Phylogenetic analysis and arsenate reduction effect of the arsenic-reducing bacteria enriched from contaminated soils at an abandoned smelter site

Microbial reduction of As(V)(i.e.,arsenate)plays an important role in arsenic(As)mobilization in aqueous environment.In this study,we investigated As(V)reduction characteristics of the bacteria enriched from the arsenic-contaminated soil at an abandoned smelter site.It was found that As(V)was completely reduced to As(III)(i.e.,arsenite)in 21 h.After 3-d incubation,a yellow solid was precipitated and the concentration of As(III)decreased sharply.After 150 h incubation,ca.65%of soluble arsenic was removed fro...     

Bacterial reduction and release of adsorbed arsenate on Fe(Ⅲ)-, Al- and coprecipitated Fe(Ⅲ)/Al-hydroxides

Mobilization of arsenic under anaerobic conditions is of great concern in arsenic contaminated soils and sediments. Bacterial reduction of As(V) and Fe(Ⅲ) influences the cycling and partitioning of arsenic between solid and aqueous phase. We investigated the impact of bacterially mediated reductions of Fe(Ⅲ)/Al hydroxides-bound arsenic(V) and iron(Ⅲ) oxides on arsenic release. Our results suggested that As(V) reduction occurred prior to Fe(Ⅲ) reduction, and Fe(Ⅲ) reduction did not enhance the release of arsenic. Instead, Fe(Ⅲ) hydroxides retained their dissolved concentrations during the experimental process, even though the new iron mineral-magnetite formed. In contrast, the release of reduced As(Ⅲ) was promoted greatly when aluminum hydroxides was incorporated. Thus, the substitution of aluminum hydroxides may be responsible for the release of arsenic in the contaminated soils and sediments, since aluminum substitution of Fe(Ⅲ) hydroxides universally occurs under natural conditions.     

Arsenic species analysis in porewaters and sediments using hydride generation atomic fluorescence spectrometry

It was observed that the atomic fluorescence emission due to signal during the determination of As（Ⅲ） in the mixture of As（Ⅲ） and As（V） could has a 10% to 40% of fluorescence emission As（V）. Besides, interferes from heavy metals such as Pb（Ⅱ）, Cu（Ⅱ） can cause severe increase of the signals as compared to the insignificant effects caused by Cd（Ⅱ）, Zn（Ⅱ）, Mn（Ⅱ） and Fe（Ⅲ）. On the basis of further studies, the masking agent of 8-hydroxyquinoline was used as an efficient agent to eliminate interference of As（V） emission and the heavy metal of Cu^2＋ and Pb^2＋ in the measurements of arsenic species, After a series standard additions and CRM researches, a sensitive and interference-free analytical procedure was developed for the speciation of arsenic in samples of porewaters and sediments in Poyang Lake, China.     

Anaerobic oxidation of arsenite by bioreduced nontronite

The redox state of arsenic controls its toxicity and mobility in the subsurface environment. Understanding the redox reactions of arsenic is particularly important for addressing its environmental behavior. Clay minerals are commonly found in soils and sediments, which are an important host for arsenic. However, limited information is known about the redox reactions between arsenic and structural Fe in clay minerals. In this study, the redox reactions between As(III)/As(V) and structural Fe in nontronite NAu-2 were investigated in anaerobic batch experiments. No oxidation of As(III) was observed by the native Fe(III)-NAu-2. Interestingly, anaerobic oxidation of As(III) to As(V) occurred after Fe(III)-NAu-2 was bioreduced. Furthermore, anaerobic oxidization of As(III) by bioreduced NAu-2 was significantly promoted by increasing Fe(III)-NAu-2 reduction extent and initial As(III) concentrations. Bioreduction of Fe(III)-NAu-2 generated reactive Fe(III)-O-Fe(II) moieties at clay mineral edge sites. Anaerobic oxidation of As(III) was attributed to the strong oxidation activity of the structural Fe(III) within the Fe(III)-O-Fe(II) moieties. Our results provide a potential explanation for the presence of As(V) in the anaerobic subsurface environment. Our findings also highlight that clay minerals can play an important role in controlling the redox state of arsenic in the natural environment.     

