat or 
other energy source. Another way of saying this is that the self-ignition temperature for a 
pyrophoric substance or mixture is lower than room (ambient) temperature. 

Organo-metals and organo-metalloids may be suspected of being pyrophores, as well as their 
derivatives. Also organo-phosphines and their derivatives, hydrides and their derivatives, 
haloacetylene derivatives, and complex acetylides may show pyrophoricity (Urben, 2007). 
Furthermore, powders or fine particles of metals could be pyrophoric. However, although many 
solid metallic substances, like e.g. aluminium, would be suspected of being pyrophoric when 
considering their general reactivity, they form a protective oxide-coat upon reaction with air. 
This thin coat of metal oxide prevents the metal from reacting further, and hence such 
substances may not show pyrophoric behaviour in reality.  

There are also pyrophoric solids that do not belong to the above mentioned groups of 
chemicals, i.e. the list above is not exhaustive. Since pyrophoric solids ignite spontaneously in 
air, pyrophoricity is a very dangerous property. In case of doubt it should therefore be 
thoroughly investigated whether a given solid is pyrophoric. More information on pyrophoric 
solids can e.g. be found in Bretherick’s Handbook of Reactive Chemical Hazards (Urben, 2007). 

2.10.2.  Definitions and general considerations for the classification pyrophoric 

solids 

The definition in CLP for pyrophoric solids is as follows: 

Annex I: 2.10.1.     Definition  

Pyrophoric solid means a solid substance or mixture which, even in small quantities, is liable 
to ignite within five minutes after coming into contact with air. 

Special consideration on particle size 

Annex I: 2.10.2.1. 

 […] 

Note: The test shall be performed on the substance or mixture in its physical form as 
presented. If for example, for the purposes of supply or transport, the same chemical is to 
be presented in a physical form different from that which was tested and which is considered 
likely to materially alter its performance in a classification test, the substance shall also be 
tested in the new form. 

The finer the particle size of a solid, the greater the area exposed to air will be, and since 
pyrophoricity is a reaction with the oxygen in air, the particle size will greatly influence the 
ability to spontaneously ignite. Hence it is very important that pyrophoric properties for solids 
are investigated on the substance or mixture as it is actually presented (including how it can 
reasonably be expected to be used, see Article 8 (6) of CLP). This is indicated by the Note cited 
in CLP Annex I, 2.10.2.1. 

 
 
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2.10.3.  Relation to other physical hazards  

Pyrophoric solids will react spontaneously with air already in small amounts and more or less 
instantaneously (within minutes). This differentiates them from self-heating substances and 
mixtures, which also react spontaneously with air but only when in larger amounts and after an 
extended period of time (hours or days). A solid which is not classified as a pyrophoric solid 
may thus belong to the hazard class self-heating substances and mixtures, and should be 
considered for classification in that hazard class, see Chapter 2.11 of this guidance. 

Pyrophoricity may be expected for certain reactive metals and some of their compounds (e.g. 
hydrides and other organo-metal compounds). Many of these substances will also react 
vigorously with water under the production of flammable gases. Such substances may thus be 
classified in the hazard class substances and mixtures which in contact with water emit 
flammable gases in addition see Chapter 2.12 of this guidance. It should be noted in this 
context that water-reactive substances or mixtures may also to some extent react with the 
humidity in air, although such a reaction is seldom vigorous. A substance that spontaneously 
ignites in air in accordance with the test procedures is to be considered pyrophoric, regardless 
of the reaction mechanism. 

Solids not classified as pyrophoric may still be able to burn rapidly if subjected to enough 
initiating energy, such as the flame from a gas burner, to start the reaction. Therefore they may 
be subject to classification in the hazard class flammable solids, see Chapter 2.7 of this 
guidance, i.e. they may be 'readily combustible solids'. 

2.10.4.  Classification of substances and mixtures as pyrophoric solids 

2.10.4.1.  Identification of hazard information  

Since the tests to determine pyrophoricity are simple and require no special equipment, see 
Section 2.10.4.4 below, there is in general no reason to go to data sources instead of 
performing tests. Furthermore, the possibilities of waiving tests are ample both for known 
pyrophores and for substances and mixtures known not to be pyrophoric, see Section 2.10.4.2 
below. If information is taken from literature or other data sources anyway, it is of utmost 
importance that the correct physical form is considered, see Section 2.0.4. Naturally, all data 
sources should be carefully evaluated with regard to reliability and scientific validity. 

2.10.4.2.  Screening procedures and waiving of testing 

In case a solid is known from practical handling to be pyrophoric no testing is necessary. Such 
solids are classified as pyrophoric solids without testing. This would also be the case if the solid 
spontaneously ignites upon opening of the receptacle when trying to perform the tests for 
classification. 

According to the additional classification considerations in CLP Annex I, 2.10.4, the classification 
procedure for pyrophoric solids need not be applied when experience in manufacture or 
handling shows that the substance or mixture does not ignite spontaneously on coming into 
contact with air at normal temperatures (i.e. the substance or mixture is known to be stable at 
room temperature for prolonged periods of time (days)). 

2.10.4.3.  Classification criteria  

Section 2.10.2.1 of Annex I of CLP specifies the classification criteria:  

Annex I: Table 2.10.1 

Criteria for pyrophoric solids 

Category 

Criteria 

 
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1 

The solid ignites within 5 minutes of coming into contact with air. 

2.10.4.4.  Testing and evaluation of hazard information  

In Section 2.10.2.1 of Annex I of CLP reference to the test-methods are made: 

Annex I: 2.10.2.1. A pyrophoric solid shall be classified in a single category for this class 
using test N.2 in part III, sub-section 33.3.1.4 of the UN RTDG, Manual of Tests and Criteria 
in accordance with Table 2.10.1: 

UN Test N.2 for pyrophoricity is quite simple and sufficiently described in Part III, Section 33 of 
the UN-MTC. No special equipment is needed. Essentially the solid is exposed to air to see if it 
ignites.  

It is important that samples for testing of pyrophoric properties are carefully packed and sealed. 
Furthermore, the material offered for testing should be freshly prepared, since the reactive 
properties may diminish due to aging or agglomeration. Whenever experiments are to be done 
one should be careful – a pyrophoric solid may well ignite already upon opening the receptacle! 

It should be noted that the mechanism of oxidation is, in general, very complex, and that the 
humidity of air might influence the rate of reaction. It is known that certain metals will not react 
in dry air, whereas in the presence of moisture the reaction is almost instantaneous (often even 
trace amounts of moisture are sufficient). Therefore a false negative may result when 
performing the tests in an extremely dry environment, and this condition must be avoided when 
performing the tests for classification for pyrophoricity.  

2.10.4.5.  Decision logic  

Classification of pyrophoric solids is done according to decision logic 2.10.4.1 as included in the 
GHS. 

  NOTE: The person responsible for the classification of pyrophoric solids should be 

experienced in this field and be familiar with the criteria for classification. 

2.10.4.5.1.  Decision logic for pyrophoric solids 

Figure 2.8  Decision logic for pyrophoric solids (Decision logic 2.10 of GHS) 

The substance/mixture is a solid 

Category 1 

Does it ignite within 5 min after exposure to air? 

Yes 

No 

Danger 

Not classified 

 
 
 
 
 
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2.10.5.  Hazard communication for pyrophoric solids  

2.10.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

Annex I: 2.10.3 Table 2.10.2 

Label elements for pyrophoric solids 

Classification 

GHS Pictogram 

Signal Word 

Hazard Statement 

Precautionary Statement Prevention 

Category 1 

Danger 

H250: Catches fire spontaneously if 
exposed to air 

P210 
P222 

P231 + P232 

P233 
P280 

Precautionary Statement Response 

P302 + P335 + P334 
P370 + P378 

Precautionary Statement Storage 

Precautionary Statement Disposal 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

2.10.6.  Relation to transport classification 

Division 4.2 within Class 4 of the UN RTDG Model Regulations covers pyrophoric solids, liquids 
and self-heating substances and mixtures. The UN Tests N.2 that is used for classification for 
pyrophoricity for solids according to CLP is also used for classification in the subdivision 
pyrophoric substances and mixtures in Division 4.2: Substances liable to spontaneous 
combustion according to the UN RTDG Model Regulations. The criteria for Category 1 according 
to CLP (which is the only category for pyrophoric solids) and for packing group I in Division 4.2 
according to the modal transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) are also 
exactly the same. Furthermore, all pyrophoric substances and mixtures are assigned to packing 
group I within Division 4.2, which is used exclusively for pyrophoric substances and mixtures. 

Therefore, any solid substance or mixture assigned to Division 4.2, packing group I according to 
the modal transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) will be classified in 
Category 1 of the hazard class pyrophoric solids according to CLP. See Annex VII for additional 
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2.10.7.  Examples of classification for pyrophoric solids 

Please note that the substance and mixture names in this chapter are fictitious.  

2.10.7.1.  Examples of substances and mixtures fulfilling the classification 

criteria  

2.10.7.1.1.  Example 1 

Name:  

Pyroferil 

Physical state: 

Solid 

Pyrophoric properties:  Pyroferil is known to self-ignite upon contact with air at ambient conditions. 

Classification:  

Pyrophoric solid, Category 1 

2.10.7.1.2.  Example 2 

Name:  

Zorapyrole 

Physical state: 

Solid 

Pyrophoric properties:  Unknown, therefore the UN Test N.2 of the UN-MTC was applied. 

Test result:  

When poured from one meter height according to the test procedure, 
Zorapyrole self-ignited after two minutes already in the first trial. 

Classification:  

Pyrophoric solid, Category 1 

2.10.7.2.  Examples of substances and mixtures not fulfilling the classification 

criteria  

2.10.7.2.1.  Example 3 

Name:  

Nonopyr 

Physical state: 

Solid 

Pyrophoric properties:  Nonopyr has been handled extensively in air and has never self-ignited. 

From the chemical structure no pyrophoricity is expected. 

Classification:  

Not a pyrophoric solid 

 
 
 
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2.10.7.2.2.  Example 4 

Name:  

Pyronot 

Physical state: 

Solid 

Pyrophoric properties:  Unknown, therefore UN Test N.2 of the UN-MTC was applied. 

Test result:  

When poured from one meter height according to the test procedure no 
ignition occurred within five minutes. The procedure was repeated six times 
and each time the result was negative. 

Classification:  

Not a pyrophoric solid 

2.10.8.  References 

Urben, Peter G. (2007). Bretherick's Handbook of Reactive Chemical Hazards, Volumes 1-2 (7th 
Edition). Elsevier. 

 
 
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2.11.  SELF-HEATING SUBSTANCES AND MIXTURES 

2.11.1.  Introduction 

The criteria for ‘Self-heating substances and mixtures’ are found in Annex I, Section 2.11 of CLP 
and are identical to those in Chapter 2.11 of GHS.  

Self-heating is the result of an exothermic reaction of a substance or mixture with the oxygen in 
the air. Initially, the reaction rate may be very low. However, when the heat produced cannot 
be removed rapidly enough (i.e. heat accumulation), the substance or mixture will self-heat, 
with the possible consequence of self-ignition. The phenomenon can occur only where a large 
surface of substance or mixture is in contact with air or oxygen (for example, piles of powders, 
crystals, splinters, any other rough surface etc.). The initiation occurs usually at or near the 
centre of the substance or mixture pile with the available air in the interspace between the 
particles. 

Since the surface area of a solid substance or mixture exposed to air increases with decreasing 
particle size, it follows that particle size and shape will greatly influence the propensity of a 
substance or mixture to self-heat. Therefore it is very important that self-heating properties for 
solids, and especially powders, are determined for the substance or mixture in the form it is 
supplied and expected to be used. 

2.11.2.  Definitions and general considerations for the classification of self-

heating substances and mixtures 

The definitions in CLP for self-heating substances and mixtures are as follows: 

Annex I: 2.11.1.1. A self-heating substance or mixture is a liquid or solid substance or 
mixture, other than a pyrophoric liquid or solid, which, by reaction with air and without energy 
supply, is liable to self-heat; this substance or mixture differs from a pyrophoric liquid or solid 
in that it will ignite only when in large amounts (kilograms) and after long periods of time 
(hours or days). 

2.11.1.2. Self-heating of a substance or a mixture is a process where the gradual reaction of 
that substance or mixture with oxygen (in the air) generates heat. If the rate of heat 
production exceeds the rate of heat loss, then the temperature of the substance or mixture 
will rise which, after an induction time, may lead to self-ignition and combustion.  

2.11.3.  Relation to other physical hazards 

Pyrophoric solids and liquids should not be considered for classification as self-heating 
substances and mixtures. 

2.11.4.  Classification of self-heating substances and mixtures 

2.11.4.1.  Identification of hazard information 

Self-heating is a very complex phenomenon which is influenced by many parameters (some of 
them being volume, temperature, particle shape and size, heat conductivity and bulk density). 
Therefore, self-heating behaviour cannot be predicted from any theoretical model. In some 
cases, properties might even differ between producers of seemingly very similar substances or 
mixtures. Differences in self-heating behaviour are especially to be anticipated where surface 
treatment occurs in the production process. Hence, all data sources should be carefully 
evaluated with regard to reliability and scientific validity.  

It is of utmost importance that in compliance with Articles 5 and 6 of CLP authentic and 
representative material in the correct form and physical state be used for testing. In many 

 
 
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cases, a simple screening test (see Section 2.11.4.2) can be used to determine whether self-
heating occurs or not. 

2.11.4.2.  Screening procedures and waiving of testing 

Annex I: 2.11.4.2. The classification procedure for self-heating substances or mixtures 
need not be applied if the results of a screening test can be adequately correlated with the 
classification test and an appropriate safety margin is applied. Examples of screening tests 
are: 

(a)     The Grewer Oven test (VDI guideline 2263, part 1, 1990, Test methods for the De-
termination of the Safety Characteristics of Dusts) with an onset temperature 80 K above 
the reference temperature for a volume of 1 l; 

(b)     The Bulk Powder Screening Test (Gibson, N. Harper, D.J. Rogers, R. Evaluation of the 
fire and explosion risks in drying powders, Plant Operations Progress, 4 (3), 181-189, 1985) 
with an onset temperature 60 K above the reference temperature for a volume of 1 l. 

EU test method A.16 as described in Regulation (EC) No 440/2008 checks for self-heating 
properties. However, the method used is generally inappropriate for a sound assessment, and 
the findings do not lead to a classification. Therefore, special care must be taken if results from 
EU test method A.16 are interpreted towards a CLP classification for self-heating substances and 
mixtures. 

In general, the phenomenon of self-heating applies only to solids. The surface of liquids is not 
large enough for reaction with air and the test method is not applicable to liquids. Therefore 
liquids are not classified as self-heating. However, if liquids are adsorbed on a large surface 
(e.g. on powder particles), a self-heating hazard should be considered.  

Substances or mixtures with a low melting point (< 160 °C) should not be considered for 
classification in this class since the melting process is endothermic and the substance-air 
surface is drastically reduced. However, this criterion is only applicable if the substance or 
mixture is completely molten up to this temperature.  

2.11.4.3.  Classification criteria  

A self-heating substance or mixture must be classified in one of the two categories for this class 
if, in a test performed in accordance with UN Test N.4 in Part III, Sub-section 33.3.1.6 of the 
UN-MTC, the result meets the criteria according to following table: 

Annex I: Table 2.11.1 

Criteria for self-heating substances and mixtures 

Category  Criteria 

1 

A positive result is obtained in a test using a 25 mm sample cube at 140 °C 

2 

(a)  a positive result is obtained in a test using a 100 mm sample cube at 140 °C 
and a negative result is obtained in a test using a 25 mm cube sample at 
140 °C and the substance or mixture is to be packed in packages with a volume 
of more than 3 m3; or 

(b)  a positive result is obtained in a test using a 100 mm sample cube at 140 °C 
and a negative result is obtained in a test using a 25 mm cube sample at 
140 °C, a positive result is obtained in a test using a 100 mm cube sample at 
120 °C and the substance or mixture is to be packed in packages with a volume 
of more than 450 litres; or 

 
 
 
 
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(c)  a positive result is obtained in a test using a 100 mm sample cube at 140 °C 
and a negative result is obtained in a test using a 25 mm cube sample at 140 
°C and a positive result is obtained in a test using a 100 mm cube sample at 
100 °C. 

184 

Note 

The test shall be performed on the substance or mixture in its physical form as presented. 
If, for example, for the purposes of supply or transport, the same chemical is to be presented 
in a physical form different from that which was tested and which is considered likely to 
materially alter its performance in a classification test, the substance shall also be tested in the 
new form. 

2.11.2.3. Substances and mixtures with a temperature of spontaneous combustion higher than 
50 °C for a volume of 27 m³ shall not be classified as a self-heating substance or mixture. 

2.11.2.4. Substances and mixtures with a spontaneous ignition temperature higher than 50 °C 
for a volume of 450 litres shall not be assigned to Category 1 of this class. 

2.11.4.4.  Testing and evaluation of hazard information  

A self-heating substance or mixture must be classified in one of the two categories for this class 
using UN Test N.4 in Part III, Sub-section 33.3.1.6 of the UN-MTC. 

2.11.4.4.1.  General remarks 

If self-heating behaviour cannot be ruled out by a screening test, further testing becomes 
necessary. UN Test N.4 as described in the latest version of the UN-MTC should be used. 

Explosive substances and mixtures should not be tested according to this method. For safety 
reasons, it is advisable to test for explosive and self-reactive properties and to rule out 
pyrophoric behaviour before performing this test. The oven should be equipped with an 
appropriate pressure-release device in case an energetic decomposition is triggered by a 
temperature rise. For samples containing flammable solvents explosion protection measures 
have to be taken. 

The tests may be performed in any order. It is suggested to start with the 25 mm sample cube 
at 140 °C. If a positive result is obtained, the substance or mixture must be classified as a self-
heating substance or mixture, Category 1, and no further testing is necessary. 

The test procedure need not be applied if the substance or mixture is completely molten at 160 
°C. 

2.11.4.4.2.  Sample preparation 

The sample (powder or granular) in its commercial form should be used and should not be 
milled or ground. It should be filled to the brim of the sample container and the container 
tapped several times. If the sample settles, more is added. If the sample is heaped it should be 
levelled to the brim. The sample container is placed in the oven as described in the UN-MTC. 

2.11.4.4.3.  Criteria and evaluation 

A positive result is obtained if spontaneous ignition occurs or if the temperature of the sample 
exceeds the oven temperature by 60 K. The testing time is 24 hours. The time count starts 
when the temperature in the centre of the sample has reached a value of 2 K below the oven 
temperature. This is especially important when the sample contains solvents which evaporate 
under the test conditions or when larger test volumes are used for extrapolation purposes (see 
below). 

Before starting UN Test N.4, the decomposition behaviour of the sample should be known. In 
general, it is sufficient to perform a screening with Differential Scanning Calorimetry. Special 
care with respect to the interpretation of the test data is necessary when exothermic 

 
 
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decomposition may occur at the test temperatures. In such cases, a test under an inert 
atmosphere (i.e. nitrogen) should be run to determine the temperature rise due to 
decomposition. Careful flushing with the chosen inert gas is essential in such cases since 
otherwise much air may be retained between the crystals of the sample in the container. 

2.11.4.5.  Decision logic  

The following decision logic for self-heating substances and mixtures is applicable according to 
CLP.  

  NOTE: The person responsible for the classification of self-heating substances and mixtures 

should be experienced in this field and be familiar with the criteria for classification. 

 
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Annex I: Figure 2.11.1. 

Self-heating substances and mixtures 

SUBSTANCE/MIXTURE 

Does it undergo dangerous self-heating when 
tested in a 100 mm sample cube at 140 °C? 

NOT CLASSIFIED 

NO 

YES 

Does it undergo dangerous self-heating when 
tested in a 25 mm sample cube at 140 °C? 

YES 

NO 

Is it packaged in more than 3 m3? 

YES 

NO 

Category 1 

Danger 

Category 2 

Warning 

Does it undergo dangerous self-heating when 
tested in a 100 mm sample cube at 120 °C? 

NO 

NOT CLASSIFIED 

YES 

Category 2 

Is it packaged in more than 450 litres volume? 

YES 

NO 

Does it undergo dangerous self-heating when 
tested in a 100 mm sample cube at 100 °C? 

YES 

NO 

NOT CLASSIFIED 

Warning 

Category 2 

Warning 

2.11.4.6.  Exemption 

The following exemptions apply (see Section 2.11.4.3): 

•  Substances and mixtures with a temperature of spontaneous combustion higher than 50 
°C for a volume of 27 m³ must not be classified as a self-heating substance or mixture. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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•  Substances and mixtures with a spontaneous ignition temperature higher than 50 °C for 

a volume of 450 litres must not be assigned to Category 1 of this class. 

However, the UN-MTC does not provide any guidance on how these values should be 
determined. The UN test regime is based on the assumption of a cubic sample shape. For the 
extrapolation to larger volumes, an improved model has to be used. According to Grewer 
(Grewer, 1994), plotting the logarithm of the volume to surface ratio (log (V/A)) versus the 
reciprocal temperature gives good results without knowledge of the Frank-Kamenetzskii (Frank-
Kamenetzskii, 1969) shape factor. 

The critical temperature for a volume of 450 l or 27 m³ can be found by extrapolation of the 
critical temperature in a log (V/A) vs. 1/T plot (see Figure 2.9): 

Figure 2.9  Extrapolation towards large volumes  

The test setup is essentially the same as in UN Test N.4 of the UN-MTC but now the sample size 
and possibly the shape are systematically varied. The criteria of Section 2.11.4.3 apply as well. 

The critical temperature must be determined over a range of at least four different volumes and 
with a volume not smaller than 16 ml. If possible, larger volumes should be also tested. The 
borderline temperature should be determined as precisely as possible. For small volumes (< 1 
litre), the temperature rise due to self-heating may be considerably less than 60 K; in this case 
a noticeable temperature rise is interpreted as a positive result. 

A conservative approach is required for the evaluation. The uncertainty of measurement must 
be taken into account. The extrapolation must be based on a linear regression of the negative 
and positive borderline data sets in the log (V/A) vs. 1/T diagram. The maximum permissible 
difference between a positive and a negative result should be 5 K. An exemption may be 
claimed if the more conservative endpoint for the particular volume is well beyond 50 °C (i.e. 
55 °C or higher). 

400 mL100 L50607080901001201401601802002202401,6 L110 mL16 mL1 m310 m327 m3-3,0-2,8-2,6-2,4-2,2-2,0-1,8-1,6-1,4-1,2-1,0-0,8-0,6-0,40,00190,00200,00210,00220,00230,00240,00250,00260,00270,00280,00290,00300,0031log(V/A) in mTemperature in °CSample volumereciprocal abs. Temperature in 1/K    positive result    negative resultNote: sample gave positiveresult at 140 °C / 1 literLinear regression linesExtrapolation to 27 m³ 
 
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2.11.5.  Hazard communication for self-heating substances and mixtures 

2.11.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

Annex I: Table 2.11.2 

Label elements for self-heating substances and mixtures 

Classification 

Category 1 

Category 2 

GHS Pictograms 

Signal Word 

Danger 

Warning 

Hazard Statement 

Precautionary Statement 
Prevention 

Precautionary Statement Response 

Precautionary Statement Storage 

Precautionary Statement Disposal 

H251: Self-heating; may 
catch fire 

H252: Self-heating in large 
quantities; may catch fire 

P235 
P280 

P407 
P413 
P420 

P235 
P280 

P407 
P413 
P420 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

2.11.6.  Relation to transport classification 

Division 4.2 – substances and mixtures liable to spontaneous combustion – within Class 4 of the 
UN RTDG Model Regulations comprises the following entries: 

a.  pyrophoric substances and mixtures ; 

b.  self-heating substances and mixtures. 

Whereas pyrophoric substances and mixtures in the modal transport regulations (ADR, RID, 
ADN and IMDG Code, ICAO TI) are assigned to packing group I, self-heating substances and 
mixtures are assigned to packing groups II and III. In cases where a substance or mixture is 
classified in Division 4.2, packing group II or III, the translation into the CLP system is 
straightforward. 

It should be kept in mind that transport classification is based on prioritisation of hazards (see 
UN RTDG Model Regulations, Section 2.0.3) and that self-heating substances and mixtures have 
a relatively low rank in the precedence of hazards. Therefore, the translation from the modal 
transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) to CLP should be only done if a 
transport classification as self-heating is explicitly available. The conclusion that a substance or 
mixture not classified as self-heating for transport should not be classified as a self-heating 

 
 
 
 
 
 
 
 
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substance or mixture according to CLP is, in general, not correct. See Annex VII for additional 
information on transport classification in relation to CLP classification. 

2.11.7.  Examples of classification for self-heating substances and mixtures 

2.11.7.1.  Examples of substances and mixtures fulfilling the classification 

criteria  

•  many organometallic compounds, especially substances or mixtures containing transition 

metals; 

•  many organic substances or mixtures; the tendency to self-heat increases with 

decreasing particle size; 

•  many metals, especially catalysts. 

2.11.7.2.  Examples of substances and mixtures not fulfilling the classification 

criteria  

In general, liquids show no self-heating behaviour unless adsorbed on a large surface. 

Scientific background 

A basic model for the thermal explosion of solids was first developed by Frank-Kamenetzskii 
(Frank-Kamenetzskii, 1969). It is based on the assumption that only the heat loss by thermal 
conduction is relevant for the phenomenon. In this case, the critical criterion for a thermal 
runaway reaction can be described as a linear relationship between the reciprocal absolute 
temperature and the logarithm of volume. 

The classification scheme of the UN for self-heating substances and mixtures is based on 
charcoal as a reference system. The critical temperature for a 1 litre cube of charcoal is 140 °C 
and for a cube of 27 m³ 50 °C. When a parallel line is drawn in the 1/T vs. logarithm of volume 
diagram from the reference points 1 litre / 120 °C and 1 litre / 100 °C, the corresponding 
volumes for a critical temperature of 50 °C are found to be 3 m³ and 450 l, respectively (see 
Figure 2.10). The black dotted line in Figure 2.10 separates Category 1 from Category 2. For 
examples of results following the Test N.2 see Section 33.3.1.4.5 of UN-MTC. 

However, the slope of the line in the 1/T vs. volume diagram depends on the individual 
activation energy of the substance or mixture, and therefore it may vary within certain limits. It 
must be born in mind that this test regime has been developed to facilitate classification and 
that it may not suffice to solve safety issues in storage.  

 
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Figure 2.10   Volume dependency of the critical temperature for charcoal 

2.11.8.  References 

Grewer, T. (1994). Thermal hazards of chemical reactions, Elsevier. 

Frank-Kamenetzskii, D.A. (1969). Diffusion and heat transfer in chemical kinetics, 2nd edition, 
Plenum Press, New York, London. 

0,0020,00220,00240,00260,00280,0030,00320,0010,010,1110100100010000100000Temperature (°C)5060708090100120140160180200220Volume (liter)recipr.Temp.Charcoalreferenceline(UN Manual T + C)Not self-heatingExemption< 3 m³Exemption< 450 ltrCat. 1Cat. 2YellowdotssymbolizeUN Manual test pointsGrewer test 
 
 
 
 
 
 
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2.12.  SUBSTANCES AND MIXTURES WHICH, IN CONTACT WITH WATER, 

EMIT FLAMMABLE GASES 

2.12.1.  Introduction 

The criteria for ‘Substances and mixtures which, in contact with water, emit flammable gases’ 
are found in Annex I, Section 2.12 of CLP and are identical to those in Chapter 2.12 of GHS.  

Depending on the chemical structure and/or the physical state (e.g. particle size) substances or 
mixtures may be able to react with water (even damp / air humidity) under normal ambient 
temperature conditions. Sometimes this reaction can be violent and/or with significant 
generation of heat. Especially if gases are evolved this reaction may become very dangerous 
during use. In addition, it is important to know whether a substance or mixture emits 
flammable gases after contact with water because special precautions are necessary especially 
with regard to explosion protection. 

Examples are demonstrated in the following table. 

Table 2.1  Examples of hazards, depending on the property of the emitted gas, when 
substances and mixtures are in contact with water 

Type of 
emitted gas  

Gas  
(in general) 

Example of the hazard  

CLP Reference 

•  Heating up of the substance 

•  Splashing of the substance and thus e.g. 

contact with skin etc. or additional risk during 
fire fighting 

Annex II, 1.1.3: 
Supplemental hazard 
information: 

EUH014* 

Flammable gas 

• 

• 

• 

Pressure rise and bursting of e.g. the 
packaging, tank 

Ignition  

Flash of fire 

Toxic gas 

•  Damage to health: intoxication (acute) 

Annex I, 2.12: 
H260/H261 

Annex II, 1.2.1: 
Supplemental hazard 
information: 

EUH029 

* For supplemental hazard information: see Section 2.12.4.2 

2.12.2.  Definitions and general considerations for the classification of 

substances and mixtures which, in contact with water, emit flammable 
gases 

The following definition is given in CLP for substances and mixtures which, in contact with 
water, emit flammable gases (CLP Annex I, 2.12). 

Annex I: 2.12.1. Substances or mixtures which, in contact with water, emit flammable gases 
means solid or liquid substances or mixtures which, by interaction with water, are liable to 
become spontaneously flammable or to give off flammable gases in dangerous quantities. 

2.12.3.  Relation to other physical hazards 

If the chemical identity of the emitted gas is unknown, the gas must be tested for flammability 
(unless it ignites spontaneously). Other than under DSD/DPD, pyrophporic liquids and 

 
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pyrophoric solids have to be considered for classification in this hazard class as well and data 
about pyrophoric properties are needed prior to testing for this hazard class. 

2.12.4.  Classification of substances and mixtures which, in contact with 

water, emit flammable gases 

2.12.4.1.  Identification of hazard information  

For the classification of substances and mixtures which, in contact with water, emit flammable 
gases the following data are needed, if applicable: 

• 

chemical structure; 

•  water solubility; 

• 

chemical identity and flammability of the emitted gas; 

•  pyrophoric properties of the tested substance or mixture; 

•  particle size in case of solids; 

• 

friability in case of solids;  

•  hazard properties in general; 

• 

information concerning the experience in production or handling.  

See also IR & CSA, Chapter R.7a: Endpoint specific guidance, Section R.7.1.7 (Water solubility), 
R.7.1.14 (Granulometry). 

Information about the chemical structure is used to check whether the substance or mixture 
contains metals and/or metalloids. 

The water solubility is used to decide whether the substance or mixture is soluble in water to 
form a stable mixture. This may also be decided based on information concerning experience in 
handling or use, e.g. the substance or mixture is manufactured with water or washed with water 
(see Section 2.12.4.4.1). 

The chemical identity of the emitted gas is used to decide whether the evolved gas is flammable 
or not. If the chemical identity of the emitted gas is unknown, the gas must be tested for 
flammability (see Section 2.2). 

In case of pyrophoric substances and mixtures the UN Test N.5 of the UN-MTC, Part III, Section 
33.4.1.3.1 must be executed under nitrogen atmosphere. Therefore, data about pyrophoric 
properties are needed prior to testing. 

The melting point, boiling point and information about viscosity are necessary to identify the 
physical state of the substance or mixture. See also IR & CSA, Chapter R.7a: Endpoint specific 
guidance, Section R.7.1.2 (Melting point/freezing point), R.7.1.3 (Boiling point), R.7.1.18 
(Viscosity). 

Even though the UN Test N.5 can be applied to both, solids and liquids, these data are 
necessary to decide whether information concerning the friability (for solids) in accordance with 
the test method is necessary.  

The particle size and the friability of a solid substance or mixture are crucial parameters for the 
classification of substances and mixtures which, in contact with water, emit flammable gases. 
These parameters have a significant effect on the test result. Thus specific requirements 
regarding the particle size and the friability are prescribed in the UN Test N.5. For further details 
regarding the test procedure see Section 2.12.4.4.1. 

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2.12.4.2.  Screening procedures and waiving of testing 

For the majority of substances and mixtures, flammability as a result of contact with water is 
not a typical property and testing can be waived based on a consideration of the structure and 
experiences in handling and use. 

Annex I: 2.12.4.1. The classification procedure for this class need not be applied if: 

a) the chemical structure of the substance or mixture does not contain metals or metalloids; 

or 

b) experience in handling and use shows that the substance or mixture does not react with 

water, e.g. the substance is manufactured with water or washed with water; or 

c) the substance or mixture is known to be soluble in water to form a stable mixture. 

2.12.4.3.  Classification criteria  

Annex I: Table 2.12.1 

Criteria for substances or mixtures which in contact with water emit flammable gas 

Category  Criteria 

Any substance or mixture which reacts vigorously with water at ambient 
temperatures and demonstrates generally a tendency for the gas produced to 
ignite spontaneously, or which reacts readily with water at ambient temperatures 
such that the rate of evolution of flammable gas is equal to or greater than 10 
litres per kilogram of substance over any one minute. 

Any substance or mixture which reacts readily with water at ambient temperatures 
such that the maximum rate of evolution of flammable gas is equal to or greater 
than 20 litres per kilogram of substance per hour, and which does not meet the 
criteria for Category 1. 

Any substance or mixture which reacts slowly with water at ambient temperatures 
such that the maximum rate of evolution of flammable gas is equal to or greater 
than 1 litre per kilogram of substance per hour, and which does not meet the 
criteria for Categories 1 and 2. 

1 

2 

3 

Note: 

The test shall be performed on the substance or mixture in its physical form as presented. If 
for example, for the purposes of supply or transport, the same chemical is to be presented in 
a physical form different from that which was tested and which is considered likely to 
materially alter its performance in a classification test, the substance must also be tested in 
the new form. 

2.12.2.2. A substance or mixture shall be classified as a substance or mixture which in 
contact with water emits flammable gases if spontaneous ignition takes place in any step of 
the test procedure. 

2.12.4.4.  Testing and evaluation of hazard information  

2.12.4.4.1.  Testing procedure 

Care must be taken during testing as the emitted gas might be toxic or corrosive. 

 
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The testing procedure for substances and mixtures which in contact with water emit flammable 
gases is sensitive to a number of influencing factors and therefore must be carried out by 
experienced personnel. Some of these factors are described in the following: 

2.  Apparatus / measuring technique 

In UN Test N.5 no special laboratory apparatus / measuring technique to determine the rate of 
gas evolution is required and no reference material is prescribed. As demonstrated in the past 
by a round robin test (Kunath, K. et al. 2011), the gas evolution rate measured by different 
apparatuses may vary widely. Therefore in order to avoid measuring and classification errors 
adequate quality control measures are necessary to validate the results and should be noted in 
the test report. 

3.  Particle size and/or friability 

The particle size of a solid has a significant effect on the test result. Therefore, if for solids the 
percentage of powder with a particle size of less than 500 µm constitutes more than 1 % of the 
total mass, or if the substance or mixture is friable, then the complete sample must be ground 
to a powder before testing to account for a possible reduction in particle size during handling 
and transport.  

In certain cases, grinding may not be applicable and/or the sample cannot be ground 
completely to a particle size of less than 500 µm (e.g. metal granules). 

Information on these pre-treatments and the respective procedures, the particle size and the 
friability has to be provided in the test report. 

4.  Atmospheric parameters  

Variations of the atmospheric parameters (mainly air pressure and temperature) during the test 
have a considerable influence on the test result. Therefore the substance or mixture must be 
tested at 20 °C, i.e. make sure that the test apparatus is acclimatised to 20 °C. 

On the other hand it is difficult to regulate and stabilise the air pressure during the testing. To 
characterise this influencing factor and to avoid false positive results, an additional ‘blank test’ 
is highly recommended. The results of the blank test should be noted in the test report. 

5.  Test with demineralised (distilled) water  

The UN Test N.5 is performed with demineralised (distilled) water. In practice, contact with 
water can be to water in the liquid state (fresh water, sea water) or humid air, respectively. 
Note that the reactivity and thus the gas evolution rate observed in practice may differ from the 
gas evolution rate value measured using demineralised water. This should be taken into account 
when handling substances and mixtures which in contact with water emit flammable gases. 

6.  Stirring procedures during the test 

Stirring of the sample or water mixture during the test may have a considerable effect on the 
test result (e.g. significant increase or decrease of the gas evolution rate). Therefore, the 
sample or water mixture should not be stirred continuously during the test, e.g. by an 
automatic magnetic stirrer, even if the test sample has hydrophobic properties and moistening 
of the sample becomes impossible (see Kunath K. et al., 2011). 

7.  Spontaneous ignition 

Spontaneous ignition of the evolved gas without contact with an additional ignition source, i.e. 
without the flame of the gas burner results in classification as Category 1. This does not 
necessarily mean that the evolved gas is pyrophoric but often the heat of reaction is sufficient 
to ignite the evolved gas (e.g. the hydrogen evolved when sodium reacts with water). 

 
 
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2.12.4.4.2.  Evaluation of hazard information 

In order to accurately interpret the test results the evaluating person must have sufficient 
experience in the application of the test methods and in the disturbing / influencing factors as 
described above. 

The evaluation of data comprises two steps:  

•  evaluation of all available data; and 

• 

identification of the study or studies giving rise to the highest concern (key studies). 

The criteria for assignment to Category 2 or 3 are gas evolution rates  of 20 and 1 litre per 
kilogram of substance or mixture per hour, respectively, but for Category 1 the relevant 
criterion is 10 litres per kilogram of substance or mixture over any one minute period (if the gas 
does not ignite spontaneously). This has to be considered while testing and for correct 
evaluation of the test results. 

The assignment to the respective hazard class/category will further determine the technical 
means to be taken to avoid dangerous events which, in combination with other safety 
characteristics such as i) explosion limits, ii) flash points (applicable only for liquids) or iii) self-
ignition temperature, can lead to clear restrictions in the conditions of use.  

2.12.4.5.  Decision logic  

Classification of substances and mixtures which, in contact with water, emit flammable gases is 
done according to decision logic 2.12.4.1 as included in the GHS. 

  NOTE: The person responsible for the classification of substances and mixtures which, in 

contact with water, emit flammable gases should be experienced in this field and be familiar 
with the criteria for classification. 

 
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Figure 2.11   Decision logic for substances and mixtures which, in contact with water, emit 
flammable gases (Decision logic 2.12 of GHS) 

Substance/mixture 

In contact with water, does it react slowly at ambient temperatures such 
that the maximum rate of evolution of flammable gas is ≥ 1 litre per kg 
of substance per hour? 

No 

Not classified  

Yes 

In contact with water, does the substance react vigorously with water at 
ambient temperatures and demonstrate generally a tendency for the gas 
produced to ignite spontaneously, or does it react readily with water at 
ambient temperatures such that the rate of evolution of flammable gas is 
≥ 10 litres per kg of substance over any one minute? 

Yes 

No 

In contact with water, does it react readily with water at ambient 
temperatures such that the maximum rate of evolution of flammable 
gas is ≥ 20 litres per kg of substance per hour? 

Yes 

No 

Category 1 

Danger 

Category 2 

Danger 

Category 3 

Warning 

 
 
 
 
 
 
 
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2.12.5.  Hazard communication for substances and mixtures which, in contact 

with water, emit flammable gases 

2.12.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements for substances and mixtures  

Annex I: Table 2.12.2 

Label elements for substances or mixtures which in contact with water emit 
flammable gases 

Classification 

Category 1 

Category 2 

Category 3 

GHS Pictograms 

Signal Word 

Danger 

Hazard Statement 

H260: 

Danger 

H261: 

Warning 

H261: 

In contact with water 
releases flammable 
gases which may 
ignite spontaneously 

In contact with 
water releases 
flammable gases 

In contact with 
water releases 
flammable gases 

Precautionary 
Statement 
Prevention 

P223 

P223 

P231 + P232 

P231 + P232 

P231 + P232 

P280 

P280 

P280 

Precautionary 
Statement Response 

P302 + P335 + P334 

P370 + P378 

P302 + P335 + 
P334 

P370 + P378 

P370 + P378 

Precautionary 
Statement Storage 

Precautionary 
Statement Disposal 

P402 + P404 

P402 + P404 

P402 + P404 

P501 

P501 

P501 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

2.12.5.2.  Additional labelling provisions 

Annex II of CLP provides the following additional labelling provisions for water-reactive 
substances and mixtures. These statements must be assigned in accordance with CLP, Article 
25 (1), to substances and mixtures classified for physical, health or environmental hazards. 
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Annex II: 1.1.3.     EUH014 – 'Reacts violently with water' 

For substances and mixtures which react violently with water, such as acetyl chloride, alkali 
metals, titanium tetrachloride.  

Annex II: 1.2.1.     EUH029 - 'Contact with water liberates toxic gas' 

For substances and mixtures which in contact with water or damp air, evolve gases classified 
for acute toxicity in category 1, 2 or 3 in potentially dangerous amounts, such as aluminium 
phosphide, phosphorus pentasulphide. 

2.12.6.  Relation to transport classification 

Division 4.3 within Class 4 of the UN RTDG Model Regulations covers substances and mixtures 
which in contact with water emit flammable gasses. Substances and mixtures which are 
classified and/or labelled in Division 4.3 in the modal transport regulations (ADR, RID, ADN and 
IMDG Code, ICAO TI) are classified as substances and mixtures which, in contact with water, 
emit flammable gases under CLP. See Annex VII for additional information on transport 
classification in relation to CLP classification. 

2.12.7.  Examples of classification for substances and mixtures which, in 

contact with water, emit flammable gases 

2.12.7.1.  Example of a substance fulfilling the classification criteria  

Many different types of chemicals may belong to the hazard class of substances and mixtures 
which, in contact with water, emit flammable gases, for example, alkali metals, alkyl aluminium 
derivatives, alkyl metals, metal hydrides, metal phosphides, certain metal powders. A 
comprehensive list can be found in Bretherick’s Handbook of Reactive Chemical Hazards (Urben, 
2007).  

2.12.7.1.1.  Example 1 

PYROPHORIC SUBSTANCE FULFILLING THE CRITERIA FOR CLP CLASSIFICATION 

Substance: 

Magnesium alkyls (Index No. 012-003-00-4) 

Chemical structure:  

Flammable gas: 

R2Mg  

Hydrogen 

Gas evolution rate:  

not applicable 

Spontaneous ignition:  

not possible due to the nitrogen atmosphere during the 
UN Test N.5  

DSD classification:  

F; R14-17  

Transport classification:  

- 

Reference:  

Former Annex I to DSD and Annex VI to CLP 

 CLP Classification:  

Water-react. 1;  H260  

Pyr. Sol. 1;  H250 

Supplemental Hazard Information: 

EUH014 

 
 
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2.12.7.2.  Example of a substance not fulfilling the classification criteria  

2.12.7.2.1.  Example 2 

MANGANESE ETHYLENE BIS (DITHIOCARBAMATE) COMPLEX WITH ZINC SALT 88 % 
(MANCOZEB) 

Gas evolution rate:  

0 litres per kilogram of substance per hour. 

Spontaneous ignition:  

not applicable 

Transport classification:  

not Class 4.3 

Reference: 

UN Test N.5, UN-MTC Table 33.4.1.4.5 

 CLP Classification:  

Not classified as substance which, in contact with 
water, emit flammable gases 

2.12.8.  References 

William M. Haynes et al. (2012) CRC Handbook of Chemistry and Physics 93rd Edition. CRC 
Press, Taylor and Francis, Boca Raton, FL  

GESTIS-database on hazardous substances: 
http://www.dguv.de/bgia/en/gestis/stoffdb/index.jsp  

O'Neil, Maryadele J. et al. (2016, 2012) The Merck Index - An Encyclopaedia of Chemicals, 
Drugs, and Biologicals (14th Edition – Version 14.9). Merck Sharp & Dohme Corp., a subsidiary 
of Merck & Co., Inc. 

Urben, Peter G. (2007). Bretherick's Handbook of Reactive Chemical Hazards, Volumes 1-2 (7th 
Edition). Elsevier. 

Kunath, K., Lüth, P., Uhlig, S. (2011). Interlaboratory test on the method UN Test N.5 / EC A.12 
“Substances which, in contact with water, emit flammable gases” 2007.Short report. BAM 
Bundesanstalt für Materialforschung und –prüfung. Berlin. ISBN 978-3-9814634-1-5. 
http://www.bam.de/de/service/publikationen/publikationen_medien/short__report_rv_un_n_5.
pdf  

 
 
 
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2.13.  OXIDISING LIQUIDS  

2.13.1.  Introduction 

The criteria for ‘Oxidising liquids’ are found in Annex I, Section 2.13 of CLP and are identical to 
those in Chapter 2.13 of GHS.  

The hazard class oxidising liquids comprises liquid substances and mixtures whose hazard is 
characterised by the fact that, in contact with other materials, they are able to cause or 
contribute to the combustion of those materials. The other materials do not necessarily have to 
belong to a certain hazard class in order to be able to be affected by the presence of oxidising 
substances or mixtures. This is for example the case when a solid material (e.g. wood) is 
soaked with an oxidising liquid.  

Certain combinations of combustible materials and oxidising substances or mixtures may even 
result in spontaneous combustion, thermal instability or form an explosive mixture, this means 
that they may have explosive properties or may be regarded as self-reactive substances or 
mixtures. 

Although widely known as oxidising materials, their hazard and behaviour might be better 
understood by considering them to be fire enhancing substances or mixtures.  

The hazards communication of oxidising liquids intends to communicate the property that it may 
cause fire or explosion or that it may intensify fire. 

Apart from the combustion hazard, the production of toxic and/or irritating fumes may cause an 
additional hazard. For example, when nitrates are involved in a fire, nitrous fumes may be 
formed. 

The testing procedure and criteria for oxidising substances or mixtures do not work properly for 
ammonium nitrate compounds or solutions, ammonium nitrate based fertilizers and ammonium 
nitrate emulsions, suspensions or gels. Therefore for classification and labelling of substances or 
mixtures containing ammonium nitrate, known experience should be used and expert 
judgement should be sought. For the classification procedures for ammonium nitrate emulsions, 
suspensions or gels – intermediate for blasting explosives, see Chapter 2.1 of this guidance. 

Annex I: 2.13.4.3  

In the event of divergence between test results and known experience in the handling and 
use of substances or mixtures which shows them to be oxidising, judgments based on known 
experience shall take precedence over test results. 

2.13.2.  Definitions and general considerations for the classification of 

oxidising liquids 

The CLP text comprises the following definition for oxidising liquids. 

Annex I: 2.13.1.     Definition 

Oxidising liquid means a liquid substance or mixture which, while in itself not necessarily 
combustible, may, generally by yielding oxygen, cause, or contribute to, the combustion of 
other material. 

2.13.3.  Relation to other physical hazards 

Oxidising liquids that are mixed with combustible materials or reducing agents may have 
explosive properties and should be considered for classification in the hazard class Explosives 
(including the applicable screening procedures), see Chapter 2.1 of this guidance. 

 
 
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In rare cases, mixtures with oxidising liquids may exhibit self-reactive behaviour, see Chapter 
2.8 of this guidance. Expert judgement should be sought in case of doubt. 

The classification procedure and criteria for oxidising substances or mixtures is not applicable 
for organic peroxides. Under DSD organic peroxides were considered to be oxidising substances 
or mixtures because of the presence of the –O–O– bond. The majority of the organic peroxides 
do not possess oxidising properties; their main hazards are reactivity and flammability. Under 
CLP organic peroxides are comprised in a separate hazard class (CLP Annex I, 2.15) and they 
must not be considered according to the procedures described for oxidising liquids. Organic 
peroxides were classified as oxidising (O; R7) according to the DSD, which was not appropriate 
since the vast majority of them do not exhibit oxidising properties.  

Inorganic oxidising liquids are not flammable and therefore do not have to be subjected to the 
classification procedures for the hazard classes flammable liquids or pyrophoric liquids. Also 
other liquids that are classified as oxidising liquids are normally not flammable, although a few 
exemptions may exist. Expert judgement should be sought in case of doubt. 

2.13.4.  Classification of substances and mixtures as oxidising liquids  

2.13.4.1.  Identification of hazard information  

Oxidising liquids may cause, or contribute to, the combustion of other material. Although the 
definition states that they generally do this by yielding oxygen, halogens can behave in a similar 
way. Therefore, any substance or mixture containing oxygen and/or halogen atoms should in 
principle be considered for inclusion into the hazard class oxidising liquids. This does not 
necessarily mean that every substance or mixture containing oxygen and/or halogen atoms 
should be subjected to the full testing procedure.  

2.13.4.1.1.  Screening procedures and waiving of testing 

Liquids that are classified as explosives should not be subjected to the testing procedures for 
oxidising liquids. 

Organic peroxides should be considered for classification within the hazard class organic 
peroxides, see Chapter 2.15 of this guidance. 

Experience in the handling and use of substances or mixtures which shows them to be oxidising 
is an important additional factor in considering classification as oxidising liquids. In the event of 
divergence between test results and known experience, judgement based on known experience 
should take precedence over test results. 

Before submitting a substance or a mixture to the full test procedure, an evaluation of its 
chemical structure may be very useful as it may prevent unnecessary testing. The person 
applying this procedure should have sufficient experience in testing and in theoretical evaluation 
of hazardous substances and mixtures. The following text provides a guideline for the 
theoretical evaluation of potential oxidising properties on basis of its composition and chemical 
structure. In case of doubt, the full test must be performed. 

For organic substances or mixtures the classification procedure for this hazard class need not to 
be applied if: 

a.  the substance or mixture does not contain oxygen, fluorine or chlorine; or 

b.  the substance or mixture contains oxygen, fluorine or chlorine and these elements 

are chemically bonded only to carbon or hydrogen. 

For inorganic substances or mixtures, the classification procedure for this hazard class need not 
be applied if they do not contain oxygen or halogen. 

On basis of this theoretical evaluation only a distinction can be made between ‘potentially 
oxidising’ (i.e. further testing required) and ‘non-oxidising’ (i.e. no further testing for this 

 
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hazard class required). It is not possible to assign a hazard category on basis of a theoretical 
evaluation. 

Any substance or mixture that complies with the above waiving criteria can be safely regarded 
to have no oxidising properties and, hence, needs not to be tested and needs not to be 
regarded as an oxidising liquid. However, such a substance or mixture may still possess other 
hazardous properties that require classification into another hazard class.  

In case a mixture of an oxidising substance and a non-hazardous inert substance is offered for 
classification, the following should be taken into account: 

•  An inert material by definition does not contribute to the oxidising capability of the 
oxidising substance. Hence, the mixture can never be classified into a more severe 
hazard category. 

• 

If an oxidising substance is mixed with an inert material, the oxidising capability of the 
mixture does not linearly decrease with decreasing content of oxidising substance. The 
relationship is more or less logarithmic and depends on the characteristics of the 
oxidising substance. For instance, a mixture containing 50 % of a strong oxidiser and 50 
% of an inert material may retain 90 % of the oxidising capability of the original 
oxidising component. Non-testing classification of mixtures based solely on test data for 
the original oxidising substance should therefore be done with extreme care and only, if 
sufficient experience in testing exists. 

•  The determination of the oxidising properties of an aqueous solution of solid oxidising 

substances and the classification as an oxidising mixture is not necessary provided that 
the total concentration of all solid oxidisers in the aqueous solution is less than or equal 
to 20 % (w/w).  

2.13.4.2.  Classification criteria 

The testing procedures for oxidising liquids are based on the capability of an oxidising liquid to 
enhance the combustion of a combustible material. Therefore, substances and mixtures that are 
submitted for classification testing are mixed with a combustible material. In principle, dried 
fibrous cellulose is used as a combustible material. The mixture of the potentially oxidising 
liquid and cellulose is then ignited and its behaviour is observed and compared to the behaviour 
of reference materials. 

For liquids the mixture with cellulose is ignited under confinement in an autoclave and the 
pressure rise rate that is caused by the ignition and the subsequent reaction is recorded. The 
pressure rise rate is compared to that of three reference material mixtures. The higher the 
pressure rise rate, the stronger the oxidising capability of the liquid tested. 

Annex I: 2.13.2.1.  

An oxidising liquid shall be classified in one of the three categories for this class using test 
O.2 in Part III, sub-section 34.4.2 of the UN RTDG, Manual of Tests and Criteria in 
accordance with Table 2.13.1: 

Table 2.13.1 

Criteria for oxidising liquids 

Category  Criteria 

1 

Any substance or mixture which, in the 1:1 mixture, by mass, of substance (or 
mixture) and cellulose tested, spontaneously ignites; or the mean pressure 
rise time of a 1:1 mixture, by mass, of substance (or mixture) and cellulose is 
less than that of a 1:1 mixture, by mass, of 50 % perchloric acid and cellulose. 

 
 
 
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2 

3 

Any substance or mixture which, in the 1:1 mixture, by mass, of substance (or 
mixture) and cellulose tested, exhibits a mean pressure rise time less than or 
equal to the mean pressure rise time of a 1:1 mixture, by mass, of 40 % 
aqueous sodium chlorate solution and cellulose; and the criteria for Category 1 
are not met. 

Any substance or mixture which, in the 1:1 mixture, by mass, of substance (or 
mixture) and cellulose tested, exhibits a mean pressure rise time less than or 
equal to the mean pressure rise time of a 1:1 mixture, by mass, of 65 % 
aqueous nitric acid and cellulose; and the criteria for Category 1 and 2 are not 
met. 

For additional information regarding the use of non-testing data see Section 2.13.4.3 below and 
Urben, 2007 (see Section 2.13.7). 

2.13.4.3.  Testing and evaluation of hazard information 

The test methods for oxidising liquids are designed to give a final decision regarding their 
classification. Apart from testing, also experience in the handling and use of substances or 
mixtures which shows them to be oxidising is an important additional factor in considering 
classification in this hazard class. In the event of divergence between test results and known 
experience, judgement based on known experience should take precedence over test results. 
However, a substance or mixture must not be classified into a less severe Category based on 
experience only. 

2.13.4.4.  Decision logic  

Classification of oxidising liquids is done according to decision logic 2.13 as included in the GHS. 

  NOTE: The person responsible for the classification of oxidising liquids should be 

experienced in this field and be familiar with the criteria for classification. 

 
 
 
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Figure 2.12   Decision logic for oxidising liquids (Decision logic 2.13 of GHS)  

The substance/mixtures is a liquid 

Does it, in the 1:1 mixture, by mass, of substance (or mixture) 
and cellulose tested, exhibits a pressure rise ≥ 2070 kPa (gauge)? 

Yes 

Does it, in the 1:1 mixture, by mass, of substance (or mixture) 
and cellulose tested, exhibit a mean pressure rise time less than or 
equal to the mean pressure rise time of a 1:1 mixture, by mass, of 
65 % aqueous nitric acid and cellulose? 

No 

No 

Yes 

Does it, in the 1:1 mixture, by mass, of substance (or mixture) 
and cellulose tested, exhibit a mean pressure rise time less than or 
equal to the mean pressure rise time of a 1:1 mixture, by mass, of 
40 % aqueous sodium chlorate and cellulose? 

No 

Yes 

Does it, in the 1:1 mixture, by mass, of substance (or mixture) 
and cellulose tested, spontaneously ignite or exhibit a mean 
pressure rise time less than that of a 1:1 mixture, by mass, of 50 
% perchloric acid and cellulose?  

No 

Yes 

Not 
classified 

Not 
classified 

Category 3 

Warning 

Category 2 

Warning 

Category 1 

Danger 

 
 
 
 
  
 
 
  
 
  
 
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2.13.4.5.  Hazard communication for oxidising liquids 

2.13.4.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

The pictograms and hazard statements are designed to indicate that oxidising substances and 
mixtures may cause or contribute to fire or explosion and therefore in principle should be 
separated from combustible materials. 

Annex I : Table 2.13.2 

Label elements for oxidising liquids 

Category 1 

Category 2 

Category 3 

GHS Pictograms 

Signal Word 

Danger 

Danger 

Warning 

Hazard Statement 

H271: May cause fire or 
explosion; strong oxidiser 

H272: May intensify 
fire; oxidiser 

H272: May intensify 
fire; oxidiser 

Precautionary 
Statement 
Prevention 

Precautionary 
Statement 
Response 

Precautionary 
Statement 
Storage 

Precautionary 
Statement 
Disposal 

P210 
P220 
P280 

P210 
P220 
P280 

P370 + P378 

P370 + P378 

P210 
P220 
P280 
P283 

P306 + P360 
P371 + P380 + P375 
P370 + P378 

P420 

P501 

P501 

P501 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

2.13.5.  Relation to transport classification 

Division 5.1 within Class 5 of the UN RTDG Model Regulations covers oxidising liquids and 
oxidising solids, using the same tests and criteria as the CLP. Therefore, a liquid substance or 
mixture classified as Division 5.1 (sometimes referred to as Class 5.1) according to any of the 
modal transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) is normally also 
classified as an oxidising liquid according to the CLP. Packing Groups I, II and III of the 
transport regulations correspond directly to Categories 1, 2 and 3 of the CLP, respectively. See 
Annex VII for additional information on transport classification in relation to CLP classification. 

 
 
 
 
 
 
 
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2.13.6.  Examples of classification for oxidising liquids 

2.13.6.1.  Examples of substances and mixtures fulfilling the classification 

criteria  

The list of substances and mixtures fulfilling the criteria for classification is only presented for 
information purposes. This list is not exhaustive. For examples of results see Section 34.4.2.5 of 
UN-MTC. 

•  Ferric nitrate, saturated aqueous solution 

•  Lithium perchlorate, saturated aqueous solution 

•  Magnesium perchlorate, saturated aqueous solution 

•  Perchloric acid, 55 % 

•  Sodium nitrate, 45 % aqueous solution 

2.13.6.2.  Examples of substances and mixtures not fulfilling the classification 

criteria  

•  Nickel nitrate, saturated aqueous solution 

•  Potassium nitrate, 30 % aqueous solution 

•  Silver nitrate, saturated aqueous solution 

2.13.7.  Reference 

Urben, Peter G. (2007). Bretherick's Handbook of Reactive Chemical Hazards, Volumes 1-2 (7th 
Edition). Elsevier.  

 
 
 
 
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2.14.  OXIDISING SOLIDS 

2.14.1.  Introduction 

The criteria for ‘Oxidising solids’ are found in Annex I, Section 2.14 of CLP and are identical to 
those in Chapter 2.14 of GHS.  

The hazard class oxidising solids comprises substances and mixtures whose hazard is 
characterised by the fact that, in contact with other materials, they are able to cause or 
contribute to the combustion of those materials. The other materials do not necessarily have to 
belong to a certain hazard class in order to be affected by the presence of an oxidising solid. 
This is for example the case when a liquid fuel (e.g. gas oil) mixes with an oxidising solid. 
Certain combinations of combustible materials and oxidising substances or mixtures may even 
result in spontaneous combustion, thermal instability or form an explosive mixture, this means 
that they may have explosive properties or may be regarded as self-reactive substances or 
mixtures. 

Although widely known as ‘oxidising materials’, their hazard and behaviour might be better 
understood by considering them to be ‘fire enhancing substances’.  

The hazards communication of oxidising solids intends to communicate the property that it may 
cause fire or explosion or that it may intensify fire. 

Apart from the combustion hazard, the production of toxic and/or irritating fumes may cause an 
additional hazard. For example, when nitrates are involved in a fire, nitrous fumes may be 
formed. 

The testing procedure and criteria for oxidising substances or mixtures do not work properly for 
ammonium nitrate, ammonium nitrate compounds, ammonium nitrate based fertilizers and 
ammonium nitrate gels. Therefore, for classification and labelling of substances and mixtures 
containing ammonium nitrate, known experience should be used and expert judgement should 
be sought. For the classification procedures for ammonium nitrate gels – intermediate for 
blasting explosives, see Section 2.1 of this guidance. 

Annex I: 2.14.4.3  

In the event of divergence between test results and known experience in the handling and 
use of substances or mixtures which shows them to be oxidising, judgments based on known 
experience shall take precedence over test results. 

2.14.2.  Definitions and general considerations for the classification of 

oxidising solids 

The CLP text comprises the following definition for oxidising solids. 

Annex I: 2.14.1.     Definition 

Oxidising solid means a solid substance or mixture which, while in itself is not necessarily 
combustible, may, generally by yielding oxygen, cause, or contribute to, the combustion of 
other material. 

Special consideration on particle size 

The oxidising properties of a solid depend on its particle size. Smaller particles enable a more 
intimate contact between the solid oxidiser and a combustible solid. The smaller the particle 
size, the higher the oxidising capability of the solid. As a consequence, it may happen that large 
particles of a certain solid are considered to be non-hazardous, while small particles of the same 
solid need to be classified into the hazard class of oxidising solids. 

 
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Hence it is very important that oxidising properties for solids are investigated on the substance 
or mixture as it is actually presented (including how it can reasonably be expected to be used, 
see Article 8 (6) of CLP). This is indicated by the Note 2 cited in CLP Annex I, 2.14.2.1. 

Annex I: 2.14.2.1.  

[…] 

Note 2: The test shall be performed on the substance or mixture in its physical form as 
presented. If for example, for the purposes of supply or transport, the same chemical is to 
be presented in a physical form different from that which was tested and which is considered 
likely to materially alter its performance in a classification test, the substance shall also be 
tested in the new form. 

2.14.3.  Relation to other physical hazards 

Oxidising solids that are mixed with combustible materials or reducing agents may have 
explosive properties and should be considered for classification in the hazard class Explosives 
(including the applicable screening procedures), see Chapter 2.1 of this guidance. 

In rare cases, mixtures with oxidising solids may exhibit self-reactive behaviour, see Chapter 
2.8 of this guidance. Expert judgement should be sought in case of doubt. 

The classification procedure and criteria for oxidising substances and mixtures is not applicable 
for organic peroxides. Under DSD organic peroxides were considered to be oxidising substances 
because of the presence of the –O–O– bond. The majority of the organic peroxides do not 
possess oxidising properties; their main hazards are reactivity and flammability. Under CLP 
organic peroxides comprise a separate hazard class (CLP Annex I, 2.15) and they must not be 
considered according to the procedures described for oxidising solids. Organic peroxides were 
classified as oxidising (O; R7) according to the DSD, which was not appropriate since the vast 
majority of them do not exhibit oxidising properties.  

Inorganic oxidising solids are not flammable and therefore do not need to be subject to the 
classification procedures for the hazard classes flammable solids or pyrophoric solids. Also other 
solids that are classified as oxidising solids are normally not flammable, although a few 
exeptions may exist. Expert judgement should be sought in case of doubt. 

2.14.4.  Classification of substances and mixtures as oxidising solids  

2.14.4.1.  Identification of hazard information  

Oxidising solids may cause, or contribute to, the combustion of other material. Although the 
definition in Annex I: 2.14.1, quoted above, states that they generally do this by yielding 
oxygen, halogens can behave in a similar way. Therefore, any substance or mixture containing 
oxygen and/or halogen atoms should in principle be considered for inclusion into the hazard 
categories oxidising solids. This does not necessarily mean that every substance or mixture 
containing oxygen and/or halogen atoms should be subjected to the full testing procedure.  

2.14.4.1.1.  Screening procedures and waiving of testing 

Solids that are classified as explosives should not be subjected to the testing procedures for 
oxidising solids. 

Organic peroxides should be considered for classification within the hazard class organic 
peroxides, see Chapter 2.15 of this guidance. 

Experience in the handling and use of substances or mixtures which shows them to be oxidising 
is an important additional factor in considering classification as oxidising solids. In the event of 

 
 
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divergence between test results and known experience, judgement based on known experience 
should take precedence over test results. 

Before submitting a substance or a mixture to the full test procedure, an evaluation of its 
chemical structure may be very useful as it may prevent unnecessary testing. The person 
applying this procedure should have sufficient experience in testing and in theoretical evaluation 
of hazardous substances and mixtures. The following text provides a guideline for the 
theoretical evaluation of potential oxidising properties on the basis of its composition and 
chemical structure. In case of doubt, the full test must be performed. 

For organic substances or mixtures the classification procedure for this hazard class need not  
be applied if: 

a.  the substance or mixture does not contain oxygen, fluorine or chlorine; or 

b.  the substance or mixture contains oxygen, fluorine or chlorine and these elements 

are chemically bonded only to carbon or hydrogen. 

For inorganic substances or mixtures, the classification procedure for this hazard class need not 
be applied if they do not contain oxygen or halogen. 

On the basis of this theoretical evaluation a distinction can only be made between ‘potentially 
oxidising’ (i.e. further testing required) and ‘non-oxidising’ (i.e. no further testing for this 
hazard class required). It is not possible to assign a hazard category on the basis of a 
theoretical evaluation. 

Any substance or mixture that complies with the above waiving criteria can be safely regarded 
to have no oxidising properties and, hence, need not be tested and need not be regarded as an 
oxidising solid. However, such a substance or mixture may still possess other hazardous 
properties that require classification into another hazard class.  

In case a mixture of an oxidising substance and a non-hazardous inert substance is offered for 
classification, the following should be taken into account: 

• 

•  An inert material by definition does not contribute to the oxidising capability of the 
oxidising substance. Hence, the mixture can never be classified into a more severe 
hazard category. 
If an oxidising substance is mixed with an inert material, the oxidising capability of the 
mixture does not linearly decrease with decreasing content of oxidising substance. The 
relationship is more or less logarithmic and depends on the characteristics of the 
oxidising substance. For instance, a mixture containing 50 % of a strong oxidiser and 50 
% of an inert material may retain 90 % of the oxidising capability of the original 
oxidising component. Non-testing classification of mixtures based solely on test data for 
the original oxidising substance should therefore be done with extreme care and only if 
sufficient experience in testing exists. 

2.14.4.2.  Classification criteria 

The testing procedures for oxidising solids are based on the capability of an oxidising solid to 
enhance the combustion of a combustible material. Therefore, solids that are submitted to 
classification testing are mixed with a combustible material. In principle, dried fibrous cellulose 
is used as a combustible material. The mixture of the potentially oxidising solid and cellulose is 
then ignited and its behaviour is observed and compared to the behaviour of reference material 
mixtures. 

For solids the mixture with cellulose is ignited at atmospheric conditions and the time necessary 
for the combustion reaction to consume the mixture is recorded. The faster the combustion 
rate, the stronger the oxidising capability of the solid tested. 

 
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Annex I: 2.14.2.1. An oxidising solid shall be classified in one of the three categories for this 
class using test O.1 in Part III, sub-section 34.4.1 or test O.3 in Part III, sub-section 34.4 3 of 
the UN RTDG, Manual of Tests and Criteria, in accordance with Table 2.14.1: 

Table 2.14.1 

Criteria for oxidising solids 

Category  Criteria using test O.1  

Criteria using test O.3 

1 

2 

3 

Any substance or mixture which, in the 
4:1 or 1:1 sample-to-cellulose ratio (by 
mass) tested, exhibits a mean burning 
time less than the mean burning time of 
a 3:2 mixture, (by mass), of potassium 
bromate and cellulose. 

Any substance or mixture which, in the 
4:1 or 1:1 sample-to-cellulose ratio (by 
mass) tested, exhibits a mean burning 
rate greater than the mean burning rate 
of a 3:1 mixture (by mass) of calcium 
peroxide and cellulose. 

Any substance or mixture which, in the 
4:1 or 1:1 sample-to-cellulose ratio (by 
mass) tested, exhibits a mean burning 
time equal to or less than the mean 
burning time of a 2:3 mixture (by mass) 
of potassium bromate and the criteria 
for Category 1 are not met. 

Any substance or mixture which, in the 
4:1 or 1:1 sample-to-cellulose ratio (by 
mass) tested, exhibits a mean burning 
rate equal to or greater than the mean 
burning rate of a 1:1 mixture (by mass) 
of calcium peroxide and cellulose and 
the criteria for Category 1 are not met. 

Any substance or mixture which, in the 
4:1 or 1:1 sample-to-cellulose ratio (by 
mass) tested, exhibits a mean burning 
time equal to or less than the mean 
burning time of a 3:7 mixture (by mass) 
of potassium bromate and cellulose and 
the criteria for Categories 1 and 2 are 
not met. 

Any substance or mixture which, in the 
4:1 or 1:1 sample-to-cellulose ratio (by 
mass) tested, exhibits a mean burning 
rate equal to or greater than the mean 
burning rate of a 1:2 mixture (by mass) 
of calcium peroxide and cellulose and 
the criteria for Categories 1 and 2 are 
not met. 

Note 1  
Some oxidising solids also present explosion hazards under certain conditions (when stored in 
large quantities). Some types of ammonium nitrate may give rise to an explosion hazard 
under extreme conditions and the 'Resistance to detonation test' (IMSBC Code (International 
Maritime Solid Bulk Cargoes Code, IMO), Appendix 2, Section 5) can be used to assess this 
hazard. Appropriate information shall be made in the SDS. 

Note 1 may also apply to other oxidising ammonium salts. Experience indicates that the 
conditions required for ammonium nitrate to present an explosion hazard involve a combination 
of factors, such as storage in large volumes (multiple tonnes) and either contamination (e.g. 
with metals, acids, organics) or excessive heat (e.g. under conditions of fire). The resistance to 
detonation (RTD) test is extensively described in Regulation (EC) No 2003/2003 for ammonium 
nitrate. 

For additional information regarding the use of non-testing data see Section 2.14.4.3 below and 
Urben, 2007 (see Section 2.14.7). 

 
 
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2.14.4.3.  Testing and evaluation of hazard information 

The test methods51 for oxidising solids are designed to give a final decision regarding their 
classification. It should be recalled that experience in the handling and use of substances or 
mixtures, besides testing, is an important additional factor in considering classification in this 
hazard class. 

2.14.4.4.  Decision logic  

Classification of oxidising solids is done according to decision logic 2.14 as included in the GHS. 

  NOTE: The person responsible for the classification of oxidising solids should be 

experienced in this field and be familiar with the criteria for classification. 

51 As from December 2012 an alternative test method for oxidising solids, Test O.3, has been included in 
the UN MTC (see document ST/SG/AC.10/40/Add.2). Test O.3 is an improved version of Test O.1 using a 
different reference substance and gravimetric measurements of the burning rate. Reference to Test O.3 
has been included in the 5th revised edition of the GHS. 

 
 
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Figure 2.13   Decision logic for oxidising solids (Decision logic 2.14 of GHS)  

The substance/mixture is a solid 

Does it, in the 4:1 or 1:1 sample-to-cellulose, by mass, test ignite 
or burn? 

No 

Not 
classified 

Yes 

Does it, in the 4:1 or 1:1 sample-to-cellulose, by mass, test exhibit 
a mean burning time ≤ the mean burning time of a 3:7 mixture, by 
mass, by potassium bromate and cellulose? 

Or 

a mean burning rate greater than or equal to the mean burning 
rate of a 1:2 mixture, by mass, of a calcium peroxide and 
cellulose? 

Yes 

No 

Not 
classified 

Does it, in the 4:1 or 1:1 sample-to-cellulose, by mass, test exhibit 
a mean burning time ≤ the mean burning time of a 2:3 mixture, by 
mass, by potassium bromate and cellulose? 

Or 

a mean burning rate greater than or equal to the mean burning 
rate of a 1:1 mixture, by mass, of a calcium peroxide and 
cellulose? 

Category 3 

No 

Warning 

Yes 

Does it, in the 4:1 or 1:1 sample-to-cellulose, by mass, test exhibit 
a mean burning time < the mean burning time of a 3:2 mixture, by 
mass, by potassium bromate and cellulose? 

No 

a mean burning rate greater than the mean burning rate of a 3:1 
mixture, by mass, of a calcium peroxide and cellulose? 

Or 

Yes 

Category 2 

Dangerd 

Category 1 

Danger 

 
 
 
 
 
 
  
 
  
 
  
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2.14.4.5.  Hazard communication for oxidising solids 

2.14.4.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

The pictograms and hazard statements are designed to indicate that oxidising substances and 
mixtures may cause or contribute to fire or explosion and therefore in principle should be 
separated from combustible materials. 

Annex I: Table 2.14.2 

GHS Pictograms 

Label elements for oxidising solids 

Category 1 

Category 2 

Category 3 

Signal Word 

Danger 

Danger 

Warning 

Hazard Statement 

H271: May cause fire or 
explosion; strong oxidiser 

H272: May intensify 
fire; oxidiser 

H272: May intensify 
fire; oxidiser 

Precautionary 
Statement Prevention 

P210 
P220 
P280 
P283 

Precautionary 
Statement Response 

P306 + P360 
P371 + P380 + P375 
P370 + P378 

Precautionary 
Statement Storage 

Precautionary 
Statement Disposal 

P420 

P501 

P210 
P220 
P280 

P210 
P220 
P280 

P370 + P378 

P370 + P378 

P501 

P501 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

2.14.5.  Relation to transport classification 

Division 5.1 within Class 5 of the UN RTDG Model Regulations covers oxidising liquids and 
oxidising solids, using the same tests and criteria as the CLP. Therefore, a solid substance or 
mixture classified as Division 5.1 (sometimes referred to as Class 5.1) according to any of the 
modal transport regulations (ADR, RID, ADN and IMDG Code, ICAO TI) is normally also 
classified as an oxidising solid according to CLP. Packing Groups I, II and III of the transport 
regulations correspond directly to Categories 1, 2 and 3 of CLP, respectively. See Annex VII for 
additional information on transport classification in relation to CLP classification. 

 
 
 
 
 
 
 
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2.14.6.  Examples of classification for oxidising solids 

2.14.6.1.  Examples of substances and mixtures fulfilling the classification 

criteria  

The list of substances and mixtures fulfilling the criteria for classification is only presented for 
information purposes. This list is not exhaustive. For examples of results see section 34.4.1.5 of 
UN-MTC. 

•  Calcium nitrate, anhydrous 

•  Chromium trioxide 

•  Potassium nitrite 

•  Potassium perchlorate 

•  Potassium permanganate 

•  Sodium chlorate 

•  Sodium nitrite 

•  Sodium nitrate 

•  Strontium nitrate, anhydrous 

2.14.6.2.  Examples of substances and mixtures not fulfilling the classification 

criteria  

•  Calcium nitrate, tetrahydrate 

•  Cobalt nitrate, hexahydrate 

2.14.7.  Reference 

Urben, Peter G. (2007). Bretherick's Handbook of Reactive Chemical Hazards, Volumes 1-2 (7th 
Edition). Elsevier. 

 
 
 
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2.15.  ORGANIC PEROXIDES 

2.15.1.  Introduction 

The criteria for ‘Organic peroxides’ are found in Annex I, Section 2.15 of CLP and are identical to 
those in Chapter 2.15 of GHS.  

The hazard class organic peroxides is unique in the respect that it is the only category to which 
chemicals are assigned on the basis of their chemical structure. Organic peroxides cannot be 
seen as an ‘intrinsic property’; it is a family of chemical substances and mixtures which may 
have various properties. However, the type of peroxide is determined by testing. 

2.15.2.  Definitions and general considerations for the classification of organic 

peroxides  

In CLP, the following definition is given for organic peroxides. 

Annex I: 2.15.1.     Definition  

Organic peroxides means liquid or solid organic substances which contain the bivalent -O-O- 
structure and may be considered derivatives of hydrogen peroxide, where one or both of the 
hydrogen atoms have been replaced by organic radicals. The term organic peroxide includes 
organic peroxide mixtures (formulations) containing at least one organic peroxide. Organic 
peroxides are thermally unstable substances or mixtures, which can undergo exothermic self-
accelerating decomposition. In addition, they can have one or more of the following 
properties: 

(i) be liable to explosive decomposition; 

(ii) burn rapidly; 

(iii) be sensitive to impact or friction; 

(iv) react dangerously with other substances. 

2.15.1.2. An organic peroxide is regarded as possessing explosive properties when in 
laboratory testing the mixture (formulation) is liable to detonate, to deflagrate rapidly or to 
show a violent effect when heated under confinement. 

2.15.3.  Relation to other physical hazards 

In addition to the definition (CLP Annex I, 2.15.1), organic peroxides may: 

a.  be flammable; 

b.  emit flammable gas when heated. 

In general, organic peroxides do not have or have only weak oxidising properties. 

The additional (subsidiary) labelling, as indicated in the list of classified organic peroxides 
included in the UN RTDG Model Regulations, Section 2.5.3.2.4, represents the additional 
hazardous properties.  

Neither the burning properties nor the sensitivity to impact and friction form part of the 
classification procedure for organic peroxides in CLP. However, these properties may be of 
importance for the safe handling of organic peroxides (see Section 2.15.4.3.2, additional 
testing). 

In addition, the following should be noted: 

 
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The explosive properties do not have to be determined according to the CLP Annex I, Chapter 
2.1, because explosive properties are incorporated in the decision logic for organic peroxides. 
Note that organic peroxides may have explosive properties when handled under higher 
confinement.   

Flammable properties 

The hazard statement for flammable properties for liquid organic peroxides should be based on 
the appropriate category for flammable liquids, as long as the flash point is relevant, (see 
Section 2.15.4.3.2). The translation table in Annex VII to CLP can be used for this. 

2.15.4.  Classification of substances and mixtures as organic peroxides  

2.15.4.1.  Identification of hazard information  

The classification of an organic peroxide in one of the seven categories ‘Types A to G’ is 
dependent on its detonation, deflagration and thermal explosion properties, its response to 
heating under confinement, its explosive power and the concentration and the type of diluent 
added to desensitize the organic peroxide. Specifications of acceptable diluents that can be used 
safely are given in the UN RTDG Model Regulations, 2.5.3.5. The classification of an organic 
peroxide as Type A, B or C is dependent on the type of packaging in which the organic peroxide 
is tested as it affects the degree of confinement to which the organic peroxide is subjected. This 
has to be considered when handling the organic peroxide; stronger packaging may result in 
more violent reactions when the organic peroxide decomposes. This is why it is important that 
storage and transport is done in packaging, allowed for the type of organic peroxide, that 
conforms the requirements of the UN-packaging or IBC instruction (P520/IBC520) or tank 
instruction (T23). 

The traditional aspects of explosive properties, such as detonation, deflagration and thermal 
explosion, are incorporated in the decision logic of CLP Figure 2.15.1. Consequently, explosive 
property determination as prescribed for the hazard class ‘explosives’ needs not to be 
conducted for organic peroxides. 

A list of currently classified organic peroxides is included in the UN RTDG Model regulations, 
Section 2.5.3.2.4. 

2.15.4.2.  Classification criteria 

In CLP, organic peroxides are not classified as oxidisers but they are a distinct hazard class. 

Annex I: 2.15.2.1. Any organic peroxide shall be considered for classification in this class, 
unless it contains: 

a) not more than 1,0 % available oxygen from the organic peroxides when containing not 

more than 1,0 % hydrogen peroxide; or 

b) not more than 0,5% available oxygen from the organic peroxides when containing more 

than 1,0 % but not more than 7,0 % hydrogen peroxide. 

[…] 

In CLP decision logic Annex I, Figure 2.15.1, classification of organic peroxides is based on 
performance based testing both small scale tests and, where necessary, some larger scale test 
with the organic peroxide in its packaging. The concept of ‘intrinsic properties’ is, therefore, not 
applicable to this hazard class. 

Organic peroxides are classified into one of the seven categories of ‘Types A to G’ according to 
the classification criteria of CLP. The classification principles are given in decision logic Figure 

 
 
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2.15.1 of CLP and the Test Series A to H, as described in the Part II of the UN-MTC, should be 
performed.  

Annex I: 2.15.2.2. Organic peroxides shall be classified in one of the seven categories of 
‘Types A to G’ for this class, according to the following principles: 

(a) any organic peroxide which, as packaged, can detonate or deflagrate rapidly shall be 

defined as organic peroxide TYPE A; 

(b) any organic peroxide possessing explosive properties and which, as packaged, neither 
detonates nor deflagrates rapidly, but is liable to undergo a thermal explosion in that 
package shall be defined as organic peroxide TYPE B; 

(c) any organic peroxide possessing explosive properties when the substance or mixture as 
packaged cannot detonate or deflagrate rapidly or undergo a thermal explosion shall be 
defined as organic peroxide TYPE C; 

(d) any organic peroxide which in laboratory testing: 

(i) detonates partially, does not deflagrate rapidly and shows no violent effect when 

heated under confinement; or 

(ii) does not detonate at all, deflagrates slowly and shows no violent effect when 

heated under confinement; or 

(iii) does not detonate or deflagrate at all and shows a medium effect when heated 

under confinement; 

shall be defined as organic peroxide TYPE D; 

(e) any organic peroxide which, in laboratory testing, neither detonates nor deflagrates at all 

and shows low or no effect when heated under confinement shall be defined as organic 
peroxide TYPE E; 

(f) any organic peroxide which, in laboratory testing, neither detonates in the cavitated state 

nor deflagrates at all and shows only a low or no effect when heated under confinement as 
well as low or no explosive power shall be defined as organic peroxide TYPE F; 

(g) any organic peroxide which, in laboratory testing, neither detonates in the cavitated state 

nor deflagrates at all and shows no effect when heated under confinement nor any 
explosive power, provided that it is thermally stable, i.e. the SADT is 60 oC or higher for a 
50 kg package(1), and, for liquid mixtures, a diluent having a boiling point of not less than 
150 oC is used for desensitisation, shall be defined as organic peroxide TYPE G. If the 
organic peroxide is not thermally stable or a diluent having a boiling point less than 150 oC 
is used for desensitisation, the organic peroxide shall be defined as organic peroxide 
TYPE F. 

Where the test is conducted in the package form and the packaging is changed, a further test 
shall be conducted where it is considered that the change in packaging will affect the outcome 
of the test. 

(1) See UN RTDG, Manual of Test and Criteria, sub-sections 28.1, 28.2, 28.3 and Table 28.3. 

A list of currently classified organic peroxides is included in the UN RTDG Model Regulations, 
Section 2.5.3.2.4. 

 
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2.15.4.3.  Testing and evaluation of hazard information 

2.15.4.3.1.  Thermal stability tests and temperature control 

In addition to the classification tests given in decision logic Figure 2.15.1 of CLP, the thermal 
stability of the organic peroxide has to be assessed in order to determine the SADT. For the 
determination of the SADT, the testing method in UN-MTC, Part II, Section 28, may be used. 

The SADT is defined as the lowest temperature at which self-accelerating decomposition of an 
organic peroxide may occur in the packaging as used in transport, handling and storage. The 
SADT is a measure of the combined effect of the ambient temperature, decomposition kinetics, 
package size and the heat transfer properties of the organic peroxide and its packaging. 

There is no relation between the SADT of an organic peroxide and its classification in one of the 
seven categories ‘Types A to G’. The SADT is used to derive safe handling, storage and 
transport temperatures (control temperature) and alarm temperature (emergency 
temperature).   

Depending on its SADT an organic peroxide needs temperature control and the rules as given in 
CLP Annex I, 2.15.2.3, consist of the following two elements: 

4.  Criteria for temperature control: 

The following organic peroxides need to be subjected to temperature control: 

a.  Organic peroxide types B and C with a SADT ≤ 50 ° C; 

b.  Organic peroxide type D showing a medium effect when heated under confinement 

with a SADT ≤ 50 ° C or showing a low or no effect when heated under 
confinement with a SADT ≤ 45 ° C; and 

c.  Organic peroxide types E and F with a SADT ≤ 45 ° C. 

5.  Derivation of control and emergency temperatures: 

Type of receptacle 

SADT * 

Control temperature  Emergency 

temperature 

Single packagings and 
IBC’s 

20 °C or less 

20 °C below SADT 

10 °C below SADT 

over 20 °C to 35 °C 

15 °C below SADT 

10 °C below SADT 

over 35 °C 

10 °C below SADT 

5 °C below SADT 

Tanks 

< 50 °C 

10 °C below SADT 

5 °C below SADT 

* i.e. the SADT of the organic peroxide as packaged for transport, handling and storage 

It should be emphasized that the SADT is dependent on the nature of the organic peroxide 
itself, together with the volume and heat-loss characteristics of the packaging or vessel in which 
the organic peroxide is handled. The temperature at which self-accelerating decomposition 
occurs falls: 

•  as the size of the packaging or vessel increases; and 

•  with increasing efficiency of the insulation on the package or vessel.   

The SADT is only valid for the organic peroxide as tested and when handled properly. Mixing the 
organic peroxide with other chemicals, or contact with incompatible materials (including 
incompatible packaging or vessel material) may reduce the thermal stability due to catalytic 
decomposition, and lower the SADT. This may increase the risk of decomposition and has to be 
avoided. 

 
 
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2.15.4.3.2.  Additional considerations and testing 

Explosive properties 

The sensitivity of organic peroxides to impact (solids and liquids) and friction (solids only) may 
be of importance for the safe handling of the organic peroxide if they have pronounced 
explosive properties (e.g. they are liable to detonate, to deflagrate rapidly or show a violent 
effect when heated under confinement). Test methods to determine these properties are 
described in Test Series 3 of the UN-MTC (see Test 3 (a) (ii) and 3 (b) (i)). This information on 
the mechanical sensitivity should be included in the SDS. 

Burning properties 

In some national storage guidelines the burning rate is commonly used for classification for the 
purposes of storage and consequential storage requirements. Test methods are incorporated in 
these national storage regulations. 

Flash point 

The flash point for liquid organic peroxides is only relevant in the temperature range where the 
organic peroxide is thermally stable. Above the SADT of the organic peroxide determination of 
the flash point is not relevant because decomposition products are evolved. 

  NOTE: In case a flash point determination seems reasonable (expected flash point below 
the SADT) a test method using small amount of sample is recommended. In case the 
organic peroxide is diluted or dissolved, the diluent may determine the flash point. 

Auto-ignition temperature 

The determination of the auto ignition temperature is not relevant for organic peroxides. 
Available test methods are for non-decomposing vapour phases but the vapours of organic 
peroxides decompose during execution of the test and auto ignition of these organic peroxide 
vapours can never be excluded. This information should be included in the SDS.  

Self-ignition temperature 

Also the determination of the self-ignition temperature (applicable for solids) is not relevant. 
The thermal stability of organic peroxides is quantitatively given by the SADT.  

Control and Emergency temperatures 

The Control and Emergency temperatures are based on the SADT as in most cases determined 
by UN Test H.4. The Dewar vessel used in the UN Test H.4 is supposed to be representative for 
the organic peroxide handled in packages. For handling the organic peroxide in larger quantities 
(IBCs/tanks/vessels etc.) and/or in (thermally) insulated containers, the SADT has to be 
determined for that quantity with that degree of insulation. From that SADT the Control and 
Emergency temperatures can be derived (see also Section 2.15.4.3.1). 

2.15.4.3.3.  Additional classification considerations 

Currently the following properties are not incorporated in the classification of organic peroxides 
under the CLP: 

•  mechanical sensitivity i.e. impact and friction sensitivity (for handling purposes); 

•  burning properties (for storage purposes); 

• 

flash point for liquids; and 

•  burning rate for solids. 

Furthermore: 

 
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Annex I: 2.15.4.2. Mixtures of already classified organic peroxides may be classified as the 
same type of organic peroxide as that of the most dangerous component. However, as two 
stable components can form a thermally less stable mixture, the SADT of the mixture shall 
be determined. 

Note: The sum of the individual parts can be more hazardous than the individual 
components. 

Formulated commercial organic peroxides are classified according to their SADT. 

2.15.4.4.  Decision logic  

The decision logic for organic peroxides is applicable according to CLP.  

  NOTE: The person responsible for the classification of organic peroxides should be 

experienced in this field and be familiar with the criteria for classification. 

 
 
 
 
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Figure 2.14   Decision logic 2.15 for organic peroxides 

 
 
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2.15.5.  Hazard communication for organic peroxides 

2.15.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

According to CLP the following label elements must be used for organic peroxide meeting the 
criteria for this hazard class: 

Annex I: Table 2.15.1 

Label elements for organic peroxides 

Classification  Type A 

Type B 

Type C & D 

Type E & F 

Type G 

GHS 
pictograms 

Signal Word 

Danger 

Danger 

Danger 

Warning 

Hazard 
Statement 

H240: 
Heating may 
cause an 
explosion 

H241: 
Heating may 
cause a fire 
or explosion 

H242: 
Heating may 
cause a fire 

H242: 
Heating may 
cause a fire 

Precautionary 
statement 

Prevention 

P210 

P234 

P235 

P240 

P280 

P210 

P234 

P235 

P240 

P280 

P210 

P234 

P235 

P240 

P280 

P210 

P234 

P235 

P240 

P280 

Precautionary 
statement 

P370 + P372 
+ 

P370 + P380 
+ 

P370 + P378  P370 + P378 

There are no 
label elements 
allocated to 
this hazard 
category 

Response  

P380 + P373 

Precautionary 
statement 

Storage 

Precautionary 
statement 

Disposal 

P403 

P410 

P411 

P420 

P501 

P375[+ 
P378]1 

P403 

P410 

P411 

P420 

P501 

P403 

P410 

P411 

P420 

P501 

P403 

P410 

P411 

P420 

P501 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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1 See introduction to Annex I for details on the use of square brackets. 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

2.15.5.2.  Additional labelling provisions for organic peroxides 

Additional hazardous properties, resulting in additional (subsidiary) labelling, are indicated in 
the list of classified organic peroxides included in the UN RTDG Model Regulations, section 
2.5.3.2.4. 

2.15.6.  Relation to transport classification  

Division 5.2 within Class 5 of the UN RTDG Model Regulations covers organic peroxides. A list of 
currently classified organic peroxides is included in the UN RTDG Model Regulations, Section 
2.5.3.2.4. This table includes organic peroxides Type B - Type F (and some formulations Type 
G, so-called exempted organic peroxides).  

An exceptional case in this respect is a peroxyacetic acid formulation, as currently classified in 
the UN RTDG Model Regulations under UN 3149, with the following description: HYDROGEN 
PEROXIDE AND PEROXYACETIC ACID MIXTURE with acid(s), water and not more than 5 % 
peroxyacetic acid, STABILISED. In the classification procedure for organic peroxides, see 
decision logic in Section 2.15.4.4, this formulation will be assigned to organic peroxide Type G, 
and consequently no label elements are allocated. In view of the above, this formulation can be 
classified, also in accordance with CLP, as an Oxidising liquid, Category 2. See Annex VII for 
additional information on transport classification in relation to CLP classification. 

2.15.7.  Examples of classification for organic peroxides 

2.15.7.1.  Examples of substances and mixtures fulfilling the classification 

criteria 

Substance to be classified: Example Peroxide 

Molecular formula: n.a. 

According to CLP Annex I, Section 2.15.2.1, the substance has an active oxygen content of 7.40 
% and thus has to be considered for classification in the hazard class organic peroxides.  

Test results and classification according to CLP decision logic 2.15.1 for organic peroxides and 
the UN-MTC, Part II, is as follows: 

CLASSIFICATION TEST RESULTS 

1. Name of the organic peroxide:  

Example Peroxide 

2. General data 

2.1. Composition: 

Example Peroxide, technically pure (97 %) 

2.2. Molecular formula: 

2.3. Active oxygen content:  

2.4. Physical form:   

2.5. Colour:   

2.6. Density (apparent): 

n.a. 

7.18 % 

liquid 

colourless 

900 kg/m3 

 
 
 
 
 
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CLASSIFICATION TEST RESULTS 

3. Detonation (test series A) 

Box 1 of the decision logic:   

Does the peroxide propagate a detonation? 

3.1. Method: 

UN Test A.1: BAM 50/60 steel tube test 

3.2. Sample conditions: 

peroxide assay 97 % 

3.3. Observations:   

fragmented part of the tube: 18 cm 

3.4. Result:   

3.6. Exit: 

4. Deflagration (test series C) 

No 

1.3 

Box 5 of the decision logic:   

Can the peroxide propagate a deflagration? 

4.1. Method 1: 

Time/pressure test (test C.1) 

4.1.1. Sample conditions:  

ambient temperature 

4.1.2. Observations: 

4.1.3. Result: 

4.2. Method 2: 

4000 ms   

Yes, slowly 

Deflagration test (test C.2) 

4.2.1. Sample conditions:  

temperature: 25 °C 

4.2.2. Observations: 

deflagration rate: 0.74 mm/s 

4.2.3. Result: 

4.3. Final result: 

4.4. Exit: 

Yes, slowly 

Yes, slowly 

5.2 

5. Heating under confinement (test series E) 

Box 8 of the decision logic:   

What is the effect of heating it under confinement? 

5.1. Method 1: 

Koenen test (test E.1) 

5.1.1. Sample conditions: 

- 

5.1.2. Observations: 

limiting diameter: 2.0 mm 

5.1.3. Result: 

5.2. Method 2: 

fragmentation type ‘F’ 

Violent 

Dutch pressure vessel test 

(test E.2) 

5.2.1. Sample conditions:  

- 

5.2.2. Observations: 

limiting diameter: 6.0 mm (with 10 g) 

 
 
 
 
 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
 
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CLASSIFICATION TEST RESULTS 

5.2.3. Result: 

5.3. Final result: 

5.4. Exit: 

6. Explosion test in package (test series G) 

Medium 

Violent 

8.1 

Box 10 of the decision logic:  

Can it explode as packaged? 

6.1. Method: 

Thermal explosion test in package (test G.1) 

6.2. Sample conditions: 

30 litre packaging, 

6.3. Observations:    

no fragmentation (N.F.) 

6.4. Result:   

6.5. Exit: 

No 

10.2 

7. Thermal stability (outside of the decision logic) 

7.1. Method: 

Heat accumulation storage test (test H.4) 

7.2. Sample conditions: 

mass 380 g. Half life time of cooling of Dewar 
vessel with400 ml DMP: 

10.0 hrs. (representing substance in package)   

7.3. Observations:  self 

accelerating decomposition at 35 °C 

7.4. Result:   

8. General remarks: 

9. Final classification 

Hazard class: 

Label:  

Signal word:   

no self accelerating decomposition at 30 °C 

SADT 35 °C 

The decision logic is given in Figure x52 

Organic peroxide, Type C, liquid, temperature 
controlled 

Flame (GHS02) 

Danger 

Hazard statement:   

H242: Heating may cause a fire 

Temperature control: 

Needed based on SADT (35 °C, in package) 

Control temperature*: 

20 °C (in package) 

Emergency temperature*: 

25 °C (in package) 

*see UN-MTC, table 28.2. 

52 Not attached to this example. 

 
 
 
 
 
 
 
 
  
 
 
 
 
 
 
 
 
 
 
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2.15.7.2.  Additional remarks 

Explosive properties 

As shown in Section 2.15.7.1 a substance and a mixture may have explosive properties when 
handled under greater confinement and where the packaging in which it was tested in UN Test 
G.1 (see point 6 of classification test results above) is changed. Such information should be 
given in the SDS.  

The example in Section 2.15.7.1 shows a violent effect when heated under confinement (see 
point 5.3 of the above results). Consequently, also the impact sensitivity according to UN Test 
series 3, test 3 (a) (ii), BAM Fallhammer should be determined. For this example it amounts to 
20 J. Such information should be given in the SDS. 

Burning properties 

For the example in Section 2.15.7.1 the burning properties as determined by the test method 
described in the storage guidelines, currently in place in France, Germany, Netherlands and 
Sweden, is 7.0 kg/min/m². Based on this figure and the classification as organic peroxide type 
C, the storage classification can be assigned in those countries.  

Flash point 

The example substance thermally decomposes before the temperature at which the vapour can 
be ignited is reached (see Section 2.15.4.3.2) and consequently a flash point cannot be 
determined. 

 
 
 
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2.16.  CORROSIVE TO METALS  

2.16.1.  Introduction 

The criteria for ‘Corrosive to metals’ are found in Annex I, Section 2.16 of CLP and are identical 
to those in Chapter 2.16 of GHS.  

The hazard class corrosive to metals is a physico-chemical property that is new in the EU 
classification scheme and appears for the first time in CLP. So far, only the health hazard 
corrosivity to skin was considered in the classification scheme. To some extent, both properties 
relate to each other and, in the context of transport of dangerous goods, have been considered 
for classification in class 8, despite the different nature of the hazard (material damage versus 
living tissue damage).  

A substance or a mixture that is corrosive to metal under normal conditions is a substance or a 
mixture liable to undergo an irreversible electrochemical reaction with metals that leads to 
significant damage or, in some cases, even to full destruction of the metallic components. The 
corrosive to metal property is a quite complex property, since it is a substance (or mixture) 
related as well as a material (metal) related property. This means a corrosive substance or 
mixture leads to corroded material (metal), according to a number of external conditions. From 
the material side, many types of corrosion processes may occur, according to configurations, 
liquid or fluid media inducing the corrosion process, nature of metal, potential passivation 
occurring by oxide formation during corrosion.  

From the substance or mixture side, many parameters may influence the corrosion properties of 
a substance or mixture, such as the nature of the chemical or the pH. From an electochemistry 
point of view, corrosion conditions are often studied using Pourbaix diagrams, which plot the 
electrochemical potential (in Volt) that develops according to electrical charges transfer versus 
the pH-value. Such a diagram is shown for the case of iron and applies only for carbon steel 
corrosion (Jones, 1996). 

Figure 2.15   Potential pH (also called Pourbaix) diagram for iron in water at 25 °C, indicating 
stable form of the Fe element and implicitly, corrosion domains 

For the purposes of CLP, corrosion to metal will only be considered, by pure convention, for 
substances and mixtures that are liable to attack carbon steel or aluminium, two of the most 
common metals that may come in contact with chemical substances (containment material, 
reactor material). The classification scheme applied here must not be considered as a material 

 
 
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(metal) classification method for metals regarding resistance to corrosion. By no means steel or 
aluminium specimens that are treated to resist to corrosion, must be selected for testing. 

2.16.2.  Definitions and general considerations for the classification of 

substances and mixtures corrosive to metals 

CLP comprises the following definition for substances and mixtures that are corrosive to metal. 

Annex I: 2.16.1.     Definition 

A substance or a mixture that is corrosive to metals means a substance or a mixture which by 
chemical action will materially damage, or even destroy, metals. 

2.16.3.  Relation to other physical hazards 

There is no direct relation to other physical hazards.  

2.16.4.  Classification of substances and mixtures as corrosive to metals 

2.16.4.1.  Identification of hazard information 

Importance of the physical state of the test substance or mixture 

There is no reference in the definition (CLP Annex I, 2.16.1) to the physical state of the 
substances or mixtures that needs consideration for potential classification in this hazard class. 
According to the test method to be employed for considering classification under this hazard 
class, we may state at least that gases are out of the scope of the corrosive to metal hazard 
class. Neither the corrosivity of gases nor the formation of corrosive gases is currently covered 
by CLP classes and are therefore not applicable here. 

According to the classification criteria only substances and mixtures for which the application of 
the UN Test C.1 (described in part III, Section 37.4.1.1 of the UN-MTC) is relevant and needs to 
be considered. Application of classification criteria in the UN-MTC, Section 37.4 excludes solids, 
while ‘liquids and solids that may become liquids (during transport)’, have to be considered for 
such a classification. 

The wording ‘solids that may become liquids’ was developed for UN RTDG Model Regulations 
classification purposes, and needs further explanation. Solids may become liquids by melting 
(due to increase in temperature). Solids having a melting point lower than 55 °C (which is the 
test temperature required in UN Test C.1) must then be taken into consideration. The other 
physical way to transform a solid into liquid is by dissolution in water or another solvent. 
Classification of solid substances that may become liquids by dissolution is subject to further 
expert judgement, and may need adaptation of the classification criteria or test protocol (see 
Section 2.16.4.4.2). Interaction with liquids may come from air moisture or unintentional 
contact with water. Other solvent traces may result from the extraction process during 
manufacturing and these may induce corrosion in practice. 

Substances and mixtures in a liquid state must be tested without any modification before 
testing. For other cases (solids that may become liquids), appropriate testing procedures 
require further work by the Committees of experts in charge of developing and updating the 
GHS at UN level. It needs to be further specified how such substances or mixtures must be 
prepared (transformed into liquids) to be able to determine their corrosivity to metals. As an 
example, it is thought that the quantity of solvent (water or any other solvent) to liquefy the 
test substance before testing would greatly influence results of the UN Test C.1 test and may 
not necessarily represent the real life situation of a product during transport, handling or use.  

Non-testing data 

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•  melting points for solids; 

• 

chemical nature of the substances and mixtures under evaluation (e.g. strong acids);  

•  pH values (liquids). 

See also IR & CSA, Chapter R.7a: Endpoint specific guidance, Section R.7.1.2 (Melting 
point/freezing point). 

Literature may also provide information on widely used substances and liquids ‘compatibility 
tables’, taking account of the corrosiveness of the products that may serve to decide whether 
testing must be conducted before assigning the corrosive to metals hazard class, on basis of 
expert judgement. 

The following substances and mixtures should be considered for classification in this class: 

• 

• 

• 

substances and mixtures having acidic or basic functional groups; 

substances or mixtures containing halogen; 

substances able to form complexes with metals and mixtures containing such 
substances.  

2.16.4.2.  Screening procedures and waiving of testing 

Experience may have proven the corrosivity of given substances and mixtures. In such case no 
more testing is needed (see examples in Section 2.16.7).  

Generally extreme pH-values point to a higher likelihood that the substance or mixture is 
corrosive. However, it cannot lead to immediate classification in the hazard class corrosive to 
metals. As a proof of that, Figure 2.15 shows that immunity zones (where steel does not 
corrode) still exist on the full spectrum of pH values as far as carbon steel is concerned. 

Corrosivity is so complex that the evaluation of a mixture cannot be extrapolated from similar 
behaviour of constituents of a mixture. However, if one significant component of a mixture is 
corrosive to metals the mixture is likely to be corrosive to metals as well. Testing the actual 
mixture is therefore highly recommended. As already mentioned, solids are currently difficult to 
test according to the current CLP requirements, as the UN Test C.1 was designed for liquids. 

Where an initial test on either steel or aluminium indicates the substance or mixture being 
tested is corrosive, the follow up test on the other metal is not required. 

2.16.4.3.  Classification criteria 

Substances and mixtures of hazard class corrosive to metals are classified in a single hazard 
category on the basis of the outcome of the UN Test C.1 (UN-MTC, Part III, Section 37, 
paragraph 37.4). 

Annex I: Table 2.16.1 

Criteria for substances and mixtures corrosive to metals 

Category 

Criteria 

1 

Corrosion rate on either steel or aluminium surfaces exceeding 6,25 mm per 
year at a test temperature of 55 oC when tested on both materials. 

 
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2.16.4.4.  Testing and evaluation of hazard information 

2.16.4.4.1.  General considerations 

It is important to point out that the criteria of corrosion rate will never be applied in an absolute 
way, but by extrapolating the measured rate of corrosion over the test period to the annual 
assumed correlating corrosion rate. This exercise has to take account of the fact that the 
corrosion rate is not necessarily constant over time. Expert judgement may be required to 
consolidate the optimum test duration and to ascertain test results. However, the possibility of 
increasing the testing period from minimum one week to four weeks as well as the use of two 
different metals in the UN Test C.1 act as barriers against erroneous classification. 

Whatever the result of the classification may be, the classification as corrosive to metals relates 
to steel and/or aluminium only and does not provide information with regard to the corrosivity 
potential to other metals than those tested. 

Two types of corrosion phenomena need to be distinguished for classification of substances and 
mixtures in this hazard class, although not reported in CLP: the uniform corrosion attack and 
the localised corrosion (e.g. pitting corrosion, shallow pit corrosion).  

Table 2.2 (Section 37.4.1.4.1 of the UN- MTC) translates the corresponding minimum mass loss 
rates leading to classify the test substance or mixture as corrosive to metals for standard metal 
specimens (2 mm of thickness), according to time of exposure, for reasons of uniform corrosion 
process. In case of use of metal plates of a thickness that differs from the specified 2 mm (see 
comments in Section 2.4.2), the values in Table 2.2 and Table 2.3 need adjustments due to the 
fact that the corrosion process depends on the surface of specimen. 

 
 
 
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Table 2.2  Minimum mass loss of specimens after different exposure times (corresponding to 
the criterion of 6.25 mm/year) 

Exposure time 

Mass loss 

7 days 

14 days 

21 days 

28 days 

13.5 % 

26.5 % 

39.2 % 

51.5 % 

Table 2.3 (Section 37.4.1.4.2 of the UN-MTC) indicates the criteria leading to classification of 
the test substance or mixture as corrosive to metals for standard metal specimens, according to 
time of exposure, for reasons of localised corrosion process. 

Table 2.3  Minimum intrusion depths after exposure times (corresponding to the criterion of 
localized corrosion of 6.25 mm/year) 

Exposure time 

Min. intrusion depth 

7 days 

14 days 

21 days 

28 days 

120 m 

240 m 

360 m 

480 m 

It is not mentioned explicitly in the text that localised corrosion as well as uniform corrosion has 
also be taken into account. However, localised corrosion, that is entirely part of UN Test C.1 
protocol, has actually to be taken into account. In addition, although the type of corrosion is not 
reflected in the classification result, this valuable information should be given in the SDS 

. 

 
 
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2.16.4.4.2.  Additional notes on best practice for testing  

Competence required for testing 

The overall evaluation of appropriate data for considering the corrosion properties of a 
substance or a mixture and in particular for testing it according to the mentioned criteria for this 
hazard class requires certain qualifications and experience. Expertise is often needed for this 
hazard class, which relates to a complex and multi-faceted hazardous phenomenon. 

Selection of metal specimens 

CLP refers to two types of metals (carbon steel and aluminium) meeting accurate specifications 
(technical characteristics of metal sheets and plate thickness). Thicker metal sheets, such as 
cast materials, of which the thickness is reduced by any form of mechanical treatment, may 
never be used. Mechanical reduction of sheet (metal) thickness could induce corrosion enhanced 
process due to cross section heterogeneity in metal grain and impurities. It is far better to use 
slightly different specifications of metal in the correct thickness or slightly different specimen 
plate thicknesses. It is recognised that it will not always be easy to obtain metal specimens with 
the profile as described above. 

Regarding the type of aluminium or steel to be used for this test see UN-MTC, Sub-section 
37.4.1.2. 

Minimum corrosive media volume 

In order to prevent any limitation on the corrosion process due to full consumption of the 
corrosive media before the end of the testing period, a minimum volume of substance or 
mixture (1.5 L, according to the UN-MTC) has to be used. (Note: volume/surface ratio of 10 
mL/cm² is stated in DIN 50905, similar in ASTM G31–72.) 

Adjustment of the test temperature  

Corrosion processes are temperature dependent. In the context of CLP, the property corrosive 
to metals is assessed through testing metal specimens at a specified temperature of 55 °C  1 
°C. In practice, it may be difficult with standard testing equipment to stay within the 
temperature window (55 °C  1 °C) of the gas phase, all over the test period. In such case, the 
test can be performed conservatively at a slightly higher temperature and somewhat lower 
accuracy (e.g. 57 °C  3 °C).   

Selecting the appropriate test duration 

The evaluation of the criterion of 6.25 mm/year is generally based on a test duration not 
exceeding 1 month. There is, however, the option to stop the test procedure already after 1 
week (see Table 1). For the decision on test duration, the non-linear behaviour of the corrosion 
process must be taken due account of. In borderline cases a non-appropriate test duration may 
result in either false positive or false negative results. 

Specimen cleaning 

Attention must be paid to the correct cleaning of the corroded residue before measurement of 
the corrosion characteristics. In case of adhesive corroded layer, the same cleaning process 
needs to be carried out on a non corroded sample to verify if the cleaning procedure is not 
significantly abrasive. For further information see UN-MTC, Sub-section 37.4.1.3. 

Testing soluble solids 

As said in Section 2.15.4.1, for solids that may become liquids through dissolution in water or in 
a solvent, the adequate testing procedure is more complex (not explicitly describe in the UN C.1 
test protocol). In no case will simple dilution of the solid substance or mixture in any quantity of 
water lead to satisfactory testing of the substance or mixture for corrosion to metals.  

 
 
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For the specific case where the corrosion potential is linked to the presence of solvent traces 
(other than water), expert judgement is needed to determine if further testing must be 
performed (where the solid is put in interaction with the metallic part considered). 

Example of equipment relevant for the performance UN Test C.1 

Figure 2.16   Example of testing equipment available on the market to perform UN Test C.1 

 
 
 
 
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2.16.4.5.  Decision logic  

Classification of substances and mixtures corrosive to metals is done according to decision 
logics 2.16.4.1 as included in the GHS. 

  NOTE: The person responsible for the classification of substances and mixtures corrosive to 
metals should be experienced in this field and be familiar with the criteria for classification. 

Figure 2.17   Decision logic for substances and mixtures corrosive to metals (Decision logic 
2.16 of GHS) 

Substance/mixture 

Does it corrode either steel or aluminium surfaces at a rate 
exceeding 6.25 mm/year at a test temperature of 55 °C 
when tested on both materials? 

No 

Yes 

Not classified 

Category 1 

Warning 

 
 
 
 
 
 
 
  
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2.16.5.  Hazard communication for substances and mixtures corrosive to 

metals  

2.16.5.1.  Pictograms, signal words, hazard statements and precautionary 

statements 

Table 2.16.2 of CLP Annex I provides the label elements for hazard class corrosive to metals. 
The hazard statement H290, using the wording ‘may’, reflects that classification under this 
hazard class does not cover all metals (testing only considers carbon steel and aluminium). 
Thus we may find examples of substances and mixtures that are classified in this hazard class 
corrosive to metals but will not induce corrosive action on other more corrosive resistant metals 
(e.g. platinum) than those serving as reference materials.  

Label elements must be used for substances and mixtures meeting the criteria for classification 
in this hazard class in accordance with Table 2.16.2. 

Annex I: 2.16.3. Table 2.16.2 

Label elements for substances and mixtures corrosive to metals 

Classification 

GHS Pictogram 

Category 1 

Signal Word 

Hazard Statement 

Precautionary Statement, Prevention 

Precautionary Statement, Response 

Precautionary Statement, Storage 

Precautionary Statement, Disposal 

Note:  

Warning 

H290: May be corrosive to metals 

P234 

P390 

P406 

Where a substance or mixture is classified as corrosive to metals but not corrosive to skin 
and/or eyes, the labelling provisions set out in Section 1.3.6 shall be used. 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

Further, in Section 1.3.6 of CLP Annex I a derogation from labelling requirements for substances 
or mixtures classified as corrosive to metals but not corrosive to skin and/or eyes is provided. 

Annex I: 1.3.6 Substances or mixtures classified as corrosive to metals but not 
classified as skin corrosion or as serious eye damage (Catgory 1) 

Substances or mixtures classified as corrosive to metals but not classified as skin corrosion 
or as serious eye damage (Catgory 1) which are in the finished state as packaged for 
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2.16.6.  Relation to transport classification  

Class 8 of the UN RTDG Model Regulations covers substances and mixtures that are classified 
for corrosivity to skin, metals or both. Valuable information can be obtained from UN RTDG 
Model Regulations and the modal transport regulations (ADR, RID, ADN and IMDG Code, ICAO 
TI). Existing test results obtained in the context of the modal transport regulations (ADR, RID, 
ADN and IMDG Code, ICAO TI) may be applied since the UN Test C.1 serves as reference for 
testing in both classification systems. See Annex VII for additional information on transport 
classification in relation to CLP classification. 

2.16.7.  Examples of classification for substances and mixtures corrosive to 

metals  

The following table lists some examples of substances and mixtures that should be classified or 
not in Class 2.16 (according to known UN Test C.1 results) in comparison with predicted results 
for skin corrosion hazard. 

Table 2.4  Examples of classified and non classified substances and mixtures in Class 2.16 

Note:   

‘Corroded’ means corrosion attack in the sense of UN Test C.1; 

‘Not corroded’ means corrosion resistant in the sense of UN Test C.1; 

‘Positive’ or ‘Negative’ are results from skin corrosion.  

Substance or mixture 

Steel 

Aluminiu
m 

CLP Annex I, 2.16 
classification 

Skin (for 
comparison) 

Hydrofluoric acid 

Not corroded  Corroded  Classified 

Positive 

> 70 % (UN1790) 

Highly concentrated nitric 
acid (97 %)  (UN2031) 

Not corroded  Corroded  Classified 

Positive 

HNO3 red fuming (UN2032) 

Not corroded  Not 

Not classified 

Positive 

corroded 

Hydrochloric acid (diluted) 
(UN1789) 

Corroded 

Corroded  Classified 

Negative 

NaOH solutions (UN1824) 

Not corroded  Corroded  Classified 

Positive 

 
 
 
 
 
 
 
 
 
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2.16.7.1.  Example of metal specimen plates after exposure to a corrosive 

mixture 

Figure 2.18  Example of corroded metal plates after testing according to UN Test C.1 for a 
classified mixture 

Plate located in the 
liquid phase 

Plate located in the 
interface 

Plate located in the 
vapour phase 

This example shows that the corrosion may develop at different rates according to the accurate 
position of the specimen related to the corroding mixture (sunk in the liquid, placed in the gas 
phase above liquid or at the liquid/gas interface). 

2.16.8.  References 

ASTM G31-72(2004) Standard Practice for Laboratory Immersion Corrosion Testing of Metals.  

Jones, D.A., Principles and Prevention of Corrosion, 2nd edition, 1996, Prentice Hall, Upper 
Saddle River, NJ. ISBN 0-13-359993-0 Page 50-52. 

DIN 50905-1: 2007, Corrosion of metals - Corrosion testing - Part 1: General guidance 
(Korrosion der Metalle - Korrosionsuntersuchungen - Teil 1: Grundsätze). 

 
 
 
 
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3.  PART 3: HEALTH HAZARDS 

3.1.  ACUTE TOXICITY 

3.1.1.  Definitions and general considerations for acute toxicity 

Annex I: 3.1.1.1. Acute toxicity means those adverse effects occurring following oral or 
dermal administration of a single dose of a substance or a mixture, or multiple doses given 
within 24 hours, or an inhalation exposure of 4 hours. 

Acute toxicity relates to effects occurring after a single or relatively brief exposure to a 
substance or mixture. The definition in CLP reflects the fact that the evidence for acute toxicity 
is usually obtained from animal testing. In particular, acute toxicity is usually characterised in 
terms of lethality and exposure times are based around those used in experimental protocols. 
However, classification for acute toxicity can also be based on human evidence which shows 
lethality following human exposure. 

There are different hazard classes covering effects after single or brief exposure – ‘Acute 
toxicity’ and ‘STOT-SE (Specific Target Organ Toxicity – Single Exposure)’, skin 
irritation/corrosion and eye damage. These are independent of each other and may all be 
assigned to a substance or a mixture if the respective criteria are met. However, care should be 
taken not to assign each class for the same effect, essentially giving a multiple classification, 
even where the criteria for different classes are fulfilled. In such a case the most appropriate 
(the most severe hazard) class should be assigned. 

Acute toxicity classification is generally assigned on the basis of evident lethality (e.g. an 
LD50/LC50 value), or, where the potential to cause lethality can be concluded from evident 
toxicity (e.g. from the fixed dose procedure). STOT-SE should be considered where there is 
clear evidence of toxicity to a specific organ, when it is observed in the absence of a 
classification for lethality (see Section 3.8 of this Guidance). Mortalities during the first 72 h 
after first treatment (in a repeated dose study) may also be considered for the assessment of 
acute toxicity. 

For more details see Guidance on IR&CSA, Section R.7.4.1.1. 

Annex I: 3.1.1.2.  The hazard class Acute Toxicity is differentiated into: 

–  Acute oral toxicity; 
–  Acute dermal toxicity; 
–  Acute inhalation toxicity. 

The classification must be considered for each route of exposure, using the appropriate 
approach as described in Section 3.1.2.2 and Section 3.1.2.3 of this Guidance. If different 
hazard categories are assigned, the most severe hazard category must be used to select the 
appropriate pictogram and signal word on the label for acute toxicity. For each relevant route of 
exposure, the hazard statement will correspond to the classification of this specific route. 

3.1.2.  Classification of substances for acute toxicity 

3.1.2.1. 

Identification of hazard information  

3.1.2.1.1. 

Identification of human data  

Relevant information with respect to acute toxicity may be available from sources such as case 
reports, epidemiological studies, medical surveillance and reporting schemes and national 
poison centres. Human data to be considered for acute toxicity should report severe effects 

 
 
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after single exposure or exposure of less than 24h, but data on severe effects after a few 
exposures over a few days can also be considered on a case by case basis. 

For more details see Guidance on IR&CSA, Section R.7.4.3.2. 

3.1.2.1.2. 

Identification of non-human data  

Non-testing data: 

Physicochemical data 

Physico-chemical properties, such as pH, physical state, form, solubility, vapour pressure and 
particle size, can be important parameters in evaluating toxicity studies and in determining the 
most appropriate classification. This is especially valid with respect to inhalation where physical 
form and particle size can have a significant impact on toxicity (see Section 3.1.2.3.2 of this 
Guidance). 

(Q)SAR models, expert systems and grouping methods 

Non-testing data can be provided by the following approaches: a) structure-activity 
relationships (SARs) and quantitative structure-activity relationships (QSARs), collectively called 
(Q)SARs; b) expert systems incorporating (Q)SARs and/or expert rules; and c) grouping 
methods (read-across and categories. These approaches can be used to assess acute toxicity if 
they provide relevant and reliable (adequate) data for the chemical of interest. […] Compared 
with some endpoints, there are relatively few (Q)SAR models and expert systems capable of 
predicting acute toxicity.’ (Guidance on IR&CSA, Section R.7.4.3.1). 

Testing data: 

In vitro data 

There are currently no in vitro tests that have been officially adopted by the EU or OECD for 
assessment of acute toxicity (see Guidance on IR&CSA, Section R.7.4.3.1, for further 
information). Any available studies should be assessed by using expert judgement. 

Animal data 

A number of different types of studies have been used to investigate acute toxicity. Older 
standard studies were designed to determine lethality and estimate the LD50/LC50. In contrast, 
contemporary study protocols, such as the fixed dose procedure, use signs of evident toxicity 
rather than lethality as indications of acute toxicity. 

The animal studies are listed in the Guidance on IR&CSA, Section R.7.4.3.1. 

3.1.2.2.  Classification criteria  

Annex I: 3.1.2.1. Substances can be allocated to one of four hazard categories based on acute 
toxicity  by  the  oral,  dermal  or  inhalation  route  according  to  the  numeric  criteria  shown  in 
Table 3.1.1. Acute toxicity values are expressed as (approximate) LD50 (oral, dermal) or LC50 
(inhalation) values or as acute toxicity estimates (ATE). Explanatory notes are shown following 
Table 3.1.1. 

Table 3.1.1 
Acute toxicity hazard categories and acute toxicity estimates (ATE) defining the 
respective categories 

Exposure Route 

Category 1 

Category 2 

Category 3 

Category 4 

Oral (mg/kg 
bodyweight) 

See:   Note (a) 

ATE ≤ 5 

5 < ATE ≤ 50 

50 < ATE 
≤ 300 

300 < ATE 
≤ 2000 

 
 
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Dermal 
bodyweight) 

(mg/kg 

ATE ≤ 50 

50 < ATE 
≤ 200 

200 < ATE 
≤ 1000 

1000 < ATE 
≤ 2000 

100 < ATE 
≤ 500 

500 < ATE 
≤ 2500 

2500 < ATE 
≤ 20000 

0.5 < ATE ≤  
2.0 

2.0 < ATE ≤ 
10.0 

10.0 < ATE 
≤ 20.0 

See:   Note (a) 

Note (b) 

Gases (ppmV (1)) 

ATE ≤ 100 

see:   Note (a) 

Note (b) 

Note (c) 

Vapours (mg/l) 

ATE ≤ 0.5 

see:   Note (a) 

Note (b) 

Note (c) 

Note (d) 

Dusts  and  mists 
(mg/l) 

see:   Note (a) 

Note (b) 

Note (c) 

ATE ≤ 0.05 

0.05 < ATE 
≤ 0.5 

0.5 < ATE ≤ 
1.0 

1.0 < ATE ≤ 5.0 

(1) Gas concentrations are expressed in parts per million per volume (ppmV). 

Notes to Table 3.1.1: 

The acute toxicity estimate (ATE) for  the classification of a substance is derived using 

(a) 
the LD50/LC50 where available. 

The  acute  toxicity  estimate  (ATE)  for  the  classification  of  a  substance  in  a  mixture  is 

(b) 
derived using: 

- 

- 

the LD50/LC50 where available, 

the appropriate conversion value from Table 3.1.2 that relates to the results of a range test, 
or 

- 

the appropriate conversion value from Table 3.1.2 that relates to a classification category. 

(c) 
The ranges of the acute toxicity estimates (ATE) for inhalation toxicity in the table are 
based on 4-hour testing exposures. Conversion of existing inhalation toxicity data which have 
been generated using a 1-hour exposure can be carried out by dividing by a factor of 2 for 
gases and vapours and 4 for dusts and mists. 

(d) 
For some substances the test atmosphere will not just be a vapour but will consist of a 
mixture of liquid and vapour phases. For other substances the test atmosphere may consist of 
a vapour which is near the gaseous phase. In these latter cases, classification shall be based 
on ppmV as follows: Category 1 (100 ppmV), Category 2 (500 ppmV), Category 3 
(2500 ppmV), Category 4 (20 000 ppmV). 

 
 
 
 
 
 
 
 
 
 
 
 
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The terms ‘dust’, ‘mist’ and ‘vapour’ are defined as follows: 

- dust: solid particles of a substance or mixture suspended in a gas (usually air), 

- mist: liquid droplets of a substance or mixture suspended in a gas (usually air), 

- vapour: the gaseous form of a substance or mixture released from its liquid or solid state. 

Dust is generally formed by mechanical processes. Mist is generally formed by condensation 
of supersaturated vapours or by physical shearing of liquids. Dusts and mists generally have 
sizes ranging from less than 1 to about 100 µm. 

  NOTE regarding CLP Annex I, Table 3.1.1, Note (c): 

The classification criteria for acute inhalation toxicity relate to a 4-hour experimental 
exposure period. Where LC50 values have been obtained in studies using exposure 
durations shorter or longer than 4 hours these values may be adjusted to a 4-hour 
equivalent using Haber’s law (C·t=k) for direct comparison with the criteria. The 
formula may be refined to (Cn·t=k) where the value of n, which is specific to individual 
substances, should be chosen using expert judgement. If an appropriate value of n is 
not available in the literature then it may sometimes be derived from the available 
mortality data using probits (i.e. the inverse cumulative distribution functions 
associated with the standard normal distribution). Alternatively, some default values are 
recommended (Guidance on IR&CSA, Section R.7.4.4.1). 

Particular care should be taken when using Haber’s law to assess inhalation data on 
substances which are corrosive or locally active. In all cases, Haber’s law should only be 
used in conjunction with expert judgement. 

It is noted that the statements in the Guidance on IR&CSA, Section R.7.4.4.1, with 
respect to Haber’s law are not consistent with those of CLP. However, the CLP approach 
must be used for classification and labelling. 

3.1.2.2.1.  Harmonised ATE values 

From 2016 harmonised ATE values are gradually included in Annex VI. These values must 
be applied when classifying mixtures containing the substance just as any other harmonised 
item regardless of any other ATE value derived from testing of the substance. 

3.1.2.2.2.  Minimum classification 

For certain entries in Annex VI there is an asterisk indicating that it is the minimum 
classification. In case the substance has a minimum classification this is the lowest 
classification possible, however, if there is data indicating that a more stringent 
classification is warranted the classification has to be adapted accordingly. This is due to 
translation from the old DSD legislation. 

3.1.2.3.  Evaluation of hazard information  

3.1.2.3.1. 

Evaluation of human data  

The evaluation of human data often becomes difficult due to various limitations frequently found 
with the types of studies and data highlighted in Section 3.1.2.1.1 of this Guidance. These 
include uncertainties relating to exposure assessment (i.e. unreliable information on the amount 
of substance the subjects were exposed to) and uncertain exposure to other substances. As 
such, human data needs careful expert evaluation to properly judge the reliability of the 
findings. It should be acknowledged that human data often do not provide sufficiently robust 
evidence on their own to support classification. They may, however, contribute to a weight of 
evidence assessment with other available information such as data from animal studies. 

 
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The classification for acute toxicity is based primarily on the dose/concentration that causes 
mortality (the Acute Toxicity Estimate, ATE), which is then related to the numerical values in 
the classification criteria according to CLP Annex I, Table 3.1.1 (see Section 3.1.2.2 of this 
Guidance) for substances or for use in the additivity formula in CLP Annex I, 3.1.3.6.1 and 
3.1.3.6.2.3 for mixtures (see Section 3.1.3.3 of this Guidance). The ATE is usually obtained 
from animal studies but in principle suitable human data can also be used if available. Where 
human data are available, they should be used to estimate the ATE which can be used directly 
for classification as described above. 

The minimum dose or concentration or range shown or expected to cause mortality after a 
single human exposure can be used to derive the human ATE directly, without any adjustments 
or uncertainty factors. See Example 1 (methanol) in Section 3.1.5.1.1 of this Guidance. 

If there are no exact or quantitative lethal dose data the procedure described in CLP Annex I, 
3.1.3.6.2.1(b) (see Section 3.1.3.3.5 of this Guidance) would have to be followed using Table 
3.1.2 (see Section 3.1.3.3 of this Guidance) with an assessment of the available information on 
a semi-quantitative or qualitative basis.  

Expert judgement is needed in a total weight of evidence approach taking relevance, reliability, 
and adequacy of the information into account. See Example 2 (N,N-dimethylaniline) in Section 
3.1.5.1.2 of this Guidance. 

3.1.2.3.2. 

Evaluation of non-human data  

Annex I: 3.1.2.2. Specific considerations for classification of substances as acutely toxic 

Annex I: 3.1.2.2.1. The preferred test species for evaluation of acute toxicity by the oral and 
inhalation routes is the rat, while the rat or rabbit are preferred for evaluation of acute dermal 
toxicity. When experimental data for acute toxicity are available in several animal species, 
scientific judgement shall be used in selecting the most appropriate LD50 value from among 
valid, well-performed tests. 

Evaluation of non-testing and in vitro data: 

Results of (Q)SAR, grouping and read-across may be used instead of testing, and substances 
will be classified and labelled on this basis if the method fulfils the criteria described in Annex XI 
of REACH. See also the Guidance on IR&CSA, Section R.7.4.4.1. In vitro data cannot be used as 
a stand alone. However, NRU data can be used as part of a weight of evidence evaluation. 

Animal data: 

ATE – establishing: 

•  Basis LD50/LC50: An available LD50/LC50 is an ATE at first stage. 

•  Results from a range test: According to CLP Annex I, Table 3.1.2 results from range 
tests (i.e. doses/exposure concentrations that cause acute toxicity in the range of 
numeric criteria values) can be assigned to the four different categories of acute toxicity 
for each possible route of exposure (centre column). Further, CLP Annex I, Table 3.1.2 
allows allocating a single value, the converted acute toxicity point estimate (cATpE), to 
each experimentally obtained acute toxicity range estimate or classification category 
(right column), see Note (b) to Table 3.1.1. This cATpE can be used in the additivity 
formulae (CLP Annex I, 3.1.3.6.1 and 3.1.3.6.2.3) to calculate the acute toxicity of 
mixtures. 

• 

In case of multiple LD50/LC50 values or LD50/LC50 values from several species: 

Where several experimentally determined ATE values (i.e. LD50, LC50 values or ATE derived from 
studies using signs of non-lethal toxicity) are available, expert judgement needs to be used to 
choose the most appropriate value for classification purposes. Each study needs to be assessed 
for its suitability in terms of study quality and reliability, and also for its relevance to the 

 
 
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substance in question in terms of technical specification and physical form. Studies not 
considered suitable on reliability or other grounds should not be used for classification. 

In general, classification is based on the lowest ATE value available i.e. the lowest ATE in the 
most sensitive appropriate species tested. However, expert judgement may allow another ATE 
value to be used in preference, provided this can be supported by a robust justification. If there 
is information available to inform on species relevance, then the studies conducted in the 
species most relevant for humans should normally be given precedence over the studies in 
other species. If there is a wide range of ATE values from the same species, it may be 
informative to consider the studies collectively, to understand possible reasons for the different 
results obtained. This would include consideration of factors such as the sex and age of the 
animals, the animal strains used, the experimental protocols, the purity of the substance and 
form or phase in which it was tested (e.g. the particle size distribution of any dusts or mists 
tested), as well as exposure mode and numerous technical factors in inhalation studies. This 
assessment may aid selection of the most appropriate study on which to base the classification. 

If there are different LD50 values from tests using different vehicles (e.g. water vs. corn oil or 
neat substance vs. corn oil), generally the lowest valid value would be the basis for 
classification. It is not considered appropriate to combine or average the available ATE values. 
The studies may not be equivalent (in terms of experimental design such as protocol, purity of 
material tested, species of animal used, etc.) making such a collation or combination unsound. 

If there is a study available with a post-observation period of less than the 14 days, the time to 
be used according to the OECD guidelines, and effects are observed at the end of the study, the 
resulting LD50 might be misleading. Such information should be included in the weight of 
evidence consideration. 

If there is available test data from a 28 day study to 1000 mg/kg bw/day and no effects are 
seen, it can be concluded that the substance does not fullfill the criteria for acute toxicity (for 
further details see Appendx 7.4-1 to Guidance R.7a, especially Section 2.4). If a substance is 
not acutely toxic by the oral route it can also be assumed that it is not acutely toxic by the 
dermal route. 

Annex I: 3.1.2.3. Specific considerations for classification of substances as acutely toxic by 
the inhalation route  

Annex I: 3.1.2.3.1. Units for inhalation toxicity are a function of the form of the inhaled 
material. Values for dusts and mists are expressed in mg/l. Values for gases are expressed in 
ppmV. Acknowledging the difficulties in testing vapours, some of which consist of mixtures of 
liquid and vapour phases, the table provides values in units of mg/l. However, for those 
vapours which are near the gaseous phase, classification shall be based on ppmV.  

Conversions: 

Differentiation between vapour and mist will be made on the basis of the saturated vapour 
concentration (SVC) for a volatile substance, which can be estimated as follows:  

SVC [mg/l] = 0.0412 x MW x vapour pressure (vapour pressure in hPa at 20°C).  

The conversion from mg/l to ppm assuming an ambient pressure of 1 atm = 101.3 kPa and 
25°C is: ppm= 24,450 x mg/l x 1/MW. 

An LC50 well below the SVC will be considered for classification according to the criteria for 
vapours; whereas an LC50 close to or above the SVC will be considered for classification 
according to the criteria for mists (see also OECD GD 39). 

Considerations with respect to physical forms or states or bioavailability: 

Article 9(5) When evaluating the available information for the purposes of classification, the 
manufacturers, importers and downstream users shall consider the forms or physical states in 

 
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which the substance or mixture is placed on the market and in which it can reasonably be 
expected to be used. 

For further details see Sections 1.2 and 1.3 of this Guidance. 

Special considerations concerning aerosols (dusts and mists): 

Annex I: 3.1.2.3.2. Of particular importance in classifying for inhalation toxicity is the use of 
well articulated values in the highest hazard categories for dusts and mists. Inhaled particles 
between 1 and 4 microns mean mass aerodynamic diameter (MMAD) will deposit in all regions 
of the rat respiratory tract. This particle size range corresponds to a maximum dose of about 
2 mg/l. In order to achieve applicability of animal experiments to human exposure, dusts and 
mists would ideally be tested in this range in rats. 

The test guidelines for acute inhalation toxicity with aerosols require rodents to be exposed to 
an aerosol containing primarily respirable particles (with a Mass Median Aerodynamic Diameter 
(MMAD) of 1 – 4 µm), so that particles can reach all regions of the respiratory tract. The use of 
such fine aerosols helps to avoid partial overloading of extra-thoracic airways in obligate nasal 
breathing species like rats. Results from studies in which substances with particle size with a 
MMAD > 4 µm have been tested can generally not be used for classification, but expert 
judgement is needed in cases where there are indications of high toxicity. 

The use of highly respirable dusts and mists is ideal to fully investigate the potential inhalation 
hazard of the substance. However, it is acknowledged that these exposures may not necessarily 
reflect realistic conditions. For instance, solid materials are often micronised to a highly 
respirable form for testing, but in practice exposures will be to a dust of much lower 
respirability. Similarly, pastes or highly viscous materials with low vapour pressure need strong 
measures to be taken to generate airborne particulates of sufficiently high respirability, whereas 
for other materials this may occur spontaneously. In such situations, specific problems may 
arise with respect to classification and labelling, as these substances are tested in a form (i.e. 
specific particle size distribution) that is different from all the forms in which these substances 
are placed on the market and in which they can reasonably be expected to be used. 

A scientific concept has been developed as a basis for relating the conditions of acute inhalation 
tests to those occurring in real-life, in order to derive an adequate hazard classification. This 
concept is applicable only to substances or mixtures which are proven to cause acute toxicity 
through local effects and do not cause systemic toxicity (Pauluhn, 2008). 

Corrosive substances 

Annex I: 3.1.2.3.3. In addition to classification for inhalation toxicity, if data are available 
that indicates that the mechanism of toxicity was corrosivity, the substance or mixture shall 
also be labelled as ‘corrosive to the respiratory tract’ (see note 1 in 3.1.4.1). Corrosion of the 
respiratory tract is defined by destruction of the respiratory tract tissue after a single, limited 
period of exposure analogous to skin corrosion; this includes destruction of the mucosa. The 
corrosivity evaluation can be based on expert judgment using such evidence as: human and 
animal experience, existing (in vitro) data, pH values, information from similar substances or 
any other pertinent data. 

It is presumed that corrosive substances (and mixtures) will cause toxicity by inhalation 
exposure. In cases where no acute inhalation test has been performed special consideration 
should be given to the need to communicate this potential hazard. 

Corrosive substances (and mixtures) may be acutely toxic after inhalation to a varying degree 
and by different modes of action. Therefore, it is not possible to estimate the acute inhalation 
toxicity from the corrosivity data alone. 

 
 
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There are special provisions for hazard communication of acutely toxic substances by a 
corrosive effect, see Section 3.1.4.2 of this Guidance. 

3.1.2.3.3.  Weight of evidence 

In cases where there is sufficient human evidence that meets the criteria given in Section 
3.1.2.2 of this Guidance then this will normally lead to classification for acute toxicity, 
irrespective of other information available. Please refer also to the Guidance R7a and in 
particular to especially to Appendix R7.4-1. 

If there are human data indicating no classification but there are also non-human data 
indicating classification then the classification is based on the non-human data unless it is 
shown that the human data cover the exposure range of the non-human data or that the non-
human data are not relevant for humans. If the human and non-human data both indicate no 
classification then classification is not required. 

If there are no human data then the classification is based on the non-human data. 

For the role and application of expert judgement and weight of evidence determination, see CLP 
Annex I, 1.1.1. 

3.1.2.4.  Decision on classification  

The classification has to be performed with respect to all routes of exposure (oral, dermal, 
inhalation) on the basis of all adequate and reliable available information.  

3.1.2.5.  Setting of specific concentration limits  

Specific concentration limits are not applicable for acute toxicity classification. Rather, the 
relative potency of substances is implicitly taken into account in the additivity formula (see 
Section 3.1.3.3.3 of this Guidance). For this reason specific concentration limits for acute 
toxicity will not appear in CLP Annex VI, Table 3.1 or in the classification and labelling inventory 
(CLP Article 42). 

3.1.2.6.  Decision logic for classification of substances 

The decision logic below is provided as additional guidance. It is strongly recommended that the 
person responsible for classification is fully familiar with the criteria for acute toxicity 
classification before using the decision logic. 

For a complete classification of a substance, the decision logic must be worked out for each 
route of exposure for which data and/or information is available. For example, if a certain 
substance is classified in Category 1 based on an oral LD50  5 mg/kg bodyweight (the answer 
was 'Yes' in box 2 for item (a)), it is still necessary to go back to box 2 in the decision logic and 
complete the classification for the dermal (b) and inhalation (c)-(e) route of exposure, when 
data are available for one or both of these routes of exposure. In case there are data for all 
three routes of exposure, the classification for acute toxicity of the substance will include the 
three differentiations of the hazard class, which might result in three different categories being 
assigned to the different routes. The route of exposure will then be specified in the 
corresponding hazard statement. 

 
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Are there data and/or information 
(including WoE, see R.7.4-1) to evaluate 
acute toxicity? 

Yes 

No 

Classification not possible 

According to the criteria in CLP Annex I, 3.1.2 to 3.1.3.4, does it 
have an:  
(a) 

  5 mg/kg bodyweight; or 

Oral LD

50

(b) 

(c) 

(d) 

(e) 

Dermal LD

50

  50 mg/kg bodyweight; or 

Inhalation (gas) LC

50

  100 ppm; or 

Inhalation (vapour) LC

  0.5 mg/l ; or 

50

Inhalation (dust/mist) LC50  0.05 mg/l? 

Yes 

No 

According to the criteria in CLP Annex I, 3.1.2 to 3.1.3.4, does it 
have an: 
(a) 
(b) 
(c) 
(d) 
(e) 

Oral LD50 >5 but  50 mg/kg bodyweight; or 
Dermal LD50 >50 but  200 mg/kg bodyweight; or  
Inhalation (gas) LC50 >100 but < 500 ppm; or 
Inhalation (vapour) LC50 > 0.5 but < 2.0 mg/l; or 
Inhalation (dust/mist) LC50 > 0.05 but  0.5 mg/l?  

Yes 

No 

According to the criteria in CLP Annex I, 3.1.2 to 3.1.3.4, does it 
have an: 
(a) 
(b) 
(c) 
(d) 
(e) 

Oral LD50 >50 but ≤ 300 mg/kg bodyweight; or 
Dermal LD50 > 200 but ≤ 1000 mg/kg bodyweight; or 
Inhalation (gas) LC50 >500 but ≤ 2500 ppm; or 
Inhalation (vapour) LC50 >2 but ≤ 10.0 mg/l; or 
Inhalation (dust/mist) LC50 >0.5 but ≤ 1.0 mg/l?  

Yes 

No 

According to the criteria in CLP Annex I, 3.1.2 to 3.1.3.4, does it 
have an: 
(a) 
(b) 
(c) 
(d) 
(e) 

Oral LD50 >300 but ≤ 2000 mg/kg bodyweight; or  
Dermal LD50 >1000 but ≤ 2000 mg/kg bodyweight; or 
Inhalation (gas) LC50 >2500 but ≤ 20000 ppm; or 
Inhalation (vapour) LC50 >10 but ≤ 20 mg/l; or 
Inhalation (dust/mist) LC50 >1 but ≤ 5 mg/l? 

Yes 

No 

No classification 

Category 1 

Danger 

Category 2 

Danger 

Category 3 

Danger 

Category 4 

Warning 

 
 
 
 
 
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3.1.3.  Classification of mixtures for acute toxicity 

3.1.3.1.  General considerations for classification 

Annex I: 3.1.3.1. The criteria for classification of substances for acute toxicity as outlined in 
section 3.1.2 are based on lethal dose data (tested or derived). For mixtures, it is necessary 
to obtain or derive information that allows the criteria to be applied to the mixture for the 
purpose of classification. The approach to classification for acute toxicity is tiered, and is 
dependent upon the amount of information available for the mixture itself and for its 
ingredients.  

The procedure for classifying mixtures is a tiered i.e. a stepwise approach based on a hierarchy 
principle and depending on the type and amount of available data/information. If valid test data 
are available for the whole mixture they have precedence. If no such data exist, the so-called 
bridging principles have to be applied if possible. If the bridging principles are not applicable an 
assessment on the basis of ingredient information will be applied (see Sections 3.1.3.3.3, 
3.1.3.3.5, 3.1.3.3.6 and 3.1.3.4 of this Guidance). 

3.1.3.2. 

Identification of hazard information  

Where relevant and reliable toxicological information from human evidence or animal studies is 
available on a mixture, this should be used to derive the appropriate classification. Where such 
information on the mixture itself is not available, information on similar tested mixtures and, 
the component substances in the mixture must be used, as described in Section 3.1.3.3 of this 
Guidance. 

Alternatively, the hazard information on all individual components in the mixture could be 
identified as described in Section 3.1.2.2 of this Guidance. 

3.1.3.3.  Classification criteria 

Annex I: 3.1.3.2. For acute toxicity each route of exposure shall be considered for the 
classification of mixtures, but only one route of exposure is needed as long as this route is 
followed (estimated or tested) for all components and there is no relevant evidence to suggest 
acute toxicity by multiple routes. When there is relevant evidence of toxicity by multiple 
routes of exposure, classification is to be conducted for all appropriate routes of exposure. All 
available information shall be considered. The pictogram and signal word used shall reflect the 
most severe hazard category and all relevant hazard statements shall be used. 

The classification must be considered for each route of exposure. If different hazard categories 
are assigned, the most severe hazard category will be used to select the appropriate pictogram 
and signal word on the label for acute toxicity. For each relevant route of exposure, the hazard 
statement will correspond to the classification of this specific route. 

