1.0 Introduction
Heavy metal refers to any metallic chemical element that has a relatively high density and is toxic or poisonous at low concentration. Example of the heavy metals include; Mercury (Hg), Cadmium (Cd), Arsenic (As), chromium (Cr) etc. Heavy metal contamination of the environment can be caused by parent material in the soil or anthropogenic activities, including fertilization application of pesticides and traffic etc. The level of environmental pollution is a worldwide concern to both the governmental and regulatory bodies that are anxious to prevent further environmental deterioration.
Beside the natural activities, almost all human activities potentially contribute to produce heavy metals as side effects. Furthermore, Migration of these contaminants into non-contaminated areas as dust or leaching through the soil and spreading of heavy metals containing sewage sludge are a few example of events contributing toward contamination of the ecosystem.
Soil may become contaminated by the accumulation of heavy metals and metalloids through emissions from the rapidly expanding industrials areas, mine tailings, disposal of high metal waste, leaded gasoline and paints, land application of fertilizers, animal manures, sewage sludge, pesticide, wastes water irrigation, coal combustion residue, spillage of petrolchemical and atmospheric deposition.
Heavy metals constitute an ill defined group of organic chemical hazards, and those most commonly founded at contaminated sites are chromium, lead, arsenic, zinc, cadmium and mercury etc (Kabata — Pendia and Pendias, 2001).
Soil are the major sink for heavy metal released into the environment by aforementioned anthropogenic activities and unlike organic contaminants which are oxidized to carbon (iv) oxide by microbial action, most metal do not undergo microbial chemical degradation and their total concentration in soils persists for a long time after their introduction.
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