Arsenic removal from groundwater by acclimated sludge under autohydrogenotrophic conditions

Arsenic in the environment is attracting increasing attention due to its chronic health effects. Although arsenite(As(III)) is generally more mobile and more toxic than arsenate(As(V)), reducing As(V) to As(III) may still be a means for decontamination, because As(III) can be removed from solution by precipitation with sulfide or by adsorption or complexation with other metal sulfides. The performance of As(V) bio-reduction under autohydrogenotrophic conditions was investigated with batch experiments. The results showed that As(V) reduction was a biochemical process while both acclimated sludge and hydrogen were essential. Most of the reduced arsenic remained in a soluble form, although 20% was removed with no addition of sulfate, while 82% was removed when sulfate was reduced to sulfide. The results demonstrated that the reduced arsenic was re-sequestered in the precipitates, probably as arsenic sulfides. Kinetic analysis showed that pseudo first-order kinetics described the bio-reduction process better than pseudo second-order. In particular, the influences of pH and temperature on As(V) reduction by acclimated sludge under autohydrogenotrophic conditions and total soluble As removal were examined. The reduction process was highly sensitive to both pH and temperature, with the optimum ranges of pH 6.5–7.0 and 30–40°C respectively. Furthermore, Arrhenius modeling results for the temperature effect indicated that the As(V) reduction trend was systematic. Total soluble As removal was consistent with the trend of As(V) reduction.     

Arsenic biotransformation in industrial wastewater treatment residue: Effect of co-existing Shewanella sp. ANA-3 and MR-1

Shewanella sp. ANA-3 with the respiratory arsenate reductase (ArrAB) and MR-1 with ferric reduction ability always coexist in the presence of high arsenic (As)-containing waste residue. However, their synergistic impacts on As transformation and mobility remain unclear. To identify which bacterium, ANA-3 or MR-1, dominates As mobility in the coexisting environment, we explored the As biotransformation in the industrial waste residue in the presence of Shewanella sp. ANA-3 and MR-1. The incubation results show that As(III) was the main soluble species, and strain ANA-3 dominated As mobilization. The impact of ANA-3 was weakened by MR-1, probably due to the survival competition between these two bacteria. The results of micro X-ray fluorescence and X-ray photoelectron spectroscopy analyses further reveal the pathway for ANA-3 to enhance As mobility. Strain ANA-3 almost reduced 100% surface-bound Fe(III), and consequently led to As(V) release. The dissolved As(V) was then reduced to As(III) by ANA-3. The results of this study help to understand the fate of arsenic in the subsurface and highlight the importance of the safe disposal of high As-containing industrial waste.     

Arsenic methylation by an arsenite S-adenosylmethionine methyltransferase from Spirulina platensis

Arsenic-contaminated water is a serious hazard for human health. Plankton plays a critical role in the fate and toxicity of arsenic in water by accumulation and biotransformation.Spirulina platensis(S. platensis), a typical plankton, is often used as a supplement or feed for pharmacy and aquiculture, and may introduce arsenic into the food chain, resulting in a risk to human health. However, there are few studies about how S. platensis biotransforms arsenic. In this study, we investigated arsenic biotransformation by S. platensis. When exposed to arsenite(As(Ⅲ)), S. platensis accumulated arsenic up to 4.1 mg/kg dry weight.After exposure to As(Ⅲ), arsenate(As(Ⅴ)) was the predominant species making up 64% to86% of the total arsenic. Monomethylarsenate(MMA(Ⅴ)) and dimethylarsenate(DMA(Ⅴ))were also detected. An arsenite S-adenosylmethionine methyltransferase from S. platensis(Sp Ars M) was identified and characterized. Sp Ars M showed low identity with other reported Ars M enzymes. The Escherichia coli AW3110 bearing Spars M gene resulted in As(Ⅲ) methylation and conferring resistance to As(Ⅲ). The in vitro assay showed that Sp Ars M exhibited As(Ⅲ) methylation activity. DMA(Ⅴ) and a small amount of MMA(Ⅴ) were detected in the reaction system within 0.5 hr. A truncated Sp Ars M derivative lacking the last 34 residues still had the ability to methylate As(Ⅲ). The three single mutants of Sp Ars M(C59S, C186 S, and C238S) abolished the capability of As(Ⅲ) methylation, suggesting the three cysteine residues are involved in catalysis. We propose that Sp Ars M is responsible for As methylation and detoxification of As(Ⅲ) and may contribute to As biogeochemistry.     

