N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) and its Transformation Product, 6PPD-quinone; Regulatory Investigation Under the Toxic Substances Control Act (TSCA), 91299-91312 [2024-26894]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 89, Number 223 (Tuesday, November 19, 2024)]
[Proposed Rules]
[Pages 91299-91312]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-26894]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 751

[EPA-HQ-OPPT-2024-0403; FRL-11628-01-OCSPP]
RIN 2070-AL16


N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its 
Transformation Product, 6PPD-quinone; Regulatory Investigation Under 
the Toxic Substances Control Act (TSCA)

AGENCY: Environmental Protection Agency (EPA).

ACTION: Advance notice of proposed rulemaking (ANPRM).

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SUMMARY: In granting a petition filed under the Toxic Substances 
Control Act (TSCA) by Earthjustice on behalf of the Yurok Tribe, the 
Port Gamble S'Klallam Tribe, and the Puyallup Tribe of Indians, the 
Environmental Protection Agency (EPA or Agency) committed to pursuing 
an action to solicit and collect information from the public on the 
potential risks associated with N-(1,3-Dimethylbutyl)-N'-phenyl-p-
phenylenediamine (6PPD) (CASRN 793-24-8, DTXSID 9025114) and its 
transformation product, 6PPD-quinone (CASRN 2754428-18-5, DTXSID 
301034849). With this document, EPA is soliciting that information, 
along with information about potential alternatives and regulatory 
options to help inform the Agency's consideration of potential future 
regulatory actions under TSCA.

DATES: Comments must be received on or before January 21, 2025.

ADDRESSES: Submit your comments, identified by docket identification 
(ID) number EPA-HQ-OPPT-2024-0403, through https://www.regulations.gov. 
Follow the online instructions for submitting comments. Do not submit 
electronically any information you consider to be Confidential Business 
Information (CBI) or other information whose disclosure is restricted 
by statute. Additional instructions on commenting and visiting the 
docket, along with more information about dockets generally, is 
available at https://www.epa.gov/dockets.

FOR FURTHER INFORMATION CONTACT: 
    For technical information: Wyn Zenni, Existing Chemicals Risk 
Management Division (7404M), Office of Pollution Prevention and Toxics, 
Environmental Protection Agency, 1200 Pennsylvania Ave. NW, Washington, 
DC 20460-0001; telephone number: (202) 565-6294; email address: 
[email protected].
    For general information on TSCA: The TSCA Hotline, ABVI-Goodwill, 
422 South Clinton Ave., Rochester, NY 14620; telephone number: (202) 
554-1404; email address: [email protected].

SUPPLEMENTARY INFORMATION:

I. Executive Summary

A. Does this action apply to me?

    You may be potentially affected by this action if you manufacture 
(including import), process (including recycling), distribute in 
commerce, dispose of, or use 6PPD and/or 6PPD-quinone. The following 
list of North American Industry Classification System (NAICS) codes is 
not intended to be exhaustive, but rather provides a guide to help 
readers determine whether this document applies to them. Potentially 
affected entities may include:
     325130 Synthetic Dye and Pigment Manufacturing;
     325199 All Other Basic Organic Chemical Manufacturing ;
     325212 Synthetic Rubber Manufacturing;
     325998 All Other Miscellaneous Chemical Product and 
Preparation Manufacturing;
     326211 Tire Manufacturing (Except Retreading);
     326291 Rubber Product Manufacturing for Mechanical Use;
     336999 All Other Transportation Equipment Manufacturing; 
and
     424690 Other Chemical and Allied Products Merchant 
Wholesalers.
    If you have any questions regarding the applicability of this 
action to you, please consult the technical information contact listed 
under FOR FURTHER INFORMATION CONTACT.

B. What is the Agency's authority for taking this action?

    This action is being taken under the Toxic Substances Control Act 
(TSCA), 15 U.S.C. 2601 et seq.
    TSCA section 21 allows any person to petition EPA to initiate a 
rulemaking proceeding for the issuance, amendment, or repeal of a rule 
under

[[Page 91300]]

TSCA sections 4, 6, or 8 or an order under TSCA sections 4, 5(e) or 
(f). If EPA grants the petition, the Agency must promptly commence an 
appropriate proceeding.
    Under TSCA section 6(a), if EPA determines that the manufacture, 
processing, distribution in commerce, use, or disposal of a chemical 
substance presents an unreasonable risk to human health or the 
environment, it must ``apply one or more of the [TSCA section 6(a)] 
requirements . . . to the extent necessary so that the chemical 
substance . . . no longer presents such risk,'' which may range from 
prohibiting or otherwise restricting the manufacturing, processing, or 
distribution in commerce of the chemical substance (or a particular 
use), to commercial use requirements or disposal restrictions, to 
labeling and recordkeeping.

C. What action is the Agency taking?

    EPA is seeking public comment on all of the information included in 
and referenced by this ANPRM. EPA also seeks any additional information 
relevant to 6PPD, 6PPD-quinone, and potential 6PPD substitutes that 
could help inform potential future rulemakings. Topics in this ANPRM 
include but are not limited to: Information on the chemicals' 
environmental effects on aquatic and terrestrial ecosystems, potential 
human health effects, environmental fate and transport, exposure 
pathways, persistence and bioaccumulation, additional uses of 6PPD, and 
releases from consumer products (e.g., sneakers, playgrounds, rubber-
modified asphalt, reused tire or other rubber products, etc). EPA is 
also seeking comment and information related to alternatives to 6PPD, 
as well as potential chemical transformation products associated with 
potential alternatives.
    When submitting information, the Agency is interested in receiving 
quantitative information, data and/or case examples, including peer-
reviewed studies, statistical analyses, and industry, scientific, or 
technical reports describing datasets or syntheses of environmental or 
human health impacts of 6PPD, 6PPD-quinone, or potential alternatives 
for 6PPD.

D. What are the incremental costs and benefits of this action?

    This action does not propose or impose any requirements, and 
instead seeks comments and suggestions that will help inform the 
Agency's consideration of potential future actions for 6PPD and/or 
6PPD-quinone. As such, there are no incremental costs or benefits 
associated with this ANPRM. Should the Agency pursue a rulemaking in 
the future, EPA will conduct the appropriate assessments of the 
potential costs and benefits associated with the proposed action.

E. What should I consider as I prepare my comments for EPA?

1. Submitting CBI
    Do not submit CBI to EPA through https://www.regulations.gov or 
email. If you wish to include CBI in your comment, please follow the 
applicable instructions at https://www.epa.gov/dockets/commenting-epa-dockets#rules and clearly mark the information that you claim to be 
CBI. Information so marked will not be disclosed except in accordance 
with procedures set forth in 40 CFR parts 2 and 703.
2. Tips for Preparing Your Comments
    When preparing and submitting your comments, see the commenting 
tips at https://www.epa.gov/dockets/commenting-epa-dockets.html.

II. Background

A. What was requested in the TSCA section 21 petition for 6PPD?

    On August 1, 2023, Earthjustice, on behalf of the Yurok Tribe, the 
Port Gamble S'Klallam Tribe, and the Puyallup Tribe of Indians, filed a 
TSCA section 21 petition requesting that EPA establish regulations 
prohibiting the manufacturing, processing, use, and distribution of 
6PPD (CASRN 793-24-8, DTXSID 9025114) in and for tires under EPA's TSCA 
section 6(a) authority, 15 U.S.C. 2605(a). The petitioners requested 
that such regulation take effect as soon as practicable to eliminate 
the unreasonable risk 6PPD in tires presents to the environment (Ref. 
1).
    In the petition, concerns were raised that the chemical 6PPD, which 
has been used in tires since the 1960s to prevent tire degradation 
(Ref. 2), poses unreasonable risk to the environment due to the acute 
toxicity of its transformation product, 6PPD-quinone (CASRN 2754428-18-
5, DTXSID 301034849), to coho salmon (Oncorhynchus kisutch) and other 
fish species. The petition described that the presence of 6PPD-quinone 
in stormwater runoff and urban watersheds are at levels that can kill 
coho salmon (O. kisutch), steelhead trout (Oncorhynchus mykiss), and 
other aquatic organisms. The petition also referenced the presence of 
6PPD-quinone in sediments and soils, road and household dust, and the 
urine of pregnant women, with emerging science pointing to potential 
risks to human health and to a larger extent, toxicity in mammals (Ref. 
1).
    On November 2, 2023, EPA granted the petition, stating that the 
petition, along with information reasonably available to EPA, set forth 
facts establishing that it was appropriate to initiate a TSCA section 
6(a) proceeding to address risks to the environment from 6PPD and its 
transformation product, 6PPD-quinone (Ref. 3 [3]). Specifically, EPA 
committed to: (a) Issuing an ANPRM for 6PPD and 6PPD-quinone under TSCA 
section 6(a) by fall 2024; and (b) Finalizing a TSCA section 8(d) 
rulemaking by the end of 2024 that would require persons who 
manufacture (including import) 6PPD to submit lists or copies of 
unpublished health and safety studies to EPA. With this action, the 
Agency has promptly commenced an appropriate proceeding. The expected 
information resulting from this action will inform the Agency's 
consideration of future potential action though, as noted in the 
petition response, EPA cannot commit to a specific timeframe or outcome 
(Ref. 3).

