Arsenic In Groundwater Research Articles

The influence mechanism of hydrogeochemical environment and sulfur and nitrogen cycle on arsenic enrichment in groundwater: A case study of Hasuhai basin, China

Hydro-biogeochemical processes control the formation and evolution of high arsenic (As) groundwater. However, the effects of nitrogen and sulfur cycles in groundwater on As migration and transformation are not well understood. Thus, twenty-one groundwater samples were collected from the Hasuhai basin. Hydrochemistry and geochemical modeling were used to analyze the geochemical processes associated with nitrogen and sulfur cycles. An arsenic speciation model (AM) and a sulfide-As model (SAM) were constructed to verify the existence of As species and the formation mechanism of thioarsenate. A hydrous ferric oxide (Hfo)-As adsorption model (HAM) and a competitive adsorption model (CAM) were used to reveal the adsorption and desorption mechanisms of As. The results showed that high arsenic groundwater (As > 10 μg/L) was mainly distributed under reductive conditions, and the highest concentration was 231.5 μg/L. The modeling results revealed that sulfides were widely involved in the geochemical cycle of As, with H3AsO3 and H2AsO3− accounting for >70 % of the total As, and thioarsenate accounting for 30 %. S/As < 2.5 and S/Fe < l control the formation of thioarsenate. With the high correlation of NH4+, TFe, sulfide, and TAs, the co-mobilization of N and S cycles may facilitate As enrichment in groundwater. A weak alkaline reduction environment triggered by the decomposition of organic matter was the main factor leading to the transfer of As from the aquifer to the groundwater. This research contributes to the development of high-As groundwater, and the findings are of general significance for drinking water in the Hasuhai Basin.

Investigation of arsenic contamination in groundwater using hydride generation atomic absorption spectrometry.

The validated hydride generation atomic absorption spectrometry (HG-AAS) method has been used to investigate total arsenic in groundwater. Under optimal experimental conditions, the concentration of arsenic in groundwater can be analysed in the range of 0.5 to 50µg/L, with a method detection limit of 0.15µg/L. Its recovery in the field is from 96.3 to 99.8%, with high repeatability. The method was used to observe the total arsenic pollution in groundwater collected in Phu Tho Province, Vietnam. A total of 364 groundwater samples were analysed. The results showed that arsenic pollution was significant, with 15.93% of the samples higher than the maximum permissible level of arsenic. About 20.69% of the contaminated samples had a total arsenic ten times higher (100µg/L) than the maximum permissible level of arsenic. The pollution source was also considered by comparing the arsenic level in the groundwater with arsenic in the surface water in the same areas. Thus, the use of the high-accuracy and sensitive method, HG-AAS, supplies valuable data on groundwater pollution for water resources management and environmental protection.

Microbes-Assisted Arsenate Reduction Activity in Bangladesh Drinking Water Wells as Revealed by Enrichment Cultivation

Arsenate-reducing microorganisms may mobilize arsenic into groundwater. Phylogenetic DNA sequence information cannot exclusively be used to infer arsenate reduction, as the spotted homologies may not translate to biochemical activities. We here develop a cultivation-based metagenomic strategy for inferring actual activities: we complement a cultivation-independent microbial community survey covering 22 arsenic-contaminated drinking water wells in Bangladesh, with the characterization of enrichments of anaerobic arsenate reducers. All investigated samples revealed microbial arsenate reduction activity. The enriched microbial communities were phylogenetically diverse within and between the enrichments. The enrichment also unveiled species: the arsenate-reducing enrichments held 16S rRNA gene sequences closest to Dechloromonas sp., Azonexus fungiphilus, Youngiibacter fragile, Methanogenic prokaryote and Fusibacter sp., in addition to arsenate-reducing Sulfurospirillum strains NP4, b10 and dissimilatory iron-reducing Geobacter species. The enriched arsenate reductase gene (arrA) sequences were closest to sequences in known arsenate reducing Sulfurospirillum barnesii. This study bridges the knowledge gap between cultivation-independent and cultivation-dependent analyses. It clarifies the mechanism for arsenic mobilization and redistribution in rural drinking water wells, as a balance between bioremediation and harmful activities. The identified, potentially dissimilatory arsenate and iron-reducing microbes, constitute a risk for arsenic bioremediation. Appropriate metagenomic and dynamic analyses should help design and maintain safer, effective bioremediation.

