View source for Thallium

{{distinguish|Thulium}}
{{infobox thallium}}

'''Thallium '''is a [[chemical element]]; it has [[Symbol (chemistry)|symbol]] '''Tl''' and [[atomic number]] 81. It is a silvery-white [[post-transition metal]] that is not found free in nature. When isolated, thallium resembles [[tin]], but discolors when exposed to air. Chemists [[William Crookes]] and [[Claude-Auguste Lamy]] discovered thallium independently in 1861, in residues of [[sulfuric acid]] production. Both used the newly developed method of [[flame spectroscopy]], in which thallium produces a notable green spectral line. Thallium, from [[Greek language|Greek]] {{lang|el|θαλλός}}, {{lang|el-Latn|[[thallus|thallós]]}}, meaning "green shoot" or "twig", was named by Crookes. It was isolated by both Lamy and Crookes in 1862; Lamy by electrolysis and Crookes by precipitation and melting of the resultant powder. Crookes exhibited it as a powder precipitated by zinc at the [[1862 International Exhibition|international exhibition]], which opened on 1 May that year.<ref>''[http://babel.hathitrust.org/cgi/pt?id=hvd.32044103134011;view=1up;seq=7 The Mining and Smelting Magazine]'' {{Webarchive|url=https://web.archive.org/web/20210224152954/https://babel.hathitrust.org/cgi/pt?id=hvd.32044103134011;view=1up;seq=7 |date=2021-02-24 }}. Ed. Henry Curwen Salmon. Vol. iv, July–Dec 1963, p. 87.</ref>

Thallium tends to form the +3 and +1 oxidation states. The +3 state resembles that of the other elements in [[Boron Group|group 13]] ([[boron]], [[aluminium]], [[gallium]], [[indium]]). However, the +1 state, which is far more prominent in thallium than the elements above it, recalls the chemistry of [[alkali metal]]s and thallium(I) ions are found geologically mostly in potassium-based ores and (when ingested) are handled in many ways like potassium ions (K<sup>+</sup>) by ion pumps in living cells.

Commercially, thallium is produced not from potassium ores, but as a byproduct from refining of heavy-metal sulfide ores. Approximately 65% of thallium production is used in the [[electronics industry]] and the remainder is used in the [[pharmaceutical industry]] and in [[glass|glass manufacturing]].<ref name="sl2001" /> It is also used in [[infrared detector]]s. The radioisotope thallium-201 (as the soluble chloride TlCl) is used in small amounts as an agent in a [[nuclear medicine]] scan, during one type of nuclear [[cardiac stress test]].

Soluble thallium salts (many of which are nearly tasteless) are highly [[toxic]] and they were historically used in [[rat poison]]s and [[insecticide]]s. Because of their nonselective toxicity, use of these compounds has been restricted or banned in many countries. Thallium poisoning usually results in hair loss. Because of its historic popularity as a murder weapon, thallium has gained notoriety as "the poisoner's poison" and "inheritance powder" (alongside [[arsenic]]).<ref>{{cite book |last = Hasan |first = Heather |date = 2009 |title = The Boron Elements: Boron, Aluminum, Gallium, Indium, Thallium |page = 14 |isbn = 978-1-4358-5333-1 |publisher = Rosen Publishing Group}}</ref>

==Characteristics==
A thallium atom has 81 electrons, arranged in the electron configuration [Xe]4f<sup>14</sup>5d<sup>10</sup>6s<sup>2</sup>6p<sup>1</sup>; of these, the three outermost electrons in the sixth shell are valence electrons. Due to the [[inert pair effect]], the 6s electron pair is relativistically stabilised and it is more difficult to get these involved in chemical bonding than it is for the heavier elements. Thus, very few electrons are available for metallic bonding, similar to the neighboring elements [[mercury (element)|mercury]] and [[lead]]. Thallium, then, like its congeners, is a soft, highly electrically conducting metal with a low melting point, of 304&nbsp;°C.<ref name="Greenwood222">Greenwood and Earnshaw, pp. 222–224</ref>

A number of standard electrode potentials, depending on the reaction under study,<ref>{{RubberBible92nd|page=8.20}}</ref> are reported for thallium, reflecting the greatly decreased stability of the +3 oxidation state:<ref name="Greenwood222" />
{|
|-
| +0.73 ||Tl<sup>3+</sup> + 3 e<sup>−</sup>|| ↔ Tl
|-
| −0.336 ||Tl<sup>+</sup> + e<sup>−</sup>|| ↔ Tl
|}

Thallium is the first element in group 13 where the reduction of the +3 oxidation state to the +1 oxidation state is spontaneous under standard conditions.<ref name="Greenwood222" /> Since bond energies decrease down the group, with thallium, the energy released in forming two additional bonds and attaining the +3 state is not always enough to outweigh the energy needed to involve the 6s-electrons.<ref name="Greenwood224">Greenwood and Earnshaw, pp. 224–7</ref> Accordingly, thallium(I) oxide and hydroxide are more basic and thallium(III) oxide and hydroxide are more acidic, showing that thallium conforms to the general rule of elements being more electropositive in their lower oxidation states.<ref name="Greenwood224" />

Thallium is [[Ductility|malleable]] and [[Sectility|sectile]] enough to be cut with a knife at room temperature. It has a metallic luster that, when exposed to air, quickly tarnishes to a bluish-gray tinge, resembling lead. It may be preserved by immersion in oil. A heavy layer of oxide builds up on thallium if left in air. In the presence of water, thallium [[hydroxide]] is formed. [[Sulfuric acid|Sulfuric]] and [[nitric acid]]s dissolve thallium rapidly to make the [[thallium(I) sulfate|sulfate]] and [[thallium(I) nitrate|nitrate]] salts, while [[hydrochloric acid]] forms an insoluble [[thallium(I) chloride]] layer.<ref name="HollemanAF">{{cite book|publisher = Walter de Gruyter|date = 1985|edition = 91–100|pages = 892–893|isbn = 978-3-11-007511-3|title = Lehrbuch der Anorganischen Chemie|first = Arnold F.|last = Holleman|author2 = Wiberg, Egon|author3 = Wiberg, Nils|chapter =Thallium|language = de}}</ref>

