title: Use of uranium isotopes as a temporal and spatial tracer of nuclear contamination in the environment.
abstract: The Fernald Feed Materials Production Center (FFMPC) was established in 1951 to process natural uranium (U) ore, enriched uranium (EU) and depleted uranium (DU). This study tests the utility of U isotopic ratios in sediment cores and lichens as indicators of the aerial extent, degree and timing of anthropogenic U contamination, using the FFMPC as a test case. An 80-cm-long sediment core was extracted from an impoundment located approximately 6.7 km southwest of the FFMPC. Elemental concentrations of thorium (2.7-6.2 μg g(-1)) and U (0.33-1.33 μg g(-1)) as well as major and minor U isotopes were analyzed in the core. The lack of measurable (137)Cs in the deepest sample as well as a natural (235)U/(238)U signature and no measurable (236)U, are consistent with pre-FFMPC activity. Anomalously elevated U with respect to Th concentrations occur in seven consecutive samples immediately above the base of the core (62-76 cm depth). Samples with elevated U concentrations also show variable (235)U/(238)U (0.00645-0.00748), and all contain measurable (236)U ((236)U/(238)U = 2.1 × 10(-6)-3.6 × 10(-5)). Correspondence between the known releases of U dust from the FFMPC through time and variations in sediment core U concentrations, (235)U/(238)U and (236)U/(238)U ratios provide evidence for distinct releases of both DU and EU. Furthermore, these relationships demonstrate that the sediment core serves as a robust archive of past environmental U contamination events. Samples in the upper 40 cm display natural (235)U/(238)U, but measurable (236)U/(238)U ((236)U/(238)U = 5.68 × 10(-6)-1.43 × 10(-5)), further indicating the continued presence of anthropogenic U in present-day sediment. Three local lichen samples were also analyzed, and all display either EU or DU signatures coupled with elevated (236)U/(238)U, recording airborne U contamination from the FFMPC.
authors.affiliation: Department of Geology and Environmental Earth Sciences, Miami University, 114 Shideler Hall, Oxford, OH 45056, USA.
authors.forename: R
authors.initials: R
authors.lastname: Tortorello
authors.forename: E
authors.initials: E
authors.lastname: Widom
authors.forename: W H
authors.initials: WH
authors.lastname: Renwick
mesh_terms: D019015:Geologic Sediments / Q000032:analysis; D008011:Lichens / Q000737:chemistry*; D009820:Ohio; D011834:Radiation Monitoring / Q000379:methods; D011848:Radioactive Pollutants / Q000032:analysis* / Q000737:chemistry; D014501:Uranium / Q000032:analysis* / Q000737:chemistry
chemical_list: D011848:Radioactive Pollutants; D014501:Uranium
keywords: Fernald; Isotope; Lichen; Ohio; Sediment; Uranium