Quantification of anthropogenic lead in Slovak forest and arable soils along a deposition gradient with stable lead isotope ratios

Isotope ratios of Pb may provide the opportunity to determine the contribut ion of Pb from a point source to Pb concentrations in soil. Our objective w as to quantify the contribution of anthropogenic ph to total Pb and chemica l Pb fractions in contaminated soil profiles with the help of Pb-206/Pb-207 isotope ratios. We sampled 5 forest and 5 arable Cambisols along a transec t from a Cu smelter and determined Pb concentrations and Pb-206/Pb-207 isot ope ratios in total digests of all horizons and in 7 chemical fractions of the A horizons. In the organic layer under forest, Pb concentrations decrea sed from 2155 mg kg(-1) at 1.1 km distance from the smelter to 402 mg kg(-1 ) at 8 km distance; in the Ap horizons, it decreased from 126 to 72 mg kg(- 1). In the total digests, Pb-206/Pb-207 isotope ratios could be explained b y simple mixing of smelter- and background-Pb as indicated by the correlati on between the inverse of the Pb concentration and the Pb-206/Pb-207 ratio (r = 0.93). The mean proportion of smelter-Pb in soil horizons decreased wi th depth from 87% (Oi) to 21% (C) under forest and from 64% (A) to 30% (B) in the arable soils. The smelter-Pb proportions in the B horizons ranged fr om 6 to 66% and were independent of the distance from the smelter indicatin g variable leaching rates. The Pb-206/Pb-207 ratios in the chemical fractio ns could not be explained by a simple mixing model. Thus, the Pb-206/Pb-207 ratios may be used to determine the contribution of anthropogenic Pb in to tal digests but not in chemical Pb fractions.