Arsenic Uptake Research Articles

Expression of New Pteris vittata Phosphate Transporter PvPht1;4 Reduces Arsenic Translocation from the Roots to Shoots in Tobacco Plants.

Arsenic-hyperaccumulator Pteris vittata is efficient in As uptake, probably through phosphate transporters (Pht). Here, for the first time, we cloned a new PvPht1;4 gene from P. vittata and investigated its role in arsenate (AsV) uptake and transport in yeast and transgenic tobacco plants. On the basis of quantitative real-time polymerase chain reaction (qRT-PCR), PvPht1;4 was abundantly expressed in P. vittata fronds and roots, with its transcripts in the roots being induced by both P deficiency and As exposure. PvPht1;4 was localized to the plasma membrane, which complemented a yeast-mutant defective in P uptake and showed higher P transport affinity than PvPht1;3. Under AsV exposure, PvPht1;4 yeast transformants showed comparable tolerance as PvPht1;3, but higher As accumulation than PvPht1;2 transformants, indicating that PvPht1;4 had considerable AsV and P transport activity. However, in soil and hydroponic experiments, PvPht1;4 expressing tobacco lines accumulated 26-44 and 37-55% lower As in the shoots than wild type plants, with lower root-to-shoot As translocation. In the roots of PvPht1;4 lines, higher glutathione (GSH) contents and expression levels of GSH synthetase gene NtGSH2 were observed. In addition, the transcripts of AsIII-GSH transporter NtABCC1 in PvPht1;4 lines were upregulated. The data suggested that PvPht1;4 lines probably detoxified As by reducing AsV to AsIII, which was then complexed with GSH and stored in the root vacuoles, thereby reducing As translocation in transgenic tobacco. Given its strong AsV transport capacity, expression of PvPht1;4 provides a new molecular approach to reduce As accumulation in plant shoots.

Simultaneous immobilization of the cadmium, lead and arsenic in paddy soils amended with titanium gypsum

In situ immobilization of heavy metals in contaminated soils using industrial by-products is an attractive remediation technique. In this work, titanium gypsum (TG) was applied at two levels (TG-L: 0.15% and TG-H: 0.30%) to simultaneously reduce the uptake of cadmium (Cd), lead (Pb) and arsenic (As) in rice grown in heavy metal contaminated paddy soils. The results showed that the addition of TG significantly decreased the pH and dissolved organic carbon (DOC) in the bulk soil. TG addition significantly improved the rice plants growth and reduced the bioavailability of Cd, Pb and As. Particularly, bioavailable Cd, Pb and As decreased by 35.2%, 38.1% and 38.0% in TG-H treatment during the tillering stage, respectively. Moreover, TG application significantly reduced the accumulation of Cd, Pb and As in brown rice. Real-time PCR analysis demonstrated that the relative abundance of sulfate-reducing bacteria increased with the TG application, but not for the iron-reducing bacteria. In addition, 16S rRNA sequencing analysis revealed that the relative abundances of heavy metal-resistant bacteria such as Bacillus, Sulfuritalea, Clostridium, Sulfuricella, Geobacter, Nocardioides and Sulfuricurvum at the genus level significantly increased with the TG addition. In conclusion, the present study implied that TG is a potential and effective amendment to immobilize metal(loid)s in soil and thereby reduce the exposure risk of metal(loid)s associated with rice consumption.

