EPA Releases Final Supplement to 1 4-Dioxane Risk Evaluation and Seeks Public Comments for Review of 1 3-Butadiene Draft Risk Evaluation

On November 13, 2024, the U.S. Environmental Protection Agency (EPA) released its final supplement to the risk evaluation and determination for the solvent 1,4-dioxane under the Toxic Substances Control Act (TSCA). The updated assessment no longer assumes that workers are consistently using proper personal protective equipment (PPE), addressing this in the risk management process. The evaluation also highlights gaps in the 2020 review, including the omission of general population exposure via drinking water and air, aggregate risks, and potential impacts on fenceline communities.

Uses, Exposures and Risks Associated with 1,4-Dioxane

1,4-Dioxane (CAS 123-91-1) is a solvent used in a variety of commercial and industrial applications. It is found in laboratories, in cleaning products such as dish soaps and laundry detergents, and in the production or processing of chemicals such as adhesives and sealants. It is often generated as a byproduct in manufacturing processes, leading to its presence as a contaminant in consumer products.

Products containing 1,4-dioxane can contaminate surface water when washed down the drain. Exposure to this chemical may occur through consumer products, workplace environments, or contaminated water and air, often due to industrial or commercial discharges.

EPA has determined that 1,4-dioxane poses an unreasonable risk to workers, nearby communities, and those who may be more sensitive to 1,4-dioxane due to factors such as age or pre-existing health conditions, citing its links to cancer, liver toxicity, and nasal tissue damage. The risks stem from inhalation and skin exposure during industrial use and from its presence as a byproduct in commercial products.

These groups could be exposed to 1,4-dioxane in drinking water, particularly in areas where water sources include smaller or slow-flowing streams that have been contaminated by industrial discharges. Additionally, runoff from households that use products containing 1,4-dioxane, such as dish soap, laundry detergent, and surface cleaners, could contribute to contamination.

1,4-Dioxane does not pose an unreasonable risk to the environment. 

Next Steps

EPA will propose a rule under TSCA Section 6 to protect public health from the identified risks of 1,4-dioxane. In line with TSCA Section 9(b), EPA is coordinating efforts across its agencies, including potential actions under the Safe Drinking Water Act (SDWA), to manage risks related to 1,4-dioxane contamination of drinking water. Both EPA’s Office of Chemical Safety and Pollution Prevention (OCSPP) and Office of Water (OW) are working together to address these concerns.

Additional Information

Conditions of Use identified in the 2020 risk evaluation and 2024 supplement as contributing significantly to unreasonable risk include:

• Manufacture and Import
• Processing (e.g., repackaging, recycling, non-incorporative uses)
• Industrial/Commercial Use (e.g., intermediates, processing aids, metalworking fluids, adhesives, sealants, hydraulic fracturing)
• Consumer Use (e.g., dish soap, laundry detergent, paint)
• Disposal

Conditions of Use that do not significantly contribute to unreasonable risk are:

• Distribution in commerce
• Commercial use of automobile antifreeze, textile dyes, and spray polyurethane foam.

1,3-Butadiene Peer Review Will Follow Suit

On November 14, 2024, EPA announced a call for public comments on candidates to assist the Science Advisory Committee on Chemicals (SACC) in reviewing the draft Toxic Substances Control Act (TSCA) risk evaluation for 1,3-butadiene.

1,3-Butadiene (CAS 106-99-0) is a highly flammable, colorless gas with a gasoline-like odor. It is used in the manufacture of products such as rubber tires, plastics, adhesives, paints, and automotive care products.

The SACC is a scientific peer review body for EPA's Office of Chemical Safety and Pollution Prevention that provides independent advice and recommendations on risk assessments, methodologies, and pollution prevention strategies for chemicals regulated under TSCA.

The peer review will take place in early 2025 and will guide the final risk evaluation.