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for="c-sort2">Show:</label><select name="rows" id="c-sort2" form="facetForm"><option selected="" value="10">10</option><option value="20">20</option><option value="30">30</option><option value="40">40</option><option value="50">50</option></select></div></div><input type="hidden" name="start" form="facetForm" value="0"/><nav class="c-pagination"><ul><li><a href="" aria-label="you are on result set 1" class="c-pagination__item--current">1</a></li><li><a href="" aria-label="go to result set 2" class="c-pagination__item">2</a></li><li><a href="" aria-label="go to result set 3" class="c-pagination__item">3</a></li><li><a href="" aria-label="go to result set 4" class="c-pagination__item">4</a></li><li><a href="" aria-label="go to result set 5" class="c-pagination__item">5</a></li></ul></nav></div><section class="c-scholworks"><div class="c-scholworks__main-column"><ul class="c-scholworks__tag-list"><li class="c-scholworks__tag-article">Article</li></ul><div><h3 class="c-scholworks__heading"><a href="/uc/item/0kz1d31k"><div class="c-clientmarkup">Redox Dynamics of Mixed Metal (Mn, Cr, and Fe) Ultrafine Particles</div></a></h3></div><div class="c-authorlist"><ul class="c-authorlist__list"><li class="c-authorlist__begin"><a href="/search/?q=author%3ANico%2C%20Peter%20S.">Nico, Peter S.</a> </li></ul></div><div class="c-scholworks__publication"><a href="/uc/lbnl_rw">LBL Publications</a> (2008)</div><div class="c-scholworks__media"><ul class="c-medialist"></ul></div></div><div class="c-scholworks__ancillary"><a class="c-scholworks__thumbnail" href="/uc/item/0kz1d31k"><img src="/cms-assets/cc738632be8a3d1c957df40f37cbd65c514c85b44fac0f91c721221e2e8d379b" alt="Cover page: Redox Dynamics of Mixed Metal (Mn, Cr, and Fe) Ultrafine Particles"/></a></div></section><section class="c-scholworks"><div class="c-scholworks__main-column"><ul class="c-scholworks__tag-list"><li class="c-scholworks__tag-article">Article</li><li class="c-scholworks__tag-peer">Peer Reviewed</li></ul><div><h3 class="c-scholworks__heading"><a href="/uc/item/7z96h08f"><div class="c-clientmarkup">Incorporation of oxidized uranium into Fe (hydr)oxides during Fe(II) catalyzed remineralization</div></a></h3></div><div class="c-authorlist"><ul class="c-authorlist__list"><li class="c-authorlist__begin"><a href="/search/?q=author%3ANico%2C%20Peter%20S.">Nico, Peter S.</a> </li></ul></div><div class="c-scholworks__publication"><a href="/uc/lbnl_rw">LBL Publications</a> (2009)</div><div class="c-scholworks__media"><ul class="c-medialist"></ul></div></div><div class="c-scholworks__ancillary"><a class="c-scholworks__thumbnail" href="/uc/item/7z96h08f"><img src="/cms-assets/368e5df9d075e990841a82078b372ee0b2ee4a94126a88161d6f47d07b3c604a" alt="Cover page: Incorporation of oxidized uranium into Fe (hydr)oxides during Fe(II) catalyzed remineralization"/></a></div></section><section class="c-scholworks"><div class="c-scholworks__main-column"><ul class="c-scholworks__tag-list"><li class="c-scholworks__tag-article">Article</li><li class="c-scholworks__tag-peer">Peer Reviewed</li></ul><div><h3 class="c-scholworks__heading"><a href="/uc/item/99t2038s"><div class="c-clientmarkup">Iron-Mediated Oxidation of Methoxyhydroquinone under Dark Conditions: Kinetic and Mechanistic Insights</div></a></h3></div><div class="c-authorlist"><ul class="c-authorlist__list"><li class="c-authorlist__begin"><a href="/search/?q=author%3AYuan%2C%20Xiu">Yuan, Xiu</a>; </li><li><a href="/search/?q=author%3ADavis%2C%20James%20A">Davis, James A</a>; </li><li class="c-authorlist__end"><a href="/search/?q=author%3ANico%2C%20Peter%20S">Nico, Peter S</a> </li></ul></div><div class="c-scholworks__publication"><a href="/uc/ucb_postprints">UC Berkeley Previously Published Works</a> (2016)</div><div class="c-scholworks__abstract"><div class="c-clientmarkup">Despite the biogeochemical significance of the interactions between natural organic matter (NOM) and iron