Cadmium (pronEng|ˈkædmiəm) is a
chemical elementwith the symbol Cd and atomic number48. A relatively abundant (price 3.55 USD/lb as of 2008-02-15), soft, bluish-white, transition metal, cadmium is known to cause cancerand occurs with zincores. Cadmium is used largely in batteries and pigments, for example in plasticproducts.
Cadmium is a common impurity in
zinc, and it is most often isolated during the production of zinc. Zinc sulfideores are roasted in the presence of oxygen, converting the zinc sulfide to the oxide. Zinc metal is produced either by smeltingthe oxide with carbonor by electrolysisin sulfuric acid. Cadmium is isolated from the zinc metal by vacuum distillationif the zinc is smelted, or cadmium sulfate is precipitated out of the electrolysis solution. [ [http://www.webelements.com/webelements/elements/text/Cd/key.html Cadmium] at WebElements.com]
Cadmium is a soft,
malleable, ductile, toxic, bluish-white bivalent metal. It is similar in many respects to zincbut reacts to form more complex compounds.
The most common
oxidation stateof cadmium is +2, though rare examples of +1 can be found.
One particular isotope of cadmium, 113Cd, absorbs neutrons with very high probability if they have an energy below the "cadmium cutoff" and transmits them readily otherwise. The cadmium cutoff is about 0.5 eV. [cite book |last=Knoll |first=G.F. |title=Radiation Detection and Measurement, 3rd edition |publisher=Wiley |date=1999 |id=ISBN 978-0471073383 p505] Neutrons with energy below the cutoff are deemed slow neutrons, distinguishing them from intermediate and fast neutrons.
About three-quarters of cadmium is used in batteries (especially Ni-Cd batteries), and most of the remaining quarter is used mainly for pigments, coatings and plating, and as stabilizers for
plastics. Other uses include:
*In some of the lowest-melting
*In bearing alloys, due to a low
coefficient of frictionand very good fatigue resistance
*In many kinds of
*As a barrier to control
*In black and white
televisionphosphors and in the blue and green phosphors for color television picture tubes
*As a photoconductive surface coating for photocopier drums. (Cadmium Sulphide)
*In paint pigments: Cadmium forms various
salts, with cadmium sulfidebeing the most common. This sulfide is used as a yellow pigment. Cadmium selenidecan be used as red pigment, commonly called "cadmium red". To painters that work with the pigment, cadmium yellows, oranges, and reds are the most potent colours to use. In fact, during production, these colours are significantly toned down before they are ground with oils and binders, or blended into watercolours, gouaches, acrylics, and other paint and pigment formulations. These pigments are toxic, and it is recommended to use a barrier cream on the hands to prevent absorption through the skin when working with them. Cadmium blue, green, and violet do not exist.
semiconductors such as cadmium sulfide, cadmium selenide, and cadmium telluride, which can be used for lightdetection or solar cells. HgCdTeis sensitive to infrared.
*In PVC as stabilizers.
*In molecular biology, used to block voltage-dependent calcium channels from fluxing calcium ions.
:"See also ."
Latin"cadmia", Greek "καδμεία" meaning " calamine", a cadmium-bearing mixture of minerals, which was named after the Greek mythological character, Κάδμος ( Cadmus)) was discovered in Germanyin 1817 by Friedrich Strohmeyer. Strohmeyer found the new element within an impurity in zinc carbonate(calamine), and, for 100 years, Germany remained the only important producer of the metal. The metal was named after the Latin word for calamine, since the metal was found in this zinc compound. Strohmeyer noted that some impure samples of calamine changed color when heated but pure calamine did not.
Even though cadmium and its compounds are highly toxic, the
British Pharmaceutical Codexfrom 1907 states that cadmium iodidewas used as a medicineto treat "enlarged joints, scrofulous glands, and chilblains".
In 1927, the International Conference on Weights and Measures redefined the meter in terms of a red cadmium spectral line (1m = 1,553,164.13 wavelengths).Fact|date=October 2008 This definition has since been changed (see
In 2001, China was the top producer of cadmium with almost one-sixth world share closely followed by South Korea and Japan, reports the
British Geological Survey.
Cadmium-containing ores are rare and, when found, occur in small quantities. However, traces do naturally occur in phosphate, and have been shown to transmit in food through fertilizer application [http://www3.interscience.wiley.com/journal/107642962/abstract?CRETRY=1&SRETRY=0] .
Greenockite(CdS), the only cadmium mineralof importance, is nearly always associated with sphalerite(ZnS). As a consequence, cadmium is produced mainly as a byproduct from mining, smelting, and refining sulfideores of zinc, and, to a lesser degree, leadand copper. Small amounts of cadmium, about 10% of consumption, are produced from secondary sources, mainly from dust generated by recycling ironand steelscrap. Production in the United Statesbegan in 1907, but it was not until after World War Ithat cadmium came into wide use.
:"See also ."
A role of cadmium in biology has been recently discovered. A cadmium-dependent
carbonic anhydrasehas been found in marine diatoms. Cadmium does the same job as zinc in other anhydrases, but the diatoms live in environments with very low zinc concentrations, thus biology has taken cadmium rather than zinc, and made it work. The discovery was made using X-ray absorption fluoresence spectroscopy (XAFS), and cadmium was characterised by noting the energy of the X-rays that were absorbed.
