View source for Arsenic

{{About|the chemical element|the poison commonly called "arsenic"|arsenic trioxide|other uses}}
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{{Infobox arsenic}}
{{Use dmy dates|date=December 2020}}

'''Arsenic''' is a [[chemical element]]; it has [[Symbol (chemistry)|symbol]] '''As''' and [[atomic number]]&nbsp;33. It is a [[metalloid]] and one of the [[pnictogens]], and therefore shares many properties with its [[group 15]] neighbors [[phosphorus]] and [[antimony]]. Arsenic is notoriously [[toxic]]. It occurs naturally in many [[minerals]], usually in combination with [[sulfur]] and metals, but also as a pure elemental [[crystal]]. It has various [[Allotropes of arsenic|allotropes]], but only the grey form, which has a metallic appearance, is important to industry.

The primary use of arsenic is in alloys of lead (for example, in [[car batteries]] and [[ammunition]]). Arsenic is also a common n-type [[dopant]] in [[semiconductor]] electronic devices, and a component of the III–V [[compound semiconductor]] [[gallium arsenide]]. Arsenic and its compounds, especially the trioxide, are used in the production of [[pesticide]]s, treated wood products, [[herbicide]]s, and [[insecticide]]s. These applications are declining with the increasing recognition of the persistent toxicity of arsenic and its compounds.<ref name=Ullmann>{{Ullmann |last1 = Grund |first1 = Sabina C. |last2 = Hanusch |first2 = Kunibert |last3 = Wolf |first3 = Hans Uwe |title = Arsenic and arsenic compounds |doi = 10.1002/14356007.a03_113.pub2 }}</ref>

Arsenic has been known since ancient times to be poisonous to humans.<ref>{{cite web |title = Arsenic: A murderous history |series = Dartmouth Toxic Metals |publisher =  [[Dartmouth College]]  |url = https://sites.dartmouth.edu/toxmetal/arsenic/arsenic-a-murderous-history/ }}</ref> However, a few species of bacteria are able to use arsenic compounds as respiratory [[metabolite]]s. Trace quantities of arsenic have been proposed to be an essential [[Mineral (nutrient)|dietary 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.<ref name=ANut/><ref name=UEssent/> 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.

The United States' [[United States Environmental Protection Agency|Environmental Protection Agency]] states that all forms of arsenic are a serious risk to human health.<ref name="EPA1">{{cite report |last1=Dibyendu |first1=Sarkar |last2=Datta |first2=Rupali |date=2007 |title=Biogeochemistry of arsenic in contaminated soils of Superfund sites |via=EPA.gov |publisher=United States [[United States Environmental Protection Agency|Environmental Protection Agency]] |url=https://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.highlight/abstract/6015 |archive-url=https://web.archive.org/web/20180226032345/https://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.highlight/abstract/6015 |archive-date=26 February 2018 |access-date=25 February 2018 }}</ref> The United States [[Agency for Toxic Substances and Disease Registry]] ranked arsenic number&nbsp;1 in its 2001 prioritized list of [[hazardous]] substances at [[Superfund]] sites.<ref>{{cite report |last=Carelton |first=James |date=2007 |title=Biogeochemistry of arsenic in contaminated soils of Superfund sites |type=Final Report |publisher=United States [[United States Environmental Protection Agency|Environmental Protection Agency]] |url=https://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.highlight/abstract/6015/report/F |via=EPA.gov |access-date=25 February 2018 |archive-url=https://web.archive.org/web/20180728035900/https://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.highlight/abstract/6015/report/F |archive-date=28 July 2018 }}</ref> Arsenic is classified as a group-A [[carcinogen]].<ref name="EPA1" />

== Characteristics ==

=== Physical characteristics ===
{{main|Allotropes of arsenic}}
[[File:SbAs lattice.png|thumb|left|Crystal structure common to [[antimony|Sb]], [[Stibarsen|AsSb]] and grey As]]
[[File:Arsenic nodule.jpg|thumb|left|Gray arsenic nodule]]
The three most common arsenic [[Allotropy|allotropes]] are grey, yellow, and black arsenic, with grey being the most common.<ref name="Norman">{{cite book|title = Chemistry of Arsenic, Antimony and Bismuth|first = Nicholas C.|last = Norman|publisher = Springer|date = 1998|isbn = 978-0-7514-0389-3|url = https://books.google.com/books?id=vVhpurkfeN4C|page = 50}}</ref> Grey arsenic (α-As, [[space group]] R{{overline|3}}m 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 low [[Mohs 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.<ref name="Wiberg2001">{{cite book|last1 = Wiberg|first1 = Egon|last2 = Wiberg|first2 = Nils|last3 = Holleman|first3 = Arnold Frederick|title = Inorganic Chemistry|publisher = Academic Press|date = 2001|isbn = 978-0-12-352651-9}}</ref> This relatively close packing leads to a high density of 5.73&nbsp;g/cm<sup>3</sup>.<ref name="Holl" /> Grey arsenic is a [[semimetal]], but becomes a [[semiconductor]] with a [[bandgap]] of 1.2–1.4&nbsp;eV if [[wikt: amorphized|amorphized]].<ref>{{cite book|author=Madelung, Otfried |title=Semiconductors: data handbook|url=https://books.google.com/books?id=v_8sMfNAcA4C&pg=PA410|date=2004|publisher=Birkhäuser|isbn=978-3-540-40488-0|pages=410–}}</ref> Grey arsenic is also the most stable form. Yellow arsenic is soft and waxy, and somewhat similar to [[tetraphosphorus]] ({{chem2|P4}}).<ref>{{cite journal |last1=Seidl |first1=Michael |last2=Balázs |first2=Gábor |last3=Scheer |first3=Manfred |title=The Chemistry of Yellow Arsenic |journal=Chemical Reviews |volume=119 |issue=14 |pages=8406–8434 |date=22 March 2019 |doi=10.1021/acs.chemrev.8b00713|pmid=30900440 |s2cid=85448636 }}</ref> 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. 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, {{chem2|As4}}. It is rapidly transformed into grey arsenic by light. The yellow form has a density of 1.97&nbsp;g/cm<sup>3</sup>.<ref name="Holl" /> Black arsenic is similar in structure to [[black phosphorus]].<ref name="Holl" /><!--10.1002/jlac.18440490302 Ueber Allotropie bei einfachen Körpern, als eine der Ursachen der Isomerie bei ihren Verbindungen (pp. 247–264)
Jac. Berzelius Volume 49 Issue 3, Pages 247–366 (1844) Justus Liebigs Annalen der Chemie
10.1002/jlac.18671440115
10.1002/jlac.19134000206
10.1002/zaac.19020320158
10.1002/zaac.18940060139
10.1002/cber.19080410197
10.1002/zaac.18940060139
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Black arsenic can also be formed by cooling vapor at around 100–220&nbsp;°C and by crystallization of amorphous arsenic in the presence of mercury vapors.<ref>{{Cite journal|last1=Antonatos|first1=Nikolas|last2=Luxa|first2=Jan|last3=Sturala|first3=Jiri|last4=Sofer|first4=Zdeněk|date=2020|title=Black arsenic: a new synthetic method by catalytic crystallization of arsenic glass|journal=Nanoscale|volume=12|issue=9|language=en|pages=5397–5401|doi=10.1039/C9NR09627B|pmid=31894222|s2cid=209544160}}</ref> It is glassy and brittle. Black arsenic is also a poor electrical conductor.<ref>[http://www.chemicool.com/elements/arsenic.html Arsenic Element Facts]. chemicool.com</ref>

Arsenic [[Sublimation (phase transition)|sublimes]] upon heating at [[atmospheric pressure]], converting directly to a gaseous form without an intervening liquid state at {{convert|887|K|C}}. However, at 817&nbsp;°C and 28 atm, arsenic melts.<ref>{{Cite book |title=无机化合物合成手册 第一卷 |publisher=化学工业出版社 |year=1983 |page=31 |language=Chinese}}</ref> The [[triple point]] is at 3.63&nbsp;MPa and {{convert|1090|K|C}}.<ref name="Holl" /><ref name="Gokcen1989" />

=== Isotopes ===
{{Main|Isotopes of arsenic}}
Arsenic occurs naturally as a single stable isotope, <sup>75</sup>As. Synthetic radioisotopes are known from <sup>64</sup>As to <sup>95</sup>As, as well as at least 11 [[nuclear isomer|isomer]]s.<ref name="NUBASE">{{NUBASE2020}}</ref><ref name="shimizu2024">{{cite journal |last1=Shimizu |first1=Y. |last2=Kubo |first2=T. |last3=Sumikama |first3=T. |last4=Fukuda |first4=N. |last5=Takeda |first5=H. |last6=Suzuki |first6=H. |last7=Ahn |first7=D.S. |last8=Inabe |first8=N. |last9=Kusaka |first9=K. |last10=Ohtake |first10=M. |last11=Yanagisawa |first11=Y. |last12=Yoshida |first12=K. |last13=Ichikawa |first13=Y. |last14=Isobe |first14=T. |last15=Otsu |first15=H. |last16=Sato |first16=H. |last17=Sonoda |first17=T. |last18=Murai |first18=D. |last19=Iwasa |first19=N. |last20=Imai |first20=N. |last21=Hirayama |first21=Y. |last22=Jeong |first22=S.C. |last23=Kimura |first23=S. |last24=Miyatake |first24=H. |last25=Mukai |first25=M. |last26=Kim |first26=D.G. |last27=Kim |first27=E. |last28=Yagi |first28=A. |display-authors=6 |title=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 |journal=Physical Review C |date=8 April 2024 |volume=109 |issue=4 |article-number=044313 |doi=10.1103/PhysRevC.109.044313}}</ref>

The most stable of these are <sup>73</sup>As with a half-life of 80.30 days and <sup>74</sup>As with a half-life of 17.77 days, followed by <sup>71</sup>As (65.30 hours), <sup>77</sup>As (38.79 hours), <sup>76</sup>As (26.24 hours), and <sup>72</sup>As (26.0 hours). All others have half-lives under 100 minutes and most under one minute. Isotopes lighter than the stable one generally decay by [[positron emission]] or [[electron capture]] to [[Isotopes of germanium|germanium]] isotopes, while those heavier [[beta decay]] to [[Isotopes of selenium|selenium]] isotopes. A notable exception is that <sup>74</sup>As decays both ways.<ref name="NUBASE" />

=== Chemistry ===

Arsenic has a similar [[electronegativity]] and [[ionization energies]] to its lighter [[pnictogen]] [[Congener (chemistry)|congener]] phosphorus and therefore readily forms [[covalent]] molecules with most of the [[nonmetals]]. Though stable in dry air, arsenic forms a golden-bronze [[tarnish]] upon exposure to humidity which eventually becomes a black surface layer.<ref name="Greenwood552">Greenwood and Earnshaw, pp. 552–4</ref> When heated in air, arsenic [[oxidation|oxidizes]] to [[arsenic trioxide]]; the fumes from this reaction have an odor resembling garlic. This odor can be detected on striking [[arsenide]] minerals such as [[arsenopyrite]] with a hammer.<ref name="Gokcen1989" /> It burns in oxygen to form arsenic trioxide and [[arsenic pentoxide]], which have the same structure as the more well-known phosphorus compounds, and in fluorine to give [[arsenic pentafluoride]].<ref name="Greenwood552" /> Arsenic makes [[arsenic acid]] with concentrated [[nitric acid]], [[arsenous acid]] with dilute nitric acid, and [[arsenic trioxide]] with concentrated [[sulfuric acid]]; however, it does not react with water, alkalis, or non-oxidising acids.<ref>{{cite EB1911|wstitle=Arsenic |volume=2 |pages=651–654}}</ref> Arsenic reacts with metals to form [[arsenide]]s, though these are not ionic compounds containing the As<sup>3−</sup> ion as the formation of such an anion would be highly endothermic and even the group 1 arsenides have properties of [[intermetallic]] compounds.<ref name="Greenwood552" /> Like [[germanium]], [[selenium]], and [[bromine]], which like arsenic [[d-block contraction|succeed the 3d transition series]], arsenic is much less stable in the +5 [[oxidation state]] than its vertical neighbors phosphorus and [[antimony]], and hence arsenic pentoxide and arsenic acid are potent [[oxidizers]].<ref name="Greenwood552" />

== Compounds ==
{{Category see also|Arsenic compounds}}

Compounds of arsenic resemble, in some respects, those of [[phosphorus]], which occupies the same [[Group (periodic table)|group]] (column) of the [[periodic table]]. The most common [[oxidation state]]s for arsenic are: −3 in the [[arsenide]]s, which are alloy-like intermetallic compounds, +3 in the [[arsenite]]s, and +5 in the [[arsenates]] and most organoarsenic compounds. Arsenic also bonds readily to itself as seen in the square {{chem2|As4(3-)}} ions in the mineral [[skutterudite]].<ref>{{cite book |doi = 10.1016/S0080-8784(01)80151-4 |title = Recent Trends in Thermoelectric Materials Research I: Skutterudites: Prospective novel thermoelectrics |date = 2001 |last1 = Uher |first1 = Ctirad |isbn = 978-0-12-752178-7 |volume = 69 |pages = 139–253| series = Semiconductors and Semimetals |chapter = Chapter 5 Skutterudites: Prospective novel thermoelectrics }}</ref> In the +3 [[oxidation state]], arsenic is typically pyramidal owing to the influence of the [[lone pair]] of [[electron]]s.<ref name="Norman" /><!--page 30-->

=== Inorganic compounds ===

One of the simplest arsenic compounds is the [[Trihydrogen cation|trihydride]], the highly toxic, flammable, [[pyrophoricity|pyrophoric]] [[arsine]] (AsH<sub>3</sub>). This compound is generally regarded as stable, since at room temperature it decomposes only slowly. At temperatures of 250–300&nbsp;°C decomposition to arsenic and hydrogen is rapid.<ref name="Greenwood557">Greenwood and Earnshaw, pp. 557–558</ref> Several factors, such as [[humidity]], presence of light and certain [[catalyst]]s (namely aluminium) facilitate the rate of decomposition.<ref name="INRS">{{cite web |website=Institut National de Recherche et de Sécurité |title=Fiche toxicologique No. 53: Trihydrure d'arsenic |year = 2000 |url = http://www.inrs.fr/inrs-pub/inrs01.nsf/IntranetObject-accesParReference/FT%2053/$File/ft53.pdf |access-date = 2006-09-06 | archive-url = https://web.archive.org/web/20061126045357/http://www.inrs.fr/inrs-pub/inrs01.nsf/IntranetObject-accesParReference/FT%2053/$FILE/ft53.pdf |archive-date = 26 November 2006 |language=fr}}</ref> It oxidises readily in air to form arsenic trioxide and water, and analogous reactions take place with [[sulfur]] and [[selenium]] instead of [[oxygen]].<ref name="Greenwood557" />

Arsenic forms colorless, odorless, crystalline [[oxide]]s [[Arsenic trioxide|As<sub>2</sub>O<sub>3</sub>]] ("[[white arsenic]]") and [[Arsenic pentoxide|As<sub>2</sub>O<sub>5</sub>]] which are [[hygroscopic]] and readily soluble in water to form acidic solutions. [[Arsenic acid|Arsenic(V) acid]] is a weak acid and its salts, known as [[arsenate]]s,<ref name="Greenwood572" /> are a major source of [[arsenic contamination of groundwater]] in regions with high levels of naturally occurring arsenic minerals.<ref>{{cite journal |last1=Smedley |first1=P.L |last2=Kinniburgh |first2=D.G |title=A review of the source, behaviour and distribution of arsenic in natural waters |journal=Applied Geochemistry |date=May 2002 |volume=17 |issue=5 |pages=517–568 |doi=10.1016/S0883-2927(02)00018-5 |bibcode=2002ApGC...17..517S |url=https://nora.nerc.ac.uk/id/eprint/12311/1/Abstract.pdf }}</ref> Synthetic arsenates include [[Scheele's Green]] (cupric hydrogen arsenate, acidic copper arsenate), [[calcium arsenate]], and [[lead hydrogen arsenate]]. These three have been used as agricultural [[insecticide]]s and [[poison]]s.

