Cadmium: Difference between revisions

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'''Cadmium''' is a [[chemical element]] in the [[periodic table]] that has the symbol '''Cd''' and [[atomic number]] 48. A relatively rare, soft, bluish-white, toxic [[transition metal]], cadmium occurs with [[zinc]] ores and is used largely in batteries.
'''Cadmium''' is a [[chemical element]] that has the symbol '''Cd''' and [[atomic number]] 48. A relatively rare, soft, bluish-white, toxic [[transition metal]], cadmium occurs with [[zinc]] ores.  It was discovered in Germany in 1817 and for 100 years Germany remained the only important producer.<ref>[http://minerals.usgs.gov/minerals/pubs/commodity/cadmium/ Cadmium Statistics and Information] From the website of the [[U.S. Geological Survey]] (USGS)</ref>  It is used largely in batteries.
{{TOC|left}}


==Production==
==Production==
Cadmium is a common impurity in zinc, and it is most often isolated during the production of zinc. Zinc sulfide ores are roasted in the presence of oxygen converting the zinc sulfide to the oxide. Zinc metal is produced either by smelting the oxide with carbon or by electrolysis in sulfuric acid. Cadmium is isolated from the zinc metal by vacuum distillation if the zinc is smelted, or cadmium sulfate is precipitated out of the electrolysis solution.<ref>[http://www.webelements.com/webelements/elements/text/Cd/key.html Cadmium] at WebElements.com</ref>
 
Cadmium is a common impurity in zinc, and is most often isolated during the production of zinc. Greenockite (CdS), the only cadmium mineral of importance, is nearly always associated with sphalerite (ZnS). Zinc sulfide ores are roasted in the presence of oxygen converting the zinc sulfide to the oxide. Zinc is produced either by smelting the oxide with carbon or by electrolysis in sulfuric acid. Cadmium is isolated from the zinc by vacuum distillation if the zinc is smelted, or cadmium sulfate is precipitated out of the electrolysis solution.<ref>[http://www.webelements.com/webelements/elements/text/Cd/key.html Cadmium] at WebElements.com</ref>


== Notable characteristics ==
== Notable characteristics ==
Cadmium is a soft, malleable, ductile, bluish-white bivalent [[metal]] which can be easily cut with a knife. It is similar in many respects to [[zinc]] but reacts to form more complex compounds.


The most common [[oxidation state]] of cadmium is +2, though rare examples of +1 can be found.
Cadmium is a soft, malleable, ductile, bluish-white bivalent [[metal]] which can be easily cut with a knife. It is similar in many respects to zinc but reacts to form more complex compounds. The most common [[oxidation state]] of cadmium is +2, though rare examples of +1 can be found.


== Applications ==
== Applications ==
{{See also|Cadmiun compounds}}
About three-fourths of cadmium is used in [[Battery (electricity)|batteries]] (especially [[nickel-cadmium battery|Ni-Cd]] batteries) and most of the remaining one-fourth is used mainly for [[Cadmium pigments|pigments]], coatings and plating, and as stabilizers for [[plastic]]s. Other uses;
About three-fourths of cadmium is used in [[Battery (electricity)|batteries]] (especially [[nickel-cadmium battery|Ni-Cd]] batteries) and most of the remaining one-fourth is used mainly for [[Cadmium pigments|pigments]], coatings and plating, and as stabilizers for [[plastic]]s. Other uses;
*Used in some of the lowest melting [[alloy]]s.
*Used in some of the lowest melting [[alloy]]s.
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*As a barrier to control [[nuclear fission]].
*As a barrier to control [[nuclear fission]].
*Compounds containing cadmium are used in black and white [[television]] phosphors and also in the blue and green phosphors for color television picture tubes.
*Compounds containing cadmium are used in black and white [[television]] phosphors and also in the blue and green phosphors for color television picture tubes.
*Cadmium forms various [[salt]]s, with [[cadmium sulfide]] being the most common. This sulfide is used as a [[Cadmium pigments|yellow pigment]]. [[Cadmium selenide]] can be used as red pigment, commonly called ''cadmium red''. To painters who 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, casesin, acrylics and other paint and pigment formulations. These pigments are toxic and it is recommended to use a barrier cream on your hands to prevent absorbtion through the skin when working with them. There is no such thing as cadmium blue, green or violet.  
*Cadmium forms various [[salt]]s, with [[cadmium sulfide]] being the most common. This sulfide is used as a [[Cadmium pigments|yellow pigment]]. [[Cadmium selenide]] can be used as red pigment, commonly called ''cadmium red''. To painters who 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, casesin, acrylics and other paint and pigment formulations. These pigments are toxic and it is recommended to use a barrier cream on your hands to prevent absorption through the skin when working with them. There is no such thing as cadmium blue, green or violet.  
*Used in some [[semiconductor]]s such as cadmium sulfide, cadmium selenide, and [[cadmium telluride]], which can be used for [[light]] detection or [[solar cell]]s. [[HgCdTe]] is sensitive to [[infrared]].
*Used in some [[semiconductor]]s such as cadmium sulfide, cadmium selenide, and [[cadmium telluride]], which can be used for [[light]] detection or [[solar cell]]s. [[HgCdTe]] is sensitive to [[infrared]].
*Some cadmium compounds are employed in [[Polyvinyl chloride | PVC]] as stabilizers.
*Some cadmium compounds are employed in [[Polyvinyl chloride | PVC]] as stabilizers.
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*Used to block voltage-dependent calcium channels from fluxing calcium ions in molecular biology.
*Used to block voltage-dependent calcium channels from fluxing calcium ions in molecular biology.


