Reducing Redox Conditions Research Articles

A double ttrA and pduA knock-out mutant of Salmonella Typhimurium is not attenuated for mice (Mus musculus).

Despite numerous studies on Salmonella enterica subsp. enterica serovar Typhimurium, the underlying mechanisms of several aspects of its virulence are still under investigation, including the role of the pdu and ttrA genes, associated with the metabolism of 1,2-propanediol using tetrathionate as an electron acceptor respectively. Our objective was to contribute to an understanding of the role of these genes inbacterial virulence for mice (Mus musculus) using an S. Typhumirum ΔttrApduA mutant. The experiment was conducted with a group infected by the S. Typhimurium mutant and a control group infected with a wild-type strain. The mutant was not attenuated compared with the parent strain. There were no differences in the bacterial numbers recovered from the mesenteric lymph nodes and Peyer's patches but at 8-day after oral infection higher numbers were recovered from the spleen, liver, and cecum. Unlike the single pduA and ttrA mutants, the double ΔttrApduA mutation did not affect invasion and survival in mice, which highlights the need for further studies to clarify the role of these important metabolism genes under reduced redox conditions linked to Salmonella virulence.

Redox-mediated changes in the release dynamics of lead (Pb) and bacterial community composition in a biochar amended soil contaminated with metal halide perovskite solar panel waste

This study explored the redox-mediated changes in a lead (Pb) contaminated soil (900 mg/kg) due to the addition of solar cell powder (SC) and investigated the impact of biochar derived from soft wood pellet (SWP) and oil seed rape straw (OSR) (5% w/w) on Pb immobilization using an automated biogeochemical microcosm system. The redox potential (Eh) of the untreated (control; SC) and biochar treated soils (SC + SWP and SC + OSR) ranged from −151 mV to +493 mV. In SC, the dissolved Pb concentrations were higher under oxic (up to 2.29 mg L−1) conditions than reducing (0.13 mg L−1) conditions. The addition of SWP and OSR to soil immobilized Pb, decreased dissolved concentration, which could be possibly due to the increase of pH, co-precipitation of Pb with FeMn (hydro)oxides and pyromorphite, and complexation with biochar surface functional groups. The ability and efficiency of OSR for Pb immobilization were higher than SWP, owing to the higher pH and density of surface functional groups of OSR than SWP. Biochar enhanced the relative abundance of Proteobacteria irrespective of Eh changes, while the relative abundance of Bacteroidota increased under oxidizing conditions. Overall, we found that both OSR and SWP immobilized Pb in solar panel waste contaminated soil under both oxidizing and reducing redox conditions which may mitigate the potential risk of Pb contamination.

Organic geochemical heterogeneity of cretaceous mudrocks and reassessment of oil sources in the Tano Basin, Ghana

The Tano Basin in Ghana, situated within the South Atlantic margin, is a significant area for petroleum exploration. Previous studies have recognized the presence of source rocks rich in organic matter from the Cretaceous period in this basin. However, the specific origins of this organic matter, as well as the thermal maturity and depositional environment of the Cretaceous source strata, are not well characterized in existing literature. Here, geochemical data are reported on the bulk geochemical composition of 45 Maastrichtian to Albian-aged rock cuttings via pyrolysis and total organic carbon (TOC) analysis. Out of these samples, 29 were selected for further biomarker and stable carbon isotope (δ13C) analysis. The biomarker and isotopic signatures of the 29 rock extracts and 6 crude oils from the basin's productive Jubilee and TEN oil fields were compared to establish oil-oil and oil-source correlations. The Cenomanian and Turonian source rocks showed the greatest oil generation potential based on current bulk geochemical analysis. These rocks are dominated by oil-prone organic matter and are at a more favorable maturity stage compared to the Maastrichtian, Santonian, and Coniacian (M-S-C) rock suites. In contrast, the Albian rock samples, characterized by mixed Type II/III and Type III kerogen, and their high thermal maturity, indicate a high potential for the generation of gaseous hydrocarbons. The biomarker and isotope data from the Cenomanian, Turonian, and Albian (T-C-A) source rocks suggest that they were deposited in a Transitional Marine-Lacustrine environment characterized by reducing redox conditions. This environment effectively preserved organic matter from diverse sources such as bacteria, algae, and higher plants. Furthermore, biomarker ratios indicated that the T-C-A source rocks are in the early-peak mature window. On the other hand, the M-S-C source rocks appear to have been deposited under suboxic conditions in a Coastal Marine environment. Lower aquatic organisms dominate these rocks, which have an immature to marginally mature level. The analysis of lower molecular weight hydrocarbons (≤C20), characterized by an unresolved complex mixture, did not reveal any obvious correlation between the oils and the Cretaceous source rocks. However, the analysis of higher molecular weight hydrocarbons (≥C20) and isotopic ratios indicated that the commercial discoveries in the Jubilee and TEN fields share a genetic similarity and are primarily sourced from the T-C-A source rocks. Furthermore, the molecular and isotopic characteristics suggest that the M-S-C source rocks do not appear to have contributed to the oils found in the Jubilee and TEN fields. These new geochemical findings shed light on the paleoenvironmental conditions and source rock characteristics of the region, significantly contributing to our understanding of the petroleum evolution and potential of the Tano Basin.

