Analytical methods to measure microplastics in drinking water : review and evaluation of methods.
Date: 2024-03-21
Institutions: Joint Research Centre
Subjects: environmental impact, health risk, plastics, research method, research report, testing, water pollutant

ISSN 1831-9424 

Analytical methods to measure 
microplastics in drinking water 

Review and evaluation of methods 

Belz, S., Cella, C., Geiss, O., Gilliland, D., La Spina, R., 

-Kluettgen, B. 

2024 

 EUR 31885 EN 

 
 
  
  
 
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JRC136859 

EUR 31885 EN 

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How  to  cite  this  report:  European  Commission,  Joint  Research  Centre,  Belz,  S.,  Cella,  C.,  Geiss,  O.,  Gilliland,  D.,  La  Spina, 
Sokull-Kluettgen, B., Analytical methods to measure microplastics in drinking water, Publications Office of the European Union, Luxembourg, 
2024, https://data.europa.eu/doi/10.2760/109944, JRC136859. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Contents 

Abstract ...................................................................................................................................................................................................... 4 

Acknowledgements .............................................................................................................................................................................. 5 

Executive summary .............................................................................................................................................................................. 6 

1  Introduction ....................................................................................................................................................................................... 7 

2  Reported presence of microplastics in drinking water .............................................................................................. 8 

2.1  Methodology applied for the literature review ................................................................................................... 8 

2.2  Sampling sites and conditions...................................................................................................................................... 8 

2.3  Techniques used for detection and quantification ........................................................................................ 10 

2.4  Reported data on microplastics present in drinking water ....................................................................... 10 

2.4.1  Reported size and shape ................................................................................................................................ 10 

2.4.2  Reported polymers ............................................................................................................................................. 11 

2.4.3  Reported number quantities ......................................................................................................................... 13 

2.4.4  Reported mass quantities .............................................................................................................................. 17 

2.4.5  Reported background/contamination levels ........................................................................................ 17 

2.5  Key points from literature reports of microplastics in drinking water ............................................... 17 

3  Analytical techniques tested in inter-laboratory comparisons or validation exercises ....................... 19 

3.1  JRC/BAM inter-laboratory comparison study on PET in water ................................................................ 19 

3.2  Southern California Coastal Water Research Project (SCCWRP) inter-laboratory comparison 
study ................................................................................................................................................................................................... 20 

3.3  German Centre for Water Technology study for microplastics analysis in water samples ... 21 

4  Current activities in international standardisation ................................................................................................... 24 

4.1  ISO activities relating to microplastics ................................................................................................................. 24 

4.2  CEN activities relating to microplastics ................................................................................................................ 25 

4.3  ASTM activities relating to microplastics ............................................................................................................ 25 

4.4  National standardization bodies in Europe activities relating to microplastics ............................ 26 

4.5  VAMAS activities relating to microplastics ......................................................................................................... 26 

4.6  Current status of standardized methods applicable to the DWD ......................................................... 27 

5  Microplastic definitions, descriptors and metrics ...................................................................................................... 28 

5.1  Microplastic definitions ................................................................................................................................................. 28 

5.1.1  REACH restriction ................................................................................................................................................ 28 

5.1.2  Marine Strategy Framework Directive (MSFD) ................................................................................... 29 

1 

 
 
5.1.3 

ISO ............................................................................................................................................................................... 30 

5.1.4  Legislative by State of California .............................................................................................................. 31 

5.2  Descriptors for microplastics ..................................................................................................................................... 31 

5.2.1  Polymer type ......................................................................................................................................................... 31 

5.2.2  Particle size ............................................................................................................................................................ 32 

5.2.3  Shape ......................................................................................................................................................................... 33 

5.2.4  Colour ........................................................................................................................................................................ 33 

5.2.5  Surface chemistry .............................................................................................................................................. 33 

5.3  Metrics for reporting ....................................................................................................................................................... 33 

5.4  Descriptors and metrics suitable for microplastics in drinking water ................................................ 34 

6  Sampling and sample treatment ....................................................................................................................................... 35 

6.1  Sampling requirements of drinking water .......................................................................................................... 35 

6.2  Sample treatment ............................................................................................................................................................ 36 

7  Instrumental techniques to detect and quantify microplastics ........................................................................ 40 

7.1  Fluorescence microscopy ............................................................................................................................................. 40 

7.2  Spectro-microscopic techniques using IR and Raman ................................................................................. 41 

7.2.1  Data acquisition and analysis strategies .............................................................................................. 42 

7.2.2  Filter materials and filter analysis ............................................................................................................ 43 

7.2.3  Raman spectro-microscopy .......................................................................................................................... 44 

7.2.4  FTIR spectro-microscopy................................................................................................................................. 46 

7.2.5  Quantum cascade laser spectroscopy .................................................................................................... 48 

7.2.6  Data analysis and spectral databases ................................................................................................... 48 

7.3  GC/MS-based thermo-analytical techniques ..................................................................................................... 49 

7.3.1  Sample treatment for pyr-GC/MS .............................................................................................................. 49 

7.3.2  Overview of capabilities and limitations of pyr-GC/MS and TED-GC/MS ............................ 51 

8  Analysis strategies ..................................................................................................................................................................... 53 

8.1  Screening technique ........................................................................................................................................................ 53 

8.2  Single polymer-specific technique .......................................................................................................................... 53 

8.2.1  Polymer-specific number-based techniques ....................................................................................... 54 

8.2.2  Polymer specific mass-based techniques ............................................................................................ 54 

8.3  Combination of techniques ......................................................................................................................................... 54 

2 

 
 
8.4  Polymer specific indicator approach ...................................................................................................................... 55 

8.5  Tiered approach ................................................................................................................................................................. 55 

9  Summary and conclusions ..................................................................................................................................................... 56 

References ............................................................................................................................................................................................. 57 

List of abbreviations and definitions ...................................................................................................................................... 66 

List of figures ....................................................................................................................................................................................... 70 

List of tables ......................................................................................................................................................................................... 72 

Annexes ................................................................................................................................................................................................... 73 

3 

 
 
Abstract 

Article 13(6) of EU Directive 2020/2184 on the quality of water intended for human  consumption 
(recast)  states  that  within  3  years  of  its  entry  into  force  on  12th  January  2021  the  European 
Commission shall adopt a methodology to measure microplastics in drinking water. To support the 
development and adoption of such a methodology, the Joint Research Centre has undertaken a review 
of the scientific knowledge base regarding the nature, distribution and quantities of microplastics in 
drinking  water.  From  the  literature  and  supported  by  in-house  experience,  potential  instrumental 
techniques were identified and documented to summarise their technical capabilities, limitations and 
where  possible  also  information  on  sample  throughput  as  well  as  running  and  investment  costs. 
Consideration was given to the relevant activities and progress of standardization bodies relating to 
microplastic analysis methods. Finally, with a view to defining the scope of a monitoring methodology, 
including  appropriate  reporting  criteria,  the  possible  descriptors  for  microplastics  have  been 
considered   in particular particle size, particle shape and polymers of interest 
 as well as suitable 
measurement metrics (mass/number). This information, which is summarised in this report, forms the 
basis  for  making  informed  and  pragmatic  recommendations  about  the  key  parameters  to  be 
measured  and  the  most  appropriate  analytical  techniques  to  use  in  the  development  of  a 
methodology.  

4 

 
 
Acknowledgements  

The support of the following JRC colleagues for fruitful discussion, review of this report, suggestions 
for  improvements,  and  the  layout  of  this  document  is  much  appreciated  (in  alphabetical  order): 
Susanne Bremer-Hoffmann, Guillaume Bucher, Heidi Olsson, Veronique Vanherck, Stefania Vegro.  

The authors are thankful to JERB editor and reviewers for their careful reading of the manuscript and 
their insightful comments and suggestions.  

Authors   alphabetical order 

Susanne Belz, Claudia Cella, Otmar Geiss, Douglas Gilliland, Rita La Spina, Dora Mehn, Birgit 
Sokull-Kluettgen 

5 

 
 
 
Executive summary  

Directive (EU) 2020/2184 of 16th December 2020 of the European Parliament and the Council on the 
quality of water intended for human consumption (recast) entered into force on 12th January 2021. 
This Directive is referred to as the Recast-Drinking Water Directive (DWD) and within 3 years of its 
entry into force, the European Commission should adopt a methodology to measure microplastics in 
water intended for human consumption, informally also called drinking water (DW).  

To support the definition of a methodology as required by the recast-DWD, the Joint Research Centre 
(JRC) has been asked to undertake a review of the scientific knowledge base regarding the nature, 
distribution  and  quantities  of microplastics in  DW.  Secondly,  from the literature  and  supported by 
in-house experience, potential instrumental  techniques have been identified and documented with 
consideration being given to summarising their technical capabilities, limitations and where possible 
also  information  on  their  sample  throughput,  running  and  initial  investment  costs.  Thirdly, 
consideration  has  been  given  to  relevant  activities  and  progress  in  guidelines  and  method 
standardisation by international standardization bodies such as CEN, ISO and ASTM. Finally, with a 
view to establishing the scope of a monitoring methodology, including appropriate reporting criteria, 
a range of possible descriptors for microplastics have been considered 
 in particular particle size, 
 as well as suitable measurement metrics (mass/number 
particle shape and polymers of interest 
based).  

The review showed that the number concentrations of particles and fibres in drinking water varied 
across five orders of magnitude. The majority of studies reported microplastics occurrence within the 
range 100 - 0.01 particles per litre with European studies typically showing levels below 1 particle 
per litre. To obtain these results, three main categories of techniques have been used:  fluorescence 
microscopy, optical micro-spectroscopy (using Raman or Infra-Red) and thermo-analytical techniques 
(pyrolysis  and  thermal-extraction-and-desorption  coupled  with  gas  chromatography / mass 
spectrometry). Each of them has a particular combination of strengths and limitations in terms of the 
measurement  metric  (polymer  weight  or  particle  number),  sensitivity,  minimum  particle  size  and 
ability  to identify polymer  type.  Regarding  harmonization  of  analytical  methods  only two  partially 
relevant  standards  have  been  published.  The  first,  ASTM  D8332-20,  is  a  Standard  Practice  for 
Collection of Water Samples for the Identification of Microplastics  while the second, ISO 24187, sets 
out the key principles to be followed in the development of sampling, sample treatment and detection 
procedures.  Neither  of  the  standards  adequately  satisfies  the  needs  of  a  methodology  tailored 
specifically for monitoring microplastics in drinking water. 

It has been concluded that no single analytical technique can yet be considered fully  suited to the 
task  of  identifying  and  quantifying  microplastics  contaminants  in  drinking  water  for  monitoring 
purposes. Consequently, the adoption of a methodology will require some degree of compromise and 
pragmatic  choices  must  be  made  regarding  the  critical  parameters  to  monitor.  Key  factors  in 
determining a suitable method or combination of methods will be sensitivity and specificity but for 
routine widespread monitoring aspects such as  comparability of measurement results obtained in 
different  laboratories,  investment  costs,  sample  throughput  and  cost  per  sample  should  also  be 
considered.  

The information collated in this report is part of the JRC science-for-policy role to assist the process 
of making informed and pragmatic recommendations about the key parameters to be measured and 
subsequently to identify suitable methodologies for achieving this. 

6 

 
 
1 

Introduction  

Microplastics are persistent pollutants which increasingly are present in land, water and air. It is well 
known that they produce harmful effects on the environment and concerns arise that they potentially 
also may have effects on human health. Plastics as such are generally considered to have low toxicity, 
but the effects of microplastic particles is not yet known. In addition, microplastics can carry additives, 
residual  monomers,  biofilm  and  adsorbed  chemicals,  some  of  which  are  of  toxicological  concern. 
Following ingestion, such compounds may be released in the gastrointestinal tract  and potentially 
taken up by the body. Because the information about exposure of humans to microplastic particles 
and/or associated compounds is scarce, a valid risk assessment is currently not possible1. 

There  has  been much debate  on  what  needs  to  be done  to  understand  and  reduce the  impact  of 
microplastics  with  numerous  international  calls  for  action  on  the  issue  (for  instance  from  United 
Nations  UN,2  World  Health  Organization  WHO,1  Organisation  for  Economic  Co-operation  and 
Development OECD3). The European Commission (EC) has responded in key policy documents such as 
the Green Deal and the European Plastics Strategy and is now driving the development of legislation 
though  a  recently  published  restriction  under  the  Registration,  Evaluation,  Authorisation  and 
Restriction of Chemicals (REACH)4 or as part of the review of legislation such as the Drinking Water 
Directive (Recast-DWD).  

The recast of Directive (EU) 2020/2184 of 16th December 2020 of the European Parliament and the 
Council  on  the  quality  of  water  intended  for  human  consumption,5  informally  referred  to  as  the 
Drinking Water Directive (DWD), requires that the European Commission shall adopt a methodology 
to measure microplastics in water intended for human consumption, informally called drinking water 
(DW), by 12th January 2024, as detailed in Article 13 Paragraph 6 of the Directive.   

Directive by adopting a methodology to measure microplastics with a view to including 

Accordingly,  the  Joint  Research  Centre  (JRC)  of  the  European  Commission,  in  its  role  of  scientific 
support  for  the  policy,  has  been  asked  to  describe  the  key  considerations  for  identifying  possible 
analytical methods for detecting and quantifying microplastic contaminants in DW. Firstly, a review 
of the scientific knowledge base regarding the nature, distribution and quantities of microplastics in 
DW was undertaken. This serves to provide key information on the range of concentrations, sizes and 
types of microplastics which could be expected to be found in real-life DW samples. Secondly, from 
the literature and supported by in-house experience, analytical techniques have been identified and 
documented with consideration being given to summarising their technical  capabilities, limitations 
and, where possible, also information on their sample throughput, running and initial investment costs. 
In addition, the scientific literature was screened to  identify commonly used sampling approaches 
and sample treatment procedures for the analysis of DW. Thirdly, in addition to scientific literature, 
consideration  has  been  given  to  any  relevant  activities  and  progress  in  guidelines  and  method 
standardisation by European and international standardization bodies such as European Committee 
for  Standardization  (CEN),  International  Organisation  for  Standardization  (ISO)  and  ASTM 
International. Finally, with a view to establishing the scope of a monitoring methodology, including 
appropriate reporting criteria, a range of possible descriptors for microplastics have been considered 
 in particular particle size, particle shape, polymers of interest 
 as well as measurement metrics 
(mass/number) so that informed and pragmatic recommendations about the key parameters to be 
measured and reported will be made. 

7 

 
 
 
 
2  Reported presence of microplastics in drinking water  

Evaluating the suitability of analytical methods for detecting and characterising microplastics requires 
an understanding of the expected levels of contamination. To this end, the scientific literature was 
screened  for  studies  on  the  detection  of  such  particles  in  relevant  water  samples.  In  particular, 
peer-reviewed  articles  specifically  reporting  the  analysis  of  microplastics  sampled  from  DW  were 
identified and evaluated. The objective of this review was to extract key information regarding the 
nature of microplastics in DW, their concentration, the analytical techniques used for their detection 
and quantification as well as the sampling methods applied. 

2.1  Methodology applied for the literature review 

The literature search was performed in December 2021 with the bibliographic databases Scopus and 

and water and 

key words. The search resulted in 207 articles published between 2013 and 2022. These articles were 
then analysed for relevance to this literature review leaving 21 articles, which reported studies of DW 
collected  from  the  following  sources:  public  and  private  institutions,  households,  residential  and 
commercial  areas,6 20  city  plumbing  system,21  hydrants22,23  and  fountains24;  two  articles  analysing 
water sampled at various points in the water distribution network25,26.  

2.2  Sampling sites and conditions 

Sampling sites, from which data are reported in the literature, are spread over four continents, namely 
Europe, America, Asia, and Africa (see Figure 1). While most studies focussed on the investigation of 
DW  in  single  countries,  Mukotaka  et  al.15  and  Kosuth  et  al.11  collected  their  samples  in  different 
countries. The 11 studies that investigated DW samples from Europe, reported data from Germany 
(5 studies), France (2), United Kingdom (2), Denmark (1), Finland (1), Iceland (1), Italy (1), Norway (1), 
Slovakia (1), Sweden (1), and Switzerland (1). 

Figure 1. Number of studies investigating DW samples from different geographical regions. Total number of 
studies is 21, of which two included samples collected from more than one region. 

Source: own production 

8 

 
 
 
The samples were taken at different points of the water supply chain, including: 

  Water tap, where a consumer collects water for daily use;  
  Hand-over point between the water supply system; 
  Private site (building or plot); 
  Public fountain/well. 

The sample collection was generally carried out in one of two different ways:  

a)  container  sampling:  water  was  collected  into  containers  followed  by  filtration  off-line 

(14 studies);  

b)  at-source filtering: a filtering device was directly attached to the water supply (8 studies).  

This includes one study (Yuan et al.)6, which used both sampling procedures.  

The  volume  sampled  varied  substantially  between  studies  and  depended  on  the  type  of  sample 
collection  (see  Table  1).  In  case  of  at-source  on-line  filtering,  quite  large  volumes  of  water  were 
collected,  the  filtered  volume  being  between  9  litres  and  2250  litres  (average:  907  litres, 
median: 900 litres). In case of container sampling, the volume of the water samples varied between 
0.5 litres and 100 litres (average: 11 litres, median: 1 litre).  

Table 1. Volumes sampled by the different studies, split up into studies with at-source filtration and 
container sampling. Yuan et al.6 used both sampling procedures. 

At-source filtering 

Container sampling 

Author(s) 

Volume [L] 

Author(s) 

Volume [L] 

Johnson et al.26 

Mintenig et al.10  

Pittroff et al.17  

Gomiero et al.22 

Weber et al.18  

Kirstein et al.23 

Feld et al.13  

Yuan et al.6 

2250 

1850 

1300 

1000 

900 

750 

50 

9 

Chanpiwat et al.25 

Ásmunddóttir et al.21 

Shen et al.16  

Yuan et al.6 

Zhang et al.12  

Chu et al.7 

Ferraz et al.19  

Lam et al.20  

Tong et al.8  

Shruti et al.24 

Kankanige et al.9  

Pratesi et al.14  

Mukotaka et al.15  

Kosuth et al.11  

100 

22.5 

10 

9 

4.5 

1 

1 

1 

1 

1 

1 

0.5 

0.5 

0.5 

Source: own production 

9 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2.3  Techniques used for detection and quantification 

After  filtration,  the  nature  and  the  quantity  of  plastic  particles  were  determined  using  different 
techniques.  Figure  2  gives  an  overview  about  the  frequency  of  techniques  or  combination  of 
techniques applied. Various combinations of techniques were used, including spectroscopic techniques 
(Fourier  Transform 
spectro-microscopy  µ-FTIR,  Attenuated  Total  Reflectance 
Fourier-Transform Infrared Spectroscopy ATR-FTIR or/and Raman spectro-microscopy µ-Raman) with 
other  optical  techniques,  such  as  optical  microscopy  (OpMic)  or/and  fluorescence  microscopy 
(FluoMic), or Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis (SEM-EDX). 

Infrared 

Figure 2. Number of studies using various techniques for analysing the particles found. Combination of 
techniques explained in the text. Acronyms of techniques: see list of abbreviations (page 66). 

Source: own production 

The determination of the number of microplastic particles was more frequently used than quantifying 
the mass of the particles. Among the number-based techniques, µ-FTIR and a combination of OpMic 
and µ-FTIR were most frequently used, followed by µ-Raman and FluoMic. Mass measurements were 
carried out in only three studies, two of which used pyrolysis gas chromatography-mass spectrometry 
(pyr-GC/MS) alone21,22 and one which used both pyr-GC/MS and µ-FTIR23. 

2.4  Reported data on microplastics present in drinking water 

2.4.1  Reported size and shape 

Most of the authors reported the size range they applied for detecting microplastic particles. Figure 
3 (logarithmic vertical scale) shows that the size ranges varied to quite some extent and that there 
was no obvious common approach for choosing them.  

10 

 
 
 
Figure 3. Particle size rages covered by the different studies7 10,13 16,18 20,24,25,27. Due to the wide variety of size 

a thinned-out top end. 

Source: own production 

The  lower  boundaries  of  the  considered  size  ranges  were  between  1  and  500  µm,  which  mainly 
depended on the pore size of the filter used for filtration and/or the size limit of detection of the 
instrumental technique applied. The majority of studies used filters with cut-off values of 10 µm or 
more and consequently could provide no information about the presence of smaller microplastics. 
The  upper  size  boundaries  of  reported  particle  size  varied  from  50  µm  to  5 mm.  However,  some 
studies did not explicitly describe size ranges and in particular the upper limit but reported that the 
sizes  of  the  found  microplastics  were  above  or  below  a  specific  size.  Approximately  half  of  the 
studies7 9,12,13,15,16,20,21,24,25  reported  the  size  of  microplastics  split  up  into  size  classes.  A  direct 
comparison of results is not possible, since each publication used different size classes in terms of 
number (from two to five) and in size range for each classes.  

In all the reported studies, the analysed particles were collected by filtration and so the analysis data 
is representative of the fraction whose size is above the cut-off of the finest filter. However, the lack 
of harmonisation of reported size (ranges) makes it impossible to draw firm conclusions about the 
average size of the microplastics in DW. 

Regarding  the  par
ver  all  the  studies,  particle  counting  showed  the  majority  of 
microplastic particles in DW to be fibres (50%) or fragments (44%), while spherical particles (5%) 
and films (1%) were found infrequently. 

2.4.2  Reported polymers   

Several  studies,  using  instrumental  techniques  able  to  identify  the  chemical  composition  of  the 
microplastics, reported the type and the percentage of microplastics found in DW samples. In some 

11 

 
 
 
cases, the studies presented the percentage of all the identified objects in the  sample and in  the 
blank, including the non-plastic particles. The main items reported in the studies that were classified 
as  non-plastic  consisted  of  cellulose,  protein,  cellophane,  polybutadiene,  epoxy  resins,  rubber  and 
precipitated dyes. For the purpose of this analysis, the percentages of the objects were recalculated 
by considering only the plastic particles and excluding the other contaminants. 

From Figure 4 it can be seen that polyethylene (PE), polyethylene terephthalate (PET), polyester other 
than PET (PEST) and polypropylene (PP) were the most frequently found polymers in DW samples. 
Other polymers detected were polystyrene (PS), polyvinylchloride (PVC) and polyamide (PA).  

Figure 4. Percentage (particle number) of microplastics polymers found in DW samples. The columns show 
the percentage of specific polymer types within the total population of microplastics reported in the individual 
articles. For the acronyms, refer to the list of abbreviation (page 66) The sub-

compounds (AC), acrylonitrile butadiene styrene (ABS), copolymer polyethylene-polypropylene (co PE+PP), 
Styrene-Ethylene-Butadiene-Styrene (SEBS), polyacrylamide (PAM), polyurethane (PU), polyphenylene sulphide 
(PPS), poly(isoprene) (PI), polytetrafluoroethylene (PTFE), poly(methyl phenyl siloxane) (PMPS), polymethyl 
methacrylate (PMMA) 

Source: own production 

12 

 
 
 
 
 
Evaluation  of  sample  blanks,  which  is  an  indication  of  the  level  of  background  contamination,  is 
dominated by the same polymers with PE, PP, PET and PEST making up 75% of the reported polymer 
contaminants. 

