Criteria for safe working with iodine-125

Radio-immunoassay and other saturation assay tests involving the use of iodine-125 are finding wide application for the determination of hormone concentrations in biological fluids. In such tests, iodinations involving concentrations of a milli-curie per micro-litre are common. Iodine-125 presents a problem from the monitoring standpoint because of its low energy photon emission (27 and 35 keV). Iodine is preferentially taken up by the thyroid gland and work involving moderate amounts of radio-iodine may give rise to a significant hazard in an accident situation. The general precautions which should be taken in work with unsealed radioactive substances are briefly summarized, working limits for iodine-125 are identified, and methods of personal protection and monitoring in an emergency situation described. (author)