Risks to human health and estuarine ecology posed by pulling out creosote-treated timber on oyster farms

Five oyster farms in Port Stephens, Australia were studied to identify consequences of using creosote-treated posts and the risks posed by removing the posts. Gas chromatography coupled with mass spectrometry (GC/MS) was used to measure polycyclic aromatic hydrocarbons (PAHs) and phenols in sediments, timber, water and oyster tissue. Before posts were removed, the total PAHs in surface sediment on farms was 24.1 mg kg−1 dry weight. This increased to 45.5 mg kg−1 dry weight after the posts were pulled out and remained significantly higher 6 months later at 59.7 mg kg−1 dry weight. A similar increase was found in deeper sediments. The sediment attached to creosote-treated posts had a total concentration of PAHs of 484-2642 mg kg−1 dry weight, while the corresponding value for the sediment on tar-treated posts was only 30.7 mg kg−1 dry weight. The surface timber of creosote-treated posts had high levels of PAHs and an average post contained 43 g of PAHs. The total PAHs dispersed to the environment when a creosote-treated post was pulled out was at least 0.67 g. The main species were PAHs with low-molecular weights: fluoranthene, phenanthrene, pyrene, acenaphthylene and chrysene. Benzo(a)pyrene represented 1-10% of PAHs in most samples. Bioassays with creosote-contaminated sediment revealed that Sydney rock oysters (Saccostrea glomerate) and Pacific oysters (Crassostrea gigas) accumulated PAHs at (mg kg−1 wet tissue weight): 11.3-15.3 and 35.5-47.9, respectively, when exposed for 5 days to water with <1 μg l−1 PAHs. Wild oysters growing on creosote-treated posts had high levels of phenols (0.09-6.92 mg kg−1 wet weight) and PAHs (0.59-1.01 mg kg−1 wet weight). The dilemma posed by removing creosote-treated posts and dispersing carcinogenic, bioavailable contaminants needs to be managed in light of risks to human health and estuarine ecology.