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Groundwater fluoride across the Punjab plains of Pakistan and India: Distribution and underlying mechanisms
Abstract
Chronic exposure from drinking well-water with naturally high concentrations of fluoride (F⁻) has serious health consequences in several regions across the world including South Asia, where the rural population is particularly dependent on untreated groundwater pumped from private wells. An extensive campaign to test 28,648 wells was conducted across the Punjab plains of Pakistan and India by relying primarily on field kits to document the scale of the problem and shed light on the underlying mechanisms. Groundwater samples were collected from a subset of 712 wells for laboratory analysis of F⁻ and other constituents. A handful of sites showing contrasting levels of F⁻ in groundwater were also drilled to determine if the composition of aquifer sediment differed between these sites. The laboratory data show that the field kits correctly classified 91% of the samples relative to the World Health Organization guideline for drinking water of 1.5 mg/L F⁻. The kit data indicate that 9% of wells across a region extending from the Indus to the Sutlej rivers were elevated in F⁻ relative to this guideline. Field data indicate an association between the proportion of well-water samples with F⁻ > 1.5 mg/L and electric conductivity (EC) > 1.5 mS/cm across six floodplains and six intervening doabs. Low Ca²⁺ concentrations and elevated bicarbonate (HCO3⁻ > 500 mg/L) and sodium (Na⁺ > 200 mg/L) in high F⁻ groundwater suggest regulation by fluorite. This could be through either the lack of precipitation or the dissolution of fluorite regulated by the loss of Ca²⁺ from groundwater due to precipitation of calcite and/or ion exchange with clay minerals. Widespread salinization of Punjab aquifers attributed to irrigation may have contributed to higher F⁻ levels in groundwater of the region. Historical conductivity data suggest salinization has yet to be reversed in spite of changes in water resources management.
... Its genesis and distribution depends on the presence of F − bearing minerals such as fluorite, biotite, muscovite, fluoroapatie illite, cryolite, apatite, topaz, muscovite, and mica (Durrani & Farooqi, 2021). Furthermore, groundwater F − mobilization and precipitation is driven chemically by Na + , K + , Ca +2 , Mg +2 , Cl − , alkalinity, TDS, EC, salinity and pH (Khattak et al., 2022), physically by residence time, aquifer recharge, depth, porosity and type, and environmentally by temperature, precipitation and topography . However, Hydrogeochemical processes responsible for groundwater F − contamination are dissolution, hydrolysis, precipitation, adsorption, ion exchange, and biochemical reactions (Ali et al., 2023;Chandrajith et al., 2020;Kitterod et al., 2022;Kumar et al., 2024). ...
... This was supported by variations in aquifer characteristics. High elevation areas has hard rock aquifers (recharging zones) with less secondary sediment deposits as compared to the alluvial aquifers (discharging zones) with increase thickness of fined clayey sediment materials (Durrani & Farooqi, 2021;Khattak et al., 2022;Wang et al., 2024). Negative correlation R 2 (− 0.052) of SO −2 4 indicated that F − was not coming from anthropogenic source such as fertilizers input rather it had geogenic origin. ...
... Very high F − was associated to Na-HCO 3 , Na-Cl and Ca-Mg-Cl while low F − was driven by Ca-HCO 3 (Durrani & Farooqi, 2021). In this study area, high F − was driven by Na-HCO 3 type water and found in the valley plain while low F − made good association with Ca-HCO 3 type water found at the surrounding mountains (Khattak et al., 2022). All the samples in the Chloro alkaline indices fall in the negative value ranging from − 1.52 to − 13.69 for CAI1 and − 1.82 to − 13.04 for CAI2 (Fig. 6), indicating reverse ion exchange that means Na + and K + ions in water are removed by abundance of weak divalent Ca +2 and Mg +2 this happens when fresh water is interacting with the aquifer material thus making the dissolution and dissociation of calcite or dolomite minerals. ...
Around 2.6 billion people are at risk of tooth carries and fluorosis worldwide. Quetta is the worst affected district in Balochistan plateau. Endemic abnormal groundwater fluoride ( F - ) lacks spatiotemporal studies. This research integrates geospatial distribution, geochemical signatures, and data driven method for evaluating F - levels and population at risk. Groundwater F - ranged from 0 to 3.4 mg/l in (n = 100) with 52% samples found unfit for drinking. Through geospatial IDW tool hotspot areas affected with low and high groundwater F - levels were identified. Geochemical distribution in geological setups recognized sediment variation leads to high F - (NaHCO3) and low F - (CaHCO3) water types in low elevation (central plain) and high elevation (mountain foot) respectively. Results of the modified water quality index identified 60% samples to be unsuitable for drinking. Support vector machine (SVM), random forest regression (RFR) and classification and regression tree (CART) machine learning models found Na + , Salinity and Ca + 2 as important contributing variables in groundwater F - prediction. CART model with R2 value of 0.732 outperformed RFR and SVM in predicting F - . Noncarcinogenic health risk vulnerability from F - increased from Adults < Teens < Children < Infants. Infants and children with hazard quotient values of 11.3 and 4.2 were the most vulnerable population at risk for consuming F - contaminated groundwater. The research emphasizes on both nutritional need and hazardous effect of F - , and development of desirable limit for F - .
... To overcome some of the limitations of a patchwork of local studies, a large-scale well survey was conducted across the Punjab Plains on both sides of the Pakistan-India border using field kits . The testing was part of a transboundary project covering the Punjab Plains that considered geogenic contamination of groundwater by As as well as fluoride (Kumar et al., 2020;Khattak et al., 2022). This survey showed that the wells in the floodplain of the Ravi River were particularly prone to As contamination compared to other drainages, which contrasts with a prediction of high levels of As contamination across all floodplains of the Indus region (Podgorski et al., 2017). ...
... In most of the villages covered by the Pakistan survey, and all of the 11 villages selected for drilling, well water was tested in the field not only for As but also for electrical conductivity (EC) and pH with Eutech Instruments EC-PCSTestr35 probes (http://www.eutechinst.com/). Calibration of the probes was monitored daily (Khattak et al., 2022). With the exception of 1082 wells in 10 villages in the Sutlej and Ravi floodplains (RAV42 and RAV89), wells (n = 20,331) were tested for dissolved Fe using the visual HANNA field kit (no. ...
... Field measurements of EC and dissolved Fe, and SO 4 for almost 19,447 wells across the study region help set the stage for interpreting the drilling results. One previously recognized feature is that EC is generally lower in floodplains compared to the doabs of the region that are less frequently flushed with fresh water (Greenman et al., 1967;Khattak et al., 2022). Combining measurements by formation shows that the proportion of wells with EC > 1 mS/cm averages 39 % in floodplains and 69 % in doab areas (interfluves) including our expanded data set (Fig. 2). ...
... Among them, fluorite dissolution has been recognized as the primary driver of high-F groundwater (Kimambo et al., 2019;Wang et al., 2020). Since Ca-depleted groundwater may promote fluorite dissolution (Li et al., 2017;Harkness and Jurgens, 2022), processes of calcite precipitation (Currell et al., 2011;Brahman et al., 2013) and cation exchange of Ca 2+ with Na + may reduce Ca 2+ concentrations, facilitating F − release (Chen et al., 2020;Khattak et al., 2022). In addition, alkaline environments with high groundwater pH and HCO 3 − concentrations may also compete with sediment F − and contribute to elevated F − concentration (Su et al., 2013;Harkness and Jurgens, 2022). ...
... Upon As release, the fate of the released As is subject to adsorption onto sediments (Fendorf et al., 2010;Gao et al., 2020). F-bearing minerals (especially fluorite) being weathered from igneous rocks should be the dominant source of groundwater F − (Chowdhury et al., 2019), which has been well documented in previous studies Han et al., 2021;Khattak et al., 2022). In the North China Plain, the presence of fluorite in sediments have been reported . ...
... This is similar to the observations in the Datong Basin, showing more oxidizing environments induced by vertical surface water recharge lowered As concentrations but enhanced F − mobility (Pi et al., 2015). Khattak et al. (2022) have also concluded that anoxic conditions may restrain the release of F − into groundwater, because of the negative correlation between dissolved Mn and F − concentrations. ...
Genesis of the contrasting distributions of high arsenic (>10 μg/L) and fluoride (>1 mg/L) groundwater and their negative correlations remain poorly understood. We investigated spatial distributions of groundwater arsenic and fluoride concentrations in the lower reaches of the Yellow River basin, Henan Province, China, using bivariate statistical analyses and geochemical simulations. Results suggest that high arsenic and fluoride groundwater showed contrasting distributions with few overlapped area. Groundwater arsenic concentrations were significantly negatively correlated with oxidation-reduction potential (ORP) values and positively with NH4⁺ and Fe(II) concentrations, while the opposites were true for groundwater fluoride concentrations. These may suggest that high arsenic groundwater is related to stronger organic matter degradation and Fe(III) oxide reduction, while groundwater fluoride enrichment occurs with less extent of organic matter degradation. Geochemical calculations supported that groundwater fluoride enrichment was governed by extent of fluorite dissolution, which was constrained by varied saturation indices of fluorite in groundwater. However, groundwater arsenic mobility may be explained by different solubility of Fe(III) oxides. Higher Fe(III) oxide solubility corresponding to goethite and lepidocrocite was related to higher arsenic concentrations, while hematite was too low in solubility to produce high arsenic groundwater. The study presented both geochemical and modeling evidences for the contrasting behaviors of groundwater arsenic and fluoride concentrations in anoxic aquifers.
... Groundwater chemical conditions such as elevated alkalinity, reduced calcium levels, and sodium bicarbonate water type favor dissolution and desorption of metal oxides, causing F − enrichment. Additionally, arid and semiarid climatic zones have also reported increased F − concentrations (8,9) due to enhanced cation exchange capacity, dissolution from F − -bearing minerals and longer groundwater residence times, thereby increasing the interaction between the rock-water interface (10,11). Besides the natural factors, anthropogenic activities, including phosphate fertilizer application, sewage and sludge dumping, mining, coal combustion, and excess groundwater extraction, also contribute to high F − levels (11,12). ...
... Although these attributes are often measured during groundwater monitoring assessments, some were missing from the datasets collected from different sources. Data collected from research papers (8,41,42) did not contain all of this information and, hence, was not included in the final database. In comparison, almost all variables were present in data collected from BGS, CUPB, and CGWB. ...
Introduction
Rising fluoride levels in groundwater resources have become a worldwide concern, presenting a significant challenge to the safe utilization of water resources and posing potential risks to human well-being. Elevated fluoride and its vast spatial variability have been documented across different districts of Punjab, India, and it is, therefore, imperative to predict the fluoride levels for efficient groundwater resources planning and management.
Methods
In this study, five different models, Support Vector Machine (SVM), Random Forest (RF), Extreme Gradient Boosting (Xgboost), Extreme Learning Machine (ELM), and Multilayer Perceptron (MLP), are proposed to predict groundwater fluoride using the physicochemical parameters and sampling depth as predictor variables. The performance of these five models was evaluated using the coefficient of determination ( R ² ), mean absolute error (MAE), and root mean square error (RMSE).
Results and discussion
ELM outperformed the remaining four models, thus exhibiting a strong predictive power. The R ² , MAE, and RMSE values for ELM at the training and testing stages were 0.85, 0.46, 0.36 and, 0.95, 0.31, and 0.33, respectively, while other models yielded inferior results. Based on the relative importance scores, total dissolved solids (TDS), electrical conductivity (EC), sodium (Na ⁺ ), chloride (Cl ⁻ ), and calcium (Ca ²⁺ ) contributed significantly to model performance. High variability in the target (fluoride) and predictor variables might have led to the poor performance of the models, implying the need for better data pre-processing techniques to improve data quality. Although ELM showed satisfactory results, it can be considered a promising model for predicting groundwater quality.
... Moreover, desorption processes of Fe-oxides, Al-oxides, oxyhydroxides, and hydrous metal oxides can also increase F − concentration (Xiao et al., 2015). Hydroxy-minerals, such as muscovite and biotite, are also widely distributed in both BSR and BXR, which are regarded as potential sources for fluoride release by providing the appreciable amounts of exchangeable F − (Khattak et al., 2022). ...
... Besides anion exchange mentioned in section 4.3.1, cation exchange can also contribute to F − release by exchange of Na + adsorbed on the clay minerals with Ca 2+ and Mg 2+ in groundwater (Khattak et al., 2022). The negative correlation relationship between (HCO 3 − + SO 4 2--Ca 2+ -Mg 2+ ) and (Cl − -Na + -K + ) for the samples in BXR (R 2 = 0.96) is more significant than it in BSR (R 2 = 0.18) (Fig. 5). ...