Dynamics of Spatiotemporal Variation of Groundwater Arsenic Due to Salt-Leaching Irrigation and Saline-Alkali Land

Determining the link between the evolution of salt-leaching irrigation, saline-alkali land, and groundwater arsenic (As) is essential to prevent groundwater arsenic pollution and implement appropriate soil salinization control projects. The objectives of our study were to explore the spatiotemporal correlation of saline-alkali land and salt-leaching irrigation with groundwater As in the Hetao Plain. Therefore, groundwater As concentrations during Period I (2006–2010) and Period II (2016–2020) were collected by historical data and chemical measurements. Salt-leaching irrigation area and saline-alkali land area in Period I and Period II were extracted through remote sensing data. With the increase of the salt-leaching irrigation area level (SLIAL) and saline-alkali land area level (SALAL), the variation trend in groundwater As concentration slightly fluctuated, with an increase in the SLIAL at the low SALAL, which may be because short-term flooding may not considerably enhance As mobilization. Lower groundwater As concentrations appeared in regions with higher SLIAL and lower SALAL. A larger saline-alkali land area (higher SALAL) increased the groundwater As concentration. The path analysis model confirmed that salt-leaching irrigation may increase groundwater salinity to affect groundwater As levels and to decrease the saline-alkali land area. From Periods I to II, the difference in path analysis results may imply that the decrease in the saline-alkali land area may have influenced As mobilization due to competitive adsorption caused by the increase in total dissolved solids (TDS) in groundwater. Our results provide new insights for the impacts of saline-alkali land and salt-leaching irrigation both on groundwater As concentration and the geochemical processes of As enrichment in arid and semi-arid areas with more serious salinization.

Analysis of the geological control on the spatial distribution of potentially toxic concentrations of As and F- in groundwater on a Pan-European scale

The distribution of the high concentrations of arsenic (As) and fluoride (F-) in groundwater on a Pan-European scale could be explained by the geological European context (lithology and structural faults). To test this hypothesis, seventeen countries and eighteen geological survey organizations (GSOs) have participated in the dataset. The methodology has used the HydroGeoToxicity (HGT) and the Baseline Concentration (BLC) index. The results prove that most of the waters considered in this study are in good conditions for drinking water consumption, in terms of As and/or F- content. A low proportion of the analysed samples present HGT≥ 1 levels (4% and 7% for As and F-, respectively). The spatial distribution of the highest As and/or F- concentrations (via BLC values) has been analysed using GIS tools. The highest values are identified associated with fissured hard rock outcrops (crystalline rocks) or Cenozoic sedimentary zones, where basement fractures seems to have an obvious control on the distribution of maximum concentrations of these elements in groundwaters.

Remediation of arsenic contaminated groundwater by electrocoagulation: Process optimization using response surface methodology

Elevated arsenic in groundwater is a serious health hazard and needs attention. In this study, electrocoagulation was investigated in an effort to find the optimum condition for samples having a mixture of As3+ and As5+. A two-level full factorial design was used to investigate the effects of three independent process variables on the response variable (arsenic removal efficiency), namely (i) pH (6.5–8.5), (ii) As (III) = (100–400) ppb, and (iii) treatment time (2–9) min. Three factors (As3+ concentration, As5+ concentration, and treatment time) were used to design centre composite design (CCD) experiments, and the effect of each variable on arsenic removal efficiency was studied using response surface methodology (RSM) with a fixed current density (CD) of 10 A/m2 and an initial pH of 7.4. Arsenic removal from the samples was confirmed by Raman spectroscopy, which showed the multiple peaks of iron and arsenic compounds in the sludge sample. Arsenic removal was also indicated by the amorphous structure of flocs of iron oxide/hydroxide, observed in scanning electron microscopy (SEM) images of sludge and evidenced from X-ray diffraction studies.