Review on heterogeneous oxidation and adsorption for arsenic removal from drinking water

The long term exposure of arsenic via drinking water has resulted in wide occurrence of arsenisim globally, and the oxidation of the non-ionic arsenite (As(III)) to negatively-charged arsenate (As(V)) is of crucial importance for the promising removal of arsenic. The chemical oxidants of ozone, chlorine, chlorine dioxide, and potassium permanganate may achieve this goal; however, their application in developing countries is sometimes restricted by the complicate operation and high cost. This review paper focuses on the heterogeneous oxidation of As(III) by solid oxidants such as manganese oxide, and the adsorption of As(V) accordingly. Manganese oxide may be prepared by both chemical and biological methods to achieve good oxidation performance towards As(III). Additionally, manganese oxide may be combined with other metal oxides, e.g., iron oxide, to improve the adsorption capability towards As(V). Furthermore, manganese oxide may be coated onto porous materials of metal organic frameworks to develop novel adsorbents for arsenic removal. To achieve the application in engineering works, the adsorbents granulation may be achieved by drying and calcination, agglomeration, and the active components may also be in situ coated onto the porous materials to maintain the oxidation and adsorption activities as much as possible. The novel adsorbents with heterogeneous oxidation and adsorption capability may be carefully designed for the removal of arsenic in household purifiers, community-level decentralized small systems, and the large-scale drinking water treatment plants (DWTPs). This review provides insight into the fundamental studies on novel adsorbents, the development of innovative technologies, and the demonstration engineering works involved in the heterogeneous oxidation and adsorption, and may be practically valuable for the arsenic pollution control globally.     

Shewanella oneidensis MR-1对不同价态砷的生物转化与甲基化

在实验室纯培养条件下,通过分别向培养基中投加As(Ⅲ)和As(Ⅴ),探讨Shewanella oneidensis MR-1对不同价态砷的生物转化与甲基化作用.结果表明,S.oneidensis MR-1介导下不同价态砷的生物转化与微生物对砷的耐受和代谢特性有着密切联系,在投加As(Ⅲ)时,由于细胞自身的解毒作用会产生少量的As(Ⅴ),同时在酶的作用下As(Ⅲ)与甲基供体结合生成甲基砷;而在投加As(Ⅴ)时,遵循Challenge机制,先产生一甲基砷后生成二甲基砷.此外,弱酸性环境比碱性更有利于甲基砷的产生;温度30℃时甲基砷的产生量较高,过低或过高的培养温度砷甲基化率下降.     

