EPA Releases Draft Risk Evaluation for 1,1-Dichloroethane and Draft Hazard Assessment of 1,2-Dichloroethane for Public Comment and Peer Review

On July 1, 2024, the U.S. Environmental Protection Agency (EPA) announced the release of the draft risk evaluation for 1,1-dichloroethane (1,1-DCE) and the draft human health hazard assessment supporting the draft risk evaluation for 1,2-dichloroethane (1,2-DCE, also known as ethylene dichloride) prepared under the Toxic Substances Control Act (TSCA). EPA states that it “preliminarily determined 1,1-dichloroethane poses unreasonable risk to human health (of workers) and the environment.” According to EPA, the effects to people from exposure to 1,1-DCE and 1,2-DCE are “kidney and other cancers, as well as harmful non-cancer renal, nasal, immune system, and reproductive effects.” Publication of a notice of availability in the Federal Register will begin a 60-day comment period.

1,2-Dichloroethane

According to EPA, although 1,1-DCE and 1,2-DCE have different uses, the chemicals are very similar in terms of their physical structure. EPA states that 1,2-DCE is the better studied of the two chemicals, and therefore there are more data available on its toxicity. EPA seeks feedback on the draft human health hazard assessment for 1,2-DCE because it used data on the toxicity of 1,2-DCE to fill gaps in the understanding of the toxicity of 1,1-DCE for the draft risk evaluation. Feedback on the draft hazard assessment for 1,2-DCE will also help inform the full 1,2-DCE draft risk evaluation.

According to EPA, environmental releases of 1,1-DCE primarily end up in the air, with lesser amounts in water, sediment, and soil. EPA states that given the relatively low quantity directly released to water, “surface water will generally not be an important source of exposure other than direct and continuous releases of 1,1-dichloroethane into deep slower moving or stagnant surface waters.” EPA notes that although 1,1-DCE has been detected in the environment and in organisms such as fish exposed to contaminated surface water, “it does not appear to bioaccumulate and thus is not measured in people or animals at greater concentrations than exist in the environment.”

EPA states that it used hazard data for 1,2-DCE as the best available candidate to provide analogous human health data for the 1,1-DCE risk evaluation because of its structural, physical, chemical, metabolic, and cancer and non-cancer toxicological similarities, since there was inadequate human health hazard data available on 1,1-DCE. According to EPA, its draft risk evaluation preliminarily shows that exposure to 1,1-DCE may increase the risk of kidney and other cancers, as well as harmful non-cancer renal, nasal, immune system, and reproductive effects to workers. EPA preliminarily found no unreasonable risk to the general population from breathing air where 1,1-DCE was released from facilities or from ingesting drinking water or surface water or soil from 1,1-DCE disposed to land (i.e., direct disposal to landfills or land applied biosolids from public wastewater treatment works treating 1,1-DCE-containing wastewater). EPA notes that in its analyses, it also accounted for and found no unreasonable risk to potentially exposed and susceptible subpopulations (PESS), which included infants exposed to drinking water during formula bottle feeding, subsistence and tribal fishers, pregnant women and people of reproductive age, and individuals with compromised immune systems or neurological disorders. EPA did not assess consumer or bystander exposures because there are no commercial or consumer products or articles that contain 1,1-dichlorethane.

EPA states that its draft risk evaluation preliminarily shows that chronic exposure to 1,1-DCE contributes to the unreasonable risk to aquatic species, including invertebrates and algae, from the manufacturing, processing, and disposal of 1,1-DCE. EPA preliminarily determined that there is no unreasonable risk of injury to aquatic and terrestrial species from acute exposures to 1,1-DCE.

Next Steps

Publication of the Federal Register notice will begin a 60-day comment period. EPA’s Science Advisory Committee on Chemicals (SACC) will peer review the draft documents and associated unresolved scientific issues. EPA will hold a virtual public meeting for the SACC to discuss the draft documents September 17-20, 2024. EPA will post registration instructions for the meeting on the SACC website later this summer, including information about how to register to present oral comments during the meeting. In addition, EPA will hold a preparatory virtual public meeting on August 27, 2024, for the SACC and the public to consider and ask questions regarding the scope and clarity of the draft charge questions. EPA will consider any feedback received from the public and the SACC to inform the final risk evaluations for 1,1-DCE and 1,2-DCE.

Commentary

The Acta Group (Acta^®) encourages entities that have an interest in TSCA or are regulated under TSCA to read carefully EPA’s assessments on 1,1-DCE and 1,2-DCE and the underlying support documents. These documents provide, for the first time, EPA’s approach with publicly communicating differing scientific opinions (DSO) within EPA on its TSCA Section 6 activities. Acta applauds EPA for its approach for addressing the DSOs and communicating professionally and transparently these issues to the public. Acta believes that the issues raised in the DSOs may ultimately have far-reaching implications for EPA’s TSCA activities. We discuss several of the identified issues below.

