Arsenite Solution Research Articles

Hidden in plain sight: revisiting the synthesis, characterisation, degradation and the intricate relationship between Scheele’s green and Emerald green

Carl Wilhelm Scheele's notorious toxic pigment, commonly referred to as “Scheele's green” often resulted in a mixture of products with unknown chemical composition. Positive identification of the pigment has been limited to Raman spectroscopy and indirect analysis using FTIR and XRD methods. Despite these techniques, reported occurrences of the pigment in heritage samples are scarce, suggesting that Scheele’s green is rarely reported due to challenges in its characterisation rather than infrequent use. Regarding the degradation of Cu-As green pigments, common assumptions suggest dissociation in acidic pH conditions, generating mobile arsenic and copper ions, followed by oxidation to As(V), which can co-precipitate with Fe, Al, and Ca ions. This study reproduces the fabrication of Scheele's green using historical recipes, focusing on maintaining the pH of the arsenite solution at 9.3. The research explores its relationship with Emerald green, the challenges associated with their identification, and addresses common misconceptions about the degradation of such pigments. Maintaining the pH at 9.3 proved influential in obtaining a crystalline product with an intense Raman signal, aligning with the widely accepted spectra of Scheele’s green. However, Raman spectra from amorphous Cu-As samples consistently exhibited broad bands at 288 and 845 cm−1, prompting a proposed modification for a dual representation of the pigment: the “common” form with broad bands and the “uncommon” or crystalline form as reported in the literature. Demonstrating that the crystalline form shares nearly identical Raman and FTIR spectra implies an identical chemical composition to Trippkeite. Evidence presented highlights that Cu-As based pigments contain free copper, arsenite and arsenate ions prone to migration, challenging commonly described degradation pathways. The hypothesis presented here, that Emerald green synthesis may inadvertently yield small amounts of Scheele’s green urges caution in pigment identification using Raman spectroscopy. Additionally, the study reveals, for the first time, the occurrence of Scheele’s green in a book, with particles exhibiting a spherulite form, challenging identification of Emerald green solely based on morphology.

H16 Arsenic to biologics: psoriasis treatment through the ages

Abstract In the 19th century when arsenic was the recommended treatment for psoriasis, little consideration was given to the toxic side-effects of the potent carcinogen. Thomas Girdlestone, an English physician, is said to have been the first to advocate for the use of arsenic to treat psoriasis. Girdlestone prescribed Fowler’s solution, a solution of potassium arsenite 1%. In 1876, Alexander John Balmanno Squire inadvertently discovered dithranol, a known treatment for ringworm, to be efficacious in treating psoriasis. However, it was Eugen Galewsky, in 1916, who then went on to synthesize anthralin, a synthetic form of dithranol, to target psoriasis. A key historical figure was William H. Geockerman, an American dermatologist, who developed Goekerman therapy—a regimen that combined the use of coal tar and ultraviolet (UV) light to treat moderate-to-severe plaque psoriasis. In 1953, John Ingram, an English dermatologist, discovered that the beneficial effects of dithranol paste could be enhanced by adding it to coal tar and UV light—later coined the ‘Ingram regimen’. Philip Showalter Hench, Edward Calvin Kendall and Tadeus Reichstein received the Nobel Prize in Medicine and Physiology for the development of cortisone; it proved to be useful in topically treating many skin diseases, but it had a limited effect on psoriasis. The production of synthetic corticosteroids soon followed, which, conversely, proved to be successful in treating psoriasis. However, the daunting side-effects of corticosteroids limited their long-term use. In 1951, a patient with rheumatoid arthritis showed dramatic improvement in their psoriasis when treated with aminopterin, as recorded by Richard Gubner, a New York cardiologist. PUVA was developed in the 1970s—a photochemotherapy for psoriasis that combined psoralen with UVA radiation to clear skin lesions. Interestingly, in 1500 Bc, the ancient Egyptians were known to use a combination of psoralen and sunlight to treat vitiligo. Furthermore, in the 1980s, researchers noted complete clearance of psoriasis in a patient with osteoporosis who was prescribed an oral form of vitamin D. This chance observation then led to the development of topical vitamin D analogues for the treatment of psoriasis that work by encouraging normal skin growth and slowing down overproduction of skin cells. Finally, in 2003, the first biologic treatments were approved for psoriasis by the US Food and Drug Administration—a significantly safer and more efficacious alternative to the controversial arsenic treatments that were used over 200 years ago.

