THE ASSESSMENT OF HUMAN EXPOSURE TO RADIONUCLIDES FROM A URANIUM MILL TAILINGS RELEASE AND MINE DEWATERING EFFLUENT

An assessment was made of human exposure to radiation from a river system contaminated by radionuclides of the 238U decay series released through a dam break at a U mill tailings pond and by the continuous discharge of dewatering effluent from 2 U mines. The in vivo analyses of radionuclides in 6 Navajo Indians who lived near the river indicated no detectable elevations above background concentrations. Dose estimates for inhalation of suspended river sediment indicated a maximum annual 50 yr dose commitment of 204 mrem to the endosteum. Estimates of doses (50 yr dose commitments) from the ingestion of livestock ranged between 1 mrem (to liver)-79 mrem (to bone) suggesting that the major contribution to human exposure was from mine dewatering effluent that had been continuously released into the river system for many years. Although the estimated exposures did not exceed existing state or federal regulations, their magnitude justified further measurement of radionuclides in animals and in the natural environment and the consideration of strategies to reduce radiation exposure to humans and animals.