Health risks of shallow groundwater in the five basins of Shanxi, China: Geographical, geological and human activity roles

Rapid economic development often leads to groundwater degradation, posing health risks to those who rely on it. The groundwater discharge conditions in basins are poor. The health risk of shallow groundwater in basins needs more attentions. The health risk of shallow groundwater in the five basins of Shanxi Province, China was discussed based on the hydrochemical evolution of shallow groundwater and the water quality assessment. The results showed that arsenic (As) and chromium (Cr) in the shallow groundwater of the basins caused prominent health risks followed by fluoride (F) and nitrate (NO3−). The non-carcinogenic risks of As, F and NO3- to children were higher than that to adults, and the carcinogenic risks of As and Cr were higher for adults than children. Various hydrogeochemical reactions, geological conditions, climatic factors, and human activities are closely related to groundwater health risks, and basin topography is considered as one of key factors. Water-rock interaction, dedolomitization and cation exchange are the natural processes in the evolution of groundwater hydrochemistry, while agricultural and mining activities are the anthropogenic factors causing groundwater degradation. The leaching/dilution effects of infiltration precipitation in the basin-mountain systems cause distinct temporal changes in the chemical composition and health risks of the groundwater in the basins. Differences in climate and farming practices among the basins further complicate the spatio-temporal changes. The basin-mountain system is conducive to the convergence and enrichment of water flow and solutes in the basins, which aggravates the degradation of groundwater quality. This study highlights that the combined influences of geographical and geological factors and anthropogenic activities amplify the human health risks of groundwater in the basins.

Plant Waste as Green Reinforcement for Polymer Composites: A Case Study of Pteris Vittata Roots

ABSTRACT Pteris vittata is a hyperaccumulator fern able to uptake arsenic by roots accumulating it in the fronds. Recent studies showed that Pteris vittata can be used efficiently for arsenic-contaminated water treatment, paving the way for long-lasting decontamination strategies established on nature-based solutions. This raises the issue of biomass disposal, which rather than being incinerated could represent a valuable untapped source of fibers for sustainable and higher-value biocomposites. Here, Pteris vittata waste roots were collected and used to develop composites based on high-density polyethylene. Composites with two amounts of filler (10 wt.% and 20 wt.%) added with 5 wt.% of maleic anhydride grafted polyethylene, were manufactured and tested in terms of mechanical and thermal properties. Mechanical property analysis showed that, compared to neat high-density polyethylene, composites at 20 wt.% filler content with coupling agent displayed an increase around 54% in tensile strength, 100% in Young’s modulus, 46% in flexural strength and 45% in flexural modulus. These results demonstrate the potential of Pteris vittata waste roots application for sustainable composite materials production.

Thiosulfate driving bio-reduction mechanisms of scorodite in groundwater environment

Reductive dissolution of scorodite results in the release and migration of arsenic (As) in groundwater. The purpose of this study was to explore the possible abiotic and biotic reduction of scorodite in groundwater environment and the effect of microbial-mediated sulfur cycling on the bio-reduction of scorodite. Microcosm experiments consisting of scorodite with bacterium Citrobacter sp. JH012-1 or free sulfide were carried out to determine the effects of thiosulfate on the mobilization of As/Fe. The results show arsenic release is positively correlated with iron reduction. The arsenate [As(V)] released can agglomerate with Fe(II) on the surface of scorodite to form crystalline parasymplesite, while no parasymplesite was detected in the abiotic reduction of scorodite by sulfide. The reduction of scorodite and As(V) was affected by thiosulfate. When 0.5 mM thiosulfate was added, the Fe(III) reduction rate increased from 32% to 82%, and the As(V) reduction rate rose from 54% to 64%. When the addition of thiosulfate was increased from 0.5 mM to 2 mM and 5 mM, Fe(III) reduction rate added 4% and 8%, and As(V) reduction rate increased 11% and 16%, respectively. In addition, the presence of thiosulfate promoted the scorodite almost completely converting to parasymplesite. Therefore, the effect of microbial-mediated sulfur cycling should be considered in arsenic migration and reduction from scorodite.

Enrichment of High Arsenic Groundwater Controlled by Hydrogeochemical and Physical Processes in the Hetao Basin, China.

Based on 447 samples collected from a shallow aquifer (depths from 0 to 150 m) in the Hetao Basin, Northern China, an integrated hydrogeochemical approach was used in this study to conceptualize the enrichment of high arsenic groundwater in the Hetao Basin. An unconventional method of distinguishing hydrogeochemical and physical processes from a dataset was tested by investigating the cumulative frequency distribution of ionic ratios expressed on a probability scale. By applying cumulative frequency distribution curves to characterize the distribution of ionic ratios throughout the Hetao Basin, hydrogeochemical indicators were obtained that distinguish the series of hydrogeochemical processes that govern groundwater composition. All hydrogeochemical processes can basically be classified as recharge intensity of groundwater, evaporation concentration intensity, and reductive degree controlling the spatial distribution of arsenic. By considering the three processes, we found that the concentration of arsenic was more than 10 μg/L when the (HCO3-+CO32-)/SO42- ratio was over 4.1 (strong reductive area). As the evaporation concentration intensity increased, the median value of arsenic increased from 10.74 to 382.7 μg/L in the median reductive area and rapidly increased from 89.11 to 461.45 μg/L in the strong reductive area. As the river recharge intensity increased (with the intensity index increasing from 0 to 5), the median value of arsenic dropped from 40.2 to 6.8 μg/L in the median reductive area and decreased more markedly from 219.85 to 23.73 μg/L in the strong reductive area. The results provide a new insight into the mechanism of As enrichment in groundwater.

