Chromium and certain chromium compounds are known carcinogens. Long-term exposure of workers to airborne levels of chromium higher than those in the natural environment has been associated with lung cancer. Compounds containing hexavalent chromium - chromium(VI) - is believed to be the major problem when inhaled. Evidence for other chromium compounds is inconclusive. Inhalation exposure to chromium may result in additional adverse effects on the respiratory system and may affect the immune system.
Chromium is a naturally occurring element that is found in soil and in volcanic dust and gases. It is found in the environment in three major states: chromium(0), chromium(III), and chromium(VI). Chromium(III) occurs naturally in the environment, while chromium(VI) and chromium(0) are generally produced by industrial processes. The metal chromium(0) is a steel-grey solid with a high melting point. Chromium is used mainly for making steel and other alloys. In the form of the mineral chromite, it is used by the refractory industry to make bricks for metallurgical furnaces. Chromium compounds produced by the chemical industry are used for chrome plating, the manufacture of pigments, leather tanning, wood treatment, and water treatment.
The three major forms of chromium differ in their effects on health. One major form, hexavalent chromium - chromium(VI) - is irritating and short-term, high-level exposure can result in adverse effects at the site of contact, such as ulcers of the skin, irritation of the nasal mucosa and irritation of the gastrointestinal tract. Chromium(VI) may also cause adverse effects in the kidney and liver. The second major form of chromium, trivalent chromium - chromium(III) - does not result in these effects and is the form that is thought to be an essential food nutrient when ingested in small amounts, although very large doses may be harmful. Chromium in food is mostly trivalent. The third major form is metallic chromium - chromium(0). Exposure to chromium(0) is less common and is not well characterized in terms of levels of exposure or potential health effects.
Chromium is considered to be an essential nutrient that helps to maintain normal metabolism of glucose, cholesterol, and fat in humans. Signs of chromium deficiency in humans include weight loss and impairment of the body's ability to remove glucose from the blood, as measured by the glucose tolerance test. The minimum human daily requirement of chromium for optimal health is not known, but a daily ingestion of 50-200 micrograms (ug) per day (0.0007-0.003 milligram of chromium per kilogram of body weight per day) has been estimated to be safe and adequate. Brewer's yeast and fresh foods are good sources of chromium. Individuals eating diets containing large amounts of highly processed foods, especially white bread and refined sugar, may consume less than the suggested dietary level of chromium. The long-term effects of eating diets low in chromium are difficult to evaluate.
Most chromium enters the body from dietary intake. Some chromium exposure occurs from breathing air and drinking water, but exposure from these sources is normally small compared to intake from food. However, exposure from breathing chromium may increase for people living near industrial sites where chromate is produced or used, and exposure from drinking water may increase due to passage of corrosive water through steel alloy pipes or plumbing containing chromium.
Much higher exposure to chromium occurs to people working in certain chromium industries (occupational exposure) and to people who smoke cigarettes. The two largest sources of chromium emission in the atmosphere are from the chemical manufacturing industry and combustion of natural gas, oil, and coal. Other sources of chromium exposure are as follows: cement-producing plants, since cement contains chromium; the wearing down of asbestos brake linings from automobiles or similar sources of wind-carried asbestos, since asbestos contains chromium; incineration of municipal refuse and sewage sludge; exhaust emission from catalytic converters in automobiles; emissions from air conditioning cooling towers that use chromium compounds as rust inhibitors; waste waters from electroplating, leather tanning, and textile industries when discharged into lakes and rivers; and solid wastes from the manufacture of chromium compounds, or ashes from municipal incineration, when disposed of improperly in landfill sites. Some consumer products that contain small amounts of chromium are: some inks, paints, and paper; some rubber and composition floor coverings; some leather materials; magnetic tapes; stainless steel and a few other metal alloys; and some toner powders used in copying machines. Occupational sources of chromium exposure mainly occur in industries that produce the following: stainless steel products (from welding); chromates (chemicals made from chromium and used in chemical industries); chrome-plated products; ferrochrome alloys; chrome pigments; and leather (from tanning). Examples of additional occupations that have potential for chromium exposure include: painters; workers involved in the maintenance and servicing of copying machines and in the disposal of some toner powders from copying machines; battery makers; candle makers; dye makers; printers; and rubber makers.
In 1994, chromium chemicals were banned as coolants in cooling towers. Around 800 cooling towers at 400 sources were affected.