Iodine-131
Encyclopedia
Iodine-131 also called radioiodine (though many other radioactive isotopes of this element are known), is an important radioisotope of iodine
. It has a radioactive decay half-life of about eight days. Its uses are mostly medical and pharmaceutical. 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 Japanese nuclear crisis. This is because I-131 is a major uranium
, plutonium
fission product
, comprising nearly 3% of the total products of fission (by weight). See fission product yield
for a comparison with other radioactive fission products. I-131 is also a major fission product of uranium-233, produced from thorium
.
Due to its mode of beta decay
, iodine-131 is notable for causing 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 I-131 for thyroid adenomas had a detectable increase in thyroid cancer, but children treated with a much higher dose did not. Likewise, most studies of very-high-dose I-131 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 I-131 absorption at moderate doses. 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 (i.e., 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 are preferred in situations when only nuclear imaging is required. The isotope I-131 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 I-131 have not shown any increase in thyroid cancer. The low-cost availability of I-131, in turn, is due to the relative ease of creating I-131 by neutron bombardment of natural tellurium in a nuclear reactor, then separating I-131 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 reactor radiation of expensive capsules of pressurized xenon
gas.
Much smaller incidental doses of iodine-131 than are used in medical therapeutic uses, are thought to be the major cause of increased thyroid cancers after accidental nuclear contamination. These cancers happen from residual tissue radiation damage caused by the I-131, and usually appear years after exposure, long after the I-131 has decayed.
of a natural tellurium target. Irradiation of natural tellurium produces almost entirely I-131 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, Te-130 (34% of natural Te) absorbs a neutron to become tellurium-131, which beta-decays with a half-life of 25 minutes, to I-131.
A tellurium compound can be irradiated while bound as an oxide to an ion exchange column, and evolved I-131 then eluted into an alkaline solution. More commonly, powdered elemental tellurium is irradiated and then I-131 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 I-131 as iodide and hypoiodate (which is soon reduced to iodide).
of 8.02 days with beta
and gamma
emissions. This nuclide
of iodine atom
has 78 neutron
s in nucleus, the stable nuclide 127I has 74 neutrons. On decaying, 131I most often (89% of the time) expends its 971 keV of decay energy by transforming into the stable 131Xe
(Xenon) in two steps, with gamma decay following rapidly after beta decay:
+ 606 keV
+ 364 keV
The primary emissions of 131I decay are thus beta particles with a maximal energy of 606 keV (89% abundance, others 248 – 807 keV) and 364 keV gamma rays (81% abundance, others 723 keV). Beta decay, as always in this process, also produces an antineutrino, which carries off variable amounts of the beta decay energy.
The beta particles, due to their high mean energy (190 keV, with typical beta-decay spectra present) have a tissue penetration of 0.6 to 2 mm.
131I is a fission product
with a yield
of 2.878% from uranium-235
, and can be released in nuclear weapons tests and nuclear accidents. 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 I-131.
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 131I 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 high levels of 131I is the chance occurrence of radiogenic thyroid cancer
in later life. Other risks include the possibility of non-cancerous growths and thyroiditis
.
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.
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 tissues and lowering the relative proportion of radioactive iodine. However, such supplements were not distributed to the population living nearest to the Chernobyl
nuclear power plant after the disaster, though they were widely distributed to children in Poland.
Within the USA, the highest 131I fallout doses occurred during the 1950s and early 1960s to children having consumed fresh sources of milk contaminated as the result of above-ground testing of nuclear weapons. The National Cancer Institute
provides additional information on the health effects from exposure to 131I in fallout, 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
.
On 27 March 2011, the Massachusetts Department of Public Health reported that 131I was detected in very low concentrations in rainwater from samples collected in Massachusetts, USA, and that this likely originated from the Fukushima power plant. Farmers near the plant dumped raw milk, while testing in the United States found 0.8 pico-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
from radioiodine. The most common method of treatment is to give potassium iodide to those at risk. The dosage for adults is 130 mg potassium iodide per day, given in one dose, or divided into portions of 65 mg twice a day. This is equivalent to 100 mg of iodide, and is about 700 times bigger than the nutritional dose of iodide, which is 0.15 mg per day (150 microgram
s per day). See potassium iodide
for more information on prevention of radioiodine absorption by the thyroid during nuclear accident, or for nuclear medical
reasons.
