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 characters including a penis on females) were measured in gastropods Nassarius (Hinia) reticulatus (L.) at localities in south-west England. Since tributyltin (TBT) was thought to cause imposex, concentrations in tissues and sea-water were also-determined. Measurements made prior to the 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/water) 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 and in this respect N. reticulatus appears less sensitive to TBT than the dog-whelk Nucella lapillus. As result of the TBT restrictions, concentrations in sea-water and tissues at some of the more polluted sites decreased by factors of 5-10 times between 1987 and 1993. However, population imposex declined very slowly. This was attributed to the longevity of the snails, the slow decline of penis-length in older females and the limited recruitment of less-affected females. It was concluded that N. reticulatus is a useful alternative to N. lapillus as an imposex-based TBT indicator at contaminated sites. However, when environmental TBT concentrations are declining fairly rapidly, analysis of N. reticulatus tissues provides a far better indication of change than measurements of population imposex.