species, considerable uncertainty still remains as to the exact processes contributing to the rates and extents of complexation and redox reactions between these important and complex environmental components. Investigations on the reactivity of low-molecular-weight quinones, which are believed to be key redox active compounds within NOM, toward iron species, could provide considerable insight into the kinetics and mechanisms of reactions involving NOM and iron. In this study, the oxidation of 2-methoxyhydroquinone (MH2Q) by ferric iron (Fe(III)) under dark conditions in the absence and presence of oxygen was investigated within a pH range of 4-6. Although Fe(III) was capable of stoichiometrically oxidizing MH2Q under anaerobic conditions, catalytic oxidation of MH2Q was observed in the presence of O2 due to further cycling between oxygen, semiquinone radicals, and iron species. A detailed kinetic model was developed to describe the predominant mechanisms, which indicated that both the undissociated and monodissociated anions of MH2Q were kinetically active species toward Fe(III) reduction, with the monodissociated anion being the key species accounting for the pH dependence of the oxidation. The generated radical intermediates, namely semiquinone and superoxide, are of great importance in reaction-chain propagation. The kinetic model may provide critical insight into the underlying mechanisms of the thermodynamic and kinetic characteristics of metal-organic interactions and assist in understanding and predicting the factors controlling iron and organic matter transformation and bioavailability in aquatic systems.</div></div><div class="c-scholworks__media"><ul class="c-medialist"></ul></div></div><div class="c-scholworks__ancillary"><a class="c-scholworks__thumbnail" href="/uc/item/99t2038s"><img src="/cms-assets/eba5ed47a6ea589c4e1505270308acc6d270d1eac2ae9bfe092007766f9ca4e6" alt="Cover page: Iron-Mediated Oxidation of Methoxyhydroquinone under Dark Conditions: Kinetic and Mechanistic Insights"/></a></div></section><section class="c-scholworks"><div class="c-scholworks__main-column"><ul class="c-scholworks__tag-list"><li class="c-scholworks__tag-article">Article</li><li class="c-scholworks__tag-peer">Peer Reviewed</li></ul><div><h3 class="c-scholworks__heading"><a href="/uc/item/8cb868hk"><div class="c-clientmarkup">Are oxygen limitations under recognized regulators of organic carbon turnover in upland soils?</div></a></h3></div><div class="c-authorlist"><ul class="c-authorlist__list"><li class="c-authorlist__begin"><a href="/search/?q=author%3AKeiluweit%2C%20Marco">Keiluweit, Marco</a>; </li><li><a href="/search/?q=author%3ANico%2C%20Peter%20S">Nico, Peter S</a>; </li><li><a href="/search/?q=author%3AKleber%2C%20Markus">Kleber, Markus</a>; </li><li class="c-authorlist__end"><a href="/search/?q=author%3AFendorf%2C%20Scott">Fendorf, Scott</a> </li></ul></div><div class="c-scholworks__publication"><a href="/uc/ucb_postprints">UC Berkeley Previously Published Works</a> (2016)</div><div class="c-scholworks__abstract"><div class="c-clientmarkup">Understanding the processes controlling organic matter (OM) stocks in upland soils, and the ability to management them, is crucial for maintaining soil fertility and carbon (C) storage as well as projecting change with time. OM inputs are balanced by the mineralization (oxidation) rate, with the difference determining whether the system is aggrading, degrading or at equilibrium with reference to its C storage. In upland soils, it is well recognized that the rate and extent of OM mineralization is affected by climatic factors (particularly temperature and rainfall) in combination with OM chemistry, mineral–organic associations, and physical protection. Here we examine evidence for the existence of persistent anaerobic microsites in upland soils and their effect on microbially mediated OM mineralization rates. We corroborate long-standing assumptions that residence times of