CONTINUING IMPACT OF TBT, PREVIOUSLY USED IN MARICULTURE, ON DOGWHELK (NUCELLA-LAPILLUS L) POPULATIONS IN A SCOTTISH SEA LOCH

The degree of development of a penis and vas deferens in adult female dogwhelks as a result of exposure to tributyltin (TBT) compounds, and concentrations of total tin in homogenised soft parts of these individuals, have been investigated for three consecutive years (1986-1988) in a Scottish sea loch where TBT anti-foulants were used in mariculture until 1987. Results of these surveys, which included the examination of sub-adults and juveniles, and of adults transplanted from a site with low imposex levels to two sites within Loch Laxford, have indicated that, even though the use of TBT paints in mariculture was prohibited in the UK in 1987, low residual concentrations of TBT were still present in the loch during 1988-1989. A mathematical model describing the penis-length-shell-length relationships in individuals of all size ranges, from selected populations in 1987 and 1988, has shown that penis growth was stimulated in males, as well as females, in response to exposure to TBT; and that there was a smaller degree of imposex development in the sub-adult and juvenile dogwhelks in 1988, than in 1987. The decrease in imposex development suggests that although TBT was present in 1988, the concentrations were lower than in the previous year, suggesting that the 1987 legislation curtailing the use of TBT in mariculture was beginning to be reflected in the imposex condition of dogwhelk populations.