Q.01

What are EPA Work Plan chemicals?

EPA Work Plan chemicals are the existing chemicals on EPA's TSCA Work Plan for Chemical Assessments. This is the list the Office of Pollution Prevention and Toxics (OPPT) built in 2012 to decide which existing chemicals to assess first under the Toxic Substances Control Act. EPA published 83 chemicals in 2012 and updated the list to 90 in October 2014 (EPA, 2014 Update). Being on the list is not a risk finding. EPA says it "indicates only that the Agency intends to consider it for assessment" (same source, p. 2).

How chemicals were selected

  • Screening factors: EPA scored chemicals on hazard, exposure (including uses), and persistence and bioaccumulation. It focused on chemicals with one or more of these features:

    • potential concern for children's health (for example reproductive or developmental effects)
    • neurotoxic effects
    • persistent, bioaccumulative and toxic (PBT)
    • probable or known carcinogen
    • use in children's products or products children may be highly exposed to
    • detection in biomonitoring programs

    The full method is in the TSCA Work Plan Chemicals Methods Document.

  • Two-step screen (2012): 1,235 candidates were found. Some were excluded, for example because they are not subject to TSCA or are already significantly regulated. That left 345 for scoring.

  • 2014 update: EPA re-ranked exposure using 2012 Chemical Data Reporting (CDR) and 2011 Toxics Release Inventory (TRI) data. It removed 15 chemicals (13 because they are no longer in commerce) and consolidated one. It added 23, including five Action Plan chemicals or groups:

    • BPA
    • decaBDE
    • HBCD
    • nonylphenols/nonylphenol ethoxylates
    • seven phthalates

  • Assessments completed before the 2014 update: TCE, methylene chloride, HHCB and antimony trioxide.

Why it still matters under the 2016 amendments to TSCA (Lautenberg Act)

  • The first 10 chemicals EPA designated for risk evaluation in December 2016 (81 FR 91927) "were drawn from the 2014 update of EPA's TSCA Work Plan" [1].
  • EPA's prioritization page states that "at least 50% of all chemical substances on which risk evaluations are being conducted by the Administrator are drawn from the 2014 Update of the TSCA Work Plan" (EPA, Prioritization of Existing Chemicals).
  • On the same page, EPA is directed to prefer Work Plan chemicals with persistence and bioaccumulation scores of three, and known human carcinogens with high acute and chronic toxicity.
  • The pre-2016 Work Plan documents are still the starting point for current risk evaluations. Examples:
    • The 1,4-dioxane final risk evaluation cites the 2015 "TSCA Work Plan Chemical Problem Formulation and Initial Assessment" [2].
    • Methylene chloride's problem formulation cites the 2014 Work Plan risk assessment for paint stripping [3].
    • The TBBPA draft risk evaluation lists a 2015 Work Plan problem formulation in its assessment history [4].

Approach: I searched EPA's TSCA section 6(b) risk evaluation documents and its prioritization register, then read EPA's 2014 Work Plan update and its prioritization page. I did not read the TSCA section 6(b) text itself in an official US Code or public-law source, so the 50% rule above is as EPA's page states it.

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Q.02

How does high-priority status differ from low-priority status?

Under TSCA section 6(b), a High-Priority Substance is one EPA concludes "may present an unreasonable risk" and must go to a full risk evaluation. A Low-Priority Substance is one EPA concludes, "based on information sufficient to establish," does not meet that high-priority standard, so no risk evaluation is "warranted at that time." Neither label is a finding about actual risk. A high-priority designation "is not a finding of unreasonable risk" [5], and EPA says low-priority designations are not indications of safety (EPA search summary of its prioritization pages).