Some studies which had found particulates of PE, PVC or PA in DW also noted that these polymers 
were commonly used in the water pipes and fittings of the supply network being investigated. As 
none of the studies was able to identify conclusively the origin of the particles, it remains uncertain 
if the construction materials of water distribution network may be contributing to the presence of 
microplastics or if these were originally in the source water and avoided capture when passing though 
in the water treatment plant. 

2.4.3  Reported number quantities  

For the reporting of the number of microplastic particles, different units were used such as particles 
per  litre,  particles  per  cubic  metre  or  particles  per  sample.  To  enable  the  comparison  of  the  data 
produced in different studies, all number-based results were recalculated (normalised) to obtain data 
expressed  as  particles  per  litre.  In  the  case  where  authors  reported  the  number  of  microplastic 
particles separately for different size ranges or/and different polymers, all sub-results for one sample 
were summed. For studies reporting the number of particles per sampling site or at different times 
during the year, the average of the single results was calculated.  

Figure 5 shows a comparison of the number-based study results (average of all study samples and 
blank values), normalised as described above. The amount of microplastic particles found in DW vary 
between  0.0001  and  440  particles  per  litre,  which  represents  a  difference  of  about  6  orders  of 
magnitude between the highest and the lowest value. Such a huge variation between studies may be 
caused by differences in the sampling location (country and site of sampling, see paragraph 2.2), but 
also  by  procedural  differences.  The  latter  comprise  the  volume  and  type  of  sampling  ( container 
)  and/or  the  applied  detection  technique.  In  addition,  the  quality 
assurance measures applied by the laboratory as well as variations in the measured background level 
and the approach on how to deal with it (whether or not subtracting it from the measurement results) 
might have been factors impacting the results.   

  or 

-

13 

 
 
 
 
Figure 5. Number of microplastic (MP on vertical axis) particles found in samples (as mean) and blanks 
(where indicated in the study description); an estimated total (open circles) was calculated in cases where the 
study authors stated having subtracted the blank from the sample result and the blank value was reported. 
Due to the wide variety of size ranges applied, vertical axis is logarithmic. For Yuan et al., the data for the two 
different sampling procedures are shown separately: (1) container sampling; (2) at-source filtering. 

Source: own production 

14 

 
 
 
 
 
The data from the studies focussing on specific countries (see Figure 6) suggest that on average the 
measured levels of microplastics present in DW seem to be lower in Europe (0.000-0.6 particles per 
litre) than in America (12-316 particles per litre) and Asia (0.7-440 particles per litre). For Europe, 
less than one microplastic particle per litre of DW was found 
 a result which was associated with 
higher sampling volumes (50-2250 litres) and sample collection by at-source filtering. Only one other 
study (Yuan et al.6, Canada) applied the same type of sampling, while all other author groups used 
container collection which risks of higher background contamination (see also below).  

Figure 6. Measured microplastic (MP on vertical axis) number concentration (including error bars) by country 
and region as reported by the studies focussing on one country. Due to the wide variety of size ranges 
applied, vertical axis is logarithmic. 

Source: own production 

When  plotting  the  number  of  microplastic  particles  found  as  a  function  of  the  volume  of  water 
sampled and the type of sampling (Figure 7), it looks like there is some sort of correlation. While a 
direct impact of the water volume seems unlikely, an influence of the sampling procedure is much 
more plausible, because at-source filtering is carried out in a closed system, while during container 
sampling the sample is   to some extent   exposed to ambient air (which may carry a certain load of 
microplastics).  Accordingly,  the measurement  results  for  at-source  filtering  (blue  dots in  Figure  7) 
tend to be lower than for container sampling (yellow dots) across all studies. 

15 

 
 
 
 
Figure 7. Number concentration of microplastic particles (MP on vertical axis) reported in relation to the 
water volume filtrated and the applied sampling procedure. Container sampling (yellow dots); at-source 
filtering (blue dots). Due to the wide variety of size ranges applied, vertical axis is logarithmic. 

Source: own production 

Figure 8. Number concentration of microplastic particles (MP on vertical axis) found in blank samples 
(background level) in relation to the water volume filtrated and the applied sampling procedure. Container 
sampling (yellow dots); at-source filtering (blue dots). Due to the wide variety of size ranges applied, vertical 
axis is logarithmic. 

Source: own production 

16 

 
 
 
 
  even  though  varying  quite 
It  can  be  assumed  that  contamination  during  sample  processing 
substantially across studies (see Figure 8)   is generally independent from the sampled volume. Under 
this  assumption,  it  would  seem  likely  that  concentration  values  determined  from  the  analysis  of 
small-volume  samples  are  dominated  by  the  presence  of  microplastic  contaminants  introduced 
during processing/analysis rather than the number of microplastics originally in the DW. To reduce 
this effect, sampling volumes should be as high as practically feasible. As it will be noted later (see 
section  4),  this  volume  range  (or  even  a  higher  one)  is  already  a  recommendation  in  the  ASTM 
standard D8332-2028 on sampling water for microplastics analysis (1500 L).  

Consequently,  the  low  level  of  microplastics  expected  in  European  DW  suggests  that  to  reduce 
analytical uncertainty and the impact of background contamination during sample processing (see 
below), a high sample volume should be analysed, probably around 1000 litres. 

2.4.4  Reported mass quantities  

The three studies21 23 in which mass-based measurements were carried out reported plastic contents 
of the analysed water of 0.52 ng/L, 6.1 ng/L and 7.2 µg/L. The range of variation in the measurement 
results  is  less  pronounced  than  in  the  case  of  number  concentrations,  but  with  four  orders  of 
magnitude it is still very high. 

2.4.5  Reported background/contamination levels 

The level of background contamination was reported for 13 out of 21 studies that produced number-
based results. The (normalised)  levels  of contamination were reported to be  between 0.0002 and 
22 particles per litre (see Figure 5, yellow dots); the majority (70%) of author groups stated to have 
a background between 0.1 and 10 particles per litre.  

For mass-based results, only one out of three studies reported a blank value, even though all author 
groups stated that they analysed (procedural or field) blanks. Kirstein et al.23 calculated estimates of 
mass values from particle number-size data. The estimated mass in the blanks ranged from 1-784 ng 
depending on the water supply line sampled. All other author groups, which produced mass-based 
results, reported their limits of detection (LOD) for the different polymers covered by their method 
being 1 µg21, 0.5-1.1 µg22 and 1.2-5.2 µg23, respectively. 

2.5  Key points from literature reports of microplastics in drinking water 

The examination of the literature has provided a valuable insight into the current knowledge about 
the occurrence of microplastics in DW as well as the sampling and analytical requirements that will 
have  to  be  considered  in  establishing  a  methodology  which,  within  the  limitations  of  current 
technology, can best satisfy the needs of monitoring. 

  With  the  exception  of  a  few  studies  in  China,  Thailand  and  Brazil  particle  number 
concentrations are low with results being at most a few tens of particles per litre. In particular, 
studies in European countries resulted in levels, which were a further 1-3 orders of magnitude 
lower than in the other countries/regions on a particle-per-litre basis (below 1 particle per 
litre).  

  Most  studies  used  microscopy  and  spectro-microscopy-based  methods  and  thus  report 
microplastic  particle  numbers.  Only  10%  of  reports  provided  particle  mass  by  thermo-
analytical techniques. 

17 

 
  Particle counting techniques used were equally divided between the ones using chemically 
specific  spectroscopy,  which  could  positively  identify  a  particle  as  being  a  polymer, 
(µ-FTIR 28% and µ-Raman 21% of the studies) as well as non-chemically specific techniques 
(OpMic 7% and FluoMic 17%).  

  Particle counting studies using larger water volumes (>50 litres) and filtration directly from 
the  water  supply  (at-source  filtering)  generally  reported  lower  calculated  particle 
concentrations (<1 particle/litre), with values generally being close to background levels.  
  Sampling volumes should be as high as practically feasible, probably around 1000 litres, to 
reduce the analytical uncertainty and the impact of background contamination during sample 
processing. 
It was found that seven common synthetic polymers (PE, PET, PEST, PP, PS, PVC and PA) make 
up close to 90% of the microplastics found in DW.  

 

  The classification of microplastics shapes showed that predominantly fibres and fragments 

were found.  

  Although the majority of studies used techniques based on microscopy rather than thermal 
analysis, very little information on particles size distributions of the polymer particles was 
available. Most studies reported only total particle numbers or particle numbers across a few 
broad size bins. Similarly, there was no information regarding the size distribution of different 
polymer types. 

18 

 
 
 
3  Analytical  techniques  tested  in  inter-laboratory  comparisons  or 

validation exercises  

The scientific literature contains many publications, which report the analyses of microplastics in a 
wide range of different matrices using methodologies relying on the three most common classes of 
techniques  (optical  microscopy,  vibrational  spectroscopy  and  thermo-analytical  techniques). 
Unfortunately, only a few of these studies have undertaken a systematic evaluation or validation of 
the techniques despite the importance of such activities in achieving reproducible and reliable data 
being highlighted by the scientific community.29 Such studies provide an important insight into the 
capabilities  and  limitations  of  analytical  procedures  and  the  related  instrumental  techniques 
themselves.  In  the  literature,  6  inter-laboratory  studies30 35  were  identified  which  evaluated 
techniques  for  microplastics  in  aqueous  media  but  only  the  three  examples  described  below 
(paragraphs  3.1,  3.2  and  3.3)  were  judged  to  be  particularly  relevant  to  the  monitoring  of 
microplastics in DW.  

There are a number of other such initiatives planned in the future within ongoing projects, such as 
those  in  the  Horizon  2020  research  cluster  CUSP36  comprising  five  microplastic  projects. 
Unfortunately, the outcomes from these initiatives may not be available before the conclusion of the 
projects (4 projects will end 31st March 2025 and one 31st March 2026) and therefore beyond the 
time frame set by the DWD for the identification of a methodology. 

3.1  JRC/BAM inter-laboratory comparison study on PET in water 

In 2021, an inter-laboratory comparison (ILC) study32 on sample containing PET particles in (clean) 
water was carried  out by the JRC in collaboration with the German Federal Institute for Materials 
Research and Testing (BAM) with nearly 100 participating laboratories from 28 countries. It was left 
to the participants to choose the analysis method, including whether to identify the polymer of the 
particles  found  and  whether  to  determine  particle  number  or/and  mass.  In  addition  to  the 
measurement  results,  information  was  collected  on  the  practices  applied  for  sample  treatment, 
measurement conditions, instrument settings, data analysis strategies and so on, including strategies 
to prevent contamination during sample processing. 98 datasets could be used for evaluation and 
provided a comprehensive overview of the state of the art of microplastic analysis in water and in 
particular the quantification of the PET particles flake-shaped fragments present in the samples.37 

The  study  participants  used  a  variety  of  different  analysis  techniques.  For  identification  and 
quantification of the PET particles present in the samples, predominantly µ-FTIR was used (37 out of 
62  laboratories)  followed  by  µ-Raman  (15)  and,  for  mass  measurements,  pyr-GC/MS  (9).  Simpler 
techniques (OpMic, FluoMic, gravimetric analysis) were employed as well, but only to determine the 
In  addition, 
emerging or less frequently described techniques, such as LDIR, NMR and HPLC, the latter only being 
applicable for hydrolysable polymers like PET, were used.  

The measurement results in this study scattered almost evenly over the range of reported values of 
about three orders of magnitude. This applies to both, number- and mass-based results as well as 
across the different analysis techniques employed.  

-FTIR and µ-Raman users obtained PET number concentrations that fell within 
the indicative range of expected results, no conclusions about the effect of measurement parameters 
on  polymer  identification  performance  could  be  drawn,  as  the  identity  of  the  material  (PET)  was 
known to the participants. In the case of the thermo-analytical techniques, the few results that were 

19 

 
submitted indicate that GC/MS after pyrolysis, with or without an intermediate sorption-desorption 
step, is a suitable technique for the identification and the quantification of PET in aqueous matrices. 
However,  the  analysis  of  methodological  details  (contamination  prevention,  sample  treatment, 
measurement conditions, instrument set-up, parameter settings etc.) showed that a huge variety of 
conditions  were  applied  and  thus  there  is  ample  room  for  harmonisation.  This  correlates  with 
statements made elsewhere33,38 40 about the further need for harmonisation and standardisation in 
the field.  

Relevance to DWD methodologies: Even thought this study was not specifically designed for the 
investigation of microplastics in DW, it shows 
as  matrix  without  any  intentionally  added  non-polymeric  materials  and  for  which  the  identity  of 
particles (PET) was known, the scatter of measurement results was still very high. This low inter-
laboratory reproducibility was largely independent of the analysis technique applied  and was also 
observed when only individual techniques such as µ-FTIR, µ-Raman or pyr-GC/MS were considered. 
This  is  a  severe  problem  for  the  comparability  of  measurement  results  generated  by  different 
laboratories.  However,  specific  aspects  of  the  general  laboratory  practices,  sample  treatment, 
measurement  conditions  or  data  analysis  contributing  to  this  outcome  of  the  study  could  not  be 
identified and, thus, no recommendations could be provided for future harmonisation. 

3.2  Southern  California  Coastal  Water  Research  Project  (SCCWRP)  inter-

laboratory comparison study  

This study was undertaken by the Southern California Coastal Water Research Project (SCCWRP)30,41 
to  support  California  Senate  Bill  1422,  which  requires  the  development  of  State-approved 
standardized  methods  for  quantifying  and  characterizing  microplastics  in  DW.  Accordingly,  an 
inter-laboratory  microplastic  method  evaluation  study  was  carried  out  with  22  participating 
laboratories  from  six  countries,  to  evaluate  the  performance  of  the  commonly  used  techniques: 
optical  microscopy,  Fourier-transform 
(µ-FTIR),  and  Raman 
spectro-microscopy (µ-Raman). The study did not contemplate the use of the pyrolysis techniques for 
the analysis of the samples. An important additional aspect of the study was that the participants 
also provided information regarding the time required in both sample treatment and analysis.  

infrared  spectro-microscopy 

)  spiked  with  microplastic 
Three  samples  of  simulated  clean  water  (
particles and a laboratory blank were sent to each laboratory with a prescribed standard operating 
procedure for particle extraction, quantification, and characterization. The samples contained known 
amounts of microparticles over four size fractions (1
four  polymer  types  (PE,  PS,  PVC,  and  PET),  three  shapes  (fragments,  spheres  and  fibres)  and  six 
colours  (clear,  white,  green,  blue,  red,  and  orange).  The  total  particle  number  per  sample  was 
609 (±132) of which 249 (±60) wer
 The samples also included around 
80 false positives (natural hair, fibres, and shells) as example of particles which can be mistaken for 
microplastics.  Particles  were  collected  via  filtering/sieving  and  the  subsequent  analysis  included 
optical microscopy, which was used to count all particles above 20 µm with characterisation of size, 
shape and colour. Chemical characterisation by µ-FTIR or µ-Raman was done on a sub-sample of the 
collected particles. 

0

Among the participating laboratories, mean particle recovery determined using stereomicroscopy was 
76% ± 10% (standard error, SE). For particles in the three largest size fractions, mean recovery was 
92% ± 12% (standard deviation, SD). On average, laboratory contamination from blank samples was 
91 particles (± 141 particles SD). µ-FTIR and µ-Raman accurately identified microplastics by polymer 
type for 95% and 91% of analysed particles, respectively. Per particle, µ-FTIR required the longest 

20 

 
time for analysis (12 min ± 9 min SD). Participants demonstrated good recovery for particles greater 
than 50 µm and excellent chemical identification for particles greater than 2
notable 
increases in accuracy and precision being possible following training and further method refinement. 
This work has formed the basis for the methods being applied for microplastics monitoring in DW in 
the State of California. 

Relevance  to  DWD  methodologies:  This  study  was  specifically  designed  to  evaluate  methods 
applicable for the monitoring of  DW and has utilised sample spikes, which were heterogeneous in 
composition,  density,  colour,  size  and  shapes.  Furthermore,  the  inclusion  of  non-plastic  materials 
which could result in possible false positives was an additional and relevant complicating factor which 
would be expected to occur in real-life samples. The number and size ranges of the microplastics 
used  were  realistic  considering  what  could  be  expected  to  be  recovered  by  filtration  from  larger 
volume sampling of DW. 

Method performance was highly dependent on particle size, with good recovery for particles >5
Both µ-FTIR and µ-Raman were effective at identifying microplastic particles and differentiating them 
from non-plastics but there were performance differences based on particle size. µ-FTIR could only 
µ-Raman  could  do  so  for 

issue could be of concern for monitoring DW systems since water treatment plants has shown to be 
42 and the primary target size relevant to health may 
effective only in filtering particles above 
be particles smaller than this size.  

It was concluded that both µ-Raman and µ-FTIR were accurate (>90%) in determining the nature and 
number of particles in the size fraction above 20 µm. When applied to particles in range 1-20 µm the 
method  using  µ-FTIR  showed  an  important  decrease  in  accuracy  and  recovery  to  around  30%.  In 
contrast, the method applying µ-Raman could maintain a good level of accuracy down to 1 µm. An 
important  additional  outcome  of  the  study  was  information  about  the  realistic  time  required  for 
sample analysis based on the experience of the participant laboratories. It was found that average 
analysis time per sample was 10 hours for µ-FTIR and 19 hours for µ-Raman. It was noted that time 
and time-related costs for all stages of microplastic sample analysis are currently barriers to routine, 
effective  monitoring.  Overcoming  barriers  will  require  new  approaches  for  automation  and 
incorporation  of  tiered  monitoring  that  uses  less  expensive  methodologies  for  screening  level 
questions. 

3.3  German Centre for Water Technology study for microplastics analysis 

in water samples  

This comparative study by Müller et al.31 from the German Centre for Water Technology (Technologie 
Zentrum Wasser, TZW) served as a first step to assess the suitability and comparability of the most 
frequently  used  analytical  techniques  in  microplastic  research  -  µ-FTIR,  µ-Raman  and  thermal 
decomposition  techniques.  Samples  comprised  up  to  five  different  types  of  microplastic  particles 
(PMMA, PVC, PET, PE, PS) with diameters ranging from 8 µm to 140  m suspended in ultrapure water. 
 one with a large-size 
The participants were supplied with two distinct  sample types  to  examine 
fraction ( 50 µm) and moderate particle 
-900 particles) of each type of polymer and 
one  with  a  small-size  fraction  (<50  µm)  and large  number  of  particles  (2000-11000)  from  three 
specific  polymer  types  (PMMA,  PS,  PE).  In  comparison  with  the  SCCWRP  study  (section  3.2),  the 
samples did not contain any  non-plastic materials, which could  give a false  positive response. No 
specific instructions were given to the participants and no factors were evaluated except the analytical 
techniques. Results from 17 laboratories from eight different countries were compared. Microscopy, 

21 

 
Fourier-transform  infrared  spectro-microscopy  ( -FTIR),  Raman  spectro-microscopy  ( -Raman), 
thermal-extraction-and-desorption or pyrolysis combined with gas chromatography coupled to mass 
spectrometry (TED-GC/MS and Pyr-GC/MS, respectively), scanning electron microscopy and the use of 
a particle counter were compared for total particle number, polymer type, number of particles and/or 
particle mass for each polymer type.  

Relevance to DWD methodologies: The organizers of the study have evaluated the results based 
on three features. First, identification of the polymer type, which describes the ability of a method to 
correctly determine the polymer type of a particle. Second, quantification of mass, which describes 
the relative deviation of a result from the theoretical mass content of microplastic particles in the 
sample. Third, quantification of total particle number and detailed particle number per polymer type.  

The overall outcome is summarised in Figure 9. 

Figure 9 Comparison of techniques performance. Results of technique comparison for identification of 
polymer type, quantification of particle mass, quantification of particle number per polymer type and 
quantification of total particle number. The average evaluation of each technique is indicated in the figure as 
insufficient (light blue), sufficient (dark blue) and questionable (both colours in different percentage). For 
acronyms see the relative list (page 66).  

Source: own production 

Identification 

-Raman and pyr-GC/MS for both size fractions but is 
-FTIR. Optical microscopy was effective in determining particle number in both size 
fractions but was not capable of distinguishing polymer types. The quantification of polymer mass 
for identified polymer types was evaluated as questionable for pyr-GC/MS and TED-GC/MS while the 
other  techniques  clearly  failed  to  determine  the  correct  polymer  mass.  Quantification  of  particle 
-FTIR in the large size fraction 
-Raman  it  was 
evaluated to be questionable for both size fractions. The quantification of total particle numbers with 
-FTIR was judged sufficient in both sizes with better overall performance being found for the small 
fraction.  -Raman  yielded  questionable  results  in  both  size  fractions.  Finally,  probably  the  most 
-FTIR  to  be 
important  result  for  DW,  the  quantification  of  particle  numbers  and  type 

and  questionable  in  the  small  size  fraction  (<50  µm)

22 

 
 
 
acceptable only for the larger size fraction while for the smaller fraction it was judged questionable. 
Surprisingly,  considering  the  good  performance  in  identifying  particle polymer  type,  -Raman  was 
judged to be questionable in both size ranges but this may be influenced by effects in the trial which 
are not related to the intrinsic capabilities of the technique.  

Overall, the suitability of a method strongly relates to the research question. µ-Raman for instance is 
a  highly  sensitive,  but  comparatively  slow  analytical  technique,  which  usually  requires  an 
extrapolation of measured particles as only a subarea of the filter area is  analysed.  -FTIR on the 
other hand might discriminate against small particles (< 2
particles in the same time period and thus may not require any or a smaller extrapolation factor. This 
-FTIR for total particle numbers and only mediocre 

-Raman for both size fractions.  

23 

 
 
 
4  Current activities in international standardisation  

It  is  widely  acknowledged  that  harmonization  and  standardization  of  analytical  methods  is  a  key 
requirement  for  the  field  of  microplastics  and  there  are  currently  a  number  of  activities  by 
standardization  bodies  or  similar  entities  around  the  globe.  In  the  following  sections,  the  current 
status on these activities is summarised. 

4.1  ISO activities relating to microplastics  

For the requirements of the DWD it would be advantageous to have the option of recommending a 
method or a set of methods which have already been through a rigorous international standardization 
procedure.  

In  recent  years,  efforts  have  been  made  to  develop  international  standards  in  the  area  of 
microplastics  and  a  number  of  projects  were  put  on  the  work  programme  of  the  International 
Organization for Standardization (ISO). A first output of this work  was 
Environmental  aspects 
subsequent  standard 
(ISO 24187:2023)44. 

