No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Arsenic in Groundwater: Testing Pollution Mechanisms for Sedimentary Aquifers in Bangladesh
Water Resources Research
Abstract
In the deltaic plain of the Ganges-Meghna-Brahmaputra Rivers, arsenic
concentrations in groundwater commonly exceed regulatory limits (>50 μg L-1) because
FeOOH is microbially reduced and releases its sorbed load of arsenic to groundwater.
Neither pyrite oxidation nor competitive exchange with fertilizer phosphate contribute to
arsenic pollution. The most intense reduction and so severest pollution is driven by
microbial degradation of buried deposits of peat. Concentrations of ammonium up to 23
mg L-1 come from microbial fermentation of buried peat and organic waste in latrines.
Concentrations of phosphorus of up to 5 mg L-1 come from the release of sorbed
phosphorus when FeOOH is reductively dissolved and from degradation of peat and
organic waste from latrines. Calcium and barium in groundwater come from dissolution of
detrital (and possibly pedogenic) carbonate, while magnesium is supplied by both
carbonate dissolution and weathering of mica. The 87Sr/86Sr values of dissolved strontium
define a two-component mixing trend between monsoonal rainfall (0.711 ± 0.001) and
detrital carbonate (<0.735).
... The content of the Clu 8 (arsenic) domain is mainly related to the study of arsenic contamination, which is closely related to the large-scale arsenic contamination incident in Bangladesh, including the mechanism of arsenic contamination [37,38] and redox process of arsenic migration in groundwater [39]. ...
... In the area of ecological alteration, scholars focus on the impact of factors, such as [13,15,16,25,26,28,29,35,37,38,[46][47][48][49][50][51][52]. ...
... The most frequently referenced literature in GCS relates to climate change in the Brahmaputra basin [13]. The second most cited article is related to arsenic [37]. The most cited literature in LCS is also the earliest SCI literature on watersheds, which was published in the field of geology in Semantic Geology [46]. ...
In this study, we visualize and analyze the literature on the Brahmaputra river using a spectral clustering algorithm, tracking research trends over time. We found that the focus of research on the Brahmaputra has changed over time in the last decade, with a shift from geology to hydrology and geochemistry and a rapid growth in climate change research in recent years. In the future, potential hot topics may be “water resource management” and other topics related to transboundary water resource management and cooperation. At the same time, this study also analyzes in detail the keywords and clusters “geohydrology” and “ecological risk and sustainable development”, among other topics. We believe that future research should carefully consider the potential effects of transdisciplinary research trends. For instance, it is urgent that transborder governance and management regimes be renovated through joint efforts and cross-border effective actions carried out by multifaceted and multi-scalar agencies along this river.
... Thatta district is a part of Indus delta and has been formed primarily by deposition of Late Holocene (7000-10,000 years BP) sediments carried by Indus River from Himalaya which host aquifers in the area (Giosan et al., 2006;Clift, 2002). The deltaic soil constitutes fine grained sediments, rich in organic matter containing high amount of arsenic, which is supposed to become part of aquifers by various geochemical processes (McArthur et al., 2001;Nickson et al., 2005). ...
... The bacterial contamination of groundwater in the study area may be due to unlined sanitation, open pit toilet systems, waste water ponds, open air excretion and free roaming cattle which may also trigger the mobilization of arsenic in groundwater by creating local redox zonation in the aquifers (McArthur et al., 2001;Husain, 2009;Cole et al., 2005;Nickson et al., 2005). Elevated levels of arsenic in Ghulamullah groundwaters may be due to weak positive correlation of As with HCO 3(r=0.26) ...
... Biogenic reductive dissolution of Feoxyhydroxides is another important mechanism that put arsenic into groundwater of the alluvial aquifer under reducing conditions Ahmed et al., 2004;McArthur et al., 2001;Nickson et al., 1998;Bhattacharya et al., 1997). The unlined sanitation and sewage contamination in the study area has also resulted in the degradation of organic matter by microorganisms in the Holocene aquifers of the study area, causing heterogeneous local reducing conditions in the aquifers and generating high concentration of HCO 3¯and dissolved organic matter in the groundwater Bhattacharya and Mukherjee, 2002). ...
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.
... Arsenic can enter the environment through anthropogenic activities such as mining, burning fossil fuels, metal extraction, timber preservatives, etc., or naturally occurring processes like atmospheric emissions or the desorbed and dissolved state of naturally occurring minerals rich in arsenic (Bhattacharya et al., 1997;Bhattacharya et al., 2002;Bhattacharya et al., 2003). One explanation for the high levels of arsenic found in the groundwater of BDP may be broken-down grains rich in iron and arsenic adsorbed authigenic secondary oxide/hydroxide precipitates, also known as arsenic traps (Bhattacharya et al., 1997;Bhattacharya et al., 2002;Bhattacharya et al., 2003;Desbarats et al., 2011;McArthur et al., 2008;McArthur et al., 2001). During iron oxide reduction, Fe(III) that is present on the surface of BDP sediments may adsorb Fe(II). ...
... 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.
... 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.
... 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.
... Long-term exposure to arsenic from drinking-water and food may cause cancer and skin lesions and is also associated with cardiovascular disease and diabetes in human [50]. Throughout the world and particularly in southern, south-eastern, and eastern parts of Asia, large tracts of the unconfined aquifers in alluvial and deltaic plains are reported with elevated concentration of arsenic [1,7,10,23,24,26,35]. ...
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.
... Arsenic is liberated in reducing conditions by bacteria in the presence of organic carbon. 26 ...
Groundwater is a major source of drinking water for millions of people across the globe. Most of these sources are reported to contain elevated levels of arsenic. Human health and ecosystems are adversely affected by arsenic-contaminated drinking water. So, arsenic-contaminated groundwater has become a major global health concern. This paper reviews groundwater contamination sources and gives an outline of arsenic contamination in different places in Nepal. It also critically reviews the health hazards associated with arsenic poisoning. A comparative study has been made regarding different aspects of conventional and recent technologies , and the one that is the most suitable for remediation of contaminated water has been recommended.
... In addition, hydrogeochemistry and biogeochemical processes are responsible for the As load and mobilization in the groundwater of Bangladesh (Raessler, 2018). As contamination occurs in the groundwater due to the geological processes, including erosion of As-containing rocks (volcanic and sedimentary) and mineral weathering (McArthur et al., 2001). This contaminated groundwater is being extensively utilized for drinking and irrigation worldwide. ...
Arsenic (As) is a recognized naturally hazardous metalloid that has long been linked to human poisoning. Bangladesh is now dealing with a major public health crisis, with arsenic contamination in drinking water and food crops putting millions of people at risk. Arsenic accumulates in large quantities in Bangladesh’s farmlands. Arsenic accumulates in edible tissues ingested by people and animals when vegetables and other crops are cultivated in As-contaminated irrigation water and soil. Various ongoing mitigation methods have been implemented in Bangladesh to reduce arsenic exposure and consumption. Some strategies have shown to be successful on their own, while others remain contentious.
... 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 . ...
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
... Groundwater As T concentrations appear to be negatively correlated with C:N ratio of groundwater DOM ( Figure 1A) consistent with previous studies (Mladenov et al., 2015). Aromatic and humic-like DOM has been linked with As mobilization as it serves as electron donor (McArthur et al., 2001) for heterotrophic microbial metabolism (such as iron reduction), forms aqueous complexes with iron and arsenic and catalyzes arsenic mobilization via electron shuttling (Kulkarni et al., 2018). Groundwater samples appeared to have higher total coliform count with increasing C:N ratio ( Figure 1B) which indicates that carbonaceous organic matter may favor the growth of coliform bacteria in groundwater. ...
... The microbial process of organic matter reduction can result in the creation of optimum conditions for the solubility of arsenic in iron oxyhydroxide minerals in a reductive condition. It has been hypothesized that buried peat deposits play a role in creating favorable redox conditions for the liberation of arsenic ions from iron oxyhydroxide (FeOOH) minerals [104]. The Bengal basin shows a large distribution of peat deposits [105]. ...
The presence of arsenic in Indian groundwater poses a significant threat to both the ecosystem and public health. This review paper comprehensively addresses the topic, encompassing the underlying causes and potential solutions. Health consequences examines the serious health risks of drinking water contaminated with arsenic. Arsenic's complex geochemical processes of mobilization, transport, and distribution in groundwater are investigated. Mathematical models, geographical analysis, and data-driven modeling are discussed in the context of Indian groundwater. A comprehensive assessment of removal methodologies and the various factors influencing the mobility of arsenic is addressed. It was documented that community water purifiers and plants have successfully eliminated approximately 90% of arsenic, and the implementation of rainwater collection systems has also enhanced the overall quality of water. This review aims to address existing knowledge gaps and assess various strategies aimed at ensuring a more secure and sustainable water supply for the regions in question. The ultimate goal is to enhance the overall well-being of the population and protect the integrity of local ecosystems.
... The two outliers (>10 μg L − 1 ) were the samples taken from industrial sites. A higher correlation between DIC and dissolved As (Fig. 6b) may be because the higher DIC concentration lowers the pH and DIC involves in the dissolution of FeOOH-As mineral (Mahimairaja et al., 2005;McArthur et al., 2001;Nickson et al., 2000). In addition, negatively charged HCO 3 − and CO 3 2− ions of DIC better compete to adsorb to solids with negatively charged arsenate or arsenite ions. ...