''See also [[:Category:Cadmium compounds|Cadmium compounds]].''
== History ==


== History ==
Cadmium ([[Latin]] ''cadmia'', [[Greek language|Greek]] ''kadmeia'' meaning "[[calamine]]") was [[discovery of the chemical elements|discovered]] in Germany in 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.
Cadmium ([[Latin]] ''cadmia'', [[Greek language|Greek]] ''kadmeia'' meaning "[[calamine]]") was [[discovery of the chemical elements|discovered]] in [[Germany]] in [[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 Codex]] from 1907 states that [[cadmium iodide]] was used as a [[medicine]] to treat "enlarged joints, scrofulous glands, and chilblains".
Although cadmium and its compounds are highly toxic, the [[British Pharmaceutical Codex]] from 1907 states that [[cadmium iodide]] was used as a medicine to treat "enlarged joints, scrofulous glands, and chilblains".


In [[1927]], the [[International Conference on Weights and Measures]] redefined the [[metre|meter]] in terms of a red cadmium spectral line (1m = 1,553,164.13 wavelengths). This definition has since been changed (see [[krypton]]).
In 1927, the [[International Conference on Weights and Measures]] redefined the [[metre|meter]] in terms of a red cadmium spectral line (1m = 1,553,164.13 wavelengths). This definition has since been changed (see [[krypton]]).


== Occurrence ==
== Occurrence ==
[[Image:CadmiumMetalUSGOV.jpg|thumb|left|Cadmium metal]]
 
Cadmium-containing ores are rare and when found they occur in small quantities. [[Greenockite]] (Cd[[sulfur|S]]), the only cadmium [[mineral]] of importance, is nearly always associated with [[sphalerite]] ([[zinc|Zn]]S). Consequently, cadmium is produced mainly as a byproduct from mining, smelting, and refining [[sulfide]] ores of zinc, and to a lesser degree, [[lead]] and [[copper]]. Small amounts of cadmium, about 10% of consumption, are produced from secondary sources, mainly from dust generated by recycling [[iron]] and [[steel]] scrap.  Production in the [[United States]] began in [[1907]] but it was not until after [[World War I]] that cadmium came into wide use.
Cadmium-containing ores are rare and when found they occur in small quantities. [[Greenockite]] (Cd[[sulphur|S]]), the only cadmium [[mineral]] of importance, is nearly always associated with [[sphalerite]] ([[zinc|Zn]]S). Consequently, cadmium is produced mainly as a byproduct from mining, smelting, and refining [[sulfide]] ores of zinc, and to a lesser degree, [[lead]] and [[copper]]. Small amounts of cadmium, about 10% of consumption, are produced from secondary sources, mainly from dust generated by recycling [[iron]] and [[steel]] scrap.  Production in the USA began in 1907, but it was not until after [[World War I]] that cadmium came into wide use.
;''See also [[:Category:Cadmium minerals]].''