OM tend to be greater in soil domains with limited oxygen supply (aggregates or peds). Moreover, the particularly long residence times of reduced organic compounds (e.g., aliphatics) are consistent with thermodynamic constraints on their oxidation under anaerobic conditions. Incorporating (i) pore length and connectivity governing oxygen diffusion rates (and thus oxygen supply) with (ii) ‘hot spots’ of microbial OM decomposition (and thus oxygen consumption), and (iii) kinetic and thermodynamic constraints on OM metabolism under anaerobic conditions will thus improve conceptual and numerical models of C cycling in upland soils. We conclude that constraints on microbial metabolism induced by oxygen limitations act as a largely unrecognized and greatly underestimated control on overall rates of C oxidation in upland soils.</div></div><div class="c-scholworks__media"><ul class="c-medialist"></ul></div></div><div class="c-scholworks__ancillary"><a class="c-scholworks__thumbnail" href="/uc/item/8cb868hk"><img src="/cms-assets/4c35685aacbcf231691f7ecaf1e7dac7e1b9a54891a5e47425b484093560424d" alt="Cover page: Are oxygen limitations under recognized regulators of organic carbon turnover in upland soils?"/></a></div></section><section class="c-scholworks"><div class="c-scholworks__main-column"><ul class="c-scholworks__tag-list"><li class="c-scholworks__tag-article">Article</li><li class="c-scholworks__tag-peer">Peer Reviewed</li></ul><div><h3 class="c-scholworks__heading"><a href="/uc/item/4336q892"><div class="c-clientmarkup">Iron and Carbon Dynamics during Aging and Reductive Transformation of Biogenic Ferrihydrite</div></a></h3></div><div class="c-authorlist"><ul class="c-authorlist__list"><li class="c-authorlist__begin"><a href="/search/?q=author%3ACismasu%2C%20A%20Cristina">Cismasu, A Cristina</a>; </li><li><a href="/search/?q=author%3AWilliams%2C%20Kenneth%20H">Williams, Kenneth H</a>; </li><li class="c-authorlist__end"><a href="/search/?q=author%3ANico%2C%20Peter%20S">Nico, Peter S</a> </li></ul></div><div class="c-scholworks__publication"><a href="/uc/ucb_postprints">UC Berkeley Previously Published Works</a> (2016)</div><div class="c-scholworks__abstract"><div class="c-clientmarkup">Natural organic matter is often associated with Fe(III) oxyhydroxides, and may be stabilized as a result of coprecipitation or sorption to their surfaces. However, the significance of this association in relation to Fe and C dynamics and biogeochemical cycling, and the mechanisms responsible for organic matter stabilization as a result of interaction with minerals under various environmental conditions (e.g., pH, Eh, etc.) are not entirely understood. The preservation of mineral-bound OM may be affected by OM structure and mineral identity, and bond types between OM and minerals may be central to influencing the stability, transformation and composition of both organic and mineral components under changing environmental conditions. Here we use bulk and submicron-scale spectroscopic synchrotron methods to examine the in situ transformation of OM-bearing, biogenic ferrihydrite stalks (Gallionella ferruginea-like), which formed following injection of oxygenated groundwater into a saturated alluvial aquifer at the Rifle, CO field site. A progression from oxidizing to reducing conditions during an eight-month period triggered the aging and reductive transformation of Gallionella-like ferrihydrite stalks to Fe (hydroxy)carbonates and Fe sulfides, as well as alteration of the composition and amount of OM. Spectromicroscopic measurements showed a gradual decrease in reduced carbon forms (aromatic/alkene, aliphatic C), a relative increase in amide/carboxyl functional groups and a significant increase in carbonate in the stalk structures, and the appearance of organic globules not associated with stalk structures. Biogenic stalks lost ∼30% of their initial organic carbon content. Conversely, a significant increase in bulk organic matter accompanied these transformations. The character of bulk OM changed in parallel with mineralogical transformations, showing an increase in aliphatic, aromatic and amide functional groups. These changes likely occurred as a result of an increase in microbial activity, or biomass production under anoxic conditions. By the end of this experiment, a substantial fraction of organic matter remained in identifiable Fe containing stalks, but carbon was also present in additional pools, for example, organic matter globules and iron carbonate minerals.