The [[protonation]] steps between the arsenate and arsenic acid are similar to those between [[phosphate]] and [[phosphoric acid]]. Unlike [[phosphorous acid]], [[arsenous acid]] is genuinely tribasic, with the formula As(OH)<sub>3</sub>.<ref name="Greenwood572">Greenwood and Earnshaw, pp. 572–578</ref>

A broad variety of sulfur compounds of arsenic are known. Orpiment ([[arsenic trisulfide|As<sub>2</sub>S<sub>3</sub>]]) and realgar ([[tetraarsenic tetrasulfide|As<sub>4</sub>S<sub>4</sub>]]) are somewhat abundant and were formerly used as painting pigments. In As<sub>4</sub>S<sub>10</sub>, arsenic has a formal oxidation state of +2 in As<sub>4</sub>S<sub>4</sub> which features As-As bonds so that the total covalency of As is still 3.<ref>{{cite web|url=http://www.webelements.com/webelements/compounds/text/As/As4S4-12279902.html|title=Arsenic: arsenic(II) sulfide compound data|access-date=2007-12-10|publisher=WebElements.com| archive-url= https://web.archive.org/web/20071211100733/http://www.webelements.com/webelements/compounds/text/As/As4S4-12279902.html| archive-date= 11 December 2007|url-status = live}}</ref> Both orpiment and realgar, as well as As<sub>4</sub>S<sub>3</sub>, have [[selenium]] analogs; the analogous As<sub>2</sub>Te<sub>3</sub> is known as the mineral [[kalgoorlieite]],<ref>
{{cite web |url=https://www.mindat.org/min-47039.html |title=Kalgoorlieite |date=1993–2017 |website=Mindat |publisher=Hudson Institute of Mineralogy |access-date=2 September 2017}}</ref> and the anion As<sub>2</sub>Te<sup>−</sup> is known as a ligand in [[cobalt]] complexes.<ref name="Greenwood578">Greenwood and Earnshaw, pp. 578–583</ref>

All trihalides of arsenic(III) are well known except the astatide, which is unknown. [[Arsenic pentafluoride]] (AsF<sub>5</sub>) 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. (The [[Arsenic pentachloride|pentachloride]] is a kind of yellow solid that is only stable below −50&nbsp;°C, at which temperature it decomposes to the trichloride, releasing chlorine gas.<ref name="Holl" />)

==== Alloys ====

Arsenic is used as the group 5 element in the [[III-V semiconductor]]s [[gallium arsenide]], [[indium arsenide]], and [[aluminium arsenide]].<ref>{{cite journal |doi = 10.1016/j.taap.2003.10.019 |title = Toxicity of indium arsenide, gallium arsenide, and aluminium gallium arsenide |date = 2004 |last1 = Tanaka |first1 = A. |journal = Toxicology and Applied Pharmacology |volume = 198 |issue = 3 |pages = 405–411 |pmid = 15276420|bibcode = 2004ToxAP.198..405T }}</ref> The valence electron count of GaAs is the same as a pair of Si atoms, but the [[Electronic band structure|band structure]] is completely different which results in distinct bulk properties.<ref>{{cite book |url=https://books.google.com/books?id=pkuuvlNjRtsC&pg=PA1 |title=Light Emitting Silicon for Microphotonics |isbn = 978-3-540-40233-6|last1=Ossicini |first1=Stefano |last2=Pavesi |first2=Lorenzo |last3=Priolo |first3=Francesco |year=2003 |publisher=Springer |access-date=2013-09-27}}</ref> Other arsenic alloys include the II-V semiconductor [[cadmium arsenide]].<ref>{{cite book |doi = 10.1109/SMELEC.1998.781173 |date = 1998 |last1 = Din |first1 = M. B. |last2 = Gould |first2 = R. D. |title = ICSE'98. 1998 IEEE International Conference on Semiconductor Electronics. Proceedings (Cat. No. 98EX187) |chapter = High field conduction mechanism of the evaporated cadmium arsenide thin films |isbn = 978-0-7803-4971-1 |pages = 168–174|s2cid = 110904915 }}</ref>

=== Organoarsenic compounds ===
{{Main|Organoarsenic chemistry}}
[[File:Trimethylarsine-2D.png|left|upright=0.4|thumb|[[Trimethylarsine]]]]

A large variety of organoarsenic compounds are known. Several were developed as [[Chemical weapon|chemical warfare agents]] during World War I, including [[Blister agent|vesicants]] such as [[lewisite]] and vomiting agents such as [[adamsite]].<ref name="Ellison2007">{{cite book|last=Ellison|first=Hank D.|title=Handbook of chemical and biological warfare agents|date=2007|publisher=[[CRC Press]]|isbn=978-0-8493-1434-6}}</ref><ref name="Girard2010">{{cite book|last=Girard|first=James|title=Principles of Environmental Chemistry|date=2010|publisher=Jones & Bartlett Learning|isbn=978-0-7637-5939-1}}</ref><ref name="Somani2001">{{cite book|last=Somani|first=Satu M.|title=Chemical warfare agents: toxicity at low levels|date=2001|publisher=CRC Press|isbn=978-0-8493-0872-7}}</ref> [[Cacodylic acid]], which is of historic and practical interest, arises from the [[methylation]] 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 Greek ''κακωδία'' "stink" for its offensive, garlic-like odor; it is very toxic.<ref name="Greenwood584">Greenwood, p. 584</ref>
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== Occurrence and production ==
{{See also|:Category:Arsenide minerals|l1=Arsenide minerals|:Category:Arsenate minerals|l2=Arsenate minerals}}
[[File:Native arsenic.jpg|upright=0.9|thumb|A large sample of native arsenic from [[Sainte-Marie-aux-Mines]], France]]

Arsenic is the 53rd most abundant element in the [[Earth's crust]], comprising about 1.5&nbsp;[[parts per million]]&nbsp;(0.00015%).<ref>{{Cite book |last=Emsley |first=John |url=https://books.google.com/books?id=dGZaDwAAQBAJ&dq=%2253rd+most+abundant+element%22&pg=PA52 |title=Nature's Building Blocks: An A-Z Guide to the Elements |date=2011-08-25 |publisher=Oxford University Press |isbn=978-0-19-257046-8 |language=en}}</ref> Typical background concentrations of arsenic do not exceed 3&nbsp;ng/m<sup>3</sup> in the atmosphere; 100&nbsp;mg/kg in soil; 400&nbsp;μg/kg in vegetation; 10&nbsp;μg/L in freshwater and 1.5&nbsp;μg/L in seawater.<ref>{{Cite book|last=Rieuwerts|first=John |title=The Elements of Environmental Pollution|date=2015|publisher=Earthscan Routledge |isbn=978-0-415-85919-6|location=London and New York|page=145 |oclc=886492996}}</ref> Arsenic is the 22nd most abundant element in seawater<ref>{{Cite journal |last1=Papry |first1=Rimana Islam |last2=Omori |first2=Yoshiki |last3=Fujisawa |first3=Shogo |last4=Al Mamun |first4=M. Abdullah |last5=Miah |first5=Sohag |last6=Mashio |first6=Asami S. |last7=Maki |first7=Teruya |last8=Hasegawa |first8=Hiroshi |display-authors=6 |date=2020-05-01 |title=Arsenic biotransformation potential of marine phytoplankton under a salinity gradient |journal=Algal Research |volume=47 |article-number=101842 |doi=10.1016/j.algal.2020.101842 |bibcode=2020AlgRe..4701842P }}</ref> and ranks 41st in abundance in the universe.<ref>{{Cite web |last=Helmenstine |first=Anne |date=2022-06-28 |title=Composition of the Universe - Element Abundance |url=https://sciencenotes.org/composition-of-the-universe-element-abundance/ |access-date=2024-06-13 |website=Science Notes and Projects |language=en-US}}</ref>{{Unreliable source?|date=December 2024}}

Minerals with the formula MAsS and MAs<sub>2</sub> (M = [[Iron|Fe]], [[Nickel|Ni]], [[Cobalt|Co]]) are the dominant commercial sources of arsenic, together with [[realgar]] (an arsenic sulfide mineral) and native (elemental) arsenic. An illustrative mineral is [[arsenopyrite]]<!--, also unofficially called mispickel,<ref>{{cite journal|journal = Geology Today|volume = 18|issue = 2|pages = 72–75|title = Minerals explained 35: Arsenopyrite|first =R. J.|last = King|year = 2002|doi = 10.1046/j.1365-2451.2002.t01-1-00006.x}}</ref>--> ([[iron|Fe]]As[[sulfur|S]]), which is structurally related to [[iron pyrite]]. Many minor As-containing minerals are known. Arsenic also occurs in various organic forms in the environment.<ref name="geosphere">{{cite journal|journal = The Science of the Total Environment|volume = 249|date = 2000|pages = 297–312| doi = 10.1016/S0048-9697(99)00524-0|title = Arsenic in the geosphere – a review|first = Jörg|last = Matschullat|pmid = 10813460|issue = 1–3|bibcode = 2000ScTEn.249..297M}}</ref>

[[File:World Arsenic Production 2006.svg|thumb|upright=1.15|Arsenic output in 2006<ref name="USGSCS2006">{{cite web|url =https://minerals.er.usgs.gov/minerals/pubs/commodity/arsenic/mcs-2008-arsen.pdf|first = William E.|last = Brooks| publisher = United States Geological Survey|access-date = 2008-11-25 |title = Mineral Commodity Summaries 2007: Arsenic| archive-url= https://web.archive.org/web/20081217031511/http://minerals.er.usgs.gov/minerals/pubs/commodity/arsenic/mcs-2008-arsen.pdf| archive-date= 17 December 2008|url-status = live}}</ref>]]

In 2014, China was the top producer of white arsenic with almost 70% world share, followed by Morocco, Russia, and Belgium, according to the [[British Geological Survey]] and the [[United States Geological Survey]].<ref name="USGSCS2016" /> 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.<ref name="USGSYB2007" /> Arsenic is the main impurity found in copper concentrates to enter [[copper smelting]] facilities.<ref name=sona>{{Cite report |title=Fundiciones de Cobre en Chile |date=2015-06-10 |url=https://www.sonami.cl/v2/wp-content/uploads/2016/07/FCM-20150610-Com-Miner%C3%ADa-y-Energia-Senado-Fundiciones.pdf |last=Costabal M. |first=Francisco|author-link=Francisco Costabal |access-date=2025-03-23 |publisher=[[SONAMI]] |language=es}}</ref> There has been an increase in arsenic in copper concentrates over the years since copper mining has moved into deep high-impurity [[ore]]s as shallow, low-arsenic copper deposits have been progressively depleted.<ref>{{Cite web |title=Arsénico y Minería |url=https://www.ecometales.cl/difusion/arsenico/arsenico-y-mineria |access-date=2025-03-21 |website=ecometales.cl |language=es |quote=Hoy se extrae más arsénico que antes debido al agotamiento de los minerales de más alta ley de cobre y sin impurezas, lo que obliga a explotar yacimientos de mayor profundidad con más arsénico.|trans-quote=More arsenic is being mined today than before due to the depletion of higher-grade copper ores without impurities, which requires the exploitation of deeper deposits with more arsenic.}}</ref>

On [[Roasting (metallurgy)|roasting]] arsenopyrite in air, arsenic sublimes as arsenic(III) oxide leaving iron oxides,<ref name="geosphere" /> while roasting without air results in the production of gray arsenic. Further purification from sulfur and other chalcogens is achieved by [[Sublimation (phase transition)|sublimation]] in vacuum, in a hydrogen atmosphere, or by distillation from molten lead-arsenic mixture.<ref>{{cite journal|title = Separation of Sulfur, Selenium, and Tellurium from Arsenic|journal = Journal of the Electrochemical Society|volume = 107|issue = 12|pages = 982–985|date = 1960|first1 = J. M.|last1 = Whelan|doi = 10.1149/1.2427585|last2 = Struthers|first2 = J. D.|last3 = Ditzenberger|first3 = J. A.|doi-access = free}}</ref><!-- 10.1023/A:1012370808738-->

{|class="wikitable sortable"
|-
! Rank !! Country !! 2014 [[Arsenic trioxide|As<sub>2</sub>O<sub>3</sub>]] Production<ref name="USGSCS2016">{{cite web|url =https://minerals.usgs.gov/minerals/pubs/commodity/arsenic/mcs-2016-arsen.pdf|first = Daniel L.|last = Edelstein |publisher = United States Geological Survey|access-date = 2016-07-01 |title = Mineral Commodity Summaries 2016: Arsenic}}</ref>
|-
| 1 || {{CHN}} || 25,000 T
|-
| 2 || {{MAR}} || 8,800 T
|-
| 3 || {{RUS}} || 1,500 T
|-
| 4 || {{BEL}} || 1,000 T
|-
| 5 || {{BOL}} || 52 T
|-
| 6 || {{JAP}} || 45 T
|-
| — || '''World Total (rounded)''' || '''36,400 T'''
|}

== History ==
[[File:Mineraly.sk - realgar.jpg|thumb|Realgar]]
[[File:Arsenic symbol.svg|upright=0.35|thumb|[[Alchemical symbol]] for arsenic]]

The word ''arsenic'' has its origin in the [[Syriac language|Syriac]] word {{lang|arc|ܙܪܢܝܟܐ}} ''zarnika'',<ref name="etymonline.com">{{OEtymD|arsenic|access-date = 2010-05-15}}</ref><ref name="oed |arsenic">{{oed |arsenic}}</ref> from Arabic al-zarnīḵ {{lang|ar|الزرنيخ}} 'the [[orpiment]]', based on [[Persian language|Persian]] zar ("gold") from the word {{lang|fa|زرنيخ}} ''zarnikh'', meaning "yellow" (literally "gold-colored") and hence "(yellow) orpiment". It was adopted into [[Greek language|Greek]] (using [[folk etymology]]) as ''arsenikon'' ({{lang|grc|ἀρσενικόν}}) – a neuter form of the Greek adjective ''arsenikos'' ({{lang|grc| ἀρσενικός}}), meaning "male", "virile".

[[Latin]]-speakers adopted the Greek term as {{Lang|la|arsenicum}}, which in French ultimately became {{Lang|fr|arsenic}}, whence the English word "arsenic".<ref name="oed |arsenic"/>
Arsenic sulfides (orpiment, [[realgar]]) and oxides have been known and used since ancient times.<ref name="Curiosa">{{cite journal |last1=Bentley |first1=Ronald |last2=Chasteen |first2=Thomas G. |title=Arsenic Curiosa and Humanity |journal=The Chemical Educator |date=April 2002 |volume=7 |issue=2 |pages=51–60 |doi=10.1007/s00897020539a }}</ref> [[Zosimos of Panopolis|Zosimos]] ({{circa|300 AD}}) describes roasting ''sandarach'' (realgar) to obtain ''cloud of arsenic'' ([[arsenic trioxide]]), which he then [[redox|reduces]] to gray arsenic.<ref>{{cite book|title= Makers of Chemistry|author= Holmyard John Eric|publisher= Read Books|date= 2007|isbn= 978-1-4067-3275-7}}</ref> As the symptoms of [[arsenic poisoning]] are not very specific, the substance was frequently used for murder until the advent in the 1830s 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".<ref>{{cite journal |doi = 10.1177/0960327107084539 |date = 2007 |title = Arsenic neurotoxicity – a review |volume = 26 |issue = 10 |pages = 823–832 |pmid = 18025055 |journal = Human & Experimental Toxicology |last1 = Vahidnia |first1 = A. |last2 = van der Voet |first2 = G.B. |last3 = De Wolff |first3 = F.A. |bibcode = 2007HETox..26..823V |s2cid = 24138885}}</ref> Arsenic became known as "the inheritance powder" due to its use in killing family members in the [[Renaissance era]].<ref name=Ketha-Garg-2020>{{cite book |last1=Ketha |first1=Hema |last2=Garg |first2=Uttam |year=2020 |chapter=An introduction to clinical and forensic toxicology |title=Toxicology Cases for the Clinical and Forensic Laboratory |pages=3–6 |isbn=978-0-12-815846-3 |doi=10.1016/B978-0-12-815846-3.00001-6 }}</ref>{{efn|
Arsenic was nicknamed 'the inheritance powder' as it was commonly used to poison family members for a fortune in the Renaissance era.<ref name=Ketha-Garg-2020/>
}}

[[File:The Arsenic Labyrinth at Botallack Mine - geograph.org.uk - 490315.jpg|thumb|left|The arsenic labyrinth, part of [[Botallack Mine]], Cornwall]]

During the [[Bronze Age]], arsenic was melted with copper to make [[arsenical bronze]].<ref>{{cite journal |last = Lechtman |first = H. |year = 1996 |title = Arsenic bronze: Dirty copper or chosen alloy? A view from the Americas |journal = Journal of Field Archaeology |volume = 23 |issue = 4 |pages = 477–514 |doi = 10.2307/530550 |jstor = 530550 }}</ref><ref>{{cite journal |last=Charles |first=J.A. |year= 1967 |title= Early Arsenical Bronzes—A Metallurgical View |journal= American Journal of Archaeology |volume= 71 |issue= 1 |pages= 21–26 |jstor = 501586 |doi = 10.2307/501586}}</ref>
[[Jabir ibn Hayyan]] described the isolation of arsenic before 815 AD.{{efn|
"We find in his [<nowiki/>[[Jabir ibn Hayyan|ibn Hayyan's]]<nowiki/>] writings [...] preparation of various substances (e.g., basic lead carbonatic, arsenic and antimony from their sulphides).<ref name=Sarton>{{cite book |last=Sarton |first=G. |author-link=George Sarton |title=Introduction to the History of Science}}</ref>{{full citation needed|date=April 2025}}
}}
[[Albertus Magnus]] (Albert the Great, 1193–1280) later isolated the element from a compound in 1250, by heating soap together with [[arsenic trisulfide]].<ref name="BuildingBlocks451-3">{{cite book |last= Emsley |first= John |year= 2001 |title= Nature's Building Blocks: An A-Z guide to the elements |pages= 43, 513, 529 |publisher= [[Oxford University Press]] |location= Oxford, UK |isbn= 978-0-19-850341-5 }}</ref> In 1649, [[Johann Schröder (physician)|Johann Schröder]] published two ways of preparing arsenic.<ref>{{cite book |last1= Fourcroy |first1= Antoine-François |author-link1 = Antoine-François de Fourcroy |year= 1804  |title= A general system of chemical knowledge, and its application to the phenomena of nature and art |page = 84 |publisher= Cadell and Davies |url= https://books.google.com/books?id=PTgwAAAAYAAJ&pg=PA84}}</ref> Crystals of elemental (native) arsenic are found in nature, although rarely.