3.1.3.3.1.  When data are available for the complete mixture 

Annex I: 3.1.3.4.1. Where the mixture itself has been tested to determine its acute toxicity, 
it shall be classified according to the same criteria as those used for substances, presented in 
Table 3.1.1. […] 

In general, where a mixture has been tested those data should be used to support classification 
according to the same criteria as used for substances (as described in Section 3.1.2.3 of this 
Guidance). However, there should be some consideration of whether the test is appropriate. For 
instance, if the mixture contains a substance for which the test species is not considered 
appropriate (for instance a mixture containing methanol tested in rats which are not sensitive to 

 
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methanol toxicity), then the appropriateness of these data for classification should be 
considered using expert judgement.  

With respect to the classification of mixtures in the form of dust or mist for acute inhalation 
toxicity, the particle size can affect the toxicity and the resulting classification should take this 
into account (see Section 3.1.2.3.2 of this Guidance). 

3.1.3.3.2.  When data are not available for the complete mixture: bridging principles 

Annex I: 3.1.3.5.1. Where the mixture itself has not been tested to determine its acute 
toxicity, but there are sufficient data on the individual ingredients and similar tested mixtures 
to adequately characterise the hazards of the mixture, these data shall be used in accordance 
with the bridging rules set out in section 1.1.3. 

In order to apply bridging principles, there needs to be sufficient data on similar tested mixtures 
as well as the ingredients of the mixture (see Section 1.6.3 of this Guidance). 

When the available identified information is inappropriate for the application of bridging 
principles then the mixture should be classified based on its ingredients as in Section 3.1.3.3.3, 
3.1.3.3.5, 3.1.3.3.6 and 3.1.3.4 of this Guidance. 

3.1.3.3.3.  When data are available for all ingredients  

Annex I: 3.1.3.3. 

(c) If the converted acute toxicity point estimates for all components of a mixture are within 
the same category, then the mixture should be classified in that category. 

(d) When only range data (or acute toxicity hazard category information) are available for 
components in a mixture, they may be converted to point estimates in accordance with Table 
3.1.2 when calculating the classification of the new mixture using the formulas in sections 
3.1.3.6.1 and 3.1.3.6.2.3. 

Annex I: 3.1.3.6. Classification of mixtures based on ingredients of the mixture (Additivity 
formula) 

Annex I: 3.1.3.6.1. Data available for all ingredients 

In order to ensure that classification of the mixture is accurate, and that the calculation need 
only be performed once for all systems, sectors, and categories, the acute toxicity estimate 
(ATE) of ingredients shall be considered as follows: 

(a) 

include ingredients with a known acute toxicity, which fall into any of the acute hazard 
categories shown in Table 3.1.1; 

(b) 

ignore ingredients that are presumed not acutely toxic (e.g., water, sugar); 

(c) 

ignore components if the data available are from a limit dose test (at the upper 
threshold for Category 4 for the appropriate route of exposure as provided in Table 
3.1.1) and do not show acute toxicity. 

Components that fall within the scope of this section are considered to be components with a 
known acute toxicity estimate (ATE). See note (b) to Table 3.1.1 and section 3.1.3.3 for 
appropriate application of available data to the equation below, and section 3.1.3.6.2.3. 

The ATE of the mixture is determined by calculation from the ATE values for all relevant 
ingredients according to the following formula below for Oral, Dermal or Inhalation Toxicity: 

 
 
 
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where: 
= 
Ci 
= 
i 
n 
= 
ATEi  = 

concentration of ingredient i (% w/w or % v/v) 
the individual ingredient from 1 to n 
the number of ingredients  
Acute Toxicity Estimate of ingredient i. 

In case an ingredient has a harmonised ATE this value must be used in the formula above. If no 
harmonised  ATE  is  available,  then  the  ATE  should  be  derived  as  stated  in  3.1.2.3.  The  cATpE 
(mentioned  in  3.1.2.3.2)  is  used  when  ATE  values  are  not  known.  If  there  is  a  harmonised 
classification  and  the  only  known  ATE  value  does  not  support  classification  in  that  hazard 
category, then the cATpE should be considered. 

3.1.3.3.4. 

Special case for acute inhalation toxicity  

For mixtures containing some substance(s) tested for inhalation toxicity as vapours and others 
as dust/mist or gas, the additivity formula cannot be used directly as the ATE ranges are 
different. Therefore for acute inhalation toxicity additivity has initially to be used separately for 
each relevant physical form (i.e. gas, vapour and/or dust/mist), using the appropriate category 
limit in CLP Annex I, Table 3.1.1. As a first step, the fraction of toxicity is calculated for each 
form/state:  

fraction = ∑ (limit / ATE) x concentrations /100 

Where limit = the upper border of the range of ATE values of a hazard category (Table 3.1.1 of 
CLP) for the state/form in question and concentrations = the concentration (%) of components 
tested for this state/form.  

The most severe category where the sum of fractions for the three states/forms are ≥ 1 would 
apply (see example 13 in section 3.1.5.5).  

In case of > 10% of ingredient(s) with unknown acute toxicity, the value is corrected as 1 
minus concentration of unknowns/100. 

In case no ATE values but only classification of the ingredients is known, the converted Acute 
Toxicity point Estimates (cATpEs) as shown in Table 3.1.2 of Annex I (see below) should be 
used. 

In addtiton to the new example 13, examples 12a and 12b are also provided in section 3.1.5 
(see note to the examples). 

Annex I: Table 3.1.2 

Conversion from experimentally obtained acute toxicity range values (or acute 
toxicity hazard categories) to acute toxicity point estimates for use in the formulas 
for the classification of mixtures 

Exposure 
routes 

Classification category or experimentally 
obtained acute toxicity range estimate 

Converted acute toxicity point 
estimate (see Note 1) 

Oral 
(mg/kg 
bodyweight) 

0 < Category 1  5 

5 < Category 2  50 

50 < Category 3  300 

300 < Category 4  2000 

0.5 

5 

100 

500 

 =niimixATEC  ATE100 
 
250 

Dermal 
(mg/kg 
bodyweight) 

Gases 
(ppmV) 

Vapours 
(mg/l) 

Dust/mist 
(mg/l) 

Note 1: 

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0 < Category 1  50 

50 < Category 2  200 

200 < Category 3  1000 

1000 < Category 4  2000 

0 < Category 1  100 

100 < Category 2  500 

500 < Category 3  2500 

2500 < Category 4  20000 

0 < Category 1  0,5 

0,5 < Category 2  2 

2,0 < Category 3  10,0 

10,0 < Category 4  20,0 

0< Category 1  0,05 

0,05 < Category 2  0,5 

0,5 < Category 3  1,0 

1,0 < Category 4  5,0 

5 

50 

300 

1100 

10 

100 

700 

4500 

0,05 

0.5 

3 

11 

0,005 

0,05 

0,5 

1,5 

These values are designed to be used in the calculation of the ATE for classification of a 
mixture based on its components and do not represent test results. 

Some cATpEs are equal to the upper limit of the next lower category, for example the cATpE of 
oral Category 2 (5 mg/kg bw) is equal to the upper limit of oral Category 1 (also 5 mg/kg bw). 

This can lead to a problem when using the cATpE values for calculating the acute toxicity of 
mixtures. For instance, using the cATpEs for a mixture containing only substances classified in 
Category 2 actually results in a Category 1 classification for the mixture. Similarly, a mixture 
containing substances classified as Category 3 for dust/mist results in a Category 2 
classification. Clearly these outcomes are incorrect and are an unintended side-effect of the 
approach. In such cases, CLP Annex I, 3.1.3.3.(c) should be applied. 

Annex I: 3.1.3.3.(c) If the converted acute toxicity point estimates for all components of a 
mixture are within the same category, then the mixture should be classified in that category. 

As a result, the mixtures in the examples highlighted above would be classified in Categories 2 
and 3, respectively.  

Annex I: 3.1.3.3.(b) where a classified mixture is used as an ingredient of another mixture, 
the actual or derived acute toxicity estimate (ATE) for that mixture may be used, when 
calculating the classification of the new mixture using the formulas in section 3.1.3.6.1 and 
paragraph 3.1.3.6.2.3. 

It is important that the downstream user has sufficient information in order to enable him to 
perform a correct classification of mixtures. 

 
 
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3.1.3.3.5.  When data are not available for all ingredients 

Annex I: 3.1.3.6.2.1. Where an ATE is not available for an individual ingredient of the 
mixture, but available information such as that listed below can provide a derived conversion 
value such as those laid out in Table 3.1.2, the formula in paragraph 3.1.3.6.1 shall be 
applied. 

This includes evaluation of: 

extrapolation between oral, dermal and inhalation acute toxicity estimates (1). Such an 

(a) 
evaluation could require appropriate pharmacodynamic and pharmacokinetic data; 

evidence from human exposure that indicates toxic effects but does not provide lethal 

(b) 
dose data; 

evidence from any other toxicity tests/assays available on the substance that indicates 

(c) 
toxic acute effects but does not necessarily provide lethal dose data; or 

(d) 

data from closely analogous substances using structure/activity relationships.  

_______________ 

(1) When mixtures contain components that do not have acute toxicity data for each route of 
exposure, acute toxicity estimates may be extrapolated from the available data and applied to 
the appropriate routes (see Section 3.1.3.2). However, specific legislation may require testing 
for a specific route. In those cases, classification shall be performed for that route based upon 
the legal requirements. 

Derivation of ATEs from available information: 

When ingredients have a known acute toxicity (LC50 or LD50 values), this value has to be used in 
the additivity formula. However, for many substances, acute toxicity data will not be available 
for all exposure routes.  

CLP allows for two ways of deriving acute toxicity conversion values. One option is to use the 
converted acute toxicity point estimates supplied in CLP Annex I, Table 3.1.2. The other option, 
based on expert judgement in substantiated cases, is the use of the directly derived ATE values.  

a.  Route-to-route extrapolation (CLP Annex I, 3.1.3.6.2.1.(a)) 

Route-to-route extrapolation is defined as the prediction of the total amount of a substance 
administered by one route that would produce the same systemic toxic response as that 
obtained by a given amount of a substance administered by another route. Thus, route-to-route 
extrapolation is only applicable for the evaluation of systemic effects. It is not appropriate to 
assess direct local effects.  

This extrapolation is possible if certain conditions are met, which substantiate the assumption 
that an internal dose causing a systemic effect at the target is related to an external 
dose/concentration; preferably the absorption can be quantified. Therefore information on the 
physico-chemical and biokinetic properties should be available and assessed in order to allow 
such a conclusion and performing an extrapolation across routes. In the absence of any 
information on absorption, 100% absorption has to be presumed as a worst case for the dermal 
and inhalation route. Extrapolating from the oral route to other routes, the assumption of an 
absorption of 100% for the oral route is, however, not a worst case. Absorption of less than 
100% by the oral route will lead to lower ATEs. Another important factor is the local and 
systemic metabolic pathways; in particular it must be ensured that no route-specific 
metabolism/degradation of substance occurs. 

If extrapolating from oral data, the influence of first-pass metabolism in the stomach/intestines 
and the liver should be considered, especially if the substance is detoxified. Such first pass 
metabolism is unlikely to occur to any significant extent by the dermal or inhalation routes, and 

 
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so this would lead to an underestimate of toxicity by these routes. Thus if based on kinetic or 
(Q)SAR data a specific first-pass effect is excluded, oral data may be used for extrapolation 
purposes.   

For an extrapolation to the dermal route, information on the potential skin penetration may be 
derived from the chemical structure (polar vs. nonpolar structure elements, Log Pow, molecular 
weight) if kinetic data are not available which would allow a quantitative comparison. When no 
such information is available 100% dermal absorption should be presumed. Further information 
and guidance on dermal absorption can be found on the OECD and EFSA websites – OECD 
(http://www.oecd.org/chemicalsafety/testingofchemicals/48532204.pdf) and EFSA 
(http://www.efsa.europa.eu/en/efsajournal/doc/2665.pdf). 

Similarly for an extrapolation to the inhalation route if there is no quantitative information on 
absorption then 100% absorption should be presumed. Inhalation volatility is an important 
factor which on the one hand may increase the exposure, but on the other hand may reduce 
absorption due to higher exhalation rates. The solubility (in water and non-polar solvents) has 
to be considered, as well as particle size, which plays a particularly important role in inhalation 
toxicity. 

Route-to-route extrapolation is not always appropriate. For example where there is a 
substantial difference in absorption between oral and inhalation uptake (e.g. poorly soluble 
particles, substances that decompose within the gastro intestinal-tract), or where the substance 
causes local effects, the toxicity by different routes may be significantly different, and route-to-
route extrapolation may not be appropriate (ECETOC TR 86, 2003). 

i.  Extrapolation oral → inhalation 

If the mentioned conditions are met an extrapolation from oral data would be performed as 
follows: 

Incorporated dose = concentration x respiratory volume x exposure time 

1 mg/kg bw = 0.0052 mg/l/4h 

using a respiratory volume for a 250 g rat of 0.20 l/min and 100 % absorption and postulating 
100% deposition and absorption (Guidance on IR&CSA, Chapter R7c, Table R.7.12-10). 

Valid information indicating that the deposition and/or absorption rate for the extrapolated route 
is lower would allow a higher equivalent derived ATE (see Section 3.1.5.1.9 Example 9 of this 
Guidance).  

ii.  Extrapolation oral→ dermal 

If based on kinetic or SAR data a high penetration rate can be assumed and a specific first pass-
effect is excluded, oral and dermal toxicity might be regarded as equivalent. This is rarely the 
case. 

Solids themselves may have a very low absorption rate, but if diluted in an appropriate solvent 
there may be an appreciable absorption of the substance. Thus, depending on the kinetic and 
physico-chemical properties and kind of mixture, varying ATEs will result. For example, butyn-
1,4-diol causes no mortality in rats when dermally applied as a solid at 5000 mg/kg bw, 
whereas when an aqueous solution of butyn-1,4-diol is administered, a dermal LD50 of 659 and 
1240 mg/kg bw in male and female rats, respectively, and an oral LD50 of about 200 mg/kg bw 
in both sexes can be determined. 

For more details on inter-route extrapolation see the Guidance on IR&CSA, Section R.7c. 
12.2.4. examples 8 and 9 which illustrate this approach. 

b.  Evidence from human exposure 

Human evidence can be used to derive an appropriate ATE to use in the additivity approach for 
mixtures (CLP Annex I, 3.1.3.6.1 and 3.1.3.6.2.3). Therefore it is necessary to extrapolate from 

 
 
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adequate and reliable data and by taking into account the potency (i.e. the magnitude of the 
lethal dose reported) of the effects in humans. Thus an equivalent ATE may be derived on the 
basis of valid human toxicity data (minimum dose/concentration) and used directly in the 
additivity formulae (see Section 3.1.5.1.1 Example 1 of this Guidance). The alternative to the 
derivation of an equivalent ATE is the allocation to a category. The category should be justified 
by semi-quantitative or qualitative data and a subsequent derivation of a converted ATE 
(cATpE) according to CLP Annex I, Table 3.1.2 and subsequent use in the formulae (see Section 
3.1.5.1.2 Example 2 of this Guidance). See also Section 3.1.2.3.1 of this Guidance for more 
details. 

c.  Evidence from other toxicity tests 

Standard acute toxicity studies should be the primary source of information for acute toxicity 
classification. However, when such data are not available or only data from non-reliable studies 
exist, information from studies conducted for other endpoints can be used for acute toxicity 
classification. For example, data on early effects from repeated dose testing can be used. These 
studies will not usually provide an exact ATE value that can be used directly for classification, 
but they may provide enough information to allow an estimate of acute toxicity to be made, 
which would be sufficient to support a decision on classification. Furthermore, it can also be 
concluded that no classification is warranted for instance by a 28-day repeated dose toxicity 
study that is performed with 1000 mg/kg bw/day and no adverse effects are observed (refer to 
Appendix 7.4-1 of Guidance R.7a). In addition, a substance not acutely toxic after oral exposure 
is not considered as acutely toxic via dermal exposure (see Guidance R.7a). 

Example: 

Available information: In a range finding study with respect to repeated dose toxicity daily oral 
doses of 1000 mg/kg bw over 5 days prove to be neither lethal nor cause serious symptoms in 
rats at the end of the observation period of 14 days. 

Conclusion: the ATE is >2000 mg/kg bw since 2 doses following (within roughly) 24 h are not 
lethal (see Section 3.1.2.2 of this Guidance). Thus this ingredient can be ignored in the 
additivity procedure. 

d.  Use of (Q)SAR 

LD50/LC50 values predicted by a highly reliable model (see Section 3.1.2.3.2 of this Guidance) 
may be used according to Note (a) to CLP Annex I, Table 3.1.1 directly as LD50/LC50=ATE in the 
additivity formula CLP Annex I, 3.1.3.6.1. If the assessment using (Q)SARs gives a more 
general result a cATpE according to Table 3.1.2 may be derived. It has to be emphasised that 
these approaches generally require substantial technical information, and expert judgement, to 
reliably estimate acute toxicity. 

Further guidance on how to apply this provision is given in Section 3.1.3.3.6 of this Guidance. 

Annex  I:  3.1.3.6.2.3.  If  the  total  concentration  of  the  relevant  ingredient(s)  with  unknown 
acute toxicity is ≤ 10 % then the formula presented in section 3.1.3.6.1 shall be used. If the 
total concentration of the relevant ingredient(s) with unknown toxicity is > 10 %, the formula 
presented  in  section 3.1.3.6.1  shall  be  corrected  to  adjust  for  the  total  percentage  of  the 
unknown ingredient(s) as follows: 

=−niimixumknownATECATE10%ifC100 
 
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3.1.3.3.6. 

Ingredients that should be taken into account for the purpose of 
classification 

Annex I: 3.1.3.3.(a) the ‘relevant ingredients’ of a mixture are those which are present in 
concentrations of 1 % (w/w for solids, liquids, dusts, mists and vapours and v/v for gases) or 
greater, unless there is a reason to suspect that an ingredient present at a concentration of 
less than 1 % is still relevant for classifying the mixture for acute toxicity (see Table 1.1). 

When a mixture contains a ‘relevant’ ingredient (i.e. constituting ≥ 1%; CLP Annex I, 3.1.3.3 
(a)) for which there is no adequate acute toxicity data then the mixture must be classified on 
the basis of the ingredients with known toxicity, with an additional statement on the label and in 
the SDS to indicate that the mixture consists of ‘x percent’ of component(s) of unknown acute 
toxicity (CLP Annex I, 3.1.3.6.2.2). The determination of the classification depends on what 
proportion of the mixture such ingredients of unknown toxicity constitute. If these ingredients 
constitute ≤10% of the total mixture, the additivity formula in CLP Annex I, 3.1.3.6.1 must be 
used. However, in cases where these ingredients constitute over 10%, a modified additivity 
formula in CLP Annex I, 3.1.3.6.2.3 must be used, which adjusts for the presence of a 
significant proportion of ingredients of unknown toxicity. This reflects the greater uncertainty as 
to the true toxicity of the mixture). 

Annex I: Excerpt of Table 1.1 

Generic cut-off values 

Hazard class 

Generic cut-off values to be taken into account 

Acute Toxicity: 

-  Category 1-3 

-  Category 4 

0,1 % 

1 % 

Note: Generic cut-off values are in weight percentages except for gaseous mixtures for those 
hazard classes where the generic cut-off values may be best described in volume percentages. 

As indicated in CLP Annex I, Table 1.1, when components are present in low concentrations 
they do not need to be taken into account when determining the classification of the mixture, 
according to the approaches detailed in CLP Annex I, 3.1.3.6.1 and 3.1.3.6.2.3 (see Section 
3.1.5.3.1 Example 11 of this Guidance). Accordingly, all components classified in Categories 1-3 
at a concentration <0.1% and Category 4 <1% are not taken into account. Similarly unknown 
ingredients present at <1% are not taken into account. 

3.1.3.3.7.  Non-classified components 

For mixtures containing ingredients with ATE values that are more than 2000 mg/kg (i.e. non-
classified components), such ingredients need not be considered in the calculation of ATEs with 
the formula presented in CLP Annex I: 3.1.3.6.1. However, in cases where no acute toxicity data 
are available for some ingredients or a mixture contains ingredients with unspecified ATE values 
which could fall within the classifiable limits, then the formula of CLP Annex I: 3.1.3.6.2.3 has to 
be used for calculation of ATEs to adjust for the concentrations of ingredients with unknown acute 
toxicities. 

 
 
 
 
 
 
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3.1.3.4.  Generic concentration limits for substances triggering classification 

of mixtures 

Generic concentration limits as such are not applicable for acute toxicity classification; therefore 
specific concentration limits are also not applicable (see Section 3.1.2.5 of this Guidance). 
Nevertheless, according to CLP Annex VI, 1.2.1 the classification for entries with the reference * 
in the column specific concentration limits is of special concern; the * means that those entries 
had an SCL in CLP Annex VI, Table 3.2 originating from Annex I to DSD. When assessing a 
mixture according to the procedure set out in CLP Annex I, a thorough search for the data 
(animal, human experience or other information) is necessary. The assessment must take all 
available information into account using a weight of evidence approach and expert judgement 
with special emphasis on possibly available human experience or information. These validated 
data will then be used in the additivity formula in CLP Annex I, 3.1.3.6.1 as ATEs or cATpEs 
(CLP Annex I, Table 3.1.2). 

3.1.3.5.  Decision on classification  

The assessment of classification has to be performed with respect to all the relevant routes of 
exposure (oral, dermal, inhalation) on the basis of all adequate reliable data. If there is 
evidence of toxicity by multiple routes of exposure classification is warranted for all these 
routes, however the label should include one pictogram and a signal word reflecting the most 
severe hazard category. If, for example, a mixture fulfils the criteria for oral toxicity Category 4 
and for inhalation Category 2, then the mixture will be classified in Category 4 for oral toxicity 
and Category 2 for inhalation toxicity and assigned the corresponding hazard statements; it will 
be labelled with the acute toxicity Category 2 pictogram (skull and cross bones) and the signal 
word ‘Danger’ and both the hazard statements for inhalation Category 2 (H330) and oral 
Category 4 (H302) (see CLP Annex I Table 3.1.3 in next section 3.1.4.1 of this Guidance). 

3.1.3.6.  Decision logic for classification of mixtures 

The decision logic is provided as additional guidance. It is strongly recommended that the 
person responsible for classification study the criteria for classification before and during use of 
the decision logic. 

 
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Does the mixture as a whole have 
data/information to evaluate acute 
toxicity? 

Yes 

Classify in appropriate 
category according to CLP 
Annex I, Table 3.1.1 toxicity 

No 

Can bridging principles be applied? 

Yes 

Classify in appropriate 
category  

No 

Is acute toxicity data available for all 
ingredients of mixture?  

Yes 

Apply the acute toxicity 
estimate calculation to 
determine the ATE of 
the mixture 

No 

Is it possible to estimate missing 
ATE(s) of the ingredient(s), i.e. can 
conversion value(s) be derived? 

Yes 

where: 

No 

Is the total concentration of the 
ingredient(s) with unknown acute 
toxicity ≤ 10%?  

Yes 

No 

ATE mix to 
Decision 
logic in 
3.1.2.6 

Ci  =  concentration  of 
ingredient i  

i  = 
the 
ingredient from 1 to n 

individual 

n  = 
ingredients  

the  number  of 

Toxicity 
ATEi = Acute 
Estimate of ingredient i. 

Apply the acute toxicity estimate calculation (i.e. when the 
total concentration of ingredients with unknown acute 
toxicity is > 10%): 

ATE mix to Decision 
logic in 3.1.2.6 

 
 
 
 
 
 
  
  
 
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3.1.4.  Hazard communication in the form of labelling for acute toxicity 

3.1.4.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

Annex I: Table 3.1.3 

Acute toxicity label elements 

Classification 

Category 1 

Category 2 

Category 3 

Category 4 

GHS Pictograms 

Signal Word 

Danger 

Danger 

Danger 

Warning 

Hazard Statement: 

– Oral 

– Dermal 

H300: Fatal 
if swallowed 

H300: Fatal 
if swallowed 

H301: Toxic 
if swallowed 

H302: Harmful if 
swallowed 

H310: Fatal 
in contact 
with skin 

H310: Fatal 
in contact 
with skin 

H311: Toxic 
in contact 
with skin 

H312: Harmful in 
contact with skin 

– Inhalation 

(see Note 1) 

H330: Fatal 
if inhaled 

H330: Fatal 
if inhaled 

H331: Toxic 
if inhaled 

H332: Harmful if 
inhaled 

Precautionary  Statement 
Prevention (oral) 

P264 

P270 

P264 

P270 

P264 

P270 

P264 

P270 

Precautionary  Statement 
Response (oral) 

Precautionary  Statement 
Storage (oral) 

Precautionary  Statement 
Disposal (oral) 

Precautionary  Statement 
Prevention (dermal) 

P301 + P310 

P301 + P310 

P301 + P310 

P301 + P312 

P321 

P330 

P405 

P321 

P330 

P405 

P321 

P330 

P405 

P330 

P501 

P501 

P501 

P501 

P280 

P280 

P262 

P264 

P270 

P280 

P262 

P264 

P270 

P280 

Precautionary  Statement 
Response (dermal) 

P302 + P350 

P302 + P350 

P302 + P352 

P302 + P352 

P310 

P310 

P312 

P312 

 
 
 
 
 
 
 
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P322 

P361 

P363 

P322 

P361 

P363 

P322 

P361 

P363 

P322 

P363 

Precautionary  Statement 
Response (dermal) 

P302 + P352 

P302 + P352 

P302 + P352 

P302 + P352 

P310 

P321 

P310 

P321 

P312 

P321 

P312 

P321 

P361 + 

P361 + 

P361 + 

P362 +P364 

Precautionary  Statement 
Storage (dermal) 

Precautionary  Statement 
Disposal (dermal) 

Precautionary  Statement 
Prevention (inhalation) 

P364 

P405 

P364 

P405 

P364 

P405 

P501 

P501 

P501 

P501 

P260 

P271 

P284 

P260 

P271 

P284 

P261 

P271 

P261 

P271 

Precautionary  Statement 
Response (inhalation) 

P304 + P340 

P304 + P340 

P304 + P340 

P304 + P340 

P310 

P320 

P310 

P320 

P311 

P321 

P312 

Precautionary  Statement 
Storage (inhalation) 

Precautionary  Statement 
Disposal (inhalation) 

Note 1 

P403 + P233 

P403 + P233 

P403 + P233 

P405 

P501 

P405 

P501 

P405 

P501 

In addition to classification for inhalation toxicity, if data are available that indicates that 
the mechanism of toxicity is corrosivity, the substance or mixture shall also be labelled as 
EUH071: ‘corrosive to the respiratory tract’ — see advice at 3.1.2.3.3. In addition to an 
appropriate acute toxicity pictogram, a corrosivity pictogram (used for skin and eye 
corrosivity) may be added together with the statement ‘corrosive to the respiratory tract’. 

Note 2 

In the event that an ingredient without any useable information at all is used in a mixture 
at a concentration of 1 % or greater, the mixture shall be labelled with the additional 
statement that ‘x percent of the mixture consists of ingredient(s) of unknown toxicity’ — 
see advice at 3.1.3.6.2.2. 

EUH071 can also be applied to inhaled corrosive substances not tested for acute inhalation 
toxicity according to CLP Annex II, Section 1.2.6 

If a substance or a mixture fulfils the classification criteria with respect to different routes the 
pictogram and signal word will be based on the most severe one, however the hazard 
statements for each route must be included on the label.  

 
 
 
 
 
 
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Article 26 1 (b)  

If the hazard pictogram ‘GHS06’ applies, the hazard pictogram ‘GHS07’ shall not appear. 

3.1.4.2.  Additional labelling provisions 

In addition to the statement required under CLP Annex I, 3.1.3.6.2.2, it would be appropriate to 
specify the relevant exposure route of toxicity concerned on a case-by-case basis: For example 
‘x percent of the mixture consists of component(s) of unknown acute oral toxicity’. In the case 
of different values being available for the % of ingredients having unknown acute toxicity (as a 
result of different route of exposure), the % value to be included in the sentence on the label 
should be selected based on the route where the % of ingredients having unknown toxicity is 
the highest. 

Annex I: 3.1.3.6.2.2. In the event that a component without any useable information for 
classification is used in a mixture at a concentration ≥ 1 %, it is concluded that the mixture 
cannot be attributed a definitive acute toxicity estimate. In this situation the mixture shall be 
classified based on the known components only, with the additional statement on the label 
and in the SDS that: “x percent of the mixture consists of component(s) of unknown acute 
toxicity”, taking into account the provisions set out in section 3.1.4.2. 

Annex I: 3.1.4.2 

The acute toxicity hazard statements differentiate the hazard based on the route of 
exposure. Communication of acute toxicity classification should also reflect this 
differentiation. If a substance or mixture is classified for more than one route of exposure 
then all relevant classifications should be communicated on the safety data sheet as 
specified in Annex II to Regulation (EC) No 1907/2006 and the relevant hazard 
communication elements included on the label as prescribed in section 3.1.3.2. If the 
statement “x % of the mixture consists of ingredient(s) of unknown acute toxicity” is 
communicated, as prescribed in section 3.1.3.6.2.2, then, in the information provided in the 
safety data sheet, it can also be differentiated based on the route of exposure. For example, 
“x % of the mixture consists of ingredient(s) of unknown acute oral toxicity” and “x % of the 
mixture consists of ingredient(s) of unknown acute dermal toxicity 

In case section 3.1.3.6.2.2 applies and the statement ‘x % of the mixture consists of 
ingredient(s) of unknown acute toxicity’ has to be communicated, the same statement can be 
differentiated on the basis of the route of exposure in the safety data sheet (SDS) in accordance 
with CLP Annex I 3.1.4.2.  For example on the label and in the SDS the following should 
appear: ‘x % of the mixture consists of ingredient(s) of unknown acute toxicity’; in the SDS the 
route of exposure can also be specified, for example ‘x % of the mixture consists of 
ingredient(s) of unknown acute oral toxicity’ and ‘x % of the mixture consists of ingredient(s) of 
unknown acute dermal toxicity’. In case of different values being available for the % of 
ingredients having unknown toxicity (as a result of a different route of exposure), the % value 
to be included in the sentence on the label should be selected based on the route where the % 
of ingredients having unknown toxicity is the highest.  

 
 
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Corrosivity: 

Annex I: 3.1.2.3.3.  

In addition to classification for inhalation toxicity, if data are available that indicates that the 
mechanism of toxicity was corrosivity, the substance or mixture shall also be labelled as 
‘corrosive to the respiratory tract’ (see note 1 in 3.1.4.1). Corrosion of the respiratory tract is 
defined by destruction of the respiratory tract tissue after a single, limited period of exposure 
analogous to skin corrosion; this includes destruction of the mucosa. The corrosivity 
evaluation can be based on expert judgment using such evidence as: human and animal 
experience, existing (in vitro) data, pH values, information from similar substances or any 
other pertinent data. 

In addition to the application of the classification for acute inhalation toxicity, the substance or 
mixture must also be labelled as EUH071 where data are available which indicate that the mode 
of toxic action was corrosivity (see Note 1 to Table 3.1.3). Such information can be derived 
from data which warrant classification as corrosive according to the hazard skin 
corrosion/irritation (see Chapter 3.2 of this Guidance). In this case the substance or mixture 
has to be classified and labelled for skin corrosion with the pictogram for corrosivity, GHS05, 
hazard statement H314 and also labelling with EUH071 (for criteria, see CLP Annex II) is 
required (see Chapter 3.2.4.2 of this Guidance). 

Annex II: 1.2.6. EUH071 — ‘Corrosive to the respiratory tract’  

For substances and mixtures in addition to classification for inhalation toxicity, if data are 
available that indicate that the mechanism of toxicity is corrosivity, in accordance with Section 
3.1.2.3.3 and Note 1 of Table 3.1.3 in Annex I.  

For substances and mixtures in addition to classification for skin corrosivity, if no acute 
inhalation test data are available and which may be inhaled.  

Corrosive substances and mixtures may be acutely toxic after inhalation to a varying degree, 
although this is only occasionally proved by testing. In case no acute inhalation study is 
available for a corrosive substance or mixture, and such substance or mixture may be inhaled, a 
hazard of respiratory tract corrosion may exist. As a consequence, substances and mixtures 
have to be supplementarily labelled with EUH071, if there is a possibility of exposure via 
inhalation taking into consideration the saturated vapour concentration and the possibility of 
exposure to particles or droplets of inhalable size as appropriate (see also Chapter 3.8.2.5 of 
this Guidance. It is strongly recommended to apply the precautionary statement P260: Do not 
breathe dust/fume/gas/mist/vapours/spray.  

Toxic by eye contact: 

Annex II:  1.2.5  EUH070 — ‘Toxic by eye contact’  

For substances or mixtures where an eye irritation test has resulted in overt signs of systemic 
toxicity or mortality among the animals tested, which is likely to be attributed to absorption of 
the substance or mixture through the mucous membranes of the eye. The statement shall 
also be applied if there is evidence in humans for systemic toxicity after eye contact.  

The statement shall also be applied where a substance or a mixture contains another 
substance labelled for this effect, if the concentration of this substance is equal to, or greater 
than 0,1 %, unless otherwise specified in part 3 of Annex VI. 

In cases where a substance or mixture has shown clear signs of severe systemic toxicity or 
mortality in an eye irritation study a supplemental labelling phrase EUH070 ‘Toxic by eye 
contact’ is required. This additional labelling, based on relevant data, is independent of any 
classification in an acute toxicity category. 

 
 
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Liberation of toxic gases 

Annex II: 1.2.1. EUH029 — ‘Contact with water liberates toxic gas’  

For substances and mixtures which in contact with water or damp air, evolve gases classified 
for acute toxicity in category 1, 2 or 3 in potentially dangerous amounts, such as aluminium 
phosphide, phosphorus pentasulphide.  

Annex II: 1.2.1 EUH031 — ‘Contact with acids liberates toxic gas’  

For substances and mixtures which react with acids to evolve gases classified for acute 
toxicity in category 3 in dangerous amounts, such as sodium hypochlorite, barium 
polysulphide.  

Annex II: 1.2.3. EUH032 — ‘Contact with acids liberates very toxic gas’  

For substances and mixtures which react with acids to evolve gases classified for acute 
toxicity in category 1 or 2 in dangerous amounts, such as salts of hydrogen cyanide, sodium 
azide.  

 
 
 
 
 
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3.1.5.  Examples of classification for acute toxicity 

  NOTE: The classification proposals for the examples refer only to acute toxicity. 

3.1.5.1.  Examples of substances fulfilling the criteria for classification  

3.1.5.1.1. 

Example 1: Methanol 

Application 

Use  of  adequate  and  reliable  human  data  allowing  derivation  of  an 
equivalent  ATE  according  to  CLP  Annex  I,  Table  3.1.1.  Animal  data  not 
appropriate. 

Test Data 

Classification  Rationale  

Available 
information 

Animal data: 

Oral LD50 rat ≥ 5000 mg/kg 
bw 

Classification 
not possible 

Human experience: 

Category 3 

Methanol is known to cause 
lethal intoxications in 
humans (mostly via 
ingestion) in relatively low 
doses: ‘…minimal lethal dose 
in the absence of medical 
treatment is between 300 
and 1000 mg/kg bw’ (IPCS, 
Environmental Health 
Criteria 196, Methanol, 
WHO, 1997) 

The rat is known to be 
insensitive to the toxicity of 
methanol and is thus not 
considered to be a good 
model for human effects 
(different effect/mode of 
action) 

The minimum lethal dose 
reported of 300 mg/kg bw is 
used as equivalent ATE; 
according to CLP Annex I, 
Table 3.1.1 the resulting 
classification is Category 3  

Remarks 

Test data in rats from mixtures containing methanol should not be used directly 
in additivity formula 

3.1.5.1.2. 

Example 2: N,N-Dimethylaniline 

Application  Use of qualitative human data and of SAR information with extrapolation 
to an ATE (CLP Annex I, 3.1.3.6.2.1(b) and Table 3.1.2). Animal data are 
not appropriate. 

Test Data 

Classification  Rationale  

Available 
information 

Animal data: 

Category 4 

Acute dermal toxicity: LD50 
values > 1690 mg/kg bw 
rabbit. 

Human experience: 

Broad human experience, 
reported in many case 

Category 3 
(oral, dermal, 
inhalation) 

The extensive and consistent 
human experience is 
considered to be sufficiently 
robust by expert judgement to 

 
 
 
 
 
 
 
 
 
 
 
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reports, demonstrating 
death from MetHB 
following relatively low 
oral/dermal/inhalation 
exposure to aromatic 
amines such as N,N-
dimethylaniline. For N,N-
Dimethyl -aniline itself  no 
exact human toxicity 
values are available. 

be used for classification into 
Category 3. The rabbit LD50 
suggests lower sensitivity to 
MetHB formation than humans 
which is consistent with what 
is known from other rabbit 
tests with substances known to 
induce MetHB in humans. The 
rabbit data are therefore not 
considered to be adequate for 
acute toxicity classification. 
Therefore the human data on 
this and structurally 
related substances are used to 
give a converted Acute Toxicity 
point Estimate (cATpE) 
according to CLP Annex I, 
Table 3.1.2 for Category 3; 
e.g. cATpE dermal = 300 
mg/kg bw, which then falls 
into a higher category than the 
rabbit data. 

Remarks 

none 

3.1.5.1.3. 

Example 3 

Application  No exact LD50 value available. Expert judgement needed. 

Test Data 

Classification  Rationale  

Available 
information 

Corrosive volatile liquid (not 
classified for skin corrosion). 

Category 4 

Animal data: 

In a GLP-compliant acute 
oral toxicity study in rats, 
the following results were 
observed: 

At a test dose of 200 
mg/kg bw: no mortality, 
only transient symptoms 
and no necropsy findings. 

At a test dose of 500 
mg/kg: 100% mortality, 
symptoms: poor general 
state; necropsy findings: 
hyperemia in stomach 
(due to local irritation 
/corrosivity), no other 
organs affected. 

Since at a dose of 200 mg/kg 
bw no mortality and only 
slight transient symptoms 
without necropsy findings 
were observed, and at 500 
mg/kg bw the high 
amount/concentration of the 
corrosive substance caused 
serious effect only at the site 
of action and mortality, based 
on expert judgement it can be 
assumed that the likely LD50 is 
> 300 mg/kg bw. Therefore, 
the Acute Toxicity Estimate 
(ATE) value for classification 
purpose is between 300 and 
500 mg/kg bw, corresponding 
to Category 4 classification for 
acute toxicity. 

Remarks 

Labelling (in addition to the labelling provisions for Acute tox Cat. 4): Corrosive 
pictogram (pictogram is not mandatory, it may be added) (see Annex I: Note 1 
of Table 3.1.3) 

Additional Hazard statement: EUH071 Corrosive to the respiratory tract 

 
 
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3.1.5.1.4. 

Example 4 

Application 

Use of non-standard-guideline test data. 

Test Data 

Classification  Rationale  

Rationale for classification: 
Since the dermal LD50 is 
above 50 mg/kg bw and less 
than 200 mg/kg bw, 
Category 2 classification is 
warranted (see CLP Annex I, 
Table 3.1.2) 

Available 
information 

Animal data: 

Category 2  

A study to evaluate the 
acute dermal 
(percutaneous) toxicity 
was performed in rabbits. 
The following test data 
results were reported: 

- At the dose level of 50 
mg/kg bw: no mortality 
was observed 

- At 200 mg/kg bw: 100% 
mortality  

Therefore, the LD50 was 
estimated to be between 
50 mg/kg bw and 200 
mg/kg bw 

Remarks 

none 

3.1.5.1.5. 

Example 5  

Application 

Use of CLP Annex I, Table 3.1.1 and experimentally obtained LC50 value 

Test Data 

Classification  Rationale  

Available 
information 

A gas 

Animal data: 

Category 4 

A GLP-compliant test for 
acute inhalation toxicity 
(gaseous form) was 
performed in accordance 
with OECD TG 403 in rats. 
The following LC50 was 
calculated: 

LC50: 4500 ppm/4h 

Rationale for classification: 
LC50 = 4500 ppm is 
considered an Acute Toxicity 
Estimate (ATE) for 
classification purposes; 
according to the classification 
criteria for acute inhalation 
toxicity for gases (CLP Annex 
I, Table 3.1.1), this value 
corresponds to Category 4. 
Therefore Category 4 Acute 
Inhalation Toxicity 
classification is warranted. 

Remarks 

none 

3.1.5.1.6. 

Example 6  

Application 

Time extrapolation; Note (c) in CLP Annex I, Table 3.1.1; Haber’s law 

Test Data 

Classification  Rationale  

Available 
information 

Solid substance  

Category 3  

Animal data: 

The classification criteria for 
acute inhalation toxicity in 
CLP Annex I, Table 3.1.1 
refer to a 4h exposure time; 

 
 
 
 
 
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The acute inhalation 
toxicity was studied in rats 
in a GLP-compliant study 
performed in principle 
according to OECD TG 403 
in rats, but with respect 
for transport only with 1-h 
exposure. The LC50 (1-h) 
of 3 mg/l was calculated. 

therefore to classify a 
substance, existing inhalation 
toxicity data generated from 
1-hour exposure should be 
converted accordingly: LC50 
values with 1h have to be 
converted by dividing by 4 
(Haber’s rule/law, dusts and 
mists) 

LC50 (4-h) = (LC50 (1-h) : 4) 
= (3 mg/l : 4) = 0.75 mg/l, 
thus Category 3 classification 
is warranted according to CLP 
Annex I, Table 3.1.1. 

Remarks 

none 

3.1.5.1.7. 

Example 7: 2,3-Dichloropropene 

Application 

Discrimination from STOT-SE 

Test Data 

Classification  Rationale  

Category 3 oral 
and Category 3 
inhalation 

Classification according to 
criteria for acute inhalation 
and oral toxicity in CLP 
Annex I, Table 3.1.1. 

Available 
information 

Animal data: 

- Oral LD50, rat 250-320 
mg/kg bw (assumption: 
results from different 
tests; lowest LD50 is valid) 

- Inhalation LC50 rat 2.3 
mg/l/4h (vapour) 

Observations: 

extensive liver and kidney 
damage following oral and 
inhalation exposure to 
lethal doses (insufficient 
information) 

Remarks 

The substance is classified for acute toxicity and not for STOT-SE, since the 
observed organ toxicity is clearly the cause of the lethality 

 
 
 
 
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3.1.5.1.8. 

Example 8 

Application 

Route-to-route extrapolation: oral to inhalation (Section 3.1.3.3.5 of this 
Guidance). Expert judgement. 

Test Data 

Extrapolated 
inhalation 
ATE/CATpE 

Rationale  

Available 
information 

Animal data: 

LD50 oral rat: 250 mg/kg 
bw (Category 3) 

100 % oral absorption 
assumed 

a) No specific kinetic 
information 

b) Robust kinetic information 
allows the conclusion that 
only 50% is absorbed due to 
an exhalation rate of 50 %. 

0.5 mg/l/4h 
(cATpE) 

2.6 mg/l/4h 
(ATE) 

a) Using the extrapolation 
formula 1 mg/kg bw = 
0.0052 mg/l/4h: 
250 x 0.0052 mg/l/4h  = 1.3 
mg/l/4h → Category 2 
according to CLP Annex I, 
Table 3.1.2 

b)Based on the 50% 
inhalation absorption rate the 
equivalent ATE would be 2.6 
(2 x 1.3) → Category 3 
according to CLP Annex I, 
Table 3.1.2 

Remarks 

Robust kinetic and other information would allow the use of directly derived 
ATEs in the additivity formulae by expert judgement 

3.1.5.1.9. 

Example 9 

Application  Route-to-route  extrapolation:  oral  to  dermal  (Section  3.1.3.3.5  of  this 

Guidance). Expert judgement. 

Test Data 

Extrapolated 
dermal 
ATE/cATpE 

Rationale  

Available 
information 

Animal data: 

LD50 rat oral: 270 mg/kg 
bw; 100 % oral absorption 
assumed 

a) Assumed dermal 
absorption rate: 100% 

b) Dermal absorption rate 
based on robust kinetic/SAR 
information: 25% 

300 mg/kg bw 

LD50 dermal 
1080 mg/kg 
bw 

a) Based on the assumption of 
100% dermal absorption the 
converted dermal ATE will be 
derived by using Table 3.1.2 
for Category 3 → 300 mg/kg 
bw as cATpE. 

b) Since dermal absorption is 
only 25%, the dermal ATE has 
to be accordingly increased → 
4x270 mg/kg bw = 1080 
mg/kg bw. This is regarded as 
an equivalent ATE which can 
be directly used in the 
additivity formulae. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Remarks 

Robust kinetic and other information would allow the use of directly derived ATEs 
in the additivity formulae by expert judgement 

3.1.5.2.  Examples of substances not fulfilling the criteria for classification 

3.1.5.2.1. 

Example 10 

Application 

Available data are of different quality. Expert judgement. WoE. 

Test Data 

Classification  Rationale  

No classification  With 3 different available 

values a validity check 
proved that the study with 
LC50 = 19 mg/l is not fully 
valid in contrast to the two 
others; thus in a weight of 
evidence approach it is 
concluded that the LC50 = 
ATE > 20 mg/l/4h. The 
criteria for Category 4 are 
not fulfilled. 

Available 
information 

A liquid 

Animal data: 

Three studies for acute 
inhalation toxicity (vapour) 
in rats are described. Two 
studies were performed in 
accordance with test 
guideline 403 and were 
GLP-compliant. One study 
has deficiencies with 
respect to study 
methodology and 
description of study 
performance and 
documentation of the test 
results; no GLP-
compliance. The LC50 were 
as follows:  

– LC50: 19 mg/l/4h (no GLP) 

– LC50: 23 mg/l/4h (TG 403, 

GLP) 

– LC50: 28 mg/l/4h (TG 403, 

GLP) 

Remarks 

none 

 
 
 
 
 
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3.1.5.3.  Example of mixtures fulfilling the criteria for classification 

3.1.5.3.1. 

Example 11 

Application  Application of the ‘Relevant ingredient’ (CLP Annex I, 3.1.3.3 (a)) and ‘Generic 
cut-off  values  to  be  taken  into  account’  concepts  (CLP  Annex  I,  Table  1.1)  for 
mixtures with data gaps using the equation in CLP Annex I, 3.1.3.6.2.3. 

For  dermal  and  inhalation  routes,  there  is  no  acute  toxicity  data  available  for 
ingredients 2 and 4. For ingredients 1, 3 and 5 the data indicates no classification 
for acute toxicity. 

Test Data 

Classification 
(ingredient) 

Rationale  

Available 
information 

Animal data (oral 
rat): 

Ingredient 1 
(4%) 

LD50:            125 
mg/kg bw 

Oral Category 3 

Apply the equation in CLP Annex I, 3.1.3.6.2.3: 

Ingredient 2 
(92%) 

Ingredient 3 
(3%) 

Ingredient 4 
(0.9%) 

No data available 

- 

LD50:           

Oral Category 4 

1500 mg/kg bw 

No data available 

- 

Ingredient 5 
(0.2%) 

LD50:              10 
mg/kg bw 

Oral Category 2 

=

ATEmix = 148 mg/kg bw 

→ Category 3 

Remarks 

Rationale for classification of the mixture in Category 3: 

1. Classification via application of substance criteria is not possible since acute toxicity 
test data was not available for the complete mixture (CLP Annex I, 3.1.3.4). 

2. Classification via the application of bridging principles is not possible since data on a 
similar mixture was not available (CLP Annex I, 3.1.3.5.1). 

3. Classification based on ingredient data for the mixture can be considered (CLP Annex 
I, 3.1.3.6). 

4. Applying the ‘relevant ingredients’ concept from CLP Annex I, 3.1.3.3 (a) means that 
Ingredient 4 is excluded from the ATEmix calculation since its concentration is < 1%. The 
same reasoning cannot apply to Ingredient 5, though its concentration is below the 
‘relevant ingredients’ threshold of 1% but it is higher than the cut-off value of 0.1% for a 
Category 2 ingredient in CLP Annex I, Table 1.1. 

5. The total concentration of ingredients with unknown acute toxicity (i.e., Ingredient 2) 
is 92%; therefore, the ATEmix equation in CLP Annex I, 3.1.3.6.2.3 must be used. This 
corrected calculation adjusts for the total percentage of the ingredient with unknown 
acute toxicity. 

6. Ingredients 1, 3 and 5 are included in the ATEmix calculation because they have data 
that fall within a CLP acute toxicity category, CLP Annex I, 3.1.3.6.1 (a). 

7. Applying the guidance in Note (b) to CLP Annex I, Table 3.1.1 results in using the 
actual LD50 data for Ingredients 1, 3 & 5 in the ATEmix calculation since data is available. 

Additional Labelling: ‘92% of the mixture consists of components of unknown acute 
toxicity.’ (See Section 3.1.4.2 of this guidance)  

=−niimixunknownATECATEifC%)10(100=++=−102.015003125492100mixATE054.002.0002.0032.0=++ 
 
 
 
 
 
 
 
 
 
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3.1.5.3.2. 

Example 12a 

Note: Examples 12a and 12b assume that it is known that only one physical form (i.e. mist in 
example 12a and vapour in example 12b) can occur during any reasonably expected use of the 
mixture  including  when  the  mixture  is  used  to  produce  a  new  mixture.  This  would  need  to  be 
justified. If toxicity data for more than one form is used, the converted ATE value has to be used 
even if an ATE value is available, according to these examples. 

Application 

Different phases in inhalation exposure. Extrapolation. 

Test Data  

Classification  Rationale  

Available 
information 

Use/exposure as aerosol 
(mist) 

Animal data (rat): 
LC50 (mg/L/4 h) 

Ingredient 1 
solid (6%) 

Ingredient 2  
solid (11%) 

Ingredient 3 
solid (10%) 

Ingredient 4 
liquid (40%) 

Ingredient 5 
(33%) 

Category 4 

Conv. ATE (mg/L/4 h) =  
1.5 mg/L/4 h 

0.6 

Category 3 

ATE = LC50 

6 (dust) 

- 

11 (vapour) 

Category 4 

Neglected, since not classified 
in any acute category 

Conv. ATE (mg/L/4 h) = 1.5 
mg/L/4 h, assuming identical 
category for vapour and mist 
by expert judgement 

- 

Water; neglected 

Remarks 

Classification: Category 4 

No test data available for the whole mixture. 

Bridging principles not applicable since no test data on similar mixtures available. 

Classification therefore based on ingredients. 

Use additivity formula in Annex I, 3.1.3.6.1, as information is available for all 
ingredients. 

100/ATEmix = (6/1.5) + (11/0.6) + 0 + (40/1.5) + 0 = 49 

→ ATEmix = 2.04 mg/L/4 h → Category 4 

NOTE: The mixture of Example 12a has to be classified formally in Category 4 
with respect to inhalation toxicity. It is notable that this classification is only 
derived from the calculation for the aerosol phase, not for the vapour phase. 

3.1.5.4.  Examples of mixtures not fulfilling the criteria for classification 

3.1.5.4.1. 

Example 12b 

See Note under example 12a. 

 
 
 
 
 
 
 
 
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Application 

Different phases in inhalation exposure. Extrapolation. 

Test Data  

Classification  Rationale  

Available 
information 

Use/exposure as vapour 

Animal data (rat): 
LC50 (mg/L/4 h) 

Ingredient 1 
solid (6%) 

Ingredient 2 
solid (11%) 

Ingredient 3 
solid (10%) 

Ingredient 4 
liquid (40%) 

Ingredient 5 
(33%) 

Category 4 

A solid with no sublimation, 
therefore not present in the 
vapour phase; neglected 

0.6 (dust) 

Category 3 

As Ingredient 1 

6 (dust) 

- 

Neglected, since not classified 
in any acute category 

11 (vapour) 

Category 4 

ATE = LC50 

- 

Water; not relevant 

Remarks 

Classification: NC 

Inhalation is appropriate route since one hazardous ingredient with appreciable 
vapour pressure. 

No test data on the whole mixture. 

Bridging principles not applicable since no test data on similar mixtures available. 

Classification is therefore based on ingredients. 

Use additivity formula in CLP Annex I, 3.1.3.6.1 as information is available for all 
ingredients. 

There are no contributions from ingredients 1 and 2 in the formula since the 
diluted solid ingredients do not sublime, and thus are not present in the vapour 
phase; ingredient 3 is in addition not classified in any acute toxicity category. 
Ingredient 5 does not show acute toxicity. 

100/ATEmix = 0 + 0 + 0 + 40/11 + 0 = 3.64 → ATEmix =27.5 mg/L/4 h, which is 
above the upper generic concentration limit for vapour → NC 

3.1.5.5.  Example of the application of the additivity method for mixtures for 

acute inhalation toxicity with ingredient substances in different 
physical forms (gas, vapour, mist or dust). 

3.1.5.5.1. 

Example 13 

Application 

Information on acute inhalation toxicity for all ingredients 

Test  data  (LC50 
acute 
inhalation) 

Tested form  Classification 

Reference 

(ingredient) 

 
 
 
 
 
 
 
 
 
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Nicotine 
(1.9%) 

0.19 mg/L 

mist 

Category 2 

RAC 2015 

Diacetyl (6%)  2.25 < LC50 < 5.2 

vapour 

Category 3 

mg/L [4-hr] 

Propylene 
glycol (65%) 

Not acutely toxic 

BASF. 1993. Study on 
the acute inhalation 
toxicity LC50 of Diacetyl 
FCC as a vapor in rats 4 
hour exposure. Project 
No. 1310247/927010. 
BASF 

REACH registration 

Glycerine 
(27.1%) 

Rationale 

Not acutely toxic 

REACH registration 

1.  No test information on the mixture 
2.  No test information on similar mixtures 
3.  Sufficient information on all ingredients. Therefore the summation method 

is applicable. 

As the two ingredients which are acutely toxic have test data for different 
forms (mist and vapour), it is not clear which ATE range is applicable to the 
mixture. Therefore, the fraction of the acute toxicity of the mixture is 
calculated for each ingredient substance and category and added. When the 
sum of the fractions is one or higher for a category, that category is 
applicable to the mixture. (See also 3.1.3.3.4) 

For diacetyl, no LC50 was derived but only a range. Therefore, the converted 
ATE value in accordance with Table 3.1.2 was applied resulting in an ATE of 3 
mg/L which is inside the observed LC50 range. 

Applied formula:  

((limit/ATE) * concentration/100)mist + ((limit/ATE) x concentration/100)vapour 

limit= the upper border of ATE values for a hazard category (Table 3.1.1., 
Annex I, CLP) 

concentration= concentration of a component tested in a state/form 

Category 1 is not applicable as none of the ingredients are classified as 
category 1. 

Category 2: (0.5/0.19) * 1.9/100 (nicotine) + (2/3) * 6/100 (diacetyl) = 

0.05 + 0.04 = 0.09 which is below 1 meaning not category 2. 

Category 3: (1.0/0.19) * 1.9/100 (nicotine) + 10/3 * 6/100 (diacetyl) = 

0.10 + 0.20 = 0.30 which is below 1 meaning not category 3. 

Category 4: (5/0.19) * 1.9/100 (nicotine) + (20/3) * 6/100 (diacetyl) = 

0.50 + 0.40 = 0.90 which is below 1 meaning not category 4. 

 
 
 
 
 
 
 
 
 
 
 
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No classification for acute toxicity by the inhalation route is warranted 

3.1.6.  References 

OECD (2009) Series on testing and assessment number 39: Guidance document on acute 
inhalation toxicity testing ENV/JM/MONO(2009)28 (21 July 2009). 

ECETOC (2003) TR 86: European Centre for Ecotoxicology and Toxicology of Chemicals, 
Brussels, Belgium, Technical report N°86. 

Pauluhn, J. (2008) Inhalation toxicology: methodological and regulatory challenges. Exp Toxicol 
Pathol. 60(2-3):111-24. 

 
 
 
 
 
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3.2.  SKIN CORROSION/IRRITATION 

3.2.1.  Definitions for classification for skin corrosion/irritation 

Annex I: 3.2.1.1. Skin Corrosion means the production of irreversible damage to the skin; 
namely, visible necrosis through the epidermis and into the dermis, following the application 
of a test substance for up to 4 hours. Corrosive reactions are typified by ulcers, bleeding, 
bloody scabs, and, by the end of observation at 14 days, by discolouration due to blanching of 
the skin, complete areas of alopecia, and scars. Histopathology shall be considered to 
evaluate questionable lesions. 

Skin Irritation means the production of reversible damage to the skin following the application 
of a test substance for up to 4 hours. 

3.2.2.  Classification of substances for skin corrosion/irritation 

3.2.2.1. 

Identification of hazard information 

3.2.2.1.1. 

Identification of human data 

CLP Article 7(3) specifies that testing on humans is not allowed for the purposes of CLP; 
however it does acknowledge that existing human data obtained from other sources can be 
used for classification purposes. 

Human data may be retrieved from a number of sources, e.g. epidemiological studies, clinical 
studies, well-documented case reports, poison information units and accident databases or 
occupational experience. 

In this context the quality and relevance of existing human data for hazard assessment should 
be critically reviewed. There may be a significant level of uncertainty in human data due to poor 
reporting and lack of specific information on exposure. Diagnosis confirmed by expert physicians 
may be missing. Confounding factors may not have been accounted for. Small group sizes may 
flaw the statistical strength of evidence. Many other factors may compromise the validity of 
human data. In clinical studies (e.g. for diagnostic purposes) the selection of individuals and the 
control groups must be carefully considered. A critical review of the value of human studies is 
provided in the Guidance on IR&CSA Section R.4.3.3 and more specific considerations for skin 
corrosion/irritation are given in the Guidance on IR&CSA Section R.7.2.4.2. 

Data indicates that human skin is, in most cases, less sensitive than the skin of rabbits 
(ECETOC, 2002). 

3.2.2.1.2. 

Identification of non human data 

Non human data include physico-chemical properties, results from (Q)SARs and models based 
on combinations of (Q)SARs and databases (expert systems), and results from in vitro and in 
vivo tests. Available skin corrosion/irritation information on substances may include existing 
data generated by the test methods in the Test Methods Regulation (Commission Regulation 
(EC) No 440/2008) or by methods based on internationally recognised scientific principles.  

Before using the non-testing methods as referred to in the following sections, it should be 
checked whether the methods are sufficiently validated (or considered valid in case of (Q)SAR 
and expert systems) against the criteria for classification according to CLP (and not validated 
against the old DSD criteria which differed slightly from the CLP criteria). 

3.2.2.1.2.1.  Consideration of physico-chemical properties 

Substances with oxidising properties can give rise to highly exothermic reactions in contact with 
other substances and human tissue. High temperatures thus generated may damage/destroy 

 
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biological materials. This applies, for example, to organic peroxides, which can be assumed to 
be skin irritants, unless evidence suggests otherwise (Guidance on IR&CSA Section R.7.2.3.1).  

Thus, in the absence of evidence to the contrary, classification as Skin Irritation Category 2 
should be considered for peroxides, whereas the classification for a hydroperoxide would 
normally be Skin Corrosive Category 1. Appropriate evidence must be provided in order to 
consider no classification of substances with oxidising properties. 

3.2.2.1.2.2.  pH and acid/alkaline reserve 

Annex I: 3.2.2.2.5. Likewise, pH extremes like ≤ 2 and ≥ 11,5 may indicate the potential to 
cause skin effects, especially when associated with significant acid/alkaline reserve (buffering 
capacity). Generally, such substances are expected to produce significant effects on the skin. 
In the absence of any other information, a substance is considered as corrosive to skin (Skin 
Corrosion Category 1) if it has a pH ≤ 2 or a pH ≥ 11,5. However, if consideration of 
alkali/acid reserve suggests the substance may not be corrosive despite the low or high pH 
value, this needs to be confirmed by other data, preferably by data from an appropriate 
validated in vitro test. 

Prediction of skin corrosivity based on pH extremes shows a very high specificity (˃90%) and 
therefore a low number of false positives (R.7.2.4.1, IR&CSA guidance). The acid/alkaline 
reserve is a measure of the buffering capacity of chemicals. For details of the methodology, see 
Young et al, 1988, and Young and How, 1994. The higher the buffer capacity, the higher in 
general the potential for corrosivity. 

3.2.2.1.2.3.  Non-testing methods: (Q)SARs and expert systems 

Non-testing methods such as (Q)SARs and expert systems (a diverse group of models 
consisting of combinations of SARs, QSARs and databases) may be considered on a case-by-
case basis. Structural alerts are substructures in the substance that are considered to reflect 
some kind of chemical or biochemical reactivity that underlies the toxicological effect. The 
occurrence of a structural alert for a substance suggests the presence of an effect, based on the 
notion that structural analogues that have exhibited corrosion (or irritation) potential can be 
used to predict a corrosive or irritant effect for the substance of interest, or to tailor further 
testing and assessment. The absence of one of the known structural alerts for irritation and 
corrosion alone does not prove absence of effect, as knowledge of structural alerts for irritation 
and corrosion might be incomplete. 

(Q)SAR systems that also account for skin effects are for example ACD Percepta, Hazard Expert, 
CASE Ultra, Discovery studio Acellrys (former TOPKAT). Derek Nexus is a knowledge-based 
expert system that gives toxicity predictions. These systems go beyond the structural similarity 
considerations encompassing also other parameters such as topology, geometry and surface 
properties. Not all of the models were developed with EU regulatory purposes in mind, so it is 
important to assess in each case whether the endpoint or effect being predicted corresponds to 
the regulatory endpoint of interest. 

The expert system BfR-DSS53 has been recommended in the Guidance on IR&CSA Section 
R.7.2.4 since there is currently no other model that sufficiently describes the absence of effects. 
The BfR rules to predict skin irritation and corrosion have been integrated in the internet tool 
‘toxtree’, https://eurl-ecvam.jrc.ec.europa.eu/laboratories-
research/predictive_toxicology/qsar_tools/toxtree. The BfR alerts (“inclusion rules”) for 
corrosion and irritation have also been incorporated into the OECD QSAR Toolbox 
(http://www.qsartoolbox.org/). 

53 Decision Support System (DSS) developed by the German Federal Institute for Risk Assessment (BfR) to 
assess certain hazardous properties of pure chemicals. 

 
 
 
 
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In the absence of any other existing data, conclusion on the presence of an effect can be 
reached if the (Q)SAR or expert system has been shown to adequately predict the presence of 
the classified effect. In case of negative (Q)SAR data the need for classification cannot be 
excluded. 

If existing other data (e.g. in vitro or in vivo data) contradicts these conclusions on the 
presence or absence of an effect then a weight of evidence approach must be applied. The 
suitability of the model (reliability, relevance) should be very carefully checked to make sure 
that the prediction is fit for purpose, and the applicability of the model to the substance should 
also be justified. 

Since a formal adoption procedure for the non-testing methods (as mentioned above) is not 
foreseen and no formal validation process is in place, appropriate documentation is very 
important. In order to achieve acceptance under REACH the documentation must conform the 
so-called QSAR Model Reporting Format (QMRF). For more details consult the Guidance on 
IR&CSA Section R.6.1. 

3.2.2.1.2.4.  Testing methods: in vitro methods 

Table R.7.2-2 in the Guidance on IR&CSA lists the status of validation and regulatory 
acceptance for in vitro test methods for skin corrosion and skin irritation. The information given 
below is current at the time of publication, however further information on newly adopted OECD 
Test Guidelines can be found on the OECD website 
(http://www.oecd.org/env/chemicalsafetyandbiosafety/testingofchemicals/oecdguidelinesforthet
estingofchemicals.htm). Furthermore, up to date information on OECD and EU test guidelines 
can be found also on the ECHA website (https://www.echa.europa.eu/support/oecd-eu-test-
guidelines). 

In vitro methods for skin corrosion 

 The OECD has accepted guidelines for in vitro skin corrosion tests as alternatives for the 
standard in vivo rabbit skin test (OECD TG 404). Accepted in vitro tests for skin corrosivity are 
found in the EU Test Methods Regulation (EC) No 440/2008 and in OECD Test Guidelines (OECD 
TG): 

•  The transcutaneous electrical resistance (TER; using rat skin) test (OECD TG 430 / TM 

B.40) 

•  Reconstructed human epidermis (RHE) tests (OECD TG 431 / TM B.40 bis) 

•  The in vitro membrane barrier test method (OECD TG 435) 

Positive in vitro results on corrosivity do not generally require further testing and can be used 
for classification. Negative in vitro corrosivity responses must be subject to further evaluation. 

Whereas the TER test at present does not allow subcategorisation within the corrosive category, 
the membrane barrier test allows for the differentiation into the three Categories 1A, 1B and 
1C. The reconstructed human epidermis (RHE) models included in the OECD TG 431 i.e. 
EpiDermTM SCT, EpiskinTM, SkinEthicTM RHE and epiSC® support the sub-categorisation into 
Category 1A, however they cannot discriminate between Categories 1B and 1C. The applicability 
domain of the three tests outlined here (TER-, RHE- and membrane barrier test) with regard to 
the alkalinity and acidity of the tested substance should be carefully considered to decide which 
test(s) are most appropriate for the actual substance. 

The TER and the RHE assays have been validated for the classification of skin corrosion. The 
results of this validation are well founded, because the CLP criteria for skin corrosion are 
identical with the ones referred to in the past validation study. 

The membrane barrier method has been endorsed as a scientifically validated test for a limited 
range of substances – mainly acids, bases and their derivatives (ECVAM/ESAC, 2000). 

In vitro methods for skin irritation 

 
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The OECD has adopted an in vitro skin irritation test guideline i.e. OECD TG 439 (TM B. 46) that 
currently contains four test methods i.e. EpiDermTM SIT, EpiSkinTM, SkinEthicTM RHE and LabCyte 
EPI – MODEL24 SIT. These test methods can reliably distinguish non-classified from classified 
substances but cannot distinguish between corrosives and irritants when used alone. Thus, in 
the case of positive results, the potential corrosive properties should be excluded or confirmed 
based on data obtained from an in vitro skin corrosion test. It should be noted that conclusions 
on the applicability domain of the four methods rest mainly on the optimisation and validation 
data set. All four methods are valid for the classification of substances for skin irritation 
according to CLP criteria. 

Information on the current developments of in vitro tests and methodology can be found on the 
ECVAM website (http://ihcp.jrc.ec.europa.eu/our_labs/eurl-ecvam ).  

Other suitable in vitro methods 

Positive data from other suitable in vitro methods may be used in a weight of evidence 
approach to determine classification as irritant, while negative data are not conclusive for no 
classification. In this context ‘suitable’ means sufficiently well-developed according to 
internationally agreed development criteria (see REACH Annex XI, section 1.4). 

3.2.2.1.2.5.  Testing methods: In vivo data  

The in vivo test in rabbits according to OECD TG 404 (TM B.4) is the standard in vivo test for 
the hazard assessment under REACH. However, according to Annex VIII of REACH (at or above 
10 tonnes/year) an in vivo test should only be performed in case the in vitro studies (as 
required in Annex VII) are not applicable or the results of these studies are not adequate for 
classification.   

Until 1987 the OECD standard protocol used occlusive patching for the application of the test 
substance, which resulted in more rigorous test conditions compared to the semi-occlusive 
patching used today. Especially in borderline cases of classification the method of application 
should be accounted for in the evaluation of effects. 

Studies performed according to the USA Federal Hazardous Substances Act (US-FHSA), may be 
used for classification purposes although they deviate in their study protocol from the OECD TG 
404. They do not include a 48-hour observation time and involve a 24-hour test material 
exposure followed by observations at 24 hour and 72 hours. Moreover, the test material is 
patched both on abraded and on intact skin of six rabbits. Studies usually are terminated after 
72 hours. In case of no or minimal responses persisting until the 72 hours time points it is 
feasible to use such data for classification by calculating the mean values for erythema and 
oedema on the basis of only the 24 and 72 hours time points. Calculation of mean scores should 
normally be restricted to the results obtained from intact skin. In case of pronounced responses 
at the 72 hours time point an expert judgement is needed as to whether the data is appropriate 
for classification. 

Data on skin effects on animals may be available from tests that were conducted for other 
primary purposes than the investigation of skin corrosion / irritation. Such information may be 
gained from acute or repeated dose dermal toxicity studies on rabbits or rats (OECD TG 402; 
OECD TG 410), guinea pig skin sensitisation studies (OECD TG 406) and from irritation studies 
in hairless mice. 

 
 
 
 
 
 
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3.2.2.2.  Classification criteria  

Annex I: 3.2.2.1.1. Skin corrosion 

Annex I: 3.2.2.1.1.1. A substance is corrosive to skin when it produces destruction of skin 
tissue, namely, visible necrosis through the epidermis and into the dermis in at least one 
tested animal after exposure for up to 4 hours. 

Annex I: 3.2.2.1.1.2. Corrosive substances shall be classified in Category 1 where data is 
not sufficient for sub-categorisation. 

Annex I: 3.2.2.1.1.3. When data are sufficient substances shall be classified in one of the 
three sub-categories 1A, 1B, or 1C in accordance with the criteria in Table 3.2.1. 

Annex I: 3.2.2.1.1.4. Three sub-categories are provided within the corrosion category: sub-
category 1A – where corrosive responses are noted following up to 3 minutes exposure and 
up to 1 hour observation; sub-category 1B – where corrosive responses are described 
following exposure greater than 3 minutes and up to 1 hour and observations up to 14 days; 
and sub-category 1C – where corrosive responses occur after exposures greater than 1 hour 
and up to 4 hours and observations up to 14 days. 

Category 

Category 11 

Table 3.2.1 

Skin corrosion category and subcategories 

Criteria 

Destruction of skin tissue, namely, visible necrosis through the 
epidermis and into the dermis, in at least one tested animal after 
exposure ≤ 4 h 

Sub-Category 1A 

Corrosive responses in at least one animal following exposure ≤ 3 
min during an observation period ≤ 1 h 

Sub-Category 1B 

Corrosive responses in at least one animal following exposure > 3 
min and ≤ 1 h and observations ≤ 14 days 

Sub-Category 1C 

Corrosive responses in at least one animal after exposures > 1 h 
and ≤ 4 h and observations ≤ 14 days 

1 See the conditions for the use of Category 1 in paragraph (a) of Section 3.2.2. 

Annex I: 3.2.2.1.2. Skin irritation 

Annex I: 3.2.2.1.2.1. A substance is irritant to skin when it produces reversible damage to 
the skin following its application for up to 4 hours. The major criterion for the irritation 
category is that at least 2 of 3 tested animals have a mean score of ≥ 2.3 and ≤ 4.0. 

Annex I: 3.2.2.1.2.2. A single irritation category (Category 2) is presented in Table 3.2.2, 
using the results of animal testing. 

Annex I: 3.2.2.1.2.3. Reversibility of skin lesions is also considered in evaluating irritant 
responses. When inflammation persists to the end of the observation period in 2 or more test 
animals, taking into consideration alopecia (limited area), hyperkeratosis, hyperplasia and 
scaling, then a material shall be considered to be an irritant. 

Annex I: 3.2.2.1.2.4. Animal irritant responses within a test can be variable, as they are with 
corrosion. A separate irritant criterion accommodates cases when there is a significant irritant 
response but less than the mean score criterion for a positive test. For example, a test 
material might be designated as an irritant if at least 1 of 3 tested animals shows a very 

 
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elevated mean score throughout the study, including lesions persisting at the end of an 
observation period of normally 14 days. Other responses could also fulfil this criterion. 
However, it should be ascertained that the responses are the result of chemical exposure. 

Category 

Irritation 
(Category 
2) 

Table 3.2.2 

Skin irritation categorya 

Criteria 

(1)  Mean score of ≥ 2,3 - ≤ 4,0 for erythema/eschar or for oedema in at 

least 2 of 3 tested animals from gradings at 24, 48 and 72 hours after 
patch removal or, if reactions are delayed, from grades on 3 consecutive 
days after the onset of skin reactions; or 

(2) 

(3) 

Inflammation that persists to the end of the observation period normally 
14 days in at least 2 animals, particularly taking into account alopecia 
(limited area), hyperkeratosis, hyperplasia, and scaling; or 

In some cases where there is pronounced variability of response among 
animals, with very definite positive effects related to chemical exposure 
in a single animal but less than the criteria above. 

a) Grading criteria are understood as described in Regulation (EC) No 440/2008. 

3.2.2.3.  Evaluation of hazard information 

Annex I: 3.2.2.2.1. A tiered approach to the evaluation of initial information shall be 
considered, where applicable, recognising that not all elements may be relevant. 

Annex I: 3.2.2.2.7. The tiered approach provides guidance on how to organize existing 
information on a substance and to make a weight of evidence decision about hazard 
assessment and hazard classification. 

Although information might be gained from the evaluation of single parameters within a tier 
(see Section 3.2.2.2.1), consideration shall be given to the totality of existing information and 
making an overall weight of evidence determination. This is especially true when there is 
conflict in information available on some parameters. 

The tiered approach for the evalution of the information applied in order to make a decision about 
the skin corrosion/skin irritation hazard properties is illustrated in Figure 3.1 below. The approach 
in  the  figure  was  adopted  by  the  UNSCEGHS  in  December  2012  (with  exception  of  the  added 
footnotes g) and h)).  

 
 
 
 
 
 
 
 
 
 
 
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Figure 3.1 Tiered evaluation for skin corrosion/skin irritation 

Step 

Parameter 

Finding 

Conclusion 

1a: 

Existing human or animal 

skin corrosion/irritation 

data a 

Not 

corrosive/Insufficient/Inco

nclusive/No data 

1b: 

Existing human or animal 

skin corrosion/irritation 

data a 

Not irritant/Inconclusive 

Insufficient//No data 

Skin corrosive 

Classify as skin 

corrosive b 

Skin irritant 

Classify as skin 

irritant g 

1c: 

Existing human or animal 

skin corrosion/irritation 

Not skin corrosive or 

Not classified g 

data a 

skin irritant 

No/Inconclusive 

Insufficient/ data 

2: 

Other, existing skin data in 

Yes; other existing 

  May be deemed to be  

animals c 

data showing that 

skin corrosive b or  

substance may cause 

skin irritant g 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Step 

Parameter 

Finding 

Conclusion 

skin corrosion or skin 

irritation 

No/Negative/ 

Insufficient/Inconclusive 

data 

3: 

Existing ex vivo/in vitro 

Positive: Skin 

Classify as skin 

corrosivity data d 

corrosive 

corrosive b 

No/Negative/ 

Insufficient/Inconclusive 

data 

Existing ex vivo/in vitro 

irritation data 

No/ 

Insufficient/Inconclusive 

data 

Positive: Skin irritant 

Classify as skin 

irritant g 

  Negative: not skin 

Not classified g 

irritant 

4: 

pH-based assessment (with 

pH ≤  2 or  ≥ 11.5 i 

Classify as skin 

consideration of 

with high 

corrosive g 

acid/alkaline reserve of the 

acid/alkaline reserve 

chemical) e 

or no data for 

acid/alkaline reserve 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Step 

Parameter 

Finding 

Conclusion 

Not pH extreme, no pH data 

or extreme pH with data 

showing low/no 

acid/alkaline reserveh 

5: 

Validated Structure Activity 

Skin corrosive 

Deemed to be skin 

Relationship (SAR) methods 

corrosive b 

Skin irritant 

Deemed to be skin 

irritant  

No/Inconclusive 

Insufficient/data 

6: 

Consideration of the total 

Skin corrosive 

Deemed to be skin 

weight of evidence f 

corrosive b 

       Skin irritant 

Deemed to be skin 

irritant  

7: 

Not classified 

(a) 

Existing human or animal data could be derived from single or repeated exposure(s), for example in 
occupational,  consumer,  transport  or  emergency  response  scenarios;  or  from  purposely-generated 
data from animal studies conducted according to validated and internationally accepted test methods. 
Although human data from accident or poison centre databases can provide evidence for classification, 
absence of incidents is not itself evidence for no classification as exposures are generally unknown or 
uncertain. 

(b)  Classify in the appropriate category/sub-category, as applicable. 

(c) 

All existing animal data should be carefully reviewed to determine if sufficient skin corrosion/irritation 
evidence is available. In evaluating such data, however, the reviewer should bear in mind that the 
reporting of dermal lesions may be incomplete, testing and observations may be made on a species 
other than the rabbit, and species may differ in sensitivity in their responses. 

(d)  Evidence  from  studies  using  validated  protocols  with  isolated  human/animal  tissues  or  other,  non-

tissue-based, though validated, protocols should be assessed.   

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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(e)  Measurement  of  pH  alone  may  be  adequate,  but  assessment  of  acid  or  alkali  reserve  (buffering 

capacity) would be preferable.   

(f) 

(g) 

All information that is available should be considered and an overall determination made on the total 
weight  of  evidence.  This  is  especially  true  when  there  is  conflict  in  information  available  on  some 
parameters.  Expert  judgment  should  be  exercised  prior  to  making  such  a  determination.  Negative 
results  from  applicable  validated  skin  corrosion/irritation  in  vitro  tests  are  considered  in  the  total 
weight of evidence evaluation. 

In case there is a conflict in available data, e.g. negative/irritation human data but positive/corrosive 
in vitro data, a weight of evidence assessment should be performed, see footnote f. (This footnote 
was not included in the figure in the 5th rev of GHS, but is based on 3.2.1.2. and 3.2.2.2.7, Annex I, 
CLP ). 

(h)  Non  corrosivity  needs  to  be  confirmed  by  other  data  and  preferably  by  data  from  an  appropriate 
validated in vitro test. (This footnote was not included in the figure in the 5th rev of GHS, but is based 
on 3.2.2.2.5, Annex I, CLP). 

(i) 

For the case of mixtures with no human or animal data on skin corrosion/irritation but with extreme 
pH see Figure 3.3 in 3.2.3.2.1.1. 

3.2.2.3.1. 

Evaluation of human data  

The usefulness of human data for classification purposes will depend on the extent to which the 
effect, and its magnitude, can be reliably attributed to the substance of interest and on the 
extent and duration of the exposure. Further guidance on evaluation of human data for skin 
corrosion/irritation can be found in the Guidance on IR&CSA Section R.7.2.4.2. 

The criteria in CLP Annex I, Tables 3.2.1 and 3.2.2 are not applicable to human data. 

3.2.2.3.2. 

Evaluation of non human data  

3.2.2.3.2.1.  In vitro data 

In evaluation of data from in vitro tests the applicability domain has to be taken into account. 
For instance, the in vitro membrane barrier test method is mainly applicable for acids and bases 
and is not applicable for solutions with pH values between 4.5 and 8. Normally, 
recommendations for classification according to GHS criteria based on the results of an in vitro 
test are mentioned in the corresponding OECD test guideline. In particular OECD TG 431 
concludes that some results fall in the category 1B/1C. Category 1B/1C is not an option in CLP. 
However, a WoE assessment may lead to a conclusion about the subcategory but if this is not 
the case, category 1 should be assigned54. 

3.2.2.3.2.2.  In vivo data 

Tests in albino rabbits (OECD TG 404) 

Evaluation criteria for local effects on the skin are severity of the damage and reversibility. 

For the severity of damage the responses are evaluated according to the Draize score ranking 
from ‘0’ (‘no response’) up to ‘4’ (‘severe response’). Evaluation takes place separately for 
erythema and oedema. 

Reversibility of skin lesions is the other decisive factor in evaluating responses in the animal 
test. The criteria are fulfilled if, for  

• 

corrosion 

54  Please,  note  that  the  issue  concerning  the  subcategorization  of  skin  corrosivity  is  currently  under 
discussion. 

 
 
 
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o 

the full thickness of the skin is destroyed resulting in ulcers, bleeding, bloody scabs 
discoloration, complete areas of alopecia and scars. In questionable cases a 
pathologist should be consulted. One animal showing this response at the end of the 
observation period is sufficient for the classification as corrosive. 

• 

irritation  

o 

o 

a limited degree of alopecia, hyperkeratosis, hyperplasia and scaling occurs. Two 
animals showing this response are sufficient for the classification as irritant. 

very elevated mean scores throughout the study are revealed, including lesions 
persisting at the end of an observation period of normally 14 days. One animal 
showing this response throughout and at the end of the observation period is 
sufficient for the classification as irritant (In cases of suspected corrosives, existing 
test data may only be available for one animal due to testing restrictions, see 
Example 2.). 

With regard to severity the main criterion for classification of a substance as irritant to skin, is 
the mean score per animal for either erythema/eschar or oedema. During the observation 
period following the removal of the patch each animal is scored on erythema and oedema. For 
each of the three test animals the average scores for three consecutive days (usually 24, 48 
and 72 hours) are calculated separately for oedema and erythema. If 2/3 animals exceed the 
cut-off-values defined in the CLP, the classification has to be done accordingly. 

With regard to reversibility the test report must prove that these effects are transient i.e. the 
affected sites are repaired within the observation period of the test (see Example 1). 

Non-classification as corrosive can only be justified if the test was performed with at least three 
animals and the test results were negative for all three animals. 

Tests that have been conducted with more than three animals 

Current guidelines foresee a sequential testing of rabbits until a response is confirmed. 
Typically, up to 3 rabbits may be used. The basis for a positive response is the individual rabbit 
value averaged over days 1, 2, and 3. The mean score for each individual animal is used as a 
criterion for classification. Skin Irritation Category 2 is used if at least 2 animals show a mean 
score of 2.3 or above. Other test methods, however, have used up to 6 rabbits. This is also the 
case for the studies performed according to the US-FSHA. 

For existing test data with more than three animals, specific guidance needs to be applied 
(adopted by the UNSCEGHS in June 2011):  

The average score is determined per animal (see Example 3, Section 3.2.5.1.3).  

In the case of 6 rabbits the following applies: 

a.  Classification as skin corrosive – Category 1 if destruction of skin tissue (visible 

necrosis through the epidermis and into the dermis) occurs in at least one animal 
after exposure up to 4 hours. 

b.  Classification as skin irritant – Category 2 if at least 4 out of 6 rabbits show a mean 

score per animal of  2.3 ≤ 4.0 for erythema/eschar or for oedema;  

In the case of 5 rabbits the following applies: 

a.  Classification as skin corrosive – Category 1 if destruction of skin tissue (visible 

necrosis through the epidermis and into the dermis) occurs in at least one animal 
after exposure up to 4 hours. 

b.  Classification as skin irritant – Category 2 if at least 3 out of 5 rabbits show a mean 

score per animal of  2.3 ≤ 4.0 for erythema/eschar or for oedema;  

 
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In the case of 4 rabbits the following applies: 

a.  Classification as skin corrosive – Category 1 if destruction of skin tissue (visible 

necrosis through the epidermis and into the dermis) occurs in at least one animal 
after exposure up to 4 hours. 

b.  Classification as skin irritant – Category 2 if at least 3 out of 4 rabbits show a mean 

score per animal of  2.3 ≤ 4.0 for erythema/eschar or for oedema;  

Other dermal tests on animals 

Relevant data may also be available from animal studies that were conducted for other primary 
purposes than the investigation of skin corrosion/irritation. For example, in line with Section 
3.2.2.2.3 of Annex I to CLP, acute dermal toxicity data may be used for classification as skin 
corrosion/irritation. However, due to the different protocols and the interspecies differences in 
sensitivity, the use of such data in general needs to be evaluated on a case-by-case basis. 
These are considered significant if the effects seen are comparable to those described above.  

If the substance is proven to be either an irritant or a corrosive in an acute dermal toxicity test 
carried out with rabbits with the undiluted test substance (liquids) or with a suitable suspension 
(solids), the following applies. In case of signs of skin corrosion, classify as Skin Corrosive 
(subcategorisation as 1A, 1B or 1C, where possible). In all other cases: calculate or estimate 
the amount of test substance per cm2 and compare this to the test substance concentration of 
80 μl or 80 mg/cm2 employed in the EU B.4/OECD TG 404 for dermal corrosion/irritation test 
with rabbits. If in the same range and adequate scoring of skin effects is provided, classify or 
not as Skin Irritant Category 2. If not in the same range and inadequate scoring of skin effects, 
use the data in a Weight-of-Evidence analysis and proceed.  

In case the test was performed in other species, which may be less sensitive (e.g. rat), 
evaluation must be made with caution. Usually, the rat is the preferred species for toxicity 
studies within the EU. The limit dose level of 2000 mg/kg bw of a solid is normally applied as a 
50% suspension in a dose volume of 4 ml/kg bw onto a skin surface area of about 5x5 cm. 
Assuming a mean body weight of 250 g, a dose of 1 ml of the suspension will be applied to an 
area of 25 cm2, i.e 20 mg test substance per cm2. In case of an undiluted liquid, 0.5 ml is 
applied to 25 cm2, i.e. 20 μl/cm2. Considering the fact that (i) the rat skin is less sensitive 
compared to rabbit skin, (ii) much lower exposures are employed and (iii), in general, the 
scoring of dermal effects is performed less accurately, the results of dermal toxicity testing in 
rats will not be adequate for classification with respect to skin irritation. Only in case of 
evidence of skin corrosivity in the rat dermal toxicity test can the test substance be classified as 
Skin Corrosive Category 1. All other data should be used in a Weight of Evidence.  

Regarding data from skin sensitisation studies, the skin of guinea pigs is less sensitive than that 
of rats which is, in turn, is less sensitive than that of rabbits. Only in the case of evidence of skin 
corrosivity in the sensitisation test (Maximisation or Buhler) with the neat material or dilutions of 
solids in water, physiological  saline  or vegetable  oil,  should the test  substance be  classified as 
Skin Corrosive Category 1. However, care should be exercised when interpreting findings from 
guinea  pig  studies,  particularly  from  maximisation  protocols,  as  intradermal  injection  with 
adjuvant  readily  causes  necrosis.  All  other  data  should  be  used  for  Weight  of  Evidence  only. 
Information on irritant properties from skin sensitisation tests cannot be used to conclude on a 
specific  classification  regarding  acute  skin  irritation  but  may  be  used  in  a  Weight-of-Evidence 
analysis. In general, irritation data from the Local Lymph Node Assay are not usable. The test 
substance is applied to the dorsum of the ear by open topical application, and specific vehicles 
for enhancement of skin penetration are used. 

3.2.2.3.3.  Weight of evidence 

According to Article 9(1) CLP, the criteria should be applied to available data. However, 
sometimes it is not straightforward or simple to apply the criteria and according to Article 9(3) a 

 
 
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weight of evidence and expert judgement should be applied in such cases when the criteria 
cannot be applied directly. 

A weight of evidence determination means that all available and scientifically justified 
information bearing on the determination of hazard is considered together, such as physico-
chemical parameters (e.g., pH, reserve alkalinity/acidity), information from the application of 
the category approach (grouping, read-across), (Q)SAR results, the results of suitable in vitro 
tests, relevant animal data, skin irritation information/data on other similar mixtures, human 
experience such as occupational data and data from accident databases, epidemiological and 
clinical studies and well-documented case reports and observations. The quality and consistency 
of the data should be given appropriate weight. Both positive and negative results should be 
assembled together in a single weight of evidence determination (see 1.1.1.3, Annex I, CLP and 
Section 1.4 in this guidance). Note that non testing methods may normally not enable 
subcategorsation of corrosive substances. 

Evaluation must be performed on a case-by-case basis and with expert judgement. However, 
normally positive results that are adequate for classification should not be overruled by negative 
findings. 

Annex I: 1.1.1.4. For the purpose of classification for health hazards (Part 3) established 
hazardous effects seen in appropriate animal studies or from human experience that are 
consistent with the criteria for classification shall normally justify classification. Where 
evidence is available from both humans and animals and there is a conflict between the 
findings, the quality and reliability of the evidence from both sources shall be evaluated in 
order to resolve the question of classification. Generally, adequate, reliable and 
representative data on humans (including epidemiological studies, scientifically valid case 
studies as specified in this Annex or statistically backed experience) shall have precedence 
over other data. However, even well-designed and conducted epidemiological studies may 
lack a sufficient number of subjects to detect relatively rare but still significant effects, to 
assess potentially confounding factors. Therefore, positive results from well-conducted animal 
studies are not necessarily negated by the lack of positive human experience but require an 
assessment of the robustness, quality and statistical power of both the human and animal 
data. 

The following Figure 3.2 provides an illustration of the assessment of available data, in the case 
of conflicting results, to decide the weight to be assigned to different types of data (see also 
Figure 3.1). It needs to be noted that the relative weights indicated in the figure assume 
comparable quality of the data. WoE considerations need to take into account, on a case-by-
case basis, the quality, nature, relevance and applicability domain of the different types of data 
available. The figure illustrates a decreasing weight of the information from top to bottom. 

Figure 3.2 Simplified illustration of the relative weight of the available information 

 
 
 
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Existing human data

Existing animal data

In vitro data

Other sources (e.g. (Q)SAR)

Extreme pH 
sufficient for 
Skin Corr 
classification 
in absence of 
other data

When  contradicting  data  of  comparable  quality  belongs  to  different  “hierarchical  levels”,  the 
following considerations should be made:  

-  When there are positive data which belong to a higher level in the hierarchy than the 
available negative data, more weight should normally be given to the positive data.  
-  When the negative data belong to a level which is higher than the positive data, the full 
available dataset should be assessed in a WoE approach (as, for example, existing good 
quality positive animal data could overrule negative human data and negative good 
quality in vitro data could overrule positive QSAR data). 

More information and guidance on the relevance of the different types of information, as well as 
on quality assessment, is provided in OECD guidance no 20355 and in the Guidance R.7a. 

For additional guidance, if both human and animal data are available, see the Guidance on 
IR&CSA Section R.7.2.3.2. 

3.2.2.4.  Decision on classification  

Where the comparison of the information with the criteria leads to a decision that the  
substance is classified as a skin corrosive but the data used for classification does not allow 
differentiation between the skin corrosion subcategories 1A/1B/1C, then the substance should 
be assigned Skin Corrosion Category 1. 

3.2.2.5.  Setting of specific concentration limits  

Article 10(1) Specific concentration limits and generic concentration limits are limits 
assigned to a substance indicating a threshold at or above which the presence of that 
substance in another substance or in a mixture as an identified impurity, additive or individual 
constituent leads to the classification of the substance or mixture as hazardous. 

55 Available at 
http://www.oecd.org/officialdocuments/publicdisplaydocumentpdf/?cote=env/jm/mono(2014)19&doclangu
age=en. See in particular section B, part 2, module 8. 

 
 
 
 
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Specific concentration limits shall be set by the manufacturer, importer or downstream user 
where adequate and reliable scientific information shows that the hazard of a substance is 
evident when the substance is present at a level below the concentrations set for any hazard 
class in Part 2 of Annex I or below the generic concentration limits set for any hazard class in 
Parts 3, 4 and 5 of Annex I. 

[..] 

It is more difficult to prove the absence of a hazardous property; the legal text states that:  

Article 10(1)  

[..] 

In exceptional circumstances specific concentration limits may be set by the manufacturer, 
importer or downstream user where he has adequate, reliable and conclusive scientific 
information that a hazard of a substance classified as hazardous is not evident at a level 
above the concentrations set for the relevant hazard class in Part 2 of Annex I or above the 
generic concentration limits set for the relevant hazard class in Parts 3, 4 and 5 of that Annex. 

A specific concentration limit (SCL) set in accordance with the above mentioned provisions shall 
take precedence over the generic concentration limit (GCL) set out in Tables 3.2.3 and 3.2.4 of 
Annex I to CLP (Article 10(6)). Furthermore, such an SCL is substance-specific and should be 
applicable to all mixtures containing the substance instead of any GCL that otherwise would 
apply to a mixture containing the substance. 

What type of information may be the basis for setting a specific concentration limit?  

Existing human data may in certain cases (especially if dose-response information is available) 
indicate that the threshold for the irritation hazard in humans for a substance in a mixture, 
would be higher or lower than the GCL. A careful evaluation of the usefulness and the validity of 
such human data, as well as their representativeness and predictive value (IR&CSA, sections 
R.4.3.3. and R.7.2.4.2), should be performed. As pointed out in 1.1.1.4 (Annex I to CLP), 
positive results from well-conducted animal studies are not necessarily negated by the lack of 
positive human experience but require an assessment of robustness, quality and a degree of 
statistical certainty of both the human and animal data. 

The aim of the standard test method for ‘Acute Dermal Irritation/Corrosion’ OECD TG 404 56 is to 
identify potential skin corrosion or irritation. The test material is generally administered 
undiluted, thus, no dose-response relationship can be obtained from an individual test. 

However, if there are adequate, reliable, relevant and conclusive existing data from other 
already performed animal studies with a sufficient number of animals tested to ensure a high 
degree of certainty, and with information on dose-response relationships, such data may be 
considered for setting a lower or, in exceptional cases, a higher SCL on a case-by-case basis. 

It should be noted that generating data specifically for the purpose of setting SCLs is not a 
requirement according to the CLP Regulation. Article 8(1) CLP specifies that new tests may only 
be performed (in order to determine the hazard of a substance or mixture) if all other means of 
generating information has been exhausted and Article 7(1) specifies that where new tests are 
carried out, tests on animals must be undertaken only when no other alternatives, which 
provide adequate reliability and quality of data, are possible. The GCLs must be applied for the 
classification of a mixture on the basis of its ingredient substances classified for skin irritation 
and corrosivity, if there are no already existing specific data justifying an SCL which is lower or, 
in exceptional cases, higher than the GCL (see Article 10(1), CLP). Therefore, information will 

56 TO NOTE: In OECD TG 404 test substance refers to the test material, test article or test item.  The term 
substance may be used differently from the REACH/CLP definition. 

 
 
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always be available, for mixtures containing substances already classified for skin 
corrosion/irritation, making it possible to identify the hazard for the mixture by using the GCLs 
(Article 9(4), CLP).  

The possibilities to use in vitro test methods are being explored as a basis for setting SCLs, but 
an accepted common approach is not yet available. Thus, at the present point in time, it is not 
possible to provide guidance for the use of in vitro methods for the purpose of setting SCLs. 
However, this does not exclude that a method to set SCLs based on in vitro tests could be 
developed in the future, as they provide a promising option for SCL setting. An SCL should 
apply to any mixture containing the substance instead of the GCL (that otherwise would apply 
to the mixture containing the substance). Thus, if the SCL is based on data derived from tests 
with dilutions of the substance in a specific solvent, it has to be considered that the derived 
concentration should be applicable to all mixtures for which the SCL should apply. 

Annex VI Part 3 (Table 3.1) to CLP includes examples of substances for which a higher or lower 
SCL was set under Directive 67/548/EEC (old DSD system) and which were transferred to CLP. 

3.2.2.6.  Decision logic for classification of substances 

The decision logic, which is based on the one provided in the GHS, is reported as additional 
guidance here below. It is strongly recommended that the person responsible for classification, 
studies the criteria for classification, as well as the guidance above, before and during use of the 
decision logic. 

 
 
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Are there data and/or information to 
evaluate skin corrosion/irritation? 

No 

Classification not possible 

Yes 

(b) 
(c) 

Is the substance corrosive (see criteria in CLP Annex I, 3.2.1.1, 
3.2.2.1.1, 3.2.2.2 and Figure 3.1 in this guidance) consideringa: 
Existing  human  data  showing  irreversible  damage  to 
(a) 
skin; 
Destruction of skin in one or more test animals; 
Other existing animal data indicating skin corrosion after 
single or repeated exposure; 
Existing ex vivo/in vitro data; 
pH extremes of ≤2 or ≥11.5b; 
Information  available  from  validated  Structure  Activity 
Relationship methods? 

(d) 
(e) 
(f) 

No 

Is the substance an irritant (see criteria in CLP, Annex I, 3.2.1.1, 
3.2.2.1.2, 3.2.2.2 and Figure 3.1 in this guidance) considering: 
(a) 
(b) 
(c) 

Existing human data, single or repeated exposure; 
Skin irritation data from an animal study;  
Other  existing  animal  data  including  single  or  repeated 
exposure; 
Existing in vitro data; 
Information  available  from  validated  Structure  Activity 
Relationship methods? 

(d) 
(e) 

Yes 

Category 1, 
Subcategory 
1A, 1B or 1C 

Danger 

Yes 

Category 2 

Warning 

No 

No classification 

a Taking into account consideration of the total weight of evidence if necessary. 

b Not applicable if consideration of pH and acid/alkaline reserve indicates substances may not be corrosive and 
confirmed by other data, preferably by data from an appropriate validated in vitro test.  

3.2.3.  Classification of mixtures for skin corrosion/irritation 

3.2.3.1. 

Identification of hazard information 

As for substances, the procedure for evaluating mixtures for classification purposes, is a tiered, 
i.e. a stepwise, approach based on a hierarchy principle and depending on the type and amount 
of available data/information starting from evaluating existing human data on the mixture, 
followed by a thorough examination of the existing in vivo data, in vitro data and finally 
physico-chemical properties available on the mixture. (The tiered approach to evaluate data for 
skin corrosion/irritation as illustrated in Figure 3.1, should be taken into account also for 
mixtures in case of relevant and reliable data on the complete mixture). 

 
 
 
 
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For mixtures that have been on the market for a long time, human data and experience may 
exist that may provide useful information on the skin irritation potential of the respective 
mixtures. Although human data from accident or poison centre databases can provide evidence 
for classification, absence of incidents is not itself evidence for no classification, as exposures 
may be unknown or uncertain. See Section 3.2.2.1 of this Guidance for further information on 
the identification of human data. 

If valid test data are available for the whole mixture they have precedence. If no such data 
exist, the so called bridging principles should be applied if possible. If the bridging principles are 
not applicable, an assessment on the basis of data for the components of the mixture must be 
applied. 

3.2.3.2.  Classification criteria for mixtures 

Based on available information, the approaches below should be used for classification of a 
mixture for skin corrosivity and irritation in the following sequence (Article 9, CLP and Figure 
1.1): 

a.  Classification derived using data on the mixture itself, by applying the substance criteria 

of Annex I to CLP; 

b.  Classification based on the application of bridging principles, which make use of test data 

on similar tested mixtures and ingredient substances; 

c.  Classification based on ingredients as described in 3.2.3.3, Annex I, CLP.  

3.2.3.2.1.  When data are available for the complete mixture 

Annex I: 3.2.3.1.1. The mixture shall be classified using the criteria for substances, taking 
into account the tiered approach to evaluate data for this hazard class. 

Annex I: 3.2.3.1.2. When considering testing of the mixture, classifiers are encouraged to 
use a tiered weight of evidence approach as included in the criteria for classification of 
substances for skin corrosion and irritation (section 3.2.1.2 and 3.2.2.2), to help ensure an 
accurate classification as well as to avoid unnecessary animal testing. In the absence of any 
other information, a mixture is considered corrosive to skin (Skin Corrosion Category 1) if it 
has a pH ≤ 2 or a pH ≥ 11.5. However, if consideration of acid/alkaline reserve suggests the 
mixture may not be corrosive despite the low or high pH value, this needs to be confirmed by 
other data, preferably by data from an appropriate validated in vitro test. 

Additional simplified guidelines for the assessment of available data on the mixture when WoE 
needs to be applied, is provided in Section 3.2.2.3.3 (see Figure 3.2).  

There is a range of available in vitro test systems that have been validated for their suitability in 
assessing skin corrosion/irritation potential of substances. Some but not all test systems have 
been validated for mixtures and not all available in vitro test systems work equally well for all 
types of mixtures. Prior to testing a mixture in a specific in vitro assay for classification 
purposes, it has to be ensured that the respective test has been previously shown to be suitable 
for the prediction of skin corrosion/irritation properties for the type of mixture to be evaluated. 

3.2.3.2.1.1.  Mixtures with extreme pH  

As a general rule, mixtures with a pH of ≤ 2 or ≥ 11.5 should be considered as corrosive. 
However, assessment of the buffering capacity of the mixture indicated by its acid or alkali 
reserve should be considered.  

Low values of acid or alkaline reserve indicate a low buffer capacity. Mixtures showing a low 
buffer capacity are less or even not corrosive or irritant. The relation is quantitatively expressed 
by: - pH + 1/12 alkaline reserve >= 14.5 or pH - 1/12 acid reserve <= -0.5. If the sums are 

 
 
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>= 14.5 or <= -0.5 the mixture has to be considered as corrosive (see Decision logic 3.2.3.4, 
step 1a).  

If the additional consideration of the acid/alkaline reserve according to Young et al. (1987, 
1994) suggests that classification for corrosion may not be warranted, this needs to be 
confirmed by other data, preferably by data from an appropriate and validated in vitro test, 
applicable  for the mixture. The consideration of acid/alkali reserve should not be used alone to 
exonerate mixtures from classification. 

Where it is decided to base the classification of a mixture upon consideration of pH alone, Skin 
Corrosion Category 1 should be applied.  

Where the mixture has an extreme pH value but the only corrosive/irritant ingredient present in 
the mixture is an acid or base with an assigned SCL (either in CLP Annex VI or set by supplier 
according to Article 10(1)), then the mixture should be classified according to the SCL. In this 
instance, pH of the mixture should not be considered a second time since it would have already 
been taken into account when deriving the SCL for the substance.  

If this is not the case, then the steps to be taken into consideration when classifying a mixture 
with pH  2 or  11.5 are described in the following decision logic: 

Figure 3.3 Mixture without human or animal data on skin corrosion/irritation or relevant data 
from similar tested mixtures, pH is  2 or  11.5 

Does the acid alkaline reserve indicate that the mixture may 
not be corrosive? 

NO ➔ 

YES 

 

Is  the  mixture  tested  in  an  OECD  adopted  in  vitro  skin 
corrosivity  test,  considered  valid  and  applicable  for  the 
mixture? 

NO ➔ 

YES 

 

Does  the  mixture  demonstrate  corrosive  properties  in  an 
OECD  adopted  in  vitro  skin  corrosivity  test  considered  valid 
and applicable for the mixture? 

           YES ➔ 

NO 

 

Classify 
Corrosion Category 1. 

as 

corrosive,  Skin 

Classify 
Corrosion Category 1  

as 

corrosive,  Skin 

as 

corrosive. 

Classify 
If 
discrimination between Skin Corr. 
1A/1B/1C  is  not  possible,  Skin 
Corr. 1 must be chosen. 

Does the mixture demonstrate irritant properties in an OECD 
adopted  in  vitro  skin  irritation  test  considered  valid  and 
applicable for the mixture? 

Classify  as  skin  irritant,  Skin 
Irritation Category 2 

                                                                        YES ➔ 

NO 

 

Consideration of the total weight of all available evidence, in 
particular in case of conflicting data, including the extreme 

 
 
 
 
 
 
 
 
 
 
 
 
 
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pH,  negative/inconclusive results from e.g. validated skin 
corrosion/irritation in vitro tests, and the results from the 
application of the methods based on the ingredients in the 
mixture in CLP Annex I, sections 3.2.3.3.2-3.2.3.3.3 (Table 
3.2.3)/3.2.3.3.4.1-3.2.3.3.4.3 (Table 3.2.4)                   
➔                                                                                                                                                  

Classify:  Category  1,  2,  no 
classification  

The mixture must be classified as Skin corrosion Category 1 should the supplier decide not to 
carry out the required confirmatory testing. 

It is also important to note that the use of the pH-acid/alkali reserve approach, potentially 
leading to a change of the classification from corrosive to irritant, or from irritant to not 
classified, assumes that the potential corrosivity or irritancy is due to the effect of the ionic 
entities. When this is not the case, especially when the mixture contains non-ionic (non-
ionisable) substances themselves classified as corrosive or irritant, then the pH-acid/alkali 
reserve method cannot be a basis for modifying the classification but should be considered in 
the weight of evidence analysis.  

If a mixture with corrosive constituents also contains surfactants (e.g. tensids or detergent 
substances), it can be assumed that corrosivity might be amplified (Kartono & Maibach 2006). 
Even if only one corrosive substance with an assigned SCL is present in such a mixture, the 
possible synergistic effect has to be taken into account when classifying the mixture. 

Where the mixture has an extreme pH value and contains some other corrosive/irritant 
ingredients (some of which may have SCLs assigned) in addition to an acid or base with or 
without an assigned SCL, then the steps described in the above decision logic should be 
followed. 

3.2.3.2.2.  When data are not available for the complete mixture: bridging principles 

Annex I: 3.2.3.2.1. Where the mixture itself has not been tested to determine its skin 
corrosion/irritation potential, but there are sufficient data on the individual ingredients and 
similar tested mixtures to adequately characterise the hazards of the mixture, these data shall 
be used in accordance with the bridging rules set out in section 1.1.3. 

In order to apply bridging principles, there needs to be sufficient data on similar tested mixtures 
as well as the ingredients of the mixture (see Section 1.6.3.2 of this Guidance). 

When the available identified information is inappropriate for the application of the bridging 
principles then the mixture should be classified based on its ingredients as described in Sections 
3.2.3.2.3 and 3.2.3.3 of this Guidance. 

3.2.3.2.3.  When data are available for all ingredients or only for some ingredients 

3.2.3.2.3.1.  Ingredients that should be taken into account for the purpose of 

classification 

Annex I: 3.2.3.3.1. […] The ‘relevant ingredients’ of a mixture are those which are present 
in concentrations ≥ 1% (w/w for solids, liquids, dusts, mists and vapours and v/v for gases), 
unless there is a presumption (e.g., in the case of corrosive ingredients) that an ingredient 
present at a concentration < 1% can still be relevant for classifying the mixture for skin 
corrosion/irritation. 

3.2.3.2.3.2.  The additivity approach is applicable 

Annex I: 3.2.3.3.2. In general, the approach to classification of mixtures as corrosive or 
irritant to skin when data are available on the ingredients, but not on the mixture as a 
whole, is based on the theory of additivity, such that each skin corrosive or skin irritant 
ingredient contributes to the overall skin corrosive or skin irritant properties of the mixture 

 
 
 
 
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in proportion to its potency and concentration. A weighting factor of 10 is used for skin 
corrosive ingredients when they are present at a concentration below the generic 
concentration limit for classification with Category 1, but are at a concentration that will 
contribute to the classification of the mixture as skin irritant. The mixture is classified as 
corrosive or irritant to skin when the sum of the concentrations of such components exceeds 
a concentration limit. 

Annex I: 3.2.3.3.3. Table 3.2.3 provides the generic concentration limits to be used to 
determine if the mixture is considered to be corrosive or irritant to the skin. 

When the supplier is unable to derive the classification using either data on the mixture itself or 
bridging principles, he must determine the skin corrosion/irritation properties of the mixture 
using data on the individual ingredients. Although the general approach is the additivity 
principle, which has been successfully used under the DPD and more recently, the supplier must 
ascertain whether the additivity approach is applicable. The first step would then be to identify 
all the relevant ingredients in the mixture (i.e. their name, chemical type, concentration level, 
hazard classification and any SCLs) and the pH of the mixture. In addition it is important to also 
consider effects that could occur in the mixture, such as surfactant interaction, neutralisation of 
acids/bases when identifying the properties of the complete mixture (including pH and the 
acid/alkaline reserve) in addition to considering contributions of individual ingredients.  

Additivity may not apply where the mixture contains substances mentioned in CLP Annex I, 
3.2.3.3.4.1-3.2.3.3.4.3, see Section 3.2.3.2.3.3 of this Guidance. 

Application of SCLs when applying the additivity approach 

The generic concentration limits (GCLs) are specified in CLP Annex I, Table 3.2.3. However, 
according to CLP Article 10(6), SCLs take precedence over GCLs. Thus, if a given substance has 
an SCL set in accordance with Article 10(1), CLP, then this limit has to be taken into account 
when applying the summation (additivity) method for skin corrosion/irritation (see Examples 4 
and 5). 

In cases where additivity applies for skin corrosion/irritation to a mixture with two or more 
substances some of which may have SCLs assigned, then the following formula should be used: 

The mixture is classified for skin corrosion/irritation if the: 

Sum of (ConcA / clA) + (ConcB / clB) + …. + (ConcZ / clZ) is   1 

Where   ConcA = the concentration of substance A in the mixture; 

      clA = the concentration limit (either specific or generic) for substance A; 

            ConcB = the concentration of substance B in the mixture; 

      clB = the concentration limit (either specific or generic) for substance B; etc. 

The formula should be used in a stepwise procedure in the following order: 

1.  Should the mixture be classified in Category 1 A?  Only Cat. 1A ingredient 

substances are added. 

2.  Should the mixture be classified in Category 1B? Cat. 1A and 1B ingredient 

substances are added. 

3.  Should the mixture be classified in Category 1C? Cat. 1A, 1B and 1C ingredient 

substances are added. 

4.  Should the mixture be classified in Category 1? Cat. 1A, 1B, 1C and 1 ingredient 

substances are added. 

3.2.3.2.3.3.  The additivity approach is not applicable 

Annex I: 3.2.3.3.4.1. Particular care must be taken when classifying certain types of 
mixtures containing substances such as acids and bases, inorganic salts, aldehydes, phenols, 

 
 
 
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and surfactants. The approach explained in Sections 3.2.3.3.1 and 3.2.3.3.2 may not be 
applicable given that many of such substances are corrosive or irritant to the skin at 
concentrations < 1%. 

Annex I: 3.2.3.3.4.2. For mixtures containing strong acids or bases the pH shall be used as 
a classification criterion (see Section 3.2.3.1.2) since pH is a better indicator of skin corrosion 
than the concentration limits in Table 3.2.3. 

Annex I: 3.2.3.3.4.3. A mixture containing ingredients that are corrosive or irritant to the 
skin and that cannot be classified on the basis of the additivity approach (Table 3.2.3), due to 
chemical characteristics that make this approach unworkable, shall be classified as Skin 
Corrosion Category 1 if it contains ≥ 1% of an ingredient classified as Skin Corrosion or as 

Skin Irritation (category 2) when it contains ≥ 3% of a skin irritant ingredient. Classification of 
mixtures with ingredients for which the approach in Table 3.2.3 does not apply is summarised 
in Table 3.2.4. 

Annex I: 3.2.3.3.5. On occasion, reliable data may show that the skin corrosion/irritation 
hazard of an ingredient will not be evident when present at a level at or above the generic 
concentration limits mentioned in Tables 3.2.3 and 3.2.4 in Section 3.2.3.3.6. In these cases 
the mixture shall be classified according to that data (see also Articles 10 and 11). On other 
occasions, when it is expected that the skin corrosion/irritation hazard of an ingredient is not 
evident when present at a level at or above the generic concentration limits mentioned in 
Tables 3.2.3 and 3.2.4, testing of the mixture shall be considered. In those cases the tiered 
weight of evidence approach shall be applied, as described in Section 3.2.2.2. 

Annex I: 3.2.3.3.6. If there are data showing that (an) ingredient(s) is/are corrosive or 
irritant to skin at a concentration of < 1 % (skin corrosive) or < 3 % (skin irritant), the 
mixture shall be classified accordingly. 

3.2.3.3.  Generic concentration limits for substances triggering classification 

of mixtures 

3.2.3.3.1.  When the additivity approach is applicable 

Annex I: Table 3.2.3 

Generic concentration limits of ingredients classified as skin corrosion (Category 1, 
1A, 1B or 1C)/skin irritation (Category 2) that trigger classification of the mixture 
as skin corrosion/skin irritation where the additivity approach applies 

Sum of ingredients classified as: 

Concentration triggering classification of a mixture 
as: 

Skin Corrosion 

Skin Irritation 

Category 1 (see note below) 

Category 2 

Skin corrosion Sub-Category 1A, 1B, 
1C or Category 1 

 5% 

 1% but < 5% 

Skin irritation Category 2 

 10% 

 
 
 
 
 
 
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(10 x Skin corrosion Sub-Category 
1A, 1B, 1C or Category 1) + Skin 
irritation Category 2 

Note 

295 

 10% 

The sum of all ingredients of a mixture classified as Skin Corrosion Sub-Category 1A, 1B or 
1C respectively, shall each be ≥ 5% respectively in order to classify the mixture as either 
Skin Corrosion Sub-Category 1A, 1B or 1C. If the sum of the ingredients classified as Skin 
Corrosion Category 1A is < 5% but the sum of the ingredients classified as Skin Corrosion 
Category 1A+1B is ≥ 5%, the mixture shall be classified as Skin corrosion Category 1B. 
Similarly, if the sum of the ingredients classified as Skin Corrosion Category 1A+1B 
ingredients is < 5% but the sum of the ingredients classified as Sub-Category 1A+1B+1C 
ingredients is ≥ 5% the mixture shall be classified as Skin Corrosion Category 1C. Where at 
least one relevant ingredient in a mixture is classified as Category 1 without sub-
categorisation, the mixture shall be classified as Category 1 without sub-categorisation if the 
sum of all ingredients corrosive to skin is ≥ 5 %. 

3.2.3.3.2.  When the additivity approach is not applicable 

Annex I: Table 3.2.4 

Generic concentration limits of ingredients of a mixture that trigger classification 
of the mixture as skin corrosion/skin irritation, where the additivity approach does 
not apply 

Ingredient: 

Concentration: 

Mixture classified as:  

Acid with pH ≤ 2 

Base with pH ≥ 11,5 

Other skin corrosive (Sub-Categories 1A, 
1B, 1C or Category 1) ingredients 

Other skin irritant (Category 2) 
ingredients, including acids and bases 

≥ 1% 

≥ 1% 

≥ 1% 

≥ 3% 

Skin corrosion Category 1 

Skin corrosion Category 1 

Skin corrosion Category 1 

Skin irritation Category 2 

3.2.3.4.  Decision logic for classification of mixtures 

The decision logic, based on the one provided in the GHS, is presented here below as additional 
guidance. It is strongly recommended that the person responsible for classification, study the 
criteria for classification, as well as the guidance above, before and during use of the decision 
logic. 

 
 
 
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Does the mixture as a whole or its ingredients have 
data/information to evaluate skin corrosion/irritation? 

No 

Classification not possible 

Yes 

Does  the  mixture  as  a  whole  have  data/information  to 
evaluate skin corrosion/irritation? 

No 

Can bridging principles be applied? 

No 

Is pH of the mixture ≤ 2 or ≥ 11.5? 

Yes 

Yes 

See decision 
logic 3.2.2.6 

Classify in 
appropriate 
category or sub-
category 

Yes 

Follow decision logic in 
Section 3.2.3.2.1.1 of 
this guidance and 
classify accordingly 

No 

Category 1 

Does the mixture contain ≥ 1%a of an ingredient which is 
corrosive when the additivity approach may not apply? 

Yes 

No 

Does the mixture contain one or more corrosive ingredients 
when the additivity approach applies and where the sum of 
concentrations ingredients classified as Skin Corr. 1 (or any 
subcategory) ≥ 5%? 

Danger 

Category 1, 
Subcategory 
1A, 1B or 1Cb 

Yes 

No 

Danger 

 
 
 
 
 
 
 
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Does the mixture contain ≥ 3% a of an ingredient which is 
irritant and when the additivity approach may not apply? 

Yes 

No 

Does the mixture contain one or more corrosive or irritant 
ingredients when the additivity approach applies and 
where the sum of concentrations of ingredients classified 
as: 

Yes 

(a) Skin Corr. Category 1 ≥ 1% but < 5%; or 
(b) Skin Irrit. Category 2 ≥ 10%; or 
(c) (10 x Skin Corr.Cat. 1) + Skin Irrit. Cat. 2 ≥ 10%? 

Category 2 

Warning 

Category 2 

Warning 

No 

Not classified 

a Where relevant < 1%, see Section 3.2.3.3.1 of Annex I of CLP.  

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3.2.4.  Hazard communication in form of labelling for skin corrosion/irritation  

3.2.4.1.  Pictograms, signal words, hazard statements and precautionary 

statements 

Annex I: 3.2.4.1. Label elements shall be used for substances or mixtures meeting the criteria 
for classification in this hazard class in accordance with Table 3.2.5. 

Table 3.2.5 

Label elements for skin corrosion/irritation 

Sub-Categories 1A / 1B / 
1C and Category 1 

Category 2 

Classification 

GHS Pictograms 

Signal Word 

Hazard Statement 

Precautionary Statement 
Prevention 

Danger 

Warning 

H314: Causes severe skin 
burns and eye damage 

H315: Causes skin 
irritation 

P260 

P264 

P280 

P264 

P280 

Precautionary Statement 
Response 

P301 + P330 + P331 

P302 + P352 

P303 + P361 + P353 

P321 

P332 + P313 

P362 + P364 

P363 

P304 + P340 

P310 

P321 

P305 + P351 + P338 

P405 

P501 

Precautionary Statement 
Storage 

Precautionary Statement 
Disposal 

Article 26 1 (d)  

If the hazard pictogram ‘GHS05’ applies, the hazard pictogram ‘GHS07’ shall not appear for 
skin and eye irritation. 

 
 
 
 
 
 
 
 
 
 
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3.2.4.2.  Additional labelling provisions 

Annex II: 1.2.6. EUH071 — Corrosive to the respiratory tract 

For substances and mixtures in addition to classification for inhalation toxicity, if data are 
available that indicate that the mechanism of toxicity is corrosivity, in accordance with section 
3.1.2.3.3 and Note 1 of Table 3.1.3 in Annex I. 

For substances and mixtures in addition to classification for skin corrosivity, if no acute 
inhalation test data are available and which may be inhaled. 

Corrosive substances (and mixtures) may be acutely toxic after inhalation to a varying degree, 
which is only occasionally proved by testing. In case no acute inhalation study is available for a 
corrosive substance (or mixture) and such substance (or mixture) may be inhaled, a hazard of 
respiratory tract corrosion may exist. As a consequence, such substances and mixtures have to 
be supplementary labelled with EUH071, if there is a possibility of exposure via inhalation taking 
into consideration the saturated vapour concentration and the possibility of exposure to 
particles  or droplets of inhalable size as appropriate, (see also Chapter 3.8.2.5 of this 
Guidance). Moreover, in such a case it is strongly recommended to apply the precautionary 
statement P260: ‘Do not breathe dust/fume/gas/mist/vapours/spray.’  

Annex II: 1.2.4. EUH066 — Repeated exposure may cause skin dryness or cracking 

For substances and mixtures which may cause concern as a result of skin dryness, flaking or 
cracking but which do not meet the criteria for skin irritancy in section 3.2 of Annex I, based 
on either: 

— practical observations; or 

— relevant evidence concerning their predicted effects on the skin. 

3.2.5.  Examples of classification for skin corrosion/irritation 

3.2.5.1.  Examples of substances fulfilling the criteria for classification 

3.2.5.1.1. 

Example 1: Standard test according to OECD TG 404 with three animals 

In a guideline test according to OECD TG 404 the test substance was applied for three minutes 
and 1 hour. No scars or other irreversible effects were found. The scoring results obtained after 
a 4-hour application time are listed in the following table: 

Animal 

Nr. 

Degree of erythema after 
[observation time] 

Degree of oedema after 
[observation time] 

 24/48/72 h 
2.3 ? 

1h  24h  48h 

72h 

7d 

14d  1h  24h 

48h 

72h 

7d 

14d  Erythe-

1 

3 

3 

3 

2 

0 

1 

2 

2 

2 

0 

ma 

Yes 

Oede-
ma 

No 

 24/48/72 h = 2.7 

 24/48/72 h =  2.0 

=>’positive 
Responder’ 

2 

3 

3 

3 

3 

0 

1 

2 

2 

1 

0 

Yes 

No 

 24/48/72 h =  3 

 24/48/72 h = 1.7 

=>’positive 
Responder’ 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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3 

1 

1 

1 

0 

0 

1 

1 

1 

1 

0 

No 

No 

 24/48/72 h = 
0.66 

 24/48/72 h = 1 

Classification: Skin Irritation Category 2 

Rationale: The classification is made on the basis of 2/3 ‘positive responder’ exceeding 2.3 
mean score for erythema. 

3.2.5.1.2. 

Example 2: Test carried out with one animal with a test substance which 
is suspected as corrosive 

Due to the unprecedented structure the biological effects of the substance cannot be 
anticipated. Therefore, the test according to OECD TG 404 was started with one animal only in 
line with testing restrictions. Exposure times were 3 min and 1h. The following scores/effects 
were observed: 

Exposure 
time 

Degree of erythema after 
……[observation time] 

Degree of oedema after 
……[observation time] 

Visible 
necrosis, 
irreversible 
skin damage 

1h  24h 

48h 

72h 

... 

1h 

24h  48h  72h 

... 

After 14d 

3 min 

1h 

0 

0 

0 

1 

0 

2 

0 

3 

0 

0 

0 

2 

0 

2 

0 

3 

No 

Yes 

Classification: Skin Corrosion Category 1B 

Rationale: The classification is based on the destruction of the tissue after 1 hour of exposure. 

3.2.5.1.3. 

Example 3: Test carried out with more than three animals 

A substance was tested on acute skin irritation / corrosion according to OECD TG 404. Contact 
time was 4 hours. No effects were seen after a contact time of 3 min and one hour. The 
following scores were obtained after a contact time of 4 hours: 

1h  24h 

48h  72h  7d 

14d  1h  24h 

48h 

72h 

7d 

14d 

Observation time 

Animal 
Nr 

Erythema 

Oedema 

1 

2 

3 

4 

3 

3 

2 

2 

3 

2 

2 

2 

2 

2 

1 

1 

2 

2 

1 

1 

1 

1 

1 

1 

0 

0 

0 

0 

2 

2 

2 

2 

3 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

1 

1 

1 

1 

0 

0 

0 

0 

Pos 
responder 

Eryth
e-ma 

Oed-
ema 

Yes 

Yes 

No 

No 

No 

No 

No 

No 

Evaluation is made based on the average score per animal. 

Only 1/4 of the animals reached the cut-off value of 2.3, i.e. only animal No 1 is a positive 
responder. No classification is warranted with regard to skin irritation. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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3.2.5.2.  Examples of mixtures fulfilling the criteria for classification 

Where the mixture is made up of ingredients with no assigned SCLs, the appropriate 
summation(s) and generic concentration limits from CLP Annex I, Table 3.2.3 should be used. 

3.2.5.2.1. 

Example 4: Mixture without extreme pH, with ingredients with SCLs 

Ingredient 

Skin corrosion / irritation 
classification 

Concentration 
(% w/w) 

SCL 

Substance A 

Skin Irrit. 2  

Substance B 

Not classified 

Base E 

Skin Corr. 1B 

Substance D 

Not classified 

Substance F 

Skin Corr. 1B 

3.8 

0.5 

5.4 

4 

2 

Not assigned 

C ≥ 10 %: Skin Corr. 1B 

5 % ≤ C < 10 %: Skin Irrit. 2 

Not assigned 

Water  

Not classified 

84.3 

pH of the mixture is 10.5 – 11.0, thus extreme pH provisions do not apply. The mixture 
contains a base but not any surfactant. Additivity is considered to apply. 

Substance B, substance D and water can be disregarded as they are not classified for skin 
corrosion/irritation. 

SCLs are neither assigned to substance F nor substance A, thus GCLs apply for these 
ingredients. SCLs are assigned to Base E (see Section 3.2.3.2.3.2 of this Guidance, Application 
of SCLs when applying the additivity approach). 

Skin Corr. 1: 

(% substance F/GCL) + (% base E/SCL) = (2/5) + (5.4/10) = 0.94   < 1, thus the mixture is 
not classified as Skin Corr. 1 

Skin Irrit. 2: 

(% substance F/GCL) + (% base E/SCL) + (% substance A/GCL) = (2/1) + (5.4/5) + (3.8/10) 
= 3.46 which is > 1, thus the mixture is classified Skin Irrit. 2 

3.2.5.2.2. 

Example 5: Mixture without extreme pH, and non-applicability of the 
additivity approach  

Ingredient 

Wt% 

Classification 

Information 

Ingredient 1 

Ingredient 2 

Ingredient 3 

Ingredient 4 

4 

5 

5 

86 

Skin Corr. 1A 

pH = 1.8 

Skin Irr. 2 

Skin Irr. 2 

- 

- 

- 

No data available 

 
 
 
 
 
 
 
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The pH of the mixture is 4.0, thus extreme pH provisions do not apply. There are no test data 
on the mixture (apart from a pH). Bridging principles do not apply since data on a similar 
mixture was not available. Classification of the mixture based on ingredient data can be 
considered.  

Ingredient 1 with a pH = 1.8 is an ingredient for which additivity might not apply (see 
3.2.3.3.4.1-2-3 and Table 3.2.4, Annex I, CLP). Expert judgment would be needed to determine 
whether or not additivity applies. Knowledge of the components is important. Given the limited 
information in this example, the classifier of this mixture chose to apply non-additivity as a 
conservative approach. Without information on the mode of action of Ingredient 1, the mixture 
could be corrosive regardless of the overall pH. Therefore, the criteria described in paragraph 
3.2.3.3.4.1-2-3 were applied (including “A mixture containing ingredients that are corrosive or 
irritant to the skin and that cannot be classified on the basis of the additivity approach (Table 
3.2.3), due to chemical characteristics that make this approach unworkable, shall be classified 
as Skin Corrosive Category 1A, 1B or 1C if it contains ≥ 1% of a an ingredient classified in 
Category 1A, 1B or 1C respectively or as Category 2 when it contains ≥ 3% of an irritant 
ingredient.”). 

Thus, the mixture should be classification as Skin Corrosion Category 1A because the mixture 
contains an ingredient 1 (Skin Corr. 1A) at a concentration ≥ 1%. 

3.2.5.3.  Examples of mixtures not fulfilling the criteria for classification 

3.2.5.3.1. 

Example 6: Mixture without extreme pH, with ingredients with SCLs 

Ingredient 

Skin corrosion / 
irritation classification 

Concentration 
(% w/w) 

SCL 

Surfactant C  

Skin Irrit. 2 

Substance G 

Skin Irrit. 2 

Substance A 

Skin Irrit. 2 

Substance H 

Skin Corr. 1A 

Substance D 

Not classified 

Water 

Not classified 

0.4 

3.0 

0.7 

3.0 

2 

90.9 

Not assigned 

Not assigned 

Not assigned 

C ≥ 70 %: Skin Corr. 1A 

50 % ≤ C < 70 %: Skin Corr. 
1B 

35 % ≤ C < 50 %: Skin Irrit. 2 

pH of the mixture is: 2.5 – 3.0, thus extreme pH provisions do not apply. The mixture contains 
one surfactant. Additivity is considered to apply57. 

Substance D and water can be disregarded as they are not classified for skin 
corrosion/irritation. Also surfactant C and substance A can be disregarded as both are present 
at below 1%. 

No SCL is assigned to substance G, thus GCL apply for this ingredient. 

Skin Corr. 1: 

57 Please note that in cases where a mixture with corrosive constituents also contains surfactans, it can be 
assumed that corrosivity migh be amplified. 

 
 
 
 
 
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The mixture contains 3% substance H, the only ingredient classified as Skin Corr. 1. As this is 
below the 50% SCL for substance H, the mixture is not classified as Skin Corr. 1. 

Skin Irrit. 2: 

(% substance H/SCL) + (% substance G/GCL) = (3/35) + (3/10) = 0.39 which is < 1, thus the 
mixture is not classified Skin Irrit. 2. 

3.2.6.  References 

ECETOC (2002), Use of human data in hazard classification for irritation and sensitisation, 
Monograph No 32, Brussels ISSN 0773-6374-32 

ECVAM/ESAC (2000) Statement on the application of the CORROSITEX® Assay for skin 
corrositivity testing. Online:  http://ihcp.jrc.ec.europa.eu/our_labs/eurl-ecvam  

ECVAM/ESAC (2007) Statement on the validity of in-vitro tests for skin irritation. Online: 
http://ecvam.jrc.it/ 

ECVAM/ESAC (2008) Statement on the validity of in-vitro tests for skin irritation testing. Online: 
http://ecvam.jrc.it/ 

ECVAM/ESAC (2009) Statement on the performance under UN GHS of three in-vitro assays for 
skin irritation testing and the adaptation of the reference chemicals and defined accuracy values 
of the ECVAM skin irritation performance standards. Online: http://ecvam.jrc.it/ 

Kartono F & Maibach H. (2006) Irritants in combination with a synergistic or additive effect on 
the skin response: an overview of tandem irritation studies. Contact Dermatitis 54(6), 303-12. 

Spielmann, H., Hoffmann, S., Liebsch, M.,  Botham, P., Fentem, J., Eskes, C., Roguet, R., 
Cotovió, J., Cole, T., Worth, A., Heylings, J., Jones, P., Robles, C., Kandárová, H., Gamer, A., 
Remmele, M., Curren, R., Raabe, H., Cockshott, A., Gerner, I. and Zuang, V. (2007) The ECVAM 
International Validation Study on In Vitro Tests for Acute Skin Irritation: Report on the Validity 
of the EPISKIN and EpiDerm Assays and on the Skin Integrity Function Test. ATLA 35, 559-601. 

Young J.R., How M.J., Walker A.P., Worth W.M.H. (1988): Classification as corrosive or irritant 
to skin of preparations containing acidic or alkaline substances, without test on animals. 
Toxicology in Vitro 2, 19-26. 

Young J.R., How M.J. (1994): Product classification as corrosive or irritant by measuring pH and 
acid / alkali reserve. In Alternative Methods in Toxicology vol. 10 - In Vitro Skin Toxicology: 
Irritation, Phototoxicity, Sensitization, eds. A.Rougier, A.M. Goldberg and H.I Maibach, Mary Ann 
Liebert, Inc. 23-27. 

 
 
 
 
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3.3.  SERIOUS EYE DAMAGE/EYE IRRITATION 

It should be noted that if a substance or mixture is classified as Skin corrosion Category 1 then 
serious damage to eyes is implicit as reflected in the hazard statement for skin corrosion (H314: 
Causes severe skin burns and eye damage). Thus, the corrosive substance or mixture is also 
classified, but the corresponding hazard statement (H318: Causes serious eye damage) is not 
indicated on the label to avoid redundancy. 

3.3.1.  Definitions for classification for serious eye damage/eye irritation 

Annex I: 3.3.1.1. Serious eye damage means the production of tissue damage in the eye, or 
serious physical decay of vision, following application of a test substance to the anterior 
surface of the eye, which is not fully reversible within 21 days of application. 

Eye irritation means the production of changes in the eye following the application of test 
substance to the anterior surface of the eye, which are fully reversible within 21 days of 
application. 

3.3.2.  Classification of substances for serious eye damage/eye irritation 

3.3.2.1. 

Identification of hazard information 

3.3.2.1.1. 

Identification of human data 

Existing data on eye effects in humans may include well-documented epidemiological studies, 
clinical studies, case reports, and data from poison information units and accident databases or 
occupational experience. Their quality and relevance for hazard assessment should be 
thoroughly reviewed. A critical review of the value of human studies is provided in the Guidance 
on IR&CSA Section R.4.3.3 and more specific considerations for eye damage/irritation are given 
in the Guidance on IR&CSA Section R.7.2.9. 

3.3.2.1.2. 

Identification of non human data 

Available serious eye damage/eye irritation information on substances may include existing data 
generated by the test methods in the Test Methods Regulation or by methods based on 
internationally recognised scientific principles. 

Before using the methods as referred to in the following sections, it should be checked whether 
the methods are sufficiently validated (or considered valid in case of (Q)SAR and expert 
systems) against the criteria for classification according to CLP (and not validated against the 
old DSD criteria which differed slightly from the CLP criteria). 

3.3.2.1.3. 

Consideration of physico-chemical properties 

Substances with oxidising properties can give rise to highly exothermic reactions in contact with 
other substances and human tissue. High temperatures thus generated, or direct oxidative 
impact, may damage/destroy biological materials. This applies, for example, to organic 
peroxides, which can be assumed to be eye irritants, unless evidence suggests otherwise 
(Guidance on IR&CSA Sections R.7.2.8 and R.7.2.4.1). 

Thus, in the absence of evidence to the contrary, a hydro peroxide should be considered to be 
classified as Eye Damage Category 1, whereas Eye Irritation Category 2 should be considered 
for peroxides. Appropriate evidence must be provided in order to consider no classification of 
substances with oxidising properties. 

3.3.2.1.4. 

pH and the acid/alkaline reserve  

Annex I: 3.3.2.2.4. Likewise, pH extremes like ≤ 2 and ≥ 11,5 may produce serious eye 
damage, especially when associated with significant acid/alkaline reserve (buffering capacity). 

 
 
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Generally such substances are expected to produce significant effects on the eyes. In the 
absence of any other information, a substance is considered to cause serious eye damage 
(Category 1) if it has a pH ≤ 2 or ≥ 11,5. However, if consideration of acid/alkaline reserve 
suggests the substance may not cause serious eye damage despite the low or high pH value, 
this needs to be confirmed by other data, preferably by data from an appropriate validated in 
vitro test. 

Substances can be predicted to be corrosive, if the pH is  2 or  11.5. Where extreme pH is the 
only basis for classification as serious eye damage, it is important to take into consideration the 
acid/alkaline reserve, a measure of the buffering capacity (Young et al, 1988, and Young and 
How, 1994). However, lack of or low buffering capacity should not be used alone to exonerate 
from classification as corrosive, which needs to be confirmed by other data, preferably by a 
validated in vitro test (see also Section 3.2.3.2 of this Guidance). 

Further information and/or reasoning is needed to conclude whether the substance causes eye 
irritation. 

3.3.2.1.5.  Non-testing methods: (Q)SARs and expert systems 

Non-testing methods such as (Q)SARs and expert systems (a diverse group of models 
consisting of combinations of SARs, QSARs and databases) may be considered on a case-by-
case basis. (Q)SARs are in general not very specific for eye irritancy. In many cases rules are 
used in a similar manner to those used for skin irritation and corrosion as alerts to indicate an 
effect. (Q)SAR systems that also account for eye effects are for example ACD Percepta, CASE 
Ultra, Discovery studio Accelrys (former TOPKAT), Derek Nexus. For more detailed guidance, 
consult the Guidance on IR&CSA Section R.6 (‘QSAR and grouping of chemicals’). OECD QSAR 
Toolbox and ToxTree contain BfR rules58 for eye irritation/corrosion. 

In the absence of any other existing data, conclusions on the presence or absence of an effect 
can be made if the (Q)SAR or expert system has been shown to make an adequate prediction 
(see Figure 3.4). The suitability of the model (reliability, relevance) should be very carefully 
checked to make sure that the prediction is fit for purpose, and the applicability of the model to 
the substance should also be justified. The predicted endpoint should be adequate for 
classification and labelling. In case of negative QSAR data the need for classification cannot be 
excluded. 

Since a formal adoption procedure for non-testing methods is not foreseen and no formal 
validation process is in place, appropriate documentation is crucial. In order to achieve 
acceptance under REACH, the documentation must conform to the so-called QSAR Model 
Reporting Format (QMRF). For more details consult the Guidance on IR&CSA Section R.6.1. 

3.3.2.1.5.1.  Testing methods: in vitro methods 

The OECD has at present adopted five in vitro test guidelines for assessing eye hazard potential. 
Four in vitro tests methods have been adopted for the identification of substances inducing 
serious eye damage, i.e. the Isolated Chicken Eye (ICE) test (OECD TG 438; TM B.48), the 
Bovine Corneal Opacity and Permeability (BCOP) test (OECD TG 437; TM B.47), the Fluorescein 
Leakage (FL) test (OECD TG 460), the short time exposure (STE) test (OECD TG 491). In 
addition, there are three validated test methods without an OECD test guideline i.e. Cytosensor 
Microphysiometer (CM)59 test, Isolated Rabbit Eye (IRE) test and the Hen's Egg Test on Chorio-

58 The German Federal Institute for Risk Assessment (BfR) has developed a Decision Support System 
(DSS) to assess certain hazardous properties of pure chemicals. 

59 A draft OECD TG available at 
http://www.oecd.org/env/ehs/testing/DRAFT%20Cytosensor%20TG%20(V9)%2021%20Dec%2012_clean.
pdf. 

 
 
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allantoic Membrane (HET-CAM) test60.  These tests are recommended for use as part of a tiered-
testing strategy for regulatory classification and labelling (e.g. Top-Down Approach 61). A 
substance can be considered as causing serious eye damage (Category 1) based on positive 
results in the ICE test, the BCOP test, the FL test, the STE test, CM test IRE test or the HET-
CAM test62. Four adopted OECD TGs can be used for identifying substances not causing serious 
eye damage/eye irritation which are the ICE test, BCOP test, STE test and Reconstructed 
human Cornea-like Epithelium (RhCE) (OECD TG 492). In addition, the validated CM test 
method can be used for identifying substances not causing serious eye damage or eye irritation. 
Negative results from the ICE, BCOP, STE, RhCE and CM test methods can be used for 
classification purposes, i.e. ‘bottom-up approach’8. For other test methods the negative in vitro 
corrosivity responses in these tests must be followed by further testing (see section R.7.2.9.1 in 
the Guidance on IR&CSA). 

There are no in vitro tests with regulatory acceptance for eye irritation at present.  

Further information on newly adopted OECD Test Guidelines can be found on the OECD website:  
(http://www.oecd.org/env/chemicalsafetyandbiosafety/testingofchemicals/oecdguidelinesforthet
estingofchemicals.htm).   

Information on the current developments of in vitro tests and methodology can be found on the 
ECVAM website (http://ihcp.jrc.ec.europa.eu/our_labs/eurl-ecvam). 

3.3.2.1.5.2.  Testing methods: In vivo methods 

Testing for eye irritation should not be carried out on substances known or predicted to be 
corrosive to skin and classified as such. Such substances are automatically considered to be 
severely damaging to the eye and are classified but not labelled for serious eye damage in 
addition to skin corrosion. 

The in vivo test in rabbits according to OECD TG 405 (TM B.5) is the standard in vivo test for 
the hazard assessment under REACH. 

The Low Volume Eye Test (LVET; Griffith et al 1980) is a modification of the standard OECD TG 
405 test method. The differences being: 

• 

the test material is placed directly on the cornea in the LVET test,  instead of introducing 
it in the conjunctival sac inside the lower lid; 

•  a reduction in the volume of test material applied (0.01 ml (or corresponding weight for 

solids) in the LVET test, as compared with the standard 0.1 ml). 

No new tests should be performed according to LVET as stated by ESAC in its conclusion on the 
use of LVET data for the purpose of classification and labelling in 2009  (ECVAM/ESAC, 2009b).  

Existing data from the LVET test could be considered for the purpose of classification and 
labelling, but must be carefully evaluated. The differences mentioned above may result in a 
classification in a lower category (or no classification) based on LVET data, than if the 
classification were based on data derived from the standard in vivo test (OECD TG 405 (TM 
B.5)). Thus, positive data from the LVET test could be a trigger for considering classification in 

60 ICCVAM published a report on the HET-CAM in 2010 
http://iccvam.niehs.nih.gov/docs/ocutox_docs/InVitro-2010/Body.pdf. 

61 The top-down approach should be used when available information suggests that the substance may 
cause serious eye damage. The bottom-up approach, on the other hand, should be followed only when 
available information suggests that the substance may not be irritant to the eye.  

62 ICCVAM published a report on the HET-CAM in 2010 
http://iccvam.niehs.nih.gov/docs/ocutox_docs/InVitro-2010/Body.pdf. 

 
 
 
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Category 1 on its own, but data from this test indicating Category 2 classification or no 
classification are not conclusive for a category 2 classification or no classification respectively.  

Consideration should be given on a case-by-case basis to the limited use of LVET data as 
supplementary in vivo data in a weight of evidence determination in order to assess if the 
criteria for classification are met. A weight of evidence could include, for example, the results of 
appropriate validated in vitro tests, relevant and conclusive human and animal data, extreme 
pH. The applicability domain is limited to detergent and cleaning products (ECVAM/ESAC, 
2009b). 

3.3.2.2.  Classification criteria 

Annex I: 3.3.2.1.1. Serious eye damage (Category 1) 

3.3.2.1.1.1. A single hazard category (Category 1) is adopted for substances that have 
potential to seriously damage the eyes. This hazard category includes as criteria the 
observations listed in Table 3.3.1. These observations include animals with grade 4 cornea 
lesions and other severe reactions (e.g., destruction of cornea) observed at any time during 
the test, as well as persistent corneal opacity, discoloration of the cornea by a dye substance, 
adhesion, pannus, and interference with the function of the iris or other effects that impair 
sight. In this context, persistent lesions are considered those which are not fully reversible 
within an observation period of normally 21 days. Hazard classification as Category 1 also 
contain substances fulfilling the criteria of corneal opacity ≥ 3 or iritis > 1,5 observed in at 
least 2 of 3 tested animals, because severe lesions like these usually do not reverse within a 
21 days observation period. 

[…] 

Table 3.3.1 

Serious eye damagea 

Category 

Criteria 

Category 1 

A substance that produces: 

(a) in at least one animal effects on the cornea, iris or conjunctiva that are not          

expected to reverse or have not fully reversed within an observation period 
of normally 21 days; and/or 

(b) in at least 2 of 3 tested animals, a positive response of: 

(i) corneal opacity ≥ 3 and/or 

(ii) iritis > 1,5 

   calculated as the mean scores following grading at 24, 48 and 72 hours  after   

installation of the test material. 

a Grading criteria are understood as described in Regulation (EC) No 440/2008 

Annex I: 3.3.2.1.2. Eye irritation (Category 2) 

3.3.2.1.2.1.  Substances  that  have  the  potential  to  induce  reversible  eye  irritation  shall  be 
classified in Category 2 (eye irritation). 