Consequential modulation of mitochondrial K+- and H+-driven ATP synthase activity under excess cytoplasmic NA+ and oxidative stress mimicking heart failure: Modeling studies.

Previously we demonstrated that mitochondrial ATP synthesis by F1Fo ATP synthase can be driven by K+ and H+ while regulating matrix volume and energy supply-demand matching under normal physiological conditions. In this new scenario, under conditions prevalent during heart failure such as Na+ accumulation and oxidized redox, we explored computationally the bioenergetic impact of mitochondrial Ca2+ levels and redox status on K+ transport and ATP synthesis. We utilized a computational model of mitochondrial function encompassing TCA cycle, oxidative phosphorylation (OxPhos), ionic transport, ROS production and ROS scavenging. Simulations were performed at increasing cytoplasmic Na+ concentrations (Nai) as means of changing mitochondrial Ca2+ in oxidized or reduced redox environments. The simulation protocol comprised consecutive pulses of increasing concentrations of ADP and cytoplasmic Ca2+ (ADP-Ca pulses). Under oxidizing redox environment, mitochondrial membrane potential (ΔΨm), matrix K+ and Ca2+ exhibit maladaptively decreased magnitudes as a function of Nai, both during baseline state 4 (absence of ADP) as well as following ADP-Ca pulses. In contrast, under reduced vs oxidized redox conditions, these variables exhibit adaptively larger transient amplitudes following the ADP-Ca pulses. OxPhos fluxes under state 4 were similar regardless of the redox state. However, during the successive ADP-Ca pulses, the lower the Nai the larger the increase in respiration, K+ uptake, and total ATP synthesis fluxes both under oxidized and reduced redox conditions. Also, at the lowest Nai, respiration can reach a 60% larger flux at the same ADP-Ca under reduced vs oxidized conditions. The simulation results predict that under heart failure conditions, the interplay between the cardiac redox status and cytoplasmic Na+ concentration significantly influences the mitochondrial energetic response, as assessed by ATP supply and degree of oxidative stress.

Orogenic Au deposits with atypical metal association (Cu, Co, Ni): Insights from the Pohjanmaa Belt, western Finland

The Laivakangas Au-Cu metallogenic area is characterised by orogenic Au deposits with both Au-only and with atypical (Au ± Cu, Co, Ni) metal associations. Here we study and compare four examples to better constrain the parameters controlling enrichment in base metals in addition to Au. We selected two typical Au-only deposits, the Laivakangas and the Huhta deposits and two orogenic Au deposits with atypical metal association, the Jouhineva Au-Cu-Co-Ag and the Kurula Au-Co deposits. All four deposits record multiple successive mineralisation events with local variations in their respective metal association. Two auriferous mineralisation events are identified, (1) a ubiquitous As-Au-(Co, Ni) event close to peak metamorphism (620–430 °C) where Au occurs either as invisible Au in arsenides or as inclusion in arsenopyrite; (2) a later Cu(-Au)-rich sulfide event on the retrograde path where Au locally occurs as free, native grains along with chalcopyrite. From S isotope studies of the sulfide and sulfarsenide minerals and relations between the deposits and surrounding rocks, we propose that the variation in metal association of the ore fluid is linked to the diversity of lithologies involved in metamorphic fluid production. Multi-event hydrothermal mineralisation and relatively reduced redox conditions appear critical to increase the Au endowment in a deposit and to introduce atypical metals. Results of this study provide a new comprehension of the variability of metal association in orogenic Au deposits of the Laivakangas Au-Cu metallogenic area and elsewhere.

