Abstract
In 1982 TBT compounds leached from antifouling agents were identified as a possible cause of poor oyster (Crassostrea gigas) growth in the UK. A programme of research and monitoring by MAFF at Burnham-on-Crouch confirmed that low concentrations (0.1-0.2 \mug l-1) of TBT occurred in enclosed estuaries with high numbers of pleasure craft, and produced low meat yields and shell thickening in C. gigas. Information gathered on the extent of the oyster problem and an examination of biological effects in other species has led to concern about the wider environmental impact of TBT. The action taken to control the use of TBT in the UK is discussed.