The primary use of arsenic is in alloys of lead (for example, incar batteries andammunition). Arsenic is also a common n-typedopant insemiconductor electronic devices, and a component of the III–Vcompound semiconductorgallium arsenide. Arsenic and its compounds, especially the trioxide, are used in the production ofpesticides, treated wood products,herbicides, andinsecticides. These applications are declining with the increasing recognition of the toxicity of arsenic and its compounds.[15]
Arsenic has been known since ancient times to be poisonous to humans.[16] However, a few species of bacteria are able to use arsenic compounds as respiratorymetabolites. Trace quantities of arsenic have been proposed to be an essentialdietary element in rats, hamsters, goats, and chickens. Research has not been conducted to determine whether small amounts of arsenic may play a role in human metabolism.[17][18] However,arsenic poisoning occurs in multicellular life if quantities are larger than needed.Arsenic contamination of groundwater is a problem that affects millions of people across the world.
Crystal structure common toSb,AsSb and grey AsGray arsenic nodule
The three most common arsenicallotropes are grey, yellow, and black arsenic, with grey being the most common.[21] Grey arsenic (α-As,space group R3m No. 166) adopts a double-layered structure consisting of many interlocked, ruffled, six-membered rings. Because of weak bonding between the layers, grey arsenic is brittle and has a relatively lowMohs hardness of 3.5. Nearest and next-nearest neighbors form a distorted octahedral complex, with the three atoms in the same double-layer being slightly closer than the three atoms in the next.[22] This relatively close packing leads to a high density of 5.73 g/cm3.[23] Grey arsenic is asemimetal, but becomes asemiconductor with abandgap of 1.2–1.4 eV ifamorphized.[24] Grey arsenic is also the most stable form.Yellow arsenic is soft and waxy, and somewhat similar totetraphosphorus (P4).[25] Both have four atoms arranged in atetrahedral structure in which each atom is bound to each of the other three atoms by a single bond. This unstable allotrope, being molecular, is the most volatile, least dense, and most toxic. Solid yellow arsenic is produced by rapid cooling of arsenic vapor,As4. It is rapidly transformed into grey arsenic by light. The yellow form has a density of 1.97 g/cm3.[23] Black arsenic is similar in structure toblack phosphorus.[23]Black arsenic can also be formed by cooling vapor at around 100–220 °C and by crystallization of amorphous arsenic in the presence of mercury vapors.[26] It is glassy and brittle. Black arsenic is also a poor electrical conductor.[27]
Arsenicsublimes upon heating atatmospheric pressure, converting directly to a gaseous form without an intervening liquid state at 887 K (614 °C). Thetriple point is at 3.63 MPa and 1,090 K (820 °C).[23][4]
Arsenic occurs in nature as one stableisotope,75As, and is therefore called amonoisotopic element.[28] As of 2024, at least 32radioisotopes have also been synthesized, ranging inatomic mass from 64 to 95.[29][30] The most stable of these is73As with ahalf-life of 80.30 days. All other isotopes have half-lives of under one day, with the exception of71As (t1/2=65.30 hours),72As (t1/2=26.0 hours),74As (t1/2=17.77 days),76As (t1/2=26.26 hours), and77As (t1/2=38.83 hours). Isotopes that are lighter than the stable75As tend to decay byβ+ decay, and those that are heavier tend to decay byβ− decay, with some exceptions.
At least 10nuclear isomers have been described, ranging in atomic mass from 66 to 84. The most stable of arsenic's isomers is68mAs with a half-life of 111 seconds.[28]
Arsenic has a similarelectronegativity andionization energies to its lighterpnictogencongener phosphorus and therefore readily formscovalent molecules with most of thenonmetals. Though stable in dry air, arsenic forms a golden-bronzetarnish upon exposure to humidity which eventually becomes a black surface layer.[31] When heated in air, arsenicoxidizes toarsenic trioxide; the fumes from this reaction have an odor resembling garlic. This odor can be detected on strikingarsenide minerals such asarsenopyrite with a hammer.[4] It burns in oxygen to form arsenic trioxide andarsenic pentoxide, which have the same structure as the more well-known phosphorus compounds, and in fluorine to givearsenic pentafluoride.[31] Arsenic makesarsenic acid with concentratednitric acid,arsenous acid with dilute nitric acid, andarsenic trioxide with concentratedsulfuric acid; however, it does not react with water, alkalis, or non-oxidising acids.[32] Arsenic reacts with metals to formarsenides, though these are not ionic compounds containing the As3− ion as the formation of such an anion would be highly endothermic and even the group 1 arsenides have properties ofintermetallic compounds.[31] Likegermanium,selenium, andbromine, which like arsenicsucceed the 3d transition series, arsenic is much less stable in the +5oxidation state than its vertical neighbors phosphorus andantimony, and hence arsenic pentoxide and arsenic acid are potentoxidizers.[31]
Compounds of arsenic resemble, in some respects, those ofphosphorus, which occupies the samegroup (column) of theperiodic table. The most commonoxidation states for arsenic are: −3 in thearsenides, which are alloy-like intermetallic compounds, +3 in thearsenites, and +5 in thearsenates and most organoarsenic compounds. Arsenic also bonds readily to itself as seen in the squareAs3−4 ions in the mineralskutterudite.[33] In the +3oxidation state, arsenic is typically pyramidal owing to the influence of thelone pair ofelectrons.[21]
One of the simplest arsenic compounds is the trihydride, the highly toxic, flammable,pyrophoricarsine (AsH3). This compound is generally regarded as stable, since at room temperature it decomposes only slowly. At temperatures of 250–300 °C decomposition to arsenic and hydrogen is rapid.[34] Several factors, such ashumidity, presence of light and certaincatalysts (namely aluminium) facilitate the rate of decomposition.[35] It oxidises readily in air to form arsenic trioxide and water, and analogous reactions take place withsulfur andselenium instead ofoxygen.[34]
A broad variety of sulfur compounds of arsenic are known. Orpiment (As2S3) and realgar (As4S4) are somewhat abundant and were formerly used as painting pigments. In As4S10, arsenic has a formal oxidation state of +2 in As4S4 which features As-As bonds so that the total covalency of As is still 3.[38] Both orpiment and realgar, as well as As4S3, have selenium analogs; the analogous As2Te3 is known as the mineralkalgoorlieite,[39] and the anion As2Te− is known as a ligand incobalt complexes.[40]
All trihalides of arsenic(III) are well known except the astatide, which is unknown.Arsenic pentafluoride (AsF5) is the only important pentahalide, reflecting the lower stability of the +5 oxidation state; even so, it is a very strong fluorinating and oxidizing agent. (Thepentachloride is stable only below −50 °C, at which temperature it decomposes to the trichloride, releasing chlorine gas.[23])
A large variety of organoarsenic compounds are known. Several were developed aschemical warfare agents during World War I, includingvesicants such aslewisite and vomiting agents such asadamsite.[44][45][46]Cacodylic acid, which is of historic and practical interest, arises from themethylation of arsenic trioxide, a reaction that has no analogy in phosphorus chemistry.Cacodyl was the first organometallic compound known (even though arsenic is not a true metal) and was named from the Greekκακωδία "stink" for its offensive, garlic-like odor; it is very toxic.[47]
Arsenic is the 53rd most abundant element in theEarth's crust, comprising about 1.5 parts per million (0.00015%).[48] Typical background concentrations of arsenic do not exceed 3 ng/m3 in the atmosphere; 100 mg/kg in soil; 400 μg/kg in vegetation; 10 μg/L in freshwater and 1.5 μg/L in seawater.[49] Arsenic is the 22nd most abundant element in seawater[50] and ranks 41st in abundance in the universe.[51][unreliable source?]