The ingestion of prophylaxis iodide & iodate
is not without its dangers, There is reason for caution about taking potassium iodide or iodine supplements, as their unnecessary use can cause conditions such as the Jod-Basedow phenomena, and the Wolff-Chaikoff effect
, trigger and/or worsen hyperthyroidism
and hypothyroidism
, and ultimately cause temporary or even permanent thyroid conditions. It can also cause sialadenitis
(an inflammation of the salivary gland), gastrointestinal disturbances, allergic reactions and rashes. Potassium iodide is also not recommended for those who have had an allergic reaction to iodine, and people with dermatitis herpetiformis and hypocomplementemic vasculitis, conditions that are linked to a risk of iodine sensitivity.
The administration of known goitrogen
substances can also be used as a prophylaxis in reducing the bio-uptake of iodine (whether it be non-radioactive iodine-127 or radioactive iodine-131, as the body cannot discern between the different iodine isotopes). Perchlorate
ions, a common water contaminant in the USA due to the aerospace industry, has been shown to reduce iodide uptake. Perchlorate is a competitive inhibitor of the process by which iodide, is actively deposited into thyroid follicular cells. A study involving healthy adult volunteers determined that at levels above 0.007 milligrams per kilogram per day (mg/(kg·d)), perchlorate begins to temporarily inhibit the thyroid gland’s ability to absorb iodine from the bloodstream ("iodide uptake inhibition", thus perchlorate is a known goitrogen).
The purposeful addition of ~ 250 ppb
of perchlorate ions to a regions water supply, for approximately three months, immediately after a radioiodine release, could thus be beneficial to the population in preventing radioiodine bioaccumulation
, independent of the availability of Iodate
or Iodide
drugs. In the event of a radioiodine release the ingestion of potassium iodide or iodate, if available, would rightly take precedence and would be the first line of defense in protecting the population from a radioiodine release. However in the event of a radioiodine release too massive and widespread to be mediation by the limited stock of iodide & iodate prophylaxis drugs, then the addition of perchlorate ions to the water supply would serve as a cheap, efficacious, second line of defense against radioiodine bioaccumulation.
The ingestion of goitrogen
drugs is also not without its dangers, such as hypothyroidism
. In all these cases however, despite the risks, the prophylaxis benefits of intervention with iodide, iodate and perchlorate outweigh the serious cancer risk from radioiodine bioaccumulation
in conditions of radioiodine contamination of the environment.
therapeutically and can also be seen with diagnostic scanners if it has been used therapeutically. Use of the 131I as iodide salt exploits the mechanism of absorption of iodine by the normal cells of the thyroid
gland. Examples of its use in radiation therapy
are those where tissue destruction is desired after iodine uptake by the tissue.
Major uses of 131I include the treatment of thyrotoxicosis (hyperthyroidism) and some types of thyroid cancer
that absorb iodine. The 131I is thus used as direct radioisotope therapy to treat 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 131I isotope is also used as a radioactive label for certain radiopharmaceuticals that can be used for therapy, e.g. 131I-metaiodobenzylguanidine (131I-MIBG) for imaging and treating pheochromocytoma
and neuroblastoma
. In all of these therapeutic uses, 131I destroys tissue by short-range 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 131I is also a gamma-emitter.
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 131I as a medical isotope has been blamed for a routine shipment of biosolids being rejected from crossing the Canada—U.S. border. Such material can enter the sewers directly from the medical facilities, or by being excreted by patients after a treatment.
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 be 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 themselves physically isolated from others. This minimizes accidental exposure by family members, especially children. 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. Airborne I-131 may cause a greater risk of second-hand exposure, spreading contamination over a wide area.
Many airports now have radiation detectors to detect the smuggling of radioactive materials that may be used in nuclear weapons manufacture. 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 131I.
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
. It has a radioactive decay half-life of about eight days. Its uses are mostly medical and pharmaceutical. It also plays a major role as a radioactive isotope present in nuclear fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
products, and was a significant contributor to the health hazards from open-air atomic bomb testing in the 1950s, and from the Chernobyl disaster
Chernobyl disaster
The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine , which was under the direct jurisdiction of the central authorities in Moscow...
