الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
One of the serious problems in the world is the environmental pollution by heavy metals. The mobilization of heavy metals through extraction from ores and subsequent processing for different applications has led to the release of these elements into the environment. Human activities such as smelting, mining, energy and fuel production electroplating, power transmission, melting operations, agricultural activities, sludge dumping, as well as disturbance of natural biogeochemical cycles with increasing industrialization leads to magnification of heavy metals pollution problems.Heavy metals (HMs) are metals with a density higher than 5 g cm-3, there are 53 HMs from 92 naturally occurring elements, but all of them are not biologically important. Seventeen HMs may be available for living cells and are important for organisms and ecosystem under physiological conditions based on their solubility (Schu¨tzendubel and Polle, 2002). Heavy metals are classified as essential and non-essential regarding to their role in biological systems. Living organisms need essential HMs in minute quantities for vital biochemical and physiological functions. Examples of essential heavy metals are Cu Fe, Mn, Ni and Zn (Cempel and Nikel, 2006). Examples of non-essential heavy metals are As, Cd, Cr, Hg and Pb (Dabonne et al., 2010). Interfere of HMs with the normal functioning of living systems has adverse effects on health of living organisms when their concentration beyond threshold limits.