Minerals with the formula MAsS and MAs2 (M =Fe,Ni,Co) are the dominant commercial sources of arsenic, together withrealgar (an arsenic sulfide mineral) and native (elemental) arsenic. An illustrative mineral isarsenopyrite (FeAsS), which is structurally related toiron pyrite. Many minor As-containing minerals are known. Arsenic also occurs in various organic forms in the environment.[52]
In 2014, China was the top producer of white arsenic with almost 70% world share, followed by Morocco, Russia, and Belgium, according to theBritish Geological Survey and theUnited States Geological Survey.[54] Most arsenic refinement operations in the US and Europe have closed over environmental concerns. Arsenic is found in the smelter dust from copper, gold, and lead smelters, and is recovered primarily from copper refinement dust.[55]
Onroasting arsenopyrite in air, arsenic sublimes as arsenic(III) oxide leaving iron oxides,[52] while roasting without air results in the production of gray arsenic. Further purification from sulfur and other chalcogens is achieved bysublimation in vacuum, in a hydrogen atmosphere, or by distillation from molten lead-arsenic mixture.[56]
The wordarsenic has its origin in theSyriac wordܙܪܢܝܟܐzarnika,[57][58] from Arabic al-zarnīḵالزرنيخ 'theorpiment', based onPersian zar ("gold") from the wordزرنيخzarnikh, meaning "yellow" (literally "gold-colored") and hence "(yellow) orpiment". It was adopted intoGreek (usingfolk etymology) asarsenikon (ἀρσενικόν) – a neuter form of the Greek adjectivearsenikos (ἀρσενικός), meaning "male", "virile".
Latin-speakers adopted the Greek term asarsenicum, which in French ultimately becamearsenic, whence the English word "arsenic".[58]Arsenic sulfides (orpiment,realgar) and oxides have been known and used since ancient times.[59]Zosimos (c. 300 AD) describes roastingsandarach (realgar) to obtaincloud of arsenic (arsenic trioxide), which he thenreduces to gray arsenic.[60] As the symptoms ofarsenic poisoning are not very specific, the substance was frequently used for murder until the advent in the 1830s of theMarsh test, a sensitive chemical test for its presence. (Another less sensitive but more general test is theReinsch 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".[61][62] Arsenic became known as "the inheritance powder" due to its use in killing family members in theRenaissance era.[63]
During theBronze Age, arsenic was melted with copper to makearsenical bronze.[64][65]Jabir ibn Hayyan described the isolation of arsenic before 815 AD.[66]Albertus Magnus (Albert the Great, 1193–1280) later isolated the element from a compound in 1250, by heating soap together witharsenic trisulfide.[67] In 1649,Johann Schröder published two ways of preparing arsenic.[68] Crystals of elemental (native) arsenic are found in nature, although rarely.
Satirical cartoon byHonoré Daumier of a chemist giving a public demonstration of arsenic, 1841
In theVictorian era, women would eat "arsenic" ("white arsenic" or arsenic trioxide) mixed with vinegar andchalk to improve thecomplexion of their faces, making their skin paler (to show they did not work in the fields).[70] The accidental use of arsenic in the adulteration of foodstuffs led to theBradford sweet poisoning in 1858, which resulted in 21 deaths.[71] From the late-18th century wallpaper production began to use dyes made from arsenic,[72]which was thought to increase the pigment's brightness.[73] One account of the illness and1821 death ofNapoleon I implicates arsenic poisoning involving wallpaper.[74]
Two arsenic pigments have been widely used since their discovery –Paris Green in 1814 andScheele's Green in 1775. After the toxicity of arsenic became widely known, these chemicals were used less often as pigments and more often as insecticides. In the 1860s, an arsenic byproduct of dye production, London Purple, was widely used. This was a solid mixture of arsenic trioxide, aniline, lime, and ferrous oxide, insoluble in water and very toxic by inhalation or ingestion[75] But it was later replaced withParis Green, another arsenic-based dye.[76] With better understanding of the toxicology mechanism, two other compounds were used starting in the 1890s.[77]Arsenite of lime andarsenate of lead were used widely as insecticides until the discovery ofDDT in 1942.[78][79][80]
In small doses, soluble arsenic compounds act asstimulants, and were once popular as medicine by people in the mid-18th to 19th centuries;[23][81][82] this use was especially prevalent for sport animals such asrace horses orwork dogs and continued into the 20th century.[83]A 2006 study of the remains of the Australian racehorsePhar Lap determined that its 1932 death was caused by a massive overdose of arsenic. Sydney veterinarian Percy Sykes stated, "In those days, arsenic was quite a common tonic, usually given in the form of a solution (Fowler's Solution) ... It was so common that I'd reckon 90 per cent of the horses had arsenic in their system."[84]
Roxarsone is a controversial arsenic compound used as a feed ingredient for chickens.
