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PubMed1994

Dose-dependent disposition of sodium arsenate in mice following acute oral exposure.

The effect of dose on arsenate disposition was studied in adult female B6C3F1 mice, dosed po with 0.5 to 5000 micrograms/kg [73As]-arsenate in water. Urine was collected at 1, 2, 4, 8, 12, 24, and 48 hr and feces at 24 and 48 hr postexposure. The mice were euthanized at 48 hr and tissues were removed. Recovery of arsenate-derived radioactivity ranged from 83 to 89%; 66-79% of the dose was excreted in urine, 10-18% in feces, and < 1% remained in the tissues. Although dose had no effect on the 48-hr excretion of radioactivity, the level of radioactivity in several tissues increased significantly with dose. The urine was analyzed for arsenic metabolites by using ion chromatography to analyze for arsenate, methylarsonic acid (MMA), and dimethylarsinic acid (DMA); ion-pairing high-performance liquid chromatography was used for arsenite analysis. Arsenate elimination ranged from 3 to 15%. DMA was the predominant metabolite excreted (51-64% of dose), but no effect of dose on its elimination was detected. As the dose of arsenate increased, the amount of MMA excreted (0.1-1.0% of dose) significantly increased. At 5000 micrograms/kg arsenate, a significant increase in arsenite excretion was observed. At doses of arsenate < or = 500 micrograms/kg, peak elimination of DMA occurred within 4 hr postexposure. At the 5000 micrograms/kg dose, DMA peak elimination shifted to 8 hr and a lower amount was excreted. In addition, at the 5000 micrograms/kg dose, there was an increase of arsenate and arsenite in the 1- and 2-hr urines. These results suggest that an acute dose of arsenate can affect the metabolism of arsenicals. High doses lead to the accumulation of intermediates that are more reactive than DMA, and this response may lead to increased toxicity.

Administration, Oral↗
PubMed2000

Two new arsenate/sulfate-reducing bacteria: mechanisms of arsenate reduction.

Two sulfate-reducing bacteria, which also reduce arsenate, were isolated; both organisms oxidized lactate incompletely to acetate. When using lactate as the electron donor, one of these organisms, Desulfomicrobium strain Ben-RB, rapidly reduced (doubling time = 8 h) 5.1 mM arsenate at the same time it reduced sulfate (9.6 mM). Sulfate reduction was not inhibited by the presence of arsenate. Arsenate could act as the terminal electron acceptor in minimal medium (doubling time = 9 h) in the absence of sulfate. Arsenate was reduced by a membrane-bound enzyme that is either a c-type cytochrome or is associated with such a cytochrome; benzyl-viologen-dependent arsenate reductase activity was greater in cells grown with arsenate/sulfate than in cells grown with sulfate only. The second organism, Desulfovibrio strain Ben-RA, also grew (doubling time = 8 h) while reducing arsenate (3.1 mM) and sulfate (8.3 mM) concomitantly. No evidence was found, however, that this organism is able to grow using arsenate as the terminal electron acceptor. Instead, it appears that arsenate reduction by the Desulfovibrio strain Ben-RA is catalyzed by an arsenate reductase that is encoded by a chromosomally-borne gene shown to be homologous to the arsC gene of the Escherichia coli plasmid, R773 ars system.

Adenosine Triphosphatases↗
PubMed1997

Dissimilatory arsenate and sulfate reduction in Desulfotomaculum auripigmentum sp. nov.

