Is used to make bricks and linings for furnaces. Compounds are used for chrome plating (chromic acid), manufacture of dyes (soluble chromates), wood treatment and water treatment.
Substance name: Chromium (VI) compounds
CASR number: 7440-47-3 (Cr metal), 18540-29-9 (Cr (VI))
Molecular formula: Cr6+
Synonyms: Chromium (VI) is an oxidation state of the element chromium. Other common oxidation states of chromium include 0 (the metallic element chromium), and III (the state in which chromium is found in nature. Chromium (III) compounds are dealt with elsewhere in the NPI). Hexavalent chromium compounds (VI) include ammonium dichromate, barium chromate, calcium chromate, chromium trioxide, lead chromate, sodium dichromate, strontium chromate, potassium chromate, potassium dichromate, sodium chromate, and zinc chromate.
Vary widely depending on the particular compound, for example:
Most Cr(VI) compounds are soluble in water, however, barium chromate (a yellow powder with specific gravity = 4.49) and lead chromate (an orange-yellow powder with specific gravity = 6.3) are insoluble in water, and calcium chromate (a yellow powder) is slightly soluble in water. Sodium dichromate is in the form of red to orange crystals, with specific gravity = 2.35, and is soluble in water. Chromic acid (H2CrO4) exists only as salts (e.g. lead chromate, barium chromate) or in solution.
Chromic acid is very reactive. Most Cr(VI) solutions are powerful oxidising agents in acidic conditions, but much less oxidising under alkaline conditions. Chromium trioxides are soluble in alcohol, ethanol, sulfuric acid, and nitric acid; when heated to decomposition chromium trioxides emit smoke and irritating fumes. Lead chromate is insoluble in water, acetic acid, and ammonia, but is soluble in acid and alkalies; when heated to decomposition emits toxic fumes of lead. Potassium chromate and potassium dichromate are soluble in cold and hot water and insoluble in alcohol. Sodium dichromate is soluble in cold and hot water and insoluble in alcohol; toxic fumes of sodium monoxide are emitted when this compound is heated to decomposition. Strontium chromate is soluble in cold and hot water, hydrochloric acid, nitric acid, acetic acid, and ammonium salts. Zinc chromate is insoluble in cold water and acetone, dissolves in hot water, and is soluble in acid and liquid ammonia.
The National Pollutant Inventory (NPI) holds data for all sources of chromium (VI) compounds emissions in Australia.
Compounds of two species of chromium are on the NPI reporting list, chromium (VI) and chromium (III). The health effects of chromium (VI) compounds will be quite different from that of chromium (III) compounds.
Very small quantities of chromium (III) compounds are essential for your health and well-being. Chromium VI compounds are usually highly toxic. Breathing in chromium (VI) compounds can damage and irritate your nose, throat, lungs, stomach and intestines. It may lead to asthma and other allergic reactions. Exposure to chromium (VI) can cause stomach upsets, ulcers, convulsions, kidney and liver damage. Long-term exposure to airborne chromium (VI) can have adverse effects on the respiratory and the immune systems and can cause cancer. Skin contact with liquids and solids may lead to skin ulcers, redness and swelling. A US expert panel investigated chromium-contaminated soils in a residential area and concluded that soil concentrations of 2,800mg/kg (i.e. 2.8 g/kg) chromium (III) and 180 mg/kg (i.e. 0.18 g/kg) chromium (VI) do not pose a health hazard following acute or chronic exposure for residents living on or near the contaminated sites. These findings and recent reports of Health-Based Soil Action Levels and case studies involving human exposure to chromium (VI) in soil and ground water put the relative toxicity of chromium (III) and chromium (VI) into perspective. Chromium (VI) is more toxic than chromium (III) but low levels can be tolerated. The human studies showed that the gastrointestinal tract can reduce ingested chromium (VI) to chromium (III) at concentrations up to 10 mg chromium (VI)/L and soil concentrations of 1240 ppm chromium (VI) do not result in allergic contact dermatitis in 99.9% of the general population.
Entering the body
Air-borne particles can be breathed in. Skin exposure to chromium (VI) will be especially noticed by those individuals with skin allergies.
Dangerous exposure to chromium (VI) happens mostly from breathing workplace air, from welding, chrome plating and handling some chromate chemicals.
Workplace exposure standards
Safe Work Australia sets the workplace exposure standard for chromium (VI) compounds through the workplace exposure standards for airborne contaminants:
- Maximum eight hour time weighted average (TWA): 0.05 mg/m3
These standards are only appropriate for use in workplaces and are not limited to any specific industry or operation. Make sure you understand how to interpret the standards before you use them.