Effect of irrigation water containing arsenic on elemental composition of bean and lettuce plants cultivated in calcareous sandy soil

BackgroundThe uptake of arsenic by vegetables from soil irrigated with arsenic enriched groundwater poses a major health hazard. The edible portion of these vegetables transfer arsenic to the human beings. The uptake of arsenic was studied in bean (Phaseolus vulgaris L.) and lettuce (Lactuca sativa L.) in a controlled greenhouse pot culture with calcareous sandy soil as substrate. The plants were irrigated with water containing sodium arsenate at concentrations 0.1, 0.25 and 0.5 mg L− 1. The total arsenic concentration of the different plants parts was determined by ICP-MS, following microwave-assisted acid digestion. The change in plant biomass production and essential macroelements (Mg, P, K) and microelements concentration (Fe, Mn, Cu, Zn) was also studied.ResultsThe As concentration in the bean was in the order: root>stem>leaf>bean fruit and in lettuce: root>leaves. At the highest dose (0.5 mg L− 1) the As concentration in the bean fruit and lettuce leaves was 22.1 μg kg− 1 and 1207.5 μg kg− 1 DW, respectively. Increasing As concentration in the irrigation water resulted in decreased edible biomass production in bean, while in lettuce the edible biomass production increased. Neither plant exhibited any visible toxicity symptoms. No significant change was observed in the macro and microelements concentration. The total and the water-soluble arsenic in soil amounted to 3.5 mg kg− 1 and 0.023 mg kg− 1, respectively. The transfer factor was found to increase with increase in the As treatment applied. The transfer factor range for bean from root to fruit was 0.003–0.005, and for lettuce from root to leaves was 0.14–0.24.ConclusionConsidering the FAO-WHO recommended maximum tolerable daily intake (MTDI) limit of 2.1 μg kg− 1 body weight, and the biomass production, both plants should not be cultivated at As treatment level higher than 0.1 mg L− 1.Graphical abstract

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.

Azadirachta indica and Ocimum sanctum leaf extracts alleviate arsenic toxicity by reducing arsenic uptake and improving antioxidant system in rice seedlings.

In the present study the potentials of aqueous extracts of the two plants, neem (Azadirachta indica) and Tulsi (Ocimum sanctum) were examined in alleviating arsenic toxicity in rice (Oryza sativa L.) plants grown in hydroponics. Seedlings of rice grown for 8days in nutrient solution containing 50μM sodium arsenite showed decline in growth, reduced biomass, altered membrane permeability and increased production of superoxide anion (O2 ·-), H2O2 and hydroxyl radicals (·OH). Increased lipid peroxidation marked by elevated TBARS (thiobarbituric acid reactive substances) level, increased protein carbonylation, alterated levels of ascorbate, glutathione and increased activities of enzymes SOD (superoxide dismutase), CAT (catalase), APX (ascorbate peroxidase) and GPX (glutathione peroxidase) were noted in the seedlings on As treatment. Exogenously added leaf aqueous extracts of Azadirachta indica (0.75mgmL-1, w/v) and Ocimum sanctum (0.87mgmL-1, w/v) in the growth medium considerably alleviated As toxicity effects in the seedlings, marked by reduced As uptake, restoration of membrane integrity, reduced production of ROS, lowering oxidative damage and restoring the levels of ascorbate, glutathione and activity levels of antioxidative enzymes. Arsenic uptake in the seedlings declined by 72.5% in roots and 72.8% in shoots, when A. indica extract was present in the As treatment medium whereas with O. sanctum extract, the uptake declined by 67.2% in roots and 70.01% in shoots. Results suggest that both A. indica and O. sanctum aqueous extracts have potentials to alleviate arsenic toxicity in rice plants and that A. indica can serve as better As toxicity alleviator compared to O. sanctum.

Effect of extracellular polymeric substances on arsenic accumulation in Chlorella pyrenoidosa