[[Cadet's fuming liquid]] (impure [[cacodyl]]), often claimed as the first synthetic [[Organometallic chemistry|organometallic compound]], was synthesized in 1760 by [[Louis Claude Cadet de Gassicourt]] through the reaction of [[potassium acetate]] with [[arsenic trioxide]].<ref>{{cite journal |first = Dietmar |last = Seyferth |year = 2001 |title = Cadet's fuming arsenical liquid and the cacodyl compounds of Bunsen |journal = Organometallics |volume = 20 |issue = 8 |pages = 1488–1498 |doi = 10.1021/om0101947 |doi-access = free }}</ref>

[[File:A chemist gives a demonstration involving arsenic Wellcome V0011761.jpg|thumb|Satirical cartoon by [[Honoré Daumier]] of a chemist giving a public demonstration of arsenic, 1841]]

In the [[Victorian era]], women would eat "arsenic" ("[[white arsenic]]" or arsenic trioxide) mixed with vinegar and [[chalk]] to improve the [[complexion]] of their faces, making their skin paler (to show they did not work in the fields).<ref>{{cite news |last=Fould |first=H.S. |date=13 February 1898 |title=Display ad&nbsp;48 – no title |quote=LADIES" [in large print at the top]; [advertises] "Dr. Campbell's Safe Arsenic Complexion Wafers and Fould's Medicated Arsenic Complexion Soap |newspaper=[[The Washington Post]] |page=28 |place=Washington, DC |id={{ProQuest|143995174}} }}</ref> The accidental use of arsenic in the adulteration of foodstuffs led to the [[1858 Bradford sweets poisoning|Bradford sweet poisoning]] in 1858, which resulted in 21 deaths.<ref name=Food>{{cite journal |first = Alan |last = Turner |year = 1999 |title = The story so far: An overview of developments in UK food regulation and associated advisory committees |department=Viewpoint |journal = [[British Food Journal]] |volume = 101 |issue = 4 |pages = 274–283 |doi =10.1108/00070709910272141}}</ref> From the late 18th&nbsp;century wallpaper production began to use dyes made from arsenic,{{efn|
"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."
<ref name=Whorton-2010>
{{cite book
 |last1             = Whorton    |first1 = James C.
 |date              = 28 January 2010
 |orig-date         = 2010
 |chapter           = Walls of death
 |title             = The Arsenic Century: How Victorian Britain was poisoned at home, work, and play
 |edition           = reprint
 |publication-place = Oxford, UK
 |publisher         = Oxford University Press
 |page              = 205
 |isbn              = 978-0-19-162343-1
 |chapter-url       = https://books.google.com/books?id=YnVNX3drptkC
 |access-date       = 1 October 2023
 |quote             = }}
</ref>
}}
which was thought to increase the pigment's brightness.<ref>{{cite book |last = Hawksley |first = Lucinda |year= 2016 |title= Bitten by Witch Fever: Wallpaper & arsenic in the Victorian home |publisher= Thames & Hudson |location= New York, NY }}</ref> One account of the illness and [[Napoleon#Death|1821 death]] of [[Napoleon]] implicates arsenic poisoning involving wallpaper.{{efn|
"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 [[Saint Helena]], revealed arsenic concentrations of about 0.12&nbsp;g/m<sup>2</sup>."<ref>
{{cite book
 |last        = Cullen  |first = William R.
 |year        = 2008
 |chapter     = 4.7.1 Was it the arsenic in the wallpaper?
 |title       = Is Arsenic an Aphrodisiac?: The sociochemistry of an element
 |publisher   = Royal Society of Chemistry
 |page        = 146
 |isbn        = 978-0-85404-363-7
 |chapter-url = https://books.google.com/books?id=yyaTdY4UGLMC
 |access-date = 1 October 2023
}}
</ref>
}}

Two arsenic pigments have been widely used since their discovery – [[Paris Green]] in 1814 and [[Scheele'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<ref>{{cite web|url= https://cameochemicals.noaa.gov/chemical/3779|title= London purple|access-date= 24 June 2023|publisher=  National Oceanic and Atmospheric Administration}}</ref> But it was later replaced with [[Paris Green]], another arsenic-based dye.<ref>{{cite journal | title = Colour in the Garden: 'Malignant Magenta' | first = Susan W. | last = Lanman | journal = Garden History | volume = 28 | issue = 2 | date = 2000 | pages= 209–221 |jstor= 1587270 | doi = 10.2307/1587270}}</ref> With better understanding of the toxicology mechanism, two other compounds were used starting in the 1890s.<ref>{{cite journal | doi = 10.1021/ie50201a018 | title = Insecticides and Fungicides | date = 1926 | last1 = Holton | first1 = E. C. | journal = Industrial & Engineering Chemistry | volume = 18 | issue = 9 | pages = 931–933}}</ref> [[calcium arsenate|Arsenite of lime]] and [[arsenate of lead]] were used widely as insecticides until the discovery of [[DDT]] in 1942.<ref>{{cite journal |doi = 10.1016/S0048-9697(98)00180-6 | title = An assessment of the amounts of arsenical pesticides used historically in a geographical area | date = 1998 | last1 = Murphy | first1 = E. A. | last2 = Aucott | first2 = M. | journal = Science of the Total Environment | volume = 218 | issue = 2–3 | pages = 89–101 | bibcode = 1998ScTEn.218...89M }}</ref><ref>{{cite book | url = https://archive.org/details/CAT85816421 |page= [https://archive.org/details/CAT85816421/page/n5 5] | title = Important Insecticides: Directions for Their Preparation and Use | publisher = U.S. Department of Agriculture | last1 = Marlatt | first1 = C. L. | date = 1897}}</ref><ref>{{cite book | url =https://books.google.com/books?id=eIJVHFCBI_wC&pg=PA248 |title = Paradise Under Glass: An Amateur Creates a Conservatory Garden |isbn = 978-0-06-199130-1 |last1 = Kassinger |first1 = Ruth |year= 2010|publisher = Harper Collins }}</ref>

In small doses, soluble arsenic compounds act as [[stimulant]]s, and were once popular  as medicine by people in the mid-18th to 19th centuries;<ref name=Holl>{{cite book |first1 = Arnold F. |last1 = Holleman |last2 = Wiberg |first2 = Egon |last3 = Wiberg |first3 = Nils |year = 1985 |chapter = Arsen |trans-chapter = Arsenic |title = Lehrbuch der Anorganischen Chemie |trans-title=Textbook of Inorganic Chemistry |edition = 91–100te |pages = 675–681 |language = de |publisher = Walter de Gruyter |isbn = 978-3-11-007511-3 }}</ref><ref>{{cite journal |last =Haller |first =John S. |year=1975 |title=Therapeutic mule: The use of arsenic in the nineteenth century ''Materia Medica'' |journal=Pharmacy in History |volume=17 |issue=3 |pages=87–100 |jstor=41108920 |pmid=11610136 }}</ref><ref>{{cite book |last=Parascandola |first=John |year=2011 |chapter=Chapter&nbsp;5: What kills can cure – arsenic in medicine |title=King of Poisons: A history of arsenic |isbn=978-1-59797-809-5 |oclc=817901966 |pages=145–172 |chapter-url=https://muse.jhu.edu/chapter/1650011 |via=[[Project MUSE]] |url=https://muse.jhu.edu/book/42297 |publisher=University of Nebraska Press |language=en |publication-place=[[Lincoln, Nebraska|Lincoln]], NB }}</ref> this use was especially prevalent for sport animals such as [[race horses]] or [[work dog]]s and continued into the 20th century.<ref>{{cite book |doi=10.1016/B978-0-12-420227-6.00014-1 |chapter=Metalloids |title=Veterinary Toxicology for Australia and New Zealand |date=2017 |last1=Cope |first1=Rhian |pages=255–277 |isbn=978-0-12-420227-6 }}</ref>
A 2006 study of the remains of the Australian racehorse [[Phar Lap]] determined that its 1932 death was caused by a massive overdose of arsenic. Sydney veterinarian Percy Sykes stated,<ref>{{cite news |title=Phar Lap arsenic claims premature: Expert |date=2006-10-23 |publisher=[[ABC News (Australia)|ABC News]] |place=Australia |url=https://www.abc.net.au/news/2006-10-23/phar-lap-arsenic-claims-premature-expert/1292814 |via=abc.net.au |access-date=2016-06-14}}</ref>
<blockquote>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&nbsp;per cent of the horses had arsenic in their system.</blockquote>

== Applications ==

=== Agricultural ===
[[File:Roxarsone.png|thumb|[[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 a [[wood preservative]].<ref>{{cite journal |doi = 10.2134/jeq2004.0173 |last1 = Rahman |first1 = F. A. |last2 = Allan |first2 = D. L. |last3 = Rosen |first3 = C. J. |last4 = Sadowsky |first4 = M. J. |title = Arsenic availability from chromated copper arsenate (CCA)-treated wood |journal = Journal of Environmental Quality |volume = 33 |issue = 1 |pages = 173–180 |date = 2004 |pmid = 14964372}}</ref> In the 1930s, 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. 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.<ref>{{cite book|title = Environmental Chemistry: Green Chemistry and Pollutants in Ecosystems|editor = Lichtfouse, Eric|editor2 = Schwarzbauer, Jan|editor3 = Robert, Didier|date = 2004|isbn = 978-3-540-22860-8|chapter-url = https://books.google.com/books?id=IDGLh_cWAIwC|chapter = Electrodialytical Removal of Cu, Cr and As from Threaded Wood|first = Eric|last = Lichtfouse |publisher = Springer|location = Berlin}}</ref><ref name="round">{{cite journal|journal = Talanta|volume = 58|issue = 1|date = 2002|pages = 201–235|doi = 10.1016/S0039-9140(02)00268-0|title = Arsenic round the world: a review|first1 = Badal Kumar|last1 = Mandal|pmid = 18968746|last2 = Suzuki|first2 = K. T.}}</ref> However, CCA remains in heavy use in other countries (such as on Malaysian rubber plantations).<ref name = Ullmann />

Arsenic was also used in various agricultural insecticides and poisons. For example, [[lead hydrogen arsenate]] was a common insecticide on [[fruit tree]]s,<ref>{{cite conference|last = Peryea|first = F. J.|title = Historical use of lead arsenate insecticides, resulting in soil contamination and implications for soil remediation|conference = 16th World Congress of Soil Science|place = Montpellier, France|date = 20–26 August 1998|url = http://soils.tfrec.wsu.edu/leadhistory.htm|archive-url = https://web.archive.org/web/20081207174027/http://soils.tfrec.wsu.edu/leadhistory.htm|archive-date = 7 December 2008}}</ref> 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) and [[disodium 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.<ref name="Federal Register">{{cite web |title=Organic Arsenicals; Notice of Receipt of Requests to Voluntarily Cancel or to Amend to Terminate Uses of Certain Pesticide Registrations |url=https://www.govinfo.gov/content/pkg/FR-2009-07-08/html/E9-16054.htm |website=Federal Register |publisher=Government Printing Office |access-date=18 July 2023}}</ref><ref>{{cite web |title=Monosodium Methanearsonate (MSMA), an Organic Arsenical |date=22 April 2015 |url=https://www.epa.gov/ingredients-used-pesticide-products/monosodium-methanearsonate-msma-organic-arsenical |publisher=Environmental Protection Agency |access-date=18 July 2023}}</ref>

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 ({{chem2|AsO3(3-)}}) is more soluble than arsenate ({{chem2|AsO4(3-)}}) 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.<ref>{{Cite web|url=https://www.crcpress.com/Trace-Elements-in-Soils-and-Plants-Third-Edition/Kabata-Pendias/p/book/9780849315756|title=Trace Elements in Soils and Plants, Third Edition|website=CRC Press|date=8 November 2000 |access-date=2016-08-02|archive-url=https://web.archive.org/web/20160821154852/https://www.crcpress.com/Trace-Elements-in-Soils-and-Plants-Third-Edition/Kabata-Pendias/p/book/9780849315756|archive-date=21 August 2016}}</ref>

Arsenic is used as a feed additive in [[Poultry farming|poultry]] and [[Pig farming|swine production]], in particular it was used in the U.S. until 2015 to increase weight gain, improve [[feed conversion ratio|feed efficiency]], and prevent disease.<ref>{{cite journal|journal = Environmental Health Perspectives|date = 2005|volume = 113|issue = 9|pages = 1123–1124|doi = 10.1289/ehp.7834|pmid = 16140615|pmc = 1280389|title = Arsenic: A Roadblock to Potential Animal Waste Management Solutions|first1 = Keeve E.|last1 = Nachman|last2 = Graham|first2 = Jay P.|last3 = Price|first3 = Lance B.|last4 = Silbergeld|first4 = Ellen K.| bibcode=2005EnvHP.113.1123N }}</ref><ref>{{cite web |url=http://www.atsdr.cdc.gov/toxprofiles/tp2-c5.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.atsdr.cdc.gov/toxprofiles/tp2-c5.pdf |archive-date=2022-10-09 |url-status=live |title=Arsenic |at=Section 5.3, p. 310 |publisher=Agency for Toxic Substances and Disease Registry }}</ref> An example is [[roxarsone]], which had been used as a [[broiler]] starter by about 70% of U.S. broiler growers.<ref>{{cite journal|title =A Broad View of Arsenic|date = 2007|volume = 86|pages = 2–14|journal = Poultry Science|first = F. T.|last =Jones|pmid =17179408|issue =1|doi=10.1093/ps/86.1.2|doi-access =free}}</ref> 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.<ref name="FDAQ&A">{{cite web |author=Staff |title=Questions and Answers Regarding 3-Nitro (Roxarsone) |url=https://www.fda.gov/AnimalVeterinary/SafetyHealth/ProductSafetyInformation/ucm258313.htm |archive-url=https://web.archive.org/web/20110612145259/http://www.fda.gov/AnimalVeterinary/SafetyHealth/ProductSafetyInformation/ucm258313.htm |archive-date=12 June 2011 |date=8 June 2011 |publisher=[[U.S. Food and Drug Administration]] |access-date=2012-09-21 }}</ref> A successor to Alpharma, [[Zoetis]], continued to sell [[nitarsone]] until 2015, primarily for use in turkeys.<ref name="FDAQ&A" />

=== Medical use ===

During the 17th, 18th, and 19th centuries, a number of arsenic compounds were used as medicines, including [[arsphenamine]] (by [[Paul Ehrlich]]) and [[arsenic trioxide]] (by [[Thomas Fowler (inventor)|Thomas Fowler]]), for treating diseases such as cancer or [[psoriasis]].<ref name="ITOM">{{cite book |last1=Gibaud |first1=Stéphane |last2=Jaouen |first2=Gérard |title=Medicinal Organometallic Chemistry |chapter=Arsenic-Based Drugs: From Fowler's Solution to Modern Anticancer Chemotherapy |date=2010 |volume=32 |pages=1–20 |doi= 10.1007/978-3-642-13185-1_1 |series=Topics in Organometallic Chemistry |isbn=978-3-642-13184-4|bibcode=2010moc..book....1G }}</ref> Arsphenamine, as well as [[neosalvarsan]], was indicated for [[syphilis]], but has been superseded by modern [[antibiotics]]. However, arsenicals such as [[melarsoprol]] are still used for the treatment of [[trypanosomiasis]] in spite of their severe toxicity, since the disease is almost uniformly fatal if untreated.<ref>{{cite journal | pmid = 28673422 | doi=10.1016/S0140-6736(17)31510-6 | volume=390 | issue=10110 | title=Human African trypanosomiasis | year=2017 |vauthors=Büscher P, Cecchi G, Jamonneau V, Priotto G | journal=Lancet | pages=2397–2409| s2cid=4853616 }}</ref> In 2000 the US [[Food and Drug Administration]] approved arsenic trioxide for the treatment of patients with [[acute promyelocytic leukemia]] that is resistant to [[all-trans retinoic acid]].<ref>{{cite journal|last = Antman |first = Karen H.|date = 2001| title = The History of Arsenic Trioxide in Cancer Therapy|volume = 6|issue =Suppl 2|pages = 1–2|pmid = 11331433|doi = 10.1634/theoncologist.6-suppl_2-1|journal = The Oncologist|doi-access = free}}</ref>

A 2008 paper reports success in locating tumors using arsenic-74 (a positron emitter). This isotope produces clearer [[Positron emission tomography|PET scan]] images than the previous radioactive agent, [[iodine]]-124, because the body tends to transport iodine to the thyroid gland producing signal noise.<ref>{{cite journal|journal = Clinical Cancer Research|date = 2008|volume = 14|pages =1377–1385|doi = 10.1158/1078-0432.CCR-07-1516|title = Vascular imaging of solid tumors in rats with a radioactive arsenic-labeled antibody that binds exposed phosphatidylserine |last1 = Jennewein |first1 =Marc|pmid = 18316558|issue = 5|last2 = Lewis|first2 = M. A.|last3 = Zhao|first3 = D.|last4 = Tsyganov |first4 = E.|last5 = Slavine |first5 = N. |last6 = He |first6 = J. |last7 = Watkins |first7 = L. |last8 = Kodibagkar |first8 = V. D.|last9 = O'Kelly |first9 = S.|first10=P. |last10=Kulkarni|first11=P. |last11=Antich|first12=A. |last12=Hermanne|first13=F. |last13=Rösch |first14=R. |last14=Mason |first15=Ph. |last15=Thorpe |display-authors=6 |pmc = 3436070}}</ref> [[Nanoparticle]]s of arsenic have shown ability to kill cancer cells with lesser [[cytotoxicity]] than other arsenic formulations.<ref>{{cite journal |last1=Subastri |first1=Ariraman |last2=Arun |first2=Viswanathan |last3=Sharma |first3=Preeti |last4=Preedia babu |first4=Ezhuthupurakkal |last5=Suyavaran |first5=Arumugam |last6=Nithyananthan |first6=Subramaniyam |last7=Alshammari |first7=Ghedeir M. |last8=Aristatile |first8=Balakrishnan |last9=Dharuman |first9=Venkataraman |last10=Thirunavukkarasu |first10=Chinnasamy  |display-authors=6 |title=Synthesis and characterisation of arsenic nanoparticles and its interaction with DNA and cytotoxic potential on breast cancer cells |journal=Chemico-Biological Interactions |date=November 2018 |volume=295 |pages=73–83 |doi=10.1016/j.cbi.2017.12.025 |pmid=29277637 |bibcode=2018CBI...295...73S |s2cid=1816043 }}</ref>

=== Alloys ===

The main use of arsenic is in alloying with lead. Lead components in [[Automotive battery|car batteries]] are strengthened by the presence of a very small percentage of arsenic.<ref name = Ullmann /><ref>{{cite journal|doi =10.1016/0378-7753(94)01973-Y|title =Lead alloys: Past, present and future|date =1995|last1 =Bagshaw|first1 =N. E.|journal =Journal of Power Sources|volume =53|issue =1|pages =25–30|bibcode = 1995JPS....53...25B }}</ref> [[Selective leaching|Dezincification]] of [[brass]] (a copper-zinc alloy) is greatly reduced by the addition of arsenic.<ref>{{cite book|chapter-url = https://books.google.com/books?id=1hSJcC9zwFIC&pg=PA123|pages =123–124| chapter = Dealloying|title = Copper: Its Trade, Manufacture, Use, and Environmental Status|isbn = 978-0-87170-656-0|last1 = Joseph|first1 = Günter|last2 = Kundig|first2 = Konrad J. A|last3 = Association|first3 = International Copper|date = 1999|publisher =ASM International}}</ref> "Phosphorus Deoxidized Arsenical Copper" with an arsenic content of 0.3% has an increased corrosion stability in certain environments.<ref>{{cite book |url = https://books.google.com/books?id=cXkNMB1vBesC&pg=SA5-PA6| page = 6 |title = The Metals Databook |isbn = 978-0-07-462300-8 |author1 = Nayar |date = 1997| publisher = McGraw-Hill }}</ref> [[Gallium arsenide]] is an important [[semiconductor]] material, used in [[integrated circuit]]s. Circuits made from GaAs are much faster (but also much more expensive) than those made from [[silicon]]. Unlike silicon, GaAs has a [[direct bandgap]], and can be used in [[laser diode]]s and [[LED]]s to convert electrical energy directly into light.<ref name = Ullmann />

