View source for Iodine-131

{{Short description|Isotope of iodine}}
{{Infobox isotope
 | alternate_names =radioiodine
 | symbol =I
 | mass_number =131
 | mass =130.90612638(65){{AME2020 II|ref}}
 | num_neutrons =78
 | num_protons =53
 | abundance =
 | halflife ={{val|8.0249|(6)|u=days}}{{NUBASE2020|ref}}
 | error_halflife =
 | image =Iodine-131.svg
 | decay_product = xenon-131
 | decay_symbol = Xe
 | decay_mass = 131
 | decay_mode1 = [[beta decay|β<sup>−</sup>]] + [[Gamma ray#Radioactive decay (gamma decay)|γ]]
 | decay_energy1 = 0.970789
 | decay_mode2 =
 | decay_energy2 =
 | decay_mode3 =
 | decay_energy3 =
 | decay_mode4 =
 | decay_energy4 =
 | parent =
 | parent_symbol =
 | parent_mass =
 | parent_decay =
 | parent2 =
 | parent2_symbol =
 | parent2_mass =
 | parent2_decay =
 | spin = 7/2+<ref name="NUBASE2020"/>
 | excess_energy = 
 | binding_energy =
}}

'''Iodine-131''' ('''<sup>131</sup>I''', '''I-131''') is an important [[radioisotope]] of [[iodine]] discovered by [[Glenn Seaborg]] and [[John Livingood]] in 1938 at the University of California, Berkeley.<ref>{{cite web |date=April 2008 |url=http://uwlbrachycourse.wikifoundry.com/page/Iodine-131 |title=UW-L Brachy Course |publisher=wikifoundry |access-date=2014-04-11 |archive-date=15 April 2019 |archive-url=https://web.archive.org/web/20190415035202/http://uwlbrachycourse.wikifoundry.com/page/Iodine-131 |url-status=dead }}</ref> It has a radioactive decay half-life of about eight days. It is associated with nuclear energy, medical diagnostic and treatment procedures, and natural gas production. It also plays a major role as a radioactive isotope present in [[nuclear fission]] products, and was a significant contributor to the health hazards from open-air atomic bomb testing in the 1950s, and from the [[Chernobyl disaster]], as well as being a large fraction of the contamination hazard in the first weeks in the [[Fukushima Daiichi nuclear disaster|Fukushima nuclear crisis]]. This is because <sup>131</sup>I is a major [[fission product]] of [[uranium]] and [[plutonium]], comprising nearly 3% of the total products of fission (by weight). See [[fission product yield]] for a comparison with other radioactive fission products. <sup>131</sup>I is also a major fission product of [[uranium-233]], produced from [[thorium]].

Due to its mode of [[beta decay]], iodine-131 causes [[mutation]] and death in cells that it penetrates, and other cells up to several millimeters away. For this reason, high doses of the isotope are sometimes less dangerous than low doses, since they tend to kill [[thyroid]] tissues that would otherwise become cancerous as a result of the radiation. For example, children treated with moderate dose of <sup>131</sup>I for thyroid adenomas had a detectable increase in thyroid cancer, but children treated with a much higher dose did not.<ref>{{Cite journal|last1=Dobyns|first1=B. M.|last2=Sheline|first2=G. E.|last3=Workman|first3=J. B.|last4=Tompkins|first4=E. A.|last5=McConahey|first5=W. M.|last6=Becker|first6=D. V.|date=June 1974|title=Malignant and benign neoplasms of the thyroid in patients treated for hyperthyroidism: a report of the cooperative thyrotoxicosis therapy follow-up study|journal=The Journal of Clinical Endocrinology and Metabolism|volume=38|issue=6|pages=976–998|doi=10.1210/jcem-38-6-976|issn=0021-972X|pmid=4134013}}</ref> Likewise, most studies of very-high-dose <sup>131</sup>I for treatment of [[Graves' disease]] have failed to find any increase in thyroid cancer, even though there is linear increase in thyroid cancer risk with <sup>131</sup>I absorption at moderate doses.<ref name="Rivkees">{{cite journal |title=The Management of Graves' Disease in Children, with Special Emphasis on Radioiodine Treatment |year=1998 |last1=Rivkees |first1=Scott A. |first2=Charles |last2=Sklar |first3=Michael |last3=Freemark |journal=Journal of Clinical Endocrinology & Metabolism |volume=83 |issue=11 |pmid=9814445 |pages=3767–76|doi=10.1210/jcem.83.11.5239 |doi-access=free }}</ref> Thus, iodine-131 is increasingly less employed in small doses in medical use (especially in children), but increasingly is used only in large and maximal treatment doses, as a way of killing targeted tissues. This is known as "therapeutic use".

