Bioavailability and form of copper in wood treated with copper-based preservative

The biological performance of copper-treated wood is related to the amount and form of copper available in treated wood. The amount of copper biologically available in wood treated with copper-based wood preservatives such as micronized copper azole, micronized copper quat, alkaline copper quat, copper chrome arsenic and copper azole was estimated by using non-sequential chemical extraction method. DI water, KNO₃, KF, Na₄P₂O₇, EDTA disodium salt and HNO₃ solutions were used to extract copper from treated wood in an ultrasonic bath. The extracts and water washings were collected, centrifuged and analyzed to determine the amount of copper. High amount of copper was extracted with EDTA disodium salt and HNO₃ solutions followed by sodium pyrophosphate, while that extracted with KNO₃, KF and DI water was low. EDTA disodium salt and sodium pyrophosphate are known as good complexing/chelating agents, capable of chemically reacting with copper in treated wood, to form water-soluble copper salts. HNO₃ was capable of extracting almost 100% of copper from copper-treated wood because of its low pH capable of solubilizing solid, unfixed and fixed copper in wood. KNO₃ reacted with exchangeable form of copper, while KF is responsible for the extraction of physically adsorbed copper. DI water mostly removed soluble form of copper from treated wood. The amount of copper bioavailability from copper-treated wood can be estimated by the amount of copper extracted using DI water, KNO₃ and KF solutions under given environmental conditions. The amount of bioavailable copper extracted from micronized copper–treated wood using DI water, KNO₃ and KF solutions, although found to be low as compared with that extracted from ACQ, CCA and CA wood, was sufficient to prevent the growth of wood-destroying fungi.