Geochemical evaluation of fluoride contamination in groundwater from Shanmuganadhi River basin, South India: implication on human health

Pan India fluoride hazard assessment in groundwater

Fluoride (F¯) contamination in groundwater in India has gained global attention due to human health hazards. India's hydrogeological heterogeneity, spatio-temporal variability of F¯, and health hazards due to geogenic and geo-environmental control pose unique challenges. Addressing these with only a single region-specific study is not possible. Therefore, this study provides an in-depth, holistic analysis of pan India F¯ contamination, controlling factors, and health hazards using a coupled advanced geostatistical and geospatial approach. Alarming F¯ contaminations are identified in Rajasthan, Telangana, Western Andhra Pradesh, Eastern Karnataka, Parts of Haryana, Gujarat, Madhya Pradesh, Tamil Nadu, Uttar Pradesh, Jharkhand, Bihar, and Chhattisgarh. Probabilistic health-risk evaluation using hot-spot, showed similar spatio-temporal distribution of F¯ contamination. The hazard quotient (HQ) for high F¯ shows more adversity to children than adults. Nationally, 8.65 % and 7.10 % of pre- and post-monsoon sites exceed the recommended safe limit of 1.50 mg/L. The highest average F¯ concentration is in Rajasthan. Very high-risk skeletal fluorosis is possible at around ≤ 2 %, whereas dental caries due to deficiency in F¯ concentration is approximately 40 %. A decisive hierarchy of lithology, geomorphology, soils, and lineaments control are identified on F¯ contamination. Climatic conditions are pivotal in governing all these controlling variables. Thus, in arid/semi-arid dry western regions, F¯ contamination is much higher than in the humid areas. Integration of strengths, weaknesses, opportunities, and threats (SWOT) analysis with the results can aid policymakers and government authorities in achieving sustainable remedial measures for future adaptability.

Prediction of arsenic and fluoride in groundwater of the North China Plain using enhanced stacking ensemble learning

Chronic exposure to elevated geogenic arsenic (As) and fluoride (F-) concentrations in groundwater poses a significant global health risk. In regions around the world where regular groundwater quality assessments are limited, the presence of harmful levels of As and F- in shallow groundwater extracted from specific wells remains uncertain. This study utilized an enhanced stacking ensemble learning model to predict the distributions of As and F- in shallow groundwater based on 4,393 available datasets of observed concentrations and forty relevant environmental factors. The enhanced model was obtained by fusing well-suited Extreme Gradient Boosting, Random Forest, and Support Vector Machine as the base learners and a structurally simple Linear Discriminant Analysis as the meta-learner. The model precisely captured the patchy distributions of groundwater As and F- with an AUC value of 0.836 and 0.853, respectively. The findings revealed that 9.0% of the study area was characterized by a high As risk in shallow groundwater, while 21.2% was at high F- risk identified as having a high risk of fluoride contamination. About 0.2% of the study area shows elevated levels of both of them. The affected populations are estimated at approximately 7.61 million, 34.1 million, and 0.2 million, respectively. Furthermore, sedimentary environment exerted the greatest influence on distribution of groundwater As, with human activities and climate following closely behind at 29.5%, 28.1%, and 21.9%, respectively. Likewise, sedimentary environment was the primary factor affecting groundwater F- distribution, followed by hydrogeology and soil physicochemical properties, contributing 27.8%, 24.0%, and 23.3%, respectively. This study contributed to the identification of health risks associated with shallow groundwater As and F-, and provided insights into evaluating health risks in regions with limited samples.

Cerium-based metal-organic-frameworks with ligand tuning of the microstructures for fluoride adsorption: linear and nonlinear kinetic and isotherm adsorption models

We present the synthesis and characterisation of three Ce-based metal-organic frameworks (Ce-MOFs) using fumaric acid (Fu), terephthalic acid (BDC), and trimesic acid (H3BTC) as linkers. The use of different linkers influenced the size of the MOF particles, surface area, crystallinity, and microporous structure. The successful implementation of Ce-Fu, Ce-BDC, and Ce-H3BTC MOFs for fluoride ion removal from wastewater was carried out, in which Ce-Fu MOFs exhibited a maximum adsorption capacity (AC) of 64.2 mg g-1. The study also reveals that the use of ultrasound as a mediator for adsorption study over conventional method gives rapid adsorption rate, in which 85% of the fluoride uptake took place just in 10 min and achieved maximum AC in 30 min. The kinetics data were most accurately explained by the pseudo-second-order model (PSO). The existence of co-ions such as NO3-, Cl-, HCO3-, SO42-, Br-, CO32-, and PO43- has a substantial effect on fluoride removal. The mechanism between the fluoride ions and the MOF surface took place via the electrostatic force and the ion exchange process, confirmed using X-ray photoelectron spectroscopy (XPS) and delsa nano. The material is sustained its relatively higher F- ions removal efficiency up to the five cycles. This research might help in the development of novel microporous Ce-based MOFs since it possesses a highly stable crystalline structure in water, suggesting a promising role in aqueous applications.

Assessment of groundwater fluoride and human health effects in a hard rock province of south India: Implications from Pollution Index Model (PIM) and Geographical Information System (GIS) techniques

This research examines whether the groundwater in the Sivakasi Region of South India is suitable for consumption, and assesses the possible health hazards for various age demographics including infants, children, teenagers, and adults. A total of 77 groundwater samples were gathered, covering a total area of 580 km2 and analyzed for major and minor ions. The hydrogen ion concentration (pH) of the samples indicates neutral to marginally alkaline. The total dissolved solids (TDS) fluctuate from 255 to 2701 mg/l and electrical conductivity varies from 364 to 3540 µS/cm. A wide range of fluoride concentration was detected (0.1 to 3.2 mg/l) with nearly 38% groundwater samples surpassing the proposed limit (1.5 mg/l) suggested by the World Health Organization in 2017. Gibbs plot analysis suggested that most of the samples were influenced by geogenic factors, primarily rock weathering in this region. Correlation analysis showed that most of the samples were impacted by both natural and human sources. The pollution index of groundwater (PIG) fluctuated from 0.67 to 2.60 with approximately 30% and 53% of samples falling into insignificant and low pollution categories, respectively. Furthermore, 10% and 5% of total samples were characterized as moderate and high pollution levels, and 2% as very high pollution category. Spatial analysis using GIS revealed that 440.63 km2 were within safe fluoride levels according to the WHO standards, while 139.32 km2 were identified as risk zone. The principal component analysis (PCA1) showed strong positive loadings on EC (0.994), TDS (0.905), Mg2+ (0.910), Cl- (0.903) and HCO3- (0.923) indicating rock water interaction. PCA2 accounts the high positive factor loading on HCO3- (0.864) indicating ion exchange and mineral leaching. The PCA1 and PCA2 indicated that variables such as mineral leaching and rock water interaction are the major mechanisms contributing to the chemical signatures in groundwater, which may support for the elevated fluoride levels in certain areas. Risk assessments, including Hazard Quotient results showed that 71%, 61% 38%, and 34% of groundwater samples exceeded the permissible THI limit (THI > 1) for infants, children, teenagers, and adults, respectively. The study recommends implementing measures such as denitrification, defluorination, rainwater harvesting, and improved sanitation infrastructure to enhance the health conditions in the study region. Additionally, it suggests introducing educational programs in rural areas to create awareness about the health dangers due to consumption of water with high fluoride levels.