B. What is 6PPD?

1. Physical and Chemical Use Properties
    6PPD is the organic compound N-(1,3-dimethylbutyl)-N'-phenyl-p-
phenylenediamine (CASRN 793-24-8, DTXSID 9025114), which is added to 
tires and other rubber products to prevent degradation. As a solid, 
6PPD is dark brown with violet flakes and is generally sold as pellets, 
pastilles, or in liquid form (Refs. 4 and 5). 6PPD can diffuse easily 
to the surface of a rubber product and quickly react with ozone 
(O3) to protect the rubber polymers from oxidation (Ref. 5). 
This chain of events occurs quickly enough to effectively protect the 
rubber but slowly enough to last for the lifetime of the product, which 
has made 6PPD a useful antidegradant for use in rubber products (Ref. 
6).
2. 6PPD's Use in Tires
    6PPD has been used globally since the 1960s as an antidegradant and 
antiozonant to prevent automobile tire degradation caused by exposure 
to ozone, oxygen, and temperature fluctuations (Refs. 2 and 7). By 
continuously migrating to the surface of the tire to fill microcracks 
and react with oxygen and ambient ozone in the environment, 6PPD 
protects the tire's rubber polymers from becoming brittle and cracked 
over time (Ref. 4). In doing so, 6PPD increases tire longevity, safety, 
and performance due to its ability to protect tires from premature 
degradation (Ref. 4).

[[Page 91301]]

    Products that use recycled tire crumbs or pieces such as rubber-
modified asphalt, playgrounds (rubber mulch), artificial turf, and 
sneakers may also contain 6PPD (Refs. 8 and 9).
3. 6PPD's Use in Other Products
    6PPD is also used as an additive in other rubber goods (e.g., 
conveyor and transmission belts, hoses, and gaskets), other automotive 
parts (e.g., engine mounts, grommets, bushings, and seals), polymers, 
lubricants, dyes, and other house-hold or recycled rubber products 
(Refs. 4, 10, and 11). Little information on the release of 6PPD and/or 
6PPD-quinone from these non-tire products currently exists.
4. Environmental Fate and Transport of 6PPD
    Although more information is needed on the environmental fate and 
transport of 6PPD, one source of 6PPD in the environment occurs through 
the release of tire wear particles (TWP) from tires containing 6PPD 
(Refs. 12, 13, 14, and 15). Though limited data suggest 6PPD has a 
short half-life (hours to several days) in aqueous solutions (Ref. 16), 
TWP are continuously being emitted into the environment, especially as 
cars brake, accelerate, or turn (Refs. 17, 18, and 19). It is believed 
that TWP reach soils and aquatic media close to roadways, with a small 
fraction emitted into the atmosphere or sorbed to sediments (Refs. 4 
and 19). During rainfall events, TWP can be mobilized from roads and 
road dust into nearby waterbodies (Ref. 20). For example, one study in 
Denmark investigating the annual TWP generated in a local road network 
and released into the aquatic environment found that 8-40 percent of 
the TWP from the roads reached surface waters after storm events 
depending on the stormwater treatment system (Ref. 21).
    Once TWP containing 6PPD enter the environment, it is hypothesized 
that the environmental transformation of 6PPD primarily occurs through 
hydrolysis (water breaking down chemical bonds) or by reaction with 
oxygen and ozone and photodegradation from exposure to sunlight and air 
(Ref. 4). The more frequent detection of 6PPD in extractions from TWP 
but not road runoff suggests that these reactions occur on the surface 
of the tire or road and/or that 6PPD rapidly transforms once released 
from the tire (Ref. 4). However, fully understanding these processes 
since 6PPD is such a reactive compound remains an information gap.
    Abiotic degradation of 6PPD occurs in water and the atmosphere. In 
water, 6PPD is highly reactive and can be affected by the water's pH, 
temperature, available sunlight, and other constituents in water such 
as metals (Ref. 4). Reported half-lives in water have ranged between 
3.4 hours to less than a day, with warmer waters containing more heavy 
metals leading to a shorter half-life of 6PPD (Refs. 4 and 16). In the 
atmosphere, 6PPD can degrade quickly via indirect photodegradation, 
with a half-life in air between 1-2 hours, further limiting the gas 
phase dispersal of the unreacted chemical (Ref. 22). Direct entry into 
the environment in the gas phase is likely limited given the low vapor 
pressure of 6PPD (Ref. 22).
    As for 6PPD's degradation in sediments, very little is known. 
Initial indications suggest that 6PPD is likely to adsorb to organic 
matter such as soil, sediments, and suspended particulate matter once 
released into the environment. This suggests that it may persist in 
aquatic and terrestrial sediments unless it undergoes photodegradation 
and hydrolysis through resuspension (Ref. 4). There are no available 
data on how 6PPD adheres to and binds to soil under different 
environmental conditions, but leaching of 6PPD through soil to 
groundwater is anticipated to be unlikely (Ref. 4). EPA's Estimation 
Program Interface (EPI) Suite estimates 6PPD's half-life to be 75 days 
in soil with photodegradation likely being the main process in which it 
is lost in surface soils (Refs. 4 and 23).
5. 6PPD's Transformation Products
    Both in tires and in TWP, 6PPD reacts at the rubber's surface with 
ambient ozone (O3) and possibly secondary O3-
related oxidants (e.g., OH-). 6PPD has less reactivity with molecular 
oxygen (O2) and other ambient air constituents (Refs. 18 and 
22). 6PPD's high reactivity with ozone triggers chemical reactions, 
resulting in the formation of transformation products (TPs) as the 
chemical undergoes structural changes and/or the formation of 
degradants as the chemical breaks down into smaller molecules (Refs. 18 
and 24). The resulting transformation products can be more or less 
mobile and more or less toxic in the environment than their parent 
compound, with 6PPD-quinone generally being more toxic to fish, more 
stable, and more mobile than 6PPD according to available data (Refs. 
18, 25, and 24). Studies have identified 25-38 ozonation transformation 
products for 6PPD that form depending on the environmental conditions, 
but more research on the hazard traits and behaviors of these 
transformation products is needed as data are still insufficient (Refs. 
18 and 26). One recent study identified four of 6PPD's most abundant 
transformation products, including 6PPD-quinone, as the most 
environmentally relevant because they were observed in roadway runoff, 
indicating that they may be ubiquitous contaminants in roadway-impacted 
environments and need further investigation (Ref. 26).

C. What is 6PPD-quinone?

1. Physical and Chemical Properties
    One of 6PPD's transformation products is 6PPD-quinone, or 2-
anilino-5-(4-methylpentan-2-ylamino) cyclohexa-2,5-diene-1,4-dione 
(CASRN 2754428-18-5, DTXSID 301034849). Due to 6PPD's highly reactive 
nature, it is thought that 6PPD is continually reacting with ozone at 
the surface of tires to form 6PPD-quinone (Refs. 6 and 27). As 6PPD-
quinone forms on the surface of the tire, it adds to the protective 
film that 6PPD naturally creates, providing further protection from 
cracking of the tire rubber (Refs. 6, 27, and 28). However, this also 
means that 6PPD-quinone and 6PPD are likely present in most TWP that 
are common in the environment (Refs. 12, 29, and 30).
2. Environmental Fate and Transport
    There are currently little data available to describe the 
environmental fate and transport of 6PPD-quinone, but data from several 
monitoring studies suggest that it persists longer in the environment 
than 6PPD (Ref. 31). One study found that 6PPD-quinone had a half-life 
of 33 hours in dechlorinated tap water compared to 5 hours for 6PPD 
(Ref. 16). The longer persistence of 6PPD-quinone in water indicates 
more potential exposure time to induce toxic effects in aquatic life 
(Ref. 16). Another study found that leachate from TWP remained toxic 
after exposure to extreme heat (80 [deg]C) for 72 hours, suggesting 
that 6PPD-quinone is stable under extreme heat conditions (Ref. 32). It 
is also likely that the polar carbonyl groups (added oxygen atoms from 
oxidation) may make 6PPD-quinone more mobile in the environment than 
6PPD (Ref. 33).

