COMMISSION STAFF WORKING DOCUMENT Progress report on the assessment and management of combined exposures to multiple chemicals (chemical mixtures) and associated risks Accompanying the document COMMUNICATION FROM THE COMMISSION TO THE EUROPEAN PARLIAMENT, THE COUNCIL, THE EUROPEAN ECONOMIC AND SOCIAL COMMITTEE AND THE COMMITTEE OF THE REGIONS Chemicals Strategy for Sustainability Towards a Toxic-Free Environment
Date: 2020-10-14
Institutions: Directorate-General for Environment, European Commission
Subjects: EU strategy, chemical compound, chemical product, chemicals legislation, environmental protection, international cooperation, product safety, public health, research and development, toxic substance

EN 

  EN 

   EUROPEAN COMMISSION  Brussels, 14.10.2020  SWD(2020) 250 final  COMMISSION STAFF WORKING DOCUMENT Progress report on the assessment and management of combined exposures to multiple chemicals (chemical mixtures) and associated risks Accompanying the document COMMUNICATION FROM THE COMMISSION TO THE EUROPEAN PARLIAMENT, THE COUNCIL, THE EUROPEAN ECONOMIC AND SOCIAL COMMITTEE AND THE COMMITTEE OF THE REGIONS   Chemicals Strategy for Sustainability  Towards a Toxic-Free Environment   {COM(2020) 667 final} - {SWD(2020) 225 final} - {SWD(2020) 247 final} - {SWD(2020) 248 final} - {SWD(2020) 249 final} - {SWD(2020) 251 final}  
 
 
Contents 

1. INTRODUCTION ............................................................................................................................... 2 

2. WHY ARE MIXTURES A CONCERN? ........................................................................................... 6 

3. REGULATORY FRAMEWORKS AND REQUIREMENTS REGARDING MIXTURES ............ 10 

3.1 Intentional mixtures ..................................................................................................................... 12 

3.2 Unintentional mixtures ................................................................................................................ 14 

3.3 Grouping approaches ................................................................................................................... 17 

3.4 Aggregate Exposure .................................................................................................................... 18 

3.5 Conclusions on existing legal requirements for intentional and unintentional mixtures, grouping 
and aggregate exposure ..................................................................................................................... 19 

4.  PROGRESS ON GUIDANCE AND REGULATORY ASSESSMENT ......................................... 20 

5.  CASES OF REGULATORY ASSESSMENT OF MIXTURES ...................................................... 21 

6.   INTEGRATED AND CO-ORDINATED ASSESSMENT OF MIXTURES ACROSS 
DIFFERENT PIECES OF LEGISLATION .......................................................................................... 23 

6.1 Interface between different pieces of legislation ......................................................................... 23 

6.2 Case studies on priority mixtures ................................................................................................ 25 

7.   CLOSING THE KNOWLEDGE GAPS – RECENT ACHIEVEMENTS ...................................... 26 

7.1 Effect, exposure and hazard data ................................................................................................. 27 

7.2 Knowledge on mode of action, grouping, interactions and drivers of mixture toxicity .............. 29 

7.3 Remaining knowledge gaps ......................................................................................................... 32 

7.4 Future research and development priorities................................................................................. 35 

8.   INTERNATIONAL ACTIVITIES .................................................................................................. 37 

9.   POSSIBLE WAYS FORWARD TO ADDRESS CHALLENGES IN THE REGULATORY 
CONTEXT ............................................................................................................................................ 38 

10.  CONCLUSIONS ............................................................................................................................ 43 

1 

 
 
 
 
 
1.  INTRODUCTION 

Humans as well as other organisms are exposed to a  great variety of chemicals occurring in 
combinations also referred to as ‘mixtures’. Scientific evidence of the strengthened toxicity of 
such mixtures is mounting.1 Real-life examples of such mixtures are the different chemicals 
appearing  simultaneously  or  sequentially  in  e.g.  human  blood  or  in  a  water  body.  The  total 
risk related to the exposure to a combination of chemicals typically exceeds the risk related to 
the  exposure  to  each  of  the  individual  chemicals  in  the  mixture  on  their  own,  at  their 
respective  concentration  in  the  mixture2.  Therefore,  exposure  to  a  mixture  can  give  rise  to 
adverse  health  and  environmental  effects,  even  at  levels  of  exposure  which  are  considered 
‘safe’ for the individual chemicals on their own.  

Science  demonstrates  that  in  the  majority  of  the  cases,  the  toxicity  of  the  mixture  can  be 
assessed by adding up the toxicities of the individual chemicals in the mixture. This is called 
the  ‘concentration  addition  model’.  In  relatively  rare  cases,  so  called  ‘interactions’  are 
observed,  where  the  toxicity  of  the  mixture  is  stronger  or  weaker  than  what  would  be 
expected from applying concentration addition3. 

A  distinction  can  be  made  between  intentional  and  unintentional  mixtures.  Intentional 
mixtures  are  intentionally  manufactured  and  often  have  a  known  composition  and  are 
contained  in  one  product.  Typical  examples  are  products  like  paint,  glue  and  detergents. 
Unintentional mixtures arise spontaneously or coincidentally, for example in air, water, soil, 
as  well  as  in  humans  and  other  organisms  as  a  result  of  co-exposure.  They  arise  whenever 
chemicals are used on their own, as components in different intentional mixtures or in objects 
(i.e. complex products). Hence, an unintentional mixture typically includes chemicals from a 
variety of sources. Their compositions are usually more or less unknown and may vary over 
time and in space. Due to the very large number of possible combinations of chemicals, the 
risk  assessment  and  management  of  unintentional  mixtures  (sometimes  also  called 
‘coincidental  mixtures’  or  ‘combination  of  chemicals’)  represents  a  particular  scientific  and 
regulatory challenge.  
Regarding  EU  policy,  already  the  White  Paper  for  a  Future  Chemicals  Policy4  from  2001 
highlighted exposure to mixtures of chemicals as a research priority to cover knowledge gaps 
and achieve the goals set out. In 2009, the Environment Council adopted Conclusions5 on the 
‘combination effects of known chemicals’, which recognised the difficulties and deficiencies 
surrounding  the  regulation  of  mixtures.  It  also  invited  the  Commission  ‘to  assess  how  and 
whether relevant existing Community legislation adequately addresses risks from exposure to 
multiple  chemicals  from  different  sources  and  pathways,  and  on  this  basis  to  consider 
appropriate modifications, guidelines and assessment methods, and report back to the Council 
by early 2012 at the latest’.  

1 Kortenkamp, A. and Faust M. (2018) ‘Regulate to reduce chemical mixture risk - regulatory systems must better provide for 
risks from exposure to multiple chemicals’, Science: 361 (6399):224-225; July 2018; DOI: 10.1126/science.aat9219, with 
supplemental material. https://science.sciencemag.org/content/361/6399/224.full  
2 Kortenkamp, A., Backhaus, T., Faust, M., ‘State of the Art Report on Mixture Toxicity, Final Report, Executive Summary’ 
22 December 2009, European Commission Study Contract Number 070307/2007/485103/ETU/D.1. 
http://ec.europa.eu/environment/chemicals/effects/pdf/report_mixture_toxicity.pdf  
3  Interactions,  involving  either  stronger  (synergism)  or  lower  (antagonism)  effects,  appear  when  the  chemicals  involved 
interact on the molecular level. This is relatively rare and its effects relatively small, largely confined to mixture with only a 
few components.  
4  Commission  of  the  European  Communities  ‘White  Paper.  Strategy  for  a  future  Chemicals  Policy’  COM(2001)  88  final. 
https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52001DC0088&from=EN  
5  Council  conclusions  on  combination  effects  of  chemicals’,  2988th  Environment  Council  meeting  Brussels,  22  December 
2009. https://www.consilium.europa.eu/uedocs/cms_data/docs/pressdata/en/envir/112043.pdf 

2 

 
 
                                                           
The Commission responded to the Council through a Communication in 20126, drawing upon 
the  joint  opinion  of  three  EU  Scientific  Committees7  and  taking  into  account  the 
comprehensive  State  of  the  Art  Report  on  Mixture  Toxicity8.  In  the  Communication,  the 
Commission reviewed the scientific knowledge and the regulatory requirements regarding the 
assessment  of  mixtures  and  committed  itself  to  several  actions  and  to  presenting  a  report 
reviewing the progress and experience associated with the actions in the Communication.  
The  EU  7th  Environment  Action  Program9  stressed  the  need  for  appropriate  regulatory 
approaches to address  combination effects of chemicals. Recent resolutions of the European 
Parliament10,  11,  12,  13,  the  Conclusions  of  the  Environment  Council  on  the  chemicals  policy 
adopted in June 201914, and the Commission Communication on endocrine disruptors adopted 
in November 201815, all confirmed the need to better take into account the combined effects 
of  different  chemicals  for  the  protection  of  human  health  and  the  environment.  Further,  the 
Commission identified the combination effects of chemicals as a target action to be addressed 
in a Chemicals Strategy for Sustainability as part of the European Green Deal16.  

The  purpose  of  the  present  report  is  to  describe  the  progress  made  since  2012  on  the 
assessment of mixtures (combinations of chemicals) – both intentional and unintentional – to 
deliver on the follow-up action announced in the Communication and to provide background 
information  and  evidence  base  to  actions  announced  in  the  Chemicals  Strategy  for 
Sustainability.  This  report  presents  the  relevant  legal  requirements,  guidance  documents, 
methodologies and knowledge base as well as the remaining challenges.  It  also  provides an 
overview  of  suggestions  made  by  Member  States,  scientists  and  other  stakeholders  on 
possible ways forward.  

Box 1. Terminology17, 18, 19, 20, 21 

6  Communication  from  the  Commission  to  the  Council,  ‘The  combination  effects  of  chemicals,  Chemical  mixtures’ 
COM(2012) 252 final.  https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52012DC0252&from=EN  
7  Scientific  Committee  on  Health  and  Environmental  Risks  (SCHER),  Scientific  Committee  on  Emerging  and  Newly 
Identified Health Risks (SCENHIR) and Scientific Committee on Consumer Safety (SCCS). ‘Joint Opinion on the Toxicity 
and Assessment of Chemical Mixtures adopted on 14th December 2011’. https://doi.org/10.2772/21444  
8 Kortenkamp, A., Backhaus, T., Faust, M ‘State of the Art Report on Mixture Toxicity’, Final Report, Executive Summary, 
22 December 2009.  http://ec.europa.eu/environment/chemicals/effects/pdf/report_mixture_toxicity.pdf  
9  Decision  No  1386/2013/EU  of  the  European  Parliament  and  of  the  Council  of  20  November  2013  on  a  General  Union 
Environment  Action  Programme  to  2020  ‘Living  well,  within  the  limits  of  our  planet’.  https://eur-lex.europa.eu/legal-
content/EN/TXT/PDF/?uri=CELEX:32013D1386&from=EN  
10  European  Parliament,  ‘Resolution  of  17  April  2018  on  the  implementation  of  the  7th  Environment  Action  Programme’ 
(2017/2030(INI)).  http://www.europarl.europa.eu/doceo/document/TA-8-2018-0100_EN.pdf  
11  European  Parliament  ‘Resolution  on  Towards  a  comprehensive  European  Union  framework  on  endocrine  disruptors’ 
(2019/2683(RSP)) of April 15, 2019. http://ec.europa.eu/transparency/regdoc/rep/1/2018/EN/COM-2018-734-F1-EN-MAIN-
PART-1.PDF  
12  European  Parliament  ‘Resolution  on  Chemicals  strategy  for  sustainability’  of    July  8-10  European  Parliament  (2020) 
(2020/2531(RSP)) https://www.europarl.europa.eu/committees/fr/envi/documents/motions-for-resolution  
13  European  Parliament  resolution  of  10  July  2020  on  the  Chemicals  Strategy  for  Sustainability  (2020/2531(RSP)) 
https://www.europarl.europa.eu/doceo/document/TA-9-2020-0201_EN.pdf  
14  Council  conclusions:  Towards  a  Sustainable  Chemicals  Policy  Strategy  of  the  Union,  10713/19,  26  June  2019. 
http://data.consilium.europa.eu/doc/document/ST-10713-2019-INIT/en/pdf 
15  European  Commission,  ‘Communication  to the Parliament  and  the  Council:  Towards  a  comprehensive  European  Union 
framework on endocrine disruptors’, November 2018  (COM(2018) 734 final).  
http://ec.europa.eu/transparency/regdoc/rep/1/2018/EN/COM-2018-734-F1-EN-MAIN-PART-1.PDF 
16  Communication  from  the  Commission  to  the  European  Parliament,  the  European  Council,  the  Council,  the  European 
Economic  and  Social  Committee  and  the  Committee  of  the  Regions.  ‘The  European  Green  Deal’  ,  COM(2019)  640  final 
https://ec.europa.eu/info/sites/info/files/european-green-deal-communication_en.pdf  
17 Bopp, S., Richarz, A., Worth, A., Berggren, E. and Whelan, M. ‘Something from nothing? Ensuring the safety of chemical 
mixtures’ , JRC Science for Policy Brief May 2018. https://op.europa.eu/en/publication-detail/-/publication/4bd117ac-6d22-
11e8-9483-01aa75ed71a1/language-en   

3 

 
 
 
                                                           
  Mixture: (or chemical mixture) in this report means any set of chemicals to which an 

organism may be jointly exposed, and which may potentially cause an adverse 
combination effect, regardless of sources and exposure routes.  

  Intentional mixture: a mixture or solution which is composed of two or more 
substances (Article 3(2) REACH, Article 2(8) CLP), normally referring to a 
formulated product (mixture), manufactured and marketed as such, or the result of 
intentional use of different products (mixtures) together, where the composition is 
normally known.  

  Unintentional mixture: mixtures of chemicals co-occurring in environmental media 

(water, soil, air), biota, feed, food, or human tissues as a result of releases from various 
sources and through multiple routes of exposure (the synonym term ‘coincidental 
mixture’ is sometimes used). Unintentional mixtures include degradation and 
transformation products of chemicals released into the environment. The composition 
of unintentional mixtures is often unknown and varying in time and space. 

  Priority mixture: a chemical combination/mixture) of high concern to human or 
environmental health, which is a priority to identify and further assess for risk 
reduction.  

  Combined exposure: simultaneous or sequential exposure to multiple substances via 
single or multiple pathways/routes (the synonym ‘cumulative exposure’ is sometimes 
used) 

  Aggregate exposure: exposure to a single substance from multiple sources and via 

multiple pathways/routes.  

  Combination effect (sometimes referred to as ‘cumulative’ or ‘mixture effect’): 

(eco)toxicological effect on an organism arising from exposure to a chemical mixture. 
Type and strength of the effect will vary depending on the composition of the mixture 
and the level of exposure. 

  Sources: places of release of chemicals (e.g. industrial installations, diffuse sources 

such as products). 

  Routes of exposure: ways of entering the organism (dermal, oral, inhalation, normally 

referring to human health). 

  Compartment: (environmental) media where chemicals are taken up (air, water, 

sediment, soil, food/feed). 

  Exposure pathway: includes fate and transport processes by which chemicals move 

from the original point of release through the environment, and the 
routes/interaction(s) through which populations or individuals are exposed 
(oral/ingestion, inhalation, dermal) via various media (water, sediment, soil, air, 
food/feed, products).   

18 Kienzler, A., Bopp, S., van der Linden, S., Berggren, E., Worth, A., ‘Regulatory assessment of chemical mixtures: 
Requirements, current approaches and future perspectives’, Regulatory Toxicology and Pharmacology 
Volume 80, October 2016, Pages 321-334.  
19  Meek, M.E. (Bette), Boobis, A.R., Crofton, K.M., Heinemeyer, G., van Raaij, M., Vickers, C.,‘Risk assessment of 
combined exposure to multiple chemicals: A WHO/IPCS framework’ Regulatory Toxicology and Pharmacology 60 (2011) 
S1–S14.   https://pubmed.ncbi.nlm.nih.gov/21466831/ 
20 OECD (2018). ‘Considerations for Assessing the Risks of Combined Exposure to Multiple Chemicals’, Series on Testing 
and  Assessment  No. 
Environment  Directorate. 
http://www.oecd.org/chemicalsafety/risk-assessment/considerations-for-assessing-the-risks-of-combined-exposure-to-
multiple-chemicals.pdf 
21  Swedish  Government  Inquiries  (2019).  ‘Future  chemical  risk  management  Accounting  for  combination  effects  and 
assessing  chemicals  in  groups’,  Swedish  Government  Official  Reports,  SOU  2019:45  https://www.government.se/legal-
documents/2019/11/sou-201945/  

Environment,  Health 

Safety  Division, 

296, 

and 

4 

 
 
                                                                                                                                                                                     
  Mode of action (MOA):  the way a chemical exerts its biological effects. A common 
mode of action is assumed to involve one or several key events between the chemical 
and its biological target(s), leading to an (eco)toxicological effect.  

  Interaction: an event where the joint effect of different chemicals in a mixture causes 
either an enhanced or weaker effect than that is expected based on the application of 
models such as concentration addition or independent action to predict the toxicity of 
the mixture.  

  Synergism: an interaction between chemicals that enhances the toxicological effect 
beyond that is expected based on the toxicity of the individual components in the 
mixture.  

  Antagonism: an interaction between chemicals that weakens the toxicological effect 
compared to what is expected based on the toxicity of the individual components in 
the mixture.  

  Whole mixture testing: an approach where a sample or chosen media containing a 
mixture of chemicals is tested experimentally for one or several toxicological 
endpoints. 

  Component-based approaches: methods for calculating mixture toxicity based on 

information on the toxicity and exposure to the individual compounds in the mixture. 
The two common models for mixture assessment are concentration (or dose) addition, 
and independent action.  

  Concentration (or dose) addition: method/model for calculating mixture toxicity, 
based on the toxicity and concentration of the individual substances and under the 
assumption that they do not interact and have similar mode(s) of action.  

  Independent action: assumes that mixture components contribute to a common 
endpoint via dissimilar and fully independent sequences of events, from an initial 
interaction with different molecular target sites to different diseases or different 
adverse effects seen at the level of individuals or populations. Consequently, the 
individual effects can be considered to be independent events in probabilistic sense. 
  Toxicological Equivalence Factor (TEF): the toxicity weighted summation of the 
relevant mixture components.  The TEF is in some regulations referred to as the 
‘Summation Method’ and may be used to assess if the sum exceeds a pre-defined 
effect threshold.  

  Default safety factor: a factor (sometimes referred to as default uncertainty factor), 
normally applied in the hazard and risk assessment of chemicals. Depending on the 
regulation different uncertainty factors may be applied. It may be used in the 
extrapolation from experimental animal studies to potential harmful effects on 
humans. Uncertainty factors may also be applied when choosing the part of the 
population that represents the exposure used in a study, as input to the risk assessment, 
as well as for the allocation of exposure to different sources. Various factors are also 
used in deriving predicted no-effect concentrations (PNECs) in environmental risk 
assessment.  

  Mixture Assessment Factor (MAF): sometimes also called ‘Mixture Allocation 
Factor’, is an additional safety factor that can be applied in the risk assessment of 
single chemicals, in order to generically cover for combined exposure without 
performing a mixture-specific assessment. The possible use of MAFs in risk 
assessment has long been discussed, but the approach has so far not been applied for 
regulatory purposes at EU level. 

5 

 
 
2. WHY ARE MIXTURES A CONCERN? 

Chemicals  normally  appear  as  mixtures.  They  are  intentionally  blended  to  form  products, 
such as paints, cosmetics, pesticides and biocides, as well as more or less complex materials 
like  plastics  and  textiles.  Chemicals  may  also  be  used  together  (e.g.  for  plant  protection 
purposes  or  when  different  biocidal  products  are  combined)  and  unintentionally  emitted  in 
combination  and/or  sequentially  (e.g.  as  discharges  during  their  manufacturing  and  use  as 
well  as  from  waste  management  and  sewage  treatment  plants).  Hence,  humans,  biota  and 
environmental  compartments  are  constantly  exposed  to  such  mixtures,  often  of  unknown 
composition, from various sources and via different pathways.  

The occurrence of combination effects of chemicals is long known and has accordingly been 
an area of scientific research, and to some extent subject to regulatory action22. A well-known 
example  is  the  interaction  between  different  pharmaceuticals  when  a  patient  is  treated  with 
two or more medicines simultaneously.  

It  is  widely  documented  that  the  combined  exposure  to  multiple  chemicals  can  trigger 
stronger  (or  occasionally  weaker)  (eco)toxicological  effects  than  exposure  to  individual 
chemicals  alone23,  24,  25.  Even  exposures  at  concentrations  regarded  as  safe  (i.e.  where  no 
effects  are  expected)  for  the  individual  chemical  can  result  in  adverse  (eco)toxicological 
effects when several chemicals occur together in a mixture26.  

Current  regulatory  approaches  to  the  risk  assessment  of  single  chemicals  normally  involves 
establishing  a  level  of  exposure  considered  reasonably  safe  in  relation  to  the  inherent 
hazardous properties of the particular chemical27, 28. When extrapolating from animal test data 
to  a safe level  of  exposure for humans or organisms  in  the environment,  safety margins  are 
applied.  The  purpose  is  to  take  account  of  differences  in  sensitivity  between  animals  and 
humans,  i.e.  between  different  species  as  well  as  between  individuals.  In  the  model  for 
humans  applied  under  REACH,  these  safety  margins  add  up  to  a  default  safety  (or 
uncertainty)  factor  of  100,  commonly  used  in  single  chemicals  risk  assessment.  Similar 
factors of different magnitude are used to establish safe levels of exposure in environmental 
hazard  and  risk  assessment.  However,  these  default  uncertainty  factors  do  not  take  into 
account the effect of combined exposures on humans29 or the environment30.  

22 Monosson, E., ‘Chemical Mixtures: Considering the Evolution of Toxicology and Chemical Assessment’, Environ Health 
Perspect. 2005 Apr; 113(4): 383–390.  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1278475/ 
23 Backhaus, T., Karlsson, M., ‘Screening level mixture risk assessment of pharmaceuticals in STP effluents’, Water 
Research, Volume 49, 1 February 2014, Pages 157-165. 
https://www.sciencedirect.com/science/article/pii/S0043135413009044?via%3Dihub 
24 Kortenkamp A., Faust, M., ‘Combined exposures to anti-androgenic chemicals: steps towards cumulative risk assessment’, 
International Journal of Andrology, Volume 33 (2):463-474, April 2010.  
https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2605.2009.01047.x  
25 De Brouwere K, Cornelis C, Arvanitis A, Brown T, Crump D, Harrison P, Jantunen, M, Price. P, Torfs R., ‘Application of 
the maximum cumulative ratio (MCR) as a screening tool for the evaluation of mixtures in residential indoor air’, The 
Science of the Total Environment 2014, 479-480, 267–76. https://pubmed.ncbi.nlm.nih.gov/24565859/  
26  This  was  confirmed  by  the  Scientific  Committee  on  Emerging  and  Newly  Identified  Health  Risks,  the  Scientific 
Committee on Health and Environmental Risks, and the and Scientific Committee on Consumer Safety  in a joint statement 
from 2011  (see Box 2).   
27 Risk characterisation is often performed in terms of a risk quotient (RQ) or risk characterisation ratio (RCR). In general, 
the quotient denotes the ratio between an observed or predicted exposure level and a regulatory acceptable exposure level, 
which is considered reasonably safe. There are numerous variants and specifications of this approach, depending on the 
specific protection goals (e.g. human health or the environment) and the specific regulatory context).  
28 ECHA (2016). Guidance on information requirements and chemical safety assessment Part E: Risk characterisation. 
ECHA-2016-G-04-EN.  https://echa.europa.eu/documents/10162/13632/information_requirements_part_e_en.pdf  
29 Martin, O.V., Scholze, M., Kortenkamp, A. (2013), ‘Dispelling urban myths about default uncertainty factors in chemical 
risk assessment – sufficient protection against mixture effects?’, Environmental Health 2013, 12:53 
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3708776/pdf/1476-069X-12-53.pdf  

6 

 
 
                                                           
A  large  body  of  research  in  the  EU  and  internationally  over  the  past  decades,  including 
laboratory  experiments,  human  and  environmental  monitoring  and  epidemiological  studies 
provides a growing body of evidence clearly showing that exposure to mixtures of chemicals 
of anthropogenic origin is the norm in the human and natural environment. Further, research 
shows  that  combination  effects  do  occur,  in  real  life  exposure  situations  as  well  as  in 
experimental studies involving realistic exposure levels (see cases in Box 2).  

