Introduction Environmental degradation due to the disposal of industrial and urban wastes generated by human activities has become a major environmental concern. Controlled and uncontrolled disposal of wastes to agricultural soils are responsible for the migration of contaminants into non-contaminated sites [1]. Soil contamination by heavy metals may pose a threat to human health, if the metals enter the food chain [2]. Soil remediation is therefore needed to eliminate risk to humans from these toxic metals [3]. Biosphere pollution by heavy metals and nucleotides was accelerated dramatically during the last few decades due to mining, smelting, manufacturing, treatment of agricultural soils with agrochemicals and soil sludge, etc. Problems associated with the contamination of soil and water such as animal welfare, health, fatalities and disruptions of natural ecosystems are well documented [4]. Heavy metals such as Pb, Cr, As, Cu, Cd, and Hg, being added to our soils through industrial, agricultural and domestic effluents, persist in soils and can either be adsorbed in soil particles or leached into ground water. Human exposure to these metals through ingestion of contaminated food or uptake of drinking water can lead to their accumulation in humans, plants and animals. Lead, copper, zinc and cadmium are also found naturally in soils and they can cause significant damage to environment and

human health as a result of their mobility and solubilities. They can occur in soil and water in several forms and their speciation in soils are determined by sequential extraction using specific extractants, which solubilize different phases of metals [5]. The physical and chemical characteristics of soil determine the speciation and mobility of heavy metals [6].