Arsenic

Notable characteristics

Arsenic is very similar chemically to its predecessor, stimulants, and were once popular in small doses as medicinals by people in the mid 18th century.

When heated in air it density of the yellow form is 1.97 g/cm³; rhombohedral 'gray arsenic' is much denser with a density of 5.73 g/cm³; the other metalloidal forms are similarly dense.

Applications

Lead hydrogen arsenate has been used, well into the 20th century, as an insecticide on fruit trees (sometimes resulting in brain damage to those working the sprayers), and 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 wood which 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 century as a structural, and outdoor building material, where there was a risk of rot, or insect infestation in untreated timber. Although widespread bans followed the publication of studies which showed low-level leaching from in-situ timbers (such as children's playground equipment) into surrounding soil, the most serious^{[citation needed]} 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). Scrap CCA construction timber continues to be widely burnt through ignorance, in both commercial and domestic fires. Protocols for safe disposal of CCA timber are still in place only patchily; there is concern in some quarters about the widespread landfill disposal of such timber.

During the 18th, 19th, and 20th centuries, a number of arsenic compounds have been used as medicines, including arsenic trioxide (by Thomas Fowler). Arsphenamine as well as 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 US ATRA.^[3] It was also used as Fowler's solution in psoriasis.^[4]

Copper acetoarsenite was used as a green arsenic poisonings.

Other uses;

• Various agricultural insecticides, termination and poisons.
• Used in animal feed, particularly in the US as a method of disease prevention and growth stimulation.
• light.
• Also used in bronzing and pyrotechny.

Occupational Exposures

Exposure to higher-than-average levels of arsenic can occur in some occupations placing workers at risk. Industries that use inorganic arsenic and its compounds include wood preservation, glass production, nonferrous metal alloys, and electronic semiconductor manufacturing. Inorganic arsenic is also found in coke oven emissions associated with the smelter industry. ^[5]

History

The word arsenic is borrowed from the Persian word زرنيخ Zarnikh meaning "yellow 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 murder one another and its 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 bronze, which made the alloy harder (so-called "arsenical bronze").

Albertus Magnus (Albert the Great, 1193-1280) is believed to have been the first to isolate the element in 1250^[6]. In 1649 Johann Schröder published two ways of preparing arsenic.

 

In the Victorian era, 'arsenic' (colourless, crystalline, soluble 'white arsenic') was mixed with vinegar and chalk and eaten by women to improve the complexion of their faces, making their skin paler to show they did not work in the fields. Arsenic was also rubbed into the faces and arms of women to 'improve their complexion'. The accidental use of arsenic in the adulteration of foodstuffs led to the Bradford sweet poisoning in 1858, which resulted in approximately 20 deaths and 200 people taken ill with arsenic poisoning.

Occurrence

    In 2005, China was the top producer of white arsenic with almost 50% world share followed by Chile and Peru, reports the British Geological Survey.

mineral. On roasting in air, the arsenic sublimes as arsenic (III) oxide leaving iron oxides.

The most important compounds of arsenic are arsenic (III) oxide, As₂O₃, ('erythrite, Co₃(AsO₄)₂. 8H₂O, and more rarely arsenites ('arsenite' = arsenate(III), AsO₃^3- as opposed to arsenate (V), AsO₄^3-). 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.

Nickernuts are said to contain arsenic. See also Arsenate minerals.

Toxicity

Main article: Arsenic poisoning

Arsenic and many of its compounds are especially potent poisons. Arsenic disrupts apoptosis. A post mortem reveals brick red colored mucosa, due to severe hemorrhage. Although arsenic causes toxicity, it can also play a protective role.^[7].

Elemental arsenic and arsenic compounds are classified as "toxic" and "dangerous for the environment" in the European Union under directive 67/548/EEC.

The IARC recognizes arsenic and arsenic compounds as carcinogens.

