| Homepage | Imprint |
|
||
 |
Arsenic
Arsenic is a chemical elementin the periodic tablethat has the symbol As and atomic number33. This is a notoriously poisonous metalloidthat has three allotropicforms; yellow, black and grey. Arsenic and its compounds are used as pesticides, herbicides, insecticidesand various alloys.
Notable characteristicsArsenic is very similar chemically to its predecessor phosphorus, so much so that it will partly substitute for phosphorusin biochemical reactions and is thus poisonous. When heated it rapidly oxidizesto arsenic trioxide, which has a garlic odor. Arsenic and some arsenic compounds can also sublimeupon heating, converting directly to a gaseous form. Elemental arsenic is found in two solid forms: yellow and gray/metallic, with specific gravitiesof 1.97 and 5.73, respectively. This is somewhat heavy for a metalloid. ApplicationsLead hydrogen arsenatehas been used, well into the 20th century, as an insecticideon fruit trees(resulting in neurological damageto those working the sprayers), and Scheele's Greenhas even been recorded in the 19th centuryas a coloring agentin sweets. In the last half century, monosodium methyl arsenate(MSMA), a less toxic organic form of arsenic, has replaced lead arsenate's role in agriculture. The application of most concern to the general public is probably that of woodwhich has been treated with chromated copper arsenate("CCA", or "Tanalith", and the vast majority of older "pressure treated" wood). CCA timber is still in widespread use in many countries, and was heavily used during the latter half of the 20th centuryas a structural, and outdoor building material, where there was a risk of rot, or insectinfestation in untreated timber. Although widespread bans followed the publication of studies which showed low-level leaching from in-situ timbers (such as children's playgroundequipment) into surrounding soil, the most serious risk is presented by the burning of CCA timber. Recent years have seen fatal animal poisonings, and serious human poisonings resulting from the ingestion - directly or indirectly - of wood ash from CCA timber (the lethal human dose is approximately 20 grams of ash - roughly a tablespoon). Scrap CCA construction timber continues to be widely burnt through ignorance, in both commercial, and domestic fires. Safe disposal of CCA timber remains patchy, and little practiced, there is concern in some quarters about the widespread landfilldisposal of such timber. During the 18th, 19th, and 20th centuries, a number of arsenic compounds have been used as medicines, including arsphenamine(by Paul Ehrlich) and arsenic trioxide(by Thomas Fowler). Arsphenamine as well as Neosalvarsanwas indicated for syphilisand trypanosomiasis, but has been superseded by modern antibiotics. Arsenic trioxide has been used in a variety of ways over the past 200 years, but most commonly in the treatment of cancer. The FDAin 2000 approved this compound for the treatment of patients with acute promyelocytic leukemiathat is resistant to ATRA.[{{fullurl:Template:FULLPAGENAME}}#endnote_ArsTriChemo] But arsenic isn't always good for cancer. Some studies show that if you use arsenic you have a high risk for cancer. Copper acetoarsenite was used as a green pigmentknown under many different names, including Paris Greenand Emerald Green. It caused numerous arsenic poisonings. Other uses;
HistoryThe word arsenic is borrowed from the Persianword ????? Zarnikh meaning "yellow orpiment". Zarnikh was borrowed by Greekas arsenikon. Arsenic has been known and used in Persiaand elsewhere since ancient times. As the symptoms of arsenic poisoningwere somewhat ill-defined, it was frequently used for murderuntil the advent of the Marsh test, a sensitive chemical test for its presence. (Another less sensitive but more general test is the Reinsch test.) Due to its use by the ruling class to bump each other off and its incredible potency and discreetness, arsenic has been called the Poison of Kings and the King of Poisons. During the Bronze Age, arsenic was often included in the bronze (mostly as an impurity), which made the alloy harder. Albertus Magnusis believed to have been the first to isolate the element in 1250. In 1649Johann Schroederpublished two ways of preparing arsenic. Image:Arsenic-symbol.pngThe alchemicalsymbol for arsenic is shown opposite. In Victorian times, arsenic was mixed with vinegarand chalkand eaten by women to improve the complexionof their faces, making their skin more fair to show they did not work in the fields. Arsenic was also rubbed into the faces and arms of women to improve their complexion. There is a massive epidemic of arsenic poisoning in Bangladesh[{{fullurl:Template:FULLPAGENAME}}#endnote_bangladesh], where it is estimated that approximately 57 million people are drinking groundwaterwith arsenic concentrations elevated above the World Health Organization's standard of 50 parts per billion. The arsenic in the groundwater is of natural origin, and is released from the sediment into the groundwater due to the anoxic conditions of the subsurface. This groundwater began to be used after western NGOsinstigated a massive tube welldrinking-water program in the late twentieth century. This program was designed to prevent drinking of bacterially-contaminated surface waters, but unfortunately failed to test for arsenic in the groundwater.(2) Many other countries in South East Asia, such as Vietnam, Cambodia, and Tibet, are thought to have geological environments similarly conducive to generation of high-arsenic groundwaters. OccurrenceImage:Native arsenic.jpg Arsenopyritealso called mispickel (FeSAs) is the most common mineralfrom which, on heating, the arsenic sublimes leaving ferrous sulfide. Other arsenic minerals include realgar, mimetite, cobaltiteand erythrite. The most important compounds of arsenic are white arsenic, its sulfide, Paris Green, calcium arsenate, and lead hydrogen arsenate. Paris Green, calcium arsenate, and lead arsenate have been used as agriculturalinsecticidesand poisons. It is sometimes found native, but usually combined with silver, cobalt, nickel, iron, antimony, or sulfur. In addition to the inorganic forms mentioned above, arsenic also occurs in various organic forms in the environment. Inorganic arsenic and its compounds, upon entering the food chain, are progressively metabolised to a less toxic form of arsenic through a process of methylation. PrecautionsArsenic and many of its compounds are especially potent poisons. Arsenic kills by massively disrupting the digestive system, leading to death from shock. See arsenic poisoning. Arsenic and its compounds inhibit the enzymelipothiamide pyrophosphate, which is an important enzyme of metabolism. In animals, the toxicity is manifested a severe gastroenteritisand diarrhoea, which is described as rice gruel type. The post mortemreveals brick red colored mucosa, due to severe haemorrhage. Elemental arsenic and arsenic compounds are classified as toxic and dangerous for the environment in the European Unionunder directive 67/548/EEC. The IARCrecognizes arsenic and arsenic compounds as group 1 carcinogens, and the EU lists arsenic trioxide, arsenic pentoxideand arsenatesalts as category 1 carcinogens. Growing the Brake (fern)Pteris vittatawill remove arsenic from the soil. See also
Compounds
References
Endnotes
External linksImage:Commons-logo.svg
Wikimedia Commonshas media related to:
[[Commons:{{{1|Special:Search/Arsenic}}}|{{{2|{{{1|Arsenic}}}}}}]]
Image:Wiktionary-logo-en.png
Look up [[wiktionary:{{{1|Special:Search/Arsenic}}}|{{{2|{{{1|Arsenic}}}}}}]] in Wiktionary, the free dictionary
Categories: Metalloids| Pnictogens| Toxicology| Chemical elements
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
