Proposed Definition of Microplastics
in Drinking Water
TABLE OF CONTENTSPROPOSED DEFINITION OF ‘MICROPLASTICS IN DRINKING WATER’* .................................... 2
EXECUTIVE SUMMARY .................................................................................................... 3
CURRENT DEFINITIONS OF MICROPLASTICS AND RELATED ITEMS IN REGULATORY AGENCIES..................................................................................................................................... 7
California Natural Resources Agency: Ocean Protection Council ............................ 8
California Environmental Protection Agency: State Water Resources; Control Board
Division of Water Quality .......................................................................................... 8
California Environmental Protection Agency: Department of Toxic Substances
Control ..................................................................................................................... 8
United States Environmental Protection Agency ...................................................... 9
National Oceanic and Atmospheric Administration .................................................. 9
European Marine Strategy Framework Directive...................................................... 9International Joint Group of Experts on the Scientific Aspects of Marine
Environmental Protection ......................................................................................... 9
European Chemicals Agency ................................................................................... 9
RATIONALE FOR DEFINING CRITERIA .............................................................................. 13
Defining Criteria: Substance .................................................................................. 13
Exclusions .......................................................................................................... 18
Defining Criteria: State ........................................................................................... 18
Defining Criteria: Dimensions ................................................................................. 19
Non-defining Criteria: Morphology and Color ......................................................... 21
Non-criteria: Solubility ............................................................................................ 22
PLASTIC-ASSOCIATED CHEMICALS REGULATED IN DRINKING WATER IN CALIFORNIA ............ 23
REFERENCES ............................................................................................................... 25
Contact Information:
Scott Coffin, Ph.D.
Research Scientist III
Regulatory Development Unit, Division of Drinking Water
State Water Resources Control Board
Scott.Coffin@waterboards.ca.gov

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PROPOSED DEFINITION OF ‘MICROPLASTICS IN DRINKING WATER’

Proposed Definition of ‘Microplastics in Drinking Water’*‘Microplastics in Drinking Water’ are defined as solid1 polymeric materials2 to which
chemical additives or other substances may have been added, which are particles2
which have at least two dimensions that are greater than 1 and less than 5,000
micrometers (µm). Polymers that are derived in nature that have not been chemicallymodified (other than by hydrolysis) are excluded.
*Evidence concerning the toxicity and exposure of humans to microplastics is nascentand rapidly evolving, and the proposed definition of ‘Microplastics in Drinking Water’ issubject to change in response to new information. The definition may also change in
response to advances in analytical techniques and/or the standardization of analyticalmethods.

1‘Solid’ means a substance or mixture which does not meet the definitions of liquid orgas.
‘Liquid’ means a substance or mixture which (i) at 50 degrees Celsius (˚C) has a vapor
pressure less than or equal to 300 kPa; (ii) is not completely gaseous at 20 ˚C and at astandard pressure of 101.3 kPa; and (iii) which has a melting point or initial melting point
greater than 20 ˚C at a standard pressure of 101.3 kPa.
‘Gas’ means a substance which (i) at 50 ˚C has a vapor pressure greater than 300 kPa(absolute); or (ii) is completely gaseous at 20 ˚C at a standard pressure of 101.3 kPa.
2
‘Polymeric material’ means either (i) a particle of any composition with a continuous
polymer surface coating of any thickness, or (ii) a particle of any composition with asynthetic polymer content of greater than or equal to 1% by mass.
‘Particle’ means a minute piece of matter with defined physical boundaries; a defined
physical boundary is an interface.
‘Polymer’ means a substance consisting of molecules characterized by the sequence of
one or more types of monomer units. Such molecules must be distributed over a rangeof molecular weights wherein differences in the molecular weight are primarily
attributable to differences in the number of monomer units. A polymer comprises thefollowing: (a) a simple weight majority of molecules containing at least three monomer
units which are covalently bound to at least one other monomer unit or other reactant;(b) less than a simple weight majority of molecules of the same molecular weight.
‘Monomer unit’ means the reacted form of a monomer substance in a polymer.
‘Monomer’ means a substance which is capable of forming covalent bonds with asequence of additional like or unlike molecules under the conditions of the relevant
polymer-forming reaction used for the particular process.
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Executive Summary
Health and Safety Code (HSC) section 116376 requires the State Water Resources
Control Board (State Water Board) to adopt a definition of microplastics in drinking
water on or before July 1, 2020. The adopted definition will be used in successive
regulatory efforts concerning microplastics in drinking water as required by HSC
116376. Although the State Water Board will be the first regulatory agency in the world
to specifically define ’Microplastics in Drinking Water’, other governmental agencies
have defined ‘microplastics’ in other contexts, including the European Chemicals
Agency (ECHA), which has recently proposed a definition related to intentional uses of‘microplastics’ (European Chemicals Agency 2019).
Evidence concerning the hazards and exposure of humans to ‘microplastics’ is nascentand rapidly evolving, and currently no standardized methods for the detection of‘microplastics’ exist. Accordingly, the proposed definition of ’Microplastics in Drinking
Water’ is subject to change in response to new information. With respect to publichealth, hazards of microplastics in humans is poorly understood (World HealthOrganization 2019). Three primary routes of exposure of humans to microplastics are
known – air, food and water (Zhang et al. 2020). However, the relative magnitude of
exposure from these and other sources are not fully understood and may varysignificantly between individuals and groups (Zhang et al. 2020). Few studies havemeasured microplastics in drinking water, and available information indicatesgroundwater wells are likely to contain very low (if any) levels of microplastics (Mintenig
et al. 2019), however surface water sources are known to contain microplastics at highdetection frequencies, and at a range of levels (Eerkes-Medrano, Leslie, and Quinn2019). Additionally, test methods are in early stages of development.
The following criteria must all be satisfied to define a particle as ’Microplastics in
Drinking Water’: substance, state, and dimensions. Additional characteristics should berecorded in the characterization of ’Microplastics in Drinking Water’, including
morphology and color, but are not critical to the definition. The proposed definition of’Microplastics in Drinking Water’ is based on the definition of ‘microplastics’ proposed by
ECHA (2019), however with a few notable differences in dimensions, and substance.
The substance criterion is based on the substance criterion in the proposed definition of‘microplastics’ by ECHA (2019) with one exception: ‘biodegradable polymers’ arespecifically excluded by ECHA, whereas no such exclusion is included here. The
proposed definition of ’Microplastics in Drinking Water’ does not exclude biodegradable
polymers due to (i) the lack of adopted standards within the State Water Board todetermine biodegradability and (ii) uncertainties regarding the human health effects ofbiodegradable polymers. Currently, the proposed definition of ’Microplastics in Drinking
Water’ excludes “polymers that are derived in nature that have not been chemicallymodified (other than by hydrolysis).” Examples of such natural polymers include
cellulose, natural rubber, DNA, proteins, wool, and silk. Substance criteria for a