One-Pot synthesis of MWCNTs/Fe-MOFs nanocomposites for enhanced adsorption of As(V) in aqueous solution

Arsenic is a toxic carcinogen, and arsenic pollution in groundwater is one of the most serious environmental problems in the world. Thus, it is an urgent problem to efficient removal of arsenic from groundwater. In this work, a novel MWCNTs/MIL-53(Fe) nanocomposite was successfully synthesized to improve the water stability of MIL-53(Fe) by incorporation of carboxylated multi-walled carbon nanotubes (MWCNTs) using a one-pot hydrothermal method, and was then used to efficiently adsorb As(V) ions from groundwater. Adsorption experimental results demonstrated an ultrafast adsorption rate of As(V) on the MWCNTs/MIL-53(Fe) nanocomposites in solution pH values of 3 to 10, and the adsorption equilibrium could be reached in circa 20 min with an adsorption capacity of 27.24 mg·g−1 in a low As(V) concentration of 10 mg·L−1. The adsorption kinetics of As(V) on the MWCNTs/MIL-53(Fe) was found in line with the pseudo-second-order (PSO) kinetic model, and was simultaneously controlled by both internal diffusion and liquid film diffusion. The adsorption isotherm data conformed to the Redlich-Peterson isotherm model, indicating both physical and chemical adsorption occurred at heterogeneous interfaces. Moreover, the postulated adsorption mechanism of As(V) on MWCNTs/MIL-53(Fe) nanocomposites was ascribed to hydrogen-bond interaction, electrostatic attraction and chemical complexation. Therefore, the as-prepared MWCNTs/MIL-53(Fe) nanocomposites not only exhibit superior water stability and outstanding adsorption performance in removing arsenic-contaminated groundwater, but also offer a novel insight for rational preparation of water-stable MOF-based composites.

Assessment of Zerovalent Iron Nanoparticle (nZVI) Efficiency for Remediation of Arsenic-Contaminated Groundwater: Two Laboratory Experiments

Zerovalent iron nanoparticle (nZVI) technology has been found to be promising and effective for soil and groundwater remediation. This paper shows the results of two batch tests (Test A and Test B) carried out to assess the capacity of nZVI to remediate arsenic (As)-contaminated water. Test A, performed with batches of tap water contaminated by arsenic, with a concentration equal to 10 mg ∗ L−1, showed a significant reduction of the As concentrations in solution, with a maximum removal rate up to 98% (Batch 3). Test A lasted 26 h. At the same time, Test B was performed with a sample of arsenic-contaminated sediment, with a concentration equal to 100 mg ∗ Kg−1 (ca). Test B lasted 72 h. Test B also confirmed an excellent reduction of the As concentrations in solution, up to a maximum removal rate of 99% (Batch 3). These results show the effectiveness of nZVI for the remediation of water contaminated by arsenic. However, as the As–nZVI interaction time increased, there was a decrease in the available sites for arsenic immobilization, and so the As concentrations in solution became constant. In fact, as the dose of nZVI (mnZVI) used in the batches increased, the mass concentration of residue As in the solution at the equilibrium decreased (cAse) and therefore the concentration of As absorbed (cAs0–cAse) on the nZVI increased due to the immobilization action of the nanoparticles. The results show concentrations of As absorbed (cAs0–cAse) on the nZVI with a range between 5.10 mg ∗ L−1 (mnZVI = 0.05 g) and 9.54 mg ∗ L−1 (mnZVI = 0.5 g) for Test A, and with a range between 0.029 mg ∗ L−1 (mnZVI = 0.05 g) and 0.058 mg ∗ L−1 (mnZVI = 0.7 g) for Test B. Therefore, these results underline the need to monitor As concentrations during applications in the field, in order to verify the demand for injecting new active nanoparticles for arsenic removal.

