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MODELING HUMAN EXPOSURES AND DOSE USING A 2-DIMENSIONAL MONTE-CARLO MODEL (SHEDS)
Citation:
Ozkaynak, A H., J Xue, V Zartarian, J M. Burke, AND S E. Graham. MODELING HUMAN EXPOSURES AND DOSE USING A 2-DIMENSIONAL MONTE-CARLO MODEL (SHEDS). Presented at Society for Risk Analysis, Baltimore, MD, December 7-10, 2003.
Impact/Purpose:
The primary objective of this research is to produce a documented version of the aggregate SHEDS-Pesticides model for conducting reliable probabilistic population assessments of human exposure and dose to environmental pollutants. SHEDS is being developed to help answer the following questions:
(1) What is the population distribution of exposure for a given cohort for existing scenarios or for proposed exposure reduction scenarios?
(2) What is the intensity, duration, frequency, and timing of exposures from different routes?
(3) What are the most critical media, routes, pathways, and factors contributing to exposures?
(4) What is the uncertainty associated with predictions of exposure for a population?
(5) How do modeled estimates compare to real-world data?
(6) What additional human exposure measurements are needed to reduce uncertainty in population estimates?
Description:
Since 1998, US EPA's National Exposure Research Laboratory (NERL) has been developing the Stochastic Human Exposure and Dose Simulation (SHEDS) model for various classes of pollutants. SHEDS is a physically-based probabilistic model intended for improving estimates of human exposure and dose to multimedia, multipathway pollutants and incorporates a two-dimensional Monte-Carlo simulation methodology implemented using SAS software. The two dimensional Monte-Carlo feature of the model is used to characterize population distributions of exposure and dose by explicitly quantifying the variability and the uncertainty in model inputs, parameters, and outputs. In particular, SHEDS-Pesticides combines human activity data (from national time/activity diary surveys and videography studies) with pesticide residue and concentration measurements in media contacted, exposure factors, and pharmacokinetic rate constants. Incurred exposure and dose are predicted for user-specified cohorts via eating contaminated foods or drinking water, inhaling contaminated air, touching contaminated surface residues, and ingesting residues from hand- or object-to-mouth activities. SHEDS-PM (i.e., particulate matter and its associated constituents) and SHEDS-ATOX (i.e., air toxics) use the same modeling approach as the SHEDS-Pesticides model, however the primary focus is on inhalation exposure and dose. The SHEDS model is designed to investigate the intensity, duration, frequency, route, and timing of exposures; to identify critical exposure factors and how to effectively reduce exposures; and to verify estimates with available biomarkers.
This work has been wholly funded by the United States Environmental Protection. It has been subjected to Agency review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.