National Institute for Public Health
and the Environment
Ministry of Health, Welfare and Sport

Microplastics in soil systems, from
source to path to protection goals
State of knowledge on microplastics in soil
RIVM report 2021-0224
M. Rutgers et al.

Microplastics in soil systems, from source
to path to protection goals
State of knowledge on microplastics in soil
RIVM report 2021-0224

RIVM report 2021-0224

Colofon

© RIVM 2022
Parts of this publication may be reproduced, provided acknowledgement
is given to the: National Institute for Public Health and the Environment,
and the title and year of publication are cited.
RIVM attaches a great deal of importance to the accessibility of its
products. However, it is at present not yet possible to provide this
document in a completely accessible form. If a part is not accessible, it
is mentioned as such. Also see www.rivm.nl/en/accessibility
DOI 10.21945/RIVM-2021-0224
M. Rutgers (author), RIVM
M. Faber (author), RIVM
S.L. Waaijers-van der Loop (author), RIVM
J.T.K. Quik (author), RIVM
Contact:
Michiel Rutgers
Centrum voor Duurzaamheid, Milieu en Gezondheid
Michiel.Rutgers@rivm.nl
This investigation was performed by order and for the account of
Ministry of Infrastructure and Water Management, directie Duurzame
Leefomgeving en Circulaire Economie (DLCE) en directie Waterkwaliteit,
Ondergrond en Marien (DWOM)

Published by:
National Institute for Public Health
and the Environment, RIVM
P.O. Box 1 | 3720 BA Bilthoven
The Netherlands
www.rivm.nl/en

Page 2 of 110

RIVM report 2021-0224

Synopsis

Microplastics in soil systems, from source to path to protection
goals
State of knowledge on microplastics in soil
Microplastics are small plastic particles less than five millimetres across.
More and more microplastics are ending up in the environment. They
are everywhere: not just in water and air but also in soil, including in
urban areas, on farms and in nature reserves. There are indications that
microplastics pose a risk to the health of humans, plants, animals and
soil life. An increasing number of publications on microplastics in the soil
have featured in the scientific literature recently. And yet there is still a
lack of clarity on whether or not there are potential risks.
This is why the National Institute for Public Health and the Environment
(RIVM) deems further clarification important. Consequently, it has
summarised the available knowledge for policymakers and risk assessors.
This information proves to be fragmentary, incomplete and sometimes
even contradictory, as a result of which it cannot (or cannot yet) be used
to arrive at a reliable risk assessment. For example, there are no
measurements available of microplastics in Dutch soils. This is largely
down to the fact that no reliable, practical, standard techniques exist to
analyse microplastics in the soil. These need to be developed.
More knowledge will be required to reliably gauge the environmental
risks presented by microplastics. RIVM recommends better charting of
the sources from which microplastics are released and how they are
dispersed in the environment. In addition, a greater degree of insight is
needed into the rate at which various types of plastic break down as well
as the rate at which microplastics break down into harmless compounds.
This is necessary for the purposes of gauging exposure. To support
efforts to this end, the RIVM has created a ‘conceptual model’.
Another recommendation is to simultaneously assess the risks posed to
the soil by various types of microplastic. The substance risk assessment
frameworks currently in place are unsuitable for this as microplastics
occur in various forms and compositions. Finally, a list has been drawn
up of what is known about measures geared towards reducing the
release of microplastics. Examples include a ban on free plastic bags and
deposits on PET bottles.
Keywords: microplastic, biodegradation, ecological risks, human risks,
review, conceptual model, mitigation, framework.

Page 3 of 110

RIVM report 2021-0224

Page 4 of 110

RIVM report 2021-0224

Publiekssamenvatting

Microplastics in de bodem: van bron, via pad naar
beschermdoelen
Kennisoverzicht van microplastics in de bodem
Microplastics zijn kleine kunststof deeltjes; kleiner dan vijf millimeter. Er
komen steeds meer microplastics in het milieu terecht. Ze zitten overal:
niet alleen in water en lucht, maar ook in de bodem, en dus ook in de
bodem van stad-, landbouw- en natuurgebieden. Er zijn aanwijzingen
dat microplastics schadelijk kunnen zijn voor de gezondheid van
mensen, planten, dieren en bodemorganismen. De laatste tijd
verschijnen er steeds meer publicaties over microplastics in de bodem in
de wetenschappelijke literatuur. Toch is het nog onbekend wat de
mogelijke risico’s zijn.
Het RIVM vindt het belangrijk dat er meer duidelijkheid komt. Het heeft
daarom voor beleidsmakers en risicobeoordelaars de beschikbare kennis
samengevat. Deze blijkt gefragmenteerd en niet volledig te zijn en
bevindingen zijn soms zelfs tegenstrijdig. De informatie is daardoor (nog)
niet te gebruiken voor een betrouwbare risicobeoordeling. Er zijn
bijvoorbeeld nog geen metingen beschikbaar van microplastics in
Nederlandse bodems. Dit komt vooral omdat er geen betrouwbare,
praktische (standaard)technieken bestaan om microplastics in de bodem
te analyseren. Deze moeten verder ontwikkeld worden.
Meer kennis is nodig om risico’s van microplastics voor het milieu
betrouwbaar in te schatten. Het RIVM beveelt aan beter in kaart te
brengen door welke bronnen microplastics worden uitgestoten en hoe ze
zich in het milieu verspreiden. Verder is meer inzicht nodig in de
snelheid waarin verschillende soorten plastic gefragmenteerd worden en
als microplastic afgebroken worden tot onschadelijke verbindingen. Dat
is nodig om de blootstelling te kunnen schatten. Als ondersteuning
hiervoor heeft het RIVM een ‘conceptueel model’ gemaakt.
Een andere aanbeveling is om de risico’s van verschillende soorten
microplastics voor de bodem tegelijk te beoordelen. De bestaande
kaders voor risicobeoordelingen van stoffen zijn er niet voor geschikt,
omdat microplastics verschillende vormen en samenstellingen hebben.
Tot slot is op een rij gezet wat bekend is over maatregelen om de
uitstoot te verminderen. Voorbeelden zijn een verbod op gratis plastic
tassen en statiegeld op petflessen.
Kernwoorden: microplastic, biodegradatie, ecologische risico’s, humane
risico’s, review, conceptueel model, mitigatie, raamwerk

Page 5 of 110

RIVM report 2021-0224

Page 6 of 110

RIVM report 2021-0224

Contents

Summary — 9
1

Introduction — 13
Classification of microplastics — 14
Objectives and scope — 15
Current state of publications — 15
Readers guide and highlights — 17

2

Origin and types of microplastics in soil — 21
Definitions and types — 21
Polymers identified in soils — 22
Chemical identity — 22
Morphological characteristics – physical identity — 24
Biological characteristics — 24
Methods for the extraction, separation, identification and quantification
of microplastic in soil — 25

3

Source, emission, behaviour and fate of microplastics in
soil — 27
Source and emission — 27
Introduction — 27
Soil specific estimates — 29
Overall environmental estimates — 29
Data gaps — 31
Observations in soil – behaviour and fate — 31
Modelling microplastic transport and fate in soil — 32
Applicability of existing models — 33
Next steps and knowledge gaps — 34

4

(Bio)degradation of (micro)plastics — 37
Introduction — 37
Determinants for (bio)degradation — 38
Chemical properties — 38
Physical properties — 39
Environmental conditions — 40
Biodegradable plastics — 41
Biodegradation standards — 41
Uncertainties associated with biodegradation testing — 46
Which plastics are biodegradable according to literature? — 47
Implications for estimating microplastics fate — 48

5

Impacts and risks of microplastics in soil — 51
Introduction — 51
Ecosystem effects of microplastics — 51
Microplastic particles — 51
Uptake by plants — 52
Leaching of chemicals from microplastics — 52
Interactions of microorganisms with microplastics — 52
A Trojan Horse — 52
Conclusion on ecosystem effects — 53
Page 7 of 110

RIVM report 2021-0224

6

6.6.1.1
6.6.1.2
7

State of knowledge and perspectives for action — 55
Introduction — 55
Conceptual model of microplastics in the soil system — 55
Knowledge and information gaps — 57
National and international projects — 59
Looking for potential mitigation options — 59
Source-oriented solutions — 61
End-of-pipe and remediation solutions — 64
Pathway to quality criteria for microplastic in soils — 66
Criteria for microplastic in soil and sediments — 66
Netherlands — 66
Flanders — 67
Towards soil quality criteria for microplastics — 68
Conclusion and Recommendations — 69
Conclusions — 69
Recommendations and reflections — 70
Literature sources — 73
Annex 1 Abbreviations of polymer types — 87
Annex 2 Biodegradation of microplastics — 88
Annex 3 Methods for extraction, separation, identification and
quantification of microplastic in soil — 94

Page 8 of 110

RIVM report 2021-0224

Summary

Microplastics research is mainly focused on freshwater and marine
environmental compartments, but soil systems are expected to receive a
far larger amount of these particles annually. For this reason, it is crucial
to increase our understanding of the sources, the release and emission
pathways, and the further fate and transport of microplastics in soil
systems (see figure 1). Knowledge on all of these topics is required to
assess the potential risks on human and environmental health
Sources

Release and
emission

Fate and
transport

Exposure
and effect

Risk

Figure 1 Diagram showing the relevant topics to address in order to assess risk of
microplastics and other substances and materials. This study mainly addresses
knowledge leading up to assessing exposure, thus not focusing on the available
knowledge about effects or risk.

In this report, we summarize the current knowledge of microplastics
with respect to sources, release and emission, and fate and transport,
with specific attention given to (bio)degradation and potential mitigation
options. These aspects are discussed using the main issues highlighted
in 45 recent review studies, most published in 2020 and 2021, and the
requirements for any future risk assessments of microplastics.
Microplastics are defined here as solid polymers with a size smaller than
5 mm.
A major issue hampering current research on microplastics in soil is the
large range in the chemical, morphological, physical and biological
characteristics of polymers that are considered microplastics, the
analytical challenges to separate particles from the complex solid soil
matrix, and the detection and quantification of different microplastic
types. Nevertheless, several measurement methods have been
developed. It is likely that a combination of some contrasting methods
would provide the most reliable data. It is essential, for this research
field and for the implementation of policies, to work towards a
harmonized protocol, describing which (set of) method(s) are best to
use for which purpose, taking into account required quality standards.
Once emitted to terrestrial ecosystems, microplastics accumulate in soils
and can migrate to marine and fresh waters through runoff, erosion and
atmospheric transport, and to the groundwater and deep soil through, for
example, leaching, bioturbation and farming activities. In this dynamic
environment, microplastics’ physical, chemical and biological properties
can change through different processes, such as fragmentation,
(bio)degradation and other interactions with the soil matrix.
Some quantitative estimates of the release of microplastics to soils are
available, but these do not cover all major sources and data is only
Page 9 of 110

RIVM report 2021-0224

available for a few regions. This means an overview of emissions to soil
systems in the EU is missing and data for the Netherlands are virtually
absent.
Modelling will play an important role in coping with the complexity of
microplastics due to the range of MP properties (e.g. polymer type, size,
shape) and the limitations of measurement methods. Several modelling
approaches are already available for estimating the emission of
microplastics to the environment from different sources. Modelling
approaches are readily applicable to microplastics, but data on source
volumes and release rates from different events (e.g. painting, driving
and weathering of plastics) are lacking. After estimating the emission of
microplastics to the soil system, exposure to organisms is often
assessed using fate and transport modelling approaches. Several models
are available that include fate in soil and are at least partially applicable
to microplastics. However, there are several key issues that need further
attention since most of these models were designed for much smaller
sized nanomaterials. Input data such as fragmentation and degradation
rates are often also highly uncertain.
The degradation and fragmentation of microplastics is important for
estimating the fate of microplastics in soil systems. On the one hand, it
means a reduction of microplastics due to mineralization or a complete
breakdown to harmless compounds. On the other hand, degradation can
occur partially, resulting in the fragmentation of microplastics to smaller
particles, e.g. nanoplastics. Fragmentation is also thought to be one of
the most important processes resulting in microplastics: formation of
secondary microplastics due to fragmentation of meso- and
macroplastics. Complete or incomplete degradation depends on three
major aspects: 1) the chemical properties (e.g. polymer type and
additives) , 2) the physical properties (e.g. shape and crystallinity) of a
microplastic and 3) the environmental abiotic (e.g. temperature, light,
oxygen) and biotic conditions (e.g. microbial composition). The first
steps have been taken to determine the biodegradation rates for
different plastics. However, there are still many uncertainties with
respect to determining these degradation rates reliably under different
environmental conditions.
It is essential to assess the rate and degree to which microplastics
degrade in order to adequately model the fate of microplastics in soil
systems. There are several existing test guidelines for assessing the
(bio)degradability of chemicals, e.g. by ISO or OECD. However, none of
these were created with (micro)plastics in mind, which could cause
some uncertainty regarding the applicability of the tests and use of the
results. Nevertheless, a testing strategy has been proposed by the
European Chemicals Agency Risk Assessment Committee (RAC) for the
restriction of intentionally added microplastics in order to determine the
biodegradability of microplastics. In the restriction, biodegradable
microplastics are derogated. The proposed strategy consists of screening
level tests and more advanced tests in soil, water and sediment in order
to test under environmentally realistic conditions. The restriction has yet
to be adopted by the European Commission. Within other regulatory
domains, e.g. related to fertilizers, mulch films or composting,
standardized test guidelines have also been proposed and/or have been
Page 10 of 110

RIVM report 2021-0224

recently developed. While available data from biodegradability studies
often does not fit within fate models, data generated by standardized
test methods is not yet available. Consequently, further investment in
research into the biodegradation of microplastics is required.
Since the persistence of microplastics and their large-scale emission to
soil are evident, and as there are indications of potential microplastic
risks, it is clear that action should be taken to mitigate these emissions.
Preferably, these actions should aim to reduce emissions based on
source-oriented or end-of-pipe solutions. As a last resort, soil
remediation type solutions can be applied to reduce microplastic
exposure. However, there are many gaps in the state of knowledge and
information needed to fully assess the behaviour, fate and effects of
microplastics in soil, making it unfeasible to derive risk-based soil
quality criteria for microplastics in this study. It is advised that, in
parallel to work on mitigation options, our understanding on several
broad knowledge gaps should be further developed, such as:
• Data on sources and emissions of microplastics to soil is still
scattered, meaning there is a lack of data on microplastic
emissions, including fragmentation of macroplastics, to the
environment.
• Consistent data on microplastic concentrations and particle
abundance in different soil types and land uses are absent and
are needed to better understand the current extent of
microplastic pollution in Dutch soils.
• Robust, reliable, standardized analytical methods are not yet
available. These are needed to gather and compare data on
microplastic concentrations in soils, including their
characteristics, such as polymer type, size and shape.
• The knowledge about the exposure and potential effects of
microplastics, additives and other adsorbed compounds in soil
systems is very scattered and largely unknown.
• There is a lack of refined understanding of the link between
microplastic properties and soil fate, exposure and uptake in
plants and organisms. Insight is missing on the interaction of
microplastics with the soil matrix. This should inform safe-bydesign approaches.
• The (bio)degradation mechanisms and degradation rates of
microplastics are largely unclear, also due to the lack of
validated, standardized (bio)degradation test methods. Research
conducted to understand biodegradation mechanisms and the
development and use of standardized tests should result in
improved quantification of degradation rates for fate modelling.
• The long-term implications of microplastic persistence and
mobility in soil systems (worldwide spread/detection) are as yet
unknown.
In conclusion, there is a need for:
1. Filling all of the above-mentioned knowledge gaps according to
smart research approaches, e.g. using read-across and
modelling.
2. Quantification of sources and emissions to soil is needed for the
prioritization of mitigation options and the assessment of
exposure as part of risk assessment.
Page 11 of 110

RIVM report 2021-0224

3. Exploring possibilities for a policy and management framework
for (micro)plastics in soil systems (or more broadly) in order to
minimize the emission of microplastics where possible and to
mitigate ecological and human health risks where needed.
The environmental issue of microplastics in soils is complex and much
more research is needed to reduce uncertainties and build up scientific
evidence. It is, however, certain that microplastics (and nanoplastics)
are present ubiquitously in urban, natural and agricultural soils
worldwide and that, due to their persistence, spreading, the continuous
emissions, and society’s dependency on plastic, microplastics will be
present in the environment for a long time. Steps can be taken to
mitigate and reduce microplastic emissions into the environment,
adapted to the latest knowledge developments, to reduce the growing
amount of pollution while improving our overview and understanding of
the problem.

Page 12 of 110

RIVM report 2021-0224

1

Introduction

The Dutch Ministry of Infrastructure and Water Management (IenW)
wants to develop adequate policies to counteract current and future
problems for human health and ecosystems. In line with the European
Circular Action Plan and Plastic Strategy, microplastics are one of the
prioritized environmental issues that needs to be addressed and goals
are being set to minimize and mitigate emissions to the environment. 1
The soil system used as a sink for microplastic accumulation was
acknowledged in the recently published EU soil Strategy for 2030. 2
The accumulation of microplastics in soil and water systems has been
considered an environmental concern from different perspectives
(Waaijers-van der Loop et al., 2022). For instance, the release of
microplastics:
1. can create a hazard for human health and ecosystems in the long
term (the risk-based perspective), as is described in many
reviews on microplastics; or
2. should be avoided at all reasonable costs because of violating the
intrinsic value of our environment (the zero-pollution based
perspective); or
3. is considered as material losses in a circular economy. 3
The optimal mitigation measures and policy actions to deal with
microplastic emissions can be different, depending on the perspective.
In this report, we focus on microplastics in soil systems and aim to
provide an overview of the available knowledge. This knowledge can
serve as a basis to establish mitigation options from any perspective.
The state of knowledge will reflect the current understanding of
microplastic sources, release and emission pathways, transport,
behaviour, and fate in the environment. This structure fits the commonly
used source-path-receptor diagrams, which can be used to assess the
potential risk of microplastics (Figure 1). Most research so far has been
on (micro)plastic litter in the water compartment, ephemerally labelled
the ‘plastic soup’ in oceans (Hammer et al., 2012; Andrady, 2011;
McFedries, 2012). Research was subsequently expanded to cover other
compartments, such as air, soils, groundwater, surface waters and
sediments (viz. Verschoor et al., 2014; Verschoor, 2015; Horton et al.,
2017; Xu et al., 2020a; Xu et al., 2020b; Quik et al., 2021). In this
report, we look at the state of knowledge about microplastics in soils,
since it is still limited.
We will follow the same order of topics as in the source-path-receptor
diagrams to structure this review, with the aim of identifying specific
information gaps. The focus will be on the source-path, with a brief

1
EU plastics strategy. ec.europa.eu/environment/strategy/plastics-strategy_en
2 EU Soil strategy for 2030, COM(2021) 699. https://ec.europa.eu/environment/publications/eu-soil-strategy2030_en
3
IenW (2018) Kamerbrief, betreft Gezamenlijke aanpak plastic zwerfafval
Kenmerk IENW/BSK-2018/232541 Datum 6 november 2018, Den Haag

Page 13 of 110

RIVM report 2021-0224

reflection on receptor (effects). We also use this approach for the
construction of a more detailed conceptual model in Chapter 6.
Sources

e.g tyres
• Industrial
e.g. pellets
• Construction
e.g. pipes
• Agriculture
and textiles
• Waste
(mis)management

Release and
emission

Fate and
transport

Exposure

Risk

• Direct release
to soil
e.g. due to
abrasion and
wear, irrigation or
soil improvement
e.g. composts,
manure, digestate
• Indirect release
to soil
e.g. release to air
with deposition
to soil

• Deposition
from air
• Attachment and
agglomeration
• (Bio)degradation
• Fragmentation
• Transport in soil
e.g. bioturbation,

• Particle toxicity
e.g. shape or size
• Chemical toxicity
e.g. polymer type
• Biological hazards
e.g. pathogenic
activity

• Hazard
identification
• Exposure
assessment
measurements
modelling emission,
fate and transport
• Hazard assessment
species sensitivity
distribution
ecotoxicity tests
• Dose metrics
e.g. surface area
or particle
number

drainage or
erosion
ecocoating

Figure 1 Research topics for microplastics in soil systems classified in a sourcepath-effect-risk model approach. Explanation to a few terms: Dose metrics is the
effective description of the dose to which organisms are exposed. Eco coating is
the attachment of organic macromolecules and biofilms onto the particle surface.
Natural attenuation is a variety of physical, chemical, or biological processes as
part of fate and transport processes that reduce the mass, toxicity, mobility,
volume, or concentration of contaminants

Classification of microplastics
Plastics can be made of different types of polymers (e.g. polypropene,
polyethylene, polystyrene, polyvinylchloride) and can be divided based
on their size into macro-, meso-, micro-, and nanoplastic. In the last
decade, several slightly differing definitions for microplastics have been
proposed (Verschoor, 2015). In this report, the recent definition used in
the context of the proposed restriction on intentionally added
microplastics is considered to be most relevant. The European Chemicals
Agency (ECHA) Risk Assessment Committee (RAC), in its opinion on the
restriction, defined microplastics as ‘particles containing solid polymer to
which additives or other substances may have been added, and in which
≥ 1% w/w of particles have (i) all dimensions ≤ 5 mm, or (ii) a length of
≤ 15 mm and a length to diameter ratio of >3 (ECHA, 2020). The
definition does not discriminate on the type of polymer used and sets no
lower size limit. While the upper size limit for microplastic is widely
accepted, the lower size limit is still under debate (Möller et al., 2020).
This is also the case for the definition proposed in the restriction; ECHA
initially proposed 100 nm as the lower size limit and, while RAC
recommended setting no lower size limit in its opinion, the sister
committee for Socio-economic Analysis (SEAC) recommended defining a
lower limit size of 1 nm, and a temporary limit of 100 nm in order to
ensure the enforceability of the restriction (ECHA 2020).

Page 14 of 110

RIVM report 2021-0224

Objectives and scope
One objective of this report is to identity and summarize the current
knowledge on microplastics in the soil system with respect to sources,
types, emissions, fate, accumulation, attenuation (including
degradation) and potential mitigation options. This information can be
used in current and future research to start estimating the potential
risks of microplastics in soils. Also, the information and quantitative data
can be used in modelling to better understand the (relative) extent of
microplastic sources and emission to soils.
Consequently, the objectives and scope for this report are:
1. To summarize sources and emissions of microplastics in the soil
system for major microplastic types.
2. To compile the current distribution and dispersal of the
microplastic types in soil systems by different mechanisms of
fate, such as transport routes and degradation mechanisms.
3. To describe gaps in our knowledge and available information that
hamper a reliable analysis and assessment of the risk of
microplastics in soil systems.
4. To collect ideas to mitigate the effects of microplastics in soil
systems through source or effect-oriented solutions and current
criteria for (micro)plastic-contaminated soil.
Current state of publications
Over the last 20 years, the number of publications on the issue of
plastics in the aquatic environment has steadily increased and reached
more than 5,000 publications per year in 2020 (data not shown). For
soil, the number is considerably smaller (Figure 2). In contrast, the
environmental topic ‘microplastic’ (including the hyphenated expression)
has received significant interest only in the last 7 years, which
demonstrates a rapid exponential increase. He et al. (2020) noticed the
same trends. With respect to the environmental compartment of
interest, the yearly number of publications focused on water systems
outcompeted the yearly number on the soil system (Figure 2). Having
said that, in 2021 there was a considerable flow of publications focused
on microplastics in soil systems, i.e. more than one per day.
At the moment, nanoplastic research is also rapidly increasing and is
obviously linked to the broader environmental issue of ‘nanomaterials’
and ‘nanotechnology’ (data not shown).

Page 15 of 110

RIVM report 2021-0224

Figure 2 Number of scientific publications per year showing the publication trends
(Scopus 25 October 2021): ‘Microplastic and soil’ (orange), ‘microplastic and
water’ (grey) and ‘plastic and soil’ (blue) in the title, keywords and abstract

An interesting observation was the large number of literature reviews
(45 reviews in our search) that were published in 2020 and 2021,
covering the issue of microplastics in the soil system. Of the 45
publications that were found with ‘microplastic’ and ‘soil’ in the title and
‘review’ in the field ‘title/keyword/abstract’, five reviews have already
received more than 50 quotes (Scopus 8 August 2021). Considering that
these reviews were produced in parallel, it is inevitable that repeated
information on the issue is presented by the different publications.
About 85% of all publications on microplastics in soil systems is
produced in only two regions: 65% in Asia and 20% in Europe (Xu et
al., 2020b, He et al., 2020).
Zhang et al. (2021b) provided an overview of the locations and type of
research in which microplastics in soil were studied (Figure 3). The map
shows that Asia and Europe are the dominant regions for research of
microplastics in soils. Arable systems are represented most (Pie diagram
in Figure 3).

Page 16 of 110

RIVM report 2021-0224

Figure 3 Studies on microplastics in the soil under controlled conditions in
laboratories (green part of the pie) and from field samplings (red part of the pie).
The majority of the publications dealt with arable soils (blue part of the pie).
Figure reproduced from Zhang et al. (2021b).

Recently, 45 reviews dealing with microplastics in soil were produced. It
was considered not effective to comprehensively review the available
literature again in order to collect the current state-of-the-art. Instead,
we provide a general overview of the state of knowledge, based
primarily on the published reviews and focused on the interpretation of
the results and some subsequent steps needed for risk assessment.
When needed, the original publications were consulted. This was further
supplemented with information from interviews of experts working on
microplastics research.
In this report, we have viewed the current knowledge from the
perspective of how it can be used to improve our understanding of
microplastics and their behaviour in the environment. We collected
generalized information on emissions, transport, and the behaviour of
microplastics in soil. The focus of the latter was specifically on natural
attenuation, and specifically the (bio)degradation of microplastics in soil
(Figure 1), as these processes are considered critical to conducting a
meaningful fate analysis of microplastic accumulation in soil. We reflect
on the state of this knowledge and on what this may mean for further
research. Finally, mitigation options aimed at emission reduction and
pathways to risk or quality-based criteria for soils are discussed.
Readers guide and highlights
Several of the published reviews provided key messages on the topic of
microplastics in soil systems (viz: Li et al., 2020a; Kumar et al., 2021;
Horton et al., 2017; Dioses-Salinas et al., 2020; Hurley and Nizzetto,
2018; Sun et al., 2022; Wang et al., 2019; Wang et al., 2020; Wang et
al., 2021a; Wang et al., 2021b; Xu et al., 2020b; Yang et al., 2021;
Zhang et al., 2020; Zhang et al., 2021a; Zhang et al., 2021b; Zhou et
al., 2020; Zhu et al., 2019; Rillig and Lehmann 2020). To assist in
reading this report, we used already published key messages and
supplemented them with the key findings from our research to yield ten
Page 17 of 110

RIVM report 2021-0224

highlights. These highlights provide a reading guide, as they present a
synopsis of each new topic discussed in Chapters 2 to 8. Each new topic
starts with a highlight (in bold font), followed by a detailed analysis of
the specific topic, including the knowledge gaps. After discussing the
results in the first chapters, we reflect on these findings and give an
outlook and perspectives for action in Chapters 6 and 7. The complete
set of highlights is given below:
1. The past decades, microplastics in soil systems have been largely
overlooked. Nowadays, microplastics are detected in all
environmental compartments worldwide: in air, marine waters,
fresh waters, sediments and terrestrial systems. Considering
release and migration to agricultural, urban and industrial soils
and the analytical data, the yearly global release of microplastics
to soils is likely much higher than that to rivers and oceans.
2. Microplastics are a very diverse group of synthetic particles,
consisting of different polymer types and additives, and having
different sizes, densities, shapes and colours. Microplastics can
also acquire biological characteristics, caused by the attachment
of microorganisms, including pathogens, on the (weathered)
particles.
3. The absence of a suitable method for analysis of the type and
quantity of microplastics in soil is a big hindrance to research.
Although a number of analytical methods have been developed,
an efficient, robust, fast and low-cost analytical method for soils
is still not available, especially for the isolation of the polymers
and particles from the complex, organic matter containing a solid
soil matrix (sample clean-up). Data on the abundance and
distribution of microplastics in soils are still limited, and results
obtained from studies differ significantly.
4. In a variety of studies, microplastic emission sources are
identified, such as tyres, agricultural plastic films, textile, seed
coatings, personal care products, cosmetics, paints (e.g. on roads
and buildings), artificial turfs, landfill, litter, packaging and
construction materials. Both primary and secondary microplastics
are released to the environment, but secondary microplastics are
the dominant source.
5. Once emitted to terrestrial ecosystems, microplastics can migrate
to marine and fresh waters through runoff, with erosion and by
atmospheric transport, and to the groundwater and deep soil
through leaching, bioturbation and farming activities, to name a
few. After microplastics enter the soil system, microplastics’
physical, chemical and biological properties change through
fragmentation and (bio)degradation.
6. Polymer type, shape, and particle-size-dependent modelling of
microplastics’ fate and behaviour is important for coping with the
complexity of microplastics in the environment. Studies for the
modelling of microplastics’ emissions, transport and fate in water
are available, however there are not yet adequate for the
investigation of the soil system.
7. Published biodegradation data for (micro)plastics differ greatly
between studies. The (bio)degradation potential of microplastic
particles depends on three major aspects, namely 1) their
chemical composition, 2) their physical properties and 3) the
environmental conditions to which they are exposed to. The
Page 18 of 110

RIVM report 2021-0224

limited data on (bio)degradation and monitoring show that
microplastics can accumulate in the environment, including soil
systems. However, the actual accumulation rates are uncertain,
not only due to the scarcity of data in combination with a large
variation between measured (bio)degradation rates, but also
simply due to the lack of standardized methods suitable to assess
the fragmentation and degradation of microplastic particles under
environmentally relevant conditions, as well as the vast range of
polymer types and identities.
8. High amounts of microplastics in soils can alter the fundamental
physicochemical and biological properties of the soil system. Soil
health and function may be impaired and trophic transfer in food
chains may also occur. This may lead to adverse effects on
ecosystems. To address the potential ecological impact on soil
systems, (further) research is needed on the (direct and indirect)
effects of microplastics on the viability, development, fertility and
mortality of soil organisms. In addition to such effect studies,
improved insights into the exposure, bioavailability and uptake of
microplastics by organisms and humans are necessary. The
current information on the impact of microplastics on the
functioning of soil organisms and the ecosystem is incomplete
and is sometimes conflicting.
9. Overall, research on the emissions to and fate of microplastics in
soil systems, and their effects on terrestrial ecosystems, is still
limited but is increasing rapidly, demonstrated by increasing
publication rates. This motivates an active monitoring of the
progress of the knowledge required for risk assessment.
10. Some studies provided specific recommendations for policy
development and land quality management. The need to act on
the prevention and reduction of microplastic accumulation is
motivated based on the persistence, the potential adverse effects
and the widespread detection of microplastics. Preventing and
reducing the impact of microplastic soil contamination requires a
large set of measures for a large variety of stakeholders. In
several countries, measures are being implemented to reduce the
release (of mostly primary microplastics) at the source (source
control) and to reduce emissions at end-of-pipe (emission
control), both of which results in the reduction of emissions to
terrestrial ecosystems.

