As-contaminated Soils Research Articles

Mobility of arsenic in soil amended with biochar derived from biomass with different lignin contents: Relationships between lignin content and dissolved organic matter leaching

• Lignin content is inversely proportional to DOM release from the biochar. • Biochar pyrolyzed sawdust with more lignin extracted less Fe from soil. • Sawdust biochar with less lignin can enhance the As leaching from soil. Biochar is widely used material whose physical and chemical characteristics been widely investigated. Nevertheless, dissolved organic matter (DOM) released from biochar has received relatively little attention. In particular, little research has been conducted to understand the effects of feedstock biomass components on biochar DOM release. To control the amount of DOM released from biochar, this study focuses on the role of lignin, a component of biomass. To this end, samples of sawdust containing different lignin contents and a binary mixture of cellulose and lignin were pyrolyzed at 400 and 700 °C, and then the physico-chemical properties of the resulting biochar, and Fe(II) and As mobility were investigated in arsenic-contaminated soil amended by the biochar. This study showed that lignin is an critical factor in controlling the release of DOM. The amount of DOM released from the sawdust biochar with the lowest lignin content was 33% (400 °C) and 44% (700 °C) lower than those produced from lignin-rich biochar (sawdust without the extraction of lignin). The amount of oxalic acid in DOM decreased with increased lignin content. In addition, As mobility and the transformation of Fe(II) were minimized when lignin-rich biochar was applied to the As-contaminated soil. More importantly, these results suggest that controlling the lignin content of biomass can be universally applied to predict DOM concentrations of the biochars produced.

Factors of Soil Properties and Elements in Tissues Influencing on Extent of Arsenic Accumulation in Brown Rice

Recently, As-contaminated soil management has started dealing with phytoavailable As content instead of total As content in soils. Phytoavailable As content is known to consider food safety more than the management of the environment. This study aims to predict As content in brown rice using phytoavailable As concentration in soil and soil properties and to see the relationship between element contents in tissues and As in brown rice. As-contaminated soils were collected, and their total and phytoavailable As content and soil properties were analyzed. Mehlich3 extraction method was used for phytoavailable As analysis. After the analysis, correlations among total and phytoavailable As concentrations in soils, As content in rice and soil properties were analyzed. Then, a prediction model of As content in brown rice was developed through multiple stepwise regression. Also, correlation analysis between nutrients and As contents in rice was conducted to identify the factors affecting As accumulation in brown rice. The modelling equation for estimating As concentration in brown rice was [Log (As in brown rice) = 2.45 + 0.13 × Log (As_Mehlich3) – 0.99 × Log (CEC) + 0.50 × Log (avail.-P)] (r = 0.49, p < 0.001). Soil avail.P concentration and CEC were valid variables for As accumulation in brown rice. In addition, Cu, Zn, Mo and Na in shoot were revealed to influence governing translocation of As from shoot to grain. Regression models for estimating As concentration in brown rice using total and phytoavailable As content in paddy soils, combined with soil avail.-P and CEC values. Parameter r p value Log (As_R†) = 2.98 ‒ 0.08×Log (Total As_S†) 0.13 0.318 Log (As_R) = 2.15 ‒ 0.06×Log (Total As_S) + 0.42×Log (avail.-P) 0.31 0.041 Log (As_R) = 2.63 + 0.01×Log (Total As_S) + 0.59×Log (avail.-P) ‒ 1.00×Log (CEC) 0.44 0.004 Log (As_R) = 2.15 + 0.17×Log (As_M3§) 0.28 0.022 Log (As_R) = 2.89 + 0.18×Log (As_M3) ‒ 0.72×Log (CEC) 0.38 0.008 Log (As_R) = 2.45+ 0.13×Log (As_M3) ‒ 0.99×Log (CEC) + 0.50×Log (avail.-P) 0.49 0.001 †As concentration in brown rice†Total As concentration in soil§Mehlich3-extractable As concentration in soil

The bioaccessibility and fractionation of arsenic in anoxic soils as a function of stabilization using low-cost Fe/Al-based materials: A long-term experiment

