As-contaminated Groundwater Research Articles

Synergistic ultra-high adsorption and oxidation of arsenic in groundwater by iron-modified biochar: Mechanisms and potential application

This study explores the potential of low-cost biochar modified with ferrihydrite and goethite for the remediation of heavily As-polluted groundwater. Combining batch experiments and synchrotron radiation-based characterization, we investigated the mechanisms of As(III) adsorption and oxidation. The modified biochars exhibited significant adsorption capacities, achieving fitted qmax of 45.7 ± 3.9 mg/g for ferrihydrite-modified biochar (FhGM) and 20.2 ± 1.5 mg/g for goethite-modified biochar (GtGM) at a dosage of 1.0 g/L and an initial concentration of 10 mg/L As(III) over 24 h. Biochar facilitated approximately 30 % As(V) generation from As(III) due to enhanced electron transfer. Moreover, over 90 % of As(III) was oxidized to As(V) following the addition of H2O2, with scanning transmission X-ray microscopy revealing the distribution of As(III), and As(V) on the solid phase. In the GtGM-H2O2 system, reactive oxidation species, primarily O2•–, served as the main oxidant. In the FhGM-H2O2 system, Fe(IV) likely acted as the primary oxidizing agent. Column experiments with 0.64 g of FhGM demonstrated that, when treating 50 mg/L As-contaminated groundwater, the effluent total As concentration remained below the maximum allowable limit of 10 μg/L after 21 h. Furthermore, in the presence of H2O2, the system managed to treat 200 mg/L As-contaminated groundwater, and the effluent total As concentration exceeded 10 μg/L after 11 h. This study provides valuable insights and practical results for the remediation of high-concentration arsenic-contaminated groundwater, highlighting the effectiveness of iron-modified biochar in this application.

Arsenic redox disequilibrium in geogenic contaminated groundwater: Bioenergetic insights from organic molecular characterization and gene-informed modeling

Biotransformation of arsenic (As) influences its speciation and mobility, obscuring mechanistic comprehension on spatiotemporal variation of As concentration in geogenic contaminated groundwater. In particular, unresolved processes underlying As redox disequilibrium in comparison to major redox couples discourage practical efforts to rehabilitate the As-contaminated groundwater. Here, quantitative metagenomic sequencing and ultrahigh-resolution mass spectrometry (FT-ICR-MS) were jointly applied to reveal the links between vertical distribution of As metabolic gene assemblages and that of free energy density of dissolved organic matter (DOM) in As-contaminated groundwater of Datong Basin. Observed small excess of Gibbs free energy available by DOM relative to that required for As(V)-to-As(III) reduction exerts thermodynamic constraint on metabolism-mediated redox transformation of As. Accordingly, the vertical distribution of dissolved As(V)/As(III) ratio correlated significantly with that of ars+acr3 and arr encoding As(V) reduction and aio encoding As(III) oxidation in the moderately/strongly reducing groundwater. Further gene-informed biogeochemical modeling suggests that a net effect of these kinetics-restricted bidirectional metabolic pathways leads to co-preservation of As(V) and As(III) even at relatively high rates of ars+acr3 encoded As(V) reduction. This study therefore provides new insights into bioenergetic constraints on As hydrobiogeochemical behavior, with implications for other redox-sensitive contaminants in the groundwater systems.

Magnetite enhances As immobilization during nitrate reduction and Fe(II) oxidation by Acidovorax sp. strain BoFeN1