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.

Evaluating hydrogeochemical controls and noncarcinogenic health risk assessment of fluoride concentration in groundwater of Palacode and Pennagaram taluk, Dharmapuri district, Tamil Nadu, India

This study focuses on assessing hydrochemical characteristics and non-carcinogenic health risks associated with fluoride contamination in groundwater within the Palacode and Pennagaram taluks of Dharmapuri district. The presence of fluoride in drinking water is a significant concern due to its potential health impacts on both adults and children. We collected a total of 158 groundwater samples during both the summer (SUM) and monsoon (MON) seasons in 2021 to evaluate the suitability of water for drinking purposes in this region. During the SUM season, groundwater exhibits alkaline characteristics with a pH range of 6.70 to 8.73 and a mean value of 7.43, while the MON season falls within the neutral pH range with values ranging from 6.60 to 7.60 and a mean of 7.00. Hydrogeochemical analysis reveals that fluoride concentrations during the SUM season range from 0.13 to 2.7 mg/L, with a mean of 0.82 mg/L, whereas the MON season exhibits concentrations ranging from 0.08 to 1.6 mg/L, with a mean of 0.5 mg/L. Spatial distribution analysis indicates a gradual increase in fluoride concentrations from the northeast to the central and southern parts of the study area during both seasons. Residents in these areas have been exposed to high fluoride levels for an extended period, leading to health issues related to fluorosis. Our hydrogeochemical analysis attributes fluoride dominance to the Cl--SO42- water type in both seasons. Furthermore, the relationship between fluoride and pH, HCO3-, Ca2+, and Na+ suggests the influence of geological factors in fluoride dissolution under alkaline conditions, while a reverse cation exchange process and increasing calcium concentration inhibit fluoride concentration. Saturation indices indicate that the unsaturated state of gypsum dissolution contributes to elevated fluoride levels in groundwater. Additionally, Gibbs plots highlight rock-water interactions as a significant factor influencing groundwater chemistry in the study area. Based on our hazard quotient (HQ) investigation, children are at a higher risk during both seasons compared to adults, with the central and northern regions showing alarming HQ values. These findings underscore the urgent need for enhanced groundwater quality monitoring and a comprehensive assessment of health risks, providing valuable insights for groundwater safety management in vulnerable areas of this region.

Probabilistic modelling is superior to deterministic approaches in the human health risk assessment: an example from a tribal stretch in central India

This case drew national attention in 2018. About 100 people died and more than 300 hospitalized in a span of few years in a village of 1200 people in a tribal stretch in central India. Medical teams visiting the area reported severe renal failure and blamed the local eating and drinking habits as causative factors. This human health assessment based on geochemical investigations finds nitrate (NO3-) and fluoride (F-) pollution as well in village's groundwater. Both deterministic and probabilistic techniques are employed to decipher the contamination pathways and extent of contamination. Source apportionments of NO3- and F- and their relationship with other ions in groundwater are carried out through chemometric modelling. Latent factors controlling the hydrogeochemistry of groundwater too are explored. While hazard quotients ([Formula: see text]) of the chemical parameters ([Formula: see text] and [Formula: see text]) identify ingestion as the prominent pathway, the calculated risk certainty levels (RCL) of the hazard index (HI) values above unity are compared between the deterministic and probabilistic approaches. Deterministic model overestimates the HI values and magnify the contamination problems. Probabilistic model gives realistic results that stand at infants ([Formula: see text] = 34.03%, [Formula: see text] = 24.17%) > children ([Formula: see text] = 23.01%, [Formula: see text] = 10.56%) > teens ([Formula: see text] = 13.17%, [Formula: see text] = 2.00%) > adults ([Formula: see text] = 11.62%, [Formula: see text] = 1.25%). Geochemically, about 90% of the samples are controlled by rock-water interaction with Ca2+-Mg2+-HCO3- (~ 56%) as the dominant hydrochemical facies. Chemometric modelling confirms Ca2+, Mg2+, HCO3-, F-, and SO42- to originate from geogenic sources, Cl- and NO3- from anthropogenic inputs and Na+ and K+ from mixed factors. The area needs treated groundwater for human consumption.

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.

The assessment of groundwater quality through the water quality and nitrate pollution indexes in northern Türkiye

Groundwater is contaminated by anthropogenic factors such as industry, domestic waste, and excessive fertilizers. Groundwater samples, which were obtained from 50 different wells in July 2020, were used in this study. Thirteen hydrochemical properties, including electrical conductivity (EC), pH, total dissolved solids (TDS), total hardness (TH), nitrate NO3-, anions, and cations were analyzed. Also, types of groundwater were investigated via the Piper diagram. The groundwater was also evaluated for irrigation suitability using the sodium percentage (Na%), sodium adsorption ratio (SAR), Kelly's index (KI), residual sodium carbonate (RSC), potential salinity, magnesium hazard (MR), and permeability index (PI). The samples were assessed for drinking the suitability using the water quality index (WQI) and the nitrate pollution index (NPI). Geographic information systems (GIS) were used to create spatial distribution maps of irrigation water quality indices, WQI, and NPI values. The results of major cations varied sodium 28.69-211.80 mg/L, calcium 78.74-258.89 magnesium 27.78-161.30 mg/L, and potasium 0.10-3.57 mg/L. The results from the study area showed that 62.70 of EC, 32.40% of PI, 20.09% of RSC, 51.55% of PS, and 49.36% of MR were inappropriate for irrigation purposes. The NPI data ranged from - 0.75 to 9.65, and 21.06% of the study areas were heavily polluted. The WQI showed that almost 62.90% of the experimental area was categorized as poor, very poor, and inappropriate for drinking water purposes, whereas 37.10% of the areas were categorized as good and excellent.

