On January 14, 2025, the U.S. Environmental Protection Agency (EPA) issued a proposed rule to address the unreasonable risk of injury to human health presented by Color Index (C.I.) Pigment Violet 29 (PV29) under its conditions of use (COU) as documented in EPA’s January 2021 risk evaluation and September 2022 revised risk determination. 90 Fed. Reg. 3107. The proposed rule states that the Toxic Substances Control Act (TSCA) requires that EPA address by rule any unreasonable risk of injury to health or the environment identified in a TSCA risk evaluation and apply requirements to the extent necessary so the chemical no longer presents unreasonable risk. To address the identified unreasonable risk, EPA proposes requirements to protect workers during manufacturing and processing, certain industrial and commercial uses of PV29, and disposal, while also allowing for a reasonable transition period prior to enforcement of said requirements. Comments are due February 28, 2025. EPA notes that under the Paperwork Reduction Act (PRA), comments on the information collection provisions are best assured of consideration if the Office of Management and Budget (OMB) receives comments on or before February 13, 2025.

As reported in our January 25, 2021, memorandum, pursuant to TSCA Section 6(b), EPA determined that PV29 presents an unreasonable risk of injury to health, without consideration of costs or other nonrisk factors, including an unreasonable risk to potentially exposed or susceptible subpopulations (PESS) identified as relevant to the 2021 risk evaluation for PV29 under the COUs. EPA notes that the term “conditions of use” is defined in TSCA Section 3(4) to mean the circumstances under which a chemical substance is intended, known, or reasonably foreseen to be manufactured, processed, distributed in commerce, used, or disposed of. To address the unreasonable risk, EPA proposes, under TSCA Section 6(a), to:

• Require use of assigned protection factor (APF) 50 respirators and equipment and area cleaning to address the risk from inhalation exposure to dry powder PV29 (also referred to as regulated PV29), where dry powder PV29 is expected to be present, for the following COUs:

   

  • Domestic manufacture;

     

  • Import;

     

  • Incorporation into formulation, mixture, or reaction products in paints and coatings;

     

  • Incorporation into formulation, mixture, or reaction products in plastic and rubber products;

     

  • Intermediate in the creation or adjustment of color of other perylene pigments;

     

  • Recycling;

     

  • Industrial and commercial use in automobile (original equipment manufacturer (OEM) and refinishing) paints and coatings;

     

  • Industrial and commercial use in coatings and basecoats paints and coatings;

     

  • Industrial and commercial use in merchant ink for commercial printing; and

     

  • Disposal.

     

• Require manufacturers (including importers), processors, and distributors in commerce of regulated PV29 to provide downstream notification of the requirements.

   

• Require recordkeeping.

EPA notes that not all TSCA COUs of PV29 are subject to the proposed rule. As described in the 2021 risk evaluation and the September 2022 revised unreasonable risk determination, four COUs do not contribute to the unreasonable risk: distribution in commerce; industrial/commercial use in plastic and rubber products — automobile plastics; industrial/commercial use in plastic and rubber products — industrial carpeting; and consumer use in professional quality watercolor and acrylic artist paint. Consumer use in professional quality watercolor and acrylic artist paint was the only consumer COU evaluated as part of the 2021 risk evaluation. More information on EPA’s September 2022 revised unreasonable risk determination is available in our September 9, 2022, memorandum.

EPA requests public comment on all aspects of the proposed rule. According to EPA’s December 20, 2024, press release, EPA “is especially interested in hearing perspectives from the public on the feasibility and effectiveness of the proposed requirements for worker protections, including from workers and entities that would be required to implement the workplace protections.”

Commentary

EPA’s evaluation of PV29 was expected to be “easy” when it was identified as one of the first ten chemicals selected for risk evaluation. PV29 is a poorly soluble, low toxicity (PSLT) particle. EPA’s approach to PSLTs has been evolving over the years and has been the subject of controversy, including whether carcinogenicity in rats from “kinetic lung overload…[where the] dust overwhelms the lung clearance mechanisms over time” is relevant to humans.

