Arsenic Volatilization Research Articles

Microbial Arsenic Methylation in Soil and Uptake and Metabolism of Methylated Arsenic in Plants: A Review.

Arsenic (As) poses a risk to the human health in excess exposure and microbes play an important role in the toxicity of As. Arsenic methylation mediated by microbes is a key driver of As toxicity in the environment and this paper reviews the role of microbial arsenic methylation and volatilization in the biogeochemical cycle of arsenic. In specific, little is presently known about the molecular mechanism and gene characterization of arsenic methylation. The uptake of methylated arsenic in plants is influenced by microbial arsenic methylation in soil, thus enhancing the volatilization of methylated arsenic is a potential mitigation point for arsenic mobility and toxicity in the environment. On the other hand, the potential risk of methylated arsenic on organisms is also discussed. And the directions for future research, theoretical reference for the control and remediation of arsenic methylation, are presented.

Arsenic volatilization in roxarsone-loaded digester: Insight into the main factors and arsM genes

The extensive use of roxarsone (ROX) in livestock and poultry husbandry causes the production of arylarsenic-contaminated manure/wastewater. Anaerobic digestion is a conventional technique for livestock manure/wastewater treatment. However, the factors affecting arsenic volatilization are poorly understood in arylarsenic-loaded anaerobic reactors. The main factors such as ROX loading, exposure time of anaerobic granular sludge (AGS) to ROX, and volatile fatty acid (VFA) levels, affecting arsenic volatilization were investigated in this study. The results indicated that ROX loading of 5.70 mg-As·L−1 triggered the maximum volatile arsenic yield of 6.78 ng-As·g−1-VSS·d−1, which was 4.95 times higher compared to the ROX-free assay. The conversion of ROX into inorganic arsenic was an essential step for arsenic volatilization. The 160-day and 270-day exposure of AGS to ROX caused 6-fold and 8-fold increase in volatile arsenic yield, respectively, compared to the 0-day exposure. With the longer-time exposure to ROX, AGS provided more available arsenic for volatilization and its arsenic-volatilizing capacity was significantly enhanced. VFA level was positively associated with arsenic volatilization (r = 0.832–0.950; p < 0.05). The abundance of arsM genes in AGS increased by 34.62–129.05% after the 100-day incubation, and was strongly correlated to arsenic volatilization. Based on these results, possible pathway of arsenic volatilization in ROX-loaded digesters were proposed. The result from this study improves a better understanding of the potential of arsenic volatilization in arylarsenic-contaminated environments.

Growth and Thermal Characterization of TbAs Nanoparticles Grown by Inert Gas Condensation

Incorporation of lanthanide arsenide (Ln-As) nanoparticles in III–V semiconductor films can alter the optoelectronic properties of the nanocomposite thin film. We report the growth and characterization of TbAs nanoparticles grown by inert gas condensation. TbAs nanoparticles were characterized by transmission electron microscopy and x-ray diffraction. Thermogravimetric analysis of TbAs nanoparticles indicates arsenic volatilization occurred at approximately 240°C and formed Tb2O3 by 500°C. Using mass balance, the composition of the TbAs nanoparticle powder was calculated to be TbAs:As2O3 of 0.53:0.47. We speculate that, unlike bulk Ln-As, Ln-As nanoparticles may be thermally unstable at low temperatures.

Structural Destruction of As–Sb Solid Solution through a Selective Oxidation Process in the Presence of CaO and Its Effect on As Removal from the As–Sb Dust

As–Sb dust from metallurgical processes causes serious environmental issues due to the presence of the toxic element As. In this study, a facile method for removing As through the destruction of the As–Sb solid solution structure from the dust using CaO under an oxidizing atmosphere was processed. The effects of the variables, including the amount of CaO added, roasting temperature and time, and oxygen partial pressure, on the volatilization of As and Sb were investigated. Under an oxidizing atmosphere in the presence of CaO, the formation of the vitreous material (As–Sb–O) was hindered through the transformation of Sb2O3 and (As, Sb)2O3 in the untreated dust into Sb2O4, Sb2O5, Sb6O13, and Ca2Sb2O7, and the volatilization of arsenic was promoted, as a result. The volatilization attained for As was 91.53% whereas that for Sb was only 4.30% under the following optimum conditions: 5 mass % CaO, a roasting temperature of 550 °C, an O2 partial pressure of 21 vol % (air), and a roasting time of 80 min.