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microplastic particle is defined principally as being ‘polymeric material’3, and includes
synthetic polymer composites, co-polymers, modified natural polymers (i.e. synthetic
polymer-encapsulated natural polymers or natural polymers with synthetic polymer
content greater than or equal to 1% by mass). Additionally, particles comprised of<99% additives are included4.
The state criterion considers the practicality of measuring particles5 that are ‘solid’ atroom temperature (20 ˚C) and standard pressure (101.3 kPa). The Globally
Harmonized System for Classification and Labelling of Chemicals (GHS) considers
melting temperature (Tm) a defining criterion for solids and liquids. Some polymers(e.g. amorphous polymers) lack a specific Tm or may have a Tm above 20 ˚C but have a
glass transition temperature (TG) below 20 ˚C and would therefore behave in many
regards as a “solid” but may be classified as “semi-solid”. For these reasons, ‘solid’ isdefined as a substance or mixture which does not meet the definitions of liquid6 or gas7
and would therefore include such ‘semi-solid’ polymers. This criterion is identical to thestate criterion in the definition of ‘microplastics’ proposed by ECHA (2019).
The dimensions8 criterion in the proposed ‘definition of microplastics in drinking water’ isbased on considerations of health hazards, other existing regulations, and current andanticipated analytical technical feasibilities. Current toxicological knowledge suggeststhat smaller particles are more hazardous. However, below the lower size limit of 1 µm,
particles may not be characterized directly using light-based microscopy, thus requiring
fundamentally different techniques and instrumentation. The upper size limit of 5 mmcorresponds with the lower size limit for the requirement of particle filtration by “fullcapture systems” in storm drains as required by the Water Quality Control Plan for
Ocean Waters of California, and thus representing a de facto upper dimensions limited
regulatory definition for “trash” by the State Water Board. Further, the upper size limit
matches the upper size limit in the ‘microplastic’ definition proposed by ECHA, with the3‘Polymeric material’ means either (i) a particle of any composition with a continuous
polymer surface coating of any thickness, or (ii) a particle of any composition with asynthetic polymer content of greater than or equal to 1% by mass.
4
According to the definition, “…to which additives or other substances may have been
added…”.
5
Particle is defined as a minute piece of matter with defined physical boundaries; adefined physical boundary is an interface (ECHA 2019).
6‘Liquid’ means a substance or mixture which (i) at 50 degrees Celsius (˚C) has a vapor
pressure less than or equal to 300 kPa; (ii) is not completely gaseous at 20 ˚C and at astandard pressure of 101.3 kPa; and (iii) which has a melting point or initial melting point
greater than 20 ˚C at a standard pressure of 101.3 kPa.
7
‘Gas’ means a substance which (i) at 50 ˚C has a vapor pressure greater than 300
kPa (absolute); or (ii) is completely gaseous at 20 ˚C at a standard pressure of 101.3
kPa.
8“…have at least two dimensions greater than 1 and less than 5,000 micrometers(µm)…”
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exception that ECHA includes an additional size criteria for “fibres”. The requirementthat two dimensions meet threshold criteria would exclude fibers and films that may
have dimensions longer than 5 mm.
A criterion for solubility is not included. This omission is congruous with the ECHA
definition of ‘microplastics’ (2019), despite the inclusion in previous definitions and otherrecommendations (Hartmann et al. 2019; COM 2017). The omission of solubility criteria
in the proposed definition of ’Microplastics in Drinking Water’ is intentional andacknowledges that limited toxicological information is available for soluble polymers,
and that such polymers may be found in ‘solid’ form in water through agglomeration withother particles and other mechanisms (Arp and Knutsen 2019).

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Background
The State Water Board is responsible for the administration of provisions related todrinking water to protect public health. The California Safe Drinking Water Act (SDWA)
authorizes the State Water Board to conduct research, studies, and demonstration
programs to ensure provision of a dependable, safe supply of drinking water, which may
include improving methods to identify and measure the existence of contaminants indrinking water and the source of the contaminants (California Code of Regulations[CCR] 1996). The SDWA also grants the State Water Board the authority to implement
regulations that may include monitoring of contaminants and requirements for notifying
the public of the quality of the water delivered to customers (CCR 1996).
On September 28, 2018, Senate Bill No. 1422 was filed with the Secretary of State,adding section 116376 to California’s Health and Safety Code (HSC), and requiring theState Water Board to adopt a definition of ’Microplastics in Drinking Water’ on or before
July 1, 2020. HSC section 116376 also requires the State Water Board on or before
July 1, 2021, to accomplish the following:(1) adopt a standard methodology to be used in the testing of drinking water for
microplastics;(2) adopt requirements for four (4) years of testing and reporting of microplastics indrinking water, including public disclosure of those results;(3) consider issuing a notification level or other guidance to aid consumer interpretationof results; and(4) accredit qualified California laboratories to analyze microplastics.
HSC section 116376 allows the State Water Board to implement these requirements
through adoption of a Policy Handbook.
On January 31, 2020, the State Water Board submitted the proposed definition of
microplastics in drinking water to the Southern California Coastal Water Research
Project (SCCWRP), who then facilitated a peer review of the scientific basis of thedefinition through an external panel of experts. Following the formal adoption of thedefinition by the State Water Board on or before July 1, 2020, the proposed definition
may be re-evaluated in response to new information and may be further reviewed byadditional expert panels.
To date, there is no universally agreed-upon definition for “microplastics” (GESAMP2019). Few studies are available regarding human exposure and health hazards ofplastic particles, and significant data gaps remain (World Health Organization 2019).
Plastic particles are a diverse contaminant suite and may be differentiated by a varietyof criteria such as substance, state at a given temperature and pressure (e.g., solid atroom temperature and standard pressure), dimensions, shape and structure(morphology), and color (Rochman et al. 2019). The influence of these parameters in
the environmental fate, transport, and human health impacts of microplastics are notfully understood. To prioritize the protection of public health in light of the significant

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PROPOSED DEFINITION OF ‘MICROPLASTICS IN DRINKING WATER’scientific uncertainties, the ’Microplastics in Drinking Water’ should be defined broadly,
and with as few exclusions as possible, to ensure that policies, regulations, andstandardized methodologies based on the definition capture a wide diversity of plastic
particle types. Furthermore, while technological limitations in the measurement ofplastic particles may be informative to a regulatory definition, it should be observed thatsuch limitations are likely transient and serve only as a rough guide for prospective
technical and economic feasibility of sampling and monitoring.

Current Definitions of Microplastics and Related Items in Regulatory
Agencies
The term “microplastics” has been defined by several national and international
regulatory agencies and scientific bodies in varying contexts. Some agencies use theterm “microplastics” in reports, yet do not include a definition. Additionally, someagencies define related items, such as trash, marine debris, microfibers, etc. Most
agencies’ definitions of “microplastics” include criteria for dimensions, however few
include criteria for substance or state.
Staff have reviewed the work in this regard of other state and federal agencies as wellas other organizations and agencies. Highlight of the work of the following
organizations is provided below:
1. California Natural Resources Agency: Ocean Protection Council
2. California Environmental Protection Agency: State Water Resources; Control
Board Division of Water Quality
3. California Environmental Protection Agency: Department of Toxic Substances
Control
4. United States Environmental Protection Agency
5. National Oceanic and Atmospheric Administration
6. European Marine Strategy Framework Directive
7. International Joint Group of Experts on the Scientific Aspects of Marine
Environmental Protection
8. European Chemicals Agency

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PROPOSED DEFINITION OF ‘MICROPLASTICS IN DRINKING WATER’California Natural Resources Agency: Ocean Protection Council
The Ocean Protection Council (OPC), in collaboration with the National Oceanicand Atmospheric Administration (NOAA) and Sea Grant California, define microplastics
as “materials smaller than 5 mm” in a 2018 report on the California Ocean Litter
Prevention Strategy (OPC and NOAA 2018). The OPC is mandated by Public
Resources Code 35635 to develop and implement a Statewide Microplastics Strategy(California Code of Regulations 2018b); however, no further criteria (e.g. substance,state, solubility, lower dimensions limit, etc.) for the definition of microplastics areprovided in the statute or in additional OPC reports (Holly Wyer, personalcommunication, October 31, 2019).

