Assessment of Potential Human Health Risks from Arsenic in CCA-Treated Wood

ABSTRACT

Chromated copper arsenate (CCA) is a chemical preservative used to treat wood for a variety of outdoor uses, including decks, fencing, and play structures. This article describes a methodology to quantify exposures to arsenic from CCA-treated wood. Exposure was evaluated for ingestion and dermal contact with arsenic-containing residue on treated wood surfaces (dislodgeable arsenic), and ingestion, dermal contact, and inhalation of soil containing arsenic originating from treated wood structures. Standard approaches were used to quantify exposures to arsenic in soil. In the absence of standard approaches for exposures to dislodgeable residue, an empirical approach was developed, extrapolating from studies of soil loadings on hands and soil ingestion rates to estimate the amount of dislodgeable residue on hands that is subsequently ingested. Results from animal studies were used to develop relative bioavailability estimates for dislodgeable and soil arsenic. A focused sensitivity analysis demonstrated that the assumptions used regarding hand loading and subsequent incidental ingestion of dislodgeable arsenic had the most significant impact on the results. This assessment indicates low uptake of arsenic into the body, resulting in incremental lifetime cancer risks within USEPA's target risk levels. We compare this approach to other methodologies used to assess exposures to treated wood.

Keywords:

• CCA
• treated wood
• human health risk assessment
• dislodgeable residue
• soil arsenic
• arsenic.

ACKNOWLEDGMENTS

Preparation of this manuscript was funded in part by the Wood Preservative Science Council (WPSC), an industry-sponsored organization comprised of Arch Wood Protection, Inc., Chemical Specialties Inc., and Osmose Inc. The WPSC supports scientific research and analysis regarding the wood preservative chromated copper arsenate. We also recognize Terri Forgach for her help in formatting and organizing the production of this manuscript.

Notes

*Sieved soil data was used for the Virginia Beach site, which had wood chips and other ground cover.

¹Data for three coupons were not included in analysis because were incomplete.

²Based on 95% Chebyshev upper confidence limit (USEPA 2002b).

³Based on non-transformed data.

*The fraction of intake parameter (FI) describes the fraction of daily intake of either dislodgeable residue or impacted soil, and is based on the proportion of daily waking hours (assumed to be 12 hours/day) that a receptor may be exposed to these media via incidental ingestion. Dermal exposure to either dislodgeable residue or impacted soil was quantified as a daily event because it's assumed that dermal uptake can continue post exposure. Inhalation exposure to soil particulate for the residential scenario (including both children and adults) is based on a 24-hour averaging time and is assumed to occur 24 hours/day.

**The hand transfer efficiency (HTE) parameter describes the fraction of dislodgeable residue on the hands that is incidentally ingested on a daily basis.

***Assumes 1/3 of the total surface area of both hands (and feet for a child ages 2–6 years old) is available for contact with a treated wood surface.

*The fraction of intake parameter (FI) describes the fraction of daily intake of either dislodgeable residue or impacted soil, and is based on the proportion of daily waking hours (assumed to be 12 hours/day) that a receptor may be exposed to these media via incidental ingestion. Dermal exposure to either dislodgeable residue or impacted soil was quantified as a daily event because it's assumed that dermal uptake can continue post exposure. Inhalation exposure to soil particulate for the different playground scenarios is based on a 24-hour averaging time and is assumed to occur only during the time a receptor is outside at a playground.

**The hand transfer efficiency (HTE) parameter describes the fraction of dislodgeable residue on the hands that is incidentally ingested on a daily basis.

***Assumes 1/3 of the total surface area of both hands (and feet for child ages 2–6 years old) is available for contact with a treated wood surface.

^a Source: USEPA (1994). Tables 2–7., pp. 2–40.

^b Ratio is based on dividing the IEUBK default soil ingestion estimate by the maximum soil ingestion estimate of 135 mg/day.

^c These values were calculated by multiplying the ingestion ratio by the median soil ingestion estimate of 45 mg/day from Stanek and Calabrese (1995).