Geochemical modeling, source apportionment, health risk exposure and control of higher fluoride in groundwater of sub-district Dargai, Pakistan

Hydrogeochemical characteristics, stable isotopes, positive matrix factorization, source apportionment, and health risk of high fluoride groundwater in semiarid region

Chronic exposure to high fluoride (F-) levels in groundwater causes community fluorosis and non-carcinogenic health concerns in local people. This study described occurrence, dental fluorosis, and origin of high F-groundwater using δ2H and δ18O isotopes at semiarid Gilgit, Pakistan. Therefore, groundwater (n = 85) was collected and analyzed for F- concentrations using ion-chromatography. The lowest F- concentration was 0.4 mg/L and the highest 6.8 mg/L. F- enrichment is linked with higher pH, NaHCO3, NaCl, δ18O, Na+, HCO3-, and depleted Ca+2 aquifers. The depleted δ2H and δ18O values indicated precipitation and higher values represented the evaporation effect. Thermodynamic considerations of fluorite minerals showed undersaturation, revealing that other F-bearing minerals viz. biotite and muscovite were essential in F- enrichment in groundwater. Positive matrix factorization (PMF) and principal component analysis multilinear regression (PCAMLR) models were used to determine four-factor solutions for groundwater contamination. The PMF model results were accurate and reliable compared with those of the PCAMLR model, which compiled the overlapping results. Therefore, 28.3% exceeded the WHO permissible limit of 1.5 mg/L F-. Photomicrographs of granite rocks showed enriched F-bearing minerals that trigger F- in groundwater. The community fluorosis index values were recorded at > 0.6, revealing community fluorosis and unsuitability of groundwater for drinking.

Uncovering nano-bonechar for attenuating fluoride in naturally contaminated soil

Fluoride ion (F-) is one of the major geogenic contaminants in water and soil. Excessive consumption of these geogenic contaminants poses serious health impacts on humans and plants. In this study, a novel carbonaceous material, nano-bonechar, was synthesized from cow bones and applied as a soil amendment at rates of 0, 0.5, 1, and 2% to remediate and revitalize naturally F--contaminated soil. The results revealed that the nano-bonechar significantly reduced the mobility and bioavailability of F- by 90% in the contaminated soil, and improved the soil quality by increasing the soil water holding capacity, soil organic matter, and the bioavailable contents of PO43-, Ca2+, and Na+. Subsequently, the pot experiment results showed a significant reduction in the uptake of F- by 93% in Zea mays plants. Moreover, the nano-bonechar application improved the plant's growth, as indicated by the higher fresh and dry weights, root and shoot lengths, and total content of PO43-, Ca2+, and K+ than those of un-amended soil. The F-immobilization in soil was mainly due to the presence of the hydroxyapatite [Ca10(PO4)6(OH)2] mineral in the nano-bonechar. Ion exchange between OH- (of nano-bonechar) and F- (of soil), and the formation of insoluble fluorite (CaF2) contributed to the attenuation of F- mobility in the soil. It is concluded that nano-bonechar, due to its size and enrichment in hydroxyapatite, could successfully be utilized for the rapid remediation and revitalization of F--contaminated agricultural soil.

Analysis of the distribution across media, migration, and related driving factors of fluoride in cold and arid lakes during the freezing period

Fluoride pollution in water has become a global challenge. This challenge especially affects China as a country experiencing serious fluoride pollution. While the have been past studies on the spatial distribution of fluoride, there has been less attention on different forms of fluoride. This study collected 176 samples (60, 40, and 76 ice, water, and sediment samples, respectively) from Lake Ulansuhai during the freezing period. The occurrence and spatial distribution characteristics of fluoride in lake ice-water-sediment were explored using Kriging interpolation, Piper three-line diagram, and Gibbs diagram analysis methods. The migration and transformation of fluoride during the freezing period were revealed and the factors influencing fluoride concentration in the water body were discussed considering the hydrochemical characteristics of lake surface water. The results showed that the average fluoride concentrations in the upper ice, middle ice and lower ice were 0.18, 0.09, and 0.12 mg/L, respectively, decreasing from north to south in the lake. The average concentrations of fluoride in surface water and bottom water were 0.63 and 0.83 mg/L, respectively. The concentrations of fluoride in ice and water were within the World Health Organisation drinking water threshold of 1.50 mg/L and the Class III Chinese surface water standard (GB3838-2002). The average sediment total fluorine was 1344.38 ± 200 mg/kg, significantly exceeding the global average (321 mg/kg) and decreasing with depth. The contents of water soluble, exchangeable, Fe/Mn bound, organic bound, and residual fluorides were 40.22-47.18, 13.24-43.23, 49.52-160.48, and 71.59-173.03 mg/kg, respectively. There was a significant positive correlation between fluoride concentration in ice and that in water. The change in fluoride concentration in water was mainly due to specific climatic and geographical conditions, pH, hydrochemical characteristics and ice sealing. This study is of great significance for the management of high-fluorine lakes in arid and semi-arid areas.

A comprehensive review of human health risks of arsenic and fluoride contamination of groundwater in the South Asia region

The present study found that ∼80 million people in India, ∼60 million people in Pakistan, ∼70 million people in Bangladesh, and ∼3 million people in Nepal are exposed to arsenic groundwater contamination above 10 μg/L, while Sri Lanka remains moderately affected. In the case of fluoride contamination, ∼120 million in India, >2 million in Pakistan, and ∼0.5 million in Sri Lanka are exposed to the risk of fluoride above 1.5 mg/L, while Bangladesh and Nepal are mildly affected. The hazard quotient (HQ) for arsenic varied from 0 to 822 in India, 0 to 33 in Pakistan, 0 to 1,051 in Bangladesh, 0 to 582 in Nepal, and 0 to 89 in Sri Lanka. The cancer risk of arsenic varied from 0 to 1.64 × 1-1 in India, 0 to 1.07 × 10-1 in Pakistan, 0 to 2.10 × 10-1 in Bangladesh, 0 to 1.16 × 10-1 in Nepal, and 0 to 1.78 × 10-2 in Sri Lanka. In the case of fluoride, the HQ ranged from 0 to 21 in India, 0 to 33 in Pakistan, 0 to 18 in Bangladesh, 0 to 10 in Nepal, and 0 to 10 in Sri Lanka. Arsenic and fluoride have adverse effects on animals, resulting in chemical poisoning and skeletal fluorosis. Adsorption and membrane filtration have demonstrated outstanding treatment outcomes.

Hydrogeochemistry and prediction of arsenic contamination in groundwater of Vehari, Pakistan: comparison of artificial neural network, random forest and logistic regression models

Arsenic contamination in the groundwater occurs in various parts of the world due to anthropogenic and natural sources, adversely affecting human health and ecosystems. The current study intends to examine the groundwater hydrogeochemistry containing elevated arsenic (As), predict As levels in groundwater, and determine the aptness of groundwater for drinking in the Vehari district, Pakistan. Four hundred groundwater samples from the study region were collected for physiochemical analysis. As levels in groundwater samples ranged from 0.1 to 52 μg/L, with an average of 11.64 μg/L, (43.5%), groundwater samples exceeded the WHO 2022 recommended limit of 10 μg/L for drinking purposes. Ion-exchange processes and the adsorption of ions significantly impacted the concentration of As. The HCO3- and Na+ are the dominant ions in the study area, and the water types of samples were CaHCO3, mixed CaMgCl, and CaCl, demonstrating that rock-water contact significantly impacts hydrochemical behavior. The geochemical modeling indicated negative saturation indices with calcium carbonate and other salt minerals, encompassing aragonite, calcite, dolomite, and halite. The dissolution mechanism suggested that these minerals might have implications for the mobilization of As in groundwater. A combination of human-induced and natural sources of contamination was unveiled through principal component analysis (PCA). Artificial neural networks (ANN), random forest (RF), and logistic regression (LR) were used to predict As in the groundwater. The data have been divided into two parts for statistical analysis: 20% for testing and 80% for training. The most significant input variables for As prediction was determined using Chi-squared analysis. The receiver operating characteristic area under the curve and confusion matrix were used to evaluate the models; the RF, ANN, and LR accuracies were 0.89, 0.85, and 0.76. The permutation feature and mean decrease in impurity determine ten parameters that influence groundwater arsenic in the study region, including F-, Fe2+, K+, Mg2+, Ca2+, Cl-, SO42-, NO3-, HCO3-, and Na+. The present study shows RF is the best model for predicting groundwater As contamination in the research area. The water quality index showed that 161 samples represent poor water, and 121 samples are unsuitable for drinking. Establishing effective strategies and regulatory measures is imperative in Vehari to ensure the sustainability of groundwater resources.

