|Pronunciation|| / /|
|Appearance||silvery bluish-gray metallic|
|Standard atomic weight Ar, std(Cd)||112.414(4)|
|Cadmium in the periodic table|
|Atomic number (Z)||48|
|Element category||Post-transition metal, alternatively considered a transition metal|
|Electron configuration||[ Kr ] 4d10 5s2|
|Electrons per shell||2, 8, 18, 18, 2|
|Phase at STP||solid|
|Melting point||594.22 K (321.07 °C,609.93 °F)|
|Boiling point||1040 K(767 °C,1413 °F)|
|Density (near r.t.)||8.65 g/cm3|
|when liquid (at m.p.)||7.996 g/cm3|
|Heat of fusion||6.21 kJ/mol|
|Heat of vaporization||99.87 kJ/mol|
|Molar heat capacity||26.020 J/(mol·K)|
| Vapor pressure |
|Oxidation states||−2, +1, +2 (a mildly basic oxide)|
|Electronegativity||Pauling scale: 1.69|
|Atomic radius||empirical:151 pm|
|Covalent radius||144±9 pm|
|Van der Waals radius||158 pm|
|Spectral lines of cadmium|
|Crystal structure|| hexagonal close-packed (hcp)|
|Speed of sound thin rod||2310 m/s(at 20 °C)|
|Thermal expansion||30.8 µm/(m·K)(at 25 °C)|
|Thermal conductivity||96.6 W/(m·K)|
|Electrical resistivity||72.7 nΩ·m(at 22 °C)|
|Magnetic susceptibility||−19.8·10−6 cm3/mol|
|Young's modulus||50 GPa|
|Shear modulus||19 GPa|
|Bulk modulus||42 GPa|
|Brinell hardness||203–220 MPa|
|Discovery and first isolation||Karl Samuel Leberecht Hermann and Friedrich Stromeyer (1817)|
|Named by||Friedrich Stromeyer(1817)|
|Main isotopes of cadmium|
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of its compounds, and like mercury, it has a lower melting point than the transition metals in groups 3 through 11. Cadmium and its congeners in group 12 are often not considered transition metals, in that they do not have partly filled d or f electron shells in the elemental or common oxidation states. The average concentration of cadmium in Earth's crust is between 0.1 and 0.5 parts per million (ppm). It was discovered in 1817 simultaneously by Stromeyer and Hermann, both in Germany, as an impurity in zinc carbonate.
Cadmium occurs as a minor component in most zinc ores and is a byproduct of zinc production. Cadmium was used for a long time as a corrosion-resistant plating on steel, and cadmium compounds are used as red, orange and yellow pigments, to color glass, and to stabilize plastic. Cadmium use is generally decreasing because it is toxic (it is specifically listed in the European Restriction of Hazardous Substances) and nickel-cadmium batteries have been replaced with nickel-metal hydride and lithium-ion batteries. One of its few new uses is in cadmium telluride solar panels.
Although cadmium has no known biological function in higher organisms, a cadmium-dependent carbonic anhydrase has been found in marine diatoms.
Cadmium is a soft, malleable, ductile, silvery-white divalent metal. It is similar in many respects to zinc but forms complex compounds.Unlike most other metals, cadmium is resistant to corrosion and is used as a protective plate on other metals. As a bulk metal, cadmium is insoluble in water and is not flammable; however, in its powdered form it may burn and release toxic fumes.
Although cadmium usually has an oxidation state of +2, it also exists in the +1 state. Cadmium and its congeners are not always considered transition metals, in that they do not have partly filled d or f electron shells in the elemental or common oxidation states.Cadmium burns in air to form brown amorphous cadmium oxide (CdO); the crystalline form of this compound is a dark red which changes color when heated, similar to zinc oxide. Hydrochloric acid, sulfuric acid, and nitric acid dissolve cadmium by forming cadmium chloride (CdCl2), cadmium sulfate (CdSO4), or cadmium nitrate (Cd(NO3)2). The oxidation state +1 can be produced by dissolving cadmium in a mixture of cadmium chloride and aluminium chloride, forming the Cd22+ cation, which is similar to the Hg22+ cation in mercury(I) chloride.
The structures of many cadmium complexes with nucleobases, amino acids, and vitamins have been determined.
