The US EPA must assess the risk of pesticide exposure to the general populace from potential dietary sources - food and drinking water � as part of the pesticide registration process under the Federal Insecticide Fungicide and Rodenticide Act. The models and methodology used in food exposure assessments has evolved over time to become quite sophisticated. The EPA has a well-defined, tiered scheme that incorporates use of more of the available data in more complex analyses; applying probabilistic methods as an assessment progresses through the tiers. In contrast, the estimation of chemical concentrations in drinking water most often relies on models parameterized to produce screening level estimates. As a result, it is not uncommon that EPA risk assessments suggest drinking water is a significant source of pesticide exposure despite evidence to the contrary. Recent changes in EPA policy regarding estimation of drinking water residues have exacerbated the dichotomy between modeled estimates and actual observed concentrations. The distorted estimates of exposure can lead to misallocation of resources as well as providing the public with a flawed understanding of sources of exposure. This presentation will examine modeling to monitoring comparisons, statistical interpretation of monitoring data to account for uncertainty in unsampled intervals, uncertainty analysis necessary for improved risk communication and the regulatory impact of simply grossing exposure concentrations up during the risk assessment process. Dietary risk assessment could be greatly improved if EPA were to establish tiers of refinement for drinking water exposure estimation comparable to existing tiers for food to account appropriately for dietary contribution to aggregate exposure in tolerance assessments.

Improvements in drinking water exposure estimates

248th National Meeting (2014)

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