Reduction Of Arsenite Research Articles

Functional traits and health implications of the global household drinking-water microbiome retrieved using an integrative genome-centric approach

The biological safety of drinking water plays a crucial role in public health protection. However, research on the drinking water microbiome remains in its infancy, especially little is known about the potentially pathogenic bacteria in and functional characteristics of the microbiome in household tap water that people are directly exposed to. In this study, we used a genomic-centric approach to construct a genetic catalogue of the drinking water microbiome by analysing 116 metagenomic datasets of household tap water worldwide, spanning nine countries/regions on five continents. We reconstructed 859 high-quality metagenome-assembled genomes (MAGs) spanning 27 bacterial and 2 archaeal phyla, and found that the core MAGs belonging to the phylum Proteobacteria encoded the highest metabolic functional diversity of the 33 key complete metabolic modules. In particular, we found that two core MAGs of Brevibacillus and Methylomona encoded genes for methane metabolism, which may support the growth of heterotrophic organisms observed in the oligotrophic ecosystem. Four MAGs of complete ammonia oxidation (comammox) Nitrospira were identified and functional metabolic analysis suggested these may enable mixotrophic growth and encode genes for reactive oxygen stress defence and arsenite reduction that could aid survival in the environment of oligotrophic drinking water systems. Four MAGs were annotated as potentially pathogenic bacteria (PPB) and thus represented a possible public health concern. They belonged to the genera Acinetobacter (n = 3) and Mycobacterium (n = 1), with a total relative abundance of 1.06 % in all samples. The genomes of PPB A. junii and A. ursingii were discovered to contain antibiotic resistance genes and mobile genetic elements that could contribute to antimicrobial dissemination in drinking water. Further network analysis suggested that symbiotic microbes which support the growth of pathogenic bacteria can be targets for future surveillance and removal.

Treatment of arsenic contaminated groundwater using Arachis hypogaea

Arsenic has a detrimental effect on both the environment and humans. In many parts of the world, arsenic has been detected in drinking water sources above acceptable levels. Considering the fact that millions of people are at high risk of arsenic poisoning via water intake, arsenic remediation from drinking water has become a global issue of serious concern. Chemical coagulants are already being used for treatment but their enormous cost, human and environmental issues associated with their use have led to searching for alternatives like natural coagulants (plant-based). In this study, laboratory scale studies using jar test experiments were performed on synthetic arsenite contaminated groundwater to analyse the efficiency of Arachis hypogaea (groundnut seed) on the treatment of arsenic contaminated water. Experiments were carried out using synthetic arsenite contaminated borehole water with pH kept constant at 7.30. Results indicated that groundnut seed extract was able to significantly reduced arsenite in water either as primary coagulant or as coagulant aid (using alum as primary coagulant). As primary coagulant, above 90% arsenite reduction was achieved and as a coagulant aid about 99.97% arsenite reduction was achieved. The pH of the treated water was within neutral (basic) due to the buffering capacity of the seed extract. Therefore, results from this study revealed that groundnut seed has potential for use as primary coagulant or as coagulant aid (with alum as primary coagulant) for the treatment of arsenic contaminated groundwater.

Immobilization of size variable Au nanoparticles on surfactant-modified silica and their catalytic application toward 4-nitrophenol reduction: A comparative account of catalysis

