Deep Dive into Plastic Monomers, Additives, and Processing Aids

Abstract

A variety of chemical substances used in plastic production may be released throughout the entire life cycle of the plastic, posing risks to human health, the environment, and recycling systems. Only a limited number of these substances have been widely studied. We systematically investigate plastic monomers, additives, and processing aids on the global market based on a review of 63 industrial, scientific, and regulatory data sources. In total, we identify more than 10'000 relevant substances and categorize them based on substance types, use patterns, and hazard classifications wherever possible. Over 2'400 substances are identified as substances of potential concern as they meet one or more of the persistence, bioaccumulation, and toxicity criteria in the European Union. Many of these substances are hardly studied according to SciFinder (266 substances), are not adequately regulated in many parts of the world (1'327 substances), or are even approved for use in food-contact plastics in some jurisdictions (901 substances). Substantial information gaps exist in the public domain, particularly on substance properties and use patterns. To transition to a sustainable circular plastic economy that avoids the use of hazardous chemicals, concerted efforts by all stakeholders are needed, starting by increasing information accessibility.

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Deep Dive into Plastic Monomers, Additives, and Processing Aids
Helene Wiesinger,*Zhanyun Wang,*and Stefanie Hellweg
Cite This: https://doi.org/10.1021/acs.est.1c00976
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ABSTRACT: A variety of chemical substances used in plastic
production may be released throughout the entire life cycle of the
plastic, posing risks to human health, the environment, and
recycling systems. Only a limited number of these substances have
been widely studied. We systematically investigate plastic
monomers, additives, and processing aids on the global market
based on a review of 63 industrial, scientific, and regulatory data
sources. In total, we identify more than 10'000 relevant substances
and categorize them based on substance types, use patterns, and
hazard classifications wherever possible. Over 2'400 substances are
identified as substances of potential concern as they meet one or
more of the persistence, bioaccumulation, and toxicity criteria in
the European Union. Many of these substances are hardly studied
according to SciFinder (266 substances), are not adequately regulated in many parts of the world (1'327 substances), or are even
approved for use in food-contact plastics in some jurisdictions (901 substances). Substantial information gaps exist in the public
domain, particularly on substance properties and use patterns. To transition to a sustainable circular plastic economy that avoids the
use of hazardous chemicals, concerted efforts by all stakeholders are needed, starting by increasing information accessibility.
KEYWORDS: plastic products, plasticizers, plastic pollution, chemical inventory, production volume, substances of concern,
circular economy, regulatory status
1. INTRODUCTION
Plastics are widely used in various industrial sectors including
packaging, construction, automotive, electronics, textiles, house-
hold items, and toys, with the current global production reaching
over 350 million tonnes per year (t/yr).
1
These synthetic
materials can be molded or shaped and are made of an organic
polymer matrix and chemical additives. In their production and
processing, a variety of chemical substances are used.
2−5
The
basis of plastics, organic polymers, is made from repeating
monomer units.
4
Additives help to maintain, enhance, and
impart specific properties (e.g., antioxidants for maintaining the
polymer matrix against oxidative conditions, plasticizers for
enhancing flexibility, and flame retardants for imparting fire
resistance).
6,7
Processing aids enable or ease the production or
processing of plastics (e.g., polymerization catalysts, solvents, or
lubricants).
8,9
In addition to these intentionally used chemicals,
many nonintentionally added substances (NIASs) can also be
present in plastics, including byproducts, breakdown products,
and contaminants.
10,11
Thus, plastics contain many substances that are not
chemically bound to the polymer matrix, including unreacted
monomers, residual processing aids and additives. These
substances may be released during the plastic life cycle, resulting
in human and environmental exposure.
12−20
Adverse health
effects have been observed for consumers, workers in the plastic
production and recycling industries, and communities and
ecosystems that are near production and recycling facilities.
21−25
In addition, substances present in plastics may also hamper the
transition to a circular economy, by impairing recycling
processes and the safety and quality of recycled materials.
26−30
Despite growing scientific evidence and public concern,
current research and regulatory actions have focused on a
limited selection of substances, mostly well-known hazardous
ones
31−33
or those commonly known for their presence in
plastics.
34,35
This phenomenon is partially because information
on plastic monomers, additives, and processing aids is limited
and scattered in the public domain. A recent review looked into
substances used in plastic packaging and identified more than
4'000 potentially relevant substances, more than half lacked
hazard classifications and a majority lacked detailed use
descriptions.
13
Currently, such an extensive assessment is
lacking for plastics used in other industrial sectors. While recent
development of nontarget analysis using high-resolution mass
spectrometry provides new possibilities to look into a larger set
of substances in plastics, the wide application of such techniques
Received: February 9, 2021
Revised: May 31, 2021
Accepted: May 31, 2021
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is still limited, in part because of challenges in interpreting the
overwhelming amount of data generated.
14,36−41
Some
researchers have suggested the use of so-called suspect lists to
enhance substance identification.
36,42
Hence, to inform future studies and action on substances
present in plastics, this study systematically collects and analyzes
publicly available information on intentionally added substances
(i.e., monomers, additives, and processing aids) in plastics of all
industrial sectors. In particular, this study investigates chemical
identities, uses patterns (functions, compatible polymer types,
industrial sectors of use, geographical distribution, and
production volumes), and reported hazard classifications.
Furthermore, based on reported hazard classifications, produc-
tion volumes, and regulatory status, substances of potential
concern are identified. Major lessons learned, including critical
data and knowledge gaps, are then highlighted, followed by an
outlook on possible ways forward.
