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July 31, 2023

Draft Supplement to Risk Evaluation and Draft Revised TSCA Risk Determination for 1,4-Dioxane for Public Comment

The ACTA Group

On July 10, 2023, the U.S. Environmental Protection Agency (EPA) announced the availability of 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 requests public comment on the analysis presented in the draft supplement to the risk evaluation for 1,4-dioxane. Comments on the draft supplement are due September 8, 2023.

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 the Toxic Substances Control Act (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 states that it specifically seeks 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. Comments on the draft revised risk determination are due September 8, 2023.

Draft Supplement to the Risk Evaluation

According to EPA’s July 7, 2023, press release, 1,4-dioxane is a solvent used in a variety of commercial and industrial applications such as the manufacture of other chemicals (e.g., adhesives, sealants) or as a processing aid or laboratory chemical. EPA states that it is also “produced as a byproduct in several manufacturing processes that then results in its presence as a contaminant in commercial and consumer products like dish soaps and detergents.”

As reported in our January 13, 2021, memorandum, EPA’s 2020 risk evaluation for 1,4-dioxane identified health risks to workers, occupationally exposed non-users, consumers, bystanders, and the general population. EPA notes that it did not evaluate general population exposures to 1,4-dioxane in drinking water or air; did not evaluate all the ways people could be exposed to 1,4-dioxane as a byproduct; did not evaluate the potential for simultaneous exposure to more than one source of 1,4-dioxane (aggregate risk); and did not evaluate potential exposures to fenceline communities (in accordance with TSCA’s requirement to evaluate risk to potentially exposed or susceptible subpopulations). According to EPA, these omissions “led several Scientific Advisory Committee on Chemicals (SACC) members to say that EPA’s ‘failure to assess 1,4-dioxane exposure in the general population may leave substantial portions of the population at risk. This is particularly concerning for drinking water.’”

In addition to the risks identified in the 2020 risk evaluation, EPA states that the draft supplemental analysis found:

  • Cancer risk estimates higher than one in 10,000 for a range of occupational exposure scenarios associated with 1,4-dioxane produced as a byproduct; and
  • Cancer risk estimates higher than one in one million for a range of general population exposure scenarios, including to fenceline communities, associated with drinking water sourced downstream of release sites and for air within one kilometer (km) of releasing facilities.

According to EPA, it addressed previous feedback from the TSCA SACC and public comments by:

  • Incorporating SACC recommendations and public comments on the 2020 draft risk evaluation for 1,4-dioxane to consider general population exposures through air and water and to consider exposure to 1,4-dioxane as a byproduct;
  • Incorporating SACC recommendations on EPA’s Draft Screening Level Approach for Assessing Ambient Air and Water Exposures to Fenceline Communities Version 1.0 to evaluate aggregate risks from multiple sources releasing 1,4-dioxane to air or water; and
  • Incorporating SACC recommendations to use of multiple years of data on releases to air and water and consideration of releases to groundwater.

EPA notes that the occupational risk scenarios evaluated do not reflect an assumption that workers always and appropriately wear personal protective equipment (PPE), even though some facilities might be using PPE as one means to reduce workers’ exposure. EPA states that its decision “should not be viewed as an indication that EPA believes there is widespread non-compliance with applicable Occupational Safety and Health Administration (OSHA) standards.” According to EPA, not assuming use of PPE in its baseline exposure scenarios reflects its recognition that certain subpopulations of workers exist that may be highly exposed because:

  • They are not covered by OSHA standards (e.g., self-employed individuals and public sector workers who are not covered by a state plan);
  • Their employers are out of compliance with OSHA standards; or
  • OSHA describes its chemical-specific permissible exposure limits (largely adopted in the 1970s) as being “outdated and inadequate for ensuring protection of worker health.”

EPA additionally notes that some of the occupational monitoring data for 1,4-dioxane available is several decades old, and thus may not reflect current industry practices. EPA “would particularly welcome public comments that include specific descriptions or exposure data that reflect any updates to these practices.”

EPA states that it is seeking external peer review from SACC on issues related to environmental release from industrial sources, application of occupational exposure modeling approaches and monitoring data for industrial and commercial operations, sources of environmental releases from hydraulic fracturing operations, modeling concentrations of 1,4-dioxane in surface water and groundwater, and exposure from multiple sources of 1,4-dioxane in air or water. SACC will consider and review the draft supplement at a virtual public meeting on September 12-15, 2023. Registration instructions for the meeting will be announced in August 2023 on the SACC website.

Draft Revised Risk Determination

EPA in its July 25, 2023, press release stated that its previously published risk determination found that 13 out of 24 COUs of 1,4-dioxane presented unreasonable risks to workers and occupationally exposed non-users as part of the 2020 risk evaluation. In the draft revised risk determination, EPA states that it proposes “some important changes” to the 2020 risk determination:

  • EPA has preliminarily determined that the better way to characterize the unreasonable risk from 1,4-dioxane is as a whole chemical, rather than COU-specific risk determinations;
  • EPA proposes that the risk determination should not assume, as the 2020 risk determination did, that workers always and appropriately wear PPE, even though some facilities might use PPE as one way to reduce workers’ exposure;
  • Based on the draft supplement to the risk evaluation, several additional COUs would also contribute to the unreasonable risk determination due to worker inhalation and dermal risks from exposure to 1,4-dioxane as a byproduct; and
  • EPA proposes, based on its evaluation of air-related and drinking water-related risks to the general population and fenceline communities from 1,4-dioxane, that drinking water sourced from surface water contaminated with 1,4-dioxane contributes to the unreasonable risk from 1,4-dioxane. According to EPA, many COUs contribute to general population or fenceline communities’ exposures to 1,4-dioxane in surface water, including industrial releases from a range of COUs (including where 1,4-dioxane is produced as a byproduct).