D. What are the ecological effects caused by 6PPD and 6PPD-quinone?

1. Aquatic Ecosystem Effects
    The number of studies on 6PPD and/or 6PPD-quinone's impacts on 
aquatic ecosystems has increased since 6PPD-quinone from TWPs was 
identified in 2020 as the likely causative agent for urban runoff 
mortality syndrome (URMS) (Ref. 32). URMS has been occurring in the 
Pacific Northwest at

[[Page 91302]]

least since it was first reported between 1999-2001, and refers to the 
death of adult fish (particularly coho salmon) that return to urban 
waterways to spawn (Refs. 32 and 34). However, much is still unknown 
about the chemicals' effects on aquatic life generally. As of December 
2023, there were 16 available studies on the hazard effects of 6PPD on 
aquatic species and 26 available studies on the hazard effects of 6PPD-
quinone that were identified by and included in the EPA's ECOTOX 
Knowledgebase (Ref. 35). Those studies along with additional online 
publications (as of July 2024) have primarily evaluated 6PPD-quinone's 
acute mortality impacts on aquatic species (i.e., lethal concentration 
(LC) values) due to its higher reported toxicity, with the majority 
focusing on fish species, compared to aquatic invertebrates and plant 
species.
    For the hazard effects of 6PPD on aquatic species, there are acute 
toxicity data for nine freshwater species as of December 2023. The 
following acute toxicity data includes both the author-reported 
mortality values (LC50) and the EPA-adjusted values (if 
needed) to account for observed chemical loss in studies that only 
measured exposure concentrations at the beginning of the study or not 
at all (Ref. 36). Of the nine studied species, Medaka (Oryzias latipes) 
(author-reported LC50 of 28 [mu]g/L after 96 hours of 
exposure), rare minnows (Gobiocypris rarus) (author-reported 
LC50 of 162 [mu]g/L after 96 hours of exposure; EPA-adjusted 
LC50 of 94.94 [mu]g/L), coho salmon (Oncorhynchus kisutch) 
(author-reported juvenile LC50 of 251 [mu]g/L after 24 hours 
of exposure; EPA-adjusted LC50 of 143.7 [mu]g/L), and 
amphipods (Hyalella azteca) (author-reported juvenile LC50 
of 250 [mu]g/L after 96 hours of exposure; EPA-adjusted LC50 
of 159.7 [mu]g/L) were the most sensitive aquatic species to acute 6PPD 
exposure (Refs. 16, 37, 38, 39, and 40). As for 6PPD's chronic effects 
on aquatic species, data are available for only two aquatic species: 
Medaka (Oryzias) (author-reported lowest observed effect concentration 
(LOEC) of 11 [mu]g/L after an early-life stage test of unknown 
duration) and fathead minnows (Pimephales) (author-reported 
LC50 of 150 [mu]g/L after 28 days of exposure) (Refs. 37 and 
41). Although additional research on the chronic effects of 6PPD will 
be important, acute toxicity is expected to be a more important driver 
for aquatic risk compared to chronic toxicity given the quick 
degradation of 6PPD. In addition, studies on 6PPD's effects on 
estuarine and marine species, as well as algae and vascular plants, are 
extremely limited.
    For the hazard effects of 6PPD-quinone on aquatic species, coho 
salmon (O. kisutch) are the most sensitive species to acute 6PPD-
quinone exposure identified to date, with an author-reported lethal 
concentration (LC50; the concentration that is lethal to 50 
percent of tested organisms) value of 0.041 [mu]g/L for juveniles in 
less than 24 hours (EPA-adjusted LC50 of 0.036 [mu]g/L) 
(Refs. 42 and 43) and up to 0.095 [mu]g/L for adults after 24 hours 
(EPA-adjusted LC50 of 0.092 [mu]g/L) (Refs. 43 and 44), 
indicating potential age-related differences in sensitivity. Other 
identified fish species that are acutely sensitive to 6PPD-quinone 
include: lake trout (Salvelinus namaycush) (LC50 of 0.5 
[mu]g/L after 24 hours of exposure; EPA-adjusted LC50 of 
0.5186 [mu]g/L) (Ref. 45), white-spotted char (Salvelinus leucomaenis 
pluvius) (<1 year juvenile LC50 of 0.80 [mu]g/L after 24 
hours; EPA-adjusted LC50 of 0.5709 [mu]g/L) (Refs. 43 and 
46), brook trout (Salvelinus fontinalis) (~1 year juvenile 
LC50 of 0.59 [mu]g/L after 24 hours) (Ref. 47), rainbow 
trout (Oncorhynchus mykiss) (~2 month juvenile LC50 of 0.64 
[mu]g/L; EPA-adjusted LC50 of 0.2961 [mu]g/L) (~2 year 
juvenile LC50 of 1.00 [mu]g/L after 96 hours) (Refs. 38, 43, 
and 47), and chinook salmon (Oncorhynchus tshawytscha) (582-day old 
LC50 of 82.1 [mu]g/L after 24 hours; EPA-adjusted 
LC50 of 65.68 [mu]g/L) (Refs. 43 and 48).
    These LC50 values for both chemicals were also used to 
support EPA's published screening values for acute 6PPD and 6PPD-
quinone exposure for freshwater fish species (published June 2024) 
which are 8.9 and 0.011 [mu]g/L, respectively (Refs. 36 and 43). EPA's 
acute screening values (published under Clean Water Act Section 
304(a)(2)) are the maximum concentrations of 6PPD and 6PPD-quinone (not 
in mixtures) with associated frequency and duration specifications that 
are expected to support protection of aquatic life from acute effects 
in freshwaters based on currently available scientific data (Refs. 36 
and 43). For comparison, one study that measured the concentration of 
6PPD-quinone in roadway runoff, stormwater-affected creeks, and 
watersheds throughout the U.S. west coast found a widespread occurrence 
of 6PPD-quinone at concentrations ranging from 0.3-19 [mu]g/L following 
storm events, which exceeds EPA's published acute screening value for 
6PPD-quinone (Refs. 32 and 43). Overall, although there is available 
information on the acute LC50 values and impacts on multiple 
fish species, more studies identifying the concentrations of 6PPD and 
6PPD-quinone measured in U.S. waterbodies, the sublethal and chronic 
effects of 6PPD and 6PPD-quinone exposure, and additional toxicity data 
on other aquatic species are important.
    Studies have also identified that certain fish species appear to be 
significantly more sensitive to 6PPD-quinone exposure than other 
species. For example, studies show that coho, steelhead, and chinook 
salmon are sensitive to 6PPD-quinone exposure; however, sockeye and 
chum salmon lacked a similar response and were not significantly 
affected by 6PPD-quinone (Refs. 12 and 49). The modes of action driving 
the large variation in the toxicity of 6PPD-quinone across species 
remains unknown, but one study suggests that a tissue-specific 
disruption of mitochondrial respiration is involved. Increased 
ventilation and gasping of sensitive species (coho salmon, brook trout, 
rainbow trout) was observed after exposure, suggesting that 6PPD-
quinone exposure (5-80 [mu]g/L) impacts cellular respiration and the 
oxygen consumption rate (Ref. 50). Another study found that the large 
increases in hematocrit commonly associated with coho salmon mortality 
after being exposed to roadway runoff could be due to a disruption in 
the blood-brain barrier since plasma leakage from the 
cerebrovasculature was observed (Ref. 51). This early research 
indicates that neurologic, metabolic, and mitochondrial disruption may 
be involved (Refs. 50, 51, and 52), but more research and tests are 
needed to confirm the specific modes of action for 6PPD-quinone and why 
it is acutely toxic to certain species. The mode of action driving 
6PPD's toxicity may be different from 6PPD-quinone's, as 6PPD is toxic 
to many tested aquatic organisms but never reaches the high toxicity 
exerted by 6PPD-quinone to selected species.
    Further, although EPA's published acute screening values for 6PPD 
and 6PPD-quinone in freshwater provided critical concentrations for 
protecting aquatic life from the two chemicals, the reports suggest 
that additional research will be important to fully characterize the 
toxicity of 6PPD-quinone and other key transformation products and 
degradants of 6PPD to aquatic life (Refs. 36 and 43). For example, the 
reports indicated that additional research that includes analytical 
confirmation of 6PPD-quinone is needed, as some of the available 
studies lacked analytical measurements of 6PPD-quinone at the end of 
the tests, which is important given the uncertainty of 6PPD-quinone's 
fate in lab water. In addition, the screening value reports noted that 
most of the available aquatic species' tests on

[[Page 91303]]