</div></div><div class="c-scholworks__media"><ul class="c-medialist"></ul></div></div><div class="c-scholworks__ancillary"><a class="c-scholworks__thumbnail" href="/uc/item/4336q892"><img src="/cms-assets/2571ea32f9b0c168cf69a15f189df03486bfeb35ec8fd802c0b9019e3546ac60" alt="Cover page: Iron and Carbon Dynamics during Aging and Reductive Transformation of Biogenic Ferrihydrite"/></a></div></section><section class="c-scholworks"><div class="c-scholworks__main-column"><ul class="c-scholworks__tag-list"><li class="c-scholworks__tag-article">Article</li><li class="c-scholworks__tag-peer">Peer Reviewed</li></ul><div><h3 class="c-scholworks__heading"><a href="/uc/item/88q1z652"><div class="c-clientmarkup">Complexation and Redox Buffering of Iron(II) by Dissolved Organic Matter</div></a></h3></div><div class="c-authorlist"><ul class="c-authorlist__list"><li class="c-authorlist__begin"><a href="/search/?q=author%3ADaugherty%2C%20Ellen%20E">Daugherty, Ellen E</a>; </li><li><a href="/search/?q=author%3AGilbert%2C%20Benjamin">Gilbert, Benjamin</a>; </li><li><a href="/search/?q=author%3ANico%2C%20Peter%20S">Nico, Peter S</a>; </li><li class="c-authorlist__end"><a href="/search/?q=author%3ABorch%2C%20Thomas">Borch, Thomas</a> </li></ul></div><div class="c-scholworks__publication"><a href="/uc/ucb_postprints">UC Berkeley Previously Published Works</a> (2017)</div><div class="c-scholworks__abstract"><div class="c-clientmarkup">Iron (Fe) bioavailability depends upon its solubility and oxidation state, which are strongly influenced by complexation with natural organic matter (NOM). Despite observations of Fe(II)-NOM associations under conditions favorable for Fe oxidation, the molecular mechanisms by which NOM influences Fe(II) oxidation remain poorly understood. In this study, we used X-ray absorption spectroscopy to determine the coordination environment of Fe(II) associated with NOM (as-received and chemically reduced) at pH 7, and investigated the effect of NOM complexation on Fe(II) redox stability. Linear combination fitting of extended X-ray absorption fine structure (EXAFS) data using reference organic ligands demonstrated that Fe(II) was complexed primarily by carboxyl functional groups in reduced NOM. Functional groups more likely to preserve Fe(II) represent much smaller fractions of NOM-bound Fe(II). Fe(II) added to anoxic solutions of as-received NOM oxidized to Fe(III) and remained organically complexed. Iron oxidation experiments revealed that the presence of reduced NOM limited Fe(II) oxidation, with over 50% of initial Fe(II) remaining after 4 h. These results suggest reduced NOM may preserve Fe(II) by functioning both as redox buffer and complexant, which may help explain the presence of Fe(II) in oxic circumneutral waters.</div></div><div class="c-scholworks__media"><ul class="c-medialist"></ul></div></div><div class="c-scholworks__ancillary"><a class="c-scholworks__thumbnail" href="/uc/item/88q1z652"><img src="/cms-assets/1f6f8863532fb41e6693b08ef16db9e691d70fd34fe4b7dfd9d64195dbecefb2" alt="Cover page: Complexation and Redox Buffering of Iron(II) by Dissolved Organic Matter"/></a></div></section><section class="c-scholworks"><div class="c-scholworks__main-column"><ul class="c-scholworks__tag-list"><li class="c-scholworks__tag-article">Article</li><li class="c-scholworks__tag-peer">Peer Reviewed</li></ul><div><h3 class="c-scholworks__heading"><a href="/uc/item/1zt6x3mz"><div