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In this study, a soil incubation experiment was conducted to explore the influence MgO-treated corn straw biochar (MCB) on the bioavailability and chemical forms of cadmium (Cd), lead (Pb), and arsenic (As), alongside the impact on the bacterial community within paddy soil subjected to both flooded and non-flooded conditions. Raw corn straw biochar (CB) served as the unmodified biochar control, aiding in the understanding of the biochar's role within the composite. The results showed that even at a minimal concentration of 0.5 %, MCB exhibited higher effectiveness in reducing the bioavailability of Pb and Cd compared to 1 % CB. In non-flooded conditions, 0.5 % MCB reduced the bioavailable Pb and Cd by 99.7 % and 87.4 %, respectively, while NaH 2 PO 4 -extracted As displayed a 14.5 % increase. With increasing MCB concentrations (from 0.5 % to 1.5 %), soil pH, DOC, EC, available phosphorus, and bioavailable As increased, while bioavailable Pb and Cd exhibited declining tendencies. Flooding did not notably alter MCB's role in reducing Pb and Cd bioavailability, yet it systematically amplified As release. Heavy metal fractions extracted by acetic acid increased in the MCB groups under flooding conditions, especially for As. The inclusion of 0.5 % MCB did not noticeably affect bacterial diversity, whereas higher doses led to reduced diversity and substantial changes in community composition. Specifically, the groups with MCB showed an increase in the Bacteroidetes and Proteobacteria phyla, accompanied by a decrease in Acidobacteria. These alterations were primarily attributed to the increased pH and EC resulting from MgO hydrolysis. Consequently, for Pb/Cd stabilization and soil bacterial diversity, a low dosage of MgO-treated biochar is recommended. However, caution is advised when employing MgO-treated biochar in soils with elevated arsenic levels, particularly under flooded conditions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Arsenic (As) is a toxic metalloid that is ubiquitous in paddy soils, where passivation is the most widely used method for remediating As contamination. Recently, anaerobic methane oxidation coupled with arsenate (As(V)) reduction (AOM-AsR) has been shown to act as a critical driver for As release in paddy fields. However, the effect and mechanism of the passivators on the AOM-AsR process remain unclear. In this study, we incubated arsenate-contaminated paddy soils under anaerobic conditions. Using isotopically labelled methane and different passivators, we found that an iron-based passivator containing calcium sulfate and iron oxide (9:1, m/m) named IBP showed a much better performance than the other passivators. Adding IBP decreased the arsenite (As(III)) concentration in the soil solution by 78% and increased the AOM rate by 55%. Furthermore, we employed high-throughput sequencing and real-time quantitative polymerase chain reaction (qPCR) to investigate the ability of IBP to control As release mediated by AOM-AsR in paddy fields, as well as its underlying mechanism. Our results showed that IBP addition significantly increased anaerobic methanotrophic (ANME) archaea (ANME-2a-c, ANME-2d, and ANME-3) by 91%, and increased the methane-oxidizing bacterium Methylobacter by 262%. Similarly, IBP addition significantly increased the Fe(III) concentration in soil solution by 39% and increased the absolute abundance of Fe(III)-reducing bacteria (Geobacteraceae) by 21 times in soil. Adding IBP may significantly promote AOM coupled with Fe(III) reduction, significantly reducing electron transfer from AOM to As(V) reduction. Hence, IBP may be used as an efficient passivator to remediate As-contaminated soil using an active AOM-AsR process. These results provide a novel insight into controlling soil As release by regulating an active and critical As mobilization pathway in the environment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Cadmium (Cd) and Arsenic (As) in rice grains are a primary exposure source for human beings. However, the simultaneous stabilization of Cd and As in soil becomes difficult due to the opposite properties of those. In this study, we investigated the simultaneous effects of biochar-supported nanoscale zero-valent iron (nZVI-BC) and water management on the decrease of Cd and As bioaccumulation in rice grain. Compared to the control, 0.25-1.00% nZVI-BC coupled with alternate wetting and drying (AWD) management simultaneously decreased the bioaccumulation of Cd and As in rice grains by 15.85-69.16% and 23.06-59.45%, respectively. The cancer risk associated with rice consumption effectively reduced by 15.60-52.41% after the application of nZVI-BC, and the lowest cancer risk was detected in 1.00% nZVI-BC under AWD management. Furthermore, rice cultivated under AWD management had a lower total cancer risk than that cultivated under continuous flooded (CF) management with the same amendment of type and dose. The reduction of soil Cd and As availability and the formation