Modifying humus-phosphorus-arsenic interactions in sludge composting: The strengthening of phosphorus availability and arsenic efflux detoxification mechanisms.

Arsenic (As) in sewage sludge poses a significant threat to environmental and human health, which has attracted widespread attention. This study investigated the value of adding sodium percarbonate (SP) on phosphorus (P) availability and As efflux detoxification through HS-P-As interactions. Due to the unique structure of humus (HS) and the similar chemical properties of P and As, the conditions for HS-P-As interaction are provided. This study discussed the content, morphology and microbial communities of HS, P and As by using metagenomic and correlation analysis. The results showed that the humification index in the experiment group (SPC) was 2.34 times higher than that in the control group (CK). The available phosphorus (AP) content of SPC increased from 71.09 mg/kg to 126.14 mg/kg, and SPC was 1.11 times that of CK. The relative abundance of ACR3/ArsB increased. Pst, Actinomyces and Bacillus commonly participated in P and As conversion. The correlation analysis revealed that the humification process was enhanced, the AP was strengthened, and the As was efflux detoxified after SP amendment. All in all, this study elucidated the key mechanism of HS-P-As interaction and put forward a new strategy for sewage sludge resource utilization and detoxification.

Involvement of Arsenic Atom of AsF3 in Five Pnicogen Bonds: Differences between X-ray Structure and Theoretical Models.

Bonding within the AsF3 crystal is analyzed via quantum chemical methods so as to identify and quantify the pnicogen bonds that are present. The structure of a finite crystal segment containing nine molecules is compared with that of a fully optimized cluster of the same size. The geometries are qualitatively different, with a much larger binding energy within the optimized nonamer. Although the total interaction energy of a central unit with the remaining peripheral molecules is comparable for the two structures, the binding of the peripherals with one another is far larger in the optimized cluster. This distinction of much stronger total binding within the optimized cluster is not limited to the nonamer but repeats itself for smaller aggregates as well. The average binding energy of the cluster rises quickly with size, asymptotically approaching a value nearly triple that of the dimer.

Harmless Treatment of High Arsenic Tin Tailings and Environmental Durability Assessment.

The treatment of arsenic (As) in tin tailings (TT) has been an urgent environmental problem, and stabilization/solidification (S/S) treatment is considered an effective technology to eliminate contamination of As. In this study, we developed a low-carbon and low-alkalinity material to S/S of As, and the results showed that the leaching concentration of As after treatment was lower than the Chinese soil environmental quality standard (0.1 mg/L). Based on a series of characterization tests, we found that OH- promoted the dissolution of As(III)-S, Fe-As(V), and amorphous As(III)-O species and formed Ca-As(III) and Ca-(V) species with Ca2+. Simultaneously, hydration produces calcium silicate hydrate (C-S-H) gel and ettringite by the form of adsorption and ion exchange to achieve S/S of As. We also assessed the durability of this material to acidity and temperature, and showed that the leaching concentration of As was below 0.1 mg/L at pH = 1-5 and temperature 20-60 °C. The method proposed in this study, S/S of As, has excellent effect and environmental durability, providing a new solution for harmless treatment of TT and its practical application.

The enhanced removal of arsenite from water by double-shell CuOx@MnOy hollow spheres (DCMHS): behavior and mechanisms.