Arsenic (As)-contaminated soils occur widely worldwide. In the present study, three low-cost Fe/Al-based materials, including red soil (RS), sponge iron filter (SIF) and Al-based water treatment sludge (WTS), were applied as amendments to remediate As-contaminated soils under anoxic conditions. After 180d of incubation, the proportion of the sum of nonspecifically absorbed As (F1) and specifically absorbed As (F2) to the total As was reduced by 6%, 52% and 13% with 5% of RS, SIF and WTS addition, respectively, compared to the control soil (31%). The results showed that among the three amendments, SIF was the most effective at decreasing As bioaccessibility in soils. Compared with RS and WTS, SIF intensified the decrease of labile fractions and the increase of unlabile fractions, and the redistribution of the amorphous oxide-bound fraction (F3) and crystalline hydrous oxide-bound fraction (F4) occurred in the SIF-amended soil. Moreover, the As stabilization processes were divided into two stages in the control and RS-amended soil, while the processes were divided into three stages in both SIF- and WTS-treated soil. The As stabilization processes in all treated soils were characterized by the transformation of labile fractions into more immobilizable fractions, except for F4 transforming into F3 in the first stage in SIF-amended soil. Correspondingly, inner-surface complexation and occlusion within Fe/Al hydroxides were the common driving mechanisms for the transformation of As fractions. Therefore, taking into consideration the results of this study, SIF could be a more promising alternative than the other two materials to passivate As in anoxic soils.

Effects of arbuscular mycorrhizal fungi, biochar, selenium, silica gel, and sulfur on arsenic uptake and biomass growth in Pisum sativum L.

Arsenic (As) is carcinogenic and highly toxic to plants. Crops accumulate As when grown in field soils irrigated with As-contaminated groundwater. The accumulation of As in roots, shoots, and grains of pea varieties can negatively affect human health via the food chain. This research is focused on the biomass growth and alleviation of As accumulation in roots, shoots, and grains of pea varieties in high As soil amended with arbuscular mycorrhizal fungi (AMF), biochar (BC), selenium (Se), silica gel (Si-gel), and sulfur (S). Root, shoot, and grain masses were found higher in pea grown in As soil amended with AMF, Se, Si-gel, and S. Amendments with rice husk and sawdust BC was found less effective to increase growth parameters in Bangladesh Agricultural Research Institute (BARI) Motor 2. Arsenic in grains was reduced by 77%, 71%, and 69% by AMF, Se, and Si-gel, respectively. It is recommended that soil amendments with AMF, S, and Se have great potential for improving biomass production of pea grown in As-contaminated soil, as well as reducing As transfer to humans through the food chains.

Efficiency of Fe-zeolite and Fe-bentonite on co-stabilization of As, Cd and Pb in Contaminated Soil

Lead (Pb), Cadmium (Cd) and Arsenic (As) have been known as a malicious environment and their toxic effects for plants, animals and humans has been demonstrated. This metals in soil have a different behaviours. The normal concentrations of Cd, As and Pb in agricultural soil were 1.1, 20 and 67 mg.kg-1 respectively. In situ immobilization of Lead and Cadmium (by zeolite and bentonite) and Arsenic (by iron) in soil is well recognized. However, studies on soils that are simultaneously contaminated with lead, cadmium and arsenic are fewer, and assessment of the sorbents effectiveness on co-stabilization of As, Cd and Pb is also necessary. In this study, local bentonite and zeolite were converted to Fe-zeolite and Fe-bentonite. A Pb-, Cd- and As-contaminated soil has been treated with modified bentonite and zeolite separately in 1 and 6 wt% rate. After one month of incubation in at 80% of field capacity moisture, Sunflower (Helianthus annuus. L) plant was transplanted into each pot. The result showed that Fe-zeolite and Fe-bentonite decreased concentration of Pb and Cd extractable with DTPA-TEA; however, Fe-bentonite in the soil reduced water-soluble arsenate, but Fe-zeolite increased it. Finally application of Fe-bentonite can be an effective approach to co-stabilize Pb, Cd and As, in contaminated soils.

