Microbial reductive mobilization of As(V) in solid phase coupled with the oxidation of sulfur compounds: An overlooked biogeochemical reaction affecting the formation of arsenic-contaminated groundwater

Dissimilatory As(V)-respiring prokaryotes (DARPs) are recognized as having a crucial role in the formation of arsenic-contaminated groundwater. DARPs use small-molecule organic acids as electron donor to directly reduce As(V) in solid phase to more mobile As(III). Therefore, DARPs are considered to be heterotrophic bacteria. However, these cannot explain why high concentrations of As(III) are produced in environments lacking soluble organic carbon. We thus propose that reduced sulfur compounds may also be utilized by DARPs and affect the DARPs-mediated arsenic mobilization. This study sought to confirm this hypothesis. Metagenomic investigations on the DARP population derived from As-contaminated soil indicated that approximately 84 % of DARP MAGs possess the enzymes potentially catalyzing the oxidation of S2-, S0, SO32-, or S2O32-. Functional analysis of DARP population and a cultivable strain suggested that DARPs, in addition to small-molecule organic carbon, can effectively use sulfur compounds as electron donor to reduce As(V) to mobile As(III). Arsenic release experiments using DARP population and a cultivable DARP strain showed that DARPs indeed utilized sulfur compounds as the sole electron donors under autotrophic and anaerobic conditions to directly reduce adsorbed As(V) in the soils to mobile As(III). These findings provide new insights into the microbial mechanism responsible for the variation of As(III) concentrations in contaminated groundwater.

Arsenic accumulation in two Pteris vittata ecotypes: Insights into transpiration, spore As/P ratios, and arsenic metabolism gene expression

Arsenic (As) contamination in soils poses a potential risk to human health. The arsenic-hyperaccumulator Pteris vittata has been utilized for phytoremediation of As-contaminated soils. Though P. vittata from different regions all accumulates As, their accumulation ability varies among ecotypes. Typically, ecotypes with greater transpiration and lower As levels in their habitat show greater As accumulation, but the underlying molecular mechanisms remain unclear. Here, we assessed the As contents, As speciation, and As metabolism-related genes in two ecotypes of P. vittata from Kunming and Hangzhou in Southwest and Southeast China. After 30 days of growth in sand media with 50 µM As, the Kunming ecotype with greater transpiration accumulated 1.5-fold more As in the fronds than Hangzhou, which was negatively correlated with its spore As contents but positively correlated with its spore P contents. Besides, the arsenite (AsIII) content in P. vittata fronds of Kunming ecotype was 1.5-fold greater than Hangzhou ecotype. The greater As and AsIII contents in the fronds of Kunming ecotype were probably due to the greater expression of As metabolism genes, including 2.8-fold greater in P transporter PvPht1;3 (As uptake), 1.8-fold greater in arsenate reductase PvHAC2 (As reduction) and 2.9-fold greater in arsenite antiporter PvACR3;2 (As translocation), being critical genes for As accumulation by P. vittata. This is the first examination of genes related to As metabolism in different P. vittata ecotypes, providing valuable insights to select P. vittata with greater As accumulation for more efficient phytoremediation.

The spatiotemporal evolution of dissolved-phase NAPL plumes revealed by the integrated groundwater quality and machine learning models

Rapid prediction of dissolved-phase contamination plume distributions is crucial for emergency remediation of aquifers contaminated with non-aqueous phase liquids (NAPLs). However, collecting and analyzing contaminated groundwater samples is expensive and undertaken infrequently. Additionally, the heterogeneous features and complex biogeochemical reactions in aquifers often limit the application of traditional numerical modeling. This study developed a novel machine learning (ML) prediction framework incorporating sliding window-based time-series prediction and general regression prediction. The goal was to predict the spatiotemporal distribution of the dissolved-phase NAPL plumes based on low-cost and easily measured in-situ groundwater quality parameters (iWQP), including pH, dissolved oxygen, oxidation-reduction potential, and electrical conductivity. The framework was applied to hypothetical but realistic field-scale reactive transport model cases, showing different hydrogeological conditions and various dissolved-phase NAPL plumes. First, a sliding window-based Random Forest (RF) model was constructed to predict the iWQP at a target time using the historical continuous-time data of iWQP. Then, four ML models, namely RF, eXtreme Gradient Boosting, Multilayer Perceptron and Long Short-Term Memory (LSTM) were employed to predict the spatial distribution of NAPL plumes at the target time using predicted iWQP and low-frequency sampled historical datasets of dissolved-phase NAPL plumes. The prediction results revealed that the LSTM model showed the best performance (R2 > 0.92) and maintained temporal validity for the longest duration. Based on the permutation feature importance approach, pH was identified as the key iWQP for predicting dissolved-phase NAPL plumes. Overall, the findings inform the subsequent development of data-driven models for real-time monitoring and pre-estimation of dissolved-phase NAPL levels in groundwater using iWQP sensors, and can assist in swift decision-making for groundwater remediation in NAPL-contaminated zones.

Rapid screening of inorganic arsenic in groundwater on-site by a portable three-channel colorimeter

Rapid screening of inorganic arsenic (iAs) in groundwater used for drinking by hundreds of millions of mostly rural residents worldwide is crucial for health protection. Most commercial field test kits are based on the Gutzeit reaction that uses mercury-based reagents for color development, an environmental concern that increasingly limits its utilization. This study further improves the Molybdenum Blue (MB) colorimetric method to allow for faster screening with more stable reagents. More importantly, a portable three-channel colorimeter is developed for screening iAs relative to the WHO drinking water guideline value (10 µg/L). Adding the reducing reagents in sequence not only prolongs the storage time to > 7 days, but also accelerates the color development time to 6 min in conjunction with lowering the H2SO4 concentration in chromogenic reagents. The optimal pH ranges from 1.2 to 1.3 and is achieved by acidifying groundwater to 1% (V/V) HCl. With detection limits of 3.7 µg/L for inorganic arsenate (iAs(V)) and 3.8 µg/L for inorganic arsenite (iAs(III)), testing groundwater with ∼10 µg/L of As has a precision < 20%. The method works well for a range of phosphate concentrations of 48-950 µg/L (0.5-10 µmol/L). Concentrations of total_iAs (6-300 µg/L), iAs(V) (6-230 µg/L) and iAs(III) (0-170 µg/L) for 14 groundwater samples from Yinchuan Plain, Pearl River Delta, and Jianghan Plain, are in excellent agreements (linear regression slope: 0.969-1.029) with the benchmark methods. The improved chemistry here lays the foundation for the MB colorimetric method to become a commercially viable screening tool, with further engineering and design improvement of the colorimeter.

A critical review on arsenic and antimony adsorption and transformation on mineral facets

Arsenic (As) and antimony (Sb), with analogy structure, belong to VA group in the periodic table and pose a great public concern due to their potential carcinogenicity. The speciation distribution, migration and transformation, enrichment and retention, as well as bioavailability and toxicity of As and Sb are influenced by several environmental processes on mineral surfaces, including adsorption/desorption, coordination/precipitation, and oxidation/reduction. These interfacial reactions are influenced by the crystal facet of minerals with different atomic and electronic structures. This review starts with facets and examines As and Sb adsorption and transformation on mineral facets such hematite, titanium dioxide, and manganese dioxide. The main focus lies on three pressing issues that limit the understanding of the environmental fate of As and Sb: the facet-dependent intricacies of adsorption and transformation, the mechanisms underlying facet-dependent phenomena, and the impact of co-existing chemicals. We first discussed As and Sb adsorption behaviors, structures, and bonding chemistry on diverse mineral facets. Subsequently, the reactivity of various mineral facets was examined, with particular emphasis placed on their significance in the context of environmental catalysis for the oxidation of As(III) and Sb(III). Finally, the impact of co-existing cation, anion, or organic substances on the processes of adsorption and transport of As and Sb was reviewed. This comprehensive review enhances our understanding of the facet-dependent phenomena governing adsorption, transformation, and fate of contaminants. It underscores the critical role of mineral facets in dictating environmental reactions and paves the way for future research in this intriguing field.

High through-put groundwater arsenic speciation analysis using an automated flow analyzer

The occurrence of geogenic arsenic (As) in groundwater is a global public health concern. However, there remain large gaps in groundwater As data, making it difficult to identify non-compliant domestic wells, partly due to lack of low-cost methods capable of rapid As analysis. Therefore, the development of high through-put and reliable on-site determination methods for inorganic As is essential. Herein, a portable automated analyzer was developed for the determination of arsenite (As(III)), arsenate (As(V)) and phosphate in As contaminated groundwater based on a previously adapted method for molybdenum blue spectrophotometry. After the optimization of the chemical reactions and flow manifold, the system demonstrated a high sample through-put (4.8/h for As(III), As(V) and phosphate analysis), allowing this system to screen 125 samples in 24 h. Other advantages include low operational costs (0.3 CNY per sample), appropriate sensitivity for contaminated groundwater (detection limits of 4.7 µg/L, 8.3 µg/L and 5.4 µg/L for As(III), As(V) and phosphate, respectively), good linearity (R2 > 0.9996 at As concentrations up to 1600 µg/L) and high precision (relative standard deviations of 3.5% and 2.8% for As(III) and As(V), respectively). The portable system was successfully used for As speciation analysis in 5 groundwater samples collected from multi-level wells at Yinchuan Plain, northwestern China, with total As concentrations ranging from 75.7 to 295.0 µg/L, independently assessing As speciation, providing a promising novel method for the rapid on-site screening of As in tens of millions of domestic wells worldwide.

