Assessing the Impact of Tin and TBT in Estuaries and Coastal Regions

Research during the last few years has demonstrated the toxic nature of tributyltin (TBT), particularly to molluscs. In the UK this has led to restrictions on the uses of TBT in antifouling preparations, initially in an attempt to achieve an environmental quality target (EQT) of 20 ng l-1, and subsequently one of 2 ng l-1. No equivalent target has been set for sediments and to date the bioavailability and effects of tin compounds (inorganic and organic) associated with particulates are largely unknown. The results presented here demonstrate the exceptionally high bioavailability of sediment-bound TBT, relative to inorganic tin, notably among estuarine sediment-dwelling species such as the clam, Scrobicularia plana (da Costa). Despite strong evidence of impact at contaminated sites, proof that sediment-bound TBT is the sole cause of detrimental effects in clams is, however, still required. In contrast, measurement of TBT-induced reproductive abnormalities in dogwhelks, Nucella lapillus (L.), provides an extremely specific and sensitive means of monitoring the biological impact of this contaminant in coastal waters. Application of such indices in a TBT-polluted area of the south coast of England is discussed.