Arsenic (As) pollution, is a global problem, threatening human health and ecological security, especially in the bay environment with dense population and human activities. Among potential pathways of As into the bay, submarine groundwater discharge (SGD) has not received adequate attention due to its invisibility. We determined As and 222Rn activity concentrations in different water mass. Spatial variation of dissolved As concentration in the groundwater was large and attributed to the adjacent local industries. By combining 222Rn mass balance modeling with As concentrations measured, the SGD-derived As fluxes was conservatively estimated to be 1310 kg As d−1 and 5880 kg As d−1 in the dry and wet seasons, respectively. The migration of arsenic may be enhanced by rainfall and dissolved carbon. The amount of SGD derived As input to the bay was greater than the total combined As input from river discharge, atmosphere, sewage drainage, and diffusion from sediment.
... In the RRD, the results show that the age of Holocene sediments affects the groundwater As concentration and these results are similar to the results of previous studies in the South Asia [35,36,37,38,39,40] or in South East Asia [13,16,41]. Sedimentary age affects geochemistry in two different ways. ...
The Red River Delta (RRD) has a high population density with about 19 million inhabitants. Water supply is from surface water and groundwater resources, in which surface water is from rivers and groundwater is mainly taken from aquifers in Quaternary sediments. Last two-decade research’s results show that groundwater in some areas in the RRD are contaminated with high elevated levels of Arsenic. Many research studies investigating Arsenic pollution have found that concentrations in water samples surveyed in Hung Yen, Hanoi, Ha Nam etc exceed the permissible value for domestic use as WHO guideline and Vietnam standard as well. The key factors controlling the distribution of Arsenic in the groundwater from previous studies are formation environment, sedimentary facies, sedimentary age, salinity of pore water and even neo-tectonic activity. However, which factor is more important for controlling groundwater arsenic distribution in the RRD need to be clarified. Therefore, the objective of this study is to determine the degree of controlling factors on the distribution of Arsenic in groundwater in the RRD. An overview of previous studies on the origin of Arsenic in groundwater is the first step to analyse the factors affecting the distribution of Arsenic in groundwater. A method of superposition of the controlling factors on the basis of ArcGIS was applied. Each controlling factor was classified and assigned a certain value. The weights of the factors were determined based on expert opinions and analytical hierarchical process (AHP) method. The results of model calibration based on the current distribution of Arsenic concentration map of the Holocene and Pleistocene aquifers allow confirming the reliability of the weights of controlling factors. Research results show that the groundwater Arsenic concentration in the RRD depends mainly on the distribution of Holocene alluvium and its age. The remaining factors are very insignificant in this case.
... Fluoride content in groundwater can rise due to the leaching of fluoride-containing minerals present in geological formations with groundwater, a phenomenon not directly linked to groundwater over-extraction. Similarly, in West Bengal, there were widespread incidences of high levels of arsenic in groundwater, threatening drinking water supplies and public health (McArthur et al., 2001). Though there are many competing theories 2 , it is seldom attributed to over-exploitation. ...
... Fluoride content in groundwater can rise due to the leaching of fluoride-containing minerals present in geological formations with groundwater, a phenomenon not directly linked to groundwater over-extraction. Similarly, in West Bengal, there were widespread incidences of high levels of arsenic in groundwater, threatening drinking water supplies and public health (McArthur et al., 2001). Though there are many competing theories 2 , it is seldom attributed to over-exploitation. ...
The book offers a thorough analysis of the groundwater availability and use situation in South Asia with particular focus on the regional patterns; provides a critical assessment of how over the years various public policies have impacted the access to and use of groundwater by various segments of the farming communities, particularly the equity in access to groundwater and efficiency in use for agricultural production; critically reviews the resource assessment methodologies adopted by official agencies, highlight their flaws and shows how such flaws can lead to wrong management decisions; and critically evaluates several schemes implemented in different parts of the sub-continent, some of which touted as ‘highly successful’ and some controversial, for their effectiveness in checking groundwater depletion using sound principles in water management, and shows how the past analyses of their impacts on the resource condition have been misleading and flawed. Drawing definite clues from South Asian experience, especially those from India, Pakistan and Bangladesh, and outside the region, the author presents some viable alternatives for groundwater management for the distinct socio-ecologies that exist in the sub-continent, built on strong conceptual and theoretical foundations, and discuss how they can be implemented. Finally, some policy lessons for other countries especially from Africa that are at an earlier stage in the groundwater development trajectory are provided
... The release of As from iron (Fe) minerals is primarily attributed to the microbialmediated dissolution of Fe-oxide coatings on sand grains and clay minerals, fueled by labile organic matter [7][8][9][10][11][12][13][14][15][16][17]. While the reductive dissolution of Fe-oxides can explain a significant proportion of the As released to solution, it is worth noting that secondary minerals, including Fe-oxides, are diagenetically formed within the sediment. ...
Sedimentary arsenic (As) in the shallow aquifers of Bangladesh is enriched in finer-grained deposits that are rich in organic matter (OM), clays, and iron (Fe)-oxides. In Bangladesh, sediment color is a useful indicator of pore water As concentrations. The pore waters of orange sediments are usually associated with lower As concentrations (<50 µg/L) owing to abundant Fe-oxides which sorb As. Using this color signal as a guide, spectroscopic measurements alongside thermal treatment were extensively utilized for analyzing the properties of both Fe-oxides and clay minerals. This study uses Fourier transform infrared (FTIR) and diffuse reflectance (DR) measurements along with thermal treatment to evaluate the solid-phase associations of As from sediment collected along the Meghna River in Bangladesh. The samples analyzed in this study were chosen to represent the various lithologies present at the study site and included riverbank sands (1 m depth), silt (6 m depth), aquifer sand (23 m depth), and a clay aquitard (37 m depth). The concentrations of sedimentary As and Fe were measured by X-ray fluorescence, and the spectroscopic measurements were taken on the samples prior to the thermal treatment. For the thermal treatment, sediment samples were placed in a preheated furnace at 600 • C for 3 h. The thermal treatment caused a deepening of reddish-brown hues in all samples, and the greatest change in color was observed in the finer-grained samples. The FTIR spectral analysis revealed that the clay minerals were composed primarily of illite, smectite, and kaolinite. The DR results indicate that the majority of Fe in sands was present as goethite; however, in the clay and silt samples, Fe was incorporated into the structure of clay minerals as Fe(II). The amount of structural Fe(II) was strongly positively correlated with the sedimentary As concentrations, which were highest in the finer-grained samples. After thermal treatment, the concentrations of As in the finer-grained samples decreased by an average of 40%, whereas the change in the As concentrations of the sand samples was negligible. These findings indicate that significant proportions of solid-phase As may be retained by OM and Fe(II)-bearing clay minerals.
... Data from recent Govt. of India report (CGWB, 2019) was used to assess the drinking water quality in the case of NO 3 -, F -, and Fe (NO 3 ranges from 0.96 mg/l to 1.7 mg/l, Franges from 0.09 to 0.18 mg/l and Fe ranges from nil to 0.22 mg/l). Since As and Fe show significant positive correlation (Rosas et al., 1999;McArthur et al., 2001;Mukherjee et al., 2006), from the low concentration of Fe it can be inferred that the concentrations of As will be insignificant, if present. ...
Springs present around Pasighat in the Himalayan foothill region are a major source of water for the local people. Study of groundwater chemistry of the river terrace springs of the Himalayan region is scarce. These springs tap the river terrace aquifers and have different chemical characteristics as compared to other types of springs present in the Himalayan region. This study aims to understand the chemical characteristics of the spring water in terms of water types and rock-water interaction. This study shows that the spring water has low concentration of dissolved ions and the pH is slightly acidic. Also, the groundwater of this area belongs to Ca-Mg-HCO3 type and recharge water type. Principal component analysis, correlation matrix and scatter plots show that silicate weathering, weathering of Cl-rich amphiboles and biotites, weathering of feldspars and ferromagnesian minerals and ion-exchange are the major operational processes in the area. Low concentration of dissolved constituents within the desirable limits makes the groundwater suitable for drinking, and other household purposes. Also, due to geological similarity of terrace deposits along the Himalayan foothills it is inferred that river terrace springs in other parts of Himalayan foothills may have similar groundwater characteristics.
... Hydrological, atmospheric, climatic, topographical, and lithological factors are all natural influences on groundwater quality (Panaskar et al. 2016;Islam et al. 2017a;Uddin et al. 2021). The escalating groundwater contamination and scarcity crisis is a global issue (McArthur et al. 2001;Macdonald et al. 2016). This scenario necessitates the judicious management of groundwater resources to guarantee their viability. ...
