Impact of Surface Water Conditions on Preservative Leaching and Aquatic ...

...Toxicity from Treated Wood ProductsSpeaker:
Brajesh Dubey, Ph.D., Department of Civil and Environmental Engineering,
Faculty of Engineering, University of AucklandAbstract:
As of January 2004, wood treated with chromated copper arsenate (CCA) was no longer manufactured for most residential uses in United States. This phase out was prompted by risk assessments which indicated an elevated human health risk from arsenic (As) which could be ingested during direct contact with the wood. The primary active ingredients in most of the As-free alternatives formulations include copper (Cu) and an organic co-biocide, among which alkaline copper quaternary (ACQ) and copper boron azole (CBA) are the most popular wood preservatives in current use for the residential market. These Cu-based alternatives have been reported to leach several times more Cu (greater concentrations as well as higher percent leaching) than CCA-treated wood and the aquatic toxicity measured was found to correlate with total Cu concentrations. Due to the higher levels of Cu in the new alternative wood preservatives, it is suspected that it can promote aquatic toxicity in natural water systems. Earlier work focused on evaluating toxicity using laboratory generated leaching solutions (e.g., de-ionized water). In this study, the impact on preservative leaching and aquatic toxicity from treated wood products was evaluated using natural surface waters including waters from two rivers, three lakes, two wetlands, and one seawater, in addition to synthetic moderate hard water and de-ionized water. Blocks of wood treated with Cu based alternatives such as alkaline copper quaternary (ACQ) and copper boron azole (CBA), along with chromated copper arsenate (CCA) treated wood, were leached under quiescent conditions and total Cu, labile Cu and heavy metal toxicity were measured. Results show that ACQ- and CBA-treated wood leach approximately ten and twenty times more total Cu relative to CCA-treated wood and that the presence of organic and inorganic ligands in natural waters lowered the labile fraction of Cu relative to that from laboratory generated leaching solutions. Aquatic toxicity was found to correlate with the labile Cu fraction and hence, the aquatic toxicity of the treated wood leachates was lower in natural waters in comparison to laboratory leaching solutions. The results of the present study suggest that studies designed to evaluate the impacts of treated wood should therefore consider the role of complexation in reducing the labile Cu fraction and its potential role in decreasing toxicity.

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