Hexavalent chromium

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A Hexavalent chromium compound: Chromium(VI)-oxide
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, but due to their toxicity they are being replaced by alternatives.

Hexavalent chromium is recognized as a human carcinogen via inhalation.[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, cut or grind chromium-containing metals such as stainless steel.

Contents

[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] Permissible Exposure Limit (PEL or OSHA PEL)

The OSHA PEL for Hexavalent Chromium is 5 µg/m3 (0.005 mg/m3).[2]

[edit] Vitamin C

Researchers have recently reported discovering that vitamin C reacts inside human lung cells with chromium 6, causing massive DNA damage. Low doses of chromium 6, combined with vitamin C, produce up to 15 times as many chromosomal breaks and up to 10 times more mutations, compared with cells lacking vitamin C. Outside cells, vitamin C actually protects against the cellular damage caused by hexavalent chromium. [3]

[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. Michael Fumento claims the scientific evidence doesn't back her up.[3]

[edit] References

  1. ^ 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.” 
  2. ^ OSHA: Small Entity Compliance Guide for the Hexavalent Chromium Standards
  3. ^ Fumento, Michael. "'Erin Brockovich,' Exposed", The Wall Street Journal, Dow Jones & Company, Inc., 2000-03-28. Retrieved on 2007-03-11.

[edit] External links

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