ISO/FDIS 24899

• Abstract:

  This document specifies a laboratory method for the extraction of microplastics from compost matrices originating from industrial or home composting. The method outlines various extraction steps assuring polymer stability, and high recovery rate. This extraction process separates microplastics from the compost matrix that can be further analysed either by number-based or by mass-based techniques. The method is applicable for microplastics up to 1 mm in size, see Clause 4. The method is applicable for microplastics with densities lower than 1,4 g/cm3. This document does not specify downstream detection methods for the identification and quantification. The method in this document has not been validated for microplastic extraction from other matrices, except for composts.

• Status: Not Published
• ICS: 83.080.01 - Plastics in general
• Technical Committee: ISO/TC 61/SC 14 - Environmental aspects
• Drafting Committee: ISO/TC 61/SC 14/WG 4 - Characterization of plastics leaked into the environment (including microplastics) and quality control criteria of respective methods
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 15-Sep-2026
• Completion Date: 15-Sep-2026

Overview

ISO/FDIS 24899: Plastics - Method for the Extraction of Microplastics from Compost Samples is an international standard developed by the International Organization for Standardization (ISO). This document specifies a laboratory procedure for extracting microplastics from compost matrices originating from both industrial and home composting. The method prioritizes high polymer stability and recovery rates to ensure the accurate separation of microplastics from organic compost materials. Extracted microplastics can be further analyzed using number-based or mass-based quantification techniques.

This standard applies specifically to microplastics sized up to 1 mm and with densities less than or equal to 1.4 g/cm³. It is intended solely for compost samples and does not cover downstream detection or quantification methods or extraction from other matrices, such as soil or sediments.

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Key Topics

• Purpose and Scope

  • Outlines a standardized laboratory method for extracting microplastics from compost.
  • Addresses the growing need for consistent, comparable data in microplastic analysis.

• Applicability

  • Suitable for microplastics in the 20 µm to 1 mm size range.
  • Covers microplastics with densities ≤ 1.4 g/cm³, including common polymers like PE, PP, PET, PC, PS, PA, PMMA, PU, PLA, and PBAT.
  • Not validated for composts containing high-density polymers like some types of PVC or PTFE.

• Extraction Principles

  • Deagglomeration: Breaking apart compost clusters via ultrasonication.
  • Fenton Oxidation: Using hydrogen peroxide and iron catalyst to digest organic matter, isolating microplastics.
  • Density Separation: Employing high-density salt solutions (such as CaCl₂) to separate plastics from heavier inorganic compost constituents.

• Quality Control

  • Incorporates method blanks, unspiked matrix samples, and spiked sample recovery tests to ensure reliability and reproducibility.
  • Specifies cleaning protocols to minimize sample contamination from laboratory environments or equipment.

• Performance Criteria

  • Stipulates a ≥ 60% recovery rate for microplastics < 100 µm and ≥ 80% for those > 100 µm.
  • Recommends rigorous validation, matrix-specific reporting, and regular evaluation of laboratory performance.

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Applications

• Compost Quality Assessment

  • Enables composting facilities and regulators to verify that compost meets environmental quality standards by accurately assessing microplastic contamination.

• Environmental Impact Studies

  • Supports research and monitoring programs by providing a consistent method for tracking microplastics in compost that may be applied to agricultural soils.

• Product Testing

  • Useful for manufacturers and quality assurance laboratories evaluating the degradation and fragmentation behavior of plastics in compostable products.

• Regulatory Compliance

  • Assists environmental authorities in implementing and enforcing limits on microplastic pollution in compost, aiding the move toward safer, cleaner organic waste recycling practices.

This method ensures reliable and comparable results across different laboratories and jurisdictions, paving the way for uniform reporting and greater confidence in regulatory and research outcomes.

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Related Standards

• ISO 16094-2: Microplastics analysis in environmental matrices-methods for mass-based quantification.
• ISO 16094-3: Methods for the identification and quantification of microplastics using advanced techniques.
• ISO 472:2013: Plastics-Vocabulary.
• ISO 14644-1: Cleanrooms and associated controlled environments.
• ISO/TR 21960: Plastics-Environmental aspects-State of knowledge and methodologies.

These related standards offer additional guidance for microplastics detection, mass and number quantification, terminology, and laboratory best practices, expanding the practical application of ISO/FDIS 24899 within the broader plastics and environmental analysis field.

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Keywords: ISO/FDIS 24899, microplastics extraction, compost analysis, laboratory method, polymer recovery, microplastics contamination, ISO microplastics standards, compost quality, density separation, Fenton oxidation, environmental plastics testing

FINAL DRAFT
International
Standard
ISO/TC 61/SC 14
Plastics — Method for the
Secretariat: DIN
extraction of microplastics from
Voting begins on:
compost samples
2026-09-15
Voting terminates on:
2026-11-10
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 61/SC 14
Plastics — Method for the
Secretariat: DIN
extraction of microplastics from
Voting begins on:
compost samples
Voting terminates on:
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
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Published in Switzerland Reference number
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviations . 1
3.1 Terms and definitions .1
3.2 Symbols and abbreviated terms .3
4 General . 3
5 Extraction of microplastics from compost . 4
5.1 Principle .4
5.2 Materials, reagents and consumables .5
5.3 Precautions for the laboratory environment, apparatus and materials .6
5.3.1 Operating precautions linked to the laboratory environment .6
5.3.2 Precautions and cleaning protocol for materials .6
5.4 Laboratory qualification .7
5.4.1 Method blank .7
5.4.2 Unspiked matrix sample . .7
5.4.3 Limits of quantification, detection and reporting .8
5.4.4 Verification of microplastics recovery rate .8
5.4.5 Particle stability tests . .9
5.5 Deagglomeration .10
5.6 Fenton oxidation .11
5.7 Density separation .11
6 Performance criteria and method verification .12
7 Test report .13
Annex A (informative) Sampling from compost and homogenisation of raw samples .15
Annex B (informative) Analysis of extracted microplastics .18
Annex C (informative) Method improvement and validation . 19
Annex D (informative) High density salt solutions .29
Bibliography .30

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
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with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
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This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 14, Environmental
aspects.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
Microplastics are ubiquitous in the environment, occurring also in complex environmental (e.g. soil,
sediments) and technical (e.g. compost) matrices. The compost, be it of industrial or home composting
origin, is primarily made from organic materials, however contamination can occur if non-compostable
plastic waste is not properly separated from the organic materials before composting. Plastic materials can
fragment into smaller microplastics, while some polymeric materials may undergo complete biodegradation.
When compost is used as fertiliser in agricultural soils plastic fragments can enter the environment.
Consequently, the presence of plastic fragments may impact compost quality and may pose a risk to biota
when compost is applied in natural settings.
To analyse microplastics in compost, it is essential to ensure a quantitatively and qualitatively representative
extraction. This involves evaluation of plastic particle and polymer stability and high recovery rate, whilst
minimising sample contamination. Generally, the extraction of microplastics from compost is poorly
comparable between scientific studies due to inconsistent methodologies used and a lack of quality
assessments. Therefore, there is a growing need for a standardised method for microplastics extraction
from compost for regulatory and standardisation purposes.
This document provides a method for extraction of microplastics from compost, including quality control
measures such as recovery and stability tests. Solely the extraction is part of this document. Mass-based or
number-based analytical techniques (e.g. according to ISO 16094-2 and ISO 16094-3) commonly used for
microplastic quantification can be employed afterwards. It is important demonstrating that the compost
extract does not contain (particulate) substances likely to be misidentified as microplastics by both,
spectroscopic and thermal techniques.
This document covers microplastics from 20 µm to 1 000 µm (in alignment with ISO 16094-2) and with
densities up to 1,4 g/cm (therefore not all types of PVC or PTFE are covered with the current version of
this method). Fragments from biodegradable polymeric materials may also be extracted with this method,
depending on their physical integrity at the time of sampling.

