Arsenic Immobilization Research Articles

Synergistic effect between biochar and nitrate fertilizer facilitated arsenic immobilization in an anaerobic contaminated paddy soil

Nitrate nitrogen fertilizer was usually used to mitigate arsenic (As) release and mobilization in the anaerobic contaminated paddy soil. However, the effect of the interplay between nitrate fertilizer and biochar on As availability as well as the involved mechanism were poorly understood. Herein, the effects and mechanisms of biochar, nitrate fertilizer, and biochar-based nitrate fertilizer on the availability of As in the contaminated paddy soil were investigated via a microcosm incubation experiment. Results indicated that the application of biochar-based nitrate fertilizer significantly lessened the available As concentration in the contaminated paddy soil from 3.01 ± 0.03 (control group) to 2.24 ± 0.08 mg kg−1, which presented an immobilization efficiency of 26.6 % better than those of individual biochar (13.5 %) and nitrate fertilizer (17.6 %), exhibiting a synergistic effect. Moreover, the biochar-based nitrate fertilizer also facilitated the transformation of more toxic arsenite in the contaminated soil to less toxic arsenate. Further, biochar-based nitrate fertilizer increased soil redox potential (Eh), dissolved organic carbon, organic matter, and nitrate yet decreased soil pH and ammonium, which changed the microbial community in the soil, enhancing the relative abundance of Bacillus, Arthrobacter, and Paenibacillus. These functional microorganisms drove the coupled transformation between nitrate denitrification and Fe(II) or As(III) oxidation, favoring As immobilization in the anaerobic paddy soil. Additionally, the co-application of biochar offset the negative effect of single nitrate fertilizer on microbial community diversity. Overall, biochar-based nitrate fertilizer could be a promising candidate for the effective immobilization of As in the anaerobic paddy soil. The current research can provide a valuable reference to the remediation of As-contaminated paddy soil and the production of safe rice.

Reclamation of co-pyrolyzed dredging sediment as soil cadmium and arsenic immobilization material: Immobilization efficiency, application safety, and underlying mechanisms

The safe management of toxic metal-polluted dredging sediment (DS) is imperative owing to its potential secondary hazards. Herein, the co-pyrolysis product (DS@BC) of polluted DS was creatively applied to immobilize soil Cd and As to achieve DS resource utilization, and the efficiency, safety, and mechanism were investigated. The results revealed that the DS@BC was more effective at reducing soil Cd bioavailability than the DS was (58.9–73.2% vs. 21.8–27.4%), except for the dilution effect, whereas the opposite phenomenon occurred for soil As (25.5–35.7% vs. 35.7–42.8%). The DS@BC immobilization efficiency was dose-dependent for both Cd and As. Soil labile Cd and As were transformed to more stable fractions after DS@BC immobilization. DS@BC immobilization inhibited the transfer of soil Cd and As to Brassica chinensis L. and did not cause excessive accumulation of other toxic metals in the plants. The appropriate addition of the DS@BC (8%) sufficiently alleviated the oxidative stress response of the plants and enhanced their growth. These findings indicate that the DS@BC was safe and effective for soil Cd and As immobilization. DS@BC immobilization decreased the diversity and richness of the rhizosphere soil bacterial community because of the dilution effect. The DS@BC immobilized soil Cd and As via direct adsorption, and indirect increasing soil pH, and regulating the abundance of specific beneficial bacteria (e.g., Bacillus). Therefore, the use of co-pyrolyzed DS as a soil Cd and As immobilization material is a promising resource utilization method for DS. Notably, to verify the long-term effects and safety of DS@BC immobilization, field trials should be conducted to explore the effectiveness and risk of harmful metal release from DS@BC immobilization under real-world conditions.