Box  2:  Growing  evidence  of  health  and  environmental  concern  relating  to  exposure  to 
unintentional mixtures 

Since 2012, the body of evidence indicating that exposure to mixtures is a cause of health and 
environmental  concern  has  grown  considerably.  Several  studies  show  that  mixtures  are  a 
cause  of  concern  at  real-life  exposure  levels  and  can  be  linked  to  effects  through 
epidemiological  and  experimental  means.  Below  are  some  selected  examples  from  recent 
studies.  

JRC review of mixture risk case studies  
A  2016  report  from  the  Commission’s  Joint  Research  Centre31  reviews  21  case  studies  on 
mixture  risk  assessment  conducted  since  2014.  The  case  studies  include  human  health  and 
environmental  risk  assessments  and  cover  several  classes  of  chemical  compounds  (e.g. 
pesticides,  phthalates,  parabens,  polybrominated  diphenyl  ethers  (PBDEs),  pharmaceuticals, 
food  contact  materials,  dioxin-like  compounds  and  anti-androgenic  chemicals).  All  selected 
studies  involved  testing  of  either  real  samples  or  realistic  artificial  samples.  The  reviewed 
case  studies  included  unintentional  mixtures  like  contaminants  in  breast  milk,  chemicals  in 
indoor  air  and  in  environmental  media,  such  as  surface  water,  ground-water  and  drinking 
water.  Several  of  the  case  studies  indicated  that  exposure  to  the  assessed  mixtures  posed 
concerns, especially regarding vulnerable populations. The review thus  clearly demonstrates 
that  unintentional  chemical  mixtures,  also  across  chemical  classes  and  legislative  sectors, 
need 
include  possible 
interactions/synergism,  bioaccumulation  and  effects  of  metabolites  appearing  in  mixtures  as 
well as data gaps hampering a more refined assessment.  

to  be  better  addressed.  Aspects  needing  further  attention 

Exposure of children, unborn children and pregnant women to endocrine 
disruptors and neurotoxic substances  
In 2017, the Danish Environmental Protection Agency published a report32 on the exposure of 
children  under  the  age  of  three,  unborn  children  and  pregnant  women  to  selected  endocrine 
disrupting  and  neurotoxic  chemical  substances.  The  study  included  37  endocrine  disrupting 
chemicals (e.g. phthalates, perfluoro-substances, bisphenols and UV filters) and 39 neurotoxic 
chemicals (e.g. heavy metals, bisphenol A, PCBs, dioxins and perfluoro-substances), of which 
seven  substances  were  relevant  for  both  endpoints.  Data  regarding  exposure  via  food, 
drinking  water,  indoor  and  outdoor  environment,  cosmetics  and  various  consumer  products 
were combined with human biomonitoring data to estimate exposure levels. The overall risk 

30 Swedish Chemicals Agency KEMI (2015). An additional assessment factor (MAF) – A suitable approach for improving 
the regulatory risk assessment of chemical mixtures; Report 5/15 https://www.kemi.se/global/rapporter/2015/rapport-5-
15.pdf 
31 Bopp, S. K , A. Kienzler, S. van der Linden, L. Lamon, A. Paini, N. Parissis, A.-N. Richarz, J. Triebe, A. Worth (2016). 
‘Review of case studies on the human and environmental risk assessment of chemical mixtures’ EUR 27968 EN; JRC report; 
doi:10.2788/272583 http://publications.jrc.ec.europa.eu/repository/bitstream/JRC102111/jrc102111_jrc_tech-
rep_mix%20case%20studies_2016_vf.pdf  
32  Danish  Environmental  Protection  Agency  (2017).  ‘Exposure  of  children  and  unborn  children  to  selected  chemical 
substances’. Survey of chemical substances in consumer products No. 158, 2017.   
http://orbit.dtu.dk/files/136888869/Eksponeringsrapport_ENG_.pdf 

7 

 
 
 
                                                                                                                                                                                     
associated  with  the  combined  exposure  was  calculated  through  a  concentration  addition 
approach, establishing risk quotients  (RQtotal) for the mixtures.33 The results of the  Danish 
study indicate that the overall exposure of children under 3 years old to mixtures of endocrine 
disrupting chemicals  is  of concern (RQtotal  >2) with  respect  to  all three types of disruptive 
effects  (anti-androgenic,  estrogenic  and  thyroid  hormone  disrupting)  already  at  average 
exposure levels. Similarly, for pregnant women and unborn children there were indications of 
possible  concern  (RQtotal≈1)  already  at  average  levels  of  exposure  to  combinations  of 
endocrine  disruptors.  Also  considering  the  exposure  to  combinations  of  neurotoxic 
substances,  results  indicate  concern  regarding  children  under  3  years  old  (RQtotal  61.1)  as 
well as pregnant women and unborn children (RQtotal 7.9).  

Environmental risks of pesticide mixtures in inland waters  
A  study  by  Gustavsson  et  al.  from  201734  (part  of  the  EU-funded  SOLUTIONS  project), 
evaluates  the  environmental  risks  associated  with  complex  pesticide  mixtures  occurring  in 
freshwater  ecosystems.  It  is  based  on  1308  individual  samples  collected  between  2002  and 
2013 from rivers and streams in an agricultural area in southern Sweden, monitoring for 141 
different pesticides. The study demonstrated that pesticides are present as mixtures, with up to 
53  pesticides  found  in  the  same  sample,  with  most  commonly  eight  pesticides  per  sample. 
These  findings  correspond  with  multiple  studies  demonstrating  the  presence  of  complex 
pesticide mixtures in surface waters in other areas.  

Evaluation  of  the  eco-toxicological  effects  of  the  pesticides  mixtures,  applying  a  statistical 
method (the Kaplan-Meier method), and based on an assessment using concentration addition 
and  the  water  quality  objectives  established  for  the  individual  pesticides,  shows  that  the 
environmental risk exceeded acceptable levels in 73% of the samples. Further, no clear time-
trend in the level of risk was detected, but risk appears to remain relatively constant, despite 
regulatory  interventions.  A  conclusion  is  that  current  single-substance  risk  assessment  and 
mitigation is insufficient to manage risks related to the total and overall use of pesticides.  

A limited number of pesticides explains the largest  share of toxicity of the mixture (i.e. so-
called  risk  drivers).  However,  the  composition  of  the  mixtures  of  pesticides  varies 
considerably between samples. Hence, 83 of the 141 monitored pesticides has to be included 
in the assessment to account for 95% of the risk at all sites and years. This highlights the need 
for continuous monitoring as a component of risk assessment and mitigation. The study also 
shows that pesticides, in particular insecticides, even if they are only present at concentrations 
close  to  detection  limits,  still  contribute  to  the  overall  toxicity  of  the  mixture.  Further,  the 
component-based  approaches  applied in  the study  do not  take account  of the whole picture, 
including  e.g.  interactions.  Therefore,  the  authors  suggest  complementary  approaches, 
including effect-based monitoring and in-situ experiments.  

Prenatal exposure to chemical mixtures linked to impaired sexual 
development, neurodevelopment and metabolism in children  

The  EDC-MixRisk  research  project (funded  through  the  EU  research  programme  Horizon 
2020)  studied  health  and  development  of  early  life-exposure  to  complex  mixtures  of 

33 In toxicology, the so called Risk Quotient (RQ) is the ratio between the measured exposure in a predicted exposure 
situation, and the exposure at which no toxic effect on humans is expected (‘derived no effect level’, DNEL). A RQ for an 
individual substance, or the summarised RQ’s of the components in a mixture (RQtotal), above the value one (1) is normally 
regarded as indicating risk. 
34 Gustavssons, M., Kreuger, J., Bundschuhb, M., Backhaus, T., ‘Pesticide mixtures in Swedish streams: Environmental risks, 
contributions of individual compounds and consequences of single-substance oriented risk mitigation’, Science of The Total 
Environment, Volume 598, 15 November 2017, Pages 973-983; 
https://reader.elsevier.com/reader/sd/pii/S0048969717309580?token=57C5E26D539F6B8CD650794BA2105715A136C7D2
A770C5EDC93B67A2A1FBED772D43EBA34076330B7633FC1D7BAC57C8 

8 

 
 
                                                           
endocrine  disrupting  chemicals  (EDC)  through  a  combination  of  approaches.  Baseline 
chemicals exposure data were derived from a pregnancy cohort (SELMA). Out of 54 potential 
endocrine disruptors analysed in blood and urine from the 2,300 pregnant women, 41 (75%) 
were  found  above  detection  levels  in  a  majority  of  the  samples.  The  researchers  used 
epidemiological and statistical methods to identify which of these chemicals (i.e. in mixtures) 
are associated with adverse health outcomes in children, with regard to sexual development, 
neurodevelopment and metabolism/growth. 

The  identified  mixtures  were  tested  in  experimental  models  to  uncover  mechanisms  and 
pathways  behind  the  health  outcomes  and  the  analysed  dose-response  relationships.  Hence, 
the EDC-MixRisk project demonstrated that exposure to the identified mixtures caused effects 
and dysfunctions in cell and animal models at levels similar to those measured in the SELMA 
cohort.  Observations  in  the  experimental  studies  included  morphological  changes  to 
reproductive  organs,  interference  with  thyroid  hormone  signalling,  changes  in  gene 
expression  associated  with  autism  spectrum  disorder  and  intellectual  disability  in  humans, 
behavioural  changes  as  well  as  changes  in  fat  cell  differentiation  and  birth  weight. 
Researchers could also link some of the experimentally induced biomarkers to adverse health 
outcomes in the exposed children of the cohort.  

Finally,  the  human  biomonitoring  data  from  the  SELMA  cohort  and  the  experimental  data 
were compared and analysed using new statistical/analytical approaches developed as part of 
EDC-MixRisk. Results showed that the approaches developed in the project, comparing and 
integrating  human  biomonitoring  data  and  experimental  models  were  more  sensitive  (i.e. 
indicated risk for adverse effects at lower exposure levels) than traditional additivity or single 
substance  risk  assessment  approaches,  at  least  for  some  endpoints.  It  also  showed  that  the 
regulatory  guideline  values  for  most  of  the  assessed  chemicals  seem  to  be  insufficiently 
protective against combined exposures to multiple substances. 

Box 3: The joint statement of 2011 by the Scientific Committee on Health and 
Environmental Risks, the Scientific Committee on Emerging and Newly Identified 
Health Risks and the Scientific Committee on Consumer Safety35 

Regarding  impacts  of  mixtures  on  human  health,  the  Scientific  Committees  concluded  that, 
under certain conditions, chemicals in a mixture with a similar mode of action may act jointly 
and produce a combination effect that is larger than that from each component of the mixture 
used singly, and hence represent a health concern.  

No robust evidence was available at the time of the drafting of the opinion for substances with 
different modes of action to indicate that exposure to such mixtures of chemicals is a health 
concern if the individual chemicals are present at or below their estimated zero-effect levels. 
The  Committees  concluded  on  the  possible  health  concerns  of  such  mixtures,  that  ‘if  the 
intended level of protection is achieved for each individual substance, the level of concern for 
mixtures of dissimilarly acting substances should be assumed to be negligible’.  

However,  for  the  ecological  effects  of  chemical  mixtures,  the  Scientific  Committees 
concluded that not only exposure to mixtures of chemicals with similar modes of action was a 
concern.  Combinations  of  dissimilarly  acting  substances  should  also  be  considered  as  a 
possible  concern,  even  if  the  exposure  to  all  the  substances  involved  is  at  a  level  where  no 

35  Scientific  Committee  on  Health  and  Environmental  Risks  (SCHER),  Scientific  Committee  on  Emerging  and  Newly 
Identified Health Risks (SCENHIR) and Scientific Committee on Consumer Safety (SCCS). ‘Joint Opinion on the Toxicity 
and Assessment of Chemical Mixtures adopted on 14th December 2011’ https://doi.org/10.2772/21444  
35  Kortenkamp,  A.,  Backhaus,  T.,  Faust,  M.  (2009):  State  of  the  Art  Report  on  Mixture  Toxicity,  Final  Report,  Executive 
Summary, 22 December 2009. http://ec.europa.eu/environment/chemicals/effects/pdf/report_mixture_toxicity.pdf  

9 

 
 
 
                                                           
effects  are  predicted  for  the  individual  substances  (i.e.  below  the  individual  Predicted  No-
Effect Concentrations - PNECs).  

3.  REGULATORY FRAMEWORKS AND REQUIREMENTS 

REGARDING MIXTURES  

The  Commission  Communication  of  2012  concluded  that  current  EU  legislation  does  not 
provide  for  a  comprehensive  and  integrated  assessment  of  the  combination  effects  (the 
Communication uses the synonym term cumulative effects) of different chemicals taking into 
account  different  routes  of  exposure.  It  also  concluded  that  ‘where  a  mixture  of  concern  is 
identified  and  where  such  a  mixture  contains  chemical  substances  regulated  under  different 
pieces  of  EU  legislation,  no  mechanism  currently  exists  for  promoting  an  integrated  and 
coordinated assessment  across the different  pieces  of legislation’  (the latter aspect  is  further 
described in section 6).  
In  2014,  the  European  Commission  Joint  Research  Centre  (JRC)36  published  a  Report 
reviewing the existing regulatory requirements for the assessment of mixtures in current 
EU  chemicals-related  legislation.  The  Report  investigated  such  requirements  in  selected 
pieces of the three main categories of chemicals-related EU legislation:  

 

 

 

legislation  focused  on  chemical  substances  and/or 
intentional/commercial 
mixtures, normally involving prospective  (pre-marketing)  assessment,  e.g. industrial 
feed  additives, 
and  consumer  chemicals,  pesticides,  biocides, 
pharmaceuticals and cosmetics (12 legislative pieces),  
legislation  mainly  oriented  towards  (or  specific  to)  the  use  of  chemicals  in 
products,  normally  not  involving  prospective  (pre-marketing  assessment),  e.g.  food 
contact materials and toys (2 legislative pieces), and 
legislation  focused  on  chemical  emissions  from  certain  activities,  e.g.  industrial 
emissions and the presence of pollutants in food/feed, at work place and in certain 
environmental media, e.g. air, water (13 legislative pieces).  

food  and 

Most pieces of legislation in the first category include some provisions for the assessment of 
the  exposure  to  and  risks  from  intentional/commercial  mixtures,  for  which  the  added 
chemicals are normally well-known and subject to a prospective risk assessment37 (see below: 
Intentional  mixtures).  However,  none  of  the  pieces  of  legislations  in  this  category  includes 
any  requirements  for  the  assessment  of  unintentional  mixtures,  except  for  Plant  Protection 
Products  and  Biocidal  Product  Regulation  in  which  cumulative  and  synergistic  effects  are 
covered  more  generally  without  making  a  distinction  whether  they  refer  to  intentional  and 
unintentional mixtures (see below: Intentional and Unintentional mixtures).  

Regarding legislation in the second category, a specific provision regarding the assessment of 
intentional mixtures exists in the Toy Safety Directive38. The directive considers any toy to be 
a mixture as regards the presence of substances which are carcinogenic, mutagenic and, toxic 
to  reproduction  (CMR).  CMRs  are  prohibited  by  default  in  toys,  but  by  derogation  may  be 
present  in  a  toy  up  to  the  generic  or  specific  concentration  limit  (whichever  is  stricter), 

36 Aude Kienzler, Elisabet Berggren, Jos Bessems, Stephanie Bopp, Sander van der Linden, Andrew Worth (2014), 
‘Assessment of Mixtures – Review of regulatory Requirements and Guidance’, JRC Science and Policy Report, EUR 26675 
EN. http://publications.jrc.ec.europa.eu/repository/bitstream/JRC90601/lb1a26675enn.pdf  
37  ‘Prospective  risk  assessment’  is  performed  in  the  context  of  pre-marketing  assessment/authorisation  of  a  chemical  (as 
distinct to ‘retrospective risk assessment’, which is generally aimed to identify the causes of adverse effects that have already 
occurred).  
38 Directive 2009/48/EC on the safety of toys (Toys Safety Directive) 

10 

 
 
                                                           
specified  in  the  CLP  Regulation.  There  is  however  no  reference  to  the  assessment  of 
unintentional mixtures in any piece of the analysed products-focused legislation.  

The  emission  and  pollution  focused  legislation  mainly  looks  at  the  environmental  exposure 
and  sometimes  risk  resulting  from  the  use  of  chemicals,  including  to  unintentional 
contaminants  present  in  these  chemicals  as  well  as  breakdown  and  transformation  products 
that  might  form.  In  line  with  this,  it  does  not  include  any  requirements  for  the  prospective 
assessment  of  single  chemicals  or  intentional  mixtures39.  However,  some  of  the  pieces  of 
legislation  in  this  category  include  legal  requirements  for  the  assessment  of  unintentional 
mixtures  (see  below:  Unintentional  mixtures).  The  legislation  focused  on  protection  of 
workers  from  chemicals  at  work  place  contains  explicit  requirement  to  assess  risks  of 
unintentional  mixture  present  at  the  work  place  such  chemicals  in  combination  (see  below: 
Unintentional mixtures).  

Of  the  27  pieces  of  chemicals-related  legislation  assessed,  10  do  not  include  any  explicit 
reference  to  the  assessment  of  either  intentional  or  unintentional  mixtures40,41.  However, 
mixtures are sometimes considered on an ad hoc basis also under these pieces of legislation, 
particularly focussing on groups of substances. There are examples of such cases, for instance 
in  the  area  of  plastics  materials  regulation  for  food  contact  materials42,  but  this  is  the 
exception rather than the rule.  

The  regulatory  requirements  for  mixtures  have  not  changed  in  any  significant  respect  since 
2012. Hence, chemicals-related legislation is still largely focused on the risk assessment and 
management  of  single  chemicals.  The  background  to  this  predominantly  substance-by-
substance  approach  to  risk  assessment  is  that  many  pieces  of  legislation  were  developed  to 
provide marketing and use provisions for chemicals used for specific purposes, and to define 
the  responsibilities  of  individual  economic  actors  involved  (i.e.  producers,  importers  and 
users).   

The  prevailing  need  to  better  address  chemical  mixtures  has  however  resulted  in  the 
development  of  common  approaches  to  assess  related  hazards,  exposures  and  risks.  Several 
guidance documents for such assessments have also been developed. However, to what extent 
these  approaches  are  actually  applied  in  the  absence  of  specific  legal  requirements  is  not 
known. (see examples in section 4).  

39  Under  the  Water  Framework  Directive  (2000/60/EC),  Article  16,  a  single-substance  risk  assessment  is  required  for  the 
review of so called ‘priority substances’, which might influence e.g. reauthorisation processes under the respective pieces of 
legislation under which the uses of these substances are regulated.  
40 Regulation (EC) No 1333/2008  on food additives;  Directive (2010/75/EC) on Integrated pollution prevention and control 
(IPPC)  (now  replaced  by  the  Directive  2010/75/EU    on  industrial  emissions  (integrated  pollution  prevention  and  control); 
Directive  2008/98/EC  on  waste  and  repealing  certain  Directives  (including  the  Waste  Stream  Directives);  Directive 
2006/118/EC  on  the  protection  of  groundwater  against  pollution  and  deterioration;  Directive  2008/56/EC  establishing  a 
framework  for  community  action  in  the  field  of  marine  environmental  policy  (Marine  Strategy  Framework  Directive); 
Council Directive 98/83/EC on the quality of water intended for human consumption (Drinking Water Directive); Directive 
2008/50/EC  on  ambient  air  quality  and  cleaner  air  for  Europe;  Regulation  (EC)  No  1935/2004  on  materials  and  articles 
intended  to  come  into  contact  with  food  and  repealing  Directives  80/590/EEC  and  89/109/EEC  (Food  Contact  Material 
Regulation), Council Regulation (EEC) No 315/93 of 8 February 1993 laying down Community procedures for contaminants 
in food (Food Contaminant Regulation); Directive 2002/32/EC on undesirable substances in animal feed (Feed Contaminant 
Directive).  
41 The Ground Water Directive and the Drinking Water Directive sets out Environmental Quality Standards for individual as 
well  as  total  presence  of  pesticides.  These  are  not  based  on  an  assessment  of  the  combined  risk  of  the  pesticides  (i.e.  the 
unintentional mixture), but still contributes to controlling the risk of combination effects.  
42  Commission  Regulation  (EU)  No  10/2011  on  plastic  materials  and  articles  intended  to  come  into  contact  with  food. 
Examples  of  cases  of  regulation  of  chemical  mixtures  in  plastics  for  food  contact  purposes  include  the  groups  primary 
aromatic amines, aromatic isocyanates, organotins and phthalates. (EU 10/2011) 

11 

 
 
 
                                                           
3.1 Intentional mixtures 

the  12  pieces  of 

Various kinds of references to the assessment of intentional mixtures appear in 11 legislative 
acts  out  of 
legislation  focused  on  chemical  substances  and/or 
intentional/commercial  mixtures  assessed.    Eight  of  these  refer  to  such  assessment  for  both 
human health and the environment43 and three for only human health44.  These delimitations 
usually  coincide  with  the  overall  scope  of  the  legislation  regarding  health  and  the 
environment,  e.g.  environment is  out  of scope of the Cosmetics Regulation, which refers to 
REACH regarding environmental risks.    

An example of legislation requiring assessment of mixtures with regard to both human health 
and the environment is the regulation on biocidal products. The regulation on plant protection 
products  considers  effects  on  human  health  both  related  to  dietary  exposure  (food,  feed, 
drinking  water)  and  to  non-dietary  exposure  (workers,  residents,  bystanders).  Biocidal  and 
plant  protection  products  are  normally  intentional  mixtures,  which  apart  from  the  active 
substance(s) might include solvents, synergists (adjuvants), safeners and surfactants.  
The Plant Protection Products (PPP) Regulation45 covers both the approval of the individual 
substances  used  in  plant  protection  products  and  the  formulated  products  (i.e.  intentional 
mixtures). Active substances used in PPPs are approved in a procedure at the EU level. This 
normally involves testing and risk assessment of the individual substances, and in some cases 
testing  of  the  whole  formulation  for  the  purpose  of  environmental  risk  assessment  for 
particular  organism  groups.  The  authorisation  also  includes  the  requirement  to  assess 
maximum residue levels (MRL) of pesticides in food and feed with regard to human health. 
MRLs  are  set  based  on  scientific  advice  of  the  European  Food  Safety  Authority  (EFSA) 
according to Regulation (EC) No. 396/2005.  Formulated plant protection products, in which 
an  approved  active  substances  is  used  together  with  other  (formulating)  substances,  are 
authorised at the Member State level. The whole formulations are generally assessed only for 
acute  toxicity  to  humans  and  for  organisms  in  the  environment  that  might  come  into  direct 
contact with the product, but Member States have the possibility to require submission of any 
other information they consider necessary. Data to be provided are either from direct testing 
of  the  product  itself  (whole-mixtures  approach),  data  on  all  components  of  the  plant 
protection product, or in some cases the application of a non-animal test method.  
The  Biocidal  Products  (BPR) Regulation46 covers the approval  of  active substances  and the 
authorisation  of  formulated  biocidal  products  (i.e.  intentional  mixtures).  In  both  cases  the 
regulation  requires  ‘cumulative  and  synergistic  effects’  to  be  taken  into  account  under 
‘realistic  worst  case  conditions  of  use’  (Article  19(2)).  It  also  requires  that  ‘for  biocidal 
products that are intended to be authorised for use with other biocidal products, the risks to 

43  Regulation  (EC)  No  1107/2009  concerning  the  placing  of  plant  protection  products  on  the  market  (Plant  protection 
Products  (PPPs)  Regulation);  Commission  Regulation  (EU)  No 283/2013  setting  out  the  data  requirements  for  active 
substances,  in  accordance  with  Regulation  (EC)  No 1107/2009  concerning  the  placing  of  plant  protection  products  on  the 
market;  Commission  Regulation  (EU)  No 284/2013    setting  out  the  data  requirements  for  plant  protection  products,  in 
accordance  with  Regulation  (EC)  No 1107/2009  concerning  the  placing  of  plant  protection  products  on  the  market; 
Regulation  (EU)  No 528/2012  concerning  the  making  available  on  the  market  and  use  of  biocidal  products  (Biocides 
Regulation); Regulation (EC) No 1272/2008 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  (CLP  regulation); 
Regulation  (EC)  No  1907/2006  concerning  the  Registration,  Evaluation,  Authorisation  and  Restriction  of  Chemicals 
(REACH); Regulation (EC) No 1831/2003 on additives for use in animal nutrition (Feed Additive Regulation); Regulation 
(EC) No 429/2008 as regards the preparation and the presentation of applications and the assessment and the authorisation of 
feed additives.  
44 Directive 2001/83/EC on the Community code relating to medicinal products for human use (Human Medicines Directive); 
Directive 2001/82/EC on the Community  code relating to veterinary  medicinal products (Veterinary Medicines Directive); 
Regulation (EC) No 1223/2009 on cosmetic products (Cosmetics Regulation).  
45 Plant protection products Regulations (Regulations (EC) 1107/2009, (EU) 283/2013, (EC) 284/2013). 
46 Biocidal Products Regulation (EC) 528/2012.  