, as well as being a large fraction of the contamination hazard in the first weeks in the Japanese nuclear crisis. This is because I-131 is a major uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
, plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...
fission product
Fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The...
, comprising nearly 3% of the total products of fission (by weight). See fission product yield
Fission product yield
Nuclear fission splits a heavy nucleus such as uranium or plutonium into two lighter nuclei, which are called fission products. Yield refers to the fraction of a fission product produced per fission.Yield can be broken down by:#Individual isotope...
for a comparison with other radioactive fission products. I-131 is also a major fission product of uranium-233, produced from thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
.
Due to its mode of beta decay
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
, iodine-131 is notable for causing mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
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
Thyroid
The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage...
tissues that would otherwise become cancerous as a result of the radiation. For example, children treated with moderate dose of I-131 for thyroid adenomas had a detectable increase in thyroid cancer, but children treated with a much higher dose did not. Likewise, most studies of very-high-dose I-131 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 I-131 absorption at moderate doses. 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
Nuclear medicine
In nuclear medicine procedures, elemental radionuclides are combined with other elements to form chemical compounds, or else combined with existing pharmaceutical compounds, to form radiopharmaceuticals. These radiopharmaceuticals, once administered to the patient, can localize to specific organs...
imaging techniques (i.e., gamma camera
Gamma camera
A gamma camera, also called a scintillation camera or Anger camera, is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy...
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 are preferred in situations when only nuclear imaging is required. The isotope I-131 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 I-131 have not shown any increase in thyroid cancer. The low-cost availability of I-131, in turn, is due to the relative ease of creating I-131 by neutron bombardment of natural tellurium in a nuclear reactor, then separating I-131 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 reactor radiation of expensive capsules of pressurized xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
gas.
Much smaller incidental doses of iodine-131 than are used in medical therapeutic uses, are thought to be the major cause of increased thyroid cancers after accidental nuclear contamination. These cancers happen from residual tissue radiation damage caused by the I-131, and usually appear years after exposure, long after the I-131 has decayed.
Production
Most I-131 production is from nuclear reactor neutron-irradiationIrradiation
Irradiation is the process by which an object is exposed to radiation. The exposure can originate from various sources, including natural sources. Most frequently the term refers to ionizing radiation, and to a level of radiation that will serve a specific purpose, rather than radiation exposure to...
of a natural tellurium target. Irradiation of natural tellurium produces almost entirely I-131 as the only radionuclide with a half-life longer than hours, since most lighter isotopes of tellurium
Isotopes of tellurium
There are 38 known isotopes and 17 nuclear isomers of tellurium with atomic masses that range from 105 to 142. These are listed in the table below.Naturally occurring tellurium on Earth consists of eight isotopes...
become heavier stable isotopes, or else stable iodine or xenon. However, the heaviest naturally-occurring tellurium nuclide, Te-130 (34% of natural Te) absorbs a neutron to become tellurium-131, which beta-decays with a half-life of 25 minutes, to I-131.
A tellurium compound can be irradiated while bound as an oxide to an ion exchange column, and evolved I-131 then eluted into an alkaline solution. More commonly, powdered elemental tellurium is irradiated and then I-131 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 I-131 as iodide and hypoiodate (which is soon reduced to iodide).
Radioactive decay
131I decays with a half-lifeHalf-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of 8.02 days with beta
Beta particle
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...
and gamma
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
emissions. This nuclide
Nuclide
A nuclide is an atomic species characterized by the specific constitution of its nucleus, i.e., by its number of protons Z, its number of neutrons N, and its nuclear energy state....
of iodine atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
has 78 neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s in nucleus, the stable nuclide 127I has 74 neutrons. On decaying, 131I most often (89% of the time) expends its 971 keV of decay energy by transforming into the stable 131Xe
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
(Xenon) in two steps, with gamma decay following rapidly after beta decay:
+ 606 keV + 364 keVThe primary emissions of 131I decay are thus beta particles with a maximal energy of 606 keV (89% abundance, others 248 – 807 keV) and 364 keV gamma rays (81% abundance, others 723 keV). Beta decay, as always in this process, also produces an antineutrino, which carries off variable amounts of the beta decay energy.
