ABSTRACT
Chromium is a naturally occurring transition metal that is an essential nutrient in its trivalent oxidation state, but a toxicant in its hexavalent state. It has been shown to be a carcinogen by the U.S. National Toxicology Program (NTP), and its concentration in drinking water is regulated by the U.S. Environmental Protection Agency (EPA). High concentrations of Cr(VI) in natural waters are usually derived from industrial Cr-containing wastes, or possibly from the oxidation of certain forms of Cr(III) in soils or sediments. Chromite ore (FeO.Cr2O3) is roasted under alkaline, high-temperature conditions to oxidize Cr2O3) to soluble Cr(VI), which is used as a starting material for production of stainless steel, pressure-treated lumber, chrome-tanned leather, pigments, chrome-plated metals, and other common products used in modern societies. Cr(VI) remaining in industrial by-products, such as chromite ore processing residue, chrome plating bath waste, paint aerosols, and other industrial wastes, may enrich soils and contaminate surface waters and groundwater that are water supplies for domestic uses, irrigation, and industrial processes.