v
FINAL DRAFT International Standard ISO/FDIS 24899:2026(en)
Plastics — Method for the extraction of microplastics from
compost samples
1 Scope
This document specifies a laboratory method for the extraction of microplastics from compost matrices
originating from industrial or home composting. The method outlines various extraction steps assuring
polymer stability, and high recovery rate. This extraction process separates microplastics from the compost
matrix that can be further analysed either by number-based or by mass-based techniques.
The method is applicable for microplastics up to 1 mm in size, see Clause 4.
The method is applicable for microplastics with densities lower than 1,4 g/cm .
This document does not specify downstream detection methods for the identification and quantification.
The method in this document has not been validated for microplastic extraction from other matrices, except
for composts.
2 Normative references
There are no normative references in this document.
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1.1
compost
organic soil conditioner obtained by biodegradation of a mixture consisting principally of various vegetable
residues, occasionally with other organic material, and having a limited mineral content
[SOURCE: ISO 472:2013, 2.1735]
3.1.2
microplastics
solid plastic or synthetic polymer particle insoluble in water with the largest dimension between 1 μm and
5 mm
Note 1 to entry: Microplastics may show various shapes.
Note 2 to entry: This definition encompasses the ISO/TR 21960 definitions of large microplastics and microplastics
Note 3 to entry: The term “microplastics” covers the sum of several individual microplastic particles.
[SOURCE: ISO 16094-2:2025, 3.1.1]

3.1.3
sample
small portion of a material or small group of units taken from a larger quantity of material or collection of
units and intended to be representative of the whole
[SOURCE: ISO 472:2013, 2.899]
3.1.4
subsample
defined portion of a sample obtained by suitable sample division and identical in terms of composition
[SOURCE: ISO/TS 20612:2007, 3.4]
3.1.5
method blank
aliquot of reagent water that is treated exactly as a sample through the complete analytical procedure
including extraction, clean-up, identification and quantification including all the relevant reagents and
materials
[SOURCE: ISO 17858:2007, 3.1.11]
3.1.6
unspiked matrix sample
compost subsample processed through the analytical procedure without the addition of spiked microplastics,
used to determine the background concentration of microplastics in the matrix for interpretation of
spike-recovery experiments
3.1.7
spiked sample
compost subsample in which a known amount of analyte has been added, used for recovery, precision, bias,
matrix effects
3.1.8
Fenton’s reagent
2+
solution of hydrogen peroxide (H O ) and an iron catalyst, typically ferrous iron (Fe ) sulfate, used to
2 2
generate hydroxyl radicals (•OH) for the oxidation of organic compounds
3.1.9
particle-free water
water not containing microplastics (3.1.2) or with the lowest possible concentration of microplastics (3.1.2)
[SOURCE: ISO 16094-2:2025, 3.1.6]
3.1.11
targeted analysis
analysis approach in which predefined analytes are specifically identified and quantified using appropriate
reference standards and calibration procedures
3.1.10
untargeted analysis
analysis approach performed without restriction to predefined analytes, aiming to detect and, where
possible, identify a broad range of compounds or particles present in the sample

3.2 Symbols and abbreviated terms
CaCl Calcium chloride
DANS 4-dimethylamino-4’-nitrostilbene
FTIR Fourier transform infrared
HCl Hydrochloric acid
H O Hydrogen peroxide
2 2
H SO Sulfuric acid
2 4
ILT Interlaboratory trial
LDIR Laser direct infrared
(LD)PE (Low density) polyethylene
LOQ Limit of quantification
NaI Sodium iodide
PA Polyamide
PBAT Polybutylene adipate terephthalate
PC Polycarbonate
PET Polyethylene terephthalate
PLA Polylactic acid
PMMA Polymethyl methacrylate
PP Polypropylene
PS Polystyrene
PTFE Polytetrafluoroethylene
PU Polyurethane
PVC Polyvinyl chloride
Py-GC/MS Pyrolysis gas chromatography-mass spectrometry
SPT Sodium polytungstate
TED-GC/MS Thermal extraction desorption gas chromatography-mass spectrometry
TGA Thermogravimetric analysis
XPS X-ray photoelectron spectroscopy
ZnCl Zinc chloride
4 General
This method is intended for extracting microplastics from compost matrices generated from either
industrial or home composting processes.
The method takes into consideration:
a) the extraction of microplastics from 20 µm to 1 000 µm in size;
b) retrieval of microplastics with densities ≤ 1,4 g/cm , such as polyethylene (PE), polypropylene (PP),
polyethylene terephthalate (PET), polycarbonate (PC), polystyrene (PS), polyamide (PA), polymethyl
methacrylate (PMMA), polyurethane (PU), as well as biodegradable polymers with densities < 1,4 g/cm
such as polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT);
c) the heterogeneity of the test compost;
d) solely the extraction of the particles. An informative section on sampling is included in Annex A. Several
analytical methods were applied in the laboratories during the method’s development. These methods
are deemed reliable, and are outlined in Annex B;

e) minimized destructive effects on particle size, number, mass, or chemical composition;
f) reduction of microplastics loss during extraction, due to extensively optimized procedural steps
throughout the extraction method;
g) minimization of plastic contamination of sample analysed by excluding, where possible, the use of
plastic materials and equipment;
h) control measurements for microplastic contamination, including method blank and the unspiked matrix
sample, as well as stability and recovery tests for microplastics and findings from the interlaboratory
trial as described in Annex C;
NOTE Microplastics with densities > 1,4 g/cm , such as some types of polyvinyl chloride (PVC) and
polytetrafluoroethylene (PTFE) are not covered with the current version of this method.
5 Extraction of microplastics from compost
5.1 Principle
The extraction method for microplastics from the compost involves several sequential steps. It starts
with the deagglomeration of the compost particles and the oxidation of the organic material using Fenton
oxidation. Microplastics are collected following density separation using a high-density CaCl salt solution.
The extraction procedure has been optimized by an interlaboratory trial, as referenced in Annex C, which
ensures a higher level of quality and reliability of this document. If any steps of the extraction are omitted,
the performance criteria provided in Clause 4 and Clause 6 become invalid, since the same level of quality
(extraction efficiency and matrix removal efficiency) in the extraction cannot be guaranteed.
A detailed overview of steps, duration of the extraction of microplastics from compost, as well as reagents
and materials needed are specified in Table 1.