Although groundwater is the primary drinking water source in northern of China, little is known about generation mechanisms and related health risks of high fluoride groundwater at the geomorphic transition zones. Thus, 419 groundwater samples were collected from Zhangjiakou region, where is a typically geomorphic transition zone of the North China Plain and the Inner Mongolia Plateau, to conduct the hydrochemical analysis, geochemical modeling, multivariate statistical analysis, and health risks assessment. From the results, F⁻ concentration in groundwater had a range of 0.05–9.71 mg L⁻¹. About 37.1% and 26.2% of groundwater samples from Bashang region (BSR) and Baxia region (BXR), respectively, were over the 1.50 mg L⁻¹, which were mainly distributed in the groundwater flow retardation area and/or evaporation discharge area. Thermodynamic simulations demonstrated that F-bearing minerals dissolution and Ca²⁺/Mg²⁺ removal via calcite/dolomite precipitation primarily governed high-F⁻ groundwater formation in the whole study area. Competitive adsorption, evaporation, evaporites dissolution and salt-effect also affected F⁻ enrichment in BSR. Desorption in alkaline environment, ion exchange and human activities played a vital role in F⁻ enrichment at BXR. The multivariate statistical analysis revealed that the origin of F⁻ contamination was geogenic in BSR; whereas, it was geogenic and anthropogenic in BXR. Besides, more than 71.8%, 51.0%, 36.1% and 25.5% of the study area exceeded the acceptable level (health index>1) for infants, children, adult males, and females, respectively. The health risks for different groups of people varied significantly and ranked: infants > children > males > females, suggesting that younger people were more susceptible to fluoride contamination. Meanwhile, females were more resistant to fluoride contamination than males. These findings are vital to providing insights on high-F⁻ groundwater formation, investigate the situation of health risks, and conduct the integrated management for high fluoride groundwater in geomorphic transition zones at northern China.
... The main cation in groundwater changed from Ca 2+ to Na + due to cation exchange occurred. This transformation process as a drive force can promote the dissolution of fluorine-bearing minerals and increasing of F − (Cao et al. 2023b;Khattak et al. 2022). Moreover, the coefficient between F − and HCO 3 − was 0.22 (p < 0.05) illustrated that the existing of competitive adsorption (Fig. 6b). ...
The North Henan Plain in the lower reaches of the Yellow River is one of the areas where the Yellow River burst and changed course most frequently. The presence of several inferior components in groundwater of this area has negatively affected the utilization of groundwater. However, the main controlling factors and the sources of environmental impacts that lead to the deterioration of groundwater quality and human health risk are still unclear. The improved water quality index and health index were calculated to assess levels of the groundwater quality condition and health risks. The hydrochemistry analysis, Sr isotope and positive matrix factorization (PMF) model were used to identify the main environmental factors affecting the groundwater quality and human health. The results showed that the increasing of Fe and As concentrations were significant factors in the deterioration of water quality. 6.97%-13.94% and 28.48%-34.55% of groundwater posed non-carcinogenic and carcinogenic risks to the population where children and female posing higher health risks than male. The groundwater was mainly affected by five factors: anthropogenic activities (37%), redox environment (3.7%), soil types (9.3%), weathering of minerals (33.4%) and water–rock interaction or competitive adsorption (16.6%). However, redox environment instead of the anthropogenic activity was the determining factor controlling the health risk. This study indicated that the risk of groundwater probably can be reduced by influencing redox conditions like groundwater table regulation.
... Naturally occurring fluoride refers to fluoride ions found in nature, primarily as minerals like fluorite (CaF₂) or in groundwater, often as sodium fluoride or other fluoride salts (Khattak, 2022). Both fluorosilicic acid and naturally occurring fluoride can dissociate in water to release fluoride ions (Nicholson, 2008), which are believed to be the active components responsible for dental health benefits. ...
This critical review examines the methodologies and search strategies employed in systematic reviews that informed the 2017 public health statement of the effects of water fluoridation. The analysis highlights significant inconsistencies in the search strategies for dental caries versus broader health effects, including outdated search dates and variations in search syntax that may limit the comprehensiveness of the evidence base. The review emphasises the importance of rigorous methodological standards, such as standardised protocols and transparent reporting, to mitigate biases and enhance the reliability of findings. Notably, the lack of differentiation between various fluoridation agents and the exclusion of certain health outcomes, such as dental fluorosis, raises concerns about the objectivity and comprehensiveness of existing reviews. Furthermore, the review underscores the necessity of updating search strategies and criteria to capture emerging research, advocating for a more nuanced understanding of the health implications associated with water fluoridation. By addressing these methodological shortcomings, future systematic reviews can contribute to a more informed and equitable public health discourse.
Keywords: water fluoridation; health effects; dental caries; public health; policy
... Numerous graphical techniques and interpretations of numerous indicators can be used to assess the quality of groundwater and determine the distinct processes of hydrogeochemistry characteristics that influence groundwater chemistry (Van Green et al. 2019;Kumar & Singh 2020;Mallick et al. 2021;Dashora et al. 2022;Khattak et al. 2022). Researchers point out that groundwater characterization is a powerful tool for addressing a variety of geochemical issues. ...
The primary source of drinking water in Ethiopia's semi-arid mountainous regions is groundwater. The present study aims to assess the hydrogeochemical characteristics of low-grade basement rocks dominated by mountainous catchments. Moreover, it examines the suitability of the groundwater quality for drinking purposes in Irob, Tigray, northern Ethiopia. However, relatively little is known about the water chemistry and groundwater quality of the resources in the area. Fifteen samples of groundwater were collected and examined for ions according to standard procedures. The outcomes were assessed against the World Health Organization (WHO) requirements for water drinking quality. To identify the source of dissolved ions and the process involved, graphic interpretations were applied. The results show that Ca–Mg–SO4–HCO3 and Ca–SO4–HCO3 were the dominant water types. Gibbs plots and ionic ratios reveal that silicate weathering, carbonate dissolution and ion exchange control water chemistry. Furthermore, the findings reveal that 60, 80, 46.67, 46.67, 60, 6.67, 60 and 53.33% of samples are above the safe limits of the WHO for hardness, alkalinity, total dissolved solids, electrical conductivity, calcium (Ca2+), potassium (K+), bicarbonate (HCO3-) and sulfate (SO42-), respectively. Consequently, the groundwater quality assessment demonstrates that the water sources in lower parts of the catchment are unsuitable for drinking.
... Volcanic rock has a high fluorine content of 1000 to 6000 mg kg −1 [4], granite has an average fluorine content of 800 mg kg −1 [5], and sedimentary rocks like limestone and dolomite have a comparatively low fluorine content of 300 mg/kg on average [5,6]. Release of just 0.04% of total fluoride from rocks and sediments, considering sediment porosity of 0.2 and sediment density of 2.5 gcc −1 , would be sufficient to raise fluoride (F − ) concentration in groundwater by about 1.5 mg l −1 [7]. Long-term exposure to F − may result in a number of health issues including dental and skeletal fluorosis as a prominent one along wither productive, developmental, endocrine, renal, neurological problem [8]. ...
... Geographically, the area lies between latitude 31.23157 • N and longitude 73.95181 • E. The people in the village consume groundwater, which is highly contaminated with F − (15 mg L − 1 , i.e. 10 times greater than the WHO permissible limit of 1.5 mg L − 1 ) for drinking and irrigation purposes (Khan et al., 2022;Khattak et al., 2022). After collection, the soil was air-dried for one week and then passed through a 2 mm sieve to obtain the homogenized soil sample. ...
... It was reasonable to inferred, therefore, that semi-arid climate and evaporite dissolution in Zone IV can lead to elevation of F − concentration in groundwater. In addition, positive cation exchange of replacing Ca 2+ and Mg 2+ in groundwater by Na + and K + adsorbed on the clay minerals in aquifer can promote F − release into groundwater (Khattak et al., 2022). Therefore, positive cation exchange in Zone IV groundwater caused decreasing concentration of Ca 2+ which can further accelerate the hydrolysis of fluorite, ultimately resulting in elevated concentration of F − in groundwater. ...
... The basic water quality parameters like pH, total dissolved solids (TDS), and electrical conductivity (EC) were examined using multi-parameter analyzer (Hanna HI9829), following 32 . The groundwater samples were shifted immediately to a standard water quality laboratory Pakistan Council of Research on Water Resources (PCRWR), to measure the concentration of major cations, anions and (As). ...
Arsenic (As), contamination in drinking groundwater resources is commonly environmental problem in many developing countries including Pakistan, with significant human health risk reports. In order to examine the groundwater quality concerning As contamination, its geochemical behavior along with physicochemical parameters, 42 samples were collected from community tube wells from District Bahawalpur, Punjab, Pakistan. The results showed the concentration of elevated As, its source of mobilization, and associated public health risk. The As concentration detected in groundwater samples varied from 0.12 to 104 µg/L with an average value of 34.7 µg/L. Among 42 groundwater samples, 27 samples were beyond the permitted limit of 10 µg/L recommended by World Health Organization (WHO), for drinking purposes. Statistical analysis result show that the groundwater cations values are in decreasing order such as: Na⁺ > Mg²⁺ > Ca²⁺ > K⁺, while anions were HCO3– > SO42– > Cl– > NO3–. Hydrochemical facies result depict that the groundwater samples of the study area, 14 samples belong to CaHCO3 type, 5 samples belong to NaCl type, 20 samples belong to Mixed CaMgCl type, and 3 samples belong to CaCl2 type. It can be accredited due to weathering and recharge mechanism, evaporation processes, and reverse ion exchange. Gibbs diagram shows that rock water interaction controls the hydrochemistry of groundwater resources of the study area. Saturation Index (SI) result indicated the saturation of calcite, dolomite, gypsum, geothite, and hematite mineral due their positive SI values. The principal component analysis (PCA) results possess a total variability of 80.69% signifying the anthropogenic and geogenic source of contamination. The results of the exposure-health-risk-assessment method for measuring As reveal significant potential non-carcinogenic risk (HQ), exceeding the threshold level of (> 1) for children in the study area. Water quality assessment results shows that 24 samples were not suitable for drinking purposes.
... In table 2 we presented the As and F from different groundwater aquifers of south-east Asia. Similar inferences are drawn by other studies form different parts of the globe (Guo et al., 2012;Pi et al., 2015;Liu et al., 2015;Zabala et al., 2016;Podgorski et al., 2018;Rashid et al., 2018;Qiao et al., 2020;Khattak et al., 2022). ...
... However, anthropogenic activities, such as pesticides and fertilizers application, mining activities, and industrial activities will exacerbate fluoride contamination in aquifers, making the groundwater quality further worsened (Kumar et al., 2018;Li et al., 2020;Qiao et al., 2022). Kumar et al. (2018), Khattak et al. (2022), Li et al. (2018), Li et al., (2017), andLiu et al. (2018) separately investigated the geochemical characterization, spatial distribution patterns, main hydrogeological processes that controlling the local scale F − enrichment in groundwater, which are all helpful for researchers to identify the factors regulating the spatial patterns and pollution sources of F − in groundwater. Zeng et al. (2023a), Qiu et al. (2023b), Qu et al. (2021), Qu et al. (2022), Zhang et al. (2023), and Yang et al. (2022) applied different innovative techniques/approaches, such as positive matrix factorization (PMF) model, Monte Carlo simulation, self-organizing maps, and factor analysis, efficiently processing complex hydrochemical datasets and help gain a full understanding of the mechanisms that regulate the fluoride enrichment, transport, and human health risk prediction in groundwater. ...
Fluoride enrichment (> 1.5 mg/L) in groundwater has become a global threat, particularly given the hazards to human health. This study collected 58 unconfined groundwater samples from Fengpei Plain in June 2022 for hydrochemical and stable isotope analyses combined with multiple methods to explore sources, influencing factors, and potential health hazards of groundwater F⁻. The results showed that groundwater F⁻ concentration ranged from 0.08 to 8.14 mg/L, with an average of 1.91 mg/L; over 41.4% of them exceeded the acceptable level of 1.5 mg/L prescribed by the World Health Organization (WHO). The dominant hydrochemical facies changed from Ca·Mg-HCO3 and Ca·Mg-SO4·Cl type in low-F– groundwater to Na-HCO3 and Na-SO4·Cl water types in high-F– groundwater. The Self-Organizing Map (SOM) and ionic correlation analysis indicated that F⁻ is positively correlated to pH, EC, Na⁺, K⁺, SO4²⁻, and TDS, but negatively to Ca²⁺ and δ¹⁸O. Groundwater F⁻ accumulation was primarily driven by F⁻-bearing minerals dissolution such as fluorite. Simultaneously, the carbonates precipitation, positive cation exchange processes, and salt effect were conducive to groundwater F⁻ enrichment. However, competitive adsorption between OH⁻/HCO3⁻ and F⁻, evaporation, and anthropogenic activities only had a weak effect on the F⁻ enrichment in groundwater. The hazard quotient (HQ) assessment results show that 67.2% of groundwater samples pose a non-carcinogenic risk (HQ > 1) for infants, followed by 53.4% for children, 32.8% for females, and 25.9% for males. The Monte Carlo simulation results agreed with those of the deterministic model that minors are more susceptible than adults. These findings are vital to providing insights into the geochemical behavior, driving factors, and drinking water safety of high-F⁻ groundwater worldwide.
Graphical abstract
... Similarly, there are approximately 2.17 million quality-affected habitations in India, with more than half impacted by excess iron, followed by fluoride, salinity, nitrate, and arsenic (Khattak et al. 2022;Podgorski et al. 2018). In addition, there are 11 million cases of typhoid fever with 117,000 deaths, 3 million cases of cholera with an estimated 95,000 deaths, and 1.7 billion cases of diarrhea among children under the age of five reported each year (Bureau of Indian Standards 2012). ...
