The role of pollution versus natural geological sources for lead enrichment in recent lake sediments and surface forest soils

This paper assesses the role of airborne pollution and natural geological s ources for lead enrichment in lake sediments and in surface soils of boreal forests. This assessment is based on analyses of stable lead isotopes (Pb- 206 and Pb-207) and lead concentrations in sediment cores (> 30 lakes), omb rotrophic peat and soil samples in Sweden. The Pb-206/Pb-207 ratio and conc entration profiles in the sediment cores change synchronously over the last 3,000 years in different lakes, temporal concentration changes in sediment s and peat deposits are very consistent, and these temporal concentration c hanges coincide well with the history of lead production in Europe. The Pb- 206/Pb-207 ratio is almost the same in all soil mor samples (1.152 +/-0.009 ; n=94), and similar to values recorded in aerosols, despite very high and different Pb-206/Pb-207 ratio of the mineral soil in the C-horizon (1.3-1.7 ). This study provides evidence that lead enrichment in recent sediments an d peat, and in the mor layer are caused by deposition of pollution lead and not natural processes.