Interaction Of Arsenate Research Articles

Nano-ferrihydrite colloidal particles mediated interfacial interactions of arsenate and cadmium: Implications for their fate under iron-rich geological settings

Arsenic (As) and cadmium (Cd) often coexist in paddy soils. Nano-ferrihydrite colloidal particles (NFPs) are ubiquitous at redox active interfaces of the paddy system and are well-known to play a critical role in controlling the solubility and bio-availability of As and Cd. However, the mutual interaction between As and Cd on NFPs remains elusive. Herein, batch experiments and in-situ spectroscopic techniques were used to investigate the effects of the interaction pattern (sequential reaction) of Cd(II) and As(V) on their respective adsorption on the surfaces of NFPs. Two scenarios were designed: Cd(II) pre-saturated NFPs and As(V) pre-saturated NFPs. Adsorption of Cd(II) was increased by 1.67, 4.08, and 5.21 times in As(V)-saturated NFPs, but only by 1.05, 1.11, and 1.15 times for As(V) in Cd(II)-saturated NFPs. Further, we determined the pH-dependent mutually beneficial cooperation pathways as mediated by the surface of NFPs. At lower pH (5), As(V) tended to promote Cd(II) adsorption, whereas Cd(II) tended to enhance As(V) adsorption at higher pH (> 5.5). X-ray photoelectron spectroscopy (XPS) indicated that both pre-saturated Cd(II) and As(V) altered the local coordination environment of their counterpart ions. Furthermore, results from in-situ attenuated total reflection-Fourier-transform infrared spectroscopy (ATR-FTIR) and second derivative peak shape fitting revealed two types of ternary surface complexes, namely Cd(II)-bridged and As(V)-bridged complexes, which were responsible for the distinct Cd(II) and As(V) co-adsorption behavior on the surface of NFPs under different conditions. These findings help us understand how co-presence Cd and As behave in an iron-rich geological setting and will aid in the development of related restoration technologies.

Mechanisms of arsenate and cadmium co-immobilized on ferrihydrite inferred from ternary surface configuration

Elucidating the interfacial interactions of arsenate (AsO43-) and cadmium (Cd) on minerals can better reveal their environmental behavior under various geological settings. Herein, the adsorption of Cd on ferrihydrite (Fh) in the presence of arsenate was investigated through batch experiments, surface complexation, and spectroscopic techniques. We determined the concentration-dependent interactions of Cd (II) and As (V) on each other’s behavior on Fh. Cadmium and arsenate tended to co-precipitate at high Cd/As ratios, whereas adsorption dominated at low Cd/As ratios. Compared with the single-ion system, the coexistence of Cd(II) and As on Fh significantly reduces the respective mobility of Cd(II) and As(V). The results of in situ attenuated total reflection–Fourier-transform infrared spectroscopy and charge distribution multisite complexation modeling revealed that the synergistic effects originated from electrostatic interactions and the formation of a ternary complex. The curve fitting of the spectra revealed three deconvolution peaks at ~ 765 cm−1, ~813 cm−1, and ~ 870 cm−1, which were assigned to As–OX (X = H+, cations, and H2O), As–O–Fe, and As–Oumcomplexed, respectively. After the addition of Cd(II), the intensity of As–OX increased at different pH values, indicating the formation of an As–O–Cd ternary complexes. We infer that two types of surface complex were assembled on the surface of Fh: namely anion-bridged Fe–As–Cd and cation-bridged Fe–Cd–As. These results contribute to our understanding of the behavior of multiple contaminates in an iron-rich environment and are helpful for the development of the corresponding restoration technology.

A Novel Insight into the Adsorption Interactions of Arsenate with a Fe–Si Binary Oxide

In the current investigation, a new insight into the adsorptive interaction of iron–silicon mixed oxide with arsenate was proposed through comparative studying the behavior of arsenate on the mixed oxide and on the parent oxides, i.e., iron hydroxide and silica. All the oxides were characterized by using different physiochemical methods. The arsenate concentration, pH, temperature, co-ion effect, and calcination of adsorbents were the key parameters of this investigation. The Langmuir model was used for the interpretation of the adsorption data. The thermodynamic parameters and spectroscopic evidences of the samples before and after arsenate adsorption confirmed that the mechanisms of arsenate adsorption by Fe(OH)3 and mixed oxide showed close similarity.