Highly sensitive detection of arsenic in groundwater by paper-based electrochemical sensor modified with earth-abundant material

The toxicity of arsenic and its hazards to the human body are well known and its timely, accurate, and cost-effective detection in water and foodstuffs and other environmental matrices is highly essential. Herein, we present a simple and easy method for the synthesis of reduced graphene oxide-ceria (rGO-CeO2) nanocomposite and its use for low-level detection of As(III) in water up to 0.93 μg/L. The presence of CeO2 on rGO surface is attributed to the enhanced electron transfer rate. The material characterization was performed with different analytical techniques including scanning electron microscopy (SEM), Raman spectroscopy, and X-ray diffraction (XRD), Infrared spectroscopy (FTIR) and Electrochemical Impedance Spectroscopy (EIS). The electrochemical behaviour of the rGO-CeO2 modified screen-printed electrodes (SPE) has been investigated by using Cyclic Voltammetry (CV) and Differential Pulse Stripping Voltammetry (DPSV). A highly linear response with a correlation coefficient of 0.9986 is achieved with a detection limit of 0.39 μg/L. Finally, the sensor was also tested with real-world groundwater samples collected from the arsenic-contaminated areas and acceptable recoveries were observed in the range of 85–95% as compared to Inductively Coupled Plasma Mass Spectrometer (ICP-MS) analysis. The electroanalytical performances of rGO-CeO2 modified SPE confirm that the as prepared sensor can be used for practical applications owing to its high sensitivity, good selectivity, robustness, low cost, high reproducibility, reusability, and ease of high scale production.

Evaluation of the factors affecting arsenic distribution using geospatial analysis techniques in Dongting Plain, China

Due to high toxicity, arsenic is regarded as a major global environmental pollutant. The present study is investigated the potential factors influencing to elevate concentration of arsenic in groundwater, surface water, and soil of the Dongting basin. The arsenic contamination potential prediction map and categories were developed using various GIS techniques such as Ordinary Kriging and the Quantile method. Then the “Raster calculator” tool was applied to verify the impact of the factors on arsenic. Eighty-four single-factor, bi-factor, and multi-factor models were established to investigate effective combinations among factors of each phase. Additionally, statistical tests were computed to evaluate arsenic between classes and factors. The arsenic value varies in groundwater from 0.0001 to 0.1582 mg/l, while in surface water between 0.0001–0.0287 mg/l and soil sediments range from 1.8–45.69 mg/kg. JunShan and GongAn groundwater resources have been identified as posing a high risk to human health. The single factors showed the best match frequency of arsenic with a population density of 66.86% in water and land use depicted match frequency of arsenic 73.19% in soil. The statistical calculations with percentage frequency factors also depicted positive trends. The correlation of the factors with arsenic in soil and water showed slow oxidation and reduction in the groundwater system. Treated portable water could be the best option to reduce the health risk of the local community.

Spatial distribution and risk identification of arsenic contamination in water and soil through GIS-based interpolation techniques in Jianghan Plain, Central China

Arsenic is considered a poison because of its seriously toxic effects on the human body; elevated concentrations of arsenic in drinking water have been reported in different parts of the world. Investigating the arsenic distributions in soil, surface water (SW), and groundwater (GW) is an interesting topic of research, along with probing its correlations with local factors of the ecosystem and other hydrogeochemical parameters. This study mainly aims to investigate the impacts of various factors on elevated arsenic concentrations in water and soil. The following factors are assessed for their relationship to the propagation of arsenic in Jianghan Plain, which is the study area: population density, pumping rate, rain, land use, surface elevation, water level, and heavy metal contamination. The arsenic contamination potential prediction map and categories were developed using GIS-based techniques, such as ordinary kriging and quantile methods. Then, the “raster calculator” tool was applied to verify the impacts of the abovementioned factors on arsenic concentration. Eighty-four single-factor, bi-factor, and multi-factor models were established to investigate the effective combinations among the factors. Land use and pumping rate were identified from the soil through an equal frequency tool, whereas water population density and pumping rate were obtained with high matching percentages. The arsenic concentrations varied in the ranges of 0.0001–0.1582 mg/L in GW, 0.0003–0.05926 mg/L in SW, and 1.820–46.620 mg/kg in soil sediment. The single factors showed the best equal frequency of arsenic concentration in water for population density (68.62%) and in soil for land use (65.57%) and pumping (63.66%). Statistical calculations with percentage frequency factors also depicted a positive trend. Arsenic was reported to have high correlations with Fe in GW (r2 = 0.4193), with EC in SW (r2 = 0.4817), and with Cu in soil (r2 = 0.623). It is observed that the alkaline behaviors of water bodies are associated with arsenic mobility. Elevated arsenic values were observed in grids along surface flows with high anthropogenic activities and urbanization. Additionally, low concentrations of Fe depicted reduced activities in aquifer systems. Filtering drinking water as well as controlling the suspected sources and factors affecting concentrations of arsenic in the three phases are options for reducing the health risks of the local populations.