43)  and  a 

Besides  such  general  guidelines,  three  projects45 47  have  recently  been  included  in  the  ISO  work 
programme that are relevant for the analysis of microplastics in drinking water (working titles as of 
February 2024): 

Water quality 
with low content of suspended solids including drinking water (ISO 16094-1)45 

 Analysis of microplastic in water 

 Part 1: General and sampling for waters 

Water quality 
for waters with low content of suspended solids including drinking water (ISO 16094-2)46 

 Analysis of microplastic in water 

 Part 2: Vibrational spectroscopy methods 

Water  quality 
waters with low content of suspended solids including drinking water (ISO 16094-3)47 

  Analysis  of  microplastic  in  water 

  Part  3:  Thermo-analytical  methods  for 

These standards are expected to be published by mid-2025 as part of a series of documents that 
may be extended by additional standards if needed. 

Already earlier, ISO started a series of standards on the collection of water samples from all kinds of 
sources, of which some are of importance to drinking water: 

ISO  5667-1:2023  Water  quality 
programmes and sampling techniques48 

  Sampling 

  Part  1:  Guidance  on  the  design  of  sampling 

ISO 5667-3:2018 Water quality   Sampling   Preservation and handling of water samples49 

ISO  5667-5:2006  Water  quality 
treatment works and piped distribution systems50 

  Sampling 

  Guidance  on  sampling  of  drinking  water  from 

It  is  planned  to  amend  this  series  of  standards  by  a  new  document  focussing  specifically  on 
microplastics: 

Water  quality 
(ISO 5667-27, working title as of February 2024)51 

  Sampling 

  Part  27:  Guidance  on  sampling  for  microplastics  in  water 

24 

 
 
 
A number of other ISO standards have been issued or are in preparation, which focus on the collection 
and  analysis  of  microplastic  fibres  that  are  shed  from  textiles  and  released  into  the  wash  water 
during laundering and therefore have less relevance for the determination of microplastics in DW.  

4.2  CEN activities relating to microplastics 

At  the  European  level,  the  European  Committee  for  Standardization  (CEN)  is  following  selected 
projects run at ISO to be prepared to incorporate, where relevant, published ISO standards into the 
European scheme of standards via the so-called Vienna agreement (a). 

In  this  context,  a  number  of  ISO  standards  relevant  to  microplastics  have  been  transposed  into 
European standards: 

EN ISO 24187:2023 

EN ISO 5667-1:2023 

EN ISO 5667-3:2018 

Likewise, the methodological draft standards of ISO mentioned in paragraph 4.1 have been taken up 
into the CEN work programme: 

prEN ISO 16094-1 

prEN ISO 16094-2 

prEN ISO 16094-3 

4.3  ASTM activities relating to microplastics 

At this time, there are no ASTM standards or test guideline specifically designed for the detection and 
quantification  of  microplastics  in  DW  but  there  is  relevant  documentation  available  regarding the 
sampling and sample treatment of a range of water types for subsequent analysis for microplastics, 
i.e.  

ASTM D8332-20: Standard Practice for Collection Of Water Samples With High, Medium, Or Low 
Suspended Solids For Identification And Quantification Of Microplastic Particles And Fibers28 

ASTM D8333-20: Standard Practice for Preparation of Water Samples with High, Medium, or Low 
Suspended Solids for Identification and Quantification of Microplastic Particles and Fibers Using 
Raman Spectroscopy, IR Spectroscopy, or Pyrolysis-GC/MS52 

These  standards  provide  for  the  collection  of  water  samples  and  the  sample  treatment  for  the 
determination and characterisation of microplastic particles and fibres. The procedures have been 
designed for the collection of samples from DW, surface waters, influent and effluent (secondary and 
tertiary) of wastewater treatment plants, and marine waters. While the procedures are not limited to 
these particular types of water, the applicability to other aqueous matrices must be demonstrated.  

(a) AGREEMENT ON TECHNICAL CO-OPERATION BETWEEN ISO AND CEN (Vienna Agreement), 

https://boss.cen.eu/media/CEN/ref/vienna_agreement.pdf 

25 

 
                                                 
 
The sample collection procedure D8332-20 describes in detail the use of a filter cascade to collect 
particulates  from  DW  using  an  apparatus  which  is  open  to  atmosphere  and  thus  risks  significant 
contamination from the surrounding environment. For DW applications where microplastics levels are 
normally  very  low,  a  closed  filtration  cascade  is  preferable  to  reduce  contact  with  the  local 
atmosphere to minimise airborne contamination.  

The  sample  preparation  procedure  D8333-20  covers  the  sample  preparation  of  collected  water 
samples  by  an  oxidation  with  hydrogen  peroxide  and  enzymatic  digestion  to  remove  interfering 
organic constituents. Such steps can be useful if the water to be investigated is known to have a high 
load of such compounds, but should normally not be necessary for DW. 

An additional  ASTM standard describes the preparation of reference samples that can be  used to 
support the evaluation of microplastic detection and imaging  techniques for a variety of matrices 
including DW: 

ASTM  D8402-23:  Standard  Practice  for  Development  of  Microplastic  Reference  Samples  for 
Calibration and Proficiency Evaluation in All Types of Water Matrices with High to Low Levels of 
Suspended Solids53 

4.4  National standardization bodies in Europe activities relating to 

microplastics 

The German national standardization organization (DIN) has issued Technical Specifications for the 
analysis of microplastics in food: 

DIN/TS 10068:2022-09 Food - Determination of microplastics - Analytical methods54 

This document explicitly excludes the application to tap water from its scope and thus has limited 
relevance for DW analysis. DIN has also provide a German translation of the ISO standard 24187, 
with title: Grundsätze für die Analyse von Mikroplastik in der Umwelt (DIN EN ISO 24187:2024-04).55  

The  French  national  standardisation  organisation  (AFNOR)  is  developing  a  standard  method  for 
analysing  microplastics  in  water  with  low  solids  content  such  as  domestic  DW,  groundwater  or 
commercially available bottled water (title translated into English):  

Water quality   Analysis of microplastics in water for human consumption and groundwater 
- Part 1: Method using vibrational spectroscopy (PR NF T90-600)56 

This method uses vibrational spectroscopy to identify and count particulates and forms the basis of 
the previously mentioned ISO project 16094-2 (see above). The timeline of the AFNOR project is not 
known. It is understood that the eventual availability of an equivalent ISO standard would supersede 
the French standard.  

4.5  VAMAS activities relating to microplastics 

Versailles Project on Advanced Materials and Standards (VAMAS) supports world trade in products 
dependent on advanced materials technologies, through International collaborative projects aimed at 
providing the technical basis for harmonized measurements, testing, specifications, and standards. 
VAMAS created a technical working area (TWA) on Micro and Nano Plastics in the Environment.57 In 
December 2022, the TWA launched an inter-laboratory comparison study, which had some relevance 
to DW, by using a well-defined mass of microplastics embedded in pressed pills. At this time, however, 
there has not been made public any output from this activity. 

26 

 
4.6  Current status of standardized methods applicable to the DWD 

At  this  time,  none  of  the  principle  international  standardisation  bodies  has  published  relevant 
standards  which  may  be  used  directly  or  which  can  be  adapted  to  the  need  of  establishing  a 
methodology for implementing article 13(6) of the DWD. As detailed previously in section 4.1, ISO 
initiated three projects relevant to DW in mid-2022. However, with a planned duration of three years, 
these may not deliver before mid-2025. Moreover, if ILC activities are undertaken as part of these 
projects, the duration may be further extended.  

27 

 
 
 
5  Microplastic definitions, descriptors and metrics    

The DWD does not provide a definition of microplastics. However, the specification of a measurement 
methodology  must  inevitably  contain  at  least  a  description  of  what  it  has  to  be  measured  and 
descriptors (properties) to be reported as output from any monitoring program. In addition, it will be 
necessary to establish a metric for the reporting. Such a metric would ideally be the most appropriate 
to risk assessment but may, in practice, be primarily a consequence of the analytical technique applied 
for detection and quantification.  

The scientific community has still to reliably demonstrate the existence of any specific hazards posed 
to humans by ingestion of microplastics. Consequently, it is not yet known exactly what are the most 
relevant properties to be reported as an outcome of the measurement procedure used in a monitoring 
program for DW. Despite the limited knowledge about effects and risks it will be necessary to consider 
the key descriptors and the following sections will outline key points from existing definitions.  

5.1  Microplastic definitions 

While it is very challenging to develop a comprehensive definition for microplastics, it is desirable to 
maintain consistency across EU legislation. Where possible and appropriate, it would be logical to give 
priority to the use or adaption of descriptors and terminology available in existing EU legislation or 
foreseen legislation which is at an advanced stage of development. Where this is not available or not 
appropriate, alignment with other national or international legislation or standardisation documents 
should be considered. 

5.1.1  REACH restriction 

The definition of a microplastic, which has been developed for the REACH restriction4, is probably the 
most advanced and comprehensive in use at this time and contains many elements, which may be 
used directly or suitably adapted for the implementation of the DWD. The most important aspects of 
this definition are quoted below. 

Microplastic means particles containing solid polymer, to which additives or other substances may 
have been added, and where the particles fulfil the following:4  

All dimensions of the particles are equal to or less than 5 mm or the length of the particles 
is equal to or less than 15 mm and their length to diameter ratio is greater than 3.  

Particles  containing  solid  polymer  means  either  (i)  particles  of  any  composition  with  a 
continuous solid polymer surface coating of any thickness or (ii) particles of any composition 

by weight.   

Polymer means a substance consisting of molecules characterised by the sequence of one or 
more types of monomer units. Such molecules must be distributed over a range of molecular 
weights wherein differences in the molecular weight are primarily attributable to differences 
in the number of monomer units. (b) 

(b)  see no. 5 in article 3 of the REACH Regulation (EC) No. 1907/2006. 

28 

 
                                                 
 
It is to be noted that the definition of the REACH restriction does not specify a lower size dimension 
but stipulates that single molecules are not particles. Instead, the regulation sets a pragmatic size of 
0.1 µm (0.3 µm for fibres) to be the lower size limit of microplastics for the purpose of enforcing the 
restriction under the condition that a quantification cannot be done by available analytical methods 
or accompanying documentation. Another aspect of the proposed legislation is the exclusion of certain 
specific categories of polymers: 

Natural polymers 
place in nature and where these polymers have not been chemically modified. 

 polymers that are the result of a polymerisation process that has taken 

Biodegradable polymers   polymers that are (bio)degradable in accordance with tests specified 
in the text of the restriction.  

Water  soluble  polymers 
  polymers  that  have  a  solubility  in  water  greater  than  2  g/L  as 
determined according the tests specified in the text of the restriction (referring to OECD Test 
Guidelines 10558 and 12059).  

Inorganic polymers   polymers that do not contain carbon atoms in their chemical structure. 

5.1.2  Marine Strategy Framework Directive (MSFD) 

The Marine Strategy Framework Directive (MSFD, Directive 2008/56/EC)60 

litative descriptors 

The annex in Commission Decision 2017/84861 (Descriptor 10) sets criteria among which is micro-

-litter (particles < 5 

persistent, manufactured or processed solid material that is discarded, disposed of, or abandoned in 
62).  

In  the  context  of  the  MSFD,  microplastics,  even  though  not  explicitly  referred  to  as  such,  are 
considered as a specific type of litter in the form of solid and persistent particles below a size of 
5 mm (largest dimension) made of artificial polymer materials. No lower size limit is considered, but 
for monitoring the lowest size is normally determined by the sampling procedure, including capturing 
device (usually some sort of net). The European MFSD Working Group on Good Environmental Status, 
in collaboration with JRC, has published a 
(JRC83985)63 which, for generic microlitter, recommends using an upper size limit of 5 mm for the 
largest dimension of the particles even though this is not explicitly stated in Commission Decision 
2017/84861.  Additionally,  it  divides  plastic  litter  into  four  dimension  classes  based  on  biological 
relevance  and  analytical  limitations:  macroplastics  (>25 mm),  mesoplastics  (5  to  25  mm),  large 
microplastics (1 to 5 mm), and small microplastics (20 
With reference to the two classes 
of microplastics the authors rationalize separating them into two sub-fractions (small and large) due 
to the relative ease of separating and quantifying visually recognizable 1-5 mm particles compared 
to the more technically challenging aspects of pa
 in size. The upper 
limit of 5 mm is also consistent with the upper limit of micro-litter (including microplastics) specified 
in the more recent Commission Decision (EU) 2017/84861 used for the implementation of the MSFD60 
of the European Parliament and of the Council of 17 June 2008. 

Regarding  the  measurement  of  micro-litter  (including  microplastics),  the  Commission  Decision 

29 

 
(m²) for surface lay

. 

5.1.3  ISO  

ISO has recently started to provide definitions relating to microplastics (see ISO/TR 21960:202043):  

Microplastic   any solid plastic particle insoluble in water with any di

. 

Large microplastic   any solid plastic particle insoluble in water with any dimension between 
1 mm and 5 mm. 

Nanoplastic   

  1  mm  and 
This  way,  ISO  has  chosen  to 
 5 mm) instead of the more commonly used single range with an upper boundary of 5 mm.64 
1 mm 
For the ISO 
 rubber is not included and that 
the  defined  dimension  is  related  to  the  longest  dimension  of  the  particle  (but  strangely  not  for 

size  classes  (1  µm 

should apply). Like this, there are a number of differences between the ISO terminology and that of 
some  other  pre-existing  practices  by  national  (NOAA)64,  international  bodies  such  as  the  United 
Nations65 and the European Commission61 and the REACH restriction (see paragraph 5.1.1). 

Further related terms are defined with reference to the general ISO standard on Plastics Vocabulary 
(ISO 472:2013)66 in the same document as follows: 

Polymer   chemical compound or mixture of compounds consisting of repeating structural 
units created through polymerization and in practice above 10,000 Dalton. Polymers comprise 
both plastics and elastomers.  

  material  which  contains  as  an  essential  ingredient  a  high polymer  and  which,  at 
Plastic 
some stage in its processing into finished products, can be shaped by flow. Plastics consist 
mainly polymers and minor contents of additives. Plastics comprise both thermoplastic and 
thermoset materials (but not elastomers like rubber).  

Thermoplastic   plastic that has thermoplastic properties.  

Thermoset   plastic which, when cured by heat or other means, changes into a substantially 
infusible and insoluble product.  

Elastomer   macromolecular material which returns rapidly to its initial dimensions and shape 
after  substantial  deformation  by  a  weak  stress  and  release  of  the  stress  (examples  of 
elastomers are rubber and synthetic rubber). 

By  defining 
as  plastic  particles,  these 
definitions exclude elastomeric polymers and consequently would not consider particulates of rubber 
 a major component in the total quantity of man-made polymer 
resulting from vehicle tyre wear 
particles released to the environment.    

30 

 
 
 
 
5.1.4  Legislative by State of California 

For the purpose of testing DW for microplastics in the United States - State of Southern California   
the following definition was adopted67: 

additives or other substances may have been added, which are particles which have at least 
three dimensions that are greater than 1 nm and less than 5,000 micrometers (µm). Polymers 
that are derived in nature that have not been chemically modified (other than by hydrolysis) 

polymer surface coating of any thickness, or (ii) a particle of any composition with a synthetic polymer 

consisting of molecules characterized by the sequence of one or more types of monomer units. Such 
molecules must be distributed over a range of molecular weights wherein differences in the molecular 
weight are primarily attributable to differences in the number of monomer units. A polymer comprises 
the  following:  (a)  a  simple  weight  majority  of molecules  containing  at  least  three  monomer  units 
which are covalently bound to at least one other monomer unit or other reactant. 

5.2  Descriptors for microplastics 

Microplastics monitoring under the DWD should allow the production of inter-comparable data about 
the  microplastics  effectively  present  in  DW  in  the  EU  Member  States.  To  achieve  this,  relevant 
descriptors of microplastics in DW must be established. The following sub-sections outline the most 
commonly  cited  descriptors  for  microplastics  with  consideration  being  given  to  their  possible 
relevance to any interactions with biological systems. 

5.2.1  Polymer type  

At  this  time,  there  is  no  clear  evidence  about  whether  the  type  of  polymer,  which  a  microplastic 
particle is composed of, has an influence on any adverse biological response. However, knowledge of 
the polymer type(s)  of microplastic particles present in DW may  have relevance in identifying the 
origin of microplastic contamination in the supply chain and verifying effects of any remedial action. 
In addition, some types of plastic tend to contain additives more harmful than plastics. 

Considering the results of the literature review regarding the types of polymers most often found in 
DW (see paragraph 2.4.2), the following types seem to be of highest relevance:  polyethylene (PE), 
polyethylene terephthalate (PET), polyester other than PET (PEST) and polypropylene (PP). 

Biodegradability 

In  the  definition  of  microplastics  developed  for  the  REACH  restriction  (see  paragraph  5.1.1), 
biodegradable plastics are specifically excluded as the objective of this action is to reduce the release 
to the environment of persistent polymers, whose lifetime is measured in years or decades rather 
than in months as in the case of biodegradable polymers. In the DWD the exclusion of such materials 
in monitoring is probably not justified as their ability to break-down more rapidly does not necessarily 
reduce the risk of provoking undesirable biological responses when ingested. In fact, there is little 
information to indicate whether man-made biodegradable polymer particles are more or less harmful 
than  persistent  plastics  when  ingested  nor  is  their  in-vivo  degradation  behaviour  known.  In  the 

31 

 
 
absence of relevant toxicological data the application of the precautionary principle would justify also 
reporting such polymers once identified in DW.  

Solubility 

Solubility, although a factor considered in relation to the REACH restriction, is probably not a relevant 
factor for microplastics in DW. Water soluble polymers, assuming the normal practice of sampling by 
filtration, should not normally be recovered from the DW supply network, however it should be noted 
that such polymers may interact with other chemical species in the water to form insoluble composite 
particles. In the case that such particulates are identified they should be included in the reported data. 

5.2.2  Particle size  

The size range which defines a microplastic is first to be considered in terms of the upper size limit 
and  in  this  it  would  be  advantageous  to  harmonise  it  with  existing  legislation  and/or  commonly 
accepted scientific conventions. On this basis, it would be reasonable to consider microplastics in DW 
to be the particles that have all dimensions less than 5 mm or 15 mm if the length-to-diameter ratio 
is above 3, as applied by the relevant REACH restriction (see paragraph 5.1.1).  

In  contrast  to  the  relative  simplicity  of  establishing  a  suitable  upper  size,  there  remains  much 
 intrinsically imply a limitation 

 1000 µm, 

of the size range to 1 
cover particles up to 5 mm as well as sub-micron sized particles or even nanoparticles. Although the 
presence  of  secondary  microplastics  (i.e.  microplastics  originated  from  the  degradation  of  bigger 
plastic items) with sizes down to the low micron range has been amply demonstrated, the limitations 
of  analytical  techniques  and  the  complexity  of  reliably  extracting  smaller  particles  from  real-life 
sample matrices  has  impeded  progress  with  smaller  sub-micron  or  nano-plastics.  As  the  issue  of 
these plastic pollutants has become more studied and technology has advanced, a growing body of 
evidence suggests the presence of sub-micron plastics in environmental samples, which presumably 
derive from degradation of larger particles. It would therefore be a logical precautionary measure to 
consider microplastics to extend below 1 µm. Furthermore, as it is not yet clearly known how particle 
size influences biological responses in vivo, there is no clear evidence which can help to establish any 
lower size limit on a health risk basis. It would therefore be reasonable to maintain harmony with the 
REACH restriction (see paragraph 5.1.1) and not impose any lower size limitation on what constitutes 
a microplastic in the context of the DWD. 

As mentioned above (see paragraph 5.1.1) the REACH restriction, instead of specifying a lower size 
dimension, sets a pragmatic size of 0.1 µm (i.e. 100 nm) to be the lower size limit of microplastics for 
the  purpose  of  enforcing  the  restriction.  This  lower  size  has  been  proposed  as  it  is  currently  not 
possible  to  characterise  or  identify  smaller  microplastics  by  existing  analytical  techniques  or 
accompanying documentation. It should be noted that although current state-of-the-art technology 
could potentially identify man-made polymer particles of size as low as 100 nm68 70 the measurement 
procedures  and  equipment  required  are extremely  specialised  and  with  complexity  and  costs  that 
cannot be realistic options for routine monitoring by water suppliers and official control laboratories.  

In the case of the DWD, the same approach of specifying pragmatic fit-for-purpose lower limits for 
implementation could be adopted as well. However, in this case, the limits must not be  based on 
considerations  of  what  is  technically  possible  with  state-of-the-art  instrumentation  and  one-off 
samples.  Instead,  it must consider  practical  sampling  procedures  and  analytical  techniques  which: 
i) are widely available commercially, ii) have known demonstrated capabilities and iii) permit levels 
of throughput and costs per sample which are acceptable for widespread monitoring. On this basis, it 

32 

 
would not be reasonable to consider a lower limit of 100 nm for reporting, but rather a more realistic 
lower size of around 20 µm, which would be compatible with the detection and throughput limitations 
of analytical techniques based on optical microscopy techniques.71   

It should be noted though that particle size is not an intrinsic limitation with the mass based thermo-
analytical techniques, but rather with the sampling process where large volumes of water have to 
pass through fine filters for the collection of microplastics. If smaller particles are to be retained for 
analysis, then a finer filter must be used and this, firstly, limits the speed of filtration and, secondly, 
the volume which may be processed due to rapid clogging of the filter.  

5.2.3  Shape 

The  shape  of  microplastic  particulates  is  a  potentially  relevant  parameter,  which  could  have  an 
influence on the interaction with living systems. At this time, no widely accepted way of categorising 
particle shape is known but a simple, minimum requirement could be to classify as particles or fibres 
based on their aspect ratio as follows:  

  Particles   particulates of any shape, including pseudo spherical or irregularly shaped frag-

guish them from fibres. 

  Fibres   particulates, of which the length to diameter ratio is >3. 

Such a categorisation would be practical only in the case of using optical microscopy-based methods, 
such as fluorescence microscopy, µ-FTIR or µ-Raman.  

5.2.4  Colour 

In an environmental context, the colour of a particle may influence the tendency for fauna to ingest 
the particles through aspects of feeding instincts. However, in the context of monitoring microplastics 
in DW, reporting the colour of the particles may be of limited value. Still, it may have a relevance in 
helping tracing the origins of particulates. 

5.2.5  Surface chemistry 

Surface  chemistry  is  likely  to  be  a  factor  influencing  the  behaviour,  stability,  fate  and  biological 
activity  of  microplastic  particles,  but  at  this  time  a  link  to  hazard  or  risk  from  DW  has  not  been 
established. Currently, the technology and knowledge required to obtain relevant data about particle 
surface chemistry would add complexity, analysis time and cost which cannot be easily justified for 
monitoring of DW.  

5.3  Metrics for reporting 

The  quantity  of  microplastics  present  in  a  sample  of  DW  may  be  reported  in  two  principal  ways 
depending on the analytical techniques used for particle detection and quantification. In the case of 
the  spectroscopy-based  techniques,  the  particles  are  analysed  one-by-one  and  consequently 
microplastic  content  would  be  reported  as  number  of  particles  identified  as  microplastic  per  unit 
volume of sampled water. In the case of the thermo-analytical techniques, the result obtained is the 
mass of detected polymers present in a sample and consequently the reported data would be the 
mass per unit volume of sampled water.  

