At least three isotopes of iodine are important. 129I, 131I (Radioiodine) and 132I. An overview of iodine exposure in the USA (resulting from bomb tests) can be seen at [1]. Open air nuclear testing and the Chernobyl disaster both released iodine-131.
Per capita thyroid doses in the continental United States of iodine-131 resulting from all exposure routes from all atmospheric nuclear tests conducted at the Nevada Test Site. See also Downwinders.
The short-lived isotopes of iodine are particularly harmful because the thyroid collects and concentrates iodide -- radioactive as well as non-radioactive -- for use in the production of metabolic hormones. Absorption of radioiodine can lead to acute, chronic, and delayed effects. Acute effects from high doses include thyroiditis, while chronic and delayed effects include hypothyroidism, thyroid nodules, and thyroid cancer. It has been shown that the active iodine released from Chernobyl and Mayak[4] has resulted in an increase in the incidence of thyroid cancer in the former Soviet Union.
One measure which may protect against this risk is taking large doses of potassium iodide before exposure to radioiodine -- the non-radioactive iodide 'saturates' the thyroid, causing less of the radioiodine to be stored in the body. Because this countermeasure simply takes advantage of the pharmacokinetics regarding iodide uptake, it affords no protection against other causes of radiation poisoning.
Administering potassium iodide reduces the effects of radio iodine by 99%, and is a prudent, inexpensive supplement to sheltering. The Food and Drug Administration (FDA) has approved potassium iodide as an over-the-counter medication. As with any medication, individuals should check with their doctor or pharmacist before using it.
A low-cost alternative to commercially available iodine pills is a saturated solution of potassium iodide. It usually possible to obtain several thousand doses for prices near US$ 0.01/dose. Long term storage of KI is normally in the form of reagent grade crystals, which are convenient and available commercially. The purity is superior to "pharmacologic grade". Its concentration depends only on temperature, which is easy to determine, and the required dose is easily administered by measuring the required volume of the liquid. At room temperature, the U.S. standard adult radiological protective dose of 130 mg is four drops of a saturated solution. A baby's dose is 65 mg, or two drops. It should be noted that these doses are sufficient to cause nausea and sometimes emesis in most individuals. It's normally administered in a ball of bread, because it tastes incredibly bad. Use is contraindicated in individual known to be allergic to iodine; for such persons sodium perchlorate is one alternative (see chap 13, Kearney).
