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Mechanism of Arsenic Release to Groundwater, Bangladesh and West Bengal
Abstract
In some areas of Bangladesh and West Bengal, concentrations of As in groundwater exceed guide concentrations, set internationally and nationally at 10 to 50 μg l−1 and may reach levels in the mg l−1 range. The As derives from reductive dissolution of Fe oxyhydroxide and release of its sorbed As. The Fe oxyhydroxide exists in the aquifer as dispersed phases, such as coatings on sedimentary grains. Recalculated to pure FeOOH, As concentrations in this phase reach 517 ppm. Reduction of the Fe is driven by microbial metabolism of sedimentary organic matter, which is present in concentrations as high as 6% C. Arsenic released by oxidation of pyrite, as water levels are drawn down and air enters the aquifer, contributes negligibly to the problem of As pollution. Identification of the mechanism of As release to groundwater helps to provide a framework to guide the placement of new water wells so that they will have acceptable concentrations of As.
... Depending on the composition of the sediments, along with other environmental variables such as salinity and degree of anthropogenic stress, As levels in estuarine sediments have been reported in the milligram range. For example, in Bangladesh, India, Nickson et al. [5] reported As concentrations between 10 and 196 mg/kg of sediment, while Chakraborti et al. [6] found Sustainability 2024, 16, 9728 2 of 12 values ranging from 9.0 to 28.0 mg/kg in sediments from the Ganges delta, India. Bai et al. [7] estimated sediment As concentrations of 8.79-13.73 ...
... A deeper understanding of estuarine fauna behavior may help inform conservation strategies, habitat management, and ecosystem restoration, ensuring that natural processes maintain biodiversity and ecosystem services in alignment with human activities. This study also highlighted that As concentrations may affect the behavioral traits of estuarine benthic fauna within the range of As concentrations reported previously as environmentally relevant, e.g., [5][6][7][8][9], emphasizing the need to continuously monitor and analyze As ecological impact [44]. As a legacy contaminant, the delivery and updating of data (as obtained here) may be capable of being framed in directives (such as the Marine Strategy Framework Directive, MSFD) to better address the sustainability and protection of ecosystems or even make public health considerations. ...
Estuaries are dynamic ecosystems exposed to a wide range of stressors, including metal (loid) contamination. The assessment of the behavioral characteristics of the species inhabiting these ecosystems may provide a new point of view on chemical contamination since these behaviors generally regulate population dynamics and ecosystem stability. Therefore, this study aimed to investigate the changes in behavioral patterns of three estuarine benthonic species (the native polychaete Hediste diversicolor, the non-native polychaete Arenicola marina, and the native clam Scrobicularia plana) when exposed to different concentrations of the metalloid arsenic (0, 0.5, 1.5, 4.5, 13.5, 40.5 mg/kg sediment). Behavioral assessment included bioturbation activity (measured by fluorescent particle remobilization) and determination of the maximum penetration depth by each species, both after 1 and 21 days of exposure. After 21 days of exposure, the ability of each species to burrow was evaluated. Results showed that the bioturbation activity of S. plana was immediately reduced by exposure to As (day 1) but disappeared with exposure time (day 21), whereas A. marina bioturbation activity was significantly increased from day 1 to day 21, expressing their highest values in sediments of 4.5, 13.5, and 40.5 mg of As/kg on day 21. For H. diversicolor, no changes were observed within each time or between the times. Results of the burrowing assay showed that A. marina nearly doubled its burrowing time, as well as increased in double its maximum penetration depth at As concentrations ≥1.5 mg/kg sediment. These results suggest that native species can be quite resilient to chemical contamination over time. However, the greater particle remobilization by the non-native species A. marina when exposed to As may cause displacement of the native fauna, disrupting the natural mutualism created in these environments, and possibly decreasing estuary functionality and biodiversity. Behavioral assessments under chemical exposure may improve the establishment of more feasible protection goals for more sustainable estuaries.
... It is seen that aquifer having either reducing or oxidizing conditions are associated with high As in groundwater (Bhattacharya et al., 1997;Peter et al., 1999). During reduced anaerobic conditions in the aquifer, As-rich Fe oxyhydroxide coatings on sedimentary grains dissolve reductively, controlled by bacterial breakdown of organic material (Nickson et al., 1998;Nickson et al., 2000;Polizotto et al., 2008). Studies found that As release from the Himalayan sediments is initiated at the transition of aerobic and anaerobic conditions (Fendorf et al., 2010). ...
... We propose that the shallow groundwater in the Ganges delta undergoes this reductive release of Mn. Fe, on the other hand, is spatially correlated with HCO 3 due to the reductive dissolution of Fe oxyhydroxides in existence of organic material (e.g., Nickson et al., 2000;McArthur et al., 2001;Mukhopadhyay et al. 2006;Sengupta et al., 2022) (Fig. 9). ...
Geochemical studies of groundwater from 302 tubewells and aquifer sediments of the Ganges delta plain of Quaternary age are conducted. The geochemical behaviour of Fe, Mn, SO4, arsenic (As), REEs, and Eu parameters in groundwater indicates two contrasting environments: (i) a more oxic condition in the fluvial environment of the Jalangi River in the northern part, and (ii) a less oxidizing/reducing environment in the paleo-lacustrine environment towards south of the study area. Arsenic concentration in groundwater is more in paleo-lacustrine environment due to (i) reductive desorption from Fe-oxyhydroxide in the high pH reducing environment and (ii) mobilization by ion exchange with the help of fertilizer used in agricultural activities. Both these phenomena are attributed to the strong spatial correlation of arsenic (As) with pH, PO4, and SO4. However, the dissimilar nature of REE pattern in groundwater and aquifer sediment indicates that REE geochemistry of groundwater is being modified by the “reductive dissolution of Fe-oxyhydroxides” in sediment which releases REE into the groundwater. We conclude that desorption and “reductive dissolution of Fe-oxyhydroxide” controls release of As and REE into the groundwater in both oxic and reducing aquifer conditions in the Ganges delta.
... The cause of local-scale heterogeneity of the As distribution is still unresolved 236 but might be related to the distribution of alluvium along flood plains 209 , sedimentation patterns 237 , micro-topographic variability 120,122,124 , palaeosol distributions 238,239 , local-scale groundwater flow 185,240 and/or recharge pathways 155,191,241 . Arsenic is hypothesized to be mobilized by microbially mediated 57,149,240 , redox-dominated dissolution of metal (oxyhydr)oxides 47,112,117,127,148 existing mostly as surface coatings on finer-grained sediments 146,234,242 and accentuated by massive irrigation pumping 118,165,182,185,190,191 . Earlier plausible hypotheses that were unsupported by ground observations suggested possible As release from the oxidation of sulfide minerals 243 and competitive ion exchange with dissolved phosphate from fertilizer 244 . ...
... For example, fluvial patterns and sedimentation control As and U distributions in South Asian flood plains and deltas, with greater accumulation within younger fine-grained sediments and channel scrolls than in interfluves, uplands and erosional surfaces 117,122-124 (Fig. 3). In the Bengal Basin, the late Quaternary geomorphology is suggested to strongly influence groundwater As distribution as a result of changes in sedimentation patterns induced by Holocene sea-level change 120,125,126 , which modified the coastal morphology through the formation of wetlands and peat swamps that form conducive geochemical environments for As accumulation and sequestration 59,119,125,127,128 . Pervasive As distribution is also documented in the arid uplands and plateaus of the Altiplano-Cordilleran basins 107,121,129 . ...
Geogenic groundwater contaminants (GGCs) affect drinking-water availability and safety, with up to 60% of groundwater sources in some regions contaminated by more than recommended concentrations. As a result, an estimated 300-500 million people are at risk of severe health impacts and premature mortality. In this Review, we discuss the sources, occurrences and cycling of arsenic, fluoride, selenium and uranium, which are GGCs with widespread distribution and/or high toxicity. The global distribution of GGCs is controlled by basin geology and tectonics, with GGC enrichment in both orogenic systems and cratonic basement rocks. This regional distribution is broadly influenced by climate, geomorphology and hydrogeochemical evolution along groundwater flow paths. GGC distribution is locally heterogeneous and affected by in situ lithology, groundwater flow and water-rock interactions. Local biogeochemical cycling also determines GGC concentrations, as arsenic, selenium and uranium mobilizations are strongly redox-dependent. Increasing groundwater extraction and land-use changes are likely to modify GGC distribution and extent, potentially exacerbating human exposure to GGCs, but the net impact of these activities is unknown. Integration of science, policy, community involvement programmes and technological interventions is needed to manage GGC-enriched groundwater and ensure equitable access to clean water. Sections
... there are various possible explanations for the high concentration of dissolved as. among them is the participation of competing anions in the release of sorbed arsenate, as-oxidation pyrite with high redox potential, reduction of freely adsorbed arsenate to arsenite, and reductive dissolution of iron hydroxides containing arsenic at low redox potential [5][6][7][8][9][10]. ...
Soil collected from random areas of non-ferrous mines and smelters was studied in order to develop a low-cost but effective method for quantifying arsenic (III), arsenic (V), and total arsenic in contaminated soil. Hydrochloric acid microwave extractions have been used as a method to digest arsenic from soil in a form of solution suitable for speciation. Arsenic (III) is selectively extracted into benzene as arsenic trichloride from a highly concentrated hydrochloric acid solution. This was followed by the arsenic being extracted back into water. The total inorganic content of arsenic (V) can be directly determined by anodic oxidation of a gold screen-printed electrode using electrochemical detection. The amount of available Arsenic (III) in the sample is determined by pre-oxidation with KMnO4 directly added to the electrochemical cell or by directly increasing the pH of the medium. ICP-MS was used to confirm all analyses for the various arsenic species as well as the discovery of total arsenic in the soil. It was discovered that the electrochemical method used allows for the cheap, quick, and selective determination of micro amounts of arsenic forms in contaminated soils.
... Approximately 61% of the groundwater samples in wet season and almost 97% samples exceeded the BDWS limit for manganese in dry season. Microbial activity in organic-rich sediments and peats in shallow aquifers creates reductive conditions that promote the dissolution of manganese oxides and hydroxides, resulting in elevated manganese concentrations under anoxic or suboxic conditions [52,[71][72][73]. Despite its critical role in enzymatic processes associated with fatty acids and cholesterol metabolism, excessive manganese in groundwater remains a significant health concern [44]. ...
Introduction
Groundwater contamination by potentially toxic elements (PTEs) poses serious health risks in Bangladesh, yet limited studies have addressed their seasonal and spatial variability. In the Barind Tract, Rajshahi, groundwater is a critical resource for drinking and irrigation, emphasizing the need for a comprehensive evaluation of contamination patterns and health implications.
