How A Dose Of Iodine Could Kill You (Or Save Your Life)

potassium iodide tablets ftloscience post

Ever since the advent of nuclear warfare during World War II, the threat posed by weapons of mass destruction continuously makes its way into headlines. The devastation that nuclear reactions can achieve is undeniable. However, their effects can propagate beyond the immediacy of blast damage and thermal radiation. Another danger lurks in the form of radioactive isotopes, such as iodine-131, with the threat of both short and long-term adverse health effects.

Nuclear Fission

Nuclear technology aims to manipulate the very energy that holds the nucleus of an atom together. Huge amounts of energy can be released either by splitting them apart (fission) or putting these elements together (fusion). While nuclear fusion technology is primitive at best, nuclear fission has been harnessed to create weapons and power entire cities (it is both of interest and concern which one came first).

Nuclear fission occurs when an atom’s nucleus splits, resulting in two smaller atoms. This process can happen on its own or forcefully induced by ‘bombarding’ heavy atoms with neutrons. Each atom that is split in this way can release even more free neutrons, which trigger even more fission events, eventually leading to a nuclear chain reaction. Atoms that are able to achieve this reaction are known as ‘fissile’ and are used as nuclear fuels; U-235 and Pu-239 are by far the most common isotopes used. The number after the element denotes its atomic mass.

uranium 235 decay energies
Neutrons released in this manner are able to trigger further fission events in nearby atoms.

Nuclear Power

A nuclear reactor is able to capture the energy released as heat from such fission events, which generates steam from water. The steam is forced through a turbine, generating electricity. This is identical to the inside of a traditional power plant, in which fossil fuels are burnt to release energy. However, burning nuclear fuel this way produces millions of times more usable energy per unit mass than coal, making it an efficient and cleaner form of energy.

nuclear power plant steam
In many countries, nuclear power plants provide an alternative source of green energy.

The reason that nuclear power plants are not widely used is because of the dangers they can pose if something goes wrong. Major accidents such as the Chernobyl (1986) and Fukushima disasters (2011) are well documented. While the nuclear material used in power plants does not have the potential to generate substantial explosive power, it can still release radioactive material into the atmosphere, causing a nuclear fallout in the surrounding areas.

Radioactive Decay

When a heavy atom splits, the smaller atoms that are formed are simply statistical probabilities. One of the major byproducts of U-235 fission happens to be an isotope of iodine (specifically, I-131) with a 2.878% chance to form with each fission event1. However, the fission products of U-235 also include atoms of Ba, Kr, Sr, Cs, Xe, I and other elements with atomic masses between 95 and 135. Many of these isotopes are unstable and spontaneously decay, releasing ionizing radiation.

radioactive decay alpha beta gamma
Processes of nuclear decay, releasing ionizing radiation. (LibreTexts)

Of the decay types, beta decay is most common amongst fission products, as their nucleus tends to contain an unstable ratio of protons and neutrons. A neutron can spontaneously transform into a proton (and vice versa) to form a more stable nucleus, releasing either an electron or a positron. After alpha or beta decay, the nucleus is usually left in a high-energy ‘excited’ state. Obviously, they would rather be in a lower energy state and they achieve this by emitting a high-energy gamma-ray photon, a process called gamma decay. These forms of decay are what allow us to perform radiometric dating.

But wait a minute, if all those isotopes go about their business decaying without care, what is it that makes iodine-131 so special?

Iodine-131 Health Risks

Iodine is readily taken up by the body and is stored in the thyroid gland where it is needed for the production of hormones. Under normal circumstances, we are exposed to I-127, the ‘stable’ isotope of iodine. However, our body doesn’t discriminate between the stable I-127 or the radioactive I-131 as they are so similar in size. In the event of I-131 being released into the atmosphere from a nuclear event, our body will happily absorb it and store it in our thyroid.

This becomes a problem when combined with the fact that I-131 has a relatively short half-life of just 8 days, emitting high-energy beta radiation that can penetrate through cells. Once ingested, I-131 has an extremely high likelihood of causing damage to thyroid tissue and increasing the victim’s risk of thyroid cancer.

radioactivity levels chernobyl
Radioactivity measured after the Chernobyl disaster – I-131 levels in the environment remained high even 10 days after the event.

A study of the people affected by the Chernobyl disaster fallout showed that I-131 was absorbed through contaminated milk, and accumulated in the thyroid glands of the population, mostly children. Cases of pediatric thyroid cancer, likely caused by absorption of I-131 into the thyroid gland, increased in Ukraine and Belarus 3 to 4 years after the accident2.

Ten years after the Chernobyl accident, thyroid damage caused by I-131 was virtually the only adverse health effect that could still be measured. Studies undertaken by the US Nuclear Regulatory Commission showed that “except for thyroid cancer, there has been no confirmed increase in the rates of other cancers, including leukemia, among the… public, that have been attributed to releases from the accident3.”

Researchers at the World Health Organization continued long-term monitoring of the victims from Chernobyl and were shocked to find an increase in thyroid cancer cases up to 500 km from the accident site, far beyond emergency planning zones. Up till 2002—almost 30 years after the incident—over 11,000 cases have been reported4, with that number likely to have increased in subsequent years.

Iodine Tablets

There is, however, a simple defense against I-131 in the event of nuclear fallout. To counteract I-131 accumulation in the thyroid gland, the body can be overloaded with the stable isotope of iodine, I-127. This is taken up by the thyroid gland and saturates it, meaning the body absorbs less of the radioactive I-131, excreting it instead. I-127 is supplied in the form of potassium iodide (KI) tablets and saturated solutions of potassium iodide, as elemental iodine is too toxic to be ingested directly.

The effectiveness of iodine tablets was shown during the Chernobyl crisis; the population living in irradiated areas where KI was not available developed thyroid cancer at epidemic levels. In neighboring Poland, where solutions of KI were administered to 10.5 million children and 7 million adults, the observed levels of I-131 activity were much lower than expected.

iosat potassium iodide tablets
Standard KI tablets that can easily be found (even on Amazon!)

Lucky for us, potassium iodide is stocked by many governments in the event of a nuclear disaster. If you feel like you should take matters into your own hands, tablets can also be bought over the counter and online. In the spirit of chemistry, a solution of KI can be easily made in the lab by dissolving the highly soluble KI salt in pure water until no more crystals dissolve. A standard I-131 blocking dose consists of 1-2 drops made this way (50-100 mg iodide). Something you can try at home?


  1. Braverman, E. R., Blum, K., Loeffke, B., Baker, R., Kreuk, F., Yang, S. P., & Hurley, J. R. (2014). Managing terrorism or accidental nuclear errors, preparing for iodine-131 emergencies: a comprehensive review. International journal of environmental research and public health11(4), 4158-4200.
  2. Cardis, E., Howe, G., Ron, E., Bebeshko, V., Bogdanova, T., Bouville, A., … & Drozdovitch, V. (2006). Cancer consequences of the Chernobyl accident: 20 years on. Journal of radiological protection26(2), 127.
  3. US Nuclear Regulatory Commission. (1998). Assessment Of The Use Of Potassium Iodide (KI) as a Public Protective Action During Severe Reactor Accidents-Draft Report For Comment. NUREG-1633, Washington, DC: NRC.
  4. Hatch, M., E. Ron, A. Bouville, L. Zablotska, and G. Howe. “The Chernobyl disaster: cancer following the accident at the Chernobyl nuclear power plant.” Epidemiologic reviews 27, no. 1 (2005): 56-66.

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