Description
Chromium metal is used as an alloying element to harden steel and to manufacture stainless steel. Chromium compounds are used for chrome plating (e.g. protective coatings for automotive and equipment accessories), as dyes, as inorganic paint pigments, for leather tanning, as fungicides and wood preservatives, and as catalysts. More applications are in the photographic industry (sensitiser), in industrial water treatment (including treatment of cooling tower water), as medicinal astringents and antiseptics, and in nuclear and high temperature research. Chromium (III) compounds are employed as pigment, as catalyst, as tanning agent in the tanning industry, in the production of pure chromium metal and chromium (VI) compounds, and in the production of refractory bricks. More specifically, chromium (III) oxide is used as a paint pigment, a fixative for certain textile dyes and as a catalyst. Chromium (III) acetate is used to fix certain textile dyes, to harden photographic emulsions and as a catalyst. Chromium (III) nitrate is used in the preparation of chrome catalysts, in textile printing operations, and as a corrosion inhibitor. Chromic sulfate is used in tanning, green paints, inks and text dyes and in ceramics.
Substance details
Substance name: Chromium (III) compounds
CASR number: 16065-83-1
Molecular formula: Cr3+
Synonyms: Chromic ion, Chromium ion, Trivalent chromium
Trivalent chromium compounds include:
chromic oxide (CASR# 1308-38-9),
chromium acetate (CASR# 1066-30-4),
chromium nitrate (CASR# 13548-38-4),
chromium chloride (CASR# 10025-73-7),
chromium phosphate (CASR# 7789-04-0), and
chromium sulfate (CASR# 10101-53-8)
Physical properties
Chromium is a white, hard, lustrous and brittle metal that is extremely resistant to ordinary corrosive agents.
Atomic Number: 24
Atomic Mass: 52.0
Melting Point: about 1860°C
Boiling Point: about 2670°C
Specific Gravity: 7.2
Properties vary widely depending on the particular compound. Chromic oxide is a bright green hygroscopic powder with melting point of 2435°C, boiling point of 4000°C and specific gravity of 5.2. Chromium acetate is a grey-green to blue green pasty mass. Chromium nitrate is a pale green powder. Chromium chloride is a hygroscopic compound with melting point of 1152°C and specific gravity of 2.8. All chromium compounds have no taste or odour.
Chemical properties
The most stable oxidation state of the element chromium is chromium (III), found in chromite. Chromite is the most important chromium ore mined for the recovery of chromium. Another oxidation state of practical importance is chromium (VI) (CASR# 18540-29-9), but whilst there are some natural sources for chromium (VI), the majority originates from industrial activities. Chromium is chiefly found in its trivalent form in natural environments, except in sea water where chromium in its hexavalent state is prevailing, but at extremely low concentrations. Compared to chromium (III), chromium (VI) is assumed to be about 100 to 1000 times more toxic. Although each form can be converted to the other form under certain conditions, chromium (III) is not oxidised to chromium (VI) in the natural soil environment. Water solubility of chromium and its salts ranges from low to high, e.g chromium (III) oxide is insoluble in water, and chromic (III) acetate, chromium (III) nitrate and chromium (III) sulfate are soluble in water. Pure chromium metal (oxidation state of 0) which dissolves readily in non-oxidising mineral acids such as hydrochloric and sulfuric acids is not found in nature. Chromium (VI) compounds are dealt with elsewhere in the NPI.
Further information
The National Pollutant Inventory (NPI) holds data for all sources of chromium (III) compounds emissions in Australia.
Description
This depends on how much chromium a person has been exposed to, for how long, the nature of the chromium compound(s), and current state of health. Trivalent chromium compounds are considerably less toxic than the hexavalent compounds and are neither irritating nor corrosive under normal conditions. However, all forms of chromium can be toxic at high levels. People who are allergic to chromium may have asthma attacks after breathing high levels of chromium (III) in air. Repeated or prolonged skin contact may cause irritation. In severe cases, skin allergy can occur with itching, redness and/or an eczema-like rash.
Entering the body
Chromium can be inhaled or ingested.
Exposure
Chromium(III) is an essential nutrient in the diet of humans and animals in very small amounts. Very small amounts of chromium (III) are in everyday foods. Other forms of chromium are not needed by living organisms. The general population is exposed to chromium (III) in food, drinking water and in air. Atmospheric contamination is caused by the combustion of natural gas, oil and coal.
