The hull of a ship is a perfect home for marine species such as algae and barnacles. But these so-called fouling organisms slow down ships, increase fuel consumption, and reduce ship durability.
People have long used various chemicals to keep their ships free of fouling organisms. In the 1960s, the modern chemicals industry developed organotins - toxic chemicals that can be added to paint which kill anything that attaches to the ship.
The problem is, these chemicals leach from the paint into sea water, and are absorbed by marine organisms. Persistent and bioaccumulative, they can remain in the environment and increase in concentration up the food chain.
And tributyl tin (TBT), one of the most effective organotins, is considered by many to be the most toxic chemical deliberately released into the marine environment.
TBT has hormone-disrupting properties. Even at low concentrations it causes deformations in oysters and genital changes in snails. The decline of commerical oysters along the Atlantic coast of France and the UK in the 1970s is attributed to TBT contamination.
Since the 1970s, increased levels of organotins have been found world-wide in marine organisms further up the food chain, such as fish, seabirds, and marine mammals, where it can cause severe damage to reproduction or immune systems. Humans also become contaminated after eating contaminated fish and marine mammals, and could also face health risks.