Arsenic (pronounced /ˈɑrsənɪk/, ARS-ə-nik; also /ɑrˈsɛnɪk/, ar-SEN-ik when attributive) is the chemical element that has the symbol As, atomic number 33 and atomic mass 74.92. Arsenic was first documented by Albertus Magnus in 1250.[4] Arsenic is a notoriously poisonous metalloid with many allotropic forms, including a yellow (molecular non-metallic) and several black and grey forms (metalloids). Three metalloidal forms of arsenic, each with a different crystal structure, are found free in nature (the minerals arsenic sensu stricto and the much rarer arsenolamprite and pararsenolamprite). However, it is more commonly found as arsenide and in arsenate compounds, several hundred of which are known. Arsenic and its compounds are used as pesticides, herbicides, insecticides and in various alloys.

History

The word arsenic was borrowed from the Syriac word ܠܐ ܙܐܦܢܝܐ (al) zarniqa [5] and the Persian word زرنيخ Zarnikh, meaning "yellow orpiment", into Greek as arsenikon (Αρσενικόν). It is also related to the similar Greek word arsenikos (Αρσενικός), meaning "masculine" or "potent". The word was adopted in Latin arsenicum and Old French arsenic, from which the English word arsenic is derived.[5] Arsenic sulfides (orpiment, realgar) and oxides have been known and used since ancient times.[6] Zosimos (circa 300 AD) describes roasting sandarach (realgar) to obtain cloud of arsenic (arsenious oxide) which he then reduces to metallic arsenic.[7] As the symptoms of arsenic poisoning were somewhat ill-defined, it was frequently used for murder until the advent of the Marsh test, a sensitive chemical test for its presence. (Another less sensitive but more general test is the Reinsch test.) Owing 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.[8]

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 by heating soap together with arsenic trisulfide.[4] In 1649, Johann Schröder published two ways of preparing arsenic.
Alchemical symbol for arsenic

Cadet's fuming liquid (impure cacodyl), the first organometallic compound, was synthesized in 1760 by Louis Claude Cadet de Gassicourt by the reaction of potassium acetate with arsenic trioxide.[9]

In the Victorian era, "arsenic" (colourless, crystalline, soluble "white arsenic" trioxide) 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.[10]

Characteristics

Isotopes
Main article: Isotopes of arsenic

Naturally occurring arsenic is composed of one stable isotope, 75As.[11] As of 2003, at least 33 radioisotopes have also been synthesized, ranging in atomic mass from 60 to 92. The most stable of these is 73As with a half-life of 80.3 days. Isotopes that are lighter than the stable 75As tend to decay by β+ decay, and those that are heavier tend to decay by β- decay, with some exceptions.

At least 10 nuclear isomers have been described, ranging in atomic mass from 66 to 84. The most stable of arsenic's isomers is 68mAs with a half-life of 111 seconds.[11]

Allotropes
Structure of yellow arsenic As4 and white phosphorus P4

Like phosphorus, arsenic is an excellent example of an element that exhibits allotropy, as its various allotropes have strikingly different properties. The three most common allotropes are metallic grey, yellow and black arsenic.[12]

The most common allotrope of arsenic is grey arsenic. It has a similar structure to black phosphorus (β-metallic phosphorus) and has a layered crystal structure somewhat resembling that of graphite. It consists of many six-membered rings which are interlinked. Each atom is bound to three other atoms in the layer and is coordinated by each 3 arsenic atoms in the upper and lower layer. This relatively close packing leads to a high density of 5.73 g/cm3.[13]

Yellow arsenic (As4) is soft and waxy, not unlike P4. Both have four atoms arranged in a tetrahedral structure in which each atom is bound to each of the other three atoms by a single bond, resulting in very high ring strain and instability. This form of arsenic is the least stable, most reactive, most volatile, least dense, and most toxic of all the allotropes. Yellow arsenic is produced by rapid cooling of arsenic vapour with liquid nitrogen. It is rapidly transformed into the grey arsenic by light. The yellow form has a density of 1.97 g/cm3.[13]

Black arsenic is similar in structure to red phosphorus.[13]

Chemical

The most common oxidation states for arsenic are −3 (arsenides: usually alloy-like intermetallic compounds), +3 (arsenates(III) or arsenites, and most organoarsenic compounds), and +5 (arsenates: the most stable inorganic arsenic oxycompounds). Arsenic also bonds readily to itself, forming square As3−4 ions in the arsenide skutterudite. In the +3 oxidation state, the stereochemistry of arsenic is affected by the presence of a lone pair of electrons.

