EPA Releases Final Supplement to the Risk Evaluation and Revised Unreasonable Risk Determination for 1,4-Dioxane

On November 13, 2024, the U.S. Environmental Protection Agency (EPA) announced the release of its final supplement to the risk evaluation and revised unreasonable risk determination for 1,4-dioxane under the Toxic Substances Control Act (TSCA). 89 Fed. Reg. 89993. EPA states in the Federal Register notice that it “used the best available science to prepare this final supplement to the risk evaluation and has determined that 1,4-dioxane poses unreasonable risk to human health.” EPA notes that under TSCA, it now must initiate risk management actions to address the unreasonable risk.

Background

As reported in our July 31, 2023, memorandum, in July 2023, EPA released the draft supplement to the risk evaluation for 1,4-dioxane for public comment and peer review. 88 Fed. Reg. 43562. EPA states in its July 7, 2023, press release that the draft supplement to the 2020 risk evaluation considers air and water exposure pathways that were excluded from the earlier risk evaluation and exposure to 1,4-dioxane generated as a byproduct. The draft supplement estimates risks to the general population, including to people living in fenceline communities, and aggregate exposures from multiple facilities located in the same area. EPA requested public comment on the analysis presented in the draft supplement to the risk evaluation for 1,4-dioxane.

On July 26, 2023, EPA released for public comment a draft revision to the risk determination for the 1,4-dioxane risk evaluation issued under TSCA. 88 Fed. Reg. 48249. In its July 25, 2023, press release, EPA notes that the draft revised risk determination evaluates 1,4-dioxane as a whole chemical substance to make one overall risk determination rather than evaluating each condition of use (COU) separately and making individual risk determinations. The draft revision incorporates the occupational and consumer exposures from EPA’s 2020 risk evaluation, as well as additional exposure pathways to the general public (including fenceline communities) and from 1,4-dioxane generated as a byproduct from the draft supplement to the risk evaluation. EPA specifically sought public comment on several aspects of the 2023 draft unreasonable risk determination, including its finding that general population exposure to 1,4-dioxane in drinking water contributes to the determination that 1,4-dioxane presents an unreasonable risk, and whether the risks to the general population from drinking water exposure can be attributed to specific COUs of 1,4-dioxane.

Unreasonable Risk Determination

In the Federal Register notice, EPA states that it has determined that 1,4-dioxane presents an unreasonable risk of injury to human health under the COUs. According to EPA, the unreasonable risk to human health is based on cancer and non-cancer risks (from liver toxicity and effects in the olfactory epithelium) to workers and occupational non-users (ONU) from inhalation and dermal exposures, and cancer risks to the general population, including fenceline communities, from exposures to 1,4-dioxane in drinking water sourced from surface water contaminated with industrial discharges of 1,4-dioxane (including when it is generated as a byproduct) and down-the-drain disposals of commercial and consumer products that are contaminated with 1,4-dioxane generated as a byproduct.

Consistent with the statutory requirements of TSCA Section 6(a), EPA will propose risk management regulatory actions “to the extent necessary so that 1,4-dioxane no longer presents an unreasonable risk to health.” According to the notice, EPA expects to focus on the COUs that significantly contribute to the unreasonable risk. EPA notes that under TSCA Section 6(a), it “is not limited to regulating the specific activities found to contribute significantly to unreasonable risk and may select from among a suite of risk management requirements in TSCA section 6(a) related to manufacture (including import), processing, distribution in commerce, commercial use, and disposal as part of its regulatory options to address the unreasonable risk.” EPA states that “[a]s a general example, [it] may regulate upstream activities (e.g., processing, distribution in commerce) to address downstream activities (e.g., consumer uses) contributing significantly to unreasonable risk, even if the upstream activities do not contribute significantly to the unreasonable risk.”