Methods
A total of 244 groundwater samples (122 per season) were analyzed for As, Al, Cu, Mn, Cr, and B using Atomic Absorption Spectrophotometry and VIS Spectrophotometry. Contamination was assessed using Metal Evaluation Index (MEI), Nemerow Pollution Index (NPI), Contamination Degree (CD), and Poseidon Index (PoS). Statistical analyses included ANOVA, effect size (η², f²), PCA, and HCA. Monte Carlo simulation (10,000 iterations, 95% CI) estimated probabilistic health risks for adults and children.
Results
Boron (1.034 mg L⁻¹) and manganese (0.824 mg L⁻¹) dominated during the wet season, while manganese (0.735 mg L⁻¹) and aluminum (0.605 mg L⁻¹) were highest in the dry season. MEI, NPI, and CD indices indicated significant contamination in Sirajganj, Chapai Nawabganj, and Natore, with Chapai Nawabganj (PoS 9.01) and Natore (PoS 8.223) showing extensive groundwater degradation. Statistical analyses confirmed significant seasonal variations, with aluminum, copper, chromium, and boron showing the most fluctuation due to hydrological and geochemical changes. Health risk assessments identified 64 samples unsafe for children and 32 for adults, with Monte Carlo simulations indicating hazard indices reaching up to 4.68 for children in certain hotspots.
Conclusions
Pronounced seasonal variations in groundwater contamination underscore the necessity of targeted, season-specific monitoring and mitigation measures. Tailored interventions are essential to safeguard public health, especially for children who face higher exposure risks. The findings offer critical insights for policy-makers and stakeholders, promoting sustainable groundwater management in the Barind Tract.
... The interaction between groundwater and aquifer sediments significantly influences the abundance and distribution of trace elements (Nickson et al., 2000). Geochemical processes within the subsurface environment lead to the exchange of different elements between groundwater and sediments (Mukherjee et al., 2016). ...
A geochemical investigation on occurrence of trace elements in the shallow aquifer of Bhanga Upazila of Faridpur District has been carried out which has not been done in this area before. Six environmentally hazardous metals (Pb, Cu, Cd, Co, Ni, Zn) were measured in the shallow aquifer sediments using Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). Sediment samples (n = 7) were collected from two boreholes and analyzed for the elemental abundance, pollution status, and probable ecotoxicological risk. Three environmental pollution indices namely the enrichment factor (EF), geo-accumulation (I geo) and pollution load index (PLI) were estimated to assess the contamination level. The different indices suggest that the sediments are contaminated with Cd, Pb, Ni, and Co which may cause acute-chronic health problems. These are likely contributed from both anthropogenic and lithogenic (rock weathering, leaching, and cation exchange) sources. However, inversely the enrichment of hazardous elements in the sediment may indicate that the aquifer sediments may have very good absorption capacity and inhibit the metals to be released in the groundwater. The outcome of this study suggests a potential threat to the environment as well as to the community health of nearby inhabitants in case the elements are released in the environment. Thus, strict regulation and efficient management should be focused on monitoring and appraisal of heavy metals in the shallow aquifer of the area.
... The Fe Total concentration in river water is within BDS limit. Groundwater containing high levels of As is commonly found in shallow groundwater (<100 m) beneath the Quaternary-Recent Ganges, Brahmaputra and Meghna (GBM) floodplains (BGS and DPHE, 2001;Nickson et al., 2000;Smedley et al., 2002;van Geen et al., 2003;Hasan et al., 2007). No study has reported the presence of a relatively high concentration of As WHO limit (>10 µg/L) in the hill districts of Chittagong. ...
The people living in the Kaptai-Lichubagan roadcut area of Kaptai Upazila in Rangamati Hill District, Bangladesh, rely on groundwater for drinking. This study aims to investigate the hydrochemistry of groundwater and river water, associated hydrochemical processes and to assess drinking water quality. In total, 26 water samples were collected for laboratory analysis; 22 from groundwater at depths ranging from 9 to 198 meters, and 4 from Karnaphuli river. Both groundwater and river water pH levels suggest acidic to neutral water. Electrical conductivity (EC) values also indicate mostly fresh groundwater and river water, and EC of groundwater varies both spatially and vertically. The total hardness (TH) of groundwater suggests moderately hard to very hard water, whereas the river water is mostly soft. Most groundwater samples are either Ca-Mg-HCO3 type or mixed Ca-Na-HCO3 and Ca-Mg-SO4-Cl type. In contrast, all the river water samples are Ca-Mg-HCO3 type. Groundwater exhibit variable polygonal shapes in stiff diagrams, characterized by relatively low to moderate major ions. However, there is one sample which shows higher cations suggesting anthropogenic influence. River water show similar patterns but smatter shapes characterized by relatively low major ions. Groundwater is primarily influenced by water-rock interaction andsilicate weathering is the dominant controlling factor of groundwater chemistry, followed by carbonate dissolution. Groundwater samples are mostly undersaturated with minerals - calcite, dolomite, gypsum, and siderite, which possess the potential for dissolution. None samples exceed the Bangladesh drinking standard (BDS) for As (50 µg/L). River water is also As safe. While As shows no spatial variability, FeTotal shows significant spatial variability in the study area. Water Quality Index (WQI) indicates about 90% water samples including most groundwater and all river water samples is of excellent quality for consumption Routine monitoring of the water quality in this area is recommended to ensure its continued safety. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 13(2), 2024, P 31-47
... Elevated level of As in the human body causes long-term health effects such as skin cancers, muscle fatigue and digestive system disturbance [14][15][16]. In Bangladesh, the geogenic process under natural reducing conditions is the main reason to release of As in groundwater, which deteriorates the groundwater quality [17][18][19][20][21]. Further, several studies stated that the processes of mobilization were also involved with groundwater abstraction [22][23][24]. ...
Quantification of the non-linear relationship between arsenic (As) and physico-chemical parameters in groundwater through a Self-Organizing Map (SOM) was performed for the first time in Chapai-Nawabganj, Bangladesh. Due to the continuous assessment of groundwater quality, the spatial distribution of As with associated elements was observed for the aerial extent of contaminated groundwater. The results exhibited that 57 % and 31 % of groundwater samples (n = 35) exceeded the allowable limit of As according to the WHO recommended drinking water standard (10 μg/L) and Bangladesh Drinking Water Standard (BDWS) (50 μg/L), respectively. The spatial distribution map of As demonstrated that a higher concentration of As in groundwater was found in the central portion of the study area and less amount was observed in the eastern part. Whereas 83 % of the samples for iron (Fe) concentration in groundwater surpassed the WHO guideline limit (0.3 mg/L) and were distributed all over the area except in the central part. Moreover, manganese (Mn) concentration varied from place to place within the allowable limit of WHO. The SOM analysis elucidated the non-linear relationship of As with other elements in two-dimensional planes of having 49 nodes (7 × 7), which incorporated with Spearman's correlation coefficient quantified the positive correlation among As, Mn and Ca, and negative correlation among As, Fe, EC and pH. In accordance with human health risk was also explained in terms of non-carcinogenic and carcinogenic risk. Health risk assessment demonstrated that higher health hazard (HQ) values in 57 % of the samples exceeded the threshold value for adults through the oral route, which implied the potential non-carcinogenic health risk, while 63 % of the samples for cancer risk (CR) was higher than the allowable limit indicating the considerable cancer risk zone for the residents of the area. This analysis provides information to the planners for formulating effective groundwater resources management and minimizing health sustainably.
... As was adsorbed on the surface of Fe and Mn oxides. The bicarbonate solution can effectively extract As adsorbed on the surface of iron hydroxide, indicating that the bicarbonate solution can activate As in sediments, thereby replacing As on the surface of sediments and minerals and releasing it into the groundwater [29,30]. Therefore, F2 represented the adsorption release factor. ...
The Aksu River Basin is located in the western region of the middle part of the southern foothills of the Tianshan Mountains and the northwestern edge of the Tarim Basin in Xinjiang, China. High-arsenic (As)/high-fluoride (F) groundwater is widely distributed in this area and is harmful to the life of local residents and to agricultural production. It is of great importance to understand the distribution and causes of As-F co-enrichment in the groundwater in this area. Based on the test results of 138 groundwater samples in the plain area of the Aksu River Basin, the hydrochemical characteristics of groundwater and the spatial distribution of As-F co-enrichment groundwater were analyzed under the following conditions: a single-structure phreatic aquifer (SSPA), a phreatic aquifer in a confined groundwater area (PACGA), a shallow confined aquifer (SCA), and a deep confined aquifer (DCA), all in a recharge area, transition area, and an evaporation area. The hydrogeochemical processes affecting the source, migration, and enrichment of As-F in the groundwater were revealed. The results showed that the chemical types of groundwater in the study area were mainly HCO3·SO4-Ca·Mg and SO4·Cl-Na·Mg. Horizontally, high-As-F groundwater was mainly distributed in the transition area and evaporation area in the middle and lower reaches of the Aksu River Basin. The area is close to the edge of the desert, where the groundwater runoff is sluggish and in an alkaline-reducing groundwater environment. Vertically, high-As groundwater was mainly distributed in the PACGA at a depth of 10–20 m and in the SCA at a depth of 80–100 m. High-F groundwater was mainly concentrated in the PACGA at a depth of 10–30 m and in the SCA at a depth of 80–100 m, and As-F co-enrichment groundwater was mainly concentrated in the PACGA at a depth of 10–20 m and in the SCA at a depth of 80–100 m. The hydrochemical characteristics of the groundwater in the Aksu River Basin were closely related to geological conditions, hydrogeological conditions, and the hydrochemical environment of the groundwater. As-F co-enriched groundwater was mainly affected by the combination of a small topographic gradient, a shallow groundwater burial depth, a weak reducing alkaline groundwater environment, strong evaporation and concentration, the weathering and dissolution of evaporated salt rock, and the alternating adsorption of cations.
... Arsenic is commonly found in shallow aquifers, with its sources attributed to the reductive dissolution of iron oxyhydroxide and altered mica. Metal-reducing bacteria also play a significant role in mobilizing arsenic in sediments [30,68]. Manganese is present in both shallow and deep aquifers and is released into groundwater through the oxidation of organic matter and peat. ...
Groundwater is the main source of potable water in rural regions of Bangladesh. Still, contamination with potentially harmful metals due to natural processes and anthropogenic activities leads to various health impacts. The focus of this research was to determine the extent of metal contamination in shallow groundwater from three southwestern districts of Bangladesh and the health hazards associated with it. A comprehensive analysis of metal, including metalloid, copper (Cu), aluminum (Al), chromium (Cr), Arsenic (As), Manganese (Mn), and boron (B) was performed on a set of 51 samples. Groundwater samples were analyzed for contamination using Atomic Absorption Spectroscopy and a UV–VIS Spectrophotometer, with pollution levels assessed via indices like the Metal Evaluation Index, Nemerow Pollution Index, and Contamination Index. Human health risks were evaluated through Chronic Daily Intake, Hazard Quotient, and Hazard Index calculations following USEPA guidelines. The results indicate that arsenic levels exceeded 25 samples and manganese levels exceeded 34 samples in accordance with WHO drinking water standards. Boron (B) concentrations exceeded the threshold in seven samples, whereas Al, Cu, and Cr exceeded limits in only two samples. The metal evaluation index (MEI), Nemerow pollution index (NI), and degree of contamination (Cd) revealed moderate to severe contamination in groundwater and unsuitability for drinking purposes. Out of the 51 analyzed samples, 48 samples exhibited potential non-carcinogenic health risks for adults, while all samples exceeded the hazard index (HI) threshold value (01) for children. Concentrations of As and Mn were identified as the main contributing factors to the higher HI values in both adults and children. However, the concentrations of Cu, Al, Cr, and B in groundwater were not individually found to be as risky. This study provided valuable insights to conduct a future comprehensive investigation of the designated region to delineate safe and hazardous zones for the installation of shallow tubewells. Furthermore, there's a need to enhance public awareness regarding the long-term ramifications of consuming contaminated water.
