Iodine ingested iodine and retain it for periods longer than this isotope's radiological half-life of eight days. For this reason, people at risk of exposure to environmental radioactive iodine (iodine-131) in fallout may be instructed to take non-radioactive potassium iodide tablets. The typical adult dose is one 130 mg tablet per 24 hours, supplying 100 mg (100,000 micrograms) of ionic iodine. (The typical daily dose of iodine for normal health is of order 100 micrograms; see "Dietary Intake" below.) Ingestion of this large dose of non-radioactive iodine minimises the uptake of radioactive iodine by the thyroid gland. As an element with
Tincture of iodine Lugol's iodine, by contrast, has no alcohol, and has twice the mass of potassium iodide as of elemental iodine. Alcohol content in the tincture of iodine can be determined by the methods of Alcock, Roscoe - Schorlemmer and Thurston - Thurston. As both USP solutions contain elemental iodine, which is moderately toxic when ingested in amounts larger than those required to disinfect water, tincture of iodine is sold labelled “for external use only,” and used primarily as a disinfectant. Tincture of iodine is often found in emergency survival kits, used both to disinfect wounds and to sanitize surface water for