Fluoride Contamination In Groundwater Research Articles

Analyzing the Relationship of Fluoride Contamination with Groundwater Temperatures in India

In this paper an attempt has been made to address fluoride contamination in groundwater of India from 2000-2020, along with its relationship with depth to water level and hots springs. Fluoride pollution has been widespread throughout India for decades. Because groundwater is India's primary supply of drinking water, fluoride pollution is a concern. The permissible limit of fluoride concentration by WHO is 0.6-1.5 mg/l while Bureau of Indian Standards (BIS) prescribes rather less vibrant range of fluoride 1-1.5 mg/l. Present study is review of fluoride concentration change in groundwater in past two decades of Indian states as well as validating the relation of fluoride concentrations with Depth to water level. With increasing depth to water level, the fluoride concentration in groundwater increases in 80% of the cases reviewed. Concentration of fluoride in Guwahati which is near the Brahmaputra River is higher (0.18 – 6.88 mg/l) than Nalbari (0.02 – 1.56 mg/l) which is away from Brahmaputra. There has been no significant change in the fluoride concentration in cases of Yavatamal & Guntur district during past two decades. In Nagaur district of Rajasthan fluoride concentration decreased from 8.5-28 mg/l in (2010) to 0.5-8.5 mg/l in (2013). In Unnao district fluoride concentration has increased from 1.45-3.75 mg/l in (2002) to 0.8-13.9 mg/l (2010). In case of Bihar, the areas of hard rock formations, the fluoride concentration were found to be higher while in the alluvial formations there were lesser cases of fluoride exceeding the required limit which is 1.5 mg/l. In Vellore district of Tamil Nadu fluoride concentration was found to be increasing within a period of 1 year from 0.2 – 3 mg/l in (2017) to 2.15 – 4.91 mg/l in (2018).

Hydrochemical appraisal of fluoride contamination in groundwater and human health risk assessment at Isa Khel, Punjab, Pakistan

Fluoride contamination in the groundwater of Pakistan is widespread with serious potential health consequences. We determine the groundwater of Isa Khel Tehsil upper Indus plain for drinking purposes and fluoride contamination by collecting 236 water samples from the water supply schemes supplied with groundwater. Results show that the majority of the parameters exceed the standard concentration of potable water. The concentration of fluoride ranges from 0.02 to 5.35 mg/L with an average of 1.8 mg/L, and about 58.5% of the collected samples have higher fluoride concentration than the allowed limit for drinking purposes. Fluoride pollution index results show that about 48.73% of samples have a high level of risk, 41.95% samples of the study area have medium level and only 9.32% of the water samples show low level of fluoride contamination. The health risk assessment due to fluoride contamination was computed based on chronic daily intake (CDI) and hazard quotient (HQ). For adult’s variation in CDI and HQ ranges from 0.001–0.15 mg/kg/day and 0.001–2.55 respectively whereas in children it ranges from 0.001–0.29 mg/kg/day and 0.02–4.84. Health risk assessment parameters indicate that in the case of adults, about 40.25% of samples exceeded the maximum allowed value of hazard quotient i.e., HQ > 1, while for children, about 66.95% of samples have HQ > 1, which means that children are at higher risk than adults because of higher vulnerability to fluoride contamination in drinking water. Thus, there is a need for effective groundwater monitoring and management in the study region to safeguard residents from various illnesses associated with drinking water with varying fluoride concentrations. • Worldwide in groundwater, fluoride contamination is becoming a challenge. • Higher fluoride level in drinking water cases dental and skeletal fluorosis at alarming rate. • Evaluation of two hundred and thirty-six water samples indicate more than 50 percent samples not fit for drinking.

Spatial assessment of groundwater quality using CCME-WQI and hydrochemical indices: a case study from Talupula Mandal, Ananthapuramu district, South India