12 

 
 
                                                           
human  health,  animal  health  and  the  environment  arising  from  the  use  of  these  product  in 
combinations shall be assessed’ (Annex III Section I Point 8.5.4). Further, common principles 
for  the  evaluation  of  biocidal  products,  including  several  references  to  cumulative  and 
synergistic  effects,  are  set  out  in  Annex  VI.  The  risk  assessment  of  the  formulated  biocidal 
products  is  normally  based  on  data  for  the  individual  components  addressing  all  relevant 
endpoints  as  required  by  the  data  requirements  for  biocides  in  Annex  VI  to  the  Biocidal 
Products  Regulation.  Guidance  documents  for  human  health  and  environmental  risk 
assessment relating to biocidal products are available (see Section 4).  

Assessment  of  intentional  mixtures  is  generally  conducted  in  connection  with  the  hazard 
based  classification  and  labelling  under  the  Classification,  Labelling  and  Packaging  (CLP) 
Regulation47.  This  process  relies  firstly  on  test  data  on  the  whole  mixture  when  such  are 
available48. Alternatively, the classification can be based on bridging principles, i.e. the use of 
data  on  a  similar  mixture.      Finally,  in  the  absence  of  information  on  the  mixture  itself, 
classification  can  be  based  on  the  toxicological  properties  of  the  ingredients  in  the  mixture 
and application of the summation rule or concentration addition method.  
The  REACH  Regulation49  covers,  in  principle,  all  intentionally  manufactured  chemical 
substances,  on  their  own,  in  mixtures  or  in  products,  unless  they  are  specifically  exempted 
under  REACH  due  to  being  regulated  by  sector  or  product-related  legislation  (e.g. 
pharmaceuticals  and  food  additives)  or  are  radioactive  substances  or  waste.  It  requires  the 
producer/importer to register a chemical to be marketed or imported in quantities above 1 ton 
per year and in this context provide test data, hazard assessment and a risk assessment of the 
identified uses. REACH registration requirements apply to each of the individual chemicals in 
an  intentional  mixture,  but  not  to  the  mixture  itself.  The  registration  must  include  a  hazard 
assessment of the chemical and a risk assessment for all identified uses. The risk assessment 
must  cover  the  use  of  a  substance  in  a  mixture  if  this  is  placed  on  the  market  and  be 
documented in a chemical safety report.  

REACH is mainly focused on individual substances and contains no specific methodology for 
the  assessment  of  intentional  mixtures,  beyond  multi-constituent  substances  (MCSs)  and  so 
called UVCBs (see below). In principle, it is however possible to take into account combined 
effects  of  intentional  mixtures,  e.g.  during  the  assessment  of  substances  for  restriction  and 
authorisation  (this  is  also  true  for  intentional  mixtures,  see  section  5).  Further,  REACH 
obliges the supplier of a mixture to provide the downstream user of that mixture with a safety 
data  sheet  (SDS), 
is  classified  as  hazardous.  The  SDS  contains 
(eco)toxicological  information  and  a  chemical  safety  assessment  for  the  mixture,  if  one  has 
been performed.    

the  mixture 

if 

Under  several  pieces  of  legislation  (e.g.  CLP,  REACH,  biocides,  cosmetics),  special 
consideration  is  given  to  impurities  in  a  substance  or  a  constituent  in  a  multi-constituent 
substance  (MCS)  as  well  as  in  the  so-called  UVCBs  (Substances  of  Unknown  or  Variable 
composition,  Complex reaction products  or  Biological  materials).  Although such substances 
can  be  seen  as  mixtures  from  a  toxicological  point  of  view,  they  are  considered  substances 
from a legal point of view (e.g. the REACH definition50). Hence, they are registered as one 

47 Classification, Labelling and Packaging (CLP) Regulation (EC) 1272/2008. 
48  The  CLP  regulation  6(3)  and  (4)  include  special  requirements  for  CMRs,  biodegradability  and  bioaccumulation.  Tests 
should not be performed for such endpoints, but the information on the individual ingredient of the mixture should be used 
instead. 
49 Regulation on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) (EC) 1907/2006.  
50 The REACH substance definition: ‘Substance means a chemical element and its compounds in the natural state or obtained 
by any manufacturing process, including any additive necessary to preserve its stability and any impurity deriving from the 
process used, but excluding any solvent which may be separated without affecting the stability of the substance or changing 
its composition.’ 

13 

 
 
                                                           
substance  under  REACH.  Procedures  for  assessing  such  substances  are  described  in  the 
REACH  and  CLP  guidance.  The  approach  generally  involves  the  testing  of  the  substance 
itself, but might also involve methods for predicting the overall risk, based on information on 
the individual components, in particular for CMR properties.  

In  conclusion,  most  pieces  of  legislation  focusing  on  chemicals  and  intentional/commercial 
mixtures  require  a  hazard  and/or  risk  assessment  of  these.  The  scope  and  level  of  detail  in 
these  provisions  vary,  including  whether  human  health  and/or  environment  are  considered. 
Methodologies and guidance documents are generally available, and assessments are usually 
performed  through  applying  whole  mixture  approaches  or  based  on  information  on  the 
individual components in the mixture.  

3.2 Unintentional mixtures  

The European Commission Joint Research Centre (JRC) report from 2014 analysed whether 
12  pieces  of  legislation  focused  on  chemical  substances  and  intentional  mixtures  include 
requirements for the assessment of unintentional mixtures. Such requirements were found to 
be absent from all these pieces of legislation, except for the Plant Protection Products and the 
Biocidal  Product  Regulations  which  require  the  consideration  of  cumulative  and  synergistic 
effects (see Box 4). The Plant Protection Product Regulation include such a specific reference 
only  regarding  human  health  (dietary  and  non-dietary  (for  workers,  residents,  bystanders)), 
while the Biocidal Product Regulation regarding human health and the environment.  

The JRC report also analysed 15 further pieces of legislation (products, pollution, food, work-
place and environmental-media related legislation) regarding requirements for the assessment 
of unintentional mixtures. Nine pieces of legislation51 have no reference to the assessment of 
unintentional mixtures, while six of them include some reference to such assessment.  

  Two pieces of legislation mention the assessment of unintentional mixtures in relation 
to both human health and the environment in the operative text (Environmental Impact 
Assessment Directive, and Water Framework Directive)52, 53.  

  One piece of legislation mentions the assessment of unintentional mixtures in relation 
to only the environment in the operative text, while human health is only mentioned in 
a recital (Environmental Quality Standards Directive)54. However, its consideration is 
implicit through the link the Water Framework Directive.  

  Three  pieces  of  legislation  include  such  a  reference  only  regarding  human  health 
(Maximum Pesticide Residue Levels Regulation, Protection of the Health of Workers 
Directive and Toy Safety Directive)55, 56.  

51  Integrated  pollution  prevention  and  control  (IPPC)  (Dir  2010/75/EC),  now  replaced  by  the  Directive  2010/75/EU  on 
industrial  emissions),  Waste  and  waste  streams  (Dir  2008/98/EC),  Groundwater  Directive  (Dir  2006/118/EC),  Marine 
Strategy  (Dir  2008/56/EC),  Drinking  water  (Dir  98/83/EC),  Ambient  Air  quality  and  cleaner  air  for  Europe  (Dir 
2008/50/EC),  Food  Contact  material  (Reg  1935/2004),  Food  contaminant  (Reg  315/93/EEC),  Feed  contaminant  (Dir 
2002/32/EC).  
52  Directive  2011/92/EU  on  the  assessment  of  the  effects  of  certain  public  and  private  projects  on  the  environment 
(Environmental Impact Assessment (EIA) Directive); Directive 2000/60/EC establishing a framework for Community action 
in the field of water policy (Water Framework Directive (WFD)).  
53 WFD (Dir 98/83/EC) includes only a mentioning of the assessment of unintentional mixtures in the guidance, but not in 
detail. 
54 Environmental Quality Standards (EQS) (Dir 2013/39/EU).  
55 Plant Protection Products  (PPPs)  Regulation  (1107/2009);  Regulation  (EC)  No 396/2005 on  maximum  residue  levels  of 
pesticides  in  or  on  food  and  feed  of  plant  and  animal  origin  (Maximum  Residue  Levels  (MRLs)  Regulation);  Directive 
98/24/EC on the protection of the health and safety of workers from the risks related to chemical agents at work); Directive 
2009/48/EC on the safety of toys (Toy Safety Directive).  

14 

 
 
 
                                                           
The  references  to  assessment  of  unintentional  mixtures  in  products,  pollution  and 
environmental media related legislation are however in most cases vague and general. There 
is  usually  a  lack  of  detailed  and  explicit  provisions  or  guidance  on  when  and  how  such 
assessment should be performed. As a result, unintentional mixtures are seldom subject to any 
regulatory assessment, and when this happens, it is on an ad hoc basis.   

The  most  explicit  requirement  to  perform  assessment  of  unintentional  mixtures  is  in  the 
Directive  on  the  protection  of  the  health  and  safety  of  workers  from  the  risks  related  to 
chemical agents at work57. It includes an obligation to assess the combined risks to workers of 
all hazardous chemical agents in the workplace58 (see Box 4).  

The  regulation  on  the  maximum  residues  levels  of  pesticides  in  food  and  feed  (MRL 
Regulation)59 includes also a relatively clear general requirement for taking into account the 
possible presence of pesticide residues arising from sources other than current plant protection 
uses of active substances, and their known cumulative and synergistic effects (see Box 4).  

For  three  of  the  analysed  pieces  of  legislation,  the  requirement  to  assess  unintentional 
mixtures refers exclusively to  particular  groups  of substances. This  is  true for the  Industrial 
Emissions Directive60, which requires assessment  of mixtures of chemicals belonging to the 
groups  Dioxins  and  Furans.  The  Food  Contaminants  Regulation61  and  its  guidance 
document62 requires the same for chemicals of the group poly-aromatic hydrocarbons (PAHs). 
The  Ambient  Air  Quality  and  Cleaner  Air  for  Europe  Directive63    also  assess  PAHs  as  a 
group, using benzo(a)pyrene  as  a marker  for the carcinogenic risk from  the whole  group of 
PAHs in the setting of target values.  

Waste  and  industrial  emissions  are  unintentional  mixtures  with  a  more  or  less  complex 
composition,  which  may  exhibit  considerable  variability.  Hence,  applying  the  principles  of 
mixtures assessment might be challenging, but relevant in these contexts. For emissions and 
wastes originating from e.g. particular industrial processes, the composition can be estimated 
or measured with some accuracy, while more mixed waste streams like household waste are 
more complicated.  

Under the Waste Framework Directive (2008/98/EC), specific waste streams are classified as 
hazardous  or  non-hazardous  to  ensure  that  waste  management  can  be  carried  out  without 
endangering  human  health  or  harming  the  environment  by  safely  handling  hazardous 
properties  materials.  The  classification  of  waste  is  largely  based  on  the  hazard  classes  and 
criteria in the CLP Regulation. Given that waste generally constitutes mixtures of substances, 
mixture classification rules apply, and are described in Annex III of the Directive. For certain 
hazardous properties, direct testing of waste is also an option. Calculation and test methods to 
classify  waste  are  used  in  conjunction  with  the  so-called  ‘List  of  Waste’  (Decision 
2000/532/EC)64. The list covers over 800 specific waste types and specifies the classification 

56 The Plant Protection Products (PPPs) Regulation is in this report considered to include a requirement for the assessment of 
unintentional mixture with regard to human health (the JRC report 2014 did not make this interpretation). 
57 Protection of the health of workers from chemical agents at work (Directive 98/24/EC).  
58  Article  4.4  in  the  chemical  agents  directive:  ‘In  the  case  of  activities  involving  exposure  to  several  hazardous  chemical 
agents, the risk shall be assessed on the basis of the risk presented by all such chemical agents in combination.’ 
59 Regulation on the Maximum residue levels of pesticides (396/2005). 
60 Industrial Emissions Directive (2010/75/EU).  
61 Food Contaminants Regulation (315/93/EEC),. 
62 Website of the European Union, guidance documents for the Food Contaminants Regulation 
https://ec.europa.eu/food/safety/chemical_safety/contaminants/sampling_analysis_en.   
63 Ambient Air quality and cleaner air for Europe Directive (2008/50/EC). 
64 Commission Decision ((2000/532/EC) of 3 May 2000 replacing Decision 94/3/EC establishing a list of wastes pursuant to 
Article  1(a)  of  Council  Directive  75/442/EEC  on  waste  and  Council  Decision  94/904/EC  establishing  a  list  of  hazardous 
waste pursuant to Article 1(4) of Council Directive 91/689/EEC on hazardous waste.  

15 

 
 
                                                                                                                                                                                     
as hazardous and non-hazardous. Detailed guidance on how to characterise and classify waste 
according to the List of Waste has been issued by the Commission in its notice on technical 
guidance on the classification of waste (2018/C 124/01)65.  

Box 4: Legal requirements for the assessment of unintentional mixtures in the worker 
protection, pesticides and biocides legislation  

Directive  on  the  protection  of  the  health  and  safety  of  workers  from  the  risks  related  to 
chemical agents at work 

Under this Directive, the employer has the responsibility to assess any risk to the safety and 
health of workers arising from the presence of hazardous chemical agents at the work place, 
taken into consideration the level, type and duration of exposure, and to set out the necessary 
preventive and protective measures. Article 4 specifically requires that: 

‘In  the  case  of  activities  involving  exposure  to  several  hazardous  chemical  agents,  the  risk 
shall  be  assessed  on  the  basis  of  the  risk  presented  by  all  such  chemical  agents  in 
combination’. 
A  Commission  guidance66  document  on  the  application  of  a  simplified  risk  assessment 
methodology (the Homogeneous Exposure Group (HEG) methodology) is available. 

Pesticides legislation 

The Regulation on the Maximum Residues Levels (MRL) of pesticides in food and feed and 
the Regulation on the placing on the market of Plant Protection Products (PPP)67 have general 
requirements for the assessment of unintentional mixtures of pesticides.  

The setting of the MRL have to take into account:  

‘Human  exposure  to  combinations  of  active  substances  and  their  cumulative  and  possible 
aggregate and synergistic effects on human health’ (preamble point 6).  

‘The  possible  presence  of  pesticide  residues  arising  from  sources  other  than  current  plant 
protection uses of active substances, and their known cumulative and synergistic effects, when 
the methods to assess such effects are available.’ (Article 14, (2) (b)).  

A  plant  protection  product  shall  meet,  according  to  the  PPP  Regulation,  among  others,  the 
following requirements: 

’It  shall  have  no  immediate  or  delayed  harmful  effect  on  human  health,  including  that  of 
vulnerable groups, or animal health, directly or through drinking water (taking into account 
substances  resulting  from  water  treatment),  food,  feed  or  air,  or  consequences  in  the 
workplace  or  through  other  indirect  effects,  taking  into  account  known  cumulative  and 
synergistic  effects  where  the  scientific  methods  accepted  by  the  Authority  to  assess  such 
effects are available; or on groundwater;’ (Article 4(3) (b).  

Until now, cumulative risk assessment according to the requirements in these regulations has 
not  been  systematically  performed  for  regulatory  purposes,  as  the  methodology  is  not  yet 
available.  The  European  Food  Safety  Agency  (EFSA)  has,  however,  taken  several  steps 

on 

guidance 

65  Notices  from  European  Union  institutions,  bodies,  offices  and  agencies.  European  Commission.  Commission  notice  on 
technical 
https://eur-lex.europa.eu/legal-
of  waste 
the 
content/EN/TXT/PDF/?uri=CELEX:52018XC0409(01)&from=EN  
66  European  Commision  (2006).  Practical  guidelines  of  a  non-biding  nature  on  the  protection  of  the  health  and  safety  of 
workers from the risks related to chemical agents at work. https://op.europa.eu/en/publication-detail/-/publication/b8827eb0-
bb69-4193-9d54-8536c02080c1/language-en  
67 Plant Protection Products (PPPs) Regulation (1107/2009)  

classification 

(2018/C 

124/01) 

16 

 
 
 
                                                           
regarding the development of a methodology and presented a guidance document68 focussing 
on  human  health  risks  from  dietary  exposure  to  chemicals  and  on  environmental  risks  of 
chemicals falling under its remit - i.e. pesticides, food and feed additives. EFSA has published 
the results of its two first pilot assessments on the risks posed to humans (effects on nervous 
system and thyroid) by residues of multiple pesticides in food. 69,70 

Biocides legislation 

The Biocidal Products Regulation has provisions for the assessment of unintentional mixtures 
of biocides.  

Article 19 (2) requires that ‘the evaluation of whether a biocidal product fulfils the criteria for 
authorisation shall take into account cumulative and synergistic effects’.  

Article 8 (3) further specifies, that  ‘where the evaluating competent authority considers that 
there  are  concerns  for  human  health,  animal  health  or  the  environment  as  a  result  of  the 
cumulative  effects  from  the  use  of  biocidal  products  containing  the  same or  different  active 
substances, it shall document its concerns in accordance with the requirements of the relevant 
parts of Section II.3 of Annex XV to Regulation (EC) No 1907/2006 and include this as part of 
its conclusions.  

3.3 Grouping approaches  

Assessing and managing chemicals in groups, rather than substance by substance, contributes 
to  addressing  risks  from  exposures  to  some  unintentional  mixtures71,72,73,74.  Chemicals  are 
usually grouped for regulatory purposes based on:  

  Similarities in their chemical structure as a proxy for their similarity of toxicity; 
  Common  intrinsic  properties  such  as  toxicity/hazard  classification,  and  exposure 

related properties, e.g. persistence, bioaccumulation and environmental mobility 

on 

on 

the 

the 

EFSA 

EFSA 

effects 

Journal 

Journal 

Report. 

chronic 

system. 

thyroid, 

Scientific 

2020;18(4):6087. 

68 EFSA (European Food Safety Authority) (2019) Guidance on harmonised methodologies for human health, animal health 
and  ecological  risk  assessment  of  combined  exposure  to  multiple  chemicals.  EFSA  Journal  17:5634  (77  pp). 
https://doi.org/10.2903/j.efsa.2019.5634  
69  EFSA  (European  Food  Safety  Authority)  (2020)  Cumulative  dietary  risk  characterisation  of  pesticides  that  have  acute 
effects 
2020;18(4):6087 
EFSA 
nervous 
https://www.efsa.europa.eu/en/efsajournal/pub/6087  
70 EFSA (European Food Safety Authority) (2020) Cumulative dietary risk characterisation of pesticides that 
have 
https://www.efsa.europa.eu/en/efsajournal/pub/6088  
71 Bopp, S.K., R. Barouki, W. Brack, S. Dalla Costa, J.-L.C.M. Dorne, P. E. Drakvik, M. Faust, T.K. Karjalainen, S. 
Kephalopoulos, J. van Klaveren, M. Kolossa-Gehring, A. Kortenkamp, E. Lebret, T. Lettieri, S. Nørager, J. Rüegg, J.V. 
Tarazona, X. Trier, B. van de Water, J. van Gils, Å. Bergman (2018): Current EU research activities on combined exposure 
to multiple chemicals; Environment International 120 (2018) 544–562 
https://www.sciencedirect.com/science/article/pii/S0160412018308420  
72 Stephanie K. Bopp, Aude Kienzler, Andrea-Nicole Richarz, Sander C. van der Linden, Alicia Paini, Nikolaos Parissis & 
Andrew P. Worth (2019) ‘Regulatory assessment and risk management of chemical mixtures: challenges and ways forward, 
Critical Reviews in Toxicology’, 49:2, 174-189, DOI: 10.1080/10408444.2019.1579169. 
https://doi.org/10.1080/10408444.2019.1579169  
73  Bunke,  D.,  Groß,  R.,  Kalberlah,  F.,  Oltmanns,  J.,  Schwarz,  M.,  Reihlen,  A.,  Reineke,  N.,  2014.  4M,  ‘Mixtures  in  the 
Environment. Development of assessment strategies for the regulation of chemicals under REACH’, Environmental Research 
of  the  Federal  Ministry  for  the  Environment,  Nature  Conservation  and  Nuclear  Safety.  Project  No  (FKZ)  3711  63  429 
https://www.umweltbundesamt.de/sites/default/files/medien/378/publikationen/texte_65_2014_aust_hassold_mixtures_in_th
e_environment.pdf  
74  Evans,  R.E.,  O.V.  Martin,  M.  Faust,  A.  Kortenkamp  (2016):  Should  the  scope  of  human  mixture  assessment  span 
legislative/regulatory 
757-764. 
of 
https://www.sciencedirect.com/science/article/pii/S0048969715309785  

the  Total  Environment 

chemicals?  Science 

2020;18(4):6088 

Journal 

(2016): 

silos 

543 

for 

17 

 
 
 
                                                           
  Common  exposure  routes  and/or  potential  for  emission/exposure,  e.g.  chemicals 

which workers are exposed to in occupational settings 

  Common  areas  of  use  and/or  technical  functionalities,  e.g.,  chemicals  occurring  in 

certain consumer products. 

Chemicals  belonging  to  such  groups  may  be  more  likely  to  occur  together  and  hence  be 
subject  to  co-exposure,  or have similar toxicities and hence demonstrate  cumulative effects. 
Thus,  risk  management  of  such  groups  of  chemicals  contributes  to  management  of  some 
unintentional mixtures. 

There are some examples of legal provisions applying grouping approaches in the assessment 
or  regulation  of  certain  chemicals  together  based  on  physical-chemical  (and/or  structural) 
similarities  combined  with  common  routes  of  exposure  and/or  potential  for  co-exposure. 
These  provisions  address  some  particular  cases  of  exposure  to  specific  mixtures  and/or 
aggregate exposure, without requiring an actual mixture assessment.  

One  example  is  the  Drinking  Water  Directive  (98/83/EC),  which  establishes  standards  for 
individual substances and groups of substances, like pesticides. In the context of the revision 
of the Directive, the possibility of requiring actual mixture assessments was discussed. It was 
however finally decided to keep the approach with lists of substances rather than move toward 
assessments  of  combined exposure for individual water supplies. The revised Directive will 
however  require  risk  assessments  and  monitoring  of  two  additional  groups  of  substances: 
PFAS  and  haloacetic  acids.  The  Groundwater  Directive  also  includes  a  standard  for  total 
pesticides. 

The  Industrial  Emissions  Directive  (IED)  (2010/75/EU)  lacks  detailed  provisions  for  risk 
assessment of  chemical  pollution. The assessment  may be based on knowledge produced in 
other contexts (e.g. under REACH). This can include grouping or concepts for the assessment 
of  mixtures  of  structurally  similar  substances  for  the  setting  of  limit  values,  e.g.  toxic 
equivalency factors (TEF), which has been used for the dioxin-group. The same approach has 
been used for dioxins also under the Water Framework Directive.  