Page 19 of 110

RIVM report 2021-0224

Page 20 of 110

RIVM report 2021-0224

2

Origin and types of microplastics in soil

In past decades, microplastics in soils have been largely overlooked
(highlight 1). Nowadays, microplastics are found in all environmental
compartments worldwide: in air, marine waters, fresh waters, sediments
and terrestrial systems. Considering the release and migration to
agricultural, urban and industrial soils and the analytical data, the yearly
global release of microplastics to soils is likely much higher than the
release to oceans and rivers.
Definitions and types
Microplastics are a very diverse group of synthetic particles, consisting of
different polymer types and additives, and having different sizes,
densities, shapes and colours (highlight 2). Microplastics can also acquire
biological characteristics, caused by the attachment of microorganisms,
including pathogens, on the (weathered) particles.
‘Plastic’ is defined as being synthesized from solid materials that can be
moulded and that contain a considerable number of carbon-based
polymers. Reversible moulding refers to rubber as a specific plastic
material. One of the more recent definitions of ‘microplastic’ is: ‘particles
containing solid polymer, to which additives or other substances may
have been added, and in which ≥ 1% w/w of particles have (i) all
dimensions 0.1μm ≤ x ≤ 5 mm, or (ii) a length of 0.3μm ≤ x ≤ 15mm
and a length to diameter ratio of >3 (ECHA, 2020). 4
Referring to this definition, microplastics are:
• synthetic materials containing polymers with carbon in their
structure;
• solid at ambient temperature;
• smaller than 5 mm;
• insoluble in water; and
• relatively inert, persistent, poorly or non(bio)degradable (this
varies among the types of the polymers).
Microplastics are universally classified as primary and secondary
substances (e.g. Fu and Wang 2019):
• Primary microplastics are particles that are synthesized
intentionally at defined small sizes for commercial applications.
Microbeads from cosmetics and personal care products, seed
coatings, and pre-production pellets used as intermediates in
plastic production are all significant sources for primary
microplastics worldwide.
• Secondary microplastics are fragmentation products of larger
plastic debris, which are broken down by UV-radiation and
mechanical abrasion (Wagner et al., 2014). The sources of
secondary microplastics are composed of fishing nets, films,
4
Note that the definition is proposed by RAC (Risk Assessment Committees) with regard to the restriction on
intentionally used microplastics. SEAC (Committee for Socio-Economic Analysis) has proposed a different
definition (no lower limit size for the particles). The final definition has not been chosen yet by the European
Commission.

Page 21 of 110

RIVM report 2021-0224

household items, tyres, textile, paints, littering, industrial raw
materials and other discarded plastic debris (e.g. Eerkes-Medrano
et al., 2015; Verschoor and de Valk, 2018).
The most widely used plastics according to Shah et al. (2008) consist of
one or more of the following polymers: polyethylene (PE: LDPE, MDPE,
HDPE and LLDPE), polypropylene (PP), polystyrene (PS: PS and EPS),
polyvinyl chloride (PVC), polyurethane (PUR), polyethylene
terephthalate (PET), polybutylene terephthalate (PBT), and poly
amide/nylons (PA). Examples of biodegradable plastics are: polylactide
(PLA), poly-3-hydroxybutyrate (PHB), polypropiolactone (PPL), poly-εcaprolactone (PCL), polyethylene succinate (PES), polybutylene
succinate(PBS), poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV)
and polyester carbonate (PEC).
Zhang et al. (2021b) reviewed 170 publications on microplastics and
soils extracted from the Web of Science covering the period 1950–2020.
They found that these studies were mainly carried out in Asia (60%) and
Europe (23%), and most focused on arable soils (69%) (Figure 3). The
microplastics most frequently found in soils were: PE (79% of the
studies), PP (79%), and PS (46%), with particle sizes ranging between
20 – 5000 μm. Of the soil samples taken, 64% contained microplastics:
1,000 – 4,000 particles per kg soil. This does not imply that only these
polymer types where present, as there may be bias or a limitation in
sampling, extraction and/or detection methods (see Annex 3).
Polymers identified in soils
The widespread use of plastics in all possible applications has resulted in a
wide dispersion of polymers in ecosystems around the globe, especially in
inhabited areas. Since these polymers have different sources, identities
and behaviour, the composition of the accumulated material varies
strongly. For instance, agricultural use of land occupies the largest share
of managed soil systems worldwide. Consequently, microplastics
associated with agriculture management also demonstrate the highest
appearance level in managed soil systems worldwide, i.e. the classic
plastics such as PA, PP, PE, PS, PET and PVC. It should be noted that
some other plastics did not appear very often, such as fluoropolymers and
natural or synthetic rubbers. Obviously, rubber from abrasion of tyres is
found or estimated to locally have high concentrations along roads
(Baensch-Baltruschat et al., 2021; Sieber et al., 2020).
Chemical identity
Figure 4 illustrates estimates of relative abundance of polymer types for a
microplastics mass flow modelling study in Switzerland for seven common
polymer types (Kawecki and Nowack, 2019). Soil microplastic
measurements indicate globally that PA (Polyamide nylon), PP, PE and PS
accounted for most polymers found while PVC and PET were found to a
lesser extent (Xu et al., 2020b). For example, PA and PP were two major
polymer types in soils from the farmland of Wuhan, with percentages of
33% and 29% (from Chen et al., 2020). PP, polycarbonate and
acrylonitrile butadiene styrene were confirmed as major microplastics in
soils from Guiyu, an E-waste dismantling zone in China (Chai et al.,
2020). PP and PE represented 51% and 43% in shallow and deep soils in
Page 22 of 110

RIVM report 2021-0224

the farmland of Shanghai, respectively (Liu et al., 2018). Likewise, PE
covered 63% of microplastic polymers in agricultural farmland in
southeast Germany, while PP and PS accounted for 25% and 13%,
respectively (Piehl et al., 2018). This was consistent with soils from ricefish coculture stations in Shanghai. PE was predominantly present (61%)
followed by PP (36%) and PVC (3.5%) (Lv et al., 2019).

Fraction of total MPs released to soil

In addition to field observations, a modelling approach can be taken to
identify the dominant polymer types expected in soils. Such modelling is
based on Material Flow Analysis, which follows material flows through
the technosphere by quantifying the material flow from the application
of plastics, processes generating microplastics (e.g. sawing) up to the
eventual releases of microplastics to the environment (Kawecki and
Nowack, 2019).
30%
25%
20%
15%
10%
5%
0%

PP

LDPE

Agricultural soil (MP)

PVC

HDPE

Residential soil (MP)

PET

Subsurface (MP)

PS

EPS

Natural soil (MP)

Figure 4 Relative mass flow of microplastics estimated to be released to three soil
types and the soil subsurface in Switzerland, for seven common polymer types
(data from Kawecki and Nowack, 2019).

In one of the first studies that models the release of microplastics to the
environment, Kawecki and Nowack (2019) followed the application of
seven common polymer types. This resulted in estimates of microplastic
releases divided over four different soil compartments: agricultural soil,
residential soil, natural soil and the soil subsurface 5 based on the (micro)
plastic application (Figure 4). The data show trends for MP release per
polymer type to different soil types for Switzerland. Although this cannot
literally be translated to other locations, it is likely that the largest
sources and waste management processes are similar to other locations,
such as those in the Netherlands, resulting in a similar division of
polymer types between soil types.
It is not strange that PP, LDPE, HDPE and PVC are polymer types
estimated to be most abundantly present in the environment because

5

For instance the soil in which construction pipes are laid under a road.
Page 23 of 110

RIVM report 2021-0224

these polymers are estimated to have the highest production volumes
(Geyer et al., 2017). 6
Morphological characteristics – physical identity
The physical identity is characterized by the dimensions, density, shape
and colour of the microplastic particles. Overall, fibres were the
dominant shape of microplastics in the majority of the soils (Xu et al.,
2020b). Of the four dominant shapes in the arable soils of Shanghai, the
average percentage of fibres was highest (53%), followed by fragments
(38%), film (6.7%) and pellets (2.1%) in shallow soil. In deep soil, the
average percentage of fibres was still highest (38%), but close to films
and fragments (34% and 28% respectively), while pellets were present
to a small extent (0.32%) (from Liu et al., 2018). Fibres made up 92%
of soil samples from Yunnan China and fragment and film only
accounted for 4.0% and 3.0%, respectively (Zhang and Liu, 2018; Lv et
al., 2019).
The accumulation of microfibres may result from the application of
sewage sludge and waste water from household washing processes as
fertilizer. Synthetic fibres have been proposed as an indicator of sludge
application (Zubris and Richards, 2005). The abundance of fibres in
sewage sludge could reach 38,080 particles/kg dry weight and waste
water containing clothing fibres may be discharged directly for irrigation
(Zhang and Liu, 2018). 1,000–4,000 particles of microplastics per kg of
dry mass was found in arable sites in European countries (Zubris and
Richards, 2005). In other studies, microbeads and fibres accounted for
48% and 37% of the accumulation in the arable land of Wuhan, China
(Chen et al., 2020). To a large extent, microplastics <1 mm are
present: for instance sizes between 0.03−1 mm occupied 49% and 60%
of shallow and deep soils in arable land of China (Liu et al., 2018).
Microplastics with sizes of less than 0.2 mm represented over 70%
found in soil samples from Wuhan, China, followed by 0.5−1 mm (13%),
0.2−0.5 mm (9%) and 1.0–3.0 mm (7%) (Chen et al., 2020). Ninetyfive per cent of sampled plastic particles from planted soils in Yunnan
were in the size of 0.05−1 mm, only 5% were larger than 1 mm (Zhang
and Liu, 2018)
Most microplastic particles were reported to have different colours.
Transparent and black particles were dominant in both rice-fish coculture soils and farmland soils in Shanghai, China (Liu et al., 2018;
Lv et al., 2019). Red, black, green, blue, brown and transparent
particles were observed in the suburbs of Wuhan (Chen et al., 2020).
White, transparent, and blue were dominant colours for the particles
found in arable land from southeast Germany (Piehl et al., 2018).
Besides other characteristics such as shape and dimensions, information
on the colour of particles can be useful for things such as determining
the source or whether ingestion by organisms as a result of active
foraging is induced by certain colours.
Biological characteristics
In the case of microplastic in soil, it might be useful to define the
biological characteristics as well. Microplastics consist of particles of
6

https://ourworldindata.org/grapher/plastic-production-polymer

Page 24 of 110

RIVM report 2021-0224

different sizes and shapes to which organisms, such as bacteria, and, as
in the case of larger particles, (multicellular) organisms like nematodes
and algae can adhere (Wang et al., 2021a). Also, microplastic particles
can adhere to the roots of plants and may affect the uptake of water
and nutrients (Zhang et al., 2021b). Microplastics can also be taken up
by plants and accumulate in plant tissue (Li et al., 2020b; Zhang et al.,
2021b). However, not much is known about this and methods to
determine this characteristic are not broadly available.
Methods for the extraction, separation, identification and
quantification of microplastic in soil
The absence of a suitable method for the analysis of the type and
quantity of microplastics in soil is a big hindrance for research
(highlight 3). Although a number of analytical methods have been
developed, an efficient, robust, fast and low-cost analytical method for
soils is still not available, especially for the isolation of the polymers and
particles from the complex, organic-matter-containing solid soil matrix
(sample clean-up). Data on the abundance and distribution of
microplastics in soils are still limited and results obtained from studies
differ significantly.
There is currently no standardized method for separating microplastics
from a soil matrix, nor a standardized analysis and identification protocol.
In Annex 3, we provide a brief overview of the methods developed and
used in scientific literature for the different steps of measuring
microplastics in complex environmental samples with a special focus on
their applicability for the analysis of soil samples. These steps comprise
sampling, extraction, separation, purification, identification and
quantification (detection). Some steps have several possible methods to
use. Each method has its benefits, its specificity for certain polymers,
differential applicability for solid matrices and some uncertainty attached.
The biggest hurdle is the extraction and clean-up method. This is a
challenging step because of the presence of various, abundant and
complex organic substances in the soil organic matter fraction (Bläsing
and Amelung, 2018; Li et al., 2020a; Ruggero et al., 2020; Möller et al.,
2020). Often applied techniques are based on the extraction of
microplastics with a salt solution through density differences (Table 1)
between the microplastics, the other soil constituents and most of the
organic matter. Different salt solutions can be used for different
polymers. With saturated NaCl, the light polymers can be extracted,
while with NaI or NaBr, for example, the whole range can be extracted.
It is, however, difficult to distinguish organic compounds from
microplastics by conventional salt solution density separation,
irrespective of the soil type and structure (Li et al., 2020a). For samples
with organic matter, such as soil and sediment samples, a digestion step
is often required (Ruggero et al., 2020).
The second hurdle is to find a suitable analytical instrument for different
types or purposes (reviews e.g., by Ruggero et al., 2020 and Möller et
al., 2020). Depending on the scope of a study, one method may be
more suitable than another. For monitoring purposes, determining mass
quantities of polymers or volumes may be the best way to measure
Page 25 of 110

RIVM report 2021-0224

concentrations in the field. Whereas a toxicity laboratory test may
require another analytical methodology to determine elasticity and
aspect-ratio (both related to potential uptake). Currently, few methods
are available to provide sufficient insight into the morphology of
microplastics. No one method fits all purposes.
Combinations of methods have also been tested (see Annex 3) and
seem to be the way forward. However, most studies are still limited to
one analytical methodology. To be able to combine and compare test
results, there is a need for a harmonized or even unified protocol
describing which (set of) method(s) can best be used for which purpose,
with the needed quality standards.
Table 1 Densities of widely used plastics (data from Ruggero et al., 2020).

Plastic class

Acronym

Expanded Polystyrene
Acrylonitrile butadiene styrene
Polypropylene
Low density polyethylene
High density polyethylene
Mater-Bi
Nylon (Polyamide)
Polystyrene
Polymethyl methacrylate
Polyurethane
Polycarbonate
Polyhydroxy butyrate
Polylactic acid
Polyvinyl chloride
Polyethylene terephthalate
Polyester

EPS
ABS
PP
LDPE
HDPE
MB
(Nylon) PA
PS
PMMA
PU
PC
PHB
PLA
PVC
PET
PES

Page 26 of 110

Density
(g/cm3)
0.03–0.15
0.90–1.53
0.91–0.95
0.92
0.96
1.02
1.02–1.06
1.05
1.09–1.20
1.2
1.20–1.22
1.25
1.25
1.35–1.39
1.38–1.41
Unknown

RIVM report 2021-0224

3

Source, emission, behaviour and fate of microplastics in soil

Source and emission
In a variety of studies, microplastic emission sources are identified, such
as tyres, agricultural plastic films, textile, seed coatings, personal care
products, cosmetics, paints (e.g. on roads and buildings), artificial turf,
landfill, litter, packaging and construction materials. Both primary and
secondary microplastics are released to the environment, but the
secondary microplastics are the dominant source (highlight 4).
Introduction
The distribution of microplastics in soil systems is widespread, which has
drawn the attention of many scientists (e.g., Rillig and Bonkowski, 2018,
reviewed by Sun et al., 2022 and Xu et al., 2020b). Microplastics can
enter terrestrial systems in various ways, such as sewage sludge 7,
plastic mulch from agriculture, tyre abrasion, littering, illegal waste
dumping and fertilizers (Horton et al., 2017; Bläsing and Amelung,
2018; Li et al., 2019; Weithmann et al., 2018). Based on measurements
of microplastic abundance in soils (see Table 2), plastic mulch and
compost are considered the most significant sources for microplastic
accumulation in arable soil (Xu et al., 2020a). Another, often reported
source is sewage sludge (Corradini et al., 2019; Wang et al., 2019). In
the Netherlands, the application of municipal sewage sludge on
agriculture soil is currently restricted, but with the introduction of a new
environmental act in 2022 this ban will be partly withdrawn. 8 This could
lead to a future increase of emissions of microplastics to arable soil. In
recent decades, the increased use of single-use grocery bags and plastic
mulch has led to a predominant contamination of arable soil with
polyethylene (Ramos et al., 2015). However, recent restrictions on the
single use plastics has proven effective, e.g. in the EU 9.
Overall, the amount of microplastics discharged to soil is estimated to be
much higher than that discharged to oceans (Horton et al., 2017; Nizzetto
et al., 2016; Hurley and Nizzetto, 2018), but a consistent comparison is
lacking. It was estimated that roughly 107,000–730,000 tons of
microplastic entered arable lands annually in North America and Europe.

7

In the Netherlands, WWTP sludge is mostly burned as the sludge does not meet strict quality standards.

8

Aanvullingsregeling Bodem OMGEVINGSREGELING consolidated and updated 08-09-2021 afdeling 9.6

specifieke voorschriften omgevingsvergunning milieubelastende activiteit – het op of in de bodem brengen van
zuiveringsslib. Https://iplo.nl/regelgeving/stelsel-omgevingswet/omgevingswet-in-ontwikkeling/hoofdlijnenomgevingsregeling/
9

Directive (EU) 2019/904 of the European Parliament and of the Council of 5 June 2019 on the reduction of the

impact of certain plastic products on the environment. https://eur-lex.europa.eu/eli/dir/2019/904/oj
Page 27 of 110

RIVM report 2021-0224

Location

Table 2 Microplastics present in different soils from around the world as reported by Xu et al. 2020b.

Farmland soil in
Shanghai, China

Abundance
Polymer
(particles/kg) identification
Shallow soil:
PP (50.5%),
78.0±12.9
PE (43.4%),
PES (6.1%)

Shape

Size (mm)

Colour

Reference

Shallow soil: fibres
(53.3%), fragments
(37.6%), films (6.7%),
pellets (2.1%)

Shallow soil:
0.03-1: 48.8%

Shallow soil: black
(39.4%)

(Liu et al.,
2018)

Deep soil:
62.5±12.9

Deep soil: fibres
Deep soil:
(37.6%), films (33.8%), 0.03-1: 59.8%
fragments (28.3%),
pellets (0.32%)
Fibres and microbeads
0.02-5
predominant

Deep soil: transparent
(46.3%)
Transparent and black
dominant

(Lv et al.,
2019)

red, black, green, blue,
brown and transparent

(Chen et al.,
2020)

Not mentioned

(Zhang and Liu,
2018)

Not mentioned

(Corradini et
al., 2019)
(Fuller and
Gautam, 2016)

Rice-fish co-culture
10.3±2.2
ecosystems, Shanghai,
China
Farmland around suburbs 320-12560
of Wuhan, China

Tree-planted soils in
Yunnan, China

7100-42960

PE (61.4%),
PP (35.5%),
PVC (3.5%)
PA (32.5%),
PP (28.8%),
PS (16.9%),
PE (4.2%),
PVC (1.9%)
Not mentioned

Agricultural soil from
Chilean central valley
Municipal solid from
waste facility in Sydney,
Australia
Floodplains in Swiss
nature reserves
Agricultural farmland in
southeast Germany

1210±250

Not mentioned

Microbeads (48%),
<0.2 (70%),
fibres (37%), fragments 0.5-1 (13%),
(15%), foams (1%)
0.2-0.5 (9%),
1.0-3.0 (7%),
3-5 (<1%)
Fibres (92.0%),
0.05-1 (95%),
fragment (4.0%), film
> 1 (5%)
(3.7%)
Fibres (97.0±3.0%)
Not mentioned

300-67500

PE, PS, PVC

Not mentioned

Not mentioned

Not mentioned

~593

PE (88%), PS,
SBR, PVC
PE (62.5%),
PP (25.0%),
PS (12.5%)

Not mentioned

0.125-0.5

Not mentioned

Films (43.8%),
fragments (43.8%),
fibres (12.5%)

1-5

White (62.5%), transparent (18.75%), blue
(12.5%), green (6.25%)

0.34±0.36

± reflects the standard deviation
Page 28 of 110

(Scheurer and
Bigalke, 2018)
(Piehl et al.,
2018)

RIVM report 2021-0224

Soil specific estimates
Only recently has knowledge about the sources of microplastics in soils
grown to such an extent that quantitative estimates of release related to
specific sources can be made using modelling approaches (SAPEA,
2018). Two such studies using state-of-the-art Material Flow Analysis
approaches are briefly described here, one focusing on seven common
polymers (Kawecki and Nowack, 2019) and one on rubber from tyres
(Sieber et al., 2020) for a Swiss scenario. From these studies, the main
inputs seem to come from microplastics that originate from secondary
sources (see Table 3), e.g. from abrasion wear of tyres, construction
pipes, agricultural films and agrotextiles. But also from the sawing of
construction pipes, resulting in sawdust. Furthermore, manufacturing
(excluding textiles) releases plastic pellets, flakes and dust to residential
soils. Microplastic present in compost is expected to be a main source
for its presence in agricultural soils and gardens, but data for the
Netherlands do not exist yet (see Table 3 for data from Switzerland,).
Table 3 Distribution of microplastics sources of seven commodity polymers in
Switzerland (Kawecki and Nowack 2019).

Source

Fraction

Construction pipes

22.9%

Agricultural films

18.9%

Outdoor air

15.6%

Agrotextiles

10.7%

Non-text. manufacturing

6.6%

Compost

5.4%

Other 19 categories

19.9%

From all these sources, it is estimated that rubber released from tyres
makes up more than 10 times the microplastic release estimated for the
seven commodity plastics (PET, PP, LDPE, HDPE, PVC, PS and EPS) in
Switzerland (Sieber et al., 2020). This figure might in reality be lower,
as the fragmentation of macroplastics into microplastics is not accounted
for in the study conducted by Kawecki and Nowack (2019), as well as
some other sources which might still need to be quantified, such as
paint. Additionally, these figures do not account for spatial distribution
of these sources. For instance, tyre wear particles are thought to end up
mainly in roadside soils, whereas the abrasion of agricultural films would
mainly end up in arable land.
Verschoor et al. (2016) estimated microplastic emissions from abrasive
cleaning agents, paints and tyre wear to different environmental
compartments in the Netherlands. The authors note that the Dutch
Pollutant Release and Transfer Register (Dutch: Emissieregistratie),
which registers and calculates regionalized emissions of 375 pollutants
in the Netherlands, allocate 40% and 90% of tyre abrasion emission to
soil in urban areas and non-urban areas, respectively. For paints no
distribution was provided.
Overall environmental estimates
Within the REACH restriction on intentionally added microplastics,
estimates have been made regarding the release of (primary)
Page 29 of 110

RIVM report 2021-0224

microplastics to the environment (Table 4). Although the releases are
not specified for each receiving environmental compartment, for certain
sources it is to be expected, based on literature, that some of the
emitted microplastics will end up in soils. This will primarily be the case
for emissions from products considered under the categories ‘agriculture
and horticulture’, ‘paints and coatings’ and ‘construction products’. With
respect to agriculture and horticulture, based on the applications noted,
it is expected that most microplastics will end up in arable soils. Several
publications showed that microplastics can subsequently end up in
crops, as plants are able to take up microplastics via the roots (Zhang et
al. 2021b; Li et al., 2020b). For paints, RIVM estimated an average
fraction of 57% of microplastics end up in soils as a result of
maintenance and wear of paints in rural and urban areas (Verschoor et
al., 2016). Although the estimate is made for secondary microplastics,
primary microplastics (beads) incorporated in the matrix of paints will
also likely end up in soils via this route, although amounts are expected
to be low compared with the first estimate.
Estimated emissions of primary microplastics to soils are, however,
expected to be small compared with the secondary microplastic
emissions. The combined release of primary microplastics from
agriculture, horticulture and paints and coatings in the whole EU/EEA
(~12.700 tonnes/year – ECHA, 2020)) is only slightly higher than
expected secondary microplastic emissions to water from only landbased litter fragmentation in the Netherlands alone (~10,000 tons/year
– Verschoor and De Valk, 2018). It is unclear what amounts end up in
soils, but the method used by Verschoor and de Valk (2018) is derived
from OSPAR, which estimates 15-40% fraction of litter reaching the sea
in its catchment area. This suggests that a substantial amount of plastic
litter ends up in soils. For tyre wear particles, it was estimated that 74%
is released to road side soils and 4% to other soils (Sieber et al., 2020).
Table 4 Use and releases of intentionally added microplastics in the EU/EEA.
Derived from data from ECHA (2020).

Sector/ Product
Group

Use (tonnes/year)

Cosmetic products
Detergents and
maintenance
Agriculture and
horticulture
Oil and gas
Paints and coatings
Construction products
In vitro diagnostic
devices
Medical devices
Medicinal products
Food additives
Infill material for
synthetic pitches

8,700 (4,100-13,100)
17,000 (11,100-23,000)

Eventual release to the
environment
(tonnes/year)
3,800 (1,800-5,900)
8,500 (5,600-11,600)

10,000 (3,500-18,000)

10,000 (3,500-18,000)

1,200 (300-2,000)
5,300 (10,200)
Unknown
50 (0.5-100)

270 (~0-550)
2,700 (5,200)
Unknown
0.27 (0.25-0.29)

Unknown
2,300 (800-3,700)
Unknown
100,000 (15,400-184,800)

Unknown
1,100 (400-1,800)
Unknown
16,000 (2,000-52,000)

Page 30 of 110

RIVM report 2021-0224

Data gaps
The main sources of microplastics emitted to soils seem to have been
identified, but quantitative data is not complete. Based on data for other
environmental compartments (Verschoor and de Valk, 2018; ECHA 2020),
it seems that an adequate dataset of emission rates of microplastics to
soils is still missing. The soil-specific data seems to lack important
information, such as paints as part of construction products and
microplastic release due to the abrasion of macroplastics (litter). Manure
and compost might be another source of microplastics in soils based on
measurements taken in China (e.g., Yang et al. 2021). Furthermore, the
data is estimated for different locations, some sources quantified for
Switzerland, the EU and the OSPAR region. So a full overview of
emissions to soil for the EU or the Netherlands is still missing.
Observations in soil – behaviour and fate
Once emitted to terrestrial ecosystems, microplastics accumulate in soils
and can migrate to marine and fresh waters through runoff, with erosion,
and by atmospheric transport, and can migrate to the groundwater and
deep soil through, for example, leaching, bioturbation and farming
activities (highlight 5). After microplastics enter the soil system, the
microplastics’ physical, chemical and biological properties change through
fragmentation and (bio)degradation.
Although information on sources can be improved, it is clear that the
microplastics are found almost ubiquitously. In a survey of Swiss
floodplains, 90% of soil samples contained microplastics (Scheurer and
Bigalke, 2018) and polyethylene particles accounted for 88% of all
microplastics found. In addition to MPs being directly emitted to soils, it is
thought that indirect sources also play a role. Several studies explained
the detection of MPs in natural areas as likely coming from flooding and
air deposition (Scheurer and Bigalke, 2018; Chen et al., 2020; Liu et al.,
2018; Lv et al., 2019). Although there is some data available on
microplastics in soils, the data remains limited at the moment and data
on microplastics in soil specific to China is relatively abundant compared
with measurements taken in other locations (Xu et al., 2020b; Table 2).
There is currently no data found in scientific literature for soils in the
Netherlands. As reported in the overview by Xu et al. (2020b) (Table 2),
the abundance of microplastics in 20 arable fields in Shanghai were
78.0±12.9 and 62.5±12.9 particles/kg (sizes of 0.02 − 5 mm) in shallow
and deep soils, respectively (Liu et al., 2018). Sewage sludge is used as
fertilizer on arable fields, which is considered a primary driver of soil
microplastic pollution. Ng et al. (2018) reported a mass of microplastic
derived from sewage sludge application of up to 2.8×103 – 1.9×104 tons
annually in Australia. Microplastic counts found in 31 agricultural fields
from the Chilean central valley (600 – 10,400 particles/kg) increases
upon successive sludge applications (Corradini et al., 2019). Another
study from Wuhan, China revealed 320–12,560 particles/kg in
horticulture (Chen et al., 2020). By now, the highest abundance of
microplastics in agricultural soils was observed in soils in Yunnan
(7,100-42,960 particles/kg) (sizes of 0.02−10 mm) (Zhang and Liu,
2018). It is currently unknown whether these amounts are high or not
and what the related potential risks are.