A critical application of different methods for the vulnerability assessment of shallow aquifers in Zhengzhou City

Groundwater vulnerability can partially reflect the possibility of groundwater contamination, which is crucial for ensuring human health and a good ecological environment. The current study seeks to assess the groundwater vulnerability of Zhengzhou City by adopting an amended version of the traditional DRASTIC model, i.e., the DRASTICL model, which incorporates land use type indicators. More specifically, the AHP-DRASTICL, entropy-DRASTICL, and AE-DRASTICL models were established by optimizing weights using the analytic hierarchy process (AHP) and entropy weight method. The evaluation results for these five models were divided into five levels: very low, low, medium, high, and very high. Using Spearman's rank correlation coefficient, the nitrate concentration was used to verify the groundwater vulnerability assessment results. The AE-DRASTICL model was found to perform the best, with a Spearman correlation coefficient of 0.78. However, the AHP and entropy weight method effectively improved the accuracy of vulnerability assessment results, making it more suitable for the study area. This study provides important insights to inform the design of strategies to protect groundwater in Zhengzhou.

Spatial distribution, health risk assessment, and public perception of groundwater in Bahawalnagar, Punjab, Pakistan: a multivariate analysis

The current study investigated the hydrogeochemical behavior of groundwater quality attributes including arsenic (As) and their associated health risks in unexplored groundwater aquifers of Bahawalnagar, Punjab, Pakistan. The groundwater samples were collected from 40 colonies of Bahawalnagar city from electric/hand pumps, tube wells and turbines installed at varying depth (20 to > 100 m). The groundwater possessed the highest concentrations of PO₄ (0.5 mg/L), HCO₃ (425 mg/L), Cl (623 mg/L), NO₃ (136.68 mg/L) and SO₄ (749.7 mg/L) concentrations. There was no difference in concentration of As in shallow and deep aquifers. Interestingly, none of the water samples showed As concentration higher than the WHO limit of 10 µg/L for drinking water with groundwater As concentration spanning from 2.5 to 7.9 µg/L. The HQ values for As were less than 1 and there was no apparent non-carcinogenic risk from the long-term consumption of As contaminated water. The questionnaire survey indicated that 82% respondents believe that drinking water quality affects human health and 55% of respondents considered that groundwater in the area is not suitable for drinking. Survey results revealed that 29.11, 22.78, 17.08, 15.19, 7.59, 5.06 and 3.16% respondents/family members suffered from hepatitis, skin problems, diabetes, tuberculosis, kidney disorders, muscular weakness and gastro, respectively. However, the data cannot be correlated with As contamination and disease burden in the local community and it can be anticipated that the groundwater may contain other potentially toxic ions that are deteriorating the water quality and compromising human health. The hydrogeochemical analysis revealed Na-Cl/SO₄, K-SO₄ type of groundwater suggesting the potential role of sulfate containing minerals in releasing As in the groundwater aquifers.

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.

Hydrogeochemical characteristics of groundwater uses for agricultural and drinking and groundwater quality of pollution index in the western part of Telangana, South India

A total of fifty groundwater samples were collected in the western part of Nizamabad district, Telangana State, India. The results obtained were compared with the IS 10500 standard, which shows more than 80% of the samples are unfit for drinking purposes. The results were also analyzed to know the irrigation suitability, where about 80% of the samples are fit for agricultural use. For the major ions in groundwater quality for irrigation and drinking, contradictory locations exist which are majorly caused by geogenic (silicate weathering minerals) and anthropogenic (fertilizers, manure, and industrial effluents) sources. The hydrochemical facies of CaCl and mixed CaMgCl and NaCl water types were dominant in pre- and post-monsoon seasons. The spatial distribution diagrams of the major ions were high concentration in northern areas followed by western and south-western portions. As per the groundwater quality of pollution index (GQPI), most of the study region (62%) comes under the low contamination zone and the rest (38%) under the moderate to unacceptable zone. Factor analysis reveals that the study region is predominant of weathering, ion exchange, and anthropogenic inputs of major contamination of groundwater quality.

Geochemical characterization and health risk assessment in two diversified environmental settings (Southern Italy)

An integrated approach using chemical and microbial indicators has been tested in two different sites of the Campania Plain (Southern Italy) with different land use covering and different hydrogeological features in order: (1) to define the water-rock interaction processes, (2) to differentiate sources of pollution in a detailed way (3) to evaluate the degree of water quality in the studied alluvial aquifer and (4) to identify the most worrying elements for human's health. Groundwater have showed a HCO₃-Ca signature for both investigated sites, and a progressive enrichment in alkali ions has been highlighted moving from the boundary of the plain toward the coastal areas, due to groundwater interaction with volcanic rocks along the flow path. The application of the Factor Analysis allowed to identify different sources of pollution, which were attributed to (a) leaks in the sewer system for the Agro-Aversano Area and also the spreading of manure as fertilizers in agricultural activities for the Caiazzo Plain. Furthermore, it has been highlighted that the use of major elements, trace elements and microbiological indicators, allows to accurately differentiate contamination processes in progress. In fact, from the results of the Factor Analysis applied in the Agro-Aversano area, no significant statistically relationships between major elements and microbiological indicators of fecal contamination were highlighted, unlike the Caiazzo plain where statistically significant correlations have been found between major and trace elements and microbiological indicators. The use of a Groundwater Quality Index has shown general poor water quality for the majority of analyzed samples due to the high amount of Nitrate and Fecal indicators. The use of a Health Risk Assessment highlighted that Nitrate coupled with Fluoride represent the most important concern for human health compared to the all investigated parameters in both sites.

Fluoride contamination, spatial variation, and health risk assessment of groundwater using GIS: a high-density survey sampling in Weifang City, North China

The present study, with the aid of GIS, utilizes high-density groundwater (GW) sampling data (1398 samples) to analyze the spatial variation characteristics of GW fluoride in Weifang City (WFC), and evaluate the health risks associated with drinking water routes. The concentration of fluoride in the GW of WFC is observed to be between 0.08 and 9.16 mg/L, with a mean value of 0.62 mg/L. The fluoride concentration of a total of 192 GW samples exceeded the limit of China's GW quality standards (1 mg/L), accounting for 14.74%. The GW fluoride concentration in most areas of WFC is less than 1 mg/L. However, the relatively high-value zones are mostly concentrated in the upper reaches of Wen River, the east of Shouguang, the southeast of Anqiu, the east of Qingzhou, the east of Fangzi, and the southeast and northwest of Gaomi. The hydrochemical types of GW in WFC are mostly HCO₃-Ca·Mg and SO₄·Cl-Ca·Mg, while GW samples with hydrochemical types HCO₃-Na and SO₄·Cl-Na are characterized by high fluoride content. The hydrochemical characteristics of GW in WFC are mostly dominated by rock weathering. In addition, the northern coastal plain is evidently influenced by seawater intrusion. The concentration of fluoride in GW is affected by the dissolution of fluorine-containing minerals, cation exchange, and alkaline environmental factors. The effect of GW by seawater intrusion and very high content of Na⁺ will decrease the fluoride content of the GW through cation exchange. Health risk assessment demonstrated that the mean values of non-carcinogenic hazard quotient (HQ) for infants, children, teenagers, and adults were 0.52, 0.35, 0.31, and 0.30, respectively. In addition, the distribution characteristics of GW fluoride in high health risk areas (HQ > 1) in WFC are further consistent with the spatial variation of GW fluoride content. Overall, the health risk distribution area of GW fluoride in WFC is decreasing in the following order: infants > children > teenagers > adults.