Groundwater resource analysis is an important technological means of avoiding disease and controlling water pollution. In this field of study, water quality assessments are conducted using sequential parametric values collected in real time. For evaluation reasons, several state-of-the-art water quality evolution mechanism typically employs a single time-invariant model to determine the quality of Water. As a result, it is challenging to illustrate the importance of randomness and contingency in the process of water quality assessment, leading to variations and errors in the procedure of quality assessment. In consideration of these limitations, this study proposes a Digital Twin inspired Hybrid System (DTHS) for water quality assessment in real time. In addition, the degree of water quality is offered as an indication for quantitatively assessing the health risk status. Observational data from a monitoring station in Chaheru, a locality in the Phagwara district of the Indian state of Punjab, are used to demonstrate the efficacy of the proposed approach. The experimental results demonstrate the effectiveness of the proposed framework in terms of water quality determination, computational cost, and stability. The framework has achieved higher prediction accuracy (94.14%), sensitivity (93.74%), specificity (91.47%), and f-measure (92.37%), indicating its ability to accurately determine water quality. Additionally, the framework offers reduced computational delay and improved reliability and stability, making it a trustworthy solution for timely predictions with respect to water quality.
... , and NO 3 − were analysed using a UV/ visible spectrophotometer (T80 + ). Fluoride was analysed by the HANNA (HI729) low-range fluoride portable kit, and its reliability was validated in previous studies (Khattak et al. 2022). While Na + and K + contents were measured through AAS-Flame Atomic Absorption Spectrometry (Agilent 55AA) under standard operating conditions. ...
Baluchistan’s water profile was developed by dividing it into seven zones (Northern Highlands-NH, Southern Highlands-SH, Quetta Valley-QV, Desert-D, Sibbi Plains-SP, Coastal Lasbella-CL, Coastal Gwadar-CG) based on geography, water availability, and climate of the area. A total of 106 water samples were collected from karaiz, spring water, and tube wells. Spatial distribution of EC, TDS, TH, SO42−, Cl−, Na+, and K+ showed an increasing trend in concentration from the highlands towards the desert and coastal zones. For anion, HCO3− is predominant in NH, SH, and QV, Cl− in D, CL, and CG and only SO42− in SP, whereas the cationic trend in overall zones is Na+>Ca2+>Mg2+>K+. In the NH, SH, QV, and SP zones, the physicochemical parameters met the drinking water quality guidelines; however, D, CL, and CG exceeded in almost all quality parameters. Furthermore, the drinking water quality index (WQI) shows excellent to good water quality in NH, SH, QV, and D zones, while CL and CG fall in poor to unsuitable water classes. In terms of hydrogeochemical facies, maximum water samples from NH fall in Ca-Mg-HCO3, and SH, QV, and SP in Ca-Mg-Cl type, where major ion chemistry is controlled by rock-weathering, while D, CL, and CG fall in the NaCl type, where evaporation is dominant. Similarly, irrigation water quality parameters (EC, SAR, RSC, Na%, MH%, PI, SSP, and KR) reveal that NH, SH, QV, and SP have suitable water for irrigation, and D, CL, and CG require proper treatment. Additionally, USSL and Wilcox’s diagrams indicated that NH, SH, QV, and SP have “excellent to permissible”; however, D, CL, and CG have “permissible to unsuitable” class water, requiring special management practices. Consequently, appropriate control measures and targeted water purification programmes should be implemented to protect the public health and sustainability of water resources in Baluchistan.
... However, studies from other South American countries are limited (Gomez et al., 2009;Alarcón-Herrera et al., 2013;Martins et al., 2018). While in Asia, China, Mongolia, and Indian subcontinents have often recorded high F‾ (Wu et al., 2015;Ali et al., 2016;2019;2022;Rahman et al., 2020;Khattak et al., 2022;Ling et al., 2022). For example, Chandrajith et al. (2020) investigated drinking wells in Sri Lanka and found that F‾ contaminates nearly 50% of the wells in dry zones. ...
Groundwater contamination by fluoride (F¯ >1.5 mg/L) is pervasive and typically confined to arid and semi-arid regions. Therefore, several parts of India are contaminated by F¯. However, the genesis, sources, and mobilization of F¯ in groundwater are unclear or evaluated based often on studies conducted at a local scale. To understand the severity of F¯ contamination at the national scale and to devise remedial strategies, we performed a statistical evaluation between F¯ and its influencing factors, including geology, hydro-meteorology, and potential hydro-chemical parameters based on a large dataset (n = ∼2000) published in the last two decades throughout India. Results revealed that (a) alkalinity plays a pivotal role in the mobilization of F¯ into groundwater from the sediments/rocks, (b) high F¯ in groundwater is more pronounced in the arid and semi-arid areas of alluvial plains than hard rock regions, and (c) positive correlation of elevated F¯ with SiO2 and K+ indicates the dominance of geogenic sources linked to the weathering of fluorine bearing silicates. Investigations show that one-third of the Indian drinking water wells are contaminated by F¯, thereby risking the health of over millions of people through the drinking water pathway. Findings from this study have addressed the most possible sources, pathways, and regional prevalence of F¯ contamination in the groundwater of India, and suggested the remediation measures suitable based on prevailing surface and sub-surface conditions. The review will also address challenges and propose future research directions to tackle high fluoride groundwater and ensure safe drinking water supply in India.
... For the past two decades, contamination of groundwater by F − and NO 3 − has been a significant public health concern (Qasemi et al. 2023). Many studies on the groundwater quality related to elevated F − have been conducted in arid and semi-arid regions around the world (Alam and Ahmad 2014;Khattak et al. 2022;Lanjwani et al. 2022;Mwiathi et al. 2022;Su et al. 2013Su et al. , 2015. The World Health Organization (WHO 2022) recommends a permissible level of 1.5 mg/L of F − in groundwater for human consumption. ...
Consumption of high fluoride (F⁻) and nitrate (NO3⁻) containing water may pose serious health hazards. One hundred sixty-one groundwater samples were collected from drinking wells in Khushab district, Punjab Province, Pakistan, to determine the causes of elevated F⁻ and NO3⁻ concentrations, and to estimate the human health risks posed by groundwater contamination. The results showed pH of the groundwater samples ranged from slightly neutral to alkaline, and Na⁺ and HCO3⁻ ions dominated the groundwater. Piper diagram and bivariate plots indicated that the key factors regulating groundwater hydrochemistry were weathering of silicates, dissolution of evaporates, evaporation, cation exchange, and anthropogenic activities. The F⁻ content of groundwater ranged from 0.06 to 7.9 mg/L, and 25.46% of groundwater samples contained high-level fluoride concentration (F⁻ > 1.5 mg/L), which exceeds the (WHO Guidelines for drinking-water quality: incorporating the first and second addenda, WHO, Geneva, 2022) guidelines of drinking-water quality. Inverse geochemical modeling indicates that weathering and dissolution of fluoride-rich minerals were the primary causes of F⁻ in groundwater. High F⁻ can be attributed to low concentration of calcium-containing minerals along the flow path. The concentrations of NO3⁻ in groundwater varied from 0.1 to 70 mg/L; some samples are slightly exceeding the (WHO Guidelines for drinking-water quality: incorporating the first and second addenda, WHO, Geneva, 2022) guidelines for drinking-water quality. Elevated NO3⁻ content was attributed to the anthropogenic activities revealed by PCA analysis. The high levels of nitrates found in the study region are a result of various human-caused factors, including leaks from septic systems, the use of nitrogen-rich fertilizers, and waste from households, farming operations, and livestock. The hazard quotient (HQ) and total hazard index (THI) of F⁻ and NO3⁻ showed high non-carcinogenic risk (> 1) via groundwater consumption, demonstrating a high potential risk to the local population. This study is significant because it is the most comprehensive examination of water quality, groundwater hydrogeochemistry, and health risk assessment in the Khushab district to date, and it will serve as a baseline for future studies. Some sustainable measures are urgent to reduce the F⁻ and NO3⁻ content in the groundwater.
... The contents of chloride (Cl − ) and fluoride (F − ) were determined using the "Mohr's technique and Fluoride Analyzer" ionselective electrode (ISE) (HANNA Instruments, Japan, Model No. HI 5222 and HI 4110, type Solid-state; Combination) [37]. The principal cations in the GW samples, including Ca 2+ , magnesium (Mg 2+ ), sodium (Na + ), and potassium (K + ), were measured using a flame atomic absorption spectrophotometer (Varian Spectra AA-240, Australia) under standard operating settings [38]. To assess the analytical precision and correctness of the GW data, the ionic charge balance of cation and anion errors (ICBE) was determined. ...
Fluoride (F −) contamination in drinking groundwater is a significant human health risk in Pakistan. Moreover, high fluoride pollution in drinking water causes a variety of disorders, including dental, neurological, and skeletal fluorosis. The aim of this research was to evaluate the health risk of elevated fluoride in groundwater and its suitability assessment for drinking purposes. The total of (n = 37) samples were collected from community tube wells of Quetta Valley, Balochistan, Pakistan. The results show a mean pH value of 7.7, TDS of 404.6 mg/L, EC of 500 µs/cm, depth of 96.8 feet, and turbidity of 1.7 nephelometric turbidity units. The mean values of HCO3 − , Ca 2+ , Mg 2+ , and Na + , were 289.5, 47.5, 30.6, and 283.3 mg/L, respectively. The mean values of SO4 2− , NO3 − , K + , Cl − , and Fe 2+ , were 34.9, 1.0, 1.6, 25.6, and 0.01 mg/L, respectively. The F − concentration in the groundwater varied between 0.19 and 6.21, with a mean value of 1.8 mg/L, and 18 samples out of 37 were beyond the WHO recommended limit of 1.5 mg/L. The hydrochemical analysis results indicated that among the groundwater samples of the study area, 54% samples were Na-HCO3 type and 46% were mixed CaNaHCO3 type. The saturation indices of the mineral phases reveal that the groundwater sources of the study area were saturated with CaCO3 and halide minerals due to their positive (SI) values. Such minerals include calcite, dolomite, gypsum, and fluorite. The principal component analysis results reveal that the groundwater sources of the study area are contaminated due to geological and anthropogenic actions. The health risk assessment results of the F − concentrations show the ranges of ADDingestion for children, females, and males in the Quetta Valley, and their mean values were observed to be 0.093052, 0.068825, and 0.065071, respectively. The HQingestion mean values were 1.55086, 1.147089, and 1.084521 for children, females, and males, respectively. It was noticed that children had the highest maximum and average values of ADDingestion and HQingestion in the research area, indicating that groundwater fluoride intake poses the greatest health risk to children. The water quality index (WQI) analyses show that 44% of the samples belong to the poor-quality category, 49% were of good quality, and 8% of the samples of the study area belong to the excellent category. Citation: Ullah, Z.; Xu, Y.; Zeng, X.-C.; Rashid, A.; Ali, A.; Iqbal, J.; Almutairi, M.H.; Aleya, L.; Abdel-Daim, M.M.; Shah, M. Non-Carcinogenic Health Risk
... So both studies advocate that the people living in the plains of Punjab are at risk due to arsenic-contaminated water. There are millions of wells that need to be tested in the Punjab plains of the subcontinent to decrease the avoidable toxic exposures (Khattak et al. 2022). Imran et al. (2017a, b) corroborated that the people living in the As-risk zones of Lahore have some kind of As-based diseases. ...
The exposure variation of arsenic from different ground and surface water sources has remained unpredictable which may cause severe human health problems. The current study is, therefore, designed to analyze the spatial variability of arsenic contamination in shallow aquifer and assess the potential human health risks. For this purpose, a total of 55 groundwater, 10 drain water, 4 river water, and 6 sediment samples were collected along zero to 5 km stretch of the River Ravi, Lahore. All water samples were tested for As, pH, and total dissolved solids (TDS), whereas sediments were only tested for As. Health risk models were used to predict cancer and non-cancer risk in adults and children. Among water samples, highest median (minimum–maximum) concentrations (µg/L) of As were recorded 53.32 (1.98–1555) in groundwater, followed by 53.04 (1.58–351.5) in drain water, and 4.80 (2.13–8.67) in river water, respectively, whereas As concentration (mg/kg) in river sediments was 6.03 (5.56–13.92). Variation of As in groundwater was non-significant (P > 0.05) among every 1-km stretch from the Ravi River. However, maximum median concentrations (µg/L) of 60.18 and 60.08 were recorded between 2–3 and 0–1 km from River Ravi, respectively, reflecting possible mixing of river water with shallow aquifers. A very high cancer and non-cancer risk (HI > 1.0 × 10−4) through groundwater As exposure was predicted for both children and adults. The current study concluded that prevalence of As above WHO prescribed limits in shallow aquifer along the urban stretch of the River Ravi is posing serious health risk to the exposed population.
... The contents of chloride (Cl − ) and fluoride (F − ) were determined using the "Mohr's technique and Fluoride Analyzer" ionselective electrode (ISE) (HANNA Instruments, Japan, Model No. HI 5222 and HI 4110, type Solid-state; Combination) [37]. The principal cations in the GW samples, including Ca 2+ , magnesium (Mg 2+ ), sodium (Na + ), and potassium (K + ), were measured using a flame atomic absorption spectrophotometer (Varian Spectra AA-240, Australia) under standard operating settings [38]. To assess the analytical precision and correctness of the GW data, the ionic charge balance of cation and anion errors (ICBE) was determined. ...
