THE DIVERSITY OF POTENTIALLY TOXIC ATMOSPHERIC PARTICULATE ASSOCIATED WITH THE MIDNITE URANIUM MINE, SPOKANE INDIAN RESERVATION: A SCANNING ELECTRON MICROSCOPY INVESTIGATION OF PINUS PONDEROSA BARK

The Midnite Uranium Mine, located on the Spokane Indian Reservation of Washington State, was abandoned in 1981 after 26 years of operation, leaving a legacy of uncovered ore piles, pits, and potential health issues. The Environmental Protection Agency (EPA) has demonstrated extensive contamination of the water and soil (e.g. presence of radionuclides and heavy metals), and declared the mine a Superfund Site in 2000. High rates of cancer, auto-immune disease, renal failure, and stillbirths exist on the reservation. One potential cause for these diseases is the inhalation of atmospheric particulate from the mine yet little to no work has been done to evaluate the nature and extent of atmospheric pollution on the reservation. To assess atmospheric dispersal, bark was sampled from 77 Pinus ponderosa trees approximately 40-150 years in age throughout the reservation. Samples were investigated using a scanning electron microscope equipped with backscatter detection, energy dispersive spectroscopy and elemental mapping capabilities. Particles of interest and their characteristics include (1) widespread iron silicates as both spherules and irregular particles varying from <1 μm to 6 μm in diameter: As, Mn, and Cr were observed in particles near the mine access roads and mill site); (2) barite spherules in mill site samples; (3) widespread rare earth element (REE) phosphates predominantly 1-2 μm in diameter: Th is observed as being a common trace element along with rare occurrences of U, Cs, and Pb; (4) REE calcium silicates in mill site and mine access road samples varying from 4-10 μm in diameter; (5) Pb-Cr was observed as flakey/microcrystalline overgrowths (<500 nm) on a <10 μm silicate particle; (6) Adjacent gold and tin particles with diameters of ≤1 μm in one mine access road sample; (7) Fe-Ni particles ranging from 1-4 μm diameter in one mine access road sample; and (8) a U-Nb phase in mill site samples with particles varying from 1-2 μm in diameter: mapping of one such particle revealed detectable amounts of U, Nb, Ca, Si, O, Mg, Al, Fe, P, and K, however U and Nb were the dominant EDS peaks. This preliminary investigation of tree bark on the Spokane Indian Reservation indicates atmospheric particulate potentially poses a health risk. Work on elemental concentrations in tree bark and geospatial correlations is ongoing.