2. METHODS
This study was conducted in four steps: (1) identification of
relevant data sources, (2) inclusion of relevant substances and
information, (3) categorization of substance types and use
patterns, and (4) identification of substances of potential
concern (Figure 1). Individual steps are summarized in the
following subsections, and additional details are provided in the
Supporting Information files, Supporting Information S1 and
Supporting Information S2.
2.1. Identification of Relevant Data Sources. Relevant
data sources were identified from (1) target scientific
literature,
13,43,44
(2) a bibliographic search of the keywords
“plastic additives”,“plastic”, and “polymer”in the Web of
Science, Scopus, and Google Scholar, and (3) a search of
manufacturers’,distributors’, and regulators’websites and
databases. In the bibliographic search, books and review articles
were manually selected, and individual research articles were
excluded due to time and resource constraints. Sources were
excluded that deal solely with polymers but are irrelevant for
plastics; similarly, sources that deal exclusively with NIASs were
excluded, as this study deals with substances intentionally added
to plastics. The internet search focused on sources that include
explicit use information.
In total, 190 relevant sources were identified and categorized
based on information content, data accessibility, and source type
(i.e., regulatory, scientific, and industrial), see Sheet S1 in
Supporting Information S1. Among them, 63 sources provided
readily accessible information and were further processed; the
rest were not used, as they referred only to general groups of
substances (e.g., phenolic antioxidants and fatty acid esters) or
were not machine-processable (e.g., information embedded in
unstructured texts; only in print versions). Data treatment and
retrieval processes varied for the 63 sources; for details, see Sheet
S1 in Supporting Information S1.
2.2. Inclusion of Relevant Substances and Informa-
tion. Plastic monomers, additives, or processing aids were
identified by searching for plastic-related keywords in the
respective use descriptions of individual substances (for details,
see Sheet S1 in Supporting Information S1). Some NIASs may
also be included where the keywords appeared in their use
descriptions, but no specificefforts were made to distinguish
them. Only substances for which the assigned Chemical Abstract
Service Registry Numbers (CASRNs) were provided in the
sources were included for further analysis, and the rest were
excluded, due to the high workload and uncertainties associated
with finding their corresponding CASRNs.
Identified CASRNs were verified using the check-digit
method (Section S1.2 in Supporting Information S2).
45,46
Furthermore, the status of identified CASRNs and their
connected CASRNs assigned by the Chemical Abstracts Service
(i.e., “active”,“deleted”,or“alternate”) were retrieved from
SciFinder.
46
Confidence in identifying target substances was assessed using
a weighted scoring approach. First, individual sources were
scored based on their information origin and outlet control, as
well as the identification method used and data processing needs
Figure 1. Schematic overview of the workflow in this study. CASRNs = Chemical Abstracts Service Registry Numbers; SMILES = simplified
molecular-input line-entry system; REACH = Regulation on Registration, Evaluation, Authorisation and Restriction of Chemicals; PBT = persistent,
bioaccumulative and toxic; EU = European Union.
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in this study (Table S2 in Supporting Information S2). Then,
substance confidence scores were assigned by taking the highest
score of their individual sources; for those substances that were
identified through multiple first-hand information sources, a
combined confidence score was calculated (Section S1.2.3 in
Supporting Information S2).
Use descriptions (including information on functions,
compatible polymer types, and relevant industrial sectors)
were retrieved from the original sources. Additional information
was retrieved for the identified substances using all CASRNs
(including deleted and alternate ones), namely, structural
identifiers [that is, CAS names, molecular formula, and
simplified molecular-input line-entry system (SMILES) entries],
reported hazard classifications, production volumes, regional use
status, and regulatory status in specific regions. Details on the
retrieval of information can be found in Sheet S2 in Supporting
Information S1.
CAS names and molecular formulas were retrieved from
SciFinder.
46
SMILES entries representing molecular structures
were retrieved from the CompTox Chemicals Dashboard.
47
Two types of reported hazard classifications were retrieved
(details in Sheet S2 in Supporting Information S1): (1) those
that were harmonized by regulatory agencies, hereafter referred
to as “regulator-harmonized”, and (2) those that were reported
by individual companies to regulators, or “company-reported”.
Regulator-harmonized hazard classifications were retrieved from
the International Agency for Research on Cancer (IARC)
Classified Agents List,
48
the Australian Hazardous Chemicals
Information System (HCIS),
49
the Japanese GHS classification
results,
50
the European Union Classification and Labelling
Inventory (EU C&L InventoryHarmonized C&L),
51
and the
concluded assessments under the EU Registration, Evaluation,
Authorisation and Restriction of Chemicals (REACH) regu-
lation. Assessments under REACH include the authorization
list,
52
the candidate list of substances of very high concern
(SVHC) list,
53
the persistent, bioaccumulative and toxic
substances (PBT) assessment list,
54
and the endocrine disruptor
(EDC) assessment list.
55
Company-reported hazard classifica-
tions were retrieved from the EU REACH (REACH
Registration C&L Data) and C&L (CLP Notification C&L
Data) registration dossiers,
56
and the Organisation for
Economic Co-operation and Development (OECD) eChem-
Portal.
57
No additional hazard classification was conducted in
this study. Hazard data from different sources were checked for
consistency.