Naturally occurring cadmium is composed of 8 isotopes. Two of them are radioactive, and three are expected to decay but have not done so under laboratory conditions. The two natural radioactive isotopes are 113Cd (beta decay, half-life is 7.7×1015 y) and 116Cd (two-neutrino double beta decay, half-life is 2.9×1019 y). The other three are 106Cd, 108Cd (both double electron capture), and 114Cd (double beta decay); only lower limits on these half-lives have been determined. At least three isotopes – 110Cd, 111Cd, and 112Cd – are stable. Among the isotopes that do not occur naturally, 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 of less than 2.5 hours, and the majority have half-lives of less than 5 minutes. Cadmium has 8 known meta states, with the most stable being 113mCd (t1⁄2 = 14.1 years), 115mCd (t1⁄2 = 44.6 days), and 117mCd (t1⁄2 = 3.36 hours).
The known isotopes of cadmium range in atomic mass from 94.950 u (95Cd) to 131.946 u (132Cd). For isotopes lighter than 112 u, the primary decay mode is electron capture and the dominant decay product is element 47 (silver). Heavier isotopes decay mostly through beta emission producing element 49 (indium).
One isotope of cadmium, 113Cd, absorbs neutrons with high selectivity: With very high probability, neutrons with energy below the cadmium cut-off will be absorbed; those higher than the cut-off will be transmitted. The cadmium cut-off is about 0.5 eV, and neutrons below that level are deemed slow neutrons, distinct from intermediate and fast neutrons.
Cadmium is created via the s-process in low- to medium-mass stars with masses of 0.6 to 10 solar masses, over thousands of years. In that process, a silver atom captures a neutron and then undergoes beta decay.
Cadmium (Latin cadmia, Greek καδμεία meaning "calamine", a cadmium-bearing mixture of minerals that was named after the Greek mythological character Κάδμος, Cadmus, the founder of Thebes) was discovered simultaneously in 1817 by Friedrich Stromeyerand Karl Samuel Leberecht Hermann, both in Germany, as an impurity in zinc carbonate. Stromeyer found the new element as 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, because it was found in this zinc ore. Stromeyer noted that some impure samples of calamine changed color when heated but pure calamine did not. He was persistent in studying these results and eventually isolated cadmium metal by roasting and reducing the sulfide. The potential for cadmium yellow as pigment was recognized in the 1840s, but the lack of cadmium limited this application.
Even though cadmium and its compounds are toxic in certain forms and concentrations, the British Pharmaceutical Codex from 1907 states that cadmium iodide was used as a medication to treat "enlarged joints, scrofulous glands, and chilblains".
In 1907, the International Astronomical Union defined the international ångström in terms of a red cadmium spectral line (1 wavelength = 6438.46963 Å). This was adopted by the 7th General Conference on Weights and Measures in 1927. In 1960, the definitions of both the metre and ångström were changed to use krypton.
After the industrial scale production of cadmium started in the 1930s and 1940s, the major application of cadmium was the coating of iron and steel to prevent corrosion; in 1944, 62% and in 1956, 59% of the cadmium in the United States was used for plating.In 1956, 24% of the cadmium in the United States was used for a second application in red, orange and yellow pigments from sulfides and selenides of cadmium.
The stabilizing effect of cadmium chemicals like the carboxylates cadmium laurate and cadmium stearate on PVC led to an increased use of those compounds in the 1970s and 1980s. The demand for cadmium in pigments, coatings, stabilizers, and alloys declined as a result of environmental and health regulations in the 1980s and 1990s; in 2006, only 7% of to total cadmium consumption was used for plating, and only 10% was used for pigments.At the same time, these decreases in consumption were compensated by a growing demand for cadmium for nickel-cadmium batteries, which accounted for 81% of the cadmium consumption in the United States in 2006.
Cadmium makes up about 0.1 ppm of Earth's crust. It is much rarer than zinc, which makes up about 65 ppm. No significant deposits of cadmium-containing ores are known. The only cadmium mineral of importance, greenockite (CdS), is nearly always associated with sphalerite (ZnS). This association is caused by geochemical similarity between zinc and cadmium, with no geological process likely to separate them. Thus, cadmium is produced mainly as a byproduct of mining, smelting, and refining sulfidic 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 wide use began after World War I.
