title: Mechanisms controlling lateral and vertical porewater migration of depleted uranium (DU) at two UK weapons testing sites.
abstract: Uranium associations with colloidal and truly dissolved soil porewater components from two Ministry of Defence Firing Ranges in the UK were investigated. Porewater samples from 2-cm depth intervals for three soil cores from each of the Dundrennan and Eskmeals ranges were fractionated using centrifugal ultrafiltration (UF) and gel electrophoresis (GE). Soil porewaters from a transect running downslope from the Dundrennan firing area towards a stream (Dunrod Burn) were examined similarly. Uranium concentrations and isotopic composition were determined using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Multi-Collector-Inductively Coupled Plasma-Mass Spectrometry (MC-ICP-MS), respectively. The soils at Dundrennan were Fe- and Al-rich clay-loam soils whilst at Eskmeals, they were Fe- and Al-poor sandy soils; both, however, had similar organic matter contents due to the presence of a near-surface peaty layer at Eskmeals. These compositional features influenced the porewater composition and indeed the associations of U (and DU). In general, at Dundrennan, U was split between large (100kDa-0.2μm) and small (3-30kDa) organic colloids whilst at Eskmeals, U was mainly in the small colloidal and truly dissolved fractions. Especially below 10cm depth, association with large Fe/Al/organic colloids was considered to be a precursor to the removal of U from the Dundrennan porewaters to the solid phase. In contrast, the association of U with small organic colloids was largely responsible for inhibiting attenuation in the Eskmeals soils. Lateral migration of U (and DU) through near-surface Dundrennan soils will involve both large and small colloids but, at depth, transport of the smaller amounts of U remaining in the porewaters may involve large colloids only. For one of the Dundrennan cores the importance of redox-related processes for the re-mobilisation of DU was also indicated as Mn(IV) reduction resulted in the release of both Mn(II) and U(VI) into the truly dissolved phase.
authors.affiliation: School of GeoSciences, Crew Building, University of Edinburgh, The King's Buildings, West Mains Road, Edinburgh, EH9 3JN, United Kingdom. Margaret.Graham@ed.ac.uk
authors.forename: Margaret C
authors.initials: MC
authors.lastname: Graham
authors.forename: Ian W
authors.initials: IW
authors.lastname: Oliver
authors.forename: Angus B
authors.initials: AB
authors.lastname: MacKenzie
authors.forename: Robert M
authors.initials: RM
authors.lastname: Ellam
authors.forename: John G
authors.initials: JG
authors.lastname: Farmer
mesh_terms: D005618:Fresh Water / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*; D006113:United Kingdom; D014501:Uranium / Q000032:analysis*; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis*; D054041:Weapons
chemical_list: D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; D014501:Uranium