基于多采样点的南京市PM2.5中的水溶性砷分析

对南京市的18个采样点进行PM_(2.5)样品采集,并利用电感耦合等离子体质谱仪以及液相电感耦合等离子体质谱联用仪分别对样品中的总砷和4种水溶性砷进行测量,在此基础上研究PM_(2.5)中砷的形态及其时空分布特征.结果表明:南京市PM_(2.5)中的砷以无机砷为主,有机砷为辅.无机砷以三价砷(As(III))为主,五价砷(As(V))为辅,As(III)/As(V)的平均值为0.39±0.03.有机砷以二甲基胂酸(DMAs(V))为主,所有样品均未检出甲基胂酸(MMAs(V)).总砷(As_T)、As(III)、As(V)和DMAs(V)的年平均浓度分别为6.90、0.99、3.20和0.03 ng·m~(-3).PM_(2.5)中的砷浓度具有明显季节变化:总砷和As(V)最大浓度出现在冬季,As(III)最大浓度出现在夏季,DMAs(V)只在夏季出现.T检验表明:As(III)、总砷和DMAs(V)年平均浓度在城区和郊区之间存在显著差异.空间变异系数的计算结果表明DMAs(V)的空间变化最大,其空间变异系数为0.6.总砷和3种水溶性砷年平均浓度由大到小排列为:农村郊区城区.道路采样点和城市背景点的总砷年平均浓度比为0.92,说明城区交通源对PM_(2.5)中砷污染的贡献不明显.As(III)和As(V)的主要排放源可能为燃煤电厂和钢铁冶炼厂,而DMAs(V)可能主要来源于生物挥发产物的二次生成.     

Arsenic retention and transport behavior in the presence of typical anionic and nonionic surfactants

The massive production and wide use of surfactants have resulted in a large amount of surfactant residuals being discharged into the environment,which could have an impact on arsenic behavior.In the present study,the influence of the anionic surfactant sodium dodecyl benzene sulfonate(SDBS) and nonionic surfactant polyethylene glycol octylphenyl ether(Triton X-100) on arsenic behavior was investigated in batch and column tests.The presence of SDBS and Triton X-100 reduced arsenic retention onto ferrihydrite(FH),enhanced arsenic transport through FH coated sand(FH-sand) columns and promoted arsenic release from the FH surface.With coexisting surfactants in solution,the equilibrium adsorbed amount of arsenic on FH decreased by up to 29.7% and the adsorption rate decreased by up to 52.3%.Pre-coating with surfactants caused a decrease in the adsorbed amount and adsorption rate of arsenic by up to 15.1% and 58.3%,respectively.Because of the adsorption attenuation caused by surfactants,breakthrough of As(Ⅴ) and As(Ⅲ) with SDBS in columns packed with FH-sand was 23.8% and 14.3%faster than that in those without SDBS,respectively.In columns packed with SDBS-coated FH-sand,transport of arsenic was enhanced to a greater extent.Breakthrough of As(Ⅴ) and As(Ⅲ) was 52.4% and 43.8% faster and the cumulative retention amount was 44.5% and 57.3% less than that in pure FH-sand column systems,respectively.Mobilization of arsenic by surfactants increased with the increase of the initial adsorbed amount of arsenic.The cumulative release amount of As(Ⅴ) and As(Ⅲ) from the packed column reached 10.8% and 36.0%,respectively.     

磁性吸附材料CuFe2O4吸附砷的性能

根据Cu(Ⅱ)和Fe(Ⅲ)都对砷有较强的亲和性,制备了同时含有Cu(Ⅱ)和Fe(Ⅲ)的、可用磁分离方法进行分离回收的磁性吸附材料CuFe₂O₄,并对其进行了表征及吸附砷的性能研究.结果表明,该吸附剂对砷的吸附能力与溶液pH有关,在弱酸性及中性条件下,吸附砷的能力最强,而对As(V)的吸附能力比对As(Ⅲ)更强些,在平衡浓度为10μg/L时,其吸附容量可达10mg/g左右,可以很容易地将水中浓度为1～20mg/L的As(V)降到10μg/L以下.实验考察了几种无机阴离子对吸附砷的影响,表明较高浓度(砷浓度的20倍)的硫酸盐对As(Ⅲ)和As(V)的吸附均有一定影响,盐酸盐及磷酸盐则影响不明显;负载的As(V)可较容易地用0.1mol/L NaOH洗脱下来,使吸附剂再生,而As(Ⅲ)则难以洗脱,这与2种价态砷的吸附机理不同有关.     