class="c-clientmarkup">HTO and selenate diffusion through compacted Na-, Na–Ca-, and Ca-montmorillonite</div></a></h3></div><div class="c-authorlist"><ul class="c-authorlist__list"><li class="c-authorlist__begin"><a href="/search/?q=author%3AFox%2C%20Patricia%20M">Fox, Patricia M</a>; </li><li><a href="/search/?q=author%3ATournassat%2C%20Christophe">Tournassat, Christophe</a>; </li><li><a href="/search/?q=author%3ASteefel%2C%20Carl">Steefel, Carl</a>; </li><li class="c-authorlist__end"><a href="/search/?q=author%3ANico%2C%20Peter%20S">Nico, Peter S</a> </li></ul></div><div class="c-scholworks__publication"><a href="/uc/ucb_postprints">UC Berkeley Previously Published Works</a> (2024)</div><div class="c-scholworks__abstract"><div class="c-clientmarkup">Radionuclide transport in smectite clay barrier systems used for nuclear waste disposal is controlled by diffusion, with adsorption significantly retarding transport rates. While a relatively minor component of spent nuclear fuel, 79Se is a major driver of the safety case for spent fuel disposal due to its long half-life (3.3 × 105 yr) and its low adsorption to clay (KD < 10 L/kg), thus a thorough understanding of Se diffusion through clay is critical for understanding the long-term safety of spent fuel disposal systems. Through-diffusion experiments with tritiated water (HTO, conservative tracer) and Se(VI) were conducted with a well-characterized, purified montmorillonite source clay (SWy-2) under a constant ionic strength (0.1 M) and three different electrolyte compositions: Na+, Ca2+, and a Na + -Ca2+ mixture at pH 6.5 in order to probe the effects of electrolyte composition and interlayer cation composition on clay microstructure, Se(VI) aqueous speciation, and ultimately diffusion. The results were modeled using a reactive transport modeling approach to determine values of porosity (ε), De (effective diffusion coefficient), and KD (distribution coefficient for adsorption). HTO diffusive flux was higher in Ca-montmorillonite (De = 1.68 × 10−10 m2 s−1) compared to Na-montmorillonite (De = 7.83 × 10−11 m2 s−1). This increase in flux is likely due to a greater degree of clay layer stacking in the presence of Ca2+ compared to Na+, which leads to larger inter-particle pores. Overall, the Se(VI) flux was much lower than the HTO flux due to anion exclusion, with Se(VI) flux following the order Ca (De = 1.03 × 10−11 m2 s−1) > Na–Ca (De = 2.12 × 10−12 m2 s−1) > Na (De = 1.28 × 10−12 m2 s−1). These differences in Se(VI) flux are due to a combination of factors, including (1) larger accessible porosity in Ca-montmorillonite due to clay layer stacking and smaller electrostatic effects compared to Na-montmorillonite, (2) larger accessible porosity for neutral-charge CaSeO4 species which makes up 32% of aqueous Se(VI) in the pure Ca system, and (3) possibly higher Se(VI) adsorption for Ca-montmorillonite. Through a combination of experimental and modeling work, this study highlights the compounding effects that electrolyte and counterion compositions can have on radionuclide transport through clay. Diffusion models that neglect these effects are not transferable from laboratory experimental conditions to in situ repository conditions.</div></div><div class="c-scholworks__media"><ul class="c-medialist"><li class="c-medialist__pdf">1 supplemental PDF</li></ul></div></div><div class="c-scholworks__ancillary"><a class="c-scholworks__thumbnail" href="/uc/item/1zt6x3mz"><img src="/cms-assets/6563be2d119f9582d41aae9431f5e123c0c085208e1cf39351f96dbd25ae7946" alt="Cover page: HTO and selenate diffusion through compacted Na-, Na–Ca-, and Ca-montmorillonite"/></a><a href="https://creativecommons.org/licenses/by-nc/4.0/" class="c-scholworks__license"><img class="c-lazyimage" data-src="/images/cc-by-nc-small.svg" alt="Creative Commons 'BY-NC' version 4.0 license"/></a></div></section><section class="c-scholworks"><div class="c-scholworks__main-column"><ul class="c-scholworks__tag-list"><li