Arsenic in the environment: Biology and Chemistry

In-situ groundwater treatment for arsenic removal: laboratory pilot scale study with 3-D tank packed porous media as subsurface

The ex-situ treatment of arsenic is widely adopted; however, there are emerging concerns related to system maintenance, material replacement, and waste generation. There is a scope to explore in-situ arsenite [As (III)] remediation in the aquifers. The main objective of this study is to evaluate the performance of in-situ synthesised FeS in immobilising As (III) in the natural groundwater when transported through a three-dimensional (3-D) porous media system. In this study, a 3-D tank of 0.50 m × 0.30 m × 0.30 m (L × W × H) was packed with natural sand to represent the subsurface porous media system. The homogeneous packing and uniform flow were ensured before synthesising FeS in-situ, where a total of 1.5 pore volumes (PVs) of 20 mM sodium sulfide (Na2S) and 20 mM ferrous sulfate (FeSO4) reagent solutions were injected alternatively into the pre-saturated porous media. Finally, 300 ± 15 μg/L of As (III) spiked natural groundwater was passed through the porous media, and the samples were collected through several sampling ports for analysing for total As and Fe. The result suggests that the concentration of As (III) reaches below 11 μg/L within 644 min (4 PVs) of injection of reagents. Furthermore, almost 88.4% of As (III) get immobilised after passing 31 PVs of contaminated water. In brief, almost 406 L of As contaminated groundwater can be treated by injecting 21 L of reagents with a reagent-to-treated water ratio of 1:20.

SUMOylation modification of FTO facilitates oxidative damage response of arsenic by IGF2BP3 in an m6A-dependent manner

N6-methyladenosine (m6A) is the most common form of internal post-transcriptional methylation observed in eukaryotic mRNAs. The abnormally increased level of m6A within the cells can be catalyzed by specific demethylase fat mass and obesity-associated protein (FTO) and stay in a dynamic and reversible state. However, whether and how FTO regulates oxidative damage via m6A modification remain largely unclear. Herein, by using both in vitro and in vivo models of oxidative damage induced by arsenic, we demonstrated for the first time that exposure to arsenic caused a significant increase in SUMOylation of FTO protein, and FTO SUMOylation at lysine (K)- 216 site promoted the down-regulation of FTO expression in arsenic target organ lung, and therefore, remarkably elevating the oxidative damage via an m6A-dependent pathway by its specific m6A reader insulin-like growth factor-2 mRNA-binding protein-3 (IGF2BP3). Consequently, these findings not only reveal a novel mechanism underlying FTO-mediated oxidative damage from the perspective of m6A, but also imply that regulation of FTO SUMOylation may serve as potential approach for treatment of oxidative damage.

Ecological and health risk assessments of heavy metals and their accumulation in a peanut-soil system

Heavy metals pollution is a notable threat to environment and human health. This study evaluated the potential ecological and health risks of heavy metals (Cu, Cr, Cd, Pb, Zn, Ni, and As) and their accumulation in a peanut-soil system based on 34 soil and peanut kernel paired samples across China. Soil As and Cd posed the greatest pollution risk with 47.1% and 17.6% of soil samples exceeding the risk screen levels, respectively, with 26.5% and 20.6% of the soil sites at relatively strong potential ecological risk level, respectively, and with the geo-accumulation levels at several soil sites in the uncontaminated to moderately contaminated categories. About 35.29% and 2.94% of soil sites were moderately and severely polluted based on Nemerow comprehensive pollution index, respectively, and a total of 32.4% of samples were at moderate ecological hazard level based on comprehensive potential ecological risk index values. The Cd, Cr, Ni, and Cu contents exceeded the standard in 11.76, 8.82, 11.76 and 5.88% of the peanut kernel samples, respectively. Soil metals posed more health risks to children than adults in the order As > Ni > Cr > Cu > Pb > Zn > Cd for non-carcinogenic health risks and Ni > Cr ≫ Cd > As > Pb for carcinogenic health risks. The soil As non-cancer risk index for children was greater than the permitted limits at 14 sites, and soil Ni and Cr posed the greatest carcinogenic risk to adults and children at many soil sites. The metals in peanut did not pose a non-carcinogenic risk according to standard. Peanut kernels had strong enrichment ability for Cd with an average bio-concentration factor (BCF) of 1.62. Soil metals contents and significant soil properties accounted for 35-74% of the variation in the BCF values of metals based on empirical prediction models.

Effects of environmental metal and metalloid pollutants on plants and human health: exploring nano-remediation approach

Metal and metalloid pollutants severely threatens environmental ecosystems and human health, necessitating effective remediation strategies. Nanoparticle (NPs)-based approaches have gained significant attention as promising solutions for efficient removing heavy metals from various environmental matrices. The present review is focused on green synthesized NPs-mediated remediation such as the implementation of iron, carbon-based nanomaterials, metal oxides, and bio-based NPs. The review also explores the mechanisms of NPs interactions with heavy metals, including adsorption, precipitation, and redox reactions. Critical factors influencing the remediation efficiency, such as NPs size, surface charge, and composition, are systematically examined. Furthermore, the environmental fate, transport, and potential risks associated with the application of NPs are critically evaluated. The review also highlights various sources of metal and metalloid pollutants and their impact on human health and translocation in plant tissues. Prospects and challenges in translating NPs-based remediation from laboratory research to real-world applications are proposed. The current work will be helpful to direct future research endeavors and promote the sustainable implementation of metal and metalloid elimination.

Assessment of the surface water quality and primary health risk in urban wastewater and its receiving river Kathajodi, Cuttack of eastern India

Kathajodi, the principal southern distributary of the Mahanadi River, is the vital source of irrigation and domestic water use for densely populated Cuttack city which receives anthropogenic wastes abundantly. This study assesses the contamination level and primary health status of urban wastewater, and its receiving river Kathajodi based on the physicochemical quality indices employing inductively coupled plasma mass spectroscopy and aligning with guidelines from the United States Environmental Protection Agency (USEPA) and WHO. The high WQI, HPI, and HEI in the catchment area (KJ2, KJ3, and KJ4) indicate poor water quality due to the influx of domestic waste through the primary drainage system and effluents of healthcare units. A high BOD (4.33-19.66 mg L-1) in the catchment indicates high organic matter, animal waste, bacteriological contamination, and low DO, resulting in deterioration of water quality. CR values beyond limits (1.00E - 06 to 1.00E - 04) in three locations of catchment due to higher Cd, Pb, and As indicate significant carcinogenic risk, while high Mn, Cu, and Al content is responsible for several non-carcinogenic ailments and arsenic-induced physiological disorders. The elevated heavy metals Cd, Cu, Fe, Mn, Ni, and Zn, in Kathajodi, could be due to heavy coal combustion, vehicle exhaust, and industrial waste. On the other hand, Cu, Fe, K, and Al could be from agricultural practices, weathered rocks, and crustal materials. Positive significant (p ≤ 0.05) Pearson correlations between physicochemical parameters indicate their common anthropogenic origin and similar chemical characteristics. A strong correlation of PCA between elements and physiological parameters indicates their role in water quality deterioration. Assessing the surface water quality and heavy metal contents from this study will offer critical data to policymakers for monitoring and managing public health concerns.

Exceptional anti-toxic growth of water spinach in arsenic and cadmium co-contaminated soil remediated using biochar loaded with Bacillus aryabhattai

Functionalized biochars are crucial for simultaneous soil remediation and safe agricultural production. However, a comprehensive understanding of the remediation mechanism and crop safety is imperative. In this work, the all-in-one biochars loaded with a Bacillus aryabhattai (B10) were developed via physisorption (BBC) and sodium alginate embedding (EBC) for simultaneous toxic As and Cd stabilization in soil. The bacteria-loaded biochar composites significantly decreased exchangeable As and Cd fractions in co-contaminated soil, with enhanced residual fractions. Heavy metal bioavailability analysis showed a maximum CaCl2-As concentration decline of 63.51% and a CaCl2-Cd decline of 50.96%. At a 3% dosage of composite, rhizosphere soil showed improved organic matter, cation exchange capacity, and enzyme activity. The aboveground portion of water spinach grown in pots was edible, with final As and Cd contents (0.347 and 0.075 mg·kg⁻¹, respectively) meeting food safety standards. Microbial analysis revealed the composite's influence on the rhizosphere microbial community, favoring beneficial bacteria and reducing plant pathogenic fungi. Additionally, it increased functional microorganisms with heavy metal-resistant genes, limiting metal migration in plants and favoring its growth. Our research highlights an effective strategy for simultaneous As and Cd immobilization in soil and inhibition of heavy metal accumulation in vegetables.