33 

 
  
As noted previously, the current knowledge about possible effects of microplastics on human health 
is  extremely  limited  and  consequently  it  is  not  yet  known  which  would  be  the  scientifically  most 
relevant metric to be used for reporting. In case the effects on biological systems, including humans, 
depend on the particulate nature of microplastics, their number and size seem important and thus a 
number-based  metric  should  be  chosen.  In  case  the  effects  of  such  particles  rather  derive  from 
substances  that  a  microplastic  particle  contains  (besides  the  polymer  itself,  also  additives  and 
potential residual monomers) and which can be released once ingested or taken up into the organism, 
the  mass  metric  may  become  more  relevant.  For  biological  effects  that  are  triggered  by  agents 
-area  appear  to  be  the  appropriate  metric. 
Thornton-Hampton  et  al.  (2022)72  analysed  the  issue  by  linking  the  measurement  metric  and  the 
toxicological effect/mechanism. They recommend to determine both number and mass concertation, 
but  also  highlight  that,  depending  on  the  specific  effect  mechanism,  other  metrics  (e.g.  volume, 
surface area) may be more informative. However, in the absence of relevant knowledge about the 
determinants  for effects on  biological  systems,  the  reporting metric  should be  determined  by  the 
analytical technique(s) used.  

It should be noted though that some degree of mathematical interconversion from a number-based 
to a mass-based metric is theoretically possible using assumptions about particle shape and density. 
However, the reliability of such procedures could not be successfully proven so far.31 

Considerations  on  the  analytical  techniques  that  can  be  used  for  detection  and  quantification  of 
microplastics in DW are described below (section 7). 

5.4  Descriptors and metrics suitable for microplastics in drinking water 

Due to the lack of knowledge about the risks of microplastic to human health and about which of 
their properties would be decisive, the descriptors and metrics for monitoring of microplastics in DW, 
at present, have to be set largely according to practical considerations. Considering the existing (legal) 
definitions the following aspects are deemed relevant for DW monitoring: 

  The metric for reporting (number or mass of particles) will depend on the technique chosen 

for quantification of the microplastics in DW. 

  An  upper  size  limit  of  5  mm  would  align  with  existing  legislative  provisions  in  Europe 
(REACH,  MSFD)  and  elsewhere  (United  States  -  State  Southern  California)  as  well  as 
commonly used practices reported in the literature.  

  A lower size limit for monitoring purposes, defined by practical considerations (pore size of 

filter used and limitations of analytical techniques), would probably be around 20 µm. 

 

 

Ideally, the type of polymer should be determined in order to support identification of the 
origin of microplastic contamination in the supply chain and verification of remedial actions. 
In case of need, the focus of analysis could be put on those polymers that have been found 
predominantly in DW so far. 

In terms of shape, it seems sufficient to distinguish two types of particulates according to 
the 
of shape is 
only possible if microscopy-based methods (e.g. fluorescence microscopy, µ-FTIR, µ-Raman) 
are used for particle identification. 

less relevance for DW or/and require complex analysis technique(s).  

34 

 
 
6  Sampling and sample treatment  

The levels of microplastics in  DW are expected to be very low (see paragraph 2.5) and  cannot be 
detected directly in the water by any existing analytical technique. To overcome this problem, larger 
volumes  of  water  must  be  collected  and  concentrated  (e.g.  by  filtering)  to  have  enough  material 
available for analysis, thus ensuring valid measurement values.  

In  practice,  any  method  for  monitoring microplastics  in  water  will  comprise  various  steps:  sample 
collection (sampling), sample treatment (including filtration), determination (detection, identification 
and quantification) and data processing. At this time, there have been few reports specifically relating 
to sampling or/and sample treatment of DW. The following sub-sections summarise the key aspects 
of sampling and sample treatment which are judged to be most relevant to DW.   

6.1  Sampling requirements of drinking water 

At present, the low levels of microplastics occurring in DW cannot be detected directly by any existing 
analytical  technique.  Consequently,  normal  practice  requires  that  an  appropriate  volume  of  water 
would be passed through filters to collect and concentrate all suspended particulate material above 
a size which is defined by the cut-off of the filter. Because of the very low expected concentration of 
microplastics in DW, collecting large (  1 m3) sample volumes seems to be the only reliable way to 
extract enough microplastic particles to stay above the quantification limit of existing methods, as 
reported in published literature.18,73 In addition, to mitigate the usually high measurement uncertainty 
(see  above,  e.g.  paragraphs  2.4  and  3.1)  and  the  omnipresent  risk  of  contamination  from  plastic 
particles present in the surrounding environment during sampling or processing (see above and in 
particular paragraph 2.4.5), large sampling volumes are likewise advisable. Consequently, the ASTM 
standard D8332-2028 published in 2020 describes procedures to recover microplastics from a range 
of different types of water and, for DW, recommends a minimum sample volume of 1.5 m3. 

The filtration devices applied in the literature for this volume range are all in-house constructed flow 
 with the common feature being the use of stainless steel filters. This material 
through solutions 
has the advantage to be chemically and mechanically resistant, plus it supports the  re-generation 
and multiple use of the filters.  

Annex A summarises the sample treatment strategies applied by various groups6,7,9 11,14 26,74 89 in the 
analysis of DW (tap water and bottled water) highlighting the relationship between sampled volumes, 
applied  filter  pore  sizes,  filter  materials,  sample  treatment  protocols,  and  expected  types  of 
contaminants.  The published  papers considered in this summary  include  the ones already cited in 
Section 2 plus a number of articles that were considered relevant in terms of approaches used for 
sample collection, treatment and analysis. The collected information shows that in all of the cases, 
where  the  sample  volume  exceeds  10 L,  the  primary  particle  collection  and  final  analysis  were 
performed on separate filters. Though the transfer from one filter to the other might lead to particle 
loss and thus affect recovery, it allows the use of filter materials that are compatible on the one hand 
with the conditions of sampling (in particular of pressure) and sample treatment that would be harsh 
and on the other hand with optical properties suitable for the analysis by OpMic, FluoMic, SEM, µ-FTIR 
or µ-Raman.  

Literature data confirms that methods using larger sample volumes (thus not only collecting a higher 
number of microplastics but also more matrix particles) involve in general more sample treatment 
steps before proceeding with the particles  detection and quantification.  

35 

 
6.2  Sample treatment 

Sample  treatment  serves  to  concentrate  the  targeted  particles  and  may  be  needed  to  reduce  or 
remove compounds present in the samples that may interfere with the detection and/or quantification 
of the target analytes, i.e. the microplastic particles. The selected procedure mainly depends on the 
type of matrix, the sampled volume and the technique(s) used for detection and quantification. 

Among processes collecting lower sample volumes (<10 L), sample treatment often consists only of 
filtration or staining and filtration, but the analysis of microplastics in samples collected from very 
large (>1000 L) volumes may not be possible without pre-treatment to remove or reduce the amount 
of non-plastic particles. This is in line with the conclusions of the article of Koelmans et al.73 which 
foresaw different sample volumes and suggested various treatment strategies depending on sample 
types. Figure 10 shows the most commonly applied procedures for DW sample treatment.  

Figure 10 Sample treatment procedures mentioned in the 37 publications examined and summarised in 
Annex A 

Source: own production 

Among the techniques available for microplastic analysis, number counting approaches are expected 
to be more sensitive to non-plastic matrix constituents, while for example pyr-GC/MS is less strongly 
influenced.  For  the  latter,  however,  some  organic  matrix  components  that  produce  similar 
decomposition products as polymers might become a source of error during data evaluation. Inorganic 
particulates,  such  as  sand,  do  not  have  considerable  effects  on  the  results.  However,  microscopic 
analysis (by  µ-FTIR,  µ-Raman,  FluoMic)  can  be  difficult if  filters  are  overloaded  with  particles  and 
result in very long (and thus impractical) measurement times. In addition, particles covered by other 
materials might be impossible to be identified spectroscopically or the formation of aggregates might 
bias size measurements. 

36 

 
 
 
Various sample treatment steps can be applied to decrease the amount of non-plastic particles. The 
liquid sample can be treated directly or the particulate material collected on a filter is treated in situ 
or after being re-suspended in a lower volume (Figure 11). The first step in the treatment of collected 
particulates  is  typically  the  removal  of  organic  materials  and  minerals,  sometimes  followed  by  a 
density separation step.90 Finally, the resulting particles are collected on a filter that is compatible 
with  the  detection/quantification  technique.  Designing  the  sample  treatment procedure(s)  requires 
careful consideration of the sample matrix.91,92 Freshwater samples or samples from the inlet of water 
treatment plants contain higher amount of organic materials (including algae, bacteria) and minerals 
(e.g. sand) compared to DW from underground sources, tap water or bottled water. For more complex 
samples, the application of multistep sample treatment 
 or low volume 
samples  only  one  step  might  be  sufficient  or  not  necessary  at  all.  In  contrast,  applying  multiple 
treatment steps might result in microplastic particle loss and thus reduced recovery. 

Figure 11 Schematic drawing on sample treatment strategies (arrow width symbolises the popularity of the 
strategy among the analysed literature sources, see Annex A) 

Source: own production 

Treated drinking water, mineral water and bottled water have usually low concentration of organic 
contaminants, but may  contain  a high concentration of minerals  such as calcium and magnesium 
carbonate,  other  calcium  and  magnesium  salts,  iron  oxides  and  precipitates  from  flocculation 
processes. These components are often suggested to be removed by treatment with inorganic acids 
(hydrochloric acid HCl, sulphuric acid H2SO4).8,10,16,18,79 However, as acid treatment is known to affect 
the recovery of some polymer types (such as PA and PET), more gentle solutions, like the application 
of  organic  acids  (acetic  acid,  citric  acid)  or  ethylenediaminetetraacetic  acid  (EDTA)  were  also 

37 

 
 
 
suggested.13,74,83 In case a treatment step needs to be used that may have an impact on the recovery 
of some polymer, the latter could be excluded from the reporting. 

The most frequently applied digestion procedure, described in the literature for water samples, was 
oxidative  treatment  with hydrogen  peroxide  (H2O2), in  some  cases  in  the  presence  of  ferrous ions 
(Fenton  reagent). The applied H2O2 concentration varied substantially from low percentages up to a 
concentration of 35%; temperatures and treatment times were also very diverse.93 With all variables, 
a highest applicable temperature of 60 °C seems to be accepted by most authors. The iron catalyst 
added  to  H2O2  might  improve  digestion  efficiency  and  decrease  treatment  times,  providing  good 
recovery for the majority of polymer types, but might attack some others, such as cellulose acetate 
(CA).94 

Enzyme digestion is specific to the organic substance(s) to be decomposed and is considered to be 
the  gentlest  among  the  various  types  of  digestion,  preserving  polymers  and  particle  integrity. 
However, it is linked with higher cost than other treatment options, especially if performed with highly 
purified enzymes.  

Other  (non-digestive)  sample  treatment  steps,  included  treatment  with  organic  solvents  such  as 
ethanol (EtOH) or hexane and various detergent solutions10,13,16,18,26 as well as sonication and density 
separation.17,19,23,25  These  are  not  supposed  to  cause  a  chemical  reaction  (decomposition)  of  the 
non-plastic  components,  but  rather  to  separate  them  based  on  hydrophobicity,  density  or  due  to 
physical forces. Mild solvents can remove adsorbed layers of contaminants from the surface of the 
particles thus for example decreasing the possibility to conceal the signal of polymers by fluorescent 
contaminants in Raman spectroscopy. Detergent solutions can help to reduce particle attachment to 
the  surface  of  filtration  apparatus/funnel,  to  supress  particle  aggregation  and  to  create  a  better 
distribution of particles on the filter surface. EtOH is also applied in some cases to reduce foaming 
during filtration in the presence of detergents.  

Sonication is a physical treatment that is applied to remove contaminants adsorbed to the particle 
surface, to disassemble particle aggregates and to detach particles from the filter surface, especially 
from  woven  mesh  filters  where  particles  might  get  trapped  in  the  filter  structure.  The  aid  for 
detachment from a filter surface is particularly useful, for example, if particles need to be transferred 
to  another  filter  (see  above).  However,  sonication  might  also  affect  particle  size  and  shape  by 
destroying larger particles and generating smaller ones. In fact, sonication is also a procedure that is 
used  to  generate microplastic  particles  from  larger plastic  objects.  As  an  alternative to  ultrasonic 
treatment,  the  application  of  (filtered)  compressed  air  was  described  to  facilitate  the  removal  of 
collected particles from the filtration device.10 

When it is desired to mechanically separate plastic particles, which are typically low-density materials, 
from  higher  density  inorganic  particles  (like  sand),  density  separation  is  commonly  used.  In  this 
procedure, the mixture of particles is placed in a liquid of intermediate density   prepared with a salt 
solution   which is then allowed to stand untouched until the less dense plastic material floats and 
separates out from the more dense inorganic material which sinks. This is usually performed in a 
cylindrical shaped vessel equipped with a central valve that 
 physically divides the 
denser inorganic material, which sediments to the bottom, from the lighter (microplastic) particles 
that floats to the surface.   

 after closing 

Because  microplastics  does not refer to a single material, but covers a group of polymers with a 
range of chemical  and physical properties and  includes particles in a wide size range, the sample 
treatment and evaluation of recovery after it is not a simple task. Chemicals used for digestion of 
matrix  particles  will  attack  different  plastics  to  a  different  extent,  and  might  shift  also  the  size 

38 

 
distribution of the particle population by consuming smaller particles - that have higher surface area 
- faster. Therefore, careful evaluation of recovery practices would be needed, but recovery values are 
rarely  published.  However,  some  reported  values  look  to  be  encouraging  (>80%)  regarding  the 
sampling of larger volumes. Lower (<80%) recovery values might be attributed to incomplete particle 
recovery from the stainless steel cartridge or to the use of too harsh sample treatment procedures, 
such as the application of chemicals like hexane or concentrated HCl.18,74   

In practice, there is no single generic method or combination of methods which can be universally 
recommended for treating solids collected from DW as the sample composition will depend on its 
origins and treatment prior to reaching the collection point. The preceding discussion highlight some 
of  the  steps  which  can  be  taken  but  the  decision  of  which,  if  any,  should  be  applied  must  be 
determined by the analyst based on knowledge about the sample and prior experience.    

39 

 
 
 
7 

Instrumental techniques to detect and quantify microplastics  

In practice, water samples may contain only low concentrations of microplastics besides particles of 
natural  organic  matter  or  minerals.  This  mixture  of  materials  means  that  any  relevant  analytical 
technique  must  be  able  to  unambiguously  distinguish  the  man-made  polymers  from  the  other 
particulate material.  

The scientific literature reporting the analysis of microplastics in various matrices is extremely broad 
and many instrumental techniques have been reported as having been applied to characterise a range 
of microplastics properties. However, for the specific application of monitoring microplastics in DW   
considering  specificity,  sensitivity,  availability,  validation  status,  cost  and  throughput -  the  viable 
options can be reduced to three, which are briefly described below.  

The first and generally  simplest technique, fluorescence microscopy (see  paragraph  7.1), relies on 
preferentially staining microplastics with a dye which i) absorbs well to hydrophobic materials such 
as  plastics  and  ii)  can  be  seen  to  fluoresce  when  illuminated  by  an  appropriate  light  source. 
Fluorescence  microscopy  can  provide  information  on  number,  size  distribution  and  shape  of  the 
stained particles. 

The  second  category  of  techniques  is  based  on  spectro-microscopy  (see  paragraph  7.2),  which 
combine optical microscopy to visualise particles with Infra-Red spectroscopy or Raman spectroscopy 
as  a  means  to  identify  the  composition  of  individual  particles.  By  these  techniques  normally 
particle-by-particle analysis is performed in combination with optical imaging and they can directly 
provide information on particle number, size distribution, shape and chemical composition.  

The  third  category  covers  thermo-analytical  techniques 
(see  paragraph  7.3)  based  on 
gas-chromatography  mass-spectrometry  (GC/MS)  which  permit  the  identification  and  mass-based 
quantification  of  plastic  materials  but  cannot  directly  provide  any  information  on  particle  size, 
morphology and number.  

Annex  B  reports  a  summary  of  the  key  aspects  of  these  instrumental  techniques  for  a  better 
comparison  of  principle,  price,  analysis  time  and  information  that  can  be  obtained  from  a  single 
analysis.  

It should be added that the scientific literature contains reports on the use of a small number of other 
techniques  such  as  scanning  electron  microscopy  (SEM,  combined  with  X-rays,  fluorescence  or 
cathode-luminescence),95  single  particle  extinction  and  scattering  (SPES)96,97  and  chromatographic 
techniques,  like  high-performance  liquid  chromatography  (HPLC).98 102  However,  none  of  these 
techniques will be considered further as they are either unable to specifically identify polymers (SEM, 
SPES)  or  are  limited  to  specific  plastic  compositions  (HPLC)  and  are  therefore  not  suited  for  a 
generalised application.  

7.1  Fluorescence microscopy 

Fluorescence microscopy (FluoMic) is a rapid screening technique of microplastics with more accuracy 
than simple visual inspection by optical microscopy, without the need of an expensive apparatus.103,104 
FluoMic  exploits  the  peculiar  properties  of  fluorescent  molecules  (fluorophores)  which  have  the 
capacity to absorb light energy and emit light at longer wavelength after few nanoseconds.105,106 The 
microscope apparatus is built with an excitation light source and a system of filters able to remove 
the signal coming from the source itself and to select the desired range of emission wavelengths. In 

40 

 
 
this way it is possible to discharge the signals coming from non-fluorescent objects or materials that 
emit at different wavelengths.105,106  

In the field of microplastic investigation, FluoMic has gained consideration since Andrady107 suggested 
the  use  of  the  Nile  Red  (NR)  dye  to  stain  particles  coming  from  environmental  samples.  NR  is  a 
hydrophobic, water insoluble dye previously used to visualize hydrophobic organic components, such 
as lipids or vesicles.103 Due to its hydrophobic properties, this molecule tends to preferentially adsorb 
on the surface of plastic particles thanks to van der Walls interactions or dipole interaction in the case 
of  polar  polymers.103,104,108  The  preferential  absorption  of  the  dye  on  plastic  with  respect  to  more 
hydrophilic  materials  (for  instance,  mineral  particles)  means  that  when  illuminated  with  an 
appropriate  light  source  the  resulting  fluorescence  permits  discrimination  between  plastic  and 
non-plastic particles.  

In the last 5 years, a series of other molecules have been also tested to stain the plastics or the 
organic residues present in the samples, with different results. The list includes molecules that are 
water soluble (i.e. Eosin B, Rose Bengal, Acridine Orange, Basic Blue 24, Crystal violet, Lactophenol 
Blue, Neutral Red, Safranin T, Tryphan blue, Rhodamine B, Fluorescein isothiocyanate, methylene blue, 
Rhodamine  6G)  or  insoluble  (i.e.  NR  and  NR  derivatives,  oil  red  ENG,  Hostasol  Yellow  3G, 
fluorescein).94,103,104,108 110  More  recently,  also  pyrene,  1-pyrenebutyric  acid  N-hydroxysuccinimidyl 
ester (PBN) and a new probe based on perylene-diimide,111 113 as well as white light emitting stanene-
oxyboride  (SnOB)  nanosheets  were  evaluated.114  However,  from  the  different studies NR  emerges 
presenting advantages with respect to other dyes, in terms of higher affinity for microplastic particles, 
reduced  staining  time,  and  lower  toxicity.94,104,108,109  Research  articles  on  the  application  of  NR  in 
microplastic investigation have been constantly increasing during the last few years.  

Some  capability  of  FluoMic  to  differentiate  between  (some  of)  types  of  plastic  via  differences  in 
fluorescence by use of NR has been reported.108,115 The dye adsorbed onto the surface of different 
polymers was shown to have slightly different colour depending on the polarity of the polymer, which 
is associated to exhibiting some differences in emission spectra. However, this approach is not well 
investigated and thus its reliability is uncertain. Due to the findings that NR may also stain natural 
polymers in environmental samples (e.g. particulates made of wood, cotton, shells), it can be assumed 
that FluoMic can lead to an overestimation of the presence of microplastics, if other organic matter 
is present.108,116,117 On the other hand, some polymers may  not be detected by FluoMic due to the 
staining being too weak or failed completely.117,118 Such flaws could potentially be avoided by carefully 
choosing  the  staining  and  measurement  conditions  as  well  as  an  appropriate  sample  treatment 
approach with the aim to remove/reduce the interfering organic matter. However, the authors of this 
report  are  not  aware  of  any  comprehensive  investigation  of  such  aspects  or  validation  of 
corresponding procedure(s). 

In  general,  after  sample  treatment,  FluoMic  can  be  used  as  screening  technique  for  microplastic 
investigation, and it is often applied for preliminary investigation of the entire sample, while only a 
portion  undergoes  to  further  evaluation  such  as  polymer  recognition  by  vibrational  microscopy 
techniques (see also paragraph 8.5).  

7.2  Spectro-microscopic techniques using IR and Raman  

Spectro-microscopic techniques allow not only the counting, sizing and morphological characterisation 
of particles collected on a filter but, in contrast to FluoMic, can also identify the chemical composition 
of individual particles   within limitations that are specific to the technique and the instrument used. 
(FTIR) 
The 

techniques  are  Raman  and  Fourier-transform 

two  most  applied 

infrared 

41 

 
spectro-microscopy with various commercial instruments available on the market. The expected limit 
of detection (LOD) of these techniques regarding detectable particle number is lower (i.e. better) than 
that for mass quantification techniques such as pyr-GC/MS. While spectro-microscopic techniques are 
supposed to be able to detect even a single 20 µm microplastic particle on a filter, the mass of a 
particle like this is below the expected LOD of pyr-GC/MS.119 On the other hand, other (non-plastic) 
particles  present  in  the  water  matrix  might  interfere  stronger  with  the  quantification  by 
spectro-microscopic 
techniques.  Additionally,  data 
collection - and in some cases also data analysis   is quite time consuming. The throughput (in terms 
of analysed samples per day) strongly depends on instrumentation and the applied strategy. Sample 
handling  is  fully  manual  (the  authors  have  no  information  about  technology  that  would  allow 
automated sample positioning); thus all measurements require sample positioning by a trained and 
skilled  operator.  In  most  cases,  also  data  analysis  needs  input  and  decisions  by  an  experienced 
operator, potentially leading to individual bias affecting the results.  

thermo-analytical 

techniques 

than  by 

While calibration is not needed for quantification (i.e. counting of particles), it is necessary for the 
spectra-based  identification.  The  latter  require  only  traditional  calibrants  for  sizing  and  the 
wavelength accuracy in spectroscopy, which are commercially available. At the moment, there is no 
existing  standardised  method  for  microplastic  analysis  using  FTIR  or  Raman  microscopy.  Ongoing 
efforts (for instance, ISO working group) are focused on providing guidelines on good practices rather 
than  developing  a  single  standardised  method  (see  paragraph  4.1),  because  of  the  diverse 
instrumental  solutions,  data  collection  and  analysis  strategies  already  applied  or  being  under 
development by the researchers of the field.  