Groundwater quality monitoring and geochemical characterization in a phreatic aquifer are critical for ensuring universal and equitable access to clean, reliable, and inexpensive drinking water for all. This research was intended to investigate the hydrogeochemical attributes and mechanisms regulating the chemistry of groundwater as well as to assess spatial variation in groundwater quality in Satna district, India. To accomplish this, the groundwater data comprising 13 physio-chemical parameters from thirty-eight phreatic aquifer locations were analysed for May 2020 by combining entropy-weighted water quality index (EWQI), multivariate statistics, geochemical modelling, and geographical information system. The findings revealed that the groundwater is fresh and slightly alkaline. Hardness was a significant concern as 57.89% of samples were beyond the permissible limit of the World Health Organisation. The dominance of ions were in the order of Ca2+ > Na+ > Mg2+ > K+ and HCO3− > SO42− > Cl− > NO3− > F−. Higher concentration of these ions is mainly concentrated in the northeast and eastern regions. Pearson correlation analysis and principal component analysis (PCA) demonstrated that both natural and human factors regulate groundwater chemistry in the region. The analysis of Q-mode agglomerative hierarchical clustering highlighted three significant water clusters. Ca–HCO3 was the most prevalent hydro-chemical facies in all three clusters. Geochemical modelling through various conventional plots indicated that groundwater chemistry in the research region is influenced by the dissolution of calcite/dolomite, reverse ion exchange, and by silicate and halite weathering. EWQI data of the study area disclosed that 73.69% of the samples were appropriate for drinking. Due to high salinity, Magnesium (Mg2+), Nitrate (NO3−), and Bicarbonate (HCO3−) concentrations, the north-central and north-eastern regions are particularly susceptible. The findings of the study may be accomplished by policymakers and groundwater managers to achieve sustainable groundwater development at the regional scale.
... This revision of the MCL recognizes the detrimental health effects associated with arsenic in drinking water, including bladder, skin, and lung cancers, diabetes, and neurological dysfunction (National Research Council, 1999). Elevated concentrations of arsenic from natural sources (>0.05 mg L -1 ) have been widely documented, for example, in Argentina, Bangladesh, Chile, West Bengal, Mexico, Taiwan, Mexico, and parts of the United States (e.g., Mandal, 1997;Nickson et al., 1998;Welch et al., 1988;Del Razo et al., 1990;McArthur et al., 2001;Rahman et al., 2001;Nordstrom, 2002). While arsenic occurs naturally, it may also be found as a result of a variety of industrial processes, including mining, metal refining, manufacture and use of arsenical pesticides and herbicides, release of industrial effluents, leather and wood treatments, and chemical waste disposal. ...
Contamination of ground-water resources by arsenic is a widespread environmental problem; consequently, there is an escalating need for developments and improvements of remedial technologies to effectively manage arsenic contamination in ground water and soils. In June 2005, a 9.1 m long, 14 m deep, and 1.8 to 2.4 m wide (in the direction of ground-water flow) pilot-scale permeable reactive barrier (PRB) was installed at a former metal smelting facility. The reactive barrier was designed to treat ground water contaminated with moderately high concentrations of both arsenite and arsenate. The reactive barrier was installed over a 3-day period using bio-polymer slurry methods and modified excavating equipment for deep trenching. The reactive medium was composed entirely of granular iron. A monitoring network of approximately 40 ground-water sampling points was installed in July 2005. Monitoring results indicate arsenic concentrations >25 mg L-1 in wells located hydraulically upgradient of the PRB. Within the PRB, arsenic concentrations are reduced to 2 to <0.01 mg L-1. After 2 years of operation, monitoring points located within 1 m of the downgradient edge of the PRB showed significant decreases in arsenic concentrations at depths intervals impacted by the emplaced zerovalent iron. Arsenic removal in the PRB results from several pathways involving adsorption to iron oxide and iron sulfide surfaces. These different uptake processes lead to multiple oxidation states and bonding environments for arsenic in the reactive medium as indicated using spectroscopic methods. This report covers aspects of site characterization, remedial design and implementation, and monitoring results for this pilot-scale PRB, including a flux-based analysis for arsenic.
... Moreover, in the meandering position and banks of river Ganga, there is a high amount of clay content in the soil, which absorbs organic carbon from river deposits. This condition favors reducing conditions, and arsenic is dissolution from the surface of Fe 2+ + hydroxides (McArthur et al., 2001). ...
Groundwater is an essential resource; around 2.5 billion people depend on it for drinking and irrigation. Groundwater arsenic contamination is due to natural and anthropogenic sources. The World Health Organization (WHO) has proposed a guideline value for arsenic concentration in groundwater samples of 10μg/L. Continuous consumption of arsenic-contaminated water causes various carcinogenic and non-carcinogenic health risks. In this paper, we introduce a geospatial-based machine learning method for classifying arsenic concentration levels as high (1) or low (0) using physicochemical properties of water, soil type, land use land cover, digital elevation, subsoil sand, silt, clay, and organic content of the region. The groundwater samples were collected from multiple sites along the river Ganga’s banks of Varanasi district in Uttar Pradesh, India. The dataset was subjected to descriptive statistics and spatial analysis for all parameters. This study assesses the various contributing parameters responsible for the occurrence of arsenic in the study area based on the Pearson correlation feature selection method. The performance of machine learning models, i.e., Extreme Gradient Boosting (XGBoost), Gradient Boosting Machine (GBM), Decision Tree, Random Forest, Naïve Bayes, and Deep Neural Network (DNN), were compared to validate the parameters responsible for the dissolution of arsenic in groundwater aquifers. Among all the models, the DNN algorithm outclasses other classifiers as it has a high accuracy of 92.30%, a sensitivity of 100%, and a specificity of 75%. Policymakers can utilize the accuracy of the DNN model to approximate individuals prone to arsenic poisoning and formulate mitigation strategies based on spatial maps.
... The lower unit is yellow to brown, oxidized, coarser-grained, and mostly developed in upland parts; the upper unit is characteristically grey, Bne to coarse-grained, often micaceous, and deposited in lower elevations. McArthur et al. (2001) suggested retreat of continental glaciers at the end of the Pleistocene leads to the rise of sea level and river base levels, and subsequent deposition of the Holocene alluvium, which later becomes the host of As-contaminated groundwater. ...
This study is based on ongoing aquifer mapping by the nodal organization of Govt. of India. It deals in role of physical environmental factors on geogenic ground water contamination. This is particularly important for formulation of management of aquifers.
... Moreover, it causes acidification and hardness in groundwater as well (Pacheco et al., 2013). It was also found that geological sources, particularly natural ones, were a contributing factor to the elevated concentrations of ammonium that occur in Bangladesh, China, Italy, the USA, and Vietnam (McArthur et al., 2001;Jiao et al., 2010;Mastrocicco et al., 2013;Jia et al., 2018). Several agricultural practices such as the application of nitrogen fertilizers, the application of wastewater to irrigate crops, and using livestock and poultry waste products are responsible for groundwater contamination with nitrate. ...
Synthetic fertilizers have been revolutionary in the way that the increased production of food crops has increased as a result of the application of synthetic fertilizers. Despite the fact that global N, P, and K consumption have increased from 64.9, 25.9, and 18.2 kg/ha in the year 2000 to 85.5, 33.2, and 20.4 kg/ha, respectively, they are still relatively low. Additionally, excessive use of inorganic fertilizers has also resulted in a deterioration of environmental systems, especially that of water resources. The presence of this toxic substance inside the human body is therefore due to the fact that it enters the body through the food chain and causes serious illnesses, such as cancer. For instance, in most countries, the maximum nitrate concentration for drinking water is restricted to between 45 and 50 mg/L. Besides promoting the use of chemicals and the application of fertilizers in farming, there should be a push to encourage the sustainable use of biofertilizers to protect the environment and human health. Composts that have been developed from various waste materials, such as poultry farms, dairy farms, and other sources, have proven to be very rich in N, P, and K. For example, compost generated from dairy farm wastes can provide a value of 45,100, 7300, and 9100 mg/kg of N, P, and K, respectively. In order to make the use of these biofertilizers in agriculture possible, it will be necessary to spread awareness among the farmers so that they can adopt the concepts of sustainable management in agriculture.
Groundwater arsenic (As) contamination is prevalent in different parts of the world to varying extents; however, its severity in India is a major concern, which has garnered significant global attention. The nature of the problem is considered to be geogenic. The identification of this crisis took place not too long ago; still it has managed to acquire the form of an endemic in the country. Millions of individual are getting vulnerable to arsenicosis on getting exposed to As polluted water. The concentration of the metalloid in the Indian groundwater reserves is often found to be as high as few thousand ppm, which is way beyond10 µg/L (10 ppb), the permissible limit of the metalloid in drinking water, set by WHO. Viable options for mitigating this problem and supply clean water to the affected populace include either identification of alternative As-free aquifers or developing new technologies for the treatment of As contaminated water. The major arsenic treatment units (ATUs) or arsenic removal plants (ARPs), installed in different As affected areas all over the country, are based on several conventional principles namely adsorption, oxidation, precipitation-filtration, coagulation-flocculation, electro-coagulation and membrane separation. Implementation of a single technology or devising an end-of-pipe solution for the remediation of As contamination seem far-fetched due to nature of the aquifers, socio-economic conditions and geo-political issues. The review aims at understanding the current scenario of the problems associated with As contaminated groundwater with respect to the Indian peninsula. It also emphasizes on the different technologies implemented for As removal, in terms of sustainability and economic feasibility.
