Assessing the Release of Copper from Nanocopper-treated and Conventional Copper-treated Lumber into Marine Waters: (2) Forms and Bioavailability

One application of nanocopper is as a wood-preserving pesticide in pressure treated lumber. Recent research has shown that pressure treated lumber amended with micronized copper azole (MCA), which contains nano-sized copper, releases copper under estuarine and marine conditions. The form of copper released (i.e., ionic, nanocopper (1 to 100 nm in size)) is not fully understood but will affect the bioavailability and toxicity of the metal. In this investigation, multiple lines of evidence, including size fractionation, ion selective electrode (ISE) electrochemistry, comparative toxicity, and copper speciation were used to determine the form of copper released from lumber blocks and sawdust. Results of all lines of evidence supported the hypothesis that ionic copper was released from MCA lumber and sawdust with little evidence that nanocopper was released. For example, copper concentrations in size fractionations of lumber block aqueous leachates including unfiltered, 0.1 μm and 3 kiloDaltons (kDa) were not significantly different suggesting the form of copper released was in the size range operationally-defined as dissolved. These results correlated with the ISE data which detects only ionic copper. In addition, comparative toxicity testing resulted in a narrow range of LC 50 s (i.e., 221 to 257 μg/L) for MCA lumber blocks and CuSO 4 . This investigation concluded ionic copper was released from the nanocopper pressure treated lumber under estuarine and marine conditions.