Iodine: Difference between revisions

'''Iodine''' is a [[chemical element]]; it has [[Chemical symbol|symbol]] '''I''' and [[atomic number]] 53. The heaviest of the stable [[halogen]]s, it exists at [[Standard temperature and pressure|standard conditions]] as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at {{convert|114|C}}, and boils to a violet gas at {{convert|184|C}}. The element was discovered by the French chemist [[Bernard Courtois]] in 1811 and was named two years later in 1813 by [[Joseph Louis Gay-Lussac]], after the [[Ancient Greek]] {{lang|grc|Ιώδης}}, meaning 'violet'.

Iodine occurs in many oxidation states, including [[iodide]] (I⁻), [[iodate]] ({{chem|IO|3|-}}), and the various [[periodate]] anions. It is the least abundant of the stable [[halogen]]s, being the 60th most abundant element. As the heaviest essential [[Mineral (nutrient)|mineral nutrient]], iodine is required for the synthesis of [[thyroid hormones]].<ref name="lpi">{{cite web|url=http://lpi.oregonstate.edu/mic/minerals/iodine|title=Iodine|publisher=Micronutrient Information Center, [[Linus Pauling Institute]], [[Oregon State University]], Corvallis|date=2015|access-date=20 November 2017|archive-date=17 April 2015|archive-url=https://web.archive.org/web/20150417055246/http://lpi.oregonstate.edu/mic/minerals/iodine|url-status=live}}</ref> [[Iodine deficiency]] affects about two billion people and is the leading preventable cause of [[Intellectual disability|intellectual disabilities]].<ref>{{cite news|url= https://query.nytimes.com/gst/fullpage.html?res=9E05E3D81231F935A25751C1A9609C8B63|work=The New York Times|title=In Raising the World's I.Q., the Secret's in the Salt| vauthors = McNeil Jr DG |date=2006-12-16|access-date=2009-07-21|url-status=live|archive-url= https://web.archive.org/web/20100712011551/http://query.nytimes.com/gst/fullpage.html?res=9E05E3D81231F935A25751C1A9609C8B63|archive-date=2010-07-12}}</ref>

In 1811, iodine was discovered by French [[chemist]] [[Bernard Courtois]],<ref name="court">{{cite journal| vauthors = Courtois B |title=Découverte d'une substance nouvelle dans le Vareck |trans-title=Discovery of a new substance in seaweed |journal=[[Annales de chimie]] |volume=88 |pages=304–310 |date=1813 |url=https://books.google.com/books?id=YGwri-w7sMAC&pg=RA2-PA304|language=French}} In French, seaweed that had been washed onto the shore was called "varec", "varech", or "vareck", whence the English word "wrack". Later, "varec" also referred to the ashes of such seaweed: the ashes were used as a source of iodine and salts of sodium and potassium.</ref><ref>{{cite journal | vauthors = Swain PA |title=Bernard Courtois (1777–1838) famed for discovering iodine (1811), and his life in Paris from 1798 |journal=Bulletin for the History of Chemistry |volume=30 |issue=2 |page=103 |date=2005 |url=http://www.scs.uiuc.edu/~mainzv/HIST/awards/OPA%20Papers/2007-Swain.pdf |access-date=2 April 2009 |archive-url=https://web.archive.org/web/20100714110757/http://www.scs.uiuc.edu/~mainzv/HIST/awards/OPA%20Papers/2007-Swain.pdf |archive-date=14 July 2010 |url-status=dead }}</ref> who was born to a family of manufacturers of [[potassium nitrate|saltpetre]] (an essential component of [[gunpowder]]). At the time of the [[Napoleonic Wars]], saltpetre was in great demand in [[France]]. Saltpetre produced from French [[Potassium nitrate|nitre beds]] required [[sodium carbonate]], which could be isolated from [[seaweed]] collected on the coasts of [[Normandy]] and [[Brittany]]. To isolate the sodium carbonate, seaweed was burned and the ash washed with water. The remaining waste was destroyed by adding [[Sulfuric acid|sulphuricsulfuric acid]]. Courtois once added excessive sulphuricsulfuric acid and a cloud of violet vapour rose. He noted that the vapour crystallised on cold surfaces, making dark black crystals.<ref name="Greenwood794">Greenwood and Earnshaw, p. 794</ref> Courtois foundsuspected that this material was a new element and he did notbut havelacked funding to pursue it further.<ref name="vdK">{{cite web |url=http://elements.vanderkrogt.net/element.php?sym=i |title=53 Iodine |publisher=Elements.vanderkrogt.net |access-date=23 October 2016 |archive-date=23 January 2010 |archive-url=https://web.archive.org/web/20100123001444/http://elements.vanderkrogt.net/element.php?sym=I |url-status=live }}</ref>

