CHAPTER ONE
INTRODUCTION
Heavy metals are found naturally in undisturbed soils and, in fact, small amounts of many metals are required by plants to remain healthy. Metals found in waste dumps exist in various forms either as the pure metal or alloyed with
various other metals. Heavy metals impairing the quality of our environment come from various sources that can be categorized into urban-industrial aerosols, liquid and solid wastes from animal and man, mining and industry and agricultural chemicals (Gerard, 1996; Ideriah et al., 2010). Heavy metals are largely present in e-wastes, especially Cu used for wires, and also Cr, Ni, Zn, Cd, and Hg as well as many other metals and rare-earth elements. Because of high air emissions or liquid leaking, significant amounts of metals are concentrated in landfills or dispersed in the environment despite recycling (Robinson, 2009). The labile fraction of particle-bound metals is considered to be more readily available to environmental receptors and hence possesses greater environmental risk than the resistant fraction. (Adamson et al.,2000; X.D. Feng et al.,2009). Soil has the ability to immobilize chemicals like heavy metals in any form introduce to it. The immobilization of xenobiotics are mainly due to sorption properties which are determined by physicochemical properties of the soil such as: amount of clay and organic fraction, pH, water content, temperature of the soil and properties of the particular metal ion (Dube et al.,2000). The most important heavy metals with regard to potential hazards and occurrence in contaminated soils are: arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), lead (Pb), antimony (Sb), molybdenum (Mo) and zinc (Zn) (Asio, 2007). Asio, (2007) further stated that the sources of heavy metal pollutants are metal mining, metal smelting, metallurgical industries, and other metal-using industries, waste disposal, corrosion of metals in use, agriculture and forestry, fossil fuel combustion, and sports and leisure activities. Heavy metals may be found in water, soil, sediments and plants in divers amounts this may be as a result of natural or anthropogenic. Chemicals found in the environment may contain some amounts of heavy metals and this may be absorbed by the components of the soil profile. The mechanism by which the heavy metals are transported through the soil profile has long presented great interest to both environmental and soil scientists because of the possibility of groundwater contamination through metal leaching. The protection of soils is and should be a principal objective of environmental policy makers to prevent pollution of soils.
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