Severe Disease Burden and the Mitigation Strategy in the Arsenic-Exposed Population of Kaliprasad Village in Bhagalpur District of Bihar, India

The present study was carried out in the village Kaliprasad of Bhagalpur district of Bihar to know the arsenic exposure effect in the exposed population. A total of n = 102 households were studied, and their water and biological samples such as urine and hair were collected and analyzed in a graphite furnace atomic absorption spectrophotometer (GF-AAS). The assessment of arsenic-exposed village population reveals that the villagers were suffering from serious health-related problems such as skin manifestations (hyperkeratosis and melanosis in their palm and soles), breathlessness, general body weakness, mental disorders, diabetes, hypertension (raised blood pressure), hormonal imbalance, neurological disorders, and few cancer cases. About 77% of household hand pump water had arsenic level more than the WHO recommended level of 10 µg/L, with highest level of 523 µg/L. Moreover, in 60% individual's urine samples, arsenic concentration was very high with maximum 374 µg/L while in hair 64% individuals had arsenic concentration above the permissible limit with maximum arsenic concentration of 11,398 µg/kg. The hazard quotient (HQ) was also calculated to know the arsenic risk percentage in children as 87.11%, in females as 83.15%, and in males as 82.27% by groundwater. This has surpassed the threshold value of 1 × 10 - 6 for carcinogenic risk (CR) in children, female, and male population group in the village. Hence, the exposed population of Kaliprasad village are at very high risk of the disease burden.

Multilevel Regulation of Membrane Proteins in Response to Metal and Metalloid Stress: A Lesson from Yeast

In the face of flourishing industrialization and global trade, heavy metal and metalloid contamination of the environment is a growing concern throughout the world. The widespread presence of highly toxic compounds of arsenic, antimony, and cadmium in nature poses a particular threat to human health. Prolonged exposure to these toxins has been associated with severe human diseases, including cancer, diabetes, and neurodegenerative disorders. These toxins are known to induce analogous cellular stresses, such as DNA damage, disturbance of redox homeostasis, and proteotoxicity. To overcome these threats and improve or devise treatment methods, it is crucial to understand the mechanisms of cellular detoxification in metal and metalloid stress. Membrane proteins are key cellular components involved in the uptake, vacuolar/lysosomal sequestration, and efflux of these compounds; thus, deciphering the multilevel regulation of these proteins is of the utmost importance. In this review, we summarize data on the mechanisms of arsenic, antimony, and cadmium detoxification in the context of membrane proteome. We used yeast Saccharomyces cerevisiae as a eukaryotic model to elucidate the complex mechanisms of the production, regulation, and degradation of selected membrane transporters under metal(loid)-induced stress conditions. Additionally, we present data on orthologues membrane proteins involved in metal(loid)-associated diseases in humans.

Source, toxicity and carcinogenic health risk assessment of heavy metals

Heavy metals are chemical elements with unique properties that are toxic even in low concentrations and affect human health with different functions. Agricultural and industrial activities, improper disposal of household solid waste and residues related to industrial producers, discharge of household wastewater and agricultural fertilizers are the most important ways in which toxic heavy metals enter the environment, which harms human health and life. A narrative review of the literature was done from 2000 to 2022 based on searched databases included Google Scholar, PubMed, Springer, Web of Science, and Science Direct (Scopus). All relevant studies published 2000 until 2022 gathered. According to the databases, 820 articles were retrieved. 186 and 50 articles were found and selected based on records identified through database searching and additional records identified through other sources. In the next stage, 97 studies were screened after review and 64 full-text articles entered into the analysis process. Finally, 45 articles were selected in this study. Adverse effects of heavy metals on various conditions in the body depend on a number of factors, including dose, route of exposure and chemical species, as well as age, sex, genetics, nutritional status, and duration of exposure to the heavy metal. The existence of significant relationships between long-term and short-term exposure to toxic heavy metals and their adverse effects, including carcinogenicity, has been extensively studied and proven through numerous experiments. However, the mechanisms associated with this complication have not been properly identified, so in future research, there is a great need for comprehensive studies on the carcinogenicity of heavy metals.

Characterisation of arsenic levels in acid-treated arsenic-containing sludge after steel slag-fly ash gel curing

Arsenic-containing sludge (ABG) is a common hazardous waste in the metallurgical industry and poses a serious threat to environmental safety. However, its instability and mobility have a significant impact on the environment. Traditional curing methods are time-consuming and costly, often resulting in incomplete curing. In this study, we introduce a curing/stabilisation method with a steel slag-fly ash gel material after ABG acid treatment. The toxic leaching of arsenic from ABG was reduced to 220 mg/kg by treating the sludge with acids (H2SO4-H3PO4) at different solid-to-liquid ratios. Afterward, H2O2 was added to oxidise As(III) to As(V). The ABG was cured/stabilised using an alkali-activated steel slag-fly ash gel material. The cured product exhibited optimal arsenic fixation under an ABG/steel slag/fly ash mass ratio of 1:4:2, a curing temperature of 60°C, a curing time of 20 h, and an ambient pH of 12.5. Under these conditions, steel slag-fly ash facilitated Ca-As precipitation, resulting in a hydration reaction that produced C-S-H gel. Additionally, the reaction generated calcium hydroxide, calcium and iron pyroxene, silica, and iron ferrite, which adsorbed part of the free arsenic, completing the curing of the acid-treated ABG and stabilising arsenic leaching toxicity. The leaching of arsenic in the ABG was much lower than the Chinese 'Hazardous Wastes Leaching Toxicity Identification Standard' (GB5085.3-2007) (5 mg/L), with an arsenic curing rate exceeding 99%. The mechanism of arsenic solidification involves the combined effects of chemical precipitation, physical encapsulation, and adsorption. Collectively, our findings demonstrated that the use of steel slag-fly ash gel as a functional material for ABG curing holds considerable environmental and economic benefits. Therefore, this study provides theoretical guidance and provides insights into the experimental feasibility of ABG treatment.

Degradation of algae promotes the release of arsenic from sediments under high-sulfate conditions

Sulfate concentrations in eutrophic waters continue to increase; however, the transformations of arsenic (As) in sediments under these conditions are unclear. In this study, we constructed a series of microcosms to investigate the effect of algal degradation on As transformations in sediments with high sulfate concentrations. The results showed that both the elevated sulfate levels and algal degradation enhanced the release of As from sediments to the overlying water, and degradation of algal in the presence of elevated sulfate levels could further contribute to As release. Sulfate competed with arsenate for adsorption in the sediments, leading to As desorption, while algal degradation created a strongly anaerobic environment, leading to the loss of the redox layer in the surface sediments. With high sulfate, algal degradation enhanced sulfate reduction, and sulfur caused the formation of thioarsenates, which may cause re-dissolution of the arsenides, enhancing As mobility by changing the As speciation. The results of sedimentary As speciation analysis indicated that elevated sulfur levels and algal degradation led to a shift of As from Fe2O3/oxyhydroxide-bound state to specifically adsorbed state at the sediment water interface. This study indicated that algal degradation increases the risk of As pollution in sulfate-enriched eutrophic waters.

Historical contamination with a current problem: Can mining tailings enhance coastal arsenic pollution?

The coast of Espírito Santo state (Southeast Brazil) is recognized for its environmental arsenic (As) enrichment and, over the years, mining operations have potentialized it. We aimed to evaluate the effect of Rio Doce discharge on As inputs and the role of iron ore tailings from the Fundão dam disaster in enhancing As contamination in the marine sediment. Two scenarios were evaluated: Predisaster and Postdisaster; dry and wet conditions were considered in each period. High As concentrations were found in the Predisaster (28.44 ± 13.53 µg g-1 ), but a significant increase in As was remarkable during the Postdisaster in the wet season, one year after the disaster (maximum of 58.39 µg g-1 ; geoaccumulation index (Igeo ) Class 3, moderately severe pollution). On that occasion, iron (Fe) oxy-hydroxides from tailings were remobilized from the Rio Doce channel and deposited on the continental shelf bottom. Therefore, chemical interactions among Fe, As, and carbonates were enhanced, resulting in As and Fe coprecipitation and the trapping by carbonate adsorption. Rio Doce discharge seems to be the main factor in As inputs to the inner continental shelf when flooding do not occur previously in samplings, which allows further dispersion of contaminants, although this hypothesis should be tested further. Integr Environ Assess Manag 2024;20:159-168. © 2023 SETAC.

Machine learning based prediction and experimental validation of arsenite and arsenate sorption on biochars

Arsenic (As) contamination in water is a significant environmental concern with profound implications for human health. Accurate prediction of the adsorption capacity of arsenite [As(III)] and arsenate [As(V)] on biochar is vital for the reclamation and recycling of polluted water resources. However, comprehending the intricate mechanisms that govern arsenic accumulation on biochar remains a formidable challenge. Data from the literature on As adsorption to biochar was compiled and fed into machine learning (ML) based modelling algorithms, including AdaBoost, LGBoost, and XGBoost, in order to build models to predict the adsorption efficiency of As(III) and As(V) to biochar, based on the compositional and structural properties. The XGBoost model showed superior accuracy and performance for prediction of As adsorption efficiency (for As(III): coefficient of determination (R2) = 0.93 and root mean square error (RMSE) = 1.29; for As(V), R2 = 0.99, RMSE = 0.62). The initial concentrations of As(III) and As(V) as well as the dosage of the adsorbent were the most significant factors influencing adsorption, explaining 48 % and 66 % of the variability for As(III) and As(V), respectively. The structural properties and composition of the biochar explained 12 % and 40 %, respectively, of the variability of As(III) adsorption, and 13 % and 21 % of that of As(V). The XGBoost models were validated using experimental data. R2 values were 0.9 and 0.84, and RMSE values 6.5 and 8.90 for As(III) and As(V), respectively. The ML approach can be a valuable tool for improving the treatment of inorganic As in aqueous environments as it can help estimate the optimal adsorption conditions of As in biochar-amended water, and serve as an early warning for As-contaminated water.

