Oysters as biomonitors of butyltins in the Gulf of Mexico.

The concentration of total butyltins and tributyltin in oysters has been measured at 59 Gulf of Mexico sites. The concentration has decreased at 85% of the sites after passage of the Organotin Paint Control Act. At 5% of the sites there was no measurable decrease in butyltin concentration, and 10% had increases in concentration between 1989 and 1990. It appears that the limitation on butyltin usage in anti-fouling paints is causing a measurable reduction in its environmental loading. Estimates of the rate of environmental decrease and determination of the new level of environmental loading resulting from butyltins usage on larger vessels will require continued sampling.