Iodine-131 can be "seen" by [[nuclear medicine]] imaging techniques (e.g., [[gamma camera]]s) whenever it is given for therapeutic use, since about 10% of its energy and radiation dose is via gamma radiation. However, since the other 90% of radiation (beta radiation) causes tissue damage without contributing to any ability to see or "image" the isotope, other less-damaging radioisotopes of iodine such as [[iodine-123]] (see [[isotopes of iodine]]) are preferred in situations when ''only'' nuclear imaging is required. The isotope <sup>131</sup>I is still occasionally used for purely diagnostic (i.e., imaging) work, due to its low expense compared to other iodine radioisotopes. Very small medical imaging doses of <sup>131</sup>I have not shown any increase in thyroid cancer. The low-cost availability of <sup>131</sup>I, in turn, is due to the relative ease of creating <sup>131</sup>I by neutron bombardment of natural [[tellurium]] in a nuclear reactor, then separating <sup>131</sup>I out by various simple methods (i.e., heating to drive off the volatile iodine). By contrast, other iodine radioisotopes are usually created by far more expensive techniques, starting with cyclotron radiation of capsules of pressurized [[xenon]] gas.<ref>{{cite journal |last1=Rayyes |first1=Al |last2=Hamid |first2=Abdul |title=Technical meeting of project counterparts on cyclotron production of I-123 |url=https://inis.iaea.org/search/search.aspx?orig_q=RN:33007368 |website=International Nuclear Information System |publisher=[[IAEA]] |language=English |format=pdf |date=2002}}</ref>

Iodine-131 is also one of the most commonly used gamma-emitting [[radioactive tracer#Applications|radioactive industrial tracer]]. Radioactive tracer isotopes are injected with [[hydraulic fracturing]] fluid to determine the injection profile and location of fractures created by hydraulic fracturing.<ref name="Reis_iodine">Reis, John C. (1976). ''Environmental Control in Petroleum Engineering.'' Gulf Professional Publishers.</ref>

Much smaller incidental doses of iodine-131 than those used in medical therapeutic procedures, are supposed by some studies to be the major cause of [[radiation-induced cancer|increased thyroid cancer]]s after accidental nuclear contamination. These studies suppose that cancers happen from residual tissue radiation damage caused by the <sup>131</sup>I, and should appear mostly years after exposure, long after the <sup>131</sup>I has decayed.<ref name="Simon">{{cite journal|last1=Simon|first1=Steven L.|first2=André |last2=Bouville |first3=Charles E. |last3=Land|title=Fallout from Nuclear Weapons Tests and Cancer Risks|journal=American Scientist|date=January–February 2006|volume=94|pages=48–57| doi=10.1511/2006.1.48 |quote=In 1997, NCI conducted a detailed evaluation of dose to the thyroid glands of U.S. residents from I-131 in fallout from tests in Nevada. (...) we evaluated the risks of thyroid cancer from that exposure and estimated that about 49,000 fallout-related cases might occur in the United States, almost all of them among persons who were under age 20 at some time during the period 1951–57, with 95-percent uncertainty limits of 11,300 and 212,000.}}</ref><ref>{{cite web |url=https://ntsi131.nci.nih.gov/ |title=National Cancer Institute calculator for thyroid cancer risk as a result of I-131 intake after nuclear testing before 1971 in Nevada |publisher=Ntsi131.nci.nih.gov |access-date=2012-06-17 |archive-url=https://web.archive.org/web/20120723085146/https://ntsi131.nci.nih.gov/ |archive-date=23 July 2012 |url-status=dead  }}</ref> Other studies did not find a correlation.<ref>{{cite journal|last1=Guiraud-Vitaux|first1=F.|last2=Elbast|first2= M.|last3= Colas-Linhart|first3= N.|last4= Hindie|first4= E.|title=Thyroid cancer after Chernobyl: is iodine 131 the only culprit ? Impact on clinical practice|journal=Bulletin du Cancer|date=February 2008|volume=95|issue=2|pages=191–5|pmid=18304904|doi=10.1684/bdc.2008.0574|doi-broken-date=1 November 2024 <!-- reported to DOI 2025-02-10 -->}}</ref><ref>{{cite book|title=The Hanford Thyroid Disease Study|year=2002|url=https://www.cdc.gov/nceh/radiation/hanford/htdsweb/pdf/htdsreport.pdf|author=Centre for Disease Control|access-date=17 June 2012|quote=no associations between Hanford's iodine-131 releases and thyroid disease were observed. [The findings] show that if there is an increased risk of thyroid disease from exposure to Hanford's iodine-131, it is probably too small to observe using the best epidemiologic methods available|author-link=Centre for Disease Control}} [https://www.cdc.gov/nceh/radiation/hanford/htdsweb/pdf/htds_aag.pdf Executive summary]</ref>

==Production==
Most <sup>131</sup>I production is from neutron [[irradiation]] of a natural tellurium target in a nuclear reactor. Irradiation of natural tellurium produces almost entirely <sup>131</sup>I as the only radionuclide with a half-life longer than hours, since most lighter [[isotopes of tellurium]] become heavier stable isotopes, or else stable iodine or xenon. However, the heaviest naturally occurring tellurium nuclide, <sup>130</sup>Te (34% of natural tellurium) absorbs a neutron to become tellurium-131, which beta decays with a half-life of 25 minutes to <sup>131</sup>I.