Table 1 — Detailed overview of steps and duration of the extraction of microplastics from the
compost
Reagents and material
Extraction step Purpose Time needed
needed
Deagglomeration Break-up of agglomer- 5 min for sample set-up, Particle-free water
ates in which microplas-
5 min ultrasonication Beaker (borosilicate glass,
tics could be retained
≥ 100 ml)
Ultrasonication device
2+
Fenton oxidation Removal of the majority 10 min preparation of the Fe Beaker (borosilicate glass,
of organic material from solution. ≥ 500 ml)
the compost
5 additions of Fenton reagent: 5x Overhead stirrer with glass
2+
2 min addition of the Fe solution rod or orbital shaker
and H O , followed by 30 min con-
pH meter
2 2
tinuous stirring.
Thermometer
Final stirring lasts 60 min. After-
1 mol/l HCl or H SO
2 4
wards reaction is not apparent from
Iron (II) sulfate heptahy-
heat/bubbles.
drate
Dispersion is left to sediment for
Hydrogen peroxide (30 %
60 min.
mass fraction)
260 min in total.
Metal filter (20 µm)
Density separation Removal of the compost 2 days in total PTFE squeeze bottle or a
components that have glass pipette
5 min mixing,
a higher density than
Separating funnel (borosil-
18 h sedimentation,
microplastics, such as
icate glass, ≥ 1 l)
6 h removal of the high-density
inorganic matter
Glass funnel
fraction,
Collection of microplas-
Calcium chloride dihydrate
5 min re-fill,
tics
(≥ 99 %)
18 h sedimentation (two density
Particle-free water
separation steps in CaCl solution
lead to removal of >90 % mass frac- Ethanol (analytical grade)
tion of particles with ρ > 1,4 g/cm ),
6 h removal of the high-density frac-
tion, and retrieval of microplastics.
30 min filtration and retrieval of the
analytical sample
NOTE The steps of homogenisation, representative sampling, and subsequent detection of particles (identification
and quantification of microplastics) are not part of this document. For further information on these two steps, refer to
Annexes A and B.
5.2 Materials, reagents and consumables
The particle-free water and all chemicals listed in Table 1 shall be checked for the presence of microplastics
by applying the method blank approach in 5.4.1. The limits of quantification, detection and reporting are
defined by the background contamination and the analytical technique used, as outlined in 5.4.3. The
particle number or mass in the analysed compost sample shall be 10 times higher than the background
contamination determined by the method blank measurements to be reported as a value. If the number
or mass of particles in the sample is lower than 10 times of the method blank, “≤ LOQ” shall be reported.
In case of high method blank contamination, microplastics in the chemical solutions shall be removed by
filtration (for example, through a cellulose filter, metal filter or another non-polymeric membrane with a
pore size of max. 10 µm) to achieve a lower limit of quantification/reporting limit. Alternatively, all solutions
and reagents used during sample preparation may be filtered through 0,2 µm filters prior to use and stored
in glass containers until required. In case of targeted analysis, no equipment made of the target polymer
shall be used.
5.3 Precautions for the laboratory environment, apparatus and materials
5.3.1 Operating precautions linked to the laboratory environment
The space dedicated to preparing and filtering samples should be free from polymer coatings or materials.
Regular cleaning of the laboratory environment is mandatory (e.g. hood and lab bench). To do this, ethanol,
detergent, particle-free water and suitable polymer free wipes may be used. Ideally, the work should be
done in a laminar flow hood, e.g. ISO 14644-1.
In particular, operators shall:
— check potential sample contamination by microplastics and chemicals which may cause spectral
interference with microplastics via the method blank measurements;
— use new gloves to avoid or minimize the unwanted release of microplastics from the laboratory safety
equipment;
— wash their hands prior to starting the manipulations with samples, especially after washing the outsides
of containers and when entering rooms dedicated to handling samples;
— wear a cotton lab coat or, if necessary, a clean anti-static lab coat (e.g. characterised regarding on the
materials/polymer in order to exclude the type of polymer from the sample results report);
— not wear face masks made of synthetic polymers (where face masks are required, masks made of natural
fibres (e.g. cotton) or non-shedding materials shall be used); not wear clothing made of synthetic fibres
(fleece jackets for example), body cleansing and other personal care products or cosmetics are likely to
release microplastics in the laboratory environment (e.g. nail varnish, foundations).
The laboratory personnel should protect the sample from all contamination coming from the working
environment especially when transporting the sample between the preparation workstation and the analysis
workstation, and during this final analysis stage. Containers, in particular beakers, containing the sample
shall be kept covered at all times using a suitable non-plastic cover (e.g. aluminium foil, inverted glass Petri
dish, or watch glass). The cover shall only be removed when strictly necessary and for the shortest possible
duration. Items carrying the sample, such as filters, shall be stored in an appropriate closed container.
5.3.2 Precautions and cleaning protocol for materials
Laboratory equipment that can release microplastics, such as those analysed (PP, PC, PA, etc.), should not be
used.
All items (glassware, metal, etc.) getting in contact with the samples, including containers for sampling,
shall be subject to special attention and shall be cleaned thoroughly, by applying the following protocol or
other suitable cleaning procedures:
Immerse the glass items in a suitable non-ionic detergent solution, with a sufficient contact time. Then rinse
the items with a suitable product (e.g. 50 % ethanol or a neutralising agent) and complete rinsing with
particle-free water of known quality. Leave the equipment to air dry. Do not wipe it dry.
As an alternative, glass items can be filled with particle-free water of known quality and non-ionic surfactant
and put in an ultrasonic bath for 5 min. Remove the water and repeat the entire procedure two times more.
The external surface of the glass item should be rinsed with particle-free water as well to remove potential
contamination on the outside. Do not wipe dry.
Containers, glassware and utensils may be calcined at 480 °C for 2 h or 450 °C for 6 h. If calcination
is applied, it should be performed after the cleaning procedure described above, in order to remove any
residual organic contamination. Calcination should be carried out prior to the first use of the equipment and
thereafter at regular intervals or whenever increased background contamination is observed (e.g. based on
method blank results).
After cleaning, glassware and metal parts shall be stored in glass or metal containers or under a laminar
flow hood. Contamination of particles can be minimized by storing glassware covered with aluminium foil
or in glass Petri dishes.
5.4 Laboratory qualification
5.4.1 Method blank
Although a clean room is not mandatory for the extraction outlined in this document, all measures shall be
taken to avoid contamination of the samples. In addition, method blanks shall be analysed to determine the
microplastic background from the surrounding area and laboratory equipment. While plastic equipment
should generally be avoided, it may be used in exceptional cases for targeted analysis of specific polymer
types, provided that the plastic material the equipment is made of can be distinguished from the target
analyte(s).
To create a method blank sample, the extraction steps outlined in 5.5 to 5.7 shall be simulated in the absence
of compost.
First, a 40 ml particle-free water shall be added to a beaker (e.g. 100 ml) and ultrasonicated with a delivered
power of 15,0 W to 20,0 W for 5 min (corresponding to 4 500 J to 6 000 J). Once the ultrasonication is
complete, the ultrasonication tip shall be removed and rinsed with 10 ml of particle-free water directly into
the same beaker containing the 40 ml sonicated particle-free water. If sonication is performed with a device
that does not require inserting a tip or similar into the sample, 10 ml of particle-free water shall be added
directly to the sonicated particle-free water. Transfer the resulting sample to a beaker (e.g. 500 ml to 600 ml,
⌀ 8 cm) and stir using an overhead stirrer with a ceramic or glass rod. Rinse the 100 ml beaker with 50 ml
particle-free water. Continuously stir the resulting 100 ml sample of particle-free water for 200 min.
Afterwards, the dispersion shall be left to sediment in the beaker for 60 min. In the meantime, 50 ml H O
2 2
(30 % mass fraction, liquid) shall be filtered through a 20 µm metal filter. The filtrate shall be discarded
and the prepared dispersion is carefully filtered through the same 20 µm metal filter. Discard the filtrate
2+
and filter 25 ml of the 0,036 mol/l Fe solution (as described in 5.6) through the same 20 µm metal filter.
To ensure complete transfer of the microplastics, the particles on the 20 µm metal filter shall be rinsed
back into the beaker that was used for stirring the particle-free water using 100 ml of 55 % mass fraction
CaCl dihydrate solution. To simulate the density separation (5.7), a separating funnel shall be filled with
prepared 100 ml CaCl dihydrate solution. The sample in the beaker shall be transferred into the separating
funnel, and the beaker shall be rinsed with 200 ml of CaCl dihydrate solution, dispensed directly from a
PTFE squeeze bottle or glass pipette into the funnel.
Next, the mixture shall first be swirled horizontally, then left to settle for 18 h. Then, the main proportion
of the salt solution in the separating funnel shall be discarded and only the last 100 ml of the separating
funnel content shall be left in the funnel. Add another 200 ml salt solution to the separating funnel, and the
funnel is horizontally swirled in circles and left to sediment for the second time. After 18 h, 200 ml of the
salt solution is removed again by opening the valve at the bottom of the separating funnel. The remaining
100 ml of the supernatant with floating microplastics shall be retained in a 250 ml glass bottle. Rinse the
separating funnel first with 50 ml particle-free water followed by 100 ml ethanol into the same 250 ml glass
bottle. To remove any remaining solid residues which might disturb the analysis, the sample shall be filtered
through a metal filter with a pore size of 20 µm. Next, a PTFE squeeze bottle or glass pipette containing
100 ml of particle-free water shall be used to rinse the particles from the filter back into the 250 ml sample
container. The entire content of the 250 ml bottle shall be analysed. The number/mass of microplastics
present corresponds to the background of microplastic number/mass in the final 100 ml analytical sample
after the 20 µm filtration step. When only a fraction of the actual compost extract (e.g. a subsample or part
of the filter surface) is analysed, the results shall be scaled to represent the total extract in order to enable
comparison with the method blank, which shall be analysed in its entirety.
5.4.2 Unspiked matrix sample
For spike-recovery tests, it is crucial to perform unspiked matrix sample measurements. The unspiked
matrix sample comprises a 1 g compost sample that does not have any intentionally spiked microplastics or
plastic test items. This 1 g compost subsample shall be sourced from the same compost sample of which later