The use of boron nitride to impose reduced redox conditions in experimental petrology

Abstract Boron nitride (BN) is a commonly used pressure-transmitting material in experimental petrology. It is often considered to be as inert as MgO or Al2O3, and its redox potential is seldomly discussed. It is generally implied that, when used as a capsule sleeve, BN may impose relatively reduced conditions, similar to the effect of the fayalite-magnetite-quartz (FMQ) buffer. However, sediment melting experiments performed at 1050 °C and 3 GPa with BN as the capsule sleeve, produced a hydrous rhyolitic melt with dissolved H2S and CH4 (Li et al. 2021). The resulting fO2 estimate is significantly more reduced than that for the magnetite-wüstite (MW)-buffered experiment where H2S and CH4 were undetected (Li et al. 2021), possibly to the extent of the quartz-iron-fayalite (QIF) buffered conditions produced when BN is used as a capsule or crucible (Wendlandt et al. 1982). To establish an explanation for such a discrepancy, we have conducted further investigation to better constrain the fO2 imposed by BN, when used as a capsule sleeve. Here we report results on analyses of Fe content in Au capsules, a comparative experiment using a QIF buffer and an experiment with an Fe-(Mg,Fe) O sensor for direct analysis of fO2. The calibration of the equilibrium between FeO in melt and Fe in the Au capsule, from Ratajeski and Sisson (1999) appears to be inadequate in constraining fO2 for our experiments. However, we were able to obtain Fe diffusion coefficients in Au from the Fe diffusion profiles observed in the capsule of the Fe-(Mg,Fe)O sensor experiment, and both the inner and outer capsules of the MW-buffered experiment, with resulting values of 1 × 10–13 m2/s, 3 × 10–14 m2/s, and 5 × 10–14 m2/s, respectively. The QIF-buffered and Fe-(Mg,Fe)O sensor experiments provide several lines of evidence supporting the observation that BN imposes QIF-like redox conditions. First, the Fe-(Mg,Fe)O sensor returned an fO2 value of QIF. Second, the “apparent” partition coefficients between FeO content in melt and Fe in the Au capsules are similar between the BN experiment and the QIF-buffered experiment. Third, we observe CH4 and H2O peaks with similar intensities in the Raman spectra of melts from these two experiments, suggesting similar H2 and thus O2 fugacity. As our experiments were performed on a cubic press with the experimental assembly encased in a pyrophyllite cube, we interpret that the significantly reduced conditions imposed by BN are likely due to high H2O activity maintained by dehydration of pyrophyllite, which can be explained using the reaction 2BN + 3H2O = B2O3 + N2 + 3H2. Lower H2O activity will reduce or inhibit the oxidation of BN and its fO2 buffering ability. If heat-treated, BN acts as a highly efficient H2 barrier, as shown by Truckenbrodt et al. (1997). Through our efforts to determine the fO2 imposed by using BN as a capsule sleeve in our experimental assembly, we are able to demonstrate the reducing ability of BN as an assembly component and, furthermore, shed light on the process by which BN imposes such reduced fO2. We hereby present what we have learned during the course of this investigation in the hope that the effect of BN on fO2 control is both recognized and further exploited in future experimental studies.

Condensation of cometary silicate dust using an induction thermal plasma system

Glass with embedded metal and sulfides (GEMS), the major components of chondritic-porous interplanetary dust particles (CP-IDPs), is one of the most primitive materials in the Solar System and may be analogous to the amorphous silicate dust observed in various astronomical environments. Mineralogical characteristics of GEMS should reflect their formation process and condition. In this study, synthetic experiments in the sulfur-bearing system of Fe–Mg–Si–O–S were performed with a systematic change in redox conditions using thermal plasma systems to reproduce the mineralogy and textures of GEMS. The resulting condensates were composed of amorphous silicates with Fe-bearing nano-inclusions. The Fe content and texture in the amorphous silicates as well as the mineral phases of the nanoparticles correlate with redox conditions. Fe dissolved in the amorphous silicate as FeO in oxidizing conditions formed Fe-metal nanoparticles in intermediate redox conditions, and gupeiite (Fe3 Si) nanoparticles in reducing conditions. In intermediate to reducing redox conditions, Fe-poor amorphous silicate formed a biphasic texture with Mg- and Si-rich regions, indicating liquid immiscibility during the melt phase. Most Fe-metal particles were surrounded by FeS and formed on the surface of amorphous silicate grains. Condensates produced in intermediate to slightly reducing redox conditions resemble GEMS in that they have similar mineral assemblages and chemical compositions to amorphous silicate, except that the Fe-metal grains are absent from the interior of the amorphous silicate grains. This textural difference can be explained by the sulfidation at high temperatures in this study, in contrast to sulfidation occurring at low temperatures in the presence of H2 in natural GEMS formation. Based on the two-liquid structures observed in the experimental products and in GEMS, also recognized in infrared spectra, we propose that GEMS condensed as silicate melt under limited redox conditions followed by incorporation of multiple metal grains into the silicate melt or by aggregation of coreshell structured grains before sulfidation of the metallic iron. Condensates produced in oxidizing conditions are similar to GEMS-like material in the matrices of primitive carbonaceous chondrite meteorites, indicating the possibility that they form by direct condensation from nebula gas in relatively oxidizing conditions compared to GEMS.