Fluoride contamination in groundwater is known from different villages of Talupula Mandal. In the present study in part of SoI toposheet no.57 J/8) of Ananthapuramu district, Andhra Pradesh, the magnitude and credible geogenic sources of the fluoride contamination in groundwater are studied. The present study carried out includes 30 groundwater samples covering an area of 442.89 sq km using (GIS) and (CCME-WQI) techniques. Problem is causally related to fluoride intoxication of human beings and animals through drinking waters. Well waters in the Talupula Mandal surrounded areas carry a high level of fluoride concentrations, much above the internationally decided safety limits. ‘Fluorosis’ is imminent as a result of prolonged intake of waters with more than 1 to 1.5 ppm of fluoride. Fluoride testing results of groundwater from borewell pump using fluoride test kit reveal that about 50% groundwater samples show fluoride concentration more than 4.0 mg/l, 30% samples show between 2.0 and 3.0 mg/l and 20% samples show fluoride concentration is 1–2 mg/l and above (BIS permissible limit: 1.5 mg/l). Agriculture indices are as follows: sodium percentage (Na%) was found between ranges (20.04–55.26), sodium absorption ratio varies from 0.86 to 3.91), Kelly's ratio (KR) varies from 0.22 to 1.16, residual sodium carbonate varies from − 4.12 to 20.66), permeability index (PI) varies from 39.00 to 82.28, magnesium hazard varies from 52.83 to 85.47, potential salinity varies from (0.71–3.15); results shown that the majority of the groundwater samples were suitable for irrigation uses. According to Gibbs’ ratio samples Gibbs ratio 1 (0.04–0.45) and Gibbs ratio 2 (0.44–0.81) fall in the rock dominance. Major ion compositions plotted on a Piper tri-linear diagram indicate that the water is of Ca-HCO3 type and is mixed Ca–Mg–Cl type. The present study indicates that the groundwater chemistry is mostly controlled by geogenic processes (weathering, dissolution and ion exchange) and some extent of anthropogenic activities.

Monitoring and prediction of high fluoride concentrations in groundwater in Pakistan

Concentrations of naturally occurring fluoride in groundwater exceeding the WHO guideline of 1.5 mg/L have been detected in many parts of Pakistan. This may lead to dental or skeletal fluorosis and thereby poses a potential threat to public health. Utilizing a total of 5483 fluoride concentrations, comprising 2160 new measurements as well as those from other sources, we have applied machine learning techniques to predict the probability of fluoride in groundwater in Pakistan exceeding 1.5 mg/L at a 250 m spatial resolution. Climate, soil, lithology, topography, and land cover parameters were identified as effective predictors of high fluoride concentrations in groundwater. Excellent model performance was observed in a random forest model that achieved an Area Under the Curve (AUC) of 0.92 on test data that were not used in modeling. The highest probabilities of high fluoride concentrations in groundwater are predicted in the Thar Desert, Sargodha Division, and scattered along the Sulaiman Mountains. Applying the model predictions to the population density and accounting for groundwater usage in both rural and urban areas, we estimate that about 13 million people may be at risk of fluorosis due to consuming groundwater with fluoride concentrations >1.5 mg/L in Pakistan, which corresponds to ~6% of the total population. Both the fluoride prediction map and the health risk map can be used as important decision-making tools for authorities and water resource managers in the identification and mitigation of groundwater fluoride contamination.

Evaluation of the groundwater quality index (GWQI) and the human health risk (HHR) on fluoride concentration in Namakkal district, South India

This research aims to determine the health consequences of fluoride contamination of groundwater in the Namakkal region in south India using the groundwater quality index (GWQI). Study area latitude and longitude: 11° 00' and 11° 30' in the north, and 77° 45' and 78° 15' in the east. Statewide, it is among the largest districts in the state. The study region occupies an area of 3406.37 km2. The geology of the studied area is mainly based on the Archaean crystalline and metamorphic complex. The district's major aquifer systems are composed of crystalline rocks that are weathered and fractured and of colluvial deposits. Alluvium and colluvium are examples of porous formations in the cross-section. Only the main river channels have alluvial deposits. The phreatic properties of groundwater Depending on the topography, these aquifers may reach 5 m saturation thickness. Groundwater samples were obtained from 58 bore well sites across the study area during the North-East Monsoon (NEM) of 2015. pH concentrations in suitable drinking water regions during the seasons assist in limiting the availability of groundwater for drinking purposes. TDS are an important factor in determining water suitability for various purposes. The groundwater sample in the study area shows cation domination in ascending order of Na+ > Ca2+ > Mg2+ > K+ due to the dissolution of aquifer minerals in rainfall in the study area. In the NEM seasons, rock dominance and anthropogenic contributions to higher Na+ > Mg2+ > Ca2+ > K+ values. Fluoride concentration differentiates into three groups such as < 0.5 indicates low risk, 0.5 to 1.5 indicates moderate risk, and > 1.5 means high risk. More than 2 fluoride implies very high risk, whereas fluoride in the range of 1.5 to 2.24 suggests a very high risk. The appraisal of non-carcinogenic risk was done to stress the health issues that succeed due to the intake and dermal contact of drinking water in the Namakkal district. The percentage of risk HQ >1 shows that 48 men groundwater samples, followed by 46 groundwater samples women and 30 groundwater samples children, constitute possible health hazards. Overall, health risk estimation results showed that all the groundwater samples have surpassed the permissible limit of HQ <1 for children.

