Evaluation of environmental levels and biological impact of TBT in Malta (central Mediterranean).

Chemical monitoring for butyltins in bulk seawater, surface microlayer and superficial sediments determined that the two main local sources of marine contamination by tributyltin (TBT) compounds in Malta are ship-repairing dockyards and marinas. In bulk seawater, TBT values ranged from below the detection limit of 5 ng Sn l(-1) to 300 ng Sn l(-1); in sediments derived from the most polluted areas, TBT concentrations as high as 1500 ng Sn g(-1) were measured. At TBT levels found in local harbours, several sublethal biological responses are possible and were observed, including a significant reduction in MFO enzyme system activities of fish; digestive cell atrophy in the oyster Ostrea edulis; and induction of imposex in the snail Hexaplex trunculus. The latter two responses are evident at TBT concentrations below the environmental quality standard (20 ng TBT l(-1)). The ecological implications of these results are discussed and it is concluded that exposure of marine organisms to TBT in local harbours may be expected to lead to a reduction in the long-term survival of a number of such organisms. For these reasons, both the use of TBT-based antifouling paints for pleasure boats as well as drydock practices need to be controlled by appropriate regulations and their enforcement.