Environmental impact of wood preservative leachates

Wood preservatives are used to protect wood products from decay to prolong their effective service life. Due to health and environmental concerns, one of the preservatives with very effective protective characteristics, CCA (chromated copper arsenate), was phased out for residential use and slowly replaced by alternatives such as ACQ (alkaline copper quaternary) and CA (copper azole). While it is assumed that these new preservatives have lower health and environmental impacts than CCA, relatively little work has been done to assess the leaching characteristics and eco-toxicity effects of these preservatives.; Depending on the physical and chemical characteristics of soil, adsorption of inorganic components of leachates from preservative treated wood can limit movement of contaminants to other compartments (soil as a "sink") and reduce their toxic effect by limiting bioavailability. Estimated adsorption maxima of Cu CCA in organic and clay soils were the same or higher than for Cu ACQ and Cu CA. However, soil has a limited capacity for adsorption and after long exposure to slight contamination this capacity could be exceeded resulting in more widespread impacts.; There was much higher leaching of Cu from ACQ and CA treated wood than from CCA treated samples indicating that ACQ treated wood may result in higher risk to aquatic organisms. CCA components were more effectively bound in soil than copper from copper amine systems. Coating treatments reduced leaching of all elements from 32 to 91 % and identification of appropriate coating systems will result in the potential to reduce impacts of preservative leachates.; The presence of preservative components in the soil decreased the yield and increased their accumulation in ryegrass. Uptake of As, Cu, and Cr in rye grass was just as well predicted by total soil content as with any of the "bioavailable" estimates. ACQ leachate showed higher toxicity to germination of ryegrass seeds and Daphnia magna toxicity; it had a lower effect on ryegrass growth than CCA leachate. Reaction of ACQ leachate with sandy soil components resulted in reduced toxicity to Daphnia magna . None of the contaminated soils had a measurable effect on earthworms, although there was some preservative uptake in the worms. CCA and ACQ had similar effects on soil microflora/fauna respiration. CA leachate had lower toxicity to Daphnia magna and similar toxicity to other organisms as ACQ.