Addressing  groups  of  substances  is  possible  and  is  increasingly  becoming  normal  practice 
under  REACH,  which  contains  specific  provisions  for  grouping..  The  grouping  of  similar 
substances is mentioned in connection with substance evaluation (Article 47). The testing and 
assessment  requirements  may  be  modified  for  a  group  of  structurally  similar  substances, 
hence  limiting  the  testing  to  one  or  a  few  substances,  while  predicting  the  properties  of  the 
other  substances  in  the  group  based  on  these  tests  (Article  13;  Annex  I  point  0.4  and; 
preamble  of  Annexes  VII  to  X  Annex  XI).  REACH  Article  62(3)  allows  submitting 
applications  for  authorisations  for  groups  of  substances.  There  are  several  examples  of 
authorisations  and  restrictions  of  groups  of  similar  substances  such  as  metal  compounds, 
PAHs, phthalates and PFASs (see examples of restriction in Section 5).  

3.4 Aggregate Exposure 

Aggregate exposure refers to the exposure to the same substance from different independent 
sources  and/or  via  different  pathways.  It  is  related  to  and  hence  often  considered  in 
connection  with  unintentional  chemical  mixtures.  Clear  legal  requirements  for  performing 
aggregate  exposure  assessments  across  different  regulatory  sectors  currently  exist  only  in 
some  pieces  of  chemicals  legislation  (i.e.  legislation  focused  on  chemical  substances  and 
intentional mixtures), and is hence not normally and systematically taken into account.  

18 

 
 
 
Under REACH, aggregate exposure may be assessed when authorities evaluate a substance or 
consider authorisation (REACH, Title VII). There are examples of restrictions under REACH 
that are based on aggregate exposure of particular chemicals, such as perfluorooctanoic acid 
and phthalates.  

The  Cosmetics  Regulation  requires  the  consideration  of  aggregate  exposure  in  the  human 
health risk assessment of certain  ingredients  in  cosmetics. According to  the guidelines from 
the  Scientific  Committee  on  Consumer  Safety  (SCCS)75,  the  evaluation  of  a  cosmetic 
ingredient  for  the  product  safety  report  must  take  into  account  aggregate  exposure  of  the 
ingredient from different types of cosmetic products.  

The Regulation on food contact materials also requires a consideration of different sources of 
exposure  to  the  same  substance  or  group  of  substance  to  which  a  specific  migration  limit 
(SML)  is  applied.  Consequently,  several  substances  regulated  in  particular  in  plastic  food 
contact  materials  acknowledge  this  and  include  an  allocation  factor  that  further  restricts  the 
amount of substance permitted to migrate into food. 

Legislation  oriented  towards  pollution  and  certain  environmental  media  (e.g.  water  and  air 
related  pieces  of  legislation)  normally  consider  the  aggregate  exposure  to  a  substance, 
regardless  of  source.  However,  it  does  usually  not  consider  exposure  via  all  relevant 
environmental media or pathways.  

3.5  Conclusions  on  existing  legal  requirements  for  intentional  and 

unintentional mixtures, grouping and aggregate exposure 

Regarding intentional  mixtures, there are requirements in  place in  most  pieces of chemicals 
legislation  (chemical  substance  and  intentional/commercial  mixture  focused  legislation)  as 
well as in one piece of products-specific legislation, namely the Toy Safety Directive.  

Requirements  on  the  assessment  of  unintentional  mixtures  are  broadly  absent  in  chemical 
substance  and  mixture  focused  legislation.  The  only  exceptions,  where  requirements  for  the 
assessment  of  cumulative  exposure  to  unintentional  mixtures  exist,  is  the  directive  on  the 
protection  of  the  health  and  safety  of  workers  from  the  risks  related  to  chemical  agents  at 
work,  the  regulation  on  the  maximum  residues  levels  of  pesticides  in  food,  the  Plant 
Protection  Products  regulation  and  the  Biocidal  Product  regulation.  The  requirements  under 
the  regulations  on  maximum  residues  levels  and  the  Plant  Protection  Products  are  however 
not yet implemented as the methodology is still under development.  

Requirements for the assessment of unintentional mixtures exist in a few additional pieces of 
legislation  focused  on  products,  pollution  and  environmental  media.  Out  of  the  15  assessed 
pieces of such legislation, six include a reference to the assessment of unintentional mixtures, 
regarding  human  health  or  the  environment,  or  both.  These  references  are  however  usually 
vague  and  general,  with  a  lack  of  provisions  and/or  guidance  for  how  to  perform  the 
assessment,  and  hence  rarely  implemented.  In  four  of  these  pieces  of  legislation,  the 
requirement only refers to particular groups of substances, e.g. dioxins or PAHs.  

A  few  pieces  of  legislation  provide  for  grouping  approaches  in  the  assessment  of  certain 
functionally  or  structurally  similar  substances,  without  requiring  an  actual  mixture 
assessment.  Aggregate  exposure  to  the  same  substance  from  different  sources  and/or  via 
different routes of exposure can be considered in substance evaluation and when considering 

75 SCCS notes for guidance point 3.4.3 
https://ec.europa.eu/health/sites/health/files/scientific_committees/consumer_safety/docs/sccs_o_224.pdf  

19 

 
 
 
                                                           
authorisation  and  restriction  under  REACH  as  well  as  in  the  regulations  on  cosmetics  and 
biocides. It is not considered in any other pieces of chemicals or products related legislation. . 
However,  aggregate  exposure  is  normally  considered  in  pollution  and  environmental  media 
focused legislation, but  usually  limited to  the particular environmental media or pathway in 
scope of the legislation.  

Overall, the progress on legal requirements for the assessment of unintentional mixtures has 
been limited since 2012.  

4.  PROGRESS ON GUIDANCE AND REGULATORY ASSESSMENT  

In  the  2012  Communication  (Section  5.3,  paragraph  2),  the  Commission  commits  to 
coordinate the development of technical guidelines in order to promote a consistent approach 
for the assessment of priority mixtures across different pieces of EU legislation.  

Some  overarching  guidance  documents  to  support  consistent  methodologies  were 
recently  developed.  These  are  based  on  the  framework  for  the  assessment  of  combined 
exposures to multiple chemicals presented by WHO/IPCS in 201176, and the methodology is 
summarized  in  the  State  of  the  Art  Report  in  2012.  EFSA77,  likewise,  published  a 
comprehensive  guidance  document  on  mixture  risk  assessments  in  2019,  to  support 
harmonised methodologies for the environment, animal and human health in the fields falling 
within  EFSA’s  competence.  The  Commission  also  contributed  to  the  2018  Organisation  for 
Economic  Co-operation  and  Development  (OECD)  report  on  risk  assessment  of  combined 
exposure78, which describes all essential steps to be considered, independent of the legislative 
framework,  the  complexity  of  the  mixture  (intentional  or  unintentional),  the  scope  of  the 
assessment, and the assessor.  

The approach for the assessment of chemical mixtures is in principle common to all guidance 
developed so far and applicable to both intentional and unintentional mixtures. It includes:  

  Prioritisation  methods  and/or  grouping  approaches  to  select  the  components  to  be 

considered; 

  Options  to  use  (eco)toxicity  and  exposure  data  on  the  single  components  to  predict 
mixture  hazard  and/or  risks,  through  component-based  approaches  (Concentration 
Addition or Independent Action); 

  Options to test the whole mixture as such and assess hazard and/or risk based on the test 

data; 

  Tiered  approaches  to  refine  the  assessment  depending  on  the  availability  and  quality  of 

data and information on the mode of action.  

Further legislation-specific guidance documents for the assessment of mixtures have been 
developed  for  some  pieces  of  EU  legislation  in  recent  years.  Currently,  such  guidance  is 
and  veterinary 
available 

for  plant  protection  products79,  biocidal  products80, 

76 M.E. (Bette) Meek, Alan R. Boobis, Kevin M. Crofton, Gerhard Heinemeyer, Marcel van Raaij, Carolyn Vickers ‘Risk 
assessment of combined exposure to multiple chemicals: A WHO/IPCS framework’ Regulatory Toxicology and 
Pharmacology 60 (2011) S1–S14   https://pubmed.ncbi.nlm.nih.gov/21466831/ 
77 https://doi.org/10.2903/j.efsa.2019.5634 https://doi.org/10.2903/j.efsa.2019.5634  
78 OECD (2018). ‘Considerations for Assessing the Risks of Combined Exposure to Multiple Chemicals’, Series on Testing 
and Assessment No. 296, Environment, Health and Safety Division, Environment Directorate. 
http://www.oecd.org/chemicalsafety/risk-assessment/considerations-for-assessing-the-risks-of-combined-exposure-to-
multiple-chemicals.pdf  
79 EFSA Guidance documents on risk assessment of plant protection products for mammals (2009) and bees (2013), EFSA 
Scientific  Opinions  (GDs  for  bees  and  birds  and  mammals,  Scientific  Opinions  on  risk  assessment  of  plant  protection 

20 

 
 
                                                           
pharmaceuticals81,  in  all  cases  including  references  to  the  risk  assessment  of  intentional 
mixtures regarding either human health or the environment.  

For  human  health  assessment,  guidance  documents  are  also  available  for  plant  protection 
products  and  their  residues  with  respect  to  Cumulative  Assessment  Groups  (CAGs)82,83  and 
probabilistic modelling84 as well as for biocidal products85.  Moreover, technical guidance on 
the classification of waste86, which includes aspects of mixture assessment, was published in 
2018 (see section 3).  

In conclusion, there has been some progress on the availability of both general and legislation 
specific guidance since 2012. All the legislation specific guidance documents presented refer 
to  the  assessment  of  intentional  mixtures,  except  for  the  guidance  on  pesticide  residues  in 
food and feed and some elements in the guidance on classification of waste.   

5.  CASES OF REGULATORY ASSESSMENT OF MIXTURES 

The  2012  Communication  concluded  that  methodologies  for  the  identification  of  chemical 
mixtures of potential concern as well as for the assessment of chemical mixtures are available, 
although the extent of the assessment is limited by knowledge and data gaps. It also foresaw 
that information collected in the context of EU legislation, in particular REACH registration 
will contribute to reducing these gaps.  

In  2014,  the  Commission  (JRC)  conducted  a  survey  on  methodologies  for  assessing  the 
combined effect of chemicals87, answered by 58 experts in risk assessment from 21 countries, 
representing  among  others,  authorities,  academia  and  industry,  with  experience  in  mixture 
risk assessment, in most cases for regulatory purposes.  According to responses to the survey, 
most  of  the  practical  experience  with  mixture  assessments  exists  in  the  area  of  plant 
protection products and, as regards intentional mixtures in the context of CLP and REACH. 
Concentration addition appeared as the most commonly used component-based approach.  

on 

(Vol. 

products 

combination 

(Parts  BþC) 

pharmaceutical 

(2005)  Guideline 

evaluation’,  European  Chemicals  Agency,  Helsinki,  Finland. 

products for aquatic organisms (2013), sediment organisms (2015), non-target terrestrial plants (2014),  non-target arthropods 
(2015) https://www.efsa.europa.eu  
80  European Chemicals Agency (ECHA) (2017), ‘Guidance on the Biocidal Products Regulation - Volume IV Environment - 
II). 
assessment  & 
https://echa.europa.eu/documents/10162/23036412/bpr_guidance_vol_iii_part_a_en.pdf/05e4944d-106e-9305-21ba-
f9a3a9845f93  
81  EMA 
(EMEA/CVMP/83804/2005). 
fixed 
https://www.ema.europa.eu/en/documents/scientific-guideline/guideline-pharmaceutical-fixed-combination-products_en.pdf  
82 EFSA Panel on Plant Protection Products and their residues (PPR). 2013. Scientific opinion on the relevance of dissimilar 
mode of action and its appropriate application for cumulative risk assessment of pesticides. EFSA Journal. 2013;11(12):3472 
https://www.efsa.europa.eu/en/efsajournal/pub/3472  
83  EFSA  Panel  on  Plant  Protection  Products  and  their  Residues  (PPR).  2013.  Scientific  Opinion  on  the  identification  of 
pesticides  to be  included  in  cumulative  assessment  groups  on  the  basis  of  their  toxicological  profile  (2014 update).  EFSA 
Journal 2013;11(7):3293, 131:3293. https://www.efsa.europa.eu/en/efsajournal/pub/3293  
84 EFSA (2012) Panel on Plant Protection Products and their Residues (PPR); Guidance on the Use of Probabilistic 
Methodology for Modelling Dietary Exposure to Pesticide Residues. EFSA Journal;10(10):2839.  
doi:10.2903/j.efsa.2012.2839 https://www.efsa.europa.eu/en/efsajournal/pub/2839  
85 ECHA (European Chemicals Agency) (2017). Guidance on the biocidal products regulation, Volume III Human health - 
assessment & evaluation, Parts B and C, ECHA-17-G-25-EN 
https://echa.europa.eu/documents/10162/23036412/biocides_guidance_human_health_ra_iii_part_bc_en.pdf/30d53d7d-
9723-7db4-357a-ca68739f5094  
86 Commission notice on technical guidance on the classification of  waste (2018/C 124/01). https://eur-lex.europa.eu/legal-
content/EN/TXT/PDF/?uri=CELEX:52018XC0409(01)&from=EN  
87 Bopp S, Berggren E, Kienzler A, van der Linden S, Worth A (2015): Scientific methodologies for the combined effects of 
chemicals  –  a  survey  and 
report  EUR  27471  EN;  doi:10.2788/093511 
https://publications.jrc.ec.europa.eu/repository/bitstream/JRC97522/jrc_tech_rep_sci%20meth%20for%20mix_final.pdf  

review;  JRC 

technical 

literature 

21 

 
 
                                                                                                                                                                                     
Cases  of  mixture  risk  assessment  based  on  combined  exposure  and  combined  effects  for 
regulatory  purposes  are  generally  important  benchmarks  for  future  action.  A  recent  case  of 
risk  management  for  mixtures  is  the  restriction  of  the  four  phthalates  DEHP,  BBP,  DBP, 
DIBP  under  REACH88.  The  risk  assessment  of  these,  considering  combined  exposure,  was 
based  on  biomonitoring  data.  The  limit  value  of  this  restriction  refers  to  the  combined 
unintentional exposure to the four substances in articles. This is the first clear-cut example of 
a REACH restriction where the risk assessment considers combined exposure to structurally 
similar  chemicals  (i.e.  in  this  report  referred  to  as  an  unintentional  mixture).  A  similar 
restriction is being introduced in food contact materials on the basis of the assessment of co-
exposure to these phthalates by EFSA89. 

There are also some cases where groups of substances were considered and restricted together 
as a group, without actually assessing the risk from their combined exposure. Instead, the joint 
restrictions  were  based  on  similarities  in  their  chemical  structure  (e.g.  lead  compounds  and 
poly-aromatic  hydrocarbons),  hazard  profile  (e.g.  CMR  in  consumer  mixtures),  uses  (e.g. 
CMR  in  textiles)  and  exposure  pathways.  Further  examples  include  the  restriction  of  the 
phthalates  DINP90,  DIDP91  and  DNOP92  in  toys  and  childcare  articles93,  and  the  ongoing 
restrictions of chemicals in tattoo inks94 and PFAS. Such restrictions can manage some risks 
related to combined exposure, but are also motivated by other aspects,  e.g. the avoidance of 
regrettable substitution.  

In  addition,  some  experience  relating  to  the  risk  assessment  of  unintentional  mixtures, 
probabilistic modelling, and grouping of chemicals in cumulative assessment groups (CAGs) 
has  been  gained  under  the  Regulation  on  Maximum  Residue  Levels  of  Pesticides.  The  first 
CAGs for pesticides that have acute effects on the nervous system95 and chronic effects on the 
thyroid system96 were recently published (see also Box 4).  

Further cases of combined exposure to chemicals considered in a regulatory context relate to 
the  area  of  food  contaminants.  These  were  mineral  oil  saturated  hydrocarbons97, 
hexabromocyclododecanes98,  non-ortho  polybrominated  biphenyls99,  marine  biotoxins100,101, 

88 ECHA (2017). Committee for Risk Assessment (RAC) and Committee for Socio-economic Analysis (SEAC) Opinion  
on an Annex XV dossier proposing restrictions on four phthalates (DEHP, BBP, DBP, DIBP);  ECHA/RAC/RES-O-
0000001412-86-140/F, March 2017 https://echa.europa.eu/documents/10162/e39983ad-1bf6-f402-7992-8a032b5b82aa  
89 https://efsa.onlinelibrary.wiley.com/doi/epdf/10.2903/j.efsa.2019.5838 
90 diisobutyl phthalate.  
91 di-“isodecyl” phthalate (CAS No 68515-49-1) as well as 1,2benzenedicarboxylic acid, di-C9-11-branched alkyl esters, 
C10-rich (CAS No 26761-40-0) 
92 di-n-octyl phthalate 
93 ECHA (2013): Evaluation of new scientific evidence concerning DINP and DIDP in relation to entry 52 of Annex XVII to 
REACH Regulation (EC) No 1907/2006 
https://www.echa.europa.eu/documents/10162/13579/201308_echa_review_dinp_didp_final_report_en.pdf  
94 ECHA website (2019): Substances in tattoo inks and permanent make up 
https://www.echa.europa.eu/web/guest/registry-of-restriction-intentions/-/dislist/details/0b0236e180dff62a  
95  EFSA  (European  Food  Safety  Authority)  (2020)  Cumulative  dietary  risk  characterisation  of  pesticides  that  have  acute 
2020;18(4):6087 
EFSA 
nervous 
effects 
https://www.efsa.europa.eu/en/efsajournal/pub/6087  
96 EFSA (European Food Safety Authority) (2020) Cumulative dietary risk characterisation of pesticides that 
have 
https://www.efsa.europa.eu/en/efsajournal/pub/6088  
97 EFSA Panel on Contaminants in the Food Chain (CONTAM), 2012a; Scientific Opinion on Mineral Oil Hydrocarbons in 
Food. EFSA Journal 2012; 10(6):2704, 185 pp. doi:10.2903/j.efsa.2012.2704 164.  
https://www.efsa.europa.eu/en/efsajournal/pub/2704  
98  EFSA  Panel  on  Contaminants  in  the  Food  Chain  (CONTAM);  Scientific  Opinion  on  Hexabromocyclododecanes 
(HBCDDs) 
doi:10.2903/j.efsa.2011.2296 
Journal 
Food. 
https://www.efsa.europa.eu/en/efsajournal/pub/2296  
99 EFSA Panel on Contaminants in the Food Chain (CONTAM), 2005. Scientific opinion on a request from the Commission 
related to the presence of non-dioxin-like polychlorinated biphenyls (PCB) in feed and food. The EFSA Journal 2005, 284, 
137 pp. doi:10.2903/j.efsa.2005.284. https://www.efsa.europa.eu/en/efsajournal/pub/284   

2020;18(4):6087. 

2020;18(4):6088 

2011;9(7):2296, 

Scientific 

thyroid, 

system. 

chronic 

Report. 

Journal 

Journal 

Journal 

effects 

EFSA 

EFSA 

EFSA 

118 

pp. 

the 

the 

on 

on 

in 

22 

 
 
                                                           
ergot  alkaloids102,  polyaromatic  hydrocarbons103,  pyrrolizidine  alkaloids104  and,  more 
recently, PFAS105. 

Lastly, lists of known synergists (chemicals interacting so that (eco)toxicological effects are 
enhanced in cases of co-exposure) are being compiled and are supposed to be included in the 
respective  Annexes  of  the  Biocides  and  Plant  Protection  Products  Regulations,  to  better 
address and regulate these compounds.  

The findings in  the JRC survey and other developments  referred to  above, demonstrate that 
knowledge,  methods  for  the  assessment  of  mixtures  and  experience  in  applying  them  are 
available  in  several  areas.  Regarding  the  MRL  Regulation,  knowledge  and  methodology 
(CAGs) are still being developed. However, as the development has proven to be extremely 
complex, CAGs are not yet applied for regulatory purposes under that Regulation.  

Hence, there is  in  several  areas an  established methodology in  principle ready to  apply in  a 
more systematic manner, although often limited by factors such as data gaps and absence of 
specific  guidance.  Grouping  approaches  can  contribute  to  addressing  some  unintentional 
mixtures, and have been applied much more frequently than actual assessments of mixtures, 
e.g. under REACH and in the area of food contaminants. 

6.  INTEGRATED AND CO-ORDINATED ASSESSMENT OF 

MIXTURES ACROSS DIFFERENT PIECES OF LEGISLATION  

6.1 Interface between different pieces of legislation  

As  already  concluded  in  2012  by  the  Commission,  EU  legislation  does  not  provide  for  a 
comprehensive  and  integrated  assessment  of  combined  effects  of  different  chemicals  across 
the different pieces of legislation.  
In  2016106,  the  JRC  reviewed  21  published  case  studies  on  risk  assessments  of  real-life 
mixtures  for  human  health  and  the  environment,  all  conducted  between  2014  and  2016. 
Assessed  cases  covered  a  range  of  different  substance  classes  and  media.  All  studies 
addressed  unintentional  mixtures  (apart  from  one  looking  at  aggregate  exposure).  Most  of 
them  were  based  on  monitoring  data,  a  few  on  modelled  exposure.  Seven  of  the  cases 

in  Shellfish  –  Saxitoxin  Group.  The  EFSA  Journal 

100 EFSA Panel on Contaminants in the Food Chain (CONTAM), 2009a. Scientific Opinion on a request from the European 
Commission  on  Marine  Biotoxins 
  2009,  1019,  1–76. 
doi:10.2903/j.efsa.2009.1019.  https://www.efsa.europa.eu/en/efsajournal/pub/1019  
101 EFSA Panel on Contaminants in the Food Chain (CONTAM), 2009b. Scientific Opinion of the Panel on Contaminants in 
the Food Chain on a request from the European Commission on marine biotoxins in shellfish – pectenotoxin group. The 
EFSA Journal 2009, 1109, 47 pp. doi:10.2903/j.efsa.2009.1109. 
https://efsa.onlinelibrary.wiley.com/doi/abs/10.2903/j.efsa.2009.1109  
102 EFSA Panel on Contaminants in the Food Chain (CONTAM), 2012b. Scientific Opinion on Ergot alkaloids in food and 
feed. EFSA Journal 2012;10(7):2798, 158 pp. doi:10.2903/j.efsa.2012.2798. 
https://www.efsa.europa.eu/en/efsajournal/pub/2798  
103 EFSA Panel on Contaminants in the Food Chain (CONTAM), 2008. Scientific Opinion on a request from the European 
Commission on Polycyclic Aromatic Hydrocarbons in Food. The EFSA Journal 2008, 724, pp. doi:10.2903/j.efsa.2008.724. 
https://www.efsa.europa.eu/en/efsajournal/pub/724  
104 EFSA Panel on Contaminants in the Food Chain (CONTAM), 2011; Scientific Opinion on Pyrrolizidine alkaloids in food 
and feed. EFSA Journal 2011;9(11):2406, 134 pp. doi:10.2903/j.efsa.2011.2406. 
https://efsa.onlinelibrary.wiley.com/doi/abs/10.2903/j.efsa.2011.2406  
105 EFSA (2020), Public consultation on the draft scientific opinion on the risks to human health related to the presence of 
perfluoroalkyl  substances 
food  https://www.efsa.europa.eu/en/consultations/call/public-consultation-draft-scientific-
opinion-risks-human-health  
106 Bopp, S. K.; A. Kienzler, S. van der Linden, L. Lamon, A. Paini, N. Parissis, A.-N. Richarz, J. Triebe, A. Worth (2016), 
Review of case studies on the human and environmental risk assessment of chemical mixtures. JRC EUR 27968 EN; 
https://publications.jrc.ec.europa.eu/repository/bitstream/JRC102111/jrc102111_jrc_tech-
rep_mix%20case%20studies_2016_vf.pdf  

in 

23 

 
 
                                                                                                                                                                                     
involves chemicals across different classes and legislative sectors. Available risk assessment 
tools were successfully used in all the reviewed cases. The concept of Concentration Addition 
was  applied  as  default  to  predict  mixture  toxicities,  while  the  Maximum  Cumulative  Ratio 
approach  was  often  used  for  prioritisation  purposes  and  to  decide  whether  only  certain 
substances or a larger number of chemicals were responsible for the mixture risks. Several of 
the  case  studies  identified  potential  risks  from  mixtures  for  human  health  and/or  the 
environment (see Box 2).  

