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Lead isotopic studies in soils provide an efficient tool for tracing the sources of lead pollution. Five different extraction/digestion techniques (0.05 M EDTA, 0.5 M HNO(3), 2 M HNO3, aqua regia, total digestion) were used for lead isotopic composition (206Pb/207Pb) determination in three forest soil profiles with different kinds of prevailing Pb contamination (unpolluted area, smelting area and vicinity of a motorway). The results obtained showed that all extraction/digestion methods used for the determination of 206Pb/207Pb ratios in surface horizons containing high organic matter contents gave statistically identical values (according to the Tukey test). In mineral soil horizons, differences between the individual extraction/digestion methods could be observed (the lowest 206Pb/207Pb ratios were obtained from EDTA extracts, corresponding to weakly bound anthropogenic lead, and the highest 206Pb/207Pb ratios were obtained from total digestion). The combination of total digestion and EDTA extraction (labile lead fraction) seems to be the optimal combination for 206Pb/207Pb ratio determination and optimal result interpretation.

The Pb isotopic composition (206Pb/207Pb and 208Pb/206Pb) in smelter-impacted soils was measured using a quadrupole-based ICP-MS. Four forest/tilled soil profiles were sampled according to the distance from the lead smelter in Príbram (Czech Republic), prevailing wind direction, geological background and soil type. The results were compared with the Pb isotopic composition of bedrocks and waste materials from Pb metallurgy (smelting slags, air-pollution-control residues). The isotopic composition of soils confirms the predominant role of metallurgy on the general pollution in the area. The highly contaminated soils from the vicinity of the smelter contain up to 35,300 mg Pb kg(-1) and exhibit an isotopic composition close to that of car battery processing (206Pb/207Pb up to 1.177). A coupled concentration/isotopic study of soil profiles showed that the smelter-induced pollution had penetrated even to the mineral soil horizons, indicating an important vertical mobility of Pb contaminant within the soil profile. The calculated downward penetration rate of Pb in soils ranges from 0.3 to 0.36 cm year(-1).