Page 31 of 110

RIVM report 2021-0224

As an example of the fate and behaviour of microplastics in arable soil,
we have selected the investigations of Yu et al. (2021), who studied
microplastic distribution in a greenhouse vegetable production base in
Northern China (Shouguang City, Shandong Province). Samples of
greenhouse agricultural soil, open-field agricultural soil, and agricultural
plastic mulch film were collected to investigate the distribution
characteristics, influencing factors, and discharging sources of
microplastics.
The abundance of microplastics at all sampling sites ranged from 310 to
5,698 items/kg, with an average value of 1,444 ± 986 items/kg. The
main size category of microplastics was less than 0.5 mm and the
contribution of microplastic particles with sizes <0.5 mm in the 10–25 cm
layer of greenhouse agricultural soils was significantly higher (p < 0.05)
than that found in the 0–5 cm soil layer, which indicated that small
microplastic particles tended to migrate to deeper soil layers. The
prevailing shapes of microplastics were fragments, while polypropylene,
ethylene-propylene copolymer, and polyethylene dominated among
chemical compositions with a total of 85%. This correlates to the
widespread use of these plastics in agriculture in China (Zhang et al.,
2019) and similar results have been found in other studies (Liu et al.,
2018; Ding et al., 2020). Other microplastics measured were: polystyrene
(PS), polyester fibres (PES), cellophane, polyurethane (PU), rayon,
acrylonitrile-butadiene-styrene copolymer (ABS), and polymethyl
methacrylate (PMMA).
The fractions of silty and sandy particles in soils were correlated with the
abundance of MPs in those soils. The microplastic abundance in sandy
loam was significantly higher (p < 0.05) than that found in silty loam or
loam. Therefore, the soil texture may affect the distribution of
microplastic particles in local agricultural soils. In addition, the age of
the greenhouse was positively correlated with microplastic-particle
abundance in the soil, while there was no significant difference in the
abundance of microplastics in greenhouse agricultural soils under
different irrigation regimes.
Modelling microplastic transport and fate in soil
Polymer type, shape and particle-size-dependent modelling of
microplastics’ fate and behaviour is important for coping with the
complexity of microplastics in the environment (highlight 6). Studies for
the modelling of microplastic emissions, transport and fate in water are
available, but these are not yet sufficient for an investigation of the soil
system.
Modelling can play an important role in coping with the complexity of
microplastics due to the range of MP properties (e.g. polymer type, size,
shape), affecting their fate in soils and the environment. However,
studies modelling the fate of microplastics in soil are not yet sufficient.
For instance, recent research provides modelling approaches to deal
with the various sizes, shapes and densities of microplastics (Kooi and
Koelmans, 2019). There are various types of models, each with
particular benefits and shortcomings, but each of them are optimized to
typically answer one question. Here we focus specifically on those
Page 32 of 110

RIVM report 2021-0224

models aimed at estimating microplastic release, transport and fate in
the soil system. Typical models available today are able to estimate:
• The emission to the environmental compartments (air, water,
soil) of substances and materials, for instance Material Flow
Analysis (MFA) models (Kawecki and Nowack, 2019; Sieber et
al., 2020).
• Background concentrations of substances (Hollander et al., 2016)
and materials (Meesters et al., 2014) at a screening level.
• Spatially and time resolved concentrations of substances and
materials (Besseling et al., 2017).
Some of these models have already been applied and adapted for use
with microplastics, others still require some work to account for the
specific needs that come with modelling microplastics in the
environment. Here we will briefly discuss some of the modelling tools
already available and the remaining knowledge gaps.
Applicability of existing models
Existing models fit for organic compounds or metals need to be adapted
in order to be fit for use with microplastics. That changes are required is
partly based on existing knowledge about the behaviour of particles
(nanoparticles or colloids) compared with dissolved compounds in the
environment (Meesters et al., 2013). And on existing knowledge about
the behaviour of microplastics in the environment (Koutnik et al., 2021).
For this reason, the first modelling studies conducted on microplastics
(Besseling et al., 2017) were based on models developed for
nanomaterials (Quik et al., 2015). However, none of the modelling
studies on microplastics included the fate in soil and they focused largely
on the aquatic environment. At most, the release to soil is quantified
(Kawecki and Nowack, 2020; Sieber et al., 2020), but not the fate and
behaviour in order to estimate exposure levels in soil. This is a
significant knowledge gap, because it has been estimated that the
emission of microplastics to soil is likely to be almost tenfold the
emission to rivers and oceans (Kawecki and Nowack, 2019; Sieber et
al., 202; Zubris and Richards, 2005).
Models aimed at describing nanomaterial fate can, for the most part,
already be applied to microplastics and the following models include fate
in the soil compartment:
• SimpleBox4nano (Meesters et al., 2014);
• MendNano (Liu and Cohen, 2014);
• NanoFATE (Garner et al., 2017);
• NanoFASE WSO (Lofts et al., 2019).
These models are developed for materials at the nanoscale (1-100 nm)
with an applicability domain of 1 nm to 10 µm sized particles. This falls
within the stokes regime of particle movement in another medium (e.g.
sedimentation/deposition). For larger microplastics (>10 µm), it might be
necessary to test some of the underlying theories, such as the application
of stokes law for describing the movement of particles in another
medium. However, this particular issue is probably not as relevant for
particle movement in soil compared with air and water. In soil, larger
particles will get trapped more easily in soil pores, thereby greatly
reducing their mobility. Another uncertainty is the parametrization of
Page 33 of 110

RIVM report 2021-0224

microplastic degradation because many nanomaterial models were
initially developed with metal particles in mind. As such, dissolution to an
alternate form is sometimes included, but in practice degradation and, in
particular, fragmentation is not included in these models.
Some studies on microplastics have already started to indicate that the
fragmentation and degradation of microplastics is an essential process
for modelling microplastics in the environment (Koelmans et al., 2017;
Koutnik et al., 2021; Kaandorp et al., 2021; Chamas et al., 2020). Soil,
together with water and sediment, is considered a sink for microplastics,
and therefore it is a relevant process which may largely define the
accumulation level of microplastics in soil. As an example of how the full
degradation can be described for modelling, degradation rate constants
from Chamas et al. (2020) are further examined in Annex 2.
Next steps and knowledge gaps
In order to estimate microplastic exposure concentrations in soil using
modelling tools, the basic steps are first to estimate the emission to soil,
and then to estimate the microplastic concentration in soil. Microplasticrelevant models that estimate the emission to soil, as well as to air and
water, are already available based on material flow analysis (Kawecki et
al., 2019; Sieber et al., 2020). The currently missing link is an
extrapolation of the modelling study from Switzerland to other regions
of interest, such as the Netherlands and the entire EU. In addition,
further effort might be needed to estimate emission in a spatially
resolved manner in order to estimate local emissions. This means the
major shortcoming is not the lack of models or tools, but rather data to
include all important sources and material flows. Gathering these data
takes a lot of effort, but the inclusion of uncertainty by applying a
probabilistic approach can be very useful.
Following a sufficient estimation of the emission rates (tonnage per
year), the further fate in the soil compartment can be modelled. To do
this, existing models fit for nanomaterials can be applied first. These
models can then be optimized based on validation and calibration with
microplastic measurements/observations to include potentially relevant
microplastic specific fate processes and physico-chemical descriptors,
such as approaches to cope with the large variety in shapes, sizes and
polymer types.
These modelling efforts will result in essential exposure data for soildwelling organisms, plants, but also for further studies on human
exposure through the environment.
Overall, the main knowledge gaps for modelling the fate of microplastics
in soil are related to:
• Estimating emissions to soil at the EU level by applying the
existing framework applied in Switzerland and including some
other major sources, such as emissions from macroplastic litter
and paint, in addition to already included sources (see
Section 3.1.2).
• Quantifying the fragmentation and degradation process (see
Chapter 4 and Annex 2).
Page 34 of 110

RIVM report 2021-0224

•

Validating and improving existing fate modelling tools for use
with microplastics.

Some of these issues are likely to be tackled in some of the recently
started EU research projects, such as LEON-T, Papillions and MINAGRIS.
(see Section 6.4)

Page 35 of 110

RIVM report 2021-0224

Page 36 of 110

RIVM report 2021-0224

4

(Bio)degradation of (micro)plastics

Published biodegradation data for (micro)plastics differ greatly between
studies (highlight 7). The (bio)degradation potential of microplastic
particles depends on three major aspects, namely 1) their chemical
composition, 2) their physical properties and 3) the environmental
conditions to which they are exposed. The limited data available on
(bio)degradation and monitoring data show that microplastics can
accumulate in the environment, including soil systems. However, the
actual accumulation rates are uncertain, not only due to the scarcity of
data in combination with a large variation between measured
(bio)degradation rates, but simply also due to the lack of standardized
methods suitable to assess the fragmentation and degradation of
microplastic particles under environmentally relevant conditions, and the
vast range of polymer types and identities.
Introduction
One of the advantages of using plastics is their resistance to
environmental influences. Nevertheless, the degradation of macro- and
microplastics is shown to occur over time depending on the intrinsic
properties of the (micro)plastic (e.g. size, type of polymer and additives)
and the extrinsic properties of the environmental and biological conditions
(e.g. microbiome, acidity, temperature and UV radiation) (EC, 2020;
Maier, 2018; Tokiwa et al., 2009). Processes that induce degradation can
be physical (e.g. UV-light), chemical (e.g. hydrolysis) or biological (e.g.
microorganisms, such as bacteria and fungi) in nature (Klein et al., 2018).
(Bio)degradation is a process that causes the breakup of the polymer
structure and any of the additives present in the microplastic particle
through biotic and abiotic processes. This can yield smaller sized
(micro)plastic particles whose polymer structure is still largely intact, a
process termed fragmentation. It is this process of the fragmentation of
macroplastics which is found to be the largest contribution to microplastic
emissions to the environment (Verschoor and de Valk, 2018) (see
Chapter 3.1 on sources and emissions). Fragmentation can be the first
step in a (bio)degradation cascade, as fragmented particles have been
shown to be more susceptible to further (bio)degradation (Mohanan et
al., 2020). However, there have been types of plastics designed that only
fragment to a certain degree and that have been banned for that reason
(e.g. oxo-degradable plastics – conventional plastics containing additives
which promote the oxidation of the material). 10
(Bio)degradation can also lead to a more complete disintegration of the
polymer structure, yielding oligomers, monomers and other degradation
products. While the microplastic particles are no longer present, other
chemicals become available. The process whereby the polymer and
additives are fully metabolized, yielding carbon dioxide, is termed

10
DIRECTIVE (EU) 2019/904 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 5 June 2019
on the reduction of the impact of certain plastic products on the environment. https://eur-lex.europa.eu/legalcontent/EN/TXT/PDF/?uri=CELEX:32019L0904&from=EN

Page 37 of 110

RIVM report 2021-0224

mineralization. Mineralization is also known as complete or ultimate
degradation.
There is an increasing interest in (bio)degradable (micro)plastics as a
solution for certain uses of (micro)plastics (e.g. single use products,
seed coatings). As such, the development of biodegradable plastics is
considered one of the technological innovations which could reduce the
potential effects of future emissions of microplastics (EC, 2020; Maier,
2018). However, caution is needed, as accumulation in the environment
can still occur if the (bio)degradation does not occur under
environmentally relevant conditions and within reasonable timeframes.
Different terms, such as partially or completely biodegradable,
degradable and compostable, are used simultaneously to describe the
(bio)degradability, i.e. the ability of a material to breakdown, of
materials and products. In practice, these claims can mean various
(bio)degradation events occurring under different biotic and abiotic
conditions. In that respect, it is important to understand what the
drivers of (bio)degradation are and to have suitable testing methods and
standards to characterize the biodegradability of microplastics.
In the remainder of this chapter, we discuss in more detail the main
determinants for (bio)degradation (4.2), the issues associated with
allowing (bio)degradable microplastics for certain uses (4.3) and finally
the implications for estimating microplastic fate in the environment (4.4).
Determinants for (bio)degradation
The (bio)degradation rates of plastics depend on three major aspects: 1)
the chemical properties of a material, 2) the physical properties of the
material and 3) the environmental abiotic and biotic conditions to which
the material is exposed. Each aspect includes multiple variables, the
most important of which – and thus not the extensive list of all
parameters – are discussed below.
Chemical properties
Polymers
Polymers contained in microplastics often have long backbones with many
carbon-carbon bonds, but can also contain other atoms such as oxygen,
hydrogen, fluoride and silicon. Carbon-carbon bonds are difficult to break,
as the dissociation energy required for it is high, with increasing energy
needed for increasing bond order (Blanksby and Ellison, 2003). The
addition of fluoride creates even more stable structures (Reddy, 2015).
(Bio)degradation by microorganisms or environmental processes will
therefore be slow. Some polymers are (undesirably) prone to deteriorate
due to abiotic processes (e.g. the colouring of polyurethane of mattresses
from white to yellow over time through photo-oxidation) which initially
leads to superficial breakdown effects. Plastics can also be designed to
deteriorate under certain conditions, but care should be taken that the
plastics really (bio)degrade and not only fragment as is the case with oxodegradable plastics (Abdelmoez et al., 2021). While some structures, e.g.
esters, are expected to be easily broken down (Iwata, 2015), their
(bio)degradation potential can vary greatly under environmentally
relevant conditions, with PET being hardly degraded (Hiraga et al., 2019),
PLA being compostable through hydrolysis that occurs under the
Page 38 of 110

RIVM report 2021-0224

prevailing high temperatures (Gorassi and Pantani, 2017), and the
microbial polyester PHA being enzymatically degradable by bacteria and
fungi under ambient conditions (Ong et al., 2017). This illustrates that
theoretical considerations alone are not sufficient to underpin the
degradation potential of substances. It also suggests that naturally
occurring polyesters might be more prone to (bio)degradation than
synthetic polyesters. Moore and Saunders (1998) further note that the
addition of hydrophilic groups foster biodegradation. These functional
groups promote the attachment of bacterial cells and, simultaneously, the
accessibility of secreted enzymes to the surface of polymers (Wilkes and
Aristilde, 2017).
Additives and contaminants
Plastics often contain additives to optimize the material properties and to
stabilize the polymers. These additives are blended in the polymer during
production processes. Commonly used additives include stabilizers, UVblockers, fillers, plasticizers, colouring agents and flame retardants
(ECHA, 2021; Hahladakis et al., 2018). During the lifetime of a plastic
material, other contaminants can also adhere. For example, during usage,
as well as afterwards when it has become waste and/or ends up in the
environment. The presence of additives and contaminants generally
hampers breakdown processes, but additives could be added that
accelerate the breakdown (e.g., for PLA; Gorassi and Pantani 2017).
Physical properties
Shape
Primary microplastics are produced in a manner that enables them to
serve their purpose for the intended production processes. They can be
produced in different sizes and shapes, and will have similar physical
properties in each batch. Secondary microplastics are formed due to
weathering and the fragmentation of larger plastics. These plastics will be
heterogeneous and can have all kinds of shapes and sizes. This directly
affects the potential to degrade, as roughness of the surface area and size
of the surface area are positively related to (bio)degradation (Moore and
Saunders, 1998). If it is assumed that microplastics are impenetrable for
organisms, biodegradation can only occur on the surface of a particle. The
ratio between surface area (SA) and volume (V) will therefore determine
how fast a particle can biodegrade. A high ratio will lead to a large surface
area available for biodegradation and a relatively fast degradation rate,
compared with a low ratio for which the reverse applies. This also applies
for abiotic degradation.
Molecular weight
The molecular weight of a polymer depends on the degree of
polymerization (the length) and the weight of the repeating unit (Balani
et al., 2015). In general, the molecular weight is inversely related to the
degradability. During (bio)degradation, polymers are converted into
simple, low-weight molecules, such as monomers, CO2 and H2O. Highweight polymers contain greater mass and have a higher degree of
entanglement with other polymers, making them more rigid but also
(chemically) more resistant, and as such more effort is needed to
degrade these polymers down to these basic molecules.

Page 39 of 110

RIVM report 2021-0224

Crystallinity
In crystalline polymers, the polymer chains are regularly aligned, in
contrast with amorphous polymers, in which the chains are
unstructured. The crystallinity of a polymer influences the density and
hardness of a material. Aligned polymers are dense and rigid (e.g.
HDPE), while semi-crystalline polymers contain both amorphous and
aligned polymers and are less dense and more flexible (e.g. LDPE).
Crystallinity lowers the rate of microbial degradation, as it limits the
movability of polymer chains and as such the accessibility of polymer
chains to microbes (Mohanan et al., 2020; Moore and Saunders, 1998;
Tokiwa et al., 2009).
Density
The density of plastics varies between around 0.8 to 2.3 kg/dm3
(Omnexus, 2021). As the density of water is around 1 kg/dm3, plastics <
1 kg/dm3 will primarily float, while plastics > 1 kg/dm3 will sink. Based on
these differences, plastics end up in different parts of the environment
and are exposed to different influences. Sinking plastics, such as PET, PVC
and PLA, will likely end up directly in sediment after entering water
systems. These plastics will be affected by the abiotic characteristics and
the microbiota present in these sediments. Floating plastics, such as
HDPE, LDPE and PP, may be transported longer distances and are
vulnerable to weathering processes such as photo-oxidation, storms and
the turbulence caused by waves and tides. The fate of microplastics in
soils is less apparent based on its density.
In soils, the fate of microplastics is less determined by the density of the
material, while agglomeration/aggregation plays an important role, as it
affects the surface area and bioavailability.
Environmental conditions
Temperature
Biological activity is positively related to temperature, as temperature
induces microbial growth. Each microbe has a range of temperatures in
which it is active and, within this range, an optimal temperature to
thrive in. Pischedda et al. (2019) showed that, for a commercial plastic
(containing biodegradable polyester (65%), starch (28%) and a natural
plasticizer (~6%)) in soil, the mineralization rate increased with
temperature (28°C>20°C>15°C). Around 80% of mineralization was
achieved after 400 days at 28°C, while around 40% and 30% was
achieved at 20°C and 15°C, respectively. Also, for films made from the
polymer PLA, it was observed that increasing temperature from 25°C to
37°C and 50°C significantly enhanced the degradation rates in soil and
compost, on top of that abiotic chemical hydrolysis that occurs at these
temperatures (Karamanlioglu, 2013). Increasing temperature may also
limit biodegradation in soil, as was observed by Nishide et al. (1999);
the bioplastic PHB/PV underwent a slower degradation at 52°C
compared with 30°C under aerobic conditions.
pH and soil organic matter
Although no studies could be found that have investigated the effect of pH
on biodegradation rates, the pH of soils will most likely impact these
rates. For example, the pH affects the availability of nutrients, toxins and
metals and will have an influence on the composition of micro-organisms
Page 40 of 110

RIVM report 2021-0224

present and subsequently the biodegradation rates. A study of Zhao et al.
(2021) demonstrated that the presence of microplastics can alter the soil
pH as well. The results indicate that the pH of soils containing different
types and shapes of microplastics (0.4% w/w) in most cases increases
over time. The rise in pH is explained as a potential increase in porosity
and soil aeration after the addition of the microplastics to the soil and due
to an alteration of the biota after the leaching of chemical compounds
from the microplastics (Zhao et al., 2021).
Light
Light and other types of electromagnetic radiation can induce degradation
(Yousif and Haddad, 2013), as it is a source of energy. When polymers
absorb photons (small light particles), photochemical reactions can occur,
leading to breakdown. This type of degradation is also known as
photodegradation. UV-blockers are frequently added to plastics to prevent
photodegradation. In the environment, photodegradation will occur
mainly due to exposure to UV radiation. The process is primarily
explained by two mechanisms, i.e. photoionization and chain scissions
(Niaounakis, 2015). These mechanisms lead to a shortening of polymer
chain sizes and the formation of oxidized groups, which facilitate
biodegradation (Ghatge et al., 2020). Lee et al. (1991), for example,
showed that UV-treated polyethylene films were biodegraded (by different
bacteria) to a larger extent than heat-treated films and control films.
Taghavi et al. (2021) demonstrated increased biodegradation of PS and
PE after UV pretreatment. Note that in soils there is limited exposure of
microplastics to UV light and photodegradation will therefore be a minor
factor.
Microbial composition
There is great variation between microorganism community compositions
in environmental compartments (marine, freshwater, sediment, soil), but
also within an environmental compartment. The microbial composition
depends on the characteristics of the environment, with important soil
parameters being the oxygen level, the carbon content, the presence of
(trace) metals, the pH, the moisture level, the C:N:P ratio, salt
concentration and the temperature range. Besides, environmental
constraints and the large variation in microorganisms can at least partially
explain why degradation rates can differ so much between environments.
It should also be noted that microorganisms compete with each other, but
also with other organisms (e.g., plants), for the available nutrients.
Microorganisms being able to use (micro)plastics as carbon and an energy
source can give a competitive advantage to other organisms. Under ratelimiting conditions, adaptations could occur, but this is rather speculative
and has so far not been shown to occur for conventional plastics (PE, PET,
PS) under environmentally relevant conditions, while during the last 50
years increasing levels of plastics can be found in the environment. More
information on the ability of microorganisms to degrade microplastics can
be found in Annex 2.
Biodegradable plastics
Biodegradation standards
Whether or not a material is considered biodegradable, differs between
legal frameworks. In most frameworks, internationally standardized ISO
Page 41 of 110

RIVM report 2021-0224

and OECD test guidelines are laid down to assess and justify the
biodegradability of materials and products. For plastics as a diverse
group of materials, it is still difficult to assess biodegradability. Most
frameworks have not (yet) established (definitive) criteria to earmark
plastics as biodegradable. Nevertheless, there is broad consensus on the
overall definition of biodegradable plastics, that being plastics that are
either mineralized to CO2 and converted to biomass, or are degraded to
small molecules that do not exhibit hazardous properties.
Reach restriction
The ECHA proposed restriction on intentionally added microplastics limits
the use of primary microplastics in products in the EU/EEA (ECHA,
2020). It is expected that the restriction will reduce primary microplastic
emissions significantly. The restriction does not restrict all microplastic
uses and derogates biodegradable polymers from the restriction, as they
do not meet the concerns raised on persistency. Within the restriction, a
testing strategy has been proposed to assess the biodegradability of
microplastics as put on the market. The tests are grouped in five
categories, with the most stringent test methods in the higher groups.
In Annex 2, an overview of the groups and test guidelines is available.
The lower groups (1-3) consist of screening level tests (ready, enhanced
ready and inherent biodegradability tests according to OECD test
guidelines). These tests are considered conservative and if full
mineralization occurs within the timeframe of a test, it can be assumed
that the microplastics will also degrade under environmentally relevant
conditions within a reasonable time frame (thus not meeting the (very)
persistent criteria as laid down in REACH). The drawback of these tests
is that they were not designed for particles and, as such, might be less
suitable for assessing the biodegradability of microplastics. For PHBV,
two screening level biodegradation tests according to OECD TG 301B
and 301F have been reported, in which PHBV was found to be readily
biodegradable (reported in ECHA, 2020). These tests support the
usability of the OECD screening level test for assessing the
biodegradability of microplastics.
Group 4 consists of ISO test methods designed for testing the
biodegradability of plastics in water, soil and sediments. In these tests,
biodegradation is assessed by comparison with a reference item. Within
the proposed restriction, these tests are similarly considered screening
level tests, meaning that passing the criteria of any of the tests rules out
the persistency of a (micro)plastic. It is, however, unclear how the
outcomes of these studies can be compared to the persistence criteria
since, for example, the duration of the tests is longer (up to 24 months in
soil) and because degradation is assessed relative to a reference material.
Group 5 consists of OECD simulation degradation tests that are used to
assess the degradability of substances under environmentally realistic
conditions. These test guidelines allow the derivation of degradation
rates in surface waters, sediment water systems and soils. However, as
with the OECD screening level tests, there is some uncertainty regarding
the testing of particles and how this affects the comparison between
compartments. These uncertainties have been noted in the RAC opinion
on the proposed restriction.
Page 42 of 110

RIVM report 2021-0224

The RAC opinion (ECHA, 2020) examined how the above tests can be
best used to determine if microplastics are biodegradable. Out of the
eight presented scenarios, the following was considered to be the most
suitable. When the criteria of the screening tests (groups 1-3) are not
met, tests in multiple environmental compartments from either group 4
or group 5 should be performed (and passed) to justify a derogation.
Considering the uncertainties, both the dossier submitter and the RAC
proposed a review of the conditions of the derogation be conducted five
years after entry of the restriction. It is expected that once the
restriction is adopted and tests are conducted, more knowledge will be
gained on the usability and comparability of the different tests. Whether
substantial biodegradation data in soils will be generated has yet to be
seen. The proposed restriction foresees that screening level data (group
1-3) will be sufficient to justify a derogation. Only if these OECD
screening level tests are not passed, ISO tests (group 4) and OECD
simulation tests from group 5 can be performed, whereby all relevant
environmental compartments have to be tested, including soil (EN ISO
17556:2019 (Group 4) and OECD TG 307:2002 (Group 5).
Fertilizer product regulation
Biodegradable polymers are also exempted in fertilizer products by the
upcoming regulation (EC) No 2019/1009. 11 This regulation lays down
rules to make fertilizers available on the European market and will come
into force in July 2022. Each fertilizer has to contain one or multiple
materials that belong to a component material group (CMC). 12 One
component material group is on polymers, i.e. CMC 9: Polymers other
than nutrient polymers. It allows the addition of biodegradable polymers
from this group to a fertilizer, however these polymers have to fulfil a
certain purpose, e.g. increasing the water retention capability of a
fertilizer. 13,14 A recent amendment has further allowed the presence of
biodegradable polymers in CMC 1 (Virgin material substances and
mixtures), CMC 8 (Nutrient polymers) and CMC 11 (By-products within
the meaning of Directive 2008/98/EC) (EC, 2021).
Criteria and test methods used to assess biodegradability have not yet
been established in the regulation. These will be assessed by 16 July
2024 and, where appropriate, laid down in criteria. It is stated in the
regulation that future criteria must ensure that 90% of the organic
carbon has to be converted to carbon dioxide within 48 months after the
claimed functionality, as compared with an appropriate standard. This
matches the criteria of the proposed ISO test for soils in group 4 of the
restriction on intentionally added microplastics. In addition, the
11

Regulation (EU) No 2019/1009, 2019. REGULATION (EU) 2019/1009 OF THE EUROPEAN PARLIAMENT AND
OF THE COUNCIL of 5 June 2019 laying down rules on the making available on the market of EU fertilising
products and amending Regulations (EC) No 1069/2009 and (EC) No 1107/2009 and repealing Regulation (EC)
No 2003/2003, Official Journal of the European Union p. 114.
12
In total 11 CMC are laid down in Regulation (EC) No 2019/1009. An initiative has been set out to extend the
list with two additional CMC. https://ec.europa.eu/info/law/better-regulation/have-your-say/initiatives/12163Fertilising-products-precipitated-phosphate-salts-and-derivates_en
13
An EU fertilizing product may contain polymers other than nutrient polymers only in cases where the purpose
of the polymer is (Regulation (EU) No 2019/1009, 2019).
(a) to control the water penetration into nutrient particles and thus the release of nutrients (in which case the
polymer is commonly referred to as a ‘coating agent’),
(b) to increase the water retention capacity or wettability of the EU fertilizing product, or
(c) to bind material in an EU fertilizing product belonging to PFC 4 (Growing medium).
14
By 16 July 2024, the Commission shall carry out a review in order to assess the possibility of determining
biodegradability criteria for mulch films, and the possibility of incorporating them into component material
category 9 in Part II of Annex I. (Regulation (EU) No 2019/1009, 2019).
Page 43 of 110

RIVM report 2021-0224

regulation specifies that the polymer ultimately needs to decompose and
that it does not accumulate in the environment. 15
Polymers from CMC 9 (except for those that serve as binder) have to
comply with the biodegradability criteria by 16 July 2026 and onwards.
If no criteria are established by then, fertilizers are not allowed to
contain these polymers when placed on the market.
Mulch films
Plastic mulch films are used on agricultural lands to ‘modify soil
temperature, limit weed growth, prevent the loss of moisture, improve
crop yield and precocity’ (BASF, 2021). In 2018, the European standard
EN17033:2018 16 for biodegradable mulch films for use in agriculture and
horticulture was introduced. The European standard replaced national
standards, although these were only available for France (NFU 52001:2005) and Italy (UNI 11495:2013). At that moment, no ISO
standard to determine the biodegradability of mulch films was available
yet. In 2021, an ISO standard was published as well (ISO 23517:2021).
In order for mulch films to comply with these standards, 90% of the
organic carbon in the material has to be converted to CO2 (absolute or
relative to a positive control) within two 2 years under ambient soil
conditions (Hayes and Flury, 2018). The time frame is similar to the ISO
test in soil, proposed in the restriction on intentionally added
microplastics.
In the fertilizer product regulation (Regulation (EU) No 2019/1009), it is
stated that by 16 July 2024 a review shall be carried out to ‘assess the
possibility of determining biodegradability criteria for mulch films, and
the possibility of incorporating them into component material category 9
in Part II of Annex II’. Currently, the methods to assess biodegradability
have not been decided on.
Other test standards for plastics in soils
Beside the aforementioned standards, two more standards were found
that describe how to determine the biodegradability of plastics in soils.
The first, ASTM D 5988-12, was developed by ASTM International to
determine the aerobic biodegradation of plastic materials in soils. The
methodology is considered to be equivalent to the ISO 17556 test
(ASTM, 2018). The second is UNI 11462:2012, published by the Ente
Nazionale Italiano di Unificazione (UNI). This document specifies test
methods to assess the biodegradability of plastics mostly used in
agriculture (UNI, 2012).
Composting standards
The terms biodegradable and compostable are often used interchangeably
when describing the breakdown potential of a product or material,
although these terms describe the same process under different
environmental conditions. Biodegradable indicates the capability of a
15

1) The polymer is capable of undergoing physical and biological decomposition in natural soil conditions and
aquatic environments across the Union, so that it ultimately decomposes only into carbon dioxide, biomass and
water. 2) the use of polymers does not lead to accumulation of plastics in the environment.
16
17033:2018 – Plastics – Biodegradable mulch films for use in agriculture and horticulture – requirements and
test methods
Page 44 of 110

RIVM report 2021-0224

material or product to be decomposed by microorganisms under
environmentally relevant conditions in the environment (e.g., surface
water, sediment and soil), compostability implies that this process occurs
under specific conditions that are discussed below (EEA, 2020; European
Bioplastics, 2016). Standards are available for composting processed at
two typical locations and corresponding environmental conditions: 1)
industrial and 2) home. These are also discussed below.
Industrial composting
ISO 16929:2021 describes a test method used to determine the aerobic
compostability of plastic materials on a pilot scale (ISO, 2021). This test
is part of an ISO evaluation scheme (ISO 17088:2021) used to assess
the industrial compostability of plastics. The latter includes four aspects
that are assessed in combination.
Standard EN 13432:200017 has been established to assess the
compostability or anaerobic treatability of packaging materials. For
plastic materials, the standard EN 14995:200718 has been established.
Both standards have been harmonized in Europe and materials that fulfil
the requirements of these standards are considered processable in
industrial composting facilities.
The capability of the plastics to biodegrade is measured relative to the
biodegradation potential of cellulose. At least 90% of the organic carbon
has to be converted to CO2 or 90% biodegradation compared with
cellulose has to be achieved within six months after start of the test. In
addition, 70% of the cellulose has to be converted to CO2 within six
months in order for the test to be valid (Degli-Innocenti, 2002). It is
also required that the material disintegrates by 12 weeks after starting
the test and more than 90% of the material should be smaller than
2 mm (BPF, 2021). Environmental conditions such as humidity,
temperature (58 ± 2° C) and oxygen level are kept constant during the
test period in order to resemble industrial composting conditions
(BioBasedEconomy, 2021; Degli-Innocenti, 2002). While tests are
performed under these standardized conditions, composting processes in
industrial composting facilities can occur under divergent environmental
conditions. In the Netherlands, the composting process takes place
during 2-3 weeks, which is less than 1/6th of the duration of the test
protocol (Vrins and Costenoble, 2019). This implies that, although
materials can be certified as compostable, materials can be composted
to a limited degree in practice. An example is compostable cutlery,
which is discarded with the residual waste in the Netherlands as these
are unwanted in the composting process. 19
Home composting
There are different certification schemes used to assess whether plastics
are compostable at home at a national and continental level. Most of the
standards have pass criteria similar to the industrial composting
standards. Environmental conditions deviate from industrial composting
standards; test temperatures are lower and test durations are shorter in
17