Methylation of arsenic in rice: Mechanisms, factors, and mitigation strategies

Arsenic contamination in rice poses a significant health risk to rice consumers across the globe. This review examines the impact of water source and type on the speciation and methylation of arsenic in rice. The review highlights that groundwater used for irrigation in arsenic-affected regions can lead to higher total arsenic content in rice grains and lower proportions of methylated arsenic species. The methylation of As in rice is influenced by microbial activity in groundwater, which can methylate arsenic that is taken up by rice plants. Reclaimed water irrigation can also increase the risk of arsenic accumulation in rice crops, although the use of organic amendments and proper water management practices can reduce arsenic accumulation. Different water management regimes, such as continuous flooding irrigation, alternate wetting and drying, aerobic rice cultivation, and subsurface drip irrigation, can affect the speciation and methylation of As in rice. Continuous flooding irrigation reduces methylation of As due to anaerobic conditions, while alternate wetting and drying and aerobic rice cultivation promote methylation by creating aerobic conditions that stimulate the activity of arsenic-methylating microorganisms. Subsurface drip irrigation reduces total arsenic content in rice grains and increases the proportion of less toxic methylated arsenic species. The review also discusses the complex mechanisms of As-methylation and transport in rice, emphasizing the importance of understanding these mechanisms to develop strategies for reducing arsenic uptake in rice plants and mitigating health risks. The review addresses the impact of water source and type on arsenic speciation and methylation in rice and highlights the need for proper water management and treatment measures to ensure the safety of the food supply as well as aiding future research and policies to reduce health risks from rice consumption. The critical information gaps that this review addresses include the specific effects of different water management regimes on As-methylation, the role of microbial communities in groundwater in As-methylation, and the potential risks associated with the use of reclaimed water for irrigation.

Health risk assessment of toxic metal(loids) (As, Cd, Pb, Cr, and Co) via consumption of medicinal herbs marketed in Malawi

This study aimed to assess the potential health risks associated with consuming three commonly consumed medicinal herbs in Malawi: Azadirachta indica, Mondia whitei, and Moringa oleifera. The concentrations of five metal(loids) (As, Cd, Pb, Cr, and Co) were determined using inductively coupled plasma mass spectrometry, while their safety was assessed by comparing the measured values with the legislated maximum contaminant levels (MCL)and reported metal(loids) concentrations in other countries. The results indicated significant variations of metal(loids) concentrations amongst the studied medicinal herbs, with Azadirachta indica containing the highest mean As (0.078 ± 0.010 mg kg-1) and Cd (0.049 ± 0.05 mg kg-1) concentrations and Mondia whitei and Moringa oleifera contained the highest mean Co (1.01 ± 0.05 mg kg-1) and Cr (1.42 ± 1.18 mg kg-1) concentrations, respectively. However, the mean concentrations of As, Cd, Pb, Cr, and Co fell below the MCL set by World Health Organization (WHO), Alimentarius Commissions, and European Commission. The estimated daily intake (EDI) for each metal(loid) was less than 1, indicating that the studied medicinal herbs do not pose serious health risks to non-regular consumers. The study also emphasizes the importance of assessing the potential risks associated with consuming medicinal herbs contaminated with heavy metals or metalloids, as it can seriously threaten human health.

Combined Effects of Fluoride and Arsenic on Mitochondrial Function in the Liver of Rat

Biochemical and/or molecular mechanisms of arsenic or fluoride toxicity in experimental animals have been widely investigated in the recent past. However, their combined effects on target cells/organelle are poorly understood. The present study was executed to delineate their combined effects on mitochondrial function in the liver of rat. Female Wistar rats (140 ± 20 g) were force fed individually or in combination with sodium arsenate (4 mg/kg body weight) and sodium fluoride (4 mg/kg body weight) for 90 days. Thereafter, established markers of mitochondrial function viz. mitochondrial lipid peroxidation, oxidative phosphorylation, ATPase, succinic dehydrogenase, and caspase-3 activity were determined. Cytochrome C release and oxidative DNA damage were also estimated in the liver of respective groups of rats. The study showed significant differences in these results amongst the three groups. Observations on parameters viz. LPO, cytochrome-C, caspase-3, and 8-OHdG suggested an antagonistic relationship between these two elements. Results on ATPase, SDH, and ADP:O ratio indicated synergism. It is concluded that AsIII + F in combination may express differential effects on signalling pathways and proapoptotic/antiapoptotic proteins/genes that contribute to liver cell death. Interaction of As and F with mitochondria.

An insight into the binding and inhibition of eye ζ-crystallin by the environmental toxin arsenic: implications in eye diseases

Arsenic contamination is highly prevalent in food chain, soil and groundwater. Continuous exposure to elevated levels of this environmental toxin is a global concern. Studies have reported enriched accumulation of arsenic in the eyes compared to other body organs leading to various eye diseases. Here, the impact of arsenic exposure on the enzymatic eye ζ-crystallin has been investigated. Arsenic inhibited the activity of the enzyme with an IC50 value of 35 µM. It decreased the free thiol group content of ζ-crystallin due to protein oxidation. The binding of arsenic with ζ-crystallin was explored using biophysical and computational tools. The enzyme undergoes some conformational changes upon arsenic binding. The binding constant (Kb) was determined to be 1.2 × 102 M-1. Thermodynamic parameters were determined by isothermal titration calorimetry (ITC) and the binding energy (ΔG) was calculated to be -3.52 kcal/mol. Molecular docking studies helped in visualizing the amino acid residues (especially Cys165) of the enzyme involved in binding with arsenic. Continuous arsenic exposure is expected to increase the eye crystallin-related abnormalities, elevating the risk of cataractogenesis. Therefore, proper measures need to be taken by authorities to control the contamination of arsenic in the environment and groundwater.Communicated by Ramaswamy H. Sarma.

Effects of microplastics and arsenic on plants: Interactions, toxicity and environmental implications

Microplastics are emerging pollutants that are ubiquitously present in environment. Occurrence and dispersion of microplastics in the soil can pose a considerable risk to soil health and biodiversity, including the plants grown in the soil. Uptake and bioaccumulation of microplastics can have detrimental effects on different plant species. Additionally, the co-presence of microplastics and arsenic can cause synergistic, antagonistic, or potentiating toxic impacts on plants. However, limited studies are available on the combined effects of microplastics and arsenic on plants. This paper elucidates both the individual and synergistic effects of microplastics and arsenic on plants. At the outset, the paper highlighted the presence and degradation of microplastics in soil. Subsequently, the interactions between microplastics and plants, accumulation, and influences of microplastics on plant growth and metabolism were explained with underlying mechanisms. Combined effects of microplastics and arsenic on plant growth, metabolism, and toxicity were discussed thereafter. Combined toxic effects of microplastics and arsenic on plants can have detrimental implications on environment, ecosystems and biodiversity. Further investigations on food chain and human health are needed in the context of microplastic-arsenic interactions.

Analysis of gut bacteriome of in utero arsenic-exposed mice using 16S rRNA-based metagenomic approach

Introduction

Approximately 200 million people worldwide are affected by arsenic toxicity emanating from the consumption of drinking water containing inorganic arsenic above the prescribed maximum contaminant level. The current investigation deals with the role of prenatal arsenic exposure in modulating the gut microbial community and functional pathways of the host.

Method

16S rRNA-based next-generation sequencing was carried out to understand the effects of in utero 0.04 mg/kg (LD) and 0.4 mg/kg (HD) of arsenic exposure. This was carried out from gestational day 15 (GD-15) until the birth of pups to understand the alterations in bacterial diversity.

Results

The study focused on gestational exposure to arsenic and the altered gut microbial community at phyla and genus levels, along with diversity indices. A significant decrease in firmicutes was observed in the gut microbiome of mice treated with arsenic. Functional analysis revealed that a shift in genes involved in crucial pathways such as insulin signaling and non-alcoholic fatty liver disease pathways may lead to metabolic diseases in the host.

Discussion

The present investigation may hypothesize that in utero arsenic exposure can perturb the gut bacterial composition significantly as well as the functional pathways of the gestationally treated pups. This research paves the way to further investigate the probable mechanistic insights in the field of maternal exposure environments, which may play a key role in epigenetic modulations in developing various disease endpoints in the progeny.

Identification of possible sources for potentially toxic elements and polycyclic aromatic hydrocarbons and their spatially varying relationships in urban soils of Dublin, Ireland

Potentially toxic elements (PTEs) and polycyclic aromatic hydrocarbons (PAHs) harm the ecosystem and human health, especially in urban areas. Identifying and understanding their potential sources and underlying interactions in urban soils are critical for informed management and risk assessment. This study investigated the potential sources and the spatially varying relationships between 9 PTEs and PAHs in the topsoil of Dublin by combining positive matrix factorisation (PMF) and geographically weighted regression (GWR). The PMF model allocated four possible sources based on species concentrations and uncertainties. The factor profiles indicated the associations with high-temperature combustion (PAHs), natural lithologic factors (As, Cd, Co, Cr, Ni), mineralisation and mining (Zn), as well as anthropogenic inputs (Cu, Hg, Pb), respectively. In addition, selected representative elements Cr, Zn, and Pb showed distinct spatial interactions with PAHs in the GWR model. Negative relationships between PAHs and Cr were observed in all samples, suggesting the control of Cr concentrations by natural factors. Negative relationships between PAHs and Zn in the eastern and north-eastern regions were related to mineralisation and anthropogenic Zn-Pb mining. In contrast, the surrounding regions exhibited a natural relationship between these two variables with positive coefficients. Increasing positive coefficients from west to east were observed between PAHs and Pb in the study area. This special pattern was consistent with prevailing south-westerly wind direction in Dublin, highlighting the predominant influences on PAHs and Pb concentrations from vehicle and coal combustion through atmospheric deposition. Our results provided a better understanding of geochemical features for PTEs and PAHs in the topsoil of Dublin, demonstrating the efficiency of combined approaches of receptor models and spatial analysis in environmental studies.

