Lead contamination of the Seine River, France: Geochemical implications of a historical perspective

International audienceFour sediment cores collected in the Seine River basin and dated between 1916 and 2003 were analyzed for lead concentrations and isotopic composition. In all four cores, the measured Pb concentration (up to 460 mg kg$^{-1}$) lies significantly above the natural background (27–40 mg kg$^{-1}$), although a significant decrease (down to 75 mg kg$^{-1}$) was observed during the second half of the 20th century which can be explained by the reduction of lead emissions. The $^{206}$Pb/$^{207}$Pb ratio measured in these samples indicates that the main source of Pb used in the Paris conurbation is characterized by a “Rio Tinto” signature (defined as $^{206}$Pb/$^{207}$Pb = 1.1634 $\pm$ 0.0001). A high contribution, up to 25%, from the leaded gasoline (characterized by 206Pb/207Pb = 1.08 $\pm$ 0.02) is revealed in the Seine River downstream Paris, indicating that lead from the leaded gasoline is preferentially released to the river.The dominating Pb signature in the Paris conurbation that is currently sampled through incinerators fumes (206Pb/207Pb = 1.1550 $\pm$ 0.0005) and waste water treatment plant ($^{206}$Pb/$^{207}$Pb = 1.154 $\pm$ 0.002), represents a mixture of highly recycled lead from the Rio Tinto mine and lead from leaded gasoline (imprinted by the low 206Pb/207Pb of the Broken Hill mine). This signature is called “urban” rather than “industrial”, because it is clearly distinct from the Pb that is found in areas contaminated by heavy industry, i.e. the heavy industries located on the Oise River which used lead from European ores characterized by high $^{206}$Pb/$^{207}$Pb ratios ($\sim$1.18–1.19) and possibly a minor amount of North American lead ($^{206}$Pb/$^{207}$Pb ratios > 1.20). The “urban” signature is also found in a rural area upstream of Paris in the 1970’s. At the Seine River mouth in 2003, Pb with an urban signature represents 70% of the total Pb sediment content, with the 30% remaining corresponding to natural Pb