Arsenic is very similar chemically to its predecessor in the Periodic Table, phosphorus. Like phosphorus, it forms colourless, odourless, crystalline oxides As2O3 and As2O5 which are hygroscopic and readily soluble in water to form acidic solutions. Arsenic(V) acid is a weak acid. Like phosphorus, arsenic forms an unstable, gaseous hydride: arsine (AsH3). The similarity is so great that arsenic will partly substitute for phosphorus in biochemical reactions and is thus poisonous. However, in subtoxic doses, soluble arsenic compounds act as stimulants, and were once popular in small doses as medicine by people in the mid 18th century.[13]

When heated in air, arsenic oxidizes to arsenic trioxide; the fumes from this reaction have an odour resembling garlic. This odour can be detected on striking arsenide minerals such as arsenopyrite with a hammer. Arsenic (and some arsenic compounds) sublimes upon heating at atmospheric pressure, converting directly to a gaseous form without an intervening liquid state. The liquid state appears at 20 atmospheres and above, which explains why the melting point is higher than the boiling point.[13]

Compounds
See also: Category:Arsenic compounds

Arsenic compounds resemble in many respects those of phosphorus as both arsenic and phosphorus occur in the same group (column) of the periodic table.

The most important compounds of arsenic are arsenic(III) oxide, As2O3, ("white arsenic"), the yellow sulfide orpiment (As2S3) and red realgar (As4S4), Paris Green, calcium arsenate, and lead hydrogen arsenate. The latter three have been used as agricultural insecticides and poisons.

Whilst arsenic trioxide forms during oxidation of arsenic, arsenic pentoxide is formed by the dehydration of arsenic acid. Both oxides dissolve in strong alkaline solution, with the formation of arsenite AsO3−3 and arsenate AsO3−4 respectively. The protonation steps between the arsenate and arsenic acid are similar to those between phosphate and phosphoric acid. However, arsenite and arsenous acid contain arsenic bonded to three oxygen and not hydrogen atoms, in contrast to phosphite and phosphorous acid (more accurately termed 'phosphonic acid'), which contain non-acidic P-H bonds. Arsenous acid is genuinely tribasic, whereas phosphonic acid is not.

A broad variety of sulfur compounds of arsenic are known, As4S3, As4S4, As2S3 and As4S10. All arsenic(III) halogen compounds (except with astatine) are known and stable. For the arsenic(V) compounds the situation is different: only the arsenic pentafluoride is stable at room temperature. Arsenic pentachloride is only stable at temperatures below −50 °C and the pentabromide and pentaiodide are unknown.[13]

Arsenic is used as group 5 element as part of the III-V semiconducting compounds. Gallium arsenide, indium arsenide and aluminium arsenide are used as semiconductor material when the properties of silicon are not suitable for the application and the higher price of the compounds is acceptable. Other arsenic compounds include:

* 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 has a formal oxidation state of +2 in As4S4, realgar. This is achieved by pairing As atoms to produce dimeric cations [As-As]2+, so the total covalency of As is still in fact three.[14]

Occurrence
See also: Arsenide minerals and Arsenate minerals
A large sample of native arsenic.

Arsenopyrite, also unofficially called mispickel,[15] (FeAsS) is the most common arsenic-bearing mineral. In the lithosphere, the minerals of the formula M(II)AsS, with M(II) being mostly Fe, Ni and Co, are the dominant arsenic minerals.
Realgar

Orpiment and realgar were formerly used as painting pigments, though they have fallen out of use owing to their toxicity and reactivity. Although arsenic is sometimes found native in nature, its main economic source is the mineral arsenopyrite mentioned above; it is also found in arsenides of metals such as silver, cobalt (cobaltite: CoAsS and skutterudite: CoAs3) and nickel, as sulfides, and when oxidised as arsenate minerals such as mimetite, Pb5(AsO4)3Cl and erythrite, Co3(AsO4)2·8H2O, and more rarely arsenites ('arsenite' = arsenate(III), AsO33− as opposed to arsenate (V), AsO43−).

