State of knowledge report
Environment Australia, 2001
ISBN 0 6425 4739 4
Cadmium and compounds
|Substance name:||Cadmium and compounds|
|Molecular formula:||Cadmium: Cd
Cadmium Chloride: CdCl2
Cadmium oxide: CdO
Cadmium sulfide: CdS
|Synonyms:||Cadmium: colloidal cadmium
Cadmium sulfide: greenockite, hawleyite
Cadmium oxide: monteponite
Pure cadmium, the metal, is a soft silver-white colour. Cadmium is most often found combined with other elements, in compounds such as cadmium chloride, cadmium oxide and cadmium sulfite.
Melting point: Cadmium: 320.9°C, Cadmium Chloride: 568°C, Cadmium oxide: 900°C (decomposes)
Boiling point: Cadmium: 765°C, Cadmium chloride: 967°C, Cadmium oxide: 1385°C
Vapour density: Cadmium: 3.9, Cadmium chloride: 6.3, Cadmium oxide: does not apply
Cadmium and its compounds are stable. Some compounds (eg cadmium chloride) are freely soluble in water; others (eg cadmium oxide) are almost insoluble in water. As a fine powder, cadmium metal will burn, releasing toxic fumes of cadmium oxide.
Cadmium compounds are used in the metal plating and battery industry, and as stabilising agents in many polyvinyl chloride (PVC) products. Cadmium metal is alloyed with copper in the production of automobile radiators. Cadmium chloride is used in the dyeing and printing of fabrics, in electronics component manufacture and in photography. Cadmium oxide is used in electroplating, in semiconductors, and in glass and ceramic glazes. Cadmium sulfide is used in the electronics industry for photocells and light-emitting diodes. It is also used as a curing agent in tyres. Cadmium is a component of petrol, diesel fuel and lubricating oils.
Cadmium is obtained as a byproduct from the treatment of zinc, copper, lead, and iron ores, so facilities that treat these ores may emit cadmium compounds to the environment (mainly water). Coal and oil burning power plants may emit cadmium compounds to air.
Diffuse sources, and point sources included in aggregated emissions data
Small industrial domestic use of cadmium products will emit low levels of cadmium to the environment. Tobacco smoke will be an indoor source of cadmium.
Cadmium is a naturally occurring element in the crust of the earth. Coal and other fossil fuels contain cadmium, and their combustion releases the element into the atmosphere. Cadmium is found naturally in various ores: lead and copper containing zinc, some iron ores, and sulfide ore. These can result in emissions to water. Volcanic emissions contain cadmium-enriched particles.
The combustion of motor fuels (petrol) in cars, trucks, and planes results in emissions to air; particles from tyre wear may result in emissions to air, land and water.
Consumer products that may contain cadmium and compounds
Cadmium is found in many domestic products (eg tobacco products, phosphate fertilisers, PVC products, photocells, petrol, oils, tyres, automobile radiators, some textile dyes and colours, electronic components, heating elements in electric kettles and hot water systems, batteries, and ceramic glazes).
How might I be exposed to cadmium and compounds?
Workers in the industries that use or produce cadmium and/or cadmium compounds are at risk of exposure. Consumers can be exposed to cadmium and or cadmium compounds by exposure to air from production and processing facilities that use cadmium and or cadmium compounds. For most members of the general public, the most significant route of exposure is through food: plants take up and retain cadmium from the soil; fish and shellfish take up and retain cadmium from the water, etc. Smoking is an important source of cadmium: tobacco, like other plants, takes up cadmium, which is then inhaled in the smoke.
By what pathways might cadmium and compounds enter my body?
Cadmium and/or cadmium compounds will enter the body if we breathe in contaminated air, eat contaminated foods, or drink contaminated water.
National Occupational Health and Safety Commission (NOHSC):
- TWA (eight-hour time weighted average) exposure limit in the workplace: 0.01 mg/m³.
Cadmium is listed as a substance under review for the establishment of an exposure standard for respirable particulate mass by the NOHSC.
Australian Drinking Water Guidelines (NHMRC and ARMCANZ 1996):
- Maximum of 0.002 mg/L (ie 0.000002 g/L).
What effect might cadmium and compounds have on my health?
There is evidence of cadmium, especially cadmium oxide, causing prostate and kidney cancer in humans; cadmium has been shown to cause lung and testicle cancer in animals. It is classified by the NOHSC as a Category 2 carcinogen (substance which should be regarded as if it is carcinogenic to humans). It is also a teratogen, and may cause reproductive damage. Inhalation of smoke from burning cadmium or from cadmium oxide is toxic to the respiratory system. It is unlikely that this sort of exposure would occur except in cases of unusual industrial accidents. Repeated low exposures can cause permanent kidney damage, which may go unnoticed. Lung scarring can occur from a single high exposure or repeated low exposures. Long-term exposures can cause anaemia, fatigue and loss of the sense of smell. High exposures can cause rapid lung damage, shortness of breath, chest pain, and a build-up of fluid in the lungs. In severe cases, death or permanent lung damage occurs. High exposure may also cause nausea, vomiting, cramps, and diarrhoea. High exposures are unlikely to occur except in cases of unusual industrial accidents.
Cadmium acts like other particles when in the atmosphere and is subject to deposition caused by rain or wind. The expected lifetime for particles in the atmosphere is about 5-15 days. Some cadmium compounds are able to leach through soils into groundwater. When cadmium compounds bind to the sediments in water (rivers, lakes, bore water), they are less likely to be bioavailable.
Industrial emissions of cadmium and/or cadmium compounds can produce elevated, but still low-level, concentrations in the atmosphere around the source. Motor vehicles may also produce elevated levels of cadmium in areas of higher traffic. Tobacco smoke is the primary source of cadmium indoors; because of their short life expectancy in the atmosphere, cadmium and its compounds are expected to be confined to the local area in which they are emitted.
Australian Water Quality Guidelines for Fresh and Marine Waters (ANZECC 1992):
- Freshwater: maximum of 0.0002 to 0.002 mg/L (ie 0.0000002 to 0.000002 g/L)
- Marine water: maximum of 0.002 mg/L (ie 0.000002 g/L).
What effect might cadmium and compounds have on the environment?
In freshwater, cadmium toxicity is influenced by the hardness of the water: the softer the water, the greater the toxicity. Cadmium has high short and long-term toxicity to aquatic life. No data are available on the short-term or long-term effects of cadmium on plants, birds or land animals, except in test animals, which did develop lung and testicle cancers. The same scarring of the lungs as found in humans will be present in very high doses in other mammals. Cadmium is highly persistent in the environment and will concentrate or bioaccumulate in aquatic animals.
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