3.3.2.1.2.2.  For  those  substances  where  there  is  pronounced  variability  among  animal 
responses, this information shall be taken into account in determining the classification  

 
 
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Table 3.3 2 

Eye irritationa 

Category 

Criteria 

Category 2 

Substances  that  produce  in  at  least  in  2  of  3  tested  animals,  a  positive 
response of: 

(a) corneal opacity ≥ 1 and/or 

(b) iritis ≥ 1, and/or 

(c) conjunctival redness ≥ 2 and/or 

(d) conjunctival oedema (chemosis) ≥ 2 

calculated as the mean scores following grading at 24, 48 and 72 hours 
after installation of the test material, and which fully reverses within an 
observation period of 21 days 

a Grading criteria are understood as described in Regulation (EC) No 440/2008 

The classification criteria apply to results of the standard animal in vivo test, OECD TG 405, and 
are possible to apply to the results of the LVET. However, the differences between the LVET and 
OECD TG 405 test methods, may result in a classification in a lower category (or no 
classification) based on LVET data, than if the classification were based on data derived from 
the standard in vivo test (OECD TG 405 (TM B.5)). See also 3.3.2.1.5.2 above. 

3.3.2.3.  Evaluation of hazard information 

Annex I: 3.3.2.2.1. A tiered approach to the evaluation of initial information shall be 
considered where applicable, recognising that not all elements may be relevant. 

Annex I: 3.3.2.2.6. The tiered approach provide guidance on how to organize existing 
information and to make a weight of evidence decision about hazard assessment and hazard 
classification. Animal testing with corrosive substances shall be avoided whenever possible. 
Although information might be gained from the evaluation of single parameters within a tier 
(see 3.3.2.1.1), consideration should be given to the totality of existing information and 
making and overall weight of evidence determination. This is especially true when there is 
conflict in information available in some parameters.   

The  tiered  approach  for  the  evaluation  of  the  information  applied  in  order  to  make  a  decision 
about  the  serious  eye  damage/eye  irritation  hazard  properties  is  illustrated  by  the  Figure  3.4 
below. The figure was adopted by the UNSCEGHS in December 2012 (with exception of the added 
footnotes g) and h)). 

 
 
 
 
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Figure 3.4 Tiered evaluation for serious eye damage/eye irritation63 

(see also Figure 3.1) 

Step  Parameter 

  Finding 

  Conclusion 

1a: 

Existing  human  or  animal 
serious  eye  damage/eye 
irritation data a 

  Serious eye damage 

  Classify  as  causing  serious 

eye damage 

Eye irritant 

Classify as eye irritant f 

Negative/Insufficient/Inconcl
usive/No data 

1b: 

Existing  human  or  animal 
data, skin corrosion 

Skin corrosion 

Deemed  to  cause  and  classify 
as serious eye damage 

Negative 
/Insufficient/Inconclusive/No 
data 

1c: 

Existing human or animal 
serious eye damage/eye 
irritation data a 

No/Insufficient/Inconclusive 
data 

2: 

Other, existing skin/eye data 
in animals b 

Not classified f 

Existing data 
showing that 
substance does not 
cause serious eye 
damage or eye 
irritation 

Yes; other existing 
data showing that 
substance may 
cause serious eye 
damage  

Yes; other existing 
data showing that 
substance may 
cause eye irritation 

May be deemed to cause 
serious eye damage 

May be deemed to be an eye 
irritant f 

No/Insufficient/Inconclusive 
data 

63 Adopted by the UNSCEGHS in December 2012. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Figure 3.4 Tiered evaluation for serious eye damage/eye irritation63 

(see also Figure 3.1) 

Step  Parameter 

  Finding 

  Conclusion 

3: 

Existing  ex  vivo/in  vitro  eye 
data c 

Positive:  serious  eye 
damage 

Classify  as  causing  serious 
eye damage  

Positive: eye irritant   

Classify as eye irritant  f, h 

Negative: not eye           

   Not classified f 

irritant 

No/Insufficient/Inconclusive 
data 

4: 

pH-based  assessment  (with 
consideration of acid/alkaline 
reserve of the chemical) d 

Not pH extreme, no pH data 
or  extreme  pH  with  data 
showing low/no acid/alkaline 
reserveg 

pH ≤  2 or  ≥ 11.5i 
with high 
acid/alkaline reserve 
or no data for 
acid/alkaline reserve 

Classify  as  causing  serious 
eye damage f 

Serious eye damage   

Deemed to  cause  serious  eye 
damage 

5: 

Validated  Structure  Activity 
Relationship (SAR) methods 

Eye irritant 

Deemed to be eye irritant  

Skin corrosive 

Deemed to cause serious eye 
damage 

No/Insufficient/Inconclusive 
data 

6: 

Consideration  of  the  total 
weight of evidence e 

Serious eye damage   

Deemed to cause serious eye 
damage 

Eye irritant 

Deemed to be eye irritant  

7: 

Not classified 

(a)  Existing human or animal data could be derived from single or repeated exposure(s), for example in 
occupational,  consumer,  transport,  or  emergency  response  scenarios;  or  from  purposely-generated 
data from animal studies conducted according to validated and internationally accepted test methods. 
Although human data from accident or poison centre databases can provide evidence for classification, 
absence of incidents is not itself evidence for no classification as exposures are generally unknown or 
uncertain; 

(b)  Existing  animal  data  should  be  carefully  reviewed  to  determine if  sufficient  serious  eye  damage/eye 
irritation  evidence  is  available  through  other,  similar  information.  It  is  recognized  that  not  all  skin 
irritants are eye irritants. Expert judgment should be exercised prior to making such a determination; 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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(c)  Evidence from studies using validated protocols with isolated human/animal tissues or other non-tissue-
based, validated protocols should be assessed. A positive test result from a validated in vitro test on 
skin corrosion would lead to the conclusion to classify as causing serious eye damage; 

(d)  Measurement of pH alone may be adequate, but assessment of acid/alkaline reserve (buffering capacity) 

would be preferable; 

(e)  All information that is available on a substance should be considered and an overall determination made 
on the total weight of evidence. This is especially true when there is conflict in information available on 
some  parameters.  The  weight  of  evidence  including  information  on  skin  irritation  may  lead  to 
classification for eye irritation. Negative results from applicable validated in vitro tests are considered 
in the total weight of evidence evaluation. 

(f)  In case of contradicting data, e.g. negative/irritation human data but positive/serious eye damage in-
vitro data, a weight of evidence assessment should be performed, see footnote e. (This footnote  was 
not included in Figure 3.4 in the 5th rev of GHS, but is based on  3.3.1.2 and 3.3.2.2.6, Annex I, CLP) 

(g)  Non corrosivity needs to be confirmed by other data preferably by data from an appropriate validated 
in  vitro  test.  (This  footnote  was  not  included  in  Figure  3.4  in  the  5th  rev  of  GHS,  but  is  based  on  
3.3.2.2.4, Annex I, CLP) 

(h)  Note: currently there are no scientifically valid or internationally accepted in vitro test methods for the 

direct identification of Cat 2 eye irritants. 

(i)  For the cases of mixtures with no human or animal data on serious eye damage/eye irritation but with 

extremeoH, see Figure 3.5 in section 3.3.3.2.1.1 for additional guidance. 

3.3.2.3.1. 

Evaluation of human data 

Quality data on substance-induced eye irritation in humans are likely to be rare. Where human 
data are available, the usefulness of such data for classification purposes will depend on the 
extent to which the effect, and its magnitude, can be reliably attributed to the substance of 
interest. The extent and duration of the exposure needs also to be taken into account as 
absence of effect may be due to washing off the eyes shortly after exposure. In such cases the 
absence of effects may not indicate the absence of hazard. The quality and relevance of such 
data for hazard assessment should be critically reviewed. 

If a substance is diagnostically confirmed by a physician to be the cause for decay in vision with 
the effects not being transient but persistent this should lead to the most serious eye 
classification, i.e. Eye Damage Category 1. 

Further information on the evaluation of human data for eye irritation can be found in the 
Guidance on IR&CSA Section R7.2.4.2. 

3.3.2.3.2. 

Evaluation of non-human data 

3.3.2.3.2.1.  Ex vivo/in vitro data 

A substance can be considered as causing serious eye damage (Category 1) based on positive 
results in the ICE test, the BCOP test, FL test, STE test, IRE test, CM test or the HET-CAM test64. 
Negative results from the ICE, BCOP, STE, RhCE and CM test methods can be used for 
classification purposes i.e. ‘bottom-up approach’, but for other test methods the negative in 
vitro corrosivity responses in these tests must be followed by further testing (Guidance on 
IR&CSA Section R.7.2.9). Normally, recommendations for classification according to GHS 
criteria based on the results of an in vitro test are mentioned in the corresponding OECD test 
guideline. 

There are currently no validated in vitro eye irritation test methods available.  

64 ICCVAM published a report on the HET-CAM in 2010 
http://iccvam.niehs.nih.gov/docs/ocutox_docs/InVitro-2010/Body.pdf. 

 
 
 
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3.3.2.3.2.2.  In vivo data 

Tests in albino rabbits (OECD TG 405) 

Evaluation criteria for local effects on the eye are severity of the damage and reversibility.  

For the severity of damage the degree of inflammation is assessed. Responses are graded 
according to the grading of ocular lesions in OECD TG 405. 

Evaluation takes place separately for cornea, iris and conjunctiva (erythema and swelling). If 
the scoring meets the criteria in CLP Annex I, Tables 3.3.1 and 3.3.2, the substances are 
classified as Category 1 for serious eye damage or Category 2 for eye irritation, respectively. 

Reversibility of eye lesions is the other decisive factor in evaluating responses in the animal 
test. If the effects are not transient within the observation time of 21 days but cause persistent 
damage, they are considered irreversible and the test substance needs to be classified into 
Category 1. In the case of studies with a shorter observation period with irreversible effects, 
classification based on WoE should be considered. 

If considered as reversible, the test report must prove that these effects are transient, i.e. the 
affected sites are repaired within the observation period of the test (see Example 1, Section 
3.3.5.1.1). Evaluation of reversibility or irreversibility of the observed effects does not need to 
exceed 21 days after instillation for the purpose of classification. 

According to OECD TG 405, in cases of suspected serious eye damage, the test is started with 
one animal only. If effects in this animal are irreversible until the end of the observation period, 
sufficient information is available to classify the substance for serious eye damage. For a 
decision on no classification for serious eye damage and/or irritation or for a decision on 
classification as irritant, two additional animals have to be tested. 

For each of the three test animals the average scores for three consecutive days (usually 24, 48 
and 72 hours) are calculated separately for the cornea, iris and conjunctiva (erythema and 
swelling). If the mean scores for 2 out of 3 animals exceed the values in CLP Annex I, Tables 
3.3.1 and 3.3.2, classification has to be assigned accordingly. 

Tests that have been conducted with more than three animals 

Older test methods used up to six rabbits. In such cases, the current UNSCEGHS Guidance 
needs to be applied (adopted in June 2011) (see also Example 2, section 3.3.5.1.2): 

In the case of 6 rabbits, the following applies: 

a.  Classification for serious eye damage – Category 1 if: 

i.  at least in one animal effects on the cornea, iris or conjunctiva that are not expected 
to reverse or have not fully reversed within an observation period of normally 21 
days; and/or(ii) at least 4 out of 6 rabbits show a mean score per animal of  3 for 
corneal opacity and/or   > 1.5 for iritis 

b.  Classification for eye irritation – Category 2 if at least 4 out of 6 rabbits show a mean 

score per animal of: 

i.   1 for corneal opacity and/or 

ii.   1 for iritis and/or 

iii.   2 conjunctival erythema (redness) and/or 

iv.   2 conjunctival oedema (swelling) (chemosis) 

and which fully reverses within an observation period of normally 21 days. 

In the case of 5 rabbits, the following applies: 

c.  Classification for serious eye damage – Category 1 if: 

 
 
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i.  at least in one animal effects on the cornea, iris or conjunctiva that are not expected 
to reverse or have not fully reversed within an observation period of normally 21 
days; and/or 

d.  at least 3 out of 5 rabbits show a mean score per animal of  3 for corneal opacity 

and/or > 1.5 for iritis. 

i.  Classification for eye irritation – Category 2 if at least 3 out of 5 rabbits show a mean 

score per animal of: 

ii.   1 for corneal opacity and/or 

iii.   1 for iritis and/or 

iv.   2 conjunctival erythema (redness) and/or 

v.   2 conjunctival oedema (swelling) (chemosis) 

and which fully reverses within an observation period of normally 21 days. 

In the case of 4 rabbits, the following applies: 

e.  Classification for serious eye damage – Category 1 if: 

i.  at least in one animal effects on the cornea, iris or conjunctiva that are not expected 
to reverse or have not fully reversed within an observation period of normally 21 
days;  and/or 

ii.  at least 3 out of 4 rabbits show a mean score per animal of 

 3 for corneal opacity and/or 

> 1.5 for iritis 

f.  Classification for eye irritation – Category 2 if at least 3 out of 4 rabbits show a mean 

score per animal of: 

i.   1 for corneal opacity and/or 

ii.   1 for iritis and/or 

iii.   2 conjunctival erythema (redness) and/or 

iv.   2 conjunctival oedema (swelling) (chemosis) 

and which fully reverses within an observation period of normally 21 days. 

In this case the irritant categories 1 and 2 are used if 4 of 6 rabbits show a mean score per 
animal as outlined in the criteria. Likewise, if the test was performed with 4 or 5 animals, for at 
least 3 individuals the mean score per animal must exceed the values laid down in the 
classification criteria. A single animal showing irreversible or otherwise serious effects consistent 
with corrosion will necessitate classification as serious eye damage Category 1 irrespective of 
the number of animals used in the test.  

Other animal tests 

The LVET uses the same scoring system as for results from the OECD TG 405. However, the 
differences between the LVET and OECD TG 405 test methods, may result in a classification in a 
lower category (or no classification) based on LVET data, than if the classification was based on 
data derived from the standard in vivo test (OECD TG 405 (TM B.5)). See also 3.3.2.1.5.2 
above. 

Note that in case there are test data that originate from non-OECD tests and scoring has not 
been performed according to the Draize system, the values in CLP Annex I, Tables 3.3.1 and 
3.3.2 are not applicable for classification purposes. However these data from non-OECD tests 
should be considered in a weight of evidence determination. 

 
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3.3.2.3.3.  Weight of evidence 

According to Article 9(1) CLP, the criteria should be applied to available information. However, 
sometimes it is not straightforward or simple to apply the criteria and according to Article 9(3) a 
weight of evidence and expert judgement should be applied in such cases when the criteria 
cannot be applied directly. 

A weight of evidence determination means that all available and scientifically justified 
information bearing on the determination of hazard is considered together, such as human 
experience (including occupational data and data from accident databases, epidemiological and 
clinical studies, and well-documented case reports and observations), relevant animal data, skin 
irritation information/data, physico-chemical parameters (e.g. pH, reserve alkalinity/acidity), 
the results of suitable in vitro tests, information from the application of the category approach 
(grouping, read-across), QSAR results. The quality and consistency of the data shall be given 
appropriate weight. Both positive and negative results shall be assembled together in a single 
weight of evidence determination. Evaluation must be performed on a case-by-case basis and 
with expert judgement. However, normally positive results that are adequate for classification 
should not be overruled by negative findings (see also 1.1.1.3, Annex I, CLP and Section 1.4 of 
this guidance). 

Annex I: 1.1.1.4. For the purpose of classification for health hazards (Part 3) established 
hazardous effects seen in appropriate animal studies or from human experience that are 
consistent with the criteria for classification shall normally justify classification. Where 
evidence is available from both humans and animals and there is a conflict between the 
findings, the quality and reliability of the evidence from both sources shall be evaluated in 
order to resolve the question of classification. Generally, adequate, reliable and representative 
data on humans (including epidemiological studies, scientifically valid case studies as specified 
in this Annex or statistically backed experience) shall have precedence over other data. 
However, even well-designed and conducted epidemiological studies may lack a sufficient 
number of subjects to detect relatively rare but still significant effects, to assess potentially 
confounding factors. Therefore, positive results from well-conducted animal studies are not 
necessarily negated by the lack of positive human experience but require an assessment of 
the robustness, quality and statistical power of both the human animal data. 

For additional guidance, if both human and animal data are available, see the Guidance on 
IR&CSA Section R.7.2.3.2. 

Additional guidelines on the assessment of available information when WoE needs to be applied 
is provided in Section 3.2.2.3.3 (see Figure 3.2). 

3.3.2.4.  Decision on classification 

A skin corrosive substance is also classified for serious eye damage which is indicated in the 
hazard statement for skin corrosion (H 314: Causes severe skin burns and eye damage). 
However, although classification for both endpoints (Skin Corr. 1 and Eye Dam. 1) is required 
and has to be addressed in the safety data sheet, the hazard statement H318 ‘Causes serious 
eye damage’ is not indicated on the label because of redundancy (CLP Article 27). 

In other cases, if the comparison of the information related to serious eye damage/eye irritation 
with the criteria shows that the criteria are met, the substance is classified for serious eye 
damage or eye irritation.  

3.3.2.5.  Setting of specific concentration limits 

Article 10(1) Specific concentration limits and generic concentration limits are limits 
assigned to a substance indicating a threshold at or above which the presence of that 

 
 
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substance in another substance or in a mixture as an identified impurity, additive or individual 
constituent leads to the classification of the substance or mixture as hazardous. 

Specific concentration limits shall be set by the manufacturer, importer or downstream user 
where adequate and reliable scientific information shows that the hazard of a substance is 
evident when the substance is present at a level below the concentrations set for any hazard 
class in Part 2 of Annex I or below the generic concentration limits set for any hazard class in 
Parts 3, 4 and 5 of Annex I. 

[…] 

It is more difficult to prove the absence of a hazardous property, the legal text states that: 

Article 10(1)  

[…] 

In exceptional circumstances specific concentration limits may be set by the manufacturer, 
importer or downstream user where he has adequate, reliable and conclusive scientific 
information that a hazard of a substance classified as hazardous is not evident at a level 
above the concentrations set for the relevant hazard class in Part 2 of Annex I or above the 
generic concentration limits set for the relevant hazard class in Parts 3, 4 and 5 of that Annex. 

A specific concentration limit (SCL) set in accordance with the above mentioned provisions shall 
take precedence over the generic concentration limit (GCL) set out in Tables 3.2.3 and 3.2.4 of 
Annex I to CLP (Article 10(6)). Furthermore, such an SCL is substance-specific and should be 
applicable to all mixtures containing the substance instead of any GCL that otherwise would 
apply to a mixture containing the substance. 

What type of information may be the basis for setting a specific concentration limit?  

Existing human data may in certain cases (especially if dose-response information is available) 
indicate that the threshold for the irritation hazard in humans for a substance in a mixture, 
would be higher or lower than the GCL. A careful evaluation of the usefulness and the validity of 
such human data as well as their representativeness and predictive value (IR&CSA, sections 
R.4.3.3. and R.7.2.4.2) should be performed. As pointed out in Section 1.1.1.4 of Annex I, CLP, 
positive results from well-conducted animal studies are not necessarily negated by the lack of 
positive human experience but require an assessment of robustness, quality and a degree of 
statistical certainty of both the human and animal data.  

The aim of the standard test method for ‘Acute Eye Irritation/Corrosion’ OECD TG 405 65 is to 
identify potential serious eye damage or eye irritation. The test material is generally 
administered undiluted. Thus, no dose-response relationship can be obtained from an individual 
test.  

However, if there are adequate, reliable, relevant and conclusive existing data from other 
already performed animal studies with a sufficient number of animals tested to ensure a high 
degree of certainty, and with information of dose-response relationships, such data may be 
considered for setting a lower or, in exceptional cases, a higher SCL on a case-by-case basis. 

It should be noted that generating data specifically for the purpose of setting SCLs is not a 
requirement according to the CLP Regulation. Article 8(1) of CLP specifies that new tests may 
only be performed (in order to determine the hazard of a substance or mixture) if all other 
means of generating information has been exhausted and Article 7(1) specifies that where new 
tests are carried out, test on animals shall be undertaken only when no other alternatives, 

65 TO NOTE: In OECD TG 404 the term test substance refers to the test material, test article or test item.  
The term substance may be used differently from the REACH/CLP definition. 

 
 
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which provide adequate reliability of data, are possible. The GCLs must be applied for the 
classification of a mixture on the basis of its ingredient substances classified as causing serious 
eye damage or as an eye irritant, if there are no already existing specific data justifying an SCL 
which is lower or, in exceptional cases, higher than the GCL (see Article 10(1), CLP). Therefore, 
information will always be available, for mixtures containing substances already classified for 
serious eye damage/eye irritation, making it possible to identify the hazard for the mixture by 
using the GCLs (Article 9(4), CLP).  

The possibilities to use in vitro test methods as a basis for setting SCLs have not yet been 
explored and therefore, at the present point in time, it is not possible to provide guidance for 
the use of in vitro methods for the purpose of setting SCLs. However, this does not exclude that 
a method to set SCLs based on in vitro tests could be developed in the future, and these tests 
may provide a promising option for SCL setting. An SCL should apply to any mixture containing 
the substance instead of the GCL (that otherwise would apply to the mixture containing the 
substance). Thus, if the SCL is based on data derived from tests with dilutions of the substance 
in a specific solvent, it has to be considered that the derived concentration, should be applicable 
to all mixtures for which the SCL should apply.  

Annex VI Part 3 to CLP Regulation includes examples of substances for which a higher or lower 
SCL  was  set  under  Directive  67/548/EEC  (old  Dangerous  Substances  Directive  (DSD)  system) 
which have been included in CLP.  

3.3.2.6.  Decision logic for classification of substances 

The decision logic, based on that provided by the GHS, is reported as additional guidance below. 
It is strongly recommended that the person responsible for classification study the criteria for 
classification before and during use of the decision logic. 

 
 
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Are there data and/or information to 
evaluate serious eye damage/eye irritation? 

No 

Classification not possible 

Yes 

Does the substance have potential to cause serious eye damage  
(see criteria in CLP, Annex I, 3.3.1, 3.3.2.1.1, 3.3.2.2 and Figure 
3.4 in this guidance) consideringa:  
(a) 
(b) 
(c) 
(d) 

Existing human eye data; 
Irreversible eye damage in one or more test animals; 
Existing human or animal data indicating skin corrosion; 
Other  existing  animal  eye  data  including  single  or 
repeated exposure; 
Existing ex vivo/in vitro eye data; 
pH extremes of ≤2 or ≥11.5b; 
Information  available  from  validated  Structure  Activity 
Relationship methods? 

(e) 
(f) 
(g) 

No 

Is  the  substance  an  eye  irritant  (see  criteria  in  CLP,  Annex  I, 
3.3.1,  3.3.2.1.2,  3.3.2.2  and  Figure  3.4  in  this  guidance) 
consideringa: 
(a) 
(b) 
(c) 

Existing human data, single or repeated exposure; 
Eye irritation data from an animal study;  
Other  existing  animal  eye  data  including  single  or 
repeated exposure; 
Existing ex vivo/in vitro data; 
Information  available  from  validated  Structure  Activity 
Relationship methods? 

(d) 
(e) 

Category 1 

Yes 

Danger 

Yes 

Category 2 

Warning 

No 

No classification 

a Taking into account consideration of the total weight of evidence as needed. 

b Not applicable if consideration of pH and acid/alkaline reserve indicates the substance may not cause serious eye 
damage and confirmed by other data, preferably by data from an appropriate validated in vitro test. 

3.3.3.  Classification of mixtures for serious eye damage/eye irritation 

3.3.3.1. 

Identification of hazard information 

As for substances, the procedure for classifying mixtures is a tiered i.e. a stepwise approach 
based on a hierarchy principle and depending on the type and amount of available 
data/information starting from evaluating existing human data on the mixture, followed by a 
thorough examination of the existing in vivo data, ex vivo/in vitro and finally physico-chemical 
properties, available on the mixture (as illustrated in Figure 3.4, above).  

 
 
 
 
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If valid test data are available for the whole mixture they have precedence. If no such data 
exist, the so called bridging principles should be applied if possible. If the bridging principles are 
not applicable an assessment on the basis of data for the components of the mixture must be 
applied. 

For mixtures that have been on the market for a long time, some human data and experience 
may exist that could provide useful information on the eye irritation potential of the respective 
mixtures. However, lack of data on effects in humans may be due to, for example, poor 
reporting or adequate preventive measures. Therefore, lack of human data cannot be taken as 
evidence of the mixture being non-hazardous. See Section 3.3.2.1.1 of this Guidance for further 
information on the identification of human data. 

Where it is decided to base the classification of a mixture upon consideration of pH alone, Eye 
Damage Category 1 should be applied. In this case no further retrieval of information on the 
mixture itself is needed. 

3.3.3.2.  Classification criteria for mixtures 

The information available related to serious eye damage and eye irritation, will determine if the 
mixture should be classified using the approaches below in the following sequence (CLP Article 
9): 

a.  Classification derived using data on the mixture itself, by applying the substance criteria 

of Annex I to CLP  

b.  Classification based on the application of bridging principles, which make use of test data 

on similar tested mixtures and ingredient substances  

c.  Classification based on calculation and/or on concentration thresholds, including SCLs 

and M-factors.  

3.3.3.2.1.  When data are available for the complete mixture 

Annex I: 3.3.3.1.1. The mixture shall be classified using the criteria for substances, and 
taking into account the tiered approach to evaluate data for this hazard class. 

Annex I: 3.3.3.1.2. When considering testing of the mixture classifiers are encouraged to 
use a tiered weight of evidence approach as included in the criteria for classification of 
substances for skin corrosion and serious eye damage/eye irritation to help ensure an 
accurate classification, as well as avoid unnecessary animal testing. In absence of any other 
information, a mixture is considered to cause serious eye damage (Category 1) if it has a pH 
≤ 2,0 or ≥ 11,5. However, if consideration of alkali/acid reserve suggests the mixture may 
not cause serious eye damage despite the low or high pH value, this needs to be confirmed by 
other data, preferably data from an appropriate validated in vitro test. 

As for substances, where the criteria cannot be applied directly to available identified 
information, a weight of evidence determination using expert judgement should be used  
according to CLP Article 9(3) when evaluating the data in order to be able to apply the criteria 
to the information (according to CLP Article 9(1)) (see 3.3.2.3.3. Weight of evidence above).  

The integration of all information to come to a final hazard assessment based on weight of 
evidence in general requires in-depth toxicological expertise. 

For guidance on the assessment of the information available for mixtures when WoE needs to 
be applied, please see Figure 3.2 in Section 3.2.2.3.3.  

There are a number of available in vitro test systems that have been validated to identify 
substances causing serious eye damage (Category 1) and/or no classification (see Section 
3.3.2.1.5.1), that are considered to be valid also for mixtures. However, not all available in vitro 
test systems work equally well for all types of mixtures. The specific applicability domain, 

 
 
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including limitations of the use of the test methods for mixtures should be considered. Thus, 
prior to testing a mixture in a specific in vitro assay for classification purposes, it has to be 
ensured that the respective test has been previously shown to be suitable for the prediction of 
serious eye damage/eye irritation properties for the type of mixture to be evaluated. 

There are no in vitro tests with regulatory acceptance for eye irritation at present. A proposal to 
combine results of multiple in vitro tests to identify eye irritants has been presented in a draft 
OECD Guidance document (ref. OECD 2015).   

3.3.3.2.1.1.  Mixtures with extreme pH 

As a general rule, mixtures with a pH of ≤ 2 or ≥ 11.5 should be considered as corrosive. 
However, assessment of the buffering capacity of the mixture indicated by its acid or alkali 
reserve should be considered (see 3.2.3.2.1.1.) 

Where the mixture has an extreme pH value but the only corrosive/irritant ingredient present in 
the mixture is an acid or base with an assigned SCL (either CLP Annex VI or set by supplier 
according to Article 10(1), CLP), then the mixture should be classified according to the SCL. In 
this instance, pH of the mixture should not be considered a second time since it would have 
already been taken into account when deriving the SCL for the substance. 

If this is not the case, then the steps to be taken into consideration when classifying a mixture 
with pH  2 or  11.5 are described in the following decision logic. 

Figure 3.5 Mixture not classified as Skin Corr. 1 and without animal or human data on serious 
eye damage/eye irritation or relevant data from similar tested mixtures, pH is  2 or  11.5 

Does  the  acid/alkaline  reserve  indicate  that  the  mixture  may  not  be 
corrosive? 

 NO ➔ 

Classify  as  corrosive, 
Skin Corr. 1 and serious 
eye  damaging,  Eye 
Dam. 1. 

YES 

 

Is the mixture tested for serious eye damaging properties in an OECD 
adopted  or  internationally  accepted  scientifically  valid  in  vitro  test 
considered to be valid and applicable for the mixture? 

Classify  as  serious  eye 
damaging, Eye Dam. 1. 

YES 

 

   NO ➔ 

Does the mixture demonstrate serious eye damaging properties in an 
OECD adopted or internationally accepted scientifically valid in vitro test 
considered valid and applicable for the mixture? 

Classify  as  serious  eye 
damaging, Eye Dam. 1. 

   YES ➔ 

NO 

 

Consideration of the total weight of available evidence, in particular in 
case  of  conflicting  data,  including  extreme  pH,  negative/inconclusive 
results  from  (e.g.)  eye  irritation  in  vitro  tests  and  results  from  the 
application of the methods based on the ingredients in the mixture in 
CLP  Annex  I,  3.3.3.3.2-3.3.3.3.3  (Table  3.3.3)  /  3.3.3.3.4.1- 
3.3.3.3.4.3 (Table 3.3.4) 

➔ 

 
 
 
    
 
  
 
 
 
 
 
 
 
 
 
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Classify:  Category  1, 
Category 
no 
classification. 

2, 

Thus, if consideration of extreme pH and acid/alkaline reserve indicates the mixture may not 
have the potential to cause serious eye damage, then the supplier should carry out further 
testing to confirm this, preferably an appropriate validated in vitro test (CLP Annex I, Section 
3.3.3.1.2). The mixture must be classified as Serious Eye damage Category 1 if the supplier 
decides not to carry out the required confirmatory testing. 

If further testing confirms that the mixture should not be classified for serious eye damage 
effects, then the supplier should assess the mixture for eye irritation either using in vitro eye 
irritation test methods when available and considered appropriately valid and applicable for the 
mixture or the methods based on ingredients. 

It must be noted that the pH-acid/alkali reserve method assumes that the potential corrosivity 
or irritancy is due to the effect of the ionic entities. When this is not the case, especially when 
the mixture contains non-ionic (non-ionisable) substances themselves classified as corrosive or 
irritant, then the pH-acid/alkali reserve method cannot be a basis for modifying the 
classification but should be considered in the weight of evidence analysis. 

Where the mixture has an extreme pH value and contains some other corrosive/irritant 
ingredients (some of which may have SCLs assigned) in addition to an acid or base with or 
without an assigned SCL, then the steps described in the above decision logic shall be followed. 

3.3.3.2.2.  When data are not available for the complete mixture: bridging principles 

Annex I: 3.3.3.2.1. Where the mixture itself has not been tested to determine its skin 
corrosivity or potential to cause serious eye damage/eye irritation, but there are sufficient 
data on the individual ingredients and similar tested mixtures to adequately characterise the 
hazards of the mixture, these data shall be used in accordance with the bridging rules set out 
in section 1.1.3. 

In order to apply bridging principles, there needs to be sufficient data on similar tested mixtures 
as well as on the ingredients of the mixture (see Section 1.6.3 of this Guidance).  

When the available identified information is inappropriate for the application of the bridging 
principles then the mixture should be classified based on its ingredients as described in Sections 
3.3.3.2 and 3.3.3.3 of this Guidance. 

3.3.3.2.3.  When data are available for all ingredients or only for some ingredients of 

the mixture 

3.3.3.2.3.1.  Ingredients that should be taken into account for the purpose of 

classification 

Annex I: 3.3.3.3.1. […] The ‘relevant ingredients’ of a mixture are those which are present 
in concentrations ≥ 1% (w/w for solids, liquids, dusts, mists and vapours and v/v for gases), 
unless there is a presumption (e.g. in the case of corrosive ingredients) that an ingredient 
present at a concentration < 1% can still be relevant for classifying the mixture for serious 
eye damage/eye irritation. 

3.3.3.2.3.2.  The additivity approach is applicable 

Annex I: 3.3.3.3.2. In general, the approach to classification of mixtures as seriously 
damaging to the eye/eye irritant when data are available on the ingredients, but not on the 
mixture as a whole, is based on the theory of additivity, such that each skin corrosive or 
serious eye damaging/eye irritation ingredient contributes to the overall serious eye 

 
 
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damage/eye irritation properties of the mixture in proportion to its potency and concentration. 
A weighting factor of 10 is used for skin corrosive and serious eye damaging ingredients when 
they are present at a concentration below the generic concentration limit for classification with 
Category 1, but are at a concentration that will contribute to the classification of the mixture 
as eye irritant. The mixture is classified as seriously damaging to the eye or eye irritant when 
the sum of the concentrations of such components exceeds a concentration limit. 

Annex I: 3.3.3.3.3. Table 3.3.3 provides the generic concentration limits to be used to 
determine if the mixture shall be classified as seriously damaging to the eye or as eye irritant. 

When the supplier is unable to derive the classification using either data on the mixture itself or 
bridging principles, he must determine the serious eye damage/eye irritation properties of his 
mixture using data on the individual ingredients. Although the general approach is the additivity 
principle which has been successfully used under the DPD and more recently, the supplier must 
ascertain whether the additivity approach is applicable where all relevant ingredients should be 
considered. The first step would then be to identify all the relevant ingredients in the mixture 
(i.e. their name, chemical type, concentration level, hazard classification and any SCLs) and the 
pH of the mixture. In addition, it is important to also consider effects that could occur in the 
whole mixture, such as surfactant interaction, neutralisation of acids/bases apart from effects of 
the entire mixture (i.e. pH and the alkaline reserve) and not only consider the contribution of 
individual ingredients. 

Additivity may not apply where the mixture contains substances mentioned in CLP Annex I, 
3.3.3.3.4.1- 3.3.3.3.4.3 which may be corrosive/irritant at concentrations below 1%, see 
Section 3.3.3.2.3.3 of this Guidance. 

Application of SCLs when applying the additivity approach 

The generic concentration limits are specified in Table 3.3.3. However, CLP Article 10(5) 
indicates that specific concentration limits (SCLs) take precedence over generic concentration 
limits. Thus, if a given substance has an SCL set in accordance with Article 10(1), CLP, then this 
specific concentration limit has to be taken into account when applying the summation 
(additivity) method for serious eye damage/eye irritation (see Examples 4 and 5). 

In cases where additivity applies for serious eye damage/eye irritation to a mixture with two or 
more substances some of which may have SCLs assigned, then the following formula should be 
used: 

The mixture is classified for serious eye damage/eye irritation if the 

Sum of (ConcA / clA) + (ConcB / clB) + ….+ (ConcZ / clZ) is   1 

Where ConcA = the concentration of substance A in the mixture; 

clA = the concentration limit (either specific or generic) of substance A; 

ConcB = the concentration of substance B in the mixture; 

clB = the concentration limit (either specific or generic) of substance B; etc. 

3.3.3.2.3.3.  The additivity approach is not applicable 

Annex I: 3.3.3.3.4.1. Particular care must be taken when classifying certain types of 
mixtures containing substances such as acids and bases, inorganic salts, aldehydes, phenols, 
and surfactants. The approach explained in paragraphs 3.3.3.3.1 and 3.3.3.3.2 might not 
work given that many of such substances are seriously damaging to the eye/eye irritant at 
concentrations < 1 %. 

Annex I: 3.3.3.3.4.2. For mixtures containing strong acids or bases the pH shall be used as 
classification criteria (see section 3.3.3.1.2) since pH will be a better indicator of serious eye 

 
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damage (subject to consideration of acid/alkali reserve) than the generic concentration limits 
of Table 3.3.3. 

Annex I: 3.3.3.3.4.3. A mixture containing skin corrosive or serious eye damaging/eye 
irritant ingredients that cannot be classified based on the additivity approach (Table 3.3.3), 
due to chemical characteristics that make this approach unworkable, shall be classified as 
Serious Eye Damage (Category 1) if it contains ≥ 1 % of a skin corrosive or serious eye 

damaging ingredient and as Eye Irritation (Category 2) when it contains ≥ 3 % of an irritant 
ingredient. Classification of mixtures with ingredients for which the approach in Table 3.3.3 
does not apply is summarised in Table 3.3.4. 

Annex I: 3.3.3.3.5. On occasion, reliable data may show that the effects of serious eye 
damage/eye irritation of an ingredient will not be evident when present at a level at or above 
the generic concentration limits mentioned in Tables 3.3.3 and 3.3.4 in section 3.3.3.3.6. In 
these cases the mixture shall be classified according to those data (see also Articles 10 and 
11). On other occasions, when it is expected that the skin corrosion/irritation hazards or the 
effect of serious eye damage/eye irritation an ingredient will not be evident when present at a 
level at or above the generic concentration limits mentioned in Tables 3.3.3 and 3.3.4, testing 
of the mixture shall be considered. In those cases, the tiered weight of evidence strategy shall 
be applied. 

Annex I: 3.3.3.3.6. If there are data showing that (an) ingredient(s) may be corrosive to the 
skin or seriously damaging to the eye/eye irritating at a concentration of < 1 % (corrosive to 
the skin or seriously damaging the eye) or < 3 % (eye irritant), the mixture shall be classified 
accordingly. 

3.3.3.3.  Generic concentration limits for substances triggering classification 

of mixtures 

3.3.3.3.1.  When the additivity approach is applicable 

Annex I: Table 3.3.3 

Generic concentration limits of ingredients of a mixture classified as skin corrosion 
(Category 1, 1A, 1B or 1C) and/or serious eye damage (Category 1) or eye irritation 
(Category 2) that trigger classification of the mixture as eye damage/eye irritation 
where additivity approach applies 

Sum of ingredients classified as: 

Serious eye damage 

Eye irritation 

Concentration triggering classification of a mixture as: 

Category 1 

Category 2 

 3 % 

 1 % but < 3 % 

 10 % 

 10 % 

Skin  corrosion  Sub-Category 1A, 
1B,  1C  or  Category  1  +  Serious 
eye damage ( Category 1)(a) 

Eye irritation (Category 2) 

10  x 
(Skin  corrosion  Sub-
Category  1A,  1B,  1C  or  Skin 
corrosion  Category  1  +  Serious 
eye damage (Category 1)) + Eye 
irritation (Category 2) 

 
 
 
 
 
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(a) If an ingredient is classified as both Skin Corrosion Sub-Category 1A, 1B, 1C or Category 1 and Serious 

Eye Damage (Category 1), its concentration is considered only once in the calculation. 

3.3.3.3.2.  When the additivity approach is not applicable 

Annex I: Table 3.3.4 

Generic concentration limits of ingredients of a mixture as serious eye damage 
(Category 1) or eye irritation (Category 2), where the additivity approach does not 
apply 

Ingredient 

Acid with pH ≤ 2 

Base with pH ≥ 11,5 

Other ingredient classified as skin corrosion 
(Sub-Category 1A,  1B,  1C  or  Category  1) 
or serious eye damage (Category 1)  

Other ingredient classified as eye irritation 
(Category 2)  

Concentration 

Mixture classified as 

≥ 1% 

≥ 1% 

≥ 1% 

≥ 3% 

Serious eye damage 
(Category 1) 

Serious eye damage 
(Category 1) 

Serious eye damage 
(Category 1) 

Eye irritation (Category 
2) 

3.3.3.4.  Decision logic for classification of mixtures 

The decision logic, based on the one provided in the GHS, is presented here below as additional 
guidance. It is strongly recommended that the person responsible for classification, study the 
criteria for classification before and during use of the decision logic. 

 
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Does the mixture as a whole or its ingredients have 
data/information to evaluate serious eye damage/eye 
irritation? 

Yes 

Does the mixture as a whole have data/information to 
evaluate serious eye damage/eye irritation? 

No 

Can bridging principles be applied? 

No 

Is pH of the mixture ≤2 or ≥11.5? 

No 

Classification not possible 

See decision 
logic 3.3.2.6 

Classify in 
appropriate 
category  

No 

Yes 

Yes 

Yes 

Follow decision logic in 
Section 3.3.3.2.1.1 of 
this guidance and 
classify accordingly 

Category 1 

Yes 

Does the mixture contain ≥1%a of an ingredient which causes 
serious eye damage when additivity approach may not apply? 

No 

Does the mixture contain one or more ingredients corrosive 
or seriously damaging to the eye when the additivity approach 
applies and where the sum of concentrations ingredients 
classified as Skin Corr. Cat. 1 + Eye Dam. Cat. 1 ≥3%? 

Yes 

No 

Danger 

Category 1 

Danger 

 
 
 
 
 
 
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Does the mixture contain ≥3% a of an ingredient which is 
an eye irritant and when the additivity approach may not 
apply? 

Yes 

No 

Does the mixture contain one or more ingredients 
corrosive or seriously damaging to the eye/eye irritant 
when the additivity approach applies and where the sum of 
concentrations of ingredients classified as: 

Yes 

(a) Eye Dam. Cat. 1 + Skin Corr. Cat. 1 ≥1% but <3%; or 

(b) Eye Irrit. Cat. 2 ≥10%; or 
(c) 10 x (Skin Corr. Cat. 1 + Eye Dam. Cat. 1b) + Eye Irrit. 
Cat. 2 ≥10%? 

Category 2 

Warning 

Category 2 

Warning 

No 

Not classified 

a Where relevant < 1%, see Section 3.3.3.3.1 of Annex I of CLP. 

b If an ingredient is classified as both skin Category 1 and eye Category 1 its concentration is considered 
only once in the calculation. 

3.3.4.  Hazard communication in form of labelling for serious eye 

damage/eye irritation 

3.3.4.1.  Pictograms, signal words, hazard statements and precautionary 

statements 

Annex I: 3.3.4.1 Label elements shall be used for substances or mixtures meeting the criteria 
for classification in this hazard class in accordance with Table 3.3.5. 

Label elements for serious eye damage/eye irritation(a) 

Table 3.3.5 

Classification 

Category 1 

Category 2 

 
 
 
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Signal Word 

Danger 

Warning 

Hazard Statement 

H318: Causes serious eye damage 

H319: Causes serious eye 
irritation 

Precautionary  Statement 
Prevention 

P280 

P264 

P280 

P305 + P351 + P338 

P305 + P351 + P338 

P310 

P337 + P313 

Precautionary  Statement 
Response 

Precautionary  Statement 
Storage 

Precautionary  Statement 
Disposal 

(a) Where a chemical is classified as skin corrosion Sub-Category 1A, 1B, 1C or Category 1, labelling for 
serious  eye  damage/eye  irritation  can  be  omitted  as  this  information  is  already  included in  the  hazard 
statement for skin corrosion Category 1 (H314).' 

A skin corrosive mixture is considered to also cause serious eye damage which is indicated in 
the hazard statement for skin corrosion, H314: Causes severe skin burns and eye damage. 
Thus, in this case a mixture has to be classified for both classifications (Skin Corr. 1 and Eye 
Dam. 1) but the hazard statement H318 ‘Causes serious eye damage’ is not indicated on the 
label because of redundancy (CLP Article 27). 

3.3.5.  Examples of classification for serious eye damage/eye irritation 

3.3.5.1.  Examples of substances fulfilling the criteria for classification 

3.3.5.1.1. 

Example 1: Standard test according to OECD TG 405 with three animals 

In a study according to OECD 405 the test substance was applied on the eyes of three rabbits. 
The scoring results obtained are listed in the following table: 

Cornea: 

Animal 
No. 

Evaluation after … 

Positive responder? 

 Score … 

1 hr 

24 hrs 

48 hrs 

72 hrs 

21 days 

 1 

 3 

1 

2 

0 

2 

2 

2 

2 

 24/48/72 h animal 1 is 2 

2 

2 

2 

0 

0 

Yes 

No 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 24/48/72 h animal 2 is 2 

Yes 

No 

3 

2 

2 

1 

1 

0 

 24/48/72 h animal 3 is 1.3 

Yes 

No 

Effects are reversible 

Iris: 

Animal 
No. 

Evaluation after … 

Positive responder? 

 Score … 

1 hr 

24 hrs 

48 hrs 

72 hrs  21 days 

 1 

> 1.5 

1 

2 

3 

0 

1 

1 

1 

1 

1 

 24/48/72 h animal 1 is 1 

1 

1 

1 

 24/48/72 h animal 2 is 1 

1 

1 

1 

0 

0 

0 

Yes 

No 

Yes 

No 

 24/48/72 h animal 3 is 1 

Yes 

No 

Effects are reversible  

Conjunctiva – Erythema:  

Animal 
No. 

1 

2 

3 

Evaluation after … 

Positive responder? 

 Score … 

1 hr 

24 hrs 

48 hrs 

72 hrs  21 days 

 2 

2 

1 

1 

2 

2 

2 

 24/48/72 h animal 1 is 2 

1 

1 

1 

 24/48/72 h animal 2 is 1 

1 

1 

1 

 24/48/72 h animal 3 is 1 

0 

0 

0 

Yes 

No 

No 

Effects are reversible 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Conjunctiva – Swelling: 

Animal 
No. 

1 

2 

3 

Evaluation after … 

Positive responder? 

 Score … 

1 hr 

24 hrs 

48 hrs 

72 hrs 

21 days 

 2 

0 

2 

2 

3 

3 

3 

 24/48/72 h animal 1 is 3 

2 

2 

1 

 24/48/72 h animal 2 is 1.7 

3 

2 

2 

 24/48/72 h animal 3 is 2.3 

0 

0 

0 

Yes 

No 

Yes 

Effects are reversible 

Classification according to CLP: Eye irritant Category 2  

Rationale:   Cornea ‘positive responder’  1: 3/3 animals 

and/or  

Conjunctiva ‘positive responder’  2: 2/3 animals 

and/or  

Iris ‘positive responder’  1:  3/3 animals 

3.3.5.1.2. 

Example 2: Test carried out with more than 3 rabbits 

Cornea:  

Anim
al No. 

Evaluation after … 

Positive responder? 

 Score … 

1h 

24h 

48h 

72h 

7d 

14d 

21d 

 3 

 1 

1 

1 

2 

3 

3 

1 

1 

0 

 24/48/72h = 2.7 

no 

yes 

2 

1 

2 

2 

3 

1 

1 

0 

 24/48/72h = 2.3 

no 

yes 

3 

1 

2 

3 

3 

2 

1 

0 

 24/48/72h = 2.7 

no 

yes 

4 

1 

2 

4 

4 

2 

1 

0 

 24/48/72h = 3.3 

yes 

yes 

Effects are reversible 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Iris: 

Anim
al No. 

Evaluation after … 

Positive responder? 

 Score … 

1h 

24h 

48h 

72h 

7d 

14d 

21d 

> 1.5 

 1 

1 

0 

0 

0 

0 

0 

0 

0 

 24/48/72h = 0 

no 

no 

2 

0 

0 

0 

0 

0 

0 

0 

 24/48/72h = 0 

no 

no 

3 

0 

1 

1 

1 

1 

0 

0 

 24/48/72h = 1 

no 

yes 

4 

0 

0 

0 

0 

0 

0 

0 

 24/48/72h = 0 

no 

no 

Conjunctiva – Erythema: 

Anim
al No. 

Evaluation after … 

Positive responder? 

 Score … 

Effects are reversible 

1h 

24h 

48h 

72h 

7d 

14d 

21d 

 2 

1 

2 

2 

2 

1 

1 

1 

0 

 24/48/72h = 1.7 

2 

2 

2 

2 

1 

1 

0 

0 

 24/48/72h = 1.7 

3 

2 

2 

2 

1 

1 

1 

1 

 24/48/72h = 1.7 

4 

2 

2 

2 

1 

0 

0 

0 

 24/48/72h = 1.7 

no 

no 

no 

no 

Effects are irreversible 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Conjunctiva – Swelling: 

Anim
al No. 

Evaluation after … 

Positive responder? 

 Score … 

1h 

24h 

48h 

72h 

7d 

14d 

21d 

 2 

1 

2 

2 

2 

1 

1 

1 

0 

 24/48/72h = 1.7 

2 

2 

2 

1 

1 

1 

0 

0 

 24/48/72h = 1.3 

3 

2 

2 

2 

1 

1 

1 

1 

 24/48/72h = 1.7 

4 

2 

2 

2 

1 

1 

1 

1 

 24/48/72h = 1.7 

no 

no 

no 

no 

Effects are irreversible 

Classification according to CLP: Serious eye damage Category 1 

Rationale: Conjunctiva with irreversible effects 

3.3.5.2.  Examples of mixtures fulfilling the criteria for classification 

3.3.5.2.1. 

Example 3: Application of the additivity approach for mixtures containing 
ingredients without SCLs  

Where the mixture is made up of ingredients with no assigned SCLs, then the appropriate 
summation(s) from CLP Annex I, Table 3.3.3 should be used. 

Ingredient 

Skin / eye classification  Concentration 

SCL 

(% w/w) 

Substance A 

Eye Dam. 1 

Substance B 

Eye Irrit. 2 

Substance C 

Eye Dam. 1 

Substance D 

Not classified 

Acid E 

Water 

Skin Corr. 1A 

Not classified 

86.3 

1.8 

0.5 

5.4 

4.0 

2.0 

Not assigned 

Not assigned 

Not assigned 

Not assigned 

pH of the mixture is 9.0 – 10.0, thus extreme pH provisions do not apply. The mixture contains 
an acid but no surfactant. Additivity is considered to apply. 

Substance D and water can be disregarded as they are not classified for serious eye 
damage/eye irritation. Substance B can also be disregarded as present below 1%. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Mixture contains 7.2% Eye Dam. 1 ingredients as well as 2% acid E so the summation {Skin 
corrosion Cat 1A, 1B, 1C + Eye Dam. 1} applies and is > 3%, thus mixture is classified Eye 
Dam. 1. 

3.3.5.2.2. 

Example 4: Application of the additivity approach for mixtures containing 
ingredients which may have SCLs 

Ingredient 

Skin / eye classification 

Concentration 
(% w/w) 

SCL 

Substance A 

Eye Dam. 1 

Substance B 

Eye Irrit. 2 

Substance C 

Skin Corr. 1B 

Substance D 

Not classified 

Substance E 

Skin Corr. 1B 

Water 

Not classified 

Not assigned 

Not assigned 

C ≥ 10 %: Skin Corr. 1B 

5 % ≤ C < 10 %: Eye Irrit. 2 

Not assigned 

2.0 

0.5 

5.4 

4.0 

2.0 

86.1 

pH of the mixture is 10.5 – 11.0, thus extreme pH provisions do not apply. Additivity is 
considered to apply. 

Substance D and water can be disregarded as they are not classified for serious eye 
damage/eye irritation. Substance B can also be disregarded as present below 1%. 

SCLs are not assigned to substance E or substance A, thus generic concentration limits (GCL) 
apply for these ingredients 

Eye Dam. 1 

(% Substance A / GCL) + (% Substance C / SCL) + (% Substance E / GCL) = (2/3) + (5.4/10) 
+ (2/3) = 1.9   > 1 thus mixture is classified Eye Dam. 1 

3.3.5.2.3. 

Example 5: Application of the additivity approach for mixtures containing 
ingredients which may have SCLs 

Ingredient 

Serious eye damage/ 
eye irritation 
classification 

Concentration 
(% w/w) 

Substance B 

Eye Dam.1 

Substance C 

Eye Irrit. 2 

Substance D 

Eye Dam.1 

0.7 

74.9 

8.5 

SCL 

Not assigned 

Not assigned 

C ≥ 25 %: Eye Dam.1 

10 % ≤ C < 25 %: Eye Irrit. 
2 

Substance E 

Not classified 

15.9 

pH of the mixture is 10.0 – 10.5 (10% solution), thus extreme pH provisions do not apply. 
Additivity is considered to apply. 

Substance E can be disregarded as it is not classified for serious eye damage/eye irritation. 
Substance B can also be disregarded as present below 1%. 

 
 
 
 
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SCLs are not assigned to substance C, thus GCL apply for this ingredient 

Eye Dam. 1 

Mixture contains 8.5% substance D, the only ‘relevant’ ingredient classified as Eye Dam.1. As 
this is below the 25% SCL for substance D, the mixture is not classified Eye Dam.1 

Eye Irrit. 2  

(%substance D/ SCL) + (%substance C / GCL) = (8.5/10) + (74.9/10) which is > 1 thus 
mixture is classified Eye Irrit. 2 

3.3.6.  References 

ECVAM/ESAC (2009a) Statement on the scientific validity of cytotoxicity/cell-function based in 
vitro assays for eye irritation testing. Online: http://ecvam.jrc.it/ 

ECVAM/ESAC (2009b) Statement on the use of existing low volume eye test (LVET) data for 
weight of evidence decisions on classification and labelling of cleaning products and their main 
ingredients. Online: http://ecvam.jrc.it/ 

Griffith J.F., Nixon G.A., Bruce R.D., Reer P.J., Bannan E.A. (1980), Dose-response studies with 
chemical irritants in the albino rabbit eye as a basis for selecting optimum testing conditions for 
predicting hazard to the human eye. Toxicol Appl Pharmacol 55, 501-513. 

Scott L., Eskes C., Hoffmann S., Adriaens E., Alepée N., Bufo M., Clothier R., Facchini D., Faller 
C., Guest R., Harbell J., Hartung T., Kamp H., Varlet B.L., Meloni M, McNamee P., Osborne R., 
Pape W., Pfannenbecker U., Prinsen M., Seaman C., Spielmann H., Stokes W., Trouba K., 
Berghe C.V., Goethem F.V., Vassallo M., Vinardell P., Zuang V. (2010), A proposed eye irritation 
testing strategy to reduce and replace in vivo studies using Bottom-Up and Top-Down 
approaches. Toxicol in Vitro 24, 1-9. 

Young J.R., How M.J., Walker A.P., Worth W.M.H. (1988), Classification as corrosive or irritant 
to skin of preparations containing acidic or alkaline substances, without test on animals. Toxicol 
in Vitro 2, 19-26. 

Young J.R., How M.J. (1994), Product classification as corrosive or irritant by measuring pH and 
acid / alkali reserve. In Alternative Methods in Toxicology vol. 10 - In Vitro Skin Toxicology: 
Irritation, Phototoxicity, Sensitization, eds. A. Rougier, A.M. Goldberg and H.I Maibach, Mary 
Ann Liebert, Inc. 23-27. 

 
 
 
 
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3.4.  RESPIRATORY OR SKIN SENSITISATION 

3.4.1.  Definitions and general considerations for respiratory or skin 

sensitisation 

Annex I: 3.4.1.1. Respiratory sensitiser means a substance that will lead to hypersensitivity 
of the airways following inhalation of the substance. 

Annex I: 3.4.1.2. Skin sensitiser means a substance that will lead to an allergic response 
following skin contact. 

In terms of prevention it might be important to note that respiratory sensitisation may be 
induced not only by inhalation but also by skin contact (Dotson et al, 2015). Please refer also to 
the Guidance on IR&CSA, Section R.7.3. 

Annex I: 3.4.1.3. For the purpose of section 3.4, sensitisation includes two phases: the 
first phase is induction of specialised immunological memory in an individual by exposure to 
an allergen. The second phase is elicitation, i.e. production of a cell-mediated or antibody-
mediated allergic response by exposure of a sensitised individual to an allergen. 

Annex I: 3.4.1.4. For respiratory sensitisation, the pattern of induction followed by 
elicitation phases is shared in common with skin sensitisation. For skin sensitisation, an 
induction phase is required in which the immune system learns to react; clinical symptoms 
can then arise when subsequent exposure is sufficient to elicit a visible skin reaction 
(elicitation phase). As a consequence, predictive tests usually follow this pattern in which 
there is an induction phase, the response to which is measured by a standardised elicitation 
phase, typically involving a patch test. The local lymph node assay is the exception, directly 
measuring the induction response. Evidence of skin sensitisation in humans normally is 
assessed by a diagnostic patch test. 

Annex I: 3.4.1.5. Usually, for both skin and respiratory sensitisation, lower levels are 
necessary for elicitation than are required for induction. Provisions for alerting sensitised 
individuals to the presence of a particular sensitiser in a mixture can be found in Annex II, 
section 2.8. 

Annex I: 3.4.1.6. The hazard class Respiratory or Skin Sensitisation is differentiated into: 

- Respiratory Sensitisation and; 

- Skin Sensitisation. 

3.4.2.  Classification of substances for sensitisation 

3.4.2.1.  Classification of substances for respiratory sensitisation 

3.4.2.1.1. 

Identification of hazard information  

There are no formally recognised and validated animal or in vitro tests for respiratory 
sensitisation. However there may be data from human observations indicating respiratory 
sensitisation in exposed populations or other sufficient evidence, including read-across.  

3.4.2.1.1.1.  Identification of human data  

Relevant information with respect to respiratory sensitisation may be available from case 
reports, epidemiological studies, medical surveillance, reporting schemes. For more details see 
the Guidance on IR&CSA, Section R.7.3.9.2. 

 
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3.4.2.1.1.2.  Identification of non human data  

No formally recognised and validated animal or in vitro tests currently exist for respiratory 
sensitisation. However, data from some animal studies may be indicative of the potential of a 
substance to cause respiratory sensitisation in humans (CLP Annex I, 3.4.2.1.3) and may 
provide supportive evidence in case human evidence is available. These data may provide 
supportive evidence and should be used in a weight of evidence assessment. For further 
information see the Guidance on IR&CSA, Section R.7.3.9.1.  

3.4.2.1.2. 

Classification criteria for substances  

Annex I: 3.4.2.1. Respiratory sensitisers 

Annex I: 3.4.2.1.1. Hazard categories 

Annex I: 3.4.2.1.1.1. Respiratory sensitisers shall be classified in Category 1 where data are 
not sufficient for sub-categorisation. 

Annex I: 3.4.2.1.1.2. Where data are sufficient a refined evaluation according to 3.4.2.1.1.3 
shall allow the allocation of respiratory sensitisers into sub-category 1A, strong sensitisers, or 
sub-category 1B for other respiratory sensitisers. 

Annex I: 3.4.2.1.1.3. Effects seen in either humans or animals will normally justify 
classification in a weight of evidence approach for respiratory sensitisers. Substances may be 
allocated to one of the two sub-categories 1A or 1B using a weight of evidence approach in 
accordance with the criteria given in Table 3.4.1 and on the basis of reliable and good quality 
evidence from human cases or epidemiological studies and/or observations from appropriate 
studies in experimental animals. 

Annex I: 3.4.2.1.1.4. Substances shall be classified as respiratory sensitisers in accordance 
with the criteria in Table 3.4.1: 

Table 3.4.1 

Hazard category and sub-categories for respiratory sensitisers 

Category 

Criteria 

Category 1 

Substances  shall  be  classified  as  respiratory  sensitisers  (Category  1) 
where data are not sufficient for sub-categorisation in accordance with the 
following criteria: 

(a) 

if  there  is  evidence  in  humans  that  the  substance  can  lead  to 
specific respiratory hypersensitivity; and /or 

(b) 

if there are positive results from an appropriate animal test. 

Sub-category 1A: 

Substances  showing  a  high  frequency  of  occurrence  in  humans;  or  a 
probability of occurrence of a high sensitisation rate in humans based on 
animal or other tests (1). Severity of reaction may also be considered. 

Sub-category 1B: 

Substances  showing  a  low  to  moderate  frequency  of  occurrence  in 
humans; or a probability of occurrence of a low to moderate sensitisation 
rate  in  humans  based  on  animal  or  other  tests  (1).  Severity  of  reaction 
may also be considered. 

(1) 
At  present,  recognised  and  validated  animal  models  for  the  testing  of  respiratory 
hypersensitivity are not available. Under certain circumstances, data from animal studies may 
provide valuable information in a weight of evidence assessment. 

 
 
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There is currently no clear way of establishing sub-categories for respiratory sensitisation, 
however if compelling evidence were available such as observations in the workplace, it may be 
possible to determine a sub-category.    

Classification into sub-categories is required when data are sufficient. When Category 1A cannot 
be excluded, Category 1 should be applied instead of Category 1B. High frequency and low to 
moderate frequency cannot be defined as specific concentrations or percentages for human 
study data because, when considering human evidence, it is necessary to take into account the 
size of the exposed population and the extent and conditions of exposure, including frequency. 
It is necessary, therefore, to reach a view on a case-by-case basis.  

3.4.2.1.3. 

Evaluation of hazard information 

3.4.2.1.3.1.  Human data  

Substances shall be classified as respiratory sensitisers if there is evidence in humans or other 
sufficient evidence, including read-across that the substance can lead to specific respiratory 
hypersensitivity. 

Annex I:  3.4.2.1.2 Human evidence 

Annex I: 3.4.2.1.2.1. Evidence that a substance can lead to specific hypersensitivity will 
normally be based on human experience. In this context, hypersensitivity is normally seen 
as asthma, but other hypersensitivity reactions such as rhinitis/conjunctivitis and alveolitis 
are also considered. The condition will have the clinical character of an allergic reaction. 
However, immunological mechanisms do not have to be demonstrated.  

Annex I: 3.4.2.1.2.2.  When considering the human evidence, it is necessary for a decision 
on classification to take into account, in addition to the evidence from the cases: 

(a) the size of the population exposed; 

(b) the extent of exposure. 

[…] 

Annex I: 3.4.2.1.2.3.  The evidence referred to above could be: 

(a) clinical history and data from appropriate lung function tests related to exposure to the 
substance, confirmed by other supportive evidence which may include: 

(i) in vivo immunological test (e.g. skin prick test) 

(ii) in vitro immunological test (e.g. serological analysis); 

(iii) studies that indicate other specific hypersensitivity reactions where 
immunological mechanisms of action have not been proven, e.g. repeated low-level 
irritation, pharmacologically mediated effects; 

(iv) a chemical structure related to substances known to cause respiratory 
hypersensitivity; 

(b) data from one or more positive bronchial challenge tests with the substance conducted 
according to accepted guidelines for the determination of a specific hypersensitivity reaction. 

Annex I: 3.4.2.1.2.4. Clinical history shall include both medical and occupational history to 
determine a relationship between exposure to a specific substance and development of 
respiratory hypersensitivity. Relevant information includes aggravating factors both in the 
home and workplace, the onset and progress of the disease, family history and medical 
history of the patient in question. The medical history shall also include a note of other 
allergic or airway disorders from childhood, and smoking history. 

 
 
 
 
 
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Annex I: 3.4.2.1.2.5. The results of positive bronchial challenge tests are considered to 
provide sufficient evidence for classification on their own. It is however recognised that in 
practice many of the examinations listed above will have already been carried out. 

3.4.2.1.3.2.  Non human data  

Annex I: 3.4.2.1.3. Animal studies 

Annex I: 3.4.2.1.3.1. Data from appropriate animal studies (*) which may be indicative of 
the potential of a substance to cause sensitisation by inhalation in humans (**) may include: 

(a) measurements of Immunoglobulin E (IgE) and other specific immunological parameters in 
mice; 

(b) specific pulmonary responses in guinea pigs. 

(*) At present, recognised and validated animal models for the testing of respiratory 
hypersensitivity are not available. Under certain circumstances, data from animal studies may 
provide valuable information in a weight of evidence assessment. 

(**) The mechanisms by which substances induce symptoms of asthma are not yet fully 
known. For preventative measures, these substances are considered respiratory sensitisers. 
However, if on the basis of the evidence, it can be demonstrated that these substances 
induce symptoms of asthma by irritation only in people with bronchial hyper reactivity, they 
should not be considered respiratory sensitisers.  

No formally recognised and validated animal tests currently exist for respiratory sensitisation. 
However data from some animal studies may be indicative of the potential of a substance to 
cause respiratory sensitisation in humans (CLP Annex I, 3.4.2.1.3) and may provide supportive 
evidence in case human evidence is available (see also Section 3.4.2.1.2 above). This 
information may also be combined with information on structural alerts for respiratory 
sensitisation (see the Guidance on IR&CSA, Section R.7.3.9.1) and information on the skin 
sensitising properties of a substance and should be used in a weight of evidence assessment.  

Information on sensitizing activity of substances, such as that identified using contact sensitivity 
studies, may also be taken into consideration in a weight of evidence assessment. Based on a 
assessment including mostly non-standrad versions of the LLNA, using BALB/c instead of 
CBA/Ca strains mice, substance for which there were convincing negative data in the LLNA (at 
an appropriate test concentration and with the exception of large substances such as enzymes) 
most probably lacks the potential for respiratory allergy (Dearman R.J., 2013). It should be 
noted that negative data on skin sensitisation cannot be used to negate data fulfilling the 
classification criteria for respiratory sensitisation.    

3.4.2.1.4.  Decision on classification  

According to CLP Annex I, Section 3.4.2.1.1.4 substances fulfilling the criteria for respiratory 
sensitisation will be classified as such in Category 1 (and in Sub-category 1A or 1B when 
sufficient data are available), 

3.4.2.1.5. 

Setting of specific concentration limits 

Respiratory sensitisers cannot be identified reliably on the basis of animal tests yet, since no 
recognised validated test exists to determine sensitising potential and potency by inhalation. 
Therefore specific concentration limits (SCLs) cannot be set on the basis of animal data alone. 
Moreover, there is no concept available to set SCLs on the basis of human data for respiratory 
sensitisers. 

 
 
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3.4.2.1.6.  Decision logic for classification of substances 

It is strongly recommended that the person responsible for classification study the criteria for 
classification before and during use of the decision logic. 

Are there data and/or information to evaluate 
respiratory sensitisation? 

No 

Classification not 
possible 

Yes 

a. Is there evidence in humans that the substance can 
lead to specific respiratory hypersensitivity, and/or 

b.  Are  there  positive  results  from  an  appropriate 
animal test, and/or  

c.  Is  there  other  sufficient  evidence,  including  read-
across,  that  the  substance  can  lead  to  specific 
respiratory hypersensitivity? 

Yes 

Are data sufficient for sub-categorisation? 

Yes 

No 

Not classified 

Category 1 

No 

Danger 

Based on weight of evidence, does the substance 
show a high frequency of occurrence of respiratory 
sensitisation in humans; or a probability of 
occurrence of a high respiratory sensitisation rate in 
humans based on animal or other tests? Severity of 
reaction may also be considered. 

Yes 

No 

Based on weight of evidence, does the substance 
show a low to moderate frequency of occurrence of 
respiratory sensitisation in humans; or a probability 
of occurrence of a low to moderate respiratory 
sensitisation rate in humans based on animal or other 
tests. Severity of reaction may also be considered. 

Yes 

Sub-category 1A 

Danger 

Sub-category 1B 

Danger 

 
 
 
 
 
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3.4.2.2.  Classification of substances for skin sensitisation 

3.4.2.2.1. 

Identification of hazard information  

With respect to identification of relevant information for skin sensitisation see the Guidance on 
IR&CSA, Section R.7.3.4. 

3.4.2.2.1.1.  Identification of human data  

Relevant information with respect to skin sensitisation may be available from case reports, 
epidemiological studies, medical surveillance and reporting schemes based on human patch 
testing. For more details see the Guidance on IR&CSA, Section R.7.3.4.2. 

3.4.2.2.1.2.  Identification of non human data  

At present no formally validated non-testing systems exist to predict skin sensitising potential. 
However data such as structural alert data or data to show that the chemical structure of a 
molecule is similar to that of known sensitisers (e.g. QSARs or expert systems) may form part 
of the weight of evidence for classification (see also Guidance on IR&CSA, Section R.7.3.4). 

The subject of in vitro testing for skin sensitisation has also been dealt with in the Guidance on 
IR&CSA, Section R.7.3.4. Validated in vitro/in chemico methods exist with the aim to identify a 
sensitising potential of a chemical. These include OECD TG442C (Peptide/protein binding), 
TG442D (keratinocyte response) and TG 442E (monocytic/dendritic cell response). The in 
vitro/in chemico tests are not regarded as stand alone tests and the result from such a test 
should be used together with other data in an overall WoE assessment. Further, at present 
there is no agreed strategy on how to use in vitro/in chemico methods for direct estimation of 
sensitising potency, but data from such tests can be used in a WoE assessment together with 
other data in order to assess skin sensitisation potency. See also the Guidance on IR&CSA, 
especially Section R.7.3.4.1. 

Information on the current developments of in vitro tests and methodology can be found on the 
ECVAM website (http://ihcp.jrc.ec.europa.eu/our_labs/eurl-ecvam).  

There are three standard animal test methods used to evaluate skin sensitisation for 
substances: the mouse local lymph node assay (LLNA), the guinea pig maximisation test 
(GPMT) and the Buehler assay. They are further described in the Guidance on IR&CSA, Section 
R.7.3.4, and in the context of classification in Section 3.4.3.2 of this Guidance. 

3.4.2.2.2. 

Classification criteria for substances  

Annex I: 3.4.2.2. Skin Sensitisers 

Annex I: 3.4.2.2.1. Hazard categories 

Annex I: 3.4.2.2.1.1. Skin sensitisers shall be classified in Category 1 where data are not 
sufficient for sub-categorisation. 

Annex I: 3.4.2.2.1.2. Where data are sufficient a refined evaluation according to section 
3.4.2.2.1.3 allows the allocation of skin sensitisers into sub-category 1A, strong sensitisers, or 
sub-category 1B for other skin sensitisers. 

Annex I: 3.4.2.2.1.3. Effects seen in either humans or animals will normally justify 
classification in a weight of evidence approach for skin sensitisers as described in section 
3.4.2.2.2. Substances may be allocated to one of the two sub-categories 1A or 1B using a 
weight of evidence approach in accordance with the criteria given in Table 3.4.2 and on the 
basis of reliable and good quality evidence from human cases or epidemiological studies 
and/or observations from appropriate studies in experimental animals according to the 
guidance values provided in sections 3.4.2.2.2.1 and 3.4.2.2.3.2 for sub-category 1A and in 
sections 3.4.2.2.2.2 and 3.4.2.2.3.3 for sub-category 1B. 

 
 
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Annex I: 3.4.2.2.1.4. Substances shall be classified as skin sensitisers in accordance with 
the criteria in Table 3.4.2: 

Hazard category and sub-categories for skin sensitisers 

Table 3.4.2 

Category 

Criteria 

Category 1 

Sub-category 1A: 

Sub-category 1B: 

Substances shall be classified as skin sensitisers (Category 1) 
where data are not sufficient for sub-categorisation in accordance 
with the following criteria: 

(a) if there is evidence in humans that the substance can lead to 

sensitisation by skin contact in a substantial number of 
persons; or 

(b) if there are positive results from an appropriate animal test 

(see specific criteria in paragraph 3.4.2.2.4.1). 

Substances showing a high frequency of occurrence in humans 
and/or a high potency in animals can be presumed to have the 
potential to produce significant sensitisation in humans. Severity 
of reaction may also be considered. 

Substances showing a low to moderate frequency of occurrence in 
humans and/or a low to moderate potency in animals can be 
presumed to have the potential to produce sensitisation in 
humans. Severity of reaction may also be considered. 

Classification into sub-categories is required when data are sufficient. When Category 1A cannot 
be excluded, Category 1 should be applied instead of Category 1B. This is particularly important 
if only data are available from certain tests showing a high response after exposure to a high 
concentration but where lower concentrations, which could show the presence of effects at 
lower doses, have not been tested (in line with some test protocols where a maximised dose 
should be used).   

When considering human evidence, it is necessary to take into account the size of the 
population exposed and the extent of exposure and frequency, and thus the consideration is on 
a case by case basis. Human data should be incorporated with animal data to decide on `the 
sub-categorisation.   

Diagnostic patch testing is the gold standard in diagnosing contact allergy in dermatitis patients 
(see e.g. Johansen et al, 2015). Patch test concentrations and substances must be suitable for 
the purpose, not causing false negatives, false positives, irritant reactions or inducing contact 
allergy (skin sensitisation). The vehicle is important for the outcome of a diagnostic patch test, 
the most commonly used being petrolatum. Patch test concentrations are not based on 
concentrations used in products. The used concentrations may be too low and lead to a false 
negative reaction. Data from the testing of unselected, consecutive dermatitis patients is more 
standardised than testing which is undertaken on a specific patient group (e.g. those with facial 
eczema) or worker group (e.g. individuals with a particular type of exposure) and often involves 
patch testing with materials beyond those normally used, i.e. ‘the standard series’, as for 
example the European baseline series. To detect and confirm new sensitisers, suitable patch 
test concentrations have to be set, which is a laborious task. For many substances, 
standardised commercial patch tests are lacking. 

 
 
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For a newly identified skin sensitiser, which might also be a substance newly introduced onto 
the market, or a substance not included in the baseline diagnostic patch test series, the high 
severity of responses might be used as an indication that classification as Category 1A is 
appropriate.  For example, where the substance has caused: 

•  Hospitalisation due to acute skin reaction 

•  Chronic dermatitis (lasting > 6 months) 

•  Generalised (systemic/whole body) dermatitis 

It should be noted that the severity/strength of diagnostic patch test reactions normally cannot 
be used for this purpose. 

It should be noted that in some cases a substance may autooxidise in contact with air or 
decompose to a more hazardous form. This may warrant classification of the parent substance 
even though it in itself is not or is less hazardous. A case-by-case evaluation should be done 
considering available hazard information on humans or animals and/or the rate and extent of 
autoxidation or decomposition. 

3.4.2.2.3. 

Evaluation of hazard information 

3.4.2.2.3.1.  Human data  

The classification of a substance can be based on human evidence, such as positive data from 
patch testing, epidemiological studies showing allergic contact dermatitis caused by the 
substance, positive data from experimental studies in man and/or well documented episodes of 
allergic contact dermatitis, using a weight of evidence approach (see Section 3.4.2.2.3.7 of this 
Guidance for details).  

Criteria for sub-categorisation are listed in CLP Annex I, 3.4.2.2.2.1 and 3.4.2.2.2.2: 

Annex I: 3.4.2.2.2.1. Human evidence for sub-category 1A can include: 

(a) 

positive responses at ≤ 500 μg/cm2 (HRIPT, HMT – induction threshold); 

diagnostic patch test data where there is a relatively high and substantial incidence of 

(b) 
reactions in a defined population in relation to relatively low exposure; 

other epidemiological evidence where there is a relatively high and substantial 

(c) 
incidence of allergic contact dermatitis in relation to relatively low exposure. 

Annex I: 3.4.2.2.2.2. Human evidence for sub-category 1B can include: 

(a) 

positive responses at > 500 μg/cm2 (HRIPT, HMT – induction threshold); 

diagnostic patch test data where there is a relatively low but substantial incidence of 

(b) 
reactions in a defined population in relation to relatively high exposure; 

other epidemiological evidence where there is a relatively low but substantial 

(c) 
incidence of allergic contact dermatitis in relation to relatively high exposure. 

HRIPT: Human Repeat Insult Patch Test; HMT: Human Maximisation Test 

CLP Article 7 (3) states ‘Tests on humans shall not be performed for the purposes of this 
Regulation. However, data obtained from other sources, such as clinical studies, can be used for 
the purposes of this Regulation.’  Thus human induction studies such as HRIPT or HMT must not 
be performed, although historical data may be used as weight of evidence for the sub-
categorisation. To provide further guidance on the types of human data that may be considered 
as data from other sources, please refer to the following table: 

 
 
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Table 3.1  Types of Human Studies 

Type 

Subjects 

Endpoint studied  Comments 

Human Repeated 
Insult Patch Test 
(HRIPT) & Human 
Maximization Test 
(HMT) 

Healthy volunteers 

Induction of 
sensitisation 

Diagnostic patch test 
from individual clinics 
or collated clinic data 

Eczema patients 
attending 
dermatology clinics 

Dose response study 
(e.g. patch test serial 
dilution; repeated open 
application test) 

Sensitised 
individuals (usually 
from diagnostic 
patch tests) 

Elicitation (as an 
indicator of 
previous 
sensitisation) 

Elicitation 

Epidemiology study 

Elicitation 

Eczema patients, 
selected 
occupational 
groups, other 
selected groups, or 
general population 

This is not a clinical study and is 
only of historical relevance.  New 
studies for this regulation are not 
permitted. 

Primary source of clinical 
information on the occurrence of 
skin sensitisation 

Not yet a standardised protocol, 
but provides an indication of the 
degree of sensitivity and of safe 
limits of exposure. Mainly used as 
confirmatory tests and in 
research. 

Large general population studies 
are scarce; focused studies in 
selected populations are more 
common and provide insights on 
frequency of sensitisation 
compared to exposure 

The purpose of the material that follows is the provision of guidance concerning the evaluation 
of human data, particularly with respect to balancing considerations of exposure against the 
clinical evidence regarding the frequency of skin sensitisation.  The concept of ‘guidance’ should 
be applied generally to all of the numeric criteria – they represent indicators derived from 
expert opinion and are not to be taken as proven absolute values. Application of this guidance 
should permit sub-categorisation where the human data on exposure and sensitisation is clear.  

Table 3.2  Relatively high or low frequency of occurrence of skin sensitisation* 

Human diagnostic patch test data 

High frequency 

Low/moderate 
frequency 

General population studies 

≥ 0.2 % 

< 0.2 % 

Dermatitis patients (unselected, consecutive) 

≥ 1.0 % 

< 1.0 % 

Selected dermatitis patients (aimed testing, usually special test 
series) 

≥ 2.0 % 

< 2.0 % 

Work place studies: 

1: all or randomly selected workers 

2: selected workers with known exposure or dermatitis 

≥ 0.4 % 

≥ 1.0 % 

< 0.4 % 

< 1.0 % 

Number of published cases  

≥ 100 cases 

< 100 cases 

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The figure of 0.2% for the general population is intended to reflect that the frequency of contact 
allergy in dermatitis patients is approximately 5 (range 2-10) times higher than in the general 
population (Mirshahpanah and Maibach, 2007).  

The figure of 1% for consecutive (i.e. unselected) dermatitis patients is based on the generally 
agreed consideration that a contact allergy frequency of ≥ 1% in such patients is of high 
concern. 

The figure of 0.4% for unselected workers in a workplace is derived from the use in REACH of a 
2 times higher assessment factor for the general population than for workers.   

It is important to note that the data from the testing of unselected, consecutive dermatitis 
patients is more standardised than testing which is undertaken on a specific patient group (e.g. 
those with facial eczema) or worker group (e.g. individuals with a particular type of exposure). 
Such clinical studies may be conducted on patients selected according to a particular type of 
eczema or based on their likelihood of occupational exposure and often involves patch testing 
with materials beyond those normally used i.e. ‘the standard series’ (Andersen et al, 2011). It is 
important to consider also that there may be variations in positive patch test frequency related 
to age, gender or region.   

Table 3.3  Relatively high or low exposure * 

Exposure data 

Concentration / dose 

Relatively low exposure 
(weighting) 

Relatively high exposure 
(weighting) 

< 1.0% 

< 500µg/cm2 

(score 0) 

≥ 1.0% 

≥ 500µg/cm2 

(score 2) 

Repeated exposure 

< once/daily (score 1) 

≥ once/daily (score 2) 

Number  of  exposures  (irrespective  of 
concentration of sensitizer) 

<100 exposures (score 0) 

≥100 exposures (score 2) 

* To achieve the exposure index (see text below) a response in each row is necessary. 

The scores in Table 3.3 represent weightings whose purpose is to enable an exposure index to 
be derived which best reflects our understanding of the relative importance of dose versus 
frequency of exposure.  An additive exposure index of 1-4 equates to low exposure, whereas 5-
6 reflects high exposure.  

Careful consideration has to be given regarding the release (migration) of a sensitising 
substance from a solid object, and not the concentration.  Ideally, skin exposure is best 
expressed in dose per unit area, but it is recognised that this data is often not available, hence 
concentration may be used as a surrogate indicator of exposure. 

Table 3.4  Sub-categorisation decision table 

Relatively low frequency of 
occurrence of skin 
sensitisation 

Relatively high frequency of 
occurrence of skin 
sensitisation 

Relatively high exposure 

Sub-category 1B 

Category 1 

(score 5-6) 

or case by case evaluation 

Relatively low exposure 

Category 1 

Sub-category 1A 

(score 1-4) 

or case by case evaluation 

 
 
 
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3.4.2.2.3.2.  Non human data  

Annex  I:  3.4.2.2.3.2.  Animal  test  results  for  sub-category  1A  can  include  data  with  values 
indicated in Table 3.4.3 

Table 3.4.3 

Animal test results for sub-category 1A 

Assay 

Criteria 

Local lymph node assay 

EC3 value ≤ 2 % 

Guinea pig maximisation test 

≥ 30 % responding at ≤ 0,1 % intradermal induction 
dose or 

≥ 60 % responding at > 0,1 % to ≤ 1 % intradermal 
induction dose 

Buehler assay 

≥ 15 % responding at ≤ 0,2 % topical induction dose or 

≥ 60 % responding at > 0,2 % to ≤ 20 % topical 
induction dose 

Annex  I:  3.4.2.2.3.3.  Animal  test  results  for  sub-category  1B  can  include  data  with  values 
indicated in Table 3.4.4 below: 

Table 3.4.4 

Animal test results for sub-category 1B 

Assay 

Criteria 

Local lymph node assay 

EC3 value > 2 % 

Guinea pig maximisation test 

≥ 30 % to < 60 % responding at > 0,1 % to ≤ 1 % 
intradermal induction dose or 

Buehler assay 

≥ 30 % responding at > 1 % intradermal induction dose 

≥ 15 % to < 60 % responding at > 0,2 % to ≤ 20 % 
topical induction dose or 

≥ 15 % responding at > 20 % topical induction dose 

The CLP Regulation allows classification of skin sensitisers in one hazard category, Category 1, 
which comprises two sub-categories, 1A and 1B.  

Annex I: 3.4.2.2.1.1: Skin sensitisers shall be classified in Category 1 where data are not 
sufficient for sub-categorisation. 

Classification into sub-categories is required when data are sufficient (CLP Annex I 3.4.2.2.1.1). 
When Category 1A cannot be excluded, Category 1 should be applied instead of Category 1B. 
This is particularly important if only data are available from the guinea pig tests or from the 
rLLNA showing a high response after exposure to a high concentration but where lower 
concentrations which could show the presence of such effects at lower doses are absent or in 
the absence of adequate dose-response information.  Unless there is sufficient evidence to place 
such substances in sub category 1A or 1B, classification in category 1 should be the default 

 
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position. In other words, although the criteria in the Table 3.4.4 for classification to subcategory 
1B are fulfilled, the classification for subcategory 1A may not be excluded and therefore the 
substance should be classified as a Category 1 skin sensitiser (see also examples 6 & 7). The 
REACH information requirements (as amended by Commission Regulation (EU) 2016/1688) for 
skin sensitisation includes a requirement for a potency assessment, i.e. an assessment of 
whether a substance "can be presumed to have the potential to produce significant sensitisation 
in humans (Cat. 1A)". The only exception to this is where there is existing animal information 
available (i.e. a study which was initiated or conducted before 11 October 2016) that does not 
allow an assessment of potency and thus only a conclusion in category 1 is possible. In such 
cases no further testing to assess potency is required (further details can be found in the 
Guidance on IR&CSA, Section R.7.3). Not all substances which need to be classified are 
registered under REACH, and thus for these substances the data base can be weaker and not 
sufficient to conclude on potency and therefore subcategorization is not possible and 
classification in category 1 is warranted. 

Since it is possible to refine the evaluation of skin sensitisers on the basis of the potency of the 
sensitising effect, this guidance advises how to evaluate the potency on the basis of the 
recommended test methods. High potency is determined according to the results from the 
animal studies as given in CLP Annex I, Table 3.4.3 and low to moderate potency is determined 
according to the results from the animal studies as given in CLP Annex I, Table 3.4.4. The 
potency considerations may be used as a basis for setting specific concentration limits (see 
Section 3.4.2.2.5 of this Guidance). The three currently recognised and officially accepted 
animal test methods for skin sensitisation defined by OECD Test Guidelines are the Mouse Local 
Lymph Node Assay (LLNA) OECD TG 429 and its variations OECD TG 442A and 442B, Guinea 
Pig Maximisation Test by Magnusson & Kligman (GPMT) and the Buehler assay in the guinea pig 
OECD TG 406. The mouse and guinea pig methods differ fundamentally with respect to the 
endpoints used; whereas the mouse LLNA measures the responses provoked during the 
induction of sensitisation, the two guinea pig tests measure challenge induced elicitation 
reactions in previously sensitised animals. For new testing of substances the LLNA is now the 
animal method of first choice, in case in vitro/in chemico assays are not considered relevant. In 
the exceptional circumstance that the LLNA is not appropriate, one of the alternative tests may 
be used (Buehler or GPMT), but justification shall be provided (see the Guidance on IR&CSA, 
Section R.7.3.5.1).  

Test results from the LLNA, GPMT and the Buehler assay can be used directly for classification. 
They may also be used for potency evaluation. 

A sensitising potential of a substance is identified if a significant effect has been obtained in an 
acceptable in vivo test. A significant skin sensitising effect in each of the three recognised 
animal tests is defined as follows: 

Table 3.5  Definition of significant skin sensitising effect 

Test 

Result 

Mouse local lymph node assay (LLNA) (OECD TG 429)* 

Stimulation Index ≥ 3 

LLNA: DA (OECD TG 442A),* 

Stimulation Index ≥ 1.8 

LLNA: BrdU-ELISA (OECD TG 442B)* 

Stimulation Index ≥ 1.6 

Guinea pig maximisation test (GPMT) (OECD 406) 

Buehler assay (OECD 406) 

*See further details in the test guidelines 

Redness (Score ≥ 1) in ≥ 30% of the 
test animals 

Redness (Score ≥ 1) in ≥ 15% of the 
test animals 

 
 
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A substance may be classified as a skin sensitiser on the basis of a positive test result in one of 
the above described animal tests. A positive result obtained by another test method not 
officially recognised may also justify classification as a skin sensitiser, but can normally not 
overrule a negative result obtained in one of the three recognised, animal tests described 
above. A new animal study should not be conducted in an attempt to negate a clearly positive 
response in a test method not officially recognised particularly where there is other supporting 
evidence that the substance is a skin sensitiser. 

3.4.2.2.3.2.1.  Mouse Local Lymph Node Assay 

The LLNA is used both for determination of skin sensitising potential (hazard identification) and 
for determination of relative skin sensitisation potency (hazard characterisation). In both 
instances the metric is cellular proliferation induced in draining lymph nodes following topical 
exposure to a chemical.  Lymph node cell proliferation is causally and quantitatively correlated 
with the acquisition of skin sensitisation (Basketter et al. 2002a, 2002b). A correlation has been 
demonstrated between the concentration of a chemical required for the acquisition of skin 
sensitisation in humans according to historical predictive data and skin sensitisation potency as 
measured in the mouse LLNA (Schneider and Akkan 2004, Basketter et al. 2005b). Potency is 
measured as a function of the derived EC3-values. The EC3-value is the amount of test 
chemical (% concentration, molar value or dose per unit area) required to elicit a stimulation 
index of 3 in the standard LLNA (Kimber et al. 2003). An inverse relationship exists between 
EC3-value and potency meaning that extremely potent sensitisers have extremely low EC3-
values. The relevance of potency derives from an appreciation that skin sensitisers vary by up 
to four or five orders of magnitude with respect to the minimum concentration required inducing 
skin sensitisation. Potency is graded on the basis of these minimum concentrations each grade 
reflecting a concentration range of approximately one order of magnitude. However, it should 
be noted that if the dose interval for LLNA is too low so that all the stimulation indexes are 
below 3, it is not possible to know whether the higher doses would have generated a stimulation 
index above 3.  Also, if only high doses would be used in an LLNA test, the EC3 value may be 
associated with great uncertainty since the extrapolation is needed to low doses when the shape 
of the dose-response curve is not known. It is also known that the choice of vehicle may 
influence the EC3 value.  

Potency may be considered when setting specific concentration limits (see Section 3.4.2.2.5 of 
this Guidance). 

Different variants of the LLNA exist, namely the reduced LLNA (rLLNA) described as an option in 
OECD TG 429, the LLNA: DA (OECD TG 442A), and the LLNA: BrdU-ELISA (OECD TG 442B). The 
rLLNA uses fewer animals than the classical LLNA and should only be used in those 
circumstances where dose-response information is not required (e.g. to confirm a negative 
prediction of skin sensitising potential) and thus should not be used for sub-categorisation of 
skin-sensitisers. The last two variants avoid the use of DNA radiolabelling agent and provide 
quantitative data suitable for dose-response assessment. However, the criteria for determining 
the positive response is different from that of the traditional LLNA (OECD TG 429).  Full details 
are given in the corresponding OECD Test Guidelines. There is no guidance for sub-
categorisation. 

3.4.2.2.3.3.  Guinea Pig Maximisation Test (GPMT, OECD TG 406) 

This test has been used for over 40 years, to detect the sensitising potential of chemicals 
through a test system maximizing the sensitivity by both intradermal and epidermal induction 
and use of an adjuvant (Freund’s Complete Adjuvant). The intradermal induction is made by 
injection. Consequently the test is not suited for substances which cannot be made up into a 
liquid formulation.  

The GPMT was originally designed to maximise the ability to identify a sensitisation hazard, 
rather than to determine skin sensitisation potency. Yet, when only a GPMT test result is 
available, potency categorisation may be  possible on the basis of the concentration of test 

 
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material used for intradermal induction and the percentage of guinea pigs sensitised. However, 
it should be recognised that there is often a degree of uncertainty associated with the derivation 
of allergenic potencies from the GPMT. 

It should be noted that the guinea pig tests should be conducted at highest induction dose 
causing mild (Buehler Assay) or mild-to-moderate (GPMT) skin irritation. As a consequence, it is 
unlikely that substances (except strong irritants) would be tested at low concentration given in 
Table 3.4.4 triggering classification as a skin sensitiser in sub category 1A. 

Potency may be considered when setting specific concentration limits (see Section 3.4.2.2.5 of 
this Guidance). 

3.4.2.2.3.4.  Buehler assay (OECD TG 406) 

This test has been in use for the last 40 years, although still a sensitive test to detect skin 
sensitisers using epidermal occluded exposure. The skin barrier of the test species (guinea pig) 
is kept intact in this assay. Potency can be categorised using the results of the Buehler assay on 
the basis of the number of animals sensitised and the concentration of the test material used for 
the epidermal induction. However, it should be recognised that there is often a degree of 
uncertainty associated with the derivation of allergenic potencies from the Buehler assay.  

Potency may be considered when setting specific concentration limits (see Section 3.4.2.2.5 of 
this Guidance). 

It should be noted that the guinea pig tests should be conducted at highest induction dose 
causing mild (Buehler Assay) or mild-to-moderate (GPMT) skin irritation. As a consequence, it is 
unlikely that substances (except strong irritants) would be tested at the low concentration given 
in Table 3.4.4 triggering classification as a skin sensitiser in sub category 1A. 

3.4.2.2.3.5.  Non-guideline skin sensitisation tests 

In vivo test methods which do not comply with recognised guidelines (see Article 8(3) of CLP) 
are strongly discouraged for the identification of skin sensitisers or assessment of skin 
sensitising potency. The results of such tests may provide supportive evidence when the tests 
are scientifically well justified and carefully evaluated. If doubts exist about the validity and the 
interpretation of the results, the evaluation needs to be done by using a weight-of-evidence 
approach as described below (see Section 3.4.2.2.3.7 of this Guidance). 

3.4.2.2.3.6.  Animal test methods conducted for purposes other than sensitisation 

Occasionally signs of skin sensitisation occur in repeated dose tests. These tests are often 
dermal toxicity tests on rats. Clearly, if signs of erythema/oedema occur in animals after 
repeated application, the possibility of skin sensitisation should be considered, and ideally 
assessed in an appropriate study. 

3.4.2.2.3.7.  Weight of evidence 

Annex I: 3.4.2.2.4. Specific considerations 

3.4.2.2.4.1. For classification of a substance, evidence shall include any or all of the following 
using a weight of evidence approach: 

(a) 

(b) 

positive data from patch testing, normally obtained in more than one dermatology 
clinic; 

epidemiological studies showing allergic contact dermatitis caused by the substance. 
Situations in which a high proportion of those exposed exhibit characteristic 
symptoms are to be looked at with special concern, even if the number of cases is 
small; 

(c) 

positive data from appropriate animal studies 

 
 
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(d) 

(e) 

positive data from experimental studies in man (see section 1.3.2.4.7); 

well documented episodes of allergic contact dermatitis, normally obtained in more 
than one dermatology clinic; 

(f) 

severity of reaction may also be considered. 

Annex I: 3.4.2.2.4.2. Evidence from animal studies is usually much more reliable than 
evidence from human exposure. However, in cases where evidence is available from both 
sources, and there is conflict between the results, the quality and reliability of the evidence 
from both sources must be assessed in order to resolve the question of classification on a 
case-by-case basis. Normally, human data are not generated in controlled experiments with 
volunteers for the purpose of hazard classification but rather as part of risk assessment to 
confirm lack of effects seen in animal tests. Consequently, positive human data on skin 
sensitisation are usually derived from case-control or other, less defined studies. Evaluation of 
human data must therefore be carried out with caution as the frequency of cases reflect, in 
addition to the inherent properties of the substances, factors such as the exposure situation, 
bioavailability, individual predisposition and preventive measures taken. Negative human data 
should not normally be used to negate positive results from animal studies. For both animal 
and human data, consideration should be given to the impact of vehicle. 

Annex I: 3.4.2.2.4.3. If none of the abovementioned conditions are met, the substance need 
not be classified as a skin sensitiser. However, a combination of two or more indicators of skin 
sensitisation as listed below may alter the decision. This shall be considered on a case-by-case 
basis. 

(a)  

(b)  

(c)  

(d)  

(e)  

Isolated episodes of allergic contact dermatitis; 

epidemiological studies of limited power, e.g. where chance, bias or confounders have 
not been ruled out fully with reasonable confidence; 

data from animal tests, performed according to existing guidelines, which do not 
meet the criteria for a positive result described in section 3.4.2.2.3, but which are 
sufficiently close to the limit to be considered significant; 

positive data from non-standard methods; 

positive results from close structural analogues. 

Annex I: 3.4.2.2.4.4. Immunological contact urticaria 

Substances meeting the criteria for classification as respiratory sensitisers may in addition 
cause immunological contact urticaria. Consideration should be given to classifying these 
substances also as skin sensitisers. Substances which cause immunological contact urticaria 
without meeting the criteria for respiratory sensitisers should also be considered for 
classification as skin sensitisers. 

There is no recognised animal model available to identify substances which cause 
immunological contact urticaria. Therefore, classification will normally be based on human 
evidence which will be similar to that for skin sensitisation. 

Positive effects seen in either humans or animals for skin sensitisation will normally justify 
classification. Evidence from animal studies on skin sensitisation is usually more reliable than 
evidence from human exposure, although adequate reliable and representative human data are 
usually more relevant. In cases where evidence is available from both sources, and there is 
conflict between the results, the quality and reliability of the evidence from both sources must 
be assessed in order to decide on the classification on a case-by-case basis. Negative human 
data should not normally negate positive findings in animal studies (CLP Annex I, 3.4.2.2.4.2). 

 
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Since the data used in hazard or risk assessment should be relevant, reliable and sufficient for 
the regulatory purpose, it is necessary to base the assessment on the totality of available 
information, i.e. to apply Weight of Evidence (WoE) considerations. 

The WoE assessment can be based on the total of experimental data, as well as post-market 
surveys and/or occupational experience data.  

Non-testing data might be used to supplement and increase confidence in the available 
experimental data. In some cases, such data might be used to conclude on classification in line 
with the criteria in the absence of experimental data.  

WoE assessment can be divided into two stages: 

a.  Assessment of each single test result and, if needed, of other data. It may be helpful to 
apply criteria for reliability as defined by Klimisch et al (1997). These criteria include 
details on the recognition of the test method, reporting detail, method relevance, test 
parameters, etc. 

b.  Comparison of the weighed single test results. 

Available in vitro/in chemico tests cannot be considered as stand alone tests, but the results 
from such tests can be used together with other data in a weight of evidence assessment. There 
is currently no agreed strategy on how to use the results of these methods for potency 
assessment (see OECD TG442C-E and Guidance on IR&CSA, R.7.3.4.1) 

Good quality data on the substance itself have more weight than such data extrapolated from 
similar substances.  

3.4.2.2.4.  Decision on classification  

According to CLP Annex I, 3.4.2.2.1.4 substances fulfilling the criteria for skin sensitisation will 
be classified as such in Category 1 (or in Sub-category 1A or 1B when sufficient data are 
available). In addition substances classified for skin sensitisation can be allocated specific 
concentration limits as described in Section 3.4.2.2.5 of this Guidance. 

3.4.2.2.5. 

Setting of specific concentration limits 

SCLs for skin sensitisation can be set based on the results from animal testing as reported 
below. SCLs are set on the basis of testing of the substance and never on the basis of testing of 
a mixture containing the sensitising substance (see CLP Annex I, 3.4.3.1.1). The setting of SCL 
is based on potency; potency is already considered for the subcategorisation defining generic 
concentration limits. SCLs are generally applied for the most potent skin sensitisers classified in 
1A. 

The following schemes can be used for determination of potency categories for sensitisers.  The 
potency categories given in the 3 tables below are described in Basketter et al. (2005a). 

For the LLNA(OECD TG 429) 

Table 3.6  Skin Sensitisation Potency in the Mouse Local Lymph Node Assay 

EC3-value (% w/v) 

Potency 

Resulting sub-category (*) 

≤ 0.2 

> 0.2 - ≤ 2 

> 2 

Extreme 

Strong 

Moderate 

1A 

1A 

1B 

(*) based on Annex I Section 3.4.2.2.3.2. and Section 3.4.2.2.3.3. 

For the Guinea Pig Maximisation Test (OECD TG 406) 

 
 
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Table 3.7   Potency on basis of the Guinea Pig Maximisation Test 

Incidence sensitised 
guinea pigs (%) 

Potency 

Resulting sub-
category (*) 

Concentration for 
intradermal 
induction (% w/v) 

≤ 0.1 

≤ 0.1 

≥ 60 

Extreme 

>30 - <60 

Strong 

Strong 

>0.1 - ≤ 1.0 

≥60 

>0.1 - ≤ 1.0  

>30 - <60  

Moderate 

> 1.0  

≥ 30  

Moderate 

1A 

1A 

1A 

1B(**) 

1B(**) 

(*) based on CLP Annex I Section 3.4.2.2.3.2. and Section 3.4.2.2.3.3. 

(**) If the concentration used for intradermal induction or the incidence of sensitised guinea pigs is very 
high, care should be taken to exclude the possibility of the substance being a Cat 1A (a strong or an 
extreme) sensitiser. 

For the Buehler Assay, (OECD TG 406)  

Table 3.8  Potency on basis of the Buehler assay 

Concentration for topical 
induction (% w/v) 

Incidence 
sensitised guinea 
pigs (%) 

Potency 

Resulting sub-
category (*) 

≤ 0.2 

≤ 0.2 

≥ 60 

Extreme 

>15 - <60 

Strong 

>0.2 - ≤ 20 

≥ 60 

Strong 

1A 

1A 

1A 

>0.2 - ≤ 20 (**) 

>15 - <60  

Moderate 

1B (**) 

> 20 (**) 

≥ 15  

Moderate 

1B (**) 

(*) based on CLP Annex I Section 3.4.2.2.3.2. and Section 3.4.2.2.3.3. 

(**) If the concentration used for topical induction or the incidence of sensitised guinea pigs is very high, 
care should be taken to exclude the possibility of the substance being a Cat 1A (a strong or an extreme) 
sensitiser. 

The generic concentration limits (GCLs) for the classification of sensitisers in mixtures are given 
in CLP Annex I, Table 3.4.5 (see Section 3.4.3.3.1 of this Guidance). In some cases, the GCL 
may not be sufficiently protective and an SCL shall be set in accordance with CLP Article 10, 
which will better reflect the hazard of mixtures containing that skin sensitiser. 

SCLs shall be set when there is adequate and reliable scientific information available showing 
that the specific hazard is evident below the GCL for classification. As such the recommended 
SCL should normally be as given in Table 3.9. However, supported by reliable data the SCL 
could have some other value below the GCL. Reliable data could be human data from e.g. work 
place studies where the exposure is defined. 

It is more difficult to prove the absence of sensitising properties at certain concentration levels. 
Therefore an SCL above the GCL may only be set in exceptional circumstances, if scientific 
information is adequate, reliable and conclusive for that particular skin sensitiser. However 
there is currently no guidance on how to set an SCL above the GCL. 

 
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The concentration limits for skin sensitisers categorised according to their sensitisation potency 
in  Table 3.9 are based on the recommendations from an EU expert group on skin sensitisation 
(Basketter et al., 2005a). 

Table 3.9  Skin sensitising potency for substances and recommendations on concentration 
limits 

Potency 

Extreme 

Strong 

Moderate 

Concentration Limit (% w/v) 

0.001 (SCL) 

0.1 (GCL) 

1 (GCL) 

 
 
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3.4.2.2.6.  Decision logic for classification of substances 

It is strongly recommended that the person responsible for classification study the criteria for 
classification before and during use of the decision logic.  

“Are  there  data  and/or  information  to  evaluate  skin 
sensitisation?   

No 

Classification 
not possible 

Yes 

a. Is there evidence in humans that the substance can 
lead  to  sensitisation  by  skin  contact  in  a  substantial 
number of persons, or 

No 

b.  Are  there  positive  results  from  an  appropriate 
animal test or in vitro/in chemico test? 

Yes 

Are data sufficient for sub- categorisation? 

No 

Yes 

Based on weight of evidence, does the substance 
show a high frequency of skin sensitisation in humans 
and/or a high potency in animals? Severity of 
reaction may also be considered. 

Yes 

No 

Based on weight of evidence, does the substance 
show a low to moderate frequency of skin 
sensitisation in humans and/or a low to moderate 
potency in animals? Severity of reaction may also be 
considered. 

Yes 

Not classified 

Category 1 

Warning 

Sub-category 1A 

Warning 

Sub-category 1B 

Warning 

 
 
 
 
 
 
  
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3.4.3.  Classification of mixtures for respiratory or skin sensitisation  

3.4.3.1. 

Identification of hazard information for respiratory sensitisation 

The same principles apply as for substances (see Section 3.4.2.1.1 of this Guidance). 

3.4.3.2. 

Identification of hazard information for skin sensitisation 

For identification of the sensitisation potential of a mixture the following information may be 
available:  

a.  test results on one or more, preferably all of its potentially sensitising 

components; or  

b.  test results on the mixture itself; or 

c.  test results of a similar mixture.  

Test methods are outlined in Section 3.4.2.2.1 of this Guidance. However, these animal tests 
have been developed to identify sensitising substances and not mixtures. Therefore the results 
obtained on mixtures need to be evaluated with care. For a mixture the cut-off in the mouse 
LLNA should be seen as a threshold for identification of a sensitiser rather than as a threshold 
for sensitisation. A conclusion on the absence of sensitising potential of a mixture based on the 
negative outcome in a test must be taken with great caution. 

On the other hand test data on a mixture takes into account effects of possible interactions of 
its components. For instance, it is known that the presence of a vehicle may significantly 
influence the skin sensitising potency, by influencing the penetration of the sensitising 
component(s) through the skin, (Basketter et al. 2001, Dearman et al. 1996, Heylings et al. 
1996) or through other mechanisms involved in the acquisition of sensitisation (Cumberbatch et 
al. 1993; Dearman et al. 1996).  

Repeated exposure to mixtures, that are non-sensitising under standard LLNA exposure 
conditions, might induce skin sensitisation, if the sensitising component in the mixture has 
sufficient accumulation potential in the skin to reach the minimum concentration for a positive 
effect (De Jong et al. 2007). Uncertainty also exists about the effect of such a mixture after 
exposure on a larger skin area. Therefore additional information is important, if the outcome of 
sensitisation tests on mixtures contrasts with the classification based on the content of 
sensitising component(s). For example, the validity of a well conducted LLNA on a mixture with 
a negative outcome can scientifically be confirmed by spiking the test mixture with another 
sensitiser (positive control) at different concentrations, or by showing a dose response 
relationship. Such LLNA tests could have been designed to provide such information without use 
of extra animals. Additional animal testing for the purpose of classification and labelling shall be 
undertaken only where no other alternatives, which provide adequate reliability and quality of 
data, are possible (CLP Article 7(1)). 

Limitations apply to in chemico and in vitro methods (see the specific OECD test guidelines).  

3.4.3.3.  Classification criteria for mixtures 

When mixtures are classified as sensitizing based on the presence of a sensitizing substance at 
a concentration at or above the generic or specific concentration limit, no sub-categorisation is 
required. 

 
 
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3.4.3.3.1.  When data are available for all ingredients or only for some ingredients  

Annex I: 3.4.3.3.1. The mixture shall be classified as a respiratory or skin sensitiser when at 
least one ingredient has been classified as a respiratory or skin sensitiser and is present at or 
above the appropriate generic concentration limit as shown in Table 3.4.5 below for 
solid/liquid and gas respectively. 

Generic concentration limits of components of a mixture classified as either 
respiratory sensitisers or skin sensitisers that trigger classification of the mixture 

Table 3.4.5 

Concentration triggering classification of a mixture as: 

Component classified as: 

Respiratory sensitiser 

Skin sensitiser 

Category 1 

Category 1 

Solid/Liquid 

Gas 

All physical states 

≥ 1,0 % 

≥ 0,2 % 

≥ 0,1 % 

≥ 0,1 % 

≥ 1,0 % 

≥ 0,2 % 

Respiratory sensitiser 

Category 1 

Respiratory sensitiser 

Sub-category 1A 

Respiratory sensitiser 

Sub-category 1B  

Skin sensitiser 

Category 1 

Skin sensitiser 

Sub-category 1A 

Skin sensitiser 

Sub-category 1B 

≥ 1,0 % 

≥ 0,1% 

≥ 1,0 % 

All sensitising components of a mixture at or above their generic or specific concentration limit 
should be taken into consideration for the purpose of classification. Specific concentration limits 
(see Section 3.4.2.2.5 of this Guidance) will always take precedence over the generic 
concentration limits. 

The additivity concept is not applicable for respiratory or skin sensitisation, i.e. if one single 
classified substance is present in the mixture above the generic or specific concentration limit, 
the mixture must be classified for that hazard. If the mixture contains two substances each 
below the generic or specific concentration limits, the mixture will not be classified. 

 
 
 
 
 
 
 
 
 
 
 
 
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Annex I: 3.4.3.3.2. Some substances that are classified as sensitisers may elicit a response, 
when present in a mixture in quantities below the concentrations established in Table 3.4.5, 
in individuals who are already sensitised to the substance or mixture (see Note 1 to Table 
3.4.6). 

Concentration limits for elicitation of components of a mixture 

Table 3.4.6 

Concentration limits for elicitation 

Component classified as: 

Respiratory sensitiser 

Skin sensitiser 

Category 1 

Category 1 

Solid/Liquid 

Gas 

All physical states 

≥ 0,1 % 
(Note 1) 

≥ 0,1 % 
(Note 1) 

≥ 0,01 % 
(Note 1) 

≥ 0,01 % 
(Note 1) 

≥ 0,1 % 
(Note 1) 

≥ 0,1 % 
(Note 1) 

Respiratory sensitiser 

Category 1 

Respiratory sensitiser 

Sub-category 1A 

Respiratory sensitiser 

Sub-category 1B   

Skin sensitiser 

Category 1 

Skin sensitiser 

Sub-category 1A 

Skin sensitiser 

Sub-category 1B 

Note 1: 

≥ 0,1 % (Note 1) 

≥ 0,01 % (Note 1) 

≥ 0,1 % (Note 1) 

This concentration limit for elicitation is used for the application of the special labelling 
requirements section 2.8 of Annex II to protect already sensitised individuals. A SDS is 
required for the mixture containing a component at or above this concentration. For 
sensitising substances with specific concentration limit lower than 0,1 %, the concentration 
limit for elicitation should be set at one tenth of the specific concentration limit. 

Further details on the additional labelling provisions to protect already sensitised individuals are 
provided in Section 3.4.4.1 of this Guidance.  

 
 
 
 
 
 
 
 
 
 
 
 
 
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3.4.3.3.2.  When data are available for the complete mixture 

Annex I: 3.4.3.1.1. When reliable and good quality evidence from human experience or 
appropriate studies in experimental animals, as described in the criteria for substances, is 
available for the mixture, then the mixture can be classified by weight-of-evidence evaluation 
of these data. Care shall be exercised in evaluating data on mixtures, that the dose used does 
not render the results inconclusive. 

In case classification of a mixture is based on test results for the mixture as a whole, this data 
must be shown to be conclusive. Especially it should be taken into account that in the case of 
skin sensitisation current test methods are based on application of a maximised dose, which can 
only be obtained using a substance by itself and not diluted in a mixture. 

It is recognised that mixtures not showing sensitisation in a test, may still contain a low 
concentration of sensitising component. 

For specific guidance on the test methods and evaluation of the results see Section 3.4.3.2 of 
this Guidance and CLP Annex I, 3.4.3.1.1. 

3.4.3.3.3.  When data are not available for the complete mixture: Bridging Principles 

Annex I: 3.4.3.2.1. Where the mixture itself has not been tested to determine its sensitising 
properties, but there are sufficient data on the individual ingredients and similar tested 
mixtures to adequately characterise the hazards of the mixture, these data shall be used in 
accordance with the bridging rules out in section 1.1.3. 

In order to apply bridging principles, there needs to be sufficient data on similar tested mixtures 
as well as the ingredients of the mixture. 

The same limitations apply for the use of existing test results of similar tested mixtures 
generated with current test methods as those described for any mixture in sections 3.4.3.2. 
Care must be exercised in evaluating data on mixtures, that the dose used does not render the 
results inconclusive. 

Note that the following bridging principles are not applicable to this hazard class: 

• 

• 

concentration of highly hazardous mixtures 

interpolation within one hazard category 

(see CLP Annex 1, 1.1.3.3 and 1.1.3.4). 

When the available identified information is inappropriate for the application of the bridging 
principles then the mixture should be classified using the method described in Section 3.4.3.3.3 
of this Guidance. 

3.4.3.4.  Decision logic for classification of mixtures 

It is strongly recommended that the person responsible for classification study the criteria for 
classification before and during use of the decision logic.  

 
 
 
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3.4.3.4.1.  Decision logic for classification of mixtures for respiratory sensitisation 

Does the mixture as a whole or its ingredients have 
respiratory sensitisation data? 

No 

Classification not 
possible 

Does the mixture as a whole have respiratory sensitisation data? 

Yes 

No 

a. Is there evidence in humans that the mixture 
can lead to specific respiratory hypersensitivity, 
and/or 

Yes 

Yes 

Category 1 (*) 

b. Are there positive results from an appropriate 
animal test?  

Danger 

Can bridging principles be 
applied? 

Yes 

No 

Classify in 
appropriate 
category 

No 

Care shall be exercised in evaluating data on 
mixtures, that the dose used does not render 
the results inconclusive.  

No 

Not classified 

Is this the case? See Section 3.4.2.1.3 of this 
Guidance. 

Yes 

Does the mixture contain one or more ingredients classified as 
a respiratory sensitiser at: 

Category 1 

a. ≥ 0.1% w/w (solid/liquid)?, b. ≥ 1.0% w/w (solid/liquid)?;  

or 

c. ≥ 0.1% v/v (gas)?, d. ≥ 0.2% v/v (gas)?; 

or  

above a SCL set for the ingredient(s)? 

No 

Not classified 

Yes 

Danger 

(*) can be sub-categorised into 1A or 1B according to decision logic in Section 3.4.2.1.6 of this Guidance.

 
 
 
 
 
 
  
  
 
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3.4.3.4.2 

Decision logic for classification of mixtures for skin sensitisation 

Does the mixture as a whole or its ingredients have skin 
sensitisation data? 

No 

Classification 
not possible 

Yes 

Does the mixture as a whole have skin sensitisation data? 

No 

Yes 

Category 1 (*) 

a. Is there evidence in humans that the mixture 
can lead to sensitisation by skin contact in a 
substantial number or persons, or 

Yes 

b. Are there positive results from an appropriate 
animal test?  

Warning 

No 

Can bridging principles be 
applied? 

Yes 

No 

Classify in 
appropriate 
category 

Care shall be exercised in evaluating data on 
mixtures, that the dose used does not render 
the results inconclusive. 

No 

Not classified 

Is this the case? See Section 3.4.3.2 and 
3.4.3.3.2 of this Guidance. 

Yes 

Category 1 

Does the mixture contain one or more ingredients classified as 
a skin sensitiser at: 

a. ≥ 0.1%?, 

b. ≥ 1.0%? 

Yes 

or above a SCL set for the ingredient(s)? 

Warning 

No 

Not classified 

(*) can be sub-categorised into 1A or 1B according to decision logic in Section 3.4.2.2.6 of this Guidance. 

 
 
 
  
  
 
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3.4.4.  Hazard communication for respiratory or skin sensitisation 

3.4.4.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

Annex I: 3.4.4.1. Label elements shall be used for substances or mixtures meeting the criteria 
for classification in this hazard class in accordance with Table 3.4.7 

Table 3.4.7 

Respiratory or skin sensitisation label elements 

Respiratory sensitisation 

Skin sensitisation 

Classification 

Category 1 and 

Category 1 and 

sub-categories 1A and 1B 

sub-categories 1A and 1B 

GHS Pictograms 

Signal Word 

Danger 

Warning 

Hazard Statement 

H334: May cause allergy or 
asthma symptoms or breathing 
difficulties if inhaled 

H317: May cause an 
allergic skin reaction 

Precautionary Statement 
Prevention 

Precautionary Statement 
Prevention 

P261 

P285 

P261 

P284 

Precautionary Statement 
Response 

P304 + P341 

P342 + P311 

Precautionary Statement 
Response 

P304 + P340 

P342 + P311 

Precautionary Statement 
Storage 

P261 

P272 

P280 

P261 

P272 

P280 

P302 + P352 

P333 + P313 

P321 

P363 

P302 + P352 

P333 + P313 

P321 

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Precautionary Statement 
Disposal 

P501 

P501 

Article 26 1 (d)  

If the hazard pictogram ‘GHS08’ applies for respiratory sensitisation, the hazard pictogram 
‘GHS07’ shall not appear for skin sensitisation or for skin and eye irritation. 

3.4.4.2.  Additional labelling provisions  

Annex II: 2.8. Mixtures containing at least one sensitising substance 

The label on the packaging of mixtures not classified as sensitising but containing at least one 
substance classified as sensitising and present in a concentration equal to or greater than that 
specified in Table 3.4.6 of Annex I shall bear the statement: 

EUH208 – ‘Contains (name of sensitising substance). May produce an allergic reaction’. 

Mixtures classified as sensitising containing other substance(s) classified as sensitising (in 
addition to the one that leads to the classification of the mixture) and present in a 
concentration equal to or greater than that specified in Table 3.4.6 of Annex I shall bear the 
name(s) of that/those substance(s) on the label. 

Where a mixture is labelled in accordance with section 2.4 or 2.5, the statement EUH208 may 
be omitted from the label for the substance concerned. 

3.4.5.  Examples of classification for skin sensitisation 

3.4.5.1.  Example of substances and mixtures fulfilling the criteria for 

classification for skin sensitisation 

3.4.5.1.1. 

Example 1 

Substance X gave a positive result in the LLNA with an EC3-value of 10.4%. As this EC3-value is 
above the cut-off of 2%, the substance is considered to be a moderate skin sensitiser, and 
should be classified as a Category 1 (Sub-category 1B) skin sensitiser. The GCL for classification 
of mixtures containing substance X is 1%. 

3.4.5.1.2. 

Example 2 

Substance Y tested positive in the LLNA with an EC3-value of 0.5%. In the GPMT a dermal 
induction concentration of 0.375% produced a positive response in 70% of the animals. On the 
basis of both these positive results, the substance is considered to be a strong sensitiser 
requiring classification as a Category 1 (Sub-category 1A) skin sensitiser. The GCL for 
classification of mixtures containing substance Y is 0.1%. 

3.4.5.1.3. 

Example 3 

Herby is a herbicide formulation containing 28 g/l substance X, a Sub-category 1B skin 
sensitiser (see example 1). There is no sensitisation data for the formulation itself. As Herby 
contains more than the GCL (1%) of this sensitising substance, and in the absence of any 
additional information, it should be classified as a Category 1 skin sensitiser.  

3.4.5.1.4. 

Example 4 

Substance Z being an extreme sensitiser, is classified as a Sub-category 1A. It has a specific 
concentration limit with regard to skin sensitisation of 0.001%, and due to this property any 

 
 
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mixture containing the substance at a concentration ≥ 0.001% must be classified as a Category 
1 skin sensitiser.  

3.4.5.1.5. 

Example 5 

Woody is a wood preservative containing two strong sensitising substances (Sub-category 1A): 
substance A is present at 1% and substance B is present at 0.05%. There are no data for the 
formulation itself. The mixture will be classified as cat 1 H317, due to the content of substance 
A (present above the GCL of 0.1%). Substance B is present below the classification limit. The 
name of both substances should appear on the label, substance A because it determines the 
classification of the mixture, and substance B because it is present in a concentration above the 
elicitation level (1/10 of the GCL of 0.1%).  

3.4.5.1.6. 

Example 6 

Substance C was tested in a reduced LLNA test in accordance with OECD 429 using a 
concentration of 25%. This resulted in a stimulation index (SI) of 20 compared to the 
concurrent control. This is clearly above the SI of 3 required for classification. Therefore, 
classification as a skin sensitiser is required. However, the available information does not allow 
calculation of an EC3 value required to determine the sub-categorisation. Although the 
substance was clearly positive at a high concentration of 25%, it cannot be excluded that also 
at a concentration of 2% or lower the SI will be 3. Therefore, there is not sufficient data for 
sub-categorisation. The substance is classified as Skin Sens Cat 1. 

3.4.5.1.7. 

Example 7 

Substance D gave a positive response in a guinea pig maximisation test with 90 % responding 
at 50 % intradermal induction dose. In a Buehler assay 70% responded at 30 % topical 
induction dose. The response in both GPMT and Buehler assay was > 60% and the substance 
was not tested at ≤ 1 % intradermal induction dose in the guinea pig maximisation test or at ≤ 
20 % topical induction dose in the Buehler assay.  Although the criteria for classification to 
subcategory 1B are fulfilled, the classification for subcategory 1A cannot be excluded and 
therefore the substance should be classified as a Category 1 skin sensitiser. 

3.4.5.1.8. 

Example 8 

If there are contradictory results from two or more skin sensitisation tests, the following 
examples will give guidance for the classification. Since these are ideal cases, the weight of 
evidence approach should be applied if studies indicate shortcomings/are not considered fully 
reliable. 

8(a): Substance E was tested in three separate animal tests performed with different test 
methods. In a Buehler assay no responses were observed with a topical induction dose of 70%. 
In the LLNA the EC3 value was 0.8%, indicating classification for subcategory 1A. In GPMT, 30 
% response was observed with an intradermal induction dose of 0,5 %, indicating classification 
for subcategory 1B. The substance should be classified for Skin Sens. 1A unless there is 
sufficient information to discount some of the results.  

8(b): Substance F is a skin sensitiser in humans indicating classification for sub-category 1A 
and in animals indicating classification for sub-category 1B. The substance should be classified 
for Skin Sens. 1A. 

8(c): Substance G is a skin sensitiser in animal tests indicating classification for sub-category 
1A and in humans indicating classification for category 1. The substance should be classified for 
Skin Sens. 1A.  

 
 
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3.4.5.2.  Example of substances or mixtures not fulfilling the criteria for 

classification for skin sensitisation  

3.4.5.2.1. 

Example 9 

Substance H was tested at concentrations up to 50% in the LLNA using a recommended and 
appropriate vehicle. It gave a maximum stimulation index of 2.6 and evidence of a positive dose 
response. On the basis that the stimulation index was below 3 at a high dose, the substance 
does not require classification. However, had the highest concentrations been lower, e.g. 10%, 
and/or a non-standard vehicle used, then further information would have been required before 
a classification decision could be reached. 

3.4.5.2.2. 

Example 10 

Insecto super is an insecticide formulation containing 9 g/l substance X (see Example 1). 
Substance X is a Sub-category 1B skin sensitiser (generic concentration limit in mixtures 1%). 
Based on the classification of substance X, the insecticide formulation shall not be classified as 
sensitising as the concentration of the substance is below the GCL of 1%. The label must bear 
the statement EUH208.  

3.4.5.3.  Examples of substances fulfilling the criteria for classification for 

respiratory sensitisation 

3.4.5.3.1. 

Example 11 

Five case studies describe the fact that work-related exposure to substance P is associated with 
asthma or rhinitis. In all of these cases blinded specific bronchial challenge tests with substance 
P provoked the respiratory symptoms, confirming that substance P is the causal substance. 

In a cohort of 51 workers exposed to substance P, 26 (51%) were diagnosed with occupational 
asthma and 12 of those also suffered from occupational rhinitis. The diagnosis was based on 
specific bronchial challenge tests with substance P.  

There is sufficient human evidence to conclude that substance P should be classified as a 
category 1 respiratory sensitizer.  Sub-categorization was not considered as there is currently 
no clear way to establish sub-categories.  

3.4.5.3.2. 

Example 12 

Work-related exposure to substance Q was associated with occupational asthma and rhinitis in 
several case studies. In those studies specific bronchial challenges were performed with 
substance Q and respiratory allergy symptoms could be reproduced, demonstrating that 
substance Q is the causal agent. In addition, a large retrospective analysis of nine longitudinal 
studies involving 2,689 persons exposed occupationally to substance Q in a period of 35 years, 
showed that the incidences of occupational asthma caused by substance Q were 2.7-5.5% in 
the earliest studies and decreased to 0.3-0.7% in the latest studies.  

Guinea pigs were exposed to substance Q by inhalation for 3 hours a day for 5 consecutive days 
to concentrations of 4, 12, 24, and 48 mg/m3. Three weeks after the first encounter with the 
inducing agent, animals were challenged with substance Q at a concentration of 2 mg/m3.  
During challenge breathing patterns were affected already at the lowest test concentration in 
guinea pigs that were sensitized and challenged to substance Q and not in control animals. 
Additionally, pulmonary inflammation and increased specific IgG1 levels were observed in 
guinea pigs sensitized and challenged with substance Q.  

On the basis of human evidence supported by data from an animal study, substance Q should 
be classified as a Category 1 respiratory sensitizer. Sub-categorization was not considered as 
there is currently no clear way to establish sub-categories. 

 
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3.4.6.  References 

Andersen KE, White IR and Goossens A (2011) Allergens from the European Baseline Series. In 
“contact Dermatitis”, 5th edition Johansen JD, Frosch PJ and Lepoittevin J-P, Springer-Verlag, 
Heidelberg, pp545-590 

Basketter DA, Andersen KE, Liden C, Van Loveren H, Boman A, Kimber I, Alanko K, Berggren E. 
(2005a): Evaluation of the skin sensitizing potency of chemicals by using the existing methods 
and considerations for the relevance of elicitation. Contact Dermatitis 52:39-43. 

Basketter DA, Clapp C, Jefferies D, Safford R, Ryan C, Gerberick G, Dearman R, Kimber I. 
(2005b): Predictive identification of human skin sensitisation thresholds. Contact Dermatitis 
53:260-267. 

Basketter DA, Evans P, Fielder RJ, Gerberick GF, Dearman RJ, Kimber I. (2002a): Local lymph 
node assay – validation and use in practice. Food Chem Toxicol 40:593-598. 

Basketter DA, Wright ZM, Colson NR, Patlewicz GY, and Pease CK. (2002b): Investigation of the 
skin sensitizing activity of linalool. Contact Dermatitis 47(3): 161-164. 

Basketter DA, Gerberick GF, Kimber I. (2001): Skin sensitisation, vehicle effects and the local 
lymph node assay. Food Chem Toxicol 39: 621-627. 

Cumberbatch M, Scott RC, Basketter DA, Scholes EW, Hilton J, Dearman RJ, Kimber I (1993): 
Influence of sodium lauryl sulfate on 2.4-dinitrochlorobenzene-induced lymph node activation. 
Toxicology 77: 181-191. 

De Jong WH, De Klerk A, Beek MT, Veenman C, Van Loveren H. (2007): Effect of prolonged 
repeated exposure to formaldehyde donors with doses below the EC3 value on draining lymph 
node responses. J Immunotoxicol 4(3):239-46. 

Dearman RJ, Basketter DA, Kimber I (2013): Inter-relationship between different classes of 
chemical allergens. J Appl Toxicology 33(7):558-65. 

Dearman RJ, Cumberbatch M, Hilton J, Clowes HM, Heylings JR, Kimber I (1996): Influence of 
dibutyl phthalate on dermal sensitization to fluorescein isothiocyanate. Fundam Appl Toxicol 33: 
24-30. 

Dotson GS, Maier A,Siegel PD, Anderson SE, Green BJ, Stefaniak AB, Codispoti CD, Kimber I 
(2015): Setting Occupational Exposure Limits for Chemical Allergens—Understanding the 
Challenges. Journal of occupational and environmental hygiene 12:S82-S98. 

Heylings JR, Clowes HM, Cumberbatch M, Dearman RJ, Fielding I, Hilton J, Kimber I (1996): 
Sensitization to 2,4-dinitrochlorobenzene: influence of vehicle on absorption and lymph node 
activation. Toxicology 109: 57-65. 

Johansen et al. European Society of Contact Dermatitis guideline for diagnostic patch testing – 
recommendations on best practice. Contact Dermatitis 2015; 73, 195-221 

Kimber I, Basketter DA, Butler M, Gamer A, Garrigue JL, Gerberick GF, Newsome C, Steiling W, 
Vohr HW. (2003): Classification of contact allergens according to potency: Proposals. Food 
Chem Toxicol 41: 1799-1809. 

Klimisch HJ, Andreae M, Tillmann U (1997): A Systematic Approach for Evaluating the Quality of 
Experimental Toxicological and Ecotoxicological Data. Regul Toxico. Pharmacol 25:1-5. 

Mirshahpanah P and Maibach HI (2007) Relationship of patch positive in a general versus an 
eczema population. Contact Dermatitis, 56: 125-130. 

Robinson MK, Nusair TL, Fletcher ER, Ritz HL. (1990): A review of the Buehler guinea pig skin 
sensitization test and its use in a risk assessment process for human skin sensitization. Fundam 
Appl Toxicol 17: 103-119. 

 
 
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Schlede E, Eppler R. (1995): Testing for skin sensitisation according to the notification 
procedure for new chemicals. The Magnusson and Kligman test. Contact Dermatitis 32: 1-4. 

Schneider K, Akkan Z. (2004). Quantitative relationship between the local lymph node assay 
and human skin sensitization assays. Regul Toxicol Pharmacol 39: 245-255. 

 
 
 
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3.5.  GERM CELL MUTAGENICITY 

3.5.1.  Definitions and general considerations for classification for germ cell 

mutagenicity 

Annex I: 3.5.1.1. A mutation means a permanent change in the amount or structure of the 
genetic material in a cell. The term ‘mutation’ applies both to heritable genetic changes that 
may be manifested at the phenotypic level and to the underlying DNA modifications when 
known (including specific base pair changes and chromosomal translocations). The term 
‘mutagenic’ and ‘mutagen’ will be used for agents giving rise to an increased occurrence of 
mutations in populations of cells and/or organisms. 

Annex I: 3.5.1.2. The more general terms ‘genotoxic’ and ‘genotoxicity’ apply to agents or 
processes which alter the structure, information content, or segregation of DNA, including 
those which cause DNA damage by interfering with normal replication processes, or which in a 
non-physiological manner (temporarily) alter its replication. Genotoxicity test results are 
usually taken as indicators for mutagenic effects.  

Germ cell mutations are those that occur in the egg or sperm cells (germ cells) and therefore 
can be passed on to the organism's offspring. Somatic mutations are those that happen in cells 
other than the germ cells, and they cannot be transmitted to the next generation. This is an 
important distinction to keep in mind in terms of both the causes and the effects of mutation. 

Annex I: 3.5.2.1 This hazard class is primarily concerned with substances that may cause 
mutations in the germ cells of humans that can be transmitted to the progeny. However, the 
results from mutagenicity or genotoxicity tests in vitro and in mammalian somatic and germ 
cells in vivo are also considered in classifying substances and mixtures within this hazard 
class. 

Annex I: 3.6.2.2 Specific considerations for classification of substances as carcinogens 

Annex I: 3.6.2.2.6. […] Mutagenicity: It is recognised that genetic events are central in the 
overall process of cancer development. Therefore evidence of mutagenic activity in vivo may 
indicate that a substance has a potential for carcinogenic effects. 

Hazard classification for germ cell mutagenicity primarily aims to identify substances causing 
heritable mutations or being suspected of causing heritable mutations. A secondary aim is that 
the hazard class germ cell mutagenicity offers supporting information with respect to the 
classification of carcinogenic substances. This is expressed by the broad meaning of the hazard 
statements ‘H340: May cause genetic defects’ and ‘H341: Suspected of causing genetic defects’ 
which comprises heritable genetic damage as well as somatic cell mutagenicity. Thus, 
classification as a germ cell mutagen (Category 1A, 1B, and 2) classifies for the hazard heritable 
genetic damage as well as providing an indication that the substance could be carcinogenic. 

It is also warranted that where there is evidence of only somatic cell genotoxicity, substances 
are classified as suspected germ cell mutagens. Classification as a suspected germ cell mutagen 
may also have implications for potential carcinogenicity classification. This holds true especially 
for those genotoxicants which are incapable of causing heritable mutations because they cannot 
reach the germ cells (e.g. genotoxicants only acting locally, ‘site of contact’ genotoxicants). This 
means that if positive results in vitro are supported by at least one positive local in vivo, 
somatic cell test, such an effect should be considered as enough evidence to lead to 
classification in Category 2. If there is also negative or equivocal data, a weight of evidence 
approach using expert judgement has to be applied. 

 
 
 
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3.5.2.  Classification of substances for germ cell mutagenicity 

3.5.2.1. 

Identification of hazard information 

3.5.2.1.1. 

Identification of human data 

Occasionally, studies of genotoxic effects in humans exposed by, for example, accident, 
occupation or participation in clinical studies (e.g. from case reports or epidemiological studies) 
may be available. Generally, cells circulating in blood are investigated for the occurrence of 
various types of genetic alterations; see also the Guidance on IR&CSA, Section R.7.7.3.2. 

3.5.2.1.2. 

Identification of non human data 

Animal data 

There is a number of in vivo assays for genotoxicity/mutagenicity testing, with or without OECD 
TGs. Modifications to OECD protocols have been developed for various classes of substances 
and may serve to enhance the accuracy of test results. Use of such modified protocols is a 
matter of expert judgement and will vary as a function of the chemical and physical properties 
of the substance to be evaluated. Commonly used in vivo tests employ methods by which any 
tissue of an animal can be examined for effects on the genetic material, giving the possibility to 
examine site-of-contact tissues (i.e., skin, epithelium of the respiratory or gastro-intestinal 
tract) in genotoxicity testing. In addition, test methods developed over the past decades in 
Drosophila and in various species of plants and fungi are available; see also the Guidance on 
IR&CSA, Section R.7.7.366. These latter tests have, however, been deleted as OECD TGs as of 
2014. 

In vivo tests in somatic cells which provide information on genotoxicity include, for example, the 
Comet single cell gel electrophoresis assay67 for DNA strand breaks. Assays such as gene 
mutations in transgenic rodent (TGR) models68 using reporter genes or mammalian erythrocyte 
micronucleus test for chromosome aberrations can be used for mutagenicity assessment. Please 
note that of these assays TGR is suitable for germ cells. 

In vitro data  

Typically, in vitro tests are performed with cultured bacterial cells, human or other mammalian 
cells. The sensitivity and specificity of tests will vary with different classes of substances; see 
also the Guidance on IR&CSA, Section R.7.7.3. 

Use of other data 

See the Guidance on IR&CSA, Section R. 7.7.3.1. 

Existing test methods 

See the Guidance on IR&CSA, Section R. 7.7.3.1. 

66 The Guidance on IR/CSA, Chapter R.7a (version 4.1). 

67 OECD TG 489 In Vivo Mammalian Alkaline Comet Assay (26 September 2014). 

68 OECD TG 488 Transgenic Rodent Somatic and Germ Cell Gene Mutation Assays (26 July 2013).  

 
 
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3.5.2.2.  Classification criteria for substances 

Annex I: 3.5.2.2. For the purpose of classification for germ cell mutagenicity, substances are 
allocated to one of two categories as shown in Table 3.5.1. 

Table 3.5.1 

Hazard categories for germ cell mutagens 

Categories 

Criteria 

CATEGORY 1: 

Substances known to induce heritable mutations or to be regarded as if 
they induce heritable mutations in the germ cells of humans. 

Substances known to induce heritable mutations in the germ cells of 
humans. 

Category 1A: 

The classification in Category 1A is based on positive evidence from 
human epidemiological studies. 

Substances to be regarded as if they induce heritable mutations in the 
germ cells of humans. 

Category 1B: 

The classification in Category 1B is based on: 
–  positive result(s) from in vivo heritable germ cell mutagenicity tests in 

mammals; or 

–  positive result(s) from in vivo somatic cell mutagenicity tests in 

mammals, in combination with some evidence that the substance has 
potential to cause mutations to germ cells. It is possible to derive this 
supporting evidence from mutagenicity/genotoxicity tests in germ cells 
in vivo, or by demonstrating the ability of the substance or its 
metabolite(s) to interact with the genetic material of germ cells; or 
–  positive results from tests showing mutagenic effects in the germ cells 
of humans, without demonstration of transmission to progeny; for 
example, an increase in the frequency of aneuploidy in sperm cells of 
exposed people. 

CATEGORY 2: 

Substances which cause concern for humans owing to the possibility that 
they may induce heritable mutations in the germ cells of humans. 

The classification in Category 2 is based on: 
–  Positive evidence obtained from experiments in mammals and/or in 

some cases from in vitro experiments, obtained from: 
–  Somatic cell mutagenicity tests in vivo, in mammals; or 
–  Other in vivo somatic cell genotoxicity tests which are supported by 

positive results from in vitro mutagenicity assays. 

Note: Substances which are positive in in vitro mammalian mutagenicity 
assays, and which also show chemical structure activity relationship to 
known germ cell mutagens, shall be considered for classification as 
Category 2 mutagens. 

 
 
 
 
 
 
 
 
 
 
 
 
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3.5.2.3.  Evaluation of hazard information 

Annex I: 3.5.2.3.3 Classification for heritable effects in human germ cells is made on the 
basis of well conducted, sufficiently validated tests, preferably as described in Regulation (EC) 
No 440/2008 adopted in accordance with Article 13(3) of Regulation (EC) No 1907/2006 
(‘Test Method Regulation’) such as those listed in the following paragraphs. Evaluation of the 
test results shall be done using expert judgement and all the available evidence shall be 
weighed in arriving at a classification. 

3.5.2.3.1. 

Evaluation of human data 

Human data have to be assessed carefully on a case-by-case basis. The interpretation of such 
data requires considerable expertise. Attention should be paid especially to the adequacy of the 
exposure information, confounding factors, co-exposures and to sources of bias in the study 
design or incident. The statistical power of the test may also be considered (see the Guidance 
on IR&CSA, Section R.7.4.4.2). 

3.5.2.3.2. 

Evaluation of non human data 

Evaluation of genotoxicity test data should be made with care. Regarding positive findings, 
responses generated only at highly toxic/cytotoxic concentrations should be interpreted with 
caution, and the presence or absence of a dose-response relationship should be considered. In 
case of negative findings in vivo toxicokinetic and other available information should be 
considered e.g. to verify whether the substance has reached the target organ (for detailed 
guidance see the Guidance on IR&CSA, Section R.7.7.4.1). 

Read-across and (Q)SARs can be used as part of a WoE approach for germ cell mutagenicity 
classification. If there are positive in vitro data from mammalian mutagenicity assays, structural 
similarities not sufficient for grouping/read-across may still warrant classification. 

3.5.2.4.  Decision on classification 

Annex I: 3.5.2.3.1. To arrive at a classification, test results are considered from experiments 
determining mutagenic and/or genotoxic effects in germ and/or somatic cells of exposed 
animals. Mutagenic and/or genotoxic effects determined in in vitro tests shall also be 
considered. 

Annex I: 3.5.2.3.9. The classification of individual substances shall be based on the total 
weight of evidence available, using expert judgement (See 1.1.1). In those instances where a 
single well-conducted test is used for classification, it shall provide clear and unambiguously 
positive results. If new, well validated, tests arise these may also be used in the total weight 
of evidence to be considered. The relevance of the route of exposure used in the study of the 
substance compared to the most likely route of human exposure shall also be taken into 
account.  

Classification as a Category 1A mutagen 

Epidemiological studies have been to date unable to provide evidence to classify a substance as 
a Category 1A mutagen. Hereditary diseases in humans for the most part have an unknown 
origin and show a varying distribution in different populations. Due to the random distribution of 
mutations in the genome it is not expected that one particular substance would induce one 
specific genetic disorder. Therefore, it is unlikely that such evidence may be obtained by 
epidemiological studies to enable classification of a substance as a Category 1A mutagen. 

Classification as a Category 1B mutagen 

 
 
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Classification in Category 1B may be based on positive results of at least one valid in vivo 
mammalian germ cell mutagenicity test. In case there are also negative or equivocal data, a 
weight of evidence approach using expert judgement has to be applied. 

It could be argued that in a case where in vivo mutagenicity/genotoxicity is proven and the 
substance under consideration is systemically available, then that substance should also be 
considered as a Category 1B mutagen. Germ cell such as the spermatogonia are generally not 
protected from substance exposure by the blood-testes barrier formed by the Sertoli cells. In 
such circumstances the relevant criteria are as follows: 

Annex I: 3.5.2.2. (extract from Table 3.5.1) 

Category 1B 

[…] 

–  positive result(s) from in vivo somatic cell mutagenicity tests in mammals, in combination 

with some evidence that the substance has potential to cause mutations to germ cells. It is 
possible to derive this supporting evidence from mutagenicity/genotoxicity tests in germ 
cells in vivo, or by demonstrating the ability of the substance or its metabolite(s) to 
interact with the genetic material of germ cells; 

[…]  

Supporting evidence in addition to positive results of a valid in vivo somatic cell mutagenicity 
test in mammals is needed to be able to classify a substance as a Category 1B mutagen when 
no data on mammalian germ cells are available. In the examples provided in the second 
sentence in the green box, mutagenicity/genotoxicity in germ cells or data showing that the 
substance or its metabolite(s) interact with the genetic material of germ cells is mentioned. 
Moreover, genetic damage to germ cells in exposed humans, related to  substance exposure, 
may offer additional information. Thus, in such circumstances, in addition to an in vivo somatic 
cell mutagenicity test, further experimental evidence is needed to be able to classify a 
substance as a Category 1B mutagen by application of a WoE approach using expert judgement. 

Classification as a Category 2 mutagen 

Classification in Category 2 may be based on positive results of at least one in vivo valid 
mammalian somatic cell mutagenicity test, indicating mutagenic effects in somatic cells. A 
Category 2 mutagen classification may also be based on positive results of a least one in vivo 
valid mammalian somatic cell genotoxicity test, supported by positive in vitro mutagenicity 
results. Genetic damage to somatic cells in exposed humans shown to be caused by substance 
exposure supported by positive in vitro mutagenicity results may also offer information 
warranting classification as a Category 2 mutagen. In vitro results can only lead to a Category 2 
mutagen classification in a case where there is support by chemical structure activity 
relationship to known germ cell mutagens. In the case where there are also negative or 
equivocal data, a weight of evidence approach using expert judgement has to be applied. 

In general, mutations can be differentiated into gene mutations (e.g. point or frame shift 
mutation), chromosome mutations (structural chromosome changes) and genome mutations 
(loss or gain of whole chromosomes). Different mutagenicity tests may detect different types of 
mutations and genotoxic effects which have to be taken into account in the weight of evidence 
determination. For instance, a substance which only causes chromosome mutations may be 
negative in a test for detecting point mutations. A complex data situation with positive and 
negative results might still lead to classification. This is because all tests detecting a certain 
type of mutation (e.g. point mutations) have been positive and all tests detecting chromosome 
mutations have been negative. Such circumstances clearly warrant classification although 
several tests have been negative which is plausible in this case. 