Production volumes were retrieved from the OECD high
production volume chemical (HPVC) list,
58
the United States
Environmental Protection Agency (USEPA) Chemical Data
Reporting (CDR) program,
59
the EU REACH registration
dossiers,
60
and the Substances in Preparations in the Nordic
countries (SPIN) database
61
(Sheet S2 in Supporting
Information S1). Substances were labeled HPVCs when their
total reported production volumes in the EU (or in the Nordic
countries if the EU production volumes were not available) and
the US surpassed 1000 t/yr or when they were listed on the
OECD HPVC list. The retrieved production volumes comprise
the total annual amounts produced in a region for all uses, not
just the use in plastics.
The regional use status was assessed by checking the
registration status of identified substances in individual national
and regional chemical inventories around the world (Sheet S2 in
Supporting Information S1 and Figure S5 in Supporting
Information S2).
62
Regulatory status in specific regions was assessed by checking
the presence of identified substances on various regulatory lists
(Sheet S2 in Supporting Information S1). These include lists of
chemicals regulated under the Stockholm Convention, the
Montreal Protocol, and the Rotterdam Convention, as well as
the regulatory lists in the EU, Japan, Republic of Korea, and the
US (Figure S7 in Supporting Information S2). Also, the
regulatory positive lists of substances allowed in food-contact
plastics in the EU, US, and Japan were included. In some cases,
groups of chemicals [for example, perfluorooctanoic acid
(PFOA), its salts, and related compounds; cadmium com-
pounds] are regulated without explicit referencing all relevant
substances; such cases required manual searches for relevant
substance names, SMILES, or molecular formulas.
2.3. Categorization of Substance Types and Use
Patterns. Using keyword searches, identified substances were
categorized according to their substance types (e.g., organo-
metallic or organohalogen compounds) and use patterns. These
included functions (e.g., colorants and fillers), compatible
polymer types (e.g., polyethylene or PE, polyvinyl chloride or
PVC), and industrial sectors of use (e.g., automotive, packaging,
and food-contact plastics).
For substance types, categorization was made by searching for
specific chemical elements in substance names, SMILES, or
molecular formulas (Sheet S6 in Supporting Information S1).
Furthermore, specific keywords were used to identify UVCBs
(substances of unknown or variable composition, complex
reaction products, or biological materials), mixtures, and
polymers.
62
For use patterns, an iterative approach was employed,
consisting of three steps: (a) defining initial categories and
associated keywords, (b) categorizing, and (c) checking errors
and updating keywords, where steps (b) and (c) were repeated
until the observed error frequencies dropped to below 10%. The
final set of categories and the corresponding keywords can be
found in Sheets S3−S6 in Supporting Information S1.
(a) Initial categories and associated keywords were defined
for functions (using definitions in industrial hand-
books),
6,8,9,63
compatible polymer types, and industrial
sectors of use (based on recent plastic material flow
analyses).
1,64,65
Keywords included synonyms (e.g.,
“HDPE”for high-density polyethylene), hyponyms
(e.g., “fridge”for electronics and “milk bottle”for food
packaging), and hypernyms [for example, “polyolefin”for
(high- and low-density) polyethylene]. These were
refined by manually including relevant frequently used
terms in the use descriptions of identified substances
(Section S1.3 in Supporting Information S2).
(b) The categorization was conducted by carrying out regular
expression searches for keywords in the use descriptions
of identified substances.
(c) A random selection of the categorization results was
manually checked for errors (Sheet S7 in Supporting
Information S1). Error-prone keywords were deleted or
improved (e.g., using more advanced regular expressions
such as “lookbehind”and “lookahead”expressionsthe
initial keyword “PE”was changed to “PE(?!T)”to
exclusively match “PE”without matching “PET”as
well). Some errors may remain, mainly due to ambiguities
in the original use descriptions provided in individual
sources (e.g., “used in paint”without details for which
functions).
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Confidence scores were assigned to individual categorizations
based on the information origin and outlet control of individual
sources, nature of the keywords (i.e., synonym, hyponym, and
hypernym), and observed error frequency (Table S4 in
Supporting Information S2).
2.4. Identification of Substances of Potential Concern.
Substances of potential concern were identified and assigned a
level of potential concern using a simplified two-step approach,
based on hazard classifications and production volumes as
surrogate reflecting potentials for causing adverse effects and
exposure, respectively.
In the first step, substances that fulfill one or more of the
following hazard criteria under EU REACH were identified as
substances of potential concern: PBT/very persistent and very
bioaccumulative (vPvB), carcinogenicity (C), mutagenicity
(M), reproductive toxicity (R), endocrine disruption (ED),
specific target organ toxicity upon repeated exposure (
STOT-RE), and chronic aquatic toxicity (AqTox). Detailed
criteria for the different hazard classifications can be found in
Table S5 in Supporting Information S2. Substances with
insufficient hazard information or without any information at
all in the considered regulatory databases were categorized as
“unknown”, whereas those with full hazard information but that
Figure 2. Overview of the substances that are (potentially) used as plastic monomers, additives, and/or processing aids. Part (A) illustrates the
distribution of the substances identified in terms of information sources, assigned confidence scores of their use in plastics, and substance types. Part
(B) shows examples of data availability in different areas. Part (C) depicts numbers of the substances falling under the broader function categories
“monomers”,“additives”,“processing aids”, and “uncategorizable”. Part (D) exhibits numbers of the substances registered for production and/or use in
different regions and countries; for those national or regional inventories with publicly accessible information on uses, the reported uses are analyzed
whether they are linked to plastics (as defined in Sheet S1 in Supporting Information S1).
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did not meet any of the considered hazard criteria were
categorized as the “low level of concern”. In the second step,
depending on production volumes, identified substances of
potential concern were either considered the “medium level of
concern”(<1'000 t/yr) or “high level of concern”(>1'000 t/yr).