EN 13432:2000 – Packaging – Requirements for packaging recoverable through composting and
biodegradation – Test scheme and evaluation criteria for the final acceptance of packaging
18
EN 14995:2007 – Plastics – Evaluation of compostability – Test schema and specification
19
https://www.delta.tudelft.nl/article/what-happens-your-coffee-cup
Page 45 of 110

RIVM report 2021-0224

order to resemble the composting conditions at home. An overview of a
number of certification schemes can be found in Annex 2.
Uncertainties associated with biodegradation testing
As discussed above, the biodegradability of (micro)plastics can be
assessed differently between frameworks. Regardless of the framework,
standardized test guidelines are needed to obtain comparable and
regulatory relevant results. These tests should enable a differentiation
between fragmentation into smaller sized plastic particles and
degradation into (hazardless) substances and complete mineralization.
Exempting biodegradable plastics which do not (bio)degrade in the
environment must be avoided. A number of uncertainties regarding the
aforementioned frameworks and biodegradation test methods are
therefore summarized below:
1. The restriction on intentionally added microplastics still has to be
adopted. In the final RAC and SEAC proposal, a passed OECD
screening level test suffices for a derogation based on
biodegradability. These tests might not be particularly suitable for
particles and might be too stringent (as can also be the case for
the OECD simulation degradation tests). For the ISO test
methods, it still has to be decided whether these are considered
screening tests and how their outcome can be used to determine
the biodegradability of (micro)plastics. For example, the ISO soil
test (EN ISO 17556:2019) foresees a testing duration of
24 months, which greatly exceeds the persistence and very
persistence criteria used under REACH.
2. As field conditions are inherently variable, test results will likely
not represent all the different field conditions that can occur. This
is inherent to all environmental fate and toxicity testing, as
testing is performed under controlled conditions (needed for
standardization and comparison) rather than realistic
environmental conditions.
3. Some standards allow tests to be conducted with the plastic base
material instead of a product or material containing additives
(e.g. as in the case of standard EN17033:2018 for plastic mulch
films). Tests with the base material will likely result in different
biodegradability rates due to differences in physical and chemical
composition.
4. In case of industrial composting, and potentially home
composting, standards do not always characterize the processes
that take place at composting sites. As described earlier, the
duration time prescribed by the industrial composting standard is
significantly longer than the actual full-scale industrial
composting time in the Netherlands, resulting in materials that
are labelled ‘compostable’ while actual degradation may be
limited.
5. For some tests, only partial biodegradation is required for plastics
to be regarded as biodegradable. The ISO tests proposed in the
restriction on intentionally added microplastics note as pass
criteria that 90% biodegradation is achieved in comparison with
the reference material. This implies that when a minimal required
biodegradation of 60% for the reference material is achieved
during the test, only 54% of the test material has to be
mineralized during the test.
Page 46 of 110

RIVM report 2021-0224

Which plastics are biodegradable according to literature?
A categorization often used for plastics, as presented in Iwata (2015), is
that plastics are either biodegradable or non-biodegradable and either
bio-based or mineral-based. While mineral- and bio-based plastics can
be distinguished based on the source material, no information is given
by Iwata (2015) on the criteria to assign a plastic as biodegradable. The
presence of an ester group is often considered as an inherent property
making polymers biodegradable. While this appears to be the case for
certain polymers, e.g., PLA and PHA, this is certainly not always the
case, for example, for PET.
PLA
Kjeldsen et al. (2018) report a broad overview of biodegradation data
for PLA, showing that results vary greatly in soil as well when
composted. The compostability of PLA ranged from 100%
biodegradation in 28 days to only 13% after 60 days. In both cases,
temperature was kept constant at 58°C and it is unclear what underlies
the large difference. Parameters such as microbiological composition,
pH, humidity, the availability of nutrients and energy sources or other
factors could have all influenced the outcomes (see Chapter 4.2 for the
determinants for (bio)degradation). In addition, most tests have not
been performed in accordance with standardized test protocols, which
means that results could have also been influenced by the applied
methods and measurement techniques. In this study, these differences
are not further explored, but it demonstrates that interpreting and
comparing study results should be done with caution.
Several biodegradation tests were performed with PLA in soils (Kjeldsen
et al., 2018); however, most test materials contained an additional
substrate/material such as fertilizer, sisal fibres and/or starch. Additional
substrates can hamper or enhance the degradation rate of polymers as
these substrates may affect the microbiological composition. Test
conditions have to be standardized or at least similar in order to
compare degradation rates, even though other studies may still be
valuable and maybe even more representative when testing actual
environmental conditions. One test performed with solely PLA resulted in
10% degradation after 98 days in a soil with a moisture content of 30%,
while information on temperature was not given (Wu, 2012). Tests with
powdered PLA in soils resulted in 14% biodegradation in 28 days at
25°C and 60% humidity (Adhikari et al., 2016). While PLA is regularly
referred to as a biodegradable plastic, the available biodegradation data
does not support this.
PHA
Most tests with PHA-based plastics are performed with PHB
(polyhydroxy butyrate). Composting of PHB resulted in around 80%
biodegradation in 28 days at 55°C and humidity levels of 70% (Tabasi
and Ajji, 2015). Comparable results were achieved in another study,
however, at 58°C in 110 days and 50% humidity (Weng et al., 2011).
Under lab-scale conditions, more than 64% degradation was recorded
after 6 months in soil (Jain and Tiwari, 2015). In tropical soils under real
environmental conditions, up to 98% biodegradation was achieved for
PHB films, though over a longer time span (300 days) (Boyandin et al.,
Page 47 of 110

RIVM report 2021-0224

2013). But for pressed PHB pellets, degradation in tropical soils was
limited to a maximum of 55%, demonstrating the importance of the
physical properties for the biodegradation rate.
Mc Donough et al. (2017) reported 66% of mineralization after 28 days
for PHBV microparticles. The result for the copolymer of PHB was
achieved in a screening test in the laboratory. For the polymer
PHB/PHBV, 79.2% biodegradation in 28 days was reported in the
microplastics restriction (ECHA, 2020).
For PHA, lower biodegradation results were recorded than were for PHB,
with 35% biodegradation in 60 days in soil at a temperature of 35°C and
35% moisture content and 48.5% biodegradation in 280 days at 20°C
and a moisture content of 60% (Gómez and Michel Jr, 2013; Wu, 2014).
Similar to PLA, for PHA-based plastics the degradation under
environmentally relevant conditions is rather slow and PHA should not
be regarded as biodegradable (compared with the P and vP criteria as
laid down under REACH).
Implications for estimating microplastics fate
As noted in Section 4.2, there are many determinants which influence
(bio)degradation. To model the fate of microplastics in soils, these
determinants should be incorporated in relevant modelling tools. While
the importance of fragmentation and degradation for modelling has been
emphasized by different researchers (Kaandorp et al., 2021; Koelmans
et al., 2017), implementation of the underlying processes is as
important for the model to represent real-world conditions.
Initial steps have been taken to determine the biodegradation rates for
different plastics (See Annex 2 for elaboration). However, there are still
many uncertainties concerning a reliable determination of these
degradation rates under different environmental conditions. Based on
the information gathered on biodegradation, there are some issues that
have implications for estimating microplastics’ fate under relevant
environmental conditions and these issues need to be addressed for
modelling:
• The number of biodegradation tests performed with microplastics
is limited. Furthermore, only a very small fraction of these tests
were performed under environmentally relevant conditions
(simulation tests) and even fewer in soils.
• Tests performed at a screening level will not allow the derivation
of degradation rates, but the outcome (ready/not
ready/inherently biodegradable) can be used as input for
modelling tools. The usability of ISO tests remains questionable
at this stage.
• There is an urgent need for the standardization of
(bio)degradation tests that are suitable to assess the
degradability of microplastic particles. Options have to be
scrutinized and existing tests have to be adapted or
benchmarked to be comparable to available persistence criteria
(under REACH, but also other frameworks).
• A great number of variables have been determined which
influence the biodegradation rates of microplastic, including their
Page 48 of 110

RIVM report 2021-0224

•

chemical and physical properties, as well as the abiotic and biotic
conditions to which the particles are exposed. As for (initial)
modelling, it will be impossible to take into account all of these
factors. The focus should be on the variables which impact
biodegradation rates the most. Note that these variables could
also indirectly enhance biodegradation, for example, by the
fragmentation of (micro)plastics.
The size and shape of microplastics are an significant aspect
influencing the biodegradation rate. Information on size
distributions and the shapes of microplastics in the environment,
as well as degradation rates for a heterogenous set of particles,
should be determined to assess biodegradation in modelling
tools. For the time being, one could also use worst-case
assumptions for surface area (linked to size and shape) as a first
tier, and refine them when necessary based on particle size.

Note that list above is not exhaustive, but are the first steps to
implement and improve biodegradation in microplastics fate modelling.

Page 49 of 110

RIVM report 2021-0224

Page 50 of 110

RIVM report 2021-0224

5

Impacts and risks of microplastics in soil

High amounts of microplastics in soils can alter the fundamental
physicochemical and biological properties of the soil system
(highlight 8). Soil health and function may be impaired and trophic
transfer in food chains may also occur. This may lead to adverse effects
on ecosystems. In order to address the potential ecological impact on soil
systems, (further) research is needed on the (direct and indirect) effects
of microplastics on the viability, development, fertility and mortality of soil
organisms. Next to such effect studies, improved insights are necessary
on the exposure, bioavailability and uptake of microplastics by organisms
and humans. The current information on the impact of microplastics on
soil organisms and ecosystem functioning is incomplete and sometimes
conflicting.
Introduction
There are a lot of publications focused on studies of microplastics in soil,
but their usefulness for risk assessment is not yet clear. Initial results
published show that microplastic particles can be taken up into crops from
the soil. It follows that the ingestion of soil particles and the consumption
of primarily vegetables could form a potential health risk due to the
presence of microplastics in the soil. The seriousness of the health risk
due to the exposure to microplastics through soil is not yet clear.
In studies focused on ecosystem effects, unrealistically high
concentrations of microplastics and short incubation times are often
used. It is expected that these ecosystem impact estimates will soon
start to become more reliable and reflect real field conditions, in view of
the high rate of studies being published and the recent or imminent
start of new projects on effects of microplastics on the ecosystem. Here
we present some scattered observations on this issue made by the
authors of several recently published literature review studies,
illustrating the mosaic contribution of different studies.
Ecosystem effects of microplastics
Microplastic particles
It was reported that microplastics may adversely affect soil properties,
protist communities 20, plants and even agroecosystems (Li et al.,
2020b). Several studies found that bulk density, water holding capacity,
soil fertility and the stable water aggregates of soils could be affected by
microplastic contamination (de Souza Machado et al., 2018; Ma et al.,
2018), and polyester fibres exhibited the most apparent effect. A case
focused on soil protists (Rillig and Bonkowski, 2018) indicated that
protists were likely to ingest microplastic particles smaller than 1 µm.
This means microplastics could be transferred higher up the food chain
of soil organisms, e.g. by earthworms feeding on soil protists (Rillig et
al., 2017). Another study reported that microplastics could induce
damage to earthworms’ tissues and immune systems (Rodriguez-Seijo
et al., 2017). Recently, long-term adverse effects on earthworms of
20

Protists are single-celled organisms of the kingdom Protista such as protozoan or algae.
Page 51 of 110

RIVM report 2021-0224

polystyrene microplastics were reported using environmentally relevant
concentrations (Sobhani et al., 2022).
Uptake by plants
Micro- and nanoplastics are of particular concern due to their ability to
be taken up by plants (Li et al., 2020b). Recent studies have observed
the adverse effects of fragments of (biodegradable) mulches on plant
growth and rhizosphere bacterial communities (Qi et al., 2020; SerranoRuiz et al., 2021). In a toxic effect investigation on wheat, low-density
polyethylene and starch-based biodegradable plastic mulch film were
selected as microplastic residues (Qi et al., 2018). The result showed
that the growth of wheat was more affected by plastic mulch film than it
was by its polymer, polyethylene. Specifically, both the vegetative and
reproductive growth of wheat were inhibited. Plant height, the number
of fruiting bodies and the root biomass of wheat were also significantly
reduced. Microplastics also showed a high adsorption capacity for heavy
metals and antibiotics (Li et al., 2018a; Li et al., 2020b) in soil
environments. Polyamide particles could even serve as a carrier for
antibiotics. By absorbing heavy metals or antibiotics, microplastics affect
microbial communities directly.
Leaching of chemicals from microplastics
Most plastics found in soil also contain a variety of additives that may
result in enhanced ecological toxicity (Xu et al., 2020b). Plasticizers such
as phthalic acid ester (PAE) have been widely used in plastic mulch
films, which have contaminated Chinese agricultural soil (Niu et al.,
2014). Since it has been proved that they have negative effects on soil
enzyme activity and microbial diversity and are often regarded as
endocrine disrupting chemicals (Ye et al., 2010), there is a need to
study the fate of PAE in microplastics in residue arable film and the risks
of exposure through the food chain (Qi et al., 2020).
Interactions of microorganisms with microplastics
In the review of Xu et al. (2020b), significant differences in bacterial
communities from different soils related to microplastics were reported.
Consequently, microplastics can provide new ecological niches in soils
supporting microplastic-associated bacteria with surface-related life
strategies. Besides having major ecological implications, this life
strategy can theoretically support pathogenic bacteria as a disease
vector that favours infection (Chai et al., 2020).
A Trojan Horse
Finally, a ‘Trojan Horse’ effect is described in the literature, which means
that microplastics can act as carriers and accumulators for other
substances associated with plastics, such as organic substances and
metals. This results in increased exposure to other pollutants in
comparison with systems with a low abundance of microplastic particles
(Hildebrandt et al., 2021). However, a recent review of current work has
not found much evidence to substantiate the claim that this Trojan
Horse effect actually brings about chemical risks under present natural
conditions (Koelmans et al., 2021). Furthermore, cascade and food
chain effects can potentially play a role, but are largely unknown
(Abdolahpur Monikh et al., 2021; Li et al., 2020b).
Page 52 of 110

RIVM report 2021-0224

Conclusion on ecosystem effects
There is evidence that microplastics can affect ecological endpoints,
directly or indirectly, although there is uncertainty in relation to the actual
risks present in current natural conditions. In general, the quantitative
relationship, e.g. in a dose-effect relationship, between microplastic
pollution in soil and subsequent adverse effects on community and other
ecosystem properties is unclear (Abdolahpur Monikh et al., 2021; Li et al.,
2020b). Furthermore, systematic knowledge about microplastic properties
– such as polymer type, degradation or transformation state, size and
shape – affecting soil organisms is largely missing as many of the studies
lack a proper physicochemical characterization of the tested microplastics,
especially those with outdoor experiments under field conditions. This
implies there are severe knowledge gaps in the final steps of performing a
risk assessment based on the source-path-receptor framework. Many
publications demonstrate potential effects, but a quantitative
underpinning under realistic exposure conditions that capture both direct
and indirect effects remain uncertain, partly unknown and therefore
should receive more attention.

Page 53 of 110

RIVM report 2021-0224

Page 54 of 110

RIVM report 2021-0224

6

State of knowledge and perspectives for action

Overall, research on microplastic emissions to and the fate of microplastic
in soil systems, and its effects on terrestrial ecosystems is still limited, but
is increasing rapidly, demonstrated by the increasing publication rates
(highlight 9). This is motivating an active monitoring of the progress of
the knowledge required for risk assessment.
Introduction
Microplastics in the soil environment exhibit a wicked problem for
society worldwide, including the Netherlands. Large volumes of plastics
are produced that are an integral part of our daily life: they are
managed by a very diverse group of stakeholders, and they represent
versatile and diverse applications and emissions. Microplastics
accumulate everywhere in the environment because of slow or even the
absence of degradation. Understanding the degradation process in terms
of full mineralization compared with partial degradation or fragmentation
is important, but it is rather complex due to test guidelines that have
not been designed with microplastic particles in mind. Microplastics
contain a lot of different substances for which the specific fate,
behaviour and toxicity is largely unknown. Microplastics are also very
difficult to quantify, especially in soil matrices. Currently, research on
microplastics in the soil system has reached a publication rate of one
scientific article per day and is still increasing. Consequently, more data
will become available over time, although it is expected that
interpretation in a risk assessment context will remain a challenge.
To address the complexity of and streamline research on microplastics in
soil systems, we introduce a conceptual model (6.2) based on the
source, to path, to receptor approach for the assessment of health and
ecological risk. In addition, we have identified data and knowledge gaps
(6.3). This should hopefully guide recently started research projects on
these topics (6.4) in order to provide knowledge for policy and
management options to mitigate microplastic pollution. We summarize
some options for mitigation (6.5) and discuss current criteria for plastic
in soil in the Netherlands and Belgium (6.6).
Conceptual model of microplastics in the soil system
To responsibly manage microplastics, we need knowledge of the links
between sources, the environmental exposure and the (potential)
adverse effects on receptors in order to mitigate potential risks to
acceptable levels. A conceptual model showing the procession of source
through pathway to receptor (see Figure 1 in Chapter 1 for a simple
diagram) can help to provide a structure to interpret available data and
information and to structure knowledge development. It can also help to
uncover information gaps. In Figure 5, in addition to Figure 1, we have
illustrated the microplastic mass flow between microplastic sources,
release and emission to soil, microplastic fate in soil processes and the
transport process in and around soil. This is a so-called conceptual
model that promotes discussion and facilitates the recognition of
weaknesses, gaps and research needs. We used the findings of the
Page 55 of 110

RIVM report 2021-0224

review in previous chapters to draw the model from a recognition of the
most important microplastic sources, release and emission routes and
fate and transport processes in relation to soil.

Sources

Fate and
transport

Release and
emission

Air

Agriculture
Stables
Biowaste
Agricultural film
Components of machines
Others

Waste water
Irrigation
Littering

Consumer products
Personal care products
Textiles
Detergents
Packaging
Paint
Others

Traffic and industry
Tyres
Construction products
Preproduction pellets
Paint
Others

Resuspension

Wet and dry deposition
Runoffand erosion

Surface
water

Soil
Sewage sludge

Resuspension

Soil types
Natural
Agricultural
Other

Abrasion

Processes
Manure
Organic waste
Compost

Solid waste

Recycling,
Incineration
& Landfill

(Bio)degradation
Fragmentation
Bioturbation
Infiltration
and drainage

Flooding and bank interactions

Groundwater

Figure 5 Conceptual model of microplastic sources, release and emission to soil,
and further MP fate in soil (processes: (Bio)degradation, Fragmentation,
Bioturbation) and transport to and from soil. The main mass flow routes from
sources to Soil are indicated, but not prioritized. The green arrows indicate
sources linked to waste processing or litter/abrasion that ultimately lead to
emission to soil (brown arrows), and (blue arrows) air and water (not indicated
here). The purple arrows indicate the main transport processes between soil,
groundwater, surface water and air.

Each of the boxes in Figure 5 should in theory be quantified in terms of
the mass or abundance of microplastic particles (in a source or in a
technical or environmental compartment). The arrows represent the
fluxes (mass or other unit per unit time) between the sources and each
compartment. The flux of microplastics released from a source (green
arrows) to another (specific) temporary or technical compartment (e.g.
waste water or compost) via different processes (grey arrows) eventually
end up (at least partially) in environmental compartments, soil (brown
arrows), Air (blue arrows) and water (not indicated). Within and between
these environmental compartments, fate and transport processes (purple
arrows) determine the environmental exposure. The accumulation of
microplastics in soil depends on the rate of emission and transport to soil
and the rate of transport from soil and (bio)degradation. Fate processes
such as fragmentation and bioturbation mostly affect the form and mixing
of microplastics within the soil compartment.
It is possible to measure mass or abundance in some of the
compartments without direct knowledge of the fluxes. This gives an idea
of the status of microplastic pollution, but to assess the effectiveness of
Page 56 of 110

Seepage

RIVM report 2021-0224

specific mitigation options it is beneficial to quantify each flux in order to
link it to the rate of microplastic accumulation in soil or other
environmental compartments. This provides an understanding of the
dominant processes. For instance, sludge from waste water treatment
plants is known to contain microplastics as well as composts and
manure (e.g. Li et al., 2018b). Furthermore, the fragmentation of films
and fabrics and the application of seed coatings containing microplastics
is thought to contribute to the emission of microplastics to agricultural
soils as well. However, for each country and each region, the relative
contribution of different potential sources will be different. Nevertheless,
information on all significant fluxes, abundancies and mass of
microplastics, specific for the relevant polymer types, is needed for
sufficient exposure modelling and to provide valuable perspectives for
mitigation and action.
Knowledge and information gaps
Although it is clearly a cause for concern that microplastics end up in soil
and can induce adverse effects, there are many gaps in the current
state of knowledge and the information needed to fully appreciate the
behaviour, fate and effects of microplastics in soil systems. Some of the
reviews stressed the need for action, because of the recalcitrance and
persistence of microplastic particles, the current levels and trends of
microplastic emission to soil, and the indications of adverse effects on
the soil system (e.g., Ng et al., 2018). In the restriction on intentionally
added microplastics, proper data was missing to perform of a
quantitative risk assessment. But based on observations of the effects
on microbiota and their persistency in the environment, sufficient
information was available for RAC to consider the microplastics as nonthreshold substances, meaning that all releases should be minimized
(ECHA, 2020). At the same time, knowledge gaps can be filled in line
with the source through pathway to receptor diagram in order to
increase insights into and prepare for potential future human and
environmental health risks.
The following gaps and visions were recognized in the reviews and
previous chapters – overlapping partly with the highlights – as significant
hurdles to better understanding the risks of microplastics in soil (e.g., Qi
et al., 2020; Horton et al., 2017):
1. Types and environmental concentrations: Current knowledge
about the extent of microplastic pollution in terrestrial
environments is insufficient, although research is progressing.
There are few regional and international studies focused on which
polymers are most abundant and general data on how this varies
across habitats, land uses and regions is lacking. Relevant data
on microplastic concentrations in soils, as well as on agricultural
soil management for the Netherlands specifically, is needed to
better understand the current extent of microplastic pollution in
Dutch soils.
2. Auxiliary substances: Auxiliary substances such as plasticizers
(e.g. phthalic acid esters, PAE) and solvents are introduced into
our soils together with microplastic particles. The potential effects
of microplastic additives for soil ecosystems are unknown.
Microplastics can also act as carriers for other pollutants, the soPage 57 of 110

RIVM report 2021-0224

3.

4.

5.

6.

7.

8.

9.

called ‘Trojan Horse’ effect. However, the meaning of this for risk
assessment is still unknown.
Analytical methodology: There is a lack of robust, reliable,
practical and standardized methods for sampling, separating,
purifying and quantifying microplastic particles and polymers in
solid matrices. These need to be developed to measure
microplastics in different types of soils and to compare, combine
and repeat scientific findings from different studies.
Properties and behaviour: There is currently a limited
understanding of how environmental conditions and microplastic
properties (chemical, physical and biological) affect microplastic
behaviour and bioavailability for terrestrial environments. If the
dominant or deterministic properties and conditions that cause
the observed effects are understood, this can be used for
emission, effect or exposure prevention and safe-by-design
approaches.
Release and emission: Data on sources and emission is still
patchy, meaning there is a lack of understanding of the overall
relative and absolute contributions of microplastic emissions to
the environment. Measures to mitigate microplastic emissions will
be more effective if both relative and absolute fluxes (emissions)
are better understood.
Soil-microplastic interaction (fate): Insight is missing into
the contribution of specific processes that are relevant for the
fate of microplastics in soil. Studies on linkage, attachment and
other interactions of soil aggregates with microplastic particles
are needed to better estimate fate and exposure. Lessons can be
learned from nanoparticles.
(Bio)degradation (fate): A quantitative understanding in
natural attenuation and degradation are pivotal for estimating the
fate of microplastics in the soil environment under different
scenarios. This understanding is currently insufficient and
contradictory. The available methods need to be scrutinized for
their suitability in determining the fate of microplastics in soil
systems, explicitly making the difference between degradation
and fragmentation. With persistent substances, (bio)degradation
is negligible (nearly zero) or slow (some degradation observed)
but the difference may be crucial for reliable modelling of
microplastic fate and exposure.
Effects and impacts: To understand the impact and potential
risks of the presence of microplastics in terrestrial ecosystems,
data are needed on the exposure, bioavailability, uptake and
dose-effect relationships (source-path-receptor). Data do exist
and adverse effects have been identified, but the data are also
scattered, limited and/or contradictory. Testing of microplastics
that occur in the environment (weathered instead of virgin) is
needed. Improved designs of studies and more reliable and
specific data can, in turn, provide a better understanding of the
(in)direct effects on public health, ecosystem resilience and
ecosystem services.
Long-term: The environmental issue of microplastics is complex
and entails several uncertainties, particularly for soil. It may take
a lot of research to sufficiently underpin and build up scientific
evidence for the adverse effects of different microplastics under

Page 58 of 110

RIVM report 2021-0224

different conditions. Currently, however, it is certain that micro
(and nano) plastics are present in soils and agricultural land
worldwide and they will, if business continues as usual, be
continuously and increasingly emitted. Due to these emissions,
spreading and persistence, this is a persistent global contaminant
whose long-term effects cannot be fully understood at this stage.
National and international projects
Several (inter)national programmes are addressing data and knowledge
gaps. Microplastics in soil systems, often in agricultural land, are the
focus of recent national and international (EU) projects with
contributions from research at national institutes and universities.
Presented below is a shortlist of current projects with representatives in
the Netherlands. This list will not cover all scientific work that is
currently being done. These projects are expected to address some of
the knowledge gaps elucidated. The projects are:
• SoilVer platform: a soil and land research funding platform for
Europe, previously known as SNOWMAN.
• MISSOURI (MIcroplasticS in Soil and grOUndwateR: sources,
transfer, metrology and Impacts): a one year EU project with a
focus on an interlaboratory survey of microplastics in soil and
groundwater.
• SOPLAS Macro and Microplastic in Agricultural Soil Systems: EU
Innovative Training Network, Marie Skłodowska-Curie Actions.
• LeonT (Low particle emissions and low noise Tires): a three year
project focused on increasing knowledge (and the measurement)
of particle and noise emissions from tyres—and their associated
effects on public health and well-being—in order to propose
effective and efficient mitigating measures through regulation,
labelling and tyre design.
• PAPILLONS (Plastic in Agricultural Production: Impacts, Lifecycles
and LONg-term Sustainability): an EU Horizons project to
elucidate the ecological and socioeconomic sustainability of
agricultural plastics (APs) in relation to the releases and impact
of micro- and nanoplastics (MNPs) in European soils.
• MINAGRIS (MIcro an Nano plastics in AGRIcultural Soils): an EU
Horizons project to assess the impact of plastic debris in
agricultural soils on biodiversity, plant productivity and
ecosystem services and their transport and degradation in the
environment. It aims to provide tools and recommendations for
the sustainable use of plastic in agriculture at the levels of farm
and field for ensuring safe and economically viable food systems
in Europe.
Looking for potential mitigation options
Some studies provided specific recommendations for policy development
and land quality management. The need to act upon the prevention and
reduction of microplastic accumulation is motivated by the persistence,
the potential adverse effects and the widespread detection of
microplastics (highlight 10). Preventing and reducing of the impact of
microplastic soil contamination requires a large set of measures for a
large variety of stakeholders. In several countries, measures are being
implemented to reduce the release of (mostly primary) microplastics at
Page 59 of 110

RIVM report 2021-0224

the source (source control) and to reduce emissions at end-of-pipe
(emission control), both of which result in the reduction of emissions to
terrestrial ecosystems.
The management of microplastics encompasses the definition of
appropriate policy goals: avoid unacceptable risks to human health and
ecosystems. These broad protection goals can be further supported by
the ambition to move towards a situation with zero-pollution and avoid
losses in a circular economy (highlighted in Chapter 1).
In order to advise on policies based on the risk paradigm, a human or
environmental risk assessment needs to be conducted. Such a risk
assessment can be conducted within the different regulatory frameworks
already available for pollutants, but requires important adaptations in
order to apply current methods to microplastics as a specific group of
substances. The reason for this is the complex effects of microplastics,
different from chemical substances, in that they have both a chemical
and a physical identity (and potentially biological properties), as well as
the difficulty in assessing the fragmentation and degradation of the
microplastic particles. Risk assessment approaches for particles need to
take their physicochemical characteristics and related effects into
account (cf. nanoparticles).
Another approach is to limit the emission of microplastics at the source
without considering the actual or potential ecological risk posed to the
environment for specific types or groups of microplastics, thus
minimizing and preventing further microplastic environmental pollution,
and contributing to preventing losses in a circular economy.
Currently, the adverse effects of microplastics on the environment are
not yet understood (Figure 1). Particles can, however, be prioritized
based on other known criteria, such as their mobility in combination with
their persistency, which are characteristics of fate and transport
(Figure 5). Within REACH, the release of substances classified as PBT
(persistent, bioaccumulative, toxic) and/or vPvB (very persistent, very
bioaccumulative) needs to be minimized, with the goal of eventually
finding substitutes for these substances. It is expected that substances
may also be classified as PMT (persistent, mobile, toxic) and vPvM (very
persistent, very mobile) within REACH in the future, as these traits are
also considered undesirable. Similar minimalization efforts are likely. As
microplastics have similar traits (being persistent as well as mobile in
the environment), limiting the emissions could be justified without
understanding the exact ecotoxicological effects and performing the
conventional threshold-based risk assessment based on a case-by-case
assessment. Microplastics are considered non-threshold substances in
the restriction on intentionally added microplastics. Similar to PBT/vPvB
substances under REACH, this means that all releases are assumed to
result in a risk (ECHA, 2020).
Regardless of the exact policy goals, regulatory action will benefit from
looking at the whole source through pathway to receptor route (Figure 1
and Figure 5), which allows for more refined mitigation options
compared with prioritizing mitigation based only on information on the
microplastic emission sources (Mitrano and Wohlleben, 2020).
Page 60 of 110