 
 
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A positive result for somatic or germinal mutagenicity in a test using intraperitoneal 
administration only shows that the tested substance has an intrinsic mutagenic property, and 
the fact that negative results are exhibited by other routes of dosage may be related to factors 
influencing the distribution/ metabolism of the substance which may be characteristic to the 
tested animal species. It cannot be ruled out that a positive test result in intraperitoneal studies 
in rodents may be relevant to humans. Note that intraperitoneal injection is since 2016 
generally not recommended for new testing without specific scientific justification because it is 
not an intended route of human exposure. However, existing studies with intraperitoneal 
injection should be assessed as described in this and the next paragraph 

If there are positive results in at least one valid in vivo mutagenicity test using intraperitoneal 
application, or from at least one valid in vivo genotoxicity test using intraperitoneal application 
plus supportive in vitro data, classification is warranted. In cases where there are additional 
data from further in vivo tests with oral, dermal or inhalative substance application, a weight of 
evidence approach using expert judgement has to be applied in order to come to a decision. For 
instance, it may be difficult to reach a decision on whether or not to classify in the case where 
there are positive in vivo data from at least one in vivo test using intraperitoneal application but 
(only) negative test data from (an) in vivo test(s) using oral, dermal, or inhalative application. 
In such a case, it could be argued that mutagenicity/genotoxicity can only be shown at internal 
body substance concentrations which cannot be achieved using application routes other than 
intraperitoneal. However, it also has to be taken into account that there is generally no 
threshold for mutagenicity unless there is specific proof for the existence of such a threshold as 
may be the case for aneugens. Thus, if mutagenicity/genotoxicity can only be demonstrated for 
the intraperitoneal route exclusively, then this may mean that the effect in the in vivo tests 
using application routes other than intraperitoneal may have been present, but it may not have 
been detected because it was below the detection limit of the oral, dermal, or inhalative test 
assays. 

In summary, classification as a Category 2 mutagen would generally apply if only 
intraperitoneal in vivo tests show mutagenicity/genotoxicity and the negative test results from 
the in vivo tests using other routes of application are plausible. Factors influencing plausibility 
are e.g. the doses tested and putative kinetic data on the test substance. However, on a case-
by-case analysis using a weight of evidence approach and expert judgement, non-classification 
may also result. 

3.5.2.5.  Classification of substances containing CMR constituents, additives 

or impurities 

From a compositional and a toxicological point of view the situation for substances containing 
CMR constituents, additives or impurities is the same as for mixtures containing components 
classified for these endpoints. For this reason the classification procedure for CMR endpoints 
that is foreseen by CLP for mixtures containing CMR components, is considered applicable also 
to substances containing CMR constituents, additives or impurities (see Section 1.1.6.1). As 
discussed in Section 3.5.3 below, mixtures containing components classified as germ cell 
mutagens shall be normally classified using only the relevant available information for the 
individual substances in the mixture. Further, in cases where the available test data on the 
mixture itself demonstrate CMR effects which have not been identified from the information on 
the individual substances, those data shall also be taken into account. For CMR endpoints the 
lowest incidence possible to detect in the tests may be by far unacceptable in humans. Thus a 
dose as high as possible (such as maximal tolerated dose, MTD dose) is needed to be able to 
detect CMR hazards. Dilution, as would be the case if mixtures or substances containing CMR 
constituents were tested, would increase the risk that CMR hazards would not be detected.  

According to article 10 (1) substances in other substances and substances in mixtures are 
treated in the same way regarding the use of GCLs and SCLs. 

 
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3.5.2.6.  Setting of specific concentration limits  

There is no detailed and accepted guidance developed for the setting of specific concentration 
limits (SCLs) for mutagenicity, as is the case for carcinogenic substances and substances toxic 
to reproduction. Guidance such as the T25 concept for carcinogens covering all relevant aspects 
would need to be developed in order to derive SCLs for mutagens in a standardized manner. 
There are several reasons why it is considered impossible to set SCLs for mutagens without a 
comprehensive guidance, one of them being that mutagenicity tests have not been specifically 
developed for the derivation of a quantitative response. Moreover, different mutagenicity tests 
have different sensitivities in detecting mutagens. Thus, it is very difficult to describe the 
minimum data requirements which would allow a standardized SCL derivation. Another 
drawback in practice is that the results obtained for the most part do not offer sufficient 
information on dose-response, especially in the case for in vivo tests. In conclusion, the 
possibility to set SCL for germ cell mutagenicity is therefore not considered possible in the 
process of self-classification as there is no standardized methodical approach available which 
adequately takes into account all relevant information. 

 
 
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3.5.2.7.  Decision logic for classification of substances 

The decision logic which follows is provided as additional guidance. It is strongly recommended 
that the person responsible for classification study the criteria before and during use of the 
decision logic. 

Does the substance have data on mutagenicity? 

No 

Classification 
not possible 

Yes 

According to the criteria, is the substance: 

Known to induce heritable mutations in germ 

(a)  
cells of humans, or 

Yes 

Should it be regarded as if it induces heritable 

(b)  
mutations in the germ cells of humans?  

Application of the criteria needs expert judgement in 
a weight of evidence approach. 

No 

Category 1 

Danger 

Category 2 

According to the criteria, does the substance cause 
concern for humans owing to the possibility that it 
may induce heritable mutations in the germ cells of 
humans? 

Yes 

Application of the criteria needs expert judgement 
in a weight of evidence approach. 

Warning 

No 

Not classified 

 
 
 
 
 
  
 
 
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3.5.3.  Classification of mixtures for germ cell mutagenicity 

3.5.3.1.  Classification criteria for mixtures 

Classification of mixtures will be based on the available test data for the individual ingredients 
of the mixture, using concentration limits for those ingredients. Under rare circumstances, the 
classification may be modified on a case-by-case basis based on the available test data for the 
mixture as a whole or based on bridging principles (see CLP Article 6(3) and CLP Annex I, 
3.5.3.2 and 3.5.3.3). 

3.5.3.1.1.  When data are available for the complete mixture 

Annex I: 3.5.3.2.1. Classification of mixtures will be based on the available test data for the 
individual ingredients of the mixture using concentration limits for the ingredients classified as 
germ cell mutagens. On a case-by-case basis, test data on mixtures may be used for 
classification when demonstrating effects that have not been established from the evaluation 
based on the individual ingredients. In such cases, the test results for the mixture as a whole 
must be shown to be conclusive taking into account dose and other factors such as duration, 
observations, sensitivity and statistical analysis of germ cell mutagenicity test systems. 
Adequate documentation supporting the classification shall be retained and made available for 
review upon request. 

3.5.3.1.2.  When data are not available for the complete mixture: bridging principles 

Annex I: 3.5.3.3.1. Where the mixture itself has not been tested to determine its germ cell 
mutagenicity hazard, but there are sufficient data on the individual ingredients and similar 
tested mixtures (subject to paragraph 3.5.3.2.1), to adequately characterise the hazards of 
the mixture, these data shall be used in accordance with the applicable bridging rules set out 
in section 1.1.3. 

Bridging principles will only be used on a case by case basis. Note that the following bridging 
principles are not applicable to this hazard class: 

• 
• 

concentration of highly hazardous mixtures 
interpolation within one hazard category 

(see CLP Annex 1, 1.1.3.3 and 1.1.3.4) 

Note that the bridging priciples are relevant only in case of comparable tested mixtures showing 
mutagenic effects not established from the evaluation of the individual ingredients. 
Classification for CMR hazards is based on tests with the ingredients. 

3.5.3.2.  Generic concentration limits for substances triggering classification 

of mixtures  

Annex I: 3.5.3.1.1. The mixture shall be classified as a mutagen when at least one 
ingredient has been classified as a Category 1A, Category 1B or Category 2 mutagen and is 
present at or above the appropriate generic concentration limit as shown in Table 3.5.2 for 
Category 1A, Category 1B and Category 2 respectively. 

Generic concentration limits of ingredients of a mixture classified as germ cell 
mutagens that trigger classification of the mixture. 

Table 3.5.2 

Concentration limits triggering classification of a mixture as: 

 
 
 
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Ingredient classified as: 

Category 1 mutagen  

Category 2 mutagen 

Category 1A  

Category 1B  

Category 1A mutagen 

≥ 0,1 % 

— 

≥ 0,1 % 

— 

— 

— 

≥ 1,0 % 

Category 1B mutagen 

Category 2 mutagen 

— 

— 

Note 

The concentration limits in the table above apply to solids and liquids (w/w units) as well as 
gases (v/v units). 

The option to set SCL for germ cell mutagenicity is not considered possible in the process of 
self-classification as there is no standardized methodical approach available which adequately 
takes into account all relevant information (see Section 3.5.2.6 of this Guidance). 

For germ cell mutagenicity it is reasonable to assume additivity for mutagens, unless there are 
specific reasons not to do so. 

3.5.3.3.  Decision logic for classification of mixtures 

The decision logic which follows is provided as additional guidance. It is strongly recommended 
that the person responsible for classification study the criteria before and during use of the 
decision logic. This decision logic deviates (slightly) from the original GHS guidance, to meet 
CLP requirements. 

Classification based on individual ingredients of the mixture 

 
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Does the mixture contain one or more ingredients 
classified as a Category 1 mutagen at  0.1%? 

Yes 

No 

Does the mixture contain one or more ingredients 
classified as a Category 2 mutagen at  1.0%? 

Yes 

No 

Not classified 

Category 1 

Danger 

Category 2 

Warning 

Modified classification on a case-by-case basis 

Test data on mixtures may be used for classification when demonstrating effects that have not 
been established from the evaluation based on the individual ingredients (CLP Annex I, 
3.5.3.2.1, see also CLP Article 6(3)). 

 
 
 
 
 
 
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Are test data available 
for the mixture itself 
demonstrating a 
mutagenic effect not 
identified from the data 
on individual 
substances? 

Yes 

Are the test results on the 
mixture conclusive taking 
into account dose and 
other factors such as 
duration, observations 
and analysis (e.g. 
statistical analysis, test 
sensitivity) of germ cell 
mutagenicity test 
systems? 

Yes 

No 

No 

Classify in 
appropriate 
category 

Danger  

or  

Warning 

Can bridging principles 
be applied? 

Yes 

No 

See above: Classification based on 
individual ingredients of the mixture. 

 
 
 
 
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3.5.4.  Hazard communication in form of labelling for germ cell mutagenicity  

3.5.4.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

Annex I: 3.5.4.1. Label elements shall be used in accordance with Table 3.5.3, for substances 
or mixtures meeting the criteria for classification in this hazard class. 

Table 3.5.3 

Label elements of germ cell mutagenicity 

Classification 

Category 1 

Category 2 

(Category 1A, 1B) 

GHS Pictograms 

Signal Word 

Danger 

Warning 

Hazard Statement 

H340: May cause genetic 
defects (state route of exposure 
if it is conclusively proven that 
no other routes of exposure 
cause the hazard) 

H341: Suspected of causing 
genetic defects (state route of 
exposure if it is conclusively 
proven that no other routes of 
exposure cause the hazard) 

Precautionary  Statement 
Prevention 

P201 
P202 
P280 

P201 
P202 
P280 

Precautionary  Statement 
Response 

Precautionary  Statement 
Storage 

Precautionary  Statement 
Disposal 

P308 + P313 

P308 + P313 

P405 

P501 

P405 

P501 

The hazard statement to be applied for the classification germ cell mutagenicity has to be 
amended to state the route of exposure if it is conclusively proven that no other routes of 
exposure will lead to the respective effect. A conclusive proof means that valid in vivo test data 
need to be available for all three exposure routes clearly indicating that only one exposure route 
leads to positive results. Moreover, such findings should be plausible with respect to the mode 
of action. It is estimated that such circumstances rarely, if ever, exist. Therefore, amending the 
hazard statement with the route of exposure generally does not have to be considered.  

3.5.4.2.  Additional labelling provisions 

There are no additional labelling provisions for substances and mixtures classified for germ cell 
mutagenicity under the CLP Regulation. However entry 29 of Annex XVII to REACH addresses 
such substances and mixtures. The packaging of substances with a harmonised classification as 

 
 
 
 
 
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Muta 1A or 1B and that are included in Appendices 3 and 4 of Annex VII of REACH,as well as 
the packaging of mixtures containing those substances above the concentration limits leading to 
the classification of the mixture, ‘must be marked visibly, legibly and indelibly as follows: 
“Restricted to professional users”.’ Derogations from this obligation are outlined in the same 
provision. 

 
 
 
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3.6.  CARCINOGENICITY 

3.6.1.  Definitions and general considerations for classification for 

carcinogenicity 

Annex I: 3.6.1.1. Carcinogen means a substance or a mixture of substances which induce 
cancer or increase its incidence. Substances which have induced benign and malignant 
tumours in well performed experimental studies on animals are considered also to be 
presumed or suspected human carcinogens unless there is strong evidence that the 
mechanism of tumour formation is not relevant for humans. 

More explicitly, chemicals are defined as carcinogenic if they induce tumours, increase tumour 
incidence and/or malignancy or shorten the time to tumour occurrence. Benign tumours that 
are considered to have the potential to progress to malignant tumours are generally considered 
along with malignant tumours. Chemicals can potentially induce cancer by any route of 
exposure (e.g. when inhaled, ingested, applied to the skin or injected), but carcinogenic 
potential and potency may depend on the conditions of exposure (e.g., route, level, pattern and 
duration of exposure). 

Carcinogenic chemicals have conventionally been divided according to the presumed mode of 
action; genotoxic or non-genotoxic, see Section 3.6.2.3.2.(k) of this Guidance. 

Classification of a substance as a carcinogen is based on consideration of the strength of the 
evidence of available data for classification with considerations of all other relevant information 
(weight of evidence) being taken into account as appropriate. Strength of evidence involves the 
enumeration of tumours in human and animal studies and determination of their level of 
statistical significance. A number of other factors need to be considered that influence the 
overall likelihood that a substance poses a carcinogenic hazard in humans (weight of evidence 
determination). The list of factors for additional consideration is long and requires the most up-
to-date scientific knowledge. It is recognised that, in most cases, expert judgement is necessary 
to be able to determine the most appropriate category for classification for carcinogenicity. 

3.6.2.  Classification of substances for carcinogenicity 

3.6.2.1. 

Identification of hazard information 

Carcinogens may be identified from epidemiological studies, from animal experiments and/or 
other appropriate means that may include (Quantitative) Structure-Activity Relationships 
((Q)SAR) analyses and/or extrapolation from structurally similar substances (read-across). In 
addition some information on the carcinogenic potential can be inferred from in vivo and in vitro 
germ cell and somatic cell mutagenicity studies, in vitro cell transformation assays, and gap 
junction intercellular communication (GJIC) tests. 

Extensive guidance on data requirements, information sources and strategies for the 
identification of potential carcinogens are given in the Guidance on IR&CSA, Section R.7.7.9 
(Information requirements on carcinogenicity) and Section R.7.7.10 (Information and its 
sources on carcinogenicity) and for potential mutagens Section R.7.7.3 (Information and its 
sources on mutagenicity). 

For more about non testing data see Section 3.6.2.3.4 of this Guidance. 

3.6.2.2.  Classification criteria for substances 

Substances are classified according to their potential to cause cancer in humans. In some cases 
there will be direct evidence on the carcinogenicity to humans from epidemiological studies. 
However, in most cases the available information on carcinogenicity will be primarily from 

 
 
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animal studies. In this case the relevance of the findings in animals to humans must be 
considered. 

Annex I: 3.6.2.1. For the purpose of classification for carcinogenicity, substances are 
allocated to one of two categories based on strength of evidence and additional considerations 
(weight of evidence). In certain instances, route-specific classification may be warranted, if it 
can be conclusively proved that no other route of exposure exhibits the hazard. 

Table 3.6.1 

Hazard categories for carcinogens 

Categories 

Criteria 

CATEGORY 1: 

Known or presumed human carcinogens 

A substance is classified in Category 1 for carcinogenicity on the basis 
of epidemiological and/or animal data. A substance may be further 
distinguished as: 

Category 1A: 

Category 1A, known to have carcinogenic potential for humans, 
classification is largely based on human evidence, or 

Category 1B: 

Category 1B, presumed to have carcinogenic potential for humans, 
classification is largely based on animal evidence. 

The classification in Category 1A and 1B is based on strength of 
evidence together with additional considerations (see section 3.6.2.2). 
Such evidence may be derived from: 

–  human studies that establish a causal relationship between human 
exposure to a substance and the development of cancer (known 
human carcinogen); or 

–  animal experiments for which there is sufficient (1) evidence to 

demonstrate animal carcinogenicity (presumed human carcinogen). 

In addition, on a case-by-case basis, scientific judgement may 
warrant a decision of presumed human carcinogenicity derived from 
studies showing limited evidence of carcinogenicity in humans 
together with limited evidence of carcinogenicity in experimental 
animals. 

CATEGORY 2: 

Suspected human carcinogens 

The placing of a substance in Category 2 is done on the basis of 
evidence obtained from human and/or animal studies, but which is not 
sufficiently convincing to place the substance in Category 1A or 1B, 
based on strength of evidence together with additional considerations 
(see section 3.6.2.2). Such evidence may be derived either from 
limited(1) evidence of carcinogenicity in human studies or from limited 
evidence of carcinogenicity in animal studies. 

(1) 

Note: See 3.6.2.2.4. 

 
 
 
 
 
 
 
 
 
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3.6.2.3.  Evaluation of hazard information 

Annex I: 3.6.2.2.1. Classification as a carcinogen is made on the basis of evidence from 
reliable and acceptable studies and is intended to be used for substances which have an 
intrinsic property to cause cancer. The evaluations shall be based on all existing data, peer-
reviewed published studies and additional acceptable data. 

Annex I: 3.6.2.2.2. Classification of a substance as a carcinogen is a process that involves 
two interrelated determinations: evaluations of strength of evidence and consideration of all 
other relevant information to place substances with human cancer potential into hazard 
categories. 

Classification of a substance as a carcinogen requires expert judgement and consideration of 
many different factors (weight and strength of evidence) included in the hazard information on 
carcinogenicity. The guidance provides an approach to data analysis rather than hard and fast 
rules. A stepwise approach to the classification can be taken where all the factors, both weight 
and strength of evidence, that may influence the outcome are considered systematically. Such 
approach, including consideration of these factors is outlined, in McGregor et al, 2009 and 
Boobis et al, 2006. Also the IPCS ‘Conceptual Framework for Evaluating a Mode of Action for 
Chemical carcinogenesis’ (2001), ILSI ‘Framework for Human Relevance Analysis of Information 
on Carcinogenic Modes of Action’ (Meek et al., 2003; Cohen et al, 2003, 2004) and the 
International Agency for Research on Cancer (IARC, 2006 - Preamble Section B) provide a basis 
for systematic assessments which may be performed in a consistent fashion internationally; 
however they are not intended to provide lists of criteria to be checked off. 

Specific considerations that are necessary are outlined in CLP Annex I, 3.6.2.2.3 (see Section 
3.6.2.3.1 of this Guidance) and other important factors to consider in CLP Annex I, 3.6.2.2.6 
(see Section 3.6.2.3.2 of this Guidance). Further guidance on these important factors is given in 
this document. 

3.6.2.3.1. 

Specific considerations for classification 

There is a strong link between CLP and the IARC classification criteria. The definitions for 
sufficient and limited evidence as defined by IARC are part of the criteria (CLP Annex I, 
3.6.2.2.3). IARC, however, understands the criteria of ‘sufficient’ and ‘limited’ as follows: ‘It is 
recognized that the criteria for these evaluations, described below, cannot encompass all of the 
factors that may be relevant to an evaluation of carcinogenicity. In considering all of the 
relevant scientific data, the Working Group may assign the agent to a higher or lower category 
than a strict interpretation of these criteria would indicate.’ (IARC 2006 preamble Section 6, 
Evaluation and rationale). This sentence emphasises that in certain circumstances expert 
judgement may overrule the strict interpretation of the IARC criteria for ‘sufficient’ and ‘limited’. 
These same limitations apply with the current criteria in that expert judgement is necessary and 
can override the strict interpretation of the definitions. 

Annex I: 3.6.2.2.3. Strength of evidence involves the enumeration of tumours in human and 
animal studies and determination of their level of statistical significance. Sufficient human 
evidence demonstrates causality between human exposure and the development of cancer, 
whereas sufficient evidence in animals shows a causal relationship between the substance and 
an increased incidence of tumours. Limited evidence in humans is demonstrated by a positive 
association between exposure and cancer, but a causal relationship cannot be stated. Limited 
evidence in animals is provided when data suggest a carcinogenic effect, but are less than 
sufficient. The terms 'sufficient' and 'limited' have been used here as they have been defined 
by the International Agency for Research on Cancer (IARC) and read as follows: 

(a)  Carcinogenicity in humans 

 
 
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The evidence relevant to carcinogenicity from studies in humans is classified into one 
of the following categories: 

–  sufficient evidence of carcinogenicity: a causal relationship has been established 

between exposure to the agent and human cancer. That is, a positive relationship has 
been observed between the exposure and cancer in studies in which chance, bias and 
confounding could be ruled out with reasonable confidence; 

– 

limited evidence of carcinogenicity: a positive association has been observed between 
exposure to the agent and cancer for which a causal interpretation is considered to be 
credible, but chance, bias or confounding could not be ruled out with reasonable 
confidence. 

(b)  Carcinogenicity in experimental animals 

Carcinogenicity in experimental animals can be evaluated using conventional 
bioassays, bioassays that employ genetically modified animals, and other in-vivo 
bioassays that focus on one or more of the critical stages of carcinogenesis. In the 
absence of data from conventional long-term bioassays or from assays with neoplasia 
as the end-point, consistently positive results in several models that address several 
stages in the multistage process of carcinogenesis should be considered in evaluating 
the degree of evidence of carcinogenicity in experimental animals. The evidence 
relevant to carcinogenicity in experimental animals is classified into one of the 
following categories: 

–  sufficient evidence of carcinogenicity: a causal relationship has been established 

between the agent and an increased incidence of malignant neoplasms or of an 
appropriate combination of benign and malignant neoplasms in (a) two or more 
species of animals or (b) two or more independent studies in one species carried out at 
different times or in different laboratories or under different protocols. An increased 
incidence of tumours in both sexes of a single species in a well-conducted study, 
ideally conducted under Good Laboratory Practices, can also provide sufficient 
evidence. A single study in one species and sex might be considered to provide 
sufficient evidence of carcinogenicity when malignant neoplasms occur to an unusual 
degree with regard to incidence, site, type of tumour or age at onset, or when there 
are strong findings of tumours at multiple sites; 

– 

limited evidence of carcinogenicity: the data suggest a carcinogenic effect but are 
limited for making a definitive evaluation because, e.g. (a) the evidence of 
carcinogenicity is restricted to a single experiment; (b) there are unresolved questions 
regarding the adequacy of the design, conduct or interpretation of the studies; (c) the 
agent increases the incidence only of benign neoplasms or lesions of uncertain 
neoplastic potential; or (d) the evidence of carcinogenicity is restricted to studies that 
demonstrate only promoting activity in a narrow range of tissues or organs. 

For human studies, the quality and power of the epidemiology studies require expert 
consideration and would normally lead to a Category 1A classification if data of adequate quality 
shows causality of exposure and cancer development. The Guidance on IR&CSA, Section 
R.7.7.10.2, further discusses the types of human epidemiology data available and the 
limitations of the data. Where there is sufficient doubt in the human data then classification in 
Category 1B may be more appropriate. On the other hand epidemiological studies may fail, 
because of uncertainties in the exposure assessment and/or limited sensitivity and statistical 
power, to confirm the carcinogenic properties of a substance as identified in animal studies 
(WHO Working group, 2000). 

 
 
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3.6.2.3.2. 

Additional considerations for classification 

Annex I: 3.6.2.2.4. Additional considerations (as part of the weight of evidence approach 
(see 1.1.1)). Beyond the determination of the strength of evidence for carcinogenicity, a 
number of other factors need to be considered that influence the overall likelihood that a 
substance poses a carcinogenic hazard in humans. The full list of factors that influence this 
determination would be very lengthy, but some of the more important ones are considered 
here. 

Annex I: 3.6.2.2.5. The factors can be viewed as either increasing or decreasing the level of 
concern for human carcinogenicity. The relative emphasis accorded to each factor depends 
upon the amount and coherence of evidence bearing on each. Generally there is a 
requirement for more complete information to decrease than to increase the level of concern. 
Additional considerations should be used in evaluating the tumour findings and the other 
factors in a case-by-case manner. 

Annex I: 3.6.2.2.6. Some important factors which may be taken into consideration, when 
assessing the overall level of concern are: 

(a) 

tumour type and background incidence; 

(b)  multi-site responses; 

(c) 

(d) 

(e) 

(f) 

progression of lesions to malignancy; 

reduced tumour latency; 

whether responses are in single or both sexes; 

whether responses are in a single species or several species; 

structural similarity to a substance(s) for which there is good evidence of 

(g) 
carcinogenicity; 

(h) 

routes of exposure; 

comparison of absorption, distribution, metabolism and excretion between test animals 

(i) 
and humans; 

(j) 

the possibility of a confounding effect of excessive toxicity at test doses; 

(k)  mode of action and its relevance for humans, such as cytotoxicity with growth 
stimulation, mitogenesis, immunosuppression, mutagenicity. 

[…] 

As indicated above, the evaluation of animal carcinogenicity data requires consideration of a 
number of important additional factors which may increase or decrease the level of concern and 
the classification category. The list in CLP Annex I, 3.6.2.2.6 is not exhaustive. Each of these 
factors is discussed individually below. 

a.  Tumour type and background incidence 

Knowledge about the tumour type including its tumour biology is indispensable to decide on the 
relevance of observed tumours for humans.   

By default, carcinogenic effects in experimental animals are considered relevant to humans and 
are considered for classification as carcinogens. Only when there is sufficient evidence showing 
that a certain type of tumour is not relevant to humans should this tumour type be excluded for 
classification. 

Certain tumour types observed in animal carcinogenicity studies are of questionable or no 
relevance to humans. In case of multiple tumours anticipated to have no relevance for humans 

 
 
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justification should be given for each tumour type. The justification for dismissing any particular 
tumour should be presented as a scientifically robust and transparent argument.  

There are several reasons why a tumour observed in animals may be judged to be not relevant 
for humans or may be judged to be of lower concern. In most of these cases the tumour arises 
via a mode of action which does not occur in humans (see this Section part k). In some cases 
the tumour may arise in a tissue known to be overly susceptible in the species tested to 
development of certain tumours and consequently may be judged to be less relevant for 
humans. In a few cases a tumour may occur in a tissue with no equivalent in humans. 

Tumours occurring in tissues with no human equivalent 

Some of the commonly used animal species have some tissues with no equivalent in humans. 
Tumours occurring in these tissues include the following 

•  Forestomach tumours in rodents following administration by gavage of irritating or 

corrosive, non mutagenic substances. In rodents, the stomach is divided into two parts 
by the muco-epidermoid junction separating squamous from glandular epithelium. The 
proximal part, or forestomach, is non-glandular, forms a continuum with the 
oesophagus, and is lined by keratinized, stratified squamous epithelium. While humans 
do not have a forestomach, they do have comparable squamous epithelial tissues in the 
oral cavity and the upper two-thirds of the oesophagus. See also this Section (k), IARC 
(2003), and RIVM (2003). 

•  Tumours in the Zymbal’s glands. Zymbal’s glands are located beneath squamous 

epithelium at the anterior and posterior aspect of the ear canal. The external portion of 
the gland in rats is 3 to 5 millimetres in diameter. 

•  Tumours in the Harderian glands. Harderian glands are found in all vertebrates that 

possess a nictitating membrane, or third eyelid. They are located behind the eyeball in 
the orbit nictitating membrane, encircling the optic nerve. Humans have a rudimentary 
one. 

Tumours occurring in such tissues indicate that the substance has the potential to induce 
carcinogenic effects in the species tested. It cannot automatically be ruled out that the 
substance could cause similar tumours of comparable cell/tissue origin (e.g. squamous cell 
tumours at other epithelial tissues) in humans. Careful consideration and expert judgement of 
these tumours in the context of the complete tumour response (i.e. if there are also tumours at 
other sites) and the assumed mode of action is required to decide if these findings would 
support a classification. However, tumours observed only in these tissues, with no other 
observed tumours are unlikely to lead to classification. However, such determinations must be 
evaluated carefully in justifying the carcinogenic potential for humans; any occurrence of other 
tumours at distant sites must also be considered. 

Considering the background incidence and use of historical control data 

Any statistically significant increase in tumour incidence, especially where there is a dose-
response relationship, is generally taken as positive evidence of carcinogenic activity. However, 
in some cases the results involve an increase incidence of tumours in treated animals which lies 
at the borderline of biological and/or statistical significance or there is an increase in a 
spontaneous tumour type, then comparison of the tumour incidence with historical control 
tumour data is strongly encouraged. 

Historical control data provide useful information on the normal pattern and range of tumour 
types and incidences for a particular strain/species, which may not be reflected by the tumour 
findings in the concurrent controls in any individual study. This can be particularly relevant for 
animal strains which have a propensity to develop a particular type of tumour spontaneously 
with variable and potentially high incidence. In such a case the tumour incidence in the treated 
group may be significantly above the concurrent control but could still be within the historical 

 
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incidence range for that tumour type in that species and therefore may not be providing reliable 
evidence of treatment related carcinogenicity. 

Some examples of animal tissues with a high spontaneous tumour incidence are: 

•  Adrenal pheochromocytoma in male F344 rats (NTP, 2007a), Sprague-Dawley rats (NTP, 

2005; RIVM, 2001; Ozaki et al., 2002); 

•  Pituitary adenomas in F344 rats (NTP, 2007a), Sprague-Dawley rats (NTP 2005; RIVM 

2005); 

•  Mammary gland tumours (adenomas and carcinomas) in female Sprague-Dawley rats 

(NTP, 2005); 

•  Mononuclear cell leukaemia in F344 rats (NTP, 2007a; RIVM, 2005); 

•  Liver tumours in B6C3F1 mice (NTP, 2007b; Haseman et al. 1998; Battershill, J.M. and 

Fielder, R.J., 1998); 

•  Leydig cell adenomas in male F344 rats (Cook et al., 1999; Mati et al., 2002; RIVM, 

2004; EU Specialised Experts Report, 2004). 

Historical control data can also be useful to judge the biological significance of marginal 
increases in uncommon tumours. If there is a small increase in a particular tumour type which 
historical data shows to be very uncommon and unlikely to have occurred by chance then this 
may support a conclusion of carcinogenicity without the requirement for a statistically significant 
increase. 

Use of historical control data should be on a case by case basis with due consideration of the 
appropriateness and relevance of the historical control data for the study under evaluation. In a 
general sense, the historical control data set should be matched as closely as possible to the 
study being evaluated. The historical data must be from the same animal strain/species, and 
ideally, be from the same laboratory to minimise any potential confounding due to variations in 
laboratory conditions, study conditions, animal suppliers, husbandry etc. It is also known that 
tumour incidences in control animals can change over time, due to factors such as genetic drift, 
changes in diagnostic criteria for pathological changes/tumour types, and husbandry factors 
(including the standard diet used), so the historical data should be contemporary to the study 
being evaluated (e.g. within a period of up to around 5 years of the study). Historical data older 
than this should be used with caution and acknowledgement of its lower relevance and 
reliability. (RIVM, 2005; Fung et al, 1996; Greim et al, 2003). 

Even when a particular tumour type may be discounted, expert judgment must be used in 
assessing the total tumour profile in any animal. However, appearance of only spontaneous 
tumours, especially if they appear only at high dose levels, may be sufficient to downgrade a 
classification from Category 1B to Category 2, or even no classification. Where the only 
available tumour data are liver tumours in certain sensitive strains of mice, without any other 
supplementary evidence, the substance may not be classified in any of the categories, 
(Battershill and Fielder, 1998). Expert judgment is required to evaluate the relevance of the 
results. 

b.  Multi-site responses 

In general, chemicals are evaluated for carcinogenic potential in two-year bioassays conducted 
in mice and rats. The chemicals produce a spectrum of responses ranging from no effects in 
either species to induction of malignant neoplasms in multiple tissues in both species. Between 
these two extremes, there are variable responses in tissues, sexes and species, which 
demonstrate that there are important differences among the carcinogens, as well as between 
the species in which they are tested. The tumour profile observed with a substance should be 
taken into account when considering the most appropriate classification. 

 
 
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Evidence shows that substances which cause tumours in either multiple sites and/or multiple 
species tend to be more potent carcinogens than those causing tumours at only one site in one 
species (Dybing et al., 1997). This is often true for substances which are mutagenic. Also, 
where human carcinogens have been tested in two or more species, the majority have caused 
cancer in several species (Tennant, 1993). Thus, if a substance causes tumours at multiple sites 
and/or in more than one species then this usually provides strong evidence of carcinogenicity. 
Typically such a tumour profile would lead to a classification in category 1B. 

c.  Progression of lesions to malignancy 

In general, if a substance involves a treatment related increase in tumours then it will meet the 
criteria for classification as a carcinogen. 

If the substance has been shown to cause malignant tumours this will usually constitute 
sufficient evidence of carcinogenicity supporting Category 1B (CLP Annex I, 3.6.2.2.3) 

The induction of only benign tumours usually provides a lower strength of evidence for 
carcinogenicity than the induction of malignant tumours and will usually support Category 2 
(CLP Annex I, 3.6.2.2.3). However, benign tumours may also be of significant concern and the 
strength of evidence for carcinogenicity that they provide should be considered using expert 
judgement.  For instance, some benign tumours may have the potential to progress to 
malignant tumours and therefore any indication that the observed tumours have the potential to 
progress to malignancy may increase the level of concern. Also, some benign tumours, for 
example brain tumours, may be of concern in themselves. 

d.  Reduced tumour latency 

The latency of tumour development i.e. how quickly a substance induces tumours, often reflects 
the potency of a carcinogen. This is particularly true for mutagenic substances which often 
induce tumours with relatively short latency and usually more rapidly than non-genotoxic 
agents. Tumour latency is not generally investigated in detail in standard carcinogenicity 
studies, although some information may be provided if the study used serial sacrifices. 

The latency of tumour formation does not materially affect the classification and hazard 
category. Any substance causing cancer will attract classification regardless of the latency for 
tumour development. This also includes tumour responses at late treatment/life periods if 
substance-related. However unusual tumour types or tumours occurring with reduced latency 
may add to the weight of evidence for the carcinogenic potential of a substance, even if the 
tumours are not statistically significant. 

e.  Whether responses are in single or both sexes 

In general, in standard carcinogenicity studies both male and female animals are tested. There 
may be cases where tumours are only observed in one sex. 

Tumours in one sex only may arise for two broad reasons. The tumours may occur in a gender-
specific tissue, for instance the uterus or testes (sex-specific tissue), or in a non sex-specific 
tissue, in one sex only. Tumours may also be induced by a mechanism that is gender (or sex) -
specific, for instance a hormonally-mediated mechanism or one involving gender (or sex) -
specific differences in toxicokinetics. As with all cases the strength of evidence of carcinogenicity 
should be assessed based on the totality of the information available using a weight of evidence 
type approach. A default position is that such tumours are still evidence of carcinogenicity and 
should be evaluated in light of the total tumorigenic response to the substance observed at 
other sites (multi-site responses or incidence above background) in determining the 
carcinogenic potential and the classification category. 

If tumours are seen only in one sex of an animal species, the mode of action should be carefully 
evaluated to see if the response is consistent with the postulated mode of action. Effects seen 
only in one sex in a test species may be less convincing than effects seen in both sexes, unless 
there is a clear patho-physiological difference consistent with the mode of action to explain the 

 
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single sex response.  However, there is no requirement for a mechanistic understanding of 
tumour induction in order to use these findings to support classification. If there is clear 
evidence for induction of either a gender (or a sex)-specific tumour then classification in Cat 1B 
may be appropriate. However, it has to be taken into account that according to the criteria 
additional data are required to provide sufficient evidence for animal carcinogenicity (1B). 

f.  Whether responses are in single species or several species 

The criteria indicate that carcinogenicity in a single animal species (both sexes, ideally in a GLP 
study) could be sufficient evidence and could therefore lead to a Category 1B classification in 
the absence of any other data. This represents a change compared to the previous EU-system 
where such a study would rarely lead to the equivalent of a Category 1B classification.  

However, as defined under ‘sufficient’ evidence (CLP Annex I, 3.6.2.2.3 (b)), a single study in 
one species and sex might be considered to provide sufficient evidence of carcinogenicity when 
malignant neoplasms occur to an unusual degree with regard to incidence, site, type of tumour 
or age at onset, or when there are strong findings of tumours at multiple sites. Moreover a 
single study in one species and sex in combination with positive in-vivo mutagenicity data would 
be considered to provide sufficient evidence of carcinogenicity. 

Positive responses in several species add to the weight of evidence, that a chemical is a 
carcinogen. 

g.  Structural similarity or not to a chemical(s) for which there is good evidence of 

carcinogenicity 

See Section 3.6.2.3.4 of this Guidance. 

h.  Routes of exposure; 

Annex I: 3.6.2.2.8. The classification shall take into consideration whether or not the 
substance is absorbed by a given route(s); or whether there are only local tumours at the site 
of administration for the tested route(s), and adequate testing by other major route(s) show 
lack of carcinogenicity. 

The classification for carcinogenicity generally does not specify specific routes of exposure. If a 
chemical has been shown to cause tumours by any route of administration then it may require 
classification, unless there is a robust justification for dismissing the findings from a particular 
route. However, a specific hazard statement has been established in CLP, H350i; May cause 
cancer by inhalation. 

Most standard carcinogenicity studies use physiological routes of exposure for humans, namely 
inhalation, oral or dermal exposure. The findings from such routes are usually considered 
directly relevant for humans. Studies using these routes will generally take precedence over 
similar studies using other routes of exposure. 

Sometimes other non-physiological routes are used, such as intra-muscular, sub-cutaneous, 
intra-peritoneal and intra-tracheal injections or instillations. Findings from studies using these 
routes may provide useful information but should be considered with caution. Usually dosing via 
these routes provides a high bolus dose which gives different toxicokinetics to normal routes 
and can lead to atypical indication of carcinogenicity. For instance, the high local concentration 
can lead to local tumours at the site of injection. These would not normally be considered 
reliable indications of carcinogenicity as they most likely arose from the abnormally high local 
concentration of the test substance and would lead to a lower category classification or no 
classification. 

Where findings are available from studies using standard routes and non-physiological routes, 
the former will generally take precedence. Usually studies using non-standard routes provide 
supporting evidence only. 

 
 
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The hazard statement allows for identifying the route of exposure ‘if it is conclusively proven 
that no other routes of exposure cause the hazard’ (CLP Annex I, Table 3.6.3). In this case the 
hazard statement may be modified accordingly. Genotoxic carcinogens are generally suspected 
to be carcinogenic by any route.  

i.  Comparison of absorption, distribution, metabolism and excretion between test animals 

and humans; 

Annex I: 3.6.2.2.9. It is important that whatever is known of the physico-chemical, 
toxicokinetic and toxicodynamic properties of the substances, as well as any available relevant 
information on chemical analogues, i.e. structure activity relationship, is taken into 
consideration when undertaking classification.  

Consideration of absorption, distribution, metabolism and excretion (toxicokinetics) of the 
substance in the test animal species and in humans is one important consideration, including 
where a substance is metabolised to an active carcinogenic metabolite. Toxicokinetic behaviour 
is normally assumed to be similar in animals and humans, at least from a qualitative 
perspective. On the other hand, certain tumour types in animals may be associated with 
toxicokinetics or toxicodynamics that are unique to the animal species tested and may not be 
predictive of carcinogenicity in humans. Where significant qualitative and quantitative 
differences in toxicokinetics exist between animals and humans this can impact on the 
relevance of the animal findings for humans and in certain instances may influence the category 
of classification. Where a carcinogenic metabolite identified in animals is demonstrated not to be 
produced in humans, no classification may be warranted where it can be shown that this is the 
only mechanism of action for carcinogenicity. 

The use of physiologically-based pharmacokinetic (PB/PK) modelling requires more validation 
and while it may not lead directly to a modification of classification, however expert judgement 
in conjunction with PB/PK modelling may help to modify the concern for humans. 

j.  The possibility of a confounding effect of excessive toxicity at test doses  

In lifetime bioassays compounds are routinely tested using at least three dose levels to enable 
hazard identification and hazard characterisation as part of risk assessment. Of these doses, the 
highest dose needs to induce minimal toxicity, such as characterised by an approximately 10% 
reduction in body weight gain (maximal tolerated dose, MTD dose). The MTD is the highest dose 
of the test agent during the bioassay that can be predicted not to alter the animal’s normal 
longevity from effects other than carcinogenicity. Data obtained from a sub-chronic or other 
repeated dose toxicity study are used as the basis for determining the MTD. 

Excessive toxicity, for instance toxicity at doses exceeding the MTD, can affect the carcinogenic 
responses in bioassays. Such toxicity can cause effects such as cell death (necrosis) with 
associated regenerative hyperplasia, which can lead to tumour development as a secondary 
consequence unrelated to the intrinsic potential of the substance itself to cause tumours at 
lower less toxic doses. 

Tumours occurring only at excessive doses associated with severe toxicity generally have a 
more doubtful potential for carcinogenicity in humans. In addition, tumours occurring only at 
sites of contact and/or only at excessive doses need to be carefully evaluated for human 
relevance for carcinogenic hazard. For example, as indicated in this Section (a) ‘Tumour type 
and background incidence’, forestomach tumours, following administration by gavage of an 
irritating or corrosive, non-mutagenic chemical, may be of questionable relevance, both due to 
the lack of a corresponding tissue in humans, but importantly, due to the high dose direct effect 
on the tissue. However, such determinations must be evaluated carefully in justifying the 
carcinogenic potential for humans; any occurrence of other tumours at distant sites must also 
be considered. 

 
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The proceedings of a WHO/IPCS workshop on the Harmonization of Risk Assessment for 
Carcinogenicity and Mutagenicity (Germ cells) - A Scoping Meeting (IPCS, 1995; Ashby et al, 
1996), points to a number of scientific questions arising for classification of chemicals, e.g. 
mouse liver tumours, peroxisome proliferation, receptor-mediated reactions, chemicals which 
are carcinogenic only at toxic doses and which do not demonstrate mutagenicity. 

If a test compound is only found to be carcinogenic at the highest dose(s) used in a lifetime 
bioassay, and the characteristics associated with doses exceeding the MTD as outlined above 
are present, this could be an indication of a confounding effect of excessive toxicity. This may 
support a classification of the test compound in Category 2 or no classification. 

k.  Mode of action and its relevance for humans, such as mutagenicity, cytotoxicity with 

growth stimulation, mitogenesis, immunosuppression 

Carcinogenic chemicals have conventionally been divided into two categories according to the 
presumed mode of action; genotoxic or non-genotoxic. Genotoxic modes of action involve 
genetic alterations caused by the chemical interacting directly with DNA to possibly result in a 
change in the primary sequence of DNA after cell division. A chemical can also cause genetic 
alterations indirectly following interaction with other cellular processes (e.g. secondary to the 
induction of oxidative stress). Non-genotoxic modes of action include epigenetic changes, i.e. 
effects that do not involve alterations in DNA but that may influence gene expression, altered 
cell-cell communication, or other factors involved in the carcinogenic process. For example, 
chronic cytotoxicity with subsequent regenerative cell proliferation is considered a mode of 
action by which tumour development can be enhanced: the induction of urinary bladder 
tumours in rats may, in certain cases, be due to persistent irritation/inflammation, tissue 
erosion and regenerative hyperplasia of the urothelium following the formation of bladder 
stones. Other modes of non-genotoxic action can involve specific receptors (e.g., peroxisome 
proliferator-activated receptor-alpha (PPARα) which is associated with liver tumours in rodents; 
or tumours induced by various hormonal mechanisms). More detail is given in the Guidance on 
IR/CIS Section R7.7.8. 

Some modes of action of tumour formation are considered to be not relevant to humans. Where 
such a mechanism is identified then classification may not be appropriate. Only if a mode of 
action of tumour development is conclusively determined not to be operative in humans may 
the carcinogenic evidence for that tumour be discounted. However, a weight of evidence 
evaluation for a substance calls for any other tumorigenic activity to be evaluated as well. In 
addition, the existence of a secondary mechanism of action with the implication of a practical 
threshold above a certain dose level (e.g., hormonal effects on target organs or on mechanisms 
of physiological regulation, chronic stimulation of cell proliferation) may lead to a downgrading 
of a Category 1 to Category 2 classification. 

The various international documents on carcinogen assessment all note that mode of action in 
and of itself, or consideration of comparative metabolism, should be evaluated on a case-by-
case basis and are part of an analytic evaluative approach. One must look closely at any mode 
of action in animal experiments taking into consideration comparative 
toxicokinetics/toxicodynamics between the animal test species and humans to determine the 
relevance of the results to humans. This may lead to the possibility of discounting very specific 
effects of certain types of chemicals. Life stage-dependent effects on cellular differentiation may 
also lead to qualitative differences between animals and humans. 

To establish a mode of action will usually require specific investigative studies over and above 
the standard carcinogenicity study. All available data must be considered carefully to judge if it 
can be concluded with confidence that the tumours are being induced through that specific 
mechanism. The IPCS Framework for Analyzing the Relevance of a Cancer Mode of Action for 
Humans (2007) can be a useful way to construct and present a robust and transparent 
assessment of such data. 

Some mechanisms of tumour formation considered not relevant for humans: 

 
 
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•  Kidney tumours in male rats associated with substances causing α2μ-globulin 

nephropathy (IARC, 1999) 

•  Pheochromocytomas in male rats exposed to particulates through inhalation secondary 

to hypoxemia (Ozaki et al, 2002) 

•  Leydig cell adenomas induced by dopamine antagonists or gonadotropin-releasing 

hormone (GnRH) (EU Specialised Experts, 2004; RIVM, 2004) 

•  Urinary bladder tumours due to crystals in the bladder (IARC, 1999) 
•  Forestomach tumours in rodents following administration by gavage of irritating or 

corrosive, non-genotoxic substances (RIVM, 2003; IARC 2003) 

•  Certain thyroid tumours in rodents mediated by UDP glucuronyltransferase (UGT) 

induction (IARC, 1999; EU Specialised Experts, 1999) 

•  Liver tumours in rodents conclusively linked to peroxisome proliferation (IARC, 1994) 

3.6.2.3.3. 

Consideration of mutagenicity 

Annex I: 3.6.2.2.6. […] Mutagenicity: It is recognised that genetic events are central in the 
overall process of cancer development. Therefore evidence of mutagenic activity in vivo may 
indicate that a substance has a potential for carcinogenic effects. 

As indicated in Section 3.6.2.1 of this Guidance and above, carcinogenic chemicals have 
conventionally been divided according to the presumed mode of action; genotoxic or non-
genotoxic. Evidence of genotoxic activity is gained from studies on mutagenic activity. 

It should be noted that in general if a substance is mutagenic then it will be considered to be 
potentially carcinogenic in humans however mutagenicity data alone are insufficient information 
to justify a carcinogen classification. In some cases where only in vitro and in vivo mutagenicity 
are present without carcinogenicity data, a Category 2 classification can be considered when all 
factors have been considered such as type and quality of the mutagenicity data, structure 
activity relationships etc. A single positive carcinogenicity study in one species and sex in 
combination with positive in-vivo mutagenicity data would be considered to provide sufficient 
evidence of carcinogenicity. 

Lack of genotoxicity is an indicator that other mechanisms are in operation as indicated in 
Section 3.6.2.3.2.(k) of this Guidance. Thus careful analysis based on all available information is 
required to identify the mechanism and derive a classification category taking into account the 
factors leading to the tumours observed, in the animals. 

3.6.2.3.4.  Non testing data 

Annex I: 3.6.2.2.7. A substance that has not been tested for carcinogenicity may in certain 
instances be classified in Category 1A, Category 1B or Category 2 based on tumour data from 
a structural analogue together with substantial support from consideration of other important 
factors such as formation of common significant metabolites, e.g. for benzidine congener 
dyes. 

A chemical that has not been tested for carcinogenicity may in certain instances be classified as 
a carcinogen based on tumour data from a structurally similar chemical with which it is 
predicted to have similar carcinogenic activity. Such an approach must always be based on a 
robust and transparent argument to support this supposition. There may also be evidence 
demonstrating similarity in terms of other important factors such as toxicokinetics or mutagenic 
activity etc. (OECD 2004, 2005, 2007; Guidance on IR&CSA, Section R.6, QSARs and grouping 
of chemicals). 

In the absence of carcinogenicity data, read-across can be used to support a classification for 
carcinogenicity when the chemical in question is similar to a known or suspected carcinogen 
(Category 1A, 1B or 2). The similarity between chemicals is considered in terms of structural 
features, physico-chemical properties and overall toxicological profile. 

 
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In general the chemicals will share a common structural element or functional group (i.e., a 
toxophore) that has been shown to be integral to the underlying mechanism of carcinogenicity 
for chemicals with this toxiphore in well conducted studies. These toxiphores can be identified 
through expert judgement or through automated systems such as (Q)SARs. The read-across 
should also consider the physico-chemical properties of the chemical and data from other 
toxicity studies to judge the similarity between the chemicals in terms of bioavailability by 
relevant routes of exposure and toxicokinetics. The toxicity profile from other studies should 
also be compared (e.g., acute and repeated-dose toxicity and mutagenicity) and should share 
similarities in nature and severity. Data from shorter term toxicity studies may be useful, 
particularly for non-genotoxic carcinogens, to indicate that the chemicals cause the same 
underlying pathological changes (e.g., hyperplasia), and act via a common mode of action. Any 
predictions made on the basis of read-across should take into account the totality of data on the 
chemicals in question, including the physico-chemical properties, toxicological profile, 
toxicokinetics, structural analogy and the performance of any (Q)SAR models used, in a weight 
of evidence approach driven by expert judgement. The final decision must be clear, scientifically 
defensible and transparent. 

The specific category depends on the category of the known carcinogen and the degree of 
confidence in the robustness of the read-across prediction. The category will not be higher than 
the chemical used to read-across from, but normally may be the same. However a lower 
category may be applied if the read-across highlights a possible carcinogenic hazard, and thus 
supports a classification, but there is uncertainty as to the robustness of the read-across 
prediction or there is evidence, for instance from mechanistic or other studies, that the chemical 
may be of lower concern for carcinogenicity. 

If a chemical is similar to a substance known to be carcinogenic and shares the toxiphore that is 
considered to be causally related to carcinogenicity, then it is unlikely that there will be 
sufficient confidence in a prediction of no hazard (for instance based on arguments relating to 
differences in physico-chemical or steric properties), to justify no classification in the absence of 
supporting negative experimental data. However, the bioavailability of the toxiphore will need 
evaluation (Guidance on IR&CSA R.6). 

3.6.2.4.  Decision on classification 

As mentioned throughout, classification as a carcinogen is based on consideration of the 
strength of evidence with additional considerations (weight of evidence) being taken into 
account as appropriate. It is recognised that, in most cases, expert judgment is necessary to 
determine the classification category. 

3.6.2.5.  Classification of substances containing CMR constituents 

From a compositional and a toxicological point of view the situation for substances containing 
CMR constituents, additives or impurities is the same as for mixtures containing components 
classified for these endpoints. For this reason the classification procedure for CMR endpoints 
that is foreseen by CLP for mixtures containing CMR components, is considered applicable also 
to substances containing CMR constituents, additives or impurities (see Section 1.1.6.1). As 
discussed in Section 3.6.3 below, mixtures containing components classified as carcinigenic 
shall be normally classified using only the relevant available information for the individual 
substances in the mixture. Further, in cases where the available test data on the mixture itself 
demonstrate CMR effects which have not been identified from the information on the individual 
substances, those data shall also be taken into account. For CMR endpoints the lowest incidence 
possible to detect in the tests is by far unacceptable in humans. Thus a dose as high as possible 
(such as maximal tolerated dose, MTD dose) is needed to be able to detect CMR hazards. 
Dilution, as would be the case if mixtures or substances containing CMR constituents were 
tested, would increase the risk that CMR hazards would not be detected.  

 
 
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According to article 10 (1) substances in other substances and substances in mixtures are 
treated in the same way regarding the use of GCLs and SCLs. 

3.6.2.6.  Setting of specific concentration limits 

Experimental studies have revealed large variations in the doses of various carcinogenic 
substances needed to induce tumours in animals. Thus, the amounts of chemical carcinogens 
required to induce tumours vary with a factor of up to 108-109 for different compounds. It is 
reasonable to assume that there is similar variation in the potency of substances carcinogenic to 
humans (Sanner and Dybing, 2005). 

The carcinogenic properties of mixtures are normally not tested. The classification and labelling 
of mixtures for carcinogenicity is therefore based on the classification of the ingredients and the 
percentage of each ingredient in the mixture. As indicated in Section 3.6.3 of this Guidance, the 
criteria contain default percentages for classification of mixtures with carcinogenic properties 
but CLP, Article 10.1 allows the use of specific concentration limits (SCL) based on the potency 
of the carcinogen(s). The EU has adopted the T25 concept for carcinogenicity (Dybing et al., 
1997) with additional considerations as a measure for intrinsic potency and a guidance 
document (EC, 1999) to assist in establishing SCLs for carcinogens. By using this approach the 
SCL may occasionally be reduced or raised from the default generic concentration limits. 

3.6.2.7.  Decision logic for classification of substances 

The decision logic which follows is taken from the GHS Guidance. It is strongly recommended 
that the person responsible for classification, study the criteria for classification before and 
during use of the decision logic. 

Does the subststance have carcinogenicity data? 

No 

Classification not possible 

Yes 

According to the criteria, is the substance: 

a. Known to have carcinogenic potential for humans, or 

b. Presumed to have carcinogenic potential for humans? 

Yes 

Application  of  the  criteria  needs  expert  judgement  in  a 
strength and weight of evidence approach. 

No 

Category 1 

Danger 

Category 2 

According to the criteria (see Section 3.6.2), is the 
substance a suspected human carcinogen? 

Yes 

Application of the criteria needs expert judgement in a 
strength and weight of evidence approach. 

Warning 

No 

Not classified 

 
 
 
 
 
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3.6.3.  Classification of mixtures for carcinogenicity 

3.6.3.1.  Classification criteria for mixtures 

Classification of mixtures will be based on the available test data for the individual 
ingredients of the mixture, using cut-off values/concentration limits for those ingredients and 
taking into account potency consideration. The classification may on a case-by-case basis be 
based on the available test data for the mixture as a whole (see Section 3.6.3.1.2 of this 
Guidance) or based on bridging principles (see Section 3.6.3.1.3 of this Guidance). 

3.6.3.1.1.  When data are available for all ingredients or only for some ingredients 

Annex I: 3.6.3.1.1. The mixture will be classified as a carcinogen when at least one ingredient 
has been classified as a Category 1A, Category 1B or Category 2 carcinogen and is present at 
or  above  the  appropriate  generic  concentration  limit  as  shown  in  Table  3.6.2  below  for 
Category 1A, Category 1B and Category 2 respectively. 

Generic concentration limits of ingredients of a mixture classified as carcinogen 
that trigger classification of the mixture 

Table 3.6.2 

Generic concentration limits triggering classification of a 
mixture as: 

Ingredient classified as: 

Category 1 carcinogen 

Category 1A carcinogen 

 0,1 % 

— 

Category 1A 

Category 1B 

Category 2 
carcinogen 

— 

— 

 0,1 % 

— 

 1,0 % [Note 1] 

Category 1B carcinogen 

Category 2 carcinogen 

Note 

— 

— 

The concentration limits in the table above apply to solids and liquids (w/w units) as well as 
gases (v/v units). 

Note 1 

If  a  Category  2  carcinogen  is  present  in  the  mixture  as  an  ingredient  at  a  concentration 
≥ 0,1% a SDS shall be available for the mixture upon request. 

In case a SCL has been established for one or more ingredients these SCLs have precedence 
over the respective GCLs. See Section 3.6.2.6 of this Guidance for the setting of SCLs for 
substances. 

3.6.3.1.2.  When data are available for the complete mixture 

Annex I: 3.6.3.2.1. Classification of mixtures will be based on the available test data for the 
individual ingredients of the mixture using concentration limits for the ingredients classified as 
carcinogens. On a case-by-case basis, test data on mixtures may be used for classification 
when demonstrating effects that have not been established from the evaluation based on the 
individual ingredients. In such cases, the test results for the mixture as a whole must be 
shown to be conclusive taking into account dose and other factors such as duration, 
observations, sensitivity and statistical analysis of carcinogenicity test systems. Adequate 

 
 
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documentation supporting the classification shall be retained and made available for review 
upon request. 

3.6.3.1.3.  When data are not available for the complete mixture: bridging principles 

Annex I: 3.6.3.3.1. Where the mixture itself has not been tested to determine its 
carcinogenic hazard, but there are sufficient data on the individual ingredients and similar 
tested mixtures (subject to the provisions of paragraph 3.6.3.2.1) to adequately characterise 
the hazards of the mixture, these data shall be used in accordance with the applicable 
bridging rules set out in section 1.1.3. 

Bridging principles will only be used on a case by case basis (see Section 3.6.3.1 of this 
guidance). Note that the following bridging principles are not applicable to this hazard class: 

• 
• 

concentration of highly hazardous mixtures 
interpolation within one hazard category 

(see CLP Annex 1, 1.1.3.3 and 1.1.3.4) 

3.6.3.2.  Decision logic for classification of mixtures 

The decision logic which is based on the GHS Guidance is revised to meet CLP requirements. It 
is strongly recommended that the person responsible for classification, study the criteria for 
classification before and during use of the decision logic. 

Classification based on individual ingredients of the mixture 

Does the mixture contain one or more ingredients 
classified as a Category 1 carcinogen at  0.1 %, or 
above a SCL set for the ingredient(s)? 

Yes 

No 

Does the mixture contain one or more ingredients 
classified as a Category 2 carcinogen at  1.0 %, or 
above a SCL set for the ingredient(s)? 

Yes 

No 

Not classified 

Category 1 

Danger 

Category 2 

Warning 

 
 
 
 
 
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Modified classification on a case-by-case basis  

Test data on mixtures may be used for classification when demonstrating effects that have not 
been established from the evaluation based on the individual ingredients (CLP Annex I, 
3.6.3.1.1, see also CLP Article 6(3)). 

Are test data available 
for the mixture 
demonstrating a 
carcinogenic effect not 
identified from the data 
on individual 
substances? 

Yes 

Are the test results on the 
mixture conclusive taking 
into account dose and 
other factors such as 
duration, observations 
and analysis (e.g. 
statistical analysis, test 
sensitivity) of 
carcinogenicity test 
systems? 

No 

No 

Classify in 
appropriate 
category 

Yes 

Danger  

or  

Warning 

Can bridging principles 
be applied? 

Yes 

No 

See above: Classification based on 
individual ingredients of the mixture. 

 
 
 
 
 
 
 
  
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3.6.4.  Hazard communication in form of labelling for carcinogenicity 

3.6.4.1.  Pictograms, signal words, hazard statements and precautionary 

statements 

Annex I: 3.6.4.1 Label elements shall be used in accordance with Table 3.6.3, for substances 
or mixtures meeting the criteria for classification in this hazard class. 

Table 3.6.3 

Label elements for carcinogenicity 

Classification 

Category 1 

Category 2 

(Category 1A, 1B) 

GHS Pictograms 

Signal Word 

Danger 

Warning 

Hazard Statement 

H350: May cause cancer 
(state route of exposure if 
it is conclusively proven 
that no other routes of 
exposure cause the hazard) 

H351: Suspected of causing 
cancer (state route of exposure 
if it is conclusively proven that 
no other routes of exposure 
cause the hazard) 

Precautionary 
Prevention 

Statement 

Precautionary 
Prevention 

Statement 

P201 
P202 
P281 

P201 
P202 
P280 

P201 
P202 
P281 

P201 
P202 
P280 

Precautionary 
Response 

Precautionary 
Storage 

Precautionary 
Disposal 

Statement 

P308 + P313 

P308 + P313 

Statement 

P405 

Statement 

P501 

P405 

P501 

The wording of the Precautionary Statements is found in CLP Annex IV, Part 2. 

Where there is conclusive proof that cancer is caused only by certain route(s), then this route 
may be stated in the hazard statement. In case of Category 1 carcinogens where there is 
conclusive proof that cancer is caused only by inhalation, the hazard phrase ‘H350i: May cause 
cancer by inhalation’ applies (CLP Annex VII, Table 1.1). 

 
 
 
 
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3.6.4.2.  Additional labelling provisions 

There are no additional labelling provisions for carcinogenic substances and mixtures in CLP, 
however there are provisions laid out in Annex XVII to REACH. The packaging of substances 
with harmonised classification as carcinogenic Category 1A or Category 1B, or mixtures 
containing such substances at concentrations warranting classification of the mixture as 
carcinogenic Category 1A or Category 1B, ‘must be marked visibly, legibly and indelibly as 
follows: “Restricted to professional users”.’ (REACH, Annex XVII, point 28. Derogations from 
this obligation are outlined in the same provision). 

3.6.4.3.  Some additional considerations for re-classification 

There are only few situations where the direct translation may lead to different results, 
however, these are likely to be very rare. 

The first difference in applying the CLP criteria is that sufficient evidence (Carc. 1B) for 
carcinogenicity in animals can also be derived from two or more independent studies in one 
species carried out at different times or in different laboratories or under different protocols. 
The second difference applying the CLP criteria is that sufficient evidence (Carc. 1B) for 
carcinogenicity in animals can be derived from an increased incidence of tumours in both sexes 
of a single species in a well-conducted study, ideally conducted under GLP. The criteria 
according to DSD allowed classification in Carc. Cat. 2 (analogous to CLP Carc. 1B) where there 
were positive results in two animal species or clear positive evidence in one species, together 
with supporting evidence such as genotoxicity data, metabolic or biochemical studies, induction 
of benign tumours, structural relationship with other known carcinogens, or data from 
epidemiological studies suggesting an association. 

Another difference can be derived from the IARC classification as ‘possibly carcinogenic to 
humans (IARC 2B)’. This category is used for substances for which there is less than sufficient 
evidence of carcinogenicity in experimental animals. According to IARC, classification as 
‘possibly carcinogenic to humans’ may be derived from solely strong evidence from mechanistic 
and other relevant data. This means that no in vivo carcinogenicity nor (Q)SAR data need to be 
available to arrive at classification for limited evidence of carcinogenicity. 

3.6.5.  Examples of classification for carcinogenicity 

Classification for carcinogenicity involves the consideration of many different factors, as outlined 
above, and is a complex task which needs expert judgement. Therefore no examples of 
classification for carcinogenicity are included in this guidance document. 

3.6.6.  References 

Ashby J, Waters M.D., Preston J., Adlerd I.-D., Douglas G.R., Fielder R., Shelby M.D., 
Anderson D., Sofuni T., Gopalan H.N.B., Becking G. and Sonich-Mullin C.: IPCS harmonization 
of methods for the prediction and quantification of human carcinogenic/mutagenic hazard, and 
for indicating the probable mechanism of action of carcinogens. Mutation Research/Fundamental 
and Molecular Mechanisms of Mutagenesis 352 (1-2), 153-157, 1996. 

Battershill J.M. and Fielder R.J.: Mouse-specific carcinogens: an assessment of hazard and 
significance for validation of short-term carcinogenicity bioassays in transgenic mice. Hum. Exp. 
Toxicol. 17(4), 193-205, 1998. 

Boobis A.R., Cohen S.M., Dellarco V., McGregor D., Meek M.E., Vickers C., Willcocks D., 
Farland W.: IPCS framework for analyzing the relevance of a cancer mode of action for humans. 
Crit. Rev. Toxicol. 36(10), 781-92, 2006. 

Cohen S.M.; Meek M.E., Klaunig J.E.; Patton D.E., Fenner-Crisp P.A.: The Human Relevance of 
Information on Carcinogenic Modes of Action: Overview. Critical Reviews in Toxicology 33(6), 
581-589, 2003. 

 
 
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Cohen S.M.: Human carcinogenic risk evaluation: an alternative approach to the two-year 
rodent bioassay. Toxicol. Sci. 80, 225-229, 2004. 

Cook J.C., Klinefelter G.R., Hardisty J.F., Sharpe R.M., Foster P.M.: Rodent Leydig cell 
tumorigenesis: a review of the physiology, pathology, mechanisms, and relevance to humans. 
Crit. Rev. Toxicol. 29 (2), 169-261, 1999. 

Dybing E., Sanner T., Roelfzema H., Kroese D, Tennant R.W.: T25: A simplified carcinogenic 
potency index. Description of the system and study correlation between carcinogenic potency 
and species/site specificity and mutagenicity. Pharmacol. Toxicol. 80, 272-279, 1997. 

EC: Guidelines for setting specific concentration limits for carcinogens in Annex I of directive 
67/548/EEC. Inclusion of potency considerations. Commission working group on the 
classification and labelling of dangerous substances. Office for the Official Publications of the 
European Communities, Luxembourg, ISBN 92-828-7443-5, 1999. 

EU Commission Group of Specialised Experts in the fields of carcinogenicity, mutagenicity and 
reprotoxicity: Non genotoxic thyroid carcinogens in the rodent bioassay, ECBI/49/99 Add. 1 
Rev. 2 excerpt of agenda point 3.1, 1999.  

EU Commission Group of Specialised Experts in the fields of carcinogenicity, mutagenicity and 
reprotoxicity: Leydig tumours 2004, ECBI/08/04 Rev. 2, 2004  

Fung K.Y., Krewski D., and Smythe R.T: A comparison of tests for trend with historical controls 
in carcinogen bioassay. Canadian J. of Statist. 24, 431-454, 1996. 

Greim H., Gelbke H.-P., Reuter U., Thielmann H.W. and Edler L.: Evaluation of historical control 
data in carcinogenicity studies. Human Exp. Toxicol. 22:541-549, 2003. 

Haseman J.K, Hailey J.R., Morris R.W.: Spontaneous neoplasm incidences in Fischer 344 rats 
and B6C3F-1 mice in two-year carcinogenicity studies: A national toxicology program update. 
Toxicol Pathol. 26(3) 428-441, 1998. 

IARC (1994) Peroxisome. Proliferation and its role in carcinogenesis views and expert opinions 
of an IARC Working Group, Lyon, 7-11 December 1994, Technical Publication No. 24, Lyon, 
France. 

IARC (1999) Scientific Publications No. 147 Species Differences in Thyroid, Kidney and Urinary 
Bladder Carcinogenesis. 

IARC (2003). Predictive value of rodent forestomach and gastric neuroendocrine tumours in 
evaluating carcinogenic risks to humans. Views and expert opinions of an IARC Working Group, 
Lyon, 29 November – 1 December 1999. IARC Technical Publication No. 39, Lyon, France, p.1-
73. 

IARC (2006) Monographs on the Evaluation of Carcinogenic Risks to Humans, Preamble Section 
B, Lyon, France. 

http://monographs.iarc.fr/ENG/Preamble/CurrentPreamble.pdf 

IPCS (1995). Harmonization of the Assessment of Risk for Carcinogenicity and Mutagenicity 
(Germ Cells), Carshalton, UK 1995. IPCS/95.x. 

IPCS (2007) Boobis A.R., Cohen S.M., Dellarco V., McGregor D., Meek M.E., Vickers C., 
Willcocks D., Farland W.: IPCS Framework for Analyzing the Relevance of a Cancer Mode of 
Action for Humans in IPCS Harmonization Project Document No. 4, Part 1, IPCS framework for 
analysing the relevance of a cancer mode of action for humans and case-studies. 
http://www.who.int/ipcs/methods/harmonization/areas/cancer_mode.pdf  

Mati W., Lam G., Dahl C., Thorup Andersen J., Balslev E.: Leydig cell tumour – a rare testicular 
tumour. Int. Urol. Nephrol. 33(1), 103-106, 2002. 

 
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McGregor D., Binaglia M., Boobis A., Botham P., Hennes E.C., Hoffstadt L., Hubbard S., Petry T., 
Riley A., Schwartz D.: 2008 Guidance for the Classification of Carcinogens under the Globally 
Harmonised System of Classification and Labelling of Chemicals (GHS). Submitted for 
publication, 2009. 

Meek M.E., Bucher J.R., Cohen S.M., Dellarco V., Hill R.N., Lehman-McKeeman L.D., 
Longfellow D.G., Pastoor T., Seed J., Patton D.E.: A Framework for Human Relevance Analysis 
of Information on Carcinogenic Modes of Action. Critical Reviews in Toxicology 33(6), 591-653, 
2003. 

NTP (2005) Historical Control Report, Gavage, Corn oil, Sprague-Dawley, Females, 2005. 

http://ntp.niehs.nih.gov/files/HIST_2005SD_TUMOR_RATS1.pdf 

NTP (2007a) Historical Controls Report All Routes And Vehicles. RATS, October 2007.  

http://ntp.niehs.nih.gov/files/HistCont-2007-10-17-Rats_All_Routes.pdf 

NTP (2007b) Historical Controls Report All Routes And Vehicles. MICE, October 2007. 

http://ntp.niehs.nih.gov/files/HistCont-2007-10-17-Mice_All_Routes.pdf 

OECD (2004). OECD Principles for the Validation, for Regulatory Purposes, of (Quantitative) 
Structure-Activity Relationship Models. 

http://www.oecd.org/document/23/0,2340,en_2649_34379_33957015_1_1_1_1,00.html 

OECD (2005). 3.2 Guidance on the Development and Use of Chemical Categories in HPV 
Chemicals Programme 

http://www.oecd.org/document/7/0,2340,en_2649_34379_1947463_1_1_1_1,00.html 

OECD (2007). Report on the Regulatory Uses and Applications in OECD Member Countries of 
(Q)SAR Models in the Assessment of New and Existing Chemicals. ENV/JM/MONO(2006)25 

http://www.oecd.org/dataoecd/55/22/38131728.pdf 

Ozaki, K., Haseman, J.K., Hailey, J.R., Maronpot, R.R., Nyska, A.: Association of adrenal 
pheochromocytoma and lung pathology in inhalation studies with particulate compounds in the 
male F344 rat – the National Toxicology Program Experience, 2002. 

RIVM (2001) report 601516007: Factsheets for the (eco)toxicological risk assessment strategy 
of the National Institute of Public Health and the Environment (RIVM). Editors: R. Luttik and 
M.T.M. van Raaij. 

RIVM (2003) report 601516012: Factsheets for the (eco)toxicological risk assessment strategy 
of the National Institute for Public Health and the Environment - Part IV. Editors: C.E. Smit and 
M.T.M. van Raaij. 

RIVM (2004) report 601516012: Factsheets for the (eco)toxicological risk assessment strategy 
of the National Institute for Public Health and the Environment - Part IV. Editors: C.E. Smit and 
M.T.M. van Raaij. 

RIVM (2005) report 601516013: Factsheets for the (eco)toxicological risk assessment strategy 
of the National Institute for Public Health and the Environment Part V. J.W.A. Scheepmaker, 
C.E. Smit, M.T.M. van Raaij. 

Sanner T. and E. Dybing: Comparison of Carcinogen Hazard Characterisation Based on Animal 
Studies and Epidemiology Basic & Clinical Pharmacology & Toxicology 96, 66–70, 2005. 

Sonich-Mullin C., Fielder R., Wiltse J., Baetcke K., Dempsey J., Fenner-Crisp P., Grant D., 
Hartley M., Knaap A., Kroese D., Mangelsdorf I., Meek E., Rice J.M., Younes M.: IPCS 
Conceptual Framework for Evaluating a Mode of Action for Chemical Carcinogenesis., Regulatory 
Toxicology and Pharmacology 34(2), 146-152, 2001. 

 
 
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http://www.who.int/ipcs/methods/harmonization/areas/cancer/en/ 

Tennant RW. Stratification of rodent carcinogenicity bioassay results to reflect relative human 
hazard. Mutation Research 286, 111-118, 1993. 

WHO working group: Evaluation and use of epidemiological evidence for environmental health 
risk assessment: Who Guideline Document. Env. Health Perspect. 108, 997-1002, 2000. 

 
 
 
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3.7.  REPRODUCTIVE TOXICITY 

3.7.1.  Definitions and general considerations for reproductive toxicity  

Annex I: 3.7.1.1. Reproductive toxicity includes adverse effects on sexual function and 
fertility in adult males and females, as well as developmental toxicity in the offspring. The 
definitions presented below are adapted from those agreed as working definitions in IPCS/EHC 
Document N°225, Principles for Evaluating Health Risks to Reproduction Associated with 
Exposure to Chemicals. For classification purposes, the known induction of genetically based 
heritable effects in the offspring is addressed in Germ Cell Mutagenicity (section 3.5), since in 
the present classification system it is considered more appropriate to address such effects 
under the separate hazard class of germ cell mutagenicity. 

In this classification system, reproductive toxicity is subdivided under two main headings: 

(a) 

(b) 

Adverse effects on sexual function and fertility; 

Adverse effects on development of the offspring. 

Some reproductive toxic effects cannot be clearly assigned to either impairment of sexual 
function and fertility or to developmental toxicity. Nonetheless, substances with these effects, 
or mixtures containing them, shall be classified as reproductive toxicants. 

Annex I: 3.7.1.2. For the purpose of classification the hazard class Reproductive Toxicity is 
differentiated into: 

–  adverse effects 

–  on sexual function and fertility, or 
–  on development; 

–  effects on or via lactation 

Annex I: 3.7.1.3. Adverse effects on sexual function and fertility 

Any effect of substances that has the potential to interfere with sexual function and fertility. 
This includes, but is not limited to, alterations to the female and male reproductive system, 
adverse effects on onset of puberty, gamete production and transport, reproductive cycle 
normality, sexual behaviour, fertility, parturition, pregnancy outcomes, premature 
reproductive senescence, or modifications in other functions that are dependent on the 
integrity of the reproductive systems. 

Annex I: 3.7.1.4. Adverse effects on development of the offspring 

Developmental toxicity includes, in its widest sense, any effect which interferes with normal 
development of the conceptus, either before or after birth, and resulting from exposure of 
either parent prior to conception, or exposure of the developing offspring during prenatal 
development, or postnatally, to the time of sexual maturation. However, it is considered that 
classification under the heading of developmental toxicity is primarily intended to provide a 
hazard warning for pregnant women, and for men and women of reproductive capacity. 
Therefore, for pragmatic purposes of classification, developmental toxicity essentially means 
adverse effects induced during pregnancy, or as a result of parental exposure. These effects 
can be manifested at any point in the life span of the organism. The major manifestations of 
developmental toxicity include (1) death of the developing organism, (2) structural 
abnormality, (3) altered growth, and (4) functional deficiency. 

 
 
 
 
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3.7.1.1.  Special considerations on effects on or via lactation 

This classification is intended to indicate when a substance may cause harm due to its effects on 
or via lactation. This can be due to the substance being absorbed by women and adversely 
affecting milk production or quality, or due to the substance (or its metabolites) being present 
in breast milk in amounts sufficient to cause concern for the health of a breastfed child. 

Annex I: 3.7.1.5. Adverse effects on or via lactation are included under reproductive toxicity, 
but for classification purposes such effects are treated separately. This is because it is 
desirable to be able to classify substances specifically for an adverse effect on lactation so 
that a specific hazard warning about this effect can be provided for lactating mothers. 

Therefore, if the adverse effects that lead to impaired development in the offspring also occur 
after in utero exposure then the substance would also be classified for developmental toxicity. 
In other words, the classification for effects on or via lactation is independent of consideration of 
the reproductive toxicity of the substance, and a substance can be classified for effects on or via 
lactation whether or not the substance is also classified for reproductive toxicity.  

Classification for effects on or via lactation alone is not sufficient for a substance to be subject 
to harmonised classification and labelling in accordance with CLP Article 36 (1).  

3.7.2.  Classification of substances for reproductive toxicity 

3.7.2.1. 

Identification of hazard information  

3.7.2.1.1. 

Identification of human data  

Epidemiological studies as well as clinical data and case reports may be available as stated in 
CLP Annex I, 3.7.2.2.3 and further in the Guidance on IR&CSA, Section R.7.6.3.2. 

3.7.2.1.2. 

Identification of non human data  

In-vitro animal data and non-testing information used for classification is outlined in CLP Annex 
I, 3.7.2.5. and further specific references to different testing methods are listed in the Guidance 
on IR&CSA, Section R.7.6.3.1. 

3.7.2.2.  Classification criteria  

Annex I: 3.7.2.1.1. For the purpose of classification for reproductive toxicity, substances are 
allocated to one of two categories. Within each category, effects on sexual function and 
fertility, and on development, are considered separately. In addition, effects on lactation are 
allocated to a separate hazard category.  

Table 3.7.1 (a) 

Hazard categories for reproductive toxicants 

Categories 

Criteria 

CATEGORY 1 

Known or presumed human reproductive toxicant 

Substances are classified in Category 1 for reproductive toxicity when they 
are known to have produced an adverse effect on sexual function and 
fertility, or on development in humans or when there is evidence from animal 
studies, possibly supplemented with other information, to provide a strong 
presumption that the substance has the capacity to interfere with 
reproduction in humans. The classification of a substance is further 

 
 
 
 
 
 
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Category 1A 

distinguished on the basis of whether the evidence for classification is 
primarily from human data (Category 1A) or from animal data (Category 1B). 

Known human reproductive toxicant 

Category 1B 

The classification of a substance in this Category 1A is largely based on 
evidence from humans. 

Presumed human reproductive toxicant 

The classification of a substance in this Category 1B is largely based on data 
from animal studies. Such data shall provide clear evidence of an adverse 
effect on sexual function and fertility or on development in the absence of 
other toxic effects, or if occurring together with other toxic effects the 
adverse effect on reproduction is considered not to be a secondary non-
specific consequence of other toxic effects. However, when there is 
mechanistic information that raises doubt about the relevance of the effect 
for humans, classification in Category 2 may be more appropriate. 

CATEGORY 2 

Suspected human reproductive toxicant 

Substances are classified in Category 2 for reproductive toxicity when there is 
some evidence from humans or experimental animals, possibly supplemented 
with other information, of an adverse effect on sexual function and fertility, 
or on development, and where the evidence is not sufficiently convincing to 
place the substance in Category 1. If deficiencies in the study make the 
quality of evidence less convincing, Category 2 could be the more appropriate 
classification. 

Such effects shall have been observed in the absence of other toxic effects, 
or if occurring together with other toxic effects the adverse effect on 
reproduction is considered not to be a secondary non-specific consequence of 
the other toxic effects. 

3.7.2.2.1. 

Classification in the presence of parental toxicity 

3.7.2.2.1.1.  Effects to be considered in the presence of marked systemic effects 

In general all findings on reproductive toxicity should be considered for classification purposes 
irrespective of the level of parental toxicity. A comparison between the severity of the effects on 
fertility/development and the severity of other toxicological findings must be performed. 

Fertility effects 

Adverse effects on fertility and reproductive performance seen only at dose levels causing 
marked systemic toxicity (e.g. lethality, dramatic reduction in absolute body weight, coma) are 
not relevant for classification purposes. 

There is no established relationship between fertility effects and less marked systemic toxicity. 
Therefore it should be assumed that effects on fertility seen at dose levels causing less marked 
systemic toxicity are not a secondary consequence of this toxicity. However, mating behaviour 
can be influenced by parental effects not directly related to reproduction (e.g. sedation, 
paralysis), and such effects on mating behaviour may not warrant classification. 

Developmental effects:  

 
 
 
 
 
 
 
 
 
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Annex I: 3.7.2.4. Maternal toxicity 

Annex I: 3.7.2.4.1. Development of the offspring throughout gestation and during the early 
postnatal stages can be influenced by toxic effects in the mother either through non-specific 
mechanisms related to stress and the disruption of maternal homeostasis, or by specific 
maternally-mediated mechanisms. In the interpretation of the developmental outcome to 
decide classification for developmental effects it is important to consider the possible influence 
of maternal toxicity. This is a complex issue because of uncertainties surrounding the 
relationship between maternal toxicity and developmental outcome. Expert judgement and a 
weight of evidence approach, using all available studies, shall be used to determine the 
degree of influence that shall be attributed to maternal toxicity when interpreting the criteria 
for classification for developmental effects. The adverse effects in the embryo/foetus shall be 
first considered, and then maternal toxicity, along with any other factors which are likely to 
have influenced these effects, as weight of evidence, to help reach a conclusion about 
classification. 

Annex I: 3.7.2.4.2. Based on pragmatic observation, maternal toxicity may, depending on 
severity, influence development via non-specific secondary mechanisms, producing effects 
such as depressed foetal weight, retarded ossification, and possibly resorptions and certain 
malformations in some strains of certain species. However, the limited number of studies 
which have investigated the relationship between developmental effects and general maternal 
toxicity have failed to demonstrate a consistent, reproducible relationship across species. 
Developmental effects which occur even in the presence of maternal toxicity are considered to 
be evidence of developmental toxicity, unless it can be unequivocally demonstrated on a case-
by-case basis that the developmental effects are secondary to maternal toxicity. Moreover, 
classification shall be considered where there is a significant toxic effect in the offspring, e.g. 
irreversible effects such as structural malformations, embryo/foetal lethality, significant post-
natal functional deficiencies. 

Annex I: 3.7.2.4.3. Classification shall not automatically be discounted for substances that 
produce developmental toxicity only in association with maternal toxicity, even if a specific 
maternally-mediated mechanism has been demonstrated. In such a case, classification in 
Category 2 may be considered more appropriate than Category 1. However, when a substance 
is so toxic that maternal death or severe inanition results, or the dams are prostrate and 
incapable of nursing the pups, it is reasonable to assume that developmental toxicity is 
produced solely as a secondary consequence of maternal toxicity and discount the 
developmental effects. Classification is not necessarily the outcome in the case of minor 
developmental changes, when there is only a small reduction in foetal/pup body weight or 
retardation of ossification when seen in association with maternal toxicity. 

Adverse effects on postnatal survival and growth seen only at dose levels causing maternal 
toxicity may be due to lack of maternal care or other causes such as adverse effects on or via 
lactation or developmental toxicity. In case post-natal effects are caused by lack of maternal 
care classification for developmental effects may not be warranted. 

3.7.2.2.1.2.  Relevance of specific effects in the parent 

All types of reproductive toxic effects may be considered as secondary to parental toxicity. With 
current knowledge it is not possible to identify specific effects indicating toxicity in parental 
animals which do not have any relevance to reproductive toxicity (e.g. peroxisome 
proliferation). However parental toxicity that is less than marked should not influence the 
classification for reproductive toxicity independent of the specific parental effects observed. 

In general it is very difficult to prove a causal relationship between a parentally mediated 
mechanism and adverse effects in the offspring. Usually data are insufficient to conclude if an 
effect on the offspring is a direct effect or secondary to parental toxicity. In order to determine 
whether a reproductive toxic effect is independent or secondary to a parental effect, it would be 

 
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most appropriate to correlate individual data for offspring and their parents. Nevertheless, 
associations between parental and offspring effects do not by default prove a causal 
relationship. 

In cases where a causal relationship is established between reproductive and parental toxicity 
and the effects on the offspring can be proved to be secondary to maternal toxicity, they may 
still be relevant for developmental classification, dependent on the severity of the effects. 

A comparison between the severity of the maternal toxicity and the severity of the findings in 
the offspring must be performed. There are several examples showing that the developing 
organism can be more susceptible and the long-term consequences can be more severe than in 
the adult. The mother might recover while the offspring could be permanently affected. 

Annex I: 3.7.2.4.4. Some of the end points used to assess maternal effects are provided 
below. Data on these end points, if available, need to be evaluated in light of their statistical 
or biological significance and dose response relationship. 

Maternal mortality: 

an increased incidence of mortality among the treated dams over the controls shall be 
considered evidence of maternal toxicity if the increase occurs in a dose-related manner and 
can be attributed to the systemic toxicity of the test material. Maternal mortality greater than 
10 % is considered excessive and the data for that dose level shall not normally be considered 
for further evaluation. 

Mating index  

(no. animals with seminal plugs or sperm/no. mated x 100)(1) 

Fertility index:   

(no. animals with implants/no. of matings x 100) 

Gestation length  

(if allowed to deliver) 

Body weight and body weight change: 

Consideration of the maternal body weight change and/or adjusted (corrected) maternal body 
weight shall be included in the evaluation of maternal toxicity whenever such data are 
available. The calculation of an adjusted (corrected) mean maternal body weight change, 
which is the difference between the initial and terminal body weight minus the gravid uterine 
weight (or alternatively, the sum of the weights of the foetuses), may indicate whether the 
effect is maternal or intrauterine. In rabbits, the body weight gain may not be useful 
indicators of maternal toxicity because of normal fluctuations in body weight during 
pregnancy. 

Food and water consumption (if relevant): 

The observation of a significant decrease in the average food or water consumption in treated 
dams compared to the control group is useful in evaluating maternal toxicity, particularly 
when the test material is administered in the diet or drinking water. Changes in food or water 
consumption need to be evaluated in conjunction with maternal body weights when 
determining if the effects noted are reflective of maternal toxicity or more simply, 
unpalatability of the test material in feed or water. 

Clinical evaluations (including clinical signs, markers, haematology and clinical chemistry 
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The observation of increased incidence of significant clinical signs of toxicity in treated dams 
relative to the control group is useful in evaluating maternal toxicity. If this is to be used as 
the basis for the assessment of maternal toxicity, the types, incidence, degree and duration of 
clinical signs shall be reported in the study. Clinical signs of maternal intoxication include: 
coma, prostration, hyperactivity, loss of righting reflex, ataxia, or laboured breathing. 

Post-mortem data: 

Increased incidence and/or severity of post-mortem findings may be indicative of maternal 
toxicity. This can include gross or microscopic pathological findings or organ weight data, 
including absolute organ weight, organ-to-body weight ratio, or organ-to-brain weight ratio. 
When supported by findings of adverse histopathological effects in the affected organ(s), the 
observation of a significant change in the average weight of suspected target organ(s) of 
treated dams, compared to those in the control group, may be considered evidence of 
maternal toxicity. 

(1) It is recognised that the Mating index and the Fertility index can also be affected by the 
male. 

3.7.2.2.2. 

Substances causing effects on or via lactation 

Annex I: Table 3.7.1 (b) 

Hazard category for lactation effects 

EFFECTS ON OR VIA LACTATION 

Effects on or via lactation are allocated to a separate single category. It is recognised that 
for many substances there is no information on the potential to cause adverse effects on the 
offspring via lactation. However, substances which are absorbed by women and have been 
shown to interfere with lactation, or which may be present (including metabolites) in breast 
milk in amounts sufficient to cause concern for the health of a breastfed child, shall be 
classified and labelled to indicate this property hazardous to breastfed babies. This 
classification can be assigned on the: 

(a) human evidence indicating a hazard to babies during the lactation period; and/or 

(b) results of one or two generation studies in animals which provide clear evidence of 
adverse effect in the offspring due to transfer in the milk or adverse effect on the quality of 
the milk; and/or 

(c) absorption, metabolism, distribution and excretion studies that indicate the likelihood 
that the substance is present in potentially toxic levels in breast milk. 

There are the two general criteria for this classification. 

i.  …are absorbed by women and have been shown to interfere with lactation.  

This relates to effects in the mother that impact adversely on the breast milk, either in terms of 
the quantity produced or the quality of the milk produced (i.e. the composition). Any effect on 
the quantity or quality of the breast milk is likely to be due to systemic effects in the mother. 
However, overt maternal toxicity may not be seen (e.g. the substance may just affect the 
transfer of a nutrient into the milk with no consequence for the mother). The type and 
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need to be considered on a case-by-case basis to determine whether classification for effects on 
or via lactation is necessary.  

If a substance causes marked overt systemic toxicity in the mother at the same dose level then 
it is possible that this may indirectly impair milk production or impair maternal care as a non-
specific secondary effect. The type and magnitude of the maternal effects and their potential 
influence on lactation/milk production needs to be considered on a case-by-case basis using 
expert judgment. If there is robust evidence to indicate that the effects on lactation are not 
caused directly by the substance then it should not be classified as such. 

A substance which does not cause overt toxicity in the mother but which interferes with milk 
production or quality will normally be classified for effects on or via lactation because in this 
case the effect on lactation is most likely a direct substance-related effect. 

ii. 

 … may be present (including metabolites) in breast milk in amounts sufficient to cause 
concern for the health of a breastfed child. 

This relates to the ability of the substance (including metabolites), to enter the breast milk in 
amounts sufficient to cause a concern. When the effect on the offspring is caused by the 
substance (or metabolite) after transport through the milk then the maternal toxicity has no 
relevance for classification. In general, positive data should usually be available to show that a 
substance leads to an adverse effect in offspring due to effects on lactation to support 
classification. However, in exceptional circumstances, if there are substantiated grounds for 
concern that the substance may have an adverse effect via lactation then it may be classified as 
such in the absence of direct evidence. This should be based on a quantitative comparison of 
the estimated transfer via the milk and the threshold for toxicity in the pups. This might apply 
in cases where the substance has the capacity to bioaccumulate which would lead to a 
potentially higher burden in the offspring, or where there is evidence that the offspring may be 
more sensitive to the substance’s toxicity than adult.  

The mere presence of the substance in the milk alone, without a strong justification for a 
concern to offspring, would normally not support classification for effects on or via lactation.  

3.7.2.3.  Evaluation of hazard information  

Appropriate classification will always depend on an integrated assessment of all available data 
and their interrelationship using a weight of evidence approach. Individual datasets should be 
analysed case by case using expert judgment. 

3.7.2.3.1.  Use of data from standard repeat dose tests  

Fertility effects: 

Toxicological effects, including marked effects, observed in a standard repeat dose study could 
be considered valid for the pre-mating phase for adult females and the pre- and post-mating 
phase for adult males. However in case of contradictions between the standard repeat dose 
studies and reproductive studies, the result from the latter should be considered more relevant.  

For pregnant and lactating females and juveniles data from standard repeat dose studies cannot 
easily be extrapolated.  

Developmental effects: 

A detailed assessment of toxicity in pregnant animals cannot be extrapolated from studies with 
non-pregnant animals. However information from general toxicity studies might give an 
indication of the maternal toxicity that could be anticipated in a subsequent developmental 
toxicity study.  

3.7.2.3.2. 

Study design 

Assessment of the dose-response relationships of parental and reproductive toxicity end points 
and their possible interrelationship require study designs where the dose intervals are not too 

 
 
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far apart. This will improve dose-response assessment and will also reduce the chance of 
masking malformations by severe toxicity (e.g. resorptions, lethality) at high dose levels. This 
may lead to experimental designs in which more than the standard three dose groups and a 
control are tested. Endpoints from repeat dose toxicity studies may be considered useful for 
inclusion in subsequent reproductive toxicity studies. These endpoints should be evaluated both 
in parental animals and in offspring. 

3.7.2.3.3. 

Evaluation of evidence relating to effects on or via lactation 

l.  Human evidence indicating a hazard to babies during the lactation period; 

This criterion acknowledges that human data, e.g. from epidemiological studies or case reports, 
indicating a hazard to babies during the lactation period can also be used to support 
classification for effects on or via lactation. The use of human data is self-explanatory and any 
study should be assessed on its merits for which expert judgment may be required. 
Observations in humans that give evidence of adverse effects in breastfed babies of mothers 
exposed to the chemical in question should be taken to provide clear evidence supporting 
classification. Such studies which do not show an adverse effect need to be considered carefully. 
Human studies investigate the risk under the specific conditions of exposure, and a negative 
finding may just reflect inadequate methods to detect effects or insufficient exposures rather 
than prove the absence of a hazard.  

In practice, useful human data are likely to be rare due to the nature of the endpoint. More 
likely are survey type studies which measure the levels of the chemical in breast milk. Such 
studies may provide useful information on the potential for maternal exposure to lead to the 
presence of the chemical in the breast milk and so they may be of use in assessing the need for 
classification for effects on or via lactation.  

m.  Results of one or two generation studies in animals which provide clear evidence of 

adverse effect in the offspring due to transfer in the milk or adverse effect on the quality 
of the milk; 

Ideally, studies will be available which inform directly on whether the substance causes adverse 
effects in the offspring due to an adverse effect on lactation. One generation or multi-generation 
reproductive toxicity studies, which involve direct exposure or exposure via the milk of the 
offspring postnatally, usually provide information on this. The most common study performed 
today is the two-generation study, but one-generation studies with new study designs, like the 
screening study OECD TG 421/422 or the developmental neurotoxicity study OECD TG 426, also 
exist. The value of these studies is that they directly observe the pups during lactation and any 
adverse effects, such as deaths, decreased viability, clinical signs such as reduced bodyweight 
gain etc, can be directly observed and quantified. However, expert judgement is required to 
decide whether these effects in pups are due to a direct adverse effect on lactation, or are due 
to impaired nursing behaviour which is a non specific secondary consequence of maternal 
toxicity. If the impaired nursing behaviour is proven to be a substance related specific effect on 
behaviour, then classification for effects on or via lactation may be appropriate. It should also 
be noted that some developmental effects resulting from exposure in utero would only manifest 
post-natally and those should not be used for classification for effects on or via lactation. Cross-
fostering studies, where available, may help establish whether effects are due to in utero or 
lactational exposure. If there is sufficient data that animal results are not relevant to humans, 
they should not be taken into account. 

n.  Absorption, metabolism, distribution and excretion studies that indicate the likelihood 

that the substance is present in potentially toxic levels in breast milk; 

The criterion indicates that toxicokinetic studies showing that the substance can be present at 
potentially toxic levels in breast milk can support classification. The implicit assumption behind 
this clause is that the pups may receive a body burden of the toxic entity through suckling that 
is sufficient to cause toxicity when the level of the toxic entity in the milk is above a certain 
threshold level (‘a level to cause concern’). There is no robust way to estimate what this 

 
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threshold is, although the likely body burden expected in the breastfed child may be compared 
to the toxicity data in adults (e.g. an appropriate NOAEL or BMD) to indicate whether toxicity is 
likely.  The mere presence of a substance in the milk, without a robust argument that these 
levels may be potentially toxic to offspring would not normally support classification. 

The toxicokinetics of a substance and the likelihood that it will enter the breast milk may be 
predicted on the basis of the physico-chemical properties of the chemical (e.g. using pKa, logP, 
water solubility, and molecular weight etc) and this information could be used as part of the 
argumentation outlined above. The potential of a substance to bioaccumulate following repeated 
exposure may also be an important factor to consider as this may contribute to the body burden 
reaching a potentially toxic level in the offspring. Studies where the offspring/neonates have 
extended exposure, such as multi-generation studies, implicitly allow for bioaccumulation and 
so findings from these studies can, in themselves, be taken to provide information on the 
potential effects of bioaccumulation. Where these types of studies are not available, potential 
bioaccumulation can be taken into consideration as part of the toxicokinetic assessment using 
expert judgement. 

There may be toxicokinetic and toxicodynamic reasons why neonates may potentially be more 
or less vulnerable to a particular adverse effect than adults due to the fact that certain systems 
(e.g. the immune and metabolic systems) and tissues/organs are immature and are still 
developing. Whether the neonate is more or less vulnerable than adults will depend on the 
specific chemical and will be determined by factors such as the hazardous properties of the 
chemical, its’ physico-chemical properties and how it is metabolised.  Therefore, the relative 
sensitivity of neonates and adults to a substance must be judged on a case by case basis using 
expert judgement. In the absence of any reliable and robust information to inform on this, it 
should be assumed that neonates and adults are equivalent in terms of sensitivity to the 
substance.  

Overall, classification for effects on or via lactation can be assigned on the basis of toxicokinetic 
data or a well substantiated estimate of the exposure through the milk alone provided that it is 
supported by an argument clearly justifying that the level present in the breast milk would be 
likely to harm developing offspring.  

3.7.2.4.  Decision on classification  

According to CLP Annex I, Section 3.7.2.1.1, reproductive toxic substances are allocated to 
either Category 1A, 1B or 2. Effects on lactation are allocated to a separate hazard category and 
should be ascribed to a substance irrespective if it classified in any other category for 
reproductive toxicity or not. 

3.7.2.5.  Classification of substances containing CMR constituents 

From a compositional and a toxicological point of view the situation for substances containing 
CMR constituents, additives or impurities is the same as for mixtures containing components 
classified for these endpoints. For this reason the classification procedure for CMR endpoints 
that is foreseen by CLP for mixtures containing CMR components, is considered applicable also 
to substances containing CMR constituents, additives or impurities (see Section 1.1.6.1). As 
discussed in Section 3.7.3 below, mixtures containing components classified as germ cell 
mutagens shall be normally classified using only the relevant available information for the 
individual substances in the mixture. Further, in cases where the available test data on the 
mixture itself demonstrate CMR effects which have not been identified from the information on 
the individual substances, those data shall also be taken into account. For CMR endpoints the 
lowest incidence possible to detect in the tests is by far unacceptable in humans. Thus a dose as 
high as possible (such as maximal tolerated dose, MTD dose) is needed to be able to detect 
CMR hazards. Dilution, as would be the case if mixtures or substances containing CMR 
constituents were tested, would increase the risk that CMR hazards would not be detected.  

 
 
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According to article 10 (1) substances in other substances and substances in mixtures are 
treated in the same way regarding the use of GCLs and SCLs. 

3.7.2.6.  Setting of specific concentration limits  

Article 10(1) Specific concentration limits and generic concentration limits are limits 
assigned to a substance indicating a threshold at or above which the presence of that 
substance in another substance or in a mixture as an identified impurity, additive or individual 
constituent leads to the classification of the substance or mixture as hazardous. 

Specific concentration limits shall be set by the manufacturer, importer or downstream user 
where adequate and reliable scientific information shows that the hazard of a substance is 
evident when the substance is present at a level below the concentrations set for any hazard 
class in Part 2 of Annex I or below the generic concentration limits set for any hazard class in 
Parts 3, 4 and 5 of Annex I. 

In exceptional circumstances specific concentration limits may be set by the manufacturer, 
importer or downstream user where he has adequate, reliable and conclusive scientific 
information that a hazard of a substance classified as hazardous is not evident at a level 
above the concentrations set for the relevant hazard class in Part 2 of Annex I or above the 
generic concentration limits set for the relevant hazard class in Parts 3, 4 and 5 of that Annex. 

3.7.2.6.1. 

Procedure  

The available data from animal and human studies are evaluated to establish the reproductive 
toxicity dose descriptor, ED10 (effective dose with a 10% effect level above the background), as 
described below. A preliminary conclusion as to whether the substance shows high, medium or 
low potency is taken based on the ED10 data. The preliminary potency evaluation may be 
modified after due consideration of a number of modifying factors as described in Chapter 
3.7.2.6.5. This results in the final potency group. Each final potency group is connected with a 
generic concentration limit (GCL) or a specific concentration limit (SCL). In this way SCLs are 
then set taking into account all relevant considerations. See Figure 3.6. A background document 
containing the justification of the boundaries of the potency groups and the SCLs is available in 
Annex VI to this document. 

It is noted that there may be alternative approaches to assess potency, such as basing it on the 
BMD Methodology (Bench Mark Dose). However such alternative methods are not elaborated in 
this current guidance, although this does not exclude their use.  If alternative approaches are 
used, they have to be clearly justified from a scientific and regulatory point of view (see Article 
10, CLP) and they must be able to provide robust scientific proposals and justifications.  

Figure 3.6  Procedure for setting SCL for reproductive toxicity 

Determine ED10 using the available data 

Determine preliminary potency group 

Determine final potency group considering the modifying factors 

Determine SCL 

 
 
 
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3.7.2.6.2. 

Cases where potency evaluation is difficult or unfeasible 

The process for evaluating potency assumes the availability of certain types of data. However, 
these data may not always be available. Also, the classification of substances as reproductive 
toxicants may be based on information such as grouping, read-across and the use of QSARs 
(Guidance IR&CSA, sections R.6 and R.7.2.3.1). In such cases, no direct estimate of the 
reproductive toxicity potency based on an ED10 value is possible. While there are often good 
reasons for extrapolation of the hazardous properties from one or more substances to another, 
the expected potency of the individual substances within the group may vary. In these cases a 
potency evaluation may be difficult or impossible. However, determination of the classification 
and the potency using non-testing methods is possible in some cases. These cases could include 
interpolation of an ED10 within a group of substances with comparable structures and effects or 
correction for molecular weight in case of extrapolation between different salts with comparable 
availability. If the classification of a substance in Category 2 is done on the basis of ‘limited 
evidence’, the quality of the available data will in such cases determine whether a potency 
assessment is possible. In cases where no further evaluation is possible, the generic 
concentration limits of CLP apply. In general, more conclusive evidence is required when moving 
a substance to a lower potency group than to a higher potency group. 

3.7.2.6.3.  Determination of the ED10 value 

The ED10 value (as used for reprotoxicity SCLs) is the lowest dose which induces reproductive 
toxic effects which fulfil the criteria for classification for reproductive toxicity with an incidence 
or magnitude of 10% after correction for the spontaneous incidence (see in Section 
3.7.2.6.3.2).  

Determining exactly which effect or combination of effects is the one that fulfils the 
classification criteria may seem difficult. However, for the majority of substances in the 
database, the developmental effect(s) observed at the lowest dose level was(/were) an increase 
in malformations and/or lethalities of the offspring. The ED10 for effects on sexual function and 
fertility is mainly based on effects on fertility and histopathological changes of the reproductive 
organs. These effects clearly fulfil the classification requirements. Also, allocation to the final 
SCLs is based on a limited number of potency groups and not on the exact ED10 value. 
Therefore, in practice, it is likely that the ED10 values for several different effects fall into the 
same potency grouping, resulting in the same SCL. 

The ED10 may be obtained either directly or by linear interpolation from experimental data or 
estimated using Bench Mark Dose (BMD) software. The use of BMD software will result in a 
more precise estimate of the ED10 because all data from the dose-response curve are used. The 
use of BMD software is needed when an ED10 cannot be determined using linear interpolation 
due to the absence of a NOAEL when the LOAEL has an effect size above 10%. In general, 
however, the use of BMD software is not required because of the wide potency groups used for 
setting the SCLs. However, it could be important for substances which are close to the boundary 
of a potency group. When an ED10 cannot be calculated by direct or linear interpolation from 
experimental data or by the use of BMD software, interpolation between the control group and 
the LOAEL should be used to determine the ED10. In such cases, only SCLs below the GCL can 
be determined and not those above the GCL, if no other reliable information is available, 
because it may be difficult in these cases to prove the absence of effects at lower dose levels. 

3.7.2.6.3.1.  Determination in practice 

In practice, often several effects on reproduction are observed in various studies, and the 
classification is based on the weight of evidence of all results. As a first step, it should be 
determined whether the classification is for effects on development, for effects on sexual 
function and fertility or both. The effects used for classification for developmental toxicity should 
be used to determine the potency for developmental toxicity only. The same applies to effects 
on sexual function and fertility. This means that for substances fulfilling the criteria for 
classification for both developmental effects and effects on sexual function and fertility, two 

 
 
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ED10 values are derived which may differ and lead eventually to different SCLs.  For both 
developmental effects and effects on sexual function and fertility, the lowest ED10 for the 
effect(s) that fulfil the criteria for classification in the different studies, is then used as the ED10 
that determines the potency of that substance. Where there are doubts as to whether a specific 
effect fulfils the classification criteria, ED10 values for different effects could be taken forward to 
the next step, when modifing factors are considered, to determine the impact.  

The calculation of the ED10 by linear interpolation requires a different approach depending on 
whether the effect is measured as an incidence (quantal data, non-parametric data), a 
magnitude (continuous data, parametric data) or both. 

3.7.2.6.3.2.  Quantal or non-parametric data 

For effects that are measured as changes in incidence, such as an increase in the number of 
malformations or resorptions, the ED10 is defined as the dose level at which 10% of the test 
population above the incidence in the concurrent control shows the effect. There may be 
occasions where the historical control data have to be taken into account (for example when the 
concurrent control data are atypical and close to the extremes of the historical data).   In the 
example in Table 3.10, the ED10 is 90 mg/kg bw/day because at this dose level 12% - 2% 
(control) = 10% of the test population shows the effect above the incidence in the control 
group. 

Table 3.10 Example of the calculation of the ED10 

Dose 

0 mg/kg 

10 mg/kg 

30 mg/kg 

90 mg/kg 

Malformations 

2% 

3% 

7% 

12% 

For some effects the results of the calculation of the ED10 based on the incidence in pups may 
be different from that based on the incidence in litters. Scientific evidence may indicate which 
parameter is more appropriate, but in the absence of such information it is not possible to 
estimate which ED10 is more appropriate for a specific effect. In such cases, both the incidence 
in offspring and the incidence in litters should be calculated, and the lower ED10 value should be 
used. 

3.7.2.6.3.3.  Continuous or parametric data 

For effects that are measured as changes in magnitude such as mean pup weight or testis 
weight, the ED10 is defined as the dose at which a change of 10%, compared to the concurrent 
control group, is observed.  In the example in Table 3.11, the ED10 is 19.3 mg/kg bw/day 
because at this dose level the mean foetal bodyweight is calculated to be 90% of the control 
value. A 10% reduction of the control value of 6.2 g gives 5.58 g. Interpolation between 10 and 
30 mg/kg bw/day to a dose level which would be expected to result in a foetal bodyweight of 
5.58 g gives a value of 19.3 mg/kg bw/day.  

Calculations:  

(30 – 10)/(6 - 5.1) = 22.2; 6.0 – 5.58 = 0.42; 0.42 x 22.2 = 9.3; 10 + 9.3 = 19.3 mg/kg 
bw/day. 

Table 3.11 Example on the calculation of the ED10 

Dose 

0 mg/kg  10 mg/kg  30 mg/kg  90 mg/kg 

Mean foetal bodyweight (g) 

6.2 

6.0 

5.1 

4.5 

NOAEL 

LOAEL 

 
 
 
 
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3.7.2.6.3.4.  Data combining incidence and magnitude 

Some effects such as histopathological changes in the testis are a combination of effects on 
incidence and magnitude (grading of the effect by a pathologist). However, calculation of an 
ED10 taking both the incidence and the magnitude into account is not possible or at least more 
complex.  The ED10 should therefore be based on the incidence of the effect below or above a 
certain magnitude. The magnitude of the effects that will be selected as a starting point has to 
be chosen carefully. Normally the particular effect size would be the lowest relevant for the 
respective classification. The ED10 is then determined as the dose level at which the incidence, 
of effects with a magnitude above that of the starting point, is 10% above the incidence in the 
control group. In practice this means that the grading system is converted into a simplified 
system where only percentages of animals in each dose group with an effect with a magnitude 
above the starting point are regarded as positive. However, it is recognised that this approach 
uses only a part of the actual data and is imprecise, and it may be appropriate that other effects 
also be considered in determining the ED10. 

Table 3.12 Example on the calculation of the ED10 for testicular effects (N=10) 

Dose (mg/kg) 

Testicular degeneration (n) 

none  slight  moderate  marked  severe 

0 

10 

30 

90 

4 

5 

5 

0 

5 

5 

4 

0 

1 

0 

1 

4 

0 

0 

0 

2 

0 

0 

0 

4 

NOAEL 

LOAEL 

For the example in Table 3.12, the effects observed in the 10 mg/kg and 30 mg/kg dose groups 
have to be considered as equivalent to the effects of the control group so the NOAEL is 30 
mg/kg. The magnitude of the testicular effect in the control group and the 10 and 30 mg/kg 
bw/day groups is slight or less. Because of the incidence observed in these three groups, the 
level of damage estimated as the starting point magnitude is ‘slight’. The ED10 is then defined as 
a 10% increase of moderate effects or more above the control. In this example the incidences 
for moderate testicular degeneration or more are 10%, 0%, 10% and 100% at respectively 0, 
10, 30 and 90 mg/kg bw/day. The ED10 is then defined as the dose level with 20% (control plus 
10%) of moderate testicular effects. The ED10 would be 36.6 mg/kg bw/day based on 
interpolation between 30 and 90 mg/kg bw/day to a dose with 20% animals with moderate 
testicular degeneration or higher. 

3.7.2.6.3.5.  Specific data types 

Non-oral studies 

In most cases only oral studies will be available and used for determination of the potency. 
However, if the classification is based on the effects seen in non-oral studies or only non-oral 
studies are available, then these data should also be used to determine the potency. This 
requires route-to-route extrapolation of the external dermal or inhalatory dose to a 
corresponding oral dose. This should be done as described in the ECHA Guidance on information 
requirements and chemical safety assessment in REACH (IR&CSA, section R.8). 

Extrapolation from dermal exposure to oral exposure should only be done when there are 
sufficient kinetic data on dermal availability because assuming a high dermal availability is not a 
worst case assumption. In cases where such data are not available a direct comparison of the 
dermal dose with the oral potency ranges could be performed in exceptional cases. However, 
such comparison should not result in moving the substance to a lower potency group (higher 

 
 
 
 
 
 
 
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ED10) – only moving the substance to a higher potency group (lower ED10) should be 
considered. 

Extrapolation from inhalatory exposure to oral exposure can only be done when there are 
sufficient kinetic data on inhaled availability because assuming a high inhaled availability is not 
a worst case assumption. If no inhalatory information on availability is available then it should 
be assumed that the inhalation and oral availability are comparable. However, such comparison 
should not result in moving the substance to a lower potency group (higher ED10) – only moving 
the substance to a higher potency group (lower ED10) should be considered. 

Human data 

The use of human data for ED10 calculation has several drawbacks including limited data on 
exposure, limited data on the size of the exposed population and limited information on whether 
the exposure included the window of sensitivity. For all these reasons, it is difficult to determine 
an ED10 based on human data. Therefore, and because in most instances animal data are also 
available for determining an ED10, these data are evaluated together on a case by case basis. 
Guidance on the use of human data for the derivation of DNELs and DMELs has been developed 
by ECHA and is available at the ECHA website, see 
http://guidance.echa.europa.eu/guidance4_en.htm 

3.7.2.6.4. 

Provisional evaluation of the potency classification 

A preliminary potency evaluation applying the ED10 value is made at this stage. 

ED10 values can be used to place substances classified as a reproductive toxicant into selected 
ranges that define potency groups. In this way, it is possible to identify reproductive toxicants 
of high, medium and low potency. For the purpose of determining the preliminary potency 
group, the boundaries in Table 3.13 are used. 

Table 3.13 Boundaries of the potency groups69. 

Potency group 

Boundaries 

High potency group 

ED10 value ≤ 4 mg/kg bw/day 

Medium potency group 

4 mg/kg bw/day < ED10 value   400 mg/kg bw/day 

Low potency group 

ED10 value   400 mg/kg bw/day. 

3.7.2.6.5.  Modifying factors 

Modifying factors are a means to account for case-specific data situations which indicate that 
the potency group for a substance as obtained by the preliminary assessment, should be 
changed. While most modifying factors would result in a higher potency group than the 
preliminary one, also the opposite could occur: If substance-specific knowledge is available 
(such as e.g. toxicokinetic information on a higher bioavailability in test animals vs. humans), 
also a lower potency class might be assigned. 

While some modifying factors should always be taken into account, other modifying factors 
could be more relevant when the potency is close to the boundary between two groups (see 
Table 3.13 above).  

Some modifying factors are of a more qualitative nature. When applied, they will simply point to 
a potency group different from the one resulting from the preliminary assessment. Other 
modifying factors might be quantifiable, at least on a semi-quantitative scale. In such cases, a 
potency group higher (or lower) than the preliminary one should be chosen if the estimated size 

69 See Annex VI of this guidance document for more details. 

 
 
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of the modifying factor exceeds the distance of the preliminary ED10 to the border of the 
relevant (higher or lower) adjacent potency group. 

Furthermore, for some substances more than one modifying factor will apply. It will then take 
expert judgement to decide on how to reasonably combine all of these individual factors into 
one overall modifying factor. In exceptional cases, such a combination of individual factors 
might even result in a change of two potency classes (e.g. assignment of the high potency 
class, where the preliminary assessment had resulted in the low potency class).   

In this context, it should be noted that several of the modifying factors may be interrelated. 
Moreover, some factors may have already been taken into account in deciding on the 
classification as a reproductive toxicant. Where such considerations have been made, care 
should be taken not to use that information again when determining the potency. For example, 
when the effects determining the ED10 were observed at dose levels also causing maternal 
toxicity, this should already have been taken into consideration during the classification and 
should not be used again to set a higher SCL.   

3.7.2.6.5.1.  Type of effect / severity 

The type of effect(s) resulting in the same classification as reproductive toxicant differs between 
substances. Some effects could be considered as more severe than others, however, ranking 
different effects based on their severity is controversial and difficult to establish criteria. 
Further, the effects of a developmental toxicant can differ between dose levels from variations 
via malformations to death of the foetuses. The adverse effects on fertility and sexual function 
of a substance can differ between dose levels from small changes in testes histopathology 
through effects on fertility to an irreversible and complete absence of fertility. As the difference 
between the dose levels is often smaller than the proposed potency groups (factor 10-100) this 
will make no difference in most cases. Also classification is in most cases based on severe 
effects like malformations or death of the foetuses for developmental toxicants and effects on 
fertility or histopathological changes of the reproductive organs for fertility toxicants. For most 
classified substances such severe effects were already observed at the lowest dose with 
reproductive effects (Muller et al, 2012). Therefore, differentiation between types of effect is 
considered to have limited added value. Exceptions can be dealt with on a case by case basis. 

For example, if the ED10 results in a preliminary conclusion for the medium potency group but is 
close to the border for the high potency group and the ED10 is based on a severe effect like 
malformations or irreversible effects on sexual function and fertility then using the higher 
potency group (lower ED10) for that substance should be considered. To determine what is ‘close 
to the border’ is to compare the distance to the next category border with the significance of 
modifying factors.  

3.7.2.6.5.2.  Data availability 

There are several aspects to this modifying factor, some of which are:  

• 

• 

limited data availability where certain test protocols are lacking and therefore certain 
parameters have not been evaluated; 

limited data availability where the spectrum of evaluated parameters is sufficient, but 
only studies with limited duration are available; and 

• 

limited data availability where only a LOAEL, but no NOAEL could be identified. 

Where only limited data are available, such as a screening study (OECD 421 and 422), a 28-day 
repeated dose toxicity study or non-OECD studies which do not exclude the presence of 
reproductive effects at lower dose levels, the calculated ED10 should not be used to set a SCL 
above the GCL.  

Furthermore it should be considered to assign a modifying factor accounting for the limitations 
in the database in a similar approach to the one used in deriving DNELs under REACH. Guidance 
regarding the potential size of such a factor can be obtained from ECHA’s Guidance on IR&CSA 

 
 
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R.8 (‘Characterisation of dose [concentration]-response for human health’). Section R.8.4.3.1 
‘Assessment of factors relating to extrapolation’, gives recommendations on how to set factors 
for extrapolating to longer study durations as well as for compensation of the lack of a NOAEL 
or of the generally poor quality of a database.  

If there are only limited data which result in an ED10 in the medium potency group which is 
close to the border for the high potency group, then using the higher potency group should be 
considered. For example an ED10 of 8 mg/kg bw/day might have been  estimated based on a 
LOAEL for malformations in the absence of a NOAEL, This ED10 is only higher by a factor of 2 
(i.e 2 times the border of the high potency group of 4 mg/kg bw/d : see. Table 3.7.2.5.4 
above), and assigning the high potency group should be considered until additional data at 
lower dose levels are available. Thus, there is uncertainty, if the ED10 based on extrapolation 
from and below the LOAEL in the absence of a NOAEL and a correction may be justified. The 
size of this uncertainty could be determined by the BMDL (Benchmark dose lower 95%-
confidence bound). In such cases, the BMDL could be used as a potency estimate instead of the 
ED10. 

3.7.2.6.5.3.  Dose-response relationship 

The ED10 will in most cases probably be in the same range as the NOAEL and LOAEL. However, 
in cases of a shallow dose effect relationship curve, the LOAEL may sometimes be clearly below 
the ED10. In such situations, if a substance would fall into a lower potency group based on the 
ED10 but into a higher potency group based on the LOAEL then the higher potency group should 
be used for that substance. 

3.7.2.6.5.4.  Mode or mechanism of action 

It is assumed that effects observed in animal studies are relevant to humans. Where it is known 
that the mode or mechanism of action is not relevant for humans or is of doubtful relevance to 
humans, this should have been taken into account in the classification and should not be used 
again as a modifying factor for potency. However, quantitative differences in toxicodynamics 
can be taken into account when not already taken into account in the classification. In cases 
where mechanistic information shows a lower sensitivity in humans than in experimental 
animals, this may move substances which are close to the potency boundaries to a lower 
potency group. In cases where mechanistic information indicates a higher sensitivity in humans 
than in experimental animals, this may move substances near the potency boundaries to a 
higher potency group. In general, more conclusive evidence is required when moving a 
substance to a lower potency group than to a higher potency group. 

3.7.2.6.5.5.  Toxicokinetics 

The toxicokinetics of a substance can differ between the tested animal species and humans. 
Where a difference is known this should be taken into account when determining the potency 
group of a substance. This should be based on a comprehensive knowledge of all involved 
toxicokinetic factors and not only on a single parameter. Also differences in kinetics between 
pregnant and non-pregnant animals and transport to the foetus should be taken into account. 
Based on the available data, quantification of this modifying factor has to be performed on a 
case by case basis. This modifying factor can work in both directions, as e.g. bioavailability in 
humans might be known to be lower or higher than in the animal species tested.. In general, 
more conclusive evidence is required when moving a substance to a lower potency group than 
to a higher potency group. 

3.7.2.6.5.6.  Bio-accumulation of substances 

The study design of, for example, developmental studies is aimed at exposure only during 
development. For substances which bio-accumulate, the actual exposure in the time window of 
sensitivity for some developmental effects may therefore be much lower than when exposure at 
the same external dose level would have started long before the sensitivity window. 
Furthermore, human exposure may occur for a long period before the sensitive window. This 

 
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should be taken into account when determining the potency group. For substances for which no 
experimental data are available with respect to their potential for accumulation, section R.7.12 
of ECHA’s IR&CSA Guidance R.7c (‘Endpoint specific guidance’) provides some hints on how to 
make an informed estimate about a respective concern. 

‘Suspected’ bio-accumulating substances should be considered as to whether they should be 
moved into the next higher potency group (lower ED10). However this should be considered on a 
case by case basis and the ‘suspected’ bio-accumulation ability should be justifed. In the case 
that the following evidence should be available, the higher potency group would not be 
necessary:  

• 

• 

the relevant studies used for the ED10 were performed in a way that internal doses could 
have been expected to have reached a steady state during a sufficiently long part of the 
study time, and in particular with developmental studies during critical time windows of 
development, or 

the increase in the internal dose caused by the accumulation versus that following a 
single administration, is smaller than the distance between the ED10 and the border to 
the next higher potency group. 

For example, if a substance preliminarily assigned to the medium potency group is known or 
suspected to be bio-accumulative and the ED10 for development has been obtained from a pre-
natal developmental study in rats without any significant pre-treatment of the dams before 
mating, assignment to the high potency category should be considered. Conversely, if reliable 
toxicokinetic data demonstrate that steady state plasma levels after prolonged repeated 
administration do not exceed those after single exposure by more than a factor of 2, while the 
preliminary ED10 is 20 mg/kg bw/d (i.e. factor 5 from the border to the high potency category) 
changing the potency class might not appear necessary. 

3.7.2.6.6. 

Assigning specific concentration limits (SCLs) 

Based upon the preliminary potency evaluation using only the ED10 and applying the modifying 
factors, a substance can be placed in the final potency group using the table below. The GCL or 
SCL of that substance can then be found in the same table. 

 
 
 
 
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Table 3.14 SCLs for substances in each potency group and classification category 

Category 1 

Category 2 

Dose 

SCL 

Dose 

Group 1  

high potency 

ED10 below 4 
mg/kg bw/day 

Group 2  

medium potency 

ED10 > 4 mg/kg 
bw/day, and < 
400 mg/kg 
bw/day 

0.03% 

(factors of 10 
lower for 
extremely 
potent 
substances B) 

0.3% (GCL) 

ED10 below 4 
mg/kg bw/day 

ED10 > 4 mg/kg 
bw/day, and < 
400 mg/kg 
bw/day 

SCL 

0.3% 

(factors of 10 
lower for 
extremely 
potent 
substances B)  

3% (GCL) 

Group 3  

low potency 

ED10 above 400 
mg/kg bw/day 

3%  

ED10 above 400 
mg/kg bw/day 

3-10% A 

A The limit of 10% may be considered in certain cases, such as for substances with a ED10 value 
above 1000 mg/kg bw/day and a NOAEL below 1000 mg/kg bw/day. 

B For substances with an ED10 more than 10 fold below 4 mg/kg bw/day, meaning an ED10 
below 0.4 mg/kg bw/day, a 10-fold lower SCL should be used. For even more potent substance 
the SCL should be lowered with a factor of 10 for every factor of 10 the ED10 is below 4 mg/kg 
bw/day. 

3.7.2.6.6.1.  Assigning two SCLs to a substance  

A substance toxic to reproduction is classified in one category for both effects on development 
and on sexual function and fertility. Within each category effects on development and on sexual 
function & fertility are considered separately. The potency and resulting concentration limits 
have to be determined separately for the two main types of reproductive toxic effects. In case 
the potency and resulting specific concentration limits are different for sexual function/fertility 
and development for a substance, the substance needs to be assigned one SCL for 
developmental toxicity and another SCL for effects on sexual function and fertility. These 
concentration limits will in all cases trigger different specifications of the hazard statements for 
the two main types of effects, to be applied to mixtures containing the substance (see also 
3.7.4.1, Annex I, CLP) 

 
 
 
 
 
 
 
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3.7.2.7.  Decision logic for classification of substances 

The decision logic which follows is provided here as additional guidance. It is strongly 
recommended that the person responsible for classification study the criteria before and during 
use of the decision logic.  

Classification of substances for fertility or developmental effects 

Does the substance have data on reproductive toxicity? 

Yes 

No 

Classification 
not possible 

Category 1 

According to the criteria, is the substance: 

(a) Known human reproductive toxicant, or 

Yes 

(b) Presumed human reproductive toxicant? 

Application of the criteria needs expert judgment in 
a weight of evidence approach. 

Danger 

No 

According  to  the  criteria,  is  the  substance  a 
suspected human reproductive toxicant? 

Yes 

Application of the criteria needs expert judgment in 
a strength and weight of evidence approach. 

No 

Not classified 

Category 2 

Warning 

Classification of substances for effects via lactation 

Does the substance according to the criteria cause 
concern for the health of breastfed children? 

Yes 

Additional 
category for 
effects on or 
via lactation 

No 

Not classified 

 
 
 
 
 
 
 
 
 
  
 
  
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3.7.3.  Classification of mixtures for reproductive toxicity  

3.7.3.1.  Classification criteria for mixtures 

Reproductive toxicity classification of mixtures is based on the presence of an ingredient 
classified for reproductive toxicity (see CLP Article 6(3) and Annex I, 3.7.3). Only in case there 
is data available for the mixture itself which demonstrate effects not retrieved from the 
ingredients, this data might be used for classification. If such data is not available for the 
mixture itself, data on a similar mixture can be used in accordance to the bridging principle (see 
CLP Annex I, 1.1.3).  

Generic concentration limits of ingredients of a mixture classified as reproduction 
toxicants or for effects on or via lactation that trigger classification of the mixture 

Annex I: Table 3.7.2 

Generic concentration limits triggering classification 
of a mixture as: 

Ingredient classified as: 

Category 1 reproductive 
toxicant   

Category 1A 

Category 1B 

Category 2 
reproductive 
toxicant 

Additional 
category for 
effects on or via 
lactation 

Category 1A  reproductive 
toxicant 

 0,3 % 
[Note 1] 

Category 1B  reproductive 
toxicant 

Category 2 
toxicant 

reproductive 

Additional  category 
for 
effects on or via lactation 

Note 

 0,3 % 
[Note 1] 

 3,0 % 
[Note 1] 

 0,3 % 
[Note 1] 

The concentration limits in Table 3.7.2 apply to solids and liquids (w/w units) as well as gases 
(v/v units). 

Note 1 

If a Category 1 or Category 2 reproductive toxicant or a substance classified for effects on or 
via lactation is present in the mixture as an ingredient at a concentration at or above 0,1 %, a 
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3.7.3.1.1.  When data are available for the individual ingredients 

Annex I: 3.7.3.1.1. The mixture shall be classified as a reproductive toxicant when at least 
one ingredient has been classified as a Category 1A, Category 1B or Category 2 reproductive 
toxicant and is present at or above the appropriate generic concentration limit as shown in 
Table 3.7.2 below for Category 1A, Category 1B and Category 2 respectively. 

Annex I: 3.7.3.1.2. The mixture shall be classified for effects on or via lactation when at 
least one ingredient has been classified for effects on or via lactation and is present at or 
above the appropriate generic concentration limit as shown in Table 3.7.2 for the additional 
category for effects on or via lactation. 

3.7.3.1.2.  When data are available for the complete mixture 

Annex I: 3.7.3.2.1 Classification of mixtures will be based on the available test data for the 
individual ingredients of the mixture using concentration limits for the ingredients of the 
mixture. On a case-by-case basis, test data on mixtures may be used for classification when 
demonstrating effects that have not been established from the evaluation based on the 
individual components. In such cases, the test results for the mixture as a whole must be 
shown to be conclusive taking into account dose and other factors such as duration, 
observations, sensitivity and statistical analysis of reproduction test systems. Adequate 
documentation supporting the classification shall be retained and made available for review 
upon request. 

3.7.3.1.3.  When data are not available for the complete mixture: bridging principles 

Annex I: 3.7.3.3.1 Subject to the provisions of paragraph 3.7.3.2.1, where the mixture itself 
has not been tested to determine its reproductive toxicity, but there are sufficient data on the 
individual ingredients and similar tested mixtures to adequately characterise the hazards of 
the mixture, these data shall be used in accordance with the applicable bridging rules set out 
in section 1.1.3. 

Bridging Principles will only be used on a case by case basis (see Section 3.7.3.1 of this 
guidance). Note that the following bridging principles are not applicable to this hazard class: 

• 

• 

concentration of highly hazardous mixtures 

interpolation within one hazard category 

(see CLP Annex 1, 1.1.3.3 and 1.1.3.4) 

 
 
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3.7.3.2.  Decision logic for classification of mixtures 

The decision logic which follows is provided here as additional guidance. It is strongly 
recommended that the person responsible for classification study the criteria before and during 
use of the decision logic.  

Classification of mixtures for fertility or developmental effects 

Classification based on individual ingredients of the mixture 

Does the mixture contain one or more ingredients 
classified as a Category 1 reproductive toxicant at  
0.3% or above the SCL? 

Yes 

No 

Does the mixture contain one or more ingredients 
classified as a Category 2 reproductive toxicant at  3 % 
or above the SCL?  

Yes 

No 

Not classified 

Category 1 

Danger 

Category 2 

Warning 

 
 
 
 
 
  
 
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Modified classification on a case-by-case basis  

Test data on mixtures may be used for classification when demonstrating effects that have not 
been established from the evaluation based on the individual ingredients (CLP Annex I, 
3.7.3.1.1, see also CLP Article 6(3)).  

Are test data available 
for the mixture itself 
demonstrating a 
reproductive toxic effect 
not identified from the 
data on individual 
substances? 

Yes 

Are the test results on the 
mixture conclusive taking 
into account dose and 
other factors such as 
duration, observations 
and analysis (e.g. 
statistical analysis, test 
sensitivity) of 
reproductive toxicity test 
systems? 

No 

No 

Classify in 
appropriate 
category 

Yes 

Danger  

or  

Warning 

Can bridging principles 
be applied? 

Yes 

No 

See above: Classification based on 
individual ingredients of the mixture. 

 
 
 
 
 
 
 
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Classification of mixtures for effects via lactation 

Classification based on individual ingredients of the mixture  

Does the mixture contain one or more 
ingredients classified for effects on or via 
lactation at  0.3 % or above the SCL? 

Yes 

Additional 
category for 
effects on or 
via lactation 

No 

Not classified 

Modified classification on a case-by-case basis 

Test data on mixtures may be used for classification when demonstrating effects that have not 
been established from the evaluation based on the individual ingredients (CLP Annex I, 3.7.3.1.1, 
see also CLP Article 6(3)).  

Are test data available 
for the mixture itself 
demonstrating effects 
on or via lactation not 
identified from the data 
on individual 
substances? 

Yes 

The test results for the 
mixture as a whole must 
be shown to be conclusive 
taking into account dose 
and other factors such as 
duration, observations, 
sensitivity and statistical 
analysis of reproductive 
toxicity test systems. 

No 

No 

Yes 

Additional 
category for 
effects on or 
via lactation 

or 

No 
classification 

Can bridging principles 
be applied? 

Yes 

No 

See above: Classification based on 
individual ingredients of the mixture. 

 
 
 
 
 
 
  
 
 
 
 
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3.7.4.  Hazard communication in form of labelling for reproductive toxicity 

3.7.4.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

Annex I: 3.7.4.1. Label elements shall be used for substances or mixtures meeting the 
criteria for classification in this hazard class in accordance with Table 3.7.3. 

Table 3.7.3 

Label elements for reproductive toxicity 

Classification 

Category 1 

Category 2 

(Category 1A, 1B) 

GHS Pictograms 

Additional category 
for effects on or via 
lactation 

No pictogram 

Signal Word 

Danger 

Warning 

No signal word 

Hazard Statement 

H360: May damage 
fertility or the unborn 
child (state specific 
effect if known)(state 
route of exposure if it is 
conclusively proven 
that no other routes of 
exposure cause the 
hazard) 

H361: Suspected of 
damaging fertility or the 
unborn child (state 
specific effect if known) 
(state route of exposure 
if it is conclusively 
proven that no other 
routes of exposure 
cause the hazard) 

H362: May cause 
harm to breast-fed 
children. 

Precautionary 
Statement 
Prevention 

P201 
P202 
P280 

P201 
P202 
P280 

P201 
P260 
P263 
P264 
P270 

Precautionary 
Statement 
Response 

Precautionary 
Statement Storage 

Precautionary 
Statement 
Disposal 

P308 + P313 

P308 + P313 

P308 + P313 

P405 

P501 

P405 

P501 

 
 
 
 
 
 
 
 
 
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Annex VII: Note 4 under Table 1.1 

Note 4  

Hazard  statements  H360  and  H361  indicate  a  general  concern  for;effects  on  fertility  and/or 
development: “May damage/Suspected of damaging fertility or the unborn child”. According to 
the criteria, the general hazard statement can be replaced by the hazard statement indicating 
the specific effect of concern in accordance with section 1.1.2.1.2. of Annex VI. When the other 
differentiation  is  not  mentioned,  this  is  due  to  evidence  proving  no  such  effect,  inconclusive 
data or no data and the obligations in Article 4(3) shall apply for that differentiation. 

Annex VI: 1.2.3 Hazard statements for reproductive toxicity 

[…]  

According to the criteria, the general hazard statement can be replaced by the hazard statement 
indicating the specific effect of concern in accordance with section 1.1.2.1.2. When the other 
differentiation  is  not  mentioned,  this  is  due  to  evidence  proving  no  such  effect,  inconclusive 
data or no data and the obligations in Article 4(3) shall apply for that differentiation.  

[…] 

Hazard statements H360 and H361 indicate a general concern for effects on fertility and/or 
development. As shown in CLP Annex I, Table 3.7.3, a substance classified as reproductive 
toxicant in Category 1A or 1B must be assigned the hazard statements H360 and a substance 
classified in Category 2 must be assigned H361. Each of these two hazard statements includes 
the mentioning of the adverse effects on sexual function and fertility or adverse effects on 
development of the offspring. 

The effects of concern should be specified in the hazard statement. Where the effect cannot be 
specified with respect to fertility or development the general statement must be applied.  

When the other differentiation is not mentioned in the CLP Annex VI, this can be due to one of 
the reasons listed in Note 4 under Table 1.1 in CLP Annex VII (see above).  In this case the 
obligations under Article 4(3) CLP must apply, i.e. classification under Title II shall be carried 
out for this differentiation.  

Self classification must take into account all available relevant data including published RAC 
documents for Harmonised Classification and Labelling (RAC opinions, background documents 
and responses to comments as available on ECHA website in section Risk Assessment 
Committee http://echa.europa.eu). 

The resulting different variants of H360 and H361 are shown in the table below, which also 
provides some examples when they can be assigned. 

Table 3.15 Hazard statements for reproductive toxicity: H360 and H361, and their specifications

H No.  

Hazard statement 

H360 

‘May damage fertility or the unborn child’ 

Example: a substance classified in Repr Cat 1 A/B but the effects cannot be specified with 
respect to fertility and/or developmental toxicity. 

H361 

‘Suspected of damaging fertility or the unborn child’ 

Example: a substance classified in Repr Cat 2 but the effects cannot be specified with 
respect to fertility and/or developmental toxicity. 

 
 
 
 
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H No.  

Hazard statement 

H360F 

‘May damage fertility’ 

Example: a substance classified in Repr Cat 1A/B on the basis of fertility effects.  For the 
effects on developmental toxicity there is evidence providing no such effect, inconclusive 
data or no data.  

H360D 

‘May damage the unborn child’ 

Example: a substance classified in Repr Cat 1A/B on the basis of developmental toxicity. For 
the effects on fertility there is evidence providing no such effect, inconclusive data or no 
data.   

H361f 

‘Suspected of damaging fertility’ 

Example: a substance classified in Repr Cat 2 on the basis of fertility effects. For the effects 
on developmental toxicity there is evidence providing no such effect, inconclusive data or no 
data.   

H361d 

‘Suspected of damaging the unborn child’ 

Example: a substance classified in Repr Cat 2 on the basis of developmental toxicity. For the 
effects on fertility there is evidence providing no such effect, inconclusive data or no data. 

H360F
D 

‘May damage fertility. May damage the unborn child.’ 

Example: a substance classified in Repr Cat 1A/B on the basis of fertility effects and 
developmental toxicity. 

H361fd 

‘Suspected of damaging fertility. Suspected of damaging the unborn child.’ 

Example: a substance classified in Repr Cat 2 on the basis of fertility effects and 
developmental toxicity. 

H360Fd 

‘May damage fertility. Suspected of damaging the unborn child.’ 

Example: a substance classified in Repr Cat 1A/B on the basis of fertility effects and which 
fulfills the criteria for Repr Cat 2 on the basis of developmental toxicity. 

H360Df 

‘May damage the unborn child. Suspected of damaging fertility.’ 

Example: a substance classified in Repr Cat 1A/B on the basis of developmental toxicity and 
which fulfills the criteria for Repr Cat 2 on the basis of fertility effects. 

According to CLP Annex I, Section 3.7.4.1, the hazard statements must be adapted by 
specifying the route of exposure if it is conclusively proven that no other routes of exposure will 
lead to an adverse effect on sexual function or fertility or development of the offspring. When 
conclusively proven, it is meant that valid in vivo test data need to be available for all three 
exposure routes clearly indicating that only one exposure route has caused positive results i.e. 
adverse effects on the reproduction. Moreover, such a finding should be considered plausible 
with respect to the mechanism or mode of action. It is estimated that such a situation would 
rarely occur. 

3.7.4.2.  Additional labelling provisions  

There are no additional labelling provisions for reproductive toxic substances and mixtures in 
CLP, however there are provisions laid out in Annex XVII to REACH. The packaging of 
substances with harmonised classification for reproductive toxicity Category 1A or Category 1B, 
and mixtures containing such substances at concentrations warranting classification of the 

 
 
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mixture for reproductive toxicity Category 1A or Category 1B, ‘must be marked visibly, legibly 
and indelibly as follows: “Restricted to professional users”.’ (REACH Annex XVII, point 30). 

3.7.5.  Examples 

3.7.5.1.  Examples of the determination of SCLs 

Four examples are given below: 

3.7.5.1.1. 

Example 1 

1.  Identification 

Substance Name:  XXXXXX 

2.  EU CLP classification 

Repro   1B 

H  360D 

3.  ED10 in animals 

3.1. Brief summary 

OECD 414, Wistar rats, GD 6-19, 0, 20, 60, 180 mg/kg bw. The number of live foetuses per litter 
was significantly reduced and the postimplantation loss was 43 % at the high dose compared to only 
8 % in the control being statistically significant.  

The mean foetal body weight was reduced by 14 %. Further, the incidence of external 
malformations (anasarca and/or cleft palate) was significantly increased. About 10 % of the high 
dose foetuses were affected (13/132 foetuses; in 7/22 litters) while no such changes were observed 
in the control. 

Skeletal malformations were also statistically significantly increased: 7.8 % affected foetuses per 
litter (7/73 foetuses in 5/21 litters) were noted in the high dose group compared to 1.1 % in the 
control. The incidences of shortened scapula (4/73 foetuses), bent radius/ulna (2/73 foetuses), 
malpositioned and bipartite sternebrae (2/73 foetuses) were statistically significantly increased. Soft 
tissue variations (dilated renal pelvis and ureter) were significantly increased in foetuses from high 
dose dams compared to controls (27.1 % vs. 6.4 %). 

At 0, 20, 60, 180 mg/kg 7.9, 14.8, 9.6, 43 % postimplantation loss was found, respectively. 

3.2. Remarks on the study used for the determination of the ED10 

Species, strain, sex:  Female Wistar rat 

Study type:  OECD 414 

Route of administration:  Oral gavage 

Effect descriptor for LOAEL:  Post-implantation loss, anasarca, cleft palate 

Mode of action:  Not known 

Genotoxicity classification:   None 

Potential to accumulate:  No data. not known 

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Control resorption rate (= postimplantation loss) is 7.9%. ED10 rate would be 17.9%. Interpolation 
between NOAEL (classification) (9.6% at 60 mg/kg) and LOAEL (classification) (43% at 180 mg/kg) 
leads to an ED10 of 89.8 mg/kg bw/d.  

Calculation: 

(180 – 60 ) / (43 – 9.6) = 3.593 mg/kg per % (steepness). Going from 9.6% to 17.9% requires 
addition of 8.3%. This equals 8.3% * 3.593 mg/kg per % = 29.8 plus 60 as the starting point = 
89.8 mg/kg bw/day.  

The ED10 for other relevant effects was above 89.8 mg/kg bw/day.   

3.4. Preliminary potency group 

Medium 

4.  Elements that may modify the preliminary potency evaluation 

4.1. Dose-response relationship 

Not relevant as ED10 not borderline. 

4.2. Type of effect / severity 

Not relevant as ED10 not borderline. 

4.3. Data availability 

Not relevant. Only one valid study available. 

4.4. Mode of action 

4.5. Toxicokinetics 

4.6. Bio-accumulation 

No data. 

No data. 

Little information, only environmental. Accumulation in 
organisms is not to be expeceted due to the calculated BCF 
at 3.16.  The substance tends not to accumulate in biota 
due to the low calculated BCF (<<500) and low measured 
log Kow (<<4). 

5.  Allocation of potency group and SCL 

medium potency, GCL 

6.  References 

Confidential 

3.7.5.1.2. 

Example 2 (developmental part only) 

1.  Identification 

Substance Name:  XXXXXX 

2.  EU CLP classification 

Repro   1B 

H  360   FD 

3.  ED10 in animals 

 
 
 
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3.1. Brief summary 

Study used for the determination of the ED10: 

Pregnant females received daily gavage doses of 0, 25, 50, 100 or 175 mg/kg during the gestation 
period (GD 6-19).   

LOAEL effect 

0 mg/kg 

25 mg/kg 

50 mg/kg 

100 mg/kg 

175 mg/kg 

Skeletal 
malformations 

2/22 (9 %)  2/17 (12 %)  5/15 (33%)  10/19 (53%)  6/12 (50%) 

Clear maternal toxicity was evident only at the highest dose level. 

3.2. Remarks on the study used for the determination of the ED10 

Species, strain, sex:  Rabbit, New Zealand White, female 

Study type:  Developmental 6-19 

Route of administration:  Gavage 

Effect descriptor for LOAEL:  Skeletal malformations (axial skeleton, ribs) 

Mode of action:  Substance is metabolised to a substance which causes the 

developmental effect 

Genotoxicity classification:   None 

Potential to accumulate:  Unknown 

3.3. Determination of the ED10 value 

ED10 was determined as 33 mg/kg. 

Control skeletal malformations is 9%. ED10 rate would be 19%. Interpolation between NOAEL 
(classification) (12% at 25 mg/kg) and LOAEL (classification) (33% at 50 mg/kg) leads to an ED10 
of 33.3 mg/kg bw/day.  