Identified substances of potential concern were further
assessed concerning their regulatory status (Section 2.2) and
the number of scientific references reported in SciFinder.
46
2.5. Quality Assurance and Quality Control. As stated
above, data quality was assured using several procedures. For
substance identification, quality assurance and quality control
(QA/QC) included assigning confidence scores to the sources
and substances (Sheet S1 in Supporting Information S1),
verifying the check digit of CASRNs,
45
and checking the
CASRN status in SciFinder (Section 2.2). For substance type
and use pattern categorization, QA/QC included iterative
keyword optimization (Section 2.3) and assigning confidence
scores to each categorization. For the identification of
substances of potential concern, QA/QC included a hazard
data consistency check (Figure S6 in Supporting Information
S2) and manually double-checking the regulatory status. The
remaining uncertainties are mostly due to misreported or
missing information and are qualitatively discussed in Section 4.
3. RESULTS
3.1. Overview of Plastic Monomers, Additives, and
Processing Aids. In total, substances with 10'547 unique active
CASRNs are identified, mostly with high confidence in their use
as plastic monomers, additives, and processing aids (Figure 2A,
Sheet S8 in Supporting Information S1). These active CASRNs
are associated with another 24'901 deleted CASRNs (i.e.,
replaced by the active CASRNs) and 22 alternate CASRNs (i.e.,
CASRNs in parallel use to the active ones). A number of these
deleted or alternate CASRNs are still being used in different
information sources.
All source types (scientific, regulatory, and industrial) are
important for substance identification (Figure 2A). A total of
4'280 CASRNs have been reported in more than one type of
source, whereas over 6'267 CASRNs have only been reported in
one type of source (note that they can occur in several sources,
but all of these belong to the same source type).
Figure 3. Overview of the substance types, compatible polymer types, industrial sector of use, production volumes, and reported hazard classifications
of the identified substances according to their function. The production volume is in tonnes per year (t/yr) and represents all uses not just the fraction
used in plastics. Data availability is the percentage of substances for which this type of data is available. Intermediates are grouped with monomers,as
they are commonly mentioned together. “Others”is an umbrella for many small, ambiguous, or only remotely plastic-related functions. UVCBs =
substances of unknown or variable composition, complex reaction products, or biological materials, and simple mixtures, or polymers, B&C = building
and construction, EEE = electrical and electronic equipment, PBT = persistence, bioaccumulation, and toxicity, CMR = carcinogenicity, mutagenicity,
or reproductive toxicity, EDC = endocrine-disrupting chemicals, AqTox = chronic aquatic toxicity, and STOT_RE = specific target organ toxicity upon
repeated exposure.
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More than 25% of the substances (2'703 CASRNs) are
UVCBs, mixtures, and polymers, whereas almost all the rest
(7'561) are individual compounds (Figure 2A). The majority of
individual compounds are organic ones (6'513), including 232
organosilicons, 228 organophosphorus, 418 organosulfurs,
1'189 organohalogens, and 1'268 organic metal(loid) salts,
metalorganics, or organometallics. For 2.5% of the identified
substances (283), their substance types are currently uncategor-
izable (Figures 2A, 3data availability) because they are
registered by their trade or trivial names [for example, Ixol M
125 (CASRN 86675-46-9), C.I. Pigment Yellow 157 (CASRN
68610-24-2)] and lack other identifiers such as SMILES or
molecular formulas that can reflect their chemical structures.
Information availability varies considerably among the 10'547
substances, with most substances having information on their
use or registration status in specific regions (>90%), followed by
production volumes (70%), functions (69%), and any reported
hazard classifications (61%). For the rest, substantial informa-
tion gaps persist: industrial sectors of use (40%), regulator-
harmonized hazard classifications (22%), and compatible
polymer types (16%). Around 3% of the substances lack any
information other than their chemical names and CASRNs
(Figure 2B).
Overall, 55% of the substances identified are categorized as
plastics additives, 39% as processing aids, and 24% as monomers,
with significant overlaps between these three categories. In
addition, due to a lack of information, 30% of the substances
remain uncategorizable regarding their functions (Figure 2C).
Overall, more than 90% of the substances are registered for
production and use in one or more of the regions or countries
considered; about 55% are registered in more than 9 countries
and regions, compared to 7% that are region/country-specific. In
individual countries or regions, 20−80% of the substances are
registered (Figure 2D). Inventories from the US, EU, and
Nordic countries (Denmark, Finland, Norway, and Sweden)
contain publicly accessible use information; our analysis shows
that many of the identified substances are seemingly registered
for uses without direct linkages to plastics in these inventories
(US: 50%, EU: 50%, and Nordic countries: 20%; Figure 2D).
Reasons for this reporting difference may be actual uses for other
purposes, ambiguity in the reporting, or under- or misreporting.
For example, tetrabromobisphenol A bis(dibromopropyl ether)
(TBBPA-BDBPE; CASRN 21850-44-2; a flame retardant) and
Tinuvin 765 (CASRN 41556-26-7; a light stabilizer) are
registered in both the SPIN and REACH databases, but their
use in plastics is reported in only one (Tinuvin 765 in the SPIN
database and TBBPA-BDBPE in the REACH database).
3.2. Overview of the Use Patterns. Functions are
identified for a majority of the substances (7'265 CASRNs,
69%), in comparison to the much lower identification of
information on compatible polymer types (3'002 CASRNs,
28%) and industrial sectors of use (4'383 CASRNs, 42%).
