You may have heard of Iodine-131, an isotope of iodine that is used in the medical field to treat thyroid cancers. However, iodine-131 is a radioactive isotope and its form of radioactive decay, beta emission (decay by way of ejecting high-speed, negatively charged electrons from the atom), is infamous for causing mutations and even death in affected cells, and care must be taken when handling or being near it.

In nature, iodine-131 has a half-life (time for half the sample to decay) of about 8 days, meaning it requires at least 54 days (almost 2 months) for 99% of it to decay and become harmless. However, if ingested or inhaled into the body, some of it may concentrate in the thyroid gland while the rest is flushed out in urine. In the thyroid gland, it has a “biological half-life” of about 100 days, and so it may take over a year for the body to fully purge the isotope from itself. During this time, it may harm the body regardless of whether it has decayed or not.

To protect yourself, we recommend wearing some form of suit made from aluminum or plastic. We advise against wearing suits or moving to areas fortified with high-density materials such as lead or tungsten, because they can produce secondary radiation. When the negatively charged beta particles hit an element with a high atomic number or density, the electrons may be blocked, but it may still irradiate the target the material was supposed to protect, according to reports from the Environmental Protection Agency.

Iodine-131 gives off much greater amounts of radiation than what we safely receive in a year’s time, and so it should actively be avoided except when in the hands of trained, medical professionals. What we are referring to by “safely receive” is the normal amount of radioactivity that penetrates the Earth’s atmosphere from deep space, that which emanates from earth, and extremely tiny amounts found naturally in food, water, and air. This “natural” radiation is perfectly safe and causes no harm, producing as much radioactivity in one year or more as Iodine-131 produces in much shorter hours or days, which is much more harmful.

We hope we have informed you about iodine-131 and how potentially dangerous it can be, and we urge you to take precaution against it.