... The arsenic contamination in soil and stream sediment at traditional gold mining Wonogiri area, Central Java reaches up to 385 mg/kg, even though the arsenic mineral is rare (Harijoko et al., 2010). The heavy metals contamination in the water is not all from anthropogenic process but some of them controlled by natural condition such as arsenic contamination in Bangladesh and West Bengal (Nickson et al., 2000) and Buyat Indonesia (Wilopo et al., 2006) In order to understand the effect of traditional gold mine and processing in Murung Raya District, Central Kalimantan to the environment especially for surface water, some water samples were taken from the field to analysis. In addition, analysis of sediment samples was also conducted to understand the source of water contaminant from human activities or natural process. ...
There are many locations for traditional gold mining in Indonesia. One of these is in Murung Raya District, Central Kalimantan Province. Mining activities involving the application of traditional gold processing technology have a high potential to pollute the environment, especially surface water. Therefore, this study aims to determine the impact of gold mining and processing on surface water quality around the mine site. Based on the results of field surveys and laboratory analysis, our data shows that the concentration of mercury (Hg) and Cyanide (CN) has reached 0.3 mg/L and 1.9 mg/L, respectively, in surface water. These values exceed the drinking water quality standards of Indonesia and WHO. Many people who live in the mining area use surface water for daily purposes including drinking, cooking, bathing and washing. This scenario is very dangerous because the effect of surface water contamination on human health cannot be immediately recognized or diagnosed. In our opinion the dissemination of knowledge regarding the treatment of gold mining wastewater is urgently required so that the quality of wastewater can be improved before it is discharged into the environment
... Compared to the Hetao Basin, soil organic carbon content was more pronounced in influencing groundwater As concentration. The aquifer sediments in Bangladesh contain OM and peat, as reported in several studies [74,75]. The degradation of OM within the aquifer generates DOC [76]. ...
Arsenic (As) contamination in groundwater represents a major global health threat, potentially impacting billions of individuals. Elevated As concentrations are found in river floodplains across south and southeast Asia, as well as in the inland basins of China, despite varying sedimentological and hydrogeochemical conditions. The specific mechanisms responsible for these high As levels remain poorly understood, complicating efforts to predict and manage the contamination. Applying hydro-chemical, geological, and soil parameters as explanatory variables, this study employs multiple linear regression (MLIR) and random forest regression (RFR) models to estimate groundwater As concentrations in these regions. Additionally, random forest classification (RFC) and multivariate logistic regression (MLOR) models are applied to predict the probability of As levels exceeding 10 μg/L in the Hetao Basin (China) and Bangladesh. Model validation reveals that RFR explains 80% and 70% of spatial variability of As concentration in the Hetao Basin and Bangladesh, respectively, outperforming MLIR, which accounts for only 35% and 32%. Similarly, RFC outperforms MLOR in predicting high As probability, achieving correct classification rates of 98.70% (Hetao Basin) and 98.25% (Bangladesh) on training datasets, and 82.76% (Hetao Basin) and 91.20% (Bangladesh) on validation datasets. The performance of the MLOR model on the validation set yields accuracy rates of 81.60% and 72.18%, respectively. In the Hetao Basin, Ca²⁺, redox potential (Eh), Fe, pH, SO4²⁻, and Cl⁻ are key predictors of As contamination, while in Bangladesh, soil organic carbon (SOC), pH, and SO4²⁻ are significant predictors. This study underscores the potential of random forest (RF) models as robust tools for predicting groundwater As contamination.
... Later on, the magnitude of groundwater arsenic contamination above 10 and 50 µg/L was reported in 148 blocks from 14 districts and 111 blocks from 12 districts, respectively Sengupta et al., 2009). The source of arsenic in groundwater is geogenic and mainly caused due to the reductive dissolution of arsenic-rich iron oxyhydroxide minerals (Nickson et al., 2000). Therefore, this natural occurrence is catalyzed with time due to excessive groundwater withdrawal and sheer negligence of the local government. ...
Groundwater arsenic contamination in West Bengal, India is a prolonged existing environmental hazard where millions of people are exposed to arsenic toxicity. At present, 132 blocks covering 12 districts in the state have groundwater arsenic concentration above its recommended limit in drinking water. Number of arsenic-affected habitations has amplified by 145% in India from the year 2015 to 2020 (https://www.downtoearth.org"xmlns:xlink="https://www.w3.org/1999/xlink">https://www.downtoearth.org. in/news/governance/arsenic-affected-habitations-in-india-up-145-in-last5-yrs-73450). The districts like Maldah, Murshidabad, Nadia, North 24 Parganas, and South 24 Parganas are most adversely affected where numerous people are suffering from arsenic-related diseases including children. Being an agriculture-dependent state, every year a huge amount of groundwater is withdrawn to reach the irrigational demand. Therefore, arsenic contamination in food chain especially through rice grain, pulses, and vegetables has become an additional health burden in recent years which is spread in apparently unexposed areas too due to the transportation of contaminated foodstuffs. However, rainwater plays an important role in scaling down of arsenic concentration in cultivable foodstuffs. According to our study, monsoonal rice grain is safer to consume than premonsoon grains as the 20former one accumulates much lesser arsenic. Post harvesting treatments of paddy grain through two-way boiling process using arsenic-contaminated groundwater increase the arsenic burden in parboiled rice grain in comparison to sunned rice grain. Cooking of raw rice with highly arsenic-contaminated water causes an entry of arsenic from water to rice while cooking with lower arsenic-contaminated water draws out arsenic from rice into gruel. Inorganic arsenic has been observed to be the dominating one among the other species in both raw and cooked rice, while for both rice and vegetables, arsenite, and arsenate are more in amounts than DMA.
... In Chapainawabganj, Northwestern Bangladesh, weathering rocks or metal sulfide oxidation may be the source of arsenic, a trace element in rocks and soils; however, there is little evidence to support this theory based on data on dissolved sulfate (Reza et al. 2010). Surface water transports released arsenic, which is highly taken up in an aquatic environment by iron oxides and sediments in streams (Nickson et al. 2000). ...
Groundwater in northwestern parts of Bangladesh, mainly in the Chapainawabganj District, has been contaminated by arsenic. This research documents the geographical distribution of arsenic concentrations utilizing machine learning techniques. The study aims to enhance the accuracy of model predictions by precisely identifying occurrences of groundwater arsenic, enabling effective mitigation actions and yielding more beneficial results. The reductive dissolution of arsenic-rich iron oxides/hydroxides is identified as the primary mechanism responsible for the release of arsenic from sediment into groundwater. The study reveals that in the research region, alongside elevated arsenic concentrations, significant levels of sodium (Na), iron (Fe), manganese (Mn), and calcium (Ca) were present. Statistical analysis was employed for feature selection, identifying pH, electrical conductivity (EC), sulfate (SO4), nitrate (NO3), Fe, Mn, Na, K, Ca, Mg, bicarbonate (HCO3), phosphate (PO4), and As as features closely associated with arsenic mobilization. Subsequently, various machine learning models, including Naïve Bayes, Random Forest, Support Vector Machine, Decision Tree, and logistic regression, were employed. The models utilized normalized arsenic concentrations categorized as high concentration (HC) or low concentration (LC), along with physiochemical properties as features, to predict arsenic occurrences. Among all machine learning models, the logistic regression and support vector machine models demonstrated high performance based on accuracy and confusion matrix analysis. In this study, a spatial distribution prediction map was generated to identify arsenic-prone areas. The prediction map also displays that Baroghoria Union and Rajarampur region under Chapainawabganj municipality are high-risk areas and Maharajpur Union and Baliadanga Union are comparatively low-risk areas of the research area. This map will facilitate researchers and legislators in implementing mitigation strategies. Logistic regression (LR) and support vector machine (SVM) models will be utilized to monitor arsenic concentration values continuously.
... Microorganisms can play a role in toxic arsenic release indirectly via the oxidation of organic carbon coupled to the reduction of arsenic-bearing iron oxyhydroxides. This then causes the opposite of the SAR process, i.e., dissolution of the arsenic-bearing iron oxyhydroxides and the subsequent release of arsenic in the more mobile arsenite form [187][188][189]. Microorganisms may also cause arsenite release directly via the utilization of arsenate as an electron acceptor [77,190]. An important factor in both processes is the organic matter that is used as an electron donor for metal reduction by the indigenous microbial community in aquifers. ...
The arsenic adsorption performance of silicon (Si), iron (Fe), and magnesium (Mg) mixed hydrous oxide containing a Si: Fe: Mg metal composition ratio of 0.05:0.9:0.05 (SFM05905) was investigated. SFM05905 was synthesized by the co-precipitation method. Batch experiments on arsenic adsorption were conducted at various temperatures and concentrations. Adsorption isotherms models were represented by a linearized equations and were insensitive to temperature change. The anion selectivity of SFM05905 at single component was high for arsenite (III), arsenate (V), and phosphate (PO4), indicating that PO4 inhibits arsenic adsorption. The adsorption amount of As (III), As (V), and PO4 were compared using a column packed with granular SFM05905, and an aqueous solution was passed by a combination of several anions that are single, binary, and ternary adsorbate systems. As (III) had the highest adsorption amount; however, As (III) and PO4 were affected by each other under the ternary mixing condition. Although the adsorption amount of As (V) was smaller than that of As (III), it was not affected by other adsorbates in the column experiments. Finally, although the adsorption of both arsenic continued, the adsorbed PO4 gradually desorbed.
... Along the Hooghly River, the concentrations of As and Fe in the riverbank sediments increased downstream (Table 1, Fig. 2), corresponding with the deposition of finer grained sediments along with increasing tidal influence. Furthermore, the riverbank lithology relates to the mineralogy of Fe in the HZ, which in turn plays an important role in regulating the mobility of As [22,29]. Within the sandy sediments, Fe exists primarily as Fe-oxides, which are a favorable adsorbent for As under near-neutral pH [12]. ...
