Abstract
Distribution and bioavailability of selected heavy metals (Pb, Cr, Cu, Ni, Zn) were investigated in subsurficial and topsoil samples from 21 sites of southeastern Po Plain. Determination of total metal contents, performed by XRF analysis, allowed identification of natural versus anthropogenic metal concentrations. EDTA extraction procedures were utilized in order to evaluate metal bioavailability.
Despite their variable, and locally very high, natural concentrations, Cr and Ni do not show remarkable enrichments from subsurficial to topsoil samples, suggesting lack of significant anthropogenic influence. By contrast, Cu and, to a lesser extent, Pb display widespread anomalies throughout the study area. Zn has an intermediate behaviour.
Metal bioavailability is proportional to metal excess, suggesting that metals of anthropogenic origin are weakly bound to soil substrate. Where no anomalies are recorded, such as in the case of Cr and Ni, metal bioavailability is very low (less than 10 ppm) regardless of total metal concentration, indicating stronger bindings of chemical elements within soil matrix. Among the metals that show anthropogenic enrichments, Cu appears to be the most bioavailable. Considerably high bioavailable fractions of Pb and Zn are recorded at distinct polluted sites.
Keywords: Bioavailability, Enrichment factor, Heavy metals, Geochemistry, Po Plain