Imposex

Imposex is a condition in which female marine gastropods develop male sexual characteristics, most notably the growth of a penis and associated ducts. It is primarily caused by exposure to organotin compounds, especially tributyltin (TBT), which were once widely used in antifouling paints for ships and underwater structures. The effect is a form of endocrine disruption and can range from partial masculinization to complete feminization, reducing reproductive capability in affected individuals.

The dog whelk (Nucella lapillus) is among the best-studied species exhibiting imposex, but the phenomenon has been reported in numerous other marine snails. Severity generally correlates with ambient TBT concentrations and exposure duration. In severe cases, imposex can lead to sterility or significant population declines in highly polluted areas. Because TBT binds strongly to sediments, imposex may persist long after emissions decrease, continuing to influence communities.

Detection and assessment typically involve scoring the degree of imposex using standardized indices or measurements, such as the length of male organs relative to body size or a categorical severity scale. These methods enable researchers to track pollution levels and ecological impacts over time, and to compare sites or monitor changes following regulatory actions.

Regulatory responses have significantly reduced TBT use. International and national measures, including bans on TBT-based antifouling paints and restrictions on ship coatings, have led to declines in imposex incidence in many regions. However, remnants of TBT in sediments and historical contamination mean that imposex remains a useful indicator of organotin pollution in some ecosystems.