Model-Based Analysis of Arsenic Retention by Stimulated Iron Mineral Transformation under Coastal Aquifer Conditions.

A multitude of geochemical processes control the aqueous concentration and transport properties of trace metal contaminants such as arsenic (As) in groundwater environments. Effective As remediation, especially under reducing conditions, has remained a significant challenge. Fe(II) nitrate treatments are a promising option for As immobilization but require optimization to be most effective. Here, we develop a process-based numerical modeling framework to provide an in-depth understanding of the geochemical mechanisms controlling the response of As-contaminated sediments to Fe(II) nitrate treatment. The analyzed data sets included time series from two batch experiments (control vs treatment) and effluent concentrations from a flow-through column experiment. The reaction network incorporates a mixture of homogeneous and heterogeneous reactions affecting Fe redox chemistry. Modeling revealed that the precipitation of the Fe treatment caused a rapid pH decline, which then triggered multiple heterogeneous buffering processes. The model quantifies key processes for effective remediation, including the transfer of aqueous As to adsorbed As and the transformation of Fe minerals, which act as sorption hosts, from amorphous to more stable phases. The developed model provides the basis for predictions of the remedial benefits of Fe(II) nitrate treatments under varying geochemical and hydrogeological conditions, particularly in high-As coastal environments.

Sulfate reduction accelerates groundwater arsenic contamination even in aquifers with abundant iron oxides.

Groundwater contamination by geogenic arsenic is a global problem affecting nearly 200 million people. In South and Southeast Asia, a cost-effective mitigation strategy is to use oxidized low-arsenic aquifers rather than reduced high-arsenic aquifers. Aquifers with abundant oxidized iron minerals are presumably safeguarded against immediate arsenic contamination, due to strong sorption of arsenic onto iron minerals. However, preferential pumping of low-arsenic aquifers can destabilize the boundaries between these aquifers, pulling high-arsenic water into low-arsenic aquifers. We investigate this scenario in a hybrid field-column experiment in Bangladesh where naturally high-arsenic groundwater is pumped through sediment cores from a low-arsenic aquifer, and detailed aqueous and solid-phase measurements are used to constrain reactive transport modelling. Here we show that elevated groundwater arsenic concentrations are induced by sulfate reduction and the predicted formation of highly mobile, poorly sorbing thioarsenic species. This process suggests that contamination of currently pristine aquifers with arsenic can occur up to over 1.5 times faster than previously thought, leading to a deterioration of urgently needed water resources.

In situ arsenic immobilisation for coastal aquifers using stimulated iron cycling: Lab-based viability assessment.

Arsenic (As) is one of the most harmful and widespread groundwater contaminants globally. Besides the occurrence of geogenic As pollution, there is also a large number of sites that have been polluted by anthropogenic activities, with many of those requiring active remediation to reduce their environmental impact. Cost-effective remedial strategies are however still sorely needed. At the laboratory-scale in situ formation of magnetite through the joint addition of nitrate and Fe(II) has shown to be a promising new technique. However, its applicability under a wider range of environmental conditions still needs to be assessed. Here we use sediment and groundwater from a severely polluted coastal aquifer and explore the efficiency of nitrate-Fe(II) treatments in mitigating dissolved As concentrations. In selected experiments >99% of dissolved As was removed, compared to unamended controls, and maintained upon addition of lactate, a labile organic carbon source. Pre- and post experimental characterisation of iron (Fe) mineral phases suggested a >90% loss of amorphous Fe oxides in favour of increased crystalline, recalcitrant oxide and sulfide phases. Magnetite formation did not occur via the nitrate-dependent oxidation of the amended Fe(II) as originally expected. Instead, magnetite is thought to have formed by the Fe(II)-catalysed transformation of pre-existing amorphous and crystalline Fe oxides. The extent of amorphous and crystalline Fe oxide transformation was then limited by the exhaustion of dissolved Fe(II). Elevated phosphate concentrations lowered the treatment efficacy indicating joint removal of phosphate is necessary for maximum impact. The remedial efficiency was not impacted by varying salinities, thus rendering the tested approach a viable remediation method for coastal aquifers.

