In Situ Immobilization of Heavy Metals in Contaminated Soil Using Two Organic Waste Materials

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Abstract

Heavy metals contamination of soil may present potential risks to humans and the ecosystem. Risk assessment studies have shown the impacts of metals to be associated with the soluble and bio-available fractions of the metals rather than their total content in the soils. This has necessitated a new approach – in situ immobilization - in mitigating heavy metals’ detrimental impacts. In situ immobilization relies on the addition of amendment(s) to a contaminated soil to effect a reduction in heavy metals’ solubility and bioavailability in the soil without the arduous necessity to remove them from the soils. This study explore the utility of two natural wastes materials – rubber sludge (RS) and palm oil mill effluent (POME) – towards immobilization of heavy metals (Zn, Mn, Pb, Cu, Cr, and Cd) in soils. Contaminated soils from automobile workshops in Sapele, Delta State Nigeria, were thoroughly mixed with different doses of organic wastes, and amended samples were incubated for 20 days at ambient temperature before soils samples were analysed for geochemical forms according to procedure describe by Salbu et al. The result suggests that amendments decreases the soluble and bio-available fractions of heavy metals in soils compared to the un-amended control. The apparent order in which these metals were rendered inactive (dormant) was Cd >Pb> Cr > Cu>Mn> Zn with the palm oil mill effluent been relatively more effective than rubber sludge.

Keywords: Bioavailability, Contaminated soil, Heavy metals,In situ immobilization, Organic amendmen

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