A tellurium compound can be irradiated while bound as an oxide to an ion exchange column, with evolved <sup>131</sup>I then [[eluted]] into an alkaline solution.<ref>{{cite journal |doi=10.1016/j.apradiso.2010.04.033 |title=Recovery of 131I from alkaline solution of n-irradiated tellurium target using a tiny Dowex-1 column |year=2010 |last1=Chattopadhyay |first1=Sankha |last2=Saha Das |first2=Sujata |journal=Applied Radiation and Isotopes |volume=68 |issue=10 |pages=1967–9 |pmid=20471848}}</ref> More commonly, powdered elemental tellurium is irradiated and then <sup>131</sup>I separated from it by dry distillation of the iodine, which has a far higher [[vapor pressure]]. The element is then dissolved in a mildly alkaline solution in the standard manner, to produce <sup>131</sup>I as iodide and hypoiodate (which is soon reduced to iodide).<ref>{{cite web |date=August 2011 |url=http://www.mds.nordion.com/documents/products/I-131_Solu_Can.pdf |title=I-131 Fact Sheet |publisher=Nordion |access-date=2010-10-26 }}{{dead link|date=September 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

<sup>131</sup>I is a [[fission product]] with a [[fission product yield|yield]] of 2.878% from [[uranium-235]],<ref>{{cite web |url=http://www-nds.iaea.org/sgnucdat/c3.htm |title=Nuclear Data for Safeguards, Table C-3, Cumulative Fission Yields |publisher=International Atomic Energy Agency |access-date=14 March 2011}} (thermal neutron fission)</ref> and can be released in [[nuclear weapons tests]] and [[nuclear accident]]s. However, the short half-life means it is not present in significant quantities in cooled [[spent nuclear fuel]], unlike [[iodine-129]] whose half-life is nearly a billion times that of <sup>131</sup>I.

It is discharged to the atmosphere in small quantities by some nuclear power plants.<ref name=":0">{{Cite book|url=https://www.ncbi.nlm.nih.gov/books/NBK201991/|title=Effluent Releases from Nuclear Power Plants and Fuel-Cycle Facilities|date=2012-03-29|publisher=National Academies Press (US)}}</ref>

==Radioactive decay==
[[File:Iodine-131-decay-scheme-simplified.svg|thumb|left|300px|Iodine-131 decay scheme (simplified)]]
<sup>131</sup>I decays with a [[half-life]] of 8.0249(6)&nbsp;days<ref name="NUBASE2020"/> with [[beta emission|beta minus]] and [[gamma ray|gamma]] emissions. This [[isotope]] of iodine has 78 [[neutron]]s in its nucleus, while the only stable nuclide, <sup>127</sup>I, has 74. On decaying, <sup>131</sup>I most often (89% of the time) expends its 971&nbsp;keV of decay energy by transforming into stable xenon-131 in two steps, with gamma decay following rapidly after beta decay:

:<chem> ^{131}_{53}I -> \beta{} + \bar\nu_e + ^{131}_{54}Xe^\ast{} + 606 keV</chem>
:<chem>^{131}_{54}Xe^\ast -> ^{131}_{54}Xe + \gamma{} + 364 keV</chem>

The primary emissions of <sup>131</sup>I decay are thus electrons with a maximal energy of 606&nbsp;keV (89% abundance, others 248–807&nbsp;keV) and 364&nbsp;keV gamma rays (81% abundance, others 723&nbsp;keV).<ref>{{cite web | url = http://hpschapters.org/northcarolina/NSDS/131IPDF.pdf | title = Nuclide Safety Data Sheet| access-date=2010-10-26}}</ref> Beta decay also produces an [[antineutrino]], which carries off variable amounts of the beta decay energy. The electrons, due to their high mean energy (190&nbsp;keV, with typical beta-decay spectra present) have a tissue penetration of {{nowrap|0.6&nbsp;to&nbsp;2&nbsp;mm}}.<ref>{{cite book |isbn=978-1-59624-021-6 |page=[https://archive.org/details/thyroiddisorders00mari/page/82 82] |title=Thyroid Disorders |series=A Cleveland Clinic Guide |first=Mario |last=Skugor |publisher=Cleveland Clinic Press |year=2006 |url-access=registration |url=https://archive.org/details/thyroiddisorders00mari/page/82 }}</ref>

==Effects of exposure==
[[File:US fallout exposure.png|right|thumb|Per capita [[thyroid]] doses in the continental United States resulting from all exposure routes from all atmospheric [[nuclear testing|nuclear tests]] conducted at the [[Nevada Test Site]] from 1951 to 1962. A [[Centers for Disease Control and Prevention]]/ [[National Cancer Institute]] study claims that nuclear fallout might have led to approximately 11,000 excess deaths, most caused by [[thyroid cancer]] linked to exposure to iodine-131.<ref>{{cite book |url=https://nap.nationalacademies.org/catalog/10621/exposure-of-the-american-population-to-radioactive-fallout-from-nuclear-weapons-tests |title=Exposure of the American Population to Radioactive Fallout from Nuclear Weapons Tests: A Review of the CDC-NCI Draft Report on a Feasibility Study of the Health Consequences to the American Population from Nuclear Weapons Tests Conducted by the United States and Other Nations |author=National Research Council |date=11 February 2003 |publisher=[[National Academies Press]] |publication-place=Washington, D.C. |access-date=10 February 2025 |doi=10.17226/10621 |pmid=25057651 |isbn=978-0-309-08713-1 }}</ref>]]