Temperature dependence of nitrate-reducing Fe(II) oxidation by Acidovorax strain BoFeN1 - evaluating the role of enzymatic vs. abiotic Fe(II) oxidation by nitrite.

Fe(II) oxidation coupled to nitrate reduction is a widely observed metabolism. However, to what extent the observed Fe(II) oxidation is driven enzymatically or abiotically by metabolically produced nitrite remains puzzling. To distinguish between biotic and abiotic reactions, we cultivated the mixotrophic nitrate-reducing Fe(II)-oxidizing Acidovorax strain BoFeN1 over a wide range of temperatures and compared it to abiotic Fe(II) oxidation by nitrite at temperatures up to 60°C. The collected experimental data were subsequently analyzed through biogeochemical modeling. At 5°C, BoFeN1 cultures consumed acetate and reduced nitrate but did not significantly oxidize Fe(II). Abiotic Fe(II) oxidation by nitrite at different temperatures showed an Arrhenius-type behavior with an activation energy of 80±7 kJ/mol. Above 40°C, the kinetics of Fe(II) oxidation were abiotically driven, whereas at 30°C, where BoFeN1 can actively metabolize, the model-based interpretation strongly suggested that an enzymatic pathway was responsible for a large fraction (ca. 62%) of the oxidation. This result was reproduced even when no additional carbon source was present. Our results show that at below 30°C, i.e. at temperatures representing most natural environments, biological Fe(II) oxidation was largely responsible for overall Fe(II) oxidation, while abiotic Fe(II) oxidation by nitrite played a less important role.

Toward a more sustainable mining future with electrokinetic in situ leaching.

Metals are currently almost exclusively extracted from their ore via physical excavation. This energy-intensive process dictates that metal mining remains among the foremost CO2 emitters and mine waste is the single largest waste form by mass. We propose a new approach, electrokinetic in situ leaching (EK-ISL), and demonstrate its applicability for a Cu-bearing sulfidic porphyry ore. In laboratory-scale experiments, Cu recovery was rapid (up to 57 weight % after 94 days) despite low ore hydraulic conductivity (permeability = 6.1 mD; porosity = 10.6%). Multiphysics numerical model simulations confirm the feasibility of EK-ISL at the field scale. This new approach to mining is therefore poised to spearhead a new paradigm of metal recovery from currently inaccessible ore bodies with a markedly reduced environmental footprint.

Fluoride release from carbonate-rich fluorapatite during managed aquifer recharge: Model-based development of mitigation strategies.

Fluoride-bearing apatite minerals such as fluorapatite (FAP: Ca10(PO4)6F2) and related carbonate-rich fluorapatites (CFA: Ca10(PO4)5(CO3,F)F2), which occur ubiquitously as trace components of rocks and sediments, may act as sources for geogenic groundwater fluoride contamination. CFA dissolution often occurs in conjunction with declining dissolved calcium concentrations. Therefore, managed aquifer recharge (MAR) operations using deionised or low calcium source water are at risk of disturbing the naturally persisting geochemical equilibrium between CFA and the ambient groundwater and induce fluoride mobilisation. In this study, we employ reactive transport modelling to investigate how an engineered manipulation of the MAR source water composition might mitigate such groundwater fluoride contamination. Based on a previously developed and calibrated model for Australia's largest groundwater replenishment operation, we investigate the efficiency of (i) raising aqueous calcium concentration through the addition of CaCl2 or Ca(OH)2 amendment, (ii) raising aqueous sodium concentrations through the addition of NaCl or sea salt amendment and (iii) raising the pH. The modelling results illustrate in detail how the geochemical zonation around injection boreholes evolves over time and how this affects fluoride release and attenuation for the different amendment types. Treatments involving the addition of calcium and sodium in the source water are both found to be effective at reducing maximum groundwater fluoride concentrations during MAR, with calcium generally producing the greatest reduction in maximum fluoride concentrations. In contrast, increasing the injectate pH was found to be inefficient in reducing fluoride concentrations significantly due to the strong pH buffering effect of the aquifer sediments.

Enhancing Roxarsone Degradation and In Situ Arsenic Immobilization Using a Sulfate-Mediated Bioelectrochemical System.

