Hexavalent chromium
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[[Image:Chrom(VI)-oxid.jpg|thumb|An example of a chromium(VI) compound: [[chromium trioxide]]]]'''Hexavalent chromium''' ('''Cr(VI)''') compounds are those which contain the element [[chromium]] in the +6 [[oxidation state]].
[[Chromate]]s, which are Chromium (VI) compounds, are often used as [[pigment]]s for [[photography]], and in [[pyrotechnic]]s, 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 coating]]s. They are used as [[corrosion inhibitor]]s, but due to their high levels of [[toxicity]] they are being replaced by alternatives.
Hexavalent chromium is recognized as a human [[carcinogen]] via inhalation.<ref>{{cite book
| author = IARC
| authorlink = International Agency for Research on Cancer
| title = Volume 49: Chromium, Nickel, and Welding
| origyear = 1990
| url = http://monographs.iarc.fr/ENG/Monographs/vol49/volume49.pdf
| format = PDF
| accessdate = 2006-07-16
| date = 1999-11-05
| id = ISBN 92-832-1249-5
| quote = 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.
}}</ref> 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.
Within the [[European Union]], the use of hexavalent chromium in electronic equipment is largely prohibited by the [[Restriction of Hazardous Substances Directive]].
==Toxicity==
In an organism's [[Cell (biology)|cell]]s, hexavalent chromium undergoes reduction, first to metastable pentavalent chromium, then to trivalent chromium. Trivalent chromium binds to proteins and creates [[hapten]]s 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-[[tanning|tanned]] [[leather]] shoes can cause or exacerbate [[contact dermatitis]].
Hexavalent chromium compounds are [[genotoxic]] [[carcinogen]]s. Chronic inhalation of hexavalent chromium compounds increases risk of [[lung cancer]] ([[lung]]s are especially vulnerable, followed by fine [[capillaries]] in [[kidney]]s and [[intestine]]). It appears that the mechanism of genotoxicity relies on pentavalent or trivalent chromium. According to some researchers, the damage is caused by [[hydroxyl radical]]s, produced during reoxidation of pentavalent chromium by [[hydrogen peroxide]] molecules present in the cell. [[Zinc chromate]] is the strongest carcinogen of the chromates used in industry. Soluble compounds, like [[chromic acid]], are much weaker carcinogens.[http://www.potters.org/subject70884.htm]
In some parts of [[Russia]], pentavalent chromium was reported as one of the factors of incidence of premature [[senility]]. <ref>[http://www.corrosion-doctors.org/Pollution/chromiumtoxicity.htm Chromium Toxicity] on the Corrosion Doctors Web site maintained by Canadian Physical Chemist, Pierre R. Roberge, PhD, P.Eng.</ref>
==Permissible Exposure Limit (PEL or OSHA PEL)==
The OSHA PEL for airborne exposures to hexavalent chromium is 5 µg/m<sup>3</sup> (0.005 mg/m<sup>3</sup>).<ref>[http://www.osha.gov/Publications/OSHA_small_entity_comp.pdf OSHA: Small Entity Compliance Guide for the Hexavalent Chromium Standards]</ref>
==Reaction with Vitamin C==
Researchers have recently reported discovering that [[vitamin C]] reacts inside human lung cells with chromium(VI), causing massive DNA damage. Low doses of chromium(VI), 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.<ref>{{cite press release | publisher = [[Brown University]] | title = Chromium 6: A Killer Compound With An Improbable Trigger | date = 2007-03-12 | url = http://www.brown.edu/Administration/News_Bureau/2006-07/06-115.html}}</ref>
==Chromium(VI) and drinking water==
Hexavalent chromium is the substance against which [[Erin Brockovich]] campaigned. It was found in drinking water in the Southern California town of [[Hinkley, California|Hinkley]]. Chromium(VI) is [[carcinogenic]] in groundwater,<ref>David Blowes, "Tracking Hexavalent Cr in Groundwater," ''Science'' '''295''': 2024 - 25 (Mar. 15, 2002).</ref> and the 0.58 ppm in the groundwater in Hinkley exceeded the Maximum Contaminant Level of 0.10 ppm currently set by the [[United States Environmental Protection Agency]].<ref>[http://www.epa.gov/safewater/dwh/c-ioc/chromium.html U.S. Environmental Protection Agency, Consumer Factsheet on: CHROMIUM.]</ref> A similar case was discovered in 2007 in [[Asopus|Asopos River]], near [[Oinofyta]], [[Greece]] and Brockovich is again focusing on it. <ref>[http://www.brockovichblog.com/2007/08/pollution_flows_in_asopos.html ''Pollution Flows in Asopos''], by Erin Brockovich, published 25 August 2007 in The Brockovich Report, a blog</ref>
==References==
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==External links==
*[http://solutions.3m.com/wps/portal/3M/en_US/OH-ESHexChrom/Hexavalent_Chromium/ 3M US: OSHA Hexavalent Chromium Standard - An overview of the Chromium Six (CrVI) standard]
*[http://www.ehjournal.net/content/5/1/5 ''Environmental Health:'' "Selected science: an industry campaign to undermine an OSHA hexavalent chromium standard"]
*[http://www.defendingscience.org/case_studies/Chromium-Case-Study.cfm Hexavalent chromium], a case study from ''[www.defendingscience.org]''
*[http://www.npi.gov.au/database/substance-info/profiles/25.html Australian National Pollutant Inventory Chromium VI fact sheet]
*[http://www.osha.gov/SLTC/hexavalentchromium/index.html US OSHA Health and Safety Topics: Hexavalent Chromium"]
*[http://www.finishingtodaymag.com/CDA/Articles/Column/acb7e54ec8adc010VgnVCM100000f932a8c0____ Finishing Today - Hexavalent Chromium: how is it affecting you?]
*[http://www.cdc.gov/niosh/topics/hexchrom/ National Institute for Occupational Safety and Health - Hexavalent Chromium]
[[Category:Chromium compounds]]
[[Category:Element toxicology]]
[[Category:IARC Group 1 carcinogens]]
[[Category:Occupational safety and health]]
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