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Embryos (stage 8–47, Nieuwkoop and Faber) of the African clawed frog (Xenopus laevis) were subjected to water-borne depleted uranium (DU) concentrations that ranged from 4.8 to 77.7 mg/L using an acute 96-h frog embryo teratogenesis assay–Xenopus (FETAX). In a chronic 64-d assay, X. laevis (from embryo through metamorphosis; stages 8–66) were subjected to concentrations of DU that ranged from 6.2 to 54.3 mg/L. Our results indicate DU is a non teratogenic metal. No effects on mortality, malformations, or growth were observed in the 96-h FETAX with concentrations of DU that ranged from 4.8 to 77.7 mg/L. From stage 8 to stage 47, X. laevis tadpoles do not actively feed and the gills are not well developed. Thus, uptake of DU was reduced despite exposure to elevated concentrations. The 64-d assay resulted in no concentration response for either mortality or malformations; however, a delay in metamorphosis was observed in tadpoles subjected to elevated DU concentrations (from 13.1 to 54.3 mg/L) compared to tadpoles in both the well-water control and reference. The delay in metamorphosis was likely due to increasing body burden of DU that ranged from 0.98 to 2.82 mg/kg.
Acknowledgments
Funding was provided by the U.S. Department of Energy/Los Alamos National Laboratory; Division of Environment, Safety, and Health; Technology Development, Evaluation, and Application; Ecology Group. Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy under contract W-7405-ENG-36. Additional support was provided by the U.S. Geological Survey, New Mexico Cooperative Fish and Wildlife Research Unit, Agricultural Experiment Station, Department of Fishery and Wildlife Sciences, and the Carlsbad Environmental Monitoring and Research Center of New Mexico State University. Personal thanks go to E. Gonzales, C. Friedman, C. Sykes, W. Knight, C. Alsworth, and C. Schloesslin for their assistance with this project.