Iodine in food is absorbed by the body and preferentially concentrated in the [[thyroid]] where it is needed for the functioning of that gland. When <sup>131</sup>I is present in high levels in the environment from [[radioactive fallout]], it can be absorbed through contaminated food, and will also accumulate in the thyroid. As it decays, it may cause damage to the thyroid. The primary risk from exposure to <sup>131</sup>I is an increased risk of [[radiation-induced cancer]] in later life. Other risks include the possibility of non-cancerous growths and [[thyroiditis]].<ref name="Rivkees"/>

The risk of thyroid cancer in later life appears to diminish with increasing age at time of exposure. Most risk estimates are based on studies in which radiation exposures occurred in children or teenagers. When adults are exposed, it has been difficult for epidemiologists to detect a statistically significant difference in the rates of thyroid disease above that of a similar but otherwise-unexposed group.<ref name="Rivkees"/><ref name="RobbinsSchneider2000">{{cite journal |last1=Robbins |first1=Jacob |last2=Schneider |first2=Arthur B. |title=Thyroid cancer following exposure to radioactive iodine |journal=Reviews in Endocrine and Metabolic Disorders |volume=1 |issue=3 |year=2000 |pages=197–203 |issn=1389-9155 |doi=10.1023/A:1010031115233 |pmid=11705004|s2cid=13575769 }}</ref>

The risk can be mitigated by taking iodine supplements, raising the total amount of iodine in the body and, therefore, reducing uptake and retention in the face and chest and lowering the relative proportion of radioactive iodine. However, such supplements were not consistently distributed to the population living nearest to the [[Chernobyl disaster|Chernobyl]] nuclear power plant after the disaster,<ref>{{cite web|url=http://www.ecolo.org/documents/documents_in_english/Causes.ChernobyJF.doc |title=The Causes of the Chernobyl Event |publisher=Ecolo.org |access-date=2012-06-17 |first=Jacques |last=Frot}}</ref> though they were widely distributed to children in Poland.

Within the US, the highest <sup>131</sup>I fallout doses occurred during the 1950s and early 1960s to children having consumed fresh milk from sources contaminated as the result of above-ground testing of nuclear weapons.<ref name="Simon"/> The [[National Cancer Institute]] provides additional information on the health effects from exposure to <sup>131</sup>I in fallout,<ref>{{cite web |title=Radioactive I-131 from Fallout |url=http://www.cancer.gov/i131 |publisher=National Cancer Institute |access-date=2007-11-14}}</ref> as well as individualized estimates, for those born before 1971, for each of the 3070 counties in the USA. The calculations are taken from data collected regarding fallout from the nuclear weapons tests conducted at the [[Nevada Test Site]].<ref>{{cite web |title=Individual Dose and Risk Calculator for Nevada Test Site fallout |url=http://ntsi131.nci.nih.gov/ |date=1 October 2007 |publisher=National Cancer Institute |access-date=2007-11-14 |url-status=dead |archive-url=https://web.archive.org/web/20071018051014/http://ntsi131.nci.nih.gov/ |archive-date=18 October 2007  }}</ref>

On 27 March 2011, the Massachusetts Department of Public Health reported that <sup>131</sup>I was detected in very low concentrations in rainwater from samples collected in Massachusetts, USA, and that this likely originated from the Fukushima power plant.<ref>{{cite web |url=http://www.thebostonchannel.com/r-video/27338488/detail.html |title=Low Concentrations Of Radiation Found In Mass. &#124; WCVB Home – WCVB Home |publisher=Thebostonchannel.com |date=2011-03-27 |access-date=2012-06-17 |url-status=dead |archive-url=https://web.archive.org/web/20120403035702/http://www.thebostonchannel.com/r-video/27338488/detail.html |archive-date=3 April 2012  }}</ref> Farmers near the plant dumped raw milk, while testing in the United States found 0.8 pico-[[Curie (unit)|curies]] per liter of iodine-131 in a milk sample, but the radiation levels were 5,000 times lower than the FDA's "defined intervention level".
The levels were expected to drop relatively quickly<ref>[http://www.latimes.com/news/nationworld/nation/la-fgw-japan-radiation-milk-20110331,0,4354119.story?track=rss "Traces of radioactive iodine found in Washington state milk" Los Angeles Times]{{dead link|date=June 2021|bot=medic}}{{cbignore|bot=medic}}</ref>

===Treatment and prevention===
{{See also|Potassium iodide}}

A common treatment method for preventing iodine-131 exposure is by saturating the thyroid with regular, stable [[iodine-127]], as an iodide or [[iodate]] salt.

