Alternatives to Chromated Copper Arsenate (CCA) for Residential Construction

For decades chromated copper arsenate (CCA) was the primary preservative for treated wood used in residential construction. However, recent label changes submitted by CCA registrants will withdraw CCA from most residential applications. This action has increased interest in arsenic-free preservative systems that have been standardized by the American Wood Preservers’ Association. These include acid copper chromate (ACC), alkaline copper quat (ACQ), copper azole (CBA-A and CA-B), copper citrate (CC), copper dimethyldithiocarbamate (CDDC), and copper HDO (CX-A). All of these CCA alternatives rely on copper as their primary biocide, although some have co-biocides to help prevent attack by copper-tolerant fungi. They have appearance and handling properties similar to CCA and are likely to be readily accepted by consumers. Prior studies indicate that these CCA alternatives release preservative components into the environment at a rate greater than or equal to that of CCA, but because these components have lower mammalian toxicity they are less likely to cause concern in residential applications. As the treated wood industry evolves it is probable that a wider range of types and retentions of wood preservatives will become available, with the treatment more closely tailored to a specific type of construction application.