Rice Industry By-Products as Adsorbent Materials for Removing Fluoride and Arsenic from Drinking Water—A Review

In drinking water, high concentrations of fluoride and arsenic can have adverse effects on human health. Waste deriving from the rice industry (rice husk, rice straw, rice bran) can be promising adsorbent materials, because they are (i) produced in large quantities in many parts of the world, (ii) recoverable in a circular economy perspective, (iii) at low cost if compared to expensive conventional activated carbon, and (iv) easily manageable even in developing countries. For the removal of fluoride, rice husk and rice straw allowed to obtain adsorption capacities in the range of 7.9–15.2 mg/g. Using rice husk for arsenic adsorption, excellent results were achieved with adsorption capacities above 19 mg/g. The best results both for fluorides and arsenic (>50 mg/g) were found with metal- or chemical-modified rice straw and rice husk. Identifying the next steps of future research to ensure the upscaling of biochar from recovered by-products, it is fundamental to perform: (i) tests on real waters for multicomponent adsorption; (ii) experiments with pilot plants in continuous operation; (iii) cost analysis/real applicability of modification treatments such as metal coupling or chemical synthesis; (iv) more studies on the biochar stability and on its regeneration or recovery after use.

Exploring a variance decomposition approach integrated with the Monte Carlo method to evaluate groundwater fluoride exposure on the residents of a typical fluorosis endemic semi-arid tract of India

This study appraised the groundwater fluoride (F^-) endemicity and the exposure levels under the Central Tendency Exposure (CTE) condition and the Reasonable Maximum Exposure (RME) condition on the residents of the semi-arid parts of the Birbhum district of Peninsular India using a Variance Decomposition (Sobol Sensitivity Indices) approach combined with Monte Carlo Simulations. The study finds the national scale drinking water standard limit for F^- (1.5 mg L^-1) is inappropriate for the present survey area where F^- concentration in groundwater varied between 0.26 and 11.82 mg L^-1 and ~54.5% of the samples (N = 400) exceeded this limit. Therefore, estimated the optimum F^- concentration of 0.733 mg L^-1 for the region using the method recommended by the World Health Organization (WHO) to calculate the optimum F^- limit at a regional scale. The average value of F^- concentrations for this region (1.71 mg L^-1) is considerably higher than the estimated optimum concentration or even the maximum permissible limits recommended for the subtropical regions (0.5-0.7 mg L^-1). The exposure analysis revealed the infants and children as potentially vulnerable populations compared to adolescents and adults of the study area for CTE and RME scenarios. The multi-exposure pathways indicated oral intake as the main exposure pathway whereas exposure through dermal contact was insignificant for the residents of all age groups of this region. Based on the first, second and total order Sobol Sensitivity Indices, F^- concentration (C) in groundwater, the groundwater ingestion rate and their combined interaction are the greatest significant parameters for the oral exposure model whereas C and its interaction effects with the proportion of the skin surface area in contact with groundwater as the utmost sensitive variables for the dermal health risks assessment model. The present study insists the inhabitants to intake defluoridated groundwater.

Geochemical characterization and assessment of fluoride sources in groundwater of Siloam area, Limpopo Province, South Africa

Siloam’s groundwater is reportedly characterized by high fluoride. In response to the reported high incidence of dental fluorosis in the area, sources of elevated fluoride in the groundwater were investigated. Total fluoride (TF) was determined using Ion Chromatograph and Fluoride Ion Selective Electrode. The mineral composition of rocks and soils were determined using X-ray Fluorescence and X-ray diffraction, respectively. Results revealed that groundwater fluoride concentration ranged from 3.92 to 4.95 mg/L. Na-Cl water type was found to be dominant in the water samples. TF content of the rocks and soils ranged from 10 to 2000 mg/L. Leachates were obtained by making a slurry from the samples at a predetermined temperature and time. TF in leachates ranged between 0.27 and 14.88 mg/L and 0.05 to 10.40 mg/L at induced, and non-induced temperatures, respectively. The possible source of fluoride has been previously inferred to be caused by fluorite minerals occurring at greater depth. However, this study proves that fluoride decreases with depth and the elevated fluoride in the groundwater is caused by smectite-kaolinite clay, muscovite and chlorite minerals abundant in the area. Geothermal temperature exhibited by the groundwater in the area is a major factor enhancing the release of fluoride from the clay materials.

Hydrogeochemical evaluation, suitability, and health risk assessment of groundwater in the watershed of Godavari basin, Maharashtra, Central India

In this investigation, the geochemical progression of a total of 31 groundwater samples of pre-monsoon season was assessed with categorization based on entropy weight water quality index and risk assessment on public health in the semi-arid area of Godavari basin, Maharashtra, Central India. Graphically, the major groundwater types identified were Ca-HCO₃, mixed Ca-Mg-Cl, and mixed Ca-Na-HCO₃. Based on [Mg²⁺/Na⁺] with [Ca²⁺/Na⁺] and [HCO₃^-/Na⁺] with [Ca²⁺/Na⁺] plots, carbonate and silicate weathering were identified as a major geochemical process governing groundwater chemistry. The presence of reverse ion exchange process was authenticated by (Ca²⁺ + Mg²⁺) vs. (HCO₃^- + SO₄^2-) and Na⁺ + K⁺-Cl^- vs. (Ca²⁺ + Mg²⁺)-(HCO₃^- + SO₄^2-) plots. The saturation index values for calcite and dolomite showed that these minerals were in dissolution state. The dissolution of gypsum, dolomite, and anhydrite increased Ca²⁺ load in groundwater which accelerated the precipitation of calcite. The high toxic level of NO₃^- (> 45 mg/L) was identified in 64.5% of the 31 groundwater samples, whereas F^- concentration exceeded the threshold value in 12.9% of samples. Based on the entropy weight water quality index values, 70% of the samples were found to have moderate quality for drinking. In addition, health risk evaluation showed that the total hazard, due to fluoride and nitrate through oral pathways, was much higher than that through the dermal pathway. Children were found to be at high risk due to the consumption of NO₃^- and F^- contaminated water. The calculated irrigation water quality index (IWQI) diverge from 7.4-89.2, expressing excellent to good quality for irrigation. Based on the irrigation water quality index, 90.3% of samples were found excellent for irrigation and 6.4% of good quality for irrigation. Authors recommend that continuous water quality monitoring programs along with effective management practices should be developed to avoid excessive extraction of groundwater.

