Sex Change in the Female Dog-Whelk, Nucella Lapillus, Induced by Tributyltin from Antifouling Paints

Imposex, the development of a penis and vas deferens in the female (Smith, 1971) is known to occur in over 30 species of marine gastropods but, to date, in only one species has this syndrome been demonstrated to have a serious deleterious effect. This species is the dog-whelk, Nucella lapillus L. Both field and laboratory observations have provided conclusive evidence that imposex in N. lapillus is initiated by tributyltin (TBT), used as a biocide in antifouling paints, at concentrations in water of less than 1 ng Sn/1. This feature is manifest in the widespread occurrence of imposex even in areas far removed from centres of boating activity (see Bryan et al. 1986). Imposex appears to have little effect on the reproductive biology of N. lapillus until this syndrome is developed to its fullest extent when it sterilises the female because the pallial oviduct becomes occluded by vas deferens tissue thus preventing expulsion of the egg capsules (Gibbs & Bryan, 1986). Laboratory experiments have indicated that this condition, found in females close to harbours and marinas, may prevail after prolonged exposure during the first few years of life to TBT levels as low as 2 ng Sn/1 (Gibbs et al. 1987). Of six organotin compounds tested by Bryan, Gibbs & Burt (1988), tributyltin chloride proved the most effective in promoting imposex in N. lapillus .