Surfactants Enhanced Soil Arsenic Phytoextraction Efficiency by Pteris vittata L.

Soil arsenic (As) pollution has become a global problem. It is urgent to improve the phytoextraction efficiency of soil As. This study found chemical activators (Span 80/SDS and GSH/Span 80/SDS) that can significantly improve the availability of As and the phytoextraction efficiency of As by Pteris vittata L. in As-contaminated soil. Compared with the control, in the soil screening experiment, Span 80/SDS and GSH/Span 80/SDS significantly increased available As in soil by 73.4% and 81.4%, respectively. And in the soil pot experiment, the Span 80/SDS and GSH/Span 80/SDS significantly increased the As concentration in the pinnae of Pteris vittata L. by 53.4% and 41.2%, respectively, and the total As amount extraction by Pteris vittata L. increased significantly by 31.7% and 94.2%, respectively. The results suggest that adding Span 80/SDS and GSH/Span 80/SDS to As-contaminated soil can be considered as an effectively method to improve the efficiency of phytoextraction.

Review on remediation technologies for arsenic-contaminated soil

Arsenic (As) is a top human carcinogen widely distributed in the environment. As-contaminated soil exists worldwide and poses a threat on human health through water/food consumption, inhalation, or skin contact. More than 200 million people are exposed to excessive As concentration through direct or indirect exposure to contaminated soil. Therefore, affordable and efficient technologies that control risks caused by excess As in soil must be developed. The presently available methods can be classified as chemical, physical, and biological. Combined utilization of multiple technologies is also common to improve remediation efficiency. This review presents the research progress on different remediation technologies for As-contaminated soil. For chemical methods, common soil washing or immobilization agents were summarized. Physical technologies were mainly discussed from the field scale. Phytoextraction, the most widely used technology for As-contaminated soil in China, was the main focus for bioremediation. Method development for evaluating soil remediation efficiency was also summarized. Further research directions were proposed based on literature analysis.

Diffusive gradients in thin films technique coupled to X-ray fluorescence spectrometry for the determination of bioavailable arsenic concentrations in soil

Many of the procedures for assessing the bioavailability of contaminant including arsenic (As) in soil are time-consuming, thus there is need to develop more effective methods. In this regard, a direct analysis of the binding resin in the diffusive gradient in thin film (DGT) by using wavelength dispersive X-ray fluorescence spectrometry (WDXRF) was tested in determining bioavailable As concentrations in soil. The binding resin obtained from the DGT was dried at room temperature in a desiccator with silica gel for 2 h, and directly analyzed by the WDXRF. The mass of As loaded in the DGT binding resin was plotted against the X-ray intensity obtained from the WDXRF analysis to a draw calibration curve, which showed good linearity (R2 = 0.997) with a limit of quantification of 0.2 μg. A correction factor (CF) for compensating the spectral interference between As-Kα and Pb-Lα was determined by considering the slope between the X-ray intensity measured at a Bragg angle of 48.781° for As-Kα and the Pb mass on the DGT binding resin. The use of the derived CF value (0.113) is reasonable to obtain As concentrations with a high accuracy. The relation between phytotoxicity of As to barley Hordeum vulgare and bioavailable As concentrations in soils, which were determined by means of the combined use of DGT and WDXRF, was observed. The study supports that the DGT-WDXRF can be a promising tool to predict soil phytotoxicity for As-contaminated soil risk management.

Passivating Effect of Dewatered Sludge and Biochar on As-Contaminated Soil

The pollution caused by As in soil menaces the health of humans. There are characteristics of waste utilization, low cost, and a wide range of materials by using dewatered sludge as the main component of soil repair agents. In this paper, dewatered sludge and biochar were used as repair agents for As pollution, which were rarely reported, and the related passivation experiments were carried out. Through the analysis of experimental data of the basic physical and chemical properties of contaminated soil, various characteristics of repair agent and As morphology were obtained, and the applicability and passivation effect of dewatered sludge-biochar compound repair agent and dewatered sludge as an individual repair agent on passivation of As pollution in soil was discussed. By comparing different passivation effects, the repairing effect increases with time, and the optimal repair time was 40 days; in the set experiment group, the best passivation effect of the individual repair agent was the S3 (dry sludge accounting for 20% of soil samples) experimental group, and the best effect of the compound repair agent was the S + B3 (dry sludge and biochar accounting for 10% and 2% of soil samples, respectively) group. As a repair agent, the dewatered sludge-biochar compound repair agent can be used to repair As-contaminated soil, which provides a new method for the recycling and waste utilization of dewatered sludge.

