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heavy metal

 
Dictionary: heavy metal
 

n.
  1. A metal with a specific gravity greater than about 5.0, especially one that is poisonous, such as lead or mercury.
  2. Music. Very loud, brash rock music, often with shouted, violent lyrics.

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Chemistry Dictionary: heavy metal
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A metal with a high relative atomic mass. The term is usually applied to common transition metals, such as copper, lead, and zinc. These metals are a cause of environmental pollution (heavy-metal pollution) from a number of sources, including lead in petrol, industrial effluents, and leaching of metal ions from the soil into lakes and rivers by acid rain.



 
Hacker Slang: heavy metal
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[Cambridge] Syn. big iron.


 

"Heavy metals" is an inexact term used to describe more than a dozen elements that are metals or metalloids (elements that have both metal and nonmetal characteristics). Examples of heavy metals include chromium, arsenic, cadmium, lead, mercury, and manganese. Generally, heavy metals have densities above 5 g/cm3. Because they cannot be degraded or destroyed, heavy metals are persistent in all parts of the environment. Human activity affects the natural geological and biological redistribution of heavy metals through pollution of the air, water, and soil. The primary anthropogenic sources of heavy metals are point sources such as mines, foundries, smelters, and coal-burning power plants, as well as diffuse sources such as combustion by-products and vehicle emissions. Humans also affect the natural geological and biological redistribution of heavy metals by altering the chemical form of heavy metals released to the environment. Such alterations often affect a heavy metal's toxicity by allowing it to bioaccumulate in plants and animals, bioconcentrate in the food chain, or attack specific organs of the body.

Heavy metals are associated with myriad adverse health effects, including allergic reactions(e.g., beryllium, chromium), neurotoxicity (e.g., lead), nephrotoxicity (e.g., mercuric chloride, cadmium chloride), and cancer (e.g., arsenic, hexavalent chromium). Humans are often exposed to heavy metals in various ways—mainly through the inhalation of metals in the workplace or polluted neighborhoods, or through the ingestion of food (particularly seafood) that contains high levels of heavy metals or paint chips that contain lead.

The three heavy metals commonly cited as being of the greatest public health concern are cadmium, lead, and mercury. There is no biological need for any of these three heavy metals. Cadmium has many commercial applications, including electroplating and the manufacture of batteries. Exposure to cadmium can occur in the workplace or from contaminated foodstuffs and can result in emphysema, renal failure, cardiovascular disease, and perhaps cancer.

Humans discovered lead more than 8,500 years ago, and over time have used lead in artwork, plumbing, gasoline, batteries, and paint. Modern-day exposure to lead occurs in the workplace or through the ingestion of lead-contaminated items such as paint chips. The primary adverse health effect from exposure to lead is permanent neurological impairment (particularly in children). Other adverse health effects associated with lead include sterility in males and nephrotoxicity.

Mercury is equally toxic. Depending on its chemical form (elemental, inorganic, or organic) mercury is able to cause a myriad of adverse health effects including neurotoxicity (elemental mercury, methylmercury), nephrotoxicity (elemental mercury, mercuric salts such as mercuric chloride), teratogenicity (methylmercury), and death (elemental mercury, methylmercury). The major source of human exposure to mercury compounds is through the consumption of seafood that contains high levels of organic mercury compounds.

The international community is beginning to recognize the adverse health effects of heavy metals. In 1998, the United Nations proposed the Protocol to the Convention on Long-range Trans-boundary Air Pollution on Heavy Metals. This protocol is designed to reduce worldwide air emissions of cadmium, lead, and mercury, but has yet to be officially adopted.

(SEE ALSO: Arsenic; Lead; Mercury)

Bibliography

Goyer, R. A. (1996). "Toxic Effects of Metals." In Casarett & Doull's Toxicology: Basic Science of Poisons, ed. C. D. Klaassen. New York: McGraw-Hill.

Hawkes, S. J. (1997). "What Is a Heavy Metal?" Journal of Chemical Education 74:1374.

United Nations (1998). Protocol to the 1979 Convention on Long-range Transboundary Air Pollution on Heavy Metals. Available at http://www.unece.org/env/lrtap/protocol/98hm.htm.

— MARGARET H. WHITAKER; BRUCE A. FOWLER



 
US Military Dictionary: heavy metal
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1. a metal of relatively high density, or of high relative atomic weight.

2. slang (in the Persian Gulf War) heavy artillery, tanks, gunships, etc.

See the Introduction, Abbreviations and Pronunciation for further details.

 
Music Encyclopedia: Heavy metal
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An Anglo-American style of rock, characterized by loud, sustained ‘power chords’ played on the electric guitar and a persistent beat that may be aggressively fast or intentionally ponderous. Lyrics (concerning sex, rebellion and violence) are delivered in an extreme, screeching and barking style between guitar chords. Exponents include Jimi Hendrix, The Who and Led Zeppelin.