Integrated approach to hydrogeochemical appraisal of groundwater quality concerning arsenic contamination and its suitability analysis for drinking purposes using water quality index

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.

Groundwater hydrogeochemistry and non-carcinogenic health risk assessment in major river basins of Punjab, India

The Indian Punjab state is drained by the four rivers, along with a well-connected network of canals, and is now dealing with a slew of water quality issues and problems. In this study, basin-wise hydrogeochemical modelling of 323 groundwater samples and identification of NO3- and F- enrichment pathways in aquifer systems of Punjab were studied using different plots and multivariate statistics. To evaluate the groundwater quality and human health risks, an entropy-based water quality index and Monte Carlo simulation were used, respectively. Spatial distribution of NO3- indicated that its very high values were prominent in parts of southwestern Punjab falling under LSRB, along with few pockets in eastern and northeastern Punjab falling under MSRB and GRB. High NO3- values (> 45.0 mg/L) were found in 15.0% of Ravi River Basin (RRB) groundwater samples, 22.86% of Beas River Basin (BRB), 23.52% of Middle Sutlej River Basin (MSRB), 36.9% of Lower Sutlej River Basin (LSRB), and 21.31% of Ghaggar River Basin (GRB). The spatial distribution of NO3- revealed elevated concentrations (> 100 mg/L) in the southwestern part of Punjab, particularly in LSRB and localized pockets in the eastern and northeastern areas of Punjab within MSRB and GRB. High F- concentration (> 1.5 mg/L) was observed in 15.12% and 21.31% groundwater samples of LSRB and GRB, respectively. Spatially southern parts falling under LSRB and GRB reflected high F- content (> 1.5 mg/L) in groundwater. In LSRB, evaporative and anthropogenic processes influence the groundwater quality. The results of interionic relationships and statistical analysis revealed that NO3- has anthropogenic origin and that is being aggravated by leaching, the evaporation processes, animal excreta, septic tanks and irrigation return flows in LSRB and GRB, while F- is geogenic in nature. Hazard index (HI) values in 14.63%, 22.2%, 24.6%, 49.58%, and 34.42% samples for adults and 21.95%, 27.7%, 42.0%, 72.3%, and 52.46% samples for children were higher than unity in RRB, BRB, MSRB, LSRB, and GRB, respectively. The basin-wise demarcation of various groundwater quality parameter and assessment of human health risk would be of significance for the management of water resources.

Fluoride in groundwater of industrial town of Sonbhadra district, Uttar Pradesh, India: probable release mechanism and potential health risk assessment

In the selected study region of Sonbhadra district, coal burning and mining activities are dominant. Previous studies reported F contamination in very few groundwater samples of this region. A detailed study is required to estimate the fluoride in groundwater of this area. Hence, a total of 128 groundwater samples were collected during post- and pre-monsoon seasons in the year 2017 to estimate the F-, its geochemistry, and health risk assessment from Renukoot and Anpara industrial clusters of Sonbhadra district, Uttar Pradesh, India. The pH of groundwater samples varied from slightly acidic to alkaline during both seasons. Almost all the major cations (Ca2+, Mg2+, Na+, and K+) and major anions (HCO3-, Cl-, SO42-, and F-) values in groundwater samples of both clusters were found within the permissible limit of World Health Organization (WHO) and Beauro of Indian standards except F- in both seasons. The scatter plots of F- with Ca2+, Na+, HCO3-, and pH are used to explain the release mechanism of fluoride in groundwater. Saturation indices (SI) calcite versus SI fluorite and SI dolomite versus SI fluorite plots of both clusters used to check the involvement of these minerals in fluoride enrichment of aquifers. F- contamination in groundwater due to coal burning in coal mining and thermal power plant dominated region is discussed globally and locally both. The non-carcinogenic health risk due to consumption of fluoride-contaminated water is estimated by using target hazard quotient (THQ). THQ values of F- showed that children are at high risk than adults in both clusters of the study area during both seasons. Pictorial representation is used to show the dental fluorosis cases in children of the study region.

Geochemical control, water quality indexing, source distribution, and potential health risk of fluoride and arsenic in groundwater: Occurrence, sources apportionment, and positive matrix factorization model

Fluoride (F-), and arsenic (As) in the groundwater cause health problems in developing countries, including Pakistan. We evaluated the occurrence, distribution, sources apportionment, and health hazards of F-, and As in the groundwater of Mardan, Pakistan. Therefore, groundwater samples (n = 130) were collected and then analyzed for F-, and As by ion-chromatography (IC) and Inductively-coupled plasma mass-spectrometry (ICP-MS). The F-, and As concentrations in groundwater were 0.7-14.4 mg/L and 0.5-11.2 µg/L. Relatively elevated F-, and As coexists with higher pH, Na+, HCO3-, SO4-2, and depleted Ca+2 due to fluoride, sulfide-bearing minerals, and anthropogenic inputs. Both F-, and/or As are transported in subsurface water through adsorption and desorption processes. Groundwater samples 45%, and 14.2% exceeded the WHO guidelines of 1.5 mg/L and 10 µg/L. Water quality indexing (WQI-model) declared that 35.7% samples are unfit for household purposes. Saturation and undersaturation of minerals showed precipitation and mineral dissolution. Groundwater contamination by PCA-MLR and PMF-model interpreted five factors. The fitting results and R2 values of PMF (0.52-0.99)>PCA-MLR (0.50-0.95) showed high accuracy of PMF-model. Human health risk assessment (HHRA-model) revealed high non-carcinogenic and carcinogenic risk for children than adults. The percentile recovery of F- and As was recorded 98%, and 95% with reproducibility ± 5% error.

Assessment of landcover impacts on the groundwater quality using hydrogeochemical and geospatial techniques

Groundwater quality is influenced by urbanization and land use land cover (LULC) changes. This study investigated their impact on groundwater quality in Quetta City, Pakistan, from 2015 to 2021. About 58 groundwater samples from monitoring wells were analyzed using hydrogeochemical and statistical methods. The water quality index (WQI), Wilcox, USSL, and various agricultural indices were employed to assess water quality trends. LULC analysis and NDVI using Sentinel-2 imagery revealed increased urban and agricultural areas and decreased barren land. Rapid urbanization was evident, with the buildup class expanding by 7.50% during this period. NDVI findings emphasized monitoring vegetation health and water quality for environmental assessments. The groundwater in Quetta was primarily classified as Cl-Ca·Mg, Cl-Ca, and Cl-Na according to the Piper diagram, with water-rock interactions and rock weathering evident. Most groundwater samples were suitable for irrigation according to the Wilcox and USSL diagrams. The WQI demonstrated overall safety for human consumption, but declining WQI values in northern parts due to urbanization are concerning. The results also revealed a moderate positive relationship between landcover classes and WQI values. It can be concluded that urbanization and excessive use of pesticides contributed to declining agricultural land quality. The spatial overlay of agricultural indices with landcover class suggested that barren land was most suitable, followed by build-up and agriculture were suitable for drinking and agriculture purposes. Moreover, agricultural indices moderately declined due to excessive fertilizers and pesticides in the agriculture landcover class. Thus, effective water resource management is crucial to address challenges. This comprehensive study serves as a baseline for future research and recommends larger-scale studies to implement efficient management strategies, urbanization planning, and safe irrigation and drinking water practices to prevent groundwater pollution.