... As polluted soil and sediments have been found in several Indian states; these areas are depicted in Fig. 1 (CGWB, 1999;CGWB, 2004;Pandey et al., 2011;Postma et al., 2007;Sharma and Sohn, 2009;Somani, 2001;Srivastava & Sharma, 2012). In the Bengal Basin, arsenic can be mobilised through a few different processes: arsenic can be released into alluvial sediments by oxidising arsenic-containing pyrite (Machlis, 1941;Mallick & Rajagopal, 1996;Raskin et al., 2000), arsenic can be released into anoxic conditions by reducing iron oxyhydroxide during sediment burial(McArthur et McArthur et al., 2001;Nickson et al., 1998;Nickson et al., 2000;Ravenscroft et al., 2005;Ravenscroft et al., 2001), or arsenic can be released into aquifer sedimentary minerals by phosphate anions used in fertilisers that are applied on the soil surface (Acharyya etal., 1999;Acharyya etal., 2000;Ravenscroft et al., 2005;Ravenscroft et al., 2001). ...
Arsenic contamination is serious issues due to the severity of arsenic contamination and the large number of people affected directly or indirectly now a days. The level of contaminant has spread over the soil and sediments from ground water and other natural resources. The world is aware of arsenic poisoning in groundwater occurrences, but the community especially the residents in affected countries is still unaware of the effects of soil contamination. Regarding arsenic contamination through crops and vegetables, people and other living forms are extremely concerned. Over time, numerous remediation technologies have been developed to examine their impacts. These technologies mostly consist of physical, chemical, and a few biological techniques. The physical and chemical approaches used for this goal are frequently ineffective, costly, and only suitable for use in aqueous systems. They also result in hazardous sludge, which raises further concerns. However, bioremediation offers appealing possibilities for biomonitoring, wastewater treatment, and the recycling of contaminated soils because it is predicated on the notion that biological organisms have the capacity to break down, detoxify, and even accumulate hazardous materials.
Widespread occurrence of geogenic groundwater contaminants, such arsenic (As), poses a significant health risk to millions of people worldwide through ingestion of contaminated drinking water. However, the (co)occurrence of other, less studied contaminants that may be sourced from similar geological settings, are less documented. Here, for the first time, we document the (co)occurrence of excess concentrations of nickel (Ni) in the intensely As-enriched groundwater from the alluvial aquifers of the Brahmaputra River Basin (BRB). Approximately 30 % of the sampled groundwater (n = 70) exceeds the drinking water guideline value of 20 µg/L for Ni, while around 20 % of samples contain both Ni (>20 µg/L) and As (>10 µg/L). Furthermore, the groundwater also has elevated levels of Fe (up to 19 mg/L) and Mn (up to ∼ 5 mg/L). The groundwater is mildly oxidizing to strongly reducing (Eh 234 mV to −72 mV), with dominant hydrogeochemical facies ranging from Ca-Mg-HCO3 to Na-HCO3 type. Linear correlation shows that Ni has a strong positive correlation with Fe (r = 0.9), As (r = 0.84), and Mn (r = 0.68) in the northern bank of the Brahmaputra River, while having a less prominent relationship with Fe (r = 0.78), As (r = -0.35) and Mn (r = 0.46) in the southern bank. We hypothesize that Ni-rich rocks from the Indus-Tsangpo suture zone and the Tidding suture serve as the primary sources of geogenic Ni in the BRB, transported and deposited by the Brahmaputra (Siang/Tsangpo) and Lohit rivers, forming the alluvial plains. We suggest that the reductive dissolution of Fe-oxyhydroxides is the primary mechanism of Ni and As release in the groundwater on the northern bank of BRB. At the same time, Fe and SO42− −reduction play an active role in the contaminant mobilization in the southern bank. The emergence of (co)occurring geogenic contaminants, such as Ni, increases the health risk for millions of residents in the study area, who are already exposed to excessive levels of As in groundwater-sourced drinking water.
Managed aquifer recharge (MAR) is an important engineering solution for achieving sustainable groundwater management. Unfortunately, if not operated properly, MAR can cause undesirable arsenic mobilization in groundwater. To avoid unexpected...
Detail studies on arsenic (As) pollution on the eastern side of the River Hugli in the Bengal Basin suggest that the concentration of As in groundwater is strongly controlled by the sub-surface distribution of palaeo-channel (PC) aquifer (depth < 70 m; As-polluted), Last Glacial Maximum Palaeosol (LGMP), at depths variable between 34 and 36 m, and palaeo-interfluvial (PI) aquifer (depth 36–70 m; As-free). The groundwater on the western side of the river is generally thought to be As-free, except in few local pockets. The present study area is one such pocket and has been reported to abstract sizeable quantity of groundwater for drinking and agricultural purposes. This study, for the first time, tries to understand whether As-pollution in the western bank of the river is similarly controlled by the distribution of PC and PI aquifers. The model is tested by mapping the colour of the well completion of 148 wells, drilling 22 boreholes up to depth of 46 m and testing 141 groundwater samples collected from depth range of 10–75 m in field and laboratory for As, Fe and Mn. The well-completion colour survey and field and laboratory testing of As reveal that wells with black stains on well completion are As-free while those with red stains on well completion are As-polluted. Drilling indicates that the shallow palaeo-channel (SPC, depth < 29 m) aquifer and deep palaeo-channel (DPC, 29–70 m) aquifer consisting of grey sands have >10 μg/L As, and PI aquifer made of brown sands have <10 μg/L As. Chemical analysis of As, Fe and Mn in groundwater samples reveals that PI aquifer and deep aquifer (>70 m depth) groundwaters have low concentrations, whereas palaeo-channel groundwaters have high concentrations of these elements. Therefore, use of PI and deep aquifers instead of PC aquifers would mitigate the health risks from consumption of As-polluted groundwater at an affordable cost.
In this work, the influence of initial solution pH on membrane performance was carried out for arsenic (III) removal using spiral wound polyethersulfone (HFN300) Nanofiltration membrane at pilot scale. The rejection percentage was found to increase from 49 % to 96 % while increasing initial solution pH from 4 to 10. Speciation of arsenic, solute-membrane affinity, electric-migration effect along with convection and diffusion were found to be dominant mechanisms for arsenic removal. Donnan Steric Pore Model was selected to estimate the membrane parameters including pore radius (0.313 nm), membrane thickness (2.17 μm), and membrane charge density (-3.56 mol/m3).Excellent agreements were found between the experimental and simulated values for all the studied pH range. Selected model works satisfactorily within 10 % of error for both rejection percentage and permeate flow. Economic feasibility study was carried out for the rural population (India) and total annualized cost was found to be USD 0.90/m3 that seems both reasonable and affordable for arsenic free drinking water. It can be concluded that annualized production cost was dependent on membrane lifespan, electricity tariff, per capita, population size, arsenic feed concentration, etc. The result obtained in the study suggests the feasibility of using the NF process in removing arsenic from contaminated water. Overall, the study provides valuable insights into the mechanisms governing arsenic (III) removal through nanofiltration process using spiral wound polyethersulfone nanofiltration membrane at pilot scale, demonstrating the effectiveness of pH optimization and membrane modelling in improving removal efficiency, which can contribute to the development of cost-effective solutions for safe drinking water in arsenic-affected rural areas.
Karst terrains provide drinking water for about 25% of the people on our planet, particularly in the southwest of China. Pollutants such as arsenic (As) in the soil can infiltrate groundwater through sinkholes and bedrock fractures in karst terrains. Despite this, the underlying mechanisms responsible for As release from karst soils under redox changes remain largely unexplored. Here, we used multiple synchrotron-based spectroscopic analyses to explore As mobilization and
sequestration in As-polluted karstic soil under biogeochemical conditions that
mimic field-validated redox conditions. We observed that As in the soil exists
primarily as As(V), which is mainly associated with Fe(oxyhydr)oxides. The
concentration of the dissolved As was high (294 μM) and As(III) was dominant
(∼95%) at low Eh (≤−100 mV), indicating the high risk of As leaching under
reducing conditions. This As mobilization was attributed to the fact that the
dissolution of ferrihydrite and calcite promoted the release and reduction of
associated As(V). The concentration of the dissolved As was low (17.0 μM) and
As(V) was dominant (∼68%) at high Eh (≥+100 mV), which might be due to the oxidation and/or sequestration of As(III) by the recrystallized ferric phase. Our results showed that the combined effects of the reductive release of As(V) from both ferric and nonferric phases, along with the recrystallization of the ferric phase, govern the redox-induced mobilization and potential leaching of As in soils within karst environments.
The exposure to groundwater arsenic contamination has ensued acute as well as chronic arsenicosis including death among more than 300 million global populations. Intake of arsenic-contaminated groundwater for drinking purpose in conjunction with crops, pulses, vegetables, and fruits cultivated with the contaminated water collectively induces toxicity in human food chain. Multiple geogenic factors have been established to shape arsenic flow in the Bengal delta plain (BDP), a recognized arsenic hotspot. Quite a few arsenic removal processes and techniques including bioremediation and phyto-remediation using hyperaccumulators with their limited advantages and specific disadvantages are currently in use. But, the overall arsenic mitigation scenario from groundwater in around the world is not praiseworthy. Site-specific remedial measures are essential in managing arsenic pollution. Maximized initiatives by the government agencies, health awareness, and participation of residents would consequence suppressing the calamity of arsenic toxicity in the world including the BDP. Further extensive research is required in this vast arena.
Keywords: Arsenic, groundwater, toxicity, health risk, sustainable management
The knowledge of arsenic (As) contamination has expanded enormously in the past two to three decades. From the very beginning of scientific research in India, the Bengal Basin attracted researchers working in the different fields. Therefore, plenty of information regarding Bengal Basin is available. Many research works have been carried out on the quantity and quality of groundwater in various parts of Bengal Basin. The ones relevant to the present study have been presented in this chapter. Here information has been gathered under broad heads according to the field of study. A few works, not exactly carried out within the present study area, but carried out in the surrounding areas and relevant to the present study, have been also incorporated here.
Groundwater is one of our most precious natural resources. Many aquifers around the world have been found to be naturally contaminated with arsenic (As), a toxic metalloid and a potent human carcinogen. Chronic exposure to arsenic is harmful to human health causing skin lesions, hepatotoxicity, vascular disease, diabetes as well as cancers of various organs. High concentrations of arsenic in groundwater, more than the permissible limit (10 µg/L as per World Health Organization, WHO) have been reported from many countries of Asia, Africa, Europe, North and South America and Australia. Around 200 million people, majority of them living in South and South-East Asia, are at risk of arsenic toxicity mainly from contaminated groundwater. Minerals, such as pyrites and arsenopyrites, have a high amount of arsenic content and release it in groundwater upon breakdown under oxic environment. Several hypotheses, such as, pyrite oxidation, iron reduction, competitive exchange and geomicrobial process, have been proposed to elucidate the release mechanism and mobilization of arsenic from sediment to groundwater. Use of groundwater laden with high concentrations of arsenic for irrigation of agricultural crops and entry of arsenic in food chain including crops has been the subject of intense research in the last decade. Some recent reports on the assessment of population’s dietary intake suggest that rice and water are significant sources of arsenic. Induction of an oxidative stress through the generation of reactive oxygen species is one of the principal mechanisms of arsenic toxicity. These reactive oxygen species results in DNA damage, lipid peroxidation and loss of antioxidant defense and induction of stress response genes. Polymorphisms in the arsenic metabolism and detoxification, antioxidant defense and DNA repair genes could also contribute to the inter-individual differences in arsenic biotransformation and consequently, influence inter-individual susceptibility to the health effects of arsenic toxicity.