acute toxicity were run for only 24 hours (standard test duration for 
acute toxicity tests are 96 hours) and occasionally in overcrowded fish 
tanks (Refs. 36 and 43).
    For these reasons, additional acute and chronic toxicity studies 
that include full analytical measurements at appropriate intervals 
across the study duration that are conducted using standard toxicity 
test guidelines would be useful. Additionally, the completion of tests 
on a broader range of aquatic taxa would provide a broader 
understanding of how these chemicals are impacting fish and other 
aquatic species (Refs. 36 and 43).
2. Terrestrial Ecosystem Effects
    There are very limited data publicly available on how 6PPD and/or 
6PPD-quinone may impact terrestrial ecosystems. As of December 2023, 
there was one available terrestrial study on the hazard effects of 6PPD 
on chicken embryos (Gallus gallus) and five available studies on the 
hazard effects of 6PPD-quinone on nematodes (Caenorhabditis elegans) 
and springtails (Folsomia candida) that passed EPA's ECOTOX screening. 
(Ref. 35).
    In the one terrestrial study focused on the hazard effects of 6PPD, 
3-day old chicken embryos were exposed to 80 different rubber tire 
chemicals in either acetone or water (Ref. 53). Exposure to 6PPD 
resulted in deaths and malformations (EC50 of 1.5 umol 11 days post-
exposure), but the authors reported an incomplete, irregular or flat 
dose-response curve for early death and malformations (Ref. 53). Given 
the incomplete dose-response characterization, more information on 
avian species and other terrestrial organisms will be important to 
further characterize the potential hazard effects of 6PPD.
    Of the five other studies on the hazard effects of 6PPD-quinone on 
terrestrial organisms, four studies investigated the chronic effects of 
6PPD-quinone exposure on nematodes (an invertebrate). One study on 
nematodes found that prolonged exposure to 6PPD-quinone at 1-10 [mu]g/L 
shortened lifespan by up to 27.4 percent due to insulin signaling 
pathway dysfunction, decreased the amount of fertilized eggs due to DNA 
and signaling pathway damage, and decreased pharyngeal pumping and 
locomotion behavior (Ref. 54). Another study by the same authors found 
that after exposing nematodes to environmentally relevant 
concentrations of 6PPD-quinone (0.1-100 [mu]g/L) for 4.5 days (from the 
larval to adult stage), several forms of abnormal locomotion behavior 
and neurodegeneration was observed, with exposure to 100 [mu]g/L 
causing 5 percent lethality (Ref. 55). A similar study on nematodes 
found that 6PPD-quinone exposure negatively affected their digestive 
systems and lipid metabolism, with evidence of lipid accumulation and 
fatty acid deposition (Ref. 56) and that plastic nanoparticles in the 
environment enhanced the neurotoxicity and accumulation of 6PPD-quinone 
in nematodes (Ref. 57). In springtails, a soil organism, one study 
found that 6PPD-quinone exposure impaired the survival of the 
organisms, with a LC50 of 16.31 [mu]g/kg after 28 days of 
exposure (Ref. 58). The studies meeting inclusion requirements for the 
EPA's ECOTOX knowledgebase primarily focus on the impacts of 6PPD-
quinone on invertebrates such as nematodes and springtails; however, 
published data in rodents that are commonly used to inform human health 
hazards and are summarized in Unit II.E.2 may also be informative of 
the ecological effects on mammalian species (Ref. 35). Overall, the 
limited studies available indicate that prolonged exposure to 
environmentally relevant concentrations of 6PPD-quinone induces a 
multisystem toxic response, including neurotoxicity, reproductive 
risks, intestinal damage, and dysfunctions in lipid metabolism with 
bioaccumulation concerns in at least terrestrial invertebrates (Refs. 
54, 55, and 57). However, more studies on the effects of 6PPD and/or 
6PPD-quinone on terrestrial organisms and ecosystems would provide a 
more comprehensive understanding of the impacts of these chemicals 
across the environment.

E. What are the potential exposures to and human health effects of 6PPD 
and 6PPD-quinone?

    There are limited data on the exposure pathways of 6PPD and 6PPD-
quinone, however several recent studies in Asia have predicted 
potential exposure through dust inhalation and ingestion. For example, 
one study in Hangzhou, China measured 6PPD and 6PPD-quinone levels in 
indoor dust and estimated the daily intake of 6PPD and 6PPD-quinone for 
children based on expected ingestion and inhalation rates for indoor 
dust (Ref. 59). The study found 6PPD and 6PPD-quinone to be the 
predominant phenylene diamine (PPD) and PPD-q in indoor dust and that 
children, especially infants, were potentially ingesting 6PPD and 6PPD-
quinone through indoor dust based on the measured concentrations and 
daily intake estimations (Ref. 59). A similar study measured 6PPD-
quinone levels in outdoor dust near roads, homes, and kindergartens in 
Guiyu, an e-waste-exposed area, and in Haojiang, a reference area, from 
2019-2021 (Ref. 60). The study found that 6PPD-quinone levels were 
significantly higher in home and kindergarten classroom dust within the 
e-waste-exposed area compared to the reference area, indicating that 
dust may be an exposure pathway for humans and that e-waste may be 
another potential source of 6PPD-quinone in the environment (Ref. 60). 
Using the measured concentrations of 6PPD-quinone in dust, the study 
also estimated that higher daily intakes of 6PPD-quinone from 
kindergarten classroom dust could be associated with lower body mass 
indexes and higher incidences of influenza and diarrhea in kindergarten 
children, although these data are potentially confounded by other 
environmental stressors and chemicals that may be found within e-waste-
exposed areas (Ref. 60). Another study in Hong Kong that measured the 
environmental occurrence of 6PPD and 6PPD-quinone in road dust to 
estimate potential pathways of human exposure found that exposure 
levels for contaminated road dust were higher for 6PPD-quinone than for 
6PPD (Ref. 61).
    Although these studies were primarily done in Asia and under unique 
exposure scenarios (i.e., near an e-waste recycling facility), these 
studies indicate environmental occurrence of 6PPD and 6PPD-quinone in 
indoor and outdoor dust, suggesting that human exposure to 6PPD and 
6PPD-quinone is plausible and may be occurring through dust ingestion, 
inhalation, and dermal absorption, with potential effects on body mass 
index (Refs. 7, 59, 60, and 61).
    A limited number of biomonitoring studies in Asia identified 6PPD-
quinone in human samples, some of which also monitored for 6PPD. 
However, it is important to note that many of these studies had a small 
sample size. In one study, after 6PPD-quinone levels were recorded in 
the cerebrospinal fluid (CSF) of 13 patients with Parkinson's disease 
(PD) and 11 control participants, researchers found that 6PPD-quinone 
levels were twice as high in PD patients compared to controls and 
confirmed through immunostaining assays that 6PPD-quinone at 
environmentally relevant concentrations exacerbated the formation of 
Lewy neurites and impaired mitochondrial activity (Ref. 62). Four other 
studies detecting PPDs and PPD-qs in human urine and blood found that 
the median concentrations of 6PPD and 6PPD-quinone were significantly 
higher than other PPD and PPD-qs measured in the study, especially in 
pregnant women and people with liver disease which may

[[Page 91304]]

indicate lipid oxidative damage (Refs. 7, 63, 64, and 65). Additional 
biomonitoring studies with larger sample sizes and in different 
locations are needed since factors influencing exposures can vary by 
region and be influenced by other environmental stressors.
    Although there are limited data available on the potential human 
health effects of 6PPD and/or 6PPD-quinone, the health effects of 6PPD 
are better characterized than 6PPD-quinone in the scientific literature 
(Refs. 4, 25, and 66). 6PPD is a known skin-sensitizer that can lead to 
contact dermatitis in sensitized individuals and is listed as a 
category 1B reproductive toxicant by the European Chemicals Agency 
(Ref. 67).
    Preliminary toxicity studies in rodents may also inform human 
health effects. For example, one study found that 6PPD and 6PPD-quinone 
bioaccumulate in the liver, with higher doses of both chemicals 
potentially causing an inflammatory response, altered hepatic 
metabolism, and hepatotoxicity in mice (Ref. 62) while another study 
identified that repeated exposure over 4 weeks to 6PPD-quinone (4 mg/
kg) caused multiple organ injury in male BALB mice (Ref. 68). These 
early mammalian toxicity studies indicate that repeated exposure to 
6PPD and 6PPD-quinone may affect organ function, metabolism, 
bioaccumulation, and inflammation in humans, but more studies are 
needed on 6PPD and 6PPD-quinone's impacts on human health.
    As for bioaccumulation potential, one study found that when lettuce 
plants were exposed to TWP-derived 6PPD and 6PPD-quinone (among other 
TWP compounds) in hydroponic solutions over 14 days in a lab, the 
chemicals were taken up and metabolized by the lettuce with 
concentrations of 6PPD and 6PPD-quinone found in the plant's roots, 
leaves, and nutrient solution (Ref. 69). Other limited studies that 
reported bioaccumulative potential of 6PPD-quinone in aquatic species 
predicted that although there is potential for uptake, the data 
suggests that 6PPD-quinone does not significantly accumulate in fish 
tissues and instead metabolizes rapidly in vivo (Refs. 38 and 70). 
Further, the predicted bioconcentration factors (BCF) for 6PPD and 
6PPD-quinone are currently below 1,000, suggesting a low to moderate 
bioaccumulative potential based on EPA policy, which identifies 
chemicals with BCFs above 1,000 as bioaccumulative (Refs. 4, 38, 70, 
and 71). That said, additional data and field studies are needed on the 
potential for bioaccumulation in plant and animal species as well as on 
the potential for 6PPD to metabolize to 6PPD-quinone within humans.
    Overall, more research on the effects, characteristics, relevant 
exposure pathways, and dose-response data are needed to identify the 
potential human health impacts from exposure to 6PPD and 6PPD-quinone. 
This is of particular importance for pregnant women and children, 
communities and workers near roadways, people with existing medical 
conditions, populations that participate in subsistence activities 
(i.e., fishing, hunting), and communities with environmental justice 
concerns.