EPA states that in addition, as part of its evaluation, it “has determined that 1,4-dioxane in drinking water sourced from surface water contaminated with industrial discharges of 1,4-dioxane (including when it is generated as a byproduct) and down-the-drain disposals of commercial and consumer products that are contaminated with 1,4-dioxane significantly contribute to the unreasonable risk from 1,4-dioxane.” EPA notes that TSCA Section 9(b) requires it to coordinate TSCA actions with actions taken under other Agency authorities. According to the notice, in coordinating regulatory action under TSCA with other offices at EPA, the Agency considered the authorities of the Safe Drinking Water Act (SDWA) and has determined that certain regulatory actions under the SDWA may also be appropriate. As described in more detail in a memorandum included in the online docket, and consistent with TSCA Section 9(b)(1), the Office of Chemical Safety and Pollution Prevention (OCSPP) “has memorialized this agreement for coordinated action on risks from 1,4-dioxane contamination in drinking water through actions under both TSCA section 6(a) and, for Office of Water consideration of remaining risks and appropriate action, under SDWA.”

Commentary

Readers may be surprised and a bit confused by the different conclusions from EPA’s draft versus final unreasonable risk determinations. EPA stated that these differences were “based on changes in the 2024 Supplement as a result of SACC [Science Advisory Committee on Chemicals] peer review and public comments.” We provide some representative examples below.

The Acta Group (Acta^®) reviewed the underlying basis for these differences, which shed light on EPA’s final risk determinations. EPA’s exposure estimates were obtained mostly from the New York State Department of Environmental Conservation’s (NYSDEC) database of waivers for a New York law that went into effect in December 2022. The New York law limits the maximum concentration of 1,4-dioxane in cleaning and personal care products to 2 parts per million (ppm) by the end of 2022 and 1 ppm by the end of 2023.

The New York law permitted manufacturers to “apply to the [NYDEC] for up to two, one-year waivers of the maximum 1,4-dioxane trace concentrations…upon such proof that the manufacturer has taken steps to reduce the concentration of 1,4-dioxane in that product and is unable to comply with the requirements.” The applicability of the waivers was limited to December 30, 2023, for the 2 ppm limit, and December 30, 2024, for the 1 ppm limit. This context is important for understanding EPA’s use of the 1,4-dioxane concentrations reported in the non-compliant products listed in the waivers database.

EPA reviewed non-compliant products in the waivers database that were effective through December 30, 2023. For example, EPA identified laundry detergent in the database with 1,4-dioxane concentrations that ranged from 2.0 to 129 ppm (see “Lapsed Waivers” tab at cells C57 to C59). EPA stated without further explanation that it “used this maximum concentration of 129 ppm in the occupational dermal exposure assessment….” EPA determined there were unreasonable cancer risks to workers from high-end dermal exposures assuming lifetime exposures to laundry detergents with concentrations of 1,4-dioxane at 129 ppm. The range of 1,4-dioxane concentrations for the New York law waivers on 1,520 non-compliant products, which were effective from December 31, 2022, and ended on December 30, 2023 (i.e., the now “Lapsed Waivers”), was 1.8 to 129.1 ppm. In comparison, the range of 1,4-dioxane concentrations for waivers on 1,075 non-compliant products, which were effective from December 31, 2023, and will end on December 30, 2024 (i.e., “Active Waivers”), is 1.03 to 8.8 ppm. EPA’s assessment is, therefore, based on past levels of 1,4-dioxane that are nearly 15-fold higher than, and would be violative of, the current New York compliance requirements.

EPA’s assessment of general population risks from drinking water contaminated with 1,4-dioxane from hydraulic fracturing took a different approach. For example, EPA stated that “while estimated well life ranges from 5 to 70 years, because the current hydraulic fracturing-led production surge is somewhat recent, it is not known how much and for how long these wells will ultimately produce…Therefore, it is unlikely that there will be exposures that result in the 95% percentile lifetime cancer risks, whether based on 33 years or a full lifetime.” It is not, however, clear why EPA made the “unlikely” determination for hydraulic fracturing, while at the same time concluding that lifetime worker dermal exposures to laundry detergents will contain 1,4-dioxane at concentrations up to 129 ppm. The New York law’s required compliance date of December 31, 2024, for the currently “Active Waivers” supports that chronic exposure at the concentration EPA assumes is unlikely.