Typically, substances can fulfill several functions (on average,
two to three functions), be used in multiple polymer types
(particularly in similar polymer types such as polyolefins), and
be used in multiple industrial sectors (Figure 3). A total of 2'263
CASRNs are reported for use in the following applications with
high exposure potential: 2'109 in food-contact applications, 522
in toys, and 247 in medical items including masks (Sheet S8 in
Supporting Information S1 under the “industrial_sector”).
Based on the production volumes reported in the EU, the US,
and the Nordic countries and the OECD HPVC list, about 4'000
substances are HPVCs (i.e., >1'000 t/yr; Figure 3); however,
these represent their total production volumes for all uses and
not just the fractions used in plastics. If production volumes in
other regions were available, more substances might be
identified as HPVCs. Furthermore, the production volumes of
many substances have been reported as “confidential”; their
share was the largest for antioxidants (10%), flame retardants
(11%), and uncategorizable substances (12%).
3.3. Substances of Potential Concern and Their
Regulatory Status. In total, reported hazard classifications
Table 1. Overview of Substances of Potential Concern Used as Plastic Monomers, Additives, or Processing Aids
a
vPvB = very persistent and very bioaccumulative, PBT = persistence, bioaccumulation, and toxicity, CMR = carcinogenicity, mutagenicity, or
reproductive toxicity, EDC = endocrine-disrupting chemicals, AqTox = chronic aquatic toxicity, and STOT_RE = specific target organ toxicity
upon repeated exposure.
b
HPVC = high production volume chemical, that is, production volume larger than 1'000 t/yr. Only their total production
volumes for all uses (including ones other than in plastics) are available.
c
Under any of the regulations considered in this study (Sheet S2 in
Supporting Information S1).
d
The percentage of the total number of chemicals within that hazard group.
e
The percentage of the number of
chemicals from regulator-harmonized hazard data within that hazard group.
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are available for about 6'400 substances (61%), whereas about
4'100 substances (39%) lack any reported hazard classifications
in the considered regulatory databases (unknown level of
concern). Most substances with unknown levels of concern lack
information about their functions (Figure 2B), are not HPVCs
in the EU or the US or in the OECD countries, and belong to
UVCBs, mixtures, and polymers (Figure S19 in Supporting
Information S2).
In total, 3'950 substances (37%) do not meet any of the
considered hazard criteria, while their hazard classifications are
available; these are designated as substances of a low level of
concern. Another 2'486 substances (24%) meet one or more of
the hazard criteria considered and are identified as substances of
potential concern; among them, 1'254 substances (12%) are also
HPVCs and thus of a high level of concern. The remaining 1'232
substances (12%) are of a medium level of concern.
An overview of all substances of potential concern is provided
in Table 1, and the entire substance list is provided in Sheet S9 in
Supporting Information S1. In short, 22 substances are PBT and
another 35 are vPvB substances. A total of 2'368 substances
show toxicity of concern, including 951 CMR toxicants, 30
EDCs, 1'646 substances that can cause chronic aquatic toxicity,
and 891 substances that may cause specific target organ toxicity
upon repeated exposure.
Around 53% of the substances of potential concern are not
subject to any sort of management measures under one or more
of the regulations considered in this study (Table 1). Five
percent (136 CASRNs) of the substances of potential concern
are regulated under the Stockholm Convention, the Rotterdam
Convention, or the Montreal protocol. Additionally, 960 of the
substances of potential concern are subject to national/regional
restrictions (EU: 135; Republic of Korea: 46; and Japan: 16),
authorizations (EU: 53; Republic of Korea: 362; and Japan: 15),
or prohibitions in specific areas (EU, toys: 440 and EU,
electronic waste: 102). Surprisingly, despite having highly
problematic hazardous properties, 901 substances of concern
also appear on the regulatory positive lists for use in food-
contact plastics (EU: 225; Japan: 568; and US: 667; see columns
under “RegulationFood-contact positive lists”in Sheet S9 in
Supporting Information S1).
The number of scientific references that are linked in
SciFinder varies greatly per substance (range = 0−1'086'797
and median = 1'410; see Figures S16 and S24 in Supporting
Information S2). Around 10% of the identified substances of
potential concern lack any scientific references in SciFinder,
indicating that they may have been poorly studied (Table 1), of
these 10% most are UVCBs, mixtures, and polymers.
4. DISCUSSION
4.1. Numbers of Plastic Monomers, Additives, and
Processing Aids on the Market. This study has identified
over 10'000 CASRNs that are or may potentially be used as
plastic monomers, additives, and processing aids. This number is
much higher than previous studies because of the broader scope,
whereas earlier studies have focused on plastic packaging (4'000
substances)
13
and plastic additives with registered tonnages
above 100 t/yr in the EU (400 substances).
12
Even so, these
10'000 identified substances might still be an underestimate of
the total number of substances present in plastics, mainly due to
the following three clusters of reasons:
I There is a general lack of transparency regarding
substances present in plastics.
66,67
Existing practices of
national/regional chemical inventories provide limited
help on this matter, due to (1) limited public accessibility
of production and use information (e.g., only three of the
21 investigated inventories made use information public;
much of the information reported in these three
inventories is claimed to be “confidential business
information”) and (2) incompleteness (e.g., reduced
reporting requirements for low production volume or
“non-hazardous”chemicals
62
). Currently, several initia-
tives targeting better communication of information on
chemicals in products along supply chains have been
initiated, for example, the EU Sustainable Product Policy
Initiative,
67,68
the Substances of Concern In articles or
Products database (SCIP database) hosted by the
European Chemicals Agency (ECHA),
69
and the HolyG-
rail Project led by P&G (under the New Plastics Economy
program of the Ellen MacArthur Foundation).
