Cadmium compounds are used in the metal plating and battery industry, and as stabilizing 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 tires. Cadmium is a component of petrol, diesel fuel and lubricating oils.
Substance name: Cadmium and compounds
CASR number: 7440-43-9
Molecular formula: Cd
Cadmium Chloride: CdCl2
Cadmium oxide: CdO
Cadmium sulfide: CdS
Synonyms: 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, which produces 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. In water some of the compounds will be quite soluble (cadmium chloride) and others will be insoluble (cadmium oxide). As fine powder cadmium metal will burn, releasing toxic fumes of cadmium oxide.
The National Pollutant Inventory (NPI) holds data for all sources of cadmium and compounds emissions in Australia.
Cadmium, especially cadmium oxide is a 'probable carcinogen'. There is evidence of it causing prostate and kidney cancer in humans, it has been shown to cause lung and testicle cancer in animals. 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 that 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.
Entering the body
Cadmium and or cadmium compounds will enter the body if we breathe in contaminated air, eat contaminated foods, or drink contaminated water.
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 using cadmium and or cadmium compounds. The most significant route of exposure to cadmium and or cadmium compounds for most members of the general public is through food, since food materials tend to take up and retain cadmium. Plants take up cadmium from the soil, fish and shellfish take up cadmium from the water, etc. Smoking is also an important source of cadmium. Tobacco, like other plants takes up cadmium, which is then inhaled in the smoke.
Workplace exposure standards
Safe Work Australia sets the workplace exposure standard for cadmium and compounds through the workplace exposure standards for airborne contaminants:
- Maximum eight hour time weighted average (TWA): 0.01 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 0.002 milligrams (2 micrograms) per litre of water for health purposes
In fresh water, cadmium toxicity is influenced by the hardness of the water, the softer the water the greater the toxicity. It has high short and long-term toxicity to aquatic life. No data are available on the short-term effects, or long term effects of cadmium on plants, birds, or land animals, excepting 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.
Entering the environment
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 usually confined to the local area within which it is emitted.
Where it ends up
Cadmium acts like other particles when in the atmosphere and will be subject to deposition caused by rain or wind. The expected lifetime for particles in the atmosphere will be about 5 to 15 days. Some cadmium compounds are able to leach through soils into ground water. When cadmium compounds do bind to the sediments in water (rivers, lakes, bore water) they are less likely to be bioavailable.
Australian Water Quality Guidelines for Fresh and Marine Waters: (ANZECC, 1992):
Fresh water: Maximum of 0.0002 to 0.002 mg/L (i.e. 0.0000002 to 0.000002 g/L)
Marine water: Maximum of 0.002 mg/L (i.e. 0.000002 g/L)
Cadmium is obtained as a by-product from the treatment of zinc, copper, lead, and iron ores, therefore 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 industry sources included in diffuse 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 in 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 result in emissions to air, and particles from tire wear may result in emissions to air, land and water.
Cadmium is found in many domestic products, e.g. tobacco products, phosphate fertilisers, polyvinyl chloride (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.
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