Ships in the 1960s were often coated in a chemical called TBT to prevent sea critters like snails from clinging to the hull. After researchers found that the toxic chemical caused female sea snails to grow penises (alongside equally frightening effects in other species) the stuff was banned in 2008. Now, six years later, things are starting to look up for the snails.
Fed Up With Fouling

Ship builders have long struggled with the problem of fouling, whereby mollusks and barnacles hitch onto a hull, causing boat damage and creating drag that drives up fuel costs. Starting in the 1960s, a chemical called tributyltin (TBT) was painted on ships to keep them free from aquatic hitchhikers. It was toxic and therefore did the trick, as described in a 2002 report [pdf] from the International Maritime Organization:

As a biocide in anti-fouling paint, it proved extremely effective at keeping smooth and clean the hulls of ships and boats. And when it was introduced into anti-fouling paints, it was considered less harmful than biocides used in anti-fouling systems at the time: such as DDT and arsenic.

But as the chemical began to leach off the ships and accumulate in marine environments, especially around shipping ports, scientists started seeing negative effects on aquatic plants and animals.

Shellfish and sea snail populations were hit especially hard. Female whelks, for example, started growing penises and vas deferens (the tubes that directs sperm from the testes). This left the snails sterile—a condition called “imposex.” In Australia in 2004, for example, between 43 and 100 percent of snails studied were found to be imposex.

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