70
How-
ever, their effective implementation is currently hindered
by factors such as (claims of) complex supply chains,
diverging interests and technical capacities of actors
within supply chains, and data storage and transfer
issues.
71,72
II Not all data in the public domain are readily machine-
accessible and processable; in this study, substances for
which the assigned CASRNs are not provided are
excluded from the analysis, including ions for ionizable
substances or structural isomers (see Section 2.2). This is
largely due to a combination of the following reasons: (1)
the wide use of nonmachine-readable data formats; (2)
current limitations in reporting all relevant substances,
including the common use of ambiguous trivial names and
group names such as phenolic antioxidants without
specifying relevant substances, the wide use of different
names for the same substances, the underuse of unique
identifiers such as assigned CASRNs, SMILES, and
InChI(Key),
62
and common mixed reporting of neutral,
ionized substances, isotopologues, and other isomers
using the same identifiers such as CASRNs and chemical
names; and (3) a lack of standardized terminology for use
patterns across jurisdictions. Concerted efforts to address
these problems are necessary to improve, harmonize, and
foster nonambiguous reporting of substance identities
and use patterns by all stakeholders across the world,
building on existing initiatives.
3,73−76
In addition,
advances in information technologies (such as optical
character recognition, natural language processing, and
cheminformatics tools) to unambiguously recognize
different types of chemical identifiers in the text and
convert between them may help collect information that
currently requires manual processing.
77−81
III Besides the intentionally added substances considered in
this study, also NIASs are highly relevant for plastics
because (1) they have been frequently reported in
measurements, (2) plastics in many applications are
prone to contamination from production, processing, and
use, and (3) substance transformation is an integral part of
fulfilling specific functions (e.g., formation of quinones
from oxidization of phenolic antioxidants).
10,41,82−84
However, NIASs are not yet comprehensively under-
stood, their identification remains challenging, not least
because of a dearth of clarity on plastic compositions and
conditions during production and use, and analytical
difficulties of unequivocally identifying substances at low
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concentrations remain.
10,11,41
To improve NIAS identi-
fication and quantification, measures such as increasing
product transparency through company reporting,
obligatory provision of analytical standards, and stand-
ardization of sample treatment, separation, and data
treatment procedures may be taken.
41
Meanwhile, for the 10'000 substances identified here, some
uncertainties may remain regarding their use in plastics and their
commercial relevance despite several measures for QA. For
example, the keyword search in substance identification
(Section 2.2) might have yielded substances that are relevant
for polymers in uses other than plastics (e.g., polymeric
adhesives) or substances used for plastic-related functions but
appearing in other materials (e.g., flame retardants in fabrics and
plasticizers in concrete formulations). In addition, in the analysis
of regional registrations and production volumes (Section 2.2),
the current commercial status is not fully covered, as some
substances may no longer be in use or might only be used in
materials other than plastics (see the next subsection).
4.2. Interpretation of Use Patterns and Their Un-
certainties. In line with earlier research, many of the substances
identified in this study can be used for different functions in
multiple polymer types and industrial sectors.
12,13
Regarding
substances in food-contact applications, a comparison with the
recently compiled database of intentionally added food-contact
chemicals (FCCdb) showed that despite identifying fewer
substances, this study has a good overlap with the FCCdb (this
study: 2'109 CASRNs; FCCdb: 11'609 CASRNs; overlapping
substances identified by both: 2'026 CASRNs).
85
The results regarding use patterns (Section 3.2, especially
Figure 3) need to be interpreted with caution, as only the
number of substances potentially used for different functions
(dominated by 3'663 colorants and 1'833 fillers) and the total
production volume for all uses (including uses for other
functions and in other materials) is presented. A recent market
study based on global production volumes shows a different
picture that plasticizers, flame retardants, and heat stabilizers
dominate the plastic additive market.
86,87
In addition, solid use
data remain lacking for many of the identified substances,
especially concerning relevant industrial sectors (missing for
58% of the substances) and compatible polymer types (missing
for 72%). Furthermore, uncertainties may be expected for some
of the identified uses for the following reasons:
I Reported uses may be incomplete, outdated, or
inaccurate. For example, diethyl phthalate (DEP,
CASRN 84-66-2) is still frequently reported as a
plasticizer in the scientific literature,
33,88−90
while the
industry has reported phase-out of its use as a plasticizer
(it is now primarily used as a solvent in cosmetics and
other personal care products).
91
Thus, DEP may be
relevant for legacy plastic products and recycled plastics,
but not for new virgin plastics. Minimizing such
uncertainties requires not just gathering more informa-
tion from different sources but rather more stringent
monitoring of industrial activities and comprehensive QC
of existing data (including verifying and updating
information sources on a regular basis).
II Some of the keywords used in the identification process in
this study may still be incomprehensive or inaccurate,
despite efforts to eliminate errors using an iterative
learning approach (Section 2.5). This is because a simple
keyword search cannot take the whole context into
account, cannot distinguish ambiguous terms, and
requires large manual efforts to include infrequent
keywords. An example of the lack of context sensitivity
is benzo[a]pyrene (CASRN 50-32-8). It was first
incorrectly identified as a cross-linking agent, a filler,
and a lubricant; a closer look revealed that it was reported
as a contaminant or byproduct in substances fulfilling
these functions. To more accurately categorize use
patterns, future efforts need to be made both on
developing advanced search algorithms (e.g., using
semantic searches and natural language processing) and
on standardizing use descriptors.
