Origin and evolution of Pb in sediments of Lake Geneva (Switzerland-France). Establishing a stable Pb record

Ph isotopes and Pb concentrations were measured in two sediment cores sampled in Lake Geneva (i) at the center of the basin (central plain) and (ii) in an area which receives the effluents of the wastewater treatment plant of Lausanne as well as runoff inputs. The presence of an anthropogenic contribution is observed over all the sampled period (similar to 150 years), even at the center of the lake. At both sites, the maximum contamination of Pb occurred in the late 1970s, and has declined to present. The site close to Lausanne received much more Pb than the one at the center of the lake. Surprisingly, the Pb isotopes show that gasoline-derived Ph has had a minor influence, at least over the last 20 years. Instead, deposition of Pb from industrial (and domestic) activities predominates. This study demonstrates that one of the major limitations of the isotopic method is the poor (or partial) knowledge of how the isotopic compositions of potential sources have evolved through the past. A simple method of sample dissolution, based on HNO(3) leaching assisted by microwave, is also presented. We believe that this sample preparation can be extensively used because it provides a reliable estimate of Pb having an anthropogenic origin.