To facilitate removing As(III) from water through an "oxidation-adsorption" process, the double-shell CuOx@MnOy hollow spheres (DCMHS) have been fabricated via a two-step co-precipitation route combined with the soft-template method. The surface characterization results showed that Mn oxides were formed without segregation and uniformly distributed on the surface of CuOx hollow spheres. DCMHS could achieve outstanding performance to remove As(III) with an As maximum adsorption capacity of 32.15 mg/g. Meanwhile, the kinetics results illustrated that the oxidative activity of DCMHS was strengthened due to its specific structure, and part of As(III) was converted to As(V) during the adsorption process. Also, air aeration could further enhance As(III) oxidation and thus improving As removal. The As(III) removal performance could be maintained under neutral and weak alkaline conditions. Phosphate, silicate, and carbonate anions could depress the removal performance, while chloride ions and sulfate anions barely influenced As removal. Moreover, DCMHS could be regenerated using NaOH and KMnO4 solutions without breaking the hollow sphere structure. Based on the spectroscopic analysis results, As(III) molecules were converted to As(V) via two pathways, including the oxidation by Mn oxides or superoxide radicals. The Cu-Mn synergistic effect could not only enhance the oxidative activity of Mn oxides but also produce superoxide radicals via the activation of surface-adsorbed oxygen molecules. Afterwards, the newly formed As(V) could be attached to the hydroxyl groups through surface complexation. Therefore, this work has provided insights into the morphology design of Mn-oxide-containing adsorbents and supplemented the interface reaction mechanisms for enhancing As(III) removal.

Enhanced arsenic removal using lateritic bauxite modified by heating and blending.

The use of bauxite to remove arsenic from wastewater has been confirmed to be effective, but its removal efficiency in literature is not up to 90%, hence the need to devise a more effective method to remove arsenic from wastewater. In this study, a novel material was prepared by thermally modifying and blending yellow and red lateritic bauxite to form thermally modified and blended yellow and red lateritic bauxite (TYB + TRB). The adsorption isotherm, morphology and chemical composition of the novel material were determined by the Langmuir and Freundlich models, Scanning Electron Microscopy (SEM) and X-ray Fluorescence (XRF), respectively. Application of the novel material in arsenic removal resulted in >97% removal efficiency within 60 min. The arsenic adsorption by TYB + TRB conformed to the Freundlich model. The SEM image depicted a compacted earth material after use of the TYB + TRB to remove arsenic from the wastewater. The XRF results also showed a drastic reduction in the chemical composition of the novel bauxite except Ti, thus suggesting the occurrence of multiple mechanisms during the arsenic removal. This study demonstrated the potential of TYB + TRB to be developed and used as the most suitable material for wastewater treatment.

Arsenene Nanodots with Selective Killing Effects and their Low-Dose Combination with ß-Elemene for Cancer Therapy.

Arsenical drugs have achieved hallmark success in treating patients with acute promyelocytic leukemia, but expanding their clinical utility to solid tumors has proven difficult with the contradiction between the therapeutic efficacy and the systemic toxicity. Here, leveraging efforts from materials science, biocompatible PEGylated arsenene nanodots (AsNDs@PEG) with high monoelemental arsenic purity that can selectively and effectively treat solid tumors are synthesized. The intrinsic selective killing effect of AsNDs@PEG is closely related to high oxidative stress in tumor cells, which leads to an activated valence-change of arsenic (from less toxic As0 to severely toxic oxidation states), followed by decreased superoxide dismutase activity and massive reactive oxygen species (ROS) production. These effects occur selectively within cancer cells, causing mitochondrial damage, cell-cycle arrest, and DNA damage. Moreover, AsNDs@PEG when applied in a multi-drug combination strategy with ß-elemene, a plant-derived anticancer drug, achieves synergistic antitumor outcomes, and its newly discovered on-demand photothermal properties facilitate the elimination of the tumors without recurrence, potentially further expanding its clinical utility. In line of the practicability for a large-scale fabrication and negligible systemic toxicity of AsNDs@PEG (even at high doses and with repetitive administration), a new-concept arsenical drug with high therapeutic efficacy for selective solid tumor therapy is provided.

Evaluation of the nuclear reaction cross sections via proton induced reactions on 72Ge and 76Se to produce 72As: A potential entrant for the theranostic pairs.