3,74−76,79,80,92
III Some important factors concerning use reporting (such as
registrants’knowledge on the topic, information process-
ing before reporting, and potential ulterior motives
influencing reporting) could not be taken into account.
For example, ulterior motives may play a role in the
comprehensiveness and accuracy of reporting (such as
missed or wrong reporting of risk-related information and
exaggeration of the number of applicable uses).
93,94
4.3. Substances of Potential Concern and Associated
Uncertainties. More than 2'400 substances of potential
concern used in plastics are identified in this study; it may
well still be an underestimate of the number of substances of
concern, as it is only based on reported hazard classification. For
example, many more substances than considered in this study
may be persistent and/or bioaccumulative, as only the
substances with the PBT assessment outcome of fulfilling (or
not fulfilling) all PBT or both vPvB criteria were separately listed
in the REACH PBT assessment list and considered in this
study.
95
Thus, substances that are registered under REACH
fulfilling the P and/or B criteria are not identified in this study,
due to time and resource constraints to individually check their
REACH registration dossiers.
Surprisingly, about 350 substances of potential concern
appear on both negative (e.g., authorization requested for
specific uses and bans in certain applications) and positive (i.e.,
approval for use in food-contact plastics) regulatory lists. For
example, while authorization is required for use of dibutyl
phthalate (CASRN 84-74-2) in the EU and Republic of Korea, it
is approved for use in food-contact plastics in the EU, US, and
Japan. This regulatory inconsistency needs to be properly
addressed, for example, through closer collaboration among
regulatory domains and agencies.
96
In this study, the production volume is used as a rough
surrogate to reflect exposure potential of a chemical. More
realistic exposure estimates for a large set of chemicals are
currently not possible to make due to a lack of substance- and
use-specific information in the public domain.
37,97
Substance-
specific information is particularly lacking for metal-containing
organic substances (30% of the identified substances) and
surfactants, as measurements or estimations of substance
properties such as partition and diffusion coefficients remain
difficult to do or make for these substances.
98,99
Future work
may focus on, for example, developing new approaches for
measuring or estimating partition and diffusion coefficients of all
substances and generating and releasing detailed use informa-
tion such as used volumes, product contents, and release
potential concerning individual uses.
100
The screening of regulations in this study reveals some gaps
and inconsistencies; this effort is not comprehensive. This is
partially due to (1) a lack of easy information access to
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regulations in many parts of the world, (2) a common listing of
groups of substances using generic descriptions without
specifying individual substances, and (3) general challenges in
identifying all relevant substances by manual list curation or
manual search. An example of (2) is that the listing of PFOA-
related compounds under the Stockholm Convention refers to
“any substances that degrade to PFOA, including any substances
(including salts and polymers) having a linear or branched
perfluoroheptyl group with the moiety (C7F15)C as one of the
structural elements”; the recognition of individual substances
such as “alkyl iodides, C10−12,γ,ω-perfluoro”(CASRN 68390-
33-0) as PFOA-related compounds currently requires expert
knowledge. Therefore, facilitating information access to
regulations around the world, for example, through a global
virtual knowledge base and further developing cheminformatics
tools that help identify whether a substance is listed based on its
molecular structure can be highly useful. Specifically, data
engines that are capable of identifying all related CASRNs,
chemical names, and structures and of indexing them based on
InChI(Keys) could prove to be beneficial in this work.
5. POSSIBLE WAYS FORWARD
This study identifies over 10'000 plastic-related substances and
details several critical knowledge and data gaps, particularly in
terms of substance- and use-specific information. This scale of
chemicals to be addressed may be much greater than previously
expected according to previously published assessments. Here,
we highlight the following overarching areas that warrant
concerted international efforts, in order to address these
chemicals efficiently and effectively. This study can also serve
as a starting point of immediate action, for example, by
prioritizing substances of potential concern and the critical
knowledge and data gaps identified above. Furthermore, while
this study focuses on plastic monomers, additives, and
processing aids, many of the lessons learned may also be used
to enhance the general sound management of chemicals.
5.1. Establishing a Centralized Knowledge Base.
Information on chemicals is scattered throughout the public
domain, resulting in numerous difficulties in understanding the
presence of chemicals in plastics and other products and their
properties and risks, as illustrated above. It may be worthwhile to
consider establishing an open and transparent centralized
knowledge base of chemicals in products with inputs and
support from all relevant stakeholders along the supply chains
(e.g., chemical and material producers, product designers,
retailers, and waste managers). It can contribute to a better
overview of relevant chemicals and related information and thus
provide a basis for prioritization of future work, for example,
based on production volumes and/or hazardous properties.
Such a knowledge base could build on this work and other
existing public databases (e.g., PubChem, SciFinder, OECD
eChemPortal, CAS Common Chemistry, and USEPA Comp-
Tox Chemicals Dashboard) and industrial transparency
initiatives [for example, Global Automotive Declarable Sub-
stance List (GADSL), the HolyGrail project led by P&G].
70
The
costs of establishing and maintaining such a large database can
be perceived an impediment, as well as questions around data
ownership (e.g., CASRNs are intellectual properties of the
Chemical Abstracts Service and may require licensing for
publication).
101
Options to navigate these barriers to access may
include cofunding such an initiative through public−private
partnerships, as a part of companies’corporate social
responsibility and commitments to the human right to science,
and harmonizing information exchange standards across the
existing major databases to allow easy retrieval and compilation
of information at one central place.
