Rates of emission from CCA-treated wood in the marine environment: measurement, modelling and requirements for further research
S M Cragg, C J Brown, R A Albuquerque, R A Eaton
Accurate estimates of rates of emission of leachate from preservative treated wood are crucial for realistic predictions of the environmental impact of its use in maritime construction. Estimates are available for some commonly used preservatives, but these vary widely. Though variable, these measurements suggest that emission generally decreases exponentially with time. Part of the variation is due to differences in methodology employed. Physical and chemical characteristics of the seawater used (e.g. temperature, salinity, pH and oxygen content) affect emission rate. So too do the specifics of the treatment process especially the preservative formulation used, and pre- and post-treatment handling of the wood. The nature of the treated wood samples is also important, with misleadingly high estimates being obtained from samples with unrepresentatively high proportions of cross-cut surfaces. A suggested strategy for developing an informative and standardised methodology is discussed. To form useful models of impacts of leaching, emission rates need to be considered in conjunction with site-specific information regarding a) water exchange rates between the area where leaching occurs and the sea, and b) the extent of partitioning of leachate between the water column, biota and sediment. The risk of environmental impact may be reduced by modification to treatment procedures and by careful planning of installation.
Keywords: RATES OF EMISSION; LEACHATE; REALISTIC PREDICTIONS; ENVIRONMENTAL IMPACT; MARITIME CONSTRUCTION; SEAWATER; TEMPERATURE; SALINITY; PH; OXYGEN CONTENT; PRESERVATIVE FORMULATION; PRE- TREATMENT; POST-TREATMENT; WATER EXCHANGE RATES; WATER COLUMN; BIOTA; SEDIMENT