According  to  the  JRC  review,  the  relatively  few  cases  where  regulatory  assessment  of 
unintentional  mixtures  is  actually  performed  (see  also  Section  3),  are  usually  limited  to 
mixtures consisting of chemicals that fall under the same particular piece of legislation. Thus, 
no  systematic  identification,  of  (unintentional)  real-life  priority  mixtures  is  currently 
performed.  The  regulatory  risk  assessment  or  risk  management  of  real-life  unintentional 
mixtures  is  accordingly  performed  only  rarely  and  on  an  ad  hoc  basis,  while  available 
scientific case studies are isolated examples.  

The  2016  JRC  review  concluded  that  ‘so  far  there  is  no  prospective  risk  assessment 
concerning  chemical  substances  related  to  various  regulatory  sectors  and/or  uses,  and 
although numerous chemicals fall under several regulatory frameworks (biocides, pesticides, 
REACH...), the potential for co-exposure is hardly assessed or taken into account in their risk 
assessment.’  

A  related  issue  is  how  to  address  aggregate  exposure  to  the  same  chemical  when  this  is 
regulated under different pieces of legislation. An example is the restriction of four phthalates 
under  REACH  (see  also  Section  5).  The  exposure  to  one  of  these  phthalates  (DEHP)  from 
food intake was identified as the major source of exposure according to the assessment. This 
part of the exposure, falling under the Food Contact Materials Regulation107, or other sources 
of exposure such as environmental contamination or food contaminants was not addressed in 
the REACH restriction.  

Article 16(2) of the Water Framework Directive (WFD) specifies how risk assessments under 
existing legislation should be used as a basis for listing priority substances in surface waters. 
It  also  allows  the  use  of  a  simplified  risk-based  assessment  procedure  taking  into  account 
evidence regarding the intrinsic hazard of the substance (aquatic toxicity and human toxicity 
via aquatic exposure routes), evidence from monitoring and other factors which may indicate 
widespread environmental  contamination,  such as production volumes or use patterns. Such 
risk-based  assessments  inevitably  consider  aggregate  risk  from  different  uses  of  the  same 
substance,  and  in  some  cases  also  several  substances  if  they  are  in  a  group  for  which  the 
Environmental  Quality  Standard  (EQS)  is  set  for  a  marker  substance  or  the  sum  of  the 
concentrations  of related substances. The listing  of substances in  the priority substances list 
under  the  WFD  on  the  basis  of  such  risk-based  assessments  should  be  taken  into  account 
when substances are approved/authorised or reviewed under several of the relevant pieces of 
sectoral  legislation, in  particular if the monitoring data subsequently obtained show that the 
EQS  are  still  not  being  met.  There  are  references  to  the  WFD  objectives  in  those  pieces  of 
legislation, and the obligation to consider the WFD findings was further specified in Article 
7a  of  the  EQS  Directive  in  2013.  The  risk-based  assessment  under  WFD  does  not  consider 
exposure via other routes, e.g. air, nor combined effects from unrelated substances (although a 
quality  standard  for  the  broad  grouping  of  “pesticides”  is  set  under  the  Groundwater 
Directive). 

107 ECHA (2017) Committee for Risk Assessment (RAC) Committee for Socio-economic Analysis (SEAC) Opinion on 
phthalates restriction, Opinion on an Annex XV dossier proposing restrictions on four phthalates (DEHP, BBP, DBP, DIBP), 
ECHA/RAC/RES-O-0000001412-86-140/F, Agreed 16 March 2017. https://echa.europa.eu/documents/10162/e39983ad-
1bf6-f402-7992-8a032b5b82aa 

24 

 
 
                                                           
The above findings and examples highlight the remaining need to develop risk management 
measures and coordination across all relevant sectors and uses, when chemicals involved are 
regulated  through  different  pieces  of  legislation.  Such  an  approach  would  require  mutual 
acceptance or  alignment  of procedures and decisions  on substances  and  mixtures as well as 
improved  co-operation,  including  the  sharing  of  data  between  involved  EU  agencies  and 
Member State authorities.    

The Commission has recently engaged in a number of evaluations of  EU chemicals related 
legislation,  which  in  several  cases  look  at  challenges  related  to  combined  exposure  and 
assessment  of  mixtures,  including  mixtures  consisting  of  chemicals  from  across  regulatory 
areas. Evaluations looking at several pieces of legislation together, and the interplay between 
these, include the fitness check of most chemicals legislation except REACH108, 109 (covering 
over  40  pieces  of  legislation),  the  fitness  check  of  the  EU  water  legislation110,111,  the 
evaluation of the EU legislation on plant protection products and pesticides residues112 as well 
as  the  fitness  check  of  the  EU  legislation  on  endocrine  disruptors113.  Evaluations  of  single 
pieces  of  legislation  that  consider  how  they  address  mixtures  include  those  of  the 
Occupational Safety and Hygiene (OSH) Directive114 and the Detergents Regulation115.  

Several  of  these  evaluations  point  to  the  need  to  develop  the  assessment  of  mixtures, 
including across regulatory areas. As such integrated assessment of chemical mixtures has not 
been achieved yet, further efforts are needed, including closing interface gaps between pieces 
of legislation, improve data availability, harmonise approaches and conduct further regulatory 
and scientific case studies on mixture assessment.   

6.2 Case studies on priority mixtures  

In the 2012 Communication, the Commission committed to develop a consistent approach to 
the  assessment  of  priority  mixtures  across  the  different  pieces  of  EU  legislation.  The 
Commission referred to  a set of criteria and methodologies that could be applied to identify 
chemical  combinations/mixtures  that  are  priorities  for  further  assessment  proposed  by  its 

and  Floods  Directive.  SWD(2019) 

108      European  Commission  (2019).  Report  from  the  Commission  to  the  European  Parliament,  the  Council,  the  European 
Economic  and  Social  Committee  and  the  Committee  of  the  regions,  Findings  of  the  Fitness  Check  of  the  most  relevant 
chemicals legislation (excluding REACH) and identified challenges, gaps and weaknesses. COM(2019) 264 final. https://eur-
lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52019DC0264&from=EN  
109 European Commission (2019), Fitness Check of the most relevant chemicals legislation (excluding REACH), as well as 
related  aspects  of  legislation  applied  to  downstream  industries.  SWD(2019)  199  final/2.  https://eur-lex.europa.eu/legal-
content/EN/TXT/PDF/?uri=CELEX:52019SC0199R(01)&from=EN  
110 European Commission (2019). Executive Summary of the Fitness Check of the Water Framework Directive, Groundwater 
final 
Directive,  Environmental  Quality  Standards  Directive 
https://ec.europa.eu/environment/water/fitness_check_of_the_eu_water_legislation/documents/SWD_2019_440_F1_SWD_F
ITNESS_CHECK_EXECUTIVE_SUMMARY_EN_V4_P1_1058675.pdf  
111 European Commission (2019). Fitness Check Evaluation of the Water Framework Directive and the Floods Directive. 
Executive Summary of the Support Study. 
https://ec.europa.eu/environment/water/fitness_check_of_the_eu_water_legislation/documents/Study%20report%20exec%20
summary%20EN%20%20-%20TRI%20TEC6327EU.pdf  
112 European Commission (2020), Commission staff working document accompanying the document report from the 
commission to the European Parliament and the Council. Evaluation of Regulation (EC) No 1107/2009 on the placing of 
plant protection products on the market and of Regulation (EC) No 396/2005 on maximum residue levels of pesticides. 
SWD/2020/87 final https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52020SC0087&from=EN  
113 European Commission (2020), Commission staff working document on endocrine disruptors SWD (2020) 249 final. 
114 European Commission (2017) Ex-post evaluation of the European Union occupational safety and health Directives 
(REFIT evaluation). SWD(2017) 10 final. 
file:///C:/Users/Boijeur/AppData/Local/Packages/Microsoft.MicrosoftEdge_8wekyb3d8bbwe/TempState/Downloads/2_EN_
autre_document_travail_service_part1_v3%20(2).pdf  
115 European Commission (2019), Executive Summary of the Evaluation of Regulation (EC) No 648/2004 of the European 
Parliament and of the Council of 31 March 2004 on detergents. SWD(2019) 299 final. 
https://ec.europa.eu/transparency/regdoc/rep/10102/2019/EN/SWD-2019-299-F1-EN-MAIN-PART-1.PDF  

440 

25 

 
 
                                                           
Scientific Committees SCHER, SCENIHR and SCCS in 2012116. The criteria proposed were 
intended to facilitate a focus on mixtures of potential concern. They included aspects such as: 
commercial mixtures with several components of concern; potential serious adverse effects of 
one or more chemicals at the likely exposure levels; likely large-scale and frequent exposure 
of  humans  or  the  environment;  persistence  in  the  body  or  the  environment;  information  on 
potential interactions; prediction of similar modes of action; and mixtures containing one or 
more components without an effect threshold.  
An experimental laboratory study from 2014117 evaluated the effects of realistic mixtures of 
14-19  different  chemicals  falling  under  different  pieces  of  legislation  (pesticides,  industrial 
chemicals,  biocides  and  pharmaceuticals)  which  may  jointly  occur  in  surface  waters.  These 
were  analysed  in  concentrations  based  on  their  respective  individual  environmental  quality 
standard  (EQS)  in  35  different  standardised  in  vitro  and  in  vivo  test  systems.  Although  the 
individual  chemicals  were  all  present  at  concentrations  considered  safe  under  current 
legislative practices, clear adverse effects of the mixtures were demonstrated in a number of 
organisms, including fish, frogs, crustaceans, algae and micro-organisms. Further, some EU-
funded research projects have identified risks of mixtures to the environment, on the basis of 
available monitoring/exposure modelling methodology and hazard data (SOLUTIONS)118, or 
to human health, based on measurements of human blood samples and in vitro and in vivo test 
systems (EDC-MixRisk)119 (see two cases described in Box 2).   

The selection of cases for the assessment of mixtures is usually driven by the availability of 
data on toxicity and exposure. Therefore, a limited selection of well-studied chemicals tend to 
be  overrepresented  in  current  case  studies,  which  are  hence  unlikely  to  be  representative  of 
human  and  environmental  exposures.  To  circumvent  this,  a  more  systematic  analysis  of 
cases of mixture risk assessments is warranted.  

In  conclusion,  the  assessment  of  unintentional  chemical  mixtures  across  regulatory  areas  as 
well  as  assessments  to  identify  priority  mixtures  are  rare  and  only  performed  on  an  ad  hoc 
basis.  Reasons  for  this  include  lack  of  regulatory  requirements  and  coordination  between 
sectors and regulatory bodies as well as absent or incomplete toxicity and exposure data.  

7.  CLOSING 

THE  KNOWLEDGE  GAPS 

– 

RECENT 

ACHIEVEMENTS  

To  address  remaining  knowledge  gaps,  the  2012  Communication120  set  out  that  the 
Commission  would  work  further  for  a  better  understanding  of  the  chemicals  mixtures  to 
which human populations and the environment are actually exposed. This includes reviewing 
data on toxicity and exposure collected under EU legislation or generated in research projects. 

116  SCHER/SCENHIR/SCCS  (2012):  Scientific  Committee  on  Health  and  Environmental  Risks  (SCHER),  Scientific 
Committee  on  Emerging  and  Newly  Identified  Health  Risks  (SCENHIR)  and  Scientific  Committee  on  Consumer  Safety 
(SCCS).  Joint  Opinion  on  the  Toxicity  and  Assessment  of  Chemical  Mixtures.  Adopted  on  14th  December  2011.  DOI: 
https://doi.org/10.2772/21444   
117 Carvalho, R.N., A. Arukwe, S. Ait-Aissac, A. Bado-Nilles, S. Balzamo, A. Baun, S. Belkin, L. Blaha, F. Brion, D. Conti, 
N. Creusot, Y. Essig, V. E. V. Ferrero, V. Flander-Putrle, M. Fuerhacker, R. Grillari-Voglauer, C. Hogstrand, A. Jonas, J. B. 
Kharlyngdoh, R. Loos, A.-K. Lundebye, C. Modig, P.-E. Olsson, S. Pillai, N. Polak, M. Potalivo, W. Sanchez, A. Schifferli, 
K. Schirmer, S. Sforzini, S.R. Stuerzenbaum, L. Søfteland, V. Turk, A. Viarengo, I. Werner, S. Yagur-Kroll, R. Zounkov, T. 
Lettieri (2014), ‘Mixtures of Chemical Pollutants at European Legislation Safety Concentrations: How Safe Are They?’, 
Toxicological Sciences, 141(1), 2014, 218–233; doi: 10.1093/toxsci/kfu118. https://pubmed.ncbi.nlm.nih.gov/24958932/   
118 Research project funded under EUs 7th Framework Program for Research and Innovation.   
119 Research project funded under EUs Research and Innovation Program Horizon 2020.  
120 Operational follow-up (Section 5.3, paragraph 3) 

26 

 
 
                                                           
The  Communication  also  committed  to  the  creation  of  a  platform  for  chemical  monitoring 
data, e.g. to help link exposure and epidemiological data on humans and the environment.  

Further, the Communication also set out how to address some of the other knowledge gaps, in 
particular:  (i)  The  mode  of  action  of  chemicals;  (ii)  Criteria  for  grouping  chemicals  into 
categories  or  assessment  groups;  (iii)  Predicting  interactions;  and  (iv)  Identifying  chemical 
substances that are the main drivers of mixture toxicity. Below is a brief summary of progress 
in these areas.  

The Communication also concluded that the assessment of chemical mixtures must be carried 
out  with  respect  to  the  principle  of  reducing,  refining  and  replacing  testing  on  vertebrate 
animals. 

To  address  the  identified  gaps,  the  Commission  has  among  other  activities  funded  several 
research  projects,  most  of  them  under  its  Research  and  Innovation  Program  Horizon  2020. 
The outcome of these projects  was  recently  summarised in two scientific publications121, 122 
and is further described below.  Some of the findings from two of these research projects are 
also described in Box 2.  

7.1 Effect, exposure and hazard data  

the  Information  Platform  for  Chemical  Monitoring 
The  Commission  developed 
(IPCHEM)123  in  response  to  the  major  lack  of  monitoring  and  epidemiological  data  to 
understand  the  co-exposures  of  humans,  animals  and  the  environment  to  chemicals,  as 
identified in the 2012 Communication. IPCHEM was launched in a demonstration version in 
2014 and in a full, publicly available version in 2015 (see Box5).   

Recent  EU-funded  research  projects  also  provide  some  comprehensive  data  sets  on 
epidemiological data (e.g. EDCMixRisk, EuroMix, HBM4EU, all funded via Horizon 2020) 
and  chemical  monitoring  and  co-exposure  modelling  data  for  the  environment  (e.g. 
SOLUTIONS funded under the 7th Framework Programme for research and innovation).  

An  important  step  forward  regarding  the  availability  of  chemicals  toxicity  data  is  the 
finalisation  of  the  three  major  rounds  of  registration  of  chemicals  on  the  EU  market  under 
REACH.  However,  significantgaps  remain  in  this  area  (cf.  below,  Remaining  knowledge 
gaps).  

Currently,  databases  of  the  respective  European  agencies  working  in  the  chemicals  field 
provide data on exposure, uses, compositions, substance properties and hazards for regulatory 
purposes  under  different  frameworks.  These  include  the  ECHA  databases  for  REACH  and 
biocides, the EFSA data warehouse, the EEA databases on water as well as data from Member 
States. Moreover, the EU is also continuously contributing to international activities to bring 
hazard  databases  together,  such  as  the  OECD  eChemPortal  and  OECD  activities  towards  a 
‘Global Chemicals Knowledge Base’124 .  

121 Bopp, S.K., R. Barouki, W. Brack, S. Dalla Costa, J.-L.C.M. Dorne, P. E. Drakvik, M. Faust, T.K. Karjalainen, S. 
Kephalopoulos, J. van Klaveren, M. Kolossa-Gehring, A. Kortenkamp, E. Lebret, T. Lettieri, S. Nørager, J. Rüegg, J.V. 
Tarazona, X. Trier, B. van de Water, J. van Gils, Å. Bergman, ‘Current EU research activities on combined exposure to 
multiple chemicals’; Environment International 120 (2018) 544–562. 
https://www.sciencedirect.com/science/article/pii/S0160412018308420  
122 Stephanie K. Bopp, Aude Kienzler, Andrea-Nicole Richarz, Sander C. van der Linden, Alicia Paini, Nikolaos Parissis & 
Andrew P. Worth (2019) ‘Regulatory assessment and risk management of chemical mixtures: challenges and ways forward, 
Critical Reviews in Toxicology’, 49:2, 174-189, DOI: 10.1080/10408444.2019.1579169. 
https://doi.org/10.1080/10408444.2019.1579169  
123 https://ipchem.jrc.ec.europa.eu/ 
124 OECD (2019) ‘A Proposed Vision for a Global Chemicals Knowledge Base, including the evolution of existing related 
OECD tools’. ENV/JM(2020)2.  

27 

 
 
                                                           
The improved exchange of available data across regulatory areas and bodies involved is also 
crucial  for  the  risk  assessment  of  mixtures.  To  explore  the  possibility  of  enhancing  the 
transparency  and  exchange  of  data,  the  Commission  has  launched  a  feasibility  study  on  a 
common  open  platform  for  chemical  safety  data  based  on  a  request  from  the  European 
Parliament125.  

Box 5. The European Commission Information Platform for Chemical 
Monitoring (IPCHEM) 

The 2012 Communication highlighted the need to  improve the understanding of human and 
environmental exposure  to  chemical  mixtures.  One of the operational  follow-ups set  out  in 
response to this need was to promote a more coherent approach to the generation, collection, 
storage and use of chemicals monitoring data, through the creation of a platform for such data. 
The Commission developed the Information Platform for Chemical Monitoring (IPCHEM) in 
direct response to this.  

The  overall  purpose  of  IPCHEM  is  to  help  identify  links  between  chemical  exposure, 
including co-exposure, and the impact on human and ecosystem health. The objectives of the 
platform include improving access to monitoring data for policy makers and scientists, to host 
such  data  and  to  make  it  available  at  a  defined  quality  (regarding  spatial,  temporal, 
methodological and metrological traceability). IPCHEM also aims at improving data quality 
and  comparability,  thereby  facilitating  risk  assessment  practices  under  EU  policies.  Other 
areas where the platform can be useful includes evaluation of policy effectiveness, the design 
of future monitoring programmes and for the analysing of collected data.  

IPCHEM  provides  a  single  access  point  for  a  wide  range  of  chemical  monitoring  data, 
originating  from  European  Commission  bodies  and  Member  States,  as  well  as  international 
and national organisations and the research community. An example is the EU-funded human 
biomonitoring  project  HBM4EU126,  which  shares  collected  data  through  the  platform. 
IPCHEM  is  cross-linked  with  other  reference  information  systems  (e.g.  the  OECD  eChem 
Portal,  ECHA-REACH  info  card,  PubChem),  thus  also  facilitating  the  search  for  chemicals 
hazard data relevant to the environment and human health. 

IPCHEM  is  structured  into  four  thematic  modules:  environmental  monitoring,  human 
biomonitoring,  food  and  feed,  products  and  indoor  air.  From  the  platform,  it  is  possible  to 
search  by  chemical  substance,  environmental  media  and  country.  IPCHEM  also  includes  a 
search  tool  for  joint-occurrences  of  multiple  chemicals  at  a  particular  location,  which  is 
particularly useful in relation to mixtures.   

At present, IPCHEM provides access to over 450 million data records, and continues to grow. 
The main challenges include harmonising the data and ensure their quality. To address these, 
specific rules and procedures are implemented, and guidance is provided to data providers as 
well as end users.  

125  European  Commmission  (2019)  ‘Feasibility  Study  on  a  Common  Open  Platform  on  Chemical  Safety  Data’. 
https://etendering.ted.europa.eu/cft/cft-display.html?cftId=5516 
126 www.hbm4eu.eu  

28 

 
 
 
                                                           
The  Commission  in  2017  arranged  a  workshop  specifically  aimed  at  enhancing  the  use  of 
IPCHEM  for  the  assessment  of  mixtures.  The  resulting  report127  identifies  the  need  for  a 
tighter  collaboration  and  data  sharing  between  research  projects,  scientific  committees, 
Commission  services  and  EU  agencies.  To  enable  this,  there  is  a  need  to  find  solutions  for 
limiting  the  access  to  restricted  data  to  specific  user  groups.  This  requires  legal,  privacy  or 
contractual obligations, as well as streamlining the efforts to harmonise the management and 
sharing of data between the different EU institutions involved. 

7.2 Knowledge on mode of action, grouping, interactions and drivers 

of mixture toxicity  

The areas mentioned in this sub-section relate to some of the knowledge gaps highlighted in 
the 2012 Communication (see above) and progress related to these. Improved knowledge in 
these  areas  is  important  to  understand  and  assess  the  risks  related  to  mixture  toxicity, 
including  what  methodologies  to  apply.  It  is  also  essential  to  manage  data  gaps  and  to 
prioritise which chemicals to consider in mixtures assessments.  

Information on the mode of action (MOA) of chemicals is used to predict possible adverse 
outcomes, to group chemicals based on their properties, or to close toxicological knowledge 
gaps via read-across approaches. Some improvements for an easier identification of the mode 
of action of chemicals have been made by using computer-based methods (sometimes called 
in  silico  methods,  e.g.  QSAR),  as  well  as  in  vitro  approaches  and  the  Adverse  Outcome 
Pathway concept128.  

Grouping of chemicals into categories is important to decide which components to consider 
in a mixture assessment. The grouping may be based on (eco)toxicological properties, mode 
of actions, chemical  structure or physicochemical  properties, as well as the type of product, 
use or exposure scenarios,e.g. joint exposures129 (see also section 3.3).  
In  2018,  the  Commission  (JRC)  published  a  dedicated  report130  on  the  MOA  of  existing 
priority substances under the Water Framework Directive and the possible use of effect-based 
methods in assessing chemical status. The report discusses how such methods could cover a 
wider  range  of  chemical  substances  than  currently  included  in  the  list  by  focusing  more  on 
their  effects  than  on  individual  concentrations.  The  methods  might  be  used  in  future  for 
exploratory monitoring (e.g. for watch-list substances) or to capture better the true chemical 
status  of  surface  waters  based  on  appropriate  trigger  values  for  an  adequate  range  of 
representative chemical-effect types or MOAs. Knowledge of MOA is important for linking 
exposure and eco-toxicological effects in the aquatic environment.   