Arsenic (As) contamination in groundwater persists in South Asia. Precipitated amorphous Fe(III)-oxides regulate the mobilization of aqueous As and iron (Fe) within the hyporheic zone (HZ). Depending on the chemical stability of these Fe(III)-oxides, this so-called Natural Reactive Barrier (NRB) can function as a sink or source of aqueous As and Fe within shallow alluvial aquifers under influences of tidal and seasonal fluctuations of river stage. The extent to which surficial lithology influences the As mobility along a riverine (upstream) to tidal (downstream) continuum is uncertain. To explore this process along a tidally fluctuating river, two new study sites with contrasting surface lithology were characterized along the banks of Hooghly River. The upstream sandy riverbank aquifer experiences robust mixing with oxygen-rich surface water under influences of tidal fluctuations which maintain oxic conditions in the riverbank aquifer. Introduced riverine dissolved oxygen (DO) drives the in-situ precipitation of crystalline Fe(III)-oxides which remove dissolved As and Fe from groundwater before discharging to the river. Although sediment from the downstream silt-capped riverbank contains higher concentrations of sedimentary As and Fe compared to the sandy site, lower proportions of crystalline Fe(III)-oxide minerals were observed. Arsenic was more easily mobilized from the aluminosilicate clay minerals to which the As was primarily bound at the silt-capped riverbank, compared to the As bound to Fe(III)-oxides at the sandy site. Thus, aluminosilicates can be an important source of dissolved As. These findings demonstrate that the surficial lithology of a riverbank along a tidally and seasonally fluctuating river regulates the mobility of As and its mineralogical association within riverbank sediments in shallow riverbank aquifers.
Availability of safe drinking water in the face of arsenic contamination of groundwater has become a global concern, and India is no exception to this alarming problem. Buxar district in the state of Bihar, India, has four blocks affected by arsenic contamination. Groundwater system of the area consists of multiple aquifers, with an arsenic-infested shallow aquifer system and an arsenic-safe deeper aquifer system, separated by a discontinuous clay layer of variable thickness. In response to the increasing demand of potable water, there is a recent trend of either constructing new wells that tap the deeper aquifer or deepening of the existing tube wells. However, unregulated exploitation of the deeper aquifer poses a significant risk, as it can disrupt the hydrodynamics of the entire groundwater system, leading to increased threats of cross-contamination of the deeper arsenic-safe aquifer from the overlying arsenic-contaminated aquifer. In the present study, modelling of the piezometric head of the deeper confined aquifers through distance drawdown analysis using the Theis non-equilibrium equation has been carried out. Findings indicate that the hydraulic head of the deeper aquifer rests at higher level than the water level of the shallow aquifer, thereby acting as a natural flow-pattern defence against the movement of contamination from the shallow aquifer to the deeper aquifer. To address this concern and understand the hydrodynamic balance within the aquifer system, an aquifer response modelling based on Theis non-equilibrium equation has been attempted. This model employs field-determined aquifer parameters to determine the optimal pumping discharge and spacing between wells constructed in the deeper arsenic safe aquifer. The objective is to devise a strategy for keeping the deeper arsenic-safe aquifers protected from any threats of cross-contamination from the overlying arsenic-contaminated aquifer. The results of the study suggest that water supply schemes in the arsenic-affected areas should be designed with a maximum discharge of 50 m³/h. Additionally, a minimum spacing of 2 km between two adjacent high discharge community water supply wells is recommended. The approach presented in the study can be used to determine the safe discharge and optimal spacing criteria between high discharge community water supply wells for pumping the arsenic safe confined aquifers in similar hydrogeological settings. Implementation of the suggested measures is crucial to ensure safe and clean drinking water for present and future generations in the arsenic contaminated areas.
This study examined how socio-economic driving forces influence households’ choice of water, ranging from a piped water supply provided by Veolia to untreated sources contaminated with high levels of arsenic and pathogens. Households fall into three cluster groups based on variations in socio-economic status and physical, infrastructure, and institutional elements. About 64% of the variations are related to differences in awareness, willingness, and ability to pay for safe water sources. Families with higher monthly income showed interest in accepting Veolia’s house connection options, resulting in the shutdown of six community tap points and ultimately affecting the low-income households’ accessibility to Veolia water. A causal loop diagram showed five feedback loops influencing the choice of drinking contaminated water. Bayesian Network models were sensitive to the ability, accessibility, and willingness to pay for safe water, deep tube well distributions, installation and maintenance costs, ownership of tube wells, household income level, and the level of awareness. Results suggest that the risks of drinking contaminated water can be minimized by raising awareness; accepting arsenic removal techniques; sharing expenses; training for deep tube well installations and maintenance; increasing Veolia pipeline coverage; and redesigning the tap point distributions. These results help identify the relative importance of such interventions to improve water security in safe water-poor areas.
Elevated metal(loid) concentrations in soil and foodstuffs is a significant global issue for many densely populated countries like Bangladesh, necessitating reliable estimation for sustainable management. Therefore, a comprehensive data synthesis from the published literature might help to provide a wholistic view of metal(loid) contamination in different areas in Bangladesh. This study provided a clearer view of metal(loid) contamination status and their associated ecological and health risks in different land use and ecosystems in Bangladesh. Comprehensive analyses were performed on data gathered from 143 published articles using multiple statistical techniques including meta-analysis. Considering the potential loading of metal(loid), the data were summarized under various groups, including coastal, rural, urban and industrial regions. Also, the concentrations of seven metal(loid)s, e.g., cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), zinc (Zn), and arsenic (As) in soil, sediment, cereal, vegetable, fruit, surface water and groundwater were included. Results showed that the relative concentrations of metal(loid)s in comparison to the maximum permissible limit (MPL) were mostly less than one, although they varied significantly for locations and individual metal(loid). However, the normalized cumulative relative concentrations over the MPL for all seven metal(loid)s across different environmental samples were 4.75, 2.97, 1.51 and 2.79 for coastal, industrial, rural and urban areas, respectively, which was due to the higher concentration of Cd, Cr and Cu. Similar to the metal(loid) concentrations, the average of cumulative median non-cancer risks for all metal(loid)s was in the order of industrial (6.46) > urban (4.05) > rural (3.83) > coastal (2.41). This research outcome will provide a foundation for future research on metal(loid)s and will help in pertinent policy-making by the relevant authorities in Bangladesh.
Inorganic and organic contaminants pollute streams daily. Pollution and other manmade disruptions change aquatic ecosystems. Water pollution may come from wastewater, industrial effluents, contaminated sediments, nutrients, flame retardants, persistent organic pollutants, medicines and illegal substances, emerging contaminants, and others (such as microplastics and engineered nanoparticles), herbicides, pesticides, and endocrine disruptors. Organic and heavy metal pollution can have negative effects on ecosystems, marine life, and humans. Pollutants stress and deplete aquatic ecosystems. The most effective strategy is phytoremediation using aquatic plants. Despite the extreme pollution and harsh conditions, certain macrophytes in water are able to persist. The following aquatic plant species help keep waterways clean: lemna, eichhornia, azolla, potamogeton, wolfia, spirodela, and wolfialla. Using these plants in phytoremediation or bioremediation helps clean up contaminated water. Macrophytes are resistant to certain chemicals, including strong concentrations of metals, phenols, formaldehydes, acids, and oxalates. One fascinating method for assessing pollution in aquatic ecosystems is biomonitoring. The purpose of using bioindicators is to monitor environmental changes and quality over time. One kind of bioindicator is macrophytes. More and more people are turning to clean up polluted land and water. When dealing with sites polluted by metals, phytoremediation is a novel and economical approach to removing persistent environmental toxins. Recent studies on the gene overexpression associated with the absorption, transport, and sequestration of metals have enhanced the potential of phytoremediation. This chapter covers aquatic pollution categories and the biomonitoring status of macrophytes.
Arsenic is found in significant quantities within the alluvial aquifers. Bangladesh heavily relies on the alluvial aquifers of the Bengal Basin as a source of irrigation and drinking water. Due to the flat topography, arsenic within an aquifer is not easily flushed out of the system. Additionally, continuous, unregulated pumping causes arsenic from deeper aquifers to migrate to shallower levels. This study simulates groundwater and contaminant transport in the alluvial aquifers of the Bengal Basin by comparison between two scenarios prior to human intervention with different sea levels, employing a combination of MODFLOW, MODPATH and MT3DMS. The simulations demonstrate that the hydraulic gradient and flow rates were higher during periods of considerably lower sea levels than they are at present. Additionally, it would require 5,600 years for the Holocene aquifer and 3,300 years for the Last Glacial Period aquifer to flush arsenic to the Bangladesh standard concentrations in drinking water in a 100-m-thick contaminated aquifer. This implies that if the sea level continues to rise with climate change, it will be difficult to remove arsenic from the alluvial aquifers in the Bengal Basin by natural flushing, which means artificial interventions need to be done in that region in the interest of the nation's health.
The hydrogeochemical evolution of groundwater in peri-urban agricultural areas is influenced by the convergence of natural processes, agricultural practices, and industrial activities. Understanding the combination of these influences is essential for assessing groundwater quality and human health risks. The study, taking the peri-urban agricultural areas in Guixi, China as a case, investigated the major components and heavy metals in groundwater and analyzed their spatial distribution patterns, sources, controlling factors, and human health risks. HCO3⁻ and Ca²⁺ are the most prevalent anions and cations in groundwater, with average concentrations of 136.74 and 34.07 mg/L, respectively. Heavy metal concentrations follow the sequence: Fe > Ba > Mn > Al > As > Pb. Groundwater compositions exhibit moderate to strong spatial variability, and most of the groundwater in the area presents moderate to significant health risks, with Cl⁻, As, Al, and Mn being the primary risk factors. Rock weathering by carbonic acid and industrial waste gypsum dissolution emerge as primary factors driving groundwater hydrogeochemical evolution. Fe and Mn correlate with SO4²⁻, sourced from industrial waste gypsum, while As and Al correlate with HCO3-, indicating a geological origin. Pb originates from transportation inputs, and Ba exhibits contrasting correlations with NO3⁻ and SO4²⁻, reflecting the dual influence of agricultural and industrial activities. These findings highlight groundwater hydrogeochemistry evolutions in peri-urban agricultural areas are intricately influenced by the combination of natural processes and a variety of human activities, rather than just the additive effect of these factors.
The transformation of metastable ferrihydrite to stable hematite has been linked to the magnetic enhancement in soils and sediments. However, the magnetic and structural characteristics associated with the transformation of...
