Radioactive contamination of atmospheric dust over southeastern New Mexico

Aerosol particle samples were collected at three sites located near the Waste Isolation Pilot Plant (WIPP), a deep underground nuclear waste-storage facility, and they were analyzed to investigate the spatial and temporal variations in the concentrations of selected radionuclides and inorganic substances. The activities of 238Pu, 239,240Pu,241Pu and 241Am were determined by alpha spectrometry following a series of chemical separations, and the concentrations of Al, U and Th were determined in a separate set of samples by inductively-coupled plasma mass spectrometry. There was no evidence for impacts of the WIPP on radionuclide activity concentrations. Rather, the activities of both naturally-occurring (U and Th) and man-made (241Am and 239,240Pu) radionuclides in the aerosols peaked in spring and tracked the loadings of Al, an indicator of mineral dust. More than half of the variability in the 239,240Pu at the sampling site closest to the WIPP could be explained by the seasonal cycles of atmospheric dust. For U and Th, the predictive value of Al was even higher: 66% to over 90% of the variance in these nuclides could be explained by their relationship to dust. Extrapolation of the data to a global scale suggests that 0.02% of the total 239,240Pu from nuclear weapons’ fallout currently recirculates between the earth and atmosphere each year. In terms of monitoring releases from nuclear facilities, the results presented here demonstrate that elemental data provide information directly relevant to understanding causes for variability in the activities of atmospheric radionuclides.