Fluoride contamination of groundwater and its threat to health of villagers and their domestic animals and agriculture crops in rural Rajasthan, India.

In India, Rajasthan is the largest state and has seven divisions, namely Ajmer, Bharatpur, Bikaner, Jaipur, Jodhpur, Kota and Udaipur. Villagers of these regions, generally, used groundwater for drinking and irrigation purposes. The basic sources of groundwater in rural areas are hand pumps, step wells and borewells. Water of most of these sources is contaminated with fluoride (F) with varying amounts. Water of > 60% these sources has F beyond the recommended country standard (1.0 or 1.5ppm) especially in tribal rural areas of Rajasthan. The highest F range, 0.1-34.0ppm, has been found in groundwater of these sources in the villages of Ajmer division and the lowest 0.1-6.8ppm in the Kota. Drinking of fluoridated groundwater for a long time is not safe for health and causes serious fluorosis disease in humans and domestic animals. In Rajasthan, around 40 lakh people are affected with fluorosis which is the highest in the country. At the F range of 1.3-6.7ppm, the maximum prevalence of dental and skeletal fluorosis in villagers and bovine animals was found 84.0% and 32.7% and 88.9% and 37.8%, respectively. Using fluoridated groundwater in irrigation is also harmful and reduces crops productivity. In this communication, division-wise F distribution in groundwater of rural Rajasthan, F-induced diverse adverse health consequences in villagers and their domesticated animals and agriculture crops and preventive measures for control of F intoxication are critically reviewed. Findings of this review are useful in implementation of health policy for the mitigation of F poisoning in rural Rajasthan.

Groundwater fluoride removal by novel activated carbon/aluminium oxide composite derived from raffia palm shells: Optimization of batch operations and field-scale point of use system evaluation

Fluoride contamination of groundwater is endemic in several countries of the world. Ingestion of fluoride laden water is linked with varying human health consequences. However, deployment of efficient and optimally performing groundwater defluoridation systems in affected regions still require concerted research efforts. Thus in this study, Response Surface Methodology (RSM) is employed to infer the effects of process conditions including adsorbent dosage (0.5–2.5 g/L), contact time (30–150 min), solution pH (3–11) and starting fluoride concentration (2–10 mg/L) on the batch-mode fluoride removal using a novel raffia palm shell activated carbon-aluminium oxide composite. The predicted optimal conditions were used to verify its efficacy for F-removal in actual fluoride ladened groundwater. Furthermore Point of Use (PoU) adsorption filters made of the raffia palm shell activated carbon-aluminium oxide composite and a Commercial Activated Carbon (CAC) was tested for fluoride containment in groundwater. The optimum conditions for defluoridation of synthetic fluoride solution were 5.9, 4.0 mg/L, 2.0 g/L and 120 min for pH, initial fluoride concentration, adsorbent dosage and contact time respectively and resulted to F-removal efficiency of 99.1% and uptake capacity of 2.0 mg/g. Test with actual fluoride ladened groundwater at the suggested optimum conditions indicated removal efficiencies of 92.83 and 85.65% for groundwater sourced from Kaltungo and Langtang areas respectively. Performance of the raffia palm shell activated carbon-aluminium oxide composite-based and CAC-based PoU filters were found to be 14.0 and 7.8 mg/g, 700 and 500 L, 112 and 80 h and 55.88 and 54.47% for average adsorption capacity, treated volume at breakthrough, breakthrough time and average removal efficiency respectively. Exhausted raffia palm shell activated carbon-aluminium oxide composite was regenerated by recoating the spent media with aluminium oxide and was reused in the PoU filters for up to 5 cycles with a marginal decrease in all performance indices.Thus the novel raffia palm shell activated carbon-aluminium oxide composite was found to be an excellent groundwater defluoridation media in both the batch and PoU modes of operation.

