Distribution and Fate of Tributyltin in Surface and Deep Waters of the Northwestern Mediterranean

Tributyltin (TBT) contamination of marine organisms collected in the open sea or in deep seawaters has been considered in several studies but not the contamination levels in these waters far from pollutant sources. This study conducted in June 1998 measured TBT concentrations in the open sea in the northwestern part of the Mediterranean. Samples were obtained in surface waters as well as along three vertical profiles between 25 and 2500 m. The analytical and sampling techniques used were calibrated to be significant for a concentration of 0.01 ng L - 1 TBT ions. Contamination of surface waters was as high as 0.47 ng L - 1 20 km from shore and never lower than 0.08 ng L - 1 in the open sea. Contamination of abyssal deep waters reached a maximum of 0.04 ng L - 1 at a depth of 1200 m and was always significant at 2500 m. A comparison of the vertical profiles of TBT and salinity allowed assumptions to be made about the source of contamination. The presence of TBT in deep waters was attributed to the circulation of water masses during winter, while the vertical transport of particulate matter was considered to be of little importance. Contrary to results for coastal experiments, the half-life of TBT in this oligotrophic environment was estimated to be several years. The ubiquity and persistence of TBT in these waters is a new source of concern for environmentalists.