天然菱铁矿改性及强化除砷研究

我国高砷地下水分布广泛,经济、高效地饮用水除砷技术受到广泛关注.静态批实验采用资源丰富、价格便宜的天然菱铁矿为主要原材料,考虑灼烧温度、时间及添加黏合剂等因素确定最优改性条件使除砷效果达到最佳.结果表明,在加铝量为10 mg.g-1、350℃下恒温灼烧90 min后造粒达到强度要求并除砷效果较优.25℃、固液比为0.5 g∶50 mL、As(Ⅲ)和As(Ⅴ)初始浓度为5 mg.L-1时,吸附后溶液中残留As浓度均<10μg.L-1.静态吸附批实验结果表明,25℃时,接触反应时间为12 h可达到吸附平衡,吸附过程较好地符合Lagergren假二级吸附速率方程;最优改性天然菱铁矿对砷的吸附规律可用Langmuir和Freundlich等温吸附模型很好地描述,As(Ⅲ)、As(Ⅴ)饱和吸附容量分别可以达到1 039、1 026μg.g-1.结合XRD、SEM等研究方法和比表面及孔结构分析初步探讨天然菱铁矿改性以及除砷的主要机制.分析表明,改性后天然菱铁矿比表面积大幅度增大,孔径减小,且在表面活化生成一层圆球状的含Fe(Ⅱ)和Fe(Ⅲ)的化合物.改性天然菱铁矿是一种值得进一步研究并实际应用的除砷材料.     

草酸盐介导下含As(V)黄钾铁矾的相转化过程与As(V)的再分配行为

黄钾铁矾能够通过吸附和共沉淀作用固定酸性矿山废水（AMD）中的重（类）金属（如砷）,降低其迁移性和生物可利用性.草酸盐广泛存在于天然水环境中,其具有的羧酸官能团能改变铁矿物的稳定性,进而影响吸持的重（类）金属的再分配行为.利用水热法合成含As（V）黄钾铁矾,探究其在不同草酸盐浓度与pH条件下的溶解、重结晶和共沉淀As（V）的行为.研究结果表明,草酸盐与含As（V）黄钾铁矾表面Fe（III）活性位点配位形成的可溶性强络合物是促进矿物溶解的第一步和关键;在pH 2.5时,含As（V）黄钾铁矾的溶解速率随草酸盐浓度增加而增加,伴随大量As（V）释放到溶液,反应过程中只有少量As（V）重新吸附到固相上,这是由于草酸盐与As（V）竞争矿物表面的同一活性位点;在pH 6.5条件下,草酸盐促进含As（V）黄钾铁矾的重结晶,经X射线衍射分析表明针铁矿和纤铁矿为主要产物,能有效地吸附释放的As（V）.研究结果有助于揭示在AMD环境下黄钾铁矾沉积物与含羧酸官能团有机酸共存时对As（V）的释放和固定机理,对AMD环境中As（V）污染控制有重要意义.     

Effect of ionic strength on adsorption of As(Ⅲ) and As(V) on variable charge soils

The study was to investigate the adsorption behavior of arsenite (As(III)) and arsenate (As(V)) on two variable charge soils, i.e., Haplic Acrisol and Rhodic Ferralsol at dierent ionic strengths and pH with batch methods. Results indicated that the amount of As(III) adsorbed by these two soils increased with increasing solution pH, whereas it decreased with increasing ionic strength under the acidic condition. This suggested that As(III) was mainly adsorbed on soil positive charge sites through electrostati...     

Arsenic release from microbial reduction of scorodite in the presence of electron shuttle in flooded soil

Scorodite (FeAsO₄·H₂O) is a common arsenic-bearing (As-bearing) iron mineral in nearsurface environments that could immobilize or store As in a bound state.In flooded soils,microbe induced Fe(Ⅲ) or As(Ⅴ) reduction can increase the mobility and bioavailability of As.Additionally,humic substances can act as electron shuttles to promote this process.The dynamics of As release and diversity of putative As(Ⅴ)-reducing bacteria during scorodite reduction have yet to be investigat...     