Stabilization of Arsenic and Heavy Metal Contaminated Soil Using Fishery By-Products and Evaluation of Heavy Metal Uptake in Crops

Objectives : Heavy metals eluted from mine waste pollute surrounding soil and water systems, which can spread to crops and have a harmful effect on the human body. The purpose of this study was to evaluate the feasibility of recycling discarded mussel shells(MS) and manila clam shells (MC) as stabilizers for the immobilization of arsenic(As) and heavy metals(Pb, Zn) in soil.Methods : MS and MC were processed with -#10 mesh natural material, -#20 mesh natural material, and -#10 mesh calcined material and treated at 0-10 wt%. After 1 week or 4 weeks of wet curing, it was eluted with 0.1 N HCl and the concentrations of As, Pb, and Zn in the soil were analyzed through inductively coupled plasma optical emission spectroscopy(ICP-OES) analysis. In addition, red lettuce was cultivated in the stabilized soil and the concentration of heavy metals that were transferred to crops was evaluated. The stabilization mechanism was investigated by scanning electron microscopy-energy dispersive X-ray spectroscopy(SEM-EDX) analysis.Results and Discussion : The stabilization efficiency for arsenic and heavy metals was in the order of natural -#10 mesh < natural -#20 mesh < calcined -#10 mesh. The calcined stabilizer showed a high stabilization efficiency of 98% at a 2 wt% treatment level. Pb was not detected in the red lettuce grown in the stabiliz ed soil, and the standard for leafy vegetables (Pb-0.3 mg/kg or less) was satisfied according to the Ministry of Food and Drug Safety. The SEM-EDX analysis revealed that As was stabilized through Ca-As precipitation and heavy metals(Pb, Zn) were stabilized through pozzolanic reactions.Conclusion : Stabilizers developed from MS and MC can be effectively applied to the stabilization of As and heavy metal-contaminated soil, and are expected to be used as economical and environmentally friendly stabilizers.

Cerium(III)-induced structural transformation of hexagonal birnessite: Effect of mineral phase transition on arsenite transport and valence changes

The widespread mining and application of rare earth elements (REEs) have led to their continuous accumulation in the environment, with increasing concentrations in soil. The interaction between the most abundant REEs, cerium (Ce), and the prevalent hexagonal birnessite (HB) in the environment is worth attention. HB is one of the most effective metal oxides for the oxidation of arsenite [As(III)] and subsequent adsorption, and thus for arsenic (As) immobilization. Therefore, in this study, we investigated the effect of the presence of Ce(III) ion on the HB formation process and the influence of generating minerals on the oxidation and removal of As(III). Research has found that the interfacial reactions of REEs in manganese (Mn) minerals not only affect their cycling but also alter the properties of the Mn minerals, thereby affecting the environmental fate of As. The results indicated that the presence of Ce ions affected the structure of HB during mineral synthesis and reduced the crystallinity of the conversion products. Their substitution for Mn(IV) in the lattice increased the specific surface area of minerals, reduced particle size, and produced more hydroxyl groups that were conducive to the immobilization of As(III). Meanwhile, Ce(III) was oxidized to Ce(IV) during the formation of Ce-bearing hexagonal birnessite (Ce-HB), and CeO2 nanoparticles were formed on the mineral surface and the removal rate of As(III) by Ce-HB was greatly improved. When the As concentration was lower than 6 mg·L−1, the removal effect of Ce-HB could reach the drinking water standard. However, the oxidation rate decreased due to the decrease in the proportion of Mn(IV). This study fundamentally reveals the behavior of HB coexisting with Ce in the migration and transformation of As(III) in the environment.

Activated carbon-mediated arsenopyrite oxidation and arsenic immobilization: ROS formation and its role