Fluoride (F −) contamination in drinking groundwater is a significant human health risk in Pakistan. Moreover, high fluoride pollution in drinking water causes a variety of disorders, including dental, neurological, and skeletal fluorosis. The aim of this research was to evaluate the health risk of elevated fluoride in groundwater and its suitability assessment for drinking purposes. The total of (n = 37) samples were collected from community tube wells of Quetta Valley, Balochistan, Pakistan. The results show a mean pH value of 7.7, TDS of 404.6 mg/L, EC of 500 µs/cm, depth of 96.8 feet, and turbidity of 1.7 nephelometric turbidity units. The mean values of HCO3 − , Ca 2+ , Mg 2+ , and Na + , were 289.5, 47.5, 30.6, and 283.3 mg/L, respectively. The mean values of SO4 2− , NO3 − , K + , Cl − , and Fe 2+ , were 34.9, 1.0, 1.6, 25.6, and 0.01 mg/L, respectively. The F − concentration in the groundwater varied between 0.19 and 6.21, with a mean value of 1.8 mg/L, and 18 samples out of 37 were beyond the WHO recommended limit of 1.5 mg/L. The hydrochemical analysis results indicated that among the groundwater samples of the study area, 54% samples were Na-HCO3 type and 46% were mixed CaNaHCO3 type. The saturation indices of the mineral phases reveal that the groundwater sources of the study area were saturated with CaCO3 and halide minerals due to their positive (SI) values. Such minerals include calcite, dolomite, gypsum, and fluorite. The principal component analysis results reveal that the groundwater sources of the study area are contaminated due to geological and anthropogenic actions. The health risk assessment results of the F − concentrations show the ranges of ADDingestion for children, females, and males in the Quetta Valley, and their mean values were observed to be 0.093052, 0.068825, and 0.065071, respectively. The HQingestion mean values were 1.55086, 1.147089, and 1.084521 for children, females, and males, respectively. It was noticed that children had the highest maximum and average values of ADDingestion and HQingestion in the research area, indicating that groundwater fluoride intake poses the greatest health risk to children. The water quality index (WQI) analyses show that 44% of the samples belong to the poor-quality category, 49% were of good quality, and 8% of the samples of the study area belong to the excellent category. Citation: Ullah, Z.; Xu, Y.; Zeng, X.-C.; Rashid, A.; Ali, A.; Iqbal, J.; Almutairi, M.H.; Aleya, L.; Abdel-Daim, M.M.; Shah, M. Non-Carcinogenic Health Risk
... For instance, nitrate, fluoride, and arsenic were frequently recorded as the main contributors to groundwater contamination worldwide Adimalla 2021;Natasha et al., 2021;Mwiathi et al., 2022). Research work has been conducted in the past, concerning groundwater quality and its hydrochemistry worldwide (Huang et al., 2018a;van Geen et al., 2019;Kumar and Singh 2020;Mallick et al., 2021a;Mallick et al., 2021b;Dashora et al., 2022;Khattak et al., 2022). Thus, it is very crucial to investigate and monitor the groundwater quality and detail hydrochemistry, to protect the health of the exposed local population, especially in highly contaminated areas of Sindh, Pakistan. ...
Arsenic (As) contamination in drinking groundwater sources is a common environmental problem in Pakistan. Therefore, we collected a total of (n = 81) drinking groundwater samples from various groundwater sources, from two districts’ namely Ghotki (n = 44) and Nawab Shah (n = 37) of Sindh, Province, Pakistan. The current research aimed to investigate the hydrogeochemistry of groundwater with elevated arsenic (As), its effect on the health of local population living in the study area, potential sources of groundwater variables, and the suitability of groundwater for ingestion motive. The results showed that groundwater sample variables of both districts had moderate to high concentration levels. The cations concentrations were observed in decreasing order of Na⁺ > Ca⁺ > Mg⁺ > K⁺, for both districts, while anions abundance was HCO3 ⁻ > Cl⁻ > SO4 ²⁻ > F⁻ > NO3 ⁻ in the Ghotki, and HCO3 ⁻ > SO4 ²⁻ > Cl⁻ > NO3 ⁻ > F⁻ in the Nawab Shah, respectively. Arsenic (As) had low to high concentration levels in both districts, observed with average values of 10.1 μg/L and 21.0 μg/L in the Ghotki and Nawab Shah, respectively. The water type was mixed CaMgCl type in both districts, while the groundwater sources were saturated for CO3 minerals indicated by the saturation indices results. Principal component analysis showed the geogenic source of ion exchange, dissolution of minerals, weathering of host rocks and anthropogenic input of industrial activities, agricultural practices and domestic waste for groundwater contamination. The water quality index (WQI) exhibits that majority of groundwater samples (73.6% of Ghotki and 65.7% of Nawab Shah) were suitable for drinking. The non-carcinogenic risk (HQ) values of As were (>1) in groundwater samples of the Ghotki and Nawab Shah, while a high mean HQ value (8.78 × 10⁰) was recorded for children in Nawab Shah. The carcinogenic risk (CR) values of As were significantly higher than the maximum threshold CR value (1 × 10–4). This study emphasized that monitoring strategies are substantially needed to mitigate the As contamination to reduce the potential health risk.
... Compared to the previous nationwide representation of fluoride at the sub-tehsil-scale (Khan et al., 2002), the novel maps presented here have a 3-4 order of magnitude higher spatial resolution (250 m), are based on much larger new datasets, and predict the probability of high groundwater fluoride for areas where data are lacking. Also in relation to a recent study by Khattak et al. that contains clusters of many groundwater fluoride measurements across much of Punjab (Khattak et al., 2021), the new maps identify hotspots, e.g. in the Sargodha Division, that that study did not uncover. ...
Concentrations of naturally occurring fluoride in groundwater exceeding the WHO guideline of 1.5 mg/L have been detected in many parts of Pakistan. This may lead to dental or skeletal fluorosis and thereby poses a potential threat to public health. Utilizing a total of 5483 fluoride concentrations, comprising 2160 of new measurements as well as those from other sources, we have applied machine learning techniques to predict the probability of fluoride in groundwater in Pakistan exceeding 1.5 mg/L at a 250 m spatial resolution. Climate, soil, lithology, topography, and land cover parameters were identified as effective predictors of high fluoride concentrations in groundwater. Excellent model performance was observed in a random forest model that achieved an Area Under the Curve (AUC) of 0.92 on test data that were not used in modeling. The highest probabilities of high fluoride concentrations in groundwater are predicted in the Thar Desert, Sargodha Division, and scattered along the Sulaiman Mountains. Applying the model predictions to the population density and accounting for groundwater usage in both rural and urban areas, we estimate that about 13 million people may be at risk of fluorosis due to consuming groundwater with fluoride concentrations >1.5 mg/L in Pakistan, which corresponds to ~6% of the total population. Both the fluoride prediction map and the health risk map can be used as important decision-making tools for authorities and water resource managers in the identification and mitigation of groundwater fluoride contamination.
This paper evaluated fluoride (F⁻) pollution in drinking groundwater sources, which causes severe fluorosis and other human health concerns in Swabi, Pakistan. We determined F⁻ concentration, prevalence, enrichment, distribution, and health hazards from water ingestion in Swabi, Pakistan. Therefore, 126 groundwater and 18 surface water samples were collected to analyze F⁻ and other geochemical tracers to understand groundwater enrichment and F⁻ mobilization in aquatic systems. The range and mean values of F⁻ in groundwater were 0.02 to 14.2 and 4.0 mg/L, and those in surface water were 1.12–0.8 and 1.4 mg/L. Most residents used groundwater for drinking purposes. Thus, groundwater results showed that 72.2% of samples had surpassed the WHO guidelines of F⁻ 1.5 mg/L. The fluoride pollution index (FPI) declared that 48.73% of samples showed a higher risk, 41.95% medium risk, and 9.32% lower risk. Mineral phases using PHREEQC interactive software determined mineral saturation revealing the dissolution of host rock minerals and unsaturation showed precipitation of minerals within the aquifer. The principal component analysis multilinear regression (PCA-MLR) model showed a five-factor solution: (a) geogenic processes, (b) mixed geogenic and anthropogenic inputs, (c) geochemical processes, (d) agriculture pollution, and (e) industrial effluents which would release F⁻ in the aquifer. The health hazard due to higher F⁻ revealed that children showed high-risk levels compared to adults in endemic areas. The spatial distribution of F⁻ in drinking groundwater increases towards the northern side and decreases in the south to the southeastern side. Therefore, effective water management techniques would be required to safeguard groundwater resources and secure human health from dental and skeletal fluorosis and other associated problems caused by high F⁻ groundwater with varying fluoride concentrations. This study will help the water management authority to safeguard depleted groundwater for drinking demands.
Globally, groundwater contamination by fluoride (F−) is a threat to the safe drinking water supply. Nevertheless, our understanding of the geochemical processes of F− mobilization to the groundwater by linking groundwater and aquifer material chemistry is limited. We therefore characterized that in the hard-rock aquifers of Central India, an area that has not been investigated thoroughly despite the known severity of the problem. Exploratory drilling of boreholes (n = 45) and lithostratigraphic modeling identified weathered basalt, vesicular basalt, fractured basalt, sandstone of Lameta, and fractured granite as major aquifers in the study area. The groundwater contamination by F− (concentration >1.5 mg/L) mainly occurred at depths >35 m bgl (at elevations <500 m amsl) of the fractured basalt and fractured granite aquifers, while samples collected from the shallow basalt, sandstone of Lameta, and shallow granite were mostly safe. The F− contamination of groundwater was primarily governed by the chemical evolution of groundwater along the flow path. Solute mass balance in groundwater, in conjunction with the mineralogical characterization of the aquifer materials, suggests that weathering of silicate and carbonate minerals was the dominant form of mineral dissolution in aquifers, which consumed dissolved CO2 along the flow path and resulted in an alkaline pH (>8) in groundwater of the deeper aquifers. The mobilization of F− in the groundwater could primarily be attributed to the ion exchange between OH− in water and structural F− in fluorapatite and F-bearing mica/amphibole. By assessing water quality and aquifer properties, this study suggests that primarily, the sandstone of Lameta and weathered and vesicular basalts can be targeted for F-safe drinking water supply in the study area. Targeting shallow aquifers can be an option for F-safe drinking water supply in other affected areas with similar geological and environmental settings.
GRACE (Gravity Recovery and Climate Experiment) has been widely used to evaluate terrestrial water storage (TWS) and groundwater storage (GWS). However, the coarse‐resolution of GRACE data has limited the ability to identify local vulnerabilities in water storage changes associated with climatic and anthropogenic stressors. This study employs high‐resolution (1 km²) GRACE data generated through machine learning (ML) based statistical downscaling to illuminate TWS and GWS dynamics across twenty sub‐regions in the Indus Basin. Monthly TWS and GWS anomalies obtained from a geographically weighted random forest (RFgw) model maintained good consistency with original GRACE data at the 25 km² grid scale. The downscaled data at 1 km² resolution illustrate the spatial heterogeneity of TWS and GWS depletion within each sub‐region. Comparison with in‐situ GWS from 2,200 monitoring wells shows that downscaling of GRACE data significantly improves agreement with in‐situ data, evidenced by higher Kling‐Gupta Efficiency (0.50–0.85) and correlation coefficients (0.60–0.95). Hotspots with the highest TWS and GWS decline rate between 2002 and 2023 were Dehli Doab (−442, −585 mm/year), BIST Doab (−367, −556 mm/year), Rajasthan (−242, −381 mm/year), and BARI (−188, −333 mm/year). Based on a general additive model, 47%–83% of the TWS decline was associated with anthropogenic stressors mainly due to increasing trends of crop sown area, water consumption, and human settlements. The decline rate of TWS and GWS anomalies was lower (i.e., −25 to −75 mm/year) in upstream sub‐regions (e.g., Yogo, Gilgit, Khurmong, Kabul) where climatic factors (downward shortwave radiations, air temperature, and sea surface temperature) explained 72%–91% of TWS/GWS changes. The relative influences of climatic and anthropogenic stressors varied across sub‐regions, underscoring the complex interplay of natural‐human activities in the basin. These findings inform place‐based water resource management in the Indus Basin by advancing the understanding of local vulnerabilities.
Fluoride contamination in the groundwater is a threat to water security. This is highly dangerous in arid and semi-arid regions which comprises one-third of the world region where more than 20% of the population resides. Elevated levels of fluoride in the groundwater are largely reported from these areas which is widely used for drinking without any prior treatment. It is of great concern as the consumption of elevated levels of fluoride causes dental fluorosis and skeletal fluorosis to humans. Furthermore, insufficient rainfall and high evapotranspiration vis-à-vis longer water–rock interactions are noticeably responsible for the elevated levels of fluoride in these regions. Unluckily, most of these regions fall in the developing world, and thus, governing policies are many times inefficient in providing sustainable water supply for drinking. Therefore, more feasible and practical solutions in conjunction with strong policy intervention are required to solve this global contaminant issue. This chapter highlights various facets of fluoride contamination and discusses various challenges in providing fluoride-free water in contaminated arid and semi-arid regions.