===Isotopes===
{{main|Isotopes of thallium}}
Thallium has 41 [[isotope]]s which have [[atomic mass]]es that range from 176 to 216. <sup>203</sup>Tl and <sup>205</sup>Tl are the only [[stable isotope]]s and make up nearly all of natural thallium. The five short-lived isotopes <sup>206</sup>Tl through <sup>210</sup>Tl inclusive occur in nature, as they are part of the natural [[decay chain]]s of heavier elements. <sup>204</sup>Tl is the most stable [[radioisotope]], with a [[half-life]] of 3.78 years.<ref name="Audi">{{NUBASE 2003}}</ref> It is made by the [[neutron activation]] of stable thallium in a [[nuclear reactor]].<ref name="Audi" /><ref>{{cite web|url = http://www-pub.iaea.org/MTCD/publications/PDF/te_1340_web.pdf|title = Manual for reactor produced radioisotopes|publisher = [[International Atomic Energy Agency]]|date = 2003|access-date = 2010-05-13|archive-date = 2011-05-21|archive-url = https://web.archive.org/web/20110521072530/http://www-pub.iaea.org/MTCD/publications/PDF/te_1340_web.pdf|url-status = live}}</ref> The most useful radioisotope, <sup>201</sup>Tl (half-life 73 hours), decays by electron capture, emitting X-rays (~70–80&nbsp;keV), and photons of 135 and 167&nbsp;keV in 10% total abundance;<ref name="Audi" /> therefore, it has good imaging characteristics without an excessive patient-radiation dose. It is the most popular isotope used for thallium nuclear [[cardiac stress test]]s.<ref>{{cite book|chapter-url = https://books.google.com/books?id=CqQgnHrDxrUC&pg=PA173|chapter = Detection, Evaluation, and Risk Stratification of Coronary Artery Disease by Thallium-201 Myocardial Perfusion Scintigraphy 155|first1 = Jamshid|last1 = Maddahi|first2 = Daniel|last2 = Berman|title = Cardiac SPECT imaging|edition = 2nd|publisher = Lippincott Williams & Wilkins|date = 2001|isbn = 978-0-7817-2007-6|pages = 155–178|access-date = 2016-09-26|archive-date = 2017-02-22|archive-url = https://web.archive.org/web/20170222122246/https://books.google.com/books?id=CqQgnHrDxrUC&pg=PA173|url-status = live}}</ref>

==Compounds==
{{See also|Category:Thallium compounds|Thallium halides}}

===Thallium(III)===
Thallium(III) compounds resemble the corresponding aluminium(III) compounds. They are moderately strong oxidizing agents and are usually unstable, as illustrated by the positive reduction potential for the Tl<sup>3+</sup>/Tl couple. Some mixed-valence compounds are also known, such as Tl<sub>4</sub>O<sub>3</sub> and TlCl<sub>2</sub>, which contain both thallium(I) and thallium(III). [[Thallium(III) oxide]], Tl<sub>2</sub>O<sub>3</sub>, is a black solid which decomposes above 800&nbsp;°C, forming the thallium(I) oxide and oxygen.<ref name="HollemanAF" />

The simplest possible thallium compound, [[thallane]] (TlH<sub>3</sub>), is too unstable to exist in bulk, both due to the instability of the +3 oxidation state as well as poor overlap of the valence 6s and 6p orbitals of thallium with the 1s orbital of hydrogen.<ref>{{cite journal|last=Andrew|first=L.|author2=Wang, X. |title=Infrared Spectra of Thallium Hydrides in Solid Neon, Hydrogen, and Argon|journal=J. Phys. Chem. A|year=2004|volume=108|issue=16|pages=3396–3402|doi=10.1021/jp0498973|bibcode=2004JPCA..108.3396W}}</ref> The trihalides are more stable, although they are chemically distinct from those of the lighter group 13 elements and are still the least stable in the whole group. For instance, [[thallium(III) fluoride]], TlF<sub>3</sub>, has the [[bismuth(III) fluoride|β-BiF<sub>3</sub>]] structure rather than that of the lighter group 13 trifluorides, and does not form the {{chem|Tl|F|4|-}} complex anion in aqueous solution. The trichloride and tribromide [[disproportionation|disproportionate]] just above room temperature to give the monohalides, and [[thallium triiodide]] contains the linear [[triiodide]] anion ({{chem|I|3|-}}) and is actually a thallium(I) compound.<ref name="Greenwood239">Greenwood and Earnshaw, p. 239</ref> Thallium(III) sesquichalcogenides do not exist.<ref name="Greenwood254">Greenwood and Earnshaw, p. 254</ref>

===Thallium(I)===
The [[thallium halides|thallium(I) halides]] are stable. In keeping with the large size of the Tl<sup>+</sup> cation, the chloride and bromide have the [[caesium chloride]] structure, while the fluoride and iodide have distorted [[sodium chloride]] structures. Like the analogous silver compounds, TlCl, TlBr, and TlI are [[photosensitive]] and display poor solubility in water.<ref name="Greenwood241">Greenwood and Earnshaw, p. 241</ref> The stability of thallium(I) compounds demonstrates its differences from the rest of the group: a stable [[thallium(I) oxide|oxide]], [[thallium(I) hydroxide|hydroxide]], and [[thallium(I) carbonate|carbonate]] are known, as are many chalcogenides.<ref name="Greenwood246">Greenwood and Earnshaw, pp. 246–7</ref>

The [[double salt]] {{chem|Tl|4|(OH)|2|CO|3|}} has been shown to have hydroxyl-centred triangles of thallium, {{chem|[Tl|3|(OH)]|2+}}, as a recurring motif throughout its solid structure.<ref>{{cite journal|title = Hydroxocentered {{chem|[(OH)Tl|3|]|2+}} triangle as a building unit in thallium compounds: synthesis and crystal structure of {{chem|Tl|4|(OH)|2|CO|3}}|first1 = Oleg I.|last1 = Siidra|first2 = Sergey N.|last2 = Britvin|first3 = Sergey V.|last3 = Krivovichev|journal = [[Z. Kristallogr.]]|volume = 224|issue = 12|pages = 563–567|doi = 10.1524/zkri.2009.1213|year = 2009|bibcode = 2009ZK....224..563S|s2cid = 97334707}}</ref>

The metalorganic compound thallium ethoxide (TlOEt, TlOC<sub>2</sub>H<sub>5</sub>) is a heavy liquid (ρ {{val|3.49|u=g·cm<sup>−3</sup>}}, m.p. −3&nbsp;°C),<ref>{{Cite book|title=Handbook of inorganic compounds|date=1995|publisher=CRC Press|others=Perry, Dale L., Phillips, Sidney L.|isbn=0-8493-8671-3|location=Boca Raton|oclc=32347397}}</ref> often used as a basic and soluble thallium source in organic and organometallic chemistry.<ref>{{Cite journal|last1=Frank|first1=Scott A.|last2=Chen|first2=Hou|last3=Kunz|first3=Roxanne K.|last4=Schnaderbeck|first4=Matthew J.|last5=Roush|first5=William R.|date=2000-08-01|title=Use of Thallium(I) Ethoxide in Suzuki Cross Coupling Reactions|journal=Organic Letters|volume=2|issue=17|pages=2691–2694|doi=10.1021/ol0062446|pmid=10990429|issn=1523-7060}}</ref>

===Organothallium compounds===
{{See also|Organothallium chemistry}}

Organothallium compounds tend to be thermally unstable, in concordance with the trend of decreasing thermal stability down group 13. The chemical reactivity of the Tl–C bond is also the lowest in the group, especially for ionic compounds of the type R<sub>2</sub>TlX. Thallium forms the stable [Tl(CH<sub>3</sub>)<sub>2</sub>]<sup>+</sup> ion in aqueous solution; like the isoelectronic [[dimethylmercury|Hg(CH<sub>3</sub>)<sub>2</sub>]] and [Pb(CH<sub>3</sub>)<sub>2</sub>]<sup>2+</sup>, it is linear. Trimethylthallium and triethylthallium are, like the corresponding gallium and indium compounds, flammable liquids with low melting points. Like indium, thallium [[cyclopentadienyl]] compounds contain thallium(I), in contrast to gallium(III).<ref name="Greenwood262">Greenwood and Earnshaw, pp. 262–4</ref>