High levels of fluoride in groundwater from Northern parts of Indo-Gangetic plains reveals detrimental fluorosis health risks

Fluoride contamination in groundwater is a worldwide phenomenon. Excess fluoride in drinking water causes serious health risks, and as a result, fluoride contamination of water resources is a global concern. In this study, an attempt has been made to provide the distribution of fluoride and related non-carcinogenic health hazards to local individual groups (males, females, and children separately) in the fluoride endemic region of Patiala, Punjab located in the Northern Indo-Gangetic Plain (IGP). The study shows that the dissolved groundwater fluoride concentration ranged between 1.5 and 9.2 mg/L with ∼98% of the sampling locations having fluoride levels higher than the permissible limit. Samples collected from deeper aquifers (>284 m bgl) showed ∼27% more fluoride contamination compared to those collected from <284 m bgl. Maximum incidence of elevated fluoride concentrations was observed in the eastern part of the study area in-sync with groundwater movement. The hazard quotient of fluoride (HQFluoride) calculated to assess the non-carcinogenic health risk was higher than the unitary value in all individual groups suggesting a prevalence of distressful fluorosis and chronic health risk. Results show that the children are the most vulnerable to fluoride toxicity followed by males and females. Our results are consistent with the recent trends in an increase in dental, skeletal fluorosis, and liver functional damage problems reported in children and adults of the studied region. The study area, therefore, needs the urgent attention of policymakers and government agencies to implement proper water management and cost-effective fluoride remedial measures to reduce the current and future chronic health risks associated with high fluoride intake.

Spatio-temporal variation of fluoride in groundwater and agricultural soil and crops of Unnao district, UP: Monitoring and assessment

Fluoride (F−) contamination in groundwater of Unnao district, Uttar Pradesh was reported for the first time in 1994, however comprehensive monitoring of F− in different environmental matrices remains to be undertaken. The presented study reports spatio-temporal monitoring of F− content in groundwater, crops and soil from F− affected district Unnao, in pre-monsoon (PRM), monsoon (MO) and post-monsoon (PMO), to establish F− groundwater-soil-plant continuum. More than 80% of groundwater samples were contaminated with F−> 1.0 mg L−1 with highest level (mg L−1), at Patiyara (3.6 ± 0.64), during PRM > Pathakpur (2.73 ± 0.57) during PMO > Sarukheda (2.40 ± 0.43) during PRM. High Cr in groundwater was observed in Jajmau (7.08 ± 1.42). The level of F− (mg Kg−1) in agricultural soils followed 3.4 ± 0.71 at Patiyara (MO) > 2.9 ± 0.14 at Badlikheda (PRM) 1.89 ± 0.28 at Jagatkhera (PRM). Among the different edible parts of crops in selected sites, highest F− content (mg Kg−1), F− level in grains of Oryza sativa ranged between 0.23 ± 0.02 to 2.01 ± 0.24. Whereas in the edible fruit of Trichosanthes diocia contained 1.47 ± 0.32 and Momordica charantia 1.47 ± 0.02. Leaf of spinach (1.03 ± 0.22) and seed of Brassica juncea (0.73 ± 0.08). Overall, comparing across all the three seasons, level of F− was highest in all the plants during MO, as compared to PRM and PMO. The regression analysis of physiochemical properties of groundwater show negative relationship between Na+ and F− whereas soil alkalinity exhibited strong influence in soil F−. The high F− content in soil and groundwater at Patiyara and Shekhpur also coincided with presence of several brick kilns, possibly contributing to the high F−.