The toxicity of arsenic to insects, bacteria, and fungi led to its use as awood preservative.[85] In the 1930s, a process of treating wood withchromated copper arsenate (also known as CCA orTanalith) was invented, and for decades, this treatment was the most extensive industrial use of arsenic. An increased appreciation of the toxicity of arsenic led to a ban of CCA in consumer products in 2004, initiated by the European Union and United States.[86][87] However, CCA remains in heavy use in other countries (such as on Malaysian rubber plantations).[15]
Arsenic was also used in various agricultural insecticides and poisons. For example,lead hydrogen arsenate was a common insecticide onfruit trees,[88] but contact with the compound sometimes resulted in brain damage among those working the sprayers. In the second half of the 20th century,monosodium methyl arsenate (MSMA) anddisodium methyl arsenate (DSMA) – less toxic organic forms of arsenic – replaced lead arsenate in agriculture. These organic arsenicals were in turn phased out in the United States by 2013 in all agricultural activities except cotton farming.[89][90]
The biogeochemistry of arsenic is complex and includes various adsorption and desorption processes. The toxicity of arsenic is connected to its solubility and is affected by pH. Arsenite (AsO3−3) is more soluble than arsenate (AsO3−4) and is more toxic; however, at a lower pH, arsenate becomes more mobile and toxic. It was found that addition of sulfur, phosphorus, and iron oxides to high-arsenite soils greatly reduces arsenic phytotoxicity.[91]
Arsenic is used as a feed additive inpoultry andswine production, in particular it was used in the U.S. until 2015 to increase weight gain, improvefeed efficiency, and prevent disease.[92][93] An example isroxarsone, which had been used as abroiler starter by about 70% of U.S. broiler growers.[94] In 2011, Alpharma, a subsidiary of Pfizer Inc., which produces roxarsone, voluntarily suspended sales of the drug in response to studies showing elevated levels of inorganic arsenic, a carcinogen, in treated chickens.[95] A successor to Alpharma,Zoetis, continued to sellnitarsone until 2015, primarily for use in turkeys.[95]
A 2008 paper reports success in locating tumors using arsenic-74 (a positron emitter). This isotope produces clearerPET scan images than the previous radioactive agent,iodine-124, because the body tends to transport iodine to the thyroid gland producing signal noise.[99]Nanoparticles of arsenic have shown ability to kill cancer cells with lessercytotoxicity than other arsenic formulations.[100]
The main use of arsenic is in alloying with lead. Lead components incar batteries are strengthened by the presence of a very small percentage of arsenic.[15][101]Dezincification ofbrass (a copper-zinc alloy) is greatly reduced by the addition of arsenic.[102] "Phosphorus Deoxidized Arsenical Copper" with an arsenic content of 0.3% has an increased corrosion stability in certain environments.[103]Gallium arsenide is an importantsemiconductor material, used inintegrated circuits. Circuits made from GaAs are much faster (but also much more expensive) than those made fromsilicon. Unlike silicon, GaAs has adirect bandgap, and can be used inlaser diodes andLEDs to convert electrical energy directly into light.[15]
As much as 2% of produced arsenic is used in lead alloys forlead shot and bullets.[109]
Arsenic is added in small quantities to alpha-brass to make itdezincification-resistant. This grade of brass is used in plumbing fittings and other wet environments.[110]
Arsenic is also used fortaxonomic sample preservation. It was also used in embalming fluids historically.[111]
Arsenic was used in thetaxidermy process up until the 1980s.[112]
Arsenic was used as an opacifier in ceramics, creating white glazes.[113]
Until recently, arsenic was used in optical glass. Modern glass manufacturers have ceased using both arsenic and lead.[114][115][116]
Some species of bacteria obtain their energy in the absence of oxygen byoxidizing various fuels whilereducing arsenate to arsenite. Under oxidative environmental conditions some bacteria use arsenite as fuel, which they oxidize to arsenate.[117] Theenzymes involved are known asarsenate reductases (Arr).[118]
In 2008, bacteria were discovered that employ a version ofphotosynthesis in the absence of oxygen with arsenites aselectron donors, producing arsenates (just as ordinary photosynthesis uses water as electron donor, producing molecular oxygen). Researchers conjecture that, over the course of history, these photosynthesizing organisms produced the arsenates that allowed the arsenate-reducing bacteria to thrive. Onestrain, PHS-1, has been isolated and is related to thegammaproteobacteriumEctothiorhodospira shaposhnikovii. The mechanism is unknown, but an encoded Arr enzyme may function in reverse to its knownhomologues.[119]
In 2011, it was postulated that theHalomonadaceae strainGFAJ-1 could be grown in the absence of phosphorus if that element were substituted with arsenic,[120] exploiting the fact that thearsenate andphosphate anions are similar structurally. The study was widely criticised and subsequently refuted by independent researcher groups.[121][122]
Arsenic may be an essential trace mineral in birds, involved in the synthesis of methionine metabolites.[123] However, the role of arsenic in bird nutrition is disputed, as other authors state that arsenic is toxic in small amounts.[124]
Some evidence indicates that arsenic is an essential trace mineral in mammals.[17][18]
Arsenic has been linked toepigenetic changes, heritable changes in gene expression that occur without changes inDNA sequence. These include DNA methylation, histone modification, andRNA interference. Toxic levels of arsenic cause significant DNA hypermethylation of tumor suppressor genesp16 andp53, thus increasing risk ofcarcinogenesis. These epigenetic events have been studiedin vitro using humankidney cells andin vivo using ratliver cells and peripheral bloodleukocytes in humans.[125]Inductively coupled plasma mass spectrometry (ICP-MS) is used to detect precise levels of intracellular arsenic and other arsenic bases involved in epigenetic modification of DNA.[126] Studies investigating arsenic as an epigenetic factor can be used to develop precise biomarkers of exposure and susceptibility.