Regulation of arsenite toxicity in lettuce by pyrite and glutamic acid and the related mechanism

Compared with the effect of a single substance on arsenic plant toxicity, the effect of coexisting pyrite and natural organic matter can better reflect actual environmental conditions. In this study, the interaction between pyrite and glutamic acid in arsenite solution was explored, the influence of pyrite and glutamic acid on arsenite plant toxicity was evaluated, and the metabolic regulation mechanism of pyrite and glutamic acid on the arsenite phytotoxic effect was clarified by metabolomics analysis. Combined pyrite and glutamic acid treatment fixed more arsenic by forming chemical bonds such as AsS, AsO, and As-O-OH in culture solution and reduced inorganic arsenic levels in plants. Compared with glutamic acid alone and pyrite alone, the combined treatment reduced the inorganic arsenic concentration in plants by 4.7 % and 40.0 %, respectively. The combined treatment limited plant ROS accumulation and maintained the leaf chlorophyll content by increasing SOD synthesis. Compared with the effect of As(III) alone, the chlorophyll content increased by 15.1–21.0 % on average under the combined treatment. The combined treatment promoted the absorption of Ca, Cu, Fe, Mo and Zn in lettuce, enhanced plant adaptation to As(III) and significantly improved plant nutritional quality. Compared with glutamic acid alone, the combined treatment increased the VC, fiber and protein contents by 128.9 %, 202.8 % and 36.7 %, respectively. Metabolomics analysis indicated that in the combined treatment group, the upregulation of tyrosine, pyruvate and N metabolism increased the plant chlorophyll content. The upregulation of S metabolism increases VC synthesis in plants and inhibits ROS accumulation, thus maintaining normal plant growth and development. The upregulation of glutathione and glycine metabolism enhances plant stress resistance. This study will provide a new way to scientifically and rationally evaluate the ecological risk of arsenic and regulate its toxicity.

Analisis Tingkat Pencemaran Air Sungai Berdasarkan Kadar Fluorida Di Kota Mataram Menggunakan Metode Spektrofotometri UV-Vis

River water pollution levels can be analysed based on fluoride levels. Excessive fluoride levels will cause fluorosis of the bones. While fluoride deficiency will cause brittleness of teeth and thinning of bones. The purpose of this study was to determine the level of river water pollution based on fluoride levels in Mataram City. Fluoride levels were tested by adding a solution of zirconyl alizarin as a reagent and a solution of Na arsenite, which was then analysed by UV-Vis spectrophotometry with a wavelength of 535 nm. The results showed that the fluoride levels in the 7 tested samples met the fluoride quality standards. The highest fluoride content of river water in Mataram city is 1.046 mg/L, while the lowest is 0.213 mg/L. From this study it can be concluded that based from 7 points location water river sample in Mataram City are not polluted by fluoride.

