The legislation on organotin-based antifouling paints, including the International Convention on the
Control of Harmful Anti-fouling Systems on Ships (AFS Convention) is here summarized. Concentrations of
TBT and TPhT in the marine environment and toxicities of TBT and TPhT to mainly marine organisms are also
overviewed, as is the relevant legislation. As one of the most typical toxicological effects of TBT and TPhT,
imposex in gastropod mollusks is reviewed. Imposex is a superimposition of male-type genitalia (penis and vas
deferens) in females and is considered an irreversible pseudohermaphroditic condition. It is typically induced by
very low concentrations (~1 ng/L) of TBT, TPhT, or both. Reproductive failure occurs in the severe stages of
imposex, either because of oviduct blockage by the formation of vasa deferentia or because of ovarian disorder
(spermatogenesis as well as suppressed production of matured oocytes), and eventually results in population
decline or mass extinction. Globally, approximately 200 species of mesogastropods and neogastropods are
affected by imposex. Imposex among gastropods has been recognized as a clear manifestation of endocrine
disruption. Five main hypotheses of the mechanisms by which organotins induce imposex in gastropods have
been proposed: (1) an increase in androgen (e.g., testosterone) levels due to TBT-mediated inhibition of
aromatase; (2) TBT-mediated inhibition of the excretion of androgen sulfate conjugates; (3) TBT interference in
the release of penis morphogenetic/retrogressive factor from the pedal/cerebropleural ganglia; (4) an increase in
the level of alanine-proline-glycine-tryptophan (APGW)amide neuropeptide in response to TBT; and (5)
involvement of the retinoid X receptor (RXR), a nuclear receptor. Each hypothesis is critically reviewed.
Keywords: AFS Convention (International Convention on the Control of Harmful Anti-fouling Systems on Ships),
bioconcentration factor- ADI (acceptable daily intake)- imposex, aromatase inhibition- APGW amide (alanineproline-
glycine-tryptophan amide)- RXR (retinoid X receptor)- 9CRA (9-cis retinoic acid).
