Arsenate Anions Research Articles

Synthesis and evaluation of chromate and arsenate anions extraction ability of a N-methylglucamine derivative of calix[4]arene immobilized onto magnetic nanoparticles

In this study, 5,17-bis-[(N-methylglucamine)methyl]-25,26,27,28-tetrahydroxy-calix[4]arene (3) was synthesized by the treatment of calix[4]arene with a secondary amine N-methylglucamine and formaldehyde. The calixarene derivative (3) was characterized by a combination of FTIR, (1)H NMR and elemental analyses. Followingly, using the macrocyclic building block, the compound 3 was immobilized by [3-(2,3-epoxypropoxy)propyl]trimethoxysilane-modified Fe(3)O(4) magnetite nanoparticles (EPPTMS-MN). The prepared calix[4]arene immobilized material was characterized by a combination of Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and thermogravimetric analyses (TGA). Moreover, the studies regarding the removal of arsenate and dichromate ions from the aqueous solutions were also carried out by using the compound in solid-liquid extraction experiments. It was found that the calix[4]arene-based magnetic material has high extraction ability towards dichromate and arsenate anions in 66% (at pH 1.5) and in 86% (at pH 3.5), respectively.

Raman spectroscopic study of the hydrogen‐arsenate mineral pharmacolite Ca(AsO3OH)·2H2O—implications for aquifer and sediment remediation

AbstractThe removal of arsenate anions from aqueous media, sediments and wasted soils is of environmental significance. The reaction of gypsum with the arsenate anion results in pharmacolite mineral formation, together with related minerals. Raman and infrared (IR) spectroscopy have been used to study the mineral pharmacolite Ca(AsO3OH)· 2H2O. The mineral is characterised by an intense Raman band at 865 cm−1 assigned to the ν1 (AsO3)2− symmetric stretching mode. The equivalent IR band is found at 864 cm−1. The low‐intensity Raman bands in the range from 844 to 886 cm−1 provide evidence for ν3 (AsO3) antisymmetric stretching vibrations. A series of overlapping bands in the 300‐450 cm−1 region are attributed to ν2 and ν4 (AsO3) bending modes. Prominent Raman bands at around 3187 cm−1 are assigned to the OH stretching vibrations of hydrogen‐bonded water molecules and the two sharp bands at 3425 and 3526 cm−1 to the OH stretching vibrations of only weakly hydrogen‐bonded hydroxyls in (AsO3OH)2− units. Copyright © 2009 John Wiley & Sons, Ltd.

Comparison of Arsenate, Lead, and Cadmium Adsorption onto Aged Biofilter Media

Many biological water treatment plants for removal of iron and manganese from groundwater are in place for quite a long time, and thus their filters are aged—naturally coated with metal oxides and associated biomass. The particular reactivity and high adsorption capacity of these biogenic surface coatings make them potentially applicable for cost effective removal of arsenic and other heavy metals from contaminated water. However, the nature of interaction between various toxic elements and the composite materials in biological filters is not well understood. This study combines macroadsorption experiments with electron probe analysis to evaluate the adsorption properties of the biogenic surface coatings of an aged biofilter medium (BFM) for cationic lead and cadmium as well as arsenate anion. Results of batch adsorption showed that BFM has higher adsorption capacity for lead and cadmium as compared to arsenate anion. At pH 5.5, the maximum adsorption capacities of the medium for As(V), Pb(II), and Cd(II) were 17.03-, 80.77-, and 179.05-mg/g surface coatings, respectively. However, the column performance of BFM for Cd(II) was rather low. In particular, the breakthrough adsorption capacities (qb) of the BFM for As(V), Pb(II), and Cd(II) were 0.247-, 31.168-, and 4.084-mg/g surface coatings, respectively. These values represent about 1.5, 38.6, and 2.3% of the respective theoretical maximum adsorption capacities (qmax) of BFM for these metals. Data from the X-ray electron probe analysis corroborated well with that of the macroadsorption experiments. Results of this study strongly suggest that the Mn/Fe ratio and the presence of preadsorbed competing ions were two of the principal characteristics of the BFM, governing its affinity and adsorption capacity for different toxic metals.