==History==
Thallium ([[Greek language|Greek]] {{lang|el|θαλλός}}, {{lang|el-Latn|thallos}}, meaning "a green shoot or twig")<ref>Liddell, Henry George and Scott, Robert (eds.) "[http://perseus.mpiwg-berlin.mpg.de/cgi-bin/resolveform?lookup=qallos&type=begin&lang=greek&searchText=&options=Sort+Results+Alphabetically&.submit=Submit&formentry=1&lang=greek θαλλος] {{Webarchive|url=https://web.archive.org/web/20160415174207/http://perseus.mpiwg-berlin.mpg.de/cgi-bin/resolveform?lookup=qallos&type=begin&lang=greek&searchText=&options=Sort+Results+Alphabetically&.submit=Submit&formentry=1&lang=greek |date=2016-04-15 }}", in ''[[A Greek–English Lexicon]]'', Oxford University Press.</ref> was discovered by [[William Crookes]] and [[Claude Auguste Lamy]], working independently, both using flame spectroscopy (Crookes was first to publish his findings, on March 30, 1861).<ref>* Crookes, William (March 30, 1861) "On the existence of a new element, probably of the sulphur group," ''Chemical News'', vol. 3, [https://archive.org/details/bub_gb_6QcAAAAAMAAJ/page/n197 pp. 193–194]; reprinted in: {{cite journal|url=https://books.google.com/books?id=OhyQnaPXF5QC&pg=RA1-PA301|date=April 1861|doi=10.1080/14786446108643058|title=XLVI. On the existence of a new element, probably of the sulphur group|volume=21|issue=140|pages=301–305|journal=Philosophical Magazine|last1=Crookes|first1=William|access-date=2016-09-26|archive-date=2014-07-01|archive-url=https://web.archive.org/web/20140701065556/http://books.google.com/books?id=OhyQnaPXF5QC&pg=RA1-PA301|url-status=live}};
* Crookes, William (May 18, 1861) "Further remarks on the supposed new metalloid," ''Chemical News'', vol. 3, [https://archive.org/details/bub_gb_6QcAAAAAMAAJ/page/n307 p. 303].
* Crookes, William (June 19, 1862) "Preliminary researches on thallium," ''Proceedings of the Royal Society of London'', vol. 12, pages 150–159.
* Lamy, A. (May 16, 1862) "De l'existencè d'un nouveau métal, le thallium," ''Comptes Rendus'', vol. 54, [http://gallica2.bnf.fr/ark:/12148/bpt6k30115.image.r=Comptes+Rendus+Hebdomadaires.f1254.langFR pages 1255–1262] {{Webarchive|url=http://arquivo.pt/wayback/20160515195019/http://gallica2.bnf.fr/ark:/12148/bpt6k30115.image.r=Comptes+Rendus+Hebdomadaires.f1254.langFR |date=2016-05-15 }}.</ref> The name comes from thallium's bright [[green]] spectral [[emission line]]s<ref>{{cite journal| doi = 10.1021/ed009p2078| title = The discovery of the elements. XIII. Supplementary note on the discovery of thallium| date = 1932| last1 = Weeks| first1 = Mary Elvira|author-link1=Mary Elvira Weeks| journal = Journal of Chemical Education| volume = 9| issue = 12| page = 2078|bibcode = 1932JChEd...9.2078W }}</ref> derived from the Greek 'thallos', meaning a green twig.<ref>{{cite web |url=https://www.rsc.org/periodic-table/element/81/thallium |website=Royal Society of Chemistry |access-date=2 February 2024 |title=Thallium - Element information, properties and uses &#124; Periodic Table }}</ref>

After the publication of the improved method of flame spectroscopy by [[Robert Bunsen]] and [[Gustav Kirchhoff]]<ref>{{cite journal|title = Chemische Analyse durch Spectralbeobachtungen|pages = 337–381|author = G. Kirchhoff|author2 = R. Bunsen|doi = 10.1002/andp.18611890702|journal = [[Annalen der Physik und Chemie]]|volume = 189|issue = 7|date = 1861|bibcode = 1861AnP...189..337K| hdl=2027/hvd.32044080591324 |url = http://archiv.ub.uni-heidelberg.de/volltextserver/15657/1/spektral.pdf|access-date = 2018-04-20|archive-date = 2020-11-14|archive-url = https://web.archive.org/web/20201114043136/http://archiv.ub.uni-heidelberg.de/volltextserver/15657/1/spektral.pdf|url-status = live}}</ref> and the discovery of [[caesium]] and [[rubidium]] in the years 1859 to 1860, flame spectroscopy became an approved method to determine the composition of minerals and chemical products. Crookes and Lamy both started to use the new method. Crookes used it to make spectroscopic determinations for [[tellurium]] on selenium compounds deposited in the [[Lead chamber process|lead chamber]] of a sulfuric acid production plant near [[Abberode|Tilkerode]] in the [[Harz|Harz mountains]]. He had obtained the samples for his research on selenium cyanide from [[August Wilhelm von Hofmann|August Hofmann]] years earlier.<ref>{{cite journal|title = Preliminary Researches on Thallium|first = William|last = Crookes|journal = Proceedings of the Royal Society of London|volume = 12|date = 1862–1863|pages = 150–159|jstor = 112218|doi = 10.1098/rspl.1862.0030|bibcode = 1862RSPS...12..150C|doi-access = free}}</ref><ref>{{cite journal|title = On Thallium|first = William|last = Crookes|journal = Philosophical Transactions of the Royal Society of London|volume = 153|date = 1863|pages = 173–192|jstor = 108794|doi = 10.1098/rstl.1863.0009|url = https://zenodo.org/record/1432438|doi-access = free|access-date = 2019-09-12|archive-date = 2020-03-13|archive-url = https://web.archive.org/web/20200313143322/https://zenodo.org/record/1432438|url-status = live}}</ref> By 1862, Crookes was able to isolate small quantities of the new element and determine the properties of a few compounds.<ref name="DeKosky">{{cite journal|title = Spectroscopy and the Elements in the Late Nineteenth Century: The Work of Sir William Crookes|first = Robert K.|last = DeKosky|journal = The British Journal for the History of Science|volume = 6|issue = 4|date = 1973|pages = 400–423|jstor = 4025503|doi = 10.1017/S0007087400012553|s2cid = 146534210}}</ref> [[Claude-Auguste Lamy]] used a spectrometer that was similar to Crookes' to determine the composition of a selenium-containing substance which was deposited during the production of [[sulfuric acid]] from [[pyrite]]. He also noticed the new green line in the spectra and concluded that a new element was present. Lamy had received this material from the sulfuric acid plant of his friend [[Charles Frédéric Kuhlmann|Frédéric Kuhlmann]] and this by-product was available in large quantities. Lamy started to isolate the new element from that source.<ref>{{cite journal|title = De l'existencè d'un nouveau métal, le thallium|journal = Comptes Rendus|date = 1862|first = Claude-Auguste|last = Lamy|volume = 54|pages = 1255–1262|url = http://gallica2.bnf.fr/ark:/12148/bpt6k30115.image.r=Comptes+Rendus+Hebdomadaires.f1254.langFR|access-date = 2008-11-11|archive-date = 2016-05-15|archive-url = http://arquivo.pt/wayback/20160515195019/http://gallica2.bnf.fr/ark:/12148/bpt6k30115.image.r=Comptes+Rendus+Hebdomadaires.f1254.langFR|url-status = live}}</ref> The fact that Lamy was able to work ample quantities of thallium enabled him to determine the properties of several compounds and in addition he prepared a small ingot of metallic thallium which he prepared by remelting thallium he had obtained by electrolysis of thallium salts.{{citation needed|date=March 2021}}