another 1 g subsample will be spiked with the target analyte. To assess microplastic contamination in this
unspiked matrix sample, the complete extraction process outlined in 5.5 to 5.7 shall be conducted, and the
analysis shall employ the same analytical technique that will be used for the spiked samples. The unspiked
matrix sample assessment is only possible for the spike-recovery tests and is identical to the sample that
needs to be analysed for microplastic content.
5.4.3 Limits of quantification, detection and reporting
The size range as well as the quantitative limits for microplastics are inherently dependent on the applied
analytical methods and therefore cannot be defined normatively in this document.
The current document is considered robust for a size range of 20 µm to 1 000 µm.
For mass-based methods, analytical performance is typically described using the limit of detection (LOD)
and the limit of quantification (LOQ). The LOD is the lowest concentration at which the analyte can be
reliably distinguished from background noise, while the LOQ represents the lowest concentration at which
quantitative results can be obtained with acceptable accuracy. According to ISO 16094-3, a signal-to-noise
ratio of 3 is commonly used to estimate the LOD and a signal-to-noise ratio of 10 for the LOQ. These limits
are often constrained by weighing accuracy rather than by the intrinsic sensitivity of the detection system
and should be determined in the presence of the relevant matrix.
For number-based methods, the concept of a reporting limit is more appropriate than a conventional LOQ.
The reporting limit depends on the analysed fraction of the sample or filter, the minimum particle size
claimed by the method, the polymer type, and the level of background contamination. ISO 16094-2 specifies
that reporting limits are derived from analytical control blanks, typically based on the mean blank value
plus three times the standard deviation, and may be defined separately for different size classes and polymer
types.
The determination and interpretation of quantitative limits strongly depend on the control of background
contamination. Method blanks are therefore essential, particularly at low microplastic concentrations.
ISO 16094-2 requires that blanks are analysed in the same way as samples and explicitly states that blank
values shall not be subtracted from the sample results. If contamination exceeds acceptable levels, the
analytical sequence might need to be repeated after corrective measures.
Background contamination is inherently heterogeneous, both in terms of particle number and particle
characteristics. Therefore, evaluation based solely on total particle number or total mass can be misleading.
The background contamination should be assessed in a polymer-specific and, where applicable, size-
resolved manner. Differences in polymer type, particle size, and other characteristics may indicate different
sources and should be considered when comparing samples and blanks.
In addition, matrix-related interferences can affect both number-based and mass-based approaches.
Spectroscopic techniques can be influenced by substances with similar spectral features (e.g. proteins,
pigments or long-chain hydrocarbons), while thermo-analytical techniques can be affected by co-extracted
matrix components. These effects should be considered when establishing method-specific detection and
reporting limits.
Overall, quantitative limits for microplastics shall be considered method-specific, matrix-dependent and
closely linked to laboratory performance. Their establishment requires appropriate validation, including
replicate analyses and blank evaluation, and is therefore outside the normative scope of this document.
5.4.4 Verification of microplastics recovery rate
Verification of the successful implementation of the extraction method shall be checked using at least two
3 3
microplastic materials of a known type (one with a density < 1 g/cm and one with a density > 1 g/cm ).
The use of commercial polymer/microplastic standards (e.g. labelled plastics or standards used for flow
cytometry) or a reference prepared by the laboratory (by friction, grinding, etc.) is possible. The spiking
material shall be representative of the microplastics claimed to be quantified and shall therefore be selected
to reflect the size range, polymer chemistry, and particle morphology relevant to the intended field of
application.
Number characterization of the prepared spike sample may take place using a different analytical technique
(e.g. flow cytometry, optical counting, Micro-FTIR, Micro-Raman, SEM) from the one used for quantification
after extraction.
At least three samples of an unspiked matrix sample (5.4.2) shall be spiked with a known mass or number
of microplastics of different types and sizes to cover the field of application claimed by the method. The
complete extraction process outlined in 5.5 to 5.7 shall then be conducted for the spiked and three unspiked
matrix samples, and the analysis shall employ the same analytical technique that will be used for the
unspiked matrix sample.
The recovery rate is calculated according to Formula (1) for a number-based recovery or Formula (2) for a
mass-based recovery:
NN
spikedsample unspikedmatrixsample
 
R  1000 (1)
N
spiked

where
R is the recovery rate in per cent;
N is the particle number measured in the spiked sample after extraction;
(spiked sample)
N is the particle number measured in the unspiked matrix sample after extraction;
(unspiked matrix sample)
N is the known particle number that was deliberately spiked into in the unspiked matrix sample.
(spiked)
mm
spikedsample, measured unspiked matrixsample, meaasured
 
R  100 (2)
m
spiked

where
m is the particle mass measured in the spiked sample after extraction;
(spiked sample)
m is the particle mass measured in the unspiked matrix sample after extraction;
(unspiked matrix sample)
m is the known particle mass that was deliberately spiked into in the unspiked matrix sample.
(spiked)
It shall be ensured that the recovery rate is ≥ 60 % for particles < 100 µm and ≥ 80 % for particles > 100 µm.
If the recovery rate is below these limits, the laboratory shall identify and eliminate potential sources of loss
or systematic error (e.g. particle loss during extraction, insufficient matrix removal or analytical bias), and
the method shall be optimized accordingly. The recovery test shall then be repeated until the acceptance
criteria are met. For values above 100 % the laboratory shall perform a cause analysis. The proposed
recovery criteria are considered scientifically justified – recognizing, based on the conducted ILT and
further literature, that the recovery and quantification of particles < 100 µm remain a significant analytical
challenge – and are deemed appropriate for reliable application within the scope of this method.
5.4.5 Particle stability tests
Several types of microplastics and fragments from biodegradable polymers (e.g. based on PBAT and PLA)
were tested during method development regarding their stability towards the specific sonication and Fenton
oxidation conditions applied in this document (results shown in Annex C). If any other type of microplastic
or more complex materials, such as multicomponent materials containing fillers and not predominantly
composed of pure polymers, shall be investigated using this document, stability tests shall be conducted
on the target analyte. This type of stability test shall be conducted once in each laboratory unless literature
data for the target analyte is available.
Particle stability shall be evaluated by comparing the particle size distribution and the total particle number
or mass before and after application of the extraction procedure. Changes in particle size distribution shall
be assessed based on size-class–resolved particle numbers (or mass fractions), rather than a single summary
parameter.
A distinction shall be made between:
— uniform particle loss, defined as a comparable decrease in particle number or mass across all size classes
without a change in distribution shape; and
— fragmentation, defined as a redistribution of particles towards smaller size classes.
The particles shall be considered stable if:
— the total particle number or mass is not reduced by more than 10 %, and
— no significant redistribution of particles between size classes (> 10 % relative change per size class) is
observed.
If stability test results indicate changes between 10 % and 30 %, either in total particle number/mass or
within individual size classes, the impact on the reported results shall be evaluated and discussed in the test
report. If the alteration exceeds 30 %, either as overall particle loss or as a significant shift in particle size
distribution (e.g. systematic increase in smaller size classes), the target analyte shall be considered unstable
under the applied conditions and cannot be extracted using this protocol.
To test the stability of the microplastic type of interest under the conditions of the described extraction
procedure (5.5 to 5.7), a suspension of the microplastics of interest in particle-free water (in the absence
of any compost), shall be subjected to the different steps of the process as foreseen in this document. The
particle size distribution or mass of each particle (polymer) type shall be analysed before and after applying
the extraction procedure and the results shall be compared.
It is also possible to test the particle stability in single extraction steps only (e.g. 5.6 Fenton oxidation) to
identify the most critical step for the stability of the microplastic type of interest.
The minimum requirement for analysis is to compare the particle size distribution (e.g. laser diffraction:
Fraunhofer evaluation for particles > 50 µm, Mie scattering evaluation for particles 1 µm to 50 µm) or
mass of the microplastic type before and after carrying out the whole procedure (or steps of it). Additional
analyses can be conducted based on the specific microplastic type and research question. Examples of
additional analyses include gel permeation chromatography for molar mass distribution (applicable only to
non-crosslinked types of microplastics), (ATR-FT) IR and/or XPS for surface chemistry, optical microscopy
or SEM for surface texture and shape, and DSC for crystallinity.
5.5 Deagglomeration
After homogenization and subsampling, any agglomerates of microplastic and compost particles are broken
down and dispersed using ultrasound. To achieve this, add 1 g of compost subsample and 40 ml particle-free
water to a beaker (e.g. 100 ml, borosilicate glass) and ultrasonicated with a delivered power of 15,0 W to
20,0 W for 5 min (corresponding to 4 500 J to 6 000 J) to effectively break up the agglomerates. The device
used for ultrasonication shall have its delivered power measured using the calorimetric method described in
Reference [17]. The temperature during the sonication treatment shall not exceed 50 °C. The sample can be
cooled using a water or ice bath to stay below 50 °C, if needed. Once the ultrasonication is complete, remove
the ultrasonication tip and rinse with 10 ml of particle-free water directly into the same beaker containing
the
...