=== Military ===

After [[World War I]], the United States built a stockpile of 20,000 tons of [[Chemical warfare|weaponized]] [[lewisite]] (ClCH=CHAsCl<sub>2</sub>), an [[organoarsenic]] [[vesicant]] (blister agent) and [[lung]] irritant. The stockpile was neutralized with [[Sodium hypochlorite|bleach]] and dumped into the [[Gulf of Mexico]] in the 1950s.<ref>{{cite web|url = http://library.thinkquest.org/05aug/00639/en/w_chemical_blister.html|publisher = Code Red – Weapons of Mass Destruction |title = Blister Agents|access-date = 2010-05-15 }}</ref> Lewisite, the chemical warfare agent, is known for its acute toxicity to aquatic organisms.  However, studies assessing the environmental impact of this disposal in the Gulf are lacking.<ref>{{Cite journal |last1=Czub |first1=Michał |last2=Nawała |first2=Jakub |last3=Popiel |first3=Stanisław |last4=Brzeziński |first4=Tomasz |last5=Maszczyk |first5=Piotr |last6=Sanderson |first6=Hans |last7=Maser |first7=Edmund |last8=Gordon |first8=Diana |last9=Dziedzic |first9=Daniel |last10=Dawidziuk |first10=Barbara |last11=Pijanowska |first11=Joanna |last12=Fabisiak |first12=Jacek |last13=Szubska |first13=Marta |last14=Lang |first14=Thomas |last15=Vanninen |first15=Paula |display-authors=6 |date=2021-01-01 |title=Acute aquatic toxicity of arsenic-based chemical warfare agents to Daphnia magna |journal=Aquatic Toxicology |volume=230 |article-number=105693 |doi=10.1016/j.aquatox.2020.105693 |pmid=33310671 |bibcode=2021AqTox.23005693C |issn=0166-445X|doi-access=free }}</ref> During the [[Vietnam War]], the United States used [[Agent Blue]], a mixture of [[sodium cacodylate]] and its acid form, as one of the [[rainbow herbicides]] to deprive North Vietnamese soldiers of foliage cover and rice.<ref>{{cite journal|doi = 10.1016/0006-3207(72)90043-2|title = Herbicides in war: Current status and future doubt|date = 1972|last1 = Westing|first1 = Arthur H.|journal = Biological Conservation|volume = 4|issue = 5|pages = 322–327| bibcode=1972BCons...4..322W }}</ref><ref>{{cite journal|last1 = Westing| first1 = Arthur H.|title =Forestry and the War in South Vietnam|journal = Journal of Forestry|volume = 69|pages = 777–783|date = 1971| issue = 11| doi = 10.1093/jof/69.11.777|url = http://www.ingentaconnect.com/content/saf/jof/1971/00000069/00000011/art00008}}</ref><!--https://www.google.com/books/edition/_/agsAAAAAMBAJ?hl=en&gbpv=1&pg=PA37-->

=== Other uses ===
* Copper acetoarsenite was used as a green [[pigment]] known under many names, including [[Paris Green]] and Emerald Green. It caused numerous [[arsenic poisoning]]s. [[Scheele's Green]], a copper arsenate, was used in the 19th century as a [[food dye|coloring agent]] in [[sweets]].<ref>{{cite book|title = The Poison Paradox: Chemicals as Friends and Foes|chapter = Butter Yellow and Scheele's Green|first = John|last = Timbrell|publisher = Oxford University Press|date = 2005|isbn = 978-0-19-280495-2|chapter-url = https://books.google.com/books?id=qYYOtQU37jcC|url-access = registration|url = https://archive.org/details/poisonparadoxche0000timb}}</ref> Interestingly, some people believe that [[Napoleon]] died from the wallpaper on the wall where he was imprisoned.<ref>{{Cite web |title=拿破仑死于潮湿的壁纸？ |url=https://www.ilovemedicine.net/sys-nd/3474.html }}{{Dead link|date=August 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> This wallpaper was painted with this green pigment, which will be decomposed by bacteria in a humid environment to produce highly toxic [[arsine]].<ref>{{Cite book |title=化学之书 |publisher=重庆大学出版社 |year=2019 |isbn=978-7-5689-1057-6 |page=47 |language=Chinese |trans-title=The Chemistry Book}}</ref>
* Arsenic is used in [[bronzing]].<ref>{{cite journal|doi = 10.1007/BF02519786|title = Industrial exposure to arsenic|date = 1979|last1 = Cross|first1 = J. D.|last2 = Dale|first2 = I. M.|last3 = Leslie|first3 = A. C. D.|last4 = Smith|first4 = H.|journal = Journal of Radioanalytical Chemistry|volume = 48|issue = 1–2|pages = 197–208| bibcode=1979JRNC...48..197C |s2cid = 93714157}}</ref>
* As much as 2% of produced arsenic is used in lead alloys for [[lead shot]] and bullets.<ref>{{cite book|title = Engineering Properties and Applications of Lead Alloys|chapter = XIV. Ammunition|first = Sivaraman|last = Guruswamy|publisher = CRC Press|date = 1999|isbn = 978-0-8247-8247-4|chapter-url = https://books.google.com/books?id=TtGmjOv9CUAC|pages = 569–570}}</ref>
* Arsenic is added in small quantities to alpha-brass to make it [[Selective leaching|dezincification-resistant]]. This grade of brass is used in plumbing fittings and other wet environments.<ref>{{cite book|chapter-url = https://books.google.com/books?id=sxkPJzmkhnUC&pg=PA390|chapter = Dealloying|page =390|isbn = 978-0-87170-726-0|title = Copper and copper alloys|last1 = Davis |first1=Joseph R. |author2 = Handbook Committee, ASM International|year= 2001| publisher=ASM International }}</ref>
* Arsenic is also used for [[Taxonomy|taxonomic]] sample preservation.<!--https://www.google.com/books/edition/_/aRI9MrpXLqYC?hl=en&gbpv=1&pg=PA93 --> It was also used in embalming fluids historically.<ref>{{Cite book |last=Quigley |first=Christine |url={{Google books|ZMSSCgAAQBAJ|page=6|plainurl=yes}}|page=6 |title=Modern Mummies: The Preservation of the Human Body in the Twentieth Century |date=2006 |orig-date=First published 1998 |publisher=McFarland |isbn=978-1-4766-1373-4 |language=en}}</ref>
* Arsenic was used in the [[taxidermy]] process up until the 1980s.<ref>{{cite journal| last1=Marte | first1=Fernando | last2=Pequignot | first2=Amandine| title=Arsenic in Taxidermy Collections: History, Detection, and Management |journal=Collection Forum|year=2006| url=https://repository.si.edu/handle/10088/8134|hdl=10088/8134|volume=21|issue=1–2|pages=143–150}}</ref>
* Arsenic was used as an opacifier in ceramics, creating white glazes.<ref>{{cite book |last1=Parmelee |first1=Cullen W. |title=Ceramic Glazes |date=1947 |publisher=Cahners Books |location=Boston|page=61 |edition=3rd}}</ref>
* Until recently, arsenic was used in optical glass. Modern glass manufacturers have ceased using both arsenic and lead.<ref>{{cite book|chapter-url = https://books.google.com/books?id=Qt7sNqoP_CkC&pg=PA68|page =68|title = Pollution technology review 214: Mercury and arsenic wastes: removal, recovery, treatment, and disposal|publisher = William Andrew|date = 1993|isbn = 978-0-8155-1326-1|chapter = Arsenic Supply Demand and the Environment|author=United States Environmental Protection Agency}}</ref><ref>{{Cite journal |last1=Kumar |first1=Mahendra |last2=Seth |first2=Aparna |last3=Singh |first3=Alak Kumar |last4=Rajput |first4=Manish Singh |last5=Sikandar |first5=Mohd |date=2021-12-01 |title=Remediation strategies for heavy metals contaminated ecosystem: A review |journal=Environmental and Sustainability Indicators |volume=12 |article-number=100155 |doi=10.1016/j.indic.2021.100155 |doi-access=free |bibcode=2021EnvSI..1200155K }}</ref><ref>{{Citation |last=Humans |first=IARC Working Group on the Evaluation of Carcinogenic Risks to |title=Exposures in the Glass Manufacturing Industry |date=1993 |url=https://www.ncbi.nlm.nih.gov/books/NBK499748/ |work=Beryllium, Cadmium, Mercury, and Exposures in the Glass Manufacturing Industry |volume=58 |pages=347–375 |access-date=2024-01-12 |publisher=International Agency for Research on Cancer |language=en |pmid=8022057|pmc=7681308 }}</ref>

== Biological role ==
{{Main|Arsenic biochemistry}}

=== Bacteria ===
Some species of bacteria obtain their energy in the absence of oxygen by [[redox|oxidizing]] various fuels while [[redox|reducing]] arsenate to arsenite. Under oxidative environmental conditions some bacteria use arsenite as fuel, which they oxidize to arsenate.<ref>{{cite journal|last1 = Stolz|first1 = John F.|last2 = Basu|first2 = Partha|last3 = Santini|first3 = Joanne M.|last4 = Oremland|first4 = Ronald S.|s2cid = 2575554|title = Arsenic and Selenium in Microbial Metabolism|journal = Annual Review of Microbiology|volume = 60|pages = 107–130|date = 2006|doi = 10.1146/annurev.micro.60.080805.142053|pmid=16704340| bibcode=2006ARvMb..60..107S }}</ref> The [[enzyme]]s involved are known as [[Arsenate reductase (glutaredoxin)|arsenate reductases]] (Arr).<ref>{{cite journal |doi = 10.1111/j.1574-6976.2002.tb00617.x |title = Microbial arsenic: From geocycles to genes and enzymes |date = 2002 |last1 = Mukhopadhyay |first1 = Rita |last2 = Rosen |first2 = Barry P. |last3 = Phung |first3 = Le T. |last4 = Silver |first4 = Simon |journal = FEMS Microbiology Reviews |volume = 26 |issue = 3 |pages = 311–325 |pmid = 12165430| doi-access = free }}</ref>

In 2008, bacteria were discovered that employ a version of [[photosynthesis]] in the absence of oxygen with arsenites as [[electron donor]]s, 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. One [[strain (biology)|strain]], PHS-1, has been isolated and is related to the [[gammaproteobacterium]] ''[[Ectothiorhodospira shaposhnikovii]]''. The mechanism is unknown, but an encoded Arr enzyme may function in reverse to its known [[homology (biology)|homologues]].<ref>{{cite journal |last1=Kulp |first1=T.R |last2= Hoeft |first2= S.E. |last3= Asao |first3= M. |last4= Madigan |first4= M.T. |last5= Hollibaugh |first5= J.T. |last6= Fisher |first6= J.C. |last7= Stolz |first7= J.F. |last8= Culbertson |first8= C.W. |last9= Miller |first9= L.G.|first10=R.S. |last10=Oremland |display-authors=6 |year = 2008 |title = Arsenic(III) fuels anoxygenic photosynthesis in hot spring biofilms from Mono Lake, California|journal = [[Science (journal)|Science]]|volume = 321 |issue = 5891|pages = 967–970|doi = 10.1126/science.1160799 |pmid= 18703741 |s2cid = 39479754|bibcode = 2008Sci...321..967K}}
{{cite magazine |first=Fred |last=Campbell |date=11 August 2008 |title=Arsenic-loving bacteria rewrite photosynthesis rules |magazine=Chemistry World |url=https://www.chemistryworld.com/news/arsenic-loving-bacteria-rewrite-photosynthesis-rules/3000398.article }}</ref>

In 2010, researchers reported the discovery of a strain of the bacterium ''[[Halomonas]]'' (designated [[GFAJ-1]]) that was allegedly capable of substituting arsenic for phosphorus in its biomolecules, including DNA, when grown in an arsenic-rich, phosphate-limited environment. This claim, published in ''Science'', suggested that arsenic could potentially serve as a building block of life in place of phosphorus, challenging long-standing assumptions about biochemical requirements for life on Earth.<ref>{{Cite journal |last1=Wolfe-Simon |first1=Felisa |last2=Blum |first2=Jodi Switzer |last3=Kulp |first3=Thomas R. |last4=Gordon |first4=Gwyneth W. |last5=Hoeft |first5=Shelley E. |last6=Pett-Ridge |first6=Jennifer |last7=Stolz |first7=John F. |last8=Webb |first8=Samuel M. |last9=Weber |first9=Peter K. |last10=Davies |first10=Paul C. W. |last11=Anbar |first11=Ariel D. |last12=Oremland |first12=Ronald S. |date=2011-06-03 |title=A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus |url=https://www.science.org/doi/10.1126/science.1197258 |journal=Science |volume=332 |issue=6034 |pages=1163–1166 |doi=10.1126/science.1197258|pmid=21127214 |bibcode=2011Sci...332.1163W |osti=1016932 }}{{Retracted|doi=10.1126/science.adu5488|pmid=40705905|https://retractionwatch.com/2025/07/24/science-retraction-arsenic-life-nasa-astrobiology/ ''Retraction Watch''|intentional=yes}}</ref>

The claim was met with widespread skepticism. Subsequent studies provided evidence contradicting the initial findings. One follow-up study published in ''Science'' in 2011 demonstrated that GFAJ-1 still requires phosphate to grow and does not incorporate arsenate into its DNA in any biologically significant way.<ref>{{Cite journal |last1=Cotner |first1=James B. |last2=Hall |first2=Edward K. |date=2011-06-03 |title=Comment on "A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus" |url=https://www.science.org/doi/10.1126/science.1201943 |journal=Science |volume=332 |issue=6034 |page=1149 |doi=10.1126/science.1201943|pmid=21622705 |bibcode=2011Sci...332R1149C |url-access=subscription }}</ref> Another independent investigation in 2012 used more sensitive techniques to purify and analyze the DNA of GFAJ-1 and found no detectable arsenate incorporated into the DNA backbone. The authors concluded that the original observations were likely due to experimental contamination or insufficient purification methods.<ref>{{Cite journal |last1=Erb |first1=Tobias J. |last2=Kiefer |first2=Patrick |last3=Hattendorf |first3=Bodo |last4=Günther |first4=Detlef |last5=Vorholt |first5=Julia A. |date=2012-07-27 |title=GFAJ-1 Is an Arsenate-Resistant, Phosphate-Dependent Organism |url=https://www.science.org/doi/10.1126/science.1218455 |journal=Science |volume=337 |issue=6093 |pages=467–470 |doi=10.1126/science.1218455|pmid=22773139 |bibcode=2012Sci...337..467E |url-access=subscription }}</ref> Together, these studies reaffirmed phosphorus as an essential element for all known forms of life. In 2025, the journal ''Science'' formally retracted the original paper, citing a lack of sufficient experimental support for its key conclusions,<ref>{{Cite journal |last=Thorp |first=H. Holden |date=2025-07-24 |title=Retraction |url=https://www.science.org/doi/10.1126/science.adu5488 |journal=Science |volume=389 |issue=6758 |page=357 |doi=10.1126/science.adu5488|pmid=40705905 |bibcode=2025Sci...389..357T |url-access=subscription }}</ref> though the authors continued to stand by their data.<ref>{{Cite journal |last=Wolf |first=Lauren |date=2025-07-24 |title=Controversial 'arsenic life' paper retracted after 15 years — but authors fight back |url=https://www.nature.com/articles/d41586-025-02325-z |journal=Nature |volume=643 |issue=8074 |pages=1163–1164 |language=en |doi=10.1038/d41586-025-02325-z |pmid=40715714 |bibcode=2025Natur.643.1163W |issn=1476-4687|url-access=subscription }}</ref>

=== Potential role in higher animals ===

Arsenic may be an essential trace mineral in birds, involved in the synthesis of methionine metabolites.<ref>{{cite journal |last1=Živkov Baloš |first1=M. |last2=Jakšić |first2=S. |last3=Ljubojević Pelić |first3=D. |date=September 2019 |title=The role, importance and toxicity of arsenic in poultry nutrition |journal=World's Poultry Science Journal |volume=75 |issue=3 |pages=375–386 |doi=10.1017/S0043933919000394 }}</ref> However, the role of arsenic in bird nutrition is disputed, as other authors state that arsenic is toxic in small amounts.<ref>{{cite journal | last = Aljohani | first = A.S. | year = 2023 | title=Heavy metal toxicity in poultry: A comprehensive review | journal=Frontiers in Veterinary Science | volume=10 | article-number = 1161354 | pmid=37456954 | pmc=10340091 | doi=10.3389/fvets.2023.1161354 | doi-access=free }}</ref>

Some evidence indicates that arsenic is an essential trace mineral in mammals.<ref name=ANut>Anke M. (1986) "Arsenic", pp. 347–372 in Mertz W. (ed.), ''Trace elements in human and Animal Nutrition'', 5th ed. Orlando, FL: Academic Press</ref><ref name=UEssent>
{{cite journal
 |last1=Uthus |first1=Eric O.
 |year=1992
 |title= Evidency for arsenical essentiality
 |journal= Environmental Geochemistry and Health 
 |volume=14 |issue=2 |pages=55–58
 |pmid=24197927  |bibcode=1992EnvGH..14...55U
 |s2cid=22882255 |doi=10.1007/BF01783629
}}
{{cite book
 |last=Uthus |first=E.O.
 |year=1994
 |section=Arsenic essentiality and factors affecting its importance
 |editor1-last=Chappell  |editor1-first=W.R.
 |editor2-last=Abernathy |editor2-first=C.O.
 |editor3-last=Cothern   |editor3-first=C.R.
 |title=Arsenic Exposure and Health
 |pages=199–208
 |place=Northwood, UK
 |publisher=Science and Technology Letters
}}
</ref>