In situ high-resolution insights into the dynamics of arsenic (As) species and heavy metals across the sediment-water interface in a deep karst reservoir

Arsenic (As) and heavy metal contamination in aquatic systems pose critical environmental challenges, particularly in reservoirs. This study utilized dual-sided high-resolution diffusive gradients in thin films (DGT) probes on-site to investigate the spatial distribution and mobility of As species and heavy metals (Cd, Cr, Cu, Ni, Pb, Sb, and Zn) in the Hongfeng Reservoir, a deep karst reservoir in southwest China. Results revealed that As mobility was primarily governed by redox-sensitive processes, including the reduction of As(V) to As(III) and the reductive dissolution of Fe/Mn oxides. As(III) dominated porewater under reducing conditions, while As(V) was prevalent in overlying water under oxidative environments. Sulfate reduction significantly influenced As mobility, and competitive adsorption with P enhanced As release in eutrophic conditions. Heavy metals exhibited distinct spatial profiles and inter-element correlations, shaped by redox variability. Flux analysis identified sediments as sources for As, Fe, Mn, P, and S, and as sinks for most heavy metals. As(III) fluxes in the North Central reflected strong reducing conditions, while As(V) fluxes in the South Central highlighted localized oxidative processes. These findings offer valuable insights into geochemical processes in karst reservoirs, aiding in the understanding of contaminant dynamics and providing guidance for managing sediment pollution and protecting water quality.

The interaction between metals and catecholamines: oxidative stress, DNA damage, and implications for human health

The interaction between metals and catecholamines plays a pivotal role in the generation of reactive oxygen species (ROS), leading to oxidative stress and DNA damage. ROS are linked to several diseases, including neurodegenerative disorders such as Parkinson's and Alzheimer's diseases. This review examines how essential metals (iron, copper, zinc, manganese) and a few non-essential metal(loid)s (mercury, chromium, arsenic, aluminum, cadmium, and nickel) contribute to oxidative stress in the presence of catecholamines. In the presence of metals, catecholamines can cause oxidative DNA modification, possibly resulting in cell apoptosis, by taking part in redox reactions and oxidizing to the corresponding aminochrome with simultaneous ROS production. Essential metals are vital for physiological functions, but imbalances in their homeostasis can be harmful. Furthermore, non-essential metals, commonly encountered through environmental or occupational exposure, can exhibit significant toxicity. Previous studies on catecholamine-induced oxidative stress focused on copper and iron, but this review emphasizes the need to investigate other neurotoxic metals and expand existing knowledge on the interactions between metals, catecholamines, and DNA damage. Results from such research could help prioritizing the development of new assessment methods associated with adverse outcome pathways, to reliably predict harmful effects on human health, aiding in the development of therapeutical strategies. The present work will help to shed light on the interplay of metals, catecholamines, and DNA damage in different diseases hopefully fostering new research in this still understudied topic. Future research should investigate the molecular mechanisms through which these metals affect neuronal health and contribute to disease pathogenesis.

Unveiling the dual role of calcium peroxide in enhancing green rust-catalyzed arsenite oxidation and stabilization

Iron oxyhydroxide redox processes coupled with reactive oxygen species (ROS) generation play a critical role in the transformation of arsenic (As). However, low ROS generation limits the detoxification and stabilization of As(III). In this study, we propose a novel strategy by integrating Fe(II) rich green rust (GR) with calcium peroxide (CaO2) for the efficient transformation of As(III) under oxic conditions. The results demonstrate that the introduction of CaO2 greatly enhances the oxidation and immobilization of As(III) by GR. Quenching experiments reveal that H2O2, ·O2-, and 1O2 are the primary ROS responsible for the oxidation of As(III). Importantly, CaO2 significantly boosts the production of key ROS in the GR/CaO2 system. Additionally, the introduction of CaO2 facilitates the transformation of both non-specific and specific adsorbed As into non-extractable As, improving the stability of immobilized As. Our findings unveil that CaO2 serves a dual role in promoting GR-catalyzed As(III) oxidation and stabilization by enhancing ROS production and forming iron-arsenic-calcium complexes. Moreover, the application of GR/CaO2 in As-contaminated soil can rapidly reduce the risk of As leaching in different scenarios. Therefore, this study provides a new strategy using CaO2 coupled with iron redox process to enhance oxidation and stabilization of arsenic in water and soil.

Boosting arsenic removal with metastable Fe2+/Mn3+ redox process in MnFe2O4/rGO composites for high capacity and stability

Fe-Mn oxides exhibit significant potential in the application of chemical and electrochemical remediation of groundwater arsenic contamination. However, the mechanism controlling the equilibrium between chemisorption inhibition and capacitive adsorption enhancement at ferromanganese oxide electrodes is unclear, posing significant challenges to achieving both electrochemical arsenic removal efficiency and cycle stability. Here, we introduce for the first time a defect engineering strategy to synthesize defect-rich, reduced graphene oxide-anchored MnFe2O4 composites (MnFe2O4/rGO). The electrochemically efficient arsenic removal capacity (102.6 mg·g-1) and sustained cycling stability (30 cycles with >95 % efficiency) are achieved through the synergistic pseudocapacitive effect of metastable Fe-Mn bimetallic. 80 % of the arsenic removal is due to pseudocapacitive effects driven by reversible redox reactions of metastable Fe2+/Mn3+ in MnFe2O4 tetrahedral coordination revealed by X-ray photoelectron spectrum (XPS). The electronic microenvironment of iron site is modulated by Mn atom reducing the arsenic adsorption energy on MnFe2O4/rGO electrode based on electronic impedance spectrum (EIS) and density function theory (DFT). Continuous flow experiments reveal that this electrochemical system deeply purifies 5 L arsenic-laden groundwater (1 mg·L-1) below World Health Organization's (WHO) drinking water guidelines with lower energy consumption and high selectivity. This study provides valuable insights for tailoring effective, stable electrodes in electrochemical arsenic removal.

As(III) removal from drinking water using FMCTO@Fe3O4 in the adsorption-magnetic separation-sand filtration equipment: Trade-off between As removal efficiency and adsorbent utilization rate

Due to the carcinogenicity and high environmental mobility of arsenic (As), its contamination in the groundwater environment is widespread, continuously threatening human health through the food chain. The adsorption technologies for As removal, which demonstrate simplicity and cost-effectiveness, have received much attention. Despite these merits, the difficult separation between adsorbent and As-contaminated water in traditional adsorption limited the development of large-scale applications. An adsorbent of Fe-Mn-Cu ternary oxide modified with magnetite (FMCTO@Fe3O4) was synthesized to develop a highly efficient As removal device based on an Adsorption-magnetic separation integrated safety device. Its safety and applicability were evaluated by optimizing the reactor design parameters using dynamic experiments. X-ray photoelectron spectroscopy, X-ray diffraction, and zeta potential results show that FMCTO@Fe3O4 has high adsorption and oxidation performance, in which 77 % of As(III) in the section was oxidized to As(V). As particle (As-p) electrostatically adsorbed to the surface of the material, with a removal efficiency of 84 % in the magnetic separation section and manganese sand filtration section. In this process, FMCTO@Fe3O4 isolated from magnetic separation section showed far stronger adsorption capacity. Specifically, FMCTO@Fe3O4, after being used 2 or 3 times, achieved an 80 % As(tot) removal efficiency. The section B functional area recycled Fe (99.24 %), Cu (98.2 %), and Mn (98.6 %), which demonstrated the equipment with higher stability and economic recovery. This device is promising in groundwater As removal, providing theoretical support and application innovation for drinking water safety and security.

In situ bioelectrochemical remediation of contaminated soil and groundwater: A review

Contamination of the subsurface environment poses a serious hazard to the environment and human health. Recently, the bioelectrochemical system (BES) has drawn great attention in soil and groundwater remediation as it does not necessitate the addition of chemicals and exhibits minimal energy consumption to facilitate microbial degradation of pollutants. However, the complexity of the subsurface environment and the design parameters of the BES significantly affect the remediation performance and the current literature on BES primarily concentrates on its application in wastewater treatment, with a lack of summary of that in the subsurface environment. Therefore, the purpose of this review was to provide the current status, challenges, and outlooks of BES in situ treatment of pollutants from soil and groundwater. Firstly, the principles and efficacies of BES in treating the typical pollutants from the subsurface environment were discussed. Secondly, the factors that impact the BES treatment efficiencies, especially soil properties, the distinctive and pivotal factors for BES in situ application, were discussed specifically. Finally, the challenges and outlooks of BES for the in situ remediation of the contaminated soil and groundwater were addressed. BES is a green and sustainable in situ remediation technology and future advancements may necessitate the integration with complementary technologies and innovative system configurations to advance the practical implementation of BES.