class="c-scholworks__tag-article">Article</li><li class="c-scholworks__tag-peer">Peer Reviewed</li></ul><div><h3 class="c-scholworks__heading"><a href="/uc/item/0sj9z4fj"><div class="c-clientmarkup">Shale as a Source of Organic Carbon in Floodplain Sediments of a Mountainous Watershed</div></a></h3></div><div class="c-authorlist"><ul class="c-authorlist__list"><li class="c-authorlist__begin"><a href="/search/?q=author%3AFox%2C%20Patricia%20M">Fox, Patricia M</a>; </li><li><a href="/search/?q=author%3ABill%2C%20Markus">Bill, Markus</a>; </li><li><a href="/search/?q=author%3AHeckman%2C%20Katherine">Heckman, Katherine</a>; </li><li><a href="/search/?q=author%3AConrad%2C%20Mark">Conrad, Mark</a>; </li><li><a href="/search/?q=author%3AAnderson%2C%20Carolyn">Anderson, Carolyn</a>; </li><li><a href="/search/?q=author%3AKeiluweit%2C%20Marco">Keiluweit, Marco</a>; </li><li class="c-authorlist__end"><a href="/search/?q=author%3ANico%2C%20Peter%20S">Nico, Peter S</a> </li></ul></div><div class="c-scholworks__publication"><a href="/uc/ucb_postprints">UC Berkeley Previously Published Works</a> (2020)</div><div class="c-scholworks__abstract"><div class="c-clientmarkup">Shales contain high levels of organic carbon (OC) and represent a large fraction of the Earth's reduced carbon stocks. While recent evidence suggests that shale-derived OC may be actively cycled in riverine systems, this process is poorly understood and not currently considered in global C models. Through the use of sediment density fractionations, extractions, radiocarbon measurements, and chemical characterization, we provide information on the abundance, chemistry, and mobility of shale-derived OC in floodplain sediments of a shale-rich mountainous watershed. The heavy fraction of the sediment, representing mineral-associated OC, is the largest (84 ± 6% of TOC) and oldest (Δ14C values −224 to −853‰) OC pool. Evidence of shale-derived OC is observed in all sediment C pools (i.e., occluded light fraction, water-soluble, and pyrophosphate-extractable) except the free light fraction, which is entirely modern. Relatively consistent chemistry was observed across samples for extracted and density-separated OC, despite wide ranges of Δ14C values. Carbon spectroscopy revealed that floodplain sediments had a higher degree of functionalized aromatic groups and lower carbonate content compared to shale collected nearby, consistent with chemical alteration and mixing with other C sources in the floodplain. We estimate that approximately 23–34% of sediment OC is derived from shale, with implications for other shale-derived elements (e.g., N). This study demonstrates the important contribution of shale-OC, particularly in environments with low litter inputs. The large impact of radiocarbon-dead shale-OC, which has a thermally altered chemical structure distinct from plant litter, on Δ14C values and reactivity of sediment-OC must be considered.</div></div><div class="c-scholworks__media"><ul class="c-medialist"></ul></div></div><div class="c-scholworks__ancillary"><a href="https://creativecommons.org/licenses/by-nc/4.0/" class="c-scholworks__license"><img class="c-lazyimage" data-src="/images/cc-by-nc-small.svg" alt="Creative Commons 'BY-NC' version 4.0 license"/></a></div></section><section class="c-scholworks"><div class="c-scholworks__main-column"><ul class="c-scholworks__tag-list"><li class="c-scholworks__tag-article">Article</li><li class="c-scholworks__tag-peer">Peer Reviewed</li></ul><div><h3 class="c-scholworks__heading"><a href="/uc/item/3z09f7hd"><div class="c-clientmarkup">Competitive sorption of microbial metabolites on an iron oxide mineral</div></a></h3></div><div class="c-authorlist"><ul class="c-authorlist__list"><li class="c-authorlist__begin"><a href="/search/?q=author%3ASwenson%2C%20Tami%20L">Swenson, Tami L</a>; </li><li><a href="/search/?q=author%3ABowen%2C%20Benjamin%20P">Bowen, Benjamin P</a>; </li><li><a href="/search/?q=author%3ANico%2C%20Peter%20S">Nico, Peter