EPA Releases Draft Supplement for 1,4-Dioxane

In July 2023, EPA announced the release of a draft supplement to the Risk Evaluation for 1,4-dioxane for public comment and peer review.  1,4-dioxane is solvent used to manufacture other chemicals such as adhesives and sealants.  It is also used as a processing aid and laboratory chemical. In addition, some manufacturing processes, such as the process used for making commercial and consumer dish soaps, result in the chemical being present as a byproduct.

The draft supplement focuses on air and water exposure pathways that were not included in the 2020 Risk Evaluation.  The 2020 Risk Evaluation focused on health risks to workers, consumers, and the general public, but not from drinking water, the air, or exposure where 1,4-dioxane is present as a byproduct.  The omission was identified by the Scientific Advisory Committee on Chemicals (SACC) as an oversight.  The SACC informed EPA that failure to assess the risks posed to the general population from exposure to the chemical may present a risk to human health – with an emphasis on drinking water as an exposure pathway.

The draft supplement identified cancer risk estimates higher than 1 in 10,000 for 1,4-dioxane present as a byproduct and higher than 1 in 1 million for general population exposure scenarios associated with 1,4-dioxane in drinking water sourced downstream of release sites and in air within 1 km of releasing facilities.

The draft supplement did note that the risk estimates include inherent uncertainties and the overall confidence in specific risk estimates fluctuates.  However, the document also stated that the information is beneficial in helping the Agency make a determination on whether the chemical poses an unreasonable risk to people with occupational exposure, through sources of drinking water, and breathing air near release sites.