Thermodynamic parameters for the protonation and the interaction of arsenate with Mg2+, Ca2+ and Sr2+: Application to natural waters

Thermodynamic parameters for the protonation of AsO43− and for the interaction with Mg2+, Ca2+ and Sr2+ were reported, comprehensive also of their dependence on ionic strength, considering the 0.1 ≤ I ≤ 1 M range and using NaCl as background salt. The same speciation models were obtained for Mg2+, Ca2+ and Sr2+ systems, with the formation of three different species: ML, MLH and MLH2 (L = AsO43−). Mono- and di-protonated species were very weak, with formation constant values (log K) ranging from 1.45 to 3.23. In order to have a complete picture of thermodynamic properties of the systems under study and to fill the shortage of thermodynamic data on arsenate complex systems, the ligand protonation and metal complex enthalpies were also determined by calorimetric titrations, at t = 25 °C and in NaCl at I = 0.7 M (for H+-AsO43- species also at I = 0.1 M). On the light of the proposed speciation models, examples of As(V) distribution in some natural waters are reported.

Phosphate-arsenate relations to affect arsenic concentration in plant tissues, growth, and antioxidant efficiency of sunflower (Helianthus annuus L.) under arsenic stress.

Relations between phosphate and arsenate are important but inconsistent to influence arsenic (As) phytotoxicity depending on many plant and soil factors. Present research aimed to investigate the phosphate and arsenate interactions in sunflower (Helianthus annuus L.) grown in alkaline calcareous soil for 18weeks under natural environmental conditions at three arsenate [0 (As0), 40 (As40), and 80 (As80)mgAskg-1 soil as sodium arsenate] and three phosphate [0 (P0), 100 (P100), and 200 (P200)mgP2O5kg-1 soil as diammonium phosphate] levels. The plants were grown in pots according to completely randomized design with five replications. Ionic and physiological parameters were measured at 40days after treatment completion. Arsenic contamination with As40 and As80 increased root and shoot As concentration with relatively higher concentration in roots, malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) while decreased plant P, chlorophyll, protein, and glutathione (GSH), and consequently plant growth, yield, and yield attributes. Addition of P100 and P200 under As stress reduced As transfer from soil to roots to shoots, MDA concentration, SOD, CAT, and POD activities while increased GSH, leaf protein, chlorophyll, and growth characteristics as well as achene yield compared to As-treated plants without additional P. In conclusion, P-induced inhibition of As transfer from soil to roots to shoots and reduction in MDA concentration accompanied with an increase in the synthesis of protein, chlorophyll, and GSH could be the main mechanisms responsible for lowered As toxicity in sunflower, leading to mitigation of potential risks of As contamination to food chain and human health.

Antioxidant enzymes responses in shoots of arsenic hyperaccumulator, Isatis cappadocica Desv., under interaction of arsenate and phosphate

ABSTRACTThe present study investigated the effects of arsenate and phosphate interaction on growth, lipid peroxidation, arsenic (As) accumulation, phosphorus (P) accumulation, and the activities of some antioxidant enzymes in Isatis cappadocica. Plants were exposed to (50–1200 μmol L−1) arsenate and (5–1600 μmol L−1) phosphate for 28 days in a hydroponic system. At a phosphate concentration of 1600 µM, biomass production and chlorophyll content increased, demonstrating clearly that phosphate was able to provide protection against As toxicity. In case of joint application of 1600 µM phosphate with arsenate, the As accumulation and then lipid peroxidation were decreased when compared to samples treated with arsenate and 5 µM phosphate. The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) increased with increasing arsenate supply levels. Addition of P decreased activities of SOD, APX and CAT, while high phosphate treatments had a positive effect on GR activity, which may be due to regulation of glutathione biosynthesis within the plants. In conclusion, high arsenate treatment (800-1200 µM) could cause an increasing oxidative stress, which can be scavenged by the antioxidant enzyme. Furthermore, P may affect As-induced oxidative stress through nutrient condition and As accumulation.

Understanding the adsorptive interactions of arsenate-iron nanoparticles with curved fullerene-like sheets in activated carbon using a quantum mechanics/molecular mechanics computational approach.

