Incidence of imposex in thais orbita from Port Phillip Bay (Victoria, Australia), following 10 years of regulation on use of TBT.

Imposex, the phenomenon in which induced male sex characteristics are superimposed on normal females, still occurs widely in the gastropod Thais orbita from Port Philip Bay, and its incidence is greatest in areas that have high boating and shipping activities. Compared to 1992, both the extent and severity of imposex has reduced. By inference, this means that pollution by tributyltin (TBT) in Port Phillip Bay has decreased and that the bans limiting its use to vessels greater than 25 m in length, in place since 1989, have been effective. However, TBT pollution is still an issue at locations that are adjacent to major ports, such as the Port of Melbourne, where TBT from large ships and ship maintenance activities continues to pollute fish habitats. It is anticipated that the incidence of imposex, and therefore TBT pollution, will continue to decrease in Port Phillip Bay as long as the bans currently in place continue to be observed. If the trends observed in the present study continue, then it is unlikely, with the notable exception of commercial ports, that TBT will pose a threat to the health of fish habitats in Port Phillip Bay.