Metals are a unique class of toxicants that occur naturally and persist in nature, but their chemical forms may be changed because of physicochemical, biological, or anthropogenic activities. Their toxicity may be markedly altered as these elements assume different chemical forms. Most metals are of 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, others 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.