Environmental Impacts of CCA-Treated Wood: A Summary from Seven Years of Study Focusing on the U.S. Florida Environment

IRG/WP 03-50205

H M Solo-Gabriele, T G Townsend, J D Schert

Wood treated with chromated copper arsenate (CCA) was identified in 1995 as the cause of elevated arsenic concentrations within wood fuel used for cogeneration within Florida. Since this time a research team from the University of Miami and University of Florida has evaluated the environmental impacts of CCA-treated wood within the State. Research has focused on two distinct areas: in-service leaching of the CCA chemical and disposal pathways for the discarded product. In-service leaching was evaluated by sampling soils located below 9 pre-existing decks (8 CCA treated and 1 not CCA treated) and 2 decks (one CCA treated and one untreated) constructed over a leachate collection system. Results showed that CCA-treated decks leach chemicals in quantities that will impact soil quality. For the pre-existing decks, the average background soil arsenic concentrations were 1.5 mg/kg. Immediately below the pre-existing decks the average soil arsenic concentration was 28.5 mg/kg. Runoff for the decks constructed over a leachate collection system contained over 1 mg/L arsenic and chromium. Arsenic in the runoff was predominately in the +5 valence; however, some As(III) has been measured. A considerable effort by this research team has been placed on evaluating the fate of CCA-treated wood upon disposal. The research has shown that the quantities of discarded CCA-treated wood will increase significantly in the future. Current disposal pathways for CCA-treated wood include construction and demolition (C&D) debris landfills (which are generally unlined in Florida) or inadvertent mixing within mulch and wood fuel that is produced from recycled C&D wood. Samples collected from C&D debris facilities located in Florida indicate that CCA-treated wood can represent up to 30% of the recycled wood by weight. Research has shown that the CCA chemical is capable of leaching from CCA-treated wood (both in the unburned form and as ash) in quantities that exceed regulatory thresholds established by the U.S. Environmental Protection Agency, thereby suggesting that discarded CCA-treated wood should in many cases be managed as a hazardous waste. When CCA-treated wood represents 5% or more of a recycled wood mixture, the ash from its combustion will typically be characterized as a toxicity characteristic (TC) hazardous waste. Both new and weathered CCA-treated wood has been found in a majority of cases to leach arsenic at concentrations greater than the TC regulatory limit. Results from chemical speciation analysis indicate that unburned wood leaches arsenic primarily in the +5 valence and chromium in the +3 valence. Chemical speciation of the ash however was much more variable with some samples showing significant amounts of As(III) and Cr(VI). Commercial mulch purchased at retail establishments in Florida also was shown to leach arsenic at levels that exceeded the State’s risk-based Groundwater Cleanup Target Levels. The presence of leachable arsenic within the mulch was attributed to the presence of CCA-treated wood. Potential solutions to the CCA-disposal problem have been explored including options for waste minimization and disposal-end management of the treated wood. Waste minimization focuses on the use of alternative wood treatment preservatives that do not contain arsenic. Non-arsenical chemicals evaluated include ACQ, CBA, CC, and CDDC. These alternatives were shown to leach less arsenic but more copper than CCA-treated wood. Options for disposal-end management explored through this study include sorting technologies to separate CCA-treated wood from other wood types. Sorting technologies explored included the use of a chemical stain and two systems based upon the use of lasers or x-rays. Chemical stains were found to be effective for sorting small quantities of CCA-treated wood. Both the laser and x-ray systems were shown to be a very promising technologies for sorting large quantities of wood in a more automated fashion.

Keywords: Chromated copper arsenate, CCA, disposal, alternatives, leaching

Conference: 03-05-18/23 Brisbane, Australia

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