Utsunomiya, SatoshiSatoshiUtsunomiyaKersting, Annie B.Annie B.KerstingEwing, Rodney C.Rodney C.Ewing2026-03-312026-03-312009-02-26https://www.scopus.com/pages/publications/64349094214https://scholars.lib.ntu.edu.tw/handle/123456789/736912Colloid-like nanoparticles in groundwater have been shown to facilitate migration of several radionuclides: 239,240Pu, 137Cs, 152,154,155Eu, and 60Co (1). However, the exact type of nanoparticle and the speciation of the associated radionuclides has remained unknown. We have investigated nanoparticles sampled from the far-field at the Nevada Test Site, Nevada, utilizing advanced electron microscopy techniques, including high-angle annular dark-field scanning TEM (HAADF-STEM). Fissiogenic elements: Cs, rare earth elements (REE), activation elements: Co; and actinides: U and Th, were detected. Cesium is associated with U-forming cesium uranate with a Cs/U atomic ratio of ∼0.12. Light REEs and Th are associated with phosphates, silicates, or apatite. Cobalt occurs as a metallic aggregate, associated with Cr, Fe, Ni, and ± Mo. Uranyl minerals; Na-boltwoodite and oxide hydrates are also present as colloids. Because of these chemical associations with nanoscale particles, in the size range <100 nm, these particles may facilitate transport, and a variety of trace nanoscale phases may be responsible for the migration of fissiogenic and actinide elements in groundwater. To accurately model the transport of these contaminants, predictive transport models should include consideration of nanoparticle-facilitated transport.ColloidsElementsMotionNanoparticlesNevadaRadioisotopesSoilUranium CompoundsWater SupplyNorth AmericaUnited StatesActinidesCesiumChromiumCobaltColloid chemistryEuropiumGroundwaterHydratesHydrogeologyMolybdenumNanostructured materialsPhosphate mineralsPlutoniumRadiometrySilicatesSodiumTrace elementsUnderground reservoirsUraniumactinidecobaltground waternanoparticleorganic carbonradioisotopeActinide elementsAtomic ratiosChemical associationsFacilitated transportsFar fieldsHaadf stemsHigh-angle annular dark fieldsMicroscopy techniquesNano-scaleNano-scale particlesNevada test sitesOxide hydratesPredictive transportsRadionuclide transportsRare-earth elementsScanning temSize rangescesiumgroundwaterpollutant transportradionucliderare earth elementspeciation (chemistry)articlenanoanalysisnuclear wastetransmission electron microscopyjournal article10.1021/es802181t