Mobility and bioavailability of heavy metals in selected soils of Iowa and Nigeria

Environmental pollution due to release of heavy metals from various sources is a widespread problem throughout the world. This research was conducted to investigate the behavior of heavy metals released to soils from sewage-sludge application and ore mining. The distribution, chemical forms, bioavailability and microenvironment of Zn, Cu, Pb, and Ni in sewage-sludge-amended Ultisols from southeastern Nigeria, and Pb and Zn in Alfisols of an abandoned mine in northeast Iowa, were investigated using field studies and microanalytical techniques to complement standard bulk analytical methods. After 37 years of sludge amendment, the soil chemical properties had changed enough to wan-ant a reclassification of the Nigerian soil from an Ultisol to an Alfisol. High contents of Zn and Cu and low contents of Pb and Ni in the amended soil compared to a control soil reflected the concentrations of the metals in the sludge. Enrichment of Zn and Cu down the profile indicated that metals had moved from the zone of incorporation. At the abandoned Pb and Zn mine in Iowa, mining influenced pedogenesis in the immediate mining areas and resulted in redistribution of Pb in the soils. Pb was localized mainly in Fe oxide nodules and in residual fractions. The native vegetation had taken up more Pb and Zn at the contaminated site than at the control site. DTPA, total metal content and sequential extractions were strongly correlated with plant uptake of Zn, but none of the extractions showed a conclusive linear relationship with plant uptake of Pb. Pedological approaches offers great possibilities for assessing heavy metal problems in soils.