F. What are the potential impacts on Tribal Nations?

    In their petition, the Yurok Tribe, the Port Gamble S'Klallam 
Tribe, and the Puyallup Tribe of Indians present many potential impacts 
of 6PPD's transformation product, 6PPD-quinone, on their resources. 
They explain that their health, wellbeing, and culture are intimately 
connected to the health of their waters and ecosystems. The petition 
states that many Tribes share an important connection with their 
waterbodies, rendering them culturally significant and protected 
resources. The petitioners, along with additional Tribes that EPA 
engaged with related to this action, all emphasized that thriving 
shellfish and abundant salmonids are essential for their subsistence, 
cultural, and economic lifeways and has been one of their most 
important resources since time immemorial (Refs.1, 72, and 73).
    The petition further explains that ``exposure to 6PPD-q[uinone] can 
kill a coho salmon within hours, and the chemical is responsible for 
`urban runoff mortality syndrome,' which kills up to 100% of coho 
returning to spawn in urban streams'' (Refs. 1 and 32). Petitioners 
state that the decline of coho salmon has negatively impacted their 
access to commercial fishing income, food security, health, and 
wellbeing and has affected their ability to pass on traditional 
ceremonial and ecological knowledge to future generations. Decreased 
fish populations and diminished water quality have also meant a loss of 
cultural identity and have led to increased reliance on expensive, 
less-healthy food sources, especially in rural, low-income communities 
(Refs. 1, 72, and 73).
    Petitioners also assert that Tribal Treaty Rights, such as the 
Treaty of Point No Point, ``guarantees the Tribe[s] access to salmon . 
. . and that any action that reduces the number of salmon available for 
harvest by Tribal members is a violation of its rights under this 
treaty.''
    The Tribes also conclude that, ``salmon and steelhead populations, 
central to the ecosystems, Tribal cultures, and economies of the West 
Coast, have already declined dramatically, due in part to exposure to 
6PPD-q[uinone], and they cannot recover without its removal from the 
environment . . . We therefore call on EPA to exercise its authority 
under TSCA to protect the environment from the unreasonable risk 
presented by the use of 6PPD in tires'' (Ref. 1).

G. What are the potential sources and geographic extent of 6PPD and/or 
6PPD-quinone contamination in the environment?

    Studies have shown that one source of 6PPD and 6PPD-quinone 
contamination in the environment is from TWP that are constantly 
entering the environment as tires roll across the road's surface (Ref. 
30). These chemicals can also enter the environment from tire rubber if 
tires are disposed of in or near waterways. Tires and tire pieces are 
sometimes used as parts of dams, embankments, and erosion-control 
infrastructure, but little is known about whether 6PPD and 6PPD-quinone 
leach from these structures into the environment (Ref. 74). E-waste 
recycling and rubber-modified asphalt have been identified as other 
potential sources (Refs. 60 and 75). For example, a recent study found 
that rubber-modified asphalt containing 6PPD was acting as a sorbent 
for tire-derived 6PPD-quinone that released 6PPD-quinone into the 
environment after simulated rainfall events, with 0.0015-0.0049 [mu]g/L 
of 6PPD-quinone recorded in the rainfall runoff (Refs. 76 and 77).
    Additionally, although 6PPD has been identified in other non-tire 
rubber products (described in Unit II.B.3.) (Refs. 78, 79, and 80), 
more research is needed to determine the full suite of products that 
may contain 6PPD and the extent to which these products may be 
contributing to environmental contamination and exposure.
    Monitoring studies have measured both 6PPD and 6PPD-quinone in air 
(Refs. 61 and 81), water (Ref. 61), outdoor and indoor dust (Refs. 82 
and 59), sediments, and soil (Ref. 61), indicating that 6PPD and 6PPD-
quinone contamination is widespread across multiple media (Ref. 83). 
Overall, 6PPD and 6PPD-quinone have been measured in environmental 
media around the world and a limited number of studies have shown both 
chemicals in human biomonitoring samples (Refs. 62, 63, 64, and 65).

[[Page 91305]]

H. What actions can be taken under TSCA section 6?

    TSCA section 6 requires EPA to take action to address unreasonable 
risks of injury to human health or the environment from a chemical 
substance or mixture to the extent necessary so that the chemical 
substance or mixture no longer presents such risk. If EPA determines 
that a chemical substance presents unreasonable risk to health or the 
environment, it must promulgate requirements under TSCA section 6(a) 
that can include one or more of the following actions, alone or in 
combination, to the extent necessary such that the chemical no longer 
presents the unreasonable risk:
     Prohibit or otherwise restrict the manufacturing 
(including import), processing, or distribution in commerce of the 
substance, or limit the amount of such substance or mixture which may 
be manufactured, processed, or distributed in commerce (TSCA section 
6(a)(1)).
     Prohibit or otherwise restrict the manufacturing, 
processing, or distribution in commerce of the substance for a 
particular use or above a specific concentration for a particular use 
(TSCA section 6(a)(2)).
     Limit the amount of the substance which may be 
manufactured, processed, or distributed in commerce for a particular 
use or above a specific concentration for a particular use (TSCA 
section 6(a)(2)).
     Require clear and adequate minimum warning and 
instructions with respect to the substance, distribution in commerce, 
or disposal, or any combination of those activities, to be marked on or 
accompanying the substance (TSCA section 6(a)(3)).
     Require manufacturers and processors of the substance to 
make and retain certain records or conduct certain monitoring or 
testing (TSCA section 6(a)(4)).
     Prohibit or otherwise regulate any manner or method of 
commercial use of the substance (TSCA section 6(a)(5)).
     Prohibit or otherwise regulate any manner or method of 
disposal of the substance, or any article containing such substance, by 
its manufacturer or processor or by any person who uses or disposes of 
it for commercial purposes (TSCA section 6(a)(6)), and
     Direct manufacturers or processors of the substance to 
give notice of the unreasonable risk determination to distributors, 
certain other persons, and the public, and to replace or repurchase the 
substance (TSCA section 6(a)(7)).
    Per TSCA section 6(c)(2)(B), in selecting among prohibitions and 
other restrictions, EPA must factor in, to the extent practicable, the 
effects of the substance on human health and the environment, any 
benefits of uses of the substance, and the reasonably ascertainable 
economic consequences of the rule.
    In addition, TSCA section 6(g) allows EPA to grant an exemption 
from a requirement of a TSCA section 6(a) rule for a specific condition 
of use of a chemical substance or mixture, if the Administrator finds 
that: the specific condition of use is a critical or essential use for 
which no technically and economically feasible safer alternative is 
available; compliance with the requirement, as applied with respect to 
the specific condition of use, would significantly disrupt the national 
economy, national security, or critical infrastructure; or the specific 
condition of use of the chemical substance or mixture, as compared to 
reasonably available alternatives, provides a substantial benefit to 
health, the environment, or public safety.

I. What are the alternatives to 6PPD for use in tires?

    At this time, an effective alternative to 6PPD's use in tires has 
not been identified, but multiple researchers, states, and tire 
manufacturers are studying potential replacements. For example, in 
October 2023, California's Department of Toxic Substances Control 
(DTSC) listed tires containing 6PPD as a Priority Product under the 
Safer Consumer Products Regulations (SCPR, Cal. Code Regs. Tit. 22, 
Sec.  69511.7). Manufacturers of tires which contain 6PPD and are 
entered into the stream of commerce in California have submitted 
Preliminary Alternatives Analysis Reports to California DTSC, including 
a submission from the United States Tire Manufacturers Association's 
(USTMA) consortium of over 30 tire manufacturers (Refs. 2 and 84). Many 
of the identified potential alternatives in phase I of USTMA's 
alternatives analysis were other PPDs or non-PPD alternatives, 
including: 7PPD (CASRN 3081-01-4; DTXSID 5027516), IPPD (CASRN 101-72-
4; DTXSID 1025485), 77PD (CASRN 3081-14-9; DTXSID 2024618), CCPD (CASRN 
4175-38-6; DTXSID 8063335), and NA (an unnamed, specialized graphene 
nano-platelet). According to the report, early data suggests that these 
potential alternatives would have reduced impacts on salmonids and 
overall hazard relative to 6PPD based on screening level performance 
data and acceptable physical and chemical properties indicative of 
exposure potential (Ref. 2). California has granted a Notice of 
Compliance for the Preliminary (Stage 1) Alternatives Analysis report, 
and manufacturers will proceed with a Stage 2 Alternatives Analysis to 
confirm their list of possible alternatives, assess the potential 
impacts of these options, and initiate a more detailed review of the 
chemicals' potential hazards and exposure-related properties (Ref. 85).
    Similarly, Washington State's Department of Ecology recently 
published a 6PPD Alternatives Assessment Hazard Criteria and an 
Alternatives Assessment (AA) Guide for them and other businesses to use 
when conducting an AA for 6PPD in tires (Ref. 86). The State of 
Washington also included 6PPD as a proposed priority chemical under 
their Safer Products of Washington law which will result in a list of 
products containing 6PPD in 2025 (Ref. 87).
    Efforts are also underway to analyze other potential alternatives. 
For example, researchers are investigating gallates (antioxidant food 
preservative), lignins (plant-based polymer), Durazone-37 (another 
existing rubber antiozonant), Graphene, and N,N'-dicyclohexyl-1,4-
phenylene diamine (CCPD) as potential replacements for 6PPD in tires 
(Ref. 88). USTMA and the U.S. Geological Survey are testing the 
toxicity of potential 6PPD alternatives and refining methods for 
evaluating potential alternatives, including the ones identified in 
USTMA's alternatives analysis report in California (Ref. 89). The U.S. 
Department of Agriculture's Western Regional Research Center and 
Flexsys are collaborating to explore a bio-based alternative to 6PPD 
(Ref. 90). EPA is funding multiple research efforts to test and 
identify potential alternatives, including EPA-funded Small Business 
Innovation Research (SBIR) grants (Ref. 91). Efforts are also underway 
to identify other potential solutions to reducing the risks posed by 
6PPD and 6PPD-quinone, including reformulating tires using natural 
rubbers without 6PPD or modifying 6PPD molecules to avoid 
transformation into 6PPD-quinone (Ref. 88).

