CONICET | Buscador de Institutos y Recursos Humanos

Soil pollution by heavy metals, particularly lead, is an important environmental concern; the bioavailability of such pollutantsis strongly dependent on their chemical form. Here, the speciation of Pb(II) in soil fractions as a function of time shortlyafter its incorporation is studied, using a selective sequential extraction method. The sample came from an ArgentineanPampas region and was extensively characterised, including Rietveld analysis of the silt+clay fraction XRD pattern to findthe major mineral components. Experiments were run twice, once in the winter and once in the summer. The results showdifferent speciation time profiles in both cases, showing faster changes in winter due to the higher water content. Thesummer experiment corresponds to an earlier stage in the speciation profile evolution compared with winter. The soluble/exchangeable fraction decreases with time in summer but shows a lower and constant value in the winter. A high proportionis found to be adsorbed onto the stable (aluminosilicates+quartz) mineral fraction. The results strongly suggest that, even ata short time following soil pollution with Pb, a high proportion is adsorbed onto the mineral fraction, with only a low fractionbeing bioavailable. The most stable (mineral incorporated) form is observed to increase with time. Soil water content appearsto be more important than temperature in determining the differences between the two.