Coupling hydrogeochemistry and stable isotopes (δ2H, δ18O and δ13C) to identify factors affecting arsenic enrichment of surface water and groundwater in Precambrian sedimentary rocks, eastern salt range, Punjab, Pakistan

The study area is a part of the Salt Range, where water quality is being deteriorated by natural and anthropogenic sources. This research integrates water quality assessment, arsenic enrichment, hydrogeochemical processes, groundwater recharge and carbon sources in aquifer. Total dissolved solid (TDS) contents in springs water, lake water and groundwater are in range of 681-847 mg/L, 2460-5051 mg/L and 513-7491 mg/L, respectively. The higher concentrations of magnesium and calcium in water bodies next to sodium are because of carbonates, sulfates, halite and silicates dissolution. The average concentrations of ions in groundwater are in order of HCO3- > SO42- > Cl- > Na+  > Mg2+ > Ca2+ > K+ > NO3-, virtually analogous to springs water, but different from lake water, categorized as poor quality and unfit for drinking purposes. Based on major ions hydrochemistry, NaCl and mixed Ca-Mg-Cl type hydrochemical facies are associated with concentration of arsenic (4.2-39.5 µg/L) in groundwater. Groundwater samples (70%) having arsenic concentration (11 ≤ As ≤ 39.5 µg/L) exceeded from World Health Organization (WHO) guideline (As ≤ 10 µg/L) in near neutral to slightly alkaline (6.7 ≤ pH ≤ 8.3), positive Eh(6 ≤ Eh ≤ 204 mV), signifying its oxic condition. Eh-pH diagrams for arsenic and iron indicate that 80% of groundwater for arsenic and iron were in compartments of HAsO42- and Fe(OH)3, unveil oxic environment. Arsenic is moderately positive correlated with TDS, sodium, chloride, bicarbonate, nitrate, sulfate and weak negative with δ13CDIC in surface and groundwater, forecasting multiple sources of arsenic to aquifer. Stable isotopes of waters show recharge of groundwater from local rain and lake water. The lower δ13CDIC values of groundwater are modified by influx of CO2 produced during biological oxidation of soil natural organic matter.

Unraveling Therapeutic Opportunities and the Diagnostic Potential of microRNAs for Human Lung Cancer

Lung cancer is a major public health problem and a leading cause of cancer-related deaths worldwide. Despite advances in treatment options, the five-year survival rate for lung cancer patients remains low, emphasizing the urgent need for innovative diagnostic and therapeutic strategies. MicroRNAs (miRNAs) have emerged as potential biomarkers and therapeutic targets for lung cancer due to their crucial roles in regulating cell proliferation, differentiation, and apoptosis. For example, miR-34a and miR-150, once delivered to lung cancer via liposomes or nanoparticles, can inhibit tumor growth by downregulating critical cancer promoting genes. Conversely, miR-21 and miR-155, frequently overexpressed in lung cancer, are associated with increased cell proliferation, invasion, and chemotherapy resistance. In this review, we summarize the current knowledge of the roles of miRNAs in lung carcinogenesis, especially those induced by exposure to environmental pollutants, namely, arsenic and benzopyrene, which account for up to 1/10 of lung cancer cases. We then discuss the recent advances in miRNA-based cancer therapeutics and diagnostics. Such information will provide new insights into lung cancer pathogenesis and innovative diagnostic and therapeutic modalities based on miRNAs.

Crystallization-based upcycling of iron oxyhydroxide for efficient arsenic capture in contaminated soils

Arsenic (As)-contaminated soil inevitably exists in nature and has become a global challenge for a sustainable future. Current processes for As capture using natural and structurally engineered nanomaterials are neither scientifically nor economically viable. Here, we established a feasible strategy to enhance As-capture efficiency and ecosystem health by structurally reorganizing iron oxyhydroxide, a natural As stabilizer. We propose crystallization to reorganize FeOOH-acetate nanoplatelets (r-FAN), which is universal for either scalable chemical synthesis or reproduction from natural iron oxyhydroxide phases. The r-FAN with wide interlayer spacing immobilizes As species through a synergistic mechanism of electrostatic intercalation and surface chemisorption. The r-FAN rehabilitates the ecological fitness of As-contaminated artificial and mine soils, as manifested by the integrated bioassay results of collembolan and plants. Our findings will serve as a cornerstone for crystallization-based material engineering for sustainable environmental applications and for understanding the interactions between soil, nanoparticles, and contaminants.

Potentially Toxic Element Contamination in Soils Affected by the Antimony Mine Spill in Northwest China

This study provides a comprehensive assessment of the potential ecological and health risks in the area of the antimony mine spill in Longnan, Northwest China, and identifies the sources of potentially toxic elements (PTEs) in the soil as a result of the spill. The geo-accumulation index and enrichment factor show that the study area is highly contaminated with arsenic (As), mercury (Hg) and antimony (Sb). The ecological risk index in the tailings spill area ranged from 320.43 to 5820.46 (mean: 1489.82), indicating a very-high potential ecological risk, with mean values of 104.86, 1118.87 and 248.84 for As, Hg and Sb, respectively. The multivariate statistical analysis suggested that Sb and Hg come from tailings leakage, while copper (Cu), nickel (Ni) and zinc (Zn) may be imported from natural sources, and As and lead (Pb) originate from agricultural activities. In addition As and Sb pose a high health risk. With the exception of the non-carcinogenic risk in adults, all other risks are significantly exceeded in other populations, with children being the highest-risk group. These findings provide important quantitative information for the assessment and management of PTE contamination in other tailings spill areas.

Human health risk apportionment from potential sources of heavy metals in agricultural soils and associated uncertainty analysis

Evaluating heavy metal pollution level in the soils and apportioning the source-specific health risk of heavy metals are critical for proposing environmental protection and remediation strategies to protection human health. This study explored heavy metal pollution and associated source-specific health risks in a typical rural industrial area, southwestern China. A total of 105 topsoil samples were collected and the concentrations of heavy metals, including As, Cd, Cr, Cu, Ni, Pb and Zn, were determined. Pollution load index and enrichment factors were used to evaluate the pollution level of heavy metals. Positive matrix factorization (PMF) model was applied to apportion the heavy metals and the associated source-specific health risks to adults and children were estimated via combining the PMF model with the health risk assessment. The results indicated that the soils were highly polluted by multiple heavy metals, especially for Cd, with the EF values of 24.94 and 22.55 in the upstream and downstream areas, respectively. Source apportionment results showed that atmospheric deposition, smelting activities, fertilizer and sewage application, and agrochemical utilization were the main anthropogenic sources, with the contributions of 37.11%, 23.69%, 19.69%, and 19.51%, respectively. Source-specific risk assessment identified atmospheric deposition as the priority source for the non-carcinogenic (NCR) and carcinogenic risks (CR) in the study area, with the contribution of 43.71% and 52.52% for adults, and 44.29% and 52.58% for children, respectively. Moreover, non-carcinogenic and carcinogenic risks posed to children (NCR: 2.84; CR: 1.31 × 10^-4) from four sources was higher than those posed to adults (NCR: 0.29; CR: 5.86 × 10^-5). The results of source-specific health risk assessment provided the valuable information on the priority sources for pollution preventing and risk controlling.

Arsenic in Mining Areas: Environmental Contamination Routes

The emission and accumulation of toxic elements such as arsenic in various environmental compartments have become increasingly frequent primarily due to anthropogenic actions such as those observed in agricultural, industrial, and mining activities. An example of environmental arsenic contamination in Brazil exists in the city of Paracatu, MG, due to the operation of a gold mine. The aim of this work is to evaluate the routes and effects of arsenic contamination in environmental compartments (air, water, and soil) and environmental organisms (fish and vegetables) from mining regions as well as the trophic transfer of the element for a risk assessment of the population. In this study, high levels of arsenic were found in the waters of the Rico stream ranging from 4.05 µg/L during the summer season to 72.4 µg/L during the winter season. Moreover, the highest As concentration was 1.668 mg kg^-1 in soil samples, which are influenced by seasonal variation and by proximity to the gold mine. Inorganic and organic arsenic species were found above the allowed limit in biological samples, indicating the transfer of arsenic found in the environment and demonstrating a great risk to the population exposed to this area. This study demonstrates the importance of environmental monitoring to diagnose contamination and encourage the search for new interventions and risk assessments for the population.