Potentially toxic metals contamination, health risk, and source apportionment in the agricultural soils around industrial areas, Firozabad, Uttar Pradesh, India: a multivariate statistical approach

Potentially toxic metals (PTMs) contamination in the soil poses a serious danger to people's health by direct or indirect exposure, and generally it occurs by consuming food grown in these soils. The present study assessed the pollution levels and risk to human health upon sustained exposure to PTM concentrations in the area's centuries-old glass industry clusters of the city of Firozabad, Uttar Pradesh, India. Soil sampling (0-15 cm) was done in farmers' fields within a 1 km radius of six industrial clusters. Various environmental (geo-accumulation index, contamination factor, pollution load index, enrichment factor, and ecological risk index) and health risk indices (hazard quotient, carcinogenic risk) were computed to assess the extent of damage caused to the environment and the threat to human health. Results show that the mean concentrations of Cu (33 mg kg^-1), Zn (82.5 mg kg^-1), and Cr (15.3 mg kg^-1) were at safe levels, whereas the levels of Pb, Ni, and Cd exceeded their respective threshold limits. A majority of samples (88%) showed considerable ecological risk due to the co-contamination of these six PTMs. Health risk assessment indicated tolerable cancer and non-cancer risk in both adults and children for all PTMs, except Ni, where adults were exposed to potential threat of cancer. Pearson's correlation study revealed a significant positive correlation between all six metal pairs and conducting principal component analysis (PCA) confirmed the common source of metal pollution. The PC score ranked different sites from highest to lowest according to PTM loads that help to establish the location of the source. Hierarchical cluster analysis grouped different sites into the same cluster based on similarity in PTMs load, i.e., low, medium, and high.

Groundwater pollutants characterization by geochemometric technique and geochemical modeling in tropical savanna watershed

Multiple interactions of geogenic and anthropogenic activities can trigger groundwater pollution in the tropical savanna watershed. These interactions and resultant contamination have been studied using applied geochemical modeling, conventional hydrochemical plots, and multivariate geochemometric methods, and the results are presented in this paper. The high alkalinity values recorded for the studied groundwater samples might emanate from the leaching of carbonate soil derived from limestone coupled with low rainfall and high temperature in the area. The principal component analysis (PCA) unveils three components with an eigenvalue > 1 and a total dataset variance of 67.37%; this implies that the temporary hardness of the groundwater and water-rock interaction with evaporite minerals (gypsum, halite, calcite, and trona) is the dominant factor affecting groundwater geochemistry. Likewise, the PCA revealed anthropogenic contamination by discharging [Formula: see text] [Formula: see text][Formula: see text] and [Formula: see text] from agricultural activities and probable sewage leakages. Hierarchical cluster analysis (HCA) also revealed three clusters; cluster I reflects the dissolution of gypsum and halite with a high elevated load of [Formula: see text] released by anthropogenic activities. However, cluster II exhibited high [Formula: see text] and [Formula: see text] loading in the groundwater from weathering of bicarbonate and sylvite minerals. Sulfate ([Formula: see text]) dominated cluster III mineralogy resulting from weathering of anhydrite. The three clusters in the Maiganga watershed indicated anhydrite, gypsum, and halite undersaturation. These results suggest that combined anthropogenic and natural processes in the study area are linked with saturation indexes that regulate the modification of groundwater quality.

Groundwater fluoride and nitrate contamination and associated human health risk assessment in South Punjab, Pakistan

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.

Hydrochemical evaluation of groundwater for drinking and irrigation purposes using multivariate indices along Indus Suture Zone, North Pakistan

The present study is aimed to investigate the hydrochemical characteristics, spatial distribution and suitability of groundwater for drinking and irrigation purposes along the Indus Suture Zone (ISZ), north Pakistan. Physicochemical parameters and hazardous trace elements (HTEs) like Cd, Co, Cu and Mn were determined following standard methods. The mean and median concentrations were found below the World Health Organization (WHO) drinking water guidelines values. Hydrochemical results indicate that groundwater sources were mainly attributed to rock-water interaction category. Piper diagram shows that most of the groundwater samples fall in Ca-HCO₃^─ class presenting weak-alkaline proportion type. The drinking water quality index (DWQI) ranking was categorized as good to excellent, indicating the overall quality of the groundwater may pose no health hazard concern. Based on irrigation WQI (SAR, Na%, MAR, KR), the groundwater was found fit for irrigation except SAR whereas 36% of the groundwater samples fall within the poor class. The total HI values through dermal contact exceeded the safe non-carcinogenic threshold of HI = 1. Therefore, there is required an effective groundwater monitoring and management facility in the study area to safeguard residents from various illnesses associated with varying HTEs concentrations in drinking water. The major response actions needed for groundwater bodies restoration are including the installation of a continuous groundwater monitoring network and control of agricultural fertilizers that seems to be the most effective and tangible for immediate action.

Geochemical evidence of fluoride behavior in loess and its influence on seepage characteristics: An experimental study

High background levels of fluorine in groundwater and soil in arid and semi-arid loess regions pose a severe threat to socio-economic development and human health, necessitating the evaluation of fluorine migration in loess. In this study, static leaching and dynamic seepage tests as well as scanning electron microscopy, mercury intrusion porosimetry, and X-ray fluorescence analyses were conducted using loess as the porous medium. Additionally, simulations using PHREEQC software were performed. The results indicated that the studied loess had a high background level of fluorine. Geochemical processes closely related to fluorine include dissolution of gypsum and dolomite, precipitation/dissolution of calcite and fluorite, and ion exchange between CaX and NaX. Under seepage of water with high fluorine levels, soil particles flocculated and formed aggregates; furthermore, the contact area between soil particles reduced, resulting in point-to-point contact between particles. Consequently, pores changed from small (intra- and inter-particle pores) to large (intra- and inter-granular pores) scale pores. Permeability initially decreased rapidly, then remained relatively stable, and subsequently rapidly increased with the passage of time. This was attributed to the dissolution of calcium minerals in loess, yielding Ca²⁺, which induced the precipitation of fluorite and promoted the dissolution of carbonates. Cation exchange and dissolution of other components were also important factors influencing permeability. The findings of this study can elucidate the coupling between loess microstructure, seepage behavior, and geochemical actions under the influence of high‑fluorine water, and are of great significance for in-situ regional research in loess areas.

Assessment of groundwater vulnerability by applying the improved DRASTIC model: a case in Guyuan City, Ningxia, China

Groundwater is the main source of production and living in most arid and semi-arid areas, and it plays an increasingly critical role in achieving local urban development. There is a serious issue regarding the contradiction between urban development and groundwater protection. In this study, we used three different models to assess the groundwater vulnerability of Guyuan City, including DRASTIC model, analytical hierarchy process-DRASTIC model (AHP-DRASTIC) and variable weight theory-DRASTIC model (VW-DRASTIC). The groundwater vulnerability index (GVI) of the study area was calculated in ArcGIS. Based on the magnitude of GVI, the groundwater vulnerability was classified into five classes: very high, high, medium, low, and very low using the natural breakpoint method, and the groundwater vulnerability map (GVM) of the study area was drawn. In order to validate the accuracy of groundwater vulnerability, the Spearman correlation coefficient was used, and the results showed that the VW-DRASTIC model performed best among the three models (ρ=0.83). The improved VW-DRASTIC model shows that the variable weight model effectively improves the accuracy of the DRASTIC model, which is more suitable for the study area. Finally, based on the results of GVM combined with the distribution of F^- and urban development planning, suggestions were proposed for further sustainable groundwater management. This study provides a scientific basis for groundwater management in Guyuan City, which can be an example for similar areas, particularly in arid and semi-arid areas.

Groundwater quality evaluation based on water quality indices (WQI) using GIS: Maadher plain of Hodna, Northern Algeria

In a semi-arid region of Maadher, central Hodna (Algeria), groundwater is the main source for agricultural and domestic purposes. Anthropogenic activities and the presence of climate change's effects have a significant impact on the region's groundwater quality. This study's goals were to use water quality indices to evaluate the groundwater's quality and its suitability for drinking and irrigation, as well as to identify contaminated wells using a geographic information system (GIS) and the spatial interpolation techniques of ordinary kriging and inverse distance weighting (IDW). The results reveal that all water samples exceeded the World Health Organization's standards for nitrate ions and had alarming concentrations of calcium, chlorine, and sulfate (WHO). According to Piper's diagram, the groundwater hydrochemical facies is composed of the elements sulfate-chloride-nitrate-calcium (SO₄^2--Cl^-NO₃^--Ca²⁺ water type). The majority of samples fall into the poor water category, slightly more than 10% fall into the very poor water category, and less than 10% fall into the good to the excellent quality category, per the water quality indices, which classify samples in a similar manner. According to irrigation water indices, every sample is suitable for irrigation. Depending on the direction of groundwater flow, the spatial distributions of Ca²⁺, Na⁺, Mg²⁺, SO₄^2-, and Cl^- show that their concentrations are high north of the area and relatively low south of Maadher village (Fig. 3). Nitrate concentrations are high in the majority of samples, particularly those close to the Bousaada wadi. In most samples, particularly those close to the Bousaada wadi, nitrate levels are high. Various water quality models were described, and GIS spatial distribution maps were created using standard kriging and inverse distance weighting (IDW) techniques through selected semi-variograms predicted against measurements. To determine the origin of mineralization and the chemical processes that take place in the aquifer-which include the precipitation and dissolution of dolomite, calcite, aragonite, gypsum, anhydrite, and halite-the groundwater saturation index was calculated.

