Speciation of Lead in Contaminated Soils

Lead contaminated soils from various origins were sampled and analyzed for total Pb content, dissolved Pb, soil pH, soil organic matter content and Mo-reactive phosphate in solution. The concentration of free Pb2+ ionic species in solution was determined using differential pulse anodic stripping voltammetry (ASV), assuming that ASV-labile Pb excludes organo–Pb complexes. The dataset shows the solubility relationships between the various soil characteristics for 84 soils covering a wide range of soil properties; pH (3.5 to 8.1), total Pb (10 to 15 000 mg Pb kg−1), dissolved Pb (0.6 to 124 μg Pb litre−1), free Pb2+ activity (10−10.4 to 10−6.8 M) and soil organic matter (4.5 to 108 g C kg-1). Non-linear regression analysis shows that free Pb2+ in soil solution can be predicted simply using the log of total soil Pb and pH with no significant contributions from the soil organic matter content or the concentration of phosphate in solution. In the case of dissolved Pb, log of total Pb, soil pH and solution phosphate are significant parameters, but soil organic matter does not contribute to the regression. About 60–80% of the dissolved Pb is present as organo–Pb complexes, this percentage is lower in soils with low pH or high total Pb content.