Roxarsone (ROX) is widely used in animal farms, thereby producing organoarsenic-bearing manure/wastewater. ROX cannot be completely degraded and nor can its arsenical metabolites be effectively immobilized during anaerobic digestion, potentially causing arsenic contamination upon discharge to the environment. Herein, we designed and tested a sulfate-mediated bioelectrochemical system (BES) to enhance ROX degradation and in situ immobilization of the released inorganic arsenic. Using our BES (0.5 V voltage and 350 µM sulfate), ROX and its metabolite, 4-hydroxy-3-amino-phenylarsonic acid (HAPA), were completely degraded within 13-22 days. In contrast, the degradation efficiency of ROX and HAPA was <85% during 32-day anaerobic digestion. In a sulfate-mediated BES, 75.0-83.2% of the total arsenic was immobilized in the sludge, significantly more compared to the anaerobic digestion (34.1-57.3%). Our results demonstrate that the combination of sulfate amendment and voltage application exerted a synergetic effect on enhancing HAPA degradation and sulfide-driven arsenic precipitation. This finding was further verified using real swine wastewater. A double-cell BES experiment indicated that As(V) and sulfate were transported from the anode to the cathode chamber and coprecipitated as crystalline alacranite in the cathode chamber. These findings suggest that the sulfate-mediated BES is a promising technique for enhanced arsenic decontamination of organoarsenic-bearing manure/wastewater.

Process-based modeling of arsenic(III) oxidation by manganese oxides under circumneutral pH conditions.

Numerous experimental studies have identified a multi-step reaction mechanism to control arsenite (As(III)) oxidation by manganese (Mn) oxides. The studies highlighted the importance of edge sites and intermediate processes, e.g., surface passivation by reaction products. However, the identified reaction mechanism and controlling factors have rarely been evaluated in a quantitative context. In this study, a process-based modeling framework was developed to delineate and quantify the relative contributions and rates of the different processes affecting As(III) oxidation by Mn oxides. The model development and parameterization were constrained by experimental observations from literature studies involving environmentally relevant Mn oxides at circumneutral pH using both batch and stirred-flow reactors. Our modeling results highlight the importance of a transitional phase, solely evident in the stirred-flow experiments, where As(III) oxidation gradually shifts from fast reacting Mn(IV) to slowly reacting Mn(III) edge sites. The relative abundance of these edge sites was the most important factor controlling the oxidation rate, whereas surface passivation restricted oxidation only in the stirred-flow experiment. The Mn(III) edge sites were demonstrated to play a crucial role in the oxidation and therefore in controlling the long-term fate of As. This study provided an improved understanding of Mn oxide reactivity and the significance in the cycling of redox-sensitive metal(loid)s in the environment.

Model-Based Analysis of Reactive Transport Processes Governing Fluoride and Phosphate Release and Attenuation during Managed Aquifer Recharge.

In water-scarce areas, the reclamation of wastewater through advanced water treatment and subsequent reinjection into depleted aquifers is an increasingly attractive water management option. However, such injection can trigger a range of water-sediment interactions which need to be well understood and quantified to ensure sustainable operations. In this study, reactive transport modeling was used to analyze and quantify the interacting hydrogeochemical processes controlling the mobilization of fluoride and phosphate during injection of highly treated recycled water into a siliciclastic aquifer. The reactive transport model explained the field-observed fluoride and phosphate transport behavior as a result of the incongruent dissolution of carbonate-rich fluorapatite where (i) a rapid proton exchange reaction primarily released fluoride and calcium, and (ii) equilibrium with a mineral-water interface layer of hydrated dibasic calcium phosphate released phosphate. The modeling results illustrated that net exchange of calcium on cation exchange sites in the sediments postbreakthrough of the injectant was responsible for incongruent mineral dissolution and the associated fluoride and phosphate release. Accordingly, amending calcium chloride into the injectant could potentially reduce fluoride and phosphate mobilization at the study site. Insights from this study are broadly applicable to understanding and preventing geogenic fluoride mobilization from fluoride-bearing apatite minerals in many other aquifers worldwide.