Experimental studies in rodents and livestock have shown that arsenic deprivation can lead to impaired growth, reduced reproductive performance, and abnormal glucose metabolism, suggesting it may play a role in essential metabolic processes.<ref>{{Cite book |url=https://nap.nationalacademies.org/catalog/6444/arsenic-in-drinking-water |title=Arsenic in Drinking Water |date=1999-06-14 |publisher=National Academies Press |isbn=978-0-309-06333-3 |location=Washington, D.C.|doi=10.17226/6444 |pmid=25101451 |author1=National Research Council (US) Subcommittee on Arsenic in Drinking Water |bibcode=1999nap..book.6444N }}</ref> Arsenic has been proposed to participate in [[methylation]] reactions, possibly influencing gene regulation and detoxification pathways.<ref>{{Cite journal |last1=Abernathy |first1=C O |last2=Liu |first2=Y P |last3=Longfellow |first3=D |last4=Aposhian |first4=H V |last5=Beck |first5=B |last6=Fowler |first6=B |last7=Goyer |first7=R |last8=Menzer |first8=R |last9=Rossman |first9=T |last10=Thompson |first10=C |last11=Waalkes |first11=M |date=July 1999 |title=Arsenic: health effects, mechanisms of actions, and research issues. |journal=Environmental Health Perspectives |volume=107 |issue=7 |pages=593–597 |doi=10.1289/ehp.99107593 |pmc=1566656 |pmid=10379007|bibcode=1999EnvHP.107..593A }}</ref> However, because the threshold between beneficial and toxic exposure is extremely narrow, arsenic is not currently classified as an essential element for humans, and its physiological role in higher animals remains uncertain.<ref>{{Cite journal |last=Hughes |first=Michael F. |date=2002-07-07 |title=Arsenic toxicity and potential mechanisms of action |journal=Toxicology Letters |volume=133 |issue=1 |pages=1–16 |doi=10.1016/s0378-4274(02)00084-x |issn=0378-4274 |pmid=12076506 |bibcode=2002ToxL..133....1H }}</ref>

=== Heredity ===

Arsenic has been linked to [[epigenetics|epigenetic changes]], heritable changes in gene expression that occur without changes in [[DNA sequence]]. These include DNA methylation, histone modification, and [[RNA]] interference. Toxic levels of arsenic cause significant DNA hypermethylation of tumor suppressor genes [[p16 (gene)|p16]] and [[p53]], thus increasing risk of [[carcinogenesis]]. These epigenetic events have been studied ''in vitro'' using human [[kidney]] cells and ''in vivo'' using rat [[liver]] cells and peripheral blood [[leukocytes]] in humans.<ref>{{cite journal|last1=Baccarelli|first1=A.|date=2009|title=Epigenetics and environmental chemicals|journal=Current Opinion in Pediatrics |issue=2 |volume=21 |pages=243–251 |doi=10.1097/MOP.0b013e32832925cc |pmid=19663042|last2=Bollati|first2=V.|pmc=3035853}}</ref> [[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.<ref>{{cite journal|last1=Nicholis|first1=I.|date=2009|title=Arsenite medicinal use, metabolism, pharmacokinetics and monitoring in human hair| journal=Biochimie| pmid=19527769| doi=10.1016/j.biochi.2009.06.003 |last2=Curis |last3=Deschamps|last4=Bénazeth|volume=91|first2=E.|first3=P.|first4=S.|issue=10|pages=1260–1267}}</ref> 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 in [[phytoremediation]].<ref>{{Cite journal
| volume = 156
| journal = New Phytologist
| title = Arsenic Distribution and Speciation in the Fronds of the Hyperaccumulator Pteris vittata
| issue = 2
| pages = 195–203
| jstor = 1514012
| doi = 10.1046/j.1469-8137.2002.00512.x
| year = 2002 |first5 = S. P.
| last5 = McGrath
 |first2 = F.-J.
| last2 = Zhao
| first1 = E.
| last3 = Fuhrmann |first3 = M. |first4 = L. Q.
| last4 = Ma
| last1 = Lombi
| pmid = 33873285
| doi-access = free
| bibcode = 2002NewPh.156..195L
}}
</ref>

=== Biomethylation ===
[[File:ArsenobetainePIC.svg|thumb|[[Arsenobetaine]]]]

Inorganic arsenic and its compounds, upon entering the [[food chain]], are progressively metabolized through a process of [[methylation]].<ref name="Biomethylation">{{cite journal|title = Biomethylation of Arsenic is Essentially Detoxicating Event|journal = Journal of Health Science|date = 2003|first1 = Teruaki Sakurai|volume = 49|issue = 3|pages = 171–178| doi = 10.1248/jhs.49.171|last1 = Sakurai|doi-access = free}}</ref><ref>{{cite book|last=Reimer|first=K. J.|author2=Koch, I.|author3=Cullen, W.R.|date=2010|title=Organoarsenicals. Distribution and transformation in the environment|volume=7 |pages=165–229|isbn=978-1-84755-177-1|pmid=20877808|doi=10.1039/9781849730822-00165|series=Metal Ions in Life Sciences}}</ref> For example, the mold ''[[Scopulariopsis brevicaulis]]'' produces [[trimethylarsine]] if inorganic arsenic is present.<ref>{{cite journal |first1 = Ronald |last1 = Bentley |last2 = Chasteen |first2 = T.G. |year = 2002 |title = Microbial methylation of metalloids: Arsenic, antimony, and bismuth |journal = Microbiology and Molecular Biology Reviews |volume = 66 |issue = 2 |pages = 250–271 |doi = 10.1128/MMBR.66.2.250-271.2002 |pmid = 12040126 |pmc = 120786}}</ref> 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&nbsp;μg/day. Values about 1000&nbsp;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.<ref>{{cite journal |first1 = William R. |last1 = Cullen |last2 = Reimer |first2 = Kenneth J. |year = 1989 | title = Arsenic speciation in the environment |journal = Chemical Reviews |volume = 89|issue = 4|pages =713–764|doi = 10.1021/cr00094a002 |hdl = 10214/2162|hdl-access = free}}</ref>

== Environmental issues ==

=== Exposure ===

Naturally occurring sources of human exposure include [[volcanic ash]], weathering of minerals and ores, and mineralized groundwater. Arsenic is also found in food, water, soil, and air.<ref>{{cite report |title=Arsenic toxicity exposure pathways |series = Case Studies in Environmental Medicine (CSEM) |publisher = Agency for Toxic Substances & Disease Registry |url = https://www.atsdr.cdc.gov/csem/csem.html |access-date = 2010-05-15 |archive-date = 4 February 2016|archive-url = https://web.archive.org/web/20160204174821/http://www.atsdr.cdc.gov/csem/csem.asp?csem=7&po=7 }}</ref> Arsenic is absorbed by all plants, but is more concentrated in leafy vegetables, rice, apple and grape juice, and seafood.<ref>{{cite web|url=https://www.webmd.com/diet/features/arsenic-food-faq|access-date=2010-04-11 |date=5 December 2011|title=Arsenic in Food: FAQ}}</ref> An additional route of exposure is inhalation of atmospheric gases and dusts.<ref name="atsdr.cdc.gov">{{cite web |title=Arsenic |publisher=The Agency for Toxic Substances and Disease Registry |year=2009 |url=https://wwwn.cdc.gov/TSP/index.aspx?toxid=3 }}</ref>
During the [[Victorian era]], arsenic was widely used in home decor, especially wallpapers.<ref>{{cite AV media |title=How Victorians were poisoned by their own homes |series=Hidden Killers |publisher=Absolute Victory ([[YouTube]]) |medium=video |url=https://www.youtube.com/watch?v=MvxnXOoFl20 |archive-url=https://web.archive.org/web/20190919033145/https://www.youtube.com/watch?v=MvxnXOoFl20&gl=US&hl=en |archive-date=19 September 2019 |via=Ghostarchive |access-date=18 September 2019 }}<br/>{{cite web |title=alternate archived video |via=[[Internet Archive|Wayback Machine]] (archive.org) |url=https://www.youtube.com/watch?v=MvxnXOoFl20&gl=US&hl=en |archive-url=https://web.archive.org/web/20190919033145/https://www.youtube.com/watch?v=MvxnXOoFl20&gl=US&hl=en |archive-date=2019-09-19 }}</ref> In Europe, an analysis based on 20,000&nbsp;soil samples across all 28&nbsp;countries show that 98% of sampled soils have concentrations less than 20&nbsp;mg/kg. In addition, the arsenic hotspots are related to both frequent fertilization and close distance to mining activities.<ref>{{cite journal |last1=Fendrich |first1=Arthur Nicolaus |last2=Van Eynde |first2=Elise |last3=Stasinopoulos |first3=Dimitrios M. |last4=Rigby |first4=Robert A. |last5=Mezquita |first5=Felipe Yunta |last6=Panagos |first6=Panos |date=2024-03-01 |title=Modeling arsenic in European topsoils with a coupled semiparametric (GAMLSS-RF) model for censored data |journal=Environment International |language=en |volume=185 |article-number=108544 |doi=10.1016/j.envint.2024.108544|doi-access=free |pmid=38452467 |bibcode=2024EnInt.18508544F }}</ref> Chronic exposure to arsenic, particularly through contaminated drinking water and food, has also been linked to long-term impacts on cognitive function, including reduced verbal IQ and memory.<ref>{{Cite journal |last1=Kapaj |first1=Simon |first2=Hans | last2 = Peterson |first3=Karsten | last3 = Liber |last4=Bhattacharya |first4=Prosun |date=2006-10-01 |title=Human Health Effects From Chronic Arsenic Poisoning–A Review |url=https://www.tandfonline.com/doi/full/10.1080/10934520600873571 |journal=Journal of Environmental Science and Health, Part A |volume=41 |issue=10 |pages=2399–2428 |doi=10.1080/10934520600873571 |pmid=17018421 |bibcode=2006JESHA..41.2399K |issn=1093-4529|url-access=subscription }}</ref>

=== Occurrence in drinking water ===
{{Main|Arsenic contamination of groundwater}}

Extensive arsenic contamination of groundwater has led to widespread [[arsenic poisoning]] in [[Water supply and sanitation in Bangladesh|Bangladesh]]<ref>{{cite book |first = Andrew |last = Meharg |year= 2005 |title = Venomous Earth – How arsenic caused the world's worst mass poisoning |isbn = 978-1-4039-4499-3 |publisher = Macmillan Science |url-access = registration|url = https://archive.org/details/venomousearthhow00meha}}</ref> and neighboring countries.<!--As of this writing,{{when|date=June 2012}}{{citation needed|date=June 2012}} 42&nbsp;major incidents around the world have been reported on groundwater arsenic contamination.--> It is estimated that approximately 57&nbsp;million people in the Bengal basin are drinking [[groundwater]] with arsenic concentrations elevated above the [[World Health Organization]]'s standard of 10&nbsp;[[Concentration#"Parts-per" notation|parts per billion]] (ppb).<ref>{{cite book |url = https://books.google.com/books?id=hMA70VU36qUC&pg=PA317 |page = 317 |title = Arsenic: Environmental Chemistry, Health Threats and Waste Treatment |isbn = 978-0-470-02758-5 |last1 = Henke |first1 = Kevin R. |date = 28 April 2009|publisher = John Wiley & Sons }}</ref> However, a study of cancer rates in [[Taiwan]]<ref>{{cite journal |doi=10.1289/ehp.8704 |journal=Environ. Health Perspect. |volume=114 |issue=7 |pages=1077–1082 |date=2006 |pmid=16835062 |pmc=1513326 |last1=Lamm |first1=S. H. |last2=Engel |first2=A. |last3=Penn |first3=C. A. |last4=Chen |first4=R. |last5=Feinleib |first5=M. |title=Arsenic cancer risk confounder in southwest Taiwan dataset |bibcode=2006EnvHP.114.1077L }}</ref> suggested that significant increases in cancer mortality appear only at levels above 150&nbsp;ppb. The arsenic in the groundwater is of natural origin, and is released from the sediment into the groundwater, caused by the [[Dead zone (ecology)|anoxic conditions]] of the subsurface. This groundwater was used after local and western [[Non-governmental organization|NGOs]] and the Bangladeshi government undertook a massive shallow tube [[Water well|well]] 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 as [[Vietnam]] and [[Cambodia]], have geological environments that produce groundwater with a high arsenic content. [[Arsenic poisoning#Arsenicosis: chronic arsenic poisoning from drinking water|Arsenicosis]] was reported in [[Nakhon Si Thammarat]], Thailand, in 1987, and the [[Chao Phraya River]] probably contains high levels of naturally occurring dissolved arsenic without being a public health problem because much of the public uses [[bottled water]].<ref>{{cite journal |first = Andrew |last = Kohnhorst |year=2005 |title=Arsenic in groundwater in selected countries in south and southeast Asia: A review |journal=J Tropical Medicine and Parasitology |volume=28 |page=73  |url=http://antispam.kmutt.ac.th/index.php/JTMP/article/view/14749 |archive-url=https://web.archive.org/web/20140110085919/http://antispam.kmutt.ac.th/index.php/JTMP/article/view/14749 |archive-date=2014-01-10}}</ref> In Pakistan, more than 60&nbsp;million people are exposed to arsenic polluted drinking water indicated by a 2017 report in [[Science (journal)|''Science'']]. Podgorski's team investigated more than 1200&nbsp;samples and more than 66% exceeded the [[World Health Organization|WHO]] contamination limits of 10 micrograms per liter.<ref>{{cite journal |title=Arsenic in drinking water threatens up to 60&nbsp;million in Pakistan |date=2017-08-23 |journal=[[Science (journal)|Science]] |publisher=[[American Association for the Advancement of Science|AAAS]] |url=https://www.science.org/content/article/arsenic-drinking-water-threatens-60-million-pakistan |access-date=2017-09-11 |language=en }}</ref>

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.<ref name="Well Water Arsenic Exposure, Arsenic Induced Skin-Lesions and Self-Reported Morbidity in Inner Mongolia">{{cite journal |last1=Xia |first1=Yajuan |last2=Wade |first2=Timothy |last3=Wu |first3=Kegong |last4=Li |first4=Yanhong |last5=Ning |first5=Zhixiong |last6=Le |first6=X. Chris |last7=He |first7=Xingzhou |last8=Chen |first8=Binfei |last9=Feng |first9=Yong |last10=Mumford |first10=Judy |display-authors=6 |title=Well Water Arsenic Exposure, Arsenic Induced Skin-Lesions and Self-Reported Morbidity in Inner Mongolia |journal=International Journal of Environmental Research and Public Health |date=9 March 2009 |volume=6 |issue=3 |pages=1010–1025 |doi=10.3390/ijerph6031010 |pmid=19440430 |pmc=2672384 |doi-access=free }}</ref> A 2009 research study observed an elevated presence of skin lesions among residents with well water arsenic concentrations between 5 and 10&nbsp;μg/L, suggesting that arsenic-induced toxicity may occur at relatively low concentrations with chronic exposure.<ref name="Well Water Arsenic Exposure, Arsenic Induced Skin-Lesions and Self-Reported Morbidity in Inner Mongolia" /> Overall, 20 of China's 34 provinces have high arsenic concentrations in the groundwater supply, potentially exposing 19&nbsp;million people to hazardous drinking water.<ref name="Lall">{{Cite journal|last1=Lall|first1=Upmanu|last2=Josset|first2=Laureline|last3=Russo|first3=Tess|date=2020-10-17|title=A Snapshot of the World's Groundwater Challenges|journal=Annual Review of Environment and Resources|language=en|volume=45|issue=1|pages=171–194|doi=10.1146/annurev-environ-102017-025800|doi-access=free }}</ref>

A study by [[IIT Kharagpur]] found high levels of Arsenic in groundwater of 20% of India's land, exposing more than 250&nbsp;million people. States such as [[Punjab]], Bihar, [[West Bengal]], Assam, [[Haryana]], Uttar Pradesh, and [[Gujarat]] have highest land area exposed to arsenic.<ref>{{cite news |title=IIT Kharagpur Study Finds 20% of India Has High Arsenic Levels in Groundwater |url=https://science.thewire.in/health/iit-kharagpurs-ai-study-finds-20-of-india-has-toxic-levels-of-arsenic-in-groundwater/ |access-date=2023-05-23 |work=[[The Wire (India)|The Wire]] |agency=PTI |date=2021-02-11}}</ref>

In the United States, arsenic is most commonly found in the ground waters of the southwest.<ref name="test">{{cite web|url = http://h2oc.com/pdfs/Occurrence.pdf|title = Arsenic in Drinking Water: 3. Occurrence in U.S. Waters|access-date = 2010-05-15|archive-url = https://web.archive.org/web/20100107171246/http://h2oc.com/pdfs/Occurrence.pdf|archive-date = 7 January 2010}}</ref> Parts of [[New England]], [[Michigan]], [[Wisconsin]], [[Minnesota]] and the Dakotas are also known to have significant concentrations of arsenic in ground water.<ref>{{cite journal |doi=10.1111/j.1745-6584.2000.tb00251.x |title=Arsenic in Ground Water of the United States: Occurrence and Geochemistry |date=2000 |last1=Welch |first1=Alan H. |last2=Westjohn |first2=D. B. |last3=Helsel |first3=Dennis R. |last4=Wanty |first4=Richard B. |journal=Ground Water |volume=38 |issue=4 |pages=589–604|bibcode=2000GrWat..38..589W |s2cid=129409319 }}</ref> Increased levels of skin cancer have been associated with arsenic exposure in Wisconsin, even at levels below the 10&nbsp;ppb drinking water standard.<ref>{{cite journal |title=Association of arsenic-contaminated drinking-water with prevalence of skin cancer in Wisconsin's Fox River Valley |journal=J. Health Popul Nutr |volume=24 |issue=2 |pages=206–213 |date=2006 |pmid=17195561|last1=Knobeloch |first1=L. M. |last2=Zierold |first2=K. M. |last3=Anderson |first3=H. A.|hdl=1807/50099 |hdl-access=free }}</ref> 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, more than 20% of the wells may contain levels that exceed established limits.<ref>{{cite web |url=http://www.dartmouth.edu/~toxmetal/InSmallDoses/ |title=In Small Doses:Arsenic|work=The Dartmouth Toxic Metals Superfund Research Program. Dartmouth College}}</ref>

Low-level exposure to arsenic at concentrations of 100&nbsp;ppb (i.e., above the 10&nbsp;ppb drinking water standard) compromises the initial immune response to [[Influenza A virus subtype H1N1|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 from the virus.<ref>{{cite journal|last1=Courtney|first1=D.|date=2009|title=Low Dose Arsenic Compromises the Immune Response to Influenza A Infection in vivo|pages=1441–1447|pmid=19750111|pmc=2737023|issue=9|doi=10.1289/ehp.0900911|volume=117|last2=Ely|first2=Kenneth H.|last3=Enelow|first3=Richard I.|last4=Hamilton|first4=Joshua W.|journal=Environmental Health Perspectives|bibcode=2009EnvHP.117.1441K }}</ref>

