Watching Chernobyl miniseries and a nuclear physicist gave a girl “stable iodine” saying it would prevent her thyroid from absorbing radioactive iodine, any attempt to Google this question got me results on radiation therapy.
Edit: I’m not asking about radiation treatment or iodine pills, I want to know why iodine specifically is so dangerous to our bodies when irradiated as opposed to other elements/molecules our bodies regularly use.
In: Biology
Radioactive iodine-131 is one of the products of nuclear fission. The human body can’t tell the difference between radioactive iodine-131 and stable iodine-127. So the body will absorb and hold onto iodine-131. Like a trojan horse, now the individual will have radioactive elements within them irradiating their thyroid and bloodstream. Additionally iodine is absorbed and used slowly so it would hang around for a while before it could be replaced with the non radioactive iodine-127
The largest concentrations of iodine in the body are found in the thyroid. Your thyroid makes use of iodine in order to produce some of the hormones it makes. The main reason radioactive is iodine is such a major risk is because its one of the few byproducts of nuclear fission whose stable, less dangerous isotopes play an important biological role and is thus absorbed by the body.
Because it’s not that common in the environment, so your thyroid has evolved to be very good at grabbing it out of your blood stream.
Iodine is a common product when uranium fissions so a good portion–like several percent–of the radioactivity is from iodine. The isotopes also have short half lives, and combined with it’s abundance causes a huge amount of radioactivity. Your thyroid concentrating it makes things even worse. It creates an intense source (because of all the iodine) at close range (inside your body) which will give big doses to organs like your brain, lungs, and bone marrow in your ribs. Those big doses are what out you at risk of cancer. It’s the same reason other isotopes like cobalt-60 or strontium-90 are bad. Your biological processes hold on to them and keep them inside you.
They way the pill works is by flooding your system with stable, non-radioactive iodine so that your thyroid is “full” and doesn’t absorb the radioactive variety so your kidneys can remove it and you pee it out.
During nuclear fission you split Uranium, Thorium or Plutonium into smaller fission products. But these tends to be unstable isotopes. Some of these will have a very short half life, this makes them emit a lot of radiation but also become harmless very fast. Others have very long half lives meaning they will emit radiation for millions of years but never very much. There are also different types of radiation with alpha radiation being very harmful if you get it inside your body but not to anything else, then beta radiation and lastly gamma radiation which goes through almost anything but that means it will not stop to cause much damage. So even though there are lots of fission products being spread in a nuclear disaster we mostly focus on the medium half life radiation sources.
And about 2-3% of the fission products will be Iodine-131 with a half life of 8 days emitting beta radiation. So it will be a big source of the radiation in the weeks after a nuclear disaster. Especially since Iodine is a nutritional mineral. And isotopes are chemically indistinguishable from each other. So plants will absorb iodine in the dust and people will eat the plants in addition to dust that have fallen on food and the body will absorb this Iodine and carry it off to the thyroid for storage and processing. You need about 150µg of Iodine a day but can store much more then that. The body have no way of knowing that it is absorbing the radioactive isotope of Iodine and that it will slowly kill it. The way you prevent this from happening is to make sure the body have an excess of non-radioactive Iodine. If you do this then it will not take up more iodine and will flush it out in the urine. And this is what you see they do in the show.
Every radioactive element releases a certain amount of energy as it decays. Some elements decay in fractions of a second, so they release a ton of energy. Other elements decay over thousands to millions of years, so they release the energy very slowly. Iodine decays slowly enough for it to travel through the environment and potentially be absorbed by people, but quickly enough that it releases quite a bit of energy which is damaging to the body.
Iodine specifically is dangerous because it is one of the only radioactive fission products that is used by the body. There are radioactive versions of other elements, but they are not inherently radioactive, they are induced because of neutrons. Hence the occurrence of these versions is extremely low, and they can’t accumulate in quantities large enough to cause any harm
It’s a combination of the fact that your body craves iodine (and will eagerly uptake it out of anything in the environment), stores it in a dicey location (your thyroid gland), and the half-life of the radioactive iodine-131 (8 days) is really short relative to its biological half-life (12 days), so it’ll have a chance to spew a lot of radiation into you before your body gets rid of it.
So it’s a particularly vulnerable fission product for acute (short-term) exposure. It is not the only worrisome fission product by a long-shot, but among the short-term ones it is a really nasty combination of factors that makes it dangerous and hard to avoid (without taking the iodine pills that will make your body stop up-taking it).
The other fission products that are biologically worrisome tend to have longer half-lives (e.g., Sr-90 = 28 years) which means that they are more chronic risks than acute ones.
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