How do different arsenic species affect the joint toxicity of perfluorooctanoic acid and arsenic to earthworm Eisenia fetida: A multi-biomarker approach

Perfluorooctanoic acid (PFOA) and arsenic are widely distributed pollutants and can coexist in the environment. However, no study has been reported about the effects of different arsenic species on the joint toxicity of arsenic and PFOA to soil invertebrates. In this study, four arsenic species were selected, including arsenite (As(III)), arsenate (As(V)), monomethylarsonate (MMA), and dimethylarsinate (DMA). Earthworms Eisenia fetida were exposed to soils spiked with sublethal concentrations of PFOA, different arsenic species, and their binary mixtures for 56 days. The bioaccumulation and biotransformation of pollutants, as well as eight biomarkers in organisms, were assayed. The results indicated that the coexistence of PFOA and different arsenic species in soils could enhance the bioavailability of arsenic species while reducing the bioavailability of PFOA, and inhibit the arsenic biotransformation process in earthworms. Responses of most biomarkers in joint treatments of PFOA and As(III)/As(V) showed more significant variations compared with those in single treatments, indicating higher toxicity to the earthworms. The Integrated Biomarker Response (IBR) index was used to integrate the multi-biomarker responses, and the results also exhibited enhanced toxic effects in combined treatments of inorganic arsenic and PFOA. In comparison, both the biomarker variations and IBR values were lower in joint treatments of PFOA and MMA/DMA. Then the toxic interactions in the binary mixture systems were characterized by using a combined method of IBR and Effect Addition Index. The results revealed that the toxic interactions of the PFOA/arsenic mixture in earthworms depended on the different species of arsenic. The combined exposure of PFOA with inorganic arsenic led to a synergistic interaction, while that with organic arsenic resulted in an antagonistic response. Overall, this study provides new insights into the assessment of the joint toxicity of perfluoroalkyl substances and arsenic in soil ecosystems.

Geochemical accumulation and source tracing of heavy metals in arable soils from a black shale catchment, southwestern China

Heavy metal enrichment in soils has been linked to the weathering of lithologies with high geochemical backgrounds, such as black shale. Therefore, this study conducted a typical sampling of surface soils in a black shale catchment in southwestern China to characterize the accumulation and sources of the heavy metals As, Cd, Co, Cr, Cu, Ni, Pb, Zn, Mo and Tl. Elevated concentrations of most heavy metals in the soils underlain by black shale are determined to exceed the regional soil background values, even the risk screening values, especially for Mo, As and Cd. Sequential extraction analysis, together with previous results, reveals that most heavy metals in soils are mainly bound in the residual fraction (> 65 %) as a result of the fixation of stable aluminosilicates (e.g., clay minerals). In contrast, Cd mainly occurs in relatively labile proportions as exchangeable (24.42 %), carbonate (24.48 %) and Fe/Mn oxide fractions (26.60 %) due to the non-specific adsorption of soil colloids and the precipitation of carbonates and Fe/Mn oxides. Pb isotopic tracing and APCS/MLR receptor model suggest that heavy metals in the urban surface soils (SG1) have a mixed source of black shale weathering, vehicle exhaust and agricultural input, while heavy metals in the rural surface soils (SG2) are a geogenic source of black shale weathering. Overall, this study provides new insights into contamination management, land use planning and health risk assessment in regions with high geochemical backgrounds.

Arsenic and cadmium leaching in co-contaminated agronomic soil and the influence of high rainfall and amendments

Arsenic (As) and cadmium (Cd) co-contaminate agricultural systems worldwide and threaten water resources, food security and human health. This column leaching study examined As and Cd mobility in an acidic sandy loam Alfisol soil collected from the dry zone of Sri Lankafor four co-contaminant concentration combinations (spiked and 1 year aged As at 20 & 100 mg kg^-1 with co-added Cd at 3 & 20 mg kg^-1) i, and under the influence of high rainfall (RF), phosphorus fertilizer (P) and lime amendments. In almost all treatments a synergistic co-contaminant adsorption effect was evident which reduced leaching of both elements, significantly in the higher spiked soil concentration treatments. The magnitude of leaching decrease varied with treatment but was greater for As due to its weaker retention in the soil. The co-sorbing effects, evident even under RF, were attributed to electrostatic sorption interactions, the formation of ternary bridging complexes and surface precipitation at higher concentrations. Liming significantly retarded mobilisation of both elements in all treatments, whereas P enhanced As leaching but suppressed Cd leaching, and both amendments moderated co-contaminant effects. An antagonistic effect of Cd on As sorption was evident in two treatments which showed increased As leaching with added Cd: the RF low spike concentration treatment, accredited to washout of stable As-Cd soluble complexes; the P high concentration treatment considered due to P disruption of As-Cd bridging complexes. This work is important for effective risk mitigation in these widely occurring co-contaminated agronomic systems, and demonstrates a strong system effect on synergistic or antagonistic co-contaminant interactions.

Ecotoxicological risk assessment in soils contaminated by Pb and As 20 years after a mining spill

This study evaluates the potential toxicity of the soils of the Guadiamar Green Corridor (GGC) affected by the Aznalcóllar mine spill (Andalusia, Spain), one of the most important mining accidents in Europe in recent decades. Twenty years after the accident, although the area is considered to be recovered, residual contamination in soils persists, and the bioavailability of some contaminants, such as As, is showing trends of increasing. Therefore, the potential residual toxicity in 84 soil samples was evaluated by bioassays with lettuce (Latuca sativa L.), earthworms (Eisenia andrei) and determining the microbial activity by basal respiration and metabolic quotient. The selected soils sampled along the GGC were divided into 4 types according to their physicochemical properties. In the closest part of the mine two soil types appear (SS1 and SS2), originally decarbonated and loamy, with a reduction in lettuce root elongation of 57% and 34% compared to the control, as well as a the highest metabolic quotient (23.9 and 18.1 ng Cc_O2 μg Cmicrob^-1 h^-1, respectively) with the highest risk of Pb and As toxicity. While, located in the middle and final part of the affected area of the spill (SS3 and SS4), soils presented alkaline pH, finer textures and the lowest metabolic quotient (<9.5 ng Cc_O2 μg Cmicrob^-1 h^-1). In addition, due to Pb and As exceeded the Guideline values established in the studied area, the human toxicity risk was determined according to US-EPA methodology. Although the total contents were higher than the Guidelines established, the obtained hazard quotients for both contaminants were less than one, so the risk for human health was discarded. However, monitoring over time of the toxicity risks of the GGC soils would be advisable, especially due to the existence of areas where residual contamination persist, and soil hazard quotient obtained for As in children was higher and close to unity.

Rethinking quantified methods for arsenic speciation and risk in a biowaste hydrothermal liquefaction system

Controversy exists to quantify the fate and speciation of Arsenic (As). We investigated its characteristics by As-containing algae in various pH hydrothermal liquefaction (HTL) system, specifically via two classical methods, i.e. the European Community Bureau of Reference (BCR) and Wenzel's method. Solid residue immobilized 11.23-16.55% of As, and 88.07-82.44% was in aqueous by the pH regulators (e.g., CH₃COOH, HCl, and KOH). ICP-MS and XRD analysis revealed that As (V) was converted into As (III) and As (0) in the solid residue, while the As (V) was mainly converted into As (III) in the aqueous phase during HTL. When the classified forms of As in solid residue are compared, Wenzel's method was more appropriate for dividing the bio-availability forms of As, whereas BCR was better for estimating the toxic-potential forms of As. Subsequently, pH regulators raised the risk of As in solid residue associated with the increasing of unstable forms. The amide was hydrolyzed to carboxylic acid with acidic additives, which weakened the reducing environment in the HTL process. In contrast, the amide was hydrolyzed to ammonia with the alkaline additives, which enhanced the reducing environment and increased the risk of As in products. This work provided a new insight in systematically evaluating the risk and speciation of As in HTL.

Evolution Mechanism of Arsenic Enrichment in Groundwater and Associated Health Risks in Southern Punjab, Pakistan

Arsenic (As) contamination in groundwater is a worldwide concern for drinking water safety. Environmental changes and anthropogenic activities are making groundwater vulnerable in Pakistan, especially in Southern Punjab. This study explores the distribution, hydrogeochemical behavior, and pathways of As enrichment in groundwater and discusses the corresponding evolution mechanism, mobilization capability, and health risks. In total, 510 groundwater samples were collected from three tehsils in the Punjab province of Pakistan to analyze As and other physiochemical parameters. Arsenic concentration averaged 14.0 μg/L in Vehari, 11.0 μg/L in Burewala, and 13.0 μg/L in Mailsi. Piper-plots indicated the dominance of Na+, SO42-, Ca2+, and Mg2+ ions in the groundwater and the geochemical modeling showed negative saturation indices with calcium carbonate and salt minerals, including aragonite (CaCO3), calcite (CaCO3), dolomite (CaMg(CO3)2), and halite (NaCl). The dissolution process hinted at their potential roles in As mobilization in groundwater. These results were further validated with an inverse model of the dissolution of calcium-bearing mineral, and the exchange of cations between Ca2+ and Na+ in the studied area. Risk assessment suggested potential carcinogenic risks (CR > 10-4) for both children and adults, whereas children had a significant non-carcinogenic risk hazard quotient (HQ > 1). Accordingly, children had higher overall health risks than adults. Groundwater in Vehari and Mailsi was at higher risk than in Burewala. Our findings provide important and baseline information for groundwater As assessment at a provincial level, which is essential for initiating As health risk reduction. The current study also recommends efficient management strategies for As-contaminated groundwater.