== Isotopes ==
== Isotopes ==
[[Image:HeCd laser.jpg|thumb|left|150px|Image of the violet light from a [[helium]] [[cadmium]] metal vapor [[laser]]. The highly [[monochromatic]] color arises from the 441.563 nm transition [[spectral line|line]] of cadmium.]]
Naturally occurring cadmium is composed of 8 [[isotope]]s. For two of them, natural [[radioactivity]] was observed, and other three are predicted to be [[radioactive]] but their decays were never observed, due to extremely long [[half-life]] times. The two natural radioactive isotopes are <sup>113</sup>Cd ([[beta decay]], [[half-life]] is 7.7 X 10<sup>15</sup> years) and <sup>116</sup>Cd (two-neutrino [[double beta decay]], [[half-life]] is 2.9 X 10<sup>19</sup> years). Other three ones are <sup>106</sup>Cd, <sup>108</sup>Cd ([[double electron capture]]), and <sup>114</sup>Cd ([[double beta decay]]); only lower limits on their [[half-life]] times have been set. At least three isotopes - <sup>110</sup>Cd, <sup>111</sup>Cd, and <sup>112</sup>Cd - are absolutely stable. Among the isotopes absent in the natural cadmium, the most long-lived are <sup>109</sup>Cd with a half-life of 462.6 days, and <sup>115</sup>Cd with a half-life of 53.46 hours. All of the remaining [[radioactive]] isotopes have half-lifes that are less than 2.5 hours and the majority of these have half-lifes that are less than 5 minutes. This element also has 8 known [[meta state]]s with the most stable being <sup>113m</sup>Cd (t<sub>½</sub> 14.1 years), <sup>115m</sup>Cd (t<sub>½</sub> 44.6 days) and <sup>117m</sup>Cd (t<sub>½</sub> 3.36 hours).


The known isotopes of cadmium range in [[atomic weight]] from 96.935 [[atomic mass unit|u]] (<sup>97</sup>Cd) to 129.934 amu (<sup>138</sup>Cd). The primary [[decay mode]] before the second most abundant stable isotope, <sup>112</sup>Cd, is [[electron capture]] and the primary modes after are [[beta emission]] and [[electron capture]]. The primary [[decay product]] before <sup>112</sup>Cd is element 47 ([[silver]]) and the primary product after is element 49 ([[indium]]).
Naturally occurring cadmium is composed of eight [[isotope]]s. For two of them, natural [[radioactivity]] has been observed, and another three are predicted to be [[radioactive]] but their decay has never been observed, due to their having extremely long [[half-life|half-lives]]. The two natural radioactive isotopes are <sup>113</sup>Cd ([[beta decay]], half-life is 7.7 X 10<sup>15</sup> years) and <sup>116</sup>Cd (two-neutrino [[double beta decay]], [[half-life]] is 2.9 X 10<sup>19</sup> years). The other three are <sup>106</sup>Cd, <sup>108</sup>Cd ([[double electron capture]]), and <sup>114</sup>Cd ([[double beta decay]]); only lower limits on their [[half-life]] times have been set. At least three isotopes, <sup>110</sup>Cd, <sup>111</sup>Cd, and <sup>112</sup>Cd, are absolutely stable. Among the isotopes absent in the natural cadmium, the most long-lived are <sup>109</sup>Cd with a half-life of 462.6 days, and <sup>115</sup>Cd with a half-life of 53.46 hours. All of the remaining [[radioactive]] isotopes 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 eight known [[meta state]]s with the most stable being <sup>113m</sup>Cd (t<sub>½</sub> 14.1 years), <sup>115m</sup>Cd (t<sub>½</sub> 44.6 days) and <sup>117m</sup>Cd (t<sub>½</sub> 3.36 hours).
 
The known isotopes of cadmium range in atomic weight from 96.935 [[atomic mass unit|amu]] (<sup>97</sup>Cd) to 129.934 amu (<sup>138</sup>Cd). The primary [[decay mode]] before the second most abundant stable isotope, <sup>112</sup>Cd, is [[electron capture]] and the primary modes after are [[beta emission]] and electron capture. The primary [[decay product]] before <sup>112</sup>Cd is element 47 (silver) and the primary product after is element 49 ([[indium]]).


== Precautions ==
== Precautions ==
{{main|Cadmium poisoning}}
[[Image:Skull and crossbones.svg|120px|thumb|Cadmium is toxic]]
Cadmium has no constructive purpose in the [[human]] body. This element and solutions of its compounds are extremely [[toxic]] even in low concentrations, and will [[bioaccumulate]] in organisms and [[ecosystem]]s. One possible reason for its toxicity is that it interferes with the action of [[zinc]]-containing enzymes. Zinc is an important element in biological systems, but cadmium, although similar to zinc chemically in many ways, apparently does not substitute or "stand in" for it well at all. Cadmium may also interfere with biological processes containing [[magnesium]] and [[calcium]] in a similar fashion.  Pathways of human contact include [[soil contamination]] from industrial releases or [[landfill]] and associated [[leachate]] processes.


