Seasonal variations in degradation of tributyltin in the brest naval harbour waters in relation to water temperature and insolation

Changes of the concentrations of tributyltin (TBT) and its degradation prod ucts were monitored in Brest naval harbour waters from September 1993 to De cember 1997. But for some exceptional values, the levels of contamination w ere more or less the same during the tour year study period. Dibutyltin (DB T) concentrations showed seasonal variations, and these are discussed in re lation with the seasonal changes of water temperature and the total number of sunlight hours preceding sampling dates. The extent oi the phase shift b etween the peaks of DBT concentrations and the sunlight hours is much highe r than the residence time of waters in the study zone, suggesting that phot olysis is unlikely to be an important factor in the degradation of TBT.