Arsenic exposure activates microglia, inducing neuroinflammation and promoting the occurrence and development of Alzheimer's disease-like neurodegeneration in mice

Health damage caused by environmental arsenic pollution has attracted widespread attention, with Alzheimer's disease (AD) thought to be one of the adverse effects of long-term arsenic exposure. In this study, we sought to investigate the relationship between arsenic exposure and AD-like neurodegeneration and to determine the role of microglia in the process of AD-like neurodegeneration induced by arsenic exposure. The relationship between arsenic exposure and AD-like neurodegeneration was investigated using cognitive assessments and biological experiments. Arsenic exposure induced memory impairment in C57BL/6 mice and resulted in a significant increase in the number of Aβ+ and pTau+ cells in the entorhinal cortex and hippocampus with neuronal granular vacuolar degeneration and necroptosis, accompanied by upregulated expression of related proteins, which showed dose- and time-response relationships. Arsenic exposure intensified memory decline in FAD4T mice with accelerated AD-like neurodegeneration. Correlation analysis showed a negative correlation between memory impairment and neurodegeneration in the entorhinal cortex and hippocampus in mice. Arsenic exposure also activated microglia in the entorhinal cortex and hippocampus, with enlargement of the cytosol, shortened and thickened cell protrusions, hypertrophic changes, and abnormal proliferation, as well as upregulated expression of the pro-inflammatory cytokines TNF-α and IL-1β. Arsenic exposure induced overactivation of microglia in the entorhinal cortex and hippocampus of FAD4T mice, resulting in de-branching or bulbous protrusions and fragmented cytoplasm. Our findings suggest that arsenic exposure promotes the occurrence and development of AD-like neurodegeneration via the activation of microglia, which induces neuroinflammation in mice.

Health risk assessment upon exposure to groundwater arsenic among individuals of different sex and age groups of Vaishali district, Bihar (India)

Availability of safe drinking water is one of the requirements for maintaining good health. Unfortunately, inhabitants of many nations suffer from adverse health effects due to the intake of arsenic-contaminated groundwater. The Vaishali district of Bihar (India) is the part of Ganga River Basin, a hotspot of arsenic contamination and hence, risk assessment among its individuals is highly pertinent. This study aimed to evaluate the extent of arsenic contamination in the ground waters of Bidupur block under Vaishali district, followed by an assessment of health risk, both non-cancer and cancer, within the arsenic-exposed adult females, adult males and children. Estimation of groundwater arsenic was done in 68 duplicate samples through an MQuant test kit (Merck, Germany). For this, Microsoft Office Excel and ArcGIS software were used as a tool. The results showed that only one-fourth of the groundwater samples exceeded the WHO permissible limit of arsenic with a high contamination factor. The total hazard index (HI), representing the non-cancer risk, was found above the threshold value (>1) among all individuals, which was high among the adults, more in adult females (3.21) than adult males (2.97), and low among the children (2.02). The cancer risk, expressed in terms of cancer index (CI), was also beyond the acceptable limit (10-4 to 10-6) among all sex and age groups, ranging from 0.91 × 10-3 to 1.45 × 10-3. Conclusively, arsenic was found to pose both high non-cancer and cancer risks in the population even at its low level due to long-term exposure.

Detection of arsenate in colored grains using an interference-free dual-signal ratiometric HEC sensor

The design of novel homogeneous electrochemical (HEC) sensors with dual-signal ratiometric response holds great potential for highly sensitive and reliable detection of arsenic in food matrices. Herein, COF-based hybrids were prepared by integrating methylene blue (MB) signals and MnO2 nanozyme coatings, possessing the advantages of high signal loading, oxidase-mimicking activity, and ascorbic acid (AA)-specific recognition to realize ratiometric HEC detection of arsenate. The hydrolysate AA, produced from ALP-catalyzed AAP hydrolysis, could decompose MnO2 coatings into Mn2+, and regulate MB release and o-phenylenediamine oxidation to 2,3-diaminophenazine (DAP). Furthermore, arsenate specifically inhibited ALP, subsequently restraining AA formation and MnO2 decomposition. Consequently, a decreased MB current and an increased DAP current with opposite responses were regulated by arsenate compared with those without arsenate. Thus, this dual-signal ratiometric HEC sensor achieved sensitive detection of arsenate, with a LOD of 0.509 ppb. It was successfully applied to reliable detection of arsenate in complex food matrices.

Three Decades of Change in Potentially Toxic Elements in Brown Algae in the Northeast Atlantic Ocean

Marine pollution from potentially toxic elements (PTEs) threatens coastal ecosystems, making long-term assessments essential. This study analyzes trends in Al, Cr, Fe, Ni, Cu, Zn, As, Cd, and Hg using 446 samples of Fucus ceranoides, F. spiralis, and F. vesiculosus collected between 1990 and 2021 at 173 coastal sites in NW Spain. A consistent resampling approach revealed significant declines in most anthropogenic PTEs, including Cu (-84.7%), Cr (-84.6%), Hg (-49.6%), and Cd (-36.7%) over time. In contrast, arsenic increased by 36.1%, but the underlying causes remain unclear, with potential factors including changes in sediment inputs, bioavailability, or emerging sources such as groundwater discharges. Higher PTE levels were detected in inner estuarine areas, but no consistent latitudinal patterns emerged. Overall, the results suggest effective mitigation of coastal pollution, with reduced bioavailable PTEs entering the food web via Fucus spp. However, rising As levels and complex contamination dynamics underscore the need for continued monitoring. This study offers the most comprehensive standardized assessment of long-term PTE trends in brown algae to date, providing valuable insights for environmental policy and coastal management.

Microbial diversity and capacity for arsenic biogeochemical cycling in aquifers associated with thermal mobilization

Thermal recovery technologies for in-situ bitumen extraction can result in the heating of surrounding aquifers, potentially mobilizing arsenic naturally present in the sediments to the groundwater. The relative toxicity of dissolved arsenic is related to its speciation, with As(V) being less toxic than As(III). Microorganisms have various mechanisms of arsenic detoxification and metabolism, which include genes for efflux, methylation, and reduction/oxidation of As(V)/As(III). We characterized the microbial communities along two aquifer transects associated with thermally mobilized arsenic near Northeastern Alberta oil sands deposits. 16S rRNA amplicons and metagenomic sequencing data of biomass from filtered groundwater indicated major changes in the dominant taxa between wells, especially those currently experiencing elevated arsenic concentrations. Annotation of arsenic-related genes indicated that efflux pumps (arsB, acr3), intracellular reduction (arsC) and methylation (arsM) genes were widespread among community members but comparatively few organisms encoded genes for arsenic respiratory reductases (arrA) and oxidases (arxA, aioA). While this indicates that microbes have the capacity to exacerbate arsenic toxicity by increasing the relative concentration of As(III), some populations of iron oxidizing and sulfate reducing bacteria (including novel Gallionella and Thermodesulfovibrionia populations) show potential for indirect bioremediation through formation of insoluble iron/sulfide minerals which adsorb or coprecipitate arsenic. An unusually high proportional abundance of a single Paceibacteria population that lacked arsenic resistance genes was identified in one high‑arsenic well, and we discuss hypotheses for its ability to persist. Overall, this study describes how aquifer microbial communities respond to thermal and arsenic plumes, and predicts potential contributions of microbes to arsenic biogeochemical cycling under this disturbance.

Arsenic-induced circASXL1 regulates 16HBE cell proliferation through the P65 signaling axis

Arsenic is a well-known environmental toxicant, strongly associated with severe toxicity across multiple organs, including the lungs. Circular RNAs (circRNAs) are critical in various cellular processes and linked to disease due to their highly stable covalent closed-loop structure, making them potential therapeutic targets. This study aimed to investigate the expression of circASXL1 under arsenic exposure and its role in 16HBE cell proliferation upon circASXL1 knockdown. Treatment with sodium arsenite increased circASXL1 expression in 16HBE cells, while metabolites had no effect. Notably, circASXL1 knockdown enhanced cell viability and proliferation, concomitant with coordinated activation of STAT3 and P65. Although the precise mechanism requires further validation, our Western blot analyses suggested that STAT3 activation may promote P65 transcriptional activity, as evidenced by upregulated expression of its downstream targets PCNA, BCL2, BCL-XL, and CIAP1. Intriguingly, combinatorial treatment with arsenic and circASXL1-specific siRNAs attenuated both cell proliferation and P65 activation. Our findings propose that arsenic modulates circASXL1 to engage STAT3-P65 crosstalk. This study establishes the arsenic-circASXL1 axis as a novel regulator of STAT3/P65 signaling networks, providing mechanistic insights for combating arsenic-induced pulmonary pathologies.

Reducing arsenic mobilization in sediments: A synergistic effect of oxidation and adsorption with zirconium-manganese binary metal oxides

Remediation of arsenic (As)-contaminated sediments is challenging, due to surface sediment often being subjected to hypoxic/anoxic conditions where As(Ⅲ) is the dominant species. In this study, a novel capping material comprising zirconium-manganese binary oxides (ZMBO) was synthesized and its feasibility in controlling sedimentary As release investigated using high-resolution sampling, X-ray absorption near edge structure (XANES) spectroscopy, and scanning electron microscopy (SEM) techniques. Results showed ZMBO exhibited both high oxidation efficiency (94 %) and strong adsorption capacity (151.8 mg As/g) for As(Ⅲ). Capping As-contaminated sediments with ZMBO resulted in a negative diffusive flux of -0.08 ng/cm2/s, effectively maintaining low As levels in the overlying water over 150 days. XANES spectra showed As in surface sediments existed predominantly As(V), consistent with high-resolution data indicating ∼90 % of labile As(Ⅲ) was oxidized and adsorbed by ZMBO. Furthermore, ZMBO also promoted Fe(Ⅱ) oxidation to stable hematite in sediments, providing additional adsorption sites for As. By comparing with current capping materials, ZMBO exhibited a balanced performance in terms of its cost-effectiveness, adsorption capacity, remediation effects, and environmental adaptability. This study highlights the potential of ZMBO as a promising capping material for remediating As-contaminated sediments through combined chemical oxidation and adsorption mechanisms, offering sustainable solutions for improving water quality management worldwide.

