Imposex

Imposex is a disorder observed in certain marine and freshwater gastropod mollusks, where female individuals develop male sexual characteristics, such as a penis and vas deferens, due to exposure to specific environmental pollutants. This condition is primarily induced by organotin compounds, notably tributyltin (TBT), which have been widely used in antifouling paints for ships to prevent biofouling. Unlike intersex conditions that involve gonadal ambiguity, imposex results in the superimposition of male genitalia onto otherwise functional female reproductive anatomy, often leading to sterility and population declines in affected species.

The phenomenon was first documented in the 1960s and has since been identified in over 260 gastropod species worldwide. Imposex serves as a sensitive bioindicator for monitoring organotin pollution in marine environments. The severity of imposex is often quantified using the Vas Deferens Sequence Index (VDSI), which assesses the progression of male organ development in females.

In response to the ecological risks posed by TBT, international regulations have been implemented to restrict its use. The International Maritime Organization (IMO) adopted a global ban on TBT-based antifouling paints, which came into effect in 2008. Subsequent studies have shown a decline in imposex prevalence in some regions, indicating partial recovery of affected gastropod populations. However, the persistence of TBT in marine sediments continues to pose challenges for the complete eradication of imposex effects.