A newly discovered arsenate-reducing bacterium, strain OREX-4, differed significantly from strains MIT-13 and SES-3, the previously described arsenate-reducing isolates, which grew on nitrate but not on sulfate. In contrast, strain OREX-4 did not respire nitrate but grew on lactate, with either arsenate or sulfate serving as the electron acceptor, and even preferred arsenate. Both arsenate and sulfate reduction were inhibited by molybdate. Strain OREX-4, a gram-positive bacterium with a hexagonal S-layer on its cell wall, metabolized compounds commonly used by sulfate reducers. Scorodite (FeAsO42. H2O) an arsenate-containing mineral, provided micromolar concentrations of arsenate that supported cell growth. Physiologically and phylogenetically, strain OREX-4 was far-removed from strains MIT-13 and SES-3: strain OREX-4 grew on different electron donors and electron acceptors, and fell within the gram-positive group of the Bacteria, whereas MIT-13 and SES-3 fell together in the epsilon-subdivision of the Proteobacteria. Together, these results suggest that organisms spread among diverse bacterial phyla can use arsenate as a terminal electron acceptor, and that dissimilatory arsenate reduction might occur in the sulfidogenic zone at arsenate concentrations of environmental interest. 16S rRNA sequence analysis indicated that strain OREX-4 is a new species of the genus Desulfotomaculum, and accordingly, the name Desulfotomaculum auripigmentum is proposed.

Arsenates↗
PubMed1984

113Cd NMR. Arsenate binding to Cd(II) alkaline phosphatase.

Alkaline phosphatase from Escherichia coli contains three metal binding sites (A, B, and C) located at sites forming a triangle with sides of 4, 5, and 7 A (Wyckoff, H.W., Handschumacher, M., Murthy, K., and Sowadski, J.M. (1983) Adv. Enzymol. 55, 453). When all three sites are occupied by Cd(II) the enzyme has a very low turnover; at least 10(3) slower than the native Zn(II) enzyme. The slow turnover number has made the Cd(II) enzyme useful in NMR studies of the mechanism of alkaline phosphatase. The binding of arsenate to two forms of Cd(II) alkaline phosphatase (Cd(II)2alkaline phosphatase and Cd(II)6alkaline phosphatase) has been studied by 113Cd NMR. Cd(II)2alkaline phosphatase, pH 6.3, binds arsenate at only one monomer of the dimeric enzyme and causes migration of Cd(II) from the A site of one monomer to the B site of the arsenylated monomer. This same migration has previously been observed to accompany metal ion-dependent phosphate binding, but is much more rapid in the case of arsenate. The acceleration of migration induced by arsenate supports the conclusion based on the phosphate data that the substrate anion binds to the A site metal ion of one monomer prior to migration and that only the metal ion at A site is required for phosphorylation (arsenylation) of serine 102. The 113Cd chemical shifts of A and B site metal ions are very sensitive to the form of the bound arsenate, i.e. covalent (E-As) or noncovalent (E X As) complex. Like the analogous phosphate derivatives, the change of chemical shift of A site (to which phosphate is coordinated in the E X P complex) is much greater than that of the B site metal ion, when the arsenate shifts between the two intermediates, suggesting that arsenate is also coordinated to A site in the E X As intermediate. The chemical shifts of A and B site 113Cd(II) ions are considerably different in the arsenate and phosphate derivatives, while the C site 113Cd(II) ions have nearly identical chemical shifts. Thus the substrate appears to interact closely with both A and B sites, while C site appears relatively unimportant in phosphomonoester hydrolysis. The analogous behavior of arsenate and phosphate at the active center as evaluated by 113Cd NMR supports the validity of using the heavier arsenate derivative in x-ray diffraction studies.

Alkaline Phosphatase↗
PubMed2005

Energetics of arsenate sorption on amorphous aluminum hydroxides studied using flow adsorption calorimetry.