Synthesis of the cotton cellulose based Fe(III)-loaded adsorbent for arsenic(V) removal from drinking water

A novel macroporous bead adsorbent, Fe(III)-loaded ligand exchange cotton cellulose adsorbent [Fe(III)LECCA], is synthesized for selective adsorption of arsenate anions [As(V)] from drinking water in batch and column systems. As(V) adsorption on Fe(III)LECCA was independent of pH, especially in drinking water pH range. Film diffusive control mechanism will benefit As(V) exchange with Fe(III)LECCA whether in batch or in column experiments. When treating the tap water at 26.0 BV/h, the column still preserves 83% of the original saturation adsorption capacity of the As(V) aqueous solution. These results have indicated that Fe(III)LECCA has the potential to act as an adsorbent for the removal of As(V) from drinking water considering its availability, nontoxicity and cost-effectiveness.

Synthesis of di-substituted calix[4]arene-based receptors for extraction of chromate and arsenate anions

The article describes the synthesis of a family of novel calix[4]arene ionophores, 25,27-bis-(2-aminomethylpyridine-propoxy)-26,28-dihydroxycalix[4]arene ( 5a), 25,27-bis-(3-aminomethylpyridine-propoxy)-26,28-dihydroxycalix[4]arene ( 5b) and two chromogenic calix[4]arenes, 5,17-dinitro-25,27-bis-(2-aminomethylpyridine-propoxy)-26,28-dihydroxycalix[4]arene ( 5c), 5,17-dinitro-25,27-bis-(3-aminomethylpyridine-propoxy)-26,28-dihydroxycalix[4]arene ( 5d) bearing pyridinium units. In the synthesis, the upper and lower rims of p- tert-butylcalix[4]arene were modified in order to acquire binding sites for the recognition of arsenate and dichromate anions. It has been observed that protonated alkylammonium forms of the ionophores showed high affinity toward dichromate and arsenate anions.

Arsenic removal by goethite and jarosite in acidic conditions and its environmental implications

Schwertmannite (Fe 8O 8(OH) 5.5(SO 4) 1.25), jarosite (KFe 3(SO 4) 2(OH) 6) and goethite (FeOOH) control natural attenuation of arsenic in acid mine drainage (AMD) impacted areas. Batch experiments were conducted to examine the sorption capacity of synthetic goethite and synthetic jarosite at highly acidic pH (1.5–2.5), at two ionic strengths (0.02–0.15 mol dm −3, NaCl) and at sulphate concentrations in the range of 5 × 10 −3 to 2.8 × 10 −1 mol dm −3. In the absence of competitive effects of other anions, K-jarosite presents better removal efficiency than goethite for As(V). The maximum sorption capacity is estimated to be 1.2 × 10 −4 and 7.0 × 10 −6 mol m −2 for jarosite and goethite, respectively, under similar experimental conditions. The variation of arsenic sorbed on goethite as a function of the equilibrium arsenic concentration in solution fits a non-competitive Langmuir isotherm. In the case of K-jarosite, sorption data could not fit a Langmuir or Freundlich isotherm since sulphate–arsenate anion exchange is probably the sorption mechanism. Ionic strength and pH have little effect on the sorption capacity of goethite and jarosite in the small range of pH studied. The presence of sulphate, which is the main anion in AMD natural systems, has a negative effect on arsenic removal since sulphate competes with arsenate for surface sorption sites. Moreover, mobilization of arsenic in the transformation of schwertmannite to jarosite or goethite at pH 2–3 is proposed since the sorption capacities of goethite and K-jarosite are considerably lower than those reported for schwertmannite.

Characterization of Surface-Bound Zr(IV) and Its Application to Removal of As(V) and As(III) from Aqueous Systems Using Phosphonic Acid Modified Nanoporous Silica Polyamine Composites

Silica polyamine composites (SPC) made from silanized amorphous nanoporous silica gel and poly(allylamine) (BP-1) were functionalized with phosphorus acid using the Mannich reaction, resulting in a phosphonic acid modified composite (BPAP). Successful immobilization of the phosphonic acid ligand was confirmed by mass gain, elemental analysis, IR, and solid-state NMR. The modified composite had a ligand loading of 1.5 mmol/g, corresponding to N/P ratio of 0.73. Zirconium(IV) was immobilized on BPAP with a loading of 1.12 mmol/g. Zirconium loading was analyzed by mass gain, ICP/AES, and SEM/EDX. Arsenate anions strongly adsorbed on the ZrBPAP composite in the pH range 2−8, while arsenite only adsorbed well at pH 10. The sorption mechanism is a chelation between arsenate or arsenite and Zr(IV)−phosphonic acid complex of BPAP. Adsorption isotherm data were found to be well modeled by the Langmuir equation for As(V) at pH 4 with Kads = 0.016 L/g and Qm = 98 mg/g; and at pH 6 with Kads = 0.018 L/g and Qm = 56 mg/g. Regeneration of the resin was carried out successfully for As(V) and As(III) using 2M-H2SO4. Four adsorption/desorption cycles were performed for As(V) at pH 4 without significant decrease in the uptake performance. ZrBPAP capture capacity and kinetics for arsenate were tested for longevity over 1000 cycles with only a marginal loss of performance. This composite is highly selective for arsenate over sulfate (As/SO42− = 50/1) and selenate (As/Se = 20/1); lower selectivity was observed with Fe(III) and Th(IV) loaded BPAP. The significance of the observed selectivity is discussed in terms of the chemical properties of the anion and the nature of the interactions with the immobilized metal site.

