Mechanism of Imposex Induced by Organotins in Gastropods

Certain environmental chemicals cause feminization of males and/or masculinization of females, and such phenomena are generally called endocrine disruption (Colborn et al. 1996). The current status of studies of endocrine disruption both in wildlife and humans is reviewed by the International Programme on Chemical Safety (IPCS) under the joint work of the United Nations Environment Programme (UNEP), the International Labour Organization (ILO) and the World Health Organization (WHO) (International Programme on Chemical Safety 2002). Here, the author will review the masculinization of female gastropod mollusks, called imposex, in terms of the basic biology and induction mechanism of imposex.

The first report of masculinized female gastropods was made by Blaber (1970), describing a penis-like outgrowth behind the right tentacle in spent females of the dog-whelk,

Nucella lapillus

around Plymouth, UK. The term

imposex

, however, was coined by Smith (1971) to describe the syndrome of a superimposition of male type genital organs, such as the penis and vas deferens, on female gastropods. Imposex is thought to be irreversible (Bryan et al. 1986). Reproductive failure may occur in females with severe imposex, resulting in population decline or even mass extinction (Gibbs and Bryan 1986, 1996). In some species, imposex is typically induced by tributyltin (TBT) and triphenyltin (TPT), chemicals released from antifouling paints used on ships and fishing nets (Bryan et al. 1987, 1988; Gibbs et al. 1987; Horiguchi et al. 1995, 1997a).