III. Specific Requests for Comment, Data, and Information

    EPA is seeking public comment on all information included or 
referenced in this ANPRM and is also seeking any other information 
relevant to 6PPD and/or 6PPD-quinone. The Agency is particularly 
interested in receiving quantitative information, data and/or case 
examples (e.g., peer-reviewed studies and industry scientific and 
technical reports describing datasets and/or syntheses of environmental 
and

[[Page 91306]]

human health impacts that include statistical analyses) addressing the 
following topics and questions. To avoid duplicative submissions, 
studies that have already been cited in this ANPRM or that have been 
submitted through another regulatory reporting requirement are not 
being requested via this ANPRM.

A. What information is the Agency requesting on environmental effects 
of 6PPD and/or 6PPD-quinone on aquatic ecosystems?

    EPA is interested in all information regarding 6PPD and/or 6PPD-
quinone's effects on aquatic ecosystems (such as aquatic toxicity 
data). Adherence to standard guidelines or laboratory practices (e.g., 
EPA's 850 Ecological Effects Test Guidelines, American Society for 
Testing and Materials (ASTM) methods, or Organization for Economic Co-
operation and Development (OECD) methods) is preferred but not 
required. Note that high-quality analytical measurements throughout 
toxicity tests are important because of the instability of 6PPD and 
6PPD-quinone under conditions relevant to aquatic environments.
    1. To ensure that EPA has robust, reasonably available data and 
information that is consistent with the best available science, EPA 
requests monitoring data reporting 6PPD and/or 6PPD-quinone 
concentrations and detection frequency in groundwater, surface waters, 
wastewater, saltwater, or estuaries across the United States. 
Specifically, EPA is requesting information and data on the volumes, 
locations, sources, dates/timeframes, and types of 6PPD and/or 6PPD-
quinone contamination in impacted surface waters and sediments (e.g., 
through TWP or direct contact with the tire), including the 
concentration, field methods/SOPs for collection of the data, and 
analytical methods used to detect the chemicals (including 
quantification limits and other quality assurance details) when 
available.
    2. EPA is interested in information and data concerning the acute 
exposure hazard effects of 6PPD and/or 6PPD-quinone on a broader range 
of aquatic species than are discussed in Unit II.D.1 of this ANPRM, as 
well as chronic effects on all aquatic taxa. Even for species and 
effects that have been investigated previously, repeated high-quality 
tests with analytical measurements following testing guidelines are 
desired. Such hazard information includes, but it is not limited to, 
mortality (lethal concentrations), growth, developmental, behavioral, 
reproductive, hormonal, immunological, neurological, cardiovascular, 
respiratory, and renal effects from the cellular level to the 
organismal and population levels that might inform lethal and sub-
lethal physiological, histological, and accumulative effects as well as 
any other hazard information that may be relevant to 6PPD and/or 6PPD-
quinone. EPA seeks hazard effects information for any aquatic species, 
including but not limited to:
     Fish species (e.g., Salmonidae, Cyprinidae, Centrarchidae, 
Serranidae, Percidae, Ictaluridae, Acipenseridae, etc.);
     Aquatic studies done using new approach methodologies such 
as fish cell line assays or in vitro methods;
     Species of Tribal or cultural significance such as lamprey 
and mussels;
     Aquatic plants (including vascular and non-vascular 
(algae) species);
     Aquatic invertebrates (including benthic species);
     Aquatic and aquatic-dependent vertebrates other than fish 
(e.g., mammals, amphibians, reptiles, birds);
     Bacteria/microbiome; and
     Any other potentially sensitive species.
    3. EPA is requesting information and data concerning known 
concentrations of 6PPD and/or 6PPD-quinone found in aquatic animal and 
plant tissue that may indicate the bioaccumulation of 6PPD and/or 6PPD-
quinone in these species, particularly in species which are culturally 
significant to Tribes or subsistence fisher populations. This 
information may have important implications for potential exposure 
through the consumption of affected plant and animal species.

B. What information is the Agency requesting on environmental effects 
of 6PPD and/or 6PPD-quinone on terrestrial ecosystems?

    EPA is interested in all information regarding 6PPD and/or 6PPD-
quinone's effects on terrestrial ecosystems (such as terrestrial 
toxicity data). Data collected by any means is requested. Adherence to 
standard guidelines or laboratory practices (e.g., EPA's 850 Ecological 
Effects Test Guidelines, American Society for Testing and Materials 
(ASTM) methods, or Organization for Economic Co-operation and 
Development (OECD) methods) is preferred but not required.
    1. To ensure that EPA has robust, reasonably available data and 
information that is consistent with the best available science, EPA 
requests monitoring information and data reporting for 6PPD and/or 
6PPD-quinone concentrations and detection frequency in air, soil, and 
other terrestrial media. Specifically, EPA is requesting information 
and data on the volumes, locations, sources, dates/timeframes/
pollutographs, and types of 6PPD and/or 6PPD-quinone contamination 
(e.g., through TWP or direct contact with the tire) in terrestrial 
environments, including the concentration and field methods and 
analytical methods used to detect the chemicals (including 
quantification limits) when available.
    2. EPA is also interested in information and data concerning the 
hazard effects of 6PPD and/or 6PPD-quinone on a broader range of 
terrestrial species than are discussed in Unit II.D.2 of this ANPRM. 
Such hazard information includes, but it is not limited to, data on 
mortality (lethal concentrations), growth, development, genetics, 
behavior, and reproduction as well as data on the cellular, hormonal, 
immunological, neurological, accumulative, histological, and 
physiological effects of 6PPD and/or 6PPD-quinone and any other hazard 
information. EPA seeks hazard effects information for any terrestrial 
species, including:
     Terrestrial vertebrates (e.g., mammals, birds, reptiles, 
amphibians);
     Soil fauna (e.g., worms, microbes, nematodes) with an 
emphasis on roadside soil fauna;
     Land invertebrates (e.g., insects, worms, slugs, snails, 
spiders);
     Terrestrial plants (including nonvascular plants such as 
moss and lichen) with an emphasis on roadside plants;
     Fungi;
     Bacteria/microbiome; and
     Potentially sensitive species.
    3. EPA is requesting information and data concerning known 
concentrations of 6PPD and/or 6PPD-quinone found in terrestrial animal 
and plant tissue that may indicate the bioaccumulation of 6PPD and/or 
6PPD-quinone in these species, particularly in species which are 
culturally significant to Tribes or subsistence fisher populations. 
This information may have important implications for potential exposure 
through the consumption of affected species.
    4. EPA is requesting information and data on any used methods of 
detection of 6PPD and/or 6PPD-quinone in biota, sediments, and soils.

C. What are the potential human health and Tribal effects of 6PPD and/
or 6PPD-quinone?

    1. As discussed in Unit II.E. of this ANPRM, there are limited data 
on the

[[Page 91307]]

