arsenate

File:Adamite-209883.jpg, a naturally occurring arsenate mineral.]]

Arsenates occur naturally, in hydrated and anhydrous form, in a variety of minerals. Examples of arsenate-containing minerals include adamite, alarsite, annabergite, erythrite and legrandite.{{Cite web |title=The mineralogy of Arsenic |url=https://www.mindat.org/element/Arsenic |website=Mindat.org}} When two arsenate ions balance the charge in a formula, it is called diarsenate for example zinc diarsenate, {{chem2|Zn3(AsO4)2}}.

Arsenate-based pesticides such as lead hydrogen arsenate were commonly used until their replacement by newer pesticides such as DDT and subsequent ban by multiple regulatory bodies due to health concerns.{{Cite web |title=The Evolution of Chemical Pesticides |url=https://www.fishersci.ca/ca/en/publications/lab-reporter/2016/issue-4/the-evolution-chemical-pesticides.html |access-date=2023-04-02 |website=www.fishersci.ca}}{{Cite web |title=The Global Problem of Lead Arsenate Pesticide |url=https://lead.org.au/lanv10n3/lanv10n3-7.html |access-date=2023-04-02 |website=lead.org.au}}

Transition metal arsenate compounds are often brightly coloured and have been used to make pigments. Copper arsenate was a minor compound used in the Egyptian blue pigment used by the ancient Egyptians and Romans.{{Cite journal |last1=Dariz |first1=Petra |last2=Schmid |first2=Thomas |date=2021-05-28 |title=Trace compounds in Early Medieval Egyptian blue carry information on provenance, manufacture, application, and ageing |journal=Scientific Reports |language=en |volume=11 |issue=1 |pages=11296 |doi=10.1038/s41598-021-90759-6 |pmid=34050218 |pmc=8163881 |bibcode=2021NatSR..1111296D |issn=2045-2322}} Cobalt violet pigment was made from cobalt arsenate before its toxicity led to its replacement by cobalt phosphate.{{Cite journal |last1=Corbeil |first1=Marie-Claude |last2=Charland |first2=Jean-Pierre |last3=Moffatt |first3=Elizabeth A. |date=2002 |title=The Characterization of Cobalt Violet Pigments |url=https://www.jstor.org/stable/1506784 |journal=Studies in Conservation |volume=47 |issue=4 |pages=237–249 |doi=10.2307/1506784 |jstor=1506784 |issn=0039-3630|url-access=subscription }}{{Cite web |title=Cobalt violet |url=https://colourlex.com/project/cobalt-violet/ |access-date=2023-04-10 |website=ColourLex |language=en-US}}{{Cite web |title=Cobaltous arsenate - CAMEO |url=https://cameo.mfa.org/wiki/Cobaltous_arsenate |access-date=2023-04-10 |website=cameo.mfa.org |language=en}}

Chromated copper arsenate (CCA) has been a widely used wood preservative since the 1930s.{{Citation |last=Barton |first=C. |title=CCA-Treated Wood |date=2014-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780123864543002724 |encyclopedia=Encyclopedia of Toxicology (Third Edition) |pages=751–752 |editor-last=Wexler |editor-first=Philip |access-date=2023-04-10 |place=Oxford |publisher=Academic Press |language=en |isbn=978-0-12-386455-0}} Safety concerns have led to the phasing out of CCA-treated wood for residential projects in many countries. CCA remains a common and economical treatment choice for non-residential uses such as agriculture. {{Cite journal |last1=Likar |first1=M |last2=Schauer |first2=P |last3=Japelj |first3=M |last4=Globokar |first4=M |last5=Oklobdzija |first5=M |last6=Povse |first6=A |last7=Sunjić |first7=V |date=1970-01-01 |title=Synthesis and antimicrobial activity of some thenoyl amides |url=https://doi.org/10.1021/jm00295a053 |journal=Journal of Medicinal Chemistry |volume=13 |issue=1 |pages=159–161 |doi=10.1021/jm00295a053 |issn=1520-4804 |pmid=5412102|url-access=subscription }}

File:Pourbaix_diagram_of_arsenic.jpg showing the distribution of arsenate and arsenite species in water. Oxygenated waters have a high pe value and arsenate species dominate. In deoxygenated water, with low pe, arsenite species dominate.{{Cite journal |last1=Marinho |first1=Belisa A. |last2=Cristóvão |first2=Raquel O. |last3=Boaventura |first3=Rui A. R. |last4=Vilar |first4=Vítor J. P. |date=2019-01-01 |title=As(III) and Cr(VI) oxyanion removal from water by advanced oxidation/reduction processes—a review |url=https://doi.org/10.1007/s11356-018-3595-5 |journal=Environmental Science and Pollution Research |language=en |volume=26 |issue=3 |pages=2203–2227 |doi=10.1007/s11356-018-3595-5 |pmid=30474808 |bibcode=2019ESPR...26.2203M |s2cid=53783178 |issn=1614-7499|url-access=subscription }}{{Citation |last1=Jekel |first1=M. |title=Chapter 11 - Arsenic removal during drinking water treatment |date=2006-01-01 |url=https://www.sciencedirect.com/science/article/pii/S1573428506800803 |work=Interface Science and Technology |volume=10 |pages=193–206 |editor-last=Newcombe |editor-first=Gayle |access-date=2023-04-15 |series=Interface Science in Drinking Water Treatment |publisher=Elsevier |language=en |last2=Amy |first2=G. L. |doi=10.1016/S1573-4285(06)80080-3 |isbn=978-0-12-088380-6 |editor2-last=Dixon |editor2-first=David|url-access=subscription }}]]