7.2.1  Data acquisition and analysis strategies 

The strategy selected for particle recognition and polymer identification by spectro-microscopy users 
depends strongly on the specific combination of hardware, analysis software and spectral library(ies). 
However, the choice can be also affected by the targeted particle size classes, matrix properties or 
polymer types to be analysed. In general, two main measurement strategies can be adopted with the 
spectro-microscopic techniques (Figure 12): i) single spot analysis of preselected individual particles 
and ii) chemical mapping by scanning over extended areas with post-measurement data analysis to 
locate and identify particles.   

Figure 12. Summary of typical data acquisition strategies in spectro-microscopic methods. Yellow boxes 
indicate the preferred options. 

Source: own production 

42 

 
 
 
In the first case, particles are recognised in the optical image of the filter surface typically based on 
optical contrast between the particles and the filter. Then, all particles or a selected set of particles 
are  chosen  for  data  acquisition,  which  is  done  at  multiple  individual  positions  (coordinates  that 
correspond to the single particles). Morphological analysis and sizing is based on the optical image. 
This  image  can  be  collected  in  transmission  or  reflection  mode,  depending  on  the  instrument.  If 
reflection mode is used, dark field illumination might be beneficial in order to improve the optical 
contrast  between  particles  and  the  filter.78  Composition  of  the  particles  is  typically  evaluated  by 
comparing the acquired spectrum from a particle to the spectra in a spectral library or applying a 
decision algorithm developed for a certain sample type.120  

In the second case, the full or a representative partial filter area is covered by the instrument acquiring 
a spectrum for each of an array of spots on the filter surface investigated. The resulting hyperspectral 
image is a kind of  chemical map  composed of spectra corresponding to the individual points of the 
covered surface. Chemical mapping is supported by FTIR instruments using focal plane or linear array 
detectors  that  allow  faster  data  collection.  It  is  possible  to  apply  this  strategy  also  in  Raman 
microscopy using very short integration times or for FTIR instruments equipped with single element 
detector if a limited filter area is mapped. Particles size and morphology can be analysed based on 
optical  image,  based  on  their  chemical  image,  (i.e.  the  group  of  pixels  touching  each  other  and 
corresponding to the same polymer or polymer group) or based on their combination with the help of 
an operator. Composition of the particles can be evaluated by comparing the spectra of each pixel to 
a spectral library or using more complex approaches like principal component analysis or machine 
learning based approaches.121 124 

Both optical and chemical images are two dimensional and carry no information about the thickness 
of the particles. Still, some authors suggest that volume of particles can be estimated supposing a 
certain theoretical ratio between their 2D projection and thickness. The calculated volume multiplied 
with the density of the identified polymer type gives the estimated mass of the particle.125 

7.2.2  Filter materials and filter analysis 

In spectro-microscopical methods, particles are usually directly analysed on the surface of a filter. 
Thus, the selection of the filter material is crucial, as in transmission mode or working with small 
particles very close to the support surface, the filter material itself might contribute to the signals of 
the acquired spectra. Because of this, the use of polymer based filters is not recommended. Raman 
users often apply aluminium-oxide, silicon, metal coated, or cellulose based filters.32 Working with 
µ-FTIR in transmission mode requires a filter material that is transparent for IR light. Such materials 
are  silicon  that  is  fully  transparent  in  the  spectral  range  of  interest  or  aluminium-oxide  that  is 
transparent  above  1250  cm-1.  The  loss  of  the  part  of  the  spectrum  below  that  wavenumber  is 
balanced by the advantage that the thin aluminium oxide filters are also partially transparent for 
visible light. This helps better focusing and condenser adjustments and allows to collect good contrast 
optical  image  of  the  sample  in  transmission  mode.  Based  on  these  partial  transmission  spectra, 
polymeric materials can still be well identified. 

Pore  size,  diameter,  roughness  and  flatness  of  the  filter  are  also  very  important  parameters 
determining lower particle-size cut-off, affecting clogging, optical imaging, particle recognition, data 
collection and analysis times. Scanning only partial filter areas is a common strategy to decrease 
analysis times. However, as particles are usually not evenly distributed on the filter surface but tend 
to accumulate close to the borders or certain areas, the non-homogeneity of their spatial distribution 
may affect the quantification. The work of Schymanski et al.78 highlights the most reliable strategies 
for  subdividing  the  total  area  of  a  filter (Figure  13).  In  case  of  the  first model,  radial  sectors  are 

43 

 
selected for measurement.78 The second model selects multiple small rectangles following a spiral 
track, while the third model uses random single particle selection.  

Figure 13. Strategies for subdividing the filter area for spectro-microscopic analysis  

Source: Schymanski et al.78 

The second model might be the best solution in cases when selection of partial areas is not the free 
choice of the operator, but the software allows only to map  rectangular area(s)  of interest or the 
analysis software is not able to deal with more complex data than a simple spectral hypercube.  

7.2.3  Raman spectro-microscopy 

Raman spectro-microscopy (µ-Raman) combines the capabilities of an optical microscope to visualise 
objects (down to 1 µm) with the analytical capabilities of Raman spectroscopy (Figure 14). The filter, 
on which the particles are collected, is placed on the (motorised) stage of the microscope and after 
imaging the filter, Raman spectra are  acquired at single  particle positions or the selected  area of 
interest is mapped (see paragraph 7.2.2).  

Figure 14. Schematic drawing of Raman spectro-microscopy.  

Source: JRC, Technical report JRC12538332 

During spectrum acquisition, monochromatic laser light is focused on the material, using the same 
objective as for imaging, or using an objective with larger magnification. In general, long distance 
objectives are recommended for signal  collection, and the applied objective and possible  confocal 
features will determin

44 

 
 
 
 
 
reflected  laser  light  is  collected.78  Raman  microscopes  are  reported  to  detect  single  microplastic 
particles even with diameters below 1 µm, but proper sizing of objects in this size range is not feasible 
due to the limitations of optical microscopy.126 The reflected laser light might pass a confocal pinhole 
if  data  collection  from  very  small  particles  is  required,  or  if  confocal  mode  helps  to  decrease 
background  fluorescence.  Finally,  the  reflected  light  passes  a  monocromator  and  arrives  to  the 
detector or passes a grating that sends the light to different pixels of a charge-coupled device (CCD) 
camera (Figure 14). The resulting Raman spectrum is unique for a specific polymer (or other material 
with Raman active vibrations) and serves as a fingerprint in chemical identification by comparison 
with spectra of a spectral library.  

The main advantage of µ-Raman compared to µ-FTIR is its higher spatial resolution but also that it is 
less sensitive to the presence of water. On the other hand, in the analysis of dry filters, this advantage 
is  less  relevant;  at  the  same  time,  the  weakness  of  Raman  spectroscopy,  being  disturbed  by 
fluorescence  emission,  becomes  more  significant.  Fluorescence  in  microplastic  particles  might 
originate  from  additives  (such  as  dyes  and  filler  materials)  of  the  plastic,  but  also  from  matrix 
components  even in  case of  such  simple matrices  as  clean  water.  Algae  and other microbes  that 
contain chlorophyll or other plant pigments, might be present in water samples and interact with the 
exciting laser light. Proper selection of the applied laser wavelength can help to decrease interference 
by  fluorescence,  but  such  a  choice  might  not  always  be  possible  due  to  the  specification  of  the 
instrument used. Photo-bleaching is another known strategy to decrease the effect of fluorescence, 
but  in  case  of  automatic  or  semi-automatic  analysis  of  large  number  of  particles  the  tailored 
treatment of individual particles is not realistic.  

Both data collection at selected particle positions and chemical mapping (Figure 12) are applied in 
the  analysis  of  microplastic  particles  by  µ-Raman  as  confirmed  also  by  the  inter-laboratory 
comparison study run by JRC in 2021.32 However, because of practical reasons, more Raman users 
combine optical image analysis for sizing with identification from single spot measurements.126  

µ-Raman can be equipped with one or more laser sources. Instruments constructed for general use 
with non-specific application are most often equipped with a 532 nm or 785 nm laser; less often a 
633 nm light source is applied. Raman spectra of polymeric materials do not depend strongly on the 
selected excitation wavelength. The position of the spectral peaks does not change, but variations in 
intensity ratios might happen   with potential impact on the chemical identification by comparison to 
the spectra in the applied database. This means that spectral databases from literature or provided 
by instrument manufacturers can be still used also when spectra are accumulated applying another 
laser.  However,  proper  calibration  of  the  instrument  before  measurements,  or  post-accumulation 
correction of the data is indispensable to get spectral features at their proper position.  

Various light sources might work at very different laser power (milliwatt, mW) and transmit different 
amount  of energy to the  analysed  particles per  accumulation  time.  Too  high  laser  power  settings 
might result in thermal decomposition of dry heat-sensitive materials in air. Small polymeric particles 
with a high surface area are vulnerable from this point of view.  

The recorded spectral range depends on the laser wavelength as well as the type and position of the 
optical grating. When applying a 532 nm laser, the full wavenumber range containing the fingerprint 
region and also C-H stretching vibrations at around 3000 cm-1 is typically covered at a single, well 
selected grating position.  

45 

 
7.2.4  FTIR spectro-microscopy  

In Fourier Transform Infrared spectro-microscopy (µ-FTIR), the polychromatic IR light beam source 
and interferometer is usually coupled with a standard microscope set-up equipped with an automated 
stage for scanning large areas (Figure 15). When IR light interacts with a sample, a certain portion of 
the  IR  radiation  is  absorbed  due  to  the  interaction  with  the  vibrational  modes  of  the  irradiated 
molecules. The non-absorbed light is transmitted by or reflected from the sample. Depending on the 
instrument  set-up,  transmitted  or  reflected  light  is  captured  by  the  detector.  The  resulting 
interferogram  is  transformed  by  an  algorithm,  called  Fourier-transformation,  to  a  spectrum.  The 
features  of  the  FTIR  spectrum  serve  as  a  fingerprint  in  chemical  identification  of  materials  by 
comparison with spectra of a spectral library.  

As both Raman and FTIR spectroscopy provide information on vibrational energies in the material, 
Raman  and  FTIR  spectra  of  molecules  contain  features  at  the  same  spectral  positions,  but  the 
intensity ratios of the peaks in the Raman and FTIR spectra of the same molecule are different. FTIR 
spectroscopy is sensitive to hetero-nuclear functional group vibrations and polar bonds, among them 
the O-H stretching in water. Because of this, FTIR cannot be used for the analysis of wet samples. 

Similarly to µ-Raman, FTIR spectra can be collected at single particle positions or the selected area 
of interest is mapped (see Figure 12). Special array detectors (focal plane array   FPA, and line array 
detectors) capable of simultaneously acquiring spectra at several portions (pixels) of the surface, can 
be added to the system to speed-up analysis time. This makes µ-FTIR more suitable for chemical 
mapping.  The  spatial  resolution  of  µ-FTIR  is  lower  than  that  of  µ-Raman,  which  means  that  with 
µ-Raman  smaller  particles  can  be  investigated  than  with  µ-FTIR.  The  spatial  resolution  depends 
strongly on instrument configuration and measurement settings, but achievable values reported  in 
literature  for  µ-FTIR  in  routine  measurements  are  in  the  range  of  10-20  µm.71,126  The  schematic 
drawing of a FTIR spectro-microscope (in transmission mode) is presented in Figure 15. 

Figure 15. Schematic drawing of FTIR spectro-microscope (in transmission mode) 

Source: own production 

Depending on the instrument set-up, FTIR spectro-microscopes can be used in transmission, reflection 
and  attenuated-total-reflectance  (ATR)  mode.  All  of  them  have  their  inherent  advantages  and 
disadvantages. The main advantage of measuring in transmission mode is that most of the available 

46 

 
 
 
spectral databases contain reference spectra acquired in this mode. Disadvantage is that above a 
certain size, plastic particles are no longer transparent for the IR light. Very low transmission values 
appear as truncated peaks in the absorbance spectrum, distorting the ratios between the peaks of 
the spectral fingerprint. This leads to lower scores at comparison to reference spectra and possible 
 like 
misinterpretation or false negatives. If the full optical cross-section of the particle is scanned 
in chemical mapping 
 and each particle is covered by more chemical image pixels, there is better 
chance to collect some good quality spectra at the edges of the particle where the total thickness of 
the material is lower. Searching for more transparent regions in large particles can be also done by 
manual measurements with a single element detector.  

Because of the limited IR transmission of thick samples, measuring in reflection mode is frequently 
chosen as strategy of automatic analysers. In this case, reflected IR light is collected by the same 
objective that is used to focus the beam on the sample. In case of a flat, well reflecting surface, the 
resulting  spectra  are  reflectance  spectra  that  can  be  transformed  into  a  classical  absorbance 
spectrum using the Kramers-Kronig transformation. Unfortunately, microplastic particles are usually 
far from being flat and well reflecting. The light reaching the particle is often partially transmitted 
and  reflected  from  various  curved  surfaces  before  leaving  the particle 
  and  interacting  with  the 
reflected light. The resulting spectrum is a so-called transflectance spectrum. As it is strongly affected 
by  the  geometrical  features  of  the  particle,  no  commercial  databases  exist  to  compare  in-house 
results  with  reference  transflectance  data.  Thus,  FTIR  instrument  users  applying  reflectance 
measurement mode are advised to build their own database   containing more spectra of the same 
polymer or other material. 

ATR measurements are possible with a special objective, containing an IR transparent crystal with a 
very fine tip. This means that preliminary imaging of the filter should be done with a normal objective, 
and the ATR crystal is pressed on the sample at the selected measurement positions and acts as a 
kind of solid immersion lens. The very fine tip allows to get high quality spectra and good spacial 
resolution. However, scanning large areas or large number of particles by ATR is much more time 
consuming because of the crystal has to be lifted and landed again at the various positions. Moreover, 
it might also be contaminated by particles that are not strongly attached to the surface. Additionally, 
ATR  provides  reflectance  spectra.  Therefore,  polymer  identification  usually  requires  further 
transformations or the use of a home built database. All in all, ATR is not the technique of choice for 
high number of loosely attached microparticles on a filter, but might become useful for the individual 
analysis of larger objects that are not transparent enough in transmission measurements. 

Basic µ-FTIR and automatic instruments are usually equipped with a single element detector. These 
detectors  allow  the  collection  of  spectra  at  selected  measurement  positions.  For  more  efficient 
mapping, instruments can be equipped with line array or focal plane array (FPA) detectors. They create 
high-resolution images of a defined pixel format and the collected pixel groups are later stitched to 
larger spectral images. Spatial resolution of an FPA detector depends on the size of the individual 
detector pixels while the covered area depends on the number of pixels. Averaging the spectra of 

accompanied by the decrease of spatial resolution. Mapping by FPA detectors is much faster than by 
single  element  detectors  and  allows  to  scan  full  filters  or  larger  representative  filter  areas  in 
reasonable  time.  Moreover,  microplastic  particles  might  be  identified  based  on  more  pixels,  more 
spectra belonging to the same visible object. 

The recorded wavelength range should cover the spectral fingerprint region(s) used for identification. 
Usually,  the  400-4000  cm-1  range  is  applied  also  by  most  of  available  spectral  databases.  The 
recorded spectral range might be also wider: for example, in case of reflectance spectra the wider 

47 

 
spectral  range  (up  to  8000  cm-1)  helps  to  improve  the  quality  of  approximations  during 
Kramers-Kronig transform. The final spectral range considered at spectral identification might be also 
different:  for  example,  the  always  changing  peaks  of  carbon  dioxide  (CO2)  gas  that  appear  in  a 
spectral region 2200-2500 cm-1 - and do not carry any information on the sample - or regions where 
the sample or reference spectrum values are not available can be excluded from the calculation. 

7.2.5  Quantum cascade laser spectroscopy  

from  selected 

Quantum cascade laser infrared (QCL-IR) spectroscopy127 uses a tunable laser as the IR light source. 
It operates at lower power than lasers used in Raman spectroscopy, thus there is less probability for 
damaging the sample. The only commercially available instrument to date, applies a detector that is 
cooled electrically, thus no liquid nitrogen is needed. For microplastic analysis, the instrument offers 
an automated workflow including an initial scan of a large surface area in reflection mode using IR 
light at a fixed wavelength to determine the location, size, and shape of particles. Spectra are then 
library.  Like  all 
collected 
single-spot-measurement strategies, it has the advantage of faster  spectrum acquisition, analysis 
speed and lower data object size. The lower size detection limit for microplastics is reported to be 
10 µm and is thus similar to µ-FTIR. However, the covered spectral range that is used for determining 
the  chemical  identity  is  limited  (about  950-1800 cm-1)  which  makes  the  identification  of  certain 
polymers (for example polyamides) less trustable. The instrument acquires transflection spectra. As 
reported in the previous paragraph, this makes the use of commercial spectral databases difficult. 
Moreover, to this date, there is no information about specific open source QCL-IR spectral databases 
on polymers. 

locations  and  compared 

the  spectral 

to 

7.2.6  Data analysis and spectral databases 

As  mentioned  above,  Raman  databases  collected  using  different  laser  sources  are  applicable  in 
general, independently from instrumentation, at least in the 532-785 nm laser wavelength range. For 
Raman and transmission-FTIR spectra, instrument providers usually offer also commercial databases 
including spectra of pure polymer and other materials alike. Thus, the most convenient choice is to 
use an already existing, quality controlled database that is compatible with the search features of 
the instrument s software applied by the user. However, experts of the field suggest - and also the 
findings of the JRC ILC study confirmed - that microplastics quantification results are better, if the 
database contains more than one spectrum for a certain polymer as well as spectra of weathered 
plastic,  particles  with  various  sizes  and  possible  matrix  components.32,78,120  In  case  of  commercial 
databases,  software  features  usually  allow  to  run  a  search  using  several  databases,  thus  other 
materials, like inorganic crystalline materials or dye databases can also be  used in addition to the 
polymer spectra database. In case of in-house databases, the laboratory should consider not only 
collecting the spectra of other materials that might appear in the sample, but possibly also to record 
more  spectra  of  the  same  type  of  material  obtained  from  different  sources  and/or  at  different 
weathering stages. Other materials that can be found in DW samples include carbonates (calcium 
and  magnesium  salts),  oxides  (sand,  iron  oxide)  and  all  possible  materials  that  might  appear  as 
contaminants from sample treatment process (e.g. cellulose from paper, plastic contaminants).120 

For some FTIR data formats, free-to-use software solutions are available together with microplastic 
specific databases and documentation in scientific literature.128 Other open or free databases might 
be also available online or from literature.129,130 In combination with certain FTIR instrument types, a 
commercial software solution was applied which is based on a machine learning approach developed 
specifically for microplastic quantification by chemical image analysis.122  

48 

 
7.3  GC/MS-based thermo-analytical techniques  

Thermo-analytical  techniques  such  as  thermal  extraction  desorption  GC/MS  (TED-GC/MS)  and 
pyrolysis  GC/MS  (pyr-GC/MS,  Figure  16)  were  introduced  relatively  recently  for  the  mass-based 
quantification  of  microplastics.95,131 134  In  these  techniques,  high  temperatures  and  oxygen-free 
conditions  lead  to  the  thermal  cracking  of  polymers  (pyrolysis)  and  the  production  of  a  range  of 
volatile  decomposition  products  characteristic  of  each  polymer.  Their  subsequent  gas 
chromatographic (GC) separation and mass spectrometric (MS) detection enable the identification and 
quantification of individual polymer types.  

Both methods share a common analytical principle (GC/MS) for the identification and quantification 
of the pyrolysis products, but they vary in how the thermal products are generated and introduced 
into the GC/MS. The traditional pyr-GC/MS method involves a direct coupling of the pyrolyser unit to 
the GC/MS. This unit heats the sample in an inert atmosphere, producing volatile pyrolytic products 
that are immediately fed into the GC/MS system for analysis. 

The  TED-GC/MS  system,  developed  more  recently,  decouples  the  pyrolysis  and  GC/MS  steps.  First, 
sample pyrolysis is carried out in a thermogravimetric analyser, with volatile decomposition products 
purged from the furnace and transferred to a solid sorbent material for capture. In the second and 
separate  step, the  sorbent  material  is  transferred  to  the  thermal  desorption (TD)  unit  of  a GC/MS 
analysis system. Polymer breakdown markers are thermally desorbed in the TD unit and transferred 
to the GC/MS system for determination. By decoupling the two steps the TED-GC/MS can simplify 
sample handling and can be applied to larger, more complex samples.   

Figure 16. Configuration of a typical pyr-GC/MS system  

Source: own production 

7.3.1  Sample treatment for pyr-GC/MS 

Following  filtration  to  collect  the microplastic particles  from  the  water  sample,  the  entire  filter  or 
part(s) thereof is/are transferred to the sample holder which is subjected to pyrolysis. The selection 
of appropriate filter materials is important because filters pyrolyze along with the sample and could 
produce interferences with the decomposition products of the polymeric materials. Some of the most 
common filter types are aluminium oxide membranes, borosilicate glass fibre filters or stainless steel 
filters.32  Pyrolysis  requires  solid  samples.  Therefore,  wet  samples  must  be  dried  before  analysis. 

49 

 
 
Besides this, if the DW to be analysed contains very low levels of natural organic solids, no additional 
sample treatment (e.g. matrix removal) is required. 

in  this  process 

A  crucial  step 
is  the  transfer  of  the  sample  to  the  sample  holder 
(cup/vial/crucible/beaker),  which  is  then  transferred  to  the  pyrolysis  device.  This  can  be  done  in  a 
number of ways. One possibility is to pyrolyze all or parts of the filter containing the sample. For 
example, alumina-based filters can be crushed/homogenized, followed by pyrolysis of known aliquots 
of this homogenised material. Thin, small (
15 mm) glass fibre filters can be folded and 
pyrolyzed as a whole. However, this depends on the size/capacity of the pyrolysis sample holder. A 
second way to transfer the sample material is to dissolve the particles caught on the filter surface 
with  a  suitable  solvent.  The  resulting  solution (or  an  aliquot thereof)  is  transferred  to  the  sample 
holder, the solvent is evaporated and the residue is pyrolyzed. The difficulty here is choosing the right 
solvent, as each polymer requires a different solvent. With an unknown sample, this latter approach 
is  rather  impracticable,  unless  only  a  specific  (limited  set  of)  polymer(s)  shall  be  detected  and 
quantified. 

Measurement procedure, calibration and data analysis 

The sample holder containing the loaded filter or the polymer solution, as appropriate, is transferred 
to the pyrolysis unit, which can be of different designs, comprising a furnace or a filament. The sample 
is then pyrolyzed at temperatures typically around 600°C. This temperature is maintained until the 
sample  has  undergone  complete  pyrolysis.  The  volatile  compounds  formed  during  the  cracking 
process are transferred to a gas chromatographic column, where they are separated by boiling points 
and  affinity  for  the  stationary  phase,  and  finally  detected  with  a  mass-selective  detector 
(mass spectrometry).  

