All Publications

  • Environmental impact of solution pH on the formation and migration of iron colloids in deep subsurface energy systems. The Science of the total environment Spielman-Sun, E., Bland, G., Wielinski, J., Frouté, L., Kovscek, A. R., Lowry, G. V., Bargar, J. R., Noël, V. 2023: 166409


    Deep subsurface stimulation processes often promote fluid-rock interactions that can lead to the formation of small colloidal particles that are suspected to migrate through the rock matrix, partially or fully clog pores and microfractures, and promote the mobilization of contaminants. Thus, the goal of this work is to understand the geochemical changes of the host rock in response to reservoir stimulation that promote the formation and migration of colloids. Two different carbonate-rich shales were exposed to different solution pHs (pH = 2 and 7). Iron and other mineral transformations at the shale-fluid interface were first characterized by synchrotron-based XRF mapping. Then, colloids that were able to migrate from the shale into the bulk fluid were characterized by synchrotron-based extended X-ray absorption structure (EXAFS), scanning electron microscopy (SEM), and single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-icpTOF-MS). When exposed to the pH = 2 solution, extensive mineral dissolution and secondary precipitation was observed; iron-(oxyhydr)oxide colloids colocated with silicates were observed by SEM at the fluid-shale interfaces, and the mobilization of chromium and nickel with these iron colloids into the bulk fluid was detected by sp-icpTOF-MS. Iron EXAFS spectra of the solution at the shale-fluid interface suggests the rapid (within minutes) formation of ferrihydrite-like nanoparticles. Thus, we demonstrate that the pH neutralization promotes the mobilization of existing silicate minerals and the rapid formation of new iron colloids. These Fe colloids have the potential to migrate through the shale matrix and mobilize other heavy metals (such as Cr and Ni, in this study) and impacting groundwater quality, as well produced waters from these hydraulic fracturing operations.

    View details for DOI 10.1016/j.scitotenv.2023.166409

    View details for PubMedID 37597537

  • Structure and composition of natural ferrihydrite nano-colloids in anoxic groundwater. Water research Engel, M., Noel, V., Pierce, S., Kovarik, L., Kukkadapu, R. K., Pacheco, J. S., Qafoku, O., Runyon, J. R., Chorover, J., Zhou, W., Cliff, J., Boye, K., Bargar, J. R. 2023; 238: 119990


    Fe-rich mobile colloids play vital yet poorly understood roles in the biogeochemical cycling of Fe in groundwater by influencing organic matter (OM) preservation and fluxes of Fe, OM, and other essential (micro-)nutrients. Yet, few studies have provided molecular detail on the structures and compositions of Fe-rich mobile colloids and factors controlling their persistence in natural groundwater. Here, we provide comprehensive new information on the sizes, molecular structures, and compositions of Fe-rich mobile colloids that accounted for up to 72% of aqueous Fe in anoxic groundwater from a redox-active floodplain. The mobile colloids are multi-phase assemblages consisting of Si-coated ferrihydrite nanoparticles and Fe(II)-OM complexes. Ferrihydrite nanoparticles persisted under both oxic and anoxic conditions, which we attribute to passivation by Si and OM. These findings suggest that mobile Fe-rich colloids generated in floodplains can persist during transport through redox-variable soils and could be discharged to surface waters. These results shed new light on their potential to transport Fe, OM, and nutrients across terrestrial-aquatic interfaces.

    View details for DOI 10.1016/j.watres.2023.119990

    View details for PubMedID 37146398

  • Dynamic development of geochemical reaction fronts during hydraulic stimulation of shale APPLIED GEOCHEMISTRY Noel, V., Druhan, J. L., Gundogar, A., Kovscek, A. R., Brown Jr, G. E., Bargar, J. R. 2023; 148
  • Nitrate Controls on the Extent and Type of Metal Retention in Fine-Grained Sediments of a Simulated Aquifer. Environmental science & technology Engel, M., Noel, V., Kukkadapu, R. K., Boye, K., Bargar, J. R., Fendorf, S. 2022


    Aquifer groundwater quality is largely controlled by sediment composition and physical heterogeneity, which commonly sustains a unique redox gradient pattern. Attenuation of heavy metals within these heterogeneous aquifers is reliant on multiple factors, including redox conditions and redox-active species that can further influence biogeochemical cycling. Here, we simulated an alluvial aquifer system using columns filled with natural coarse-grained sediments and two domains of fine-grained sediment lenses. Our goal was to examine heavy metal (Ni and Zn) attenuation within a complex aquifer network and further explore nitrate-rich groundwater conditions. The fine-grained sediment lenses sustained reducing conditions and served as a sink for Ni sequestration─in the form of Ni-silicates, Ni-organic matter, and a dominant Ni-sulfide phase. The silicate clay and sulfide pools were also important retention mechanisms for Zn; however, Ni was associated more extensively with organic matter compared to Zn, which formed layered double hydroxides. Nitrate-rich conditions promoted denitrification within the lenses that was coupled to the oxidation of Fe(II) and the concomitant precipitation of an Fe(III) phase with higher structural distortion. A decreased metal sulfide pool also resulted, where nitrate-rich conditions generated an average 20% decrease in solid-phase Ni, Zn, and Fe. Ultimately, nitrate plays a significant role in the aquifer's biogeochemical cycling and the capacity to retain heavy metals.