So Courtois gave the samples to his friends, [[Charles Bernard Desormes]] (1777–1838) and [[Nicolas Clément]] (1779–1841), to continue research. He also gave some of the substance to chemist [[Joseph Louis Gay-Lussac]] (1778–1850), and to [[physicist]] [[André-Marie Ampère]] (1775–1836). On 29 November 1813, Desormes and Clément made Courtois' discovery public. Theyby describeddescribing the substance to a meeting of the Imperial [[Institut de France|Institute of France]].<ref>Desormes and Clément made their announcement at the Institut impérial de France on 29 November 1813; a summary of their announcement appeared in the ''Gazette nationale ou Le Moniteur Universel'' of 2 December 1813. See:

* {{cite journal |vauthors=Chattaway FD |title=The discovery of iodine |journal=Chemical News and Journal of Industrial Science |date=23 April 1909 |volume=99 |issue=2578 |pages=193–195 |url=https://books.google.com/books?id=Rco_AQAAIAAJ&pg=PA193 }}</ref> On 6 December 1813, Gay-Lussac found and announced that the new substance was either an element or a compound of [[oxygen]] with an another element and he found that it is an element without any oxygen in it.<ref name="Gay-Lussac">{{cite journal |vauthors=Gay-Lussac J |title=Sur un nouvel acide formé avec la substance décourverte par M. Courtois |trans-title=On a new acid formed by the substance discovered by Mr. Courtois |journal=Annales de Chimie |volume=88 |pages=311–318 |date=1813 |url=https://books.google.com/books?id=YGwri-w7sMAC&pg=PA311 |language=French |access-date=2 May 2021 |archive-date=19 March 2024 |archive-url=https://web.archive.org/web/20240319070023/https://books.google.com/books?id=YGwri-w7sMAC&pg=PA311#v=onepage&q&f=false |url-status=live }}</ref><ref>{{cite journal |vauthors=Gay-Lussac J |title=Sur la combination de l'iode avec d'oxigène |trans-title=On the combination of iodine with oxygen |journal=Annales de Chimie |volume=88 |pages=319–321 |date=1813 |url=https://books.google.com/books?id=YGwri-w7sMAC&pg=PA319 |language=French |access-date=2 May 2021 |archive-date=19 March 2024 |archive-url=https://web.archive.org/web/20240319070022/https://books.google.com/books?id=YGwri-w7sMAC&pg=PA319#v=onepage&q&f=false |url-status=live }}</ref><ref>{{cite journal| vauthors = Gay-Lussac J |title=Mémoire sur l'iode |trans-title=Memoir on iodine |journal=Annales de Chimie |volume=91 |pages=5–160|date=1814 |url=https://books.google.com/books?id=Efms0Fri1CQC&pg=PA5|language=French}}</ref> Gay-Lussac suggested the name "iode" (Englished[[Anglicisation (linguistics)|anglicized]] as "iodine"), from the [[Ancient Greek]] {{lang|grc|Ιώδης}} ({{transliteration|grc|iodēs}}, "violet"), because of the colour of iodine vapourvapor.<ref name="court" /><ref name="Gay-Lussac" /> Ampère had given some of his sample to British chemist [[Humphry Davy]] (1778–1829), who experimented on the substance and noted its similarity to [[chlorine]] and also found it as an element.<ref>{{cite journal |vauthors=Davy H |author-link=Humphry Davy |title=Sur la nouvelle substance découverte par M. Courtois, dans le sel de Vareck |trans-title=On the new substance discovered by Mr. Courtois in the salt of seaweed |journal=Annales de Chimie |volume=88 |pages=322–329 |date=1813 |url=https://books.google.com/books?id=YGwri-w7sMAC&pg=PA322 |language=French |access-date=2 May 2021 |archive-date=19 March 2024 |archive-url=https://web.archive.org/web/20240319070024/https://books.google.com/books?id=YGwri-w7sMAC&pg=PA322#v=onepage&q&f=false |url-status=live }}</ref> Davy sent a letter dated 10 December to the [[Royal Society|Royal Society of London]] stating that he had identified a new element called iodine.<ref>{{cite journal| vauthors = Davy H |author-link=Humphry Davy |title=Some experiments and observations on a new substance which becomes a violet coloured gas by heat |journal=Philosophical Transactions of the Royal Society of London |volume=104 |pages=74–93 |date=1 January 1814 |doi=10.1098/rstl.1814.0007 |doi-access=free }}</ref> Arguments erupted between Davy and Gay-Lussac over who identified iodine first, but both scientists found that both of them identified iodine first and also knew that Courtois is the first one to isolate the element.<ref name="vdK" />