Arsenic (As) cycling in groundwater is commonly coupled to the biogeochemical cycling of iron (Fe) and the associated transformation of Fe minerals present. Numerous laboratory studies suggested that Fe minerals can act as nucleation sites for further crystal growth and as catalysts for abiotic Fe(II) oxidation. In view of the widespread existence of magnetite in anoxic environments where As is often dissolved, we firstly exploited magnetite to enhance As immobilization during nitrate-reducing Fe(II) oxidation (NRFO) induced by Acidovorax sp. strain BoFeN1, a mixotrophic nitrate-reducing Fe(II)-oxidizing bacterium that can oxidize Fe(II) through both enzymatic and abiotic pathways. Subsequently, we investigated how magnetite affects NRFO and As immobilization. Results demonstrated a significant increase in As(III) removal efficiency from 75.4 % to 97.2 % with magnetite, attributed to the higher amount of NRFO and As(III) oxidation promoted by magnetite. It was found that magnetite stimulated the production of extracellular polymeric substances (EPS), which could decrease the diffusion of nitrate in the periplasm of bacteria and shield them against encrustation, resulting in a more rapid reduction of nitrate in the system with magnetite than that without magnetite. Meanwhile, Fe(II) was almost completely oxidized in the presence of magnetite during the whole 72 h experiment, while in the absence of magnetite, 47.7 % of Fe(II) remained, indicating that magnetite could obviously accelerate the chemical oxidation of Fe(II) with nitrite (the intermediates of nitrate bioreduction). Furthermore, the formation of labile Fe(III), an intermediate product of electron transfer between Fe(II) and magnetite, was reasonably deduced to be vital for anoxic As(III) oxidation. Additionally, the XPS analysis of the solid phase confirmed the oxidation of 43.8 % of As(III) to As(V). This study helps to understand the biogeochemical cycling of Fe and As in the environment, and provides a cost-effective and environmentally friendly option for in situ remediation of As-contaminated groundwater.

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

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

A mechanistic approach to arsenic adsorption and immobilization in aqueous solution, groundwater, and contaminated paddy soil using pine-cone magnetic biochar

Arsenic (As) poisoning in groundwater and rice paddy soil has increased globally, impacting human health and food security. There is an urgent need to deal with As-contaminated groundwater and soil. Biochar can be a useful remedy for toxic contaminants. This study explains the synthesis of pinecone-magnetic biochar (PC-MBC) by engineering the pinecone-pristine biochar with iron salts (FeCl3.6H2O and FeSO4.7H2O) to investigate its effects on As(V) adsorption and immobilization in water and soil, respectively. The results indicated that PC-MBC can remediate As(V)-contaminated water, with an adsorption capacity of 12.14 mg g−1 in water. Isotherm and kinetic modeling showed that the adsorption mechanism involved multilayer, monolayer, and diffusional processes, with chemisorption operating as the primary interface between As(V) and biochar. Post-adsorption analysis of PC-MBC, using FTIR and XRD, further revealed chemical fixing and outer-sphere complexation between As(V) and Fe, O, NH, and OH as the main reasons for As(V) adsorption onto PC-MBC. Recycling of PC-MBC also had excellent adsorption even after several regeneration cycles. Similarly, PC-MBC successfully immobilized As in paddy soil. Single and sequential extraction results showed the transformation of mobile forms of As to a more stable form, confirmed by non-destructive analysis using SEM, EDX, and elemental dot mapping. Thus, Fe-modified pine-cone biochar could be a suitable and cheap adsorbent for As-contaminated water and soil.

Valorization of invasive plant and leaf litter wastes into biochar: Production, properties and potential for arsenic removal

