Alternatives to Chromated Copper Arsenate for Residential Construction

Book excerpt: 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 dimethyldithio-carbamate (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. These alternative treatments have appearance and handling properties‍?similar to those of CCA and are likely to be readily accepted by consumers. Prior studies indicate that these treatments release preservative components into the environment at a rate greater than or equal to that of CCA, but because their 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.