of iron plaque dominated the decrease of Cd and As uptake by rice grains. The elevated soil pH was responsible for Cd adsorption, and the dominant mechanism for As immobilization was the formation of complexes. The iron plaque was double-edged, promoting and inhibiting Cd uptake by rice, wherein the inhibition was predominant under aerobic conditions. In addition, iron plaque was a barrier to preventing the As accumulation by rice, a larger amount of As was immobilized on the iron plaque with nZVI-BC treatment. This study sheds new insights on the simultaneous remediation of Cd and As co-contaminated paddy fields., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Simultaneous stabilization of cadmium (Cd) and arsenic (As) in co-contaminated soil is challenging in environmental remediation because of their opposite properties. In this study, biochar-supported nanoscale zero-valent iron (nZVI-BC) was designed for simultaneously decreasing the soil availability of Cd and As and their bioaccumulation in vegetables. It was found that nZVI-BC exhibited remarkable performance for the stabilization of Cd and As in soil, and their availability decreased by 34.93% and 32.64% compared to the control sample, respectively, under 1.00% nZVI-BC treatment. The increase of soil pH and complexation dominated the Cd remediation process, while the formation of precipitation together and surface complexes transformed labile As into stable forms. Pot experiments showed that nZVI-BC application inhibited the bioaccumulation of Cd and As in vegetables by 23.63-36.48% and 43.09-45.10%, respectively, and hence effectively decreased the cancer risks by 38.19-42.93% related with vegetable consumption (P < 0.05). This study revealed that nZVI-BC is a promising amendment for achieving the simultaneous remediation of Cd and As co-contaminated farmland soil., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Global warming severely hinders both rice (Oryza sativa L.) quality and yield by increasing arsenic (As) bioavailability in paddy soils. However, details regarding As biotransformation and migration in the rice-soil system at elevated temperatures remain unclear. This study investigated the effects of increasing temperature on As behavior and translocation in rice grown in As-contaminated paddy soil at two temperature treatments (33 °C warmer temperature and 28 °C as control). The results showed that increasing temperature from 28 °C to 33 °C significantly favored total As, arsenite (As(III)) and arsenate (As(Ⅴ)) release into the soil pore-water. This increase in As bioavailability resulted in significantly higher As(III) accumulation in the whole grains at warmer treatment relative to the control. Moreover, the results suggest that increasing temperature to 33 °C promoted As(III) migration from the roots to the whole grains. Furthermore, the As(V)-reducing Xanthomonadales order and Alcaligenaceae family, and As(V) reductase-encoding arsC gene were enriched in the rhizosphere soils incubated at 33 °C. This suggests that the increase in As bioavailability in that treatment was due to enhanced As(V) reductive dissolution into the soil pore-water. Overall, this study provides new insights on how warmer future temperatures will exacerbate As accumulation in rice grains., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Contaminations by heavy metals in the environment always exist as a mixture of both metal and metalloid. Thus, it is a challenge to simultaneously remove both components due to their adverse chemical behaviors. Herein, effective cadmium (Cd) and arsenic (As) removal in aqueous solution was achieved by use of a novel composite, which was synthesized by Bacillus sp. K1 loaded onto Fe 3 O 4 biochar (MBB). The combination with Bacillus sp. K1 provided new biosorption sites such as amine and hydroxyl groups in the composite surface, which significantly increasing the removal capability of Cd(II) by 230% when compared with the raw magnetic biochar. Both competition and synergy effects were found in binary system. Adsorption of As(III) extended active sites for capturing Cd(II), which appeared on the surface of the MBB as type B ternary surface complexes. The maximum adsorption capacity of Cd(II) and As(III) reached 25.04 and 4.58 mg g -1 in a binary system, respectively. In summary, this environmentally friendly composite is promising for simultaneous Cd(II) and As(III) remediation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The present study used calcium-based magnetic biochar (Ca-MBC), a novel material made through pyrolyzing rice straw impregnated with iron oxide (Fe 3 O 4 ) and calcium carbonate (CaCO 3 ) under oxygen-limited conditions, to reduce arsenic (As) accumulation in rice plants (Oryza sativa L.) through a 130-day pot experiment. The BCR (European Community Bureau of Reference) sequential extraction confirmed that Ca-MBC decreased the unstable fraction of As through transforming to the stable fraction at both tillering stage and maturity. The addition