Fractionation of 238U/235U by reduction during low temperature uranium mineralisation processes

Murphy, Melissa J.; Stirling, Claudine H.; Kaltenbach, Angela; Turner, Simon; Schaefer, Bruce F.

doi:10.1016/j.epsl.2013.11.034

Cited by 71 publications

(63 citation statements)

References 36 publications

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“…The reproducibility of these standards was about 0.05‰ at Hannover and 0.1‰ at ASU (Table S7; all delta values there are reported relative to CRM-112A). The delta values for all standards used agree with those previously published (9,11,18,19,36) (Table S7).…”

Section: Methodssupporting

confidence: 86%

“…This isotopic signature has been measured in low-temperature paleo-environments, enabling the use of U isotope fractionation as a proxy for the redox conditions of ancient atmosphere and oceans (14)(15)(16). A recent study (17) observed enrichment of the heavier 238 U isotope in the products of biogenic U reduction, consistent with findings in nature (8,10,11,18) and in agreement with ab initio calculations (19,20).…”

supporting

confidence: 70%

“…4). The results of this study suggest that, in many sedimentary deposits, enzymatic U reduction was a major driver for authigenic U enrichment, including marine sediments and shales (10,14), as well as sandstone tabular and roll-front U deposits (8,11,36). For example, in the modern Black Sea, U isotope fractionation (Δ 238 U) of ∼0.7‰ between the authigenic U in the sediment and that in the deep water column was observed (10,13,37).…”

Section: Discussionmentioning

confidence: 76%

“…Moreover, permil-level fractionations of the two abundant and primordial uranium isotopes are reported in association with U(VI) to U(IV) redox transitions through the accumulation of the heavy isotope ( 238 U) rather than the light isotope ( 235 U) in the reduced product (8)(9)(10)(11)(12)(13). This isotopic signature has been measured in low-temperature paleo-environments, enabling the use of U isotope fractionation as a proxy for the redox conditions of ancient atmosphere and oceans (14)(15)(16).…”

mentioning

confidence: 99%

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Uranium isotopes fingerprint biotic reduction

Stylo

Neubert

Wang

et al. 2015

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

133

153

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Knowledge of paleo-redox conditions in the Earth’s history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U), i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth’s crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. Additionally, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium.

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Section: Methodssupporting

confidence: 86%

supporting

confidence: 70%

Section: Discussionmentioning

confidence: 76%

mentioning

confidence: 99%

See 2 more Smart Citations

Uranium isotopes fingerprint biotic reduction

Stylo

Neubert

Wang

et al. 2015

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

133

153

View full text Add to dashboard Cite

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“…For these samples, the predominant fractionation mechanism has been generally assumed to be the NFS effect in the case of U(VI)/ U(IV) redox reactions. 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.…”

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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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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