Theranostic applications of radiopharmaceuticals have revolutionized present era specially, dealing with cancer diseases. Increase in the uses of radionuclides in nuclear medicine has resulted in the demands of optimized new radionuclides to be produced focussing on the economy, simplicity and maximum yield. Two radionuclides of arsenic offer a well agreed theranostic systems namely 77As and 72As. Some arsenic radionuclides are capable of positron-emission, with range of hour to weeks half-lives and have potential to be used for nuclear medicine. Present work will elucidate the production of 72As on Germanium and Selenium via proton induced nuclear reactions. The experimental results obtained by several nuclear reactions were analyzed. The results of nuclear model codes namely ALICE-IPPE, EMPIRE-3.2.3 and TALYS-1.9 are compared with the experimental cross sections to generate recommended cross section data. Recommended excitation functions are used to compute the thick target yields (TTY) of 72As. Assessment of radionuclidic impurities are also studied and comparison of several radionuclidic impurities is done. To produce 72As,72Ge (p, n)72As, 73Ge (p, 2n)72As, 74Ge (p, 3n)72As and 76Se (p, x)72As reactions in different energy ranges are discussed. We have identified 72Ge (p, n)72As reaction; gives pre-eminent yield with least impurities mark it as feasible entrant to be applied in Positron Emission Tomography (PET) and theranostic applications.

Removal of As(III) from Biological Fluids: Mono- versus Dithiolic Ligands.

Arsenic is one of the inorganic pollutants typically found in natural waters, and its toxic effects on the human body are currently of great concern. For this reason, the search for detoxifying agents that can be used in a so-called "chelation therapy" is of primary importance. However, to the aim of finding the thermodynamic behavior of efficient chelating agents, extensive speciation studies, capable of reproducing physiological conditions in terms of pH, temperature, and ionic strength, are in order. Here, we report on the acid-base properties of meso-2,3-dimercaptosuccinic acid (DMSA) at different temperatures (i.e., T = 288.15, 298.15, 310.15, and 318.15 K). In particular, its capability to interact with As(III) has been investigated by experimentally evaluating some crucial thermodynamic parameters (ΔH and TΔS), stability constants, and its speciation model. Additionally, in order to gather information on the microscopic coordination modalities of As(III) with the functional groups of DMSA and, at the same time, to better interpret the experimental results, a series of state-of-the-art ab initio molecular dynamics simulations have been performed. For the sake of completeness, the sequestering capabilities of DMSA-a simple dithiol ligand-toward As(III) are directly compared with those recently emerged from similar analyses reported on monothiol ligands.

Elevated Arsenic and Lead Concentrations in Natural Healing Clay Applied Topically as a Treatment for Ulcerative Dermatitis in Mice.

Ulcerative dermatitis in laboratory mice remains an ongoing clinical problem and animal welfare issue. Many products have been used to treat dermatitis in mice, with varying success. Recently, the topical administration of healing clays, such as bentonite and green clays, has been explored as a viable, natural treatment. We found high concentrations of arsenic and lead in experimental samples of therapeutic clay. Given the known toxic effects of these environmental heavy metals, we sought to determine whether the topical administration of a clay product containing bioavailable arsenic and lead exerted a biologic effect in mice that potentially could introduce unwanted research variability. Two cohorts of 20 singly housed, shaved, dermatitis free, adult male CD1 mice were dosed daily for 2 wk by topical application of saline or green clay paste. Samples of liver, kidney and whole blood were collected and analyzed for total arsenic and lead concentrations. Hepatic and renal concentrations of arsenic were not different between treated and control mice in either cohort; however, hepatic and renal concentrations of lead were elevated in clay treated mice compared to controls in both cohorts. In addition, in both cohorts, the activity of δ-aminolevulinate acid dehydratase, an enzyme involved with heme biosynthesis and a marker of lead toxicity, did not differ significantly between the clay-treated mice and controls. We have demonstrated that these clay products contain high concentrations of arsenic and lead and that topical application can result in the accumulation of lead in the liver and kidneys; however, these concentrations did not result in measurable biologic effects. These products should be used with caution, especially in studies of lead toxicity, heme biosynthesis, and renal α2 microglobulin function.

A Water-Stable Ionic MOF for the Selective Capture of Toxic Oxoanions of SeVI and AsV and Crystallographic Insight into the Ion-Exchange Mechanism.