The Chinese brake fern (Pteris vittata) hyperaccumulates arsenic from the soil into its leaves and has a proposed use inphytoremediation.[127]
Inorganic arsenic and its compounds, upon entering thefood chain, are progressively metabolized through a process ofmethylation.[128][129] For example, the moldScopulariopsis brevicaulis producestrimethylarsine if inorganic arsenic is present.[130] The organic compoundarsenobetaine 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.[131]
Naturally occurring sources of human exposure includevolcanic ash, weathering of minerals and ores, and mineralized groundwater. Arsenic is also found in food, water, soil, and air.[132] Arsenic is absorbed by all plants, but is more concentrated in leafy vegetables, rice, apple and grape juice, and seafood.[133] An additional route of exposure is inhalation of atmospheric gases and dusts.[134]During theVictorian era, arsenic was widely used in home decor, especially wallpapers.[135] In Europe, an analysis based on 20,000 soil samples across all 28 countries show that 98% of sampled soils have concentrations less than 20 mg kg-1. In addition, the As hotspots are related to frequent fertilization and close distance to mining activities.[136]
Extensive arsenic contamination of groundwater has led to widespreadarsenic poisoning inBangladesh[137] and neighboring countries. It is estimated that approximately 57 million people in the Bengal basin are drinkinggroundwater with arsenic concentrations elevated above theWorld Health Organization's standard of 10parts per billion (ppb).[138] However, a study of cancer rates inTaiwan[139] suggested that significant increases in cancer mortality appear only at levels above 150 ppb. The arsenic in the groundwater is of natural origin, and is released from the sediment into the groundwater, caused by theanoxic conditions of the subsurface. This groundwater was used after local and westernNGOs and the Bangladeshi government undertook a massive shallow tubewell drinking-water program in the late twentieth century. This program was designed to prevent drinking of bacteria-contaminated surface waters, but failed to test for arsenic in the groundwater. Many other countries and districts in Southeast Asia, such asVietnam andCambodia, have geological environments that produce groundwater with a high arsenic content.Arsenicosis was reported inNakhon Si Thammarat, Thailand, in 1987, and theChao Phraya River probably contains high levels of naturally occurring dissolved arsenic without being a public health problem because much of the public usesbottled water.[140] In Pakistan, more than 60 million people are exposed to arsenic polluted drinking water indicated by a 2017 report inScience. Podgorski's team investigated more than 1200 samples and more than 66% exceeded the WHO minimum contamination level.[141]
Since the 1980s, residents of the Ba Men region of Inner Mongolia, China have been chronically exposed to arsenic through drinking water from contaminated wells.[142] A 2009 research study observed an elevated presence of skin lesions among residents with well water arsenic concentrations between 5 and 10 μg/L, suggesting that arsenic induced toxicity may occur at relatively low concentrations with chronic exposure.[142] Overall, 20 of China's 34 provinces have high arsenic concentrations in the groundwater supply, potentially exposing 19 million people to hazardous drinking water.[143]
A study byIIT Kharagpur found high levels of Arsenic in groundwater of 20% of India's land, exposing more than 250 million people. States such asPunjab, Bihar,West Bengal, Assam,Haryana, Uttar Pradesh, andGujarat have highest land area exposed to arsenic.[144]
In the United States, arsenic is most commonly found in the ground waters of the southwest.[145] Parts ofNew England,Michigan,Wisconsin,Minnesota and the Dakotas are also known to have significant concentrations of arsenic in ground water.[146] Increased levels of skin cancer have been associated with arsenic exposure in Wisconsin, even at levels below the 10 ppb drinking water standard.[147] According to a recent film funded by the USSuperfund, millions of private wells have unknown arsenic levels, and in some areas of the US, more than 20% of the wells may contain levels that exceed established limits.[148]
Low-level exposure to arsenic at concentrations of 100 ppb (i.e., above the 10 ppb drinking water standard) compromises the initial immune response toH1N1 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 from the virus.[149]
Some Canadians are drinking water that contains inorganic arsenic. Private-dug–well waters are most at risk for containing inorganic arsenic. Preliminary well water analysis typically does not test for arsenic. Researchers at the Geological Survey of Canada have modeled relative variation in natural arsenic hazard potential for the province of New Brunswick. This study has important implications for potable water and health concerns relating to inorganic arsenic.[150]
Epidemiological evidence from Chile shows a dose-dependent connection between chronic arsenic exposure and various forms of cancer, in particular when other risk factors, such as cigarette smoking, are present. These effects have been demonstrated at contaminations less than 50 ppb.[151] Arsenic is itself a constituent oftobacco smoke.[152]
Analyzing multiple epidemiological studies on inorganic arsenic exposure suggests a small but measurable increase in risk for bladder cancer at 10 ppb.[153] According to Peter Ravenscroft of the Department of Geography at the University of Cambridge,[154] roughly 80 million people worldwide consume between 10 and 50 ppb arsenic in their drinking water. If they all consumed exactly 10 ppb 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 processes for removing dissolved arsenic from drinking water demonstrated the efficacy of co-precipitation with either iron or aluminium oxides. In particular, iron as a coagulant was found to remove arsenic with an efficacy exceeding 90%.[155][156] Several adsorptive media systems have been approved for use at point-of-service in a study funded by theUnited States Environmental Protection Agency (US EPA) and theNational Science Foundation (NSF). A team of European and Indian scientists and engineers have set up six arsenic treatment plants inWest Bengal based on in-situ remediation method (SAR Technology). This technology does not use any chemicals and arsenic is left in an insoluble form (+5 state) in the subterranean zone by recharging aerated water into the aquifer and developing an oxidation zone that supports arsenic oxidizing micro-organisms. This process does not produce any waste stream or sludge and is relatively cheap.[157]
Another effective and inexpensive method to avoid arsenic contamination is to sink wells 500 feet or deeper to reach purer waters. A recent 2011 study funded by the US National Institute of Environmental Health Sciences' Superfund Research Program shows that deep sediments can remove arsenic and take it out of circulation. In this process, calledadsorption, arsenic sticks to the surfaces of deep sediment particles and is naturally removed from the ground water.[158]
Magnetic separations of arsenic at very low magnetic fieldgradients with high-surface-area andmonodispersemagnetite (Fe3O4) nanocrystals have been demonstrated in point-of-use water purification. Using the high specific surface area of Fe3O4 nanocrystals, the mass of waste associated with arsenic removal from water has been dramatically reduced.[159]
Epidemiological studies have suggested a correlation between chronic consumption of drinking water contaminated with arsenic and the incidence of all leading causes of mortality.[160] The literature indicates that arsenic exposure is causative in the pathogenesis of diabetes.[161]
Chaff-based filters have recently been shown to reduce the arsenic content of water to 3 μg/L. This may find applications in areas where the potable water is extracted from undergroundaquifers.[162]
For several centuries, the people ofSan Pedro de Atacama in Chile have been drinking water that is contaminated with arsenic, and some evidence suggests they have developed some immunity.[163][164][165]
Around one-third of the world's population drinks water from groundwater resources. Of this, about 10 percent, approximately 300 million people, obtains water from groundwater resources that are contaminated with unhealthy levels of arsenic or fluoride.[166] These trace elements derive mainly from minerals and ions in the ground.[167][168]
Arsenic is unique among the tracemetalloids and oxyanion-forming trace metals (e.g. As, Se, Sb, Mo, V, Cr, U, Re). It is sensitive to mobilization at pH values typical of natural waters (pH 6.5–8.5) under both oxidizing and reducing conditions. Arsenic can occur in the environment in several oxidation states (−3, 0, +3 and +5), but in natural waters it is mostly found in inorganic forms as oxyanions of trivalent arsenite [As(III)] or pentavalent arsenate [As(V)]. Organic forms of arsenic are produced by biological activity, mostly in surface waters, but are rarely quantitatively important. Organic arsenic compounds may, however, occur where waters are significantly impacted by industrial pollution.[169]
Arsenic may be solubilized by various processes. When pH is high, arsenic may be released from surface binding sites that lose their positive charge. When water level drops andsulfide minerals are exposed to air, arsenic trapped in sulfide minerals can be released into water. When organic carbon is present in water, bacteria are fed by directly reducing As(V) to As(III) or by reducing the element at the binding site, releasing inorganic arsenic.[170]
The aquatic transformations of arsenic are affected by pH, reduction-oxidation potential, organic matter concentration and the concentrations and forms of other elements, especially iron and manganese. The main factors are pH and the redox potential. Generally, the main forms of arsenic under oxic conditions areH3AsO4,H2AsO−4,HAsO2−4, andAsO3−4 at pH 2, 2–7, 7–11 and 11, respectively. Under reducing conditions,H3AsO4 is predominant at pH 2–9.
