Distribution of natural and anthropogenic lead in Mediterranean soils

The concentrations and isotopic composition of Pb have been combined with a selective sequential dissolution procedure to track the distribution of an thropogenic and natural Pb in the soil of semiarid climate and the penetrat ion pathway of petrol-Pb within the soil profile. Soil samples were collect ed from soil profiles adjacent to a major highway (8-23 m) and from soil pr ofiles 500 m away from the same highway. The selective sequential dissoluti on procedure was used to determine the distribution of Pb between the diffe rent soil components: soil carbonate, organic matter, Fe-oxides and hydrous oxides, and aluminosilicates. Natural Pb is associated mainly with alumino silicates (similar to 60%) and Fe-oxides (similar to 30%), and only a small fraction with the soil carbonate and organic matter (similar to 10%). In c ontrast to the distribution of natural Pb, the distribution of anthropogeni c Pb, which accumulates mainly in the upper part of the soil profile, is si milar to 40% with the soil carbonate, similar to 10% with organic matter, s imilar to 35% with Fe-oxides, and only similar to 15% with alumino silicate s. On the basis of concentration and isotopic composition of total Pb, the deeper horizon of the roadside soil (10-30 cm) and the soil sampled 500 m f rom the highway seem uncontaminated. However, the isotopic composition of t he labile components in the soil (Pb-carb, Pb-org, and PbFe-ox) indicates t hat these soils are actually contaminated. This contamination implies that over the period of vehicle pollution (similar to 40 yr), petrol-Pb has pene trated through the entire roadside soil profile (25-30 cm). Furthermore, Pb isotopes in aluminosilicates of the upper part of the roadside soil indica te that this Pb too is anthropogenic. Measurements of Pb concentration and isotopic composition in roadside soil profiles sampled in 1997 and archived samples collected at the same location in 1982 provided a unique opportuni ty to trace petrol-Pb penetration into the soil. Copyright (C) 2001 Elsevie r Science Ltd.