Reduction in toxicity of chromated copper arsenate (CCA)-treated wood as assessed by community study

Panels of chromated copper arsenate (CCA)-treated wood and control (untreated) wood were placed into an estuary and examined after one month for differences in settlement of organisms. The community on the CCA wood exhibited greatly reduced species richness, biomass, and diversity. When the community on each panel (treated and untreated) was removed and the boards replaced into the estuary, the epibiota settling during the following month showed a smaller difference between the CCA panels and the control wood. After removal of the community and immersion of the wood for a third month, there were no statistically significant differences in the community that formed on the two materials. However, qualitative differences were still visible, particularly in the growth of the alga Enteromorpha and the bryozoan Conopeum. Differences in algal and bryozoan cover persisted after a year of submersion. The decreased toxicity of the CCA wood with repeated trials is probably related to decreased rate of leaching, as observed earlier in laboratory experiments, and suggests that the treated wood would have reduced environmental impact if it were soaked out at the treatment facility before being marketed for use in the aquatic environment. Bioaccumulation of the metals in the epibiota on the CCA wood generally declined over time, but remained far above control levels.