Oxidation and reduction affects the migration of arsenic in subsurface environments. Arsenite is the most stable soluble form of arsenic in reducing environments and arsenate, which is less mobile than arsenite, is dominant in oxidizing environments at neutralpH. Therefore, arsenic may be more mobile under reducing conditions. The reducing environment is also rich in organic matter which may enhance the solubility of arsenic compounds. As a result, theadsorption of arsenic is reduced and dissolved arsenic accumulates in groundwater. That is why the arsenic content is higher in reducing environments than in oxidizing environments.[171]
The presence of sulfur is another factor that affects the transformation of arsenic in natural water. Arsenic canprecipitate when metal sulfides form. In this way, arsenic is removed from the water and its mobility decreases. When oxygen is present, bacteria oxidize reduced sulfur to generate energy, potentially releasing bound arsenic.
Redox reactions involving Fe also appear to be essential factors in the fate of arsenic in aquatic systems. The reduction of iron oxyhydroxides plays a key role in the release of arsenic to water. So arsenic can be enriched in water with elevated Fe concentrations.[172] Under oxidizing conditions, arsenic can be mobilized frompyrite or iron oxides especially at elevated pH. Under reducing conditions, arsenic can be mobilized by reductive desorption or dissolution when associated with iron oxides. The reductive desorption occurs under two circumstances. One is when arsenate is reduced to arsenite which adsorbs to iron oxides less strongly. The other results from a change in the charge on the mineral surface which leads to the desorption of bound arsenic.[173]
Some species of bacteria catalyze redox transformations of arsenic. Dissimilatory arsenate-respiring prokaryotes (DARP) speed up the reduction of As(V) to As(III). DARP use As(V) as the electron acceptor of anaerobic respiration and obtain energy to survive. Other organic and inorganic substances can be oxidized in this process.Chemoautotrophic arsenite oxidizers (CAO) andheterotrophic arsenite oxidizers (HAO) convert As(III) into As(V). CAO combine the oxidation of As(III) with the reduction of oxygen or nitrate. They use obtained energy to fix produce organic carbon from CO2. HAO cannot obtain energy from As(III) oxidation. This process may be an arsenicdetoxification mechanism for the bacteria.[174]
Equilibrium thermodynamic calculations predict that As(V) concentrations should be greater than As(III) concentrations in all but strongly reducing conditions, i.e. wheresulfate reduction is occurring. However, abiotic redox reactions of arsenic are slow. Oxidation of As(III) by dissolved O2 is a particularly slow reaction. For example, Johnson and Pilson (1975) gavehalf-lives for the oxygenation of As(III) in seawater ranging from several months to a year.[175] In other studies, As(V)/As(III) ratios were stable over periods of days or weeks during water sampling when no particular care was taken to prevent oxidation, again suggesting relatively slow oxidation rates. Cherry found from experimental studies that the As(V)/As(III) ratios were stable in anoxic solutions for up to 3 weeks but that gradual changes occurred over longer timescales.[176] Sterile water samples have been observed to be less susceptible to speciation changes than non-sterile samples.[177] Oremland found that the reduction of As(V) to As(III) in Mono Lake was rapidly catalyzed by bacteria with rate constants ranging from 0.02 to 0.3-day−1.[178]
As of 2002, US-based industries consumed 19,600 metric tons of arsenic. Ninety percent of this was used for treatment of wood withchromated copper arsenate (CCA). In 2007, 50% of the 5,280 metric tons of consumption was still used for this purpose.[55][179] In the United States, the voluntary phasing-out of arsenic in production of consumer products and residential and general consumer construction products began on 31 December 2003, and alternative chemicals are now used, such asAlkaline Copper Quaternary,borates,copper azole,cyproconazole, andpropiconazole.[180]
Although discontinued, this application is also one of the most concerning to the general public. The vast majority of olderpressure-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 outdoorbuilding 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 surroundingsoil (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.[181] Scrap CCA lumber from construction and demolition sites may be inadvertently used in commercial and domestic fires. Protocols for safe disposal of CCA lumber are not consistent throughout the world. Widespreadlandfill disposal of such timber raises some concern,[182] but other studies have shown no arsenic contamination in the groundwater.[183][184]
One tool that maps the location (and other information) of arsenic releases in the United States isTOXMAP.[185] TOXMAP is a Geographic Information System (GIS) from the Division of Specialized Information Services of theUnited States National Library of Medicine (NLM) funded by the US Federal Government. With marked-up maps of the United States, TOXMAP enables users to visually explore data from theUnited States Environmental Protection Agency's (EPA)Toxics Release Inventory andSuperfund Basic Research Programs. TOXMAP's chemical and environmental health information is taken from NLM's Toxicology Data Network (TOXNET),[186]PubMed, and from other authoritative sources.
Physical, chemical, and biological methods have been used to remediate arsenic contaminated water.[187] Bioremediation is said to be cost-effective and environmentally friendly.[188] Bioremediation of ground water contaminated with arsenic aims to convert arsenite, the toxic form of arsenic to humans, to arsenate. Arsenate (+5 oxidation state) is the dominant form of arsenic in surface water, while arsenite (+3 oxidation state) is the dominant form in hypoxic to anoxic environments. Arsenite is more soluble and mobile than arsenate. Many species of bacteria can transform arsenite to arsenate in anoxic conditions by using arsenite as an electron donor.[189] This is a useful method in ground water remediation. Another bioremediation strategy is to use plants that accumulate arsenic in their tissues viaphytoremediation but the disposal of contaminated plant material needs to be considered.
Bioremediation requires careful evaluation and design in accordance with existing conditions. Some sites may require the addition of an electron acceptor while others require microbe supplementation (bioaugmentation). Regardless of the method used, only constant monitoring can prevent future contamination.
