|Classification and external resources|
Chromium toxicity refers to the fact that chromium is toxic.
Water-insoluble chromium(III) compounds and chromium metal are not considered a health hazard, while the toxicity and carcinogenic properties of chromium(VI) have been known for a long time. An investigation into hexavalent chromium release into drinking water was the basis of the true story of Erin Brockovich, dramatised as Erin Brockovich (film).
Because of the specific transport mechanisms, only limited amounts of chromium(III) enter the cells. Several in vitro studies indicated that high concentrations of chromium(III) in the cell can lead to DNA damage. Acute oral toxicity ranges between 1900 and 3300 µg/kg. The proposed beneficial effects of chromium(III) and its use in dietary supplements yielded some controversial results, but recent reviews suggest that moderate uptake of chromium(III) through dietary supplements poses no risk.
The World Health Organization-recommended maximum allowable concentration in drinking water for chromium (VI) is 0.05 milligrams per litre. Hexavalent chromium is also one of the substances whose use is restricted by the European Restriction of Hazardous Substances Directive.
The LD50 for chromium(VI) ranges between 50 and 150 mg/kg. In the body, chromium(VI) is reduced by several mechanisms to chromium(III) already in the blood before it enters the cells. The chromium(III) is excreted from the body, whereas the chromate ion is transferred into the cell by a transport mechanism, one by which sulfate and phosphate ions also enter the cell. The acute toxicity of chromium(VI) is due to its strong oxidative properties. After it reaches the bloodstream, it damages blood cells by oxidation reactions. Hemolysis, and subsequently kidney and liver failure, are the results of this damage. Aggressive dialysis can improve the situation.
The carcinogenity of chromate dust has been known for a long time, and in 1890 the first publication described the elevated cancer risk of workers in a chromate dye company. Three mechanisms have been proposed to describe the genotoxicity of chromium(VI). The first mechanism includes highly reactive hydroxyl radicals and other reactive radicals which are byproducts of the reduction of chromium(VI) to chromium(III). The second process includes the direct binding of chromium(V), produced by reduction in the cell, and chromium(IV) compounds, to the DNA. The last mechanism attributes the genotoxicity to the binding to the DNA of the end product of the chromium(III) reduction.
Chromium salts (chromates) are also the cause of allergic reactions in some people. Chromates are often used to manufacture, among other things, leather products, paints, cement, mortar, and anti-corrosives. Contact with products containing chromates can lead to allergic contact dermatitis and irritant dermatitis, resulting in ulceration of the skin, sometimes referred to as "chrome ulcers". This condition is often found in workers that have been exposed to strong chromate solutions in electroplating, tanning and chrome-producing manufacturers.
As chromium compounds were used in dyes and paints and the tanning of leather, these compounds are often found in soil and groundwater at abandoned industrial sites, now needing environmental cleanup and remediation per the treatment of brownfield land. Primer paint containing hexavalent chromium is still widely used for aerospace and automobile refinishing applications.
Monitoring excessive human exposure
Overexposure to chromium can occur in welders and other workers in the metallurgical industry, persons taking chromium-containing dietary supplements, patients who have received metallic surgical implants, and individuals who ingest chromium salts. Chromium concentrations in whole blood, plasma, serum or urine may be measured to monitor for safety in exposed workers, to confirm the diagnosis in potential poisoning victims, or to assist in the forensic investigation in a case of fatal overdosage.
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