Analysis of multiple pathways and levels of fluoride intake in fluorosis areas of Southwest China

In the coal-burning fluorosis areas of China, over 10 million people suffer from dental fluorosis caused by multiple pathways of fluoride intake. However, the link between dental fluorosis prevalence, the geochemical distribution of fluoride, and contributions of different exposure pathways remain unclear. Here, we aimed to quantify the various fluoride exposure pathways and establish the association between dental fluorosis and fluoride intake in Southwest China. Epidemiological data on the peak time of fluorosis prevalence were combined with geochemical analyses of the fluoride content in coal and clay over a large scale, the amounts and ratios of fluoride intake through different exposure pathways were calculated, and the association between the total daily fluoride intake (TDFI) and dental fluorosis severity was analyzed. The prevalence of dental fluorosis was not significantly correlated with the fluoride geo-background of coal and clay on a large scale (P > 0.05). The co-combustion of coal and clay contained in hand-made briquettes is the main pathway of fluoride contamination, which occurs through the inhalation of polluted air and consumption of contaminated roasted products. Furthermore, the TDFI per person ranged from 2.78 to 17.32 mg, and it was significantly positively correlated with the prevalence of dental fluorosis (P < 0.05). The TDFI from breathing and eating was 1.1-3.2 mg and 1.1-15.1 mg, which accounted for 9%-54% and 40%-90% of the total TDFI, respectively. The combination of living habits and soil geochemical fluoride anomalies resulted in the higher prevalence of fluorosis in rural areas of Southwest China.

Prediction of elevated groundwater fluoride across India using multi-model approach: insights on the influence of geologic and environmental factors

Elevated fluoride in groundwater is a severe problem in India due to its extensive occurrence and detrimental health impacts on the large population that thrives on groundwater. Although fluoride is primarily a geogenic pollutant, existing model-based studies lack the amalgamation of the influence of geologic factors, specifically tectonics, for identifying groundwater fluoride distribution. This drawback encourages the present study to investigate the association of the tectonic framework with fluoride in a multi-model approach. We have applied three machine learning models (random forest, boosted regression tree, and logistic regression) to predict elevated groundwater fluoride based on fluoride measurements across India. The random forest model outperformed other models with an accuracy of 93%. Tectonics was found to be one of the most important predictors alongside "depth to water table." Two major areas of high risk identified were the northwest parts and the south-southeast cratonic peninsular region. The random forest model also performed significantly well over the validation dataset. We estimate that nearly 257 million people are exposed to elevated fluoride risk in India. We endeavor that the findings of our study would be an effective tool for identifying the areas at risk of elevated fluoride and also assist in undertaking effective groundwater management strategies.

Identifying the geochemical evolution and controlling factors of the shallow groundwater in a high fluoride area, Feng County, China

Understanding how groundwater is formed and evolves is critical for water resource exploitation and utilization. In this study, hydrochemistry and stable isotope tracing techniques were adopted to determine the key factors influencing groundwater chemical evolution in Feng County. A total of fourteen wells and five surface water samples were investigated in November 2021. The δD and δ¹⁸O compositions show that both surface water and groundwater are recharged from atmospheric precipitation. The dominating order of cations and anions in groundwater appears to be Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ and HCO₃^- > SO₄^2- > Cl^- > NO₃^- > F^-, respectively. The groundwater hydrochemical facies are mainly characterized by HCO₃-Ca-Mg and SO₄-Cl-Na types. The chemical evolution of groundwater is dominated by water-rock interaction and cation exchange reactions. The major ions in groundwater are mainly controlled by various geogenic processes including halite, gypsum, calcite, dolomite, Glauber's salt, feldspar, and fluorite dissolution/precipitation. Furthermore, the abundant fluoride-bearing sediments, together with low Ca²⁺, promote the formation of high F^- groundwater. Approximately 85.7% and 28.6% of groundwater samples exceeded the permissible limit for F^- and NO₃^- respectively. Apart from geogenic F^-, human interventions (i.e., industrial fluoride-containing wastewater discharge and agricultural phosphate fertilizer uses) also regulate the F^- enrichment in the shallow groundwater. Nitrate pollution of the groundwater may be attributed to domestic waste and animal feces. Our findings could provide valuable information for the sustainable exploitation of groundwater in the study area and the development of effective management strategies by the authorities.

Groundwater Quality, Health Risk Assessment, and Source Distribution of Heavy Metals Contamination around Chromite Mines: Application of GIS, Sustainable Groundwater Management, Geostatistics, PCAMLR, and PMF Receptor Model

Groundwater contamination by heavy metals (HMs) released by weathering and mineral dissolution of granite, gneisses, ultramafic, and basaltic rock composition causes human health concerns worldwide. This paper evaluated the heavy metals (HMs) concentrations and physicochemical variables of groundwater around enriched chromite mines of Malakand, Pakistan, with particular emphasis on water quality, hydro-geochemistry, spatial distribution, geochemical speciation, and human health impacts. To better understand the groundwater hydrogeochemical profile and HMs enrichment, groundwater samples were collected from the mining region (n = 35), non-mining region (n = 20), and chromite mines water (n = 5) and then analyzed using ICPMS (Agilent 7500 ICPMS). The ranges of concentrations in the mining, non-mining, and chromite mines water were 0.02-4.5, 0.02-2.3, and 5.8-6.0 mg/L for CR, 0.4-3.8, 0.05-3.6, and 3.2-5.8 mg/L for Ni, and 0.05-0.8, 0.05-0.8, and 0.6-1.2 mg/L for Mn. Geochemical speciation of groundwater variables such as OH^-, H⁺, Cr⁺², Cr⁺³, Cr⁺⁶, Ni⁺², Mn⁺², and Mn⁺³ was assessed by atomic fluorescence spectrometry (AFS). Geochemical speciation determined the mobilization, reactivity, and toxicity of HMs in complex groundwater systems. Groundwater facies showed 45% CaHCO₃, 30% NaHCO₃, 23.4% NaCl, and 1.6% Ca-Mg-Cl water types. The noncarcinogenic and carcinogenic risk of HMs outlined via hazard quotient (HQ) and total hazard indices (THI) showed the following order: Ni > Cr > Mn. Thus, the HHRA model suggested that children are more vulnerable to HMs toxicity than adults. Hierarchical agglomerative cluster analysis (HACA) showed three distinct clusters, namely the least, moderately, and severely polluted clusters, which determined the severity of HMs contamination to be 66.67% overall. The PCAMLR and PMF receptor model suggested geogenic (minerals prospects), anthropogenic (industrial waste and chromite mining practices), and mixed (geogenic and anthropogenic) sources for groundwater contamination. The mineral phases of groundwater suggested saturation and undersaturation. Nemerow's pollution index (NPI) values determined the unsuitability of groundwater for domestic purposes. The EC, turbidity, PO₄^-3, Na⁺, Mg⁺², Ca⁺², Cr, Ni, and Mn exceeded the guidelines suggested by the World Health Organization (WHO). The HMs contamination and carcinogenic and non-carcinogenic health impacts of HMs showed that the groundwater is extremely unfit for drinking, agriculture, and domestic demands. Therefore, groundwater wells around the mining region need remedial measures. Thus, to overcome the enrichment of HMs in groundwater sources, sustainable management plans are needed to reduce health risks and ensure health safety.