Arsenic removal technologies for middle- and low-income countries to achieve the SDG-3 and SDG-6 targets: A review

• Over 230 million population are suffering from ‘As’ laced drinking water and its associated health hazards worldwide. • To achieve SDG- 3 (Good health and well-being’) and SDG-6 (Safe and clean water and sanitation) ‘As’ problem needs to be managed. • Low and middle income countries have a challenge to implement highly efficient As removal technologies. • Chemical and biological technologies, adsorption, and hybrid technologies with running cost <1 US$/m 3 can be applied in low/middle income countries. • Regular monitoring of As, community participation, research on cost effective As-removal models coupled with policy level intervention is most needed. Contamination of arsenic (As) in groundwater has increased across the world with prominence in the middle- and low-income countries. The United Nations ‘Sustainable Development Goals’ (SDG's)- ‘good health and well-being’ (SDG 3) and ‘safe and clean water and sanitation for all’ (SDG 6), cannot be achieved without monitoring and remediating ‘As’ pollution in groundwater. Over 230 million people worldwide are affected due to arsenic-contaminated drinking water. More than 200 articles discussing the ‘As’ contamination, toxicity and cost effective technology were reviewed in this study focusing on economic status of the affected nation as per World bank report. Cost budget analysis suggested that chemical oxidation followed by precipitation (0. 043-0. 076 US$/m 3 ), low cost adsorbent (0. 1 US$/m 3 ), hybrid treatment technologies (0. 15-0. 17 US$/m 3 ) and biological oxidation (0. 2 US$/m 3 ) can be applied in low income countries through community based models to mitigate the health problem related to As contamination in order to achieve SDG 3 and SDG 6 targets. This study recommends further research on budget friendly ‘As’ remediation systems and policy level interventions in the affected nations to cater safe drinking water to all.

Assessment of Arsenic Contamination in Groundwater and Associated Human Health Risk

Drinking water contamination by arsenic (As) is of significant concern due to its potential cause of cancer and arsenicosis. In this study, out of the 200 samples (n = 200), the mean As concentrations ranged from below detection limit (BDL) to 3.30, 4.81, 4.42 and 3.85 µg L−1 in small residential, roadside, industrial and household areas, respectively. From 200 total samples, 9% of the groundwater samples showed As levels higher than the WHO safe guideline limit of 10 μg L−1. Human health risk was assessed using average daily intake (ADD), hazard quotient (HQ) and cancer risk (CR) values which were found to be greater than the recommended values by the United States Environmental Protection Agency (1.0 and 10−6) for health risk assessment. The CR were ranged from 0–5.7 × 10−1, 4.0 × 10−1, 2.0 × 10−1 and 1.0 × 10−1 in small residential areas for children, adolescents, males and females, respectively. In roadside areas, the values ranged from 0–2.8 × 10−1, 4.0 × 10−1, 2.0 × 10−1 and 2.8 × 10−1 for children, adolescents, males and females, while 0–5.9 × 10−1, 4.1 × 10−1, 2.1 × 10−1 and 1.6 × 10−1 in industrial areas and 0–8.0 × 10−1, 2.91 × 10−1, 2.6 × 10−1 and 3.9 × 10−1 were calculated in household sites. All the CR values were found to be exceeding the US-EPA limit (10−6) recommending that the people in the study area are more prone to carcinogenic risk. Overall, it was concluded that due to presence of As in drinking water, these areas tend to be at higher cancer risks. To provide safe drinking water for the people living in these As-affected areas, urgent remedial and management steps are required.

