United States Environmental Protection Agency Office of Research and Development National Exposure Research Laboratory Research Abstract Government Performance Results Act (GPRA) Goal 4 Annual Performance Measure 225, 229 Significant Research Findings: A Probabilistic Exposure Model Assessment for Children Who Contact CCA-Treated Playsets and Decks Scientific Concerns have been raised regarding the safety of young children who may Problem and contact arsenic and chromium residues while playing on and around Chromated Policy Issues Copper Arsenate (CCA)-treated wood playground structures and decks. Although CCA registrants voluntarily canceled the production of treated wood for residential use effective December 31, 2003, the potential for exposure from existing treated wood structures and surrounding soil still poses CAA exposure concerns. The EPA's Office of Research and Development (ORD), National Exposure Research Laboratory (ORD/NERL) developed and applied the probabilistic Stochastic Human Exposure and Dose Simulation model for wood preservatives (SHEDS-Wood) to estimate children's absorbed dose of the arsenic and chromium components of CCA. Skin contact with, and non-dietary ingestion of, arsenic and chromium in soil and wood residues were considered for the population of children in the United States who frequently contact CCA-treated wood playsets and decks. Model analyses were conducted to assess the range and uncertainty in population estimates, key model inputs, and the impact of various potential mitigation strategies such as the use of sealants and hand washing after play events. ORD/NERL presented the draft assessment to the EPA Office of Pesticide Programs" (OPP) Scientific Advisory Panel in December 2003. OPP used the results to determine the potential short-term, intermediate-term, and lifetime cancer risks for children in the United States who frequently contact treated wood playsets and decks in public and residential locations. The results from the draft probabilistic exposure and dose analysis showed predicted central values for lifetime annual average daily dose values for arsenic ranging from 10"6 to 10"5 mg/kg/day, with predicted 95th percentiles on the order of 10"5 mg/kg/day. There were several orders of magnitude difference between the lowest and highest (upper) percentiles of predicted population estimates. Residue ingestion via hand-to-mouth contact was determined to be the most significant exposure route for most scenarios. The following key variables were also found to influence the model estimates: Research Approach Results and Impact 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 • time spent on/around treated residential decks Alternative scenarios did not significantly impact the baseline results, except for the impact of greatly reducing wood residue concentrations through hypothetical wood sealant applications. The SHEDS-Wood CCA probabilistic results were found to compare well to the results from other deterministic CCA exposure assessments. Draft reports for the exposure and risk assessments can be found on the EPA website for the December 3-5, 2003 Scientific Advisory Panel meeting: www. epa. gov/scipolv/sap. The final OPP/ORD human health risk assessment will be pivotal in the risk management and CCA re-registration eligibility decisions, and in advising the public on how to minimize health risks from existing treated wood structures. The EPA's ORD/NERL collaborated closely with the EPA's OPP in the Office of Prevention, Pesticides, and Toxic Substances (OPPTS) to conduct this probabilistic exposure assessment. OPP provided guidance on model input and output specifications to include population definition, exposure scenarios, and model inputs. ORD/NERL conceived the probabilistic exposure model methodology, coded the SHEDS model for the wood preservative scenario, developed model inputs, and applied the model for the CCA assessment. OPP used ORD's SHEDS model results as inputs to their CCA risk assessment. ORD and OPP jointly presented the CCA exposure modeling methodology and exposure/risk assessments at several OPP Scientific Advisory Panel meetings. ManTech Environmental Technology, Inc. provided contractor assistance in coding the exposure model and preparing the report. This research has been presented in several international and national conference presentations, and in the following technical reports: Zartarian,V.G., Xue J., Ozkaynak H., Dang W., Glen G., Smith L., Stallings C., "Probabilistic Exposure Assessment for Children Who Contact CCA-Treated Playsets and Decks Using the Stochastic Human Exposure and Dose Simulation Model for the Wood Preservative Exposure Scenario (SHEDS-Wood)," Draft Preliminary Report, prepared for EPA Office of Pesticide Programs FIFRA (Federal Insecticide, Fungicide, Rodenticide Act) Science Advisory Panel (SAP) meeting, December 3-5, 2003. Zartarian V.G., Xue J., Ozkaynak H., Glen G., Stallings C., Smith L., Dang W., Cook N., Aviado D., Mostaghimi S., Chen J., 2002, "Technical Manual: Using SHEDS-Wood (Stochastic Human Exposure and Dose Simulation Model for a Wood Preservative Scenario) for the Assessment of Children's Exposure and Dose from Treated Wood Preservatives on Playsets and Residential Decks," prepared for EPA Office of Pesticide Programs FIFRA (Federal Insecticide, Fungicide, Rodenticide Act) Science Advisory Panel meeting, August 30,2002. Future Research ORD/NERL is refining the SHEDS-Wood model inputs for CCA and will be performing more comprehensive uncertainty analyses that will consider model and scenario uncertainties. We will also be updating the CCA exposure assessment Research Collaboration and Research Products ------- with new information on key model inputs and parameters, including any new data on effectiveness of different sealants. With appropriate wood and soil residue data, the SHEDS-Wood model described here could be applied to evaluate alternate wood preservatives in addition to CCA. This research is part of a larger on-going effort in ORD to develop models that improve our understanding of the magnitude, range, uncertainty, and contributing factors for multimedia, multipathway pollutant exposure, especially to children. Contacts for Questions and inquiries on ORD/NERL's wood-preservative exposure-modeling Additional research can be directed to Information Valerie Zartarian, Ph.D. US EPA National Exposure Research Laboratory (MD E205-02) Research Triangle Park, NC 27711 Phone: 617-918-1541 zartarian.valerie@,epa.gov ------- |