NASSARIUS-RETICULATUS (NASSARIIDAE, GASTROPODA) AS AN INDICATOR OF TRIBUTYLTIN POLLUTION BEFORE AND AFTER TBT RESTRICTIONS

Between 1984 and 1993, levels of imposex (the induction of male charac ters including a penis on females) were measured in gastropods Nassari us (Hinia) reticulatus (L.) at localities in south-west England. Since tributyltin (TBT) was thought to cause imposex, concentrations in tis sues and sea-water were also-determined. Measurements made prior to th e restriction of TBT usage in 1987 showed that intensities of imposex were related to TBT levels in females. Tissue concentrations were also related to those of sea-water and concentration factors (dry tissue/w ater) were approximately 30,000 at 10 ng Sn l-1 and 75,000 at 1 ng Sn l-1. Penis development in females was initiated at about 1 ng Sn l-1 a nd in this respect N. reticulatus appears less sensitive to TBT than t he dog-whelk Nucella lapillus. As result of the TBT restrictions, conc entrations in sea-water and tissues at some of the more polluted sites decreased by factors of 5-10 times between 1987 and 1993. However, po pulation imposex declined very slowly. This was attributed to the long evity of the snails, the slow decline of penis-length in older females and the limited recruitment of less-affected females. It was conclude d that N. reticulatus is a useful alternative to N. lapillus as an imp osex-based TBT indicator at contaminated sites. However, when environm ental TBT concentrations are declining fairly rapidly, analysis of N. reticulatus tissues provides a far better indication of change than me asurements of population imposex.