On July 20, 2022, the U.S. Environmental Protection Agency (EPA) announced the availability of and requested public comment on a draft revision to the risk determination for the 1-bromopropane (1-BP) risk evaluation issued under the Toxic Substances Control Act (TSCA). 87 Fed. Reg. 43265. EPA states that the draft revision to the 1-BP risk determination reflects its announced policy changes to ensure the public is protected from unreasonable risks from chemicals in a way that is supported by science and the law. In the draft revision, EPA finds that 1-BP, as a whole chemical substance, presents an unreasonable risk of injury to health when evaluated under its conditions of use (COU). Comments are due August 19, 2022.

In addition, the revised risk determination does not reflect an assumption that all workers always appropriately wear personal protective equipment (PPE). EPA states that it understands that there could be occupational safety protections in place at workplace locations. According to EPA, not assuming use of PPE reflects EPA’s recognition that unreasonable risk may exist for subpopulations of workers who may be highly exposed because they are not covered by Occupational Safety and Health Administration (OSHA) standards, or their employers are out of compliance with OSHA standards, or because OSHA has not issued a permissible exposure limit (PEL) (as is the case for 1-BP).

In its July 20, 2022, press release, EPA states that 23 of the 25 COUs that EPA evaluated would drive the 1-BP whole chemical unreasonable risk determination. Removing the assumption that workers always and appropriately wear PPE in making the whole chemical risk determination for 1-BP would result in seven COUs in addition to the original 16 driving the unreasonable risk for 1-BP. Additional risks of cancer from dermal exposures would also drive the unreasonable risk to workers in six COUs; additional risks for non-cancer effects from acute and chronic inhalation exposures would also drive the unreasonable risk to workers in two COUs; and additional risks for non-cancer effects and cancer from acute and chronic inhalation and dermal exposures to workers would also drive the unreasonable risk in one COU. EPA notes that two out of 25 COUs would not drive the unreasonable risk: the commercial and consumer use of 1-BP in insulation for building and construction materials, and distribution in commerce.

Separately, EPA is conducting a screening approach to assess potential risks from the air and water pathways for several of the “first 10” chemicals, including 1-BP. For 1-BP, certain exposure pathways that were or could be regulated under another EPA-administered statute were excluded from the 2020 risk evaluation. According to EPA, this resulted in the air exposure pathway not being fully assessed. EPA states that its screening approach will identify if there are risks that were unaccounted for in the risk evaluation for 1-BP. While this analysis is underway, EPA is not incorporating the screening-level approach into this draft revised unreasonable risk determination. If the results suggest there is additional risk, EPA will determine if the risk management approach being contemplated for 1-BP will protect against these risks or if the risk evaluation will need to be formally supplemented or revised.

Commentary

As reported in our July 12, 2022, memorandum on the draft revisions to the risk determinations for perchloroethylene (PCE), N-methylpyrrolidone (NMP), methylene chloride (MC), and trichloroethylene (TCE), Bergeson & Campbell, P.C. (B&C^®) identified several common issues that EPA did not address as comprehensively as it might, namely, using a systematic review method that failed to meet the scientific standards under TSCA Section 26, making a whole chemical risk determination that conflicts with 40 C.F.R. Subpart B, and making a baseline assumption of the absence of PPE, a decision that many believe ignores reasonably available information in violation of TSCA. These same issues are common to the draft revised risk determination for 1-BP and the underlying final risk evaluation. We, therefore, have focused the following discussion on several representative issues in the final risk evaluation on 1-BP that would alter the findings of unreasonable risk or at a minimum the magnitude of those risks in the draft revised risk determination on 1-BP.

B&C notes that it agrees with EPA about “the irreversible health effects (specifically developmental toxicity and cancer)” that may occur with 1-BP under its COUs if exposures are not adequately mitigated. We do not, however, agree with EPA’s dermal exposure assessment for workers, its decision to disregard its own guidance for reducing uncertainty when deriving inhalation points of departure (POD), nor its failure to acknowledge the questionable human relevance of mouse lung tumors (i.e., the basis for its cancer assessment). In our view, each of these decisions appears to ensure the identification of risks, rather than to inform an objective determination of whether unreasonable risks are associated with the assessed COUs.

For the dermal exposure assessment for workers, EPA incorporated a fraction absorbed parameter as a modification to its “EPA/OPPT 2-Hand Dermal Exposure to Liquids Model.” This parameter was used to account for the volatility of 1-BP. EPA also used, however, surrogate data on cooking oil as default values to estimate the amount of 1-BP remaining on the skin. The impact of this decision is best visualized by considering how much cooking oil would remain on one’s hand after dipping it in cooking oil and then partially removing the liquid with a dry cloth versus doing the same with water. Though this is a simplified summary of how EPA derived its default values, it demonstrates how the amount of a highly viscous substance (e.g., cooking oil) remaining on the skin, even after wiping, would be significantly higher than the amount of a substance remaining, like 1-BP, that has a viscosity comparable to that of water.

For inhalation assessments, EPA followed its own guidance on calculating inhalation PODs for humans, but it did not follow the same guidance that also recommends reducing the associated uncertainty when making such extrapolations (i.e., rodents to humans), leading to a risk threshold that was, in most cases, three times more stringent. EPA’s explanation (related to the irritating property of 1-BP) for not reducing the uncertainty is that rodents and humans respond differently to respiratory tract irritation. Yet EPA reduced the associated uncertainty in its final risk evaluation for 1,4-dioxane, a substance that causes direct effects on the respiratory tract, including irritation. This inconsistency, like many others, calls into question the thoroughness and quality of EPA’s risk evaluations, and thus causes us to question the evaluation’s scientific integrity.

For the cancer assessment, EPA summarized data that showed 1-BP caused tumors in rodents at multiple sites, including the skin (male rats), the large intestines (female rats), and the lungs (female mice), following whole-body inhalation. This discussion, however, lacked reference to more recent evaluations that explore (and raise questions about) the relevance of mouse lung tumors to humans (e.g., Smith et al., 2018 and Cohen et al., 2020). We recognize that EPA may not agree with these evaluations, but EPA should have included reference to this work and a discussion of the relevance to its 1-BP risk evaluation. B&C does not question the carcinogenic potential of 1-BP. We, however, are puzzled by EPA’s decision not to characterize the human relevance of the tumors identified in rodents, particularly the lung tumors in female mice only.