ISO/TC 61/SC 14/WG 4
Secretariat: DIN
Date: 2026-07-3008-31
Plastics – A — Method for the extraction of microplastics from
compost samples
FDIS stage
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
EmailE-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviations . 1
3.1 Terms and definitions . 1
3.2 Symbols and abbreviated terms . 3
4 General. 3
5 Extraction of microplastics from compost . 4
5.1 Principle . 4
5.2 Materials, reagents and consumables . 5
5.3 Precautions for the laboratory environment, apparatus and materials . 6
5.4 Laboratory qualification . 7
5.5 Deagglomeration . 11
5.6 Fenton oxidation . 11
5.7 Density separation . 12
6 Performance criteria and method verification . 13
7 Test report . 14
Annex A (informative) Sampling from compost and homogenisation of raw samples . 16
Annex B (informative) Analysis of extracted microplastics . 20
Annex C (informative) Method improvement and validation . 21
Annex D (informative) High density salt solutions . 36
Bibliography . 37

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 14,
Environmental aspects.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
Microplastics are ubiquitous in the environment, occurring also in complex environmental (e.g. soil,
sediments) and technical (e.g. compost) matrices. The compost, be it of industrial or home composting origin,
is primarily made from organic materials, however contamination can occur if non-compostable plastic waste
is not properly separated from the organic materials before composting. Plastic materials can fragment into
smaller microplastics, while some polymeric materials may undergo complete biodegradation. When compost
is used as fertiliser in agricultural soils plastic fragments can enter the environment. Consequently, the
presence of plastic fragments may impact compost quality and may pose a risk to biota when compost is
applied in natural settings.
To analyse microplastics in compost, it is essential to ensure a quantitatively and qualitatively representative
extraction. This involves evaluation of plastic particle and polymer stability and high recovery rate, whilst
minimising sample contamination. Generally, the extraction of microplastics from compost is poorly
comparable between scientific studies due to inconsistent methodologies used and a lack of quality
assessments. Therefore, there is a growing need for a standardised method for microplastics extraction from
compost for regulatory and standardisation purposes.
This document provides a method for extraction of microplastics from compost, including quality control
measures such as recovery and stability tests. Solely the extraction is part of this document. Mass-based or
number-based analytical techniques (e.g. according to ISO 16094-2 and ISO 16094-3) commonly used for
microplastic quantification can be employed afterwards. It is important demonstrating that the compost
extract does not contain (particulate) substances likely to be misidentified as microplastics by both,
spectroscopic and thermal techniques.
This document covers microplastics from 20 µm to 1 000 µm (in alignment with ISO 16094-2) and with
densities up to 1,4 g/cm (therefore not all types of PVC or PTFE are covered with the current version of this
method). Fragments from biodegradable polymeric materials may also be extracted with this method,
depending on their physical integrity at the time of sampling.
v
Plastics – A — Method for the extraction of microplastics from
compost samples
1 Scope
This document specifies a laboratory method for the extraction of microplastics from compost matrices
originating from industrial or home composting. The method outlines various extraction steps assuring
polymer stability, and high recovery rate. This extraction process separates microplastics from the compost
matrix that can be further analysed either by number-based or by mass-based techniques.
The method is applicable for microplastics up to 1 mm in size, see Clause 4Clause 4.
The method is applicable for microplastics with densities lower than 1,4 g/cm .
This document does not specify downstream detection methods for the identification and quantification.
The method in this document has not been validated for microplastic extraction from other matrices, except
for composts.
2 Normative references
There are no normative references in this document.
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1.1 3.1.1
compost
organic soil conditioner obtained by biodegradation of a mixture consisting principally of various vegetable
residues, occasionally with other organic material, and having a limited mineral content
[SOURCE: ISO 472:2013, 2.1735]
3.1.2 3.1.2
microplastics
solid plastic or synthetic polymer particle insoluble in water with the largest dimension between 1 μm and
5 mm
Note 1 to entry: Microplastics may show various shapes.
Note 2 to entry: This definition encompasses the ISO/TR 21960 definitions of large microplastics and microplastics
Note 3 to entry: The term “microplastics” covers the sum of several individual microplastic particles.
[SOURCE: ISO 16094-2:2025, 3.1.1]
3.1.3 3.1.3
sample
small portion of a material or small group of units taken from a larger quantity of material or collection of
units and intended to be representative of the whole
[SOURCE: ISO 472:2013, 2.899]
3.1.4 3.1.4
subsample
defined portion of a sample obtained by suitable sample division and identical in terms of composition
[SOURCE: ISO/TS 20612:2007, 3.4]
3.1.5 3.1.5
method blank
aliquot of reagent water that is treated exactly as a sample through the complete analytical procedure
including extraction, clean-up, identification and quantification including all the relevant reagents and
materials
[SOURCE: ISO 17858:2007, 3.1.11]
3.1.6 3.1.6
unspiked matrix sample
compost subsample processed through the analytical procedure without the addition of spiked microplastics,
used to determine the background concentration of microplastics in the matrix for interpretation of
spike-recovery experiments
3.1.7 3.1.7
spiked sample
compost subsample in which a known amount of analyte has been added, used for recovery, precision, bias,
matrix effects
3.1.8
matrix blank
compost subsample in which no analyte is present, and unspiked, used only as a reference for matrix
interference correction
3.1.8 3.1.9
Fenton’s reagent
2+
solution of hydrogen peroxide (H O ) and an iron catalyst, typically ferrous iron (Fe ) sulfate, used to generate
2 2
hydroxyl radicals (•OH) for the oxidation of organic compounds
3.1.9 3.1.10
particle-free water
water not containing microplastics (3.1.2(3.1.2)) or with the lowest possible concentration of microplastics
(3.1.2(3.1.2))
[SOURCE: ISO 16094-2:2025, 3.1.6]
3.1.10 3.1.11
targeted analysis
analysis approach in which predefined analytes are specifically identified and quantified using appropriate
reference standards and calibration procedures
3.1.11 3.1.12
untargeted analysis
analysis approach performed without restriction to predefined analytes, aiming to detect and, where possible,
identify a broad range of compounds or particles present in the sample
3.2 Symbols and abbreviated terms
CaCl Calcium chloride
DANS 4-dimethylamino-4’-nitrostilbene
FTIR Fourier transform infrared
HCl Hydrochloric acid
H O Hydrogen peroxide
2 2
H SO Sulfuric acid
2 4
ILT Interlaboratory trial
LDIR Laser direct infrared
(LD)PE (Low density) polyethylene
LOQ Limit of quantification
NaI Sodium iodide
PA Polyamide
PBAT Polybutylene adipate terephthalate
PC Polycarbonate
PET Polyethylene terephthalate
PLA Polylactic acid
PMMA Polymethyl methacrylate
PP Polypropylene
PS Polystyrene
PTFE Polytetrafluoroethylene
PU Polyurethane
PVC Polyvinyl chloride
Py-GC/MS Pyrolysis gas chromatography-mass spectrometry
SPT Sodium polytungstate
TED-GC/MS Thermal extraction desorption gas chromatography-mass spectrometry
TGA Thermogravimetric analysis
XPS X-ray photoelectron spectroscopy
ZnCl Zinc chloride
4 General
This method is intended for extracting microplastics from compost matrices generated from either industrial
or home composting processes.
The method takes into consideration:
a) a) the extraction of microplastics from 20 µm to 1 000 µm in size;
b) b) retrieval of microplastics with densities ≤ 1,4 g/cm , such as polyethylene (PE), polypropylene
(PP), polyethylene terephthalate (PET), polycarbonate (PC), polystyrene (PS), polyamide (PA),
polymethyl methacrylate (PMMA), polyurethane (PU), as well as biodegradable polymers with densities
< 1,4 g/cm such as polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT);
c) c) the heterogeneity of the test compost;
d) d) solely the extraction of the particles. An informative section on sampling is included in
Annex AAnnex A. Several analytical methods were applied in the laboratories during the method’s
development. These methods are deemed reliable, and are outlined in Annex BAnnex B;;
e) e) minimized destructive effects on particle size, number, mass, or chemical composition;
f) f) reduction of microplastics loss during extraction, due to extensively optimized procedural
steps throughout the extraction method;
g) g) minimization of plastic contamination of sample analysed by excluding, where possible, the