127 Silvia Dalla Costa, Stylianos Kephalopoulos, Stephanie Bopp, Aude Kienzler, Andrea Richarz, Sander Van der Linden, 
Peter Korytar, Thomas Backhaus, Erik Lebret, Jacob Van Klaveren, Hilko Van der Voet (2018), ‘JRC Workshop on 
IPCHEM supporting the assessment of Chemical Mixtures - Final report’, European Commission, Joint Research Centre, 
Ispra, PUBSY No.112434.  
https://ipchem.jrc.ec.europa.eu/RDSIdiscovery/ipchem/documents/JRC112434_ipchem_mixtures_workshop_final_report_v1
2_final.pdf  
128 Adverse Outcome Pathway Knowledge Base (AOP-KB). https://aopkb.oecd.org/index.html 
129 Stephanie K. Bopp, Aude Kienzler, Andrea-Nicole Richarz, Sander C. van der Linden, Alicia Paini, Nikolaos Parissis & 
Andrew P. Worth (2019) ‘Regulatory assessment and risk management of chemical mixtures: challenges and ways forward, 
Critical Reviews in Toxicology’, 49:2, 174-189, DOI: 10.1080/10408444.2019.1579169. 
https://doi.org/10.1080/10408444.2019.1579169  
130  Dorota  Napierska,  Isabella  Sanseverino,  Robert  Loos,  Livia  Gómez  Cortés,  Magdalena  Niegowska  and  Teresa  Lettieri, 
(2018) ‘Modes of action of the current Priority Substances list under the Water Framework Directive and other substances of 
interest, Review of the Relevant Modes of Action’, JRC Technical Report. EUR 29008 EN  
https://publications.jrc.ec.europa.eu/repository/bitstream/JRC110117/jrc_tech_report_moa_final__31may2018(8).pdf  

29 

 
 
 
 
                                                           
Recent  research in  the area of pesticide residues has advanced the  Cumulative Assessment 
Groups method, which is based on the chemicals involved having common target organs and 
effects (see also section 4). Developing such approaches can also help to assess and manage 
combined  exposure,  for  instance  to  a  group  of  structurally  similar  substances  that  are 
considered  to  have  similar  toxicological  properties.  This  kind  of  approach  can  often  be 
applied  without  performing  an  actual  mixture  assessment  which  involves  the  calculation  of 
mixture toxicity (e.g. some REACH restrictions take this approach, see section 5). In addition 
to the specific usefulness of grouping approaches in connection with mixture assessment, they 
also  contribute  to  the  filling  of  data  gaps  (i.e.  through  the  use  of  read-across  and  QSAR 
methods), to avoid regrettable substitution and to limit the need for animal testing131. Several 
studies  on  interactions  have  been  performed  during  the  last  decade.  Higher  or  lower 
mixture toxicities than predicted by the usual additivity approach may occasionally occur due 
to  interactions  between  the  individual  chemicals,  for  example  if  chemicals  influence  each 
other’s metabolism and thus (de)toxification processes in an organism. These phenomena are 
commonly  referred  to  as  synergisms  or  antagonisms.  Several  authors  have  reviewed  the 
evidence of such interactions in real life mixtures. They concluded that interactions are rare at 
lower  concentrations  such  as  exposure  via  the  environment.  In  observed  cases,  the 
interactions  have  also  led  to  relatively  small  deviations,  usually  over  or  underestimations 
within a factor of four132,133 compared to additivity-based predictions.  

A systematic literature review on the topic of prediction of interactions was finalised in 2019, 
through a contract study for the Commission134. The review analysed 1220 eco-toxicological 
as well as  mammalian/human health studies related to  mixtures which were published since 
2007. For a subset of 388 studies involving claims of interaction or providing indications of 
this, a quantitative reappraisal of the authors’ evaluation was conducted. The results indicate 
that relatively few of the studies claiming synergistic or antagonistic effects show a deviation 
of  observed  mixture  effects  of  more  than  two-fold  from  concentration  addition  based 
predictions  if  re-evaluated.  However,  a  small  proportion  of  the  reviewed  experiments  that 
indicated synergism was considered significant and of regulatory relevance. No clear trend in 
factors, including chemical composition, that tend to be involved in cases of synergism was 
detected.  However,  the  review  confirmed  earlier  indications  that  synergism  is  particularly 
frequent  among  pesticide  combinations.  A  conclusion  of  the  study  is  that  the  concentration 
addition  concept  can  be  applied  as  default  for  predictive  assessment  of  chemical  mixtures. 
This  can  be  complemented  on  a  case-by-case  basis  by  specific  considerations  for  mixtures 
where interactions are anticipated based on the components.  

The  above  finding  confirms  the  recommendation  by  EFSA’s  Scientific  Committee  in  its 
guidance for risk assessment of mixtures, to use Concentration Addition for the assessment of 
chemicals  with  similar  as  well  as  dissimilar  modes  of  action  in  the  context  of  both  human 
health and environmental risk assessment135. 

131  Swedish  Government  Inquiries  (2019)  ‘Future  chemical  risk  management  Accounting  for  combination  effects  and 
assessing  chemicals  in  groups’,  Swedish  Government  Official  Reports,  SOU  2019:45  https://www.government.se/legal-
documents/2019/11/sou-201945/  
132  Boobis  A,  Budinsky  R,  Collie  S,  Crofton  K,  Embry  M,  Felter  S,  Hertzberg  R,  Kopp  D,  Mihlan  G,  Mumtaz  M,  et  al. 
(2011) ‘Critical analysis of literature on low-dose synergy for use in screening chemical mixtures for risk assessment’. Crit 
Rev. Toxicol. 41(5):369–383. https://pubmed.ncbi.nlm.nih.gov/21309635/  
133 Cedergreen N. (2014), ‘Quantifying synergy: a systematic review of mixture toxicity studies within environmental 
toxicology’, PLoS ONE. 9(5): e96580. doi:10.1371/journal.pone.0096580. 
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0096580  
134  European  Commission  2019,  ‘Systematic  Review  of  Ten  Years  of  Research  on  Interactions  in  Chemical  Mixtures  of 
Environmental  Pollutants  -  Final  Report  Service  Contract  CCR.F.933992.X0’.  Olwenn  Martin,  Martin  Scholze,  Sibylle 
Ermler, Joanne McPhie, Andreas Kortenkamp  
135 EFSA Scientiﬁc Committee (2019): More SJ, Bampidis V, Benford D, Bennekou SH, Bragard C, Halldorsson TI, Hernandez-
Jerez AF, Koutsoumanis K, Naegeli H, Schlatter JR, Silano V, Nielsen SS, Schrenk D, Turck D, Younes M, Benfenati E, Castle L, 

30 

 
 
                                                           
Tools  and  criteria  for  prioritising  chemicals  and  identifying  the  main  drivers  of  mixture 
toxicity  are  also  available.  In  recent  EU-funded  research  projects,  a  selection  of  prioritising 
approaches  were  applied136.  The  ‘Maximum  Cumulative  Ratio’  (MCR)137,138,139  approach  is 
often used during regulatory and scientific assessments of intentional, as well as unintentional 
mixtures.  In  the  context  of  human  health  assessment,  information  on  Adverse  Outcome 
Pathways  and  statistical  and  pharmacokinetic  modelling  is  used.  In  the  context  of 
environmental assessment, the SOLUTIONS140 project has proposed the use of different lines 
of  evidence  based  on  ecological,  effect-based  and  chemical  monitoring  to  identify  priority 
pollutants in surface waters141. 

To  reduce  costs,  improve  efficiency  and  replace  animal  testing,  alternative  experimental 
and  computational  approaches  have  increasingly  been  introduced  into  (eco)toxicological 
assessments.  In  a  2014  Commission  (JRC)  survey  on  scientific  methodologies  for  the 
combined effect of chemicals142, experts confirmed that there is a high potential in further use 
of available novel tools and scientific methodologies for the assessment of chemical mixtures. 
Such  methods  include  methods  using  e.g.  cell  cultures  and  biological  molecules  (in  vitro), 
computer-based simulation methods (i.e. in silico) and modelling approaches143, which can be 
used  in  integrated  approaches.  They  allow  meaningful  information  on  individual  mixture 
components  or  whole  mixtures  to  be  derived,  enabling  a  better  understanding  of  the 
underlying mechanisms  of mixture effects  and prediction  of combined effects  and risks. On 
the same theme, the EU-funded project EuroMix144 has proposed a tiered framework for the 
assessment of mixtures with a combination of in silico and in vitro tools.  

In conclusion, there has been considerable progress in the development of the calculation and 
monitoring methods for mixture assessment, as well as approaches to manage data gaps and 
methods for prioritising substances for assessment. These methodologies so far mainly appear 
to  be  used  in  the  research  context,  less  for  regulatory  purposes.    This  situation  is  a 

to 

from 

multiple 

exposures 

Cedergreen N, Hardy A, Laskowski R, Leblanc JC, Kortenkamp A, Ragas A, Posthuma L, Svendsen C, Solecki R, Testai E, 
Dujardin B, Kass GEN, Manini P, Jeddi MZ , Dorne J-LCM and Hogstrand C, ‘Guidance on harmonised methodologies for 
human health, animal health and ecological risk assessment of combined exposure to multiple chemicals’, EFSA Journal 
2019;17(3):5634,77 pp. https://www.efsa.europa.eu/en/efsajournal/pub/5634 
136 Bopp, S.K., R. Barouki, W. Brack, S. Dalla Costa, J.-L.C.M. Dorne, P. E. Drakvik, M. Faust, T.K. Karjalainen, S. 
Kephalopoulos, J. van Klaveren, M. Kolossa-Gehring, A. Kortenkamp, E. Lebret, T. Lettieri, S. Nørager, J. Rüegg, J.V. 
Tarazona, X. Trier, B. van de Water, J. van Gils, Å. Bergman, ‘Current EU research activities on combined exposure to 
multiple chemicals’; Environment International 120 (2018) 544–562.  
https://www.sciencedirect.com/science/article/pii/S0160412018308420  
137 Price, P., Han, X., 2011, ‘Maximum cumulative ratio (MCR) as a tool for assessing the value of performing a cumulative 
risk assessment’, Int. J. Environ. Res. Public Health 2011 (8), 2212–2225. https://doi.org/10.3390/ijerph8062212 
138 Price, P., Dhein, E., Hamer, M., Han, X., Heneweer, M., Junghans, M., Rodriguez, C., 2012, ‘A decision tree for assessing 
2012. 
substances’, 
eﬀ ects 
https://enveurope.springeropen.com/articles/10.1186/2190-4715-24-26  
139 MCR is the ratio of the cumulative toxicity received by an individual from exposure to multiple chemical stressors to the 
largest  toxicity  from  a  single  chemical  stressor.  The  MCR  is  a  quantitative  measure  of  the  difference  in  an  individual’s 
toxicity estimated using a chemical-by-chemical approach and using an additive model of toxicity. 
140 https://www.solutions-project.eu/  
141 Brack et al. (2015), ‘The SOLUTIONS project: challenges and responses for present and future emerging pollutants in 
land and water resources management’, Sci Total Environ. 2015 Jan 15;503-504:22-31. doi: 10.1016/j.scitotenv.2014.05.143. 
https://pubmed.ncbi.nlm.nih.gov/24951181/  
142 Bopp S, Berggren E, Kienzler A, van der Linden S, Worth A (2015), ‘Scientific methodologies for the combined effects 
of chemicals – a survey and literature review’, JRC technical report EUR 27471 EN; doi:10.2788/093511.  
https://publications.jrc.ec.europa.eu/repository/bitstream/JRC97522/jrc_tech_rep_sci%20meth%20for%20mix_final.pdf  
143  The  JRC  report  mentions  the  adverse  outcome  pathway  (AOP)  concept,  in  vitro  methods,  omics  techniques,  in  silico 
approaches such as quantitative structure activity relationships (QSARs) and read-across, toxicokinetic and dynamic energy 
budget (DEB) modelling, and integrated approaches to testing and assessment (IATA). 
144 S. Rotter, A. Beronius, A. R. Boobis, A. Hanberg, J. van Klaveren, M. Luijten, K. Machera, D. Nikolopoulou, H. van der 
Voet, J. Zilliacus & R. Solecki (2019), ‘Overview on legislation and scientific approaches for risk assessment of combined 
exposure 
in  Toxicology,  DOI: 
10.1080/10408444.2018.1541964. https://www.tandfonline.com/doi/pdf/10.1080/10408444.2018.1541964?needAccess=true  

the  potential  EuroMix  contribution’,  Critical  Reviews 

to  multiple  chemicals: 

Environ. 

Eur. 

Sci. 

24, 

26 

31 

 
 
                                                                                                                                                                                     
consequence of a limitation of the methodologies, which require detailed, sensitive and high 
quality  data  on  both  toxicity  and  exposure,  which  is  rarely  available.  This  will  continue  to 
hamper the certainty of mixture assessment (see 7.3 Remaining knowledge gaps), as detailed 
data needed will be lacking also in foreseebale future.  

One  of  the  most  significant  scientific  advancement  in  recent  years,  with  direct  regulatory 
implications,  is  that  Concentration  Addition  can  be  used  as  the  default  method  for  the 
assessment of chemical mixtures with similar as well as dissimilar modes of action, in relation 
to risks to both human health and environment.  

7.3 Remaining knowledge gaps 

Progress has been made on the development of assessment methodologies, test methods and 
modelling  approaches,  as  well  as  on  improving  the  quality  of  and  access  to  knowledge  on 
toxicity  and  exposure  to  chemicals,  as  described  above.  Despite  this  progress,  significant 
knowledge  and  data  gaps  still  remain  in  a  number  of  areas,  which  will  continue  to 
hamper  the  assessment  and  risk  management  of  mixtures.  These  knowledge  and  data 
gaps,  and  the  challenges  in  closing  them,  are  linked  to  the  wide  variety  of  chemicals  from 
different sources occurring in mixtures to which humans and the environment are exposed.  

An important finding is that normally, a limited number of chemicals are responsible for the 
majority of the toxicity of a mixture. These chemicals are referred to as ‘drivers of toxicity’. 
However,  the  identities  of  these  chemicals  and  how  much  they  contribute  to  the  overall 
toxicity  (their  potencies)  vary  greatly  between  various  mixtures  and  exposure  situations. 
Hence,  it  is  not  sufficient  to  gather  data  only  on  high  volume  or  ‘priority  chemicals’. 
Additional toxicity data will still be needed for a large number of substances to successfully 
assess mixtures, e.g. through calculation methods and in-silico modelling.145 
The  Communication  of  2012146,  drawing  upon  the  joint  opinion  of  three  EU  Scientific 
Committees147  and  the  State  of  the  Art  Report  on  Mixture  Toxicity148,  highlighted  that 
extensive  knowledge  gaps  on  toxicities  and  exposures  to  chemicals  were  limiting  how 
accurately  chemical  mixtures  could  be  risk  assessed.  The  Communication  mentioned  that 
information  to  be  collected  in  the  context  of  EU  legislation,  in  particular  REACH,  would 
contribute to reducing these uncertainties. 

Indeed, the overall quality of and access to toxicity data has improved considerably during the 
last decade. The registration under REACH of chemicals present on the market (i.e. phase-in 
chemicals),  was  finalised  with  the  registration  deadline  in  May  2018149.  Hence,  a  total  of 
23,023  unique  chemicals,  placed  on  the  EU  market  in  quantities  over  1  tonne  per 
producer/importer and year, had been registered by June 2020. This number will continue to 
grow  as  new  chemicals  produced  or  imported  to  the  EU  are  continuously  registered.  The 
REACH database is the most comprehensive available worldwide.  

145 Van Broekhuizen FA., Posthuma L., Traas TP. (2016). Addressing combined effects of chemicals in environmental safety 
assessment  under  REACH  –  A  thought  starter.  National  Institute  for  Public  Health  and  the  Environment,  Bilthoven,  The 
Netherlands, RIVM Report 2016-0162. www.rivm.nl/bibliotheek/rapporten/2016-0162.pdf 
146 Communication from the Commission to the Council, ‘The combination effects of chemicals, Chemical mixtures’ 
COM(2012) 252 final  https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52012DC0252&from=EN  
147  Scientific  Committee  on  Health  and  Environmental  Risks  (SCHER),  Scientific  Committee  on  Emerging  and  Newly 
Identified Health Risks (SCENHIR) and Scientific Committee on Consumer Safety (SCCS). ‘Joint Opinion on the Toxicity 
and Assessment of Chemical Mixtures adopted on 14th December 2011’ https://doi.org/10.2772/21444  
148 Kortenkamp, A., Backhaus, T., Faust, M ‘State of the Art Report on Mixture Toxicity’, Final Report, Executive Summary, 
22 December 2009  http://ec.europa.eu/environment/chemicals/effects/pdf/report_mixture_toxicity.pdf  
149 https://echa.europa.eu/-/21-551-chemicals-on-eu-market-now-registered 

32 

 
 
                                                           
Despite this progress, hazardous properties and occurrence is sufficiently well characterised to 
allow appropriate mixture risk assessment only for a fraction of all chemicals produced and 
used. A general challenge is that chemicals are often transformed to other forms along their 
life-cycles (e.g. during use, through degradation in the environment and upon uptake in living 
organisms).  Further,  in  addition  to  the  exposure  to  chemicals  in  current  use,  there  is  also 
exposure  to  legacy  chemicals,  still  occurring  in  and  released  from  products  and  waste,  and 
accumulating in humans and the environment.  

It is not known exactly how many chemicals are produced and used worldwide, but estimates 
span from between 85,000 to over 140,000150, 151, 152. These chemicals can in principle occur 
in  the  human  and  natural  environment.  Another  recent  study  shows  that  a  total  of 
approximately  350,000  individual  chemicals  and  commercial/intentional  mixtures  are 
registered  under  different  jurisdictions  and  traded  globally.153  It  should  be  noted  that 
chemicals of relevance for assessment of unintentional mixtures and combination effects are 
not only the ones subject to e.g. registration under REACH, but all kinds of chemicals that can 
occur in the environment, including pesticides, biocides, pharmaceuticals and chemicals used 
and imported in different kinds of products.  

In line with the above findings, several authors conclude that risk assessment of unintentional 
mixtures continue to be hampered by gaps in, or lack of access to, hazard and exposure data 
on  the  individual  chemicals  that  are  the  components  of  mixtures154,155,156,157.  For  many 
chemicals  known  or  suspected  to  appear  in  environmental  media,  information  on  uses, 
releases and toxicity is either absent, unavailable or of poor quality. This problem relates to 
chemicals  across  uses  and  regulatory  areas.  In  particular  hazard  characterizations  are 
frequently incomplete, especially for specific endpoints. This problem is associated with the 
type and level of information required under different pieces of legislation as well as the lack 
of alignment of such requirements across legislation158, 159.  

from: 

(ECHA), 

and  Labelling 

Inventory’.  Available 

150 UNEP (United Nations Environment Programme) (2019b) ‘Global chemicals outlook II – from legacies to innovative 
solutions: Implementing the 2030 agenda for sustainable development’. 
https://www.unenvironment.org/resources/report/global-chemicals-outlook-ii-legacies-innovative-solutions  
151 The European Environment Agency’s (EEA) (2019). The European environment – state and outlook 2020. Knowledge for 
transition 
to  a  sustainable  Europe  https://www.eea.europa.eu/publications/soer-2020/chapter-10_soer2020-chemical-
pollution/view  
152  European  Chemicals  Agency 
‘Classification 
https://echa.europa.eu/information-on-chemicals/cl-inventory-database 
153  Zhang,  X.,  Sun,  X.,  Jiang,  R.,  Zeng,  E.Y.,  Sunderland,  E.M.,  and  Muir,  D.,  Screening  New  Persistent  and 
Bioaccumulative Organics in China’s Inventory of Industrial Chemicals. Environmental Science & Technology 2020 54 (12), 
7398-7408 DOI: 10.1021/acs.est.0c01898 https://pubs.acs.org/doi/10.1021/acs.est.0c01898?ref=pdf 
154 Bopp, S.K., R. Barouki, W. Brack, S. Dalla Costa, J.-L.C.M. Dorne, P. E. Drakvik, M. Faust, T.K. Karjalainen, S. 
Kephalopoulos, J. van Klaveren, M. Kolossa-Gehring, A. Kortenkamp, E. Lebret, T. Lettieri, S. Nørager, J. Rüegg, J.V. 
Tarazona, X. Trier, B. van de Water, J. van Gils, Å. Bergman (2018): Current EU research activities on combined exposure 
to multiple chemicals; Environment International 120 (2018) 544–562 
https://www.sciencedirect.com/science/article/pii/S0160412018308420  
155 Bopp, S. K. , A. Kienzler, S. van der Linden, L. Lamon, A. Paini, N. Parissis, A.-N. Richarz, J. Triebe, A. Worth (2016); 
Review of case studies on the human and environmental risk assessment of chemical mixtures; EUR 27968 EN; JRC report; 
doi:10.2788/272583 http://publications.jrc.ec.europa.eu/repository/bitstream/JRC102111/jrc102111_jrc_tech-
rep_mix%20case%20studies_2016_vf.pdf  
156 Kortenkamp, A. and M. Faust (2018) ‘Regulate to reduce chemical mixture risk - regulatory systems must better provide 
for risks from exposure to multiple chemicals’, Science: 361 (6399):224-225; July 2018; DOI: 10.1126/science.aat9219, with 
supplemental material. https://science.sciencemag.org/content/361/6399/224.full 
157  Swedish  Government  Inquiries  (2019).  ‘Future  chemical  risk  management  Accounting  for  combination  effects  and 
assessing  chemicals  in  groups’,  Swedish  Government  Official  Reports,  SOU  2019:45.  https://www.government.se/legal-
documents/2019/11/sou-201945/  
158  European  Commission  (2019),  ‘Report  from  the  Commission  to  the  European  Parliament,  the  Council,  the  European 
Economic  and  Social  Committee  and  the  Committee  of  the  regions,  Findings  of  the  Fitness  Check  of  the  most  relevant 
chemicals  legislation  (excluding  REACH)  and  identified  challenges,  gaps  and  weaknesses’,  COM(2019)  264  final. 
https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52019DC0264&from=EN  

33 

 
 
                                                           
An  issue  related  to  the  REACH  registration  requirements  is  the  usually  low  level  of 
knowledge and/or availability of data on substances produced and used in smaller volumes (1-
10  tonnes  per  producer/importer  and  year)160.  Such  substances  can  represent  a  problem  for 
mixture  risk  assessment  as  they  despite  being  produced  and  used  in  low  volumes  can  still 
appear  as  components  of  a  mixture  and  thereby  contribute  to  its  toxicity.  Further,  some 
categories  of  chemicals  including  e.g.  polymers  and  pharmaceuticals  are  exempted  from 
registration under REACH. There are also issues related to a high degree of non-compliance 
and  the  low  quality  of  registration  dossiers  under  REACH161,162.  Further,  the  publically 
available knowledge on  occurrence and  concentration of chemicals  in  articles163 and related 
exposure  is  insufficient.    Overall,  there  is  a  lack  of  knowledge  of  the  actual  amounts  of 
individual  chemicals  produced,  how  much  is  used  for  different  purposes  and  how  much  is 
released into different environmental media.   
Case studies conducted as part of the SOLUTIONS research project164 illustrate the toxicity 
knowledge  gaps.  In  one  example,  a  total  of  227  chemicals  were  monitored  at  different 
locations  in  the  river  Danube.  For  27%  of  these  chemicals,  experimental  toxicity  data  for 
acute  toxicity  was  available,  assessed  through  the  most  common  bioassay  (Daphnia 
magna)165.  For  any  other  bioassay  or  test  species  and  for  chronic  effects,  data  was 
considerably scarcer. 

Regarding exposure data, knowledge of the composition of the mixtures to which humans 
and wildlife are exposed and their effects, is  often missing. Overall, the extent of human 
and environmental monitoring of chemicals is still insufficient to provide adequate knowledge 
on  exposure  and  occurrence  of  chemicals  in  humans,  biota  and  environmental  media. 
Chemical monitoring also has its limitations. For instance, generally only chemicals suspected 
to be present are detected by targeted or suspect screening analyses. Hence, the chemicals not 
analysed,  including  breakdown  products  or  metabolites,  which  can  contribute  to  a  mixture 
effects  might  be  overlooked.  In  addition,  monitoring  data  allow  retrospective  assessments 
only, while detection of rising levels and effects will be delayed by years or decades after the 
emissions took place. In order to prospectively model co-exposure to unintentional mixtures, 
more information on the types and quantities of chemical uses is needed.  

Examples  of  ongoing  initiatives  at  the  EU  level  that  will  contribute  to  improved  chemicals 
exposure  knowledge  and  data  access  includes  HBM4EU  and  IPCHEM  (see  Section  7.1). 
Approaches  that  can contribute to  filling toxicity data  gaps include  grouping  and modelling 
methodologies. 

