Fouling organisms as indicators of the environmental impact of marine preservative-treated wood
R M Albuquerque, S M Cragg
This study evaluates the use of fouling organisms (epibiota) to assess the environmental impact of preservative treated wood. This paper presents initial findings from treated panels exposed for 6 months at Sagres, Algarve, Portugal. Panels were treated with CCA, two copper-containing quaternary ammonium (ACQ) formulations and creosote, with nominal retentions from 10 to 40 kg/m³ (creosote 25 pcf). The presence of an abundant, diverse and healthy epibiotic community growing on treated wood was used as an indication that the preservative treatment had a relatively low impact on its immediate environment. Algae and mussels (Mytilus galloprovincialis) were the dominant members of the fouling community which developed on all preservative treated wood panels. The biomass (dry weight of organisms) and species diversity of epibiota scraped from the surface of preservative treated wood panels showed the following order CCA > Creosote > ACQ 1:1 > ACQ 2:1. No difference was detected concerning the shell dimension of mussels between treatments, but mussel biomass was much lower on ACQ-treated test samples, indicating that mussel settlement was affected by ACQ treatment, but growth was not. Algal biomass was highest on creosotetreated panels, with biomass on other panels fitting the following sequence: Creosote > CCA > ACQ 1:1 > ACQ 2:1. Copper, chromium and arsenic contents of algae were determined by atomic absorption spectroscopy (AAS). Elevated levels of Cu, Cr and As were found in the macroalgal mat from CCA-treated panels. These levels showed significant positive linear regressions with panel preservative retention levels. Higher levels of copper were found in macroalgal mats from ACQ-treated wood, but showed no linear relationship to panel preservative loadings. Copper levels did not exceed 9 ppm in algal tissue, chromium and arsenic levels were below 1 ppm.