use of plastic materials and equipment;
h) h) control measurements for microplastic contamination, including method blank and the
unspiked matrix sample, as well as stability and recovery tests for microplastics and findings from the
interlaboratory trial as described in Annex CAnnex C;;
NOTE Microplastics with densities > 1,4 g/cm, such as some types of polyvinyl chloride (PVC) and
polytetrafluoroethylene (PTFE) are not covered with the current version of this method.
5 Extraction of microplastics from compost
5.1 Principle
The extraction method for microplastics from the compost involves several sequential steps. It starts with the
deagglomeration of the compost particles and the oxidation of the organic material using Fenton oxidation.
Microplastics are collected following density separation using a high-density CaCl salt solution.
The extraction procedure has been optimized by an interlaboratory trial, as referenced in Annex CAnnex C,,
which ensures a higher level of quality and reliability of the standard.this document. If any steps of the
extraction are omitted, the performance criteria provided in Clause 4Clause 4 and Clause 6Clause 6 become
invalid, since the same level of quality (extraction efficiency and matrix removal efficiency) in the extraction
cannot be guaranteed.
A detailed overview of steps, duration of the extraction of microplastics from compost, as well as reagents and
materials needed are specified in Table 1Table 1.
Table 1 — Detailed overview of steps and duration of the extraction of microplastics from the
compost
Reagents and
Extraction step Purpose Time needed
material needed
Deagglomeration Break-up of 5 min for sample set-up, Particle-free water
agglomerates in which
5 min ultrasonication Beaker (borosilicate glass,
≥ 100 ml)
Reagents and
Extraction step Purpose Time needed
material needed
microplastics could be Ultrasonication device
retained
2+
Fenton oxidation Removal of the majority 10 min preparation of the Fe Beaker (borosilicate glass,
of organic material solution. ≥ 500 ml)
from the compost
5 additions of Fenton reagent: 5x Overhead stirrer with
2+
2 min addition of the Fe solution glass rod or orbital shaker
O , followed by 30 min
and H2 2
pH meter
continuous stirring.
Thermometer
Final stirring lasts 60 min.
1 Mmol/l HCl or H2SO4
Afterwards reaction is not
Iron (II) sulfate
apparent from heat/bubbles.
heptahydrate
Dispersion is left to sediment for
Hydrogen peroxide (30 %
60 min.
mass fraction)
260 min in total.
Metal filter (20 µm)
Density separation Removal of the compost 2 days in total PTFE squeeze bottle or a
components that have a glass pipette
5 min mixing,
higher density than
Separating funnel
18 h sedimentation,
microplastics, such as
(borosilicate glass, ≥ 1 l)
6 h removal of the high-density
inorganic matter
Glass funnel
fraction,
Collection of
Calcium chloride
5 min re-fill,
microplastics
dihydrate (≥ 99 %)
18 h sedimentation (two density
Particle-free water
separation steps in CaCl solution
lead to removal of >90 % mass Ethanol (analytical grade)
fraction of particles with ρ >
1,4 g/cm ),
6 h removal of the high-density
fraction, and retrieval of
microplastics.
30 min filtration and retrieval of
the analytical sample
NOTE The steps of homogenisation, representative sampling, and subsequent detection of particles (identification
and quantification of microplastics) are not part of this document. For further information on these two steps, refer to
Annexes AAnnexes A and BB.
5.2 Materials, reagents and consumables
The particle-free water and all chemicals listed in Table 1Table 1 shall be checked for the presence of
microplastics by applying the method blank approach in 5.4.15.4.1. The limits of quantification, detection and
reporting are defined by the background contamination and the analytical technique used, as outlined in
5.4.35.4.3. The particle number or mass in the analysed compost sample shall be 10 times higher than the
background contamination determined by the method blank measurements to be reported as a value. If the
number or mass of particles in the sample is lower than 10 times of the proceduralmethod blank, “≤ LOQ” shall
be reported. In case of high method blank contamination, microplastics in the chemical solutions shall be
removed by filtration (for example, through a cellulose filter, metal filter or another non-polymeric membrane
with a pore size of max. 10 µm) to achieve a lower limit of quantification/reporting limit. Alternatively, all
solutions and reagents used during sample preparation may be filtered through 0,2 µm filters prior to use and
stored in glass containers until required. In case of targeted analysis, no equipment made of the target polymer
shall be used.
5.3 Precautions for the laboratory environment, apparatus and materials
5.3.1 Operating precautions linked to the laboratory environment
The space dedicated to preparing and filtering samples should be free from polymer coatings or materials.
Regular cleaning of the laboratory environment is mandatory (e.g. hood and lab bench). To do this, ethanol,
detergent, particle-free water and suitable polymer free wipes may be used. Ideally, the work should be done
in a laminar flow hood, e.g. ISO 14644-1. In particular, operators shall:
In particular, operators shall:
— — check potential sample contamination by microplastics and chemicals which may cause spectral
interference with microplastics via the method blank measurements;
— — use new gloves to avoid or minimize the unwanted release of microplastics from the laboratory safety
equipment;
— — wash their hands prior to starting the manipulations with samples, especially after washing the
outsides of containers and when entering rooms dedicated to handling samples;
— — wear a cotton lab coat or, if necessary, a clean anti-static lab coat (e.g. characterised regarding on the
materials/polymer in order to exclude the type of polymer from the sample results report);
— — not wear face masks made of synthetic polymers (where face masks are required, masks made of
natural fibres (e.g. cotton) or non-shedding materials shall be used); not wear clothing made of synthetic
fibres (fleece jackets for example), body cleansing and other personal care products or cosmetics are likely
to release microplastics in the laboratory environment (e.g. nail varnish, foundations).
The laboratory personnel should protect the sample from all contamination coming from the working
environment especially when transporting the sample between the preparation workstation and the analysis
workstation, and during this final analysis stage. Containers, in particular beakers, containing the sample shall
be kept covered at all times using a suitable non-plastic cover (e.g. aluminium foil, inverted glass Petri dish, or
watch glass). The cover shall only be removed when strictly necessary and for the shortest possible duration.
Items carrying the sample, such as filters, shall be stored in an appropriate closed container.
5.3.2 Precautions and cleaning protocol for materials
Laboratory equipment that can release microplastics, such as those analysed (PP, PC, PA, etc.).), should not be
used.
All items (glassware, metal, etc.) getting in contact with the samples, including containers for sampling, shall
be subject to special attention and shall be cleaned thoroughly, by applying the following protocol or other
suitable cleaning procedures:
Immerse the glass items in a suitable non-ionic detergent solution, with a sufficient contact time. Then rinse
the items with a suitable product (e.g. 50 % ethanol or a neutralising agent) and complete rinsing with
particle-free water of known quality. Leave the equipment to air dry. Do not wipe it dry.
As an alternative, glass items can be filled with particle-free water of known quality and non-ionic surfactant
and put in an ultrasonic bath for 5 min. Remove the water is removed, and repeat the entire procedure is
repeated two times more. The external surface of the glass item should be rinsed with particle-free water as
well to remove potential contamination on the outside. Do not wipe dry.
Containers, glassware and utensils may be calcined at 480 °C for 2 h or 450 °C for 6 h. If calcination is applied,
it should be performed after the cleaning procedure described above, in order to remove any residual organic
contamination. Calcination should be carried out prior to the first use of the equipment and thereafter at
regular intervals or whenever increased background contamination is observed (e.g. based on method blank
results).
After cleaning, glassware and metal parts shall be stored in glass or metal containers or under a laminar flow
hood. Contamination of particles can be minimized by storing glassware covered with aluminumaluminium
foil or in glass Petri dishes.
5.4 Laboratory qualification
5.4.1 Method blank
Although a clean room is not mandatory for the extraction outlined in this document, it is however important
to take all measures shall be taken to avoid contamination of the samples. In addition, it is essential to analyse
method blanks shall be analysed to determine the microplastic background from the surrounding area and