The prevalence of global arsenic groundwater contamination has driven widespread research on developing effective treatment systems including adsorption using various sorbents. The uptake of arsenic-based contaminants onto established sorbents such as activated carbon (AC) can be effectively enhanced via immobilization/impregnation of iron-based elements on the porous AC surface. Recent suggestions that AC pores structurally consist of an eclectic mix of curved fullerene-like sheets may affect the arsenic adsorption dynamics within the AC pores and is further complicated by the presence of nano-sized iron-based elements. We have therefore, attempted to shed light on the adsorptive interactions of arsenate-iron nanoparticles with curved fullerene-like sheets by using hybridized quantum mechanics/molecular mechanics (QMMM) calculations and microscopy characterization. It is found that, subsequent to optimization, chemisorption between HAsO42- and the AC carbon sheet (endothermic process) is virtually non-existent - this observation is supported by experimental results. Conversely, the incorporation of iron nanoparticles (FeNPs) into the AC carbon sheet greatly facilitates chemisorption of HAsO42-. Our calculation implies that iron carbide is formed at the junction between the iron and the AC interface and this tightly chemosorbed layer prevents detachment of the FeNPs on the AC surface. Other aspects including electronic structure/properties, carbon arrangement defects and rate of adsorptive interaction, which are determined using the Climbing-Image NEB method, are also discussed.

Effect of humic acid on as redox transformation and kinetic adsorption onto iron oxide based adsorbent (IBA).

Due to the importance of adsorption kinetics and redox transformation of arsenic (As) during the adsorption process, the present study elucidated natural organic matter (NOM) effects on As adsorption-desorption kinetics and speciation transformation. The experimental procedures were conducted by examining interactions of arsenate and arsenite with different concentrations of humic acid (HA) as a model representative of NOM, in the presence of iron oxide based adsorbent (IBA), as a model solid surface in three environmentally relevant conditions, including the simultaneous adsorption of both As and HA onto IBA, HA adsorption onto As-presorbed IBA, and As adsorption onto HA-presorbed IBA. Experimental adsorption-desorption data were all fitted by original and modified Lagergren pseudo-first and -second order adsorption kinetic models, respectively. Weber’s intraparticle diffusion was also used to gain insight into the mechanisms and rate controlling steps, which the results suggested that intraparticle diffusion of As species onto IBA is the main rate-controlling step. Different concentrations of HA mediated the redox transformation of As species, with a higher oxidation ability than reduction. The overall results indicated the significant effect of organic matter on the adsorption kinetics and redox transformation of As species, and consequently, the fate, transport and mobility of As in different environmentally relevant conditions.

Structural and functional consequences of phosphate-arsenate substitutions in selected nucleotides: DNA, RNA, and ATP.

A recent finding of a bacterial strain (GFAJ-1) that can rely on arsenic instead of phosphorus raised the questions of if and how arsenate can replace phosphate in biomolecules that are essential to sustain cell life. Apart from questions related to chemical stability, there are those of the structural and functional consequences of phosphate-arsenate substitutions in vital nucleotides in GFAJ1-like cells. In this study we selected three types of molecules (ATP/ADP as energy source and replication regulation; DNA–protein complexes for DNA replication and transcription initiation; and a tRNA–protein complex and ribosome for protein synthesis) to computationally probe if arsenate nucleotides can retain the structural and functional features of phosphate nucleotides. Hydrolysis of adenosine triarsenate provides 2–3 kcal/mol less energy than ATP hydrolysis. Arsenate DNA/RNA interacts with proteins slightly less strongly than phosphate DNA/RNA, mainly due to the weaker electrostatic interactions of arsenate. We observed that the weaker arsenate RNA–protein interactions may hamper rRNA assembly into a functional ribosome. We further compared the experimental EXAFS spectra of the arsenic bacteria with theoretical EXAFS spectra for arsenate DNA and rRNA. Our results demonstrate that while it is possible that dried GFAJ-1 cells contain linear arsenate DNA, the arsenate 70S ribosome does not contribute to the main arsenate depository in the GFAJ-1 cell. Our study indicates that evolution has optimized the inter-relationship between proteins and DNA/RNA, which requires overall changes at the molecular and systems biology levels when replacing phosphate by arsenate.

