Environmental Microbiology Laboratory (EML), EPFL-ENAC-IIE-EML, Ecole Polytechnique Federale de Lausanne (EPFL), Station 6, Lausanne CH-1015, Switzerland.
Center for Applied Geoscience (ZAG), Eberhard Karls Universitaet Tuebingen, Sigwartstrasse 10, Tuebingen 72076, Germany.
Environ Sci Technol. 2020 Apr 21;54(8):4840-4846. doi: 10.1021/acs.est.9b07186. Epub 2020 Mar 30.
Uranium (U) bioremediation has been investigated as a cost-effective strategy to tackle U contamination in the subsurface. While uraninite was believed to be the only product of bioreduction, numerous studies have revealed that noncrystalline U(IV) species (NCU(IV)) are dominant. This finding brings into question the effectiveness of bioremediation because NCU(IV) species are expected to be labile and susceptible to oxidation. Thus, understanding the stability of NCU(IV) in the environment is of crucial importance. Fe(II) minerals (such as FeS) are often associated with U(IV) in bioremediated or naturally reduced sediments. Their impact on the stability of NCU(IV) is not well understood. Here, we show that, at high dissolved oxygen concentrations, FeS accelerates NCU(IV) reoxidation. We hypothesize that either highly reactive ferric minerals or radical S species produced by the oxidation of FeS drive this rapid reoxidation of NCU(IV). Furthermore, we found evidence for the contribution of reactive oxygen species to NCU(IV) reoxidation. This work refines our understanding of the role of iron sulfide minerals in the stability of tetravalent uranium in the presence of oxygen in a field setting such as contaminated sites or uranium-bearing naturally reduced zones.
铀（U）的生物修复已被研究作为一种经济有效的策略，用于解决地下水中的 U 污染问题。虽然人们认为沥青铀矿是生物还原的唯一产物，但许多研究表明，非晶质 U(IV)物种（NCU(IV)）是主要存在的。这一发现使得生物修复的有效性受到质疑，因为预计 NCU(IV)物种不稳定且易被氧化。因此，了解 NCU(IV)在环境中的稳定性至关重要。在生物修复或自然还原沉积物中，Fe(II)矿物（如 FeS）通常与 U(IV)相关。然而，它们对 NCU(IV)稳定性的影响尚未得到充分理解。在这里，我们表明，在高溶解氧浓度下，FeS 会加速 NCU(IV)的再氧化。我们假设，FeS 氧化产生的高反应性的铁矿物或自由基 S 物种驱动了 NCU(IV)的快速再氧化。此外，我们发现证据表明活性氧物种对 NCU(IV)再氧化有贡献。这项工作深化了我们对含硫铁矿物在含氧条件下稳定四价铀的作用的理解，这种情况在污染场地或含铀自然还原带等野外环境中经常出现。