Inorganic arsenic (iAs) in its dominant dissolved phase in the environment is known to pose major threats to ecological and human health. While the biological effects in many arsenic-bearing freshwaters have been extensively studied, the behavior and bioaccumulation of dissolved iAS in the presence of extracellular polymeric substances (EPS) still remains to be a critical knowledge gap. In this study, the uptakes and kinetic characteristics of iAs were studied using Chlorella pyrenoidosa (a typical freshwater green algae) by addressing the different effects of EPS on arsenite (AsШ) and arsenate (AsV). The arsenic uptake capacity increased as the exposure concentration increased from 0 to 300 µmol L−1, and the uptake rate constants (Ku) in the Bio-dynamic model were greater for AsV than AsШ (0.63–11.57 L g−1 h−1 vs. 0.44–5.43 L g−1 h−1). The toxic effects as mitigated by EPS were observed through the morphological changes of algal cells by TEM and SEM. When compared with the EPS-free algal cells (EPS-F), EPS-covered cells (EPS-C) had a higher arsenic adsorption capacity through EPS-enhanced surface adsorption and reduced intracellular uptake. The overall decrease (35% and 23.3% for AsШ and AsV, respectively) in the maximum uptake capacity in intact algae cells favors cell’s tolerance to the toxic effects of iAs. These observed discrepancies between AsШ and AsV and between EPS-C and EPS-F were further elucidated through morphological images (TEM and SEM) and molecular/atomic spectroscopic data that combine three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Altogether, the spectroscopic evidence revealed the interactions of iAs with C–O–C, C–O–H and –NH2 functional groups in EPS’ tyrosine- and tryptophan-like proteins as the binding sites. Overall, this study for the first time provides comprehensive evidence on the iAs-EPS interactions. Such insights will benefit our understanding of the biogeochemical processes of iAs and the strategic development of bioremediation techniques involving microalgae in the natural and engineered systems.

Surface functionalized Philippine natural zeolite for arsenic adsorption in an aqueous solution

This study shows the effectiveness of the natural zeolite and its surface modified form in adsorbing arsenic from deep well water sources and irrigated waters in some rural areas in the Philippines. It aims to compare the arsenic adsorption efficiency between, pre-conditioned sodium modified natural [Na-Philippine natural zeolites (PNZ)] and surface-modified Na-PNZ (SM-PNZ) with varying concentrations of 100% and 330% of the external cation exchange capacity (ECEC) of the PNZ. Characterization of the adsorbents were conducted such as X-ray diffraction (XRD) (mineralogy using X-ray diffraction), XRF (chemical composition using X-ray fluorescence), Fourier-transform Infrared for functionalization test and wettability tests (contact angle and water penetration tests). Arsenic adsorption studies were conducted using the Atomic absorption spectroscopy to determine the arsenic uptake of the adsorbents at varying contact times. The results proved that the adsorbent modified with surfactant, cetyltrimethylammonium bromide, at 100% ECEC has the highest arsenic uptake compared with Na-PNZ.

Influence of different arsenic species on uptake, speciation and efflux of arsenic in hydroponic rice plants

Uptake, translocation and speciation of As in rice plants have been investigated through hydroponic cultivations under stress from different As species. After germination, rice seedlings were treated with arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMA) or dimethylarsinic acid (DMA) at concentrations of 50, 100, 150, 200 and 250 μg/L for 24 days. Only inorganic As species were detected in the rice plants treated with As(III) or As(V), indicating that rice seedlings could not methylate inorganic As in hydroponic culture. As(V) in the rice roots was readily reduced to As(III) after uptake; thus, As(III) was the dominant species in the rice roots (>60%) and shoots (>80%) regardless of As(III) or As(V) treatment. The increased As(III) proportion in the nutrient solutions was due to the efflux of As(III) from the rice roots. MMA with relatively low stability in the blank nutrient solution was demethylated to As(III). Moreover, demethylation and methylation of MMA might occur simultaneously in rice plants. Specific proportions of MMA and AsB were observed in the rice roots treated with DMA, implying that MMA and AsB were the DMA metabolites in rice roots after detoxification.

