Definition

Chromium is a hard steel-gray metal that is highly resistant to oxidation, even at high temperatures. It is the sixth most abundant element in the earth's crust, where it is combined with iron and oxygen in the form of chromite ore.

Uses

Chromium is used in three basic industries

• metallurgical,
• chemical, and
• refractory (heat-resistant applications).

These industries are the most important industrial sources of chromium in the atmosphere [EPA 1998; ATSDR 2000].
In the metallurgical industry, chromium is an important component of stainless steels and various metal alloys. Metal joint prostheses made of chromium alloys are widely used in clinical orthopedics.
In the chemical industry, chromium is used

• primarily in
  • chrome plating,
  • leather tanning,
  • paint pigments (chromium compounds can be red, yellow, orange, and green), and
  • wood treatment;
• smaller amounts in
  • catalysts,
  • copy machine toner,
  • corrosion inhibitors,
  • drilling muds,
  • magnetic tapes,
  • photographic chemicals,
  • safety matches, and
  • water treatment.

Refractory uses of chromium include magnesite-chrome firebrick for metallurgical furnace linings and granular chromite for various other heat-resistant applications.

Different Valence States

Chromium exists in a series of oxidation states from -2 to +6 valence. The most important stable states are 0 (elemental metal), +3 (trivalent), and +6 (hexavalent).

Chromium in chromite ore is in the trivalent state; industrial processes also produce the elemental metal and hexavalent chromium.

The health effects of chromium are primarily related to the valence state of the metal at the time of exposure. Trivalent (Cr[III]) and hexavalent (Cr[VI]) compounds are thought to be the most biologically significant. Cr(III) is an essential dietary mineral in low doses. Cr(VI) compounds are carcinogenic. Cr(VI) is generally considered 1,000 times more toxic than Cr(III) [EPA 1998; ATSDR 2000; Dayan and Paine 2001].

Essential Dietary Nutrient

Cr(III) is an essential dietary nutrient. It is required to potentiate insulin and for normal glucose metabolism. Cr(III) deficiency has been associated with

• cardiovascular disease,
• decreased lean body mass,
• decreased sperm count,
• elevated percent body fat,
• fasting hyperglycemia,
• glucosuria,
• impaired fertility,
• impaired glucose tolerance, and
• maturity-onset diabetes.

Cr(III) is found in most fresh foods and drinking water. Dietary sources rich in Cr(III) include

• breads,
• cereals,
• fish,
• fresh vegetables,
• meats, and
• spices.

Other significant sources of Cr(III) are mineral supplements, brewer's yeast, and beer.

The National Academy of Sciences has established a safe and adequate daily intake for Cr(III) in adults of 50-200 micrograms per day. On the average, adults in the United States take in an estimated 60-80 micrograms of Cr(III) per day in food. Therefore, many people's diets may not provide enough Cr(III) [ATSDR 2000].

The biologically active form of an organic Cr(III) complex, often referred to as glucose tolerance factor (GTF), is believed to function by facilitating the interaction of insulin with its cellular receptor sites. Studies have shown that the Cr(III) supplementation in deficient and marginally deficient subjects can result in the rapid reversal of many of the symptoms of chromium-deficiency [Cohen, Kargacin et al. 1993; Mertz 1993].

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