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Federal Register / Vol. 86, No. 40 / Wednesday, March 3, 2021 / Rules and Regulations Other supplementary sources of finished water occurrence data from UCM Rounds 1 and 2 indicate that the occurrence of 1,1-dichloroethane in PWSs is likely to be low to non-existent USEPA, 2021a. 1,1-Dichloroethane occurrence data for ambient water from NAWQA and NWIS are consistent with those for finished water USEPA, 2021a.
c Meaningful Opportunity The Agency has determined that regulation of 1,1-dichloroethane does not present a meaningful opportunity for health risk reduction for persons served by PWSs based on the estimated exposed populations, including sensitive populations. UCMR 3 findings indicate that the estimated population exposed to 1,1-dichloroethane at levels of public health concern is 0%, based on lack of detections at levels greater than 12 the HRL 500 mg/L or the HRL
1,000 mg/L. As a result, the Agency finds that an NPDWR for 1,1dichloroethane does not present a meaningful opportunity for health risk reduction.
d Summary of Public Comments on 1,1-Dichloroethane and Agency Responses EPA received several comments on the Agencys evaluation of 1,1dichloroethane under section 1412b1A of SDWA, all of which were in support of its preliminary determination not to regulate 1,1dichloroethane. EPA agrees with the comments that are in support of the negative regulatory determination.
C. Acetochlor
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1. Description Acetochlor is a chloroacetanilide pesticide that is used as an herbicide for pre-emergence control of weeds. It is registered for use on corn crops field corn and popcorn and has been approved for use on cotton as a rotational crop. Synonyms for acetochlor include 2-chloro-2-methyl-6ethyl-N-ethoxymethylacetanilide USEPA, 2021a. Acetochlor is expected to have low to moderate persistence in water due to its biodegradation half-life, as well as susceptibility to photolysis USEPA, 2021a.
2. Agency Findings The Agency is making a determination not to regulate acetochlor with an NPDWR. Acetochlor 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 acetochlor may have adverse effects on the health of persons. Subchronic and chronic oral studies have demonstrated adverse effects on the liver, thyroid secondary to the liver effects, nervous system, kidney, lung, testes, and erythrocytes in rats and mice USEPA, 2006b; USEPA, 2018c. There was evidence of carcinogenicity in studies conducted with acetochlor in rats and mice and a non-mutagenic mode of action was demonstrated for nasal and thyroid tumors in rats USEPA, 2006b. Cancer effects include nasal tumors and thyroid tumors in rats, lung tumors and histiocytic sarcomas in mice, and liver tumors in both rats and mice Ahmed and Seely, 1983; Ahmed et al., 1983;
Amyes, 1989; Hardisty, 1997a; Hardisty, 1997b; Hardisty, 1997c; Naylor and Ribelin, 1986; Ribelin, 1987; USEPA, 2004b; USEPA, 2006b; and Virgo and Broadmeadow, 1988. No biologically sensitive human subpopulations have been identified for acetochlor.
Developmental and reproductive toxicity studies do not indicate increased susceptibility to acetochlor exposure at early life stages in test animals USEPA, 2006b.
The study used to derive the oral RfD
is a 1-year oral chronic feeding study conducted in beagle dogs. This study describes a NOAEL of 2 mg/kg/day, and a LOAEL of 10 mg/kg/day, based on the critical effects of increased salivation;
increased levels of alanine aminotransferase ALT and ornithine carbamoyl transferase OTC; increased triglyceride levels; decreased blood glucose levels; and alterations in the histopathology of the testes, kidneys, and liver of male beagle dogs USEPA, 2018c; ICI, Inc., 1988. The UF applied was 100 10 for intraspecies variation and 10 for interspecies extrapolation.
The EPA OPP RfD for acetochlor of 0.02
mg/kg/day, based on the NOAEL of 2
mg/kg/day from the 1-year oral chronic feeding study in beagle dogs, is expected to be protective of both noncancer and cancer effects.
EPA calculated an HRL of 100 mg/L
based on the EPA OPP RfD for noncancer effects for acetochlor of 0.02 mg/
kg/day USEPA, 2018c using 2.5 L/day drinking water ingestion, 80 kg body weight, and a 20% RSC factor.
b Occurrence EPA has determined that acetochlor 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 acetochlor
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are from the first Unregulated Contaminant Monitoring Regulation UCMR 1 assessment monitoring AM
20012003 and the second Unregulated Contaminant Monitoring Regulation UCMR 2 screening survey SS 20082010. Acetochlor was not detected at levels greater than 12 the HRL 50 mg/L, the HRL 100 mg/L, or the MRL 2 mg/L in any of the 33,778
UCMR 1 assessment monitoring samples from 3,869 PWSs USEPA, 2008;
USEPA, 2021a or in any of the 11,193
UCMR 2 screening survey samples from 1,198 PWSs USEPA, 2015; USEPA, 2021a.
Findings from the available ambient water data for acetochlor are consistent with the results in finished water.
Ambient water data in NAWQA show that acetochlor was detected in between 13% and 23% of samples from between 3% and 10% of sites. While maximum values in NAWQA Cycle 2 20022012
and Cycle 3 20132017 monitoring exceeded the HRL 215 mg/L in 2004 and 137 mg/L in 2013 only one sample in each of those two cycles exceeded the HRL, 90th percentile levels of acetochlor remained below 1 mg/L. More than 10,000 samples were collected in each cycle. Non-NAWQA NWIS data 19912016, which included limited finished water data in addition to the ambient water data, show no detected concentrations greater than the HRL
USEPA, 2021a.
c Meaningful Opportunity The Agency has determined that regulation of acetochlor does not present a meaningful opportunity for health risk reduction for persons served by PWSs based on the estimated exposed populations, including sensitive populations. The estimated population exposed to acetochlor at levels of public health concern is 0%
based on UCMR 1 finished water data gathered from 2001 to 2003 and UCMR
2 finished water data gathered from 2008 to 2010. As a result, the Agency finds that an NPDWR for acetochlor does not present a meaningful opportunity for health risk reduction.
d Summary of Public Comments on Acetochlor and Agency Responses EPA received several comments on the Agencys evaluation of acetochlor under section 1412b1A of SDWA, all of which were in support of its preliminary determination not to regulate acetochlor. EPA agrees with the comments that are in support of the negative regulatory determination.

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