Iodine is the fourth [[halogen]], being a member of group 17 in the periodic table, below [[fluorine]], [[chlorine]], and [[bromine]]; it is the heaviest stable member of its group. (The fifth and sixth halogens, the radioactive [[astatine]] and [[tennessine]], are not well-studied due to their expensivenessexpense and inaccessibility in large quantities, but appear to show various unusual properties for the group due to [[Relativistic quantum chemistry|relativistic effects]].) Iodine has an electron configuration of [Kr]4d¹⁰5s²5p⁵, with the seven electrons in the fifth and outermost shell being its [[valence electron]]s. Like the other halogens, it is one electron short of a full octet and is hence an oxidising agent, reacting with many elements in order to complete its outer shell, although in keeping with [[periodic trends]], it is the weakest oxidising agent among the stable halogens: it has the lowest [[electronegativity]] among them, just 2.66 on the Pauling scale (compare fluorine, chlorine, and bromine at 3.98, 3.16, and 2.96 respectively; astatine continues the trend with an electronegativity of 2.2). Elemental iodine hence forms [[diatomic molecule]]s with chemical formula I₂, where two iodine atoms share a pair of electrons in order to each achieve a stable octet for themselves; at high temperatures, these diatomic molecules reversibly dissociate a pair of iodine atoms. Similarly, the iodide anion, I⁻, is the strongest reducing agent among the stable halogens, being the most easily oxidised back to diatomic I₂.<ref name="Greenwood800">Greenwood and Earnshaw, pp. 800–4</ref> (Astatine goes further, being indeed unstable as At⁻ and readily oxidised to At⁰ or At⁺.)<ref>{{cite book | series = Gmelin Handbook of Inorganic and Organometallic Chemistry | title = 'At, Astatine', System No. 8a | edition=8th | year = 1985 | publisher = Springer-Verlag | isbn = 978-3-540-93516-2 | vauthors = Kugler HK, Keller C | volume = 8 }}</ref>

Iodine is quite reactive, but it is much less reactive than the other halogens. For example, while [[chlorine]] gas will [[Halogenation|halogenate]] [[carbon monoxide]], [[nitric oxide]], and [[sulfur dioxide|sulphur dioxide]] (to [[phosgene]], [[nitrosyl chloride]], and [[sulfuryl chloride|sulphuryl chloride]] respectively), iodine will not do so. Furthermore, iodination of metals tends to result in lower oxidation states than chlorination or bromination; for example, [[rhenium]] metal reacts with chlorine to form [[Rhenium(VI) chloride|rhenium hexachloride]], but with bromine it forms only rhenium pentabromide and iodine can achieve only rhenium tetraiodide.<ref name="Greenwood800" /> By the same token, however, since iodine has the lowest ionisation energy among the halogens and is the most easily oxidised of them, it has a more significant cationic chemistry and its higher oxidation states are rather more stable than those of bromine and chlorine, for example in [[iodine heptafluoride]].<ref name="Greenwood804" />

The simplest compound of iodine is [[hydrogen iodide]], HI. It is a colourless gas that reacts with oxygen to give water and iodine. Although it is useful in [[Halogenation|iodination]] reactions in the laboratory, it does not have large-scale industrial uses, unlike the other hydrogen halides. Commercially, it is usually made by reacting iodine with [[hydrogen sulfide|hydrogen sulphide]] or [[hydrazine]]:<ref name="Greenwood809">Greenwood and Earnshaw, pp. 809–12</ref>

