Iodine-131 bioaccumulation in regions where radioiodine has sufficiently contaminatated the environment. Iodine-131 is used for unsealed source radiotherapy in nuclear medicine to treat several conditions. It can also be detected by gamma cameras for diagnostic imaging, however it is rarely administered for diagnostic purposes only, imaging will normally be done following a therapeutic dose. Use of the I as iodide salt exploits the mechanism of absorption of iodine by the normal cells of the thyroid gland. Major uses of I include the treatment of thyrotoxicosis (hyperthyroidism) due to Graves' disease, and sometimes hyperactive thyroid nodules (abnormally active thyroid tissue that is
Iodine and iodate anions are often used for quantitative volumetric analysis, for example in iodometry and the iodine clock reaction (in which iodine also serves as a test for starch, forming a dark blue complex), and aqueous alkaline iodine solution is used in the iodoform test for methyl ketones. The iodine test for starch is still used to detect counterfeit banknotes printed on starch-containing paper. The spectra of the iodine molecule, I, consists of (not exclusively) tens of thousands of sharp spectral lines in the wavelength range 500-700 nm. It is therefore a commonly used wavelength reference (secondary standard). By measuring