 

Type of rock music marked by highly amplified, distorted "power chords" on electric guitar, a hard beat, thumping bass, and often dark lyrics. It evolved in Britain and the U.S. in the late 1960s from the heavy, blues-oriented music of Steppenwolf, Jimi Hendrix, and others. In the 1970s the genre was defined by the music of bands such as Led Zeppelin, Black Sabbath, Kiss, AC/DC, and Aerosmith. After a period of decline, a new generation of bands such as Def Leppard, Iron Maiden, Mötley Crüe, and Van Halen revived heavy metal in the 1980s, along with the careers of many of its pioneers, including Ozzy Osbourne of Black Sabbath.

For more information on heavy metal, visit Britannica.com.

 
Blogs: Related blogs on: heavy metal
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Wikipedia: Heavy metal (chemistry)
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A heavy metal is a member of an ill-defined subset of elements that exhibit metallic properties, which would mainly include the transition metals, some metalloids, lanthanides, and actinides. Many different definitions have been proposed—some based on density, some on atomic number or atomic weight, and some on chemical properties or toxicity.[1] The term heavy metal has been called "meaningless and misleading" in an IUPAC technical report due to the contradictory definitions and its lack of a "coherent scientific basis".[1] There is an alternative term toxic metal, for which no consensus of exact definition exists either. As discussed below, depending on context, heavy metal can include elements lighter than carbon and can exclude some of the heaviest metals. One source defines heavy metal as one of the "common transition metals, such as copper, lead, and zinc. These metals are a cause of environmental pollution (heavy-metal pollution) from a number of sources, including lead in petrol, industrial effluents, and leaching of metal ions from the soil into lakes and rivers by acid rain."[2] Another common definition is based on the density of the metal (hence the name heavy metal), classifying all metals weighing more than 5000 kg/m3, such as lead, zinc and copper, as heavy metals. Heavy metals occur naturally in the ecosystem with large variations in concentration. Nowadays anthropogenic sources of heavy metals, i.e. pollution, have been introduced to the ecosystem. Waste derived fuels are especially prone to contain heavy metals so they should be a central concern in a consideration of their use.

Contents

Relationship to living organisms

Living organisms require varying amounts of "heavy metals." Iron, cobalt, copper, manganese, molybdenum, and zinc are required by humans. Excessive levels can be damaging to the organism. Other heavy metals such as mercury, plutonium, and lead are toxic metals that have no known vital or beneficial effect on organisms, and their accumulation over time in the bodies of animals can cause serious illness. Certain elements that are normally toxic are, for certain organisms or under certain conditions, beneficial. Examples include vanadium, tungsten, and even cadmium.[3]

Heavy metal pollution

Motivations for controlling heavy metal concentrations in gas streams are diverse. Some of them are dangerous to health or to the environment (e.g. Hg, Cd, As, Pb, Cr), some may cause corrosion (e.g. Zn, Pb), some are harmful in other ways (e.g. Arsenic may pollute catalysts). Within the European community the 13 elements of highest concern are As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sn and Tl, the emissions of which are regulated in waste incinerators. Some of these elements are actually necessary for humans in minute amounts (Co, Cu, Cr, Ni) whilst others are carcinogenic or toxic, affecting, among others, the central nervous system (Hg, Pb, As), the kidneys or liver (Hg, Pb, Cd, Cu) or skin, bones or teeth (Ni, Cd, Cu, Cr).[4]

Heavy metal pollution can arise from many sources but most commonly arises from the purification of metals, e.g., the smelting of copper and the preparation of nuclear fuels. Electroplating is the primary source of chromium and cadmium. Through precipitation of their compounds or by ion exchange into soils and muds, heavy metal pollutants can localize and lay dormant. Unlike organic pollutants, heavy metals do not decay and thus pose a different kind of challenge for remediation. Currently, plants or microrganisms are tentatively used to remove some heavy metals such as mercury. Plants which exhibit hyper accumulation can be used to remove heavy metals from soils by concentrating them in their bio matter. Some treatment of mining tailings has occurred where the vegetation is then incinerated to recover the heavy metals.

Some well-documented environmental disasters associated with heavy metals are:

In medicine

In medical usage, heavy metals are loosely defined[1] and include all toxic metals irrespective of their atomic weight: "heavy metal poisoning" can possibly include excessive amounts of iron, manganese, aluminium, mercury or beryllium (the fourth lightest element) or such a semi-metal as arsenic. This definition excludes bismuth, the heaviest of stable elements, because of its low toxicity.

Early farming in New Zealand suffered from bush sickness which was later discovered to be a deficiency in cobalt

Hazmats

Heavy metals in a hazardous materials (or "hazmat") setting are for the most part classified in "Misc." on the UN model hazard class, but they are sometimes labeled as a poison when being transported.

References

  1. ^ a b c John H. Duffus ""Heavy metals" a meaningless term? (IUPAC Technical Report)" Pure and Applied Chemistry, 2002, Vol. 74, pp. 793-807. doi:10.1351/pac200274050793
  2. ^ A Dictionary of Chemistry. Oxford University Press, 2000. Oxford Reference Online.Oxford University Press.
  3. ^ Lane TW, Morel FM. A biological function for cadmium in marine diatoms. 
  4. ^ Ron Zevenhoven, Pia Kilpinen: Control of Pollutants in Flue Gases and Fuel Gases. TKK, Espoo 2001.

 
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Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
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