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.<ref name="GSC-2009">{{cite web|last1=Klassen |first1=R. A. |last2=Douma |first2=S. L. |last3=Ford |first3=A. |last4=Rencz |first4=A. |last5=Grunsky |first5=E. |title=Geoscience modeling of relative variation in natural arsenic hazard in potential in New Brunswick |url=http://geogratis.cgdi.gc.ca/eodata/download/part6/ess_pubs/247/247834/cr_2009_07_gsc.pdf |date=2009 |publisher=[[Geological Survey of Canada]] |access-date=2012-10-14 |archive-url=https://web.archive.org/web/20130502043721/http://geogratis.cgdi.gc.ca/eodata/download/part6/ess_pubs/247/247834/cr_2009_07_gsc.pdf |archive-date=2 May 2013 }}</ref>

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&nbsp;ppb.<ref>{{cite journal |title=Arsenic exposure and its impact on health in Chile |journal=J Health Popul Nutr |volume=24 |issue=2 |pages=164–175 |date=2006 |pmid=17195557|last1=Ferreccio |first1=C. |last2=Sancha |first2=A. M.|hdl=1807/50095 |hdl-access=free }}</ref> Arsenic is itself a constituent of [[tobacco smoke]].<ref name="TalhoutSchulz2011">{{cite journal|last1=Talhout|first1=Reinskje|last2=Schulz|first2=Thomas|last3=Florek|first3=Ewa|last4=Van Benthem|first4=Jan|last5=Wester|first5=Piet|last6=Opperhuizen|first6=Antoon|title=Hazardous Compounds in Tobacco Smoke|journal=International Journal of Environmental Research and Public Health|volume=8|issue=12|year=2011|pages=613–628|doi=10.3390/ijerph8020613|pmid=21556207|pmc=3084482|doi-access=free}}</ref>

Analyzing multiple epidemiological studies on inorganic arsenic exposure suggests a small but measurable increase in risk for bladder cancer at 10&nbsp;ppb.<ref>{{cite journal |last1=Chu|first1= H. A. |last2 = Crawford-Brown|first2= D. J. |title=Inorganic arsenic in drinking water and bladder cancer: a meta-analysis for dose-response assessment |journal=Int. J. Environ. Res. Public Health |volume=3 |issue=4 |pages=316–322 |date=2006 |pmid=17159272 |doi=10.3390/ijerph2006030039|doi-access=free |pmc=3732405 }}</ref> According to Peter Ravenscroft of the Department of Geography at the University of Cambridge,<ref>{{cite news |url = https://www.usatoday.com/news/world/2007-08-30-553404631_x.htm|title = Arsenic in drinking water seen as threat – USATODAY.com|access-date = 2008-01-01 |work=USA Today|date=30 August 2007}}</ref> roughly 80&nbsp;million people worldwide consume between 10 and 50&nbsp;ppb arsenic in their drinking water. If they all consumed exactly 10&nbsp;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.

<!-- RECENTISM, local university news: Several arsenic kits are available in the market which uses toxic mercury bromide, also required expensive machinery to read the outputs. A new test instrument called whole-cell arsenic bio-sensor, a cheap and non-toxic one, has been designed at the University of Edinburgh.<ref>[http://www.cam.ac.uk/research/news/new-test-to-detect-arsenic-contamination-in-drinking-water/ New test to detect arsenic contamination in drinking water – Research – University of Cambridge]. Cam.ac.uk (2012-06-01). Retrieved 2012-06-20.</ref> -->
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%.<ref>{{cite journal|title=Removal of Arsenic (V) from Water by Adsorption on Aluminum and Ferric Hydroxides|journal=J. Am. Water Works Assoc.| volume=65| issue=8|pages=548–552|date=1973|last1 = Gulledge| first1 = John H.| last2 = O'Connor|first2 = John T.|doi=10.1002/j.1551-8833.1973.tb01893.x|bibcode=1973JAWWA..65h.548G }}</ref><ref>{{cite news| url = http://www.h2oc.com/pdfs/Removal.pdf| title = Arsenic in Drinking Water: 4. Removal Methods| last1 = O'Connor| first1 = J. T.| last2 = O'Connor| first2 = T. L.| archive-url = https://web.archive.org/web/20100107182531/http://h2oc.com/pdfs/Removal.pdf| archive-date = 7 January 2010}}</ref> Several adsorptive media systems have been approved for use at point-of-service in a study funded by the [[United States Environmental Protection Agency]] (US 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 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.<ref>{{cite web|url = https://www.insituarsenic.org|title = In situ arsenic treatment|work=insituarsenic.org|access-date = 2010-05-13 }}</ref>

Another effective and inexpensive method to avoid arsenic contamination is to sink wells 500&nbsp;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, called ''adsorption'', arsenic sticks to the surfaces of deep sediment particles and is naturally removed from the ground water.<ref>{{cite journal |doi=10.1038/ngeo1283 |title=Arsenic migration to deep groundwater in Bangladesh influenced by adsorption and water demand |date=2011|last1=Radloff|first1=K.A. |last2=Zheng |first2=Y. |last3=Michael |first3=H.A. |last4=Stute |first4=M. |last5=Bostick |first5=B.C. |last6=Mihajlov |first6=I. |last7=Bounds|first7=M. |last8=Huq|first8=M. R. |last9=Choudhury |first9=I.|first10=M. |last10=Rahman|first11=P. |last11=Schlosser |first12=K. |last12=Ahmed |first13=A. |last13=van Geen |display-authors=6 |journal=Nature Geoscience |volume=4 |issue=11 |pages=793–798 |pmid=22308168 |pmc=3269239 |bibcode = 2011NatGe...4..793R}}</ref>

Magnetic separations of arsenic at very low magnetic field [[gradient]]s with high-surface-area and [[monodisperse]] [[magnetite]] (Fe<sub>3</sub>O<sub>4</sub>) nanocrystals have been demonstrated in point-of-use water purification. Using the high specific surface area of Fe<sub>3</sub>O<sub>4</sub> nanocrystals, the mass of waste associated with arsenic removal from water has been dramatically reduced.<ref>{{cite journal|last1 = Yavuz|first1 = Cafer T.|title = Low-field magnetic separation of monodisperse Fe<sub>3</sub>O<sub>4</sub> nanocrystals |journal = Science |year = 2005 |doi = 10.1126/science.1131475 |volume = 314 |issue = 580 1|pages = 964–967 |pmid = 17095696|last2 = Mayo|first2 = J.T. |last3 = Yu |first3 = W.W. |last4 = Prakash |first4 = A. |last5 = Falkner |first5 = J. C.|last6 = Yean|first6 = S.|last7 = Cong | first7 = L. |last8 = Shipley |first8 = H.J. |last9 = Kan |first9 = A. |first10=M. |last10=Tomson |first11=D. |last11=Natelson |first12=V.L. |last12=Colvin |display-authors=6 |s2cid = 23522459}}</ref>

Epidemiological studies have suggested a correlation between chronic consumption of drinking water contaminated with arsenic and the incidence of all leading causes of mortality.<ref>{{cite journal |pmc = 1797014 |last1 = Meliker |first1 = J. R. |last2 = Wahl |first2 = R. L. |last3 = Cameron |first3 = L. L. |last4 = Nriagu |first4 = J. O. |title = Arsenic in drinking water and cerebrovascular disease, diabetes mellitus, and kidney disease in Michigan: A standardized mortality ratio analysis |volume = 6 |page = 4 |doi = 10.1186/1476-069X-6-4 |journal = Environmental Health |year = 2007 |issue = 1 |pmid = 17274811 |bibcode = 2007EnvHe...6....4M |doi-access = free }}</ref> The literature indicates that arsenic exposure is causative in the pathogenesis of diabetes.<ref>{{cite journal |doi=10.1289/ehp.00108847 |title=Long-term arsenic exposure and incidence of non-insulin-dependent diabetes mellitus: A cohort study in arseniasis-hyperendemic villages in Taiwan |year=2000 |last1=Tseng |first1=Chin-Hsiao |last2=Tai |first2=Tong-Yuan |last3=Chong |first3=Choon-Khim |last4=Tseng |first4=Ching-Ping |last5=Lai |first5=Mei-Shu |last6=Lin |first6=Boniface J. |last7=Chiou |first7=Hung-Yi |last8=Hsueh |first8=Yu-Mei |last9=Hsu |first9=Kuang-Hung |last10=Chen |first10=C. J. |display-authors=6 |journal=Environmental Health Perspectives |volume=108 |issue=9 |pages=847–851 |pmid=11017889 |pmc=2556925|bibcode=2000EnvHP.108..847T }}</ref>

Chaff-based filters have recently been shown to reduce the arsenic content of water to 3&nbsp;μg/L. This may find applications in areas where the potable water is extracted from underground [[aquifer]]s.<ref>{{cite news |url=http://mno.hu/gazdasag/szenzacios-magyar-talalmany-1068315 |title=Newspaper article |archive-url=https://web.archive.org/web/20120417212726/http://mno.hu/gazdasag/szenzacios-magyar-talalmany-1068315 |archive-date=17 April 2012 |language=Hungarian |publisher=[[Magyar Nemzet]] |date=15 April 2012 }}</ref>

==== San Pedro de Atacama ====
{{see also|Atacama people|Chinchorro mummies}}
For several centuries, the people of [[San Pedro de Atacama]] in Chile have been drinking water that is contaminated with arsenic, and some evidence suggests they have developed some immunity.<ref>{{cite journal |last1=Goering |first1=P. |last2=Aposhian |first2=H.V. |last3=Mass |first3=M.J. |last4=Cebrián |first4=M. |last5=Beck |first5=B.D. |last6=Waalkes |first6=M.P. |title=The enigma of arsenic carcinogenesis: role of metabolism |journal=Toxicological Sciences |date=May 1999 |volume=49 |issue=1 |pages=5–14 |doi=10.1093/toxsci/49.1.5 |pmid=10367337 }}</ref><ref>{{cite journal |date=1996 |last1=Hopenhayn-Rich |first1=C. |last2=Biggs |first2=M. L. |last3=Smith |first3=Allan H. |last4=Kalman |first4=D. A. |last5=Moore |first5=Lee E. |title=Methylation study of a population environmentally exposed to arsenic in drinking water |journal=Environmental Health Perspectives |volume=104 |issue=6 |pages=620–628 |doi=10.1289/ehp.96104620 |pmid=8793350 |pmc=1469390 |bibcode=1996EnvHP.104..620H }}</ref><ref>{{cite journal |last1=Smith |first1=A.H. |last2=Arroyo |first2=A.P. |last3=Mazumder |first3=D.N. |last4=Kosnett |first4=M.J. |last5=Hernandez |first5=A L |last6=Beeris |first6=M. |last7=Smith |first7=M.M. |last8=Moore |first8=L.E. |display-authors=6 |title=Arsenic-induced skin lesions among Atacameño people in Northern Chile despite good nutrition and centuries of exposure. |journal=Environmental Health Perspectives |date=July 2000 |volume=108 |issue=7 |pages=617–620 |doi=10.1289/ehp.00108617 |pmid=10903614 |pmc=1638201 |bibcode=2000EnvHP.108..617S }}</ref> Genetic studies indicate that certain populations in this region have undergone natural selection for gene variants that enhance arsenic metabolism and detoxification. This adaptation is considered one of the few documented cases of human evolution in response to chronic environmental arsenic exposure.<ref>{{Cite journal |last1=Schlebusch |first1=Carina M. |last2=Gattepaille |first2=Lucie M. |last3=Engström |first3=Karin |last4=Vahter |first4=Marie |last5=Jakobsson |first5=Mattias |last6=Broberg |first6=Karin |date=2015-06-01 |title=Human Adaptation to Arsenic-Rich Environments |url=https://academic.oup.com/mbe/article/32/6/1544/1074042 |journal=Molecular Biology and Evolution |volume=32 |issue=6 |pages=1544–1555 |doi=10.1093/molbev/msv046 |pmid=25739736 |issn=0737-4038|doi-access=free |url-access=subscription }}</ref>

==== Hazard maps for contaminated groundwater ====
Around one-third of the world's population drinks water from groundwater resources. Of this, about 10 percent, approximately 300&nbsp;million people, obtains water from groundwater resources that are contaminated with unhealthy levels of arsenic or fluoride.<ref>{{citation | date = 2017 | orig-date = January 2015 | title = Geogenic Contamination Handbook – Addressing Arsenic and Fluoride in Drinking Water | editor-first1 = C. Annette | editor-last1 = Johnson | editor-first2 = Anja | editor-last2 = Bretzler | publisher = Swiss Federal Institute of Aquatic Science and Technology (Eawag) | location = Dübendorf, Switzerland | page = 5 | url = http://www.eawag.ch/en/research/humanwelfare/drinkingwater/wrq/geogenic-contamination-handbook/ | archive-url = https://web.archive.org/web/20171220105720/http://www.eawag.ch/en/research/humanwelfare/drinkingwater/wrq/geogenic-contamination-handbook/ | archive-date = 20 December 2017 | access-date = 18 August 2025 | url-status = dead }}</ref> These trace elements derive mainly from minerals and ions in the ground.<ref>{{cite journal | last1=Amini |first1=M.|last2=Abbaspour |first2=K.C. |last3=Berg |first3=M. |last4=Winkel |first4=L. |last5=Hug |first5=S.J. |last6=Hoehn |first6=E. |last7= Yang |first7=H. |last8=Johnson |first8=C.A. |display-authors=6 | year = 2008 | title = Statistical modeling of global geogenic arsenic contamination in groundwater | journal = Environmental Science and Technology | volume = 42 | issue = 10| pages = 3669–3675 | doi = 10.1021/es702859e | pmid = 18546706 | bibcode = 2008EnST...42.3669A | doi-access = free }}</ref><ref>{{cite journal |last1=Winkel |first1=Lenny |last2=Berg |first2=Michael |last3=Amini |first3=Manouchehr |last4=Hug |first4=Stephan J. |last5=Annette Johnson |first5=C. |title=Predicting groundwater arsenic contamination in Southeast Asia from surface parameters |journal=Nature Geoscience |date=August 2008 |volume=1 |issue=8 |pages=536–542 |doi=10.1038/ngeo254 |bibcode=2008NatGe...1..536W |url=https://www.dora.lib4ri.ch/eawag/islandora/object/eawag%3A5777 |url-access=subscription }}</ref>

=== Redox transformation of arsenic in natural waters ===

Arsenic is unique among the trace [[metalloids]] 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.<ref>{{cite journal |last1=Smedley |first1=P.L |last2=Kinniburgh |first2=D.G |title=A review of the source, behaviour and distribution of arsenic in natural waters |journal=Applied Geochemistry |date=May 2002 |volume=17 |issue=5 |pages=517–568 |doi=10.1016/S0883-2927(02)00018-5 |bibcode=2002ApGC...17..517S |url=https://nora.nerc.ac.uk/id/eprint/12311/1/Abstract.pdf }}</ref>

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 and [[sulfide]] 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.<ref>[https://web.archive.org/web/20110308104034/http://www.civil.umaine.edu/macrae/arsenic_gw.htm How Does Arsenic Get into the Groundwater]. Civil and Environmental Engineering. [[University of Maine]]</ref>

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 are {{chem2|H3AsO4}}, {{chem2|H2AsO4-}}, {{chem2|HAsO4(2-)}}, and {{chem2|AsO4(3-)}} at pH 2, 2–7, 7–11 and 11, respectively. Under reducing conditions, {{chem2|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 neutral [[pH]]. 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, the [[adsorption]] 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.<ref>Zeng Zhaohua, Zhang Zhiliang (2002). "The formation of As element in groundwater and the controlling factor". Shanghai Geology 87 (3): 11–15.</ref>

The presence of sulfur is another factor that affects the transformation of arsenic in natural water. Arsenic can [[precipitate]] 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.<ref>{{cite journal |title=Redox control of arsenic mobilization in Bangladesh groundwater |doi=10.1016/j.apgeochem.2003.09.007 |volume=19 |issue=2 |journal=Applied Geochemistry|pages=201–214|bibcode=2004ApGC...19..201Z |year=2004 |last1=Zheng |first1=Y. |last2=Stute |first2=M. |last3=van Geen |first3=A. |last4=Gavrieli |first4=I. |last5=Dhar |first5=R. |last6=Simpson |first6=H.J. |last7=Schlosser |first7=P. |last8=Ahmed |first8=K.M.  |display-authors=6 }}</ref> Under oxidizing conditions, arsenic can be mobilized from [[pyrite]] 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.<ref>Thomas, Mary Ann (2007). [https://pubs.usgs.gov/sir/2007/5036/pdf/sir20075036_web.pdf "The Association of Arsenic With Redox Conditions, Depth, and Ground-Water Age in the Glacial Aquifer System of the Northern United States"]. U.S. Geological Survey, Virginia. pp. 1–18.</ref>

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) and [[heterotrophic]] 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 CO<sub>2</sub>. HAO cannot obtain energy from As(III) oxidation. This process may be an arsenic [[detoxification]] mechanism for the bacteria.<ref>{{cite journal|author=Bin, Hong |year=2006|title=Influence of microbes on biogeochemistry of arsenic mechanism of arsenic mobilization in groundwater|journal= Advances in Earth Science |volume=21 |issue=1|pages= 77–82|url=http://www.adearth.ac.cn/EN/abstract/abstract3466.shtml}}</ref>

