Examining India's groundwater quality management

Groundwater quality prediction and risk assessment in Kerala, India: A machine-learning approach

Despite its critical importance for health, agriculture, and the economy, and its key role in supporting climate change adaptation, groundwater quality remains vulnerable to contamination and is often neglected until significant deterioration. The groundwater resources of Kerala, one of the southernmost states of India, are under escalating stress and scarcity, despite a high well density with 62% of the population relying on groundwater from approximately 6.5 million open wells. This study investigates the detailed hydrogeochemistry and predicts groundwater quality zones of the state using machine-learning techniques viz, extreme gradient boosting (XGBoost), support vector regression (SVR), artificial neural network (ANN) and random forest (RF) regression. The hydrogeochemical analysis reveals varying groundwater quality across the state. Among the different machine learning models, RF shows higher goodness of fit (R2: 0.922) with minimal prediction error (root mean square error: 6.29 and mean absolute error: 3.12). The predicted groundwater quality was validated using the spatially distributed stiff diagrams, visually representing water composition trends of each well. The very good, good, moderate and poor groundwater quality zones occupy 31.7%, 40.4%, 20.4%, and 7.4% of the state aligning accurately with the groundwater quality scenario of the state. Additionally, groundwater drinking risk assessment was conducted, considering that 7.4% of the state experiences poor-quality groundwater. Integrating groundwater quality maps with population data, the study assessed potential health risks due to consuming untreated water. Nearly 0.59 million people across 252 local self-government bodies (LSGs) are susceptible to consuming poor quality groundwater, which may pose potential health risks. This observation provides valuable insights for sustainable groundwater management and public health safeguarding and the findings of the present study are useful for achieving sustainable development goal (SGD) 6 (clean water and sanitation) and long-term groundwater management in Kerala.

Occurrence and Health Risk Assessment of Phthalates in Municipal Drinking Water Supply of a Central Indian City

In this study, the occurrence of phthalates in the municipal water supply of Nagpur City, India, was studied for the first time. The study aimed to provide insights into the extent of phthalate contamination and identify potential sources of contamination in the city's tap water. We analyzed fifteen phthalates and the total concentration (∑15phthalates) ranged from 0.27 to 76.36 µg L-1. Prominent phthalates identified were di-n-butyl phthalate (DBP), di-isobutyl phthalate (DIBP), benzyl butyl phthalate (BBP), di (2-ethylhexyl) phthalate (DEHP), di-n-octyl phthalate (DNOP), and di-nonyl phthalate (DNP). Out of the fifteen phthalates analyzed, DEHP showed the highest concentration in all the samples with the median concentration of 2.27 µg L-1, 1.39 µg L-1, 1.83 µg L-1, 2.02 µg L-1, respectively in Butibori, Gandhibaag, Civil Lines, and Kalmeshwar areas of the city. In 30% of the tap water samples, DEHP was found higher than the EPA maximum contaminant level of 6 µg L-1. The average daily intake (ADI) of phthalates via consumption of tap water was higher for adults (median: 0.25 µg kg-1 day-1) compared to children (median: 0.07 µg kg-1 day-1). The hazard index (HI) calculated for both adults and children was below the threshold level, indicating no significant health risks from chronic toxic risk. However, the maximum carcinogenic risk (CR) for adults (8.44 × 10-3) and children (7.73 × 10-3) was higher than the threshold level. Knowledge of the sources and distribution of phthalate contamination in municipal drinking water is crucial for effective contamination control and management strategies.

Isotopic tracing of leachate percolation from municipal solid waste dump sites to groundwater in diverse climatic zones of India

Groundwater resources in tropical regions are largely dependent on recharge by rainwater infiltration through soil layers with variable time. However, the rainwater infiltration through soil is a serious concern in urban tropics where it interacts with landfills at the dumpsites, potentially contaminating adjoining groundwater. In this study, the stable isotopic compositions of oxygen and hydrogen (δ18O and δ2H, respectively) in groundwater and leachates, adjoining municipal dumpsites in urban tropics (Bangalore, Kolkata and Durgapur located in diverse rainfall zonation of India), were analyzed to investigate their recharge sources and trace the possible mixing of leachate contaminants under three diverse climatology. The measured values of δ18O and δ2H suggested that the groundwater in these sites reflects higher recharge by rainwater. However, the d-excess values indicated secondary effects suggesting the groundwater has experienced significant modifications. The end member analysis using δ18O-d-excess relation pinpointed an additional leachate contribution from adjoining dumpsites. The critical fraction of leachate infiltration to groundwater quantified using two component mixing model ranged between (i) 1 and 33% in Bangalore, (ii) 5 and 13% in Kolkata and (iii) 18 and 76% in Durgapur, with its variability dependent on seasonality and aquifer connectivity. This information is crucial for groundwater management to secure water quality and to quantify potential hydrological contaminants particularly in drier seasons and drier regions, when and where the demand for groundwater is high, respectively.

A construction strategy of Kriging surrogate model based on Rosenblatt transformation of associated random variables and its application in groundwater remediation

When using simulation-optimization models for optimizing the design of groundwater pumping-treatment plans for pollution, building a surrogate model for the numerical simulation model has become an effective means of overcoming the computational load of such models. However, previous studies often treated pumping time as a single optimization variable, leading to unnecessary excessive pumping. This paper considers the location, pumping rate, start time, and end time of each candidate pumping well as optimization variables, and proposes a Rosenblatt-transform-based optimal Latin hypercube sampling method for the associated random variables to ensure that the start time is less than or equal to the end time. This method is coupled with an adaptive sampling method based on batch local optimal solutions to construct a dynamic adaptive Kriging surrogate model for the numerical model, ensuring that the true value of the optimal remediation scheme is not lost. The results show that, at the final stage of remediation, the pollutant concentration in the 4 scenarios achieves comprehensive compliance. However, when considering the minimization of remediation costs as the evaluation criterion, the remediation scheme in scenario 1 (the pumping start and end times are independent optimization variables for all candidate pumping wells) is optimal. In the optimization design of groundwater pumping-treatment plans, the pumping wells should be arranged in the midstream and downstream regions of the contaminant plume and parallel to the regional flow direction. This paper provides a method reference for the construction and adaptive updating of surrogate models involving associated random variables, as well as guidance for the dynamic optimization of groundwater pumping and treatment at contaminated sites.