California Environmental Protection Agency: State Water Resources;
Control Board Division of Water Quality“Microplastics and microfibers” are identified as an issue that may be addressedin coming years in the Final Staff Report of the State Water Board’s 2019 Review of theWater Quality Control Plan for Ocean Waters of California (Ocean Plan), which includes
a non-regulatory description of microplastics as, “…a variety of both types and forms ofplastic” (Dolan et al. 2019). The State Water Board-adopted 2019 Review of the Ocean
Plan does not include “microplastics” as a priority issue (State Water Board 2019).
In 2015, the State Water Resources Control Board adopted an Amendment to
the Water Quality Control Plan for Ocean Waters of California to Control Trash (“TheTrash Provisions”), and defines water quality objectives for trash, which is defined as
all improperly discarded solid material from any production, manufacturing, orprocessing operation, including, but not limited to, products, product packaging,or containers constructed of plastic, steel, aluminum, glass, paper, or othersynthetic or natural materials. (State Water Board 2016b)
Based on the understanding that small particles are difficult to remove from theenvironment, the State Water Board’s definition of trash specifically does not include
criteria for dimensions (State Water Board 2016b). However, included in the Trash
Provisions is the requirement to implement a “full capture system” that, “…traps all
particles that are 5 mm or greater” (State Water Board 2016a), thus effectively leaving a
regulatory gap for trash that falls below this size limit.

California Environmental Protection Agency: Department of Toxic
Substances Control
The Department of Toxic Substances Control (DTSC) does not specificallydescribe “microplastics” or a related term; however, DTSC observes particle sizes andfiber sizes as hazard traits:(a) The particle dimensions or fiber dimension hazard trait is defined as theexistence of a chemical substance in the form of small particles or fibers or the

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PROPOSED DEFINITION OF ‘MICROPLASTICS IN DRINKING WATER’propensity to form into such small-sized particles or fibers with use orenvironmental release.
(b) Evidence for the particle dimensions or fiber dimension hazard trait includes,
but is not limited to: measures of particle dimensions less than or equal to 10
micrometers in mass median aerodynamic diameter for inhalation exposure, orless than 10 micrometers in any dimension for dermal or ingestion exposure, or
fibers with a 3:1 aspect ratio and a width less than or equal to 3 micrometers.(22CCR § 69405.7. Particle Size or Fiber Dimension 2011, 7)

United States Environmental Protection Agency
The United States Environmental Protection Agency (U.S. EPA) defines microplastics
broadly as “plastic particles <5 mm in dimensions in any one dimension” (Murphy 2017).

National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration (NOAA) defines microplastics as“plastic particles smaller than 5mm” (Courtney Arthur, Baker, and Bamford 2008). Thismaximum size was chosen based on possible ecological effects other than physicalblockage of gastrointestinal tracts (Courtney Arthur, Baker, and Bamford 2008).

European Marine Strategy Framework Directive
A report published in 2013 by the European Marine Strategy Framework Directive(MFSD) Working Group on Good Environmental Status defines plastic litter into four
dimensions classes based on biological relevance and analytical limitations:macroplastics (>25 mm), mesoplastics (5 to 25 mm), large microplastics (1 to 5 mm),and small microplastics (20 µm to 1 mm) (Institute for Environment and Sustainability(Joint Research Centre) , MSFD Technical Subgroup on Marine Litter 2013). The
MFSD rationalizes separating microplastics into two subfractions (small and large) due
to the relative ease of separating and quantifying visually recognizable 1-5 mm particles
compared to the more technically challenging aspects of particles between 20 µm and
1 mm (Institute for Environment and Sustainability (Joint Research Centre) , MSFD
Technical Subgroup on Marine Litter 2013).

International Joint Group of Experts on the Scientific Aspects ofMarine Environmental Protection
Microplastics are defined by the International Joint Group of Experts on the Scientific
Aspects of Marine Environmental Protection (GESAMP) as “plastic particles < 5 mm indiameter, which include particles in the nano-dimensions range (1 nm)” (GESAMP2019). No apparent state or substance criteria are included.

European Chemicals Agency
In 2017, the European Commission requested the European Chemicals Agency(ECHA), an agency which manages the technical and administrative aspects of theimplementation of Registration, Evaluation, Authorisation and Restriction of Chemicals(REACH), to develop a restriction proposal for the intentional uses of microplastics inPage | 9

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PROPOSED DEFINITION OF ‘MICROPLASTICS IN DRINKING WATER’consumer products9, which ECHA then defined as “synthetic water-insoluble polymersof 5mm or less in any dimension” (COM 2017). In March 2018 ECHA adopted an
updated working definition for ‘microplastics’: “any polymer or polymer-containing, solidor semi-solid particle having a size of 5mm or less in at least one external dimension”(ECHA 2018). In all versions of ECHA’s definitions of ‘microplastics’, ‘polymer’ isdefined according to the REACH definition for polymers (REACH 2006).
After requesting and reviewing stakeholder input on the March 2018 working definitionof ‘microplastics,’ ECHA proposed a revised definition for ‘microplastics’ in August 2019
(European Chemicals Agency 2019). The proposed definition follows a similar
approach to the definition presented by Hartmann et al. (2019), and includes four
criteria which must all be met, including substance, state, morphology, and dimensions(European Chemicals Agency 2019). In the proposed definition, ECHA defines‘microplastics’ as:
A material consisting of solid polymer-containing particles, to which additives orother substances may have been added, and where ≥ 1% w/w of particles have(i) all dimensions 1nm ≤ x ≤ 5mm, or (ii), for fibres, a length of 3nm ≤ x ≤ 15mm
and length to diameter ratio of >3. Polymers that occur in nature that have notbeen chemically modified (other than by hydrolysis) are excluded, as arepolymers that are (bio)degradable. (European Chemicals Agency 2019)
Where ‘polymer’ is defined in Article 3(5) of Regulation (EC) No 1907/2006 (REACH)as:
A substance consisting of molecules characterised by the sequence of one ormore types of monomer units. Such molecules must be distributed over a rangeof molecular weights wherein differences in the molecular weight are primarily
attributable to differences in the number of monomer units. A polymer comprises
the following:(a) a simple weight majority of molecules containing at least three monomer
units which are covalently bound to at least one other monomer unit or otherreactant;(b) less than a simple weight majority of molecules of the same molecular weight.
In the context of this definition a ‘monomer unit’ means the reacted form of amonomer substance in a polymer;
monomer: means a substance which is capable of forming covalent bonds with asequence of additional like or unlike molecules under the conditions of therelevant polymer-forming reaction used for the particular process. (REACH 2006)9