Determination of Arsenic Uptake Potential in An Edible Plant Species (Trigonellna foenum- granecum) and Assessment of Human Health Risk

Arsenic is a carcinogenic and toxic element that possesses a high health risk from its presence in crops, water, and soil. The present study has been conducted by fenugreek (Trigonella foenum-granecum) seeds which is a very common spice used for cooking, especially in India. An equal number of seeds have been germinated in laboratory conditions. Three concentrations e.g. 1, 2, and, 3 mg/L of arsenite (As+3) and arsenate (As+5) salt solutions were used throughout the experiments for the treatment of plants. After 10 days of germination, the concentration of the arsenic accumulated into the plant edible parts was estimated and health risk was assessed. Effects of arsenic concentration were observed through estimating the total chlorophyll (a, b, c), carotenoid content, and taking the fresh weight and dry weight of both the control and treatment plants. The results of the biochemical analysis revealed that chlorophyll and carotenoid contents were decreased than that of control plants. Moreover, fresh weight and dry weight results also showed lower values in treatments than in controls. The bioaccumulation factor results demonstrated that an increased level of soil arsenic doesn’t certainly result in high arsenic uptake by the Fenugreek plants. From the concentration estimated in the plant body, the health risk was assessed in adults and children and found that both adults and children having a potential health risk upon consumption of fenugreek. Moreover, Incremental Life Time Cancer Risk was found high (< 10-4) which indicates the presence of potential cancer risk. Hence, it is possible to conclude from the present study that fenugreek can bio-accumulate arsenic and it may be used as an indicator plant for arsenic-contaminated areas.

Biomimetic System for the Application of Nanomaterials in Fluid Purification: Removal of Arsenic with Ferrihydrite.

The use of nanomaterials has transformed fields such as medicine and electronics. However, aggregation of nanomaterials in aqueous solutions, difficult recovery of spent nano-adsorbents from reactors, and a tremendous pressure loss caused by nano-adsorbents in adsorption columns have prevented the wide-scale use of nano-adsorbents in industrial applications for water purification. An over-reliance on traditional adsorption media for fluid purification practices has slowed innovation in this field. This study serves as a proof of concept for a new approach in utilizing nano-adsorbents in water treatment. A system based on the concept of renal dialysis was used to treat a solution of arsenite using two-line ferrihydrite (Fh) under environmental conditions. The performance was compared to traditional batch studies, and environmental variables pH and Eh were monitored. The system removed 67 and 91% of arsenite at 1.22 and 2.61 g/L Fh loadings, respectively, in comparison to batch experiments that removed 82 and 94% for similar loadings. Operational conditions and the physical design of the vessel limited the extent of removal that could be obtained with the system. Design advantages, shortcomings, and required improvements are discussed.

As(III) Removal from Aqueous Solution by Calcium Titanate Nanoparticles Prepared by the Sol Gel Method.

Arsenic (As) contamination of water is a serious problem in developing countries. In water streams, arsenic can be as As(V) and As(III), the latter being the most toxic species. In this work, an innovative adsorbent based on CaTiO3 nanoparticles (CTO) was prepared by the sol-gel technique for the removal of As(III) from aqueous solution. X-ray diffraction of the CTO nanoparticles powders confirmed the CTO phase. Transmission electron microscopy observations indicated an average particle size of 27 nm, while energy dispersive X-ray spectroscopy analysis showed the presence of Ca, Ti, and O in the expected stoichiometric amounts. The surface specific area measured by Brunauer, Emmett, and Teller (BET) isotherm was 43.9 m2/g, whereas the isoelectric point determined by Zeta Potential measurements was at pH 3.5. Batch adsorption experiments were used to study the effect of pH on the equilibrium adsorption of As(III), using an arsenite solution with 15 mg/L as initial concentration. The highest removal was achieved at pH 3, reaching an efficiency of up to 73%, determined by X-ray fluorescence from the residual As(III) in the solution. Time dependent adsorption experiments at different pHs exhibited a pseudo-second order kinetics with an equilibrium adsorption capacity of 11.12 mg/g at pH 3. Moreover, CTO nanoparticles were regenerated and evaluated for four cycles, decreasing their arsenic removal efficiency by 10% without affecting their chemical structure. X-ray photoelectron spectroscopy analysis of the CTO surface after removal experiments, showed that arsenic was present as As(III) and partially oxidized to As(V).