RIVM report 2021-0224

Overall mitigation to reduce environmental contamination with
microplastics can span a large set of measures, since plastics are
applied in and originate from a great variety of production processes,
applications and uses. Below we reflect on ‘source-oriented solutions’ to
control microplastic release, and on ‘end-of-pipe and remediation
solutions’ to manage microplastic emission to and fate and exposure in
soils. Note that the options and measures described are not exhaustive
and should be regarded as a starting point for further work on mitigation
options when research gaps are filled.
Source-oriented solutions
There is a great variety in the sources of microplastics that end up in soils
(Figure 5). To effectively address microplastic emissions, it is important
to quantify sources of microplastics to determine the main contributors of
the polymers in the environment. Measures to address these sources will
likely have most effect. However, it also depends on the emission routes.
A source may contribute heavily to the presence of microplastics in the
aquatic environment, but to a limited extent in soils, e.g. when emissions
enter the aquatic compartment directly. Because microplastics are found
in all environments and microplastics can migrate to other compartments
and are therefore often cross-border, an integral approach should be
pursued to tackle microplastic emissions.
As mentioned before, microplastics found in soils can be divided
between primary and secondary microplastics, the latter represents the
largest share (see Chapter 3). Currently, knowledge about the
magnitude of emissions is mainly derived from estimates and models,
while data to support these numbers is very limited. Without reliable
numbers, the effects of source control cannot be evaluated. Source
control for both types are discussed below.
Primary microplastics
In the past, substantial steps have been taken to address the problem of
primary microplastic emissions. One of the first initiatives was the ‘Beat
the Microbead’ campaign, which stimulates producers of cosmetics to
voluntarily remove microplastics from personal care 21 products. It also
informs consumers about products that are microplastic-free. However,
this will mainly impact the emissions to aquatic compartments as the
sewage system is one of the main emission routes. More noteworthy is
the upcoming ECHA restriction on intentionally added microplastics. The
restriction, which according to the planned timetable should be adopted
in 2022 22, restricts the placing of intentional (primary) microplastics in
the EU/EEA on the market and affects the use of these microplastics in
important sources of microplastic emissions to soils, such as products
used in agriculture, horticulture and construction. A large decline in
primary microplastic emissions is expected, but it should be noted that a
number of derogations and the final definition of ‘microplastic’ may still
result in the weakening of measures. Currently, it is unclear whether
microplastics will have a lower limit for size; when a lower size limit is
attributed, small particles may still be used in products. Another
uncertainty is addressed in Chapter 4; biodegradable polymers are
21
22

https://www.beatthemicrobead.org/
https://echa.europa.eu/nl/hot-topics/microplastics
Page 61 of 110

RIVM report 2021-0224

exempted from the restriction, but the tests to assess biodegradability
were either not designed for microplastic particles or, if designed for
plastics, their outcome cannot be compared to the existing persistence
criteria. This rather complicates the biodegradability assessment.
Uses at industrial sites, in medicinal products for human or veterinary
use, and substances or mixtures containing food additives are examples
of derogations. For derogated uses, a reporting requirement will be
effective, not of the amounts used (what was initially proposed), but
rather the quantities released to the environment. (Downstream) users,
excluding consumers and professional users, are responsible for
delivering information on the use and emissions of microplastics to
ECHA. In addition, suppliers should provide instructions on use and
disposal, and the effectiveness of this information should be monitored.
All information is used to assess the risks arising from microplastic uses
in the future. From a regulatory perspective, action is already being
taken to reduce primary microplastic emissions, but the restriction is not
yet definitive and could be modified by the European Commission in the
adaption process. When data becomes available, the effectiveness of the
restriction can be assessed.
Secondary microplastics
Verschoor and de Valk (2018) estimated that microplastic emissions in
catchments areas in the Netherlands mainly derive from litter
fragmentation, tyre abrasion, and paint abrasion; three sources of
secondary microplastics. In earlier research, distribution to different
environmental compartments was estimated for emissions from paints
(rural and urban areas) and tyres (Verschoor et al., 2016). Based on
these estimations, a large proportion of the emitted microplastics end up
in soils. For this compartment, it is therefore important to reduce
microplastic emissions from these sources. Relevant measures known
are discussed very briefly below. In addition, measures to reduce
secondary microplastic emissions from sludge and compost, as well as
from agricultural films and textiles, are discussed because these are
widely recognized as sources in the literature.
Litter fragmentation
In recent years, regulatory measures have been taken against littering
(of plastics). Examples of initiatives are the EU ban on single-use
plastics (Directive (EU) 2019/904), the EU Plastic Bags Directive
(Directive (EU) 2015/720) to reduce the use of lightweight plastic carrier
bags, and the introduction of a deposit on small plastic bottles in the
Netherlands. 23 All these initiatives were implemented during recent
years. The direct results of most measures therefore will only become
clear in the years to come. Implementation of the EU Plastics Bags
Directive led to a reduction of 70% in issued plastic bags, yet
600 million plastic carrier bags were still issued in 2018. 24 It can be
expected that these measures will not completely diminish intentional
and unintentional littering, and it is questionable whether this can be
achieved. Most of the additional solutions will therefore exist in end-of23

Kamerbrief besluitvorming statiegeld flesjes en uitvoering moties blikjes. Kenmerk IENW/BSK-2020/64322.
Rapport ‘Evaluatie verbod op gratis plastic draagtassen’.
https://www.rijksoverheid.nl/documenten/rapporten/2020/03/02/bijlage-1-evaluatie-verbod-op-gratis-plasticdraagtassen
24

Page 62 of 110

RIVM report 2021-0224

pipe solutions (Chapter 6.5.2). In the design phase, there are some
options to reduce the effects of microplastic emissions, e.g. the use of
biodegradable polymers or the use of alternative materials that do not
contain plastics. Another approach is to promote behavioural change by
providing information and education. Behavioural interventions,
education and raising awareness within the European Marine Strategy
Framework Directive, as well as several campaigns 25 have already
proved to be effective in reducing litter(ing). 26
Paints
Recently, RIVM asked stakeholders in the paint sector which measures
have been and could be taken to avoid microplastic emissions (Faber et
al., 2021). The paint sector believes that polymers are needed in paints
to sustain the beneficial features of current products. Relatively few few
paint products are available without polymers and these are not (yet)
suitable for all paint applications. Indirect measures, such as optimizing
durability, have been realized by the paint producers, but the effects of
these type of measures cannot be quantified.
The REACH restriction will have limited effects on the use of primary
microplastics in paints. Film-forming, which occurs after paints are
applied, is derogated as the physical properties are permanently
modified and the microplastics are permanently incorporated in a solid
matrix. In addition, the restriction does not address secondary
microplastics, which is the main source of microplastics from paints. No
information on types and amounts used will become available through
the ECHA restriction, only the emission of primary microplastics.
However, the European Strategy for Plastics in a Circular Economy does
specify that policy options for reducing the unintentional release of
microplastics from paint (and tyres and textiles) are to be developed. 27
Tyres
Tyres are made of synthetic rubber. Both rubber and plastics are
polymers and abrasion results in the formation of microplastics.
Verschoor and de Valk (2018) have investigated the effects of measures
to reduce emissions of microplastics. Although the focus was on
emissions to water, the study recognizes that most emissions will end
up in soils. A number of measures (e.g. legal threshold for tyre abrasion
and tyre label with abrasion indicator) for source control were identified
and reduction potentials were estimated. In 2020, the EU Regulation on
the labelling of tyres was adopted (Regulation (EU) No 2020/740). 28 The
need for measures to reduce microplastics, addressed by the European
Commission 29, is mentioned in the Regulation. The regulation specifies
25

e.g. Nederlandschoon (https://www.nederlandschoon.nl/zwerfafvalaanpakken/aanpakken/campagnes/) and
Rijkswaterstaat (https://zwerfafval.rijkswaterstaat.nl/actueel/nieuwsbrief/2021/gratis-beschikbaar-campagneplek-schoon/)
26
Brief regering – Voortgang beleidsprogramma microplastics d.d. 25th of June, 2021. Tweede Kamer,
vergaderjaar 2020–2021, 30 872, nr. 261.
27
ANNEXES to the Communication from the Commission to the European Parliament, the Council, the
European Economic and Social Committee and the Committee of the Regions. A European Strategy for Plastics
in a Circular Economy. https://ec.europa.eu/environment/pdf/circular-economy/plastics-strategy-annex.pdf
28
Regulation (EU) No 2020/740, 2020. REGULATION (EU) 2020/740 OF THE EUROPEAN PARLIAMENT AND OF
THE COUNCIL of 25 May 2020 on the labelling of tyres with respect to fuel efficiency and other parameters,
amending Regulation (EU) 2017/1369 and repealing Regulation (EC) No 1222/2009, Official Journal of the
European Union p. 31.
29
A European Strategy for Plastics in a Circular Economy.
Page 63 of 110

RIVM report 2021-0224

that ‘once reliable, accurate and reproducible methods to test and
measure tyre abrasion and mileage are available, the Commission
should assess the feasibility of adding information on tyre abrasion and
mileage to the tyre label’. The additional information regarding tyre
abrasion and mileage to end-users may reduce microplastic releases
when durability becomes an important criterion for selecting tyres.
Agricultural films and textiles
Agricultural films and agricultural textiles have different functions in
agriculture. Depending on the function and the environment degradation
(or fragmentation), rates differ. In general, agricultural textiles have a
longer lifespan than films. One of options to reduce the impact of these
materials is to apply biodegradable films. However, until now,
biodegradable films do not meet the criteria for mechanical strength. For
a few years now, a biodegradability standard for mulch films has been
available (see Section 4.3.1).
Infill of synthetic materials in soccer sport fields
Artificial turf sports fields are increasingly enriched with synthetic infill
materials – often granulated rubber from tyres – in order to enhance
performance and endurance. There is concern about the health and
ecosystem risks from substances leaching from the particles. 30
Microplastic emissions are also an issue for these fields. Potentially, the
use of these infill materials will also be banned by the upcoming
restriction on intentionally added microplastics.
End-of-pipe and remediation solutions
End-of-pipe mitigation options can, in addition to source control, reduce
emissions of microplastics to soil. Microplastics can be removed
biologically, physically and/or chemically. As an ultimate mitigation
option, soil remediation might be able to lower microplastic abundance,
however this often comes with negative trade-offs, such as high-costs,
high energy usage and (temporal) associated damage to the ecosystem.
The best known methods to remove microplastics from a matrix are
related to the aquatic environment. Examples are waste water
treatment plants (WWTPs), the bubble barrier 31 and the shoreliner. 32 As
examples of End-of-pipe measures two tyre wear related options and
sludge and compost treatment are briefly discussed below. Although the
authors currently do not know many pragmatic methods to remove
microplastics from soils, some techniques for dealing with contaminated
soil may also lead to a reduction in microplastics in soil, both for
contaminated sites and for the reuse of (excavated) topsoil, briefly
discussed below.
Tyre wear
Verschoor and de Valk (2018) have proposed two measures that may
reduce emissions to the environment: 1) Replacement of top layer of
asphalt of motorways by another type which retains more wear particles
30

ANNEX XV REPORT: AN EVALUATION OF THE POSSIBLE HEALTH RISKS OF RECYCLED RUBBER GRANULES
USED AS INFILL IN SYNTHETIC TURF SPORTS FIELDS Substance Names: Substances in recycled rubber
granules used as infill material in synthetic turf. Submitter: ECHA. Version number: 1.01 Date: 28 February
2017. https://echa.europa.eu/documents/10162/13563/annex-xv_report_rubber_granules_en.pdf/dbcb4ee61c65-af35-7a18-f6ac1ac29fe4
31
https://thegreatbubblebarrier.com
32
https://www.tauw.nl/op-welk-gebied/circulaire-economie/shoreliner-plastic-soup-oplossing.html
Page 64 of 110

RIVM report 2021-0224

and 2) street cleaning campaigns in urban areas. According to the
calculations, both measures will have effect on a limited fraction (<25%)
of the microplastic emissions to soil.
Sludge and compost
In the literature, sludge is also mentioned as an important source of
microplastics in agricultural soils. In many countries, sludge from waste
water treatment plants (WWTP) is applied as fertilizer. A large proportion
of microplastics is removed in the WWTP and end up in this sludge. In the
Netherlands, WWTP sludge is mostly burned as the sludge does not meet
regulatory quality standards. In some cases, ‘clean’ sludge from WWTP
can be used as fertilizer (e.g. some WWTP of food manufacturers). As the
processed materials are food-grade, it is expected that these sludges will
not contain (substantial amounts of) microplastics. However, no
standards are available for microplastics in food while recent research has
demonstrated that plants are able to take up microplastics (Li et al.,
2020b) and food products can contain microplastics (Rainieri and
Barranco, 2019). In contrast to WWTP sludge, compost is applied by
farmers and consumers and can contain microplastics. Although
(macro)plastics are removed as far as possible, in the Netherlands,
microplastics can still be found in compost (van Schothorst et al., 2021).
The sources of microplastics in compost are most likely to be plastic
materials that are discarded by households. In the past, some issues were
identified with compostable plastic materials; these materials were
labelled as compostable while the Dutch compost installations are not
able to degrade these materials. Without prior removal, these plastic
materials can fragment and in time result in the formation of
microplastics.
Soil remediation of a microplastic-contaminated site
Since 1987, soil protection, soil quality management and remediation
have been integrated into Dutch legislation. Many soil remediation
techniques and soil management schemes have been developed to
reduce the risks of contaminated sites for human and environmental
health (Pijls and Marnette, 2020). Some of these will be applicable in the
effort to reduce microplastics in soils as well. For instance, excavated
soil can be treated with heat, which may result in oxidation of
microplastics (Brand et al., 2021). However, soil remediation often
comes with negative trade-offs, such as high-costs, high energy usage
and (temporal) associated damage to the ecosystem. Trade-offs should
be weighed against each other to determine whether remediation is
preferred. Contaminated soils can be transferred to a waste disposal
site, can be applied under controlled conditions or can be treated, for
instance, with heat or incineration in order to end up as thermally
cleaned soil. Additionally, soils can be treated on the spot, although
available remediation techniques might not be feasible to remove
microplastics. One remediation technique that does not remove
microplastics, but may lower their impact, is covering contaminated soil
with a layer of clean topsoil, a so-called living layer. Such a layer limits
unwanted exposure of the ecosystem to microplastics. Concerning
microplastics, no standards have been included in Dutch soil regulations.
Microplastics are not included in the list of substances for soil
management and investigations. This means that microplastic
Page 65 of 110

RIVM report 2021-0224

contaminated soil can only be remediated on the basis of the ‘due
diligence’ (in Dutch: ‘zorgplicht’) article in the Soil Quality Decree.
Restrictions on the reuse of microplastic-contaminated soil
Parallel to the development of remediation techniques, restrictions on
the reuse of excavated soil were developed. Slightly polluted soil can
only be reused when the level of the contamination and the sensitivity of
the land use do not lead to an unacceptable risk for human health and
the ecosystem. This can be made instrumental through so-called soil
quality criteria for the reuse of soil containing microplastics. This is
described in the next section.
Pathway to quality criteria for microplastic in soils
A soil quality criterion (e.g. standard) is a policy instrument that
contributes to a sustainable management of soil systems. With soil
quality standards, the protection of ecosystems and human health as
the two overarching endpoints can be put in place. However, the current
state of the art in microplastic research is insufficient for reliable criteria
setting. There is an urgent need for reliable and practical analytical
methods for microplastic determination in soils, and for data on the
impact of microplastics on different ecosystem parameters.
Today there is a growing awareness about the harmfulness of
microplastics for human health and ecosystems. Societal concerns are
about the potential effect that these large-scale, accumulating
substances can have on ecosystem integrity and human health.
Consequently, there is a plea for action in reducing the emission of
plastics and particularly microplastic to vulnerable ecosystems, including
the soil. We summarize current policies to arrive at (criteria for)
acceptable levels of plastics in soil in the Netherlands and Flanders.
6.6.1.1

Criteria for microplastic in soil and sediments
Netherlands
An excavated top layer of soils and sediments generally contains
materials such as timber, rubble and manmade fragments, and other
evidence of human activities. In many cases, these materials, although
not entirely from a natural origin, do not pose problems for ecosystem
quality or human risks. Nevertheless, it is necessary to limit these
materials to a certain level. In the Soil Protection Act of the Netherlands,
this is incorporated in Article 34 of the Soil Quality Decree 33 and the
second part of Article 1.1. in the Directions for Soil Quality. 34 All
substances that are intentionally added to the soil or sediment are
excluded from the Soil Quality Decree.
When applying soil or sediment, a maximum of 20% (w/w) of nonnatural material may be present: i.e. wood and stony fragments. These
fragments must already be contained in the soil or sediment before
excavating the soil or collecting the sediment, and it must not be
possible to remove these materials. Under the act, local authorities can
apply stricter maximum percentages in local legislation.
Substances other than wood or stony fragments, such as plastic and
expanded polystyrene, may only be present when it is “sporadically”
33
34

Besluit bodemkwaliteit: https://wetten.overheid.nl/BWBR0022929/2021-01-01
Regeling bodemkwaliteit: https://wetten.overheid.nl/BWBR0023085/2021-01-21

Page 66 of 110

RIVM report 2021-0224

present in the soil or sediment before excavating and harvesting, and
only when it is not reasonable to demand clean-up of the soil or
sediment before application. The term ‘sporadically’ is not stringently
defined. The term is explained in the overview of changes to the Soil
Quality Regulation. 35 In that context, the term 'sporadically' indicates
that small amounts of other foreign material may be present in the
excavated soil or dredging sludge to be used, because this cannot
always be prevented. The term sporadically was chosen as there are no
precise criteria, such as a certain percentage by weight, to determine
the maximum amount of other foreign material that may be present in
excavated soil or dredging sludge. (Expanded) polystyrene, for example,
is a light material for which the percentage by weight is not a suitable
criterion. In addition, the content of this term is partly determined by
what can reasonably be removed during careful excavation or before
application. In practice, however, it is not necessary to define boundary
limits for foreign materials; what is important is that effective action can
be taken in cases where it is evident that more than sporadic foreign
matter occurs in soil or dredging sludge.
In the policy letters of the Ministry of the Environment, VROM and IenW 36,
it is stated: “… this means that non-natural substances or materials other
than woody and stony fragments in the soil are not allowed, such as
plastic and expanded polystyrene” and in the Soil Quality Decree34 and the
Guidance on soil quality35: “The amount of plastic should be restricted to
a minimum. This is accomplished through a visual estimation.” Note that
this visual examination is not meant to accurately assess microplastic
content, but is used as a rough inspection method.
When the criteria cannot be met, application of the excavated soil and
sediment is restricted by the Soil Quality Decree. As a solution to
overcome the restriction, soil sieving is proposed to reduce the number
of artificial substances. This solution may help for the larger wood and
stony fragments but will not be practically applicable to remove the
majority of microplastic in contaminated soils or sediments.
The second policy letter (IenW 2018 (37)) was added by the government
because of multiple applications of contaminated soil in deep lakes with
large amounts of plastics. This is in violation of Article 7 (due diligence
or “Zorgplicht” article) in the Soil Quality Decree.
6.6.1.2

Flanders
In Flanders the policies regarding excavated, microplastic-contaminated
soils are similar to those in the Netherlands (OVAM/VLAREBO) 37. There
are no practical criteria for microplastic-contaminated soil. However, there
is a quantitative criterion for non-natural materials other than stones or
stony fragments. These substances include plastic and microplastic: the
maximum acceptable level in soil and sediment is 1% (w/w) and 1%
(v/v) in mass percentage and volume percentage, respectively.
https://zoek.officielebekendmakingen.nl/stcrt-2018-68042.html.
VROM (2010) Kamerbrief 30 015, Voortgang bodemsanering Nr. 39, brief van de Minister van
Volkshuisvesting, Ruimtelijke Ordening en Milieubeheer, Den Haag, en IenW (2018) Kamerbrief, betreft
Gezamenlijke aanpak plastic zwerfafval. Kenmerk IENW/BSK-2018/232541 Datum 6 november 2018, Den
Haag.
37
VLAREBO (2008) Bodemsanering. Besluit van de Vlaamse Regering houdende vaststelling van het Vlaams
reglement betreffende de bodemsanering en de bodembescherming, afd. III Voorwaarden voor het gebruik van
bodemmaterialen. Gebruik van bodemmaterialen als bodem. art 161. https://ovam.be/bodemdecreet-envlarebo
35
36

Page 67 of 110

RIVM report 2021-0224

Towards soil quality criteria for microplastics
At the moment, it seems difficult to establish soil quality criteria for
microplastics which are feasible in practice and which are perceived to
have only limited risks for humans and ecosystems. There are various
issues which need improvement before deriving these standards:
• Improved analytical instruments, (i) for separating polymers from
the soil matrix and (ii) for robust and practical quantitative
analyses of all types of polymers and (iii) that can practically and
reliably determine the shape and dimension of aggregates (see
Annex 3 for more information).
• Data that can support the quantification of the fate of
microplastics in the environment – polymer and aggregate
dependent – such as natural attenuation and transport
processes.
• Data on the effects of polymers on ecosystem parameters beyond
the standard tests for substances and that are meaningful for
ecological endpoints (species, processes and integrity) under
realistic field conditions and ready for a risk assessment.
• Data on the impact of microplastics on human health.
Considering the current interest of the scientific community in
microplastic research, as seen from the exponential increase of
publications on the subject in the last five years, it is expected that some
gaps can be partly covered with new innovations in the near future.

Page 68 of 110

RIVM report 2021-0224

7

Conclusion and Recommendations

Conclusions
Microplastic accumulation in soil systems is a complex phenomenon, due
to the heterogeneity in composition and dynamics of both soils and
microplastics, and the large amounts emitted, combined with slow or
absent degradation. In contrast to air and water, the soil system
generally reacts slowly to environmental pressures and recovery is even
slower. Combined with obstacles from inadequate analytical techniques,
it is no surprise that there is a substantial gap in our knowledge. We are
not yet able to perform a proper risk assessment of microplastics in soil
for human health or ecosystems.
A particular gap in our knowledge is related to the fate and behaviour
characteristics of microplastics in the soil environment, i.e. natural
attenuation, especially the processes of fragmentation and
(bio)degradation. The pragmatic definition – that microplastics
encompass (mainly) non-biodegradable polymers – can be understood
from a precautionary point of view, but it is not useful for constructing a
risk-based perspective on what the accumulation of polymers means.
Secondary microplastics often originate from the fragmentation of mesoand macro-plastic particles. In dedicated experiments, many polymers
have been demonstrated to be (bio)degradable, albeit often at slow
rates. Still, microplastic particles containing additives and having specific
sizes and shapes might display different (bio)degradation potential in
the environment. Understanding degradation is important for
understanding microplastics in soils. A further use of biodegradable
plastics can be part of the solution to reduce the accumulation of
microplastics in soils. However, if plastics and polymers are not
degraded completely or fast enough under environmentally relevant
conditions, microplastics will continue to accumulate.
A suite of degradation tests is available. Some tests have been designed
specifically for (micro)plastics, but their outcome is difficult to compare
with the available persistence criteria, while tests designed for substances
need to be scrutinized for their usability to assess microplastic particles.
Furthermore, screening level tests determine (bio)degradation by
measuring carbon dioxide formed during the complete break-down
(taking into account that a part is converted into biomass) under
standardized conditions. In a simulation test, primary degradation can be
monitored, but it remains complicated to distinguish between the intact
polymer, shorter pieces of polymer, oligomer and monomers. The biotic
and abiotic degradation processes resulting in partial degradation need to
be explicitly quantified, as this can result in a major source of
microplastics. In addition, these processes may foster biodegradation. To
what extent these processes and different environmental conditions
contribute to degradation, has yet to be investigated.
For modelling of the fate and behaviour of microplastics in soils and
cross-cutting environmental boundaries, tools are available, but reliable
data to run the models are missing. For instance, models for describing
Page 69 of 110

RIVM report 2021-0224

general particle behaviour are fit for use, although some adaptation to
microplastics might be needed, e.g. the inclusion of the fragmentation
process.
The conceptual model produced in this report can help organize the
information needed to mitigate potential risks to acceptable levels. Firstly,
fluxes of microplastics and polymers should be quantified for different
sources, (e.g. by measuring release and modelling emissions), and for
different soil types and locations (e.g. based on land use and scale: site, a
region or continent). This will also improve our knowledge about potential
successful mitigation options. At the moment, the ‘source control’
mitigation options are expected to be more effective than ‘end of pipe
solutions’. Nevertheless, in a few restricted serious cases, remediation of
a site followed by a soil treatment can be opted for.
Secondly, sufficient exposure and toxicity data for human health and
ecosystems are absent and therefore it is not possible to perform a risk
assessment and to arrive at reliable risk-based soil quality criteria. We
need research that pragmatically solves the problem of the complexity
of microplastics’ fate, behaviour, exposure and toxicity for different soil
systems and organisms. We need to work towards a generic approach
whereby we study which biological, physical and chemical properties,
under which environmental conditions, are responsible for any observed
effects. This is only possible if reliable analytical methods are developed
to quantify microplastics in soil. This should pave the way for deriving
soil quality criteria for (micro-)plastics.
As can be concluded from the trends in the literature, research on
microplastics in soil is increasing rapidly and many national and
international projects have recently started or will be started soon;
many of them with a focus on agricultural soils or on large emissions
such as from abrasion of tyres. Therefore, the harmonization of
methodologies and data reporting, as well as a common language and
overview, is of utmost importance to ensure that new results can be
validated and made useful.
Recommendations and reflections
The following recommendations and reflections were articulated:
Prioritization and filling of knowledge gaps
There is a lack of data and knowledge of almost every aspect on the
issue of microplastics in the soil system. Although some initial data have
become available, the way to interpret the data for application in risk
assessment, or for effective emission reduction, is still a big challenge. It
is important to deal effectively with the complexity of microplastics in
soil systems, for instance with over-arching approaches, and to set
priorities in the details because time and resources are limited.
For more accurate modelling, there is a need for practical, robust,
affordable and sensitive analytical methods that take polymer type, form
and size into account. For a better understanding of the sources,
emissions, fate and behaviour, and for fuelling the risk assessment
schemes, interpreted data on microplastics are needed with respect to
source, emission, transport rate, polymer type, size and shape, natural
Page 70 of 110

RIVM report 2021-0224

attenuation and (bio)degradation rate in order to establish realistic
exposure scenarios for relevant end-points. For the latter specifically,
tests have to be scrutinized and optimized to assess the biodegradation
of microplastics.
For the hazard estimates, we need data on direct and indirect (toxic,
food chain and other) effects of microplastics on ecosystem elements,
such as species, processes, resilience and resistance phenomena. Data
are especially lacking on the toxicity of ‘environmental ’microplastics
which have been exposed to physical and chemical stressors, rather
than the fabricated particles which are generally tested.
Quantifying sources
Quantitative information on emissions from specific sources is relevant for
the prioritization of policy management. Emission modelling by linking
human activities (e.g. sawing or driving) to the application of plastics
(pipes or tyres) is already applied to estimate secondary microplastic
release (Sieber et al. 2020; Kawecki and Nowack, 2019). To obtain a
more complete overview for the EU, there is a need to (i) expand these
modelling approaches to the whole EU (i.e. studies are for Switzerland
only), (ii) extend the modelling with other important release routes, such
as 'natural' incomplete fragmentation of plastic products discarded in the
environment or applied in the environment for long periods (e.g. building
materials) and (iii) include other (potentially) relevant sources coupled
with activities that induce wear (e.g. paints and sanding).
Policy and management framework
We have seen during this study that, although data can be scattered
and a better overview is needed, results show that microplastics are
widespread in soil systems. While improving our knowledge and
understanding, steps can be taken now to minimize and mitigate
emissions throughout the environment. We thus recommend exploring
the possibilities for a policy and management framework for
(micro)plastics in soil systems (or broader) in order to minimize
microplastic emission where possible and to mitigate ecological and
human health risks where needed. To this end, collaboration and
knowledge exchange with a wide range of stakeholders is required. Our
conceptual model in Figure 5 (see Section 6.2) can help to start
discussions, obtain an overview and prioritize microplastic sources and
routes that can be addressed. The framework should be sufficiently
versatile to accommodate all the different aspects of microplastics in the
soil system, including their behaviour as particles, source control for
zero emission, source control for avoiding emergent risks, or the
mitigation of ecosystem and human health effects. tTo establish such a
framework with all stakeholders, requires a multi-actor, multi-effort type
of collaborative work.
A long-lasting environmental issue
The environmental issue of microplastics in soils is complex and has
many uncertainties, in particular for soil. It may take muchresearch to
sufficiently underpin and build up scientific evidence. It is, however,
certain that micro- (and nano)plastics are present everywhere in urban,
natural and agricultural soils worldwide and that, due to their
persistence, spreading, emission rates, and society’s dependence on
Page 71 of 110

RIVM report 2021-0224

plastic, microplastics will be a contaminant in our environment for a long
time. Steps to mitigate and reduce microplastic emissions to the
environment can be taken to prevent pollution, while improving our
overview and understanding.

Page 72 of 110

RIVM report 2021-0224

Acknowledgements

The authors would like to thank all the experts that agreed to an
interview, reviewers M. Marinković, P.F. Otte and W.J.G.M. Peijnenburg
for their input and reflection and J. Ridder for assisting in the literature
search.