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 high exposure of fluoride and arsenic in the groundwater of India is a serious challenge that is currently threatening human health, agriculture, livestock, and livelihood. The increased dependency on groundwater due to monsoonal uncertainties amplifies the risk by several folds. Due to the high population density in the affected regions, policies on prevention, monitoring, and mitigation have become extremely challenging to implement. The pursuit of improved human health in the affected regions cannot be completed until and unless there is sufficient urbanization and industrialization to support the livelihood, which again aggravates the situation due to improper disposal of anthropogenic contaminants owing to the lack of knowledge about the natural cycle of contaminants. The present review article is an attempt to understand the problem of fluoride and arsenic in the scenario of Indian floodplains by first explaining the globally identified mobilization mechanisms of these contaminants and then developing a compendium of knowledge through which the risk on the Indian floodplains can be analysed. Then the study compares the similarity/dissimilarity in the enrichment mechanism followed by a detailed investigation of the available mitigation techniques. In totality, the present study adds a new dimension to our understanding of the risk due to contaminants.
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.
Concentrations of potentially toxic elements (PTEs) like arsenic, uranium, iron, and nitrate in the groundwater of the Majha Belt (including Tarn Taran, Amritsar, Gurdaspur, and Pathankot districts) in Punjab, India were measured to evaluate the health risks associated with its consumption and daily use. The average concentrations of these elements in some locations exceeded the WHO-recommended values. Arsenic and iron toxicity levels were found to be higher in the Amritsar district, while uranium toxicity was more prevalent in Tarn Taran. The Trace Element Evaluation Index suggests that Amritsar is one of the districts most affected by toxic elements. According to the US Environmental Protection Agency’s (USEPA) guidelines, the HQ values of U, Fe, and nitrate were less than one, indicating that there is no non-carcinogenic health risk for adults and children. However, the hazard quotient (HQ) value for arsenic was greater than one, indicating a higher possibility of health risk due to arsenic in the study area. The total hazard index values of 44.10% of samples were greater than four for arsenic, indicating that people in the Majha Belt are at a very high health risk due to the usage of water for drinking and domestic purposes. The cancer risk assessment values for arsenic in children (5.69E + 0) and adults (4.07E + 0) were higher than the accepted limit of USEPA (10⁻⁴ to 10⁻⁶) in the Majha Belt. The average radiological cancer risk values of U for children and adults were 8.68E-07 and 9.45E-06, respectively, which are well below the permissible limit of 1.67 × 10⁻⁴ suggested by the Atomic Energy Regulatory Board of DAE, India. The results of this study confirm that the residents of the Majha Belt who use contaminated groundwater are at a serious risk of exposure to arsenic in the Amritsar district and uranium in Tarn Taran district.
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.
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.
Dissolved organic matter (DOM) plays a crucial role in the biogeochemical processing of reactive nitrogen in groundwater systems. However, the impacts of DOM on release of geogenic ammonium and transport and transformation of reactive nitrogen including nitrate attenuation under dynamics in groundwater level characteristic for floodplain environments remain unclear. In this study, we have identified the influence of riparian water level fluctuations on changes in the redox conditions, groundwater geochemical composition including the DOM mobilization in the piedmont recharge and the discharge area along groundwater flow paths. We have also evaluated the pivotal roles of DOM degradation in transport and transformation of nitrogen species including geogenic ammonium enrichment, nitrate attenuation, and dissolved nitrous oxide (N2O) production combining the stable carbon isotopic signatures and the optical characteristics of DOM. Along groundwater flow paths, the seasonal amplitudes of surface water levels were higher in the piedmont recharge area than those in the plain discharge area, and four DOM fluorescent components were identified through the parallel factor analysis (PARAFAC), with two terrestrial humic-like components (C1 and C2) in the piedmont recharge area, and two microbial humic-like components (C3 and C4) in the plain transition-discharge area. A positive correlation between stable dissolved inorganic carbon isotopic signatures (δ13C-DIC) and ammonium-nitrogen concentrations indicated that microbial degradation processes of DOM concomitantly promote the release of geogenic ammonium into groundwater. Ammonium enrichment and nitrate attenuation trend in groundwater was noted as one moved from the recharge area to the discharge area. Evidently, a clear correlation emerged where elevated dissolved N2O concentrations were linked to diminished ammonium-nitrogen levels and elevated nitrate-nitrogen levels. Additionally, groundwater exhibited higher dissolved N2O levels in the piedmont recharge area compared to the plain discharge area. These findings revealed that the impacts of groundwater DOM degradation on nitrate attenuation and dissolved N2O production in similar geogenic ammonium-affected Quaternary alluvial aquifers along groundwater flow paths, and established the theoretical basis for ensuring the security of local groundwater supply.
At a great many locations worldwide, the safety of drinking water is not assured due to pollution with arsenic. Arsenic toxicity is a matter of both systems chemistry and systems biology: it is determined by complex and intertwined networks of chemical reactions in the inanimate environment, in microbes in that environment, and in the human body. We here review what is known about these networks and their interconnections. We then discuss how consideration of the systems aspects of arsenic levels in groundwater may open up new avenues towards the realization of safer drinking water. Along such avenues, both geochemical and microbiological conditions can optimize groundwater microbial ecology vis-à-vis reduced arsenic toxicity.
In alluvial aquifers with near-neutral pH and high dissolved arsenic (As) concentrations, the presence and character of sedimentary organic matter (SOM) regulates As mobility by serving as an energetically variable source of electrons for redox reactions or forming As–Fe-OM complexes. Near tidally and seasonally fluctuating rivers, the hyporheic zone (HZ), which embodies the mixing zone between oxic river water and anoxic shallow groundwater, may precipitate (or dissolve) iron (Fe)-oxides which sequester (or mobilize) As. To understand what is driving the mobilization of As within a shallow aquifer and riverbank sands adjacent to the tidally fluctuating Meghna River, we characterized the chemical reactivity of SOM from the sands, and a silt and clay layer, underlying the HZ and aquifer, respectively. Dissolved As (50–500 μg/L) and Fe (1–40 mg/L) concentrations increase with depth within the shallow aquifer. Similar vertical As and Fe concentration gradients were observed within the riverbank sands where concentrations of the products of reductive dissolution of Fe-oxides increase with proximity to the silt layer. Compared to all other sediments, the SOM in the clay aquitard contains older, more recalcitrant, terrestrially-derived material with high proportions of aromatic carboxylate functional groups. The shallow silt layer contains fresher SOM with higher proportions of amides and more labile polysaccharide moieties. The SOM in both the riverbank and aquifer is terrestrially-derived and humic-like. The labile SOM from the silt layer drives the microbially mediated reductive dissolution of As-bearing Fe-oxides in the HZ. In contrast, the carboxylate-rich SOM from the clay aquitard maintains dissolved As concentrations at the base of the aquifer by complexing with soluble As and Fe. This highlights that SOM-rich fine (silt or clay) layers in the Bengal basin drive As and Fe mobility, however, the specific processes mobilizing As and Fe depend on the lability of the SOM.
Arsenic (As) pollution, is a global problem, threatening human health and ecological security, especially in the bay environment with dense population and human activities. Among potential pathways of As into the bay, submarine groundwater discharge (SGD) has not received adequate attention due to its invisibility. We determined As and 222Rn activity concentrations in different water mass. Spatial variation of dissolved As concentration in the groundwater was large and attributed to the adjacent local industries. By combining 222Rn mass balance modeling with As concentrations measured, the SGD-derived As fluxes was conservatively estimated to be 1310 kg As d−1 and 5880 kg As d−1 in the dry and wet seasons, respectively. The migration of arsenic may be enhanced by rainfall and dissolved carbon. The amount of SGD derived As input to the bay was greater than the total combined As input from river discharge, atmosphere, sewage drainage, and diffusion from sediment.
Selective removal of trace, highly toxic arsenic from water is vital to ensure an adequate and safe drinking water supply for over 230 million people around the globe affected by arsenic contamination. Here, we developed an Fe-based metal-organic framework (MOF) with a ferrocene (Fc) redox-active bridge (termed Fe-MIL-88B-Fc) for the highly selective removal of As(III) from water. At a cell voltage of 1.2 V, Fe-MIL-88B-Fc can selectively separate and oxidize As(III) into the less harmful As(V) state in the presence of a 100- to 1250-fold excess of competing electrolyte, with an uptake capacity of >110 mg-As g-1 adsorbent. The high affinity between the uncharged As(III) and the μ3-O trimer (-36.55 kcal mol-1) in Fe-MIL-88B-Fc and the electron transfer between As(III) and redox-active Fc+ synergistically govern the selective capture and conversion of arsenic. The Fe-based MOF demonstrates high selectivity and capacity to remediate arsenic-contaminated natural water at a low energy cost (0.025 kWh m-3). This study provides valuable guidance for the tailoring of effective and robust electrodes, which can lead to a wider application of electrochemical separation technologies.