Depending on the pH, arsenate can be found as trihydrogen arsenate (that is arsenic acid {{chem2|H3AsO4}}), dihydrogen arsenate ({{chem2|H2AsO4-}}), hydrogen arsenate ({{chem2|HAsO4(2-)}}), or arsenate ({{chem2|AsO4(3-)}}).{{Cite book |last=Pollutants |first=National Research Council (US) Committee on Medical and Biological Effects of Environmental |url=https://www.ncbi.nlm.nih.gov/books/NBK231019/ |title=Chemistry of Arsenic |date=1977 |publisher=National Academies Press (US) |language=en}} Trihydrogen arsenate is also known as arsenic acid. At a given pH, the distribution of these arsenate species can be determined from their respective acid dissociation constants.

:{{chem2|H3AsO4 + H2O ⇌ H2AsO4− + [H3O]+}}{{pad|3em}}(pK_a1 = 2.19)

:{{chem2|H2AsO4− + H2O ⇌ HAsO4(2−) + [H3O]+}}{{pad|3em}}(pK_a2 = 6.94)

:{{chem2|HAsO4(2−) + H2O ⇌ AsO4(3−) + [H3O]+}}{{0|H}}{{pad|3em}}(pK_a3 = 11.5)

These values are similar to those of phosphoric acid. Hydrogen arsenate and dihydrogen arsenate predominate in aqueous solution near neutral pH.

The reduction potential (pe) of a solution also affects arsenate speciation. In natural waters, the dissolved oxygen content is the main factor influencing reduction potential. Arsenates occur in oxygenated waters, which have a high pe, while arsenites are the main arsenic species in anoxic waters with a low pe.

A Pourbaix diagram shows the combined influence of pH and pe on arsenate speciation.

Arsenates, along with arsenites, are a significant source of contamination in some natural water sources and can lead to arsenic poisoning with repeated exposure.{{Cite journal |last1=Sánchez-Rodas |first1=Daniel |last2=Luis Gómez-Ariza |first2=José |last3=Giráldez |first3=Inmaculada |last4=Velasco |first4=Alfredo |last5=Morales |first5=Emilio |date=2005-06-01 |title=Arsenic speciation in river and estuarine waters from southwest Spain |url=https://pubmed.ncbi.nlm.nih.gov/15919540/ |journal=The Science of the Total Environment |volume=345 |issue=1–3 |pages=207–217 |doi=10.1016/j.scitotenv.2004.10.029 |issn=0048-9697 |pmid=15919540|bibcode=2005ScTEn.345..207S }}{{Cite web |title=Arsenic |url=https://www.who.int/news-room/fact-sheets/detail/arsenic |access-date=2023-04-15 |website=www.who.int |language=en}} Countries with high levels of arsenic minerals in sediment and rock, such as Bangladesh, are especially at risk of arsenate contamination.{{Cite web |last=UCL |date=2022-05-10 |title=Reducing population exposure to groundwater arsenic in Bangladesh |url=https://www.ucl.ac.uk/earth-sciences/news/2022/may/reducing-population-exposure-groundwater-arsenic-bangladesh |access-date=2023-04-15 |website=UCL Earth Sciences |language=en}}

Arsenate is harmful to humans and animals as it interferes with the normal functioning of glycolysis and the Krebs cycle. Arsenate replaces inorganic phosphate in the step of glycolysis that produces 1,3-bisphosphoglycerate from glyceraldehyde 3-phosphate. This yields 1-arseno-3-phosphoglycerate instead, which is unstable and quickly hydrolyzes, forming the next intermediate in the pathway, 3-phosphoglycerate. Therefore, glycolysis proceeds, but the ATP molecule that would be generated from 1,3-bisphosphoglycerate is lost – arsenate is an uncoupler of glycolysis, explaining its toxicity.{{Cite web |date= 21 June 2022|title=How does arsenic kill? |url=https://www.livescience.com/how-does-arsenic-kill |access-date=2023-03-31 |website=livescience.com |language=en}}{{Cite journal |last=Hughes |first=Michael F. |date=2002-07-07 |title=Arsenic toxicity and potential mechanisms of action |url=https://pubmed.ncbi.nlm.nih.gov/12076506/ |journal=Toxicology Letters |volume=133 |issue=1 |pages=1–16 |doi=10.1016/s0378-4274(02)00084-x |issn=0378-4274 |pmid=12076506}}

As with other arsenic compounds, arsenate binds to lipoic acid, inhibiting the conversion of pyruvate into acetyl-CoA, blocking the Krebs cycle and therefore resulting in further loss of ATP.

• :Category:Arsenates

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{{Wiktionary|arsenate|arsenation}}

Category:Arsenic(V) compounds

Category:Pnictogen oxyanions