The oxidative dissolution of arsenopyrite (FeAsS) is a significant source of arsenic contamination in nature. Activated biochar (AC), a widely used environmental remediation agent, is prevalent in ecosystems and participated in various geochemical processes of arsenic and iron-containing sulfide minerals. However, the impact of AC-arsenopyrite association on reactive oxidation species (ROS) generation and its contribution to As transformation were rarely explored. Here, ROS formation and the redox conversion of As during the interaction between AC and arsenopyrite were investigated. AC-mediated arsenopyrite oxidation was a two-stage process. At stage I, the heterogeneous electron transfer from arsenopyrite facilitated O2 reduction on AC, enhancing arsenopyrite dissolution and ROS formation. TBA, PBQ and catalase inhibited 86.40 %, 79.39 % and 49.66 % of As(III) oxidation, respectively, indicating indicated that HO˙, (O2•)- and H2O2 were responsible for As(III) oxidation. However, at stage II, the mobility of As was highly restricted, especially increasing AC addition. Besides adsorption, AC retained appreciable As through catalyzing insoluble ferric arsenate formation and growth by promoting Fe(II) and As(III) oxidation and functioning as nuclei. These findings deepen our understanding of the coupling behavior of AC-arsenopyrite and its influence on geochemical cycling of arsenic in mined surroundings, which has important implications for mitigating arsenic pollution.

Arsenic immobilization from high-As sulfide copper ores through high-pressure leaching with ferric and sodium chloride media

The processing of high-impurity ores has become increasingly common in recent years. Enargite (Cu3AsS4) is an important source of copper, but it is notorious for its high arsenic content, posing serious environmental concerns. This study explores the potential of a high-pressure leaching system for treating high-arsenic-containing copper ores. The leaching behavior of enargite was studied to elucidate the role of ferric sulfate and NaCl in enhancing the dissolution of enargite and the fixation of As in the residue. Under optimized leaching conditions of 160 °C, 1.0 MPa, 0.1 mol/L Fe2(SO4)3, and 0.34 mol/L NaCl, excellent copper extractions (97 %) and immobilization of arsenic (98 %) was achieved. The Fe/As ratio in the feed significantly influenced arsenic removal minerals, with lower ratios of less than 1 favoring scorodite precipitation, while higher ratios (Fe/As > 1) promoted arsenic removal through sorption and co-precipitation with natrojarosite. Sodium chloride addition enhanced natrojarosite precipitation, reducing the total dissolved iron in the leachate. Arsenic attenuation onto jarosite was found to be difficult to form in the absence of NaCl and was more effective with mixed minerals (enargite, chalcopyrite, and pyrite) as opposed to only enargite. A relationship was established between Fe and free acidity in the leachate when NaCl was used, with a correlation coefficient of 0.992. Additionally, a correlation coefficient of 0.921 was obtained between final Fe and As concentrations in the leachate suggesting that As tenors can be managed by controlling free acidity. Evaluation of the environmental stability of the leach residue using the TCLP test showed an As leachability of 5.84 mg/L.

Arsenic immobilization and greenhouse gas emission depend on quantity and frequency of nitrogen fertilization in paddy soil

Nitrogen (N) fertilization in paddy soils decreases arsenic mobility and methane emissions. However, it is unknown how quantity and frequency of N fertilization affects the interlinked redox reactions of iron(II)-driven denitrification, iron mineral (trans-)formation with subsequent arsenic (im-)mobilization, methane and nitrous oxide emissions, and how this links to microbiome composition. Thus, we incubated paddy soil from Vercelli, Italy, over 129 days and applied nitrate fertilizer at different concentrations (control: 0, low: ∼35, medium: ∼100, high: ∼200 mg N kg−1 soil−1) once at the beginning and after 49 days. In the high N treatment, nitrate reduction was coupled to oxidation of dissolved and solid-phase iron(II), while naturally occurring arsenic was retained on iron minerals due to suppression of reductive iron(III) mineral dissolution. In the low N treatment, 40 μg L−1 of arsenic was mobilized into solution after nitrate depletion, with 69 % being immobilized after a second nitrate application. In the non-fertilized control, concentrations of dissolved arsenic were as high as 76 μg L−1, driven by mobilization of 36 % of the initial mineral-bound arsenic. Generally, N fertilization led to 1.5-fold higher total GHG emissions (sum of CO2, CH4 and N2O as CO2 equivalents), 158-fold higher N2O, and 7.5-fold lower CH4 emissions compared to non-fertilization. On day 37, Gallionellaceae, Comamonadaceae and Rhodospirillales were more abundant in the high N treatment compared to the non-fertilized control, indicating their potential role as key players in nitrate reduction coupled to iron(II) oxidation. The findings underscore the dual effect of N fertilization, immobilizing arsenic in the short-term (low/medium N) or long-term (high N), while simultaneously increasing N2O and lowering CH4 emissions. This highlights the significance of both the quantity and frequency of N fertilizer application in paddy soils.

