Chromium (pronounced /ˈkroʊmiəm/, KROH-mee-əm) is a chemical...

Chromium (pronounced /ˈkroʊmiəm/, KROH-mee-əm) is a chemical element which has the symbol Cr and atomic number 24, first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odourless, tasteless, and malleable. The name of the element is derived from the Greek word "chr¨­ma" (¦Ö¦Ñ¦Ø¦Ì¦Á), meaning color, because many of its compounds are intensely colored. It was discovered by Louis Nicolas Vauquelin in the mineral crocoite (lead chromate) in 1797. Crocoite was used as a pigment, and after the discovery that the mineral chromite also contains chromium this latter mineral was used to produce pigments as well.

Chromium was regarded with great interest because of its high corrosion resistance and hardness. A major development was the discovery that steel could be made highly resistant to corrosion and discoloration by adding chromium and nickel to form stainless steel. This application, along with chrome plating (electroplating with chromium) are currently the highest-volume uses of the metal. Chromium and ferrochromium are produced from the single commercially viable ore, chromite, by silicothermic or aluminothermic reaction or by roasting and leaching processes. Although trivalent chromium (Cr(III)) is required in trace amounts for sugar and lipid metabolism in humans and its deficiency may cause a disease called chromium deficiency, hexavalent chromium (Cr(VI)) is toxic and carcinogenic, so that abandoned chromium production sites need environmental cleanup.
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Hexavalent chromium refers to chemical compounds that contain the element chromium in the +6 oxidation state. Virtually all chromium ore is processed via conversion to sodium dichromate. Approximately 136,000,000 kilograms (300,000,000 lb) of hexavalent chromium were produced in 1985.[1] Other hexavalent chromium compounds are chromium trioxide and various salts of chromate and dichromate. Hexavalent chromium is used for the production of stainless steel, textile dyes, wood preservation, leather tanning, and as anti-corrosion and conversion coatings as well as a variety of niche uses.

Hexavalent chromium is recognized as a human carcinogen via inhalation.[2] Workers in many different occupations are exposed to hexavalent chromium. Problematic exposure is known to occur among workers who handle chromate-containing products as well as those who arc weld stainless steel.[2] Within the European Union, the use of hexavalent chromium in electronic equipment is largely prohibited by the Restriction of Hazardous Substances Directive.
For the Erin Brockovich fans out there the above was what she was fighting against
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contamination of drinking water with hexavalent chromium, also known as chromium(VI), in the southern California town of Hinkley. At the center of the case was a facility called the Hinkley Compressor Station, part of a natural gas pipeline connecting to the San Francisco Bay Area constructed in 1952. Between 1952 and 1966, PG&E used hexavalent chromium to fight corrosion in the cooling tower. The wastewater dissolved the hexavalent chromium from the cooling towers and was discharged to unlined ponds at the site. Some of the wastewater percolated into the groundwater, affecting an area near the plant approximately two miles long and nearly a mile wide.[4] The case was settled in 1996 for $333 million, the largest settlement ever paid in a direct action lawsuit in U.S. history.