    View details for DOI 10.1021/acs.est.2c03403

    View details for PubMedID 36206030

  • Simulation of anoxic lenses as exporters of reactivity in alluvial aquifer sediments GEOCHIMICA ET COSMOCHIMICA ACTA Babey, T., Boye, K., Tolar, B., Engel, M., Noel, V., Perzan, Z., Kumar, N., Francis, C. A., Bargar, J. R., Maher, K. 2022; 334: 119-134
  • Mechanism of Arsenic Partitioning During Sulfidation of As-Sorbed Ferrihydrite Nanoparticles. ACS earth & space chemistry Kumar, N., Noël, V., Besold, J., Planer-Friedrich, B., Boye, K., Fendorf, S., Brown, G. E. 2022; 6 (7): 1666-1673


    Knowledge of how arsenic (As) partitions among various phases in Fe-rich sulfidic environments is critical for understanding the fate and mobility of As in such environments. We studied the reaction of arsenite and arsenate sorbed on ferrihydrite nanoparticle surfaces with dissolved sulfide at varying S/Fe ratios (0.1-2.0) to understand the fate and transformation mechanism of As during sulfidation of ferrihydrite. By using aqueous As speciation analysis by IC-ICP-MS and solid-phase As speciation analysis by synchrotron-based X-ray absorption spectroscopy (XAS), we were able to discern the mechanism and pathways of As partitioning and thio-arsenic species formation. Our results provide a mechanistic understanding of the fate and transformation of arsenic during the codiagenesis of As, Fe, and S in reducing environments. Our aqueous-phase As speciation data, combined with solid-phase speciation data, indicate that sulfidation of As-sorbed ferrihydrite nanoparticles results in their transformation to trithioarsenate and arsenite, independent of the initial arsenic species used. The nature and extent of transformation and the thioarsenate species formed were controlled by S/Fe ratios in our experiments. However, arsenate was reduced to arsenite before transformation to trithioarsenate.

    View details for DOI 10.1021/acsearthspacechem.1c00373

    View details for PubMedID 35903782

    View details for PubMedCentralID PMC9310089

  • Call for Papers for the Environmental Redox Processes and Contaminant and Nutrient Dynamics Special Issue ACS EARTH AND SPACE CHEMISTRY Kumar, N., Noel, V., Schenkeveld, W. 2022
  • Mechanism of Arsenic Partitioning During Sulfidation of As-Sorbed Ferrihydrite Nanoparticles ACS EARTH AND SPACE CHEMISTRY Kumar, N., Noel, V., Besold, J., Planer-Friedrich, B., Boye, K., Fendorf, S., Brown Jr, G. E. 2022
  • Ligand-Induced U Mobilization from Chemogenic Uraninite and Biogenic Noncrystalline U(IV) under Anoxic Conditions. Environmental science & technology Chardi, K. J., Satpathy, A., Schenkeveld, W. D., Kumar, N., Noel, V., Kraemer, S. M., Giammar, D. E. 2022


    Microbial reduction of soluble hexavalent uranium (U(VI)) to sparingly soluble tetravalent uranium (U(IV)) has been explored as an in situ strategy to immobilize U. Organic ligands might pose a potential hindrance to the success of such remediation efforts. In the current study, a set of structurally diverse organic ligands were shown to enhance the dissolution of crystalline uraninite (UO2) for a wide range of ligand concentrations under anoxic conditions at pH 7.0. Comparisons were made to ligand-induced U mobilization from noncrystalline U(IV). For both U phases, aqueous U concentrations remained low in the absence of organic ligands (<25 nM for UO2; 300 nM for noncrystalline U(IV)). The tested organic ligands (2,6-pyridinedicarboxylic acid (DPA), desferrioxamine B (DFOB), N,N'-di(2-hydroxybenzyl)ethylene-diamine-N,N'-diacetic acid (HBED), and citrate) enhanced U mobilization to varying extents. Over 45 days, the ligands mobilized only up to 0.3% of the 370 muM UO2, while a much larger extent of the 300 muM of biomass-bound noncrystalline U(IV) was mobilized (up to 57%) within only 2 days (>500 times more U mobilization). This work shows the potential of numerous organic ligands present in the environment to mobilize both recalcitrant and labile U forms under anoxic conditions to hazardous levels and, in doing so, undermine the stability of immobilized U(IV) sources.

    View details for DOI 10.1021/acs.est.1c07919

    View details for PubMedID 35522992

  • Bioavailability of chromium, nickel, iron and manganese in relation to their speciation in coastal sediments downstream of ultramafic catchments: A case study in New Caledonia. Chemosphere Merrot, P., Juillot, F., Flipo, L., Tharaud, M., Viollier, E., Noel, V., Le Pape, P., Fernandez, J., Moreton, B., Morin, G. 2022: 134643