Evaluation of Shallow Groundwater Quality at Regional Scales Using Adaptive Water Quality Indices

Groundwater, which is the main source of water for human consumption in many rural areas, has its quality determined by the complex interaction of environmental factors and anthropogenic activities. The present study evaluated the quality of shallow groundwater (1 to 25 m depth) in the rural area of the Târgovişte Plain, a densely populated area (200 inhabitants/km²) using 80 water samples collected from public wells. In order to explain the spatial distribution of the concentrations of the 19 physicochemical parameters considered (including heavy metals), the evaluation of groundwater quality for human consumption and potential impact on human health was conducted using the Water Quality Index (WQI), Integrated Weight Water Quality Index (IwWQI), Total Hazard Index (THI), and cumulative carcinogenic risk (CCR). For the WQI/IwWQI the comparative analysis of the two indices showed that for the WQI, it is important to select an optimal set of parameters, because use of a large number of physicochemical parameters can eclipse the values that exceed WHO guideline limits. In contrast, the use of entropy in the calculation of the IwWQI did not lead to eclipsing of exceedance, no matter the number of parameters used. Areas with poor and very poor groundwater quality according to the WQI/IwWQI overlapped, with a moderate risk to human health (THI > 1) for noncarcinogenic contaminants and also a risk of developing cancer according to the CCR average value (1.15 × 10^-2). The health of 43% of the rural population in the Târgovişte Plain can be affected if they drink contaminated groundwater, and it is estimated that about 600 people can develop cancer during their lifetime. If the risk of developing cancer is reduced only in the rural population that does not have access to a water source from a centralized and verified network, the results suggest that 385 people (1.15%) can develop cancer as a result of consuming groundwater contaminated with heavy metals based on the average value of CCR. This value is lower than the general mortality rate in areas with high CCR and below the average number of cancer patients in Romania (2.65%). The quality of groundwater and the risk of developing diseases and cancer due to water consumption is directly proportional to the intensity of agricultural land use and inversely proportional to the depth of the groundwater layer, the distance from the main hydrographic network and the reservoirs, and the distance from the main city, Târgovişte. The complex and integrated analysis of groundwater quality using quality indices and indicators of health risk for the population, validated by hot-spot analysis and compared to the mortality rate, is an approach with practical applicability. This integrated approach allows public authorities, policymakers, and health services to implement an efficient monitoring program and optimize anthropogenic activities in order to prevent groundwater contamination and finally improve the quality of life for the residents in the area of this study.

Moisture movement, soil salt migration, and nitrogen transformation under different irrigation conditions: Field experimental research

Irrigation and fertilizer application can lead to significant changes in groundwater quality. In this study, a field irrigation experiment was carried out from April 9 to 23, 2021 under irrigation and fertigation conditions to understand the mechanisms of moisture movement, soil salt migration, and nitrogen transformation in the soil profile. Continuous in-situ monitoring and sampling of soil and irrigation water, as well as stable isotopes, chemical parameters, and soluble salt analyses, were performed in this research. The results showed that the time cost by the irrigation water in the vadose zone was about 5 h. The infiltrated irrigation water was accompanied by high concentrations of soluble salts, leached from the soil layers of 20-80 cm and 100-150 cm, which is associated with the leaching of Na⁺, Cl^-, SO₄^2-, and Ca²⁺ and the dissolution of minerals such as gypsum and halite. Furthermore, the variations in nitrogen concentrations (NH₄⁺ and NO₃^-) in the soil profile suggested that fertilizer application was the main source of NO₃^- in the soil and groundwater, while irrigation was the biggest driving force for nitrogen transport and transformation in soil. The application of urea fertilizer can increase the content of ammonium nitrogen at the soil layer of 0-80 cm. This nitrogen form can be subsequently transformed to nitrate nitrogen during the water transport to the groundwater. The current study provides a strong scientific basis for the protection and management of groundwater and soil quality in agricultural areas.

Anthropogenic arsenic menace in contaminated water near thermal power plants and coal mining areas of India

Coal mining and coal combustion in thermal power plants (TPPs) are the major anthropogenic sources of arsenic (As) contamination in many different industrial regions. In this study of industrial regions of West Bengal and Singrauli, it is observed that there is an anthropogenic contribution to the contamination from As-bearing coal. Up to 14.53 mg/kg of As is obtained in coal of West Bengal which also has very high average Fe concentration (16,095 mg/kg) along with high concentration of Cu, Mn and Hg. Similar observations are also found in Singrauli Industrial Region where 3.14 mg/kg of As with very high concentration of Fe 43,867 mg/kg along with high Cu, Mn and Hg concentration is found in coal samples. This low-grade bituminous coal contains arsenopyrite as observed by SEM-EDX. Arsenopyrite is converted to arsenolite upon combustion in these TPPs as observed in XRD. The fly ash has average As concentration of 1.53 mg/kg for West Bengal and 2.38 mg/kg for Singrauli Industrial Region and high concentration of toxic elements. The soil near these TPPs and mining areas is enriched in As, Fe, Hg, Cu and Mn. Not only As but high concentrations of Fe, Hg, Mn are also observed from analysis of water which relates to the anthropogenic inputs. The dissolution of arsenolite in reducing environments caused by periodic flooding releases As into water. Hence, the As contamination in the study area also has anthropogenic origin from coal consumption in TPPs.