Although high levels of geogenic ammonium in groundwater have been widely reported, the mechanisms controlling its heterogeneous distribution are not yet well understood. In this study, a comprehensive investigation of hydrogeology, sediments, and groundwater chemistry was coupled with a set of incubation experiments to reveal the contrasting mechanisms of groundwater ammonium enrichment at two adjacent monitoring sites with different hydrogeologic settings in the central Yangtze River basin. Significant differences were found in the ammonium concentrations of groundwater at two monitoring sites, with the ammonium concentrations in the Maozui (MZ) section (0.30-5.88 mg/L; average of 2.93 mg/L) being much higher than those in the Shenjiang (SJ) section (0.12-2.43 mg/L; average of 0.90 mg/L). For the SJ section, the aquifer medium had a low organic matter (OM) content and a weak mineralization capability, leading to a limited potential for geogenic ammonium release. Moreover, due to the presence of alternating silt and continuous fine sand layers (with coarse grains) above the underlying confined aquifer, the groundwater was in a relatively open environment with oxidizing conditions, which may have promoted the removal of ammonium. For the MZ section, the aquifer medium had a high OM content and a strong mineralization capability, leading to a much higher potential for geogenic ammonium release. Furthermore, due to the presence of a thick and continuous muddy clay layer (aquitard) above the underlying confined aquifer, the groundwater was in a closed environment with strong reducing conditions, which was conductive to the storage of ammonium. Larger sources of ammonium in the MZ section and greater consumption of ammonium in the SJ section contributed collectively to the significant differences in groundwater ammonium concentrations. This study identified contrasting mechanism of groundwater ammonium enrichment in different hydrogeologic settings, which can help explain the heterogeneous distribution of ammonium levels in groundwater.
The study of microbial community in groundwater systems is considered to be essential to improve our understanding of arsenic (As) biogeochemical cycling in aquifers, mainly as it relates to the fate and transport of As. The present study was conducted to determine the microbial community composition and its functional potential using As-contaminated groundwater from part of the Bengal Delta Plain (BDP) in West Bengal, India. Geochemical analyses indicated low to moderate dissolved oxygen (0.42-3.02 mg/L), varying As (2.5-311 µg/L) and Fe (0.19-1.2 mg/L) content, while low concentrations of total organic carbon (TOC), total inorganic carbon (TIC), nitrate, and sulfate were detected. Proteobacteria was the most abundant phylum, while the indiscriminate presence of an array of archaeal phyla, Euryarchaeota, Crenarchaeota, Nanoarchaeota, etc., was noteworthy. The core community members were affiliated to Sideroxydans, Acidovorax, Pseudoxanthomonas, Brevundimonas, etc. However, diversity assessed over multiple seasons indicated a shift from Sideroxydans to Pseudomonas or Brevundimonas dominant community, suggestive of microbial response to seasonally fluctuating geochemical stimuli. Taxonomy-based functional potential showed prospects for As biotransformation, methanogenesis, sulfate respiration, denitrification, etc. Thus, this study strengthened existing reports from this region by capturing the less abundant or difficult-to-culture taxa collectively forming a major fraction of the microbial community.
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.
Gas occurrences in irrigation wells have been reported from most parts of the counry, and in some parts of the southeast region, gas occurrences have become a limiting factor for groundwater development. Methane is the main component of water well gases and is readily identified by its ignition characteristics. It has been found that conditions required for gas formation, such as the amount of total organic carbon and organic matter, depth of burial, hydrothermal gradient and degree of compaction, are all favourable for the generation of biogenic gases in the deltaic regions of the Bengal Basin. Biogenic gas from water wells contains only methane as the hydrocarbon gas and along with more than one per cent (by volume) of carbon dioxide. On theother hand thermogenic gas from deep wells contains methane and other higher hydrocarbon gases along with less than one per cent of carbon dioxide. Areas marked by high groundwater salinity generates more methane than other parts of the country and this is suggestive of estuarine environment of deposition of the aquifer materials in those areas.
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.
The people of Bangladesh used to rely on surface water for drinking, which was often infected with cholera and other life-threatening diseases. To reduce the incidences of these diseases, millions of tubewells were installed in Bangladesh over the last 27 years. This recent transition from surface water to groundwater has significantly reduced deaths from water-borne pathogens; however, recent evidence suggests disease and death from arsenic and potentially other metals in groundwater are impacting large areas of Bangladesh.
In this preliminary assessment the areal and vertical distribution of arsenic and other inorganic chemicals in the groundwater was mapped throughout Bangladesh. The study suggests that a major source of this arsenic may be one or more phosphate minerals containing arsenate as an impurity. Evidence for other potentially toxic heavy metals in groundwater was also discovered. Several appropriate treatment technologies were evaluated.
Few wetland studies from temperate North America have related either spe- cies richness or plant community composition to any direct measure of nutrient availability, or examined changes in species composition following experimental nutrient additions. Studies of wetlands in western Europe and of other terrestrial ecosystems in North America frequently show that nutrient enrichment leads to changes in species composition, declines in overall plant species diversity, and loss of rare and uncommon species. We therefore used an extensive literature survey and analysis of data on plant species composition, species richness, productivity or standing crop, and C:N:P stoichiometry in plant tissues and surface soils to draw conclusions about the nature of nutrient limitation in temperate North American bogs, fens, marshes, and swamps, and to infer their potential response to nutrient enrichment. We searched all major bibliographic data bases for studies containing such data (through March 1998) and added relevant data from our own ongoing research. We analyzed plant and soil data sets by wetland type and by wetland soil type, and the plant data set also by growth form. Existing studies appear to confirm common generalizations: (1) plant community type changes across broad nutrient gradients; (2) species richness declines as various indicators of nutrient availability increase beyond some threshold; and (3) rare and uncommon species are almost always associated with species-rich communities. However, (1) these general- izations do not always hold within community types; (2) for many community types, the threshold beyond which richness declines has not been established, and high or low diversity may occur below that threshold; and (3) the failure of many studies to include bryophytes precludes drawing strong conclusions about nutrient availability and diversity in peatlands. Marshes had significantly lower mean nitrogen : phosphorus (N:P) ratios in live tissue than other wetland types (bogs, fens, and swamps), which did not differ significantly from each other. Mean N:P ratios in live tissues were significantly higher in peatlands than in mineral-soil wetlands. Nitrogen : phosporus ratios in litter did not differ significantly between peatlands and mineral-soil wetlands but were higher than in live tissues. Among growth forms, the highest mean N:P ratios in live tissues occurred in bryophytes, and the lowest in vascular herbaceous species. Only bryophyte live tissues differed significantly from other growth forms; litter N:P ratios were not significantly different among growth forms. Average N:P ratios in surface soils were lower in marshes and swamps than in bogs and fens. Wetlands on mineral soils had lower average N:P ratios than wetlands on peat soils. Average surface soil N:P ratios rose sharply at high soil organic-matter contents ( $90%) and were generally greater than 16 at organic-matter concentrations above 20%. In combination, plant tissue and surface soil N:P ratios suggest that a large proportion of North American wetlands are either P limited or co-limited by N and P, especially those occurring on organic soils. Only marshes have N:P ratios in both live tissues and surface soils that consistently indicate N limitation, although soils data suggest that the majority of swamps are also N limited. Vascular herbaceous species appear to be N limited, but no pattern is apparent among other growth forms. Inferences drawn from N:P stoichiometry need to be verified by examining ecosystem response to experimental fertilization. High variances in plant and soil N:P ratios suggest that understanding nutrient limitation at both the community and individual-species level may be necessary to predict changes in species composition and richness with nutrient enrichment.
Long-term studies along a 30-yr nutrient-enrichment gradient in the northern part of the subtropical Everglades fen allowed us to assess the effects of nitrogen (N) and phosphorus (P) additions on plant community structure and chemical qualities of wetland plants. Areas in the highest P-enriched zones (>1000 mgP/kg), once dominated by open-water sloughs and surrounding monocultures of sawgrass (Cladium jamaicense, a stress-tolerant low-nutrient-status species), are now dominated by cattail (Typha domingensis, a competitive, high-nutrient-status species). Areas of moderate (750-500 mg/kg) and low (<500 mg/kg) P soil concentrations have maintained their original plant composition. Analysis of nutrient-use efficiency indicates that sawgrass is highly efficient in nutrient resorption and nutrient proficiency, but this efficiency decreases at high soil P concentrations. Both indices indicate that suboptimal concentrations of P, which limit growth and optimize retention of P within the plant, exist in the Everglades. This information, when coupled with the low levels of P found in the plants, soil, and pore water of the unenriched portions of the Everglades, indicates that this ecosystem is extremely P limited. High molar N:P leaf ratios suggested P limitations for sawgrass at unenriched sites, but not in highly enriched areas. Intermediate P loadings resulted in either N or P limitations. Increased leaf P concentrations correspond to decreased phenolic content of sawgrass leaves, suggesting that this species' metabolic growth response follows the carbon-nutrient balance hypothesis of decreased production of phenolics with increased nutrient supply. Concomitant with decreased foliar phenolic content at high P enrichment was an increase in herbivory and fungal infections.
Geomicrobiology : Interactions between microbes and minerals Eds J.F. Banfield and K.H. Nealson Reviews in Mineralogy vol 35, Mineralogical Society of America.
As stated throughout this book and effectively described in the various chapters Geomicrobiological research has made major discoveries in the last few years which has profound implications. Many of these relate to microbial mineral interactions and we are becoming aware of the global significance of these interactions and the probable role this has played in the evolution of our planet. This is coupled with discoveries of microbial populations deep within the Earth’s crust and of inorganically drivern anaerobic ecosystems completely independent of photosynthetically fixed organic carbon. All of this elequently demonstrates the intimate coupling between the biosphere and geosphere, which has thrown the previously disparate disciplines of microbiology and geology together and has proved that the early disciples of Geomicrobiology to be fully justified. Some of these aspects are described in this book, but not all, and in that sense the book doesn’t cover Geomicrobiology, but a sub set concerned with microbe:mineral interactions. Yet, there is more than just microbes and minerals. In the first two chapters there is a concise introduction to bacteria, their activity and diversity and importantly whats new in each. There are detailed chapters on the cryrstal structure, geochemistry, formation and dissolution/weathering of minerals, providing intriguing details of minerals as a potential microbial habitat, providing a substrate, energy source, nutirients and sometimes protection and a home. The biomineral home becomes exquisite with exoskeletons of calcium carbonate secreting algae and diatoms and we are treated to a description of the fine cellular control of these elegant structures, only to find out that for calcium carbonate producers it might just be a cleaver way of maximising limiting carbon dioxide for photosynthesis, but why the species specific delicate structures ?
