Degradation of tributyltin in San Diego Bay, California, waters

Unlabelled or carbon-14 labelled tributyltin (TBT), an antifouling toxicant in boat paints, were added to water samples from 2 sites. Unlabelled TBT degradation to dibutyltin (DBT) and monobutyltin (MBT) was measured using hydride generation and atomic absorption. Labelled TBT degradation was determined using liquid scintillation counting and autoradiography. The effects of light and dark conditions were examined. Calculated half-lives in water from one site, a yacht harbour, (ambient concentration of 0.5 ug TBT per litre) were 6 and 7 days for light and dark conditions, respectively. Half-lives from the clean-water site (ambient concentration less than 0.03 ug TBT per litre) were 9 and 19 days. The principal degradation product was DBT. Complete mineralization occurred with a half-life of 50-75 days. High concentrations (744 ug per litre) of TBT were not degraded in sunlight, indicating that microbial metabolism was the principal degradative process for TBT at low ambient concentrations.