Powering biological nitrogen removal from the environment by geobatteries

Geobatteries are redox-active substances that can take up, store, and release electrons reversibly. Provided that their redox activity can be maintained by fluctuations of oxidizing and reducing redox conditions, geobatteries could also improve the performance of engineered systems, such as in biological nitrogen removal from wastewater or constructed wetlands.

Mineral thermobarometry and its implications for petrological constraints on Mesoarchean granitoids from the Carajás Province, Amazonian Craton (Brazil)

This paper describes the first investigation of the crystallization parameters of the Mesoarchean granitoids from Ourilândia do Norte, which is located in the midwestern part of the Carajás Province. These rocks are divided into three major groups: (i) sanukitoids composed of amphibole-bearing granitoids and associated intermediate to mafic rocks; (ii) potassic granites composed of biotite monzogranites and associated high-Ti granodiorite; and (iii) subordinated TTG-affinity granitoids (amphibole-bearing trondhjemites and biotite-bearing tonalitic xenoliths). These rocks were formed from different sources at different depths, including enriched mantle (sanukitoids), continental crust (monzogranite), mantle-crust mixture (high-Ti granodiorite) and oceanic crust (TTG-affinity granitoids). Potassic granites and porphyritic sanukitoid facies have high magnetite contents, and consequently high magnetic susceptibility (MS), compared to the equigranular sanukitoid facies and trondhjemite. Thermometers based on apatite saturation in whole-rock indicate liquidus temperatures above 800 °C for all granitoids, reaching 959 °C in the high-Ti granodiorite. Amphibole-based and Si-sensitive geothermometers indicate solidus temperatures from 785 to 738 °C for sanukitoids and 892 to 772 °C for trondhjemite, with estimated emplacement pressures varying from 297 to 80 MPa and 580 to 263 MPa, respectively. Because the potassic granites display an amphibole-free assemblage, no geothermobarometric estimate based on amphibole composition was possible. However, potassic granites are associated with coeval sanukitoids (2.88 Ga), which indicates similar pressure conditions and emplacement depths for these rocks. Crystallization constraints from the Ourilândia sanukitoids are comparable to those of the geochemically similar Rio Maria sanukitoids of the Carajás Province, although the pressure estimates and water content show differences. The Fe/(Fe + Mg) ratios of both biotite and amphibole indicate high to intermediate redox conditions for the sanukitoids and potassic granites, which are mostly above that of nickel-nickel oxide (+1.0 < NNO < + 1.9), although less oxidized conditions are estimated for the trondhjemite (– 0.5 < NNO < + 1.0). High water content was estimated for the sanukitoid-related granitoids (> 5%) relative to the TTG-affinity granitoids (< 4%) using amphibole-based water calibrations. Compared with sanukitoids from other Archean cratons, the Ourilândia sanukitoids crystallization constraints show similarities with the more oxidized members from the Baltic Shield, the Closepet-type granites and the Matok-type sanukitoids but differ from the reduced redox conditions of the Elan-type granitoids from the East Sarmatian orogen.

Chemical intervention for enhancing growth and reducing grain arsenic accumulation in rice.

Arsenic (As) is a ubiquitous environmental carcinogen that enters the human food chain mainly through rice grains. In the present study, we evaluated the potential of thiourea (TU; non-physiological reactive oxygen species scavenger) in mitigating the negative effects of arsenic (As) stress in indica rice variety IR64, with the overall aim to reduce grain As accumulation. At seedling stage, As+TU treatment induced the formation of more numerous and longer crown roots compared with As alone. The As accumulation in main root, crown root, lower leaf and upper leaf was significantly reduced to 0.1-, 0.14-, 0.16-, 0.14-fold, respectively in As+TU treated seedlings compared with those of As alone. This reduced As accumulation was also coincided with light-dependent suppression in the expression levels of aquaporins and photosynthesis-related genes in As+TU treated roots. In addition, the foliar-supplemented TU under As-stress maintained reducing redox conditions which decreased the rate of As accumulation in flag leaves and, eventually grain As by 0.53-fold compared with those of As treatment. The agronomic feasibility of TU was validated under naturally As contaminated sites of Nadia (West Bengal, India). The tiller numbers and crop productivity (kg seed/ha) of TU-sprayed plants were increased by 1.5- and 1.18-fold, respectively; while, grain As accumulation was reduced by 0.36-fold compared with those of water-sprayed control. Thus, this study established TU application as a sustainable solution for cultivating rice in As-contaminated field conditions.

