ABSTRACT
Metals are a unique class of toxicants. They occur and persist in nature, but their chemical forms may be changed because of physicochemical, biological, or anthropogenic activities. Their toxicity may be drastically altered as they assume different chemical forms. Most of them have some value to humans because of their varied use in industry, agriculture, or medicine. Some are essential elements, required in various biochemical/physiological functions. On the other hand, they may pose health hazards to the public because of their presence in food, water, or air, and to workers engaged in mining, smelting, and a variety of industrial activities.