EPA’s unreasonable risk determinations for consumer COU was also surprising based on its draft versus final unreasonable risk determinations. Several examples are shown below.

Aside from EPA’s exposure and release assumptions, the primary driver for its unreasonable risk determinations across all COUs is its application of a linear low-dose extrapolation (i.e., no threshold) for quantifying potential cancer risks from exposures to 1,4-dioxane. During the comment period on the 2023 draft supplement, members of the public referred EPA to the conclusions of other competent authorities that performed independent evaluations on the carcinogenicity of 1,4-dioxane and determined that it is a threshold carcinogen. For example, Health Canada (HC) concluded in its 2021 Guideline Technical Document for Public Consultation on 1,4-Dioxane in Drinking Water that “Since 1,4-dioxane acts through a non-genotoxic MOA and demonstrates dose-related non-linear kinetics, a non-linear (threshold) risk assessment approach is considered appropriate.” More recently, the European Chemicals Agency’s (ECHA) Committee for Risk Assessment (RAC) concluded in its 2022 Opinion on Scientific Evaluation of Occupational Exposure Limits for 1,4-Dioxane that “A non-linear (threshold) risk assessment approach is considered appropriate.” EPA’s response to public comments on the 2023 Draft Supplement was silent on the conclusions of HC and the ECHA RAC, despite these conclusions post-dating EPA’s 2020 final risk evaluation for 1,4-dioxane. EPA further dismissed the most recent published evaluation of the carcinogenic mode of action (MOA) for 1,4-dioxane (i.e., Lafranconi et al., 2023), stating that it “does not provide novel data and relies primarily on studies that were already considered by the EPA in the MOA analysis published in 2020.” EPA’s dismissal failed to consider the integrated assessment of these data, which provides an updated MOA for 1,4-dioxane. Further, EPA did not include charge questions on the 2023 Draft Supplement to obtain the TSCA SACC’s advice on whether these newer evaluations warranted application of a threshold approach. EPA’s perfunctory rejection of others’ scientific views seemingly would not comply with EPA’s Scientific Integrity Policy and, what’s more, undermines the scientific legitimacy of the risk determination.

Given that EPA had to assume unrealistically high exposures from products that violate current New York 1,4-dioxane product standards and a questionable concern level, EPA’s determination of unreasonable risk raises serious questions. There are circumstances in which there might be an unreasonable risk, especially in areas with polluted water sources, and OCSPP’s plans to work with the Office of Water to promulgate limits on 1,4-dioxane in drinking water are laudable. Doing so will be more protective because it will protect the public from both new exposures (from the down-the-drain exposure to very small amounts of 1,4-dioxane in products) and legacy 1,4-dioxane pollution. EPA could have come to this conclusion even with more supportable levels in products and with a threshold carcinogen point of departure.

Under ordinary circumstances, EPA would have one year from publication of the final risk evaluation, in this case the final 2024 Supplement, to issue a proposed risk management rule on 1,4-dioxane. These are not, however, ordinary circumstances. The forthcoming change in administration may lead to significant scrutiny on this and other recent EPA work products. For example, on January 20, 2021, President Biden issued Executive Order (EO) 13990, which required “Immediate Review of Agency Actions Taken Between January 20, 2017, and January 20, 2021.” The EO instructed the heads of agencies to consider suspending, revising, or rescinding agency actions that were not “guided by the best science” and were not “protected by processes that ensure the integrity of Federal decision-making.” We anticipate that the Trump-Vance Administration will issue a similar EO on or about January 20, 2025.