Metallic cadmium can be found in the Vilyuy River basin in Siberia.
Rocks mined for phosphate fertilizers contain varying amounts of cadmium, resulting in a cadmium concentration of as much as 300 mg/kg in the fertilizers and a high cadmium content in agricultural soils. Coal can contain significant amounts of cadmium, which ends up mostly in flue dust. Cadmium in soil can be absorbed by crops such as rice. Chinese ministry of agriculture measured in 2002 that 28% of rice it sampled had excess lead and 10% had excess cadmium above limits defined by law. Some plants such as willow trees and poplars have been found to clean both lead and cadmium from soil.
Typical background concentrations of cadmium do not exceed 5 ng/m3 in the atmosphere; 2 mg/kg in soil; 1 μg/L in freshwater and 50 ng/L in seawater. Concentrations of cadmium above 10 μg/l may be stable in water having low total solute concentrations and p H and can be difficult to remove by conventional water treatment processes.
The British Geological Survey reports that in 2001, China was the top producer of cadmium with almost one-sixth of the world's production, closely followed by South Korea and Japan.
Cadmium is a common impurity in zinc ores, and it is most often isolated during the production of zinc. Some zinc ores concentrates from sulfidic zinc ores contain up to 1.4% of cadmium.In the 1970s, the output of cadmium was 6.5 pounds per ton 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 from the electrolysis solution.
Cadmium is a common component of electric batteries, pigments,coatings, and electroplating.
In 2009, 86% of cadmium was used in batteries, predominantly in rechargeable nickel-cadmium batteries. Nickel-cadmium cells have a nominal cell potential of 1.2 V. The cell consists of a positive nickel hydroxide electrode and a negative cadmium electrode plate separated by an alkaline electrolyte (potassium hydroxide). The European Union put a limit on cadmium in electronics in 2004 of 0.01%, with some exceptions, and reduced the limit on cadmium content to 0.002%. Another type of battery based on cadmium is the silver-cadmium battery.
Cadmium electroplating, consuming 6% of the global production, is used in the aircraft industry to reduce corrosion of steel components.This coating is passivated by chromate salts. A limitation of cadmium plating is hydrogen embrittlement of high-strength steels from the electroplating process. Therefore, steel parts heat-treated to tensile strength above 1300 MPa (200 ksi) should be coated by an alternative method (such as special low-embrittlement cadmium electroplating processes or physical vapor deposition).
Titanium embrittlement from cadmium-plated tool residues resulted in banishment of those tools (and the implementation of routine tool testing to detect cadmium contamination) in the A-12/SR-71, U-2, and subsequent aircraft programs that use titanium.
Cadmium is used in the control rods of nuclear reactors, acting as a very effective neutron poison to control neutron flux in nuclear fission.When cadmium rods are inserted in the core of a nuclear reactor, cadmium absorbs neutrons, preventing them from creating additional fission events, thus controlling the amount of reactivity. The pressurized water reactor designed by Westinghouse Electric Company uses an alloy consisting of 80% silver, 15% indium, and 5% cadmium.
QLED TVs have been starting to include cadmium in construction. Some companies have been looking to reduce the environmental impact of human exposure and pollution of the material in televisions during production.
Complexes based on heavy metals have great potential for the treatment of a wide variety of cancers but their use is often limited due to toxic side effects. However, scientist are advancing on the field and new promising cadmium complex compounds with reduced toxicity have been discovered.
Cadmium oxide was used in black and white television phosphors and in the blue and green phosphors of color television cathode ray tubes.Cadmium sulfide (CdS) is used as a photoconductive surface coating for photocopier drums.
Various cadmium salts are used in paint pigments, with CdS as a yellow pigment being the most common. Cadmium selenide is a red pigment, commonly called cadmium red. To painters who work with the pigment, cadmium provides the most brilliant and durable yellows, oranges, and reds — so much so that during production, these colors are significantly toned down before they are ground with oils and binders or blended into watercolors, gouaches, acrylics, and other paint and pigment formulations. Because these pigments are potentially toxic, users should use a barrier cream on the hands to prevent absorption through the skineven though the amount of cadmium absorbed into the body through the skin is reported to be less than 1%.