Galvanic replacement reaction (GRR) is a widely used powerful synthesis technique to produce different hollow nanoparticles. In the present work, As(0) nanoparticles in two different size ranges (e.g. 50±7 and 70±10 nm) are synthesized by sodium borohydride reduction of arsenite under controlled pH, and subsequently they are used as templates for GRR reaction to produce two different sized hollow gold nanoparticles (HGNPs), which are designated as RHGNPs and BHGNPs (because of their red and blue colors respectively), with average diameter 55±7 and 72±7 nm, respectively. The unique feature of the reduction of arsenite to As(0) and not to AsH3, is the control of medium pH at 7-9. Now the use of RHGNPs and BHGNPs in homogeneous phase restricts them to recollect and reuse properly. So a soft solid template, cationic surfactant-modified silica (SMS) having positive charge in the surface has been considered to ‘adsolubilize’ the RHGNPs and BHGNPs. The ionic attraction between negatively charged surface of both the HGNPs (which arises due to the in-situ stabilization by surface adsorbed H2AsO4⁻) and the positively charged SMS holds them tightly. SMS after the adsorption of RHGNPs on to it looks pinkish-red and the material is designated as RG-SMS. Similarly, SMS after the adsorption of BHGNPs looks bluish-purple and the material is called BG-SMS. This is a unique procedure to prepare RG-SMS and BG-SMS. The catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of sodium borohydride has been studied using RG-SMS and BG-SMS (i.e. red and blue HGNPs immobilized in the solid phase) as the catalyst to examine the size effect. While both the nanoparticles exhibit excellent catalytic activity, the smaller particles (Au present in RG-SMS) are observed to be more effective than the larger ones (Au present in BG-SMS). The reaction is carried out with varying catalyst doses and initial 4-NP concentrations and the reaction follows first order kinetics in all cases. The first order rate constant values obtained are 0.0667 min−1 and 0.0257 min−1 for RG-SMS and BG-SMS respectively at a dose of 0.041 g L−1 and at 4-NP concentration 9.9 × 10−5 M. The turnover frequency (TOF) obtained at a dose 0.041 g L−1 are 0.0159 per minute and 0.0079 per min for the catalytic reaction using RG-SMS and BG-SMS, respectively. The results suggest that RG-SMS bears ∼2 times higher catalytic activity than that of BG-SMS. The reusability of both catalysts up to the 4th cycle has been checked. The catalytic activity of the HGNPs in the solution phase and the solid phase (i.e. on SMS) are compared. It has been observed that solution phase catalysts are better in terms of activity but solid supported catalysts are better in terms of their shelf-life and ease of application.

Removal of arsenite by reductive precipitation in dithionite solution activated by UV light

This study investigates the removal of arsenite (As(III)) from water using dithionite activated by UV light. This work evaluated the removal kinetics of As(III) under UV light irradiation as affected by dithionite dose and light intensity, and characterized the nature of the precipitated solids using XPS and SEM-EDS. Photolysis of dithionite was observed by measuring dithionite concentration using UV absorbance at 315nm. This study also investigated the effect of UV light path length on soluble As concentrations to understand resolubilization mechanisms. Total soluble As concentrations were observed to decrease with reaction time due to reduction of arsenite to form solids having a yellow-orange color. The removal mechanism was found to be reductive precipitation that formed solids of elemental arsenic or arsenic sulfide. However, these solids were observed to resolubilize at later times after dithionite had been consumed. Resolubilization of As was prevented and additional As removal was obtained by frequent dosing of dithionite throughout the experiment. As(III) removal is attributed to photolysis of dithionite by UV light and production of reactive radicals that reduce As(III) and convert it to solid forms.

Electrochemical Investigation of Arsenic Redox Processes on Pyrite.

The specific Eh-pH conditions and mechanism(s) for the reduction of arsenite, As(III), by pyrite are incompletely understood. A fundamental question is what role the pyrite surface plays in the reduction process. We used electrochemical methods to evaluate the reduction of As(III) under controlled redox conditions. As(III) reduction to elemental As(0) occurs on the pyrite surface under suboxic-reducing conditions and is promoted at low pH. Remarkably, As(III) reduction on pyrite occurs at similar potentials to those for reduction on platinum metal, suggesting a similar mechanism and kinetics for these surfaces. The onset for As(III) reduction at pH ≤ 3.5 coincides with the potential for hydrogen electroadsorption on pyrite, E ≈ +0.1 V (versus RHE). Batch reactions show that As(III) is reduced on pyrite at the Eh-pH predicted by the electrochemical study. X-ray photoelectron spectroscopy reveals that, at pH ≤ 3.5, a significant fraction of the surface arsenic (30-60%) has an oxidation state consistent with As(0). Here, we propose a mechanism whereby atomic hydrogen that forms on ferric (hydr)oxide surface layers promotes As(III) reduction at low Eh and pH. Insights provided by this study will have implications for understanding the controls on dissolved As(III) concentrations in suboxic-anoxic environments.