Figure 17.  Characteristic fingerprint chromatograms and specific indicator ions of exemplary polymers: 
polyethylene (PE), polypropylene (PP), polystyrene (PS) and polyamide-6. 

Source: own production 

Each polymer produces specific decomposition products (Figure 17) that can be used for identification. 
Polymer  identity  is  confirmed  by  the  specific  marker  fragment  ions  of  the  characteristic 
decomposition  product,  the  respective  qualifier  ions  and  the  retention  time.  The  intensity  of  the 
specific  maker  fragment  ions  is  proportional  to  the  amount  of  pyrolyzed  product  and  is  used  for 

50 

 
 
 
quantification  against  external  calibration  curves  generated  with  pure  polymers  of  known 
composition. 

Each  polymer  to  be  studied  necessitates  its  own  individual  calibration  curve.  There  are  various 
methods  for  creating  calibration  curves,  one  of  which  involves  weighing  known  quantities  of  pure 
polymer  into  sample  holders  with  the  help  of  an  ultra-microbalance,  which  can  provide  accurate 
measurements to within about 5 µg. For smaller masses, finely ground powders made up of small 
particles can be  mixed with inert  materials like silica or calcium carbonate to achieve the desired 
measurements.  A  microplastic  calibration  standard  (Frontier  Lab)135  has  recently  become 
commercially  available.  This  standard  includes  12  commonly  used  polymers  that  are  uniformly 
dispersed  with  a  solid  diluent  for  easy  weighing  on  microbalances.  Another  method  for  creating 
calibration  curves  involves  dissolving  precise  amounts  of  polymers  in  solvents.  Aliquots  of  these 
solutions are then transferred to sample holders, and after the solvent has evaporated, the remaining 
polymer residues are pyrolyzed. It is important to note that each polymer requires a different solvent, 
and dissolution is often only achievable under harsh conditions. 

7.3.2  Overview of capabilities and limitations of pyr-GC/MS and TED-GC/MS 

Pyr-GC/MS  has  been  applied  for  the  analysis  of  polymers  for  a  long  time.136  However,  its  use  to 
identify  and  quantify  microplastics  is  relatively  new  (~  5  years)  and  is  currently  still  in  the 
development stage. It is relevant to note that that many existing GC/MS instruments can be upgraded 
with  a  pyrolyzer  as  an  instrument  accessory.  The  use  of  the  alternative  TED-GC/MS  to  analyse 
microplastics is also a recent evolution but in this case the higher cost and the lower availability of 
suitable instruments has limited the more widespread use in the field. The information that can be 
obtained  from  the  GC/MS  based  thermo-analytical  techniques  includes  absolute  mass  and 
identification of polymers, while it does not offer information on particle shape,  size and number. 
Compared  to  the  spectroscopic  techniques,  thermo-analytical  ones  provide  information  about  the 
properties of the entire particle and are less sensitive to interferences such as pigments or surface 
oxidation phenomena. In case of interference by (organic) matrix compounds, it may be necessary to 
reduce their presence by sample treatment procedures such as digestion, density separation and/or 
filtration (see paragraph 6.2).  

The  limit  of  quantification  of  microplastics  using  thermo-analytical  techniques  is  typically  around 
0.1 µg ( 1 spherical particle of 60 µm in diameter)   theoretically higher than the equivalent mass 
of single particles detectable by spectro-microscopical techniques (1-5 µm by µ-Raman). However, as 
the limit of quantification is also polymer dependent (0.02 µg   4 µg) high sampling volumes may be 
required to compensate for the reduced sensitivity to some common polymers such as PE and PET. If 
robustness is proven, these techniques might allow higher throughput (lower analysis time) compared 
to most of the other techniques. However, the techniques are still in the developmental stage and no 
routine methods, standards or standard operating procedures are available for microplastics analysis.  

In addition, the technique requires reference materials for the calibration that allows quantification. 
No  specific  size  or  shape  of  the  particles  is  required,  but  the  most  convenient  calibrants  are 
homogeneous polymer powders that are not easy to dose, particularly for pyr-GC/MS, which has more 
stringent  limits  on  the  maximum  acceptable  size  of  sample.  The  calibration  procedure  can  be 
challenging,  especially  if  more  than  one  polymer  is  present  in  the  sample.  Interference  between 
common polymer types (PVC and PET) during pyrolysis is also known from literature.137 

In the case of TED-GC/MS, decoupling the pyrolysis and GC/MS steps can simplify sample handling 
and permit the introduction of larger, more representative, and more complex samples in the pyrolysis 
stage. In particular, the additional flexibility in the thermal processing of the sample can be exploited 

51 

 
to  help  reduce  the  presence  of  interfering  organic  matter.  Non-volatile  residues  never  enter  the 
analysis system. The main disadvantages of TED-GC/MS, compared to pyr-GC/MS are the much higher 
equipment  cost,  the more  limited  availability  in  existing laboratories  and the longer  analysis  time 
(2h for a complete analysis cycle vs 45 mins for pyr-GC/MS).  

Finally, it should be noted that the thermo-analytical techniques are destructive: samples cannot be 
re-analysed or transferred for further analysis with an orthogonal technique. 

52 

 
 
 
8  Analysis strategies 

In practice, the most complex, time consuming and costly step of an analytical methodology is the 
instrumental  technique  applied  for  detection  and  quantification  of  the  microplastic  particles.  As 
discussed previously (section 7), there are a limited number of techniques available and each has 
different capabilities in terms of specificity, measurement metric, detectable size range, sensitivity, 
throughput and cost. Unfortunately, no single technique has clear advantages in all of these aspects.   

The consequence of this is that it will be necessary to either accept, as component of the analysis 
process, a single technique (paragraphs 7.1, 7.3, 7.2.3 or 7.2.4) with certain limitations or to combine 
two (or even three) different techniques to obtain more complete information. The following options 
describe  possible  strategies  which  could  be  considered  as  a  means  to  either  compensate  for  the 
technical limitations of individual analytical techniques or to minimise the financial and manpower 
burden. This latter is specifically significant for routine monitoring, where it is relevant also to consider 
cost and time.  

8.1  Screening technique 

An option to reduce cost and time would be  to pre-screen samples using the previously described 
fluorescence  microscopy  to produce number size distributions. A discrimination between plastic 
and  non-plastic  particles  is  often  possible  due  to  the  ability  of  the  fluorescent  dye  to  bind  to 
hydrophobic surfaces, like most synthetic polymers. Size and shape of the particles can be determined 
as well. The technique, if supported by microscope automation and image analysis, could allow the 
analysis of entire filters in time periods of less than 1 hour per sample (plus the timing for sample 
treatment).  Since the detection  limit is  theoretically  one  particle  and  size  detection  limit  of  a  few 
microns is achievable, the mass detection limit could be in the sub-pg range. Additional advantages 
are that the cost of materials and instrumentations are relatively low compared to other methods, in 
particular spectroscopic techniques, as previously described in this report. 

However, the disadvantage of using this technique alone is that it cannot determine polymer identity 
and potentially will produce an undefined number of false positive or/and false negative results. Little 
or  no  reliable  information  on  the  performance  of  such  method  in  validation  or  inter-laboratory 
comparison  studies  is  available  in  the  open  literature.  Consequently,  it  would  be  necessary  to 
investigate 
be valuable but complex, as it would require the consideration of real-life samples which would have 
to be thoroughly analysed using techniques that can id
such as µ-FTIR 
or µ-Raman, for comparison with the results gained from fluorescence microscopy. 

Other  potential  screening  techniques  which  may  be  applicable  in  principle  (e.g.  thermogravimetry, 
Differential  Scanning  Calorimetry,  determination  of  Total  Organic  Carbon)  are  even  less  well 
investigated for the analysis of microplastics. 

8.2  Single polymer-specific technique  

Another strategy would be to apply either a method using a single type of spectro-microscopy for 
particle  counting  or  a  single  thermo-analytical  technique  for  determining  polymer  mass.  Key 
discriminating  factors  in  the  final  choice  would  be  the  relevance  of  mass  or  number  based  data, 
sensitivity, cost, throughput and particle size range. Subsequently, it would be necessary to accept 
the specific limitations which are intrinsic to each of the method categories.  

53 

 
8.2.1  Polymer-specific number-based techniques 

composition (polymer type), there are only two classes of techniques in routine use at the moment: 
infra-red spectro-microscopy (µ-FTIR and QCL-IR) or Raman spectro-microscopy (µ-Raman). 
They permit the identification of the polymer composition of individual particle and the counting of 
all particles of interest. Additionally, these techniques permit the determination of particle size and 
shape, both of which might be factors influencing biological responses.     

As  discussed  in  section  7.2,  spectro-microscopy  techniques  have  the  advantage  of  high  absolute 
sensitivity and can provide particle identification as well as number size distributions and this would 
normally make them a good choice for monitoring applications. However, solids recovered from DW 
by filtration usually contain only a few plastic particles mixed together with many other non-plastic 
particulates.  Consequently,  obtaining  statistically  significant  data138  may  require  that  several 
thousand individual particles be analysed. This makes methods using spectro-microscopy techniques 
time consuming. For routine monitoring, rather than basis research, sample throughput is a factor 
which must be taken into consideration. An additional disadvantage of these techniques is that they 
have minimum size limits which allow them to cover only a part of the particle size range which may 
be present in DW. In routine operation, as particle size decreases below 10 µm, first µ-FTIR and then 
µ-Raman methods become increasingly ineffective until at around 1 µm even µ-Raman identification 
becomes difficult or impossible. It should be noted that these size values are indicative and in practice 
depend on factors such instrument type and specification, operator skill and the nature of sample.  

Both  classes  of  techniques  have  medium-high  investment  costs  and  have  a  low  throughput 
(typically 1-2  sample/day)  but  deliver  more  reliable  and  more  extensive  information  about  the 
targeted particles than the screening methods.  

8.2.2  Polymer specific mass-based techniques  

The  thermo-analytical  techniques such  as  pyrolysis  gas  chromatography/mass  spectrometry 
(pyr-GC/MS) or thermal-extraction-and-desorption gas chromatography/mass spectrometry 
(TED-GC/MS) have a higher per-sample throughput139 and, in the specific case of pyr-GC/MS, lower 
investments  costs  than  methods  using  micro-spectroscopic  techniques.  However,  the  calibration 
which is required to obtain quantitative data is time consuming and challenging as it needs to be 
done for each type of polymer, which has to be quantified. Furthermore, real-life samples may contain 
mixtures  of  polymers  and  unknown  quantities  of  natural  organic  matter  both  of  which  can  have 
unpredictable effects on the reliability of the measurement. The thermo-analytical techniques have 
poorer  detection  limits  (mass)  than  the  optical  spectroscopic  techniques,  which  may  be  a  critical 
limitation in the case of the low microplastics levels expected in DW. Thermo-analytical techniques 
are as such not dependent on the particle  size and thus can be  used for the  analysis of smallest 
particles, provided that their number are high enough to exceed the (mass-based) detection limit. On 
the other hand this means that, in contrast to the microscopy-
(and shape) cannot be determined with these techniques.   

8.3  Combination of techniques 

Multiple orthogonal techniques could be combined to compensate their individual disadvantages. For 
example, a filter cascade with different pore sizes (e.g. 100 µm, 20 µm and 1 µm) could be used to 
separate particulates into size ranges most appropriate for the two categories of techniques applied. 
The fraction 1-20 µm could be analysed using pyr-GC/MS while the fractions above 20 µm would then 

54 

 
be investigated by micro-spectroscopy techniques such as µ-FTIR, QCL-IR or µ-Raman. The advantage 
of this approach is that it would provide information on the presence of microplastics over a much 
wider size range and, in particular, the sub-micron range which may have higher probability of being 
taken up by the human body though the gastro-intestinal system. The disadvantages of this approach 
are  the  significant  increase  in  cost  from  the  need  to  invest  in  two  different  techniques  and  the 
technical difficulties of sampling using fine filters with large volumes of water. Additionally, the use 
of  multiple  filters  of  different  nominal  sizes  does  not  guarantee  correct  size  separation,  as 
phenomena such as filter cake formation may result in the retention of particles which are smaller 
than  the  nominal  size  cut-off  of  a  filter.  At  this  time  the  relevance  of  size  to  risk  and  hazard 
assessment is not clearly known and thus the benefits of this more complex and costly approach 
remain uncertain.  

8.4  Polymer specific indicator approach 

The analysis strategy would target the detection and quantification of a limited number of polymer 
types  which  are  most  commonly  found  in  DW 
particularly beneficial for the thermo-analytical techniques as it would simplify the time-consuming 
calibration steps. In the case of the spectro-microscopy it may provide some more limited benefit by 
simplifying the data analysis and thus decrease the analysis time. The disadvantage is that polymers 
not among the pre-

8.5  Tiered approach 

On the basis that the primary confirmatory technique would be spectro-microscopy and that these 
techniques have high cost and low throughput, it could be relevant to consider a tiered approach to 
the  analysis.  In  such  an  approach,  a  screening  technique,  e.g.  fluorescence  microscopy,  would  be 
carried out first (1st tier). If a pre-set threshold is not exceeded, no further analysis is done, while in 
case  the  threshold  is  exceeded,  a  more  specific  analysis  (µ-FTIR  or  µ-Raman)  is  carried  out 
subsequently (2nd tier). Under the assumption that the threshold will not be passed in many (most of 
the) cases, the overall cost is much lower than applying spectroscopic techniques for all samples. The 
2nd tier analysis may be even outsourced to another (specialised) laboratory. 

To apply such a tiered approach, thresholds would need to be established and the selection of relevant 
values  will  pose  some  challenges.  Considerations  for  setting  the  thresholds  should  include  the 
-plastic materials   i.e. the probability 

of false positive and false negative results 
compensate  for  the  impact  of  the  sample  matrix  and  other  factors  causing  deviations  from  the 
probability estimates. Since, to date, reliable information regarding such factors is not available in 
the  scientific  literature,  some  research  is  needed  to  establish  the  knowledge  for  setting  suitable 
thresholds.  In  addition,  the  omission  of  the  second  tier,  re  precise  analysis,  triggered  by  a  false 
negative result in the first (screening) step, should not lead to a risk for human health. However, there 
is still very little information  on the latter either. Consequently, it is likely that scientifically based 
threshold values will not be available in the next 1-2 years.   

55 

 
 
 
 
 
9  Summary and conclusions 

Globally, microplastics were shown to be present in drinking water (DW) with sizes ranging from a 
few µm to several mm. Reported concentrations typically ranged from several hundred particles per 
litre to values which are often much less than the equivalent of 0.1 particle per litre. In Europe, the 
analysis of particle composition indicated that about 90% were distributed amongst 7 polymer types 
with no single polymer type constituting more than 25% of the particle number. When considering 
specifically studies of EU water supplies, the particle concentrations were all below 1 particle per litre 
and the majority were significantly below 0.1 particle per litre. These low levels mean that instrument 
sensitivity  will  be  a  key  limiting  factor  in  establishing  a  suitable  methodology  for  monitoring  the 
occurrence of microplastics in drinking water in the EU. 

Studies using small (<10 litres) sample volumes, typically reported higher calculated values of particle 
concentration (above 1 particle per litre) compared to when larger sampling volumes (>50 litres) were 
adopted. This is likely attributable to higher relative influence of background contamination (from 
sample processing and handling) on the final concentration values when the sample volumes are low. 
To  reduce  this  source  of  error,  large  sampling  volumes  are  a  likely  necessity  with  a  minimum  of 
500-1000 litres being advisable. 

In all the reported studies, the particles to be analysed were collected by passing DW through one or 
more filter(s) and thus reported only those particulates with a size above the cut-off of the finest 
filter. The majority of studies used filters with cut-off values of 5-10 µm or above and consequently 
there was little information about the presence of smaller microplastic particulates as these were not 
retained for subsequent analysis. Although the majority of studies used particle counting methods 
based  on  microscopy,  very  little  information  about  particles  size  distributions  was  available  with 
studies reporting only total particle numbers or particle numbers in a few broad size bins. Similarly, 
there was no information of the size distribution in relation to actual polymer types. 

A  detailed  examination  of  the  literature  showed  that  there  are  four  main  analytical  techniques 
currently used in microplastic analysis. Each of these have specific strengths and limitations in terms 
of the measurement metric (polymer weight or particle number), sensitivity, minimum particle size 
and ability to identify the polymer type (see Annex A and Annex B). Overall, it appeared that no single 
analytical  technique  was  fully  suited  to  characterise  the  nature  and  extent  of  microplastic 
contaminants  in  drinking  water.  Consequently,  the  adoption  of  a  methodology  will  require  some 
degree of compromise and pragmatic choices must be made regarding the parameters to monitor. 
Key  factors  in  determining  the  most  suitable  method  or  combination  of  methods  will  be  the 
measurement  metric,  size  range,  sensitivity  and  reliability  (specificity,  accuracy,  precision),  but 
additionally the throughput and cost per sample should also be considered.  

56 

 
 
References  

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

Geneva: World Health Organization. Microplastics in drinking-water. Licence: CC BY-NC-SA 3.0 
IGO. (2019). 

United  Nations  Environment  Assembly.  Draft  resolution.  End  plastic  pollution:  Towards  an 
international legally binding instrument UNEP/EA.5/L.23/Rev.1. (2022). 

Policies to Reduce Microplastics Pollution in Water. (OECD, 2021). doi:10.1787/7ec7e5ef-en. 

European Commission Directorate-General for Internal Market Industry Entrepreneurship and 
SMEs. Commission Regulation (EU) 2023/2055 of 25 September 2023 amending Annex XVII 
to Regulation (EC) No 1907/2006 of the European Parliament and of the Council. OJ L 238 
67 88 (2023). 

European Parliament Council of the European Union. Directive (EU) 2020/2184 of the European 
Parliament  and  of  the  Council  of  16  December  2020  on  the  quality  of  water  intended  for 
human consumption (recast). in OJ L 435 1 62 (2020). 

Yuan, C., Almuhtaram, H., McKie, M. J. & Andrews, R. C. Assessment of microplastic sampling 
and extraction methods for drinking waters. Chemosphere 286, (2022). 

Chu, X. et al. Occurrence and distribution of microplastics in water supply systems: In water 
and pipe scales. Sci. Total Environ. 803, (2022). 

Tong, H., Jiang, Q., Hu, X. & Zhong, X. Occurrence and identification of microplastics in tap water 
from China. Chemosphere 252, 126493 (2020). 

Kankanige,  D.  &  Babel,  S.  Identification  of  micro-plastics  (MPs)  in  conventional  tap  water 
sourced from Thailand. J. Eng. Technol. Sci. 52, 95 107 (2020). 

10.  Mintenig, S. M., Löder, M. G. J., Primpke, S. & Gerdts, G. Low numbers of microplastics detected 
in drinking water from ground water sources. Sci. Total Environ. 648, 631 635 (2019). 

11. 

12. 

13. 

14. 

Kosuth, M., Mason, S. A. & Wattenberg, E. V. Anthropogenic contamination of tap water, beer, 
and sea salt. PLoS One 13, 1 18 (2018). 

Zhang, M. et al. Distribution Characteristics and Influencing Factors of Microplastics in Urban 
Tap Water and Water Sources in Qingdao, China. Anal. Lett. 53, 1312 1327 (2020). 

Feld, L., Silva, V. H. Da, Murphy, F., Hartmann, N. B. & Strand, J. A study of microplastic particles 
in danish tap water. Water (Switzerland) 13, (2021). 

Pratesi,  C.  B.  et  al.  Presence  and  quantification  of  microplastic  in  urban  tap  water:  A  pre-
screening in brasilia, Brazil. Sustain. 13, (2021). 

15.  Mukotaka,  A.,  Kataoka,  T.  &  Nihei,  Y.  Rapid  analytical  method  for  characterization  and 
quantification of microplastics in tap water using a Fourier-transform infrared microscope. Sci. 
Total Environ. 790, (2021). 

16. 

17. 

Shen,  M.  et  al.  Presence  of  microplastics  in  drinking  water  from  freshwater  sources:  the 
investigation in Changsha, China. Environ. Sci. Pollut. Res. 28, 42313 42324 (2021). 

Pittroff,  M.  et  al.  Microplastic  analysis  in  drinking  water  based  on  fractionated  filtration 
sampling and Raman microspectroscopy. Environ. Sci. Pollut. Res. 28, 59439 59451 (2021). 

18.  Weber,  F.,  Kerpen,  J.,  Wolff,  S.,  Langer,  R.  &  Eschweiler,  V.  Investigation  of  microplastics 

57 

 
 
19. 

20. 

21. 

22. 

23. 

24. 

25. 

26. 

27. 

28. 

29. 

30. 

contamination in drinking water of a German city. Sci. Total Environ. 755, (2021). 

Ferraz,  M.,  Bauer,  A.  L.,  Valiati,  V.  H.  &  Schulz,  U.  H.  Microplastic  concentrations  in  raw  and 
drinking water in the sinos river, southern brazil. Water (Switzerland) 12, 1 10 (2020). 

Lam, T. W. L., Ho, H. T., Ma, A. T. H. & Fok, L. Microplastic contamination of surfacewater-sourced 
tap water in Hong Kong - A preliminary study. Appl. Sci. 10, (2020). 

Ásmundsdóttir, Á. M., Gomiero, A. & Øysæd, K. B. Microplastics and Nanoplastics Occurrence 
and Composition in Drinking Water from Akureyri Urban Area, Iceland. in Proceedings of the 
2nd International Conference on Microplastic Pollution in the Mediterranean Sea (eds. Cocca, 
M. et al.) (Springer International Publishing) 106 111 (2020). doi:10.1007/978-3-030-45909-
3_18. 

Gomiero, A., Øysæd, K. B., Palmas, L. & Skogerbø, G. Application of GCMS-pyrolysis to estimate 
the levels of microplastics in a drinking water supply system. J. Hazard. Mater. 416, (2021). 

Kirstein,  I.  V  et  al.  Drinking  plastics? 
drinking water distribution systems by µFTIR and Py-GCMS. Water Res. 188, (2021). 

  Quantification  and  qualification  of  microplastics  in 

Shruti, V. C., Pérez-Guevara, F. & Kutralam-Muniasamy, G. Metro station free drinking water 
Environ.  Pollut.  261, 
fountain- 
(2020). 

Chanpiwat, P. & Damrongsiri, S. Abundance and characteristics of microplastics in freshwater 
and treated tap water in Bangkok, Thailand. Environ. Monit. Assess. 193, (2021). 

Johnson, A. C.  et al. Identification and Quantification of Microplastics in Potable Water and 
Their Sources within Water Treatment Works in England and Wales. Environ. Sci. Technol. 54, 
12326 12334 (2020). 

Kosuth, M., Mason, S. A. & Wattenberg, E. V. Anthropogenic contamination of tap water, beer, 
and sea salt. PLoS One 13, (2018). 