Histopathological Changes and Antioxidant Enzymes Status in Oxidative Stress Induction Using Sodium arsenite in Rats

Introduction: Arsenic toxicity has posed troublesome health concerns in the world and many of the toxic effects of arsenic are related to its effect on oxidative stress. The aim of the present study is to evaluate histopathological and antioxidant enzymes changes in oxidative stress status induced by sodium arsenite in rats. Materials and Methods: All experiments were carried out in male Wistar rats. Animal were divided into 2 groups of eight animals in each: Rats consumed distilled water (control group). Group 2: Rats consumed a solution of sodium arsenite (100 ppm) daily (arsenic group). At the end of day 28 arsenic exposure, the enzyme level in rat liver and kidney tissues was measured using the assay kits. The remaining liver, kidney, and heart tissue were fixed in 10% neutral-buffered formalin and used for histological observation. Results: The results showed a significant decrease in values of glutathione peroxidase (GPx), superoxide dismutase (SOD), total antioxidant capacity (TAC) and catalase (CAT) in serum and tissue in kidney and liver rat (P < 0.05). But, malondialdehyde (MDA) levels were increased significantly (P < 0.05). Arsenic caused severe degenerative changes in tubular cells and acute tubular necrosis, hepatocyte cell degeneration, severe hemorrhage, and infiltration and formation of Kupffer cells nodules, fragmentation, and degeneration of muscle fibers with pyknotic nuclei in heart tissue. Conclusions: The finding of the present study revealed that the administration of Sodium arsenite caused significant oxidative stress, decreased antioxidant enzymes activity and severe tissue damage.

Fluoride concentration in drinking water samples in Fiji

Objective:The main aim of this study was to determine the content of fluoride in drinking water from sources within the sampling areas for the National Oral Health Survey (NOHS) 2011 from the Central, Northern, Western and Eastern Divisions in the Fiji Islands. Method:Drinking water samples were collected from taps, a waterfall, wells, creeks, streams, springs, rivers, boreholes and rain water tanks in a diverse range of rural and urban areas across the Fiji Islands. A total of 223 areas were sampled between December 2014 and June 2015. Samples were analysed for fluoride using a colorimetric assay with the Zirconyl‐SPADNS Reagent. The samples were pre‐treated with sodium arsenite solution prior to analysis to eliminate interference from chlorine. Results:Measured fluoride concentrations ranged from 0.01 to 0.35 ppm, with a mean concentration across all samples of 0.03 + 0.04 ppm. No samples achieved the optimal level for caries prevention (0.7 ppm). The Western Division had the highest fluoride levels compared to the other Divisions. The highest single fluoride concentration was found in Valase. The drinking water for this rural area located in the Western Division is from a borehole. The lowest concentrations of fluoride were in reticulated water samples from rural areas in the Central Division, which were consistently less than those recorded in the Northern, Eastern and Western Divisions. Conclusion:All samples had fluoride concentrations below the optimum level required to prevent dental caries. Implications for public health:This research forms part of the objectives of the 2011 National Oral Health Survey in Fiji. At present, Fiji lacks water fluoridation and therefore a baseline of the fluoride content in drinking water supplies is essential before water fluoridation is implemented. The results from this study would be beneficial in designing caries‐preventive strategies through water fluoridation and for comparing those strategies with caries prevalence overtime.

Effect of pH, temperature, and oxygenation on arsenic phytofiltration by aquatic moss (Warnstorfia fluitans)