    Coastal sediments downstream of ultramafic catchments can show Ni and Cr concentration well above sediment quality guidelines. Despite their potential ecological impact, the bioavailability of these trace metals in such sedimentary settings has been poorly investigated. In this study, we tried to fill this gap by performing kinetic EDTA-extractions across a shore-to-reef gradient in lagoon sediments downstream of an ultramafic catchment in New Caledonia and interpreting the results in regard of synchrotron-derived speciation. Measured bioavailability ranged from very low for Cr (below 1% of total Cr) to medium for Ni (below 5% of total Ni). Both trace metals showed a decreasing shore-to-reef bioavailability gradient reflecting the larger deposition of ultramafic sediments close to the shore. According to synchrotron-derived speciation data, the very low bioavailability of Cr is attributed to its major occurrence as Cr(III)-bearing Fe-(oxyhydr)oxides and phyllosilicates, with no evidence of Cr(VI). Considering the low occurrence of Fe-sulfides, the medium bioavailability of Ni is considered to arise mainly from the reductive dissolution of Ni-bearing Fe-(oxyhydr)oxides during early diagenesis. This reaction also explains the medium bioavailability of Fe (up to 15% of total Fe) and the positive correlation observed with Total Organic Carbon (TOC). In this regard, this latter parameter appears as a major driver of Ni and Fe bioavailability in coastal sediments downstream of ultramafic catchments. On the opposite, in the absence of Mn-oxides, TOC has no influence on Mn bioavailability (up to 30% of total Mn) that appears more likely driven by sediment sources. From an ecological point of view, considering the Australian and New-Zealand High Interim Sediment Quality Guidelines (ANZ-ISQG-H), Cr should not represent a significant risk towards benthic communities in coastal sediments downstream of ultramafic catchments. On the opposite, Ni, Fe and Mn might represent an ecological risk that should be further investigated in such sedimentary settings.

    View details for DOI 10.1016/j.chemosphere.2022.134643

    View details for PubMedID 35483664

  • Reply to the Comment on "FeS colloids - formation and mobilization pathways in natural waters" by S. Peiffer, D0EN00967A ENVIRONMENTAL SCIENCE-NANO Noel, V., Kumar, N., Boye, K., Lezama-Pacheco, J. S., Brown, G. E., Bargara, J. R. 2021; 8 (6): 1817-1821

    View details for DOI 10.1039/d1en00278c

    View details for Web of Science ID 000662712900024

  • Simulated Aquifer Heterogeneity Leads to Enhanced Attenuation and Multiple Retention Processes of Zinc. Environmental science & technology Engel, M., Boye, K., Noel, V., Babey, T., Bargar, J. R., Fendorf, S. 2021


    Alluvial aquifers serve as one of the main water sources for domestic, agricultural, and industrial purposes globally. Groundwater quality, however, can be threatened by naturally occurring and anthropogenic metal contaminants. Differing hydrologic and biogeochemical conditions between predominantly coarse-grained aquifer sediments and embedded layers or lenses of fine-grained materials lead to variation in metal behavior. Here, we examine processes controlling Zn partitioning within a dual-pore domain-reconstructed alluvial aquifer. Natural coarse aquifer sediments from the Wind River-Little Wind River floodplain near Riverton, WY, were used in columns with or without fine-grained lenses to examine biogeochemical controls on Zn concentrations, retention mechanisms, and transport. Following the introduction of Zn to the groundwater source, Zn preferentially accumulated in the fine-grained lenses, despite their small volumetric contributions. While the clay fraction dominated Zn retention in the sandy aquifer, the lenses supported additional reaction pathways of retention-the reducing conditions within the lenses resulted in ZnS precipitation, overriding the contribution of organic matter. Zinc concentration in the groundwater controlled the formation of Zn-clays and Zn-layered double hydroxides, whereas the extent of sulfide production controlled precipitation of ZnS. Our findings illustrate how both spatial and compositional heterogeneities govern the extent and mechanisms of Zn retention in intricate groundwater systems, with implications for plume behavior and groundwater quality.

    View details for DOI 10.1021/acs.est.0c06750

    View details for PubMedID 33570404

  • FeS colloids - formation and mobilization pathways in natural waters ENVIRONMENTAL SCIENCE-NANO Noel, V., Kumar, N., Boye, K., Barragan, L., Lezama-Pacheco, J. S., Chu, R., Tolic, N., Brown, G. E., Bargar, J. R. 2020; 7 (7): 2102–16

    View details for DOI 10.1039/c9en01427f

    View details for Web of Science ID 000549099000015

  • Sulfur Loading and Speciation Control the Hydrophobicity, Electron Transfer, Reactivity, and Selectivity of Sulfidized Nanoscale Zerovalent Iron. Advanced materials (Deerfield Beach, Fla.) Xu, J., Avellan, A., Li, H., Liu, X., Noel, V., Lou, Z., Wang, Y., Kaegi, R., Henkelman, G., Lowry, G. V. 2020: e1906910


    Sulfidized nanoscale zerovalent iron (SNZVI) is a promising material for groundwater remediation. However, the relationships between sulfur content and speciation and the properties of SNZVI materials are unknown, preventing rational design. Here, the effects of sulfur on the crystalline structure, hydrophobicity, sulfur speciation, corrosion potential, and electron transfer resistance are determined. Sulfur incorporation extended the nano-Fe0 BCC lattice parameter, reduced the Fe local vacancies, and lowered the resistance to electron transfer. Impacts of the main sulfur species (FeS and FeS2 ) on hydrophobicity (water contact angles) are consistent with density functional theory calculations for these FeSx phases. These properties well explain the reactivity and selectivity of SNZVI during the reductive dechlorination of trichloroethylene (TCE), a hydrophobic groundwater contaminant. Controlling the amount and speciation of sulfur in the SNZVI made it highly reactive (up to 0.41 L m-2 d-1 ) and selective for TCE degradation over water (up to 240 moles TCE per mole H2 O), with an electron efficiency of up to 70%, and these values are 54-fold, 98-fold, and 160-fold higher than for NZVI, respectively. These findings can guide the rational design of robust SNZVI with properties tailored for specific application scenarios.