Arsenic Bio-volatilization by Engineered Yeast Promotes Rice Growth and Reduces Arsenic Accumulation in Grains

Arsenic is listed as the most extensive environmental carcinogens. The present report demonstrated that yeast expressing WaarsM gene encoding arsenic methyltransferase from soil fungus Westerdykella aurantiaca removes arsenic from contaminated soil. We investigated the potential use of yeast as a plant growth-promoting agent to stimulate rice plant growth. The genetically engineered (GE) Saccharomyces cerevisiae showed high arsenic methylation and volatilization activity under arsenic stress. Rice seeds bio-primed with GE yeast showed higher seedling vigor index compared to untreated control. Yeast also promotes the growth of rice plants in control condition while GE yeast significantly (P < 0.05) increased shoot length, ca 29%, root length, ca 47% and panicle length, ca 38%, of plants grown in arsenic-contaminated soil. The application of yeast significantly increases the photosynthetic pigments of rice plants in the control condition while in the presence of arsenic; the photosynthetic pigments were increased in plants inoculated with GE yeast only. Plants inoculated with GE yeast, grown in soil irrigated with arsenic-containing water accumulates about 37%, 36% and 28% lower arsenic in the root, shoot and grains, respectively, compared to non-inoculated plants. Thus, volatilization of arsenic from contaminated soil is possible with GE yeast and could be the instrumental agent for reducing arsenic content from the soil and agricultural products.

Arsenic volatilization in flooded paddy soil by the addition of Fe-Mn-modified biochar composites

We investigated the potential role of Fe-Mn-modified biochar composites (FMBCs) in the volatilization of toxic arsenic (As) in flooded paddy soil, by considering As fractionation, enzyme activities, and bacterial abundance. The results indicated that the addition of FMBCs reduced As volatilization from polluted soil, and this effect was more pronounced at higher dosages. Two types of FMBCs (i.e., FMBC1 and FMBC2) were analyzed, and FMBC2 exhibited a superior performance to FMBC1. Maximum volatilization was achieved in the fourth week and was followed by stabilization. In addition, the majority of As in the soil corresponded to crystalline and residual phases. Furthermore, the addition of FMBCs had little influence on the activities of various enzymes, although FMBC1 significantly affected catalase and peroxidase activities (P < 0.05). Moreover, FMBC application changed the relative abundances of different bacteria, where the abundances of Firmicutes were reduced, but a 2 g dose of FMBCs in highly polluted soil increased the bacterial abundance. In addition, the As volatilization, As fractionation, and enzyme activities displayed some correlation, in that As volatilization was negatively correlated to the presence of residual As phases but positively correlated to amorphous and poorly crystalline hydrous oxides of Fe and Al. As such, As fractionation and an improvement in soil properties are important mechanisms for reducing As volatilization.

Arsenic volatilization by Aspergillus sp. and Penicillium sp. isolated from rice rhizosphere as a promising eco-safe tool for arsenic mitigation

Arsenic (As) is a non-threshold human carcinogenic. This element can be volatilized either by nature or anthropogenic sources. In the present study, the analytical performance of an As volatile species trapping system was evaluated to assess the As volatilization promoted by Penicillium sp. and Aspergillus sp., both isolated from rice rhizosphere, and Aspergillus niger sp. considered as a reference. The study was conducted for 60 days (sampling of volatile As species from 1st to 30th day and from 31st to 60th day). The efficiency of As-volatilization was associated with the fungal growth. The highest As volatilization occurred from 31st to 60th day. Penicillium sp., Aspergillus sp. and A. niger were capable of producing 57.8, 46.4, and 5.2% of volatile arsenic species, respectively. The speciation analysis has shown trimethylarsine (TMAs) as the main volatilized As-form, followed by mono- and dimethylarsine (MMAs and DMAs). The results are following the “Challenger pathway”. Therefore, the tested fungi isolated from rice rhizosphere have shown promising properties concerning bio-volatilization with potential use for As-mitigation in paddy soils.

Removal of arsenic from a denitration catalyst by reduction using methanol as a carbon source

Reduction–volatilization of arsenic from a denitration catalyst obtained from a coal-fired power plant using a gaseous reducing agent was investigated to develop a dry arsenic removal process.