Phytofiltration of arsenic (As)-contaminated water could reduce As in irrigation and surface water. In a previous study, we found that the aquatic moss Warnstorfia fluitans efficiently removes arsenic from water contaminated with arsenate and arsenite. This work investigates how factors such as pH, temperature, and oxygenation influence As removal, since these factors vary in the environment. Plants were grown in a medium with 5 or 10 μM arsenite or arsenate and: 1) a pH of 2.5, 6.5, or 9.5; 2) a temperature of 12, 20, or 30 °C; and 3) oxygenation of <2 or 13 mg O2 L−1. Removal of As was monitored over 48–96 h, and the content and speciation of As were analysed in moss plants at the termination of the experiments. Results indicate that As removal was faster in arsenite than arsenate solutions. Arsenic removal from arsenite solution was the fastest, i.e., 80–90% within 2 h, at pH 6.5 and 9.5 and at 20 and 30 °C. At pH 2.5, plants were stressed and the net removal was low throughout the treatment period. Arsenic removal was more efficient at low than high oxygenation levels. Besides this, no As net efflux process was seen in the water system except after 48 h in arsenate-treated medium in high-temperature (30 °C) regimes. Regardless of As species added, usually only arsenite was found in the plants after treatment. Most internal As, i.e., 95% in the arsenate and 85% in the arsenite treatments, was firmly bound to the tissue. The study found that at 20 °C, neutral pH, and low oxygenation, this aquatic moss has great potential for As phytofiltration.

Coexisting arsenate and arsenite adsorption from water using porous pellet adsorbent: Optimization by response surface methodology

Mesoporous pellet adsorbent developed from mixing at an appropriate ratio of natural clay, iron oxide, iron powder, and rice bran was used to investigate the optimization process of batch adsorption parameters for treating aqueous solution coexisting with arsenate and arsenite. Central composite design under response surface methodology was applied for optimizing and observing both individual and interactive effects of four main influential adsorption factors such as contact time (24-72 h), initial solution pH (3-11), adsorbent dosage (0-20 g/L) and initial adsorbate concentration (0.25-4.25 mg/L). Analysis of variance suggested that experimental data were better fitted by the quadratic model with the values of regression coefficient and adjusted regression coefficient higher than 95%. The model accuracy was supported by the correlation plot of actual and predicted adsorption efficiency data and the residual plots. The Pareto analysis suggested that initial solution pH, initial adsorbate concentration, and adsorbent dosage had greater cumulative effects on the removal system by contributing the percentage effect of 47.69%, 37.07% and 14.26%, respectively. The optimum values of contact time, initial solution pH, adsorbent dosage and initial adsorbate concentration were 52 h, 7, 10 g/L and 0.5 mg/L, respectively. The adsorption efficiency of coexisting arsenate and arsenite solution onto the new developed adsorbent was over 99% under the optimized experimental condition.

A simple standard technique for labyrinthectomy in the rat: A methodical communication with a detailed description of the surgical process.

Aims Labyrinthectomized rats are suitable models to test consequences of vestibular lesion and are widely used to study neural plasticity. We describe a combined microsurgical-chemical technique that can be routinely performed with minimum damage. Methods Caudal leaflet of the parotis is elevated. The tendinous fascia covering the bulla is opened frontally from the sternomastoid muscle's tendon while sparing facial nerve branches. A 4mm diameter hole is drilled into the bulla's hind lower lateral wall to open the common (in rodents) mastoid-tympanic cavity. The cochlear crista (promontory) at the lower posterior part of its medial wall is identified as a bony prominence. A 1mm diameter hole is drilled into its lower part. The perilymphatic/endolymphatic fluids with tissue debris of the Corti organ are suctioned. Ethanol is injected into the hole. Finally, 10µL of sodium arsenite solution (50µM/mL) is pumped into the labyrinth and left in place for 15min. Simple closure in two layers (fascia and skin) is sufficient. Results and conclusion All rats had neurological symptoms specific for labyrinthectomy (muscle tone, body position, rotatory movements, nystagmus, central deafness). Otherwise, their behavior was unaffected, drinking and eating normally. After a few days, they learned to balance relying on visual and somatic stimuli (neuroplasticity).

