Sources of heavy metals:
Xenobiotics are those which are foreign to biological systems,originated either by biogenic or anthropogenic activities, (Kapri et al., 2011). Metals stand at prior position among xenobiotics, playing a pivotal role in the development of human civilizations. They pose severe threat to all sorts of life forms due to their improper management and extensive use.
Heavy metals are group of metals whose atomic density is greater than 5 g/cm (Gadd, 1992). Heavy metals exists in nature in soils, rocks, water and biota at low concentration, having deleterious effect on all kind of organism (Nies, 2003). All heavy metals, including those, that are essential micronutrients (e.g. copper, zinc, etc.), are toxic at high concentrations. Some of these elements are actually necessary for humans in minute amounts (cobalt, copper, chromium, manganese, nickel) while others are carcinogenic or toxic, affecting central nervous system (manganese, mercury, lead, arsenic), the renal/liver (mercury, lead, cadmium, copper) skin, bones or teeth (nickel, cadmium, copper, chromium) (Zevenhoven and Kilpinen, 2001).
Usage of lead acetate for sweeting of wine, in building materials, pigments for glazing ceramics, and in water transporting pipes defines its intervention with mankind at least for 5000 years. In addition usage of mercury in treating syphilis and cadmium pigment by Claude Monet a French impressionist painter shows the negligence on the management and ignorance in usage of metal ions from early dates of human civilization (L Järup, 2003) with all these, addition of hexavalent chromium enormously in to the ecosystem (Lauwerys et al. 2007 & Marsh and McInerney 2001 in Mechanisms of Hexavalent Chromium Resistance and Removal by Microorganisms) highlights the continued mismanagement of toxic heavy metal like lead, cadmium, mercury and chromium even after understanding their effects on human health and ecosystem.
Heavy metal pollution of biosphere has accelerated dramatically since the beginning of the industrial revolution. As a result of human activities such as mining and smelting of metals, electroplating, gas exhaust, energy and fuel production, fertilizer, sewage and pesticide application and municipal waste generation.