The beta particles, due to their high mean energy (190 keV, with typical beta-decay spectra present) have a tissue penetration of 0.6 to 2 mm.
131I is a fission product
Fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The...
with a yield
Fission product yield
Nuclear fission splits a heavy nucleus such as uranium or plutonium into two lighter nuclei, which are called fission products. Yield refers to the fraction of a fission product produced per fission.Yield can be broken down by:#Individual isotope...
of 2.878% from uranium-235
Uranium-235
- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...
, and can be released in nuclear weapons tests and nuclear accidents. However, the short half-life means it is not present in significant quantities in cooled spent nuclear fuel
Spent nuclear fuel
Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor...
, unlike iodine-129
Iodine-129
Iodine-129 is long-lived radioisotope of iodine which occurs naturally, but also is of special interest in the monitoring and effects of man-made nuclear fission decay products, where it serves as both tracer and potential radiological contaminant....
whose half-life is nearly a billion times that of I-131.
Effects of exposure
Thyroid
The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage...
where it is needed for the functioning of that gland. When 131I is present in high levels in the environment from radioactive fallout
Fallout
Fallout or nuclear fallout is the residual radiation hazard from a nuclear explosion.Fallout may also refer to:*Fallout , a 1997 post-apocalyptic computer role-playing game released by Interplay Entertainment...
, 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 high levels of 131I is the chance occurrence of radiogenic thyroid cancer
Thyroid cancer
Thyroid neoplasm is a neoplasm or tumor of the thyroid. It can be a benign tumor such as thyroid adenoma, or it can be a malignant neoplasm , such as papillary, follicular, medullary or anaplastic thyroid cancer. Most patients are 25 to 65 years of age when first diagnosed; women are more affected...
in later life. Other risks include the possibility of non-cancerous growths and thyroiditis
Thyroiditis
Thyroiditis is the inflammation of the thyroid gland. The thyroid gland is located on the front of the neck below the laryngeal prominence, and makes hormones that control metabolism.-Classification:...
.
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.
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 tissues and lowering the relative proportion of radioactive iodine. However, such supplements were not distributed to the population living nearest to the Chernobyl
Chernobyl disaster
The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine , which was under the direct jurisdiction of the central authorities in Moscow...
nuclear power plant after the disaster, though they were widely distributed to children in Poland.
Within the USA, the highest 131I fallout doses occurred during the 1950s and early 1960s to children having consumed fresh sources of milk contaminated as the result of above-ground testing of nuclear weapons. The National Cancer Institute
National Cancer Institute
The National Cancer Institute is part of the National Institutes of Health , which is one of 11 agencies that are part of the U.S. Department of Health and Human Services. The NCI coordinates the U.S...
provides additional information on the health effects from exposure to 131I in fallout, 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
Nevada Test Site
The Nevada National Security Site , previously the Nevada Test Site , is a United States Department of Energy reservation located in southeastern Nye County, Nevada, about northwest of the city of Las Vegas...
.
On 27 March 2011, the Massachusetts Department of Public Health reported that 131I was detected in very low concentrations in rainwater from samples collected in Massachusetts, USA, and that this likely originated from the Fukushima power plant. Farmers near the plant dumped raw milk, while testing in the United States found 0.8 pico-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
Treatment and prevention
A common treatment method for preventing iodine-131 exposure is by saturating the thyroid with regular, non-radioactive iodine-127, as an iodide salt. Free elemental iodine should not be used for saturating the thyroid because it is a corrosive oxidant and therefore is toxic to ingest in the necessary quantities. The thyroid will absorb very little of the radioactive iodine-131 after it is saturated with non-radioactive iodide, thereby avoiding the damage caused by radiationRadiation poisoning
Acute radiation syndrome also known as radiation poisoning, radiation sickness or radiation toxicity, is a constellation of health effects which occur within several months of exposure to high amounts of ionizing radiation...