Coagulation andflocculation are closely related processes common in arsenate removal from water. Due to the net negative charge carried by arsenate ions, they settle slowly or not at all due to charge repulsion. In coagulation, a positively charged coagulent such as iron and aluminum (commonly used salts: FeCl3,[190] Fe2(SO4)3,[191] Al2(SO4)3[192]) neutralize the negatively charged arsenate, enable it to settle. Flocculation follows where a flocculant bridges smaller particles and allows the aggregate to precipitate out from water. However, such methods may not be efficient on arsenite as As(III) exists in uncharged arsenious acid, H3AsO3, at near-neutral pH.[193]
The major drawbacks of coagulation and flocculation are the costly disposal of arsenate-concentrated sludge, and possiblesecondary contamination of environment. Moreover, coagulents such as iron may produce ion contamination that exceeds safety levels.[190]
Arsenic and many of its compounds are especially potent poisons (e.g.arsine). Small amount of arsenic can be detected by pharmacopoial methods which includes reduction of arsenic to arsenious with help of zinc and can be confirmed with mercuric chloride paper.[195]
Arsenic is known to causearsenicosis when present in drinking water, "the most common species being arsenate [HAsO2−4; As(V)] and arsenite [H3AsO3; As(III)]".
In the United States since 2006, the maximum concentration in drinking water allowed by theEnvironmental Protection Agency (EPA) is 10 ppb[196] and the FDA set the same standard in 2005 for bottled water.[197] The Department of Environmental Protection for New Jersey set a drinking water limit of 5 ppb in 2006.[198] TheIDLH (immediately dangerous to life and health) value for arsenic metal and inorganic arsenic compounds is 5 mg/m3 (5 ppb). TheOccupational Safety and Health Administration has set thepermissible exposure limit (PEL) to a time-weighted average (TWA) of 0.01 mg/m3 (0.01 ppb), and theNational Institute for Occupational Safety and Health (NIOSH) has set therecommended exposure limit (REL) to a 15-minute constant exposure of 0.002 mg/m3 (0.002 ppb).[199] The PEL for organic arsenic compounds is a TWA of 0.5 mg/m3.[200] (0.5 ppb).
In 2008, based on its ongoing testing of a wide variety of American foods for toxic chemicals,[201] the U.S.Food and Drug Administration set the "level of concern" for inorganic arsenic in apple and pear juices at 23 ppb, based on non-carcinogenic effects, and began blocking importation of products in excess of this level; it also required recalls for non-conforming domestic products.[197] In 2011, the nationalDr. Oz television show broadcast a program highlighting tests performed by an independent lab hired by the producers. Though the methodology was disputed (it did not distinguish between organic and inorganic arsenic) the tests showed levels of arsenic up to 36 ppb.[202] In response, the FDA tested the worst brand from theDr.Oz show and found much lower levels. Ongoing testing found 95% of the apple juice samples were below the level of concern. Later testing byConsumer Reports showed inorganic arsenic at levels slightly above 10 ppb, and the organization urged parents to reduce consumption.[203] In July 2013, on consideration of consumption by children, chronic exposure, and carcinogenic effect, the FDA established an "action level" of 10 ppb for apple juice, the same as the drinking water standard.[197]
Concern about arsenic in rice in Bangladesh was raised in 2002, but at the time only Australia had a legal limit for food (one milligram per kilogram, or 1000 ppb).[204][205] Concern was raised about people who were eating U.S. rice exceeding WHO standards for personal arsenic intake in 2005.[206] In 2011, the People's Republic of China set a food standard of 150 ppb for arsenic.[207]
In the United States in 2012, testing by separate groups of researchers at the Children's Environmental Health and Disease Prevention Research Center atDartmouth College (early in the year, focusing on urinary levels in children)[208] andConsumer Reports (in November)[209][210] found levels of arsenic in rice that resulted in calls for the FDA to set limits.[211] The FDA released some testing results in September 2012,[212][213] and as of July 2013, is still collecting data in support of a new potential regulation. It has not recommended any changes in consumer behavior.[214]
Consumer Reports recommended:
That the EPA and FDA eliminate arsenic-containing fertilizer, drugs, and pesticides in food production;
That the FDA establish a legal limit for food;
That industry change production practices to lower arsenic levels, especially in food for children; and
That consumers test home water supplies, eat a varied diet, and cook rice with excess water, then draining it off (reducing inorganic arsenic by about one third along with a slight reduction in vitamin content).[210]
Evidence-based public health advocates also recommend that, given the lack of regulation or labeling for arsenic in the U.S., children should eat no more than 1.5 servings per week of rice and should not drink rice milk as part of their daily diet before age 5.[215] They also offer recommendations for adults and infants on how to limit arsenic exposure from rice, drinking water, and fruit juice.[215]
An improved rice cooking approach to maximise arsenic removal while preserving nutrient elements[216]
In 2020, scientists assessed multiple preparation procedures of rice for their capacity to reduce arsenic content and preserve nutrients, recommending a procedure involvingparboiling and water-absorption.[217][216][218]
Arsenic isbioaccumulative in many organisms, marine species in particular, but it does not appear to biomagnify significantly in food webs.[221] In polluted areas, plant growth may be affected by root uptake of arsenate, which is a phosphate analog and therefore readily transported in plant tissues and cells. In polluted areas, uptake of the more toxic arsenite ion (found more particularly in reducing conditions) is likely in poorly-drained soils.
Arsenic's toxicity comes from the affinity of arsenic(III) oxides forthiols. Thiols, in the form ofcysteine residues andcofactors such aslipoic acid andcoenzyme A, are situated at the active sites of many importantenzymes.[15]
Arsenic disruptsATP production through several mechanisms. At the level of thecitric acid cycle, arsenic inhibitslipoic acid, which is a cofactor forpyruvate dehydrogenase. By competing with phosphate, arsenate uncouplesoxidative phosphorylation, thus inhibiting energy-linked reduction ofNAD+, mitochondrial respiration and ATP synthesis. Hydrogen peroxide production is also increased, which, it is speculated, has potential to form reactive oxygen species and oxidative stress. These metabolic interferences lead to death from multi-systemorgan failure. The organ failure is presumed to be fromnecrotic cell death, notapoptosis, since energy reserves have been too depleted for apoptosis to occur.[222]
Occupational exposure andarsenic poisoning may occur in persons working in industries involving the use of inorganic arsenic and its compounds, such as 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.[223]
The conversion between As(III) and As(V) is a large factor in arsenic environmental contamination. According to Croal, Gralnick, Malasarn and Newman, "[the] understanding [of] what stimulates As(III) oxidation and/or limits As(V) reduction is relevant forbioremediation 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.[224]
Treatment of chronic arsenic poisoning is possible. British anti-lewisite (dimercaprol) is prescribed in doses of 5 mg/kg up to 300 mg every 4 hours for the first day, then every 6 hours for the second day, and finally every 8 hours for 8 additional days.[225] However the USA'sAgency for Toxic Substances and Disease Registry (ATSDR) states that the long-term effects of arsenic exposure cannot be predicted.[134] Blood, urine, hair, and nails may be tested for arsenic; however, these tests cannot foresee possible health outcomes from the exposure.[134] Long-term exposure and consequent excretion through urine has been linked tobladder andkidney cancer in addition to cancer of the liver, prostate, skin, lungs, andnasal cavity.[226]
^abArblaster JW (2018).Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International.ISBN978-1-62708-155-9.