A Soluble Humic Substance for the Simultaneous Removal of Cadmium and Arsenic from Contaminated Soils.

With abundant oxygen-containing functional groups, a humic substance (HS) has a high potential to remediate soils contaminated by heavy metals. Here, HS was first extracted from a leonardite and analyzed for its chemical compositions and spectroscopic characteristics. Then it was assessed for its ability as a washing agent to remove Cd and As from three types of soils (red soil, black soil, and fluvo-aquic soil) that were spiked with those contaminants (Cd: 40.5–49.1 mg/kg; As: 451–584 mg/kg). The operational washing conditions, including the pH and concentration of the HS, washing time and cycles, and liquid–soil ratio, were assessed for Cd and As removal efficiency. At pH 7, with an HS concentration (3672 mg C/L) higher than its critical micelle concentration and a liquid–soil ratio of 30, a single washing for 6–12 h removed 41.9 mg Cd/kg and 199.3 mg As/kg from red soil, 33.5 mg Cd/kg and 291.5 mg As/kg from black soil, and 30.4 mg Cd/kg and 325.5 mg As/kg from fluvo-aquic soil. The removal of Cd and As from the contaminated soils involved the complexation of Cd and As with the carboxyl and phenolic groups of HS. Outcomes from this research could be used to develop a tailor-made HS washing agent for the remediation of Cd- and As-contaminated soils with different properties.

Spraying silicon to decrease inorganic arsenic accumulation in rice grain from arsenic-contaminated paddy soil

Addition of Si to soil can reduce As uptake and accumulation in rice, while also enhancing As release from soil particles via competing sorption sites in soil minerals with As. Foliar application of Si might be an alternative pathway to reduce As accumulation in rice. It is not clear which growing stage would be better for spraying different types of Si solution to reduce inorganic As in edible parts of rice. Soil pot experiments were conducted to investigate whether total As and inorganic As accumulation in rice grains was alleviated via spraying Si in As-contaminated paddy soil. The results showed that foliar Si application at the tillering or jointing stage significantly reduced As concentrations in rice husks and grain via inhibiting the translocation of As from straw to husk or grain compared with other growing stages. Spraying of Si at the tillering stage markedly decreased the concentrations of inorganic As in rice bran and polished rice, accounting for 27.3% and 61.4% respectively. Furthermore, spraying Si solution mixed with surfactant-Tween 80 not only dramatically reduced the total As in rice tissues by 48.8%, but also significantly alleviated the accumulation of inorganic As in rice grain by 49.2%. Spraying Si restricted inorganic As in rice grain through the mechanism by which foliar Si application at tillering stage increased the Si concentrations in shoot and root, which downregulated Si transporters of Lsi1 and Lsi2 in the root and Lsi6 in the blade and sheath significantly, and finally decreased As uptake and transport. Therefore, spraying Si is an alternative and efficient pathway to reduce inorganic As accumulation of rice grain in As-contaminated soil.

Soil Microbial Communities Involved in Reductive Dissolution of Arsenic from Arsenate-Laden Minerals with Different Carbon Sources.