Arsenic is known to cause arsenicosis due to its manifestation in drinking water, “the most common species being arsenate [HAsO₄^2- ; As(V)] and arsenite [H₃AsO₃ ; As(III)]”. The ability of arsenic to undergo redox conversion between As(III) and As(V) makes its availability in the environment possible. According to Croal, Gralnick, Malasarn, and Newman, “[the] understanding [of] what stimulates As(III) oxidation and/or limits As(V) reduction is relevant for bioremediation of contaminated sites (Croal). The study of chemolithoautotrophic As(III) oxidizers and the heterotrophic As(V) reducers can help the understanding of the oxidation and/or reduction of arsenic.^[8]

Arsenic in drinking water

Main article: Arsenic contamination of groundwater

Arsenicosis was reported in Nakhon Si Thammarat, Thailand in 1987, and the dissolved arsenic in the Chao Phraya River is suspected of containing high levels of naturally occurring arsenic, but has not been a public health problem due to the use of bottled water.^[10]

The northern United States, including parts of Michigan, Wisconsin, Minnesota and the Dakotas are known to have significant concentrations of arsenic in ground water. Increased levels of skin cancer has been associated with arsenic exposure in Wisconsin, even at levels below the 10 part per billion drinking water standard.^[11]

Epidemiological evidence from Chile shows a dose dependent connection between chronic arsenic exposure and various forms of cancer, particularly when other risk factors, such as cigarette smoking, are present. These effects have been demonstrated to persist below 50 parts per billion. ^[12]

A study of cancer rates in Taiwan ^[13] suggested that significant increases in cancer mortality appear only at levels above 150 parts per billion.

Analyzing multiple epidemiological studies on inorganic arsenic exposure suggests a small but measurable risk increase for bladder cancer at 10 parts per billion.^[14] According to Peter Ravenscroft, of the Department of Geography at the University of Cambridge ^[15] roughly 80 million people worldwide consume between 10 and 50 parts per billion arsenic in their drinking water. If they all consumed exactly 10 parts per billion arsenic in their drinking water, the previously cited multiple epidemiological study analysis would predict an additional 2,000 cases of bladder cancer alone. This represents a clear underestimate of the overall impact, since it does not include lung or skin cancer, and explicitly underestimates the exposure. Those exposed to levels of arsenic above the current WHO standard should weigh the costs and benefits of arsenic remmediation.

Arsenic can be removed from drinking water through coprecipitation of iron minerals by oxidation and filtering. When this treatment fails to produce acceptable results, adsorptive arsenic removal media may be utilized. Several adsorptive media systems have been approved for point of service use in a study funded by the United States Environmental Protection Agency (U.S.EPA) and the National Science Foundation (NSF).

Magnetic separations of arsenic at very low magnetic field gradients have been demonstrated in point-of-use water purification with high–surface area and monodisperse magnetite (Fe₃O₄) nanocrystals. Using the high specific surface area of Fe₃O₄ nanocrystals the mass of waste associated with arsenic removal from water has been dramatically reduced. ^[16]

Compounds

• Arsenic acid (H₃AsO₄)
• Arsenous acid (H₃AsO₃)
• Arsenic trioxide (As₂O₃)
• Arsine (Arsenic Trihydride AsH₃)
• Cadmium arsenide (Cd₃As₂)
• Gallium arsenide (GaAs)
• Lead hydrogen arsenate (PbHAsO₄)

Arsenic also occurs in the II oxidation state, but only in the As₂⁴⁺ cation, As(II) is never found otherwise.^[17]

See also Arsenic compounds.

Isotopes

Main article: isotopes of arsenic

Arsenic has been proposed as a "fallout for several hours.^{[citation needed]} Such a weapon is not known to have ever been built, tested, or used.

Notes

References

• Los Alamos National Laboratory – Arsenic

See also

• Aqua Tofana
• Arsenic poisoning
• Arsenicosis
• Fowler's solution
• Grainger challenge
• Black arsenic
• White arsenic