Dublet, GabrielleWorms, IsabelleFrutschi, ManonBrown, AshleyZund, Giada C.Bartova, BarboraSlayeykoya, Vera I.Bernier-Latmani, Rizlan2019-09-142019-09-142019-09-142019-08-2010.1021/acs.est.9b01417https://infoscience.epfl.ch/handle/20.500.14299/161177WOS:000482521600004Uranium (U) speciation was investigated in anoxically preserved porewater samples of a natural mountain wetland in Gola di Lago, Ticino, Switzerland. U porewater concentrations ranged from less than 1 mu g/L to tens of mu g/L, challenging the available analytical approaches for U speciation in natural samples. Asymmetrical flow field-flow fractionation coupled with inductively coupled plasma mass spectrometry allowed the characterization of colloid populations and the determination of the size distribution of U species in the porewater. Most of the U was associated with three fractions: <0.3 kDa, likely including dissolved U and very small U colloids; a 1-3 kDa fraction containing humic-like organic compounds, dispersed Fe, and, to a small extent, Fe nanoparticles; and a third fraction (5-50 nm), containing a higher amount of Fe and a lower amount of organic matter and U relative to the 1-3 kDa fraction. The proportion of U associated with the 1-3 kDa colloids varied spatially and seasonally. Using anion exchange resins, we also found that a significant proportion of U occurs in its reduced form, U(1V). Tetravalent U was interpreted as occurring within the colloidal pool of U. This study suggests that U(IV) can occur as small (1-3 kDa), organic-rich, and thus potentially mobile colloidal species in naturally reducing wetland environments.Engineering, EnvironmentalEnvironmental SciencesEngineeringEnvironmental Sciences & Ecologyspatial-distributionorganic-matterwaterspeciationfieldsoiltransportmobilityelementsreleasetext::journal::journal article::research article