Flow adsorption calorimetry was used to investigate the energetics of arsenate sorption on amorphous aluminum hydroxide (AHO) and its effect on surface charge and ion exchange. Arsenate sorption at pH 5.7 was exothermic and the molar heats of adsorption were quite variable, ranging from -3.0 to -66 kJ/mol. Repetitive exposure of the same sample to arsenate in the calorimeter showed that the AHO was able to regenerate a considerable amount of reactive surface over time periods as short as 15 to 20 min. The large variability in heats of arsenate adsorption and the ability to regenerate reactive surface is believed to result from the amorphous nature of the AHO used. Heats of Cl/NO3 exchange were much smaller and more consistent, ranging from about 3.0 to 6.0 kJ/mol. The molar ratio of exchangeable Cl:Al was about 6:1 for the AHO, indicating a highly porous material. At pH 5.7, arsenate sorption neutralized surface positive charge as measured by Cl/NO3 exchange. Only at the two highest loadings (>60,000 mg/kg) did arsenate sorption result in any negative surface charge as measured by Na/K exchange. These results showed that most of the arsenate was adsorbed by a mechanism that involved no increase in surface negative charge. The PZNC of the AHO decreased by about 1 pH unit when exposed to arsenate in the flow calorimeter. Exposure to arsenate in a batch system decreased the PZNC about 4 pH units. This difference in behavior between batch and flow systems was related to differences in the amount of arsenate adsorbed.

Journal Article↗
PubMed2004

Isolation and characterization of arsenate-reducing bacteria from arsenic-contaminated sites in New Zealand.

Two environmental sites in New Zealand were sampled (e.g., water and sediment) for bacterial isolates that could use either arsenite as an electron donor or arsenate as an electron acceptor under aerobic and anaerobic growth conditions, respectively. These two sites were subjected to widespread arsenic contamination from mine tailings generated from historic gold mining activities or from geothermal effluent. No bacteria were isolated from these sites that could utilize arsenite or arsenate under the respective growth conditions tested, but a number of chemoheterotrophic bacteria were isolated that could grow in the presence of high concentrations of arsenic species. In total, 17 morphologically distinct arsenic-resistant heterotrophic bacteria isolates were enriched from the sediment samples, and analysis of the 16S rRNA gene sequence of these bacteria revealed them to be members of the genera Exiguobacterium, Aeromonas, Bacillus, Pseudomonas, Escherichia, and Acinetobacter. Two isolates, Exiguobacterium sp. WK6 and Aeromonas sp. CA1, were of particular interest because they appeared to gain metabolic energy from arsenate under aerobic growth conditions, as demonstrated by an increase in cellular growth yield and growth rate in the presence of arsenate. Both bacteria were capable of reducing arsenate to arsenite via a non-respiratory mechanism. Strain WK6 was positive for arsB, but the pathway of arsenate reduction for isolate CA1 was via a hitherto unknown mechanism. These isolates were not gaining an energetic advantage from arsenate or arsenite utilization, but were instead detoxifying arsenate to arsenite. As a subsidiary process to arsenate reduction, the external pH of the growth medium increased (i.e., became more alkaline), allowing these bacteria to grow for extended periods of time.

Acinetobacter↗
PubMedDate not supplied

The metabolism of arsenite and arsenate by the rat.

Differences in distribution and metabolism of arsenite and arsenate were studied in rats and in rat liver and kidney slices and hepatocytes. Five minutes after i.v. administration of 4.8 nmol arsenite or arsenate to male Sprague-Dawley rats, blood levels of arsenic were only 10 percent of the initial dose. Blood arsenic levels then rose: by 4 hours about 67 percent of the initial dose of arsenite and 28 percent of the initial dose of arsenate were in the blood compartment. The predominant form of arsenic in the RBC was dimethylarsinic acid (DMA). Arsenite was rapidly distributed to both liver and kidney; arsenate was rapidly distributed to kidney only. After 4 hours of exposure to arsenite, liver slices had taken up six times more arsenic and kidney slices two times more arsenic than after exposure to arsenate. Isolated hepatocytes took up as much as 20 times more arsenic after arsenite exposure. DMA was found in the medium of the liver slices and hepatocytes exposed to arsenite, but very little DMA was found in the medium of the arsenate-exposed liver slices and hepatocytes. However, five times more DMA was found in the medium of the kidney slices exposed to arsenate than in the medium of the liver slices. Phosphate inhibited uptake and metabolism of arsenate by kidney slices. These studies indicate that inorganic arsenic is rapidly taken up by liver and kidney and methylated. Arsenite is methylated by both organs, whereas arsenate may be methylated by kidney only.