Volatilization of toxic elements from coal samples of Thar coal field, after burning at different temperature and their mobility from ash: Risk assessment

In present study, the volatilization of arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb) by the burning of coal samples in the electric furnace was evaluated. The coal samples were obtained from different blocks of newly developed Thar coal field, Pakistan. The replicate coal samples were heated/burned in an electric furnace at laboratory scale for three temperature intervals (200, 400 and 900 °C). The ash obtained after each temperature intervals were analyzed for selected toxic elements. The resulted data indicated that the total contents of As, Cd, and Pb in coal samples of block X and XI were found in the range of 16.8–18.5, 4.21–4.72, and 14.2–18.8 mg/kg, respectively. Whereas, 67.8–79.7%, 34.3–36.8% and 9.89–10.8% of As, Cd, and Pb, respectively, were volatized out after combustion of coal samples at 900 °C. The total contents of Hg in selected coal samples of block X and XI were observed in the range of 0.985–1.46 and 0.992–1.41 mg/kg, respectively. The contents of Hg volatilized out via burning in a furnace at 200 °C and 400 °C, were observed in the range of 32.0–36.5% and >91.0% of its total contents, respectively, whereas at 900 °C, it was not detected in ash. The partitioning and mobility of studied toxic elements in residue termed as (laboratory made ash) obtained after burning at 900 °C, was carried out by three-step sequential extraction scheme. The resulted data of present study will give a better knowledge about the quality of coal and its burning product, which may help to take measure to reduce the adverse effects on the environment in future.

Size dependent arsenic volatilization in ErAs nanoparticle powders

The thermal stability of ErAs nanoparticles and bulk-like powders, synthesized by pulsed laser ablation and direct reaction, respectively, is investigated up to 700 °C in N2. Thermogravimetric analysis and XRD are used to monitor the decomposition temperatures and crystalline compositions of the synthesized powders, respectively. Degradation of unagglomerated nanoparticle powders is observed at 350 °C accompanied by the crystallization of amorphous Er2O3. Mass balance analysis suggests that the mass loss occurs as a result of arsenic volatilization rather than congruent sublimation of ErAs. Conversely, micron-sized agglomerated particles grown by direct reaction show little evidence for degradation under similar thermal processing conditions. This significant decrease in ErAs stability compared to agglomerated powders suggests a size dependence on the degradation characteristics of ErAs.

Separation of arsenic and antimony from dust with high content of arsenic by a selective sulfidation roasting process using sulfur

The separation of arsenic and antimony from dust with high content of arsenic was conducted via a selective sulfidation roasting process. The factors such as roasting temperature, roasting time, sulfur content and nitrogen flow rate were investigated using XRD, EPMA and SEM–EDS. In a certain range, the sulfur addition has an active effect on the arsenic volatilization because the solid solution phase ((Sb,As)2O3) in the dust can be destroyed after the Sb component in it being vulcanized to Sb2S3 and this generated As2O3 continues to volatile. In addition, an amorphization reaction between As2O3 and Sb2O3 is hindered through the sulfidation of Sb2O3, which is also beneficial to increasing arsenic volatilization rate. The results show that volatilization rates of arsenic and antimony reach 95.36% and only 9.07%, respectively, under the optimum condition of roasting temperature of 350 °C, roasting time of 90 min, sulfur content of 22% and N2 flow rate of 70 mL/min. In addition, the antimony in the residues can be reclaimed through a reverberatory process.

Insights into the effect of chlorine on arsenic release during MSW incineration: An on-line analysis and kinetic study

The effect of chlorine on arsenic (As) release dynamics during municipal solid waste (MSW) incineration in a fluidized bed was studied on the basis of an on-line analysis system. This system can continuously and quantitatively measure the concentrations of trace elements in flue gas. Chlorine addition increases obviously the concentration of arsenic in flue gas, indicating a promoting effect of chlorine on arsenic release during MSW incineration. Based on the temporal concentration of arsenic in flue gas, the overall kinetic parameters of arsenic release during MSW incineration were calculated. A second-order kinetic law r(x) = 81.6e−66.9/RT (−1.05x2 − 0.01x + 1.03) was ascertained for arsenic release during MSW incineration without chlorine addition, and r(x) = 177.3e−65.3/RT (−0.68x2 − 0.43x + 1.08) for arsenic release with chlorine addition. Thermodynamic calculations were performed to predict the partitioning behavior of arsenic during MSW incineration. The addition of chlorine can not only compete with gaseous arsenic to react with mineral, but is also able to increase the volatilization of arsenic by forming volatile arsenic chlorides, thereby affecting the release kinetics of arsenic during MSW incineration.