Photocatalytic Oxidation of Arsenite Using Goethite and UV LED

Arsenic (As) has been considered as the most toxic one among various hazardous materials and As contamination can be caused naturally and anthropogenically. Major forms of arsenic in groundwater are arsenite [(As(III)] and/or arsenate [(As(V)], depending on redox condition: arsenite and arsenate are predominant in reduced and oxidized environments, respectively. Because arsenite is much more toxic and mobile than arsenate, there have been a number of studies on the reduction of its toxicity through oxidation of As(III) to As(V). This study was initiated to develop photocatalytic oxidation process for treatment of groundwater contaminated with arsenite. The performance of two types of light sources (UV lamp and UV LED) was compared and the feasibility of goethite as a photocatalyst was evaluated. The highest removal efficiency of the process was achieved at a goethite dose of 0.05 g/L. Based on the comparison of oxidation efficiencies of arsenite between two light sources, the apparent performance of UV LED was inferior to that of UV lamp. However, when the results were appraised on the basis of their emitting UV irradiation, the higher performance was achieved by UV LED than by UV lamp. This study demonstrates that environmentally friendly process of goethite-catalytic photo-oxidation without any addition of foreign catalyst is feasible for the reduction of arsenite in groundwater containing naturally-occurring goethite. In addition, this study confirms that UV LED can be used in the photo-oxidation of arsenite as an alternative light source of UV lamp to remedy the drawbacks of UV lamp, such as long stabilization time, high electrical power consumption, short lifespan, and high heat output requiring large cooling facilities. Key words: Arsenite [As(III)], Arsenate [As(V)], Photocatalytic Oxidation, UV Lamp, UV LED, Goethite

Thiol reduction of arsenite and selenite: DFT modeling of the pathways to an as-se bond.

The reactivity of arsenite and selenite with biological thiols plays an important role in the toxicity of these elements. However, toxic effects are eliminated when the species are coadministered, due to the antagonistic relationship between selenium and arsenic. The reduction of arsenous acid and selenious acid by thiol and the formation of an As-Se species have been modeled using density functional theory (DFT) and solvent-assisted proton exchange (SAPE), a microsolvation technique that uses a network of water molecules to mimic the participation of bulk solvent in proton transfer processes. Activation barriers and relative energies were calculated for the stepwise thiol reduction of arsenite to form As(SR)3 and selenious acid to first form a selenotrisulfide (Se(SR)2) and then H2Se. Several pathways were explored for the formation of an As-Se bond: the nucleophilic attack of selenide or selenopersulfide on As(OH)3, (RS)As(OH)2, and (RS)2AsOH to form (RS)2AsSeH. On the basis of the lower activation barrier and bioavailability of (RS)2AsOH, the reaction of H2Se with (RS)2AsOH is deemed the most favorable, consistent with previous experimental studies.

Cyclic voltammetry of arsenic-doped cysteine-capped ceramic nanoparticles

Development of new nanoparticle compositions is of the greatest concern to derive alternative successful applications in different fields. Little is known, however, about the electrochemical characterization of the arsenic-doped cysteine-capped ceramic-based nanoparticles. In this work, several arsenic-doped cysteine-capped thoria-/zirconia-based nanoparticles were prepared for the first time and used as electrode material for its characterization by cyclic voltammetry. This approach takes advantage particularly of the quantitative oxidation of arsenic to arsenite, after previous reduction of arsenite to arsenic. Besides, electroanalytical sensing of cysteine, together with additional information about the cysteine and arsenic interactions were also clearly demonstrated.

Intraparticle Reduction of Arsenite (As(III)) by Nanoscale Zerovalent Iron (nZVI) Investigated with In Situ X-ray Absorption Spectroscopy

While a high efficiency of contaminant removal by nanoscale zerovalent iron (nZVI) has often been reported for several contaminants of great concern, including aqueous arsenic species, the transformations and translocation of contaminants at and within the nanoparticles are not clearly understood. By analysis using in situ time-dependent X-ray absorption spectroscopy (XAS) of the arsenic core level for nZVI in anoxic As(III) solutions, we have observed that As(III) species underwent two stages of transformation upon adsorption at the nZVI surface. The first stage corresponds to breaking of As-O bonds at the particle surface, and the second stage involves further reduction and diffusion of arsenic across the thin oxide layer enclosing the nanoparticles, which results in arsenic forming an intermetallic phase with the Fe(0) core. Extended X-ray absorption fine-structure (EXAFS) data from experiments conducted at different iron/arsenic ratios indicate that the reduced arsenic species tend to be enriched at the surface of the Fe(0) core region and had limited mobility into the interior of the metal core within the experimental time frame (up to 22 h). Therefore, there was an accumulation of partially reduced arsenic at the Fe(0)/oxide interface when a relatively large arsenic content was present in the solid phase. These results illuminate the role of intraparticle diffusion and reduction in affecting the chemical state and spatial distribution of arsenic in nZVI materials.