The natural microbial communities involved in arsenic (As) extraction under biostimulated conditions are still unclear. In this study, soil slurry was incubated with arsenate [As(V)]-laden Fe(III) or Al (hydr)oxides with lactate or acetate. After 40 d, dissolved As released from As(V)-laden Fe(III) accounted for 54% of the initial solid-phase As in lactate-amended slurries, while much less As was released from acetate-amended slurries. As was released more rapidly from As(V)-laden Al, but the total release was relatively low (45%). High-throughput Illumina sequencing of 16S rRNA genes revealed that dissimilatory metal(loid) reducers such as Desulfitobacterium became predominant in lactate-amended slurries. Moreover, anaerobic fermenters in the Sporomusaceae family were predominant. Interestingly, a Sporomusaceae bacterial strain isolated from the slurry was capable of releasing As from both As(V)-laden (hydr)oxides in the presence of lactate. The strain first released As as As(V) and subsequently reduced it to As(III) in the aqueous phase. These results suggest that lactate is a suitable carbon source for As extraction by natural microbial communities, and that both dissimilatory metal(loid) reducers and certain anaerobic fermenters play significant roles in As extraction. Microbial reductive dissolution of As may be expected to be a cost-effective restoration technique for As-contaminated soils.

Investigating arsenic toxicity in tropical soils: A cell cycle and DNA fragmentation approach

Arsenic (As) is a metalloid and a toxicant that is found naturally in many environmental compartments, soils included. Soils with high levels of As occur worldwide and might pose a threat not only to humans, but also to many ecosystems. Considering the scarcity of studies regarding cytogenotoxic effects of model plants in As-contaminated soil, mainly in tropical areas, this study proposes the use of Allium cepa root tip bioassays for a fast-track assessment of As toxicity in tropical soils. For this end, root tip cells of A. cepa were exposed to an Oxisol, an Inceptisol and a Tropical Artificial Soil (TAS) contaminated with increasing doses of As (0, 8, 14.5, 26, 46.5, 84, 150, and 270 mg kg−1). The effects of As on cell cycle, micronucleus formation, and DNA fragmentation were evaluated. In general, root tip cells exposure to As increases the frequency of chromosome abnormalities and micronucleus, in turn, decreasing the frequency of mitotic index. As-treated cells also presented an increase in the percentage of DNA damage observed in comet assay. Overall, the effects of As in TAS were more pronounced, than in the Oxisol, being the Inceptisol the less toxic. A discussion of each As effect in cells and the link with the soil type is presented and reveals that clastogenic effects of As in A. cepa cells seemed to be the mode of action of this soil contaminant.

Complete stabilization of severely As-contaminated soil by a simple H2O2 pre-oxidation method combined with non-toxic TMT-15 and FeCl3·6H2O

The stabilization of severely As-polluted soil has been a challenge, especially for the extremely toxic As(III) contaminants. In this study, soil with a high As concentration (26084 mg/kg) was availably stabilized by a H2O2 pre-oxidation assisted TMT-15 (Na3S3C3N3 solution with a mass fraction of 15%) and FeCl3·6H2O stabilization method. The results showed that the combination of the two stabilizers (i.e., TMT-15 and FeCl3·6H2O) presented a better stabilization behavior than either stabilizer used individually. The use of the H2O2 pre-oxidation assisted TMT-15 and FeCl3·6H2O stabilization approach not only converted the As(III) to As(V) but also reduced the toxic leaching concentration of As to 1.61 mg/L, which is a safe level, when the additions of TMT-15 and FeCl3·6H2O were 2 mL and 0.20 g, respectively. Thus, using only a simple H2O2 pre-oxidation to combine clean stabilization with non-toxic stabilizers TMT-15 and FeCl3·6H2O could render the severely As-contaminated soil safe for disposal in a landfill.

Lead isotopes combined with geochemical and mineralogical analyses for source identification of arsenic in agricultural soils surrounding a zinc smelter

As-contaminated soil samples were chosen to identify As sources near a Zn smelter where Zn contamination in soils was found to be of smelter origin. Based on the As concentrations and Pb isotopic compositions, high As levels in soils were originated from the geogenic source. There was no consistent trend in As concentrations with either depth or distance from the smelter, while the Pb isotopic compositions in soils varied regardless of As levels and were quite different from those of smelter origin. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) suggested that the high As concentrations were due to arsenopyrite and its alteration minerals, which were easily found but heterogeneously distributed within host rocks. A detailed investigation of As levels and Pb isotropic compositions along the predominant wind direction also supported that the As contamination was of geogenic origin unlike the Zn contamination. The atmospheric emissions from the smelter increased the Zn concentrations and decreased the 206Pb/207Pb ratios at surface layers, while the As concentrations occasionally exceeded the worrisome level at deep layers. According to the Pb isotropic compositions, about 21% of the As-contaminated soils were impacted by the smelter, in particular at the surface layer.