Worker Risks

EPA’s proposed changes to the risk determination include:

  • Two additional COUs in addition to the original 13 COUs from the 2020 risk evaluation would contribute to the unreasonable risk from 1,4-dioxane;
  • Several additional COUs from the draft supplement, which were not assessed in 2020, would also contribute to the unreasonable risk due to worker inhalation and dermal risks; and
  • Overall, based on the revised risk determination, EPA’s preliminary findings include that worker exposure to 1,4-dioxane from all but four occupational COUs contribute to the unreasonable risk from 1,4-dioxane.

Consumer Risks

EPA states that in the 2020 risk evaluation, it evaluated risks to consumers from eight COUs and found that the use of the evaluated products did not present an unreasonable risk to consumers or bystanders. In the 2023 draft revised unreasonable risk determination, EPA does not propose to identify the consumer COUs as contributing to the unreasonable risk determination from 1,4-dioxane. EPA notes that the manufacture of those consumer products, and, in some cases, the commercial use of similar products, does contribute to the unreasonable risk determination, however, due to worker risks of cancer and non-cancer effects from inhalation and dermal exposures and risk to fenceline communities from exposures to drinking water sourced from surface water contaminated with 1,4-dioxane discharged from industrial facilities.

General Population and Fenceline Community Risks

In the 2023 draft supplement, EPA evaluated exposures via ingestion of drinking water sourced from surface water or groundwater contaminated with 1,4-dioxane from facility-specific releases, down-the-drain releases of consumer and commercial products that contain 1,4-dioxane as a byproduct, hydraulic fracturing releases, and leaching from landfills. EPA states that it proposes to include the risks to the general population and fenceline communities from drinking water sourced from surface water contaminated with 1,4-dioxane that is discharged from industrial facilities (including where it is produced as a byproduct) as contributing to the unreasonable risk determination.


As with EPA’s other TSCA Section 6 actions, EPA’s proposed supplement to the 1,4-dioxane risk evaluation also suffers from the flaws in the systematic review process that EPA followed. For example, EPA has yet to provide a robust rebuttal of the several evaluations by other competent authorities, including Health Canada, the European Union, and the Commonwealth of Australia, that concluded that 1,4-dioxane is a threshold carcinogen by the oral route. Given EPA’s departure from this long history, it is unclear whether EPA has met its burden under TSCA Section 26 to justify considering 1,4-dioxane a genotoxic carcinogen warranting a linear low-dose extrapolation. EPA’s lone assessment of 1,4-dioxane’s carcinogenicity is troubling as it disregards reasonably available information on the threshold carcinogenic mode of action for 1,4-dioxane.

Even more problematic is EPA’s decision to issue its revised risk determination for 1,4-dioxane with a public comment deadline on the same day (i.e.September 8, 2023) as the deadline for its proposed supplement to the 1,4-dioxane risk evaluation. This suggests that EPA has pre-determined the outcome it seeks, rather than following the best available science. This is not an isolated instance. For example, during the peer review of the draft 1,4-dioxane risk evaluation, a public commenter expressed concern because EPA was holding the peer review on the draft document prior to the close of the public comment period. The public commenter noted that “this approach is a case of either the arbitrary deadline for a decision [being] more important than the integrity of the information going into the decision, or this is a mechanism to discourage comments from the stakeholder community which desires to see a standardized risk evaluation process allowed, and followed, or both.”

Another concern relates to EPA’s use of new methods and novel applications of existing methods in the proposed supplement to the 1,4-dioxane risk evaluation. EPA seeks comment on these novel approaches and on the outcome of EPA’s assessment using these novel approaches. Typically, EPA would seek review of the proposed novel methods to ensure they are fit-for-purpose before employing such methods in a regulatory action. While it is clear that EPA is seeking to expedite completion of its proposed supplement to the 1,4-dioxane risk evaluation so that it can propose risk management measures that are already overdue, EPA is increasing the burden on reviewers by requiring the use of the new policies while also preparing comments on the revised risk determination based on those very novel methods.

We agree with EPA’s view that the primary exposure pathway for 1,4-dioxane is through drinking water. EPA’s risk evaluation and likely risk management actions will be complicated by the fact that there are sources of 1,4-dioxane, both legacy sources and non-TSCA sources, such as personal care products, that EPA cannot assess or eliminate in a TSCA action. This is a case in which EPA will likely have to rely upon its authority under the Safe Drinking Water Act and set a Maximum Contaminant Level to ensure that exposure to 1,4-dioxane from all sources is below the concern threshold.

We encourage stakeholders to pay careful attention to this risk evaluation. It will likely be the model for the “Next 20” risk evaluations that will begin rolling out later this year.