Inorganic arsenic speciation in water samples by miniaturized solid phase microextraction using a new polystyrene polydimethyl siloxane polymer in micropipette tip of syringe system

The polymer, polystyrene polydimethyl siloxane was loaded into the micropipette tip of the syringe system as an adsorbent to developed miniaturized solid phase microextraction. Standard solutions of arsenate and arsenite were passed through the adsorbent loaded in micropipette tip to check the adsorption behaviors. It was observed that arsenate adsorbed on the polystyrene polydimethyl siloxane in the pH rang of 6–8, while arsenite was directly passed through the micropipette tip of syringe system. The adsorbed arsenate in micropipette tip of syringe system were eluted by 1.0M hydrochloric acid. The total inorganic arsenic contents were obtained by the addition of oxidizing agent potassium permanganate into the studied samples before passing to the micropipette tip of syringe system. Arsenite concentration in water samples were measured by subtracting arsenate from total inorganic arsenic concentration. Different characteristics which effect the determination of arsenate specie like amount of adsorbent, adsorption capacity, pH, pulled and pushed cycles for adsorption and desorption, volume of sample, eluent type and it volume were also studied in detail. Enrichment factor and detection limit of arsenate by desired method were 218 and 6.9ngL−1 respectively. The relative standard deviation was 4.1% (n=10, C=0.12µgL−1). Accuracy of the desired technique was confirmed by analysis of the CRMs (Lake Ontario Water TM-28.3 and Riverine Water NRCC-SLRS-4). Desired technique was significantly useful for determination of the total arsenic, arsenate, and arsenite contents in different natural water samples.

Determination of As by UV-photochemical generation of its volatile species with AAS detection

This work was focused on the development of an analytical method for determination of arsenic in liquid (aqueous solutions of arsenite) by UV-photochemical generation of its volatile compounds. The study contains the optimization, method characterisation and also a study of the influence of selected compounds on the signal measured. The method involves a combination of flow injection analysis, UV-photochemical generation of volatile compounds of arsenic in flow injection arrangement and atomic absorption spectrometry using an externally heated quartz tube atomizer. The attained absorbance was very low after the optimization. In the next step, the influence of selected compounds on UV-photochemical generation was investigated with the aim to find a suitable reaction modifier that would improve the sensitivity of arsenic determination. Bi(III) was found as the best reaction modifier not only for causing the increase of the signal of arsenic measured but also for its persisting effect. The activation with concentration of 10 mg dm−3 of Bi(III) increases the absorbance of arsenic approximately eleven times compared to signals without activation. Following method characteristics were achieved under the optimum experimental conditions: the limit of detection of 18 µg dm−3, the repeatability of 4.5 % expressed as % RSD at 200 µg dm−3, and linear dynamic range 60–500 µg dm−3 of arsenic.

Effective treatment of arsenic-bearing water by a layered double metal hydroxide: Iowaite

Iowaite with designed Mg/Fe ratios of 2.5, 3.0, 3.5, 4.0 and 5.0 was synthesized for treating both arsenate- and arsenite-spiked waters in this study. The experimental results show that there is a positive correlation between the molar ratio of Fe to Mg of synthetic iowaite and its arsenic uptake capacity. The dearsenication mechanisms were investigated based on the XRD, SEM and EDX analyses of solid samples before and after reaction with arsenic-bearing solutions. When the initial solution concentration of arsenic is not higher than 7500 μg/L, anion exchange between arsenate or arsenite in solution and chloride in the interlayer regions of iowaite is the primary mechanism for arsenic removal. However, at a very high initial arsenic concentration in solution (750 mg/L), the dissolution of iowaite and subsequent formation of new minerals, such as scorodite and karibibite, are responsible for the substantial removal of arsenic from water. Iowaite is superior to other types of layered double metal hydroxides (LDHs) such as hydrotalcite and hydrocalumite in terms of water dearsenication, and therefore promising for treatment of arsenic-rich waters, either naturally occurring waters or industrial wastewaters.