Effect of nanomaterials on arsenic volatilization and extraction from flooded soils

Herein, we utilize sequential extraction and high-throughput sequencing to investigate the effects of nanomaterial additives on As volatilization from flooded soils. We reveal that maximum volatilization is achieved in the fourth week and is followed by stabilization. The extent of volatilization decreased in the order of control > nano-zerovalent iron >40-nm hydroxyapatite > nano-Fe3O4 > 20-nm hydroxyapatite > multilayer graphene oxide > high-quality graphene oxide. The most abundant forms of As in soil corresponded to As-Fe and Al oxides. In soil with low levels of As pollution, the contents of these species increased after treatment with graphene oxides but decreased after treatment with other nanomaterials, with an opposite trend observed for soil with high levels of As pollution. The addition of nanomaterials influenced the activity of soil enzymes, e.g., hydroxyapatites affected the activities of urease and alkaline phosphatase, whereas graphene oxides significantly impacted that of peroxidase (P < 0.05). The addition of nanomaterials (which can potentially inhibit microbial growth) affected As levels by influencing the amount of As volatilized from polluted soil. Moreover, As volatilization, enzyme activity, and As speciation were observed to be mutually correlated (e.g., volatilization was negatively correlated to peroxidase activity and the contents of amorphous crystalline hydrous oxides of As-Fe and Al).

Effect of Volatile and Ash Contents in Coal on the Volatilization of Arsenic during Isothermal Coal Combustion

The effects of the temperature, volatile content, and ash content on the volatilization kinetics of arsenic were discussed. Six Chinese coals were tested in an isothermal thermogravimetric reactor at 600–1300 °C. Sequential chemical extraction analysis was employed to know the speciation transformation of arsenic during coal combustion. Results show that the volatilization ratio of arsenic increases with the temperature, and most arsenic volatilizes between 700 and 1000 °C. The volatile content has a positive effect on the volatilization rate of arsenic in the initial stage of combustion. With the same level of ash content, high-volatile coals (>30%) own a larger volatilization rate of arsenic (0.55–0.6% s–1) than the low-volatile coals (<12%) (0.25% s–1). In contrast, coals with a higher ash content tend to obtain a lower volatilization rate of arsenic during the process. Despite the effect of volatile and ash contents on the volatilization rate of arsenic, the final volatilization ratio of arsenic large...

Arsenic loss during metallurgical processing of arsenical bronze

The chemical composition of ancient copper-based metal changes over time due to repetitive recycling and mixing of old metal. Prehistoric copper usually contains impurities from the copper ores themselves, and some have been used as evidence of anthropomorphically induced chemical change. Research into these changes has historically relied upon the assumption of element loss linearity, which is highly misleading and in fact varies with a multitude of factors. To illustrate the complexity of such losses for prehistoric alloys, we have selected arsenical bronze (Cu-As alloys) for study. The mass loss of several Cu-As-alloys under reducing atmosphere was measured by DTA/TGA. From our comparison of the experimental results to thermodynamic calculations and literature data, it was unclear whether weight losses were solely caused by the elemental loss of arsenic. However, a prolonged time temperature-cycling run demonstrated that mainly arsenic volatilizes; hence, the non-linear mass loss from the alloy can be directly attributed to arsenic.

Simultaneous volatilization characteristics of arsenic and sulfur during isothermal coal combustion

Six coals that with different rank and sulfur contents were chosen for the isothermal combustion experiments at 900°C and 1300°C. By changing the residence time, the volatilization ratio and rate of arsenic with time were obtained. Effects of residence time, temperature, coal type and sulfur content on arsenic volatilization characteristics were discussed. The emission concentration of SO2 was also obtained through online monitoring by flue gas analyzer. Furthermore, the curves of arsenic volatilization, SO2 emission and mass loss of coal were compared together to study the simultaneous volatilization characteristics of arsenic and sulfur. Results show that coals with higher sulfur content tend to have a larger proportion of sulfide bound arsenic, which could have a positive effect on arsenic volatilization. With the increase of residence time, the volatilization ratio of arsenic increases gradually with various volatilization rate. One volatilization peak of arsenic is observed for all the coals. The volatilization peak of arsenic moves forward with higher temperature and lower coal rank. The peak rate of arsenic increases with higher temperature while varies much in different coals. At 900°C, coals with lower coal rank tend to have a higher peak rate of arsenic, while at 1300°C, coals with larger proportion of sulfide bound arsenic tend to have a higher peak rate of arsenic. As for SO2, all the coals have one emission peak at 900°C while two emission peaks at 1300°C, which is similar to the mass loss characteristics of coals. The simultaneous releasing behavior of arsenic and sulfur is observed at 900°C due to the moderate mass loss of coal and at 1300°C due to the decomposition of As-bearing sulfides.