Acute toxicity of fluoride and aluminium on the freshwater fish, &lt;em&gt;Cyprinus carpio&lt;/em&gt; L

Fluoride is a trace element which has beneficial effect at lower concentration but detrimental at higher concentration. The fluoride contamination in ground water is a major global problem. Similarly, aluminium is the most abundant metal of the earth, highly toxic to all organisms. In the present study, we investigated the acute toxicity of fluoride and aluminium on three month old fingerlings of Cyprinus carpio L. in hard water (Hardness 125 mg/L of CaCO3) under static renewal bioassay. The 96 h LC50 value of the fluoride and aluminium were 675.615 and 224.214 mg/L, respectively. There was a significant correlation (P <0.01) between mortality rate of C. carpio with all concentrations of fluoride as well as aluminium. The exposure time (24, 48, 72 and 96 h) and different concentration of fluoride (680, 684, 686 and 692 mg/L) and aluminium (228, 229, 231 and 232 mg/L) was also significantly correlated (P <0.05). The different abnormal behaviour displayed by the fluoride and aluminium exposed fishes were erratic swimming movements, rapid opercular activity and excessive secretion of mucous. The safe level of concentrations of fluoride and aluminium were 6.75 and 2.24 µg/L, respectively. The LC50 values of fluoride and aluminium of the present study may be useful in deriving water quality standards in West Bengal.

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 9.16mg/L, with a mean value of 0.62mg/L. The fluoride concentration of a total of 192 GW samples exceeded the limit of China's GW quality standards (1mg/L), accounting for 14.74%. The GW fluoride concentration in most areas of WFC is less than 1mg/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.

Assessment of fluoride contamination in groundwater and its impact on human health

Assessment of fluoride contamination in groundwater and its impact on human health

Fluoride Contamination in Groundwater and Its Effect on Human Health: Case Study of Baramati Tehsil Area, India

Baramati Tehsil is the rural part of the Pune district which have an arid to semi-arid region. Groundwater is the main source of drinking water for the people living in this area. The groundwater is being removed from a dug well and borewells in the study area for drinking purposes. The present study studied, fluoride from Dug well water of the Baramati Tehsil area. A total of 15 groundwater samples of dug well were collected in post-monsoon (POM) winter 2015 to pre-monsoon (PRM) summer 2017 for four seasons by using standard methods of American Public Health Association (APHA). The various physico-chemical parameters such as pH, Electrical conductivity (EC), Total Dissolved Solids (TDS), Total Hardness (TH), Calcium (Ca2+), Magnesium (Mg2+), Sodium (Na+), Potassium (K+), Bicarbonate (HCO3-), Chloride (Cl-), Sulphate (SO42-) and Fluoride (F-) were determined using standard procedures of APHA suggested for determination of the water quality for drinking purpose. The results obtained from the analysis was used for interpretation of fluoride and other ions concentration and the effect on human health. Results obtained indicate that the fluoride concentrations in POM and PRM were within the maximum permissible limit of WHO and BIS recommended for drinking. World Health Organization (WHO 2006) has fixed a safe limit of fluoride from 0.5 to 1.5 mg/l in drinking water. The maximum fluoride concentration in the study area was 0.68 mg/l while the minimum was 0.12 mg/l and the average fluoride concentration was 0.41 mg/l in all four seasons. The drinking water intake with fluoride content less than 0.5 mg/l can cause tooth decay. The groundwater of all wells was suitable for drinking purposes without treatment for fluoride removal at the time of analysis.

Senna auriculata L. flower petal biomass: An alternative green biosorbent for the removal of fluoride from aqueous solutions

Fluoride contamination in groundwater is a major concern in many parts of India and all over the world. Researches paying attention for the removal of fluoride through the application of biosorbents prepared from different parts of plants are finding greater scope and importance. The present research work focuses on Senna auriculata L., flower petal biomass as biosorbent, and evaluated its feasibility for fluoride ion elimination from aqueous solutions. Batch experiments were conducted to remove fluoride under different experimental conditions have been optimized for the maximum removal of fluoride; 80% removal was observed at pH: 6, sorbent dosage: 0.25 g/100 mL, time of agitation: 90 min, and initial concentration of the fluoride ions: 5 mg/L. Characterization studies of the biosorbent revealed its favorability towards the sorption of fluoride. In the isothermal modeling studies, Langmuir isotherm model was obeyed by the biosorption process with R2 value of 0.98 and from a kinetic perspective, the biosorption of fluoride onto the biosorbent observed the pseudo-second-order reaction with R2 value of 0.98. The developed biosorbent has been applied to real field fluoride-contaminated water samples and found to be successful.

A holistic study on fluoride-contaminated groundwater models and its widespread effects in healthcare and irrigation.