human health effects of 6PPD and/or 6PPD-quinone, including toxicity 
studies (in vivo and in vitro) on carcinogenicity, reproductive and 
developmental effects, genotoxicity, neurotoxicity, immunotoxicity, 
endocrine effects, and other systemic toxicity and toxicokinetics 
(absorption, distribution, metabolism, or elimination), including 
modelling studies in humans. To ensure that EPA has robust, reasonably 
available data and information that are consistent with the best 
available science, EPA requests information and data on the human 
health effects of 6PPD and/or 6PPD-quinone on the general population, 
and on specific subpopulations including the following:
     Pregnant women and children;
     Workers, including roadway workers, auto repair workers, 
racetrack maintenance crews, tire manufacturers or recyclers, and 
others who may be more frequently exposed to tires, TWP, vehicle dust, 
and road dust that may contain 6PPD and/or 6PPD-quinone; and
     Other potentially exposed or susceptible subpopulations 
(PESS), which may include:
    --Communities that engage in subsistence fishing and/or gathering 
activities (e.g., Tribal communities and other populations engaging in 
fishing in urban or semi-urban waterways);
    --Near-roadway communities that may be more frequently exposed to 
tires, TWP, vehicle dust, and road dust that may contain 6PPD and/or 
6PPD-quinone;
    --Communities living near goods-movement facilities, such as 
seaports, inland ports, land ports of entry, intermodal facilities and 
warehouse distribution centers;
    --Populations with existing disabilities or medical conditions 
whose inhalation or ingestion of 6PPD and/or 6PPD-quinone may 
exacerbate existing medical concerns; and
    --Populations that are otherwise vulnerable or experiencing 
multiple environmental stressors; and
     Studies showing the composition and purity of test 
substances should be reported, if available.
    2. As discussed in Unit II.E. of this ANPRM, there is also limited 
data on relevant human exposure pathways (the ways a person can be 
exposed to 6PPD and/or 6PPD-quinone), including inhalation, ingestion, 
or direct contact with the chemicals in media such as air, water, soil, 
and dust. To ensure that EPA has robust, reasonably available data and 
information that is consistent with the best available science, EPA 
requests information and data on human exposure pathways of 6PPD and/or 
6PPD-quinone on the general population, and especially for the 
following:
     Pregnant women and children;
     Disproportionately affected workers, including roadway 
workers, auto repair workers, and others who may be more frequently 
exposed to tires, TWP, vehicle dust, and road dust that may contain 
6PPD and/or 6PPD-quinone; and
     Other potentially exposed or susceptible subpopulations 
(PESS), which may include:
    --Communities that engage in subsistence fishing and/or gathering 
activities (e.g., Tribal communities and other populations engaging in 
fishing in urban or semi-urban waterways);
    --Near-roadway communities that may be more frequently exposed to 
tires, TWP, vehicle dust, and road dust that may contain 6PPD and/or 
6PPD-quinone;
    --Populations with existing disabilities or medical conditions 
whose inhalation or ingestion of 6PPD and/or 6PPD-quinone may 
exacerbate existing medical concerns; and
    --Populations that are otherwise vulnerable or experiencing 
multiple environmental stressors.
    3. EPA is requesting information on the cultural, political, 
economic, and environmental justice impacts of 6PPD and 6PPD-quinone 
contamination on Tribes.
    4. EPA is requesting information and data on the detection of 6PPD 
and/or 6PPD-quinone contamination in drinking water. Specifically, EPA 
is requesting information on the volumes, locations, sources, and types 
of 6PPD and/or 6PPD-quinone contamination in drinking water, including 
the concentration and analytical method used to detect the chemicals 
(including quantification and detection limits) when available.

D. What is 6PPD's use in tires, releases of 6PPD and/or 6PPD-quinone 
into the environment, and remediation technologies?

    1. To help inform EPA's understanding of how 6PPD from tires and/or 
TWP enters the environment, EPA is requesting information on the use of 
6PPD in tires, including quantity and concentration. For example, this 
information includes but is not limited to the following:
     How many and what types of businesses are engaged in 
importing, manufacturing, processing, distributing in commerce, using, 
and disposing of 6PPD?
     What percent by weight of 6PPD meets the minimum criteria 
for the chemical's function within tires? Since the concentration of 
6PPD in tires is not necessarily equivalent to the concentration that 
is released by tires, due to varying tire structures and designs, the 
amount and production of 6PPD's transformation products such as 6PPD-
quinone and other degradants may be among the considerations for this 
response.
     What concentration of 6PPD is currently used during the 
tire manufacturing process? How does this vary across tire 
manufacturing companies and processes, as well as across different 
types of tire use (e.g., cars vs. large trucks, electric vehicles vs. 
gas powered)?
     What is the rate of release of 6PPD and 6PPD-quinone from 
tires on electric vehicles vs. gas-powered vehicles?
     What is the concentration of 6PPD in the finished tire and 
where in the tire is 6PPD present (i.e., in the sidewalls, tread, inner 
liner, etc)? Include the different concentrations for different types 
of tires, if applicable.
     How does the concentration of 6PPD in the tire change over 
time during normal wear and tear--after one year of use, versus after 5 
years, etc over the normal lifespan of a tire? Does the 6PPD 
concentration decrease steadily, or are there seasonal or other 
variations?
     Whether, and if so how, 6PPD content in tires has changed 
over the last several decades. Specifically, has 6PPD content changed 
on a per-pound basis? Or has it changed on a per-tire basis given that 
tire size and formulation can vary for light versus heavy duty 
vehicles?
     Has the trend toward increased specialization in light 
duty vehicle tires altered 6PPD use/content in tires? In particular, 
has the use of high-performance summer tires, winter tires, and tires 
with off-road capability increased over time?
     What are the water discharges from tire manufacturing 
facilities, including wastewater from processing and stormwater 
originating from these sites? Are monitoring data from near such sites 
available?
     What are the water discharges from other aquatic and 
terrestrial sites that use or reuse tires, including but not limited to 
artificial reefs, playgrounds that use crumb rubber or artificial turf, 
and/or tire dumps? Are monitoring data from near such sites available?
    2. EPA is requesting data and information concerning the 
contribution of tire disposal, tire recycling, and tire reuse on 
environmental releases of, and

[[Page 91308]]

wildlife exposures to 6PPD and 6PPD-quinone.
    3. For EPA to better understand the fate and transport of 6PPD and 
6PPD-quinone, EPA is requesting data and information on 6PPD as it 
moves from tires into the environment, reacts with ozone, and evolves 
into multiple transformation products, such as 6PPD-quinone. EPA is 
requesting information and data regarding the fate and transport of 
6PPD and/or 6PPD-quinone in and for use in tires, as well as the fate 
and transport of TWP containing 6PPD and/or 6PPD-quinone. For example, 
EPA is requesting information on, but not limited to, the following:
     What factors influence the transformation of 6PPD to 6PPD-
quinone and other transformation products (e.g., how does the 
concentration of ozone in ambient air impact the reaction rate of 6PPD 
to 6PPD-quinone and other products)?
     What are the degradation and transformation products of 
6PPD, how do they move through the environment (e.g., via TWP, road 
dust, etc), and how are they absorbed in aqueous media, air, and soil/
sediments? For aqueous fate and transport, conditions of interest under 
variable water quality conditions could include but are not limited to 
a broad range of pH (5-9), dissolved oxygen (2-10 mg/L), conductivity 
(0-50,000 [micro]S/cm), and temperature (0-30C).
     How do 6PPD and 6PPD-quinone react with water quality 
sampling equipment (i.e., water grab and passive samplers) such as 
resins, filtration media with plastic or silica-based tubs, caulking, 
or tubing (polytetrafluoroethylene--lined and others), deployment 
times, or flow rate meters?
    4. To gain a better understanding of 6PPD's uses, EPA is requesting 
information and data regarding other products that contain 6PPD and the 
potential for 6PPD and/or 6PPD-quinone contamination from these other 
sources, some of which are mentioned in Unit II.G. (sneakers, plumbing 
seals, elastics, etc).
    5. EPA is requesting information and data on successful water, air, 
soil, or sediment remediation and mitigation technologies that help 
reduce 6PPD and/or 6PPD-quinone exposure, such as green infrastructure, 
bioinfiltration basins, or technologies that capture TWP before they 
enter the environment, including methods that reduce 6PPD and/or 6PPD-
quinone bound to airborne particulate matter. EPA is interested in 
information on remediation technologies once 6PPD and/or 6PPD-quinone 
has entered the environment and the scalability and feasibility of 
implementing those remediation approaches for reducing 6PPD and/or 
6PPD-quinone in the environment.
    6. EPA is requesting information and data regarding the cost and 
efficacy of technologies for remediating water sources that have been 
contaminated with 6PPD and/or 6PPD-quinone. EPA is particularly 
interested in examples or case studies of remediation efforts that have 
addressed 6PPD and/or 6PPD-quinone contamination, and cost and efficacy 
comparisons with other remediation efforts.