[[Iodine oxide]]s are the most stable of all the halogen oxides, because of the strong I–O bonds resulting from the large electronegativity difference between iodine and oxygen, and they have been known for the longest time.<ref name="King" /> The stable, white, [[Hygroscopy|hygroscopic]] [[iodine pentoxide]] (I₂O₅) has been known since its formation in 1813 by Gay-Lussac and Davy. It is most easily made by the dehydration of [[iodic acid]] (HIO₃), of which it is the anhydride. It will quickly oxidise carbon monoxide completely to [[carbon dioxide]] at room temperature, and is thus a useful reagent in determining carbon monoxide concentration. It also oxidises [[nitrogen oxide]], [[ethylene]], and [[hydrogen sulfide|hydrogen sulphide]]. It reacts with [[sulfur trioxide|sulphur trioxide]] and peroxydisulphurylperoxydisulfuryl difluoride (S₂O₆F₂) to form salts of the iodyl cation, [IO₂]⁺, and is reduced by concentrated [[sulfuric acid|sulphuric acid]] to iodosyl salts involving [IO]⁺. It may be fluorinated by [[fluorine]], [[bromine trifluoride]], [[sulfur tetrafluoride|sulphur tetrafluoride]], or [[chloryl fluoride]], resulting [[iodine pentafluoride]], which also reacts with [[iodine pentoxide]], giving iodine(V) oxyfluoride, IOF₃. A few other less stable oxides are known, notably I₄O₉ and I₂O₄; their structures have not been determined, but reasonable guesses are I^III(I^VO₃)₃ and [IO]⁺[IO₃]⁻ respectively.<ref name="Greenwood851">Greenwood and Earnshaw, pp. 851–3</ref>

They are thermodymically and kinetically powerful oxidising agents, quickly oxidising Mn²⁺ to [[permanganate|{{chem|MnO|4|-}}]], and cleaving [[Diol|glycols]], α-[[Dicarbonyl|diketones]], α-[[Hydroxy ketone|ketols]], α-[[Alkanolamine|aminoalcohols]], and α-[[diamine]]s.<ref name="Greenwood872" /> Orthoperiodate especially stabilises high oxidation states among metals because of its very high negative charge of −5. [[Periodic acid|Orthoperiodic acid]], H₅IO₆, is stable, and dehydrates at 100&nbsp;°C in a vacuum to [[Periodic acid|Metaperiodic acid]], HIO₄. Attempting to go further does not result in the nonexistent iodine heptoxide (I₂O₇), but rather iodine pentoxide and oxygen. Periodic acid may be protonated by [[sulfuric acid|sulphuric acid]] to give the {{chem|I(OH)|6|+}} cation, isoelectronic to Te(OH)₆ and {{chem|Sb(OH)|6|-}}, and giving salts with bisulfate and sulfate.<ref name="King" />

When iodine dissolves in strong acids, such as fuming sulphuricsulfuric acid, a bright blue [[Paramagnetism|paramagnetic]] solution including {{chem|I|2|+}} cations is formed. A solid salt of the diiodine cation may be obtained by oxidising iodine with [[antimony pentafluoride]]:<ref name="King" />

The salt I₂Sb₂F₁₁ is dark blue, and the blue [[tantalum]] analogue I₂Ta₂F₁₁ is also known. Whereas the I–I bond length in I₂ is 267&nbsp;pm, that in {{chem|I|2|+}} is only 256&nbsp;pm as the missing electron in the latter has been removed from an antibonding orbital, making the bond stronger and hence shorter. In [[fluorosulfuric acid|fluorosulphuric acid]] solution, deep-blue {{chem|I|2|+}} reversibly dimerises below −60&nbsp;°C, forming red rectangular diamagnetic {{chem|I|4|2+}}. Other polyiodine cations are not as well-characterised, including bent dark-brown or black {{chem|I|3|+}} and centrosymmetric ''C''_2''h'' green or black {{chem|I|5|+}}, known in the {{chem|AsF|6|-}} and {{chem|AlCl|4|-}} salts among others.<ref name="King" /><ref name="Greenwood842">Greenwood and Earnshaw, pp. 842–4</ref>