Since EPA first issued its 1994 document titled “Methods for Derivation of Inhalation Reference Concentrations (RfCs) and Application of Inhalation Dosimetry,” scientific advances in mechanistic modeling of inhalation dosimetry have matured. The scientific understanding of the most appropriate dose metric for PSLTs (i.e., retained dose, not deposited dose) has also evolved. In 1994, EPA developed the regional deposited dose ratio (RDDR) model, an empirical model that provides predictions of deposited dose. In 2021, EPA developed an update to the multiple-path particle dosimetry (MPPD) model (i.e., MPPD EPA 2021 v.1.01). This model is an improvement over the RDDR model because it incorporates the best available science, including “some dose metric predictions…based on mechanistic descriptions instead of empirical fitting…[and] providing prediction of retained mass….” Prior to this update, MPPD was already recognized as a superior model versus RDDR for inhalation dosimetry. For example, EPA’s Integrated Risk Information System used MPPD when developing an inhalation reference concentration for benzo[a]pyrene in January 2017; the National Institute for Occupational Safety and Health also used MPPD for developing its recommended exposure limit for carbon nanotubes in April 2013.

EPA used the MPPD model in the revised draft risk evaluation for PV29. EPA subsequently used the RDDR model in the Final PV29 risk evaluation. EPA stated that “The change in model [i.e., RDDR rather than MPPD] resulted in unreasonable risk determinations for all [occupational nonusers] ONUs and industrial and commercial use in automobile paint [original equipment manufacturer] OEM and refinishing condition of use” (emphasis added). EPA justified this change by stating “The MPPD model was not thought to be appropriate because the particle size data was not robust enough and the MPPD model cannot calculate [human equivalent concentrations] HECs for the hamster data…, while the RDDR model can accept hamster data input.” We find this justification hollow. EPA did not state why the particle size data were robust enough for the RDDR model but not the MPPD model. Further, EPA did not use the hamster data as the basis for its point of departure (POD) in the Final PV29 risk evaluation. We suspect this change was based on a preferred outcome (i.e., unreasonable risks), rather than an objective scientific evaluation to determine if there is unreasonable risk.

Interestingly, EPA calculated an existing chemical exposure limit (ECEL) of 0.014 mg/m³ for PV29, but it did not provide the underlying documentation for this value. Instead, EPA only stated that it chose not to propose an ECEL for PV29 because EPA was unable to identify a “method with a limit of detection lower than the calculated ECEL….” Without the underlying documentation, it is impossible to determine if EPA’s proposed regulatory action is based on the best available science or if the protective measures meet the requirement to protect workers “to the extent necessary” to mitigate the risk identified.

EPA derived PODs based on the HEC of 0.28 mg/m³ derived from rats and the HEC of 0.16 mg/m³ that it derived from hamsters, but these PODs are based on a dose metric (i.e., deposited dose) that does not represent the best available science (i.e., retained dose). EPA should have used the results of the rat inhalation study (the most sensitive species) and calculated the HEC based on the retained dose. That would provide a POD that would be both health protective and based on the best available science. Without that POD and an appropriate benchmark margin of exposure (MOE), EPA cannot justify its proposed regulatory action.

The proposed PV29 risk management rule has the potential to be more impactful than other EPA risk management rules because of the thousands of PSLTs listed on the TSCA Inventory. If either of EPA’s proposed risk management options is issued in final, it will set a bad precedent by serving as the basis for all of EPA’s risk evaluations for PSLTs when respirable particles are formed. Stakeholders need to be aware and be engaged. It is critically important that the rule be based on the best available science. This is a good opportunity for EPA to work with the U.S. Occupational Safety and Health Administration (OSHA) to revise the permissible exposure limit (PEL) for particulates not otherwise regulated (PNOR) (PSLTs fall into this category), given the immense number of opportunities for exposure to PSLT dust in the workplace, many of which are not under TSCA authority.