Micro-determination of arsenic in aqueous samples by image scanning and computational quantification

Arsenic is highly toxic in all of its forms found in natural groundwater. An improved method for the estimation of inorganic arsenic at low levels (μg L−1) in water has been proposed. The method involves the generation of arsine in a specially designed cell by borohydride reduction of arsenite (AsO21−). The resulting arsine is passed through a filter paper pre-dipped in mercuric bromide solution giving a yellowish brown complex. The color intensity of the spots is calculated by scanning the spotted paper and analyzing the image using specially designed software. The method was found to be effective at trace levels having a linear response at the concentration range 2–20μg L−1 (8–80ng). The detection limit of the proposed method is 1 μg L−1 (4 ng) which can be reduced further by making some modifications to the apparatus. The method was successfully applied to the analysis of synthetic samples and field samples of water.

A Microbial Sensor Based on Direct Electron Transfer at Shewanella Sp. Drop‐Coated Screen‐Printed Carbon Electrodes

AbstractAerobically grown Shewanella sp. bacterial suspension drop‐coated on a disposable screen‐printed carbon electrode was found to possess electroactivity without the aid of redox mediator. Cyclic voltammetric studies revealed the characteristics of a mixed diffusion adsorption‐controlled electrochemical process for direct electron transfer at the bacteria‐modified electrode. Both FE‐SEM and ATR FT‐IR experiments were carried out to investigate the surface characteristics. The electroanalytical applicability was further demonstrated for electrocatalytic reduction of arsenite, hydrogen peroxide and nitrite. Low cost and very simple manufacturing procedure allow for the proposed bacterial sensor to be applied as disposable devices.

Optimization of a Flow Injection System with Amperometric Detection for Arsenic Determination

A selective and sensitive analytical procedure for rapid arsenic determination by gas-diffusion flow injection analysis with amperometric detection was developed. The method is based on the arsenite reduction by NaBH(4). Derived arsine diffuses through a PTF membrane into the acceptor flow stream and is amperometrically determined on a platinum working electrode. The limit of detection (3 sigma) at room temperature was 5 microg/dm(3) of As(III). The relative standard deviation for a 1 mg/dm(3) As(III) standard was 1.96% for six repetitive injections. Arsenic(V) was determined after its prereduction with potassium iodide. Arsenic determination was not interferred with by 1 mg/dm(3) Sb(III), 5 mg/dm(3) Sn(II), 10 mg/dm(3) Se(IV), 1 mg/dm(3) As(V), 1 mg/dm(3) hydrasine, 1 mg/dm(3) Fe(II) or 0.5 mg/dm(3) Fe(III) solution. The throughput of this method was 60 analyses per hour. This method was successfully applied to arsenic determination in some power plant waste water samples.

Electrochemical Determination of Arsenite Using a Gold Nanoparticle Modified Glassy Carbon Electrode and Flow Analysis

A flow analysis electrochemical system has been developed, characterized, and optimized for the determination of arsenite (As(III)). Sensitivity was significantly improved by the electrochemical deposition of gold nanoparticles on a dual glassy carbon electrode, which was inserted into a cross-flow thin-layer electrochemical cell. The electrochemical system was linear up to 15 ppb with a detection limit of 0.25 ppb. Gold deposition was evident from cyclic voltammetry measurements, whereas atomic force microscopy and scanning electron microscopy revealed the size and distribution of deposited gold nanoparticles. The size and density of the nanoparticles were related to the gold salt concentration, deposition time, and potential as well as the electrode position. The response to arsenite was directly related to the frequency, increment, and amplitude of the square wave voltammetry as well as the deposition time and potential. Estimated reproducibility was +/-1.1% at 95% confidence interval for 40 repeated analyses of 8 ppb arsenite during continuous analysis. The reproducibility was far superior if the electrochemical reduction of arsenite was performed in nitric acid instead of hydrochloric or sulfuric acid. The electrochemical system was applicable for analysis of spiked arsenic in mineral water containing a significant amount of various ion elements.