Groundwater contaminants from natural and anthropogenic sources pose a serious threat to the ecological environment and public health. In this study, 30 groundwater samples were collected from shallow wells at a large central water source in the North Anhui Plain, eastern China. Hydrogeochemical methods, positive matrix factorization (PMF) model, and Monte Carlo simulation were used to determine the characteristics, sources, and human health risks of inorganic and organic analytes in groundwater. The groundwater was weakly alkaline with high total hardness and was dominated by HCO3-Mg·Ca, HCO3-Ca·Mg, and HCO3-Ca·Mg·Na hydrochemical facies. The concentration of naphthalene was at a safe level, while the concentrations of F-, NO3- and Mn in 16.7 %, 26.7 % and 40 % of the samples, respectively, exceeded threshold risk-based values based on Chinese groundwater quality standards. Hydrogeochemical methods revealed that water-rock interactions (including weathering of silicate minerals, dissolution of carbonates, and cation exchange), acidity, and runoff conditions control the migration and enrichment of these analytes in groundwater. The PMF model indicated that local geogenic processes, hydrogeochemical evolution, agricultural activities, and petroleum-related industrial sources were the main factors affecting groundwater quality, with contributions of 38.2 %, 33.7 %, 17.8 %, and 10.3 %, respectively. A health risk evaluation model based on Monte Carlo simulation indicated that 77.9 % of children were exposed to a total noncarcinogenic risk above safe thresholds, about 3.4 times higher than the risk to adults. The main contributor to human health risk was F- originating from geogenic processes; thus, F- was identified as a priority for control. This study demonstrates the feasibility and reliability of combining source apportionment techniques and health risk assessment to evaluate groundwater quality.
The Yudong Plain is in the eastern part of Henan Province, China, where there is little rain and high evaporation. Compared to other areas in Henan Province, the groundwater fluorine content is generally high, which affects the health of residents. Based on the systematic analysis of water chemistry data of shallow and mid-depth groundwater samples in the Yudong Plain, the causes of shallow and mid-depth high-fluorine groundwater in the Yudong Plain were explored using mathematical statistics, spatial interpolation, and ion ratios. The results show that the fluorine contents of both shallow and mid-depth groundwater in the study area are high. The shallow samples had fluorine contents ranging from 0.1 to 4.89 mg/L, with an exceedance rate of 48% and an average content of 1.15 mg/L. The fluorine content of mid-depth samples ranged from 0.14 to 3.32 mg/L, with an exceedance rate of 68% and an average content of 1.33 mg/L. The shallow high-fluorine groundwater is mainly distributed in the central low-lying area, and its main hydrochemical type is HCO3-Na·Mg; the mid-depth high-fluorine groundwater is mainly distributed in strips in the north and east of the study area, and its main water chemistry type is HCO3-Na. Fluorine enrichment in shallow groundwater in the study area is controlled by rock weathering, evaporation concentration, and competitive adsorption, while leaching and dissolution of fluorine-containing minerals in sedimentary strata are the main factors influencing fluorine enrichment in mid-depth groundwater. The results of the human health risk assessment (HRA) showed that the mean non-carcinogenic hazard quotients (HQs) in shallow groundwater were 0.95, 0.64, 0.57, and 0.55 for infants, children, teenagers, and adults, respectively, while the mean non-carcinogenic HQs in mid-depth groundwater were 1.11, 0.74, 0.66, and 0.63, respectively. The study provides a scientific basis for the rational development and use of groundwater in the area and offers theoretical support for the prevention and control of groundwater pollution.
Fluoride contamination in groundwater is a global issue. Nanoscale oxides of Zr(IV), Al(III), and Ti(IV) can form the inner-sphere complex with fluoride through ligand exchange, offering a new chance for efficient groundwater purification. However, pilot-scale field demonstration of nanotechnology in groundwater defluoridation is very rare. Herein, we conducted a 150-day field defluoridation study using the nanocomposite [email protected], which was prepared by encapsulating nano-hydrated zirconium oxide (HZO) inside the strongly basic anion exchanger D201. The [email protected] beads were packed in five-stage series columns (40 L for each column), and the groundwater was pumped through the columns sequentially. The effective treatment amount for the single column ([F-] < 1.0 mg/L) exceeded ∼3000 bed volume (BV). The exhausted [email protected] was fully refreshed through ex situ treatment with NaOH-NaCl solution for repeated use without significant loss in defluoridation reactivity. Owing to the specific interaction with HZO, the fluoride concentration could be steadily reduced below 1.0 mg/L throughout the 150-day field demonstration, while the common anions coexisting in groundwater (K+, Na+, Ca2+, Mg2+, SO42-, Cl-, etc.) remained almost unchanged. The operational cost for deep defluoridation was estimated as 0.574 RMB per ton of groundwater, much less than that of the widely studied reverse osmosis. TEM, XPS, and Fourier transform infrared (FTIR) analysis indicated that negligible change occurred in the structure and chemical composition of [email protected] after the long-term field assay. This study may inspire more attempts at the pilot scale and engineering demonstration of nano-enabled water treatment techniques.
Groundwater fluoride contamination in some parts of the study region was long recognized as a water quality issue. For this purpose, groundwater samples were collected from different groundwater abstraction units (14 sampling sites and 28 years data 1990–2018) and analyzed using standard protocols. The results of water quality index (WQI) showed that 86% and 14% of sampling sites fall within the class of “good” and “poor” quality, respectively. Non-carcinogenic health risk (NCHR) assessment (using hazard quotient (HQ)) and sensitivity analysis for three age groups were also carried out using Monte Carlo simulation technique. The estimated levels of HQoral were greater in magnitude than those estimated from HQdermal; thus, the main source of fluoride toxicity is oral ingestion. Amongst the three age groups studied, children > female > male were found to be more prone to NCHR with HQoral ranging from (0.13 to 5.45), (0.07 to 2.97), and (0.06 to 2.51), respectively. Sensitivity analyses indicated that fluoride concentration, ingestion rate, shower exposure time, and fractional skin contact with water were the most relevant variables in the model to reduce the potential health effect.
Fluoride has received much attention for its predominant bone toxicity in the human body. However, the toxic mechanism of bone injury caused by fluoride exposure remains largely unclear. Bone marrow mesenchymal stem cells (BMSCs) are widely used as model cells for evaluating bone toxicity after environmental toxicant exposure. In this study, BMSCs were exposed to fluoride at 1, 2, and 4 mM for 24 h, and fluoride significantly inhibited cell viability at 2 and 4 mM. A multiomics analysis combining transcriptomics with metabolomics was employed to detect alterations in genes and metabolites in BMSCs treated with 2 mM fluoride. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of transcriptomics profiles identified “lysosomes” as the top enriched pathway, which was severely damaged by fluoride exposure. Lysosomal damage was indicated by decreases in the expression of lysosomal associated membrane protein 2 (LAMP 2) and cathepsin B (CTSB) as well as an increase in pH. Upregulation of the lysosome-related genes Atp6v0b and Gla was observed, which may be attributed to a compensatory lysosomal biogenesis transcriptional response. Interestingly, inhibition of glutathione metabolism was observed in fluoride-treated BMSCs at the metabolomic level. Moreover, an integrative analysis between altered genes, metabolites and lysosome signaling pathways was conducted. Palmitic acid, prostaglandin C2, and prostaglandin B2 metabolites were positively associated with Atp6v0b, a lysosome-related gene. Overall, our results provide novel insights into the mechanism responsible for fluoride-induced bone toxicity.
The objective of this study was to understand the drinking water quality state in the Inner Mongolia Autonomous Region from 2014 to 2018 and to derive information that will provide a basis for improving the drinking water quality in the region. Monitoring data for drinking water from the Inner Mongolia Autonomous Region for 2014 to 2018 were analyzed and the results were compared with GB 5749-2006, the Standard Test Method for Drinking Water, and GB 5749-2006, the Drinking Water Quality Standards. Data for a total of 30,613 water samples were assessed. Of the data for the microbiological index, sensory trait and general chemical index, and toxicological index, 89, 80, and 69% were qualified, respectively. For the toxicological index, the fluoride and nitrate nitrogen data were the least compliant. The water quality in all the cities was generally very suitable for drinking. However, there were marked differences in the qualified rates of drinking water in different areas and the qualified rates of the data for the three indexes were lower in rural areas than in urban areas. Given the varied issues with the drinking water quality, the relevant departments of League cities should implement appropriate and effective treatment measures to improve the drinking water quality and ensure it is safe for residents. HIGHLIGHTS
The values of the microbial, sensory trait and general chemical, and toxicological indexes for drinking water in the Inner Mongolia Autonomous Region have increased over the period from 2014 to 2018.;
The compliance of the three indexes for drinking water from various sources and cities were different, which required appropriate measures to improve.;
The quality of drinking water is lower in rural areas than in urban areas.;
Fluoride is capable of inducing developmental neurotoxicity, but the mechanisms involved remain unclear. We aimed to explore the role of autophagosome-lysosome fusion in developmental fluoride neurotoxicity, particularly focusing on the interaction between ATG14 and the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex. We developed in vivo models of Sprague–Dawley rats exposed to sodium fluoride (NaF) from the pregnancy of parental rats until the offspring were two months old and in vitro models of NaF and/or Ad-ATG14-treated SH-SY5Y cells. We assessed neurobehavioral changes in offspring and further investigated the effects of NaF exposure on autophagic flux, apoptosis, autophagosome-lysosome fusion, and the interaction between ATG14 and the SNARE complex. NaF exposure impaired offspring learning and memory capabilities and induced the accumulation of autophagosomes and autophagic flux blockage and apoptosis, as indicated by increased LC3-II, p62, and cleaved-caspase-3 expression in vivo and in vitro. In addition, NaF treatment downregulated the protein expression of ATG14 and the SNARE complex and induced autophagosome-lysosome fusion blockage as evidenced by decreased ATG14, STX17, SNAP29, and VAMP8 expression and diminished colocalization of autophagosomes and lysosomes in vivo and in vitro. Furthermore, ATG14 upregulation enhanced the interaction of ATG14 and the SNARE complex to facilitate autophagosome-lysosome fusion, thereby restoring autophagic flux and alleviating NaF-induced apoptosis. In conclusion, NaF exhibited developmental neurotoxicity by restraining the interaction of ATG14 with the SNARE complex and hindering autophagosome-lysosome fusion, thereby participating in the occurrence and development of fluoride neurotoxicity. Notably, ATG14 upregulation protects against developmental fluoride neurotoxicity, and ATG14 may serve as a promising biomarker for further epidemiological investigation.
Millions of villagers in Bangladesh are exposed to arsenic by drinking contaminated water from private wells. Testing for arsenic can encourage switching from unsafe wells to safer sources. This study describes results from a cluster randomized controlled trial conducted in 112 villages in Bangladesh to evaluate the effectiveness of different test selling schemes at inducing switching from unsafe wells. At a price of about US0.60, only one in four households purchased a test. Sales were not increased by informal inter-household agreements to share water from wells found to be safe, or by visual reminders of well status in the form of metal placards mounted on the well pump. However, switching away from unsafe wells almost doubled in response to agreements or placards relative to the one in three proportion of households that switched away from an unsafe well with simple individual sales.
The Gilgit-Baltistan Province and Azad Kashmir regions are rich in mineral and natural resources. The gemstones, marbles and many other economic mineralizations are significant but these regions are relatively far from central and southern commercial areas of Pakistan. The gemstones of Gilgit-Baltistan Province are famous worldwide especially from Hunza and Skardu regions. The Azad Kashmir region also has a share of gemstone especially from the upper approaches of Neelam valley and marble, construction materials, coal, clays and other minerals found from different areas of Azad Kashmir. There is no common previous availability of comprehensive papers providing mineral data of Gilgit-Baltistan Province and Azad Kashmir regions. This report provides a quick view of mineral resources occurred in the Gilgit-Baltistan and Azad Kashmir regions.
Hydrogeochemistry and factor analysis were conducted together to assess the distribution and the major geochemical processes in fluoride-contaminated shallow groundwater in the Yuncheng Basin. Spatially, fluoride concentration was low (< 1.5 mg/L) in the southern piedmont plain, medium (< 4 mg/L) in the central basin, and high (up to 14.1 mg/L) in Kaolao lowland areas in shallow aquifers. A three-factor principal component analysis model explained over 75.1% of the total variance. Sediment weathering leaching and evapotranspiration were recognized as the first primary hydrochemical processes response for the groundwater chemistry and explained the largest portion (42.1%) of the total variance. Factor two reflects the negative influence of human activities, with a positive loading of NO3⁻ and HCO3⁻, and negative loading of well depth. Fluoride-bearing mineral dissolution and alkaline condition was ranked as the third factors responding for groundwater chemistry and explained 11.2% of the total variance.
In the present study 134 children were studied for comparison and correlation between an endemic fluorotic village Rukh Mudke (RM), n = 74 , and a non-fluorotic village Ottawa (OTW), n = 60 . The children were aged between 7-18 years and selected for the estimation of fluoride in their household water, body fluids (urine-serum), dental fluorosis and thyroid hormones (Free tri-iodothyronine (FT 3 ) free tetra iodothyronine (FT 4 ) and thyroid stimulating hormone (TSH) respectively . Mean concentration of water fluoride in subjects of RM was 4.6 ×10 ⁶ ng/L, urine fluoride 2.59 ×10 ⁶ ng/L, serum fluoride 6.0 ×10 ⁴ and dental fluorosis 90.5% respectively. Significant elevation ( P = 0.000) in the concentration of three out of these four variables ( P < 0.01) was observed (except in serum fluoride) in subjects of RM compared to those in the control group (OTW). Mean FT 4 , FT 3 and TSH concentrations in RM subjects was 18.3 pmol/L, 5.06 pmol/L and 3.2 mlU/L respectively. No marked difference in FT 4 and FT 3 ( P = 0.17 and P = 0.7) was found compared to the control (OTW) group, while significant elevation in TSH ( P < 0.05) was found in. 22% of the children in the RM group, portrayed well defined thyroid hormonal aberrations. A negative correlation between water fluoride - FT 4 (r = - 0.24); a strong positive between water, urine, serum, dental fluorosis and TSH (r = 0.94, 0.87, 0.88, 0.74 and 0.8) and moderate correlation between water fluoride - FT 3 (r = 0.52) was observed. Results of this study indicate that the fluoride intoxication through drinking water is not only increasing fluoride level in body fluids and deteriorating teeth but also destroying thyroid function in a large number of children.
About 20 million rural Bangladeshis continue to drink well-water containing >50 ug/L arsenic (As). This analysis argues for re-prioritizing interventions on the basis of a survey of wells serving a population of 380,000 conducted one decade after a previous round of testing overseen by the government. The available data indicate that testing alone reduced the exposed population in the area in the short term by about 130,000 by identifying the subset of low As wells that could be shared at a total cost of <US30 per person whose exposure was reduced. In contrast, the installation of over 900 deep (>150 m) wells and a single piped-water supply system by the government reduced exposure of little more than 7,000 inhabitants at a cost of US$150 per person whose exposure was reduced. The findings make a strong case for long-term funding of free well testing on a massive scale with piped water or groundwater treatment only as a last resort.
The groundwater quality of Indus Basin around Sargodha and adjacent areas of Punjab Plain is known for its poor-quality in multiple aquifers at different depths. The poor-quality water is being used for domestic and irrigation purposes, causing significant health hazards to communities, ecosystem, livestock, and crops. The aquifer water, sediment analysis, and surface drainage system, including river beds and dormant meanders, have been analyzed during different studies. The subsoil data points had not been concluded or established the geological reason or created a model impacting the quality of groundwater. In the past, limited work has been recognized in multiple source areas and remained focused only to Salt Range outcrops. The geological significance of Kirana-Chiniot Hillocks has not been considered and it has remained to its existing localized exposures. The aquifer solvents support the existence of near to far distance geological formations that are consistently charging the aquifers in Doabs (the area between two rivers). The present study comprises subsurface rock data, composition and geometry below the alluvial cover to speculate geological model which is contributing to alter groundwater composition after dilution and distribution to aquifers. The east-west trending zone of 200-220 km length stretches from Lahore to Khisor Range while its width in the north-south direction is about 60-80 km around Sargodha-Chinot-Sangla Hillocks. The hypothetical model is based on sub-crop rock distribution drilled wells for oil and gas, 2D-Seismic reflection data, regional gravity mapping and geology of Kirana-Chinot-Sangla Hillocks. Cambrian and Precambrian lithologies and associated minerals after dilution with recharging waters are controlling the groundwater quality in Doabs.
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 dataset 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 non-managed 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.
Hydrogeochemical and stable isotope analyses and geochemical modeling were carried out to identify the major geochemical processes controlling the groundwater chemistry and fluoride contamination in the aquifers of the Yuncheng Basin, China, an area with complex hydrogeochemical conditions and severe fluoride contamination of the groundwater. The major findings of this case study include the following: 1) Cation exchange and salt effects are vital controls on the enrichment of fluoride in groundwater in the area by reducing the activity of Ca²⁺/F⁻ in groundwater via ion complexation. Cation exchange increased the fluoride concentration by 2.7 mg/L when the Na/Ca molar ratio increased from 0.24 to 9.0, while the salt effect led to a ca. 5–10% increase in complex F⁻ in groundwater due to the further dissolution of fluoride-bearing minerals in the aquifers, as suggested by a model calculation. 2) Anthropogenic contamination from pesticide and fertilizer use and industrial waste discharge is also a main source of fluoride in the groundwater. 3) Evaporation and ion effects favor the enrichment of fluoride in groundwater by encouraging the removal of Ca via precipitation. 4) The desorption of fluoride from mineral/organic matter surfaces is enhanced under alkaline conditions and a high HCO3 content in groundwater.
The Indo-Gangetic aquifer is one of the world's most important transboundary water resources, and the most heavily exploited aquifer in the world. To better understand the aquifer system, typologies have been characterized for the aquifer, which integrate existing datasets across the Indo-Gangetic catchment basin at a transboundary scale for the first time, and provide an alternative conceptualization of this aquifer system. Traditionally considered and mapped as a single homogenous aquifer of comparable aquifer properties and groundwater resource at a transboundary scale, the typologies illuminate significant spatial differences in recharge, permeability, storage, and groundwater chemistry across the aquifer system at this transboundary scale. These changes are shown to be systematic, concurrent with large-scale changes in sedimentology of the Pleistocene and Holocene alluvial aquifer, climate, and recent irrigation practices. Seven typologies of the aquifer are presented, each having a distinct set of challenges and opportunities for groundwater development and a different resilience to abstraction and climate change. The seven typologies are: (1) the piedmont margin, (2) the Upper Indus and Upper-Mid Ganges, (3) the Lower Ganges and Mid Brahmaputra, (4) the fluvially influenced deltaic area of the Bengal Basin, (5) the Middle Indus and Upper Ganges, (6) the Lower Indus, and (7) the marine-influenced deltaic areas.
© The Author(s) 2017.
In several parts of India, groundwater is the only reliable, year round source for drinking water. Prevention of fluorosis, a chronic disease resulting from excess intake of fluoride, requires the screening of all groundwater sources for fluoride in endemic areas. In this paper, the authors present a field deployable colorimetric analyzer based on an inexpensive smartphone embedded with digital camera for taking photograph of the colored solution as well as an easy-fit, and compact sample chamber (Akvo Caddisfly). Phones marketed by different smartphone makers were used. Commercially available zirconium xylenol orange reagent was used for determining fluoride concentration. A software program was developed to use with the phone for recording and analyzing the RGB color of the picture. Linear range for fluoride estimation was 0-2mgl(-1). Around 200 samples, which consisted of laboratory prepared as well as field samples collected from different locations in Karnataka, India, were tested with Akvo Caddisfly. The results showed a significant positive correlation between Ion Selective Electrode (ISE) method and Akvo Caddisfly (Phones A, B and C), with correlation coefficient ranging between 0.9952 and 1.000. In addition, there was no significant difference in the mean fluoride content values between ISE and Phone B and C except for Phone A. Thus the smartphone method is economical and suited for groundwater fluoride analysis in the field.
The element fluorine has long been recognised to have benefits for dental health: low-fluoride intake has been linked to development of dental caries and the use of fluoride toothpastes and mouthwashes is widely advocated in mitigating dental health problems. Fluoridation of water supplies to augment naturally low fluoride concentrations is also undertaken in some countries. However, despite the benefits , optimal doses of fluoride appear to fall within a narrow range. The detrimental effects of ingestion of excessive doses of fluoride are also well documented. Chronic ingestion of high doses has been linked to the development of dental fluorosis, and in extreme cases, skeletal fluorosis. High doses have also been linked to cancer (Marshall 1990), although the association is not well-established (Hamilton 1992).
There is discrepancy about intervals of fluoride monitoring in groundwater resources by Iranian authorities. Spatial and temporal variability of fluoride in groundwater resources of Larestan and Gerash regions in Iran were analyzed from 2003 to 2010 using a geospatial information system and the Mann-Kendall trend test. The mean concentrations of fluoride for the 8-year period in the eight cities and 31 villages were 1.6 and 2.0 mg/l, respectively; the maximum values were 2.4 and 3.8 mg/l, respectively. Spatial, temporal, and spatiotemporal variability of fluoride in overall groundwater resources were relatively constant over the years. However, results of the Mann-Kendall trend test revealed a monotonic trend in the time series of one city and 11 villages for the 8-year period. Specifically, one city and three villages showed positive significant Kendall's Tau values, suggesting an upward trend in fluoride concentrations over the 8-year period. In contrast, seven villages displayed negative significant Kendall's Tau values, arguing for a downward trend in fluoride concentrations over the years. From 2003 to 2010, approximately 52 % of the Larestan and Gerash areas have had fluoride concentrations above the maximum permissible Iranian drinking water standard fluoride level (1.4 mg/l), and about 116,000 people were exposed to such excess amounts. Therefore, our study supports for a close monitoring of fluoride concentrations from health authorities in monthly intervals, especially in villages and cities that showed positive trend in fluoride concentrations. Moreover, we recommend simultaneous implementation of cost-effective protective measures or interventions until a standard fluoride level is achieved.
Arsenicosis and fluorosis, two endemic diseases known to result from exposure to their elevated concentrations in groundwater of north China used by many rural households for drinking, have been major public health concerns for several decades. Over the last decade, a large number of investigations have been carried out to delineate the spatial distribution and to characterize the chemical compositions of high As and F groundwaters with a focus on several inland basins in north China. Findings from these studies, including improved understanding of the hydrogeological and geochemical factors resulting in their enrichments, have been applied to guide development of clean and safe groundwater in these endemic disease areas. Survey efforts have led to the recognition of iodine in groundwater as an emerging public health concern. This paper reviews the new understandings gained through these studies, including those published in this special issue, and points out the direction for future research that will shed light on safe guarding a long-term supply of low As and F groundwater in these water scarce semi-arid and arid inland basins of north China.
This study was conducted to evaluate the clinical reversal of dental fluorosis with various combinations of calcium, vitamin D3, and ascorbic acid, along with changes in levels of certain biochemical parameters concerned with dental fluorosis. The role of fluoride level of drinking water in the etiology of dental fluorosis and the prevalence of dental fluorosis in both dentitions and teeth were also assessed.
A total number of 50 patients with clinical features of dental fluorosis without trauma and any adverse habits were selected. Of these, in 30 co-operative patients, estimation of water fluoride level and pretreatment and post-treatment serum and urine fluoride levels were done with ion selective electrode method. The selected 30 patients were divided into three groups, that is, group A, group B, and group C, and were given various combinations of medications like calcium with vitamin D3 supplements, ascorbic acid with vitamin D3 supplements, and chlorhexidine mouthwash (placebo) for three months, respectively. These 30 patients were assessed for any change in the clinical grading of dental fluorosis.
No change in clinical grading of dental fluorosis was noted. Considerable reduction in serum and urine fluoride levels was noted in both group A and group B patients. Dental fluorosis was noted in permanent teeth more commonly than deciduous teeth, and permanent maxillary central incisors had the highest prevalence rate.
This study comprises only 30 patients with three months of follow-up. So, this sample of patients and duration of follow-up period are conclusive to observe changes in biochemical parameters but not sufficient to observe changes in clinical grading.
To assess the relationship between exposure to different drinking water fluoride levels and children's intelligence in Madhya Pradesh state, India.
This cross-sectional study was conducted among 12-year-old school children of Madhya Pradesh state, India. The children were selected from low (< 1.5 parts per million) and high (≥1.5 parts per million) fluoride areas. A questionnaire was used to collect information on the children's personal characteristics, residential history, medical history, educational level of the head of the family, and socioeconomic status of the family. Levels of lead, arsenic, and iodine in the urine and the levels of fluoride in the water and urine were analyzed. The children's intelligence was measured using Raven's Standard Progressive Matrices. Data analysis was done using the chi-square, one way analysis of variance, simple linear regression, and multiple linear regression tests. P value <0.05 was considered statistically significant.
Differences in participant's sociodemographic characteristics, urinary iodine, urinary lead, and urinary arsenic levels were statistically not significant (P>0.05). However, a statistically significant difference was observed in the urinary fluoride levels (P 0.000). Reduction in intelligence was observed with an increased water fluoride level (P 0.000). The urinary fluoride level was a significant predictor for intelligence (P 0.000).
Children in endemic areas of fluorosis are at risk for impaired development of intelligence.
The relationship between environmental fluoride and human health has been studied for over 100years by researchers from a
wide variety of disciplines. Most scientists believe that small amounts of fluoride in the diet can help prevent dental caries
and strengthen bones, but there are a number of adverse affects that chronic ingestion at high doses can have on human health,
including dental fluorosis, skeletal fluorosis, increased rates of bone fractures, decreased birth rates, increased rates
of urolithiasis (kidney stones), impaired thyroid function, and lower intelligence in children. Chronic occupational exposure
to fluoride dust and gas is associated with higher rates of bladder cancer and variety of respiratory ailments. Acute fluoride
toxicity and even death from the ingestion of sodium fluoride pesticides and dental products have also been reported. The
distribution of fluoride in the natural environment is very uneven, largely a result of the geochemical behavior of this element.