Page 73 of 110

RIVM report 2021-0224

Page 74 of 110

RIVM report 2021-0224

Literature sources

Abdelmoez, W., Dahab, I., Ragab, E. M., Abdelsalam, O. A., & Mustafa,
A. (2021) Bio‐and oxo‐degradable plastics: Insights on facts and
challenges. Polymers for Advanced Technologies, 32(5), 1981-1996
Abdolahpur Monikh, F., Chupani, L., Vijver, M.G., Peijnenburg, W. (2021_
Parental and trophic transfer of nanoscale plastic debris in an assembled
aquatic food chain as a function of particle size. Environmental Pollution
269, 116066
Adhikari, D., Mukai, M., Kubota, K., Kai, T., Kaneko, N., Araki, K.S., Kubo,
M. (2016) Degradation of bioplastics in soil and their degradation effects
on environmental microorganisms. Journal of Agricultural Chemistry and
Environment 5, 23
Andrady, A.L. (2011) Microplastics in the marine environment. Marine
Pollution Bulletin Volume 62(8): 1596-1605
ASTM. American Society for Testing and Materials (2018) Standard Test
Method for Determining Aerobic Biodegradation of Plastic Materials in Soil.
https://www.astm.org/d5988-12.html. Accessed on: 02-02-2022
Auta, H.S., Emenike, C.U., Jayanthi, B., Fauziah, S.H. (2018) Growth
kinetics and biodeterioration of polypropylene microplastics by Bacillus sp.
and Rhodococcus sp. isolated from mangrove sediment.
Marine Pollution Bulletin 127: 15-21
Baensch-Baltruschat, B., Kocher, B., Kochleus, C., Stock, F., &
Reifferscheid, G. (2021). Tyre and road wear particles-a calculation of
generation, transport and release to water and soil with special regard to
German roads. Science of the Total Environment, 752, 141939.
Balani, K., Verma, V., Agarwal, A., Narayan, R., 2015. Physical, thermal,
and mechanical properties of polymers. Biosurfaces: A Materials Science
and Engineering Perspective 329
BASF (2021) Mulch Films.
https://agriculture.basf.com/global/en/business-areas/crop-protectionand-seeds/use-areas/agricultural-films/mulch-films.html. Accessed on:
16-09-2021
Besseling, E., Quik, J.T., Sun, M., Koelmans, A.A. (2017) Fate of nanoand microplastic in freshwater systems: A modelling study. Environmental
Pollution, 220(Pt A): 540-548
BioBasedEconomy (2021) Developing standards for bio-based industries.
https://www.biobasedeconomy.eu/developing-standards-bio-basedindustries/. Accessed on: 16-09-2021
Blanksby, S.J., Ellison, G.B., (2003) Bond dissociation energies of organic
molecules. Accounts of chemical research 36, 255-263
Page 75 of 110

RIVM report 2021-0224

Bläsing, M., Amelung, W. (2018) Plastics in soil: analytical methods
and possible sources. Sci. Total Environ. 612: 422−435
Boyandin, A.N., Prudnikova, S.V., Karpov, V.A., Ivonin, V.N., Đỗ, N.L.,
Nguyễn, T.H., Lê, T.M.H., Filichev, N.L., Levin, A.L., Filipenko, M.L. (2013)
Microbial degradation of polyhydroxyalkanoates in tropical soils.
International Biodeterioration & Biodegradation 83, 77-84
BPF. (2021). British Plastics Federation. Packaging Waste Directive &
Compostable Packaging.
https://www.bpf.co.uk/topics/Standards_for_compostability.aspx.
Accessed on: 12-01-2022
Brand, E., Rutgers, M., Schouten, T., Versluijs, K., Negash, A., Dijkstra,
J., Comans, R., Breure, T., P. Otte, P. (2021) Toepassing van thermisch
gereinigde grond. Een evaluatie en opties voor een toepassingskader.
Briefrapport 2021-0168, RIVM, Bilthoven.
Chai, B., Li, X., Liu, H., Lu, G., Dang, Z., Yin, H. (2020) Bacterial
communities on soil microplastic at Guiyu, an E-Waste dismantling zone
of China. Ecotoxicology and Environmental Safety 195: art.no. 110521
Chamas, A., Moon, H., Zheng, J., Qiu, Y., Tabassum, T., Jang, J. H., AbuOmar, M., Scott, S. L., Suh, S (2020) Degradation rates of plastics in the
environment. ACS Sustainable Chemistry and Engineering 8(9): 34943511
Chen, Y., Leng, Y., Liu, X., Wang, J. (2020) Microplastic pollution in
vegetable farmlands of suburb Wuhan, central China. Environmental
Pollution 257: art.nr. 113449
Corradini, F., Meza, P., Eguiluz, R., Casado, F., Huerta-Lwanga, E.,
Geissen, V. (2019) Evidence of microplastic accumulation in agricultural
soils from sewage sludge disposal. Science of the Total Environment 671:
411-420. DOI: 10.1016/j.scitotenv.2019.03.368
De Souza Machado, A.A., Kloas, W., Zarfl, C., Hempel, S., Rillig, M.C.
(2018) Microplastics as an emerging threat to terrestrial ecosystems.
Global Change Biology 24(4): 1405-1416
Degli-Innocenti, F. (2002) BIODEGRADABILITY AND COMPOSTABILITY –
The International Norms 7th World Conference on Biodegradable
Polymers & Plastics. Tirrenia – Pisa, Italy, p. 14
Ding, L., Zhang, S., Wang, X., Yang, X., Zhang, C., Qi, Y., Guo, X. (2020)
The occurrence and distribution characteristics of microplastics in the
agricultural soils of Shaanxi Province, in north-western China.
Science of the Total Environment 720: art. no. 137525
Dioses-Salinas, D.C., Pizarro-Ortega, C.I., De-la-Torre, G.E. (2020)
A methodological approach of the current literature on microplastic
contamination in terrestrial environments: Current knowledge and
baseline considerations. (2020) Science of the Total Environment 730:
art.no. 139164
Page 76 of 110

RIVM report 2021-0224

EC. European Commission. (2020) Biodegradability of plastics in the open
environment. Group of Chief Scientific Advisors’ Scientific Opinion No.10,
December 2020. doi: 10.2777/284409. ISBN 978-92-76-23785-3
EC. European Commission (2021) DRAFT ANNEXES to the COMMISSION
DELEGATED REGULATION amending, for the purpose of adaptation to
technical progress, Annexes I, II, III and IV to Regulation (EU)
2019/1009 of the European Parliament and of the Council laying down
rules on the making available on the market of EU fertilising products.
ECHA. The European Chemicals Agency (2020) Committee for Risk
Assessment (RAC) Committee for Socio-economic Analysis (SEAC)
Opinion on an Annex XV dossier proposing restrictions on intentionallyadded microplastics p. 172.
https://echa.europa.eu/documents/10162/a513b793-dd84-d83a-9c06e7a11580f366
ECHA. The European Chemicals Agency (2021) Mapping exercise – Plastic
additives initiative. https://echa.europa.eu/nl/mapping-exercise-plasticadditives-initiative. Accessed on: 21-09-2021
EEA. European Environmental Agency (2020) Biodegradable and
compostable plastics — challenges and opportunities.
https://www.eea.europa.eu/publications/biodegradable-and-compostableplastics. Accessed on: 22-09-2021
Eerkes-Medrano, D., Thompson, R.C., Aldridge, D.C. (2015) Microplastics
in freshwater systems: A review of the emerging threats, identification of
knowledge gaps and prioritisation of research needs.
Water Research 75: 63-82
European Bioplastics. (2016). What is the difference between
‘biodegradable’ and ‘compostable’?. https://www.europeanbioplastics.org/faq-items/what-is-the-difference-between-biodegradableand-compostable/ Accessed on: 25-09-2021
Faber, M., Marinković, M., de Valk, E., Waaijers-van der Loop, S. (2021)
Paints and microplastics. Exploring the possibilities to reduce the use and
release of microplastics from paints. Feedback from the paint sector.
Fu, Z., Wang, J. (2019) Current practices and future perspectives of
microplastic pollution in freshwater ecosystems in China. Science of the
Total Environment 691: 697-712
Fuller, S., Gautam, A. (2016) A Procedure for Measuring Microplastics
using Pressurized Fluid Extraction. Environmental Science & Technology
50, 5774-5780
Garner, K.L., Suh, S., Keller, A.A. (2017) Assessing the risk of engineered
nanomaterials in the environment: Development and application of the
nanoFate model. Environmental Science & Technology 51: 5541–5551
Geyer, R., Jambeck, J.R., Law, K.L. (2017) Production, use and fate of all
plastics ever made. Science Advances 3(7): e1700782
Page 77 of 110

RIVM report 2021-0224

Ghatge, S., Yang, Y., Ahn, J.-H., Hur, H.-G. (2020) Biodegradation of
polyethylene: a brief review. Applied Biological Chemistry 63, 1-14
Gómez, E.F., Michel Jr, F.C. (2013) Biodegradability of conventional and
bio-based plastics and natural fibre composites during composting,
anaerobic digestion and long-term soil incubation. Polymer Degradation
and Stability 98, 2583-2591
Gorrasi, G., & Pantani, R. (2017) Hydrolysis and Biodegradation of Poly
(lactic acid). Synthesis, Structure and Properties of Poly (lactic acid), 119151
Hahladakis, J.N., Velis, C.A., Weber, R., Iacovidou, E., Purnell, P. (2018)
An overview of chemical additives present in plastics: Migration, release,
fate and environmental impact during their use, disposal and recycling.
Journal of Hazardous Materials 344, 179-199
Hammer, J., Kraak, M.S., Parsons, J. (2012) Plastics in the marine
environment: the dark side of a modern gift. In: D.M. Whitacre, Editor,
Reviews of Environmental Contamination and Toxicology 2012, Springer
New York. pp. 1-44
Hayes, D.G., Flury, M. (2018) Summary and Assessment of EN
17033:2018, a New Standard for Biodegradable Plastic Mulch Films,
Report No. EXT-2018-01 ed, p. 7
He, D., Bristow, K., Filipović, V., Lv, J., He, H. (2020)
Microplastics in terrestrial ecosystems: A scientometric analysis.
Sustainability (Switzerland) 12(20), art. no. 8739
Hildebrandt, L., Nack, F.L., Zimmermann, T., Pröfrock, D. (2021)
Microplastics as a Trojan horse for trace metals. Journal of Hazardous
Materials Letters. 2: art.no. 100035 DOI: 10.1016/j.hazl.2021.100035
Hiraga, K., Taniguchi, I., Yoshida, S., Kimura, Y., & Oda, K. (2019)
Biodegradation of waste PET: A sustainable solution for dealing with
plastic pollution. EMBO reports, 20(11), e49365
Hollander, A., Schoorl, M., van de Meent, D. (2016) SimpleBox 4.0:
Improving the model while keeping it simple. Chemosphere 148, 99-107
Horton, A.A., Walton, A., Spurgeon, D.J., Lahive, E., Svendsen, C. (2017)
Microplastics in freshwater and terrestrial environments: Evaluating the
current understanding to identify the knowledge gaps and future research
priorities. Science of the Total Environment 586: 127-141
Hurley, R.R., Nizzetto, L. (2018) Fate and occurrence of
micro(nano)plastics in soils: Knowledge gaps and possible risks.
Current Opinion in Environmental Science and Health 1: pp. 6-11
ISO. International Organization for Standardization (2021) ISO
16929:2021(en) Plastics — Determination of the degree of disintegration
of plastic materials under defined composting conditions in a pilot-scale
test.
Page 78 of 110

RIVM report 2021-0224

Iwata, T. (2015) Biodegradable and bio‐based polymers: future prospects
of eco‐friendly plastics. Angewandte Chemie International Edition 54,
3210-3215
Jain, R., & Tiwari, A. (2015). Biosynthesis of planet friendly bioplastics
using renewable carbon source. Journal of Environmental Health Science
and Engineering, 13(1), 1-5
Kaandorp, M.L.A., Dijkstra, H.A., Van Sebille, E. (2021) Modelling size
distributions of marine plastics under the influence of continuous
cascading fragmentation. Environmental Research Letters.
doi:10.1088/1748-9326/abe9ea
Karamanlioglu, M. (2013) Environmental degradation of the compostable
plastic packaging material poly(lactic) acid and its impact on fungal
communities in compost. The University of Manchester (United Kingdom)
Kawecki, D., Nowack, B. (2019) Polymer-specific modelling of the
environmental emissions of seven commodity plastics as macro- and
microplastics. Environmental Science and Technology 53(16): 9664-9676
Kawecki, D., Nowack, B. (2020) A proxy-based approach to predict
spatially resolved emissions of macro- and microplastic to the
environment. Science of the Total Environment 748: art.no. 141137
Kjeldsen, A., Price, M., Lilley, C., Guzniczak, E., Archer, I. (2018) A
Review of Standards for Biodegradable Plastics. Ind. Biotechnol. Innov.
Cent. IBioIC 33
Klein, S., Dimzon, I.K., Eubeler, J., Knepper, T.P. (2018) Analysis,
occurrence, and degradation of microplastics in the aqueous environment,
Freshwater microplastics. Springer, Cham, pp. 51-67
Kooi, M., Koelmans, A.A. (2019) Simplifying microplastic via continuous
probability distributions for size, shape and density. Environmental
Science & Technology Letters 6(9): 551-557
Koelmans, A.A., Diepens, N.J., Nor, N.H.M. (2021) Weight of Evidence for
the Microplastic Vector Effect in the Context of Chemical Risk Assessment.
Microplastic in the Environment: Pattern and Process
Koelmans, A.A., Kooi, M., Law, K.L., Van Sebille, E. (2017) All is not lost:
deriving a top-down mass budget of plastic at sea. Environmental
Research Letters 12, 114028
Koutnik, V.S., Leonard, J., Alkidim, S., DePrima, F.J., Ravi, S., Hoek,
E.M.V., Mohanty, S.K. (2021) Distribution of microplastics in soil and
freshwater environments: Global analysis and framework for transport
modelling. Environmental Pollution 274: 116552

Page 79 of 110

RIVM report 2021-0224

Kumar, M., Chen, H., Sarsaiya, S., Qin, S., Liu, H., Awasthi, M.K., Kumar,
S., Singh, L., Zhang, Z., Bolan, N.S., Pandey, A., Varjani, S., Taherzadeh,
M.J. (2021) Current research trends on micro- and nano-plastics as an
emerging threat to global environment: A review. Journal of Hazardous
Materials 409: art.no. 124967
Lee, B., Pometto III, A.L., Fratzke, A., Bailey Jr, T.B. (1991)
Biodegradation of degradable plastic polyethylene by Phanerochaete and
Streptomyces species. Applied and Environmental Microbiology 57, 678685
Li, J., Zhang, K., Zhang, H. (2018a) Adsorption of antibiotics on
microplastics. Environmental Pollution 237: 460-467
Li, X., Chen, L., Mei, Q., Dong, B., Dai, X., Ding, G., Zeng, E.Y. (2018b)
Microplastics in sewage sludge from the waste water treatment plants in
China. Water Research 142, 75–85
Li, Q., Wu, J., Zhao, X., Gu, X., Ji, R. (2019) Separation and identification
of microplastics from soil and sewage sludge. Environmental Pollution
254: art.no. 113076
Li, J., Song, Y., Cai, Y. (2020a) Focus topics on microplastics in soil:
Analytical methods, occurrence, transport, and ecological risks
(2020a) Environmental Pollution 257: art.no. 113570
Li, L., Luo, Y., Li, R., Zhou, Q., Peijnenburg, W.J.G.M., Yin, N., Yang, J.,
Tu, C., Zhang, Y. (2020b) Effective uptake of submicrometre plastics by
crop plants via a crack-entry mode. Nature Sustainability 3(11): 929-937
Liu, H.H., Cohen, Y. (2014) Multimedia environmental distribution of
engineered nanomaterials. Environmental Science & Technology 48:
3281–3292
Liu, M., Lu, S., Song, Y., Lei, L., Hu, J., Lv, W., Zhou, W., Cao, C., Shi, H.,
Yang, X., He, D. (2018) Microplastic and mesoplastic pollution in farmland
soils in suburbs of Shanghai, China. Environmental Pollution 242: 855862
Lofts, S., Dumont, V., Keller, R., Williams, R., Manders, A., Van den Brink,
N.W., Praetorius, A., Loureiro, S., Stoll, S., Lynch, I., et al. (2019)
Specification for the NanoFASE model. H2020 NanoFASE Project
Deliverable 2.1. Swindon (UK): Natural Environment Research Centre
(NERC)
Lv, W., Zhou, W., Lu, S., Huang, W., Yuan, Q., Tian, M., Lv, W., He, D.
(2019) Microplastic pollution in rice-fish co-culture system: A report of
three farmland stations in Shanghai, China. Science of the Total
Environment 652: 1209-1218
Ma, D., Chen, L., Qu, H., Wang, Y., Misselbrook, T., Jiang, R. (2018)
Impacts of plastic film mulching on crop yields, soil water, nitrate and
organic carbon in North-western China: A meta-analysis. Agricultural
Water Management 202: 166-173
Page 80 of 110

RIVM report 2021-0224

Maier, N. (2018) Biodegradable Plastics Approaches and experiences from
16 Members of the EPA Network. European Network of the Heads of
Environment Protection Agencies
McDonough, K., Itrich, N., Casteel, K., Menzies, J., Williams, T., Krivos,
K., & Price, J. (2017). Assessing the biodegradability of microparticles
disposed down the drain. Chemosphere, 175, 452-458
McFedries, R. (2012) Littered with 'plastic soup'. Maritime by Holland
61(4): 14-16
Meesters, J.A.J., Veltmant, K., Hendriks, A.J., Van de Meent, D. (2013)
Environmental exposure assessment of engineered nanoparticles: why
REACH needs adjustment. Integrated Environmental Assessment and
Management 9(3): e15-26
Meesters, J.A.J., Koelmans, A.A., Quik, J.T.K., Hendriks, A.J., van de
Meent, D. (2014) Multimedia Modelling of Engineered Nanoparticles with
SimpleBox4nano: Model Definition and Evaluation. Environmental Science
& Technology 48, 5726-5736
Mitrano, D.M., Wohlleben, W. (2020) Microplastic regulation should be
more precise to incentivize both innovation and environmental safety.
Nature Communications 11: art.no. 5324
Mohanan, N., Montazer, Z., Sharma, P. K., & Levin, D. B. (2020) Microbial
and enzymatic degradation of synthetic plastics. Frontiers in
Microbiology 11: art.no. 2837
Möller, J.N., Löder, M.G.J., Laforsch, C. (2020) Finding Microplastics in
Soils: A Review of Analytical Methods. Environmental Science &
Technology 54: 2078−2090
Moore, G., Saunders, S. (1998) Advances in biodegradable polymers.
iSmithers Rapra Publishing
Ng, E.-L., Huerta Lwanga, E., Eldridge, S.M., Johnston, P., Hu, H.-W.,
Geissen, V., Chen, D. (2018) An overview of microplastic and nanoplastic
pollution in agroecosystems. Science of the Total Environment 627: 13771388
Niaounakis, M. (2015) Biopolymers: applications and trends. William
Andrew
Nishide, H., Toyota, K., Kimura, M. (1999) Effects of soil temperature and
anaerobiosis on degradation of biodegradable plastics in soil and their
degrading microorganisms. Soil Science and Plant Nutrition 45, 963-972
Niu, L., Xu, Y., Xu, C., Yun, L., & Liu, W. (2014) Status of phthalate esters
contamination in agricultural soils across China and associated health
risks. Environmental Pollution, 195, 16-23.

Page 81 of 110

RIVM report 2021-0224

Nizzetto, L., Futter, M., Langaas, S. (2016) Are Agricultural Soils Dumps
for Microplastics of Urban Origin? Environmental Science and Technology
50(20): 10777-10779
Nowak, B., Pajak, J., Drozd-Bratkowicz, M., Rymarz, G. (2011)
Microorganisms participating in the biodegradation of modified
polyethylene films in different soils under laboratory conditions.
International Biodeterioration and Biodegradation 65(6): 757-767
Omnexus (2021) Density of Plastics: Technical Properties
Piehl, S., Leibner, A., Loder, M.G.J., Dris, R., Bogner, C., Laforsch, C.
(2018) Identification and quantification of macro- and microplastics on an
agricultural farmland. Scientific Reports 8, 17950
Ong, S. Y., Chee, J. Y., & Sudesh, K. (2017). Degradation of
polyhydroxyalkanoate (PHA): a review. Journal of Siberian Federal
University Biology 10: 211–225
Piehl, S., Leibner, A., Löder, M.G.J., Dris, R., Bogner, C., Laforsch, C.
(2018) Identification and quantification of macro- and microplastics on an
agricultural farmland. Scientific Reports 8(1): 17950
Pijls, G.J.M., Marnette, E.C.L. (2020) 40 jaar bodemsaneringstechnologie:
saneringstechnieken in
verleden en toekomst. Tijdschrift Bodem 30(6): 14-16
Pischedda, A., Tosin, M., Degli-Innocenti, F. (2019) Biodegradation of
plastics in soil: The effect of temperature. Polymer Degradation and
Stability 170: art.no. 109017
Qi, Y., Yang, X., Pelaez, A.M., Huerta Lwanga, E., Beriot, N., Gertsen, H.,
Garbeva, P., Geissen, V. (2018) Macro- and micro- plastics in soil-plant
system: Effects of plastic mulch film residues on wheat (Triticum
aestivum) growth. Science of the Total Environment 645: 1048-1056
Qi, R., Jones, D.L., Li, Z., Liu, Q., Yan, C. (2020) Behaviour of
microplastics and plastic film residues in the soil environment: A critical
review. Science of the Total Environment 703: 134722
Quik, J.T.K., De Klein, J.J.M., Koelmans, A.A. (2015) Spatially explicit fate
modelling of nanomaterials in natural waters. Water Research 80: 200208
Quik, J.T.K., Waaijers-van der Loop, S. (2021) Microplastics in indoor air,
a literature review. Letter report 2021-0059, RIVM, Bilthoven
Rainieri, S., Barranco, A. (2019) Microplastics, a food safety issue? Trends
in Food Science & Technology 84, 55-57
Ramos, L., Berenstein, G., Hughes, E.A., Zalts, A., Montserrat, J.M.
(2015) Polyethylene film incorporation into the horticultural soil of small
peri-urban production units in Argentina. Science of the Total
Environment 523: 74-81
Page 82 of 110

RIVM report 2021-0224

Reddy, P. V. (2015). Organofluorine compounds in biology and medicine.
Chapter 2. Newnes
Rillig, M.C., Bonkowski, M. (2018) Microplastic and soil protists: A call for
research. Environmental Pollution 241: 1128-1131
Rillig, M.C., Lehmann, A. (2020) Microplastic in terrestrial ecosystems
Research shifts from ecotoxicology to ecosystem effects and Earth system
feedbacks. Science 368 (6498): 1430-1431
Rillig, M.C., Ziersch, L., Hempel, S. (2017) Microplastic transport in soil by
earthworms. Scientific Reports 7(1): art.no. 1362
Rodriguez-Seijo, A., Lourenço, J., Rocha-Santos, T.A.P., da Costa, J.,
Duarte, A.C., Vala, H., Pereira, R. (2017) Histopathological and molecular
effects of microplastics in Eisenia andrei Bouché. Environmental Pollution
220: 495-503
Ruggero, F., Gori, R., Lubello, C. (2020) Methodologies for microplastics
recovery and identification in heterogeneous solid matrices: A review.
Journal of Polymers and the Environment 28(3): 739-748
SAPEA (2018). A Scientific Perspective on Microplastics in Nature and
Society. Berlin, Science Advice for Policy by European Academies
(SAPEA).
Scheurer, M., Bigalke, M. (2018) Microplastics in Swiss floodplain soils.
Environmental Science & Technology 52: 3591–3598
Serrano-Ruiz, H., Martin-Closas, L., Pelacho, A.M. (2021). Biodegradable
plastic mulches: Impact on the agricultural biotic environment. Science of
the Total Environment 750: art.no. 141228
Shah, A. A., Hasan, F., Hameed, A., & Ahmed, S. (2008). Biological
degradation of plastics: a comprehensive review. Biotechnology
Advances, 26(3), 246-265
Sieber, R., Kawecki, D., Nowack, B. (2020) Dynamic probabilistic material
flow analysis of rubber release from tires into the environment.
Environmental Pollution 258: art.no. 113573
Sobhani, Z., Panneerselvan, L., Fang, C., Naidu, R., Megharaj, M. (2022)
Chronic and transgenerational effects of polyethylene microplastics at
environmentally relevant concentrations in earthworms. Environmental
Technology and Innovation 25: art.no. 102226. DOI:
10.1016/j.eti.2021.102226
Sun, Q., Li, J., Wang, C., Chen, A., You, Y., Yang, S., Liu, H., Jiang, G.,
Wu, Y., Li, Y. (2022) Research progress on distribution, sources,
identification, toxicity, and biodegradation of microplastics in the ocean,
freshwater, and soil environment. Frontiers of Environmental Science and
Engineering 16(1): art. no. 1

Page 83 of 110

RIVM report 2021-0224

Tabasi, R.Y., Ajji, A. (2015) Selective degradation of biodegradable blends
in simulated laboratory composting. Polymer Degradation and Stability
120, 435-442
Taghavi, N., Zhuang, W.-Q., Baroutian, S. (2021) Enhanced
biodegradation of non-biodegradable plastics by UV radiation: Part 1.
Journal of Environmental Chemical Engineering, 106464
Tokiwa, Y., Calabia, B.P., Ugwu, C.U., Aiba, S. (2009) Biodegradability of
plastics. International Journal of Molecular Sciences 10(9): 3722-3742
UNI. Ente Nazionale Italiano di Unificazione (2012) Norma UNI. UNI
11462:2012. http://store.uni.com/catalogo/uni-11462-2012. Accessed
on: 02-02-2022
van Schothorst, B., Beriot, N., Huerta Lwanga, E., & Geissen, V. (2021)
Sources of light density microplastic related to two agricultural practices:
the use of compost and plastic mulch. Environments, 8(4), 36
Verschoor, A., De Poorter, L. Dröge, R., Kuenen, J., De Valk, E. (2016)
Emission of microplastics and potential mitigation measures
Abrasive cleaning agents, paints and tyre wear. Report 2016-0026, RIVM,
Bilthoven
Verschoor, A., De Poorter, L., Roex, E., Bellert, B. (2014) Inventarisatie
en prioritering van bronnen en emissies van microplastics. Report 20140110, RIVM, Bilthoven
Verschoor, A.J., De Valk, E. (2018) Potential measures against
microplastic emissions to water. Report 2017-0193, RIVM, Bilthoven
Verschoor, A.J. (2015) Towards a definition of microplastics.
Considerations for the specification of physico-chemical properties.
Letter Report 2015-0116, RIVM, Bilthoven
Vrins, M., Costenoble, O. (2019) Report on standardization proposals
delivered and impacts realised. Work Package 5 D5.4
Waaijers-van der Loop, S., Van Bruggen, A., Beijer, N.R.M., Sips, A.C., De
Roda Husman, A., Cassee, F., Peijnenburg, W. (2022) Improved sciencebased transformation pathways for the development of safe and
sustainable plastics. Environment International 160: 107055.
Wagner, M., Scherer, C., Alvarez-Muñoz, D., Brennholt, N., Bourrain, X.,
Buchinger, S., Fries, E., Grosbois, C., Klasmeier, J., Marti, T., RodriguezMozaz, S., Urbatzka, R., Vethaak, A.D., Winther-Nielsen, M.,
Reifferscheid, G. (2014) Microplastics in freshwater ecosystems: what we
know and what we need to know. Environmental Sciences Europe 26 (1):
art.no. 12, pp. 1-9
Wang, J., Liu, X., Li, Y., Powell, T., Wang, X., Wang, G., Zhang, P. (2019)
Microplastics as contaminants in the soil environment: A mini-review.
Science of the Total Environment 691: 848-857
Page 84 of 110

RIVM report 2021-0224

Wang, W., Ge, J., Yu, X., Li, H. (2020) Environmental fate and impacts of
microplastics in soil ecosystems: Progress and perspective. Science of the
Total Environment 708, art.no. 134841
Wang, C., Zhao, J., Xing, B. (2021a) Environmental source, fate, and
toxicity of microplastics. Journal of Hazardous Materials 407: art. no.
124357
Wang, L., Wub, W., Bolan, N.S., Tsang, D.C.W., Li, Y., Qin, M.,
Hou, D. (2021b) Environmental fate, toxicity and risk management
strategies of nanoplastics in the environment: Current status and future
perspectives. Journal of Hazardous Materials 401 (2021) 123415
Weithmann, N., Möller, J.N., Löder, M.G.J., Piehl, S., Laforsch, C., Freitag,
R. (2018) Organic fertilizer as a vehicle for the entry of microplastic into
the environment. Science Advances 4(4): art.no. eaap8060
Weng, Y.-X., Wang, X.-L., Wang, Y.-Z. (2011) Biodegradation behaviour
of PHAs with different chemical structures under controlled composting
conditions. Polymer testing 30, 372-380
Wu, C.-S. (2014) Preparation and characterization of
polyhydroxyalkanoate bioplastic-based green renewable composites from
rice husk. Journal of Polymers and the Environment 22, 384-392
Wu, C.S. (2012) Preparation, characterization, and biodegradability of
renewable resource‐based composites from recycled polylactide bioplastic
and sisal fibres. Journal of Applied Polymer Science 123, 347-355
Xu, B., Liu, F., Cryder, Z., Huang, D., Lu, Z., He, Y., Wang, H., Lu, Z.,
Brookes, P.C., Tang, C., Gan, J., Xu, J. (2020a) Microplastics in the soil
environment: Occurrence, risks, interactions and fate–A review. Critical
Reviews in Environmental Science and Technology 50(21): 2175-2222
Xu, C., Zhang, B., Gu, C., Shen, C., Yin, S., Aamir, M., Li, F. (2020b)
Are we underestimating the sources of microplastic pollution in terrestrial
environment? Journal of Hazardous Materials 400: art.no. 123228
Yang, J., Li, R., Zhou, Q., Li, L., Li, Y., Tu, C., Zhao, X., Xiong, K.,
Christie, P., Luo, Y. (2021) Abundance and morphology of microplastics in
an agricultural soil following long-term repeated application of pig
manure. Environmental Pollution, 272, 116028.
doi:10.1016/j.envpol.2020.116028
Ye, J., Zhao, M.R., Liu, J., Liu, W.P. (2010) Enantioselectivity in
environmental risk assessment of modern chiral pesticides. Environmental
Pollution, 158(7): 2371–2383
Yu, L., Zhang, J., Liu, Y., Chen, L., Tao, S., Liu, W. (2021)
Distribution characteristics of microplastics in agricultural soils from the
largest vegetable production base in China. Science of the Total
Environment 756: art. no. 143860