Immobilization capacity of element arsenic in alkali-activated slag-arsenic tailing system during self-healing process

The utilization of alkali-activated slag systems for encapsulating hazardous tailings to produce polymers can effectively reduce the leaching of hazardous elements. Nevertheless, the propensity of these polymers to develop cracks during service poses a risk of secondary release of hazardous elements. For this reason, this study focused on the development of polymer materials using calcium carbide residue (CCR), phosphogypsum (PG), ground granulated blast furnace slag (GGBS), superabsorbent polymers (SAP), and arsenic-containing tailings. The self-healing behavior of the alkali-activated slag system after cracking was analyzed, specifically targeting arsenic immobilization. Additionally, the crack width, crack area, and mechanical properties of the polymers was tested to evaluate their self-healing potential. The results revealed that the main healing products consisted of calcium silicate hydrate (C–S–H), ettringite (AFt), and calcite. These products covered the inner surfaces of the cracks, resulting in a reduction by 78.1–95.9% in arsenic leaching concentration after healing for 56 days. The incorporation of PG led to increased generation of AFt and facilitated secondary hydration reactions for self-healing. This enhanced crack closure and promoted strength recovery while simultaneously improving the pore structure of the crack walls. As a result, the leaching of arsenic from the cracked polymer was effectively inhibited. The mechanism of arsenic immobilization by polymers during self-healing process was as follows: i) adsorption of AsO43− by C–S–H; ii) ion exchange of AFt with AsO43−; iii) physical encapsulation of mixed products including C–S–H, AFt, calcite, and swollen SAP.

Nanoconfined Fe(II) releaser for long-term arsenic immobilization and its sustainability assessment

Ferrous (Fe(II))-based oxygen activation for pollutant abatements in soil and groundwater has attracted great attention, while the low utilization and insufficient longevity of electron donors are the primary challenges to hinder its practical applications. Herein, we propose a nanoconfined Fe(II) releasing strategy that enables stable long-term electron donation for oxygen activation and efficient arsenic (As) immobilization under oxic conditions, by encapsulating zero-valent iron in biomass-derived carbon shell (ZVI@porous carbon composites; ZVI@PC). This strategy effectively enhances the generation of reactive oxygen species, enabling efficient oxidation and subsequent immobilization of As(III) in soils. Importantly, this Fe(II) releaser exhibits strong anti-interference capability against complex soil matrices, and the accompanying generation of Fe(III) enables As immobilization in soils, effectively lowering soil As bioavailability. Soil fixed-bed column experiments demonstrate a 79.5 % reduction of the total As in effluent with a simulated rainfall input for 10 years, indicating the excellent long-term stability for As immobilization in soil. Life cycle assessment results show that this Fe(II) releaser can substantially mitigate the negative environmental impacts. This work offers new insights into developing green and sustainable technologies for environmental remediation.

Effect of porous media heterogeneity and FeS re-generation for multiple cycles on arsenic immobilization under in-situ conditions