Thermodynamics of Dimethylarsinic Acid and Arsenate Interactions with Hydrated Iron-(Oxyhydr)oxide Clusters: DFT Calculations

Dimethylarsinic Acid (DMA) belongs to an important class of organoarsenical compounds commonly detected in arsenic speciation studies of environmental samples and pyrolysis products of fossil fuels. Transformation of DMA under certain conditions leads to the formation of other forms of arsenic, which could be more toxic than DMA to biota, and more efficient in deactivating catalysts used in petrochemical refining. Published surface sensitive X-ray and infrared spectroscopic work suggested that DMA simultaneously forms inner- and outer-sphere complexes with iron-(oxyhydr)oxides. Computational work on the complexation of arsenicals with various surfaces of environmental and industrial interest provides useful information that aids in the interpretation of experimental spectroscopic data as well as predictions of thermodynamic favorability of surface interactions. We report herein Gibbs free energies of adsorption, ΔG(ads), for various ligand exchange reactions between hydrated complexes of DMA and Fe-(oxyhydr)oxide clusters calculated using density functional theory (DFT) at the B3LYP/6-311+G(d,p) level. Calculations using arsenate were also performed for comparison. Calculated As-(O,Fe) distances and stretching frequencies of As-O bonds are also reported for comparison with experimental spectroscopic data. Gibbs free energies of desorption, ΔG(des), due to reactions with phosphorus species at pH 7 are reported as well. Our results indicate that the formation of both inner- and outer-sphere DMA complexes is thermodynamically favorable, with the former having a more negative ΔG(ads). Values of ΔG(des) indicate that desorption favorability of DMA complexes increases in this order: bidentate < mondentate < outersphere. The significance of our results for the overall surface complexation mechanism of DMA is discussed.

Normalization, comparison, and scaling of adsorption data: Arsenate and goethite

Various approaches for analyzing adsorption data were examined to determine the best method for reporting and interpreting the results of adsorption experiments and ultimately extrapolating laboratory measurements to the field. The interactions of arsenate and goethite were used as representative adsorbate and adsorbent, respectively, although the general principles are applicable to other adsorbate–adsorbent systems as well. A modeling exercise was conducted first to determine the theoretical principles governing the comparison and scaling of adsorption data. These principles were then tested on a suite of experimental data, both new and previously published. Log K D is significantly more sensitive to variations in adsorbate (As T) or adsorbent (Fe T) concentrations than either adsorbed concentration ( q) or percentage adsorbed. The sensitivity of K D relative to q occurs due to the non-linearity of the adsorption isotherm at a given pH, since as the equilibrium aqueous concentration approaches zero, q also approaches zero while K D approaches infinity. Varying As T and Fe T while keeping As T/Fe T fixed yields more consistent values of percentage adsorbed, log K D , and q, although the adsorbate-to-adsorbent ratios used in laboratory studies often have a rather narrow range compared to those possible in the field. Specific surface area is also a better scaling parameter than the mass of adsorbent, especially between systems with differing adsorbents with markedly different specific surface areas (e.g., natural versus synthetic goethite). Our results have significant implications to contaminant transport modeling, as the constant K D approach is the most common method of modeling contaminant transport, while contaminant concentrations in the field are typically low, precisely the conditions where K D is most sensitive.

Reduction of Arsenic Oxidative Toxicity By Phosphate Is Not Related To Arsenate Reductase Activity In Wheat Plants

ABSTRACT Arsenic toxicity to plants is thought to be induced through the generation of reactive oxygen species. The response of arsenate reductase (AR) activity as well as the oxidative stress to the interaction of arsenate and phosphate in wheat seedlings was studied in this experiment. The results showed that AR activity increased by 108% with arsenate exposure under P-deficient condition and by 130% under P-sufficient condition; but AR activity showed no significant response to P treatment. Hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentrations increased significantly under arsenate exposure, especially in P-deficient plants, increasing by 180% for H2O2 and 51% for MDA. Superoxide dismutase (SOD) and peroxidase (POD) activity decreased significantly; catalase (CAT) activity decreased under P-deficient condition and increased under P-sufficient condition. Glutathione (GSH), Ascorbate (AsA) and Non-protein thiols (NPT) concentrations all increased when exposed to arsenate under P-deficient condition. Arsenate exposure induced oxidative stress in wheat and P-deprivation increased the damage of oxidative stress.