E. What are the alternatives to 6PPD's use in tires?

    1. There are multiple efforts underway investigating potential 
alternatives to 6PPD in tires, many of which are summarized in Unit IV 
of this ANPRM. EPA is requesting information and data on potential 
alternatives and their associated transformation or degradation 
products, including those not identified in this ANPRM, that may 
replace 6PPD as an antiozonant in tires. In addition to identifying 
potential alternatives, EPA is requesting information and data on the 
following:
     What concentration of the potential alternative would be 
used during the tire manufacturing process and what concentration would 
be present in the finished tire? How would this vary across different 
types of tire use (e.g., car tires vs. large truck tires)?
     What are the degradation and transformation products of 
the potential alternative, how do they move through the environment 
(e.g., via TWP, road dust, etc.), and how are they absorbed in aqueous 
media, air, and soil/sediments once they're in the environment?
     What are the risks posed by potential alternatives to 6PPD 
on human health and the environment, including but not limited to 
hazard and toxicity effects of the parent and/or its transformation and 
degradation products on humans, aquatic and terrestrial species and 
ecosystems, and on air quality, greenhouse gas emissions, and potential 
disposal;
     What are relevant considerations to include when 
evaluating an alternative that might replace 6PPD in tires (e.g., the 
standards used to assess the efficacy of potential alternatives); 
 What is the durability of the alternative (how long would it 
last as an antidegradant in the tire) and what is its ability to 
protect tires from degradation compared to 6PPD;
     Are there any potential non-chemical alternatives to 6PPD, 
such as, but not limited to, bio-based alternatives, self-healing 
polymers, or making physical changes to the tire or 6PPD molecule that 
could result in less release into the environment of 6PPD or TWP; and
     Any other exposure information, properties, or 
considerations of the potential alternatives.
    2. More generally, EPA is requesting information and data on the 
potential challenges and timelines of transitioning to using an 
alternative to 6PPD as a tire antiozonant, such as:
     What is a timeframe for finding an alternative that 
presents no/less hazards than 6PPD?
     Once an alternative is identified, how long would it take 
for the alternative to be screened for feasibility in terms of its use 
in tires (e.g. ability to incorporate into manufacturing processes at 
large scale, ability to protect the tires from degradation)?
     What safety testing and approval processes need to occur 
on the alternative to ensure it passes federal highway safety 
regulations? What are the relevant timeframes for completing those 
processes?
     Once there is a feasible alternative that has passed 
initial safety screenings and is scalable, how might an extended 
phaseout be implemented to replace tires currently in use that contain 
6PPD with the new tires?
     How much time would be necessary for tire and rubber 
manufacturers to phase out and/or replace 6PPD as an antiozonant from 
their production cycle once a safe and feasible alternative was ready 
to be implemented?
     What is a reasonable timeframe to phase out existing 
stocks of 6PPD that have already been produced for use in tires? Can 
existing stocks of 6PPD that have not been added to tires yet be safely 
disposed of (include associated methodologies)?
     What is a reasonable timeframe to phase out existing 
stocks of 6PPD-containing tires?
     How can 6PPD-containing tires be disposed of or repurposed 
(include associated methodologies) and what are the potential impacts 
of such actions?
     What is a reasonable timeframe to phase out the need for 
further introduction into commerce of 6PPD-containing tires?
     What transition periods (e.g., 3, 5, 10 years) would be 
necessary and what would the likely associated impact be on the price 
or supply of tires and rubber products?
     If a ban on the use of 6PPD in tires were in place, how 
long would it take to replace all tires currently in use given the 
expected lifespan of current tires (7-10 years)? EPA is requesting 
information

[[Page 91309]]

and data regarding impacts on human health or the environment that 
might result from the phase out or restricted use of 6PPD as a tire 
additive and antiozonant (e.g., reduced tire safety, disposal issues 
due to more frequent changing of tires).
    3. EPA is requesting information and data on the economic 
considerations and tradeoffs of removing 6PPD from tires and switching 
to an alternative formulation, process, or chemical.
    4. EPA is requesting information and data based on actual releases 
to the environment of potential alternatives and their associated 
transformation products and degradants; including degree of 
contamination, and the cost and efficacy of the technologies available 
to remediate such contamination. Specifically, EPA is requesting, to 
the extent possible, information on the volumes, concentrations, 
locations, sources, and types of contamination from potential 
alternatives in water, soil, and air.

F. What actions could the Agency take under TSCA?

    As explained in this ANPRM, EPA is gathering information on a 
potential rulemaking. EPA requests comment on:
    1. If the Agency moves forward with a proposed rule after the ANPRM 
is published, what potential actions could EPA take under TSCA section 
6(a)? Potential options include:
     Regulate the manufacturing, processing, or distribution in 
commerce of the chemical, including a complete ban of any such activity 
or limiting the amounts of the chemical manufactured, distributed, and/
or included in tires;
     Regulate the manufacturing, processing, or distribution in 
commerce of the chemical for particular uses, including banning any 
such activity for a particular use; limiting the concentration of the 
chemical that may be used; or limiting the amounts of the chemical for 
particular uses;
     Require warning statements and/or instructions for use 
with respect to the chemical's use in tires and non-tire materials 
(e.g., rubber modified asphalt, sneakers, elastics, etc.), distribution 
in commerce, and/or disposal of the chemical or products containing the 
chemical;
     Require manufacturers/processors to make and retain such 
records of the manufacturing process and/or monitor or conduct tests to 
ensure compliance with a TSCA section 6 rule;
     Prohibiting or regulating any manner or method of 
commercial use of the chemical;
     Prohibit or regulate the disposal of the chemical; and
     Require manufacturers/processors to provide warnings to 
distributors or users and to replace or repurchase the chemical.
    2. TSCA provides EPA authority to select a combination of TSCA 
section 6(a) actions and limit the geographic application of a rule 
under TSCA section 6(a). EPA is requesting comment on whether, and if 
so, where EPA should consider limits to the geographical scope of any 
potential action under TSCA section 6(a)?
    3. TSCA section 9 provides that the EPA Administrator shall consult 
and coordinate with the heads of other appropriate federal executive 
departments or agencies to achieve maximum enforcement of TSCA, while 
imposing the least burden of duplicative requirements. The 
Administrator is also directed to coordinate actions taken under TSCA 
with actions taken under other federal laws administered by the EPA, 
such as the Resource Conservation and Recovery Act, the Clean Air Act 
and the Clean Water Act. Are there other statutory authorities 
administered by EPA that could be used to eliminate or reduce to a 
sufficient extent any risk identified?
    4. As discussed in Unit II.H., TSCA section 6(g) allows EPA to 
grant an exemption from a requirement of a TSCA section 6(a) rule for a 
specific condition of use of a chemical substance or mixture, if the 
Administrator finds that: the specific condition of use is a critical 
or essential use for which no technically and economically feasible 
safer alternative is available; compliance with the requirement, as 
applied with respect to the specific condition of use, would 
significantly disrupt the national economy, national security, or 
critical infrastructure; or the specific condition of use of the 
chemical substance or mixture, as compared to reasonably available 
alternatives, provides a substantial benefit to health, the 
environment, or public safety. What should EPA consider regarding a 
potential TSCA section 6(g) exemption for 6PPD use in tires? If so, 
what conditions may be necessary to protect health and the environment 
while achieving the purposes of an exemption?

IV. References

    The following is a list of the documents that are specifically 
referenced in this document. The docket includes these documents and 
other information considered by EPA, including documents that are 
referenced within the documents that are included in the docket, even 
if the referenced document is not physically located in the docket. For 
assistance in locating these other documents, please consult the 
technical person listed under FOR FURTHER INFORMATION CONTACT.

1. Earthjustice, ``Citizen Petition under TSCA section 21 to 
Prohibit 6PPD in Tires,'' August 1, 2023. [Online]. Available: 
https://www.epa.gov/system/files/documents/2023-08/TSCA%20Section%2021%20Petition%20to%20EPA%20re%206PPD%20in%20tires.pdf.
2. U.S. Tire Manufacturers Association (USTMA), ``Preliminary (Stage 
1) Alternatives Analysis Report Motor Vehicle Tires Containing N-
(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD),'' March 25, 
2024. [Online]. Available: https://www.ustires.org/sites/default/files/2024-03/USTMA%20Consortium%206PPD%20AA%20Preliminary%20Report_3-25-24.pdf.
3. U.S. EPA, ``Final EPA Response to Section 21 Petition Regarding 
N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (CASRN 793-24-8, 
aka 6PPD) in Tires,'' November 2, 2023. [Online]. Available: https://www.epa.gov/system/files/documents/2023-11/pet-001845_tsca-21_petition_6ppd_decision_letter_esigned2023.11.2.pdf.
4. Oslo and Paris Convention (OSPAR) Commission, ``Hazardous 
Substances Series 4-(dimethylbutylamino)diphenylamine (6PPD),'' 2005 
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5. PubChem, ``N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine 
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10. Joined Fortune Chemical, ``6PPD Rubber Antioxidant: 
Characteristics, Applications, Combinations, and

[[Page 91310]]

Considerations for Commercial Procurement,'' June 25, 2023. 
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Particle Leachate Recreates an Urban Runoff Mortality Syndrome in 
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& Technology, vol. 57, no. 14, p. 5621-5632, 2023.
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Chemosphere, vol. 181, pp. 250-258, August 2017.

[[Page 91311]]

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V. Statutory and Executive Order Reviews

    Additional information about these statutes and executive orders 
can be found at https://www.epa.gov/regulations/laws-and-executive-orders.

A. Executive Order 12866: Regulatory Planning and Review and Executive 
Order 14094: Modernizing Regulatory Review

    This action is not a significant regulatory action as defined in 
Executive Order 12866 (58 FR 51735, October 4, 1993), as amended by 
Executive Order 14094 (88 FR 21879, April 11, 2023), and was therefore 
not subject to a requirement for Executive Order 12866 review.

B. Other Regulatory Assessment Requirements

    Because this action does not impose or propose any requirements, 
the various other review requirements in statutes and Executive Orders 
that apply when an agency imposes or proposes requirements do not apply 
to this ANPRM. Should EPA subsequently determine to pursue a 
rulemaking, EPA will address the requirements in the statutes and 
executive orders as applicable to that rulemaking.

List of Subjects in 40 CFR Part 751

    Chemicals, Environmental protection, Exports, Hazardous substances, 
Imports, Reporting and recordkeeping requirements.

Michael S. Regan,
Administrator.
[FR Doc. 2024-26894 Filed 11-18-24; 8:45 am]
BILLING CODE P