# Presentation: 574013

## Applying an ORD Probabilistic Exposure Model (SHEDS) to Help Conduct a Health Risk Assessment for Children who Contact Chromated Copper Arsenate on Treated Playsets and Decks

- Halûk Özkaynak1, Valerie Zartarian1, Mark Mason2
- U.S. Environmental Protection Agency, Office of Research and Development, 1National Exposure Research Laboratory; 2National Risk Management Research Laboratory

- Concerns have been raised regarding the safety of young children contacting arsenic and chromium residues while playing on and around CCA-treated wood playground structures and decks.  Although CCA registrants voluntarily canceled treated wood for residential use effective December 31, 2003, the potential for exposure from existing treated wood structures and surrounding soil still poses child health hazard concerns.
- The science questions addressed by this research are:
- What are the real world aggregate exposures to arsenic and chromium of children who frequently contact Chromated Copper Arsenate (CCA)-treated wood in playsets and home decks and CCA-contaminated soil around these structures?
- What key variables contribute to these exposures?
- How can the exposures and risks from CCA-treated playsets and decks be mitigated?
- How effective are different wood coatings for reducing dermal exposures to arsenic and chromium residues?

**Research Goals**

**Methods/Approach**

**Impact and Outcomes**

**Results/Conclusions**

**Future Directions**

**Science Questions**

- The primary goals of this ORD research were:
- To conduct a probabilistic aggregate exposure and dose assessment that could help EPA’s Office of Pesticide Programs (OPP) determine the potential health risks to children from frequent contact with CCA-treated wood in playsets and home decks and CCA-contaminated soil around these structures;  and
- To determine the impact of various wood coatings on reducing available residues, in order to help OPP provide information to the public on how to reduce/eliminate exposures to arsenic and chromium from CCA-treated structures.

- The predicted central values for lifetime annual average daily dose values for arsenic, which is a carcinogen, 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 (Figure 1). Residue ingestion via hand-to-mouth contact was the most significant exposure route for most scenarios (Figure 2). The key variables influencing 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 (Figure 3). Analyses of model uncertainties resulting from uncertainties in either the model inputs or selected parameters indicated only modest amount of error (about factor of 4) in model predictions (Figure 4). Special analyses did not significantly impact the baseline results, except for reducing wood residues through hypothetical wood sealant applications (Figure 5).

- It is anticipated that the outcome of this research will be pivotal in OPP’s risk management and reregistration eligibility decisions for CCA, and in advising the public how to minimize health risks from existing treated wood structures such as playsets and decks.  The model sensitivity and uncertainty analyses conducted through this research (See Figure 4)  have helped identify key variables for which more data are needed (e.g., residue dermal transfer coefficients, time  children spend contacting treated wood, frequency of outdoor hand-to-mouth contact, saliva removal efficiency for arsenic residues on skin).  This project has also fostered new ORD research to quantify model and scenario uncertainty, in addition to parameter uncertainty, that can be applied to other EPA aggregate and cumulative exposure and risk modeling efforts.

- ORD is conducting ongoing research to evaluate both model uncertainty for the CCA assessment and the effectiveness of different wood coatings.  The models and methods developed through this research could be applied in the future to CCA alternatives.
- OPP has conducted a preliminary draft risk assessment on children's risks to CCA. OPP plans to complete their risk assessment using the final results of ORD’s exposure and dose modeling analyses, to determine the potential short-term, intermediate-term, and lifetime cancer risks for the population of interest.

**References**

- Zartarian,V.G., Xue J., Özkaynak H., Dang W., Glen G., Smith L., Stallings C., “ Probabilistic Exposure Assessment for Children Who Contact CCA-Treated Playsets and Decks Using the SHEDS-Wood Model,” Draft Preliminary Report. Reviewed at the EPA Office of Pesticide Programs FIFRA (Federal Insecticide, Fungicide, Rodenticide Act) Science Advisory Panel (SAP) meeting, December 3-5, 2003. EPA/600/X-04/089.
- Zartarian, V., Xue, J., Ozkaynak, A.H., Glenn, G., Smith, L., Dang, W., Cook, N., Aviado, D., Mostaghimi, S., and Chen, J. Technical Manual: Using SHEDS for the assessment of children's exposure and dose from treated wood preservatives on playsets and residential decks. Reviewed at the EPA OPP FIFRA SAP meeting, August 30, 2002.

***Applying a probabilistic model (SHEDS) to answer the following questions:***

**Figure 4.  What is the uncertainty in modeled estimates?**

**Figure 1.  What is population distribution of exposure, accounting for variability in activities, pesticide levels contacted, other factors?**

**Figure 2.  Which are the most important routes and pathways of exposure?**

**Figure 3.  Which model inputs are most important?**

**Figure 5.  What is the impact of potential mitigation strategies?**

- Sensitivity Analysis, Arsenic short-term ADD, warm,
- scaling by factor 1/2 and 2

***Assess Efficacy of Different Wood Sealants***

- The EPA’s Office of Research and Development (ORD), National Exposure Research Laboratory (ORD/NERL) developed and applied the probabilistic _S_tochastic _H_uman _E_xposure and _D_ose _S_imulation model for wood preservatives (SHEDS-Wood) to estimate children’s absorbed dose of the arsenic and** **chromium components of CCA. Two bounding climate scenarios (warm throughout year and cold throughout year); three exposure time periods (short-term, intermediate-term, and lifetime); and four exposure pathways (skin contact with, and ingestion of, arsenic and chromium in both soil and wood residues) were considered for a population of children in the United States who frequently contact CCA-treated wood playsets and decks, simulated using EPA's Consolidated Human Activity Database (CHAD).
- Model inputs include wood surface residue concentrations and wood-to-skin residue transfer efficiencies using CCA-treated deck and playground samples from various U.S. locations collected and analyzed by the American Chemistry Council and the Consumer Product Safety Commission.  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 SHEDS-Wood methodology to the EPA Office of Pesticide Programs’ (OPP) Scientific Advisory Panel (SAP) in August 2002 and presented the draft exposure and dose assessment to the SAP in December 2003.  The final assessment, which addresses SAP comments, is planned during 2005.
- ORD’s National Risk Management Research Laboratory (NRMRL) has been conducting a two-year study to evaluate the efficacy of actual wood coatings on reducing available arsenic residues in treated wood and surrounding soil. The sealants research has been conducted under field conditions using 40 outdoor mini-decks at the EPA-RTP complex.
- From more than 150 products, ORD/NRMRL selected twelve coatings that are available to consumers, require no sanding or stripping preparation, and span a range of product types including, clear, opaque, semitransparent, and toned stains and sealants, as well as two paints and two products advertised to encapsulate CCA treated wood. The products were applied according to manufacturer's instructions to mini-decks constructed from CCA decking collected from two and six year-old in-service decks. Dislodgeable arsenic concentrations are determined periodically using a wipe technique developed by the Consumer Product Safety Commission (CPSC).
- Data collected through fifteen months of outdoor weathering will be compiled in a data base and undergo statistical evaluation.  A draft interim project report will be prepared by the contractor and delivered to EPA in February, 2005.  After internal review and revision by EPA project staff, the interim report will be distributed for wider review within EPA and with CPSC staff. This project is conducted as a collaboration between ORD, OPP, and the CPSC.