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Federal Register / Vol. 86, No. 165 / Monday, August 30, 2021 / Rules and Regulations
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for children 1 to less than 2 years old and dermal and inhalation postapplication exposures for adults from exposure to mosquitocide uses. The Agency combined post-application exposures for children 1 to less than 2
years old for dermal, inhalation, and incidental oral exposure routes because these routes all share a common toxicological endpoint. EPA used the post-application exposures and risk estimates resulting from the golfing scenarios in its aggregate exposure and risk assessment.
VIII. Aggregate Risk Assessment and Conclusions Regarding Safety for Chlorpyrifos The final step in the risk assessment is the aggregate exposure assessment and risk characterization. In this step, EPA combines information from the first three steps hazard identification, level of concern LOC/dose-response analysis, and human exposure assessment to quantitatively estimate the risks posed by a pesticide. The aggregated exposure assessment process considers exposure through multiple pathways or routes of exposure e.g., food, water, and residential for different sub-populations e.g., infants, children ages 16 and exposure duration or types of effects e.g., acute noncancer effects single dose, chronic noncancer effects, and cancer. The aggregated exposure assessments can be deterministic levels of exposure for each pathway are point estimates, probabilistic levels of exposure are a distribution for a given population, or a combination of the two and are dependent on the level of refinement or assessment tier.
As noted above, EPA evaluates aggregate exposure by comparing combined exposure from all relevant sources to the safe level. Where exposures exceed the safe level, those levels exceed the risk cup and are of potential concern. There are risk cups for each pertinent duration of exposure for a pesticide because the amount of exposure that can be incurred without adverse health effects will vary by duration e.g., acute, short-term, chronic. The risk cup is equal to the PAD either acute, chronic, or steadystate, or the maximum safe exposure for shortand intermediate-term durations.
Whether risks will exceed the risk cup i.e., whether exposures are expected to exceed safe levels is expressed differently, depending on the type of level of concern the Agency has identified. For dietary assessments, the risk is expressed as a percentage of the acceptable dose i.e., the dose which EPA has concluded will be safe.

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Dietary exposures greater than 100% of the percentage of the acceptable dose are generally cause for concern and would be considered unsafe within the meaning of FFDCA section 408b2B. For non-dietary and combined dietary and non-dietary risk assessments of threshold effects, the toxicological level of concern is typically not expressed as an RfD/PAD, but rather in terms of an acceptable or target Margin of Exposure MOE
between human exposure and the PoD.
The margin that is being referred to in the term MOE is the ratio between the PoD and human exposure which is calculated by dividing human exposure into the PoD. An acceptable MOE is generally considered to be a margin at least as high as the product of all applicable safety factors for a pesticide.
For example, when the Agency retains the default uncertainty factors for dietary or aggregate risk a 10X
interspecies uncertainty factor, a 10X
intraspecies uncertainty factor, and a 10X FQPA safety factor, the total uncertainty factors or level of concern is 1000, and any MOE above 1000
represents exposures that are not of concern. Like RfD/PADs, specific target MOEs are selected for exposures of different durations and routes. For nondietary exposures, EPA typically examines short-term, intermediate-term, and long-term exposures. Additionally, target MOEs may be selected based on both the duration of exposure and the various routes of non-dietary exposuredermal, inhalation, and oral.
Target MOEs for a given pesticide can vary depending on the characteristics of the studies relied upon in choosing the PoD for the various duration and route scenarios.
In addition, in a DWLOC aggregate risk assessment, the calculated DWLOC
is compared to the EDWC. Where EPA
has calculated a DWLOC, EPA can determine whether drinking water exposures will result in aggregate risks of concern by comparing estimated pesticide concentrations in drinking water to the DWLOC. As noted above, an aggregate DWLOC represents the amount of allowable safe residues of pesticide in drinking water because it represents the room remaining in the risk cup after accounting for the food and residential exposures. The DWLOC
provides an estimate of the allowable safe concentrations of pesticides in drinking water for comparison to EDWCs. When the EDWC is less than the DWLOC, there are no risk concerns for aggregate exposures because the Agency can conclude that the contribution from drinking water when
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aggregated with food and nonoccupational exposures will not exceed save levels of exposure. Conversely, an EDWC at or exceeding the DWLOC
would indicate a risk of concern, as those exposures to chlorpyrifos in drinking water, when aggregated with exposures from food and residential exposures, would exceed safe levels of exposure. Ref. 31.
A. Dietary Risks From Food Exposures As noted above, EPAs acute and steady state dietary exposures assessments for chlorpyrifos were highly refined and incorporated monitoring data for almost all foods.
The Agency assessed food exposures based on approved registered uses of chlorpyrifos. This includes field uses of chlorpyrifos but not potential exposure from food handling establishment uses since the Agency did not identify any registered food handling establishment uses. Ref. 9 at 3336.
Considering food exposures alone, the Agency did not identify risks of concern for either acute or steady state exposures. Acute dietary food only risk estimates, which are based on risk from a single exposure event in the 2020
HHRA were all below 100 percent of the acute population adjusted dose for food aPADfood at the 99.9th percentile of exposure and are not of concern. The population with the highest risk estimate was females 1349 years old at 3.2% aPADfood. Steady-state dietary food only risk estimates, which are based on the potential risk from a 21day exposure duration using a 3-week rolling average sliding by day across the year, were also all below 100% of the steady state PAD for food ssPADfood at the 99.9th percentile of exposure and are not of concern. The population with the highest risk estimate was children 12 years old at 9.7% ssPADfood.
Although EPAs most recent risk assessment calculated two sets of risk estimates as a result of the dual approach to assess the range of risks that would occur if the Agency determined reliable data existed to support a 1X
FQPA safety factor, EPA has determined that it is appropriate to retain the 10X
FQPA safety factor, see Unit VI.C.3.
Therefore, the risk estimates associated with the 1X FQPA are not relevant to todays action.
B. Non-Occupational, Non-Dietary Residential Risks Because there are some uses of chlorpyrifos that may result in residential exposures, EPA assessed risk from those uses. All residential postapplication risk estimates for the registered uses of chlorpyrifos were
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