Uranium in vitro bioassay action level used to screen workers for chronic inhalation intakes of uranium mill tailings

A uranium in vitro bioassay (urinalysis) action level was derived for use at the Department of Energy's Uranium Mill Tailings Remedial Action Project sites to identify chronic inhalation intakes of uranium mill tailings causing 0.5 mSv (50 mrem) annual effective dose equivalent. All radionuclides in the 238U decay chain that contribute 1% or more to the annual effective dose equivalent from an inhalation intake of uranium mill tailings were included in the derivation of the urinalysis action level. Using a chronic inhalation intake model, the uranium urinalysis action level for a 24-h urine sample, collected on a quarterly schedule, was calculated to be 1.5 micrograms.