Background: Research over past two decades has indicated the presence of Arsenic with consumption f rice and wheat. The present research was conducted on human health effects, including chronic toxicity of arsenic in West Bengal, India. Results: Arsenic content in the Haringhata region samples were found as 55 ug/l in Ground water, 41 ug/l in Soil sample, 30 ug/l in Boro Rice, 20 ug/l in Wheat, 24 ug/l in Potato. Arsenic content in the Chakdaha region samples were found as 50 ug/l in Ground water, 44 ug/l in Soil sample, 35 ug/l in Boro Rice, 19 ug/l in Wheat, 25 ug/l in Potato. Arsenic content in the Ranaghat region samples were found as 56 ug/l in Ground water, 39 ug/l in Soil sample, 30 ug/l in Boro Rice, 20 ug/l in Wheat, 25 ug/l in Potato. Arsenic content in the Shantipur region samples were 55 ug/l in Ground water, 45 ug/l in Soil sample, 34 ug/l in Boro Rice, 25 ug/l in Wheat, 27 ug/l in Potato. Arsenic content in the Krishna Nagar region samples were found as 54 ug/l in Ground water, 43 ug/l in Soil sample, 32 ug/l in Boro Rice, 21 ug/l in Wheat, 24 ug/l in Potato. Conclusion: This research reveals that Levels of arsenic content were highest in the groundwater compared to soil, in all the selected regions. The arsenic content in groundwater increases the arsenic contamination which affects serious threats to human health. Keywords: Arsenic; toxicity; health effects; analysis Background: Research over past two decades has indicated the presence of Arsenic with consumption f rice and wheat. The present research was conducted on human health effects, including chronic toxicity of arsenic in West Bengal, India. Results: Arsenic content in the Haringhata region samples were found as 55 ug/l in Ground water, 41 ug/l in Soil sample, 30 ug/l in Boro Rice, 20 ug/l in Wheat, 24 ug/l in Potato. Arsenic content in the Chakdaha region samples were found as 50 ug/l in Ground water, 44 ug/l in Soil sample, 35 ug/l in Boro Rice, 19 ug/l in Wheat, 25 ug/l in Potato. Arsenic content in the Ranaghat region samples were found as 56 ug/l in Ground water, 39 ug/l in Soil sample, 30 ug/l in Boro Rice, 20 ug/l in Wheat, 25 ug/l in Potato. Arsenic content in the Shantipur region samples were 55 ug/l in Ground water, 45 ug/l in Soil sample, 34 ug/l in Boro Rice, 25 ug/l in Wheat, 27 ug/l in Potato. Arsenic content in the Krishna Nagar region samples were found as 54 ug/l in Ground water, 43 ug/l in Soil sample, 32 ug/l in Boro Rice, 21 ug/l in Wheat, 24 ug/l in Potato. Conclusion: This research reveals that Levels of arsenic content were highest in the groundwater compared to soil, in all the selected regions. The arsenic content in groundwater increases the arsenic contamination which affects serious threats to human health. Keywords: Arsenic; toxicity; health effects; analysis
Arsenic (As) contamination of shallow alluvial aquifers in deltas of major rivers (Ganga, Meghna, Brahmaputra, Sutlej, Indus, etc.) in south Asia is the result of the microbially mediated reductive dissolution of iron (Fe)- and As-rich sediments, which are eroded from Himalayan rocks and transported to the deltas by rivers. The reductive dissolution is fueled by labile sedimentary and dissolved organic matter (OM). However, a very limited number of studies investigated the interactions between Fe, As, and DOC or OM in the Himalayan region. We hypothesize that the sediments transported by the Himalayan rivers shall contain elevated concentrations of Fe and As. We collected and analyzed riverbank sediment, river water, and sediment pore water samples from six locations along the Beas River in Himachal Pradesh (India), a major contributor to Sutlej-Indus River delta. Our results showed that the river sediments contained 12 ± 3 g/kg of total Fe, 4 ± 1 mg/kg of As, and 264 ± 122 mg/kg of Mn as measured by XRF. These As concentrations are approximately twice the crustal abundance of As, which is 2 mg/kg. The findings of this study will advance our understanding of how As is mobilized from the source to the delta.
Problem of natural arsenic (As) in groundwater is of growing concern to the health of people worldwide because of its carcinogenic properties. Arsenic contamination in groundwater affects the Indus alluvial and deltaic plains in Punjab and Sindh including Thatta district, where people are suffering from arsenic ingested diseases. Groundwater samples were collected from deltaic areas of Ghulamullah and Gujjo in Thatta district, where large section of population depends on groundwater for drinking and irrigation purpose. These water samples were analyzed to determine their arsenic contents, physicochemical and microbiological characteristics. Arsenic concentrations in groundwaters of Ghullamullah and Gujjo are in the range of 10-200 µg/L and 10-20 µg/L respectively. Most of As contaminated wells have also been found sewage impacted, which may be due to reducing conditions in the aquifers created by microbial degradation which favor As mobilization into groundwater. To determine the mobilization mechanism and source of arsenic, 11 soil samples were also collected from near the well sites and analyzed for their mineralogical and elemental composition using XRD and AAS techniques. Average concentrations of As in the soil of Ghulamullah and Gujjo areas are 73 and 65 µg/kg respectively. Higher As concentrations in Ghulamullah groundwater are due to dominance of clayey soil and presence of arsenic rich minerals particularly muscovite and phloghopite than in Gujjo area. The data reveal that the dominant hydrofacies in the study area are Na-Cl type indicating the impact of recent or ancient sea water intrusion. Arsenic distribution in shallow aquifers of Thatta district is patchy and seems to be controlled by degradation of organic matter by natural and anthropogenic sources.
One of the biggest environmental worries in the world today is the risk of arsenic (As) contamination in groundwater. The Atomic Absorption Spectrometer (AAS) was used in this work to assess the As content in groundwater samples from 38 shallow (27 m) tubewells in northwest Bangladesh to determine the existing situation, potential source(s), and likely health risk of As and other important water quality parameters. The range of arsenic concentrations (μgL⁻¹) was troublesome and greater than the WHO recommended level for drinking water, ranging from 0.50 to 164 (mean ± SD: 20.22 ± 36.46). In groundwater, the concentrations of Fe, and Mn vary from 0.04 to 52.75 mgL⁻¹ (mean ± SD: 4.23 ± 9.68), and 0.23 to 3.27 mgL⁻¹ (mean ± SD: 1.10 ± 0.67). The obtained groundwater samples have pH values ranging from 5.9 to 7.1, which indicates a somewhat acidic to neutral character. Major cations have an average abundance that is as follows: Ca²⁺ > Mg²⁺ > Na⁺ > K⁺, while major anions have an average abundance that is as follows: HCO3⁻ > Cl⁻ > SO4²⁻ > NO3⁻; Ca²⁺ and HCO3⁻ are the main cation and anion, respectively. The groundwater in the Rajarampur village was deemed unfit for drinking or irrigation based on analyses of water quality performed using the entropy water quality index. The Ca–HCO3 type of water, in which Ca²⁺ and HCO3⁻ are the main positive ions and negative ions, is suggested by the Piper tri-linear diagram. It was discovered that silicate weathering regulates the hydro-geochemical activities in groundwater using a bi-variate examination of several hydro-chemical variables. Four major clusters were observed for the water sample. According to reductive dissolution processes and principal component analysis, the arsenic in groundwater is geogenic in origin. Arsenic is discharged from sediment to groundwater by reductive dissolution of FeOOH and MnOOH, as shown by the modest connection between As, Fe, and Mn. The United Nations Environmental Protection Agency's (USEPA) suggested value for probable cancer risk assessment was 10⁻⁶, however the probable cancer risk assessment found a higher value, indicating that the population in the study region was at high risk for cancer. Remedial measures for arsenic mitigation include removing arsenic from groundwater after it is extracted, searching for alternative aquifers, and implementing various water-supply technologies such as dugwells, deep tubewells, pond-sand filters, and rainwater harvesting systems.
A pumice-maghemite (P-maghemite) composite was developed using the chemical coprecipitation method with a 20% iron loading ratio by weight. The characterization of the composite using SEM and XRD indicated the effective loading and dispersion of nano-particles on the surface of the developed base materials. Thereafter, in situ sequestration experiments were conducted in the laboratory for an arsenic-polluted aquifer system using two well-integrated permeable reactive barrier (PRB) modules filled with the developed composite. A vertical fixed-bed column setup was used for the columnar PRB, whereas a sand tank experimental setup was employed for the well-screen-integrated PRB; both PRB systems were fed by a synthetic solution representing the arsenic-contaminated groundwater. More than 99% arsenic removal was observed in the columnar PRB, with an average effluent concentration of 4 μg/L at the end of the experiment, which is well below the acceptable limit of drinking water for arsenic (<10 μg/L). Removal of arsenic by the 4 cm wide well-screen-integrated PRB from 652 μg/L to less than 20 μg/L shows a great potential of the developed composite for arsenic remediation at slower groundwater flow rates. A maximum arsenic removal of 99% was attained at the start of the experiment, which decreased to 97% after 1 month of PRB operation. The effluent concentration of all other major ions also was reduced considerably in the PRB modules. The hydraulic conductivity of the developed media was reduced by 35% in the columnar PRB and by approximately 20% in the well-screen-integrated PRB. The high arsenic removal efficiency in continuous flow-through remediation systems indicates the applicability of the developed PRB system in in-situ remediation of arsenic-contaminated groundwater.
The arsenic-affected areas of West Bengal are lying on a sediment of Younger Deltaic Deposition (YDD). The same sediment extends eastwards towards Bangladesh, covering the approximate area of 34 districts out of a total of 64 districts in Bangladesh. We suspect that the groundwater of these 34 districts of Bangladesh may be arsenic-contaminated. So far, we have collected 3106 water samples for analysis from 28 out of these 34 districts and in 27 districts 38% of the water samples we had analysed contain arsenic above 0.05 mg/l. Area and population of these 27 districts are 51,000 km2 and 36 million respectively. Out of these 27 districts, so far, we have surveyed 20 districts for arsenic patients, and in 18 districts we have identified people having arsenical skin lesions such as melanosis, leucomelanosis, keratosis, hyperkeratosis, dorsum, non-petting oedema, gangrene and skin cancer. During our preliminary field survey in 45 arsenic-affected villages in 18 districts, from a random examination of 1630 people, including children, 57.5% have arsenical skin-lesions. While comparing the West Bengal arsenic scenario with the available data of Bangladesh, it appears that Bangladesh's arsenic calamity may be more severe. If our prediction that the groundwater of Bangladesh's 34 district is likely to be arsenic-contaminated comes true, then more than 50 million people would be at risk. To combat the situation, Bangladesh needs a proper utilization of its vast surface and rain water resources. Proper watershed management is required urgently.