Arsenic (As) is an emerging pollutant and because of its toxicity, long-term persistence, elevated mobility, and high bioavailability, it has contaminated groundwaters of countries including India, China, and USA. Recently, biochars have emerged as a promising method for remediation of As. In the present study, biochars were prepared from invasive plants and leaf/plant litter waste at 300–700 °C temperatures. Further, the study assessed the impact of these feedstocks on physico-chemical properties and As removal efficiency of biochars. Based on high yield and As removal efficiency, the ones produced at 500 °C (LCB500 for Lantana camara-based biochar and LLB500 for leaf litter-based biochar) were chosen for advanced functional, morphological, and parameter optimization studies. Biochars showed a porous surface with high stability, mineral content, and surface functionality. Batch adsorption studies showed As adsorption capacity of 5.47 mg g−1 for LCB500 (at 4 mg L−1 initial concentration, 0.6 g L−1 dosage, 25 °C, 90 min contact time, and pH 8) and 6.36 mg g−1 for LLB500 (at 6 mg L−1 initial concentration, 0.8 g L−1 dosage, 25 °C, 90 min contact time, and pH 7). Emergence and disappearance of peaks in FTIR spectra and XRD diffractograms and isotherm, kinetic, and thermodynamic studies indicated a favourable multi-layer As adsorption with participation of both physisorption and chemisorption. Under optimized conditions, biochars showed removal of >75% As from As-contaminated groundwater samples collected from Sahibganj (Jharkhand). The recycling of spent LCB500 and LLB500 showed high reusability up to five cycles. Meanwhile, inconsequential impacts of co-existing ions were observed, indicating substantial efficacy for practical environmental applications. Cost analysis demonstrated considerable techno-economic feasibility and promotion of circular economy via development of value-added products through utilisation of waste. The present study recommends valorization of invasive plants and leaf litter wastes into sustainable biochars which could be used for effective removal of As from groundwaters.

Adsorptive behavior of Fe/Zn-modified nanobiochar for arsenic removal from naturally contaminated groundwater

Global groundwater is frequently discovered to have high arsenic (As) concentrations, critically endangered and potentially toxic to aquatic organisms and humans. This work investigates As(V) adsorption using raw nanobiochar (RnBC) and activated magnetic nanobiochar (AMnBC), which are synthesized via pre-treating rice straw biomass with ZnCl2 and FeCl3 and pyrolyzing at 500 °C, followed by ball milling. The highest adsorption capacity for AMnBC and RnBC was 130 μg/g and 38.67 μg/g, respectively, at alkaline water chemistry to mimic natural groundwater conditions. Different functional groups contributed by modifications are evident with As(V) adsorption using RnBC and AMnBC. Multilayer chemisorption may explain the adsorption of As(V) on biochar surfaces, as Freundulich isotherm and pseudo-second-order kinetic model are suggested. The synthesis cost for AMnBC and RnBC was $0.0147/g and $0.0099/g, respectively, which helped to determine the most effective and efficient method for As(V) adsorption. In this study, natural As-contaminated groundwater collected from Patna, Bihar (India), was treated for As(V) removal using AMnBC in natural environments. Thus, this study recommends that cost-effective modified biochar can effectively be used for As(V) elimination from naturally contaminated groundwater as well as surface water.

Metagenomic and culture-dependent approaches unveil active microbial community and novel functional genes involved in arsenic mobilization and detoxification in groundwater

BackgroundArsenic (As) and its species are major pollutants in ecological bodied including groundwater in Bangladesh rendering serious public health concern. Bacteria with arsenotrophic genes have been found in the aquifer, converting toxic arsenite [As (III)] to less toxic arsenate [As (V)] that is easily removed using chemical and biological trappers. In this study, genomic and metagenomic approaches parallel to culture-based assay (Graphical abstract) have made it possible to decipher phylogenetic diversity of groundwater arsenotrophic microbiomes along with elucidation of their genetic determinants.ResultsSeventy-two isolates were retrieved from six As-contaminated (average As concentration of 0.23 mg/L) groundwater samples from Munshiganj and Chandpur districts of Bangladesh. Twenty-three isolates harbored arsenite efflux pump (arsB) gene with high abundance, and ten isolates possessing arsenite oxidase (aioA) gene, with a wide range of minimum inhibitory concentration, MICAs (2 to 32 mM), confirming their role in arsenite metabolism. There was considerable heterogeneity in species richness and microbial community structure. Microbial taxa from Proteobacteria, Firmicutes and Acidobacteria dominated these diversities. Through these combinatorial approaches, we have identified potential candidates such as, Pseudomonas, Acinetobacter, Stenotrophomonas, Achromobacter, Paraburkholderia, Comamonas and Klebsiella and associated functional genes (arsB, acr3, arsD, arsH, arsR) that could significantly contribute to arsenite detoxification, accumulation, and immobilization.ConclusionsCulture-dependent and -independent shotgun metagenomic investigation elucidated arsenotrophic microbiomes and their functions in As biogeochemical transformation. These findings laid a foundation for further large-scale researches on the arsenotrophic microbiomes and their concurrent functions in As biogeochemical transformation in As-contaminated areas of Bangladesh and beyond.