Animals↗
PubMed1999

Signal transduction pathways regulated by arsenate and arsenite.

Arsenate and arsenite activate c-Jun N-terminal kinase (JNK), however, the mechanism by which this occurs is not known. By expressing inhibitory mutant small GTP-binding proteins, p21-activated kinase (PAK) and mitogen-activated protein kinase/extracellular signal-regulated kinase kinase kinases (MEKKs), we have identified specific proteins that are involved in arsenate- and arsenite-mediated activation of JNK. We observe a distinct difference between arsenate and arsenite signaling, which demonstrates that arsenate and arsenite are capable of activating unique proteins. Both arsenate and arsenite activation of JNK requires Rac and Rho. Neither arsenate nor arsenite signaling was inhibited by a dominant-negative mutant of Cdc42 or Ras. Arsenite stimulation of JNK requires PAK, whereas arsenate-mediated activation of JNK was unaffected by inhibitory mutant PAK. Of the four MEKKs tested, only MEKK3 and MEKK4 are involved in arsenate-mediated activation of JNK. In contrast, arsenite-mediated JNK activation requires MEKK2, MEKK3 and MEKK4. These results better define the mechanisms by which arsenate and arsenite activate JNK and demonstrate differences in the regulation of signal transduction pathways by these inorganic arsenic species.

Arsenates↗
PubMed2001

Bacillus subtilis arsenate reductase is structurally and functionally similar to low molecular weight protein tyrosine phosphatases.

Arsenate is an abundant oxyanion that, because of its ability to mimic the phosphate group, is toxic to cells. Arsenate reductase (EC; encoded by the arsC gene in bacteria) participates to achieve arsenate resistance in both prokaryotes and yeast by reducing arsenate to arsenite; the arsenite is then exported by a specific transporter. The crystal structure of Bacillus subtilis arsenate reductase in the reduced form with a bound sulfate ion in its active site is solved at 1.6-A resolution. Significant structural similarity is seen between arsenate reductase and bovine low molecular weight protein tyrosine phosphatase, despite very low sequence identity. The similarity is especially high between their active sites. It is further confirmed that this structural homology is relevant functionally by showing the phosphatase activity of the arsenate reductase in vitro. Thus, we can understand the arsenate reduction in the light of low molecular weight protein tyrosine phosphatase mechanism and also explain the catalytic roles of essential residues such as Cys-10, Cys-82, Cys-89, Arg-16, and Asp-105. A "triple cysteine redox relay" is proposed for the arsenate reduction mechanism.

Amino Acid Sequence↗
PubMed1982

Energetics of plasmid-mediated arsenate resistance in Escherichia coli.

Plasmid R773, which codes for resistances to arsenate, arsenite, and antimony, was introduced into Escherichia coli strain AN120, a mutant deficient in the H+-translocating ATPase of oxidative phosphorylation. Cultures depleted of endogenous energy reserves were loaded with 74AsO3-4, and arsenate efflux was measured after dilution into medium containing various energy sources and inhibitors. Rapid extrusion of arsenate occurred when glucose was added. Arsenate was extruded both against and down a concentration gradient. In this strain glucose allows formation of both ATP via substrate-level phosphorylation and an electrochemical proton gradient (or protonmotive force) via oxidation of the products of glycolysis. When oxidation was inhibited by cyanide, glucose metabolism still produced arsenate efflux. Energy sources such as succinate, which supplies a protonmotive force but not ATP, did not result in efflux. Measurement of intracellular ATP concentration under each set of conditions demonstrated a direct correlation between the rate of efflux and ATP levels. Osmotically shocked cells lost the ability to extrude arsenate; however, no arsenate-binding activity was detected in osmotic shock fluid from induced cells. These results suggest that the arsenate efflux system is coupled to cellular ATP rather than an electrochemical proton gradient, possibly by an arsenate-translocating ATPase.