Composition of Reduced Mantle Fluids: Evidence from Modeling Experiments and Fluid Inclusions in Natural Diamond

Abstract —Experimental modeling in the C–O–H, C–O–H–N, and peridotite–C–O–H–N systems, combined with analyses of fluid inclusions in natural diamonds, is used to reconstruct the compositions of fluids that can be stable in the reduced mantle. Hydrocarbons (HCs) in the upper mantle can form either by reactions of carbonates with iron/wüstite and water or by direct hydrogenation of carbon phases (graphite, diamond, and amorphous carbon) interacting with reduced fluids. Carbon required for the formation of HCs can come from diamond, graphite, or carbonates. Mainly light alkanes are stable at the mantle pressures and temperatures in the C–O–H and C–O–H–N systems as well as in the peridotite–fluid system under ultrareduced to moderately reduced redox conditions at the oxygen fugacity from –2 to +2.5 lg units relative to the IW (Fe–FeO) buffer. Some oxygenated HCs can be stable in fluids equilibrated with carbonate-bearing peridotite. Ammonia and, to a lesser degree, methanimine (CH3N) are predominant nitrogen species in reduced fluids in the conditions of the subcratonic lithosphere or the Fe0-bearing mantle. The presence of HCs as common constituents of reduced mantle fluids is supported by data on inclusions from natural diamonds hosted by kimberlites of the Yakutian province and from placer diamonds of the northeastern Siberian craton and the Urals. Fluid inclusions have minor amounts of H2O, methane, and other light alkanes but relatively high concentrations of oxygenated hydrocarbons, while the H/(H + O) ratio varies from 0.74 to 0.93. Hydrocarbon-bearing fluids in some eclogitic diamonds have high CO2 concentrations. Also, the fluid inclusions have significant percentages of N2 and N-containing species, Cl-containing HCs, and S-containing compounds. Both the experimental results and the analyses of fluid inclusions in natural diamonds indicate that HCs are stable in the upper mantle conditions. The set of hydrocarbons, mainly light alkanes, might have formed in the mantle from inorganic substances. Further research should focus on the causes of the difference between experimental and natural fluids in the contents of methane, light alkanes, oxygenated hydrocarbons, and water and on the stability of N-, S-, and Cl-containing fluid components.

Ore genesis of the Zhuxi supergiant W-Cu skarn polymetallic deposit, South China: Evidence from scheelite geochemistry

Scheelite is the main ore mineral in skarn-type tungsten deposits, which can be used to track the ore-forming processes and sources. The Zhuxi W-Cu deposit (3.44 Mt WO3 at 0.54% and 0.10 Mt Cu at 0.57%), located in the northern part of the Jiangnan orogen, is one of the largest tungsten deposits in the world. Skarn and orebodies occur mainly within the contact zone between the Mesozoic highly fractionated intrusions and Carboniferous carbonate sediments (Huanglong and Chuanshan formations). Our data reveal that the REEs of scheelite are mainly controlled by the substitution mechanism 3Ca2+ = 2REE3+ + □Ca. Scheelites from the Zhuxi deposit show negative Eu anomalies in the prograde skarn stage, but positive Eu anomalies in the retrograde skarn stage in the chondrite-normalized REE patterns. Variation of Eu anomalies recorded the ore-forming processes. The negative Eu anomalies were inherited from the Mesozoic granites and the positive ones formed under more reduced redox conditions. The decrease of Mo concentrations, along with increase of δEu and δCe of scheelite from prograde to retrograde skarn stage, support a temporal decrease in oxygen fugacity of the mineralization fluids. The scheelites from the Zhuxi deposit are characterized by low εNd(t) values (−10.1 to −7.0) and high initial 87Sr/86Sr ratios (0.71231–0.72371), which are different from the scheelites hosted in vein-type Au-W deposits contributed mainly by mantle. The Nd-Sr isotopes of scheelites are consistent with the results of the three Mesozoic granites, indicating their genetic relationship. However, the scheelites show variable Nb/Ta compositions, which straddle between the values of Mesozoic granites and the country rock of Shuangqiaoshan Group meta-sedimentary rocks, indicating the Shuangqiaoshan Group also has contributed to mineralization. This is different from a commonly accepted model that the ore-forming fluids and metals were exsolved exclusively from the granite plutons.