laboratory equipment. While plastic equipment should generally be avoided, it may be used in exceptional
cases for targeted analysis of specific polymer types, provided that the plastic material the equipment is made
of can be distinguished from the target analyte(s).
To create a method blank sample, the extraction steps outlined in 5.55.5 to 5.75.7 shall be simulated in the
absence of compost.
First, a 40 ml particle-free water areshall be added to a beaker (e.g. 100 ml) and ultrasonicated with a
delivered power of 15,0 W to 20,0 W for 5 min (corresponding to 4 500 J to 6 000 J). Once the ultrasonication
is complete, the ultrasonication tip isshall be removed and rinsed with 10 ml of particle-free water directly
into the same beaker containing the 40 ml sonicated particle-free water. If sonication is performed with a
device that does not require inserting a tip or similar into the sample, 10 ml of particle-free water areshall be
added directly to the sonicated particle-free water. Transfer the resulting sample is transferred to a beaker
(e.g. 500 ml to 600 ml, ⌀ 8 cm) and stirredstir using an overhead stirrer with a ceramic or glass rod. Rinse the
100 ml beaker is rinsed with 50 ml particle-free water. Continuously stir the resulting 100 ml sample of
particle-free water is continuously stirred for 200 min.
Afterwards, the dispersion isshall be left to sediment in the beaker for 60 min. AtIn the meantime, 50 ml H O
2 2
(30 % mass fraction, liquid) areshall be filtered through a 20 µm metal filter. The filtrate isshall be discarded
and the prepared dispersion is carefully filtered through the same 20 µm metal filter. Discard the filtrate is
2+
discarded and filter 25 ml of the 0,036 mol/l Fe solution (as described in 5.65.6) are filtered) through the
same 20 µm metal filter. To ensure complete transfer of the microplastics, the particles on the 20 µm metal
filter areshall be rinsed back into the beaker that was used for stirring the particle-free water using 100 ml of
55 % mass fraction CaCl dihydrate solution. To simulate the density separation (5.7(5.7),), a separating funnel
isshall be filled with prepared 100 ml CaCl dihydrate solution. The sample in the beaker isshall be transferred
into the separating funnel, and the beaker isshall be rinsed with 200 ml of CaCl dihydrate solution, dispensed
directly from a PTFE squeeze bottle or glass pipette into the funnel.
Next, the mixture isshall first be swirled horizontally, then left to settle for 18 h. FollowingThen, the main
proportion of the salt solution in the separating funnel isshall be discarded and only the last 100 ml of the
separating funnel content isshall be left in the funnel. Add another 200 ml salt solution is then added to the
separating funnel, and the funnel is horizontally swirled in circles and left to sediment for the second time.
After 18 h, 200 ml of the salt solution is removed again by opening the valve at the bottom of the separating
funnel. The remaining 100 ml of the supernatant with floating microplastics isshall be retained in a 250 ml
glass bottle. Rinse the separating funnel is rinsed first with 50 ml particle-free water followed by 100 ml
ethanol into the same 250 ml glass bottle. To remove any remaining solid residues which might disturb the
analysis, the sample isshall be filtered through a metal filter with a pore size of 20 µm. Next, a PTFE squeeze
bottle or glass pipette containing 100 ml of particle-free water isshall be used to rinse the particles from the
filter back into the 250 ml sample container. It is essential to analyse The entire content of the 250 ml bottle
shall be analysed. The number/mass of microplastics present corresponds to the background of microplastic
number/mass in the final 100 ml analytical sample after the 20 µm filtration step. When only a fraction of the
actual compost extract (e.g. a subsample or part of the filter surface) is analysed, the results shall be scaled to
represent the total extract in order to enable comparison with the method blank, which shall be analysed in
its entirety.
5.4.2 Unspiked matrix sample
For spike-recovery tests, it is crucial to perform unspiked matrix sample measurements. The unspiked matrix
sample comprises a 1 g compost sample that does not have any intentionally spiked microplastics or plastic
test items. This 1 g compost subsample shall be sourced from the same compost sample of which later another
1 g subsample will be spiked with the target analyte. To assess microplastic contamination in this unspiked
matrix sample, the complete extraction process outlined in 5.55.5 to 5.75.7 shall be conducted, and the analysis
shall employ the same analytical technique that will be used for the spiked samples. The unspiked matrix
sample assessment is only possible for the spike-recovery tests and is identical to the sample that needs to be
analysed for microplastic content.
5.4.3 Limits of quantification, detection and reporting
The size range as well as the quantitative limits for microplastics are inherently dependent on the applied
analytical methods and therefore cannot be defined normatively in this document.
The current document is considered robust for a size range of 20 µm to 1 000 µm.
For mass-based methods, analytical performance is typically described using the limit of detection (LOD) and
the limit of quantification (LOQ). The LOD is the lowest concentration at which the analyte can be reliably
distinguished from background noise, while the LOQ represents the lowest concentration at which
quantitative results can be obtained with acceptable accuracy. According to ISO 16094-3, a signal-to-noise
ratio of 3 is commonly used to estimate the LOD and a signal-to-noise ratio of 10 for the LOQ. These limits are
often constrained by weighing accuracy rather than by the intrinsic sensitivity of the detection system and
should be determined in the presence of the relevant matrix.
For number-based methods, the concept of a reporting limit is more appropriate than a conventional LOQ. The
reporting limit depends on the analysed fraction of the sample or filter, the minimum particle size claimed by
the method, the polymer type, and the level of background contamination. ISO 16094-2 specifies that
reporting limits are derived from analytical control blanks, typically based on the mean blank value plus three
times the standard deviation, and may be defined separately for different size classes and polymer types.
The determination and interpretation of quantitative limits strongly depend on the control of background
contamination. Method blanks are therefore essential, particularly at low microplastic concentrations.
ISO 16094-2 requires that blanks are analysed in the same way as samples and explicitly states that blank
values shall not be subtracted from the sample results. If contamination exceeds acceptable levels, the
analytical sequence maymight need to be repeated after corrective measures.
Background contamination is inherently heterogeneous, both in terms of particle number and particle
characteristics. Therefore, evaluation based solely on total particle number or total mass can be misleading. It
is recommended thatThe background contamination isshould be assessed in a polymer-specific and, where
applicable, size-resolved manner. Differences in polymer type, particle size, and other characteristics may
indicate different sources and should be considered when comparing samples and blanks.
In addition, matrix-related interferences maycan affect both number-based and mass-based approaches.
Spectroscopic techniques can be influenced by substances with similar spectral features (e.g. proteins,
pigments or long-chain hydrocarbons), while thermo-analytical techniques can be affected by co-extracted
matrix components. These effects should be considered when establishing method-specific detection and
reporting limits.
Overall, quantitative limits for microplastics mustshall be considered method-specific, matrix-dependent and
closely linked to laboratory performance. Their establishment requires appropriate validation, including
replicate analyses and blank evaluation, and is therefore outside the normative scope of this document.
5.4.4 Verification of microplastics recovery rate
Verification of the successful implementation of the extraction method shall be checked using at least two
3 3
microplastic materials of a known type (one with a density < 1 g/cm and one with a density > 1 g/cm ).
The use of commercial polymer/microplastic standards (e.g. labelled plastics or standards used for flow
cytometry) or a reference prepared by the laboratory (by friction, grinding, etc.) is possible. The spiking
material shall be representative of the microplastics claimed to be quantified and shall therefore be selected
to reflect the size range, polymer chemistry, and particle morphology relevant to the intended field of
application.
Number characterization of the prepared spike sample may take place using a different analytical technique
(e.g. flow cytometry, optical counting, Micro-FTIR, Micro-Raman, SEM) from the one used for quantification