Groundwater is a key resource in the world. Its importance is often undermined, despite the various applications which include irrigation, drinking, sanitation, and industrial uses. One of the contaminants of groundwater is fluoride or the fluorine ion. Fluoride is a common pollutant of water, carrying potential benefits and costs to various sectors. Fluoride contamination of groundwater can impact humans, animals, healthcare, and the agricultural sector in direct or indirect ways. This paper aims to establish the definition of fluoride contamination of groundwater and simultaneously provide an outline of a few common sources that may cause fluoride contamination. Furthermore, this study will lay out the impacts of fluoride-contaminated groundwater on two sectors: healthcare and agriculture/irrigation. This study will also summarize various other research projects conducted across the world, which deliver promising evidence to support the points made throughout the paper. In addition to a detailed analysis of the impacts of fluoride on the healthcare and agricultural sector, this study also evaluates few other challenges which this issue poses and how to overcome them in the near future. A summation of deflouridation techniques is included, along with the future scope pertaining to the field of fluoride contamination. Another objective of the study is to spread awareness about the various health impacts that fluoride contamination poses and encourages consumption of fluoride in accordance with the set limit of 0.5-1.5 mg/L. The motivation behind writing this review is to compile and document various researches, along with an address on this prevalent issue to minimize the detrimental impacts and potential health risks on the society. The results of this study help to minimize risks in the future and encourage scientists to come up with mitigation strategies to ensure a safer environment.

Synergistic removal of fluoride from groundwater by seed crystals and bacteria based on microbially induced calcium precipitation

A new hypothesis that seed crystals (SC) and bacteria based on microbially induced calcium precipitation (MICP) synergistically remove fluoride (F−) from groundwater was proposed, with a focus on evaluating the defluoridation potential of this method and revealing its F− removal mechanism. The crucial conditions were optimized to reduce preparation and operation costs. SC furnished more available binding sites due to the existence of bacteria, and the reuse experiments showed that the defluoridation efficiency of SC still remained a high level after 14 cycles (70.10%), with a residual F− concentration of 0.96 mg L−1. The SEM-EDS, FTIR and XRD analyses indicated the predominant F− removal mechanism of SC could be ascribed to the chemisorption, ion exchange, and co-precipitation. Moreover, ion exchange and co-precipitation (PO43− involvement) were validated more contributive than chemisorption (CaCO3 and CaSO4 involvement). As a feasible, reusable, and eco-friendly technique, SC suggests promising applications in the treatment of fluoride-contaminated groundwater.

Predicting geogenic groundwater fluoride contamination throughout China

Endemic fluorosis exists in almost all provinces of China. The long-term ingestion of groundwater containing high concentrations of fluoride is one of the main causes of fluorosis. We used artificial neural network to model the relationship between groundwater fluoride concentrations from throughout China and environmental variables such as climatic, geological. and soil parameters as proxy predictors. The results show that the accuracy and area under the receiver operating characteristic curve of the model in the test dataset are 80.5% and 0.86%, respectively, and climatic variables are the most effective predictors. Based on the artificial neural network model, a nationwide prediction risk map of fluoride concentrations exceeding 1.5 mg/L with a 0.5 × 0.5 arc minutes resolution was generated. The high risk areas are mainly located in western provinces of Xinjiang, Tibet, Qinghai, and Sichuan, and the northern provinces of Inner Mongolia, Hebei and Shandong. The total number of people estimated to be potentially at risk of fluorosis due to the use of untreated high fluoride groundwater as drinking water is about 89 million, or 6% of the population. The high fluoride groundwater risk map helps the authorities to prioritize areas requiring mitigation measures and thus facilitates the implementation of water improvement and defluoridation projects.

Prediction on the fluoride contamination in groundwater at the Datong Basin, Northern China: Comparison of random forest, logistic regression and artificial neural network