Promoting artificial recharge to enhance groundwater potential in the lower Bhavani River basin of South India using geospatial techniques

The artificial recharge is an alternative technique to augment surface water and groundwater and for providing continuous supply of water to the demand regions. The scope of contemporary study helps in evaluation of groundwater potential zones and to find proper zones and sites for groundwater recharge using geospatial and multi-criteria decision analysis (MCDA) techniques. In this study, the pragmatic methodology was proposed for the implementation of water harvesting structures. The satellite and conventional datasets with field inferences were systematically processed to obtain various thematic information of the study area. The analytical hierarchical process (AHP) in geographical information system (GIS) was utilized to assign the geometric mean and the normalized weight for the individual features. Further, groundwater potential zones were identified, and they were categorized into four types viz. very high (523.58 km²), high (798.22 km²), moderate (646.04 km²) and low (456.66 km²). Nearly, 54.52% of the study area falls in the 'very high' to 'high' potential categories. The GIS-based Boolean logical method was also executed to identify suitable areas for creating recharge structures such as check dams (127.47 km²), percolation ponds (115.23 km²), flood and furrows (63.01 km²) and ditch and furrows (1046.31 km²). Based on the above results, 36 water harvesting structures were promoted to augment the groundwater resources of the basin. The highest priority was given to check dams (19 Nos), followed by percolation ponds (7 Nos), flood and furrows (5 Nos) and ditch and furrows (5 Nos). The suggested structures would improve the groundwater availability for agriculture and domestic purposes in the study area. Further, the outcomes could deliver a scientific procedure to the decision makers and water scientists for effective water resources development and management planning. Overall, the integrated remote sensing, GIS and MCDA methods are an efficient and useful tool for planning and improving groundwater recharge in the basin scale.

Groundwater quality evolution based on geochemical modeling and aptness testing for ingestion using entropy water quality and total hazard indexes in an urban-industrial area (Tiruppur) of Southern India

This study used geochemical modeling to understand the chemical evolution of groundwater, entropy water quality index to assess the aptness of groundwater for human consumption, and total hazard index to determine the possible non-carcinogenic risks among children, women, and men in an urban-industrial area (Tiruppur region) of southern India. For the above purposes, 40 groundwater samples were collected from tube and dug wells, and they were tested for various physicochemical parameters. Fluoride and nitrate levels ranged from 0.10 to 2.70 mg/l and 10 to 290 mg/l, respectively. Nearly, 50% of the fluoride samples and 58% of the nitrate samples exceeded the WHO limits of 1.5 and 45 mg/l, respectively. The majority of the groundwater samples (22.5%) represented Ca²⁺-Na⁺-Cl^- water type while the remaining samples exhibited mixed water types. Approximately, 85% of the samples indicated high levels of salinization since they had Revelle index > 0.5 meq/l. The saturation index (SI) revealed that mineral weathering; dissolution of halite, gypsum, and anhydrite; and precipitation of calcite and dolomite contributed to groundwater chemistry. Based on the entropy water quality index (EWQI), none of the groundwater samples was characterized as excellent or good water quality while 57.5% of the samples had medium water quality, and 32.5% and 10% of the samples exhibited poor and extremely poor water qualities, respectively. The last two categories are designated as unfit for consumption. The cumulative health risk (nitrate and fluoride together) ranged from 0.97 to 11.16 for children, 0.60 to 10.54 for women, and 0.39 to 6.92 for men. These values represent health risks among 88%, 80%, and 73% of the groundwater samples for children, women, and men, respectively. Therefore, proper measures should to be done to reduce the health risks associated with high nitrate and fluoride in the groundwater of the study area, which is used for drinking purposes.

Appraisal of subsurface hydrogeochemical processes in a geologically heterogeneous semi-arid region of south India based on mass transfer and fuzzy comprehensive modeling

The main aim of the present study was to examine the quality of the groundwater and decipher the sources of groundwater fluoride through mass balance modeling based on fluoride exposure in a geologically heterogeneous semi-arid region of southern India. This was achieved by hydrogeochemical analysis, graphical methods, and mass transfer modeling approaches. Fuzzy comprehensive technique was applied to evaluate the quality of groundwater for groundwater management. In this regard, 61 groundwater samples were obtained from open wells and bore wells and analyzed for different physicochemical parameters. The major cation and anion abundances follow the order Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ and Cl^- > HCO₃^- > SO₄^2- > NO₃^- > PO₄^3-. About 88.4% and 34.4% of the total water samples were dominated with Na⁺ and Cl^- ions in this region, respectively. The fluoride level in groundwater ranged from 0.10 to 3.30 mg/l with a mean value of 1.04 mg/l. Nearly 25% of the groundwater samples collected from 15 villages showed fluoride concentrations exceeding the maximum permissible limit of 1.5 mg/l as per the World Health Organization recommendations for human intake. More than 85% of the samples fell under strong acid (Cl^- and SO₄^2-) type. The amount of groundwater salinization in this region was 70.5% since the Revelle index (RI) was excess in the groundwater samples (RI > 0.5 meq/l). Silicate weathering, cation exchange, and gypsum dissolution were the dominant geogenic processes in the aquifer system influencing groundwater chemistry and nullified the possibility of carbonate dissolution. Saturation indices revealed the contribution of sequestration of CaCO₃ in F^- enrichment. Total dissolved solids showed strong positive correlations with Na⁺, Ca²⁺, Mg²⁺, Cl^-, SO₄^2- and NO^3- indicating the contribution of anthropogenic inputs to groundwater chemistry in addition to geogenic sources. The results of the fuzzy comprehensive method indicated that 33% of the groundwater samples fell under fair water type, 2% and 11% of the samples fell under poor and very poor quality water types, respectively. Therefore, this work will be helpful for the decision-makers to plan for the sustainable management of groundwater resources.