Subcellular Partitioning of Arsenic Trioxide Revealed by Label-Free Imaging

Subcellular partitioning of therapeutic agents is highly relevant to their interactions with target molecules and drug efficacy, but studying subcellular partitioning is an enormous challenge. Here, we describe the application of nanoscale secondary ion mass spectrometry (NanoSIMS) analysis to define the subcellular pharmacokinetics of a cytotoxic chemotherapy drug, arsenic trioxide (ATO). We reasoned that defining the partitioning of ATO would yield valuable insights into the mechanisms underlying ATO efficacy. NanoSIMS imaging made it possible to define the intracellular fate of ATO in a label-free manner─and with high resolution and high sensitivity. Our studies of ATO-treated cells revealed that arsenic accumulates in the nucleolus. After prolonged ATO exposure, ∼40 nm arsenic- and sulfur-rich protein aggregates appeared in the cell nucleolus, nucleus, and membrane-free compartments in the cytoplasm, and our studies suggested that the partitioning of nanoscale aggregates could be relevant to cell survival. All-trans retinoic acid increased intracellular ATO levels and accelerated the nanoscale aggregate formation in the nucleolus. This study yielded fresh insights into the subcellular pharmacokinetics of an important cancer therapeutic agent and the potential impact of drug partitioning and pharmacokinetics on drug activity.

Removal of hazardous ions from aqueous solutions: Current methods, with a focus on green ion flotation

Hazardous ions, like those of heavy metals, cause significant health and environmental problems when they are discharged into water resources naturally or through various industrial processes. Removing these ions from water is of significant importance in the provision of high-quality water for drinking and agricultural usage. This work discusses current techniques that are frequently used for the removal of heavy-metal ions from aqueous solutions by absorption, particularly the use of biodegradable surfactants in ion flotation. Certain new surfactants promise high efficiency in their use in the ion-flotation process and in their application in industrial-water treatment to remove heavy metals. As an example, this work demonstrates the high efficiency of surfactants based on an amino-acid (L-cysteine) in removing a range of heavy-metal ions in a simple, single-stage ion-flotation process. High foaming ability, the ability to operate in various temperatures and pHs, decomposing into natural products and high binding affinity for heavy-metal ions make the cysteine-based surfactants a highly suitable compound to replace current commercial surfactants in ion- and froth-flotation processes. Removal of particular ions can also be achieved in ion flotation; a suitable choice of parameters, such as pH and surfactant concentration, favours the surfactant binding to those ions. Further intensive work is required to develop an optimal process to recover valuable elements from waste solutions.

Transformation of arsenic species by diverse endophytic bacteria of rice roots

Rice growing in flooded paddy soil often accumulates considerable levels of inorganic and organic arsenic (As) species, which may cause toxicity to plants and/or pose a risk to human health. The bioavailability and toxicity of As in soil depends on its chemical species, which undergo multiple transformations driven primarily by soil microbes. However, the role of endophytes inside rice roots in As species transformation remains largely unknown. We quantified the abundances of microbial functional genes involved in As transformation in the endosphere and rhizosphere of rice roots growing in three paddy soils in a pot experiment. We also isolated 46 different bacterial endophytes and tested their abilities to transform various As species. The absolute abundances of the arsenate reductase gene arsC and the dissimilatory arsenate reductase gene arrA in the endosphere were comparable to those in the rhizosphere, whereas the absolute abundances of the arsenite methylation gene arsM and arsenite oxidation gene aioA in the endosphere were lower. After normalization based on the bacterial 16S rRNA gene, all four As transformation genes showed higher relative abundances in the endosphere than in the rhizosphere. Consistent with the functional gene data, all of the 30 aerobic endophytic isolates were able to reduce arsenate, but only 3 strains could oxidize arsenite. Among the 16 anaerobic endophytic isolates, 4 strains belonging to Desulfovibrio, Terrisporobacter or Clostridium could methylate arsenite and/or methylarsenite. Six strains of aerobic endophytes could demethylate methylarsenite, among which three strains also could reduce and demethylate methylarsenate. None of the isolates could demethylate dimethylarsenate. These results suggest that diverse endophytes living inside rice roots could participate in As species transformation and affect As accumulation and species distribution in rice plants.

A catchment-scale model of river water quality by Machine Learning

Water quality is a concern in most river basins worldwide due to the widespread release of pollutants which impacts the freshwater ecosystems. Exploring the relationships between drivers and water quality parameters at the regional scale is key in the identification of appropriate actions for the reduction of water pollution. Regional models are the appropriate tool to achieve this, though their development poses relevant challenges because of the complexity and non-linearity of such relationships. Among the available approaches, Machine Learning (ML) is promising because of its capability to detect complex nonlinear relationships and flexibility in the parameterization, which is learned from data. In this work, we developed regional models of water temperature, dissolved oxygen, arsenic, sulfate and chloride concentrations, as well as electrical conductivity, by using two ML algorithms, Random Forest and Deep feed-forward Neural Network, and compared their performances against the standard Linear Regression model. Our results indicate that the two ML algorithms are much more accurate models for such variables than the classical Linear Regression model, with Deep feed-forward Neural Network being the most effective in identifying the reciprocal importance of the drivers and capturing nonlinear relationships between drivers and water quality variables. Our analysis also revealed that the Julian day and year at which the sample was taken surrogate the air temperature in modeling water temperature and dissolved oxygen, with only a slight performance reduction. Arsenic, sulfate, and chloride show more complex behaviors in which geogenic and anthropogenic sources are intertwined. Dilution exerts a role chiefly for arsenic concentration, which suggests a non-uniform, in space, geogenic origin for this variable.

New Insights in factors affecting ground water quality with focus on health risk assessment and remediation techniques

Groundwater is considered as the primary source of water for the majority of the world's population. The preponderance of the nation's drinking water, as well as agricultural and industrial water, comes from groundwater. Groundwater level is becoming increasingly challenging to replenish due to climate change. Fertilizer application and improper processing of industrial waste are the two major anthropogenic drivers of groundwater pollution. Arsenic and cadmium are two of the principal heavy metal pollutants that have affected groundwater quality by human activity. When people are exposed to both non-carcinogenic and carcinogenic contaminants for an extended period, toxic effects might occur. It can have detrimental health effects from long-term exposure to contaminants, even in low amounts. As a result, metal contamination concentrations and fractions can be used to determine potential health concerns. At the same time, contaminants also need to be removed or converted to harmless products by groundwater remediation. Remediation of groundwater quality can be accomplished in several ways, including natural and artificial means. The purpose of this review is to explore a wide range of factors that affect groundwater quality, including their possible health effects. This communication provides state-of-the-art information about remediation approaches for groundwater contamination including hindrances and perspectives in this area of research. The in-depth information provided in different sections of this communication would expand the scope of interdisciplinary research.

Integrated environmental factor-dependent growth and arsenic biotransformation by aquatic microalgae: A review

Arsenic (As) is a toxic metalloid posing harming the human food chain through trophic transfer. Microalgae are primary producers, ensuring bioaccumulation and biogeochemical cycling of As in water environment. They are highly efficient at removing As from the environment, making these microscopic organisms eco-friendly and money saving method in As remediation process. However, microalgal growth and As biotransformation potential relies greatly on individual and integrated environmental factors. This review scrutinizes the available literature on the As biotransformation potentials of various marine and freshwater microalgae under individual and integrated stresses of such factors. Various combinations of important factors such as temperature, salinity, concentrations of As (V) and PO₄^3─, pH, light intensity, and length of exposure period are summarized along with the optimum conditions for different microalgae. The effects of environmental factors on microalgal growth, changes in cell shape, and the relationship between As biotransformation and other activities are discussed in detail. Time-dependent As speciation pattern by aquatic microalgae are reviewed. Conceptual models highlighting the microalgal species particularly linked with environmental factor-dependent As biotransformation mechanisms are also summarized. This review will contribute to an in depth understanding of the connection between environmental factors, As uptake, and the biotransformation mechanism of marine and freshwater microalgae from the perspective of As remediation process.

Clean Water Production Enhancement through the Integration of Small-Scale Solar Stills with Solar Dish Concentrators (SDCs)—A Review

The conventional solar still, as a water treatment technique, has been reported to produce water at a low working temperature where various thermal resistance pathogens could survive in their distillate. In this work, the reviews of previous research on the quality of water produced by passive solar stills and their productivities in initial basin water temperatures were first presented and discussed. The next review discussed some recent studies on the performances of small-scale solar stills integrated with SDCs (with and without sun-tracking systems (STSs)) to observe the operating temperatures from early hours until the end of operations, daily water yield, and cost per liter. Based on these findings, it was revealed that SDCs with STSs indicated an instant increase in the absorber water temperature up to 70 °C at the starting point of the experiments in which this temperature range marked the unbearable survival of the pathogenic organisms and viruses, particularly the recent SARS-CoV-2. Furthermore, disinfection was also observed when the absorbers’ water temperature reached beyond the boiling point until the end of operations. This indicates the effectiveness of SDCs with STS in reflecting a large amount of sun’s rays and heat to the small-scale absorbers and providing higher operating absorbers temperatures compared to immobile SDCs. Daily productivities and costs per liter of the SDCs with STSs were found to be higher and lower than those of the other previous passive and active solar stills. Therefore, it is recommended that small-scale absorbers integrated with SDCs and STS can be used as a cost-effective and reliable method to produce hygienic pathogen-free water for the communities in remote and rural areas which encounter water scarcity and abundant annual bright sunshine hours.