Some drawbacks of using organoiodine compounds as compared to organochlorine or organobromine compounds is the greater expense and toxicity of the iodine derivatives, since iodine is expensive and organoiodine compounds are stronger alkylating agents.<ref>{{cite web|publisher = Oxford University|title = Safety data for iodomethane|url = http://msds.chem.ox.ac.uk/IO/iodomethane.html|access-date = 12 December 2008|archive-date = 10 August 2010|archive-url = https://web.archive.org/web/20100810211004/http://msds.chem.ox.ac.uk/IO/iodomethane.html|url-status = dead}}</ref> For example, [[iodoacetamide]] and [[iodoacetic acid]] denature proteins by irreversibly alkylating [[cysteine]] residues and preventing the reformation of [[disulfide|disulphide]] linkages.<ref>{{cite journal | vauthors = Polgár L | title = Deuterium isotope effects on papain acylation. Evidence for lack of general base catalysis and for enzyme--leaving-group interaction | journal = European Journal of Biochemistry | volume = 98 | issue = 2 | pages = 369–374 | date = August 1979 | pmid = 488108 | doi = 10.1111/j.1432-1033.1979.tb13196.x | doi-access = free }}</ref>

Iodine is the least abundant of the stable halogens, comprising only 0.46&nbsp;[[Parts-per notation|parts per million]] of Earth's crustal rocks (compare: [[fluorine]]: 544&nbsp;ppm, [[chlorine]]: 126&nbsp;ppm, [[bromine]]: 2.5&nbsp;ppm) making it the 60th most abundant element.<ref name="Greenwood795">Greenwood and Earnshaw, pp. 795–796.</ref> Iodide minerals are rare, and most deposits that are concentrated enough for economical extraction are iodate minerals instead. Examples include [[Calcium iodate|lautarite]], Ca(IO₃)₂, and dietzeite, 7Ca(IO₃)₂·8CaCrO₄.<ref name="Greenwood795" /> These are the minerals that occur as trace impurities in the [[caliche]], found in [[Chile]], whose main product is [[sodium nitrate]]. In total, they can contain at least 0.02% and at most 1% iodine by mass.<ref name="Elzea">{{cite book |title = Industrial Minerals & Rocks: Commodities, Markets, and Uses |publisher = SME |date = 2006 |isbn = 978-0-87335-233-8 |url = https://books.google.com/books?id=zNicdkuulE4C |pages = 541–552 | veditors = Kogel JE, Trivedi NC, Barker JM, Krukowski ST }}</ref> [[Sodium iodate]] is extracted from the caliche and reduced to iodide by [[sodium bisulfite|sodium bisulphite]]. This solution is then reacted with freshly extracted iodate, resulting in comproportionation to iodine, which may be filtered off.<ref name="Greenwood800" />

The caliche was the main source of iodine in the 19th century and continues to be important today, replacing [[kelp]] (which is no longer an economically viable source),<ref>{{cite journal |url = https://books.google.com/books?id=wW8KAAAAIAAJ&pg=PA185 | vauthors = Stanford EC |journal = Journal of the Society of Arts |title = On the Economic Applications of Seaweed |date = 1862 |pages = 185–189}}</ref> but in the late 20th century [[brine]]s emerged as a comparable source. The Japanese [[Minami Kantō gas field]] east of [[Tokyo]] and the American [[Anadarko Basin]] gas field in northwest [[Oklahoma]] are the two largest such sources. The brine is hotter than 60&nbsp;°C from the depth of the source. The [[brine]] is first [[List of purification methods in chemistry|purified]] and acidified using [[sulfuric acid|sulphuric acid]], then the iodide present is oxidised to iodine with [[chlorine]]. An iodine solution is produced, but is dilute and must be concentrated. Air is blown into the solution to [[Evaporation|evaporate]] the iodine, which is passed into an absorbing tower, where [[sulfur dioxide|sulphur dioxide]] reduces the iodine. The [[hydrogen iodide]] (HI) is reacted with chlorine to precipitate the iodine. After filtering and purification the iodine is packed.<ref name="Elzea" /><ref>{{cite journal |journal = Geochemical Journal |volume = 40 |page = 475 |date = 2006 |title = Chemical and isotopic compositions of brines from dissolved-in-water type natural gas fields in Chiba, Japan | vauthors = Maekawa T, Igari SI, Kaneko N |doi = 10.2343/geochemj.40.475 |issue = 5 |bibcode = 2006GeocJ..40..475M|doi-access = free }}</ref>

