Isotope fractionation of 238U and 235U during biologically-mediated uranium reduction

Stirling, Claudine H.; Andersen, Morten B.; Warthmann, R.; Halliday, Alex N.

doi:10.1016/j.gca.2015.03.017

Cited by 95 publications

(83 citation statements)

References 75 publications

(157 reference statements)

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“…Biotic reduction studies have demonstrated the uranium isotopic fractionation during the reduction of U(VI) to U(IV) mediated by bacteria (33)(34)(35). However, in agreement with results reported for other mammalian cells (58-61), we can exclude U(VI) reduction in the case of the SH-SY5Y cells used in this study.…”

Section: Discussionsupporting

confidence: 90%

“…NFS effect leads to the enrichment of the heavy 238 U isotope into the U(IV) species (30)(31)(32). Some studies reported that these redox reactions can be mediated by sulfatereducing bacteria (33)(34)(35), but, in these cases, only extracellular uranium was analyzed, and the potential processes occurring inside the bacteria were not investigated. The reductases involved in these reactions are thought to be electron-carrier proteins or enzymes, such as different c-type cytochromes, in the outer membrane, within the periplasm, and/or in the external part of the cytoplasmic membrane (36).…”

Section: Significancementioning

confidence: 99%

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Evidence of isotopic fractionation of natural uranium in cultured human cells

Paredes

Avazeri

Malard

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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The study of the isotopic fractionation of endogen elements and toxic heavy metals in living organisms for biomedical applications, and for metabolic and toxicological studies, is a cutting-edge research topic. This paper shows that human neuroblastoma cells incorporated small amounts of uranium (U) after exposure to 10 μM natural U, with preferential uptake of the 235 U isotope with regard to 238 U. Efforts were made to develop and then validate a procedure for highly accurate n( 238 U)/n( 235 U) determinations in microsamples of cells. We found that intracellular U is enriched in 235 U by 0.38 ± 0.13‰ (2σ, n = 7) relative to the exposure solutions. These in vitro experiments provide clues for the identification of biological processes responsible for uranium isotopic fractionation and link them to potential U incorporation pathways into neuronal cells. Suggested incorporation processes are a kinetically controlled process, such as facilitated transmembrane diffusion, and the uptake through a highaffinity uranium transport protein involving the modification of the uranyl (UO 2 2+ ) coordination sphere. These findings open perspectives on the use of isotopic fractionation of metals in cellular models, offering a probe to track uptake/transport pathways and to help decipher associated cellular metabolic processes.isotopic fractionation | uranium | neuronal cells | analytical procedure development | microsamples

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Section: Discussionsupporting

confidence: 90%

Section: Significancementioning

confidence: 99%

Evidence of isotopic fractionation of natural uranium in cultured human cells

Paredes

Avazeri

Malard

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…Uranium isotope measurements of aragonite and high‐Mg calcite primary precipitates exhibit no offset from seawater (Romaniello et al, ). Laboratory‐precipitated calcite and aragonite at pH ∼8.5 showed only minor (<0.13‰) fractionation between the liquid medium and the solid (Chen, Romaniello, Herrmann, Wasylenki, & Anbar, ; Stirling, Andersen, Warthmann, & Halliday, ). At pH ∼7.5, the precipitates of both polymorphs exhibit no fractionation (Chen et al, ).…”

Section: Stratigraphic Variation Of U Concentrationsmentioning

confidence: 99%

Global marine redox changes drove the rise and fall of the Ediacara biota

et al. 2019

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The role of O2 in the evolution of early animals, as represented by some members of the Ediacara biota, has been heavily debated because current geochemical evidence paints a conflicting picture regarding global marine O2 levels during key intervals of the rise and fall of the Ediacara biota. Fossil evidence indicates that the diversification the Ediacara biota occurred during or shortly after the Ediacaran Shuram negative C‐isotope Excursion (SE), which is often interpreted to reflect ocean oxygenation. However, there is conflicting evidence regarding ocean oxygen levels during the SE and the middle Ediacaran Period. To help resolve this debate, we examined U isotope variations (δ238U) in three carbonate sections from South China, Siberia, and USA that record the SE. The δ238U data from all three sections are in excellent agreement and reveal the largest positive shift in δ238U ever reported in the geologic record (from ~ −0.74‰ to ~ −0.26‰). Quantitative modeling of these data suggests that the global ocean switched from a largely anoxic state (26%–100% of the seafloor overlain by anoxic waters) to near‐modern levels of ocean oxygenation during the SE. This episode of ocean oxygenation is broadly coincident with the rise of the Ediacara biota. Following this initial radiation, the Ediacara biota persisted until the terminal Ediacaran period, when recently published U isotope data indicate a return to more widespread ocean anoxia. Taken together, it appears that global marine redox changes drove the rise and fall of the Ediacara biota.

