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Chromium (Cr) is an element found naturally in rocks, soil, plants, and animals, including people. It occurs in combination with other elements as chromium salts, some of which are soluble in water. The pure metallic form does not occur naturally. Chromium does not evaporate, but it can be present in air as particles.
Chromium is used to make steel and other alloys, for chrome plating, and as an additive to limit corrosion. Named for its colored compounds, chromium has also been used to make dyes and pigments for paints, make refractory bricks for furnaces, tan leather, and preserve wood.
Chromium is abundant in nature. Its valence states range from -2 to +6, but in natural environments, it is generally found as trivalent chromium [Cr(III)] or hexavalent chromium [Cr(VI)]. Trivalent chromium occurs naturally in many fresh vegetables, fruits, meat, grains, and yeast and is often added to vitamins as a dietary supplement. Hexavalent chromium (CASRN 18540-29-9) is most often produced by industrial processes and may be an indicator of environmental contamination. This form exists in oxidizing conditions and can move down through soil to underlying groundwater. The concentration of naturally occurring chromium in U.S. soils ranges from 1 to 2,000 parts per million (ppm). Hexavalent chromium concentrations in air are generally low because it can react with dust and other air pollutants to form trivalent chromium and can be removed by atmospheric fallout and precipitation. In air, the concentrations generally range between 0.01 and 0.03 microgram per cubic meter (µg/m3). Drinking water levels are generally less than 2 parts per billion (ppb).
Hexavalent chromium can be toxic. When inhaled, it can damage the lining of the nose and throat and irritate the lungs. Based on studies of workers in chromium processing factories, hexavalent chromium is classified as a known human carcinogen due to chronic inhalation exposures. When swallowed, it can upset the gastrointestinal tract and damage the liver and kidneys, however evidence suggests hexavalent chromium does not cause cancer when ingested, most likely because it is rapidly converted to the trivalent form after entering the stomach.
EPA regulates chromium and its compounds under the Clean Air Act, Clean Water Act; Comprehensive Environmental Response, Compensation, and Liability Act; Resource Conservation and Recovery Act; Safe Drinking Water Act, Emergency Planning and Community Right-to-Know Act of 1986; Federal Insecticide, Fungicide, and Rodenticide Act; and Toxic Substances Control Act.
Environmental Impacts of Preservative-treated Wood, 8-11 February 2004, Orlando, Florida [Proceedings]
Florida Center for Environmental Solutions, Gainesville. 387 pp, 2004
These conference papers and abstracts address the impacts of wood-preserving compounds containing chromium, copper, and arsenic on environmental media and biota, human health effects, disposal approaches, and innovative remediation technologies applicable to treated wood waste.
Groundwater Information Sheet: Chromium VI
California State Water Resources Control Board, 8 pp, 2009.
This brief groundwater information sheet provides general information (fate and transport, health effects, testing and remediation methods) and identifies where high levels of the compound are found in California. The information is pulled from a variety of sources, and a bibliography is provided.
State of the Science of Hexavalent Chromium in Drinking Water
McNeill, L., J. McLean, M. Edwards, and J. Parks.
Water Research Foundation (WaterRF). 36 pp, 2012 Update
This review briefly summarizes what is known about Cr(VI) and points out gaps in current knowledge. The review does not cover all aspects of Cr(VI) health effects.
ATSDR Toxicological Profile for Chromium
Agency for Toxic Substances and Disease Registry, 2012