Arsenic level in drinking water, its correlation with water quality parameters, and associated health risks.

This study aimed to evaluate the occurrence and likelihood of health risks related to arsenic in drinking water of all counties of the Hamadan province in the northwest of Iran. In this work, 370 samples were collected from all of the water resources of urban and rural regions, during 5years (2017 to 2021). Oracle Crystal Ball software was used to perform the Monte Carlo simulation and investigate the potential health risks. According to the results, the average values of arsenic in the nine counties were in the order Kabudarahang (40.1ppb), Malayer (13.1ppb), Nahavand (6.1ppb), Bahar (2.05ppb), Famenin (0.41ppb), Asadabad (0.36ppb), Tuyserkan (0.28ppb), Razan (0.14ppb), and Hamadan (< 0.1ppb). The highest concentration of arsenic occurred in Kabudarahang with a maximum value of 185ppb. In the spring season, the average concentration of the cations, including calcium, magnesium, sodium, lead, cadmium, and chromium, obtained 109.51mg/l, 44.67mg/l, 20.50mg/l, 88.76ppb, 0.31ppb, and 0.02ppb, respectively. Based on the Delphi classification, the P 90% of oral lifetime cancer risk, in Hamadan province, were within level II (low risk) to VII (extremely high risk). The risk analysis revealed there was a possible carcinogenic risk to humans from oral exposure to As-contaminated groundwater, especially in Kabudarahang county. Therefore, there is an urgent need for management and precise measures in contaminated areas to reduce and prevent the adverse health effects of arsenic.

Accumulation of arsenic and other metals in soil and human consumable foods of Meherpur district, southwestern Bangladesh, and associated health risk assessment

Groundwater and soil contaminated with arsenic (As) are significant environmental health concerns worldwide and have become a serious health issue for millions of Bangladeshis. This contaminated groundwater is commonly used for Boro rice production during the dry season in Bangladesh, leading to long-term As deposition in soils. The consequences of long-term irrigation with As-contaminated groundwater for bioaccumulation in food crops and hence dietary exposure to As and other metals are a threat to the resident. Highly arsenic (292 µg L−1) contaminated groundwater used to irrigate in the study area increases the As content (mean: 24.5 mg kg−1) in irrigated soil than non-irrigated soil (mean: 8.43 mg kg−1). The high enrichment factor (mean: 16.8) and geo-accumulation index (mean: 2.33) revealed that the soil of that particular area is strongly contaminated by As. In paddy, roots showed the maximum As concentration (mean: 139.8 mg kg−1) followed by straws (mean: 5.25 mg kg−1) and grains (mean: 1.23 mg kg−1) where 85–95% As exist in the roots of paddy, and only 0.8–1% As translocate to the harvesting part of the rice in the study area. In food samples, two rice grains (R-1, R-3) and a drumstick (FS-5) exceed the Indian standard of As concentration (As: 1.1 mg kg−1) in food. According to World Health Organization, the metals concentrations in all food samples exceeded the permissible limit except for Cu and Pb in red amaranth; Cr, Cd, and Pb in guava; and Cu and Cd in drumsticks. Higher values of bioaccumulation factor (BAF: 2.94) and the net translocation coefficient (NTC: 6.17) indicate As-accumulation in food from adjacent contaminated soil. Daily metal intake from food consumption suggests that the heavy metal(loid)s like As, Ni, and Pb represent high concentrations and exceed the daily ingestion limits (As: 3 µg kg−1 day−1, Ni: 1.3 µg kg−1 day−1, and Pb: 3.57 µg kg−1 day−1) developed by the Food and Agriculture Organization and European Food Safety Authority. Carcinogenic (> 10–6) and non-carcinogenic (HQ > 1) health risks of As, Pb, Cd, and Cu suggest that the community was at potential health risk according to the United States Environmental Protection Agency.