Heterologous Expression of Pteris vittata Phosphate Transporter PvPht1;3 Enhances Arsenic Translocation to and Accumulation in Tobacco Shoots.

Arsenic-hyperaccumulator Pteris vittata is efficient in As accumulation and has been used in phytoremediation of As-contaminated soils. Arsenate (AsV) is the predominant As species in aerobic soils and is taken up by plants via phosphate transporters (Pht) including P. vittata. In this work, we cloned the PvPht1;3 full length coding sequence from P. vittata and investigated its role in As accumulation by yeast and plants. PvPht1;3 complemented a yeast P uptake mutant strain and showed a stronger affinity and transport capacity to AsV than PvPht1;2. In transgenic tobacco, PvPht1;3 enhanced AsV absorption and translocation, increasing As accumulation in the shoots under both hydroponic and soil experiments. On the basis of the expression patterns via qRT-PCR, PvPht1;3 was strongly induced by P deficiency but not As exposure. To further understand its expression pattern, transgenic Arabidopsis thaliana and soybean expressing the GUS reporter gene, driven by PvPht1;3 promoter, were produced. The GUS staining showed that the reporter gene was mainly expressed in the stele cells, indicating that PvPht1;3 was expressed in stele cells and was likely involved in P/As translocation. Taken together, the data suggested that PvPht1;3 was a high-affinity AsV transporter and was probably responsible for efficient As translocation in P. vittata. Our results suggest that expressing PvPht1;3 enhances As translocation and accumulation in plants, thereby improving phytoremediation of As-contaminated soils.

Stabilization of Arsenic-Contaminated Soils Using Fe-Mn Oxide Under Different Water Conditions

Fe-Mn oxide (FM) was used to evaluate its stabilization effects on three typical arsenic (As)-contaminated soils in southern China under different water conditions (dry soil, moist soil, and flooded soil). With an increase in moisture content, the toxicity characteristic leaching procedure (TCLP) results for As decreased by 34.78%, 47.62%, and 13.64%, respectively,in Shaoguan,Hechi, and Changde, and then increased by 310.34%, 185.22%, and 23.38%, respectively. The results showed that adding a certain amount of water (30%) had a positive effect on decreasing the As concentration in the TCLP, but excessive amounts (80%) led to As re-release into the soil. The application of FM under flooding conditions has obvious advantages. In the three soils of Shaoguan,Hechi, and Changde, FM significantly reduced the As concentration in the TCLP by more than 99.00%, and reduced the soil available As content by 55.40%, 40.05%, and 16.92%, respectively. FM increased the specificandnon-specific adsorption of As to stabilize the bound fractions of hydrated iron-aluminum oxide, thus significantly reducing the biological effectiveness of soil As and soil environmental risk.FM reduced the available P in the soil in Shaoguan,Hechi, and Changde by 0.60%-6.67%, 15.74%-50.00%, and 32.48-40.39%, respectively. Our study revealed that FM can absorb a small amount of available P, which may limit P uptakeby agricultural products in P-deficient areas, while effectively inhibiting the non-point source pollution of soil to surrounding water bodiesin P-rich areas. The variation in pH after FM application in the three soils was only 0.04-0.07, which had little effect on the soil environment. FM has good prospects for stabilization of flooded As-contaminated soil. The results of this study provide an important scientific basis for soil As stabilization in China.

Expressing Arsenite Antiporter PvACR3;1 in Rice (Oryza sativa L.) Decreases Inorganic Arsenic Content in Rice Grains.