Arsenic exposure is associated with elevated sweat chloride concentration and airflow obstruction among adults in Bangladesh: A cross-sectional study

Arsenic is associated with lung disease and experimental models suggest that arsenic-induced degradation of the chloride channel CFTR (cystic fibrosis transmembrane conductance regulator) is a mechanism of arsenic toxicity. We examined associations between arsenic exposure, sweat chloride concentration (measure of CFTR function), and pulmonary function among 269 adults in Bangladesh. Participants with sweat chloride ≥ 60 mmol/L had higher arsenic exposures than those with sweat chloride < 60 mmol/L (water: median 77.5 µg/L versus 34.0 µg/L, p = 0.025; toenails: median 4.8 µg/g versus 3.7 µg/g, p = 0.024). In linear regression models, a one-unit µg/g increment in toenail arsenic was associated with a 0.59 mmol/L higher sweat chloride concentration, p < 0.001. Among the entire study population, after adjusting for covariates including age, sex, smoking, education, and height, toenail arsenic concentration was associated with increased odds of airway obstruction (OR: 1.97, 95%: 1.06, 3.67, p = 0.03); however, sweat chloride concentration did not mediate this association. Our findings suggest that sweat chloride concentration may serve as novel biomarker for arsenic exposure, warranting further investigation in diverse populations, and that arsenic likely acts on the lung through mechanisms other than inducing CFTR dysfunction. Alternative mechanisms by which environmental arsenic exposure may lead to obstructive lung disease, such as arsenic-induced direct lung injury and/or increase lung proteinase activity, require additional exploration in future work.

Electrochemistry and Molecular Compositions Reflect Electron Shuttling of Dissolved Organic Matter in High Arsenic Groundwater

Little is known about the electron shuttle ability of dissolved organic matter (DOM) and its effects on arsenic (As) mobilization, which makes the underlying mechanism of groundwater As enrichment elusive. In this study, both the electrochemical properties and molecular compositions of DOM in high As groundwater were quantified in the Hetao Basin, China. We found that, along the flow path, the average electron-transferring capacity (ETC) of DOM, including the capacities of electron-accepting and electron-donating, continuously increased from 2.85 to 3.59 mmole-/gC along with As concentrations. The increasing ETC reflected an increase in electron shuttle ability of DOM. Furthermore, the increasing electron shuttle ability was mainly attributed to the recalcitrant compounds in DOM, especially CHOS and CHONS formulas in highly unsaturated structures with high oxygen (HUSHO) and CHO and CHON formulas in aromatic structures (AS). The significantly positive correlation between As concentration and ETC indicated that recalcitrant DOM promoted groundwater As enrichment through electron shuttling for inducing the reductive dissolution of As-containing Fe(III) oxide minerals, which was further supported by our culture experiments showing that goethite was more reduced [133 μM Fe(II)] in the presence of DOM with a higher ETC (3.35 mmole-/gC) as electron shuttling than that [65.2 μM Fe(II)] with a relatively lower ETC (2.41 mmole-/gC). Our study highlights that recalcitrant DOM compounds with unsaturated and AS have high electron shuttle ability, promoting As enrichment in groundwater.

The role of SLC7A11 in arsenite-induced oncogenic phenotypes of human bronchial epithelial cells: A metabolic perspective

Chronic arsenic exposure enhances the probability of lung cancer with the underlying mechanisms remain unknown. Glutamine-driven synthetic metabolism, including nucleotide synthesis, amino acid production, TCA cycle replenishment, glutathione synthesis, and lipid biosynthesis, is crucial for both cancer initiation and progression. This study demonstrated that chronic exposure to 0.1 μM arsenite for as long as 36 weeks induced malignant transformation in human bronchial epithelial cells (BEAS-2B). Metabolomics were used to systematically disclose metabolic characteristics in arsenic-transformed malignant (As-TM) cells. Significantly changed metabolites were enriched in alanine, aspartate and glutamate metabolism, arginine biosynthesis, glutamine and glutamate metabolism, glutathione metabolism, butanoate metabolism, TCA cycle, and arginine and proline metabolism. It is worth noting that glutamate located at the intersection of the enriched metabolism pathways. Glutamine deprivation attenuated the oncogenic phenotypes, including capacity of wound healing and proliferation, in As-TM cells. And the expression levels of mRNA and proteins associated with glutamine metabolism-related transporters and enzymes, including SLC7A11, GCLM, and GCLC, were significantly increased, with SLC7A11 exhibiting the most substantial increase. Moreover, arsenite transformation progressively elevated SLC7A11 mRNA and protein levels over time. The SLC7A11 inhibitor sulfasalazine remarkably attenuated arsenite-induced oncogenic phenotypes. Collectively, our data suggest that chronic arsenite exposure enhances glutamine metabolism through upregulation of SLC7A11, thereby promoting cell proliferation and malignant transformation. These results provide new insights for preventive and therapeutic strategies for lung cancer linked to arsenic exposure.

The kinetics of aqueous thiolated arsenic oxidation

Thiolated arsenic (As) compounds have been identified in various natural and engineered environments worldwide and are important for the biogeochemical cycling of As, yet quantitative data regarding their stability and transformation rates remains scarce. This study investigates the oxidation kinetics of mono-, di-, and tri-thioarsenate at varying pH, Fe, and (thio-)As concentrations in the aqueous phase. Experiments conducted over four weeks revealed that all thioarsenates were oxidized faster at lower pH, with rates of up to several μmoles/L/d at a pH of 3. Trithioarsenate demonstrated approximately two orders-of-magnitude faster oxidation rates than di- and monothioarsenate and these rates exhibited a higher sensitivity to pH and dissolved As and Fe concentrations. The presence of Fe enhanced the oxidation rates of trithioarsenate but had less impact on di- and monothioarsenate. Kinetic data were subsequently used to parameterize oxidation rate equations and determine reaction orders, and to calibrate a kinetic model that was leveraged to determine rate constants. The fundamental insights and kinetic parameters derived for thio-As oxidation in this study are important for predicting the mobility of thio-As compounds and for assessing the potential environmental impacts of As across ambient aquatic systems.

Removal of arsenic from water by silver nanoparticles and Fe-Ce mixed oxide supported on polymeric anion exchanger

By encapsulating nanoscale particles of goethite (α-FeO(OH)), hydrous ceric oxide (CeO2·H2O, HCO) and silver nanoparticles (AgNPs) in the pores of polystyrene anion exchanger D201, a novel nanocomposite FeO(OH)-HCO-Ag-D201 was prepared for the effective removal of arsenic from water. The isotherm study shows that FeO(OH)-HCO-Ag-D201 has excellent adsorption performance for As(III) and As(V), with an increased adsorption capacity of As(III) to 40.12 mg/g compared to that of 22.03 mg/g by the composite adsorbent without AgNPs (FeO(OH)-HCO-D201). The adsorption kinetics data showed that the sorption rate of FeO(OH)-HCO-Ag-D201 for As(III) is less than that for As(V), and the adsorption of As(III) and As(V) were consistent with the pseudo-second-order model and the pseudo-first-order model, respectively. Neutral or basic conditions are favored for the adsorption of As(III/V) by FeO(OH)-HCO-Ag-D201. Compared with nitrate/chloride/bicarbonate, sulfate/silicate/phosphate showed more remarkable inhibition of arsenic removal by FeO(OH)-HCO-Ag-D201, whereas natural organic matter showed no interference to the arsenic removal. The As(V) adsorption involved different interactions such as electrostatic attraction and surface complexation, while the adsorption of As(III) involved the part oxidization of As(III) to As(V) and the simultaneous adsorption of As(III) and As(V). In addition to the Ce(IV) in CeO2·H2O acted as an oxidant, the synergistic effect of α-FeO(OH) and AgNPs also contributed to the oxidization of As(III) to As(V). Moreover, the reusable property suggested that this FeO(OH)-HCO-Ag-D201 nanocomposite has great potential for arsenic-contaminated water purification.

Arsenic and heavy metals contamination by effluent dam rupture in a subtropical coastal lagoon

Dam accidents, often resulting from inadequate structural monitoring, pose significant environmental risks. In southern Brazil, the rupture of an evaporation-infiltration lagoon released over 500,000 m3 of treated domestic effluent into a coastal lagoon, raising concerns about potential contamination from nutrients and heavy metals. This study aimed to (1) assess the environment's self-purification capacity regarding dissolved nutrients, (2) determine total heavy metal concentrations in water and sediments throughout the coastal lagoon using inductively coupled plasma mass spectrometry, (3) correlate variables influencing heavy metal availability to identify potential sources, and (4) evaluate environmental risks by comparing concentrations to established water and sediment quality guidelines. Potential sources of contamination included natural origins, boat traffic associated with fuel leaks and antifouling paints, and the irregular discharge of domestic effluents into the lagoon. The results revealed nutrient self-purification and elevated arsenic levels in the water, likely from natural sources. However, manganese and zinc concentrations exceeded water quality limits, while zinc and copper levels were notably high in northern sediments, with no definitive association to the dam's sludge. These findings highlight significant toxicity risks to biota and emphasize the need for continuous monitoring. Mitigation strategies should be implemented, particularly in the most contaminated areas, given the lagoon's intense use for recreation and seafood harvesting. Overall, the results reinforce the threat of pollution to biodiversity, ecosystem services, the livelihoods of fishing communities, and the local economy, emphasizing the importance of this study in guiding management actions amidst significant challenges.

