In November 2024, the EPA released the final revised risk determination and final supplement to the risk evaluation for 1,4-dioxane. The evaluation determines that 1,4-dioxane presents an unreasonable risk of injury to health under the conditions of use.

Dmitry Kalinovsky / Shutterstock.com

This chemical is used primarily as a solvent in a variety of commercial and industrial applications, such as the manufacture of other chemicals, as a processing aid, in laboratory chemicals, and in adhesives and sealants.

“This final risk determination is based on the information in the 2020 Risk Evaluation and the 2024 Supplement to the Risk Evaluation for 1,4-Dioxane, including the appendices and supporting documents. This determination was made in accordance with TSCA section 6(b), as well as TSCA’s best available science (TSCA section 26(h)) and weight of scientific evidence standards (TSCA section 26(i)), and relevant implementing regulations in 40 CFR part 702,” the unreasonable risk determination says. The “EPA’s final determination is based on cancer and non-cancer risks (from liver toxicity and effects in the olfactory epithelium) to workers and occupational non-users (ONUs) 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).”

The EPA identified the following conditions of use from the 2020 Risk Evaluation and the 2024 Supplement to the Risk Evaluation as significantly contributing to the unreasonable risk from 1,4-dioxane:

• Manufacture (including domestic manufacture and import)
• Processing (including repackaging, recycling, non-incorporative, as a reactant, and as a byproduct, including ethoxylation processing and polyethylene terephthalate (PET) manufacturing)
• Industrial/commercial use: intermediate
• Industrial/commercial use: processing aid
• Industrial/commercial use: functional fluids (open and closed system): metalworking fluid, cutting and tapping fluid, polyalkylene glycol fluid, hydraulic fluid
• Industrial/commercial use: laboratory chemicals
• Industrial/commercial use: adhesives and sealants: film cement
• Industrial/commercial use: other uses: spray polyurethane foam
• Industrial/commercial use: other uses: printing and printing compositions
• Industrial/commercial use: other uses: dry film lubricant
• Industrial/commercial use: other uses: hydraulic fracturing
• Industrial/commercial use: arts, crafts, and hobby materials: textile dye
• Industrial/commercial use: cleaning and furniture care products: surface cleaner
• Industrial/commercial use: laundry and dishwashing products: dish soap
• Industrial/commercial use: laundry and dishwashing products: dishwasher detergent
• Industrial/commercial use: laundry and dishwashing products: laundry detergent
• Industrial/commercial use: paints and coatings: paint and floor lacquer
• Consumer use: cleaning and furniture care products: surface cleaner
• Consumer use: laundry and dishwashing products: dish soap
• Consumer use: laundry and dishwashing products: dishwasher detergent
• Consumer use: laundry and dishwashing products: laundry detergent
• Consumer use: paints and coatings: paint and floor lacquer
• Disposal

The determination didn’t find unreasonable risk from 1,4-dioxane under the following conditions of use:

• Distribution in commerce
• Commercial use of automobile antifreeze
• Consumer use of textile dyes
• Consumer use of automobile antifreeze
• Consumer use of spray polyurethane foam

TSCA review process

The Toxic Substances Control Act (TSCA) was amended in 2016 under the Frank R. Lautenberg Chemical Safety for the 21st Century Act. This established a three-step chemical review process for the EPA to use in evaluating the safety of chemicals under specific types of use. Those three steps are:

• Prioritization
• Risk evaluation
• Risk management

In the first step, chemicals are designated as either “low priority” or “high priority.” High-priority chemicals are then moved to the risk evaluation stage, where the EPA determines whether the chemicals present unreasonable risks to humans or the environment under the specific conditions of use for which the chemicals are typically used. If an “unreasonable risk” determination is made, the Agency then moves to create regulations to manage those risks.

History

“1,4-Dioxane was prioritized for review by the EPA in December 2016 as one of the first 10 chemicals evaluated under the TSCA amendments. … The EPA issued its draft risk evaluation for 1,4-Dioxane in 2019 (Draft Risk Evaluation), in which it reviewed the hazards and exposures that the use of 1,4-Dioxane in industrial and commercial uses poses. The EPA issued the final risk evaluation for 1,4-Dioxane in December 2020,” according to law firm Holland & Knight. “The 2020 Final Risk Evaluation concluded that 1,4-Dioxane did not pose an unreasonable risk of injury to human health or the environment under several conditions of use. … However, it identified several manufacturing, processing, industrial, commercial and disposal uses that present an unreasonable risk to health.

“In 2021, [the EPA] concluded that a supplement to the 2020 Final Risk Evaluation for potential 1,4-Dioxane exposures was needed to consider exposure pathways that it had not previously evaluated. Following this supplemental evaluation, the EPA issued a Draft Revised Final Risk Evaluation and Risk Determination in 2023 (2023 Draft) that preliminarily concluded that 1,4-Dioxane presents an unreasonable risk to human health and the environment.”

TSCA regulations require the EPA to publish a proposed risk management rule by November 14, 2025. However, the Agency historically misses these regulated dates, and the upcoming administration change is also expected to cause delays.