To the knowledge of the State Water Board, REACH has not adopted a definition for‘microplastics’ specifically in the context of drinking water or other environmental
matrices, and that the proposed definition of ‘microplastics’ by ECHA mentioned within
this report is meant to apply to the intentional uses of microplastics in consumer
products (European Chemicals Agency 2019).
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PROPOSED DEFINITION OF ‘MICROPLASTICS IN DRINKING WATER’and‘Particle’ is defined as, “a minute piece of matter with defined physicalboundaries; a defined physical boundary is an interface”;‘Polymer-containing particle’ means “either(i) a particle of any composition with a continuous polymer surface coating of any
thickness; or(ii) a particle of any composition with a polymer content of ≥ 1% w/w”;‘Solid’ means, “a substance or a mixture which does not meet the definitions ofliquid or gas”;‘Gas’ means, “a substance which(i) at 50 ˚C has a vapour pressure greater than 300 kPa (absolute); or(ii) is completely gaseous at 20 ˚C at a standard pressure of 101.3 kPa;
‘Liquid’ means, “a substance or mixture which(i) at 50 ˚C has a vapour pressure of not more than 300 kPa (3 bar);(ii) is not completely gaseous at 20 ˚C and at a standard pressure of 101.3 kPa;and(iii) which has a melting point or initial melting point of 20 ˚C or less at a standard
pressure of 101.3 kPa.” (European Chemicals Agency 2019)
Note that the August 2019 proposed definition of ‘microplastics’ by ECHA does notinclude any explicit state-defining criteria for polymers that lack melting points (i.e.
amorphous polymers) other than that such polymers would fall under the definition of‘solid’ based on their inability to fit the definition of either ‘liquid’ or ‘gas.’ In contrast, theearlier, March 2018 working definition of ‘microplastics’ state criteria include specificcriteria for particles that are either “solid or semi-solid”, whereby:
The ‘solid’ form of a polymer in the environment (at ambient temperature andpressure of 101.3 kPa) may, for example, be defined via a melting point above
20 °C (includes waxes). Thermosetting plastics, however, will decompose rather
than melt above 20 °C.
‘Semi-solid’ refers to a material which is in a physical state between a solid and aliquid. A polymer can, for example, be defined to be a semi-solid when its
melting point (at ambient temperature and pressure of 101.3 kPa) is above 20 °C
and its glass transition temperature is below 20 °C. (European Chemicals
Agency 2019; ECHA 2018)
These definitions for ‘solid’ and ‘semi-solid’ were based upon the GHS definitions forsolids and liquids, which utilize Tm as a defining threshold. Since some polymers (e.g.
amorphous polymers) lack a specific Tm or may have a Tm above 20 ˚C but have a TG
below 20 ˚C, they would behave in many regards like a “solid” but could be classified asa “semi-solid”. In the August 2019 proposed definition, ECHA revised the state criteriasuch that ‘solid’ is defined as “a substance or mixture which does not meet the

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definitions of liquid or gas”10 and would therefore include such “semi-solid” polymers.
Although the August 2019 ECHA definition of “solid” does not depend on more explicit
defining properties suggested by Hartmann et al. to classify state, such as “TG, viscosity,
modulus of elasticity, or tension at constant elongation” (2019), the state criteria is likely
to be highly inclusive of particle diversities while remaining technically feasible.
ECHA acknowledges that conventional threshold-based risk assessments cannot be
reliably conducted for microplastics due to an insufficient amount of information;
therefore, it has defined microplastics based on dimensions and persistence, which areclassified as persistent, bioaccumulating and toxic (PBT) and/or very persistent andvery bioaccumulating (vPvB) (European Chemicals Agency 2019).Therefore, naturally
occurring polymers that have not been chemically modified (other than by hydrolysis),and “biodegradable” polymers are excluded from their proposed definition of‘microplastics’ (European Chemicals Agency 2019). In the ECHA definition of‘microplastics’, criteria for the demonstration of biodegradation of microplastics areincluded, in which several standardized test methods are recommended (European
Chemicals Agency 2019). ECHA acknowledges that commonly used plastics do notdegrade rapidly or primarily through biological mechanisms, rather under photooxidationor hydrolysis, resulting in extremely long resistance time in the environment (decades tohundreds of years) (European Chemicals Agency 2019; Duis and Coors 2016; Klein etal. 2018). ECHA further cites that although some plastics are available which rapidly
biodegrade, such as PHBV (66-88% mineralization after 28 days using a modified
standardized method) (McDonough et al. 2017), there is a high variability in thebiodegradation potential of different types of plastic in the environment (European
Chemicals Agency 2019).
ECHA included solubility criteria in a previous working definition of ‘microplastics’, suchthat only “water-insoluble” were included (COM 2017). ECHA has since removed
solubility criteria from subsequent working and proposed definitions, despite critiquesthat solubility parameters are important for risk assessment, that soluble polymers “donot contribute to the microplastics concern”, and analytical techniques may not detectcertain soluble polymers (ECHA 2018; European Chemicals Agency 2019). ECHA’s
rationale for the removal of solubility criteria is explained in a response to these
critiques:
Whilst soluble polymers may be considered as not contributing to the‘microplastic’ concern, this is not equivalent to a conclusion that they do not pose
any risk to the environment….However, we need to explore if appropriate
10

Where liquid’ means a substance or mixture which (i) at 50 degrees Celsius (˚C) has
a vapor pressure less than or equal to 300 kPa; (ii) is not completely gaseous at 20 ˚Cand at a standard pressure of 101.3 kPa; and (iii) which has a melting point or initial
melting point greater than 20 ˚C at a standard pressure of 101.3 kPa.
‘Gas’ means a substance which (i) at 50 ˚C has a vapor pressure greater than 300 kPa(absolute); or (ii) is completely gaseous at 20 ˚C at a standard pressure of 101.3 kPa.
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PROPOSED DEFINITION OF ‘MICROPLASTICS IN DRINKING WATER’standard methods are available and whether there should be threshold (cut-off)values for demonstrating solubility. (ECHA 2018)
The restriction proposal dossier for the intentional uses of microplastics in consumer
products was open to public consultation from March to September 2019. The dossier
is expected to be submitted to the European Commission in spring 2020, who will thendecide whether to amend REACH’s regulations with the proposed restrictions andformally adopt the proposed definition of ‘microplastics’ in the context of intentionallyadded microplastics in products (European Commission 2019).

Rationale for Defining Criteria
Defining Criteria: Substance
The substance of plastic is a fundamental defining characteristic for a definition of‘microplastics’; however varying threshold criteria exist within research and regulatory
agencies. For instance, according to the ISO, plastic is a “material which contains as an
essential ingredient a high molecular weight polymer and which, at some stage in its
processing into finished products, can be shaped by flow” (ISO 2013). (ISO 2013).
Similar to the ISO definition, ASTM International defines ‘plastic(s)’ as, “a material that
contains as an essential ingredient one or more organic polymeric substances of large
molecular weight, is solid in its finished state, and at some stage in its manufacture orprocessing into finished articles, can be shaped be flow…rubber, textiles, adhesives,and paint, which may in some cases meet this definition, are not considered plastics…”(ASTM 2020). ECHA (2019) critiques the ISO definition of ‘plastic’ for its dependence onterms which are not defined by ISO nor are universally accepted or standardized (i.e.,‘material’, ‘high molecular weight polymer’, and “shaped by flow”). Further, the ISO
definition of ‘plastic’ has been criticized for being too narrow, as while it would include
common, high-production classes of polymers such as thermoplastics and thermosets,some elastomers (e.g. anthropogenic rubbers) would be excluded (Hartmann et al.
2019). The ASTM definition is more narrow than the ISO definition due to their explicit
exclusion of rubber, textiles, adhesives, and paint (ASTM 2020).
‘Polymer’ is a fundamental term in the ISO definition of ‘plastic,’ although it lacks adiscrete, robust definition by ISO. Alternatively, a widely accepted definition for‘polymer’ is defined by IUPAC as; “molecule of high relative molecular mass, thestructure of which essentially comprises the multiple repetition of units derived, actuallyor conceptually, from molecules of low relative molecular mass” (IUPAC 2008).
Typically, anthropogenic polymers are created with a molecular mass >10,000 g mol-1(Lechner et al. 2003) resulting in a high likelihood for most polymers to be least 1 µm in
one dimension. The IUPAC definition of ‘polymer’ is relatively widely inclusive, andwould include copolymers, which are produced from “more than one species ofmonomer” (IUPAC 2008). Yet, an even more inclusive definition of ‘polymer’ is definedby REACH and used in the definition of ‘microplastics’ proposed by ECHA (2019):‘Polymer’ means a substance consisting of molecules characterized by thesequence of one or more types of monomer units. Such molecules must be
distributed over a range of molecular weights wherein differences in the