Reactive transport calculations to evaluate sulphide fluxes in the near-field of a SF/HLW repository

Radioactive waste is planned to be disposed in a deep geological repository in the Opalinus Clay (OPA) rock formation in Switzerland. Cu coating of the steel disposal canister is considered as potential a measure to ensure complete waste containment of spent nuclear fuel (SF) and vitrified high-level waste (HLW) or a period of 100,000 years. Sulphide is a potential corroding agent to Cu under reducing redox conditions. Background dissolved sulphide concentrations in pristine OPA are low, likely controlled by equilibrium with pyrite. At such concentrations, sulphide-assisted corrosion of Cu would be negligible. However, the possibility exists that sulphate reducing bacteria (SRB) might thrive at discrete locations of the repository’s near-field. The activity of SRB might then lead to significantly higher dissolved sulphide concentrations. The objective of this work is to employ reactive transport calculations to evaluate sulphide fluxes in the near-field of the SF/HLW repository in the OPA. Cu canister corrosion due to sulphide fluxes is also simplistically evaluated.

Redox behavior and solubility of plutonium under alkaline, reducing conditions

Abstract The solubility and redox behavior of hydrous Pu(IV) oxide was comprehensively investigated by an experimental multi-method approach as a function of different redox conditions in 0.1 M NaCl solutions, allowing a detailed characterization of Pu(IV) and Pu(III) solubility and solid phase stability in these systems. Samples were prepared at ~3≤pHm≤~6 (pHm=–log m H + ) ${{\text{m}}_{{{\text{H}}^{\text{ + }}}}})$ and ~8≤pHm≤~13 at T=(22±2)°C under Ar atmosphere. No redox buffer was used in one set of samples, whereas mildly and strongly reducing redox conditions were buffered in two series with hydroquinone or SnCl2, respectively, resulting in (pe+pHm)=(9.5±1) and (2±1). XRD, XANES and EXAFS confirmed the predominance of Pu(IV) and the nanocrystalline character of the original, aged PuO2(ncr,hyd) solid phase used as a starting material. Rietveld analysis of the XRD data indicated an average crystal (domain) size of (4±1) nm with a mean cell parameter of (5.405±0.005) Å. The solubility constant of this solid phase was determined as log ∗ ​ K ° s , 0 $^ * K{^\circ _{{\text{s}},0}}$ =–(58.1±0.3) combining solubility data in acidic conditions and redox speciation by solvent extraction and CE–SF–ICP–MS. This value is in excellent agreement with the current thermodynamic selection in the NEA-TDB. Synchrotron-based in-situ XRD, XANES and EXAFS indicate that PuO2(ncr,hyd) is the solid phase controlling the solubility of Pu in hydroquinone buffered samples. Under these redox conditions and ~8≤pHm≤~13, the solubility of Pu is very low (~10−10.5 m) and pH-independent. This is consistent with the solubility equilibrium PuO2(am,hyd)+2H2O(l)⇔ Pu(OH)4(aq). Although in-situ XRD unequivocally shows the predominance of PuO2 in Sn(II)-buffered systems, XANES analyses indicate a significant contribution of Pu(III) (30±5%) in the solid phases controlling the solubility of Pu at (pe+pHm)=(2±1). For this system, EXAFS shows a systematic shortening of Pu–O and Pu–Pu distances compared to the starting Pu material and hydroquinone-buffered systems. The solubility of Pu remains very low (~10−10.5 m) at pHm&gt;9, but shows a very large scattering (~10−9–10−10.5 m) at pHm=8. Experimental observations collected in Sn(II) buffered systems can be explained by the co-existence of both PuO2(ncr,hyd) and Pu(OH)3(am) solid phases, but also by assuming the formation of a sub-stoichiometric PuO2−x (s) phase. This extensive study provides robust upper limits for Pu solubility in alkaline, mildly to strongly reducing conditions relevant in the context of nuclear waste disposal. The potential role of Pu(III) in the solid phases controlling the solubility of Pu under these conditions is analysed and discussed in view of the current NEA-TDB thermodynamic selection, which supports the predominance of PuO2(am,hyd) and constrains the formation of Pu(OH)3(am) at pHm&gt;8 outside the stability field of water.

