Pollution of environment is one of the most horrible ecological crisis to which we are subjected today. One of the main sources of pollution in the
environments is metallic compounds. Metals and metalloids have long been mined and used in numerous applications. This has led to a significant
increase of metal pollutions. Metals can accumulate in all environmental matrices at either high or trace levels of concentration. Heavy metals are
naturally occurring elements that have a high atomic weight and a density. Therefore amount of various kinds of metals are present in soil, plants,
air, lakes, animals, oceanic regions, even in foodstuffs and human beings. Their widespread distribution, especially heavy metals, became serious
problems because of their toxicities for animals, human health and the environment. Their toxicity of heavy metals depends on several factors
including the dose, route of exposure and chemical species, as well as the age, gender, genetics and nutritional status of exposed individuals.
Because of their high degree of toxicity, lead, cadmium, chromium, zinc, nickel, arsenic and mercury rank among the priority metals that are of
public health significance. Metals generally enter in the ecosystem in a relatively non-toxic form and generally become intrinsic components
of the environment in such a way that it is difficult to remove them from the environment. Some of them are converted into toxic forms through
the environmental reactions involving various micro-organisms and non-biological pathways. For example, methylated compounds like dimethyl
mercury, (CH3)2Hg, are more toxic than their inorganic forms. In the present investigation more attention has been given to heavy metals like lead,
cadmium, nickel and zinc. Although, the term “heavy metals” refer to any metallic element that has a relatively high density and is toxic or poisonous
at low concentrations. Examples of heavy metals include Pb, Cd, Hg, As, Cr and Ti etc. This review provides an analysis of their environmental
occurrence, production and use, potential for human exposure and molecular mechanisms of toxicity, genotoxicity and carcinogenicity.