of Ca-MBC decreased while the pristine biochar increased the concentrations of NH 4 H 2 PO 4 - and BCR-extracted As. The μ-XRF test revealed that iron oxide on the Ca-MBC played an important role in decreasing As bioavailability. The addition of Ca-MBC greatly decreased As concentration in rice grains, mainly due to (1) the decreases in bioavailability of As in soil and (2) adsorption of As in pore water by Ca-MBC; and (3) the enhanced formation of iron plaque that acted as a barrier for plant As uptake. Furthermore, the addition of Ca-MBC at 1% but not 2% promoted plant growth. The results suggest that Ca-MBC can be used as an efficient material to lower As accumulation in grains and promote plant growth in rice paddy fields., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Arsenic (As) is a potential contaminant in sewage sludge that may affect waste treatment and limit the use of these waste materials as soil amendments. Anaerobic digestion (AD) is an important and effective process for the treatment of sewage sludge and the chemical speciation of As is particularly important in sludge AD. However, the biotransformation genes of As in sludge during AD has not been fully explored. In this study, the influent and effluent sludge of anaerobic digester in a wastewater treatment plant (WWTP) was collected to investigate the species transformations of As, the abundance and diversity of As biotransformation genes was explored by real-time PCR (qPCR) and metagenomic sequencing, separately. The results showed that arsenite [As(III)] and arsenate [As(V)] were predominant in the influent sludge, whereas the relative abundance of monomethylarsenic acid (MMA) increased by 25.7% after digestion. As biotransformation genes were highly abundant, and the As(III) S-adenosylmethionine methyltransferase (arsM) gene was the predominant which significantly increased after AD by qPCR analysis. Metagenomic analysis indicated that the diversity of the arsM-like sequences also increased significantly after AD. Most of the arsM-like sequences in all the influent and effluent sludge samples were related to Bacteroidetes and Alphaproteobacteria. Furthermore, co-occurrence network analysis indicated a strong correlation between the microbial communities and As. This study provides a direct and reliable reference on As biotransformation genes and microbial community in the AD of sludge., Competing Interests: Declaration of Competing Interest The authors declare that there are no conflicts of interest., (Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.)

This study developed a novel calcium-based magnetic biochar by pyrolysing rice straw mixed with calcium carbonate and iron oxide for stabilization of contamination of multiple metals. A 160-day incubation study was conducted to investigate its performance in stabilization of cadmium and arsenic co-contamination in soil. Both biochar and Ca-MBC treatments increased soil pH, decreased the bioavailability of cadmium. Ca-MBC decreased but biochar enhanced the bioavailability of arsenic. The BCR (European Community Bureau of Reference) sequential extraction confirmed Ca-MBC facilitated the transformation of the unstable fraction of arsenic to stable fractions. The stabilization mechanisms were explored through synchrotron-based micro X-ray fluorescence and X-ray absorption near edge structure. The results show that Ca-MBC remediated the dual contamination of arsenic and cadmium through (1) elevated pH and cation exchange capacity (for Cd); (2) the formation of bi-dentate chelate and ternary surface complexes on the surface of iron oxide; (3) enhanced adsorption ability of porous biochar. In addition, Ca-MBC increased the abundance and diversity of bacterial community, and modified the relative abundances of bacterial taxa, leading to a shift of the composition. These new insights provide valuable information for stabilization of co-contamination of arsenic and cadmium in soil using the potential material Ca-MBC., Competing Interests: Declaration of Competing Interest The authors declare that there are no conflicts of interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

In situ immobilization of heavy metals in contaminated soils using industrial by-products is an attractive remediation technique. In this work, titanium gypsum (TG) was applied at two levels (TG-L: 0.15% and TG-H: 0.30%) to simultaneously reduce the uptake of cadmium (Cd), lead (Pb) and arsenic (As) in rice grown in heavy metal contaminated paddy soils. The results showed that the addition of TG significantly decreased the pH and dissolved organic carbon (DOC) in the bulk soil. TG addition significantly improved the rice plants growth and reduced the bioavailability of Cd, Pb and As. Particularly, bioavailable Cd, Pb and As decreased by 35.2%, 38.1% and 38.0% in TG-H treatment during the tillering stage, respectively. Moreover, TG application significantly reduced the accumulation of Cd, Pb and As in brown rice. Real-time PCR analysis demonstrated that the relative abundance of sulfate-reducing bacteria increased with the TG application, but not for the iron-reducing bacteria. In addition, 16S rRNA sequencing analysis revealed that the relative abundances of heavy metal-resistant bacteria such as Bacillus, Sulfuritalea, Clostridium, Sulfuricella, Geobacter, Nocardioides and Sulfuricurvum at the genus level significantly increased with the TG addition. In conclusion, the present study implied that TG is a potential and effective amendment to immobilize metal(loid)s in soil and thereby reduce the exposure risk of metal(loid)s associated with rice consumption., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