Highly Sensitive Detection of Arsenite Based on Its Affinity toward Ruthenium Nanoparticles Decorated on Glassy Carbon Electrode

Metallic ruthenium nanoparticles (Ru NPs) are formed on the glassy carbon electrode (GC) at electrodeposition potential of -0.75 V, as observed from X-ray photoelectron spectroscopy. Thus formed Ru NPs have the arsenite selective surface and conducting core that is ideally suited for designing a highly sensitive and reproducible response generating matrix for the arsenite detection at an ultratrace concentration in aqueous matrices. Contrary to this, arsenate ions sorb via chemical interactions on the ruthenium oxide (RuO2 and RuO3) NPs formed at -0.25 V, but not on the Ru NPs. For exploring a possibility of the quantification of arsenite in the ultratrace concentration range, the Ru NPs have been deposited on the GC by a potentiostatic pulse method of electrodeposition at optimized -0.75 V for 1000 s. Arsenite preconcentrates onto the Ru surface just by dipping the RuNPs/GC into the arsenite solution as it interacts chemically with Ru NPs. Electrochemical impedance spectroscopy of As(III) loaded RuNPs/GC shows a linear increase in the charge transfer resistance with an increase in As(III) conc. Using a differential pulse voltammetric technique, arsenite is oxidized to arsenate leading to its quantitative determination without any interference of Cu(2+) ions that are normally encountered in the water systems. Thus, the use of RuNPs/GC eliminates the need for a preconcentration step in stripping voltammetry, which requires optimization of the parameters like preconcentration potential, time, stirring, inferences, and so on. The RuNPs/GC based differential pulse voltammetric (DPV) technique can determine the concentration of arsenite in a few min with a detection limit of 0.1 ppb and 5.4% reproducibility. The sensitivity of 2.38 nA ppb(-1) obtained in the present work for As(III) quantification is considerably better than that reported in the literature, with a similar detection limit and mild conditions (pH = 2). The RuNPs/GC based DPV has been evaluated for its analytical performance using the lake water, ground water, and seawater samples spiked with known amounts of As(III).

Anabaena sp. mediated bio-oxidation of arsenite to arsenate in synthetic arsenic (III) solution: Process optimization by response surface methodology

Blue green algae Anabaena sp. was cultivated in synthetic arsenite solution to investigate its bio-oxidation potential for arsenic species. Response surface methodology (RSM) was employed based on a 3-level full factorial design considering four factors, viz. initial arsenic (III) concentration, algal dose, temperature and time. Bio-oxidation (%) of arsenic (III) was considered as response for the design. The study revealed that about 100% conversion of As (III) to As (V) was obtained for initial As (III) concentration of 2.5–7.5mg/L at 30°C for 72h of exposure using 3g/L of algal dose signifying a unique bio-oxidation potential of Anabaena sp. The dissolved CO2 (DCO2) and oxygen (DO) concentration in solution was monitored during the process and based on the data, a probable mechanism was proposed wherein algal cell acts like a catalytic membrane surface and expedites the bio-oxidation process. Bioaccumulation of arsenic, as well as, surface adsorption on algal cell was found considerably low.Lipid content of algal biomass grown in arsenite solution was found slightly lower than that of algae grown in synthetic media. Toxicity effects on algal cells due to arsenic exposure were evaluated in terms of comet assay and chlorophyll a content which indicated DNA damage to some extent along with very little decrease in chlorophyll a content. In summary, the present study explored the potential application of Anabaena sp. as an ecofriendly and sustainable option for detoxification of arsenic contaminated natural water with value-added product generation.