A Deep Alteration and Oxidation Profile in a Shallow Clay Aquitard: Example of the Tégulines Clay, East Paris Basin, France

The oxidation profile of a surficial clay aquitard was studied on a 35-meter borecore from the Albian Tégulines Clay near Brienne-le-Château (Paris Basin, France). Mineralogical, geochemical, and petrophysical data showed evidences of gradual oxidation taking place down to a depth of 20 m. Below 20 m, the clay material was nonplastic and nonfractured, and it inherited reduced redox conditions from bacterial sulfate reduction that occurred after sediment deposition. Above 20 m, the clay material was plastic. Up to a depth of 10-11 m, only rare yellowish aggregates of glauconite attested to limited oxidation, and pore water chemistry was unmodified. The 5–11 m depth interval was characterized by intensive pyrite oxidation, calcite dissolution, and formation of sulfate and iron hydroxide minerals. The upper 2-3 m was ochrous and entirely oxidized. These mineralogical changes were mirrored with pore water chemistry modifications such as an increase of alkalinity and sulfate concentration in the upper part of the profile. The presence of siderite at ~11 m evinced the reactivity of Fe(II) in the structure of clay minerals with dioxygen from meteoric waters that infiltrated into the Tégulines Clay through vertical fractures.

Sediment core data reconstruct the management history and usage of a heavily modified urban lake in Berlin, Germany.

Urban surface waters face several stressors associated with industry and urban water management. Over much of the past century, the wastewater treatment in Berlin, Germany, relied on inefficient sewage farms, which resulted in severe eutrophication and sediment contamination in the recipient surface waterbodies. A prominent example is Lake Tegel, where a multitude of management measures were applied in the last decades for the purpose of ecosystem restoration. In this study, we analyzed sediment cores of three lakes with X-ray fluorescence spectroscopy: Lake Tegel, Lake Großer Wannsee, which is environmentally similar but has a different management history, and Lake Userin, which serves as a reference located in a nature protection area. Multivariate statistical methods (principal component analysis, k-means clustering, and self-organizing maps) were used to assess the sediment quality and to reconstruct the management history of Lake Tegel. Principal component analysis established two main gradients of sediment composition: heavy metals and lithogenic elements. The impact of the management measures was visualized in the lake sediment composition changing from high abundance of heavy metals and reducing redox conditions to less-impacted sediments in recent layers. The clustering techniques suggested heterogeneity among sites within Lake Tegel that probably reflect urban water management measures. The abundance of heavy metals in recent lake sediments of Lake Tegel is similar to a lake with low urban impact and is lower than in Lake Großer Wannsee suggesting that the management measures were successful in the reduction of heavy metals, which are still a threat for surface waters worldwide.

Assessing the chemical contamination dynamics in a mixed land use stream system

Traditionally, the monitoring of streams for chemical and ecological status has been limited to surface water concentrations, where the dominant focus has been on general water quality and the risk for eutrophication. Mixed land use stream systems, comprising urban areas and agricultural production, are challenging to assess with multiple chemical stressors impacting stream corridors. New approaches are urgently needed for identifying relevant sources, pathways and potential impacts for implementation of suitable source management and remedial measures. We developed a method for risk assessing chemical stressors in these systems and applied the approach to a 16-km groundwater-fed stream corridor (Grindsted, Denmark). Three methods were combined: (i) in-stream contaminant mass discharge for source quantification, (ii) Toxic Units and (iii) environmental standards. An evaluation of the chemical quality of all three stream compartments – stream water, hyporheic zone, streambed sediment – made it possible to link chemical stressors to their respective sources and obtain new knowledge about source composition and origin. Moreover, toxic unit estimation and comparison to environmental standards revealed the stream water quality was substantially impaired by both geogenic and diffuse anthropogenic sources of metals along the entire corridor, while the streambed was less impacted. Quantification of the contaminant mass discharge originating from a former pharmaceutical factory revealed that several 100 kgs of chlorinated ethenes and pharmaceutical compounds discharge into the stream every year. The strongly reduced redox conditions in the plume result in high concentrations of dissolved iron and additionally release arsenic, generating the complex contaminant mixture found in the narrow discharge zone. The fingerprint of the plume was observed in the stream several km downgradient, while nutrients, inorganics and pesticides played a minor role for the stream health. The results emphasize that future investigations should include multiple compounds and stream compartments, and highlight the need for holistic approaches when risk assessing these dynamic systems.

