239,240Pu and inorganic substances in aerosols from the vicinity of a waste isolation pilot plant:: The importance of resuspension

Aerosol samples were collected and analyzed to characterize the spatial and temporal variations in the concentrations of plutonium and selected inorganic substances in the atmosphere around the Waste Isolation Pilot Plant (WIPP). High-volume aerosol sampling was conducted at three sites: (1) On Site, (2) Near Field, and (3) Cactus Flats. Pu-239,Pu-240 was determined by alpha spectrometry following chemical separations; mass loadings were determined gravimetrically. A separate set of low-volume aerosol samples was analyzed for major ions using ion chromatography and for trace elements by inductively-coupled plasma emission spectrometry and mass spectrometry. The average Pu-239,Pu-240 activity concentrations in total suspended particle (TSP) samples (12 to 16 nBq m(-3)) were consistent with those previously reported, but they varied strongly with season, with the highest values generally in spring. Further, the Pu-239,Pu-240 activity concentrations were comparable among the three sites, and therefore there was no evidence for elevated Pu-239,Pu-240 activities due to WIPP operations. The fraction of the Pu-239,Pu-240 activity concentrations in the PM10 samples (particles less than 10 mum diameter) relative to TSP was lower than the corresponding PM10/TSP ratios of either high-volume mass or several inorganics (sulfate, aluminum or lead), indicating that Pu-239,Pu-240 tends to be on large particles. Aerosol mass loadings (mug m(-3)) and Pu-239,Pu-240 activity concentrations were correlated for all sets of samples, but at On Site, the TSP samples showed higher mass to Pu-239,Pu-240 ratios than the other sites. Thus activities or processes occurring at or near the WIPP site evidently produced aerosols that contributed to the mass loadings but contained less Pu-239,Pu-240 than ambient aerosols. About 63% of the variability in Pu-239,Pu-240 activity concentrations was explained by wind travel, sampling location, length of the sampling interval, and aerosol mass. Pu-239,Pu-240 activity concentrations also were correlated with aluminum (an indicator of mineral dust), further implicating the resuspension of soils as an important determinant of Pu-239,Pu-240 in aerosols. The Pu-239,Pu-240/Al ratios for the aerosols were higher than in soils, and this could be explained by the preferential binding of Pu-239,Pu-240 to small soil particles that have large surface area to mass ratios and also have higher aluminum contents than larger particles.