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A PROBABILISTIC EXPOSURE ASSESSMENT FOR CHILDREN WHO CONTACT CCA-TREATED PLAYSETS AND DECKS USING THE STOCHASTIC HUMAN EXPOSURE AND DOSE SIMULATION (SHEDS) MODEL FOR THE WOOD PRESERVATIVE EXPOSURE SCENARIO
Zartarian, V, J Xue, A H. Ozkaynak, W. Dang, G. Glenn, L. Smith, AND C Stallings. A PROBABILISTIC EXPOSURE ASSESSMENT FOR CHILDREN WHO CONTACT CCA-TREATED PLAYSETS AND DECKS USING THE STOCHASTIC HUMAN EXPOSURE AND DOSE SIMULATION (SHEDS) MODEL FOR THE WOOD PRESERVATIVE EXPOSURE SCENARIO. Presented at International Society of Exposure Analysis 14th Annual Conference, Philadelphia, PA, October 17-21, 2004.
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?
The U.S. Environmental Protection Agency has conducted a probabilistic exposure and dose assessment on the arsenic (As) and chromium (Cr) components of Chromated Copper Arsenate (CCA) using the Stochastic Human Exposure and Dose Simulation model for wood preservatives (SHEDS-Wood). A draft assessment was presented to OPP's Scientific Advisory Panel in December, 2003 and is currently being finalized. This assessment is part of the Agency's health risk assessment for children who frequently contact CCA-treated wood in playsets and home decks and CCA-contaminated soil around these structures. Two bounding estimate climate scenarios; three exposure time periods (short-term, intermediate-term, and lifetime); and four pathways (dermal contact with, and ingestion of, As and Cr in both soil and wood residues) were considered. Variability, sensitivity, and uncertainty analyses were conducted, as well as special analyses considering different subpopulations (e.g., pica children) and exposure reduction scenarios (e.g., sealants, hand washing). The draft assessment was presented to OPP's Scientific Advisory Panel in December, 2003 and is currently being finalized. The results from this probabilistic exposure and dose analysis showed that the predicted central values for lifetime annual average daily dose values for arsenic were on the order of 10-6 to 10-5 mg/kg/day, with the predicted 95th percentiles on the order of 10-5 mg/kg/day. There was several orders of magnitude difference between the lower and the upper percentiles of predicted population exposure and dose variability estimates. Residue ingestion via hand-to-mouth contact was the most significant exposure route for most scenarios. The key variables that were found to influence model estimates were: wood surface residue-to-skin transfer efficiency, wood surface residue concentrations, fraction of hand surface area mouthed, hand washing events, soil concentrations near treated playsets, daily soil ingestion rate, and time spent on/around treated residential decks. Alternative scenarios did not significantly impact the baseline results, except for the impact of greatly reducing wood residues through hypothetical wood sealant applications. Finally, the SHEDS-Wood CCA probabilistic results were found to compare well to results from other deterministic CCA exposure assessments.
Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy.