砷浓度、形态及碳酸氢盐对蜈蚣草吸收砷的影响

大同盆地是典型的高砷地下水分布区。利用从地方性砷中毒严重病区山阴县采集的高砷地下水样品,用稀释培养法实验研究了外加砷源对地下水中微生物数量的影响;同时基于生物学可培养法和16S rDNA序列比对法,选取代表性高砷水样,研究了耐砷菌的种群特征。结果表明,外加砷源对地下水中微生物数量影响显著,高浓度砷会抑制大部分微生物生长,使微生物数量减少;低浓度砷对微生物生长具有一定促进作用。通过多次分离、纯化从3个不同砷含量地下水样中分离到多株砷抗性菌,经鉴定属于主要为Bacillus、Pseudomonas、Paenibacillus、Aeromonas、Enterobacter5个属。从RDP(Ribosomal Database Project)分析显示3个水样可培养微生物组成不同,都有生存能力强能够耐低浓度NaAsO₂的Bacillales,优势耐砷菌是γ-proteobacteria,其中Enterbacter具有耐高浓度NaAsO₂的能力。     

砷浓度、形态及碳酸氢盐对蜈蚣草吸收砷的影响

为了探讨超富集植物蜈蚣草在处理高砷地下水方面的可行性,研究了水培条件下砷的浓度、形态和碳酸氢盐(HCO-3)对超富集植物蜈蚣草吸收砷的影响。实验中使用了浓度为0.1～100mg·L-1的As(III)和As(V)溶液。HCO-3处理中,HCO-3浓度范围为0.5～20mmol·L-1,As(III)或As(V)的浓度为5mg·L-1。结果表明,在水培条件下,蜈蚣草具有明显的耐高砷特征。当介质砷含量高达100mg·L-1时,砷的去除率可达到80%,且对As(III)的吸收效率高于As(V)。植物体内砷形态研究表明,蜈蚣草体内2种形态砷的含量与外源砷形态有一定的关系,As(V)处理条件下,植物体中的As(V)比例较As(III)处理高。高浓度的HCO-3(20mmol·L-1)处理对蜈蚣草地上部分生物量没有明显影响,但是抑制了地下部分的生长,并且对砷的吸收表现出明显的抑制作用。     

Removal of arsenic by Acidothiobacillus ferrooxidans bacteria in bench scale fixed-bed bioreactor system

In the present study arsenic contaminated simulated water and groundwater was treated by the combination of biological oxidation of tri-valent arsenite [As (III)] to penta-valent arsenate [As (V)] in presence of Acidothiobacillus ferrooxidans bacteria and its removal by adsorptive filtration in a bioreactor system. This method includes the immobilisation of A.ferrooxidans on Granulated Activated Carbon (GAC) capable of oxidising ferrous [Fe (II)] to ferric [Fe (III)]. The Fe (III) significantly converts the As (III) to As (V) and ultimately removed greater than 95% by the bed of GAC, limestone, and sand. The significant influence of Fe (II) concentration (0.1–1.5?gL^?1), flowrate (0.06–0.18?Lh^?1), and initial As (III) concentration (100–1000?µgL^?1) on the arsenic removal efficiency was investigated. The simulated water sample containing the different concentration of As (III) and other ions was used in the study. The removal of other co-existing ions present in contaminated water was also investigated in column study. The concentration of arsenic was found to be <10?µgL^?1 which is below Maximum Contaminant Level (MCL) as per WHO in treated water. The results confirmed that the present system including adsorptive-filtration was successfully used for the treatment of contaminated water containing As (III) ions.     

Phytoextraction of Cr(VI) from soil using Portulaca oleracea

Cr(VI) represents an environmental challenge in both soil and water as it is soluble and bioavailable over a wide range of pH. In previous investigations, Portulaca oleracea (a plant local to the United Arab Emirates (UAE)) demonstrated particular ability for the phytoextraction of Cr(VI) from calcareous soil of the UAE. In this publication, the results of the evaluation of P. oleracea phytoextraction of Cr(VI) from UAE soil at higher concentrations are reported. P. oleracea was exposed to nine different concentrations of Cr(VI) in soil from 0 to 400 mg kg^?1. The uptake of Cr(VI) increased as its concentration in soil increased between 50 and 400 mg kg^?1, with the most efficient removal in the range from 150 to 200 mg kg^?1. The total chromium concentrations exceeded 4600 mg kg^?1 in roots and 1400 mg kg^?1 in stems, confirming the role of P. oleracea as an effective Cr(VI) accumulator. More than 95% of the accumulated Cr(VI) was reduced to the less toxic Cr(III) within the plant.     

Toxicity of tri- and penta-valent arsenic, alone and in combination, to the cladoceran Daphnia carinata: the influence of microbial transformation in natural waters

The acute toxicity of arsenic(III) and arsenic(V) alone and in combination to a cladoceran, Daphnia carinata, was studied in both cladoceran culture medium and natural water collected from a local suburban stream. As(III) was found to be more toxic than As(V) to Daphnia survival. The LC₅₀ values for As(III), As(V), and As(III) + As(V) were 0.554, 1.499, and 0.692 mg l⁻¹, respectively. Although various species of As, particularly As(III) and As(V) co-exist together in natural waters, the existing guidelines for water quality are based on individual As species. The results of this investigation suggest that As(III) and As(V) can interact either synergistically or additively resulting in an increase in the overall toxicity of the mixture compared to individual As species. Also, indigenous microorganisms in natural water may play a significant role in the transformation of As, thereby influencing the toxicity of As in receiving waters. This study clearly suggests that the joint action of As species should be considered in the development of water quality guidelines. To our knowledge this is the first study on the interactive effect of As(III) and As(V) to a cladoceran. Thus, this study suggests that these two species of As, when present together above 0.1 mg l⁻¹ concentration, are toxic to fresh water invertebrates; therefore, pollution with these compounds may adversely affect natural ecosystems.     

碳纳米管影响无机砷(As(III)和As(V))对大型蚤毒性的研究：特定砷形态的作用

作为一种新兴的纳米材料,羟基多壁碳纳米管(OH-MWCNTs)可能与其他污染物在水环境中共存,并进一步影响它们的毒性、输移和归趋。因此,评价碳纳米管存在下砷的毒性变化需要得到更多的关注。该试验探索了在不同pH值条件下,OH-MWCNTs诱导砷(As(III)和As(V))对水生生物大型蚤的毒性变化的潜在机制。发现了H₂AsO₃^-和H₂AsO₄^-是对大型蚤毒性最大的As(III)和As(V)。比较As(III)和As(V)的结果,发现pH值是影响砷毒性最重要的因素。此外,OH-MWCNTs影响砷对大型蚤毒性的结果表明,OH-MWCNTs的存在可以提高砷的毒性。通过吸附实验进一步研究了砷与OH-MWCNTs的相互作用。OH-MWCNTs 对As(V)吸附容量高于As(III)。总而言之, OH-MWCNTs对某些形态砷的吸附是解释砷毒性增强的可靠证据。
精选自Xinghao Wang, Ruijuan Qu, Ahmed A. Allam, Jamaan Ajarem, Zhongbo Wei, Zuoyao Wang. Impact of carbon nanotubes on the toxicity of inorganic arsenic [As(III) and As(V)] to Daphnia magna: the role of the certain arsenic species. Environmental Toxicology and Chemistry: Volume 35, Issue 7, pages 1852–1859, July 2016. DOI: 10.1002/etc.3340
详情请见http://onlinelibrary.wiley.com/doi/10.1002/etc.3340/full
     

As(V)-reduction to As(III) by arsenic-resistant Bacillus spp. bacterial strains isolated from low-contaminated sediments of the Oliveri-Tindari Lagoon,Italy

Five arsenic-resistant bacterial strains designated MT1, MT2, MT3, V1 and V2 were isolated from sediments of the Oliveri-Tindari Lagoon (Italy), which comprises six small lakes whose sediments contain low arsenic concentrations. Phylogenetic analysis of the 16S rRNA gene sequences assigned them to the genus Bacillus. Bacillus sp. strain MT3 showed higher tolerance to As(III) and As(V), as indicated by minimum inhibitory concentrations of 14 and 135 mmol^?1, respectively. Bacillus sp. strain V1 showed growth inhibition at 14 mmol^?1 in the presence of As(III) and at 68 mmol^?1 in the presence of As(V), whereas the arsenic resistance of Bacillus sp. strain MT1 was 10 and 27 mmol^?1 for As(III) and As(V), respectively. The strains Bacillus spp. MT2 and V2 showed low levels of As(III) and As(V) resistance, as it was unable to grow at concentrations>7 and 14 mmol^?1, respectively. The isolated arsenic-resistant Bacillus spp. strains were able to reduce As(V) to As(III), especially Bacillus spp. strain MT3. This study suggests that the isolated bacterial strains play a role in the arsenic biogeochemical cycle of arsenic-poor sediments in the Oliveri-Tindari Lagoon.     

Arsenic accumulation by ferns: a field survey in southern China

The objective of this study reported here was to characterize arsenic (As) accumulation by Pteris ferns by comparing 3 of the ferns of this genus with each other as well as with four non-Pteris ferns growing on seven sites in southern China with different As levels. A total of 112 samples, including 78 Pteris vittata, 13 P. cretica, 3 P. multifida and 18 ferns from other non-Pteris genera, with the soils in which they grew were collected for As and other elemental analyses. P. vittata was found to be the most dominant species and the most efficient As-accumulator, whereas P. multifida was the lowest As-accumulator among the Pteris ferns, with 4.54–3599, 28.7–757 and 11.2–341 mg kg^–1 As recorded in the fronds of P. vittata, P. cretica and P. multifida, respectively. Arsenic concentrations in non-Pteris ferns were generally much lower than those in Pteris ferns, with 0.81–1.32, 3.59, 10.7, 6.17–24.3 mg kg^–1 in the fronds of Blechumum orientale, Dicranopteris dichotoma, Pteridium aquilinum and Cyclosorus acuminatus, respectively. For P. vittata, the As bioaccumulation factor (ratio of As in fronds to that in soils) changed, whereas the As translocation factor (ratio of As in fronds to that in roots) remained unchanged among the different sites. The concentrations of Fe were very high in all of the collected fern sample, with the exception of B.␣orientale, with 207–6865, 637–3369, 375–1856, 1876, 493-6865 and 492 mg kg^–1 in the fronds of P. vittata, P. cretica, P. multifida, C. acuminatus, P. aquilinum and D. dichotoma, respectively. The association between Fe accumulation and As accumulation and tolerance in these ferns indicates the unique role of Fe in As-hyperaccumulation.     

Redox potential and uranium sorption onto sediments: kinetic and thermodynamic characteristics

ABSTRACT

The effects of the flooding and initial Eh of sediments on the sorption of uranium onto the sediments were analysed by flooding and static experiments. The changes in uranium species with Eh and kinetic and thermodynamic characteristics of the uranium sorption onto the sediments were investigated. The flooding experiment indicates that the initial Eh of the sediment gradually decreased with the increase in flooding time. Based on the redox potential in the flooding experiment, simulation results obtained using the geochemical simulation software PHREEQC show that the concentration of U (VI) decreased. In contrast, the concentrations of U (III), U (IV), and U (V) gradually increased. The pseudo-second-order kinetic model well fitted the experimental data, which shows that the sorption was mainly chemical sorption. The thermodynamic parameters suggest that the entropy and enthalpy under the used conditions were positive and that ΔG^θ was negative. A thermodynamic analysis shows that the sorption was endothermic and spontaneous. These results are useful for the understanding of the sorption mechanism and migration of uranium onto the sediment under different initial sediment redox potentials and provide a good theoretical foundation for radioactive pollution remediation.     

Differentiation in low molecular weight organic acids exudation into rhizosphere and their creation in Ulmus laevis Pall organs treated by As – pot experiment

Two-year old Ulmus laevis Pall (U. laevis) seedlings were cultivated in a three-month hydroponic experiment with inorganic (aresenite – As(III) and arsenate – As(V)) and organic (dimethylarsenic acid – DMA(V)) arsenic forms, at 0.06 and/or 0.6?mM concentrations. Further, the profile and content of total low molecular weight organic acids (LMWOAs) were investigated in the rhizosphere, roots and leaves of U. laevis. Obtained results showed that the addition of As(III) or As(V) individually or in a mixture led to increased LMWOAs concentration in the rhizosphere, especially of oxalic and malonic acids, in comparison to the control, while in roots the overall content of the profiled LMWOAs decreased. In both rhizosphere and roots, addition of the DMA(V) form resulted in the inhibition of LMWOAs exudation into the rhizosphere and their creation in plant roots. Leaves were characterised by a higher content of LMWOAs than in the rhizosphere and roots for all experimental systems, where the profile and content of LMWOAs was strictly correlated with the analysed As forms. Our study indicated that creation of LMWOAs in U. laevis organs and their exudation to the rhizosphere could be responsible for the As toxicity tolerance of the plants.     

Arsenite oxidation by <Emphasis Type="Italic">Alcaligenes</Emphasis> sp. strain RS-19 isolated from arsenic-contaminated mines in the Republic of Korea

Arsenite [As(III)]-oxidizing bacteria play important roles in reducing arsenic [As] toxicity and mobility in As-contaminated areas. As-resistant bacteria were isolated from the soils of two abandoned mines in the Republic of Korea. The isolated bacteria showed relatively high resistances to As(III) up to 26 mM. The PCR-based 16S rRNA analysis revealed that the isolated As-resistant bacteria were close relatives to Serratia marcescensa, Pseudomonas putida, Pantoea agglomerans, and Alcaligenes sp. Among the five As-resistant bacterial isolates, Alcaligenes sp. strain RS-19 showed the highest As(III)-oxidizing activity in batch tests, completely oxidizing 1 mM of As(III) to As(V) within 40 h during heterotrophic growth. This study suggests that the indigenous bacteria have evolved to retain the ability to resist toxic As in the As-contaminated environments and moreover to convert the species to a less toxic form [e.g., from As(III) to As(V)] and also contribute the biogeochemical cycling of As by being involved in speciation of As.     

Removal of arsenic from aqueous solution by two types of nano TiO2 crystals

Titanium dioxide (TiO₂) is a promising sorbent for As removal. There are two main and physico-chemically distinct polymorphs of TiO₂ in nature, namely anatase and rutile. Since the difference of arsenic removal by the two polymorphs of TiO₂ is now well known, study on the arsenic removal efficiency and the underlying mechanism is of great significance in developing new remediation strategies for As-polluted waters. Here batch experiments were carried out in combination with instrumental analysis of X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) to investigate the effects, influential factors and mechanisms of As removal from aqueous solution by two types of nano TiO₂ crystals. The adsorption behavior of anatase and rutile for As(V) and As(III) are well described by Freundlich equations. Anatase had higher As removal efficiency and adsorption capacity than rutile. Solution pH had no influence on the As adsorption of anatase TiO₂, whereas the As removal by rutile TiO₂ was increased by 7?C18% with pH from 4 to 10. Presence of accompanying anions such as phosphate, silicate, nitrate and sulfate, decreased the As(V) and As(III) removal by both crystals, with phosphate being the most effective. However, removal of As by rutile TiO₂ was greatly enhanced in the presence of divalent cations i.e. Ca²⁺ and Mg²⁺. Shading of light decreased the removal of As(V) and As(III) of anatase by 15.5% and 17.5%, respectively, while a slight increase of As removal was observed in the case of Rutile TiO₂. FT-IR characterization of As(V) or As(III)-treated nano TiO₂ crystals indicated that both Ti-O and As-O groups participated in As adsorption. Both FT-IR and XPS analysis demonstrated that As(III) was photooxidated into As(V) when adsorbed by anatase under the light condition. Thus, the effect of crystal types and light condition on As removal should be taken into consideration when nano TiO₂ is applied for As removal from water.     

水稻根系吸收砷的动力学特征及硅的缓解机制（Uptake Kinetics of Arsenic Species in Two Genotypes of Rice Plants and Mitigatory Mechanism of Silicon）

采用室内模拟的方法,研究了两种基因型水稻(硅突变体和野生型)根系吸收As的动力学特征以及Si对水稻吸收As的影响.结果表明,两种基因型水稻根系对As(III)和As(V)的吸收均可以用Freundlich模型较好地模拟.外源Si的加入可显著降低水稻根系对As(III)和As(V)的吸收.在20μmol·L-1As处理下,与不加Si处理相比,加1.0mmol·L-1Si处理导致水稻根系吸收As(III)和As(V)分别降低94.1%和92.2%(野生型);74.4%和90.2%(突变体).在100μmol·L-1As处理下,水稻根系吸收As(III)和As(V)则分别降低64.5%和91.2%(野生型);76.1%和90.6%(突变体).     

Effect of arsenic compounds on Vibrio fischeri light emission and butyrylcholinesterase activity

The effect of organic arsenic compounds and inorganic As(V) and As(III) on Vibrio fischeri luminescence and butyrylcholinesterase activity were evaluated using Microtox and microcalorimetric analysis. Organic arsenic compounds were arsenocholine (AsC), arsenobetaine (AsB), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA) and the antibiotic 4-hydroxy-3-nitrobenzene arsonic acid (HNAA, Roxarsone^(R)). HNAA, As(III) and As(V) were found to inhibit Vibrio fischeri light emission whereas MMA, DMA, AsC and AsB produced only a slight effect. By contrast, only AsC, AsB and As(III) were found to inhibit butyrylcholinesterase activity. Selected article from the 6th European Meeting on Environmental Chemistry, University of Belgrade, Serbia and Montenegro organized by Prof. Dr. Branimir Jovancicevic (www.research.plymouth.ac.uk/ace).     

Sources,spatial variation,and speciation of heavy metals in sediments of the Tamagawa River in Central Japan

Subsurface geochemical behavior of As(V) with Fe(II) was studied under strict anoxic conditions. Abiotic reduction of As(V) (0.1 mM) to As(III) by aqueous Fe(II) and sorbed Fe(II) in pH range 5.0–7.0 and Fe(II)_aq concentration (0.6–1.2 mM) was investigated along with the effect of As(V) on the oxidation of Fe(II) by dissolved oxygen (DO). Although the reduction was thermodynamically feasible for homogeneous chemical conditions, practically no As(V) reduction by aqueous Fe(II) was observed. Similarly, no sorbed As(V) reduction was observed under the heterogeneous experimental conditions by sorbed Fe(II) onto synthetic iron oxide (hematite, α-Fe₂O₃). Experimental results on Fe(II) oxidation by DO in the presence of 0.1 mM As(V) showed a significantly slower Fe(II) oxidation, which might be due to the formation of Fe(II)–As(V) complex in the aqueous phase. The results of this study demonstrate that As(V) is relatively stable in the presence of Fe(II) under subsurface environment and interfere the oxidation of Fe(II).     

Effect of arsenic species on the growth and arsenic accumulation in <Emphasis Type="Italic">Cucumis sativus</Emphasis>

The effects of arsenic (As) species, such as As(III), As(V) and dimethylarsinic acid (DMA), on the accumulation of As in cucumber (Cucumis sativus), as well as on its growth in a soil mesocosm were evaluated. When Cucumis sativus was cultivated in soils contaminated with 20 and 50 mg/kg of As(III), As(V) or DMA for 40 days, the growth was markedly inhibited by the inorganic As (As(III) and As(V)) rather than the organic As (DMA). Irrespective of the As species, the As concentrations accumulated in Cucumis sativus increased with increasing As concentration in the soil. The As bioaccumulation factors from soil into the tissue of Cucumis sativus were 17.5–35.4, 29.3–42.7 and 17.6–25.7 for As(III), As(V) and DMA, respectively. In addition, the As translocation factors from the roots to shoots were 0.025–0.031, 0.018–0.032 and 0.014–0.026 for As(III), As(V) and DMA, respectively. In conclusion, Cucumis sativus mainly accumulated As in its roots rather than its shoots and easily accumulated inorganic rather than organic As from the soil into its tissue.     

Enhanced adsorption of arsenate on titanium dioxide using Ca and Mg ions

In this study, we report the effects of pH and divalent cations on the adsorption of arsenate (As(V)) by titanium dioxide (TiO₂) nanoparticles. The extent of As(V) adsorption on TiO₂ decreased with increasing pH due to the decrease of positively charged binding sites on the TiO₂ surface. The Langmuir maximum uptake capacity at pH 4 is about three times higher than that at pH 7. Here we show that the relatively low As(V) uptake at circumneutral pH could be substantially enhanced by the addition of common divalent cations such as magnesium and calcium. At a concentration of approximately 7 mM, magnesium and calcium increased the extent of As(V) adsorption from 2.1 to 6.5 and 7.7 mg As(V)/g TiO₂, respectively.     

Regulation of soil enzyme activities in constructed wetlands under a short-term drying period

The activities of extracellular enzymes are important in understanding decomposition of soil organic matter in wetlands subjecting to drying. The activity of soil extracellular enzymes (β-glucosidase, N-acetylglucosaminidase, and phosphatase), and related physicochemical parameters were monitored in constructed freshwater wetlands during a one-month drying manipulation. Drying increased redox potential and decreased soil water content significantly (P<0.05). Higher content of soil organic matter (P<0.05) and higher concentrations of inorganic N (nitrate, P<0.01; and ammonia, P<0.001) were also observed significantly under drying condition. Soil hydrolase enzyme activities were stimulated significantly (β-glucosidase, P<0.05; N-acetylglucosaminidase, P<0.01; and phosphatase, P<0.001), and a two-phase pattern of enzyme activities was revealed under drying condition. The increase of soil enzyme activities under drying condition was significantly related to soil redox potential (P<0.001). Drying strongly affected soil enzyme activities only when soil water content remained above an optimal level for enzymatic catalysis (higher than 23% w/w), corresponding to redox potentials below 250–300 mV. Our results suggest that, under drying condition, potential enzyme activities may be regulated by redox potential, in respect to soil moisture, and consequently alter nutrient availability in wetlands.     

Migration of manganese and iron during the adsorption-regeneration cycles for arsenic removal

Fe-Mn binary oxide incorporated into porous diatomite (FMBO-diatomite) was prepared in situ and regenerated in a fixed-bed column for arsenite [As(III)] and arsenate [As(V)] removal. Four consecutive adsorption cycles were operated under the following conditions: Initial arsenic concentration of 0.1 mg·L^-1, empty bed contact time of 5 min, and pH 7.0. About 3000, 3300, 3800, and 4500 bed volumes of eligible effluent (arsenic concentration≤0.01 mg·L^-1) were obtained in four As(III) adsorption cycles; while about 2000, 2300, 2500, and 3100 bed volumes of eligible effluent were obtained in four As(V) adsorption cycles. The dissection results of FMBO-diatomite fixed-bed exhibited that small amounts of manganese and iron were transferred from the top of the fixed-bed to the bottom of the fixed-bed during As(III) removal process. Compared to the extremely low concentration of iron (<0.01 mg·L^-1), the fluctuation concentration of Mn²⁺ in effluent of the As(III) removal column was in a range of 0.01–0.08 mg·L^-1. The release of manganese suggested that manganese oxides played an important role in As(III) oxidation. Determined with the US EPA toxicity characteristic leaching procedure (TCLP), the leaching risk of As(III) on exhausted FMBO-diatomite was lower than that of As(V).