Arsenic (As) contamination in groundwater is a well-established concern. Several studies have explored the possibility of immobilizing arsenite [As (III)] in-situ within the aquifer. Recent studies show a uniform distribution of ferrous sulfate (FeS) synthesized within homogenous porous media and demonstrated promising performance in immobilizing As(III). Upscaling from bench-scale to field-scale systems involves the integration of physical and chemical heterogeneities. Thus, the distribution of reducing agent (i.e., FeS), subsequent capturing of As(III) in the upscaled heterogeneous porous media system is a complex and uncertain phenomenon. Therefore, this study focuses on assessing the performance of FeS when synthesized for multiple cycles under constant flow and constant head conditions for immobilization of As(III) through a heterogeneous porous media system. A 3-D heterogenous porous media system is first simulated using a sequential indicator simulator model (SISIM). Then, the same heterogeneous media is prepared in the laboratory by packing three different-sized sand within a 3-D tank (0.67 m × 0.40 m × 0.40 m) which is subdivided into a total of 150 grids (0.096 m × 0.08 m × 0.08 m). FeS is synthesized in-situ by sequential injection of sodium sulfide (Na2S) and ferrous sulfate (FeSO4‧6H2O), as detailed in the previous study. The outcome of the study suggests that flow within the model subsurface porous media is non-uniform and follows an inter-connected preferential flow path. The progression of in-situ synthesized FeS is faster in the areas of higher hydraulic conductivity. The immobilization of As (88%) is promising by FeS synthesized within heterogeneous porous media. An overall reduction of porosity (7.7%) and hydraulic conductivity (68.3%) are observed, which is more predominant along the preferential flow path where deposition of FeS is significantly higher. To maintain constant flow rate, 60% increase in head difference is required. Whereas the flow rate decreases by 47.2% when constant head condition is adopted. Overall, the newly synthesized FeS shows promising performance in immobilizing As(III) within heterogeneous model subsurface porous media; however, there might be some possibility of pore-clogging and bypassing of flow due to deposition and subsequent retention of As, which may impact the As removal efficiency in the longer run.

Mechanistic studies of adsorption and ion exchange of Si(OH)4 molecules on the surface of scorodites

Scorodites are commonly used for arsenic immobilization, and it is also the main component of arsenic bearing tailings. Alkali-activated geopolymers are commonly used to landfill arsenic-bearing minerals. However, there no previous studies have explored the interaction between geopolymer molecules and the surface of scorodite. In this paper, Si(OH)4 as a monomer molecule of geopolymer, the mechanism of adsorption and ‘ion exchange’ between Si(OH)4 molecule and the surface of scorodite during alkali-activation is studied. Results show that the Fe-terminated scorodite (010) surface has high stability. Si(OH)4 are more easily adsorbed on the hollow site of an Fe-terminated scorodite (010) surface, which is described as chemisorption. Compared with Si(OH)4, NaOH is easier to adsorb on an Fe-terminated scorodite (010) surface. The co-adsorption of NaOH and Si(OH)4 on the Fe-terminated scorodite (010) surface was studied, and also belongs to chemical adsorption. When the hydroxyl binds to the As atom, the adsorbed Si(OH)4 is more likely to undergo an ‘ion exchange’ reaction with the surface, and the reaction is barrierless. The intermediate As(OH)4 produced by the ‘ion exchange’ reaction can be deprotonated to form an arsenate molecule, which can occur spontaneously. This work reveals that the interaction mechanism of geopolymer molecules on surface of scorodite.

Scorodite synthesis process using solid iron oxides

The immobilization of arsenic in the form of scorodite (FeAsO4·2H2O), which has excellent chemical stability, is attracting attention as a method for treating wastewater containing high concentrations of arsenic generated at nonferrous metal smelting plants. Scorodite, with its low solubility and high arsenic content per volume, is expected to be an environmentally friendly arsenic fixation method suitable for final disposal. Various scorodite synthesis methods have been studied. The first synthesis method proposed is the hydrothermal method using an autoclave to synthesize highly crystalline scorodite. Although the hydrothermal method is capable of synthesizing scorodite with good crystallinity, from an economic point of view, scorodite synthesis under ambient pressure and at low temperatures is more attractive. As a low-temperature scorodite synthesis method under atmospheric pressure, the oxidation of Fe(II) process by O2 bubbling was proposed. In this method, ferrous sulfate is added to an arsenic-containing solution as a Fe ion source, and in situ oxidation of Fe(II) by O2 or air bubbling to form scorodite with good crystallinity. In addition to temperature, other conditions, pH, Fe/As ratio, and reaction time have been reported to affect scorodite crystallization. Recently, scorodite synthesis using solid iron oxide as the Fe source for scorodite synthesis, instead of aqueous Fe salt solutions, has attracted much attention. In this presentation, we will report on the investigation of reaction parameters, such as the type of iron oxide and reaction temperature, for the scorodite synthesis using solid iron oxide.