Both soil and underground water of the southwestern Bangladesh has already been threatened with arsenic contamination affecting health of millions of people. An estimated 44% of total area of Bangladesh (34 districts) and 53 million rural people are at risk of arsenic poisoning. In the southwestern and some parts of eastern Bangladesh, arsenic content in soil and underground water has identified higher contamination. The experts at Bangladesh Council for Scientific and Industrial Research (BCSIR) found the highest contamination, 14mg/l of shallow tube well water in Pabna, a northern district and 220mg/kg of soil in Sylhet area of Bangladesh. The World Health Organization (WHO) standard for arsenic in drinking water is 0.01mg/l . However, the maximum permissible limit of arsenic in drinking water of Bangladesh is 0.05mg/l. Worsening contamination of groundwater aquifer and sufferings of the millions of people demand extensive research in this field.This study is a preliminary evaluation of our ongoing research on current state of the subsurface contamination of arsenic in Bangladesh. Last decade water resources management has been analyzed to cope with the problem in the source level. Possible geo-hydrological and geo-chemical occurrences of arsenic in subsurface are discussed. The concentration of arsenic and the stratigraphic occurrence are presented. It is observed that arsenic concentration in tubewell water of 31 districts of Bangladesh contain above the maximum permissible limit. And the concentration of arsenic in tubewell water decreases with the depth of subsurface.
Arsenic is ubiquitous in the environment, being present in small amounts in all rock, soil, dust, water and air. It is associated with many types of mineral deposits and in particular those containing sulphide minerals. The most common arsenic mineral is arsenopyrite, FeAsS 2 . Elevated concentrations are sometimes found in fine grained argillaceous sediments and phosphorites. Some marine sediments may contain as much as 3000 mg kg ⁻¹ . Arsenic is co-precipitated with iron hydroxides and sulphides in some sedimentary rocks, and is precipitated as ferric arsenate in soil horizons rich in iron.
This paper reviews current knowledge on the natural geochemical sources of arsenic in several countries where high concentrations in soils, dusts, surface and groundwaters may present a hazard to human health. The chemistry and behaviour of arsenic within the weathering zone are discussed in relation to pathways leading to human exposure.
Measurements of degree of pyritisation require an estimate of sediment iron which is capable of reaction with dissolved sulphide to form pyrite, either directly or indirectly via iron monosulphide precursors. Three dissolution techniques (buffered dithionite, cold 1 M HCl, boiling 12 M HCl) were examined for their capacity to extract iron from a variety of iron minerals, and iron-bearing sediments, as a function of different extraction times and different grain sizes. All the iron oxides studied are quantitatively extracted by dithionite and boiling HCl (but not by cold HCl). Both HCl techniques extract more iron from silicates than does dithionite but probably about the same amounts as are potentially capable of sulphidation. Modern sediment studies indicate that most sedimentary pyrite is formed rapidly from iron oxides, with smaller amounts formed more slowly from iron silicates (if sufficient geologic time is available). It is therefore recommended that the degree of pyritisation be defined with respect to the dithionite-extractable (mainly iron oxide) pool and/or the boiling HCl-extractable pool (which includes some silicate iron) for the recognition of iron-limited pyritisation.
The first eight chapters of this book treat the main chemical processes that affect groundwater composition. Examples are provided of how natural groundwaters have obtained their composition, and the effects of pollution are discussed. Under ideal field conditions a single chemical reaction may adequately describe the evolution of groundwater composition, but in general, the interplay of several processes must be considered. The remaining chapters present the systematics of transport in aquifers and how to couple transport to chemical reactions. It treats the basics of writing computer programs to calculate the combined effects of transport and chemical reactions. Applications of hydrogeochemical transport modelling of complex systems are demonstrated and geochemical approaches to aquifer clean-up schemes are evaluated. -from Authors
Sediment and groundwater samples from Kachua and Itina, N-24 Parganas, West Bengal were analysed and found to be contaminated with arsenic. In an attempt to investigate on the probable source areas of the arsenious sediments, eleven borehole samples were collected from these two villages up to 50 metres depth. Heavy mineral suites of the arsenious sediments were studied in detail. Altogether four assemblages viz. A, B/I, II and III were detected. Assemblages B/I, II and III reflect the potential source area of the arsenious sediments to be the metamorphic terrains of the Bihar plateau region. Assemblage A indicates the corresponding sediments to belong to a mixed provenance of Himalayan (dominantly igneous) and Bihar plateau (dominantly metamorphic regions. Arsenic appears to be cogenetic with the sedimentation. -Authors
The author subdivided the recent sediments and discussed the landforms and sedimentary environment in the Bengal Lowland based on the analysis of the sediments. The recent sediments are subdivided into five members, and the sealevel curve in the region is similar to so-called “Sheperd curve” with regression during a certain period between ca.12, 000 and 10, 000 yBP. During the maximum epoch of the last glacial age, the rivers flowing in the Bengal Lowland deposited gravels on the valley floors. After the period, the sea level rose up to about 45m below present level, and the lower member deposited by ca. 12, 000 yBP. During ca.12, 000 and 10, 000 yBP, the delta and flood plain surface was slightly dissected according to the regression of the sealevel. After the regression, the middle member characterized by fine sediments in the deltaic condition deposited. The upper member deposited during 10, 000 (or 8, 000) yBP and 6, 000 (5, 000) yBP. After ca. 5, 000 yBP, broad peat land or wet land developed widely in the Bengal Lowland.
Arsenic in groundwater above the WHO maximum permissible limit of 0.05 mg l(-1) has been found in six districts of West Bengal covering an area of 34 000 km(2) with a population of 30 million. At present, 37 administrative blocks by the side of the River Ganga and adjoining areas are affected. Areas affected by arsenic contamination in groundwater are all located in the upper delta plain, and are mostly in the abandoned meander belt. More than 800 000 people from 312 villages/wards are drinking arsenic contaminated water and amongst them at least 175 000 people show arsenical skin lesions. Thousands of tube-well water in these six districts have been analysed for arsenic species. Hair, nails, scales, urine, liver tissue analyses show elevated concentrations of arsenic in people drinking arsenic-contaminated water for a longer period. The source of the arsenic is geological. Bore-hole sediment analyses show high arsenic concentrations in only few soil layers which is found to be associated with iron-pyrites. Various social problems arise due to arsenical skin lesions in these districts. Malnutrition, poor socio-economic conditions, illiteracy, food habits and intake of arsenic-contaminated water for many years have aggravated the arsenic toxicity. In all these districts, major water demands are met from groundwater and the geochemical reaction, caused by high withdrawal of water may be the cause of arsenic leaching from the source. If alternative water resources are not utilised, a good percentage of the 30 million people of these six districts may suffer from arsenic toxicity in the near future.
NETPATH is an interactive Fortran 77 computer program used to interpret net geochemical mass-balance reactions between an initial and final water along a hydrologic flow path. Alternatively, NETPATH computes the mixing proportions of two to five initial waters and net geochemical reactions that can account for the observed composition of a final water. The program utilizes previously defined chemical and isotopic data for waters from a hydrochemical system. For a set of mineral and (or) gas phases hypothesized to be the reactive phases in the system, NETPATH calculates the mass transfers in every possible combination of the selected phases that accounts for the observed changes in the selected chemical and (or) isotopic compositions observed along the flow path. The calculations are of use in interpreting geochemical reactions, mixing proportions, evaporation and (or) dilution of waters, and mineral mass transfer in the chemical and isotopic evolution of natural and environmental waters. Rayleigh distillation calculations are applied to each mass-balance model that satisfies the constraints to predict carbon, sulfur, nitrogen, and strontium isotopic compositions at the end point, including radiocarbon dating. DB is an interactive Fortran 77 computer program used to enter analytical data into NETPATH, and calculate the distribution of species in aqueous solution. This report describes the types of problems that can be solved, the methods used to solve problems, and the features available in the program to facilitate these solutions. Examples are presented to demonstrate most of the applications and features of NETPATH. The codes DB and NETPATH can be executed in the UNIX or DOS1 environment. This report replaces U.S. Geological Survey Water-Resources Investigations Report 91-4078, by Plummer and others, which described the original release of NETPATH, version 1.0 (dated December, 1991), and documents revisions and enhancements that are included in version 2.0. 1 The use of trade, brand or product names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.
Phosphorites from the continental shelf off Morocco have been analysed for major elements and Fe, Mn, V, Cu, Ni, Zn, As, Na, Sr, S, and for carbonate. In pyritic phosphorites Cu, Ni, Zn, and As are present mainly in minor pyrite and organic carbon. In ferruginous phosphorites As, Mn, and V are associated with goethite. In the ferruginous phosphorites Cu, Ni, and Zn may have been introduced in association with organic matter and pyrite during phosphorite formation and been retained during subsequent destruction of these phases by weathering. In all phosphorites Na and Sr are present mainly in carbonate-fluorapatite. Sulphur in the ferru-ginous phosphorites occurs only in carbonate-fluorapatite. In the pyritic samples it is partitioned between pyrite and francolite (carbonate-fluorapatite).
Unusually high As and U concentrations (>100 μg/L) are widespread in shallow ground water beneath the southern Carson Desert. The high concentrations, which locally exceed 1000 μg/L, are of concern from a human health standpoint because the shallow ground water is used for domestic supply. Possible affects on wildlife are also of concern because the ground water flows into shallow lakes and marshes within wildlife refuges.Arsenic and U concentrations in ground water of the southern Carson Desert appear to be affected by evaporative concentration, redox reactions, and adsorption. The relation of these elements with Cl suggest that most of the high concentrations can be attributed to evaporative concentration of Carson River water, the primary source of recharge.Some ground water contains higher As and U concentrations that cannot be explained by evaporative concentration alone. Oxidation-reduction reactions, involving metal oxides and sedimentary-organic matter, appear to contribute As, U, inorganic C, Fe and Mn to the ground water. Arsenic in Fe-oxide was confirmed by chemical extraction and is consistent with laboratory adsorption studies. Uranium in both sedimentary-organic C and Fe-oxide coatings has been confirmed by fission tracks and petrographic examination.Arsenic concentrations in the ground water and chemical extracts of aquifer sediments are broadly consistent with adsorption as a control on some dissolved As concentrations. An apparent loss of As from some ground water as evaporative concentration proceeds is consistent with adsorption as a control on As. However, evidence for adsorption should be viewed with caution, because the adsorption model used values for the adsorbent that have not been shown to be valid for the aquifer sediments throughout the southern Carson Desert.Hydrologic and geochemical conditions in the Carson Desert are similar to other areas with high As and U concentrations in ground water, including the Salton Sea basin and southern San Joaquin Valley of California. Hydrologic and geochemical conditions that produced some sandstone-type U-ore deposits, including those in the non-marine, closed-basin sediments of the Morrison Formation near Grants, New Mexico, suggest that the Carson Desert may be a modern analog for those systems.