A combined amendment (CF) consisting of 90% calcium sulfate (CaSO 4 ) and 10% ferric oxide (Fe 2 O 3 ) was used to investigate the feasibility, active principles, and possible mechanisms of the immobilization of heavy metals in paddy soil. A soil incubation experiment, two consecutive pot trials, and a field experiment were conducted to evaluate the effectiveness and persistence of CF on metal(loid) immobilization. Soil incubation experiment results indicated that the application of CF significantly decreased the concentrations of cadmium (Cd), lead (Pb), and arsenic (As) in soil solution. CF treatments simultaneously reduced the accumulation of Cd, Pb, and As in two consecutive pot trials. The total Cd, Pb, and As concentrations in the rice grains were respectively 0.02, 2.08, and 0.62 mg kg -1 in the control treatment in the second year, which exceeded the safety limits of contaminants in food products in China. However, a high amount of CF amendment (CF-H, 0.3%) effectively decreased Cd, Pb, and As by 75.0%, 75.5%, and 46.8%, respectively. Further, with the CF amendment, the bioavailable Cd and Pb in the soil and the accumulation of Cd, Pb, and As in rice grain in the field experiment were also significantly decreased. The concentrations of Cd, Pb, and As in grains were respectively 0.02, 0.03, and 0.39 mg kg -1 in the control treatment in the field experiment, which decreased to 0.01, 0.01, and 0.22 mg kg -1 with CF addition, suggesting that grains produced in the field could pose less health risk. In conclusion, these results implied that CF was an effective and persistent combined amendment to immobilize heavy metals in soil and thereby can reduce the exposure risk of metal(loid)s associated with rice consumption.

A novel calcium-based magnetic biochar (Ca-MBC), made by pyrolyzing the mixture of rice straw, iron oxide (Fe 3 O 4 ) and calcium carbonate (CaCO 3 ), was developed in this study for remediation of co-pollution of arsenic and cadmium. Characteristics of the material showed that Fe 3 O 4 and CaCO 3 were adhered on the surface of biochar. The experiments on the effects of pH, adsorption kinetics and isotherm revealed that the Ca-MBC had a great ability to adsorb arsenic and cadmium within 0.5 h for cadmium and 12 h for arsenic with a maximum adsorption capacity of 6.34 and 10.07 mg g -1 , respectively, and that the adsorption of both metals was pH-dependent from 2 to 12 with an optimal pH of pH 5. The mechanism of co-adsorption of Cd(II) and As(III) included both competitive and synergistic effects. The presence of As(III) enhanced Cd(II) adsorption by 3-16% while Cd(II) addition suppressed As(III) adsorption by 15-33%. The synergistic effects on As(III) and Cd(II) adsorption had resulted from the electrostatic interaction and the formation of type B ternary surface complexes. These new insights provide valuable information for the application of Ca-MBC as a potential adsorbent in treatment of water contaminated with As(III) and Cd(II)., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Although methylation is regarded as one of the main detoxification pathways for arsenic (As), current knowledge about this process during manure composting remains limited. In this study, two pilot-scale compost piles were established to treat manure contaminated with As. An overall accumulation of methylated As occurred during 60 day-composting time. The concentration of monomethylarsonic acid (MMA) increased from 6 to 190 μg kg -1 within 15 days and decreased to 35 μg kg -1 at the end of the maturing phase; while the concentration of dimethylarsinic acid (DMA) continuously increased from 33 to 595 μg kg -1 over the composting time. The arsM gene copies increased gradually from 0.08 × 10 9 to 6.82 × 10 9 copies g -1 dry mass over time and correlated positively to the concentrations of methylated As. 16S rRNA gene sequencing and arsM clone library analysis confirmed the high abundance and diversity of arsM genes. Many of these genes were related to those from known As-methylating microbes, including Streptomyces sp., Amycolatopsis mediterranei and Sphaerobacter thermophiles. These results demonstrated that As methylation during manure composting is significant and, for the first time, established a linkage between As biomethylation and the abundance and diversity of the arsM functional genes in composting manure.

