Distribution and fate of tributyltin in surface and deep waters of the northwestern Mediterranean

Tributyltin (TBT) contamination of marine organisms collected in the open s ea 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 wa ters as well as along three vertical profiles between 25 and 2500 m. The an alytical and sampling techniques used were calibrated to be significant far a concentration of 0.01 ng L-1 TBT ions. Contamination of surface waters w as 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 c omparison of the vertical profiles of TBT and salinity allowed assumptions to be made about the source of contamination. The presence of TBT in deep w aters was attributed to the circulation of water masses during winter, whil e the vertical transport of particulate matter was considered to be of litt le importance. Contrary to results for coastal experiments, the half-life o f TBT in this oligotrophic environment was estimated to be several years. T he ubiquity and persistence of TBT in these waters is a new source of conce rn for environmentalists.