Publication Abstract

A critical appraisal of the evidence for tributyltin-mediated endocrine disruption in molluscs

P. Matthiessen and P. Gibbs

This paper reviews the field and laboratory evidence for endocrine disruption in gastropod molluscs caused by tributyltin (TBT). There are abundant and undisputed field data to link TBT, and to a lesser degree some other organotin compounds, with a sexual abnormality in many species of female neogastropod snails, known as 'imposex'. This phenomenon is a masculinization process involving the development of male sex organs, notably a penis and a vas deferens; in certain species the imposition of a vas deferens disrupts oviducal structure and function, preventing normal breeding activity and causing population disappearance. In some species, oogenesis is supplanted by spermatogenesis. A related condition referred to as intersex' has been reported in littorinid mesogastropods, and these too become unable to lay eggs. Field evidence clearly associates these syndromes with the use of TBT as an antifoulant, chiefly on boat hulls, and dose related effects can be replicated in laboratory exposures to environmentally-relevant concentrations of TBT compounds. It has now been established that imposex and intersex are a form of endocrine disruption caused by elevated testosterone titres that masculinize TBT-exposed females. The precise mechanism by which increased levels of testosterone are produced has not yet been fully described, but the weight of evidence suggests that TBT acts as a competitive inhibitor of cytochrome P450-mediated aromatase. Aromatase inhibition has been shown to reduce the formation of estradiol from testosterone, thereby leading to a build-up of the latter in affected females. Some recent data suggest TBT may also inhibit the formation of sulfur conjugates of testosterone and its active metabolites, thus interfering with its excretion. However, more information on this mode of action is needed before its relative importance can be assessed. In summary, TBT-induced masculinuization in gastropods - imposex and intersex - is the clearest example of endocrine disruption described in invertebrates to date that is unequivocally linked to a specific environmental pollutant.

Reference:

P. Matthiessen and P. Gibbs, 1998. A critical appraisal of the evidence for tributyltin-mediated endocrine disruption in molluscs. Environmental Toxicology and Chemistry 17(1): 37-43