Calculation: 

(50– 25 ) / (33 – 12) = 1.19 mg/kg per % (steepness). Going from 12% to 19% requires addition 
of 7%. This equals 7% * 1.19 mg/kg per % = 8.3 plus 25 as the starting point = 33.3 mg/kg 
bw/day. 

3.4. Preliminary potency group 

Medium potency group. 

4.  Elements that may modify the preliminary potency evaluation 

4.1. Dose-response relationship 

The effect on which the classification is based is the 
occurrence of malformations.  As the lowest ED10 was the 
ED10 for skeletal malformations, this ED10 was chosen as the 
basis for the SCL.  The dose effect relationship is clear.  The 
ED10 (33 mg/kg) is not borderline with the LOAEL.  There is 
no reason to consider the dose-response relationship to 
modify the potency of the substance.  

 
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4.2. Type of effect / severity 

4.3. Data availability 

4.4. Mode of action 

4.5. Toxicokinetics 

The effect on which the classification is based is the 
occurrence of malformations, which is a severe effect. 
Moving the substance to a higher potency group should be 
considered. 

Not relevant.  Different studies are available showing a 
developmental effect on different species (rat, mouse, 
rabbit). 

The toxic metabolite has been extensively investigated and 
established as a strong embryotoxicant and teratogen.  
There is no mechanistic information showing a higher or a 
lesser sensitivity in humans than in experimental animals. 

Human and rat liver microsomal preparations (mixtures) 
have been shown to produce qualitatively and quantitively 
similar oxidative metabolic products suggesting that the 
human pathways for this substance may be similar to those 
observed in experimental animals.   

4.6. Bio-accumulation 

Unknown 

5.  Allocation of potency group and SCL 

Skeletal malformations0102030405060050100150200mg/kg% malformations 
 
 
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The effect on which the classification is based is the occurrence of malformations. This is a severe 
effect.   

Due to the fact that the ED10 (33 mg/kg) is not a borderline case, it is not justified to move the 
substance to the highest potency group although the ED10 is based on a severe effect like 
malformations.  

Medium potency, GCL. 

6.  References 

Confidential 

3.7.5.1.3. 

Example 3 (limited to developmental toxicity) 

1. 

Identification 

Substance Name:  XXXXXX 

2.  EU CLP classification 

Repro   1B 

H  360   fD 

3.  ED10 in animals 

3.1. Brief summary 

Several studies in rats were available for the evaluation of the developmental effect of this 
substance. These included 2-generation studies, developmental toxicity studies, and studies with 
exposure in sensitive periods during gestation. The most relevant study for the evaluation of 
potency was considered to be a two-generation study performed according to the revised OECD 
Test Guideline 416. In this study the substance was administered in the diet. Developmental 
toxicity was evident as reduced absolute and adjusted AGD in F1 and F2 offspring as well as and 
reduced foetal and testicular weight in offspring. The NOAEL was 50 mg/kg bw/day based on 
reduced AGD from 250 mg/kg bw/day. These effects were reported in the absence of marked 
maternal toxicity. Effects on the reproductive organs were also reported in male offspring in the 
developmental toxicity studies at higher doses. 

3.2. Remarks on the study used for the determination of the ED10 

Species, strain, sex:  CD(Sprague-Dawley) rats male and female 

Study type:  2-generation according to OECD 416 

Route of administration:  Oral in feed 

Effect descriptor for LOAEL:  Overall: reduced anogenital distance 

Classification: increase in areolae in males 

Mode of action:  Antiandrogenic effect, mechanism relevant for humans 

Genotoxicity classification:   Not classified for germ cell mutagenicity 

Potential to accumulate:  No 

3.3. Determination of the ED10 value 

 
 
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Calculation of the ED10 value: 416 mg/kg bw/day 

Dose (mg/kg bw/day) 

% male F1 with areola 

0 

50 

250 (NOAEL) 

750 (LOAEL) 

2.63 

0.0 

0.76 

32.3 

The ED10 is calculated by interpolation between 250 and 750 mg/kg bw/day to a dose level with 
10% above control level. Roughly, an increase of 30% above control was found at 750 mg/kg 
bw/day. Interpolation between 250 and 750 mg/kg bw/day results in a dose of 16.67 mg/kg 
bw/day for each % of increase in areola ((750-250)/30). A 10% increase (ED10) is expected at 250 
+ 10 * 16.67 = 416 mg/kg bw/day. 

3.4. Preliminary potency group 

Low potency 

4.  Elements that may modify the preliminary potency evaluation 

4.1. Dose-response relationship  A dose-response relationship on decreased AGD was 

4.2. Type of effect / severity 

evident for decrease in AGD in the two-generation study. 
(AGD was decreased in male offspring in a dose-related 
pattern from 250 mg/kg bw/day (1. 89 mm at 250 mg/kg 
bw/day and 1.70 mm at 750 mg/kg bw/day (control: 2.06 
mm)). 

Development: reduced anogenital distance (absolute and 
adjusted) from 250 mg/kg bw/day in F1 and F2 offspring. 
Weight changes in the reproductive organs in F1 and F2 
male offspring, and macroscopic and microscopic lesions in 
the reproductive organs in male offspring at 750 mg/kg 
bw/day. 

Maternal toxicity: organ weight changes, and 
histopahological lesions in the liver graded as minimal in 
females at 750 mg/kg bw/day. 

NOAEL for developmental effects: 50 mg/kg bw/day based 
on reduced anogenital distance from 250 mg/kg bw/day in 
F1 and F2 offspring. 

NOAEL for maternal toxicity: 250 mg/kg bw/day. 

4.3. Data availability 

4.4. Mode of action 

A two-generation study is considered relevant for the 
assessment of development toxicity. 

The mechanism (antiandrogen activity) is considered 
relevant for humans. 

 
 
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4.5. Toxicokinetics 

When metabolites are measured in urine, they are related 
to the day before exposure. The metabolites of the 
substance in rats differ quantitatively from those in 
humans. In several studies the pattern of malformations 
induced by some of the metabolites were similar to that 
produced by the substance, suggesting that the metabolic 
products may be responsible for the developmental toxicity.  

Although there is a difference in toxicokinetics between rats 
and humans, this difference is not expected to result in a 
difference in potency between rats and humans as the 
available data indicate comparable effects and potency of 
the metabolites. 

4.6. Bio-accumulation 

Low to medium bioaccumulation 

5.  Allocation of potency group and SCL 

The ED10 was 416 mg/kg bw/day. The elements that may modify the potency evaluation were 
considered to not modify the potency. This substance is shown to have a low potency.  Therefore 
an SCL of 3 % should be applied. 

6.  References 

Confidential 

3.7.5.1.4. 

Example 4  

1.  Identification 

Substance Name:  XXXXXX 

2.  EU CLP classification 

Repro   2 

H  361f 

3.  ED10 in animals 

3.1. Brief summary 

Only two repeated dose studies are available for this substance and no fertility studies. In the 
inhalatory repeated dose study testicular lesions were observed after exposure to 2.87 mg/l for 4 
exposures of 16 to 20 hours per week during 11 weeks. Other dose levels were not tested. In the 
oral 90 day study, effects on the testes were observed after exposure to 660 mg/kg bw/day. Other 
dose levels were not tested. 

3.2. Remarks on the study used for the determination of the ED10 

Species, strain, sex:  Rats, CD(SD)BR males 

Study type:  90 days, 5 days per week, 120 day observation period 

Route of administration:  gavage 

Effect descriptor for LOAEL: 

testicular atrophy in 50% of the animals 

 
 
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Mode of action:  A metabolite is assumed to be causing the testicular effects. 

A direct effect of this metabolite on the Sertoli cells is 
postulated. 

Genotoxicity classification:   none 

Potential to accumulate:  unknown 

3.3. Determination of the ED10 value 

The dose level of 660 mg/kg bw/day is considered as the LOAEL but in the absence of a NOAEL an 
ED10 cannot be determined by interpolation or the BMD approach because only one dose level was 
tested. An ED10 can be estimated based on interpolation between 660 mg/kg bw/day (50% of the 
animals affected) and the control (0 % of the animals affected). This results in an ED10 of 132 
mg/kg bw/day by interpolation. 

3.4. Preliminary potency group 

Medium potency group 

4.  Elements that may modify the preliminary potency evaluation 

4.1. Dose-response relationship 

There is no data available on the dose response 
relationship. 

4.2. Type of effect / severity 

There are clear testicular effects. It is unknown whether 
these effects will result in functional effects on fertility as 
this has not been tested. 

4.3. Data availability 

4.4. Mode of action 

There is only limited data available at one exposure level.. A 
LOAEL can be determined but it in the absence of a NOAEL 
it cannot be excluded that effects on sexual organs occur at 
levels below the LOAEL. The available data are considered 
as limited. 

A metabolite is assumed to be the cause of the testicular 
effects. A direct effect of this metabolite on the Sertoli cells 
is postulated. 

4.5. Toxicokinetics 

Unknown 

4.6. Bio-accumulation 

Unknown 

5.  Allocation of potency group and SCL 

An ED10 can only be estimated using interpolation between the only dose tested and the controls. 
The resulting ED10 indicates medium potency. However, there is only very limited data. As there is 
only an LOAEL and no NOAEL, it cannot be excluded that testicular effects can be induced at lower 
levels. However, there is no evidence that this substance can induce testicular effects at dose levels 
below 4 mg/kg bw/day. Therefore, a medium potency is considered the best estimate based on the 
available data. 

6.  References 

Confidential 

 
 
 
 
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3.8.  SPECIFIC TARGET ORGAN TOXICITY – SINGLE EXPOSURE (STOT-

SE) 

3.8.1.  Definitions and general considerations for STOT-SE  

Annex 1: 3.8.1.1. Specific target organ toxicity (single exposure) is defined as specific, non 
lethal target organ toxicity arising from a single exposure to a substance or mixture. All 
significant health effects that can impair function, both reversible and irreversible, immediate 
and/or delayed and not specifically addressed in Chapters 3.1 to 3.7 and 3.10 are included 
(see also 3.8.1.6). 

There are two hazard classes for single exposure toxicity: ‘Acute toxicity’ and ‘STOT-SE’. These 
are independent of each other and both may be assigned to a substance or a mixture if the 
respective criteria are met. Acute toxicity refers to lethality and STOT-SE to non lethal effects. 
However, care should be taken not to assign both classes for the same toxic effect, essentially 
giving a ‘double classification’, even where the criteria for both classes are fulfilled. In such a 
case the most appropriate class should be assigned. 

Acute toxicity classification is generally assigned on the basis of evident lethality (e.g. an 
LD50/LC50 value) or where the potential to cause lethality can be concluded from evident toxicity 
(e.g. from fixed dose procedure). STOT-SE should be considered where there is clear evidence 
of toxicity to a specific organ especially when it is observed in the absence of lethality. 

Furthermore, specific toxic effects covered by other hazard classes are not included in STOT-SE. 
STOT-SE should only be assigned where the observed toxicity is not covered more appropriately 
by another hazard class. For example, specific effects caused after a single exposure like 
corrosion of skin or effects on the reproductive organs should be used for classification for skin 
corrosion or reproductive toxicity, respectively, but not for STOT-SE. 

Annex 1: 3.8.1.4. Assessment shall take into consideration not only significant changes in a 
single organ or biological system but also generalised changes of a less severe nature 
involving several organs. 

Annex I: 3.8.1.5. Specific target organ toxicity can occur by any route that is relevant for 
humans, i.e. principally oral, dermal or inhalation. 

Annex I: 3.8.1.7. The hazard class Specific Target Organ Toxicity – Single Exposure is 
differentiated into: 

Specific target organ toxicity – single exposure, Category 1 and 2; 

Specific target organ toxicity – single exposure, Category 3. 

The hazard class STOT-SE has 3 categories, with Categories 1 and 2 being distinct from 
Category 3 in terms of the toxicity they cover and the criteria. Categories 1 and 2 for non lethal 
‘significant and/or severe toxic effects’ are the basis for classification with the category 
reflecting the dose level required to cause the effect. Category 3 covers ‘transient effects’ 
occurring after single exposure, specifically respiratory tract irritation (RTI) and narcotic effects 
(NE). The relationship between Categories 1/2 vs. Category 3 is discussed in Sections 3.8.2.4.3 
and 3.8.2.4.2 of this Guidance.  

 
 
 
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3.8.2.  Classification of substances for STOT-SE 

3.8.2.1. 

Identification of hazard information  

Annex 1: 3.8.2.1.5. The information required to evaluate specific target organ toxicity 
comes either from single exposure in humans, such as: exposure at home, in the workplace 
or environmentally, or from studies conducted in experimental animals.  

CLP does not require testing of substances or mixtures for classification purposes. The 
assessment is based on the respective criteria together with available adequate and robust test 
data/information. Generally, information relevant to STOT-SE can be obtained from human 
experience or acute toxicity studies in animals.  

3.8.2.1.1. 

 Identification of human data  

Relevant information with respect to toxicity after single exposure may be available from case 
reports, epidemiological studies, medical surveillance and reporting schemes and national 
poisons centres. 

Data on sensory irritation of the airways may be available from volunteer studies including 
objective measurements of RTI such as electrophysiological responses, data from lateralization 
threshold testing, biomarkers of inflammation in nasal or bronchoalveolar lavage fluids 
(Guidance on IR&CSA, Section 7.2.3.2). For more details see the Guidance on IR&CSA, Section 
7.4.3.2 and R.7.2. 

3.8.2.1.2. 

 Identification of non human data  

Annex 1: 3.8.2.1.5 The standard animal studies in rats or mice that provide this information 
are acute toxicity studies which can include clinical observations and detailed macroscopic and 
microscopic examination to enable the toxic effects on target tissues/organs to be identified. 
Results of acute toxicity studies conducted in other species may also provide relevant 
information.  

Annex 1: 3.8.2.1.7.3. Evidence from appropriate studies in experimental animals can furnish 
much more detail, in the form of clinical observations, and macroscopic and microscopic 
pathological examination, and this can often reveal hazards that may not be life-threatening 
but could indicate functional impairment. Consequently all available evidence, and relevance to 
human health, must be taken into consideration in the classification process, … 

Non-testing data 

Physicochemical data 

Physicochemical properties, such as pH, physical form, solubility, vapour pressure, particle size, 
can be important parameters in evaluating toxicity studies and in determining the most 
appropriate classification especially with respect to inhalation where physical form and particle 
size can have a significant impact on toxicity. 

(Q)SAR models, Read-across 

‘Non-testing’ data (i.e. data not obtained from experimental methods) can be provided by the 
use of techniques such as grouping/category formation, Quantitative and qualitative Structure 
Activity Relationship (Q)SAR models and expert systems, which generally relate physico-
chemical properties and chemical structure to toxicity. The use of these methods is described in 
more detail in Section 1.4 of this Guidance and in the Guidance on IR&CSA, Section R.7.4.4.1. 

The potential use of (Q)SAR models for predicting effects relevant to STOT-SE Categories 1/2 is 
currently quite limited and may only be applicable in specific cases. However, they may be 

 
 
 
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somewhat more useful for STOT-SE Category 3 where there are some well established 
relationships between physicochemical properties or chemical structure and effects such as 
narcosis and respiratory tract irritation. For instance substances such as aldehydes, unsaturated 
carbonic esters and reactive inorganic compounds are generally found to be respiratory tract 
irritants. 

In addition, there are systems which can predict the metabolism of substances. These can be 
useful in providing information on the potential for the substance to be metabolised to 
substances with known toxicity. An example is certain esters, which after enzymatic cleavage to 
carbonic acids and alcohols in the nasal region, cause respiratory irritation. 

For more details see the Guidance on IR&CSA, Section 7.4.3.1. 

Testing data 

Animal data 

The standard tests on acute toxicity are listed in the Guidance on IR&CSA, Section R.7.4.3.1. 

For Category 1 and 2, in general terms, most studies involving single exposure via any 
relevant route of exposure, such as acute toxicity studies, can be used for classification 
purposes. Older acute toxicity studies which tended to only measure lethality as an 
observational endpoint (e.g. to determine LD50/LC50) will generally not provide useful 
information for STOT-SE. However, newer acute toxicity test protocols, such as the fixed-dose 
and up-down procedures, have a wider range of observations on signs of toxicity and therefore 
may provide information relevant for STOT-SE. Other standard studies, e.g. neurotoxicity tests, 
or ad-hoc studies designed to investigate acute toxicity, can also provide valuable information 
for STOT-SE. 

Care must be taken not to classify for STOT-SE for effects which are not yet lethal at a certain 
dose, but would lead to lethality within the numeric classification criteria. In other words, if 
lethality would occur at relevant doses then a classification for acute toxicity would take 
precedence and STOT-SE would not be assigned. 

Although classification in Category 3 is primarily based on human data, if available, animal 
data can be included in the evaluation. These animal data on RTI and NE will generally come 
from standard acute inhalation studies, although it is possible that narcosis could be observed in 
studies using other routes. Standard acute toxicity tests are often more useful for Category 3 
than for STOT-SE Categories 1/2 because overt findings of narcosis and RTI are more often 
reported in clinical observations. 

The Alarie test gives specific information on the potential for sensory irritation. Further, 
information on this test and its limitations can be found in the Guidance on IR&CSA, Section 
R.7.2. 

Furthermore the Inhalation Hazard Test (Annex to OECD TG 403) might give information on the 
potential for RTI of volatile substances. Though the focus of STOT-SE is on effects caused by 
single exposure, data from studies with repeated exposure might give additional valuable 
information, especially with respect to the underlying mode of action of RTI. 

In vitro data 

Since there are currently no in vitro tests that have been officially adopted by the EU or OECD 
for assessment of acute toxicity, there are also no useful test systems for STOT-SE (see the 
Guidance on IR&CSA, Section R.7.4.3.1). Any available studies should be assessed using expert 
judgement. 

3.8.2.2.  Classification criteria for Categories 1 and 2 

Annex I: 3.8.2.1.1. Substances are classified for immediate or delayed effects separately, by 
the use of expert judgement (see 1.1.1) on the basis of the weight of all evidence available, 

 
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including the use of recommended guidance values (see 3.8.2.1.9). Substances are then 
placed in Category 1 or 2, depending upon the nature and severity of the effect(s) observed 
(Table 3.8.1). 

Categories for specific target organ toxicity-single exposure 

Table 3.8.1 

Categories 

Criteria 

Substances that have produced significant toxicity in humans or that, on the 
basis of evidence from studies in experimental animals, can be presumed to 
have the potential to produce significant toxicity in humans following single 
exposure 

Substances are classified in Category 1 for specific target organ toxicity (single 
exposure) on the basis of: 

Category 1 

a.  reliable and good quality evidence from human cases or epidemiological 

studies; or 

b.  observations from appropriate studies in experimental animals in which 

significant and/or severe toxic effects of relevance to human health were 
produced at generally low exposure concentrations. Guidance 
dose/concentration values are provided below (see 3.8.2.1.9) to be used as 
part of weight-of-evidence evaluation. 

Substances that, on the basis of evidence from studies in experimental animals 
can be presumed to have the potential to be harmful to human health following 
single exposure 

Substances are classified in Category 2 for specific target organ toxicity (single 
exposure) on the basis of observations from appropriate studies in 
experimental animals in which significant toxic effects, of relevance to human 
health, were produced at generally moderate exposure concentrations. 
Guidance dose/concentration values are provided below (see 3.8.2.1.9) in order 
to help in classification. 

In exceptional cases, human evidence can also be used to place a substance in 
Category 2 (see 3.8.2.1.6). 

Category 2 

Note:  Attempts shall be made to determine the primary target organ of toxicity and to 
classify for that purpose, such as hepatotoxicants, neurotoxicants. The data shall be carefully 
evaluated and, where possible, secondary effects should not be included (e.g. a hepatotoxicant 
can produce secondary effects in the nervous or gastro-intestinal systems). 

Annex I: 3.8.2.1.2. The relevant route or routes of exposure by which the classified 
substance produces damage shall be identified (see 3.8.1.5). 

STOT-SE Category 1 and 2 is assigned on the basis of findings of ‘significant’ or ‘severe’ toxicity. 
In this context ‘significant’ means changes which clearly indicate functional disturbance or 
morphological changes which are toxicologically relevant. ‘Severe’ effects are generally more 
profound or serious than ‘significant’ effects and are of a considerably adverse nature with 
significant impact on health. Both factors have to be evaluated by weight of evidence and 
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3.8.2.2.1.  Guidance values 

Annex I: 3.8.2.1.9.1 In order to help reach a decision about whether a substance shall be 
classified or not, and to what degree it shall be classified (Category 1 or Category 2), 
dose/concentration ‘guidance values’ are provided for consideration of the dose/concentration 
which has been shown to produce significant health effects.  

Annex I: 3.8.2.1.9.3. The guidance value (C) ranges for single-dose exposure which has 
produced a significant non-lethal toxic effect are those applicable to acute toxicity testing, as 
indicated in Table 3.8.2. 

Guidance value ranges for single-dose exposures a 

Table 3.8.2 

Guidance value ranges for:* 

Route of exposure 

Units 

Category 1 

Category 2 

Category 3 

Oral (rat) 

Dermal (rat or 
rabbit) 

mg/kg body 
weight 

mg/kg body 
weight 

C ≤ 300 

2000 ≥ C > 300 

Guidance values do 
not apply b 

C ≤ 1000 

2000 ≥ C > 1000 

Inhalation (rat) gas 

ppmV/4h 

C ≤ 2500 

20000 ≥ C > 2500 

Inhalation (rat) 
vapour 

Inhalation (rat) 
dust/mist/fume 

Note 

mg/l/4h 

C ≤ 10 

20 ≥ C > 10 

mg/l/4h 

C ≤ 1.0 

5,0 ≥ C >1,0 

a.  The guidance values and ranges mentioned in Table 3.8.2 above are intended only for 

guidance purposes, i.e. to be used as part of the weight of evidence approach, and to assist 
with decision about classification. They are not intended as strict demarcation values. 

b.  Guidance values are not provided for Category 3 substances since this classification is 

primarily based on human data. Animal data, if available, shall be included in the weight of 
evidence evaluation. 

  * NOTE: There is a misprint in Annex I, Table 3.8.2; the heading 'Guidance value ranges 

for:' should also belong to the column 'Category 1'. 

Where significant or severe toxicity has been observed in animal studies, the dose/exposure 
level causing these effects is compared to the guidance values provided to determine if 
classification in Category 1 or 2 is most appropriate.  

In cases of inhalation studies with exposure times different to 4 hours an extrapolation can be 
performed similar to the one described in Section 3.1 of this Guidance for Acute Toxicity.  

 
 
 
 
 
 
 
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3.8.2.3.  Classification criteria for Category 3: Transient target organ effects 

Currently, the criteria for classification in Category 3 only cover the transient effects of 
‘respiratory tract irritation’ and ‘narcotic effects’. 

Annex I: Table 3.8.1 (continued) 

Categories for specific target organ toxicity-single exposure 

Categories 

Criteria 

Category 3 

Transient target organ effects 

This category only includes narcotic effects and respiratory tract irritation. 
These are target organ effects for which a substance does not meet the 
criteria to be classified in Categories 1 or 2 indicated above. These are 
effects which adversely alter human function for a short duration after 
exposure and from which humans may recover in a reasonable period 
without leaving significant alteration of structure or function. Substances are 
classified specifically for these effects as laid down in 3.8.2.2 

Annex I: 3.8.2.2.1 Criteria for respiratory tract irritation 

The criteria for classifying substances as Category 3 for respiratory tract irritation are: 

(a)  respiratory irritant effects (characterized by localized redness, oedema, pruritis and/or 
pain) that impair function with symptoms such as cough, pain, choking, and breathing 
difficulties are included. This evaluation will be based primarily on human data. 

(b)  subjective human observations could be supported by objective measurements of clear 
respiratory tract irritation (RTI) (such as electrophysiological responses, biomarkers of 
inflammation in nasal or bronchoalveolar lavage fluids).  

(c)  he symptoms observed in humans shall also be typical of those that would be produced in 
the exposed population rather than being an isolated idiosyncratic reaction or response 
triggered only in individuals with hypersensitive airways. Ambiguous reports simply of 
“irritation” shall be excluded as this term is commonly used to describe a wide range of 
sensations including those such as smell, unpleasant taste, a tickling sensation, and 
dryness, which are outside the scope of classification for respiratory irritation. 

(d)  there are currently no validated animal tests that deal specifically with RTI, however, 

useful information may be obtained from the single and repeated inhalation toxicity tests. 
For example, animal studies may provide useful information in terms of clinical signs of 
toxicity (dyspnoea, rhinitis etc) and histopathology (e.g. hyperemia, edema, minimal 
inflammation, thickened mucous layer) which are reversible and may be reflective of the 
characteristic clinical symptoms described above. Such animal studies can be used as part 
of weight of evidence evaluation. 

(e)  this special classification would occur only when more severe organ effects including in the 

respiratory system are not observed. 

It is clearly indicated in the CLP that there are currently no validated animal tests that deal 
specifically with RTI, but that animal studies can be used as a part of weight of evidence 
evaluation (CLP Annex I, 3.8.2.2.1.2(d)). However when there are no data in human and animal 
data suggesting RTI effects, expert judgement is needed to estimate the severity of the effects 
observed in animals, the conditions of the test, the physical-chemical properties of the 
substance and whether those considerations alone might be sufficient for a classification in 
Category 3 for RTI.  

 
 
 
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The generic term RTI covers two different effects: ‘sensory irritation’ and ‘local cytotoxic 
effects’. Classification in STOT-SE Category 3 for respiratory tract irritation is generally limited 
to local cytotoxic effects.  

Sensory irritation refers to the local and central reflex interaction of a substance with the 
autonomic nerve receptors, which are widely distributed in the mucosal tissues of the eyes and 
upper respiratory tract. It helps to minimize exposure by decreasing the respiration-time-
volume and inducing the exposed to leave the areas of irritant concentrations, if possible. 
Sensory irritation-related effects are fully reversible given that its biological function is to serve 
as a warning against substances that could damage the airways. 

Local cytotoxic irritant effects induce tissue changes at the site of contact which can be detected 
by clinico-pathological or pathological methods. Such effects may induce long lasting functional 
impairment of the respiratory system. 

The basic mechanisms underlying morphological changes comprise cytotoxicity and induction of 
inflammation. Based on the quality and severity of morphological changes, the function of the 
respiratory system could be impaired, which may lead to the development of consequential 
systemic effects, i.e. there might be consequences on distal organs by a diminution of the 
oxygen supply. As the functional impairment is seldom evaluated by experimental inhalation 
studies in animals, data on functional changes will mainly be available from experience in 
humans. 

Further see the Guidance on IR&CSA, Section R.7.2. 

Annex I: 3.8.2.2.2. Criteria for narcotic effects  

The criteria for classifying substances as Category 3 for narcotic effects are: 

(a) 

(b) 

central nervous system depression including narcotic effects in humans such as 
drowsiness, narcosis, reduced alertness, loss of reflexes, lack of coordination, and 
vertigo are included. These effects can also be manifested as severe headache or 
nausea, and can lead to reduced judgment, dizziness, irritability, fatigue, impaired 
memory function, deficits in perception and coordination, reaction time, or sleepiness. 

narcotic effects observed in animal studies may include lethargy, lack of coordination, 
loss of righting reflex, and ataxia. If these effects are not transient in nature, then they 
shall be considered to support classification for Category 1 or 2 specific target organ 
toxicity single exposure. 

3.8.2.4.  Evaluation of hazard information on STOT-SE for substances 

3.8.2.4.1. 

Evaluation of human data  

Annex I: 3.8.2.1.6. In exceptional cases, based on expert judgement, it is appropriate to 
place certain substances with human evidence of target organ toxicity in Category 2: 

(a)  when the weight of human evidence is not sufficiently convincing to warrant Category 1 

classification, and/or 

(b)  based on the nature and severity of effects. 

Dose/concentration levels in humans shall not be considered in the classification and any 
available evidence from animal studies shall be consistent with the Category 2 classification. 
In other words, if there are also animal data available on the substance that warrant Category 
1 classification, the substance shall be classified as Category 1. 

Annex I: 3.8.2.1.7.2. Evidence from human experience/incidents is usually restricted to 
reports of adverse health consequence, often with uncertainty about exposure conditions, and 

 
 
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may not provide the scientific detail that can be obtained from well-conducted studies in 
experimental animals. 

Annex I: 3.8.2.1.10.2. When well-substantiated human data are available showing a specific 
target organ toxic effect that can be reliably attributed to single exposure to a substance, the 
substance shall normally be classified. Positive human data, regardless of probable dose, 
predominates over animal data. Thus, if a substance is unclassified because specific target 
organ toxicity observed was considered not relevant or significant to humans, if subsequent 
human incident data become available showing a specific target organ toxic effect, the 
substance shall be classified. 

Human data are potentially very valuable for determining an appropriate classification as they 
provide direct evidence on the effects of a substance in humans. However, the evaluation of 
human data is often made difficult by various limitations frequently found with the types of 
studies and data highlighted in Section 3.8.2.4.1 of this Guidance. These include uncertainties 
relating to exposure assessment (i.e. unreliable information on the amount of a substance the 
subjects were exposed to or ingested) and confounding exposures to other substances. As a 
result it should be acknowledged that human data often do not provide sufficiently robust 
evidence on their own to support classification but may contribute to a weight of evidence 
assessment with other available information such as animal studies. 

Categories 1 and 2 

In general, where reliable and robust human data are available showing that the substance 
causes significant target organ toxicity these take precedence over other data, and directly 
support classification in Category 1. Available animal data may support this conclusion but do 
not detract from it (e.g. if the same effect is not observed in animals). 

In exceptional cases, where target organ toxicity is observed in humans but the data reported 
are not sufficiently convincing to support Category 1 because of the lack of details in the 
observations or in the exposure conditions, and/or with regard to the nature and  the severity of 
the effects observed, then classification in Category 2 could be justified (CLP Annex I, 
3.8.2.1.6). In this case, any animal data must also be consistent with Category 2 and not 
support Category 1 (see below). In this case, if the animal data support Category 1, they will 
take precedence over the human data. This is because the reliability of the human data in this 
case is probably lower than the reliability of data from standard well conducted animal studies 
and should accordingly have less weight in the assessment.  

When using human data, there is no consideration of the human dose/exposure level that 
caused those effects.  

Category 3 

Respiratory Tract Irritation 

Human evidence for RTI often comes from occupational case reports where exposure is 
associated with signs of RTI. Such reports should be interpreted carefully using expert 
judgement to ensure that they provide reliable information. For instance, there should be a 
clear relationship between exposure and the development of signs of RTI, with RTI appearing 
relatively soon after the start of exposure. A solid substance which causes RTI due to 
physical/mechanical irritation when inhaled as a dust should not be classified. For more details 
on RTI, see the Guidance on IR&CSA Chapter R7a.7.2.1, and example n° 3 for sulfur dioxide. 

 
 
 
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Narcotic Effects 

Narcotic effects may range from slight dizziness to deep unconsciousness and may be caused by 
several mechanisms: 

•  pharmaceutical drugs (designed effect; often receptor-mediated; effective dose usually 
low; patient under professional observation; limited importance for industrial chemicals 
and their safety assessment.) 

•  unspecific effects of many organic industrial chemicals on CNS-membranes at high dose 

levels (often solvent vapours, ≥ 6000 ppm in respired air volume). Such effects can be 
expected at high exposure levels due to otherwise low toxicity. 

•  organic chemicals with similarities to and interference with CNS-transmitters; often 
metabolic transformation necessary; certain solvents, e.g. butandiol, butyrolactone, 
methoxyethanol; medium levels of effective dose. Children may be considerably more 
susceptible than adults. 
chemicals with high specific CNS toxicity; narcotic effects usually close to near-lethal 
doses (example: H2S). 

• 

Narcotic effects are usually readily reversible on cessation of exposure with no permanent 
damage or changes. 

Human evidence relating to narcosis should be evaluated carefully. Often the reporting of 
clinical signs is relatively subjective and reports of effects such as severe headache and 
dizziness should be interpreted carefully to judge if they provide robust evidence of narcosis. 
Where relevant human data do not mirror realistic exposure conditions, for instance in case 
reports from accidental over-exposure situations, supportive information may be needed to 
corroborate the observed effects. A single case report from accidental or deliberate exposure 
(i.e. abuse) is unlikely to provide sufficiently robust evidence to support classification without 
other evidence. For more details on evaluation of available human information see also Section 
3.1.2.3.1 of this Guidance and the Guidance on IR&CSA, Section R.7.4 (especially R.7.4.4.2). 
Example n° 4 for toluene illustrates the procedure. 

3.8.2.4.2. 

Evaluation of non human data  

Annex I: 3.8.2.1.5. The standard animal studies in rats or mice that provide information are 
acute toxicity studies which can include clinical observations and detailed macroscopic and 
microscopic examination to enable the toxic effects on target tissues/ organs to be identified. 
Results of acute toxicity studies conducted in other species may also provide relevant 
information. 

Annex I: 3.8.2.1.10.1. When a substance is characterised only by use of animal data (typical 
of new substances, but also true for many existing substances), the classification process 
includes reference to dose/concentration guidance values as one of the elements that 
contribute to the weight of evidence approach. 

Annex I: 3.8.2.1.10.3. A substance that has not been tested for specific target organ toxicity 
may, where appropriate, be classified on the basis of data from a validated structure activity 
relationship and expert judgement-based extrapolation from a structural analogue that has 
previously been classified together with substantial support from consideration of other 
important factors such as formation of common significant metabolites. 

The type of evidence mentioned in CLP Annex I, 3.8.2.1.7 and 3.8.2.1.8 to support or not to 
support classification (e.g. clinical biochemistry, changes in organ weights with no evidence of 
organ dysfunction) is rarely obtained from animal tests designed to measure acute 
lethality/toxicity (see Section 3.8.2.1.2 of this Guidance). 

 
 
 
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Generic guidance on data evaluation is presented in the Guidance on IR&CSA, Sections R.7.4 
and R.7.4.4.2. All available animal data which are of acceptable quality should be used in a 
weight of evidence approach based on a comparison with the classification criteria described 
above. The assessment should be done for each route of exposure.  

For each study the effects seen in each sex at or around the guidance values (GV) for Category 
1 and Category 2 should be compared with the effects warranting classification in Category 1 
and 2. In general findings in the most sensitive sex would be used to determine the 
classification. If the NOAEL from the study is above the GV, the results of that study do not 
indicate classification for that category (situations 1 and 2 in Figure 3.7). If the NOAEL is below 
the GV then the effective dose (ED) level, the lowest dose inducing significant/severe target 
organ toxicity as defined in Section 3.8.2.2.1 of this Guidance should be determined based on 
the criteria described above. If the ED is below the GV then this study indicates that 
classification is warranted (situations 2 and 4 in Figure 3.7).  

In a case where the ED is above a GV but the NOAEL is below the GV (situations 3 and 5 in 
Figure 3.7) then interpolation between the ED and the NOAEL is required to determine whether 
the effects expected at or below the GV would warrant classification.  

Figure 3.7  Comparison between the NOAEL and the ED versus the guidance values 

Situation 1 

Situation 2 

Situation 3 

Situation 4 

Situation 5 

GV 

Category 2 

GV 

Category 1 

- NOAEL 1 

- ED 3 

- ED 2 

- NOAEL 3 

- NOAEL 2 

- ED 5 

- ED 4 

- NOAEL 5 

- NOAEL 4 

NC 

Category 2 

Interpolation 

Category 1 

Interpolation 

Where a number of studies are available these should be assessed using a weight of evidence 
approach to determine the most appropriate classification. Where the findings from individual 
studies would lead to a different classification then the studies should be assessed in terms of 
their quality, species and strain used, nature of the tested substance (including the impurity 
profile and physical form) etc to choose the most appropriate study to support classification. In 
general, the study giving the most severe classification will be used unless there are good 
reasons that it is not the most appropriate. If the effects observed in animals are not considered 
relevant for humans then these should not be used to support classification. Similarly, if there is 
robust evidence that humans differ in sensitivity or susceptibility to the effect observed in the 
study then this should be taken into account, possibly leading to an increase or decrease in the 

 
 
 
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classification assigned. The final classification based on non human data will be the most severe 
classification of the three exposure routes. 

Category 3 

There are no similar guidance values for Category 3. Therefore, if the study shows clear 
evidence for narcotic effects or respiratory tract irritation at any dose level then this could 
support classification with Category 3.  

In evaluating inhalation studies a differentiation of respiratory tract effects and systemic effects 
should always be attempted. In addition, the region in the respiratory tract and the qualitative 
nature of observed effects is pivotal. Often, the lesions observed are representing stages of a 
reaction pattern leading to severe and irreversible functional and structural alterations. 
Therefore reversibility of effects is a significant discriminator. For further details see also Section 
3.8.2.3 of this Guidance. 

3.8.2.4.3. 

Evaluation of non-testing and in vitro data 

Non-testing and in vitro data can contribute to the weight of evidence supporting a 
classification. As described in Annex XI of REACH approaches such as (Q)SAR, grouping and 
read-across can provide information on the hazardous properties of substances in place of 
testing and can be used for classification purposes. Also see the Guidance on IR&CSA R7.4.4.1. 

3.8.2.4.4. 

Conversions 

The guidance values are given in mg/kg bodyweight. Where the doses in a study are given in 
different units they will need to be converted as appropriate. For instance the dosages in 
feeding and drinking water studies are often expressed in ppm, mg test substance/ kg (feed) or 
mg (test substance)/l (drinking water).  

The conversion from mg/l to ppm assuming an ambient pressure of 1 at 101.3 kPa and 25°C is 
ppm = 24,450 x mg/l  1/MW. 

3.8.2.4.5.  Weight of evidence 

Annex I: 3.8.2.1.6. In exceptional cases, based on expert judgement, it is appropriate to 
place certain substances with human evidence of target organ toxicity in Category 2: 

when the weight of evidence is not sufficiently convincing to warrant Category 1 

1) 
classification, and/or 

2) 

based on the nature and severity of effects. 

Dose/concentration levels in humans shall not be considered in the classification and any 
available evidence from animal studies shall be consistent with the Category 2 classification. In 
other words, if there are also animal data available on the substance that warrant Category 1 
classification, the substance shall be classified as Category 1. 

The available information should be considered using expert judgement and a weight of 
evidence assessment, as described in CLP Annex I, 1.1.1 and Module 1 and in the approach 
described in Section 3.8.2.3 of this Guidance. 

If there are no human data then the classification is based on the non-human data. If there is 
human data indicating no classification but there is also non-human data indicating classification 
then the classification is based on the non-human data unless it is shown that the human data 
cover the exposure range of the non-human data and that the non-human data are not relevant 
for humans. If the human and non-human data both indicate no classification then classification 
is not required.  

 
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3.8.2.5.  Decision on classification of substances  

Decision on classification for STOT-SE is based on the results of weight of evidence approach 
described in Section 3.8.2.4.5. 

STOT-SE and acute toxicity are independent of each other and both may be assigned to a 
substance if the respective criteria are met. However, care should be taken not to assign each 
class for the same effect, in other words a double classification for the same effect has to be 
avoided. STOT-SE will be considered where there is clear evidence for a specific organ toxicity 
especially in absence of lethality, see examples no 1 and no 3 (methanol and 
tricresylphosphate). 

If no classification has been warranted for acute toxicity despite significant toxic effect, the 
substance should be considered for classification as STOT-SE. 

Normally, the assignment of STOT-SE Category 1 or 2 is independent to the assignment of 
Category 3. Therefore, a substance may be classified in both Category 1/2 and Category 3 if the 
respective criteria are met, for instance, in the case of a neurotoxic substance that also causes 
transient narcotic effects. If Category 1/2 is assigned on the basis of effects in the respiratory 
tract then Category 3 should not be assigned as this would provide no additional information. 

Classification as acutely toxic and/or corrosive is considered to cover and communicate the 
specific toxicological effect(s) adequately. An additional classification as specific target organ 
toxicant (single exposure, Category 1 or 2) is not indicated if the severe toxicological effect is 
the consequence of the local (i.e. corrosive) mode of action. 

It is a reasonable assumption that corrosive substances may also cause respiratory tract 
irritation when inhaled at exposure concentrations below those causing frank respiratory tract 
corrosion. If there is evidence from animal studies or from human experience to support this 
then Category 3 may be appropriate. In general, a classification for corrosivity is considered to 
implicitly cover the potential to cause RTI and so the additional Category 3 is considered to be 
superfluous, although it can be assigned at the discretion of the classifier. The Category 3 
classification would occur only when more severe effects in the respiratory system are not 
observed.  

Category 3 effects should be confined to changes, whether functional or morphological, 
occurring in the upper respiratory tract (nasal passages, pharynx and larynx). Localized 
irritation with associated adaptive responses (e.g., inflammation, epithelial metaplasia, goblet 
cell hyperplasia, proliferative effects) may occur and are consistent with Category 3 responses. 
Injury of the olfactory epithelium should be distinguished in terms of irritation-related (non-
specific) and metabolic/ non-irritant (specific).  

3.8.2.6.  Setting of specific concentration limits for STOT-SE  

Article 10(1) Specific concentration limits and generic concentration limits are limits 
assigned to a substance indicating a threshold at or above which the presence of that 
substance in another substance or in a mixture as an identified impurity, additive or individual 
constituent leads to the classification of the substance or mixture as hazardous. 

Specific concentration limits shall be set by the manufacturer, importer or downstream user 
where adequate and reliable scientific information shows that the hazard of a substance is 
evident when the substance is present at a level below the concentrations set for any hazard 
class in Part 2 of Annex I or below the generic concentration limits set for any hazard class in 
Parts 3, 4 and 5 of Annex I. 

In exceptional circumstances specific concentration limits may be set by the manufacturer, 
importer or downstream user where he has adequate, reliable and conclusive scientific 
information that a hazard of a substance classified as hazardous is not evident at a level 

 
 
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above the concentrations set for the relevant hazard class in Part 2 of Annex I or above the 
generic concentration limits set for the relevant hazard class in Parts 3, 4 and 5 of that Annex. 

Specific concentration limits (SCLs) for STOT-SE may be set by the supplier in some situations 
according to Article 10 of CLP. For STOT-SE, this may only be done for substances inducing 
STOT-SE Category 1 at a dose level or concentration clearly (more than one magnitude) below 
the guidance values according to Table 3.8.2, e.g. below 30 mg/kg bodyweight from the oral 
single exposure study. This will be mainly based on data in experimental animals but can also 
be based on human data if reliable exposure data are available. The SCL (SCL Cat. 1) for a 
Category 1 substance triggering classification of a mixture in Category 1 can be determined 
using the following formula: 

Equation 3.8.2.6.a 

SCL Cat 1: 0.7 mg/kgbw/300 mg/kgbw x 100%=0.23% --> 0.2% 

In this formula the ED is the dose of the Category 1 substance inducing significant specific 
target organ toxicity and GV1 is the guidance value for Category 1 according to Table 3.8.2 of 
Annex I. The resulting SCL is rounded down to the nearest preferred value70  (1, 2 or 5). 

Example of determining STOT-SE SCL for a Category 1 substance: 

  = 0.23% --> 0.2% 

Though  classification  of  a  mixture  in  Category  1  is  not  triggered  if  a  Category  1  constituent  is 
present in lower concentrations than the established SCL, a classification in Category 2 should be 
considered. 

The SCL (SCL Cat. 2)for a Category 1 substance triggering classification of a mixture in Category 
2 can be determined using the following formula: 

Equation 3.8.2.6.b 

In this formula the ED is the dose of the Category 1 substance inducing specific target organ 
toxicity and GV2 is the upper guidance value for Category 2 according to Table 3.8.2 of Annex I. 
The resulting SCL is rounded down to the nearest preferred values (1, 2 or 5). However, if the 
calculated SCL for classification in Category 2 is above 1%, which is the Generic Concentration 
Limit, then no SCL should be set. 

Example for a substance in SCL Category 2:  

= 0.035 --> 0.02% (rounded down) 

For example, a Category 1substance inducing specific target organ toxicity at 0.7 mg/kg bw/day 
in an acute oral study would generate an SCL for classification of mixtures in Category 1 at 
0.2% and in Category 2 at 0.02% (Cat1: C ≥ 0.2% ; Cat 2: 0.02% ≤ C < 0.2%). 

It is not appropriate to determine SCLs for substances classified in Category 2 since ingredients 
with a higher potency (i.e. lower effect doses than the lower guidance values of Category 2) will 

70 This is the “preferred value approach” as used in EU and are values to be established preferentially as 
the numerical values 1,2 or 5 or multiples by powers of ten.  

%10011.=GVEDSCLCat%100/300/7.0=kgbwmgkgbwmg%10022.=GVEDSCLCat%100/2000/7.0=kgbwmgkgbwmg 
 
 
 
 
 
 
 
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be classified in Category 1; substances with higher effect doses than the upper guidance value 
of Cat2 will generally not be classified.  

Classification in STOT-SE Category 3 for RTI and narcotic effects does not take potency into 
account and consequently does not have any guidance values. A pragmatic default GCL of 20% 
is suggested, although a lower or higher SCL may be used where it can be justified. Therefore, 
an SCL can be determined on a case-by-case basis for substances classified as STOT-SE 
Category 3 and expert judgement shall be exercised.  

Specific concentration limits for each of the hazard classes skin and eye irritation, and STOT-SE 
Category 3 for respiratory tract irritation need to be addressed separately, while unjustified 
read-across of SCLs from one hazard class to another is not acceptable.  

For narcotic effects, the factors to be taken into consideration in order to set lower or higher 
SCLs are the effective dose/concentration, and in addition for liquids, the volatility (saturated 
vapour concentration) of the substance. 

3.8.2.7.  Decision logic for classification of substances 

The decision logic is provided as additional guidance. It is strongly recommended that the person 
responsible  for  classification  study  the  criteria  for  classification  before  and  during  use  of  the 
decision logic. 

This decision logic deviates slightly from the original  GHS in separating the connection between 
Category 2 and Category 3, since, different from the procedure in other hazard classes, they have 
to be regarded as independent. 

 
 
 
 
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Classification in Category 1 and Category 2 

Does the substance have data and/or information to evaluate 
specific target organ toxicity following single exposure? 

No 

Classification 
not possible 

Yes 

Following single exposure, 

Category 1 

(a) Can the substance produce significant toxicity in humans, or  

(b)  Can  it  be  presumed  to  have  the  potential  to  produce 
significant  toxicity  in  humans  on  the  basis  of  evidence  from 
studies in experimental animals? 

Yes 

See  CLP  Annex  I,  3.8.2  for  criteria  and  guidance  values. 
Application of the criteria needs expert judgment in a weight of 
evidence approach. 

Danger 

No 

Category 2 

Following single exposure, 

Can  the  substance  be  presumed  to  have  the  potential  to  be 
harmful to human health on the basis of evidence from studies 
in experimental animals? 

Yes 

See  CLP  Annex  I,  3.8.2  for  criteria  and  guidance  values. 
Application of the criteria needs expert judgment in a weight of 
evidence approach. 

Warning 

No 

Not classified 

 
 
 
 
 
 
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Classification in Category 3 

Does the substance have data and/or information to 
evaluate specific target organ toxicity following single 
exposure with relevance for RTI or narcotic effects? 

No 

Yes 

Following single exposure, 

Can the substance produce respiratory tract irritation or 
narcotic effects? 

Yes 

See  CLP  Annex  I,  3.8.2  for  criteria.  Application  of  the 
criteria  needs  expert  judgment  in  a  weight  of  evidence 
approach. 

Classification 
not possible 

Category 3 

Warning 

No 

Not classified 

3.8.3.  Classification of mixtures for STOT-SE  

3.8.3.1. 

Identification of hazard information  

Where toxicological information is available on a mixture this should be used to derive the 
appropriate classification. Such information may be available from the mixture manufacturer. 
Where such information on the mixture itself is not available information on similar mixtures 
and/or the component substances in the mixture must be used, as described below. 

3.8.3.2.  Classification criteria for mixtures 

Annex I: 3.8.3.1. Mixtures are classified using the same criteria as for substances, or 
alternatively as described below.  

3.8.3.2.1.  When data are available for the complete mixture 

Annex I: 3.8.3.2.1. When reliable and good quality evidence from human experience or 
appropriate studies in experimental animals, as described in the criteria for substances, is 
available for the mixture, then the mixture shall be classified by weight of evidence evaluation 
of these data (see 1.1.1.3). Care shall be exercised in evaluating data on mixtures, that the 
dose, duration, observation or analysis, do not render the results inconclusive 

In cases where test data for mixtures are available, the classification process is exactly the 
same as for substances.  

 
 
 
 
 
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3.8.3.2.2.  When data are not available for the complete mixture: bridging principles 

Annex I: 3.8.3.3.1. Where the mixture itself has not been tested to determine its specific 
target organ toxicity, but there are sufficient data on the individual ingredients and similar 
tested mixtures toadequately characterise the hazards of the mixture, these data shall be 
used in accordance with the bridging principles set out in section 1.1.3. 

In order to apply bridging principles, there needs to be sufficient data on similar tested mixtures 
as well as the ingredients of the mixture (see Section 1.6.3 of this Guidance). 

When the available identified information is inappropriate for the application of the bridging 
principles then the mixture should be classified using the calculation method or concentration 
thresholds as described in Sections 3.8.3.2.3, 3.8.3.2.4 and 3.8.3.3 of this Guidance. 

3.8.3.2.3.  When data are available for all ingredients or only for some ingredients of 

the mixture 

Annex I: 3.8.3.4.1. Where there is no reliable evidence or test data for the specific mixture 
itself, and the bridging principles cannot be used to enable classification, then classification of 
the mixture is based on the classification of the ingredient substances. In this case, the 
mixture shall be classified as a specific target organ toxicant (specific organ specified), 
following single exposure, when at least one ingredient has been classified as a Category 1 or 
Category 2 specific target organ toxicant and is present at or above the appropriate generic 
concentration limit as mentioned in Table 3.8.3 below for Category 1 and 2 respectively. 

A mixture not classified as corrosive but containing a corrosive ingredient should be considered 
for classification in Category 3 RTI on a case-by-case basis following the approach explained 
above (see Section 3.8.2.3 of this Guidance). More information on classification of mixtures into 
Category 3 is provided below (Section 3.8.3.3 of this Guidance). 

3.8.3.2.4. 

Components of a mixture that should be taken into account for the 
purpose of classification 

Components with a concentration equal to or greater than the generic concentration limits (1% 
for Category 1 components and 10% for Category 2. See CLP Annex I, Table 3.8.3), or with a 
Specific Concentration Limit (see Section 3.8.2.6 of this Guidance) will be taken into account for 
classification purposes. For Category 3, the GCL is 20%. Specific concentration limits have 
preference over the generic ones.  

3.8.3.3.  Generic concentration limits for substances triggering classification 

of mixtures for STOT-SE 

The STOT-SE hazard class does not foresee summation of Category 1 or 2 substances in the 
classification process of a mixture. Furthermore, as Category 1 and 2 depict different hazards 
than Category 3 the assessment must be done independently from each other.  

 
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Annex I: Table 3.8.3 

Generic concentration limits of ingredients of a mixture classified as a specific target 
organ toxicant that trigger classification of the mixture as Category 1 or 2 

INGREDIENT CLASSIFIED 
AS: 

Generic concentration limits triggering classification 

of the mixture as : 

Category 1 

Category 2 

Category 1 

Concentration  10% 

1.0%  concentration  10% 

Specific Target Organ Toxicant 

Category 2 

Specific Target Organ Toxicant 

Note 1: 

Concentration  10% 

[(Note 1)] 

If a Category 2 specific target organ toxicant is present in the mixture as an ingredient at a 
concentration ≥ 1.0% a SDS shall be available for the mixture upon request. 

Annex I: 3.8.3.4.4. Care shall be exercised when toxicants affecting more than one organ 
system are combined that the potentiation or synergistic interactions are considered, because 
certain substances can cause target organ toxicity at < 1% concentration when other 
ingredients in the mixture are known to potentiate its toxic effect. 

Annex I: 3.8.3.4.5. Care shall be exercised when extrapolating toxicity of a mixture that 
contains Category 3 ingredient(s). A generic concentration limit of 20% is appropriate; 
however, it shall be recognised that this concentration limit may be higher or lower depending 
on the Category 3 ingredient(s) and that some effects such as respiratory tract irritation may 
not occur below a certain concentration while other effects such as narcotic effects may occur 
below this 20% value. Expert judgement shall be exercised. Respiratory tract irritation and 
narcotic effects are to be evaluated separately in accordance with the criteria given in section 
3.8.2.2. When conducting classifications for these hazards, the contribution of each 
component should be considered additive, unless there is evidence that the effects are not 
additive. 

Categories 1 and 2 

Each single classified component in a concentration range given in CLP Annex I, Table 3.8.3 
triggers the classification of the mixture, i.e. additivity of the concentrations of the components 
is not applicable. 

Category 3 

When a mixture contains a number of substances classified with Category 3 and present at a 
concentration below the GCL (i.e. 20%), an additive approach to determine the classification of 
the mixture as a whole should be applied unless there is evidence that the effects are not 
additive. In the additive approach the concentrations of the individual substances with the same 
hazard (i.e. RTI or narcotic effects) are totalled separately. If each individual total is greater 
than the GCL then the mixture should be classified as Category 3 for that hazard. A mixture 
may be classified either as STOT-SE 3 (RTI) or STOT-SE 3 (narcotic effects) or both.  

Example  

The following example shows whether or not additivity should be considered for Specific Target 
Organ Toxicity – Single Exposure (STOT-SE) Category 3 transient effects. 

Ingredient information: 

 
 
 
 
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Ingredient 

Wt%  Classification 

Ingredient 1 

0.5 

- 

Ingredient 2 

3.5 

Category 3 – Respiratory Tract Irritation 

Ingredient 3 

15 

Category 3 – Narcotic effects 

Ingredient 4 

15 

Category 3 – Narcotic effects 

Ingredient 5 

66 

- 

Answer: 

Mixture is Category 3 – Narcotic effects 

∑%Category 3 – Narcotic effects = 15% + 15% = 30% which is > 20%, therefore classify 
as Category 3 – Narcotic Effects 

∑%Category 3 – Respiratory Irritation = 3.5%, which is < 20%, not classified for 
Respiratory Irritation 

Rationale: 

a.  Classification via application of substance criteria is not possible since test data was not 

provided for the mixture (CLP Annex I, 3.8.3.2);  

b.  Classification via the application of bridging principles is not possible since data on a 

similar mixture was not provided (CLP Annex I, 3.8.3.3.1); 

c.  Application of CLP Annex I, 3.8.3.4.5 is used for classification. Expert judgement is 

necessary when applying this paragraph. CLP Annex I, 3.8.3.4.5 notes that a cut-off 
value/concentration limit of 20% has been suggested, but that the cut-off 
value/concentration limit at which effects occur may be higher or less depending on the 
Category 3 ingredient(s). In this case, the classifiers judged that 30% is sufficient to 
classify. 

SCLs 

In the case where a specific concentration limit has been established for one or more 
ingredients these SCLs have precedence over the generic concentration limit. 

3.8.3.4.  Decision logic for classification of mixtures 

A mixture should be classified either in Category 1 or in Category 2, according to the criteria 
described above. The corresponding hazard statement (H370 for Category 1 or H371 for 
Category 2) should be used without specifying the target organs, except if the classification of 
the mixture is based on data available for the complete mixture, in which case the target organs 
may be given. In the same way, the route of exposure should not be specified, except if data 
are available for the complete mixture and it is conclusively demonstrated that no other routes 
of exposure cause the hazard.  

If the criteria are fulfilled to classify also the mixture in Category 3 for respiratory irritation or 
narcotic effects, only the corresponding hazard statement (H335 and/or H336) will be added in 
hazard communication. 

The decision logic is provided as additional guidance. It is strongly recommended that the 
person responsible for classification study the criteria for classification before and during use of 
the decision logic.  

 
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This decision logic deviates slightly from the original GHS in separating the connection between 
Category 2 and Category 3, since different from the procedure in other hazard classes they 
have to be regarded as independent. 

Classification in Category 1 or 2 

Does the mixture as a whole have data/information to 
evaluate specific target organ toxicity following single 
exposure? 

Yes 

No 

Can bridging principles be applied? 

Yes 

No 

Does the mixture contain one or more ingredients 
classified as a Category 1 specific target organ 
toxicant at a concentration  10%? 

Yes 

No 

See decision 
logics for 
substances 

Classify in 
appropriate 
category 

Categorie 1 

Danger 

Categorie 2 

Does  the  mixture  contain  one  or  more  ingredients 
classified as a Category 1 specific target organ toxicant 
at a concentration of  1.0 and < 10%? 

Yes 

Or  

One  or  more  ingredients  classified  as  a  Category  2 
specific target organ toxicant at a concentration  10%? 

Warning 

No 

Not classified 

 
 
 
 
 
 
 
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Classification in Category 3 

Does the mixture as a whole have data and/or 
information to evaluate specific target organ toxicity 
following single exposure with relevance for RTI or 
narcotic effects? 

No 

Can bridging principles be applied? 

No 

Yes 

Yes 

Does the mixture contain one or more ingredients 
classified as a Category 3 specific target organ 
toxicant at a concentration  20%? 

Yes 

No 

Not classified 

See decision 
logics for 
substances 

Classify in 
appropriate 
category 

Categorie 3 

Warning 

 
 
 
 
 
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3.8.4.  Hazard communication in form of labelling for STOT-SE 

3.8.4.1.  Pictograms, signal words, hazard statements and precautionary 

statements  

Annex I: 3.8.4.1. Label elements shall be used in accordance with Table 3.8.4., for substances 
or mixtures meeting the criteria for classification in this hazard class. 

Label elements for specific target organ toxicity after single exposure 

Table 3.8.4 

Classification 

Category 1 

Category 2 

Category 3 

GHS Pictograms 

Signal Word 

Danger 

Warning 

Warning 

Hazard statement 

H370: Causes damage 
to organs (or state all 
organs affected, if 
known) (state route of 
exposure if it is 
conclusively proven 
that no other routes of 
exposure cause the 
hazard) 

H371: May cause 
damage to organs (or 
state all organs 
affected, if known) 
(state route of 
exposure if it is 
conclusively proven 
that no other routes of 
exposure cause the 
hazard) 

H335: May cause 
respiratory irritation; 

or 

H336: May cause 
drowsiness or 
dizziness 

Precautionary 
Statement 
Prevention 

Precautionary 
Statement 
Response 

Precautionary 
Statement 
Response 

P260 
P264 
P270 

P307 + P311 
P321 

P308 + P311 
P321 

Precautionary 
Statement Storage 

Precautionary 
Statement Disposal 

P405 

P501 

P260 
P264 
P270 

P309 + P311 

P308 + P311 

P405 

P501 

P261 
P271 

P304 + P340 
P312 

P304 + P340 
P312 

P403 + P233 
P405 

P501 

The hazard statement should include the primary target organ(s) of toxicity. Organs in which 
secondary effects were observed should not be included. The route of exposure should not be 

 
 
 
 
 
 
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specified, except if it is conclusively demonstrated that no other routes of exposure cause the 
hazard. When a mixture is classified for STOT-SE on basis of test data, the hazard statement 
will specify the target organs, in the same way as for a substance.  If a mixture is classified on 
basis of the ingredients, the hazard statement (H370 for Category 1 or H371 for Category 2) 
may be used without specifying the target organs, as appropriate. 

In the same way, the route of exposure should not be specified, except if data are available for 
the complete mixture and if it is conclusively demonstrated that no other routes of exposure 
cause the hazard. It is recommended to include no more than three primary target organs for 
practical reasons and because the classification is for specific target organ toxicity. If more 
target organs are effected it is recommended that the overall systemic damage should be 
reflected by using the phrase ‘damage to organs’. 

3.8.4.2.  Additional labelling provisions 

Annex I: 3.8.2.1.10.4 

Saturated vapour concentration shall be considered, where appropriate, as an additional 
element to provide for specific health and safety protection. 

According to CLP Annex I, 3.8.2.1.10.4 the saturated vapour concentration shall be considered 
as an additional element for providing specific health and safety protection. Thus if a classified 
substance is highly volatile a supplementary precautionary advice (e.g. ‘Special/additional care 
should be taken due to the high saturated vapour pressure’) might be given in order to 
emphasize the hazard in case it is not already covered by the general precautionary statements. 
(As a rule, the supplementary precautionary advice would normally be given for substances for 
which the ratio of the effect concentration at ≤ 4h to the SVC at 20° C is ≤1/10). 

Diluted corrosive substances (may) exhibit an irritation potential with respect to the respiratory 
tract if they have a sufficient saturated vapour concentration. Expert judgement is needed for a 
decision with respect to a classification in STOT-SE Category 3. In these cases a switch from 
one hazard class (skin corrosion/irritation) to another (STOT-SE) would be justified. 

3.8.5.  Examples of classification for STOT-SE 

3.8.5.1.  Examples of substances fulfilling the criteria for classification  

3.8.5.1.1. 

Example 1: Methanol 

Application  Use  of  adequate  and  reliable  human  data,  where  animal  data  are  not 
appropriate. Independent classification for STOT-SE and Acute toxicity due to 
different effects 

Available 
information 

Test Data 

Animal data: 

LD50 rat > 5,000 (mg/kg bw)  

No specific target organ toxicity 
(impairment of seeing ability) 
observed in rats, even in high 
doses. 

Classification  Rationale  

Classification 
not possible 

The rat is known to be 
insensitive to the toxicity of 
methanol and is thus not 
considered to be a good 
model for human effects 
(different effect/mode of 
action) 

Human experience: 

Broad human experience from 
many case reports about blindness 
following oral intake. Methanol is 

STOT-SE 
Category 1 

The classification criteria for 
Category 1 are fulfilled: clear 
human evidence of a specific 
target organ toxicity effect 

 
 
 
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known to cause lethal intoxications 
in humans (mostly via ingestion) in 
relatively low doses: ‘ …minimal 
lethal dose in the absence of 
medical treatment is between 300 
and 1000 mg/kg bw’ (IPCS) 

which is not covered by 
Acute toxicity. 

Remarks 

The standard animal species for single exposure (acute) tests, the rat, is not 
sensitive, i.e. no appropriate species for this specific target organ effect. Methanol is 
classified independently for acute toxicity, since the impairment of vision is not 
causal for the lethality, i. e. there are different effects. 

Labelling:  

Pictogram GHS 08; Signal word: Danger; Hazard statement: H370 Causes 
damage to the eye. 

3.8.5.1.2. 

Example 2: Tricresyl phosphate 

Application 

Use of valid human evidence supported by animal data 

Test Data 

Classification  Rationale  

STOT-SE 
Category 1 

The classification criteria are 
clearly fulfilled based on 
human experience as well as 
on results of animal studies 

Available 
information 

Human experience: 

There are well documented case 
reports about severe neurotoxic 
effects 

Animal experiments: 

Severe neurotoxic effects 
(Paralysis) were observed after 
single exposure of doses < 200 
mg/kg bw 

LD50 rat oral 3000 - 3900 mg/kg 
bw 

Remarks 

Labelling: 

Pictogram GHS 08; Signal word: Danger; Hazard Statement: H370 Causes 
damage to the central nervous system. 

3.8.5.1.3. 

Example 3: Sulfur dioxide 

Application 

Use of valid human evidence 

Test Data 

Classification  Rationale  

Available 
information 

Human experience: 

Broad, well documented human 
experience on irritating effect to 
respiratory system. 

STOT-SE 
Category 3  

The classification criteria for 
Category 3 (Respiratory Tract 
Irritation) are fulfilled based 
on well documented 
experience in humans 

Remarks 

Labelling: 

Pictogram GHS 07; Signal word: Warning; Hazard statement: H335 May 
cause respiratory irritation 

 
 
 
 
 
 
 
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3.8.5.1.4. 

Example 4: Toluene  

Application 

Use of valid animal data 

Test Data 

Classification 

Rationale  

Available 
information 

Animal data: 

In valid animal experiments 
narcotic effects (transient 
effect on nervous system) 
at ≥ 8 mg/l were observed. 

STOT-SE 
Category 3  

The classification criteria for 
Category 3 (Narcotic Effects) 
are fulfilled based on well 
documented results in animal 
experiments 

Remarks 

Labelling: 

Pictogram GHS 07; Signal word: Warning; Hazard statement: H336 May 
cause drowsiness and dizziness 

3.8.5.2.  Examples of substances not fulfilling the criteria for classification  

3.8.5.2.1. 

Example 5: ABC  

Application 

No classification for STOT-SE in case same effect leading to Acute toxicity 
classification 

Available 
information 

Test Data 

Animal data: 

In a study in rats after single 
exposure at 2,000 mg/kg bw 
severe damage in liver 
(macroscopic examination) and 
mortality in 6/10 animals were 
observed 

Classification  Rationale  

No 
classification 
in STOT- SE  

Though a specific organ is 
damaged, the substance will 
be classified in Acute Toxicity 
(Category 4), since lethality 
was observed which was due 
to the liver impairment. It is 
assumed that the LD50=ATE 
is ≤ 2,000 mg/kg bw. There 
should be no double 
classification for the same 
effect/mechanism causing 
lethality by impairment of a 
specific organ, thus no 
classification for STOT-SE 

 
 
 
 
 
 
 
 
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3.8.5.2.2. 

Example 6: N,N-Dimethylaniline 

Application 

No classification for STOT-SE in case  same  effect leading toAcute toxicity 
classification 

Available 
information 

Test Data 

Animal data: 

Acute oral toxicity: LD50 values 
> 1,120-1,300 mg/kg bw oral 
rat and 1,690 mg/kg bw dermal 
rabbit; ca. 50 mg/kg are lethal 
in cats due to high Met HB 
formation; no specific target 
organ toxicity (blood toxicity) 
observed in rats. 

Human experience: 

Broad human experience from 
many case reports about lethal 
intoxications caused by 
methemoglobinemia following 
oral/dermal/inhalation exposure 
to aromatic amines  

Classification 

Rationale  

No  classification 
in STOT-SE  

No  classification 
in STOT-SE  

The criteria for STOT-SE 
classification are not fulfilled 
despite a clear specific 
target organ effect in 
humans and in a relevant 
animal species. The 
substance is classified in 
Category 3 Acute Toxicity 
since the Met HB formation 
is causative for the lethality 
in humans and in animals 
(cats) in low doses. 

Remarks 

The standard animal species for single exposure (acute) tests, the rat, is not 
sensitive, i.e. no appropriate species for this specific effect. 

 
 
 
 
 
 
 
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3.9.  SPECIFIC TARGET ORGAN TOXICITY – REPEATED EXPOSURE 

(STOT-RE) 

3.9.1.  Definitions and general considerations for STOT-RE 

Annex I: 3.9.1.1. Specific target organ toxicity (repeated exposure) means specific, target 
organ toxicity arising from a repeated exposure to a substance or mixture. All significant 
health effects that can impair function, both reversible and irreversible, immediate and/or 
delayed are included. However, other specific toxic effects that are specifically addressed in 
Chapters 3.1 to 3.8 and Chapter 3.10 are not included here. 

According to CLP Annex I, 3.9.1.1, specific toxic effects covered by other hazard classes are not 
included in STOT-RE. STOT-RE should only be assigned where the observed toxicity is not 
covered more appropriately by another hazard class. For example specific effects like tumours 
or effects on the reproductive organs should be used for classification for carcinogenicity or 
reproductive toxicity, respectively, but not for STOT-RE. 

Annex I: 3.9.1.3. These adverse health effects include consistent and identifiable toxic 
effects in humans, or, in experimental animals, toxicologically significant changes which have 
affected the function or morphology of a tissue/organ, or have produced serious changes to 
the biochemistry or haematology of the organism and these changes are relevant for human 
health.  

Annex I: 3.9.1.4. Assessment shall take into consideration not only significant changes in a 
single organ or biological system but also generalised changes of a less severe nature 
involving several organs. 

Annex I: 3.9.1.5. Specific target organ toxicity can occur by any route that is relevant for 
humans, i.e. principally oral, dermal or inhalation. 

Annex I: 3.9.2.2. The relevant route or routes of exposure by which the classified substance 
produces damage shall be identified. 

The purpose of STOT-RE is to identify the primary target organ(s) of toxicity (CLP Annex I, 
3.9.1.4) for inclusion in the hazard statement. Where possible secondary effects are observed in 
other organs, they should be carefully considered for the classification. The STOT-RE 
classification should identify those routes by which the substance causes the target organ 
toxicity (CLP Annex I, 3.9.1.5 and 3.9.2.2). This is usually based on the available evidence for 
each route. There are no compelling reasons to do route-to-route extrapolation to attempt to 
assess the toxicity by other routes of exposure for which there are no data. 

Annex I: 3.9.1.6. Non-lethal toxic effects observed after a single-event exposure are 
classified as described in Specific target organ toxicity — Single exposure (section 3.8) and 
are therefore excluded from section 3.9. 

Where the same target organ toxicity of similar severity is observed after single and repeated 
exposure to a similar dose, it may be concluded that the toxicity is essentially an acute (i.e. 
single exposure) effect with no accumulation or exacerbation of the toxicity with repeated 
exposure. In such a case classification with STOT-SE only would be appropriate. 

 
 
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3.9.2.  Classification of substances for STOT-RE 

3.9.2.1. 

Identification of hazard information  

Annex 1: 3.9.2.5. The information required to evaluate specific target organ toxicity comes 
either from repeated exposure in humans, such as exposure at home, in the workplace or 
environmentally, or from studies conducted in experimental animals.  

CLP does not require testing of substances and mixtures for classification purposes. The 
assessment is based on the respective criteria and consideration of all available adequate and 
reliable information, primarily such relating to repeated-dose exposures but also taking into 
account the general physico-chemical nature of the substance. The most useful information is 
generally from human epidemiology, case studies and animal studies, but information obtained 
using read-across from similar substances and from appropriate in vitro models can also be 
used, where appropriate. 

3.9.2.1.1. 

Identification of human data 

Relevant information with respect to repeated dose toxicity may be available from case reports, 
epidemiological studies, medical surveillance and reporting schemes, and national poisons 
centres. 

Details are given in the Guidance on IR&CSA, Section 7.5.3.2. 

3.9.2.1.2. 

Identification of non human data  

Annex 1: 3.9.2.5. …. The standard animal studies in rats or mice that provide this 
information are 28 day, 90 day or lifetime studies (up to 2 years) that include haematological, 
clinicochemical and detailed macroscopic and microscopic examination to enable the toxic 
effects on target tissues/organs to be identified. Data from repeat dose studies performed in 
other species shall also be used, if available. Other long-term exposure studies, such as on 
carcinogenicity, neurotoxicity or reproductive toxicity, may also provide evidence of specific 
target organ toxicity that could be used in the assessment of classification. 

Non-testing data 

Physico-chemical data 

Physicochemical properties, such as pH, physical form, solubility, vapour pressure, and particle 
size, can be important parameters in evaluating toxicity studies and in determining the most 
appropriate classification especially with respect to inhalation where physical form and particle 
size can have a significant impact on toxicity. 

(Q)SAR models 

Structurally or mechanistically related substance(s), read-across/grouping/chemical category 
and metabolic pathway approach: A (Q)SAR analysis for a substance may give indications for a 
specific mechanism of action and identify possible organ or systemic toxicity upon repeated 
exposure. Overall, (Q)SAR approaches are currently not well validated for repeated dose 
toxicity. (Guidance on IR&CSA, Section R7.5.4.1). Data on structurally analogous substances 
may be available and add to the toxicity profile of the substance under investigation. The 
concept of grouping, including both read-across and the related chemical category concept has 
been developed under the OECD HPV chemicals program. For certain substances without test 
data the formation of common significant metabolites or information with those of tested 
substances or information from precursors may be valuable information. (For more details see 
the Guidance on IR&CSA, Sections R.6.1 and R.6.2.5.2 and OECD (2004)). OECD Principles for 
the Validation, for Regulatory Purposes, of (Quantitative) Structure-Activity Relationship 
Models) 

 
 
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Testing data 

Animal data 

‘The most appropriate data on repeated dose toxicity for use in hazard characterisation and risk 
assessment are primarily obtained from studies in experimental animals conforming to 
internationally agreed test guidelines. In some circumstances repeated dose toxicity studies not 
conforming to conventional test guidelines may also provide relevant information for this 
endpoint’ (Guidance on IR&CSA, Section R.7.5.3.1). Studies not performed according to 
Standard Test Guidelines and/or GLP have to be evaluated on case by case basis by expert 
judgement and in the context of a total weight of evidence assessment if there are more data 
(for more information see Section 3.9.2.3.4 of this Guidance and the Guidance on IR&CSA, 
Section R.7.5.4.1. 

The standard test guidelines are described in the Gudiance on IR&CSA, Section R.7.5.4.1. There 
may also be studies employing different species and routes of exposure. In addition, special 
toxicity studies investigating further the nature, mechanism and/or dose relationship of a critical 
effect in a target organ or tissue may also have been performed for some substances. Other 
studies providing information on repeated dose toxicity: although not aiming at investigating 
repeated dose toxicity per se and other available EU/OECD test guideline studies involving 
repeated exposure of experimental animals may provide useful information on repeated dose 
toxicity, e.g reproduction toxicity or carcinogenicity studies. For more details see the Guidance 
on IR&CSA, Section R .7.5.4.1 (ECHA, 2008). 

In vitro data 

At present available in vitro data is not useful on its own for regulatory decisions such as 
classification and labelling. However, such data may be helpful in the assessment of repeated 
dose toxicity, for instance to detect local target organ effects and/or to clarify the mechanisms 
of action. Since, at present, there are no validated and regulatory accepted in vitro methods, 
the quality of each of these studies and the adequacy of the data provided should be carefully 
evaluated(Guidance on IR&CSA, Section R.7.5.4.1). 

3.9.2.2.  Classification criteria for substances 

Annex 1: 3.9.2.1. Substances are classified as specific target organ toxicants following 
repeated exposure by the use of expert judgement (see 1.1.1), on the basis of the weight of 
all evidence available, including the use of recommended guidance values which take into 
account the duration of exposure and the dose/concentration which produced the effect(s), 
(see 3.9.2.9), and are placed in one of two categories, depending upon the nature and 
severity of the effect(s) observed (Table 3.9.1). 

Categories for specific target organ toxicity-repeated exposure 

Table 3.9.1 

Categories 

Criteria 

 
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Substances that have produced significant toxicity in humans or that, on the 
basis of evidence from studies in experimental animals, can be presumed to 
have the potential to produce significant toxicity in humans following repeated 
exposure. Substances are classified in Category 1 for target organ toxicity 
(repeat exposure) on the basis of: 

Category 1 

reliable and good quality evidence from human cases or epidemiological studies; 
or 

observations from appropriate studies in experimental animals in which 
significant and/or severe toxic effects, of relevance to human health, were 
produced at generally low exposure concentrations. Guidance 
dose/concentration values are provided below (see 3.9.2.9), to be used as part 
of a weight-of- evidence evaluation. 

Substances that, on the basis of evidence from studies in experimental animals 
can be presumed to have the potential to be harmful to human health following 
repeated exposure. Substances are classified in category 2 for target organ 
toxicity (repeat exposure) on the basis of observations from appropriate studies 
in experimental animals in which significant toxic effects, of relevance to human 
health, were produced at generally moderate exposure concentrations. 
Guidance dose/concentration values are provided below (see 3.9.2.9) in order 
to help in classification.  

In exceptional cases human evidence can also be used to place a substance in 
Category 2 (see 3.9.2.6). 

Category 2 

Note  

Attempts shall be made to determine the primary target organ of toxicity and classify for that 
purpose, such as hepatotoxicants, neurotoxicants. One shall carefully evaluate the data and, 
where possible, not include secondary effects (a hepatotoxicant can produce secondary effects 
in the nervous or gastro-intestinal systems). 

  NOTE: In the Note above (in green box) ‘classify’ would mean to identify the primary target 

organ. 

STOT-RE is assigned on the basis of findings of ‘significant’ or ‘severe’ toxicity.  In this context 
‘significant’ means changes which clearly indicate functional disturbance or morphological 
changes which are toxicologically relevant. ‘Severe’ effects are generally more profound or 
serious than ‘significant’ effects and are of a considerably adverse nature which significantly 
impact on health. Both factors have to be evaluated by weight of evidence and expert 
judgement. 

Annex I: 3.9.2.9.4. The decision to classify at all can be influenced by reference to the 
dose/concentration guidance values at or below which a significant toxic effect has been 
observed. 

Annex I: 3.9.2.9.6. Thus classification in Category 1 is applicable, when significant toxic 
effects observed in a 90-day repeated-dose study conducted in experimental animals are 
seen to occur at or below the guidance values (C) as indicated in Table 3.9.2 below: 

Guidance values to assist in Category 1 classification 

Table 3.9.2 

 
 
 
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Route of exposure 

Units 

Guidance values 
(dose/concentration) 

Oral (rat) 

mg/kg body weight/day 

Dermal (rat or rabbit) 

mg/kg body weight/day 

Inhalation (rat) gas 

ppmV/6h/day 

Inhalation (rat) vapour 

mg/litre/6h/day 

Inhalation (rat) dust/mist/fume 

mg/litre/6h/day 

C ≤ 10 

C ≤ 20 

C ≤ 50 

C ≤ 0,2 

C ≤ 0,02 

Annex I: 3.9.2.9.7. Classification in Category 2 is applicable, when significant toxic effects 
observed in a 90-day repeated-dose study conducted in experimental animals are seen to 
occur within the  guidance value ranges as indicated in Table 3.9.3 below: 

Guidance values to assist in Category 2 classification 

Table 3.9.3 

Route of Exposure 

Units  Guidance 

Value Ranges: 
(dose/concentration) 

Oral (rat) 

mg/kg body weight/day 

10 < C ≤ 100 

Dermal (rat or rabbit) 

mg/kg body weight/day 

20 < C ≤ 200 

Inhalation (rat) gas 

ppmV/6h/day 

50 < C ≤ 250 

Inhalation (rat) vapour 

mg/litre/6h/day 

0,2 < C ≤ 1,0 

Inhalation (rat) dust/mist/fume 

mg/litre/6h/day 

0,02 < C ≤ 0,2 

Annex I: 3.9.2.9.8. The guidance values and ranges mentioned in paragraphs 3.9.2.9.6 and 
3.9.2.9.7 are intended only for guidance purposes, i.e., to be used as part of the weight of 
evidence approach, and to assist with decisions about classification. They are not intended as 
strict demarcation values. 

Annex I: 3.9.2.9.5.The guidance values refer to effects seen in a standard 90-day toxicity 
study conducted in rats. They can be used as a basis to extrapolate equivalent guidance 
values for toxicity studies of greater or lesser duration, using dose/exposure time 
extrapolation similar to Haber’s rule for inhalation, which states essentially that the effective 
dose is directly proportional to the exposure concentration and the duration of exposure. The 
assessment shall be done on a case-by-case basis; for a 28-day study the guidance values 
below is increased by a factor of three.  

Haber’s rule is used to adjust the standard guidance values, which are for studies of 90-day 
duration, for studies of longer or shorter durations. It should be used cautiously with due 
consideration of the nature of the substance in question and the resulting value produced. 

 
 
 
 
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In particular, care should be taken when using Haber’s rule to assess inhalation data on 
substances which are corrosive or local active or have the potential to accumulate with repeated 
exposure. 

One particular problem to note is that when adjusting the guidance value for very short study 
durations this can lead to very high guidance values which are not appropriate. For instance, for 
a 4 day exposure a guidance value of 2250 mg/kg bw/day for classification as STOT-RE 
category 2 could potentially be produced. This is above the limit for acute toxicity of 2000 
mg/kg bw and it does not make sense to have a guidance value for repeated dose toxicity that 
is above the guidance value for mortality after acute exposure. To address this problem a 
pragmatic approach is proposed. For studies with exposure durations shorter than 9 days (i.e 
10% of the 90 days to which the default general guidance value applies) the guidance value 
used should be no greater than 10 times the default guidance value. For example, the effects in 
an oral range-finding study of 9 days or less should be compared with a guidance value of 1000 
mg/kg bw/day for STOT-RE Category 2. 

Expert judgement is needed for the establishment of equivalent guidance values because one 
needs to know about the limitations of the applicability of the proportionality. In the following 
table the equivalents for 28-day and 90-day studies according to Haber's rule are given: 

Table 3.16 Equivalent guidance values for 28-day and 90-day studies 

Study type 

Species 

Unit 

Category 1 
90-day 

Category 1 
28-day 

Category 2 
90-day 

Category 2 
28-day 

Oral 

Rat 

Dermal 

Rat 

Inhalation, gas 

Rat 

Inhalation, 
vapor 

Inhalation, 
dust/mist/fume 

Rat 

Rat 

mg/kg 
bw/d 

mg/kg 
bw/d 

ppmV/6 
h/d 

mg/l/6 
h/d 

mg/l/6 
h/d 

≤ 10 

≤ 30 

≤ 100 

≤ 300 

≤ 20 

≤ 60 

≤ 200 

≤ 600 

≤ 50 

≤ 150 

≤ 250 

≤ 750 

≤ 0.2 

≤ 0.6 

≤ 1 

≤ 3 

≤ 0.02 

≤ 0.06 

≤ 0.2 

≤ 0.6 

Annex I: 3.9.2.9.9. Thus it is feasible that a specific profile of toxicity occurs in repeat-dose 
animal studies at a dose/concentration below the guidance value, such as < 100 mg/kg bw/day 
by the oral route, however the nature of the effect, such as nephrotoxicity seen only in male 
rats of a particular strain known to be susceptible to this effect may result in the decision not 
to classify. Conversely, a specific profile of toxicity may be seen in animal studies occurring at 
or above a guidance value, such as ≥ 100 mg/kg bw/day by the oral route, and in addition 
there is supplementary information from other sources, such as other long-term administration 
studies, or human case experience, which supports a conclusion that, in view of the weight of 
evidence, classification is the prudent action to take. 

3.9.2.3.  Evaluation of hazard information  

Annex I: 3.9.2.4. […] Evaluation shall be based on all existing data, including peer-reviewed 
published studies and additional acceptable data. 

 
 
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3.9.2.3.1. 

Evaluation of human data  

Annex I: 1.1.1.4. For the purpose of classification for health hazards (Part 3) established 
hazardous effects seen in appropriate animal studies or from human experience that are 
consistent with the criteria for classification shall normally justify classification. Where 
evidence is available from both humans and animals and there is a conflict between the 
findings, the quality and reliability of the evidence from both sources shall be evaluated in 
order to resolve the question of classification. Generally, adequate, reliable and representative 
data on humans (including epidemiological studies, scientifically valid case studies as specified 
in this Annex or statistically backed experience) shall have precedence over other data. 
However, even well-designed and conducted epidemiological studies may lack a sufficient 
number of subjects to detect relatively rare but still significant effects, to assess potentially 
confounding factors. Therefore, positive results from well-conducted animal studies are not 
necessarily negated by the lack of positive human experience but require an assessment of 
the robustness, quality and statistical power of both the human and animal data.  

Annex I: 3.9.2.7.2. Evidence from human experience/incidents is usually restricted to 
reports of adverse health consequence, often with uncertainty about exposure conditions, and 
may not provide the scientific detail that can be obtained from well-conducted studies in 
experimental animals. 

Where relevant human data do not mirror realistic exposure conditions, supportive information 
may be needed to corroborate the observed effects. A single case report from deliberate 
exposure (i.e. abuse) is unlikely to provide sufficiently robust evidence to support classification 
without other evidence.  

The Guidance on IR&CSA, Section R.7.5.4.2 gives a detailed description on the use of human 
hazard information 

3.9.2.3.2. 

Evaluation of non human data  

Annex I: 3.9.2.7.3. Evidence from appropriate studies in experimental animals can furnish 
much more detail, in the form of clinical observations, haematology, clinical chemistry, and 
macroscopic and microscopic pathological examination, and this can often reveal hazards that 
may not be life-threatening but could indicate functional impairment. 

All available animal data which are of acceptable quality should be used in a weight of evidence 
approach based on a comparison with the classification criteria described above. This should be 
done separately for each route for which data are available. 

For each study the effects seen in each sex at or around the guidance values for Category 1 and 
Category 2 should be compared with the effects warranting classification in Category 1 and 
Category 2. In general findings in the most sensitive sex would be used to determine the 
classification.  If the NOAEL from the study is above the guidance value (GV), the results of that 
study do not indicate classification for that category (situations 1 and 2 in Figure 3.8 below). If 
the NOAEL is below the GV then the effective dose level (ED), i.e. the lowest dose inducing 
significant/severe target organ toxicity as defined in Section 3.9.2.2 of this Guidance, should be 
determined based on the criteria described above. If the ED is below the GV then this study 
indicates that classification is warranted (situations 2 and 4 in Figure 3.8).  

In a case where the ED is above a GV but the NOAEL is below the GV (situations 3 and 5 Figure 
3.8) then interpolation between the ED and the NOAEL is required to determine whether the 
effects expected at or below the GV would warrant classification.  

 
 
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Figure 3.8  Comparison between the NOAEL and the ED versus the guidance values 

Situation 1 

Situation 2 

Situation 3 

Situation 4 

Situation 5 

GV 

Category 2 

GV 

Category 1 

- NOAEL 1 

- ED 3 

- ED 2 

- NOAEL 3 

- NOAEL 2 

- ED 5 

- ED 4 

- NOAEL 5 

- NOAEL 4 

NC 

Category 2 

Interpolation 

Category 1 

Interpolation 

Where a number of studies are available these should be assessed using a weight of evidence 
approach to determine the most appropriate classification. Where the findings from individual 
studies would lead to a different classification then the studies should be assessed in terms of 
their quality, species and strain used, nature of the tested substance (including the impurity 
profile and physical form) etc to choose the most appropriate study to support classification. In 
general, the study giving the most severe classification will be used unless there are good 
reasons that it is not the most appropriate. If the effects observed in animals are not considered 
relevant for humans then these should not be used to support classification. Similarly, if there is 
robust evidence that humans differ in sensitivity or susceptibility to the effect observed in the 
study then this should be taken into account, possibly leading to an increase or decrease in the 
classification assigned. 

If there are differences in effects at the GV between studies with different duration then more 
weight is usually given to studies of a longer duration (28 days or more). This is because 
animals may not have fully adapted to the exposure in studies of shorter durations and also 
because longer duration studies tend to include more thorough and extensive investigations 
(e.g. in terms of detailed pathology and haematological effects etc) which can generally give 
more substantial information compared to shorter duration studies. If a 90-day as well as a 28-
day study are available expert judgement has to be used and not just Haber's rule. 

If there are differences in effects between good quality data in the same sex, species and strain 
then other variables such as particle size, vehicle, substance purity and impurities and 
concentration should be considered. If the results are considered to be depending on a specific 
impurity then different classifications depending on the concentration of the impurity could be 
considered. 

Any information pertaining to the relevance of findings in animals to humans must be taken into 
account and may be used to modify the classification from how it would be if based on the 
available animal data. For instance, it may be shown that the findings in animals are not 
relevant for humans, for example if the toxicity in animals is mediated by a mode of action that 
does not occur in humans. This would potentially provide a supporting case for no classification. 

 
 
 
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Similarly, evidence may suggest that the potency of the substance may be higher or lower in 
humans than in animals, for example because of differences in toxicokinetics/toxicodynamics 
between the species. Such evidence could be used to increase or decrease the severity of the 
classification as appropriate. It should be noted that such arguments for modifying the 
classification must be robust and transparent (see Section 3.9.2.3.4 of this Guidance). 

The final classification based on non human data will be the most severe classification of the 
three routes. If it is shown that classification for this endpoint is not required for a specific route 
then this can be included in the hazard statement (see Section 3.9.2.4 of this Guidance). 
Evaluation of non human data can result in no classification, STOT RE 1 or STOT RE 2. The 
results of the evaluation in non human data should be used in combination with the results of 
the evaluation of human data. 

3.9.2.3.3. 

Conversions  

The guidance values are giving in mg/kg bw. Where the doses in a study are given in different 
units they will need to be converted as appropriate. For instance the dosages in feeding and 
drinking water studies are often expressed in ppm, mg test substance/ kg (feed) or mg (test 
substance)/l (drinking water).  

Where insufficient information is reported in the study to perform the conversion, Table 3.17 
and Table 3.18 can be used as ‘Approximate relations’. These tables are derived from the 
following documents: Guidance on IR&CSA, Chapter 8, Table 17; and OECD ENV/JM/MONO 
(2002)19, 04-Sep-2002, Table 1; L.R. Arrington (Introductory Laboratory Animal Science, 
1978).  

Table 3.17 Food conversion 

Animal 

Weight (kg)  Food consumed per day (g) 

Factor 1mg/kgbw/d 
equivalent to ppm in diet 

Rat, young 

Rat, older 

Mouse 

Dog 

0.10 

0.40 

0.02 

10 

10 

20 

3 

250 

10 

20 

7 

40 

Table 3.18 Conversion drinking water 

Animal 

Weight (kg) 

Rat, young 

Rat, older 

0.25 

0.40 

Drinking water 
consumed per 
day(g) 

28 (25-30) 

28 (25-30) 

Mouse 

0.025 

5 (4-7) 

Dog 

13 

350 

Factor 1mg/kgbw/d equivalent 
to ppm in drinking water 

9 

14 

8 

37 

The conversion is performed according to the following simple equation: 

mg/kg bw   =   ppm/factor 

Example:  

 
 
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In a 4 week study rats received the 1000 ppm test substance in feed 

Dosage (mg/kg bw): 1000:10= 100 mg/kg bw. 

In any case a calculation of the average substance intake based on measured bodyweight and 
consumption data is preferable and should be performed where possible. 

Gases: mg/l into ppm: 

Effect doses from gases given in the unit mg/l have to be converted into the unit ppm as used 
by the CLP via the following simplified formula assuming values for ambient pressure of 1 atm = 
101.3 kPa and 25 ° c: 

3.9.2.3.4.  Weight of evidence 

mg/l   =   ppm   x   MW   x   1/24,450 

Annex I: 3.9.2.3. Classification is determined by expert judgment (see section 1.1.1), on the 
basis of the weight of all evidence available including the guidance presented below. 

Annex I: 3.9.2.4. Weight of evidence of all data (see section 1.1.1), including human 
incidents, epidemiology, and studies conducted in experimental animals, is used to 
substantiate specific target organ toxic effects that merit classification. This taps the 
considerable body of industrial toxicology data collected over the years. Evaluation shall be 
based on all existing data, including peer-reviewed published studies and additional 
acceptable data. 

Annex I: 3.9.2.10.2. When well-substantiated human data are available showing a specific 
target organ toxic effect that can be reliably attributed to repeated or prolonged exposure to 
a substance, the substance shall normally be classified. Positive human data, regardless of 
probable dose, predominates over animal data. Thus, if a substance is unclassified because 
no specific target organ toxicity was seen at or below the dose/concentration guidance value 
for animal testing, if subsequent human incident data become available showing a specific 
target organ toxic effect, the substance shall be classified. 

Annex I: 3.9.2.10.3. A substance that has not been tested for specific target organ toxicity 
may, where appropriate, be classified on the basis of data from a validated structure activity 
relationship and expert judgment-based extrapolation from a structural analogue that has 
previously been classified together with substantial support from consideration of other 
important factors such as formation of common significant metabolites. 

In cases where there is sufficient human evidence that meets the criteria given in CLP Annex I, 
Table 3.9.1 to support classification then this will normally lead to classification in Category 1, 
irrespective of other information available.  

Where human evidence does not meet this criterion, for example when the weight of evidence is 
not sufficiently convincing (limited number of cases or doubt on causal relationship) or because 
of the nature and severity of the effects (CLP Annex I, 3.9.2.7.3 and 3.9.2.8.1), then 
classification is based primarily on the non-human data  

If there are no human data then the classification is based on the non-human data. If there is 
human data indicating no classification but there is also non-human data indicating classification 
then the classification is based on the non-human data unless it is shown that the human data 
cover the exposure range of the non-human data and that the non-human data are not relevant 
for humans. If the human and non-human data both indicate no classification then classification 
is not required.  

 
 
 
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3.9.2.4.  Decision on classification 

Annex I: 3.9.2.7.1. Reliable evidence associating repeated exposure to the substance with 
a consistent and identifiable toxic effect demonstrates support for the classification. 

Annex I: 3.9.2.7.3. Evidence from appropriate studies in experimental animals can furnish 
much more detail, in the form of clinical observations, haematology, clinical chemistry, and 
macroscopic and microscopic pathological examination, and this can often reveal hazards that 
may not be life-threatening but could indicate functional impairment. Consequently all 
available evidence, and relevance to human health, shall be taken into consideration in the 
classification process, including but not limited to the following toxic effects in humans and/or 
animals: 

(a)  morbidity or death resulting from repeated or long-term exposure. Morbidity or death 
may result from repeated exposure, even to relatively low doses/concentrations, due 
to bioaccumulation of the substance or its metabolites, and/or due to the 
overwhelming of the de-toxification process by repeated exposure to the substance or 
its metabolites. 

(b) 

(c) 

(d) 

significant functional changes in the central or peripheral nervous systems or other 
organ systems, including signs of central nervous system depression and effects on 
special senses (e.g., sight, hearing and sense of smell). 

any consistent and significant adverse change in clinical biochemistry, haematology, or 
urinalysis parameters. 

significant organ damage noted at necropsy and/or subsequently seen or confirmed at 
microscopic examination. 

(e)  multi-focal or diffuse necrosis, fibrosis or granuloma formation in vital organs with 

regenerative capacity. 

(f) 

(g) 

morphological changes that are potentially reversible but provide clear evidence of 
marked organ dysfunction (e.g., severe fatty change in the liver). 

evidence of appreciable cell death (including cell degeneration and reduced cell 
number) in vital organs incapable of regeneration. 

Annex I: 3.9.2.8. Effects considered not to support classification for specific target organ 
toxicity following repeated exposure 

Annex I: 3.9.2.8.1. It is recognised that effects may be seen in humans and/or animals that 
do not justify classification. Such effects include, but are not limited to: 

(a) Clinical observations or small changes in bodyweight gain, food consumption or water 
intake that have toxicological importance but that do not, by themselves, indicate “significant" 
toxicity. 

(b) Small changes in clinical biochemistry, haematology or urinalysis parameters and/or 
transient effects, when such changes or effects are of doubtful or minimal toxicological 
importance 

(c) Changes in organ weights with no evidence of organ dysfunction. 

(d) Adaptive responses that are not considered toxicologically relevant.  

(e) Substance-induced species-specific mechanisms of toxicity, i.e. demonstrated with 
reasonable certainty to be not relevant for human health, shall not justify classification. 

If the evaluation of available data on a substance shows that the criteria for classification in a 
category are fulfilled then the substance shall be classified in that category for STOT-RE.  

 
 
 
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If the data show that classification is warranted in Category 1 for one route and in Category 2 
for another route then the substance shall only be classified in Category 1.  

Hazard statements are provided in Section 3.9.4.1 of this Guidance and can specify the route(s) 
of exposure according to Table 3.9.2.4.1 below. If only data is available for one route showing 
that classification is warranted then no route should be stated in the hazard statement. If the 
data conclusively show that no classification for STOT-RE is warranted for a specific route then 
the remaining routes should be stated. If the data show that classification is warranted in 
Category 1 for one route and in Category 2 for another route then the hazard statement for 
Category 1 should include both routes because substances are placed in one of two categories. 

Table 3.19 Inclusion of route of exposure in Hazard statement 

Route 1 

Route 2 

Route 3  H-statement H372 

Category 1 

Category 2 

unknown  Causes  damage  to  organs  through  prolonged  or 

repeated exposure 

Category 1 

Category 2 

NC 

Causes damage to organs via route 1 and 2 

Category 1 

NC 

unknown  Causes  damage  to  organs  through  prolonged  or 

repeated exposure 

Category 1 

unknown 

unknown  Causes  damage  to  organs  through  prolonged  or 

repeated exposure 

Category 1 

NC 

NC 

Causes damage to organs via route 1 

3.9.2.5.  Additional considerations 

In the following sections some special aspects in the decision process on classification are 
described in more detail. 

3.9.2.5.1. 

Irritating/corrosive substances 

Substances (or mixtures) classified as corrosive may cause severe toxicological effects following 
repeated exposure, especially in the lungs following inhalation exposure. In such cases, it has to 
be evaluated whether the severe effect is a reflection of true repeated exposure toxicity or 
whether it is in fact just acute toxicity (i.e. corrosivity). One way to distinguish between these 
possibilities is to consider the dose level which causes the toxicity. If the dose is more than half 
an order of magnitude lower than that mediating the evident acute toxicity (corrosivity) then it 
could be considered to be a repeated-dose effect distinct from the acute toxicity. In this case, 
classification as specific target organ toxicant (repeated exposure) would be warranted even if 
the substance (or mixture) is also classified as acutely toxic and/or corrosive.  

In assessing non systemic effects caused by irritating/corrosive substances it should be kept in 
mind, that the guidance values /criteria for STOT-RE of the CLP were derived from acute toxicity 
criteria (lethality based) assuming that systemic effects show a time dependent increase of 
severity due to accumulation of toxicity and taking also adaptive and detoxification processes 
into account. The effect considered in this context was lethality. This indicates that classification 
was intended for the presence of severe health damage, only. (see ECBI/67/00, (2000) in EU 
Commission Summary Record of Meeting of the Commission Working Group on C&L of 
Dangerous Substances ECBI/44/01). 

3.9.2.5.2.  Hematotoxicity  

Methaemoglobin generating agents 

 
 
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Methaemoglobinemia has often been regarded as an acute clinical symptom resulting from the 
action of methemoglobin-generating agents. If lethality is observed in humans or in animals71 or 
can be predicted (QSAR), methemoglobin generating substances should be classified in the 
Acute Toxicity Hazard Class. Since this effect is difficult to detect in rodents, expert judgement 
should be used (cf. Guidance on Acute toxicity, Example2). If methemoglobinemia does not 
result in lethality but exposure to methaemoglobin generating agents results in signs of damage 
to the erythrocytes and  haemolysis, anaemia or hypoxemia, the formation of  methaemoglobin 
shall be classified accordingly either in STOT-SE or STOT-RE (Muller A. et al., 2006). 

Haemolytic anaemia  

The guidance developed for classification of substances inducing haemolytic anaemia according 
to 67/548/EEC (Muller A. et al., 2006) cannot directly be used under CLP because of the 
changes in criteria (see CLP Annex I, 3.9.2.7.3 c and 3.9.2.8.b, d ). The major criterion for 
haemolytic anaemia changed: 

From ‘Any consistent changes in haematology which indicate severe organ dysfunction.’ 

To ‘Any consistent and significant adverse changes in haematology.’ 

This indicates that less adverse effects are considered for classification according to CLP. This is 
consistent with the changes in the other criteria for classification for repeated exposure.  

Adaptation towards the criteria according to CLP results in the following guidance: 

It is evident that anaemia describes a continuum of effects, from sub-clinical to potentially 
lethal in severity. Overall, the interpretation of study findings requires an assessment of the 
totality of findings, to judge whether they constitute an adaptive response or an adverse 
toxicologically significant effect. If a haemolytic substance induces one or more of the serious 
health effects listed as examples below within the critical range of doses, classification is 
warranted. It is sufficient for classification that only one of these criteria is fulfilled. 

Annex I: 3.9.2.7.3. 

(a) morbidity or death resulting from repeated or long-term exposure. Morbidity or death may 
result from repeated exposure, even to relatively low doses/concentrations, due to 
bioaccumulation of the substance or its metabolites, and/or due to the overwhelming of the 
de-toxification process by repeated exposure to the substance or its metabolites; 

Example: 

Premature deaths in anaemic animals that are not limited to the first three days of treatment in 
the repeated dose study (Mortality during days 0–3 may be relevant for acute toxicity).  

Clinical signs of hypoxia, e.g. cyanosis, dyspnoea, pallor, in anaemic animals that are not 
limited to the first three days of treatment in the repeated dose study. 

(b) significant functional changes in the central or peripheral nervous systems or other organ 
systems, including signs of central nervous system depression and effects on special senses 
(e.g. sight, hearing and sense of smell); 

(c) any consistent and significant adverse effect in clinical biochemistry, haematology or 
urinalysis parameters; 

Examples: 

71 Observation of lethality following methemoglobin formation is not usual, as several animals are more 
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Reduction in Hb at ≥20%. 

Reduction in functional Hb at ≥20% due to a combination of Hb reduction and MetHb increase. 

Haemoglobinuria that is not limited to the first three days of treatment in the repeated dose 
study in combination with other changes indicating significant haemolytic anaemia (e.g. a 
reduction in Hb at ≥10%). 

Haemosiderinuria supported by relevant histopathological findings in the kidney in combination 
with other changes indicating significant haemolytic anaemia (e.g. a reduction in Hb at ≥10%). 

(d) significant organ damage noted at necropsy and/or subsequently seen or confirmed at 
microscopic examination; 

(e) multifocal or diffuse necrosis, fibrosis or granuloma formation in vital organs with 
regenerative capacity; 

Example: 

Multifocal or diffuse fibrosis in the spleen, liver or kidney. 

(f) morphological changes that are potentially reversible but are clear evidence of marked 
organ dysfunction (e.g. severe fatty change in the liver) 

Example: 

Tubular nephrosis 

(g) evidence of appreciable cell death (including cell degeneration and reduced cell number) in 
vital organs incapable of regeneration. 

In the case where multiple less severe effects with regenerative capacity were observed, the 
classification should apply as “Assessment shall take into consideration not only significant 
changes in a single organ or biological system but also generalised changes of a less severe 
nature involving several organs.” (CLP Annex I, 3.9.1.4). 

Example: 

Marked increase of haemosiderosis in the spleen, liver or kidney in combination with other 
changes indicating significant haemolytic anaemia (e.g. a reduction in Hb at ≥10%) in a 28 day 
study. 

Significant increase in haemosiderosis in the spleen, liver or kidney in combination with 
microscopic effects like necrosis, fibrosis or cirrhosis. 

Annex I: 3.9.2.8.1. It is recognised that effects may be seen in humans and/or animals that 
do not justify classification. Such effects include, but are not limited to: 

(a) clinical observations or small changes in bodyweight gain, food consumption or water 
intake that have toxicological importance but that do not, by themselves, indicate ‘significant’ 
toxicity; 

(b) small changes in clinical biochemistry, haematology or urinalysis parameters and/or 
transient effects, when such changes or effects are of doubtful or minimal toxicological 
importance; 

Example: 

Significant decrease in Hb without any other significant indicators of haemolytic anaemia. 

 
 
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Minimal to slight increase in MetHb formation without any other indications of significant 
haemolytic anaemia. 

(c) changes in organ weights with no evidence of organ dysfunction; 

(d) adaptive responses that are not considered toxicologically relevant. 

Example: 

Only adaptive or compensating effects without significant signs of haemolytic anaemia. 

(e) substance-induced species-specific mechanisms of toxicity, i.e. demonstrated with 
reasonable certainty to be not relevant for human health, shall not justify classification. 

3.9.2.5.3.  Mechanisms not relevant to humans (CLP Annex I, 3.9.2.8.1. (e)) 

In general, valid data from animal experiments are considered relevant for humans and are 
used for hazard assessment/classification. However, it is acknowledged that there are cases 
where animal data are not relevant for humans and should not be used for that purpose. This is 
the case when there is clear evidence that a substance – induced effect is due to a species-
specific mechanism which is not relevant for humans. Examples for such species differences are 
described in this section. 

-2-μ globulin nephropathy in male rats 

The protein α-2-μ globulin, which is primarily synthesized in male rats, has the capability to 
bind to certain chemicals. The resultant adducts accumulate as droplets in the kidneys and 
causes progressive renal toxicity within a few weeks which can ultimately lead to kidney 
tumours. This specific mechanism is unique to male rats and has no relevance for humans. 
Examples of chemicals causing -2-μ globulin nephropathy are: unleaded gasoline, chlorinated 
paraffins, isophorone, d-limonene.  

Specific thyroid toxicity via liver enzyme induction 

Certain chemicals cause induction of liver enzymes and are interfering with the regulation of 
thyroid hormones. An increase in the activity of hepatic UDPG-transferase results in increased 
glucuronidation of thyroid hormones and increased excretion. It is known that rodents are 
highly sensitive to a reduction in thyroid hormone levels (T4), resulting in thyroid toxicity (e.g. 
hypertrophy, hyperplasia) after repeated stimulation / exposure of this organ. This in turn is 
related to an increase in the activity of hepatic UDPG-transferase. Humans, unlike rodents, 
possess a T4 binding protein that greatly reduces susceptibility to plasma T4 depletion and 
thyroid stimulation. Thus, such a mechanism/effect cannot be directly extrapolated to humans, 
i.e. these thyroid effects observed in rodents caused by an increase in hepatic UDPG-transferase 
are therefore considered of insufficient concern for classification (see ECBI/22/98 Add1, EU 
Commission Meeting of the Commission Working Group on C&L of Dangerous Substances 
ECBI/27/98 Rev.2). 

Peroxisome induction/proliferation 

Peroxisomes are cell-organelles which can be induced to a specifically high level in rats and 
mice under certain conditions, e.g. by repeated exposure to long chain and branched fatty 
acids. Peroxisome proliferation which is especially occurring in the liver causes liver toxicity 
(e.g. hyperplasia, oxidative stress) and can ultimately after long-term exposure also may lead 
to tumours. There is no evidence of e.g. hepatomegaly from clinical studies in humans treated 
with peroxisome proliferators (I.H.F. Purchase, Human & Experimental Toxicology (1994), 13, 
Suppl. 2 S47-S48). Examples are Clofibrat and Diethylhexylphthalate (DEHP). 

Lung Overload 

 
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The relevance of lung overload in animals to humans is currently not clear and is subject to 
continued scientific debate.  

3.9.2.5.4. 

Adaptive responses (CLP Annex I, 3.9.2.8.1. (d)) 

Adaptive (compensatory) changes generally constitute a normal biochemical or physiological 
response to a substance or to the effect of the substance (e.g. in response to methaemoglobin 
formation), usually manifested as an increase in background processes such as metabolism or 
erythropoiesis etc, which are generally reversible with no adverse consequences on cessation of 
exposure. In some cases the adaptive response may also be associated with pathological 
changes which reflect the normal response of the target tissue to substances: for example, liver 
hypertrophy in response to enzyme induction, increase in alveolar macrophages following 
inhalation of insoluble particles that must be cleared from the lungs, or development of 
epithelial hyperplasia and metaplasia in the rat larynx in response to inhalation of irritants.  

Determination of whether adaptive changes support a classification requires a holistic 
assessment of the nature and severity of the observations and their dose-response relationship 
using expert judgement. Exposure to a substance can lead to a spectrum of effects which vary 
in incidence and severity with dose. At lower doses there may be adaptive changes which are 
not considered to be toxicologically significant or adverse, whereas at higher doses these 
changes may become more severe and/or other effects may occur which together constitute 
frank toxicity. Also, sometimes the adaptive effect is observed but the primary effect is not 
because the relevant parameter is not determined or not determined at the right time. For 
example, irritation of the larynx after inhalation of irritants is not observed at the end of a 
repeated dose study because of the quick response. The adaptive effect can then be used as an 
indication of the primary effect. It is often difficult to clearly distinguish between changes which 
are adaptive in nature and those which represent clear overt toxicity and this assessment 
requires expert judgement. Where the response to a substance is considered to be purely 
adaptive at dose levels relevant for classification then no classification would be appropriate. 

3.9.2.5.5. 

Post-observation periods in 28 day and 90 day studies 

For subacute/subchronic testing protocols, the usual guideline procedure is to sacrifice the 
exposed animals immediately after the end of the exposure period (d 29 or 91).  

Japanese agencies often require a 14 days postobservation period for 28 day studies (OECD TG 
407). This means that 10 more animals in the top dose and 10 more animals as an additional 
control group are then necessary.  

The reversibility of organotoxic effects can often be estimated by the pathologist from histologic 
findings without a post-observation period. 

•  Certain effects are entirely reversible such as simple irritation or many forms of liver, 

testicular and hematotoxicity. 

•  Other effects may be reversible in morphological terms but the reserve capacity of the 

organism may be irreversibly compromised (such as in the case of kidney toxicity with a 
persistent loss in kidney nephrons). 

•  Some forms of tissue toxicity may be fundamentally irreversible, such as CNS- and 

neuro-toxicity with specific histological findings, cardiac toxicity and lung toxicity. Often, 
such effects do not return to normal morphology and may deteriorate even after the end 
of exposure.  

3.9.2.6.  Setting of specific concentration limits    

Specific concentration limits (SCLs) for STOT-RE may be set by the supplier in some situations 
according to Article 10.1 of CLP. For STOT-RE, this may only be done for substances inducing 
target organ toxicity at a dose level or concentration clearly (more than one magnitude) below 
the guidance values according to CLP Annex I, Table 3.9.2, that corresponds to ED below 1 

 
 
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mg/kg bw from the 90-day oral study. Where the exposure duration is not 90 days the ED has 
to be adjusted to an equivalent for 90 days using Haber’s law and expert judgement (as 
described above). This will be mainly based on data in experimental animals but can also be 
used for human data if reliable exposure data are available. Setting of SCLs above the GCL is 
not applicable for STOT-RE because classification for STOT-RE is based on potency. Substances 
with a low potency do not require classification for this hazard class and substances with a 
medium or high potency are classified in a category defined by the GV.  

The SCL for a Category 1 substance (SCL Cat.1) can be determined using the following formula:  

Equation 3.9.2.6.a 

SCL Cat 1: 0.12 mg/kg bw/10 mg/kg bw x 100%= 1.2% --> 1% 

ED (effective dose) is the dose inducing specific target organ toxicity and GV1 is the guidance 
value for Category 1 according to CLP Annex I, Table 3.9.2 of Annex I corrected for the 
exposure duration. The resulting SCL is rounded down to the nearest preferred value72 (1, 2 or 
5). 

Though classification of a mixture in Category 1 is not triggered if a Category 1 constituent is 
present in lower concentrations than the established SCL, a classification in Category 2 should 
be considered. The SCL for classification of a mixture in Category 2 (SCLCat. 2) based on 
substances classified in Category 1 can be determined using the following formula: 

Equation 3.9.2.6.b 

SCL Cat 2: 0.12 mg/kg bw/100 mg/kg bw x 100%=0.12% --> 0.1% 

In this formula the ED (effective dose) is the dose inducing specific target organ toxicity and 
GV2 is the upper guidance value for Category 2 according to CLP Annex I, Table 3.9.3 corrected 
for the exposure duration. The resulting SCL is rounded down to the nearest preferred values 
(1, 2 or 5). 

It is not appropriate to determine SCLs for substances classified in Category 2 since ingredients 
with a higher potency (i.e. lower effect doses than the guidance values of Category 2) will be 
classified in Category 1 and substances with respective higher effect doses will generally not be 
classified. For example, a substance inducing significant specific target organ toxicity at 0.12 
mg/kg bw/day in a 90-day oral study would require a SCL for Category 1 of 1% and for 
Category 2 of 0.1%. 

72 This is the “preferred value approach” as used in EU and are values to be established preferentially as 
the numerical values 1, 2 or 5 or multiples by powers of ten. 

%10011.=GVEDSCLCat%10022.=GVEDSCLCat 
 
 
 
 
 
 
 
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3.9.2.7.  Decision logic for classification of substances 

The decision logic which follows is provided as additional guidance to the criteria. It is strongly 
recommended  that  the  person  responsible  for  classification,  study  the  criteria  for  classification 
before and during use of the decision logic. 

Does the substance have data and/or information to evaluate 
specific target organ toxicity following repeated exposure? 

No 

Classification 
not possible 

Yes 

Following repeated exposure, 

Category 1 

Can the substance produce significant toxicity in humans, or  

Can  it  be  presumed  to  have  the  potential  to  produce  significant 
toxicity  in  humans  on  the  basis  of  evidence  from  studies  in 
experimental animals? 

Yes 

See  3.9.2  for  criteria  and  guidance  values.  Application  of  the 
criteria needs expert judgment in a weight of evidence approach. 

Danger 

No 

Following repeated exposure, 

Can the substance be presumed to have the potential to be 
harmful to human health on the basis of evidence from studies in 
experimental animals? 

Yes 

See 3.9.2 for criteria and guidance values. Application of the 
criteria needs expert judgment in a weight of evidence approach. 

Warning 

Category 2 

No 

Not classified 

 
 
 
 
 
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3.9.3.  Classification of mixtures for STOT-RE  

3.9.3.1. 

Identification of hazard information  

Where toxicological information is available on a mixture this should be used to derive the 
appropriate classification. Such information may be available from the mixture manufacturer. 
Where such information on the mixture itself is not available information on similar mixtures 
and/or the component substances in the mixture must be used, as described below. 

Further, the hazard information on all individual components in the mixture could be identified 
as described in Section 3.9.3.3.2 of this Guidance. 

3.9.3.2.  Classification criteria for mixtures   

Annex I: 3.9.3.1. Mixtures are classified using the same criteria as for substances, or 
alternatively as described below. As with substances, mixtures shall be classified for specific 
target organ toxicity following repeated exposure. 

3.9.3.3. 

 When data are available for the complete mixture 

Annex I: 3.9.3.2.1. When reliable and good quality evidence from human experience or 
appropriate studies in experimental animals, as described in the criteria for substances, is 
available for the mixture (see 1.1.1.3), then the mixture shall be classified by weight of 
evidence evaluation of these data. Care shall be exercised in evaluating data on mixtures, that 
the dose, duration, observation or analysis, do not render the results inconclusive. 

In cases where test data for mixtures are available, the classification process is exactly the 
same as for substances.  

3.9.3.3.1.  When data are not available for the complete mixture: bridging principles 

Annex I: 3.9.3.3.1. Where the mixture itself has not been tested to determine its specific 
target organ toxicity, but there are sufficient data on the individual ingredients and similar 
tested mixtures to adequately characterise the hazards of the mixture, these data shall be 
used in accordance with the bridging principles set out in section 1.1.3. 

In order to apply bridging principles, there needs to be sufficient data on similar tested mixtures 
as well as the ingredients of the mixture (see Section 1.6.3 of this Guidance).  

When the available identified information is inappropriate for the application of the bridging 
principles then the mixture should be classified based on its ingredients as described in Sections 
3.9.3.3.2, 3.9.3.3.3 and 3.9.3.4 of this Guidance. 

3.9.3.3.2.  When data are available for all ingredients or only for some ingredients of 

the mixture 

Annex I: 3.9.3.4.1. Where there is no reliable evidence or test data for the specific mixture 
itself, and the bridging principles cannot be used to enable classification, then classification of 
the mixture is based on the classification of the ingredient substances. In this case, the 
mixture shall be classified as a specific target organ toxicant (specific organ specified), when 
at least one ingredient has been classified as a Category 1 or Category 2 specific target organ 
toxicant and is present at or above the appropriate generic concentration limit as laid out in 
Table 3.9.4 below for Category 1 and 2 respectively. 

 
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3.9.3.3.3. 

Components of a mixture that should be taken into account for the 
purpose of classification 

Components with a concentration equal to or greater than the generic concentration limits (see 
CLP Annex I, Table 3.9.4) or with a specific concentration limit (see also Section 3.9.3.5 of this 
Guidance) will be taken into account for classification purposes. Specific concentration limits 
have preference over the generic concentration limits. 

3.9.3.4.  Generic concentration limits for substances triggering classification 

of mixtures    

Generic concentration limits of ingredients of a mixture classified as a specific 
target organ toxicant that trigger classification of the mixture. 

Annex I: Table 3.9.4 

Ingredient classified as: 

Generic concentration limits triggering 
classification of the mixture as: 

Category 1 

Category 2 

Category 1 

Concentration  10% 

Specific Target Organ Toxicant 

Category 2 

Specific Target Organ Toxicant 

Note 1  

1.0%  concentration 
 10% 

Concentration  10% 
(Note 1) 

If a Category 2 specific target organ toxicant is present in the mixture as an ingredient at a 
concentration ≥ 1,0 % a SDS shall be available for the mixture upon request. 

Annex I: 3.9.3.4.4. Care shall be exercised when toxicants affecting more than one organ 
system are combined that the potentiation or synergistic interactions are considered, because 
certain substances can cause target organ toxicity at < 1% concentration when other 
ingredients in the mixture are known to potentiate its toxic effect. 

In the case a specific concentration limit has been established for one or more ingredients these 
SCLs have precedence over the respective generic concentration limit. 

When classifying a mixture for STOT-RE the additive approach, where the concentrations of 
individual components with the same hazards are summed, is not used. If any individual 
component is present at a concentration higher than the relevant generic or specific 
concentration limit then the mixture will be classified. 

3.9.3.5.  Decision logic for classification of mixtures  

A mixture should be classified either in Category 1 or in Category 2, according to the criteria 
described above. When a mixture is classified for STOT-RE on the basis of test data, the hazard 
statement will specify the target organs, in the same way as for a substance.  If a mixture is 
classified on basis of the ingredients, the hazard statement (H372 for Category 1 or H373 for 
Category 2) may be used without specifying the target organs, as appropriate. In the same 
way, the route of exposure should not be specified, except if data are available for the complete 
mixture and if it is conclusively demonstrated that no other routes of exposure cause the 
hazard. 

 
 
 
 
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The decision logic which follows is provided as additional guidance to the criteria. It is strongly 
recommended that the person responsible for classification study the criteria for classification 
before and during use of the decision logic.  

Does the mixture have data and/or information to evaluate? 

No 

Can bridging principles be applied? 

No 

Yes 

Yes 

Does the mixture contain one or more ingredients classified as a 
Category 1 specific target organ toxicant at a concentration of ≥ 
10% ? 

Yes 

No 

Does  the  mixture  contain  one  or  more  ingredients  classified  as  a 
Category 1 specific target organ toxicant at a concentration of ≥ 1.0 
and <10%? 

OR  

Yes 

Does  the  mixture  contain  one  or  more  ingredients  classified  as  a 
Category  2  specific  target  organ  toxicant  at  a  concentration  of  ≥ 
10%? 

(A SDS is required if a cat 2 substance is present at or above 1%) 

See 
Substances 

Classify in 
appropriate 
category 

Category 1 

Danger 

Category 2 

Warning 

No 

Not classified 

 
 
 
 
  
 
 
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3.9.4.  Hazard communication in form of labelling for STOT-RE   

3.9.4.1.  Pictograms, signal words, hazard statements and precautionary 

statements    

Annex I: 3.9.4.1. Label elements shall be used in accordance with Table 3.9.5 for substances 
or mixtures meeting the criteria for classification in this hazard class. 

Table 3.9.5 

Label elements for specific target organ toxicity after repeated exposure 

Classification 

Category 1 

Category 2 

GHS Pictograms 

Signal word 

Danger 

Warning 

Hazard statement 

H372: Causes damage to 
organs (state all organs 
affected, if known) through 
prolonged or repeated 
exposure (state route of 
exposure if it is conclusively 
proven that no other routes of 
exposure cause the hazard) 

H373: May cause damage to 
organs (state all organs 
affected, if known) through 
prolonged or repeated 
exposure (state route of 
exposure if it is conclusively 
proven that no other routes of 
exposure cause the hazard) 

Precautionary statement 
prevention 

Precautionary statement 
response 

Precautionary statement 
storage 

Precautionary statement 
disposal 

P260 
P264 
P270 

P314 

P260 

P314 

P501 

P501 

The hazard statement should include the primary target organ(s) of toxicity. Organs in which 
secondary effects were observed should not be included. The route of exposure should not be 
specified, except if it is conclusively demonstrated that no other routes of exposure cause the 
hazard. 

When a mixture is classified for STOT-RE on basis of test data, the hazard statement will specify 
the target organs, in the same way as for a substance.  If a mixture is classified on basis of the 
ingredients, the hazard statement (H372 for Category 1 or H373 for Category 2) may be used 
without specifying the target organs, as appropriate. 

 
 
 
 
 
 
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In the same way, the route of exposure should not be specified, except if data are available for 
the complete mixture and if it is conclusively demonstrated that no other routes of exposure 
cause the hazard.  

It is recommended to include no more then three primary target organs for practical reasons 
and because the classification is for specific target organ toxicity. If more target organs are 
affected it is recommended that the overall systemic damage should be reflected by using the 
more general term ‘damage of organs’.  

3.9.4.2.  Additional labelling provisions  

Annex I: 3.9.2.10.4 Saturated vapour concentration shall be considered, where appropriate, 

as an additional element to provide for specific health and safety protection. 

According to CLP Annex I, 3.9.2.10.4 the saturated vapour concentration shall be considered as 
an additional element for providing specific health and safety protection. Thus if a classified 
substance is highly volatile a supplementary precautionary advice (e.g. ‘Special/additional care 
should be taken due to the high saturated vapour pressure’) might be given in order to 
emphasize the hazard in case it is not already covered by the general P statements. (As a rule 
substances for which the ratio of the effect concentration at ≤ 4h to the SVC at 20° C is ≤ 
1/10). 

Although not according to the criteria of STOT-RE, the following EU-special hazard statement 
‘Repeated exposure’ may be used when appropriate: 

EUH066- ‘Repeated exposure may cause skin dryness or cracking’ (see Section 3.2 of this 
Guidance on Skin Corrosion/Irritation). 

3.9.5.  Examples of classification for STOT-RE 

  NOTE: The classification proposals for the examples refer only to STOT-RE. 

Labelling is done only with respect to hazard statements (statement with respect of 
organs affected = target organs). 

3.9.5.1.  Examples of substances fulfilling the criteria for classification 

3.9.5.1.1. 

Example 1: Hydroxylamine / Hydroxylamonium salts (CAS no. 7803-49-
8) 

Application of criteria for evaluation/classification and decision on classification: Use of studies 
with different duration; Haber’s rule; Expert judgement 

Available information:  

6.  Human experience: No information available 

7.  Animal data: 

Background: 

Hydroxylamine and its salts are direct MetHb producers in contrast to aromatic amines, which 
require metabolic activation (XI/484/92). 

Several studies are available for the assessment of the toxicity after repeated administration: 

•  4-week drinking water study (BASF, 1989) 

•  3-month drinking water study (BASF, 1989) 

•  Combined chronic/carcinogenicity study in drinking water in rats (BASF, 2001) 

 
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Though not explicitly stated in the criteria the "... study with the longest duration should 
normally be used". 

• 

In the 3-month-study at the dose level of 21 mg/kg bw only ‘slight to moderate 
hematotoxic effects’ were observed. Thus this dose would not be a sufficient ED causing 
‘significant/severe’ effects, but it can be concluded that via interpolation an  ED would 
result within the Guidance Value Range for Cat 2 (10-100 mg/kg bw). 

•  A classification in Category 2 would be warranted based on the 3-month-study. 

In the combined chronic/carcinogenicity study (BASF, 2001), the effects observed after 12 and 
24 months are to be considered separately: 

12 month study: 

•  0 ppm (control): hemosiderin storage of low degree in males and females (spleen) 

•  5 ppm (males 0.3 mg and females 0.4 mg/kg bw/day): No substance-induced effects; 
hemosiderin storage of low degree in males and females, comparable to controls. 

•  20 ppm (males 1.1 mg and females 1.6 mg/kg bw/day): Here, hemosiderin deposits with 

the gradation of moderate was observed in the spleens of the males; hemosiderin 
storage of low degree in females comparable to controls. This effect is not to be regarded 
as serious since hematology did not reveal any findings whatsoever with regard to 
anemia. This is supported by the fact that no substantial (1/10 moderate, but 1/10 
severe in the male control group) extramedullary hematopoiesis was observed in this 
group. In the histopathological examination, the spleen was not found to be impaired 
morphologically. Thus, this dose is to be regarded as the NOAEL for males whereas it is 
the NOEL for females. 

•  80 ppm (males 4.5 mg and females 6.2 mg/kg bw/day): The clinicochemical findings are 

assessed as mild anemia in the males (e.g. decrease of RBC, HB and HT (< 10%); MCV 
increased at the beginning and compensatory normalization later) and, also as mild 
anemia in the females (decrease in RBC < 12%, HB < 10% and HT < 10%). The 
increase of MCV, PLT and RET and of Howell-Jolly bodies is regarded as a compensatory 
effect, and the bone marrow still reacts, i.e. it does not demonstrate ‘... decreased bone 
marrow production of red blood cells’ within the meaning of the criteria. The only slight 
increase of the Heinz bodies is considered to be a sign of a weak hematotoxic effect. 
From the point of view of histopathology, the effects (hemosiderin storage, 
extramedullary hematopoesis) can be regarded as signs of anemia, but not within the 
meaning of ‘serious’ (the effect was more pronounced in the females than in the males). 
The extramedullary hematopoiesis observed is thus again compensatory in the sense of 
a functional counterreaction. 

Assessment: 

For a 12-month study, cut-off values of 25 and 2.5 mg/kg bw/day (100 mg/kg bw/day: 4) have 
to be regarded for STOT-RE Category 1 vs. Category 2 respectively. At the dose level of 1.1 (m) 
or 1.6 mg/kg bw/day (f), no hematotoxic effects whatsoever or extramedullary hematopoiesis 
were observed, nor substantial hemosiderin deposits. The effects at 4.5 (f) and 6.2 (m) mg/kg 
bw/day are regarded as mild anemia; however, more distinct effects may be expected to occur 
up to the cut-off value (25 mg/kg bw/day). Therefore, a classification in Category 2 seems 
justified. 

24-month study:  

In contrast to the 12-month study, no complete hematological examination was carried out, i.e. 
only morphological parameters were evaluated, yet full histopathology. The following findings 
relevant to classification – with the exception of the neoplasias – were obtained: 

•  ppm (males 0.2 mg and females 0.4 mg/kg bw/day): No non-neoplastic effects 

 
 
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•  20 ppm (males 1 mg and females 1.6 mg/kg bw/day): Increased proportion of 
hemosiderin deposits in the spleens of the females, but no extramedullary 
hematopoiesis, which demonstrates that there was no clear anemia before. 

Remark:  

The fact that, at this dose level, hemosiderin was detected only in the males in the 12-month 
study and an increased proportion of it only in the females in the 24-month study shows that 
this effect was only borderline. 

•  80 ppm (males 3.7 mg and females 6.2 mg/kg bw/day): Again hemosiderin storage and 
extramedullary hematopoesis were observed, yet no serious effects in hematology nor 
histopathology. Furthermore, the results of the study do not indicate that any animal 
died prematurely as a result of the anemia.  

Remark:  

No effects were observed neither in kidneys nor in liver in the 12-month study. In the 3 month 
study only in the highest dose the relative liver weights were increased in the males; in the 3 
month as well as in the 24-month study only marginal effects (diffuse hemosiderin storage in 
the liver) in both sexes was observed in the highest dose. 

Assessment: 

The results of the 24 month study show that effects as seen after 12 month exposure are not 
substantially increased.  

Classification & Labelling: 

Classification: Based on the evaluation of the 3-month-study and the more relevant 12-month-
study by expert judgement a classification in Category 2 is warranted. 

Labelling: Hazard statement: H373 May cause damage to blood system through prolonged or 
repeated exposure 

(See also ECBI/ 14/3/ Add 3 (2003) and ECBI/56/04 Rev 1 in EU Commission Meeting of the 
Commission Working Group on C&L of Dangerous Substances ECBI/139/04 Rev.2) 

3.9.5.1.2. 

Example 2: But-2-yn-1,4-diol (EC No 203-788-6; CAS No 110-65-6) 

Application of criteria for evaluation/classification and allocation of hazard statements with 
respect to specific target organs and route of exposure 

Available information:  

8.  Human experience: no information available 

9.  Animal data: 

•  28d oral study 

•  28d inhalation study  

•  Acute oral toxicity: LD50 rat 132 (males) and 176 (females) mg/kg bw -> 

Category 3 

•  Acute dermal toxicity: LD50 424 (males) and 983 (females) mg/kg bw-> Category 

3 

•  Acute inhalation toxicity: LC50 rat 0.69 mg/l -> Category 2  

•  Corrosivity in animal experiments (Category 1) 

STOT-RE oral: 

28d rat oral (gavage): doses 0; 1; 10; 50 mg/kg bw/d 

 
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•  1 mg/kg bw: NOEL 

•  10 mg/kg bw: LOEL 

• 

Increased liver weight (not statistically significant) 

•  Hepatic and spleenic changes (no clear desription of severity given) 

•  Diminished RBC counts in females, yet no other changes in blood chemistry 

•  Histopathology: in 2/10 males and 3/10 females swelling of parenchymal cells 
and increased  polymorphism of the hepatocyte nuclei and the nuclear cells. 
These effects are regarded as not “significant/severe toxic effects” 

•  50 mg/kg bw: mortality (3/8 males; 3/8 females); hepato- and nephrotoxicity 
responsible for mortality; no distinct hepato- and nephrotoxicity described for 
survivors 

•  Hematology: decrease in RBC count ca. 20% and 21% in HB both in males and 

females; decrease in Hematocrite 11%. These effects are regarded as “moderate 
hematotoxicity”. 

Conclusion for the highest dose group: severe effects. 

Assessment: 

The substance has a high acute toxicity (s.a.). Since the factor between the acute LD50 and the 
subacute lethal dose (20 applications) is only 2-3, it can be assumed that the substance has a 
low cumulative potential. On the other hand there is a steep dose response in the 4 week study, 
thus it can be concluded by interpolation that at 30 mg/kg bw moderate but no 
‘significant/severe’ toxicity could be expected; 30 mg/kg bw is the guidance value for Category 
1 in a 4 week study according to Haber’s rule: 10 mg/kg bw x 3 )  

STOT-RE inhalation 

In a valid 4 week inhalation study (vapour) rats were exposed to 0.5; 5; and 25 mg/m3/6h/d. 

•  0.5 mg/m3:  NOAEC for local effects in the respiratory tract  

•  mg/m3: minimal-slight focal squamous metaplasia and inflammation in the larynx 

•  25 mg/m3: minimal-slight focal squamous metaplasia and inflammation in the larynx 

•  25 mg/m3:  NOAEC for systemic effects including hematology, clinical chemistry, 

histopathology and neuropathology examinations 

Assessment: 

Up to the highest concentration tested there were no systemic effects. Since the substance is 
classified as corrosive an irritation of the respiratory tract by the vapour could be expected and 
has been observed in minimal-slight degree at 5-25 mg/m3. It is assumed that the irritation 
would increase with higher concentrations. The corrosive/irritation potential is covered by the 
classification as ‘corrosive’ Category 1, thus no classification as STOT-RE with respect to the 
inhalation route would result. 

Classification & Labelling: 

Classification: Category 2  for the oral route is proposed since within the guidance values of 30-
300 mg/kg bw in a 4 week study serious effect occurred. According to a total weight of evidence 
approach it is concluded that these significant effects would not be observed below 30 mg/kg 
bw, the concentration limit for Category 1. 

Classification via the inhalation route is not warranted, since at the highest concentration tested 
only local effects, but no systemic effects, were observed. The local effects 
(corrosivity/irritancy) are covered by the respective classification. 

 
 
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Labelling: Hazard statement: H373 May cause damage to liver and kidney through prolonged or 
repeated exposure. 

To note: Since the substance is classified as STOT-RE via the oral route and specific toxicity has 
not been conclusively excluded for the dermal route (rather it can be expected due to high 
dermal absorbtion in acute toxicity, Category 3) the Hazard statement for STOT-RE in total 
without specifying a route has to be applied based on the classification via the oral route. 

(See also Risk assessment report BUT-2YNE-1,4-DIOL; EC 2005. Available at ECHA website: 
http://echa.europa.eu/documents/10162/49324502-03ba-4005-8800-b2bebf924d2d) 

3.9.5.1.3. 

Example 3: XYZ  

Application of criteria for evaluation/classification and allocation of hazard statements with 
respect to specific target organs and route of exposure. 

Available information: 

•  Human experience: No information available 

•  Animal data: 

Key chronic toxicity data (underlined for EU classification) 

Type of study - Effects 

NOAEL 
ppm (mg/kg 
bw/d) 

LOAEL 
ppm (mg/kg 
bw/d) 

CLP Repeated 
Exposure (STOT) 
classification 

mouse, oral 28 days 

M: no NOAEL 

M: 300 (51-58) 

0, 300, 600, 1200 ppm 

F: 300 (59-66) 

F: 600 (111-127) 

Category 2 based on 
the effects on blood 

(M:  0,  51-58,  101-115,  177-226 
mg/kg bw/d, F: 0, 59-66, 111-127, 
221-281 mg/kg bw/d) 

hematological changes in M (  RBC 
count, Hb, Ht) 

rat, oral 13 weeks 

50  

500  

0, 50, 500, 1000 ppm 

(M: 3.5, F: 4) 

(M: 38, F: 38) 

Category 2 based on 
the effects on blood 

(M: 0, 3.5, 38, 67 mg/kg bw/d, F: 
0, 4, 38, 80 mg/kg bw/d) 

hematological changes in F (  RBC 
count, Hb, Ht) 

male rat, oral 30, 60, 90 days 

0,  5,  10,  25  mg/kg  bw/d  (by 
gavage) 

(open literature) 

mortality  at 5 (5/25), 10 (7/25) & 
25 (8/25) mg/kg bw 

No classification is 
proposed on the basis 
of this study because 
the mortality observed 
in the 3 groups are in 
contradiction with the 
other relevant 
experiments in this 
species (mortality not 
dose related, some 
animals (2/6) already 
died after 30 days at 5 
mg/kg bw) 

 
 
 
 
 
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CLP Repeated 
Exposure (STOT) 
classification 

Category 2 based on 
the effects on blood 
(haemolytic anaemia 
accompanied by 
compensatory 
mechanisms) 

No classification 
(effects above the cut-
off values) 

Category 2 based on 
the effects on blood 
and nervous system 

Key chronic toxicity data (underlined for EU classification) 

Type of study - Effects 

NOAEL 
ppm (mg/kg 
bw/d) 

LOAEL 
ppm (mg/kg 
bw/d) 

rat, oral 2 years 

30  

150  

0, 30, 150, 300 ppm 

(M: 1.46, F: 1.8) 

(M: 7.31, F: 8.86) 

(M:  0,  1.46,  7.31,  14.66  mg/kg 
bw/d, F : 0, 1.8, 8.86, 18.57 mg/kg 
bw/d) 

eyelid masses: 1 F/50 at 150 ppm, 
5 M/50 & 3 F/49 at 300 ppm 

changes in erythroid parameters ( 
RBC count,  MC Hb,  MCV in F at 
300 ppm) 

extramedullary hemopoiesis in liver 
(M: 150 & 300 ppm, F: 300 ppm), 
spleens 

  myeloid  hyperplasia  in  BM,  in 
femur & sternum of F at 300 ppm 

  i.  hemorrhages  w/i  mesenteric 
lymph nodes at 150 & 300 ppm 

rat, oral 80 weeks 

M: 0, 5, 20, 52 mg/kg bw/d 

F: 0, 6, 26, 67 mg/kg bw/d 

(open literature) 

ataxic  syndrom  in  F  at  67  mg/kg 
bw/d (unusual gait). The condition 
of  these  rats  worsened,  leading to 
paralysis  posterior  to  the  lumbar 
region, atrophy of the hing legs. No 
specific  hystopathological  lesion  of 
CNS or PNS. 

rat, oral, 104 weeks 

0, 3, 30, 300 ppm 

(M: 0, 0.1, 1.2, 11.6 mg/kg bw/d, 
F: 0, 0.1, 1.4, 13.8 mg/kg bw/d) 

(open literature) 

anemia  in  300  ppm  (F)  (not  in  30 
ppm) 

regressive changes of sciatic nerve 
(degeneration)  +  atrophy  of  calf 
muscle  in  F  at  300  ppm,  but  no 
neurologcal signs 

progression of myocardial lesions at 
300 ppm 

 
 
 
 
 
 
 
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CLP Repeated 
Exposure (STOT) 
classification 

Category 2 based on 
the effects on blood. 

Category 2 based on 
the effects on the 
retina 

Key chronic toxicity data (underlined for EU classification) 

Type of study - Effects 

NOAEL 
ppm (mg/kg 
bw/d) 

LOAEL 
ppm (mg/kg 
bw/d) 

mouse, oral, 97/98 weeks 

15 

M : 0, 15, 150, 300 ppm ( 0, 3, 24, 
50 mg/kg bw/d) 

(M: 5.2, F: 3.1) 

F : 0, 15, 300, 600 ppm (0, 3, 57, 
112 mg/kg bw/d) 

retinal atrophy at  150 ppm ( or 
absence of outer nuclear cell layer 
of retina) 

 turnover of erythrocytes 

Classification & Labelling: 

Classification for XYZ: STOT-RE Category 2 

Labelling:  

•  Symbol: GHS08 

•  Signal word: warning 

•  Hazard statement: H373 May cause damage to the blood and nervous systems through 

prolonged or repeated exposure. 

Justification: The effects on blood are reported in the 2 species (mouse, rat), at doses low 
enough to justify Category 2. The effects on NS are reported in the rat at doses low enough to 
justify Category 2. 

3.9.5.2.  Examples of substances not fulfilling the criteria for classification   

3.9.5.2.1. 

Example 4: MCCPs (Medium Chain Chlorinated Paraffins) = Alkanes, C14-
17, Chloro- (EC No 287-477-0; CAS No 85535-85-9) 

Application of criteria for evaluation/classification with regard to mechanisms not relevant to 
humans (see Section 3.9.2.5.3 of this Guidance) 

Available information: 

•  Human experience: No information available 

•  Animal data: see summary 

KEY CHRONIC TOXICITY DATA: SUMMARY OF DATA FOR REPEATED EXPOSURE 

The only available data relate to a number of oral dosing studies (up to 90 days duration) 
that have investigated the repeated dose toxicity of MCCPs (C14-17, 40% or 52% 
chlorinated paraffins) in rodents. However, only two studies emerge as providing helpful 
dose-response information in respect of classification and labelling (IRDC 1984, Poon et al. 
1995). The others, all presented in more detail in the ESR RAR, were generally 
mechanistic studies on the interplay between liver and thyroid and the relevance of effects 
on these organs to human health, conducted at relatively high exposure levels.  

In rats, the liver, thyroid and kidney are the target organs for repeated dose toxicity of 
MCCPs.  

 
 
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KEY CHRONIC TOXICITY DATA: SUMMARY OF DATA FOR REPEATED EXPOSURE 

For the liver, increases in weight and changes in enzyme activity are seen in rats at 
exposure levels of 36 mg/kg bw/day or more (Poon et al., 1995). These effects are 
considered part of an adaptive response to an increase in metabolic demand. There is also 
the possibility that peroxisome proliferation plays a role. These findings were not 
considered to justify classification. At higher exposure levels (around 360 mg/kg bw/day), 
single cell necrosis was observed in rats (Poon et al., 1995), but this is above the cut-off 
level for classification. 

Increased thyroid weight was observed in a 90-day study only at the highest exposure 
level tested, 625 mg/kg bw/day (IRDC 1984). Histopathologically, lesions such as 
hyperplasia have been observed down to the lowest exposure levels tested (eg. 0.4 mg/kg 
bw/day by Poon et al., 1995) with an exposure-related increase in severity. However, the 
severity only ranged from ‘mild’ to ‘moderate’ even with an increase in exposure of 3 
orders of magnitude. The thyroid changes (increased weight and follicular hypertrophy and 
hyperplasia) are considered to occur as a result of repeated stimulation of this organ 
caused by the well-characterised negative feedback control effect arising from plasma T4 
depletion. This in turn is related to an increase in the activity of hepatic UDPG-transferase. 
Humans, unlike rodents, possess a T4 binding protein that greatly reduces susceptibility to 
plasma T4 depletion and thyroid stimulation. The thyroid effects observed in rats are 
therefore considered of insufficient concern for classification. 

No adverse renal effects were seen in males and female rats at 0.4 mg/kg bw/day in a 90-
day study (Poon et al., 1995). Inner medullary tubular dilatation was seen at 4 mg/kg 
bw/day in the kidneys of females only. These lesions were slight, with changes increasing 
only marginally in severity and incidence at higher levels (up to 420 mg/kg bw/day for 
females). An exposure-related increase in the incidence and severity of a mixed population 
of interstitial inflammatory cells, tubular regeneration and minimal degenerative changes 
in the tubular epithelium was seen in treated males and females at 10 mg/kg bw/day or 
more. At 10 mg/kg bw/day the severity of these changes was graded as ‘trace’, and even 
at the highest exposure level, 625 mg/kg bw/day it was only ‘mild’. As the effects 
observed in the highest dose group do not seem to be severe, no classification is proposed 
for repeated-exposure effects. 

Mechanistic studies conducted using short-chain chlorinated paraffins (SCCPs, C10-13) 
indicate deposition of β2μ-globulin in proximal convoluted tubules and this may be the 
primary mechanism for renal toxicity in male rats. 

