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.