As both scientists discovered thallium independently and a large part of the work, especially the isolation of the metallic thallium was done by Lamy, Crookes tried to secure his own priority on the work. Lamy was awarded a medal at the International Exhibition in London 1862: ''For the discovery of a new and abundant source of thallium'' and after heavy protest Crookes also received a medal: ''thallium, for the discovery of the new element.'' The controversy between both scientists continued through 1862 and 1863. Most of the discussion ended after Crookes was elected [[Fellow of the Royal Society]] in June 1863.<ref name="James">{{cite journal|title =Of 'Medals and Muddles' the Context of the Discovery of Thallium: William Crookes's Early|first = Frank A. J. L.|last = James|journal =Notes and Records of the Royal Society of London|volume = 39|issue = 1|date = 1984|pages = 65–90|jstor = 531576|doi =10.1098/rsnr.1984.0005|doi-access = free}}</ref><ref name="Murder">{{cite book|title = The Elements of Murder: A History of Poison|chapter = Thallium|first = John|last = Emsley|publisher = Oxford University Press|date = 2006|isbn = 978-0-19-280600-0|chapter-url = https://books.google.com/books?id=BACSR7TXWhoC|pages = 326–327|access-date = 2016-09-26|archive-date = 2020-03-07|archive-url = https://web.archive.org/web/20200307115513/https://books.google.com/books?id=BACSR7TXWhoC|url-status = live}}</ref>
<!-- historic use as rat poison and for night sweat of tuberculosis and for hair removal Thallium Toxicity and the Role of Prussian Blue in Therapy 10.1016/S1383-5742(97)00022-7 10.1007/BF01684859 http://quod.lib.umich.edu/cgi/t/text/text-idx?c=nal;idno=17038117.0238.001-->

The dominant use of thallium was the use as poison for rodents. After several accidents the use as poison was banned in the United States by [[Executive order (United States)|Presidential Executive Order]] 11643 in February 1972. In subsequent years several other countries also banned its use.<ref name="USGS1972">{{cite book|author=Staff of the Nonferrous Metals Division|title=Minerals yearbook metals, minerals, and fuels|date=1972|publisher=United States Geological Survey|volume=1|page=1358|chapter=Thallium|access-date=2010-06-01|chapter-url=http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/EcoNatRes-idx?type=goto&id=EcoNatRes.MinYB1972v1&page=1358&isize=XL|archive-url=https://web.archive.org/web/20140322013525/http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/EcoNatRes-idx?type=goto&id=EcoNatRes.MinYB1972v1&page=1358&isize=XL|archive-date=2014-03-22|url-status=live}}</ref>

==Occurrence and production==
Thallium [[Abundance of elements in Earth's crust | concentration in the Earth's crust]] is estimated to be 0.7&nbsp;mg/kg,<ref name="USGS-CS2010">{{cite web|first = David E.|last = Guberman|title = Mineral Commodity Summaries 2010: Thallium|url = http://minerals.usgs.gov/minerals/pubs/commodity/thallium/mcs-2010-thall.pdf|access-date = 2010-05-13|publisher = United States Geological Survey|archive-date = 2010-07-15|archive-url = https://web.archive.org/web/20100715162053/http://minerals.usgs.gov/minerals/pubs/commodity/thallium/mcs-2010-thall.pdf|url-status = live}}</ref> mostly in association with [[potassium]]-based [[mineral]]s in [[clay]]s, [[soil]]s, and [[granite]]s. The major source of thallium for practical purposes is the trace amount that is found in [[copper]], [[lead]], [[zinc]], and other heavy-metal-[[sulfide]] [[ore]]s.<ref>{{Cite journal| doi = 10.1007/BF01684859| title = Thallium: Occurrence in the environment and toxicity to fish| year = 1975| last1 = Zitko | first1 = V.| last2 = Carson | first2 = W. V.| last3 = Carson | first3 = W. G.| journal = Bulletin of Environmental Contamination and Toxicology| volume = 13| pages = 23–30| pmid = 1131433| issue = 1| bibcode = 1975BuECT..13...23Z| s2cid = 40955658}}</ref><ref name="Vira">{{cite journal|doi = 10.1016/j.envint.2004.09.003|title = Thallium: a review of public health and environmental concerns|date = 2005|last1 = Peter|first1 = A.|last2 = Viraraghavan|first2 = T.|journal = [[Environment International]]|volume = 31|pages = 493–501|pmid = 15788190|issue = 4| bibcode=2005EnInt..31..493P }}</ref>

[[File:Hutchinsonite-131710.jpg|thumb|left|alt=A close view of a rock crusted with groups of glassy, lustrous, silvery-blue [[hutchinsonite]], in tight clusters of loosely aligned needle-like crystals, among smaller clusters of tiny orange-brown crystals|Crystals of [[hutchinsonite]] ((Tl,Pb)<sub>2</sub>As<sub>5</sub>S<sub>9</sub>)]]
Thallium is found in the minerals [[crookesite]] TlCu<sub>7</sub>Se<sub>4</sub>, [[hutchinsonite]] TlPbAs<sub>5</sub>S<sub>9</sub>, and [[lorándite]] TlAsS<sub>2</sub>.<ref>{{cite journal|doi = 10.1016/0016-7037(52)90003-3|title = The geochemistry of thallium|date = 1952|last1 = Shaw|first1 = D.|journal = Geochimica et Cosmochimica Acta|volume = 2|issue = 2|pages = 118–154 |bibcode = 1952GeCoA...2..118S }}</ref> Thallium also occurs as a trace element in [[iron pyrite]], and thallium is extracted as a by-product of roasting this mineral for the production of [[sulfuric acid]].<ref name="sl2001">{{cite web|title=Chemical fact sheet&nbsp;– Thallium|publisher=Spectrum Laboratories|date=April 2001|url=http://www.speclab.com/elements/thallium.htm|access-date=2008-02-02|archive-date=2008-02-21|archive-url=https://web.archive.org/web/20080221222321/http://www.speclab.com/elements/thallium.htm|url-status=dead}}</ref><ref name="Downs">{{cite book|title = Chemistry of aluminium, gallium, indium, and thallium|first = Anthony John|last = Downs|publisher = Springer|date = 1993|isbn = 978-0-7514-0103-5|pages = 90 and 106|url = https://books.google.com/books?id=v-04Kn758yIC|access-date = 2016-09-26|archive-date = 2017-02-22|archive-url = https://web.archive.org/web/20170222131541/https://books.google.com/books?id=v-04Kn758yIC|url-status = live}}</ref>