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molecular weight are primarily attributable to differences in the number ofmonomer units. A polymer comprises the following:(a) a simple weight majority of molecules containing at least three monomer units
which are covalently bound to at least one other monomer unit or other reactant;(b) less than a simple weight majority of molecules of the same molecular weight.
‘Monomer unit’ means the reacted form of a monomer substance in a polymer.
‘Monomer’ means a substance which is capable of forming covalent bonds with asequence of additional like or unlike molecules under the conditions of therelevant polymer-forming reaction used for the particular process. (REACH 2006)
Since the REACH definition of ‘polymer’ is more inclusive than the IUPAC definition, theREACH definition should be considered to be more health-protective based on its ability
to characterize a wider breadth of constituents, and is therefore considered for adoption
into the proposed definition of ’Microplastics in Drinking Water’.
It is worth noting that the REACH definition of ‘polymer’ includes both naturally occurringand synthetic (i.e. anthropogenic) polymers. ECHA observes that, “the microplastic
concern is, in general, associated with synthetic polymers” (2019). As such, the ECHA
definition specifically excludes, “Polymers that occur in nature that have not beenchemically modified (other than by hydrolysis)” (2019). While there is no clear scientificconsensus regarding the importance of a polymer’s origin/persistence in determining its
toxicity and behavior in the environment, recent evidence suggests that synthetic
polymers are more toxic to various biota (Scherer et al. 2020; Le Guen et al. 2020;
Schür et al. 2019). Still, few toxicological studies have compared synthetic polymers
with natural polymers, resulting in strong uncertainties (Backhaus and Wagner 2019).
Despite these marked uncertainties, most definitions of ‘microplastics’ refer to either‘synthetic polymers’ and/or to specific polymer classes (e.g. thermosets11,
thermoplastics12, chemically- or mechanically- modified elastomers13) and/or to certain
polymer characteristics (e.g. those that retain their shape during use) (European
Chemicals Agency 2019; Hartmann et al. 2019). In maintaining consistency with nearly
all academic and regulatory definitions of ‘microplastics,’ the proposed State Water
11

Thermoset polymers are polymers that are irreversibly hardened by curing, which
results in cross-linked polymer chains. When exposed to high temperatures, thermoset
polymers do not melt, but will decompose. Thermoset polymers cannot be reshaped,
thus preventing most forms of recycling (The Open University (UK) 2000). Examples ofthermoset polymers includes vulcanized rubber, polyester resins, epoxy resins, siliconresins. Some polymers, such as polyurethane, can be either thermoplastic or thermoset.
12
Thermoplastic polymers are associated by intermolecular forces, meaning that they
are chemically reversible and will soften when heated and become fluid with additional
heat. Thermoplastics are produced at relatively high volumes and as such are found athigh quantities in the environment. Thermoplastics may be recycled through re-melting
and forming via injection molding. Thermoplastic polymers can be petroleum- or biobase. Examples include polylactic acid, nylon, polyethylene, polypropylene,
polyethylene terephthalate, polystyrene, and polyvinyl chloride.
13
Elastomer is defined as a polymer that exhibits elastic properties (IUPAC 2008).
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Board definition of ’Microplastics in Drinking Water’ includes a criterion for chemical
origin such that only polymeric materials that are derived in nature and have not beenchemically modified (other than by hydrolysis) are excluded. Note that the State Water
Board definition uses the term, “derived in nature” as opposed to the ECHA (2019) term,“occur in nature”. This difference in wording is intentional and is aimed to reduce
potential loopholes in the interpretation of this exception, as chemically modified
anthropogenic polymers are clearly occur in nature as a result of environmental
contamination.
ECHA’s 2017 working definition of ‘microplastics’ in the context of intentionally added
microplastics to products includes criterion for polymer origin under the term, “synthetic”(COM 2017). “Synthetic” is later removed from ECHA’s proposed definition for‘microplastics’, and is replaced with a statement to exclude “polymers that occur innature that have not been chemically modified (other than by hydrolysis)… [and] arepolymers that are (bio)degradable”, under the rationale that persistence is a principle
defining characteristic of problems associated ‘microplastics’ (European Chemicals
Agency 2019). It is worth noting that “biodegradable” polymers (e.g. poly-lactic acid
[PLA]) have demonstrated in vivo toxic effects similar or equivalent to their conventional,
non-biodegradable counterparts (Green et al. 2017; 2016). Due to a lack of refined andwidely accepted standards to determine biodegradability as well as uncertainties
regarding the human toxicological effects of biodegradable polymers, the proposedState Water Board definition of ’Microplastics in Drinking Water’ does not exclude“biodegradable” polymers.
To further clarify the types of polymers included in the proposed definition of’Microplastics in Drinking Water’, a discrete, non-exhaustive list of polymer types andmonomer units are listed, along with examples, in Table 1. The substance criteria in the
proposed definition of ’Microplastics in Drinking Water’ could be summarized as being
an expansion of the ISO definition of ‘plastic’14 in which ‘polymer’ (as it appears in the
ISO definition) would include the IUPAC definition15, but additionally includes
anthropogenic polymers that are not shaped by flow (e.g. elastomers). The proposed
substance criteria include all forms of thermoplastic and thermoset polymers, in addition
to anthropogenic elastomers, anthropogenic inorganic/hybrid polymers, and elastomers
and inorganic/hybrid polymers that have been chemically modified. The proposed
substance criteria includes polymers in which least one base monomer unit is derived
from petroleum or non-petroleum biologically-derived chemicals (except for naturalpolymers that have not been chemically modified other than by hydrolysis), and would
also include chemically-modified inorganic chemicals, inorganic-organic hybrid
chemicals/polymers, chemically-modified natural rubber, and chemically-modified
cellulose. Several examples of polymer categories are in Table 116.
14

(ISO 2013).
(IUPAC 2008).
16
It is important to note that the listed polymer categories in this section and Table 1 arenot exhaustive and are only provided for additional guidance in the interpretation of this
proposed definition.
15

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Rationale for the inclusion of chemically-modified natural polymers, chemically-modified
natural rubber, and cellulose that have been further processed to produce a final
polymer (i.e. chemically-modified) is that these particles have been heavily modified
such that their toxicological properties and environmental fate and transport are likely
altered (Hartmann et al. 2019).