Critical role of vegetation and human activity indicators in the prediction of shallow groundwater quality distribution in Jianghan Plain with LightGBM algorithm and SHAP analysis

Groundwater serves as an indispensable resource for freshwater, but its quality has experienced a notable decline over recent decades. Spatial prediction of groundwater quality (GWQ) can effectively assist managers in groundwater remediation, management, and risk control. Based on the traditional intrinsic groundwater vulnerability (IGV) model (DRASTIC) and three vegetation (V) indicators (NDVI, EVI, and kNDVI) and four human activity (H) indicators (land use, GDP, urbanization index, and nighttime light), we constructed four models for GWQ spatial prediction in the Jianghan Plain (JHP), namely DRASTI, DRASTIH, DRASTIV, and DRASTIVH, excluding the conductivity (C) indicator due to its uniformly low values. LightGBM algorithm, Tree-structured Parzen Estimator (TPE) optimization method, and SHapley Additive exPlanations (SHAP) analysis are used for model setting, calibration, and interpretation, respectively. The results show that nitrogen-related GWQ parameters have higher weights, and the model performs exceptionally well when considering all the indicators (accuracy = 0.840, precision = 0.824, recall = 0.832, F1 score = 0.828, AUROC = 0.914). Notably, the introduced indicators (NDVI, EVI, kNDVI, nighttime light, GDP, and urbanization index) rank as the top six in terms of importance, while traditional DRASTI and land use indicators show lower significance. Based on SHAP analysis, poor GWQ primarily occurs in areas with either extremely high or extremely low GDP and urbanization index values, and human activities are the primary cause of poor GWQ in JHP, potentially involving urbanization, industrial and agricultural activities, as well as fertilizer usage. Finally, the methodological framework proposed in this study is encouraged to be applied to diverse regions, such as plains, karst areas, mountainous regions, and coastal areas, to support effective future groundwater management.

Unveiling PFAS hazard in European surface waters using an interpretable machine-learning model

Per- and polyfluoroalkyl substances (PFAS), commonly known as "forever chemicals", are ubiquitous in surface waters and potentially threaten human health and ecosystems. Despite extensive monitoring efforts, PFAS risk in European surface waters remain poorly understood, as performing PFAS analyses in all surface waters is remarkably challenging. This study developed two machine-learning models to generate the first maps depicting the concentration levels and ecological risks of PFAS in continuous surface waters across 44 European countries, at a 2-km spatial resolution. We estimated that nearly eight thousand individuals were affected by surface waters with PFAS concentrations exceeding the European Drinking Water guideline of 100 ng/L. The prediction maps identified surface waters with high ecological risk and PFAS concentration (>100 ng/L), primarily in Germany, the Netherlands, Portugal, Spain, and Finland. Furthermore, we quantified the distance to the nearest PFAS point sources as the most critical factor (14%-19%) influencing the concentrations and ecological risks of PFAS. Importantly, we determined a threshold distance (4.1-4.9 km) from PFAS point sources, below which PFAS hazards in surface waters could be elevated. Our findings advance the understanding of spatial PFAS pollution in European surface waters and provide a guideline threshold to inform targeted regulatory measures aimed at mitigating PFAS hazards.

Co-oxidation of arxB response by As(III), Fe(II), and Mn(II)-oxidizing bacteria in As-contaminated tap water

Iron pipe corrosion can be caused by tap water contamination with arsenic (As), heavy metals, and symbiotic microorganisms. In this study, we performed laboratory experiments on drinking water samples collected from Yanbian University of Science and Technology, Jilin Province, eastern China, to evaluate the mechanism of heavy metal oxidation by microbes. The experiments revealed corrosion of the entire water pipe, heavy metal contamination, and microbial co-oxidation of As(III), iron (Fe(II)), and manganese (Mn(II)). Pipe corrosion was observed in several university buildings, with particularly high levels of As (4.3 μg/L), Fe (143.4 μg/L), Mn (0.6 μg/L), and bacteria (1,200 CFU/100 mL) in the Engineering building. The As(III), Fe(II), and Mn(II) co-oxidation activity of As(III)-resistant and Fe(II)- and Mn(II)-oxidizing bacteria was investigated based on frvA, aioE, boxA, arsB, and arxB gene activities in Burkholderia glathei strain YUST-DW12 (NCBI accession No.: HM640291). Batch experiments revealed that YUST-DW12 completely co-oxidized 1 mM As(III) to As(V), 5 mM Fe(II) to Fe(III), and 5 mM Mn(II) to Mn(IV) within 45-50 h, 10 h, and 25 h, respectively. Co-oxidation related to arxB gene activity significantly contributed to As, Fe, and Mn bioremediation and mobility in tap water, indicating that As, Fe, and Mn oxidases in bacteria control the biogeochemical cycle of contaminated public tap water affected by iron pipe corrosion. This research provides novel insights into the role of microbial arxB in As(III), Fe(II), and Mn(II) co-oxidation in corroded iron pipes, enhancing our understanding of the co-oxidative removal of As from contaminated tap and bottled water.

Mechanism of arsenic regulation of mitochondrial damage and autophagy induced synaptic damage through SIRT1 and protective effect of melatonin in HT22 cell

Arsenic (As), a widespread environmental pollutant, can induce severe neurological damage worldwide; however, the underlying mechanisms remain unclear. Sirtuin 1 (SIRT1) has been reported to exert neuroprotective effects against various neurological diseases by resisting mitochondrial damage and autophagy through deacetylation. In this study, we established a model of HT22 cells exposed to NaAsO2 and examined the levels of mitochondrial, autophagy, and synaptic damage in HT22 cells and HT22 cells with high expression of SIRT1 (pre-treated with the agonist SRT1720) 24 h after exposure. Our results suggest that NaAsO2 exposure induces down-regulation of SIRT1, causing mitochondrial damage and activation of autophagy, which in turn leads to synaptic damage. Notably, melatonin (Mel) intervention upregulated SIRT1 and attenuated mitochondrial damage and autophagy, restoring synaptic damage. In conclusion, the results of the present study indicate that As causes neurotoxicity by decreasing SIRT1 production, causing mitochondrial damage and activating autophagy, which provides fundamental data for further study of arsenic neurotoxicity. In addition, blocking this pathway attenuated the synaptic damage of arsenic exposure, which provides a new therapeutic avenue for arsenic neurotoxicity.

Rainwater-Derived Reactive Oxygen Species Diminish Environmental Risk from Arsenic in Paddy Rice Systems

It has been previously observed that rainwater input into paddy rice soils reduced the level of grain-borne arsenic, and it is hypothesized that a Fenton-like reaction triggered by interaction between rainwater-borne hydrogen peroxide and ferrous iron in paddy soils is responsible for microbially mediated impediment of As uptake by rice plants. However, this hypothesis remains untested. This study tested the hypothesis through mesocosm experiments, confirming that rainwater-borne hydrogen peroxide triggered hydroxyl radical (•OH) generation, elevating soil redox potential, and oxidizing arsenite to less phytoavailable arsenate in soil porewater, thereby reducing As uptake by rice and As accumulation in rice grain. Comparison between two crops of rice cultivation with different fluxes of rainwater-borne hydrogen peroxide confirms that seasonal rainfall variation has an impact on accumulation of rice grain-borne arsenic, with paddy soil receiving more rainfall having a lower arsenic concentration in the rice grain compared to that receiving less rainfall. Using China's major rice-producing region as an example, it is demonstrated that spatial variation in rainfall regime could impact the geographical distribution of rice grain-borne As at a national scale. The findings have implications for the assessment and management of the environmental risk from arsenic-contaminated rice grains.

Global soil pollution by toxic metals threatens agriculture and human health

Toxic metal pollution is ubiquitous in soils, yet its worldwide distribution is unknown. We analyzed a global database of soil pollution by arsenic, cadmium, cobalt, chromium, copper, nickel, and lead at 796,084 sampling points from 1493 regional studies and used machine learning techniques to map areas with exceedance of agricultural and human health thresholds. We reveal a previously unrecognized high-risk, metal-enriched zone in low-latitude Eurasia, which is attributed to influential climatic, topographic, and anthropogenic conditions. This feature can be regarded as a signpost for the Anthropocene era. We show that 14 to 17% of cropland is affected by toxic metal pollution globally and estimate that between 0.9 and 1.4 billion people live in regions of heightened public health and ecological risks.

Magnetic Nanofibers in Heavy Metal Arsenic(V) Pollution Control Research

In this experiment, PAN/Fe3O4@CTAB magnetic nanofibers (average diameter of 386 nm) were prepared by electrospinning for the removal of As(V) from an aqueous solution. Material characterization was analyzed using phase analysis of X-ray diffraction (XRD), a Fourier transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), and thermogravimetric analysis (TG), which demonstrated that the magnetic nanoparticles were successfully incorporated into the fiber membrane. Batch adsorption experiments revealed that the process followed pseudo-second-order kinetics and Langmuir isotherm models, achieving a maximum adsorption capacity of 138.66 mg/g, higher than that of unmodified PAN/Fe3O4 (93.59 mg/g). The adsorption efficiency of this adsorbent was high (97% removal in 300 min) and remained at 91% after five regeneration cycles (initial value of 98.65%). The response surface methodology (RSM) was also employed to construct and analyze the model to investigate the effects of three critical adsorption parameters, pH, adsorption time, and adsorbent concentration, on As(V). The optimal conditions for adsorption were determined to be a pH of 3.81, an adsorption time of 342 min, and an adsorbent concentration of 1.36 g/L, achieving an arsenic ion removal rate of 98.62%. The experimental results were found to be in accordance with the theoretical parameters, thereby providing further evidence that the synthesized material is an excellent adsorbent for the treatment of water pollution.