from radioiodine. The most common method of treatment is to give potassium iodide to those at risk. The dosage for adults is 130 mg potassium iodide per day, given in one dose, or divided into portions of 65 mg twice a day. This is equivalent to 100 mg of iodide, and is about 700 times bigger than the nutritional dose of iodide, which is 0.15 mg per day (150 microgram
Microgram
In the metric system, a microgram is a unit of mass equal to one millionth of a gram , or 1/1000 of a milligram. It is one of the smallest units of mass commonly used...
s per day). See potassium iodide
Potassium iodide
Potassium iodide is an inorganic compound with the chemical formula KI. This white salt is the most commercially significant iodide compound, with approximately 37,000 tons produced in 1985. It is less hygroscopic than sodium iodide, making it easier to work with...
for more information on prevention of radioiodine absorption by the thyroid during nuclear accident, or for nuclear medical
Nuclear medicine
In nuclear medicine procedures, elemental radionuclides are combined with other elements to form chemical compounds, or else combined with existing pharmaceutical compounds, to form radiopharmaceuticals. These radiopharmaceuticals, once administered to the patient, can localize to specific organs...
reasons.
The ingestion of prophylaxis iodide & iodate
Iodate
An iodate is a conjugate base of iodic acid. In the iodate anion, iodine is bonded to three oxygen atoms and the molecular formula is IO3−. The molecular geometry of iodate is trigonal pyramidal....
is not without its dangers, There is reason for caution about taking potassium iodide or iodine supplements, as their unnecessary use can cause conditions such as the Jod-Basedow phenomena, and the Wolff-Chaikoff effect
Wolff-Chaikoff effect
The Wolff–Chaikoff effect is a reduction in thyroid hormone levels caused by ingestion of a large amount of iodine.It is an autoregulatory phenomenon that inhibits organification in the thyroid gland, the formation of thyroid hormones inside the thyroid follicle, and the release of thyroid...
, trigger and/or worsen hyperthyroidism
Hyperthyroidism
Hyperthyroidism is the term for overactive tissue within the thyroid gland causing an overproduction of thyroid hormones . Hyperthyroidism is thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood. Hyperthyroidism and thyrotoxicosis are not synonymous...
and hypothyroidism
Hypothyroidism
Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or...
, and ultimately cause temporary or even permanent thyroid conditions. It can also cause sialadenitis
Sialadenitis
Sialadenitis is inflammation of a salivary gland. It may be subdivided temporally into acute, chronic and recurrent forms.Alternate spelling:Sialoadenitis-Acute Form:Predisposing factors:* decreased flow * poor oral hygiene...
(an inflammation of the salivary gland), gastrointestinal disturbances, allergic reactions and rashes. Potassium iodide is also not recommended for those who have had an allergic reaction to iodine, and people with dermatitis herpetiformis and hypocomplementemic vasculitis, conditions that are linked to a risk of iodine sensitivity.
The administration of known goitrogen
Goitrogen
Goitrogens are substances that suppress the function of the thyroid gland by interfering with iodine uptake, which can, as a result, cause an enlargement of the thyroid, i.e., a goitre.-Goitrogenic drugs and chemicals:...
substances can also be used as a prophylaxis in reducing the bio-uptake of iodine (whether it be non-radioactive iodine-127 or radioactive iodine-131, as the body cannot discern between the different iodine isotopes). Perchlorate
Perchlorate
Perchlorates are the salts derived from perchloric acid . They occur both naturally and through manufacturing. They have been used as a medicine for more than 50 years to treat thyroid gland disorders. They are used extensively within the pyrotechnics industry, and ammonium perchlorate is also a...
ions, a common water contaminant in the USA due to the aerospace industry, has been shown to reduce iodide uptake. Perchlorate is a competitive inhibitor of the process by which iodide, is actively deposited into thyroid follicular cells. A study involving healthy adult volunteers determined that at levels above 0.007 milligrams per kilogram per day (mg/(kg·d)), perchlorate begins to temporarily inhibit the thyroid gland’s ability to absorb iodine from the bloodstream ("iodide uptake inhibition", thus perchlorate is a known goitrogen).
The purposeful addition of ~ 250 ppb
PPB
PPB can stand for:* Party political broadcast, a type of political programming in the United Kingdom* parts-per-billion, a unit of concentration* Portland Police Bureau, a police agency for the city of Portland...
of perchlorate ions to a regions water supply, for approximately three months, immediately after a radioiodine release, could thus be beneficial to the population in preventing radioiodine bioaccumulation
Bioaccumulation
Bioaccumulation refers to the accumulation of substances, such as pesticides, or other organic chemicals in an organism. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost...