Selectively capturing toxic oxoanions of selenium and arsenic is highly desired for the remediation of hazardous waste. Ionic metal-organic frameworks (iMOFs) especially cationic MOFs (iMOF-C) as ion-exchange materials, featuring aqueous phase stability, present a robust pathway for sequestration of the oxoanions owing to their ability to prevent leaching because of their ionic nature. On account of scarcity of water-stable cationic MOFs, the capture of oxoanions of selenium and arsenic has been a major challenge and has not been investigated using iMOFs. Herein, we demonstrate large scale synthesis of cationic MOF, viz. iMOF-1C that exhibits selective capture of oxoanions of SeVI (SeO42- ) and AsV (HAsO42- ) in water with a maximum sorption capacity of 100 and 85 mg g-1 , respectively. This represents among the highest uptake capacities observed for selenate oxoanion in MOFs. Further, the ion-exchange mechanism was directly unveiled by single crystal analysis, which revealed variable modes of host-guest binding.

Effect of phosphorus-modified biochars on immobilization of Cu (II), Cd (II), and As (V) in paddy soil.

Novel phosphorus-modified biochars were produced by pyrolyzing biomass feedstocks (wood, bamboo, cornstalk and rice husk) pre-impregnated with potassium phosphate (K3PO4). The soil heavy metal immobilization performance and mechanisms of modified biochars were investigated. Incubation experiments showed that impregnation with phosphorous can decrease the extraction of Cu (II) and Cd (II) by 2 to 3 times. Phosphorus-modified biochars enhanced the transformation of Cu (II) and Cd (II) ions from acid soluble to more stable forms. Characterization results showed that phosphorus (P) compounds in modified biochar played a vital role to immobilize Cu (II) and Cd (II) by forming precipitates or complexes with them. Additionally, the modified rice husk and cornstalk biochars have in the average 14-24% and 19-33% higher immobilization efficiency for Cd (II) and Cu (II) than the other two P-assisted biochars. However, regardless of the feedstock, both the extraction and mobility of As (V) were increased by phosphorous. This study indicates that the P-modified biochar can serve as a novel remediation agent for heavy metal polluted soils.

GaAs-Based InPBi Quantum Dots for High Efficiency Super-Luminescence Diodes.

InPBi exhibits broad and strong photoluminescence at room temperature, and is a potential candidate for fabricating super-luminescence diodes applied in optical coherence tomography. In this paper, the strained InPBi quantum dot (QD) embedded in the AlGaAs barrier on a GaAs platform is proposed to enhance the light emission efficiency and further broaden the photoluminescence spectrum. The finite element method is used to calculate the strain distribution, band alignment and confined levels of InPBi QDs. The carrier recombinations between the ground states and the deep levels are systematically investigated. A high Bi content and a flat QD shape are found preferable for fabricating super-luminescence diodes with high efficiency and a broad emission spectrum.

Arsenic accumulation in edible vegetables and health risk reduction by groundwater treatment using an adsorption process.

The heavy metals transfer from the soil, where they accumulate, to the edible parts of the plants, and then, their entrance in the food chain can represent a source of concern for human health. Among heavy metals, arsenic is one of the most widespread in the soil of Lazio (central region of Italy), where the phytoavailable geogenic arsenic enters the food chain, with a dangerous exposition of the local population. In the first part of this work, plants of radish (Raphanus sativus L.) and lettuce (Lactuca sativa L.) were grown in protected culture in the experimental farm of CREA-AA, where they were daily treated with different concentrations of sodium arsenate dibasic heptahydrate in order to investigate differences in their arsenic accumulation capacities. In order to confirm the results achieved, in the second part of this study, the arsenic concentration was determined in commercial products obtained from contaminated areas of Lazio, and the potential exposition risk for human health through consumption of these widely consumed vegetables was estimated. The highest arsenic concentrations were found in the samples of lettuce. To evaluate the potential health risk from consumption of L. sativa and R. sativus, the estimated daily intake (EDI) for adults, adolescents, and elderly was calculated, finding that HRI (health risk index) index value for arsenic was low (< 1) in the case of chronic consumptions for all samples of radishes, and for the lettuces grown in the area of Viterbo. On the contrary, the lettuces obtained from Tuscania and Tarquinia presented very high concentrations of arsenic and a worrying HRI value. In order to reduce the risk of As toxicity in the people through consumption of the vegetables, the irrigation water should contain less than 0.1 mg As L-1. For this reason, the authors tested the application of red mud (RM) to remove As from groundwater before using it for the irrigation of radish and lettuce in greenhouse production.