Arsenates↗
PubMed2001

Phytochelatins are involved in differential arsenate tolerance in Holcus lanatus.

Arsenate tolerance is conferred by suppression of the high-affinity phosphate/arsenate uptake system, which greatly reduces arsenate influx in a number of higher plant species. Despite this suppressed uptake, arsenate-tolerant plants can still accumulate high levels of As over their lifetime, suggesting that constitutive detoxification mechanisms may be required. Phytochelatins are thiol-rich peptides, whose production is induced by a range of metals and metalloids including arsenate. This study provides evidence for the role of phytochelatins in the detoxification of arsenate in arsenate-tolerant Holcus lanatus. Elevated levels of phytochelatin were measured in plants with a range of tolerance to arsenate at equivalent levels of arsenate stress, measured as inhibition of root growth. The results suggest that arsenate tolerance in H. lanatus requires both adaptive suppression of the high-affinity phosphate uptake system and constitutive phytochelatin production.

Adaptation, Physiological↗
PubMed1969

Arsenic-lipid complex formatinon during the active transport of arsenate in yeast.

In studying formation of an arsenic-lipid complex during the active transport of (74)As-arsenate in yeast, it was found that adaptation of yeast to arsenate resulted in cell populations which showed a deficient inflow of arsenate as compared to the nonadapted yeast. Experiments with both types of cells showed a direct correlation between the arsenate taken up and the amount of As-lipid complex formed. (74)As-arsenate was bound exclusively to the phosphoinositide fraction of the cellular lipids. When arsenate transport was inhibited by dinitrophenol and sodium azide, the formation of the As-lipid complex was also inhibited. Phosphate did not interfere with the arsenate transport at a non-inhibitory concentration of external arsenate (10(-9)m). The As-adapted cells but not the unadapted cells were able to take up phosphate when growing in the presence of 10(-2)m arsenate.

Adaptation, Biological↗
PubMed2007

The cymA gene, encoding a tetraheme c-type cytochrome, is required for arsenate respiration in Shewanella species.

In Shewanella sp. strain ANA-3, utilization of arsenate as a terminal electron acceptor is conferred by a two-gene operon, arrAB, which lacks a gene encoding a membrane-anchoring subunit for the soluble ArrAB protein complex. Analysis of the genome sequence of Shewanella putrefaciens strain CN-32 showed that it also contained the same arrAB operon with 100% nucleotide identity. Here, we report that CN-32 respires arsenate and that this metabolism is dependent on arrA and an additional gene encoding a membrane-associated tetraheme c-type cytochrome, cymA. Deletion of cymA in ANA-3 also eliminated growth on and reduction of arsenate. The DeltacymA strains of CN-32 and ANA-3 negatively affected the reduction of Fe(III) and Mn(IV) but not growth on nitrate. Unlike the CN-32 DeltacymA strain, growth on fumarate was absent in the DeltacymA strain of ANA-3. Both homologous and heterologous complementation of cymA in trans restored growth on arsenate in DeltacymA strains of both CN-32 and ANA-3. Transcription patterns of cymA showed that it was induced under anaerobic conditions in the presence of fumarate and arsenate. Nitrate-grown cells exhibited the greatest level of cymA expression in both wild-type strains. Lastly, site-directed mutagenesis of the first Cys to Ser in each of the four CXXCH c-heme binding motifs of the CN-32 CymA nearly eliminated growth on and reduction of arsenate. Together, these results indicate that the biochemical mechanism of arsenate respiration and reduction requires the interactions of ArrAB with a membrane-associated tetraheme cytochrome, which in the non-arsenate-respiring Shewanella species Shewanella oneidensis strain MR-1, has pleiotropic effects on Fe(III), Mn(IV), dimethyl sulfoxide, nitrate, nitrite, and fumarate respiration.