Arsenic stress on photosynthesis and growth in Ipomoea aquatica

An experiment was conducted to understand the effect of arsenic (As) on photosynthetic pigments in Ipomoea aquatica leaves, its growth performance and As uptake in edible plant parts. The experiment was designed with three levels of As treatments, viz. 10, 20, and 40 mg As kg-1 soil along with control, and three biological replications. I. aquatica was grown for six weeks after seed germination. Chlorophyll-a, chlorophyll-b, carotenoid, plant height and weight increased at lower rate of As application (10 mg kg-1) in soil. Higher As (20 and 40 mg As kg-1 soil) in soil significantly decreased all the parameters except carotenoid. Both plant height and weight were significantly reduced at 20 mg As kg-1 in soil. Chlorophyll-a and chlorophyll-b content were significantly reduced at 40 mg As kg-1 in soil. Arsenic concentration in plant parts increased significantly at higher As concentration and exceeded the maximum limit of As (0.5 mg kg-1) for vegetables at 20 mg As kg-1 soil and above. Arsenic uptake (µg plant-1) also increased significantly with elevated levels of soil As (40 mg kg-1). Considering the growth performance, I. aquatica should not be recommended to grow where the soil As concentration is 20 mg kg-1 and above.

Involvement of glutathione and glutathione metabolizing enzymes in Pistia stratiotes tolerance to arsenite

Glutathione is essential for plant tolerance to arsenic but few studies have focused on the coordination between the enzymes involved in its metabolism. We exposed Pistia stratiotes to four treatments (control, 5, 10 and 20 µM AsIII) for 24 h to evaluate the role of glutathione metabolism in arsenic response and determined the arsenic uptake, growth, membrane integrity, glutathione concentration and enzyme activities (γ-glutamyl-cysteine synthetase, glutathione reductase, glutathione peroxidase, and glutathione-S-transferase). Despite absorbing high concentrations of AsIII, plants maintained growth and cell membrane integrity when exposed to concentrations of up to 10 µM AsIII. The maintenance of these parameters involved glutathione concentration increase due to an increase in its biosynthetic pathway (higher γ-glutamyl-cysteine synthetase). In addition, an increase in the activity of glutathione reductase, glutathione peroxidase and glutathione-S-transferase also contributed to the conserve the cellular homeostasis. However, at the concentration of 20 µM AsIII, the high toxicity of AsIII affected glutathione concentration and glutathione metabolizing enzymes activities, which resulted in drastic decrease in growth and damage to cell membranes. These results showed that not only the glutathione concentration but also the coordination of the enzymes involved in the synthesis, oxidation and reduction pathways of glutathione is essential for AsIII tolerance.

Microarray Data Analysis of as-induced Rice Roots by using Easygo and Mapman Softwares