Equilibrium thermodynamic calculations predict that As(V) concentrations should be greater than As(III) concentrations in all but strongly reducing conditions, i.e. where [[sulfate]] reduction is occurring. However, abiotic redox reactions of arsenic are slow. Oxidation of As(III) by dissolved O<sub>2</sub> is a particularly slow reaction. For example, Johnson and Pilson (1975) gave [[Half-life|half-lives]] for the oxygenation of As(III) in seawater ranging from several months to a year.<ref>{{cite journal|doi=10.1080/00139307509437429|pmid=236901 |title=The oxidation of arsenite in seawater |volume=8 |issue=2 |journal=Environmental Letters|pages=157–171|year=1975 |last1=Johnson |first1=D. L. |last2=Pilson |first2=M. E. Q. |url=https://digitalcommons.uri.edu/gsofacpubs/2090 }}</ref> 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.<ref>{{cite book|author=Cherry, J. A.|title=Contemporary Hydrogeology – the George Burke Maxey Memorial Volume|chapter=Arsenic species as an indicator of redox conditions in groundwater|doi=10.1016/S0167-5648(09)70027-9 |volume=12|pages=373–392|series=Developments in Water Science|year=1979|isbn=978-0-444-41848-7}}</ref> Sterile water samples have been observed to be less susceptible to speciation changes than non-sterile samples.<ref>{{cite journal|doi=10.1021/cr00094a002 |title=Arsenic speciation in the environment |volume=89 |issue=4 |journal=Chemical Reviews |pages=713–764|year=1989 |last1=Cullen |first1=William R |last2=Reimer |first2=Kenneth J |hdl=10214/2162 |hdl-access=free }}</ref> 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<sup>−1</sup>.<ref>{{cite journal|author1-link=Ronald Oremland|author=Oremland, Ronald S.|title=Bacterial dissimilatory reduction of arsenate and sulfate in meromictic Mono Lake, California|doi=10.1016/S0016-7037(00)00422-1 |bibcode=2000GeCoA..64.3073O|volume=64|issue=18|journal=Geochimica et Cosmochimica Acta|pages=3073–3084|year=2000|url=https://zenodo.org/record/1259591}}</ref>

=== Wood preservation in the US ===
As of 2002, US-based industries consumed 19,600 metric tons of arsenic. Ninety percent of this was used for treatment of wood with [[chromated copper arsenate]] (CCA). In 2007, 50% of the 5,280 metric tons of consumption was still used for this purpose.<ref name="USGSYB2007">{{cite web|url = https://minerals.er.usgs.gov/minerals/pubs/commodity/arsenic/myb1-2007-arsen.pdf|first = William E.|last = Brooks|publisher = [[United States Geological Survey]]|access-date = 2008-11-08 |title = Minerals Yearbook 2007: Arsenic| archive-url= https://web.archive.org/web/20081217031509/http://minerals.er.usgs.gov/minerals/pubs/commodity/arsenic/myb1-2007-arsen.pdf| archive-date= 17 December 2008|url-status = live}}</ref><ref>{{cite web|url = https://minerals.er.usgs.gov/minerals/pubs/commodity/arsenic/160302.pdf|first = Robert G. Jr.|last = Reese|publisher = [[United States Geological Survey]]|access-date = 2008-11-08 |title = Commodity Summaries 2002: Arsenic| archive-url= https://web.archive.org/web/20081217031513/http://minerals.er.usgs.gov/minerals/pubs/commodity/arsenic/160302.pdf| archive-date= 17 December 2008|url-status = live}}</ref> 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 as [[Alkaline Copper Quaternary]], [[borate]]s, [[Wood preservation#Copper azole|copper azole]], [[cyproconazole]], and [[propiconazole]].<ref>{{cite web|url=https://www.epa.gov/ingredients-used-pesticide-products/chromated-arsenicals-cca|title=Chromated Copper Arsenate (CCA)|publisher=US Environmental Protection Agency|access-date = 2018-10-15 |date=16 January 2014}}</ref>

Although discontinued, this application is also one of the most concerning to the general public. The vast majority of older [[Timber treatment|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&nbsp;grams of ash.<ref>{{Cite web|url=https://www.softwoods.com.au/blog/cca-treated-pine-safe/|title=Is CCA treated pine Safe? |website=www.softwoods.com.au|date=26 October 2010|language=en-AU|access-date=2017-02-24}}</ref> 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. Widespread [[landfill]] disposal of such timber raises some concern,<ref>{{Cite book|url=https://books.google.com/books?id=3l_LBQAAQBAJ|title=Environmental Impacts of Treated Wood|last1=Townsend|first1=Timothy G.|last2=Solo-Gabriele|first2=Helena|year=2006|publisher=CRC Press|isbn=978-1-4200-0621-6}}</ref> but other studies have shown no arsenic contamination in the groundwater.<ref>{{Cite journal|last1=Saxe|first1=Jennifer K.|last2=Wannamaker|first2=Eric J.|last3=Conklin|first3=Scott W.|last4=Shupe|first4=Todd F.|last5=Beck|first5=Barbara D.|date=2007-01-01|title=Evaluating landfill disposal of chromated copper arsenate (CCA) treated wood and potential effects on groundwater: evidence from Florida|journal=Chemosphere|volume=66|issue=3|pages=496–504|doi=10.1016/j.chemosphere.2006.05.063|pmid=16870233|bibcode=2007Chmsp..66..496S}}</ref><ref>{{Cite web|url=https://www.woodpreservativescience.org/disposal.shtml|title=CCA Treated Wood Disposal {{!}} Wood Preservative Science Council {{!}} Objective, Sound, Scientific Analysis of CCA|last=BuildingOnline|website=www.woodpreservativescience.org|access-date=2016-06-16}}</ref>

=== Mapping of industrial releases in the US ===

One tool that maps the location (and other information) of arsenic releases in the United States is [[TOXMAP]].<ref>{{cite web |url=http://toxmap.nlm.nih.gov/toxmap/tri/mapIt.do?chemicalName=arsenic |title=TRI Releases Map |publisher=Toxmap.nlm.nih.gov |access-date=2010-03-23 |archive-url=https://web.archive.org/web/20100320154547/http://toxmap.nlm.nih.gov/toxmap/tri/mapIt.do?chemicalName=arsenic |archive-date=20 March 2010 }}</ref> TOXMAP is a Geographic Information System (GIS) from the Division of Specialized Information Services of the [[United 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 the [[United States Environmental Protection Agency]]'s (EPA) [[Toxics Release Inventory]] and [[Superfund Basic Research Program]]s. TOXMAP's chemical and environmental health information is taken from NLM's Toxicology Data Network (TOXNET),<ref>[https://www.nlm.nih.gov/toxnet/index.html TOXNET – Databases on toxicology, hazardous chemicals, environmental health, and toxic releases]. Toxnet.nlm.nih.gov. Retrieved 2011-10-24.</ref> [[PubMed]], and from other authoritative sources.

=== Bioremediation ===

Physical, chemical, and biological methods have been used to remediate arsenic contaminated water.<ref name="JEM-2012">{{cite journal |last1=Jain |first1=C. K. |last2=Singh |first2=R. D. |title=Technological options for the removal of arsenic with special reference to South East Asia |doi=10.1016/j.jenvman.2012.04.016 |date=2012 |journal=Journal of Environmental Management |volume=107 |pages=1–8 |pmid=22579769|bibcode=2012JEnvM.107....1J |url=https://zenodo.org/record/1259107 }}</ref> Bioremediation is said to be cost-effective and environmentally friendly.<ref>{{cite journal |doi = 10.1007/s11270-013-1722-y |title = Bioremediation of arsenic-contaminated water: recent advances and future prospects |date = 2013 |last1 = Goering |first1 = P. |journal = Water, Air, & Soil Pollution |volume = 224 |issue = 12 |article-number=1722| bibcode = 2013WASP..224.1722B |s2cid = 97563539 }}</ref> 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.<ref>{{cite journal |doi = 10.1016/j.jhazmat.2014.10.014| pmid = 25464303 |title = Anaerobic arsenite oxidation with an electrode serving as the sole electron acceptor: A novel approach to the bioremediation of arsenic-polluted groundwater. |date = 2015 |last1 = Goering |first1 = P. |journal = Journal of Hazardous Materials |volume = 283 |pages = 617–622| bibcode = 2015JHzM..283..617P | hdl = 10256/11522 }}</ref> This is a useful method in ground water remediation. Another bioremediation strategy is to use plants that accumulate arsenic in their tissues via [[phytoremediation]] 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.

=== Arsenic removal ===

[[Coagulation (water treatment)|Coagulation]] and [[flocculation]] 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: FeCl<sub>3</sub>,<ref name="Bina 2013 17">{{cite journal |last1=Hesami |first1=Farid |last2=Bina |first2=Bijan |last3=Ebrahimi |first3=Afshin |last4=Amin |first4=MohammadMehdi |title=Arsenic removal by coagulation using ferric chloride and chitosan from water |journal=International Journal of Environmental Health Engineering |date=2013 |volume=2 |issue=1 |page=17 |doi=10.4103/2277-9183.110170 |doi-access=free }}</ref> Fe<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>,<ref>{{cite journal |last1=Sun |first1=Yuankui |last2=Zhou |first2=Gongming |last3=Xiong |first3=Xinmei |last4=Guan |first4=Xiaohong |last5=Li |first5=Lina |last6=Bao |first6=Hongliang |title=Enhanced arsenite removal from water by Ti(SO4)2 coagulation |journal=Water Research |date=September 2013 |volume=47 |issue=13 |pages=4340–4348 |doi=10.1016/j.watres.2013.05.028 |pmid=23764585 |bibcode=2013WatRe..47.4340S }}</ref> Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub><ref>{{cite journal |last1=Hering |first1=Janet G. |last2=Chen |first2=Pen-Yuan |last3=Wilkie |first3=Jennifer A. |last4=Elimelech |first4=Menachem |title=Arsenic Removal from Drinking Water during Coagulation |journal=Journal of Environmental Engineering |date=August 1997 |volume=123 |issue=8 |pages=800–807 |doi=10.1061/(ASCE)0733-9372(1997)123:8(800) |url=https://infoscience.epfl.ch/handle/20.500.14299/59147 }}</ref>) 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, H<sub>3</sub>AsO<sub>3</sub>, at near-neutral pH.<ref>{{cite journal |last1=Ng |first1=Wenfa |title=Inability to Completely Remove Trace Contaminants from Drinking Water by Adsorption |journal=Journal of Environmental Science and Public Health |date=9 March 2022 |volume=6 |issue=1 |pages=129–134 |url=https://fortuneonline.org/articles/inability-to-completely-remove-trace-contaminants-from-drinking-water-by-adsorption.html }}</ref>

The major drawbacks of coagulation and flocculation are the costly disposal of arsenate-concentrated sludge, and possible [[secondary contamination]] of environment. Moreover, coagulents such as iron may produce ion contamination that exceeds safety levels.<ref name="Bina 2013 17"/>

== Toxicity and precautions ==
{{Main|Arsenic poisoning}}
{{Chembox
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| GHSPictograms = {{GHS05}} {{GHS06}} {{GHS08}} {{GHS09}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|H301+H331|H315|H318|H350|H410}}
| PPhrases = {{PPhrases|P273|P280|P301 + P310|P302 + P352|P304 + P340 + P311|P305 + P351 + P338}}
| GHS_ref  =<ref>{{cite web |url=https://www.sigmaaldrich.com/catalog/product/aldrich/202657?lang=en&region=US| publisher=Sigma Aldrich |title =Arsenic |date=|access-date=2021-12-21}}</ref>
| NFPA-H = 3
| NFPA-F = 2
| NFPA-R = 0
| NFPA-S = 
| NFPA_ref =<ref>{{cite web |url=https://www.osha.gov/chemicaldata/528 |title=Arsenic, inorganic compounds (as As) |access-date=April 1, 2025 |website=Occupational Safety and Health Administration |date=April 3, 2024 }}</ref>}}
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Arsenic and many of its compounds ([[arsine]], for instance) are potent poisons.

=== Classification ===

Elemental arsenic and arsenic sulfate and trioxide compounds are classified as "[[toxicity|toxic]]" and "dangerous for the environment" in the European Union under [[directive 67/548/EEC]].
<!-- INDEX 033-001-00-X (arsenic) R23/25-50/53; S1/2-20/21-28-45-60-61 -->
<!-- INDEX 033-002-00-5 (other compounds) pareil -->The [[International Agency for Research on Cancer]] (IARC) recognizes arsenic and inorganic arsenic compounds as [[List of IARC Group 1 carcinogens|group 1 carcinogens]], and the EU lists arsenic trioxide, [[arsenic pentoxide]], and [[arsenate]] salts as category 1 [[carcinogen]]s.

Arsenic is known to cause [[Arsenic poisoning|arsenicosis]] when present in drinking water, "the most common species being arsenate [{{chem2|HAsO4(2-)}}; As(V)] and arsenite [{{chem2|H3AsO3}}; As(III)]"{{Citation needed|date=October 2025}}.

=== Legal limits, food, and drink ===

In the United States since 2006, the maximum concentration in drinking water allowed by the [[United States Environmental Protection Agency|Environmental Protection Agency]] (EPA) is 10&nbsp;ppb<ref>[https://www.epa.gov/dwreginfo/chemical-contaminant-rules Arsenic Rule]. U.S. [[United States Environmental Protection Agency|Environmental Protection Agency]]. Adopted 22 January 2001; effective 23 January 2006.</ref> and the FDA set the same standard in 2005 for bottled water.<ref name="fda_metals">{{cite web|url=https://www.fda.gov/Food/GuidanceRegulation/GuidanceDocumentsRegulatoryInformation/ChemicalContaminantsMetalsNaturalToxinsPesticides/ucm360023.htm |archive-url=https://web.archive.org/web/20140110092030/http://www.fda.gov/Food/GuidanceRegulation/GuidanceDocumentsRegulatoryInformation/ChemicalContaminantsMetalsNaturalToxinsPesticides/ucm360023.htm |archive-date=10 January 2014 |title=Supporting Document for Action Level for Arsenic in Apple Juice |publisher=Fda.gov |access-date=2013-08-21 }}</ref> The Department of Environmental Protection for New Jersey set a drinking water limit of 5&nbsp;ppb in 2006.<ref>{{cite web|url=https://www.state.nj.us/dep/dsr/arsenic/guide.htm |title=A Homeowner's Guide to Arsenic in Drinking Water |publisher=New Jersey Department of Environmental Protection |access-date=2013-08-21 }}</ref> The [[IDLH]] (immediately dangerous to life and health) value for arsenic metal and inorganic arsenic compounds is 5&nbsp;mg/m<sup>3</sup> (5&nbsp;ppb). The [[Occupational Safety and Health Administration]] has set the [[permissible exposure limit]] (PEL) to a time-weighted average (TWA) of 0.01&nbsp;mg/m<sup>3</sup> (0.01&nbsp;ppb), and the [[National Institute for Occupational Safety and Health]] (NIOSH) has set the [[recommended exposure limit]] (REL) to a 15-minute constant exposure of 0.002&nbsp;mg/m<sup>3</sup> (0.002&nbsp;ppb).<ref name="PGCH">{{PGCH|0038}}</ref> The PEL for organic arsenic compounds is a TWA of 0.5&nbsp;mg/m<sup>3</sup>.<ref>{{PGCH|0039}}</ref> (0.5&nbsp;ppb).

In 2008, based on its ongoing testing of a wide variety of American foods for toxic chemicals,<ref>[https://web.archive.org/web/20130330072450/http://www.fda.gov/Food/FoodScienceResearch/TotalDietStudy/default.htm Total Diet Study] and [https://www.fda.gov/Food/FoodborneIllnessContaminants/ChemicalContaminants/ucm2006907.htm Toxic Elements Program]{{dead link|date=May 2025|bot=medic}}{{cbignore|bot=medic}}</ref> the U.S. [[Food and Drug Administration]] set the "level of concern" for inorganic arsenic in apple and pear juices at 23&nbsp;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.<ref name="fda_metals" /> In 2011, the national ''[[The Dr. Oz Show|Dr. 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&nbsp;ppb.<ref>{{cite news|author=Kotz, Deborah |url=http://www.boston.com/community/moms/articles/2011/09/14/does_apple_juice_have_unsafe_levels_of_arsenic/ |title=Does apple juice have unsafe levels of arsenic? – The Boston Globe |newspaper=Boston.com |date=14 September 2011 |access-date=2013-08-21 }}</ref> In response, the FDA tested the worst brand from the ''Dr.'' ''Oz'' show and found much lower levels. Ongoing testing found 95% of the apple juice samples were below the level of concern. Later testing by [[Consumer Reports]] showed inorganic arsenic at levels slightly above 10&nbsp;ppb, and the organization urged parents to reduce consumption.<ref>{{cite web|url=http://consumerist.com/2011/11/30/consumer-reports-study-finds-high-levels-of-arsenic-lead-in-apple-juice/|title=Consumer Reports Study Finds High Levels of Arsenic & Lead in Some Fruit Juice|author=Morran, Chris|work=Consumerist|date=30 November 2011|publisher=consumerist.com|access-date=10 January 2014|archive-date=10 January 2014|archive-url=https://web.archive.org/web/20140110084956/http://consumerist.com/2011/11/30/consumer-reports-study-finds-high-levels-of-arsenic-lead-in-apple-juice/}}</ref> In July 2013, on consideration of consumption by children, chronic exposure, and carcinogenic effect, the FDA established an "action level" of 10&nbsp;ppb for apple juice, the same as the drinking water standard.<ref name="fda_metals" />

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).<ref>{{cite journal|url=https://www.nature.com/news/2002/021122/full/news021118-11.html |title= Arsenic contamination of Bangladeshi paddy field soils: Implications for rice contribution to arsenic consumption|journal=Nature |date=22 November 2002 |doi=10.1038/news021118-11 |access-date=2013-08-21 |url-access=subscription }}</ref><ref>{{cite magazine|url=https://www.newscientist.com/article/dn3141-tainted-wells-pour-arsenic-onto-food-crops.html#.UhPasx-37Vs |title=Tainted wells pour arsenic onto food crops |magazine=New Scientist |date=6 December 2002 |access-date=2013-08-21 }}</ref> Concern was raised about people who were eating U.S. rice exceeding WHO standards for personal arsenic intake in 2005.<ref>{{cite journal|author=Peplow, Mark |doi=10.1038/news050801-5 |title=US rice may carry an arsenic burden |journal= Nature News|date=2 August 2005 }}</ref> In 2011, the People's Republic of China set a food standard of 150&nbsp;ppb for arsenic.<ref>{{cite web |url = http://medicalxpress.com/news/2011-12-rice-source-arsenic-exposure.html |title = Rice as a source of arsenic exposure}}</ref>