Potential health risk assessment, spatio-temporal hydrochemistry and groundwater quality of Yamuna river basin, Northern India

Groundwater which is an essential source of freshwater for various domestic, agricultural, industrial applications is facing a severe deterioration in quality due to demographic pressure and intense industrial activities. Present study appraises the influence of human induced activities on groundwater quality of Agra-Firozabad industrial belts of Western Uttar Pradesh, Yamuna basin, India. The maximum concentrations of metals and anions found during pre and post monsoon are as follows: Lead 0.302; 0.086, calcium 672; 1260, magnesium 215; 16.8, cadmium 0.0; 0.066, chromium 0.016; 0.005, manganese 0.340; 0.076, nickel 0.044; 0.028, sulfate 514; 286, nitrate 66.7; 3.56 and fluoride 1.17; 2.02 mg/L respectively. Based on results of Water Quality Index, groundwater samples were classified under 'Poor water' category in 34.2% and 52.63% during pre and post-monsoon period, respectively. Accordingly, higher concentrations of bicarbonate and sulfate might have attributed to excess hardness, instrumental in making it unsuitable for industrial usage. However, values of Percent Sodium, Sodium Adsorption Ratio, Magnesium Hazard and Permeability Index signified that groundwater from majority of locations was fit for agricultural use. Health risk assessment studies revealed that children consuming polluted water were affected more as compared to adults. Timely action and strict compliance of regulation is recommended towards groundwater management for defined usage to avert severe health effects and to meet sustainable development goals.

Arsenic Contamination, Water Toxicity, Source Apportionment, and Potential Health Risk in Groundwater of Jhelum Basin, Punjab, Pakistan

Potable groundwater (GW) contamination through arsenic (As) is a commonly reported environmental issue in Pakistan. In order to examine the groundwater quality for As contamination, its geochemical behavior, and other physicochemical parameters, 69 samples from various groundwater sources were collected from the mining area of Pind Dadan Khan, Punjab, Pakistan. The results showed the concentration of elevated As, its source of mobilization, and linked public health risk. Arsenic detected in the groundwater samples varied from 0.5 to 100 µg/L, with an average value of 21.38 µg/L. Forty-two samples were beyond the acceptable limit of 10 µg/L of the WHO for drinking purposes. The statistical summary showed that the groundwater cation concentration was in decreasing order such as Na⁺  > Ca²⁺  > Mg²⁺ > K⁺, while anions were as follows: HCO₃^- > SO4^2- > Cl^- > NO₃^-. Hydrochemical facies results depicted that groundwater samples belong to CaHCO₃ type. Rock-water interactions control the hydrochemistry of groundwater. Saturation indices' results indicated the saturation of the groundwater sources for CO₃ minerals due to their positive SI values. Such minerals include aragonite, calcite, dolomite, and fluorite. The principal component analysis (PCA) findings possess a total variability of 77.36% suggesting the anthropogenic and geogenic contributing sources of contaminant. The results of the Exposure-health-risk-assessment model for measuring As reveal significant potential carcinogenic risk exceeding the threshold level (value > 10^-4) and HQ level (value > 1.0).

Spatiotemporal assessment of groundwater quality in the Central Ganga Plain, India, using multivariate statistical tools

In the present study, the water quality status of the Sadar block in Pratapgarh district of Uttar Pradesh, India, was calculated by Water Pollution Index (WPI) using 15 groundwater quality parameters (pH, turbidity, EC (electric conductivity), TDS (total dissolved solids), salinity, total hardness, Ca²⁺, K⁺, Mg²⁺, Na⁺, Cl^-, F^-, SO₄^2-, HCO₃^-, and NO₃^-) at 40 different study locations. It is found that 10%, 25%, and 65%, of samples, fall under the good, moderately polluted, and highly polluted category, respectively. Irrigation suitability of groundwater has also been evaluated by using irrigation suitability parameters, i.e., Sodium Absorption Ratio (SAR), Residual Sodium Carbonate (RSC), Permeability Index (PI), Kelly Ratio (KR), Percentage Sodium (% Na), and Magnesium Hazards (MH). Based on the analysis, it was determined that most of the samples were suitable for irrigation in the area. Irrigation practices are found to be unsuitable for Kelly's ratio of 37.5%, MH 60%, and RSC 55% samples. WPI and Pearson's correlation matrix (PCA) have suggested a significant linear relationship among the water quality parameters based on the test results. The Gibbs plot indicates that the majority of samples fall under the "evaporation dominance" category while the rest fall under the "rock weathering dominance" suggesting that the complex geochemical mechanisms are active in the study area. This study would be very helpful to government authorities and it would aid them to suggest alternate drinking water resources in affected areas.

Hydrogeochemical assessment of carcinogenic and non-carcinogenic health risks of potentially toxic elements in aquifers of the Hindukush ranges, Pakistan: insights from groundwater pollution indexing, GIS-based, and multivariate statistical approaches

Globally, potentially toxic elements (PTEs) and bacterial contamination pose health hazards, persistency, and genotoxicity in the groundwater aquifer. This study evaluates PTE concentration, carcinogenic and noncarcinogenic health hazards, groundwater quality indexing (GWQI-model), source provenance, and fate distribution in the groundwater of Hindukush ranges, Pakistan. The new estimates of USEPA equations record new research dimensions for carcinogenic and noncarcinogenic hazards. The principal component analysis (PCA), mineral phases, and spatial distribution determine groundwater contamination and its impacts. The average concentrations of PTEs, viz., Cd, Cu, Co, Fe, Pb, and Zn, were 0.06, 0.27, 0.07, 0.55, 0.05, and 0.19 mg/L, and E. coli, F. coli, and P. coli were 27.5, 24.0, and 19.0 CFU/100 ml. Moreover, the average values of basic minerals, viz., anhydrite, aragonite, calcite, dolomite, gypsum, halite, and hydroxyl apatite, were 0.4, 2.4, 2.6, 5.1, 0.6, and - 4.0, 11.2, and PTE minerals like monteponite, tenorite, cuprite, cuprous ferrite, cupric ferrite, ferrihydrite, goethite, hematite, lepidocrocite, maghemite, magnetite, massicot, minium, litharge, plattnerite, and zincite were - 5.5, 2.23, 4.65, 18.56, 20.0, 4.84, 7.54, 17.46, 6.66, 9.67, 22.72, - 3.36, 22.9, 3.16, - 18.0, and 1.46. The groundwater showed carcinogenic and non-carcinogenic health hazards for children and adults. The GWQI-model showed that 58.3% of samples revealed worse water quality. PCA revealed rock weathering, mineral dissolution, water-rock interaction, and industrial effluents as the dominant factors influencing groundwater chemistry. Carbonate weathering and ion exchange play vital roles in altering CaHCO3 type to NaHCO3 water. In this study, E. coli, F. coli, P. coli, EC, turbidity, TSS, PO43─, Na+, Mg+2, Ca+2, Cd, Co, Fe, and Pb have exceeded the World Health Organization (WHO) guidelines. The carcinogenic and non-carcinogenic impacts of PTEs and bacterial contamination declared that the groundwater is unfit for drinking and domestic purposes.

Fluoride enrichment mechanisms and related health risks of groundwater in the transition zone of geomorphic units, northern China

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.

Non-Carcinogenic Health Risk Evaluation of Elevated Fluoride in Groundwater and Its Suitability Assessment for Drinking Purposes Based on Water Quality Index

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^-, Ca²⁺, Mg²⁺, 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 Fe²⁺, 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 ADD_ingestion 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 HQ_ingestion 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 ADD_ingestion and HQ_ingestion 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.

APCS-MLR model: A convenient and fast method for quantitative identification of nitrate pollution sources in groundwater

Nitrate (NO₃^-) contamination in groundwater has diverse sources and complicated transformation processes. To effectively control NO₃^- pollution in groundwater systems, quantitative and accurate identification of NO₃^- sources is critical. In this work, we applied hydrochemical characteristics and isotope analysis to determine NO₃^- source apportionment. For the first time, the NO₃^- source contributions were calculated using hydrochemical indicators combined with multivariate statistical model (PCA-APCS-MLR). The results interpret that chemical fertilizers (58.11%) and natural sources (22.69%) were the primary NO₃^- sources in the vegetable cultivation area (VCA) which were rather close to the estimation by Bayesian isotope mixing model (SIAR). In particular, the contributions of chemical fertilizers in the VCA differed by only 3.79% between the two methods. Compared with previous approaches e.g. SIAR, the key advantage of the proposed PCA-APCS-MLR model is that it only requires the hydrochemical indicators which can be easily measured. A series of complicated experiments including measurement of isotope data of NO₃^- in groundwater, monitoring of in-situ pollution source information and calculation of isotopic enrichment factor can be simply avoided. The PCA-APCS-MLR model offers a much more convenient and faster method to determine the contribution rates of NO₃^- pollution sources in groundwater.