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Table 1. Examples of Substances Included in the Proposed Definition
Derived monomer or physicalconstituent
Petroleum

non-petroleum biologically derived
chemicals
Inorganic or inorganic-organic hybrid
polymers
Chemically modified natural polymers
Chemically modified natural rubber
Chemically modified cellulose
Copolymers

Polymer composites

Examplespolyethylene, polypropylene,
polyurethane, polyethylene terephthalate,polystyrene, polyvinyl chloride (PVC)
bio-polyethylene terephthalate, biopolyethylene, polylactic acid,polyhydroxyalkanoates
elastomers such as silicone
Dyed wool, dyed cotton
Tire wear particles
rayon, cellophane
acrylonitrile-butadiene-styrene [ABS],
ethylene-vinyl acetate [EVA], styrenebutadiene rubber [SBR]nylon, glass fiber-reinforced polyester,graphite reinforced epoxy, cottonpolyester or wool-polyester textile blends

Polymers containing high quantities of non-polymeric additives (e.g., PVC) are also be
included in the proposed definition per the clause, “to which additives or othersubstances may have been added”. Additive content (e.g. plasticizers, colorants,
reinforcements, fillers, flame retardants, stabilizers) varies widely in anthropogenic
polymers and may change once in the environment (Hartmann et al. 2019; Rochman etal. 2019). Additionally, many additives and monomers are known to be toxic (i.e. BPA,
DEHP) (Manikkam et al. 2013) and may contribute to the toxicity of exposure toanthropogenic polymeric particles (Lithner, Larsson, and Dave 2011).
Copolymers, or synthetic polymers produced from more than one species of monomer(e.g., acrylonitrile-butadiene-styrene [ABS], ethylene-vinyl acetate [EVA], styrenebutadiene rubber [SBR]) are also included as these polymers are not derived in nature(Hartmann et al. 2019). Notably, ABS and EVA would be considered ‘plastic’ according
to ISO (2013) as they are thermoplastics, however SBR would not be considered‘plastic’ by the ISO definition since it is an elastomer. Accordingly, these, and other
copolymers (e.g. synthetic rubber copolymers) are included in the substance criteria forthe definition of ’Microplastics in Drinking Water’.
In addition to copolymers and high-additive content polymers, polymer composite
materials such as nylon, glass fiber-reinforced polyester, graphite reinforced epoxy,
cotton-polyester or wool-polyester textile blends are included in the substance criteria
for the definition of ’Microplastics in Drinking Water’ granted they satisfy the following
criteria:

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PROPOSED DEFINITION OF ‘MICROPLASTICS IN DRINKING WATER’(i) a particle of any composition with a continuous polymer surface coating of any
thickness, or;(ii) a particle of any composition with a synthetic polymer content of greater than orequal to 1% by mass.
Exclusions
The definition of microplastics in drinking water excludes polymers derived exclusively
from natural origins and materials (e.g., DNA, proteins, wool, silk, cellulose) according
to the clause, “polymers that are derived in nature that have not been chemicallymodified (other than by hydrolysis) are excluded”. Slightly modified natural polymers(e.g., dyed wool) may be excluded so long as they satisfy the criteria of being
composed of <1% synthetic polymer by mass.

Defining Criteria: State
While it may be commonly thought that all plastic polymers are ‘solid’ materials at room
temperature and standard pressure, some polymers can be wax-like, semisolid, or
liquid. Most polymers have a vapor pressure <300 kPa (at 50 ˚C) and an initial melting
point >20 ˚C (Tm at 101.3 kPa), which would therefore be considered solids under the
GHS (United Nations 2013). While melting temperature (Tm) determines the difference
between solid and liquid state for most materials, amorphous and semicrystalline
plastics will behave differently when heated (Hartmann et al. 2019). Amorphous
polymers (e.g., polystyrene, ABS) are hard, brittle materials at temperatures below theirglass transition temperature (TG) but become viscous and free flowing above their TG(Hartmann et al. 2019). Semicrystalline polymers (e.g., polyamide, polyethylene
terephthalate, polypropylene, PVC, polyethylene, polycarbonate) have both a TG and aTM, in which they are hard and brittle below their TG; ductile, soft, and form-stable below
their TM and liquid above their TM. (Hartmann et al. 2019). While TM may adequately
predict the state of semicrystalline polymers, amorphous polymers lack a specific TM.
(Hartmann et al. 2019). Based on the lack of TM for some polymers, Hartmann et al.
propose that TG should be used to define state, with a proposed threshold of TG > 20 °C(i.e. ambient room temperature), based on practical purposes of conducting
measurements of plastic under standard laboratory conditions (2019).
A state threshold of TG > 20 °C would exclude some wax-like polymers as well as softpolymer gels. Polymer gels may be derived from natural (e.g., gelatin, agarose) orsynthetic feedstock (e.g., polyacrylamide, polyvinyl alcohol, polyethylene glycol) and areused in various applications, such as polyacrylamide copolymers which are used as
flocculation agents during wastewater treatment (Hartmann et al. 2019). In the field ofpolymer science, polymer gels are considered solids within an additional medium (i.e.,liquid) (Rogovina, Vasil’ev, and Braudo 2008). Some polymer gels or their monomericunits are known to be toxic to humans. For example, the monomeric constituent ofpolyacrylamide- acrylamide- is a potent human neurotoxicant and suspectedcarcinogen, and is regulated in drinking water by the U.S. EPA (Rudén 2004). Further,
the U.S. EPA regulates polymer applications so that dissolved acrylamide

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PROPOSED DEFINITION OF ‘MICROPLASTICS IN DRINKING WATER’concentrations do not exceed 500 ng/L (U.S. EPA 2003). Despite the documented andundocumented toxicity of polymer gels, inclusion of such constituents in the definition of’Microplastics in Drinking Water’ is not technically feasible due to the fact that inaqueous solutions, polymer gels become soft and viscous and may be difficult toseparate using traditional microplastics extraction methods17 (Hartmann et al. 2019).
ECHA included TG and Tm thresholds within the state criteria of a previous working
definition of ‘microplastics’ to define ‘solid’ and ‘semi-solid’ polymers, but later removed
TG as a defining feature in the state criteria, defining ‘solid’ as “a substance or mixture
which does not meet the definitions of liquid or gas” and would therefore include such‘semi-solid’ polymers (e.g. amorphous polymers) (European Chemicals Agency2019).The state criteria included in the proposed definition of ’Microplastics in Drinking
Water’, which is synonymous with the state criteria included in the proposed definition
by ECHA in August 2019, is likely to be highly inclusive of particle diversities whileremaining technically feasible using typical methods and instruments used tocharacterize microplastics.