Fluorine is preferentially enriched in highly evolved magmas and hydrothermal solutions, which explains why high concentrations
are often found in syenites, granitoid plutonic rocks, alkaline volcanic, and hydrothermal deposits. Fluoride can also occur
in sedimentary formations that contain fluoride-bearing minerals derived from the parent rock, fluoride-rich clays, or fluorapatite.
Dissolved fluoride levels are usually controlled by the solubility of fluorite (CaF2); thus, high concentrations are often associated with soft, alkaline, and calcium-deficient waters. Although much is known
about the occurrence and health effects of fluoride, problems persist in Third World countries, where populations have little
choice in the source of their drinking water and food. However, even in developed nations, fluoride ingestion can exceed the
recommended dose when sources other than drinking water are ignored.
The problem of high fluoride concentration in groundwater resources has become one of the most important toxicological and geo-environmental issues in India. Excessive fluoride in drinking water causes dental and skeletal fluorosis, which is encountered in endemic proportions in several parts of the world. World Health Organization (WHO) guideline value and the permissible limit of fluoride as per Bureau of Indian Standard (BIS) is 1.5 mg/L. About 20 states of India, including 43 blocks of seven districts of West Bengal, were identified as endemic for fluorosis and about 66 million people in these regions are at risk of fluoride contamination. Studies showed that withdrawal of sources identified for fluoride often leads reduction of fluoride in the body fluids (re-testing urine and serum after a week or 10 days) and results in the disappearance of non-skeletal fluorosis within a short duration of 10-15 days.
To determine the prevalence of signs and symptoms of suspected dental, skeletal, and non-skeletal fluorosis, along with food habits, addictions, and use of fluoride containing toothpaste among participants taking water with fluoride concentration above the permissible limit, and to assess the changes in clinical manifestations of the above participants after they started consuming safe drinking water.
A longitudinal intervention study was conducted in three villages in Rampurhat Block I of Birbhum district of West Bengal to assess the occurrence of various dental, skeletal, and non-skeletal manifestations of fluorosis, along with food habits, addictions, and use of fluoride containing toothpaste among the study population and the impact of taking safe water from the supplied domestic and community filters on these clinical manifestations. The impact was studied by follow-up examination of the participants for 5 months to determine the changes in clinical manifestations of the above participants after they started consuming safe drinking water from supplied domestic filters and community filter with fluoride concentration below the permissible limit. The data obtained were compared with the collected data from the baseline survey.
The prevalence of signs of dental, skeletal, and non-skeletal fluorosis was 66.7%, 4.8-23.8%, and 9.5-38.1%, respectively, among the study population. Withdrawal of source(s) identified for fluoride by providing domestic and community filters supplying safe water led to 9.6% decrease in manifestation of dental fluorosis, 2.4-14.3% decrease in various manifestations of skeletal fluorosis, and 7.1-21.5% decrease in various non-skeletal manifestations within 5 months. Following repeated motivation of participants during visit, there was also 9.7-38.1% decrease in the usage of fluoride containing toothpaste, and 9.8-45.3% and 7.3-11.9% decrease in the consumption of black lemon tea and tobacco, respectively, which are known sources of fluoride ingestion in our body and have an effect on the occurrence of various manifestations of fluorosis following drinking of safe water from domestic and community filters.
Increased prevalence of dental, skeletal, and non-skeletal fluorosis was found among the study population. Withdrawal of source(s) identified for fluoride by supplying domestic and community filters, dietary restriction, and other nutritional interventions led to decrease in manifestation of the three types of fluorosis within 5 months.
Iron oxides control the mobility of a host of contaminants in aquifer systems, and the microbial reduction of iron oxides in the subsurface is linked to high levels of arsenic in groundwater that affects greater than 150 million people globally. Paired observations of groundwater and solid-phase aquifer composition are critical to understand spatial and temporal trends in contamination and effectively manage changing water resources, yet field-representative mineralogical data are sparse across redox gradients relevant to arsenic contamination. We characterize iron mineralogy using X-ray absorption spectroscopy across a natural gradient of groundwater arsenic contamination in Vietnam. Hierarchical cluster analysis classifies sediments into meaningful groups delineating weathering and redox changes, diagnostic of depositional history, in this first direct characterization of redox transformations in the field. Notably, these groupings reveal a signature of iron minerals undergoing active reduction before the onset of arsenic contamination in groundwater. Pleistocene sediments undergoing postdepositional reduction may be more extensive than previously recognized due to previous misclassification. By upscaling to similar environments in South and Southeast Asia via multinomial logistic regression modeling, we show that active iron reduction, and therefore susceptibility to future arsenic contamination, is more widely distributed in presumably pristine aquifers than anticipated.
Recent testing has shown that shallow aquifers of the Ravi River floodplain are more frequently affected by groundwater arsenic (As) contamination than other floodplains of the upper Indus River basin. In this study, we explore the geochemical origin of this contrast by comparing groundwater and aquifer sand composition in the 10-30 m depth range in 11 villages along the Ravi and adjacent Beas and Sutlej rivers. The drilling was preceded by testing wells in the same villages with field kits not only for As but also for nitrate (NO3⁻), iron (Fe), and sulfate (SO4²⁻). Concentrations of NO3⁻ were ≥20 mg/L in a third of the wells throughout the study area, although conditions were also sufficiently reducing to maintain >1 mg/L dissolved Fe in half of all the wells. The grey to grey-brown color of sand cuttings quantified with reflectance measurements confirms extensive reduction of Fe oxides in aquifers of the affected villages. Remarkably high levels of leachable As in the sand cuttings determined with the field kit and As concentration up to 40 mg/kg measured by X-ray fluorescence correspond to depth intervals of high As in groundwater. Anion-exchange separation in the field and synchrotron-based X-ray spectroscopy of sand cuttings preserved in glycerol indicate speciation in both groundwater and aquifer sands that is dominated by As(V) in the most enriched depth intervals. These findings and SO4²⁻ concentrations ≥20 mg/L in three-quarters of the sampled wells suggest that high levels of NO3⁻, presumably from extensive fertilizer application, may have triggered the release of As by oxidizing sulfide-bound As supplied by erosion of black shale and slate in the Himalayas. Radiocarbon dating of sub-surface clay cuttings indicates that multiple episodes of inferred As-sulfide input reached the Ravi floodplain over the past 30 kyr. Why the other river basins apparently did not receive similar inputs of As-sulfide remains unclear. High NO3⁻ in groundwater may at the same time limit concentrations of As in groundwater to levels lower than they could have been by oxidizing both Fe(II) and As(III). In this particular setting, a kit can be used to analyze sand cuttings for As while drilling in order to target As-safe depths for installing domestic wells by avoiding intervals with high concentrations of As in aquifer sands with the well screen.
Most of the rural population of 90 million in Punjab province in Pakistan and Punjab state in India drinks, and cooks with, untreated water drawn from shallow wells. Limited laboratory testing has shown that groundwater in the region can contain toxic levels of arsenic. To refine this assessment, a total of 30,567 wells from 383 villages were tested with a field kit in northern Punjab province of Pakistan and western Punjab state of India. A subset of 431 samples also tested in the laboratory show that 85% of wells were correctly classified by the kit relative to the World Health Organization guideline of 10 μg/L for arsenic in drinking water. The kit data show that 23% of the tested wells did not meet the WHO guideline for arsenic but also that 87% of households with a well high in arsenic live within 100 m of a well that meets the WHO guideline. The implication is that many households could rapidly lower their exposure if the subset of safe wells could be shared. In a follow-up conducted one year later in five villages where 59% of wells were elevated in arsenic, two-thirds of households indicated that they had switched to a neighboring well in response to the testing. The blanket testing of millions of wells for arsenic in the region should therefore be prioritized over much costlier water treatment and piped water supply projects that will take much longer to have a comparable impact.
Excess exposure to fluoride causes substantive health burden in humans and livestock globally. However, few studies have assessed the distribution and controls of variability of ambient background concentrations of fluoride in soil. Ambient background concentrations of fluoride in soil were collated for Greater Melbourne, Greater Geelong, Ballarat and Mitchell in Victoria, Australia (n = 1005). Correlation analysis and machine learning techniques were used to identify environmental and anthropogenic influences of fluoride variability in soil. Sub-soils (>0.3 m deep), in some areas overlying siltstone and sandstone, and to a lesser extent, overlying basalt, were naturally enriched with fluoride at concentrations above ecological thresholds for grazing animals. Soil fluoride enrichment was predominantly influenced by parent material (mineralogy), precipitation (illuviation), leaching during palaeoclimates and marine inputs. Industrial air pollution did not significantly influence ambient background concentrations of fluoride at a regional scale. However, agricultural practices (potentially the use of phosphate fertilisers) were indicated to have resulted in added fluoride to surface soils overlying sediments. Geospatial variables alone were not sufficient to accurately model ambient background soil fluoride concentrations. A multiple regression model based on soil chemistry and parent material was shown to accurately predict ambient background fluoride concentrations in soils and support assessment of fluoride enrichment in the environment.
Groundwater beneath the alluvial plain of the Indus River, Pakistan, is reported to be widely polluted by arsenic (As) and to adversely affect human health. In 79 groundwaters reported here from the lower Indus River plain, in southern Sindh Province, concentrations of As exceeded the WHO guideline value of 10 μg/L in 38%, with 22% exceeding 50 μg/L, Pakistan's guideline value. The As pollution is caused by microbially‐mediated reductive dissolution of sedimentary iron‐oxyhydroxides in anoxic groundwaters; oxic groundwaters contain < 10 μg/L of As. In the upper Indus River plain, in Punjab Province, localised As pollution of groundwater occurs by alkali desorption as a consequence of ion‐exchange in groundwater, possibly supplemented by the use for irrigation of groundwater that has suffered ion‐exchange in the aquifer and so has values > 0 for residual sodium carbonate.
In the field area in southern Sindh, concentrations of Mn in groundwater exceed 0.4 mg/L in 11% of groundwaters, with a maximum of 0.7 mg/L, as a result of reduction of sedimentary manganese oxides. Other trace elements pose little or no threat to human health. Salinities in groundwaters range from fresh to saline (EC up to 6 mS/cm). High salinities result from local inputs of waste‐water from unsewered sanitation, but mainly from evaporation/evapotranspiration of canal water and groundwater used for irrigation. The process does not concentrate As in the groundwater owing to sorption of As to soils. Ion‐exchange exerts a control on concentrations of Na, Ca, and B, but not on As. High values of Cl/Br mass ratios (most » 288, the marine value) reflect the pervasive influence on groundwater of sewage‐contaminated water from irrigation canals through seepage loss and deep percolation of irrigation water, with additional, well‐specific, contributions from unsewered sanitation.
Access to information about environmental quality may facilitate low-cost preventive measures that protect human health. In this paper, we study the demand for information about environmental quality and the behavioral response to the information provided. With a field experiment conducted in Bihar (India), we estimate the price sensitivity of demand for diagnostic testing of drinking water wells for arsenic of natural origin - a serious threat to the health of tens of millions of villagers across South and Southeast Asia. Demand is substantial but sensitive to price; uptake falls from 68% to 31% of households over our price range (Rs. 10 to Rs. 50). We further assess how households respond to information regarding the contamination level in their wells. About one-third of households with unsafe wells switch to a safer water source. Finally, we demonstrate that households that received adverse test outcomes are more likely to selectively forget test results, and proactively remove evidence of their wells' arsenic status.
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.
High-F groundwaters are common in the dry parts of the Indian peninsula, consituting a serious health problem. The F originates mainly from hydroxypositions in biotite and hornblende and is concentrated through evapotranspiration in soil and groundwater exhibiting residual alkalinity. Such waters are common in areas with generally alkaline soils. Along the flow paths of the water from hilltops to valley bottoms, calcite, dolomite and fluorite seem to precipitate, in that order. A practical solution to the health problem may be to locate drinking water wells in upslope positions. -Authors
Groundwater is used extensively in the Central Kenya Rift for domestic and agricultural demands. In these active rift settings groundwater can exhibit high fluoride levels. In order to address water security and reduce human exposure to high fluoride in drinking water, knowledge of the source and geochemical processes of enrichment are required. A study was therefore carried out within the Naivasha catchment (Kenya) to understand the genesis, enrichment and seasonal variations of fluoride in the groundwater. Rocks, rain, surface and groundwater sources were sampled for hydrogeochemical and isotopic investigations, the data was statistically and geospatially analyzed. Water sources have variable fluoride concentrations between 0.02-75mg/L. 73% exceed the health limit (1.5mg/L) in both dry and wet seasons. F- concentrations in rivers are lower (0.2-9.2mg/L) than groundwater (0.09 to 43.6mg/L) while saline lake waters have the highest concentrations (0.27-75mg/L). The higher values are confined to elevations below 2000masl. Oxygen (δ18O) and hydrogen (δD) isotopic values range from -6.2 to +5.8‰ and -31.3 to +33.3‰, respectively, they are also highly variable in the rift floor where they attain maximum values. Fluoride base levels in the precursor vitreous volcanic rocks are higher (between 3750-6000ppm) in minerals such as cordierite and muscovite while secondary minerals like illite and kaolinite have lower remnant fluoride (<1000ppm). Thus, geochemical F- enrichment in regional groundwater is mainly due to a) rock alteration, i.e. through long residence times and natural discharge and/or enhanced leakages of deep seated geothermal water reservoirs, b) secondary concentration fortification of natural reservoirs through evaporation, through reduced recharge and/or enhanced abstraction and c) through additional enrichment of fluoride after volcanic emissions. The findings are useful to help improve water management in Naivasha as well as similar active rift setting environments.