Deterministic and probabilistic human health risk assessment for fluorides in drinking groundwater from Lukavac, Bosnia and Herzegovina

Although fluorides are essential for dental health, there are growing health concerns regarding the risk-benefit ratio of fluoride exposure. The objectives of the study were to obtain data on the amount and human health risks of fluoride in drinking groundwater, as well as to compare and evaluate the differences in the outputs obtained by two different approaches in health risk assessment (deterministic vs probabilistic). From a densely populated industrial area of north-eastern Bosnia and Herzegovina, a total of 54 groundwater samples were collected. Fluoride concentrations varied from 1.69 to 3.52 mg/L. The WHO's threshold value for fluoride in drinking water was exceeded in all the samples analysed, indicating an increased daily intake of fluoride from groundwater. Deterministic and semi-probabilistic techniques were used for exposure assessment and health risk quantification. Generally, the deterministic approach resulted in acceptable health risks in most adult exposure scenarios. However, the Monte Carlo simulation revealed that 20.6, 20.8, and 99.8% of adult males, females, and children, respectively, were above the tolerable upper intake level, indicating that both adults and children face a significant health risk. Nevertheless, small children are more vulnerable to environmental hazards than youth and adults. Hence, a more in-depth risk-benefit analysis is required to reduce/or optimize fluoride content in drinking water to prevent tooth decay and fluorosis at all ages. Considering that optimal daily intake of fluorides is a crucial factor for preserving human health, decision-makers should take steps to emphasize the importance of continuous monitoring of fluoride concentrations in drinking water.

Geochemical Modeling Source Provenance, Public Health Exposure, and Evaluating Potentially Harmful Elements in Groundwater: Statistical and Human Health Risk Assessment (HHRA)

Groundwater contamination by potentially harmful elements (PHEs) originating from the weathering of granitic and gneissic rock dissolution poses a public health concern worldwide. This study investigated physicochemical variables and PHEs in the groundwater system and mine water of the Adenzai flood plain region, in Pakistan, emphasizing the fate distribution, source provenance, chemical speciation, and health hazard using the human health risk assessment HHRA-model. The average concentrations of the PHEs, viz., Ni, Mn, Cr, Cu, Cd, Pb, Co, Fe, and Zn 0.23, were 0.27, 0.07, 0.30, 0.07, 0.06, 0.08, 0.68, and 0.23 mg/L, respectively. The average values of chemical species in the groundwater system, viz., H+, OH−, Ni2+, Mn2+, Mn3+, Cr3+, Cr6+, Cu+, Cu2+, Cd2+, Pb2+, Pb4+, Co2+, Co3+, Fe2+, Fe3+, and Zn2+, were 1.0 × 10−4 ± 1.0 × 10−6, 1.0 × 10−4 ± 9.0 × 10−7, 2.0 × 10−1 ± 1.0 × 10−3, 3.0 × 10−1 ± 1.0 × 10−3, 1.0 × 10−22 ± 1.0 × 10−23, 4.0 × 10−6 ± 2.0 × 10−6, 4.0 × 10−11 ± 2.0 × 10−11, 9.0 × 10−3 ± 1.0 × 10−2, 2.0 × 10−1 ± 2.0 × 10−3, 7.0 × 10−2 ± 6.0 × 10−2, 5.0 × 10−2 ± 5.0 × 10−2, 2.0 × 10−2 ± 1.5 × 10−2, 6.0 × 10−2 ± 4.0 × 10−2, 8.0 × 10−31 ± 6.0 × 10−31, 3.0 × 10−1 ± 2.0 × 10−4, 4.0 × 10−10 ± 3.0 × 10−10, and 2.0 × 10−1 ± 1.0 × 10−1. The mineral compositions of PHEs, viz. Ni, were bunsenite, Ni(OH)2, and trevorite; Mn viz., birnessite, bixbyite, hausmannite, manganite, manganosite, pyrolusite, and todorokite; Cr viz., chromite and eskolaite; Cu viz., CuCr2O4, cuprite, delafossite, ferrite-Cu, and tenorite; Cd viz., monteponite; Pb viz, crocoite, litharge, massicot, minium, plattnerite, Co viz., spinel-Co; Fe viz., goethite, hematite, magnetite, wustite, and ferrite-Zn; and Zn viz., zincite, and ZnCr2O4 demarcated undersaturation and supersaturation. However, EC, Ca2+, K+, Na+, HCO3−, Cr, Cd, Pb, Co, and Fe had exceeded the WHO guideline. The Nemerow’s pollution index (NPI) showed that EC, Ca2+, K+, Na+, HCO3−, Mn, Cd, Pb, Co, and Fe had worse water quality. Principal component analysis multilinear regression (PCAMLR) and cluster analysis (CA) revealed that 75% of the groundwater contamination originated from geogenic inputs and 18% mixed geogenic-anthropogenic and 7% anthropogenic sources. The HHRA-model suggested potential non-carcinogenic risks, except for Fe, and substantial carcinogenic risks for evaluated PHEs. The women and infants are extremely exposed to PHEs hazards. The non-carcinogenic and carcinogenic risks in children, males, and females had exceeded their desired level. The HHRA values of PHEs exhibited the following increasing pattern: Co > Cu > Mn > Zn > Fe, and Cd > Pb > Ni > Cr. The higher THI values of PHEs in children and adults suggested that the groundwater consumption in the entire region is unfit for drinking, domestic, and agricultural purposes. Thus, all groundwater sources need immediate remedial measures to secure health safety and public health concerns.

The Impact of Customer Experience and Customer Engagement on Behavioral Intentions: Does Competitive Choices Matters?

The study aims to analyze behavioral intentions influenced by customer engagement, experience, and identification moderated by competitive choices in the granite sector of Pakistan. The study has been carried out through primary data analysis of cross-sectional approach in the transition to a sustainable economy. In total, 400 questionnaires were distributed, for which only 216 were filled and usable with a response rate of 54%—collected data from the production managers and units. In contrast, missed mine holders and labor analyzed the data in SPSS and AMOS to run various tests, i.e., reliability, correlation analysis, regression, moderation regression, and confirmatory factor analysis. The study findings indicate a positive and significant relationship and effect among the variables. The reviews might contain some biases. Therefore, this study recommended adopting a probability sampling technique for future studies. The study results in a positive manner indicating customer service involvement as a significant factor in behavioral intention despite competitive options.

Increase in fluoride concentration in mine water in Shendong mining area, Northwest China: Insights from isotopic and geochemical signatures

Mine water poses severe threats to the quality of the water supply and ecological environment of the Shendong mining areas owing to its excessive fluoride (F^-) content. However, the geochemical behaviours and enrichment mechanisms responsible for F⁻ enrichment during mining activities are not fully understood. In total, 18 Yanan groundwater and 45 mine water samples were collected to analyse the spatial distribution, hydrogeochemical behaviours, and formation mechanisms related to elevated F^- levels by analysing the stable isotopes and water-rock interactions. In this study, F^- concentrations in mine water samples varied from 0.16 to 12.75 mg/L, with a mean value of 6.10 mg/L, and 77.78% of the mine water samples had a concentration that exceeded China's national standards (1.00 mg/L) for drinking water. The F^- concentration was markedly high in the mine water samples, with the mean F^- concentration being 1.58 times of that in the Yanan groundwater samples. The results of stable isotopes (¹⁸O_H2O, D, ³⁴S_SO4, and ¹⁸O_SO4) and water-rock interaction analyses suggested that cation exchange and competitive effects were the dominant factors responsible for elevated F^- concentration in mine water during mining activities. Thus, the weathering of F-bearing minerals, agriculture, and domestic activities do not play a significant role in the secondary enrichment of F^- concentration.