Defining Criteria: Dimensions
The proposed lower size limit for “at least two dimensions being” at least 1 µm is basedon the fundamental physical differences of plastic particles smaller than 1 µm.
Specifically, particles between 1-1,000 nm exhibit strong colloidal behavior (Gigault etal. 2016; 2018), and cannot be identified using light-based microscopy, thus requiring
fundamentally different techniques and instrumentation for characterization (Frias et al.
2018). The rationale for at least two dimensions meeting threshold criteria is to exclude
large fibers and films that would be considered microplastics under the US EPA
definition of “any one dimension.” Such fibers and films with dimensions longer than
5,000 µm are not typically considered to be microplastics and are expected to behave
fundamentally differently than smaller microplastic particles. Furthermore, defining
microplastic particles as having at least two dimensions between defined size
thresholds would require the measurement or reliable interpolation of at least two
dimensions, thus improving size-specific data for samples.
The proposed upper size limit for of 5,000 µm is the most widely used in the scientific
literature, dating back to 2003 (Hartmann et al. 2019; A. L. Andrady 2003). NOAA
adopted this upper size limit based on the likelihood of particles smaller than these
dimensions being ingested relative to larger items (C. Arthur, Baker, and Bamford
2009). Further, this upper size limit is congruous with ECHA’s definition of‘microplastics’18 (European Chemicals Agency 2019). A distinctive dimensions criterion
for fibers may be included in a future definition of ’Microplastics in Drinking Water’ if
17

Polymer gels, such as polyacrylamide, may appear as ‘solids’ in water due toagglomeration and other mechanisms. A further discussion regarding water-soluble
polymers is included on page 20.
18
Except in the case of “fibres”, which ECHA further defines as having, “a length of 3nm≤ x ≤ 15mm and length to diameter ratio of >3” (European Chemicals Agency 2019).
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PROPOSED DEFINITION OF ‘MICROPLASTICS IN DRINKING WATER’available standardized methodology, human health toxicological information, andoccurrence data suggest that such a distinction is necessary.
In 2016, California amended the Ocean Plan to include provisions for the control oftrash, including a requirement to install “full capture systems” in storm drains to restrict
trash particles larger than 5 mm (State Water Board 2016a). While it was understoodthat the smaller particles that would pass through these devices would negatively
impact water quality due to their dimensions-dependent biological hazard, 5mm(5,000 µm) was ultimately chosen based on reliability and performance sensitivity undervarying loads (State Water Board 2016b). While the State Water Board definition of’Microplastics in Drinking Water’ is not a de facto regulatory definition of microplastics inother media, the adoption of 5,000 µm as an upper limit would eliminate contrasting
definitions of ‘microplastics’ within the State Water Board or the need for developmentof another dimensions-based plastic classification.
While the occurrence of microplastics in drinking water is not considered a primaryfactor in the formulation of the dimensions criterion in the proposed ’Microplastics in
Drinking Water’, it is worthwhile to consider such occurrences. Currently there are notreatment technologies directly targeted at the removal of microplastics from drinking
water. Nevertheless, several drinking water treatment technologies have anecdotally
been found to remove microplastics, with dimensions being a significant factor (Novotna
et al. 2019). In a study that measured microplastic content (> 1 µm) at the inlet (rawsurface water) and subsequently at the outlet (treated water) of three drinking water
treatment plants, removal rates for treatment technologies were as follows:
coagulation/flocculation and sand filtration (70% removal); coagulation/flocculation,
sedimentation, sand filtration and granular activated carbon filtration (81% removal);coagulation/flocculation, flotation, sand filtration and granular activated carbon filtration(83% removal) (Pivokonsky et al. 2018). For all three drinking water treatment plants,
microplastics in the 1-5 µm range were most abundant (25-60%), followed by
microplastics between 5-10 µm (30-50%) (Pivokonsky et al. 2018). Microplastics >50µm in dimensions were virtually not detected in treated water, and no microplastics>100 µm were detected in treated water, despite their observed occurrence in raw water(Pivokonsky et al. 2018). One study found that ultrafiltration using polyvinylidene
fluoride membranes (30 nm average pore diameter) effectively rejected all polyethylene
microplastics (<500 µm) (Ma et al. 2019). Very few studies have measured
microplastics in groundwater, with the highest abundance being 0.007 microplastics/liter(>20 um), although very small microplastics were not measured (Mintenig et al. 2019).
Self-contamination during sampling and analysis of microplastics is widely reported(Scopetani et al. 2020), and, despite extensive efforts documented by Mintenig et al.
(2019), there is skepticism regarding the validity of the findings of microplastics ingroundwater (Kniggendorf, Wetzel, and Roth 2019).
While there is currently insufficient evidence to determine the risk to humans from theingestion of microplastics in drinking water due to incomplete hazard identification andPage | 20

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exposure, sufficient evidence exists to suggest that smaller microplastic particles arelikely more toxic to humans than larger particles and should therefore be prioritized formonitoring in drinking water (World Health Organization 2019).
Mammalian studies demonstrate that smaller particles have an increased efficiency totranslocate across the gut and be further distributed into target organs (Wright and Kelly
2017; Volkheimer 1975; Jani et al. 1989). Once ingested, nondegradable particles (i.e.,
microplastics) may be distributed into the gastrointestinal tract via multiple processes,
including paracellular persorption and endocytosis- which depend largely on thedimensions and shape of the particle (Wright and Kelly 2017; Volkheimer 1975).
Paracellular persorption of microplastic particles has been documented in mammalianmodels, including polyvinyl chloride (PVC) microplastic particles in dogs (Steffens 1995;
Volkheimer 1975). Following the ingestion of 5-110 µm PVC microplastics by dogs,
PVC particles were found in bile, urine, cerebrospinal fluid, tissue and organs(Volkheimer 1975). The uptake of microplastic particles (1-2.2 µm) into thegastrointestinal tract via endocytosis by Peyer’s patches has been documented in
mammalian models, including rats and mice (Jani et al. 1989; LeFevre, Boccio, and Joel
1989). Once taken up into the gastrointestinal tract, microplastic particles may befurther transported into sensitive organs via the chyle (lumen) of underlying lymph
vessels, as demonstrated for PVC particles (5-110 µm) in rats, guinea pigs, rabbits,
chickens, dogs and pigs; or by portal circulation, as demonstrated in dogs (Volkheimer1975).
In addition to the enhanced uptake and distribution of smaller microplastics, hazards
increase with smaller dimensions due to the interaction with target systems (Wu et al.
2019; Wright and Kelly 2017). The desorption rate of sorbed chemicals is inversely
correlated with size due to increased surface area (Coffin, Lee, et al. 2019; Koelmans etal. 2013). However, some externally mixed additives such as decaBDE and inorganic
pigments may mechanically separate from particles at different rates, thus larger
particles with orders of magnitude more chemical mass may also release chemicals at
relevant rates if ingested (Reche et al. 2019; De la Torre et al. 2018). Due to thebiopersistence of microplastics, interactions with cells and tissues may lead to biologicalresponses including inflammation, genotoxicity, oxidative stress, apoptosis, andnecrosis (Wright and Kelly 2017; Volkheimer 1975). If sustained, these conditions may
cause adverse health outcomes such as tissue damage, fibrosis, and carcinogenesis(Wright and Kelly 2017).

Non-defining Criteria: Morphology and Color
Morphology and color are useful descriptors for microplastics that may be relevant to
toxicological risk assessments, fate and transport models, and origin, however, are notconsidered to be defining criteria for the proposed definition of ’Microplastics in Drinking
Water’. Regardless, such non-defining criteria should be recorded, to the extent
possible, in standard methods for microplastics in drinking water. Once available, thePage | 21

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PROPOSED DEFINITION OF ‘MICROPLASTICS IN DRINKING WATER’use of standardized terminology to describe the morphology and color of identified
microplastics in drinking water should be employed.
Common classifications for the morphology of microplastics include spheres, pellets,
fragments, films, and fibers. The State Water Board is not yet aware of a standardized
taxonomy for the morphology of microplastics, and thus tentatively recommends thefollowing guidelines based on previous recommendations (Hartmann et al. 2019):
●
●
●
●
●
●

pellet - every surface point has the same distance from the center;
fiber- length to diameter ratio of >3;
fiber bundle – typically inseparable group of >2 fibers;
fragment- particle with irregular shape;
film- planar, considerably smaller in one than in the other dimensions;
black rubbery fragment- typically anthropogenic crumb rubber derived from tires
which is technically challenging to identify using common spectroscopic
techniques.