Antioxidant enzymes and transporter genes mediate arsenic stress reduction in rice (Oryza sativa L.) upon thiourea supplementation

Thiourea (TU) is a chemo-priming agent and non-physiological reactive oxygen species (ROS) scavenger whose application has been found to reduce As accumulation in rice grains along with improved growth and yield. The present field study explored TU-mediated mechanistic changes in silicon (Si) assimilation in root/shoot, biochemical and molecular mechanisms of arsenic (As) stress amelioration in rice cultivars. Gosai and Satabdi (IET-4786) rice cultivars were selected for field experiment at three different places; control field and two other As contaminated experimental fields (EF1 and EF2) in West Bengal, India. The average As reduction was observed to be 9.5% and 19.8% whereas the yield increment was 8.8% and 17.7% for gosai and satabdi, respectively among all the three experimental fields. The positive interrelation was also observed between improved internal ultrastructure anatomy and enhanced Si assimilation (36%-423%) upon TU application. The level of photosynthetic pigments was increased by 29.8%-99.2%. Further, activities of antioxidant enzymes were harmonically altered in TU supplemented plants. The expression of various As related transporter genes in flag leaf and developing grains (inflorescence) was changed in both the rice cultivars (gosai and satabdi). It was also presumably responsible for observed As reduction in grains. Thus, TU application was found to be an efficient and sustainable agronomic practice for amelioration of As toxicity in rice plants in As contaminated field conditions.

Gender difference in arsenic biotransformation is an important metabolic basis for arsenic toxicity

BACKGROUND

Arsenic metabolism enzymes can affect the toxic effects of arsenic. However, the effects of different genders on the metabolites and metabolic enzymes in liver arsenic metabolism is still unclear. This study analyzed the gender differences of various arsenic metabolites and metabolic enzymes and further explored the effects of gender differences on arsenic metabolism in liver tissues of rats.

METHODS

Rats were treated with high/medium/low doses of iAs³⁺ or iAs⁵⁺. Liver pathological changes were observed with electron microscopy. The monomethyl aracid (MMA) and dimethyl aracid (DMA) was determined by high performance liquid chromatography-hydride generation atomic fluorescence spectroscopy. S-adenosylmethionine (SAM), arsenate respiratory reductase (ARR), nicotinamide adenine dinucleotide (NAD), purine nucleoside phosphorylase (PNP), pyruvate kinase (PK), and myeloperoxidase (MPO) SAM, ARR, NAD, PNP, PK, and MPO were determined by enzyme-linked immunoassay. RT-qPCR was used to determine Arsenic (+ 3 oxidation state) methyltransferase (AS3MT).

RESULTS

The iAs³⁺ and iAs⁵⁺ at high doses induced pathological changes in the liver, such as increased heterochromatin and lipid droplets. Compared within the same group, MMA and DMA were statistically significant in iAs^{3 +} high, iAs^{3 +} medium and iAs⁵⁺ low dose groups (P < 0.05). MMA of male rats in iAs³⁺ high and medium groups was higher than that of female rats, and the DMA of male rats was lower than that of female rats. As3MT mRNA in the male iAs³⁺ high group was higher than that of females. Besides, compared between male and female, only in iAS³⁺ low dose, iAS³⁺ medium dose, iAS⁵⁺ low dose, and iAS⁵⁺ medium dose groups, there was significant difference in SAM level (P < 0.05). Compared within the same group, male rats had significantly higher PNP and ARR activities while lower PK activity than female rats (P < 0.05). Between the male and female groups, only the iAS³⁺ high dose and medium dose group had a statistically significant difference (P < 0.05). The NAD activity of females in iAS³⁺ high dose group was higher than that of males.

CONCLUSION

The gender differences in the arsenic metabolism enzymes may affect the biotransformation of arsenic, which may be one of the important mechanisms of arsenic toxicity of different sexes and different target organs.

Effect of rainwater oxidants on As volatilization in the soil-rice system

Rainwater contains multiple oxidants, such as hydrogen peroxide (H₂O₂) and perchlorate (ClO₄^-). The aim of the study was to investigate the rainwater of trace H₂O₂ and ClO₄^- affected on the arsenic (As) methylation and volatilization in the rice paddy of As contamination (arsenite (As(III)) and roxarsone (Rox)). Heavy rainfall monitoring and simulation experiments were applied in this study. The result showed that the H₂O₂ and ClO₄^- of heavy rainfall in 2017 was 5.3-51.6 μmol/L and ND - 6.1 μg/L respectively. Because of the differences in chemical properties, H₂O₂ and ClO₄^- affected As methylation and volatilization of paddy soil in different ways. H₂O₂ performed a temporary effect on As volatilization, which was mainly in the 1st-hour and restored to the controls condition finally. However, ClO₄^- showed a persistent inhibition on As volatilization which decreased 32 %-69 % in the whole test. In general, the trend of volatilization was following the order: CK ≈ H₂O₂ > ClO₄^-. The oxidants (H₂O₂ and ClO₄^-) also could decrease As(III) in 37 %-44 % and increased As(V) in 24 %-272 %. In addition, planting rice in As contamination soil could enhance As volatilization by 36 %-334 %. These suggested that planting wetland plants on As-contaminated soil probably become a potential way to increase As volatilization.

Hazardous emissions and concentrations of toxic metalloids and trace elements in charcoals from six commonly used tropical timbers for carbonization

Carbonized wood is a biofuel from cellulose pyrolysis with frequent smoke and life-threatening carcinogenic emissions. Carbon monoxide (CO), particulate matter (PM_2.5), metalloids and trace elements from charcoals from six commonly used tropical timbers for carbonization in Donkorkrom (Ghana) were assessed. During combustion, Anogeissus leiocarpa charcoal emitted the least CO (4.28 ± 1.08 ppm) and PM_2.5 (3.83 ± 1.57 μg/m³), while particulate matter was greatest for Erythrophleum ivorense (28.05 ± 3.08 ppm) and Azadirachta indica (27.67 ± 4.17 μg/m³) charcoals. Erythrophleum ivorense charcoal produced much lead (16.90 ± 0.33 ppm), arsenic (1.97 ± 0.10 ppm) and mercury (0.58 ± 0.003 ppm) but the least chromium (0.11 ± 0.01 ppm) and zinc (2.85 ± 0.05 ppm). Nickel was greatest for A. indica charcoal (0.71 ± 0.01 ppm) and least for Vitellaria paradoxa (0.07 ± 0.004 ppm). Trace elements ranged from 342.01 ± 2.54 ppm (A. indica) to 978.47 ± 1.80 ppm (V. paradoxa) for potassium and 1.74 ± 0.02% (V. paradoxa) to 2.24 ± 0.10% (A. indica) for sulphur. Besides A. leiocarpa charcoal, which ranked safest during combustion, the high PM_2.5 and CO emissions make the other biofuels hazardous indoors. Kitchens need air filters to absorb these emissions together with the use of improved cook stoves. These carcinogenic metalloids would necessitate that their ashes be properly discarded without human contact. Yet, the charcoals would be much suitable as soil amendment bio-char for plant growth quality improvement.

Geochemical distribution and speciation of Tl and other trace metals in upper Beijiang River in South China: Approach of in-situ DGT monitoring

Mining activities frequently result in severe contamination of river water. This study aimed to better understand the spatial distribution characteristics of Tl and other metals (e.g., Al, Cd, Co, Mn, Ni, Zn, Pb, V, As, Mo, and Sb), and to assess their risks to human health. Surface water samples were collected from the upper Beijiang River (South China) via grab sampling and the diffusive gradients in thin-films (DGT) technique. The concentrations of Tl measured by grab sampling and δ-MnO₂-DGT ranged from 0.045 μg L^-1 to 0.231 μg L^-1 and from 0.056 μg L^-1 to 0.131 μg L^-1, respectively. Most of the metals monitored were below the threshold levels allowed by the drinking water standard in China, except for As, Sb, and Mn at specific sampling sites. The concentrations of other metals measured by grab sampling were higher than those measured using the DGT technique because of the differences in speciation during these measurements. The hazard quotient (5.43 × 10^-4-8.0 × 10^-1 for grab sampling and 2.23 × 10^-4-2.8 × 10^-1 for DGT technique) for the monitored trace metals demonstrated minimal health risk to human beings. The pollution status of these toxic metals in the study area was generally acceptable. As was found to be potentially the most harmful metal in the studied area, with hazard quotients at some sampling sites calculated by grab sampling of >1. It has previously been suggested that As is the most important non-carcinogenic contaminant. The combination of grab sampling and the DGT technique provides a comprehensive understanding of trace metals, especially Tl, in terms of potential bioavailability and ecological assessment.