Rice is one of the most important crops in Asian countries such as China, Vietnam... Many recent reports indicate that the arsenic content in rice exceeds the threshold and affects human health. Studying of molecular mechanisms and finding the arsenic resistance genes in rice which is extremely important and urgent. In this study, we analyzed the transcriptional changes of arsenic-treated rice root cells during 24 hours by microarray technique. Results showed that a large number of the differentially expressed genes (720 genes). EasyGO and Mapman softwares are powerful tools in analyzing microarray data and classifying functional groups as well as the important metabolic pathways in the cell. Results of microarray analysis using EasyGO showed that 74 down-regulated genes related to cellular component, 200 up-regulated genes involved in catalytic activity, 93 up-regulated genes involved in biological processes as responding to environmental stress, and 64 detoxification-realted genes are increased expression such as cytochrome P450, Glutathione-S-transferase and UDP-Glycosyltransferase. Mapman's microarray analysis reaults also indicate that numerous of arsenic-tolerance genes of rice roots. These results support for searching indicated genes in the selection of As-tolerance rice varieties.
 Keywords
 Asen, EasyGO, Mapman, microarray, Oryza sativa L.
 References
 [1] S.K. Panda, R.K. Upadhyay, S. Nath, Arsenic stress in plants. Journal of Agronomy and Crop Science 196 (2010) 161-174. https://doi.org/10. 1111/j.1439-037X.2009. 00407.x.[2] M.A. Rahman, H. Hasengawa, M.M. Rahman, M.A Miah, A. Tasmin. Arsenic accumulation in rice (Oryza sativa L.): Human exposure through food chain. Ecotoxicology and Environmental Safety 69 (2008): 317-324. https://doi.org/10. 1016/j.ecoenv.2007.01.005.[3] K.A. Marrs, The function and regulation of Glutathione S-transferase in plants. Plant Mol Biol 47 (1996) 127-58. https://doi.org/10.1146/ annurev.arplant.47.1.127.[4] L.M. DelRazo, B. Quintanilla-Vega, E. Brambila-Colombres, E.S. Caldero ́n-Aranda, M. Manno, A. Albores, Stress proteins induced by Arsenic. Toxicology and Applied Pharmacology 177 (2001)132-148. https://doi.org/10.1006/taap. 2001.9291.[5] T.L. Huang, Q.T.T. Nguyen, S.F. Fu, C.Y. Lin, Y.C. Chen, H.J. Huang, Transcriptomic changes and signalling pathways induced by arsenic stress in rice roots. Plant Molecular Biology 80 (2012) 587-608. https://link.springer.com/article/10.10 07/s11103-012-9969-z.[6] O. Thimm, O. Bläsing, Y. Gibon, A. Nagel, S. Meyer, P. Krüger, J. Selbig, L.A. Müller, S.Y Rhee, M. Stitt, Mapman: a user-driven tool to display genomics data sets onto diagrams of metabolic pathways and other biological processes. The Plant Journal 37 (2004) 914-939. https://doi.org/10.1111/j.1365-313X.2004. 02016.x.[7] J. Hartley-Whitker, G. Ainsworth, A.A. Meharg, Copper- and arsenate-induced oxidative stress in Holcus lanatus L. clones with differential sensitivity. Plant, Cell and Environment 24 (2001) 713-722. https://doi.org/10.1046/j.0016-8025.2001.00721.x.[8] S. Mishara, A.B. Jha, R.S. Dubey, Arsenite treatment induces oxidative stress, upregulates antioxidant system, and causes phytochelatin synthesis in rice seedlings. Protoplasma 248 (2011) 565-577. https://doi.org/10.1007/s00709-010-0210-0.[9] M. Chabannes, A. Barakate, C. Lapierre, J.M. Marita, Strong decrease in lignin content without significant alteration of plant development is induced by simultaneous down-regulation of cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) in tobacco plants, The Plant 28 (2001): 257-270. https://doi.org/10. 1046/j.1365-313X.2001.01140.x.[10] T. Goujon, V. Ferret, I. Mila, B. Pollet, Down-regulation of the AtCCR1 gene in Arabidopsis thaliana: effects on phenotype, lignins and cell wall degradability. Planta 217 (2003) 218-228. https://doi.org/10.1007/s00425-003-0987-6.[11] C. Li, S. Feng, Y. Shoa, L. Jiang, X. Lu, X. Hou, Effects of arsenic on seed germination and physiological activities of wheat seedlings. Journal of Environmental Sciences. 19 (2007) 725-732. https://doi.org/10.1016/S1001-0742(07) 60121-1.[12] A.A. Meharg, J. Harley-Whitaker, Arsenic uptake and metabolism in arsenic resistant and nonresistant plant species. New Phytologist 154 (2002) 29-43. https://doi.org/10.1046/j.1469-8137.2002.00363.x.
 
 

Effect of Endogenous Selenium on Arsenic Uptake and Antioxidative Enzymes in As-Exposed Rice Seedlings.

Arsenic (As) and selenium (Se) are two metalloids found in the environment. As it poses a significant threat to human health and plant growth due to its prevalence and toxicity, however Se is a required micronutrient for human health. In this study hydroponic experiments were performed to investigate whether endogenous Se can mitigate As toxicity in rice (Oryza sativa L.). We found that As uptake by rice roots increased by pretreatment with selenateSe(VI) or selenite Se(IV). However, co-application of arsenate As(V) or arsenite As(III) with selenate markedly reduced the uptake of As by roots. Co- or pretreatment with Se with five µM of As(V) or one µM of As(III) significantly decreased shoot As content. Conversely, Se pretreatment before the addition of five µM of As(III) or one µM of As(V) resulted in As accumulation in the shoot compared to As and Se co-application. As translocation to the shoot was lower whereas the transfer factor was higher upon the simultaneous application of Se and As compared to Se pretreatment. Se supplementation with As(III) or pretreatment increased antioxidant enzymes: Superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) increased in the root and shoot, but decreased glutathione (GSH) and malondialdehyde (MDA) contents in the shoot. Plants under As(V) treatment showed the same trend except that CAT content decreased in the root and shoot, while MDA content increased in the shoot. These results suggest that cultivating rice in the presence of Se can reduce the accumulation of toxic As in seedlings, thus ensuring the safety of this important crop for human consumption.

Synthesis of green marine algal-based biochar for remediation of arsenic(V) from contaminated waters in batch and column mode of operation

The sorption behavior of biochar derived from green seaweed (Ulva reticulata) toward arsenic(V) ions was explored in both batch and continuous modes. The pH edge experiments indicated optimum arsenic(V) sorption observed at pH 4, with maximum sorptional capacity of 7.67 mg/g through isotherm experiments. The kinetic experimental trials indicated that arsenic(V) sorption onto biochar was a fast electrostatic attraction process, with maximum removal occurred within 30 min. The sorption isotherms were modeled using the Toth, Redlich–Peterson, Langmuir and Freundlich isotherm models while the adsorption kinetics was modeled using the pseudo-first- and pseudo-second-order kinetic equations. The three-parameter models (Redlich–Peterson and Toth) better described the isotherm data, whereas pseudo-first-order model represented kinetic data well with low error and high correlation coefficient values. Among the different alkaline and acidic elutants investigated, the solution of 0.01 M NaOH effectively desorbed arsenic(V) from spent biochar. The feasibility of the biochar in continuous remediation of arsenic(V) from contaminated waters was explored in an up-flow fixed column. The biochar exhibited arsenic(V) removal efficiency and sorptional uptake of 59.5% and 8.12 mg/g, respectively. The biochar-loaded column was effectively desorbed using NaOH (0.01 M), with desorption efficiency of 99.5%.

Hazardous Effects of Arsenic Contaminated Water on the Biological Characteristics of Fishes: A Review

The aim of the current review is to deliberate on arsenic chemistry, its existence in aquatic ecosystem and its effects on the biological systems of fishes which are regarded as potential indicators for any change in water quality. Water is a major storehouse of arsenic which is present in the form of arsenate and arsenite. Anthropogenic activities including unlimited application of arsenic pesticides, industrial activities and mining operations have increased the universal incidence of soluble arsenic above tolerable levels of 0.010 mg/L. Variations in fish behaviour, growth rate, haematological and biological parameters and organ systems have been observed in arsenic contaminated water. Data regarding these parameters indicate that the fish shows aggressive behaviour and its weight increases due to a high arsenic uptake. The production rate of biochemical compounds like carbohydrates, proteins and lipids is reduced due to arsenic bonding with their precursors. Among organ systems, skin is a highly affected organ, while muscles are the least affected due to high arsenic concentration. Low concentration of arsenic results in bioaccumulation, conspicuously in liver and kidney, upon incessant exposure to freshwater fish. This bioaccumulation turns into biomagnification and becomes the cause of lethal diseases in human beings, such as hyperglycaemia, diminution of enzymatic activities and immune system abnormalities. Keeping in view all of these above mentioned facts, it is imperative to take action against excessive arsenic usage and to develop its eco-friendly management ways.