Thallium can also be obtained from the [[smelting]] of lead and zinc ores. [[Manganese nodule]]s found on the [[ocean floor]] contain some thallium.<ref>{{cite journal|doi = 10.1016/j.marchem.2003.09.006|pages = 125–139|title = The mass balance of dissolved thallium in the oceans|date = 2004|issue = 3–4|last1 = Rehkamper|first1 = M.|journal = Marine Chemistry|volume = 85|last2 = Nielsen|first2 = Sune G.| bibcode=2004MarCh..85..125R }}</ref> In addition, several other thallium minerals, containing 16% to 60% thallium, occur in nature as complexes of sulfides or selenides that primarily contain [[antimony]], [[arsenic]], copper, lead, and [[silver]]. These minerals are rare, and have had no commercial importance as sources of thallium.<ref name="USGS-CS2010" /> The [[Allchar deposit]] in southern [[North Macedonia]] was the only area where thallium was actively mined. This deposit still contains an estimated 500&nbsp;tonnes of thallium, and it is a source for several rare thallium minerals, for example lorándite.<ref>{{cite journal|doi = 10.1016/0168-9002(88)90170-2|title = The Allchar Tl–As–Sb deposit, Yugoslavia and its specific metallogenic features|date = 1988|last1 = Jankovic|first1 = S.|journal = Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment|volume = 271|issue = 2|page = 286|bibcode = 1988NIMPA.271..286J }}</ref><!-- The "Alshar" epithermal Au-As-Sb-Tl deposit, located in southern Macedonia, is the only larger mining area 10.1134/S1075701506030020 https://www.jstor.org/pss/2843882 -->

The [[United States Geological Survey]] (USGS) estimates that the annual worldwide production of thallium is 10&nbsp;metric tonnes as a by-product from the smelting of copper, zinc, and lead ores.<ref name="USGS-CS2010" /> Thallium is either extracted from the dusts from the smelter flues or from residues such as [[slag]] that are collected at the end of the smelting process.<ref name="USGS-CS2010" /> The raw materials used for thallium production contain large amounts of other materials and therefore a purification is the first step. The thallium is leached either by the use of an alkali or sulfuric acid from the material. The thallium is precipitated several times from the solution to remove impurities. At the end it is converted to thallium sulfate and the thallium is extracted by [[electrolysis]] on [[platinum]] or [[stainless steel]] plates.<ref name="Downs" /> The production of thallium decreased by about 33% in the period from 1995 to 2009 – from about 15&nbsp;metric [[tonne]]s to about 10&nbsp;tonnes. Since there are several small deposits or ores with relatively high thallium content, it would be possible to increase the production if a new application, such as a thallium-containing [[high-temperature superconductivity|high-temperature superconductor]], becomes practical for widespread use outside of the laboratory.<ref>{{cite web|first = Gerald R.|last = Smith|title = Mineral commodity summaries 1996: Thallium|url = http://minerals.usgs.gov/minerals/pubs/commodity/thallium/thallmcs96.pdf|access-date = 2010-05-13|publisher = United States Geological Survey|archive-date = 2010-05-29|archive-url = https://web.archive.org/web/20100529192216/http://minerals.usgs.gov/minerals/pubs/commodity/thallium/thallmcs96.pdf|url-status = live}}</ref>

==Applications==

===Historic uses===
The odorless and tasteless [[Thallium(I) sulfate|thallium sulfate]] was once widely used as rat poison and ant killer. Since 1972 this use has been prohibited in the United States due to safety concerns.<ref name="USGS1972" /><ref name="sl2001" /> Many other countries followed this example. Thallium salts were used in the treatment of [[ringworm]], other [[skin infection]]s and to reduce the [[night sweat]]ing of [[tuberculosis]] patients. This use has been limited due to their narrow [[therapeutic index]], and the development of improved medicines for these conditions.<ref name="CRC" /><ref>{{cite journal|doi = 10.1111/j.1365-2133.1930.tb09395.x|pmid =20774304|pages =59–69|title = The Treatment of Ringworm of The Scalp with Thallium Acetate|date = 1930|issue = 2|last1 = Percival|first1 = G. H.|journal = British Journal of Dermatology|volume = 42|pmc = 2456722}}</ref><ref>{{cite journal|doi = 10.1016/S0378-4274(98)00126-X| pages =1–13|title = Thallium toxicity|date = 1998|last1 = Galvanarzate|first1 = S.|journal = [[Toxicology Letters]]|volume = 99|pmid = 9801025|last2 = Santamarı́a|first2 = A.|issue = 1}}</ref>

===Optics===
[[Thallium(I) bromide]] and [[thallium(I) iodide]] [[crystal]]s have been used as infrared optical materials, because they are harder than other common infrared optics, and because they have transmission at significantly longer wavelengths. The trade name [[KRS-5]] refers to this material.<ref>{{cite journal|pages = 338–346|doi = 10.1364/JOSA.46.000956|title = Refraction and Dispersion of Thallium Bromide Iodide|date = 1956|last1 = Rodney|issue = 11|first1 = William S.|last2 = Malitson|first2 = Irving H.|journal = [[Journal of the Optical Society of America]]|volume = 46|bibcode = 1956JOSA...46..956R}}</ref> [[Thallium(I) oxide]] has been used to manufacture glasses that have a high [[refractive index|index of refraction]]. Combined with sulfur or [[selenium]] and arsenic, thallium has been used in the production of high-[[density]] glasses that have low [[melting point]]s in the range of 125 and 150 Celsius°. These glasses have room-temperature properties that are similar to ordinary glasses and are durable, insoluble in water and have unique [[refractive indices]].<ref>{{cite book|url = https://books.google.com/books?id=jOOSKQHEJdwC&pg=PA52|publisher = [[CRC Press]]|title = Glasses for infrared optics|isbn = 978-0-8493-3785-7|date = 1996|first = Valentina F.|last = Kokorina|access-date = 2016-09-26|archive-date = 2020-03-11|archive-url = https://web.archive.org/web/20200311092514/https://books.google.com/books?id=jOOSKQHEJdwC&pg=PA52|url-status = live}}</ref>