In the United States in 2012, testing by separate groups of researchers at the Children's Environmental Health and Disease Prevention Research Center at [[Dartmouth College]] (early in the year, focusing on urinary levels in children)<ref>{{Cite journal|doi=10.1289/ehp.1205014|title=Rice Consumption and Urinary Arsenic Concentrations in U.S. Children|year=2012|last1=Davis|first1=Matthew A.|last2=MacKenzie|first2=Todd A.|last3=Cottingham|first3=Kathryn L.|last4=Gilbert-Diamond|first4=Diane|last5=Punshon|first5=Tracy|last6=Karagas|first6=Margaret R.|journal=Environmental Health Perspectives|volume=120|issue=10|pages=1418–1424|pmid=23008276|pmc=3491944|bibcode=2012EnvHP.120.1418D }}</ref> and [[Consumer Reports]] (in November)<ref>{{cite web|url=https://www.npr.org/2012/03/02/147781035/high-levels-of-arsenic-found-in-rice |title=High Levels of Arsenic Found in Rice |website=NPR.org |date=2 March 2012 |access-date=2013-08-21 }}</ref><ref name="cr_rice">{{cite web|url=http://www.consumerreports.org/cro/magazine/2012/11/arsenic-in-your-food/index.htm |title=Arsenic in Your Food {{pipe}} Consumer Reports Investigation |work=Consumer Reports |date=1 November 2012 |access-date=2013-08-21 }}</ref> found levels of arsenic in rice that resulted in calls for the FDA to set limits.<ref name="foodsafetynews">[http://www.foodsafetynews.com/2012/02/lawmakers-urge-fda-to-act-on-arsenic-standards/ Lawmakers Urge FDA to Act on Arsenic Standards]. Foodsafetynews.com (24 February 2012). Retrieved 2012-05-23.</ref> The FDA released some testing results in September 2012,<ref>{{cite web|url=https://www.fda.gov/forconsumers/consumerupdates/ucm319827.htm |archive-url=https://web.archive.org/web/20120921203328/http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm319827.htm |archive-date=21 September 2012 |title=FDA Looks for Answers on Arsenic in Rice |publisher=Fda.gov |date=19 September 2012 |access-date=2013-08-21 }}</ref><ref>{{cite web|url=https://www.fda.gov/Food/FoodborneIllnessContaminants/Metals/ucm319870.htm |archive-url=https://web.archive.org/web/20130423015508/http://www.fda.gov/Food/FoodborneIllnessContaminants/Metals/ucm319870.htm |archive-date=23 April 2013 |title=Arsenic in Rice |publisher=Fda.gov |access-date=2013-08-21 }}</ref> 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.<ref>{{cite web|url=https://www.fda.gov/Food/FoodborneIllnessContaminants/Metals/ucm319948.htm |archive-url=https://web.archive.org/web/20130502001130/http://www.fda.gov/Food/FoodborneIllnessContaminants/Metals/ucm319948.htm |archive-date=2 May 2013 |title=Questions & Answers: FDA's Analysis of Arsenic in Rice and Rice Products |publisher=Fda.gov |date=21 March 2013 |access-date=2013-08-21 }}</ref>

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).<ref name="cr_rice" />
# 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.<ref name="berkeleywellness">{{cite web|title=Arsenic in Rice: What You Need to Know|url=https://www.berkeleywellness.com/healthy-eating/food-safety/article/arsenic-rice-should-you-worry|website=UC Berkeley Wellness|access-date=3 September 2014}}</ref> They also offer recommendations for adults and infants on how to limit arsenic exposure from rice, drinking water, and fruit juice.<ref name="berkeleywellness" />
A 2014 [[World Health Organization]] advisory conference was scheduled to consider limits of 200–300&nbsp;ppb for rice.<ref name="cr_rice" />

====Reducing arsenic content in rice====
[[File:Improved rice cooking approach to maximise arsenic removal while preserving nutrient elements.jpg|thumb|300px|An improved rice cooking approach to maximise arsenic removal while preserving nutrient elements<ref name="cookingmethod" />]]
In 2020, scientists assessed multiple preparation procedures of rice for their capacity to reduce arsenic content and preserve nutrients, recommending a procedure involving [[Parboiling#Parboiled rice|parboiling]] and water-absorption.<ref>{{cite news |title=New way of cooking rice removes arsenic and retains mineral nutrients, study shows |url=https://phys.org/news/2020-11-cooking-rice-arsenic-retains-mineral.html |access-date=10 November 2020 |work=phys.org |language=en}}</ref><ref name="cookingmethod">{{cite journal |title=Improved rice cooking approach to maximise arsenic removal while preserving nutrient elements |journal=Science of the Total Environment |date=29 October 2020 |article-number=143341 |doi=10.1016/j.scitotenv.2020.143341 |last1=Menon |first1=Manoj |last2=Dong |first2=Wanrong |last3=Chen |first3=Xumin |last4=Hufton |first4=Joseph |last5=Rhodes |first5=Edward J. |volume=755 |issue=Pt 2 |pmid=33153748 |doi-access=free }}</ref><ref>{{cite news |title=How much arsenic is in your rice? Consumer Reports' new data and guidelines are important for everyone but especially for gluten avoiders |url=https://www.consumerreports.org/cro/magazine/2015/01/how-much-arsenic-is-in-your-rice/index.htm |access-date=15 February 2022 |work=consumerreports.org}}</ref>

=== Occupational exposure limits ===

{| class="wikitable"
!Country
!Limit<ref>{{Cite web|url = https://www.cdc.gov/niosh-rtecs/CG802C8.html|title = Arsenic|website = RTECS|date = 28 March 2018|publisher = National Institute for Occupational Safety and Health (NIOSH)}}</ref>
|-
|[[Argentina]]
|Confirmed human carcinogen
|-
|Australia
|TWA 0.05&nbsp;mg/m<sup>3</sup> – Carcinogen
|-
|[[Belgium]]
|TWA 0.1&nbsp;mg/m<sup>3</sup> – Carcinogen
|-
|[[Bulgaria]]
|Confirmed human carcinogen
|-
|Canada
|TWA 0.01&nbsp;mg/m<sup>3</sup>
|-
|[[Colombia]]
|Confirmed human carcinogen
|-
|[[Denmark]]
|TWA 0.01&nbsp;mg/m<sup>3</sup>
|-
|[[Finland]]
|Carcinogen
|-
|[[Egypt]]
|TWA 0.2&nbsp;mg/m<sup>3</sup>
|-
|[[Hungary]]
|Ceiling concentration 0.01&nbsp;mg/m<sup>3</sup> – Skin, carcinogen
|-
|India
|TWA 0.2&nbsp;mg/m<sup>3</sup>
|-
|Japan
|Group 1 carcinogen
|-
|[[Jordan]]
|Confirmed human carcinogen
|-
|Mexico
|TWA 0.2&nbsp;mg/m<sup>3</sup>
|-
|New Zealand
|TWA 0.05&nbsp;mg/m<sup>3</sup> – Carcinogen
|-
|[[Norway]]
|TWA 0.02&nbsp;mg/m<sup>3</sup>
|-
|[[Philippines]]
|TWA 0.5&nbsp;mg/m<sup>3</sup>
|-
|[[Poland]]
|TWA 0.01&nbsp;mg/m<sup>3</sup>
|-
|Singapore
|Confirmed human carcinogen
|-
|[[South Korea]]
|TWA 0.01&nbsp;mg/m<sup>3</sup><ref>[http://www.kosha.or.kr/content/safetyinfo/안전보건기술지침_제정현황1.xls Korea Occupational Safety & Health Agency] {{Webarchive|url=https://web.archive.org/web/20170123114742/http://www.kosha.or.kr/content/safetyinfo/%EC%95%88%EC%A0%84%EB%B3%B4%EA%B1%B4%EA%B8%B0%EC%88%A0%EC%A7%80%EC%B9%A8_%EC%A0%9C%EC%A0%95%ED%98%84%ED%99%A91.xls |date=23 January 2017 }}. kosha.or.kr</ref>
|-
|Sweden
|TWA 0.01&nbsp;mg/m<sup>3</sup>
|-
|[[Thailand]]
|TWA 0.5&nbsp;mg/m<sup>3</sup>
|-
|[[Turkey]]
|TWA 0.5&nbsp;mg/m<sup>3</sup>
|-
|United Kingdom
|TWA 0.1&nbsp;mg/m<sup>3</sup>
|-
|United States
|TWA 0.01&nbsp;mg/m<sup>3</sup>
|-
|[[Vietnam]]
|Confirmed human carcinogen
|}

=== Ecotoxicity ===

Arsenic is [[bioaccumulation|bioaccumulative]] in many organisms, marine species in particular, but it does not appear to biomagnify significantly in food webs.<ref>{{cite journal |last1=Gaion |first1=Andrea |last2=Sartori |first2=Davide |last3=Scuderi |first3=Alice |last4=Fattorini |first4=Daniele |title=Bioaccumulation and biotransformation of arsenic compounds in Hediste diversicolor (Muller 1776) after exposure to spiked sediments |journal=Environmental Science and Pollution Research |date=May 2014 |volume=21 |issue=9 |pages=5952–5959 |doi=10.1007/s11356-014-2538-z |pmid=24458939 |bibcode=2014ESPR...21.5952G |s2cid=12568097 }}</ref> 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.

=== Toxicity in animals ===
{| class="wikitable"
!Compound
!Animal
!LD<sub>50</sub>
!Route
|-
|Arsenic
|Rat
|763&nbsp;mg/kg
|oral
|-
|Arsenic
|Mouse
|145&nbsp;mg/kg
|oral
|-
|[[Calcium arsenate]]
|Rat
|20&nbsp;mg/kg
|oral
|-
|Calcium arsenate
|Mouse
|794&nbsp;mg/kg
|oral
|-
|Calcium arsenate
|Rabbit
|50&nbsp;mg/kg
|oral
|-
|Calcium arsenate
|Dog
|38&nbsp;mg/kg
|oral
|-
|[[Lead arsenate]]
|Rabbit
|75&nbsp;mg/kg
|oral
|}

{| class="wikitable"
!Compound
!Animal
!LD<sub>50</sub><ref name="Hughes" />
!Route
|-
|Arsenic trioxide (As(III))
|Mouse
|26&nbsp;mg/kg
|oral
|-
|Arsenite (As(III))
|Mouse
|8&nbsp;mg/kg
|im
|-
|Arsenate (As(V))
|Mouse
|21&nbsp;mg/kg
|im
|-
|MMA (As(III))
|Hamster
|2&nbsp;mg/kg
|ip
|-
|MMA (As(V))
|Mouse
|916&nbsp;mg/kg
|oral
|-
|DMA (As(V))
|Mouse
|648&nbsp;mg/kg
|oral
|-
| colspan="4" |im = injected intramuscularly
ip = administered intraperitoneally
|}

=== Biological mechanism ===

Arsenic's toxicity comes from the affinity of arsenic(III) oxides for [[thiol]]s. Thiols, in the form of [[cysteine]] residues and [[Cofactor (biochemistry)|cofactors]] such as [[lipoic acid]] and [[coenzyme A]], are situated at the active sites of many important [[enzyme]]s.<ref name="Ullmann" />

Arsenic disrupts [[Adenosine triphosphate|ATP]] production through several mechanisms. At the level of the [[citric acid cycle]], arsenic inhibits [[lipoic acid]], which is a cofactor for [[pyruvate dehydrogenase]]. By competing with phosphate, arsenate uncouples [[oxidative phosphorylation]], thus inhibiting energy-linked reduction of [[Nicotinamide adenine dinucleotide|NAD+]], 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-system [[organ failure]]. The organ failure is presumed to be from [[necrotic]] cell death, not [[apoptosis]], since energy reserves have been too depleted for apoptosis to occur.<ref name="Hughes">{{cite journal |doi = 10.1016/S0378-4274(02)00084-X |title = Arsenic toxicity and potential mechanisms of action |date = 2002 |last1 = Hughes |first1 = Michael F. |journal = Toxicology Letters |volume = 133 |pages = 1–16 |pmid = 12076506 |issue = 1|bibcode = 2002ToxL..133....1H | url = https://zenodo.org/record/1260065 }}</ref>
<!--A [[post mortem]] in an arsenic poisoning death reveals brick-red-colored [[mucosa]], owing to severe [[hemorrhage]]. copyright violation from http://rfppl.com/subscription/upload_pdf/Art%204_415.pdf if we need it there is another ref 10.1080/10643389991259227 -->

=== Exposure risks and remediation ===

Occupational exposure and [[arsenic poisoning]] may occur in people 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.<ref>{{cite web
|url= https://www.osha.gov/SLTC/arsenic/index.html
|title=OSHA Arsenic
|access-date=2007-10-08
|publisher=United States Occupational Safety and Health Administration
| archive-url= https://web.archive.org/web/20071012033424/https://www.osha.gov/SLTC/arsenic/index.html| archive-date= 12 October 2007|url-status = live}}</ref>

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 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.<ref>{{cite journal |title=The Genetics of Geochemisty |journal=Annual Review of Genetics |volume=38 |date=2004 |pages=175–206 |pmid=15568975 |doi=10.1146/annurev.genet.38.072902.091138 |last1=Croal |first1=Laura R. |last2=Gralnick |first2=Jeffrey A. |last3=Malasarn |first3=Davin |last4=Newman |first4=Dianne K. |url=http://authors.library.caltech.edu/286/ |access-date=30 August 2017 |archive-date=18 September 2021 |archive-url=https://web.archive.org/web/20210918094902/http://authors.library.caltech.edu/286/ }}</ref>

=== Treatment ===

Treatment of chronic arsenic poisoning is possible. British anti-lewisite ([[dimercaprol]]) is prescribed in doses of 5&nbsp;mg/kg up to 300&nbsp;mg every 4&nbsp;hours for the first day, then every 6&nbsp;hours for the second day, and finally every 8&nbsp;hours for 8 additional days.<ref>{{cite book|author1=Giannini, A. James |author2=Black, Henry Richard |author3=Goettsche, Roger L. |title=The Psychiatric, Psychogenic and Somatopsychic Disorders Handbook|isbn=978-0-87488-596-5 |location=New Hyde Park, NY|publisher=Medical Examination Publishing Co |date=1978 |pages=81–82}}</ref> However the USA's [[Agency for Toxic Substances and Disease Registry]] (ATSDR) states that the long-term effects of arsenic exposure cannot be predicted.<ref name="atsdr.cdc.gov" /> Blood, urine, hair, and nails may be tested for arsenic; however, these tests cannot foresee possible health outcomes from the exposure.<ref name="atsdr.cdc.gov" /> Long-term exposure and consequent excretion through urine has been linked to [[Bladder cancer|bladder]] and [[kidney cancer]] in addition to cancer of the liver, prostate, skin, lungs, and [[nasal cavity]].<ref>{{cite web |url=http://www.atsdr.cdc.gov/toxguides/toxguide-2.pdf?id=21&tid=3 |title=The tox-guide for arsenic |year=2007 |series=The US [[Agency for Toxic Substances and Disease Registry]] |publisher=U.S. [[Center for Disease Control]] |via=atsdr.cdc.gov }}</ref>

== Footnotes ==
{{notelist}}

== See also ==
* [[Aqua Tofana]]
* ''[[Arsenic and Old Lace (disambiguation)|Arsenic and Old Lace]]''
* [[Grainger challenge]]
* [[Hypothetical types of biochemistry]]

== References ==
{{reflist|25em}}

== Bibliography ==
* {{cite book
 |title=Nature's Building Blocks: An A–Z Guide to the Elements
 |last=Emsley |first=John
 |publisher=Oxford University Press
 |year=2011
 |location=Oxford, UK
 |isbn=978-0-19-960563-7
 |chapter=Arsenic
 |pages=47–55
 |chapter-url=https://books.google.com/books?id=j-Xu07p3cKwC
}}
* {{Greenwood&Earnshaw2nd}}
* {{cite book|title=The Elements of Environmental Pollution|last=Rieuwerts | first = John|publisher=Routledge, Taylor & Francis Group/Earthscan | location = London|isbn=978-0-415-85920-2|date=2015}}

== Further reading ==
* {{cite book|title=The Arsenic Century|first=James G.|last=Whorton|publisher=Oxford University Press|isbn=978-0-19-960599-6|date=2011}}

== External links ==
{{Commons}}
{{Wiktionary|arsenic}}
* [https://www.who.int/news-room/fact-sheets/detail/arsenic WHO fact sheet on arsenic]
* [https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/arsenic Arsenic] Cancer Causing Substances, U.S. National Cancer Institute.
* [http://ctdbase.org/detail.go?type=chem&acc=D001151 CTD's Arsenic page] and [http://ctdbase.org/detail.go?type=chem&acc=D001152 CTD's Arsenicals page] from the [[Comparative Toxicogenomics Database]]
* [http://www.clu-in.org/contaminantfocus/default.focus/sec/arsenic/cat/Overview/ Contaminant Focus: Arsenic] {{Webarchive|url=https://web.archive.org/web/20090901131448/http://www.clu-in.org/contaminantfocus/default.focus/sec/arsenic/cat/Overview/ |date=1 September 2009 }} by the [[United States Environmental Protection Agency|EPA]].
* [https://www.inchem.org/documents/ehc/ehc/ehc224.htm Environmental Health Criteria for Arsenic and Arsenic Compounds, 2001] by the [[World Health Organization|WHO]].
* [https://www.cdc.gov/niosh/topics/arsenic/ National Institute for Occupational Safety and Health – Arsenic Page]
* [[usgs.gov]] (Mineral Commodity Summaries 2025): [https://pubs.usgs.gov/periodicals/mcs2025/mcs2025.pdf#page=36 Arsenic]

{{Periodic table (navbox)}}
{{Arsenic compounds}}
{{Arsenides}}

{{Authority control}}

[[Category:Arsenic| ]]
[[Category:Chemical elements]]
[[Category:Metalloids]]
[[Category:Semimetals]]
[[Category:Hepatotoxins]]
[[Category:Pnictogens]]
[[Category:Endocrine disruptors]]
[[Category:IARC Group 1 carcinogens]]
[[Category:Trigonal minerals]]
[[Category:Minerals in space group 166]]
[[Category:Teratogens]]
[[Category:Fetotoxicants]]
[[Category:Suspected testicular toxicants]]
[[Category:Native element minerals]]
[[Category:Chemical elements with rhombohedral structure]]