Origin of life isotopes dip into as modest cost !
The Middendorf aquifer of South Carolina exhibits a 40-kilometer-wide zone where dissolved ferrous iron concentrations commonly exceed 1 mg/I. Downgradient of this zone, dissolved iron concentrations decrease to less than 0.05 mg/1. Geochemical and microbiologie evidence indicates that this zonation reflects the competitive exclusion of sulfate-reducing activity by Fe(IH)-reducing bacteria in the high-iron zone and the emergence of sulfate reduction as the predominant process in the low-iron zone. Viable Fe(III)- and sulfate-reducing bacteria coexist throughout the aquifer. However, the observed linear relationship between dissolved iron and dissolved inorganic carbon as well as the lack of sulfate consumption indicates that sulfate-reducing bacteria are much less active than Fe(III)-reducing bacteria in the high-iron zone. Fe(III)-reducing bacteria appear to exclude sulfate-reducing activity by maintaining dissolved hydrogen (˜1.0 nM), formate (˜2.0 μM), and acetate (˜1.0 μM) concentrations at levels lower than thresholds required by sulfate-reducing bacteria. Downgradient of the high-iron zone, Fe(III)-reducing activity becomes limited by a lack of Fe(III) oxyhydroxides as Middendorf sediments become progressively more marine in origin. Hydrogen, formate, and acetate concentrations then increase to levels (˜3.0 nM, ˜10.9, and 2.5 μM, respectively) that allow sulfate-reducing bacteria to become active. Increased sulfide production strips ferrous iron from solution by precipitating ferrous sulfides, and dissolved iron concentrations decrease. The observed high-iron zonation is thus one manifestation of microbial competition for scarce substrates. The wide occurrence of similar water-chemistry patterns implies that microbial competition mechanisms are important to the ground-water geochemistry of many hydrologie systems.
Microbial processes affect the chemical composition of groundwater and the hydraulic properties of aquifers in both contaminated and pristine groundwater systems. The patterns of water-chemistry changes that occur depend upon the relative abundance of electron donors and electron acceptors. In many pristine aquifers, where microbial metabolism is limited by the availability of electron donors (usually organic matter), dissolved inorganic carbon (DIC) accumulates slowly along aquifer flow paths and available electron acceptors are consumed sequentially in the order dissolved oxygen > nitrate > Fe(III) > sulfate > CO2 (methanogenesis). In aquifers contaminated by anthropogenic contaminants, an excess of available organic carbon often exists, and microbial metabolism is limited by the availability of electron acceptors. In addition to changes in groundwater chemistry, the solid matrix of the aquifer is affected by microbial processes. The production of carbon dioxide and organic acids can lead to increased mineral solubility, which can lead to the development of secondary porosity and permeability. Conversely, microbial production of carbonate, ferrous iron, and sulfide can result in the precipitation of secondary calcite or pyrite cements that reduce primary porosity and permeability in groundwater systems.
Himalayan rivers have very unusual Sr characteristics and their budget cannot be achieved by simple mixing between silicate and carbonate even if carbonates are radiogenic. We present Sr, O, and C isotopic data from river and rain water, bedload, and bedrock samples for the western and central Nepal Himalaya and Bangladesh, including the monsoon season. Central Himalayan rivers receive Sr from several sources: carbonate and clastic Tethyan sediments, High Himalayan Crystalline (HHC) gneisses and granitoids with minor marbles, carbonates and metasediments of the Lesser Himalaya (LH), and Miocene-Recent foreland basin sediment from the Siwaliks group and the modern flood plain. In the Tethyan Himalaya rivers have dissolved [Sr] ≈ 6 μmol/l and 87Sr/86Sr ≈ 0.717, with a large contribution from moderately radiogenic carbonate. Rivers draining HHC gneisses are very dilute with [Sr] ≈ 0.2 μmol/l and 87Sr/86Sr ≈ 0.74. Lesser Himalayan streams also have low [Sr] ≈ 0.4 μmol/l and are highly radiogenic (87Sr/86Sr ≥ 0.78). Highly radiogenic carbonates of the LH do not contribute significantly to the Sr budget because they are sparse and have very low [Sr]. In large rivers exiting the Himalaya, Sr systematics can be modeled as a mixture between Tethyan rivers, where slightly radiogenic carbonates (mean 87Sr/86Sr ≈ 0.715) are the main source of Sr, and Lesser Himalaya waters, where extremely radiogenic silicates (>0.8) are the main source of Sr. HHC waters are less important because of their low [Sr]. Rivers draining the Siwaliks foreland basin sediments have [Sr] ≈ 4 μmol/l and 87Sr/86Sr ≈ 0.725. Weathering of silicates in the Siwaliks and the flood plain results in a probably significant radiogenic (0.72–0.74) input to the Ganges and Brahmaputra (G-B), but quantification of this flux is limited by uncertainties in the hydrologic budget. The G-B in Bangladesh show strong seasonal variability with low [Sr] and high 87Sr/86Sr during the monsoon. Sr in the Brahmaputra ranges from 0.9 μmol/l and 0.722 in March to 0.3 μmol/l and 0.741 in August. We estimate the seasonally weighted flux from the G-B to be 6.5 × 108 mol/yr with 87Sr/86Sr = 0.7295.
Until recently, nonenzymatic processes were generally considered to account for much of the Fe(III) reduction in subsurface environments. However, it is now;clear that enzymatic Fe(III) reduction catalyzed by microorganisms which conserve energy to support growth by completely oxidizing organic compounds to carbon dioxide accounts for most of the Fe(III) reduction. Microbial Fe(III) reduction in deep pristine aquifers releases dissolved inorganic carbon into groundwater which may increase aquifer porosity. The Fe(II) released into the groundwater is an important groundwater quality problem in many aquifers. Microbial oxidation of organic contaminants coupled to Fe(III) reduction removes significant amounts of pollutants from many contaminated aquifers. Fe(III) reduction and hence contaminant removal can be accelerated in aquifer sediments with the addition of Fe(III) chelators or humic substances. Both of these amendments alleviate the need for Fe(III) reducers to come into direct physical contact with Fe(III) oxides in order to reduce them. Some Fe(III)-reducing microorganisms can reduce contaminant metals and metalloids such as uranium, technetium, cobalt, chromium and selenium. This metabolism may be useful for remediation of metal-contaminated subsurface environments. Fe(III) reducers and some of the insoluble Fe(II) products of Fe(III) reduction can reducively dechlorinate chlorinated contaminants. Magnetite that is similar to that produced by known Fe(III)-reducing microorganisms has been recovered at depths as great as 6.7 km on Earth and has been observed in a Martian meteorite. Thus, microbial oxidation of organic matter coupled to the reduction of Fe(III) to Fe(II) appears to be a important process in a variety of subsurface environments.
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.
A total of five hundred shallow and deep tube well samples were measured for arsenic content by spectroscopic method using both Zn/HCl and NaBH4 for arsine generation. The concentration ranged from 0 - 1.7 ppm. Spatial maps were prepared based on the results obtained. Highest arsenic concentrations were found to have occurred at a depth 60-1000 ft. Some deep tube wells also recorded arsenic in the concentration range 0.25 -0.16 ppm. Particularly, the Block Goalchamat showed arsenic in the deep tube wells (.250 ft), while the shallow layer in the block (>22 ft) recordrd no arsenic. Speciation for As+3 and As+5 done in the field showed that As+3 ranged from 88-50% of the total arsenic. It was found that in the areas which recorded high As+3 percentage even though the total arsenic may have been low (<1ppm), causes of arsenic affected persons were more prevalent. Eight persons with high arsenic content in their urine (250mg/d) were monitored on month basis and were found to be free of arsenic in their urine on administration of arsenic free drinking water. on the basis of the results obtained so far, attempts have been made to understand the biologeochemical mobilization of arsenic by various processes such as organic matter, Fe+2, S-2 ,and formation and primary productivity of paleo-oxbow lakes.
On the mitigation endeavors, a removal material based on the chemically treated laterite-Fe2O3 matrix was prepared. This was used for preparation of low cost column, domestic filter, and strainers of hand tube wells. All the systems worked efficiently at a concentration of 1.6 ppm. Domestic filters have been released in the market on trial basis. The strains for the tube wells are being installed.
Extracellular polysaccharide secretion (EPS) is a salient feature of many soil bacteria. This study investigates whether an EPS shell modulates the diffusion rate of nutrients in the immediate microenvironment of soil microorganisms. The diffusion of glucose through pure microbial polysaccharides xanthan and dextran, and through kaolinite and EPS-amended kaolinite was measured at several water potentials using a steady state method. A specific device was developed to simultaneously monitor water potential (Ψ) using polyethylene glycol (PEG) solutions, and measure diffusion rates. The diffusion rate of glucose increased with increasing Ψ and volumetric water content in both polysaccharides. At all Ψ values studied, glucose diffused faster in EPS or in EPS-amended clay than in pure clay, due to the higher volumetric water content of EPS and their water-saturated porosity. Water retention and diffusion characteristics in EPS may thus help soil bacteria to maintain physiological functions at low water potential.