159 European Commission (2019), Fitness Check of the most relevant chemicals legislation (excluding REACH), as well as 
related  aspects  of  legislation  applied  to  downstream  industries.  SWD(2019)  199  final/2.  https://eur-lex.europa.eu/legal-
content/EN/TXT/PDF/?uri=CELEX:52019SC0199R(01)&from=EN  
160   European Commission (2018) ‘Commission General Report on the operation of REACH and review of certain elements, 
Comprehensive Evaluation Report, Conclusions and Actions’, SWD(2018) 58 final, 1-7. 
https://ec.europa.eu/growth/sectors/chemicals/reach/review_en  
161 European Commission (2018) ‘Commission General Report on the operation of REACH and review of certain elements. 
Conclusions and Actions’, COM(2018) 116 final. https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=COM:2018:0116:FIN   
162 European Chemicals Agency (ECHA), ‘Evaluation under REACH: Progress Report 2017 10 years of experience’, 
Reference: ECHA-18-R-05-EN 
https://echa.europa.eu/documents/10162/13628/evaluation_under_reach_progress_en.pdf/24c24728-2543-640c-204e-
c61c36401048  
163 An ‘article’ is an object which during production is given a special shape, surface or design which determines its function 
to a greater degree than does its chemical composition’ (REACH, Article 3(3). Examples of articles are electronics, vehicles 
and pieces of clothing.  
164 https://www.solutions-project.eu/  
165 Rico, A., Van den Brink, P.J., Leitner, P., Graf, W. and Focks, A., 2016, ‘Relative influence of chemical and non-
chemical stressors on invertebrate communities: a case study in the Danube River’, Science of the Total Environment, 571, 
pp.1370-1382. file:///C:/Users/Boijeur/AppData/Local/Microsoft/Windows/INetCache/Content.Outlook/KOMTM6MB/1-
s2.0-S0048969716315339-main.pdf  

34 

 
 
                                                                                                                                                                                     
The  2018  EEA  report  ‘Chemicals  in  European  Waters  –  Knowledge  developments’166 
provides an overview of recent findings, challenges and remaining knowledge gaps related to 
the assessment of chemicals mixtures in the aquatic environment. These include knowledge of 
the  biological  actions  of  pollutants  and,  information  needed  to  establish  the  use  of  effect-
based monitoring methods under e.g. the Water Framework Directive.   

Activities  to  investigate  the  feasibility  and  potential  implementations  of  effect-based 
monitoring  method  and  tools  under  the  Common  Implementation  Strategy  for  the  Water 
Framework  Directive  started  in  2012.  The  work  to  provide  robust  methodologies  and  to 
identify  threshold  values  (trigger  values)  for  methods  developed  is  still  ongoing,  and  has 
resulted  in  one  scientific  paper167  and  one  report168,  while  another  report  will  soon  be 
published.  

7.4 Future research and development priorities 

Several  authors  and  projects  have  presented  priorities  and  recommendations  on  future 
research and development needs. The project coordinators of the recent EU research projects 
(SOLUTIONS, HBM4EU, EDC-MixRisk,  EuroMix) highlighted mixtures as a high priority 
for further research in a position paper in 2018169. The paper pointed out 12 key issues to be 
urgently tackled by scientists, regulators and industry. Their conclusions confirm the lack of 
data and difficulty to access available mixture exposure and hazard data for the components in 
a  mixture  (see  Section  7.3),  while  also  highlighting  the  need  for  validated  and  standardised 
test methods, for knowledge on the effects on vulnerable populations and on combined effects 
with other stressors as key knowledge gaps.  

The EFSA Scientific Committee in 2019, in its general guidance on assessment of combined 
exposure,  included  a  comprehensive  set  of  recommendations  on  future  research  and 
development  activities  regarding  mixture  assessment170.  These  range  from  the  development 
and validation of methods and tools for assessment to the improved access to and sharing of 
data and cooperation between scientists, EU agencies, member states and international bodies.    

Box 6 compiles priorities and recommendations on research and development activities from 
a number of publications, including the ones mentioned above.  

Box 6. Priorities and recommendations on research and development 

166 European Environment Agency (2018): Chemicals in European Waters – Knowledge developments; EEA report 18/2018; 
doi: 10.2800/265080 https://www.eea.europa.eu/publications/chemicals-in-european-waters  
167 Wernersson, A., Carere, M., Maggi, C. et al., ‘The European technical report on aquatic effect-based monitoring tools 
under the water framework directive’, Environ Sci Eur 27, 7 (2015). https://doi.org/10.1186/s12302-015-0039-4  
168 European Commission (2014), ‘Technical report on aquatic effect-based monitoring tools’, Technical Report - 2014 – 
077. https://circabc.europa.eu/sd/a/0d78bbf7-76f0-43c1-8af2-6230436d759d/Effect-
based%20tools%20CMEP%20report%20main%2028%20April%202014.pdf  
169  Altenburger,  R.,  R.  Barouki,  Å.  Bergman,  W.  Brack,  E.  Dravik,  J.  van  Klaveren,  M.  Kolossa-Gehring,  E.  Lebret,  J. 
Rűegg,  B.  van  de  Water  (2018),  ‘Position  Paper:  Preventing  risks  for  people  and  environment  from  hazardous  mixtures’.  
https://edcmixrisk.ki.se/wp-content/uploads/sites/34/2018/05/Position-paper-180417-for-the-EC.pdf 
170  EFSA  Scientiﬁc  Committee  (2019):  More  SJ,  Bampidis  V,  Benford  D,  Bennekou  SH,  Bragard  C,  Halldorsson  TI, 
Hernandez-Jerez  AF,  Koutsoumanis  K,  Naegeli  H,  Schlatter  JR,  Silano  V,  Nielsen  SS,  Schrenk  D,  Turck  D,  Younes  M, 
Benfenati E, Castle L, Cedergreen N, Hardy A, Laskowski R, Leblanc JC, Kortenkamp A, Ragas A, Posthuma L, Svendsen 
C,  Solecki  R,  Testai  E,  Dujardin  B,  Kass  GEN,  Manini  P,  Jeddi  MZ  ,  Dorne  J-LCM  and  Hogstrand  C,  ‘Guidance  on 
harmonised methodologies for human health, animal health and ecological risk assessment of combined exposure to multiple 
chemicals’, EFSA Journal 2019;17(3):5634,77 pp. https://www.efsa.europa.eu/en/efsajournal/pub/5634  

35 

 
 
 
 
                                                           
A  number  of  scientific  papers,  reports  and  position  papers171,172,173,174,175,176,177  discuss 
priorities for future research and development to support and facilitate the assessment and 
management of chemical mixtures. Some priorities and recommendations put forward in 
these include:  

  Common  efforts  to  generate  and  make  toxicity,  exposure  and  chemicals-monitoring 
data accessible. This includes data on the overall exposure of the European population.  
  Structured approaches for collecting data on simultaneous and sequential exposure to 

mixtures. 

  Research  and  development  regarding  modelling  approaches  to  support  mixture 

 

assessment.  
Increasing  the  availability  of  validated  and  standardised  test  methods  and  guidance, 
including such on how to apply new and innovative methodologies (e.g.  in vitro and 
computer based methods) for mixture assessment.  

  Develop methodologies and harmonised guidance on the grouping of chemicals.  
  Guidance  for  analysing  uncertainties  in  risk  assessment  of  combined  exposure  to 
multiple  chemicals,  e.g.  associated  with  the  grouping  into  assessment  groups  and 
assumptions concerning similar MoAs/AOPs and application of dose addition 

  Knowledge  and  methods  on  how  to  anticipate  synergisms  and  antagonisms  between 
chemicals,  predict  when  such  arise  and  need  to  be  taken  into  account,  and  the 
development of criteria/guidance on this.  

  Methodologies to integrate multiple lines of evidence, such as mixture toxicology and 

 

epidemiology, into risk assessment.  
Improve the knowledge about effects of mixture exposure on the heath and resilience 
of ecosystems, vulnerable populations and the importance of sensitive time-windows 
of exposure.  

  Knowledge  building  about  the  combination  of  chemical  stressors  with  other 

environmental and social stressors.  

171  Altenburger,  R.,  R.  Barouki,  Å.  Bergman,  W.  Brack,  E.  Dravik,  J.  van  Klaveren,  M.  Kolossa-Gehring,  E.  Lebret,  J. 
Rűegg,  B.  van  de  Water  (2018),  ‘Position  Paper:  Preventing  risks  for  people  and  environment  from  hazardous  mixtures’.  
https://edcmixrisk.ki.se/wp-content/uploads/sites/34/2018/05/Position-paper-180417-for-the-EC.pdf  
172 Bopp, S.K., R. Barouki, W. Brack, S. Dalla Costa, J.-L.C.M. Dorne, P. E. Drakvik, M. Faust, T.K. Karjalainen, S. 
Kephalopoulos, J. van Klaveren, M. Kolossa-Gehring, A. Kortenkamp, E. Lebret, T. Lettieri, S. Nørager, J. Rüegg, J.V. 
Tarazona, X. Trier, B. van de Water, J. van Gils, Å. Bergman (2018): Current EU research activities on combined exposure 
to multiple chemicals; Environment International 120 (2018) 544–562 
https://www.sciencedirect.com/science/article/pii/S0160412018308420  
173  EFSA  Scientiﬁc  Committee  (2019):  More  SJ,  Bampidis  V,  Benford  D,  Bennekou  SH,  Bragard  C,  Halldorsson  TI, 
Hernandez-Jerez  AF,  Koutsoumanis  K,  Naegeli  H,  Schlatter  JR,  Silano  V,  Nielsen  SS,  Schrenk  D,  Turck  D,  Younes  M, 
Benfenati E, Castle L, Cedergreen N, Hardy A, Laskowski R, Leblanc JC, Kortenkamp A, Ragas A, Posthuma L, Svendsen 
C,  Solecki  R,  Testai  E,  Dujardin  B,  Kass  GEN,  Manini  P,  Jeddi  MZ  ,  Dorne  J-LCM  and  Hogstrand  C,  ‘Guidance  on 
harmonised methodologies for human health, animal health and ecological risk assessment of combined exposure to multiple 
chemicals’, EFSA Journal 2019;17(3):5634,77 pp. https://www.efsa.europa.eu/en/efsajournal/pub/5634  
174 Kortenkamp, A. and M. Faust (2018) ‘Regulate to reduce chemical mixture risk - regulatory systems must better provide 
for risks from exposure to multiple chemicals’, Science: 361 (6399):224-225; July 2018; DOI: 10.1126/science.aat9219, with 
supplemental material. https://science.sciencemag.org/content/361/6399/224.full 
175  UNEP  (United  Nations  Environment  Programme)  (2019b)  ‘Global  chemicals  outlook  II  –  from  legacies  to  innovative 
solutions: Implementing the 2030 agenda for sustainable development’. 
176 S. Rotter, A. Beronius, A. R. Boobis, A. Hanberg, J. van Klaveren, M. Luijten, K. Machera, D. Nikolopoulou, H. van der 
Voet, J. Zilliacus & R. Solecki (2019), ‘Overview on legislation and scientific approaches for risk assessment of combined 
exposure to multiple chemicals: the potential EuroMix contribution’, Critical Reviews in Toxicology, DOI: 
10.1080/10408444.2018.1541964 https://www.tandfonline.com/doi/pdf/10.1080/10408444.2018.1541964?needAccess=true  
177  Swedish  Government  Inquiries  (2019).  ‘Future  chemical  risk  management  Accounting  for  combination  effects  and 
assessing  chemicals  in  groups’,  Swedish  Government  Official  Reports,  SOU  2019:45  https://www.government.se/legal-
documents/2019/11/sou-201945/  

36 

 
 
                                                           
 

Increased  collaboration  between  scientists  and  regulators  on  translating  science  into 
policy.   

  Establish long-term research programs on mixture toxicity on the EU level.  

8.  INTERNATIONAL ACTIVITIES  

An overview of international activities relating to mixture assessment, focusing on available 
guidance  documents  and  ongoing  processes  under  international  organisations,  as  well  as  on 
existing  regulation  and  guidance  in  some  countries  outside  the  EU  was  prepared  by  JRC  in 
2014178. The Commission and EU Agencies have participated in several relevant international 
activities  to  promote  consistent  and  science-based  approaches  to  the  risk  assessment  of 
mixtures. Besides the general benefit of the sharing of knowledge, experience and expertise, 
the  joint  international  activities  are  important  as  they  can  contribute  to  internationally 
harmonised approaches to mixtures assessment and management in the long perspective.  

The  Commission  contributed  to  the  2018  OECD  consideration  document  on  the  risk 
assessment of combined exposures to chemicals179, which describes the essential steps to be 
considered,  independent  of  legal  framework  and  kind  of  mixture,  scope  and  assessor  (see 
Section 4). Further, EFSA developed its 2019 guidance180 on mixture risk assessments based 
on  the  WHO/IPCS  framework181  for  the  assessment  of  combined  exposures  to  multiple 
chemicals from 2011, and organised an international consultation (see Section 4).  

The involvement of the Commission and EU Agencies in the international activities includes 
the  JRC’s  co-leading  of  a  working  group  on  Combined  Exposures  to  Multiple  Chemicals 
under  the  OECD  Working  Parties  on  Hazard  Assessment  and  on  Exposure  Assessment.  
Further,  the  JRC  together  with  several  EU  Agencies,  was  a  member  of  a  WHO  informal 
working group on combined exposure under the WHO Chemical Risk Assessment Network, 
which  was  active  on  the  mapping  activities,  facilitating  collaboration,  and  identifying 
remaining gaps. The JRC is also coordinating an informal international research group on the 
testing of mixtures.  

Further, the Commission and the EU agencies participate in international cooperation aimed 
at  improving  the  knowledge  base  on  chemical  mixtures,  toxicity  and  exposure  information. 
This includes the OECD-led projects on combining different chemicals-related databases (see 
Section  7),  e.g.  the  OECD  eChemPortal182  and  the  OECD  activities  towards  a  ‘Global 
Chemicals Knowledge Base’.  

and 

296, 

Environment,  Health 

178 Kienzler, A., Berggren, E., Bessems, J, Bopp, S., van der Linden, S., Worth, A.  (2014), ‘Assessment of Mixtures  - 
Review of regulatory Requirements and Guidance’, JRC Science and Policy Report, EUR 26675 EN. 
http://publications.jrc.ec.europa.eu/repository/bitstream/JRC90601/lb1a26675enn.pdf  
179 OECD (2018). ‘Considerations for Assessing the Risks of Combined Exposure to Multiple Chemicals’, Series on Testing 
and  Assessment  No. 
Environment  Directorate. 
http://www.oecd.org/chemicalsafety/risk-assessment/considerations-for-assessing-the-risks-of-combined-exposure-to-
multiple-chemicals.pdf  
180  EFSA  Scientiﬁc  Committee  (2019):  More  SJ,  Bampidis  V,  Benford  D,  Bennekou  SH,  Bragard  C,  Halldorsson  TI, 
Hernandez-Jerez  AF,  Koutsoumanis  K,  Naegeli  H,  Schlatter  JR,  Silano  V,  Nielsen  SS,  Schrenk  D,  Turck  D,  Younes  M, 
Benfenati E, Castle L, Cedergreen N, Hardy A, Laskowski R, Leblanc JC, Kortenkamp A, Ragas A, Posthuma L, Svendsen 
C,  Solecki  R,  Testai  E,  Dujardin  B,  Kass  GEN,  Manini  P,  Jeddi  MZ  ,  Dorne  J-LCM  and  Hogstrand  C,  ‘Guidance  on 
harmonised methodologies for human health, animal health and ecological risk assessment of combined exposure to multiple 
chemicals’, EFSA Journal 2019;17(3):5634,77 pp. https://doi.org/10.2903/j.efsa.2019.5634  
181  Meek,  M.E.  (Bette),  Boobis,  A.R.,  Crofton,  K.M.,  Heinemeyer,  G.,  van  Raaij,  M.,  Vickers,  C.  ‘Risk  assessment  of 
combined exposure to multiple chemicals: A WHO/IPCS framework’ Regulatory Toxicology and Pharmacology 60 (2011) 
S1–S14 https://pubmed.ncbi.nlm.nih.gov/21466831/ 
182 https://www.echemportal.org/echemportal/index.action 

Safety  Division, 

37 

 
 
 
                                                           
Box  6.  Legal  requirements,  guidance  and  regulatory  assessments  in  the  USA  and 
Canada  

Requirements and approaches for a risk assessment and regulation of chemical mixtures also 
exist outside the EU, including legal obligations and guidance documents183,  184. In the USA 
several  legal  acts  include  requirements  for  the  risk  assessment  of  mixtures  (e.g.  the 
Comprehensive Environmental Response Compensation and  Liability  Act,  the Food Quality 
Protection  Act,  and  the  Safe  Drinking  Water  Act),  and  several  guidance  documents  are 
available  (e.g.  health  risks  assessments  for  mixtures,  simultaneous  exposures  from  food, 
drinking water and non-occupational use of pesticides).  

In Canada, requirements to consider aggregated exposures to pesticides in human health risk 
assessments  (e.g.  Pest  Controls  Product  Act)  as  well  as  guidance  documents  (e.g.  for  the 
combined  exposures  of  contaminated  sites)  are  in  place  and  several  risk  assessments  for 
unintentional mixtures of certain groups have been performed.  

International experience of regulatory requirements and implementation of these can be useful 
in the EU context.  

9.  POSSIBLE WAYS FORWARD TO ADDRESS CHALLENGES IN 

THE REGULATORY CONTEXT     

Scientists, Member States and industry associations have repeatedly acknowledged the issue 
of mixtures and the need to address them. They have also provided several recommendations 
and proposals for approaches to address mixtures in the regulatory context.  

On the industrial side, in 2016, the European Chemical Industry Council (Cefic), published a 
guidance document on a ‘lead component identification methodology’ (LCID)185 to improve 
the  communication  of  classified  chemicals  and  mixtures  in  REACH  safety  data  sheets.  The 
methodology  is  also  intended  for  the  development  of  provisions  for  workers’  safety  and  to 
establish  which  quantities  are  environmentally  safe  to  use  during  production.  Further,  Cefic 
together with the German chemicals industry association (Verband der Chemichen Industrie, 
VCI) has published a practical  guidance and examples of how the results from applying the 
Lead  Component  Identification  (LCID)  methodology  can  be  incorporated  into  a  mixture 
Safety  Data  Sheet  (“SDS”)  under  REACH186.  Apart  from  this  ‘top-down’  LCID  method, 
another, ‘bottom-up’ approach has also been developed by industry, to identify information to 
communicate  along  the  supply  chain,  called  ‘safe  use  of  mixtures  information’  (SUMI). 
Sector  organisations  can  apply  this  to  identify  the  risk  management  measures  for  typical 
products  and  uses  within  the  sector187.  In  2018,  Cefic  also  published  a  position  paper188, 

183 Kienzler, A., Berggren, E., Bessems, J., Bopp, S., van der Linden, A., Worth, A.  (2014), ‘Assessment of Mixtures – 
Review of regulatory Requirements and Guidance’, JRC Science and Policy Report, EUR 26675 EN. 
http://publications.jrc.ec.europa.eu/repository/bitstream/JRC90601/lb1a26675enn.pdf  
184   Rotter, S., Beronius, A., Boobis, A. R., Hanberg, A., van Klaveren, J., Luijten, M., Machera, K., Nikolopoulou, D., van 
der Voet, H., Zilliacus, J.  & Solecki, R.  (2019), ‘Overview on legislation and scientific approaches for risk assessment of 
combined  exposure  to  multiple  chemicals:  the  potential  EuroMix  contribution’,  Critical  Reviews  in  Toxicology,  DOI: 
10.1080/10408444.2018.1541964. https://www.tandfonline.com/doi/pdf/10.1080/10408444.2018.1541964?needAccess=true  
185  CEFIC  (2016):  REACH  Practical  Guide  on  Safe  Use  Information  for  Mixtures  under  REACH  -  The  Lead  Component 
Identification  (LCID)  Methodology.  https://cefic.org/app/uploads/2016/03/Practical-Guide-Safe-Use-Information-
for-Mixtures-under-REACH_v6-1-1.pdf  
186 CEFIC and VCI, ‘Mixtures under REACH – exemplification of the LCID output in the Safety Data Sheet’, Final version 
1.0  –  30.  September  2019  (2016):  https://cefic.org/app/uploads/2019/11/Mixtures-under-REACH-–-Exemplification-of-the-
LCID-output-in-the-SDS-REPORT.pdf  
187 The Downstream Users of Chemicals Coordination Group (DUCC), ‘DUCC/CEFIC pilot project on Exposure 
Scenarios  and  communication  in  the  supply  chain,  Formulators  phase:  testing  the  SUMI  selection  approach 

38 

 
 
                                                           
recognizing the need to address combination effects and to engage in the use of available tools 
for identifying drivers of toxicity,  as well as prioritising and assessing mixtures via a tiered 
approach.  

Regarding  Member  State  initiatives,  the  German  Environment  Agency  in  2017  published  a 
report189  focused  on  the  risk  assessment  of  chemical  mixtures,  in  particular  in  the  aquatic 
environment,  in  the  context  of  REACH  and  its  interfaces  with  other  pieces  of  legislation. 
Different regulatory approaches for addressing mixtures are discussed in the report, including 
tiered approaches for intentional mixtures, the use of Mixture Assessment Factors (MAF) and 
the whole mixture testing approach.   

the  environment 

In 2017, the government of the Netherlands proposed a regulatory approach involving a MAF 
to account for combination effects in the environmental risk assessment of substances under 
REACH  regulation.  This  proposal  was  made  based  on  a  report  from  the  Dutch  institute  for 
(RIVM)190  providing  detailed  methodological 
public  health  and 
considerations for application of this approach.  
In 2019, the Swedish Government published a Special Inquiry Report191 on risk management 
approaches to account for combination effects and enable assessment of chemicals in groups. 
The  report  provides  11  recommendations,  including  the  introduction  of  specific  and 
crosscutting  legal  requirements  for  mixture  assessment,  the  application  of  a  MAF  in  risk 
assessment,  the  increased  use  of  grouping  approaches  in  chemicals  legislation  and  the 
improved sharing of data.  

In  2020,  a  number  of  leading  scientists  in  the  area  of  mixtures  toxicology  published  a 
statement  on  advancing  the  assessment  of  chemical  mixtures  and  their  risks.  The  statement 
highlights  the need to  strengthen the legal  basis for mixture risk management, to  strengthen 
coordination  across  regulatory  bodies  and  sectors,  to  integrate  component-based  and  whole 
mixture  testing  in  risk  assessment  frameworks  where  possible  and  to  apply  pragmatic 
approaches,  such  as  MAF,  where  conclusive  mixture  risk  assessments  cannot  be  routinely 
conducted due to significant knowledge and data gaps.192 The statement also formulates key 
enablers  for  mixture  risk  assessments,  such  as  availability  of  data  and  tools,  and  future 
research needs.  

In  2020,  the  Netherlands  together  with  the  Swedish  Chemicals  Agency  (KEMI)  hosted  a 
workshop with the aim of discussing possible pragmatic approaches to address the risks from 
combined  exposure  to  unintentional  mixtures  under  REACH.  The  participants  agreed  that  a 

of 

on 

Cefic 

Effects 

Position 

Chemicals, 

ENES  action  4.1.  –  Report’, DUCC,  13  December  2019.  https://cefic.org/app/uploads/2020/01/DUCC-CEFIC-
pilot-project-on-exposure-scenarios-and-communication-in-the-supply-chain-Pilot-Project-Report-on-
Formulators’-phase-testing-the-SUMI-selection-approach.pdf  
188 
Combination 
Paper 
https://cefic.org/app/uploads/2019/01/Combination-effects-of-chemicals-position-paper-POSITION-PAPER.pdf  
189  Bunke,  D.,  Groß,  R.,  Kalberlah,  F.,  Oltmanns,  J.,  Schwarz,  M.,  Reihlen,  A.,  Reineke,  N.,  2014.  4M,‘Mixtures  in  the 
Environment. Development of assessment strategies for the regulation of chemicals under REACH’, Environmental Research 
of  the  Federal  Ministry  for  the  Environment,  Nature  Conservation  and  Nuclear  Safety.  Project  No  (FKZ)  3711  63  429 
https://www.umweltbundesamt.de/sites/default/files/medien/378/publikationen/texte_65_2014_aust_hassold_mixtures_in_th
e_environment.pdf  
190  van  Broekhuizen,  F.A.,  L.  Posthuma,  T.P.  Traas  (2016):  Addressing  combined  effects  of  chemicals  in  environmental 
safety 
2016-0162 
thought 
under 
https://www.rivm.nl/bibliotheek/rapporten/2016-0162.pdf 
191  Swedish  Government  Inquiries  (2019)  Future  chemical  risk  management  Accounting  for  combination  effects  and 
assessing  chemicals  in  groups.  Swedish  Government  Official  Reports,  SOU  2019:45  https://www.government.se/legal-
documents/2019/11/sou-201945/  
192 Dravik et al. (2020) ’Statement on advancing the assessment of chemical mixtures and their risks for human health and the 
environment.’ Environment International, Volume 134, January 2020, 105267. 
https://www.sciencedirect.com/science/article/pii/S0160412019331538#!  

assessment 

September 

REACH 

starter; 

RIVM 

report 

Letter 

2018 

A 

- 

39 

 
 
                                                                                                                                                                                     
pragmatic approach is needed and there was a general support for the principle of applying a 
MAF. No other approaches to deal with unintentional mixtures were identified193. A follow up 
workshop is planned for the autumn 2020 to elaborate on practicalities of such approach.  

