Chemical Structure of Arsenic and Chromium in Chromated Copper Arsenate (CCA) Treated Wood

In recent years, regulatory and public attention has become focused on the potential risks associated with exposure to chromated copper arsenate (CCA)-treated wood – the most widely used wood treatment product in the United States. CCA has been used to treat lumber for over 60 years (1), mainly because of the extended lifetime of CCA-treated wood as compared to untreated wood (2-5) and the higher costs of non-wood alternatives. Since the late 1980s, U.S. production of CCA-treated wood has averaged approximately 5 x 10 ft/y (6) and by 1996, sales of treated wood products reached over $3.9 billion (1). Although in January 2004 a voluntary ban on CCA for residential use went into effect, it is estimated that 300,000 metric tons of As have been used in CCA production since 1975 with most of that product still remaining in use today (7). Because of the potential toxicity of the metal constituents of CCA, attention has become focused on the potential risks from this exposure source, and in particular, the exposure of children to arsenic from CCAtreated wood used in decks and play sets. As a result, the U.S. EPA Office of Pesticide Programs (OPP) is currently preparing a human health risk assessment for direct-contact exposures to CCA-treated wood. Using the assumptions proposed in its initial 2001 exposure evaluation methodology, the U.S. EPA suggested that the major routes of arsenic exposure to younger children, 1 to 6 years, from CCA products would be through contact with wood residues, with roughly 50% coming through dermal absorption of arsenic and 46% coming through incidental ingestion. The dermal absorption estimate was calculated by assuming that 6.4% of a dermally applied arsenic dose would be absorbed. The remaining 4% of the exposure was estimated to come from exposure to arsenic containing soils.