Potential Protective Effect of Riboflavin Against Pathological Changes in the Main Organs of Male Mice Induced by Fluoride Exposure

Long-term exposure to excessive fluorine could cause damage to various tissues and organs in human and animals. However, there is no effective antidote to prevent and cure fluorosis except for avoiding fluoride intake. As an essential nutrient, riboflavin (VB₂) has been identified to relieve oxidative stress and inflammation in animal tissues caused by other toxic substances, whether it can alleviate the damage caused by fluoride is unknown. For this, 32 ICR male mice were allocated to four groups of eight each. They were treated with 0 (distilled water), 100 mg/L sodium fluoride (NaF), 40 mg/L VB₂, and their combination (100 mg/L NaF plus 40 mg/L VB₂) via the drinking water for 90 consecutive days, respectively. The content of bone fluoride and the histomorphology of the main organs including liver, kidney, cerebral cortex, epididymis, small intestine, and colon were evaluated and pathologically scored. The results found that fluoride caused the pathological changes in liver, kidney, cerebral cortex, epididymis, small intestine, and colon at varying degrees, while riboflavin supplementation reduced significantly the accumulation of fluoride in bone, alleviated the morphological damage to cerebral cortex, epididymis, ileum, and colon. This study provides new clues for deeply exploring the mechanism of riboflavin intervention in fluorosis.

Global diagnosis of nitrate pollution in groundwater and review of removal technologies

Clean water and sanitation for the world population is one of the most important challenges established by the Sustainable Development Goals of the United Nations since worldwide, one in three people do not have access to safe drinking water. Groundwater, one of the main sources of fresh water, has been considerably damaged by human activities. Nevertheless, while numerous plants are globally aimed at removing pollutants from surface waters, a much scarcer number of facilities have focused on groundwater remediation. Nowadays, there is increasing concern about the presence of nitrates (NO₃^-) in groundwaters as a consequence of the intensive use of fertilizers and other anthropogenic sources, such as sewage or industrial wastewater discharge. In this context, the selection and development of highly effective and low-cost solutions for the sustainable management of groundwater resources need to be addressed. Thus, this work collects data from the literature regarding the presence of nitrates in groundwater, and, simultaneously, it reviews the main alternatives available to remove NO₃^- from groundwater sources. A total of 292 sites have been analyzed categorized by continents, carefully discussing the possible origins of nitrate pollution. In addition, a discussion is carried out of the different technologies currently employed to treat groundwater, highlighting the progress made and the main challenges to be overcome. Finally, the review gathers the data available in the literature for nitrate treatment plants at full-scale.

Hydrogeochemical Assessment of Groundwater and Suitability Analysis for Domestic and Agricultural Utility in Southern Punjab, Pakistan

Groundwater is a critical water supply for safe drinking water, agriculture, and industry worldwide. In the Khanewal district of Punjab, Pakistan, groundwater has severely deteriorated during the last few decades due to environmental changes and anthropogenic activities. Therefore, 68 groundwater samples were collected and analyzed for their main ions and trace elements to investigate the suitability of groundwater sources for drinking and agricultural purposes. Principal component analysis (PCA) and cluster analysis (CA) were employed to determine the major factors influencing groundwater quality. To assess the groundwater’s appropriateness for drinking and irrigation, drinking and agricultural indices were used. The pH of the groundwater samples ranged from 6.9 to 9.2, indicating that the aquifers were slightly acidic to alkaline. The major cations were distributed as follows: Na+ > Ca2+ > Mg2+ > K+. Meanwhile, the anions are distributed as follows: HCO3− > SO42− > Cl− > F−. The main hydrochemical facies were identified as a mixed type; however, a mixed magnesium, calcium, and chloride pattern was observed. The reverse ion exchange process helps in exchanging Na+ with Ca2+ and Mg2+ ions in the groundwater system. Rock weathering processes, such as the dissolution of calcite, dolomite, and gypsum minerals, dominated the groundwater hydrochemistry. According to the Weight Arithmetic Water Quality Index (WAWQI), 50% of the water samples were unsafe for drinking. The Wilcox diagram, USSL diagram, and some other agricultural indices resulted in around 32% of the groundwater samples being unsuitable for irrigation purposes. The Khanewal’s groundwater quality was vulnerable due to geology and the influence of anthropogenic activities. For groundwater sustainability in Khanewal, management strategies and policies are required.

Hydrogeochemical Investigation of Elevated Arsenic Based on Entropy Modeling, in the Aquifers of District Sanghar, Sindh, Pakistan

Arsenic (As) contamination in drinking groundwater is a common environmental problem in Pakistan. Therefore, sixty-one groundwater samples were collected from various groundwater sources in District Sanghar, Sindh province, Pakistan, to understand the geochemical behavior of elevated As in groundwater. Statistical summary showed the cations and anions abundance in decreasing order of Na+ > Ca2+ > Mg2+ > K+, and HCO3− > Cl− > SO42− > NO3−. Arsenic was found with low to high concentration levels ranging from 5 µg to 25 µg/L with a mean value of 12.9 µg/L. A major water type of groundwater samples was mixed with NaCl and CaHCO3 type, interpreting the hydrochemical behavior of rock–water interaction. Principal component analysis (PCA) showed the mixed anthropogenic and natural sources of contamination in the study area. Moreover, rock weathering and exchange of ions controlled the hydrochemistry. Chloro-alkaline indices revealed the dominance of the reverse ion exchange mechanism in the region. The entropy water quality index (EWQI) exposed that 17 samples represent poor water, and 11 samples are not suitable for drinking.

Geochemical controls on the enrichment of fluoride in the mine water of the Shendong mining area, China

Underground coal mining produces large amounts of mine water annually in the Shendong mining area of China. Due to the severe scarcity of water resources, mine water is extensively used for productive, domestic, and ecological demands. However, mine water exhibits high fluoride levels. For water-use security, reduction of fluoride exposure and environmental protection, knowledge of sources and geochemical controls of fluoride enrichment in mine water is required. The results showed that F^- concentrations of mine waters vary from 0.05 to 11.65 mg/L, with a mean value of 1.96 mg/L, and 51% of the mine waters contain F^- concentrations exceeding the Chinese drinking water standard (1 mg/L). The overall mine water quality is influenced by cation exchange, mineral dissolution, pyrite oxidation, silicate weathering and so on. The high-fluoride mine waters are all associated with Na-type, with a remarkable cation composition feature of higher Na⁺ and lower Ca²⁺ and Mg²⁺ concentrations. Overall, the high-fluoride mine waters are well-matched with the water environment with higher pH, TDS, and EC levels. PCA reveals that the geochemical controls on the enrichment of F^- in mine waters include dissolution of fluoride-bearing minerals and F^--OH^- ion exchange; the former process is mainly caused by the decrease in Ca²⁺ concentrations resulting from Na ⁺ -Ca²⁺ cation exchange and mineral precipitation, and the latter process benefits from a highly alkaline water environment, facilitating the substitution of OH^- in the mine water for F^- within or absorbed on the minerals. Evaporation also controls F^- enrichment in local areas.

Assessing Nitrate Contamination Risks in Groundwater: A Machine Learning Approach

Groundwater is one of the primary sources for the daily water requirements of the masses, but it is subjected to contamination due to the pollutants, such as nitrate, percolating through the soil with water. Especially in built-up areas, groundwater vulnerability and contamination are of major concern, and require appropriate consideration. The present study develops a novel framework for assessing groundwater nitrate contamination risk for the area along the Karakoram Highway, which is a part of the China Pakistan Economic Corridor (CPEC) route in northern Pakistan. A groundwater vulnerability map was prepared using the DRASTIC model. The nitrate concentration data from a previous study were used to formulate the nitrate contamination map. Three machine learning (ML) models, i.e., Support Vector Machine (SVM), Multivariate Discriminant Analysis (MDA), and Boosted Regression Trees (BRT), were used to analyze the probability of groundwater contamination incidence. Furthermore, groundwater contamination probability maps were obtained utilizing the ensemble modeling approach. The models were calibrated and validated through calibration trials, using the area under the receiver operating characteristic curve method (AUC), where a minimum AUC threshold value of 80% was achieved. Results indicated the accuracy of the models to be in the range of 0.82–0.87. The final groundwater contamination risk map highlights that 34% of the area is moderately vulnerable to groundwater contamination, and 13% of the area is exposed to high groundwater contamination risk. The findings of this study can facilitate decision-making regarding the location of future built-up areas properly in order to mitigate the nitrate contamination that can further reduce the associated health risks.