The potential risk assessment for different arsenic species in the aquatic environment

The different toxicity characteristics of arsenic species result in discrepant ecological risk. The predicted no-effect concentrations (PNECs) 43.65, 250.18, and 2.00 × 10³ μg/L were calculated for As(III), As(V), and dimethylarsinic acid in aqueous phase, respectively. With these PNECs, the ecological risk from arsenic species in Pearl River Delta in China and Kwabrafo stream in Ghana was evaluated. It was found that the risk from As(III) and As(V) in the samples from Pearl River Delta was low, while much high in Kwabrafo stream. This study implies that ecological risk of arsenic should be evaluated basing on its species.     

Bacterial community succession during the enrichment of chemolithoautotrophic arsenite oxidizing bacteria at high arsenic concentrations

To generate cost-effective technologies for the removal of arsenic from water, we developed an enrichment culture of chemolithoautotrophic arsenite oxidizing bacteria (CAOs) that could effectively oxidize widely ranging concentrations of As(III) to As(V). In addition, we attempted to elucidate the enrichment process and characterize the microbial composition of the enrichment culture. A CAOs enrichment culture capable of stably oxidizing As(III) to As(V) was successfully constructed through repeated batch cultivation for more than 700 days, during which time the initial As(III) concentrations were increased in a stepwise manner from 1 to 10-12 mmol/L. As(III) oxidation activity of the enrichment culture gradually improved, and 10-12 mmol/L As(III) was almost completely oxidized within four days. Terminal restriction fragment length polymorphism analysis showed that the dominant bacteria in the enrichment culture varied drastically during the enrichment process depending on the As(III) concentration. Isolation and characterization of bacteria in the enrichment culture revealed that the presence of multiple CAOs with various As(III) oxidation abilities enabled the culture to adapt to a wide range of As(III) concentrations. The CAOs enrichment culture constructed here may be useful for pretreatment of water from which arsenic is being removed.     

Removal of arsenate and arsenite from aqueous solution by waste cast iron

The removal of As(III) and As(V) from aqueous solution was investigated using waste cast iron, which is a byproduct of the iron casting process in foundries. Two types of waste cast iron were used in the experiment: grind precipitate dust (GPD) and cast iron shot (CIS). The X-ray diffraction analysis indicated the presence of Fe0 on GPD and CIS. Batch experiments were performed under different concentrations of As(III) and As(V) and at various initial pH levels. Results showed that waste cast iron was effective in the removal of arsenic. The adsorption isotherm study indicated that the Langmuir isotherm was better than the Freundlich isotherm at describing the experimental result. In the adsorption of both As(III) and As(V), the adsorption capacity of GPD was greater than CIS, mainly due to the fact that GPD had higher surface area and weight percent of Fe than CIS. Results also indicated the removal of As(III) and As(V) by GPD and CIS was influenced by the initial solution pH, generally decreasing with increasing pH from 3.0 to 10.5. In addition, both GPD and CIS were more effective at the removal of As(III) than As(V) under given experimental conditions. This study demonstrates that waste cast iron has potential as a reactive material to treat wastewater and groundwater containing arsenic.     

河水-地下水交互带内砷及金属的自然衰减过程

在简单介绍污染物自然衰减作用定义的基础上,重点分析了河水-地下水交互带内As和以矿山废水为来源的金属污染物的自然衰减行为:主要包括吸附作用,氧化还原作用,生物转化作用等。其中详细介绍了金属Fe、Al的氢氧化物/氧化物对As化合物和其他金属如Cd、Cu和Zn等的吸附作用;Ca2+、Fe2+、磷酸盐、重碳酸盐等阴阳离子和天然有机质对吸附作用的影响;金属微生物氧化还原作用以及微生物作用下As(V)与As(III)的相互转化过程。研究发现,阳离子可以增强金属的吸附作用,阴离子主要是参与竞争吸附;天然有机质对金属吸附过程的抑制作用阻碍金属的固定;交互带内氧化还原条件的变化可以引起一系列的氧化还原反应;微生物催化还原不利于As的自然衰减。最后指出目前河水-地下水交互带内金属污染物衰减过程研究存在的问题以及今后的发展方向。