EPA Releases Draft Supplement to the Risk Evaluation for 1,4-Dioxane

Released July 7, 2023

Assesses previously excluded air & water exposures to the general population, including fenceline communities, and from 1,4-dioxane generated as a byproduct

Today, the U.S. Environmental Protection Agency (EPA) released for public comment and peer review the Draft Supplement to the Risk Evaluation for 1,4-Dioxane. This 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. Once finalized, this draft supplement, along with the 2020 risk evaluation, provides the public with a more-complete understanding of the risks presented by 1,4-dioxane. The document released today does not contain the Agency’s revised draft unreasonable risk determination for 1,4-dioxane, which will also be released in the coming weeks for public comment.

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. 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. Health effects of concern for 1,4-dioxane include cancer and adverse effects to the liver and nasal tissue. 

EPA’s published 2020 risk evaluation for 1,4-dioxane identified health risks to workers, occupationally exposed non-users, consumers, bystanders, and the general population. However, 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). 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, this draft supplemental analysis found:

• Cancer risk estimates higher than 1 in 10,000 for a range of occupational exposure scenarios associated with 1,4-dioxane produced as a byproduct. 
• Cancer risk estimates higher than 1 in 1 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 1 km of releasing facilities. 

This draft supplement addresses 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.  
• Incorporating SACC recommendations to use of multiple years of data on releases to air and water and consideration of releases to groundwater. 

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. This 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. 

EPA understands there could be occupational safety protections in place at some workplace locations. However, not assuming use of PPE in its baseline exposure scenarios reflects EPA’s 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.” 

Additionally, EPA notes that some of the occupational monitoring data for 1,4-dioxane available to the Agency 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 is requesting public comment on the analysis presented in the draft supplement to the risk evaluation for 1,4-dioxane. Upon publication of the Federal Register notice, written comments on the draft supplement will be accepted for 60 days through www.regulations.gov (Docket No. EPA-HQ-OPPT-2022-0905). For additional information, please see the Federal Register notice or contact the Designated Federal Official, Dr. Alaa Kamel at kamel.alaa@epa.gov.

Finally, EPA is seeking external peer review from its Science Advisory Committee on Chemicals (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. The 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 on the SACC website.