The identification of plants with high arsenic hyperaccumulating efficiency from water is required to ensure the successful application of phytoremediation technology. Five dominant submerged plant species (Vallisneria natans (Lour.) Hara., Potamageton crispus L., Myriophyllum spicatum L., Ceratophyllum demersum L. and Hydrilla verticillata (L.f.) Royle) in China were used to determine their potential to remove As from contaminated water. V. natans had the highest accumulation of As among them. The characteristics of As accumulation, transformation and the effect of phosphate on As accumulation in V. natans were then further studied. The growth of V. natans was not inhibited even when the As concentration reached 2.0 mg L(-1). After 21 d of As treatment, the bioconcentration factor (BCF) reached 1300. The As concentration in the environment and exposure time are major factors controlling the As concentration in V. natans. After being absorbed, As(V) is efficiently reduced to As(III) in plants. The synthesis of non-enzymic antioxidants may play an important role under As stress and increase As detoxication. In addition, As(V) uptake by V. natans was negatively correlated with phosphate (P) uptake when P was sufficiently supplied. As(V) is probably taken up via P transporters in V. natans.

Vallisneria natans (Lour.) Hara, a widely distributed submerged aquatic plant, is a promising species for arsenic (As) removal from contaminated water. We investigated the effects of pH on the accumulation, subcellular distribution and detoxification of As in V. natans. The results showed that the optimum pH for submerged V. natans growth is close to 7.0. The accumulation of As in the plant increased with the increase of pH (p < 0.05). This may have been due to arsenic/phosphate transporters with a higher affinity for the more highly electronegative AsO4 (3-) than for HAsO4 (2-) and H2AsO4 (-). After As(V) was accumulated by plants, more than 80 % was reduced to As(III), but As reduction decreased with increased pH. The majority of accumulated As and reduced As(III) (47 %-66 %) was found in the vacuoles. Higher As concentrations in vacuoles could be considered as an important mechanism for As detoxification in submerged plants.

Accurate quantification of arsenic migration and accumulation in brownfield site is critical for environmental management and soil remediation. However, the researches simulating arsenic in brownfield site in China are limited due to sparse data and complex migration behaviors. In this study, we simulated historic arsenic contamination using Hydrus-3D in an abandoned brownfield site in Hebei, China, from 1972 to 2019. Atmospheric discharge, wastewater leakage, solid waste discharge and tank leakage were calculated according to the factory processes for model simulation. Based on the results of Hydrus-3D, we assessed health risk of arsenic in this site. The results showed that total arsenic input to the soil surface from 4 pathways was 24.6 tons, the solid waste discharge was the highest contributor. The accumulation process mainly occurred in the unsaturated zone due to clay and silty clay absorbed arsenic and thus slow down the migration process. While in the saturation zone, abundant groundwater promoted migration of arsenic, resulting in widespread distribution of contaminated area. The model results represented good performance between simulated and measured values. Sensitivity analysis indicated that adsorption constant and water conductivity were the most influential parameters. Heath risk assessment showed that arsenic contamination continues to threaten resident health. [Display omitted] • 58-years migration and accumulation of arsenic in site was simulated by Hydrus-3D. • Solid waste emission pathway contributed most arsenic in studied brownfield site. • Clay absorption and waterflow were the main factors affecting arsenic migration. • Risk assessment indicated that arsenic continues to threaten human health. • Our study provides a scope for contaminated site assessment and soil remediation. [ABSTRACT FROM AUTHOR]

We investigated the performance and encapsulation mechanisms of novel biochar-supported nanoscale zero-valent iron (nZVI-BC) used for the remediation of soil co-contaminated with arsenic (As), cadmium (Cd), and lead (Pb) via incubation and column experiments. Compared with the control, 0.50% of nZVI-BC significantly decreased the leakage of As, Cd, and Pb by 97.94–98.45%, 42.86–81.12%, and 82.14–92.49%, respectively. In addition, 0.50% of nZVI-BC could transform the fraction of unstable heavy metals into a stable form, which substantially decreased the availability, leachability, and bioaccessibility of the heavy metals and hence greatly reduced the human health exposure risk. Column experiments showed that 0.50% of nZVI-BC effectively restrained the leaching of As, Cd, and Pb by 95.60–99.84%, 70.82–84.18%, and 91.68–99.81%, respectively. The predominant encapsulation mechanisms of nZVI-BC included complexation, precipitation/co-precipitation, reduction, and the formation of ternary surface complexes. Based on these insights, we can devise new strategies for the remediation of soil co-contaminated with As, Cd, and Pb. [Display omitted] • nZVI-BC exhibited high applicability and time stability for soil remediation. • Leaching toxicity of soil As, Cd and Pb were suppressed by nZVI-BC. • nZVI-BC decreased bioaccessibility and human exposure risk of heavy metals. [ABSTRACT FROM AUTHOR]