Distribution and Behavior of Arsenic During the Reducing-Matting Smelting Process

The distribution and behavior of arsenic during the reducing-matting smelting process were investigated with various values of the carbon addition ratio, arsenic content, CaO/SiO2 ratio, and Fe/SiO2 ratio. The carbon addition ratio significantly affected the arsenic distribution among the phases, and most arsenic could be retained in an iron-rich matte with a carbon addition ratio greater than 20%. An increasing Fe/SiO2 ratio favored the retention and stabilization of arsenic in the iron-rich matte, and an increase in the CaO/SiO2 ratio decreased the arsenic volatilization and improved arsenic stability in the iron-rich matte and slag. It may be concluded from this study that the reducing-matting smelting process could be optimized by increasing the carbon addition ratio, CaO/SiO2 ratio, and Fe/SiO2 ratio and by decreasing the arsenic content.

Separation of Arsenic from the Antimony-Bearing Dust through Selective Oxidation Using CuO

A pyrometallurgical process of selective oxidation roasting of the antimony-bearing dust using CuO is put forward, in which the antimony component is oxidized to Sb2O4 staying in the roasted residue, and arsenic is volatilized in the form of As2O3. The addition of CuO has an active effect on the arsenic volatilization, because structures of some complicated As-Sb phases in the dust are destroyed after the “Sb” component in them is oxidized to Sb2O4, and this part of arsenic might be transformed to As2O3, which continues to volatilize. However, the arsenic volatilization rate decreases with the CuO amount in a certain range, which is attributed to the greater formation of Cu3 (AsO4)2 and Cu3As. Under the conditions of roasting temperature of 673 K (400 °C), roasting time of 100 minutes, CuO amount of 34.54 mass pct, and N2 flow rate of 30 mL/min, 91.50 pct arsenic and only 8.63 pct antimony go into the smoke.

Arsenic accumulation and volatilization in a 260-day cultured upflow anaerobic sludge blanket (UASB) reactor

Roxarsone has been extensively used as an organoarsenic feed additive. Part of supplemented roxarsone was discharged into wastewater. UASB reactor has been widely applied to treat high concentration of organics wastewater. However, there was little report about the arsenic accumulation from organoarsenic biotransformation in an UASB reactor. In this study, the accumulation and volatilization of arsenic in a 260-day cultured UASB reactor spiked with 13.2mg/L roxarsone were investigated. In the anaerobic granular sludge (AGS), the total arsenic concentrations were 5276.90±366.12mg/kg AGS at the bottom of anaerobic sludge bed and 10,661.92±539.63mg/kg AGS at the top of anaerobic sludge bed. Nearly 50% arsenic in the AGS was extracted under acidic conditions, and the main species of the extracted arsenic was arsenite (As(III)). In the aqueous phases, roxarsone was rapidly transformed into 4-hydroxy-3-aminophenylarsonic acid (HAPA) and an unknown organoarsenic, which was further converted to inorganic arsenic and monomethylarsenate (MMA(V)), in which As(III) was also the main species. Volatile arsenic from the reactor spiked with roxarsone was released at a rate of 134.93±6.61ng/d. Based on the mass balance analysis of arsenic, 23.40% of the influent arsenic was accumulated in the AGS and 0.002% was released in the form of volatile arsenic. The results from this study indicated that the operation of anaerobic digestion reactor treating organoarsenic-contaminated wastewater and the disposal of the residual AGS should be well managed.

Anaerobic Disposal of Arsenic-Bearing Wastes Results in Low Microbially Mediated Arsenic Volatilization.

The removal of arsenic from drinking water sources produces arsenic-bearing wastes, which are disposed of in a variety of ways. Several disposal options involve anaerobic environments, including mixing arsenic waste with cow dung, landfills, anaerobic digesters, and pond sediments. Though poorly understood, the production of gaseous arsenic species in these environments can be a primary goal (cow dung mixing) or an unintended consequence (anaerobic digesters). Once formed, these gaseous arsenic species are readily diluted in the atmosphere. Arsenic volatilization can be mediated by the enzyme arsenite S-adenosylmethionine methyltransferase (ArsM) or through the enzymes involved in methanogenesis. In this study, methanogenic mesocosms with arsenic-bearing ferric iron waste from an electrocoagulation drinking water treatment system were used to evaluate the role of methanogenesis in arsenic volatilization using methanogen inhibitors. Arsenic volatilization was highest in methanogenic mesocosms, but represented <0.02% of the total arsenic added. 16S rRNA cDNA sequencing, qPCR of mcrA transcripts, and functional gene array-based analysis of arsM expression, revealed that arsenic volatilization correlated with methanogenic activity. Aqueous arsenic concentrations increased in all mesocosms, indicating that unintended contamination may result from disposal in anaerobic environments. This highlights that more research is needed before recommending anaerobic disposal intended to promote arsenic volatilization.