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Arsenic is an element widely present in the environment, found in water, air, and soil. It is also released to the environment from such anthropogenic sources as mining wastes, metal smelting, glass manufacture, semiconductor manufacture, pesticides, and herbi- cide production. Several zones around the world exposure to this metalloid are high, and have been associated with skin cancer, diabetes, and peripheral neuropathy, among other pathologies. Arsenic has four oxidation states; the trivalent (arsenite) and pentavalent (arsenate) species are the most important for their known toxic effects. Arsenites bind to the sulfhydryl group of many enzymes such as pyruvate dehydrogenase and succinate dehydrogenase, which are involved in carbohydrate metabolism, while arsenates uncouple the oxidative phosphorylation chain. All these effects of arsenic appear to target the cellular pathways involved in energy production. Inhalation of industrial particulates and ingestion of contaminated foods and drinking water are the major routes for human exposure to inorganic arsenic (As).