LEAD SOURCE ASSESSMENT BY ISOTOPIC AND ELEMENTARY COMPOSITION IN THE TRANSITION FROM PRISTINE TO POLLUTED CONDITION OF COASTAL SEDIMENTS

The source assessments of metal contaminants are critical for a consistent management of coastal zones. In this work, lead (Pb) concentration and isotopic composition were determined in sediments from Angra dos Reis coast (Brazil) to evaluate the potential influence of contamination sources on Pb distribution. Estimated Pb enrichment factor up to 1.64 suggested natural source predominance. Diagrams of Pb-206/Pb-207 ratio plotted against Pb-208/Pb-206 and 1/Pb ratios indicated a binary source mixing that was explained by marine and terrigenous influences. Only some specific sites fall close to anthropogenic Pb isotopes signatures (e.g., from urban effluents and gasoline). The lower Pb concentrations were associated with a marine carbonate dilution effect, as indicated by a negative relationship between Pb and Ca. Past dredging activities contributed to explain a diffuse occurrence of anthropogenic Pb isotopic signature. The overall results reveal the beginning of a transition from pristine to slightly-polluted condition.