Amino Acid Sequence↗
PubMed2003

Accumulation and metabolism of arsenic in mice after repeated oral administration of arsenate.

Exposure to the human carcinogen inorganic arsenic (iAs) occurs daily. However, the disposition of arsenic after repeated exposure is not well known. This study examined the disposition of arsenic after repeated po administration of arsenate. Whole-body radioassay of adult female B6C3F1 mice was used to estimate the terminal elimination half-life of arsenic after a single po dose of [(73)As]arsenate (0.5 mg As/kg). From these data, it was estimated that steady-state levels of whole-body arsenic could be attained after nine repeated daily doses of [(73)As]arsenate (0.5 mg As/kg). The mice were whole-body radioassayed immediately before and after the repeated dosing. Excreta were collected daily and analyzed for arsenic-derived radioactivity and arsenicals. Whole-body radioactivity was determined 24 h after the last repeated dose, and five mice were then euthanized and tissues analyzed for radioactivity. The remaining mice were whole-body radioassayed for 8 more days, and then their tissues were analyzed for radioactivity. Other mice were administered either a single or nine repeated po doses of non-radioactive arsenate (0.5 mg As/kg). Twenty-four hours after the last dose, the mice were euthanized, and tissues were analyzed for arsenic by atomic absorption spectrometry (AAS). Whole-body radioactivity was rapidly eliminated from mice after repeated [(73)As]arsenate exposure, primarily by urinary excretion in the form of dimethylarsinic acid (DMA(V)). Accumulation of radioactivity was highest in bladder, kidney, and skin. Loss of radioactivity was most rapid in the lung and slowest in the skin. There was an organ-specific distribution of arsenic as determined by AAS. Monomethylarsonic acid was detected in all tissues except the bladder. Bladder and lung had the highest percentage of DMA(V) after a single exposure to arsenate, and it increased with repeated exposure. In kidney, iAs was predominant. There was a higher percentage of DMA(V) in the liver than the other arsenicals after a single exposure to arsenate. The percentage of hepatic DMA(V) decreased and that of iAs increased with repeated exposure. A trimethylated metabolite was also detected in the liver. Tissue accumulation of arsenic after repeated po exposure to arsenate in the mouse corresponds to the known human target organs for iAs-induced carcinogenicity.

Administration, Oral↗
PubMed2003

Mechanisms of arsenate adsorption by highly-ordered nano-structured silicate media impregnated with metal oxides.

The highly ordered mesoporous silica media, SBA-15, was synthesized and incorporated with iron, aluminum, and zinc oxides using an incipientwetness impregnation technique. Adsorption capacities and kinetics of metal-impregnated SBA-15 were compared with activated alumina which is widely used for arsenic removal. Media impregnated with 10% of aluminum by weight (designated to Al10SBA-15) had 1.9-2.7 times greater arsenate adsorption capacities in a wide range of initial arsenate concentrations and a 15 times greater initial sorption rate at pH 7.2 than activated alumina. By employing one- and two-site models, surface complexation modeling was conducted to investigate the relationship between the aluminum oxidation states in different media and adsorption behaviors shown by adsorption isotherms and kinetics since the oxidation phase of aluminum incorporated onto the surface of SBA-15 was Al-O, which has a lower oxidation state than activated alumina (Al2O3). Surface complexation modeling results for arsenate adsorption edges conducted with different pH indicated thatthe monodentate complex (SAsO(4)2-) was dominant in Al10SBA-15, while bidentate complexes (XHAsO4 and XAsO4-) were dominant in activated alumina at pH 7.2, respectively. In kinetic studies at pH 7.2 + 0.02, Al10SBA-15 had only a fast-rate step of initial adsorption, while activated alumina had fast- and slow-rate steps of arsenate adsorption. Therefore, it can be inferred that the monodentate arsenate complex, predominant in Al10SBA-15, leads to faster adsorption rates than bidentate arsenate complexes favored with activated alumina. An arsenate adsorption behavior and arsenate surface complexation were thought to be well explained by aluminum oxidation states and surface structural properties of media.