, independent of the availability of Iodate
Iodate
An iodate is a conjugate base of iodic acid. In the iodate anion, iodine is bonded to three oxygen atoms and the molecular formula is IO3−. The molecular geometry of iodate is trigonal pyramidal....
or Iodide
Iodide
An iodide ion is the ion I−. Compounds with iodine in formal oxidation state −1 are called iodides. This page is for the iodide ion and its salts. For information on organoiodides, see organohalides. In everyday life, iodide is most commonly encountered as a component of iodized salt,...
drugs. In the event of a radioiodine release the ingestion of potassium iodide or iodate, if available, would rightly take precedence and would be the first line of defense in protecting the population from a radioiodine release. However in the event of a radioiodine release too massive and widespread to be mediation by the limited stock of iodide & iodate prophylaxis drugs, then the addition of perchlorate ions to the water supply would serve as a cheap, efficacious, second line of defense against radioiodine bioaccumulation.
The ingestion of goitrogen
Goitrogen
Goitrogens are substances that suppress the function of the thyroid gland by interfering with iodine uptake, which can, as a result, cause an enlargement of the thyroid, i.e., a goitre.-Goitrogenic drugs and chemicals:...
drugs is also not without its dangers, such as hypothyroidism
Hypothyroidism
Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or...
. In all these cases however, despite the risks, the prophylaxis benefits of intervention with iodide, iodate and perchlorate outweigh the serious cancer risk from radioiodine bioaccumulation
Bioaccumulation
Bioaccumulation refers to the accumulation of substances, such as pesticides, or other organic chemicals in an organism. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost...
in conditions of radioiodine contamination of the environment.
Medical and pharmaceutical uses
It is used in nuclear medicineNuclear medicine
In nuclear medicine procedures, elemental radionuclides are combined with other elements to form chemical compounds, or else combined with existing pharmaceutical compounds, to form radiopharmaceuticals. These radiopharmaceuticals, once administered to the patient, can localize to specific organs...
therapeutically and can also be seen with diagnostic scanners if it has been used therapeutically. Use of the 131I as iodide salt exploits the mechanism of absorption of iodine by the normal cells of the thyroid
Thyroid
The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage...
gland. Examples of its use in radiation therapy
Radiation therapy
Radiation therapy , radiation oncology, or radiotherapy , sometimes abbreviated to XRT or DXT, is the medical use of ionizing radiation, generally as part of cancer treatment to control malignant cells.Radiation therapy is commonly applied to the cancerous tumor because of its ability to control...
are those where tissue destruction is desired after iodine uptake by the tissue.
Major uses of 131I include the treatment of thyrotoxicosis (hyperthyroidism) and some types of thyroid cancer
Thyroid cancer
Thyroid neoplasm is a neoplasm or tumor of the thyroid. It can be a benign tumor such as thyroid adenoma, or it can be a malignant neoplasm , such as papillary, follicular, medullary or anaplastic thyroid cancer. Most patients are 25 to 65 years of age when first diagnosed; women are more affected...
that absorb iodine. The 131I is thus used as direct radioisotope therapy to treat hyperthyroidism
Hyperthyroidism
Hyperthyroidism is the term for overactive tissue within the thyroid gland causing an overproduction of thyroid hormones . Hyperthyroidism is thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood. Hyperthyroidism and thyrotoxicosis are not synonymous...
due to Graves' disease
Graves' disease
Graves' disease is an autoimmune disease where the thyroid is overactive, producing an excessive amount of thyroid hormones...
, 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
Saul Hertz
Saul Hertz, M.D. was an American physician who discovered the use of radioactive iodine for the treatment of thyroid disease.-Early life and education:...
in 1941.