Rice (Oryza sativa) is a major food crop in the world, feeding half of the world's population. However, rice is efficient in taking up toxic metalloid arsenic (As), adversely impacting human health. Among different As species, inorganic As is more toxic than organic As. Thus, it is important to decrease inorganic As in rice to reduce human exposure from the food chain. The arsenite (AsIII) antiporter gene PvACR3;1 from As-hyperaccumulator Pteris vittata decreases shoot As accumulation when heterologously expressed in plants. In this study, three homozygous transgenic lines (L2, L4, and L7) of T3 generation were obtained after transforming PvACR3;1 into rice. At 5 μM of AsIII, PvACR3;1 transgenic rice accumulated 127%-205% higher As in the roots, with lower As translocation than wild type (WT) plants. In addition, at 20 μM of AsV, the transgenic rice showed similar results, indicating that expressing PvACR3;1 increased As retention in the roots from both AsIII and AsV. Furthermore, PvACR3;1 transgenic rice plants were grown in As-contaminated soils under flooded conditions. PvACR3;1 decreased As accumulations in transgenic rice shoots by 72%-83% without impacting nutrient minerals (Mn, Zn, and Cu). In addition, not only total As in unhusked rice grain of PvACR3;1 transgenic lines were decreased by 28%-39%, but also inorganic As was 26%-46% lower. Taken together, the results showed that expressing PvACR3;1 effectively decreased both total As and inorganic As in rice grain, which is of significance to breed low-As rice for food safety and human health.

Interaction among soil physicochemical properties, bacterial community structure, and arsenic contamination: Clay-induced change in long-term arsenic contaminated soils.

Pyrosequencing analyses to determine soil bacterial communities were conducted with forty-two soil samples collected from rice paddy and forest/farmland soils (Group A and B, respectively) at a long-term As-contaminated site. Soil physicochemical properties, such as the concentrations of As, Fe, Al, and Mn, pH, organic matter content, and clay content, were found to be significantly different with land use, and more importantly, strongly affected the bacterial community structure of the soil samples. When fitting the soil properties onto a nonmetric multidimensional scale plot of soil bacterial communities, clay content was found to be the most important factor in clustering the bacterial communities (R2 = 0.4831, p-value = 0.001). Phylum Chloroflexi (-1.03 of bioplot score) and Planctomycetes (1.31 of bioplot score) showed a significant relationship with clay content in soil samples. Interestingly, thebacterial phylotypes linked to clay content were only found in the soil samples of group B with low clay content, and had a strong relationship to As contamination in the redundancy analysis and the correlation analysis.Our results suggest that clay content seems to be negatively related to As contamination in soils, which, in turn, strongly influences the structure of bacterial communities in As-contaminated soil.

Arbuscular mycorrhizal fungi reduce arsenic uptake and improve plant growth in Lens culinaris.

Arsenic (As) is a carcinogenic and hazardous substance that poses a serious risk to human health due to its transport into the food chain. The present research is focused on the As transport in different lentil genotypes and the role of Arbuscular Mycorrhizal Fungi (AMF) in mitigation of As phyto-toxicity. Arsenic transport from soil to root, shoot and grains in different lentil genotypes was analyzed by flow injection hydride generation atomic absorption spectrophotometry. AMF were applied for the reduction of As uptake as well as the improvement of plant growth in lentil genotypes. Arsenic phyto-toxicity was dose-dependent as evidenced by relatively higher shoot length, fresh and dry weight of root and shoot in 5 and 15 mgkg-1 As-treated lentil plants than that in 100 mgkg-1 As-treated lentil. Arsenic accumulation occurred in roots and shoots of all BARI-released lentil genotypes. Arsenic accumulation in grains was found higher in BARI Mashur 1 than other lentil genotypes. AMF treatment significantly increased growth and biomass accumulation in lentil compared to that in non-AMF plants. Furthermore, AMF effectively reduced the As concentrations in roots and shoots of lentil plants grown at 8 and 45 mgkg-1 As-contaminated soils. This study revealed remarkable divergence in As accumulation among different BARI-released lentil genotypes; however, AMF could reduce As uptake and mitigate As-induced phyto-toxicity in lentil. Taken together, our results suggest a great potential of AMF in mitigating As transfer in root and shoot mass and reallocation to grains, which would expand lentil cultivation in As-affected areas throughout the world.