    View details for DOI 10.1002/adma.201906910

    View details for PubMedID 32162726

  • Chemical Speciation and Stability of Uranium in Unconventional Shales: Impact of Hydraulic Fracture Fluid. Environmental science & technology Jew, A. D., Besançon, C. J., Roycroft, S. J., Noel, V. S., Bargar, J. R., Brown, G. E. 2020


    Uranium and other radionuclides are prominent in many unconventional oil/gas shales and is a potential contaminant in flowback/produced waters due to the large volumes/types of chemicals injected into the subsurface during stimulation. To understand the stability of U before and after stimulation, a geochemical study of U speciation was carried out on three shales (Marcellus, Green River, and Barnett). Two types of samples for each shale were subjected to sequential chemical extractions: unreacted and shale-reacted with a synthetic hydraulic fracture fluid. A significant proportion of the total U (20-57%) was released from these three shales after reaction with fracture fluid, indicating that U is readily leachable. The total U released exceeds labile water-soluble and exchangeable fractions in unreacted samples, indicating that fluids leach more recalcitrant phases in the shale. Radiographic analysis of unreacted Marcellus shale thin sections shows U associated with detrital quartz and the clay matrix in the shale. Detrital zircon and TiO2 identified by an electron microprobe could account for the hot spots. This study shows that significant proportions of U in three shales are mobile upon stimulation. In addition, the extent of mobilization of U depends on the U species in these rocks.

    View details for DOI 10.1021/acs.est.0c01022

    View details for PubMedID 32401022

  • Organic compounds alter the preference and rates of heavy metal adsorption on ferrihydrite. The Science of the total environment Engel, M. n., Lezama Pacheco, J. S., Noël, V. n., Boye, K. n., Fendorf, S. n. 2020; 750: 141485


    The availability of heavy metals in terrestrial environments is largely controlled by their interactions with minerals and organic matter, with iron minerals having a particularly strong role in heavy metal fate. Because soil organic matter contains a variety of compounds that differ in their chemical properties, the underlying impact organic matter-soil mineral associations bestow on heavy metal binding is still unresolved. Here, we systematically examine the binding of Cd, Zn and Ni by a suite of organic-ferrihydrite assemblages, chosen to account for various compound chemistries within soil organic matter. We posited that organic compound functionality would dictate the extent of association with the organic-ferrihydrite assemblages. Increased heavy metal binding to the assemblages was observed and attributed to the introduction of additional binding sites by the organic functional groups with differing metal affinities. The relative increase depended on the metal's Lewis acidity and followed the order Cd > Zn > Ni, whereas the reverse order was obtained for metal binding by pristine ferrihydrite (Ni > Zn > Cd). Citric acid-, aspartic acid- and cysteine-ferrihydrite assemblages also enhanced the metal binding rate. X-ray absorption spectroscopy revealed that the organic coating contributed significantly to Zn binding by the assemblages, despite relatively low organic surface coverage. Our findings provide valuable information on the nature of heavy metal-organic-mineral interactions and metal adsorption processes regulating their bioavailability and transport.

    View details for DOI 10.1016/j.scitotenv.2020.141485

    View details for PubMedID 32862002

  • Redox Heterogeneities Promote Thioarsenate Formation and Release into Groundwater from Low Arsenic Sediments. Environmental science & technology Kumar, N. n., Noël, V. n., Planer-Friedrich, B. n., Besold, J. n., Lezama-Pacheco, J. n., Bargar, J. R., Brown, G. E., Fendorf, S. n., Boye, K. n. 2020


    Groundwater contamination by As from natural and anthropogenic sources is a worldwide concern. Redox heterogeneities over space and time are common and can influence the molecular-level speciation of As, and thus, As release/retention but are largely unexplored. Here, we present results from a dual-domain column experiment, with natural organic-rich, fine-grained, and sulfidic sediments embedded as lenses (referred to as "reducing lenses") within natural aquifer sand. We show that redox interfaces in sulfur-rich, alkaline aquifers may release concerning levels of As, even when sediment As concentration is low (<2 mg/kg), due to the formation of mobile thioarsenates at aqueous sulfide/Fe molar ratios <1. In our experiments, this behavior occurred in the aquifer sand between reducing lenses and was attributed to the spreading of sulfidic conditions and subsequent Fe reductive dissolution. In contrast, inside reducing lenses (and some locations in the aquifer) the aqueous sulfide/Fe molar ratios exceeded 1 and aqueous sulfide/As molar ratios exceeded 100, which partitioned As(III)-S to the solid phase (associated with organics or as realgar (As4S4)). These results highlight the importance of thioarsenates in natural sediments and indicate that redox interfaces and sediment heterogeneities could locally degrade groundwater quality, even in aquifers with unconcerning solid-phase As concentrations.