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“…The rationale is that, at steady state, the uranium isotopic composition of seawater should be influenced by the proportions of sediments formed under different conditions because the extent of uranium isotopic fractionation differs in anoxic, euxinic, suboxic, and oxic sediments. Work has been done over the past several years to assess uranium isotopic fractionation factors between seawater and sediments formed under various conditions (Rademacher et al, 2006;Stirling et al, 2007Stirling et al, , 2015Weyer et al, 2008;Bopp et al, 2010;Brennecka et al, 2011b;Shiel et al, 2013;Andersen et al, 2014;Goto et al, 2014;Basu et al, 2014;Murphy et al, 2014;Noordmann et al, 2015;Wang et al, 2015;this study). In all cases, these fractionation factors are derived from local case studies, and it is unknown to what extent these are representative of the diverse conditions encountered in the oceans, where accumulation rate, organic matter burial, and mineral mode can vary.…”

Section: The U Isotopic Composition Of the Ocean And The Modern Oceanmentioning

confidence: 99%

Uranium isotopic compositions of the crust and ocean: Age corrections, U budget and global extent of modern anoxia

Tissot

Dauphas

2015

Geochimica et Cosmochimica Acta

179

197

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The 238 U/ 235 U isotopic composition of uranium in seawater can provide important insights into the modern U budget of the oceans. Using the double spike technique and a new data reduction method, we analyzed an array of seawater samples and 41 geostandards covering a broad range of geological settings relevant to low and high temperature geochemistry. Analyses of 18 seawater samples from geographically diverse sites from the Atlantic and Pacific oceans, Mediterranean Sea, Gulf of Mexico, Persian Gulf, and English Channel, together with literature data (n = 17), yield a d 238 U value for modern seawater of À0.392 ± 0.005& relative to CRM-112a. Measurements of the uranium isotopic compositions of river water, lake water, evaporites, modern coral, shales, and various igneous rocks (n = 64), together with compilations of literature data (n = 380), allow us to estimate the uranium isotopic compositions of the various reservoirs involved in the modern oceanic uranium budget, as well as the fractionation factors associated with U incorporation into those reservoirs. Because the incorporation of U into anoxic/euxinic sediments is accompanied by large isotopic fractionation (D Anoxic/Euxinic-SW = +0.6&), the size of the anoxic/euxinic sink strongly influences the d 238 U value of seawater. Keeping all other fluxes constant, the flux of uranium in the anoxic/euxinic sink is constrained to be 7.0 ± 3.1 Mmol/yr (or 14 ± 3% of the total flux out of the ocean). This translates into an areal extent of anoxia into the modern ocean of 0.21 ± 0.09% of the total seafloor. This agrees with independent estimates and rules out a recent uranium budget estimate by Henderson and Anderson (2003). Using the mass fractions and isotopic compositions of various rock types in Earth's crust, we further calculate an average d 238 U isotopic composition for the continental crust of À0.29 ± 0.03& corresponding to a 238 U/ 235 U isotopic ratio of 137.797 ± 0.005. We discuss the implications of the variability of the 238 U/ 235 U ratio on Pb-Pb and U-Pb ages and provide analytical formulas to calculate age corrections as a function of the age and isotopic composition of the sample. The crustal ratio may be used in calculation of Pb-Pb and U-Pb ages of continental crust rocks and minerals when the U isotopic composition is unknown.

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Isotope fractionation of 238U and 235U during biologically-mediated uranium reduction

Cited by 95 publications

References 75 publications

Evidence of isotopic fractionation of natural uranium in cultured human cells

Evidence of isotopic fractionation of natural uranium in cultured human cells

Global marine redox changes drove the rise and fall of the Ediacara biota

Uranium isotopic compositions of the crust and ocean: Age corrections, U budget and global extent of modern anoxia

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