Editing Arsenic (section)

== 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 |url-status = dead |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=http://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 |url-status=dead |archive-url=https://ghostarchive.org/varchive/youtube/20211205/MvxnXOoFl20 |archive-date=2021-12-05 |via=Ghostarchive }}<br/>{{cite web |title=alternate arcived 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 |pages=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=PETERSON ,HANS |first3=LIBER ,KARSTEN |last4=and 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}}</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 |url-status = dead |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|url-status = dead|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 |url-status = dead|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.|url-status = dead| 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 = http://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}}
[[File:Miscanti Lagoon near San Pedro de Atacama Chile Luca Galuzzi 2006.jpg|thumb|'''Miscanti Lagoon near San Pedro de Atacama Chile Luca Galuzzi 2006''']]
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 }}</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>Eawag (2015) Geogenic Contamination Handbook – Addressing Arsenic and Fluoride in Drinking Water. C.A. Johnson, A. Bretzler (Eds.), Swiss Federal Institute of Aquatic Science and Technology (Eawag), Duebendorf, Switzerland. (download: www.eawag.ch/en/research/humanwelfare/drinkingwater/wrq/geogenic-contamination-handbook/)</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 }}</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=http://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). [http://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. }}</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 = http://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 = http://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=http://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 |url-status = dead}}</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>[http://toxnet.nlm.nih.gov/ 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 |page=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 |pages=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) }}</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"/>