Inhaling cadmium laden dust quickly leads to [[respiratory tract]] and [[kidney]] problems which can be fatal (often from [[renal failure]]). Ingestion of any significant amount of cadmium causes immediate poisoning and damage to the [[liver]] and the kidneys.  
Cadmium has no constructive purpose in the human body. This element and solutions of its compounds are extremely toxic even at low concentrations, and will accumulate in organisms and ecosystems. One possible reason for its toxicity is that it interferes with the action of zinc-containing enzymes. Zinc is an important element in biological systems, but cadmium, although similar to zinc chemically in many ways, apparently does not substitute or "stand in" for it well at all. Cadmium may also interfere with biological processes containing [[magnesium]] and [[calcium]] in a similar fashion.  Pathways of human contact include [[soil contamination]] from industrial releases or [[landfill]] and associated [[leachate]] processes.


Compounds containing cadmium are also [[carcinogen]]ic <ref>http://www.epa.gov/enviro/html/emci/chemref/7440439.html</ref>, and can induce many types of [[cancer]] <ref>http://www.cancer.wisc.edu/uwccc/article_cadmium.asp</ref>.
Inhaling cadmium laden dust quickly leads to [[respiratory tract]] and kidney problems which can be fatal (often from [[renal failure]]). Ingestion of any significant amount of cadmium causes immediate poisoning and damage to the liver and the kidneys.  


Cadmium poisoning is the cause of the [[itai-itai disease]], which literally means "pain pain" in [[Japanese language|Japanese]].  In addition to kidney damage, patients suffered from [[osteoporosis]] and [[osteomalacia]].
Compounds containing cadmium are also carcinogenic,<ref>[http://www.epa.gov/enviro/html/emci/chemref/7440439.html Chemical References: Cadmium] From the website of the [[U.S. Environmental Protection Agency]] (U.S. EPA)</ref> and can induce many types of cancer. Cadmium poisoning is the cause of the [[itai-itai disease]], which literally means "pain pain" in Japanese.  In addition to kidney damage, patients suffered from [[osteoporosis]] and [[osteomalacia]].


While working with cadmium it is important to do so under a [[fume hood]] to protect against dangerous fumes. [[Silver (element)|Silver]] [[solder]], for example, which contains cadmium, should be handled with care. Serious toxicity problems have resulted from long-term exposure to cadmium plating baths.
While working with cadmium it is important to use a [[fume hood]] to protect against dangerous fumes. Silver [[solder]], for example, which contains cadmium, should be handled with care. Serious toxicity problems have resulted from long-term exposure to cadmium plating baths.


{{wiktionarypar|cadmium}}
==Attribution==
{{Commons|Cadmium}}
{{WPAttribution}}


==References==
==References==
<references/>
<references/>
== External links ==
*[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 &ndash; Cadmium]
*[http://periodic.lanl.gov/elements/48.html Los Alamos National Laboratory &ndash; Cadmium]
[[Category:Chemical elements]]
[[Category:Transition metals]]
[[Category:Toxicology]]
[[Category:IARC Group 1 carcinogens]]
[[Category:Soil contamination]]
[[Category:Cadmium]]
[[Category:CZ Live]]
[[Category:Chemistry Workgroup]]
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[[io:Kadmio]]
[[id:Kadmium]]
[[is:Kadmín]]
[[it:Cadmio]]
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[[lt:Kadmis]]
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Cadmium
112.411(8) +2



  Cd
48
1s22s22p63s23p63d104s2 4p64d105s2 12,5,d
[ ? ] Transition metal:
Properties:
Soft, malleable, ductile, bluish-white metal
Uses:
Batteries, pigments, coatings and plating, and stabilizers for plastics
Hazard:
Toxic


Cadmium is a chemical element that has the symbol Cd and atomic number 48. A relatively rare, soft, bluish-white, toxic transition metal, cadmium occurs with zinc ores. It was discovered in Germany in 1817 and for 100 years Germany remained the only important producer.[1] It is used largely in batteries.

Production

Cadmium is a common impurity in zinc, and is most often isolated during the production of zinc. Greenockite (CdS), the only cadmium mineral of importance, is nearly always associated with sphalerite (ZnS). Zinc sulfide ores are roasted in the presence of oxygen converting the zinc sulfide to the oxide. Zinc is produced either by smelting the oxide with carbon or by electrolysis in sulfuric acid. Cadmium is isolated from the zinc by vacuum distillation if the zinc is smelted, or cadmium sulfate is precipitated out of the electrolysis solution.[2]

Notable characteristics

Cadmium is a soft, malleable, ductile, bluish-white bivalent metal which can be easily cut with a knife. It is similar in many respects to zinc but reacts to form more complex compounds. The most common oxidation state of cadmium is +2, though rare examples of +1 can be found.

