Biologically Essential and Non-Essential Elements Causing Toxicity in Environment

This paper encompasses the toxicity of abundant and trace elements present on the earth. Generally, the less abundant elements are more toxic. But even the biologically essential elements become toxic above a critical concentration. The synergistic influence of a metal on toxicity of another is also discussed for mercury selenium and zinc-cadmium pairs. A general observation is made that for biologically important elements a single oxidation states are considerably more toxic. It is known that some elements viz., C, H, O, Na, K, N, P, S, Mg, Ca, Cl are major essentials for life and B, F, Si, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Se, Mo, Sn and I are the trace elements essential for life. Cr (III) for example is essential for glucose and lipid metabolism, Mn(II) is a co-factor in a number of enzymatic reactions, Fe has major role in haemoglobin formation, Co(II) is a component of vit. B12, NI(II) has been found to be essential for mammals and Mo is an important co-factor for xanthine oxidase and aldehyde oxidase as a consequence of its different oxidation states. A minimum concentration of these elements is essential for proper growth of body, but beyond certain level of concentration these elements also become toxic. The threshold concentration is comparatively higher for the compounds of metals which have some biological function but for other metals (Pb, Cd, Hg, As, Sb etc) the tolerance limit is very low. These metals get accumulated in body because they are not biodegradable.