Tributyltin, or TBT, is an organotin compound that has been used for 40 years as a biocide in antifouling paint. These paints work, but TBT leaches into the marine environment, where it can kill organisms. In 1982, France banned the use of antifouling paints containing TBT on vessels less than 25 meters in length because of the destruction of Arcachon Bay oysters in Bordeaux.
The International Convention on the Control of Harmful Anti-fouling Systems on Ships, adopted in October 2001, prohibits the use of organotin in antifouling paints. The convention entered into force in September 2008, but TBT was expected to remain in ocean water columns and sediment for another two decades. A downside to the ban was a renewed use of copper in traditional antifouling paints. Because it kills marine organisms, copper has been prohibited in antifouling paints in parts of Sweden, Denmark and the Netherlands.
Under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), the sale or application of an antifouling paint in the United States must be approved by the U.S. Environmental Protection Agency. Copper-containing bottom paints are allowed by the U.S., but are banned by Washington state on recreational boats. California may impose its own copper restrictions at some point.
Though prohibited by the IMO, TBT antifouling paints are used today in parts of the Caribbean and elsewhere.