Comparison of As removal efficiency and health risks from aqueous solution using as-synthesized Fe0 and Cu0: modelling, kinetics and reusability.

Batch scale removal of arsenic (As) from aqueous media was explored using nano-zero valent iron (Fe0) and copper (Cu0) particles. The synthesized particles were characterized using a Brunauer-Emmett-Teller (BET) surface area analyzer, a scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR). The BET result showed that the surface area (31.5 m2/g) and pore volume (0.0415 cm3/g) of synthesized Fe0 were higher than the surface area (17.56 m2/g) and pore volume (0.0287 cm3/g) of Cu0. The SEM results showed that the morphology of the Fe0 and Cu0 was flowery microspheres and highly agglomerated with thin flakes. The FTIR spectra for Fe0 showed broad and intense peaks as compared to Cu0. The effects of the adsorbent dose (1-4g/L), initial concentration of As (2mg/L to 10mg/L) and solution pH (2-12) were evaluated on the removal of As. Results revealed that effective removal of As was obtained at pH 4 with Fe0 (94.95%) and Cu0 (74.86%). When the dosage increased from 1 to 4g L-1, the As removal increased from 70.59 to 93.02% with Fe0 and from 67 to 70.59% with Cu0. However, increasing the initial As concentration decreased the As removal significantly. Health risk indices, including estimated daily intake (EDI), hazard quotient (HQ), and cancer risk (CR) were employed and a significant decline (up to 99%) in risk indices was observed in As-treated water using Fe0/Cu0. Among the adsorption isotherm models, the values of R2 showed that isothermal As adsorption by Fe0 and Cu0 was well explained by the Freundlich adsorption isotherm model (R2 > 0.98) while the kinetic experimental data was well-fitted with the Pseudo second order model. The Fe0 showed excellent stability and reusability over five sorption cycles, and it was concluded that, compared to the Cu0, the Fe0 could be a promising technology for remediating As-contaminated groundwater.

Characterization of Groundwater Quality and Human Health Risk Assessment

The study aimed to appraise groundwater quality in the Mekong Delta using a groundwater quality index (GWQI) and estimate human health risks associated with groundwater consumption. Groundwater samples were collected at sixty wells distributed in An Giang, Kien Giang, Hau Giang and Dong Thap provinces. Twelve water quality parameters were measured, including pH, total dissolved solids (TDS), hardness, coliform, nitrate (NO3ˉ), nitrite (NO2ˉ), ammonium (NH4+), sulfate (SO42-), iron (Fe), manganese (Mn), arsenic (As) and cadmium (Cd). The results were compared with the national regulation on groundwater quality. The findings of this study indicated that groundwater in the Mekong Delta was contaminated with microorganisms and some heavy metals (Fe, Mn, and As). This was related to anthropogenic activities, such as improperly treated domestic wastewater and agricultural and industrial wastes. Based on the results of GWQI, 30% of the total groundwater samples in the Mekong Delta were classified as very good for drinking purposes. However, over 26% of all samples were unsuitable for drinking. In terms of risk assessment, children were rather susceptible to cancer risks and adverse health effects through drinking As-contaminated groundwater than adults. The cancer risks of consuming As-contaminated groundwater for children and adults were up to 4.28×10-3that is higher than the acceptable risk. The highest aggregate hazard quotient of heavy metal-contaminated groundwater for children and adults was 9.54, which means that they could suffer adverse health effects. Groundwater is an indispensable source of freshwater in the Mekong Delta; thus, home water treatments are recommended to protect public health, and an in-depth groundwater quality and health risk assessment should be conducted. Doi: 10.28991/CEJ-2023-09-03-09 Full Text: PDF