Environmental implications of one-century COPRs evolution in a single industrial site: From leaching impact to sustainable remediation of CrVI polluted groundwater

The Stoppani factory manufactured chromium for more than one century, dumping millions of tons of Chromite Ore Processing Residues (COPRs) over decades. The massive presence of COPRs resulted in an intense Cr^VI leaching and consequent contamination of percolating groundwater. The site offers a unique opportunity to follow COPRs evolution from the primary roasting process to the aged Cr-bearing mineral phases. Herein, new insights on COPRs mineralogy evolution and their role in Cr^VI release are provided by a dry sample preparation protocol, coupled with in-depth multi-technique characterization. Besides typical COPRs mineral assemblages, highly soluble Na₂CrO₄ and the first evidence of crocoite (PbCrO₄) in a COPR contaminated site are revealed. Selective extraction experiments confirmed a strong reactivity for Cr-bearing minerals as confirmed by concentrations as high as 375 mg L^-1 of leached Cr^VI. The mineralogical approach was combined with a nanotechnological solution for Cr^VI wastewater remediation. The application of naked colloidal maghemite (γ-Fe₂O₃) nanoparticles (SAMNs) on the complex industrial wastewater, led to > 90% Cr^VI removal, either under acidic or in-situ conditions. The present case study of a highly polluted site, ranging from mineral characterization to wastewater remediation, highlights the use of multidisciplinary approaches to cope with complex environmental issues.

Isotope and hydrochemical systematics of groundwater from a multi-tiered aquifer in the central parts of Indo-Gangetic Plains, India - Implications for groundwater sustainability and security

The Indo-Gangetic multi-aquifer system provides water supplies to the most populous regions of the Indian subcontinent, however precise knowledge on the sources and dynamics of groundwater is still missing. Environmental isotopes (²H, ¹⁸O, ¹³C, ³H and ¹⁴C) and hydrochemical modeling tools were used in this study in the multi-tiered aquifers underlying the Middle Gangetic Plains (MGP) to investigate the source of recharge, aquifer dynamics and inter-connectivity among aquifers. Within a depth span of 300 m, three aquifers, with contrasting recharge sources and dynamics, were delineated in this Sone-Ganga-Punpun interfluve region, with limited cross-aquifer hydraulic interconnections. The chemistry evolves from Ca-HCO₃ to Na-Ca-HCO₃ in the shallow semiconfined Aquifer-I with a mean transit time of 20-23 years. The dominant recharge to Aquifer-I is from the river inflows and rainwater percolation through paleochannels. The semi-confined to confined Aquifer-II holds fresh quality groundwater with mixed water facies (Mg/Ca-Na-HCO₃). The modeled age of Aquifer-II groundwater is found to be 205-520 years, which is supported by presence of negligible tritium and minor variations in stable isotopes. Outcrop regions of Aquifer-II sediments in the marginal alluvial areas and deep-seated paleochannels in the southwestern part are the potential zones for Aquifer-II recharge. A deep confined Aquifer-III with fresh quality of groundwater is identified below 220 m. This aquifer is characterized by old age (~3.5 to 4.7 ka BP) and enriched δ¹⁸O (-5.7‰). These results along with the existing paleoclimate records of this region infer that Aquifer-III is recharged during an arid climate. The marginal alluvial plains are the probable recharge zones for Aquifer-III. This study helped in conceptualizing the groundwater flow paths in multi-tiered aquifers of MGP. The knowledge and understanding would extend crucial inputs for the sustainable development of deep aquifers not only in the MGP but also in other regions of Indo-Gangetic Plains.

Preparation and characterization of boron-doped corn straw biochar: Fe (Ⅱ) removal equilibrium and kinetics

Nowadays, iron ions as a ubiquitous heavy metal pollutant are gradually concerned and the convenient and quick removal of excessive iron ions in groundwater has become a major challenge for the safety of drinking water. In this study, boron-doped biochar (B-BC) was successfully prepared at various preparation conditions with the addition of boric acid. The as-prepared material has a more developed pore structure and a larger specific surface area (up to 897.97 m²/g). A series of characterization results shows that boric acid effectively activates biochar, and boron atoms are successfully doped on biochar. Compared with the ratio of raw materials, the pyrolysis temperature has a greater influence on the amount of boron doping. Based on Langmuir model, the maximum adsorption capacity of 800B-BC_1:2 at 25 °C, 40 °C, 55 °C are 50.02 mg/g, 95.09 mg/g, 132.78 mg/g, respectively. Pseudo-second-order kinetic model can better describe the adsorption process, the adsorption process is mainly chemical adsorption. Chemical complexation, ions exchange, and co-precipitation may be the main mechanisms for Fe²⁺ removal.

Co-exposure to inorganic arsenic and fluoride prominently disrupts gut microbiota equilibrium and induces adverse cardiovascular effects in offspring rats

Co-exposure to inorganic arsenic (iAs) and fluoride (F^-) and their collective actions on cardiovascular systems have been recognized as a global public health concern. Emerging studies suggest an association between the perturbation of gut bacterial microbiota and adverse cardiovascular effects (CVEs), both of which are the consequence of iAs and F^- exposure in human and experimental animals. The aim of this study was to fill the gap of understanding the relationship among co-exposure to iAs and F^-, gut microbiota perturbation, and adverse CVEs. We systematically assessed cardiac morphology and functions (blood pressure, echocardiogram, and electrocardiogram), and generated gut microbiota profiles using 16S rRNA gene sequencing on rats exposed to iAs (50 mg/L NaAsO₂), F^- (100 mg/L NaF) or combined iAs and F^- (50 mg/L NaAsO₂ + 100 mg/L NaF), in utero and during early postnatal periods (postnatal day 90). Correlation analysis was then performed to examine relationship between significantly altered microbiota and cardiac performance indices. Our results showed that co-exposure to iAs and F^- resulted in more prominent effects in CVEs and perturbation of gut microbiota profiles, compared to iAs or F^- treatment alone. Furthermore, nine bacterial genera (Adlercreutzia, Clostridium sensu stricto 1, Coprococcus 3, Romboutsia, [Bacteroides] Pectinophilus group, Lachnospiraceae NC2004 group, Desulfovibrio, and two unidentified genera in Muribaculaceae and Ruminococcaceae family), which differed significantly in relative abundance between control and iAs and F^- co-exposure group, were strongly correlated with the higher risk of CVEs (correlation coefficient = 0.70-0.88, p < 0.05). Collectively, these results suggest that co-exposure to iAs and F^- poses a higher risk of CVEs, and the part of the mode of action is potentially through inducing gut microbiota disruption, and the strong correlations between them indicate a high potential for the development of novel microbiome-based biomarkers of iAs and/or F^- associated CVEs.