Applications of geochemical and multivariate statistical approaches for the evaluation of groundwater quality and human health risks in a semi-arid region of eastern Maharashtra, India

A qualitative approach, including geochemical and multivariate statistical approaches, is applied to evaluate the groundwater quality and human health risk, based on analytical data of 72 samples collected from a semi-arid region of eastern Maharashtra, India. The shifting of hydrochemical type from Ca²⁺-Na⁺-[Formula: see text] to Na⁺-Ca²⁺-Cl^- type was observed along different flow paths. The main controlling processes observed from the chemical characterisation of the groundwater are water-rock interactions, dedolomitisation and reverse ion exchange. Simulation analysis (mass transfer) exposes the dissolution of dolomite, gypsum, halite, k-feldspar and CO₂ down the simulated pathways. Around 77% of the total variance was observed from the first three principal component analyses. The high positive loadings of EC, TDS, Na⁺, K⁺, Ca²⁺, Cl^-, [Formula: see text] and [Formula: see text] of PC1 revealed silicate weathering and reverse ion exchange followed by human activities as the contamination sources. The sources identified for high positive loadings on [Formula: see text] and [Formula: see text] of PC2 are soil CO₂ and human activities. The high loadings of pH and F^- in PC3 revealed fluorite dissolution and calcite precipitation. The human health risk calculated for [Formula: see text] revealed that 58% and 44% of the total groundwater samples surpassed the tolerance limit for non-carcinogenic risk of 1.0 in children and adults. The human health risk assessment for fluoride showed high hazard index values in 40% and 23% of the total groundwater samples for children and adults, respectively. The study suggests some management measures for protection of groundwater resources.

Poor groundwater quality and high potential health risks in the Datong Basin, northern China: research from published data

Datong Basin in China is a typical arid-semiarid inland basin, with high levels and wide distributions of arsenic (As), fluoride (F^-), and iodine (I). To better understand the presence of low-quality groundwater in Datong Basin and assess the health risks for local residents, groundwater samples were collected from the shallow aquifer and in medium-deep groundwater and analyzed for As, F^-, I, and nitrate (NO₃^-). Maxima of 1932 μg/L for As, 80.89 mg/L for F^-, 2300 μg/L for I, and 3854.74 mg/L for NO₃^- were detected in shallow groundwater, which greatly exceeded the WHO limits for drinking purpose. High-As groundwater was present in both shallow and medium-deep aquifers. High-F^- and high-NO₃^- groundwater was widely distributed in the shallow aquifer, and high-I groundwater was mainly present in the medium-deep aquifers. Poor-quality groundwater in the Datong Basin is mainly caused by local geological and climatic conditions, which are characterized by strong evaporation, active water-rock interactions, thick lacustrine sediment, low groundwater flow rate, and reducing and weak alkaline environments. However, groundwater quality was further impacted by agricultural activities in some areas, as shallow groundwater was also polluted by nitrate. Datong Basin inhabitants face high health risk caused by high concentrations of As, F^-, I, and NO₃^-. The mean noncarcinogenic risk values (HQ_total) were 18.40 for children, 10.94 for adult females, and 9.47 for adult males due to exposure to contaminants in shallow groundwater; and 13.76 for children, 8.18 for adult females, and 7.08 for adult males because of exposure to medium-deep groundwater. Further, the carcinogenic risks (CR) caused by exposure to As were very high for local inhabitants, with the mean and median CR values of 4.20×10^-3 and 4.13×10^-4 in shallow groundwater and 3.44×10^-3 and 1.71×10^-4 in medium-deep groundwater, respectively.

Potential risk assessment of groundwater to address the agricultural and domestic challenges in Ordos Basin

The safety of groundwater has been a great concern for irrigation and drinking purposes in recent decades due to the increasing impacts of anthropogenic activities. There are several standards to evaluate the groundwater quality for different utilization purposes. In this paper, 804 samples covering the entire Ordos Basin across five provinces were used to evaluate the irrigation suitability and human health risks. The results showed that the sequence of cationic concentration was Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ > NH₄ ⁺, and the anion concentration was HCO₃ ^- > SO₄ ^2- > Cl^- > NO₃ ^- > F^- > NO₂ ^-. For drinking purposes, TDS, Na⁺, SO₄ ^2-, F^-, TH and NO₃ ^- exceed seriously the regulated standard in the study area. For irrigating purposes, 80% of the water in the study area belongs to "good water" according to the evaluation of salinity and alkalinity. Saline water which is not suitable for irrigation accounts for about 9%. High health risks of fluoride ions are mainly observed to the samples representing the western part of the study area, while the health risks of nitrates spread throughout the study area. Health risk is not only related to location, but also varies with age, and it is found that children suffer more threats than adults.

Chemical weathering and atmospheric carbon dioxide (CO2) consumption in Shanmuganadhi, South India: evidences from groundwater geochemistry

Chemical weathering in a groundwater basin is a key to understanding global climate change for a long-term scale due to its association with carbon sequestration. The present study aims to characterize and to quantify silicate weathering rate (SWR), carbon dioxide consumption rate and carbonate weathering rate (CWR) in hard rock terrain aided by major ion chemistry. The proposed study area Shanmuganadhi is marked with superior rainfall, oscillating temperature and runoff with litho-units encompassing charnockite and hornblende-biotite gneiss. Groundwater samples (n = 60) were collected from diverse locations and analysed for major chemical constituents. Groundwater geochemistry seems to be influenced by geochemical reactions combining dissolution and precipitation of solids, cation exchange and adsorption along with minor contribution from anthropogenic activities. The SWR calculated for charnockite and hornblende-biotite gneiss was 3.07 tons km^-2 year^-1 and 5.12 tons km^-2 year^-1, respectively. The calculated CWR of charnockite and hornblende-biotite gneiss was 0.079 tons km^-2 year^-1 and 0.74 tons km^-2 year^-1, respectively. The calculated CO₂ consumption rates via silicate weathering were 1.4 × 10³ mol km^-2 year^-1 for charnockite and 5.8 × 10³ mol km^-2 year^-1 for hornblende-biotite gneiss. Lithology, climate and relief were the key factors isolated to control weathering and CO₂ consumption rates.

Groundwater quality for potable and irrigation uses and associated health risk in southern part of Gu'an County, North China Plain

The study area is a part of the North China Plain, where groundwater is heavily abstracted for drinking and irrigation purposes. Groundwater quality is adversely affected due to rapid economic development and urbanization. Therefore, the purposes of this study were to evaluate the suitability of groundwater for drinking and irrigation purposes and to quantify the associated human health risks in the southern part of Gu'an County, North China Plain. The matter-element extension method based on entropy weight was used to evaluate the water quality for drinking, while sodium adsorption ratio, sodium percentage (%Na), residual sodium carbonate and magnesium hazard were used to evaluate the water quality for irrigation. Non-carcinogenic and carcinogenic health risks via different exposure ways were evaluated for different age groups. The study found that the quality of both deep and shallow groundwater in this area was generally suitable for drinking. Deep water quality has better quality than the shallow water. However, 8.70% and 73.92% of water samples pose non-carcinogenic health risks on adults and children, respectively. Children and adults are also at cancer risk due to Cr⁶⁺ and As in drinking groundwater in this area. The main responsible parameters for non-carcinogenic risk are Cr⁶⁺, F^- and Fe, and Cr⁶⁺ is also responsible for carcinogenic risk. These toxic elements are mainly from industries. Therefore, deterioration of groundwater quality can be prevented by strengthening the sewage management of various industries.

