Iodine (chemical symbol I) is a nonmetallic solid element. There are both radioactive and non-radioactive isotopes of iodine. Iodine-129 and -131 are the most important radioactive isotopes in the environment. Some isotopes of iodine, such as I-123 and I-124 are used in medical imaging and treatment, but are generally not a problem in the environment because they have very short half-lives.


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 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.