Naturally occurring cadmium is composed of 8
isotopes. For two of them, natural radioactivitywas observed, and three others are predicted to be radioactivebut their decays were never observed, due to extremely long half-lifetimes. The two natural radioactive isotopes are 113Cd ( beta decay, half-lifeis 7.7 × 1015 years) and 116Cd (two-neutrino double beta decay, half-lifeis 2.9 × 1019 years). The other three are 106Cd, 108Cd ( double electron capture), and 114Cd ( double beta decay); only lower limits on their half-lifetimes have been set. At least three isotopes - 110Cd, 111Cd, and 112Cd - are absolutely stable. Among the isotopes absent in the natural cadmium, the most long-lived are 109Cd with a half-life of 462.6 days, and 115Cd with a half-life of 53.46 hours. All of the remaining radioactiveisotopes have half-lives that are less than 2.5 hours, and the majority of these have half-lives that are less than 5 minutes. This element also has 8 known meta states, with the most stable being 113mCd (t½ 14.1 years), 115mCd (t½ 44.6 days), and 117mCd (t½ 3.36 hours).
The known isotopes of cadmium range in
atomic massfrom 94.950 u (95Cd) to 131.946 u (132Cd). The primary decay modebefore the second-most-abundant stable isotope, 112Cd, is electron capture, and the primary modes after are beta emissionand electron capture. The primary decay productbefore 112Cd is element 47 ( silver), and the primary product after is element 49 ( indium).
Cadmium poisoning is an
occupational hazardassociated with industrial processes such as metal plating and the production of nickel-cadmium batteries, pigments, plastics, and other synthetics. The primary route of exposure in industrial settings is inhalation. Inhalation of cadmium-containing fumes can result initially in metal fume feverbut may progress to chemical pneumonitis, pulmonary edema, and death. [ [http://www.ijmt.net/ijmt/4_5/4_5_41.html] Principles and Methods of Toxicology (fourth edition). A. Wallace Hayes. Taylor and Francis Publishing Inc.; Philadelphia, 2001.]
Cadmium is also a potential environmental hazard. Human exposures to environmental cadmium are primarily the result of the burning of fossil fuels and municipal wastes. [ [http://www.epa.gov/ttn/atw/hlthef/cadmium.html EPA summary on cadmium] ] However, there have been notable instances of toxicity as the result of long-term exposure to cadmium in contaminated food and water. In the decades following
World War II, Japanese mining operations contaminated the Jinzu Riverwith cadmium and traces of other toxic metals. As a consequence, cadmium accumulated in the rice crops growing along the riverbanks downstream of the mines. The local agricultural communities consuming the contaminated rice developed Itai-itaidisease and renal abnormalities, including proteinuriaand glucosuria. [ [http://www.springerlink.com/content/n0773057mw738u05/] Environmental cadmium exposure, adverse effects, and preventative measures in Japan. Nogowa et al. Biometals. 2004 Oct; 17(5):581-7.] Cadmium is one of six substances banned by the European Union's Restriction on Hazardous Substances (RoHS) directive, which bans carcinogens in computers.
Cadmium and several cadmium-containing compounds are known
carcinogens and can induce many types of cancer. [ [http://ntp.niehs.nih.gov/index.cfm?objectid=32BA9724-F1F6-975E-7FCE50709CB4C932 11th Report on Carcinogens] provided by the National Toxicology Program]
Current research has found that cadmium toxicity may be carried into the body by
zincbinding proteins; in particular, proteins that contain zinc fingerprotein structures. Zinc and cadmium are in the same group on the periodic table, contain the same common oxidation state (+2), and when ionized are almost the same size. Due to these similarities, cadmium can replace zinc in many biological systems, in particular, systems that contain softer ligands such as sulfur. Cadmium can bind up to ten times more strongly than zinc in certain biological systems, and is notoriously difficult to remove. In addition, cadmium can replace magnesiumand calciumin certain biological systems, although these replacements are rare.
Tobacco smoking is the most important single source of cadmium exposure in the general population. It has been estimated that about 10% of the cadmium content of a cigarette is inhaled through smoking. The absorption of cadmium from the lungs is much more effective than that from the gut, and as much as 50% of the cadmium inhaled via cigarette smoke may be absorbed.
On average, smokers have 4-5 times higher blood cadmium concentrations and 2-3 times higher kidney cadmium concentrations than non-smokers. Despite the high cadmium content in cigarette smoke, there seems to be little exposure to cadmium from
passive smoking. No significant effect on blood cadmium concentrations could be detected in children exposed to environmental tobacco smoke.
List of breast carcinogenic substances
* [http://www.atsdr.cdc.gov/csem/cadmium/ ATSDR Case Studies in Environmental Medicine: Cadmium Toxicity] U.S.
Department of Health and Human Services
* [http://www-cie.iarc.fr/htdocs/monographs/vol58/mono58-2.htm IARC Monograph "Cadmium and Cadmium Compounds"]
* [http://www.npi.gov.au/database/substance-info/profiles/17.html National Pollutant Inventory - Cadmium and compounds]
* [http://www.webelements.com/webelements/elements/text/Cd/index.html WebElements.com – Cadmium]
* [http://periodic.lanl.gov/elements/48.html Los Alamos National Laboratory – Cadmium]
* [http://publicdocs.mnr.gov.on.ca/View.asp?Document_ID=10690&Attachment_ID=25585] Warning Moose and Deer Liver
* [http://www.cdc.gov/niosh/topics/Cadmium National Institute for Occupational Safety and Health - Cadmium Page]
* [http://minerals.usgs.gov/minerals/pubs/commodity/cadmium/ USGS Comodity Report cadmium]
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