Classification & Labelling: 

Classification for MCCP’s: No classification for STOT-RE  

Justification:  

•  Effects on the liver: the effects justifying the classification (necrosis) are above the cut-

off limit values. 

•  Effects on the thyroid: the effects observed are specific for the rat and do not justify 

classification. 

•  Effects on the kidneys: the data are not detailed enough to give an idea what are the 

actual effects around the cut-off values (10-100 mg/kg bw) but probably we could come 
to the same conclusion, i.e. the effect is not enough to justify the classification in any 
category. 

 
 
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3.9.5.3.  Examples of mixtures fulfilling the criteria for classification   

3.9.5.3.1. 

Example 5 

Application of criteria for mixture classification: 'When data are available for the complete 
mixture' (see Section 3.9.3.3 of this Guidance). 

Available information:  

A mixture with a suspect ingredient (8%) has been tested in a valid 90-day oral study according 
to TG OECD 408 and GLP. At the dose of 90 mg/kg bw/day severe liver damage (necrosis) has 
been observed, at 30 mg/kg bw/day slight-moderate liver impairment. The NOAEL was 9 mg/kg 
bw/day. 

Classification & Labelling: 

Classification: STOT-RE Category 2 

Justification: The classification is based on data of a valid, appropriate animal study for the 
complete mixture. Therefore the criteria for substances (CLP Annex I, Table 3.9.3) are applied. 

3.9.5.3.2. 

Example 6 

Application of criteria for mixture classification: 'When data are available for all components' 
(see Section 3.9.3.3 of this Guidance). Components of a mixture that should be taken into 
account are listed below together with their concentrations. Generic concentration limits should 
be used, non-additivity is applied. 

Available information: 

Ingredient  % w/w 

Classification 

1 

2 

3 

4 

39 

5.5 

54 

1.5 

NC 

STOT-RE Category 1 

NC 

STOT-RE Category 2 

Classification & Labelling: 

Classification of the mixture: STOT-RE Category 2  

Justification: No test data with respect to STOT-RE are available for the complete mixture. 
Bridging principles can not be applied since no respective test data on a similar mixture are 
available. The classification of the mixture will be based on the classified ingredients (CLP Annex 
I, Table 3.9.4). 

There is one STOT-RE Category 1 ingredient in a concentration of <10%. Therefore the mixture 
is not classified in STOT-RE Category 1. There is one STOT-RE Category 1 ingredient in a 
concentration of ≥ 1% and <10%, therefore STOT-RE Category 2 is warranted. The STOT-RE 
Category 2 ingredient with 1.5% is not taken into account at all, since the concentration is < 
10%.  

3.9.5.3.3. 

Example 7 

Application of criteria for mixture classification 'When data are available for all components' 
(Section 3.9.3.3 of this Guidance). Components of a mixture that should be taken into account 
are listed below together with their concentrations. Generic concentration limits should be used, 
specific concentration limits should take precedence over generic concentration limits when 
available, and non-additivity applies. 

 
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Available information: 

Guidance on the Application of the CLP Criteria 

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Ingredient 

Classification 

Concentration 
(% w/w) 

Mixture 
Classification 

Remarks 

A 

B 

STOT-RE Category  1 

0.1 

SCL 0.2% 

STOT-RE Category 1 

9 

Classification & Labelling: 

Classification of the mixture: STOT-RE Category 2 based on 9% of B, which is ≥ 1% and < 
10%; A does not contribute to the classification of the mixture, as the concentration of A is < 
0.2% (the SCL) and additivity of the two ingredients is not foreseen. 

3.9.5.3.4. 

Example 8 

Application of criteria for mixture classification 'When data are available for all components' 
(Section 3.9.3.3 of this Guidance). Components of a mixture that should be taken into account 
are listed below together with their concentrations. Generic concentration limits should be used, 
specific concentration limits should take precedence over generic concentration limits when 
available, and non-additivity applies. 

Available information: 

Ingredient 

Classification 

Concentration (% w/w) 

Remarks 

A 

C 

STOT-RE Category 1 

STOT-RE Category 2 

0.3 

9 

SCL 0.2% 

Classification & Labelling: 

Classification of the mixture: STOT-RE Category 1 since the concentration of A, even if being 
lower than the generic concentration limit, is higher than the SCL; C does not contribute to the 
classification. 

3.9.5.4.  Example of mixtures not fulfilling the criteria for classification   

3.9.5.4.1. 

Example 9 

Application of criteria for mixture classification: 'When data are available for all components' 
(Section 3.9.3.3 of this Guidance); components of a mixture that should be taken into account 
are listed below together with their concentrations. Generic concentration limits should be used, 
non-additivity is applied: 

Available information: 

Ingredient  Concentration (% w/w) 

Classification 

1 

2 

3 

4 

39 

9 

49.5 

2.5 

NC 

STOT-RE Category2 

NC 

STOT-RE Category 2 

 
 
 
 
 
 
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Classification & Labelling: 

Classification of the mixture: NC (no classification). 

Justification: No test data with respect to STOT-RE are available for the mixture as a whole. 
Bridging principles can not be applied, since no respective test data on a similar mixture are 
available (CLP Annex I, Table 3.9.4). 

The classification of the mixture is based on the classified ingredients. No ingredient is classified 
in STOT-RE Category 1. Therefore the mixture cannot be classified in STOT-RE Category 1. 
Though the sum of the STOT-RE Category 2 ingredients (11.5 %) is above the generic 
concentration limit of 10%, the mixture is not classified. This is because for STOT-RE the no 
additivity approach applies and no individual ingredient ≥ 10% is present in the mixture. 

3.9.6.  References 

Muller, A. et al (2006) Regulatory Toxicology and Pharmacology 45, 229-241 

 
 
 
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4.  PART 4: ENVIRONMENTAL HAZARDS 

4.1.  HAZARDOUS TO THE AQUATIC ENVIRONMENT 

4.1.1.  Introduction  

Guidance  for  the  application  of  the  criteria  covering  effects  on  the  aquatic  compartment  was 
developed by OECD and incorporated as Annexes 9 and 10 in the ‘Globally Harmonised System 
of  classification  and  labelling  of  chemicals  (UN  GHS)’  (Fourth  revised  edition,  2011, 
https://www.unece.org/fileadmin/DAM/trans/danger/publi/ghs/ghs_rev04/English/ST-SG-AC10-
30-Rev4e.pdf).  

The text in part 4, even more so in some of the Annexes to this chapter, is largely based on the 
text in UN GHS. The guidance given in Annexes 9 and 10 of UN GHS relates to substances, but 
not  mixtures.  Some  parts  have  therefore  been  slightly  revised  to  take  into  account  recent 
developments and additional guidance documents provided by ECHA. Furthermore guidance on 
the classification of mixtures has been brought into this chapter as well as classification examples 
for both substances and mixtures. 

4.1.2.  Scope  

Annex  I:  4.1.1.3.1  Classification  of  substances  and  mixtures  for  environmental  hazards 
requires the identification of the hazards they present to the aquatic environment. The aquatic 
environment  is  considered  in  terms  of  the  aquatic  organisms  that  live  in  the  water,  and  the 
aquatic ecosystem of which they are part. The basis, therefore, of the identification of short-
term (acute) and long-term (chronic) hazards is the aquatic toxicity of the substance or mixture, 
although this shall be modified by taking account of further information on the degradation and 
bioaccumulation behaviour, if appropriate. 

The  classification  scheme  (CLP  Annex  I,  part  4)  has  been  developed  with  the  objective  of 
identifying those chemicals that present, through their intrinsic properties, a hazard to the aquatic 
environment covering the aquatic freshwater and marine ecosystems. For most substances, the 
majority of data available addresses this environmental compartment. The classification scheme 
is limited in scope in that it does not, as yet, include aquatic sediments, nor higher organisms at 
the  top  end  of  the  aquatic  food-chain,  although  these  may  to  some  extent  be  covered  by  the 
criteria selected. 

Although limited in scope, it is widely accepted that this compartment is vulnerable, in that it is 
the receiving compartment for many harmful substances, and the organisms that live there can 
be  very  sensitive.  It  is  also  complex  since  any  system  that  seeks  to  identify  hazards  to  the 
environment must seek to define those effects in terms of wider effects on ecosystems, rather 
than on individuals within a species or population. For practical reasons, a limited set of specific 
properties  has  been  selected  through  which  the  short-term  (acute)  and  long-term  (chronic) 
hazards  can  be  best  described:  acute  aquatic  toxicity;  chronic  aquatic  toxicity;  lack  of  rapid 
degradability; and potential for or actual bioaccumulation. Relevant definitions for aquatic hazard 
classification  of  substances  i.e.  acute  and/or  chronic  aquatic  toxicity,  availability  and 
bioavailability to the aquatic environment are  outlined in the  CLP Regulation, Annex I, Section 
4.1.1.1.  Some  further  guidance  can  be  viewed  in  IR&CSA  Chapter  R.7b  and  Annex  I  of  this 
Guidance. The rationale for the selection of these properties as the means to define the aquatic 
hazard will be described in more detail in the following sections of this guidance (e.g. see Annex 
I). 

 
 
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4.1.3.  Classification of substances hazardous to the aquatic environment 

4.1.3.1. 

Information applicable for classification of substances hazardous to 
the aquatic environment  

4.1.3.1.1. 

Substance properties used for classification 

Generally speaking, in deciding whether a substance should be classified, a search of appropriate 
databases  and  other  sources  of  data  should  be  made  for  at  least  the  following  substance 
properties:  water  solubility,  octanol/water  partition  coefficient  (log  Kow),  acute  aquatic  toxicity 
(L(E)C50),  chronic  aquatic  toxicity  (NOEC  or  equivalent  ECx
73),  degradation  (evidence  of  rapid 
degradability, hydrolysis) and bioaccumulation (preferably bioconcentration factor in fish (BCF)). 
Other information might be considered on a case-by-case basis. 

Although  not  used  directly  in  the  criteria,  the  water  solubility  and  stability  data  are  important 
since they are a valuable help in the data interpretation of the other properties. However, water 
solubility may be difficult to determine and is frequently recorded as simply being low, insoluble 
or  less  than  the  detection  limit.  This  may  create  problems  in  interpreting  aquatic  toxicity  and 
bioaccumulation studies (see also Annex III). Hydrolysis data (Test Methods Regulation (EC) No 
440/2008; OECD TG 111) and information on the hydrolysis products as well as their behaviour 
in water might be helpful as well. As an example, for substances where the degradation half-life 
(DT50) is less than 12 hours, environmental effects are likely to be attributed to the hydrolysis 
products rather than to the parent substance itself.  

4.1.3.1.2. 

Information and data availability  

Annex  I:  4.1.1.2.2  Preferably  data  shall  be  derived  using  the  standardised  test  methods 
referred  to  in  Article 8(3).  In  practice  data  from  other  standardised  test  methods  such  as 
national methods shall also be used where they are considered as equivalent. Where valid data 
are  available  from  non-standard  testing  and  from  non-testing  methods,  these  shall  be 
considered  in  classification  provided  they  fulfil  the  requirements  specified  in  section 1  of 
Annex XI  to  Regulation  (EC)  No  1907/2006.  In  general,  both  freshwater  and  marine  species 
toxicity data are considered suitable for use in classification provided the test methods used are 
equivalent. Where such data are not available classification shall be based on the best available 
data. See also part 1 of Annex I to Regulation (EC) No 1272/2008. 

The  data  used  to  classify  a  substance  can  be  drawn  from  data  required  for  other  regulatory 
purposes as well as the relevant literature. A number of internationally recognised databases exist 
which  can  act  as  a  good  starting  point.  Such  databases  vary  widely  in  quality  and 
comprehensiveness, and it is unlikely that any one database will hold all the information necessary 
for  a  classification  to  be  made.  Some  databases  specialise  in  aquatic  toxicity  and  others  in 
environmental fate. Information can also be gathered from data submitted under plant protection 
products and/or biocidal products legislation. 

Non-testing information 

Information derived from (Q)SAR and read-across, grouping and categorisation can also be used, 
see also IR&CSA Chapter R.6 (see also section 1.4 of this Guidance).  

Information sources 

73 If available, preference is given to EC10, see OECD 2006. 

 
 
 
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Section  R.3.4.1  of  IR&CSA  Chapter  R.3  specifies  a  selection  of  freely  available  databases  and 
databanks  which  might  be  consulted  for  classification  purposes.  All  ECHA  guidance  documents 
are available on the Agency’s website ( https://echa.europa.eu/support/guidance).  

Data  can  also  be  found  through  the  eChemPortal,  which  is  a  global  portal  to  information  on 
chemical substances. The eChemPortal provides access to a number of databases, including the 
OECD HPV (Existing Chemicals Database) and the SIDS UNEP (Screening Information Dataset for 
the  OECD: 
High  Volume  Chemicals).  The  eChemPortal 
(https://www.echemportal.org/echemportal/)   

is  currently  hosted  by 

Further guidance is given in Annex 0 to this document. 

4.1.3.2.  Evaluation of available information 

4.1.3.2.1.  General considerations  

The term substance covers a wide range of chemicals (consult the Guidance for identification and 
naming  of  substances  under  REACH  and  CLP,  Chapter  3)  many  of  which  pose  challenges  to  a 
classification system based on rigid criteria. This section will thus provide some guidance on how 
these challenges can be dealt with based both on experience in use and clear scientific rationale.  

The range of interpretational problems can be extensive and, as a result, such interpretation will 
always rely on the ability and expertise of the individuals responsible for classification. However, 
it  is  possible  to  identify  some  commonly  occurring  difficulties  and  provide  guidance.  Such 
difficulties can fall into a number of overlapping issues: 

a.  The difficulty in applying the current test procedures to some types of substances; 

b.  The difficulty in interpreting the data derived both from these ‘difficult to test’ substances 

(see section below) and from other substances; 

c.  The difficulty in interpretation of diverse datasets derived from a wide variety of sources 

(e.g. Weight of Evidence); 

d.  The difficulty of interpreting ‘other’ information 

Regarding the use of test data, in general, only reliable information (i.e. with a Klimisch reliability 
score  of  1  (reliable  without  restrictions)  or  2  (reliable  with  restrictions))  should  be  used  for 
classification purposes.  However, good quality  data may not always be available for all trophic 
levels. It will be necessary to consider data of lower quality for those trophic levels for which good 
quality data are not available. Consideration of such data, however, will also need to take into 
account the difficulties that may have affected the likelihood of achieving a valid result. For larger 
data sets, preference should be given to information with Klimisch score 1, while information with 
Klimisch score 2  can be used as  supporting information. For more information  on the Klimisch 
reliability scoring system, see IR&CSA Chapter R.4 section R.4.2. 

4.1.3.2.2. 

Substances difficult to test 

For many organic substances, the testing and interpretation of data presents no problems when 
applying  both  the  relevant  Test  Methods  Regulation  (EC)  No  440/2008  and/or  OECD  Test 
Guidelines and the classification criteria. There are a number of typical interpretational problems, 
however,  that  can  be  attributed  to  the  properties  of  the  substance  being  studied.  These  are 
commonly called ‘difficult to test substances’:  

a.  poorly  soluble  substances:  these  substances  are  difficult  to  test  because  they  present 
problems  in  the  preparation  of  a  test  solution,  maintenance  of  test  concentrations  and 
verification of exposure during aquatic toxicity testing. In addition, many available data 
for such substances have been produced using ‘solutions’ in excess of the water solubility 
resulting in major interpretational problems in defining the true L(E)C50 or NOEC/ECx for 
the  purposes  of  classification.  Interpretation  of  the  partitioning  behaviour  can  also  be 
problematic  where  the  poor  solubility  in  water  and  octanol  may  be  compounded  by 

 
 
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insufficient  sensitivity  in  the  analytical  method.  Water  solubility  may  be  difficult  to 
determine and is frequently recorded as simply being less than the detection limit, creating 
problems  in  interpreting  both  aquatic  toxicity  and  bioaccumulation  studies.  In 
biodegradation studies, poor solubility may result in low bioavailability and thus lower than 
expected biodegradation rates. The specific test method or the choice of procedures used 
can thus be of key importance (see also Annex I.4.2);  

b.  unstable substances: such substances that degrade (or react) rapidly in the test system 
present  both  testing  and  interpretational  problems.  It  will  be  necessary  to  determine 
whether the correct methodology in line with the guidance provided in Section 4.1.3.3 has 
been used, whether it is the substance or the degradation/reaction product that has been 
tested,  and  whether  the  data  produced  is  relevant  to  the  classification  of  the  parent 
substance (see also Annex I.4.3);  

c.  volatile substances: such substances that can clearly present testing problems when used 
in  open  systems  should  be  evaluated  to  ensure  adequate  maintenance  of  exposure 
concentrations. Loss of test material during biodegradation testing is inevitable in certain 
methods and will lead to misinterpretation of the results (see also Annex I.4.1); 

d.  complex  or  multi-constituent74  substances:  such  substances,  for  example,  complex 
hydrocarbons,  or  other  UVCB75  substances,  frequently  cannot  be  dissolved  into  a 
homogeneous  solution,  and  the  multiple  components  make  monitoring  impossible.  For 
organics,  consideration  therefore  needs  to  be  given  to  using  the  data  derived  from  the 
testing of water-accommodated fractions (WAFs) for aquatic toxicity, and the use of such 
data  in  the  classification  scheme76.  Biodegradation,  bioaccumulation,  partitioning 
behaviour  and  water  solubility  all  present  problems  of  interpretation,  where  each 
component of these complex or multi-constituent substances may behave differently (see 
also Annex I.4.5); 

e.  polymers: such substances frequently comprise a wide range of molecular masses, which 
individually  might  have  different  water  solubilities.  Special  methods  are  available  to 
determine the water soluble fraction and these data will need to be used in interpreting 
the test data against the classification criteria (see also Annex I.4.5); 

f. 

inorganic compounds and metals: such substances, which can interact with the media, can 
produce a range of aquatic toxicities dependent on factors such as pH, water hardness etc. 
Difficult  interpretational  problems  also  arise  from  the  testing  of  essential  elements  that 
are beneficial at certain levels. For metals and inorganic metal compounds, the concept of 
degradability as applied to organic compounds has limited or no meaning. Equally the use 
of bioaccumulation data should be treated with care (see also Annex IV); 

g.  surface-active substances: such substances can form emulsions in which the bioavailability 
is difficult to ascertain, even with careful preparation of solutions. Micelle formation can 
result in an overestimation of the bioavailable fraction even when ‘solutions’ are apparently 
formed. This presents significant problems of interpretation in each of the water solubility, 
partition coefficient, bioaccumulation and aquatic toxicity studies (see also Annex III.3.1); 

h.  ionisable  substances:  such  substances  can  change  the  extent  of  ionisation  according  to 
the level of counter ions in the media. Acids and bases, for example, will show radically 
different partitioning behaviour depending on the pH;  

74  Further  definitions  are provided  in  the  Guidance  for  identification  and  naming  of  substances  under  REACH  and  CLP 
(ECHA). 

75 UVCB means Substances of Unknown or Variable composition, Complex reaction products or Biological materials, see 
Chapter 4.3 of the Guidance for identification and naming of substances under REACH and CLP. 

76 Note that the toxicity is sometimes expressed as LL50, related to the lethal loading level. This loading level from the 
WSF or WAF may be used directly in the classification criteria (see also Annex I.4.5 of this guidance document). 

 
 
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i.  coloured  substances:  such  substances  can  cause  problems  in  the  algal/aquatic  plant 

testing because of the blocking of incident light; 

j. 

impurities: some substances can contain impurities that can change in percentage and in 
chemical nature between production batches. Interpretational problems can arise where 
either or both the toxicity and water solubility of the impurities are greater than the parent 
substance, thus potentially influencing the toxicity data in a significant way. In general, 
the substance as manufactured including impurities should be tested and the classification 
should  be  based  on  these  test  results.  To  assess  the  sameness  of  two  substances 
containing  the  same  impurity  in  different  amount  see  Guidance  for  identification  and 
naming of substances under REACH and CLP, Chapter 5; 

k.  essential  substances:  some  substances  are  essential  to  life,  even  though,  like  any 
substance,  excessive  concentrations  can  be  harmful.  This  can  lead  to  complex 
concentration/dose-response curves; 

l.  substances  which  can  chelate  or  sequester  essential  elements,  leading  to  the  same 

problems of interpretation as in (k). 

testing 

For  further  details  see  the  OECD  Guidance  23  Guidance  Document  on  aqueous-phase  aquatic 
2019, 
toxicity 
http://www.oecd.org/officialdocuments/publicdisplaydocumentpdf/?cote=ENV/JM/MONO(2000)6
/REV1&docLanguage=En) and also the IR&CSA Chapter R.7b, Appendix 7.8-1 and Annex I to the 
current Guidance Document. 

chemicals 

difficult 

(OECD, 

test 

of 

4.1.3.2.3. 

Interpretation  of  data 
bioaccumulation   

4.1.3.2.3.1.  Aquatic toxicity  

for  aquatic 

toxicity,  degradation  and 

Annex I: 4.1.2.7.1 Acute aquatic toxicity is normally determined using a fish 96 hour LC50, a 
crustacea species 48 hour EC50 and/or an algal species 72 or 96 hour EC50. These species cover 
a range of trophic levels and taxa and are considered as surrogate for all aquatic organisms. 
Data  on  other  species  (e.g.  Lemna  spp.)  shall  also  be  considered  if  the  test  methodology  is 
suitable. The aquatic plant growth inhibition tests are normally considered as chronic tests but 
the EC50s are treated as acute values for classification purposes (see note 2).  

Annex  I:  4.1.2.7.2  For  determining  chronic  aquatic  toxicity  for  classification  purposes  data 
generated  according  to  the  standardised  test  methods  referred  to  in  Article 8(3)  shall  be 
accepted,  as  well  as  results  obtained  from  other  validated  and  internationally  accepted  test 
methods. The NOECs or other equivalent ECx (e.g. EC10) shall be used. 

Fish, crustacea and algae or other aquatic plants are tested as surrogate species representing a 
range of trophic levels and taxa, and the test methods are highly standardised (see Annex I for 
further details). Valid data for short- and long-term tests on other species at the same trophic 
level  shall  also  be  considered,  provided  they  are  equivalent  and  suitable  in  terms  of  species 
relevance, testing conditions and test endpoints. 

The purpose of classification is to characterise both the acute and long-term hazards in the aquatic 
environment. The acute and long-term hazards represent distinct types of hazard and should be 
determined independently.  

The  lowest  available  toxicity  value(s)  between  and  within  the  different  trophic  levels  (fish, 
crustacea,  algae/aquatic  plants)  will  normally  be  used  to  define  the  appropriate  hazard 
category(ies),  although  there  may  be  circumstances  where  a  weight  of  evidence  approach  is 
required (see Section 4.1.3.2.4). 

Care  should  be  taken  when  classifying  substances  like  ionisable  organic  chemicals  or  organo-
metallic  substances  as  the  observed  results  may  express  different  toxicities  in  freshwater  and 
marine  environments  or  when  classifying  poorly  soluble  substances  (water  solubility  e.g.  <  1 

 
 
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mg/L CLP Table 4.1.0 note 4), and substances with a specific mode of action inducing effects on 
reproduction or growth instead of lethality. In the latter cases, there is evidence that acute testing 
may not provide a true measure of the intrinsic toxicity.  

Relevant descriptions of the type of acute and/or chronic aquatic toxicity tests have been outlined 
in detail in Annex I to the current Guidance and in IR&CSA Chapter R.7b, Sections R.7.8.3-R.7.8.4. 
For  classification  and  labelling  purposes,  tests  using  organisms  outside  the  specified  size 
(generally smaller) and/or tests with a differing test duration could be used if no other acceptable 
data are available.  

There  are  some  recently  validated  in  vitro  methods  available  for  use  as  alternative  data  to 
determine acute and long-term hazards. Currently, in vitro tests cannot directly substitute in vivo 
data in terms of one for one replacement for classification purposes. However, in vitro data can 
already play a role as supporting evidence in a weight of evidence approach and there are ongoing 
efforts to develop and validate further in vitro methods which may add to our understanding of 
aquatic toxicity. Although the standard guideline in vivo methods remain the most informative for 
classification  and  labelling  purposes,  all  available  and  relevant  information  on  aquatic  toxicity, 
including non-guideline methods, can be assessed on their own merits and carefully balanced in 
the overall weight of evidence. 

4.1.3.2.3.2.  Degradation 

Annex  I:  4.1.2.9.1  Substances  that  rapidly  degrade  can  be  quickly  removed  from  the 
environment. While effects of such substances can occur, particularly in the event of a spillage 
or accident, they are localised and of short duration. In the absence of rapid degradation in the 
environment a substance in the water has the potential to exert toxicity over a wide temporal 
and spatial scale. 

Annex I: 4.1.2.9.2  One way of demonstrating rapid degradation utilises the biodegradation 
screening tests designed to determine whether an organic substance is "readily biodegradable". 
Where such data are not available, a BOD(5 days)/COD ratio ≥ 0,5 is considered as indicative 
of rapid degradation. Thus, a substance which passes this screening test is considered likely to 
biodegrade "rapidly" in the aquatic environment, and is thus unlikely to be persistent. However, 
a fail in the screening test does not necessarily mean that the substance will not degrade rapidly 
in the environment. Other evidence of rapid degradation in the environment may therefore also 
be considered and are of particular importance where the substances are inhibitory to microbial 
activity  at  the  concentration  levels  used  in  standard  testing.  Thus,  a  further  classification 
criterion is included which allows the use of data to show that the substance did actually degrade 
biotically or abiotically in the aquatic environment by > 70 % in 28 days. Thus, if degradation 
is  demonstrated  under  environmentally  realistic  conditions,  then  the  criterion  of  "rapid 
degradability" is met. 

The  definition  of  degradation  covers  both  biotic  (biodegradation)  and  abiotic  degradation 
processes.  Data  on  degradation  properties  of  a  substance  may  be  available  from  standardised 
tests,  from  other  types  of  investigations,  or  they  may  be  estimated  from  the  structure  of  the 
molecules  (see  Section  1.4).  In  Annex  II.2  to  this  guidance  a  general  overview  of  relevant 
definitions on how to use different (bio)degradability tests and guidance for the interpretation of 
test  data  in  the  context  of  classification  and  labelling  is  given.  Additional  information  on 
(bio)degradation testing methods can be found in IR&CSA Chapter R.7b, section R.7.9. The OECD 
test methods 301A-F (C.4-A to F of the Test Methods Regulation 440/2008), OECD TG 310, or 
equivalent  tests,  are  commonly  used  to  determine  ‘ready  biodegradability’.  Some  guidance  on 
the  use  of  (Q)SAR  methods  for  degradability  is  presented  in  IR&CSA  Chapter  R.7b,  section 
R.7.9.3.1. 

The paragraphs below will focus on the guidance for using degradability data for classification & 
labelling under CLP. It should be noted that the guidance on degradability pertains primarily to 
individual substances. In the case of complex or multi-constituent substances, the proposed test 

 
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approaches  do  not  normally  allow  an  unequivocal  interpretation  of  the  degradability  of  the 
individual components when the test material is the multi-constituent substance as a whole. Thus, 
results of biodegradability tests on complex or multi-constituent substances should be carefully 
evaluated before use for classification purposes is considered. See Annex II.3.1 for further details. 

Annex I: 4.1.2.9.3 Many degradation data are available in the form of degradation half-lives 
and these can be used in defining rapid degradation provided that ultimate biodegradation of 
the substance, i.e. full mineralisation, is achieved. Primary biodegradation does not normally 
suffice  in  the  assessment  of  rapid  degradability  unless  it  can  be  demonstrated  that  the 
degradation  products  do  not  fulfil  the  criteria  for  classification  as  hazardous  to  the  aquatic 
environment. 

Annex I: 4.1.2.9.4 The criteria used reflect the fact that environmental degradation may be 
biotic or abiotic. Hydrolysis can be considered if the hydrolysis products do not fulfil the criteria 
for classification as hazardous to the aquatic environment. 

Annex I: 4.1.2.9.5 Substances are considered rapidly degradable in the environment if one of 
the following criteria holds true: 

(a)  if, in 28-day ready biodegradation studies, at least the following levels of degradation 

are achieved: 

(i)  tests based on dissolved organic carbon: 70 %; 

(ii) tests based on oxygen depletion or carbon dioxide generation: 60 % of theoretical  

maximum. 

These  levels  of  biodegradation  must  be  achieved  within  10  days  of  the  start  of 
degradation  which  point  is  taken  as  the  time  when  10 %  of  the  substance  has  been 
degraded;  unless  the  substance  is  identified  as  an  UVCB  or  as  a  complex,  multi-
constituent  substance  with  structurally  similar  constituents.  In  this  case,  and  where 
there is sufficient justification, the 10-day window condition may be waived and the pass 
level applied at 28 days, or 

(b)  if,  in  those  cases  where  only  BOD  and  COD  data  are  available,  when  the  ratio  of 

BOD5/COD is  0,5; or 

(c)  if other convincing scientific evidence is available to demonstrate that the substance can 
be degraded (biotically and/or abiotically) in the aquatic environment to a level > 70 % 
within a 28-day period. 

The following decision scheme may be used as a general guidance to facilitate decisions in relation 
to rapid degradability in the aquatic environment and classification of chemicals hazardous to the 
aquatic environment. 

A substance is considered to be  not rapidly degradable  unless at least one  of the following is 
fulfilled: 

a.  The  substance  is  demonstrated  to  be  readily  biodegradable  in  a  28-day  test  for  ready 
biodegradability. The pass level of the test (70 % DOC removal or 60 % theoretical oxygen 
demand) must be achieved within 10 days from the onset of biodegradation, if it is possible 
to evaluate this according to the available test data (the 10-day window condition may be 
waived for complex multi-component substances with structurally similar constituents and 
the pass level applied at 28 days, as discussed in Annex II.2.1.2 to this document). If this 
is not possible, then the pass level should be  evaluated within a 14-day time window if 
possible, or after the end of the test; or 

b.  The  substance is demonstrated to be ultimately degraded in a  surface water  simulation 
test  with  a  half-life  of  < 16  days  (corresponding  to  a  degradation  of  >  70  %  within  28 
days); or 

 
 
 
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c.  The substance is demonstrated to be primarily degraded biotically or abiotically e.g. via 
hydrolysis,  in  the  aquatic  environment  with  a  half-life  <  16  days  (corresponding  to  a 
degradation of > 70 % within 28 days), and it can be demonstrated that the degradation 
products do not fulfil the criteria for classification as hazardous to the aquatic environment. 

When these preferred data types are not available rapid degradation may be demonstrated if one 
of the following criteria is justified: 

a.  The substance is demonstrated to be ultimately degraded in an aquatic sediment or soil 
simulation test with a half-life of < 16 days (corresponding to a degradation of > 70 % 
within 28 days); or 

b.  In  those  cases  where  only  BOD5  and  COD  data  are  available,  the  ratio  of  BOD5/COD  is 
greater than or equal to 0.5. The same criterion applies to ready biodegradability tests of 
a shorter duration than 28 days, if the half-life furthermore is < 7 days; or 

c.  A weight of evidence approach based on read-across provides convincing evidence that a 

given substance is rapidly degradable.  

If none of the types of data mentioned above are available, the substance is considered as not 
rapidly degradable. This decision may be supported by fulfilment of at least one of the following 
criteria: 

i.  the substance is not inherently degradable in an inherent biodegradability test; or 

ii.  the substance is predicted to be slowly biodegradable by scientifically valid (Q)SARs, 
e.g.  for  the  Biodegradation  Probability  Program,  the  score  for  rapid  degradation 
(linear or non-linear model) < 0.5; or 

iii. the substance is considered to be not rapidly degradable based on indirect evidence, 

such as knowledge from structurally similar substances; or 

iv. no other data regarding degradability are available. 

The percentage degradation reached after 28 days in ready biodegradability tests may be used 
directly for the assessment of ‘rapid degradability’ if no specific information on the time window 
is available or if the data were derived with the MITI I test (OECD TG 301C, 2006 or C.4-E of the 
Test Methods Regulation 440/2008). In the Closed Bottle test (OECD  TG 301D, or C.4-F of the 
Test Methods Regulation 440/2008), a 14-day window may be used when measurements have 
not been made after 10 days. For some industrial chemicals that in terms of composition can be 
seen  as  multi-component  substances,  testing  for  ‘ready  biodegradability’  can  lead  to 
interpretational problems (see Annex II to this guidance).  

In  all  cases,  it  should  be  considered  that  IR&CSA  Chapter  R.7b,  section  R.7.9.4  states  that 
“…ready biodegradability tests are intended for pure substances and are generally not applicable 
for  complex  compositions  containing  different  types  of  constituents,  like  UVCBs”.  For  a  UVCB 
substance,  observed  biodegradation  may  indeed  represent  the  biodegradation  of  only  some 
constituents. In the same document, it is indicated that “it is sometimes relevant to examine the 
ready biodegradability of mixtures of structurally similar chemicals”. 

Selection of test systems  

As regards section 4.1.2.9.5 (c) in Annex I to CLP (“other convincing scientific evidence available 
to demonstrate that the substance can be degraded in the aquatic environment to a level > 70 
% within a 28-day period”), the evaluation of the fulfilment of this criterion should be conducted 
on a case-by-case basis by expert judgement. Test systems that can be used to demonstrate the 
occurrence of rapid degradability are listed in Annex II. This includes e.g. simulation tests under 
realistic conditions, mesocosms and field monitoring.  

Inherent (OECD TG 302A and B, or C.9 and C.12 of the Test Methods Regulation 440/2008) and 
sewage treatment simulation (OECD TG 303, or C.10 of the Test Methods Regulation 440/2008) 
tests  are  not  used  in  this  context,  due  to  the  high  levels  of  adapted  biomass.  Anaerobic 

 
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degradation tests (OECD TG 311/ISO 11734 and analogous tests) are not suitable because of the 
specificity  of  the  anaerobic  compartments.  Also  the    defined  category  of  ‘Enhanced  Ready 
Biodegradation (Screening) Tests’ in IR&CSA Chapter R.7b, section R.7.9 are not suitable for use 
in  classification  and  labelling,  as  they  are  designed  to  promote  biodegradation  and  are  not  as 
stringent as OECD TG 301-suite type tests. More specifically, section R.7.9.4.1 explicitly states 
that “a number of potential enhancements to the ready biodegradation test have been identified. 
These  enhancements  have  been  proposed  for  the  determination  of  persistence  in  vPvB/PBT 
assessment only but are not to be used for Classification and Labelling and quantitative exposure 
and risk assessment”. 

Use of SARs and (Q)SARs  

The  estimation  of degradation via SARs and/or  (Q)SARs for hydrolysis and biodegradation is  a 
rapidly developing field. The predictions from (Q)SAR models may be considered as contributing 
to a decision on ready biodegradability or rapid degradation for classification purposes. (Q)SAR 
models should be used with great care, taking into account the applicability domain and validation 
of the models. Current practice is to use the outcome of these biodegradation models to predict 
that a substance is not readily degradable, rather than vice versa. This is because models such 
as BIOWIN tend to predict non-ready biodegradability more certainly than ready biodegradability 
(IR&CSA Chapter R.7b, section R.7.9.4.1). However, (Q)SAR information can be used as a part 
of  expert  judgement  and  WoE  practices,  for  example  where  very  consistent  measured  and 
predicted data are available for a structurally analogous compound. More details can be found in 
IR&CSA Chapter R.7b, section R.7.9.4.1.  

General interpretation problems and substances difficult to test 

The UN GHS Annex 9 and OECD Guidance 23 (OECD 2019) discuss substances that are inherently 
difficult  to  test  for  biodegradability,  and  possible  adjustments  to  overcome  testing  problems. 
Testing or interpretational problems may occur with e.g. complex multi-constituent substances, 
surface active agents, highly volatile or insoluble substances, substances that are toxic to micro-
organisms at normal test concentrations, and unstable molecules.   

4.1.3.2.3.3.  Bioaccumulation  

Annex I: 4.1.2.8.1 Bioaccumulation of substances within aquatic organisms can give rise to 
toxic effects over longer time scales even when actual water concentrations are low. For organic 
substances  the  potential  for  bioaccumulation  shall  normally  be  determined  by  using  the 
octanol/water partition coefficient, usually reported as a log Kow. The relationship between the 
log Kow of an organic substance and its bioconcentration as measured by the bioconcentration 
factor (BCF) in fish has considerable scientific literature  support. Using a  cut-off value of log 
Kow  4  is  intended  to  identify  only  those  substances  with  a  real  potential  to  bioconcentrate. 
While this represents a potential to bioaccumulate, an experimentally determined BCF provides 
a better measure and shall be used in preference if available. A BCF in fish of ≥ 500 is indicative 
of  the  potential  to  bioconcentrate  for  classification  purposes.  Some  relationships  can  be 
observed between chronic toxicity and bioaccumulation potential, as toxicity is related to the 
body burden. 

The  potential  for  bioaccumulation  is  an  important  criterion  to  determine  whether  a  chemical 
substance  is  a  potential  hazard  to  the  environment.  Bioaccumulation  of  a  substance  into  an 
organism  is  not  a  hazard  in  itself  but  should  be  considered  in  relation  to  potential  long-term 
effects.  Chemical  concentration  and  accumulation  may  result  in  internal  concentrations  of  a 
substance in an organism (body burden), which may or may not lead to toxic effects over long-
term  exposures.  Further  guidance  on  bioaccumulation  is  given  in  Annex III  to  this  guidance. 
Bioaccumulation of metals is discussed in Annex IV. 

Information on actual bioaccumulation of a substance may be available from standardised tests 
(e.g.  Test  Methods  Regulation  (EC)  No  440/2008,  OECD  TG  305:  Bioaccumulation  in  Fish: 
Aqueous  and  Dietary  Exposure)  or  information  on  the  bioaccumulation  potential,  for  organic 

 
 
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substances, may be estimated from the structure of the molecule (see also IR&CSA Chapter R.7b, 
section R.7.10).  

In  general,  the  potential  of  an  organic  substance  to  bioconcentrate  is  primarily  related  to  the 
lipophilicity of the substance. A surrogate measure of lipophilicity is the n-octanol/water partition 
coefficient  (Kow)  which,  for  lipophilic  non-ionised  and  non-surface  active  organic  substances, 
undergoing minimal metabolism or biotransformation within the organism, is correlated with the 
bioconcentration factor. Therefore, Kow is often used for estimating the bioconcentration of non-
ionised organic substances, based on the empirical relationship between log BCF and log Kow. For 
those organic substances, estimation methods are available for calculating the Kow. Data on the 
bioconcentration properties of non-ionised organic substances may thus be:  

1.  Experimentally determined; 

2.  Estimated from experimentally determined Kow; or  

3.  Estimated from Kow values derived by use of (Q)SARs. 

Experimentally derived BCF values of high quality are preferred for classification purposes. BCF 
results from poor or questionable quality studies should not be used for classification purposes if 
high quality data on log Kow are available. If no BCF is available for fish species, high quality data 
on the BCF for some invertebrates (e.g. blue mussel, oyster and/or scallop) may be used as a 
worst case surrogate.  

For non-ionised organic substances, experimentally derived high quality Kow values are preferred. 
If  no  experimental  data  of  high  quality  are  available,  validated  Quantitative  Structure  Activity 
Relationships ((Q)SARs) for log Kow may be used in the classification process. If data are available 
but not validated, expert judgement should be used. (Q)SAR BCF values can be used as part of a 
WoE approach, but it must be noted that high quality experimental BCF and Log kow values are 
always  preferred  and  (Q)SAR  BCFs  are  not  considered  a  one  for  one  substitute  (See  Annex 
III.2.2.2  for  further  details).  BCF  estimates  based  on  in  vitro  OECD  TGs  319A  and  B  might  be 
considered in a WoE approach for bioaccumulation provided that they fulfil relevant data quality 
requirements  (IR&CSA  Chapter  R.7b,  R.11.4.1.2.10).  For  ionised  organic  substances  problems 
may  occur,  e.g. changes in pH which  may significantly affect the water  solubility and partition 
coefficient  of  the  substance.  Further  guidance  on  how  to  deal  with  such  difficulties  in 
bioaccumulation testing is provided in the OECD Guidance 23 (OECD 2019). 

4.1.3.2.4.  Using weight of evidence in evaluations in the context of C&L 

4.1.3.2.4.1.  General aspects of weight of evidence  

The weight of evidence approach is described in IR&CSA Chapter R.4, section R.4.4 as follows: 
‘The  weight  of  evidence  (WoE)  approach  is  not  a  scientifically  well-defined  term  or  an  agreed 
formalised concept. It involves assessing the relevance, reliability and adequacy of each piece of 
available  information,  holding  the  various  pieces  of  information  up  against  each  other  and 
reaching  a  conclusion  on  the  hazard.  This  process  always  involves  expert  judgement.  It  is 
important  to  document  and  communicate  how  the  evidence-based  approach  was  used  in  a 
reliable, robust and transparent manner’.  

Where  there  is  only  one  experimental  effect  value  per  endpoint,  classification  and  labelling 
decisions  are  relatively  straightforward.  However,  this  is  often  not  the  case  when  dealing  with 
data-deficient  substances  or  substances  for  which  more  than  one  valid  value  is  available  for  a 
given  endpoint.  In  both  situations,  available  information  needs  to  be  evaluated  carefully.  Data 
deficiency may occur  for substances  for which  there  are no  reliable data, or  only  experimental 
data  which  is  irrelevant  for  classification  and  labelling.  This  might  be  the  case  for  substances 
exempted  from  REACH  such  as  polymers  or  substances  manufactured  in  quantities  <  1 
tonne/annum. 

The taxa chosen, fish, crustacea and aquatic plants, that represent the ‘base-set’ in most hazard 
profiles, represent a minimum dataset for a fully valid description of hazard. The lowest of the 

 
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available toxicity values will normally be used to define the hazard category. Given the wide range 
of species in the environment, the three taxa tested can only be a rudimentary surrogate and the 
lowest value is considered to be a cautious approach for defining the hazard category. In doing 
so, it is recognised that the distribution of species sensitivity can be several orders of magnitude 
wide,  and  that  there  will  thus  be  both  more  and  less  sensitive  species  in  the  environment. 
Therefore, when data are limited, the use of the most sensitive species tested gives a cautious 
but acceptable definition of the hazard.  

There are some circumstances where it may not be appropriate to use the lowest toxicity value 
as  the  basis  for  classification.  This  will  usually  only  arise  where  it  is  possible  to  define  the 
sensitivity distribution with more accuracy than would normally be possible, such as when large 
datasets  are  available.  Such  large  datasets  should  be  evaluated  with  due  caution.  In  case  of 
multiple data points for the same effects endpoint, Guidance R.4 states that “Where there is more 
than one study for each endpoint, the greatest weight is attached to the studies that are the most 
relevant  and  reliable.  Sound  scientific  judgement  is  an  important  principle  in  considering  the 
adequacy, reliability, and relevancy of information and determining the key study”.  

Conversely, as CLP allows the use of expert judgment in employing non-testing information such 
as (Q)SARs, the classification of data-deficient substances could potentially be conducted in the 
absence of any experimental data.  

In  applying  the  WoE  approach,  the  reliability  of  the  information  under  evaluation  needs  to  be 
taken into due account. Typically, this information originates from studies which have been ranked 
according to the Klimisch criteria. The scores assigned to the studies may serve as an indication 
of the ‘weight’ that the corresponding information could have in ‘weighing the evidence’.  

4.1.3.2.4.2.  Guidance on WoE for data deficient substances  

Either  for  those  substances  for  which  the  standard  data  set  of  acute  aquatic  testing  in  fish, 
crustacea  and  algae/aquatic  plants  is  not  available  or  where  there  are  data  gaps,  REACH 
introduces  the  concept  of  an  ‘Integrated  Testing  Strategy’  (for  further  guidance  see  IR&CSA 
Chapter R.7b, Figure R.7.8-2). This outlines a stepwise approach on the use of test data and non-
testing  information,  such  as  reliable  (Q)SARs  and  in  vitro  testing.  It  outlines  how  the  relevant 
information is collected and evaluated and in the final step, expert judgement is used to reach an 
overall  assessment  of  the  aquatic  toxicity  of  the  substance  under  evaluation,  also  taking  into 
consideration metabolites, reaction products, and analogues.   

For  classification  purposes,  representative  species  should  be  chosen  which  cover  a  range  of 
trophic levels and taxonomic groups, namely fish, crustacea and primary producers. Annex  I to 
this document also provides guidance on the following where no experimental data are available: 
‘(Q)SARs can be relied upon to provide predictions of acute toxicity to fish, crustacea (Daphnia 
and  Mysid),  and  algae  for  non-electrolytes,  non-electrophilic,  and  otherwise  non-reactive 
substances. Care should be taken when evaluating the toxicity of poorly water soluble substances, 
where the quoted toxicity may be greater than the water solubility’. 

4.1.3.2.4.3.  Guidance  on  WoE  for  substances  for  which  more  than  one  valid  piece  of 

data is available for a given data element 

The  best  quality  data  should  be  used  as  the  fundamental  basis  for  classification.  Classification 
should preferably be based on primary data sources. It is essential that test conditions be clearly 
and completely articulated. 

Where multiple studies for a taxonomic group are available, all studies that are assessed to have 
sufficient quality should be taken into consideration. The study showing the highest toxicity (e.g. 
the  one  with  the  lowest  L(E)C50  or  NOEC  or  ECx)  should  normally  be  chosen  as  key  study  for 
aquatic hazard classification for that taxonomic group. However, in a WoE approach, a different 
weight may be given to studies irrespective the test results. For example: a judgement has to be 
made on a case-by-case basis whether Klimisch 1 studies in a dataset are given more weight than 
Klimisch 2 studies or valid (Q)SAR data available for the same taxonomic group.  

 
 
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Lower  quality  information  showing  no  or  low  toxicity  should  specifically  be  treated  with  care, 
especially where the quality assessment has revealed points of concern regarding methodology 
and  reporting  (e.g.  maintenance  of  test  concentrations).  In  addition  it  should  be  noted  that 
substances which are difficult to test may yield apparent results that are not indicating the true 
toxicity. Expert judgement would also be needed for classification in these cases. 

Assessment of data quality includes assessment of adequacy of the information for classification 
purposes and an assessment of both relevance and reliability. Details on the assessment of quality 
can be found in IR&CSA Chapter R.4.  

Where  more  than  one  acceptable  test  is  available  for  the  same  taxonomic  group,  the  most 
sensitive  (the  one  with  the  lowest  L(E)C50  or  NOEC/EC10)  is  generally  used  for  classification. 
However, this must be dealt with on a case-by-case basis. When larger data sets (four or more 
values) are available for the same species, the geometric mean of toxicity values may be used as 
the representative toxicity value for that species. In estimating a mean value, it is not advisable 
to combine tests of different species within a taxonomic group or in different life stages or tested 
under  different  conditions  or  duration.  This  implies  that  for  substances  where  four  or  more 
ecotoxicity data on the same species and endpoint are available, the data could be grouped, and 
the geometric mean used as a representative toxicity value for that species.  

In case of very large data sets meeting the criteria for applying the Species Sensitivity Distribution 
(SSD) approach (see IR&CSA Chapter R.10), statistical techniques (e.g. HC5 derivation) can be 
considered to estimate the aquatic toxicity reference value for classification (equivalent to using 
the lowest EC50 or NOEC), in a weight of evidence approach. 

4.1.3.2.4.4.  Outliers 

The WoE approach would also address potential outliers, since as a starting point, all data points 
for  a  specific  trophic  level/taxonomic  group  would  be  considered  to  come  from  the  same 
sensitivity  distribution.  Only  if  a  sufficiently  large  number  of  data  were  available  for  the  same 
species  and  effects  endpoint,  appropriate  statistical  tests  would  be  performed  to  confirm  or 
disprove a particular value as an outlier. 

The  issue  of  possible  ‘outliers’,  which  may  exist,  particularly  in  large  data  sets  can  be  tackled 
according to a proposal in IR&CSA Chapter R.7b, section R.7.8.4.1. 

4.1.3.2.4.5.  Weight of evidence in degradation 

Where multiple or conflicting datasets exist for a single chemical, the most reliable data should 
be selected first, and subsequently a ‘weight of evidence’ approach followed based on these data. 
This implies that if both positive (i.e. above the pass level) and negative results (below pass level) 
have  been  obtained  for  a  substance  in  rapid  degradability  tests,  then  the  data  of  the  highest 
quality and the best documentation should be used for determining the rapid degradability of the 
substance. However, given the conservative nature of ready biodegradability tests positive results 
could  be  used  irrespective  of  negative  results  when  the  scientific  quality  is  good  and  the  test 
conditions are well documented, i.e. the guideline criteria are fulfilled. See Annex  II for further 
guidance. 

4.1.3.2.4.6.  Weight of evidence in bioaccumulation 

When conflicting bioaccumulation data is available, see Annex III for further guidance. 

 
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4.1.3.3.  Classification categories and criteria 

4.1.3.3.1.  Outline of the core classification system 

Annex  I:  4.1.2.2.  The  core  classification  system  for  substances  consists  of  one  short-term 
(acute)  hazard  classification  category  and  three  long-term  (chronic)  hazard  classification 
categories. The short-term (acute) and the long-term (chronic) hazard classification categories 
are applied independently. 

Annex I: 4.1.2.3. The criteria for classification of a substance in category Acute 1 are defined 
on the basis of acute aquatic toxicity data only (EC50 or LC50). The criteria for classification of a 
substance into the categories Chronic 1 to 3 follow a tiered approach where the first step is to 
see if available information on chronic toxicity merits long-term (chronic) hazard classification. 
In absence of adequate chronic toxicity data, the subsequent step is to combine two types of 
information,  i.e.  acute  aquatic  toxicity  data  and  environmental  fate  data  (degradability  and 
bioaccumulation data) (see Figure 4.1.1). 

Figure 4.1.1 

Categories for substances long-term (chronic) hazardous to the aquatic environment 

Are there  
adequate chronic  
toxicity data available  
for all three 
trophic levels?  

Yes 

Classify according to the criteria given in Table 
4.1.0(b)(i)  or  4.1.0(b)(ii)  depending  on 
information on rapid degradation 

No 

Yes 

Are there  
adequate chronic  
toxicity data 
available  
for one or two  
trophic levels? 

No 

Are there  
adequate acute  
toxicity data  
available? 

Assess both: 

(a)    according  to  the  criteria  given  in  Table 
4.1.0(b)(i)  or  4.1.0(b)(ii)  (depending  on 
information on rapid degradation), and 

(b)  (if  for  the  other  trophic  level(s)  adequate 
acute toxicity data are available) according 
to the criteria given in Table 4.1.0(b)(iii), 

and  classify  according  to  the  most  stringent 
outcome 

Yes 

Classify according to the criteria given in Table 
4.1.0(b)(iii) 

 
 
 
 
 
 
 
 
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4.1.2.1. The system for classification recognises that the intrinsic hazard to aquatic organisms 
is represented by both the acute and chronic toxicity of a substance. For the long-term (chronic) 
hazard separate hazard categories are defined representing a gradation in the level of hazard 
identified. The lowest of the available toxicity values between and within the different trophic 
levels (fish, crustacean, algae/aquatic plants) shall normally be used to define the appropriate 
hazard category(ies). There are circumstances, however, when a weight of evidence approach 
is appropriate. 

Chronic  toxicity  data,  where  available,  are  preferred  for  determining  the  long-term  (chronic) 
hazard category. Where adequate chronic toxicity data exist for the three trophic levels and the 
lowest  chronic  toxicity  value  (that  normally  would  define  the  appropriate  hazard  category)  is 
below or equal to 1 mg/L, a long-term hazard classification is warranted. The actual category is 
also  dependent  on  the  information  on  rapid  degradation.  Chronic  toxicity  and  the  degradation 
properties  of  the  substance  should  be  considered  when  determining  the  potential  hazard 
classification.  Substances  that  do  not  rapidly  degrade  have  a  higher  potential  for  longer  term 
exposures and therefore should be classified in a more severe category than substances which 
are rapidly degradable. 

Since the introduction of chronic aquatic toxicity criteria in ATP 2 to CLP (Table 4.1.0 of Annex I 
to CLP), chronic toxicity data has become widely available.  

Chronic  toxicity  data  (ECx  or  NOEC),  where  available,  should  be  used  for  long-term  hazard 
classification. However, when assessing the adequacy of available chronic toxicity data, there may 
be  some  cases  (for  example,  data  poor  substances)  where  the  chronic  toxicity  data  do  not 
represent the species that is considered the most sensitive in available short-term toxicity tests. 
In such cases, the classification should be based on the toxicity data (acute or chronic) that gives 
the  most  strict  classification  (including  the  M-factor).  In  the  absence  of  chronic  toxicity  data, 
suitable acute toxicity data can be used to determine long-term hazard classification in addition 
to acute hazard classification (Figure 4.1.1 and Table 4.1.0(b)(iii) of Annex I to CLP ). 

A review of the existing adequate and appropriate acute toxicity data and environmental fate data 
(degradability and bioaccumulation) is required for those trophic levels where adequate chronic 
toxicity data may be absent; to decide if a long-term hazard classification may be warranted.  

While recognising that acute toxicity itself is not a sufficiently accurate predictor of chronic toxicity 
to be used solely and directly for establishing hazard, it is considered that, in combination with 
either a potential to bioaccumulate (i.e. experimentally determined BCF  500 or, if absent, the 
log Kow  4) or higher potential longer term exposure (i.e. lack of rapid degradation), it can be 
used  as  a  suitable  surrogate  for  long-term  hazard  classification  purposes.  Substances  rapidly 
degrading that show acute toxicity with a significant degree of bioaccumulation will normally show 
chronic  toxicity  at  a  significantly  lower  concentration.  Equally,  substances  that  do  not  rapidly 
degrade have a higher potential for giving rise to longer term exposures which again may result 
in long-term toxicity being realised.  

The hazard categories for acute and chronic aquatic toxicity and their related criteria are set out 
in CLP, Annex I, Section 4.1, Table 4.1.0. 

Annex I: Table 4.1.0 
Classification categories for hazardous to the aquatic environment 

 
 
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(a) Short-term (acute) aquatic hazard 

Category Acute 1: (Note 1) 

96 hr LC50 (for fish) 

48 hr EC50 (for crustacea) 

 1 mg/l and/or 

 1 mg/l and/or 

72 or 96 hr ErC50 (for algae or other aquatic plants) 

 1 mg/l. (Note 2) 

(b) Long-term (chronic) aquatic hazard 

(i) Non-rapidly degradable substances (Note 3) for which there are adequate chronic 

toxicity data available  

Category Chronic 1: (Note 1) 

Chronic NOEC or ECx (for fish) 

Chronic NOEC or ECx (for crustacea) 

 0,1 mg/l and/or 

 0,1 mg/l and/or 

Chronic NOEC or ECx (for algae or other aquatic plants)   0,1 mg/l. 

Category Chronic 2:   

Chronic NOEC or ECx (for fish) 

Chronic NOEC or ECx (for crustacea) 

 1 mg/l and/or 

 1 mg/l and/or 

Chronic NOEC or ECx (for algae or other aquatic plants)   1 mg/l. 

(ii) Rapidly degradable substances (Note 3) for which there are adequate chronic toxicity 

data available  

Category Chronic 1:  (Note 1) 

Chronic NOEC or ECx (for fish) 

Chronic NOEC or ECx (for crustacea) 

 0,01 mg/l and/or 

 0,01 mg/l and/or 

Chronic NOEC or ECx (for algae or other aquatic plants)   0,01 mg/l  

Category Chronic 2:    

Chronic NOEC or ECx (for fish) 

Chronic NOEC or ECx (for crustacea) 

 0,1 mg/l and/or 

 0,1 mg/l and/or 

Chronic NOEC or ECx (for algae or other aquatic plants)   0,1 mg/l 

Category Chronic 3:   

Chronic NOEC or ECx (for fish) 

Chronic NOEC or ECx (for crustacea) 

 1 mg/l and/or 

 1 mg/l and/or 

Chronic NOEC or ECx (for algae or other aquatic plants)   1 mg/l.  

(iii) Substances for which adequate chronic toxicity data are not available 

Category Chronic 1: (Note 1) 

96 hr LC50 (for fish) 

48 hr EC50 (for crustacea) 

 1 mg/l and/or 

 1 mg/l and/or 

72 or 96 hr ErC50 (for algae or other aquatic plants) 

 1 mg/l. 

(Note 2) 

 
 
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and the substance is not rapidly degradable and/or the experimentally determined BCF ≥ 500 

(or, if absent, the log Kow  4). (Note 3). 

Category Chronic 2:   

96 hr LC50 (for fish) 

48 hr EC50 (for crustacea) 

> 1 to  10 mg/l and/or 

> 1 to  10 mg/l and/or 

72 or 96 hr ErC50 (for algae or other aquatic plants) 

> 1 to  10 mg/l.  (Note 2) 

and the substance is not rapidly degradable and/or the experimentally determined BCF ≥ 500 

(or, if absent, the log Kow  4). (Note 3). 

Category Chronic 3:   

96 hr LC50 (for fish) 

48 hr EC50 (for crustacea) 

> 10 to  100 mg/l and/or 

> 10 to  100 mg/l and/or 

72 or 96 hr ErC50 (for algae or other aquatic plants) 

> 10 to  100 mg/l. 

(Note 2) 

and the substance is not rapidly degradable and/or the experimentally determined BCF ≥ 500 
(or, if absent, the log Kow  4). (Note 3). 

Note 1: 
is necessary at the same time to indicate then appropriate M-factor(s) (see table 4.1.3). 

When classifying substances as Acute Category 1 and/or Chronic Category 1 it 

Classification shall be based on the ErC50 [= EC50 (growth rate)]. In 
Note 2:  
circumstances where the basis of the EC50 is not specified or no ErC50 is recorded, 
classification shall be based on the lowest EC50 available. 

Note 3: 
determined or estimated data, the substance should be regarded as not rapidly degradable. 

When no useful data on degradability are available, either experimentally 

Classifications may also be made in cases where data are not available on all three trophic levels. 
In  these  cases,  the  classification  may  be  subject  to  further  information  becoming  available.  In 
general, all the data available will need to be considered prior to assigning a classification. Where 
good quality data are available for a particular species or taxa, this should be used in preference 
to  any  lower  quality  data  which  might  also  be  available  for  that  species  or  taxa.  Where  good 
quality  data  are  not  available,  lower  quality  data  will  need  to  be  considered.  In  these 
circumstances, a judgement will need to be made regarding the true level of hazard. Consideration 
of  such  data,  however,  will  also  need  to  consider  the  difficulties  that  may  have  affected  the 
likelihood of achieving a valid result. For example, the test details and experimental design may 
be  critical  to  the  assessment  of  the  usability  of  some  data,  such  as  that  from  hydrolytically 
unstable  chemicals,  while  less  so  for  other  chemicals.  Such  difficulties  are  described  further  in 
Annex I to this guidance. 

Normally, the identification of hazard, and hence the classification will be based on information 
directly obtained from testing of the substance being considered. There are occasions, however, 
where this can create difficulties, or the outcomes do not conform to common sense. For example, 
some chemicals, although stable in the bottle, will react rapidly (or slowly) in water giving rise to 
degradation products that may have different properties. Where such degradation is rapid, the 
available test data will frequently define the hazard of the degradation products since it will be 
these  that  have  been  tested.  These  data  may  be  used  to  classify  the  parent  substance  in  the 
normal  way.  However,  where  degradation  is  slower,  it  may  be  possible  to  test  the  parent 
substance  and  thus  generate  hazard  data  in  the  normal  manner.  The  subsequent  degradation 
may then be considered in determining whether an acute or long-term hazard category should be 
based  on  parent  or  degradant  data.  There  may  be  occasions  when  a  substance  tested  may 
degrade to give rise to a more hazardous degradation product under environmental conditions. 
In these circumstances, the rate of generation of the more hazardous degradation product (i.e., 

 
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quantity  produced  and  time  frame)  should  be  considered  to  assess  whether  the  classification 
should be based on data for the degradation product. OECD Guidance 23 (OECD 2019) provides 
useful information on this topic. Further information on unstable substances can be found in Annex 
I.4.1. There may also be instances where it may be necessary to  consider data obtained from 
mixtures (e.g., formulated products) when assessing hazards to the aquatic environment. In such 
cases, it is important to understand the aquatic hazard presented by other constituents in order 
to conduct an accurate  assessment  of the substance being classified. In all cases, data  on the 
substance being classified (including any relevant degradation products) is clearly preferred over 
data on mixtures. 

4.1.3.3.2. 

The ‘safety net’ 

Annex I: 4.1.2.4 The system also introduces a "safety net" classification (referred to as Chronic 
4) for use when the data available do not allow classification under the formal criteria for Acute 
1 or Chronic 1 to 3 but there are nevertheless some grounds for concern (see example in Table 
4.1.0). 

Annex I: 4.1.2.6. Table 4.1.0. continued 

‘Safety net’ classification 

Chronic Category 4 

Cases when data do not allow classification under the above criteria but there are nevertheless 
some grounds for concern. This includes, for example, poorly soluble substances for which no 
acute toxicity is recorded at levels up to the water solubility (note 4), and which are not rapidly 
degradable in accordance with Section 4.1.2.9.5 and have an experimentally determined BCF 
≥ 500  (or,  if  absent,  a  log  Kow   4),  indicating  a  potential  to  bioaccumulate,  which  will  be 
classified  in  this  category  unless  other  scientific  evidence  exists  showing  classification  to  be 
unnecessary. Such evidence includes chronic toxicity NOECs > water solubility or > 1 mg/l, or 
other evidence of rapid degradation in the environment than the ones provided by any of the 
methods listed in Section 4.1.2.9.5. 

Note 4:  ‘No acute toxicity’ is taken to mean that the L(E)C50(s) is/are above the water solubility. 
Also for poorly soluble substances, (water solubility < 1 mg/l), where there is evidence 
that the acute test does not provide a true measure of the intrinsic toxicity. 

Category  Chronic  4  is  for  example  triggered  for  some  poorly  soluble  substances,  which  are 
normally  considered  as  those  having  a  water  solubility  <  1  mg/L  where  no  acute  toxicity  is 
expressed in toxicity tests performed at the solubility limit. If for such a substance, however, the 
BCF is  500, or if absent, the log Kow is  4 (indicating a potential for bioaccumulation) and the 
substance is also not  rapidly degradable, a safety net classification,  Chronic 4 is assigned.  For 
these types of substances the exposure duration in short-term toxicity tests may well be too short 
for a steady-state concentration of the substance to be reached in the test organisms. Thus, even 
though  no  acute  toxicity  has  been  measured  in  a  short-term  (acute)  test,  it  remains  a  real 
possibility that such non-rapidly degradable and bioaccumulative substances may exert chronic 
effects, particularly since such low degradability may lead to an extended exposure period in the 
aquatic environment.   

Another example is that Chronic 4 can also be applied where a concern can be suitably justified 
for  a  given  species  or  trophic  level  (for  example,  a  mechanistic  basis  for  hazard  or  target 
organism(s) in the context of a PPP or biocide) and there is insufficient chronic toxicity data for 
the given species/trophic level to indicate that no classification is warranted. In such a case, the 
water  solubility,  rapid  degradation,  and/or  bioaccumulation  may  strengthen  the  concern. 

 
 
 
  
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Alternatively, with a robust basis for concern they may not be such important elements  of the 
assessment but this is a matter of expert judgement. 

The precise definitions of the core elements of this system are described in detail in Annexes  I-
III to this guidance document. For metals and metal compounds (those relevant for assessment 
under Annex IV according to Annex IV.1), please see Annexes IV.5.2.2.2 and IV.5.3.2.2. 

4.1.3.3.3. 

Setting an M-factor for highly toxic substances  

4.1.2.5 Substances with acute toxicities below 1 mg/l or chronic toxicities below 0,1 mg/l (if 
non-rapidly degradable) and 0,01 mg/l (if rapidly degradable) contribute as components of a 
mixture to the toxicity of the mixture even at a low concentration and shall normally be given 
increased weight in applying the summation of classification approach (see Note 1 of Table 4.1.0 
and 4.1.3.5.5). 

When  a  substance  is  classified  as  category  Acute  1  and/or  category  Chronic  1,  (a)  multiplying 
factor(s)  (M-factor)  has/have  to  be  assigned  (as  described  in  Article  10  of  CLP).  Where 
appropriate, M-factors shall be set for acute and long-term hazard classification separately and 
are considered an integral part of the classification (Article 10 of CLP). This means that, for such 
classifications, there will normally be two M-factors (one for acute and one for long-term hazard) 
for one substance. It is important to also include the M-factor(s) in the SDS as other users in the 
supply chain might need it, e.g. for classification of mixtures containing that substance. 

The  M-factor  itself  should  be  derived  using  the  table  below  (CLP,  Annex  I  Table  4.1.3)  and  is 
dependent on the toxicity band of the substances. For example, a substance with an acute toxicity 
of 0.005 mg/L  requires an acute M-factor of 100 to be assigned. Whereas a chronic toxicity of 
0.005  mg/L  requires  a  chronic  M-factor  of  10  to  be  assigned  for  a  non-rapidly  degradable 
substance and a chronic M-factor of 1 for a rapidly degradable substance.  

Annex I: Table 4.1.3  

Multiplying factors for highly toxic components of mixtures 

Acute toxicity 

M 
factor 

Chronic toxicity 

M factor 

L(E)C50 value 

NOEC value 

NRDa 

RDb 

comp
onent
s 

compo
nents 

- 

1 

10 

100 

0,1 < L(E)C50 ≤ 1 

1 

0,01 < NOEC ≤ 0,1 

0,01 < L(E)C50  0,1 

10 

0,001 < NOEC ≤ 0,01 

1 

10 

0,001 < L(E)C50  0,01  100 

0,0001 < NOEC ≤ 0,001 

100 

1000 

0,00001 < NOEC ≤ 0,0001 

1000 

0,0001  <  L(E)C50   
0,001 

0,00001  <  L(E)C50   
0,0001 

(continue in factor 10 intervals) 

(continue in factor 10 intervals) 

a 

b 

Non-rapidly degradable. 

Rapidly degradable. 

10000 

0,000001 < NOEC ≤ 0,00001  10000 

1000 

 
 
 
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The NOEC value in Table 4.1.3 (Annex I to CLP) refers to both NOEC and ECx (toxicity values are 
in mg/L). The first two columns in Table 4.1.3 refer to the classification system in Table 4.1.0 (a) 
and (b)(iii), the last three columns refer to the respective classification system in Table 4.1.0 (b)(i 
& ii). In cases where  chronic toxicity data are not available and Table 4.1.0 (b)(iii) is used  for 
defining  long-term  aquatic  hazard,  the  resulting  M-factor  derived  for  acute  aquatic  hazard 
classification  is  applied  (Table  4.1.3,  Acute  toxicity  column)  to  the  long-term  aquatic  hazard 
classification, albeit stated separately. 

For deriving the M-factors of metals and metal compounds (those relevant for assessment under 
Annex IV according to Annex IV.1), please see Annex IV.5.4. 

4.1.3.4.  Decision on classification: examples for substances 

If the evaluation shows that the criteria are fulfilled, one category for acute aquatic hazard and/or 
one for long-term aquatic hazard should be assigned, as well as (an) M-factor(s) where applicable. 
For  the  labelling  elements,  such  as  hazard  pictograms,  signal  words,  hazard  statements  and 
precautionary statements, see Section 4.1.6 of this guidance.  

Further classification examples specific to metals and metal compounds are given in Annex IV to 
this guidance document. 

The examples in this section are focussed on self-classification based on relevant data available. 
Mandatory use of harmonised classification for substances included in Table 3.1 of Annex VI, the 
use of information from the classification and labelling inventory and the use of the translation 
Table in Annex VII are not taken into account in these examples. 

After data collection, classification starts with an evaluation of the adequacy of the data collected, 
assessment  of  the  results,  and  concludes  on  the  endpoints  most  relevant  for  environmental 
hazard classification. Where the assessment shows that criteria for environmental classification 
are fulfilled, an acute aquatic hazard and/or one category for long-term aquatic hazards should 
be determined. M-factor(s) should be assigned  for classifications as Acute 1 and/or Chronic 1.  

List of the examples of substance classification included in this section: 

•  Example  A:  Hydrophilic  substance,  straightforward  classification  based  on  acute  and 

chronic toxicity data; 

•  Example B: Hydrophilic substance, straightforward classification based on acute data, no 

chronic toxicity data available; 

•  Example  C:  Moderately  water  soluble  substance,  straightforward  classification  based  on 
acute data, chronic toxicity data available for two trophic levels; combined set of (Q)SAR 
data and experimental data; 

•  Example D: Substance with several toxicity data for one trophic level; 

•  Example E: “Safety net” classification category Chronic 4; 

•  Example F: Substance difficult to test, toxicity above level of water solubility. 

Further classification examples specific to metals and metal compounds are given in Annex IV to 
this guidance. 

The examples are presented using a logical format starting with a table listing for all relevant data 
elements:  the  information  available,  followed  by  an  aquatic  hazard  assessment  for  each  data 
element, a section showing the aquatic hazard classification, a section with the reasoning behind 
the conclusions, and finally a table presenting the applicable labelling elements. 

 
 
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Explanation of data elements used in the examples: 

•  Physico-chemical properties important for evaluation of aquatic hazards for the purpose of 
classification:  Generally  this  consists  of  water  solubility  (mg/L)  and  log  octanol/water 
partition coefficient (log Kow); 

•  Acute aquatic toxicity: Generally expressed in terms of LC50 or EC50 (mg/L); 

•  Long-term aquatic toxicity: Generally expressed in terms of NOEC or ECx(mg/L); 

•  Degradation  (evidence  of  rapid  degradation):  Generally  expressed  in  terms  of  biotic  or 
abiotic degradation of organic substances (or transformation of inorganic substances). In 
case  of  rapid  primary  degradation,  information  shall  be  given  whether  the  degradation 
products can be classified as hazardous to the aquatic environment or not; 

•  Bioaccumulation: Generally expressed in terms of bioconcentration factor in fish. 

Information on reliability is not taken into account in the examples below. For the purpose of the 
examples, the reliability score is assumed to be high (e.g. for experimental tests, Klimisch score 
1 or 2) unless otherwise stated. Note that assigning a reliability score to studies is important - if 
a study is assessed as poorly reliable it is normally not usable for classification purposes. 

Besides  the  conclusion  from  studies  on  relevant  endpoints  for  classification,  the  following 
information is presented for each example in a separate column: 

•  Referral to applicable test method according to the EU Test Methods Regulation (EC) No 

440/2008 or OECD test guideline or (Q)SAR model used; 

•  Some basic information on the test design (pH of the test media, renewal regime of test 

media (static, semi-static, flow-through)); 

•  Use of measured or nominal test concentrations; 

•  Compliance of the experiment and reporting with OECD Good Laboratory Practice (GLP) 

rules; 

•  Specific information related to the relevant endpoints, as appropriate. 

This information plays a crucial role when the adequacy of the data and the assessment of the 
study results are being evaluated for their applicability in the classification and labelling scheme. 
However, in these examples this information is included mainly to make the data more realistic. 

 
 
 
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4.1.3.4.1. 

Example A: Hydrophilic substance, straightforward classification based on 
acute and chronic toxicity data 

DATA ELEMENTS 

Value 

Test  method 
((EC)  No. 
440/2008)  or  OECD  guideline 
/ remarks  

Physico-chemical properties 

Water solubility: 

1200 mg/L 

A.6. / pH:7.0, non-GLP 

Log  octanol/water  partition  coefficient 
(log Kow): 

2.75 

A.8. / pH:7.5, GLP 

Acute aquatic toxicity 

Fish               Oncorhynchus mykiss: 

12 mg/L (96 h LC50) 

C.1. / static, non-GLP 

Lepomis macrochirus: 

2.7 mg/L (96 h LC50) 

C.1. / static, GLP 

Crustacea      Daphnia magna: 

18 mg/L (48 h EC50) 

C.2. / static, non-GLP 

Algae/aquatic plants 

Scenedesmus subspicatus:  0.056 mg/L (96 h ErC50)  C.3. / static, GLP 

Lemna gibba: 

0.031 mg/L (7 d ErC50) 

C.26. / semi-static, GLP 

Chronic aquatic toxicity 

Fish 

Danio rerio: 

1.2 mg/L (21 d NOEC) 

OECD  TG  210  /  Early  Life  Stage 
toxicity test, flow-through, GLP 

Crustacea 

Daphnia magna: 

1.1 mg/L (21 d NOEC) 

C.20. / semi-static, GLP 

Algae/aquatic plants 

Scenedesmus subspicatus:  0.01 mg/L (96 h NOEC)  C.3. / static, GLP 

Degradation (evidence of rapid degradation) 

Biotic degradation: 

86 % in 28 days (10-day 
window fulfilled) 

C.4-C / pH:7.5, GLP 

Abiotic degradation, hydrolysis 

No data 

(half-life (d)): 

Bioaccumulation 

Bioconcentration factor in fish (BCF): 

No data 

Aquatic hazard assessment, conclusions and comments: 

Physico-chemical properties: 

•  The substance is readily soluble. Log Kow < 4, indicating low potential for bioaccumulation, 

which can be used in absence of BCF data. 

Acute aquatic toxicity: 

 
 
 
 
 
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•  The  acute  aquatic  toxicity  based  on  the  lowest  of  the  available  toxicity  values  (i.e., 

algae/aquatic plants) is between  0.01 and 0.1 mg/L. 

Long-term aquatic toxicity: 

•  The long-term aquatic toxicity based on the lowest of the available toxicity values (i.e., 

algae/aquatic plants) is between 0.001 and 0.01 mg/L. 

Degradation (evidence of rapid degradation): 

•  70  %  degradation  in  28  days  (10-d  window  fulfilled)  (i.e.,  86%  in  28  days,  based  on 
dissolved  organic  carbon  (DOC))  based  on  dissolved  organic  carbon  (DOC)  fulfils  the 
criteria for rapid degradation.  

Aquatic hazard classification and, where applicable, established M-factor(s): 

Acute (short-term) aquatic hazard: category Acute 1, M-factor: 10. 

Long-term aquatic hazard: category Chronic 1, M-factor: 1. 

Reasoning: 

Acute aquatic hazard: acute toxicity L(E)C50 ≤ 1 mg/L. M-factor based on L(E)C50 between 0.01 
and 0.1 mg/L. 

Long-term aquatic hazard:  

The  criteria  for  classification  of  a  substance  into  the  categories  Chronic  1  to  3  follow  a  tiered 
approach where the first step is to see if adequate information on long-term toxicity is available 
allowing long-term hazard classification. In absence of adequate chronic toxicity data for some or 
all trophic levels, the subsequent step is to combine two types of information, i.e. acute aquatic 
toxicity data and environmental fate data (degradability and bioaccumulation data). For details 
see Section 4.1.3.3 and Table 4.1.0. 

•  Adequate chronic toxicity data for all three trophic levels, long-term toxicity NOEC ≤ 0.01 
mg/L, rapidly degradable. M-factor based on NOEC between 0.001 and 0.01 mg/L (rapidly 
degradable). 

Labelling elements based on the classification: 

Element 

GHS Pictogram 

Signal Word 

Hazard Statement 

Code 

GHS09 

Wng 

H41077 

Precautionary statement(s) 

P273, P391, P501 

77 Note that in accordance with Article 27 of CLP the hazard statement H400 may be considered redundant and 
therefore not included on the label because hazard statement H410 also applies, see Section 4.1.6 of this document. 

 
 
 
 
 
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Example B: Hydrophilic substance, straightforward classification based on 
acute data, no chronic toxicity data available 

DATA ELEMENTS 

Value 

Test  method 
No. 
440/2008) or OECD guideline / 
remarks  

((EC) 

Physico-chemical properties 

Water solubility: 

1200 mg/L 

A.6. / pH:7.0, non-GLP 

Log  octanol/water  partition  coefficient 
(log Kow): 

2.75 

A.8. / pH:7.5, GLP 

Acute aquatic toxicity 

Fish               Oncorhynchus mykiss: 

12 mg/L (96 h LC50) 

C.1. / static, non-GLP 

Lepomis macrochirus: 

2.7 mg/L (96 h LC50) 

C.1. / static, GLP 

Crustacea  

Daphnia magna: 

18 mg/L (48 h EC50) 

C.2. / static, non-GLP 

Algae/aquatic plants 

Scenedesmus subspicatus:  0.056 mg/L (96 h ErC50)  C.3. / static, GLP 

Lemna gibba: 

0.031 mg/L (7 d ErC50)  C.26. / semi-static, GLP 

Chronic aquatic toxicity 

Fish: 

Crustacea: 

No data 

No data 

Algae/aquatic plants: 

NOEC not reported 

Degradation (evidence of rapid degradation) 

Biotic degradation: 

86 % in 28days (10-day 
window fulfilled) 

C.4-C / pH:7.5, GLP 

Abiotic degradation, hydrolysis 

No data 

(half-life (d)): 

Bioaccumulation 

Bioconcentration factor in fish (BCF): 

560 L/kg 

total 

C.13. / pH: 7.8, GLP, BCF (related 
to 
residues 
radioactive 
because data for parent compound 
not available) 

 
 
 
 
 
 
 
 
 
 
 
 
 
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Aquatic hazard assessment, conclusions and comments: 

Physico-chemical properties: 

•  The substance is readily soluble. Log Kow < 4, indicating low potential for bioaccumulation, 

which can be used in absence of BCF data (see bioaccumulation assessment). 

Acute aquatic toxicity: 

•  The  acute  aquatic  toxicity  based  on  the  lowest  of  the  available  toxicity  values  (i.e., 

algae/aquatic plants) is between 0.01 and 0.1 mg/L. 

Long-term aquatic toxicity: 

•  No adequate chronic toxicity data available for all three trophic levels. 

Degradation (evidence of rapid degradation): 

•  70  %  degradation  after  28  days  (10d  window  fulfilled)  (i.e.  86%  in  28  days,  based  on 
dissolved  organic  carbon  (DOC))  based  on  dissolved  organic  carbon  (DOC)  fulfils  the 
criteria for rapid degradation.  

Bioaccumulation: 

•  BCF > 500, hence high potential for bioaccumulation. BCF value overrules the use of log 

Kow value which in this case is lower than the cut-off value of 4. 

Aquatic hazard classification and, where applicable, established M-factor(s): 

Acute aquatic hazard: category Acute 1, M-factor: 10. 

Long–term aquatic hazard: category Chronic 1, M-factor: 10. 

Reasoning: 

Acute (short-term) aquatic hazard: acute toxicity L(E)C50 ≤ 1 mg/L. M-factor based on L(E)C50 
between 0.01 and 0.1 mg/L. 

Long-term aquatic hazard: 

The  criteria  for  classification  of  a  substance  into  the  categories  Chronic  1  to  3  follow  a  tiered 
approach where the first step is to see if adequate information on long-term toxicity is available 
allowing long-term hazard classification. In absence of adequate chronic toxicity data for some or 
all trophic levels, the subsequent step is to combine two types of information, i.e. acute aquatic 
toxicity data and environmental fate data (degradability and bioaccumulation data). For details 
see Section 4.1.3.3 and Table 4.1.0. 

•  No adequate chronic toxicity data available (for all three trophic levels); 

•  Lowest acute toxicity L(E)C50  ≤ 1 mg/L; 

•  Substance is rapidly degradable but the experimentally determined BCF > 500; 

•  Since the conclusion is based on Table 4.1.0 (b) (iii), therefore the M-factor is based on 
the acute toxicity between 0.01 and 0.1 mg/L. In this case, the same factor M applies for 
both acute and long-term hazard. 

 
 
 
 
 
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Labelling elements based on the classification: 

Element 

GHS Pictogram 

Signal Word 

Hazard Statement 

Code 

GHS09 

Wng 

H41078 

Precautionary statement(s) 

P273, P391, P501 

78 Note that in accordance with Article 27 of CLP the hazard statement H400 may be considered redundant and therefore 
not included on the label because hazard statement H410 also applies, see Section 4.1.6 of this document. 

 
 
 
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4.1.3.4.3. 

Example  C:  Moderately  water  soluble  substance,  straightforward 
classification based on acute data, chronic toxicity data available for two 
trophic levels only; combined set of (Q)SAR data and experimental data 

DATA ELEMENTS 

Value 

Test  method 
No. 
440/2008) or OECD guideline / 
remarks  

((EC) 

Physico-chemical properties 

Water solubility: 

25 mg/L 

A.6. / pH: 7.0, non-GLP 

Log  octanol/water  partition  coefficient 
(log Kow): 

5.75 

3.9 

A.8. / pH: 7.5, GLP 

(Q)SAR KOWINN, valid, non-GLP 

Acute aquatic toxicity 

Fish 

Oncorhynchus mykiss: 

12.3 mg/L (96 h LC50) 

C.1. / static, non-GLP 

Lepomis macrochirus: 

22.5 mg/L (96 h LC50) 

C.1. / static, GLP 

Crustacea  

Daphnia magna: 

0.79 mg/L (48 h EC50) 

C.2. / static, non-GLP 

Daphnia magna: 

1.06 mg/L (48 h EC50) 

(Q)SAR, ECOSAR, valid, non-GLP 

Algae/aquatic plants 

Scenedesmus subspicatus:  1.53 mg/L (96 h ErC50)  C.3. / static, GLP 

Chronic aquatic toxicity 

Fish 

Oncorhynchus mykiss: 

0.56 mg/L (21 d NOEC)  OECD  TG  210  /  Early  Life  Stage 

toxicity test, flow-through, GLP 

Crustacea: 

No data 

Algae/aquatic plants 

Scenedesmus subspicatus:  0.23 mg/L (96 h NOEC)  C.3. / static, GLP 

Degradation (evidence of rapid degradation) 

Biotic degradation: 

45 % in 28 days 

C.4-C / pH: 7.5, GLP 

Abiotic degradation, hydrolysis 

(half-life (d)): 

No data 

Bioaccumulation 

Bioconcentration factor in fish (BCF): 

No data 

Aquatic hazard assessment, conclusions and comments: 

Physico-chemical properties: 

•  The substance is moderately soluble. Log Kow 5.75. Based on weight of evidence, valid Kow 

estimated with (Q)SAR is overruled by valid GLP experimental data. 

 
 
 
 
 
 
 
 
 
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Note that use of experimental data and  (Q)SAR data for estimation log Kow should be carefully 
considered on a case by case basis. The validity of data may be dependent on the structure of 
the chemical. See Annex III.2.2 for more details on the use of log Kow data and Annex III.3 for 
details on chemical classes that need special attention in this respect. 

Acute aquatic toxicity: 

•  The acute aquatic toxicity based on the lowest of the available toxicity values is between 

0.1 and 1 mg/L; 

•  For  Daphnia  magna  two  valid  values  are  presented.  A  weight  of  evidence  approach  is 
applied in which the (Q)SAR data are outweighed by the valid experimental data. Hence, 
the lowest acute toxicity value of 0.79 mg/L is used for crustacea. 

Long-term aquatic toxicity: 

•  Adequate  chronic  toxicity  data  available  only  for  fish  and  algae/aquatic  plants,  not  for 

crustacea; 

•  The  chronic aquatic toxicity based on the lowest  of the available toxicity values  for fish 

and algae/aquatic plants is between 0.1 and 1 mg/L. 

Since there is adequate chronic toxicity data available for two trophic levels, assess both: 

a.  according to the criteria given in Table 4.1.0(b)(i) or 4.1.0(b)(ii) (depending on information 

on rapid degradation), and 

b.  (if for the other trophic level(s) adequate acute toxicity data are available) according to 

the criteria given in Table 4.1.0(b)(iii), 

and classify according to the most stringent outcome. 

Degradation (evidence of rapid degradation): 

•  < 70 % degradation in 28 days based on dissolved organic carbon (DOC), does not fulfil 

the criteria for rapid degradation. 

Bioaccumulation: 

•  Log  Kow  5.75,  indicating  a  high  potential  for  bioaccumulation,  which  can  be  used  in  the  

absence of BCF data. 

Aquatic hazard classification and, where applicable, established M-factor(s): 

Acute aquatic hazard: category Acute 1, M-factor: 1. 

Long-term aquatic hazard: category Chronic 1, M-factor: 1. 

 
 
 
 
 
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Reasoning: 

Acute (short-term) aquatic hazard: lowest acute aquatic toxicity L(E)C50 ≤ 1 mg/L. M-factor based 
on L(E)C50 between 0.1 and 1 mg/L. 

Long-term aquatic hazard: 

The  criteria  for  classification  of  a  substance  into  the  categories  Chronic  1  to  3  follow  a  tiered 
approach where the first step is to see if adequate information on long-term toxicity is available 
allowing long-term hazard classification. In absence of adequate chronic toxicity data for some or 
all trophic levels, the subsequent step is to combine two types of information, i.e. acute aquatic 
toxicity  data  and  environmental  fate  data  (degradability  and  bioaccumulation  data).  In  this 
example  the  absence  of  long-term  study  for  the  species/trophic  level  (i.e.  Daphnia/Crustacea) 
with the lowest acute toxicity value supports using the surrogate system. For details see Section 
4.1.3.3 and Table 4.1.0. 

•  Based  on  available  chronic  toxicity  data  (Table  4.1.0  (b)(i):  lowest  long-term  aquatic 

toxicity NOEC ≤ 1 mg/L, not rapidly degradable, hence category Chronic 2; 

•  Surrogate approach (Table 4.1.0 (b)(iii): lowest acute aquatic toxicity L(E)C50 < 1 mg/L, 

not rapidly degradable (and log Kow>4), hence category Chronic 1; 

•  Conclusion: category Chronic 1 applies following the most stringent outcome; 

•  Since the conclusion is based on the surrogate system (Table 4.1.0 (b) (iii)) the M-factor 

is based on the acute aquatic toxicity between 0.1 and 1 mg/L. 

Labelling elements based on the classification: 

Element 

GHS Pictogram 

Signal Word 

Hazard Statement 

Code  

GHS09 

Wng 

H41079 

Precautionary statement(s) 

P273, P391, P501 

79 Note that in accordance with Article 27 of CLP the hazard statement H400 may be considered redundant and 
therefore not included on the label because hazard statement H410 also applies, see Section 4.1.6 of this document. 

 
 
 
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4.1.3.4.4. 

Example D: Substance with several toxicity data for a trophic level 

DATA ELEMENTS 

Value 

((EC)  No. 
Test  method 
440/2008)  or  OECD  guideline 
/ remarks  

Physico-chemical properties 

Water solubility: 

120 mg/L 

A.6. / pH:7.0, non-GLP 

Log  octanol/water  partition  coefficient 
(log Kow): 

4.9 

A.8. / pH:7.5, GLP 

Acute aquatic toxicity 

Fish 

Lepomis macrochirus: 

108 mg/L (96 h LC50) 

C.1. / static, GLP 

Crustacea80 

Daphnia magna: 

40 mg/L (48 h EC50) 

C.2. / static, GLP 

Procambarus clarkii: 

0.12 mg/L (48 h EC50) 

Method na. / static, GLP 

Asellus aquaticus: 

0.4 mg/L (48 h EC50) 

Method na. / static, non-GLP 

Mysidopsis bahia: 

0.5 mg/L (48 h EC50) 

Method na. / static, GLP 

Chironomus tentans: 

0.8 mg/L (48 h EC50) 

Method na. / static, GLP 

Algae/aquatic plants

Pseudokirchneriella subcapitata: 

22 mg/L (96 h ErC50) 

C.3. / static, GLP 

Chronic aquatic toxicity 

Fish 

Pimephales promelas: 

1.1 mg/L (21 d NOEC) 

Crustacea 

Daphnia magna: 

1.2 mg/L (21 d NOEC) 

OECD  TG  210  /  Early  Life  Stage 
toxicity  test,  flow-through,  GLP, 
endpoint: growth 

C.20. 
endpoint: reproduction 

/ 

semi-static,  GLP, 

Algae/aquatic plants

Pseudokirchneriella subcapitata: 

8.5 mg/L (96 h NOEC) 

C.3. / static, GLP 

Degradation (evidence of rapid degradation) 

Biotic degradation 

Abiotic degradation, hydrolysis            
(half-life (d)): 

Bioaccumulation 

No data 

No data 

Bioconcentration factor in fish (BCF): 

No data 

80 Some species in this trophic level may be representatives of other taxonomic groups than crustacea e.g. the non-biting 
midge Chironomus tentans is a representative of the subphylum Hexapoda (class Insecta). 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Aquatic hazard assessment, conclusions and comments: 

Physico-chemical properties: 

•  The substance is water soluble. log Kow 4.9. 

Acute aquatic toxicity: 

•  The acute aquatic toxicity (based on the lowest of the available toxicity values) is between 
0.1 and 1 mg/L. The classification in this example should be based on the most sensitive 
species which is the crustacea Procambarus clarkii; 

Note that in general for substances for which multiple toxicity data is available for a taxonomic 
group  (in  this  case  crustacea)  on  a  case-by-case  basis  the  toxicity  data  may  be  evaluated  by 
weighting the evidence. If for example four or more acute LC50 values were available for the same 
fish species, then a geometric mean may be calculated (see Section 4.1.3.2.4.3). In this specific 
example, acute toxicity data on five separate crustacean species is available and all – except one 
– are from GLP studies that are weighed equally in a weight of evidence approach. Accordingly, 
the lowest value is used for classification purposes. 

Chronic aquatic toxicity: 

•  Adequate chronic toxicity data available only for fish and algae/aquatic plants. The chronic 
aquatic toxicity (based on the lowest of the two available toxicity values) is above 1 mg/L; 

•  For crustacea chronic toxicity data is available for Daphnia magna, which based upon the 
relatively large acute dataset is clearly the least sensitive of the species for which data is 
available. Hence, the chronic aquatic toxicity data set for aquatic invertebrates should be 
considered inadequate. 

Degradation (evidence of rapid degradation): 

•  No  data  available  for  this  substance.  In  such  cases,  the  substance  is  considered  as  not 

rapidly degradable (see Table 4.1.0, Note 3). 

Bioaccumulation: 

•  Log  Kow  4.9,  indicating  high  potential  for  bioaccumulation,  which  can  be  used  in  the 

absence of BCF data. 

Aquatic hazard classification and, where applicable, established M-factor(s): 

Acute aquatic hazard: category Acute 1, M-Factor: 1. 

Long-term aquatic hazard: category Chronic 1, M-Factor 1. 

Reasoning: 

Acute aquatic hazard: Acute aquatic toxicity L(E)C50 > 0.1 and ≤1 mg/L; 

Long-term aquatic hazard: 

The  criteria  for  classification  of  a  substance  into  the  categories  Chronic  1  to  3  follow  a  tiered 
approach where the first step is to see if adequate information on long-term toxicity is available 
allowing long-term hazard classification. In absence of adequate chronic toxicity data for some or 
all trophic levels, the subsequent step is to combine two types of information, i.e. acute aquatic 
toxicity data and environmental fate data (degradability and bioaccumulation data). For details 
see Section 4.1.3.3 and Table 4.1.0. 

•  Adequate  Chronic  toxicity  data  available  for  two  out  of  three  trophic  levels  (fish  and 
algae/aquatic plants), lowest NOEC above 1 mg/L. Conclusion for these two trophic levels: 

 
 
 
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NOEC-based system (Table 4.1.0 (b)(i): lowest long-term aquatic toxicity NOEC > 1 mg/L, 
hence not classified; 

•  Surrogate  system  (Table  4.1.0  (b)(iii)):  lowest  acute  aquatic  toxicity  L(E)C50  <  1  mg/L 
(0.12 mg/L Procambarus clarkii), not rapidly degradable (and log Kow > 4), hence category 
Chronic 1; 

•  Conclusion: category Chronic 1 applies following the most stringent outcome; 

•  Since the conclusion is based on the surrogate system (Table 4.1.0 (b) (iii)) the M-factor 

is based on the acute aquatic toxicity between 0.1 and 1 mg/L. 

Labelling elements based on the classification: 

Element 

GHS Pictogram 

Signal Word 

Hazard Statement 

Code 

GHS09 

Wng 

H41081 

Precautionary statement(s) 

P273, P391, P501 

81 Note that in accordance with Article 27 of CLP the hazard statement H400 may be considered redundant and therefore 
not included on the label because hazard statement H410 also applies, see Section 4.1.6 of this document. 

 
 
 
 
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4.1.3.4.5. 

Example E: ‘Safety net’ classification category Chronic 4 

DATA ELEMENTS 

Value 

((EC)  No. 
Test  method 
440/2008)  or  OECD  guideline 
/ remarks 

Physico-chemical properties 

Water solubility: 

0.009 mg/L 

A.6. / pH:7.0, non-GLP 

Log octanol/water partition coefficient 
(log Kow): 

5.4 

A.8. / pH:7.5, GLP 

Acute aquatic toxicity 

Fish: 

No data 

Crustacea  

Daphnia magna:  > 1 mg/L (48 h EC50) 

C.2. / static, nominal 
concentration, non-GLP 

Algae/aquatic plants: 

No data 

Chronic aquatic toxicity 

Fish: 

Crustacea: 

Algae/aquatic plants: 

No data 

No data 

No data 

Degradation (evidence of rapid degradation) 

Biotic degradation: 

Abiotic degradation, hydrolysis           
(half-life (d)): 

No data 

No data 

Bioaccumulation 

Bioconcentration factor in fish (BCF): 

No data 

Aquatic hazard assessment, conclusions and comments: 

Physico-chemical properties: 

•  The substance is poorly soluble. Log Kow > 4, indicating high potential for bioaccumulation, 

which can be used in absence of BCF data. 

Acute aquatic toxicity: 

•  Data poor substance. No acute toxicity recorded at levels up to the limit of water solubility. 

Long-term aquatic toxicity: 

•  No adequate chronic toxicity data available for all three trophic levels. 

Degradation (evidence of rapid degradation): 

•  The  substance  is  considered  not  rapidly  degradable  by  default  in  absence  of  measured 

data. 

 
 
 
 
 
 
 
 
 
 
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•  Log Kow 5.4, indicating high potential for bioaccumulation, which can be used in absence 

of BCF data. 

Aquatic hazard classification and, where applicable, established M-factor(s): 

Acute hazard: Not classified. 

Long-term hazard: ‘Safety net’ classification category Chronic 4. 

Reasoning: 

Acute hazard: No acute aquatic toxicity recorded at levels up to the limit of water solubility; 

Long-term  hazard:  No  adequate  chronic  toxicity  data  available  for  all  three  trophic  levels. 
Substance nevertheless of concern based on the following findings: 

•  Poorly soluble substance; 

•  No acute aquatic toxicity recorded at levels up to the limit of water solubility; 

•  Not rapidly degradable (by default in absence of measured data); 

•  High potential for bioaccumulation (in absence of BCF data, log Kow > 4); 

•  No evidence on NOEC being above water solubility for all three trophic levels; 

•  No other evidence of rapid degradation in the environment. 

Labelling elements based on the classification: 

Element 

GHS Pictogram 

Signal Word 

Code 

- 

- 

Hazard Statement 

H413 

Precautionary statement(s) 

P273, P501 

 
 
 
 
 
 
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4.1.3.4.6. 

Example  F:  Substance  difficult  to  test,  toxicity  above  level  of  water 
solubility 

DATA ELEMENTS 

Value 

Test  method 
No. 
440/2008) or OECD guideline / 
remarks 

((EC) 

Physico-chemical properties 

Water solubility: 

< 0.2 mg/L 

A.6. / pH: 7.0, non-GLP 

Log octanol/water partition coefficient 
(log Kow): 

No data 

Not determined due to instability 
of the substance in water 

Acute aquatic toxicity 

Fish 

Oncorhynchus mykiss:   12 mg/L (96 h LC50) 

Crustacea  

Daphnia magna: 

18 mg/L (48 h EC50) 

C.1. / static, nominal 
concentration, non-GLP 

C.2. / static, nominal 
concentration, non-GLP 

Algae/aquatic plants 

3.56 mg/L (96 h ErC50)  C.3. / static, nominal 

Pseudokirchneriella subcapitata: 

concentration, non-GLP 

Chronic aquatic toxicity 

Fish: 

Crustacea: 

Algae/aquatic plants: 

No data 

No data 

No data 

Degradation (evidence of rapid degradation) 

Biotic degradation: 

No data 

Abiotic degradation, hydrolysis         

(half-life (d)): 

< 0.5 days (longest 
half-life within pH 4-9) 

C.7. / pH: 7.0, non-GLP 

Bioaccumulation 

Bioconcentration factor in fish (BCF): 

No data 

Aquatic hazard assessment, conclusions and comments: 

Physico-chemical properties: 

•  The  water  solubility  test  is  not  considered  to  be  valid  (Klimisch  3)  as  the  substance  is 
known  to  rapidly  hydrolyse  and  this  was  not  considered  in  this  study.  Log  Kow  not 
determined.  

 
 
 
 
 
 
 
 
 
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•  This data is based on initial measured concentrations in the suspension and the reported 
EC50 values are far above the water solubility (Klimisch score 3). Tests undertaken in a 
static  regime  which  is  inappropriate  for  a  substance  which  rapidly  hydrolyses  (see  also 
IR&CSA R.7b for guidance on how to test difficult substances); 

• 

It is not clear whether the reported effects in the acute toxicity studies are due to physical 
effects  of  the  undissolved  substance  particles  in  the  test  media  on  the  test  species  or 
inherent toxicity of the substance. 

Long-term aquatic toxicity: 

•  No adequate chronic toxicity data available for all three trophic levels. 

Degradation (evidence of rapid degradation): 

• 

In  the  assessment  of  rapid  degradability  hydrolysis  can  be  considered  if  the  hydrolysis 
products do not fulfil the criteria for classification as hazardous to the aquatic environment. 
In  this  example  hydrolysis  is  sufficient  to  show  a  rapid  degradability  of  the  parent 
substance  in  the  environment  but  no  information  is  available  about  the  breakdown 
product(s). More data on degradation of this/these compound(s) would be necessary; 

• 

In absence of data to show a rapid degradation of the breakdown product(s) the parent 
substance is considered not rapidly degradable. 

Bioaccumulation: 

•  Log Kow could not be determined experimentally. The parent substance has a low potential 

for bioaccumulation due to hydrolytic instability. 

Aquatic hazard classification and, where applicable, established M-factor(s): 

Acute aquatic hazard: Not classified in absence of adequate data (data of poor quality). 

Long-term aquatic hazard: category Chronic 4. 

Reasoning: 

Acute hazard (Table 4.1.0 (a)): No acute aquatic toxicity as no adequate acute data available; 

Long-term  hazard:  No  adequate  chronic  toxicity  data  available  for  all  three  trophic  levels. 
Substance nevertheless of concern based on the following findings: 

•  Poorly soluble substance (< 0.2 mg/L); 

•  No acute aquatic toxicity recorded at levels up to the limit of water solubility; 

•  Not  rapidly  degradable  (see  Section  4.1.3.2.3.2  of  this  guidance  (CLP  Annex  I  section 

4.1.2.9.3); 

•  No evidence of NOEC being above water solubility for all three trophic levels. 

•  No  information  available  on  the  hydrolysis  products  and  hence  dataset  not  decisive 
whether these fulfil the criteria for classification as hazardous to the aquatic environment 
based upon: 

•  Toxicity; 

•  Rapid degradability; 

•  Bioaccumulation. 

 
 
 
 
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• 

In this case the safety net classification should be applied because of the large uncertainty 
on the fate and effects of the hydrolysis products.  

Labelling elements based on the classification: 

Element 

GHS Pictogram 

Signal Word 

Code 

- 

- 

Hazard Statement 

H413 

Precautionary statement(s) 

P273, P501 

 
 
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4.1.4.  Classification of mixtures hazardous to the aquatic environment  

4.1.4.1.  General considerations for classification of mixtures hazardous to the 

aquatic environment 

Note that general principles for classification of mixtures under CLP are given in Section 1.1.6.2 
and Section 1.6 of part 1 of this guidance document.  

The basic principle  of  mixture classification under CLP is shown in the green box below and in 
Figure 4.1.2 which is also explained in the text below the box.  

Annex I: 4.1.3.2 The approach for classification of aquatic environmental hazards is tiered, and 
is dependent upon the type of information available for the mixture itself and for its components. 
Figure 4.1.2 outlines the process to be followed. 

Elements of the tiered approach include: 

classification based on tested mixtures;  

classification based on bridging principles;  

the use of "summation of classified components" and/or an "additivity formula". 

Figure 4.1.2 
Tiered 
for short-term (acute) and long-term (chronic) aquatic environmental hazards 

classification 

approach 

to 

of 

mixtures 

Aquatic toxicity test data available on the mixture as a whole 

Sufficient data available on 
similar mixtures to estimate 
hazards 

No 

Either aquatic toxicity or 
classification data available for 
all relevant components 

No 

No 

Yes 

Yes 

CLASSIFY 
(acute)/long-
for  short-term 
term  (chronic)  aquatic  hazard 
(see 4.1.3.3) 
CLASSIFY 
for  short-term 
(acute)/long-
term (chronic) aquatic hazard  

Apply bridging principles  
(see 4.1.3.4.) 

CLASSIFY 
for  short-term 
term chronic) aquatic hazard  

(acute)/long-

Yes 

Apply summation Method  
(see 4.1.3.5.5) using:  

▪ Percentage  of  all  components 

classified as "Chronic" 

▪ Percentage  of 

  components 

classified as "Acute" 

▪ Percentage of components with 
acute or chronic toxicity data: 

apply  additivity  formulas  (see 
4.1.3.5.2)  and  convert 
the  
derived L(E)C50 or EqNOECm to 
the  appropriate  "Acute"  or 
"Chronic" Category 

Use available hazard data of 
known components. 

Apply 
Summation  method 
and/or  Additivity  Formula  (see 
4.1.3.5) and apply 4.1.3.6 

CLASSIFY 
for  short-term  (acute)/long-
term (chronic) aquatic hazard  

 
 
 
 
 
 
 
 
 
  
 
 
 
 
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Explanation of Figure 4.1.2: 

•  Horizontal arrow in first row: Where specific and valid test data are already available on 
the  mixture,  there  is  a  general  obligation  to  use  these  data  on  the  mixture  itself  for 
classification  purposes.  Valid  data  must  normally  then  be  available  on  each  of  fish, 
crustacea  and  algae  or  other  aquatic  plants,  unless  a  decision  to  classify  in  the  most 
stringent category(ies) (Acute 1 and/or Chronic 1) can be made without a full dataset (see 
Section 4.1.4.3 of this document). 

•  Horizontal arrows in second row: In other cases, sufficient data may be available on similar 
tested mixtures to estimate hazards using the bridging principles (see Section 4.1.4.4 of 
this document). 

•  Horizontal  arrows  in  third  row:  In  general,  however,  where  either  aquatic  toxicity  or 
classification data are available for all relevant components of a mixture the aquatic hazard 
classification  shall  be  made  through  the  identification  of  the  hazards  of  the  respective 
components  in  a  first  step,  and  then  in  a  second  step  through  the  summation  of  the 
quantities of these hazardous components, applying the summation method (see Section 
4.1.4.5 of this document). When doing so:  

•  The percentage of all components classified as Acute 1 and/or Chronic 1, 2, 3 & 4 
is  fed  straight  into  the  summation  method  (for  relevant  components  see  section 
4.1.3.1 of Annex I to CLP);  

•  For the percentage of the other components with acute or chronic toxicity data, the 
additivity formulas (see section 4.1.3.5.2 of Annex I to CLP) may be applied. The 
derived L(E)C50 or EqNOECm is converted to the appropriate "Acute" or "Chronic" 
Category and then, in a second step, fed into the summation method.82 

•  Horizontal arrows in fourth (last) row: Use available hazard data of known components.  

•  This  applies  to  mixtures  containing  unknown  components  and/or  known 
components, for which neither toxicity data nor classifications are known. In these 
cases,  apply  the  additional  statement  on  the  label  and  in  the  safety  data  sheet: 
"Contains x % of components with unknown hazards to the aquatic environment" 
(see  the  green  box  below).  For  classification  based  on  the  known  part  of  the 
mixture,  use  the  Summation  Method  and/or  the  Additivity  Formula  (see  Section 
4.1.4.5 of this document). 

Annex  I:  4.1.3.6.1  In  the  event  that  no  useable  information  on  short-term  (acute)  and/or 
long-term  (chronic)  aquatic  hazard  is  available  for  one  or  more  relevant  components,  it  is 
concluded that the mixture cannot be attributed to one or more definitive hazard category(ies). 
In this situation the mixture shall be classified based on the known components only, with the 
additional  statement  on  the  label  and  in  the  SDS  that:  "Contains  x %  of  components  with 
unknown hazards to the aquatic environment". 

4.1.4.2. 

Information requirements 

Before a classification can be made, available information on toxicity of the mixture as a whole 
as well as all the available information on the composition of the mixture and the hazard category 
of relevant components (substances) should be gathered. Note that manufacturers, importers or 
downstream users are not requested by the CLP Regulation to generate new data for determining 
the aquatic hazard classification of the mixture. Rather the supplier should be contacted if it is 

82  As  manufacturers  and  importers  are  obliged  to  classify  all  substances  placed  on  the  market  within  the  EU,  the 
summation method can usually be directly applied and the additivity formula will be of limited application. 

 
 
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considered  that  the  information  on  the  substance  or  mixture  supplied  is  not  sufficient  for 
classification purposes. 

Generally,  therefore,  the  constituent  substance  classifications  should  be  used  as  the  basis  for 
derivation of the correct hazard classification of the final mixture (see also Section 1.6.4 of this 
guidance document).  

Article  11  of  CLP  refers  to  cut-off  values.  These  values  are  the  minimum  concentrations  for  a 
substance  to  be  taken  into  account  for  classification  purposes.  The  substances  meeting  these 
criteria are relevant ingredients or relevant components. When a classified substance is present 
in a concentration above the generic cut-off value it contributes to the mixture classification even 
if it may not trigger classification of the mixture directly. 

Annex  I:  4.1.3.1.  The  classification  system  for  mixtures  covers  all  classification  categories 
which are used for substances, i.e. categories Acute 1 and Chronic 1 to 4. In order to make use 
of all available data for purposes of classifying the aquatic environmental hazards of the mixture, 
the following is applied where appropriate: 

The "relevant components" of a mixture are those which are classified "Acute 1"or "Chronic 1" 
and  present  in  a  concentration  of  0.1 %  (w/w)  or  greater,  and  those  which  are  classified 
"Chronic 2", "Chronic 3" or "Chronic 4" and present in a concentration of 1 % (w/w) or greater, 
unless there is a presumption (such as in the case of highly toxic components (see 4.1.3.5.5.5)) 
that  a  component  present  in  a  lower  concentration  can  still  be  relevant  for  classifying  the 
mixture for aquatic environmental hazards. Generally, for substances classified as "Acute 1" or 
"Chronic 1" the concentration to be taken into account is (0.1/M) %. (For explanation M-factor 
see 4.1.3.5.5.5). 

For aquatic hazards the cut-off values are further addressed under section 1.1.2.2.2 (b) of Annex 
I to CLP. The calculation referred to in (b)(i) of that section, is found in section 4.1.3.1 of Annex 
I to CLP (see the green box above). 

This  signals  that  highly  toxic  components  will  need  to  be  considered  at  lower  levels  than  the 
generic cut-off values, and this applies to any substance to which an M-factor greater than 1 has 
been assigned (see Section 4.1.4.5 of this document).  

Note that generic concentration limits (GCLs) should be given in weight percentages except for 
certain gaseous mixtures where they may be best described in volume percentage, e.g. a single 
hazardous component in an inert diluent, e.g. nitrogen or helium. 

When the information on the mixture has been gathered and validated, the following guidance 
should be followed depending on the type and level of information available. 

4.1.4.3.  Classification  criteria  for  mixtures  hazardous  to  the  aquatic 
environment based on test data on the mixture as a whole 

The testing of a mixture for aquatic toxicity is highly complex, both in terms of the conduct of the 
test, and in the interpretation of data from such testing. The different physico-chemical properties, 
such as water solubility, vapour pressure, and adsorption, make it almost impossible to prepare 
an  exposure  concentration  that  is  characteristic  of  the  mixture,  while  the  multi-component 
analysis needed to verify such an exposure concentration is both complex and expensive. 

Therefore,  before  any  such  new  testing  is  conducted,  alternative  approaches  such  as  the 
summation  method,  should  be  considered,  particularly  where  testing  would  involve  the  use  of 
vertebrate animals such as fish (see also Section 1.1.6.2 of this document). Nevertheless, there 
are  circumstances  where  test  data  may  already  be  available  and  should  then  be  examined  to 
assess  its  relevance  for  the  purposes  of  classification.  Data  which  has  been  prepared  for 
Regulatory use in compliance with standard guidelines, such as test data on plant protection or 
biocidal products, may be considered as acceptable for classification. Where such valid test data, 

 
 
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both acute and chronic, are available, they may be used in accordance with the general guidance 
below.  

Annex  I:  4.1.3.3.1  When  the  mixture  as  a  whole  has  been  tested  to  determine  its  aquatic 
toxicity, this information can be used for classifying the mixture according to the criteria that 
have  been  agreed  for  substances.  The  classification  is  normally  based  on  the  data  for  fish, 
crustacea  and  algae/plants  (see  sections  4.1.2.7.1  and  4.1.2.7.2).  When  adequate  acute  or 
chronic toxicity data for the mixture as a whole are lacking, “bridging principles” or “summation 
method” should be applied (see sections 4.1.3.4 and 4.1.3.5). 

4.1.3.3.2  The  long-term  (chronic)  hazard  classification  of  mixtures  requires  additional 
information  on  degradability  and  in  certain  cases  bioaccumulation.  Degradability  and 
bioaccumulation tests for mixtures are not used as they are  usually difficult to interpret, and 
such tests may be meaningful only for single substances. 

4.1.3.3.3 Classification for category Acute 1 

(a)  When there are adequate acute toxicity test data (LC50 or EC50) available for the mixture 

as a whole showing L(E)C50  1 mg/l: 

Classify mixture as Acute 1 in accordance with point (a) of Table 4.1.0. 

(b)  When there are acute toxicity test data (LC50(s) or EC50(s)) available for the mixture as 

a whole showing L(E)C50(s) 1 mg/l for normally all trophic levels: 

No need to classify for short-term (acute) hazard. 

4.1.3.3.4 Classification for categories Chronic 1, 2 and 3 

(a)  When there are adequate chronic toxicity data (ECx or NOEC) available for the mixture 

as a whole showing ECx or NOEC of the tested mixture ≤ 1mg/l: 

(i)  Classify the mixture as Chronic 1, 2 or 3 in accordance with point (b)(ii) of Table 
4.1.0. as rapidly degradable if the available information allows the conclusion that 
all relevant components of the mixture are rapidly degradable;  

(ii)  Classify the mixture as Chronic 1 or 2 in all other cases in accordance with point 

(b)(i) of Table 4.1.0. as non-rapidly degradable; 

(b)  When there are adequate chronic toxicity data (ECx or NOEC) available for the mixture 
as a whole showing ECx(s) or NOEC(s) of the tested mixture > 1 mg/l for normally all 
trophic levels:  

No need to classify for long-term (chronic) hazard in categories Chronic 1, 2 or 3. 

4.1.3.3.5 Classification for category Chronic 4 

If there are nevertheless reasons for concern: 

Classify the mixture as Chronic 4 (safety net classification) in accordance with Table 4.1.0. 

Where a classification is made based on test data, valid data should normally be available on each 
of  fish,  crustacea  and  algae  or  other  aquatic  plants,  unless  a  decision  to  classify  in  the  most 
stringent  category(ies)  (Acute  1  and/or  Chronic  1)  can  be  made  without  a  full  dataset.  To  be 
valid, it would normally be necessary to show that the tested organism has been exposed to the 
toxic components of the mixture in proportion to the composition of the mixture, and that this 
exposure has been maintained for the duration of the test.  If this  cannot be accomplished the 
classification should be based on information on the individual components. It is insufficient to 
simply prepare a water-accommodated fraction (WAF) for testing. 

When  there  is  adequate  toxicity  test  data  available  for  the  mixture  as  a  whole,  this  may  be 
simplified to two basic rules for each of acute and long-term hazard classification: 

 
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Classification for acute (short-term) aquatic hazard: 

i. 

ii. 

If the lowest valid acute/short-term L(E)C50 is ≤ 1 mg/L, classify as Acute 1.  

If valid acute/short-term test data are available on fish, crustacea and algae/aquatic plants 
(i.e. all three trophic levels), and all showing L(E)C50 > 1 mg/L, there is no need to classify 
for acute aquatic hazard.  

Classification for long-term aquatic hazard: 

i. 

ii. 

If the lowest valid chronic toxicity test data (NOEC or ECx) is ≤ 1 mg/L, classify as Chronic 
1,  2  or  3,  depending  on  the  information  on  components  degradability,  e.g.  if  all 
components are known to be rapidly degradable. 

If valid chronic toxicity test data are available on fish, crustacea and algae/aquatic plants 
(i.e. all three trophic levels), and all showing NOEC or ECx >1 mg/L, there is no need to 
classify for long-term aquatic hazard in Chronic 1, 2 or 3. 

4.1.4.4.  When  experimental  aquatic  toxicity  data  are  not  available  for  the 

complete mixture: bridging principles 

Annex  I:  4.1.3.4.1  Where  the  mixture  itself  has  not  been  tested  to  determine  its  aquatic 
environmental hazard, but there are sufficient data on the individual components and similar 
tested mixtures to adequately characterise the hazards of the mixture, this data shall be used 
in accordance with the bridging rules set out in Section 1.1.3. However, in relation to application 
of the bridging rule for dilution, sections 4.1.3.4.2 and 4.1.3.4.3 shall be used. 

4.1.3.4.2  Dilution:  if  a  mixture  is  formed  by  diluting  another  tested  mixture  or  a  substance 
classified for its aquatic environmental hazard with a diluent which has an equivalent or lower 
aquatic hazard classification than the least toxic original component and which is not expected 
to affect the aquatic hazards of other components, then the resulting mixture may be classified 
as equivalent to the original tested mixture or substance. Alternatively, the method explained 
in section 4.1.3.5 may be applied. 

4.1.3.4.3 If a mixture is formed by diluting another classified mixture or substance with water 
or other totally non-toxic material, the toxicity of the mixture can be calculated from the original 
mixture or substance. 

For  circumstances  where  no  or  inadequate  test  data  are  available  on  the  mixture  itself,  the 
classification of a mixture may be determined based on sufficient data for individual components 
of the mixture and on another similar tested mixture by an appropriate application of any of the 
specified ‘bridging principles’. The identified relevant information needs to be evaluated for the 
purpose of classification, by comparing it with the criteria in section 1.1.3 of Annex I to CLP. Those 
rules  allow  characterisation  of  the  hazards  of  the  mixture  without  performing  tests  on  it,  but 
rather by building on the available information on similar tested mixtures (see also Part 1, Section 
1.6.3.2 of this guidance document). 

4.1.4.5.  When  hazard  data  (information  on  toxicity  or  classification)  are 

available for all the components of the mixture 

Annex I: 4.1.3.5.1 The classification of a mixture is based on summation of the classification 
of  its  components.  The  percentage  of  components  classified  as  "Acute"  or  "Chronic"  is  fed 
straight  in  to  the  summation  method.  Details  of  the  summation  method  are  described  in 
4.1.3.5.5. 

Where no or inadequate test data on the mixture itself is available and the bridging principles are 
not applicable, the classification of the mixture is based on information on the components. The 
information  that  will  most  usually  be  available  to  aid  classification  of  a  mixture  will  be  the 

 
 
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classification applied to the individual components (substances). These data and any associated 
M-factor(s) are included in the safety data sheets (SDS) and also in the Classification and Labelling 
Inventory (C&L Inventory) established and maintained by the Agency in the form of a database 
[http://echa.europa.eu/information-on-chemicals/cl-inventory-database].  Where  M-factors  are 
not available for the harmonised classification or the SDS there is a general obligation under CLP 
Art. 10(2) to derive M-factors using available aquatic toxicity data.  In cases where the aquatic 
hazard classification of a mixture will be made based on data on the components, it is therefore 
generally the summation of the quantities of the hazardous components that should be used to 
determine a specific hazard classification of the mixture.  

Provided the classification data, in part or in total, and the % of these components in the mixture 
are known, a classification of the mixture can be made according to the summation method. The 
following text from CLP describes the application of this method. 

Annex I: 4.1.3.5.5 Summation method 

4.1.3.5.5.1 Rationale 

4.1.3.5.5.1.1  In  case  of  the  substance  classification  categories  Chronic  1  to  Chronic  3,  the 
underlying  toxicity  criteria  differ  by  a  factor  of  10  in  moving  from  one  category  to  another. 
Substances with a classification in a high toxicity band therefore contribute to the classification 
of a mixture in a lower band. The calculation of these classification categories therefore needs 
to consider the contribution of any substance classified as Chronic 1, 2 or 3. 

4.1.3.5.5.2. Classification procedure 

4.1.3.5.5.2.1  In  general  a  more  severe  classification  for  mixtures  overrides  a  less  severe 
classification, e.g. a classification with Chronic 1 overrides a classification with Chronic 2. As a 
consequence, in this example, the classification procedure is already completed if the result of 
the  classification  is  Chronic  1.  A  more  severe  classification  than  Chronic  1  is  not  possible. 
Therefore it is not necessary to undergo the further classification procedure. 

4.1.3.5.5.3 Classification for category Acute 1 

4.1.3.5.5.3.1  First  all  components  classified  as  Acute  1  are  considered.  If  the  sum  of  the 
concentrations  (in  %)  of  these  components  multiplied  by  their  corresponding  M-factors  is 
greater than 25 % the whole mixture is classified as Acute 1. 

4.1.3.5.5.3.2  The  classification  of  mixtures  for  short-term  (acute)  hazards  based  on  this 
summation of classified components is summarised in Table 4.1.1. 

 
 
 
 
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Table 4.1.1 
Classification 
based on summation of classified components 

mixture 

for 

of 

a 

short-term 

(acute) 

hazards, 

Sum of components classified as: 

Mixture is classified as: 

Acute 1  M (a) ≥ 25 % 

Acute 1 

(a) 

For explanation of the M-factor see  4.1.3.5.5.5 

4.1.3.5.5.4 Classification for the categories Chronic 1, 2, 3 and 4 

4.1.3.5.5.4.1  First  all  components  classified  as  Chronic  1  are  considered.  If  the  sum  of  the 
concentrations (in %) of these components multiplied by their corresponding M-factors is equal 
to or greater than 25 %, the mixture is classified as Chronic 1. If the result of the calculation is 
a classification of the mixture as Chronic 1, the classification procedure is completed. 

4.1.3.5.5.4.2  In  cases  where  the  mixture  is  not  classified  as  Chronic  1,  classification  of  the 
mixture as Chronic 2 is considered. A mixture is classified as Chronic 2 if 10 times the sum of 
the  concentrations  (in  %)  of  all  components  classified  as  Chronic  1  multiplied  by  their 
corresponding M-factors plus the sum of the concentrations (in %) of all components classified 
as Chronic 2 is equal to or greater than 25 %. If the result of the calculation is classification of 
the mixture as Chronic 2, the classification process is completed. 

4.1.3.5.5.4.3  In  cases  where  the  mixture  is  not  classified  either  as  Chronic  1  or  Chronic  2, 
classification of the mixture as Chronic 3 is considered. A mixture is classified as Chronic 3 if 
100  times  the  sum  of  the  concentrations  (in  %)  of  all  components  classified  as  Chronic  1 
multiplied by their corresponding M-factors plus 10 times the sum of the concentrations (in %) 
of  all  components  classified  with  Chronic  2  plus  the  sum  of  the  concentrations  (in  %)  of  all 
components classified as Chronic 3 is ≥ 25 %. 

4.1.3.5.5.4.4  If  the  mixture  is  still  not  classified  in  Chronic  1,  2  or  3,  classification  of  the 
mixture as Chronic 4 shall be considered. A mixture is classified as Chronic 4 if the sum of the 
concentrations (in %) of components classified as Chronic 1, 2, 3 and 4 is equal to or greater 
than 25 %. 

4.1.3.5.5.4.5  The  classification  of  mixtures  for  long-term  (chronic)  hazards,  based  on  this 
summation of the concentrations of classified components, is summarised in Table 4.1.2. 

 
 
 
 
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Table 4.1.2 
Classification 
based on summation of the concentrations of classified components 

a  mixture 

long-term 

for 

of 

(chronic) 

537 

hazards,  

Sum of components classified as: 

Mixture is classified as: 

Chronic 1  M (a) ≥ 25 % 

Chronic 1 

(M  10  Chronic 1) + Chronic 2 ≥ 25 %  Chronic 2 

(M  100  Chronic 1) + (10  Chronic 2)  

+ Chronic 3 ≥ 25 % 

Chronic 1 + Chronic 2 + Chronic 3  

+ Chronic 4 ≥ 25 % 

Chronic 3 

Chronic 4 

(a) 

For explanation of the M-factor, see 4.1.3.5.5.5 

4.1.3.5.5.1.2 When a mixture contains components classified as Acute 1 or Chronic 1, attention 
must be paid to the fact that such components, when their acute toxicity is below 1 mg/l and/or 
chronic  toxicity  is  below  0,1  mg/l  (if  non-rapidly  degradable)  and  0.01  mg/l  (if  rapidly 
degradable)  contribute  to  the  toxicity  of  the  mixture  even  at  a  low  concentration.  Active 
ingredients in pesticides often possess such high aquatic toxicity but also some other substances 
like  organometallic  compounds.  Under  these  circumstances  the  application  of  the  normal 
generic  concentration  limits  leads  to  an  "under-classification"  of  the  mixture.  Therefore, 
multiplying  factors  shall  be  applied  to  account  for  highly  toxic  components,  as  described  in 
section  4.1.3.5.5.5. 

For those components for  which only toxicity data are available (i.e.,  no derived classification) 
the additivity formulas offer a way for estimating what the toxicity of a mixture would be if the 
individual substance toxicities could be ‘added’ to each  other in a straightforward way. Thus it 
assumes a similar ‘mode of action’ for each component. 

To make full use of this approach access to the whole aquatic toxicity dataset and the necessary 
knowledge to select the best and most appropriate data is required. Clearly, the best use would 
be  to  add  up  separately  each  of  the  fish  toxicity  data,  the  crustacea  toxicity  data  and  the 
algae/aquatic  plants  toxicity  data  to  derive  a  specific  toxicity  value  for  each  trophic  level.  The 
lowest of the toxicity values would normally be used to define the appropriate hazard category 
for the mixture. Indeed, if it is only possible to characterise part of the mixture in this way, that 
part can be assigned a hazard category (and an M-factor for categories Acute 1 and/or Chronic 
1) and then, in a second step, be used in the summation method.  

The use of the additivity formulae is limited to those circumstances where the substance hazard 
category  is  not  known.  The  following  text  from  CLP  describes  the  application  of  the  additivity 
formula. 

 
 
 
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Annex  I:  4.1.3.5.2  Mixtures  can  be  made  of  a  combination  of  both  components  that  are 
classified  (as  Acute  1  and/or  Chronic  1,  2,  3,  4)  and  others  for  which  adequate  toxicity  test 
data is available. When adequate toxicity data are available for more than one component in 
the  mixture,  the  combined  toxicity  of  those  components  is  calculated  using  the  following 
additivity formulas (a) or (b), depending on the nature of the toxicity data: 

(a)  

Based on acute aquatic toxicity: 

where: 

Ci = concentration of component i (weight percentage); 

L(E)C50 i = (mg/l) LC50 or EC50 for component i; 

 = number of components, and i is running from 1 to n; 

L(E)C50 m = L(E) C50 of the part of the mixture with test data; 

The calculated toxicity may be used to assign to that portion of the mixture a short-term (acute) 
hazard  category  which  is  then  subsequently  used  in  applying  the  summation 
method; 

(b) 

Based on chronic aquatic toxicity: 

where: 

Ci =  

Cj =  

concentration  of  component  i  (weight  percentage)  covering  the  
rapidly degradable components; 

concentration  of  component  j  (weight  percentage)  covering  the 
non- rapidly degradable components; 

NOECi =  

NOEC  (or  other  recognized  measures  for  chronic  toxicity)  for 
component  i  covering  the  rapidly  degradable  components,  in 
mg/l; 

NOECj =  

NOEC  (or  other  recognized  measures  for  chronic  toxicity)  for 
component j covering the non-rapidly degradable components, in 
mg/l; 

n = 

number of components, and i and j are running from 1 to n; 

EqNOECm =   Equivalent NOEC of the part of the mixture with test data; 

The  equivalent  toxicity  thus  reflects  the  fact  that  non-rapidly  degrading  substances  are 
classified one hazard category level more “severe” than rapidly degrading substances. 

The calculated  equivalent toxicity may be used to assign that portion  of the mixture a long-
term  (chronic)  hazard  category,  in  accordance  with  the  criteria  for  rapidly  degradable 

+=+nnmNOECjCjNOECiCiEqNOECCjCi1,0=i50m50C)E(LCi  C)E(LCi 
 
 
 
 
 
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substances  (point  (b)(ii)  of  Table  4.1.0.),  which  is  then  subsequently  used  in  applying  the 
summation method. 

4.1.3.5.3.  When  applying  the  additivity  formula  for  part  of  the  mixture,  it  is  preferable  to 
calculate the toxicity of this part of the mixture using for  each substance toxicity values that 
relate to the same taxonomic group (i.e. fish, crustacean, algae or equivalent) and then to use 
the highest toxicity (lowest value) obtained (i.e. use the most sensitive of the three taxonomic 
groups).  However,  when  toxicity  data  for  each  component  are  not  available  in  the  same 
taxonomic group, the toxicity value  of each component is selected in  the same manner that 
toxicity values are selected for the classification of substances, i.e. the higher toxicity (from the 
most sensitive test organism) is used. The calculated acute and chronic toxicity is then used to 
assess whether this part of the mixture shall be classified as Acute 1 and/or Chronic 1, 2 or 3 
using the same criteria described for substances. 

Note:  the  chronic  additivity  formula  includes  a  factor  of  10  correction  for  the  non-rapidly 
degradable  components  to  allow  equivalent  inclusion  of  not  rapidly  and  rapidly  degradable 
components. Therefore, toxicity values are to be treated as rapidly degradable when  deriving a 
classification. That is, calculated equivalent toxicity values are compared with the criteria in Table 
4.1.0 (b)(ii) and M-factors derived from the ‘RD’ column of Table 4.1.3. Note also that generic 
concentration  limits  (GCLs)  should  be  given  in  weight  percentages  except  for  certain  gaseous 
mixtures  where  they  may  be  best  described  in  volume  percentage,  e.g.  a  single  hazardous 
component in an inert diluent, e.g. nitrogen or helium. 

  NOTICE: With the aquatic toxicity data at hand the ingredient substance classification and M-
factor(s)  could  easily  be  gained  by  a  direct  comparison  with  the  substance  criteria,  which 
then  could  be  fed  straight  into  the  summation  method.  It  will  therefore  usually  not  be 
necessary to use the additivity formulae. 

4.1.4.6.  When  hazard  data  (information  on  toxicity  or  classification)  are 

available for only some components of the mixture  

This  section  is  related  to  Figure 4.1.1  where  one  can  decide  to  apply  the  summation  method 
and/or the additivity formula (see section 4.1.3.5 of Annex I to CLP) and apply section 4.1.3.6 of 
Annex I to CLP. 

Use available hazard data of known components.  

•  This applies to mixtures containing unknown components and/or known components, for 
which  neither  toxicity  data  nor  classifications  are  known.  In  these  cases,  for  labelling 
purposes  consider  the  provisions  of  section  4.1.3.6  in  Annex  I  to  CLP.  For  classification 
based on the known part of the mixture, use the summation method and/or the additivity 
formula (see section 4.1.3.5 of Annex I to CLP).  

•  NOTE:  If  a  mixture  is  classified  in  more  than  one  way,  the  method  yielding  the  most 

stringent result should be used.  

 
 
 
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4.1.4.7.  Decision on classification: examples for mixtures 

If the evaluation shows that the criteria are fulfilled, one category for acute aquatic hazard and/or 
one category for long-term aquatic hazards should be assigned. For the labelling elements, such 
as:  hazard  pictograms,  signal  words,  hazard  statements  and  precautionary  statements,  see 
Section 4.1.6. 

List of the examples on mixtures classification included in this section: 

The  classification  system  for  mixtures  is  complex  as  different  methods  are  available.  Which 
method to use is dependent upon the type of information available.  

•  Example A: When classification data are available for some or all components of a mixture: 

straightforward application of the summation method.  

•  Example B1: When toxicity test data on the mixture as a whole are available for all three 

trophic levels: classification based on test data on the mixture. 

•  Example B2: When information on the classification of the components and test data on 
the mixture as a whole are available for some, but not all three trophic levels: classification 
based on the summation method. 

•  Example C: When no data are available on the mixture as a whole and its components, 
but  test  data  are  available  on  a  similar  tested  mixture:  use  of  the  bridging  principles  – 
dilution with water. 

•  Example  D:  When  only  test  data  are  available  for  some,  but  not  all  components  of  the 

mixture: use of the additivity formula and the summation method. 

 
 
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4.1.4.7.1. 

Example  A:  When  classification  data  are  available  for  some  or  all 
components  of  a  mixture:  straightforward  application  of  the  summation 
method 

INFORMATION ON INGREDIENTS CLASSIFICATION AND CONCENTRATION 

Acute aquatic hazard  M 

Long-term 
aquatic hazard 

M 

C (%) 

10 

Chronic 1 

10 

1 

- 

- 

- 

- 

Chronic 2 

Chronic 2 

Chronic 3 

Not classified 

Not classified 

- 

- 

- 

- 

- 

1 

3 

10 

10 

10 

66 

Astralamid 

Bastralamid 

Acute 1 

Acute 1 

Castralamid 

Not classified 

Dastralamid 

Not classified 

Estralamid 

Not classified 

Festralamid 

Not classified 

M = M-factor; C = Concentration  

Aquatic hazard classification: 

Acute aquatic hazard: Not classified. 

Long-term aquatic hazard: Category Chronic 2 

Reasoning: 

•  Valid test data on the mixture as a whole (for all three trophic levels) are not available.  

•  Valid  test  data  on  similar  tested  mixtures  are  not  available,  either,  meaning  that  any 

bridging principle cannot be used. 

Therefore,  classification  should  be  considered  based  on  individual  components  using  the 
summation method. 

Acute aquatic hazard: Information on classification including associated M-factors and the % of 
the components in the mixture are available. 

Classify for acute hazard if: ∑ (Acute 1  M) ≥ 25% 

Using the classification of the components of the mixture: (1   10) + (3  1) = 13 (which is < 
25%). Hence, no classification for acute aquatic hazard. 

Long-term aquatic hazard: 

Step 1: Classify as Chronic 1 if: ∑ (Chronic 1  M) ≥ 25% (if not, then go to Step 2). 

Step 2: Classify as Chronic 2 if: ∑ (10  Chronic 1  M) + ∑ (Chronic 2) ≥ 25% (if not, then go to 
Step 3). 

Step 3: Classify as Chronic 3 if: ∑ (100  Chronic 1  M) + ∑ (10  Chronic 2) + ∑ (Chronic 3) 
≥ 25% (if not, then go to Step 4). 

Step 4: Classify as Chronic 4 if: ∑ (Chronic 1) + ∑ (Chronic 2) + ∑ (Chronic 3) + ∑ (Chronic 4) 
≥ 25% 

Using the classification of the components of the mixture: 

 
 
 
 
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Step 1: (1  10) = 10 (which is < 25% → Step 2). 

Step 2: (10  1  10) + 3+10 = 113 (which is > 25%). Hence, classify as Category Chronic 2. 

Labelling elements based on the classification: 

Element 

GHS Pictogram 

Signal Word 

Hazard Statement 

Resulting  Labelling  Elements 
(code) 

GHS09 

- 

H411 

Precautionary statement(s) 

P273, P391, P501 

 
 
 
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4.1.4.7.2. 

Example B1: When toxicity data on the mixture as a whole is available for 
all three trophic levels: classification based on test data for the mixture 

INFORMATION ON INGREDIENTS CLASSIFICATION AND CONCENTRATION 

Acute aquatic hazard  M 

Long-term 
aquatic hazard 

M 

C (%) 

Frusthrin 

Gladobrin 

Acute 1 

Acute 1 

1 

1 

Chronic 1 

Chronic 3 

1 

- 

40 

60 

M = M-factor; C = Concentration 

Acute (short-term) aquatic toxicity 

Value 

Fish: 

Mixture (Cyprinus carpio) 

Crustacea: 

Mixture (Daphnia magna) 

19 mg/L 

(96 hr LC50) 

3.5 mg/L 

(48 hr EC50) 

Test  method  ((EC)  No. 
440/2008) 
OECD 
guideline / remarks 

or 

C.1 / static, GLP 

C.2 / static, GLP 

Algae/aquatic plants: 

15 mg/L 

C.3 / static, GLP 

Mixture (Scenedesmus subspicatus) 

(72 or 96 hr ErC50) 

Chronic (long-term) aquatic toxicity 

Fish: 

Mixture (Cyprinus carpio) 

0.09 mg/L 

(12 d NOEC) 

OECD  210  /  Early  Life  Stage, 
flow through, GLP 

Crustacea: 

0.05 mg/L 

C.20 / semi-static, GLP 

Mixture (Daphnia magna) 

(21 d NOEC) 

Algae/aquatic plants: 

1.5 mg/L 

C.3 / static, GLP 

Mixture (Scenedesmus subspicatus) 

(96 h NOEC) 

Aquatic hazard classification: 

Acute aquatic hazard: Not classified.  

Long-term aquatic hazard: Chronic 1. 

 
 
 
 
 
 
 
 
 
 
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Reasoning: 

Acute aquatic hazard: 

Valid test data for all the three trophic levels are available for the mixture as a whole, therefore 
no need to consider bridging principles or classification of individual components for acute hazard 
classification  of  the  mixture.  Test  data  showed  that  L(E)C50  >  1  mg/L.  Consequently  -  no 
classification for acute aquatic hazard. 

Long-term aquatic hazard:  

Valid test data for all the three trophic levels are available for the mixture as a whole, therefore 
no need to consider classification of individual components for long-term hazard classification of 
the  mixture.  Test  data  showed  that  NOEC  <  0.1  mg/L.  No  information  on  rapid  degradation. 
Hence,  the  mixture  is  considered  being  not  rapidly  degradable.  The  mixture  is  classified  as 
category Chronic 1.  

Labelling elements based on the classification: 

Element 

GHS Pictogram 

Signal Word 

Hazard Statement 

Resulting  Labelling  Elements 
(code) 

GHS09 

Wng 

H410 

Precautionary statement(s) 

P273, P391, P501 

 
 
 
 
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4.1.4.7.3. 

Example B2: When information on the classification of the components is 
available and toxicity data on the mixture as a whole is available for some, 
but not all three trophic levels: use of the summation method 

INFORMATION ON COMPONENTS CLASSIFICATION AND CONCENTRATION 

Acute aquatic hazard  M 

Long-term 
aquatic hazard 

M 

C (%) 

Frusthrin 

Gladobrin 

Acute 1 

Acute 1 

1 

1 

Chronic 1 

Chronic 3 

1 

- 

40 

60 

M = M-factor; C = Concentration 

Acute (short-term) aquatic toxicity 

Value 

Test  method  ((EC)  No. 
OECD 
440/2008) 
guideline / remarks 

or 

Algae/aquatic plants: 

15 mg/L 

C.3 / static, GLP 

Mixture (Scenedesmus subspicatus) 

(72 or 96 hr ErC50) 

Chronic (long-term) aquatic toxicity 

Algae/aquatic plants: 

1.5 mg/L 

C.3 / static, GLP 

Mixture (Scenedesmus subspicatus) 

(96 h NOEC) 

Aquatic hazard classification: 

Acute aquatic hazard: Acute 1.  

Long-term aquatic hazard: Chronic 1. 

Reasoning: 

•  Valid test data on the mixture as a whole are available for one, but not for all the three 
trophic levels and we don’t know if algae is clearly the most sensitive trophic level for the 
mixture.  

•  Neither is valid test data on similar tested mixtures available, meaning that the bridging 

principles could not be used.  

Therefore, classification should for both acute hazard and long-term hazard be considered based 
on individual components using the summation method. Testing should not be conducted for the 
mixture for the remaining trophic levels. 

Acute aquatic hazard: 

Information on classification including associated M-factors and the % of the components in the 
mixture are available.  

Classify for acute hazard if: ∑ (Acute 1  M) ≥ 25% 

 
 
 
 
 
 
 
 
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Using the classification of the components of the mixture: (40  1) + (60  1) = 100 (which is ≥ 
25%). Hence - category Acute 1. 

Long-term aquatic hazard: 

Information on classification including associated M-factors and the % of the components in the 
mixture are available.  

Step 1: Classify as Chronic 1 if: ∑ (Chronic 1  M) ≥ 25% (if not, then go to Step 2). 

Using the classification of the components of the mixture: 

Step 1: (40  1) = 40 (which is ≥ 25%). Hence - Category Chronic 1. 

Labelling elements based on the classification: 

Element 

GHS Pictogram 

Signal Word 

Hazard Statement 

Resulting  Labelling  Elements 
(code) 

GHS09 

Wng 

H41083 

Precautionary statement(s) 

P273, P391, P501 

83 Note that in accordance with Article 27 of CLP hazard statement H400 may be considered redundant and therefore 
not included on the label because hazard statement H410 also applies, see Section 4.1.6. 

 
 
 
 
 
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4.1.4.7.4. 

Example C: When no data are available on the mixture as a whole and its 
components, but test data are available on a similar tested mixture: use of 
the bridging principles – dilution with water 

Test Species 

Information / Data 

Fish  

Crustacea 

Algae 

No data available 

No data available 

No data available 

A reference mixture has shown a LC50 of 0.5 mg/L and adequate NOECs in the range 0.07 to < 
0.1 mg/L. Based on this data it has been classified as Category Acute 1 and Category Chronic 1. 

Subsequently, this mixture has been diluted in water by factor of 10 and the newly diluted mixture 
shall now be classified.  

Aquatic hazard classification: 

Acute aquatic hazard: Not classified. 

Long-term aquatic hazard: Category Chronic 2. 

Reasoning: 

The mixture is formed by diluting another classified mixture with water, the toxicity of the mixture 
can therefore be calculated from the original mixture. (see Section 4.1.4.4 of this document and 
CLP Annex I, section 4.1.3.4.3.) 

Acute aquatic hazard: LC50 = 5 mg/L (0.5x10). Hence - not classified. 

Long-term aquatic hazard: Adequate NOECs in the range 0.7 to < 1 mg/L (0.07 x 10 and 0.1 x 
10). Hence - category Chronic 2. 

Labelling elements based on the classification: 

Element 

GHS Pictogram 

Signal Word 

Hazard Statement 

Resulting  Labelling  Elements 
(code) 

GHS09 

- 

H411 

Precautionary statement(s) 

P273, P391, P501 

 
 
 
 
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4.1.4.7.5. 

Example D: When test data are available for some, but not all components 
of the mixture: use of the additivity formula and of the summation method 

INFORMATION ON COMPONENTS CLASSIFICATION AND CONCENTRATION 

Acute aquatic hazard  M 

Long-term 
aquatic hazard 

M 

C (%) 

Component 1 

Component 2 

Component 3 

- 

- 

- 

Component 4 

Not classified 

- 

- 

- 

- 

- 

- 

- 

Chronic 1 

- 

- 

- 

- 

50 

10 

10 

30 

COMPONENT TOXICITY DATA 

Data elements 

Component 1 

Component 2 

(50%  of  the 
mixture) 

(10%  of  the 
mixture) 

Test  method  ((EC) 
No.  440/2008)  or 
OECD  guideline  / 
remarks 

Physico-chemical properties 

Water Solubility: 

200 mg/L 

1000 mg/L 

A.6 / pH: 7.0, non-GLP 

Log octanol/water partition coefficient 
(log Kow): 

No data 

No data 

Acute (short-term) aquatic toxicity 

Fish:                Oncorhynchus mykiss 

No data 

0.3 mg/L 

C.1 / static, GLP 

(96 hr LC50) 

Crustacea:                Daphnia magna  0.55 mg/L 

No data 

C.2 /  static, non-GLP 

(48 hr EC50) 

Algae/aquatic plants:  

Scenedesmus subspicatus 

0.37 mg/L 

1.37 mg/L 

(72 hr ErC50) 

(72 hr ErC50) 

C.3 / static, GLP 

Long-term aquatic toxicity 

Fish:                Oncorhynchus mykiss  0.07 mg/L 

1.3 mg/L 

OECD 210 / semi-static 

(28 d NOEC) 

(28 d NOEC) 

Crustacea:                Daphnia magna  0.09 mg/L 

1.4 mg/L 

C.20 / semi-static, GLP 

(21 d NOEC) 

(21 d NOEC) 

 
 
 
 
 
 
 
 
 
 
 
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Algae/aquatic plants: 

Scenedesmus subspicatus 

0.13 mg/L 

0.53 mg/L 

(72 hr NOEC) 

(72 hr NOEC) 

C.3 / static, GLP 

Degradation (evidence of rapid degradation) 

Biotic  degradation  (%  degradation  in 
28 days (or, if absent, half-life in water 
(d)): 

No data 

No data 

Abiotic degradation (Hydrolysis) (half-
life (d)): 

No data 

No data 

Bioaccumulation 

Bioconcentration factor in fish (BCF):  No data 

No data 

Long-term hazard classification is known for 30% of the mixture.  