Adsorption↗
PubMed2005

Adsorption of arsenate onto ferrihydrite from aqueous solution: influence of media (sulfate vs nitrate), added gypsum, and pH alteration.

Mineral processing effluents generated in hydrometallurgical industrial operations are sulfate based; hence it is of interest to investigate the effect sulfate matrix solution ("sulfate media") has on arsenate adsorption onto ferrihydrite. In this work, in particular, the influence of media (SO4(2-) vs NO3-), added gypsum, and pH alteration on the adsorption of arsenate onto ferrihydrite has been studied. The ferrihydrite precipitated from sulfate solution incorporated a significant amount of sulfate ions and showed a much higher adsorption capacityfor arsenate compared to nitrateferrihydrite at pH 3-8 and initial Fe/As molar ratios of 2, 4, and 8. Adsorption of arsenate onto sulfate-ferrihydrite involved ligand exchange with SO4(2-) ions that were found to be more easily exchangeable with increasing pH. Added gypsum to the adsorption system significantly enhanced the uptake of arsenate by ferrihydrite at pH 8. Equilibration treatment at acidic pH and addition of gypsum markedly improved the stability of adsorbed arsenate on ferrihydrite when pH was elevated. Comparison of arsenate adsorption onto ferrihydrite to coprecipitation of arsenate with iron(III) showed the latter process to lead to higher arsenic removal.

Adsorption↗
PubMed2006

Observation of surface precipitation of arsenate on ferrihydrite.

X-ray diffraction and Raman spectroscopy were used in this study to characterize arsenate phases in the arsenate-ferrihydrite sorption system. Evidence has been obtained for surface precipitation of ferric arsenate on synthetic ferrihydrite at acidic pH (3-5) underthe following experimental conditions: sorption density of As/Fe approximately 0.125-0.49 and arsenic equilibrium concentration of <0.02-440 mg/L. Surface precipitation occurred under apparently undersaturated (in the bulk solution phase) conditions, and probably involved initial uptake of arsenate by surface complexation followed by transition to ferric arsenate formation on the surface as indicated by XRD analysis. At basic pH (i.e., pH 8), however, no ferric arsenate was observed in arsenate-ferrihydrite samples at a sorption density of As/Fe approximately 0.125-0.30 and an arsenic equilibrium concentration of 2.0-1100 mg/ L. At pH 8, arsenate is sorbed on ferrihydrite predominantly via surface adsorption, and the XRD patterns resemble basically that of ferrihydrite.

Adsorption↗
PubMed2003

Arsenate transport and reduction in the hyper-tolerant fungus Aspergillus sp. P37.

Aspergillus sp. P37 is able to grow at arsenate concentrations of 0.2 M--more than 20-fold higher than that withstood by reference microorganisms such Escherichia coli, Saccharomyces cerevisiae and Aspergillus nidulans. This paper examines the transport of arsenate and phosphate and the reduction of arsenate in Aspergillus sp. P37. These properties were compared with the corresponding properties of the archetype strain Aspergillus nidulans TS1. Both uptake and efflux of arsenate were inhibited by carbonyl cyanide-p-trifluoromethoxyphenylhydrazone, suggesting that the transport system(s) is(are) membrane-potential dependent. As uptake of arsenate and phosphate are higher in Aspergillus sp. P37 than in A. nidulans, the increase in arsenate resistance cannot be accounted for by a change in uptake. Cells of both strains loaded with arsenic slowly released the oxyanion. Speciation of the arsenic in the medium showed an enhanced level of arsenate reduction in Aspergillus sp. P37. These data suggest that increased arsenate reduction is at least in part responsible for the hyper-tolerant phenotype of this fungus.

Arsenates↗