Geochemical conditions conducive for retention of trace elements and radionuclides during shale-fluid interactions.

Produced water generated during unconventional oil and gas extractions contains a complex milieu of natural and anthropogenic potentially toxic chemical constituents including arsenic (As), chromium (Cr), and cadmium (Cd), naturally occurring radioactive materials (NORMs) including U and Ra, and a myriad of organic compounds. The human-ecological health risks and challenges associated with the disposal of produced water may be alleviated by understanding geochemical controls on processes responsible for the solubilization of potentially hazardous natural shale constituents to produced water. Here, we investigated, through a series of batch treatments, the leaching behavior of As, Se, Cu, Fe, Ba, Cr, Cd, and radioactive nuclides U, Ra from shale to produced water. Specifically, the effect of four major controls on element mobility was studied: (1) solution pH, (2) ionic strength of the solution, (3) oxic-anoxic conditions, and (4) an additive used in fracking fluid. The mobilization of metals and metalloids from shale was greatest in treatments containing sodium persulfate, an oxidant and a commonly used additive in fracture fluid. In the high ionic strength treatments, dissolved Ba concentrations increased 5-fold compared to low ionic strength treatments. Overall, anoxic conditions superimposed with low pH resulted in the largest increase of dissolved metals and radionuclides such as Ra. Overall, our results suggest that (1) limiting pore water acidification by injection of alkaline fluid in carbonate-low shale and (2) minimizing strong oxidizing conditions in shale formations may result in cost-effective in situ retention of produced water contaminants.

Nutrient distribution and structure affect the behavior and speciation of arsenic in coastal waters: A case study in southwestern coast of the Laizhou Bay, China.

The effects of nutrient distribution and structure on the behavior and speciation of dissolved inorganic arsenic (DIAs) in coastal waters were analyzed based on the data of 48 surface water samples collected in the southwestern coast of Laizhou Bay and its adjacent rivers (SWLZB). The concentration of DIAs in the SWLZB ranged from 0.016 to 0.099 µmol l-1 and generally decreased from west to south. The inshore waters exhibited higher DIAs level than the open ocean. The As5+/As3+ ratio was significantly positively correlated with the concentration of TDN, NO3-N, PO4-P, DSi, Chl-a and DO. The concentration of DIAs was strongly correlated with the concentration of PO4-P and DSi, suggesting that adsorption/desorption was an important process for regulating the total DIAs concentration. The results indicated that the distribution of nutrients might well be an important environmental factor affecting the speciation and behavior of DIAs in surface water of the SWLZB.

Ultra-fast enrichment and reduction of As(V)/Se(VI) on three dimensional graphene oxide sheets-oxidized carbon nanotubes hydrogels.

The removals of arsenic and selenium pollutants are always urgent desires for the water security. In this study, both sorption and catalysis strategies were combined for the effective removals of As(V) and Se(VI) over magnetic graphene oxide sheets (GOs)-oxidized carbon nanotubes (OCNTs) hydrogels. The sorption behavior facilitated the operation of catalysis reactions, meanwhile, the catalytic reduction promoted the release of occupied sorption sites and then restarted a new sorption-catalysis cycle. The synergic effect of sorption and catalysis realized 258.2 mg g-1 for As(V) enrichment capacity on MPG2T1, and ultra-fast sorption and catalysis equilibriums were identified within 9 min. In the case of Se(VI), a moderate enrichment performance was observed to be 46.2 mg g-1. Similarly, the ultra-fast sorption and reduction of Se(VI) were realized within 2 min. In the competition experiments, only SO42-, SO32-, and HPO42- showed interference for As(V) and Se(VI) removals. These results testified the superiority of the synergy effect of sorption and catalysis, and the feasibility of 3D magnetic GOs-OCNTs hydrogel in practical implementations.