^abcGokcen, N. A (1989). "The As (arsenic) system".Bull. Alloy Phase Diagrams.10:11–22.doi:10.1007/BF02882166.
^As(−2) has been observed in CaAs; seeHolleman AF, Wiberg, Egon, Wiberg, Nils (2008).Lehrbuch der Anorganischen Chemie (in German) (102 ed.). Walter de Gruyter. p. 829.ISBN9783110206845.
^As(−1) has been observed in LiAs; seeReinhard Nesper (1990). "Structure and chemical bonding in zintl-phases containing lithium".Progress in Solid State Chemistry (1):1–45.doi:10.1016/0079-6786(90)90006-2.
^Abraham MY, Wang Y, Xie Y, Wei P, Shaefer III HF, Schleyer Pv, Robinson GH (2010). "Carbene Stabilization of Diarsenic: From Hypervalency to Allotropy".Chemistry: A European Journal.16 (2):432–5.doi:10.1002/chem.200902840.PMID19937872.
^Ellis BD, MacDonald CL (2004). "Stabilized Arsenic(I) Iodide: A Ready Source of Arsenic Iodide Fragments and a Useful Reagent for the Generation of Clusters".Inorganic Chemistry.43 (19):5981–6.doi:10.1021/ic049281s.PMID15360247.
Uthus E.O. (1994) "Arsenic essentiality and factors affecting its importance", pp. 199–208 in Chappell W.R, Abernathy C.O, Cothern C.R. (eds.)Arsenic Exposure and Health. Northwood, UK: Science and Technology Letters.
^Wiberg E, Wiberg N, Holleman AF (2001).Inorganic Chemistry. Academic Press.ISBN978-0-12-352651-9.
^abcdefHolleman AF, Wiberg, Egon, Wiberg, Nils (1985). "Arsen".Lehrbuch der Anorganischen Chemie (in German) (91–100 ed.). Walter de Gruyter. pp. 675–681.ISBN978-3-11-007511-3.
^Antonatos N, Luxa J, Sturala J, Sofer Z (2020). "Black arsenic: a new synthetic method by catalytic crystallization of arsenic glass".Nanoscale.12 (9):5397–5401.doi:10.1039/C9NR09627B.PMID31894222.S2CID209544160.
^Shimizu Y, Kubo T, Sumikama T, Fukuda N, Takeda H, Suzuki H, Ahn DS, Inabe N, Kusaka K, Ohtake M, Yanagisawa Y, Yoshida K, Ichikawa Y, Isobe T, Otsu H, Sato H, Sonoda T, Murai D, Iwasa N, Imai N, Hirayama Y, Jeong SC, Kimura S, Miyatake H, Mukai M, Kim DG, Kim E, Yagi A (8 April 2024). "Production of new neutron-rich isotopes near the N = 60 isotones Ge 92 and As 93 by in-flight fission of a 345 MeV/nucleon U 238 beam".Physical Review C.109 (4): 044313.doi:10.1103/PhysRevC.109.044313.
^Din MB, Gould RD (1998). "High field conduction mechanism of the evaporated cadmium arsenide thin films".ICSE'98. 1998 IEEE International Conference on Semiconductor Electronics. Proceedings (Cat. No. 98EX187). pp. 168–174.doi:10.1109/SMELEC.1998.781173.ISBN978-0-7803-4971-1.S2CID110904915.
^Rieuwerts J (2015).The Elements of Environmental Pollution. London and New York: Earthscan Routledge. p. 145.ISBN978-0-415-85919-6.OCLC886492996.
^Papry RI, Omori Y, Fujisawa S, Al Mamun MA, Miah S, Mashio AS, Maki T, Hasegawa H (1 May 2020). "Arsenic biotransformation potential of marine phytoplankton under a salinity gradient".Algal Research.47: 101842.Bibcode:2020AlgRe..4701842P.doi:10.1016/j.algal.2020.101842.
^Ketha H, Garg U (2020). "An introduction to clinical and forensic toxicology".Toxicology Cases for the Clinical and Forensic Laboratory. pp. 3–6.doi:10.1016/B978-0-12-815846-3.00001-6.ISBN978-0-12-815846-3.Arsenic was nicknamed 'the inheritance powder' as it was commonly used to poison family members for a fortune in the Renaissance era.
^Lechtman H (1996). "Arsenic Bronze: Dirty Copper or Chosen Alloy? A View from the Americas".Journal of Field Archaeology.23 (4):477–514.doi:10.2307/530550.JSTOR530550.
^Charles, J. A. (1967). "Early Arsenical Bronzes—A Metallurgical View".American Journal of Archaeology.71 (1):21–26.doi:10.2307/501586.JSTOR501586.
^George Sarton,Introduction to the History of Science. "We find in his writings [...] preparation of various substances (e.g., basic lead carbonatic, arsenic and antimony from their sulphides)."
^Fould HS (13 February 1898). Written at New York. "Display Ad 48 – no Title" ["LADIES" in large print at the top; advertises "Dr. Campbell's Safe Arsenic Complexion Wafers and Fould's Medicated Arsenic Complexion Soap"].The Washington Post. Washington, DC. p. 28.ProQuest143995174.
^Turner A (1999). "Viewpoint: the story so far: An overview of developments in UK food regulation and associated advisory committees".British Food Journal.101 (4):274–283.doi:10.1108/00070709910272141.
^Whorton JC (28 January 2010) [2010]. "Walls of Death".The Arsenic Century: How Victorian Britain was Poisoned at Home, Work, and Play (reprint ed.). Oxford: Oxford University Press. p. 205.ISBN978-0-19-162343-1. Retrieved1 October 2023.At first, green papers were coloured with the traditional mineral pigment verdigris or buy mixing blues and yellows of plant origin. But once Scheele's green began to be produced in quantity, it was adopted as an improvement over the old colours and became a common constituent in wallpaper by 1800.
