Iodine and Radioactive Iodine Facts

In this section we will explore all things iodine, both radioactive and non radioactive. According to the EPA, here are the basics about iodine and radioactive iodine.

Radioactive iodine has been found in US milk as early as March 2011. Since then the amount of iodine in milk and drinking water has been increasing, not decreasing.

FukushimaHawaii & Arizona Dairy Milk Test Up To 800% Higher Than Safety Limits; via A Green Road Blog

The Basics

Who discovered iodine and radioactive iodine?

In 1811, Bernard Courtois discovered natural iodine in water that was used to dissolve certain parts of seaweed ash for use. Radioactive iodine-131 was discovered by Glenn T. Seaborg and John Livingood at the University of California – Berkeley in the late 1930’s.
Where do  radioactive iodine-129 and iodine-131 come from?
Both iodine-129 and iodine-131 are produced by the fission of uranium atoms during operation of nuclear reactors and by plutonium (or uranium) in the detonation of nuclear weapons.
What are the properties of iodine-129 and iodine-131?
Radioactive iodines have the same physical properties as stable iodine. However, radioactive iodines decay with time.
Iodine is a nonmetallic, purplish-black crystalline solid. It has the unusual property of ‘sublimation,’ which means that it can go directly from a solid to a gas, without first becoming liquid. It sublimes to a deep violet vapor at room temperature. This vapor is irritating to the eyes, nose and throat. Iodine dissolves in alcohol and in water. It melts at 236 °F.
Iodine reacts easily with other chemicals, and isotopes of iodine are found as compounds rather than as a pure elemental nuclide. Thus, iodine-129 and -131 found in nuclear facilities and waste treatment plants quickly form compounds with the mixture of chemicals present. However, iodine released to the environment from nuclear power plants is usually a gas.
Iodine-129 has a half-life of 15.7 million years; iodine-131 has a half-life of about 8 days. Both emit beta particles upon radioactive decay. There are many other long life radioactive substances;
93 Long life Radiation Contaminants, A Problem For Billions Of Years; via A Green Road Blog   
What are iodine radioisotopes used for?
Iodines are among the most widely used radionuclides, mostly in the medical field. Because of its short half-life and useful beta emission, iodine-131 is used extensively in nuclear medicine.
Its tendency to collect in the thyroid gland makes iodine especially useful for diagnosing and treating thyroid problems. Iodine-123 is widely used in medical imaging, and I-124 is useful in immunotherapy.
Iodine’s chemical properties make it easy to attach to molecules for imaging studies. It is useful in tracking the metabolism of drugs or compounds, or for viewing structural defects in various organs, such as the heart.
A less common isotope, iodine-125, is sometimes used to treat cancerous tissue.
Iodine-129 has little practical use, but may be used to check some radioactivity counters in diagnostic testing laboratories.
Exposure to Iodine-129 and Iodine-131
How do iodine-129 and iodine-131 get into the environment?
Iodine-129 and iodine-131 are gaseous fission products that form within fuel rods as they fission. Unless reactor chemistry is carefully controlled, they can build up too fast, increasing pressure and causing corrosion in the rods. As the rods age, cracks or wholes may breach the rods.
Cracked rods can release radioactive iodine into the water that surrounds and cools the fuel rods. There, it circulates with the cooling water throughout the system, ending up in the airborne, liquid, and solid wastes from the reactor. From time to time, reactor gas capture systems release gases, including iodine, to the environment under applicable regulations.
