Evaluation of impact of CCA-treated wood on the marine environment
R M Albuquerque, S M Cragg
This paper reviews the literature relating to the potential of CCA-treated wood to affect the marine environment and outlines the compounds required for a model which could be used to predict the environemental impact of maritime construction using such timber. Marine pilings require high loadings of CCA to provide protection from marine borers. Though loadings of 32-48 kg/m³ provide long-term protection, preservative content is depleted over time. A number of studies have shown that copper migrates from core regions of treated wood towards the surface and that all three elements are lost by leaching. Most studies of leaching rates in seawater indicate a considerably lower rate of leaching of chrome than for the copper and arsenic. The relatively rapid initial rate of leaching appears to tail off to a much lower level within a short period of time. When trying to predict the effect of preservative leachate, the rate of element movement per unit area of longitudinal surface is the key measurement. Leaching from cross-cut surfaces is more rapid, but such surfaces form a very small proportion of total treated surface area in the below-water portions of wooden structures such as wharfs. In the laboratory, leachate has been demonstrated to adversely affect a range of organisms, but under conditions likely to generate unusually high leachate levels. Certain field observations suggest that epibiota on treated wood and benthic organisms in nearby sediments may be adversely affected by leachate where water circulation is limited. Further realistic measurements of leaching rates and a proper understanding of the chemical and biological transformations undergone by leachate on entering the marine environmment are required before a useful predictive model of the environmental impact can be developed.
Keywords: ECOTOXICOLOGY; EMISSIONS IN WATER; MODELLING; MARINE; IN-SERVICE RISK ASSESSMENT; RESISTANCE TO LEACHATE