ASTM D8332-20 Standard Practice for Collection of Water Samples with High, Medium, or Low 
Suspended  Solids  for  Identification  and  Quantification  of  Microplastic  Particles  and  Fibers. 
https://www.astm.org/d8332-20.html (2020) doi:10.1520/D8332-20. 

SAPEA  Science  Advice  for  Policy  by  European  Academies.  A  Scientific  Perspective  on 
Microplastics in Nature and Society. (2019) doi:10.26356/microplastics. 

De Frond, H. et al. Monitoring microplastics in drinking water: An interlaboratory study to inform 
effective  methods  for  quantifying  and  characterizing  microplastics.  Chemosphere  298, 
134282 (2022). 

31.  Müller, Y. K. et al. Microplastic analysis 

 are we measuring the same ? Results on the first 
global  comparative  study for  microplastic  analysis in  a  water  sample.  Anal. Bioanal.  Chem. 
412, 555 560 (2020). 

32. 

Belz,  S.  et  al.  Current  status  of  the  quantification  of  microplastics  in  water  -  Results  of  a 
JRC/BAM  interlaboratory  comparison  study  on  PET  in  water.  JRC  Tech.  Rep.  JRC125383, 
(2021). 

33.  Mourik, L. M. Van et al. Results of WEPAL-QUASIMEME / NORMANs first global interlaboratory 
study on microplastics reveal urgent need for harmonization. Sci. Total Environ. 772, 145071 
(2021). 

34. 

Isobe, A. et al. An interlaboratory comparison exercise for the determination of microplastics 
in standard sample bottles. Mar. Pollut. Bull. 146, 831 837 (2019). 

58 

 
35. 

Becker,  R.,  Altmann,  K.,  Sommerfeld,  T.  &  Braun,  U.  Quantification  of  microplastics  in  a 
freshwater suspended organic matter using different thermoanalytical methods   outcome of 
an interlaboratory comparison. J. Anal. Appl. Pyrolysis 148, 104829 (2020). 

36. 

The CUSP cluster. www.cusp-research.eu. 

37. 

38. 

39. 

40. 

Seghers, J. et al. Preparation of a reference material for microplastics in water evaluation of 
homogeneity. Anal. Bioanal. Chem. (2021) doi:10.1007/s00216-021-03198-7. 

Allan,  J.  et  al.  Regulatory  landscape  of  nanotechnology  and  nanoplastics  from  a  global 
perspective. Regul. Toxicol. Pharmacol. 122, 104885 (2021). 

. Briefing notes (2021). 

- and 

Ivleva,  N.  P.,  Primpke,  S.  &  Lynch,  J.  M.  Advances  in  chemical  analysis  of  micro-  and 
nanoplastics. Anal. Bioanal. Chem. 415, 2869 2871 (2023). 

41. 

Southern California Coastal Water Research Project (SCCWRP). www.sccwrp.org. 

42. 

43. 

44. 

45. 

46. 

47. 

48. 

49. 

50. 

51. 

52. 

Na,  S.-H.  et  al.  Microplastic  removal  in  conventional  drinking  water  treatment  processes: 
Performance, mechanism, and potential risk. Water Res. 202, 117417 (2021). 

ISO/TR 21960:2020 Plastics - Environmental aspects - State of knowledge and methodologies. 
https://www.iso.org/standard/72300.html (2020). 

ISO  24187:2023  Principles  for  the  analysis  of  microplastics  present  in  the  environment. 
https://www.iso.org/standard/78033.html (2023). 

ISO/CD  16094-1  Water  quality  -  Analysis  of  microplastic  in  water  -  Part  1:  General  and 
sampling  for  waters  with  low  content  of  suspended  solids  including  drinking  water. 
https://www.iso.org/standard/84459.html. 

ISO/DIS  16094-2  Water  quality  -  Analysis  of  microplastic  in  water  -  Part  2:  Vibrational 
spectroscopy  methods  for  waters  with  low  content  of  suspended  solids  including  drinking 
water. https://www.iso.org/standard/84460.html. 

ISO/CD 16094-3 Water quality - Analysis of microplastic in water - Part 3: Thermo-analytical 
methods  for  waters  with  low  content  of  suspended  solids  including  drinking  water. 
https://www.iso.org/standard/84463.html. 

ISO 5667-1:2023 Water quality 
programmes and sampling techniques. https://www.iso.org/standard/84099.html (2023). 

 Part 1: Guidance on the design of sampling 

 Sampling 

ISO  5667-3:2018  Water  quality  -  Sampling  -  Part  3:  Preservation  and  handling  of  water 
samples. https://www.iso.org/standard/72370.html (2018). 

ISO 5667-5:2006 Water quality - Sampling - Part 5: Guidance on sampling of drinking water 
systems. 
from 
https://www.iso.org/standard/36694.html (2021). 

distribution 

treatment 

works 

piped 

and 

ISO/DIS 5667-27 Water quality - Sampling - Part 27: Guidance on sampling for microplastics 
in water. https://www.iso.org/standard/82612.html. 

ASTM D8333-20 Standard Practice for Preparation of Water Samples with High, Medium, or 
Low Suspended Solids for Identification and Quantification of Microplastic Particles and Fibers 
Using Raman Spectroscopy, IR Spectroscopy, or Pyrolysis-GC/MS. https://www.astm.org/d8333-
20.html (2020) doi:10.1520/D8333-20. 

53. 

ASTM  D8402-23  Standard  Practice  for Development  of  Microplastic  Reference  Samples  for 

59 

 
Calibration and Proficiency Evaluation in All Types of Water Matrices with High to Low Levels 
of Suspended Solids. https://www.astm.org/d8402-23.html (2023) doi:10.1520/D8402-23. 

54. 

55. 

56. 

DIN/TS  10068:2022-09  Food  -  Determination  of  microplastics  -  Analytical  methods. 
(2022) 
https://www.beuth.de/en/pre-standard/din-ts-10068/353579768 
doi:https://dx.doi.org/10.31030/3350580. 

Principles  for  the  analysis  of  microplastics  present  in  the  environment  (ISO  24187:2023); 
German  version  EN 
ISO  24187:2023.  https://www.beuth.de/en/standard/din-en-iso-
24187/373720466 doi:10.31030/3495706. 

PR NF T90-
- Analyse des microplastiques dans les eaux de consommation 
humaine  et  les  eaux  souterraines  -  Partie  1:  Méthode  utilisant  la  spectroscopie  vibratoire. 
https://norminfo.afnor.org/norme/nf-t90-600/qualite-de-leau-analyse-des-microplastiques-
dans-les-eaux-de-consommation-humaine-et-les-eaux-souterraines-partie-1/189976. 

57. 

VAMAS, TWA 45, Micro and Nano Plastics in the Environment. http://www.vamas.org/twa45/. 

58. 

Test No. 105: Water Solubility. (OECD, 1995). doi:10.1787/9789264069589-en. 

59. 

60. 

61. 

62. 

63. 

64. 

65. 

Test  No.  120:  Solution/Extraction  Behaviour  of  Polymers 
doi:10.1787/9789264069886-en. 

in  Water.  (OECD,  2000). 

European Parliament Council  of the European Union.  Directive 2008/56/EC of  the  European 
Parliament and of the Council of 17 June 2008 establishing a framework for community action 
in the field of marine environmental policy (Marine Strategy Framework Directive). OJ L 164 
19 40 (2008). 

European  Commission  Directorate-General  for  Environment.  Commission  Decision  (EU) 
2017/848  of  17  May  2017  laying  down  criteria  and  methodological  standards  on  good 
environmental  status  of  marine  waters  and  specifications  and  standardised  methods  for 
monitoring and assessment, and repealing Decision 2010/477/EU. OJ L 125 (2017). 

Joint Research Centre. Marine Strategy Framework Directive   Task group 10 report   Marine 
litter, April 2010. (Publications Office, 2010). doi:doi/10.2788/86941. 

Joint Research Centre (Institute for Environment and Sustainability). Guidance on monitoring 
of marine litter in European seas. (Publications Office, 2014). doi:doi/10.2788/99816. 

Baker,  A.  C.  J.  &  Bamford,  H.  Proceedings  of  the  International  Research  Workshop  on  the 
Occurrence , Effects , and Fate of Microplastic Marine Debris. in NOAA Technical Memorandum 
NOS-OR&R-30 Sept 9-11 2008 (2009). 

United Nations Environment programme. Meeting of the Ecosystem Approach Correspondence 
Group 
Litter). 
https://wedocs.unep.org/bitstream/handle/20.500.11822/39548/21wg490_8_eng.pdf?sequen
ce=1&isAllowed=y (2021). 

Monitoring 

(CORMON 

Marine 

Marine 

Litter 

on 

66. 

ISO 472:2013 Plastics 

 Vocabulary. https://www.iso.org/standard/44102.html (2018). 

67. 

(2020). 

Calif. Water Boards 1 42 

68.  Meyns,  M.,  Primpke,  S.  &  Gerdts,  G.  Library  based  identification  and  characterisation  of 
polymers with nano-FTIR and IR-sSNOM imaging. Anal. Methods 11, 5195 5202 (2019). 

69. 

Luo, H., Xiang, Y., Zhao, Y., Li, Y. & Pan, X. Nanoscale infrared, thermal and mechanical properties 
of  aged  microplastics  revealed  by  an  atomic  force  microscopy  coupled  with  infrared 
spectroscopy (AFM-IR) technique. Sci. Total Environ. 744, (2020). 

60 

 
70. 

71. 

72. 

Valsesia,  A.  et  al.  Combining  microcavity  size  selection  with  Raman  microscopy  for  the 
characterization of Nanoplastics in complex matrices. Sci. Rep. 11, 362 (2021). 

Käppler,  A.  et  al.  Analysis  of  environmental  microplastics  by  vibrational  microspectroscopy: 
FTIR, Raman or both? Anal. Bioanal. Chem. 408, 8377 8391 (2016). 

Thornton  Hampton,  L.  M.  et  al.  Characterizing  microplastic  hazards:  which  concentration 
metrics and particle characteristics are most informative for understanding toxicity in aquatic 
organisms? Microplastics and Nanoplastics 2, 20 (2022). 

73. 

Koelmans,  A.  A.  et  al.  Microplastics  in  freshwaters  and  drinking  water:  Critical  review  and 
assessment of data quality. Water Res. 155, 410 422 (2019). 

74.  Weisser, J. et al. From the well to the bottle: Identifying sources of microplastics in mineral 

water. Water (Switzerland) 13, (2021). 

75.  Wu, P., Li, J., Lu, X., Tang, Y. & Cai, Z. Release of tens of thousands of microfibers from discarded 
face masks under simulated environmental conditions. Sci. Total Environ. 806, 150458 (2022). 

76. 

77. 

78. 

79. 

80. 

81. 

Cherniak, S. L. et al. Conventional and biological treatment for the removal of microplastics 
from drinking water. Chemosphere (2021) doi:10.1016/j.chemosphere.2021.132587. 

Kankanige, D. & Babel, S. Smaller-sized micro-plastics (MPs) contamination in single-use PET-
bottled water in Thailand. Sci. Total Environ. 717, (2020). 

Schymanski, D. et al. Analysis of microplastics in drinking water and other clean water samples 
with micro-Raman and micro-infrared spectroscopy: minimum requirements and best practice 
guidelines. Anal. Bioanal. Chem. 413, 5969 5994 (2021). 

. & Klimtová, M. Occurrence and fate 
of microplastics at two different drinking water treatment plants within a river catchment. Sci. 
Total Environ. 741, (2020). 

Tong, H., Jiang, Q., Hu, X. & Zhong, X. Occurrence and identification of microplastics in tap water 
from China. Chemosphere 252, (2020). 

Dalmau-Soler, J. et al. Microplastics from headwaters to tap water: occurrence and removal in 
a drinking water treatment plant in Barcelona Metropolitan area (Catalonia, NE Spain). Environ. 
Sci. Pollut. Res. 28, 59462 59472 (2021). 

82.  Mason,  S.  A.,  Welch,  V.  G.  &  Neratko,  J.  Synthetic  Polymer  Contamination  in  Bottled  Water. 

Front. Chem. 6, (2018). 

83. 

84. 

85. 

86. 

Oßmann, B. E. et al. Small-sized microplastics and pigmented particles in bottled mineral water. 
Water Res. 141, 307 316 (2018). 

Panno, S. V. et al. Microplastic Contamination in Karst Groundwater Systems. Groundwater 57, 
189 196 (2019). 

Pivokonsky, M. et al. Occurrence of microplastics in raw and treated drinking water. Sci. Total 
Environ. 643, 1644 1651 (2018). 

Paredes, M., Castillo, T., Viteri, R., Fuentes, G. & Bodero, E. Microplastics in the drinking water 
of the Riobamba city, Ecuador. Sci. Rev. Eng. Environ. Sci. 28, 653 663 (2019). 

87.  Wang, Z., Lin, T. & Chen, W. Occurrence and removal of microplastics in an advanced drinking 

water treatment plant (ADWTP). Sci. Total Environ. 700, (2020). 

88. 

Almaiman, L. et al. The occurrence and dietary intake related to the presence of microplastics 

61 

 
in drinking water in Saudi Arabia. Environ. Monit. Assess. 193, (2021). 

89.  Madejski,  G.  R.  et  al.  Silicon  nanomembrane  filtration  and  imaging  for  the  evaluation  of 

microplastic entrainment along a municipal water delivery route. Sustain. 12, 1 14 (2020). 

90.  Mortensen, N. P., Fennell, T. R. & Johnson, L. M. Unintended human ingestion of nanoplastics 
and small microplastics through drinking water, beverages, and food sources. NanoImpact vol. 
21 at https://doi.org/10.1016/j.impact.2021.100302 (2021). 

91. 

92. 

Schwaferts, C., Niessner, R., Elsner, M. & Ivleva, N. Methods for the analysis of submicrometer- 
and nanoplastic particles in the environment. TrAC Trends Anal. Chem. 112, (2019). 

Toussaint, B. et al. Review of micro- and nanoplastic contamination in the food chain. Food 
Addit. Contam. Part A 36, 639 673 (2019). 

93.  Wang, Z. et al. Research progresses of microplastic pollution in freshwater systems. Science of 

the Total Environment vol. 795 at https://doi.org/10.1016/j.scitotenv.2021.148888 (2021). 

94. 

95. 

Prata, J. C. et al. A new approach for routine quantification of microplastics using Nile Red and 
automated software (MP-VAT). Sci. Total Environ. 690, 1277 1283 (2019). 

Fries, E. et al. Identification of polymer types and additives in marine microplastic particles 
using pyrolysis-GC/MS and scanning electron microscopy.  Environ. Sci. Process. Impacts 15, 
1949 1956 (2013). 

96. 

EOS. ANALYSIS OF POLYMERIC PARTICLES VIA SPES TECHNOLOGY - application note AN001. 
(2021). 

97.  Winkler, A. et al. Detection and formation mechanisms of secondary nanoplastic released from 

drinking water bottles. Water Res. 222, 118848 (2022). 

98.  Wang,  L.,  Zhang,  J.,  Hou,  S.  &  Sun,  H.  A  Simple  Method  for  Quantifying  Polycarbonate  and 
Polyethylene  Terephthalate  Microplastics 
in  Environmental  Samples  by  Liquid 
Chromatography Tandem Mass Spectrometry. Environ. Sci. Technol. Lett. 4, 530 534 (2017). 

99.  Müller,  A.,  Goedecke,  C.,  Eisentraut,  P.,  Piechotta,  C.  &  Braun,  U.  Microplastic  analysis  using 
chemical extraction followed by LC-UV analysis: a straightforward approach to determine PET 
content in environmental samples. Environ. Sci. Eur. 32, 85 (2020). 

100. 

et  al.  Quantitative  Determination  of  PA6  and/or  PA66  Content  in  Polyamide-

Containing Wastes. ACS Sustain. Chem. Eng. 8, 11818 11826 (2020). 

101.  Castelvetro,  V.  et al.  Quantification  of  poly(ethylene terephthalate) micro-  and nanoparticle 
contaminants in marine sediments and other environmental matrices. J. Hazard. Mater. 385, 
121517 (2020). 

102.  El  Hadri,  H., Gigault,  J.,  Mounicou,  S.,  Grassl,  B.  &  Reynaud,  S.  Trace  element  distribution  in 
marine microplastics using laser ablation-ICP-MS. Mar. Pollut. Bull. 160, 111716 (2020). 

103.  Sturm, M. T., Horn, H. & Schuhen, K. The potential of fluorescent dyes comparative study of 
Nile red and three derivatives for the detection of microplastics.  Anal. Bioanal. Chem. 413, 
1059 1071 (2021). 

104.  Shruti, V. C., Pérez-Guevara, F., Roy, P. D. & Kutralam-Muniasamy, G. Analyzing microplastics 

with Nile Red: Emerging trends, challenges, and prospects. J. Hazard. Mater. 423, (2022). 

105.  Lichtman, J. W. & Conchello, J. Fluorescence microscopy. 2, (2005). 

106.  Sanderson, M. J., Smith, I., Parker, I. & Bootman, M. D. Fluorescence Microscopy. 1042 1066 

62 

 
(2014) doi:10.1101/pdb.top071795. 

107.  Andrady,  A.  L.  Microplastics  in  the  marine  environment.  Mar.  Pollut.  Bull.  62,  1596 1605 

(2011). 

108.  Maes, T., Jessop, R., Wellner, N., Haupt, K. & Mayes, A. G. A rapid-screening approach to detect 
and  quantify  microplastics  based  on  fluorescent  tagging  with  Nile  Red.  Sci.  Rep.  7,  1 10 
(2017). 

109.  Lv, L. et al. A simple method for detecting and quantifying microplastics utilizing fluorescent 
dyes  -  Safranine  T,  fluorescein  isophosphate,  Nile  red  based  on  thermal  expansion  and 
contraction property. Environ. Pollut. 255, 113283 (2019). 

110.  Aoki, H., Torimura, M. & Habe, H. Spectroscopic Investigation of Increased Fluorescent Intensity 
of Fluorescent Dyes When Adsorbed onto Polystyrene Microparticles. Anal. Sci. 37, 773 779 
(2021). 

111.  Costa, C. Q. V. et al. Fluorescence sensing of microplastics on surfaces. Environ. Chem. Lett. 19, 

1797 1802 (2021). 

112.  Lee, E. H., Lee, S., Chang, Y. & Lee, S. W. Simple screening of microplastics in bottled waters 
and environmental freshwaters using a novel fluorophore. Chemosphere 285, 131406 (2021). 

113.  Caponetti,  V.  et  al.  A  selective  ratiometric  fluorescent  probe  for  no‐wash  detection  of  PVC 

microplastic. Polymers (Basel). 13, 1 15 (2021). 

114.  Sharma, N., Chi, C. H., Swaminathan, N., Dabur, D. & Wu, H. F. Introducing Stanene oxyboride 
nanosheets  as  white  light  emitting  probe  for  selectively  identifying  <5  µm  microplastic 
pollutants. Sensors Actuators B Chem. 348, 130617 (2021). 

115.  Sancataldo, G., Avellone, G. & Vetri, V. Nile Red lifetime reveals microplastic identity. Environ. 

Sci. Process. Impacts 22, 2266 2275 (2020). 

116.  Shim, W. J., Song, Y. K., Hong, S. H. & Jang, M. Identification and quantification of microplastics 

using Nile Red staining. Mar. Pollut. Bull. 113, 469 476 (2016). 

117.  Stanton, T. et al. Exploring the Efficacy of Nile Red in Microplastic Quantification: A Costaining 

Approach. Environ. Sci. Technol. Lett. 6, 606 611 (2019). 

118.  Erni-Cassola, G., Gibson, M. I., Thompson, R. C. & Christie-Oleza, J. A. Lost, but Found with Nile 

Environmental Samples. Environ. Sci. Technol. 51, 13641 13648 (2017). 

119.  Braun, U. et al. Analysis of Microplastics - Sampling, preparation and detection methods. Status 

Report within the framework program Plastics in the Environment. (2020). 

120.  Cowger, W. et al. Critical Review of Processing and Classification Techniques for Images and 

Spectra in Microplastic Research. Appl. Spectrosc. 74, 989 1010 (2020). 

121.  Primpke,  S.  et  al.  Toward the  Systematic  Identification  of  Microplastics in  the Environment: 
Evaluation  of  a  New  Independent  Software  Tool  (siMPle)  for  Spectroscopic  Analysis.  Appl. 
Spectrosc. 74, 1127 1138 (2020). 

122.  Hufnagl, B. et al. Computer-Assisted Analysis of Microplastics in Environmental Samples Based 
Environ. Sci. Technol. Lett. 9, 90 95 

(2022). 

123.  Primpke,  S.,  Lorenz,  C.,  Rascher-Friesenhausen,  R.  &  Gerdts,  G.  An  automated  approach  for 
microplastics analysis using focal plane array (FPA) FTIR microscopy and image analysis. Anal. 

63 

 
Methods 9, 1499 1511 (2017). 

124.  Löder, M. G. J., Kuczera, M., Mintenig, S., Lorenz, C. & Gerdts, G. Focal plane array detector-
based  micro-Fourier-transform  infrared  imaging  for  the  analysis  of  microplastics  in 
environmental samples. Environ. Chem. 12, 563 581 (2015). 

125.  Simon, M., van Alst, N. & Vollertsen, J. Quantification of microplastic mass and removal rates 
at  wastewater  treatment  plants  applying  Focal  Plane  Array  (FPA)-based  Fourier  Transform 
Infrared (FT-IR) imaging. Water Res. 142, 1 9 (2018). 

126. 

Ivleva,  N.  P.  Chemical  Analysis  of  Microplastics  and  Nanoplastics:  Challenges,  Advanced 
Methods, and Perspectives. Chem. Rev. 121, 11886 11936 (2021). 

127.  Hildebrandt, L. et al. Agilent Application Note - Fast, Automated Microplastics Analysis Using 
Laser  Direct  Chemical  Imaging.  https://www.agilent.com/cs/library/applications/application-
marine-microplastics-8700-ldir-5994-2421en-agilent.pdf (2020). 

128.  Primpke, S., Wirth, M., Lorenz, C. & Gerdts, G. Reference database design for the automated 
analysis of microplastic samples based on Fourier transform infrared (FTIR) spectroscopy. Anal. 
Bioanal. Chem. 410, 5131 5141 (2018). 

129.  Cabernard, L., Roscher, L., Lorenz, C., Gerdts, G. & Primpke, S. Comparison of Raman and Fourier 
Transform  Infrared  Spectroscopy  for  the  Quantification  of  Microplastics  in  the  Aquatic 
Environment. Environ. Sci. Technol. 52, 13279 13288 (2018). 

130.  De Frond, H., Rubinovitz, R. & R

-FTIR Spectral Libraries of Plastic Particles 
(FLOPP and FLOPP-e) for the Analysis of Microplastics. Anal. Chem. 93, 15878 15885 (2021). 