S</a>; </li><li class="c-authorlist__end"><a href="/search/?q=author%3ANorthen%2C%20Trent%20R">Northen, Trent R</a> </li></ul></div><div class="c-scholworks__publication"><a href="/uc/ucb_postprints">UC Berkeley Previously Published Works</a> (2015)</div><div class="c-scholworks__abstract"><div class="c-clientmarkup">A large fraction of soil organic matter (SOM) is composed of small molecules of microbial origin. However, the biotic and abiotic cycling of these nutrients is poorly understood and is a critical component of the global carbon cycle. Although there are many factors controlling the accessibility of SOM to microbes, sorption to mineral surfaces is among the most significant. Here, we investigated the competitive sorption of a complex pool of microbial metabolites on ferrihydrite, an iron oxide mineral, using a lysate prepared from a soil bacterium, Pseudomonas stutzeri RCH2. After a 24-h incubation with a range of mineral concentrations, more than half of the metabolites showed significant decreases in solution concentration. Phosphate-containing metabolites showed the greatest degree of sorption followed by dicarboxylates and metabolites containing both nitrogen and an aromatic moiety. Similar trends were observed when comparing sorption of metabolites with an equimolar metabolite mixture rather than a bacterial lysate. Interestingly, ectoine, lysine, two disaccharides and uracil were found not to sorb and may be more bioavailable in iron oxide-rich soils. Additionally, the highest-sorbing metabolites were examined for their ability to mobilize mineral-sorbed phosphate. All phosphate-containing metabolites tested and glutathione released phosphate from the mineral surface within 30 min of metabolite addition. These findings of preferential sorption behavior within a complex pool of microbial metabolites may provide insight into the cycling of SOM and specific nutrient availability. Finally, the release of highly-sorptive metabolites may be an underexplored mechanism utilized by microbial communities to gain access to limited environmental nutrients.</div></div><div class="c-scholworks__media"><ul class="c-medialist"></ul></div></div><div class="c-scholworks__ancillary"><a class="c-scholworks__thumbnail" href="/uc/item/3z09f7hd"><img src="/cms-assets/54abe8001567cfc65b0f0eb04896c23c37bee038fa0b3478466a865adf54afbf" alt="Cover page: Competitive sorption of microbial metabolites on an iron oxide mineral"/></a></div></section><section class="c-scholworks"><div class="c-scholworks__main-column"><ul class="c-scholworks__tag-list"><li class="c-scholworks__tag-article">Article</li><li class="c-scholworks__tag-peer">Peer Reviewed</li></ul><div><h3 class="c-scholworks__heading"><a href="/uc/item/7z76d17m"><div class="c-clientmarkup">Characterization of Chromium Bioremediation Products in Flow‐Through Column Sediments Using Micro–X‐ray Fluorescence and X‐ray Absorption Spectroscopy</div></a></h3></div><div class="c-authorlist"><ul class="c-authorlist__list"><li class="c-authorlist__begin"><a href="/search/?q=author%3AVaradharajan%2C%20Charuleka">Varadharajan, Charuleka</a>; </li><li><a href="/search/?q=author%3AHan%2C%20Ruyang">Han, Ruyang</a>; </li><li><a href="/search/?q=author%3ABeller%2C%20Harry%20R">Beller, Harry R</a>; </li><li><a href="/search/?q=author%3AYang%2C%20Li">Yang, Li</a>; </li><li><a href="/search/?q=author%3AMarcus%2C%20Matthew%20A">Marcus, Matthew A</a>; </li><li><a href="/search/?q=author%3AMichel%2C%20Marc">Michel, Marc</a>; </li><li class="c-authorlist__end"><a href="/search/?q=author%3ANico%2C%20Peter%20S">Nico, Peter S</a> </li></ul></div><div class="c-scholworks__publication"><a href="/uc/ucb_postprints">UC Berkeley Previously Published Works</a> (2015)</div><div class="c-scholworks__abstract"><div class="c-clientmarkup">Microbially mediated reductive immobilization of chromium is a possible remediation technique for sites contaminated with Cr(VI). This study is part of a broader