A Regional Approach to Assess Drinking Water Exposure. C. L. Walls, J. L. Kiwell, L. Barraj, J. L. Watters, and S. H. Youngren, Novigen Sciences, Inc., Washington DC
In establishing (or maintaining) pesticide tolerances, the Food Quality Protection Act of 1996 (FQPA) mandates that the EPA evaluate potential exposure from residues in drinking water and foods. To meet the requirements of the current legislation and maintain consistency with dietary exposure methodologies for foods, a regional approach based on a calendar method for estimating exposure from water is proposed. Currently, OPP relies on the Interim Standard Operating Procedure for Drinking Water Exposure and Risk Assessments that utilize conservative modeling techniques for estimating potential residues in drinking water. The present methodology assumes that drinking water is homogeneous throughout the nation regardless of regional differences. Although OPP is willing to replace model predictions with valid monitoring data in the risk assessments, it has concerns about adequately representing vulnerable drinking water sources. The probabilistic approach presented herein addresses regional variability in residue levels and utilizes 1) residue data from the National Water Quality Assessment Program, 2) US population distributions, and 3) USDA CSFII consumption data. To demonstrate the impact on the risk assessment, Novigen calculated dietary exposures for Chemical X utilizing the regional methodology. This approach results in more realistic estimates of dietary exposure from residues in drinking water, since actual residue and consumption data are used.
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