State of knowledge report
Environment Australia, 2001
ISBN 0 6425 4739 4
Chromium (VI) compounds
|Substance name:||Chromium (VI) compounds|
|CASR number:||7440-47-3 (Cr metal), 18540-29-9 (Cr (VI))|
|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). 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|
The physical properties of the different chromium (VI) compounds vary widely; for example, most Cr(VI) compounds are soluble in water, but barium chromate (a yellow powder with a specific gravity of 4.49) and lead chromate (an orange-yellow powder with a specific gravity of 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; it has a specific gravity of 2.35, and is soluble in water. Chromic acid (H2CrO4) exists only as salts (eg lead chromate, barium chromate) or in solution.
Chromic acid is very reactive. Most chromium (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 it 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.
Chromium (VI) 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. Chromium (VI) is also used in galvanising, printing, paints, degreasers and rust converters in Australia.
Emissions to air and water occur from the chemical manufacturing industry (eg dyes for paints, rubber and plastic products); the metal finishing industry (eg chrome plating); from manufacturers of pharmaceuticals, wood, stone, clay and glass products; from electrical and aircraft manufacturers; from steam and airconditioning supply services; from cement-producing plants (cement contains chromium); from incineration of council refuse and sewage sludge; and from the combustion of oil and coal.
Diffuse sources, and point sources included in aggregated emissions data
Facilities below the National Pollutant Inventory 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, which may oxidise to the chromium (VI) state during fuel combustion in vehicle engines).
Consumer products that may contain chromium (VI) compounds
Consumer products that may contain chromium (VI) compounds are some inks, paints and paper; some rubber and composite floor coverings; some treated (preserved) timber products; and some toner powders used in copying machines.
How might I be exposed to chromium (VI) compounds?
Dangerous exposure to chromium (VI) occurs mostly by breathing workplace air or from welding, chrome plating and handling some chromate chemicals.
By what pathways might chromium (VI) compounds enter my body?
Airborne particles can be breathed in. Skin exposure to chromium (VI) will be noticed especially by individuals with skin allergies.
National Occupational Health and Safety Commission (NOHSC):
- TWA (eight-hour time weighted average) exposure limit in the workplace:
- chromium (VI) compounds: 0.05 mg/m³.
- chromium metal (CAS No. 7440-47-3) 0.5 mg/m³.
Certain water insoluble chromium (VI) compounds are listed as substances under review for carcinogenicity by the NOHSC. Water-soluble compounds are listed as substances under review for respiratory irritation and effects on the kidneys.
Australian Drinking Water Guidelines (NHMRC and ARMCANZ 1996):
- 0.05 mg/L (ie 0.00005 g/L).
What effect might chromium (VI) compounds have on my health?
Compounds of chromium (VI) and chromium (III) are on the National Pollutant Inventory reporting list. The health effects of chromium (VI) compounds will be quite different from those of chromium (III) compounds.
Very small quantities of chromium (III) compounds are essential for health and wellbeing. Chromium (VI) compounds are usually highly toxic. Inhalation of chromium (VI) compounds can damage and irritate the nose, throat, lungs, stomach and intestine or 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 immune systems and can cause cancer. Skin contact with liquids and solids may lead to skin ulcers, redness and swelling.
A United States expert panel investigated chromium-contaminated soils in a residential area and concluded that soil concentrations of 2800 mg/kg (2.8 g/kg) chromium (III) and 180 mg/kg (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, recent reports of Health-Based Soil Action Levels and case-studies involving human exposure to chromium (VI) in soil and groundwater 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. Studies on humans showed that the gastrointestinal tract can reduce ingested chromium (VI) to chromium (III) at concentrations up to 10 mg chromium (VI) per litre; soil concentrations of 1240 ppm of chromium (VI) do not result in allergic contact dermatitis in 99.9% of the general population. Certain water-soluble chromium (VI) compounds are classified by the NOHSC as Category 1 carcinogens (substances known to be carcinogenic to humans).
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.
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.
Australian Water Quality Guidelines for Fresh and Marine Waters (ANZECC 1992):
- Freshwater: maximum concentration 0.01 mg/L (0.00001 g/L)
- Marine water: maximum concentration 0.05 mg/L (0.00005 g/L).
What effect might chromium (VI) compounds have on the environment?
Compounds of chromium (VI) and chromium (III) are on the National Pollutant Inventory reporting list. The environmental effects of chromium (VI) compounds will be quite different from those of chromium (III) compounds.
Chromium (VI) can have high to moderate acute toxic effect on plants, birds and land animals. This can mean the death of animals, birds and fish and either death or low growth rate in plants. Chromium (VI) does not break down or degrade easily; there is a high potential for accumulation of chromium (VI) in fish life.
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