Spatial distribution and human health risk assessment of soil heavy metals based on sequential Gaussian simulation and positive matrix factorization model: A case study in irrigation area of the Yellow River

The content of Cd, Cu, Pb, Zn, Cr, Ni and As from 250 soil samples was measured in agricultural soil of Ningxia section of the Yellow River. Positive matrix factorization (PMF) was to identify the main sources of these heavy metals; Sequential Gaussian Simulation (SGS) was to identify their spatial distribution and high-risk areas; and Human Health risk (HHR) model was to measure the health risk. Results showed that the average content of Cd and As exceeds the risk screening value of "Soil Environmental Quality-Agricultural Land Soil Pollution Risk Control Standard" (GB 15618-2018), which belongs to slight-level pollution. Although the content of other types of HMs (Cu, Pb, Zn, Cr, Ni) is below the risk screening value, they are still included heavily in the soil (except Cr). PMF indicated that mixed sources of agriculture and industry accounted for 27.06%, natural sources accounted for 14.12%, industrial sources accounted for 23.04%, traffic sources accounted for 21.50%, and Yellow River sedimentary sources accounted for 14.28%. PMF-HHR showed that the mixed sources of agriculture and industry are the most important factor causing non-carcinogenic risk (HI) to children (accounting for 55.75%). Industrial sources and traffic sources were the two main factors that cause HI to adults (industrial sources accounted for 25.16%, and traffic sources accounted for 28.78%). Mixed sources of agriculture and industry and natural sources were the two main factors that cause carcinogenic risk (CR) (mixed sources of agriculture and industry account for 35.34%, and natural sources account for 33.23%). SGS indicated that 0.64% and 9.32% of the total areas were posing as higher HI areas to children and adults respectively; in particular, 0.68% and 1.12% of the areas were identified as higher HI of As and Cr areas at a critical probability of 0.9.

Diversity and Metabolic Potentials of As(III)-Oxidizing Bacteria in Activated Sludge

Biological arsenite [As(III)] oxidation is an important process in the removal of toxic arsenic (As) from contaminated water. However, the diversity and metabolic potentials of As(III)-oxidizing bacteria (AOB) responsible for As(III) oxidation in wastewater treatment facilities are not well documented. In this study, two groups of bioreactors inoculated with activated sludge were operated under anoxic or oxic conditions to treat As-containing synthetic wastewater. Batch tests of inoculated sludges from the bioreactors further indicated that microorganisms could use nitrate or oxygen as electron acceptors to stimulate biological As(III) oxidation, suggesting the potentials of this process in wastewater treatment facilities. In addition, DNA-based stable isotope probing (DNA-SIP) was performed to identify the putative AOB in the activated sludge. Bacteria associated with Thiobacillus were identified as nitrate-dependent AOB, while bacteria associated with Hydrogenophaga were identified as aerobic AOB in activated sludge. Metagenomic binning reconstructed a number of high-quality metagenome-assembled genomes (MAGs) associated with the putative AOB. Functional genes encoding As resistance, As(III) oxidation, denitrification, and carbon fixation were identified in these MAGs, suggesting their potentials for chemoautotrophic As(III) oxidation. In addition, the presence of genes encoding secondary metabolite biosynthesis and extracellular polymeric substance metabolism in these MAGs may facilitate the proliferation of these AOB in activated sludge and enhance their capacity for As(III) oxidation. IMPORTANCE AOB play an important role in the removal of toxic arsenic from wastewater. Most of the AOB have been isolated from natural environments. However, knowledge regarding the structure and functional roles of As(III)-oxidizing communities in wastewater treatment facilities is not well documented. The combination of DNA-SIP and metagenomic binning provides an opportunity to elucidate the diversity of in situ AOB community inhabiting the activated sludges. In this study, the putative AOB responsible for As(III) oxidation in wastewater treatment facilities were identified, and their metabolic potentials, including As(III) oxidation, denitrification, carbon fixation, secondary metabolite biosynthesis, and extracellular polymeric substance metabolism, were investigated. This observation provides an understanding of anoxic and/or oxic AOB during the As(III) oxidation process in wastewater treatment facilities, which may contribute to the removal of As from contaminated water.

Arsenic: A Global Environmental Challenge

Arsenic is a naturally occurring metalloid and one of the few metals that can be metabolized inside the human body. The pervasive presence of arsenic in nature and anthropogenic sources from agricultural and medical use have perpetuated human exposure to this toxic and carcinogenic element. Highly exposed individuals are susceptible to various illnesses, including skin disorders; cognitive impairment; and cancers of the lung, liver, and kidneys. In fact, across the globe, approximately 200 million people are exposed to potentially toxic levels of arsenic, which has prompted substantial research and mitigation efforts to combat this extensive public health issue. This review provides an up-to-date look at arsenic-related challenges facing the global community, including current sources of arsenic, global disease burden, arsenic resistance, and shortcomings of ongoing mitigation measures, and discusses potential next steps.

A modeling approach for unveiling adsorption of toxic ions on iron oxide nanocrystals

The era of advanced computer simulations in materials science enables a great potential to design in silico computational experiments for (nano-)material performance. The adsorption efficiency of nanoparticles in various environments can be unveiled by atomistic models and computer simulations. Arsenic (As) is one of the important globally distributed contaminants with a hazardous impact on human health and environment, and it can strongly bind with iron nanocrystals (e.g., hematite (Fe₂O₃)) depending on their shape and size. Here, we developed a novel Kinetic Monte Carlo (KMC) model capable of exploring and delineating shape-efficiency dependence for Fe₂O₃ nanocrystals in contact with arsenate-contaminated water. This newly designed model demonstrated the performance of nanocrystals for removal of toxic (As) ions on their surface. The current model opens new avenues for designing further advanced KMC models for nanoparticles-toxic ions interactions, under varying environmentally relevant situations, e.g., groundwater, wetlands, and water treatment systems. In addition to bidentate adsorption complexes, implemented in the model presented, monodentate and outer-sphere adsorption complexes should be incorporated into the KMC model. Detailed environmental controls can be addressed by implementation of pH and background ions.

Statistical optimization of arsenic removal from synthetic water by electrocoagulation system and its application with real arsenic-polluted groundwater

Arsenic presence in the water has become one of the most concerning environmental problems. Electrocoagulation is a technology that offers several advantages over conventional treatments such as chemical coagulation. In the present work, an electrocoagulation system was optimized for arsenic removal at initial concentrations of 100 µg/L using response surface methodology. The effects of studied parameters were determined by a 2³ factorial design, whereas treatment time had a positive effect and current intensity had a negative effect on arsenic removal efficiency. With a p-value of 0.1629 and a confidence of level 99%, the type of electrode material did not have a significant effect on arsenic removal. Efficiency over 90% was reached at optimal operating conditions of 0.2 A of current intensity, and 7 min of treatment time using iron as the electrode material. However, the time necessary to accomplish with OMS arsenic guideline of 10 µg/L increased from 7 to 30 min when real arsenic-contaminated groundwater with an initial concentration of 80.2 ± 3.24 µg/L was used. The design of a pilot-scale electrocoagulation reactor was determined with the capacity to meet the water requirement of a 6417 population community in Sonora, Mexico. To provide the 1.0 L/s required, an electrocoagulation reactor with a working volume of 1.79 m³, a total electrode effective surface of 701 m², operating at a current intensity of 180 A and an operating cost of 0.0208 US$/day was proposed. Based on these results, electrocoagulation can be considered an efficient technology to treat arsenic-contaminated water and meet the drinking water quality standards.

Assessment of arsenic exposure in the population of Sabalpur village of Saran District of Bihar with mitigation approach

Arsenic poisoning through groundwater is the world's greatest normal groundwater catastrophe which got an immense effect on worldwide general wellbeing. India is confronting the outcomes of arsenic poisoning in the zone of Ganga Brahmaputra alluvial plains. In Bihar, out of 38 districts, 18 districts are exceptionally influenced with groundwater arsenic defilement. In the present study, we have assessed the current situation of arsenic exposure in Sabalpur village of Saran district of Bihar after reporting of breast, renal, skin and thyroid cancer cases from this village along with typical symptoms of arsenicosis. Such cancer patients were identified at our institute and were taken for the study. The present investigation deals with the quantification of arsenic in groundwater, hair and nail samples of subjects as well as the survey of entire village to know the overall health status of the village people. A total of n=128 household handpump water samples as well as n=128 human hair and nail samples were collected from over n=520 households. Using the graphite furnace atomic absorption spectrophotometer (GF-AAS), all the samples were analysed. The investigation resulted that the 61% of the analysed samples particularly the groundwater had the arsenic levels more than the permissible limit of WHO (> 10 μg/L) with 244.20 μg/L as the highest arsenic contamination in one of the handpump water sample. The exposure effect of hair sample was worst as 88% of all the collected samples were having high arsenic levels more than the permissible limit (> 0.2 mg/Kg). In case of nail samples, 92% of the samples were having high arsenic concentration more than the permissible limit (> 0.5 mg/Kg). The health survey study revealed high magnitude of disease burden in the exposed population with symptoms such as asthma, anaemia, hepatomegaly, diabetes, cardiac problem, skin fungal infections, breathlessness and mental disability. Few cancer cases of renal, skin, breast and cervix were also found among the exposed population of this village. The percentage of cancer cases in this village was 0.94% that was low, but it would be an aggravated situation in the near future if people will continue drinking arsenic-contaminated water. Therefore, a mitigation intervention was carried out in March 2020 by installing an arsenic filter plant. The health situation in the village in the present scenario is hope to improve in the coming years. However, motivation and awareness among the village population are still required.