after extraction.
At least three samples of an unspiked matrix sample (5.4.2(5.4.2)) shall be spiked with a known mass or
number of microplastics of different types and sizes to cover the field of application claimed by the method.
The complete extraction process outlined in 5.55.5 to 5.75.7 shall then be conducted for the spiked and three
unspiked matrix samples, and the analysis shall employ the same analytical technique that will be used for the
unspiked matrix sample.
The recovery rate is calculated according to Formula (1) for a number-based recovery or Formula (2)in the
following way for a mass-based recovery:
Recovery [%]
particle number/mass − particle number/mass
(spiked sample,measured) (unspiked matrix sample,measured)
= ∙ 100
particle number/mass
(spiked)
𝑁𝑁 −𝑁𝑁
(spiked sample) (unspiked matrix sample)
𝑅𝑅 = × 100
𝑁𝑁
(spiked)
(1)
where
R is the recovery rate in per cent;
N is the particle number measured in the spiked sample after extraction;
(spiked sample)
N(unspiked matrix sample) is the particle number measured in the unspiked matrix sample after extraction;
N(spiked) is the known particle number that was deliberately spiked into in the unspiked matrix sample.
𝑚𝑚 −𝑚𝑚
(spiked sample, measured) (unspiked matrix sample, measured)
𝑅𝑅 = × 100
𝑚𝑚
(spiked)
(2)
where
m(spiked sample) is the particle mass measured in the spiked sample after extraction;
m(unspiked matrix sample) is the particle mass measured in the unspiked matrix sample after extraction;
m(spiked) is the known particle mass that was deliberately spiked into in the unspiked matrix sample.
It shall be ensured that the recovery rate is ≥ 60 % for particles < 100 µm and ≥ 80 % for particles > 100 µm.
If the recovery rate is below these limits, the laboratory shall identify and eliminate potential sources of loss
or systematic error (e.g. particle loss during extraction, insufficient matrix removal or analytical bias), and the
method shall be optimized accordingly. The recovery test shall then be repeated until the acceptance criteria
are met. For values above 100 % the laboratory shall perform a cause analysis. The proposed recovery criteria
are considered scientifically justified – recognizing, based on the conducted ILT and further literature, that the
recovery and quantification of particles < 100 µm remain a significant analytical challenge – and are deemed
appropriate for reliable application within the scope of this method.
5.4.5 Particle stability tests
Several types of microplastics and fragments from biodegradable polymers (e.g. based on PBAT and PLA) were
tested during method development regarding their stability towards the specific sonication and Fenton
oxidation conditions applied in this document (results shown in Annex CAnnex C).). If any other type of
microplastic or more complex materials, such as multicomponent materials containing fillers and not
predominantly composed of pure polymers, are toshall be investigated using this standard, it is essential to
conductdocument, stability tests shall be conducted on the target analyte. This type of stability test shall be
conducted once in each laboratory unless literature data for the target analyte is available.
Particle stability shall be evaluated by comparing the particle size distribution and the total particle number
or mass before and after application of the extraction procedure. Changes in particle size distribution shall be
assessed based on size-class–resolved particle numbers (or mass fractions), rather than a single summary
parameter.
A distinction shall be made between:
— — uniform particle loss, defined as a comparable decrease in particle number or mass across all size
classes without a change in distribution shape; and
— — fragmentation, defined as a redistribution of particles towards smaller size classes.
The particles shall be considered stable if:
— — the total particle number or mass is not reduced by more than 10 %, and
— — no significant redistribution of particles between size classes (> 10 % relative change per size class) is
observed.
If stability test results indicate changes between 10 % and 30 %, either in total particle number/mass or
within individual size classes, the impact on the reported results shall be evaluated and discussed in the test
report. If the alteration exceeds 30 %, either as overall particle loss or as a significant shift in particle size
distribution (e.g. systematic increase in smaller size classes), the target analyte shall be considered unstable
under the applied conditions and cannot be extracted using this protocol.
To test the stability of the microplastic type of interest under the conditions of the described extraction
procedure (5.5(5.5 to 5.75.7),), a suspension of the microplastics of interest in particle-free water (in the
absence of any compost), shall be subjected to the different steps of the process as foreseen in this document.
The particle size distribution or mass of each particle (polymer) type shall be analysed before and after
applying the extraction procedure and the results shall be compared.
It is also possible to test the particle stability in single extraction steps only (e.g. 5.65.6 Fenton oxidation) to
identify the most critical step for the stability of the microplastic type of interest.
The minimum requirement for analysis is to compare the particle size distribution (e.g. laser diffraction:
Fraunhofer evaluation for particles > 50 µm, Mie scattering evaluation for particles 1 µm to 50 µm) or mass of
the microplastic type before and after carrying out the whole procedure (or steps of it). Additional analyses
can be conducted based on the specific microplastic type and research question. Examples of additional
analyses include gel permeation chromatography for molar mass distribution (applicable only to non-
crosslinked types of microplastics), (ATR-FT) IR and/or XPS for surface chemistry, optical microscopy or SEM
for surface texture and shape, and DSC for crystallinity.
5.5 Deagglomeration
After homogenization and subsampling, any agglomerates of microplastic and compost particles are broken
down and dispersed using ultrasound. To achieve this, add 1 g of compost subsample and 40 ml particle-free
water are added to a beaker (e.g. 100 ml, borosilicate glass) and ultrasonicated with a delivered power of
15,0 W to 20,0 W for 5 min (corresponding to 4 500 J to 6 000 J) to effectively break up the agglomerates. The
device used for ultrasonication shall have its delivered power measured using the calorimetric method
[17]
described in Reference by Taurozzi, Hackley and Wiesner (2012). The temperature during the sonication
treatment shall not exceed 50 °C. The sample can be cooled using a water or ice bath to stay below 50 °C, if
needed. Once the ultrasonication is complete, remove the ultrasonication tip is removed and rinsedrinse with
10 ml of particle-free water directly into the same beaker containing the 40 ml compost dispersion. If
sonication is performed with a device that does not require inserting a tip or similar into the sample, 10 ml of
particle-free water areshall be added directly to the compost dispersion after sonication. Transfer the
resulting dispersion is transferred to a beaker (e.g. 500 ml to 600 ml, ⌀ 8 cm, borosilicate glass) and stirredstir
continuously until and during further use (see 5.65.6)) using an overhead stirrer with a ceramic or glass rod
or an orbital shaker. Rinse the 100 ml beaker is rinsed with 50 ml particle-free water. Rinsing steps
throughout the method reduce microplastics loss due to attachment to the labware used.
NOTE The ultrasonication was tested using a sonifier with a micro-tip (6,4 mm, 1/4”, conical). To achieve the
optimal delivered energy, the compost was ultrasonicated for 5 min at 40 % intensity.
5.6 Fenton oxidation
WARNING — Fenton oxidation is a chemical reaction and requires safety precautions: perform
oxidations in a fume hood, monitor reaction intensity and temperature closely, and ensure the
temperature does not exceed 50 °C to prevent polymer degradation.
The majority of organic components of the compost willshall be removed using a Fenton oxidation procedure
at room temperature (23° C ± ± 2 °C). For safety reasons, this oxidation step shall be conducted in a fume
hood. The temperature evolution during Fenton oxidation was monitored in stability tests conducted both in
the absence and presence of compost and remained below 40 °C in all cases (see Annex C, C.2.2Annex C,
C.2.2).). Temperature monitoring shall still be performed during oxidation. If the reaction temperature
exceeds 40 °C, a water or ice bath shall be applied to maintain the temperature within the range of 21 °C to
2+
40 °C. The temperature shall not exceed 50 °C. For each extraction, a solution of 0,036 mol/l Fe (obtained by
dissolving 10,0 g iron (II) sulfate heptahydrate in 1 l of particle-free water) needs toshall be freshly prepared
and the pH will be tested and adjusted to 3 to 4 with a 1 Mmol/l HCl (liquid) or a 1 M mol/l H SO (liquid).
2 4
The oxidation of the dispersion obtained in 5.55.5 is shall be carried out in five steps. In e
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