In PVC, cadmium was used as heat, light, and weathering stabilizers.Currently, cadmium stabilizers have been completely replaced with barium-zinc, calcium-zinc and organo-tin stabilizers. Cadmium is used in many kinds of solder and bearing alloys, because it has a low coefficient of friction and fatigue resistance. It is also found in some of the lowest-melting alloys, such as Wood's metal.
Helium–cadmium lasers are a common source of blue-ultraviolet laser light. They operate at either 325 or 422 nm in fluorescence microscopes and various laboratory experiments. Cadmium selenide quantum dots emit bright luminescence under UV excitation (He-Cd laser, for example). The color of this luminescence can be green, yellow or red depending on the particle size. Colloidal solutions of those particles are used for imaging of biological tissues and solutions with a fluorescence microscope.
Cadmium is a component of some compound semiconductors, such as cadmium sulfide, cadmium selenide, and cadmium telluride, used for light detection and solar cells. HgCdTe is sensitive to infraredlight and can be used as an infrared detector, motion detector, or switch in remote control devices.
In molecular biology, cadmium is used to block voltage-dependent calcium channels from fluxing calcium ions, as well as in hypoxia research to stimulate proteasome-dependent degradation of Hif-1α.
Cadmium-selective sensors based on the fluorophore BODIPY have been developed for imaging and sensing of cadmium in cells.One of the most popular ways to monitor cadmium in aqueous environments is the use of electrochemistry, one example is by attaching a self-assembled monolayer that can help obtain a cadmium selective electrode with a ppt-level sensitivity.
Cadmium has no known function in higher organisms,but a cadmium-dependent carbonic anhydrase has been found in some marine diatoms. Administration of cadmium to cells causing the oxidative stress and increase the levels of antioxidants to protect the cells against macro molecular damage. The diatoms live in environments with very low zinc concentrations and cadmium performs the function normally carried out by zinc in other anhydrases. This was discovered with X-ray absorption fluorescence spectroscopy (XAFS).
The highest concentration of cadmium is absorbed in the kidneys of humans, and up to about 30 mg of cadmium is commonly inhaled throughout human childhood and adolescence. Cadmium is under preliminary research for its toxicity in humans, potentially affecting mechanisms and risks of cancer, cardiovascular disease, and osteoporosis.
The biogeochemistry of cadmium and its release to the environment has been the subject of review, as has the speciation of cadmium in the environment.
|GHS Signal word||Danger|
|P201, P202, P260, P264, P270, P271, P273, P280, P284, P304, P340, P310, P308, P313, P403, P233, P405, P501|
|NFPA 704 (fire diamond)|
Individuals and organizations have been reviewing cadmium's bioinorganic aspects for its toxicity.The most dangerous form of occupational exposure to cadmium is inhalation of fine dust and fumes, or ingestion of highly soluble cadmium compounds. Inhalation of cadmium fumes can result initially in metal fume fever, but may progress to chemical pneumonitis, pulmonary edema, and death.
Cadmium is also an environmental hazard. Human exposure is primarily from fossil fuel combustion, phosphate fertilizers, natural sources, iron and steel production, cement production and related activities, nonferrous metals production, and municipal solid waste incineration.Bread, root crops, and vegetables also contribute to the cadmium in modern populations.
There have been a few instances of general population poisoning as the result of long-term exposure to cadmium in contaminated food and water. Research into an estrogen mimicry that may induce breast cancer is ongoing.In the decades leading up to World War II, mining operations contaminated the Jinzū River in Japan with cadmium and traces of other toxic metals. As a consequence, cadmium accumulated in the rice crops along the riverbanks downstream of the mines. Some members of the local agricultural communities consumed the contaminated rice and developed itai-itai disease and renal abnormalities, including proteinuria and glucosuria. The victims of this poisoning were almost exclusively post-menopausal women with low iron and low body stores of other minerals. Similar general population cadmium exposures in other parts of the world have not resulted in the same health problems because the populations maintained sufficient iron and other mineral levels. Thus, although cadmium is a major factor in the itai-itai disease in Japan, most researchers have concluded that it was one of several factors.
Cadmium is one of six substances banned by the European Union's Restriction of Hazardous Substances (RoHS) directive, which regulates hazardous substances in electrical and electronic equipment, but allows for certain exemptions and exclusions from the scope of the law.
