Chromated Copper Arsenate
Chromated copper arsenate (CCA) is a pesticide that has been used as a preservative in pressure-treated wood since the 1940s. When injected into the wood, CCA protects it from rotting due to decay-causing insects and microbes. From the 1970s through 2003, most of the wood excluding cedar and redwood used in outdoor residential structures such as decks, gazebos, picnic tables, and playsets, was treated with CCA (U.S. Consumer Product Safety Commission, undated). Effective December 31, 2003, manufacturers voluntarily discontinued use of chromated arsenicals in pressure-treated wood for residential use. CCA is still used, however, in products such as utility poles, pilings, docks, and retaining structures.
CCA is an acidic mixture that commonly contains hexavalent chromium as chromic acid anhydride (CrO3), pentavalent arsenic as arsenic pentoxide (As2O5), and divalent copper as cupric oxide (CuO), often in an aqueous solution or liquid-soluble concentrate (National Center for Biotechnology Information, 2022). The copper serves as the primary fungicide, with arsenic serving as both a fungicide and insecticide. The chromium chemically fixes the copper and arsenic in the wood to limit leaching, but chromium, copper, and arsenic in CCA have the potential to leach out of the wood with time (Lebow, 1996; U.S. Consumer Product Safety Commission, undated).
Metals leached from CCA-treated wood tend to accumulate in soil because they bind with organic material or with iron, aluminum, and manganese (Lebow, 1996). However, they can be transported farther in soil with less organic material, such as clay or sandy soils. Direct spills and leaks of CCA can have a wider impact on the environment. Detections of arsenic, chromium, and copper at elevated concentrations posing a risk to human health and the environment have been found in soil, sediment, groundwater, and other media at wood treater facilities that used CCA (U.S. EPA, 2018a; U.S. EPA, 2018b; U.S. EPA, 2017).
CCA-treated wood should not be burned to avoid possible inhalation of toxic chemicals in the smoke and ash (U.S. Consumer Product Safety Commission, undated). Although wood ash is a common soil amendment used for treatment of contaminated soil in situ, the ash of wood products treated with CCA is not acceptable because of the contaminants present (U.S. EPA, 2007).
More information on chromated arsenicals, alternatives to their use, and how to dispose of wood treated with CCA is available from EPA's Office of Pesticides webpage. Information and supplemental references on the chemistry and behavior, occurrence, toxicology, detection/characterization, and treatment of arsenic and chromium are available on the CLU-IN Contaminant Areas for arsenic and hexavalent chromium. In addition, the Technology Innovation News Survey (TINS) contains abstracts of documents addressing the assessment and cleanup of contaminants such as CCA.
Lebow, S., 1996. Leaching of Wood Preservative Components and Their Mobility in the Environment: Summary of Pertinent Literature. U.S. Department of Agriculture, Forestry Service.
National Center for Biotechnology Information, 2022. PubChem Compound Summary for CID 86341922, Copper Arsenate, Chromated. Retrieved October 4, 2022.
U.S. Consumer Product Safety Commission, undated. CCA Pressure-Treated Wood: Guidance for Outdoor Wooden Structures Decks • Playgrounds • Picnic Tables. Brochure.
U.S. EPA, last updated February 4, 2022. Chromated Arsenicals (CCA) Webpage.
U.S. EPA, 2017. Record of Decision, Summary of Remedial Alternative Selection for Fairfax Street Wood Treaters Superfund Site, Jacksonville, Duval County, Florida. August.
U.S. EPA, 2007. The Use of Soil Amendments for Remediation, Revitalization and Reuse. EPA 542-R-07-013. Office of Solid Waste and Emergency Response, December.