Metagenome based analysis of groundwater from arsenic contaminated sites of West Bengal revealed community diversity and their metabolic potential

The study of microbial community in groundwater systems is considered to be essential to improve our understanding of arsenic (As) biogeochemical cycling in aquifers, mainly as it relates to the fate and transport of As. The present study was conducted to determine the microbial community composition and its functional potential using As-contaminated groundwater from part of the Bengal Delta Plain (BDP) in West Bengal, India. Geochemical analyses indicated low to moderate dissolved oxygen (0.42-3.02 mg/L), varying As (2.5-311 µg/L) and Fe (0.19-1.2 mg/L) content, while low concentrations of total organic carbon (TOC), total inorganic carbon (TIC), nitrate, and sulfate were detected. Proteobacteria was the most abundant phylum, while the indiscriminate presence of an array of archaeal phyla, Euryarchaeota, Crenarchaeota, Nanoarchaeota, etc., was noteworthy. The core community members were affiliated to Sideroxydans, Acidovorax, Pseudoxanthomonas, Brevundimonas, etc. However, diversity assessed over multiple seasons indicated a shift from Sideroxydans to Pseudomonas or Brevundimonas dominant community, suggestive of microbial response to seasonally fluctuating geochemical stimuli. Taxonomy-based functional potential showed prospects for As biotransformation, methanogenesis, sulfate respiration, denitrification, etc. Thus, this study strengthened existing reports from this region by capturing the less abundant or difficult-to-culture taxa collectively forming a major fraction of the microbial community.

Arsenic and its management in soil

Arsenic (As) is a toxic metalloid and carcinogenic element that occurs widely in environment around the world. Arsenic is introduced into soil and water through geological (weathering of rocks and minerals) and anthropogenic pathways (mining, pesticides, fertilizers, timber treatment etc). Irrigation of agricultural land with As-contaminated groundwater or wastewater, particularly in India, Bangladesh and South-East Asia resulted in the accumulation of arsenic in both soils and plants posing risks to soil ecosystems and human health. Arsenic in soil and water exists in a different valence state, but predominantly as toxic As(III) and less toxic As(V) form. Arsenic toxicity is one of the most challenging problems in drinking water, as well as food crops (Samal et al., 2021). With greater public awareness of arsenic poisoning in animals and human nutrition, there has been growing interest in remediation technologies for mitigating As-contaminated ecosystems. Remediation of As-contaminated soil improves physical, chemical and biological approaches that may achieve either partial/complete removal of arsenic from soil and water. Many technologies like bioremediation, phytoremediation, soil mixing, soil washing, soil capping, filtration, adsorption and immobilization are used for arsenic removal from soil and water. Phytoremediation is a bioremediation process that uses various types of plants to remove, transfer, stabilize, and/or destroy contaminants in the soil and groundwater. But most of the arsenic still remains in the environment and there is always a risk of leaching caused by changes in the environmental conditions. Integrated approach involving a combination of physical, chemical and biological technologies is needed for the successful and effective management of As-contaminated environment.

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.

Performance of FeS synthesized within the porous media for in-situ immobilization of arsenic under varying water chemistry and groundwater conditions