High-Priority SubstanceLow-Priority Substance
Definition (TSCA §6(b)(1)(B), 40 CFR 702.3)EPA concludes, "without consideration of costs or other non-risk factors," that the substance "may present an unreasonable risk of injury to health or the environment because of a potential hazard and a potential route of exposure under the conditions of use," including risk to a potentially exposed or susceptible subpopulation [5]EPA concludes, "based on information sufficient to establish," and without considering costs or other non-risk factors, that the substance "does not meet the standard for a High-Priority Substance" (EPA, Final Designation of Low-Priority Substances, p. 3)
What it triggersThe final designation "initiates the risk evaluation process (40 CFR 702.17)." That process ends in a finding on whether the substance presents an unreasonable risk [5]. Under §6(b)(3)(A), the designation itself counts as the start of the risk evaluation [6]"A risk evaluation is not warranted at that time (TSCA Section 6(b)(1)(A) and 40 CFR 702.15)" (same notice, p. 4). EPA says the notice "does not establish any requirements on persons or entities outside of the Agency" (p. 3)
What EPA states as the basisUnder 40 CFR 702.11, EPA "generally expects to indicate which condition(s) of use were the primary basis" for the designation [6]One screening review document per chemical, setting out the information, analysis and basis (low-priority notice, p. 8)
Ongoing pipeline dutyUnder §6(b)(3)(C), EPA must designate at least one new High-Priority Substance each time it completes a risk evaluation of a high-priority one [7]None stated in the sources I read
Designations so far25: 20 designated 2019-12-20 (84 FR 71924) and 5 designated 2024-12-18 (89 FR 102900)
Examples: formaldehyde [8], 1,3-butadiene [9], vinyl chloride [10]		20, all designated 2020-02-20 (85 FR 11069)
Examples: D-gluconic acid [11], 1-octadecanol [12], 1,2-hexanediol [13]

What both designations share

  • Screening criteria (40 CFR 702.9(a)): both go through the same screen (low-priority notice, p. 4):
    • hazard and exposure potential
    • persistence and bioaccumulation
    • potentially exposed or susceptible subpopulations
    • storage near significant sources of drinking water
    • conditions of use
    • production volume
    • other risk-based criteria
  • Process: both follow the same steps: initiation, a 90-day comment period, proposed designation, a second 90-day comment period, then final designation in the Federal Register (low-priority notice, p. 3).
  • Where low-priority candidates came from: EPA used the Safer Chemical Ingredients List as a starting point, then reviewed each candidate independently (low-priority notice, p. 9).

Still pending: five chemicals are in prioritization with no designation yet, under 89 FR 102903:

Approach: I searched EPA's TSCA prioritization register and the December 2024 high-priority designation notices, and read the 2020 low-priority designation notice and EPA's low-priority page. The low-priority text I read is EPA's pre-publication copy of the notice (published as 85 FR 11069), and I couldn't open 40 CFR part 702 on eCFR. So I have not checked whether or how a low-priority designation can later be revised.

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Q.03

Which chemicals were designated high priority most recently?

EPA's most recent High-Priority Substance designations under TSCA section 6(b) were made on 18 December 2024 (89 FR 102900). There were five chemicals in that batch, and none has been designated since.

ChemicalCASRNDocket
Acetaldehyde75-07-0EPA-HQ-OPPT-2018-0497 [19]
Acrylonitrile107-13-1EPA-HQ-OPPT-2018-0449 [20]
Benzenamine (aniline)62-53-3EPA-HQ-OPPT-2018-0474 [21]
4,4'-Methylene bis(2-chloroaniline) (MBOCA)101-14-4EPA-HQ-OPPT-2018-0464 [22]
Vinyl chloride75-01-4EPA-HQ-OPPT-2018-0448 [10]
  • Why these five: EPA's announcement calls them "five known or probable carcinogens" (EPA news release).
  • The only other batch: the register holds 25 high-priority designations in total. The other 20 were all designated on 20 December 2019.
  • No proposals yet for the next five: EPA began prioritizing benzene, ethylbenzene, naphthalene, styrene and 4-tert-octylphenol in December 2024. EPA's Prioritization Actions page, last updated 19 May 2026, still lists all five as "Initiated; Pending proposed designation" (EPA, Prioritization Actions Under TSCA).
  • Data call for those five: all of them are among the 16 chemicals covered by EPA's December 2024 final rule under TSCA section 8(d). It requires manufacturers, including importers, to report unpublished health and safety studies (EPA, 8(d) final rule).

Approach: I searched EPA's TSCA prioritization register, then checked EPA's Prioritization Actions page for anything designated after December 2024.

Sources:

Q.04