Anywhere spent nuclear fuel is handled, there is a chance that iodine-129 and iodine-131 will escape into the environment. Nuclear fuel reprocessing plants dissolve the spent fuel rods in strong acids to recover plutonium and other valuable materials. In the process, they also release iodine-129 and -131 into the airborne, liquid, and solid waste processing systems. In the U.S., spent nuclear fuel is no longer reprocessed, because of concerns about nuclear weapons proliferation.
More information about ‘recycling’ nuclear waste;
Windscale: Biggest Covered Up UK Nuclear Disaster? via A Green Road Blog
Ozyorsk – Kyshtym – Mayak Nuclear Waste Reprocessing Center Disaster And Coverup; via A Green Road Blog
La Hague; France‘s Nuclear Waste Nightmare; via A Green Road Blog 
UK Sellafield Nuclear Reprocessing Plant Loses $1.2 Billion Pounds, Then Closes; via A Green Road Blog
Hanford; Lethal And Leaking; A Race To Armageddon?  via A Green Road Blog
Rokkasho Reprocessing Plant History, Accidents And Dangers; via A Green Road Blog   
Dr. Ivan Oelrich; Nuclear Spent Fuel Reprocessing Greenwashing; via A Green Road Blog
Currently, spent nuclear fuel remains in temporary storage at nuclear power plants around the country. Wherever spent nuclear fuel is stored, the short-lived iodine-131 it contains will decay away quickly and completely. However, the long-lived iodine-129 will remain for millions of years. Keeping it from leaking into the environment, requires carefully designed, long-term safeguards.
More information about nuclear waste storage;
The Fallacy Of High Level Nuclear Waste Geological Storage; via A Green Road Blog
Dr. Chris Busby; Consequences of Burning Radioactive Waste In Japan; via A Green Road Blog
No Solutions For Nuclear Disasters Or Nuclear Waste; via A Green Road Blog
What Happens To Nuclear Waste In Your Country? via A Green Road Blog 
Huge Number Of Radiation Contaminated Sites In Just ONE US State; via A Green Road Blog
Depleted Uranium Effects In The Human Body; via A Green Road Blog 
Nuclear Plants And Radioactive Water Contamination; via A Green Road Blog
Nuclear Spent Fuel/Radioactive Waste Storage; via A Green Road Blog 
The detonation of nuclear weapons also releases iodine-129 into the environment. Atmospheric testing in the 1950’s and 60’s released radioactive iodine to the atmosphere which has disseminated around the world, and is now found at very low levels in the environment. Most I-129 in the environment came from weapons testing.
The Nuclear Fuel Chain That Leads To Nuclear Bombs; via A Green Road Blog
Alpha Radiation Dangers; Polonium, Radon, Radium, Plutonium, Uranium….
Depleted Uranium Effects In The Human Body; via A Green Road Blog 
EMP; Electromagnetic Pulse Effect And High Altitude Nuclear Bombs; via A Green Road Blog
2400 Global Nuclear Atmospheric Bomb Tests 1945-1998
Nevada National Security Site; Nuclear Bomb Testing Areas 1-30; via A Green Road Blog
Downwinders And Nuclear Bomb Testing; via A Green Road Blog
Atomic Bomb Testing Veterans; via A Green Road Blog
Nuclear Bomb Test Sites And Atomic Lake in Kazakstan, Russia; via A Green Road Blog
Hiroshima And Nagasaki; Lessons Learned? via A Green Road Blog
Windscale, Sellafield; Biggest Covered Up UK Nuclear Disaster? via A Green Road Blog
Israel‘s Secret Illegal Nuclear, Biological And Chemical Weapons
Dr. Helen Caldicott MD On Nuclear Weapons, MAD/Nuclear Armageddon; via A Green Road Blog 
Cancer – The Forbidden Cures; via A Green Road
Threads; A BBC Nuclear War Movie – What Would Life Be Like After A Nuclear War? 