These sources ensure that Chile and Japan are the largest producers of iodine today.<ref name="Greenwood795" /> AlsoAlternatively, the brine ismay be treated with [[silver nitrate]] to precipitate out iodine as [[silver iodide]], which is then decomposed by reaction with iron to form metallic silver and a solution of [[iron(II) iodide]]. The iodine is then liberated by displacement with [[chlorine]].<ref name="Greenwood799">Greenwood and Earnshaw, p. 799.</ref>

[[Ion thruster]] propulsion systems employing iodine as the [[working mass|reaction mass]] can be built more compactly, with less mass (and cost), and operate more efficiently than the [[gridded ion thruster]]s that were utilized to propel previous spacecraft, such as Japan's [[Hayabusa]] probes, ESA's [[Gravity Field and Steady-State Ocean Circulation Explorer|GOCE]] satellite, or NASA's [[Double Asteroid Redirection Test|DART]] mission, all of which used xenon for this purpose. Iodine's [[Standard atomic weight|atomic weight]] is only 3.3% less than that of xenon, while its first two [[Ionization energy|ionisation energies]] average 12% less; together, these make iodine ions a promising substitute.<ref name="ThrustMe1">{{cite journal |vauthors=Rafalskyi D, Martínez JM, Habl L, Zorzoli Rossi E, Proynov P, Boré A, Baret T, Poyet A, Lafleur T, Dudin S, Aanesland A |date=November 2021 |title=In-orbit demonstration of an iodine electric propulsion system |journal=Nature |volume=599 |issue=7885 |pages=411–415 |bibcode=2021Natur.599..411R |doi=10.1038/s41586-021-04015-y |pmc=8599014 |pmid=34789903 |quote=''Both atomic and molecular iodine ions are accelerated by high-voltage grids to generate thrust, and a highly collimated beam can be produced with substantial iodine dissociation.''}}</ref><ref name="ThrustMe2">{{cite web |url=https://www.cnet.com/news/in-a-space-first-scientists-test-ion-thrusters-powered-by-iodine/ |title=In a space first, scientists test ion thrusters powered by iodine |vauthors=Ravisetti M |date=18 November 2021 |website=[[CNET]] |publisher=[[Red Ventures]] |access-date=2021-11-29 |archive-date=27 November 2021 |archive-url=https://web.archive.org/web/20211127105437/https://www.cnet.com/news/in-a-space-first-scientists-test-ion-thrusters-powered-by-iodine/ |url-status=live }}</ref> However, iodine introduces chemical reactivity issues not present in xenon plasmas.<ref>Rogers, James Daniel. ''Hollow Cathode Materials in an Iodine Plasma EnviromentEnvironment''. Diss. The University of Alabama, 2023.</ref>

[[File:Diatrizoic acid.svg|thumb|right|[[Diatrizoate|Diatrizoic acid]], an iodine-containing radiocontrastradio[[contrast agent]]]]

The organoiodine compound [[erythrosine]] is an important food coloring agent. Perfluoroalkyl iodides are precursors to important surfactants, such as [[perfluorooctanesulfonic acid|perfluorooctanesulphonic acid]].<ref name = Ullmann/>

The daily levels of intake recommended by the [[United States]] [[National Academy of Medicine]] are between 110 and 130 [[microgram|µgμg]] for infants up to 12 months, 90&nbsp;µgμg for children up to eight years, 130&nbsp;µgμg for children up to 13 years, 150&nbsp;µgμg for adults, 220&nbsp;µgμg for pregnant women and 290&nbsp;µgμg for lactating women.<ref name="lpi" /><ref>{{cite web|url=http://iom.edu/en/Global/News%20Announcements/~/media/Files/Activity%20Files/Nutrition/DRIs/DRISummaryListing2.ashx |archive-url=https://web.archive.org/web/20091030004039/http://iom.edu/en/Global/News%20Announcements/~/media/Files/Activity%20Files/Nutrition/DRIs/DRISummaryListing2.ashx |url-status=dead |archive-date=30 October 2009 |title=Dietary Reference Intakes (DRIs): Recommended Intakes for Individuals, Vitamins |publisher=[[Institute of Medicine]] |date=2004 |access-date=9 June 2010 }}</ref> The Tolerable Upper Intake Level (TUIL) for adults is 1,100&nbsp;μg/day.<ref name="InstituteofMedicine">{{cite book| author = United States National Research Council| date = 2000| title = Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc| pages = 258–259| publisher = National Academies Press| url = http://books.nap.edu/openbook.php?record_id=10026&page=258| doi = 10.17226/10026| pmid = 25057538| isbn = 978-0-309-07279-3| access-date = 9 March 2008| archive-date = 25 July 2015| archive-url = https://web.archive.org/web/20150725203752/http://books.nap.edu/openbook.php?record_id=10026&page=258| url-status = live}}</ref> This upper limit was assessed by analyzing the effect of supplementation on [[thyroid-stimulating hormone]].<ref name="Patrick2008" />