^Hawksley L (2016).Bitten by Witch Fever: Wallpaper & Arsenic in the Victorian Home. New York: Thames & Hudson.
^Cullen WR (2008). "4.7.1 Was it the Arsenic in the Wallpaper?".Is Arsenic an Aphrodisiac?: The Sociochemistry of an Element. Royal Society of Chemistry. p. 146.ISBN978-0-85404-363-7. Retrieved1 October 2023.The wallpaper-as-arsenic-source of poison made the headlines in 1982 [...] when analysis of a sample of wallpaper from the living room in Longwood, Napoleon's residence on St. Helena, revealed arsenic concentrations of about 0.12 g/m2.
^"London purple". National Oceanic and Atmospheric Administration. Retrieved24 June 2023.
^Lanman SW (2000). "Colour in the Garden: 'Malignant Magenta'".Garden History.28 (2):209–221.doi:10.2307/1587270.JSTOR1587270.
^Holton EC (1926). "Insecticides and Fungicides".Industrial & Engineering Chemistry.18 (9):931–933.doi:10.1021/ie50201a018.
^Murphy EA, Aucott M (1998). "An assessment of the amounts of arsenical pesticides used historically in a geographical area".Science of the Total Environment.218 (2–3):89–101.Bibcode:1998ScTEn.218...89M.doi:10.1016/S0048-9697(98)00180-6.
^Haller JS (1975). "Therapeutic Mule: The Use of Arsenic in the Nineteenth Century Materia Medica".Pharmacy in History.17 (3):87–100.JSTOR41108920.PMID11610136.
^Subastri A, Arun V, Sharma P, Preedia babu E, Suyavaran A, Nithyananthan S, Alshammari GM, Aristatile B, Dharuman V, Thirunavukkarasu C (November 2018). "Synthesis and characterisation of arsenic nanoparticles and its interaction with DNA and cytotoxic potential on breast cancer cells".Chemico-Biological Interactions.295:73–83.Bibcode:2018CBI...295...73S.doi:10.1016/j.cbi.2017.12.025.PMID29277637.S2CID1816043.
^Joseph G, Kundig KJ, Association IC (1999)."Dealloying".Copper: Its Trade, Manufacture, Use, and Environmental Status. ASM International. pp. 123–124.ISBN978-0-87170-656-0.
^Živkov Baloš M, Jakšić S, Ljubojević Pelić D (September 2019). "The role, importance and toxicity of arsenic in poultry nutrition".World's Poultry Science Journal.75 (3):375–386.doi:10.1017/S0043933919000394.
^Nicholis I, Curis E, Deschamps P, Bénazeth S (2009). "Arsenite medicinal use, metabolism, pharmacokinetics and monitoring in human hair".Biochimie.91 (10):1260–1267.doi:10.1016/j.biochi.2009.06.003.PMID19527769.
^Knobeloch LM, Zierold KM, Anderson HA (2006). "Association of arsenic-contaminated drinking-water with prevalence of skin cancer in Wisconsin's Fox River Valley".J. Health Popul Nutr.24 (2):206–213.hdl:1807/50099.PMID17195561.
^Yavuz CT, Mayo JT, Yu WW, Prakash A, Falkner JC, Yean S, Cong L, Shipley HJ, Kan A, Tomson M, Natelson D, Colvin VL (2005). "Low-Field Magnetic Separation of Monodisperse Fe3O4 Nanocrystals".Science.314 (5801):964–967.doi:10.1126/science.1131475.PMID17095696.S2CID23522459.
^Goering P, Aposhian HV, Mass MJ, Cebrián M, Beck BD, Waalkes MP (May 1999). "The enigma of arsenic carcinogenesis: role of metabolism".Toxicological Sciences.49 (1):5–14.doi:10.1093/toxsci/49.1.5.PMID10367337.
^Eawag (2015) Geogenic Contamination Handbook – Addressing Arsenic and Fluoride in Drinking Water. C.A. Johnson, A. Bretzler (Eds.), Swiss Federal Institute of Aquatic Science and Technology (Eawag), Duebendorf, Switzerland. (download: www.eawag.ch/en/research/humanwelfare/drinkingwater/wrq/geogenic-contamination-handbook/)
^Winkel L, Berg M, Amini M, Hug SJ, Annette Johnson C (August 2008). "Predicting groundwater arsenic contamination in Southeast Asia from surface parameters".Nature Geoscience.1 (8):536–542.Bibcode:2008NatGe...1..536W.doi:10.1038/ngeo254.
^Zeng Zhaohua, Zhang Zhiliang (2002). "The formation of As element in groundwater and the controlling factor". Shanghai Geology 87 (3): 11–15.
^Zheng Y, Stute M, Van Geen A, Gavrieli I, Dhar R, Simpson H, Schlosser P, Ahmed K (2004). "Redox control of arsenic mobilization in Bangladesh groundwater".Applied Geochemistry.19 (2):201–214.Bibcode:2004ApGC...19..201Z.doi:10.1016/j.apgeochem.2003.09.007.
^Cherry, J. A. (1979). "Arsenic species as an indicator of redox conditions in groundwater".Contemporary Hydrogeology – the George Burke Maxey Memorial Volume. Developments in Water Science. Vol. 12. pp. 373–392.doi:10.1016/S0167-5648(09)70027-9.ISBN978-0-444-41848-7.
^Hering JG, Chen PY, Wilkie JA, Elimelech M (August 1997). "Arsenic Removal from Drinking Water during Coagulation".Journal of Environmental Engineering.123 (8):800–807.doi:10.1061/(ASCE)0733-9372(1997)123:8(800).
^Gaion A, Sartori D, Scuderi A, Fattorini D (May 2014). "Bioaccumulation and biotransformation of arsenic compounds in Hediste diversicolor (Muller 1776) after exposure to spiked sediments".Environmental Science and Pollution Research.21 (9):5952–5959.Bibcode:2014ESPR...21.5952G.doi:10.1007/s11356-014-2538-z.PMID24458939.S2CID12568097.
^Giannini, A. James, Black, Henry Richard, Goettsche, Roger L. (1978).The Psychiatric, Psychogenic and Somatopsychic Disorders Handbook. New Hyde Park, NY: Medical Examination Publishing Co. pp. 81–82.ISBN978-0-87488-596-5.
Emsley J (2011)."Arsenic".Nature's Building Blocks: An A–Z Guide to the Elements. Oxford, England: Oxford University Press. pp. 47–55.ISBN978-0-19-960563-7.
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