==Medical use==
[[File:Pheochromocytoma Scan.jpg|thumb|upright|A [[pheochromocytoma]] tumor is seen as a dark sphere in the center of the body (it is in the left adrenal gland). The image is by [[MIBG]] [[scintigraphy]], showing the tumor by radiation from radioiodine in the MIBG. Two images are seen of the same patient from front and back. The image of the thyroid in the neck is due to unwanted uptake of radioiodine (as iodide) by the thyroid, after breakdown of the radioactive iodine-containing medication. Accumulation at the sides of the head is from salivary gland due to uptake of I-131 mIBG by the sympathetic neuronal elements in the salivary glands. Meta-[I-131]iodobenzylguanidine is a radio-labeled analog of the adrenergic blocking agent guanethidine.<ref>Nakajo, M., Shapiro, B. Sisson, J.C., Swanson, D.P., and Beierwaltes, W.H. Salivary gland uptake of Meta-[I131]Iodobenzylguanidine. J Nucl Med 25:2–6, 1984</ref> Radioactivity is also seen from uptake by the liver, and excretion by the kidneys with accumulation in the bladder.]]
Iodine-131 is used for [[unsealed source radiotherapy]] in [[nuclear medicine]] to treat several conditions. It can also be detected by [[gamma camera]]s for [[diagnostic imaging]], however it is rarely administered for diagnostic purposes only, imaging will normally be done following a therapeutic dose.<ref>{{cite book |last1=Carpi |first1=Angelo |last2=Mechanick |first2=Jeffrey I. |title=Thyroid Cancer: From Emergent Biotechnologies to Clinical Practice Guidelines |date=2016 |publisher=CRC Press |isbn=9781439862223 |page=148 |url=https://books.google.com/books?id=nQwrGfR1rZoC&pg=PA148 }}</ref> Use of the <sup>131</sup>I as [[iodide]] salt exploits the mechanism of absorption of iodine by the normal cells of the [[thyroid]] gland.

=== Treatment of thyrotoxicosis ===
Major uses of <sup>131</sup>I include the treatment of [[thyrotoxicosis]] (hyperthyroidism) due to [[Graves' disease]], and sometimes hyperactive thyroid nodules (abnormally active thyroid tissue that is not malignant). The therapeutic use of radioiodine to treat hyperthyroidism from Graves' disease was first reported by [[Saul Hertz]] in 1941. The dose is typically administered orally (either as a liquid or capsule), in an [[outpatient]] setting, and is usually 400–600 [[megabecquerel]]s (MBq).<ref name="EANMablation">{{cite journal |last1=Stokkel |first1=Marcel P. M. |last2=Handkiewicz Junak |first2=Daria |last3=Lassmann |first3=Michael |last4=Dietlein |first4=Markus |last5=Luster |first5=Markus |title=EANM procedure guidelines for therapy of benign thyroid disease |journal=European Journal of Nuclear Medicine and Molecular Imaging |date=13 July 2010 |volume=37 |issue=11 |pages=2218–2228 |doi=10.1007/s00259-010-1536-8 |pmid=20625722|s2cid=9062561 }}</ref> Radioactive iodine (iodine-131) alone can potentially worsen thyrotoxicosis in the first few days after treatment. One side effect of treatment is an initial period of a few days of increased hyperthyroid symptoms. This occurs because when the radioactive iodine destroys the thyroid cells, they can release thyroid hormone into the blood stream. For this reason, sometimes patients are pre-treated with thyrostatic medications such as methimazole, and/or they are given symptomatic treatment such as propranolol. Radioactive iodine treatment is contraindicated in breast-feeding and pregnancy<ref>Brunton, Laurence L. et al. Goodman & Gilman's The Pharmacological Basis of Therapeutics, 12e. 2011. Chapter 39</ref>

===Treatment of thyroid cancer===

Iodine-131, in higher doses than for thyrotoxicosis, is used for ablation of remnant thyroid tissue following a complete [[thyroidectomy]] to treat [[thyroid cancer]].<ref>{{cite journal |last1=Silberstein |first1=E. B. |last2=Alavi |first2=A. |last3=Balon |first3=H. R. |last4=Clarke |first4=S. E. M. |last5=Divgi |first5=C. |last6=Gelfand |first6=M. J. |last7=Goldsmith |first7=S. J. |last8=Jadvar |first8=H. |last9=Marcus |first9=C. S. |last10=Martin |first10=W. H. |last11=Parker |first11=J. A. |last12=Royal |first12=H. D. |last13=Sarkar |first13=S. D. |last14=Stabin |first14=M. |last15=Waxman |first15=A. D. |title=The SNMMI Practice Guideline for Therapy of Thyroid Disease with 131I 3.0 |journal=Journal of Nuclear Medicine |date=11 July 2012 |volume=53 |issue=10 |pages=1633–1651 |doi=10.2967/jnumed.112.105148|pmid=22787108 |s2cid=13558098 |doi-access=free }}</ref><ref name="EANMablation" />