Test data is available for 60% of the mixture. 

For 10% of the mixture no information is available. 

Aquatic hazard classification: 

Acute aquatic hazard: Category Acute 1. 

Long-term aquatic hazard: Category Chronic 1. 

Reasoning: 

•  Valid test data on the mixture as a whole (for all three trophic levels) are not available.  

•  Valid  test  data  on  similar  tested  mixtures  are  not  available,  either,  meaning  that  any 

bridging principle cannot be used. 

Therefore,  classification  should  be  considered  based  on  individual  components  using  the 
summation method. 

NOTICE! 
In the case of the downstream user or importer not having the classification 
of  all  the  components,  further  dialogue  with  the  supplier  may  be  necessary  to  obtain 
additional  information.  The  suppliers  in  a  supply  chain  shall  cooperate  to  meet  the 
requirements  for  classification,  labelling  and  packaging  (see  Article  4(9)  of  CLP).  This 
particular  example,  however,  shows  what  could  be  done  if  the  classification  of  some 
components  in  any  case  is  not  available  (which,  for  example,  could  be  the  case  when 
importing certain mixtures). 

Acute aquatic hazard: 

For component 1 the most sensitive species showed a L(E)C50 0.37 mg/L. Thus, component 1, 
comprising 50% of the mixture, is classified as Acute 1; M-factor 1.  

Subsequently  used  in  the  summation  method,  more  than  25%  of  the  mixture  is  classified  as 
category Acute 1. Hence, the mixture is classified as Acute 1. 

 
 
 
 
 
 
 
 
 
 
 
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Alternatively:  You  can  calculate  the  combined  toxicity  for  components  1  and  2  applying  the 
Additivity Formula84: 

L(E)C50m = (50+10) / (50/0.37 mg/L + 10/0.3 mg/L) = 0.36 mg/L 

Assign category Acute 1. This means that 60% of this mixture is classified as category Acute 1 
and hence, subsequently used in the summation method, the whole mixture is classified as Acute 
1.  

Long-term aquatic hazard: 

Assign hazard categories for each component for which there are adequate chronic toxicity data 
available: 

Relevant information 

Category 

C (%) 

Component 1 

0.07 mg/L 

(28 d NOEC Fish); 

Assign  Chronic  1,  M-
factor 1 

50 % 

No  information  on  degradation.  Hence, 
the  substance  is  considered  not  rapidly 
degradable. 

Component 2 

0.53 mg/L 

Assign Chronic 2 

10% 

(72 hr NOEC Algae); 

No  information  on  degradation.  Hence, 
the  substance  is  considered  not  rapidly 
degradable. 

Component 3 

No data 

Component 4 

for  basis  of  classification  not 

Data 
available. 

- 

Chronic 1 

10% 

30 % 

More than 25% of the mixture is classified as category Chronic 1 and thus, the mixture is classified 
as category Chronic 1. 

Alternatively:  You  can  apply  the  Additivity  Formula85  to  calculate  the  combined  toxicity  for 
components 1 and 2 (60% of the mixture) 

EqNOECm = 60 / (50/(0.1 x 0.07) + 10/(0.1 x 1.3)) = 0.008 mg/L for fish 

EqNOECm = 60 / (50/(0.1 x 0.09)) + 10/(0.1 x 1.4)) = 0.011 mg/L for crustacea 

EqNOECm = 60 / (50/(0.1 x 0.13) + 10/(0.1 x 0.53)) = 0.015 mg/L for algae 

The lowest calculated EqNOECm is 0.008 mg/L for fish.  

Following the not rapidly degradable correction applied by use of the additivity formula (i.e., a 
factor  of  10  for  non-rapidly  degradable  components),  treat  the  values  as  those  of  a  rapidly 
degradable substance by applying point (b) (ii) of Table 4.1.0 of Annex I to CLP. Subsequently, 
use the ‘RD’ column of Table 4.1.3. In conclusion, assign category Chronic 1, M-factor 1 to that 
part of the mixture. 

84 In many cases it is possible to use the summation method straight away by assigning hazard categories 
to single components of a mixture when data is available. 

85 See also Section 4.1.4.6 of this guidance. 

 
 
 
 
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In addition component 4 of the mixture is classified as category Chronic 1 and comprises 30% of 
the mixture.  

The  long-term  hazard  category  assigned  to  that  part  of  the  mixture  the  mixture  is  then 
subsequently used in applying the summation method:  

Classify as Chronic 1 if:  

∑ (Chronic 1  M) ≥ 25% 

∑ (60  1) + 10 = 70  

Thus, the mixture is classified as category Chronic 1.  

Labelling elements based on the classification: 

Element 

GHS Pictogram 

Signal Word 

Resulting  Labelling  Elements 
(code) 

GHS09 

Wng 

Hazard Statement 

H41086 

Precautionary statement(s)  P273, P391, P501 

In  the  SDS  and  on  the  label  it  has  to  be  stated:  ‘Contains  10%  of  components  with  unknown 
hazards to the aquatic environment’. 

86 Note that in accordance with Article 27 of CLP, the hazard statement H400 may be considered redundant and therefore 
not included on the label because hazard statement H410 also applies, see Section 4.1.6 of this document. 

 
 
 
 
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4.1.5.  Metal and metal compounds  

4.1.2.10. Inorganic compounds and metals 

4.1.2.10.1.  For  inorganic  compounds  and  metals,  the  concept  of  degradability  as  applied  to 
organic compounds has limited or no meaning. Rather, such substances may be transformed 
by normal environmental processes to either increase or decrease the bioavailability of the toxic 
species. Equally the use of bioaccumulation data shall be treated with care(1). 

4.1.2.10.1. Poorly soluble inorganic compounds and metals may be acutely or chronically toxic 
in  the  aquatic  environment  depending  on  the  intrinsic  toxicity  of  the  bioavailable  inorganic 
species  and  the  rate  and  amount  of  this  species  which  enter  solution.  All  evidence  must  be 
weighed in a classification decision. This would be especially true for metals showing borderline 
results in the Transformation/Dissolution Protocol. 

_____________ 

(1)  Specific  guidance  has  been  issued  by  the  European  Chemicals  Agency  on  how  these  data  for  such 
substances may be used in meeting the requirements of the classification criteria. 

Annex IV provides the detailed guidance on the classification of metals and metal compounds. 

The guidance on classification of alloys and complex metal containing materials is limited so far. 
More guidance is needed (see also Annex IV.5.5). 

4.1.6.  Hazard communication for hazards to the aquatic environment  

A substance or mixture classified as hazardous and contained in packaging shall bear a label in 
accordance  with  the  rules  in  Title  III  of  CLP.  The  elements  to  be  included  in  labels  should  be 
specified  in  accordance  with  the  hazard  pictograms,  signal  words,  hazard  statements  and 
precautionary  statements  which  form  the  core  information  of  the  CLP  system.  For  general 
guidance  on  labelling  see  the  Introductory  Guidance  on  the  CLP  Regulation  (ECHA,  2019)  and 
also the Guidance on Labelling and Packaging in accordance with Regulation (EC) No 1272/2008 
(ECHA, 2019). 

Label elements shall be used for substances or mixtures meeting the criteria for classification in 
the hazard class Hazardous to the Aquatic Environment in accordance with Table 4.1.4 of Annex 
I to CLP. 

Pictogram 

The  hazard  pictogram  shall  satisfy  the  provisions  of  Annex  V  and  Annex  I,  part  1.2  to  the 
Regulation. 

Symbol: Environment;    Pictogram Code: GHS09 

The pictogram GHS09 is required only for substances or mixtures classified as: 

•  Aquatic Acute 1 and/or 

•  Aquatic Chronic 1 or 2 

 
 
 
 
 
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Signal word 

The  label  shall  include  the  relevant  signal  word  in  accordance  with  the  classification  of  the 
hazardous substance or mixture. The signal word relevant for the hazard class Hazardous to the 
Aquatic Environment is: 

Warning 

Signal Word Code: Wng 

The signal word ‘Warning’ is required only for substances or mixtures classified as: 

•  Aquatic Acute 1 and/or 

•  Aquatic Chronic 1 

Where  the  signal  word  ‘Danger’  is  used  on  the  label  due  to  classification  into  another  hazard 
class(es), the signal word ‘Warning’ shall not appear on the label. 

Hazard statements 

The label shall include the relevant hazard statements in accordance with the classification of the 
hazardous substance or mixture and shall be worded in accordance with Annex III to CLP. 

The hazard statements (and the Hazard statement Codes) relevant for the hazard class Hazardous 
to the Aquatic Environment are: 

•  Very toxic to aquatic life 

•  Very toxic to aquatic life with long lasting effects   

•  Toxic to aquatic life with long lasting effects 

•  Harmful to aquatic life with long lasting effects  

•  May cause long lasting harmful effects to aquatic life  

(H400) 

(H410) 

(H411) 

(H412) 

(H413) 

The hazard statement H400 is required only for substances or mixtures classified as: 

•  Aquatic Acute 1 

The  hazard  statements  H410  to  H413  are  respectively  required  for  substances  or  mixtures 
classified as: 

•  Aquatic Chronic 1, 2, 3 or 4 

Article 27 of CLP states that if a substance or mixture is classified within several hazard classes 
or differentiations of a hazard class, all hazard statements resulting from the classification shall 
appear on the label, unless there is evident duplication or redundancy. 

This means that in line with Part 1 of Annex III to CLP, where the hazard statement H410 is used 
on the label due to classification in the long-term hazard category Chronic 1, the hazard statement 
H400  does  not  need  to  appear  on  the  label.  Furthermore,  where  a  substance  or  a  mixture  is 
classified  both  in  acute  and  long-term  hazard  categories,  it  is  possible  to  use  only  hazard 
statement H410 on the label (see Table 4.1). 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Table 4.1  Hazard  statement  Codes  relevant  for  the  hazard  class  Hazardous  to  the  Aquatic 
Environment 

Aquatic hazard classification  Associated  hazard 

statement 

Associated  hazard  statement  that 
could appear on the label 

Acute 1 

H400 

H400 

Acute 1 and Chronic 1 

H400; H410 

H410 

Acute 1 and Chronic 2 

H400; H411 

H410 

Acute 1 and Chronic 3 

H400; H412 

H410 

Acute 1 and Chronic 487 

H400; H413 

H410 

Chronic 1 

Chronic 2 

Chronic 3 

Chronic 4 

H410 

H411 

H412 

H413 

H410 

H411 

H412 

H413 

Precautionary statements  

In accordance with Articles 17 and 22  of CLP the label shall include the relevant precautionary 
statements.  The  precautionary  statements  that  can  in  principle  be  used  for  the  hazard  class 
Hazardous to the Aquatic Environment according to CLP Annex I Table 4.1.4 are: 

•  Avoid release to the environment 

•  Collect spillage 

•  Dispose of contents/container to …   

(P273) 

(P391) 

(P501) 

4.1.7. 

 References  

ECHA Guidance on information requirements and chemical safety assessment (version 4.0, June 
2017), Chapter R7b 

OECD 2019: Guidance Document on aqueous-phase aquatic toxicity testing of difficult test 
chemicals. Series on Testing and Assessment Number 23 (Second Edition) 
ENV/JM/MONO(2000)6/REV1 ( 
http://www.oecd.org/officialdocuments/publicdisplaydocumentpdf/?cote=ENV/JM/MONO(2000)6
/REV1&docLanguage=En) (referred here as OECD Guidance 23)OECD 2006: Series on Testing 
and Assessment Number 54, Current approaches in the statistical analysis of ecotoxicity data: a 
guidance to application. ENV/JM/MONO(2006)18 

Guidance for identification and naming of substances under REACH and CLP

87 Please note that this combined classification only applies for mixtures. 

 
 
 
 
 
 
 
 
 
 
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5.  PART 5: ADDITIONAL HAZARDS  

5.1.  HAZARDOUS TO THE OZONE LAYER 

The criteria chapter for classification and labelling of substances and mixtures hazardous to the 
ozone layer are short and the need for guidance is limited to the actual ODP-value that would 
trigger classification for a substance. 

Annex I:  

5.1.2  Classification criteria for substances 

5.1.2.1. A substance shall be classified as Hazardous to the Ozone Layer (Category 1) if the 
available evidence concerning its properties and its predicted or observed 
environmental fate and behaviour indicate that it may present a danger to the 
structure and/or the functioning of the stratospheric ozone layer. 

5.1.3   Classification criteria for mixtures 

5.1.3.1. Mixtures shall be classified as Hazardous to the Ozone Layer (Category 1) on the 

basis of the individual concentration of the substance(s) contained therein that are 
also classified as Hazardous to the Ozone Layer (Category 1), in accordance with 
Table 5.1. 

Any substances having an Ozone Depleting Potential (ODP) greater or equal to the lowest ODP 
(i.e. 0.005) of the substances currently listed in Annex I to Regulation (EC) No 1005/200988 
should be classified as hazardous to the ozone layer (category 1). 

88 Regulation (EC) No 1005/2009 of the European Parliament and of the Council of 16 September 2009 on 
substances that deplete the ozone layer.  

 
 
 
 
 
 
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I 

ANNEX I: AQUATIC TOXICITY 

I.1 

Introduction 

The  basis  for  the  identification  of  a  hazard  to  the  aquatic  environment  for  a  substance  is  the 
aquatic  toxicity  of  that  substance.  Classification  is  predicated  on  having  toxicity  data  for  fish, 
crustacea, and algae/aquatic plant available. These taxa are generally accepted as representative 
of aquatic fauna and flora for hazard identification. Data on these particular taxa are more likely 
to  be  found  because  of  this  general  acceptance  by  regulatory  authorities  and  the  chemical 
industry. Other information on the degradation and bioaccumulation behaviour is used to better 
delineate the aquatic hazard. This section describes the appropriate tests for ecotoxicity, provides 
some  basic  concepts  in  evaluating  the  data  and  using  combinations  of  testing  results  for 
classification.  Further  detailed  guidance  is  given  in  IR&CSA  Chapter  R.7b,  sections  R.7.8.3  – 
R.7.8.5). 

I.2 

Description of tests 

For classifying substances in the harmonised system, freshwater and marine species toxicity data 
can  be  considered  as  equivalent  data.  It  should  be  noted  that  some  types  of  substances,  e.g. 
ionisable  organic  chemicals  or  organometallic  substances  may  express  different  toxicities  in 
freshwater and marine environments. Since the purpose of classification is to characterise hazard 
in the aquatic environment, the result showing the highest toxicity should normally be chosen. 
However, there are circumstances where a weight of evidence approach is appropriate. 

The  criteria  for  determining  aquatic  hazards  should  be  test  method  neutral,  allowing  different 
approaches  as  long  as  they  are  scientifically  sound  and  validated  according  to  international 
procedures  and  criteria  already  referred  to  in  existing  systems  for  the  hazard  of  concern  and 
produce mutually acceptable data. Where valid data are available from non-standard testing and 
from  non-testing  methods,  these  shall  be  considered  in  classification  provided  they  fulfil  the 
requirements specified in Section 1 of Annex XI to the REACH Regulation (EC) No 1907/2006.  

According to GHS, 2011, fourth revised  edition, Section 4.1.1.3:“Acute toxicity would normally 
be determined using a fish 96 hour LC50 (OECD Test  Guideline 203  or equivalent), a crustacea 
species 48 hour EC50 (OECD Test Guideline 202 or equivalent) and/or an algal species 72 or 96 
hour EC50 (OECD Test Guideline 201 or equivalent). These species are considered as surrogate 
for all aquatic organisms and data on other species such as the duckweed Lemna may also be 
considered if the test methodology is suitable.” 

Chronic testing involves an exposure that covers a significant period of time when compared to 
the organism´s life cycle. The term can signify periods from days to a year, or more depending 
on the reproductive cycle of the aquatic organism. Chronic tests can be done to assess certain 
information relating to growth, survival, reproduction and development. 

According  to  GHS,  2011,  fourth  revised  edition,  Section  4.1.1.3:“Chronic  toxicity  data  are  less 
available than acute data and the range of testing procedures less standardised. Data generated 
according to the OECD Test Guidelines 210 (Fish Early Life Stage), 202 Part 2 or 211 (Daphnia 
Reproduction) and 201 (Algal Growth Inhibition) or equivalent can be accepted (see also Annex 
9,  para.  A9.3.3.2).  Other  validated  and  internationally  accepted  tests  could  also  be  used.  The 
NOECs or other equivalent ECx should be used.” 

It  should  be  noted  that  several  of  the  test  guidelines  cited  as  example  tests  for  potential 
consideration for classification purposes have been revised or updated. Such revisions may lead 
to minor modifications  of test conditions  or  even introduction of the potential use of additional 
effects  endpoints  depending  on  the  regulatory  context.  Therefore,  the  expert  group  that 

 
 
 
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developed  the  harmonised  criteria  for  classification  intended  some  flexibility  in  test  duration 
and/or species and number of animals used. 

Guidelines for conducting acceptable tests with fish, crustacea, and algae can be found from many 
sources  (e.g.,  Test  Methods  Regulation  440/2008;  OECD  e.g.  the  OECD  monograph  No.11, 
Detailed Review Paper on Aquatic Toxicity Testing for Industrial Chemicals and Pesticides, 1999; 
EPA, 1996; ASTM, 1999; ISO standards; EU standards). 

Some general guidance on commonly faced issues with aquatic toxicity testing: 

•  Evidence  should  be  provided  that  test  concentrations/dose  levels  and  number  of 
concentrations  are  known  and  where  possible  evidence  should  be  provided  that 
concentrations have been maintained throughout the duration of the test. Therefore, mean 
measured  concentrations  are  preferred  over  nominal  (non-measured)  concentrations.  If 
mean measured concentrations are not within ±20% of nominal concentrations, effect values 
should  be  related  to  mean  measured  concentrations.  Where  test  concentrations  remain 
within ±20% of nominal, mean measured or nominal concentrations can be used, following 
expert judgement on a case-by-case basis. For flow-through studies the arithmetic mean of 
measured concentrations should be calculated. For static or semi-static tests the geometric 
mean of measured concentrations should be calculated (see IR&CSA Chapter R.7b, Appendix 
R.7.8—1). In some cases where only nominal concentrations are provided, expert judgement 
may be required to decide whether test concentrations are likely to have been maintained 
(Note, Nominal testing results on metals or metal compounds (those relevant for assessment 
under Annex IV according to Annex IV.1) cannot be used for hazard classification as further 
specified in Annex IV, In contrast, only nominal concentrations (from loading rates) can be 
used for multi-constituent substances tested using WAF approaches, see Annex I.4.5); 

•  Some substances, depending on their specific mode of action may produce toxic effects at 
time  points  earlier  than  those  typically  used  in  any  given  test  guideline.  In  such  cases, 
caution  should  be  exercised  and  evaluation  on  a  case-by-case  basis  is  required.  If  effect 
durations less than those indicated in the test guideline are to be accepted for classification 
purposes, the full test duration should be reported and the respective test guideline validity 
criteria for that end point must be fulfilled at the time to be used; 

•  Regarding rapidly degrading substances, studies conducted under flow-through and/or semi-
static (usually after 24 hours) conditions are preferred in order to maintain test concentration 
during  the  duration  of  the  study.  See  OECD  Guidance  23  (OECD  2019)  for  further 
information. 

•  There are instances where the only data available may lack test details described above. In 
such cases, expert judgement should be used to determine the suitability of the test for use 
in  classification  and  the  reliability  of  the  endpoint  values.  For  example,  there  should  be 
enough information to determine whether the test conditions are suitable for the organisms 
being  tested,  the  viability  of  the  test  organisms,  demonstration  of  exposure  of  the  test 
organisms,  a  suitable  concentration  range,  and  a  clear  dose  response  relationship  for 
endpoints of interest. Tests where such information is not available may not be suitable for 
classification and labelling. 

I.2.1 

Fish tests  

I.2.1.1    Acute testing 

Acute tests are generally performed with young juveniles 0.1 – 5 g in size for a period of 96 hours. 
The  observational  endpoint  in  these  tests  is  mortality.  Fish  larger  than  this  size  range  and/or 
durations  shorter  than  96  hours  are  generally  less  sensitive.  However,  for  classification,  they 
could be used if no acceptable data with the smaller fish for 96 hours are available or the results 
of  these  tests  with  different  size  fish  or  test  durations  would  influence  classification  in  a  more 

 
 
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hazardous category. Tests consistent with OECD TG 203 (Fish 96 hour LC50) or equivalent should 
be used for classification.  

The Fish Embryo Acute Toxicity (FET) Test (OECD TG 236) was adopted on the 26th July 2013 and 
its potential to fulfil the REACH information requirement on acute fish toxicity has been the subject 
of  an  ECHA  commissioned  study  (May  2015,  http://echa.europa.eu/  publications/technical-
scientific-reports), which highlighted certain regulatory limitations in its use and thus concluded 
that the FET test cannot be considered as stand-alone information for addressing the information 
requirement  for  acute  fish  toxicity  under  the  REACH  Regulation.  Based  on  current  knowledge, 
ECHA  considers  that  OECD  TG  236  might  best  be  used  within  a  Weight  of  Evidence  (WoE) 
approach together with other independent, adequate, relevant, and reliable sources of information 
for classification and labelling. However, if the only available information on the fish toxicity of a 
substance  is  the  FET,  the  test  can  be  used  for  classification,  even  if  no  other  information  for 
weight 
available 
evidence 
(https://www.echa.europa.eu/documents/10162/22931011/non_animal_approcches_en.pdf/87
ebb68f-2038-f597-fc33-f4003e9e7d7d).  

of 

is 

With regards to in vitro test methods, as new non-animal alternatives are developed (e.g. the fish 
cell line assay, OECD TG 249, adopted 2021), it may be possible to use these, as outlined for FET, 
to assess acute toxicity to fish provided that they fulfil relevant data quality requirements (IR&CSA 
Chapter R.7b, section R.7.8.4.1). 

I.2.1.2 

Chronic testing 

Chronic or long-term tests with fish can be initiated with fertilized eggs, embryos, juveniles, or 
reproductively active adults. Durations can vary widely depending on the test purpose (anywhere 
from  7  days  to  over  200  days).  Observational  endpoints  can  include  hatching  success,  growth 
(length and weight changes), spawning success, and survival. Tests consistent with OECD Test 
Guideline  210  (Fish  Early-life  Stage  Toxicity  Test,  FELS),  US  EPA  850.1500  (the  fish  life-cycle 
test),  or  equivalent  can  be  used  in  the  classification  scheme.  Currently,  other  relevant  tests 
include OECD TG 212 (Fish, Short-term Toxicity Test on Embryo and Sac-Fry Stages) and OECD 
TG 215 (Fish, Juvenile Growth Test). 

OECD TG 210 (FELS) is widely accepted as a predictor of chronic toxicity and is used as such for 
purposes of classification in the harmonised system, particularly as fish early-life stage toxicity 
data are much more available than fish life cycle or reproduction studies. Technically, the OECD 
TG 210 is not a ‘chronic’ test, but a sub-chronic test on sensitive life stages. 

However, it is preferred as it is considered to be more sensitive than the OECD TG 212 or OECD 
TG 215, covering several life stages of the fish from the newly fertilized egg, through hatch to 
early stages of growth (IR&CSA Chapter R.7b, section R.7.8.4.1). Moreover, the FELS toxicity test 
is  preferable  for  examining  the  potential  toxic  effects  of  substances  which  are,  for  example: 
expected to cause effects over a longer exposure period, which require a longer exposure period 
of time to reach steady state (in non flow-through test systems), substances that have a latency 
of effects, or a longer period to onset of maximum (often sub-lethal) effect. Regarding OECD TG 
212, care should be taken when interpreting data from this test to ensure that the test substance 
is not too lipophilic (e.g. Log Kow > 4), that there is no evidence of endocrine disrupting properties, 
or  other  specific  modes  of  action89.  For  further  guidance  on  the  use  of  OECD  TG  212  and 
information  on  the  animal  welfare  issues  related  to  this  test,  consult  OECD  171  (Fish  Toxicity 
Testing Framework). However, smaller differences in sensitivity between OECD TG 212 and 215 
would be expected for chemicals with a non-specific, narcotic mode of action (Kristensen, 1990). 

89 Following amendments to the REACH annexes (Reg (EU) 2022/477 of 24 March 2022) OECD TG 212 has been deleted 
as a new information requirement due to animal welfare concerns. However, an existing such test can be considered to 
fulfil the LT toxicity data requirement for fish at Annex IX. 

 
 
 
 
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OECD TG 215 measures the growth of juvenile fish over a fixed period of time and it is considered 
a sensitive indicator of toxicity for the growth endpoint. Although it does not cover all the sensitive 
points in the fish life cycle, as would normally be required of a chronic toxicity test such as the 
FELS test, it can be used, for example, when growth inhibition is the most relevant effect endpoint 
in fish. 

Where it has been determined that a substance has endocrine disrupting properties, tests such 
as the following may be available: 

OECD  TG  234  (Fish  Sexual  Development  Test  adopted  on  July  28th  2011)  is  in  principle  an 
enhancement  of  OECD  TG  210,  where  the  exposure  is  continued  until  the  fish  are  sexually 
differentiated, i.e. about 60 days post-hatch for Japanese medaka (Oryzias latipes), the three-
spined stickleback and zebrafish (the exposure period can be shorter or longer for other species 
that  are  validated  in  the  future),  and  endocrine-sensitive  endpoints  are  added.  OECD  TG  234 
currently  states  that  a  minimum  of  three  test  concentrations  should  be  used,  with  five  test 
concentrations recommended if the data are to be used for risk assessment. The use of five test 
concentrations is recommended in order to derive a more precise NOEC/LOEC or ECx value. It 
should be noted that vitellogenin (VTG) level is affected by exogenous oestrogen stimulation and 
cannot be used alone for aquatic hazard identification as an endpoint on its own. Rather, it can 
be used as part of a WoE approach when considered with other data on relevant related effects 
(e.g., this endpoint in combination with sex ratio endpoint can demonstrate the endocrine mode 
of action of the test substance). 

OECD TG 240 (adopted 28th July 2015) is an extended one generation test using Japanese medaka 
running  until  hatching  in  the  F2  generation.  This  test  provides  standard  long-term  toxicity 
endpoints (hatching and larval survival, growth i.e., length and body weight, etc.) but also has 
secondary  effect  endpoints  for  endocrine  disruption.  For  the  latter  (vitellogenin  etc.)  similar 
considerations as outlined for OECD TG 234 apply.  

Regarding  OECD  TG  204  (Fish,  Prolonged  Toxicity  Test:  14-day  Study),  OECD  has  deleted  the 
test  guideline  on  2nd  April  2014.  It  is  noted  that,  according  to  the  Guidance  on  Information 
Requirements and Chemical Safety Assessment (IR&CSA Chapter R.7b, section R.7.8.4.1), “tests 
performed according to OECD 204 or similar guidelines cannot be considered suitable long-term 
tests.  They  are,  in  effect,  prolonged  acute  studies  with  fish  mortality  as  the  major  endpoint 
examined”. 

I.2.2 

Tests with Aquatic Crustacea 

I.2.2.1 

Acute testing 

Acute tests with crustacea generally begin with first instar juveniles. For daphnids, test duration 
of 48 hours is used. For other crustacea, such as mysids or others, duration of 96 hours is typical. 
The  observational  endpoint  is  mortality  or  immobilisation  as  a  surrogate  to  mortality. 
Immobilisation is defined as unresponsive to gentle prodding. Tests consistent with OECD TG 202 
(Daphnia acute) or USA-EPA OPPTS 850.1035 (Mysid acute toxicity) or their equivalents should 
be used for classification.  

Although  crustacea  are  the  preferred  group  (Daphnia  magna  being  the  most  common  test 
species), other aquatic invertebrates can be considered on a case-by-case basis. As such, toxicity 
tests using aquatic insects (e.g., mayfly larvae , chironomids [OECD TG 235]) and molluscs can 
be  acceptable  for  hazard  classification,  providing  they  are  relevant  and  reliable.  Where  a 
substance has an intended target invertebrate group (e.g. insecticides), or a group of particular 
sensitivity,  data  from  such  a  group  or  species  may  be  available  in  addition  to  crustacea  (e.g., 
daphnids).  

 
 
 
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I.2.2.2 

Chronic testing 

Chronic tests with crustacea also generally begin with first instar juveniles and continue through 
maturation  and  reproduction.  Observational  endpoints  include  time  to  first  brood,  number  of 
offspring produced per female, growth, and survival. For daphnids, in particular Daphnia magna, 
21 days is sufficient for maturation and the production of at least 3 broods, while for mysids 28 
days  is  necessary,  and  Ceriodaphnia  dubia  produces  3  broods  within  7  days  (Connors  et  al., 
2022). It is recommended that tests consistent with OECD TG 211 (Daphnia reproduction), US-
EPA  850.1350  (Mysid  chronic),  ISO  20665  (chronic  toxiciy  to  Ceriodaphnia  dubia),  or  their 
equivalents be used in the classification scheme. Older data according to OECD TG 202 part II 
could in principle still be available for use pending a thorough assessment. 

Data from invertebrate  species  other than the crustacea mentioned  can be used, following the 
considerations outlined above in Annex I.2.2.1. Concerning the sediment-dwelling larvae of the 
freshwater  dipteran  Chironomus  sp.  (OECD  TG  218/219),  data  from  such  tests  can  be  used 
provided it can be demonstrated that exposure to the test material is through the water phase 
and not via sediment. For most substances, uptake from water (bioconcentration, defined as the 
net  result  of  uptake,  transformation,  and  elimination  of  a  substance  in  an  organism  due  to 
waterborne exposure) is believed to be the predominant route of exposure for aquatic organisms. 
For organic substances and metals, pore water is one of the primary exposure routes for benthic 
organisms (Di Toro et al., 1991; Ankley et al., 1991). However, for highly lipophilic compounds 
or  other  substances  that  adsorb  to  particles  (e.g.  metals),  uptake  from  food  or  sediment  may 
contribute to the overall exposure, depending on the living and feeding strategy of the exposed 
organisms. The importance of dietary exposure relative to water exposure as a cause of toxicity 
is currently not fully understood. 

In summary, factors that influence adsorption and thus distribution between sediment and water 
also influence toxicity to aquatic (pelagic and benthic) species. Generally, the substance must not 
partition to sediments to any great extent. The low sorption potential of the substance must be 
demonstrated, and the test design should use the water-spiking method. This may indicate that 
the organisms are exposed to the substance primarily via the water. When considering the life-
stage used in an available test, Chironomus spend their most sensitive larval stage (first instar) 
free swimming in the water phase and will therefore only be exposed via the water in this stage. 
Other  life-stages  will  involve  the  sediment  so  interpretation  of  results  may  be  less  straight- 
forward. Generally, where sediment is included in the test system, it must be clear what caused 
the observed toxicity, with regards to the exposure route. Test system equilibrium should favour 
exposure from the water phase. If it cannot be ruled out that the test organisms were exposed 
to the substance or metabolites adsorbed to the sediment particle surfaces, the test may not be 
relevant for classification purposes. 

I.2.3 

Algae / other aquatic plant tests 

I.2.3.1 

Tests with algae 

Algae  are  cultured  and  exposed  to  the  test  substance  in  a  nutrient-enriched  medium.  Tests 
consistent with OECD  TG 201 (Algal growth inhibition) should be used. Standard test methods 
employ  a  cell  density  in  the  inoculum  in  order  to  ensure  exponential  growth  through  the  test, 
usually 3 to 4 days duration. Annex 2 of OECD TG 201 (Algae) and IR&CSA R.7b report some of 
the species shown to be generally suitable for the testing and include green algae, diatoms, and 
cyanobacteria. 

The  algal  growth  inhibition  test  is  a  short-term  test  that  provides  both  acute  and  chronic 
endpoints. The EC50 is treated as an acute value for classification purposes. Classification shall be 
based on both, the algal growth rate reduction endpoint, ErC50 [= EC50 (growth rate)] and NOErC 
[= NOEC (growth rate)] or ECx  value, provided that the control growth is exponential (greater 
than a factor of 16) (where available, EC10 is preferred over NOEC, see 4.1.3.1.1). This endpoint 

 
 
 
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is  preferred  because  it  is  not  dependent  on  the  test  design,  whereas  the  endpoint  biomass 
(growth) inhibition (EbC50) depends on both, growth rate of the test species as well as test duration 
and other elements of test design.  

In circumstances where the basis of the EC50 is not specified and no ErC50 is recorded, classification 
shall be based  on the lowest EC50 available. Where the algal toxicity  ErC50 falls more than 100 
times below the next most  sensitive  species and results in a  classification based solely on this 
effect, consideration should be given to whether this toxicity is representative of the toxicity to 
aquatic plants. Where it can be shown that this is not the case, professional judgment should be 
used in deciding if classification should be applied. 

I.2.3.2 

Tests with aquatic macrophytes 

The most commonly used vascular plants for aquatic toxicity tests are duckweeds (Lemna gibba 
and  L.  minor).  The  tests  last  for  up  to  14  days  and  are  performed  in  nutrient  enriched  media 
similar  to  that  used  for  algae  but  may  be  increased  in  strength.  The  observational  endpoint  is 
based on change in the number of fronds produced. Tests consistent with OECD TG 221 on Lemna 
and  US-EPA  850.4400  (aquatic  plant  toxicity,  Lemna)  and  OECD  TG  238/239  (Myriophyllum 
spicatum) should be used. The observational endpoint for Myriophyllum spicatum is based on the 
vegetative growth.  Note that for tests using sediment (e.g.,  OECD TG 239), TG considerations 
regarding sediment should be followed and exposure should be from the water. 

The respective macrophyte TGs are considered to provide both acute and chronic endpoints over 
the experimental time periods specified. 

I.3 

Aquatic toxicity concepts 

This  section  addresses  the  use  of  acute  and  chronic  toxicity  data  in  classification,  and  special 
considerations for exposure regimes, algal toxicity testing, and use of (Q)SARs.  

I.3.1 

Acute toxicity 

Acute  toxicity  for  classification  purposes  refers  to  the  intrinsic  property  of  a  substance  to  be 
harmful to an organism in a short-term exposure to that substance. Acute toxicity is generally 
expressed  in  terms  of  a  concentration  which  is  lethal  to  50  %  of  the  test  organisms  (lethal 
concentration,  LC50),  causes  a  measurable  adverse  effect  to  50  %  of  the  test  organisms  (e.g. 
immobilisation  of  daphnids,  EC50),  or  leads  to  a  50  %  reduction  in  test  (treated)  organism 
responses from control (untreated) organism responses (e.g. growth rate in algae, ErC50). 

Acute aquatic toxicity is normally determined using a fish 96 hour LC50, a crustacea species 48 
hour EC50, an algal species 72 or 96 hour EC50 and/or aquatic plants 7 days EC50. These species 
cover a range of trophic levels and taxa and are considered as surrogate for all aquatic organisms. 
Data  on  other  species  shall  also  be  considered  if  the  test  methodology  is  suitable.  Since  the 
purpose of classification is to characterise hazard in the aquatic environment, the result showing 
the  highest  toxicity  should  be  chosen.  However,  there  are  circumstances  when  a  weight  of 
evidence approach is appropriate. 

Substances with an acute toxicity determined to be less than 1 mg/L are generally recognised as 
being very toxic. The handling, use, or discharge into the environment of these substances poses 
a high degree of hazard and they are classified in category Acute 1. When classifying substances 
as Acute 1, it is necessary at the same time to indicate an appropriate Multiplying factor, M-factor. 
M-factors are derived using the endpoint value used to derive the hazard category (see Section 
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I.3.2 

Chronic toxicity 

Chronic toxicity, for classification purposes, refers to the intrinsic property of a substance to cause 
adverse effects to aquatic organisms during  exposures which are determined in relation to the 
life-cycle of the organism. Such chronic effects usually include a range of sublethal endpoints and 
are generally expressed in terms of a No Observed Effect Concentration (NOEC), or an equivalent 
ECx. Observable endpoints typically include survival, growth and/or reproduction. Chronic toxicity 
exposure durations can vary widely depending on the test endpoint measured and test species 
used.  

For long-term hazard classification, a differentiation is made between rapidly degradable and non-
rapidly degradable substances. Substances that rapidly degrade are classified in category Chronic 
1 when the chronic toxicity NOEC or ECx is determined to be ≤ 0.01 mg/L. Rapidly degradable 
substances  with  a  chronic  toxicity  NOEC  or  ECx  between  0.01  and  0.1  mg/L  are  classified  in 
category Chronic 2. Rapidly degradable substances with a chronic toxicity NOEC or ECx between 
0.1 and 1.0 mg/L are classified in category Chronic 3. Finally, those rapidly degraded substances 
with chronic toxicity NOECs or ECxs over 1.0 mg/L are not classifiable for long-term hazard in any 
of the categories Chronic 1, 2 or 3.  

For substances that do not rapidly degrade, based on data or by default (i.e., default applies in 
cases where no information on rapid degradation is available), two chronic categories are used: 
category Chronic 1 if the chronic toxicity NOEC or ECx is determined to be ≤ 0.1 mg/L and category 
Chronic  2  if  the  chronic  toxicity  NOEC  or  ECx  is  determined  to  be  between  0.1  and  1.0  mg/L. 
Finally, those not rapidly degraded substances with chronic toxicity NOECs or ECxs over 1.0 mg/L 
are not classifiable for long-term hazard in any of the categories Chronic 1 or 2. Note, category 
Chronic 3 does not apply to non-rapidly degraded substances. 

When  classifying  substances  as  Chronic  1,  it  is  necessary  at  the  same  time  to  indicate  an 
appropriate M-factor. M-factors are derived using the endpoint value used to derive the hazard 
category (see Section 3). 

In the absence of chronic toxicity data, chronic hazard is identified by appropriate combinations 
of acute toxicity, lack of degradability, and/or the potential or actual bioaccumulation. However, 
where adequate chronic toxicity data exist (see section 4.1.3.3.1), this shall be used in preference 
over  the  classification  based  on  the  combination  of  acute  toxicity  with  degradability  and/or 
bioaccumulation. In this context, the following general approach should be used. 

a.  If  adequate  chronic  toxicity  data  are  available  for  all  three  trophic  levels,  this  is  used 

directly to determine an appropriate long-term hazard category. 

In cases where chronic toxicity data are available for all three trophic levels, but data are 
absent  for  the  most  acutely  sensitive  species,  the  chronic  toxicity  dataset  may  not  be 
considered  adequate  (see  Section  4.1.3.3.1).  In  such  cases,  it  may  be  appropriate  to 
derive  a  classification  using  available  acute  toxicity  data  for  the  most  acutely  sensitive 
species following the procedure outlined below (b); 

b.  If adequate chronic toxicity data are available for one or two trophic levels, it should be 
examined  if  acute  toxicity  data  are  available  for  the  other  trophic  level(s).  A  potential 
classification is made for the trophic level(s) with chronic toxicity data and compared with 
that made using the acute toxicity data for the other trophic level(s). The final classification 
shall  be  made  according  to  the  most  stringent  outcome  (Figure  4.1.1  and  Table 
4.1.0(b)(iii) of Annex I to CLP); 

c.  In  order  to  remove  or  downgrade  a  chronic  aquatic  classification,  using  chronic  toxicity 
data, it must be demonstrated that the NOEC(s) (or equivalent ECx) used would be suitable 
to remove or downgrade the concern for all taxa which resulted in classification based on 
acute data in combination with degradability, and/or bioaccumulation. This can often be 
achieved by using a long-term NOEC or ECx for the most sensitive species identified by the 
acute toxicity. Thus, if a  long-term hazard classification has been based on a fish acute 

 
 
 
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LC50, it would generally not be possible to remove or downgrade this classification using a 
long-term NOEC or ECx from an invertebrate toxicity test. In this case, the NOEC or ECx 
would normally need to be derived from a long-term fish test of the same species or one 
of  equivalent or greater sensitivity. Equally, if  classification has  resulted from the  acute 
toxicity  of  more  than  one  taxonomic  group,  it  is  likely  that  NOECs  or  ECxs  from  each 
taxonomic  group  will  be  needed.  In  case  of  classification  of  a  substance  as  Chronic  4, 
sufficient  evidence  should  be  provided  that  the  NOEC  or  ECx  or  equivalent  ECx  for  each 
taxonomic  group  is  greater  than  1  mg/L  or  greater  than  the  water  solubility  of  the 
substances under consideration. 

I.3.3 

Exposure regimes 

Three  types  of  exposure  conditions  are  employed  in  both  acute  and  chronic  tests  and  in  both 
freshwater and saltwater media: static, static-renewal (semi-static), and flow-through. The choice 
for which test type to use usually depends on test substance characteristics, test duration, test 
species, and regulatory requirements.  

I.3.4 

Test media for algae and Lemna 

Algal  and  Lemna  tests  are  performed  in  nutrient-enriched  media  and  use  of  one  common 
constituent, EDTA, or other chelators, should be considered carefully. When testing the toxicity 
of organic chemicals, trace amounts of a chelator like EDTA are needed to complex micronutrients 
in the culture medium; if omitted, growth can be significantly reduced and compromise test utility. 
However,  chelators  can  reduce  the  observed  toxicity  of  metal  test  substances.  Therefore,  for 
metal compounds, it is desirable that data from tests with high concentration of chelators and/or 
tests with stoichiometric excess of chelator relative to iron be critically evaluated. Free chelator 
may mask heavy metal toxicity considerably, in particular with strong chelators like EDTA (see 
Annex IV to this guidance on Metals and inorganic metal compounds). However, in the absence 
of  available  iron  in  the  medium  the  growth  of  algae  and  Lemna  can  become  iron  limited,  and 
consequently  data  from  tests  with  no  or  with  reduced  iron  and  EDTA  should  be  treated  with 
caution.  

I.3.5 

Use  of  substance  categorisation  (read-across  and  grouping)  and 
(Q)SARs for classification and labelling 

See Section 1.4 of this guidance. 

I.4 

Substances which are difficult to test 

The  following  paragraphs  provide  some  detailed  guidance  on  some  of  these  problems  of 
interpretation. In doing so it should be remembered that this is guidance and rigid rules cannot 
be applied. The nature of many of the difficulties means that expert judgement must always be 
applied both in determining whether there is sufficient information in a test for a judgement to 
be made on its validity, and also whether a toxicity level can be determined  that is suitable for 
use  in  applying  the  classification  criteria.  Metals  present  their  own  set  of  difficulties  and  are 
discussed separately (see Annex IV on metals). 

For classification of organic compounds, it is desirable to have stabilised and analytically measured 
test concentrations. Although measured concentrations are preferred, classification may, under 
certain circumstances, be based on studies where nominal concentrations are the only valid data 
available.  

If the material is likely to substantially degrade or otherwise be lost from the water column, care 
must be taken in data interpretation and classification should be done taking into account the loss 
of the toxicant during the test, if relevant and possible. In cases where loss of test material may 
occur,  actual  test  concentrations  are  likely  to  be  less  than  the  nominal  or  expected  test 

 
 
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concentrations  and  under-represent  the  actual  toxicity.  In  circumstances  where  a  substance  is 
known to be difficult to test, expert judgement is needed to determine the acceptability of such 
tests  for  use  in  classification.  Similarly,  caution  is  also  needed  when  deriving  appropriate  M-
factors. 

I.4.1 

Unstable substances 

While testing procedures which minimise the impacts of instability in the test media should ideally 
have  been  deployed,  in  practice,  in  certain  tests,  it  can  be  almost  impossible  to  maintain  a 
constant  concentration  throughout  the  test.  Common  causes  of  lack  of  constant  exposure 
concentration  during  the  test 
include  but  are  not  limited  to:  oxidation,  hydrolysis, 
photodegradation,  volatilisation,  sorption,  and  biodegradation.  While  the  latter  forms  of 
degradation can be more readily controlled, such controls may be absent in much existing testing. 
Nevertheless,  for  some  testing,  particularly  acute  and  chronic  fish  toxicity  testing,  a  choice  of 
exposure regimes is available to help minimise losses due to instability, and this should be taken 
into account in deciding on the test data validity. 

Where  instability  is  a  factor  in  determining  the  level  of  exposure  during  a  test,  an  essential 
prerequisite  for  data  interpretation  is  the  existence  of  measured  exposure  concentrations  at 
suitable time points throughout the test. In the absence of analytically measured concentrations 
at least at the start and end of the test, no valid interpretation can be made, and the test should 
be considered as invalid for classification purposes. Where measured data are available, a number 
of practical guidelines can be considered:  

a.  where measured data are available for the start and end of the test (as is normal for the 
acute Daphnia and algal tests), the L(E)C50, for classification purposes, may be calculated 
based  on  the  geometric  mean  concentration  of  the  start  and  end  of  test.  Where 
concentrations  at  the  end  of  the  test  are  below  the  analytical  detection  limit,  such 
concentrations shall be considered to be half of that detection limit; 

b.  where measured data are available at the start and end of media renewal periods (as may 
be available for the semi-static tests), the geometric mean for each renewal period should 
be  calculated,  and  the  mean  exposure  over  the  whole  exposure  period  calculated  from 
these data; 

c.  where  the  toxicity  can  be  attributed  to  a  degradation  breakdown  product,  and  the 
concentrations of this product are known, the L(E)C50 for classification purposes may be 
calculated based on the geometric mean of the degradation product concentration, back 
calculated to the parent substance; 

d.  similar principles may be applied to measured data in chronic toxicity testing.  

I.4.2 

Poorly soluble substances 

These substances, usually taken to be those with a solubility in water of < 1 mg/L, are frequently 
difficult to dissolve in the test media, and the dissolved concentrations will often prove difficult to 
measure at the low concentrations  anticipated. For many substances,  the true solubility in the 
test  media  will  be  unknown  and  will  often  be  recorded  as  below  the  detection  limit  in  purified 
water. Nevertheless  such substances can  show toxicity and, where no toxicity is  found,  expert 
judgement  must  be  applied  to  whether  the  result  can  be  considered  valid  for  classification. 
Judgement  should  err  on  the  side  of  caution  and  should  not  underestimate  the  hazard.  Here, 
OECD Guidance 23 (OECD 2019) provides guidance on how to proceed. 

Ideally,  tests  using  appropriate  dissolution  techniques  and  with  accurately  measured 
concentrations  within  the  range  of  water  solubility  should  be  used.  Where  such  test  data  are 
available,  they  should  be  used  in  preference  to  other  data.  It  is  normal,  however,  particularly 
when  considering  older  data,  to  find  substances  with  toxicity  levels  recorded  in  excess  of  the 
water  solubility,  or  where  the  dissolved  levels  are  below  the  detection  limit  of  the  analytical 
method.  Thus,  in  both  circumstances,  it  is  not  possible  to  verify  the  actual  exposure 

 
 
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concentrations using measured data. Where these are the only data available on which to classify, 
some practical rules can be considered by way of general guidance: 

a.  where the acute toxicity is recorded at levels in excess of the water solubility, the L(E)C50 
for classification purposes may be considered to be equal to or below the measured water 
solubility. In making this decision, due attention should be paid to the possibility that the 
excess  undissolved  substance  may  have  given  rise  to  physical  effects  on  the  test 
organisms.  Where  this  is  considered  the  likely  cause  of  the  effects  observed,  the  test 
should be considered as invalid for classification purposes; 

b.  where no acute toxicity is recorded at levels in excess of the water solubility, the L(E)C 50 
for  classification  purposes  may  be  considered  to  be  greater  than  the  measured  water 
solubility. In such circumstances, consideration should be given to whether the category 
Chronic 4 should apply. In making a decision that the substance shows no acute toxicity, 
due account should be taken of the techniques used to achieve the maximum dissolved 
concentrations. Where these are not considered as adequate, the test should be considered 
as invalid for classification purposes; 

c.  where  the  water  solubility  is  below  the  detection  limit  of  the  analytical  method  for  a 
substance, and acute toxicity is recorded, the L(E)C50 for classification purposes may be 
considered to be below the analytical detection limit. Where no toxicity is observed, the 
L(E)C50  for  classification  purposes,  may  be  considered  to  be  greater  than  the  water 
solubility. Due consideration should also be given to the quality criteria mentioned above; 

d.  where chronic toxicity data are available, the same general rules should apply. In principle, 
only data showing no observed effect concentrations at levels above the water solubility 
limit,  or  greater  than  1  mg/L  need  be  considered.  Again,  where  these  data  cannot  be 
validated  by  analytically  verified/  measured  concentrations,  the  techniques  used  to 
achieve the maximum dissolved concentrations must be considered as appropriate. 

I.4.3 

Other factors contributing to concentration loss 

A number of other factors can also contribute to losses of test material from solution and, while 
some  can  be  avoided  by  correct  study  design,  interpretation  of  data  where  these  factors  have 
contributed will be necessary. 

a.  sedimentation:  this  can  occur  during  a  test  for  a  number  of  reasons.  A  common 
explanation is that the substance has not truly dissolved despite the apparent absence of 
particulates, and agglomeration occurs during  the test leading to precipitation. In these 
circumstances, the L(E)C50 for classification purposes, may be considered to be based on 
the end of test concentrations. Equally, precipitation can occur through reaction with the 
media. This is considered under instability above; 

b.  adsorption: this can occur for substances of high adsorption characteristics such as high 
Log Koc/log Kow substances or some substances with a permanent charge (such as some 
cationic  surfactants).  Where  this  occurs,  the  loss  of  concentration  is  usually  rapid,  and 
exposure may best be characterised by the end of test concentrations; 

c.  bioaccumulation: losses may occur due to the bioaccumulation of a substance into the test 
organisms. This may be particularly important where the water  solubility is low and log 
Kow correspondingly high. The L(E)C50 for classification purposes, may be calculated based 
on the geometric mean of the start and end of test concentrations. 

I.4.4 

Perturbation of the test media 

Strong acids and bases may exert their toxicity through extreme pH. However, changes of the pH 
in aquatic systems are normally prevented by buffer systems in the test medium. If no data are 
available on a salt, the salt should generally be classified in the same way as the anion or cation, 
i.e., as the ion that receives the most stringent classification. If the effect concentration is related 

 
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to only one of the ions, the classification of the salt should take the molecular weight difference 
into  consideration  by  correcting  the  effect  concentration  by  multiplying  with  the  ratio: 
MWsalt/MWion. 

Polymers  are  typically  not  available  in  aquatic  systems.  Dispersible  polymers  and  other  high 
molecular mass materials can perturb the test system and interfere with uptake of oxygen and 
give rise to mechanical or secondary effects. These factors need to be taken into account when 
considering  data  from  these  substances.  Many  polymers  behave  like  complex  substances, 
however, having a significant low molecular mass fraction which can leach from the bulk polymer. 
This is considered further below. 

I.4.5 

Complex substances 

Complex  substances  (UVCBs  and  multi-constituent  substances)  (OECD  series  on  testing  and 
assessment  Number  23,  Guidance  Document  on  Aquatic  Toxicity  Testing  of  Difficult  to  Test 
Substances and Mixtures) are characterised by a range of chemical structures, covering a wide 
range  of  water  solubilities  and  other  physico-chemical  characteristics.  In  addition  to  water, 
equilibrium  will  be  reached  between  the  dissolved  and  undissolved  fractions  which  will  be 
characteristic  of  the  loading  of  the  substance.  For  this  reason,  such  complex  substances  are 
usually  tested  as  a  WSF  or  WAF,  and  the  L(E)C50  recorded  based  on  the  loading  or  nominal 
concentrations. Analytical support data are not normally available since the dissolved fraction will 
itself be a complex mixture of components. The toxicity parameter is sometimes referred to as 
LL50,  related  to  the  lethal  loading  level.  This  loading  level  from  the  WSF  or  WAF  may  be  used 
directly in the classification criteria. Whilst taking a constituent based approach may be required 
for  assessing  rapid  degradability  and  bioaccumulation,  in  the  absence  of  adequate  whole 
substance aquatic toxicity data the mixtures approaches (following figure 4.1.2 of CLP) can be 
followed. 

Polymers represent a special kind of complex substance, requiring consideration of the polymer 
type  and  their  dissolution/dispersal  behaviour.  Polymers  may  dissolve  as  such  without  change 
(true  solubility  related  to  particle  size),  be  dispersible,  or  portions  consisting  of  low  molecular 
weight fractions may go into solution. In the latter case, in effect, the testing of a polymer is a 
test of the ability of low molecular mass material to leach from the bulk polymer, and whether 
this leachate is toxic. It can thus be considered in the same way as a complex mixture in that a 
loading of polymer can  best characterise the  resultant leachate, and hence the toxicity can be 
related to this loading. 

I.5 

References 

Ankley GT, Schubauer-Berigan MK, Dierkes JR (1991) Predicting the toxicity of bulking to 
aquatic organisms with aqueous test fractions: Pore water vs. elutriate, Environ Toxicol Chem 
10:1359-1366. 

US EPA 1996. Ecological Effects Test Guidelines - OPPTS Harmonized Test Guidelines Series 
850.1000 -- Public Drafts, EPA 712-C-96-113. 
http://www.epa.gov/ocspp/pubs/frs/publications/OPPTS_Harmonized/850_Ecological_Effects_T
est_Guidelines/Drafts/850-1000.pdf  

ASTM 1999. Annual book of ASTM standards, Vol. 11.04. American Society for Testing and 
Materials, Philadelphia, PA 

Connors KA, Brill JL, Norberg-King T, Barron MG, Carr G, and Belanger SE (2022) Daphnia 
magna and Ceriodaphnia dubia Have Similar Sensitivity in Standard Acute and Chronic Toxicity 
Tests, Environ Toxicol Chem 41:134-147 

 
 
 
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Di Toro DM, Zarba CS, Hansen DJ, Berry WJ, Swartz RC, Cowan CE, Pavlou SP, Allen HE, 
Thomas NA, Paquin PR (1991) Technical basis for establishing sediment quality criteria for 
nonionic organic chemicals using equilibrium partitioning. Environ Toxicol Chem 10:1541-1583. 

ISO guidelines: http://www.iso.org/iso/iso_catalogue.htm 

Kristensen, P. (1990) Evaluation of the Sensitivity of Short Term Early Life Stage tests in 
relation to other FELS test methods. Final Report to the Commission of the European 
Communities, 60 pp. 

Test Methods Regulation (EC) No 440/2008. http://eur-
lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2008:142:0001:0739:en:PDF 

OECD 171: Fish Toxicity Testing Framework 
https://www.oecd.org/officialdocuments/publicdisplaydocumentpdf/?cote=ENV/JM/MONO%282
012%2916&doclanguage=en 

OECD (2019), Guidance Document on Aquatic Toxicity Testing of Difficult Substances and 
Mixtures, OECD Series on Testing and Assessment, OECD Publishing, Paris, 
https://doi.org/10.1787/0ed2f88e-en.  

 
 
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II  ANNEX II: RAPID DEGRADATION 

II.1 

Introduction 

Degradability is one of the important properties of substances that has an impact on the potential 
for  substances  to  exert  an  aquatic  hazard.  Non-degradable  substances  will  persist  in  the 
environment  and  may  consequently  have  a  potential  for  causing  long-term  adverse  effects  on 
biota. In contrast, degradable substances may be removed in the sewers, in sewage treatment 
plants or in the environment. It should be noted that data from degradability tests on mixtures 
are difficult or impossible to interpret and are therefore not used in classification and labelling. 

Classification of substances is primarily based on their intrinsic properties. However, the degree 
of degradation depends not only on the intrinsic degradability or  recalcitrance of the molecule, 
but  also  on  the  actual  conditions  in  the  receiving  environmental  compartment  such  as  redox 
potential, pH, temperature, presence of suitable micro-organisms, concentration of the substance 
and  occurrence  and  concentration  of  other  substrates.  The  interpretation  of  the  degradation 
properties  in  an  aquatic  hazard  classification  context  therefore  requires  detailed  criteria  which 
consider the intrinsic properties of the substance and the prevailing environmental conditions into 
a concluding statement on the potential for long-term adverse effects. 

The term degradation is defined in Section 4.1 of Annex I to CLP as ‘the decomposition of organic 
molecules to smaller molecules and eventually to carbon dioxide, water and salts’. For inorganic 
compounds  and  metals,  the  concept  of  degradability  has  limited  or  no  meaning.  Rather  the 
substance may be transformed by normal environmental processes to either increase or decrease 
the bioavailability of the toxic species. Therefore, the present section applies only to organic and 
organometal compounds. A separate section on the classification & labelling (C&L) of metals is 
provided in Part 4.4.1.5 and Annex IV to the CLP guidance. 

Data on degradation properties of a substance may be available from standardised tests, or from 
other types of investigations, or they may be estimated from the structure of the molecules i.e. 
via  SAR  or  (Q)SAR  approaches.  The  interpretation  of  such  degradation  data  for  classification 
purposes often requires detailed evaluation of the (test) data. The use of biodegradation data for 
classification purposes is only applicable to substances. Biodegradation data on mixtures cannot 
be used as it does not provide a reliable indication of environmental fate (CLP Annex I,  section 
4.1.3.3.1).  

II.2 

Interpretation of degradability data 

Based on the harmonised criteria (CLP I.4.1.2.9), guidance for interpretation of degradation data 
is presented below.  

II.2.1 

Ready biodegradability 

Ready biodegradability is defined in the OECD Test Guidelines No. 301 methods A-F (OECD 1992), 
OECD TG 306 (marine water) and OECD TG 310 (OECD 2006). All organic substances that degrade 
to a level higher than the pass level in a standard OECD ready biodegradability or a similar test 
should be considered readily biodegradable, and consequently also rapidly degradable. Many test 
data  found  in  the  open  literature,  however,  do  not  specify  all  of  the  conditions  that  should  be 
evaluated  to  demonstrate  whether  or  not  the  test  fulfils  the  requirements  of  a  ready 
biodegradability test. Expert judgement is therefore needed  as regards the validity of the data 
before use for classification purposes.  

Regarding marine data, OECD TG 306 series on Biodegradability in Seawater includes seawater 
variants of the Closed Bottle Test (OECD 301 D) and of the Modified OECD Screening Test (OECD 
301 E). Degradation of substances in seawater has generally been found to be slower than that 
in freshwater tests inoculated with activated sludge or sewage effluent. This is also confirmed in 

 
 
 
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the research program  conducted in CEFIC LRI  ECO11 project, where it was demonstrated that 
both magnitude and variation in the bacterial diversity were higher in the following order for the 
different environmental sources: activated sludge > rivers > estuaries > sea water. 

OECD  test  guideline  306  explicitly  indicates  that  results  of  those  tests  (shake  flask  and  closed 
bottle) "are not to be taken as indications of ready biodegradability, but are to be used specifically 
for obtaining information about the biodegradability of chemicals in marine environments". Those 
tests "are not tests for ready biodegradability since no inoculum is added in addition to the micro-
organisms already present in the seawater. Neither do the tests simulate the marine environment 
since nutrients are added and the concentration of test substance is very much higher than would 
be present in the sea". However, it is acknowledged that biodegradation in seawater is generally 
slower.  Therefore  >60%  ThOD  or  >70%  DOC  removal  in  a  Biodegradability  in  Seawater  test 
(OECD  306)  obtained  after  28  day  (Closed  Bottle  Method)  or  60  day  (Shake  Flask  Method)  is 
indicative  of  potential  for  ultimate  biodegradation  in  the  marine  environment  and  can  also  be 
regarded  as  a  piece  of  evidence  that  the  substance  is  likely  to  fulfil  the  criteria  for  ready 
biodegradability. For example, a positive OECD TG 306 test is regarded as an indication of rapid 
degradation for classification and labelling. However, if the ratio of inoculum to substrate in the 
test  system  is  enhanced  by  increasing  the  concentration  of  micro-organisms  as  it  has  been 
proposed recently in Ott et al. (2020), this also increases the degradation potential. In this case 
the test system does not resemble a pelagic water body anymore and is thus less stringent. This 
has  consequences  for  interpretation  of  the  so  produced  degradation  data  with  respect  to 
conclusion  on  ready  biodegradation  behaviour  as  such  enhancements  will  render  the  test 
unsuitable for assessing ready biodegradability (rapid degradation) under CLP. 

Before  concluding  on  the  ready  biodegradability  of  a  test  substance,  however,  at  least  the 
following parameters should be considered.  

II.2.1.1  Concentration of test substance 

Relatively high concentrations of test substance are used in the OECD ready biodegradability tests 
(2-100  mg/L).  Many  substances  may  however  be  toxic  to  the  inoculum  at  such  high 
concentrations,  resulting  in  a  low  degradation  of  the  substances  in  these  tests,  although  the 
substances  might  be  rapidly  degradable  at  lower  non-toxic  concentrations.  A  toxicity  test  with 
micro-organisms  (e.g.,  OECD  TG  209),  or  inhibition  of  the  inoculum  observed  with  a  positive 
control substance may demonstrate the toxicity of the test substance. Guidance on the selection 
of suitable microbial inhibition test methods is provided in IR&CSA Chapter R.7b, section R7.8.18. 
When it is likely that inhibition is the reason for a substance being not readily degradable, results 
from a test employing lower non-toxic concentrations of the test substance should be used when 
available.  

II.2.1.2  Time window 

The harmonised criteria include a general requirement for all of the ready biodegradability tests 
on achievement of the pass level within ten days of the onset of biodegradation. This is not in line 
with  the  OECD  TG  301  in  which  the  10-day  time  window  applies  to  the  OECD  ready 
biodegradability tests except the MITI I test (OECD TG 301C). Furthermore, in the Closed Bottle 
test (OECD TG 301D), a 14-day window may be used instead when measurements have not been 
made after ten days or are not possible due to experimental design. However, occasionally only 
limited  information  is  available  for  biodegradation  tests.  Thus,  as  a  pragmatic  approach,  the 
percentage of degradation reached after 28 days may be used directly for assessment of ready 
biodegradability  when  no  information  on  the  10-day  time  window  is  available.  This  should, 
however, only be accepted for existing  experimental studies and test results where the 10-day 
window  does  not  apply  or  is  not  available.  Tests  following  current  test  guidelines  should  allow 
assessment of the 10-day window, where appropriate.  

Where  there  is  sufficient  justification,  the  10-day  window  condition  may  be  waived  for  certain 
complex substances and the pass level is applied at 28 days. This applies to multi-constituent and 

 
 
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certain UVCB substances (such as oils and surfactants) consisting of structural similar constituents 
with different chain-lengths, degree and/or site of branching or stereoisomers, even in their most 
purified commercial forms. Testing of each individual constituent may be costly and impractical. 
If  a  test  on  such  a  complex  substance  is  performed  and  it  is  anticipated  that  a  sequential 
biodegradation of the individual constituents is taking place, then the 10-day window should not 
be  applied  to  interpret  the  results  of  the  test.  A  case  by  case  evaluation  should  however  take 
place  on  whether  a  biodegradability  test  on  such  a  substance  would  give  valuable  information 
regarding its biodegradability as such i.e. regarding the degradability of all the constituents, or 
whether instead an investigation of the degradability of carefully selected individual constituents 
of the complex substance is required (OECD 2006). 

II.2.2 

BOD5/COD 

Information  on  the  5-day  biochemical  oxygen  demand  (BOD5)  will  be  used  for  classification 
purposes only when no other measured degradability data are available. Thus, priority is given to 
data from ready biodegradability tests and from simulation studies regarding degradability in the 
aquatic  environment.  Therefore,  this  test  should  not  be  performed  anymore  for  assessment  of 
the ready biodegradability of substances. Older test data may however be used when no other 
degradability  data  are  available.  For  substances  where  the  chemical  structure  is  known,  the 
theoretical oxygen demand (ThOD) can be calculated and this value should be used instead of 
the chemical oxygen demand (COD).  

II.2.3  Other convincing scientific evidence 

Rapid degradation in the aquatic environment may be demonstrated by other data than a ready 
biodegradability  test,  or  a  BOD5/COD  ratio.  These  may  be  data  on  biotic  and/or  abiotic 
degradation. Data  on primary degradation  can only be used where it  is demonstrated that the 
degradation  products  do  not  fulfil  the  criteria  for  classification  as  hazardous  to  the  aquatic 
environment. 

The fulfilment of criterion (c) of paragraph 4.1.2.9.5 of CLP (other convincing scientific evidence) 
requires that the substance is degraded in the aquatic environment to a level of > 70 % within a 
28-day  period.  If  first-order  kinetics  are  assumed,  which  is  reasonable  at  the  low  substance 
concentrations  prevailing  in  most  aquatic  environments,  the  degradation  rate  will  be  relatively 
constant for the 28-day period. Thus, the degradation requirement will be fulfilled with an average 
degradation rate constant, k > -(ln 0.3 - ln 1)/28 = 0.043 day-1. This corresponds to a degradation 
half-life, t½ < ln 2/0.043 = 16 days.  

Moreover, as degradation processes are temperature dependent, this parameter should also be 
taken into account when assessing degradation in the environment. Data from studies employing 
environmentally realistic temperatures e.g. 5 – 25 °C should be used for the evaluation. When 
data from studies performed at different temperatures need to be compared, the traditional Q10 
approach could be used, i.e. that the degradation rate is halved when the temperature decreases 
by 10°C.  

The evaluation of data in the context of rapid degradation should be conducted on a case-by-case 
basis by expert judgement. However, guidance on the interpretation of various types of data that 
may be used for demonstrating a rapid degradation in the aquatic environment is given below. In 
general, only data from aquatic biodegradation simulation tests are considered directly applicable 
(e.g.,  OECD  TG  309).  However  simulation  test  data  from  other  environmental  compartments 
could be considered as well (e.g., OECD TG 308), but such data require in general more scientific 
judgement before use. 

II.2.3.1  Aquatic simulation tests 

Aquatic simulation tests (e.g. Aerobic Mineralisation in Surface Water – Simulation Biodegradation 
Test,  OECD  TG  309)  are  tests  conducted  in  the  laboratory,  but  simulating  environmental 

 
 
  
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conditions and employing natural samples as inoculum. Results of aquatic simulation tests may 
be  used  directly  for  classification  purposes,  when  realistic  environmental  conditions  in  surface 
waters are simulated, i.e.: 

a.  substance concentration that is realistic for the general aquatic environment (often in the 

low µg/L range); 

b.  inoculum from a relevant aquatic environment; 

c.  realistic concentration of inoculum (103-106 cells/mL); 

d.  realistic  temperature  e.g.  5  °C  to  25  °C,  with  12  °C  being  the  average  surface  water 
temperature in the EU (see Table R.16-8 in IR&CSA Chapter R.16 “Environmental exposure 
estimation”), that can be considered under CLP; 

e.  ultimate  degradation  is  determined  i.e.,  determination  of  the  mineralisation  rate  or  the 

individual degradation rates of the total biodegradation pathway. 

II.2.3.2  Field investigations 

Parallel to laboratory simulation tests are field investigations or mesocosm experiments. In such 
studies, fate and/or effects of chemicals in the environment or in environmental enclosures may 
be  investigated.  Fate  data  from  such  experiments  can  in  principle  be  used  for  assessing  the 
potential for a rapid degradation. This may, however, often be difficult, as it requires that ultimate 
degradation can be demonstrated. This may be documented by preparing mass balances showing 
that no non-degradable intermediates are formed, and which take the fractions into account that 
are removed from the aqueous system due to other processes such as sorption to sediment or 
volatilisation from the aquatic environment.  

II.2.3.3  Monitoring data 

Monitoring data may demonstrate the removal  of  contaminants from the aquatic  environment. 
Such data are, however, very difficult to use for classification purposes, although detection of an 
anthropogenic substance in groundwater could be an indication that the substance is not rapidly 
degradable. The following aspects should be considered before use: 

a.  Is  the  removal  a  result  of  degradation,  or  is  it  a  result  of  other  processes  such  as 

dilution or distribution between compartments (sorption, volatilisation)? 

b.  Is formation of non-degradable intermediates excluded? 

Only  when  it  can  be  demonstrated  that  removal  as  a  result  of  ultimate  degradation  fulfils  the 
criteria for rapid degradability, can such data be considered for use for classification purposes. In 
general, monitoring data should only be used as supporting evidence for demonstration of either 
persistence in the aquatic environment, or of rapid degradation. 

II.2.3.4  Inherent and Enhanced Ready Biodegradability tests 

Substances that are degraded more than 70% in tests  for inherent biodegradability (OECD  TG 
302) have the potential for ultimate biodegradation. However, because of the optimised conditions 
in  these  tests,  the  rapid  biodegradability  of  inherently  biodegradable  substances  in  the 
environment  cannot  be  assumed.  The  optimised  conditions  in  inherent  biodegradability  tests 
stimulate  adaptation  of  the  micro-organisms  thus  increasing  the  biodegradation  potential, 
compared  to  natural  environments.  Therefore,  positive  results  in  general  should  not  be 
interpreted as evidence for rapid degradation in the environment. 

IR&CSA Chapters R.7b and R.11 refer in the context of persistence testing to a new category of 
tests,  i.e.  the  ‘enhanced  ready  (screening)  biodegradability  tests’.  These  are  in  essence  ready 
biodegradability  tests  to  which  more  flexibility  is  given  to  demonstrate  the  occurrence  of 
degradation e.g. via prolonged testing times, larger test volumes, adaptation, etc. These methods 
are not yet validated and/or standardised for C&L.  

 
 
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II.2.3.5  Sewage treatment plant simulation tests 

Results from tests simulating the conditions in a sewage treatment plant (STP) e.g. the OECD TG 
303 (Simulation Test - Aerobic Sewage Treatment -- A: Activated Sludge Units; B: Biofilms) and 
OECD  TG  314  B  (Simulation  Tests  to  Assess  the  Biodegradability  of  Chemicals  Discharged  in 
Wastewater)  cannot  be  used  for  assessing  the  degradation  in  the  aquatic  environment,  for 
classification  purposes.  The  main  reasons  for  this  are  that  the  microbial  biomass  in  a  STP  is 
significantly different from the biomass in the environment, that there is a considerably different 
composition  of  substrates,  and  that  the  presence  of  rapidly  mineralised  organic  matter  in 
wastewater may facilitate degradation of the test substance by co-metabolism. 

II.2.3.6  Soil and sediment degradation data 

It  has  been  argued  that  for  many  non-sorptive  substances  comparable  degradation  rates  are 
found in soil and in surface water. For sorptive substances, a lower degradation rate may generally 
be expected in soil than in water due to a lower bioavailability caused by sorption. Thus, when a 
substance has been shown to be degraded rapidly in a soil simulation study, it is most likely also 
rapidly  degradable  in  the  aquatic  environment.  It  is  therefore  proposed  that  in  the  absence  of 
aquatic  degradation  data  an  experimentally  determined  rapid  degradation  in  soil  is  sufficient 
documentation for a rapid degradation in surface waters when: 

a.  no pre-exposure (pre-adaptation) of the soil micro-organisms has taken place; and 

b.  an environmentally realistic concentration of substance is tested; and 

c.  the  substance  is  ultimately  degraded  within  28  days  with  a  half-life  < 16  days 

corresponding to a degradation rate > 0.043 day-1 . 

The same argumentation is considered valid for data on degradation in sediment under aerobic 
conditions. 

II.2.3.7  Anaerobic degradation data 

Data regarding anaerobic degradation (e.g., OECD TG 311) cannot be used to decide whether a 
substance  should  be  regarded  as  rapidly  degradable  for  classification  purposes,  because  the 
aqueous  phase  of  the  aquatic  environment  is  generally  regarded  as  the  aerobic  compartment 
where  the  aquatic  organisms,  such  as  those  of  relevance  for  aquatic  hazard  classification,  are 
found. 

II.2.3.8  Hydrolysis 

Data on hydrolysis e.g. OECD TG 111 might be considered for classification purposes only when 
the  longest  half-life  t½  determined  within  the  pH  range  4-9  is  shorter  than  16  days.  However, 
hydrolysis is not an ultimate degradation and various intermediate degradation products may be 
formed,  some  of  which  may  be  only  slowly  degradable.  Only  when  it  can  be  satisfactorily 
demonstrated  that  the  hydrolysis  products  formed  do  not  fulfil  the  criteria  for  classification  as 
hazardous for the aquatic environment, data from hydrolysis studies could be considered. 

When a substance is quickly hydrolysed e.g. with t½ < a few days, this process is a part of the 
degradation  determined  in  biodegradation  tests.  Hydrolysis  may  be  the  initial  transformation 
process in biodegradation.  

II.2.3.9  Photochemical degradation 

Information on photochemical degradation e.g. OECD TG 316 is difficult to use for classification 
purposes. The actual degree of photochemical degradation in the aquatic environment depends 
on local conditions e.g. water depth, suspended solids, turbidity as well as seasonal influences, 
and  the  hazard  of  the  degradation  products  is  usually  not  known.  Probably  only  seldom  will 
adequate information be available for a thorough evaluation based on photochemical degradation. 

 
 
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II.2.3.10  Estimation of degradation 

Hydrolysis:  Certain  (Q)SARs  have  been  developed  for  prediction  of  an  approximate  hydrolysis 
half-life, which should only be considered when no experimental data are available, or in a Weight 
of Evidence approach. However, a hydrolysis half-life can only be used with great care in relation 
to classification, because hydrolysis does not concern ultimate degradability (see ‘Hydrolysis’ of 
this Section). Furthermore the  (Q)SARs developed until now have a rather limited applicability 
and are only able to predict the potential for hydrolysis on a limited number of chemical classes 
(see also IR&CSA Chapter R.7b, section R.7.9.3.1).  

Biodegradation:  In  general,  no  quantitative  estimation  method  ((Q)SAR)  for  estimating  the 
degree  of  biodegradability  of  organic  substances  is  yet  sufficiently  accurate  to  unequivocally 
predict  rapid  degradation.  However,  results  from  such  methods  may  be  used  to  predict  that  a 
substance is not rapidly degradable or be used in a Weight of Evidence approach. For example, 
when  in  the  Biodegradation  Probability  Program  e.g.  BIOWIN  version  3.67,  Syracuse  Research 
Corporation the probability is < 0.5 estimated by the linear or non-linear methods, the substances 
should be regarded as not rapidly degradable (OECD, 1994; Pedersen et al., 1995 & Langenberg 
et al., 1996). Also other (Q)SAR methods may be used as well as expert judgement, for example, 
when degradation data for structurally analogue compounds are available, but such judgement 
should be conducted with great care. See also IR&CSA Chapter R.7b, section R.7.9.3.1. 

In general, a (Q)SAR prediction that the substance is not rapidly degradable is considered a better 
justification  for  classification  than  application  of  a  default  classification,  when  no  useful 
degradation data are available.  

Degradation  data  from  structurally  related  substances  may  provide  evidence  that  a  given 
substance displays very similar degradation properties. Such information may be employed in a 
read-across or weight of evidence approach for C&L.  

II.2.3.11  Volatilisation 

Chemicals  may  be  removed  from  some  aquatic  environments  by  volatilisation.  The  intrinsic 
potential for volatilisation is determined by the Henry's Law constant (H) of the substance. Apart 
from the substance’s physical-chemical properties, volatilisation from the aquatic environment is 
also  highly  dependent  on  the  environmental  conditions  of  the  specific  water  body  in  question, 
such as the water depth, the gas exchange coefficients (depending on wind speed and water flow) 
and stratification of the water body. Because volatilisation only represents removal of a chemical 
from  the  water  phase,  and  not  degradation,  the  Henry's  Law  constant  cannot  be  used  for 
assessment  of  degradation  in  relation  to  aquatic  hazard  classification  of  substances  (see  also 
Pedersen et al., 1995). 

II.2.4  No degradation data available 

When  no  useful  data  on  degradability  are  available  -  either  experimentally  determined  or 
estimated data - the substance should be regarded by default as not rapidly degradable. 

II.3  General interpretation problems 

II.3.1 

Complex substances 

The harmonised criteria for classification of chemicals as hazardous for the aquatic environment 
refer  to  single  substances.  However,  complex  substances  also  need  to  be  considered  for 
classification and labelling and these are normally considered as single substances in a regulatory 
context.  Some  complex  substances  such  as  multi-constituent  substances  of  natural  origin, 
chemicals  that  are  produced  or  extracted  from  mineral  oil  or  plant  material,  etc.,  are  highly 
complex with a high number of constituents, many of which may be unidentified. The constituents 
of  a  complex  substance  can  be  highly  varied  and  possess  a  wide  range  of  physical-chemical 

 
 
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properties  important  for  aquatic  degradation  assessment  (e.g.,  water  solubility,  Log  kow, 
adsorption characteristics, and volatility). Therefore, it may not be possible to make a degradation 
assessment using a test on the whole complex substance  and data  on known constituents will 
need to be considered to assess the whole substance. Occasionally, complex substances may be 
defined as a homologous series of substances within a certain range of carbon chain length and/or 
degree of substitution. When this is the case, no major difference in degradability is foreseen and 
the degree of degradability can be established from tests of the complex chemical. Occasionally, 
a  borderline  degradation  is  found  because  some  of  the  individual  constituents  may  be  rapidly 
degradable  and  others  may  not  be  rapidly  degradable.  As  above,  this  requires  a  detailed 
assessment of the degradability of the individual constituents in the complex  substance. When 
the  constituents  that  are  not-rapidly-degradable  constitute  a  significant  part  of  the  complex 
substance  e.g.  more  than  20  %,  or  for  a  hazardous  constituent,  an  even  lower  content,  the 
substance should be regarded as not rapidly degradable.  

II.3.2 

Availability of the substance 

The  present  standard  methods  for  investigating  degradability  of  substances  are  developed  for 
readily soluble test compounds. However, many organic substances are only slightly soluble in 
water. As the standard tests (OECD TG 301 suite and 310) recommend 2-100 mg/L of the test 
substance, sufficient availability may not be reached for substances with low water solubility. In 
general, the DOC Die-Away test (OECD TG 301A) and the Modified OECD Screening test (OECD 
Test Guideline 301E) are less suitable for testing the biodegradability of poorly soluble substances 
since  adsorption  may  be  confused  with  degradation.  In  such  cases,  test  adaptations  may  be 
considered  with  e.g.  continuous  mixing  and/or  an  increased  exposure  time.  Also  tests  with  a 
special design, where concentrations of the test substance lower than the water solubility have 
been employed e.g. with radiolabelled test chemicals, could be relevant.  

II.3.3 

Test duration less than 28 days 

Sometimes degradation is reported for tests terminated before the 28 day period specified in the 
standards e.g. the MITI, 1992. These data are of course directly applicable when a degradation 
greater than or equal to the pass level is obtained. When a lower degradation level is reached, 
the results need to be interpreted with caution. One possibility is that the duration of the test was 
too  short  and  that  the  chemical  structure  would  probably  have  been  degraded  in  a  28-day 
biodegradability test. If substantial degradation  occurs within a short time period, the situation 
may be compared with the criterion BOD5/COD  0.5 or with the requirements on degradation 
within the 10-day time window. In these cases, a substance may be considered readily degradable 
(and hence rapidly degradable), if: 

a.  the ultimate biodegradability exceeds 50 % within 5 days; or  

b.  the  ultimate  degradation  rate  constant  in  this  period  is  greater  than  0.1  day-1 

corresponding to a half-life of 7 days.  

These criteria are proposed in order to ensure that rapid mineralisation did occur, although the 
test was ended before 28 days and before the pass level was attained. Interpretation of test data 
that  do  not  comply  with  the  prescribed  pass  levels  must  be  made  with  great  caution.  It  is 
mandatory to consider whether a biodegradability result below the pass level was due to a partial 
degradation  of  the  substance  and  not  a  complete  mineralisation.  If  partial  degradation  is  the 
probable explanation for the observed biodegradability, the substance should be considered not 
readily biodegradable. 

II.3.4 

Primary biodegradation 

In  some  tests,  only  the  disappearance  of  the  parent  compound  i.e.  primary  degradation  is 
determined  for  example  by  following  the  degradation  by  specific  or  group  specific  chemical 
analyses of the test substance. Data on primary biodegradability may be used for demonstrating 

 
 
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rapid degradability only when it can be satisfactorily demonstrated that the degradation products 
formed do not fulfil the criteria for classification as hazardous to the aquatic environment. 

II.3.5 

Conflicting results from screening tests 

Where  data  from  more  than  one  experimental  degradation  study  are  available  for  the  same 
substance, there is a possibility that the results may be conflicting. The IR&CSA Chapter R.7b, 
section  R.7.9.4.1  indicates  that  ready  biodegradability  tests  may  sometime  fail  because  of  the 
stringent test conditions, positive test results should generally supersede negative test results in 
cases  where  good  quality  experimental  studies  are  presented.  However,  when  conflicting  test 
results are reported, possible differences in the test conditions and design should be investigated. 
In particular the origin of the inoculum should be examined in order to verify whether or not there 
are differences in the adaptation of the inoculum which may explain the differences in the results 
(OECD, 2006b). Also, differing results always have to be assessed considering the test conditions, 
substance properties and reliability of the data. Good data reliability depends on the test method 
applied,  statistical  robustness  of  the  study  and  its  reporting  which  in  turn  depend  on  several 
factors, e.g. number of replicates, and number of controls. 

The  suitability  of  the  inoculum  for  degrading  the  test  substance  depends  on  the  presence  and 
amount of competent degraders. When the inoculum is obtained from an environment that has 
previously been exposed to the test substance, the inoculum may be adapted as demonstrated 
by a degradation capacity greater than that of an inoculum from a non-exposed environment. As 
far as possible the inoculum must be sampled from an unexposed environment, but for substances 
that are used ubiquitously in high volumes and released widespread or more or less continuously, 
this may be difficult or impossible. When conflicting results are obtained, the origin and density 
of the inoculum should be checked in order to clarify whether or not differences in the adaptation 
of the microbial community may be the reason.  

As mentioned above, many substances may be toxic or inhibitory to the inoculum at the relatively 
high concentrations tested in ready biodegradability tests. This is especially likely in the Modified 
MITI (I) test (OECD TG 301C) and the Manometric Respirometry test (OECD Test Guideline 301F) 
where  high  concentrations  (100  mg/L)  are  prescribed,  compared  to  the  low  test  substance 
concentrations prescribed in the Closed Bottle test (OECD Test Guideline 301D) where 2-10 mg/L 
is  used.  The  possibility  of  toxic  effects  may  be  evaluated  by  including  a  toxicity  control  in  the 
ready biodegradability test or by comparing the test concentration with toxicity test data on micro-
organisms (for test methods see IR&CSA Chapter R.7b, section R.7.8.14) or by assessing whether 
there is evidence of inhibition of intrinsic respiration in the ready biodegradability test (e.g., lower 
respiration  in  the  test  item  vessel  compared  to  the  blank  inoculum  may  be  indicative  of  an 
inhibitory effect). 

Volatile substances should only be tested in closed systems, such as the Closed Bottle test (OECD 
Test Guideline 301D), the MITI I test (OECD Test Guideline 301C) the Manometric Respirometry 
test (OECD Test Guideline 301F), or OECD 310 (CO2 in sealed vessels – Headspace Test). Results 
from other tests should be evaluated carefully and only considered if it can be demonstrated, e.g. 
by mass balance estimates, that the removal of the test substance is not a result of volatilisation.  

II.3.6 

Variation in simulation test data 

A number of simulation test data may be available for certain high priority chemicals. Often such 
data  can  provide  a  range  of  half-lives  for  various  environmental  media  such  as  soil,  sediment 
and/or surface water. The observed differences in half-lives from simulation tests performed on 
the same substance may reflect differences in test conditions, all of which may be environmentally 
relevant. A suitable conservative half-life, i.e. a realistic worst case of the observed range of half-
lives  from  such  investigations,  should  be  selected  for  classification  by  employing  a  weight  of 
evidence approach and taking the realism and relevance of the employed tests into account in 
relation  to  environmental  conditions.  In  general,  simulation  test  data  of  surface  waters  (e.g., 

 
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OECD  TG  309)  are  preferred  relative  to  aquatic  sediment  or  soil  simulation  test  data  for  the 
evaluation of rapid degradability in the aquatic environment.  

II.4  Decision scheme 

The following decision scheme may be used as a general guidance to facilitate decisions in relation 
to rapid degradability in the aquatic environment and classification of chemicals hazardous to the 
aquatic environment. 

A substance is considered to be  not rapidly degradable  unless at least one  of the following is 
fulfilled: 

c.  The  substance  is  demonstrated  to  be  readily  biodegradable  in  a  28-day  test  for  ready 
biodegradability. The pass level of the test (70 % DOC removal or 60 % theoretical oxygen 
demand) must be achieved within 10 days from the onset of biodegradation, if it is possible 
to evaluate this according to the available test data (the 10-day window condition may be 
waived for complex multi-component substances and the pass level applied at 28 days, as 
discussed in II.2.1.2). If this is not possible, then the pass level should be evaluated within 
a 14-day time window if possible, or after the end of the test; or 

d.  The  substance is demonstrated to be ultimately degraded in a  surface water  simulation 
test  with  a  half-life  of  < 16  days  (corresponding  to  a  degradation  of  >  70  %  within  28 
days); or 

e.  The substance is demonstrated to be primarily degraded biotically or abiotically e.g. via 
hydrolysis,  in  the  aquatic  environment  with  a  half-life  <  16  days  (corresponding  to  a 
degradation of > 70 % within 28 days), and it can be demonstrated that the degradation 
products do not fulfil the criteria for classification as hazardous to the aquatic environment. 

When these preferred data types are not available rapid degradation may be demonstrated if one 
of the following criteria is justified: 

a.  The substance is demonstrated to be ultimately degraded in an aquatic sediment or soil 
simulation test with a half-life of < 16 days (corresponding to a degradation of > 70 % 
within 28 days); or 

b.  In  those  cases  where  only  BOD5  and  COD  data  are  available,  the  ratio  of  BOD5/COD  is 
greater than or equal to 0.5. The same criterion applies to ready biodegradability tests of 
a shorter duration than 28 days, if the half-life furthermore is < 7 days; or 

c.  A weight of evidence approach based on read-across provides convincing evidence that a 

given substance is rapidly degradable.  

If none of the above types of data are available, then the substance is considered as not rapidly 
degradable. This decision may be supported by fulfilment of at least one of the following criteria: 

i.  the substance is not inherently degradable in an inherent biodegradability test; or 

ii.  the substance is predicted to be slowly biodegradable by scientifically valid (Q)SARs, 
e.g.  for  the  Biodegradation  Probability  Program,  the  score  for  rapid  degradation 
(linear or non-linear model) < 0.5; or 

iii. the substance is considered to be not rapidly degradable based on indirect evidence, 

such as knowledge from structurally similar substances; or 

iv. no other data regarding degradability are available. 

 
 
 
 
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II.5  References 

OECD (2006). Revised introduction to the OECD guidelines for testing of chemicals, section 3. 
OECD, 23 March 2006. 

OECD (1992), OECD Test Guidelines No. 301 methods A-F 

Ott A, Martin TJ, Acharya K, Lyon DY, Robinson N, Rowles B, Snape JR, Still I, Whale GF, 
Albright III VC, Bäverbäck P, Best N, Commander R, Eickhoff C, Finn S, Hidding B, Maischak H, 
Sowders KA, Taruki M, Walton HE, Wennberg AC, and Davenport RJ (2020) Multi-laboratory 
Validation of a New Marine Biodegradation Screening Test for Chemical Persistence Assessment, 
Environmental Science & Technology 54 (7), 4210-4220 

Pedersen, F., H. Tyle, J. R. Niemeldi, B. Guttmann, L. Lander, and A. Wedebrand (1995) 
Environmental Hazard Classification – data collection and interpretation guide. TemaNord 
1995:581 

Langenberg J.H., W.J.G.M. Peijnenburg & E. Rorije (1996). On the usefulness and reliability of 
existing QSBRs for risk assessment and priority setting. SAR and (Q)SAR in Environmental 
Research 5, 1-16 

 
 
 
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III  ANNEX III: BIOACCUMULATION 

III.1  Introduction 

Bioaccumulation  of  a  substance  by  an  organism  is  not  in  itself  a  hazard.  However,  the 
bioaccumulation of a substance should be considered in relation to the potential for that substance 
to  exert  long-term  effects.  Chemical  concentration  and  accumulation  may  result  in  internal 
concentrations of a substance in an organism (body burden), which may or may not lead to toxic 
effects  over 
from  water 
long-term  exposures.  For  most  organic  chemicals  uptake 
(bioconcentration) is believed to be the predominant route of uptake. Only for very hydrophobic 
substances  does  uptake  from  food  become  important.  The  classification  criteria  use  the 
bioconcentration factor (BCF) or, in the absence of it, the octanol/water partition coefficient (log 
Kow) as the measure of the potential for bioaccumulation. For these reasons, the present guidance 
document  mainly  considers  bioconcentration  and  does  not  discuss  in  detail  uptake  via  food  or 
other routes. However, the possibility to use information on the biomagnification factor (BMF) as 
supportive evidence for bioaccumulation of highly lipophilic substances may be taken into account 
on a case by case basis.  

Classification of a substance is primarily based on its intrinsic properties. However, the degree of 
bioconcentration also depends on factors such as the degree of bioavailability, the physiology of 
test organism, maintenance of constant exposure concentration, exposure duration, metabolism 
inside  the  body  of  the  target  organism  and  excretion  from  the  body.  The  interpretation  of  the 
bioconcentration potential in a chemical classification context therefore requires an evaluation of 
the intrinsic properties of the substance, as well as of the experimental conditions under which 
bioconcentration  factor  (BCF)  has  been  determined.  IR&CSA  Chapter  R.7c,  section  7.10.5.1 
discusses  the  suitability  of  bioconcentration  data,  log  Kow  data  and  other  information  (e.g. 
evidence  for  limited  bioaccumulation  potential)  for  classification  purposes.  Use  of  measured 
biomagnification data is discussed in relation to the screening approach in IR&CSA Chapter R.7c, 
section 7.10.4.5. Bioaccumulation of metals is discussed in Annex IV. 

Information on the bioaccumulation potential of a substance may be available from standardised 
tests  or  may  be  estimated  from  the  structure  of  the  molecule.  The  interpretation  of  such 
bioconcentration data for classification purposes often requires detailed evaluation of test data. 
Guidance has been developed in IR&CSA in order to  facilitate this evaluation.  IR&CSA  Chapter 
R.7a, section 7.1.8 gives guidance on n-octanol/water partition coefficient and IR&CSA Chapter 
R.7c,  section  7.10.4  gives  guidance  on  how  to  evaluate  laboratory  data  on  aquatic 
bioaccumulation. The use of bioaccumulation data for classification purposes is only applicable to 
substances. Bioaccumulation data on mixtures cannot be used as it does not provide a reliable 
indication of environmental fate (CLP Annex I, section 4.1.3.3.1). 

III.2  Interpretation of bioconcentration data 

Aquatic  hazard  classification  of  a  substance  is  normally  based  on  existing  data  on  its 
environmental  properties.  Test  data  will  only  seldom  be  produced  with  the  main  purpose  of 
facilitating  a  classification.  Often  a  diverse  range  of  test  data  is  available  which  does  not 
necessarily match the classification criteria. Further guidance on how to use this data is given in 
IR&CSA Chapter R.7c, section. 

Bioconcentration of an organic substance can be experimentally determined in bioconcentration 
experiments, during which BCF is measured as the concentration in the organism relative to the 
concentration  in  water  under  steady-state  conditions  and/or  estimated  from  the  uptake  rate 
constant and the elimination rate constant. In general, the potential of an organic substance to 
bioconcentrate is primarily related to the lipophilicity of the substance. A measure of lipophilicity 
is  the  n-octanol/water  partition  coefficient  (Kow)  which,  for  lipophilic  non-ionised  organic 
substances,  undergoing  minimal  metabolism  or  biotransformation  within  the  organism,  is 

 
 
 
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correlated  with  the  bioconcentration  factor.  Therefore,  Kow  is  often  used  for  estimating  the 
bioconcentration of non-ionised organic substances, based on the empirical relationship between 
log  BCF  and  log  Kow.  For  those  organic  substances,  estimation  methods  are  available  for 
calculating  the  Kow.  Data  on  the  bioconcentration  properties  of  non-ionised  organic  substances 
may thus be (i) experimentally determined, (ii) estimated from experimentally determined Kow, 
or (iii) estimated from Kow values derived by use of Quantitative Structure Activity Relationships 
((Q)SARs).  Guidance for interpretation of such data is given in  IR&CSA Chapter R.7c, sections 
7.10.4 and 7.10.5. Guidance is also given on ionised chemicals and other classes that need special 
attention (see Annex III.3.1).  

III.2.1  Bioconcentration factor (BCF) 

The bioconcentration factor is defined as the ratio on a weight basis between the concentration 
of the chemical in biota and the concentration in the surrounding medium, here water, at steady 
state.  BCF  can  thus  be  experimentally  derived  under  steady-state  conditions,  on  the  basis  of 
measured concentrations. In addition BCF can also be calculated as the ratio between the first-
order  uptake  and  elimination  rate  constants;  a  method  which  does  not  require  steady  state 
(equilibrium conditions). 

Experimentally derived BCF values of high quality studies are ultimately preferred for classification 
purposes as such data override surrogate data, e.g. Kow. High quality data are defined as data 
where the validity criteria for the test method applied are fulfilled and described. Further guidance 
is provided in IR&CSA Chapter R.7c, section 7.10.4. BCF results of poor or questionable quality 
may give an erroneous BCF value. Therefore, such data should be carefully evaluated before use 
and consideration should be given to using Kow instead. 

Different test guidelines for the experimental determination of bioconcentration in fish have been 
documented and adopted, the most generally applied being the OECD TG 305 (OECD, 2012; C.13 
in Test Methods Regulation 440/2008 is a corresponding test). If there is no BCF value for fish 
species, high-quality data on the BCF value for invertebrate species may be used. An invertebrate 
(mussel, oyster or scallop) BCF can be used as a worst case (conservative) value for fish. BCF for 
algae should not be used.  

Experimental  BCF  data  on  highly  lipophilic  substances  (e.g.  with  log  Kow  above  6)  will  have  a 
higher level of uncertainty than BCF values determined for less lipophilic substances. For highly 
lipophilic  substances,  e.g.  with  log  Kow  above  6,  experimentally  derived  BCF  values  tend  to 
decrease  with  increasing  log  Kow.  Conceptual  explanations  of  this  non-linearity  mainly  refer  to 
either reduced membrane permeation kinetics or reduced biotic lipid solubility for large molecules. 
A low bioavailability and uptake of these substances in the organism will thus occur. Other factors 
relate  to  experimental  considerations,  such  as  equilibrium  not  being  reached,  reduced 
bioavailability  due  to  sorption  to  organic  matter  in  the  aqueous  phase,  and  analytical  errors. 
Special care should thus be taken when evaluating experimental data on BCF for highly lipophilic 
substances as these data will have a much higher level of uncertainty than BCF values determined 
for less lipophilic substances. 

III.2.1.1  BCF in different test species 

BCF values used for classification are based on whole body measurements. As stated previously, 
the optimal data for classification are BCF values derived using OECD TG 305 or corresponding 
EU test guideline C.13 or internationally equivalent methods, which uses small fish. Due to the 
higher  gill  surface-to-weight  ratio  in  smaller  organisms  than  in  larger  ones,  steady-state 
conditions  will  be  reached  sooner  in  smaller  organisms  than  in  larger  ones.  The  size  of  the 
organisms (fish) used in bioconcentration studies is thus of considerable importance in relation to 
the time used in the uptake phase,  when the  reported BCF value is based  solely  on measured 
concentrations in fish and water at steady-state. Thus, if large fish, e.g. adult salmon, have been 
used in bioconcentration studies, it should be evaluated whether the uptake period was sufficiently 
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precisely. Also possible  growth dilution should  be taken into account  when calculating the BCF 
values for smaller fish that grow during the bioconcentration studies. 

Furthermore, when using existing data for classification, it is possible that the BCF values could 
be derived from several different fish or other aquatic species (e.g. clams) and for different organs 
in the fish. Thus, to compare diverse measured BCF data from different species to each other and 
to the criteria, normalisation to common basis lipid content will be required to reduce variability. 
Detailed guidance can be found in IR&CSA Chapter R.7c, section 7.10.4.1 for 'correction factors'.  

Generally, the highest valid BCF value expressed on this common lipid basis is used to determine 
the wet weight based BCF-value in relation to the cut off value for BCF of 500 of the classification 
criteria. 

III.2.1.2  Use of radio-labelled substances 

The use of radio-labelled test substances can facilitate the analytical measurements in water and 
fish samples. The BCF from radio-labelled studies should, preferentially, be based on the parent 
compound.  If  these  are  unavailable,  for  classification  purposes,  the  BCF  based  on  total  radio-
labelled  residues  can  be  used.  If  the  BCF,  in  terms  of  radio-labelled  residues,  is  ≥  1000,  the 
identification  and  quantification  of  degradation  products  documented  to  be  ≥  10  %  of  total 
residues in fish tissues at steady state, are strongly recommended. This is because when using 
radio-labelled substances, the labelling is most often placed in the stable part of the molecule, for 
which reason the measured BCF value represents both the parent substance and takes account 
of  the  radio  labelled  part  of  the  metabolites  (i.e.,  the  BCF  represents  the  whole  undegraded 
molecule).  Thus,  unless  combined  with  a  specific  analytical  method,  the  total  radioactivity 
measurements  potentially  reflect  the  presence  of  the  parent  substance  as  well  as  possible 
metabolite(s) and possible metabolised carbon, which have been incorporated in the fish tissue 
in  organic  molecules.  BCF  values  determined  by  use  of  radio-labelled  test  substances  are 
therefore  normally  overestimated.  Also,  for  some  substances  it  is  the  metabolite  which  is  the 
most  toxic  or  which  has  the  highest  bioconcentration  potential.  Therefore,  selective 
measurements of the parent substance as well as the metabolites may thus be important for the 
interpretation of the aquatic hazard (including the bioconcentration potential) of such substances. 
In experiments where radio-labelled substances have been used, high radio-label concentrations 
are often found in the gall bladder of fish. This is interpreted to be caused by biotransformation 
in the liver and subsequently by excretion of metabolites in the gall bladder (Comotto et al., 1979; 
Wakabayashi et al., 1987; Goodrich et al., 1991; Toshima et al., 1992).  

When  fish  do  not  eat,  the  content  of  the  gall  bladder  is  not  emptied  into  the  gut,  and  high 
concentrations of metabolites may build up in the gall bladder. The feeding regime may thus have 
a pronounced effect on the measured BCF. In the literature many studies are found where radio-
labelled compounds are used, and where the fish are not fed. In these studies the bioconcentration 
may  in  most  cases  have  been  overestimated.  As  these  concepts  are  of  limited  applicability  to 
metals and metal compounds (relevant for assessment for assessment under Annex IV according 
to Annex IV.1), please see Annex IV.4 for more information. 

III.2.2  Octanol-water-partitioning coefficient (Kow) 

For organic substances experimentally derived high-quality Kow values are preferred over other 
determinations  of  Kow.  When  no  experimental  data  of  high  quality  are  available,  validated 
Quantitative  Structure  Activity  Relationship  ((Q)SAR)  results  for  log  Kow  may  be  used  in  the 
classification  process.  Such  (Q)SAR  results  may  be  used  without  modification  to  the  agreed 
criteria when they meet the validity criteria indicated in IR&CSA Chapter R.6. These requirements 
include, among others, the use of a scientifically valid model and that the substance falls within 
its applicability domain. For substances like strong acids and bases, substances which react with 
the eluent, or surface-active substances, a (Q)SAR estimated value of Kow, or an estimate based 
on  individual  n-octanol  and  water  solubilities  should  be  provided  instead  of  an  analytical 
determination  of  Kow.  For  ionisable  substances,  measurements  should  be  taken  on  their  non-
ionised form (free acid or free base) only by using an appropriate buffer with pH below pK for free 

 
 
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acid  or  above  the  pK  for  free  base.  Similarly,  (Q)SAR  estimates  should  be  based  on  the  non-
ionised structure. If multiple log Kow data are available for the same substance, the reasons for 
any differences should be assessed before selecting a value. Generally, the highest valid value 
should take precedence. 

III.2.2.1  Experimental determination of Kow 

For experimental determination of Kow values, several different methods are described in standard 
guidelines. IR&CSA Chapter R.7a, section 7.1.8.3 gives guidance on direct measurement methods 
(Shake Flask Method, Generator Column Method, and Slow Stirring Method), and on one indirect 
measurement method (Reverse Phase HPLC Method).  

III.2.2.2  Use of (Q)SARs for determination of log Kow and BCF 

Numerous (Q)SARs have been and continue to be developed for the estimation of Kow and BCF. 
When  an  estimated  Kow  value  is  found,  the  estimation  method  has  to  be  taken  into  account. 
Further guidance is also provided in IR&CSA Chapter R.7a, section 7.1.8.4. (Q)SARs can also be 
used to derive BCF values. However, as CLP (I.4.1.2.8) clearly prefers experimental BCF data and 
experimental log Kow data where available, (Q)SAR BCF data can only be considered as part of a 
broader WoE approach. As for other endpoints derived using (Q)SARs, careful attention should 
be paid to the validity of the result as further detailed in IR&CSA Chapter R.6. It should be noted 
that due to the wording of  CLP (I.4.1.2.8), (Q)SAR BCF data cannot  be used as a  one  for  one 
substitute  for  experimental  BCF  or  log  Kow  data.  Furthermore,  following  the  weighting  of  data 
described above (Q)SAR BCFs derived using as input experimental data (e.g., log Kow and intrinsic 
clearance data from OECD TG 319A and B) should generally be given greater weight than those 
where  the  log  Kow  and  other  source  data  is  calculated.  Examples  of  freely  available  (Q)SAR 
software  programs  that  include  models  for  the  prediction  of  log  Kow  and  BCF  are  EPISuite 
(https://www.epa.gov/tsca-screening-tools/epi-suitetm-estimation-program-interface),  OECD 
(Q)SAR Toolbox (https://qsartoolbox.org/) and VEGA (https://www.vegahub.eu/).   

III.3  Chemical classes that need special attention with respect to BCF and Kow 

values 

There are certain physico-chemical properties of substances, which can make the determination 
of BCF or its measurement difficult. These may be substances, which do not bioconcentrate in a 
manner  consistent  with  their  other  physico-chemical  properties,  e.g.  steric  hindrance  or 
substances which make the use of descriptors inappropriate, e.g. surface activity, which makes 
both the measurement and use of log Kow inappropriate. 

III.3.1  Substances difficult to test  

The methods presented above are generally designed for non-ionised organic substances. They 
are therefore  of limited usefulness  for a large  number  of  other substances, collectively termed 
difficult  substances,  which  include  complex  mixtures  and  chemicals  that  are  charged  at 
environmental  pH  (such  as  inorganic  compounds).  Substances  difficult  to  test  may  be  poorly 
soluble  substances,  complex  mixtures,  high  molecular  weight  substances,  surface  active 
substances,  inorganic  substances,  ionisable  substances,  or  organic  substances  that  do  not 
partition to lipid. Some guidance is given in this Chapter. More detailed guidance is provided in 
IR&CSA Chapter R.7c, mainly in Appendix R.7.10-3.  

In order to bioconcentrate in aquatic organisms, an organic substance needs to be present in the 
water, available for transfer across the fish gills and soluble in lipids. Factors that may alter this 
availability will thus change the actual bioconcentration of a substance, when compared with the 
prediction.  For  example,  readily  biodegradable  substances  may  only  be  present  in  the  aquatic 
compartment  for  short  periods  of  time.  Similarly,  volatility,  and  hydrolysis  will  reduce  the 
concentration and the time during which a substance is available for uptake. A further important 

 
 
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parameter, which may reduce the actual exposure concentration of a substance, is adsorption, 
either to particulate matter or to surfaces in general.  

There are a number of substances, which have shown to be rapidly transformed in the organism, 
thus leading to a lower BCF value than expected. Substances that form micelles or aggregates 
may  bioconcentrate  to  a  lower  extent  than  would  be  predicted  from  simple  physico-chemical 
properties,  e.g.,  water  solubility.  This  is  also  the  case  for  hydrophobic  substances  that  are 
contained in micelles formed as a consequence of the use of dispersants. Therefore, the use of 
dispersants in bioaccumulation tests is discouraged. Further guidance is given in IR&CSA Chapter 
R.7c, section 7.10.3.4 on how to consider the factors that affect the bioaccumulation potential of 
many substances and that are important especially in the absence of a fully valid BCF test result. 

In general, for substances difficult to test, measured BCF and Kow values – based on the parent 
substance  –  are  a  prerequisite  for  the  determination  of  the  bioconcentration  potential. 
Furthermore, proper documentation of the test concentration is a prerequisite for the validation 
of the given BCF value. 

III.3.2  Poorly soluble and complex substances 

Special attention should be paid to poorly soluble substances. Frequently the solubility of these 
substances is recorded as less than the detection limit, which creates problems in interpreting the 
bioconcentration potential. Where the test data indicate that the concentrations in the study are 
below the limit of detection, then the test is invalid and cannot be used. For such substances the 
bioconcentration potential should be based on experimental determination of log Kow or (Q)SAR 
estimations  of  log  Kow  (see  Annex  III.2.2).  Complex  substances  contain  a  range  of  individual 
substances which can have a great variation in their physico-chemical and toxicological properties. 
It is generally not recommended to estimate an average or weighted BCF value. It is preferable 
to identify one or more representative constituents for further consideration. Further guidance is 
given in IR&CSA Chapter R.7c, Appendix R.7.10-3.  

III.3.3  High molecular weight substances 

A  number  of  regulatory  systems  use  molecular  weight  as  an  indicator  for  reduced  or  minimal 
bioconcentration.  It  is,  however,  concluded  in  IR&CSA  Chapter  R.7c,  section  7.10.3.4  that 
molecular  mass  and  size  should  not  be  used  in  isolation  as  confirmatory  evidence  of  lack  of 
bioaccumulation  (ECETOC  2005).  However,  supported  by  other  data  and  by  employing  expert 
judgement,  it  may  be  concluded  by  a  weight  of  evidence  argument  that  such  substances  are 
unlikely to have a high bioconcentration factor (regardless of the log Kow value). More details can 
be found in PBT assessment guidance (IR&CSA Chapter R.11). 

III.3.4  Surface-active substances (surfactants) 

Surfactants consist of a  non-polar, lipophilic part (most often an alkyl  chain) (the hydrophobic 
tail)  and  a  polar  part  (the  hydrophilic  headgroup).  According  to  the  charge  of  the  headgroup, 
surfactants are subdivided into classes of anionic, cationic, non-ionic, or amphoteric surfactants. 
Due  to  the  variety  of  different  headgroups,  surfactants  are  a  structurally  diverse  class  of 
compounds,  which  is  defined  by  surface  activity  rather  than  by  chemical  structure.  The 
bioaccumulation  potential  of  surfactants  should  thus  be  considered  in  relation  to  the  different 
subclasses  (anionic,  cationic,  non-ionic,  or  amphoteric)  instead  of  to  the  group  as  a  whole. 
Surface-active substances may form emulsions, in which the bioavailability is difficult to ascertain. 
Micelle formation can result in a change of the bioavailable fraction even when the solutions are 
apparently formed, thus giving problems in interpretation of the bioaccumulation potential. See 
IR&CSA Chapter R.7c, Appendix R.7.10-3 for further guidance. 

Measured (experimentally derived) BCF  values  on surfactants show that BCF tends to increase 
with increasing alkyl chain length and be dependent on the site of attachment of the head group, 
other structural features and whether the alkyl part is subject to biotransformation. 

 
 
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III.3.4.1  Octanol-water-partition coefficient (Kow) 

The octanol-water partition coefficient for surfactants cannot be determined using the shake-flask 
or  slow  stirring  method  because  of  the  formation  of  emulsions.  In  addition,  the  surfactant 
molecules will exist in the water phase almost exclusively as ions, whereas they will have to pair 
with a counter-ion in order to be dissolved in octanol. Therefore, experimental determination of 
Kow does not characterise the partition of ionic surfactants (Tolls, 1998). On the other hand, it has 
been  shown  that  the  bioconcentration  of  anionic  and  non-ionic  surfactants  increases  with 
increasing lipophilicity (Tolls, 1998). Tolls (1998) showed that for some surfactants, an estimated 
log Kow value using LOGKOW could represent the bioaccumulation potential; however, for other 
surfactants some ‘correction’ to the estimated log Kow value using the method of Roberts (1989) 
was required. These results illustrate that the quality of the relationship between log Kow estimates 
and bioconcentration depends on the class and specific type of surfactants involved. Therefore, 
the classification of the bioconcentration potential based on log Kow values should be used with 
caution. Further guidance is provided in IR&CSA Chapter R.7c, Appendix R.7.10-3. 

III.4  Conflicting data and lack of data 

III.4.1  Conflicting BCF data 

When multiple BCF data are available for the same substance, the possibility of conflicting results 
may arise. In general,  conflicting results for a  substance, which has been tested  several times 
with  an  appropriate  bioconcentration  test,  should  be  interpreted  by  a  ‘weight  of  evidence 
approach’. This implies that if experimentally determined BCF data, both ≥ and < 500, have been 
obtained for a substance, the data of the highest quality and with the best documentation should 
be used for determining the bioconcentration potential of the substance. If differences still remain, 
for example high-quality BCF values for different fish species are available, generally the highest 
valid value should be used as the basis for classification. When larger data sets (4 or more values) 
are available for the same species and life stage, the geometric mean of the BCF values may be 
used as the representative BCF value for that species (IR&CSA Chapter R.7c, section R.7.10.4.6). 

III.4.2  Conflicting log Kow data 

When  multiple  log  Kow  data  are  available  for  the  same  substance,  the  possibility  of  conflicting 
results might arise. If log Kow data both ≥ and < 4 have been obtained for a substance, then the 
data  of  the  highest  quality  and  the  best  documentation  should  be  used  for  determining  the 
bioconcentration potential of the substance. If differences still exist, generally the highest valid 
value  should  take  precedence.  In  such  situation,  (Q)SAR  estimated  log  Kow  could  be  used  as 
guidance. 

III.4.3  Expert judgement 

If no experimental BCF or log Kow data or no predicted log Kow data are available, the potential 
for bioconcentration in the aquatic environment may be assessed by expert judgement. This may 
be based on a comparison of the structure of the molecule with the structure of other substances 
for which experimental bioconcentration or log Kow data or predicted Kow are available. IR&CSA 
Chapter R.7c, gives guidance on read-across and categories in section R.7.10.3.2. 

III.5  Decision scheme 

Based on the above discussions and conclusions, a decision scheme has been elaborated which 
may facilitate decisions as to whether or not a substance has the potential for bioconcentration 
in aquatic species. A conclusion on (the potential for) bioaccumulation is required under CLP and 
a conclusion should always be presented. In the event that available data is genuinely equivocal, 

 
 
 
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a  conclusion  of  ‘inconclusive’  may  be  acceptable  but  a  positive/negative  conclusion  is  clearly 
preferred. For metals and metal compounds (relevant for assessment under Annex IV according 
to Annex IV.1), please see Annex IV.4. 

Experimentally  derived  BCF  values  of  high  quality  are  ultimately  preferred  for  classification 
purposes. BCF results from poor or questionable quality studies should preferably not be used for 
classification purposes.  If no BCF is available  for  fish species, high quality data on the BCF for 
some  invertebrates  (e.g.  blue  mussel,  oyster  and/or  scallop)  may  be  used  as  a  worst  case 
surrogate. As discussed in III.2.2.2, BCF (Q)SARs cannot be placed in the decision scheme due 
to the considerations expressed in CLP (I.4.1.2.8) but can be used as part of a WoE assessment. 

For  non-ionised  organic  substances,  experimentally  derived  high  quality  Kow  values,  or  values 
which are evaluated in reviews and assigned as the “recommended values”, are preferred. If no 
experimental  data  of  high  quality  are  available,  validated  Quantitative  Structure  Activity 
Relationships  ((Q)SARs)  for  log  Kow  may  be  used  in  the  classification  process.  Such  validated 
(Q)SARs may be used without modification in relation to the classification criteria, if restricted to 
chemicals  for  which  their  applicability  is  well  characterised.  For  difficult  substances  like  strong 
acids and bases, metal complexes, and surface-active substances a (Q)SAR estimated value of 
Kow, or an estimate based on individual n-octanol and water solubilities could be provided instead 
of an analytical determination of Kow. 

If data are available but not validated, expert judgement should be used. Attempts to  reach a 
conclusion should be made with all available data under a weight of evidence approach, where 
possible. 

As  mentioned  in  the  first  paragraph  above,  whether  or  not  a  substance  has  a  potential  for 
bioaccumulation  in  aquatic  organisms  could  thus  be  decided  in  accordance  with  the  following 
scheme: 

Valid/high quality experimentally determined BCF value → YES: 

→ BCF  ≥  500:  The  substance  has  a  potential  for  bioaccumulation  in  the  aquatic 
environment 

→ BCF < 500: The substance does not have a potential for bioaccumulation in the 
aquatic environment  

Valid/high quality experimentally determined BCF value → NO: 

→ Valid/high quality experimentally determined log Kow value → YES: 

→ log Kow ≥ 4:  The  substance has a potential for bioaccumulation in the aquatic 
environment 

→log Kow < 4: The substance does not have a potential for bioaccumulation in the 
aquatic environment 

Valid/high quality experimentally determined BCF value → NO: 

Valid/high quality experimentally determined log Kow value → NO:  

Use of validated (Q)SAR for estimating a log Kow value → YES: 

→ log Kow ≥ 4:  The  substance has a potential for bioaccumulation in the aquatic 

environment 

→ log Kow < 4: The substance does not have a potential for bioaccumulation in the 

aquatic environment 

 
 
 
 
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III.6  References 

Comotto, R,M., Kimerle, R.A., Swisher, R.D. (1979) Bioconcentration and metabolism of linear 
alkylbenzenesulfonate by Daphnids and Fathead minnows. L.L.Marking, R.A. Kimerle, Eds. 
Aquatic Toxicology (ASTM, 1979), vol. ASTM STP 667. 

EC 2008. C.13 Bioconcentration: flow-through fish test in COUNCIL REGULATION (EC) No 
440/2008 of 30 May 2008 laying down test methods pursuant to Regulation (EC) No 1907/2006 
of the European Parliament and of the Council on the Registration, Evaluation, Authorisation and 
Restriction of Chemicals (REACH). Official Journal of European Union L142: 571-589. 

ECETOC 2005. Technical Report No. 97. Alternative testing approaches in environmental safety 
assessment. ISSN-0773-8072-97.  

Goodrich, M.S., Melancon, M.J., Davis, R.A. (1991) The toxicity, bioaccumulation, metabolism 
and elimination of dioctyl sodium sulfosuccinate DSS in rainbow trout (Oncorhynchus mykiss). 
Water Res. 25: 119-124. 

OECD 1996. Bioaccumulation: Flow-through Fish Test. Organisation for Economic Cooperation 
and Development (OECD), OECD Guideline for the Testing of Chemicals No. 305, Paris, France.  

Roberts, D.W. (1989) Aquatic toxicity of linear alkyl benzene sulphonates (LAS) – a (Q)SAR 
analysis. Communicaciones Presentadas a Las Jornadas Del Comite Esponol de la Detergencia, 
20 (1989) 35-43. Also in J.E. Turner, M.W. England, T.W. Schultz and N.J. Kwaak (eds.) (Q)SAR 
88. Proc. Third International Workshop on Qualitative Structure-Activity Relationships in 
Environmental Toxicology, 22-26 May 1988, Knoxville, Tennessee, pp. 91-98. Available from 
National Technical Information Service, US Dept. of Commerce, Springfield, VA. 

Tolls, J. (1998) Bioconcentration of surfactants. Ph.D. Thesis, Utrecht University, Utrecht, The 
Netherlands. 

Toshima, S., Moriya, T., Yoshimura, K. (1992) Effects of polyoxyethylene (20) sorbitan 
monooleate on the acute toxicity of linear alkylbenzenesulfonate (C12-LAS) to fish, Ecotoxicol. 
Environ. Safety 24: 26-36. 

Wakabayashi, M., Kikuchi, M., Sato, A., Yoshida, T. 1987. Bioconcentration of alcohol 
ethoxalates in carp (Cyprinus carpio), Ecotoxicol. Environ. Safety 13, 148-163. 

 
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IV  ANNEX IV: METALS AND INORGANIC METAL COMPOUNDS 

IV.1 

Introduction 

The harmonised system for classifying chemical substances is a hazard-based system, and the 
basis of the identification of hazard is the aquatic toxicity of the substances, and information on 
the  degradation  and  bioaccumulation  behaviour  (OECD  2001).  Since  this  document  deals  only 
with the hazards associated with a given substance when the substance is dissolved in the water 
column,  exposure  from  this  source  is  limited  by  the  solubility  of  the  substance  in  water  and 
bioavailability  of  the  substance  to  organisms  in  the  aquatic  environment.  Thus,  the  hazard 
classification schemes for metals and metal compounds are limited to the acute and long-term 
hazards posed by metals and metal compounds when they are available (i.e. exist as dissolved 
metal ions, for example, as M+ when present as M-NO3), and do not take into account exposures 
to  metals  and  metal  compounds  that  are  not  dissolved  in  the  water  column  but  may  still  be 
bioavailable, such as metals in foods. This section does not take into account the non-metallic ion 
(e.g. CN-) of metal compounds which may be toxic. For such metal compounds the hazards of the 
non-metallic ions must also be considered.  

Also  organometal  compounds  may  be  of  concern  given  they  may  pose  bioaccumulation  or 
persistence  hazards.  Organometals  do  not  dissociate  or  dissolve  in  water  as  the  metal  ion,  as 
metals  and  inorganic  metal  compounds  do.  Organometals  (e.g.  methyl  mercury  or  tributyltin) 
that do not release metal ions are thereby excluded from the guidance of this section and should 
be classified according to the general guidance provided in part 4. Metal compounds that contain 
an organic component but that dissociate easily in water or dissolve as the metal ion should be 
treated in the same way as metal  compounds  and classified according to this  annex (e.g. zinc 
acetate). 

The level of the metal ion which may be present in solution following the addition of the metal 
and/or its compounds, will largely be determined by two processes: the extent to which it can be 
dissolved, i.e. its water solubility, and the extent to which it can react with the media to transform 
to water soluble forms. The rate and extent at which this latter process, known as ‘transformation’ 
for the purposes of this guidance, takes place can vary extensively between different compounds 
and the metal itself, and is an important factor in determining the appropriate hazard class. Where 
data  on  transformation  are  available,  they  should  be  taken  into  account  in  determining  the 
classification. The Protocol for determining this rate is available as Annex 10 to UN GHS. 

Generally  speaking,  the  rate  at  which  a  substance  dissolves  is  not  considered  relevant  to  the 
determination  of  its  intrinsic  toxicity.  However,  for  metals  and  many  poorly  soluble  inorganic 
metal compounds, the difficulties in achieving dissolution through normal solubilisation techniques 
are  so  severe  that  the  two  processes  of  solubilisation  and  transformation  become 
indistinguishable. Thus, where the compound is sufficiently poorly soluble that the levels dissolved 
following normal attempts at solubilisation do not exceed the available L(E)C50, it is the rate and 
extent  of  transformation,  which  must  be  considered.  The  transformation  will  be  affected  by  a 
number of factors, not least of which will be the properties of the media with respect to pH, water 
hardness, alkalinity, temperature etc. In addition to these properties, other factors such as the 
size and, in particular, the specific surface area of the particles which have been tested, the length 
of time over which exposure to the media takes place and, of course the mass or surface area 
loading  of  the  substance  in  the  media  will  all  play  a  part  in  determining  the  level  of  dissolved 
metal  ions  in  the  water.  Transformation  data  can  generally,  therefore,  only  be  considered  as 
reliable for the purposes of classification if conducted according to the standard protocol in Annex 
10 to UN GHS. This protocol aims at standardising the principal variables such that the level of 
dissolved ion can be directly related to the loading of the substance added. It is this loading level 
which yields the level of metal ion equivalent to the available L(E)C50 or NOEC/EC10 that can then 
be used to determine the acute or long-term hazard category appropriate for classification. The 
testing methodology is detailed in Annex 10 to UN GHS. The strategy to be adopted in using the 

 
 
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data from the testing protocol, and the data requirements needed to make that strategy work, 
are described in Annex IV.2, IV.3 and in more detail in Annex IV.5 of this document. 

In considering the classification of metals and metal compounds, both readily and poorly soluble, 
recognition has to be paid to a number of factors. As defined in Annex II.1, the term ‘degradation’ 
refers to the decomposition of organic molecules. For inorganic compounds and metals, clearly 
the  concept  of  degradability,  as  it  has  been  considered  and  used  for  organic  substances,  has 
limited  or  no  meaning.  Rather,  the  substance  may  be  transformed  by  normal  environmental 
processes to either increase or decrease the bioavailability of the toxic species. Equally, the log 
Kow cannot be considered as a measure of the potential to accumulate. Nevertheless, the concept 
that  a  substance,  or  a  toxic  metabolite/reaction  product  may  not  be  rapidly  lost  from  the 
environment  and/or  may  bioaccumulate,  are  as  applicable  to  metals  and  metal  compounds  as 
they are to organic substances. 

Speciation of the soluble form can be affected by pH, water hardness and other variables, and 
may yield particular forms of the metal ion which are more or less toxic. In addition, metal ions 
could be made non-available from the water column by a number of processes (e.g. mineralisation 
and  partitioning).  Sometimes  these  processes  can  be  sufficiently  rapid  to  be  analogous  to 
degradation in assessing chronic (long-term) aquatic hazard. However, partitioning of the metal 
ion from the water column to other environmental media does not necessarily mean that it is no 
longer  bioavailable,  nor  does  it  necessarily  mean  that  the  metal  has  been  made  permanently 
unavailable. 

Information pertaining to the extent of the partitioning of a metal ion from the water column, or 
the extent to which a metal has been or can be converted to a form that is less toxic or non-toxic 
is frequently not available over a sufficiently wide range of environmentally relevant conditions, 
and  thus,  a  number  of  assumptions  will  need  to  be  made  as  an  aid  in  classification.  These 
assumptions may be modified if available data show otherwise. In the first instance it should be 
assumed  that  the  metal  ions,  once  in  the  water,  are  ‘not  rapidly  partitioned’  from  the  water 
column. Underlying this is the assumption that, although speciation can occur, the species will 
remain available under environmentally relevant conditions. This may not always be the case, as 
described  above,  and  any  evidence  available  that  would  suggest  changes  to  the  bioavailability 
over the course of 28 days, should be carefully examined.  

The  bioaccumulation  of  metals  and  inorganic  metal  compounds  is  a  complex  process  and 
bioaccumulation data should be used with care. The application of bioaccumulation criteria  will 
need to be considered on a case-by-case basis taking due account of all the available data. 

A  further  assumption  that  can  be  made,  which  represents  a  cautious  approach,  is  that,  in  the 
absence of any solubility data for a particular metal compound, either measured or calculated, 
the metal compound will be assumed to be sufficiently soluble to cause toxicity at the level of the 
ecotoxicity reference value (ERV), being the acute ERV (expressed as L(E)C50), and/or the chronic 
ERV (expressed as the NOEC/ECx or an HC5 for extensive data sets)  and thus may be classified 
in the same way as other soluble salts of the metal. Again, this is clearly not always the case, and 
it may be wise to generate appropriate solubility data. Absence of solubility data on the metallic 
form for a metal for which the soluble salts are classified for the environment, will therefore lead 
to a default classification due to potential hazard concerns. 

This  Annex  IV  deals  with  metals  and  inorganic  metal  compounds.  Within  the  context  of  this 
guidance document, metals and metal compounds are characterised as follows: 

a.  metals (M0) in their elemental state are not soluble in water but may transform to yield 
the available form (e.g. Fe0 will not dissolve as such, but the Fe0 molecules present at the 
surface of a massive/powder will be first transformed into Fe2+ or Fe3+ compounds prior to 
their solubilisation). This means that a metal in the elemental state may react with water 
or  a  dilute  aqueous  electrolyte  to  form  soluble  cationic  or  anionic  products,  and  in  the 
process the metal will oxidise, or transform, from the neutral or zero oxidation state to a 
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b.  in a simple metal compound, such as an oxide or sulphide, the metal already exists in the 
oxidised state, so that further metal oxidation is unlikely to occur when the compound is 
introduced into an aqueous medium. 

Organo-metals are outside the scope of this section. 

While oxidisation may not change, interaction with the media may yield more soluble forms. A 
sparingly soluble metal compound can be considered as one for which a solubility product can be 
calculated, and which will yield a small amount of the available form by dissolution. However, it 
should  be  recognised  that  the  final  solution  concentration  may  be  influenced  by  a  number  of 
factors,  including  the  solubility  product  of  some  metal  compounds  precipitated  during  the 
transformation/dissolution test, e.g. aluminium hydroxide. 

IV.2  Application of aquatic toxicity data and solubility data for classification 

IV.2.1 

Interpretation of aquatic toxicity data  

Ecotoxicity data of soluble inorganic compounds are used and combined to define the toxicity of 
the  metal  ion  under  consideration.  The  ecotoxicity  of  soluble  inorganic  metal  compounds  is 
dependent  on  the  physico-chemistry  of  the  medium,  irrespective  of  the  original  metal  species 
released  in  the  environment.  Reading  across  metal  compounds  can  therefore  be  conducted  by 
comparing  the  soluble  metal  ion  concentration  (µg  Me/L)  causing  the  ecotoxicity  effect  and 
translating this towards the compound under investigation. A molecular weight correction of the 
ecotoxicity  reference  value  may  be  required  to  classify  soluble  metal  compounds  (MW  soluble 
substance/MW metal ion90). Poorly soluble metal compounds and metals do not require Molecular 
weight correction given the amount used for Transformation Dissolution already recognises this 
into the loading calculation. The comparison is therefore directly done by comparing the soluble 
fraction measured after Transformation Dissolution with the ecotoxicity reference values of the 
soluble metal ion (based on the UN GHS, 2009).  

When evaluating ecotoxicity data, the general guidance on the weight of evidence (see Section 
4.1.3.2.4 of this document) is also applicable to metals. 

The term adequacy covers here both the  reliability (inherent quality  of a test relating to test 
methodology  and  the  way  that  the  performance  and  results  of  a  test  are  described)  and  the 
relevance (extent to which a test is appropriate to be used for the derivation of an ecotoxicity 
reference value) of the available ecotoxicity data. 

Under the reliability criteria, metal specific considerations include the description of some abiotic 
parameters  in  the  test  conditions  for  enabling  the  consideration  of  the  bioavailable  metal 
concentration and free metal ion concentration: 

•  Description of the physical test conditions: further to the general parameters (O2, T°, 
pH, …) abiotic parameters such as dissolved organic carbon (DOC), hardness, alkalinity of 
the  water  that  govern  the  speciation  and  hence  the  metal  bioavailability  is  required.  A 
proper description of culture conditions related to the level of essential metals is required 
to avoid artefacts due to acclimatisation/adaptation (see also below); 

•  Description  of  test  materials  and  methods:  to  calculate  the  free  metal  ion 
concentration  with  speciation  models  the  concentrations  of  dissolved  major  ions  and 
cations like Al, Fe, Mg, Ca… are required; 

•  Concentration-effect relationship; hormesis: sometimes an increased performance in 
growth or reproduction is seen at low metal doses that exceed the control values, referred 
to as hormesis. Such effects can be important especially for major trace nutrients such as 

90 Note that this calculation needs to be adjusted to reflect the stoichiometry of the compound, for example for Zn3(PO4)2 
the MW metal would be multiplied by three. 

 
 
 
 
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Fe, Zn and Cu but can also occur with a wide variety of non-essential substances. In such 
cases,  positive  effects  should  not  be  considered  in  the  derivation  of  acute  ERV’s  and 
especially  chronic  ERV’s,  likely  other  models  than  the  conventional  log-logistic  dose-
response model should be used to fit the dose-response curve and consideration should 
be  given  to  the  adequacy  of  the  control  diet/exposure.  Due  to  the  essential  nutritional 
needs, caution is needed with regards to  extrapolation of the dose-response curve (e.g. 
to derive an acute ERV) below the lowest tested concentration. 

Under the relevancy criteria, certain considerations need to be made, related to the relevancy of 
the test substance and to acclimatisation/adaptation: 

•  Relevance of the test substance: soluble metal salts should be used for the purpose of 
classification of inorganic metals/metal compounds. The ecotoxicity adapted from organic 
metal compounds exposure should not be used. 

•  Acclimatisation/adaptation: for essential metals, the culture medium should contain a 
minimal concentration not causing deficiency for the test species used. This is especially 
relevant  for  organisms  used  for  long-term  toxicity  tests  where  the  margin  between 
essentiality  and  toxicity  may  become  small.  As  an  example,  for  algae,  depletion  of  the 
strong complexing agent EDTA from the medium may result in iron deficiency. 

Aquatic  toxicity  studies  carried  out  according  to  a  recognised  protocol  should  normally  be 
acceptable as valid for the purposes of classification. Annex I should also be consulted for generic 
issues  that  are  common  to  assessing  any  aquatic  toxicity  data  point  for  the  purposes  of 
classification. 

 
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IV.2.1.1  Metal complexation and speciation 

The toxicity of a particular metal in solution, appears to depend primarily on (but is not strictly 
limited to) the level of dissolved free metal ions and the physico-chemistry of the environment. 
Abiotic factors including alkalinity, ionic strength and pH can influence the toxicity of metals in 
two ways: (i) by influencing the chemical speciation of the metal in water (and hence affecting 
the  availability)  and  (ii)  by  influencing  the  uptake  and  binding  of  available  metal  by  biological 
tissues. For the classification of metals, Transformation/Dissolution is carried out over a pH range. 
Ideally both T/D  and ecotoxicity data are compared at a  similar pH  since both parameters will 
vary with pH. However, the majority of ecotoxicity tests are performed at the higher pH range 
(i.e.  >  pH  7.5)  and  ecotoxicity  data  obtained  at  lower  pH  are  often  scarce.  Bioavailability  and 
speciation models (e.g. respectively Biotic Ligand Models and WHAM (Tipping, 1994), as discussed 
below) may allow to normalise ecotoxicity data obtained at a given pH to other pH values, relevant 
to the T/D data. The applicability of the bioavailability models to the biological species for which 
data are available must be evaluated. Guidance on the Bioavailability correction for metals can 
be found in IR&CSA Chapter R.7c, section R.7.13.1).    

Where  chemical speciation is important, it may be possible to model the concentrations of the 
different chemical forms of the metal, including those that are likely to cause toxicity. Analysis 
methods  for  quantifying  exposure  concentrations,  which  are  capable  of  distinguishing  between 
the complexed and uncomplexed fractions of a test substance, may not always be available or 
economic. 

Complexation of metals to organic and inorganic ligands in test media and natural environments 
can  be  estimated  from  metal  speciation  models.  Speciation  models  for  metals,  including  pH, 
hardness,  DOC,  and  inorganic  substances  such  as  MINTEQ  (Brown  and  Allison,  1987),  WHAM 
(Tipping,  1994)  and  CHESS  (Santore  and  Driscoll,  1995)  can  be  used  to  calculate  the 
uncomplexed and complexed fractions of the metal ions. 

Alternatively,  and  when  available  for  the  metal,  the  Biotic  Ligand  Model  (BLM),  allows,  for  the 
calculation of the acute and/or chronic ERV’s of the metal ion, for different pH values, through 
integration  of  metal  speciation  and  its  interaction  with  the  organism.  The  BLM  model  has  at 
present been validated for a number of metals, organisms, and endpoints (Santore and Di Toro, 
1999). The models and formula used for the characterisation of metal complexation in the media 
should  always  be  clearly  reported,  allowing  for  their  translation  back  to  natural  environments 
(OECD,  2000).  In  case  a  metal-specific  BLM  is  available  covering  an  appropriate  pH  range,  a 
normalised comparison of aquatic toxicity data can be made using the entire effects database for 
different reference pH values. 

IV.2.2 

Interpretation of solubility data 

When  considering  the  available  data  on  solubility,  their  validity  and  applicability  to  the 
identification of the hazard of metal compounds should be assessed. In particular, the pH and the 
medium in which the data were generated should be known. 

IV.2.2.1  Assessment of existing data 

Existing data will be in one of the three forms: for soluble, insoluble metal compounds and 
the  metallic  form.  For  some  well-studied  metals,  there  will  be  solubility  products  and/or 
solubility  data  for  the  various  inorganic  metal  compounds.  It  is  also  possible  that  the  pH 
relationship of the solubility will be known. However, for many metals or metal compounds, it is 
probable that the available information will be descriptive  only,  e.g. poorly soluble or resulting 
from  the  water  solubility  test  form  the  OECD  TG  105  physico-chemical  water  dissolution  test. 
Unfortunately there appears to be very little (consistent) guidance about the solubility ranges for 
such descriptive terms. Where these are the only information available it is most probable that 
solubility data will need to be generated using the Transformation/Dissolution Protocol (Annex 10 
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IV.2.2.2  Screening T/D test for assessing solubility of metal compounds  

In the absence of solubility data, a simple ‘Screening Test’ for assessing solubility, based on the 
high rate of loading (100 mg/L) for 24 h and rigid stirring conditions, should be used for metal 
compounds as described in the Transformation/Dissolution Protocol (Annex 10 to UN GHS). The 
function  of  the  screening  test  is  to  identify  those  metal  compounds  which  undergo  either 
dissolution or rapid transformation such that they are indistinguishable from soluble forms and 
hence may be classified based on the dissolved ion concentration and those who dissolves slowly 
and can be assessed in the same way as the metallic form. Where data are available from the 
screening  test  detailed  in  the  Transformation/Dissolution  Protocol,  the  maximum  solubility 
obtained over the tested pH range should be used. Where data are not available over the full pH 
range, a check should be made that this maximum solubility has been achieved by reference to 
suitable thermodynamic speciation models or other suitable methods (see Annex IV.2.1 of this 
document).  It  should  be  noted  that  this  test  is  only  intended  to  be  used  for  inorganic  metal 
compounds. Metals should immediately be assessed at the level of the full T/D test. 

IV.2.2.3  Full T/D test for assessing solubility of metals and metal compounds 

The  Full  Transformation  Dissolution  test  should  be  carried  out  at  the  pH91  that  maximises  the 
concentration of dissolved metal ions in solution and that expresses the highest toxicity. 

Based on the data from the Full Test, it is possible to generate a concentration of the metal ions 
in solution after 7 days (short-term test) for each of the three loadings (i.e. 1 mg/L as ‘low’, 10 
mg/L as ‘medium’ and 100 mg/L as ‘high loading’) used in the test. If the purpose of the test is 
to assess the long-term hazard of the substance, then the loadings92 should be 0.01 mg/L, 0.1 
mg/L or 1 mg/L depending on the transformation rate and the duration of the test being extended 
to 28 days (long-term test). 

91 The UN GHS transformation/dissolution protocol specifies a pH range of 6-8.5 for the 7days test and 5.5 to 8.5 for the 
28 days test. Considering the difficulty in carrying out transformation/dissolution tests at pH 5.5, the OECD only validated 
the test in the pH range of 6-to 8.5.   

92 The standard protocol in Annex 10 to UN GHS presently only foresees a long-term loading rate of 1 mg/l and lower 
loading rates may not even be practically feasible for each case. While TDp testing at lower loading rates is in principle 
the best way forward it is technically often not feasible for the lower chronic loading rates. Extensive experience with the 
T/D protocol demonstrated that reliable predictions can be made for other loading rates. In order to make maximal use 
of existing Transformation Dissolution data, the 28 days results for the lower chronic loading rates (0,1 and 0,01 mg/l) 
can therefore be derived by extrapolation from TDp evidence from other loading rates. Such read-across should be justified 
on a case by case basis and supported by reliable information on the T/D at different loading rates, e.g. over 7 and/or 28 
days.  It should be noted that the relationship between loading rate and dissolved metal concentration may well not be 
linear. Therefore, extrapolation of T/D data to lower loadings should preferably be made by using the equations of section 
A10.6.1 of the UN-Annex 10 transformation dissolution protocol or alternatively by extrapolating in a precautionary way. 

The UN announced to change/update Annex 10 in the near future to bring it better in line with the chronic classification 
strategy an aim that is already anticipated in this guidance note for the CLP. 

 
 
 
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IV.2.3  Comparison of aquatic toxicity data and solubility data 

A decision on whether or not the substance is classified will be made by comparing aquatic toxicity 
data and solubility data. Depending on the available data two approaches can be followed.  

1.  When  only  a  limited  dataset  is  available  existing  data  should  be  taken  together 
irrespective of whether the toxicity and dissolution data are at the same pH and the 
lowest data point should give the basis for classification (this should be used as the 
default  approach).  This  default  approach  may  lead  to  the  lowest  toxicity  data  point 
compared with the highest Transformation Dissolution result each derived at different 
pH levels used for the purpose of classification. 

2.  When  a  more  extensive  toxicity/dissolution  dataset  is  available,  a  split  of  the 
acute and chronic ecotoxicity reference values can be performed according to their pH 
used during  T/D test. The worst case classification entry across pHs  should be used 
based on comparing TDp data with relevant ecotox data across the pH range. Meaning 
that  toxicity  data  and  transformation  data  are  in  this  case  always  compared  at  the 
same pH.  

This split of the effects data into pH classes would apply in an equal way to the acute and the 
long-term effects data sets.  

IV.3  Assessment of environmental transformation 

Environmental  transformation  of  one  species  of  a  metal  to  another  species  of  the  same  metal 
does not constitute ‘degradation’ as applied to organic compounds and may increase or decrease 
the availability and bioavailability of the toxic species. In addition naturally occurring geochemical 
processes can partition metal ions from the water column while also other processes may remove 
metal ions from the water column (e.g. by precipitation and speciation). Data on water column 
residence  time,  transformation  in  the  aquatic  environment,  and  the  processes  involved  at  the 
water  –  sediment  interface  (i.e.  deposition  and  re-mobilisation)  are  fairly  extensive  for  some 
metals. Using the principles and assumptions discussed above in Annex IV.1 of this document, it 
may therefore be possible to incorporate this approach into the classification. 

Such assessments are difficult to give guidance for and will normally be addressed on a case-by-
case approach. However, the following multiple lines of evidence that could be considered  may 
be taken into account: 

a.  Changes in speciation if they are to non-available forms, however, the potential for the 

reverse change to occur must also be considered; 

b.  Changes in speciation to species which are considerably less soluble than that of the metal 

compound being considered. 

Some caution is recommended; see Annex IV.1 of this document, the 5th and 6th paragraph. 

  Comment by ECHA:  Two workshops were held on the issue, in 2012 and 2019. The 2012 
workshop defined " types of metals in respect to Rapid Removal (RR) mechanisms: 1) metals 
that methylate and are by default not considered as rapidly transformed (e.g., Hg), 2) metals 
that quickly hydrolyse and form different products that quickly precipitate in the water column 
(Al and Fe) for which the new species can be considered as rapidly transforming and 3) metals 
for which the key question is ‘irreversibility’ (i.e., binding to a non-bioavailable form under a 
range  of  environmental  conditions).  A  second  workshop  (WS)  was  held  in  June  2019  to 
discuss the issue  of Rapid Removal (RR) for type 3  metals. The conclusion of the  WS was 
that at this stage neither RR nor the extended T/D protocol (T/Dp-E) were suitable for use 
under  CLP  (CA_68_2019)  and  that  metals  shall  only  be  assessed  on  a  case-by-case  basis 
evaluating the available evidence. This conclusion was brought to CARACAL 32, which agreed 
with the conclusion (CA_101_2019). Consequently, neither RR nor the T/Dp-E are considered 

 
 
 
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suitable for use under CLP without further technical advancements of the science and case 
by case data sets. Instead, environmental transformation as described in IV.3 shall be used 
for classification and labelling. Annex IV example D provides a practical example, taking both 
chemical transformation and potential removal mechanisms into account.   

 
 
 
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IV.4  Bioaccumulation 

While log Kow is a good predictor of BCF for certain types of organic compounds e.g. non-polar 
organic substances, it is irrelevant for inorganic substances such as inorganic metal compounds 
because  metals,  in  contrast  to  organic  substances,  are  not  lipophilic  and  are  not  passively 
transported through cellular membranes. Uptake of metal ions occurs through active processes. 