Samples of Precambrian carbonate (mostly dolomite) outcrops collected across the Lesser Himalaya have been analysed for their mineralogy, chemical composition, and isotope ratios of Sr, O, and C to assess the extent of their preservation and their role in contributing to the high radiogenic strontium isotope composition of the source waters of the Ganga, Ghaghara, and the Indus. Their Sr concentrations range from 20 to 363 ppm, δ¹⁸OPDB −1.4 to −12.8‰ and Mn 11–2036 ppm. The petrography of the samples, their low Sr concentrations, and wide range of δ¹⁸O values are suggestive of their postdepositional alteration. The ⁸⁷Sr/⁸⁶Sr of the bulk samples and their carbonate fractions are similar to one another with values ranging from 0.7064 to 0.8935 and are generally more radiogenic than that of contemporaneous seawater.
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.
A geochemical study of the groundwater of the pampa in the province of Cordoba, Argentina, is reported. Physical-chemical parameters, dissolved solids, and seven trace elements were determined in 60 selected water samples. Systematic and accurate measurements of arsenic, fluorine, and vanadium were performed for the first time. The geographic distribution of the seven trace elements was mapped and its correlation with the anion-cation composition of the water was studied. Eighty-four percent of the water analyzed showed arsenic contents over 0.05 mg/l. The maxima for arsenic, fluorine, vanadium, and uranium contents were found in the western part of the study area, in waters dominated by alkali metal cations. Maximum selenium and antimony contents were found in the eastern part of the areas, whereas molybdenum distribution showed no relationship to the other groups. The movements of the subsoil have disturbed surface and subsurface drainage, thus influencing the water salinity and trace element contents. To investigate the origin of contamination, 54 loess samples were collected at wells in depths ranging from the surface down to the water table. This loess, which has a high proportion of volcanic components, mainly rhyolitic glass, exhibits a chemical composition corresponding to that of a dacite. The loess and volcanic glass show anomalous contents of all contaminant trace elements, mainly arsenic and selenium. For this reason, loess is considered to be the most important source of contamination of this ground water area. 30 refs., 6 figs., 9 tab.
The sediment in a reservoir on the Clark Fork River in western Montana is contaminated with arsenic, copper, zinc, and other elements. This sediment is the source of groundwater contamination in the adjacent alluvial aquifer, and this study elucidates the processes transferring arsenic to the groundwater by the formation of diagenetic sulfides in the sediment. Vertical trends in a core through oxidized surface sediment into reducing sediment below show that concentration and partitioning of metals and arsenic are controlled by the redox interface. Solid phases of arsenic, copper, and zinc change from dominantly oxyhydroxide and organic phases to sulfide phases across the interface. Arsenic, copper, zinc, manganese, and iron in the pore water are controlled by the solubility of iron and manganese oxyhydroxides in the oxidized zone and metal sulfides in the reduced zone. The change in redox conditions upon burial results in a system where the growth of diagenetic copper, zinc, and arsenic sulfides controls the distribution and partitioning of metals and arsenic in the sediment and the speciation and release of arsenic to the adjacent groundwater system.
LIMNOLOGY January 1977 AND Volume 22 Number OCEANOGRAPHY Microbial methane consumption reactions and their effect on methane distributions in freshwater and marine environment? William Institute S. Reeburgh and David T. Heggk of Marine Science, University of Alaska, Fairbanks Abstract A survey of reported methane distributions in sediments and the adjacent overlying water shows distinct differences between freshwater and marine environments. These differences may be explained by the activities of sulfate-reducing bacteria and appear to be the re- sult of differences in sulfate concentration between freshwater and marine environments. Measurements of methane in freshwater an d marine environments have been re- ported by many workers over the past 20 years. Table 1 summarizes the studies that we have consulted for the water columns and sediments of both environments. Physical mixing processes are similar in lake and marine sediments, so a compari- son of methane distributions is possible and should yield information on similari- ties and differences in chemical reactions occurring in these environments. Such a comparison is more difficult for the water column, as there are few marine circulation analogs of stratified lakes. Anoxic basins are the nearest analogs, so studies on the Black Sea, the Cariaco Trench, and Lake Nitinat are included in Table 1. A great deal of emphasis has been placed on improving the precision and accuracy of gas measurements in sediments and ex- plaining the formation of methane. Much less emphasis has been placed on methane consumption. No summary of the reported methane distributions has been attempted. Although an mlusually wide variety of sampling and analytical techniques have been used in the sediment studies (e.g. Reeburgh 1968; Barnes 1973; Martens 1974), distributions from either freshwater or marine environments show reasonable internal consistency. Distinct differences in the methane distributions from freshwater and marine environments are also evident, suggesting that some general process must be responsible. We will use here the re- sults from recent laboratory and field stud- ies of the requirements, activities, and dis- tributions of aerobic methane-oxidizing bacteria, as well as bacteria capable of an- aerobic sulfate reduction, methane produc- tion, and methane oxidation, to point out the locations of the above bacterial reac- tions and to provide a general explanation of the differences in the freshwater and ma- rine methane distributions. Data The results of the studies cited in Ta- ble 1 are too numerous to plot conveniently in a single figure, so representative exam- ples of sediment methane distributions in 1 This work was supported in part by Na- tional Science Foundation grants GA-19380 and GA-41209. Contribution 277, Institute of Marine Science, University of Alaska. LIMNOLOGY AND OCEANOGRAPHY JANUARY 1977, V. 22( 1)
Recent improvements in sample collection and analytical techniques have suggested that As(III) is more prevalent in groundwater than previously believed. Indeed, reducing conditions in alluvial aquifers supplying single families may result in significant exposures to naturally occurring As(III). These results are noteworthy because As(III) is both more toxic and more mobile in the environment than As(V). The literature contains contradictory information concerning the appropriate preservation and analytical techniques for determining As(III). It appears that several previously reported occurrences of As(V) may have been predominantly As(III), but the samples were either not preserved or analyzed properly. For example, separation of arsenic species by ion exchange is apparently necessary to obtain reliable analytical results for certain environmental samples. The problems encountered with investigating As(III) in the environment are due to the complex series of geochemical reactions undergone by arsenic. The complexity of these reactions and the variable experimental conditions used by different investigators have resulted in widely different conclusions concerning both the nature of arsenic adsorption reactions and reaction kinetics. Moreover, it appears that biological reactions may play a role in certain ecosystems. In general, the mechanism promoting the mobility of As(III) in groundwater is the onset of reducing conditions in alluvium in which iron oxides have sorbed arsenic. Such conditions may result in concentrations of arsenic in groundwater as high as several hundred micrograms per liter.
Arsenian pyrite, formed during Cretaceous gold mineralization, is the primary source of As along the Melones fault zone in the southern Mother Lode Gold District of California. Mine tailings and associated weathering products from partially submerged inactive gold mines at Don Pedro Reservoir, on the Tuolumne River, contain ∼20–1300 ppm As. The highest concentrations are in weathering crusts from the Clio mine and nearby outcrops which contain goethite or jarosite. As is concentrated up to 2150 ppm in the fine-grained (<63 μm) fraction of these Fe-rich weathering products.
The partitioning of fluvial sediment load across continental margins is an important con-
trol on strata formation and sequence development; however, few quantitative sediment budgets that encompass entire dispersal systems exist. For the Ganges-Brahmaputra river system, sedi- ment discharge is estimated to be 10^9 t/yr at gauging stations ~300 km inland of the coast, but little has been known of the downstream fate of this material. Geochronological, geophysical, and stratigraphic investigations of the lowland flood plain, delta plain, and shelf help to delineate the extent of Holocene fill and allow calculation of a first-order sediment budget. Results reveal that 1500 × 109 m3 of sediment fill has been sequestered within the flood plain and delta plain since ca. 7000 yr B.P., or about one-third of the annual discharge. The remaining load appears to be apportioned between the prograding subaqueous delta (1970 × 109 m3 ) and transport to the deep-sea Bengal fan via a nearshore canyon. Modern (<100 yr) budget estimates based on short-term accretion rates indicate a similar dispersal pattern and show that contemporaneous deposition continues within these disparate depocenters. The roughly equal partitioning of sedi- ment among flood-plain, shelf, and deep-sea settings reflects the respective influence of an inland tectonic basin, a wide shelf, and a deeply incised canyon system. The findings also support new sequence stratigraphic models for these settings and indicate the important insight that modern river deltas can provide for ancient margin systems. Furthermore, results affirm that values of riverine sediment flux to the oceans may be considerably overestimated by not accounting for loss to the flood plains downstream of the gauging stations.
Fossil shells and paleosol carbonate from ancestral Himalayan river deposits provide a 87Sr/86Sr record of lowland Himalayan river water during the late Neogene. Reconstructed87Sr/86Sr river values increased sharply in the late Miocene, probably marking the beginning of exhumation of high-87Sr/86Sr metalimestones, more in the central than in the western Himalayas. These results imply that the marine 87Sr/86Sr record may not be a proxy for silicate weathering or consumption of atmospheric CO2resulting from that weathering.