Arsenic mobilization from iron oxides in the presence of oxalic acid under hydrodynamic conditions.

Oxalic acid potentially enhances pump-and-treat for groundwater As remediation by accelerating mobilization. This study examines how oxalic acid mobilizes As from Fe(III)-oxide coated sand under hydrodynamic conditions. Four columns were packed with metal-substituted ferrihydrite or goethite to 1% Fe, presorbed to 50% As surface coverage, and reacted with pH = 2.2 artificial groundwater amended with 10 mM oxalic acid at 1 m day-1. Arsenic elution was affected by both As and Fe speciation. Although the As(V) columns experienced faster substrate dissolution, As(V) elution was delayed by re-adsorption, whereas As(III) elution was rapid due to pH decrease that prevented re-adsorption. Cr-ferrihydrite and Ni-goethite dissolved both effectively initially but then diverged. The Cr-ferrihydrite columns experienced continuous stoichiometric Fe and Cr release, and As release could be sustained. The Ni-goethite columns initially experienced nonstoichiometric Fe and Ni release, and As release was extensive. Such release, however, was not sustained. We hypothesized that Ni-goethite contained sites with distinct reactivity, and oxalic acid targeted readily-dissolved, sorption-dense sites. Our data indicate that oxalic acid-enhanced pump-and-treat methods would be easier to apply to aquifers dominated by As(III), requiring less amendment to be injected; such oxalic acid-enhanced methods remove reactive sediment Fe and As, potentially preventing future groundwater contamination.

Identifying and Quantifying the Intermediate Processes during Nitrate-Dependent Iron(II) Oxidation.

Microbially driven nitrate-dependent iron (Fe) oxidation (NDFO) in subsurface environments has been intensively studied. However, the extent to which Fe(II) oxidation is biologically catalyzed remains unclear because no neutrophilic iron-oxidizing and nitrate reducing autotroph has been isolated to confirm the existence of an enzymatic pathway. While mixotrophic NDFO bacteria have been isolated, understanding the process is complicated by simultaneous abiotic oxidation due to nitrite produced during denitrification. In this study, the relative contributions of biotic and abiotic processes during NDFO were quantified through the compilation and model-based interpretation of previously published experimental data. The kinetics of chemical denitrification by Fe(II) (chemodenitrification) were assessed, and compelling evidence was found for the importance of organic ligands, specifically exopolymeric substances secreted by bacteria, in enhancing abiotic oxidation of Fe(II). However, nitrite alone could not explain the observed magnitude of Fe(II) oxidation, with 60-75% of overall Fe(II) oxidation attributed to an enzymatic pathway for investigated strains: Acidovorax ( A.) strain BoFeN1, 2AN, A. ebreus strain TPSY, Paracoccus denitrificans Pd 1222, and Pseudogulbenkiania sp. strain 2002. By rigorously quantifying the intermediate processes, this study eliminated the potential for abiotic Fe(II) oxidation to be exclusively responsible for NDFO and verified the key contribution from an additional, biological Fe(II) oxidation process catalyzed by NDFO bacteria.

Do you have a right to decide? Or do we have a right to acquiesce?

Clinicians make decisions about patient management on a daily basis and are required to act in a way that is both legally and ethically correct. To act legally requires compliance with a set of rules which reflect the values and interests of society. Ethical decisions are based on what we believe as a group to be morally right. Morals are, however, unique to the individual. Balancing the legal, ethical and moral dimensions of clinical decisions has the potential, therefore, to generate conflict for the individual practitioner. In this paper we report a case study of a patient with a high cervical spine injury resulting in quadriplegia, without prospect of a ventilator independent life. The patient, who was assessed as having capacity to make decisions, subsequently elected to have treatment withdrawn. In this case, withdrawal of treatment constituted removal of mechanical ventilation which ultimately resulted in death. The patient also requested for his organs to be donated after he was deceased. This case study, to our knowledge, is the first report of donation after cardiac death following a high cervical spinal injury in a cognitively intact patient. As such, this case study allows us to discuss the moral, ethical and legal implications of donation after cardiac death following withdrawal of medical treatment.