Page 85 of 110

RIVM report 2021-0224

Yousif, E., Haddad, R. (2013) Photodegradation and photostabilization of
polymers, especially polystyrene. SpringerPlus 2, 1-32
Wilkes, R. A., & Aristilde, L. (2017) Degradation and metabolism of
synthetic plastics and associated products by Pseudomonas sp.:
capabilities and challenges. Journal of Applied Microbiology, 123(3), 582593
Zhang, G.S., Liu, Y.F. (2018) The Distribution of Microplastics in Soil
Aggregate Fractions in Southwestern China. Science of the Total
Environment 642: 12−20
Zhang, B., Yang, X., Chen, L., Chao, J., Teng, J., Wang, Q. (2020)
Microplastics in soils: a review of possible sources, analytical methods and
ecological impacts. Journal of Chemical Technology and Biotechnology
95(8): 2052-2068
Zhang, K., Hamidian, A.H., Tubić, A., Zhang, Y., Fang, J.K.H., Wu, C.,
Lam, P.K.S. (2021a) Understanding plastic degradation and microplastic
formation in the environment: A review. Environmental Pollution 274:
art.no. 116554
Zhang, S., Wang, J., Yan, P., Hao, X., Xu, B., Wang, W., Aurangzeib, M.
(2021b) Non-biodegradable microplastics in soils: A brief review and
challenge. Journal of Hazardous Materials 409: 124525
Zhao, T., Lozano, Y.M., Rillig, M.C. (2021) Microplastics increase soil ph
and decrease microbial activities as a function of microplastic shape,
polymer type, and exposure time. Frontiers in Environmental Science 9:
art.no. 67580
Zhou, Y., Wang, J., Zou, M., Jia, Z., Zhou, S., Li, Y. (2020)
Microplastics in soils: A review of methods, occurrence, fate, transport,
ecological and environmental risks. 2020 Science of the Total
Environment 748: art.no. 141368
Zhu, F, Zhu, C., Wang, C., Gu. C. (2019) Occurrence and ecological
impacts of microplastics in soil systems: a review. Bulletin of
Environmental Contamination and Toxicology 102: 741–749
Zubris, K.A.V., Richards, B.K. (2005) Synthetic fibers as an indicator of
land application of sludge. Environmental Pollution 2: 201–211

Page 86 of 110

RIVM report 2021-0224

Annex 1 Abbreviations of polymer types

EPA
HDPE
LDPE
LLDPE
MDPE
PA
PAE
PBS
PBT
PCL
PE
PEC
PES
PET
PHA
PHB
PHBV
PLA
PP
PPL
PS
PUR
PVC
SBR

expanded polystyrene
high-density polyethylene
low-density polyethylene
linear low-density polyethylene
medium density polyethylene
poly amide/nylons
phthalic acid esters
polybutylene succinate
polybutylene terephthalate
poly-ε-caprolactone
polyethylene
polyester carbonate
polyethylene succinate
polyethylene terephthalate
polyhydroxyalkanoate
poly-3-hydroxybutyrate
poly-3-hydroxybutyrate-co-3-hydroxyvalerate
polylactide
polypropylene
polypropiolactone
polystyrene
polyurethane
polyvinyl chloride
styrene butadiene rubber

Page 87 of 110

RIVM report 2021-0224

Annex 2 Biodegradation of microplastics

A2.1

Test methods to assess biodegradation within the proposed
restriction on intentionally added microplastics
Table 4 Overview of the test methods proposed by the ECHA restriction focused on
intentionally added microplastics to determine biodegradability. Note that not all
information is given regarding the test methods. For detailed information, see
Table 22 of the Background Document to the Opinion on the Annex XV report that
proposes restrictions on intentionally added microplastics, which is the latest
document published regarding the restriction (ECHA, 2020)

Group Determines

Pass criteria

1

Ready biodegradation

60% mineralization
1. Ready biodegradability (OECD TG
measures as evolved CO2 or
301 B,C,D,F)
consumed O2 in 28 days
2. Ready biodegradability – CO2 in
sealed vessels (OECD TG 310)

2

Enhanced /
modified ready
biodegradation

60% mineralization
1. Ready biodegradability (OECD TG
measured as evolved CO2 or
301 B,C,D,F)
consumed O2 in 60 days
2. Ready biodegradability – CO2 in
sealed vessels (OECD TG 310)
3. Modified biodegradability in
Seawater (OECD TG 306)

3

Inherent biodegradation

≥ 70% mineralization
measured as O2 within 14
days

4

(Bio)degradatio
n relative to a
reference
material

Ultimate degradation of ≥
1. Ultimate aerobic biodegradability
90% relative to the
in an aqueous medium (EN ISO
degradation of the referen14852:208 or EN ISO
ce material (60%) within:
14851:2004)
1. 6 months in aquatic tests 2. Aerobic biodegradation in
(O2 consumed) or
sweater/sediment interface (EN
2. 24 months in soil (CO2
ISO 19679:2016 or EN ISO
evolved or O2 consumed)
18830:2016)
or water/sediment tests 3. Ultimate aerobic biodegradability
(CO2 evolved)
in soil (EN ISO 17556:2019)
4. Aerobic biodegradation when
exposed to marine sediment (ISO
22404:2019

5

Half-life in the 1. The degradation half-life
environment
in soil is less than 180
(under relevant
days or
environmental 2. The degradation half-life
in marine, fresh or
conditions)
estuarine sediment is
less than 180 days or
3. The degradation half-life
in marine, fresh or
estuarine water is less
than 60 days

Page 88 of 110

Permitted test methods

1. Inherent biodegradability: Modified
MITI Test (II) (OECD 302C)

1. Aerobic and anaerobic
transformation in soil (OECD TG
307:2002)
2. Aerobic and anaerobic
transformation in aquatic sediment
systems (OECD TG 308: 2002)
3. Aerobic mineralization in surface
water – simulation biodegradation
test (OECD TG 309: 2004)

RIVM report 2021-0224

Composting of plastics
Table 5 Overview of continental and national certification schemes for plastics
compostable at home. Sources: Bastioli (2020); European Bioplastics (2016);
Standards Australia (2010); TUV Austria (2019)

Standards

Country/ Target/
continent product

Test
criteria

Pass
criteria

OK compost
HOME

Europea

Plastics

T: 20-30°C
Duration:
12 months

Absolute or
relative 90%
biodegradati
on (similar
to
EN 13432,
see above)

NF T 51-800:2015 France

Plastics

Very similar to OK
compost home

prEN 17427
(2020)

Europe

Carrier
bags

Unknownb

Unknownb

AS 5810:2010

Australia

Plastics

T: 25±5°C
Duration:
12 months

90% biodegradation
absolute or
relative to
suitable
reference
substance

UNI 11355:2010
and
UNI 11183:2006

Italy

Plastics

Very similar to OK
compost Home and AS
5810

a: The label originated in Belgium at the testing institute Vinçotte.
b: The information could not be retrieved from open sources.

A2.2

Microbes and biodegradation
Strains able to degrade plastics have been reported for various
environmental compartments, including soil. For example, a polyethene
(PE) deteriorating Aspergillus terreus strain was isolated from a mangrove
tree’s (Avicennia marina) rhizosphere (Sangale et al., 2019). This strain
was reported to be a highly efficient PE deteriorating fungus, reducing the
amount of PE microplastics present in the test system by more than 50%
at pH 9.5. Other reports of PE degrading microorganisms include isolates
from waste coal, a forest and a crater in Poland (Nowak et al., 2011). The
dominant microorganisms in waste coal and crater soil were bacteria
(Bacillus mycoides, Acinetobacter baumanniia and Pseudomonas
fluorescens), while in forest soils filamentous fungi (Staphylococcus
cohnii) were detected. Experiments with these microorganisms resulted in
a weight loss of 0.13% to 17% of the modified PE film within 225 days.
Hiraga et al. (2019) isolated microbes from landfills that apparently can
synthesize PET under laboratory conditions. Auta et al. (2018) reported
that a Bacillus and a Rhodococcus strain were isolated from mangrove
sediments that could degrade PP. The structure and morphology of PP
was altered following exposure to the bacteria, as was shown with FTIR
and SEM analyses. After 40 days of incubation, weight loss of 4.0 and
6.4% was observed for the bacillus and Rhodococcus strains,
Page 89 of 110

RIVM report 2021-0224

respectively. It should be noted that the studies discussed above are
just a few examples of microorganisms that have been isolated from
soils and that have the potential to degrade different types of plastics,
e.g. PE, PET and PP. Many more examples can be found in the literature.
It remains unclear though whether these strains also effectively degrade
(micro)plastics in the environment, where suboptimal conditions occur
and where more readily available carbon sources might be present.
A2.3

Determination of degradation rates
Degradation rates are generally expressed in terms of unit loss per unit
time. Theoretically, the rate can be described as the loss of weight, size,
polymer structures or other parameters, while it could also be described
as a gain in breakdown products, for example, monomers or CO2.
It is likely that the degradation of microplastics is largely dependent on
the available surface area (Chamas et al., 2020). Therefore when it is
assumed that degradation only occurs at the surface of a polymer,
degradation can be expressed as a specific surface degradation speed
(ka.deg) in m/s, such that m is the depth of the microplastic (perpendicular
to the surface) which is degraded after a certain period of time (s). Note
that the (surface) degradation speed can also be expressed as a rate
constant (e.g. s-1), which is discussed later on. The ka.deg will differ
between polymer types, based on the susceptibility of the material to
degradation, but also between similar polymer types due, for example, to
additives and environmental conditions that hamper or accelerate
degradation. The amount of mass lost over time depends on the density
of the polymer (kg/m3) and the surface area (m2). Multiplying these
parameters with ka.deg will result in the mass-based degradation rate
(kg/s). This is the basic approach that can be taken when assuming a
constant surface area, for instance for a thin flat surface. However, the
surface area of most shapes of plastics will change over time and
therefore degradation of most plastics cannot be described by a constant
mass-based degradation rate in time.
The recent study conducted by Chamas et al. (2020) elaborated on the
surface-based degradation of microplastics and described the
degradation rate and time to complete degradation for MPs with a
constant surface area (flat, thin plastic), spherical (microbead) and
cylindrical (fibre) shapes. By including a few assumptions, the authors
derived the following equations to determine the degradation time:

𝑡𝑡𝑑𝑑 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 =
𝑡𝑡𝑑𝑑 𝑠𝑠𝑠𝑠ℎ𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 =

3 𝑉𝑉
3
� 0
2/3
6 𝑘𝑘𝑎𝑎.𝑑𝑑𝑑𝑑𝑑𝑑 𝜋𝜋

𝑡𝑡𝑑𝑑 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 =
Page 90 of 110

𝑉𝑉0
𝑘𝑘𝑎𝑎.𝑑𝑑𝑑𝑑𝑑𝑑 𝑆𝑆𝑆𝑆

𝑚𝑚 1/2
�
�
𝑘𝑘𝑎𝑎.𝑑𝑑𝑑𝑑𝑑𝑑 𝜋𝜋𝜋𝜋ℎ
1

RIVM report 2021-0224

With:
= complete degradation time (s)
td
= volume start (m3)
V0
ka.deg = surface degradation speed (m/s)
SA = surface area (m2)
m
= mass (kg)
ρ
= density (kg/m3)
h
= height (m)
*
For td cylindrical it is assumed that SA = 2 πrh instead of SA = 2 πr
(h+r).
**
Note that the ka.deg can vary over time, which is not included in the
model equations.
Because a mixture of microplastics is present in the environment,
modelling degradation will be complex. The above formulas can however
be used to estimate the degradation times of individual plastics. To do so,
physical properties are necessary, but also the ka.deg. Chamas et al.
(2020) has published an overview of ka.deg values found in the literature
for different plastics in different environmental conditions. Based on the
available data, Ka.deg values can vary up to a factor of 1,000 for a type of
plastic in an environmental compartment (e.g. soil or water). It is
expected that the variation in ka.deg may largely be allocated to the
different test conditions, especially as the results for landfill, compost and
soils are presented jointly. Under these environmental conditions, the
range of specific degradation rates seems mostly to be large for LDPE and
other plastics, although for these plastics also the most data points were
available. As the results are presented jointly for plastics containing fillers
and/or tested under accelerating conditions and for those not, it is unclear
what the individual effects of these are. On average, the ka.deg for plastics
in landfill/compost/soils seems to be around 5-10 µm/year. In Table 6,
ka.deg values are given for each plastic type (Chamas et al., 2020). For
many plastics no data was retrieved, while for some types of plastics no
degradation was observed. It is argued that the lack of degradation is
likely a result of the testing conditions. For plastics, generally long periods
of time are needed to degrade, which corresponds to low ka.deg values.
Table 6 Estimated specific surface degradation rates for different plastics (minmax, in µm/year) in landfill/compost/soil under normal buried conditions or under
influence of UV/heat. 0 = no degradation was observed. – = no published data
was found. From Chamas et al. (2020)

Polymer type
PET
HDPE
PVC
LDPE
PP
PS
Others

Estimated specific surface degradation rates
(µm/year)
Buried
Accelerated by UV/heat
0
–
1.0 (0.91-1.11)
1.3 (0.55-2.6)
0
–
11
22 (1.6-83)
–
0.51
0
–
270 (20-1400)
320

Several of the currently available fate models (Besseling et al., 2017;
Meesters et al., 2014) that are fit for use with microplastics are based
Page 91 of 110

RIVM report 2021-0224

on first-order rate constants for describing the different environmental
fate processes, such as degradation. First-order degradation rate
constants (s-1) for each type of polymer can be estimated by using the
specific surface degradation rates (zero-order degradation rates) to
calculate the degradation of a microplastic over time. As an example, a
microbead particle is used. The equation to calculate the complete
degradation time of a microbead (td spherical) takes into account that
the particle has completely shrunk over time. Chamas et al. (2020) also
formulated the equation to determine the mass of a particle as a
function of time (see below).
𝑚𝑚𝑡𝑡 = �(𝑚𝑚0 )1⁄3 −
With:
mt
m0
ka.deg
ρ
t

3

62⁄3
𝑘𝑘 (𝜋𝜋𝜋𝜋)1⁄3 𝑡𝑡�
3 𝑑𝑑

= mass at time = t (kg)
= mass at time = 0 (kg)
= specific surface degradation speed (m/s)
= density (kg/m3)
= time (s)

This equation assumes that degradation of the particle increases over
time. By modelling mt for an initial period over time (e.g. until mt =
0.5*m0), the slope of the decrease in mass can be used to determine
the degradation rate constant.
In the case of a HDPE microbead of 8mm, the following input parameters
can be used:
Size:
8 mm
Volume: 2.9 cm3
ρ:
0.950 kg/m3
0.00275 kg
m0:
1.0 µm/year (average ka.deg for HDPE in soil/landfill/compost,
ka.deg:
from Table 6).
As a result, a slope, and with that a first-order degradation rate constant,
of 1E-11 s-1 can be estimated for the first part of the degradation in time.
Although such a degradation rate constant provides insights into the
degradation rate of an individual particle in a very generic manner, a
number of aspects have to be taken into account when applying such a
constant in modelling:
• Rate constants are polymer-type-specific and dependent on
ka.deg. (Estimations for) ka.deg are currently not yet available for all
type of polymers in soils, while for some polymers limited
information is available.
• Calculated degradation rate constants depend on the different
initial particle characteristic which used as input, such as size,
density and mass (the latter of which is related to both
aforementioned characteristics).
• Besides the physical particle characteristics used as input, other
physical/chemical characteristics (e.g. presence of additives,
Page 92 of 110

RIVM report 2021-0224

•

•

smoothness of the surface) can also influence degradation and
should be considered.
The calculations do not take into account changes over time. The
specific surface degradation rate can vary over time (e.g. as a
result of changing environmental conditions or changing surface
area), which is not captured.
The specific surface degradation of each polymer depends on the
environmental conditions. As seen in Table 6, ka.deg can vary to a
great extent between studies. Note that in addition to
environmental factors, particle characteristics could also have
influenced the results.

Page 93 of 110

RIVM report 2021-0224

Annex 3 Methods for extraction, separation, identification
and quantification of microplastic in soil

A3.1

Introduction
There is no standardized method for separating microplastics from a soil
matrix, nor a standardized analysis and identification protocol. In this
Annex we provide a brief overview of the methods that have been used
in research for different steps of measuring microplastics in complex
environmental samples, with a special focus on their applicability for the
analysis of soil samples. These methods are described in more detail in
other reviews, amongst others by Bläsing and Amelung, 2018; Zhang et
al., 2018; Li et al., 2020b; Ruggero et al., 2020; Möller et al., 2020.
Some steps have several possible methods to use. Each method has its
benefits, its specificity for certain polymers, differential applicability in
solid matrices and uncertainty.
The biggest hurdle to face is the extraction and clean-up method. This is
a challenging step because of the presence of various, abundant and
complex organic substances in the soil organic matter fraction.
Commonly used techniques are based on the extraction of microplastics
with a salt solution based on density differences between the
microplastics, the other soil constituents and most of the organic matter.
Different salt solutions can be used for different polymers. With saturated
NaCl, the light polymers can be extracted, while with NaI or NaBr, for
example, the whole range can be extracted. It is, however, difficult to
distinguish organic compounds from microplastics by conventional salt
solution density separation, irrespective of the soil type and structure (Li
et al., 2020a). For samples with organic matter such as soil and sediment
samples, a digestion step is often required (Ruggero et al., 2020).
The second hurdle to overcome is to find a suitable analytical instrument
for different types or purposes (reviews e.g., by Ruggero et al., 2020 and
Möller et al., 2020). Depending on the scope of a study, one method may
be more suitable than another. For monitoring purposes, determining the
mass quantities of polymers or volumes may be the best way to measure
concentrations in the field. Whereas a toxicity laboratory test may require
another analytical methodology to determine elasticity and aspect-ratio
(both related to potential uptake). Currently, fewer methods are available
to sufficiently provide insight into the morphology of microplastics. There
is no one method that fits all purposes.

A3.2

Sampling
Soil sampling is the first step in the extraction of microplastic from the
environment. Proper soil sampling is very important to obtain
representative information, but this is unfortunately sometimes
overlooked. Different strategies exist to obtain reliable information from
a qualified sampling approach. Möller et al. (2020) summarized the main
characteristics of different approaches:
Page 94 of 110

RIVM report 2021-0224

•
•

•
•
•

•

Judgmental sampling. This is based on pre-existing information,
very effective but for that reason subjective.
Simple random sampling. Effective and flexible with rather
homogeneous sites. However, microplastics are often not
homogeneously distributed, neither are the covariables in the soil
system.
Systematic grid sampling. Simple to implement, but sometimes
too inflexible.
Unaligned grid sampling. Like grid sampling, but with more
flexibility to select sampling locations within a grid cell.
Transect sampling. This method allows a systematic identification
of the distribution of microplastic pollution in straight lines, i.e.
according to the distance to a source, parallel to roads and
streams, and other gradients in the field.
Stratified sampling. Based on a division of the sampling area into
smaller areas with homogeneous features. This is a
recommended approach with significant different strata, where
microplastics are relatively homogenously distributed compared
to the distribution in the area as a whole.

A dedicated sampling approach is required to obtain a representative set
of samples for each type and size of the landscape and for each type of
microplastic with respect to polymer composition and sizes of the
particles. Very often, constraints in budgets hamper the collection of a
robust set of samples with sufficient statistical power to detect the
impact of pollution gradients. Sometimes a combination of samples in a
composite sample may be a solution in order to reduce the number of
samples, without losing the representative nature of the information
obtained. However, there is a danger here that small differences
between samples disappear and some pollution hot spots may be missed
as a result.
More details on sampling and the preparation of samples can be found in
the literature (viz. Möller et al., 2020).
A3.3

Extraction

A3.3.1

Introduction
For an analysis of microplastics in complex environments (Möller et al.,
(2020), it is recommended that the bulk of the solid matrix be removed,
preferably isolating the microplastic particles from the matrix and
removing adhering substances. For inhomogeneous solid samples such
as soils, microplastic extraction is challenging, especially with decreasing
grain size of the soil texture (clay) and microplastic particle sizes
(Crawford and Quinn, 2017). Soil particles can form relatively stable
aggregates, which may enclose microplastic particles and obscure them
from analysis (Zhang and Liu, 2018; Bläsing and Amelung, 2018). For
this reason, developing a method for soil aggregate dispersion without
risking the destruction or artificial fragmentation of microplastic particles
is an important first step for the microplastic analysis in soil.

A3.3.2

Manual extraction
The crudest method for microplastic extraction is sieving and hand
sorting, using a stereo microscope to exclude obvious mineral or
biogenic matter, such as particles with visible cell structures. This
Page 95 of 110

RIVM report 2021-0224

method can be combined with the ‘hot needle test’ to further confine the
number of putative microplastic particles. However, manual sorting and
visual identification is extremely time and labour intensive, restricted to
sizes >500 μm and is highly prone to misidentification and bias,
rendering a subsequent reliable polymer identification indispensable.
A3.3.3

Electrostatic separation
A rather novel methodology used is the electrostatic separation of
microplastic particles from solid matter. While experiments conducted by
Hidalgo-Ruz et al. (2012) in this direction failed, Felsing et al. (2018)
managed to modify a smaller but fair demonstration device of an
electrostatic separation unit commonly used in the recycling industry to
isolate microplastics from sand and sediment samples. The method
allows a relatively high sample throughput with a mass reduction of up
to 99% and recovery rates of 90−100% for pristine microplastic
particles ranging from 63 μm to 5 mm. However, to achieve these high
recovery rates, the samples underwent the procedure three times, with
a temporal effort of 3 to 4 h per 150 g sample. Furthermore, the authors
claim that the method is independent of organic matter content, particle
density, shape, age, or biofouling. However, this method is not suitable
for moist samples (Felsing et al., 2018) and its suitability for cohesive
soil samples is questionable, due to the unavoidable formation of
aggregates. Furthermore, the applicability for very small particles must
still be verified, as the force of adhesion to the metal drum and scraper
may be higher than the gravity-force, possibly leading to significant
losses of the small microplastic fraction in the final sample.

A3.3.4

Removal of the mineral fraction
Oil extraction
Crichton et al. (2017) developed an oil extraction protocol, a simple
approach for the extraction of microplastic from solid samples, taking
advantage of the lipophilic surface properties of most plastics.
Dried sediment samples are mixed with water and canola oil, then
agitated thoroughly and left to settle until the oil, water and mineral
fractions are completely separated. Any microplastic particles coming into
contact with the oil should thus be conveyed to the oil layer, which can
easily be transferred onto a filter. According to Crichton et al. (2017),
recovery rates range from 90 to 100% for all seven tested pristine
polymer types compared using density separation methods with NaI and
CaCl2. The procedure is simple, safe, cheap and time efficient, but may
require an additional step to remove organic substances from a sample
(Crighton et al., 2017). A recent study conducted by Mani et al. (2019)
tested the oil extraction method using castor oil to separate microplastics
(0.3−1 mm) from four complex environmental matrices: fluvial and
marine suspended surface solids, marine beach sediments and
agricultural soil. The method showed high recovery rates for the four
pristine polymers: polypropylene, polystyrene, poly(methyl methacrylate,
and glycol modified polyethylene terephthalate The average recovery
rates were 99% ± 4% (mean ± SD) and a mean matrix reduction of 95%
± 4% (dry weight). For validation, non-spiked Rhine river water
suspended solids underwent the castor oil extraction protocol. Of the
978 microplastic particles found in the five examined samples, 773
microplastic particles were recovered in the upper oil phase, whereas 205
Page 96 of 110

RIVM report 2021-0224

microplastic particles were recovered from the lower aqueous and solid
phase, resulting in a recovery rate of 74% ± 13%. For organic-rich
sample matrices, an additional H2O2 digestion step was required to
achieve an adequate sample purification (Mani et al., 2019).
Density separation
The most commonly applied method for the separation of microplastics
from solid matrices is density separation. These methods use highdensity salt solutions as extraction media (Hanvey et al., 2017).
In an early study conducted by Thompson et al. (2004), a method was
devised using a saturated NaCl solution to separate microplastic from
sand. After stirring and sedimentation, the plastic-containing supernatant
is sucked into an extra flask from where it is transferred onto a filtering
system (Crawford and Quinn 2017; Thompson et al., 2004). Losses may
occur in the tubing or while decanting, which is why more sophisticated
devices have been built since. Furthermore, saturated NaCl solution can
only achieve a maximum density of 1.2 g ml-1, and several synthetic
polymers, such as polyethylene terephthalate (PET) and polyvinylchloride
(PVC), have higher densities and are not extracted by saturated NaCl
solutions. Thus, alternative salt solutions such as NaI (ρ=1.8 g·ml-1 ml-1),
Na6[H2W12O6] (ρ=1.4 g·cm−3), Zn2Cl (ρ=1.6−1.7 g·cm−3) and NaBr
(ρ=1.55 g·cm−3) were recommended, although the costs and
hazardousness of these solutions may impose a need for alternatives.
Imhof et al. (2012) developed the Munich Plastic Sediment Separator
(MPSS) to separate a diverse range of microplastics from a maximum of
6 L of sediments using a ZnCl2-solution. A removable sample chamber
equipped with a filter holder enables a direct transfer of the microplastic
particles onto a filter, separating the sample from the density solution.
As no decantation or repetitive extraction steps are required, losses and
contamination can be avoided. According to Imhof et al. (2012),
recovery rates of 95−100% can be achieved. However, Zobkov and
Esiukova (2017) evaluated the MPSS and found the recovery rates of
pristine plastics to be similarly high, as stated by Imhof et al., but the
recovery of aged plastics was significantly lower at only 13−39%.
Moreover, ZnCl2 is hazardous and corrosive, has a low pH value and
may react with the natural components of sediment, especially
carbonates, resulting in bubbling and a foam that significantly hampers
the procedure (Zobkov and Esiukova, 2017).
It is also questionable whether soil aggregates will be adequately
dispersed in the MPSS, or whether a prior dispersion is required,
especially for cohesive soils. Furthermore, the large surface area which
may corrode due to the nature of the ZnCl2 may be problematic if small
particles get caught on the rough surface and cannot rise upward,
possibly causing significant losses. Coppock et al. (2017) saw the need
for a cheaper and portable microplastic-sediment separator and devised
the Sediment-Microplastic-Isolation unit consisting of PVC tubes, a PVC
ball valve and zinc chloride agitated by a magnetic stir bar. The principle
mirrors that of the MPSS and shows similarly high recovery rates of
92−98%.
However, PVC must be excluded from the analysis as abrasion from the
PVC tubing may contaminate the samples. This may compromise the
value of the analytic results, as PVC is a relevant contaminant in
Page 97 of 110

RIVM report 2021-0224

environmental samples, such as sediments and possibly soils, and
excluding it from the analysis poses a significant loss of information.
Möller et al. (2020) considered a NaBr solution (1.55 g cm−3) as the
most suitable separation medium, due to its relatively high density and
low viscosity. Recovery rates of over 90% were reported for 10 types of
microplastics (PA, PC, PP, ABS, PE, PS, PMMA, POM, PET and PVC). PE
particles of different size ranges (100−500 μm, 500−1000 μm,
100−3000 μm) and shapes (particle, fibre, film) were tested using the
device. The recovery rates differed only marginally for the different sizes,
whereas the shape of ‘particles’, that is fragments, showed the highest
recovery rate (98.3%), as opposed to films, with the lowest recovery rate
(85%). This method appears promising for soil sample analysis for
microplastic particles >100 μm and, although particles down to 32 μm
were found in soil samples, the recovery rate (i.e. reliability) of the device
for smaller particles (e.g. 1−100 μm) must first be systematically
determined. One severe drawback of the described system is that the
separation cylinder is made of Plexiglas (i.e. PMMA). Abrasion caused by
the stirring of coarse soils may lead to an overestimation of the PMMA
contamination in the samples. Therefore a non-plastic material should be
used or PMMA excluded from the analysis.
In reviewing the above-named publications, no upper or lower size limit
for the extraction of microplastic particles using density separation has
been established (Möller et al., 2020). In general, the recovery rates of
the particles were established for size ranges lying between 40 μm 55
and 5 mm (Liu et al., 2019; Imhof et al., 2012). The applicability for
smaller microplastics and nanoplastics have not yet been analysed.
However, according to the Stokes equation, small particles have very
low settling velocities that are further reduced by high drag coefficients,
which are dependent on the particle shape. So an in-depth empirical
study of the minimum size of various microplastic particles in common
density separation fluids is called for.
Froth flotation
Another method, which is not only dependent on the density of the
polymer, but also on the hydrophobicity of its surface, is froth flotation,
commonly used in the recycling industry (Alter, 2005; Fraunholcz, 2004;
Marques and Tenório, 2000). Air bubbles will selectively attach to the
more hydrophobic particles and carry them upward, thus separating
them from the less hydrophobic matrix. According to Imhof et al.
(2012), however, the mean efficiency of the froth flotation in separating
microplastic from sediment is quite low (55 ± 28%), with high
differences between polymer types.
Magnetic extraction
Another method that relies on the hydrophobic nature of microplastic
surfaces is the method introduced by Grbic et al. (2019). By
functionalizing iron nanoparticles with hydrophobic hydrocarbon tails
(using hexadecyltrimethoxysilane (HDTMS)), the iron nanoparticles will
bind to the microplastic surfaces and allow extraction with a magnet. In
addition to water samples, the method was tested for sieved (mesh size
45 μm) benthic sediment spiked with microplastics (200 μm to 1 mm;
PP, PVC, PU, PS, and PE). The recovery rates ranged from 49% (PP) to
Page 98 of 110

RIVM report 2021-0224

90% (PE), albeit with high standard deviations within trials. This method
is a proof of concept that still has a few disadvantages: for instance,
lipophilic substances that are present in a soil’s organic matter may
result in nonspecific binding, reducing the effectiveness of the method.
The authors suggest using the method for sediment samples after
density separation or digestion, after which a further extraction method
would no longer be necessary. Furthermore, brittle microplastic particles
were shown to fragment during the procedure. In environmental
samples, where aged microplastics may be more brittle than pristine
particles, this could distort the results significantly. Grbic et al. (2019)
propose that limiting microplastic contact with the magnet may reduce
fragmentation. However, the question of the iron interfering with
possible subsequent analytical characterization methods has not been
addressed and should be further examined. While the authors describe
how sonicating the magnet in a surfactant or acid solution can remove
the iron nanoparticles from the microplastic surfaces, this method may
lead to further fragmentation of microplastic particles (Löder et al.,
2015) and is therefore undesirable.
Vertical density gradient separation
A new methodology for density separation developed for the recycling
industry uses a liquid containing colloidal ferromagnetic particles. A
magnetic field around the liquid creates a vertical density gradient, with
the highest density being at the bottom and the lowest density being at
the top of the liquid container, thus a separation of a sample into
different strata of various densities can be achieved (Hu, 2014). This
method may have potential concerning the isolation of microplastics
from environmental samples; however, no research in this field has
been conducted yet and the costs may be unjustifiably high.
In general, density separation may be useful to remove the mineral
fraction of soil samples, but methods developed for aquatic sediments
must be adjusted to the new matrix ‘terrestrial soil’, which can be
extremely heterogeneous. Special care must be taken here that no
microplastic losses occur due to enclosure in soil aggregates. Also, a
soil’s organic matter has a similar density (ρ=1−1.4 g·cm−3) to most
plastics and needs to be removed separately, as organic compounds can
impede microplastic analysis.
A3.3.5

Removal of the organic fraction
Acidic and alkaline digestion
The treatment of organic matter in soil becomes the first key to detecting
microplastics in soil. H2O2 and Fenton reagent are still common reagents
for the digestion of organic compounds. H2O2 at 70°C improves the
digestion of organic compounds (Li et al., 2019). However, studies have
found that H2O2 will reduce the extraction efficiency of microplastics
(Wang et al., 2018). NaOH and KOH are also used in the digestion of
organic matter in soil. Although they effectively remove organic matter
from soil, these two reagents can cause the discoloration and degradation
of microplastics (Maes et al., 2017; Ruggero et al., 2020). A recent study
used 98% H2SO4 to separate microplastics from farmland soil in order to
obtain pure polyethylene (Li et al., 2020b). This method can be widely
used in agriculture, although the use of large quantities of acid solution is
not preferred. Standard instruments used to detect microplastics in ocean
environments can be used in soil instead.
Page 99 of 110

RIVM report 2021-0224

Acidic and alkaline digestion methods are frequently reported in the
literature to remove the organic fraction of the sample matrix. Due to
the fact that soils contain organic matter as well, a digestive step is
imperative for an undisturbed analysis. Claessens et al. (2013)
determined that the most efficient chemical digestion of mussel tissue
was obtained by treating the sample with 22.5 M HNO3. Also, the ICES
(International Council for the Exploration of the Sea) recommends an
acid blend of HNO3:HClO4 (4:1) to digest marine animal tissue for
microplastic analysis. However, several studies state that certain strong
acids may destroy specific polymers such as polystyrene and polyamide.
Alkaline digestion is similarly discussed by many authors, especially for
the digestion of animal tissue. However, treatment with NaOH was found
to destroy polyamide and polyethylene (PE) fibres and led to the
melding or discoloration of other polymers. Foekema et al. (2013)
digested fish intestines with 10% KOH solution at room temperature for
2−3 weeks. While it is apparently successful and non-destructive to
synthetic polymers, the procedure is time-consuming and may not be
applicable to plant material or stabilized organic matter in soil.
Generally, the purification of samples with strong acidic or alkaline
solutions will lead to uncontrolled bias in the resulting microplastic
composition of the sample (Löder et al., 2017). As stated earlier, the
use of large quantities of strong acid or alkaline solutions is producing a
lot of harmful chemical waste.
Oxidation with hydrogen peroxide
Oxidation treatment with boiling hydrogen peroxide (30% H2O2) is
commonly used in soil analysis to remove a soil’s organic matter (Pansu
and Gautheyrou, 2006). It has also been used at lower temperatures to
digest organic matter in the context of microplastic isolation from organic
rich sediment matrices: Nuelle et al. (2014) allowed samples to remain in
30% H2O2 for 7 days. Around 50% of the biogenic matter was dissolved
completely, but polyamide (PA), polycarbonate (PC) and polypropylene
(PP) pellets showed visible signs of degradation such as discoloration and
size reduction. Liebezeit and Dubaish (2012) claim that a 30% H2O2
treatment overnight does not affect plastic particles; however, it is not
stated whether pristine or weathered plastic polymers were used, which
can affect the results. In a study of microplastics in marine snow, Zhao et
al. (2017) observed that 30% hydrogen peroxide treatment of organicrich samples often results in the formation of a dense foam, which may
suspend a significant portion of the microplastics sample, remaining
separated and not mixed with the reagent. Many more observations on
pristine and weathered microplastics were reviewed by Möller et al.
(2020), indicating that care must be taken since the degradation of
polymers can happen by long or hot exposure to high concentrations of
hydrogen peroxide and Fentons reagent. Nevertheless, according to
Möller et al. (2020) some promising results were obtained with Fenton’s
reagent in removing organic matter from the samples (e.g. Hurley et al.,
2018). As this method is relatively cost and time-efficient, it has potential
to become an important step in the microplastic analysis of soil samples.