Application of water quality index and chemometric methods on contamination assessment in the shallow aquifer, Ganges River basin, India

Water quality index and chemometric methods were employed to assess the groundwater quality and contamination sources in the upper Ganges basin (UGB) and lower Ganges basin (LGB) as groundwater is a sole source for drinking, domestic and agricultural uses. Groundwater samples were collected from UGB (n = 44) and LGB (n = 26) and analysed for physicochemical parameters. Groundwater in this basin is desirable (51%) to permissible (TDS < 1000 mg/l, 96%) classes for drinking. Chemical constituents in the groundwater are lower than the maximum allowable limit recommended by the WHO for drinking except K. Drinking water quality index (DWQI) values reveal that groundwater belongs to excellent (89%) and good (10%) classes. However, the high concentrations of Fe and Mn in 61 and 77% of samples, respectively, restrict the usage for drinking according to USEPA recommendations. Both LGB and UGB groundwater in shallow wells have elevated concentration of TDS, EC and other ions (Ca²⁺, Cl^- and SO₄^2- in LGB; major ions, NO₃^-, PO₄^3-, F^-, Fe and Mn in UGB) and imply the influences of anthropogenic activities. Principal component analysis and hierarchical cluster analysis reiterated that groundwater quality is affected by the anthropogenic activities as well as mineral dissolutions (carbonate and silicate minerals). This study highlighted that the infiltration of wastewater from various contamination sources likely triggered the dissolution of the minerals in the vadose zone that resulted in the accumulation of ions in the shallow aquifer. An effective management plan is essential to protect this shallow aquifer.

Source apportionment, chemometric pattern recognition and health risk assessment of groundwater from southwestern Punjab, India

The groundwater quality of southwestern Punjab, India, is a serious cause of concern due to the presence of chemical contaminants in it. However, limited studies of groundwater quality, sources of chemical contaminants and their health risks are available for the region. Hence, this study was conducted to investigate the source, distribution and potential health risk assessment of groundwater quality in three districts of southwestern Punjab, India. The spatial distribution of groundwater chemical contaminants and their potential health risks have been illustrated using inverse distance weighting interpolation technique. The concentration of fluoride (F^-; ranged from 0.08 to 4.79 mg L^-1) exceeded the WHO limit (1.5 µg L^-1) in 80 and 50% samples collected from Bathinda and Ludhiana districts, respectively. The uranium (U) concentration ranged from 0.5 to 432 µg L^-1 and shows ~ 85%, 75% and 10% of samples collected from Bathinda, Barnala and Ludhiana districts exceeded the WHO drinking water limit (30 µg L^-1), respectively. The groundwater quality of the Bathinda district is a matter of concern due to elevated levels of alkalinity, hardness, fluoride, uranium and nitrate (NO₃^-). The principal component analysis shows close association between F^- and U, which indicates their geogenic origin. Further, they also seem to be subordinately influenced by diffuse anthropogenic activities. The clustering of Cu and Pb with NO₃^- and SO₄^2- indicates their anthropogenic origin. The non-carcinogenic health risk assessment indicates that F^-, NO₃^- and U are the major health risk pollutants in the study area. The carcinogenic health risk of As and Cr exceeded the USEPA limits (10^-6) in the entire study area, but observed to be more serious for the district Bathinda (10^-3-10^-5). The spatial distribution maps illustrate that the health risk for Bathinda district inhabitants is higher than Barnala and Ludhiana districts.

Gut microbiota perturbations and neurodevelopmental impacts in offspring rats concurrently exposure to inorganic arsenic and fluoride

Many "hot spot" geographic areas across the world with drinking water co-contaminated with inorganic arsenic (iAs) and fluoride (F^-), two of the most common natural contaminants in drinking water. Both iAs and F^- are known neurotoxins and affect neurodevelopment of children. However, very few studies have investigated the neurodevelopmental effects of concurrent exposure to iAs and F^-, which could potentially pose a greater risk than iAs or F^- exposure alone. Further, perturbations of gut microbiota, which plays a regulatory role in neurodevelopment, resulting from iAs and F^- exposure has been reported in numerous studies. There is lacking of information regarding to the relationship among concurrent iAs and F^- exposure, microbiome disruption, and neurodevelopmental impacts. To fill these gaps, we treated offspring rats to iAs (50 mg/L NaAsO₂) and F^- (100 mg/L NaF), alone or combined from early life (in utero and childhood) to puberty. We applied Morris water maze test to assess spatial learning and memory of these rats and generated gut microbiome profiles using 16S rRNA gene sequencing. We showed that concurrent iAs and F^- exposure caused more prominent neurodevelopmental effects in rats than either iAs or F^- exposure alone. Moreover, Unsupervised Principal Coordinates Analysis (PCoA) and Linear Discriminant Analysis Effect Size (LEfSe) analysis of gut microbiome sequencing results separated concurrent exposure group from others, indicating a more sophisticated change of gut microbial communities occurred under the concurrent exposure condition. Further, a correlation analysis between indices of the water maze test and microbial composition at the genus level identified featured genera that were clearly associated with neurobehavioral performance of rats. 75% (9 out of 12) genera, which had a remarkable difference in relative abundance between the control and combined iAs and F^- exposure groups, showed significantly strong correlations (r = 0.70-0.90) with the water maze performance indicators. Collectively, these results suggest that concurrent iAs and F^- exposure led to more prominent effects on neurodevelopment and gut microbiome composition structures in rats, and the strong correlation between them indicates a high potential for the development of novel microbiome-based biomarkers of iAs and/or F^- associated neurodevelopmental deficits.

Organic micropollutants in groundwater of India-A review

Groundwater pollution due to organic micropollutants is a major cause of concern, especially in parts of the world where available water resources are on the decline. India is the largest user of groundwater where the presence of micropollutants in the subsurface environment has been the focus of many researchers. The objective of this study was to provide a detailed review of studies on micropollutants in Indian groundwater and to provide strategies for further work. It is found that the presence of pharmaceuticals, endocrine disrupting compounds, surfactants, phthalates, per- and poly-fluoroalkyl substances, personal care products, artificial sweeteners, and pesticides in groundwater from different parts of India is reported. Pesticides and phthalate concentrations reported exceed the standard guideline values. This review points out the regions where the groundwater is prone to contamination due to micropollutants. An assessment of temporal variation in the concentration of micropollutants in groundwater has been done only by a few researchers. This study highlighted the need for more research on the possible presence of micropollutants in groundwater, especially in the major polluted rivers in cities where more pharmaceuticals, pesticides, and plastic industries are located. PRACTITIONER POINTS: Organic micropollutants were not new contaminants into the environment but the one entered even decades ago which has threatening effect. The number of studies on organic micropollutants in groundwater is lesser than surface water or wastewater. Scarcity on the studies of micropollutants was a result of definite technical lack in its analysis and complexity in sample preparation. Most of the studies done were related to contamination sites and point sources.

