AN EVALUATION OF THE POTENTIAL OF GASTROPOD IMPOSEX AS A BIOINDICATOROF TRIBUTYLTIN POLLUTION IN PORT-PHILLIP BAY, VICTORIA

Imposex, the imposition of male sexual characteristics on female marin e snails, was used as an indicator of past and present exposure to tri butyltin (TBT) in the abundant muricid whelk Thais orbita (Gmelin). Wi ld populations of Thais orbita were surveyed for frequency and intensi ty of imposex throughout Port Phillip Bay and at two sites on the adja cent oceanic coast. Imposex indices correlated strongly with proximity to marinas or harbours. Average TBT body burdens for each population were mostly below 10 ng g-1 Sn (as TBT, wet wt) and failed to correlat e with imposex indices. Even the highest body burdens were indicative of low contemporary ambient TBT levels. Thais orbita females from a po pulation with negligible levels of imposex were transplanted to two si tes where the highest imposex indices were found. Transplants failed t o develop a significantly higher frequency or intensity of imposex tha n controls after 11 weeks. These results confirm that, as with many ot her gastropod species, imposex in T. orbita is irreversible, and may b e found in populations where TBT contamination is no longer present. N evertheless. controlled transplantation of T. orbita shows promise as a routine bioindicator of contemporary TBT contamination in southern A ustralia. Imposex in other gastropod species in Port Phillip Bay is de scribed and discussed.