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Federal Register / Vol. 86, No. 40 / Wednesday, March 3, 2021 / Rules and Regulations
statutory authorities to guide Agency decision making with respect to how the Agency evaluates and potentially regulates additional PFAS.
b Summary of Public Comments on Potential PFAS Monitoring Approaches and Agency Responses As part of the proposed preliminary regulatory determination for PFOA and PFOS, EPA solicited comment on potential monitoring approaches if the Agency were to finalize a positive regulatory determination for these contaminants. EPA presented two monitoring approaches in the Agencys preliminary Regulatory Determination for CCL 4 contaminants. Under the Standardized Monitoring Framework SMF for synthetic organic chemicals, monitoring schedules are based around the detection levels of the regulated contaminants, and state primacy agencies can also issue waivers for monitoring. The Agency also presented an alternative monitoring approach to allow state primacy agencies to require monitoring at PWSs where information indicates potential PFAS contamination, such as proximity to facilities with historical or on-going uses of PFAS.
Many commenters supported the Agencys goal of reducing potential monitoring burden for PWSs without compromising public health protection.
While there were differing views among commenters regarding which monitoring approach is best for PFAS, many urged EPA to keep evaluating different approaches as the Agency promulgates the NPDWR for PFOA and PFOS.
The Agency appreciates commenter recommendations on monitoring approaches. As the Agency promulgates the regulatory standard for PFOA and PFOS, EPA will continue to work to establish monitoring requirements in the rule that minimize burden while ensuring public health protection.
B. 1,1-Dichloroethane
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1. Description 1,1-Dichloroethane is a halogenated alkane. It is an industrial chemical and is used as a solvent and a chemical intermediate. 1,1-Dichloroethane is expected to have moderate to high persistence in water USEPA, 2021a.
2. Agency Findings The Agency is making a determination not to regulate 1,1dichloroethane with an NPDWR. It does not occur with a frequency and at levels of public health concern. As a result, the Agency finds that an NPDWR does not present a meaningful opportunity for health risk reduction.

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a Adverse Health Effects The Agency finds that 1,1dichloroethane may have adverse effects on the health of persons. Based on a 13week gavage study in rats Muralidhara et al., 2001, the kidney was identified as a sensitive target for 1,1dichloroethane, and no-observedadverse-effect level NOAEL and lowest-observed-adverse-effect level LOAEL values of 1,000 and 2,000 mg/
kg/day, respectively, were identified based on increased urinary enzyme markers for renal damage and central nervous system CNS depression USEPA, 2006a.
The only available reproductive or developmental study with 1,1dichloroethane is an inhalation study where pregnant rats were exposed on days 6 through 15 of gestation Schwetz et al., 1974. No effects on the fetuses were noted at 3,800 ppm. Delayed ossification of the sternum without accompanying malformations was reported at a concentration of 6,000
ppm.
A cancer assessment for 1,1dichloroethane is available on IRIS
USEPA, 1990a. That assessment classifies the chemical, according to EPAs 1986 Guidelines for Carcinogenic Risk Assessment USEPA, 1986, as Group C, a possible human carcinogen.
This classification is based on no human data and limited evidence of carcinogenicity in two animal species rats and mice, as shown by increased incidences of hemangiosarcomas and mammary gland adenocarcinomas in female rats and hepatocellular carcinomas and benign uterine polyps in mice NCI, 1978. The data were considered inadequate to support quantitative assessment. The close structural relationship between 1,1dichloroethane and 1,2-dichloroethane, which is classified as a B2 probable human carcinogen and produces tumors at many of the same sites where marginal tumor increases were observed for 1,1-dichloroethane, supports the suggestion that the 1,1-isomer could possibly be carcinogenic to humans.
Mixed results in initiation/promotion studies and genotoxicity assays are consistent with this classification. On the other hand, the animals from the 1,1-dichloroethane National Cancer Institute NCI, 1978 study were housed with animals being exposed to 1,2dichloroethane providing opportunities for possible co-exposure impacting the 1,1-dichloroethane results. The following groups of individuals may have an increased risk from exposure to 1,1-dichloroethane NIOSH, 1978;
ATSDR, 2015:

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Those with chronic respiratory disease, Those with liver diseases that impact hepatic microsomal cytochrome P450 functions, Individuals with impaired renal function and vulnerable to kidney stones Individuals with skin disorders vulnerable to irritation by solvents like 1,1-dichloroethane, Those who consume alcohol or use pharmaceuticals e.g., phenobarbital that alter the activity of cytochrome P
450s.
A provisional chronic RfD was derived from the 13-week gavage study in rats based on a NOAEL of 1,000 mg/
kg/day administered for five days/week and adjusted to 714.3 mg/kg/day for continuous exposure an increase in urinary enzymes was the adverse impact on the kidney. The chronic oral RfD of 0.2 mg/kg/day was derived by dividing the normalized NOAEL of 714.3 mg/kg/
day in male Sprague-Dawley rats by a combined UF of 3,000. The combined UF includes factors of 10 for interspecies extrapolation, 10 for extrapolation from a subchronic study, 10 for human variability, and 3 for database deficiencies including lack of reproductive and developmental toxicity tests by the oral route. This assessment noted several limitations in the critical study and database as a whole. Specifically, that the reporting of the results in the critical study were marginally adequate and that the database lacks information on reproductive and developmental and nervous system toxicity.
EPA calculated an HRL for 1,1dichloroethane of 1,000 mg/L, based on EPA oral RfD of 0.2 mg/kg/day, using 2.5 L/day drinking water ingestion, 80
kg body weight and a 20% relative source contribution RSC factor.
b Occurrence EPA has determined that 1,1dichloroethane does not occur with a frequency and at levels of public health concern at PWSs based on the Agencys evaluation of available occurrence information. The primary occurrence data for 1,1-dichloroethane are the 20132015 nationally representative drinking water monitoring data generated through EPAs UCMR 3. 1,1Dichloroethane was not detected in any of the 36,848 UCMR 3 samples collected by 4,916 PWSs serving 241 million people at levels greater than 12 the HRL
500 mg/L or the HRL 1,000 mg/L. 1,1Dichloroethane was detected in about 2.3% samples at or above the MRL 0.03
mg/L USEPA, 2019a; USEPA, 2021a.

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