Ecotoxicological Impacts of Organotins: An Overview

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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.