Jack Bowman: Winnipeg's contributions to the treatment and prevention of Rhesus hemolytic disease of the newborn.

Jack Bowman (1925-2005) was a Canadian pediatrician who was on the staff of the Winnipeg Children's Hospital. He was trained by Bruce Chown who had started the Rhesus (Rh) hemolytic disease of the Newborn program and in due course succeeded Chown as director of the program. Jack began as one of the three pediatricians (including his twin Bill) who performed exchange transfusions on the affected infants. In due course with his colleague in obstetrics, he was the first in North America to perform intrauterine transfusions for the babies at risk of stillbirth. He was a leader in the prevention of Rh disease by the administration of anti-Rh immunoglobulin to the Rh-negative mothers and established that this could be done safely and effectively during pregnancy. He introduced to North America the column fractionation method of preparing the immunoglobulin that produced a higher yield of a purer product that could be given intravenously. Jack Bowman successfully combined research with clinical practice throughout his career.

Attenuated secretion of very low density lipoproteins from McA-RH7777 cells treated with eicosapentaenoic acid is associated with impaired utilization of triacylglycerol synthesized via phospholipid remodeling.

In McA-RH7777 cells stably expressing human apolipoprotein (apo) B100, treatment with oleic acid (18:1(n-9)) promoted whereas treatment with eicosapentaenoic acid (EPA, 20:5(n-3)) attenuated assembly and secretion of VLDL. Under conditions where the cells were cultured in the presence of 20% serum, EPA (0.4 mM) had marginal effect on the secretion of total apoB100 (determined by pulse-chase analysis) but decreased (by 50%) secretion of triacylglycerol (TG), indicating that the inhibitory effect of EPA was exerted primarily on TG-rich VLDL. Analysis of phospholipid mass and species by tandem mass spectrometry showed increased phosphatidylethanolamine (PE) in EPA-treated cells, the increase was significant in the distal Golgi membranes (by 170%) and endoplasmic reticulum (by 116%). Lipid pulse-chase studies showed a major distinction between phospholipid species containing 20:5(n-3) and 18:1(n-9), which in turn was associated with distinct compartmentalization of TG containing 20:5(n-3) or 18:1(n-9) between cytosol and microsomes and their recruitment during VLDL assembly. Thus, 18:1-TG was secreted as VLDL but 20:5-TG was not. These results suggest that EPA attenuation of VLDL secretion is associated with impaired utilization of TG derived from phospholipid remodeling.

Rab3D and actin reveal distinct lamellar body subpopulations in alveolar epithelial type II cells.

Rab3D is a small GTP-binding protein associated with secretory vesicles in various exocrine and endocrine cells, where it has been implicated in regulated exocytosis. Data obtained previously in pancreas have suggested that rab3D is involved in the coating of secretory granules with filamentous actin. In the present study we employed Western blot analysis, immunofluorescence, and immunoelectron microscopy to examine the distribution of rab3D in rat lung. Rab3D immunoreactivity was detected in bronchiolar Clara cells and alveolar epithelial type II (AET-II) cells. In both cell types, rab3D displayed preferential localization to secretory vesicles that were identified using specific antibodies against Clara Cell Secretory Protein and p180 lamellar body protein, respectively. Interestingly, rab3D was associated with only 24% of the lamellar bodies in AET-II cells. Rab3D-positive lamellar bodies were typically in close proximity of the apical plasma membrane, where exocytosis occurs. Another subpopulation of lamellar bodies, constituting only 2%, was not only rab3D-positive but could also be labeled with the filamentous-actin probe phalloidin. A third subpopulation, constituting 9%, displayed actin coating without rab3D staining. We propose that these three lamellar body subpopulations represent consecutive intermediates along the regulated exocytotic pathway, implying that rab3D release and actin coating are intimately linked processes.

Rab3D is not required for exocrine exocytosis but for maintenance of normally sized secretory granules.