Prediction Modeling and Mapping of Groundwater Fluoride Contamination throughout India

For about the past eight decades, high concentrations of naturally occurring fluoride have been detected in groundwater in different parts of India. The chronic consumption of fluoride in high concentrations is recognized to cause dental and skeletal fluorosis. We have used the random forest machine-learning algorithm to model a data set of 12 600 groundwater fluoride concentrations from throughout India along with spatially continuous predictor variables of predominantly geology, climate, and soil parameters. Despite only surface parameters being available to describe a subsurface phenomenon, this has produced a highly accurate prediction map of fluoride concentrations exceeding 1.5 mg/L at 1 km resolution throughout the country. The most affected areas are the northwestern states/territories of Delhi, Gujarat, Haryana, Punjab, and Rajasthan and the southern states of Andhra Pradesh, Karnataka, Tamil Nadu, and Telangana. The total number of people at risk of fluorosis due to fluoride in groundwater is predicted to be around 120 million, or 9% of the population. This number is based on rural populations and accounts for average rates of groundwater consumption from nonmanaged sources. The new fluoride hazard and risk maps can be used by authorities in conjunction with detailed groundwater utilization information to prioritize areas in need of mitigation measures.

Deep urban groundwater vulnerability in India revealed through the use of emerging organic contaminants and residence time tracers

Demand for groundwater in urban centres across Asia continues to rise with ever deeper wells being drilled to avoid shallow contamination. The vulnerability of deep alluvial aquifers to contaminant migration is assessed in the ancient city of Varanasi, India, using a novel combination of emerging organic contaminants (EOCs) and groundwater residence time tracers (CFC and SF₆). Both shallow and intermediate depth private sources (<100 m) and deep (>100 m) municipal groundwater supplies were found to be contaminated with a range of EOCs including pharmaceuticals (e.g. sulfamethoxazole, 77% detection frequency, range <0.0001-0.034 μg L^-1), perfluoroalkyl substances (e.g. PFOS, range <0.0001-0.033 μg L^-1) as well as a number of pesticides (e.g. phenoxyacetic acid, range <0.02-0.21 μg L^-1). The profile of EOCs found in groundwater mirror those found in surface waters, albeit at lower concentrations, and reflect common waste water sources with attenuation in the subsurface. Mean groundwater residence times were found to be comparable between some deep groundwater and shallow groundwater sources with residence times ranging from >70 to 30 years. Local variations in aquifer geology influence the extent of modern recharge at depth. Both tracers provide compelling evidence of significant inputs of younger groundwater to depth >100 m within the aquifer system.

Removal of selected pesticides from groundwater by membrane distillation

The removal of five selected pesticide compounds in a brackish model groundwater solution was examined using a bench scale direct contact membrane distillation (DCMD) system. It was found that the rejection rate of the pesticides in DCMD is mainly influenced by its properties. Compounds with low hydrophobic characteristics and low vapour pressure showed a high rejection rate (70-99%), whereas compounds with a high vapour pressure or high hydrophobicity (LogD) showed a reduced rejection (30-50%) at a water recovery of 75%. The influence of groundwater feed solution contents such as the presence of organics (humic acid) and inorganic ions (Na⁺, Ca²⁺, Mg²⁺, Cl^- and SO₄^2-) as well as feed temperature (40, 55 and 70 °C) on the rejection of the pesticides in DCMD operation was also evaluated. The results showed that the presence of inorganic ions and organics in the feed solution influences the pesticides rejection in DCMD operation to a minor degree. In contrast, reduced rejection of pesticides with high vapour pressure was observed. A rapid small-scale column test (RSSCT) was carried out to study the removal of any remaining substances in the permeate by adsorption onto granular activated carbon (GAC). RSSCT showed promising performance of GAC as a post-treatment option.

Groundwater quality in the alluvial aquifer system of northwest India: New evidence of the extent of anthropogenic and geogenic contamination

Groundwater depletion has been widely studied in northwest India, but water quality concerns are still poorly constrained. In this study, we explore the hydrochemistry of the top 160m of the aquifer system, through detailed field studies in the Bist-Doab region, considering both anthropogenic and geogenic controls. A detailed comparison is made between sites dominated by urban and agricultural landuse. Salinity, nitrate, chloride and lead concentrations are significantly higher in the shallow (0-50m) groundwater system due to surface anthropogenic contaminant loading from agricultural and urban sources. The widespread occurrence of oxic groundwater within the aquifer system means that denitrification potential is limited and also enhances the mobility of selenium and uranium in groundwater. Geogenic trace elements (e.g. As, Se, F), are generally found at concentrations below WHO guideline drinking water values, however elevated U concentrations (50-70μg/L) are found within the deeper part of the aquifer and shallow urban aquifers associated with higher bicarbonate waters. Higher concentration of Se (10-40μg/L) are found exclusively in the shallow groundwater system where Se is mobilised from soils and transported to depth in the shallow aquifer due to the prevailing oxidising aquifer conditions. New evidence from a range of environmental tracers shows elevated concentrations of anthropogenic contaminants in the deeper part of the aquifer (50-160m deep) and demonstrates vulnerability to vertical migration of contaminants. Continued intensive groundwater abstraction from >100m deep means that water quality risks to the deep aquifer system need to be considered together with water quantity constraints.