    View details for DOI 10.1021/acs.est.9b06502

    View details for PubMedID 32069033

  • Nickel and iron partitioning between clay minerals, Fe-oxides and Fe-sulfides in lagoon sediments from New Caledonia. The Science of the total environment Merrot, P., Juillot, F., Noel, V., Lefebvre, P., Brest, J., Menguy, N., Guigner, J., Blondeau, M., Viollier, E., Fernandez, J., Moreton, B., Bargar, J. R., Morin, G. 2019; 689: 1212–27


    In the tropics, continental weathering and erosion are major sources of trace metals towards estuaries and lagoons, where early diagenesis of sediments may influence their mobility and bioavailability. Determining trace metals speciation in tropical sedimentary settings is thus needed to assess their long-term fate and potential threat to fragile coastal ecosystems. In this study, we determined Fe, Ni and S speciation across a shore-to-reef gradient in sediments from the New Caledonia lagoon that receive mixed contribution from lateritic (iron-oxyhydroxides and clay minerals), volcano-sedimentary (silicates) and marine (carbonate) sources. Sulfur K-edge XANES data indicated a major contribution of pyrite (FeS2) to S speciation close to the shore. However, this contribution was found to dramatically decrease across the shore-to-reef gradient, S mainly occurring as sulfate close to the coral reef. In contrast, Fe and Ni K-edge XANES and EXAFS data indicated a minor contribution of pyrite to Fe and Ni speciation, and this contribution could be evidenced only close to the shore. The major fractions of Fe and Ni across the shore-to-reef gradient were found to occur as Ni- and Fe-bearing clay minerals consisting of smectite (~nontronite), glauconite and two types of serpentines (chrysotile and greenalite/berthierine). Among these clay minerals, greenalite/berthierine, glauconite and possibly smectite, were considered as authigenic. The low contribution of pyrite to trace metals speciation compared to clay minerals is interpreted as a result of (1) a reduced formation rate due to the low amounts of organic carbon compared to the Fe pool and (2) repeated re-oxidation events upon re-suspension of the sediments top layers due to the specific context of shallow lagoon waters. This study thus suggests that green clay authigenesis could represent a key process in the biogeochemical cycling of trace metals that are delivered to lagoon ecosystems upon continental erosion and weathering.

    View details for DOI 10.1016/j.scitotenv.2019.06.274

    View details for PubMedID 31466160

  • Influence of redox interfaces on metal(loid) contaminant mobility in shallow alluvial groundwater aquifers Boye, K., Kumar, N., Noel, V., Bargar, J., Fendorf, S. AMER CHEMICAL SOC. 2019
  • Colloid formation driven by redox processes: Impact on groundwater quality in shallow alluvial aquifers Noel, V., Kumar, N., Barragan, L., Boye, K., Bargar, J. AMER CHEMICAL SOC. 2019
  • Isotopic Fingerprint of Uranium Accumulation and Redox Cycling in Floodplains of the Upper Colorado River Basin ENVIRONMENTAL SCIENCE & TECHNOLOGY Lefebvre, P., Noel, V., Lau, K. V., Jemison, N. E., Weaver, K. L., Williams, K. H., Bargar, J. R., Maher, K. 2019; 53 (7): 3399–3409
  • Hydrological-geochemical controls over uranium mobility in unsaturated zone sediments Bargar, J., Roycroft, S., Boye, K., Noel, V., Johnson, R., Perzan, Z. AMER CHEMICAL SOC. 2019
  • Isotopic Fingerprint of Uranium Accumulation and Redox Cycling in Floodplains of the Upper Colorado River Basin. Environmental science & technology Lefebvre, P., Noel, V., Lau, K. V., Jemison, N. E., Weaver, K. L., Williams, K. H., Bargar, J. R., Maher, K. 2019


    Uranium (U) groundwater contamination is a major concern at numerous former mining and milling sites across the Upper Colorado River Basin (UCRB), USA, where U(IV)-bearing solids have accumulated within naturally reduced zones (NRZs). Understanding the processes governing U reduction and oxidation within NRZs is critical for assessing the persistence of U in groundwater. To evaluate the redox cycling of uranium, we measured the U concentrations and isotopic compositions (delta238U) of sediments and pore waters from four study sites across the UCRB that span a gradient in sediment texture and composition. We observe that U accumulation occurs primarily within fine-grained (low-permeability) NRZs that show active redox variations. Low-permeability NRZs display high accumulation and low export of U, with internal redox cycling of U. In contrast, within high-permeability NRZs, U is remobilized under oxidative conditions, possibly without any fractionation, and transported outside the NRZs. The low delta238U of sediments outside of defined NRZs suggests that these reduced zones act as additional U sources. Collectively, our results indicate that fine-grained NRZs have a greater potential to retain uranium, whereas NRZs with higher permeability may constitute a more-persistent but dilute U source.