The objectives of the study are (i) to assess arsenic immobilization efficiency by in-situ synthesized FeS within the porous media under varying solution chemistry and (ii) the performance evaluation of FeS-sand matrix in removing arsenic under natural groundwater conditions. To achieve the objectives, column experiments were performed where FeS was synthesized within the porous media in-situ. Then the As (III) or As (V) solution was injected within the column, and the effluents were collected to measure arsenic (As) and iron (Fe) concentrations. The groundwater samples were collected from seventeen locations in West Bengal, India, and were characterized. The As removal efficiency by FeS-sand matrix from the selected groundwater samples was studied in the batch and column system. The result showed that a significant amount of arsenite [As (III), 71.7–74.9%] was immobilized in the FeS synthesized porous media. The solution pH and the concentration of As (III) have an insignificant effect on immobilizing As (III) in the porous media system in the pH range of 6–8. Arsenate [As (V)] immobilization was not very promising under the reducing condition by in-situ synthesized FeS in the porous media. The As (V) removal was slightly better at pH 6 (26.9%) compared to pH 8 (11.7%). The occurrence of As in the groundwater (ranging from 0.78 μg/L to 376 μg/L) of the region was found to be associated with aluminum (Al) and Fe. The As removal by FeS-sand matrix showed better performance at pH 6 (40.7 ± 8.6%) compared to that of pH 8 (29.2 ± 15.6%) in the batch system. The immobilization of As increased significantly (83%) when the As-contaminated groundwater (376 μg/L) was injected into the porous media containing in-situ synthesized FeS. The concentration of Fe also reduced significantly (<160 μg/L) at the effluent after 2 PVs, indicating a limited risk of release of Fe. Overall, it could be stated that in-situ synthesized FeS in the porous media has the potential to immobilize As under a reducing environment within a range of pH under the groundwater conditions.

The Enhanced Stability of Arsenic Coprecipitated with Magnetite during Aging: An XAS Investigation

The coprecipitation of magnetite (Fe3O4) with arsenic (As) is a potential remediation technique for As-contaminated groundwater that can be applied to meet increasingly stringent As drinking water limits. However, knowledge of the fate of As coprecipitated with magnetite during aging for extended periods is lacking, which is critical to predict the long-term efficiency of this As treatment strategy. In this work, I combined aqueous As measurements with solid-phase characterization by synchrotron-based Fe and As K-edge X-ray absorption spectroscopy (XAS) to track the transformation of magnetite and the speciation of coprecipitated As(V) or As(III) for up to a year in oxic or anoxic conditions. It was determined that the initial magnetite particle increased in crystallinity for all aging experiments, but some differences in solid-phase Fe speciation were detected depending on aging conditions. For the anoxic aging samples with initial As(V), a significant fraction (15% of the total Fe) of maghemite (a magnetic Fe oxide spinel with formula γ-Fe2O3) was identified, which was coupled to As(V) reduction [As(III) was ∼30% of the total sorbed As], suggesting electron transfer between magnetite and particle-bound As(V). In the oxic aging experiments, the initial particle crystallized, with a large fraction of Fe(III) (oxyhydr)oxides (i.e., maghemite and lepidocrocite, γ-FeOOH) in the final products. Despite increased crystallinity suggested by Fe XAS analysis, sorbed As was not released from the particles in any experiment (aqueous As never exceeded 1 μg/L). This remarkable stability of As coprecipitated with magnetite was revealed by As K-edge XAS to be largely due to the formation of distinct multinuclear As uptake modes [i.e., As(V) incorporation; hexanuclear 3C As(III) complexes]. These results demonstrate the unique potential of magnetite for long-term As sequestration.

Arsenic accumulation in rice: Alternative irrigation regimes produce rice safe from arsenic contamination

The natural occurrence of arsenic (As) in groundwater & soils and its bioaccumulation in rice grains is a major health concern worldwide. To combat the problem, best combination of irrigation management and suitable rice variety altering As content in grains must be ensured. With this aim, a field trial was conducted with two rice varieties and water management including alternate wetting and drying (AWD) and continuous flooding (CF) irrigation regimes with As contaminated groundwater (AsW) and temporarily stored groundwater (TSG) and river water for only CF (as control). Results revealed that As content in different portions of paddy plant was significantly different (P < 0.001) with irrigation practices and rice varieties. AWD irrigation with TSG accumulated lower As in rice grains compared with CF-AsW for both varieties. Data showed that AWD-TSG practice led to 61.37% and 60.34% grain As reduction for BRRI dhan28 and BRRI dhan29, respectively, compared with CF-AsW. For Principle Component Analysis (PCA), first principle component (PC1) explained 91.7% of the variability and irrigation water As, soil total and available As, straw As, root As and husk As were the dominating parameters. With significant (P < 0.05) variation in yields between the genotypes, AWD increased grain yield by 29.25% in BRRI dhan29 Compared with CF. However, translocation factor (TF) and bioconcentration factor (BCF) for both varieties were less than one for all the treatments. The addition of this study to our knowledge base is that, AWD-TSG with BRRI dhan29 can be an As–safe practice without compromising yields.