Simultaneous doping of anodic silicon oxide films with phosphorus and arsenic

It is established that, during the formation of anodic P- or As-doped SiO2 films on p-Si in an ethylene glycol + 0.13% H2O solution containing 14.3% H3PO4, 0.17% HNO3, and 0.0193–1.95% H3AsO4 additives, the orthophosphoric and orthoarsenic acids do not produce any combined effect upon the process of introduction of the arsenate and phosphate anions into silicon dioxide. It is suggested that the partial anodic reactions of Si with NO 3 − , OH−, AsO 4 3− , and PO 4 3− proceed with the formation of SiO2 involving As2O3, As, As2O5, P2O5, and P.

Water‐soluble polymers: Optimization of arsenate species retention by ultrafiltration

AbstractThe liquid‐phase polymer‐based retention (LPR) technique was employed to study the retention of arsenate species by poly(vinylbenzyl trimethylammonium chloride), P(ClVBTA), and poly[2‐(acryloyloxy)ethyltrimethylammonium chloride], P(ClAETA). The effect of parameters such as polymer concentration, time exposure, competition of sulfate and phosphate anions, and the use of natural systems as drinking water on the retention of As(V) species was analyzed. The mole ratios of polymer : As(V) of (31 : 1), (20 : 1), (10 : 1), (6 : 1), and (3 : 1) by using the washing method at pH 8 and 6 were assayed. The retention capacity was a function of polymer concentration and pH. The optimum mole ratio of polymer : As(V) was (20 : 1) for all pHs studied and all polymeric structures. The polymer's activity recovery assays were performed by washing at pH 2 and 3. A 95% As(V) elimination was achieved from polymers. A study of competition in the presence of other anions was performed at the same polymer : As(V) ratio (20 : 1). At pH 8 and at the same concentration of arsenate anions, sulfate, and phosphate anions, no important competition on arsenic retention was observed. Assays for P(ClVBTA) at pH 8 and mole ratio of polymer : As(V) (20 : 1), (40 : 1), and (60 : 1) using drinking water showed that the efficiency was higher under these conditions for the three As(V) retention cases. An unbuffered system with drinking water was tested for washing and enrichment methods by determining the maximum saturation capacity of the P(ClVBTA) polymer. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Novel layered uranyl arsenates, Ag6[(UO2)2(As2O7)(As4O13)] and AI6[(UO2)2(AsO4)2(As2O7)] (AI–Ag and Na): first observation of a linear As4O136− anion and structure type evolution

Three new layered uranyl arsenates with mixed arsenate anions have been prepared by high-temperature solid-state reactions: Ag6[(UO2)2(As2O7)(As4O13)] (1), Ag6[(UO2)2(AsO4)2(As2O7)] (2), Na6[(UO2)2(AsO4)2(As2O7)] (3). The crystal structures of the synthesized compounds have been solved by direct methods, and found to be based upon 2-D anionic layers with complex topology. The layers have composition [(UO2)2(As2O7)(As4O13)]6− in 1 and [(UO2)2(AsO4)2(As2O7)]6− in 2 and 3. In the structure of 1, UO7 pentagonal bipyramids share corners with linear As2O74− and zigzag-like As4O136−. Compounds 2 and 3 are isostructural and based upon corner-sharing between UO7 pentagonal bipyramids, AsO43− and As2O74−groups. The A+ cations (Ag+ in 1 and 2, Na+ in 3) are in between the layers. The zigzag-like tetramer [As4O13]6− in the structure of 1 is the first example of a linear tetramer in arsenate chemistry.