In situ arsenic immobilization by natural iron (oxyhydr)oxide precipitates in As–contaminated groundwater irrigation canals

Arsenic-contaminated groundwater is widely used in agriculture. To meet the increasing demand for safe water in agriculture, an efficient and cost-effective method for As removal from groundwater is urgently needed. We hypothesized that Fe (oxyhydr)oxide (FeOOH) minerals precipitated in situ from indigenous Fe in groundwater may immobilize As, providing a solution for safely using As-contaminated groundwater in irrigation. To confirm this hypothesis and identify the controlling mechanisms, we comprehensively evaluated the transport, speciation changes, and immobilization of As and Fe in agricultural canals irrigated using As-contaminated groundwater. The efficiently removed As and Fe in the canals accumulated in shallow sediment rather than subsurface sediment. Linear combination fitting (LCF) analysis of X–ray absorption near edge spectroscopy (XANES) indicated that As(V) was the dominant As species, followed by As(III), and there was no FeAsO4 precipitate. Sequential extraction revealed higher contents of amorphous FeOOH and associated As in shallower sediment than in the subsurface layer. Stoichiometric molar ratio calculations, SEM‒EDS, FTIR, and fluorescence spectroscopy collectively demonstrated that the microbial reductive dissolution of amorphous FeOOH proceeded via reactive dissolved organic matter (DOM) consumption in subsurface anoxic porewater environment facilitating high labile As, whereas in surface sediment, the in situ-generated amorphous FeOOH was stable and strongly inhibited As release via adsorption. In summary, groundwater Fe2+ can efficiently precipitate in benthic surface sediment as abundant amorphous FeOOH, which immobilizes most of the dissolved As, protecting agricultural soil from contamination. This field research supports the critical roles of the phase and reactivity of in situ-generated FeOOH in As immobilization and provides new insight into the sustainable use of contaminated water.

Biochar-supported zero-valent iron enhanced arsenic immobilization in a paddy soil: the role of soil organic matter

Arsenic (As) detoxification in polluted soils by iron-based materials can be mediated by the endogenous soil organic matter (SOM), nevertheless the mechanisms remain unclear. Herein, endogenous SOM in a paddy soil was substantially removed to understand its roles on As immobilization by biochar-supported zero-valent iron (ZVI/BC). The results demonstrated that ZVI/BC application significantly decreased As bioavailability by 64.2% compared with the control soil under the anaerobic condition. XPS and HR-TEM suggested As immobilization by ZVI/BC mainly invoked the formation of ternary complexes (i.e., As-Fe-SOM). However, SOM depletion compromised the efficacy of ZVI/BC for As immobilization by 289.8%. This is likely because SOM depletion increased the fulvic acid and OH− contents in soils. Besides, ZVI/BC increased the proportion of As(III) in available As fraction, but SOM depletion altered the mechanisms associated with As(V) reduction. That is, As(V) reduction resulted from the reductive capacity of ZVI in the pristine soil, but the As(V)-reducing bacteria contributed greater to As(V) reduction in the SOM-depleted soil. Additionally, SOM depletion boosted the abundances of Fe(III)- and As(V)-reducing bacteria such as Bacillus and Ammoniphilus in soils, which enhanced the dissimilatory arsenate reduction. Thus, this work highlighted the importance of SOM in the remediation of As-contaminated soils by ZVI/BC.Graphical

Mitigation of arsenic accumulation in crop plants using biofertilizer.