Effect of selenium in soil on the toxicity and uptake of arsenic in rice plant

Selenium can regulate arsenic toxicity by strengthening antioxidant potential, but the antagonism between selenite or selenate nutrient and the translocation of arsenic species from paddy soil to different rice organs are poorly understood. In this study, a pot experiment was designed to investigate the effect of selenite or selenate on arsenite or arsenate toxicity to two indica rice cultivars (namely Ming Hui 63 and Lu You Ming Zhan), and the uptake and transportation of arsenic species from paddy soil to different rice organs. The results showed that selenite or selenate could significantly decrease the arsenate concentration in pore water of soils, and thus inhibited arsenate uptake by rice roots. However, the existence of selenite or selenate didn't decrease arsenate concentration in rhizosphere pore water of two indica rice cultivars. There existed good antagonistic effect between selenite or selenate and the uptake of arsenite and arsenate in rice plant in the case of low arsenic paddy soil. However, this antagonism depended on rice cultivars, arsenic species and arsenic level in soil. There existed both synergistic and inhibiting effects between the addition of selenite or selenate and the uptake of trimethylarsinoxide and dimethylarsinic acid by two indica rice cultivars, but the mechanism was unclear. Both selenite and selenate are all effective to decrease the translocation of inorganic arsenic from the roots to their above-ground rice organs in arsenite/arsenate-spiked paddy soil, but selenate had stronger inhibiting effect on their transfer factors than selenite.

Effects of lime and sawdust on arsenic reduction in corn planted on the inside of the dyke at Quoc Thai commune, An Phu district, An Giang province

Previous research has shown that soil and crops in Quoc Thai commune, An Phu district, An Giang province are severely contaminated with arsenic. The objectives of the experiment were (1) to evaluate effects of lime and sawdust on water pH and arsenic content in soil and 2) to determine effects of lime and sawdust on arsenic uptake by corn. The experiment was carried out in the field on the inside of the dyke with 4 treatments and 4 replications. The results showed that the treatment of lime combined with sawdust increased water pH and arsenic content in soil. The arsenic content in stems and leaves (95.3 mg/kg) and in seeds (6.33 mg/kg) of the maize was lower than that of the control by 31.9% and 49.4%, respectively. In brief, the use of lime in combination with sawdust to fertilize plants increased the water pH and arsenic content in the soil, while reducing the arsenic content in plants.

Removal of arsenic from aqueous solution using microflower-like δ-Bi2O3 as adsorbent: adsorption characteristics and mechanisms

Arsenic is one of the most common and harmful pollutants in environment, causing serious damage to human health and ecosystems. Herein, the uptake of arsenic by microflower-like δ-Bi2O3 including adsorption equilibrium, kinetics, desorption, the effects of initial pH and interfering ions on removal efficiency were studied in batch experiments, and the adsorption mechanism was also elucidated by Fourier transform infrared spectra and X-ray photoelectron spectroscopy. The results showed that the maximum adsorption capacities of As(III) and As(V) were 115.05 and 33.17 mg g−1, respectively. Simultaneously, the arsenic removal by MF-δ-Bi2O3 could work well in a wide pH range of 4–11 and presented excellent sorption selectivity for arsenic in the presence of competitive anions (NO3 − and SO4 2 −). Furthermore, the adsorbent showed excellent morphological and structural stability after adsorption, which makes it easy to separate from aqueous solution and avoid secondary pollution as much as possible. The ligand exchange between arsenic ions and hydroxyl groups occupying the oxygen vacancies of MF-δ-Bi2O3 was the main adsorption mechanism. All studies in this experiment can led to a new direction for arsenic removal.

