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Chromium

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Introduction

Chromium is a naturally occurring element found in rocks, animals, plants, soil, and in volcanic dust and gases. Chromium is present in the environment in several different forms. The most common forms are chromium(0), trivalent [or chromium(III)], and hexavalent [or chromium(VI)]. Chromium(III) occurs naturally in the environment and is an essential nutrient required by the human body to promote the action of insulin in body tissues so that sugar, protein, and fat can be used by the body. Chromium(VI) and chromium(0) are generally produced by industrial processes. No known taste or odor is associated with chromium compounds. The metal chromium, which is the chromium(0) form, is a steel-gray solid with a high melting point. It is used mainly for making steel and other alloys. The naturally occurring mineral chromite in the chromium(III) form is used as brick lining for high-temperature industrial furnaces, for making metals and alloys (mixtures of metals), and chemical compounds. Chromium compounds, mostly in chromium(III) and chromium(VI) forms, produced by the chemical industry are used for chrome plating, the manufacture of dyes and pigments, leather tanning, and wood preserving. Smaller amounts are used in drilling muds, rust and corrosion inhibitors, textiles, and toner for copying machines.

Fate & Transport

Chromium enters the air, water, and soil mostly in the chromium(III) and chromium(VI) forms as a result of natural processes and human activities. Emissions from burning coal and oil, and steel production can increase chromium(III) levels in air. Stainless steel welding, chemical manufacturing, and use of compounds containing chromium(VI) can increase chromium(VI) levels in air. Waste streams from electroplating can discharge chromium(VI). Leather tanning and textile industries as well as those that make dyes and pigments can discharge both chromium(III) and chromium(VI) into waterways. The levels of both chromium(III) and chromium(VI) in soil increase mainly from disposal of commercial products containing chromium, chromium waste from industry, and coal ash from electric utilities.

In air, chromium compounds are present mostly as fine dust particles. This dust eventually settles over land and water. Rain and snow help remove chromium from air. Chromium compounds will usually remain in the air for less than 10 days. Although most of the chromium in water binds to dirt and other materials and settles to the bottom, a small amount may dissolve in the water. Soluble chromium compounds can remain in water for years before settling to the bottom. Fish do not accumulate much chromium in their bodies from water. Most of the chromium in soil does not dissolve easily in water and can attach strongly to the soil. A very small amount of the chromium in soil, however, will dissolve in water and can move deeper in the soil to underground water. The movement of chromium in soil depends on the type and condition of the soil and other environmental factors.

Exposure Pathways

You can be exposed to chromium by breathing air, drinking water, or eating food containing chromium or through skin contact with chromium or chromium compounds. The level of chromium in air and water is generally low. The concentration of total chromium in air [both chromium(III) and chromium(VI)] generally ranges between 0.01 and 0.03 microgram (ug) per cubic meter of air (ug/m3). Chromium concentrations in drinking water [mostly as chromium(III)] are generally very low, less than 2 parts of chromium in a billion parts of water (ppb). Contaminated well water may contain chromium(VI). For the general population, eating foods that contain chromium is the most likely route of chromium exposure. Chromium(III) occurs naturally in many fresh vegetables, fruits, meat, yeast, and grain. Various methods of processing, storage, and preparation can alter the chromium content of food. Acidic foods in contact with stainless steel cans or cooking utensils might contain higher levels of chromium because of leaching from stainless steel. Refining processes used to make white bread or sugar can decrease chromium levels. Chromium(III) is an essential nutriet for humans. On the average, adults in the United States take in an estimated 60 ug of chromium daily from food. You may also be exposed to chromium from using consumer products such as household utensils, wood preservatives, cement, cleaning products, textiles, and tanned leather.

People who work in industries that process or use chromium or chromium compounds can be exposed to higher-than-normal levels of chromium. An estimated 305,000 workers in the United States are potentially exposed to chromium and chromium-containing compounds in the workplace.

Occupational sources of chromium exposure (with chemical forms of interest shown in parentheses) may occur in the following industries:

· Stainless steel welding [chromium(VI)]

· Chromate production [chromium(VI)]

· Chrome plating [(chromium(VI)]

· Ferrochrome industry [chromium(III) and chromium(VI)]

· Chrome pigments [chromium(III) and chromium(VI)]

· Leather tanning [mostly chromium(III)]

Examples of other occupations that may involve chromium exposure include:

· Painters [chromium(III) and chromium(VI)]

· Workers involved in the maintenance and servicing of copying machines, and the disposal of some toner powders from copying machines [chromium(VI)]

· Battery makers [chromium(VI)]

· Candle makers [chromium(III) and chromium(VI)]

· Dye makers [chromium(III)]

· Printers [chromium(III) and chromium(VI)]

· Rubber makers [chromium(III) and chromium(VI)]

· Cement workers [chromium(III) and chromium(VI)]

You may be exposed to higher-than-normal levels of chromium if you live near the following:

· Landfill sites with chromium-containing wastes

· Industrial facilities that manufacture or use chromium and chromium-containing compounds

· Cement-producing plants, because cement contains chromium

· Industrial cooling towers that use chromium as rust inhibitors

· Waterways that receive industrial discharges from electroplating, leather tanning, and textile industries

· Busy roadways, because emissions from automobile brake lining and catalytic converters contain chromium

In addition, you may be exposed to higher levels of chromium if you use tobacco products, since tobacco contains chromium.