====Administration of I-131 for ablation====
Typical therapeutic doses of I-131 are between 2220 and 7400 [[megabecquerel]]s (MBq).<ref>{{Cite journal|last1=Yama|first1=Naoya|last2=Sakata|first2=Koh-ichi|last3=Hyodoh|first3=Hideki|last4=Tamakawa|first4=Mitsuharu|last5=Hareyama|first5=Masato|date=June 2012|title=A retrospective study on the transition of radiation dose rate and iodine distribution in patients with I-131-treated well-differentiated thyroid cancer to improve bed control shorten isolation periods|journal=Annals of Nuclear Medicine|volume=26|issue=5|pages=390–396|doi=10.1007/s12149-012-0586-3|issn=1864-6433|pmid=22382609|s2cid=19799564}}</ref> Because of this high radioactivity and because the exposure of stomach tissue to [[Beta particle|beta radiation]] would be high near an undissolved capsule, I-131 is sometimes administered to human patients in a small amount of liquid. Administration of this liquid form is usually by straw which is used to slowly and carefully suck up the liquid from a shielded container.<ref>{{cite journal | pmc = 2934601 | pmid=20844671 | doi=10.4103/0972-3919.63601 | volume=25 | issue=1 | title=Closed system vacuum assisted administration of high dose radio iodine to cancer thyroid patients: NIMS {{sic|nolink=y|reason=error in source|techniqe}} | journal=Indian J Nucl Med | pages=34–5 | last1 = Rao | first1 = V. P. | last2 = Sudhakar | first2 = P. | last3 = Swamy | first3 = V. K. | last4 = Pradeep | first4 = G. | last5 = Venugopal | first5 = N.| year=2010 | doi-access=free }}</ref> For administration to animals (for example, cats with hyperthyroidism), for practical reasons the isotope must be administered by injection. European guidelines recommend administration of a capsule, due to "greater ease to the patient and the superior radiation protection for caregivers".<ref>{{cite journal |last1=Luster |first1=M. |last2=Clarke |first2=S. E. |last3=Dietlein |first3=M. |last4=Lassmann |first4=M. |last5=Lind |first5=P. |last6=Oyen |first6=W. J. G. |last7=Tennvall |first7=J. |last8=Bombardieri |first8=E. |title=Guidelines for radioiodine therapy of differentiated thyroid cancer |journal=European Journal of Nuclear Medicine and Molecular Imaging |date=1 August 2008 |volume=35 |issue=10 |pages=1941–1959 |doi=10.1007/s00259-008-0883-1 |pmid=18670773|s2cid=81465 }}</ref>

====Post-treatment isolation====
Ablation doses are usually administered on an [[inpatient]] basis, and [[IAEA]] International Basic Safety Standards recommend that patients are not discharged until the activity falls below 1100 MBq.<ref>{{cite book|title=Nuclear medicine in thyroid cancer management: a practical approach.|date=2009|pages=1–288 |publisher=International Atomic Energy Agency|location=Vienna|isbn=978-92-0-113108-9|url=http://www-pub.iaea.org/books/IAEABooks/7947/Nuclear-Medicine-in-Thyroid-Cancer-Management-A-Practical-Approach}}</ref> [[ICRP]] advice states that "comforters and carers" of patients undergoing radionuclide therapy should be treated as members of the public for dose constraint purposes and any restrictions on the patient should be designed based on this principle.<ref>{{cite journal|last1=Valentine|first1=J.|title=ICRP Publication 94: Release of Nuclear Medicine Patients after Therapy with Unsealed Sources|journal=Annals of the ICRP|date=June 2004|volume=34|issue=2|pages=1–27|doi=10.1016/j.icrp.2004.08.003|s2cid=71901469|doi-access=free}}</ref>

Patients receiving I-131 radioiodine treatment may be warned not to have sexual intercourse for one month (or shorter, depending on dose given), and women told not to become pregnant for six months afterwards. "This is because a theoretical risk to a developing fetus exists, even though the amount of radioactivity retained may be small and there is no medical proof of an actual risk from radioiodine treatment. Such a precaution would essentially eliminate direct fetal exposure to radioactivity and markedly reduce the possibility of conception with sperm that might theoretically have been damaged by exposure to radioiodine."<ref>{{cite web | title = Radioiodine Therapy: Information for Patients | publisher = AACE | year = 2004 | url = http://www.kumc.edu/endocrine/Radioiodine_Therapy.pdf | url-status = dead | archive-url = https://web.archive.org/web/20080910235528/http://www.kumc.edu/endocrine/Radioiodine_Therapy.pdf | archive-date = 10 September 2008 | df = dmy-all }}</ref> These guidelines vary from hospital to hospital and will depend on national legislation and guidance, as well as the dose of radiation given. Some also advise not to hug or hold children when the radiation is still high, and a one- or two- metre distance to others may be recommended.<ref>{{cite web|title=Instructions for Receiving Radioactive Iodine Therapy after a Thyroid Cancer Survey |url=http://uwmedicine.washington.edu/PatientCare/MedicalSpecialties/SpecialtyCare/UWMEDICALCENTER/Radiology/instructionsthyroidcancersurvey.htm |publisher=University of Washington Medical Center |access-date=2009-04-12 |url-status=dead |archive-url=https://web.archive.org/web/20090228160844/http://uwmedicine.washington.edu/PatientCare/MedicalSpecialties/SpecialtyCare/UWMEDICALCENTER/Radiology/instructionsthyroidcancersurvey.htm |archive-date=28 February 2009 }}</ref>

