Iodine Basics | Exposure Route | Radiation Dose | Health Risks | Protection Standards

This web site focuses on iodine 131 (I-131) because large amounts of this isotope were released during the production and testing of nuclear weapons. Iodine 127 (I-127) is the only naturally occurring iodine isotope, and it is the only nonradioactive (stable) iodine isotope. All other iodine isotopes (I-123, I-125, I-129, I-131, and I-135) are radioactive. Only I-131 and I-123 are associated with medical administration.

I-131 is normally present at low levels in hospital nuclear medicine departments, patients administered radioactive iodine in the last 3 months, and in releases from nuclear power plants.

I-131 is produced during nuclear fission, which occurs during the operation of nuclear reactors or detonation of a nuclear bomb. When uranium or plutonium atoms undergo fission, about 1.5%–2% of the fission products become I-131.

Radioiodine has a strong affinity for the thyroid gland, which is the critical organ for exposure. Exposure to I-131 increases the risk for hypothyroidism, thyroid nodules, and cancer, especially in childhood. I-131 can play a specific role in the health consequences of radioactivity released into the environment, primarily related to uptake in children’s thyroid from the ingestion of milk from goats or cows that grazed on contaminated pasture land.

It is not very likely that I-131 would be a component of dirty bombs because such a bomb does not produce I-131. Also, the half-life of I-131 is a little more than 8 days, which precludes it from being added to a dirty bomb.