Groundwater Quality Assessment Using Groundwater Quality Index and Multivariate Statistical Methods and Human Health Risk Assessment in a Coastal Region of the Vietnamese Mekong Delta

This study aimed to evaluate the suitability of groundwater for drinking purposes and assess the associated human health risks for different age groups in a coastal province of Mekong Delta, Vietnam. Twenty groundwater samples were collected in Soc Trang Province, and various water quality parameters were analyzed. The data were employed to calculate entropy-weighted groundwater quality index (EWQI), principal component analysis (PCA), cluster analysis (CA), and non-carcinogenic and carcinogenic risks for adult and children health. The results revealed that groundwater in some locations, especially in GW19, was polluted by hardness, total dissolved solids, NH4+, Cl-, Fe, total coliform, and E. coli. In addition, 5 principal components from the PCA results could explain 84.5% of the total variation of groundwater quality, which also suggested that the potential groundwater pollution sources were geochemical processes, agricultural activities, domestic and industrial wastewater, seawater intrusion, and excessive nitrogen fertilizer application. The CA results showed that monitoring locations can be divided into 4 clusters based on their similarities in groundwater quality, and the most polluted group was found at cluster IV (GW19). The computed EWQI values ranged from 20.05 to 738.52, with approximately 45% of total samples classifying good to excellent water quality. The sampling points with undrinkable quality are mainly located in the northeast and center of the province. The ratio of children and adults under the threat of adverse health effects due to drinking groundwater contained non-carcinogenic substances (NH4+, NO2-, NO3-, Cd, Cu, F-, Mn, and As) ranged from 5 to 40%, and children had higher risks compared to adults. Additionally, the consumption of As-contaminated groundwater also poses carcinogenic risks for children, female and male adults ranging from 4.80×10-6 to 1.33×10-4. The findings of this study can provide helpful information for policymakers in the development of long-term water management strategies to protect community health.

Recognition method for the health risks of potentially toxic elements in a headwater catchment

The spatial association of potentially toxic elements (PTEs) in soil–crop–groundwater systems is poorly recognised. In this study, the contents of arsenic (As), cadmium (Cd), copper (Cu) and lead (Pb) in paddy soils, rice and groundwater in the Xiancha River catchment were determined. The intrinsic effects of PTEs in soils on their spatial distribution in groundwater and rice were explored. Also, the potential sources and health risks of PTEs in multi-media were investigated. Results showed that the mean contents of As and Cd in soils were 23.86 and 0.26 mg kg−1, respectively. In groundwater, the maximum (average) content of As reached 6.55 (1.84) μg L−1. Moreover, As contents in soils and groundwater showed a sound spatial correlation (q = 0.81), and this is supported by the result of the soil column experiment, indicating homology and the strong vertical migration capacity of As. The non-homologous patterns of Pb, Cu and Cd contaminations in soil–groundwater system suggested that geogenic processes influenced the distribution of these PTEs. Cd presented a poor spatial correlation in soil–rice system, as multiple factors controlled its transfer process. Multivariate statistical analysis results demonstrated that As, Cu and Pb in soils mainly came from agricultural sources, whereas high Cd levels were from mining activities. Additionally, direct consumption of As-contaminated groundwater and Cd-contaminated rice posed significant health risks to local residents. This study, which proposes a risk recognition method used to investigate target PTEs in multi-media, may serve as a valuable reference for further research involving catchments.