Groundwater fluoride concentrations in the watershed sedimentary basin of Quetta Valley, Pakistan

Litho-geochemical characteristics of low and high fluoride (F^-) groundwater along with hydrological processes were investigated to delineate its genesis and enrichment mechanism in a watershed sedimentary basin. In this study, groundwater F^- concentration ranged from 0 to 20 mg/L with a mean and standard deviation of 2.8 and ± 3.7 mg/L, respectively. Out of N = 87, 63% of samples exceeded the World Health Organization (WHO) limit of 1.5 mg/L. The order of cationic and anionic dominance in groundwater samples with mean was found in decreasing order as Na⁺  > Mg²⁺  > Ca²⁺  > K⁺ and HCO₃^-  > SO₄^2-  > Cl^-  > PO₄^3-  > NO₃^- measured in milligrams per liter. Groundwater chemistry changed from Ca-HCO₃ to Na-HCO₃ type and low to high fluoride as we moved from mountain foot towards the synclinal basin. Low fluoride groundwater reflected weathering, recharge, and reverse ion exchange processes with Ca-HCO₃- and Ca-Mg-Cl-type water while high fluoride groundwater revealed base ion exchange, mixing, and desorption as dominant hydrological processes with Na-HCO₃ and Na-Cl types of water. Gibb's diagram showed rock weathering and mineral dissolution as the major geochemical processes controlling water chemistry with an insignificant role of evaporation in the semi-arid area. Fluoride was undersaturated with mineral fluorite, indicating fluoride in groundwater is released by secondary minerals. However, due to complex geological features, groundwater fluoride enrichment was affected by a broad-scale process across a wide area such as depth, residence time, and most important geomorphological units hosting the aquifer.

Hydrogeochemistry and health hazards of fluoride-enriched groundwater in the Tarim Basin, China

Fluoride (F^-) enrichment reduces the availability of groundwater resources in the arid region, and it is thus important to investigate the hydrogeochemistry and health hazards of fluoride-enriched groundwater. Seventy-two groundwater samples (20 unconfined samples from the piedmont plain, 22 unconfined samples and 30 shallow confined samples from the alluvial plain) were collected in the Tarim Basin of China to illustrate the geochemical processes driving the F^- enrichment and the incidence of dental fluorosis. The patterns of average ions contents in groundwater are Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ and SO₄^2- > Cl^- > HCO₃^- > NO₃^- > F^-. The highest F^- concentration (average 2.16 mg/L) is observed in unconfined groundwater in the alluvial plain, while the lowest (average 0.63 mg/L) is recorded in unconfined groundwater in the piedmont plain. Approximately 5.0% of unconfined groundwater in the piedmont plain, 90.9% of unconfined groundwater and 33.3% of shallow confined groundwater in the alluvial plain contain F^- concentrations exceeding 1.0 mg/L (Chinese drinking water standard). Mineral dissolution, cation exchange, and evaporation play a significant role in the formation of solutes in groundwater. High-F^- groundwater is mostly associated with SO₄·Cl-Na·Ca, SO₄·Cl-Na·Mg, and SO₄·Cl-Na types water. Thermodynamic simulations reveal that the dissolution of F-bearing minerals (e.g., fluorite) significantly controls the F^- contents in groundwater. High concentrations of F^- are closely related to high HCO₃^-, high Na⁺, high salinity, cation exchange, and evaporation. This demonstrates that high F^- concentrations are caused by the increase in fluorite solubility due to high ionic strength, Ca²⁺ consumption and the desorption of F^- from solid surfaces under alkaline conditions. Mixing with the upper unconfined groundwater plays a vital role in the enrichment of F^- in shallow confined groundwater in the alluvial plain. The health risk assessment based on Dean's classification indicates that the percentage prevalence of fluorosis for boys aged 6 to 18 is 15.5% for Yecheng (YC), 18.4% for Zepu (ZP), 33.3% for Shache (SC), 29.8% for Maigaiti (MG), and 44.9% for Bachu (BC), while that for girls of the same age is 14.3% for YC, 24.3% for ZP, 42.2% for SC, 41.4% for MG, and 45.3% for BC. For male and female adults aged between 19 and 68, the percentage prevalence of fluorosis is: YC (11.5%, 12.0%), ZP (18.3%, 20.0%), SC (35.4%, 35.0%), MG (32.5%, 39.7%), and BC (42.4%, 44.3%). It is obvious that younger generation, especially girls, suffers from more severe dental fluorosis. This study has implications for the effective management of high-F^- groundwater in arid regions.

Hydrogeochemistry of Fluorine in Groundwater in Humid Mountainous Areas: A Case Study at Xingguo County, Southern China

The understanding of F− concentration in groundwater in humid areas is limited although there are lots of research on high-fluoride groundwater in arid areas. In this paper, with controlling factors of F− concentrations in humid areas as the focus, 130 groundwater samples, obtained from four subsystems in Northwest Xingguo County, Jiangxi Province, China, were investigated to demonstrate the controlling factors of F− concentrations in humid areas. According to analytical results, the following hydrogeochemical characteristics of the fluorine in humid mountainous areas were determined: (1) F− concentration is positively correlated with total dissolved solids (TDS), Ca2+, ${\text{HCO}}_3^{-}$ , and pH; (2) the groundwater features a high flow rate and low TDS; (3) the equilibrium constant of CaF2 is less than its solubility product constant, and the fluorine-bearing minerals in rocks are in a dissolved state; and (4) the dissolved fluoride-bearing minerals constitute the main sources of F− in the groundwater. Fluorine mainly comes from groundwater fluorine-bearing minerals in metamorphic rocks. Moreover, the low F− concentration in the groundwater mainly results from the fast flow rate of groundwater. Fluoride in groundwater has great potential hazards in humid areas.

Spatial distribution and potential health risk of fluoride in drinking groundwater sources of Huaibei, Anhui Province

Fluoride enrichment in drinking groundwater at Huaibei leads to potential health risk to the residents. A total of 49 groundwater samples from groundwater sources were collected to evaluate the potential health risk of fluoride ingestion through drinking water for children and adults in Huaibei. Results shown that the average concentration of fluoride in centralized sources is less than that of decentralized sources, which may be attributed to different geological conditions including fluoride-rich minerals, environmental conditions and high fluoride waste discharge. The corresponding health risk value of fluoride in centralized source is lower than that in decentralized one, and the HI values of fluoride in the three exposed groups varied in the same order: infants > children > adults. Infants and children were more sensitive receptors to the non-carcinogenic health hazards of fluoride than adults. Special care should be taken to infants and children for the highly prone to health risk compared to adults.

Groundwater Quality and Potential Human Health Risk Assessment for Drinking and Irrigation Purposes: A Case Study in the Semiarid Region of North China

Groundwater is a valuable water source for drinking and irrigation purposes in semiarid regions. Groundwater pollution may affect human health if it is not pretreated and provided for human use. This study investigated the hydrochemical characteristics driving groundwater quality for drinking and irrigation purposes and potential human health risks in the Xinzhou Basin, Shanxi Province, North China. More specifically, we first investigated hydrochemical characteristics using a descriptive statistical analysis method. We then classified the hydrochemical types and analyzed the evolution mechanisms of groundwater using Piper and Gibbs diagrams. Finally, we appraised the groundwater quality for drinking and irrigation purposes using the entropy water quality index (EWQI). We assessed the associated human health risks for different age and sex groups through drinking intake and dermal contact pathways. Overall, we found that (1) Ca-HCO3 and Ca·Mg-HCO3 were the dominant hydrochemical types and were mainly governed by rock weathering and water–rock interactions. (2) Based on the EWQI classifications, 67.74% of the groundwater samples were classified as medium quality and acceptable for drinking purpose. According to the values of sodium adsorption ratio (SAR), residual sodium carbonate (RSC) and soluble sodium percentage (%Na), 90.32% of the samples were suitable for irrigation, while the remaining samples were unfit for irrigation because of the high salinity in the groundwater. (3) Some contaminants in the groundwater, such as NO3−, NO2− and F−, exceeded the standard limits and may cause potential risks to human health. Our work presented in this paper could establish reasonable management strategies for sustainable groundwater quality protection to protect public health.