Comparison of environmental impacts of wood treated with chromated copper arsenate (CCA) and three different arsenic-free preservatives.

摘要

Recently, the treated wood industry phased out the use of arsenic (As)-preserved wood for residential uses in favor of copper-preserved wood. Pressure-treated wood products of CCA and three As- and Cr-free preservatives, alkaline copper quaternary (ACQ), copper boron azole (CBA), and disodium octaborate tetrahydrate (DOT), were studied, and the possible environmental impacts from these treated wood products were compared under identical in-service and disposal scenarios.; The scenario of treated wood use in an aquatic ecosystem was simulated in laboratory conditions. Part of the present study is focused on studying the effect of natural water chemistry on chemical leaching and aquatic toxicity when a treated wood structure is used in these conditions. In general, it was found that the major part of the total copper leached was present as a complex with inorganic or organic ligands present in water and was not bio-available.; The relative risks from preservative components of various wood treatment chemicals in soil for direct exposure and groundwater contamination were evaluated by using a deck and soil column experiment. Arsenic from CCA-treated wood was found to pose highest relative risk in terms of direct exposure. In terms of potential groundwater contamination boron (B) from DOT-treated wood and As from CCA-treated wood posed a greater relative risk compared to Cu and organic biocides from ACQ- and CBA-treated wood.; The impact of pressure treated wood on leachate quality when disposed in landfills was studied. Simulated C&D columns were constructed for CCA- and ACQ-treated wood co-disposal scenario and the treated wood sawdust of CCA-, ACQ-, CBA- and DOT-treated wood were leached using leachates collected from various MSW landfill sites in Florida. In batch leaching tests higher Cu concentration was measured in the extract, but Cu was below the detection limit in C&D column leachate throughout the duration of experiment. Elevated As, Cr and B concentration in both batch and column leaching tests indicate potential groundwater contamination in an unlined landfill and leachate management and treatment problem for lined landfill.