    View details for PubMedID 30807121

  • Uranium storage mechanisms in wet-dry redox cycled sediments. Water research Noel, V., Boye, K., Kukkadapu, R. K., Li, Q., Bargar, J. R. 2019; 152: 251–63


    Biogeochemical redox processes that govern radionuclide mobility in sediments are highly sensitive to forcing by the water cycle. For example, episodic draining and intrusion of oxidants into reduced zones during dry seasons can create biogeochemical seasonal hotspots of enhanced and changed microbial activity, affect the redox status of minerals, initiate changes in sediment gas and water transport, and stimulate the release of organic carbon, iron, and sulfur by oxidation of solid reduced species to aqueous oxic species. In the Upper Colorado River Basin, water-saturation of organic-enriched sediments locally promotes reducing conditions, denoted 'Naturally Reduced Zones' (NRZs), that accumulate strongly U(IV)sol. Subsequently, fluctuating hydrological conditions introduce oxidants, which may reach internal portions of these sediments and reverse their role to become secondary sources of Uaq. Knowledge of the impact of hydrological variability on the alternating import and export of contaminants, including U, is required to predict contaminant mobility and short- and long-term impacts on water quality. In this study, we tracked U, Fe, and S oxidation states and speciation to characterize the variability in redox processes and related Usol solubility within shallow fine-grained NRZs at the legacy U ore processing site at Shiprock, NM. Previous studies have reported U speciation and behavior in permanently saturated fine-grained NRZ sediments. This is the first report of U behavior in fine-grained NRZ-like sediments that experience repeated redox cycling due to seasonal fluctuations in moisture content. Our results support previous observations that reducing conditions are needed to accumulate Usol in sediments, but they counter the expectation that Usol predominantly accumulates as U(IV)sol; our data reveal that Usol may accumulate as U(VI)sol in roughly equal proportion to U(IV)sol. Surprisingly high abundances of U(VI)sol confined in transiently saturated fine-grained NRZ-like sediments suggest that redox cycling is needed to promote its accumulation. We propose a new process model, where redox oscillations driven by annual water table fluctuations, accompanied by strong evapotranspiration in low-permeability sediments, promote conversion of U(IV)sol to relatively immobile U(VI)sol, which suggests that Usol is accumulating in a form that is resistant to redox perturbations. This observation contradicts the common idea that U(IV)sol accumulated in reducing conditions is systematically re-oxidized, solubilized and transported away in groundwater.

    View details for PubMedID 30682569

  • Antimonite Binding to Natural Organic Matter: Spectroscopic Evidence from a Mine Water Impacted Peatland. Environmental science & technology Besold, J. n., Eberle, A. n., Noël, V. n., Kujala, K. n., Kumar, N. n., Scheinost, A. C., Pacheco, J. L., Fendorf, S. n., Planer-Friedrich, B. n. 2019


    Peatlands and other wetlands are sinks for antimony (Sb), and solid natural organic matter (NOM) may play an important role in controlling Sb binding. However, direct evidence of Sb sequestration in natural peat samples is lacking. Here, we analyzed solid phase Sb, iron (Fe), and sulfur (S) as well as aqueous Sb speciation in three profiles up to a depth of 80 cm in a mine water impacted peatland in northern Finland. Linear combination fittings of extended X-ray absorption fine structure spectra showed that Sb binding to Fe phases was of minor importance and observed only in the uppermost layers of the peatland. Instead, the dominant (to almost exclusive) sequestration mechanism was Sb(III) binding to oxygen-containing functional groups, and at greater depths, increasingly Sb(III) binding to thiol groups of NOM. Aqueous Sb speciation was dominated by antimonate, while antimonite concentrations were low, further supporting our findings of much higher reactivity of Sb(III) than Sb(V) toward peat surfaces. Insufficient residence time for efficient reduction of antimonate to antimonite currently hinders higher Sb removal in the studied peatland. Overall, our findings imply that Sb(III) binding to solid NOM acts as an important sequestration mechanism under reducing conditions in peatlands and other high-organic matter environments.

    View details for DOI 10.1021/acs.est.9b03924

    View details for PubMedID 31436960

  • Sulfidation mechanisms of Fe(III)-(oxyhydr)oxide nanoparticles: a spectroscopic study ENVIRONMENTAL SCIENCE-NANO Kumar, N., Pacheco, J., Noel, V., Dublet, G., Brown, G. E. 2018; 5 (4): 1012–26

    View details for DOI 10.1039/c7en01109a

    View details for Web of Science ID 000435963000016

  • Vertical transport of uranium in the unsaturated zone: A likely plume persistence mechanism Roycroft, S., Noel, V., Boye, K., Johnson, R., Dam, W., Fendorf, S., Bargar, J. AMER CHEMICAL SOC. 2018
  • Vertical changes of the Co and Mn speciation along a lateritic regolith developed on peridotites (New Caledonia) GEOCHIMICA ET COSMOCHIMICA ACTA Dublet, G., Juillot, F., Brest, J., Noel, V., Fritsch, E., Proux, O., Olivi, L., Ploquin, F., Morin, G. 2017; 217: 1–15
  • Redox Controls over the Stability of U(IV) in Floodplains of the Upper Colorado River Basin ENVIRONMENTAL SCIENCE & TECHNOLOGY Noel, V., Boye, K., Pacheco, J., Bone, S. E., Janot, N., Cardarelli, E., Williams, K. H., Bargar, J. R. 2017; 51 (19): 10954–64