As of 2000, the median intake of iodine from food in the United States was 240 to 300&nbsp;μg/day for men and 190 to 210&nbsp;μg/day for women.<ref name="InstituteofMedicine" /> The general US population has adequate iodine nutrition,<ref>{{cite journal | vauthors = Caldwell KL, Makhmudov A, Ely E, Jones RL, Wang RY | title = Iodine status of the U.S. population, National Health and Nutrition Examination Survey, 2005–2006 and 2007–2008 | journal = Thyroid | volume = 21 | issue = 4 | pages = 419–427 | date = April 2011 | pmid = 21323596 | doi = 10.1089/thy.2010.0077 | url = https://zenodo.org/record/1235283 | access-date = 29 September 2020 | archive-date = 2 December 2022 | archive-url = https://web.archive.org/web/20221202135223/https://zenodo.org/record/1235283 | url-status = live }}</ref><ref name="Lueng">{{cite journal | vauthors = Leung AM, Braverman LE, Pearce EN | title = History of U.S. iodine fortification and supplementation | journal = Nutrients | volume = 4 | issue = 11 | pages = 1740–1746 | date = November 2012 | pmid = 23201844 | pmc = 3509517 | doi = 10.3390/nu4111740 | doi-access = free }}</ref> with lactating women and pregnant women having a mild risk of deficiency.<ref name="Lueng" /> In Japan, consumption was considered much higher, ranging between 5,280&nbsp;μg/day to 13,800&nbsp;μg/day from [[wakame]] and [[kombu]] that are eaten,<ref name="Patrick2008">{{cite journal | vauthors = Patrick L | title = Iodine: deficiency and therapeutic considerations | journal = Alternative Medicine Review | volume = 13 | issue = 2 | pages = 116–127 | date = June 2008 | pmid = 18590348 | url = http://www.thorne.com/altmedrev/.fulltext/13/2/116.pdf | url-status = dead | archive-url = https://web.archive.org/web/20130531112100/http://www.thorne.com/altmedrev/.fulltext/13/2/116.pdf | archive-date = 31 May 2013 }}</ref> both in the form of kombu and wakame and kombu and wakame [[umami]] [[Extract|extracts]] for [[Stock (food)|soup stock]] and [[Potato chip|potato chips]]. However, new studies suggest that Japan's consumption is closer to 1,000–3,000&nbsp;μg/day.<ref>{{cite journal | vauthors = Zava TT, Zava DT | title = Assessment of Japanese iodine intake based on seaweed consumption in Japan: A literature-based analysis | journal = Thyroid Research | volume = 4 | pages = 14 | date = October 2011 | pmid = 21975053 | pmc = 3204293 | doi = 10.1186/1756-6614-4-14 | doi-access = free }}</ref> The adult UL in Japan was last revised to 3,000&nbsp;µgμg/day in 2015.<ref>{{cite web |title=Overview of Dietary Reference Intakes for Japanese (2015) |publisher=Minister of Health, Labour and Welfare, Japan |url=http://www.mhlw.go.jp/file/06-Seisakujouhou-10900000-Kenkoukyoku/Overview.pdf |access-date=14 March 2022 |archive-date=23 April 2021 |archive-url=https://web.archive.org/web/20210423083531/https://www.mhlw.go.jp/file/06-Seisakujouhou-10900000-Kenkoukyoku/Overview.pdf |url-status=live }}</ref>