Carcinogenic and non-carcinogenic health risk of arsenic ingestion via drinking water in Langat River Basin, Malaysia

The prolonged persistence of toxic arsenic (As) in environment is due to its non-biodegradable characteristic. Meanwhile, several studies have reported higher concentrations of As in Langat River. However, it is the first study in Langat River Basin, Malaysia, that As concentrations in drinking water supply chain were determined simultaneously to predict the health risks of As ingestion. Water samples collected in 2015 from the four stages of drinking water supply chain were analysed for As concentration by inductively coupled plasma mass spectrometry. Determined As concentrations along with the time series data (2004-2015) were significantly within the maximum limit 0.01 mg/L of drinking water quality standard set by World Health Organization. The predicted As concentration by auto-regression moving average was 3.45E-03 mg/L in 2020 at 95% level based on time series data including climatic control variables. Long-term As ingestion via household filtration water at Langat Basin showed no potential lifetime cancer risk (LCR) 9.7E-06 (t = 6.68; p = 3.37E-08) as well as non-carcinogenic hazard quotient (HQ) 4.8E-02 (t = 6.68; p = 3.37E-08) risk at 95% level. However, the changing landscape, ex-mining ponds and extensive use of pesticides for palm oil plantation at Langat Basin are considered as the major sources of increased As concentration in Langat River. Therefore, a two-layer water filtration system at Langat Basin should be introduced to accelerate the achievement of sustainable development goal of getting safe drinking water supply.

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

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

Health risks associated with fluoride intake from rural drinking water supply and inverse mass balance modeling to decipher hydrogeochemical processes in Vattamalaikarai River basin, South India

Preliminary investigation reveals that fluorosis is reported due to the continuous intake of fluoride-rich groundwater in Vattamalikarai River basin, Tamil Nadu, India. A detailed study was attempted for evaluating the health risks associated with the intake of fluoride-rich groundwater supplied to the rural community. Groundwater samples were collected from 60 and 58 dug and tube wells during winter and southwest (SW) monsoon seasons respectively. The samples were analyzed for the determination of fluoride and other chemical parameters to examine the fitness for drinking water. Spatio-temporal variation maps reveal that fluoride concentration is high during SW monsoon season when compared with the winter season in this region. The fluoride bearing minerals present in hornblende-biotite gneiss and charnockite rock formations leached into the groundwater during rock-water interaction. To understand the subsurface hydrogeochemical reactions, inverse mass balance model was developed using NETPATH code. The model output indicates that calcite dilution, silicate (hornblende and biotite) weathering, ion exchange (Ca/Na and Mg/Na) and illite precipitation are the dominant processes controlling the groundwater chemistry along the flow paths. Non-carcinogenic risks to children and adults (women and men) were evaluated by working out intake exposure of groundwater. Hazard quotient (HQ) based on fluoride intake was calculated for children and adults. It varied from 0.08 to 2.21 with an average of 1.07 for adults. For children, it varied from 0.01 to 2.99 with the mean of 1.44. About 78%, 69% and 61% of the samples fall under the risk category for children, women and men during winter season. However, more number of samples possessed health risks (83% of samples for children, 73% of samples for women and 64% of samples for men) during SW monsoon season.

Revealing drinking water quality issues and possible health risks based on water quality index (WQI) method in the Shanmuganadhi River basin of South India

The aim of the study is to address the issues and associated health risks due to consumption of high-fluoride water supplied for drinking in a rural part of Shanmuganadhi River basin, Tamil Nadu, India. In this study, 61 groundwater samples were gathered from various tube and open wells and analysed for fluoride and other physicochemical parameters. The abundance of cations is Na⁺ > Ca²⁺ > Mg²⁺ > K⁺, and that of anions is HCO₃^- > SO₄^2- > Cl^- > F^-. The fluoride concentration in drinking groundwater varied from 0.10 to 3.3 mg/l. According to the WHO standards, about 26% of the samples were unfit for drinking requirements (16 out of 61 samples) Water quality index (WQI) method was adopted to categorize the water into different classes to understand its suitability for drinking requirements. WQI signified that nearly 52% of the samples denoted poor, very poor and not suitable categories, whereas 48% of samples denoted good and excellent categories for consumption. Health risks associated with high-fluoride drinking water were assessed for various age groups of inhabitants such as children, teens and adults. The hazard quotient estimated based on the oral intake ranged from 0.00E+00 to 5.50E+00, from 0.00E+00 to 4.22E+00 and from 0.00E+00 to 3.45E+00 for children, teens and adults, respectively. It suggested that the health risks are associated with 75%, 59% and 43% of samples, respectively, among children, teens and adults. Therefore, children are more inclined towards risk than teens and adults in this region based on the intake of fluoride-rich drinking water. To improve the present scenario, groundwater should be either treated before drinking water supply or must be artificially recharged to lower the concentration of ions.

Non-carcinogenic health risk assessment with source identification of nitrate and fluoride polluted groundwater of Wardha sub-basin, central India

In order to understand the pollution status of groundwater with geochemical evolution and appraisal of its probable public health risk due to nitrate (NO₃^-) and fluoride (F^-), a total of 93 groundwater samples were collected during pre-monsoon (May) period from Wardha sub-basin, central India. By employing Piper plot, transition from Ca-HCO₃ type water (recharge waters) to Na-Cl (saline water) type water through mixed Ca-Na-HCO₃, mixed Ca-Mg-Cl (reverse ion exchange waters) and Ca-Cl types (leachate waters), were observed. The Geogenic processes such as silicate, dolomite, halite and carbonate weathering along with calcite precipitation and ion exchange process were identified as major controlling factors for evolution and alteration of groundwater chemistry. The Saturation index highlighted that the groundwater in the area is oversaturated with respect to the mineral calcite and dolomite, and under saturated with gypsum, fluorite and halite. The high NO₃^- and F^- concentration overpassing the permissible limit were found in 54.8% and 18.5% of samples. The plot of F^- with Na⁺/Ca²⁺, Na⁺/Mg²⁺ and F^-/Cl^- established fluoride bearing rock weathering is responsible for F^- contamination. Based on the cluster analysis, the groundwater was grouped into Cluster-I Ca-Na-HCO₃ type (61.3%) and Cluster-II Na-Ca-HCO₃-Cl type (30.1%). The total hazard index (HI) based on human health risk assessment (HHRA) model for cumulative NO₃^- and F^- toxicity through oral and dermal pathways were computed as 100%, 97.85% and 96.77% for children, female and male populations respectively. The HQ_(nitrate) > 1 through ingestion pathway were in 84.95%, 68.82% and 62.37%, and HQ_(fluoride) > 1 in 83.87%, 62.37% and 43.01% of the groundwater samples were recorded for children, female and male population respectively. The risk assessment study highlighted very high toxicity and severe health impact of ingestion of contaminated groundwater on public health.