===Electronics===
[[File:Thallium rod corroded.jpg|thumb|right|alt=A heavily pitted, blackish cylindrical rod, with extensive, crumbling brown-and-white corrosion|A corroded thallium rod]]
Thallium(I) sulfide's [[electrical conductivity]] changes with exposure to [[infrared light]], making this compound useful in [[photoresistor]]s.<ref name="CRC">{{cite book |author = Hammond, C. R. |title = The Elements, in Handbook of Chemistry and Physics |edition = 81st |publisher = CRC press |isbn = 978-0-8493-0485-9 |date = 2004-06-29 |url-access = registration |url = https://archive.org/details/crchandbookofche81lide }}</ref> Thallium selenide has been used in [[bolometer]]s for infrared detection.<ref>{{cite journal| bibcode = 1977ApOpt..16.2942N| title = Thallium selenide infrared detector| author = Nayer, P. S| author2 = Hamilton, O.| journal = Appl. Opt.| volume = 16| issue = 11| pages = 2942–4|date =1977| doi = 10.1364/AO.16.002942| pmid = 20174271}}</ref> [[Doping (semiconductor)|Doping]] selenium semiconductors with thallium improves their performance, thus it is used in trace amounts in [[selenium rectifier]]s.<ref name="CRC" /> Another application of thallium doping is the [[sodium iodide]] and [[cesium iodide]] crystals in [[gamma radiation]] detection devices. In these, the sodium iodide crystals are doped with a small amount of thallium to improve their efficiency as [[scintillation (physics)|scintillation]] generators.<ref>{{cite journal|pages =796–810|doi =10.1103/PhysRev.75.796|title =The Detection of Gamma-Rays with Thallium-Activated Sodium Iodide Crystals|date =1949|issue =5|last1 =Hofstadter|first1 =Robert|journal =Physical Review|volume =75|bibcode = 1949PhRv...75..796H }}</ref> Some of the electrodes in [[oxygen analyzer|dissolved oxygen analyzers]] contain thallium.<ref name="sl2001" />

===High-temperature superconductivity===
Research activity with thallium is ongoing to develop high-temperature [[Superconductivity|superconducting]] materials for such applications as [[magnetic resonance imaging]], storage of magnetic energy, [[linear motor|magnetic propulsion]], and [[electric power generation]] and transmission. The research in applications started after the discovery of the first [[thallium barium calcium copper oxide]] superconductor in 1988.<ref>{{cite journal|journal = Nature|volume = 332|issue = 6160|pages = 138–139|date = 1988|doi = 10.1038/332138a0|title = Bulk superconductivity at 120 K in the Tl–Ca/Ba–Cu–O system|first = Z. Z.|last =Sheng|author2=Hermann A. M. |bibcode=1988Natur.332..138S|s2cid = 30690410}}</ref> Thallium [[cuprate]] superconductors have been discovered that have transition temperatures above 120 K. Some mercury-doped thallium-cuprate superconductors have transition temperatures above 130 K at ambient pressure, nearly as high as the world-record-holding mercury cuprates.<ref>{{cite journal|title=Stabilization of the Tl<sub>2</sub>Ba<sub>2</sub>Ca<sub>2</sub>Cu<sub>3</sub>O<sub>10</sub> superconductor by Hg doping|author=Jia, Y. X.|author2=Lee, C. S.|author3=Zettl, A.|journal=Physica C|volume=234|issue=1–2|pages=24–28|bibcode=1994PhyC..234...24J|doi=10.1016/0921-4534(94)90049-3|date=1994|url=https://zenodo.org/record/1258633|access-date=2019-07-01|archive-date=2020-03-16|archive-url=https://web.archive.org/web/20200316222202/https://zenodo.org/record/1258633|url-status=live}}</ref>

===Nuclear medicine===
Before the widespread application of [[technetium-99m]] in [[nuclear medicine]], the [[radioactive]] isotope [[thallium-201]], with a half-life of 73 hours, was the main substance for [[Myocardial perfusion imaging|nuclear cardiography]]. The nuclide is still used for stress tests for risk stratification in patients with [[coronary artery disease]] (CAD).<ref>{{cite book |title = Essential cardiology: principles and practice |chapter = Nuclear imaging in cardiovascular medicine |first1 = Diwakar |last1 = Jain |first2 = Barry L. |last2 = Zaret |editor = Clive Rosendorff |pages = 221–222 |isbn = 978-1-58829-370-1 |publisher = Humana Press |chapter-url = https://books.google.com/books?id=cY182J9q5NoC&pg=PA222 |date = 2005 |edition = 2nd |access-date = 2016-09-26 |archive-date = 2017-02-19 |archive-url = https://web.archive.org/web/20170219095947/https://books.google.com/books?id=cY182J9q5NoC&pg=PA222 |url-status = live }}</ref><!--<ref>{{cite web|url=http://www.wramc.amedd.army.mil/departments/nuclear/PatientInfo/Thallium.htm|title=Thallium Test] from [[Walter Reed Army Medical Center]}}</ref><ref>[http://www.americanheart.org/presenter.jhtml?identifier=4743 Thallium Stress Test] from the [[American Heart Association]]</ref>--> This isotope of thallium can be generated using a transportable generator, which is similar to the [[technetium-99m generator]].<ref>{{cite journal |title = An integrally shielded transportable generator system for thallium-201 production |journal = International Journal of Applied Radiation and Isotopes |date = 1982 |volume = 33 |issue = 12 |pages = 1439–1443 |last = Lagunas-Solar |first = M. C. |author2 = Little, F. E. |author3 = Goodart, C. D. |url = http://www.medscape.com/medline/abstract/7169272 |doi = 10.1016/0020-708X(82)90183-1 |pmid = 7169272 |access-date = 2006-11-23 |archive-date = 2007-10-12 |archive-url = https://web.archive.org/web/20071012114116/http://www.medscape.com/medline/abstract/7169272 |url-status = live }}</ref> The generator contains [[lead-201]] (half-life 9.33 hours), which decays by [[electron capture]] to thallium-201. The lead-201 can be produced in a [[cyclotron]] by the bombardment of thallium with [[proton]]s or [[deuteron]]s by the (p,3n) and (d,4n) reactions.<ref>[http://www.med.harvard.edu/JPNM/physics/isotopes/Tl/Tl201/prod.html Thallium-201 production] {{Webarchive|url=https://web.archive.org/web/20060913175254/http://www.med.harvard.edu/JPNM/physics/isotopes/Tl/Tl201/prod.html |date=2006-09-13 }} from [[Harvard Medical School]]'s Joint Program in Nuclear Medicine.</ref><ref>{{cite journal | title = Thallium-201 for medical use | url = http://jnm.snmjournals.org/cgi/content/abstract/16/2/151 | pmid = 1110421 | journal = The Journal of Nuclear Medicine | volume = 16 | issue = 2 | pages = 151–5 | date = 1975 | last1 = Lebowitz | first1 = E. | last2 = Greene | first2 = M. W. | last3 = Fairchild | first3 = R. | last4 = Bradley-Moore | first4 = P. R. | last5 = Atkins | first5 = H. L. | last6 = Ansari | first6 = A. N. | last7 = Richards | first7 = P. | last8 = Belgrave | first8 = E. | access-date = 2010-05-13 | archive-date = 2008-10-11 | archive-url = https://web.archive.org/web/20081011152841/http://jnm.snmjournals.org/cgi/content/abstract/16/2/151 | url-status = live }}</ref>

====Thallium stress test====
A thallium stress test is a form of [[scintigraphy]] in which the amount of thallium in tissues correlates with tissue blood supply. Viable cardiac cells have normal [[Na+/K+-ATPase|Na<sup>+</sup>/K<sup>+</sup> ion-exchange pumps]]. The Tl<sup>+</sup> cation binds the K<sup>+</sup> pumps and is transported into the cells. Exercise or [[dipyridamole]] induces widening ([[vasodilation]]) of arteries in the body. This produces [[coronary steal]] by areas where arteries are maximally dilated. Areas of infarct or [[Ischemia|ischemic tissue]] will remain "cold". Pre- and post-stress thallium may indicate areas that will benefit from myocardial [[revascularization]]. Redistribution indicates the existence of coronary steal and the presence of ischemic [[coronary artery disease]].<ref>{{cite book |url=https://books.google.com/books?id=u_A5BSqsb20C&pg=PA100 |page=100 |title=Primary care cardiology |author=Taylor, George J. |publisher=Wiley-Blackwell |date=2004 |isbn=978-1-4051-0386-2 |access-date=2016-09-26 |archive-date=2020-03-12 |archive-url=https://web.archive.org/web/20200312164133/https://books.google.com/books?id=u_A5BSqsb20C&pg=PA100 |url-status=live }}</ref>

