LONG-TERM MONITORING OF POLYCYCLIC AROMATIC-HYDROCARBONS IN MUSSELS (MYTILUS-EDULIS) FOLLOWING THE BRAER OIL-SPILL

On January 5, 1993, 84 700 t of Norwegian Gullfaks crude oil was relea sed into the coastal region of south Shetland when the tanker MV Braer grounded at Garths Ness, A Fisheries Exclusion Zone was designated un der the Food and Environment Protection Act 1985 (FEPA), prohibiting t he taking or harvesting of fish or shellfish within the Zone so as to prevent contaminated products reaching the marketplace, The criteria s et for lifting of the Order were that the particular species must be f ree from any petrogenic taint and the concentration of polycyclic arom atic hydrocarbons (PAHs) must be within the range for reference sample s. Between April 1993 and February 1995 the Order was progressively li fted for wild fish, salmon, crustacea, excluding Nephrops norvegicus ( Norway lobster), and molluscs, with the exception of mussels, As part of the monitoring exercise, mussels from a reference site were transpl anted in June 1995 to three sites within the Zone, where they were sus pended in plastic mesh boxes from rafts to a depth of 5 m, Samples wer e collected at regular intervals over the following 12 months and the concentration and composition of PAHs mere determined by gas chromatog raphy with mass spectrometric detection, The total measured PAH concen tration at the control site increased from 13.7 to 66.1 ng g(-1) wet m ass of tissue between June 1995 and February 1996, This trend was reve rsed by July 1996 when the PAH concentration was 12.8 ng g(-1). The me an across the year for the control site was 24.0 ng g(-1) (SE = 8.9 ng g(-1), n = 6), A similar seasonal trend in PAH concentration over the year was observed at all sites within the Zone, but the PAH concentra tion was consistently greater at these sites, reaching a maximum conce ntration of 316 ng g(-1) in February 1996, Although no taint was detec ted in any of the mussels, these results meant that it was not possibl e to lift the Prohibition Order for mussels, Further monitoring at thr ee sites outwith the Zone and three sites within the Zone is under way together with investigations into the specific source of the PAHs.