Tributyltin compounds induce male characteristics on female mud snails Nassarius obsoletus = Ilyanassa obsoleta.

Superimposition of male characteristics on to normal females of this dioecious snail is prevalent near marinas in estuaries. In the laboratory it can be caused by exposure to parts per billion concentrations of three organotin biocides: tributyltin oxide, tributyltin resinate and tributyltin chloride. Occurrence of such abnormalities in natural populations is thus an indicator of organotin pollution which might present an environmental hazard.