Workplace exposure standards
Safe Work Australia sets the workplace exposure standard for chromium (III) compounds through the workplace exposure standards for airborne contaminants:
- Maximum eight hour time weighted average (TWA): 0.5 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
There is no guideline for chromium (III) compounds in the Australian Drinking Water Guidelines.
Description
Chromium (III) and chromium (VI) both have high chronic toxicity to aquatic life. No data are available on the long-term effects of chromium to plants, birds, or land animals. Chromium (III) has moderate acute toxicity to aquatic life. No data are available on the short-term effects of chromium to plants, birds, or land animals. Fish do not appear to take up or store chromium in their bodies.
Entering the environment
Chromium can be transported as particles released into the atmosphere or as dissolved compounds in natural waters.
Where it ends up
Chromium (III) can be found in nature and low background levels in air, water and food occur everywhere. Manufacturing, disposal of products or chemicals containing chromium, or burning of fossil fuels release chromium to the air, soil, and water. Chromium particles settle from air in less than 10 days. Chromium sticks strongly to soil particles. Most chromium in water sticks to dirt particles that fall to the bottom and only a small amount of chromium dissolves.
Environmental guidelines
Australian Water Quality Guidelines for Fresh and Marine Waters: (ANZECC, 1992):
Maximum of 0.01 mg/L (i.e. 0.00001 g/L) in fresh waters and 0.05 mg/L (i.e. 0.00005 g/L) in marine waters respectively. Important: These are total chromium concentrations and are based on the assumption that all chromium is in the more toxic chromium (VI) form.
Industry sources
Emissions to air and water may result from leather tanning industries, chemical manufacturing industries (e.g. dyes for paints, rubber and plastic products), metal finishing industries (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 (cement contains chromium), incineration of council refuse and sewage sludge, and combustion of oil and coal.
Diffuse sources, and industry sources included in diffuse emissions data
Emissions to air and water may result from leather tanning industries, chemical manufacturing industries (e.g. dyes for paints, rubber and plastic products), metal finishing industries (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 (cement contains chromium), incineration of council refuse and sewage sludge, and combustion of oil and coal.
Natural sources
Chromium is a relatively common element, naturally occurring in rocks, soil, plants, animals, and in volcanic dust and gases. Oil and coal contain traces of chromium (III). Chromium is chiefly found as the chromium (III) form in nature, and rarely as chromium (VI) compounds.
Transport sources
Motor vehicle exhaust may contain chromium.
Consumer products
Some textile and some leather products.
Sources used in preparing this information
- Agency for Toxic Substances and Disease Registry (ATSDR), ToxFAQs, Chromium (accessed, May, 1999)
- Australian and New Zealand Environment and Conservation Council (ANZECC) (1992), Australian Water Quality Guidelines for Fresh and Marine Waters.
- ChemFinder WebServer Project (1995), Chromium (accessed, May, 1999)
- ChemFinder WebServer Project (1995), Chromium (III) (accessed, May, 1999)
- Environmental Health Center (a division of the National Safety Council) Environment Writer - Chemical Backgrounders (July 1, 1997), Chromium and Chromium compounds (accessed, May, 1999)
- Integrated Risk Information System (IRIS, September 3, 1998), Chromium (III), insoluble salts (accessed, May, 1999)
- Kimbrough, D. E., Cohen, Y., Winer, A. M., Creelman, L., and Mabuni, C., A critical assessment of chromium in the environment, Critical Reviews in Environmental Science and Technology 29:1 (1999), 1-46.
- Merian, E. (editor, 1991), Metals and Their Compounds in the Environment – Occurrence, Analysis, and Biological Relevance, VCH.
- Technical Advisory Panel (1999), Final Report to the National Environment Protection Council.
- US EPA TTNWeb and US OAQPS UATW, Health Effects Notebook for Hazardous Air Pollutants (December 1994), Chromium and Compounds (accessed, May, 1999)
- US EPA, Office of Water, National Primary Drinking Water Regulations, Consumer Version (January 23, 1998), Factsheet on Chromium (accessed, May, 1999)
- WebElements – The periodic table on the WWW (May 1999), Chromium (accessed, May, 1999)
- 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