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Federal Register / Vol. 86, No. 165 / Monday, August 30, 2021 / Rules and Regulations contribute to a drinking water intake referred to as PCA or percent use area when considering non-agricultural uses and incorporate data on the amount of a pesticide that is actually applied within a watershed for agricultural and non-agricultural uses referred to as PCT. These refinement approaches underwent external peer review and were issued for public comment in January 2020: https www.epa.gov/
pesticide-science-and-assessingpesticide-risks/about-water-exposuremodels-used-pesticide. In addition, EPA
used average application rates, average numbers of annual applications for specific crops, and estimated typical application timing at the state-level based on pesticide usage data derived from a statistically reliable private market survey database, publicly available survey data collected by the USDA, and state-specific scientific literature from crop extension experts.
The recently developed refinements were integrated in the Updated Chlorpyrifos Refined Drinking Water Assessment for Registration Review, which was issued in September 2020.
2020 DWA Ref. 10 The updated assessment applied the new methods for considering the entire distribution of community water systems PCA
adjustment factors, integrated state level PCT data, incorporated refined usage and application data, and included quantitative use of surface water monitoring data in addition to considering state level usage rate and data information. In addition, given the 2016 DWA calculation of estimated drinking water concentrations exceeding the DWLOC of 4.0 ppb, the Agency decided to focus its refinements for the 2020 updated drinking water assessment on a subset of uses in specific regions of the United States.
The purpose of the focus on this subset of uses was to determine, if these were the only uses permitted on the label, whether or not the resulting estimated drinking water concentrations would be below the DWLOC. The subset of uses assessed were selected because they were identified as critical uses by the registrant and/or high-benefit uses to growers. That subset of currently registered uses included alfalfa, apple, asparagus, cherry, citrus, cotton, peach, soybean, sugar beet, strawberry, and wheat in specific areas of the country.
The results of this analysis indicated that the EDWCs from this subset of uses limited to certain regions are below the DWLOC. Ref. 10 at 1617. However, the 2020 DWA refined estimates did not include chlorpyrifos exposures from uses beyond that subset. In the 2020

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C. Residential Exposure to Pesticides
the amount of pesticide that transfers from the environment to humans from a defined activity e.g., hand contact with a treated surface or plant. Specific information on pesticides can include information on residue levels as well as information on environmental fate such as degradation data.
Once EPA assesses all the potential exposures from all applicable exposure scenarios, EPA selects the highest exposure scenario for each exposed population to calculate representative risk estimates for use in the aggregate exposure assessment. Those specific exposure values are then combined with the life stage appropriate exposure values provided for food and drinking water to determine whether a safety finding can be made.

1. General Approach to Assessing NonOccupational Exposures Residential assessments examine exposure to pesticides in nonoccupational or residential settings e.g., homes, parks, schools, athletic fields or any other areas frequented by the general public, based on registered uses of the pesticide. Exposures to pesticides may occur to persons who apply pesticides which is referred to as residential handler exposure or to persons who enter areas previously treated with pesticides which is referred to as post-application exposure. Such exposures may occur through oral, inhalation, or dermal routes and may occur over different exposure durations e.g., short-term, intermediate-term, long-term, depending on the type of pesticide and particular use pattern.
Residential assessments are conducted through examination of significant exposure scenarios e.g., children playing on treated lawns or homeowners spraying their gardens using a combination of generic and pesticide-specific data. To regularize this process, EPA has prepared SOPs for conducting residential assessments on a wide array of scenarios that are intended to address all major possible means by which individuals could be exposed to pesticides in a nonoccupational environment e.g., homes, schools, parks, athletic fields, or other publicly accessible locations. Ref. 18
The SOPs identify relevant generic data and construct algorithms for calculating exposure amounts using these generic data in combination with pesticidespecific information. The generic data generally involve survey data on behavior patterns e.g., activities conducted on turf and time spent on these activities and transfer coefficient data. Transfer coefficient data measure
2. Residential Exposure Assessment for Chlorpyrifos Most chlorpyrifos products registered for residential treatment were voluntarily cancelled or phased out by the registrants between 1997 and 2001;
however, some uses of chlorpyrifos remain that may result in nonoccupational, non-dietary i.e., residential exposures. Based on the remaining registered uses, the Agency has determined that residential handler exposures are unlikely. Chlorpyrifos products currently registered for residential use are limited to roach bait products or ant mound treatments.
Exposures from the application of roach bait products are expected to be negligible. The roach bait product is designed such that the active ingredient is contained within a bait station, which eliminates the potential for contact with the chlorpyrifos containing bait material. Since the ant mound treatments can only be applied professionally, residential handler exposure is also not anticipated. Ref. 9
at 3644.
There is a potential for residential post-application exposures.
Chlorpyrifos is registered for use on golf courses and as an aerial and groundbased ultra-low volume ULV mosquito adulticide applications made directly in residential areas. Based on the anticipated use patterns reviewed under the SOP, EPA assessed these exposures as steady-state residential postapplication exposures, which would be protective of shorter durations of exposure. There is a potential for dermal post-application exposures from the golf course uses for adults females 1349
years old; youths 11 to less than 16
years old; and children 6 to less than 11 years old. There is also a potential for dermal, incidental oral, and inhalation post-application exposures
DWA, EPA stated that if additional uses were added or additional geographic areas included, a new separate assessment would need to be prepared in order to evaluate whether concentrations would remain below the DWLOC. In addition to the modeling of the EDWCs for the specific subset of uses, the 2020 DWA conducted a quantitative surface water monitoring data analysis. That analysis indicated that monitored chlorpyrifos concentrations, which reflect existing uses, are above the DWLOC. Ref. 10 at 62, 75. These data would need to be considered in the context of any additional uses beyond the subset evaluated.

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