In addition to the inorganic forms mentioned above, arsenic also occurs in various organic forms in the environment.[16]

Other naturally occurring pathways of exposure include volcanic ash, weathering of the arsenic-containing mineral and ores as well as groundwater. It is also found in food, water, soil and air.[17]

Production
Arsenic output in 2006[18]

In 2005, China was the top producer of white arsenic with almost 50% world share, followed by Chile, Peru and Morocco, reports the British Geological Survey and the United States Geological Survey.[18] The arsenic was recovered mostly during mining operations, for example the production from Peru comes mostly from copper mining and the production in China is owing to gold mining. Arsenic is part of the smelter dust from copper, gold, and lead smelters.[19]

On roasting in air of arsenopyrite, arsenic sublimes as arsenic (III) oxide leaving iron oxides[16], while roasting without air results in the production of metallic arsenic. Further purification from sulfur and other chalcogens is achieved by sublimation in vacuum or in a hydrogen atmosphere or by distillation from molten lead-arsenic mixture.[20]

Applications

Wood preservation

The toxicity of arsenic to insects, bacteria, and fungi led to its use as a wood preservative. In the 1950s a process of treating wood with chromated copper arsenate (also known as CCA or Tanalith) was invented, and for decades this treatment was the most extensive industrial use of arsenic. Due to improved understanding of arsenic's high level of toxicity, most countries banned the use of CCA in consumer products. The European Union and United States led this ban, beginning in 2004.[21][22]

As of 2002, US-based industries consumed 19,600 metric tons of arsenic. 90% of this was used for treatment of wood with CCA. In 2007, 50% of the 5,280 metric tons of consumption was still used for this purpose.[19][23] In the United States, the use of arsenic in consumer products was discontinued for residential and general consumer construction on December 31, 2003 and alternative chemicals are now used, such as ACQ, borates, copper azole, cyproconazole, and propiconazole.[24]

Although discontinued, this application is also one of the most concern to the general public. The vast majority of older pressure-treated wood was treated with CCA. CCA lumber 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. Although the use of CCA lumber was banned in many areas after studies showed that arsenic could leach out of the wood into the surrounding soil (from playground equipment, for instance), a risk is also presented by the burning of older CCA timber. The direct or indirect ingestion of wood ash from burnt CCA lumber has caused fatalities in animals and serious poisonings in humans; the lethal human dose is approximately 20 grams of ash. Scrap CCA lumber from construction and demolition sites may be inadvertently used in commercial and domestic fires. Protocols for safe disposal of CCA lumber do not exist evenly throughout the world; there is also concern in some quarters about the widespread landfill disposal of such timber.[25]

Medical

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 Neosalvarsan was indicated for syphilis and trypanosomiasis, but has been superseded by modern antibiotics. Arsenic trioxide has been used in a variety of ways over the past 500 years, but most commonly in the treatment of cancer. The US Food and Drug Administration in 2000 approved this compound for the treatment of patients with acute promyelocytic leukemia that is resistant to ATRA.[26] It was also used as Fowler's solution in psoriasis.[27] Recently new research has been done in locating tumours using arsenic-74 (a positron emitter). The advantages of using this isotope instead of the previously used iodine-124 is that the signal in the PET scan is clearer as the iodine tends to transport iodine to the thyroid gland producing a lot of noise.[28]

Pigments

Copper acetoarsenite was used as a green pigment known under many different names, including 'Paris Green' and 'Emerald Green'. It caused numerous arsenic poisonings. Scheele's Green, a copper arsenate, was used in the 19th century as a colouring agent in sweets.[29]

Military

After World War I the United States built up a stockpile of 20,000 tons of lewisite; a chemical weapon, acting as a vesicant (blister agent) and lung irritant. The stockpile was neutralized with bleach and dumped into the Gulf of Mexico after the 1950s.[30] During the Vietnam War the United States used Agent Blue (a mixture of sodium cacodylate) and dimethyl arsenic acid (cacodylic acid) as one of the rainbow herbicides to deprive the Vietnamese of valuable crops.

Other uses

* Various agricultural insecticides, termination and poisons. For example Lead hydrogen arsenate was used well into the 20th century as an insecticide on fruit trees.[31] Its use sometimes resulted in brain damage to those working the sprayers. In the last half century, monosodium methyl arsenate (MSMA) and disodium methyl arsenate (DSMA), a less toxic organic form of arsenic, has replaced lead arsenate's role in agriculture.
* Used in animal feed, particularly in the US as a method of disease prevention[32][33] and growth stimulation. One example is roxarsone which was used by 69.8 and 73.9% of the broiler starter and growers between 1995 to 2000.[34]
* Gallium arsenide is an important semiconductor material, used in integrated circuits. Circuits made using the compound are much faster (but also much more expensive) than those made in silicon. Unlike silicon it is direct bandgap, and so can be used in laser diodes and LEDs to directly convert electricity into light.
* Also used in bronzing and pyrotechnics.
* Up to 2% of arsenic is used in lead alloys for lead shots and bullets.[35]
* Arsenic is added in small quantities to brass to make it dezincification resistant. This grade of brass is used to make plumbing fittings.
* Arsenic is also used for taxonomic sample preservation.
* Until recently Arsenic was used in optical glass. Modern glass manufacturers, under pressure from environmentalists, have removed it, along with Lead.[36]