Rab3D, a member of the Rab3 subfamily of the Rab/ypt GTPases, is expressed on zymogen granules in the pancreas as well as on secretory vesicles in mast cells and in the parotid gland. To shed light on the function of Rab3D, we have generated Rab3D-deficient mice. These mice are viable and have no obvious phenotypic changes. Secretion of mast cells is normal as revealed by capacitance patch clamping. Furthermore, enzyme content and overall morphology are unchanged in pancreatic and parotid acinar cells of knockout mice. Both the exocrine pancreas and the parotid gland show normal release kinetics in response to secretagogue stimulation, suggesting that Rab3D is not involved in exocytosis. However, the size of secretory granules in both the exocrine pancreas and the parotid gland is significantly increased, with the volume being doubled. We conclude that Rab3D exerts its function during granule maturation, possibly by preventing homotypic fusion of secretory granules.

Intracellular assembly of very low density lipoproteins containing apolipoprotein B100 in rat hepatoma McA-RH7777 cells.

Previous studies with McA-RH7777 cells showed a 15-20-min temporal delay in the oleate treatment-induced assembly of very low density lipoproteins (VLDL) after apolipoprotein (apo) B100 translation, suggesting a post-translational process. Here, we determined whether the post-translational assembly of apoB100-VLDL occurred within the endoplasmic reticulum (ER) or in post-ER compartments using biochemical and microscopic techniques. At steady state, apoB100 distributed throughout ER and Golgi, which were fractionated by Nycodenz gradient centrifugation. Pulse-chase experiments showed that it took about 20 min for newly synthesized apoB100 to exit the ER and to accumulate in the cis/medial Golgi. At the end of a subsequent 20-min chase, a small fraction of apoB100 accumulated in the distal Golgi, and a large amount of apoB100 was secreted into the medium as VLDL. VLDL was not detected either in the lumen of ER or in that of cis/medial Golgi where apoB100 was membrane-associated and sensitive to endoglycosidase H treatment. In contrast, VLDL particles were found in the lumen of the distal Golgi where apoB100 was resistant to endoglycosidase H. Formation of lumenal VLDL almost coincided with the appearance of VLDL in the medium, suggesting that the site of VLDL assembly is proximal to the site of secretion. When microsomal triglyceride transfer protein activity was inactivated after apoB had exited the ER, VLDL formation in the distal Golgi and its subsequent secretion was unaffected. Lipid analysis by tandem mass spectrometry showed that oleate treatment increased the masses of membrane phosphatidylcholine (by 68%) and phosphatidylethanolamine (by 27%) and altered the membrane phospholipid profiles of ER and Golgi. Taken together, these results suggest that VLDL assembly in McA-RH7777 cells takes place in compartments at the distal end of the secretory pathway.

A study of immunoglobulin G glycosylation in monoclonal and polyclonal species by electrospray and matrix-assisted laser desorption/ionization mass spectrometry.

N-linked oligosaccharides were released from human and bovine polyclonal immunoglobulin G (IgG) obtained from commercial sources and also from a monoclonal IgG(1) secreted by murine B-lymphocyte hybridoma cells (CC9C10) grown under different serum-free conditions. These conditions differed according to their steady-state dissolved oxygen concentrations. This work is based on a previous quantitative study where released glycans were characterized by fluorophore-assisted carbohydrate electrophoresis (FACE) and high-pH anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) (J. P. Kunkel, D. C. H. Jan, J. C. Jamieson, and M. Butler, 1998, J. Biotechnol. 62, 55-71). In the present article, peptide-N-glycosidase F-released glycans from different species of polyclonal IgG and murine monoclonal IgG were characterized qualitatively by high-performance liquid chromatography (HPLC) coupled to electrospray ionization mass spectrometry (ESI-MS). The glycans were also analyzed by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS). The MALDI mass spectrometer used allowed acquisition of MS and tandem MS data, which were useful in structural investigations at a more detailed level than allowed by FACE and HPAEC-PAD. Predominant N-linked structures, as determined by all techniques, were core-fucosyl asialyl biantennary chains with varying galactosylation. Minor amounts of afucosyl, bisected, and monosialyl oligosaccharides were also detected. In contrast to FACE and HPAEC-PAD, MALDI-double quadrupole/time-of-flight MS and HPLC/ESI-MS also detected low-abundance high-mannose and hybrid structures in some of the species under investigation.