Imposex in marine gastropods from the Atlantic coast of South Africa
Tributyltin (TBT) is an organotin compound used as an antifouling agent in paint that is applied to the hulls of vessels to prevent the formation of biofilms. This highly toxic antifouling compound leaches into the water and has subsequent negative effects on marine life, especially marine gastropods. One of the most serious effects of exposure to TBT is the growth of a penis/vas deferens in female gastropods; this phenomenon is referred to as imposex (imposed sex). Marine gastropods are therefore useful bioindicators as imposex is related to TBT exposure. Imposex may affect the reproduction of these organisms and thus affect coastal ecology. The consumption of TBT-contaminated foodstuffs may also pose a risk to human health. The use of antifouling paints containing organotin compounds such as TBT continues in developing countries, despite the fact that the International Maritime Organization (IMO) banned the global use of organotin compounds in antifouling paints applied to ships in 2008, by country Parties electing to do so. This is the first report of an imposex-sediment survey used to evaluate TBT contamination along South Africa’s Atlantic coastline. This was achieved by sampling caenogastropods from sites presumed impacted and non-impacted by TBT pollution and by using various biological indices: Percentage Imposex (% I), Relative Penis Length Index (RPLI), Relative Penis Size Index (RPSI), and Male:Female ratio (M:F). TBT and DBT (dibutyltin) concentrations were measured in sediments to provide additional information regarding TBT pollution as gastropods usually inhabit these sediments and imposex may be related to these concentrations. This study showed that imposex is prevalent along the coastline and high concentrations of TBT have been measured, which is of major concern. Results have shown that TBT and DBT levels are related to boating activity, including imposex prevalence. Research will make valuable information available to necessary parties so that regulations and protective measures may be enforced to protect our marine life.