1.1 BACKGROUND OF THE STUDY
Metals are substances with high electrical conductivity,malleability, and luster, which voluntarily lose their electrons to form cations. Metals are found naturally in the earth’s crust and their compositions vary among different localities, resulting in spatial variations of surrounding concentrations. The metal distribution in the atmosphereis monitored by the properties of the given metal and by various environmental factors (Khlifi & Hamza-Chaffai,2010).
Heavy metals are generally referred to as those metals which possess a specific density of more than 5 g/cm3 and adversely affect the environment and living organisms (Järup, 2003).Environmental pollution has become an extensive and dangerous problem as a consequence of industrial and human activities. Widespread low to high pollution of large areas of agricultural land is a particular problem from indiscriminate sludge discharge from industries, crude oil pollution, and wastes (Ogboi, 2012).
Human activities have dramatically changed the balance of biochemical and geological cycles of many heavy metals. An assessment of environmental risk caused by soil contamination is especially important for agricultural as well as non-cultivated areas due to the fact that metals potentially harmful to human health persist in soils for a relatively long time and may transfer into the food chain in considerable amounts (Radmila et al., 2013). The persistent nature of heavy metals in soil due to their non-biodegradability raises environmental concerns because of the interdependence between plants and animals,including humans in the ecosystem (Agbogidi, 2014).