    Aquifers in the Upper Colorado River Basin (UCRB) exhibit persistent uranium (U) groundwater contamination plumes originating from former ore processing operations. Previous observations at Rifle, Colorado, have shown that fine grained, sulfidic, organic-enriched sediments accumulate U in its reduced form, U(IV), which is less mobile than oxidized U(VI). These reduced sediment bodies can subsequently act as secondary sources, releasing U back to the aquifer. There is a need to understand if U(IV) accumulation in reduced sediments is a common process at contaminated sites basin-wide, to constrain accumulated U(IV) speciation, and to define the biogeochemical factors controlling its reactivity. We have investigated U(IV) accumulation in organic-enriched reduced sediments at three UCRB floodplains. Noncrystalline U(IV) is the dominant form of accumulated U, but crystalline U(IV) comprises up to ca. 30% of total U at some locations. Differing susceptibilities of these species to oxidative remobilization can explain this variability. Particle size, organic carbon content, and pore saturation, control the exposure of U(IV) to oxidants, moderating its oxidative release. Further, our data suggest that U(IV) can be mobilized under deeply reducing conditions, which may contribute to maintenance and seasonal variability of U in groundwater plumes in the UCRB.

    View details for PubMedID 28873299

  • Oxidation of Ni-Rich Mangrove Sediments after Isolation from the Sea (Dumbea Bay, New Caledonia): Fe and Ni Behavior and Environmental Implications ACS EARTH AND SPACE CHEMISTRY Noel, V., Juillot, F., Morin, G., Marchand, C., Ona-Nguema, G., Viollier, E., Prevot, F., Dublet, G., Maillot, F., Delbes, L., Marakovic, G., Bargar, J. R., Brown, G. E. 2017; 1 (8): 455–64
  • Thermodynamically controlled preservation of organic carbon in floodplains NATURE GEOSCIENCE Boye, K., Noel, V., Tfaily, M. M., Bone, S. E., Williams, K. H., Bargar, J. R., Fendorf, S. 2017; 10 (6): 415-+

    View details for DOI 10.1038/NGEO2940

    View details for Web of Science ID 000402579200009

  • Long-term sequestration of nickel in mackinawite formed by Desulfovibrio capillatus upon Fe(III)-citrate reduction in the presence of thiosulfate APPLIED GEOCHEMISTRY Ikogou, M., Ona-Nguema, G., Juillot, F., Le Pape, P., Menguy, N., Richeux, N., Guigner, J., Noel, V., Brest, J., Baptiste, B., Morin, G. 2017; 80: 143–54
  • Spectroscopic investigation of the mechanism and kinetics of the sulfidation of FeIII-(oxyhydr)oxide nanoparticles Kumar, N., Noel, V., Pacheco, J., Maher, K., Brown, G. AMER CHEMICAL SOC. 2017
  • Molecular controls over uranium mobility in complex redox-active sediment systems Bargar, J., Noel, V., Bone, S., Janot, N., Roycroft, S., Boye, K. AMER CHEMICAL SOC. 2017
  • Factors affecting the sorption of uranyl at mineral-aqueous solution interfaces Brown, G., Dublet, G., Noel, V., Fendorf, S., Bargar, J., Maher, K. AMER CHEMICAL SOC. 2017
  • Understanding controls on redox processes in floodplain sediments of the Upper Colorado River Basin. The Science of the total environment Noël, V., Boye, K., Kukkadapu, R. K., Bone, S., Lezama Pacheco, J. S., Cardarelli, E., Janot, N., Fendorf, S., Williams, K. H., Bargar, J. R. 2017


    Floodplains, heavily used for water supplies, housing, agriculture, mining, and industry, are important repositories of organic carbon, nutrients, and metal contaminants. The accumulation and release of these species is often mediated by redox processes. Understanding the physicochemical, hydrological, and biogeochemical controls on the distribution and variability of sediment redox conditions is therefore critical to developing conceptual and numerical models of contaminant transport within floodplains. The Upper Colorado River Basin (UCRB) is impacted by former uranium and vanadium ore processing, resulting in contamination by V, Cr, Mn, As, Se, Mo and U. Previous authors have suggested that sediment redox activity occurring within organic carbon-enriched bodies located below the groundwater level may be regionally important to the maintenance and release of contaminant inventories, particularly uranium. To help assess this hypothesis, vertical distributions of Fe and S redox states and sulfide mineralogy were assessed in sediment cores from three floodplain sites spanning a 250km transect of the central UCRB. The results of this study support the hypothesis that organic-enriched reduced sediments are important zones of biogeochemical activity within UCRB floodplains. We found that the presence of organic carbon, together with pore saturation, are the key requirements for maintaining reducing conditions, which were dominated by sulfate-reduction products. Sediment texture was found to be of secondary importance and to moderate the response of the system to external forcing, such as oxidant diffusion. Consequently, fine-grain sediments are relatively resistant to oxidation in comparison to coarser-grained sediments. Exposure to oxidants consumes precipitated sulfides, with a disproportionate loss of mackinawite (FeS) as compared to the more stable pyrite. The accompanying loss of redox buffering capacity creates the potential for release of sequestered radionuclides and metals. Because of their redox reactivity and stores of metals, C, and N, organic-enriched sediments are likely to be important to nutrient and contaminant mobility within UCRB floodplain aquifers.