===Other uses===
A mercury–thallium alloy, which forms a [[eutectic]] at 8.5% thallium, is reported to freeze at&nbsp;−60&nbsp;°C, some 20&nbsp;°C below the freezing point of mercury. This alloy is used in thermometers and low-temperature switches.<ref name="CRC" /> In organic synthesis, thallium(III) salts, as thallium trinitrate or triacetate, are useful reagents for performing different transformations in aromatics, ketones and olefins, among others.<ref>{{cite journal|pages = 956–960|doi =10.1021/ar50034a003|title = Thallium in organic synthesis|date = 1970|last1 = Taylor|issue = 10|first1 = Edward Curtis|last2 = McKillop|first2 = Alexander|journal = Accounts of Chemical Research|volume = 3}}</ref> Thallium is a constituent of the alloy in the [[anode]] plates of [[magnesium battery|magnesium seawater batteries]].<ref name="sl2001" /> Soluble thallium salts are added to [[gold plating]] baths to increase the speed of plating and to reduce grain size within the gold layer.<ref>{{cite book | url = https://books.google.com/books?id=hDwX3slSvQ4C&pg=PA113 | pages = 113–115 | title = Integrated circuit, hybrid, and multichip module package design guidelines: a focus on reliability | isbn = 978-0-471-59446-8 | author1 = Pecht, Michael | date = 1994-03-01 | publisher = John Wiley & Sons | access-date = 2016-09-26 | archive-date = 2014-07-01 | archive-url = https://web.archive.org/web/20140701063446/http://books.google.com/books?id=hDwX3slSvQ4C&pg=PA113 | url-status = live }}</ref>

A saturated solution of equal parts of thallium(I) [[formate]] (Tl(HCO<sub>2</sub>)) and thallium(I) [[malonate]] (Tl(C<sub>3</sub>H<sub>3</sub>O<sub>4</sub>)) in water is known as [[Clerici solution]]. It is a mobile, odorless liquid which changes from yellowish to colorless upon reducing the concentration of the thallium salts. With a density of 4.25&nbsp;g/cm<sup>3</sup> at 20&nbsp;°C, Clerici solution is one of the heaviest aqueous solutions known. It was used in the 20th century for measuring the density of minerals by the [[Buoyancy|flotation]] method, but its use has discontinued due to the high toxicity and corrosiveness of the solution.<ref name="jahns">{{cite journal|title=Clerici solution for the specific gravity determination of small mineral grains|url=http://www.minsocam.org/ammin/AM24/AM24_116.pdf|volume=24|page=116|date=1939|author=Jahns, R. H.|journal=American Mineralogist|access-date=2009-11-06|archive-date=2012-07-24|archive-url=https://web.archive.org/web/20120724051736/http://www.minsocam.org/ammin/AM24/AM24_116.pdf|url-status=live}}</ref><ref name="b1">{{cite book|url=https://books.google.com/books?id=tfXa13uWiRIC&pg=PA63|pages=63–64|title=Gemmology|author=Peter G. Read|publisher=Butterworth-Heinemann|date=1999|isbn=978-0-7506-4411-2|access-date=2016-09-26|archive-date=2020-03-17|archive-url=https://web.archive.org/web/20200317174113/https://books.google.com/books?id=tfXa13uWiRIC&pg=PA63|url-status=live}}</ref>
<!--
https://books.google.com/books?id=v-04Kn758yIC&pg=PA108
Chemistry of aluminium, gallium, indium, and thallium Von Anthony John Downs Uses of ThalliumSpringer, 19939780751401035
https://books.google.com/books?id=fIu58uZTE-gC&pg=PA390 Structure-property relations in nonferrous metals Von Alan M. Russell, Kok Loong Lee 9780471649526John Wiley and Sons, 2005
http://minerals.usgs.gov/minerals/pubs/commodity/thallium/mcs-2010-thall.pdf
10.1016/j.envint.2004.09.003
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Thallium iodide is frequently used as an additive in [[metal-halide lamp]]s, often together with one or two halides of other metals. It allows optimization of the lamp temperature and color rendering,<ref>{{cite journal|doi=10.1364/JOSA.54.000532|title=Characteristics of Mercury Vapor-Metallic Iodide Arc Lamps|date=1964|last1=Reiling|first1=Gilbert H.|journal=Journal of the Optical Society of America|volume=54|issue=4|page=532|bibcode=1964JOSA...54..532R}}</ref><ref>{{cite journal|doi=10.1364/AO.6.001563|title=The Effect of Thallium Iodide on the Arc Temperature of Hg Discharges|date=1967|last1=Gallo|first1=C. F.|journal=Applied Optics|volume=6|issue=9|pages=1563–5|pmid=20062260|bibcode = 1967ApOpt...6.1563G }}</ref> and shifts the spectral output to the green region, which is useful for underwater lighting.<ref>{{cite news|url=https://www.nytimes.com/1987/08/11/science/undersea-quest-for-giant-squids-and-rare-sharks.html?pagewanted=all&src=pm|title=UNDERSEA QUEST FOR GIANT SQUIDS AND RARE SHARKS|author=Wilford, John Noble|work=The New York Times |date=1987-08-11|access-date=2017-02-13|archive-date=2016-12-20|archive-url=https://web.archive.org/web/20161220102236/http://www.nytimes.com/1987/08/11/science/undersea-quest-for-giant-squids-and-rare-sharks.html?pagewanted=all&src=pm|url-status=live}}</ref>

==Toxicity==
{{main|Thallium poisoning}}
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Thallium and its compounds are extremely toxic, with numerous recorded cases of fatal thallium poisoning.<ref>{{Cite web|date=2011-02-13|title=A 15-year-old case yields a timely clue in deadly thallium poisoning|url=https://www.nj.com/news/2011/02/thallium_is_favored_method_of.html|access-date=2023-02-12|website=nj|language=en}}</ref><ref>{{cite web|url=https://arstechnica.com/science/2018/12/new-study-establishes-timeline-for-famous-thallium-poisoning-cold-case/|author=Jennifer Ouellette|title=Study brings us one step closer to solving 1994 thallium poisoning case|date=25 December 2018|work=Ars Technica|access-date=26 December 2018|archive-date=26 December 2018|archive-url=https://web.archive.org/web/20181226001509/https://arstechnica.com/science/2018/12/new-study-establishes-timeline-for-famous-thallium-poisoning-cold-case/|url-status=live}}</ref> The [[Occupational Safety and Health Administration]] (OSHA) has set the legal limit ([[permissible exposure limit]]) for thallium exposure in the workplace as 0.1&nbsp;mg/m<sup>2</sup> skin exposure over an eight-hour workday. The [[National Institute for Occupational Safety and Health]] (NIOSH) also set a [[recommended exposure limit]] (REL) of 0.1&nbsp;mg/m<sup>2</sup> skin exposure over an eight-hour workday. At levels of 15&nbsp;mg/m<sup>2</sup>, thallium is [[IDLH|immediately dangerous to life and health]].<ref>{{Cite web|title = CDC – NIOSH Pocket Guide to Chemical Hazards – Thallium (soluble compounds, as Tl)|url = https://www.cdc.gov/niosh/npg/npgd0608.html|website = www.cdc.gov|access-date = 2015-11-24|archive-date = 2015-09-24|archive-url = https://web.archive.org/web/20150924140704/http://www.cdc.gov/niosh/npg/npgd0608.html|url-status = live}}</ref>

