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Chromium Essay

2352 words - 9 pages

Chromium, the seventh most abundant element on earth is a transition metal from group VI-B .It is found in nature as the bound form constituting approximately 0.1 – 0.3 mg.g-1 of the earth’s crust. The name of the element is derived from the Greek word "chroma" meaning color, because many of its compounds are intensely colored. Cr is able to exist in several oxidation states, of which the trivalent Cr (III) and hexavalent Cr (VI) species are the most stable and abundant forms (Zayed & Terry et al., 2003).
The most stable form of chromium is its trivalent oxidation state which is primarily found geologically as chromite (FeCr2O4) (Cervantes et al., 2001). Cr (III) is naturally occurring, whereas Cr (VI) is of anthropogenic origin. This is as a result of the dissolution of chromite and the subsequent oxidation of Cr (III) to aqueous Cr (VI) in the presence of the common manganese mineral, birnessite (Oze et al., 2007). Cr (VI) usually associates with oxygen to form the oxyanions chromate (CrO42-) and dichromate (Cr2O7 2- ). Cr (VI) compounds are highly soluble and therefore mobile within aquatic systems, whereas derivatives of Cr(III) in the forms of hydroxides, oxides and sulphates, are water insoluble and exist mostly bound to organic matter in soils and aquatic systems(Cervantes,C et al.,2001; Zayed & Terry, 2003).
Chromium differs widely in physicochemical properties and biological reactivity with respect to its oxidation states. While Cr (VI) species and dichromate’s are extremely water soluble and mobile in the environment, Cr (III) species are much less soluble and comparatively immobile (Viamajala et al., 2004).

Chromium is an essential micronutrient required for the growth of many microorganisms for the maintenance of normal glucose, cholesterol and fatty acid metabolism (Thacker et al., 2006; Srivastava and Thakur et al., 2006).
The deficiency of chromium has been implicated in impaired insulin action, which can cause glucose intolerance, elevated glucose blood levels, diabetes, elevated cholesterol levels, obesity and heart diseases, as well as other conditions not yet documented. Chromium is considered the cofactor for all the actions of the hormone insulin, primarily the regulation of carbohydrate, protein and fat metabolism. Signs of chromium deficiency are widespread; they tend to be associated with aging, and are consistent with the progressive decline in body and organ content of chromium from birth onward. Chromium deficiency impairs glucose utilization and disturbs protein and lipid metabolism
The biological effect of chromium is highly dependent on its oxidation state. Cr(VI) is highly toxic and has been shown to be a mutagen and carcinogen, whereas Cr(III) is considered to be relatively innocuous, probably due to the inability of Cr(III) to penetrate cells (Cervantes et al., 2001; Codd et al., 2001).Chromate alone does not react with DNA in vitro, however, in the presence of reductants a wide variety of DNA...

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