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Less than a month after the comment period closed for EPA’s supplemental analysis of the Toxic Substances Control Act (TSCA) risk evaluation for 1,4-dioxane, the agency finalized and published the assessment in the January 8 Federal Register. As has been a continual theme in EPA’s TSCA risk assessments, the agency ignores exposures via drinking water. AMWA submitted a letter to EPA November 30 regarding the agency's supplemental analysis that included comments similar to those AMWA has made for trichloroethylene and perchloroethylene, urging the agency to include drinking water exposure within EPA's risk assessments under TSCA.

In addition to this request, AMWA asked for further explanation as to why, in this supplemental analysis, EPA reversed course to now examine exposures to the general population via ambient surface waters, but not via the drinking water pathway. The agency defended its position stating, “EPA is evaluating 1,4 dioxane through the [Safe Drinking Water Act] statutory processes for developing a National Primary Drinking Water regulation. However, EPA has not developed [Clean Water Act] section 304(a) recommended water quality criteria for the protection of aquatic life or human health for 1,4-dioxane and therefore evaluated exposures to aquatic species and the general population from ambient water in the 1,4-dioxane risk evaluation.”

EPA failed to address a related point from AMWA’s comments – why the agency declined to make a determination for 1,4-dioxane within the Office of Water’s Fourth Regulatory Determination, which cited the need for additional information including the finalization of this risk evaluation. AMWA’s letter asked for clarification as to why, “if the Office of Water is relying on this risk assessment to make a regulatory determination for 1,4-dioxane, the Office of Chemical Safety and Pollution Prevention excludes drinking water exposure from their analysis.”