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TECHNICAL MANUAL: USING SHEDS FOR THE ASSESSMENT OF CHILDREN'S EXPOSURE AND DOSE FROM TREATED WOOD PRESERVATIVES ON PLAYSETS AND RESIDENTIAL DECKS
Zartarian, V, J Xue, A H. Ozkaynak, G. Glenn, L. Smith, W. Dang, N. Cook, D. Aviado, S. Mostaghimi, AND J. Chen. TECHNICAL MANUAL: USING SHEDS FOR THE ASSESSMENT OF CHILDREN'S EXPOSURE AND DOSE FROM TREATED WOOD PRESERVATIVES ON PLAYSETS AND RESIDENTIAL DECKS.
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's (EPA) Office of Research and Development (ORD), National Exposure Research Laboratory (NERL), in conjunction with the EPA's Office of Prevention, Pesticides, and Toxic Substances (OPPTS), Office of Pesticide Programs (OPP) has developed a modeling methodology to conduct a probabilistic exposure and dose assessment for chemicals in wood treatment preservatives, and applied this methodology to a hypothetical case study for demonstration purposes. Such a methodology could be applied to help determine the potential health risks to children from contact with treated wood in playsets and home decks and contaminated soil around these structures.
In October 2001, OPP presented a proposed deterministic exposure assessment approach, specific to Chromated Copper Arsenate (CCA), to the FIFRA (Federal Insecticide, Fungicide, and Rodenticide Act) Scientific Advisory Panel (SAP). One of the primary recommendations was to use a probabilistic model to predict variability of absorbed doses in a given population of interest. Following the SAP meeting, OPP requested assistance from ORD in addressing this recommendation by using NERL's physically-based, Monte Carlo, probabilistic SHEDS model (Stochastic Human Exposure and Dose Simulation model). The methodology and assessment presented in this document focuses only on exposures and absorbed doses (both average daily doses (ADDs) and lifetime average daily doses (LADDs)); it does not address risk estimates. Absorbed doses obtained via this methodology could be used by OPP to conduct separate risk analyses.
To demonstrate the methodology, SHEDS was applied to assess the exposure and dose of 1 to 6 year-old children to a hypothetical "Chemical X" and "Chemical Y" from a wood treatment preservative via contact with playsets and home decks. The Chemical X scenario corresponds to a "lower exposure" cold climate scenario; Chemical Y to a "higher exposure" warm climate scenario. Three exposure time periods were considered: short-term (one day to one month), intermediate-term (one month to six months), and lifetime (6 years over a 75 year lifetime). Dermal contact with and ingestion of the chemical in both soil and wood residues were considered for a population of children simulated using time-location-activity diaries from EPA's Consolidated Human Activity Database (CHAD). Model algorithms and input values used by SHEDS for the wood treatment preservative scenario were selected by OPP and ORD. Recommendations by the SAP were incorporated to the extent possible in the example assessment.
The primary outputs obtained using SHEDS for the two case studies and different time periods include the following: population cumulative density functions (CDFs) of total absorbed dose (ADD and LADD) and absorbed dose by each exposure pathway; sensitivity analyses identifying critical input variables with respect to population variability; and uncertainty analyses identifying critical input variables with respect to uncertainty in percentiles of population distributions. Children contacting playsets only were considered as well as children who contact both playsets and home decks. For the chemical-specific model inputs, data were fabricated by OPP and ORD to correspond to a "lower exposure" and a "high exposure" scenario. Most of the inputs, however, such as activity-related inputs and exposure factors, are independent of the chemical being addressed. Thus, where possible, distributions were fit to the best available data sets. These data are presented in this report in addition to the general exposure assessment methodology.
The United States Environmental Protection Agency's Office of Research and Development perfomed and funded the research described here. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.