EPA transparently stated in the 1,1-DCE assessment under the Acknowledgements section (lines 996-1010) and as an Additional Note (lines 1131-1145) under the Executive Summary that “there are some significant aspects of the draft 1,1-dichloroethane risk evaluation and the draft 1,2-dichloroethane human health hazard assessment technical support document for which there is not agreement between ECRAD [Existing Chemicals Risk Assessment Division] and senior scientists and technical experts.” EPA stated the same concern nearly verbatim under the Summary (lines 232-246) of the 1,2-DCE assessment. EPA also included the DSOs as part of the draft charge questions to the SACC. The DSOs addressed multiple issues. We, therefore, limited our discussion to a few representative examples, as summarized below.

1,2-DCE Mouse Cancer Study

ECRAD proposed to use data on mice exposed to 1,2-DCE from a carcinogenicity study performed by the U.S. National Toxicology Program (NTP) in 1978 to inform its quantitative cancer risk assessment on 1,1-DCE. ECRAD requested review of these study data by senior scientists from EPA’s Office of Pesticide Programs (OPP) and its Office of Research and Development (ORD). OPP concluded that “both the male and female mice data are not of sufficient quality that they can be used for carcinogenicity assessment.” ORD concluded that “This study should not be used for carcinogenicity assessment.” To EPA’s credit, it publicly posted the written evaluations from ECRAD, OPP, and ORD. EPA also included detailed charge questions for the TSCA SACC on this study.

Analog Read-Across

ECRAD proposed an approach to use 1,2-DCE as a toxicological analog to inform the carcinogenic potential of 1,1-DCE. ECRAD provided a detailed structure-activity relationship justification for this proposed approach in the 1,1-DCE assessment and in its above-mentioned request to the OPP and ORD scientists. ECRAD noted in part that 1,1-DCE and 1,2-DCE “are close structural dichloroethane isomers…[and]…have similar physical-chemical properties which influences ADME [absorption, distribution, metabolism, and elimination] responses and toxicology….” The senior scientists from OPP and ORD were not tasked by ECRAD to comment on this justification. The senior scientists from OPP and ORD did, however, provide feedback on this, stating that they “strongly caution against this approach…[because] the two isomers demonstrate very different ADME behaviors…[and] are of low [structural] similarity (<50%).” As with the 1,2-DCE mouse cancer study, EPA publicly posted these discussions and included detailed charge questions to the TSCA SACC on the analog read-across for carcinogenicity and for non-cancer effects.

Oils Study

EPA used a dermal exposure model in the 1,1-DCE assessment that includes a key parameter of the amount of a chemical substance remaining on the skin for assessing occupational exposures. The amount remaining on the skin is based on experimental studies EPA performed using oils of different viscosities (i.e., mineral oil, cooking oil, and bath oil). For discussion, see our memorandum dated July 21, 2022. EPA originally intended to include a water/oil emulsion (50:50, water:water-soluble oil), water, and a water/ethanol (50:5) solution. EPA omitted these liquids because “an acceptable experimental procedure to address volatilization/evaporation losses could not be developed for them.” Acta notes that EPA identified 1,1-DCE as a “highly volatile organic compound (VOC).” It is questionable whether the oil study is appropriate for informing the amount of 1,1-DCE remaining on the skin, should dermal exposures occur. EPA appropriately included charge questions on the use of the oils study for informing the 1,1-DCE assessment.

The TSCA SACC’s determination on the appropriateness of EPA using the oil study data for informing the amount of a VOC remaining on the skin may have significant impacts on EPA’s draft and final risk evaluations. EPA has used the same oil study data to inform many of its risk evaluations. EPA also typically uses the oil study data to inform its risk determinations on new chemical substances under TSCA Section 5. The TSCA SACC’s feedback will, therefore, potentially impact EPA’s proposed risk management rules under TSCA Section 6 and its risk determinations under TSCA Section 5.

Concluding Observations

Acta again applauds EPA’s transparent description of the internal DSOs that exist on the 1,1- and 1,2-DCE assessments. We also commend EPA for publicly disclosing this information and seeking public comment. The DSOs reflect points of disagreement that are commonly raised by external parties, including study quality, analog selection for read-across, and EPA’s general use of the oils study, especially for VOCs. Regardless of the outcome of the TSCA SACC’s review on these issues and others, we are pleased that EPA has taken the initiative to describe its internal DSOs and to solicit broader input on these issues. Scientific disagreements are common. This is one of the most commendable actions EPA has taken in support of its commitment to meeting the scientific standards under TSCA Section 26, and we hope that this trend continues.