A standardized color palette should be employed to characterize color.

Non-criteria: Solubility
While many conventional polymers are poorly soluble in water, some synthetic polymers
readily dissolve in water (e.g., low molecular polyethylene glycol, polyvinyl alcohol). As
mentioned earlier, one such water-soluble polymer, polyacrylamide, persists in theenvironment and degrades into the potent neurotoxicant monomer- acrylamide- underanaerobic conditions (Hennecke et al. 2018; Xiong et al. 2018). Polyacrylamide is
widely used as a flocculant in water treatment, soil conditioner in agriculture, andviscosity enhancer in oil and gas drilling and fracking, with high concentrations (101,000 mg/L) reported in wastewater effluent concentrations (Xiong et al. 2018). Due tothe persistence, toxicity, and widespread use of polyacrylamide and other water-soluble
polymers, there is concern that the exclusion of water-soluble polymers from a
regulatory definition of ‘microplastics’ may cause them to be ignored (Arp and Knutsen2019).
Water-soluble polymers may appear as microscopic particles due to agglomeration withother particles, cross-linking, coating of flocculated composites, and other mechanisms(Berndt et al. 1991; Rivas, Urbano, and Sánchez 2018). Moreover, water-soluble
polymers may be measured using analytical techniques that are used to measurewater-insoluble polymers, such as dimensions exclusion chromatography, infrared
spectroscopy, and mass spectrometry (Arp and Knutsen 2019). Based on thepersistence, toxicity, and potential for detection of water-soluble polymers using avariety of analytical techniques that are also used to detect water-insoluble polymers,
there are no solubility threshold criteria in the proposed definition of ‘microplastics indrinking water.’ The exclusion of a solubility threshold is consistent with ECHA’s
proposed definition of ‘microplastics’ (2019).

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Plastic-associated chemicals regulated in drinking water in California
It is understood that plastic can transfer chemicals to biota once ingested (Koelmans etal. 2016). In aquatic biota, plastic may or may not be a relevant transfer mechanism forsuch chemicals relative to other environmental exposure media (Bakir et al. 2016; Burns
and Boxall 2018). It remains uncertain if the transfer of chemicals from a particle via
ingestion through drinking water is a relevant factor in the hazards of microplastics tohumans, despite a preliminary risk assessment based on highly conservative
assumptions (World Health Organization 2019). While not a defining feature (critical orotherwise) to the proposed definition of ’Microplastics in Drinking Water’, included here
is a discussion of chemicals associated with plastic that are currently regulated indrinking water in California (per Title 22 and 17 of the California Code of Regulations) toprovide a basis for examining potential, poorly documented hazards associated withsuch chemicals and microplastic particles in regards to human health.
Some chemicals may be intentionally added to plastic during manufacturing to be used
as a functional additive (i.e., plasticizer, flame retardant, stabilizer, antioxidant, slip
agent, lubricant, anti-static, curing agent, blowing agent, biocide), colorant (i.e. inorganic
pigment, organic pigment, soluble colorant), filler, reinforcement, or monomer(Hahladakis et al. 2018). Additionally, some compounds may be unintentionally added
to plastic through the manufacturing process or may be generated as a result of the
breakdown of plastic in the environment (Gewert, Plassmann, and MacLeod 2015; Vanet al. 2012). For the purposes of this discussion, the aforementioned attributes are
requisite criteria for a chemical to be classified as a “plastic-associated chemical.”Chemicals that sorb to plastic in the environment after the manufacturing process are
excluded from the classification of “plastic-associated chemicals” in recognition thatplastic is not the source of such chemicals, but rather a transport mechanism.
Many known plastic-associated chemicals are currently regulated in drinking water in
California (i.e., have a Maximum Contaminant Level or MCL per Title 22 and 17 of the
California Code of Regulations) and are known to leach from plastic in the environment.
These include, but are not limited to:● Di(2-ethylhexyl)phthalate (DEHP)- a commonly-used plastic additive in a wide
range of products including food packages, cosmetics, medical devices, and
PVC (Hauser and Calafat 2005);● Di(2-ethylhexyl)adipate – a reagent used to make plastic (Fasano et al. 2012);● antimony (Sb)- used in the form of antimony trioxide (Sb2O3) as an important
catalyst in the manufacture of polyethylene terephthalate (PET) plastic andknown to leach from PET water bottles (Shotyk and Krachler 2007);● methyl-tert-butyl ether (MTBE) – a reagent used to make plastic (Chang et al.
2003) that has been found to leach from plastic including cross-bonded
polyethylene (PEX) (Skjevrak et al. 2003);● styrene- a monomer used to make polystyrene plastic (Garrigós et al. 2004);● vinyl chloride- a monomer used to make PVC (Fayad et al. 1997);

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PROPOSED DEFINITION OF ‘MICROPLASTICS IN DRINKING WATER’● benzene, ethylbenzene – byproducts of the thermo-oxidation degradation
pathway of plastic (Hoff et al. 1982);● arsenic – a degradation product of arsenic-based biocides used in plastics suchas soft PVC and foamed polyurethanes (Nichols 2005);● cadmium and lead- degradation products of cadmium- and lead-based
compounds used as heat stabilizers and slip agents (Al-Malack 2001);● 2,3,7,8-TCDD (dioxin), and cyanide – released from chlorine-containing plastics(e.g., PVC) during thermal degradation (Lokensgard 2016);● fluoride – released from fluorine-containing polymers (e.g. polytetrafluoroethylene[PTFE]) and polyvinylidene fluoride) by a chain-stripping mechanism and otherdegradation pathways (Lokensgard 2016);● chromium- used as pigment (Anthony L. Andrady and Rajapakse 2016);● polychlorinated biphenyls (PCBs) including congeners 77, 110,114, and 206,
which, although generally banned for use in the United States under the Toxic
Substances Control Act of 1979, are still found in plastics produced in the UnitedStates and China likely as impurities in dyes and pigments (Coffin et al. 2018; Hu
and Hornbuckle 2010; Rodenburg et al. 2010).
It should be noted that plastic-associated chemicals range drastically in terms of use
and their ability to leach from plastics in the environment, and depend on a wide range
of factors such as polymer type, intended use, production facility, production processes,
and environmental parameters such as ultraviolet light exposure, salinity, heat, chemicalinteractions, enzymes, dissolved organic carbon, dimensions, etc. (Coffin, Huang, et al.
2019; Coffin et al. 2018; Lokensgard 2016). Extremely limited evidence regarding thetransfer of such chemicals to humans from microplastics is currently available (World
Health Organization 2019; Zhang et al. 2020).

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References
22 CCR § 69405.7. Particle Size or Fiber Dimension. 2011. California Code ofRegulations.
https://govt.westlaw.com/calregs/Document/I7AEE2BC032A411E186A4EF11E7
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Al-Malack, Muhammad H. 2001. “Migration of Lead from Unplasticized Polyvinyl
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Andrady, A. L., ed. 2003. Plastics and the Environment. Hoboken, N.J: WileyInterscience.
Andrady, Anthony L., and Nepali Rajapakse. 2016. “Additives and Chemicals in
Plastics.” In Hazardous Chemicals Associated with Plastics in the Marine
Environment, edited by Hideshige Takada and Hrissi K. Karapanagioti, 78:1–17.
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Arp, Hans Peter H., and Heidi Knutsen. 2019. “Could We Spare a Moment of the
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