**2. Sources of environmental contamination**

Heavy metals contamination of environment can come both from natural sources and from anthropogenic processes. Natural emissions of heavy metals include volcanic eruptions, rock weathering, sea-salt sprays, forest fires, biogenic sources, windborne soil particles and can be found in the nature as oxides, hydroxides, silicates, sulphates, sulphides, phosphates, organic compounds [4].

Anthropogenic processes which can release heavy metals in different environmental compartments, are industries, agriculture (insecticides, pesticides which can release As), fossil fuels combustion (Ni, V, Hg, Se, Sn), wastewater, mining, smelting (As, Cu, Zn), corrosion, metallurgical processes, residual organic matter, transportation (Pb) [4, 7, 16].
