Anthropogenic and lithogenic sources of lead in Lower Silesia (Southwest Poland): An isotope study of soils, basement rocks and anthropogenic materials
Abstrakt
To discriminate possible anthropogenic and lithogenic sources of Pb in Lower Silesia (SW Poland), the Pb isotope composition was investigated in a spectrum of rocks and anthropogenic materials as well as within 10 soil profiles. Silicate rocks in Lower Silesia have Pb-206/Pb-207 ratios that vary from 1.17 for serpentinites to 1.38 for gneisses, and this variability is reflected in the isotope composition of the mineral soil horizons.
The Pb isotope composition of coals, ores and anthropogenic materials (slags and fly ashes) is rather uniform, with Pb-206/Pb-207 ratios ranging from 1.17 to 1.18. Similar ratios were observed in ore and coal samples from Upper Silesia.
The O soil horizons also have uniform Pb-206/Pb-207 ratios of 1.17-1.18 and the heterogeneity of the Pb-206/Pb-207 ratios increases with depth in the soil profiles. Five soils, with varying Pb concentrations, analysed far from contamination centres, show consistent, approximately 2-fold enrichment in Pb concentration from the C to A horizons, which is consistent with natural re-distribution of Pb within the profiles.
The increase in the Pb concentration is accompanied by a decrease in Pb-206/Pb-207 ratios, also attributed to natural Pb isotope fractionation. Four soil profiles from industrial areas show variable enrichments in Pb concentrations and these are attributed to anthropogenic input from airborne pollutants or even slag particles at smelting sites.
The implication is that a lithogenic Pb source can deviate from the basement rock composition, and detailed isotope characteristics of the geological background and natural enrichments in soils are often needed to determine the lithogenic/anthropogenic proportions of Pb in soils.