Aggregate Exposure Assessment: Issues and Processes. H. Özkaynak, US Environmental Protection Agency, National Exposure Research Laboratory, Research Triangle Park, North Carolina
Aggregate exposure assessment must account for exposures by all media and by all significant routes. Typically, these include: inhalation, ingestion (both dietary and non-dietary), and dermal contact. The modeling methodology employed by EPA is designed to predict media- and route-specific pollutant concentrations, total estimated personal exposures, absorbed dose, and urinary or blood biomarker concentrations. Data on human activity patterns are an essential component of estimating total personal exposures to environmental contaminants. Specific objectives of EPA’s long-term research in this area include 1) use of models to identify critical pathways, parameters, and hypotheses for guiding exposure measurements; 2) combine probabilistic multimedia/multipathway exposure modeling with the dosimetric or exposure-response models being developed by collaborating institutions; and 3) provide insights into sources and mechanisms of human exposure so that EPA may develop better, scientifically-based, and cost-effective risk management approaches. The initial focus of EPA’s aggregate exposure model (SHEDS) is on exposures of infants and children to pesticides and other pollutants under the FQPA. The model examines a variety of pathways to estimate the contribution of different exposure routes and media (soil, dust, air, water, food, and surface residues) to chlorpyrifos exposure. Two-stage Monte-Carlo is used to characterize uncertainty and variability. Preliminary results show the youngest age group has the highest potential exposures. Predicted acute and short-term (i.e. following application) residential exposures and dose from chlorpyrifos residues could be many times greater than the non-acute exposure values, depending on the type of pesticide application and activities of the children. Both the variability and uncertainty of predicted exposures are found to be very high.
This work has been funded in part by the United States Environmental Protection Agency. It has been subjected to Agency review and approved for publication.
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