I-131 will be eliminated from the body over the next several weeks after it is given. The majority of I-131 will be eliminated from the human body in 3–5 days, through natural decay, and through excretion in sweat and urine. Smaller amounts will continue to be released over the next several weeks, as the body processes thyroid hormones created with the I-131. For this reason, it is advised to regularly clean toilets, sinks, bed sheets and clothing used by the person who received the treatment. Patients may also be advised to wear slippers or socks at all times, and avoid prolonged close contact with others. This minimizes accidental exposure by family members, especially children.<ref>{{cite web|title=Precautions after Out-patient Radioactive Iodine (I-131) Therapy|url=http://www.hamiltonhealthsciences.ca/documents/Patient%20Education/I131RadioactiveIodineTherapyHHS-trh.pdf|publisher=Department of Nuclear Medicine McMaster University Medical Centre|url-status=dead|archive-url=https://web.archive.org/web/20110929125700/http://www.hamiltonhealthsciences.ca/documents/Patient%20Education/I131RadioactiveIodineTherapyHHS-trh.pdf|archive-date=29 September 2011}}</ref> Use of a decontaminant specially made for radioactive iodine removal may be advised. The use of chlorine bleach solutions, or cleaners that contain chlorine bleach for cleanup, are not advised, since radioactive elemental iodine gas may be released.<ref name="Biosafety Manual for Purdue University">{{cite web |title=Biosafety Manual for Indiana University–Purdue University Indianapolis |date=May 2002 |page=7 |url=http://www.ehs.iupui.edu/biohaz_manual/biosafety_manual_v0502.pdf |publisher=[[Indiana University–Purdue University Indianapolis]] |access-date=28 April 2011 |archive-url=https://web.archive.org/web/20120323093535/http://www.ehs.iupui.edu/biohaz_manual/biosafety_manual_v0502.pdf |archive-date=23 March 2012 |url-status=dead }}</ref> Airborne I-131 may cause a greater risk of second-hand exposure, spreading contamination over a wide area. Patient is advised if possible to stay in a room with a bathroom connected to it to limit unintended exposure to family members.

Many airports have radiation detectors to detect the smuggling of radioactive materials. Patients should be warned that if they travel by air, they may trigger radiation detectors at airports up to 95 days after their treatment with <sup>131</sup>I.<ref>{{cite news  | last = Sutton | first =Jane | title = Radioactive patients | publisher = reuters | date = 29 January 2007 | url = https://www.reuters.com/article/health-SP-A/idUSN2633076820070209?pageNumber=2 | access-date = 2009-05-15 }}</ref>

=== Other therapeutic uses ===
The <sup>131</sup>I isotope is also used as a radioactive label for certain [[radiopharmaceutical]]s that can be used for therapy, e.g. <sup>131</sup>I-[[metaiodobenzylguanidine]] (<sup>131</sup>I-MIBG) for imaging and treating [[pheochromocytoma]] and [[neuroblastoma]]. In all of these therapeutic uses, <sup>131</sup>I destroys tissue by short-range [[beta decay|beta radiation]]. About 90% of its radiation damage to tissue is via beta radiation, and the rest occurs via its gamma radiation (at a longer distance from the radioisotope). It can be seen in diagnostic scans after its use as therapy, because <sup>131</sup>I is also a gamma-emitter.

===Diagnostic uses===
Because of the carcinogenicity of its beta radiation in the thyroid in small doses, I-131 is rarely used primarily or solely for diagnosis (although in the past this was more common due to this isotope's relative ease of production and low expense). Instead the more purely gamma-emitting radioiodine [[iodine-123]] is used in diagnostic testing ([[nuclear medicine]] scan of the thyroid). The longer half-lived [[iodine-125]] is also occasionally used when a longer half-life radioiodine is needed for diagnosis, and in [[brachytherapy]] treatment (isotope confined in small seed-like metal capsules), where the low-energy gamma radiation without a beta component makes iodine-125 useful. The other radioisotopes of iodine are never used in brachytherapy.

The use of <sup>131</sup>I as a medical isotope has been blamed for a routine shipment of [[biosolids]] being rejected from crossing the Canada—U.S. border.<ref>{{cite news|url=http://www.cbc.ca/news/canada/medical-isotopes-the-likely-cause-of-radiation-in-ottawa-waste-1.852645|title=Medical isotopes the likely cause of radiation in Ottawa waste|date=4 February 2009|access-date=30 September 2015|publisher=[[CBC News]]}}</ref> Such material can enter the sewers directly from the medical facilities, or by being excreted by patients after a treatment

==Industrial radioactive tracer uses==
Used for the first time in 1951 to localize leaks in a drinking water supply system of [[Munich]], Germany, iodine-131 became one of the most commonly used gamma-emitting industrial [[radioactive tracer]]s, with applications in [[isotope hydrology]] and leak detection.<ref>{{cite book|last1=Moser |last2=Rauert|first1=H.|first2=W. |title=Isotopes in the water cycle : past, present and future of a developing science|year=2007|publisher=Springer|location=Dordrecht|isbn=978-1-4020-6671-9 |editor1-last=Aggarwal|editor2-first=Joel R. |editor2-last=Gat|editor3-first= Klaus F. |editor3-last=Froehlich|access-date=6 May 2012|page=11|chapter=Isotopic Tracers for Obtaining Hydrologic Parameters|chapter-url=https://books.google.com/books?id=XKk6V_IeJbIC&pg=PA11|editor-first=Pradeep K.}}</ref><ref>{{cite book|last=Rao|first=S. M.|title=Practical isotope hydrology|year=2006|publisher=New India Publishing Agency|location=New Delhi|isbn=978-81-89422-33-2|chapter-url=https://books.google.com/books?id=E7TVDVVji0EC&q=isotope%20hydrology%20iodine&pg=PA11|access-date=6 May 2012|pages=12–13|chapter=Radioisotopes of hydrological interest}}</ref><ref>{{cite web|title=Investigating leaks in Dams & Reservoirs|url=http://www.iaea.org/technicalcooperation/documents/sheet20dr.pdf|work=IAEA.org|access-date=6 May 2012}}</ref><ref>{{cite book|last1=Araguás|first1=Luis Araguás|title=Detection and prevention of leaks from dams|year=2002|publisher=Taylor & Francis|isbn=978-90-5809-355-4|chapter-url=https://books.google.com/books?id=FXB-HMzfBnkC&pg=PA179|first2=Antonio |last2=Plata Bedmar|access-date=6 May 2012|pages=179–181|chapter=Artificial radioactive tracers}}</ref>

