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


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•	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


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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


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