Elevated levels of arsenic in crop plants have been found in various regions worldwide, especially where agricultural soils have been affected by arsenic-enriched aquifers and human activities including mining, smelting, and pesticide application. Given the highly toxic nature of arsenic, remediation should be carried out immediately to reduce this potentially toxic element transport from soil to crop plants. This study focused on the utilization of biofertilizer which is a combination of arsenic-accumulating microorganisms and adsorbent (carrier) in order to achieve high efficiency of arsenic immobilization and ability to apply in the field. Thirty-two bacterial strains were isolated from 9 soil samples collected from the Dongjin and Duckum mining areas in Korea using a nutrient medium amended with 2 mM sodium arsenite. Among isolates, strain DE12 identified as Bacillus megaterium exhibited the greatest arsenic accumulation capacity (0.236 mg/g dry biomass) and ability to resist up to 18 mM arsenite. Among the three agricultural waste adsorbents studied, rice straw was proved to have a higher adsorption capacity (0.104 mg/g) than rice husk and corn husk. Therefore, rice straw was chosen to be the carrier to form biofertilizer together with strain DE12. Inoculation of biofertilizer in soil showed a reduction of arsenic content in the edible part of lettuce, water spinach, and sweet basil by 17.5%, 34.1%, and 34,1%, respectively compared to the control group. The use of biofertilizer may open up the potential application in the field for other food plants.

Complexation and immobilization of arsenic in maize using green synthesized silicon nanoparticles (SiNPs)

Arsenic (As) is a heavy metal that is toxic to both plants and animals. Silicon nanoparticles (SiNPs) can alleviate the detrimental effects of heavy metals on plants, but the underlying mechanisms remain unclear. The study aims to synthesize SiNPs and reveal how they promote plant health in Arsenic-polluted soil. 0 and 100% v/v SiNPs were applied to soil, and Arsenic 0 and 3.2 g/ml were applied twice. Maize growth was monitored until maturity. Small, irregular, spherical, smooth, and non-agglomerated SiNPs with a peak absorbance of 400 nm were synthesized from Pycreus polystachyos. The SiNPs (100%) assisted in the development of a deep, prolific root structure that aided hydraulic conductance and gave mechanical support to the maize plant under As stress. Thus, there was a 40–50% increase in growth, tripled yield weights, and accelerated flowering, fruiting, and senescence. SiNPs caused immobilization (As(III)=SiNPs) of As in the soil and induced root exudates Phytochelatins (PCs) (desGly-PC2 and Oxidized Glutathione) which may lead to formation of SiNPs=As(III)–PCs complexes and sequestration of As in the plant biomass. Moreover, SiNPs may alleviate Arsenic stress by serving as co-enzymes that activate the antioxidant-defensive mechanisms of the shoot and root. Thus, above 70%, most reactive ROS (OH) were scavenged, which was evident in the reduced MDA content that strengthened the plasma membrane to support selective ion absorption of SiNPs in place of Arsenic. We conclude that SiNPs can alleviate As stress through sequestration with PCs, improve root hydraulic conductance, antioxidant activity, and membrane stability in maize plants, and could be a potential tool to promote heavy metal stress resilience in the field.

Optimized production of invasive animal biochar for arsenic immobilization and methane oxidation in contaminated soils using response surface methodology

The apple snail (Pomacea canaliculata Lamarck) is among the 100 worst invasive alien species worldwide. Apple snail residues discarded during daily management are potential raw materials for biochar production. This study optimized the factors for producing apple snail biochar (ASB) using response surface methodology (RSM) and analyzed the As removal capacity and soil remediation effects of the optimal ASB. The optimal ASB occurred for 348.63 °C pyrolysis temperature, 2.19 h pyrolysis time, and 2.53 Fe3+/Fe2+ molar ratio. For the optimal ASB, the maximum experimental As(III) removal ratio was 98.72%. Temperature and the Fe3+/Fe2+ molar ratio were essential factors affecting the As removal ratio of ASB. The ASB had a rough surface, and As (1.09%) was evident on its surface after adsorption. The As(III) adsorption capacity on ASB was 10.59 mg/g at 288 K, 9.75 mg/g at 298 K, and 11.82 mg/g at 308 K. The As immobilization efficiency in the 3% and 5% ASB treatments exceeded 50% after 15 d. The 5% ASB treatment increased the soil organic matter, total N, available N, total P, and available P content by 120%, 245%, 47%, 62%, and 154%, respectively. Within 15 d, the soil methane oxidation potential peaked at 4.05 μg/g/h in the 5% ASB treatment. The maximum methane oxidation rate occurred after 10 d in the 5% ASB treatment. ASB has multiple benefits for As immobilization, quality improvement, and methane oxidation in soil. This study provides a reference for optimized production and application of invasive animal biochar in contaminated soil.