The chemical composition of natural water is derived from many different sources of solutes, including gases and aerosols from the atmosphere, weathering and erosion of rocks and soil, solution or precipitation reactions occurring below the land surface, and cultural effects resulting from human activities. Broad interrelationships among these processes and their effects can be discerned by application of principles of chemical thermodynamics. Some of the processes of solution or precipitation of minerals can be closely evaluated by means of principles of chemical equilibirum, including the law of mass action and the Nernst equation. Other processes are irreversible and require consideration of reaction mechanisms and rates. The chemical composition of the crustal rocks of the Earth and the composition of the ocean and the atmosphere are significant in evaluating sources of solutes in natural freshwater. The ways in which solutes are taken up or precipitated and the amounts present in solution are influenced by many environmental factors, especially climate, structure and position of rock strata, and biochemical effects associated with life cycles of plants and animals, both microscopic and macroscopic. -from Author
Groundwater samples (n=152) were collected in the Thar Desert of the Umarkot Sub-District, Pakistan to evaluate the geochemical controls on the occurrence of high fluoride (F-) levels within the study area. Fluoride concentrations range from 0.06 to 44.4 mg/L,with mean and median values of 5.22 and 4.09 mg/L, respectively; and roughly 84 percent of the samples contain fluoride concentrations that exceed the 1.5 mg/L drinking water standard set by WHO. The overall groundwater quality reflects the influences of silicate mineral weathering and evaporation. Fluoride originates from the weathering of minerals derived from Type-A granite and possibly anion exchange (OH- for F-) on clays and weathered micas under high pH conditions. High fluoride levels are associated with Na-HCO3 type water produced by calcite precipitations and/or base ion exchange. Depleted calcium levels in groundwater allow higher fluoride concentrations to occur before the solubility limit for fluorite is reached.
Tahir Rafique, Shahid Naseem, David Ozsvath, Riaz Hussain, Muhammad Iqbal Bhanger, & Tanzil Haider Usmani
Poor water quality has become a public health issue as cases of fluorosis in Datong Basin, Northern China are increasing. This paper investigates the origin and the geochemical mechanisms of fluoride enrichment in groundwater at Datong Basin. The fluoride concentration in the groundwater samples from 70 wells selected for this study ranges from 0.1 to 8.3 mg/L (mean 2.2 mg/L), with 51% of the samples containing fluoride concentrations that exceed the WHO drinking water guideline value of 1.5 mg/L. High fluoride groundwaters are characterized by hydrochemical types HCO3Na(Mg), HCO3·SO4Na(Mg) and SO4·ClNa(Mg), with low Ca2+ and high HCO3− and Na+, and occurred in transition areas between the alluvial–pluvial mountain front plain and the alluvial–lacustrine plain of Datong Basin. Conditions favorable for fluoride enrichment in groundwater include weakly alkaline pH condition (7.2–8.2), moderate TDS, and HCO3− and Na+ as the dominant ions. The hydrolysis of F-bearing minerals in aquifer sediments is the dominant process for F− release, and facilitated by alkaline conditions and long residence time of groundwater. Calcite and fluorite are the main solubility-control minerals controlling the aqueous geochemistry of high fluoride groundwater. Evapotranspiration also favors fluoride enrichment in groundwater.
In India, as elsewhere, groundwater is a vital component of the ecosystem and its controlled use should not interfere adversely with the natural hydrologic cycle. However, its misuse causes many problems and may be observed in the Bist Doab and adjacent areas of the Punjab state where difficulties arise from water-logging, pollution by industrial toxic wates and overdraft in the phreatic aquifer. Remedial measures should include artificial recharge to groundwater in recharge areas by means of check impoundments and infiltration basins in order to overcome serious over-exploitation currently in progress.
High contents of fluoride in groundwater are a controversial issue in the dry zone of Sri Lanka. This study describes the geochemistry of residual soils from relatively fluoride-rich (< 8 mg/L; mean 2.0 mg/L) and fluoride-poor (< 1 mg/L; mean 0.4 mg/L) groundwater sites in the dry zone to identify possible sources for fluoride. Abundances of 22 major and trace elements were determined in 74 soil samples using X-ray fluorescence. The results show that soil fluoride is lower than average upper continental crust and basement rocks in both the fluoride-rich (< 411 mg/kg) and fluoride-poor (< 277 mg/kg) groundwater sites. Negative linear correlation exists between fluoride in the soil and the groundwaters, suggesting that fluoride is readily leached to water rather than being retained in the unconsolidated sandy clay loam soils. Weathering of heavy minerals such as zirconium, apatite, fluorite, monazite and garnet are the main source for the soil in the fluoride-rich groundwater districts. In these areas Zr, Nb and Th are immobile relative to the basement, and F, CaO and P2O5 are depleted, suggesting that the loss of CaO provides favorable conditions for the leaching of F to water. Conversely, soils in the relatively fluoride-poor district are enriched in TiO2, Fe2O3, MnO, Cr, V and Sc, denoting the weathering of biotite, hornblende, garnet and pyroxenes in the basement. Primary minerals present in the soils are the main cause for the enrichment of those elements. Further, fluoride levels in the soils and subsequently in the groundwaters show links with original magmatic contrast between the basement formations in each area. Soil geochemistry suggests that the meta-igneous rocks in the fluoride-rich districts may have been influenced by a fluoride-rich residual melt, whereas the fluoride-poor districts are associated with acidic meta-igneous rocks and meta-sedimentary rocks.
Pakistan's irrigation system is more than a century old. Due to the increasing population and consequent intensifying agriculture, dependence on groundwater is successively increasing. The underground reservoir that was recharged during the first half of the twentieth century by the newly built irrigation system with low cropping intensities is now being overexploited. Groundwater quality is variable, both vertically and horizontally, with the exception of areas adjacent to rivers, where it is fresh. This paper describes groundwater quality in the Lower Bari Doab Canal (LBDC) irrigation system based on 47 years of historic water quality data (TDS, SAR and RSC). Areas are delineated in the form of zones and depths. The tail end of the command is facing severe groundwater depletion, whereas in certain parts, groundwater quality deterioration with the passage of time has also been detected. Possible reasons and mechanisms of saline intrusion within the aquifer are described. Lateral saline intrusion is not a major issue due to very slow groundwater movement. But in areas with saline groundwater lying below the upper layer of irrigation leaked fresh water, mobilization of deeper saline water is taking place as a result of pumping by farmers. In addition, results of the solute transport model and MODPATH runs were evaluated in support of water quality analysis and groundwater flow rates.
Chemical analysis of groundwater and sediments was carried out to investigate causes of elevated F− (1.5–6.6 mg/L) and As concentrations (10–27 μg/L; one sample affected by local contamination with 4870 μg/L As), in groundwater from the Yuncheng Basin, northern China. Groundwater from 9 out of 73 wells contains both F and As concentrations above World Health Organisation safe drinking guidelines (>1.5 mg/L and >10 μg/L, respectively); F− concentrations above safe levels are more widespread than As (27 vs. 12 wells). The elevated As and F concentrations represent a significant health risk, as groundwater is widely used to supply agricultural and domestic water in the region. High F and As concentrations occur in shallow groundwater affected by agriculture and deep groundwater with long residence times (>13 ka) that shows little sign of anthropogenic influence. The strong positive correlation between groundwater F/Cl and As/Cl ratios (r2 = 0.98 and 0.77 in shallow and deep groundwater, respectively) indicates that these elements are mobilized and enriched by common processes. Positive correlations between F and As concentrations and Na/Ca ratios (r2 = 0.67 and 0.46, respectively) indicate that groundwater major ion chemistry plays a significant role in mobilizing F and As. Mobilization likely occurs via de-sorption of As and F anions (e.g. and F−) from hydrous metal oxides. Moderate positive correlations between pH and As and F concentrations (r2 = 0.36 and 0.17, respectively) indicate that high pH may favour de-sorption, while HCO3 may act as a sorption competitor. High groundwater Na/Ca ratios likely result from cation exchange, while pH and HCO3 contents are predominantly controlled by carbonate weathering reactions. Sediments from the area were reacted with various water solutions, producing F concentrations between 0.49 and 2.7 mg/L and As concentrations between 0.51 and 16.7 μg/L. Up to 45% more F and 35% more As were released when sediments were reacted with a Na-rich, Ca-poor solution compared to a Ca-rich solution; this is consistent with increased mobilization of F− and by Na-rich, Ca-poor groundwater. Increasing F and As concentrations across a wide area caused by high levels of pumping is a potential future health concern.
The high As and F− groundwaters from Datong Basin are mostly soda waters with a Na/(Cl+SO4) (meq) ratio greater than unity, As and F− up to 1550 μg/L and 10.4 mg/L, respectively, and with pH between 7.6 and 9.1. Geochemical modeling indicates that the waters are oversaturated with respect to calcite and clay minerals such as kaolinite, and undersaturated with respect to primary rock-forming minerals such as anorthite and albite. The water chemistry also is affected by evapotranspiration. The degree of evaporative enrichment is up to 85 in terms of Cl−. Results of the hydrogeochemical studies indicate that the occurrence of soda water at Datong is the result of incongruent dissolution of aluminosilicates at one stage of their interaction with groundwater when the water is oversaturated with respect to calcite and evapotranspiration-related salt accumulation is not too strong. Studying the genesis of soda waters provides new insights into mechanism of As and F− enrichment in the aquifer system. Due to CaF2 solubility control and OH−–F− exchange reactions, F− can be enriched in soda water. And the high pH condition of soda water favors As desorption from oxyhydroxide surfaces, thereby increasing the concentration of As in the aqueous phase.
Distribution coefficients, as a function of precipitation rate, were determined for the metals Sr2+, Co2+, Mn2+ and Cd2+in calcite. A pH-stat was used to maintain a constant degree of-saturation, and hence precipitation rate, during each coprecipitation run. The precipitation rate was proportional to the degree of supersaturation and the mass of seed crystal introduced. Distribution coefficients (λ) as a function of rate were determined using radioactive isotopes for solutions with saturations Ω = 1 to Ω = 5.5. Strontium distribution coefficients increased with increasing precipitation rate, while Co, Mn and Cd distribution coefficients decreased with increasing precipitation rate. The following rate expressions (at 25°C) were derived: logλSr = 0.249 log R −1.57logλMn = −0.266 log R + 1.35logλCo = −0.173 log R + 0.68logλCd = −0.194 log R + 1.46 where R is the observed precipitation rate in nmoles CaCO3 per mg seed crystal per min.In separate experiments the uptake of radioactive isotopes was monitored during the recrystallization of calcite seed crystals. Rates of recrystallization were from 100 to 10, 000 times slower than the pH-stat experiments, but yielded distribution coefficients consistent with the above rate expressions.Using gross estimates of biogenic crystal growth rates, aragonite to calcite transformation rates, and the above Sr rate expression, biogenic calcite and diagenetic calcite Sr contents are estimated. These experiments indicate that in addition to solution composition, precipitation rate is a significant factor influencing the trace metal content of naturally occurring calcite.
This study reexamines the notion that extensive As mobilization in anoxic groundwater of Bangladesh is intimately linked to the dissolution of Fe oxyhydroxides on the basis of analyses performed on a suite of freshly collected samples of aquifer material. Detailed sediment profiles extending to 40 to 70 m depth below the surface were obtained at six sites where local groundwater As concentrations were known to span a wide range. The sediment properties that were measured include (1) the proportion of Fe(II) in the Fe fraction leached in hot 1.2 N HCl, (2) diffuse spectral reflectance, and (3) magnetic susceptibility.
India has an increasing incidence of fluorosis, dental and skeletal, with some 62 million people at risk. High fluoride groundwaters are present especially in the hard rock areas south of the Ganges valley and in the arid north-western part of the country. The phenomenon is related to groundwater with residual alkalinity . Fluoride concentrations are governed by adsorption equilibria and by fluorite solubility. Evapotranspiration leads to a precipitation of calcite, a lowering of Ca activity and increase in Na/Ca ratios, and this allows an increase in F− levels. In southern India, Mg seems to be controlled by dolomite, while sepiolite and palygorskite are Mg sinks in Rajasthan but may then release F− under alkaline conditions. The latter two minerals are probably also important sources and sinks for F− in the hydroxy-positions. The increase in the extent of sodic soils as a result of irrigation is a contributing factor to the increasing incidence of fluorosis. Remedial measures including addition of gypsum and rainwater harvesting are needed even in areas where the sodicity does not cause structural problems in the soil.
High-F groundwaters are common in the dry parts of the Indian peninsula, constituting a serious health problem. The F originates mainly from hydroxypositions in biotite and hornblende and is concentrated through evapotranspiration in soil and groundwater exhibiting residual alkalinity. Such waters are common in areas with generally alkaline soils. Along the flow paths of the water from hilltops to valley bottoms calcite, dolomite and fluorite seem to precipitate, in that order. A practical solution to the health problem may be to locate drinking water wells in upslope positions.