Groundwater fluoride contamination and its possible health implications in Indi taluk of Vijayapura District (Karnataka State), India

Groundwater fluoride concentration and fluoride-related health problems were studied in twenty-two villages of Indi taluk of Vijayapura district, Karnataka, India. Present study (2015) was also used to compare groundwater fluoride concentration in same 22 villages with previous government report (2000). Groundwater fluoride concentrations of 62 bore wells of 22 villages were analyzed by using an ion-sensitive electrode. A total of 660 adults and 600 children were screened for fluorosis symptoms and signs. Sixty clinically suspected fluorosis patients' urine samples were further analyzed for fluoride. The mean value (1.22 ± 0.75 mg/L) of fluoride concentration of 62 bore wells and 54.83 % bore wells with ≥1.0 mg/L of fluoride concentrations in Indi taluk indicates higher than the permissible limit of drinking water fluoride concentration recommended for India. Clinical symptoms like arthritis, joint pains, gastrointestinal discomfort and lower limb deformities with high urinary fluoride concentrations in some subjects suggest fluorosis. Results also showed an increase in groundwater fluoride concentration of the same 22 villages between previous and present study. Preliminary arthritis symptom of the villagers could be due to drinking fluoride-contaminated water. Increase in fluoride concentration with time to the bore wells definitely indicates future danger.

Hydrochemical evaluation and identification of geochemical processes in the shallow and deep wells in the Ramganga Sub-Basin, India

Groundwater samples were collected from 44 wells in the Ramganga Sub-Basin (RSB), India, and analysed for major ions, nutrients and trace metals. The primary goal of this study is to evaluate the hydrochemistry and to identify the geochemical processes that govern the water chemistry in the shallow and deep tube wells in the study area using geochemical methods. The knowledge of changes in hydrochemistry of the aquifers is important for both groundwater recharge and use in the region. This study found that there are substantial differences of water chemistry between shallow and deep wells. In the shallow wells, the average concentrations of total dissolved solid (TDS), Na, K, Ca, Mg, HCO₃, Cl, SO₄, NO₃, PO₄, F, Cu, Mn, Fe and Cr are twofold higher than the deep wells. The concentrations of dissolved silica in the groundwater do not vary with the depth, which implies that the variation in the water chemistry is not due to mineral dissolution alone. Major ion ratios and saturation indices suggest that the water chemistry is predominantly controlled by dissolution of carbonate minerals, silicate weathering and ion exchange reactions. Thermodynamic evaluation (ion activity ratios and stability filed diagrams) indicates that the kaolinite and gibbsite controlled the water chemistry in the both shallow and deep wells. In addition, the groundwater chemistry in the shallow wells is affected by the vertical infiltration of contaminated water from surface contamination sources and nitrification process. In the deep wells, absence of NO₃ and low concentrations of Cl, SO₄, PO₄ and F imply the role of regional flow and denitrification in the groundwater. Results concluded that proper management plan is necessary to protect the shallow aquifer in the RSB since shallow aquifer pumping is less expensive than the deeper one.

Arsenic in groundwater of the Kolkata Municipal Corporation (KMC), India: Critical review and modes of mitigation

This study represents the first comprehensive report of groundwater arsenic contamination status in the Kolkata Municipal Corporation (KMC). During the past 23 years, 4210 groundwater samples were analysed from all 141 wards in the KMC: 14.2% and 5.2% samples had arsenic >10 μg/l and >50 μg/l, respectively, representing 77 and 37 wards. The study shows that the number of arsenic contaminated samples (and wards) in the southern part of the KMC exceeds that of other parts of the city. The daily intake of arsenic from drinking water was estimated as 0.95 μg per kg bw and the cancer risk was estimated as 1425/10⁶. Analyses of biological samples (hair, nail and urine) showed elevated concentrations of arsenic indicating the presence of subclinical arsenic poisoning, predicting an enhanced lifetime cancer risk for the population in southern part of the KMC. In the KMC, groundwater is not a sustainable source of freshwater due to arsenic, high iron, hardness and total dissolved solids. Its continued use is impelled by the lack of an adequate infrastructure to treat and supply surface water and in some wards the unaccounted for water (UFW) is even >45% incurred during distribution. The rare imposition of a water tax makes the water supply systems unsustainable and fosters indifference to water conservation. To mitigate the arsenic problem, continuous groundwater monitoring for pollutants, a treated surface water supply with strict policy implications, rainwater harvesting in the urban areas and introduction of water taxes seem to be long-term visible solutions.

Contaminant Removal from Source Waters Using Cathodic Electrochemical Membrane Filtration: Mechanisms and Implications

Removal of recalcitrant anthropogenic contaminants from water calls for the development of cost-effective treatment technologies. In this work, a novel electrochemical membrane filtration (EMF) process using a conducting microfiltration membrane as the cathode has been developed and the degradation of sulphanilic acid (SA) examined. The electrochemical degradation of SA in flow-by mode followed pseudo-first-order kinetics with the degradation rate enhanced with increase in charging voltage. Hydrogen peroxide as well as oxidants such as HO^• and Fe(IV)O²⁺ were generated electrochemically with HO^• found to be the dominant oxidant responsible for SA degradation. In addition to the anodic splitting of water, HO^• was formed via a heterogeneous Fenton process with surface-bound Fe(II) resulting from aerobic corrosion of the steel mesh. In flow-through mode, the removal rate of SA was 13.0% greater than obtained in flow-by mode, presumably due to the better contact of the contaminant with the oxidants generated in the vicinity of the membrane surface. A variety of oxidized products including hydroquinone, p-benzoquinone, oxamic acid, maleic acid, fumaric acid, acetic acid, formic acid, and oxalic acid were identified and an electrochemical degradation pathway proposed. These findings highlight the potential of the cathodic EMF process as an effective technology for water purification.

Environmental status of groundwater affected by chromite ore processing residue (COPR) dumpsites during pre-monsoon and monsoon seasons

Chromite ore processing residue (COPR) is generated by the roasting of chromite ores for the extraction of chromium. Leaching of carcinogenic hexavalent chromium (Cr(VI)) from COPR dumpsites and contamination of groundwater is a key environmental risk. The objective of the study was to evaluate Cr(VI) contamination in groundwater in the vicinity of three COPR disposal sites in Uttar Pradesh, India, in the pre-monsoon and monsoon seasons. Groundwater samples (n = 57 pre-monsoon, n = 70 monsoon) were taken in 2014 and analyzed for Cr(VI) and relevant hydrochemical parameters. The site-specific ranges of Cr(VI) concentrations in groundwater were <0.005 to 34.8 mg L^-1 (Rania), <0.005 to 115 mg L^-1 (Chhiwali), and <0.005 to 2.0 mg L^-1 (Godhrauli). Maximum levels of Cr(VI) were found close to the COPR dumpsites and significantly exceeded safe drinking water limits (0.05 mg L^-1). No significant dependence of Cr(VI) concentration on monsoons was observed.