How do iodine-129 and iodine-131 change in the environment?
Radioactive iodine can disperse rapidly in air and water, under the right conditions. However, it combines easily with organic materials in soil. This is known as ‘organic fixation’ and slows iodine’s movement in the environment. Some soil minerals also attach to, or adsorb, iodine, which also slows its movement.
The long half-life of iodine-129, 15.7 million years, means that it remains in the environment. However, iodine-131’s short half-life of 8 days means that it will decay away completely in the environment in a matter of months. Both decay with the emission of a beta particle, accompanied by weak gamma radiation.
How do people come in contact with iodine-129 and iodine-131?
Radioactive iodine can be inhaled as a gas or ingested in food or water. It dissolves in water so it moves easily from the atmosphere into humans and other living organisms. 
People are exposed to I-129 from the past testing of nuclear weapons, and I-131 from nuclear power plant emissions. Some industrial facilities also emit radioactive iodine to the environment, as well as medical institutions. 
Radioactive iodine is usually emitted as a gas, but may contaminate liquids or solid materials as well. If a family member has been treated with I-131, you may have increased exposure to it through their body fluids.
How do iodine-129 and iodine-131 get into the body?
Radioactive iodine can enter the body by ingestion or inhalation. It dissolves in water so it moves easily from the atmosphere into humans and other living organisms. For example, I-129 and -131 can settle on grass where cows can eat it and pass it to humans through their milk. It may settle on leafy vegetables and be ingested by humans. Iodine isotopes also concentrate in marine and freshwater fish, which people may then eat.
Also, doctors may give thyroid patients radioactive iodine, usually iodine-131, to treat or help diagnose certain thyroid problems. The tendency of iodine to collect in the thyroid makes it very useful for highlighting parts of its structure in diagnostic images.
Exposure from Iodine 131 (Centers for Disease Control)
What do iodine-129 and iodine-131 do once they get into the body?
When I-129 or I-131 is ingested, some of it concentrates in the thyroid gland. The rest passes from the body in urine.
Airborne I-129 and I-131 can be inhaled. In the lung, radioactive iodine is absorbed, passes into the blood stream, and collects in the thyroid. Any remaining iodine passes from the body with urine.
In the body, iodine has a biological half-life of about 100 days for the body as a whole. It has different biological half-lives for various organs: thyroid – 100 days, bone – 14 days, and kidney, spleen, and reproductive organs – 7 days.
Health Effects of Iodine-129 and Iodine-131
How can iodine-129 and iodine-131 affect people’s health?”