Computational Investigation Into the Adsorption of Pollutants Onto Mineral Surfaces: Arsenate and Dolomite

ABSTRACTComputational modeling techniques have been used to investigate the interaction of arsenate with the dolomite (211) surface. The suitability of a variety of techniques has been assessed in the context of their applicability to the problem, in order to determine the least computationally expensive method of modeling the mineral-solution interface. To this end, various methods of solvating arsenate have been investigated, and a reliable solvation energy has been determined for the molecule. The adsorption geometry of the primary arsenate ion at the dolomite surface has been determined under vacuum conditions. Additionally, solvation of the dolomite surface has studied using molecular dynamics, and results show that there is some layering 2Å above the surface, and that dissociation of the water molecules occurs in this layer.

Phosphate and arsenate interactions in the rhizosphere of canola (Brassica napus).

Arsenate [As(V)] and phosphate [P(V)] compete for the same uptake systems in plant roots. For this reason, P(V) is often added to As-contaminated soils to reduce As(V) uptake and alleviate As toxicity. However, the addition of P(V) can result in an increase in As concentrations in plant tissues, which is often attributed to an increase in As(V) availability, although direct evidence for this explanation is lacking. Rhizosphere and batch desorption experiments were conducted to investigate (i) the effect of As(V) and P(V) additions, and plant phosphorus (P) status, on As(V) uptake by canola (Brassica napus L.) and (ii), P(V) and As(V) interactions at the surface of roots and specific soil particles (goethite and kaolinite). Results showed that P-deficient canola took up more As(V) from arsenated kaolinite, but transported less As from roots to shoots, than P-adequate canola. The addition of P(V) adsorbed on substrate increased As(V) uptake by canola but desorption experiments revealed that the addition of phosphated kaolinite to arsenated kaolinite was not likely to increase As(V) availability in the rhizosphere. It was concluded that plant P status together with P(V) and As(V) interactions at the surfaces of roots and soil particles need to be considered to properly asses P(V) and As(V) interactions in the plant-soil continuum.

Mechanisms of arsenic hyperaccumulation in Pteris vittata. Uptake kinetics, interactions with phosphate, and arsenic speciation.

The mechanisms of arsenic (As) hyperaccumulation in Pteris vittata, the first identified As hyperaccumulator, are unknown. We investigated the interactions of arsenate and phosphate on the uptake and distribution of As and phosphorus (P), and As speciation in P. vittata. In an 18-d hydroponic experiment with varying concentrations of arsenate and phosphate, P. vittata accumulated As in the fronds up to 27,000 mg As kg(-1) dry weight, and the frond As to root As concentration ratio varied between 1.3 and 6.7. Increasing phosphate supply decreased As uptake markedly, with the effect being greater on root As concentration than on shoot As concentration. Increasing arsenate supply decreased the P concentration in the roots, but not in the fronds. Presence of phosphate in the uptake solution decreased arsenate influx markedly, whereas P starvation for 8 d increased the maximum net influx by 2.5-fold. The rate of arsenite uptake was 10% of that for arsenate in the absence of phosphate. Neither P starvation nor the presence of phosphate affected arsenite uptake. Within 8 h, 50% to 78% of the As taken up was distributed to the fronds, with a higher translocation efficiency for arsenite than for arsenate. In fronds, 49% to 94% of the As was extracted with a phosphate buffer (pH 5.6). Speciation analysis using high-performance liquid chromatography-inductively coupled plasma mass spectroscopy showed that >85% of the extracted As was in the form of arsenite, and the remaining mostly as arsenate. We conclude that arsenate is taken up by P. vittata via the phosphate transporters, reduced to arsenite, and sequestered in the fronds primarily as As(III).

