This presentation introduces a conceptual tiered approach to estimation of agricultural chemical residues in the drinking water component of a dietary risk assessment. Passage of the Food Quality Protection Act of 1996 required the US EPA to reassess tolerances and reregister all active ingredients. Since FQPA was adopted, the US EPA human health risk assessment considers the combined exposure potential from all routes, such as residue from food intake, drinking water, and non-occupational exposures. A tiered process has evolved for the analysis of exposure from food in a dietary risk assessment. Early tiers feature maximum exposure estimates assuming high levels of product use and consumption. More realism is introduced through inclusion of actual residue data from surveys of commodities and probabilistic assessment of exposure potential. In contrast, the assessment of exposure potential from drinking water for dietary risk assessment has not evolved considerably. The modeling tools for estimation of residues in surface water adjacent to a farm field are used to produce estimates of potential residues in reservoirs. Modeling with scenarios and input parameters consistent with a high risk for leaching are used to produce a deterministic evaluation of potential residues in groundwater. The groundwater and surface water values are used as estimates for drinking water exposure. The refinement of drinking water exposure requires monitoring, and for a few chemicals the monitoring data available is extensive. Extensive monitoring is not always practical, and statistical analysis of the available data suggest that monitoring programs can be more pragmatically designed with targeted programs that consider the temporal and spatial sampling requirements to achieve a desirable predictive power. We propose that the lessons learned since FQPA was implemented be applied in developing an approach to estimation of exposure from drinking water that is analogous to the approach used in estimation of potential exposure from food.

Improving the estimation of drinking water exposure in dietary risk assessment

246th National Meeting (2013)

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