STUDIES OF POTENTIAL HUMAN-HEALTH EFFECTS FROM BRECCIA-PIPE URANIUM MINING IN THE GRAND CANYON REGION, USA

Underground mining of breccia-pipe uranium deposits in the Grand Canyon region generates controversy for a variety of reasons, including possible effects of mining to human health. Potential health concerns related to uranium mining include radiation exposure, inhalation of dust, and toxicity from uranium and co-occurring ore-body elements, including arsenic, from inhaled or consumed material. In 2012, the U.S. Department of Interior instated a 20-year moratorium on new mining of breccia-pipe deposits in the Grand Canyon region, while allowing existing permitted mines to continue operations. Since then, the U.S. Geological Survey has conducted numerous studies to better understand the environmental and human-health effects of mining across the mine life cycle at developing, active, inactive, and reclaimed mine sites in the region. Human health-related studies include monitoring radon, dust flux, and dust chemical and mineralogic composition around some of the mine sites; establishing baseline concentrations of multiple metals in elk tissue harvested from tribal hunting grounds; and analyzing metal content of smoke from combusted vegetation collected near a uranium mine to better understand the composition of smoke potentially inhaled during ceremonial traditional use. Results indicate radon gas concentrations vary generally with size of ore storage at the surface and inversely with the amount of wind and rain at a mine site. Dust flux is greatest during periods of drought and reclamation activity. Elk liver- and muscle-tissue samples had only 1 sample each (4 out of 40 results) above quantification limits for arsenic (0.04 parts per milligrams per kilogram dry weight (mg/kg)) and uranium (0.02 parts per mg/kg). Study results of smoke from combusted vegetation are pending but involved development of a combustion chamber that directly collects smoke particulates for digestion and analysis. Our results may help inform management decisions to mitigate uptake and health effects during all phases of uranium mining in the Grand Canyon region.