Arsenic exposure provoked prostatic PANoptosis by inducing mitochondrial dysfunction in mice and WPMY-1 cells

Inorganic arsenic, a widespread environmental toxicant, significantly contributes to prostate injury. However, the exact cellular mechanisms remain unclear. This study explored the involvement of pyroptosis, apoptosis, and necroptosis (PANoptosis), and their interconnections in arsenic-induced prostate injury. Herein, by employing in vitro (WPMY-1 cells exposed to arsenic for 48 h with or without reactive oxygen species (ROS) and mitochondrial ROS scavenger treatments) and in vivo (C57BL/6 mice were orally gavaged with arsenic and/or N-acetylcysteine for 90 consecutive days) models of arsenic-induced prostate injury and intervention, we demonstrated that sodium arsenite (NaAsO2) triggered mitochondrial damage-activated PANoptosis via the Bax/Bcl-xL/caspase-3/Gasdermin E (GSDME) pathway and the Z-DNA binding protein 1/receptor-interacting protein kinases 1 (RIPK1)/RIPK3/mixed lineage kinase domain-like protein (MLKL) signaling pathway. Notably, treatment with NaAsO2, GSDME, or MLKL knockdown in WPMY-1 cells increased the phenotype of PANoptosis. Mechanistically, the GSDME-N, GSDMD-N, p-MLKL, and cleaved caspase-3 protein levels were increased (1.4-, 2.67-, 3.51-, and 2.16-fold, respectively) in NaAsO2-treated GSDME knockdown WPMY-1 cells, whereas GSDME-N and cleaved caspase-3 protein levels were increased (1.30- and 1.21-fold, respectively) in NaAsO2-treated MLKL knockdown WPMY-1 cells. Our study highlights the crucial role of mitochondrial dysfunction in the initiation of PANoptosis during arsenic-induced prostate injury. Furthermore, we provide novel insights into the connections between apoptosis, pyroptosis, and necroptosis, indicating that GSDME and MLKL proteins may act as crucial regulators and potential therapeutic targets for arsenic-induced PANoptosis.

Sulfur depletion through repetitive redox cycling unmasks the role of the cryptic sulfur cycle for (methyl)thioarsenate formation in paddy soils

Inorganic and oxymethylated thioarsenates form through the reaction of arsenite and oxymethylated arsenates with reduced sulfur, mainly as sulfide (SII-) but also as zerovalent sulfur (S0). In paddy soils, considered low-S systems, microbial reduction of the soil's "primary" sulfate pool is the principal SII- source for As thiolation. Under anoxic conditions, this primary pool is readily consumed, and the precipitation of iron (Fe) sulfides lowers SII- availability. Nonetheless, sulfate can be constantly replenished by the reoxidation of SII- coupled with the reduction of FeIII phases in the so-called cryptic S cycle (CSC). The CSC supplies a small secondary sulfate pool available for reduction and, according to previous studies, As thiolation. However, sulfate concentrations commonly found in paddy soils mask the biogeochemical processes associated with the CSC. Here, we depleted a paddy soil from excess S, Fe, and As from a paddy soil through repetitive flooding and draining (e.g., redox cycling). After 10, 20, and 30 such cycles, we followed thioarsenate formation during an anoxic incubation period of 10 days. Higher S/As ratios increased As thiolation contribution to total As up to 10-fold after 30 cycles. During the anoxic incubation, the depleted soils showed a transient first phase where the reduction of the primary sulfate pool led to inorganic thioarsenate formation. In the second phase, methylthioarsenate formation correlated with partially oxidized S species (S0, thiosulfate), suggesting CSC-driven sulfate replenishment, re-reduction, and thiolation. Methylthioarsenates formed even as inorganic thioarsenates de-thiolated, indicating thermodynamic preference under S-limited conditions. This study highlights the role of the CSC in sustaining thioarsenate formation in low-S systems.

Interactions between phosphate and arsenic in iron/biochar-treated groundwater: Corrosion control insights from column experiments

An increasing number of studies have reported the coexistence of arsenic (As) and phosphorus at high concentrations in groundwater, which threatens human health and increases the complexity of groundwater remediation. However, limited work has been done regarding As interception in the presence of phosphate in flowing systems. In this study, a series of experiments were conducted to evaluate the interactions between phosphate and As during As removal by iron (Fe)-based biochar (FeBC). The addition of phosphate promoted As removal by FeBC in the batch and column experiments. X-ray absorption near edge structure (XANES) analysis provided evidence of simultaneous oxidation and reduction of trivalent arsenic in the FeBC column experiment, accompanied by corrosive Fe oxidation. However, the addition of phosphate enhanced As stabilization, attributed to the As-incorporated Fe-Ca-phosphates precipitates. The involvement of phosphate decelerated the Fe corrosion and the formation of secondary minerals in the column, mediating the risk of passivation and clogging. The As retained by Fe-Ca-phosphate precipitates was more readily oxidized, resulting in higher proportions of pentavalent arsenic. The results of this work identify the corrosion control and sustained-release roles of phosphate in FeBC application, informing the perspective of FeBC in As-contaminated groundwater remediation and providing new insights into the interactions between phosphate and As.

Arsenic toxicity exacerbates China's groundwater and health crisis

Arsenic (As) contamination is considered a major threat to groundwater quality and human health. The uneven distribution of arsenic contributes to regional variations, creating discrimination related to arsenic enrichment and carcinogenic risk. Here, we have analyzed 2,737 groundwater samples across China, which spans a broad range of geo-environments, climates and land use types. We find that regional inequality of groundwater arsenic concentration is caused by ontology environment. By mapping the groundwater arsenic distribution across China and conducting a global meta-analysis, the spatial response of arsenic concentration to different cancer risks was revealed, and neglected As(V) should be given attention. A random forest analysis identified chemical properties (including oxidation-reduction potential, pH, total manganese ion, total iron ion, total dissolved solids, and sulfate ion) as the most influential drivers, contributing 56% to the model's explanatory power, followed by geographical factors at 28%, climatic factors at 10%, and human activities at 6%. Additionally, reducing the proportion of groundwater supply with high arsenic concentration in drinking water in regions without water treatment may help lower the potential carcinogenic risk. This study emphasizes the potential health risk associated with high arsenic groundwater, making it particularly important to roll out efficient water purification technologies given the natural enrichment of arsenic, especially rural regions.

Probabilistic Health Risk Assessment and Grading Benchmark Estimation of Atmospheric PM2.5-Bound Heavy Metals in China

The formulation of reasonable concentration classification standards can significantly enhance the protection of populations against atmospheric heavy metals, and the development of these standards should be grounded in national-level probabilistic risk assessment to establish multiple grading benchmarks. In this study, the probabilistic health risk assessment model was used for the first time to assess the health risks of hazardous metals [arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), mercury (Hg), manganese (Mn), nickel (Ni), lead (Pb), and vanadium (V)] based on a publication dataset containing 57,737 PM2.5-bound heavy metal samples from China. Our results showed that the average non-carcinogenic risk attributed to heavy metals in all provinces of China was less than 1. In contrast, the average carcinogenic risk was greater than 10-6 in all provinces. The logarithmic mean non-carcinogenic health risks for the eight non-carcinogenic metals were ranked as follows: V (- 1.55 ± 0.96) > As (- 1.79 ± 0.96) > Mn (- 1.84 ± 0.82) > Co (- 2.05 ± 0.89) > Cd (- 2.14 ± 0.94) > Ni (- 2.59 ± 0.92) > Cr (- 3.26 ± 0.93) > Hg (- 4.86 ± 0.91), while the logarithmic mean carcinogenic health risk for the seven carcinogenic metals was Cr (- 5.33 ± 0.93) > V (- 5.79 ± 0.96) > As (- 5.98 ± 0.96) > Co (- 6.32 ± 0.89) > Cd (- 6.89 ± 0.94) > Pb (- 7.02 ± 0.93) > Ni (- 7.22 ± 0.92). The metals that contributed most to the non-carcinogenic and carcinogenic risks were V (35.86%) and Cr (57.61%), respectively. Through probabilistic risk assessment, we constructed seven-level health benchmarks for carcinogenic metals (As, Cd, Co, Cr, Ni, Pb, V). These benchmarks of extremely low health risk for the seven carcinogenic metals (As, Cd, Co, Cr, Ni, Pb, V) were 0.00037 μg/m3, 0.0011 μg/m3, 0.00012 μg/m3, 0.00011 μg/m3, 0.0043 μg/m3, 0.025 μg/m3, and 0.00031 μg/m3, respectively. Overall, this study is the first nationwide comprehensive assessment of the probabilistic risk of atmospheric PM2.5-bound toxic metals and provides a theoretical basis for revising and improving China's air quality standards.