Dr. Helen Caldicott MD explains a little bit about Chernobyl and Fukushima and provides a little information about the dangers of radiation poisoning.

EPA: “Radioactive iodine can cause thyroid problems, and help diagnose and treat thyroid problems. Long-term (chronic) exposure to radioactive iodine can cause nodules, or cancer of the thyroid. However, once thyroid cancer occurs, treatment with high doses of I-131 may be used to treat it. Doctors also use lower doses of I-131 to treat overactive thyroids.
Low doses can reduce activity of the thyroid gland, lowering hormone production in the gland. Doctors must maintain the fine balance between the risks and benefits of using radioactive iodine. On one hand, this small, additional exposure may tip the balance in favor of cancer formation. On the other, this small additional exposure can restore health by slowing an overactive thyroid and improve health conditions.
Is there a medical test to determine exposure to iodine-129 and iodine-131?
Since iodine is concentrated in the thyroid gland, a radioassay of the thyroid can determine the level of exposure to many of its isotopes. However, I-129 has very low activity and emits extremely low energy beta particles, making a radioassay much more difficult. Tests for I-131 in the body should be available through most major medical centers.
Protecting People from Iodine-129
How do I know if I’m near radioactive iodine?
Living near a nuclear power plant may slightly increase your annual exposure to I-131. Detecting radioactive iodine in the environment requires specialized equipment. Most major medical centers can test for isotopes of iodine in your body.
Jeffrey Patterson MD on Nuclear Power and Human Health; via A Green Road Blog
Hot Particles (Fuel Fleas) From Fukushima Continue To Circulate Globally; via A Green Road Blog
Low dose radiation causing changes in children; via A Green Road Blog
What can I do to protect myself and my family from iodine-129 and iodine-131?
The thyroid cannot tell the difference between radioactive and non-radioactive iodine. It will take up radioactive iodine in whatever proportion it is available in the environment.
If large amounts of radioactive iodine are released during an nuclear accident, large doses of stable iodine may be distributed by government agencies to keep your thyroid gland from absorbing too much radioactive iodine: Raising the concentration of stable iodine in the blood, increases the likelihood that the thyroid will absorb it instead of radioactive iodine. (Note: Large doses of stable iodine can be a health hazard and should not be taken except in an emergency. However iodized table salt is an important means of acquiring essential non-radioactive iodine to maintain health.
What is EPA doing about iodine-129 and iodine-131?
EPA has issued a variety of regulations that limit the release of radionuclides, including I-129 and I-131, to the environment. These regulations address airborne and liquid releases from nuclear reactors, airborne emissions from a variety of industrial and governmental facilities, and allowable radioactive releases from radioactive waste disposal systems.
EPA has established Maximum Contaminant Levels that limit the concentration of radioactive iodine and other radionuclides in drinking water from public water suppliers.
Iodine-129 is one of the more important radionuclides of concern in the large inventory of spent reactor fuel and defense high-level waste. This standard limits the radiation exposure of individuals, and radionuclide concentrations in ground water from the release of I-129 and other radionuclides in the vicinity of Yucca Mountain.
This site provides information about radionuclides in drinking water and guidance to help states and water systems comply with the standard.
This site provides information about radioactive contaminants in the air.”
Recent Discoveries
Scientists are now able to find out the source of a particular cancer and whether it was caused by a nuclear accident or by ‘nature’, including thyroid cancer, caused by a nuclear accident. In Japan, the law states that a nuclear plant operator is responsible for accidents and health effects. This means that anyone getting cancer from Fukushima can now trace that cancer back to Fukushima radiation releases and sue for damages. 
“This breakthrough is the first time since the reactor accident in 1986 that scientists have been able to discriminate between the cancers caused by the radioactive contamination and those that arise naturally.”…
Link to the article about the study:
Abstract on the PNAS website:
Correspondence should be addressed. 