A review of the literature indicates that numerous microorganisms can reduce ferric iron during the metabolism of organic matter. In most cases, the reduction of ferric iron appears to be enzymatically catalyzed and, in some instances, may be coupled to an electron transport chain that could generate ATP. However, the physiology and biochemistry of ferric iron reduction are poorly understood. In pure culture, ferric iron‐reducing organisms metabolize fermentable substrates, such as glucose, primarily to typical fermentation products, and transfer only a minor portion of the electron equivalents in the fermentable substrates to ferric iron. However, fermentation products, especially hydrogen and acetate, may be important electron donors for ferric iron reduction in natural environments. The ability of some organisms to couple the oxidation of fermentation products to the reduction of ferric iron means that it is possible for a food chain of iron‐reducing organisms to completely mineralize nonrecalcitrant organic matter with ferric iron as the sole electron acceptor. The rate and extent of ferric iron reduction depend on the forms of ferric iron that are available. Most of the ferric iron in sediments is resistant to microbial reduction. Ferric iron‐reducing organisms can exclude sulfate reduction and methane production from the zone of ferric iron reduction in sediments by outcompeting sulfate‐reducing and methanogenic food chains for organic matter when ferric iron is available as amorphic ferric oxyhydroxide. There are few quantitative estimates of the rates of ferric iron reduction in natural environments, but there is evidence that ferric iron reduction can be an important pathway for organic matter decomposition in some environments. There is a strong need for further study on all aspects of microbial reduction of ferric iron.
In a laboratory study, iron oxide-coated sand showed promise as a medium for use in small systems or home-treatment units in developing areas of the world, for removing arsenic(III) and arsenic(V) from ground water. A low-cost, simple, home arsenic removal unit (material and fabrication cost: Rs. 200, cost of medium: Rs. 80, and regeneration cost: Rs. 5; 1 US dollar = Rs. 35), containing 6 kg (4 L) of iron oxide-coated sand, produced 625 and 610, and 780 and 760 L of water in two cycles of runs when the influent arsenic(III) or arsenic(V) concentration was 1.0 mg/L. A detailed study addressing the effects of some important factors (selectivity of arsenic(III) and arsenic(V) over one another for removal, water pH, concentration and type of competing anions, and cations) on the process is needed. The home arsenic removal unit should be subjected to field trial to assess long-term effects on performance.
Adsorption isotherms in solutions with ionic strengths of 0.01 at 25° C were measured over the arsenite concentration range 10-7-10-5 M and the pH range 4-10. These isotherms obeyed equations of the Langmuir type. Curves of arsenite removed by iron hydroxide from a constant volume of solution, as a function of pH, go through a maximum at approximately pH 7. The pH of the zero point of charge of the suspension was measured as a function of the amount of adsorption of arsenite and was found to decrease as more arsenite adsorbed.
Arsenic contamination in groundwater used for drinking purposes has been envisaged as a problem of global concern. Exploitation of groundwater contaminated with arsenic within the delta plains in West Bengal has caused adverse health effects among the population within a span of 8-10 years. The sources of arsenic in natural water are a function of the local geology, hydrology and geochemical characteristics of the aquifers. The retention and mobility of different arsenic species are sensitive to varying redox conditions. The delta plains in West Bengal are characterized by a series of meander belts formed by the fluvial processes comprising different cycles of complete or truncated fining upward sequences (sand-silt-clay). The arseniferous groundwater belts are mainly located in the upper delta plain and in abandoned meander channels. Mineralogical investigations have established that arsenic in the silty clay as well as in the sandy layers occurs as coatings on mineral grains. Clayey sediments intercalated with sandy aquifers at depths between 20 and 80 m are reported as a major source of arsenic in groundwater.Integrated knowledge on geological, hydrologicaland geochemical characteristics of the multi-level aquifer system of the upper delta plain is therefore necessary in predicting the origin, occurrence and mobility of arsenic in groundwater in West Bengal. This would also provide a basis for developing suitable low-cost techniques for safe drinking water supply in the region.
Elevated arsenic concentrations were found in ground water near Canal Fulton, Ohio. The hydrologie and chemical properties of the area were studied to determine the source of the arsenic and evaluate the possibility of a similar problem occurring elsewhere. Two major aquifer systems exist within the study area: the Sharon Sandstone of the upland areas; and the outwash sand and gravel deposits of the buried valleys. Ground-water flow is generally from the north, but local variations are caused by the Tuscarawas River valley on the south and west of the study area. Within the study area, there is no evidence for an anthropogenic source of arsenic to the ground water. Agricultural soils, abandoned underground coal mines, industrial impoundments to the north, and an abandoned industrial dump site within the study area were all eliminated as possible sources for the arsenic. The arsenic in Canal Fulton ground water is entirely inorganic, consisting of about equal parts of arsenate and arsenite. Reduction-oxidation (redox) considerations suggest that arsenic is controlled by an adsorption equilibrium with ferric hydroxides, and that the reduction of the ferric hydroxides by a recent lowering of Eh and/or pH in the aquifer has liberated both iron and arsenic to solution. A high correlation between ferrous iron and total dissolved arsenic supports this model. It is hypothesized that Eh conditions have been lowered in the aquifer by either the recent introduction of methane gas or the deposition of a thick layer of till during the last glacial retreat. The methane gas could be leaking from deep underground storage at the site and reducing oxidized compounds. The deposition of till would have eliminated local recharge of oxygenated waters.
Late Quaternary sediments, deposited since the lowest stand of sea-level during the last glacial maximum, in the Ganges Delta and its surrounding region were classified into five units according to their sedimentary facies. These are the lowest unit of sandy gravels, the lower unit of sand with a few gravels, and the middle, upper and uppermost units consisting mainly of sand and silt with occasional peat layers. The contact between the lower and middle units is fairly sharp, and the upper part of the lower unit is oxidized in some places. This suggests a period of subaerial exposure after the deposition of the lower unit.During the low stand of sea-level, about the time of the last glacial maximum, rivers in the Ganges Delta and its surrounding region dissected the surfaces of the region, and deposited the lowest unit on the valley floors. The lower unit was deposited over the lowest unit during an early stage of the post-glacial transgression. Between ca. 12,000 yr BP and 10,000 yr BP, the surface of the delta was slightly dissected and the top of the lower unit was weathered and oxidized. Following this period, the middle and upper units of alluvial or deltaic sand and silt with occasional peat were deposited. The coastline in the early Holocene retreated towards the central part of the present Ganges Delta. In the middle and late Holocene, the silt and clay with occasional peat layers of the uppermost unit indicate that the lowland gradually became marshy and poorly drained as the rate of transgression became slower.
A review of the occurrence and cycling of arsenic in fresh waters is presented. The fate of arsenic in natural waters has received little attention in past years, in spite of the fact that arsenic is toxic and probably carcinogenic through exposure by drinking water.The chemistry of arsenic in aqueous systems is reviewed. Thermodynamic information is summarized in an Eh pH diagram for a system including sulfur. Mechanisms for removal of arsenic from the solution phase to the sediments are discussed. The possible microbially-mediated reactions of arsenic, including oxidation of arsenite, methylation of arsenic species, and reduction of arsenate, are discussed with reference to the locale of the reaction in the water column or in the sediments and to the toxicological significance of the reaction products and the rates of reaction.A cycle of reactions for arsenic in a stratified lake is proposed and evidence is summarized relating to the occurrence and importance of particular reactions.The potential pollutional hazard of arsenic is from ingestion of drinking water with high concentrations of arsenic, rather than consuming arsenic containing aquatic organisms. Although arsenic is greatly concentrated in aquatic organisms, it is evidently not progressively concentrated along a food chain. In addition, arsenic when consumed as an organically-bound species in flesh evidently has low toxicity.The global cycle of arsenic is discussed. While volcanic activity is the original source of much of the arsenic in sedimentary rocks, in recent times weathering of arsenic has been approximately in balance with deposition of arsenic in sediments. Human activities, including the use of arsenic, the burning of fossil fuels, increased erosion of land and the mining and processing of sulfide minerals, have increased the amount of arsenic entering the oceans by at least a factor of 3. This increase will have no effect on the concentration in the oceans for many hundreds of years.However, these cultural contributions are the source of high localized concentrations in many fresh waters. Careful surveillance and increased knowledge of the fate or arsenic in the aquatic environment are needed to insure that there will be no public health hazard.
Measured pore-water concentrations of iron in interbedded pelagic and turbiditic sediments from the Nares Abyssal Plain are in excellent agreement with sediment colour and measured redox potential. The organic carbon content of these sediments appears to define the redox conditions and consequently the porewater and solid-phase concentration of constituents that are involved in early diagenetic reactions. In the turbiditic sediments the concentration of NO3− generally goes to zero within a sediment depth of 1 m, whereas at 8 m in a pelagic core from the same area the concentration of NO3− is still higher than it is in the bottom water. The pore-water concentration of Mn2+ in the turbiditic sediments increases sharply down to a depth of approximately 3 m and from thereon remains nearly constant due to saturation with respect to Mn, Ca-CO3. The pore water of the turbiditic sediments is also saturated with respect to calcite. The few “diagenetic spikes” in the pore-water concentration of NO3− and Mn2+ and the concentration/depth profile of dissolved iron, H4SiO4 and phosphate all clearly demonstrate the inhomogeneous nature of interbedded pelagic and turbiditic sediments. The simultaneous occurrence of peaks of dissolved iron/silica and of sediment intervals with a relatively high organic carbon content is attributed to enhanced early diagenetic reactions associated with the decomposition of organic matter in these specific intervals. Linked with these reactions is the irregular pore-water concentration of phosphate, which is shown to originate partly from the oxidation of organic matter, but mainly from the desorption of phosphate from iron oxide. Potential concentrations of phosphate are calculated from the stoichiometric early diagenetic reactions and compared with measured concentrations. Due to the unique combination of low porosity and relatively high sedimentation rates, the sediments from the Nares Abyssal Plain are an ideal basis for the study of such interbedded sequences of pelagic and turbiditic deposits.
The effects of As contamination in ground water in six districts of West Bengal have been studied. Some of the common symptoms observed amongst the affected people are described and the source of the As contamination is discussed. Some social problems arising from the contamination are described.
In Bangladesh and West Bengal, alluvial Ganges aquifers used for public
water supply are polluted with naturally occurring arsenic, which
adversely affects the health of millions of people. Here we show that
the arsenic derives from the reductive dissolution of arsenic-rich iron
oxyhydroxides, which in turn are derived from weathering of base-metal
sulphides. This finding means it should now be possible, by
sedimentological study of the Ganges alluvial sediments, to guide the
placement of new water wells so they will be free of arsenic.
Groundwater As in the Bengal Delta Plains: a sedimentary geochemical overview
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Arsenic in Groundwater: cause, eect and remedy
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Relation of diagenetically-available Fe and As in sedi-ments from Tungipara
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Absorption of amorphous iron hydroxide from dilute aqueous solution An interactive code (NETPATH) for modeling NET geochem-ical reactions along a ¯ow PATH
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Arsenic in the Environment, Part 1, Cycling and characterisation
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