Gender-switching in mud snails has decreased following a European Union ban on tributyltin (TBT) in ship hull paint.

TBT is an antifouling agent that was used in paint to prevent organisms from growing on the hulls of ships. Unfortunately, it was found that once it enters the water it has a toxic effect on other marine organisms. And by 2003, the use of these paints was banned by the EU.

In the mud snails Nassarius reticulatus TBT was found to cause the imposex condition, where females develop male sexual characteristics such as a penis. Milene Rato from the University of Aveiro, Portugal, and colleagues measured the penis lengths in the female snails to determine TBT pollution levels. 'The main motivation to conduct this work was to find if the legislation implemented by the EU was effective,' says Rato.

They found a decrease in the levels of imposex, and therefore a decrease in the levels of TBT, with hotspots being found within harbours that contain marinas and commercial fishing ports.  From these results the group concluded that the regulation has had a favourable impact on pollution levels.

'The data shows that some recovery has occurred over the last five years, albeit at a slow rate,' says Simon Apte, the leader of the centre of environmental contaminants research at the CSIRO in Sydney, Australia.

Although TBT levels are decreasing, they are still high, Rato comments. 'Further monitoring surveys should be carried out in order to determine whether these EU measures are sufficient to reduce environmental TBT to a safe level,' he adds.

Rebecca Brodie

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