According to Wikipedia; “Iodine-131 (131I), 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. 
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 Japanese nuclear crisis
This is because I-131 is a major uraniumplutonium 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. 
Much smaller incidental doses of iodine-131 than those used in medical therapeutic procedures, are thought to be the major cause of increased thyroid cancers after accidental nuclear contamination.[3] 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.
Most I-131 production is from nuclear reactor neutron-irradiation 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.[4] 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).[5]
Radioactive decay
Iodine-131 decay scheme (simplified)
131I decays with a half-life of 8.02 days with beta and gamma emissions. This nuclide of iodine atom has 78 neutrons 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).[6] 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.[7]
131I is a fission product with a yield of 2.878% from uranium-235,[8] 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.
Effects of exposure from atomic bomb testing
Per capita thyroid doses in the continental United States resulting from all exposure routes from all atmospheric nuclear tests conducted at the Nevada Test Site from 1951-1962.
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.[1]
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.[1]
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 distributed to the population living nearest to the Chernobyl nuclear power plant after the disaster,[9] 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 sour sources of milk contaminated as the result of above-ground testing of nuclear weapons.[10]
The National Cancer Institute provides additional information on the health effects from exposure to 131I in fallout,[11] 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.[12]
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.[13] 
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 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 micrograms 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 theJod-Basedow phenomena, and the Wolff-Chaikoff effect, trigger and/or worsen hyperthyroidism and hypothyroidism respectively, 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.[15]
The administration of known goitrogen substances can also be used as a prophylaxis in reducing the bio-uptake of iodine, (whether it be the nutritional non-radioactive iodine-127 or radioactive Iodine, radioiodine – most commonly iodine-131, as the body cannot discern between different iodine isotopes).
Perchlorate ions, a common water contaminant in the USA due to the aerospace industry, has been shown to reduce iodine uptake and thus is classifed as a goitrogen. Perchlorate ions are a competitive inhibitor of the process by which iodide, is actively deposited into thyroid follicular cells. 
Studies 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).[16] 
The reduction of the iodide pool by perchlorate has dual effects–reduction of excess hormone synthesis and hyperthyroidism, on the one hand, and reduction of thyroid inhibitor synthesis and hypothyroidism on the other. Perchlorate remains very useful as a single dose application in tests measuring the discharge of radioiodide accumulated in the thyroid as a result of many different disruptions in the further metabolism of iodide in the thyroid gland.[17]
Treatment of thyrotoxicosis (including Graves’ disease) with 600-2,000 mg potassium perchlorate (430-1,400 mg perchlorate) daily for periods of several months or longer was once common practice, particularly in Europe,[16][18] and perchlorate use at lower doses to treat thryoid problems continues to this day.[19]Although 400 mg of potassium perchlorate divided into four or five daily doses was used initially and found effective, higher doses were introduced when 400 mg/day was discovered not to control thyrotoxicosis in all subjects.[16][17]
Current regimens for treatment of thyrotoxicosis (including Graves’ disease), when a patient is exposed to additional sources of Iodine, commonly include 500 mg potassium perchlorate twice per day for 18-40 days.[16][20]
Prophylaxis with perchlorate containing water at concentrations of 17 ppm, which corresponds to 0.5 mg/kg-day personal intake, if one is 70 kg and consumes two litres of water per day, was found to reduce baseline radioiodine uptake by 67%[16] This is equivalent to ingesting a total of just 35 mg of perchlorate ions per day. In another related study were subjects drank just 1 litre of perchlorate containing water per day at a concentration of 10 ppm, i.e daily 10 mg of perchlorate ions were ingested, an average 38% reduction in the uptake of Iodine was observed.[21]
However when the average perchlorate absorption in perchlorate plant workers subjected to the highest exposure has been estimated as approximately 0.5 mg/kg-day, as in the above paragraph, a 67% reduction of iodine uptake would be expected. Studies of chronically exposed workers though have thus far failed to detect any abnormalities of thyroid function, including the uptake of iodine.[22] this may well be attributable to sufficient daily exposure or intake of healthy iodine-127 among the workers and the short 8 hr biological half life of perchlorate in the body.[16]
To completely block the uptake of iodine-131 by the purposeful addition of perchlorate ions to a populaces water supply, aiming at dosages of 0.5 mg/kg-day, or a water concentration of 17 ppm, would therefore be grossly inadequate at truly reducing radioiodine uptake. Perchlorate ion concentrations in a regions water supply, would need to be much higher, approaching 500 mg/kg or 500 ppm, to be truly beneficial to the population at preventing bioaccumulation when exposed to a radioiodine environment,[16][20] independent of the availability of iodate or iodide drugs.
The continual addition of Perchlorate to the water supply would need to continue for no less than 80-90 days, beginning immediately after the initial release of radioiodine was detected, after 80-90 days had passed released radioactive iodine-131 would have decayed to less than 0.1% of its initial quantity and thus the danger from biouptake of iodine-131 is essentially over[23].
In the event of a radioiodine release the ingestion of prophylaxis potassium iodide or iodate, if available, would rightly take precedence over perchlorate administration 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 controlled by the limited stock of iodide & iodate prophylaxis drugs, then the addition of perchlorate ions to the water supply, or distribution of perchlorate tablets would serve as a cheap, efficacious, second line of defense against carcinogenic radioiodine bioaccumulation.
The ingestion of goitrogen drugs is, much like potassium iodide is also not without its dangers, such ashypothyroidism. In all these cases however, despite the risks, the prophylaxis benefits of intervention with iodide, iodate or perchlorate outweigh the serious cancer risk from radioiodine bioaccumulation in regions were radioiodine has sufficiently contaminatated the environment.
[edit]Medical and pharmaceutical uses
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 uptake of radioiodide. Radioactivity is also seen from uptake by the liver, and excretion by the kidneys with accumulation in the bladder.
It is used in nuclear medicine 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 treatingpheochromocytoma 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.[24] 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.”[25] 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.[26]
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.[27] 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.[28] 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.[29]
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 with applications in isotope hydrology and leak detection. [30][31][32][33]
Since 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 iodine.[34][2][35] It is used to characterize the hydraulic fracturing fluid to help determine the injection profile and location of fractures created by hydraulic fracturing.[36][37][38]

Iodine and Radioactive Iodine Facts; via A Green Road Blog

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