Silicon-nanoparticles loaded biochar for soil arsenic immobilization and alleviation of phytotoxicity in barley: Implications for human health risk.

Arsenic (As)-induced environmental pollution and associated health risks are recognized on a global level. Here the impact of cotton shells derived biochar (BC) and silicon-nanoparticles loaded biochar (nano-Si-BC) was explored on soil As immobilization and its phytotoxicity in barley plants in a greenhouse study. The barley plants were grown in a sandy loam soil with varying concentrations of BC and nano-Si-BC (0, 1, and 2%), along with different levels of As (0, 5, 10, and 20mgkg-1). The FTIR spectroscopy, SEM-EDX, and XRD were used to characterize BC and nano-Si-BC. Results revealed that As treatment had a negative impact on barley plant development, grain yield, physiology, and anti-oxidative response. However, the addition of nano-Si-BC led to a 71% reduction in shoot As concentration compared to the control with 20mgkg-1 of As, while BC alone resulted in a 51% decline. Furthermore, the 2% nano-Si-BC increased grain yield by 94% compared to control and 28% compared to BC. The addition of 2% nano-Si-BC to As-contaminated soil reduced oxidative stress (34% H2O2 and 48% MDA content) and enhanced plant As tolerance (92% peroxidase and 46% Ascorbate peroxidase activity). The chlorophyll concentration in barley plants decreased due to oxidative stress. Additionally, the incorporation of 2% nano-Si-BC resulted in a 76% reduction in water soluble and NaHCO3 extractable As. It is concluded that the use of BC or nano-Si-BC in As contaminated soil for barley resulted in a low human health risk (HQ < 1), as it effectively immobilized As and promoted higher activity of antioxidants.

Functionalized organo-mineral composites of biochar for the effectual immobilization of arsenic in contaminated soil

Functionalized organo-mineral composites of biochar for the effectual immobilization of arsenic in contaminated soil

Mechanism and thermodynamics of scorodite formation by oxidative precipitation from arsenic-bearing solution

Arsenic pollution is a challenging environmental issue caused by arsenic-bearing wastes from nonferrous metallurgy. Oxidative precipitation via introducing O2 into an ionic Fe(II)–As(V) solution is an advanced method for arsenic immobilization. However, the underlying mechanism is still not well understood. This study proposed a mechanism for scorodite formation by oxidative precipitation, and its thermodynamics were calculated using Gaussian software. Scorodite formation was divided into three stages: precursor formation (3–90 min), oxidative conversion (90–270 min) and crystallization (270–720 min) from the variation in precipitates and solution characterization and parameters such as initial pH, arsenic concentration, and ferrous dosage. In the scorodite formation mechanism, the precursors originate from the coordination polymerization of aqueous Fe(H2O)62+ and H2AsO4−, which contributes to the oxidative conversion of coordinated polymers ([Fe(H2O)4(H2O)]nn+) to basic Fe(H2O)2AsO4 until regular octahedral crystals are formed via nucleation and growth during crystallization. The ΔrGmθ for polymerization varied from −491.96 kJ mol−1 to −33.30 kJ mol−1, and the ΔrGmθ of oxidative conversion changed from −982.16 kJ mol−1 to −224.82 kJ mol−1, demonstrating the feasibility in scorodite formation. This research is significant for understanding scorodite formation in As(V) solutions. It can provide schemes for controlling and modifying the conditions of arsenic-bearing waste immobilization in the laboratories and industries.