Nonlinear two-phase equilibrium model for the binding of arsenic anions to cationic micelles

The binding of arsenic ions to cationic cetylpyridinium chloride (CPC) micelles has been investigated using the semiequilibrium dialysis (SED) technique. In SED experiments, it has been shown that CPC micelles are very effective in binding arsenic ions in the retentate. At the studied pH (pH 8), the unbound and bound arsenic exists primarily as divalent anions (HAsO 4 2−) while CPC molecules exist as monovalent cations. Therefore, arsenic ions are bound electrostatically to the cationic micelle. The resultant colloid is large enough not to pass through the dialysis membrane, producing a rejection greater than 99.59%. The concentration of the unbound arsenic anions passing through the dialysis membrane is practically the same as the permeate concentration of these species in the analogous micellar-enhanced ultrafiltration (MEUF) experiments. Therefore, a nonlinear equilibrium model which combines thermodynamic relations, charge balance equations, and material balance equations with the Oosawa two-phase polyelectrolyte theory has been developed to correlate the binding of arsenic to CPC micelles in SED and MEUF. It was shown that the equilibrium model successfully accounts for the experimental data in both SED and MEUF in the absence and presence of monovalent (HCO 3 1−) and divalent co-ions (HPO 4 2−). Because of their small sizes (less than 10 nm), micelles should retain their equilibrium shapes in the presence of hydrodynamic shear typically attained in most dynamic processes. Therefore, the equilibrium model can be used to predict separation efficiencies in other ultrafiltration units such as in crossflow ultrafiltration processes.

Raman and infrared spectroscopy of arsenates of the roselite and fairfieldite mineral subgroups

Raman spectroscopy complimented with infrared spectroscopy has been used to determine the molecular structure of the roselite arsenate minerals of the roselite and fairfieldite subgroups of formula Ca 2B(AsO 4) 2·2H 2O (where B may be Co, Fe 2+, Mg, Mn, Ni and Zn). The Raman arsenate (AsO 4) 2− stretching region shows strong differences between the roselite arsenate minerals which is attributed to the cation substitution for calcium in the structure. In the infrared spectra complexity exists with multiple (AsO 4) 2− antisymmetric stretching vibrations observed, indicating a reduction of the tetrahedral symmetry. This loss of degeneracy is also reflected in the bending modes. Strong Raman bands around 450 cm −1 are assigned to ν 4 bending modes. Multiple bands in the 300–350 cm −1 region assigned to ν 2 bending modes provide evidence of symmetry reduction of the arsenate anion. Three broad bands for roselite are found at 3450, 3208 and 3042 cm −1 and are assigned to OH stretching bands. By using a Libowitzky empirical equation hydrogen bond distances of 2.75 and 2.67 Å are estimated. Vibrational spectra enable the molecular structure of the roselite minerals to be determined and whilst similarities exist in the spectral patterns, sufficient differences exist to be able to determine the identification of the minerals.

Removal of Cr(VI) and As(V) from aqueous solutions by HDTMA-modified zeolite Y

The synthesized zeolite NaY from rice husk ash (RHA) and the commercial zeolite NaY both modified with surfactants in amounts equal to 50%, 100% and 200% of their external cation exchange capacity (ECEC) were used to remove chromate and arsenate anions from aqueous solutions. While the unmodified zeolite Y had little or no affinity for the Cr(VI) and As(V) anionic species, the surfactant-modified zeolite Y (SMZY) showed significant ability to remove of these anions from the aqueous solutions. The highest chromates and arsenates adsorption efficiency was observed from solutions of pH values 3 and 8, respectively because of the dominance of the univalent species of both anions. The adsorption equilibrium data were best fitted with the Langmuir isotherm model with the highest removal capacities observed for the SMZY initially prepared considering the hexadecyltrimethyl ammonium (HDTMA) amount equal to the 100% of the ECEC of zeolite Y. Synthesized SMZY remove Cr(VI) and As(V) more than the corresponding commercial one due to its lower silica to alumina ratio. Thus, the HDTMA-covered modified zeolite Y synthesized using RHA can be used to remove Cr(VI) and As(V) from water.