Bank filtration in a coastal lake in South Brazil: water quality, natural organic matter (NOM) and redox conditions study

Bank filtration (BF) was evaluated as new treatment or pre-treatment option for drinking water production in Brazil. General water quality parameters, natural organic matter (NOM) and redox conditions were evaluated in Lagoa do Peri, a costal lake in Santa Catarina, South Brazil. Studies in two periods at two bank filtrations well systems, in a 45-m-length column and in a test filter laboratory scale set-up, were performed. The well systems and the column showed the removal of turbidity and colour from around 7 NTU and 65 Pt–Co, respectively, to below the local regulations (1 NTU and 15 Pt–Co units). Both systems demonstrated a good removal of NOM and trihalomethanes (THM) precursors with a preference removal of THM precursors. The NOM and THM precursor removal in the large column and the test filter were effectively modelled. In both cases, an easily degradable organic matter fraction was modelled; in the large column a moderate degradable fraction was identified as well. The first fraction was removed during the first days of travel time of the bank filtrate. A change to reduced redox conditions was observed in the large column experiment. The same happened in the wells system, showing the dissolution of iron, manganese and sulphide in the bank filtrate. This was the principal drawback of BF comparing with the already existing direct filtration (DF) treatment plant. BF performed slightly better in THM precursor removal (52%) than DF (42%). Therefore, BF could be a pre-treatment for the DF treatment system, and the existing facility could be adapted for iron and manganese removal.

The sulfur depot in the rhizosphere of a common wetland plant, Juncus effusus, can support long-term dynamics of inorganic sulfur transformations

The sulfur cycle in the rhizosphere of constructed wetlands is frequently interlaced with transformations of carbon and nitrogen. Knowledge about the manifold sulfur transformations may thus aid in improving treatment performance of constructed wetlands. In this study, two laboratory-scale constructed wetland models (planted fixed bed reactors; PFR1 and PFR2) were used to investigate inorganic sulfur transformations at various total loads of sulfate and organic carbon. Sulfate, sulfide and elemental sulfur were the most abundant sulfur compounds detected, thus providing evidence for the simultaneous occurrence of dissimilatory sulfate reduction and sulfide oxidation. This co-occurrence was likely enabled by oxygen micro-gradients in the root-near environment, i.e. aerobic sulfide and elemental sulfur oxidation took place mostly at the roots while sulfate and elemental sulfur reduction occurred in the pore water under reduced redox conditions. The rhizosphere was found to be first sink, then source for sulfur during the course of the experiment. Immobilization of reduced sulfur was triggered by catabolism of organic matter coupled to dissimilatory sulfate reduction and the subsequent partial oxidation of generated sulfide. Good plant status was critical for sulfur deposition in the systems. Without externally provided sulfate the sulfur depot of the rhizosphere was a prolonged source for sulfur, which was remobilized into the pore water. Oscillations between sulfide and sulfur (PFR1) or sulfide and sulfate (PFR2) suggested a dynamic interplay between plants and various microbial guilds, i.e. dissimilatory sulfate and sulfur reducers on one side and sulfide and sulfur oxidizers on the other.

Soil amendment using poplar woodchips to enhance the treatment of wastewater-originated nutrients

Vegetation filters, a nature based wastewater regeneration technology, have been reported as a feasible solution for small municipalities and scattered populations with limited access to sewage networks. However even when such a treatment is properly planned, the leaching of contaminants through the unsaturated zone may occur. The amendment of soil with a readily-labile source of carbon is supposed to ameliorate the removal of contaminants by stimulating microbial activity and enhancing sorption processes. In this study, lab-scale leaching column experiments were carried out to explore if the addition of woodchips to the soil could be a feasible strategy to be integrated in a vegetation filter. Two different types of arrangement of soil and woodchips layers were tested. The soil was collected from an operating vegetation filter treating wastewater of an office building characterised by a high nutrient load. Daily pulse of synthetic wastewater were applied into the columns and effluent samples were collected and analyzed for major ions, total nitrogen (NT), total phosphorous (PT) and chemical oxygen demand (COD). By the end of the experiment, NT, NO3-N and PT soil contents were also measured. Results indicate that amendments with woodchips enhance the elimination of wastewater-originated contaminants. NT removal in the columns with woodchips reaches a value of 99.4%. The main processes responsible for this elimination are NH4-N sorption and nitrification/denitrification. This latter fostered by the reduced redox conditions due to the enhanced microbial activity. High removal of PT (99%) is achieved independently of the woodchips presence due to retention and/or precipitation phenomena. The COD removal efficiency is not affected by the presence of the woodchips. The leaching of organic carbon occurs only during the experimental start-up period.