The mechanisms for uptake and depuration rates of metals are very complex and variable and 
there  is  at  present  no  general  model  to  describe  this.  Instead  the  bioaccumulation  of  metals 
according to the classification criteria should be evaluated on a case-by-case basis using expert 
judgement. 

While  BCFs  are  indicative  of  the  potential  for  bioaccumulation  there  may  be  a  number  of 
complications in interpreting measured BCF values for metals and inorganic metal compounds. 
For most metals and inorganic metal compounds the relationship between water  concentration 
and BCF in aquatic organisms is inverse, and bioconcentration data should therefore be used with 
care.  This  is  particularly  relevant  for  metals  that  are  biologically  essential.  Metals  that  are 
biologically  essential  are  actively  regulated  in  organisms  in  which  the  metal  is  essential 
(homeostasis).  Removal  and  sequestration  processes  that  minimise  toxicity  are  complemented 
by an ability to up-regulate concentrations for essentiality. Since nutritional requirement of the 
organisms can be higher than the environmental concentration, this active regulation can result 
in  high  BCFs  and  an  inverse  relationship  between  BCFs  and  the  concentration  of  the  metal  in 
water.  When  environmental  concentrations  are  low,  high  BCFs  may  be  expected  as  a  natural 
consequence  of  metal  uptake  to  meet  nutritional  requirements  and  can  in  these  instances  be 
viewed as a normal phenomenon. Also, while a metal may be essential in a particular organism, 
it may not be essential in other organisms. Therefore, where the metal is not essential or when 
the bioconcentration of an essential metal is above nutritional levels, special consideration should 
be given to the potential for bioconcentration and environmental concern. 

Non-essential  metals  are  also  actively  regulated  to  some  extent  and  therefore  also  for  non-
essential  metals,  an  inverse  relationship  between  the  metal  concentration  and  the  external 
concentration may be observed (McGeer et al., 2003). 

Consequently for both essential and non-essential elements, measured BCFs decline as external 
concentration increases. When external concentrations are so high that they exceed a threshold 
level, or overwhelm the regulatory mechanism, this can cause harm to the organism. 

BCF and BAF may be used to estimate metal accumulation by: 

a.  Considering information on essentiality and homeostasis of metals/ metal compounds. As 
a  result,  of  such  regulation,  the  ‘bioaccumulative’  criterion  is  not  applicable  to  these 
metals.  

b.  Assessing  bioconcentration  factors  for  non-essential  metals,  should  preferably  be  done 

from BCF studies using environmentally relevant concentrations in the test media.  

 
 
 
 
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IV.5  Classification strategies for metals and metal compounds  

IV.5.1 

Introduction 

  Notice!  

Acute and long-term hazards are assessed individually. 

For  determination  of  long-term  hazards  preference  should  be  given  in  applying  the  approach 
based  on  chronic  toxicity  data.  Such  evidence  is  often  frequently  available  for  the  bioavailable 
forms of metals.  

The schemes for the determination of acute and long-term aquatic hazards of metals and metal 
compounds are described below and summarised diagrammatically in the figures: 

IV.5.2.1 (acute hazard classification of metals); 

IV.5.2.2 (a and b) (long-term hazard of metals); 

IV.5.3.1 (acute hazard classification of metal compounds); 

IV.5.3.2 (a and b) (long-term hazard of metal compounds).  

There are several stages in these schemes where data are used for decision purposes. It is not 
the intention of the classification schemes to  generate new ecotoxicity data. In the absence  of 
valid data, it will be necessary to use all available data and expert judgement. 

In the following sections, the reference to the acute and chronic ERV’s refer to the data point(s) 
that will be used to select the hazard category(ies) for the metal or metal compound. 

When considering acute and chronic ERV’s data for metal compounds, it is important to ensure 
that the data point to be used as the justification for the classification is expressed in the weight 
of the molecule of the metal compound to be classified. This is known as correcting for molecular 
weight. Thus while most metal data is expressed in, for example,  mg/L of the metal (ion), this 
value will need to be adjusted to the corresponding weight of the metal compound. Thus: 

Acute  ERVcompound  =  acute  ERV  of  the  metal  compound  =  acute  ERV of  metal  ion  x  (Molecular 
weight of metal compound /atomic weight of the metal). 

Chronic ERVcompound = chronic ERV of the metal compound = chronic ERV of metal ion x (Molecular 
weight of metal compound /atomic weight of the metal). 

IV.5.2  Classification strategies for metals 

  Notice!  

Acute and long-term hazards are assessed individually. 

IV.5.2.1  Classification strategy for determining acute aquatic hazard for metals 

The scheme for the determination of acute aquatic hazard for metals are described in this section 
and summarised diagrammatically in Figure IV. 1. 

Where the acute ERV for the metal ions of concern is greater than 1 mg/L the metals need not 
be considered further in the classification scheme for acute hazard.  

Where the acute ERV for the metal ions of concern is less than or equal to 1 mg/L consideration 
must be given to the data available on the rate and extent to which these ions can be generated 
from the metal. Such rate and extend data, to be valid and useable should have been generated 
using the Transformation/Dissolution Protocol (Annex 10 to UN GHS) for a 7d period. 

Where 7d data from the Transformation/Dissolution protocol are available, then the results should 
be used to classify, according to the following rule: 

Classify the metal as Category Acute 1 if the dissolved metal ion concentration after a 
period of 7 days (or earlier for a significant time period) at a loading rate of 1 mg/L exceeds 

 
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that of the acute ERV, an M-factor must also be established as part of this classification 
(see IV.5.4).  

Figure IV. 1  Classification strategy for determining acute aquatic hazard for metals 

7 days T/D full test data 
available 

No  

Yes 

Not possible to 
classify for acute 
aquatic hazard 
due to insufficient 
data. 

Concentration at 1 mg/L 
loading rate ≥ acute ERV of 
dissolved form 

Yes 

Classify Acute 1 
and add M-factor 
(see IV.5.4) 

No  

Do not classify for 
acute hazard 

IV.5.2.2  Classification strategy for determining long-term aquatic hazard for metals 

The scheme for the determination of  long-term aquatic hazard for metals are described in this 
section and summarised diagrammatically in Figure IV. 2 and IV. 3.  

Metals can be classified for long-term aquatic hazards:  

1.  using chronic reference data when available; or  

2.  using the surrogate approach in absence of appropriate chronic toxicity reference data.  

In  case  relevant  chronic  ecotoxicity  data  (chronic  ERV)  are  available  the  approach  comparing 
chronic  ERV  with  28  days  transformation/dissolution  reference  should  be  applied  as  described 
under IV.5.2.2.1 while otherwise the surrogate approach (see IV.5.2.2.2) should be followed. 

IV.5.2.2.1 Approach based on available chronic toxicity reference data 

Where the chronic ERV for the metal ions of concern is greater than 1 mg/L, the metals need not 
be considered further in the classification scheme. 

Where the chronic ERV for the metal ions of concern is less than or equal to 1 mg/L consideration 
must be given to the data available on the rate and extent to which these ions can be generated 
from the metal. Such rate and extend data, to be valid and useable should have been generated 
using the Transformation/Dissolution Protocol (Annex 10 to UN GHS) for a 28 d period. 

Where  such  T/Dp  data  are  unavailable  the  surrogate  approach  should  be  applied  (see  Annex 
IV.5.2.2.2).  Where  28d  data  from  the  Transformation/Dissolution  protocol  are  available,  then, 
the results should be used to aid classification according to the following rules: 

a.  Classify  the  metal  as  Category  Chronic  1  if  the  dissolved  metal  ion  concentration 
obtained at a loading rate of 0.1 mg/L is greater than or equal to the chronic ERV, an M-
factor must also be established as part of this classification (see IV.5.4); or  

b.  Classify  the  metal  as  Category  Chronic  2  if  the  dissolved  metal  ion  concentration 

obtained at a loading rate of 1 mg/L is greater than or equal to the chronic ERV.   

 
 
 
 
 
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If there is evidence of rapid environmental transformation: 

a.  Classify  the  metal  as  Category  Chronic  1  if  the  dissolved  metal  ion  concentration 
obtained at a loading rate of 0.01 mg/L is greater than or equal to the chronic ERV, an M-
factor must also be established as part of this classification (see IV.5.4); or  

b.  Classify  the  metal  as  Category  Chronic  2  if  the  dissolved  metal  ion  concentration 
obtained at a loading rate of 0.1 mg/L is greater than or equal to the chronic ERV; or   

c.  Classify  the  metal  as  Category  Chronic  3  if  the  dissolved  metal  ion  concentration 

obtained at a loading rate of 1 mg/L is greater than or equal to the chronic ERV.   

Do not classify for long-term hazard if the dissolved metal ion concentration obtained from the 
28 day Transformation/Dissolution test at a loading rate of 1 mg/L is less than the chronic ERV 
of the metal ion. 

IV.5.2.2.2 The surrogate approach 

Where the acute ERV for the metal ions of concern is less than or equal to 100 mg/L consideration 
must be given to the data available on the rate and extent to which these ions can be generated 
from the metal. Such rate and extend data, to be valid and useable should have been generated 
using the Transformation/Dissolution Protocol (Annex 10 to UN GHS) for a 7d period. 

Where such T/Dp data are unavailable, i.e. there is no clear data of sufficient validity to show that 
the transformation to metal ions will not occur; the safety net classification (Category Chronic 4) 
should be applied since the known classifiable toxicity of these soluble forms is considered to give 
rise to sufficient concern. 

Where T/Dp data are available classification should be according to the following rules: 

a.  Classify  the  metal  as  Category  Chronic  1  if  the  dissolved  metal  ion  concentration 
obtained from the 7 day transformation test at the low loading rate (1  mg/L) is greater 
than  or  equal  to  the  acute  ERV,  an  M-factor  must  also  be  established  as  part  of  this 
classification (see IV.5.4); 

b.  Classify  the  metal  as  Category  Chronic  2  if  the  dissolved  metal  ion  concentration 
obtained  from  the  7  day  transformation  test  at  the  medium  loading  rate  (10  mg/L)  is 
greater than or equal to the acute ERV; 

c.  Classify  the  metal  as  Category  Chronic  3  if  the  dissolved  metal  ion  concentration 
obtained from the 7 day transformation test at the high loading rate (100 mg/L) is greater 
than or equal to the acute ERV. 

d.  Classify  the  metal  as  Category  Chronic  4  if  the  dissolved  metal  ion  concentration 
obtained from the 7 day transformation test at the high loading rate (100 mg/L) is lower 
than the acute ERV. 

 
 
 
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Figure IV. 2  Classification strategy for determining long-term aquatic hazard for metals 

Is chronic ERV available? 

YES 

Chronic ERV < 1 mg/L 

NO 

Do not classify for 
long term aquatic 
hazard 

YES 

Go to Figure 
IV. 3 

NO  

28 days T/D full test data available 

YES 

YES  

Is there evidence of rapid 
environmental 
transformation? 

NO  

Classify 
Chronic 1 
and add 
M-factor 
(see 
IV.5.4) 

YES  

Concentration at 0.01 mg/L 
loading rate ≥ chronic ERV 
of dissolved form 

Concentration at 0.1 mg/L 
loading rate ≥ chronic ERV 
of dissolved form 

YES 

NO  

NO  

Classify 
Chronic 1 
and add 
M-factor 
(see 
IV.5.4) 

Classify 
Chronic 2 

YES  

Concentration at 0.1 mg/L 
loading rate ≥ chronic ERV 
of dissolved form 

Concentration at 1 mg/L 
loading rate ≥ chronic ERV 
of dissolved form 

YES 

Classify 
Chronic 2 

NO  

NO  

Classify 
Chronic 3 

YES  

Concentration at 1 mg/L 
loading rate ≥ chronic ERV 
of dissolved form 

NO  

Do not classify for long term 
aquatic hazard 

 
 
 
 
 
 
 
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Figure IV. 3  Classification  strategy  for  determining  long-term  aquatic  hazard  for  metals  in 
absence of appropriate chronic toxicity reference and/or T/Dp data 

Is acute ERV available and ≤ 100 mg/L? 

Not possible to classify for 
long-term aquatic hazard due 
to insufficient data 

NO 

YES 

7 days T/D full test data available 

YES 

Classify Chronic 4 
unless Acute 1 
applies  

NO 

YES 

NO 

Is there evidence of both rapid 
environmental transformation and no 
bioaccumulation? 

Is chronic ERV available and 
≤ 1 mg/L? 

YES 

NO 

Concentration at 1 mg/L loading 
rate ≥ acute ERV of dissolved 
form 

NO 

Concentration at 10 mg/L 
loading rate ≥ acute ERV of 
dissolved form 

NO 

Classify Chronic 1 
and add M-factor    

(see IV.5.4) 

Classify 
Chronic 2 

YES 

YES 

Concentration at 100 mg/L 
loading rate ≥ acute ERV of 
dissolved form 

YES 

Classify 
Chronic 3 

NO 

Classify 
Chronic 4 

 
 
 
 
 
 
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IV.5.3  Classification strategies for metal compounds 

  Notice!  

Acute and long-term hazards are assessed individually  

A metal compound will be considered as readily soluble if: 

• 

• 

the  water solubility (measured through a 24-hour Dissolution Screening test or estimated 
e.g. from the solubility product) is greater or equal to the acute ERV of the dissolved metal 
ion concentration; or 
if such data are unavailable, i.e. there are no clear data of sufficient validity to show that 
the transformation to metal ions will not occur.  

Care  should  be  exercised  for  metal  compounds  whose  solubility  is  close  to  the  acute  toxicity 
reference value as the conditions under which solubility is measured could differ significantly from 
those of the acute toxicity test. In these cases the results of the Dissolution Screening Test are 
preferred. 

Metal  compounds  that  have  lower  water  solubility  than  the  acute  ERV  through  a  24-hour 
Dissolution  Screening  test  or  estimated  from  the  solubility  product,  are  considered  as  poorly 
soluble metal compound.  

IV.5.3.1  Classification  strategies  for  determining  acute  aquatic  hazard  for  metal 

compounds 

The scheme for the determination of acute aquatic hazard for metal compounds are described in 
this section and summarised diagrammatically in Figure IV. 4. 

Where  the  acute  ERV  for  the  metal  ions  of  concern  corrected  for  the  molecular  weight  of  the 
compound (further called as acute ERVcompound) is greater than 1 mg/L, the metal compounds need 
not to be considered further in the classification scheme for acute hazard.  

Where the acute ERVcompound is less than or equal to 1 mg/L, consideration must be given to the 
data  available  on  the  rate  and  extent  to  which  these  ions  can  be  generated  from  the  metal 
compound. Such data, to be valid and useable should have been generated using the T/D (Annex 
10 to UN GHS). 

Readily soluble metal compounds 

Classify the metal compound as Category Acute 1 if the acute ERVcompound ≤ 1 mg/L, an M-factor 
must also be established as part of this classification (see IV.5.4).   

Poorly soluble metal compounds 

Where 7d data from the Transformation/Dissolution protocol are available, then the results should 
be used to classify sparingly soluble metal compounds, according to the following rule: 

Classify the metal compound as Category Acute 1 if the dissolved metal ion concentration 
after a period of 7 days (or earlier for a significant time period) at a loading rate of 1 mg/L 
exceeds  that  of  the  acute  ERV,  an  M-factor  must  also  be  established  as  part  of  this 
classification (see IV.5.4).   

 
 
 
 
 
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Figure IV. 4  Classification strategy for determining acute aquatic hazard for metal compounds 

Is it readily soluble 
(solubility ≥ acute ERV)? 

YES  

Acute ERVcompound ≤ 1 mg/L 

Classify Acute 1 
and add M-factor 
(see IV.5.4) 

YES  

NO 

NO  

Do not classify for 
acute aquatic 
hazard 

7 days T/D full test data 
available 

NO  

Not possible to classify for acute 
aquatic hazard due to insufficient data 

YES 

Concentration at 1 mg/L 
loading rate ≥ acute 
ERV of dissolved form 

YES 

NO  

Classify Acute 1 and add M-factor         

(see IV.5.4) 

Do not classify for acute aquatic hazard 

IV.5.3.2  Classification  strategy  for  determining  long-term  aquatic  hazard  for  metal 

compounds 

The scheme for the determination of long-term aquatic hazard for metal compounds are described 
in this section and summarised diagrammatically in Figure IV. 5 and IV. 6. 

Metal compounds can be classified for long-term aquatic hazards:  

1.  using chronic reference data when available; or 

2.  using the surrogate approach in absence of appropriate chronic toxicity reference data.  

In  case  relevant  chronic  ecotoxicity  data  (chronic  ERV)  are  available  the  approach  comparing 
chronic ERV of the dissolved metal ion with release data of 28 days transformation/dissolution, 
should  be  applied  as  described  under  IV.5.3.2.1  while  otherwise  the  surrogate  approach  (see 
IV.5.3.2.2) should be followed. 

 
 
 
 
 
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IV.5.3.2.1 Approach based on available chronic toxicity reference data  

Where the chronic ERV for the metal ions of concern corrected for the molecular weight of the 
compound (further called as chronic ERVcompound) is greater than 1 mg/L, the metal compounds 
need not to be considered further in the classification scheme for long-term hazard.  

Readily soluble metal compounds 

Readily soluble metal compounds are classified on the basis of chronic ERV of the dissolved metal 
ion, corrected for the molecular weight of the compound (further called as chronic ERVcompound) . 

If there is no evidence of rapid environmental transformation:   

a.  Classify  the  metal  compound  as  Category  Chronic  1  if  the  chronic  ERVcompound  ≤  0.1 

mg/L, an M-factor must also be established as part of this classification (see IV.5.4); or  

b.  Classify the metal compound as Category Chronic 2 if the chronic ERVcompound > 0.1mg/L 

and ≤ 1 mg/L.   

If there is evidence of rapid environmental transformation:   

a.  Classify the metal compound as  Category Chronic 1 if the chronic ERVcompound ≤ 0.01 

mg/L, an M-factor must also be established as part of this classification (see IV.5.4); or  

b.  Classify  the  metal  compound  as  Category  Chronic  2  if  the  chronic  ERVcompound  > 

0.01mg/L and ≤ 0.1 mg/L; or   

c.  Classify the metal compound as Category Chronic 3 if the chronic ERVcompound > 0.1mg/L 

and ≤ 1 mg/L.   

Poorly soluble metal compounds 

Where the chronic ERV for the metal ions of concern is greater than 1 mg/L, the metals need not 
be considered further in the classification scheme. 

Where the chronic ERVcompound is less than or equal to 1 mg/L consideration must be given to the 
data  available  on  the  rate  and  extent  to  which  these  ions  can  be  generated  from  the  metal 
compound. Such rate and extend data, to be valid and useable should have been generated using 
the Transformation/Dissolution Protocol (Annex 10 to UN GHS) for a 28d period. 

Where  28d  T/Dp  data  are  unavailable,  the  surrogate  approach  should  be  applied  (see  Annex 
IV.5.3.2.2).  

Where  28d  data  from  the  Transformation/Dissolution  protocol  are  available,  then  classify 
according to the following rules: 

a.  Classify  the  metal  compound  as  Category  Chronic  1  if  the  dissolved  metal  ion 
concentration obtained from the 28 day transformation test at a loading rate of 0.1 mg/L 
is greater than or equal to the chronic ERV, an M-factor must also be established as part 
of this classification (see IV.5.4); or   

b.  Classify  the  metal  compound  as  Category  Chronic  2  if  the  dissolved  metal  ion 
concentration obtained from the 28 day transformation test at a loading rate of 1 mg/L is 
greater than or equal to the chronic ERV.   

If there is evidence of rapid environmental transformation: 

a.  Classify  the  metal  compound  as  Category  Chronic  1  if  the  dissolved  metal  ion 
concentration obtained from the 28 day transformation test at a loading rate of 0.01 mg/L 
is greater than or equal to the chronic ERV, an M-factor must also be established as part 
of this classification (see IV.5.4); or   

b.  Classify  the  metal  compound  as  Category  Chronic  2  if  the  dissolved  metal  ion 
concentration obtained from the 28 day transformation test at a loading rate of 0.1 mg/L 
is greater than or equal to the chronic ERV; or   

 
 
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c.  Classify  the  metal  compound  as  Category  Chronic  3  if  the  dissolved  metal  ion 
concentration obtained from the 28 day transformation test at a loading rate of 1 mg/L is 
greater than or equal to the chronic ERV.   

Do not classify for long-term hazard if the dissolved metal ion concentration obtained from the 
28 day Transformation/Dissolution test at a loading rate of 1 mg/L is less than the chronic ERV of 
the dissolved metal ion. 

IV.5.3.2.2  The surrogate approach 

Readily soluble metal compounds 

In  absence  of  relevant  chronic  toxicity  data,  and  unless  there  is  evidence  of  both  rapid 
environmental  transformation  and  evidence  of  no  bioaccumulation  (see  Annex  IV.3  and  IV.4), 
readily soluble metal compounds are classified as:  

a.  Category  Chronic  1  if  the  acute  ERVcompound  ≤  1  mg/L,  an  M-factor  must  also  be 

established as part of this classification (see IV.5.4); or  

b.  Category Chronic 2 if the acute ERVcompound > 1mg/L and ≤ 10 mg/L; or   

c.  Category Chronic 3 if the acute ERVcompound > 10mg/L and ≤ 100 mg/L.   

Poorly soluble metal compounds 

Where the acute ERVcompound is less than or equal to 100 mg/L consideration must be given to the 
data available on the rate and extent to which these ions can be generated from the metal. Such 
rate  and  extend  data,  to  be  valid  and  useable  should  have  been  generated  using  the 
Transformation/Dissolution Protocol (Annex 10 to UN GHS) for a 7d period. 

Where such 7d T/Dp data are unavailable, i.e. there is no clear data of sufficient validity to show 
that the transformation to metal ions will not occur; the safety net classification (Category Chronic 
4) has to be applied. 

Where T/Dp data are available but relevant chronic ERVs are absent, the results should be used 
to aid classification according to the following rules: 

a.  Classify  the  metal  compound  as  Category  Chronic  1  if  the  dissolved  metal  ion 
concentration obtained from the 7 day transformation test at the low loading rate (1 mg/L) 
is greater than or equal to the acute ERV and there is no evidence of rapid environmental 
transformation and no bioaccumulation, an M-factor must also be established as part of 
this classification (see IV.5.4); 

b.  Classify  the  metal  compound  as  Category  Chronic  2  if  the  dissolved  metal  ion 
concentration obtained from the 7 day transformation test at the medium loading rate (10 
mg/L)  is  greater  than  or  equal  to  the  acute  ERV  and  there  is  no  evidence  of  rapid 
environmental transformation and no bioaccumulation; 

c.  Classify  the  metal  compound  as  Category  Chronic  3  if  the  dissolved  metal  ion 
concentration obtained from the 7 day transformation test at the high loading rate (100 
mg/L)  is  greater  than  or  equal  to  the  acute  ERV  and  there  is  no  evidence  of  rapid 
environmental transformation and no bioaccumulation; 

d.  Classify  the  metal  compound  as  Category  Chronic  4  if  the  dissolved  metal  ion 
concentration obtained from the 7 day transformation test at the high loading rate (100 
mg/L)  is  lower  than  the  acute  ERV  and  there  is  no  evidence  of  rapid  environmental 
transformation and no bioaccumulation. 

 
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Figure IV. 5  Classification  strategy  for  determining  long-term  aquatic  hazard  for  metal 
compounds 

Is chronic ERV available? 

Yes 

No 

Is it readily soluble 
(solubility ≥ acute ERV)? 

No 

Yes 

Go to Figure IV. 6 

Classify 
Chronic 1 and 
add M-factor 
(see IV.5.4) 

Classify 
Chronic 2 

Yes 

Yes 

Yes 

Is there evidence of rapid 
environmental transformation? 

No 

Chronic ERVcompound ≤ 
0.01 mg/L 

Chronic ERVcompound ≤ 
0.1 mg/L 

No 

No 

Yes 

Classify 
Chronic 1 and 
add M-factor 
(see IV.5.4) 

Chronic ERVcompound > 
0.01mg/L and ≤ 0.1 
mg/L 

Chronic ERVcompound > 
0.1mg/L and ≤ 1 
mg/L 

Yes 

Classify 
Chronic 2 

No 

No 

Classify 
Chronic 3 

Yes 

Chronic ERVcompound > 
0.1 mg/L and ≤ 1 mg/L 

No 

Do not classify for long-
term aquatic hazard 

Chronic ERVcompound < 1 mg/L 

No 

Do not classify for long-term hazard 

Yes 

Yes 

28 days T/D full test data available 

No 

YES 

Is there evidence of rapid environmental 
transformation? 

Classify 
Chronic 1 and 
add M-factor 
(see IV.5.4) 

Yes 

Concentration at 0.01 
mg/L loading rate ≥ 
chronic ERV 

Concentration at 0.1 
mg/L loading rate ≥ 
chronic ERV 

No 

No 

Go to Figure 
IV. 6 and use 
the surrogate 
approach 

Classify 
Chronic 1 and 
add M-factor 
(see IV.5.4)   

No 

Yes 

Classify 
Chronic 2 

Yes 

Concentration at 0.1 
mg/L loading rate ≥ 
chronic ERV 

Concentration at 1 
mg/L loading rate ≥ 
chronic ERV 

Yes 

Classify 
Chronic 2 

No 

No 

Classify 
Chronic 3 

Yes 

Concentration at 1 
mg/L loading rate ≥ 
chronic ERV 

No 

Do not classify for long-term 
aquatic hazard 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Figure IV. 6  Classification  strategy  for  determining  long-term  aquatic  hazard  for  metal 
compounds in absence of appropriate chronic toxicity reference and/or T/Dp data 

Not possible to classify for long-term 
aquatic hazard due to insufficient data 

Is acute ERV available 
and ≤ 100 mg/L? 

Yes 

Is it readily soluble 
(solubility ≥ acute ERV)? 

No 

Yes 

Is there evidence of both rapid 
environmental transformation 
and no bioaccumulation? 

No 

No 

Acute ERVcompound ≤ 1 mg/L 

No 

Acute ERVcompound > 1mg/L and 
≤ 10 mg/L 

No 

Acute ERVcompound > 10 mg/L 
and ≤ 100 mg/L 

Yes 

Yes 

Yes 

Yes 

Classify 
Chronic 1 and 
add M-factor 
(see IV.5.4)   

Classify 
Chronic 2 

Classify 
Chronic 3 

7 days T/D full test 
data available? 

No 

Yes 

Classify 
Chronic 4, 
unless Acute 
1 applies 

Yes 

Is there evidence of both rapid 
environmental transformation 
and no bioaccumulation? 

Yes 

Is chronic ERV available  
and ≤ 1 mg/L? 

No 

Not possible to 
classify for long-term 
aquatic hazard due 
to insufficient data 

No 

Concentration at 1 mg/L 
loading rate ≥ acute ERV 

No 

Concentration at 10 
mg/L loading rate ≥ 
acute ERV 

No 

Concentration at 100 
mg/L loading rate ≥ 
acute ERV 

No 

Yes 

Yes 

Yes 

Classify Chronic 1 and add 
M-factor (see IV.5.4) 

Classify Chronic 2 

Classify Chronic 3 

Classify Chronic 4, unless 
Acute 1 applies 

 
 
 
 
 
 
 
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IV.5.4  Setting M-factors for metals and inorganic metal compounds 

For the hazard class “Hazardous to the Aquatic Environment”, SCLs are not applicable. Instead 
the M-factors concept is used.  

The  M-factors  are  used  in  application  of  summation  method  for  classification  of  mixtures 
containing  substances  that  are  classified  as  very  toxic.  The  concept  of  M-factors  has  been 
established to give an increased weight to very toxic substances when classifying mixtures. M-
factors  are  only  applicable  to  the  concentration  of  a  substance  classified  as  hazardous  to  the 
aquatic environment (categories Acute 1 and Chronic 1) and are used to derive by the summation 
method  the  classification  of  a  mixture  in  which  the  substance  is  present.  They  are,  however, 
substance-specific  and  it  is  important  that  they  are  being  established  already  when  classifying 
substances. 

M-factors should have been established in accordance with Article 10 of CLP and be available in 
the C&L Inventory.  

For the harmonised classifications in Annex VI to CLP, M-factors shall be set by the manufacturer, 
importer  or  downstream  user  in  case  there  is  no  M-factor  provided,  in  accordance  with  Article 
10(4) of CLP. 

For soluble metal compounds M-factors are applied as for organic substances (see Table IV. 1).  

For poorly soluble metal compounds and metals, M-factors can be estimated from the ratio of the 
soluble metal ions concentrations obtained from Transformation Dissolution (7 d at a loading of 1 
mg/L or 28 d at the loading used to determine classification as Chronic 1, i.e., 0.1 or 0.01 mg/L, 
depending on rapid/no-rapid transformation) and the ERV of the dissolved metal ion taking the 
considerations mentioned in IV.2.3 into account. If this ratio is: 

•  below 10 then an M-factor of 1 should be applied;  
•  10 and < 100 then the M-factor would be 10; 
•  100 and < 1000 then the M-factor would be 100.  

Continue in factor 10 intervals.  

Table IV. 1   M-factors for inorganic substances 

Acute ERV (mg/L) 

Multiplying factors (M) 

0,1 < Acute ERV ≤ 1 

0,01 < Acute ERV ≤ 0,1 

0,001 < Acute ERV ≤ 0,01 

0,0001 < Acute ERV ≤ 0,001 

1 

10 

100 

1000 

Continue in factor 10 intervals 

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Chronic ERV (mg/L) 

Multiplying factors (M) 

No 
environmental 
transformation 

rapid 

Rapid 
environmental 
transformation 

0,01 < Chronic ERV ≤ 0,1 

0,001 < Chronic ERV ≤ 0,01 

0,0001 < Chronic ERV ≤ 0,001 

1 

10 

100 

0,00001 < Chronic ERV ≤ 0,0001 

1000 

Continue in factor 10 intervals 

1 

1 

10 

100 

IV.5.5  Particle size and surface area 

Surface  area  is  a  crucial  parameter  in  that  any  variation  in  surface  area  tested  may  cause  a 
significant change in the levels of metals ions released in a given time window. Thus, particle size 
or  surface  area  is  fixed  for  the  purposes  of  the  transformation  test,  allowing  the  comparative 
classifications to be based solely on the loading level. Normally, the classification data generated 
would have used the smallest particle size marketed to determine the extent of transformation. 
There may be cases where data generated for a particular metal powder are not considered as 
suitable  for  classification  of  the  massive  forms.  For  example,  where  it  can  be  shown  that  the 
tested powder is structurally a different material (e.g. different crystallographic structure) and/or 
it has been produced by a special process and is not generally generated from the massive metal, 
classification  of  the  massive  can  be  based  on  testing  of  a  more  representative  particle  size  or 
surface area, if such data are available. The powder may be classified separately based on the 
data generated on the powder. However, in normal circumstances it is not anticipated that more 
than two classification proposals would be made for the same metal. 

Metals with a particle size smaller than the default diameter value of 1 mm can be tested on a 
case-by-case  basis.  One  example  of  this  is  where  metal  powders  are  produced  by  a  different 
production  technique  or  where  the  powders  give  rise  to  a  higher  dissolution  (or  reaction)  rate 
than the massive form leading to a more stringent classification. 

The  particle  sizes  tested  and/or  used  for  classification  and  labelling  depend  on  the  substance 
being assessed and are shown in the table below: 

Type 

Particle size 

Comments 

Metal compounds 

Smallest  representative 
size sold 

Never larger than 1 mm 

Metals – powders 

Smallest  representative 
size sold 

Metals – massive 

1 mm 

May need to consider different sources 
if  yielding  different  crystallographic/ 
morphologic properties 

Default  value  may  be  altered 
sufficient justification 

if 

Massives will usually be tested as 1 mm particles. Alternatively, the T/D testing of materials with 
different surface area’s may result in highly reliable dissolution kinetic equations that allows to 
define the ‘Critical Particle Diameter’ (CPD) for appropriate loadings for the acute and long-term 
hazard assessment.  

 
 
 
 
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For most metals and some metal compounds, it is possible, using the Transformation/ Dissolution 
Protocol (Annex 10 to UN GHS), to obtain a correlation between the concentration of the metal 
ion after a specified time interval as a function of the surface area loadings of the forms tested. 
Such correlations should be established for the relevant pH ranges as specified in the protocol. In 
such cases, it could then be possible to estimate the level of dissolved metal ion concentration at 
a given pH of the metal with different particles, using the critical surface area approach (Skeaff 
et al., 2000). From this correlation and a linkage to the appropriate toxicity data at corresponding 
pH level, it is possible to determine a "Critical Surface Area" (CSA) of the substance that delivers 
the L(E)C50 to the dissolution medium and then to convert the CSA to a Critical Particle Diameter 
(CPD)  (see  example).  This  CPD  at  appropriate  mass  loadings  for  acute  and  long-term  hazard 
assessment can then be used to: 

•  determine the classification category of powders based on the finest representative powder 

on the market; and  

•  determine an accurate classification of the massive metal by applying a 1 mm (default) 

diameter. 

Within  the  CSA  Approach  an  equation  is  developed  to  predict  metal  ion  release  (based  on 
previously measured metal ion release from different loadings of the metal), which is correlated 
to measured surface area, and a corresponding calculated equivalent particle diameter. The basis 
of the CSA Approach is that the release of metal ions is dependent on the surface area of 
the substance, with this release being predictable once the relationship has been established. 
The  CSA  is  the  surface  area  loading  (mm2/l)  to  a  medium  that  delivers  a  selected  ecotoxicity 
reference value to that medium. The term SA is the measured specific surface area (m2/g) of the 
metal sample. The measured specific critical surface area (SAcrit) (m2/g) is the measured specific 
surface areas for the corresponding low, medium and high loadings which are associated with the 
respective  acute  and  long-term  aquatic  toxicity  classification  categories  in  the  classification 
scheme  for  metals  and  metal  compounds.  A  typical  equation  for  this  relationship  for  a  given 
substance, aquatic medium, pH and retention time is:  

log (CMe(aq), mg/L) = a + b log(Ameas) 

CMe(aq) =   total dissolved concentration of metal ion (mg/L) at a particular length of test time (i.e. 
168 hours for acute toxicity transformation testing) under certain conditions (i.e. pH, 
specified  medium,  etc.),  as  determined  by  transformation/dissolution  testing  of 
different surface area loadings  

a, b =  

regression coefficients  

Ameas =   initial  surface  area  loading  (mm2/l)  [equals  (measured  specific  surface  area,  SA,  in 
m2/g) X (substance mass loading in g/l) X 106], where SA was measured with the BET 
nitrogen adsorption-desorption technique. 

 
 
 
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IV.5.6  Classification of mixtures of metals and metal compounds 

Simple composed metal or metal compound mixtures should be handled as mixtures and classified 
according to the mixtures rules described in Section 4.1.4 given they normally express toxicity as 
a  function  of  their  composing  ingredients.  Ores  and  concentrates  and  UVCB  inorganics  are 
considered as substances in respect to CLP but follow in general the mixture ruling to determine 
their  classification  unless  specific  ecotoxicity  data  are  available  for  the  mineral(s)  under 
consideration.  

Ores and concentrates and inorganic UVCBs are considered substances under CLP. In the absence 
of substance specific ecotoxicity data, their classification can be assessed by applying the mixtures 
rule.  The  metals  industry  has  developed  classification  tools  that  allow  for  the  hazard  ID  and 
environmental classification of these complex materials, by integrating all aspects of this guidance 
with a knowledge of their mineralogical and other typical metal properties. 

Metal  alloys  are  considered  as  mixtures  for  the  purpose  of  classification  and  labelling  (Article 
2(27) of CLP), although due to their (eco)toxicity profile differing from that of their constituents, 
they may require special consideration. Further information on how to assess the environmental 
hazard  classification  of  alloys  and  other  complex  metal  containing  materials  is  provided 
hereunder. 

IV.5.6.1  Classification of alloys and complex metal containing materials 

Metal  alloys,  or  alloy  manufacturing  products  are  not  simple  mixtures  of  metals  or  metal 
compounds, since the alloy has clearly distinctive properties compared to a classical mixture of 
its  metal  components.  Justified  by  their  intrinsic  properties,  the  solubility  properties  can  differ 
substantially from what is observed for each individual constituent in that alloy (e.g. the rate and 
extend of metals release from pure metals are different from the ones from alloys). The rate and 
extend to which the ingredients of the alloy react with the media to transform to water soluble 
in  the  same  way  as  with  metals  (by  using  the  OECD 
forms  can  be  measured 
Transformation/Dissolution test (Annex 10 to UN GHS)). However, alloys often react slowly and 
to a very limited extent, making the application of the T/D protocol more complex. Special care 
should  be  taken  in  this  respect  to  the  detection  limit  and  the  accurate  determination  of  the 
measured surface. Initial testing of alloys, using the T/D protocol, shows that this can be useful 
but further additional guidance on this aspect is recommended. 

More  complex  metals  or  metal  compounds  containing  inorganic  substances  like  e.g.  ores  and 
concentrates are not simple mixtures of metals or metal compounds. Justified by their intrinsic 
properties,  the  solubility  properties  can  differ  substantially  from  what  is  observed  for  each 
individual constituent of that complex substance (e.g. the rate and extent of metals release from 
e.g. ores/concentrates are different from the ones from simple metals). All these materials are 
typically  not  readily  soluble  in  any  aqueous  medium.  In  addition,  these  materials  are  often 
heterogeneous in size and composition on a microscopic/macroscopic scale. Therefore, adequate 
amounts  of  the  material  could  be  used  to  evaluate  the  extent  to  which  the  substances  can  be 
dissolved, i.e. its water solubility and/or the extent to which the metals can react with the media 
to  transform  to  water  soluble  forms  e.g.  through  Transformation/Dissolution  tests.  Additional 
guidance on this aspect is needed for complex metal mixtures. 

An  ecotoxicity  validation  step  may  be  important  for  alloys  and  complex  metal  containing 
materials  (e.g.  ores,  concentrates,  slags),  where  binding  of  the  metal  to  abiotic  and  biological 
binding sites will in many cases be competitive. Therefore the ‘additivity mode’ is not necessarily 
valid and additional information may be relevant.  

Therefore,  information  from  ecotoxicity  validation  steps  could  be  useful  in  cases  where  a 
significant  uncertainty  is  associated  with  the  existing  toxicity  data.  This  ecotoxicity  validation 
should have been derived from tests using most sensitive species at dissolved ion concentrations 
equivalent to those measured in the T/D medium. However, information from ecotoxicity testing 
directly  in  the  T/D  medium  is  not  recommended  because  the  composition  of  this  medium  is 
unlikely  to  meet  the  requirements  for  standard  test  media  to  ensure  proper  survival  and/or 

 
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reproduction. Therefore, ecotoxicity tests should have been conducted in standard media dosed 
at  metal  concentration  equivalent  to  the  concentration  level  actually  measured  in  the  T/D 
medium.  

IV.6  References 

Brown, D.S. and Allison, J.D. (1987). MINTEQA1 Equilibrium Metal Speciation Model: A user’s 
manual. Athens, Georgia, USEPA Environmental Research Laboratory, Office of Research and 
Development 

Farley KJ, Carbonaro RF and Di Toro DM (2007), Unit World Model Tier 1 Hazard Ranking Model 
for metals in lakes. Report prepared for the International Council of Metals and Mining (ICMM) 

McGeer JC, Brix KV, Skeaff JM, DeForest DK, Brigham SI, Adams WJ and A Green, (2003). 
Inverse relationship between bioconcentration factor and exposure concentration for 
metals: Implications for hazard assessment of metals in the aquatic environment. 
Environmental Toxicology and Chemistry 22(5), 1017-1037. 

Di Toro, M.D.; C. D. Kavvadas; R. Mathew, P.R. Paquin and R.P. Winfield . The persistence and 
availability of metals in aquatic environments. ICMM, 2001. 

OECD 2001. OECD SERIES ON TESTING AND ASSESSMENT, Number 33: HARMONISED 
INTEGRATED CLASSIFICATION SYSTEM FOR HUMAN HEALTH AND ENVIRONMENTAL HAZARDS 
OF CHEMICAL SUBSTANCES AND MIXTURES. 
OECD, Paris. http://www.oecd.org/dataoecd/48/51/37182285.pdf  

OECD, 2000. Guidance Document on Aquatic Toxicity Testing of Difficult Substances and 
Mixtures, OECD, Paris 

OECD, 2001. Guidance Document on Transformation/Dissolution of Metals and Metals 
Compounds in Aqueous Media, OECD, Paris 

Santore, R.C. and Driscoll, C.T. (1995). The CHESS Model for Calculating Chemical Equilibria in 
Soils and Solutions, Chemical Equilibrium and Reaction Models. The Soil Society of America, 
American Society of Agronomy 

Santore, R.C. and Di Toro, D.M. et al (1999). A biotic ligand model of the acute toxicity of 
metals. II. Application to fish and daphnia exposure to copper. Environ. Tox. Chem. Submitted 

Skeaff, J., Delbeke, K., Van Assche, F. and Conard, B. (2000) A critical surface are concept for 
acute hazard classification of relatively insoluble metal-containing powders in aquatic 
environments. Environ. Tox. Chem. 19:1681-1691 

Tipping, E. (1994). WHAM – A computer equilibrium model and computer code for waters, 
sediments, and soils incorporating discrete site/electrostatic model of ion-binding by humic 
substances. Computers and Geoscience 20 (6): 073-1023  

 
 
 
 
 
 
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IV.7  Decision on classification: examples for metals and metal compounds 

List of examples: 

•  Example A: Soluble metal compound with acute and chronic toxicity data and no evidence 

of rapid environmental transformation (Me2 (SO4)2). 

•  Example  B:  Poorly  soluble  metal  compound  with  acute  and  chronic  toxicity  data, 
Transformation/Dissolution data at 7 days (low loading rate) and at 28 days (only low and 
medium loading rates) and no evidence of rapid environmental transformation. 

•  Example C: Metal in powder and massive form with acute and chronic toxicity data and 
Transformation/Dissolution data at 7 days (low, medium and high loading rates) and at 
28  days  (only  the  high  loading  rate)  and  no  evidence  of  rapid  environmental 
transformation. 

o  Explanatory note to Example D - Critical Surface Area (CSA) Approach. 

•  Example D: Hazard classification of a soluble metal salt: the case of rapid environmental 

transformation through speciation in the water column. 

 
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Example  A:  Soluble  metal  compound  with  acute  and  chronic  toxicity 
data  and  no  evidence  of  rapid  environmental  transformation  (Me2 
(SO4)2). 

DATA ELEMENTS 

Value 

Test method ((EC) No. 
440/2008)  or  OECD 
guideline / remarks  

Transformation dissolution protocol evidence 

Screening  test  (24  h)  at  100  mg/L 

pH 6 : 6240 µg/L 

Metals TDp, non-GLP 

loading 

7 d TDp test 

28 d TDp test 

pH 8 : 840 µg/L 

Not applicable 

Not applicable 

MWT of the metal ion versus compound 

60 / 312 

Acute aquatic toxicity of metal ion93 

Fish: 

             Oncorhynchus mykiss  120 µg/L (96 h LC50) at pH 7,8 

C.1. / static, GLP 

106  µg/L (96 h LC50) at pH 7,8 

C.1. / static, non-GLP 

104 µg/L (96 h LC50) at pH 7,8 

C.1. / static, GLP 

78 µg/L (96 h LC50) at pH7,8 

C.1. / static, non-GLP 

(species mean: 102 µg/L at pH 
7,8 ) 

Crustacea:                  Daphnia magna  180 µg/L (48 h EC50) at pH 8 

C.2. / static, non-GLP 

Algae/aquatic plants: 

Scenedesmus subspicatus  

154 µg/L (72 h ErC50) at pH 8 

C.3. / static, GLP 

Lemna gibba 

670 µg/L (7 d ErC50) at pH 8 

C.26. / semi-static, GLP 

Chronic aquatic toxicity94 

Fish:                              Danio rerio 

24 µg/L (28 d NOEC) at pH 6 

Marine Fish 

87 µg/L (28 d NOEC) at pH 8 

1414 µg/L (28 d EC10) 

OECD  210  /  28  d  flow-
through, non-GLP 

OECD  210  /28  d  flow 
through, GLP) 

OECD  210  /28  d  flow 
through, GLP) 

93 Tests performed with readily soluble salts such as metal sulphates and metal chlorides. 

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Crustacea:                  Daphnia magna 

37 µg/L (21 d EC10) at pH 7.8 

C.20. / semi-static, GLP 

8.6 µg/L (21 d NOEC) at pH 6.4 

                                Marine decapoda 

1612 µg/L (21 d NOEC) 

C.20./semi-static 
GLP 

non-

Non-standard test 

Algae/aquatic  plants:        Scenedesmus 

21.6 µg/L (72 h NOEC) at pH 8 

C.3. / static, GLP  

subspicatus 

8.7 µg/L (72 h NOEC) at pH 6.2 

C.3. / static, non-GLP 

Degradation (evidence of rapid degradation) 

Rapid environmental transformation 

No evidence. 

Bioaccumulation 

Bioconcentration factor in fish 

+/- 200 at NOEC level 

Aquatic hazard assessment, conclusions and comments: 

Transformation Dissolution: 

•  The substance passes the 24 h screening TDp test at pH 6 given the dissolution at a loading 

of 100 mg/L is 6240 µg/L > acute ERV of the soluble ion being 102 µg/L at pH 7.8. 

Acute aquatic toxicity: 

•  The acute ecotoxicity reference value is driven by the Fish data. No data are available for 

the low pH end. 

•  The acute ERV for the metal compound is 102 * (312/(2*60)) = 265 µg/L. 

Evidence of rapid environmental transformation: 

•  No information available, so substance considered as not rapidly transformed by  normal 

environmental processes. 

Chronic aquatic toxicity: 

•  The chronic aquatic ecotoxicity reference toxicity value based on the lowest of the available 

toxicity values is slightly below 10 µg/L for Daphnia magna at pH 6,4  for the metal ion. 

•  The chronic ERV for the metal compound is 8.6 * (312/(2*60)) = 22.4 µg/L. 

Aquatic hazard classification and, where applicable, established M-factor(s): 

•  Acute (short-term) aquatic hazard: category Acute 1, M-factor: 1 
•  Long-term aquatic hazard: category Chronic 1, M-factor: 1 

Reasoning: 

Acute aquatic hazard 

•  The acute ecotoxicity reference value is driven by the Fish data. A species mean of 102 
µg/L for the metal ion, is calculated for Oncorhynchus mykiss given 4 or more toxicity data 
for the same species under comparable conditions are available. 

•  Acute aquatic hazard expressed as the ERV for the metal compound after molecular weight 

correction ≤ 1 mg/L. M-factor is 1 given the acute ERV is between 1 and 0.1 mg/L. 

•  The molecular weight correction recognises that 2 metal ions are included. 

 
 
 
 
 
 
 
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•  The substance passes the 24 h screening dissolution test by comparing acute toxicity data 
at pH 7.8 with TDp data at pH6 given an acute toxicity data set at pH 6 is lacking and the 
chronic toxicity data indicate more toxic behaviour of the metal at the lower pH end. 

Long-term aquatic hazard:  

•  Adequate information on chronic toxicity (all 3 trophic levels) is available allowing long-

term hazard classification (no use of the surrogate approach).95 

•  Marine toxicity data are not included in the chronic ERV assessment given far less sensitive 
as  freshwater  toxicity  references  and  data  for  3  trophic  levels  for  the  freshwater  are 
available. 

•  The Daphnia magna reference at pH6 is the lowest and determines the chronic ERV.  
•  A molecular weight correction is applied to the substance recognising that 2 metal ions are 

included.  

•  Rapid environmental transformation cannot be demonstrated given the lack of sufficient 

information. 

•  The M-factor of 1 is based on the chronic ERV of 22 µg/L (so between 0.01 and 0.1 mg/L.) 

without rapid environmental transformation. 

Labelling elements based on the classification: 

Element 

GHS Pictogram 

Signal Word 

Code 

GHS09 

Wng 

Hazard Statement 

H400, H410 → H41096 

Precautionary statement(s) 

P273, P391, P501 

95  In  absence  of  adequate  chronic  toxicity  data  for  all  trophic  levels,  the  subsequent  step  is  to  combine  two  types  of 
information, i.e., chronic info for the trophic level with such data and acute aquatic toxicity data and environmental fate 
information for lacking info on trophic levels. For details see Section 4.1.3.3 and Table 4.1.0. 

96  In  accordance  with  Article  27  of  CLP,  the  hazard  statement  H400  may  be  considered  redundant  on  the  label  and 
therefore not included on the label because hazard statement H410 also applies, see Section 4.1.6 of this document. 

 
 
 
 
 
 
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IV.7.2 

Example  B:  Poorly  soluble  metal  compound  with  acute  and  chronic 
toxicity data, transformation/dissolution data at 7 days (low loading 
rate)  and  at  28  days  (only  low  and  medium  loading  rates)  and  no 
evidence of rapid environmental transformation 

DATA ELEMENTS 

Value 

Test  method  ((EC)  No. 
440/2008)  or  OECD 
guideline / remarks  

Transformation dissolution protocol evidence 

Screening  test  (24  h)  at  100  mg/L 

pH 6: 74 µg/L 

Metals TDp, non-GLP 

loading 

pH 8: 34 µg/L 

7 d TDp test           at 1 mg/L loading  pH 6: 50 µg/L  

Metals TDp, non-GLP 

pH 8: 16 µg/L   

Metals TDp, non-GLP 

28 d TDp test       at 0.1 mg/L loading 

pH 6:  no data available 

Metals TDp, non-GLP 

pH 8:  no data available 

Metals TDp, non-GLP 

at 0.01 mg/L loading 

pH 6:  9 µg/L      

Metals TDp, non-GLP 

pH 8: <1 (DL)  

Metals TDp, non-GLP 

MWT of the metal ion versus compound 

MWT  of 
compound 

the  metal 

ion  versus 

60 / 91 

Acute aquatic toxicity of metal ion97 

Fish:                Oncorhynchus mykiss  186 µg/L (48 h LC50) at pH 7 

C.1. / static, non-GLP 

120 µg/L (96 h LC50) at pH 7.8 

C.1. / static, GLP 

106  µg/L (96 h LC50) at pH 7.8 

C.1. / static, non-GLP 

104 µg/L (96 h LC50) at pH 7.8 

C.1. / static, GLP 

78 µg/L (96 h LC50) at pH 7.8 

C.1. / static, non-GLP 

(species mean for four values : 
102 µg/L at pH 7.8 ) 

78 µg/L (96 h LC50) at pH 6.4 

Crustacea:                Daphnia magna  180 µg/L (48 h EC50) at pH 8 

C.2. / static, non-GLP 

106 µg/L (48 h EC50) at pH 8 

Algae/aquatic plants   Scenedesmus 

154 µg/L (72 h ErC50) at pH 8 

C.3. / static, GLP 

subspicatus 

78 µg/L (72 h ErC50) at pH 6 

                                  Lemna gibba 

670 µg/L (7 d ErC50) at pH 8 

C.26. / semi-static, GLP 

97 Tests performed with readily soluble salts such as metal sulphates and metal chlorides. 

 
 
 
 
 
 
 
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Chronic aquatic toxicity98 

Fish:                               Danio rerio 

24 µg/L (28 d NOEC) at pH 6 

87 µg/L (28 d NOEC) at pH 8 

OECD  210  /  28  d  flow-
through, non-GLP 

OECD  210  /28  d  flow 
through, GLP) 

Crustacea:                Daphnia magna  37 µg/L (21 d EC10) at pH 7.8 

C.20. / semi-static, GLP 

8.6 µg/L (21 d NOEC) at pH 6.4 

C.20.  /  semi-static,  non-
GLP 

Algae/aquatic 

plants:                 

21.6 µg/L (96 h NOEC) at pH 8 

C.3. / static, GLP 

Scenedesmus subspicatus: 

8.7 µg/L (72 h EC10) at pH 6.2 

C.3. / static, non-GLP 

Degradation (evidence of rapid degradation) 

Rapid environmental transformation 

No  data  available 
considered  as  not 
transformed. 

therefore 
rapidly 

Bioaccumulation 

Bioconcentration factor in fish 

+/- 200 at NOEC level 

Aquatic hazard assessment, conclusions and comments: 

Transformation Dissolution screening outcome:  

•  The  substance  fails  the  24  h  screening  Transformation  Dissolution  test  given  the 

dissolution at a loading of 100 mg/L : 

o  at pH 6 is 74 µg/L < acute ERV of the soluble ion being 78 µg/L (borderline case) 
o  at pH 8 is 34 µg/L < acute ERV of the soluble ion being 102 µg/L 

Acute aquatic toxicity: 

•  Adequate data on pH 6 and 8 are available allowing to derive an acute ERV for the (soluble) 

metal ion : 

o  at the lower pH end (around pH 6) :  78 µg/L  
o  at the higher pH end (around pH 8) : 102 µg/L  

7 days Transformation/Dissolution outcome :  

•  The acute release after 7 d is the highest at pH 6 (50  µg/L) being lower than the acute 

toxicity level (78 µg/L) at this corresponding pH 

•  The acute release is lower at or around pH 8 (16 µg/L), which is significantly lower than 

the acute toxicity level (102 µg/L) at this corresponding pH 

Evidence of rapid environmental transformation: 

•  No information available and therefore substance considered as not rapidly transformed 

by normal environmental processes. 

Chronic aquatic toxicity for a substance not rapidly transformed:  

98 Tests performed with readily soluble salts such as metal sulphates and metal chlorides. 

 
 
 
 
 
 
 
 
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•  The  chronic  ERV  for  the  (soluble)  metal  ion  is  8.6  µg/L  around  pH  6  and  21.6  µg/L 

around pH 8.  

28 days Transformation dissolution outcome for a substance not rapidly transformed: 

•  The release after 28 d at pH 6 at a loading of 0.1 mg/L is not available and needs to be 
extrapolated  from  the  0.01  loading  rate  assuming  a  10  times  higher  dissolution  level 
(10x9=90 µg/L), which is significantly larger than the chronic ERV at pH 6 (8.6 µg/L). 
•  The release for the 0.1  mg/L loading is also extrapolated in the same way and is much 
lower  at  pH  8.  The  calculated  release  rate  of  <  10  µg/L  is  still  lower  than  the  chronic 
toxicity  level  21.6  µg/L  at  this  pH  level.  The  calculated  release  rates  at  1  mg/L  loading 
would be < 100 µg/L which is significantly larger than the chronic ERV at pH 8. 

Aquatic hazard classification and, where applicable, established M-factor(s): 

•  Acute (short-term) aquatic hazard: no acute classification 
•  Long-term aquatic hazard: category Chronic 1, M-factor 10 

Reasoning: 

The  metal  compound  is  considered  as  poorly  soluble  since  it  fails  the  OECD  transformation 
dissolution screening test at a 100 mg/L loading. The test confirmed pH 6 as the pH of the highest 
release rate. 

Acute aquatic hazards:  

•  The acute  ecotoxicity reference value is driven by the Fish data  for the high pH and by 
algae data for the low pH level. For the high pH end (around pH 8) a species mean of 102 
µg/L for the metal ion is calculated for Oncorhynchus mykiss and a single reference of 78 
µg/L for Scenedesmus subspicatus at around pH 6. 

•  A poorly soluble substance is evaluated for classification by comparing the dissolved metal 
ion level resulting from the TDp at 7d, at a loading rate of 1 mg/L with the acute ERV as 
determined for the (soluble) metal ion. A molecular weight correction for the poorly soluble 
metal compound is consequently not required given this factor has already been included 
for the loading rate of the TDp test.  

•  The  dissolution  level  of  the  poorly  soluble  metal  compound  from  the  7d  TDp  at  1  mg 
loading is lower than the acute ERVs of the soluble metal ion for both pH levels, thereby 
not resulting in an acute classification. 

Long-term aquatic hazard:  

•  Adequate information on chronic toxicity (all 3 trophic levels) for the higher and lower pH 
levels are available allowing direct long-term hazard classification (no use of the surrogate 
approach).  

•  No valid info is available on rapid transformation by normal environmental processes, so 

the poorly soluble metal compound is considered to be not rapidly transformed. 

•  No  Molecular  Weight  Correction  is  applied  for  the  poorly  soluble  metal  compound  given 
the classification scheme is based on the comparison of the dissolved fraction of the poorly 
metal compound with the chronic ERV of the soluble metal ion at both pH 6 and pH 8. 
•  No TDp data are available for the 0.1 mg/L and 1 mg/L loading. The calculated dissolution 
level from the 28d TDp at pH 6 at 0.1mg/L loading (+/- 90 µg/L) for the poorly soluble 
metal compound is much higher than the chronic ERV’s of the soluble metal ion for pH 6 
(8.6 µg/L) warranting a chronic 1 classification. The classification is much less sensitive at 
pH 8 given a less toxic and a lower dissolution rate. 

•  The M-factor associated with the long-term hazard classification is derived by using the 
solubility level derived from the 28d TDp test at the 0,1 mg/L loading (90 µg/L at pH 6) 

 
 
 
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divided by the ERV of the dissolved metal ion (8.6 µg/L at pH 6): 90/8.6=10.45. According 
to Annex IV.5.4 the substance will get an M-factor 10, given this factor was between 10 
and 100.  

Labelling elements based on the classification: 

Element 

GHS Pictogram 

Signal Word 

Hazard Statement 

Code 

GHS09 

Wng 

H410 

Precautionary statement(s) 

P273, P391, P501 

 
 
 
 
 
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IV.7.3 

Example C: Metal in powder and massive form with acute and chronic 
toxicity  data  and  Transformation/Dissolution  data  at  7  days  (low, 
medium and high loading rates) and at 28 days (only the high loading 
rate) and no evidence of rapid environmental transformation 

DATA ELEMENTS 

Value 

Test  method  ((EC)  No. 
440/2008)  or  OECD 
guideline / remarks  

Transformation dissolution protocol evidence 

For metal in POWDER form 

Screening  test  (24  h)  at  100  mg/L 

Not applicable for metals 

Metals TDp, non-GLP 

loading 

7 d TDp test           at 1 mg/L loading 

pH 6 :  1.7 µg/L  (.) 

Metals TDp, non-GLP 

at 10 mg/L loading 

at 100 mg/L loading 

pH 8 :  3 µg/L   

pH 6 :  24 µg/L   

pH 8 :  29 µg/L   

pH 6 :  340 µg/L   

pH 8 :  280 µg/L   

28 d TDp test          at 1 mg/L loading 

pH 6:  2.3 µg/L  

Metals TDp, non-GLP 

               at 0.1 mg/L loading 

no measured data available 

at 0.01 mg/L loading 

no measured data available 

pH 8:  3.5 µg/L  

MWT of the metal 

MWT of the metal 

59 

Acute aquatic toxicity of metal ion99 

Fish: 

Large data sets available for the 
2  pH  ends  but  less  sensitive 
than crustacean at high pH end 
and Algae at low pH end 

C.1. / static, non-GLP 

C.1. / static, GLP 

Crustacea:           Ceriodaphnia dubia  Most  sensitive  species  at  high 
pH 
: 
Geometric  mean  for  6  values 
test 
under 
comparable 
conditions  (EC50  48h  ):  68  µg 
metal ion/l 

(pH  8.3-8.7) 

end 

C.2. / static, non-GLP 

99 Tests performed with readily soluble salts such as metal sulphates and metal chlorides. 

 
 
 
 
 
 
 
 
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Algae/aquatic plants: 

Pseudokirchneriella subcapitata 

Chronic aquatic toxicity100 

Fish 

Data sets available for the 2 pH 
ends  but  less  sensitive  than 
crustacean  at  high  pH  end  and 
most  sensitive  endpoint  at  low 
end. 

Most sensitive value (96 h EC10) 
at  the  low  pH  range:  120  µg 
metal ion/l 

C.3. / static, GLP 

And non-GLP 

C.26. / static, non-GLP 

Large  data  sets  available  for 
different  pHs  but  less  sensitive 
than crustacean at high and low 
pH  

Crustacea:           Ceriodaphnia dubia  Most  sensitive  species  at  high 

and low pH end: 

- At low pH (NOEC 21d): 20 µg/L  

- At high pH: (EC10 21d): 2.4 µg 
/l 

C.20.  /  semi-static,  non-
GLP 

Algae/aquatic plants: 

Large  data  sets  available  for 
different pH’s but less sensitive 
than crustacean at high and low 
pH 

C.3. / static, GLP 

C.3. / static, non-GLP 

Degradation (evidence of rapid degradation) 

Rapid environmental transformation 

No information. 

. 

Bioaccumulation 

Bioconcentration factor in fish 

<< 500 at NOEC or EC50 level 

Transformation Dissolution screening outcome: not applicable for metals 

Acute aquatic toxicity:  

•  Adequate  data  at  high  and  low  pH  are  available  allowing  deriving  an  acute  ERV  for  the 

(soluble) metal ion: 

•  at the lower pH end (around pH 6) : 120 µg/L  

•  at the higher pH end (above pH 8) : 68 µg/L  

100 Tests performed with readily soluble salts such as metal sulphates and metal chlorides. 

 
 
 
 
 
  
 
 
 
 
 
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7 days Transformation/Dissolution outcome for the powder form: 

•  The release after 7 d’s is the highest at pH 8 while lower at pH 6. The table below compares 

the TDp results with the acute ERV values at the corresponding pH ranges 

Loading         (mg 
metal ion/l) 

pH* 

Highest 
dissolution        
(mg metal/L) 

Reference 
value (mg metal/L) 

toxicity 

Dissolution > toxicity 
reference value? 

1 

10 

100 

1 

10 

100 

low 

0.0017 

low 

0.024 

low 

0.35 

high 

0.003 

high 

0.029 

high 

0.28 

0.12 

0.12 

0.12 

0.068 

0.068 

0.068 

No 

No 

Yes 

No 

No 

Yes 

* pH value at which dissolution testing was conducted and similar to the pH for the acute toxicity reference 
value 

•  The release from the metal powder101 at a loading of 100 mg/L is for both pH ranges higher 

than the acute ERV.  

7 days Transformation/Dissolution outcome for the massive form : 

•  The  CSA  Approach  can  be  used  to  calculate  a  Critical  Particle  Diameter  (CPD)  for  the 
dissolution rates from the metal powder. The metal in massive form will be classified as 
hazardous to the aquatic environment if the CPD is above or equal to 1 mm. The measured 
critical surface area (SAcrit) that releases sufficient ions to reach the acute ERV for the most 
critical  pH  (6)  is  SAcrit    0.101  m2/g  corresponding  to  an  equivalent  critical  spherical 
particle diameter (CDspec) of 6.67 m at a 100 mg/L loading rate. This is far less than 1 
mm. 

Evidence of rapid environmental transformation: 

•  No information available and therefore substance considered as  not rapidly transformed 

by normal environmental processes. 

Chronic aquatic toxicity:  

•  The  chronic  ERV  for  the  (soluble)  metal  ion  is  2.4  µg/L  at  around  pH  8  and  20  µg/L 

around pH 6 which is an inverse relationship with pH as for the acute level. 

28 days Transformation/Dissolution outcome for a substance not rapidly transformed: 

•  The release after 28 d at a loading of 1 mg/L is slightly higher at pH 8 (3.5 µg/L) than at 

pH 6 (2.3 µg/L).   

•  TDp data for lower loadings are not available and were calculated given that the rate of 
metal ion release from the metal in the OECD 203 medium at high pH at the 28 days can 
be predicted by the equation: log (CMe(aq)) = -5.144 + 1.0229log(Ameas), whereby  

Cme(aq) = total dissolved concentration of metal (mg/L) 

101 The finest representative metal powder should be used for TDp testing. 

 
 
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Ameas  =  initial  surface  area  loading  (mm2/l)  [equals  (measured  specific  surface 
area, SA, in m2/g)  (substance mass loading in g/l) X 10], where SA was 
measured with the BET nitrogen adsorption-desorption technique. 

An equal approach can be followed for the lower pH level. 

•  Measured and estimated transformation dissolution data for the  metal powder are listed 

in the table below 

Loading            
(mg metal ion/l) 

Measured  or 
calculated 

pH*  Highest 

dissolution         
(mg metal/L) 

Reference 
toxicity  value 
(mg metal/L) 

Dissolution 
> 
toxicity reference 
value? 

1 

1 

0.1 

0.1 

Measured 

low 

0.0023 

0.020 

Measured 

high  0.0035 

0.0024 

Estimated 

Low  0.00023 

0.020 

Estimated 

High  0.00035 

0.0024 

No 

Yes 

No 

No 

* pH value at which dissolution testing was conducted and similar to the pH for the acute toxicity reference 
value 

•  The release after 28 days at the 1 mg/L loading for the higher pH level slightly exceeds 
the chronic ERV, while no such effect is noted at pH 6 mainly due to the lower sensitivity 
of the species.   

Aquatic hazard classification and, where applicable, established M-factor(s): 

Acute (short-term) aquatic hazard:  

• 
• 

for the powder form: no acute hazard classification 
for the massive form: no acute hazard classification  

Long-term aquatic hazard:  

• 
• 

for the powder form: category Chronic 2 
for the massive form: no long-term hazard classification  

Reasoning: 

The single environmental classification for all  metal powders (spherical diameter ≤ 1 mm) of 
the  considered  metal  can  be  derived  by  comparing  the  transformation/dissolution  data  for  the 
smallest commercially representative metal powder with the acute and chronic toxicity reference 
values (for the soluble metal compounds). 

Acute hazard classification: 

•  The  dissolution  rate  for  the  finest  powder  on  the  market  does  not  reach  the 
concentration corresponding with the ERV, within 7 days at a loading of 1  mg/L. This is 
only  reached  at  a  loading  of  100  mg/L.  Therefore,  no  acute  hazard  classification  is 
required.  

•  The dissolution rate for the massive forms (spherical diameter > 1 mm) is lower than 
those  for  powders  given  the  lower  available  surface  area.  The  Critical  surface  area 
approach  confirms  that  above  a  diameter  of  6.7  µm  the  acute  ERV  cannot  be  reached 
within 7 days at a loading of 1 mg/L. (Not even at a 100 mg/L loading.) Thereby confirming 
no need for an acute hazard classification. More explanation on the CSA assessment of the 
powder form for this metal is included in the explanatory note to example D (see below). 

 
 
 
 
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Long-term hazard classification: 

•  The metal does not fulfil the criterion for rapid environmental transformation. 
•  T/D data are only available for 1 mg/L loading rate. The medium loading rate of 0,1 mg/L 
required for the long-term hazard assessment could be safely extrapolated from existing 
evidence given clear relationships between concentration and dissolution were established 
for both pH levels.  

•  The comparison of chronic ERV’s with the 28 days TDp results concludes that the chronic 
ERV  for  the  metal  ion  is  only  reached  at  a  loading  rate  of  1  mg/L  at  pH  8.  Therefore, 
chronic 2 hazard classification for the metal in the powder form is warranted. 
•  Given the surface of the particle reference  for massive metal is > 100 larger than for 
the  smallest  commercially  representative  form  this  corresponds  to  a  Critical  Particle 
Diameter  >  1  mm  at  the  high  loading  rate.  Therefore  there  is  no  need  to  classify  the 
massive form for long-term hazard.  

Labelling elements based on the classification for the powder form: 

Element 

GHS Pictogram 

Signal Word 

Hazard Statement 

Code  

GHS09 

none 

H411 

Precautionary statement(s) 

P273, P391, P501 

Labelling elements based on the classification for the massive form: none 

Element 

GHS Pictogram 

Signal Word 

Hazard Statement 

Code  

none 

none 

none 

Precautionary statement(s) 

none 

 
 
 
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IV.7.3.1  Explanatory note to Example C - Critical Surface Area (CSA) approach  

Acute hazard: 

For the metal powder in this example, the data showed that the concentration of metal released 
in the OECD 203 medium at pH 8 at the 168 hr can be predicted by the equation: 

log (CMe(aq)) = -5.122 + 0.9875 log (Ameas) 

CMel(aq) = total dissolved concentration of Metal ion (mg/L) at 168 hr and pH 8; 

Ameas = initial surface area loading (mm2/l) [equals (measured specific surface area, SA, 
in m2/g)  (substance mass loading in g/l)  106], where SA was measured with the 
BET nitrogen adsorption-desorption technique.  

The CSA approach can subsequently determine what surface areas and particle diameters would 
result in different levels of aquatic toxicity classification using the regression coefficients from the 
above  equation,  a  (-5.122)  and  b  (0.9875),  and  the  proposed  acute  toxicity  reference  value 
(0.068 mg Me/l) as the CMe(aq). The critical surface area (CSA) would be the Ameas at which the 
metal  ion  is  released  at  the  concentration  of  the  acute  toxicity  reference  value.  The  following 
equations can be used to derive these values for this case: 

log L(E)C50 = -5.122 + 0.9875 log CSA 

L(E)C50 = acute ecotoxicity reference value for classification (mg/L) 

CSA =  critical  surface  area  (mm2/l)  that  releases  metal  ion  in  the  concentration  of  the 

acute ecotoxicity reference value to the aquatic medium  

The CSA can be derived as follows: 

For an acute toxicity reference value of 0.068 mg Me/l, the CSA is thus 10,100 mm2/l. This is the 
surface  area  loading  of  metal  that  will  deliver  the  reference  value  amount  of  metal  ion  to  the 
OECD 203 medium at pH 8 and at a time of 168 hr.   

The  critical  specific  surface  areas,  SAcrits  for  a  loading  of  1  mg/L  will  deliver  the  acute  toxicity 
reference value to the OECD 203 medium at pH 8 and a time of 168 hr can be calculated by:  

SAcrit  =  critical  specific  surface  area  (m2/g)  corresponding  to  the  acute  ecotoxicity 

reference value  

CP = classification cut-off loading of 1 mg/L that yield a classification as acute 1) 

Thus, for the metal powder under consideration a  CSA of 10.100 mm2/l and the CP of 1 mg/L, 
the SAcrit is 10,1 m2/g.   

The equivalent critical spherical particle diameter (CDspec) associated with the acute ecotoxicity 
reference value is determined by: 

Me = density of the metal (g/cm3) 

CDspec  =  critical  diameter  of  the  sphere  (m)  corresponding  to  the  acute  ecotoxicity 

reference value 

+=9875.0122.5)(loglog50CELCSA=MeSACDspeccrit6 
 
 
 
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For the above SAcrit of 10,1 m2/g, corresponding to the 1 mg/L loading, the critical diameter would 
be 0.067 m. The EU-CLP system defines that the finest representative metal powder should be 
used for TDp testing and classification of the metal powder form.   

An acute hazard classification can therefore be assigned to all metal powders (diameter ≤ 1 mm) 
by measuring the real surface area using the BET nitrogen adsorption-desorption technique 
and comparing it to SAcrit. If the surface area of the reference material is greater than the SAcrit 
for the associated acute hazard classification then the representative metal sample would classify 
for that acute hazard category and classify all powder types of that metal in the same way. 
If the measured surface area is less than the SAcrits of all of the classification categories then all 
powders of this metal would not classify for aquatic toxicity. 

The CSA Approach can consequently be used to assign an acute hazard classification to the metal 
powders based on measured surface area using the measured surface area of0.43 m2/g for 
the smallest representative size powder on the EU market. Since this surface area is greater than 
0.1 m2/g but less than 1 m2/g, there is according to this approach no need for an acute hazard 
classification of the metal powders in this example.   

The CSA Approach can also be used to calculate a Critical Particle Diameter (CPD) to be used to 
determine  an  accurate  classification  of  the  metal  massive  (diameter  >  1  mm),  where  the 
measured surface area of the tested granules is 0.086 m2/g. This surface area is far less than all 
of the SAcrit so there is no need for an acute classification for the metal massive.   

Long-term hazard: For this example it has been shown that rate of metal ion release from the 
metal in the OECD TG 203 medium at high pH at the 672 hr can be predicted by the equation: 

log (CMe(aq)) = -5.144 + 1.0229log(Ameas) 

Cme(aq) = total dissolved concentration of metal (mg/L) 

Ameas = initial surface area loading (mm2/l) [equals (measured specific surface area, SA, 
in m2/g)  (substance mass  loading in g/l) X 106], where SA was measured with 
the BET nitrogen adsorption-desorption technique. 

The CSA Approach can determine what surface areas and particle diameter would result in chronic 
(long-term) hazard classification by using the regression coefficients from the above equation, a 
(-5.144) and b (1.0229), and the proposed chronic toxicity reference value (0.0024 mg Me/l) as 
the CMe(aq). The critical surface area (CSA) would be the Ameas at which metal ion is released at the 
concentration  of  the  chronic  toxicity  reference  value.  The  following  equations  can  be  used  to 
derive these values. 

log chronic toxicity = -5.144 + 1.0229log CSA 

chronic  toxicity  =  chronic  ecotoxicity  reference  value  for  classification  (mg/L),  using 
calculated EC10s or measured NOECs (if the EC10 is less than the NOEC) 

CSA = critical surface area (mm2/l) that releases metal in the concentration of the chronic 

toxicity reference value to the aquatic medium  

The CSA can be derived as follows: 

For  the  long-term  hazard  classification  derivation  exactly  the  same  approach  as  for  the  acute 
hazard assessment can be followed to define SAcrit and CDspec. For this metal powder example this 
results in a CSA of 3,420 mm2/l and the CP of 1 mg/L, the SAcrit is 0.342 m2/g.   

For a SAcrit of 0.342 m2/g, corresponding to the 1 mg/L loading, the critical diameter would be 2 
m.  

+=0229.1144.5loglogicitychronictoxCSA 
 
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Equivalent as for the assessment of the acute hazard the CSA Approach can be used to assign a 
long-term hazard classification to all powders based on measured surface area of the reference 
powder,  using  the  measured  surface  area  at  100  mg/L  loading  (0.43  m2/g)  for  the  smallest 
representative size powder on the EU market. Since this surface area is greater than 0.342 m2/g, 
all metal powders would be classified as Chronic 3.   

The CSA Approach can also be used to classify the massive metal (diameter > 1 mm), where 
the measured surface area of the massive at 100 mg/L loading) is 0.086 m2/g. This surface area 
is less than the chronic SAcrit so the massive metal form would not be classified for long-term 
environmental hazard. 

IV.7.4 

Example  D:  Hazard  classification  of  a  soluble  metal  salt:  the  case  of 
rapid environmental transformation  through speciation in the water 
column 

General approach  

This example was selected to: 

i. 

illustrate the use of information on the metal oxidation and resulting transformation of 
metal ions in the water column for classification decisions; 

ii.  provide further information related to testing of sparingly soluble metal salts.  

The metal ion selected for this example, Me(II), is unstable when its solutions are exposed to air, 
and  it  oxidises  to  the  Me(III),  which  then  forms  the  familiar  insoluble,  hydrated,  amorphous, 
gelatinous precipitate,  Me(OH)3 (metal hydroxide). The question then  arises as to whether the 
metal  hydroxide  precipitate  forms  rapidly  enough  to  decrease  the  concentration  of  Me(II)  and 
Me(III) ions to levels below which there is no cause for concern over the aquatic environment. 
Consideration of the rates at which Me(II) oxidises to Me(III) is relevant to this question to proof 
rapid environmental transformation.   

Additionally,  the  classification  of  substances  of  concern  for  the  aquatic  environment  requires 
evaluation of aquatic toxicity. Results for this case were evaluated against standard acceptability 
criteria for use in this classification assessment. 

Results 

Assessment of the rapid environmental transformation:  

A review of the scientific literature on the oxidation of metal sulphate reveals the following: Metal 
sulphate  reacts  with  oxygen  in  water  to  form  metal  hydroxide  (MeOH2),  moderately  insoluble, 
Ksp = 1.6  10-14) this in turn undergoes further oxidation to form metal hydroxide (MeOH3) which 
is highly insoluble (Ksp = 1  10-36). Formation of metal hydroxide at pH levels above 5.0 limits 
the presence of metal ions in aqueous systems. In sediments the metal hydroxide is expected to 
result in enriched concentrations of insoluble metal sulphide. 

The  rates  at  which  dissolved  metal  sulphate  (Me++)  oxidises  to  (Me+++)  and  forms  the  metal 
hydroxide [Me(OH)3] precipitate: 

Is highly dependent on pH (100 fold from pH 6 to 8); 

• 
•  decreases with increase in ionic strength of the aqueous medium (pristine waters contain 

less metal ions);  

increases 10-fold for a 15 C increase in temperature;  

•  dependent to some extent on the anions present in solution such as sulphate and chloride; 
• 
•  exhibits a linear dependence on the partial pressure of oxygen; and  
•  dependent  on  the  initial  concentration  of  metal  sulphate  and  exhibits  linear  reaction 
kinetics at Me(II) loadings less than ~50 micromolar (~3 mg/L). At concentrations greater 
than  50  micromolar,  rates  of  reaction  increase  with  increasing  concentration  of  metal 
sulfate (about 4 for each order of magnitude). 

 
 
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Based  on  literature  data  and  empirical  reaction  kinetics,  it  can  be  calculated  that,  at  low  pH 
(reasonable  worst  case  scenario)  in  the  OECD  203  medium  (diluted  by  10  as  per  the 
Transformation/Dissolution  Protocol),  the  half-times  for  the  oxidation  of  Me(II)  are  11,  9  and 
3.6 hr,  for  1,  10  and  100  mg/L  loadings  of  MeSO4,  respectively.  At  high  pH,  the  reaction  is 
estimated to be as short as 8 seconds. The rapid precipitation of metal ions from aqueous systems 
accounts for low ‘metal’ concentrations found in most natural aquatic systems (all except natural 
waters at very low pH values (i.e. < pH 5.5)). Under the reasonable worst case scenario of low 
pH and a low initial concentration of 1 mg/L MeSO4, the 70 % removal from solution is calculated 
to be achieved in 19hr and 90 % removal would be achieved by 36hr. Since the removal of the 
metal  sulphate  are  due  to  reaction  with  oxygen  in  water  to  form  highly  insoluble  and  non-
classifiable metal hydroxide and the half-life for the removal of the soluble species are less than 
16 days this can be  considered as  rapidly transformed in the  water  column and the substance 
considered for classification purposes as rapidly degradable.  

To support this, evidence of rapid loss of ‘Metal ions’ (and other metals) from the water column 
has been reported in mesocosm lake experiments (Perch Lake). The data are presented as half-
lives as a function of time, partition coefficient and first stability constant. Half-lives for metal ions 
in the mesocosms are calculated to be approximately 11 days under the given conditions. The 
data  support  that  half-lives  are  short  and  loss  from  the  water  column  can  be  related  to  both 
formation of the metal hydroxide but also to sorption to suspended particles that are settling.  

Aquatic Toxicity 

Acute ERV values lie in the range of 1-37 mg/L (see Table). Two values for Daphnia magna were 
less than 10 mg/L. Four Daphnia magna studies were performed and the geometric mean value 
for this species is 5.77 mg/L. The values for fish were all greater than 10 mg/L. No algal studies 
were  deemed  reliable.  All  these  values  are  expressed  as  mg/L  Me.  If  the  classification  relates 
specifically to metal sulphate of which the most common form is the heptahydrate MeSO4.7H2O. 
The  numerical  ERV  values  detailed  should  be  adjusted  according  to  the  table  below  and  the 
species under consideration to calculate the toxicity on a metal sulfate basis. 

Chemical Species 

Molecular Weight 

Ratio 

MeSO47H2O 

MeSO4H2O 

MeSO4 

Me 

278.0 

169.91 

151.90 

55.84 

4.978 

3.043 

2.720 

1.0 

The  data  cover  all  the  reliable  results  available  for  aquatic  toxicity  of  binary  ‘metal’  and  any 
observed  toxicity  effects  could  relate  to  the  Me  ion  which  could  be  in  Me(II)  or  metal  Me(III) 
oxidation states.  

Conversion of the acute ERV values for the metal ion to those appropriate for MeSO4.7H2O implies 
an acute toxicity range of 6.4 to 199 mg/L.   

 
 
 
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Table IV. 2   Acute toxicity data deemed reliable for ‘Metal’ are presented as mg/L Me 

Test substance 

Test organism 

Duration  Endpoints 

L(E)C50 (mg Me L-1) 

MeCl3.6H2O 

Pimephales promelas 

96h 

Survival 

Lepomis macrochirus 

96h 

Survival 

MeSO4.7H2O 

Oncorhynchus mykiss 96h 

Survival 

21.8 

20.3 

16.6 

Me2(SO4)3 

Oncorhynchus mykiss 96h 

Survival 

>27.9 

MeSO4 

MeSO4 

Daphnia pulex 

24h 

Immobility 

36.9 

Daphnia magna 

24h 

Immobility 

17 

MeCl3.6H2O 

Daphnia pulex 

48h 

Immobility 

12.9 

Me2(SO4)3 

Daphnia longispina 

48h 

Immobility 

11.5 

MeCl3.6H2O  

Daphnia magna 

48 h 

Immobility 

9.6 

MeSO4 

Daphnia magna 

24h 

Immobility 

5.25 

MeSO4.7H2O 

Daphnia magna 

48h 

Immobility 

1.29 

Table IV. 3   Chronic toxicity data deemed reliable for ‘Metal’ are presented as mg/L Me 

Test substance 

Test organism 

Duration  Endpoints 

NOEC/LOEC  (mg 
Me L-1) 

Fe(OH)3 

Salvelinus fontinalis 

30 days 

Hatching 

Growth 

Survival 

>10.3 

Fe(OH)3 

Oncorhynchus kisuth  30 days 

Hatching 

>10.3 

Growth 

2.81/>10.3 

Survival 

>10.3 

FeCl3.6H2O 

Pimephales promelas  33 days 

Survival 

Length 

Weight 

1.0/1.6 

1.61/2.81 

FeCl3.6H2O 

Daphnia pulex 

21 days 

Immobility 

2.51/5.01 

Total offspring 

0.63/1.26 

Brood size 

1.26/2.51 

FeCl3.6H2O 

Daphnia magna 

21 days 

Immobility 

5.9 EC50 

Reproduction 

4.4 EC16 

 
 
 
 
 
 
 
 
 
 
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Aquatic hazard classification: 

Acute hazard: Not classified. 

Long-term hazard: Not classified. 

Reasoning: 

Acute aquatic toxicity > 1 mg/L. 

Since  all  chronic  aquatic  toxicity  values  are  higher  than  1  mg/L  and  rapid  transformation  to  a 
metal hydroxide takes place by normal environmental processes, no classification is warranted. 

Labelling elements based on the classification: 

Element 

GHS Pictogram 

Signal Word 

Hazard Statement 

Precautionary statement(s) 

Code 

none 

none 

none 

none 

 
 
 
 
 
 
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V  ANNEX V: COLLECTION OF INTERNET LINKS FOR THE 

USERS OF THE GUIDANCE 

Reference/Site name 

Host 

URL 

ECHA website 

ECHA 

http://echa.europa.eu/web/guest 

UN GHS 

UN 

http://www.unece.org/trans/danger/publi/ghs/ghs
_welcome_e.html 

eChemPortal 

OECD 

http://www.echemportal.org/ 

REACH guidance 

ECHA 

http://echa.europa.eu/guidance-
documents/guidance-on-reach 

OECD Series on Testing and 
Assessment 

OECD 

http://www.oecd.org/document/30/0,3746,en_26
49_34377_1916638_1_1_1_1,00.html 

EU Test Method Regulation 
440/2008 

EC 

http://eur-
lex.europa.eu/lexuriserv/lexuriserv.do?uri=celex:
32008r0440:en:not 

OECD test guidelines 

OECD 

http://www.oecd.org/env/ehs/testing/oecdguideli
nesforthetestingofchemicals.htm l 

Public C&L Inventory 

ECHA 

http://www.echa.europa.eu/web/guest/informatio
n-on-chemicals/cl-inventory-database 

 
 
 
 
 
 
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VI  ANNEX VI: BACKGROUND DOCUMENT TO THE GUIDANCE 

FOR SETTING SPECIFIC CONCENTRATION LIMITS FOR 
SUBSTANCES CLASSIFIED FOR REPRODUCTIVE TOXICITY 
ACCORDING TO REGULATION (EC) NO 1272/2008 

VI.1  Executive summary  

Regulation (EC) No 1272/2008 on the classification, labelling and packaging of substances and 
mixtures (the CLP Regulation or CLP) contains rules including criteria for the classification of 
substances and mixtures. While the classification of substances for human health hazards is 
based on specific criteria for each hazard class, the classification of mixtures is mainly based on 
the concentration and the classification of the substances contained in the mixture. CLP includes 
generic concentration limits (GCLs) which are specific for a hazard class and category and which 
indicate a threshold above which the presence of a substance in a mixture leads to the 
classification of the mixture. However, under certain conditions specific concentration limits 
(SCLs) must or may be used . As the Regulation itself does not provide any further guidance on 
when and how to set SCLs, guidance has been developed for certain hazard classes (see the 
respective chapters on setting SCLs in Part 3 of the Guidance on the Application of the CLP 
Criteria).  

This Annex provides a background to the method for the determination of SCLs for substances 
classified as reproductive toxicants, as outlined in the guidance in Part 3. 

Potency, expressed as the dose for the induction of reproductive effects, was identified as the 
best determinant for setting SCLs. The ED10 for effects warranting classification was selected as 
the most appropriate parameter for estimating potency. The ED10 is the dose level which 
induces reproductive effects in 10% of the animals above the control group or a change of 10% 
in the effect compared to the control group. Based on the ED10, the substance is placed in a 
potency group.  However, modifying factors can alter the potency group, especially when the 
potency estimate is close to the boundary between two groups. 

The distribution of the potency of a large number of substances classified in Annex VI to CLP as 
developmental toxicants and/or substances affecting sexual function and fertility was 
determined by establishing two databases. In line with other methods for setting SCLs for other 
hazard classes, it is proposed to define three potency groups. The boundaries for the potency 
groups were determined in line with the provisions outlined in Article 10(1) of CLP, the results 
of the database analyses and policy considerations. Most substances are foreseen to fall into the 
medium potency group, which is linked to the GCL. For substances in the high and low potency 
group, the following SCLs are proposed. 

Category 1 

Dose 

High potency 
group 

ED10 below 4 
mg/kg bw/day 

Medium 
potency group 

ED10 > 4 mg/kg 
bw/day, and < 
400 mg/kg bw/day 

SCL 

0.03% 

(factors of 10 
lower for 
extremely potent 
substancesB)  

0.3% (GCL) 

Category 2 

Dose 

ED10 below 4 mg/kg 
bw/day 

ED10 > 4 mg/kg 
bw/day, and < 400 
mg/kg bw/day 

SCL 

0.3% 

(factors of 10 
lower for 
extremely potent 
substancesB)  

3% (GCL) 

Low potency 
group 

ED10 above 400 
mg/kg bw/day 

3%  

ED10 above 400 
mg/kg bw/day 

3-10% A 

 
 
 
 
 
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A The limit of 10% may be considered in certain cases, such as for substances with a ED10 value 
above 1000 mg/kg bw/day and a NOAEL below 1000 mg/kg bw/day  

B For substances with an ED10 more than 10 fold below 4 mg/kg bw/day, meaning an ED10 
below 0.4 mg/kg bw/day, a 10-fold lower SCL should be used. For even more potent substance 
the SCL should be lowered with a factor of 10 for every factor of 10 the ED10 is below 4 mg/kg 
bw/day. 

VI.2 

Introduction 

VI.2.1  General description of the classification system for reprotoxic 

substances and mixtures 

The CLP Regulation contains rules for the classification of substances and mixtures. In CLP 
Annex I, 3.7.2.1.1 Table 3.7.1 (a), the criteria are given for the classification of substances as 
reprotoxicants in one of the following categories: 

Annex I: 3.7.2.1.1. For the purpose of classification for reproductive toxicity, substances are 
allocated to one of two categories. Within each category, effects on sexual function and 
fertility, and on development, are considered separately. In addition, effects on lactation are 
allocated to a separate hazard category. 

Table 3.7.1 (a) 

Hazard categories for reproductive toxicants 

Categories 

Criteria 

CATEGORY 1 

Known or presumed human reproductive toxicant 

Substances are classified in Category 1 for reproductive toxicity when they 
are known to have produced an adverse effect on sexual function and 
fertility, or on development in humans or when there is evidence from animal 
studies, possibly supplemented with other information, to provide a strong 
presumption that the substance has the capacity to interfere with 
reproduction in humans. The classification of a substance is further 
distinguished on the basis of whether the evidence for classification is 
primarily from human data (Category 1A) or from animal data (Category 1B). 

Category 1A 

Known human reproductive toxicant 

The classification of a substance in this Category 1A is largely based on 
evidence from humans. 

Category 1B 

Presumed human reproductive toxicant 

The classification of a substance in this Category 1B is largely based on data 
from animal studies. Such data shall provide clear evidence of an adverse 
effect on sexual function and fertility or on development in the absence of 
other toxic effects, or if occurring together with other toxic effects the 
adverse effect on reproduction is considered not to be a secondary non-
specific consequence of other toxic effects. However, when there is 
mechanistic information that raises doubt about the relevance of the effect 
for humans, classification in Category 2 may be more appropriate. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
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CATEGORY 2 

Suspected human reproductive toxicant 

Substances are classified in Category 2 for reproductive toxicity when there is 
some evidence from humans or experimental animals, possibly supplemented 
with other information, of an adverse effect on sexual function and fertility, 
or on development, and where the evidence is not sufficiently convincing to 
place the substance in Category 1. If deficiencies in the study make the 
quality of evidence less convincing, Category 2 could be the more appropriate 
classification. 

Such effects shall have been observed in the absence of other toxic effects, 
or if occurring together with other toxic effects the adverse effect on 
reproduction is considered not to be a secondary non-specific consequence of 
the other toxic effects. 

Effects on or via lactation are also part of the hazard class ‘reproductive toxicity’. Classification 
for these effects is independent of the classification in the classes 1A, 1B or 2 as described 
above. The development of a method for the determination of SCLs for substances with effects 
on or via lactation is outside the scope of this document. Therefore, these effects and this 
classification are not further considered in this document. 

The classification of mixtures containing substances classified for reproductive toxicity and of 
substances containing impurities, additives or constituents classified for reproductive toxicity is 
based on the concentration of the reproductive toxic component(s). Table 3.7.2 of Annex I to 
CLP contains GCLs above which classification for reproductive toxicity is required. The GCL is 
0.3% for reprotoxicants in Category 1A and 1B and 3.0% for Category 2. However, a GCL for all 
substances may not be protective for high potency substances and may be overprotective for 
substances with a low potency. Therefore, SCLs may be needed for such substances. 

According to CLP Article 10, SCLs must be set where adequate and reliable scientific information 
shows that the hazard of a substance is evident at a level below the GCL. This results in SCLs 
below the GCLs. SCLs above the GCLs may be set in exceptional circumstances where 
adequate, reliable and conclusive scientific information shows that a hazard of a substance is 
not evident at a concentration above the GCL. Normally, substances that fulfil the criteria for 
reproductive toxicity are subject to a harmonised classification and labelling and included in 
Annex VI to CLP. In such cases, SCLs are set via the procedure for harmonisation of 
classification and labelling of substances in line with CLP Article 37. When there is no such 
harmonised entry in Annex VI to CLP, a manufacturer, importer or downstream user must self-
classify reproductive toxic substances and must set lower or may set higher SCLs than the 
GCLs, if justified according to CLP Article 10(1). He may also provide a proposal for a 
harmonised classification (CLP Article 37(2)), including an SCL where appropriate. 

VI.2.2  Description of the process for the development of a method to set 

SCLs for reproductive toxic substances 

There are no hazard-specific criteria for the setting of SCLs in CLP . According to CLP Article 10 
(7), the European Chemicals Agency (ECHA) is required to provide further guidance on the 
setting of SCLs. A working group was established to develop such guidance for the hazard class 
reproductive toxicity, with the exception of the effects on or via lactation. 

The work on the proposal for guidance on the determination of SCLs for reproductive toxicants 
was initiated by an EU working group of the TC C&L (Technical Committee on Classification and 
Labelling of Dangerous Substances), continued under the REACH Implementation Project (RIP) 
3.6 and subsequently under the auspices of ECHA.  

To get an impression of the possible parameters for potency and their distribution, two 
databases were compiled, containing several parameters for a large number of substances 

 
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classified for developmental toxicity and impaired fertility. Based on the compiled data choices 
were made for the most appropriate parameter, the boundaries of the potency groups and the 
associated SCLs.  

In the course of the guidance development, three documents have been produced. The first 
document is the actual guidance chapter included in the Guidance on the Application of the CLP 
Criteria. The second document is this annexed background document, describing the process 
and considerations and providing the rationale for the proposed guidance. The third document is 
a publication of the databases of parameters for developmental toxicants and substances with 
an effect on sexual function or fertility and the analyses of the databases [(Muller et al., 2012)]  

Chapter 2 of this document describes potency parameters and contains a number of theoretical 
considerations on the determination of the most appropriate parameter and the SCLs. A 
description of the databases and the analyses is also provided in this chapter. Chapter 4 is 
dedicated to the non-modifying factors. Chapter 5 describes and justifies the potency 
boundaries and corresponding SCLs.  

VI.2.3  Considering potency in setting specific concentration limits for 

various health hazards 

The criteria for classification for reproductive toxicity are based on the strength of scientific 
evidence that the substance can cause reproductive toxicity. In general, no specific 
considerations are given to the potency of the substance to induce reproductive toxicity.  

On the other hand, classification for several other health hazard classes is based on potency. 
Substances with different potency are classified in different categories within the hazard class. 
The classification of mixtures for that hazard class is then based on the concentration of the 
substance in the mixture and the hazard category or the potency (for acute toxicity) of the 
substance. 

For acute toxicity, the potency is based on the acute toxicity estimate (ATE). The ATE is the 
dose level which induces 50% mortality in an acute toxicity study (LD50 or LC50) or the 
estimated LD50 or LC50 using fixed dose procedure or the acute toxic class method. This value is 
used to classify a substance into one of several categories. For mixtures, the ATE value is used 
to estimate the potency of a mixture by calculation. The estimated potency is then used to 
classify the mixture into a hazard category.  

For specific target organ toxicity (STOT) after single and repeated exposure, potency is defined 
as the dose at which a substance shows significant toxic effects in a study. Based on the 
potency, a substance is either classified for STOT into one of two hazard categories or not 
classified. The classification of a mixture containing a substance classified for STOT depends on 
the percentage of the substance in the mixture and the hazard category of the substance. A 
minimal percentage is included in the criteria. SCLs have to be determined for substances with 
a very high potency.  

Classification for carcinogenicity is, as for reproductive toxicity, based on the strength of 
scientific evidence and again no specific consideration is given to the potency. The classification 
of mixtures containing a carcinogenic substance is based on the GCL unless a SCL has been 
allocated for that substance as provided in Annex VI to CLP. SCLs for carcinogenic substances 
are determined based on the potency for carcinogenic effects based on the T25. The T25 is 
defined as the daily dose (in mg/kg bw) inducing a tumour incidence of 25% upon lifetime 
exposure after correction for the spontaneous incidence. This is mainly based on animal studies. 
Substances are divided into three groups based on the T25. High potency substances have a 
T25 < 1mg/kg bw/ day, medium potency substances have a T25 between 1 -100 mg/kg 
bw/day, and T25> 100 mg/kg bw/day for low potency substances.  Besides the T25, other 
elements were included that modify the potency evaluation (Commission Working Group, date 
unknown). This method has been included in the Guidance on the Application of the CLP 
Criteria.  

 
 
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The use of potency for the classification into different categories for several other hazard classes 
and the use of the potency to set SCLs for carcinogenic substances, justifies the use of potency 
as a first approach also for setting SCLs for reproductive toxic substances. As no definition of 
potency for reproductive toxicants was available, the following definition is used as a working 
definition: 

Reproductive toxicity potency is defined as the dose which induces reproductive toxic effects 
with a specific type, incidence and magnitude, considering the study design in terms of species 
and strain, exposure route, exposure duration, exposure window in the life cycle, and possible 
concomitant parental toxicity. 

According to this definition ‘Potency’ is primarily based on applied dose and can be modified by 
consideration of ‘severity’. Within this definition the dose is defined as the amount of substance 
to which the animals or humans that showed the effect (meaning type, incidence and 
magnitude) were exposed on an mg/kg bw/day basis. The incidence is the proportion of animals 
or humans that showed the effect. The type of effect describes which property of an organ or 
system of the animal or human is affected and the magnitude describes the level of change 
compared to the control. Together, the incidence, type and magnitude describe the ‘severity’ of 
the effect, meaning how adverse the effect or combination of effects is. With specific incidence, 
type and magnitude (together specific severity) a comparable level of severity is indicated for 
different effects.  

The working definition above allows potency to be defined at different levels of specific severity, 
for example at the ED10 and the LOAEL (Lowest Observed Adverse Effect Level), and for 
different type of effects. Therefore, several possible estimates for potency were investigated. 

VI.2.4  Parameters for potency for reproductive toxicity  

A consistent database to derive potency estimates for reproductive toxicity was lacking. 
Therefore, data on substances classified for effects on reproduction were collected and 
analysed. This was done separately for substances with an effect on development and 
substances with an effect on sexual function and fertility because the types of effects clearly 
differ between these two main types of reproductive effects. Therefore, this chapter falls into 
two parts, namely one for parameters for potency of substances with developmental effects 
(chapter 2.3.1) and one for  parameters for potency of substances with effects on sexual 
function and fertility (chapter 2.3.2). As potency is primarily based on the dose in mg/kg 
bw/day at which different adverse effects are observed, a number of parameters/dose 
descriptors (e.g. NOAEL102, LOAEL103, ED10 etc.) exist for each type of adverse effect. The 
collected data included the NOAEL, LOAEL and ED10 (effective dose with a 10% incidence or 
effect level above the background) as parameters for the effect on reproduction of each 
substance. They were further divided into effects fulfilling the criteria for classification (named 
‘LOAEL (classification)’ for example) and any effects on reproduction (named ‘NOAEL (overall)’ 
for example). Together, this sub-division results in 6 different potency parameters, see Table 
VI. 1). Other data, e.g. a mutagenicity classification of a substance, the type of effect at the 
LOAEL and species used in the test, were also collected. These parameters were analysed and 
the results tabulated and plotted graphically. The results are published by Muller et al., 2012. 
As the data for these two main types of reproductive toxicity were analysed separately, the 
results are provided separately. 

VI.2.4.1  Potency parameters for developmental toxicants (Muller et al, 2012) 

Data for one or more of the parameters for development were available for 99 substances 
classified for developmental toxicity when the work on this guidance development started. For 

102 NOAEL means No Observed Adverse Effect Level. 
103 LOAEL means Lowest Observed Adverse Effect Level. 

 
 
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almost all substances a LOAEL is available but a NOAEL and ED10 were sometimes missing. The 
absence of a NOAEL is mostly caused by the absence of a dose level without an effect in the 
study or database of a substance. The absence of an ED10 value is mainly caused by the 
absence of a NOAEL and in most of those cases an ED10 could only be derived by a benchmark 
dose (BMD) approach to avoid interpolation between the LOAEL and the vehicle control. Another 
cause for the absence of ED10 values is the limited reporting of effect levels in the consulted 
study summaries or study reports. 

The difference in the average value between the highest and lowest of the 6 parameters for 
potency is a factor of 4 or less. This is very small compared to the difference in potency 
between substances for each parameter of up to 1,000,000 fold (Table VI. 2). The potency 
difference is more pronounced for a NOAEL or LOAEL compared to an ED10 mainly because for 
most potent substances only a NOAEL and/or a LOAEL was available but not an ED10. The 
available data indicate that there is a close relation between the NOAEL, LOAEL and ED10 for 
most substances. The average LOAEL is between a factor of 2 and 3 above the average NOAEL. 
The fact that it is not closer to the factor of 3 to 4 that is normally used between dose levels is 
probably due to the absence of a NOAEL for a number of substances. The average ED10 
(classification), is slightly higher than the average LOAEL (classification). The difference is more 
pronounced for the ‘overall’ values, namely approximately a factor of 2. These findings are 
caused by both the dose spacing in the studies and the limited discriminative power of the 
NOAEL approach. 

Table VI. 1   Average values (assuming log/normal distribution) (in mg/kg bw/day) and 
potency differences for parameters for all developmental toxicants of the database (Muller et 
al, 2012) 

Average  Standard 
deviation 

Lowest 
value 

Highest 
value 

Potency 
difference 

Parameter 

NOAEL (overall) 

LOAEL (overall) 

ED10 (overall) 

NOAEL 
(classification) 

LOAEL 
(classification) 

N 

68 

98 

59 

76 

12 

25 

43 

18 

97 

40 

ED10 (classification) 

63 

48 

10 

13 

6 

11 

13 

6 

0.002 

684 

342000 

0.002 

2281 

1140500 

0.3 

785 

2617 

0.002 

1100 

550000 

0.002 

2281 

1140500 

0.3 

933 

3110 

A part of the differences in average values and potency between the different parameters in 
Table VI. 1 is probably caused by the difference in the number of substances for which a 
particular variable is present. When only substances are used for which all 6 parameters were 
present, this reduces the database to 44 substances (Table VI. 2Error! Reference source not f
ound.). A part of the difference between the parameters in potency difference can be explained 
by the unusual dose levels (NOAEL 0.026 mg/kg bw/day and LOAEL 0.26 mg/kg bw/day) used 
in the study for the substance that had the lowest values for all parameters (cadmium oxide). 

Table VI. 2   Average values (assuming log/normal distribution) (in mg/kg bw/day) and 
potency differences for parameters for developmental toxicants (N=44) with all 6 parameters 
(Muller et al, 2012) 

Parameter 

Average  Standard 
deviation 

Lowest 
value 

Highest 
value 

Potency 
difference 

NOAEL (overall) 

19 

7 

0.026 

684 

26308 

 
 
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LOAEL (overall) 

ED10 (overall) 

NOAEL (classification) 

LOAEL (classification) 

ED10 (classification) 

58 

44 

25 

71 

49 

7 

5 

7 

6 

6 

0.260 

2281 

0.300 

0.026 

570 

684 

0.260 

2281 

0.300 

933 

8773 

1900 

26308 

8773 

3110 

Comparing Table VI. 1 and Table VI. 2 indicates no major changes in average, standard 
deviation and highest value for each parameter. However, the lowest value changes for several 
parameters. The resulting potency difference becomes much more comparable between the 
parameters. This indicates that the difference between the parameters in potency difference in 
Table VI. 1 is mainly due to the absence of an ED10 for some very potent substances. 

VI.2.4.2  Potency parameters for substances with an adverse effect on sexual 

function and fertility (Muller et al, 2012) 

Data for one or more of the potency parameters were available for 93 substances classified for 
adverse effects on sexual function and fertility (hereafter called fertility toxicants) when the 
work with the guidance development started. For all substances, an LOAEL was available but a 
NOAEL and an ED10 were sometimes missing. The absence of a NOAEL is mostly caused by the 
absence of a dose level without an effect in the study or database of a substance. The absence 
of an ED10 value is mainly caused by the absence of a NOAEL and in most of those cases an 
ED10 could only be derived by a Benchmark Dose (BMD) approach to avoid interpolation 
between the LOAEL and the vehicle control. Another cause for the absence of an ED10 values is 
the limited reporting of effect levels in the consulted study summaries or study reports. 

The difference in the average values between the highest and lowest of the six parameters for 
potency is less than a factor of four. This is small compared to the difference in potency 
between substances for each parameter of up to 30,000 (Table VI. 3). The difference in potency 
within the parameters is more pronounced for the NOAEL values than for the values of LOAEL 
and ED10, which is mainly due to one substance with a NOAEL of 0.032 mg/kg bw/day but an 
LOAEL of 10 mg/kg bw/day. The available data indicate that there is a close relation between 
the NOAEL, LOAEL and ED10 for most substances. The average LOAEL is between a factor 2 and 
3 above the average NOAEL. The fact that it is not closer to the factor of 3 to 4 that is normally 
used between dose levels is probably due to the absence of an NOAEL for a number of 
substances. The average ED10 is between the average NOAEL and LOAEL. 

Table VI. 3   Average values (assuming log/normal distribution) (in mg/kg bw/day) and 
potency differences for parameters for all fertility toxicants of the database 

Average  Standard 
deviation 

Lowest 
value 

Highest 
value 

Potency 
difference 

Parameter 

NOAEL (overall) 

LOAEL (overall) 

ED10 (overall) 

NOAEL 
(classification) 

LOAEL 
(classification) 

N 

68 

93 

37 

70 

20 

54 

31 

24 

93 

62 

ED10 (classification) 

37 

33 

7 

7 

5 

7 

7 

6 

0.032 

635 

19844 

0.25 

2060 

0.6 

1065 

8240 

1775 

0.032 

940 

29375 

0.33 

2060 

6242 

0.6 

1065 

1775 

 
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A part of the differences in the average values and in potency between the different parameters 
in Table VI. 3 is probably caused by the difference in the number of substances for which a 
particular parameter is present. When only substances are used for which all 6 parameters were 
present, this reduces the database to 34 substances (Table VI. 4).  

 
 
 
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Table VI. 4   Average values (assuming log/normal distribution) (in mg/kg bw/day) and 
potency differences for parameters for fertility toxicants (N=34) with all 6 parameters 

Parameter 

NOAEL (overall) 

LOAEL (overall) 

ED10 (overall) 

NOAEL(classification) 

LOAEL(classification) 

ED10 (classification) 

Average  Standard 
deviation 

Lowest 
value 

Highest 
value 

Potency 
difference 

19 

72 

35 

24 

89 

39 

6 

6 

5 

6 

6 

5 

0.3 

0.7 

1.3 

0.3 

0.7 

1.3 

250 

1000 

1065 

940 

1580 

1065 

833 

1429 

819 

3133 

2257 

819 

Comparing Table VI. 3 and Table VI. 4 indicates no major changes in average, standard 
deviation and highest value for each parameter. However, the lowest value changes for some 
parameters. The resulting potency difference becomes much more comparable between the 
parameters. This indicates that part of the differences between the parameters in potency 
difference in Table VI. 3 is due to the absence of an ED10 for some very potent substances. 

VI.2.4.3  Conclusions on the most appropriate parameter for potency 

As LOAELs are available for almost all substances, this could be considered the most useful 
informed parameter on which to base potency. However, in the absence of a NOAEL, a LOAEL is 
not a suitable parameter for potency because there is no indication to what extent the real 
LOAEL could be lower than the LOAEL observed. The lower number of substances for which an 
ED10 is available is probably due to the limitations of the available study summaries for several 
substances. Use of the ED10 requires access to a detailed summary of the study or the study 
report itself which was not available for several substances in the database.  

However, this guidance can be applied by both industry and Member State Competent 
Authorities when preparing proposals for harmonised classification and labelling, and by 
industry in case of self-classification of a reproductive toxic substance for which there is no 
entry in Annex VI to CLP.  

Companies have access to their own studies. It is expected that by the completion of the REACH 
registration deadlines, more detailed information including ED10 will be available for more 
substances than in this database used to develop this guidance.   

Member States have access to the study summaries in the registrations. The full studies could 
be requested by ECHA or by a Member State Competent Authority, according to CLP Article 
49(3).  

It should be noted that in the absence of a NOAEL, an ED10 cannot be determined by 
interpolation, in case the size of the effect at the LOAEL is more than 10%. However, an ED10 
can be estimated using bench mark dose (BMD) software when sufficient data are available. A 
NOAEL and LOAEL cannot be estimated using the BMD approach. In addition, a fixed level of 
effect of e.g. 10% (ED10) is considered to be more representative for the potency and facilitates 
comparisons of relative potency between substances to a greater extent, than a LOAEL which is 
a chosen dose level. 

For most other hazard classes, the SCLs are based on effect levels. For carcinogenicity the T25 
is used, and for skin sensitisation the EC3 value or the dose level with a certain level of 
responders is used. Therefore, the LOAEL or ED10 is considered a more appropriate parameter 
for determination of an SCL than the NOAEL.  

 
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For substances where there is a difference in the LOAEL overall (lowest dose with any effect on 
reproduction) versus the LOAEL classification (lowest dose with an effect on reproduction 
fulfilling the classification criteria), this is in most cases due to non-significant increases in 
lethalities or malformations or decreases in foetal body weight at the LOAEL overall versus 
significant increases in lethalities or malformations at the LOAEL classification. The difference 
between significant and non-significant effects will disappear if the ED10 is used as parameter 
for potency.  

The difference in parameters between ‘overall’ and ‘classification’ was sometimes due to limited 
effects that normally do not warrant classification such as a small increase in variations at the 
LOAEL and to more severe effects warranting classification at a higher dose level. To have a 
more consistent parameter for potency, it was preferred to use the parameters for effects 
warranting classification. 

Overall, the use of the ED10 for effects warranting classification is proposed as the most 
appropriate estimate for the potency. The advantage of this parameter is that it is a dose level 
with a specified level of effects of at least a certain severity. This is in line with most 
classification criteria and with other methods for the determination of SCLs.   

Furthermore, not all aspects included in the working definition of reproductive potency are fully 
taken into account in the ED10. Therefore, certain additional parameters should be considered 
which can change the potency group as determined by using the ED10, resulting in the setting of 
lower or higher concentration limits. See Chapter 4 for such modifying factors.  

VI.3  Modifying factors 

Several possible elements of reproductive toxicity were considered as elements which should 
also be taken into account when determining the potency group for reproductive toxicity of a 
substance (modifying factors). Modifying factors may change the potency group for a 
substance.  While some modifying factors should always be taken into account, other modifying 
factors could be more relevant when the potency is close to the boundary between two groups 
(see below). It should be noted that several of the elements may be interrelated.  

VI.3.1  Boundaries of the potency groups 

Table VI. 5   Boundaries of the potency groups 

Potency group 

Boundaries 

High potency group 

ED10 value ≤ 4 mg/kg bw/day 

Medium potency group 

4 mg/kg bw/day < ED10 value   400 mg/kg bw/day 

Low potency group 

ED10 value   400 mg/kg bw/day. 

Some factors may have already been taken into account in deciding on the classification as a 
reproductive toxicant. Where such considerations have been made, care should be taken not to 
use that information again when determining the potency. For example, when the effects 
determining the ED10 were observed at dose levels also causing maternal toxicity, this should 
already have been taken into consideration during the classification and should not be used 
again to set a higher SCL. Factors considered not to be used as modifying factors are included 
in section IV.4 of this Annex. The following factors are used as modifying factors:  

•  Type of effect / severity 
•  Data availability 
•  Dose-response relationship 
•  Mode or mechanism of action 

 
 
 
 
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•  Toxicokinetics 
•  Bio-accumulation of substances 

The justification of the use of these modifying factors is provided in the guidance (see Section 
3.7.2.6.5). 

VI.4  Non-modifying factors 

A wide range of parameters were considered as possible modifying factors for the determination 
of reproductive potency. Parameters selected as modifying factors are included above. 
Parameters or factors considered but not included as modifying factors are listed below:  

VI.4.1  Species and strains 

The species used to determine the ED10 could be considered as a modifying factor if it is shown 
that a certain species is generally more sensitive to reproductive toxicants, meaning showing 
effects at a lower exposure level, and this can be considered relevant to humans. However, 
comparison of the different parameters between the two most used species for developmental 
effects, rats and rabbits, did not indicate a difference in average NOAEL, LOAEL or ED10 in this 
analysis. Furthermore, almost all studies that were determinative for the classification for 
fertility were studies in rats. Therefore, species is not regarded as a modifying factor. The most 
sensitive species for each substance has to be used to determine the potency parameter unless 
there is clear evidence that the observed effects are not relevant to humans or when there is 
good evidence for a difference in sensitivity between humans and the test species. This also 
applies to different strains. 

VI.4.2  Systemic or maternal toxicity 

Adverse effects on fertility and sexual function may be caused as a secondary effect of systemic 
toxicity to other organs. Developmental effects may be caused as a secondary effect of 
maternal toxicity. However, this should have already been taken into account for classifying a 
substance in a specific category. Therefore, this should not also be used for modifying the 
concentration limit. 

VI.4.3  Mutagenicity 

Analyses of the databases [(Muller et al., 2012)] indicate that substances classified both for 
reproductive toxicity and mutagenicity have a higher potency (lower ED10) than substances 
classified for reproductive toxicity only. However, as this higher potency is already included in 
the lower ED10, there is no need to use mutagenicity as a modifying factor. 

VI.4.4  Volatility 

Volatility is a physical property related to exposure rather than to the intrinsic hazardous 
potency of a substance. However, the exposure level to a substance in a mixture is not only 
influenced by the concentration but also by the volatility of the substance. The higher the 
volatility of a substance the higher the inhalation exposure may be when handling such a 
substance in a mixture. Inhalation exposure to vapours are not covered by the experimental 
oral testing limit of 1000 mg/kg bw/day as the exposure at workplaces can be more than one 
order of magnitude above the extrapolated exposure level covered by the limit dose (Schneider 
et al., 2007). This is probably the reason why no limit dose for classification is included in the 
classification criteria (see appendix I, 3.7.2.5.4). Therefore, volatility could be considered as a 
modifying factor. 

However this argument is not specific for reproductive toxicity and should then apply to all 
relevant hazard classes. In methods for setting SCLs for other hazard classes such as 

 
 
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carcinogenicity, the volatility is not used as a modifying factor, although it is suggested to be a 
factor to take into consideration when setting SCLs for narcotic effects (STOT-SE 3). Further, 
volatility is not specifically mentioned in the criteria for classification for any other hazard class 
other than STOT-SE and -RE (CLP Annex I 3.8.2.1.10.4 and CLP Annex I 3.9.2.10.4) for which 
the guidance recommends a specific precautionary statement on the label for highly volatile 
substances. 

However for some hazard classes, volatility is taken into account in the classification of 
substances and mixtures by using different numeric criteria, (CLP Annex I Table 3.1.1: see 
section 3.1.2.2 of this Guidance) or guidance values (CLP Annex I Table 3.8.2 – see section 
3.8.2.2.1 of this Guidance and Annex I Table 3.9.2 and 3.9.3- see section 3.9.2.2 of this 
Guidance) for vapours than for dusts and mists. For STOT-SE and STOT-RE, the method for 
setting SCLs is directly depending on these guidance values. 

It was decided not to include volatility as a modifying factor because it is a physical property 
that depends also on other factors (e.g. temperature and composition of the mixture) and is 
therefore more related to exposure rather that to the intrinsic hazardous potency of the 
substance.   

VI.5  Potency groups and specific concentration limits 

VI.5.1 

Justification of the proposed potency boundaries and specific 
concentration limits 

In the following some general considerations on potency groups are first provided, followed by 
justifications for the approach taken and for the suggested boundaries of the potency groups 
and the corresponding concentration limits. 

VI.5.1.1  General considerations on potency groups 

VI.5.1.1.1  Legal requirements 

According to the second subparagraph of CLP Article 10(1): 

Article 10 (1)   

Specific concentration limits shall be set by the manufacturer, importer or downstream user 
where adequate and reliable scientific information shows that the hazard of a substance is 
evident when the substance is present at a level below the concentrations set for any hazard 
class in Part 2 of Annex I or below the generic concentration limits set for any hazard class 
in Parts 3, 4 and 5 of Annex I. 

According to the third subparagraph of CLP Article 10(1): 

Article 10 (1)  

In exceptional circumstances specific concentration limits may be set by the manufacturer, 
importer or downstream user where he has adequate, reliable and conclusive scientific 
information that a hazard of a substance classified as hazardous is not evident at a level 
above the concentrations set for the relevant hazard class in Part 2 of Annex I or above the 
generic concentration limits set for the relevant hazard class in Parts 3, 4 and 5 of that 
Annex. 

VI.5.1.1.2   Scientific results of the database analysis 

The databases with ED10 values for substances (Category 1 and 2) with an effect on 
development and with an effect on sexual function and fertility were compared to determine 

 
 
 
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whether there is a difference in potency between Category 1 and Category 2 substances 
[(Muller et al, 2012)]. The results should be carefully interpreted because of the limitations of 
the database: the database is based on a limited number of substances and the available data 
per substance is reduced to a single number (ED10) and some modifying factors. Reducing the 
data in the database would have included removal of differences in effects and doubts between 
Category 1 and Category 2. In any case, the comparisons indicate that the average potency of 
substances with an effect on development and with an effect on sexual function and fertility are 
comparable and that also the average potencies of Category 1 and 2 substances are comparable 
and certainly do not differ by a factor of 10. 

VI.5.1.1.3   Policy related considerations and proposed method 

Data derived from an insensitive test method could in some cases not be regarded as adequate, 
reliable and conclusive evidence, as mentioned in Article 10 (1) (3rd para). For example, a 
screening assay which only uses a limited number of animals and studied endpoints, cannot be 
used to set higher SCLs (but can be used to set lower SCLs). Also a study resulting in an LOAEL 
without an NOAEL cannot be used to set higher SCLs. 

Determination of the boundaries of the potency groups (see Table VI. 5) and the SCL or GCL for 
each group is a policy related issue.  CLP Article 10, the criteria in Annex I to CLP and the 
available data do not give a clear direction. Therefore, a simple system was developed. 
Furthermore, the approach taken is similar to the one developed for other hazard classes such 
as skin sensitization and carcinogenicity, which should be an appropriate justification for the 
current method.   

Determination of the potency for reproductive toxicity will in most cases be based on limited 
data from one or a few studies. It was recognised that an exact SCL for each substance that 
also differs for each substance would indicate a precision that is not realistic or scientifically 
justified. Also, Janer (2007) has shown that the variation in the NOAELs of 2-generation studies 
for one substance is considerable. Therefore, it is proposed to divide the substances into large 
potency groups with associated SCLs as it is done for other hazard classes. Three potency 
groups are proposed. As shown in Table VI. 6 below, substances with the lowest potency 
(highest ED10) fall in a group with an SCL above the GCL. Most substances should fall in the 
group with the GCL. Only substances with a very high potency (low ED10) should fall in the 
group with a SCL below the GCL. It is proposed to include approximately 70 – 80% in the GCL 
potency group and 5 to 15% in the low and high potency groups. Further, as the average 
potency of developmental toxicants and substances affecting sexual function and fertility are 
comparable, it is proposed to use the same boundaries for both types of effect. Also, the 
database shows there is no difference in potency between substances in Category 1 and 
Category 2. Therefore it is proposed to use the same boundaries for Category 1 and 2 
substances. 

VI.5.1.1.4   Other methods considered 

Several other options for a method for determining SCLs were discussed including a method 
that was used by the TC C&L in a limited number of cases in the past. This method is based on 
the limit dose of 1000 mg/kg bw/day, as described in the test guideline OECD 414 and 416.  

The concentration limit expressed as a % in mixtures is derived by dividing the NOAEL by the 
limit dose followed by multiplication by 100 (see ECBI/47/02 Add.7). This method would result 
in an individual SCL for each substance. This would indicate a precision that cannot be expected 
from standard reproduction studies. Also this would result in an SCL for most substances and in 
a GCL for only some substances. Therefore, this method was not considered. Potency groups 
are used in the proposed method because this does not give the impression of a high precision 
and allow the placing of many substances in the medium potency group with the connected 
GCL. 

 
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VI.5.1.2  Justification of the boundaries between the three potency groups 

The estimated percentages of already classified substances in each group for both Category 1 
and 2 substances with an effect on development or an adverse effect on fertility and sexual 
function are provided in the tables below.  They are based on the distribution of potencies of 
known developmental toxicants and of known fertility toxicants (Muller et al., 2012). Several 
possible values of the boundaries between the three groups are tested.  The estimations are 
based on counting the number of substances above or below a number of possible boundaries 
and applying some of the modifying factors such as the presence of a NOAEL and considering 
also the saturated vapour concentration for substances in the low potency group. However, the 
saturated vapour concentration, reflecting volatility, is not proposed as a modifying factor in the 
guidance.  

Taking into account all modifying factors for all substances would imply a full assessment of the 
potency for all substances. This was not possible within the available resources. As most 
modifying factors result in a shift from the low potency group into the medium potency group 
and from the medium potency group into the high potency group, it is likely that the 
percentages in the low potency group may decrease and the percentages in the high potency 
group may increase. (Thus, the effect of volatility on the frequencies in Table VI. 6 should be 
marginal.) 

Based on the ED10 distribution a rough estimate was made by the Working group of the optimal 
boundaries using a range of a factor of 100 for the medium potency group. Then the number of 
substances falling into several combinations of boundaries was estimated. 

 
 
 
 
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Table VI. 6   Percentages of substances in the three potency groups using the ED10 and some 
of the modifying factors for different boundaries of the potency groups and considering the 
saturated vapour concentration of low potency substances 

Boundaries of the high and low potency groups 

<2 
mg/kg 

<3 
mg/kg 

<4 
mg/kg 

<5 
mg/kg 

<6 
mg/kg 

<7 
mg/kg 

Type of 
effect 

Classifica
tion 

Potency 
group 

>200 
mg/kg 

>300 
mg/kg 

>400 
mg/kg 

>500 
mg/kg 

>600 
mg/kg 

>700 
mg/kg 

Develop
ment 

Cat 
1A/1B 

H360D 

High 
potency 

Medium 
potency 

12,1 

13,8 

17,2 

20,7 

20,7 

20,7 

75,9 

77,6 

79,3 

77,6 

79,3 

79,3 

Low potency 

12,1 

8,6 

3,4 

1,7 

0,0 

0,0 

% with SCL 

24,1 

22,4 

20,7 

22,4 

20,7 

20,7 

Cat 2 

H361d 

High 
potency 

Medium 
potency 

10,3 

13,8 

13,8 

17,2 

17,2 

20,7 

72,4 

72,4 

79,3 

75,9 

82,8 

79,3 

Low potency 

17,2 

13,8 

6,9 

6,9 

0,0 

0,0 

% with SCL 

27,6 

27,6 

20,7 

24,1 

17,2 

20,7 

Fertility 

Cat 
1A/1B 

H360F 

High 
potency 

Medium 
potency 

3,4 

3,4 

3,4 

6,9 

10,3 

13,8 

89,7 

93,1 

96,6 

93,1 

89,7 

86,2 

Low potency 

6,9 

% with SCL 

10,3 

3,4 

6,9 

0,0 

3,4 

0,0 

6,9 

0,0 

0,0 

10,3 

13,8 

Cat 2 

H361f 

High 
potency 

Medium 
potency 

6,3 

9,4 

10,9 

15,6 

15,6 

17,2 

71,9 

76,6 

81,3 

78,1 

79,7 

79,7 

Low potency 

21,9 

14,1 

7,8 

6,3 

4,7 

3,1 

% with SCL 

28,1 

23,4 

18,8 

21,9 

20,3 

20,3 

avg high 
potency 

avg medium 
potency 

avg low 
potency 

avg % with  
SCL 

8.0 

10.1 

11.3 

15.1 

16.0 

18.1 

77.5 

79.9 

84.1 

81.2 

82.9 

81.1 

14.5 

10.0 

4.5 

3.7 

1.2 

0.8 

22,5 

20,1 

15,9 

18,8 

17,1 

18,9 

All 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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As shown in Table VI. 6 boundaries of 4 to 400 mg/kg bw/day would result in the maximum 
number of substances being included in the medium potency range for most types of effects 
and classifications and for both type of effects and classifications combined. For developmental 
effects Category 1 and 2 the percentage of substances in the medium potency group is within 
the target of ca. 70-80%. For effects on sexual function and fertility Category 2 this is almost 
the case. Only for Category 1 is this not the case. The percentage of substances in the medium 
potency group could be reduced by reducing the factor of 100 between the boundaries. 
However, because of the large difference in potency of the substances classified for reproductive 
toxicity of up to a million, this was not considered necessary. The percentage of substances in 
the high potency group is higher than the percentage in the lower potency group for the 
boundaries of 4 to 400 mg/kg bw/day. However, the percentage of substances in the high 
potency group was above 15% for substances classified for an effect on development in 
Category 1. 

Following the PEG consultation, it was agreed that volatility was not considered a modifying 
factor and thus, the ED10 distribution changes as shown in Table VI. 7. Borders of 4 to 400 
mg/kg bw/day would result in the maximum number of substances being included in the 
medium potency range for most type of effects and classifications and for both type of effects 
and classifications combined. However, the same value also applies to some of the other 
borders. For developmental effects Category 1 and 2 the percentage of substances in the 
medium potency group is within the target of ca. 70-80%. For effects on sexual function and 
fertility Category 2 this is not the case. The percentage of substances in the medium potency 
group could be reduced by reducing the factor of 100 between the borders. However, because 
of the large difference in potency of the substances classified for reproductive toxicity of up to a 
million, this was not considered necessary. The percentage of substances in the high potency 
group is approximately the same as the percentage in the lower potency group for the borders 
of 4 to 400 mg/kg bw/day.  

 
 
 
 
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Table VI. 7   Percentages of substances in the three potency groups using the ED10 and some 
of the modifying factors but not volatility for different borders of the potency groups 

Borders of the high and low potency groups 

≤2 
mg/kg 

≤3 
mg/kg 

≤4 
mg/kg 

≤5 
mg/kg 

≤6 
mg/kg 

≤7 
mg/kg 

Type of 
effect 

Classifica
tion 

Potency group 

≥200 
mg/kg 

≥300 
mg/kg 

≥400 
mg/kg 

≥500 
mg/kg 

≥600 
mg/kg 

≥700 
mg/kg 

Develop
ment 

Cat 1A/1B 

High potency 

12.1 

13.8 

17.2 

20.7 

20.7 

20.7 

H360D 

Medium potency 

67.2 

74.1 

77.6 

75.9 

79.3 

79.3 

Low potency 

20.7 

12.1 

5.2 

3.4 

0 

0 

% with SCL 

32.8 

25.9 

22.4 

24.1 

20.7 

20.7 

Cat 2 

High potency 

7.3 

9.8 

9.8 

12.2 

12.2 

14.6 

H361d 

Medium potency 

68.2 

65.8 

70.7 

70.7 

75.6 

78.1 

Low potency 

24.4 

24.4 

19.5 

17.1 

12.2 

7.3 

% with SCL 

31.7 

34.2 

29.3 

29.3 

24.4 

21.9 

Fertility 

Cat 1A/1B 

High potency 

3.4 

3.4 

3.4 

6.9 

10.3 

13.8 

H360F 

Medium potency 

86.3 

89.7 

93.2 

89.7 

86.3 

86.2 

Low potency 

10.3 

6.9 

% with SCL 

13.7 

10.3 

3.4 

6.8 

3.4 

3.4 

0 

10.3 

13.7 

13.8 

Cat 2 

High potency 

6.3 

9.4 

10.9 

15.6 

15.6 

17.2 

H361f 

Medium potency 

68.7 

73.4 

78.2 

75.0 

76.6 

76.5 

All 

Low potency 

25.0 

17.2 

10.9 

9.4 

7.8 

6.3 

% with SCL 

31.3 

26.6 

21.8 

25.0 

23.4 

23.5 

avg high 
potency 

avg medium 
potency 

7.3 

9.1 

10.3 

13.9 

14.7 

16.6 

72.6 

75.7 

79.9 

77.8 

79.4 

80.0 

avg low potency 

20.1 

15.2 

9.8 

8.3 

5.9 

3.4 

avg % with  
SCL 

27.4 

24.3 

20.1 

22.2 

20.6 

20.0 

On average, combining both effect types and both classification categories, the goal of 70-80% 
of the substances in the medium potency group and 5 -15% of the substances in the low and 
high potency group was fulfilled with boundaries of 4 and 400 mg/kg bw/day. However, other 
combinations of boundaries such as 3 and 300 and 5 to 500 mg/kg bw/day also fulfill these 
requirements. Using these boundaries would result in a change of potency group for 10 to 14 
substances (5 – 7%). Further it could be considered to lower the factor of 100 between the 
borders to increase the number of substances. For example, using boundaries of 5 to 300 
mg/kg bw/day would result in 13.9% high potency substances, 15.2% low potency substances 
and 71% substances in the medium potency group. Also, the percentages provided in Table VI. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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6 and Table VI. 7 are calculated not using every modifying factor. Therefore, it can be stated 
that the choice of the boundaries is arbitrary. However, based on the available information, the 
boundaries of 4 to 400 mg/kg bw/day seem to be reasonable. 

VI.5.1.3  Concentration limits for Category 1 and Category 2 substances 

The generic concentration limit (GCL) from the respective categories will be used for medium 
potency substances (group 2). As mentioned earlier the GCL is 0.3% for reproductive toxicants 
Category 1A and 1B and 3.0% for Category 2. 

Category 1A and 1B 

Different concentration limits have to be used for the different potency groups. Substances 
classified in Category 1 in the low potency group (group 3) can have a SCL above the GCL of 
0.3%. We propose to use an SCL of 3% which is tenfold of the GCL. A factor of 10 is used often 
in CLP as difference in GCL between hazard categories. This factor is also used in the guidance 
for setting SCLs for carcinogens. For substances in group 1 (high potency), it is proposed to use 
a SCL of 0.03%. For extremely potent reproductive toxicants with an ED10 (classification) of 
more than 10 fold below the boundary limit of 4 mg/kg bw/day it is proposed to use even lower 
SCLs. For every factor of 10 below the upper limit the SCL is reduced with a factor of 10. 

Category 2 

Substances classified in Category 2 in the low potency group (group 3) can have a SCL above 
the GCL of 3%. We propose to use an SCL of 3-10% which is one to 3-fold of the GCL. An SCL 
above 10% was considered too high. The upper SCL of 10% can only be used in exceptional 
cases (NOAEL below 1000 mg/kg bw/day but ED10 above 1000 mg/kg bw/day). This would 
account for none of the substances in the database. For high potency substances (group 1), it is 
proposed to use an SCL of 0.3%. For extremely potent reproductive toxicants with an ED10 
(classification) of more than 10-fold below the boundary limit of 4 mg/kg bw/day it is proposed 
to use even lower SCLs. For every factor of 10 below the upper limit, the SCL is reduced by a 
factor of 10.  

The resulting SCLs for each potency group are presented in Table VI. 8. 

Table VI. 8   SCLs for substances in each potency group and classification category 

Category 1 

Dose 

Group 1 high 
potency 

ED10 (classification) 
below 4 mg/kg 
bw/day 

Group 2 
medium 
potency 

ED10 > 4 mg/kg 
bw/day, and < 400 
mg/kg bw/day 

SCL 

0.03% 

(factors of 10 
lower for 
extremely potent 
substancesB)  

0.3% (GCL) 

Group 3 low 
potency 

ED10 (classification) 
above 400 mg/kg 
bw/day 

3%  

Category 2 

Dose 

ED10 (classification) 
below 4 mg/kg 
bw/day 

ED10 > 4 mg/kg 
bw/day, and < 400 
mg/kg bw/day 

ED10 (classification) 
above 400 mg/kg 
bw/day 

SCL 

0.3% 

(factors of 10 
lower for 
extremely potent 
substancesB)  

3% (GCL) 

3-10% A 

A The limit of 10% may be considered in certain cases, such as for substances with an ED10 value above 
1000 mg/kg bw/day and a NOAEL below 1000 mg/kg bw/day. 

B For substances with an ED10 more than 10 fold below 4 mg/kg bw/day, meaning an ED10 below 0.4 
mg/kg bw/day, a 10-fold lower SCL should be used. For even more potent substance the SCL should be 
lowered with a factor of 10 for every factor of 10 the ED10 is below 4 mg/kg bw/day. 

 
 
 
 
 
 
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649 

Assigning two SCLs to a substance  

A reproductive toxic substance is classified in one category for both effects on development and 
on sexual function and fertility. Within each category effects on development and on sexual 
function & fertility are considered separately. The potency and resulting concentration limits 
have to be determined separately for the two main types of reproductive toxic effects. In case 
the potency and resulting specific concentration limits are different for sexual function/fertility 
and development for a substance, the substance needs to be assigned one SCL for 
developmental toxicity and another SCL for effects on sexual function and fertility. These 
concentration limits will in all cases trigger different specifications of the hazard statements for 
the two main types of effects, to be applied to mixtures containing the substance (see also 
3.7.4.1, Annex I, CLP).  

VI.5.2  Assigning SCLs 

The SCL or GCL for each substance can be determined using the final potency group of the 
substance using Table VI. 6.  

VI.6 

References 

Gemma Janer, Betty C. Hakkert, Aldert H. Piersma, Theo Vermeire and Wout Slob (2007) A 
retrospective analysis of the added value of the rat two-generation reproductive toxicity study 
versus the rat subchronic toxicity study. Reproductive Toxicology 24,103-123. 

Schneider K, Oltmans J, van Gelder R and Gebel T (2007) Suitability of the limit dose in 
evaluating reproductive toxicity of substances and preparations. International Journal of 
Toxicology, 26: 183-195. 

Regulation (EC) No 1272/2008 on the classification, labelling and packaging of substances and 
mixtures. Official Journal of the European Union L353, 31-12-2008. 

Regulation (EC) NO 1907/2006 concerning the Registration, Evaluation, Authorisation and 
Restriction of Chemicals (REACH). Official Journal of the European Union L136, 29-05-2007. 

R.8 Guidance on information requirements and chemical safety assessment. Chapter R.8: 
Characterisation of dose [concentration]-response for human health. ECHA, 2008. 

Commission Working Group on the Classification and Labelling of Dangerous Substances (date 
unknown) Guidelines for setting specific concentration limits for carcinogens in Annex I to 
Directive 67/548/EEC – Inclusion of potency considerations. 
http://ec.europa.eu/environment/archives/dansub/pdfs/potency.pdf  

Muller A, Blaude M-N, Ihlemann C, Bjorge C, Ohlsson A and Gebel T (2012) A regulatory 
approach to assess the potency of substances to the reproduction. Regulatory Toxicology and 
Pharmacology 63, 97-105. 

 
 
 
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VII   ANNEX VII: RELATION BETWEEN TRANSPORT AND CLP 
CLASSIFICATION REGARDING PHYSICAL HAZARDS 

Table VII. 1 on physical hazards only, provided in this annex, contains additional information on 
transport classifications in relation to CLP classifications that could be of added value. However, 
these comparisons have certain restrictions with regard to their applicability. In particular, the 
area of applicability of the transport regulation is different from the CLP Regulation (ADR 49 
countries, IMDG-Code, ICAO-TI international regulations). Therefore, the table should be used 
as reference for deriving CLP classifications and not vice versa. 

The transport classification of named substances or mixtures in the transport regulations 
reflects the transport conditions and therefore were not adapted to take into account the GHS 
criteria. The transport classifications may be based on experience or certain events that are 
specific to transport. The transport classification of named substances or mixtures is legally 
binding for transport and should not be used to derive a CLP classification without an expert 
review. 

The transport regulations include the concept of precedence of hazards which guarantees that 
information on the most dangerous hazards is communicated with precedence. CLP does not 
apply a precedence of hazards and therefore substances or mixtures might need to be classified 
in additional hazard classes under CLP, which in the transport classification are allocated and 
noted under the respective UN-Number (giving information on subsidiary risks, appropriate 
packaging and transport conditions). 

It needs to be noted that a substance may have more than one entry in the Dangerous Goods 
List. These are usually within the same class, but transport conditions are different because of 
different severity of the hazard for different concentrations of this substance. 

The following table refers only to physical hazards, as health hazards are not harmonised 
regarding cut-off values, and/or allowed methods. 

Tabel VII. 1  Relation between transport and CLP classifications regarding physical hazards 

  (NOTE that within transport, the term ‘substances’ covers also mixtures in CLP terms.) 

Transport classification 

Physical 
state 

CLP-classification 

Remarks 

Transport 
class and 
(sub)division 
(if 
applicable) 

Packing group, 
division, type, 
group or code 

Class 1 

Division 1.1 

Division 1.2 

Division 1.3 

Division 1.4 

Division 1.5 

Division 1.6 

Liquid or 
solid 

Hazard 
category, 
division, 
type or 
group 

Hazard class 

Explosives 

Division 1.1 

Matching criteria. 

Division 1.2 

Division 1.3 

Division 1.4 

Division 1.5 

Division 1.6 

However, if 
explosives are un-
packed or repacked, 
they have to be 
assigned to division 
1.1 unless the 
hazard is shown to 
correspond to one of 
the other divisions. 

Class 2* – 
Gases 

1 Compressed 
gas 

Gaseous 

Gases under 
pressure 

Compressed 
gas 

A correspondence 
only applies to the 

 
 
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2 Liquefied gas.   Gaseous 

3 Refrigerated 
liquefied gas 

Gaseous 

Liquefied 
gas.  

Refrigerated 
liquefied gas 

form in which the 
gas is transported. If 
it is used in a 
different form, then 
the classification has 
to be amended. 

Matching criteria 
with 2.5. Note: 
Gases may be 
packaged in other 
forms such as 
“chemical under 
pressure” or 
“adsorbed gases” 
that are not 
considered in the 
GHS/CLP. 

The transport 
classification does 
not differentiate 
between Aerosols 
Category 1 and 2 
(both are classified 
as class 2.1)  

4 Dissolved gas 

Gaseous 

Dissolved gas 

5 Aerosol 
dispensers,  

Class 2.1 

Class 2.2 

6  Other  articles 
containing 
gas 
under pressure 

7 Non-
pressurised 
gases subject to 
special 
requirements  

8 Chemicals 
under 
pressure*** 

Aerosols 

Not 
relevant 

(Articles)  

Category 1 

Category 2 

Category 3 

Gaseous 

Flammable 
gases 

Category 1 

Gaseous 

Oxidising 
gases 

Category 1 

Not 
relevant 

9 Adsorbed gas 

Gaseous 

Class 3 

Packing group I 

Liquid 

Packing group II 

Liquid 

Packing group 
III 

Liquid 

Flammable 
liquid 

Flammable 
liquid 

Flammable 
liquid 

Category 1 

Category 2 

Category 3 

Class 4.1 

Types B-F 

Solid or 
liquid 

Self-reactive 
substances 

Types B-F 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Packing group I 

Solid 

Solid 
desensitized 
explosives 

Packing group II  Solid 

Flammable 
solids 

Category 1 

Packing group 
III 

Solid 

Flammable 
solids 

Category 2 

652 

Class 4.1 
(solid 
desensitized 
explosives) 

Class 4.1 
(only readily 
combustible 
solids) 

Class 4.1 
(only readily 
combustible 
solids) 

Class 4.2 

Pyrophoric 
substances 

Packing group I 

Liquid 

Solid 

Class 4.2  

Packing group II  Solid 

Class 4.2 

Packing group 
III 

Solid 

Class 4.3 

Packing group I 

Packing group II 

Packing group 
III 

Liquid or 
solid 

Pyrophoric 
liquids 

Pyrophoric 
solids 

Self-heating 
substances 
and mixtures 

Self-heating 
substances 
and mixtures 

Substances 
which in 
contact with 
water emit 
flammable 
gases 

Category 1 

Category 1 

Category 1 

Category 2 

Category 1 

Category 2 

Category 3 

Class 5.1 

Packing group I 

Solid  

Oxidising solid  Category 1 

Packing group II 

Packing group 
III 

Class 5.1 

Packing group I 

Liquid 

Packing group II 

Packing group 
III 

Oxidising 
liquid 

Category 2 

Category 3 

Category 1 

Category 2 

Category 3 

Class 5.2  

Types B-F 

Solid or 
liquid 

Organic 
peroxides 

Types B-F 

Class 8 

Packing group 
III 

Liquid or 
solid 

Corrosive to 
metals  

Category 1 

Applies only when 
the substance or 
mixture is not 
classified as 
corrosive to skin 
and/or eye. 

 
 
 
 
 
 
 
 
 
 
 
 
 
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653 

(*) Substances and articles (except aerosols and chemicals under pressure) of Class 2 are assigned to one of 
the following transport groups according to their hazardous properties, as follows: A asphyxiant, O oxidising, F 
flammable, T toxic, TF toxic, flammable, TC toxic corrosive, TO toxic, oxidising, TFC toxic, flammable, corrosive, 
TOC toxic, oxidising, corrosive 

(**) Aerosols are assigned to one of the following transport groups according to their hazardous properties, as 
follows: A asphyxiant, O oxidising, F flammable, T toxic, C corrosive, CO corrosive, oxidising, FC flammable, 
corrosive, TF toxic, flammable, TC toxic corrosive,  TO toxic, oxidising, TFC toxic, flammable, corrosive, TOC 
toxic, oxidising, corrosive 

(***)  Chemicals  under  pressure  are  assigned  to  one  of  the  following  transport  groups  according  to  their 
hazardous properties, as follows: A asphyxiant, F flammable, T toxic, C corrosive, FC flammable, corrosive, TF 
toxic, flammable 

 
 
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