131.  Fischer, M. & Scholz-Böttcher, B. M. Microplastics analysis in environmental  samples-recent 
pyrolysis-gas  chromatography-mass  spectrometry  method  improvements  to  increase  the 
reliability of mass-related data. Anal. Methods 11, 2489 2497 (2019). 

132.  Eisentraut, P. et al. Two Birds with One Stone - Fast and Simultaneous Analysis of Microplastics: 

Microparticles Derived from Thermoplastics and Tire Wear. Environ. Sci. Technol. Lett. 5, 608
613 (2018). 

133.  Duemichen, E., Eisentraut, P., Celina, M. & Braun, U. Automated thermal extraction-desorption 
gas  chromatography  mass  spectrometry:  A  multifunctional  tool  for  comprehensive 
characterization of polymers and their degradation products.  J. Chromatogr. A 1592, 133
142 (2019). 

134.  Dümichen, E. et al. Analysis of polyethylene microplastics in environmental samples, using a 

thermal decomposition method. Water Res. 85, 451 457 (2015). 

135.  FrontierLab.  Microplastics  Calibration  Standard  set  for  MPs  analysis  using  Py-GC/MS. 

https://www.frontier-lab.com/products/multi-functional-pyrolysis-system/194709. 

136.  Rial-otero,  R.,  Galesio,  M.,  Capelo,  J.-L.  &  Simal-Gandar,  J.  A  Review  of  Synthetic  Polymer 

Characterization by Pyrolysis   GC   MS. Chromatographia 70, 339 348 (2009). 

137.  Bouzid, N. et al. Quantification of Microplastics by Pyrolysis Coupled with Gas Chromatography 
and Mass Spectrometry in Sediments: Challenges and Implications. Microplastics 1, 229 239 
(2022). 

138.  Schymanski, D., Goldbeck, C., Humpf, H.-U. & Fürst, P. Analysis of microplastics in water by 
micro-Raman spectroscopy: Release of plastic particles from different packaging into mineral 
water. Water Res. 129, 154 162 (2018). 

139.  Elert, A. M. et al. Comparison of different methods for MP detection: What can we learn from 

64 

 
them, and why asking the right question before measurements matters? Environ. Pollut. 231, 
1256 1264 (2017). 

140.  Mason,  S.  A.,  Welch,  V.  G.  &  Neratko,  J.  Synthetic  Polymer  Contamination  in  Bottled  Water. 

Front. Chem. 6, (2018). 

141. 

Microplastic  contamination  in  water  supply  and  the  removal  efficiencies  of  the  treatment 
plants: A case of Surabaya City, Indonesia. J. Water Process Eng. 43, (2021). 

142.  Schymanski, D., Goldbeck, C., Humpf, H. U. & Fürst, P. Analysis of microplastics in water by 
micro-Raman spectroscopy: Release of plastic particles from different packaging into mineral 
water. Water Res. 129, 154 162 (2018). 

65 

 
 
 
List of abbreviations and definitions 

Abbreviations 

Definitions 

ABS 

AC 

Acrylonitrile butadiene styrene  

Acrylic compounds 

AFNOR 

French Standardisation Association [Association Française de Normalisation] 

ASTM  

ASTM International, formerly known as American Society for Testing and 
Materials  

ATR-FTIR 

Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy 

BAM  

CA 

CCD 

(German) Federal Institute for Materials Research and Testing [Bundesinstitut 
für Materialforschung und -prüfung]  

Cellulose Acetate 

Charge-Coupled Device 

co PE+PP 

copolymer polyethylene-polypropylene 

CEN 

DIN 

DW 

DWD  

EC  

EDTA 

EDX  

EU  

EVA 

EtOH 

European Committee for Standardization [Comité Européen de Normalisation] 

German Standardisation Organisation [Deutsches Institut für Normung] 

Drinking Water 

Drinking Water Directive  

European Commission  

Ethylenediaminetetraacetic acid 

Energy-dispersive X-ray spectroscopy   

European Union  

Ethylene-vinyl acetate 

Ethanol 

FluoMic  

Fluorescence Microscopy  

FPA  

Focal Plane Array  

66 

 
Abbreviations 

Definitions 

FTIR  

GC  

GC/MS 

HCl 

H2O2  

H2SO4 

HPLC  

ILC  

IR  

ISO  

JRC  

KOH 

LOD 

Fourier-Transform Infrared (spectroscopy)  

Gas chromatography  

Gas-Chromatography Mass-Spectrometry (analytical techniques combining 
gas-chromatography and mass spectrometry)  

Hydrochloric acid 

Hydrogen peroxide  

Sulphuric acid 

High-performance liquid chromatography  

Inter-laboratory comparison  

Infra-Red  

International Organisation for Standardization  

Joint Research Centre  

Potassium hydroxide 

Limit of detection 

LDIR  

Laser Direct Infrared (imaging) 

m 

MP 

MS  

Minimum  

Microplastic (vertical axis in Figure 5, Figure 6, Figure 7, Figure 8) 

Mass spectrometry  

MSFD 

Marine Strategy Framework Directive 

mW 

n.a. 

NMR 

NR 

milliwatt 

Not available 

Nuclear Magnetic Resonance (spectroscopy) 

Nile Red 

67 

 
Abbreviations 

Definitions 

OECD 

OpMic  

PA  

PAM 

PAN 

PB 

PBA 

PBT  

PC  

PE  

PEST  

PET  

PI 

PMMA 

PMPS 

PMS 

PP  

PPS  

PS  

PTFE  

PTT 

PU  

PVC  

Organisation for Economic Co-operation and Development 

Optical microscopy  

Polyamide 

Polyacrylamide   

Polyacrylonitrile 

Polybutene 

Poly(butyl acrylate) 

Polybutylene terephthalate  

Polycarbonate  

Polyethylene  

Polyester other than PET 

Polyethylene terephthalate  

Poly(isoprene) 

Poly(methyl methacrylate) 

Poly(methyl phenyl siloxane) 

Poly alpha-methylstyrene 

Polypropylene  

Polyphenylene sulfide 

Polystyrene  

Polytetrafluoroethylene  

Polytrimethylene terephthalate 

Polyurethane  

Polyvinyl chloride  

68 

 
Abbreviations 

Definitions 

Pyr-GC/MS 

Pyrolysis-Gas Chromatography Mass Spectrometry  

QCL-IR 

Quantum cascade laser-Infrared (IR) spectroscopy 

SB 

SD  

Styrene-Butadiene Copolymer 

Standard Deviation 

REACH 

Registration, Evaluation, Authorisation and Restriction of Chemicals 

SCCWRP 

Southern California Coastal Water Research Project 

SE 

SEBS  

SEM  

Standard Error 

Styrene-ethylene-butyrene-styrene 

Scanning Electron Microscopy  

SEM-EDX 

Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis 

SPES 

Single particle extinction and scattering  

TED-GC/MS  

Thermal extraction and desorption gas chromatography/mass spectrometry  

TWA 

TZW 

UN 

Technical working area 

Technologie Zentrum Wasser (German Centre for Water Technology) 

United Nations 

VAMAS 

Versailles Project on Advanced Materials and Standards 

-FTIR  

Fourier-Transform Infrared spectro-microscopy (FTIR spectroscopy coupled to a 
microscope)   

-Raman  

Raman spectro-microscopy (Raman spectroscopy coupled to a microscope) 

µm 

WHO 

micrometre (micron) 

World Health Organization 

69 

 
 
 
 
 
List of figures  

Figure 1. Number of studies investigating DW samples from different geographical regions. Total 
number of studies is 21, of which two included samples collected from more than one region. ........... 8 

Figure 2. Number of studies using various techniques for analysing the particles found. Combination 
of techniques explained in the text. Acronyms of techniques: see list of abbreviations (page 66). ... 10 

Figure 3. Particle size rages covered by the different studies7 10,13 16,18 20,24,25,27. Due to the wide variety 

-out top end. ........................................................................................................................ 11 

Figure 4. Percentage (particle number) of microplastics polymers found in DW samples. The columns 
show the percentage of specific polymer types within the total population of microplastics reported 
in the individual articles. For the acronyms, refer to the list of abbreviation (page 66) The sub-group 

polyethylene-polypropylene (co PE+PP), Styrene-Ethylene-Butadiene-Styrene (SEBS), polyacrylamide 
(PAM), polyurethane (PU), polyphenylene sulphide (PPS), poly(isoprene) (PI), polytetrafluoroethylene 
(PTFE), poly(methyl phenyl siloxane) (PMPS), polymethyl methacrylate (PMMA) .......................................... 12 

Figure  5. Number of microplastic (MP on vertical  axis) particles found in samples (as mean)  and 
blanks (where indicated in the study description); an estimated total (open circles) was calculated in 
cases where the study authors stated having subtracted the blank from the sample result and the 
blank value was reported. Due to the wide variety of size ranges applied, vertical axis is logarithmic. 
For Yuan et al., the data for the two different sampling procedures are shown separately: (1) container 
sampling; (2) at-source filtering. ................................................................................................................................................ 14 

Figure 6. Measured microplastic (MP on vertical axis) number concentration (including error bars) by 
country and region as reported by the studies focussing on one country. Due to the wide variety of 
size ranges applied, vertical axis is logarithmic. ............................................................................................................... 15 

Figure 7. Number concentration of microplastic particles (MP on vertical axis) reported in relation to 
the water volume filtrated and the applied sampling procedure. Container sampling (yellow dots); at-
source filtering (blue dots). Due to the wide variety of size ranges applied, vertical axis is logarithmic.
 ....................................................................................................................................................................................................................... 16 

Figure 8. Number concentration of microplastic particles (MP on vertical axis) found in blank samples 
(background  level)  in  relation  to  the  water  volume  filtrated  and  the  applied  sampling  procedure. 
Container sampling (yellow dots); at-source filtering (blue dots). Due to the wide variety of size ranges 
applied, vertical axis is logarithmic. .......................................................................................................................................... 16 

Figure 9 Comparison of techniques performance. Results of technique comparison for identification 
of polymer type, quantification of particle mass, quantification of particle number per polymer type 
and quantification of total particle number. The average evaluation of each technique is indicated in 
the figure as insufficient (light blue), sufficient (dark blue) and questionable (both colours in different 
percentage). For acronyms see the relative list (page 66). ........................................................................................ 22 

Figure 10 Sample treatment procedures mentioned in the 37 publications examined and summarised 
in Annex A ................................................................................................................................................................................................ 36 

Figure 11 Schematic drawing on sample treatment strategies (arrow width symbolises the popularity 
of the strategy among the analysed literature sources, see Annex A) ................................................................ 37 

70 

 
Figure 12. Summary of typical data acquisition strategies in spectro-microscopic methods. Yellow 
boxes indicate the preferred options. ...................................................................................................................................... 42 

Figure 13. Strategies for subdividing the filter area for spectro-microscopic analysis ........................... 44 

Figure 14. Schematic drawing of Raman spectro-microscopy. .............................................................................. 44 

Figure 15. Schematic drawing of FTIR spectro-microscope (in transmission mode) ................................. 46 

Figure 16. Configuration of a typical pyr-GC/MS system .......................................................................................... 49 

Figure  17.    Characteristic  fingerprint  chromatograms  and  specific  indicator  ions  of  exemplary 
polymers: polyethylene (PE), polypropylene (PP), polystyrene (PS) and polyamide-6. ................................ 50 

71 

 
 
List of tables  

Table 1. Volumes sampled by the different studies, split up into studies with at-source filtration and 
container sampling. Yuan et al.6 used both sampling procedures. ............................................................................ 9 

72 

 
 
 
 
 
 
 
Annexes 

73 

 
 
Annex A 

Comparison of sample treatment in the analysis of drinking water as described in 
literature 

Pre-Treatment 

Recovery 
%* 

Pre-treatment 
directly on 
filter 

Transfer to 
analysis 
filter/unit 

Analysis 
technique 

Plastics found 
(abbreviations see page 66) 

(n.a. = data not available) 

Reference 

Sample type 
(T = tap 
water; 
B= bottled 
water) 

T 

T 

T 

T 

T 

T 

T 

T 

T 

T 

T 

T 

T 

T 

B 

T 

B 

T 

B 

T 

Sample 
volume 
(L) 

1200-2500 

1500 

1300 

1000 

1000 

200-1000 

(1) 200 

100 

100 

50 

10 

10 

9 

4-8 

2.4-6 

3 

2.5 

0.7-1.5 

1 

Size cut-off of filter 
(µm) 

3 

10 

Filter type 

(n.a. = data not 
available) 

stainless steel 

stainless steel 

compressed air, HCl, EtOH, 
H2O2 
detergent, cellulase, tripsin, 
EtOH 

5,20,100 

stainless steel 

sonication 

500-1300 

10 

stainless steel 

Hexane, concentrated HCl 

81 

55 

98.5 

58 

1,10,100 

stainless steel 

detergent, protease, H2O2, 
EtOH 

5,50 

5 

(5, 10) 20, 100, 500, 
5000 

stainless steel 

ciric acid, EtOH 

stainless steel 

EtOH, detergent, density 
separation, sonication 

stainless steel 

H2O2 30% 

50 

paper, glass fibre 

detergent, density separation, 
sonication, H2O2, 

20, 100, 300, 1000, 
3500 

stainless steel 

10 

0.22 

stainless steel 

30% acetic acid, EtOH 

90 

PTFE 

H2O2, HCl, EtOH 

10, 45, 125, 300, 500  PC, stainless steel 

KOH 10%, detergent 

10 

1.5 

0.45 

0.2 

0.2 

3 

1.7 

PC 

glass fibre 

nitrocellulose 

Nile red 

Nile red 

68 

aluminum oxide 

detergent, EtOH 

86 

PTFE 

H2O2 Fenton, 75 °C 

Au coated PC 

glass fibre 

H2O2 <1%, 24h 

74 

+ 

- 

- 

+ 

+ 

- 

- 

- 

+ 

- 

+ 

+ 

- 

- 

- 

- 

- 

- 

- 

- 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

- 

- 

- 

- 

- 

- 

- 

µ-FTIR 

µ-FTIR 

µ-Raman 

Raman 

PEST, PVC, PA, PE 

Mintenig 201910 

PS, ABS 

Johnson 202026 

PE, PET, PP, PA 

PE,PP PET, PS 

Pittroff 202117 

Weber 202118 

Pyr-GC/MS 

PE, PA, PET, PP, PS 

Gomiero 202122 

µ-FTIR 

PVC, PEST, PS, PE 

Weisser 202174 

µ-FTIR, Pyr-GC/MS 

µ-Raman 

PEST, PA, PVC, PS, PE, PP, PU, 
AC 
PP, PE PVC, PA, vinylchloride-
vinylacetate-copolymer 

Kirstein 202123 

Wu 202275 

µ-Raman 

PP, PE, PET, PS, PVC 

Chanpiwat 202125 

µ-FTIR 

µ-FTIR 

µ-FTIR, µ-Raman 

OpMic, µ-Raman 

PES, PP, PE, ABS, PA 

Dalmau-Soler 202181 

PE, PP, PET 

PE, PP, PET 

Feld 202113 

Shen 202116 

PET, PEST, PE, PAN, PP, PBT, 
PU, AC 

Cherniak 202176 

OpMic, µ-Raman 

PET, PVC, PA 

Yuan 20226 

FluoMic, µ-FTIR 

PP, PA, PS, PE, PEST 

Mason 2018140 

FluoMic, µ-FTIR, 
µ-Raman 

PET, PE, PP, PA 

Kankanige 202077 

µ-FTIR 

PE, PS 

OpMic, µ-FTIR 

PES, PE, PP, cellophane, PA, 
polytrimolithicamide 

µ-Raman 

µ-FTIR 

PET, PE, PS, PP 

PEST, PS, PA 

Weisser 202174 

Radityaningrum 
2021141 
Schymanski 2018142 

Chu 20227 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Sample type 
(T = tap 
water; 
B= bottled 
water) 

Sample 
volume 
(L) 

Size cut-off of filter 
(µm) 

Pre-Treatment 

Recovery 
%* 

Pre-treatment 
directly on 
filter 

Transfer to 
analysis 
filter/unit 

Analysis 
technique 

0.22 

nitrocellulose 

0.45, 53, 300, 500 

nitrocellulose 

T 

T 

T 

T 

B 

T 

T 

T 

T 

T 

T 

T 

T 

B 

T 

B,T 

T 

1 

1 

1 

1 

1 

1 

1 

1 

1 

0.5 

0.5 

0.5 

0.25 

0.25 

0.25 

0.2 

0.05 

0.2 

7 

2.7 

0.2 

0.7, 1.2 

0.45 

0.2, 5 

26 

na 

2.5 

2.5 

0.4 

5 

0.2 

8 

Filter type 

(n.a. = data not 
available) 

PTFE, aluminum 
oxide 

glass fibre 

glass fibre 

PC 

glass fibre 

n.a. 

PTFE 

1 M H2SO4 

KOH 15%, density separation, 
Nile red 

Rose Bengal 

Nile red 

Nile red 
HCl 

H2O2 

stainless steel 

drop of H2O2 30%, 60 °C 

n.a. 

cellulose 

cellulose 

no 

Rose Bengal 

Rose Bengal 

Al coated PC 

EDTA, detergent 

PTFE 

aluminum oxide 

H2O2 

no 

silicon nitride 

Nile red 

Source: own production 

Plastics found 
(abbreviations see page 66) 

(n.a. = data not available) 

CA, PET, PVC, PE, PP, EVA, 
PBA, PTT 

n.a. 

n.a. 

Reference 

Pivokonský 202079 

Ferraz 202019 

Lam 202020 

PTT, epoxy resin 

Shruti 202024 

SEM, µ-Raman 

FluoMic 

OpMic 

FluoMic, SEM-EDX, 
µ-Raman 

FluoMic, µ-FTIR 

PC, PE, PP, PET 

Kankanige 20209 

FluoMic 
µ-Raman 

Pyr-GC/MS 

OpMic, Pyr-GC/MS 

PE, PP, PPS, PET, PB, PMMA, 
PA, PMS, PVC, PBT, PTFE 
(by µ-Raman analysis) 

Tong 20208 

PVC, PE 

PE 

Asmundsdottir 202021 

Panno 201984 

µ-FTIR, µ-Raman 

PAM, PET, PE, PP, PVC 

Pivokonsky 201885 

PS, PP, PES, PE, SEBS, PVC 

Mukotaka 202115 

µ-FTIR 

FluoMic 

OpMic 

OpMic, FluoMic 

n.a. 

n.a. 

n.a. 

Pratesi 202114 

Kosuth 201811 

Paredes 201986 

Oßmann 201883 

µ-Raman 

PET, PE, PP, SB 

µ-Raman, SEM 

PET, PE, PP, PAM, PS, PVC 

Wang 202087 

µ-FTIR 

PE, PS, PET, PP, PU, PA 

Almaiman 202188 

FluoMic, EDX 

n.a. 

Madejski 202089 

- 

- 

+ 

- 

- 

+ 
- 

- 

- 

- 

+ 

- 

+ 

+ 

- 

- 

- 

+ 

- 

+ 

- 

+ 

- 

+ 
+ 

- 

- 

+ 

- 

- 

- 

- 

- 

+ 

- 

- 

* When recovery were reported with different values in relation to the plastic type, the minimum value was included in the table  

75 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Annex B 

Comparison of key aspects of main instrumental techniques 

Aspects 
Principle 

Price (Estimate) 

Fluorescence Microscopy 
Samples are treated with a dye 
which preferentially makes 
hydrophobic surface, such as 
plastic ones, fluorescent. When 
illuminated with light of a suitable 
wavelength and viewed through an 
optical microscope the stained 
particles (plastics) are highlighted 
with respect to the more 
hydrophilic material (such as 
mineral particles). 
20-40,000 euro 

Analysis time 

<1 hour per sample 

Information that can 
be obtained  
Min. measurable size  
Min. measurable size 
in routine operation 
Min. mass that can be 
determined 

Number, size, size-distribution, 
shape of polymer particles  
1-5 µm  
5-10 µm  

Not applicable 

Destructive/Non-
destructive 

Non-destructive, but particles are 
modified (stained)  

Main interferences 

The selectivity of the staining dye 
for polymers is not absolute and 
false positive/negative results may 
occur to an unknown extent.  

Pyrolysis GC/MS 
Thermal decomposition of polymers by 
heating in an oxygen-free atmosphere 
(pyrolysis) resulting in polymer-specific 
decomposition products, which are 
identified/quantified (mass) by gas 
chromatography-mass spectrometry (GC/MS).  

Raman Spectro-microscopy 
Particles are illuminated with monochromatic 
light from a focused laser beam. Interactions 
with the molecular bonds in the material 
generates scattered light, which has higher or 
lower wavelength than the incident light. The 
scattered light is collected and analysed by a 
spectrometer resulting in a spectrum, which is 
characteristic for the material. Comparison of 
the spectrum with a library of known spectra 
permit the identification of the material. 

Infrared Spectro-microscopy 
The material is illuminated with infra-red light 
and the transmitted or reflected light is 
collected and analysed to determine the 
relative intensity at each frequency (or 
wavelength). The resulting IR spectrum is 
characteristic for the material analysed and 
comparison with a library of known spectra 
permit the identification of the unknown 
material.  

300.000 euro 

For particles collected on a 13 mm filter: 
8-24 hours for the analysis of one sample by 
chemical mapping by µ-FTIR. Times for 
QLC-IR method is significantly less but not 
known 

Number, size, size-distribution, shape, identity 
of polymer(s) 
-10 µm 
15-20 µm 

ng  
(estimate form size and polymer density) 

Non-destructive 

200.000 euro 

Laboratories may be able to upgrade an 
existing GC/MS system by retrofitting a 
pyrolyser unit and optionally adding an 
autosampler. 
Pyrolysis unit: 30.000 euro. Autosampler for 
pyrolisis unit: 25.000 euro. GC/MS: 80.000 
euro 
Approximately 0.5-1 hour per sample 
(depends on the GC settings). In addition, at 
least one calibration curve is required with at 
least 3 points that corresponds to 0.5-1 hour 
of analysis each.  
Total time: several hours, depending on 
number of identified polymers and of points 
on the calibration curve. 
Identification of polymer(s), mass per polymer   Number, size, size-distribution, shape and 

3-6 hours for the analysis of a sample with 
about 1000 particles.  

identification of polymer(s) 

5 -

pg  
(estimate by calculation from size and 
polymer density) 
Non-destructive 
(at careful selection of laser power) 

 (None) 
 (None) 

Depends on polymer. Typically around 1 µg 
(correspond to 1 spherical particle with 
diameter 60 µm) 
Destructive BUT resulting pyrograms can be 
re-evaluated retrospectively for further 
indicator ions of new polymers (semi-
quantitative) 
Natural organic matter with decomposition 
products similar to those of plastics 

76 

Coloured particles, pigments, fluorescence, 
fatty acids, amides, proteins. Coloured 
particles and fluorescence can be seen as 
well by changing laser wavelength  

Particles loaded with carbon black. Presence 
of water, difficulty identifying mineral 
particles, protein that can be confused with 
PA, fatty acids, amides. 

 
 
 
 
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