Recommendations  on  ways  forward  including  implementation,  development  of  policy  and 
methods as well as knowledge building activities, proposed by Member States, scientists and 
other stakeholders are summarised in Box 7. 

Box  7.  Compilation  of  recommendations  by  Member  States,  scientists  and  other 
stakeholders on way forward with risk management of chemical mixtures  194, 195,  196, 197, 
198, 199, 200, 201, 202, 203, 204, 205 

  Continue/step up the implementation of current regulatory schemes, e.g. the identification 
and  risk  management  of  substances  of  very  high  concern  under  REACH,  thereby 
controlling  individual  chemicals  and  hence  reducing  some  overall  risks  of  combined 
exposure.  

  Step up the use of currently existing regulatory options and methodologies for addressing 
(assessing and managing) groups of chemicals, and further develop such approaches in the 
context of relevant legislation. 
Introduce clear and explicit legal requirements for the risk assessment and management of 
mixtures in all relevant pieces of EU legislation.  

 

  Develop  a  legal  framework  and  a  mechanism  to  improve  the  co-ordination  across 
regulatory areas to address mixtures of chemicals subject to different pieces of legislation.  

2020. 

Commission 

CA/MS/34/2020, 

193 Competent authorities of the Netherlands and Sweden (2020), Discussion paper for CARACAL provided by KEMI and 
the Netherlands. Towards a pragmatic procedure to regulate the risks of exposure to unintended combinations of chemicals in 
the EU. 34th Meeting of Competent Authorities for REACH and CLP (CARACAL) Open session, 31 March - 1 April 2020. 
Doc. 
http://files.chemicalwatch.com/24%20-
25  Mars 
European 
%20CA_MS_34_2020_a.p.10.2_Combination%20of%20chemicals.pdf 
194  Bunke,  D.,  Groß,  R.,  Kalberlah,  F.,  Oltmanns,  J.,  Schwarz,  M.,  Reihlen,  A.,  Reineke,  N.,  2014.  4M.  Mixtures  in  the 
Environment. Development of assessment strategies for the regulation of chemicals under REACH. Environmental Research 
of  the  Federal  Ministry  for  the  Environment,  Nature  Conservation  and  Nuclear  Safety.  Project  No  (FKZ)  3711  63  429 
https://www.umweltbundesamt.de/sites/default/files/medien/378/publikationen/texte_65_2014_aust_hassold_mixtures_in_th
e_environment.pdf  
195 Drakvik et al. (2019): Statement on advancing the assessment of chemical mixtures and their risks for human health and 
the environment. Environment International 134 (2020) 105267 
https://www.sciencedirect.com/science/article/pii/S0160412019331538?via%3Dihub  
196  Altenburger,  R.,  R.  Barouki,  Å.  Bergman,  W.  Brack,  E.  Dravik,  J.  van  Klaveren,  M.  Kolossa-Gehring,  E.  Lebret,  J. 
Rűegg,  B.  van  de  Water  (2018):  Position  Paper  Preventing  risks  for  people  and  environment  from  hazardous  mixtures 
https://edcmixrisk.ki.se/wp-content/uploads/sites/34/2018/05/Position-paper-180417-for-the-EC.pdf 
197 Kortenkamp, A. and Faust, M. (2018): Regulate to reduce chemical mixture risk - regulatory systems must better provide 
for risks from exposure to multiple chemicals; Science: 361 (6399):224-225; July 2018; DOI: 10.1126/science.aat9219, with 
supplemental material https://science.sciencemag.org/content/361/6399/224.full 
198  Evans,  R.E.,  O.V.  Martin,  M.  Faust,  A.  Kortenkamp  (2016):  Should  the  scope  of  human  mixture  assessment  span 
legislative/regulatory 
757-764. 
https://www.sciencedirect.com/science/article/pii/S0048969715309785  
199  van  Broekhuizen,  F.A.,  L.  Posthuma,  T.P.  Traas  (2016):  Addressing  combined  effects  of  chemicals  in  environmental 
safety 
2016-0162 
thought 
https://www.rivm.nl/bibliotheek/rapporten/2016-0162.pdf ;  
200 Swedish Chemicals Agency KEMI (2015): An additional assessment factor (MAF)  – A suitable approach for improving 
the  regulatory  risk  assessment  of  chemical  mixtures;  Report  5/15  https://www.kemi.se/global/rapporter/2015/rapport-5-
15.pdf  
201 Coors, A. et al. (2018): Prospective environmental risk assessment of mixtures in wastewater treatment plant effluents  - 
Theoretical considerations and experimental verification; Water Research 140:56-66. doi: 10.1016/j.watres.2018.04.031 
202 Bopp et al. (2019): …challenges and ways forward; Crit. Rev. Toxicol.  
203 Kortenkamp, A. and Faust, M.  (2018): Science 361  
204 European Environment Agency (2018): EEA report 18/2018  
205Cefic 
https://cefic.org/app/uploads/2019/01/Combination-effects-of-chemicals-position-paper-POSITION-PAPER.pdf 

on  Combination  Effects 

the  Total  Environment 

chemicals?  Science 

of  Chemicals. 

(2018):  Cefic 

assessment 

September 

REACH 

Position 

(2016): 

starter; 

RIVM 

report 

Letter 

Paper 

under 

2018 

silos 

543 

for 

of 

A 

- 

40 

 
 
                                                           
  Continue the development of guidance on the assessment of intentional and unintentional 
mixtures for relevant pieces of legislation, with a focus on basic methodologies, including 
component based approaches, and the selection of an appropriate methodology.  

  Combine screening for identifying combined exposures of concern and application of the 
Maximum Cumulative Ratio (MCR) approach in a tiered approach for the refinement of 
hazard and exposure assessment of combined exposures, which can be applied where data 
is available.  

  Further  elaborate,  introduce  and  apply  a  MAF  in  human  health  and  environmental 
assessment, as a science based, generic mean to take into account combined exposure.  
  Perform monitoring of use, emissions and exposure (including co-exposure) to chemicals, 
through  e.g.  human,  environmental  and  effect-based  monitoring  as  well  as  modelling 
approaches,  while  improving  public  availability  of  the  data  collected  and  promoting  the 
use of monitoring data in regulatory assessment.  

  Further develop and apply new approaches/methodologies for chemical testing, including 
read-across  and alternative methods to  animal  testing (e.g.  in  vitro  and computational/in 
silico methods).  

  Continue the mixture-related research, with a focus on applied research to harmonise and 
validate  methods  for  concrete  and  practical  approaches  (on  e.g.  modelling  and  real-life 
exposure to mixtures, methodology for risk assessment, toxicological modes of action of 
chemicals, monitoring methods and epidemiological approaches to mixtures). 

A  common  conclusion  across  many  of  the  recommendations  and  inputs  is  that  the  current 
system for risk assessment fails to take into account exposure to and effects of unintentional 
chemical  mixtures.  Given  the  large  number  of  chemicals  produced  and  used  and  the  even 
bigger number of combinations of such, to which people and the environment are exposed, it 
is  not  feasible with  an approach involving the testing, assessment and/or monitoring of vast 
number of individual unintentional mixtures. Further, although some progress has been made 
in  improving  the  quality  and  access  to  such  information  over  the  last  decade,  considerable 
knowledge  and  information  gaps  remain  regarding  the  toxicity  and  exposure  to  chemicals 
occurring in unintentional mixtures. These gaps applies to a wide range of different chemicals 
across  classes  and  areas  of  use  and  will  for  a  foreseeable  future  continue  to  hamper  the 
detailed assessment of unintentional mixtures. Therefore, to make it possible to broadly and 
systematically  address  unintentional  mixtures  in  a  relatively  near  future,  a  practical  and 
workable approach is needed, which can be implemented despite prevailing knowledge gaps. 
Several authors propose, as an element in their recommendations, the introduction of a MAF 
in relevant pieces of chemicals related legislation as such a solution (see Box 8).  

Box 8: Mixture Assessment Factor (MAF)206 ,207, 208, 209, 210 

– 

sufficient 

assessment 

206 Kortenkamp, A. and M. Faust (2018) ‘Regulate to reduce chemical mixture risk - regulatory systems must better provide 
for risks from exposure to multiple chemicals’, Science: 361 (6399):224-225; July 2018; DOI: 10.1126/science.aat9219, with 
supplemental material. https://science.sciencemag.org/content/361/6399/224.full 
207 Martin, O.V., M. Scholze, A. Kortenkamp (2013): Dispelling urban myths about default uncertainty factors in chemical 
risk 
12:53.  
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3708776/pdf/1476-069X-12-53.pdf  
208 Swedish Chemicals Agency KEMI (2015): An additional assessment factor (MAF)  – A suitable approach for improving 
the  regulatory  risk  assessment  of  chemical  mixtures;  Report  5/15.  https://www.kemi.se/global/rapporter/2015/rapport-5-
15.pdf209 Swedish Government Inquiries (2019). ‘Future chemical risk management Accounting for combination effects and 
assessing  chemicals  in  groups’,  Swedish  Government  Official  Reports,  SOU  2019:45.  https://www.government.se/legal-
documents/2019/11/sou-201945/  
209  Swedish  Government  Inquiries  (2019).  ‘Future  chemical  risk  management  Accounting  for  combination  effects  and 
assessing  chemicals  in  groups’,  Swedish  Government  Official  Reports,  SOU  2019:45.  https://www.government.se/legal-
documents/2019/11/sou-201945/  

Environmental  Health 

against  mixture 

protection 

effects?, 

41 

 
 
                                                           
The application of a ’mixture assessment factor‘ (MAF), and the related concepts of ’mixture 
allocation  factor‘  and  the  ‘risk  cup’  approach,  has  been  proposed  by  several  authors  to 
generically  take  into  account  mixture  effects  in  chemicals  risk  assessments,  where  the 
available data are insufficient to  allow an assessment of actual co-exposure situations. Such 
proposals  discuss  the  application  in  particular  under  REACH,  but  also  in  other  regulatory 
contexts.  The  MAF  is  by  its  proponents  considered  a  pragmatic  approach  to  mixture 
assessment,  in  order  to  manage  the  current  situation  of  lack  of  the  necessary  toxicity  and 
exposure  data  and  make  a  systematic  regulatory  management  of  unintentional  mixtures 
possible in a relatively near future.  

When  applying  a  MAF,  exposure  levels  that  are  considered  sufficiently  safe  for  single 
chemicals  are  reduced  by  a  certain  factor  (i.e.  by  MAF)  to  safeguard  against  risk  from 
combined exposure to multiple chemicals. Hence, the MAF approach takes into account that 
the single chemical in real-life will be a component of a mixture as soon as it is released into 
the  environment  and  that  humans  and  wild  organisms  will  be  exposed  to  such  mixtures  of 
different chemicals, all contributing to the risk. The application of the MAF in chemicals risk 
assessment would target those substances and uses that contributes the most to the toxicity of 
the  mixture  (i.e.  uses  of  substances  with  a  high  toxicity  and/or  a  high  exposure,  and 
accordingly  a  high  Risk  Quotient).  The  MAF  is  proposed  to  be  a  way  of  addressing 
unintentional  mixtures  where  sufficient  knowledge  or  data  are  not  available  to  allow  an 
assessment of actual co-exposure situations. If such knowledge or data are available, the MAF 
can be replaced by scenario-specific factors or by more specific and targeted methodologies, 
when these are available. 

The appropriate numerical value of the MAF is subject to a scientific discussion and different 
magnitudes have been proposed for its use in different contexts. An important task for science 
and  authorities  will  be  to  gain  further  knowledge  in  order  to  set  appropriate  value(s)  of  the 
factor. Further ongoing discussion relates to at what stage of risk assessment should MAF be 
applied  (to the DNEL211 and PNEC212 or to the Risk Quotient). Another question  is  how to 
use  the  MAF  for  substances  lacking  a  dose  threshold  below  which  toxic  activities  does  not 
occur (so called ‘non-threshold substances’).  

The  MAF  approach  has  been  already  successfully  applied  for  regulatory  purposes.  In  the 
USA, a ‘risk cup’ approach is applied for pesticides under the Food Quality Protection Act213. 
This approach is also the basis for the allocation factors used for the relative source allocation 
during  the  setting  of  drinking  water  standards  by  the  World  Health  Organisation.214    An 
example from the EU is the use of a MAF for the derivation of environmental quality criteria 
for single substances in the Netherlands.215  

210 Van Broekhuizen FA., Posthuma L., Traas TP. (2016). Addressing combined effects of chemicals in environmental safety 
assessment  under  REACH  –  A  thought  starter.  National  Institute  for  Public  Health  and  the  Environment,  Bilthoven,  The 
Netherlands, RIVM Report 2016-0162. www.rivm.nl/bibliotheek/rapporten/2016-0162.pdf  
211 Derived No-Effect Level 
212 Predicted No-Effect Concentration 
213 US Congress (1996),’Food Quality Protection Act of 1996’, Public Law No. 104–170, 110 Stat. 1489 (104th Congress, 3 
Aug 1996).  
214World Health Organization (WHO) 2017, ‘Guidelines for drinking-water quality, 4th edition’, 
www.who.int/water_sanitation_health/publications/drinkingwater-quality-guidelines-4-including-1st-addendum/en/   
215 Van Vlaardingen, Verbruggen, (2007), ‘Guidance for the derivation of environmental risk limits within the framework of 
‘‘International and national environmental quality standards for substances in the Netherlands’’ ‘, (INS), Revision 2007. 
RIVM report 601782001/2007, Bilthoven, The Netherlands. www.rivm.nl/bibliotheek/rapporten/601782001.pdf  

42 

 
 
                                                                                                                                                                                     
10. CONCLUSIONS  

The vast majority of chemicals are used and occur as part of chemical mixtures. Exposure 
of  humans  and  the  environment  to  mixtures  of  chemicals  (intentional  and  unintentional)  of 
anthropogenic origin is consequently the norm rather than the exception. A growing body of 
scientific evidence shows that combination effects do occur, in real-life exposure situations as 
well as in experimental studies involving realistic exposure levels, and that some of these co-
exposures represent risks to humans and the environment. 

Regulatory  requirements  and  management  of  mixtures  have  not  changed  significantly 
since  2012.  Most  pieces  of 
also 
intentional/commercial  mixtures  and  require  a  risk  assessment  of  such  mixtures,  although 
with varying scope (e.g. whether considering human health and/or the environment) and level 
of detail. Methodologies and guidance documents for the intentional/commercial mixtures are 
generally available.  

focused  on 

legislation 

chemicals 

cover 

Requirements  to  consider  unintentional  mixtures  are  broadly  absent  in  legislation 
oriented  towards  chemicals  and  intentional/commercial  mixtures.  Explicit  requirements  for 
the assessment of unintentional mixtures (i.e. cumulative effects) exist in the directive on the 
protection  of  the  health  and  safety  of  workers  from  the  risks  related  to  chemical  agents  at 
work and the regulation on Maximum Residue Levels of pesticides in food and feed, the Plant 
Protection Products and the Biocidal Products Regulations require to consider cumulative and 
synergistic  effects.  Implementation  of  the  requirements  of  the  regulation  on  Maximum 
Residue Levels of pesticides in food and feed and the Plant Protection Products has however 
not yet started, as methodology is still under development (see below).  

Some reference to  the  assessment of unintentional  mixtures as regards human health  and/or 
environmental  risks  exists  in  a  few  additional  pieces  of  legislation  focused  on  products, 
pollution  and  environmental  media.  Except  in  relation  to  aggregate  exposure  to  specific 
substances from several sources, and to certain groups of substances (e.g. dioxins or PAHs), 
many  of  these  references  are  however  rather  vague  and  general;  there  are  few  specific 
requirements or guidance on how to perform the assessment.   

Chemicals  legislation  does  not  systematically  consider  aggregate  exposure  across 
regulatory  sectors  (i.e.  the  exposure  to  one  substance  from  different  independent  sources 
and/or via different pathways). Legislation oriented towards environmental media (e.g. water 
and  air  legislation)  normally  considers  aggregate  exposure,  although  limited  to  the 
environmental media/route of exposure on which the particular piece of legislation is focused.  

Furthermore,  EU  legislation  still  does  not  provide  for  a  comprehensive  and  integrated 
assessment  of  the  combined  effects  of  different  chemicals  across  different  pieces  of 
legislation. An ad hoc working group of relevant Commission services and EU Agencies and 
Authorities  (EFSA,  ECHA,  EMA  and  EEA)  was  established  to  strengthen  co-ordination 
across the different pieces of legislation and to promote the integrated assessment of priority 
mixtures, taking into account the risks of human and environmental exposure. This group was 
used  as  a  platform  for  information  exchange  on  activities  across  the  different  pieces  of 
legislation,  while  its  core  objective,  to  coordinate  action  on  addressing  of  priority  mixtures 
across  legislation,  remains  to  be  implemented.  Tools  and  criteria  for  identifying  priority 
mixtures  and  main  drivers  of  mixture  toxicity  are  available  and  can  be  useful  if  further 
integrated into legislative and regulatory practices. 

Progress  has  been  made  since  2012  on  the  development  of  methodologies  for  mixture 
assessment.  The  concept  of  Concentration  Addition  is  widely  accepted  as  the  default 

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approach  to  predict  mixture  toxicities  for  human  health  as  well  as  the  environment.  This 
includes cases where there are indications of possible interactions (synergism or antagonism).  

In the context of setting maximum residue levels for plant protection products, EFSA opted 
for development of a specific methodology  based on cumulative assessment groups with the 
intention  of  grouping  pesticides  based  on  their  effects  on  all  major  organs/systems  and  of 
considering  cumulative  effects  within  those  groups.  So  far,  pesticides  affecting  two 
organs/systems – the thyroid and the nervous system – have been identified and grouped. A 
gradual implementation of the methodology is envisaged, starting by using existing groups to 
guide the monitoring of pesticide residues (as part of a retrospective assessment). In parallel, 
the  methodology  will  be  further  developed  in  the  coming  years  to  cover  more  organs  and 
systems  and  to  cover  prospective  risk  assessment  in  view  of  regulatory  decisions  on  MRL 
setting.  With  the  experience  gained  in  those  processes,  at  a  later  stage  expansion  to  the 
approval/authorisation processes for plant protection products could be considered, if feasible. 

There has also been progress on the development of guidance documents. The basic tools 
for  assessing  and  managing  risks  from  intentional  as  well  as  unintentional  mixtures  are 
therefore  available  to  EU  agencies  and  Member  State  authorities.  However,  despite  the 
progress on methodologies and guidance for assessing mixtures, a remaining key challenge is, 
that as long as the chemical compositions of unintentional mixtures are largely unknown, 
including  the  identity  of  the  chemicals  and  their  concentrations,  mixture  assessment 
methodologies  such  as  concentration  addition  cannot  be  generally  applied  across 
legislation. The reason can for example be that information on the composition of mixtures 
occurring in environmental media (e.g. wastewater or waterbodies) may not be available..  

Some  progress  has  been  made  in  addressing  data  gaps  on  occurrence  and  exposure  to 
chemicals. The Information Platform for Chemical Monitoring (IPCHEM) was established to 
promote a more coherent approach to the generation, collection, storage and use of chemical 
monitoring data in relation to humans and the environment. It provides centralised access to 
monitoring  data  held  by  the  Commission  Services,  EU  Agencies  and  Member  States  and 
offers a tool to assess co-occurrence of substances. The platform already provides significant 
amounts  of  data  but  more  effort  is  needed  to  finalise  making  data  from  EU  Agencies  and 
Member States available and improve the applicability of the tools available.  

Data on hazard and intrinsic properties of chemicals have also been improved. The main 
reason for this progress is that manufacturers and importers has fulfilled the obligation under 
REACH to register substances used on their own or in mixtures. The obligation was fulfilled 
in  June  2018  and  this  has  improved  the  situation  as  regards  the  availability  of  data  on  the 
toxicity and exposure to chemicals. However, despite these improvements, considerable data 
gaps on the toxicity of components of unintentional mixtures, as well as on exposure to 
such mixtures remain. The gaps relates to chemicals across uses and regulatory areas (i.e. in 
addition  to  chemicals  subject  to  REACH  registration,  also  e.g.  pesticides,  biocides, 
pharmaceuticals,  substances  in  imported  products)  that  can  occur  in  unintentional  mixtures, 
and these gaps will likely remain for a long time.  This will continue to limit the extent to 
which unintentional mixtures can be properly assessed. Approaches, such as grouping of 
chemicals,  read-across,  in-silico  and  modelling  will  be  important  to  fill  these  data  gaps, 
although a prerequisite for benefiting more from them is to improve our knowledge on where 
chemicals  are  used  and  in  what  quantities.  Effect-based  in-vitro  methods  have  also  been 
improved, and show some promise as tools to assess mixture effects across legislations, but 
would  need  to  be  further  improved  in  terms  of  sensitivity  and  their  implementation  as  risk 
management tools.  

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Significant progress  has been made in the past years to close some knowledge gaps on 
the impact of mixtures. Although basic knowledge and tools are available and ready to use, 
more  research  is  still  important  to  further  improve  the  knowledge  base,  as  well  as  develop 
assessment methodologies and legal requirements. Continued research is crucial regarding the 
toxicity  of  mixture  components,  toxicological  properties  of  and  exposure  to  mixtures, 
standardised test methods, and knowledge on the effects on the environment and vulnerable 
populations.  Further  areas  include  human  and  environmental  monitoring  methodologies  and 
improved monitoring data, knowledge on epidemiological aspects, modelling methodologies 
as well as on the combined effects with other stressors.  

The Commission and EU Agencies have actively participated in international activities 
to  promote  consistent  and  science-based  approaches  to  the  risk  assessment  of  chemical 
mixtures  at  a  global  level  and  to  promote  a  level  playing  field  around  the  world.  The 
Commission  and  the  EU  Agencies  remain  involved  in  several  on-going  international 
activities, mainly under the auspices of OECD and WHO and often assume a leading role in 
these activities.  

Additional  efforts  are  needed  to  adequately  address  the  challenges  posed  by 
unintentional mixtures. In particular, there is a need to introduce or strengthen provisions to 
take  account  of  unintentional  mixtures  in  relevant  pieces  of  legislation,  such  as  REACH, 
water,  food  additives,  toys,  food  contact  materials,  detergents  and  cosmetics.  In  the  current 
situation,  where  knowledge  and  availability  of  toxicity  and  exposure  information  on 
unintentional  mixtures  and  mixture  components  is,  and  will  remain  for  a  long  time  ahead, 
fragmented and insufficient, there is a need to apply practical and workable approaches. The 
application of a mixture assessment factor (MAF) seems to be the most pertinent for industrial 
chemicals  under  REACH,  but  it  is  applicable  also  to  other  regulatory  areas,  where  the 
available data are insufficient to allow an assessment of actual co-exposure situations. At the 
same time, there is a need to continue developing more specific and targeted methodologies, 
such as the one for pesticides, and applying them as soon as feasible.  In addition, there is a 
need  to  continue  filling  the  gaps  on  knowledge  on  exposures  and  toxicities  and  to  improve 
coordination to tackle mixtures across different regulatory areas. 

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