Biological role
Trimethylarsine
Arsenobetaine

Inorganic arsenic and its compounds, upon entering the food chain, are progressively metabolised to less toxic forms of arsenic through a process of methylation. For example, the mold Scopulariopsis brevicaulis produce significant amounts of trimethylarsine if inorganic arsenic is present.[37] The organic compound arsenobetaine is found in some marine foods such as fish and algae, and also in mushrooms in larger concentrations. The average person's intake is about 10–50 µg/day. Values about 1000 µg are not unusual following consumption of fish or mushrooms. But there is little danger in eating fish because this arsenic compound is nearly non-toxic.[38]

Some species of bacteria obtain their energy by oxidizing various fuels while reducing arsenate to arsenite. The enzymes involved are known as arsenate reductases (Arr).

In 2008, bacteria were discovered that employ a version of photosynthesis in the absence of oxygen with arsenites as electron donors, producing arsenates (just like ordinary photosynthesis uses water as electron donor, producing molecular oxygen). Researchers conjecture that historically these photosynthesizing organisms produced the arsenates that allowed the arsenate-reducing bacteria to thrive. One strain PHS-1 has been isolated and is related to the γ-Proteobacterium Ectothiorhodospira shaposhnikovii. The mechanism is unknown, but an encoded Arr enzyme may function in reverse to its known homologues.[39]

Arsenic has been linked to epigenetic changes which are heritable changes in gene expression that occur without changes in DNA sequence and include DNA methylation, histone modification and RNA interference. Toxic levels of arsenic cause significant DNA hypermethylation of tumour suppressor genes p16 and p53 thus increasing risk of carcinogenesis. These epigenetic events have been observed in in vitro studies with human kidney cells and in vivo tests with rat liver cells and peripheral blood leukocytes in humans.[40] Inductive coupled plasma mass spectrometry (ICP-MS) is used to detect precise levels of intracellular of arsenic and its other bases involved in epigenetic modification of DNA.[41] Studies investigating arsenic as an epigenetic factor will help in developing precise biomarkers of exposure and susceptibility.

Mapping of industrial releases in the United States

One tool that maps releases of arsenic [1] to particular locations in the United States[42] and also provides additional information about such releases is TOXMAP. TOXMAP is a Geographic Information System (GIS) from the Division of Specialized Information Services of the United States National Library of Medicine (NLM) that uses maps of the United States to help users visually explore data from the United States Environmental Protection Agency's (EPA) Toxics Release Inventory and Superfund Basic Research Programs. TOXMAP is a resource funded by the US Federal Government. TOXMAP's chemical and environmental health information is taken from NLM's Toxicology Data Network (TOXNET)[43] and PubMed, and from other authoritative sources.

Safety
Main articles: Arsenic poisoning and Arsenic toxicity

Arsenic and many of its compounds are especially potent poisons. Arsenic disrupts ATP production through several mechanisms. At the level of the citric acid cycle, arsenic inhibits lipoic acid which is a cofactor for pyruvate dehydrogenase; and by competing with phosphate it uncouples oxidative phosphorylation, thus inhibiting energy-linked reduction of NAD+, mitochondrial respiration, and ATP synthesis. Hydrogen peroxide production is also increased, which might form reactive oxygen species and oxidative stress. These metabolic interferences lead to death from multi-system organ failure, probably from necrotic cell death, not apoptosis. A post mortem reveals brick red coloured mucosa, owing to severe haemorrhage. Although arsenic causes toxicity, it can also play a protective role.[44]

Elemental arsenic and arsenic compounds are classified as "toxic" and "dangerous for the environment" in the European Union under directive 67/548/EEC. The International Agency for Research on Cancer (IARC) recognizes arsenic and arsenic compounds as group 1 carcinogens, and the EU lists arsenic trioxide, arsenic pentoxide and arsenate salts as category 1 carcinogens.