Page 100 of 110

RIVM report 2021-0224

Enzymatic digestion
Organic matter within soils is one of the most difficult fractions to
remove without destroying the microplastic particles (e.g. Möller et al.,
2020). An adapted enzymatic digestion may therefore be beneficial.
However, most reports on enzymatic digestion procedures were
developed for aquatic samples, removing soft animal tissue, and
exclusively use proteolytic enzymes that will not be able to remove the
stabilized plant organic matter contained in soils. For this reason, a
more promising approach was derived by Löder et al. (2017). A
sequential enzymatic digestion coupled with short-term reactions with
H2O2. The enzymes used target specific organic compounds and using
different enzymes may result in better digestion efficiencies than does,
for example, a single oxidation step using H2O2. The presented protocol
is sufficient for complex aquatic samples, but the removal of terrestrial
plant matter and stabilized organic matter in soil will probably require a
different set of enzymes; so an adaptation of this protocol may be
necessary for terrestrial samples. As proposed by Löder et al. (2017)
and Möller et al. (2020), a sequential combination of Fenton’s reagent,
SDS and specific enzymes can enhance the purification of organic
matter in soil compared with the use of Fenton’s reagent alone.
Combined methodologies
A few series of research studies depict the advantage of combined
methodologies to ensure extraction of microplastics from the bulk sample
(Ruggero et al., 2020). In particular, in most of them digestion of the
organic residues follows a previous treatment for microplastic separation.
This application was done for sediment samples after flotation with NaCl
(Nuelle et al., 2014) and after elutriation in water (Quinn et al., 2017).
These matrices, in fact, allow a proper separation from plastics due to the
high difference in density, but can require a further digestion to remove
any organic residues which float due to their lower density. In sludges,
matrix digestion is combined with a prior sieving treatment (fractions
from 60 µm to 2 mm) which ensures the removal of most of the sludges
but leaves bigger size organic residues (Lares and Ncibi, 2018). Finally,
the treatment which couples elutriation to sieving has a high efficiency in
samples of sandy soils (Kedzierski et al., 2016).
A3.4

Identification and quantification (detection)
This chapter will focus on the identification and quantitative analysis of
polymers in the soil sample containing microplastics.

A3.4.1

Visual identification and hot needle test
The earliest determination of microplastics was by means of visual
identification under a light microscope, which is rather prone to bias and
large error rates. To reduce the shortcomings of visual identification,
some publications recommend the ‘hot needle test’, which makes use of
the thermoplastic properties of many synthetic polymers. Zhang et al.
(2018) further developed this principle for a simple identification of lowdensity polymers in soils: After a density separation with water, the
residue in the supernatant is analysed by comparing microscope-images
taken prior and after heating the sample at 130 °C for 3−5 s. Melted
particles are then identified as thermoplastic polymers. While simple and
feasible, this form of identification neglects high density and
Page 101 of 110

RIVM report 2021-0224

thermosetting plastics and lacks the possibility of identifying the exact
type of polymer. Similarly, the use of polarized light microscopy under
which certain synthetic particles appear intensely illuminated, though
indiscriminate, is non-destructive. For more details and further reading,
the reader may take information from the reviews of Möller et al. (2020)
and Ruggero et al. (2020).
A3.4.2

Chromatography
Common and more sophisticated methods, which allow the qualitative
and quantitative identification of individual polymer types, include
various extraction methods coupled to a chromatographic unit.
Recommended methods in the literature include high temperature gelpermeation chromatography (HT-GPC) for the identification of
polyolefins in cosmetics, liquid extraction with size-exclusion
chromatography (SEC) for the identification and quantification of
polystyrene (PS) and polyethylene terephthalate (PET) in soil samples
(Elert et al., 2017), and pyrolysis followed by gas chromatography mass
spectrometry (Pyr GC-MS). Pyr GC-MS is a sensitive and wellestablished method for the characterization and quantification of many
polymer types and their organic additives.
Pyr GC-MS has been shown to be very suitable for the detection of
microplastics in environmental samples. However, it also has several
drawbacks. The size of the pyrolysis capsule and, accordingly, the sample
amount per run is exceedingly small: 1.5 mm (Fries et al., 2013) and
0.5 mg (Dümichen et al., 2017) respectively, which requires an extensive
sample clean-up for matrix-rich samples, making it rather unsuitable for
bulk analysis. Additionally, it is prone to contamination or even blockage.
To overcome these shortcomings, Dümichen et al. (2017) developed the
thermal extraction-desorption gas chromatography mass spectrometry
(TED GC-MS) for microplastic detection. Each run can accommodate up to
100 mg of sample, which requires no pretreatment other than grinding and
mixing in an attempt to homogenize the samples. The processing time
requires 2−3 h, which is less than most of the current spectroscopic
methods available. This new analytical method seems suitable for the fast
analysis of many different environmental sample types, including soils.
Eisentraut et al. (2018) confirmed the possibility of identifying tyre wear in
environmental samples using TED GC-MS, an achievement that is very
important to monitor the massive introduction of microplastic particles into
the environment by traffic. However, if sample grinding is necessary,
quality controls should take place, ensuring that the risk of microplastic
losses and contamination remain at a minimum. One significant drawback
of TED GC-MS, as with all extraction-chromatography methods, that it is
destructive. Hence, information on the number, size and morphology of the
plastic particles cannot be obtained, although this information may be
crucial in the context of assessing the effects of microplastics on organisms
and eco-systems: size and form may affect exposure and bioavailability. In
addition, the morphology of the microplastics may also be important in the
context of their influence on the soil structure and function.

A3.4.3

Thermogravimetric analysis
A different thermal analysis method is the thermogravimetric analysis
(TGA). Majewsky et al. (2016) coupled TGA with differential scanning
calorimetry (DSC) for the microplastic analysis of waste water. However,
Page 102 of 110

RIVM report 2021-0224

in that study, only polyethylene (PE) and polypropylene (PP) could
clearly be identified. David et al. (2018) attempted to couple TGA with
mass spectrometry (MS) in order to quantitatively analyse polyethylene
terephthalate (PET) in soil samples without sample pretreatment. While
successful, the method still requires further development and, to the
best of the author’s knowledge, is still restricted to the analysis of PET
only. Thermogravimetric analysis and chromatography bear several
promising approaches for fast mass-quantitative identification of
microplastics in soils and other complex matrices (Huppertsberg and
Knepper, 2018). However, they are limited insofar as subsequent
analyses are impossible due to the destructive nature of the methods
and the fact that the number, size and form of the particles remain
unknown, resulting in the drawbacks mentioned above in the
chromatography section.
A3.4.4

Vibrational spectroscopy
Vibrational spectroscopy, such as Raman or Fourier transform infrared
(FTIR) spectroscopy, are the most commonly used state-of-the-art
analytical methods in microplastic research, because they enable the
precise identification of polymer types, their abundance, shape and size
(Möller et al., 2020). Raman microspectroscopy enables the chemical
imaging of samples down to a pixel resolution of 500 nm, while focal
plane array (FPA) based micro-FTIR spectroscopy enables the
identification of particles in a size range from 10 to 500 μm. Larger
particles (>500 μm) can be analysed by attenuated total reflectance
(ATR)-FTIR spectroscopy (Renner et al., 2017). For general information,
the reader is referred to the reviews of Ruggero et al. (2020) and Möller
et al. (2020), and for the application modes of FTIR and Raman
spectroscopy, to the publications of Renner et al. (2017) and Kappler et
al. (2016).
Raman and FTIR-based chemical imaging complement each other and
should be chosen in accordance with the specific research questions: the
Raman imaging run time is significantly higher than FTIR imaging
(Kappler et al., 2016), but is independent of the shape, size or thickness
of the measured particles, which can influence the results in micro-FTIR
imaging. Black particles often result in unidentifiable FTIR-spectra which
is particularly problematic with soil samples rich in organic matter.
Consequently, a thorough sample purification is needed prior to placing
the concentration on the filter surface on which the analysis takes place
(Löder et al., 2017). For solid samples, this fact significantly reduces the
amount of sample that can realistically be processed. Therefore, the
need for an easy high-throughput technique for a representative amount
of solid samples, such as soils, has been recognized and solutions have
been proposed (reviewed by Möller et al. (2020) and Ruggero et al.
(2020)). In all cases and similar to the chromatographic methods, these
techniques are destructive and only allow mass-quantitative analysis,
and do not provide information on number, size and shape of the
polymer particles. Additionally, multiple polymer types in one sample
produce complex absorption spectra that may hamper identification. To
address these issues, several trials have been undertaken.
A similar, novel method was introduced by Schmidt et al.116 who used
short-wave infrared (SWIR) imaging spectroscopy to analyse surface
Page 103 of 110

RIVM report 2021-0224

water samples taken from the Teltow Canal in Berlin (Germany). The
purified (using H2O2) samples were filtered onto several glass fibre filters
each (diameter 47 mm) and scanned with a SWIR imaging spectrometer
– measurement speed: 52 048 mm2 per hour – resulting in the
measurement of 10 filters within 20 min. The lower detection limit is for
particles of size 560 μm by 280 μm (2 pixels). The evaluation of the
spectroscopic images was done automatically by the “PlaMAPP”
algorithm, yielding a 75% true detection efficiency. To achieve more
reliable results, additional manual checking was required (Schmidt et
al., 2018). While the SWIR imaging spectroscopy can process many
sample filters in comparatively little time, its drawbacks are the rather
large lower size limit and the need for improvement for correct particle
detection in the automated analysis algorithm
A3.4.5

Proton nuclear magnetic resonance spectroscopy (1H NMR)
A completely new approach for size-independent microplastic analysis
was recently described by Peez et al. (2019). Using quantitative 1H NMR
spectroscopy, model samples of polyethylene (PE) particles, polystyrene
(PS) beads, and polyethylene terephthalate (PET) fibres could
successfully be qualitatively and quantitatively analysed using a
calibration curve method. This method has the severe drawback of
having to completely remove organic matter from the sample to avoid
signal overlays (Peez et al., 2019). As a 100% removal of organic
matter from soil samples is not possible, the 1H NMR method is
unsuitable for microplastic analysis in soil samples.

A3.4.6

In-situ identification
Several attempts were undertaken to develop in-situ identification and
quantification methods. One such approach was developed by Paul et al.
(2019), who attempted to combine near-infrared (NIR) spectroscopy
(opposed to the mid-infrared range used in conventional FTIR
spectroscopy) with chemometrics to identify microplastics in soils. Nearinfrared radiation can penetrate deeper than mid-infrared radiation,
enabling analysis of particles even when coated with a thick biofilm, and
the method is generally not sensitive to water. Paul et al. (2019) were not
able to achieve a sensitive quantification of the plastic content in soil
samples. However, Corradini et al. (2019) developed a method to ‘rapidly
assess microplastic concentrations in soils without extraction’ using a
portable visible NIR spectroscope. Here the microplastic concentration is
to be estimated directly in the field, without time- and labour-consuming
extraction and detection procedures. The current low accuracy and high
detection levels are hampering the limit (which may be much higher than
realistic concentrations in natural soils), as well as the need for a training
set to accurately predict the polymer concentrations, which has to be
adapted to different soil types. Hyperspectral imaging or visible NIR
spectroscopy for microplastic analysis in environmental samples are
methods under development and have the potential for becoming rapid
automated identification methods in soil samples in the future (Corradini
et al., 2019; Karlsson et al., 2016; Serranti et al., 2018).

A3.5

Conclusion
Despite considerable efforts made and although many methods have
shown their applicability, the search for reliable, practical, robust and
Page 104 of 110

RIVM report 2021-0224

affordable methods for measuring microplastics in complex solid
matrices such as soils continues. This is not unexpected since
microplastics comprise a broad group of different synthetic polymers,
with different shapes and dimensions, which are difficult to separate
from the soil matrix. It should therefore be acknowledged that there will
be no single method that fulfils all the requirements for the
quantification of microplastics in the soil system.
Instead, one recommendation might be to combine sets of contrasting
methods, which individually do not demonstrate a fully reliable
performance, but in combination with other methods can produce a
weight of evidence for quantification.
Combinations involving sets of separation, recovery and identification
methods have also been tested and seem to be the way forward
(Ruggero et al., 2020). However, most studies are still limited to one
analytical methodology for each step. To be able to combine and
compare test results, there is a need for a harmonized protocol
describing which (set of) method(s) is/are best to use for which
purpose, with the necessary quality standards.
A3.6

Literature annex 2 and 3
Alter, H. (2005) The recovery of plastics from waste with reference to
froth flotation. Resources, Conservation & Recycling, 43(2): 119−132
Bastioli, C. (2020) Handbook of biodegradable polymers. Chapter 5.5.3.
Walter de Gruyter GmbH & Co KG
Besseling, E., Quik, J.T., Sun, M., Koelmans, A.A. (2017) Fate of nanoand microplastic in freshwater systems: A modelling study.
Environmental Pollution, 220(Pt A): 540-548
Bläsing, M., Amelung, W. (2018) Plastics in soil: analytical methods and
possible sources. Science of the Total Environment, 612: 422−435
Chamas, A., Moon, H., Zheng, J., Qiu, Y., Tabassum, T., Jang, J. H.,
Abu-Omar, M., Scott, S. L., Suh, S (2020). Degradation rates of plastics
in the environment. ACS Sustainable Chemistry and Engineering 8(9):
3494-3511
Claessens, M., Van Cauwenberghe, L., Vandegehuchte, M.B., Janssen,
C.R. (2013) New techniques for the detection of microplastics in
sediments and field collected organisms. Marine Pollution Bulletin,
70(1−2): 227−233
Coppock, R.L., Cole, M., Lindeque, P.K., Queirós, A.M., Galloway, T.S.
(2017) A small-scale, portable method for extracting microplastics from
marine sediments. Environmental Pollution, 230: 829-837
Corradini, F., Bartholomeus, H., Lwanga, E.H., Gertsen, H., Geissen, V.
(2019) Predicting soil microplastic concentration using vis-NIR
Spectroscopy. Science of the Total Environment, 650: 922−932

Page 105 of 110

RIVM report 2021-0224

Crawford, C.B., Quinn, B. (2017) Microplastic separation techniques. In
Microplastic Pollutants, pp. 203−218
Crichton, E.M., Noel, M., Gies, E.A., Ross, P.S. Novel, A. (2017) DensityIndependent and FTIR-Compatible approach for the rapid extraction of
microplastics from aquatic sediments. Analytical Methods
9 (9): 1419−1428
David, J., Steinmetz, Z., Kucerik, J., Schaumann, G.E. (2018)
Quantitative analysis of poly(ethylene terephthalate) microplastics in soil
via thermogravimetry-mass spectrometry. Analytical Chemistry
90: 8793−8799
Dümichen, E., Eisentraut, P., Bannick, C.G., Barthel, A.-K., Senz, R.,
Braun, U. (2017) Fast identification of microplastics in complex
environmental samples by a thermal degradation method.
Chemosphere, 174, pp. 572-584.
ECHA. European Chemicals Agency (2020). Committee for Risk
Assessment (RAC) Committee for Socio-economic Analysis (SEAC)
Background Document to the Opinion on the Annex XV report proposing
restrictions on intentionally added microplastics. ECHA/RAC/RES-O0000006790-71-01/F 183 pp.
https://echa.europa.eu/documents/10162/5a730193-cb17-2972-b59593084c4f39c8
Eisentraut, P., Dümichen, E., Ruhl, A. S., Jekel, M., Albrecht, M., Gehde,
M., Braun, U. (2018) Two birds with one stone – fast and simultaneous
analysis of microplastics: microparticles derived from thermoplastics and
tyre wear. Environmental Science & Technology Letters, 5(10):
608−613
Elert, A.M., Becker, R., Duemichen, E., Eisentraut, P., Falkenhagen, J.,
Sturm, H., Braun, U. (2017) comparison of different methods for mp
detection: what can we learn from them, and why asking the right
question before measurements matters? Environmental Pollution, 231:
1256−1264.
European Bioplastics. (2016). What are the required circumstances for a
compostable product to compost? https://www.europeanbioplastics.org/faq-items/what-are-the-required-circumstances-for-acompostable-product-to-compost/
Felsing, S., Kochleus, C., Buchinger, S., Brennholt, N., Stock, F.,
Reifferscheid, G. (2018) A new approach in separating microplastics
from environmental samples based on their electrostatic behaviour.
Environmental Pollution, 234: 20−28
Foekema, E M., De Gruijter, C., Mergia, M.T., Van Franeker, J.A., Murk,
A.J., Koelmans, A. A. (2013) Plastic in North Sea fish. Environmental
Science & Technology, 47: 8818−8824
Fraunholcz, N. (2004) Separation of waste plastics by froth flotation – A
review, Part I. Miner. Eng. 17:261−268
Page 106 of 110

RIVM report 2021-0224

Fries, E., Dekiff, J.H., Willmeyer, J., Nuelle, M.T., Ebert, M., Remy, D.
(2013) Identification of polymer types and additives in marine
microplastic particles using pyrolysis-GC/MS and scanning electron
microscopy. Environmental Science: Processes & Impacts 15(10):
1949−1956
Grbic, J., Nguyen, B., Guo, E., You, J.B., Sinton, D., Rochman, C.M.
(2019) Magnetic extraction of microplastics from environmental
samples. Environmental Science & Technology Letters, 6(2): 68−72
Hanvey, J.S., Lewis, P.J., Lavers, J.L., Crosbie, N D., Pozo, K., Clarke,
B.O. (2017) A review of analytical techniques for quantifying
microplastics in sediments. Analytical Methods, 9: 1369−1383
Hidalgo-Ruz, V., Gutow, L., Thompson, R. C., Thiel, M. (2012)
Microplastics in the marine environment: a review of the methods used
for identification and quantification. Environmental Science &
Technology, 46(6): 3060−3075
Hu, B. (2014) Thesis: Magnetic Density Separation of Polyolefin Wastes,
DOI: 10.4233/uuid:0c3717fa-8000-4de0-a938-d65605bf2a96.
https://doi.org/10.4233/uuid:0c3717fa-8000-4de0-a938-d65605bf2a96
Huppertsberg, S., Knepper, T. P. (2018) Instrumental analysis of
microplastics: benefits and challenges. Analytical and Bioanalytical
Chemistry, 410(25): 6343−6352
Hurley, R.R., Lusher, A.L., Olsen, M., Nizzetto, L. (2018) Validation of a
method for extracting microplastics from complex, organic-rich,
environmental matrices. Environmental Science & Technology, 52:
7409-7417
Imhof, H.K., Schmid, J., Niessner, R., Ivleva, N.P., Laforsch, C. (2012) A
novel, highly efficient method for the separation and quantification of
plastic particles in sediments of aquatic environments. Limnology and
Oceanography: Methods 10(7): 524−537
Käppler, A., Fischer, D., Oberbeckmann, S., Schernewski, G., Labrenz,
M., Eichhorn, K. J., & Voit, B. (2016) Analysis of environmental
microplastics by vibrational microspectroscopy: FTIR, Raman or Both?
Analytical and Bioanalytical Chemistry, 408(29): 8377−8391
Karlsson, T. M., Grahn, H., Van Bavel, B., Geladi, P. (2016)
Hyperspectral imaging and data analysis for detecting and determining
plastic contamination in seawater filtrates. Journal of Near Infrared
Spectroscopy, 24(2): 141−149
Kedzierski, M., Le Tilly, V., Bourseau, P., Bellegou, H., César, G., Sire,
O., Bruzaud, S. (2016) Microplastics elutriation from sandy sediments: A
granulometric approach. Marine Pollution Bulletin 107(1): 315-323
Lares, M., Ncibi, M.C. (2018) Occurrence, identification and removal of
microplastic particles and fibres in conventional activated sludge process
and advanced MBR technology. Water Research, 133:236–246
Page 107 of 110

RIVM report 2021-0224

Li, Q., Wu, J., Zhao, X., Gu, X., Ji, R. (2019) Separation and
identification of microplastics from soil and sewage sludge.
Environmental Pollution, 254: art.no. 113076
Li, J., Song, Y., Cai, Y. (2020a) Focus topics on microplastics in soil:
Analytical methods, occurrence, transport, and ecological risks.
Environmental Pollution 257: art.no. 113570
Li, W., Wufuer, R., Duo, J., Wang, S., Luo, Y., Zhang, D., Pan, X.
(2020b). Microplastics in agricultural soils: extraction and
characterization after different periods of polythene film mulching in an
arid region. Science of the Total Environment, 749: art.no. 141420
Liebezeit, G., Dubaish, F. (2012) Microplastics in beaches of the east
Frisian islands Spiekeroog and Kachelotplate. Bulletin of Environmental
Contamination and Toxicology, 89(1): 213−217
Liu, M., Song, Y., Lu, S., Qiu, R., Hu, J., Li, X., Bigalke, M., Shi, H., He,
D. (2019) A method for extracting soil microplastics through circulation
of sodium bromide solutions. Science of the Total Environment, 691:
341−347
Löder, M.G., Imhof, H K., Ladehoff, M., Löschel, L.A., Lorenz, C.,
Mintenig, S., Piehl, S., Primpke, S., Schrank, I., Laforsch, C., Gerdts, G.
(2017) Enzymatic Purification of Microplastics in Environmental Samples.
Environmental Science & Technology, 51(24): 14283−14292.
Maes, T., Van der Meulen, M.D., Devriese, L.I., Leslie, H.A., Huvet, A.,
Frère, L., Robbens, J., Vethaak, A.D. (2017) Microplastics baseline
surveys at the water surface and in sediments of the North-East
Atlantic. Frontiers in Marine Science 4 (May): art.no. 135
Majewsky, M., Bitter, H., Eiche, E., Horn, H. (2016) Determination of
microplastic polyethylene (pe) and polypropylene (pp) in environmental
samples using thermal analysis (TGA-DSC). Science of the Total
Environment, 568: 507−511
Mani, T., Frehland, S., Kalberer, A., Burkhardt-Holm, P. (2019) Using
castor oil to separate microplastics from four different environmental
matrices. Analytical Methods 11: 1788−1794
Marques, G.A., Tenório, J.A.S. (2000) Use of Froth Flotation to separate
PVC/PET mixtures. Waste Management, 20(4): 265−269
Meesters, J.A.J., Koelmans, A.A., Quik, J.T.K., Hendriks, A.J., van de
Meent, D. (2014) Multimedia Modelling of Engineered Nanoparticles with
SimpleBox4nano: Model Definition and Evaluation. Environmental
Science & Technology 48, 5726-5736
Möller, J.N., Löder, M.G.J., Laforsch, C. (2020) Finding Microplastics in
Soils: A Review of Analytical Methods. Environmental Science &
Technology, 54: 2078−2090

Page 108 of 110

RIVM report 2021-0224

Nuelle, M.T., Dekiff, J.H., Remy, D., Fries, E. (2014) A new analytical
approach for monitoring microplastics in marine sediments.
Environmental Pollution, 184: 161−169
Pansu, M., Gautheyrou, J. (2006) Handbook of soil analysis:
mineralogical, organic and inorganic methods. Springer Berlin
Heidelberg, DOI: 10.1007/978-3-540-31211-6
Paul, A., Wander, L., Becker, R., Goedecke, C., Braun, U. (2019) Highthroughput NIR spectroscopic (NIRS) detection of microplastics in soil.
Environmental Science and Pollution Research 26(8): 7364-7374
Peez, N., Janiska, M., Imhof, W. (2019) The first application of
quantitative 1 h nmr spectroscopy as a simple and fast method of
identification and quantification of microplastic particles (PE, PET, and
PS). Analytical and Bioanalytical Chemistry, 411(4): 823−833
Quinn, B., Murphy, F., Ewins, C. (2017) Validation of density separation
for the rapid recovery of microplastics from sediment. Analytical
Methods 9(9): 1491-1498
Renner, G., Schmidt, T. C., Schram, J. (2017) Characterization and
quantification of microplastics by Infrared Spectroscopy. Comprehensive
Analytical Chemistry, 75: 67−118
Ruggero, F., Gori, R., Lubello, C. (2020) Methodologies for microplastics
recovery and identification in heterogeneous solid matrices: A review.
Journal of Polymers and the Environment 28(3): 739-748
Schmidt, L.K., Bochow, M., Imhof, H.K., Oswald, S.E. (2018) MultiTemporal surveys for microplastic particles enabled by a novel and fast
application of SWIR imaging spectroscopy − Study of an urban
watercourse traversing the city of Berlin, Germany. Environmental
Pollution, 239: 579−589
Serranti, S., Palmieri, R., Bonifazi, G., Cozar, A. (2018) Characterization
of microplastic litter from oceans by an innovative approach based on
hyperspectral imaging. Waste Management, 76: 117−125
Standards Australia (2010) Australian Standard® – Biodegradable
plastics—Biodegradable plastics suitable for home composting, p. 16
Thompson, R.C., Olson, Y., Mitchell, R.P., Davis, A., Rowland, S.J., John,
A.W.G., McGonigle, D., Russell, A.E. (2004) Lost at sea: where is all the
plastic? Science 304(5672): 838
TUV Austria (2019) OK COMPOST HOME – CERTIFICATION – Home
compostability of products, p. 15
Wang, Z., Taylor, S.E., Sharma, P., Flury, M. (2018) Poor extraction
efficiencies of polystyrene nano- and microplastics from biosolids and
soil. PLoS ONE 13(11): art. no. e0208009

Page 109 of 110

RIVM report 2021-0224

Zhao, S., Danley, M., Ward, J.E., Li, D., Mincer, T.J. (2017) An Approach
for extraction, characterization and quantitation of microplastic in
natural marine snow using Raman microscopy. Analytical Methods, 9(9):
1470−1478
Zhang, G.S., Liu, Y.F. (2018) The Distribution of Microplastics in Soil
Aggregate Fractions in Southwestern China. Science of the Total
Environment, 642: 12−20.
Zhang, S., Yang, X., Gertsen, H., Peters, P., Salánki, T., Geissen, V.
(2018) A simple method for the extraction and identification of light
density microplastics from soil. Science of the Total Environment,
616−617: 1056−1065
Zobkov, M.B., Esiukova, E.E. (2017) Evaluation of the Munich Plastic
Sediment Separator efficiency in extraction of microplastics from natural
marine bottom sediments. Limnology and Oceanography: Methods,
15(11): 967-978

Page 110 of 110

RIVM
Committed to health and sustainability ­