The U.S. Environmental Protection Agency (EPA) has released the final supplemental risk assessment report for the solvent 1,4-dioxane, confirming under the Toxic Substances Control Act (TSCA) that the chemical poses an unreasonable risk to human health. Studies indicate that 1,4-dioxane can cause cancer and damage to liver and nasal tissues. Although 1,4-dioxane was one of the first ten chemicals to be reviewed under the revised TSCA, the 2020 risk assessment did not evaluate the exposure of the general population through drinking water or air, nor did it consider all pathways of exposure to 1,4-dioxane as a byproduct. The final supplemental risk assessment addresses these issues, providing a more comprehensive understanding to the public and clarifying the risks associated with 1,4-dioxane.
Use and Associated Risks of 1,4-Dioxane
1,4-dioxane is a solvent commonly used in commercial and industrial settings, widely present in laboratories, cleaning products (such as dish soaps and laundry detergents), and in the production of chemicals like adhesives and sealants. This chemical can be produced as a byproduct during manufacturing processes and exist as a pollutant in various consumer products. After the use of these products, 1,4-dioxane can be discharged into sewers, leading to surface water contamination. People may be exposed to this chemical in workplace or daily life environments through inhalation or skin contact, especially in areas with industrial emissions and water pollution. EPA's research shows that 1,4-dioxane poses serious health risks to workers, the general public, and residents of communities near chemical release sites, including risks of cancer, liver toxicity, and nasal tissue damage. Out of 26 assessed uses in industrial and commercial scenarios, 22 were found to pose significant unreasonable risks to workers.
Next Steps
To address the unreasonable risks posed by 1,4-dioxane, the EPA plans to initiate risk management measures under Section 6 of the TSCA, proposing a rule aimed at protecting the public from identified risks. Additionally, the EPA will ensure that its measures are coordinated with regulatory actions of other agencies under TSCA Section 9(b). The EPA is considering various risk management options and believes that regulatory measures under the Safe Drinking Water Act (SDWA) framework may also be appropriate for 1,4-dioxane.
Supplementary Information
Conditions of Use that Significantly Contribute to the Unreasonable Risk (based on the 2020 risk evaluation and 2024 supplement):
- 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
Conditions of Use that Do Not Significantly Contribute to the Unreasonable Risk
- Distribution in commerce
- Commercial use of automobile antifreeze
- Consumer use of textile dyes
- Consumer use of automobile antifreeze
- Consumer use of spray polyurethane foam