Iron (III) oxide nanoparticles alleviate arsenic induced stunting in Vigna radiata

Iron nanoparticles (NPs) are widely used for the removal of arsenic from water. In this study, we evaluated the interaction between arsenate (AsO43−) and Fe2O3-NPs on early seedling growth of Vigna radiata. Seedlings were raised in AsO43− and Fe2O3-NPs, alone and in combination. While Fe2O3-NPs slightly promoted seedling growth, AsO43− reduced seedling growth drastically. AsO43--induced decline in the seedling growth was recovered by Fe2O3-NPs. In contrast, equivalent concentrations of FeCl3, alone and together with AsO43−, inhibited seed germination completely. Lower arsenic content in seedlings raised in the presence of Fe2O3-NPs indicated that Fe2O3-NPs restricted arsenic uptake. Ability of Fe2O3-NPs to restrict the arsenic uptake of the seedlings was due to adsorption of AsO43−, as revealed by transmission and scanning electron microscopy. Non-toxic levels of iron in seedlings were due to restriction of Fe2O3-NPs to root-surface. AsO43− enhanced the ferric chelate reductase activity of root which was recovered by Fe2O3-NPs. The AsO43--induced oxidative stress, evident from high levels of proline, H2O2 and malondialdehyde, and lowered root oxidisability was ameliorated by Fe2O3-NPs. AsO43-induced enhancement in total antioxidant capacity, superoxide dismutase and catalase activity, and decline in guaiacol peroxidase activity were antagonized by Fe2O3-NPs. Our findings reveal that Fe2O3-NPs provide effective resistance/amelioration to arsenic toxicity by reducing arsenic availability to plants.

Indigenous strain Bacillus XZM assisted phytoremediation and detoxification of arsenic in Vallisneria denseserrulata

The symbiosis between Vallisneria denseserrulata and indigenous Bacillus sp. XZM was investigated for arsenic removal for the first time. It was found that the native bacterium was able to reduce arsenic toxicity to the plant by producing higher amount of extra cellular polymeric substances (EPS), indole-3-acetic acid (IAA) and siderosphore. Interestingly, V. denseserrulata-Bacillus sp. XZM partnership showed significantly higher arsenic uptake and removal efficiency. The shift in FT-IR spectra indicated the involvement of amide, carboxyl, hydroxyl and thiol groups in detoxification of arsenic, and the existence of an arsenic metabolizing process in V. denseserrulata leaves. The scanning electron microscopy (SEM) images further confirmed that the bacterium colonized on plant roots and facilitated arsenic uptake by plant under inoculation condition. In plant, most of the arsenic existed as As(III) (85%) and was massively (>77%) found in vacuole of particularly leaves cells. Thus, these findings are highly suggested for arsenic remediation in the constructed wetlands.

Mixed plantation of wheat and accumulators in arsenic contaminated plots: A novel way to reduce the uptake of arsenic in wheat and load on antioxidative defence of plant

Wheat (W) and accumulators (A) were planted in plots (arsenic amended soil and without arsenic) designed with ecotoxicological concern for arsenic safe-grains. For the study sixteen plots of 2 × 2 × 0.5 m (l × b × h) size were prepared. Arsenic (As) in the form of sodium arsenate was applied at 50 mg/kg in plots. Out of these sixteen plots eight plots had arsenic amended soil and rest 8 without any arsenic (C). Accumulator's viz. Pteris vittata (PV), Phragmites australis (PA) and Vetiveria zizanioides (VZ) were planted along with wheat in combination (W + PV, W + PA and W + VZ) in twelve plots (6 AWAs plots and 6 AWC plots). In the rest 4 plots (2 WAs plots and 2 WC plots), only wheat was planted. The study was conducted for two cropping seasons, where accumulators were left in the plots between the cropping seasons except that before 2nd cropping accumulators were properly pruned and extra tillers were removed. The germination % of wheat in WAs in 1st and the 2nd cropping season was found to be 55 and 57%, while in AWAs and AWC plots it was between 86 and 92% (W + VZ, 56 and 73%). The physiological activity was found to be reduced in WAs plots compared to AWAs (except for vetiver combination) and AWC plots in both cropping seasons. The antioxidant activity was enhanced in WAs compared with AWAs. The arsenic concentration in grains of wheat was within the permissible limit set by WHO and GOI in AWAs plots while it exceeded the limit in W + VZ (in 1st cropping) and WAs in both cropings.