102−104
Regardless, trans-
parency, independence, and open accessibility are crucial for
such a knowledge base, and strong leadership through national
and/or international governmental organizations (e.g., United
Nations Environment Programme, OECD, ECHA) is needed
for setting it up.
5.2. Ensuring Transition to a Safe and Sustainable
Circular Plastic Economy. Avastnumberofdiverse
substances are potentially used in the manufacture of plastics,
with over 20% being substances of potential concern. Mean-
while, current regulations, scientific and regulatory monitoring
efforts, and industry initiatives lag far behind the introduction of
these substances to the market, to ensure clean, safe, and high-
quality virgin and recycled plastics. For example, the current
European chemicals regulations mostly focus on single
substances and/or certain industrial sectors (e.g., plastics for
food-contact purposes, in toys, in electrical and electronic
equipment, and in automotive applications).
105−107
Similarly,
current industrial circular economy initiatives focus primarily on
the material level (e.g., using the same polymer for multilayer
plastics to increase recyclability), with limited attention paid to
the chemicals therein.
108−113
To ensure the transition toward a safe and sustainable circular
plastic economy, concerted efforts by all stakeholders are needed
in at least the following areas:
114
developing standardized
approaches to assessing the sustainable circularity of plastics and
chemicals therein; avoiding hazardous substances and embed-
ding sustainable circularity in the design phase of plastic
polymers, additives, processing aids, and value chains; fostering
greater transparency throughout value chains including waste
management and broadening monitoring efforts; developing
and sharing knowledge on creating sustainable circularity of
plastics and chemicals therein; and fostering innovative and
chemical management enabling business models and practices.
The information compiled in this study may help initial
screenings of safer alternatives in specific applications, followed
by more detailed alternative assessments.
115
Note that the
indispensability or “essential”use of a substance for a specific
function/performance (in a specific application) may also be
evaluated first to phase out those uses that are nonessential and
thus reduce the numbers of existing chemicals on the market and
their uses to be assessed and transitioned.
114−118
5.3. Expanding and Harmonizing Regulatory Efforts.
Current chemical regulation does not ensure global sustainable
management of chemicals for several reasons: (a) not all
substances of potential concern are listed under relevant
international or regional regulations (Section 3.3); (b)
substance-by-substance regulations may not protect against
regrettable substitutions;
119,120
(c) regional regulations might
lead to shifting chemical pollution elsewhere;
121
and (d)
negative externalities (e.g., monitoring costs, potential cleanup
costs, public health damages, and impaired ecosystem services)
of chemicals throughout their life cyles are not fully addressed by
current regulations.
122,123
Potential ways forward include (a)
increasing the number of substances under regulatory scrutiny to
cover all substances of potential concern;
124
(b) focusing on
group- or class-based regulatory approaches to avoid substitut-
ing one hazardous substance with another hazardous one in the
same group or class;
125,126
(c) fostering cooperation among
regulators from different fields
96,127
and regions
128,129
to ensure
consistent measures and avoid shifting pollution to countries
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with less stringent regulations; and (d) complementing current
regulation with market-based policy instruments to internalize
externalities and incentivize true innovation and pioneers.
114
Examples of market-based policy instruments include tradable
use permits or a Pigouvian tax, where the raised governmental
revenue is used to finance cleanup or chemical-related public
health costs and helps to create financial incentives for avoiding
the use of hazardous or unnecessary chemicals.
122,123
Overall,
concerted efforts from industry, civil society organizations, the
scientific community, regulatory agencies, and other policy-
makers are urgently needed to ensure sustainable chemicals
management in the future.
■ASSOCIATED CONTENT
*
sıSupporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.est.1c00976.
Excel file with large tables presenting data sources and
retrieval, keywords for the categorization, and overviews
of all substances and substances of potential concern
(ZIP)
PDF file presenting details on methods, additional results,
and additional discussion on chemicals on the global
market (PDF)
■AUTHOR INFORMATION
Corresponding Authors
Helene Wiesinger −Chair of Ecological Systems Design,
Institute of Environmental Engineering, ETH Zürich, 8093
Zürich, Switzerland; orcid.org/0000-0003-4154-5907;
Email: wiesinger@ifu.baug.ethz.ch
Zhanyun Wang −Chair of Ecological Systems Design, Institute
of Environmental Engineering, ETH Zürich, 8093 Zürich,
Switzerland; orcid.org/0000-0001-9914-7659;
Email: Zhanyun.wang@ifu.baug.ethz.ch
Author
Stefanie Hellweg −Chair of Ecological Systems Design, Institute
of Environmental Engineering, ETH Zürich, 8093 Zürich,
Switzerland
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.est.1c00976
Notes
The authors declare no competing financial interest.
■ACKNOWLEDGMENTS
We gratefully acknowledge the financial support of the Swiss
Federal Office for the Environment (8T20/17.0103.PJ), the
Swiss Federal Office of Public Health (18.000809), and the
Canton of Zurich’sOffice for Waste, Water, Energy and Air
(85P-1454). We thank Magdalena Klotz and Melanie Haupt
(ETH Zurich) for their valuable feedback and discussion,
Joanna Houska (EAWAG/EPFL, former ETH Zurich) for the
initial compilation of various relevant data sources and feedback
on the final manuscript, and Christopher Oberschelp (ETH
Zurich) for his valuable input regarding confidence assessment
of sources. We further thank the members of the Clean Cycle
Advisory Board for their feedback and support, the anonymous
reviewers for their comments and suggestions to improve the
manuscript, and Naomi Lubick for her technical editorial
support.
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