Metabolism

Chromium can enter your body when you breathe air, eat food, or drink water containing chromium. Chromium(VI) enters the body more easily than chromium(III), but once inside the body, chromium(VI) is changed to chromium(III). When you breathe air containing chromium, chromium particles can be deposited in the lungs. Particles that are deposited in the upper part of the lungs are likely to be coughed up and swallowed. Particles deposited deep in the lungs are likely to remain long enough for some of the chromium to pass through the lining of the lungs and enter your bloodstream. Once in the bloodstream, chromium is distributed to all parts of the body, then will pass through the kidneys, and be eliminated in the urine within a few days. Everyone normally eats or drinks a small amount of chromium daily. Most of the chromium that you swallow leaves your body within a few days through the feces and never enters your blood. A small amount (about 0.4 to 2.1 percent) will pass through the lining of the intestines and enter the bloodstream. Once in the bloodstream, chromium is distributed to all parts of the body where it is used to carry out essential functions. Chromium will then pass through the kidneys and be eliminated in the urine in a few days. Chromium(III) present in food can attach to other compounds that make it easier from chromium to enter your bloodstream from your stomach and intestines. This form of chromium is used by your body to carry out essential body functions. If your skin comes into contact with chromium, very little will enter your body unless your skin is damaged.

Health Effects

Chromium(III) is an essential nutrient that helps the body use sugar, protein, and fat. An intake of 50 to 200 ug of chromium(III) per day is recommended for adults. On the average, adults in the United States take in an estimated 60 ug of chromium per day in food. Therefore, most people in the United States take in enough chromium(III) in the food they eat, but some people's diets may not provide enough chromium(III). Without chromium(III) in the diet, the body loses its ability to use sugars, proteins, and fat properly, which may result in weight loss or decreased growth, improper function of the nervous system, and a diabetic-like condition.

The health effects resulting from exposure to chromium(III) and chromium(VI) are fairly well described in the literature. Breathin in high levels (greater than 2 ug/m3) of chromium(VI) can cause irritation to the nose, such as runny nose, sneezing, itching, nosebleeds, ulcers, and holes in the nasal septum. These effects have primarily occurred in factory workers who make or use chromium(VI) for several months to many years. Long-term exposure to chromium has been associated with lung cancer in workers exposed to levels in air that were 100 to 1,000 times higher than those found in the natural environment. Lung cancer may occur long after exposure to chromium has ended. It is not clear which form(s) of chromium is capable of causing lung cancer in workers. Chromium(VI) is believed to be primarily responsible for the increased lung cancer rates observed in workers who were exposed to high levels of chromium in workroom air. Breathing in small amounts of chromium(VI) for short or long periods does not cause a problem in most people. However, high levels of chromium in the workplace have caused asthma attacks in people who are allergic to chromium.

Breathing in chromium(III) does not cause irritation to the nose or mouth in most people. In the same way, small amounts of chromium(VI) that you swallow will not hurt you; however, accidental or intentional swallowing of larger amounts have caused stomach upsets and ulcers, convulsions, kidney and liver damage, and even death. The levels of chromium(VI) that caused these effects are far greater than those that you might be exposed to in food or water. Although chromium(III) in small amounts is an important nutrient needed by the body, swallowing large amounts of chromium(III) may cause health problems. Workers handling liquids or solids that have chromium(VI) in them have developed skin ulcers. Some people have been found to be extremely sensitive to chromium(VI) or chromium(III). Allergic reactions consisting of severe redness and swelling of the skin have been noted. Exposure to chromium(III) is less likely than exposure to chromium(VI) to cause skin rashes in chromium-sensitive people. The metal, chromium(0), is less common, and we do not know much about how it affects your health. We have no reliable information that any form of chromium has harmful effects on reproduction or causes birth defects in humans.

In animals that breathed high levels of chromium, harmful effects on the respiratory system and a lower ability to fight disease were noted. However, we do not know if similar effects could occur in humans or if chromium can lower a person's ability to fight disease. Some of the female mice that were given chromium(VI) by mouth had fewer offspring and had offspring with birth defects. Some male mice that were given chromium(VI) or chromium(III) by mouth had decreased numbers of sperm in the testes. The birth defects or the decrease in sperm occurred in mice at levels about several thousand times higher than the normal daily intake by humans. Some chromium(VI) compounds produced lung cancer in animals that breathed in the particles or had the particles placed directly in their lungs. In animals that were injected with some some chromium(VI) compounds, tumors formed at the site of the injection.

Because some chromium(VI) compounds have been associated with lung cancer in workers and caused cancer in animals, the Department of Health and Human Services has determined that certain chromium(VI) compounds (calcium chromate, chromium trioxide, lead chromate, sodium dichromate, strontium chromate, and zinc chromate) are known carcinogens. The International Agency for Research on Cancer (IARC) has determined that chromium(VI) is carcinogenic to humans, based on sufficient evidence in humans for the carcinogenicity of chromium(VI) compounds as found in chromate production, chromate pigment production, and chromium plating industries. IARC's determination is also based on sufficient evidence in experimental animals for the carcinogenicity of calcium chromate, zince chromate, strontium chromate, and lead chromate; and limited evidence in experimental animals for the carcinogenicity of chromium acid and sodium dichromate. IARC has also determined that chromium(0) and chromium(III) compounds are not classifiable as to their carcinogenicity to humans.

Information excerpted from:

Toxicological Profile for Chromium

Agency for Toxic Substances and Disease Registry
U.S. Dept. of Health and Human Services