Glyceraldehyde-3-Phosphate Dehydrogenase Inactivation by Peroxynitrite

Rabbit muscle glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was inactivated by peroxynitrite under biologically relevant conditions. The decrease of enzymatic activity followed an exponential function, and the concentration of peroxynitrite needed to inactivate 50% of 7 μM GAPDH (IC50) was 17 μM. Hydroxyl radical scavengers did not protect GAPDH from inactivation, but molecules that react directly with peroxynitrite such as cysteine, glutathione, or methionine and the substrate, glyceraldehyde 3-phosphate, afforded significant protection. Assuming simple competition kinetics between scavengers and the enzyme, we estimated a second-order rate constant of (2.5 ± 0.5) × 105M−1s−1at 25°C and pH 7.4 for the GAPDH tetramer. The loss of enzyme activity was accompanied by protein thiol oxidation (two thiols oxidized per subunit) with only one critical thiol responsible of enzyme inactivation. Indeed, the pH profile of inactivation was consistent with the reaction of GAPDH sulfhydryls (GAPDH-SH) with peroxynitrite. Peroxynitrite-inactivated GAPDH was resistant to arsenite reduction and only 15% recovered by 20 mM dithiothreitol, suggesting that GAPDH-SH has been mainly oxidized to sulfinic or sulfonic acid, with a minor proportion yielding a disulfide. On the other hand, under anaerobic conditions the peroxynitrite precursor, nitric oxide (•NO), only slowly inactivated GAPDH with a rate constant of 11 M−1s−1. The remarkable reactivity of the critical thiol group in GAPDH (Cys-149) toward peroxynitrite, which is one order of magnitude higher than that of previously studied sulfhydryls, indicate that it may constitute a preferential intracellular target for peroxynitrite.

Some observations on the application of arsenite reduction to the potentiometric determination of osmium(VIII) and to the analysis of mixtures

A rapid potentiometric method for the determination of osmium(VIII) is proposed. The method is based on the addition of arsenite to osmium(VIII) to reduce it to the metallic state. The excess of arsenite was oxidized by iodine dissolved in acetic acid. The liberated iodide was then potentiometrically titrated against mercury(II) using silver amalgam as the indicator electrode. Some binary and ternary mixtures were completely analyzed.

Application of arsenite reduction to the potentiometric determination of gold and to the analysis of mixtures and alloys

This investigation is an application of the method involving reduction with arsenite to the determination of gold. Binary and ternary gold containing mixtures as well as some important Egyptian gold alloys were completely analyzed. The reversibility of As(V) and Cu(II) toward iodide makes possible the determination of Ag and Au in presence of each other without the interference of As(V) or Cu(II). The more insoluble AgI makes possible the determination of the metal in the presence of chloride ions. The nonreactivity of both Ag(I) and Au(III) toward EDTA, makes possible the determination of Cu(II) in the presence of both cations. The present methods have the advantages over the classical ones of being simple rapid and reliable.

Use of arsenite reduction in potentiometric methods for arsenic(III) or higher valent lead, manganese, chromium, and vanadium in some industrial products

A simple, rapid, and reliable method is given for determination of As(III) based on arsenite reduction of alcoholic iodine and titration of the equivalent iodide with Hg(II) using silver amalgam as the indicator electrode. Arsenite reduction is applied to the estimation of lead in minium, manganese in duralumin, chromium in zinc chromate, and vanadium and chromium in ilmenite, the excess of arsenite being determined by the same method used for As(III). The endpoints are accurately determined with very satisfactory potential breaks.

Analysis of tungsten-containing mixtures and some alloy steels by potentiometric titration methods

Reliable potentiometric titration methods are adopted for the analysis of tungsten mixtures analogous to some industrially important alloys such as low alloy tap steel, tungsten chisel, and high speed steels. Tungsten is separated as Hg 2WO 4 and unreacted Hg(I) is titrated with KBr. The techniques of oxidation with I 2 or reduction with KI and use of the selective arsenite reduction of Cr(VI) and/or Mn(IV) in the presence of V(V) or Fe(III) make it possible to determine alloy components without tedious separations. In all titrations the potential break is sharp enough for the precise establishment of the end point.

Effect of Arsenic upon the Entry of Hydrogen into Mild Steel as Determined at Constant Electrochemical Potential

Arsenic added as arsenite to acid solutions promotes the entry of hydrogen into steel structures during cathodic polarization. The extent of the hydrogenation depends on electrochemical potential. At the corrosion potential of the steel, arsenite inhibits the entry of hydrogen; the reduction of arsenite to elemental arsenic suppresses the hydrogen evolution reaction. Only when the specimen is polarized to sufficiently cathodic potentials is there noticeable entry and permeation of hydrogen in steel. The greater the concentration of arsenite is in the solution, the greater is the extent of cathodic polarization needed to bring about measurable permeation. The entry of hydrogen does not depend on arsine formation; the greatest relative permeation occurs in the potential range where arsenic is the stable phase.