The International Agency for Research on Cancer has classified cadmium and cadmium compounds as carcinogenic to humans.Although occupational exposure to cadmium is linked to lung and prostate cancer, there is still a substantial controversy about the carcinogenicity of cadmium in low environmental exposure. Recent data from epidemiological studies suggest that intake of cadmium through diet associates to higher risk of endometrial, breast, and prostate cancer as well as to osteoporosis in humans. A recent study has demonstrated that endometrial tissue is characterized by higher levels of cadmium in current and former smoking females.
Cadmium exposure is a risk factor associated with a large number of illnesses including kidney disease,early atherosclerosis, hypertension, and cardiovascular diseases. Although studies show a significant correlation between cadmium exposure and occurrence of disease in human populations, a necessary molecular mechanism has not been identified. One hypothesis holds that cadmium is an endocrine disruptor and some experimental studies have shown that it can interact with different hormonal signaling pathways. For example, cadmium can bind to the estrogen receptor alpha, and affect signal transduction along the estrogen and MAPK signaling pathways at low doses.
The tobacco plant readily absorbs and accumulates heavy metals such as cadmium from the surrounding soil into its leaves. Following tobacco smoke inhalation, these are readily absorbed into the body of users. to 5 times greater than non-smokers and in the kidney, 2–3 times greater than in non-smokers. Despite the high cadmium content in cigarette smoke, there seems to be little exposure to cadmium from passive smoking.Tobacco smoking is the most important single source of cadmium exposure in the general population. An estimated 10% of the cadmium content of a cigarette is inhaled through smoking. Absorption of cadmium through the lungs is more effective than through the gut. As much as 50% of the cadmium inhaled in cigarette smoke may be absorbed. On average, cadmium concentrations in the blood of smokers is 4
In a non-smoking population, food is the greatest source of exposure. High quantities of cadmium can be found in crustaceans, mollusks, offal, frog legs, cocoa solids, bitter and semi-bitter chocolate, seaweed, fungi and algae products. However, grains, vegetables, and starchy roots and tubers are consumed in much greater quantity in the U.S., and are the source of the greatest dietary exposure there. mg) of metal toxins for every kilo of fertilizer. Fertilizers made from animal dung (e.g., cow dung) or urban waste can contain similar amounts of Cd. The Cd added to the soil from fertilizers (rock phosphates or organic fertilizers) become bio-available and toxic only if the soil pH is low (i.e., acidic soils).Most plants bio-accumulate metal toxins such as Cd and when composted to form organic fertilizers, yield a product that often can contain high amounts (e.g., over 0.5
Zn, Cu, Ca, and Fe ions, and selenium with vitamin C are used to treat Cd intoxication, though it is not easily reversed.
Because of the adverse effects of cadmium on the environment and human health, the supply and use of cadmium is restricted in Europe under the REACH Regulation.
The EFSA Panel on Contaminants in the Food Chain specifies that 2.5 μg/kg body weight is a tolerable weekly intake for humans.The Joint FAO/WHO Expert Committee on Food Additives has declared 7 μg/kg bw to be the provisional tolerable weekly intake level. The state of California requires a food label to carry a warning about potential exposure to cadmium on products such as cocoa powder.
The U.S. Occupational Safety and Health Administration (OSHA) has set the permissible exposure limit (PEL) for cadmium at a time-weighted average (TWA) of 0.005 ppm. The National Institute for Occupational Safety and Health (NIOSH) has not set a recommended exposure limit (REL) and has designated cadmium as a known human carcinogen. The IDLH (immediately dangerous to life and health) level for cadmium is 9 mg/m3.
|LD50: 225 mg/kg||rat||oral||n/a|
|LD50: 890 mg/kg||mouse||oral||n/a|
|LC50: 25 mg/m3||rat||n/a||30 min|
In May 2006, a sale of the seats from Arsenal F.C.'s old stadium, Highbury in London, England was cancelled when the seats were discovered to contain trace amounts of cadmium.Reports of high levels of cadmium use in children's jewelry in 2010 led to a US Consumer Product Safety Commission investigation. The U.S. CPSC issued specific recall notices for cadmium content in jewelry sold by Claire's and Wal-Mart stores.
