Hexavalent chromium

From Wikipedia, the free encyclopedia

A Hexavalent chromium compound: Chromium(VI)-oxide

Hexavalent chromium or Cr(VI) compounds are those which contain the element chromium in the +6 oxidation state. Chromates are often used as pigments for photography, and in pyrotechnics, dyes, paints, inks, and plastics. They can also be used for stainless steel production, textile dyes, wood preservation, leather tanning, and as anti-corrosion and conversion coatings. They are used as corrosion inhibitors, however due to their toxicity they are being replaced by alternatives.

Hexavalent chromium is recognized as a human carcinogen.^[1] Workers in many different occupations are exposed to hexavalent chromium. Occupational exposures occur mainly among workers who:

handle dry chromate-containing pigments
spray chromate-containing paints and coatings
operate chrome plating baths
weld or cut chromium-containing metals such as stainless steel.

1 Toxicity
2 Erin Brockovich
3 References
4 External links

[edit] Toxicity

Hexavalent chromium in contact with skin acts as both sensitizer and irritant. After entering the organism, it gets reduced to trivalent chromium, which then binds to proteins and creates haptens which trigger immune system reaction. Once developed, chrome sensitivity becomes fairly persistent; in such cases, even contact with chromate-dyed textiles or wearing of chromate-tanned leather shoes can cause or exacerbate contact dermatitis.

Hexavalent chromium compounds are carcinogens. Chronic inhalation of such compounds increases risk of lung cancer. Zinc chromate is the strongest carcinogen of the chromates used in industry. Soluble compounds, like chromic acid, are much weaker carcinogens.

Hexavalent chromium is genotoxic. It appears that the mechanism of genotoxicity relies on pentavalent or trivalent chromium, an intracellular reduction product of hexavalent chromium after its penetration into the cell. According to some researchers, the damage is caused by hydroxyl radicals, produced during reoxidation of pentavalent chromium by hydrogen peroxide molecules present in the cell. [1]

In an organism, hexavalent chromium undergoes reduction, first to metastable pentavalent chromium, then to trivalent chromium. Pentavalent chromium is a known carcinogen. If the material gets lodged in tissues (lungs are especially vulnerable here, followed by fine capillaries in kidneys and intestines), its long-term action may lead to cancerous growth. In some parts of Russia, pentavalent chromium was reported as one of the factors of incidence of premature senility. [2]

[edit] Erin Brockovich

Hexavalent chromium is the substance against which Erin Brockovich campaigned. It was found in drinking water in the Southern California town of Hinkley.

[edit] References

^ IARC [1990] (1999-11-05). Volume 49: Chromium, Nickel, and Welding (PDF). ISBN 92-832-1249-5. Retrieved on 2006-07-16. “There is sufficient evidence in humans for the carcinogenicity of chromium[VI] compounds as encountered in the chromate production, chromate pigment production and chromium plating industries.”