Contaminated sediments from the Milltown Reservoir in western Montana release arsenic and various heavy metals (e.g., Cu, Cd, Pb, Zn, Mn) into an underlying alluvial aquifer as redox conditions in the sediments change with seasonally fluctuating water levels. Porewater analyses indicate that sulfate is depleted with depth. In this study, the feasibility of inducing As(III) precipitation through bacterial reduction of sulfate was evaluated in laboratory microcosms established under strictly anaerobic conditions. As(lII), Fe(II), and sulfate concentrations were routinely monitored in the aqueous phase as sulfate was reduced to sulfide. Both As(III) and Fe(II) concentrations in the sediment microcosms decreased as sulfide was made available. Energy‐dispersive x‐ray (EDS) analysis indicated that some of the arsenic was precipitated as an iron‐arsenic‐sulfide solid phase. The precipitation of arsenic observed in this laboratory study suggests that bacterial sulfate reduction may be a process by which heavy metals are immobilized in sediments; however, even though the Milltown sediments contained sulfate‐reducing bacteria, their activity appears to be both sulfate and carbon limited.
Arsenic mobilization from aquatic sediments is an issue of concern, as water-borne arsenic can migrate into pristine areas, endangering aquatic organisms and people. Such mobilization in the Aberjona Watershed has distributed nearly 20 t of arsenic throughout river and lake sediments. To gain an understanding of possible biological mechanisms contributing to this transport, mobilization of solid-phase arsenic was investigated in upper Aberjona sediment microcosms. Microcosms catalyzed rapid dissolution of arsenic from iron arsenate, a solid-phase surrogate for sedimentary arsenic, mobilizing 20−28% of the arsenic present. Sterilization prevented this transformation. Reduction of arsenate to arsenite accompanied iron arsenate dis solution, suggesting that reduction was driving dissolution. Sediment-conditioned, filter-sterilized medium showed no arsenic-transforming activity. A native enrichment culture of sulfate-reducing bacteria possessed one-fifth of the microcosm activity, while strain MIT-13, a native arsenate-reducing microorganism, showed much greater activity, dissolving 38% of the arsenic present. Furthermore, strain MIT-13 mobilized arsenic from presterilized, unamended upper Aberjona sediments. These observations indicate that a direct microbial arsenic-mobilizing activity exists in the sedi ments, show that strain MIT-13 is a strong arsenic-transforming agent native to the sediments, and suggest that dissimilatory arsenic reduction may contribute to arsenic flux from anoxic sediments in the most arsenic-contaminated region of the Aberjona Watershed.
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.
Concentrations of naturally occurring arsenic in ground water vary regionally due to a combination of climate and geology. Although slightly less than half of 30,000 arsenic analyses of ground water in the United States were 1 μg/L, about 10% exceeded 10 μg/L. At a broad regional scale, arsenic concentrations exceeding 10 μg/L appear to be more frequently observed in the western United States than in the eastern half. Arsenic concentrations in ground water of the Appalachian Highlands and the Atlantic Plain generally are very low ( 1 μg/L). Concentrations are somewhat greater in the Interior Plains and the Rocky Mountain System. Investigations of ground water in New England, Michigan, Minnesota, South Dakota, Oklahoma, and Wisconsin within the last decade suggest that arsenic concentrations exceeding 10 μg/L are more widespread and common than previously recognized.
Arsenic release from iron oxide appears to be the most common cause of widespread arsenic concentrations exceeding 10 μg/L in ground water. This can occur in response to different geochemical conditions, including release of arsenic to ground water through reaction of iron oxide with either natural or anthropogenic (i.e., petroleum products) organic carbon. Iron oxide also can release arsenic to alkaline ground water, such as that found in some felsic volcanic rocks and alkaline aquifers of the western United States. Sulfide minerals are both a source and sink for arsenic. Geothermal water and high evaporation rates also are associated with arsenic concentrations 10g/L in ground and surface water, particularly in the west.
Until recently, nonenzymatic processes were generally considered to account for much of the Fe(III) reduction in subsurface environments. However, it is now clear that enzymatic Fe(III) reduction catalyzed by microorganisms which conserve energy to support growth by completely oxidizing organic compounds to carbon dioxide accounts for most of the Fe(III) reduction. Microbial Fe(III) reduction in deep pristine aquifers releases dissolved inorganic carbon into groundwater which may increase aquifer porosity. The Fe(II) released into the groundwater is an important groundwater quality problem in many aquifers. Microbial oxidation of organic contaminants coupled to Fe(III) reduction removes significant amounts of pollutants from many contaminated aquifers. Fe(III) reduction and hence contaminant removal can be accelerated in aquifer sediments with the addition of Fe(III) chelators or humic substances. Both of these amendments alleviate the need for Fe(III) reducers to come into direct physical contact with Fe(III) oxides in order to reduce them. Some Fe(III)-reducing microorganisms can reduce contaminant metals and metalloids such as uranium, technetium, cobalt, chromium and selenium. This metabolism may be useful for remediation of metal-contaminated subsurface environments. Fe(III) reducers and some of the insoluble Fe(II) products of Fe(III) reduction can reducively dechlorinate chlorinated contaminants. Magnetite that is similar to that produced by known Fe(III)-reducing microorganisms has been recovered at depths as great as 6.7 km on Earth and has been observed in a Martian meteorite. Thus, microbial oxidation of organic matter coupled to the reduction of Fe(III) to Fe(II) appears to be a important process in a variety of subsurface environments.
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.
A geochemical study of groundwater of the pampa in the province of Córdoba, Argentina, was performed; the area covered approximately 10,000 km2.
Physical-chemical parameters, dissolved solids, and seven trace elements were determined in 60 selected water samples. Systematic and accurate measurements of arsenic, flourine, and vanadium were performed for the first time. Three trace element contaminants not reported earlier were found: an important one, selenium, and two others of less known effects, uranium and molybdenum.
Eighty-four percent of the water analyzed showed arsenic contents over 0.05 mg/L, maximum contaminant level established by the U.S. Environmental Protection Agency (1982). The frequency distribution of trace elements was analyzed, and its fit to the lognormal distribution was proved by means of the Pearson and Kolmogorov-Smirnov test; the geographic distribution of the seven trace elements was mapped and its correlation with the anion-cation composition of the water was studied.
The maximum arsenic, fluorine, vanadium, and uranium contents were found in the western part of the area under study, in waters containing dominant alkali metals in the cation composition. Maximum selenium and antimony contents were found in the eastern part of the area, while molybdenum distribution does not show any relationship with the other two groups. In addition, the geographic distribution of the trace elements seems to be related to the subsurface structure, which has been inferred using interactive digital analysis of Landsat imagery. The movements of the subsoil have disturbed surface and subsurface drainage influencing the water salinity and trace element contents.
In order to investigate the origin of the contamination, 54 loess samples were collected in wells at depths ranging from the surface down to the water table. This loess, which has a high proportion of volcanic components, mainly rhyolitic glass, exhibits a chemical composition corresponding to that of a dacite.
The loess and the volcanic glass show anomalous contents of all contaminant trace elements, mainly arsenic and selenium. For this reason loess is considered the most important contamination source in the groundwater under study.
High concentrations of naturally occurring arsenic are present in alluvial groundwater systems in the midwestern United States. These occurrences tend to be sporadic because the arsenic is mobilized only under a narrow range of redox conditions. The reducing conditions must be sufficient to reduce and dissolve iron and manganese but not to produce sulfide. Typically, the affected aquifers are relatively high in clay content and of relatively low yield. For that reason, many of these arsenic occurrences are in aquifers supplying single families. The mechanism by which the arsenic is mobilized begins with the deposition of iron oxides during streamflow while the alluvium is being deposited. The oxides have a strong affinity for dissolved arsenic and adsorb it from the streamwater. As the alluvium is buried, it eventually becomes subject to slow groundwater movement. As conditions become more reducing, ferric oxides are reduced to soluble ferrous oxides, resulting in mobilization of the adsorbed arsenic.
High arsenic concentrations (up to 12,000 μg/L) have been measured in groundwater from a confined sandstone aquifer in eastern Wisconsin. The main arsenic source is a sulfide-bearing secondary cement horizon (SCH) that has variable thickness, morphology, and arsenic concentrations. Arsenic occurs in pyrite and marcasite as well as in iron oxyhydroxides but not as a separate arsenopyrite phase. Nearly identical sulfur isotopic signatures in pyrite and dissolved sulfate and the correlation between dissolved sulfate, iron, and arsenic concentrations suggest that sulfide oxidation is the dominant process controlling arsenic release to groundwater. However, arsenic-bearing oxyhydroxides can potentially provide another arsenic source if reducing conditions develop or if they are transported as colloids in the aquifer. Analysis of well data indicates that the intersection of the SCH with static water levels measured in residential wells is strongly correlated with high concentrations of arsenic in groundwater. Field and laboratory data suggest that the most severe arsenic contamination is caused by localized borehole interactions of air, water, and sulfides. Although arsenic contamination is caused by oxidation of naturally occurring sulfides, it is influenced by water-level fluctuations caused by municipal well pumping or climate changes, which can shift geographic areas in which contamination occurs.