Fate of over 480 million inhabitants living in arsenic and fluoride endemic Indian districts: Magnitude, health, socio-economic effects and mitigation approaches

During our last 27 years of field survey in India, we have studied the magnitude of groundwater arsenic and fluoride contamination and its resulting health effects from numerous states. India is the worst groundwater fluoride and arsenic affected country in the world. Fluoride results the most prevalent groundwater related diseases in India. Out of a total 29 states in India, groundwater of 20 states is fluoride affected. Total population of fluoride endemic 201 districts of India is 411 million (40% of Indian population) and more than 66 million people are estimated to be suffering from fluorosis including 6 million children below 14 years of age. Fluoride may cause a crippling disease. In 6 states of the Ganga-Brahmaputra Plain (GB-Plain), 70.4 million people are potentially at risk from groundwater arsenic toxicity. Three additional states in the non GB-Plain are mildly arsenic affected. For arsenic with substantial cumulative exposure can aggravate the risk of cancers along with various other diseases. Clinical effects of fluoride includes abnormal tooth enamel in children; adults had joint pain and deformity of the limbs, spine etc. The affected population chronically exposed to arsenic and fluoride from groundwater is in danger and there is no available medicine for those suffering from the toxicity. Arsenic and fluoride safe water and nutritious food are suggested to prevent further aggravation of toxicity. The World Health Organization (WHO) points out that social problems arising from arsenic and fluoride toxicity eventually create pressure on the economy of the affected areas. In arsenic and fluoride affected areas in India, crisis is not always having too little safe water to satisfy our need, it is the crisis of managing the water.

Optimization and economic analysis for a small scale nanofiltration and reverse osmosis water desalination system

This paper presents the results of a techno-economic investigation of a nanofiltration (NF) and reverse osmosis (RO) process for treating brackish water. Optimization experiments of six commercially available small scale RO and NF membranes were carried out using formulated artificial groundwater. A predictive model was developed by using response surface methodology (RSM) for optimization of input process parameters of brackish water membrane processes to simultaneously maximize water recovery and salt rejection while minimizing energy demand. A predictive model using multiple response optimization revealed that CSM RO and NF250 membranes showed the optimal efficiency with 20.24% and 18.98% water recovery, 90.22% and 70.64% salt rejection and 17.87 kWh/m3 and 9.35 kWh/m3 of specific energy consumption (SEC), respectively. Furthermore, confirmation of RSM predictions was carried out by an artificial neural network (ANN) model trained by RSM experimental data. Predicted values by both RSM and ANN modeling methodologies were compared and found within the acceptable range. Finally, a membrane validation experiment was carried out successfully at proposed optimal conditions, which proved the accuracy of the employed RSM and ANN models. Detailed analyses of the economic assessment showed that the recovery rate can play a major role in reducing the cost of a membrane system.

Arsenic and fluoride contaminated groundwaters: A review of current technologies for contaminants removal

Chronic contamination of groundwaters by both arsenic (As) and fluoride (F) is frequently observed around the world, which has severely affected millions of people. Fluoride and As are introduced into groundwaters by several sources such as water-rock interactions, anthropogenic activities, and groundwater recharge. Coexistence of these pollutants can have adverse effects due to synergistic and/or antagonistic mechanisms leading to uncertain and complicated health effects, including cancer. Many developing countries are beset with the problem of F and As laden waters, with no affordable technologies to provide clean water supply. The technologies available for the simultaneous removal are akin to chemical treatment, adsorption and membrane processes. However, the presence of competing ions such as phosphate, silicate, nitrate, chloride, carbonate, and sulfate affect the removal efficiency. Highly efficient, low-cost and sustainable technology which could be used by rural populations is of utmost importance for simultaneous removal of both pollutants. This can be realized by using readily available low cost materials coupled with proper disposal units. Synthesis of inexpensive and highly selective nanoadsorbents or nanofunctionalized membranes is required along with encapsulation units to isolate the toxicant loaded materials to avoid their re-entry in aquifers. A vast number of reviews have been published periodically on removal of As or F alone. However, there is a dearth of literature on the simultaneous removal of both. This review critically analyzes this important issue and considers strategies for their removal and safe disposal.

A concurrent exposure to arsenic and fluoride from drinking water in Chihuahua, Mexico

Inorganic arsenic (iAs) and fluoride (F-) are naturally occurring drinking water contaminants. However, co-exposure to these contaminants and its effects on human health are understudied. The goal of this study was examined exposures to iAs and F- in Chihuahua, Mexico, where exposure to iAs in drinking water has been associated with adverse health effects. All 1119 eligible Chihuahua residents (>18 years) provided a sample of drinking water and spot urine samples. iAs and F- concentrations in water samples ranged from 0.1 to 419.8 µg As/L and from 0.05 to 11.8 mg F-/L. Urinary arsenic (U-tAs) and urinary F- (U-F-) levels ranged from 0.5 to 467.9 ng As/mL and from 0.1 to 14.4 µg F-/mL. A strong positive correlation was found between iAs and F- concentrations in drinking water (rs = 0.741). Similarly, U-tAs levels correlated positively with U-F- concentrations (rs = 0.633). These results show that Chihuahua residents exposed to high iAs concentrations in drinking water are also exposed to high levels of F-, raising questions about possible contribution of F- exposure to the adverse effects that have so far been attributed only to iAs exposure. Thus, investigation of possible interactions between iAs and F- exposures and its related health risks deserves immediate attention.