Drinking water guidelines
The Australian Drinking Water Guidelines include the following guidelines for acceptable water quality:
- Maximum of 0.05 milligrams per litre of water for health purposes
- If the concentration of total chromium exceeds this value then a separate analysis for hexavalent chromium should be undertaken.
Compounds of two species of chromium are on the NPI reporting list, chromium (VI) and chromium (III). The environmental effects of chromium (VI) compounds will be quite different from that of chromium (III) compounds. Chromium (VI) can have a high to moderate, acute toxic effect on plants, birds or land animals. This can mean death of animals, birds or fish and death or low growth rate in plants. Chromium (VI) does not breakdown or degrade easily and there is a high potential for accumulation of chromium (VI) in fish life.
Entering the environment
Chromium (VI) released into the atmosphere is carried in the air as particles or dust for a period of time. As it settles it will contaminate soil and water with only small amounts dissolving. Rain will remove chromium (VI) particles from the atmosphere, depositing them in the ground, or they may be transported over long distances by wind.
Where it ends up
Chromium (VI) is released into the air, soil and water during the manufacture and disposal of products and chemicals containing chromium (VI) or the burning of fossil fuels (coal, oil or gas). Airborne chromium (VI) particles will settle in less than 10 days, depending on particle size, and will stick strongly to soil particles. Small amounts may travel from the soil to groundwater. Chromium (VI) in water will stick to dirt particles that fall to the bottom with only a small amount dissolving.
Australian Water Quality Guidelines for Fresh and Marine Waters (ANZECC, 1992):
Maximum concentration in fresh water: 0.01 mg/L (i.e. 0.00001 g/L);
Maximum concentration in marine water: 0.05 mg/L (i.e. 0.00005 g/L).
Emissions to air and water from:
Chemical manufacturing industry e.g. dyes for paints, rubber and plastic products.
Metal finishing industry e.g. chrome plating.
Manufacturers of pharmaceuticals, wood, stone, clay and glass products.
Electrical and aircraft manufacturers, steam and air conditioning supply services.
Cement producing plants as cement contains chromium.
Incineration of council refuse and sewage sludge.
Combustion of oil and coal.
Diffuse sources, and industry sources included in diffuse emissions data
Facilities below the reporting threshold.
Chromium (VI) compounds are not found in nature. Chromium is usually found as the Cr(III) form, as the mineral Chromite and in many soils.
Emission to air from the wearing down of brake linings containing chromium. Motor vehicle exhaust (crude oil contains traces of chromium (III) compounds, these may oxidise to the chromium (VI) state during fuel combustion in vehicle engines).
Some inks, paints and paper.
Some rubber and composite floor coverings.
Some treated (preserved) timber products.
Some toner powders used in copying machines.
Sources used in preparing this information
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- Agency for Toxic Substances and Disease Registry (1997), ToxFAQS (accessed, December, 1998)
- Australian and New Zealand Environment and Conservation Council (ANZECC) (1992), Australian Water Quality Guidelines for Fresh and Marine Waters.
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- Environmental Defense Fund (1998), Chromium The Chemical Scorecard (accessed, December, 1998)
- Finley, B.L. and Paustenback, D.J., J. Soil Contamination, 6(6), 649, 1997.
- Meagher, D (1991), The Macmillan Dictionary of The Australian Environment, Macmillan Education Australia Pty Ltd.
- National Environment Protection Council (1998), National Environment Protection Measure for the National Pollutant Inventory. (accessed, December 1998)
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- New Jersey Department of Health, Right to Know Program (1988), TRIFacts (accessed, December, 1998)
- Proctor, D.M., Shay, E.C. and Scott, P.K., J. Soil Contamination, 6(6), 595, 1997.
- Richardson, M (1992), Dictionary of Substances and their Effects, Royal Society of Chemistry, Clays Ltd, England.
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- US Department of Health and Human Services (1990), NIOSH Pocket Guide to Chemical Hazards, Publication No. 90-117.
- US Environmental Protection Agency and the Office of Air Quality Planning & Standards (1998), Chromium and Compounds (accessed, December, 1998)
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- Worksafe Australia (1995), Chromium toxicity in the respiratory system, author A Bonin (accessed, December, 1998)
- Worksafe Australia (1996), Hazardous Substance Chromium (accessed, December, 1998)
- Safe Work Australia, Workplace exposure standards for airborne contaminants, accessed June 2021.
- National Health and Medical Research Council (NHMRC), Australian Drinking Water Guidelines (2011) - Updated October 2017, accessed May 2018