Toxic anti-fouling agents

Butyltins (BTs) are organic tin compounds used in marine ship paints. They act as anti-fouling agents, to prevent hulls and docks from becoming encrusted with barnacles. However, repeated studies have demonstrated negative impacts of BTs on organisms such as molluscs and gastropods and, more recently, marine mammals such as dolphins.

Dead sea otters found along California coastal waters contained high levels of TBT and other BT compounds, which according to a researcher at the University of Michigan, may have contributed to immunosuppression in the otters and increased their susceptibility to infections. Sea otters which had died of infectious diseases contained greater concentrations of BTs in their tissues than those that died of trauma or unknown causes.

In 1989, tributyltin (TBT) was banned in the USA on vessels of 25 meters or less in length. However, because BTs persist in sediment for years, wildlife continues to be exposed to them. In addition, they are still used on larger vessels and aluminium-hulled boats. Large harbours such as California's Monterey Bay that handle ships greater than 25 m in length, which are legally painted with TBT, continue to experience high inputs of butyltins. These particularly affect animals such as sea otters, which are coastal and feed on such species as scallops, mussels, rock crabs and sea urchins, which accumulate high levels of butyltins.