    View details for DOI 10.1016/j.scitotenv.2017.01.109

    View details for PubMedID 28359569

  • Nickel accelerates pyrite nucleation at ambient temperature GEOCHEMICAL PERSPECTIVES LETTERS Morin, G., Noel, V., Menguy, N., Brest, J., Baptiste, B., Tharaud, M., Ona-Nguema, G., Ikogou, M., Viollier, E., Juillot, F. 2017; 5: 6–11
  • Regional importance of organic-rich sediments to uranium mobility in the upper Colorado River Basin Noel, V., Boye, K., Bargar, J., Lefebvre, P., Maher, K., Bone, S., Lezama, J., Carderelli, E., Dam, W., Johnson, R. AMER CHEMICAL SOC. 2016
  • Impact of redox conditions on interfacial uranium chemistry in complex natural sediments Bargar, J., Bone, S., Lezama-Pacheco, J., Alessi, D., Cerrato, J., Veeramani, H., Noel, V., Suvorova, E., Bernier-Latmani, R., Giammar, D., Long, P., Williams, K. AMER CHEMICAL SOC. 2016
  • Physico-Chemical Heterogeneity of Organic-Rich Sediments in the Rifle Aquifer, CO: Impact on Uranium Biogeochemistry. Environmental science & technology Janot, N., Lezama Pacheco, J. S., Pham, D. Q., O'Brien, T. M., Hausladen, D., Noël, V., Lallier, F., Maher, K., Fendorf, S., Williams, K. H., Long, P. E., Bargar, J. R. 2016; 50 (1): 46-53


    The Rifle alluvial aquifer along the Colorado River in west central Colorado contains fine-grained, diffusion-limited sediment lenses that are substantially enriched in organic carbon and sulfides, as well as uranium, from previous milling operations. These naturally reduced zones (NRZs) coincide spatially with a persistent uranium groundwater plume. There is concern that uranium release from NRZs is contributing to plume persistence or will do so in the future. To better define the physical extent, heterogeneity and biogeochemistry of these NRZs, we investigated sediment cores from five neighboring wells. The main NRZ body exhibited uranium concentrations up to 100 mg/kg U as U(IV) and contains ca. 286 g of U in total. Uranium accumulated only in areas where organic carbon and reduced sulfur (as iron sulfides) were present, emphasizing the importance of sulfate-reducing conditions to uranium retention and the essential role of organic matter. NRZs further exhibited centimeter-scale variations in both redox status and particle size. Mackinawite, greigite, pyrite and sulfate coexist in the sediments, indicating that dynamic redox cycling occurs within NRZs and that their internal portions can be seasonally oxidized. We show that oxidative U(VI) release to the aquifer has the potential to sustain a groundwater contaminant plume for centuries. NRZs, known to exist in other uranium-contaminated aquifers, may be regionally important to uranium persistence.

    View details for DOI 10.1021/acs.est.5b03208

    View details for PubMedID 26651843

  • Persistent Secondary Contaminant Sources at a Former Uranium Mill Site, Riverton, Wyoming, USA Johnson, R. H., Dam, W. L., Campbell, S., Noel, V., Bone, S. E., Bargar, J. R., Dayvault, J., Drebenstedt, C., Paul, M. TU BERGAKADEMIE FREIBERG, INST MINING & SPECIAL CIVIL ENG. 2016: 398–404
  • Use of Ferrihydrite-Coated Pozzolana and Biogenic Green Rust to Purify Waste Water Containing Phosphate and Nitrate Current Inorganic Chemistry Ruby, C., Naille, S., Ona-Nguema, G., Morin, G., Mallet, M., Guerbois, D., Barthélémy, K., Etique, M., Zegeye, A., Zhang, Y., Boumaïza, H., Al-Jaberi, M., Renard, A., Noël, V., Binda, P., Hanna, K., Despas, C., Abdelmoula, M., Kukkadapu, R., Sarrias, J., Albignac, M., Rocklin, P., Nauleau, F., Hyvrard, N., Génin, J. 2016
  • Ni cycling in mangrove sediments from New Caledonia GEOCHIMICA ET COSMOCHIMICA ACTA Noel, V., Morin, G., Juillot, F., Marchand, C., Brest, J., Bargar, J. R., Munoz, M., Marakovic, G., Ardo, S., Brown, G. E. 2015; 169: 82-98
  • EXAFS analysis of iron cycling in mangrove sediments downstream a lateritized ultramafic watershed (Vavouto Bay, New Caledonia) GEOCHIMICA ET COSMOCHIMICA ACTA Noel, V., Marchand, C., Juillot, F., Ona-Nguema, G., Viollier, E., Marakovic, G., Olivi, L., Delbes, L., Gelebart, F., Morin, G. 2014; 136: 211–28
  • Biomineralization of iron-phosphates in the water column of Lake Pavin (Massif Central, France) GEOCHIMICA ET COSMOCHIMICA ACTA Cosmidis, J., Benzerara, K., Morin, G., Busigny, V., Lebeau, O., Jezequel, D., Noel, V., Dublet, G., Othmane, G. 2014; 126: 78–96
  • XAS evidence for Ni sequestration by siderite in a lateritic Ni-deposit from New Caledonia AMERICAN MINERALOGIST Dublet, G., Juillot, F., Morin, G., Fritsch, E., Noel, V., Brest, J., Brown, G. E. 2014; 99 (1): 225-234