Dual in-aquifer and near surface processes drive arsenic mobilization in Cambodian groundwaters.

Millions of people globally, and particularly in South and Southeast Asia, face chronic exposure to arsenic from reducing groundwaters in which. Arsenic release to is widely attributed largely to reductive dissolution of arsenic-bearing iron minerals, driven by metal reducing bacteria using bioavailable organic matter as an electron donor. However, the nature of the organic matter implicated in arsenic mobilization, and the location within the subsurface where these processes occur, remains debated. In a high resolution study of a largely pristine, shallow aquifer in Kandal Province, Cambodia, we have used a complementary suite of geochemical tracers (including 14C, 3H, 3He, 4He, Ne, δ18O, δD, CFCs and SF6) to study the evolution in arsenic-prone shallow reducing groundwaters along dominant flow paths. The observation of widespread apparent 3H-3He ages of <55years fundamentally challenges some previous models which concluded that groundwater residence times were on the order of hundreds of years. Surface-derived organic matter is transported to depths of >30m, and the relationships between age-related tracers and arsenic suggest that this surface-derived organic matter is likely to contribute to in-aquifer arsenic mobilization. A strong relationship between 3H-3He age and depth suggests the dominance of a vertical hydrological control with an overall vertical flow velocity of ~0.4±0.1m·yr-1 across the field area. A calculated overall groundwater arsenic accumulation rate of ~0.08±0.03µM·yr-1 is broadly comparable to previous estimates from other researchers for similar reducing aquifers in Bangladesh. Although apparent arsenic groundwater accumulation rates varied significantly with site (e.g. between sand versus clay dominated sequences), rates are generally highest near the surface, perhaps reflecting the proximity to the redox cline and/or depth-dependent characteristics of the OM pool, and confounded by localized processes such as continued in-aquifer mobilization, sorption/desorption, and methanogenesis.

Remediation of arsenic from contaminated seawater using manganese spinel ferrite nanoparticles: Ecotoxicological evaluation in Mytilus galloprovincialis.

In the last decade different approaches have been applied for water remediation purposes, including the use of nanoparticles (NPs) to remove metals and metalloids from water. Although studies have been done on the toxic impacts of such NPs, very scarce information is available on the impacts of water after decontamination when discharged into aquatic environments. As such, in the present study we aimed to evaluate the ecotoxicological safety of seawater previously contaminated with arsenic (As) and remediated by using manganese-ferrite (MnFe2O4-NPs) NPs. For this, mussels Mytilus galloprovincialis were exposed for 28 days to different conditions, including clean seawater (control), As (1000 µg L-1) contaminated and remediated (As 70 µg L-1) seawater, water containing MnFe2O4- NPs (50 mg L-1) with and without the presence of As. At the end of exposure, concentrations of As in mussels tissues were quantified and biomarkers related to mussels' metabolism and oxidative stress status were evaluated. Results revealed that mussels exposed to water contaminated with As and to As + NPs accumulated significantly more As (between 62% and 76% more) than those exposed to remediated seawater. Regarding biomarkers, our findings demonstrated that in comparison to remediated seawater (conditions a, b, c) mussels exposed to contaminated seawater (conditions A, B, C) presented significantly lower metabolic activity, lower expenditure of energy reserves, activation of antioxidant and biotransformation defences, higher lipids and protein damages and greater AChE inhibition. Furthermore, organisms exposed to As, NPs or As + NPs revealed similar biochemical effects, both before and after water decontamination. In conclusion, the present study suggests that seawater previously contaminated with As and remediated by MnFe2O4-NPs presented significantly lower toxicity than As contaminated water, evidencing the potential use of these NPs to remediate seawater contaminated with As and its safety towards marine systems after discharges to these environments.