Metalloid Nanomaterials Alleviate Arsenic Phytotoxicity and Grain Accumulation in Rice: Mechanisms of Abiotic Stress Tolerance and Rhizosphere Behavior

Nanoenabled agriculture technology exhibits potential in reducing arsenic uptake in rice; however, a systematic understanding of the rice-soil-microorganism process of nanomaterials (NMs) is lacking. Soil amendment of metalloid NMs, including SiO2, hydroxyapatite, S0, and Se0 at 10-100 (0.1-5.0 for Se NMs) mg/kg, increased rice biomass by 76.1-135.8% in arsenic-contaminated soil (17.0 mg/kg) and decreased arsenic accumulation in plant tissues by 9.3-78.2%. The beneficial effects were nanoscale-specific and NMs type- and concentration-dependent; 5 mg/kg Se NMs showed the greatest growth promotion and decrease in As accumulation. Mechanistically, (1) Se NMs optimized the soil bacterial community structure, enhancing the abundance of arsM by 104.2% and subsequently increasing arsenic methylation by 276.1% in rhizosphere compared to arsenic-alone treatments; (2) metabolomic analyses showed that Se NMs upregulated the biosynthesis pathway of abscisic acid, jasmonic acid, and glutathione, with subsequent downregulation of the arsenic transporter-related gene expression in roots by 42.2-73.4%, decreasing the formation of iron plaque by 87.6%, and enhancing the arsenic detoxification by 50.0%. Additionally, amendment of metalloid NMs significantly enhanced arsenic-treated rice yield by 66.9-91.4% and grain nutritional quality. This study demonstrates the excellent potential of metalloid NMs for an effective and sustainable strategy to increase food quality and safety.

Geochemistry of arsenic in soils with a focus on calcareous soils: control strategies and perspectives

Arsenic (As) contamination has become a significant environmental challenge due to the global expansion of industrial, agricultural, and mining activities, which contribute to the contamination of water, air, soils, and biota with As and other metals and metalloids. This review elucidates the geochemical behavior of As in soils, focusing on the factors influencing its dynamics and the effectiveness of various remediation techniques, particularly in calcareous soils. Calcareous soils, characterized by their unique properties, exhibit intricate interactions with As, necessitating a deeper understanding of the mechanisms driving these processes. Compared to other soil types, the bioavailability of As in calcareous soils is generally lower, largely due to their elevated pH and the presence of calcium carbonate (CaCO3). These factors contribute to the enhanced adsorption of As by soil organic and mineral components, forming less soluble As-CaCO3 complexes and decreasing As solubility. Despite this, research on As geochemistry in calcareous soils and the development of effective removal techniques still needs to be completed, emphasizing the need for further study. Additionally, this review explores future research directions in the context of As contamination and remediation, integrating case studies and advanced technologies to highlight innovative approaches for mitigating As contamination in calcareous soils.

A novel environmentally friendly catalyst for the preparation and degradation of DNT in dynamite wastewater: Performance, mechanism and application

This study proposes a novel approach to sustainable recycling through the preparation of a JCA5Fe@CNs catalyst, which demonstrates excellent performance. The catalyst was synthesized by loading nZVI onto biomass carbon-based precursors using a chemical modification-pyrolysis technique, with discarded date palm as the raw material. The new catalysts were prepared for a wide range of pH conditions and neutral conditions were preferred. The catalyst was able to degrade approximately 80 % of 2,4-Dinitrotoluene (2,4-DNT, 20 mg/L) within 5 min, with a maximum degradation rate constant (k) of 1.42162 min-1. Synchrotron radiation and density functional theory (DFT) calculations confirmed that the catalytic performance and stability of nZVI were significantly enhanced when incorporated into date-palm-based biomass carbon carriers. The degradation mechanism of 2,4-DNT was investigated using EPR and quenching experiments, revealing that reactive oxygen species (ROS) generated during the reaction involved both radical and non-radical pathways. HPLC-MS analysis identified several reaction intermediates, and potential degradation pathways for 2,4-DNT were proposed. Finally, a flow wastewater model was constructed to evaluate the catalyst's performance in 2,4-DNT degradation under a flow system, assessing its practical application potential. In conclusion, the JCA5Fe@CNs catalyst, prepared using the modification-pyrolysis strategy, shows promising potential for the treatment of challenging organic wastewater.

Global and regional patterns of soil metal(loid) mobility and associated risks

Soil contamination by metals and metalloids (metal[loid]s) is a global issue with significant risks to human health, ecosystems, and food security. Accurate risk assessment depends on understanding metal(loid) mobility, which dictates bioavailability and environmental impact. Here we show a theory-guided machine learning model that predicts soil metal(loid) fractionation across the globe. Our model identifies total metal(loid) content and soil organic carbon as primary drivers of metal(loid) mobility. We find that 37% of the world's land is at medium-to-high mobilization risk, with hotspots in Russia, Chile, Canada, and Namibia. Our analysis indicates that global efforts to enhance soil carbon sequestration may inadvertently increase metal(loid) mobility. Furthermore, in Europe, the divergence between spatial distributions of total and mobile metal(loid)s is uncovered. These findings offer crucial insights into global distributions and drivers of soil metal(loid) mobility, providing a robust tool for prioritizing metal(loid) mobility testing, raising awareness, and informing sustainable soil management practices.

Metformin Mitigates the Impact of Arsenic Exposure on the Maternal and Offspring Reproductive System of Female Mice

Exposure to arsenic causes health problems and is associated with adverse effects on fertility and development. Humans are facing increasing exposure to arsenic from multiple sources, such as drinking water, food products, and industrial processes. The mechanisms behind arsenic-induced reproductive toxicity and its impact on fertility and the development of future generations are investigated by the protective role of metformin (200 mg/kg) against arsenic-induced (20 ppm As2O3) ovarian damage in both maternal and offspring generations. Results showed arsenic exposure caused significant weight loss, increased mortality, reduced serum anti-Mullerian hormone (AMH) levels, and heightened oxidative stress, indicated by increased reactive oxygen species (ROS), malondialdehyde (MDA), and reduced ovarian antioxidant activity. Gene expression changes related to apoptosis and inflammation, such as BAX, Bcl-2, Bcl-2, caspase-3, tumor necrosis factor-alpha (TNF-α), and interleukin-1 (IL-1), were also noted, along with a decrease in HO-1 expression. Arsenic exposure led to a reduction in ovarian follicles and an increase in atretic follicles and uterine thickness. However, metformin significantly reduced ROS and MDA levels, enhanced antioxidant capacity, and protected ovarian tissue by upregulating heme oxygenase-1 (HO-1) and Bcl-2, modulating apoptotic and inflammatory genes, and preserving AMH levels. The possible protective role of metformin against arsenic-induced toxicity and its detrimental effects aims to improve therapeutic approaches to alleviate the harmful consequences of environmental pollutants, especially arsenic.

Missing pieces in the puzzle of ecology of microbial arsenate reduction

Arsenic pollution and its associated health risks have raised widespread concern. Under anaerobic conditions, arsenic mobility and toxicity increase when arsenate [As(V)] is reduced to arsenite [As(III)] by microbes through the cytoplasmic and dissimilatory pathways. However, the relative importance of these two pathways in the environment remains unclear, restricting our ability to effectively predict and regulate the environmental behavior of arsenic. Here, we review reports that declared a major role of the cytoplasmic or dissimilatory pathway in the environment and point out their limitations. We then summarize the key environmental factors influencing microbial As(V) reduction. Based on studies examining the expression of genes involved in the two As(V) reduction pathways, we hypothesize that the cytoplasmic pathway predominates at relatively high environmental As(III) concentrations, while the dissimilatory pathway is more significant at low concentrations. Future research is needed to test this hypothesis, and the expression of As(V)-reducing genes as a function of As(III) concentration can be investigated with various environmental samples and gradients.

Groundwater quality evolution across China

China is facing a severe groundwater quality crisis amid economic development and climate change, yet the extent and trajectory of this crisis remain largely unknown. Here we developed a machine-learning model, incorporating natural and social-economic factors, to construct annual probabilistic maps of poor groundwater quality (PGQ, i.e., Class V based on the Chinese groundwater quality standard) across China from 1980 to 2100. Alarmingly, our findings indicate a concerning escalation in PGQ area ratio, rising from 17.3% in 1980 to 30.1% in 2000, and surging to 40.8% by 2020, adversely affecting 6.8%, 17.5%, and 36.0% of the Chinese population, respectively. The predominant drivers of this degradation were identified as agricultural discharge (contributing to 10.7% growth in PGQ area ratio), followed by groundwater exploitation (5.6%), industrial discharge (5.3%), domestic discharge (1.7%), climate change (0.5%), and land use change (-0.3%). By 2050, the PGQ area ratio could range from 37.9% to 48.3% under different socio-economic and climate scenarios. Our study highlights the urgent need for effective water resources management and conservation measures to mitigate the deteriorating trend of groundwater quality and address the challenges posed by socio-economic development and climate change, thereby safeguarding water security for China and the global community.

