COMPARATIVE PLANT UPTAKE AND ENVIRONMENTAL BEHAVIOR OF U-SERIES RADIONUCLIDES AT A URANIUM MINE-MILL

Concentrations of U, Th, Ra, Pb, and Po were determined in native vegetation and underlying substrate (soil and tailings) at various sites around a conventional open pit, acid leach uranium production operation in the Western United States. Radionuclide concentrations in substrate and vegetation were generally elevated above background at all sites disturbed by mining and milling activities. Observed plant/soil CR values for vegetation growing on exposed, weathered tailings were ordered as follows: U-238 > Th-230 > Po-210, Ra-226 > Pb-210. We suspect that in the case of sulfuric acid leached tailings, Ra and Pb are sequestered as sulfates, which are highly insoluble relative to U and Th sulfates, resulting in reduced availability for plant uptake. Soil acidity and the saturation condition at the tailings impoundment edge tend to enhance radionuclide availability for plant uptake. The transport of radionuclides to foliage and subsequent retention and absorption may play a role in plant contamination.