Groundwater Pollution and Human Health Risks in an Industrialized Region of Southern India: Impacts of the COVID-19 Lockdown and the Monsoon Seasonal Cycles

Samples of groundwater were collected during a post-monsoon period (January) and a pre-monsoon period (May) in 2020 from 30 locations in the rapidly developing industrial and residential area of the Coimbatore region in southern India. These sampling periods coincided with times before and during the lockdown in industrial activity and reduced agricultural activity that occurred in the region due to the COVID-19 pandemic. This provided a unique opportunity to evaluate the effects of reduced anthropogenic activity on groundwater quality. Approximately 17% of the wells affected by high fluoride concentrations in the post-monsoon period returned to levels suitable for human consumption in samples collected in the pre-monsoon period. This was probably due to ion exchange processes, infiltration of rainwater during the seasonal monsoon that diluted concentrations of ions including geogenic fluoride, as well as a reduction in anthropogenic inputs during the lockdown. The total hazard index for fluoride in the post-monsoon samples calculated for children, adult women, and adult men indicated that 73%, 60%, and 50% of the groundwater samples, respectively, had fluoride levels higher than the permissible limit. In this study, nitrate pollution declined by 33.4% by the pre-monsoon period relative to the post-monsoon period. The chemical facies of groundwater reverted from the Na-HCO3-Cl and Na-Cl to the Ca-HCO3 type in pre-monsoon samples. Various geogenic indicators like molar ratios, inter-ionic relations along with graphical tools demonstrated that plagioclase mineral weathering, carbonate dissolution, reverse ion exchange, and anthropogenic inputs are influencing the groundwater chemistry of this region. These findings were further supported by the saturation index assessed for the post- and pre-monsoon samples. COVID-19 lockdown considerably reduced groundwater pollution by Na+, K+, Cl-, NO3¯, and F- ions due to shutdown of industries and reduced agricultural activities. Further groundwater quality improvement during lockdown period there is evidence that the COVID-19 lockdown by increased HCO3¯ ion concentration. Overall results illustrate the positive benefits to groundwater quality that could occur as a result of measures to control anthropogenic inputs of pollutants.

Potential Human Health Risks Due to Groundwater Fluoride Contamination: A Case Study Using Multi-techniques Approaches (GWQI, FPI, GIS, HHRA) in Bilate River Basin of Southern Main Ethiopian Rift, Ethiopia

The main focus of the present research was to examine the appropriateness of groundwater resources for drinking purposes in the Bilate River Basin of Southern Main Ethiopian Rift, Ethiopia. The groundwater quality index (GWQI), fluoride pollution index (FPI), and human health risk were used to examine the human health risk factors associated with the intake of high fluoride groundwater. For this purpose, 29 groundwater samples were collected from the existing wells and were analyzed for various physicochemical parameters. The dominant cation was Na⁺, followed by Ca²⁺, Mg²⁺, and K⁺. The dominant anion was HCO₃^-, followed by Cl^-, SO₄^2-, and F^-. The Gibbs plot shows that rock-water interactions are the dominant factor controlling the groundwater chemistry. By using the GWQI, the quality of groundwater samples was 31% excellent, 21% good, 31% poor, and 17% very poor. The fluoride concentration in groundwater ranges from 0.2 to 5.60 mg/L (mean, 2.10 mg/L). 59% (i.e., 17 wells) of the groundwater samples were not suitable for drinking, because they surpassed the drinking water quality limit of 1.5 mg/L. The remaining 41% (i.e., 12 wells) of the samples were suitable for drinking. The FPI indicates that 51.72% of the wells were highly polluted by fluoride. The noncarcinogenic health risk varies from 0.75 to 8.44 for children (83%), 0.34-3.84 for women (62%), and 0.27-3.01 for men (52%), which indicates that children are at higher health risk than women and men due to the physiological condition and the rates of ingestion.

Groundwater pollution: Occurrence, detection, and remediation of organic and inorganic pollutants

Groundwater pollution is a result of natural and anthropogenic activities. While the elevated levels of various inorganic constituents could be attributed to natural processes, such as geological weathering and aquifer characteristics, many times, anthropogenic activities also substantially pollute the groundwater. On the contrary, the occurrence of organic pollutants is primarily due to various anthropogenic activities. Extensive groundwater mining, the hydraulic connection between groundwater and other surface water bodies, and leaking underground buried infrastructure also contribute to groundwater pollution. Water resources are scarce commodities, and preserving groundwater quality is of critical concern. This paper documents instances of groundwater quality impact during the year 2019 due to both natural and anthropogenic activities throughout the world. PRACTITIONER POINTS: Groundwater pollution problems reported during the year 2019 are reviewed and documented. Occurrence of organic, inorganic, and microbial pollutants in groundwater is reported. Remediation technologies for selected inorganic pollutants are reviewed and documented.

Evaluation of non-carcinogenic risks due to fluoride and nitrate contaminations in a groundwater of an urban part (Coimbatore region) of south India

Groundwater quality investigations were carried out in one of the urban parts of south India for fluoride and nitrate contaminations, with special focus on human health risk assessment for the rapidly growing and increasingly industrialized Coimbatore City. Twenty-five groundwater samples were collected and analyzed for physico-chemical parameters (EC, pH, TDS, Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^-, SO₄^2-, HCO₃^-, PO₄^3-, NO₃^-, and F^-) and the piper diagram characterized 60% of them as Ca-Mg-Cl type. Analysis of fluoride (0.1 to 2.4 mg/l) shows that 32% of the groundwater samples contain F^- over the permissible limit, affecting a region of 122.10 km². Nitrate (0.1 to 148 mg/l) is over the permissible limit in 44% of the groundwater samples spread over an area of 429.43 km². The total hazard indices (THI) of non-carcinogenic risk for children (0.21 to 4.83), women (0.14 to 3.35), and men (0.12 to 2.90) shows some of the THI values are above the permissible limit of the US Environmental Protection Agency. The THI-based non-carcinogenic risks are 60%, 52%, and 48% for children, women, and men. This investigation suggests higher health risk for children and also recommends that proper management plan should be adopted to improve the drinking water quality in this region in order to avoid major health issues in the near future.