Experimental and modelling analysis of As(V) ions adsorption on granular activated carbon

In this work the adsorption of pentavalent arsenic on a granular activated carbon (GAC) has been experimentally studied. The effects of arsenic concentration, pH, temperature and salinity on equilibrium adsorption capacity have been investigated. Experimental results show that the adsorption capacity is the highest at neutral pH conditions, low salinity levels and high temperatures. A model for the description of the arsenic adsorption mechanism is reported. This is based on the multicomponent Langmuir adsorption theory applied to the ionic species in solution. The model points out that the adsorption capacity is proportional to the concentration of arsenic anions in solution and decreases by increasing the concentration of competitive ions such as hydroxides and chlorides, allowing a correct interpretation of the pH and salinity effects on the adsorption capacity. Finally, one of the main goals of the proposed model is to preserve the exothermicity of the adsorption phenomena despite the observed trend of experimental results: the increase of adsorption capacity with temperature appears to be related to a higher arsenic dissociation.

Coprecipitation of Arsenate with Metal Oxides. 2. Nature, Mineralogy, and Reactivity of Iron(III) Precipitates

Coprecipitation of arsenic with iron or aluminum occurs in natural environments and is a remediation technology used to remove this toxic metalloid from drinking water and hydrometallurgical solutions. In this work, we studied the nature, mineralogy, and reactivity toward phosphate of iron-arsenate coprecipitates formed at As(V)/Fe(III) molar ratios (R) of 0, 0.01, or 0.1 and at pH 4.0, 7.0, and 10.0 aged for 30 or 210 days at 50 degrees C and studied the desorption of arsenate. At R = 0, goethite and hematite (with ferrihydrite at pH 4.0 and 7.0) crystallized, whereas at R = 0.01, the formation of ferrihydrite increased and hematite crystallization was favored over goethite. In some samples, the morphology of hematite changed from rounded platy crystals to ellipsoids. At R = 0.1, ferrihydrite formed in all the coprecipitates and remained unchanged even after 210 days of aging. The surface area and chemical composition of the precipitates were affected by pH, R, and aging. Chemical dissolution of the samples showed that arsenate was present mainly in ferrihydrite, but at R = 0.01, it was partially incorporated into the structures of crystalline Fe oxides. The sorption of phosphate on to the coprecipitates was affected not only by the mineralogy and surface area of the samples but also by the amounts of arsenate present in the oxides. The samples formed at pH 4.0 and 7.0 and at R = 0.1 sorbed lower amounts of phosphate than the precipitates obtained at R = 0 or 0.01, despite the former having a larger surface area and showing only a presence of short-range ordered materials. This is mainly due to the fact that in the coprecipitates at R = 0.1 arsenate occupied many sorption sites, thus preventing phosphate sorption. Less than 20% of the arsenate present in the coprecipitates formed at R = 0.1 was removed by phosphate and more from the samples synthesized at pH 7.0 or 10.0 than at pH 4.0. Moreover, we found that more arsenate was desorbed by phosphate from a ferrihydrite on which arsenate was added than from an iron-arsenate coprecipitate, attributed to the partial occlusion of some arsenate anions into the framework of the coprecipitate. XPS analyses confirmed these findings.

Capability of cationic water‐soluble polymers in conjunction with ultrafiltration membranes to remove arsenate ions

AbstractArsenic is one of the most hazardous pollutants, and is present in water, mainly, as As(V) and As(III), and in its inorganic hydrolysis species. Great efforts have been made to develop effective removal techniques. One alternative is the use of water‐soluble polymers containing functional groups to remove these toxic species. This paper presents the synthesis and characterization (FT‐IR and 1H NMR spectroscopy, as well as thermogravimetry TG‐DSC) of two cationic water‐soluble polymers containing tetra alkylammonium groups, poly[2‐(acryloyloxy)ethyl]trimethylammonium chloride, and poly[2‐acryloyloxy)ethyl]trimethylammonium methyl sulfate (P(SAETA)). The arsenate retention properties were investigated using the liquid‐phase polymer‐based retention technique. The polymer structure and the exchangeable anions' nature have been shown to be two important variables in the removal efficiency of arsenate anions from aqueous solutions. Both investigated polymers were found to efficiently remove HAsO42− species from an aqueous media, with pH ranging from 6 to 8. The exchange of methyl sulfate for the chloride anion on P(SAETA) improved arsenate ion retention ability. The modification of ionic strength by Na2SO4 addition induced a significant decrease in the cationic polymer's arsenate retention properties. The polymers' retention properties were not studied using real samples. POLYM. ENG. SCI., 47:1256–1261, 2007. © 2007 Society of Plastics Engineers