Since the late 1940s, radioactive tracers have been used by the oil industry. Tagged at the surface, water is then tracked downhole, using the appropriated gamma detector, to determine flows and detect underground leaks. I-131 has been the most widely used tagging isotope in an aqueous solution of [[sodium iodide]].<ref name="Reis iodine">{{cite book |last1=Reis |first1=John C. |year=1976 |title=Environmental Control in Petroleum Engineering |publisher=Gulf Professional Publishers|isbn=978-0-88415-273-6|page=55|chapter-url=https://books.google.com/books?id=XAseQ35m2OYC&pg=PA54|chapter=Radioactive materials}}</ref><ref>{{cite book|last=McKinley|first=R. M.|title=Temperature, radioactive tracer, and noise logging for injection well integrity|year=1994|publisher=U.S. Environmental Protection Agency|location=Washington|chapter-url=http://www.epa.gov/ogwdw/uic/pdfs/Historical/techguide_uic_temp_tracer__noise_logging_1994.pdf|access-date=6 May 2012|chapter=Radioactive tracer surveys}}</ref><ref>{{cite web|title=Radioactive-tracer log|url=http://www.glossary.oilfield.slb.com/Display.cfm?Term=radioactive-tracer%20log|work=Schlumberger.com|access-date=6 May 2012|author=Schlumberger Ltd|archive-date=3 June 2012|archive-url=https://web.archive.org/web/20120603095814/http://www.glossary.oilfield.slb.com/Display.cfm?Term=radioactive%2Dtracer%20log|url-status=dead}}</ref> It is used to characterize the [[hydraulic fracturing]] fluid to help determine the injection profile and location of fractures created by [[hydraulic fracturing]].<ref name="No5635712">{{cite patent |country=US |number=5635712 |status=patent |title=Method for monitoring the hydraulic fracturing of a subterranean formation |pubdate=1997-06-03 |inventor=Scott, George L.}}</ref><ref name="US4415805">{{cite patent |country=US |number=4415805 |status=patent |title=Method and apparatus for evaluating multiple stage fracturing or earth formations surrounding a borehole |pubdate=1983-11-15 |inventor=Fertl, Walter H.}}</ref><ref name="US5441110">{{cite patent |country=US |number=5441110 |status=patent |title=System and method for monitoring fracture growth during hydraulic fracture treatment |pubdate=1995-08-15 |inventor=Scott, George L.}}</ref>

==In popular culture==
*The use of Iodine-131 as a poison &ndash; used in small doses over a period of time to disrupt a person's ability to think and tell right from wrong &ndash; played a central role in the episode "The Case of the Melancholy Marksman" of the long-running [[CBS]] TV series ''[[Perry Mason (1957 TV series)|Perry Mason]]'' (season 5, episode 24, first broadcast March 24, 1962).

==See also==
* [[Isotopes of iodine]]
* [[Iodine in biology]]

==References==
{{Reflist|30em}}

==External links==
* {{cite web|url=http://www.ead.anl.gov/pub/doc/iodine.pdf|title=ANL factsheet|archive-url=https://web.archive.org/web/20030614211154/http://www.ead.anl.gov/pub/doc/iodine.pdf|archive-date=14 June 2003}}
* [http://www.radiologyinfo.org/en/info.cfm?pg=radioiodine RadiologyInfo – The radiology information resource for patients: Radioiodine (I −131) Therapy]
* [https://www.atsdr.cdc.gov/csem/csem.html Case Studies in Environmental Medicine: Radiation Exposure from Iodine 131]
* [https://web.archive.org/web/20051223162858/http://rsna2004.rsna.org/rsna2004/V2004/conference/event_display.cfm?em_id=4407767 Sensitivity of Personal Homeland Security Radiation Detectors to Medical Radionuclides and Implications for Counseling of Nuclear Medicine Patients]
* [http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@na+@rel+iodine,+radioactive NLM Hazardous Substances Databank – Iodine, Radioactive]

{{Isotope sequence
|element=iodine
|lighter=<sup>130</sup>I
|heavier=<sup>132</sup>I
|before=[[Tellurium-131|<sup>131</sup>Te]] '''([[beta decay|β<sup>−</sup>]])'''
|after=[[Xenon-131|<sup>131</sup>Xe]] '''(β<sup>−</sup>)'''
}}
{{Use dmy dates|date=July 2019}}
{{Radiopharmaceuticals}}
{{Therapeutic radiopharmaceuticals}}
{{Radiation oncology}}
{{Thyroid hormone receptor modulators}}

[[Category:Isotopes of iodine]]
[[Category:Antithyroid drugs]]
[[Category:Fission products]]
[[Category:Radioactive contamination]]
[[Category:Medical isotopes]]