Arsenic is known to cause arsenicosis owing to its manifestation in drinking water, “the most common species being arsenate [HAsO42- ; 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 more abundant. 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.[45]

Treatment of chronic arsenic poisoning is easily accomplished. British anti-lewisite (dimercaprol) is prescribed in dosages of 5 mg/kg up to 300 mg each 4 hours for the first day. Then administer the same dosage each 6 hours for the second day. Then prescribe this dosage each 8 hours for eight additional days.[46]

Arsenic in drinking water
Main article: Arsenic contamination of groundwater

Arsenic contamination of groundwater has led to a massive epidemic of arsenic poisoning in Bangladesh[47] and neighbouring countries. Presently 42 major incidents around the world have been reported on groundwater arsenic contamination. It is estimated that approximately 57 million people are drinking groundwater with arsenic concentrations elevated above the World Health Organization's standard of 10 parts per billion. However, a study of cancer rates in Taiwan[48] suggested that significant increases in cancer mortality appear only at levels above 150 parts per billion. The arsenic in the groundwater is of natural origin, and is released from the sediment into the groundwater owing to the anoxic conditions of the subsurface. This groundwater began to be used after local and western NGOs and the Bangladeshi government undertook a massive shallow tube well drinking-water program in the late twentieth century. This program was designed to prevent drinking of bacterially contaminated surface waters, but failed to test for arsenic in the groundwater. Many other countries and districts in South East Asia, such as Vietnam, Cambodia, and China have geological environments conducive to generation of high-arsenic groundwaters. 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 owing to the use of bottled water.[49]

In the United States, arsenic is most commonly found in the ground waters of the southwest.[50] Parts of New England, Michigan, Wisconsin, Minnesota and the Dakotas are also known to have significant concentrations of arsenic in ground water. Increased levels of skin cancer have been associated with arsenic exposure in Wisconsin, even at levels below the 10 part per billion drinking water standard.[51] According to a recent film funded by the US Superfund, millions of private wells have unknown arsenic levels, and in some areas of the US, over 20% of wells may contain levels that exceed established limits.[52]

Low-level exposure to arsenic at concentrations found commonly in US drinking water compromises the initial immune response to H1N1 or swine flu infection according to NIEHS-supported scientists. The study, conducted in laboratory mice, suggests that people exposed to arsenic in their drinking water may be at increased risk for more serious illness or death in response to infection from the virus.[53]

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.[54]

Analyzing multiple epidemiological studies on inorganic arsenic exposure suggests a small but measurable risk increase for bladder cancer at 10 parts per billion.[55] According to Peter Ravenscroft of the Department of Geography at the University of Cambridge,[56] 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 remediation.

Early (1973) evaluations of the removal of dissolved arsenic by drinking water treatment processes demonstrated that arsenic is very effectively removed by co-precipitation with either iron or aluminum oxides. The use of iron as a coagulant, in particular, was found to remove arsenic with efficiencies exceeding 90%.[57][58] 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). A team of European and Indian scientists and engineers have set up six arsenic treatment plants in West Bengal based on in-situ remediation method (SAR Technology). This technology does not use any chemicals and arsenic is left as an insoluble form (+5 state) in the subterranean zone by recharging aerated water into the aquifer and thus developing an oxidation zone to support arsenic oxidizing micro-organisms. This process does not produce any waste stream or sludge and is relatively cheap.[59]

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.[60]

Epidemiological studies have suggested a correlation between chronic consumption of drinking water contaminated with arsenic and the incidence of type 2 diabetes. However, the literature provides insufficient scientific evidence to show cause and effect between arsenic and the onset of diabetes mellitus type 2.

Occupational exposures
Main article: Arsenic poisoning

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.[61] Occupational exposure and poisoning may occur in persons working in these industries.

Arsenic: environmental chemistry, health threats and waste treatment, Kevin R. Henke

Arsenic in ground water, geochemisty and occurence, Alan H. Welch, Kenneth G. Stollenwerk

Arsenic pollution: a global synthesis, Peter Ravenscroft, H. Brammer, K. S. Richards

The arsenic century: how Victorian Britain was poisoned at home, work, and play, James C. Whorton

Managing arsenic in the environment: from soil to human health, R. Naidu

Is arsenic an aphrodisiac?: the sociochemistry of an element, William R. Cullen

See also

* Aqua Tofana
* Arsenic poisoning
* Arsenic trioxide
* Fowler's solution
* Grainger challenge
* White arsenic

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External links

* CTD's Arsenic page and CTD's Arsenicals page from the Comparative Toxicogenomics Database
* A Small Dose of Toxicology
* ATSDR - Case Studies in Environmental Medicine: Arsenic Toxicity
* Contaminant Focus: Arsenic by the EPA.
* Environmental Health Criteria for Arsenic and Arsenic Compounds, 2001 by the WHO.
* Evaluation of the carcinogenicity of arsenic and arsenic compounds by the IARC.
* National Institute for Occupational Safety and Health - Arsenic Page
* National Pollutant Inventory - Arsenic
* origen.net – CCA wood and arsenic: toxicological effects of arsenic
* WebElements.com – Arsenic