Interactions of arsenate, sulfate and phosphate with yeast mitochondria

In the presence of K +, addition of ATP or ethanol to yeast mitochondria triggers the depletion of the transmembrane potential (ΔΨ) and this is prevented by millimolar concentrations of phosphate (PO 4). Different monovalent and polyvalent anions were tested for their protective effects on mitochondria from Saccharomyces cerevisiae. Only arsenate (AsO 4) and sulfate (SO 4) were as efficient as PO 4 to protect mitochondria against the K + mediated swelling, depletion of the ΔΨ, and decrease in the ratio of uncoupled state to state 4 respiration rates. Protection by PO 4, SO 4 or AsO 4 was inhibited by mersalyl, suggesting that these anions interact with a site located in the matrix side. In addition, the effects of SO 4 and AsO 4 on the F 1F 0-ATPase were tested: both SO 4 and AsO 4 inhibited the synthesis of ATP following competitive kinetics against PO 4 and non-competitive kinetics against ADP. The mersalyl sensitive uptake of 32PO 4 was not inhibited by SO 4 or AsO 4, suggesting that the synthesis of ATP was inhibited at the F 1F 0-ATPase. The hydrolysis of ATP was not inhibited, only a stimulation was observed when AsO 4 or sulfite (SO 3) were added. It is suggested that the structure and charge similarities of PO 4, AsO 4 and SO 4 result in undiscriminated binding to at least two sites located in the mitochondrial matrix: at one site, occupation by any of these three anions results in protection against uncoupling by K +; at the second site, in the F 1F 0-ATPase, AsO 4 and SO 4 compete for binding against PO 4 leading to inhibition of the synthesis of ATP.

Interaction of Arsenate with the Molybdenum Site of Sulfite Oxidase

Interaction of Arsenate with the Molybdenum Site of Sulfite Oxidase

Arsenate Interactions with CaO: Formation of Johnbaumite

In hyperalkaline en~cironments such as concretes and alkaline wastes, the aqueous geochemistry of arsenate should be controlled by reactions of arsenate ions with alkaline phases such as portlandite, calcite and ettringite. This should result in the formation of surface complexes, and/or solid solutions of metalarsenate precipitates. At present, insufficient thermodynamic data is available to facilitate prediction of Ca-arsenate precipitates. In addition, little spectroscopic data is available for As(V) interactions with Ca mineral phases or for Ca-arsentate precipitates. The present study examined the sorption of arsenate by CaO. Examination of reaction products with direct physical methods (XRD, SEM, FTIR, Raman and XAS) indicated the formation of johnbaumite (Cas(AsO4)3(OH)).

Reduction and binding of arsenate and dimethylarsinate by glutathione: a magnetic resonance study

By observing the chemical shifts of the proton and carbon-13 nuclei of reduced glutathione, the interactions of arsenate, arsenite and dimethylarsinate with this tripeptide have been characterized. These spectral studies show the reduction and complexation of arsenic to be a two-step process. Initially, the oxidation of 2 mol of glutathione reduces arsenate to arsenite. Then, 3 mol of glutathione are consumed in the formation of a glutathione-arsenite complex. Similar experiments with arsenite identified a (glutathione) 3-arsenite complex; however, no oxidized glutathione was detected. The arsenite binding site in the glutathione-arsenite complex is the cysteinyl sulfhydryl. The glutathione-arsenite complex is stable over the pH range from 1.5 to 7.0–7.5. At higher pH, dissociation occurs releasing reduced glutathione. For a glutathione to dimethylarsinate ratio of 3, oxidized glutathione is also coupled with a reduction to trivalent dimethylarsinous acid, prior to the formation of a 1:1 glutathione-dimethylarsinite complex. The role of reduced glutathione in the metabolism of arsenic is consistent with the previously described effects of this agent on the organismic toxicity of arsenic.

Transfer of arsenite from glutathione to dithiols: a model of interaction.

The interactions of arsenate and arsenite with meso-2,3-dimercaptosuccinic acid (DMSA) have been characterized using carbon-13 nuclear magnetic resonance. These studies show that DMSA reduces arsenate to arsenite and complexes arsenite. Monitoring the carbon-13 signals of complexed DMSA and liberated glutathione shows that DMSA readily extracts arsenite from a (glutathione)3-arsenite complex, proving the affinity of arsenite for dithiols is greater than that for monothiols. Competition between DMSA (vicinal thiols) and dithioerythritol (1,4-dimercapto-2,3-butanediol) for binding of arsenite indicates that the binding affinity is inversely related to the distance between the two thiol groups. On the basis of these findings, a model for the interaction of arsenic with mono- and dithiol-containing molecules is proposed.