Applications

See also: Cadmiun compounds

About three-fourths of cadmium is used in batteries (especially Ni-Cd batteries) and most of the remaining one-fourth is used mainly for pigments, coatings and plating, and as stabilizers for plastics. Other uses;

  • Used in some of the lowest melting alloys.
  • Due to a low coefficient of friction and very good fatigue resistance, it is used in bearing alloys.
  • 6% of cadmium finds use in electroplating.
  • Many kinds of solder contain this metal.
  • As a barrier to control nuclear fission.
  • Compounds containing cadmium are used in black and white television phosphors and also in the blue and green phosphors for color television picture tubes.
  • Cadmium forms various salts, with cadmium sulfide being the most common. This sulfide is used as a yellow pigment. Cadmium selenide can be used as red pigment, commonly called cadmium red. To painters who 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, casesin, acrylics and other paint and pigment formulations. These pigments are toxic and it is recommended to use a barrier cream on your hands to prevent absorption through the skin when working with them. There is no such thing as cadmium blue, green or violet.
  • Used in some semiconductors such as cadmium sulfide, cadmium selenide, and cadmium telluride, which can be used for light detection or solar cells. HgCdTe is sensitive to infrared.
  • Some cadmium compounds are employed in PVC as stabilizers.
  • Used in the first neutrino detector.
  • Used to block voltage-dependent calcium channels from fluxing calcium ions in molecular biology.

History

Cadmium (Latin cadmia, Greek kadmeia meaning "calamine") was discovered in Germany in 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.

Although cadmium and its compounds are highly toxic, the British Pharmaceutical Codex from 1907 states that cadmium iodide was used as a medicine to 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). This definition has since been changed (see krypton).

Occurrence

Cadmium-containing ores are rare and when found they occur in small quantities. Greenockite (CdS), the only cadmium mineral of importance, is nearly always associated with sphalerite (ZnS). Consequently, cadmium is produced mainly as a byproduct from mining, smelting, and refining sulfide ores of zinc, and to a lesser degree, lead and copper. Small amounts of cadmium, about 10% of consumption, are produced from secondary sources, mainly from dust generated by recycling iron and steel scrap. Production in the USA began in 1907, but it was not until after World War I that cadmium came into wide use.

Isotopes

Naturally occurring cadmium is composed of eight isotopes. For two of them, natural radioactivity has been observed, and another three are predicted to be radioactive but their decay has never been observed, due to their having extremely long half-lives. The two natural radioactive isotopes are 113Cd (beta decay, half-life is 7.7 X 1015 years) and 116Cd (two-neutrino double beta decay, half-life is 2.9 X 1019 years). The other three are 106Cd, 108Cd (double electron capture), and 114Cd (double beta decay); only lower limits on their half-life times 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 radioactive isotopes 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 eight 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 weight from 96.935 amu (97Cd) to 129.934 amu (138Cd). The primary decay mode before the second most abundant stable isotope, 112Cd, is electron capture and the primary modes after are beta emission and electron capture. The primary decay product before 112Cd is element 47 (silver) and the primary product after is element 49 (indium).

Precautions

Cadmium has no constructive purpose in the human body. This element and solutions of its compounds are extremely toxic even at low concentrations, and will accumulate in organisms and ecosystems. One possible reason for its toxicity is that it interferes with the action of zinc-containing enzymes. Zinc is an important element in biological systems, but cadmium, although similar to zinc chemically in many ways, apparently does not substitute or "stand in" for it well at all. Cadmium may also interfere with biological processes containing magnesium and calcium in a similar fashion. Pathways of human contact include soil contamination from industrial releases or landfill and associated leachate processes.

Inhaling cadmium laden dust quickly leads to respiratory tract and kidney problems which can be fatal (often from renal failure). Ingestion of any significant amount of cadmium causes immediate poisoning and damage to the liver and the kidneys.

Compounds containing cadmium are also carcinogenic,[3] and can induce many types of cancer. Cadmium poisoning is the cause of the itai-itai disease, which literally means "pain pain" in Japanese. In addition to kidney damage, patients suffered from osteoporosis and osteomalacia.

While working with cadmium it is important to use a fume hood to protect against dangerous fumes. Silver solder, for example, which contains cadmium, should be handled with care. Serious toxicity problems have resulted from long-term exposure to cadmium plating baths.

Attribution

Some content on this page may previously have appeared on Wikipedia.

References

  1. Cadmium Statistics and Information From the website of the U.S. Geological Survey (USGS)
  2. Cadmium at WebElements.com
  3. Chemical References: Cadmium From the website of the U.S. Environmental Protection Agency (U.S. EPA)