Assessment of the environmental impacts and sediment remediation potential associated with copper contamination from antifouling paint (and associated recommendations for management)

Farm based monitoring has shown copper concentrations in sediments under salmon farms in the Huon and D’Entrecasteaux Channel are elevated relative to background conditions as a result of long-term use of copper-based antifoulants. This study was undertaken as a collaboration between researchers at the Institute for Marine and Antarctic Studies (University of Tasmania) and CSIRO, and with the cooperation of the Tasmanian Salmon farming industry to determine whether these copper concentrations have any major or long-term impacts on the local ecology or sediment function and to identify the remediation potential of these sediments and what, if any, management strategies could be used to enhance recovery. Noting that in this instance recovery was assessed as either i) a marked decline in copper over time (recovery in progress) or ii) return to background/ baseline copper concentrations (total recovery). Conditions were assessed over the short-term (12 months, this study) at sites selected for high copper loads, as well as over the longer-term (> 5 years, incorporating the results of previous farm-based assessments) at sites where the copper concentration history was well-known. Changes in background concentrations were assessed by reviewing copper data from both the farm assessments and a range of previous studies in the region, and integrating broader environmental data on prevailing conditions and exposure. Finally, targeted sedimentation studies provided data on deposition and accumulation rates that could be used to provide longer-term projections for recovery. A specific concern at the start of this study was that ongoing farming, even without the use of antifoulant nets, could increase the risk of toxicity in sediments where copper concentrations were elevated; the results of this study clearly identify that this is not the case. The results indicate that the risk of serious adverse impacts on sediment processes from current copper contamination levels is relatively low; largely because most of the copper occurs as paint flakes and can’t be easily taken up by benthic organisms. Copper can exist in a variety of forms in the sediments, with some being more toxic than others. The concentrations of relevant forms of copper were assessed, and the associated sediment conditions determined. Whilst antifoulant usage was shown to be the primary source of elevated copper concentrations within farms, local environmental conditions and certain farming practices can have a significant influence on copper accumulation and impact levels throughout the system. Consequently, it was possible to make operational management recommendations that will reduce the potential for impacts into the future. The study also recommends refined regulatory guidelines that should provide better protection with respect to chronic ecotoxicological impacts.