The 131I isotope is also used as a radioactive label for certain radiopharmaceuticals that can be used for therapy, e.g. 131I-metaiodobenzylguanidine (131I-MIBG) for imaging and treating pheochromocytoma
Pheochromocytoma
A pheochromocytoma or phaeochromocytoma is a neuroendocrine tumor of the medulla of the adrenal glands , or extra-adrenal chromaffin tissue that failed to involute after birth and secretes excessive amounts of catecholamines, usually noradrenaline , and adrenaline to a lesser extent...
and neuroblastoma
Neuroblastoma
Neuroblastoma is the most common extracranial solid cancer in childhood and the most common cancer in infancy, with an annual incidence of about 650 cases per year in the US , and 100 cases per year in the UK . Close to 50 percent of neuroblastoma cases occur in children younger than two years old...
. In all of these therapeutic uses, 131I destroys tissue by short-range beta radiation
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
. 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 131I is also a gamma-emitter.
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
Iodine-123
Iodine-123 is a radioactive isotope of iodine used in nuclear medicine imaging, including single photon emission computed tomography . The isotope's half-life is 13.22 hours; the decay by electron capture to tellurium-123 emits gamma radiation with predominant energies of 159 keV and 127 keV...
is used in diagnostic testing (nuclear medicine
Nuclear medicine
In nuclear medicine procedures, elemental radionuclides are combined with other elements to form chemical compounds, or else combined with existing pharmaceutical compounds, to form radiopharmaceuticals. These radiopharmaceuticals, once administered to the patient, can localize to specific organs...
scan of the thyroid). The longer half-lived iodine-125
Iodine-125
Iodine-125 is a radioisotope of iodine which has uses in biological assays, nuclear medicine imaging and in radiation therapy as brachytherapy to treat prostate cancer and brain tumors. It is the second longest-lived radioisotope of iodine, after iodine-129.Its half-life is around 59 days and it...
is also occasionally used when a longer half-life radioiodine is needed for diagnosis, and, in brachytherapy
Brachytherapy
Brachytherapy , also known as internal radiotherapy, sealed source radiotherapy, curietherapy or endocurietherapy, is a form of radiotherapy where a radiation source is placed inside or next to the area requiring treatment...
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 131I as a medical isotope has been blamed for a routine shipment of biosolids being rejected from crossing the Canada—U.S. border. Such material can enter the sewers directly from the medical facilities, or by being excreted by patients after a treatment.
Post-treatment isolation
Patients receiving I-131 radioiodine treatment are warned not to have sexual intercourse for one month (or shorter, depending on dose given), and women are 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." These guidelines vary from hospital to hospital and will depend also on 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.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 be 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 themselves physically isolated from others. This minimizes accidental exposure by family members, especially children. 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. Airborne I-131 may cause a greater risk of second-hand exposure, spreading contamination over a wide area.
Many airports now have radiation detectors to detect the smuggling of radioactive materials that may be used in nuclear weapons manufacture. 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 131I.
See also
- IodineIodineIodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
- Isotopes of iodineIsotopes of iodineThere are 37 known isotopes of iodine and only one, 127I, is stable. Iodine is thus a monoisotopic element.Its longest-lived radioactive isotope, 129I, has a half-life of 15.7 million years, which is far too short for it to exist as a primordial nuclide...
- Iodine in biologyIodine in biologyIodine is an essential trace element for life, the heaviest element commonly needed by living organisms, and the second-heaviest known to be used by any form of life .-The thyroid:Iodine's main role in animal biology is as constituents of the thyroid hormones, thyroxine and...
- IodideIodideAn iodide ion is the ion I−. Compounds with iodine in formal oxidation state −1 are called iodides. This page is for the iodide ion and its salts. For information on organoiodides, see organohalides. In everyday life, iodide is most commonly encountered as a component of iodized salt,...
- Potassium iodidePotassium iodidePotassium iodide is an inorganic compound with the chemical formula KI. This white salt is the most commercially significant iodide compound, with approximately 37,000 tons produced in 1985. It is less hygroscopic than sodium iodide, making it easier to work with...
External links
- ANL factsheet
- RadiologyInfo - The radiology information resource for patients: Radioiodine (I -131) Therapy
- Case Studies in Environmental Medicine: Radiation Exposure from Iodine 131
- Sensitivity of Personal Homeland Security Radiation Detectors to Medical Radionuclides and Implications for Counseling of Nuclear Medicine Patients
- NLM Hazardous Substances Databank – Iodine, Radioactive