Urinary concentrations of environmental metals and associating factors in pregnant women.

Pregnant women, a vulnerable population, can be exposed to a variety of environmental metals that may adversely affect their health at elevated concentrations. Moreover, environmental exposure and risk disparities are associated with several factors such as sociodemographic characteristics, pregnancy complications, and nutritional supplementation indicators. Our aim was to investigate whether and how the urinary metal concentrations vary according to these factors in a large pregnancy and birth cohort. Urinary levels of seven metals including manganese, zinc, selenium, arsenic, cadmium, thallium, and lead were assessed in 7359 participants across Wuhan City in China. In all, 7359 urine samples from the third trimester were analyzed and 15 sociodemographic characteristics, pregnancy complications, and nutritional supplementation indicators were assessed: maternal age, household income, multivitamin supplements during pregnancy, etc. Concentrations of Zn, As, and Cd were detected in all urine samples; Mn, Se, Tl, and Pb were detected in 95.3%, 99.8%, 99.8%, and 99.9% urine samples, respectively. The geometric mean (GM) of creatinine-adjusted urinary Mn, Zn, Se, As, Cd, Tl, and Pb concentrations were 1.42, 505.44, 18.24, 30.49, 0.64, 0.55, and 3.69 µg/g. Factors that associated with environmental metals concentration were as follows: (1) Urinary Zn and Cd concentrations increased with maternal age. (2) Pregnant women with higher education had lower Cd concentrations. (3) Pregnant women with folic acid supplementation had lower Mn and with multivitamin supplementation had higher Se and lower Tl. Our results demonstrated that the maternal age, education level, folic acid supplementation, and multivitamin supplementation were significantly associated with environmental metal concentrations. Furthermore, studies are recommended to explore the influence of diet on biological metals concentrations in more detail.

Modulation of photosynthetic parameters, sugar metabolism, polyamine and ion contents by silicon amendments in wheat (Triticum aestivum L.) seedlings exposed to arsenic.

The objective of the present investigation was to consider the effectiveness of exogenous silicate supplementation in reviving the arsenate imposed alterations on pigment content, Hill activity, photosynthetic parameters, sugar metabolism, polyamine, and ion contents in wheat (Triticum aestivum L. cv. PBW-343) seedlings. Experiments were conducted under different levels of arsenate (0, 25 µM, 50 µM, and 100 µM) in combination with silicate (0, 5 mM) in a hydroponic environment with modified Hoagland's solution for 21 days to determine the ameliorative role of silicon (Si). Arsenate exposure led to a decline in chlorophyll content by 28% and Hill activity by 30% on an average along with photosynthetic parameters. Activity of starch phosphorylase increased causing a subsequent decrease in starch contents by 26%. Degradation of starch enhanced sugar contents by 61% in the test cultivar. Dose-dependant increments in the activities of carbohydrate metabolizing enzymes viz., sucrose synthase, sucrose phosphate synthase, and acid invertase were also noted. Putrescine content was significantly enhanced along with a consequent decline in spermidine and spermine contents. The macro- and micronutrient contents declined proportionally with arsenate imposition. Conversely, silicate amendments irrespective of all arsenate concentrations brought about considerable alterations in all parameters tested with respect to arsenate treatment alone. Marked improvement in pigment content and Hill activity also improved the gas exchange parameters. Soluble sugar contents decreased and starch contents were enhanced. Increase in polyamine contents improved the ionic balance in the test cultivar as well. This study highlights the potentiality of silicon in ameliorating the ecotoxicological risks associated with arsenic pollution and the probable ability of silicon to offer an approach in mitigating arsenate-induced stress leading to restoration of growth and metabolism in wheat seedlings.