Anoxic, ethanolic, and cool – An improved method for thioarsenate preservation in iron-rich waters

Preservation of thioarsenates is challenging, especially in the presence of iron. Flash-freezing and cryo-storage, which was considered to be the best available technique, led to arsenic co-precipitation with iron upon thawing and transformation of thioarsenates to arsenite with further oxidation to arsenate. Even in the absence of iron, flash-freezing was found to be problematic when water samples were in disequilibrium. In arsenite solutions with excess sulfide increasing formation of thioarsenates was observed as an artifact upon storage. High ionic strengths were found to have a similar effect of pushing thioarsenate distribution towards equilibrium which renders it difficult to transfer a preservation method developed with synthetic thioarsenate solutions in the laboratory to any type of natural water chemistry. Addition of EDTA to complex excess iron also led to arsenite oxidation and artificial thioarsenate formation. An effective method that required minimal logistic effort was to use anoxic septum vials and store the samples at 4°C in 1% ethanol to reduce any remaining oxygen. This method preserved (thio)arsenic speciation in both synthetic and natural waters in the absence and presence of iron or excess sulfide up to one week. With the new method we were able to show that iron-rich mineral waters in Czech Republic had a much higher share of thioarsenates (up to 50%) than previously reported and that up to 26% trithioarsenate existed – a species which has not been described from iron-rich waters before.

Extraction of arsenic from arsenic-containing cobalt and nickel slag and preparation of arsenic-bearing compounds

The arsenic extraction from the arsenic-containing cobalt and nickel slag, which came from the purification process of zinc sulfate solution in a zinc smelting factory, was investigated. The alkaline leaching method was proposed according to the mode of occurrence of arsenic in the slag and its amphoteric characteristic. The leaching experiments were conducted in the alkaline aqueous medium, with bubbling of oxygen into the solution, and the optimal conditions for leaching arsenic were determined. The results showed that the extraction rate of arsenic was maximized at 99.10% under the optimal conditions of temperature 140 °C, NaOH concentration 150 g/L, oxygen partial pressure 0.5 MPa, and a liquid-to-solid ratio 5:1. Based on the solubilities of As2O5, ZnO and PbO in NaOH solution at 25 °C, a method for the separation of As in the form of sodium arsenate salt from the arsenic-rich leachate via cooling crystallization was established, and the reaction medium could be fully recycled. The crystallization rate was confirmed to reach 88.9% (calculated on the basis of Na3AsO4) upon a direct cooling of the hot leachate down to room temperature. On the basis of redox potentials, the sodium arsenate solution could be further reduced by sulfur dioxide (SO2) gas to arsenite, at a reduction yield of 92% under the suitable conditions. Arsenic trioxide with regular octahedron shape could be prepared successfully from the reduced solution, and further recycled to the purification process to purify the zinc sulfate solution. Also, sodium arsenite solution obtained after the reduction of arsenate could be directly used to purify the zinc sulfate solution. Therefore, the technical scheme of alkaline leaching with pressured oxygen, cooling crystallization, arsenate reduction by SO2 gas, and arsenic trioxide preparation, provides an attractive approach to realize the resource utilization of arsenic-containing cobalt and nickel slag.

Water‐soluble polymer and photocatalysis for arsenic removal

ABSTRACTIn this study, the photocatalytic oxidation of hazardous arsenite (As(III)) to arsenate (As(V)) and the sequential removal of arsenate from aqueous solution by liquid‐phase polymer‐based retention (LPR) were investigated. The photocatalytic oxidation of arsenite was performed using TiO2 (P25 Degussa, Germany) under UV‐A light. The optimal photocatalytic conditions to oxidize 10 mg L−1 of arsenite solution were achieved using a 0.5 g L−1 of catalyst at a pH value of 2. The As(III) oxidation reached 100% after 30 min of illumination with UV‐A light. A water‐soluble polymer containing quaternary ammonium groups, poly(3‐acrylamidopropyl)trimethylammonium chloride (P(ClAPTA)), was used as an extracting reagent in the LPR process. To obtain the optimized conditions, the removal experiments were performed at various polymer : As(V) molar ratios using 10 mg L−1 of arsenate solutions. After the oxidation of As(III) to As(V), the removal of arsenate by P(ClAPTA) was obtained in a 99% yield using a 20 : 1 polymer : As(V) molar ratio at a pH value of 9. The results demonstrate that the combination of these methods is highly useful for potential applications related to the treatment of wastewater contaminated with As(III). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40871.