TBT and intersex in periwinkles
Context of the study
Organotin compounds (like TBT) used in antifouling paints can disrupt the endocrine system of many gastropod species. Concentrations of 1 ng tin / l sea water results in imposex; the development of non-functional male reproductive organs in females. In the periwinkle however, higher concentrations of TBT (> 10ng tin/l) can also cause intersex; the transformation of the oviduct into a non-functional prostate. Both conditions can lead to female sterility. After TBT was banned in 2003, many periwinkle populations stopped displaying imposex characteristics. It remains unknown whether they still display intersex characteristics. 
Content of the study
The study investigated the occurrence of intersex in periwinkles sampled at 5 locations in the Western Scheldt estuary between 2000 and 2002.
Main results of the study
The study showed that in all sampling regions, the occurrence of intersex characteristics in periwinkles decreased during the 3 year study period. Intersex characteristics were more abundant at former TBT hot spots, located near the harbor of Antwerp and Vlissingen. The percentage of sterile females decreased in all locations during the study period. These results show that the TBT ban has positive effects on the populations. The ban has also negative effects such as an increased fuel coast due to the attachment of organisms on the hull of ships, the use of less effective antifouling paints (copper based) which need to be applied more often. It should also be considered, that copper might also be toxic at high concentrations. (See also here.) Therefore, using copper based antifouling paints instead of TBT might just replace one environmental problem by another.