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Federal Register / Vol. 86, No. 40 / Wednesday, March 3, 2021 / Rules and Regulations
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Summary of Public Comments on Strontium, 1,4-Dioxane, and 1,2,3Trichloropropane, and the Agencys Responses H. Strontium Strontium is an alkaline earth metal.
On October 20, 2014 the Agency published its preliminary regulatory determination to regulate strontium and requested public comment on the determination and supporting technical information USEPA, 2014. Informed by the public comments received, rather than making a final determination for strontium in 2016, EPA delayed the final determination to consider additional data, and to decide whether there is a meaningful opportunity for health risk reduction by regulating strontium in drinking water USEPA, 2016f. Specifically, the publication on the delayed final determination mentioned that EPA would evaluate additional studies on strontium exposure and health studies related to strontium exposure. Since 2016, EPA
has worked to identify and evaluate published studies on health effects associated with strontium exposure, sources of exposure to strontium, and treatment technologies to remove strontium from drinking water. In its March 10, 2020 document USEPA, 2020a, EPA clarified that it is continuing with its previous 2016
decision USEPA, 2016f to delay a final determination for strontium in order to further consider additional studies related to strontium exposure.
The Agency received several comments in support of a continued evaluation of strontium and not making a final determination for strontium in this action. One commenter requested that EPA complete its evaluation of strontium in a more timely manner. EPA
agrees with the comments that are in support of the continued evaluation prior to making a final regulatory determination for strontium. Regarding making a regulatory determination for strontium in this rulemaking, EPA notes that there continues to be a need for additional information and analyses before a regulatory determination can be made for strontium. While EPA
determined in 2014 that strontium may have adverse effects on the health of persons including children, the Agency continues to consider additional data, consult existing assessments such as Health Canadas Drinking Water Guideline from 2018, and evaluate whether there is a meaningful opportunity for health risk reduction by regulating strontium in drinking water.
Additionally, EPA understands that strontium may co-occur with beneficial
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calcium in some drinking water systems and treatment technologies that remove strontium may also remove calcium.
The Agency is evaluating the effectiveness of treatment technologies under different water conditions, including calcium concentrations. EPA
intends to make a determination after these data needs have been resolved as part of its regulatory determination process.
I. 1,4-Dioxane 1,4-Dioxane is used as a solvent in cellulose formulations, resins, oils, waxes, and other organic substances;
also used in wood pulping, textile processing, degreasing; in lacquers, paints, varnishes, and stains; and in paint and varnish removers.
While the health effects data suggest that 1,4-dioxane may have an adverse effect on human health and the occurrence data indicate that 1,4dioxane is occurring in finished drinking water above the current HRL in some systems, EPA has not made a preliminary determination for 1,4dioxane, as the Agency has not determined whether 1,4-dioxane occurs in public water systems with a frequency and at levels of public health concern and whether there is a meaningful opportunity for public health risk reduction by establishing an NPDWR for 1,4-dioxane USEPA, 2020a. The Final Regulatory Determination 4 Support Document USEPA, 2021a and the Occurrence Data from the Third Unregulated Contaminant Monitoring Rule UCMR 3
USEPA, 2019a present additional information and analyses supporting the Agencys evaluation of 1,4-dioxane.
The Agency received several comments in support of a continued evaluation and not making a 1,4dioxane determination at this time. One commenter provided information summarizing their belief that 1,4
dioxane has a non-linear mode of action. Another commenter requested that EPA complete its evaluation of 1,4dioxane in a more-timely manner. EPA
agrees with the comments that are in support of the continued evaluation.
Regarding making a regulatory determination for 1,4-dioxane today, EPA notes that there is a need for additional information and analyses before a regulatory determination can be made for 1,4-dioxane. Based on UCMR
3 data, EPA derived a national estimate of less than two baseline cancer cases per year attributable to 1,4-dioxane in drinking water USEPA, 2021a.
However, while the number of baseline cancer cases is relatively low, other adverse health effects following
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exposure to 1,4-dioxane may also contribute to potential risk to public health, and these analyses under SDWA
have not yet been completed. The Agency recently completed its new TSCA risk evaluation for 1,4-dioxane by the Office of Chemical Safety and Pollution Prevention OCSPP USEPA, 2020c and intends to consider it and the Canadian guideline technical document, once finalized, Health Canada, 2018 and other relevant new science relevant to drinking water contamination prior to making a regulatory determination. This evaluation may provide clarity as to whether a new HRL is appropriate for evaluating the occurrence of 1,4-dioxane and whether there is a meaningful opportunity for an NPDWR to reduce public health risk.
J. 1,2,3-Trichloropropane 1,2,3-Trichloropropane is a man-made chemical used as an industrial solvent, cleaning and degreasing agent, and synthesis intermediate.
While the UCMR 3 data indicated 1,2,3-trichloropropane occurrence was relatively low at concentrations above the MRL, the MRL 0.03 mg/L is more than 75 times the HRL 0.0004 mg/L for 1,2,3-trichloropropane. This discrepancy allows for a broad range of potential contaminant concentrations that could be in exceedance of the HRL
but below the MRL. EPA did not make a preliminary determination for 1,2,3trichloropropane due to these analytical method-based limitations. The Agency noted that it needs additional lowerlevel occurrence information prior to making a preliminary regulatory determination for 1,2,3trichloropropane. The Final Regulatory Determination 4 Support Document USEPA, 2021a and the Occurrence Data from the Third Unregulated Contaminant Monitoring Rule UCMR 3
USEPA, 2019a present additional information and analyses supporting the Agencys evaluation of 1,2,3trichloropropane.
The Agency received several comments in support of a continued evaluation and not making a 1,2,3trichloropropane determination at this time. In addition, EPA notes that several comments requested that EPA find solutions to the analytical method limitations and collect additional monitoring data with an MRL adequate to support decision-making. EPA agrees with the comments that are in support of the continued evaluation. EPA also agrees that further evaluation of 1,2,3tricholoropropane is warranted when new methods or other tools are available to do so.

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