In June 2010, McDonald's voluntarily recalled more than 12 million promotional Shrek Forever After 3D Collectible Drinking Glasses because of the cadmium levels in paint pigments on the glassware. The glasses were manufactured by Arc International, of Millville, NJ, USA.
Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard and brittle transition metal. Chromium is the main additive in stainless steel, to which it adds anti-corrosive properties. Chromium is also highly valued as a metal that is able to be highly polished while resisting tarnishing. Polished chromium reflects almost 70% of the visible spectrum, with almost 90% of infrared light being reflected. The name of the element is derived from the Greek word χρῶμα, chrōma, meaning color, because many chromium compounds are intensely colored.
A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis, the formation of cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substances are considered carcinogens, but their carcinogenic activity is attributed to the radiation, for example gamma rays and alpha particles, which they emit. Common examples of non-radioactive carcinogens are inhaled asbestos, certain dioxins, and tobacco smoke. Although the public generally associates carcinogenicity with synthetic chemicals, it is equally likely to arise in both natural and synthetic substances. Carcinogens are not necessarily immediately toxic; thus, their effect can be insidious.
Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts per million of the Earth's crust. Indium has a melting point higher than sodium and gallium, but lower than lithium and tin. Chemically, indium is similar to gallium and thallium, and it is largely intermediate between the two in terms of its properties. Indium was discovered in 1863 by Ferdinand Reich and Hieronymous Theodor Richter by spectroscopic methods. They named it for the indigo blue line in its spectrum. Indium was isolated the next year.
Manganese is a chemical element with the symbol Mn and atomic number 25. It is not found as a free element in nature; it is often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy uses, particularly in stainless steels.
Nickel is a chemical element with the symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile. Pure nickel, powdered to maximize the reactive surface area, shows a significant chemical activity, but larger pieces are slow to react with air under standard conditions because an oxide layer forms on the surface and prevents further corrosion (passivation). Even so, pure native nickel is found in Earth's crust only in tiny amounts, usually in ultramafic rocks, and in the interiors of larger nickel–iron meteorites that were not exposed to oxygen when outside Earth's atmosphere.
Toxicology is a scientific discipline, overlapping with biology, chemistry, pharmacology, and medicine, that involves the study of the adverse effects of chemical substances on living organisms and the practice of diagnosing and treating exposures to toxins and toxicants. The relationship between dose and its effects on the exposed organism is of high significance in toxicology. Factors that influence chemical toxicity include the dosage, duration of exposure, route of exposure, species, age, sex, and environment. Toxicologists are experts on poisons and poisoning. There is a movement for evidence-based toxicology as part of the larger movement towards evidence-based practices. Toxicology is currently contributing to the field of Cancer research, since some toxins can be used as drugs for killing tumor cells. One prime example of this is Ribosome Inactivating Proteins, tested in the treatment of Leukemia.
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a blue-silvery appearance when oxidation is removed. It is the first element in group 12 of the periodic table. In some respects, zinc is chemically similar to magnesium: both elements exhibit only one normal oxidation state (+2), and the Zn2+ and Mg2+ ions are of similar size. Zinc is the 24th most abundant element in Earth's crust and has five stable isotopes. The most common zinc ore is sphalerite (zinc blende), a zinc sulfide mineral. The largest workable lodes are in Australia, Asia, and the United States. Zinc is refined by froth flotation of the ore, roasting, and final extraction using electricity (electrowinning).
Metalloprotein is a generic term for a protein that contains a metal ion cofactor. A large proportion of all proteins are part of this category. For instance, at least 1000 human proteins contain zinc-binding protein domains although there may be up to 3000 human zinc metalloproteins.
Metallothionein (MT) is a family of cysteine-rich, low molecular weight proteins. They are localized to the membrane of the Golgi apparatus. MTs have the capacity to bind both physiological and xenobiotic heavy metals through the thiol group of its cysteine residues, which represent nearly 30% of its constituent amino acid residues.
Group 12, by modern IUPAC numbering, is a group of chemical elements in the periodic table. It includes zinc (Zn), cadmium (Cd) and mercury (Hg). The further inclusion of copernicium (Cn) in group 12 is supported by recent experiments on individual copernicium atoms. Formerly this group was named IIB by CAS and old IUPAC system.