Novel arsenate-respiring bacteria drive arsenic biogeochemical cycling in Tibetan geothermal springs revealed by DNA-SIP based metagenomics

Arsenic (As) is a toxic element posing health risks globally, with geothermal environment as one of the hotspots. Arsenic biotransformation is mainly mediated by microorganisms which often employ diverse metabolic strategies for survival. However, the microorganisms responsible for As cycling and their survival strategies in geothermal environment in Tibet, the Third Pole, remain unclear. To address this knowledge gap, we investigated As biotransformation in representative geothermal springs using DNA-stable isotope probing (DNA-SIP) combined with metagenomic sequencing. As(V) reduction to the more toxic As(III) was found to be prevalent. Pseudomonas and Thermincola were identified as the dominant As(V)-reducing bacteria (AsRB). Metagenome-assembled genomes (MAGs) affiliated with AsRB contained abundant genes encoding As(V)-respiratory reductase (arrA, 1044.34 transcripts per million (TPM)), nitrate reduction pathway (e.g., narG), and Wood-Ljungdahl pathway (e.g., acsA), indicating their role as dissimilatory As(V)-reducing prokaryotes (DARPs) with diverse metabolic strategies. Here, Thermincola's potential of As(V) reduction via arrA and carbon fixation via Wood-Ljungdahl pathway was observed for the first time, which was found to be widespread in various ecosystems. Our study unravels the key players driving As biogeochemical cycle in Tibetan geothermal springs and provides insights into the genetic mechanisms enabling their survival in extreme environments.

Optimisation led energy-efficient arsenite and arsenate adsorption on various materials with machine learning

The contamination of water by arsenic (As) poses a substantial environmental challenge with far-reaching influence on human health. Accurately predicting adsorption capacities of arsenite (As(III)) and arsenate (As(V)) on different materials is crucial for the remediation and reuse of contaminated water. Nonetheless, predicting the optimal As adsorption on various materials while considering process energy consumption continues to pose a persistent challenge. Literature data regarding the As adsorption on diverse materials were collected and employed to train machine learning models (ML), such as CatBoost, XGBoost, and LGBoost. These models were utilized to predict both As(III) and As(V) adsorption on a variety of materials using their reaction parameters, structural properties, and composition. The CatBoost model exhibited superior accuracy, achieving a coefficient of determination (R²) of 0.99 and a root mean square error (RMSE) of 1.24 for As(III), and an R² of 0.99 and RMSE of 5.50 for As(V). The initial As(III) and As(V) concentrations were proved to be the primary factors influencing adsorption, accounting for 27.9 % and 26.6 % of the variance for As(III) and As(V) individually. The genetic optimization led optimisation process, considering the low energy consumption, determined maximum adsorption capacities of 291.66 mg/g for As(III) and 271.56 mg/g for As(V), using C-Layered Double Hydroxide with reduced graphene oxide and chitosan combined with rice straw biochar, respectively. To further facilitate the process design for different real-life applications, the trained ML models are embedded into a web-app that the user can use to estimate the As(III) and As(V) adsorption under different design conditions. The utilization of ML for the energy-efficient As(III) and As(V) adsorption is deemed essential for advancing the treatment of inorganic As in aquatic settings. This approach facilitates the identification of optimal adsorption conditions for As in various material-amended waters, while also enabling the timely detection of As-contaminated water.

Arsenic exposure induces neural cells senescence and abnormal lipid droplet accumulation leading to social memory impairment in mice

The long-term harmful effects of arsenic exposure remain one of the important public health issues. The effects of arsenic exposure on the central nervous system, particularly concerning brain structure and function, have been garnering increasing attention. Hence, the aim of this study was to investigate the impact of chronic low-dose arsenic exposure on murine social memory and to elucidate the underlying molecular mechanisms. Male C57BL/6 mice at six months of age were randomly assigned to a control group and three treatment groups with different arsenic concentrations (50, 100, and 200 μg/L), with exposure durations of 30, 90, 180, and 360 days. The five-social memory test and three-chamber social memory test results indicated that chronic low-dose arsenic exposure disrupted social memory in mice. Further analysis revealed that arsenic exposure led to degeneration of neurons within the dorsal CA2 of the hippocampus (dCA2) and the lateral entorhinal cortex (LEC), which are pivotal for the modulation of social memory, and dCA2 neurons demonstrated structural disruptions and cytoplasmic fragmentation. In addition, arsenic exposure induced neurons and glial cells senescence in both dCA2 and LEC, with a particularly pronounced effect in microglia, and worse with dosage increasing of arsenic exposure, correlating with elevated expression levels of p16INK4A, ferritin light chain and the senescence-associated secretory factors TNF-α and IL-1β, and reduced expression of Lamin B1. Moreover, arsenic exposure triggered substantial cytoplasmic lipid droplets accumulation in neurons, astrocytes and microglia, with an upregulation of PLIN2 expression, a protein associated with lipid droplet formation in astrocytes. At the same time, the aberrant accumulation of lipid droplets further aggravated the astrocytes and microglia aging, especially microglia. Additionally, correlation analysis revealed that social memory impairment was negatively correlated with nerve cell senescence and lipid accumulation. Our findings suggest that arsenic exposure induced cellular functional abnormalities by triggering cellular senescence and the accumulation of lipid droplets, thereby exacerbated neuronal degeneration and result in impaired social memory in mice.

Competitive adsorption of arsenate and phosphate on hematite facets: Molecular insights for enhanced arsenic retention

Understanding the competition for adsorption between arsenate and other common oxyanions at mineral-water interfaces is critical for enhancing arsenate retention in the subsurface environment and mitigating exposure risks. This study investigated the competitive adsorption between arsenate and phosphate on hematite facets using batch experiments, together with in-situ infrared spectroscopy, two-dimensional correlation spectroscopy (2D-COS), and ab initio molecular dynamic (AIMD) simulations. This study's findings revealed that hematite exhibited notable selectivity for arsenate over phosphate in both adsorption capacity and rate, with selectivity significantly influenced by the exposed facets of the hematite and reaction concentrations. To wit, the (001) facet exhibited stronger selectivity for arsenate than the (110) facet, and increasing reaction concentration further enhances this selectivity. This selectivity was driven by surface hydroxy structure-mediated complexation, where both surfaces primarily formed stable inner-sphere monodentate complexes with an affinity for arsenate. On the (001) surface, the available Fe2OH featured two close-spaced iron sites (Fe - Fe ≈ 2.86 Å), enabling arsenate to interact with both sites simultaneously, significantly boosting arsenate selectivity. At higher surface loadings, the (110) surface formed partially more selective bidentate binuclear complexes, further enhancing arsenate retention. These findings emphasize the critical role of interfacial complexation, particularly the formation of inner-sphere bidentate complexes and the availability of iron sites, in controlling arsenate retention. By tailoring mineral facets and optimizing reaction conditions to improve iron site availability and promote bidentate complexation, arsenate retention can be significantly enhanced in phosphate-rich aquatic environments, such as rivers and groundwater in agricultural areas.

α-Lipoic Acid Ameliorates Arsenic-Induced Lipid Disorders by Promoting Peroxisomal β-Oxidation and Reducing Lipophagy in Chicken Hepatocyte

Liver disease poses a significant threat to global public health, with arsenic (As) recognized as a major environmental toxin contributing to liver injury. However, the specific mechanisms and the protective effects of α-lipoic acid (LA) remain unclear. Therefore, this study employs network toxicology and network pharmacology to comprehensively analyze the hepatotoxic mechanism of As and the hepatoprotective mechanism of LA, and further verifies the mechanisms of peroxisomal β-oxidation and lipophagy in the process. The network analysis results show that As induces liver damage mainly through autophagy, apoptosis, lipid metabolism, and oxidative stress, whereas LA exerts its hepatoprotective properties mainly by regulating lipid metabolism. Further verifications find that As inhibits SIRT1 expression, activates the P53 and Notch pathways, damages mitochondria, inhibits peroxisomal β-oxidation, increases lipid accumulation, and enhances lipophagy in the liver, while LA intervention alleviates As-induced lipid accumulation and enhances lipophagy by targeting SIRT1, ameliorating mitochondrial damage, enhancing peroxisomal β-oxidation, thereby alleviating As-induced liver damage. This study further clarifies the mechanism of As hepatotoxicity and provides a theoretical basis for LA as a potential hepatoprotective agent.

Application of the composite nanoparticles of selenium and chitosan for ameliorating arsenic stress in rice seedlings

Selenium nanoparticles are well known for their antioxidant and stress-mitigating properties. In our study, composite nanoformulations of selenium and chitosan have been synthesized. The synthesized composite nanoformulations were 50 nm in diameter, spherical in shape, and had higher antioxidant activities and stability than the selenium and chitosan nanoparticles. In our study, Luit rice seedlings grown in an arsenic-treated Hoagland solution showed a reduction of growth, decreased superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, ascorbate, and glutathione content. Otherwise, superoxide anion, hydrogen peroxide, and malondialdehyde content increased in arsenic-stressed conditions. The alone application of Selenium nanoparticles, chitosan nanoparticles, and their nanoformulation improved growth, reduced stress parameters, and enhanced enzymatic and non-enzymatic activity. Additionally, the reduction of superoxide anion, hydrogen peroxide, and malondialdehyde content was higher by applying composite nanoformulations in arsenic-stressed conditions than selenium and chitosan nanoparticles. The treatment of composite nanoformulation also regulated the enzymatic and non-enzymatic antioxidant activity higher than that of other nanoparticles. It might be due to the higher stability and antioxidant activity of composite nanoformulations than that of selenium and chitosan nanoparticles. Our study suggests that the composite nanoformulation enhanced the growth of rice plants by mitigating arsenic-induced reactive oxygen species and upregulating antioxidant activity.