Groundwater vulnerability assessment using DRASTIC and Pesticide DRASTIC models in intense agriculture area of the Gangetic plains, India

Delineating areas susceptible to contamination from anthropogenic sources form an important component of sustainable management of groundwater resources. The present research aims at estimating vulnerability of groundwater by application of DRASTIC and Pesticide DRASTIC models in the southern part of the Gangetic plains in the state of Bihar. The DRASTIC and Pesticide DRASTIC models have considered seven parameters viz. depth to water level, net recharge, aquifer material, soil material, topography, impact of vadose zone and hydraulic conductivity. A third model, Pesticide DRASTIC LU has been adopted by adding land use as an additional parameter, to assess its impact on vulnerability zonation. The DRASTIC model indicated two vulnerable categories, moderate and high, while the Pesticide DRASTIC model revealed moderate, high and very high vulnerable categories. Out of the parameters used, depth to water level affected the vulnerability most. The parameter caused least impact was topography in DRASTIC, while in case of Pesticide DRASTIC and Pesticide DRASTIC LU models, the parameter was hydraulic conductivity. A linear regression between groundwater NO3 concentrations and the vulnerability zonation revealed better correlation for Pesticide DRASTIC model, emphasising the effectiveness of the model in assessing groundwater vulnerability in the study region. Considering all three models, the most vulnerable areas were found to be concentrated mainly in two zones, (i) in the south-western part along Ekangarsarai-Islampur patch and (ii) around Biharsharif-Nagarnausa area in the central part. Both zones were characterised by intensive vegetable cultivation with urban areas in between.

Arsenic mobilization in the Brahmaputra plains of Assam: groundwater and sedimentary controls

Arsenic (As) mobilization to the groundwater of Brahmaputra floodplains was investigated in Titabor, Jorhat District, located in the North Eastern part of India. The groundwater and the aquifer geochemistry were characterized in the study area. The range of As concentration in the groundwater varies from 10 to 440 μg/l with mean concentration 210 μg/l. The groundwaters are characterized by high dissolved Fe, Mn, and HCO₃(-) and low concentrations of NO₃(-) and SO₄(2-) indicating the reduced conditions prevailing in the groundwater. In order to understand the actual mobilization processes in the area, six core drilling surrounding the two target tube wells (T1 and T2) with high As concentration (three drill-cores surrounds each tube well closely) was done. The sediment was analyzed its chemical, mineralogical, and elemental compositions. A selective sequential extraction suggested that most of the As in the sediment is bound to Fe oxides fractions (32 to 50%) and the competition for adsorption site by anions (PO₄(3-)) also accounts to significant fractions of the total arsenic extracted. High variability in the extraction as well as properties of the sediment was observed due to the heterogeneity of the sediment samples with different chemical properties. The SEM and EDX results indicate the presence of Fe, Mn coating along with As for most of the sample, and the presence of As associated minerals were calculated using PHREEQC. The mobilization of As into the groundwater was anticipated to be largely controlled by the reductive dissolution of Fe oxides and partly by the competitive anions viz. PO₄(3-).

Biological neutralization and biosorption of dyes of alkaline textile industry wastewater

The present work was aimed to secure biological neutralization and biosorption of dyes of an alkaline textile industrial effluent (ATIE) using an alkaliphilic bacterium, Enterococcus faecalis strain R-16 isolated from Gujarat coast. The isolate was capable and competent to bring down the pH of ATIE from 12.1 to 7.0 within 2 h in the presence of carbon and nitrogen sources. Carboxylic group concentration (CGC), NMR and FT-IR analysis revealed production of carboxylic acid as a result of neutralization. The unconventional carbon and nitrogen sources like Madhuca indica flowers or sugar cane bagasse supported the growth of bacterium with effective neutralization and biosorption of dyes from ATIE. The process proved to be efficient, inexpensive and eco-friendly as compared to conventional chemical neutralization process.

Chronic low-level arsenic exposure reduces lung function in male population without skin lesions

OBJECTIVES

The respiratory effects of chronic low-level arsenic exposure from groundwater have been investigated in West Bengal, India.

METHODS

The participants (834 non-smoking adult males) were subdivided in two groups: an arsenic-exposed group (n = 446, mean age 35.3 years) drinking arsenic-contaminated groundwater (11-50 μg/L) and a control group of 388 age-matched men drinking water containing <10 μg/L of arsenic. Arsenic in water samples was measured by atomic absorption spectroscopy. The prevalence of respiratory symptoms was documented by structured, validated questionnaire. Pulmonary function test (PFT) was assessed by portable spirometer.

RESULTS

Compared with control, the arsenic-exposed subjects had higher prevalence of upper and lower respiratory symptoms, dyspnea, asthma, eye irritation and headache. Besides, 20.6% of arsenic-exposed subjects had lung function deficits (predominantly restrictive and combined types) compared with 13.6% of control (p < 0.05). A positive association was observed between arsenic concentration in drinking water and the prevalence of respiratory symptoms, while a negative association existed between arsenic level and spirometric parameters.

CONCLUSIONS

The findings suggest that even low-level arsenic exposure has deleterious respiratory effects.

Hydrogeochemical factors affecting the mobilization of As into the groundwater of the Brahmaputra alluvial plains of Assam, Northeast India

Groundwater in the Brahmaputra river basin is known to contain an elevated concentration of naturally occurring Arsenic (As). To better understand the mobilization processes responsible for the As enrichment in the groundwater of the alluvial plains of the Brahmaputra river, the hydrochemical characteristics of the groundwater were studied in two districts, namely the Darrang and Jorhat districts of Assam. A total of 217 groundwater samples were analyzed for 20 water quality parameters. A lower As concentration was observed in the Darrang district with a mean concentration of 0.02 μg l(-1), while the Jorhat district had a higher As concentration (mean 100 μg l(-1)). The groundwater in the study areas is characterized by high concentrations of dissolved Fe, Mn, HCO3(-) and PO4(3-) and low concentrations of NO3(-) and SO4(2-). The redox potential and the groundwater composition showed reducing conditions in the groundwater. A difference in the groundwater geochemistry between the two districts was observed and was mainly controlled by the redox conditions in the subsurface, which control the mobility of As in the floodplains. The saturation indices of various As associated minerals were calculated using the geochemical code PHREEQC. The mobilization of As into the groundwater was anticipated to be largely controlled by the reductive dissolution of Fe-oxides and Mn-oxides and partly by competitive anions viz. PO4(3-).