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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 products were monitored in Brest naval harbour waters from September 1993 to December 1997. But for some exceptional values, the levels of contamination were more or less the same during the four year study period. Dibutyltin (DBT) concentrations showed seasonal variations, and these are discussed in relation with the seasonal changes of water temperature and the total number of sunlight hours preceding sampling dates. The extent of the phase shift between the peaks of DBT concentrations and the sunlight hours is much higher than the residence time of waters in the study zone, suggesting that photolysis is unlikely to be an important factor in the degradation of TBT.