Contact with skin is dangerous, and adequate ventilation is necessary when melting this metal. Thallium(I) compounds have a high aqueous solubility and are readily absorbed through the skin, and care should be taken to avoid this route of exposure, as [[cutaneous]] absorption can exceed the absorbed dose received by inhalation at the [[permissible exposure limit]] (PEL).<ref>{{Cite web|title=Surface Contamination - Overview &#124; Occupational Safety and Health Administration|url=https://www.osha.gov/surface-contamination|access-date=2023-02-12|website=www.osha.gov}}</ref> Exposure by inhalation cannot safely exceed 0.1&nbsp;mg/m<sup>2</sup> in an eight-hour time-weighted average (40-hour work week).<ref>[https://www.osha.gov/dts/chemicalsampling/data/CH_271500.html Chemical Sampling Information | Thallium, soluble compounds (as Tl)] {{Webarchive|url=https://web.archive.org/web/20140322030241/https://www.osha.gov/dts/chemicalsampling/data/CH_271500.html |date=2014-03-22 }}. Osha.gov. Retrieved on 2013-09-05.</ref> The [[Centers for Disease Control and Prevention]] (CDC) states, "Thallium is not classifiable as a carcinogen, and it is not suspected to be a carcinogen. It is unknown whether chronic or repeated exposure to thallium increases the risk of reproductive toxicity or developmental toxicity. Chronic high level exposure to thallium through inhalation has been reported to cause nervous system effects, such as numbness of fingers and toes."<ref>{{cite web|url=https://www.cdc.gov/niosh/ershdb/emergencyresponsecard_29750026.html|title=CDC – The Emergency Response Safety and Health Database: Systemic Agent: THALLIUM – NIOSH|website=www.cdc.gov|access-date=2019-12-11|archive-date=2019-11-15|archive-url=https://web.archive.org/web/20191115160632/https://www.cdc.gov/niosh/ershdb/emergencyresponsecard_29750026.html|url-status=live}}</ref> For a long time thallium compounds were readily available as rat poison. This fact and that it is water-soluble and nearly tasteless led to frequent intoxication caused by accident or criminal intent.<ref name="Murder" />

One of the main methods of removing thallium (both radioactive and stable) from humans is to use [[Prussian blue]], a material which absorbs thallium.<ref>{{cite journal |last1=Yang |first1=Yongsheng |last2=Faustino |first2=Patrick J. |last3=Progar |first3=Joseph J. |last4=Brownell |first4=Charles R. |last5=Sadrieh |first5=Nakissa |last6=May |first6=Joan C. |last7=Leutzinger |first7=Eldon |last8=Place |first8=David A. |last9=Duffy |first9=Eric P. |last10=Yu |first10=Lawrence X. |last11=Khan |first11=Mansoor A. |last12=Lyon |first12=Robbe C. |title=Quantitative determination of thallium binding to ferric hexacyanoferrate: Prussian blue |date=2008 |journal=International Journal of Pharmaceutics |volume=353 |issue=1–2 |pages=187–194 |doi=10.1016/j.ijpharm.2007.11.031 |pmid=18226478 |display-authors=3 |url=https://zenodo.org/record/1259065 |access-date=2019-07-01 |archive-date=2020-03-15 |archive-url=https://web.archive.org/web/20200315120441/https://zenodo.org/record/1259065 |url-status=live }}</ref> Up to 20&nbsp;grams per day of Prussian blue is fed by mouth to the patient, and it passes through their digestive system and comes out in their stool. [[Hemodialysis]] and [[hemoperfusion]] are also used to remove thallium from the blood serum. At later stages of the treatment, additional potassium is used to mobilize thallium from the tissues.<ref>[http://www.bt.cdc.gov/radiation/prussianblue.asp Prussian blue fact sheet] {{Webarchive|url=https://web.archive.org/web/20131020123050/http://www.bt.cdc.gov/radiation/prussianblue.asp |date=2013-10-20 }}. US [[Centers for Disease Control and Prevention]].</ref><ref>{{cite journal |last = Malbrain |first = Manu L. N. G. |author2 = Lambrecht, Guy L. Y. |author3 = Zandijk, Erik |author4 = Demedts, Paul A. |author5 = Neels, Hugo M. |author6 = Lambert, Willy |author7 = De Leenheer, André P. |author8 = Lins, Robert L. |author9 = Daelemans, Ronny |date = 1997 |title = Treatment of Severe Thallium Intoxication |journal = Clinical Toxicology |volume = 35 |issue = 1 |pages = 97–100 |doi = 10.3109/15563659709001173 |pmid = 9022660}}</ref>

According to the [[United States Environmental Protection Agency]] (EPA), artificially-made sources of thallium pollution include gaseous emission of [[Cement#Heavy metal emissions in the air|cement factories]], coal-burning power plants, and metal sewers. The main source of elevated thallium concentrations in water is the leaching of thallium from ore processing operations.<ref name="Vira" /><ref>{{cite web |url = http://www.epa.gov/safewater/pdfs/factsheets/ioc/thallium.pdf |access-date = 2009-09-15 |title = Factsheet on: Thallium |publisher = US Environmental Protection Agency |archive-date = 2012-01-11 |archive-url = https://web.archive.org/web/20120111232626/http://www.epa.gov/safewater/pdfs/factsheets/ioc/thallium.pdf |url-status = live }}</ref>

==See also==
* {{portal-inline|Chemistry}}
* [[Myocardial perfusion imaging]]

== Citations ==
{{Reflist|30em}}

== General bibliography ==
* {{Greenwood&Earnshaw2nd}}

==External links==
{{Sister project links |wikt=thallium |commons=thallium |n=no |q=no |b=no |v=Thallium atom}}
* [http://www.periodicvideos.com/videos/081.htm Thallium] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
* [http://www.emedicine.com/emerg/topic926.htm Toxicity, thallium]
* [http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@na+@rel+thallium,+elemental NLM hazardous substances databank&nbsp;– Thallium, elemental]
* [https://wwwn.cdc.gov/TSP/ToxFAQs/ToxFAQsDetails.aspx?faqid=308&toxid=49 ATSDR – ToxFAQs]
* [https://www.cdc.gov/niosh/npg/npgd0608.html CDC – NIOSH Pocket Guide to Chemical Hazards]

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