Biodegradation of dissolved organic matter and sedimentary organic matter in high arsenic groundwater system: Evidence from lipid biomarkers and compound-specific carbon isotopes

Organic matter plays important roles in arsenic mobility. Whether sedimentary or dissolved organic matter is the predominant electron donors is still on debate. To fill this gap, both sediments and groundwater were collected from the Hetao Basin, a typical arid-semiarid area hosting high arsenic groundwater, to characterize diagnostic biomarkers and compound-specific carbon isotopes of lipids in dissolved organic matter (DOM) and its depth-matched sedimentary organic matter (SOM). Results showed that SOM in both clay and sand layers were mainly sourced from terrestrial higher plants, but sand SOM had additional sources from microbial and petroleum OM. Compound-specific carbon isotope compositions of DOM and SOM showed that δ13C of low molecular weight (LMW) n-alkanes (δ13CL) were more positive than those of high molecular weight (HMW) n-alkanes (δ13CH). The δ13CH in groundwater (δ13CH-DOM) and sediments (δ13CH-SOM) fall in the range of C3 plants, indicating that DOM and SOM had similar origins. More positive δ13CL than δ13CH suggests preferential degradation of LMW compounds in both sediments and groundwater. In comparison with SOM, more microbial-derived OM was observed in groundwater DOM, especially in high‑arsenic groundwater. High arsenic groundwater was accompanied by the low ratio of n-alkanes to hopanes in depth-matched SOM, and the great difference between δ13CL and δ13CH and low terrestrial/microbial ratios (TAR) in groundwater DOM. This indicates that SOM and DOM should be utilized by indigenous bacteria to fuel the reductive dissolution of Fe oxides for arsenic release into groundwater. Furthermore, more abundant LMW compounds and weaker odd-to-even predominance in DOM than those in SOM support that DOM encountered stronger biodegradation. This study highlights that preferential biodegradation of DOM (especially LMW components and petroleum sourced OM) would provide electrons for the reductive dissolution of arsenic-bearing Fe/Mn oxides and thus induce arsenic enrichment in groundwater.

Structural, Optical, and Arsenic Removal Properties of Sol-Gel Synthesized Fe-Doped TiO2 Nanoparticles.

Pure and Fe-doped TiO2 nanoparticles were synthesized by the sol–gel method. The samples were characterized by X-ray diffraction, Raman spectroscopy, BET, UV-vis diffuse reflectance spectroscopy, and scanning electron microscopy. The results show a dependence between the crystallite size and the amount of dopant, which decreases from 13.02 to 12.81 nm. The same behavior was observed in the optical properties, where the band gap decreased from 3.2 to 2.86 eV. The arsenic (V) adsorption was tested in aqueous solution containing 5 mg/L of arsenic and 0.5 g/L of adsorbent at pH 7 and in dark conditions. The results indicate that the TiO2-B sample shows a higher arsenic removal, reaching 88% arsenic removal from the water at pH 7. Thus, it is also shown that the best performance occurs at pH 5, where it reaches an arsenic removal of 94%. Ion competition studies show that arsenic removal capacity is slightly affected by chloride, carbonate, nitrate, and sulfate ions. According to the results, the synthesized samples are a promising material for treating arsenic-contaminated water.

Parametric study of adsorption column for arsenic removal on the basis of numerical simulations

ABSTRACT Arsenic infectivity is a burning issue that causes skin infections, cancers and few hazardous impacts. This manuscript presents a computational fluid dynamic model of adsorption column using a commercially renowned CFD software FLUENT®14.2. A with 2-D geometry. The iron oxide (FeOH) was employed as an adsorbent with active reaction surface sites. Arsenic-contaminated water was lumped into single species called arsenious acid (H3AsO3) and allowed to react with FeOH particles. The turbulence parameters were modeled using the two-equations model. The governing equations for mass, momentum, energy and species transport have been solved for adsorption column. The significant parameters, for instance, adsorbent bed height (5, 10 and 15 cm), bed porosity (93%, 73%, 58% and 40%), initial concentration of arsenious acid (20–100%) and feed mass flow rate of contaminated water (0.01–0.1 Kg/s) have been investigated. The performance of adsorption column has been evaluated based on arsenic removal efficiency and pressure drop. Present results suggested that 10 cm adsorbent bed height, 58% bed porosity, 100% arsenious acid initial concentration with water and 0.01 Kg/sec contaminated water feed rate have shown remarkable performance in terms of more than 90% removal efficiency and less than 40 Pa pressure drop.