effort investigating the biogeochemical mechanisms for Cr(VI) reduction in Hanford 100H aquifer sediments using flow-through laboratory columns. It had previously been shown that reduced chromium in the solid phase was in the form of freshly precipitated mixed-phase Cr(III)-Fe(III) (hydr)oxides, irrespective of the biogeochemical conditions in the columns. In this study, the reduced Cr phases in the columns were investigated further using spectroscopy to understand the structure and mechanisms involved in the formation of the end products. Several samples representing potential processes that could be occurring in the columns were synthesized in the laboratory and characterized using X-ray absorption near edge structure (XANES) and X-ray scattering. The XANES of Cr(III) particles in the columns most closely resembled those from synthetic samples produced by the abiotic reaction of Cr(VI) with microbially reduced Fe(II). Microbially mediated Cr-Fe reduction products were distinct from abiotic Cr-Fe (hydr)oxides [CrFe(OH)] and organically complexed Cr(III) sorbed onto the surface of a mixed ferrihydrite-goethite mineral phase. Furthermore, analyses of the abiotically synthesized samples revealed that even the end products of purely abiotic, iron-mediated reduction of Cr(VI) are affected by factors such as the presence of excess aqueous Fe(II) and cellular matter. These results suggest that CrFe(OH) phases made under realistic subsurface conditions or in biotic cultures are structurally different from pure Cr(OH) or laboratory-synthesized CrFe(OH). The observed structural differences imply that the reactivity and stability of biogenic CrFe(OH) could potentially be different from that of abiotic CrFe(OH).</div></div><div class="c-scholworks__media"><ul class="c-medialist"></ul></div></div><div class="c-scholworks__ancillary"><a class="c-scholworks__thumbnail" href="/uc/item/7z76d17m"><img src="/cms-assets/b11e89bbb3a07a5daf1058c344e7c97a469c53e1eb05d900ee1b674ffb3acbc6" alt="Cover page: Characterization of Chromium Bioremediation Products in Flow‐Through Column Sediments Using Micro–X‐ray Fluorescence and X‐ray Absorption Spectroscopy"/></a></div></section><nav class="c-pagination"><ul><li><a href="" aria-label="you are on result set 1" class="c-pagination__item--current">1</a></li><li><a href="" aria-label="go to result set 2" class="c-pagination__item">2</a></li><li><a href="" aria-label="go to result set 3" class="c-pagination__item">3</a></li><li><a href="" aria-label="go to result set 4" class="c-pagination__item">4</a></li><li><a href="" aria-label="go to result set 5" class="c-pagination__item">5</a></li></ul></nav></section></main></form></div><div><div class="c-toplink"><a href="javascript:window.scrollTo(0, 0)">Top</a></div><footer class="c-footer"><nav class="c-footer__nav"><ul><li><a href="/">Home</a></li><li><a href="/aboutEschol">About eScholarship</a></li><li><a href="/campuses">Campus Sites</a></li><li><a href="/ucoapolicies">UC Open Access Policy</a></li><li><a href="/publishing">eScholarship Publishing</a></li><li><a href="https://www.cdlib.org/about/accessibility.html">Accessibility</a></li><li><a href="/privacypolicy">Privacy Statement</a></li><li><a href="/policies">Site Policies</a></li><li><a href="/terms">Terms of Use</a></li><li><a href="/login"><strong>Admin Login</strong></a></li><li><a href="https://help.escholarship.org"><strong>Help</strong></a></li></ul></nav><div class="c-footer__logo"><a href="/"><img class="c-lazyimage" data-src="/images/logo_footer-eschol.svg" alt="eScholarship, University of California"/></a></div><div class="c-footer__copyright">Powered by the<br/><a href="http://www.cdlib.org">California Digital Library</a><br/>Copyright © 2017<br/>The Regents of the University of California</div></footer></div></div></div></div> <script src="/js/vendors~app-bundle-2aefc956e545366a5d4e.js"></script> <script src="/js/app-bundle-4477d7630fb8c6f70662.js"></script> </body> </html>