Mechanisms controlling lateral and vertical porewater migration of depleted uranium (DU) at two UK weapons testing sites

• Published in: The Science of the total environment Vol. 409; no. 10; pp. 1854 - 1866
• Main Authors: Graham, Margaret C., Oliver, Ian W., MacKenzie, Angus B., Ellam, Robert M., Farmer, John G.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15.04.2011; Elsevier
• Subjects: Aluminum; Applied sciences; Aquatic colloids; Biological and physicochemical properties of pollutants. Interaction in the soil; Colloiding; Colloids; Depleted uranium; Dissolution; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Firing; Fresh Water - chemistry; Gel electrophoresis; Iron; Isotopes; Pollution; Pollution, environment geology; Soil (material); Soil and sediments pollution; Soil contamination; Soil Pollutants - analysis; Ultrafiltration; United Kingdom; Uranium; Uranium - analysis; Water Movements; Water Pollutants, Chemical - analysis; Weapons; United Kingdom; Europe; British Isles; Aquatic colloids; Ultrafiltration; Gel electrophoresis; Isotopes; Depleted uranium; Soil contamination; Radioactive pollution; Pollutant behavior; Shooting; Migration; Radioisotope; Soil pollution; Interstitial water; Transport process; Membrane separation; Armament; Colloid particle
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2011.01.011

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 (100 kDa–0.2 μm) and small (3–30 kDa) organic colloids whilst at Eskmeals, U was mainly in the small colloidal and truly dissolved fractions. Especially below 10 cm 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. ► U associations in soil porewaters at DU munitions sites were investigated. ► U distribution among colloidal/dissolved fractions varied with soil type and depth. ► U association with large Fe-Al-organic colloids led to removal from soil porewaters. ► Small organic colloidal association inhibited U removal from sandy soil porewaters. ► Reductive dissolution of Mn can release ‘truly dissolved’ U into soil porewaters.