Cationic hydrogels for toxic arsenate removal from aqueous environment

Poly(3-acrylamidopropyl)trimethylammonium chloride (p(APTMACl)) hydrogels were synthesized and utilized as absorbents for the removal of toxic arsenate from aqueous medium. The pH-dependent swelling characteristics of the hydrogel were studied, and the experimental parameters that affect the absorption efficiency were investigated. Our results demonstrate that these types of hydrogels are highly effective in removing arsenate(V) anions from the aqueous environment. A removal efficiency of approximately 99.7% was obtained be immersing 1.5 g/l hydrogel in a solution containing 50 ppm As(V) at pH 9 for 360 min. Moreover, the hydrogels are very easy to handle upon absorption, avoiding issues related to the separation of traditional powder absorbents from water after absorption.

Cationic water‐soluble polymers with the ability to remove arsenate through an ultrafiltration technique

AbstractDifferent cationic water‐soluble polymers with (R)4N+X− groups and pyridinium groups were prepared, and their arsenate retention performance was investigated with the liquid‐phase polymer‐based retention technique. Poly[3‐(methacryloylamino)propyl]trimethylammonium chloride, poly[2‐(acryloyloxy)ethyl]trimethylammonium chloride, poly(ar‐vinylbenzyl)trimethylammonium chloride, poly[2‐(acryloyloxy)ethyl]trimethylammonium methyl sulfate, poly(4‐vinyl‐1‐methyl pyridinium)bromide, and poly[3‐(methacryloylamino)propyl]dimethyl(3‐sulfopropyl)ammonium hydroxide were prepared. The synthesis of the polymers by solution radical polymerization produced a yield higher than 77%. Structural analyses were performed with Fourier transform infrared and 1H‐NMR spectroscopy and thermogravimetry/differential scanning calorimetry. Commercial poly(4‐vinyl‐1‐methyl pyridinium)bromide and poly(ar‐vinylbenzyl)trimethylammonium chloride were also used. The liquid‐phase polymer‐based retention technique was employed to study the retention of arsenate species. The polymer structure and exchange groups, such as methyl sulfate, chloride, bromide, and hydroxide, presented different properties for removing arsenate anions from aqueous solutions. The type of voluminous quaternary ammonium group present influenced arsenic retention. All the polymers could bind HAsO42− species from an aqueous solution more selectively at pHs 8 and 6 than at pH 4. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Sorption Removal of Arsenic(V) by Sn-loaded Poly(hydroxamic) Acid Chelating Resin

Sorption conditions of arsenate ions onto Sn-loaded poly (hydroxamic acid) chelating resin (Sn-PHA) have been studied. Sorption isotherms data correlated well to the Langmuir model with maximum capacity of 38.46 mg g-1 at pH 2. Sorption process follows pseudo-second order kinetics. Intraparticle diffusion was found to take part in sorption processes. The free energy (E) was 11.18 kJ mol-1 which shows the sorption is an ion-exchange process. Thermodynamic parameters, ΔH°, ΔS° and ΔG° were also calculated from the experimental data. Standard heat of sorption was found to be endothermic and entropy change value was calculated to be positive. Negative ΔG° value indicates that the sorption process for the arsenic anions onto Sn-PHA is spontaneous.

Arsenate detoxification in a Pseudomonad hypertolerant to arsenic

Pseudomonas sp. strain As-1, obtained from an electroplating industrial effluent, was capable of growing aerobically in growth medium supplemented with up to 65 mM arsenate (As (V)), significantly higher concentrations than those tolerated by other reference arsenic resistant bacteria. The majority of the arsenic was detected in culture supernatants as arsenite (As (III)) and X-ray absorbance spectroscopy suggested that 30% of this cell-bound arsenic was As (V), 65% As (III) and 5% of arsenic was associated with sulphur. PCR analysis using primers designed against arsenic resistance genes of other Gram-negative bacteria confirmed the presence of an arsenic resistance operon comprising of three genes, arsR, arsB and arsC in order of predicted transcription, and consistent with a role in intracellular reduction of As (V) and efflux of As (III). In addition to this classical arsenic resistance mechanism, other biochemical responses to arsenic were implicated. Novel arsenic-binding proteins were purified from cellular fractions, while proteomic analysis of arsenic-induced cultures identified the upregulation of additional proteins not normally associated with the metabolism of arsenic. Cross-talk with a network of proteins involved in phosphate metabolism was suggested by these studies, consistent with the similarity between the phosphate and arsenate anions.