Cadmium pigments are a class of pigments that contain cadmium. Most of the cadmium produced worldwide has been for use in rechargeable nickel-cadmium batteries, which have been replaced by other rechargeable nickel-chemistry cell varieties such as NiMH cells, but about half of the remaining consumption of cadmium, which is approximately 2,000 tonnes annually, is used to produce colored cadmium pigments. The principal pigments are a family of yellow, orange and red cadmium sulfides and sulfoselenides, as well as compounds with other metals.
Bioinorganic chemistry is a field that examines the role of metals in biology. Bioinorganic chemistry includes the study of both natural phenomena such as the behavior of metalloproteins as well as artificially introduced metals, including those that are non-essential, in medicine and toxicology. Many biological processes such as respiration depend upon molecules that fall within the realm of inorganic chemistry. The discipline also includes the study of inorganic models or mimics that imitate the behaviour of metalloproteins.
Cadmium is a naturally occurring toxic metal with common exposure in industrial workplaces, plant soils, and from smoking. Due to its low permissible exposure in humans, overexposure may occur even in situations where trace quantities of cadmium are found. Cadmium is used extensively in electroplating, although the nature of the operation does not generally lead to overexposure. Cadmium is also found in some industrial paints and may represent a hazard when sprayed. Operations involving removal of cadmium paints by scraping or blasting may pose a significant hazard. The primary use of cadmium is in the manufacturing of NiCd rechargeable batteries. The primary source for cadmium is as a byproduct of refining zinc metal. Exposures to cadmium are addressed in specific standards for the general industry, shipyard employment, the construction industry, and the agricultural industry.
Metal fume fever, also known as brass founders' ague, brass shakes, zinc shakes, galvie flu, metal dust fever, Welding Shivers, or Monday morning fever, is an illness primarily caused by exposure to chemicals such as zinc oxide (ZnO), aluminium oxide (Al2O3), or magnesium oxide (MgO) which are produced as byproducts in the fumes that result when certain metals are heated. Other common sources are fuming silver, gold, platinum, chromium (from stainless steel), nickel, arsenic, manganese, beryllium, cadmium, cobalt, lead, selenium, and zinc.
Metal toxicity or metal poisoning is the toxic effect of certain metals in certain forms and doses on life. Some metals are toxic when they form poisonous soluble compounds. Certain metals have no biological role, i.e. are not essential minerals, or are toxic when in a certain form. In the case of lead, any measurable amount may have negative health effects. Often heavy metals are thought as synonymous, but lighter metals may also be toxic in certain circumstances, such as beryllium and lithium. Not all heavy metals are particularly toxic, and some are essential, such as iron. The definition may also include trace elements when in abnormally high doses may be toxic. An option for treatment of metal poisoning may be chelation therapy, which is a technique which involves the administration of chelation agents to remove metals from the body.
Environmental toxicology is a multidisciplinary field of science concerned with the study of the harmful effects of various chemical, biological and physical agents on living organisms. Ecotoxicology is a subdiscipline of environmental toxicology concerned with studying the harmful effects of toxicants at the population and ecosystem levels.
Metalloestrogens are a class of inorganic xenoestrogens which can affect the gene expression of human cells responding to estrogen. Effects are related to the physiologic function of estrogen because metalloestrogens have shown affinity for estrogen receptors. Because they can mimic estrogen thus activating the receptor, they are considered harmful and potentially linked with breast cancer. List of metalloestrogens include aluminium, antimony, arsenite, barium, cadmium, chromium, cobalt, copper, lead, mercury, nickel, selenite, tin and vanadate.
Cobalt is a chemical element with the symbol Co and atomic number 27. Like nickel, cobalt is found in the Earth's crust only in chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.
Heavy metals are generally defined as metals with relatively high densities, atomic weights, or atomic numbers. The criteria used, and whether metalloids are included, vary depending on the author and context. In metallurgy, for example, a heavy metal may be defined on the basis of density, whereas in physics the distinguishing criterion might be atomic number, while a chemist would likely be more concerned with chemical behaviour. More specific definitions have been published, but none of these have been widely accepted. The definitions surveyed in this article encompass up to 96 out of the 118 known chemical elements; only mercury, lead and bismuth meet all of them. Despite this lack of agreement, the term is widely used in science. A density of more than 5 g/cm3 is sometimes quoted as a commonly used criterion and is used in the body of this article.
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