Groundwater fluoride is posing a health risk to humans, and analyzing groundwater quality is time-wasting and expensive. Statistical methods provide a valuable approach to study the spatial distribution of groundwater fluoride. Random Forest (RF), Artificial Neural Network (ANN), and Logistic Regression (LR) were used in this study for groundwater fluoride prediction in Datong Basin. The groundwater chemistry of 482 groundwater samples was collected and used to figure out the performance of three statistical technologies and extract the main factors controlling the enrichment of fluoride in groundwater. The data was separated into two parts for the statistical analysis, 80% for training and 20% for testing. The Chi-squared was applied to select the most relevant variables, and TDS, Cl−, NO3−, Na+, HCO3−, SO42−, K+, Zn, Ca2+, and Mg2+ were selected as best inputs for the fluoride prediction. Models were evaluated using the confusion matrix and The receiver operating characteristic area under the curve ROC (AUC). The results suggest that within ten input variables, the accuracies of RF, ANN, and LR were 0.89, 0.85, and 0.76, respectively. The mean decrease in impurity (MDI) and permutation feature demonstrates that eight of ten parameters, including TDS, Cl−, NO3−, Na+, HCO3−, SO42−, Ca2+ and Mg2+ are the variables influencing the groundwater fluoride in the study area. RF exhibited the best model with high conformity and confidence in predicting groundwater fluoride contamination in the study area.

Remediation of chromium- and fluoride-contaminated groundwater by immobilized Citrobacter sp. on a nano-ZrO2 hybrid material.

To effectively address excessive SO42-, Cr(VI), total chromium and F- in the groundwater of acidic mining areas, a facultative anaerobic bacterium, Citrobacter, with sulfate-reducing properties, tolerance to hexavalent chromium and the ability to reduce Cr(VI) to Cr(III) was isolated and domesticated. Based on microbial immobilization technology, a nano-ZrO2 polyacrylamide hybrid material was prepared as an embedding agent to form nano-ZrO2 polyacrylamide Citrobacter (ZPC) particles. ZPC was microscopically characterized, and the removal performance and mechanism of ZPC for SO42-, Cr(VI), total chromium and F- in groundwater were analyzed. The results of single-factor tests showed that the optimal reaction conditions included a reaction temperature of 35°C, Citrobacter dosage of 35% (volume ratio) in the particles and hybrid material dosage of 300 mL; under these conditions, the removal rates of SO42-, Cr(VI), total chromium and F- were 70.5%, 100%, 100% and 93.3%, respectively, and the pH value increased from 4.6 to 8.07. On this basis, the effects of the reaction layer type, influent hydraulic load and influent concentration on the removal efficiency of polluted groundwater were studied through dynamic experiments. The experimental results showed that ZPC particles were better than Citrobacter as a reaction layer; the optimal influent hydraulic load was 3.0 m3/(m2·d); the selectivity of ZPC particles to anions and anionic groups was different; and the order of adsorption selectivity was F- > Cr(VI) > SO42-.

Hydrochemical evolution and assessment of groundwater quality in fluorosis-affected area, Mandla District, central India

Deterioration of groundwater quality is a matter of serious concern today. In Mandla region of central India, fluorosis is common among the local people due to consumption of fluoride-contaminated groundwater. It is, therefore, important to understand the hydrochemical process of contamination and assess the groundwater quality of this region. A total of 173 samples (pre-monsoon and post-monsoon) were collected from borewells and dug wells of different depths for major ions analysis: K+, Na+, Ca2+, Mg2+, Cl−, CO32−, HCO3−, NO3−, SO42−, and F−; along with pH, temperature, TH (as CaCO3), TDS and EC. Broadly, three hydrogeologic units have been identified, viz. Deccan lava flows, infratrappean Lameta and Archean granite and gneiss. In Deccan, two distinct hydrostratigraphic units are Mandla and Dhuma. Mandla is the most prominent and extensive aquifer having hydraulic conductivity 5–15 mday-1 and yield 10–50 m3day−1. Water quality data vis-à-vis well-depth data indicate that Mandla aquifer, lying at a lower elevation than 500 m amsl, is fluoride-contaminated and harmful for human health. Fluoride (41.0% of total samples) and bicarbonate (54.9% of total samples) concentrations in analyzed water are above the global standard for drinking purpose. However, above 500 m msl groundwater is not contaminated with fluoride and is suitable for drinking and irrigation purpose. Fluoride concentration maps depict spatial and seasonal variation. Spatial variation of fluoride in groundwater is due to change in aquifer lithology, varying degree of rock weathering and orientation of structural lineaments. In fluoride concentration map of post-monsoon season, broadening of contour of uncontaminated zone indicates groundwater recharge, which corroborates with water fluctuation map. The fluoride-contaminated water and low-fluoride water are mainly Na–HCO3 and Ca–HCO3 type, respectively. The hydrochemical processes suggest pre-dominance of rock-water interaction; contribution of Na+ and K+ ions in groundwater is due to silicate weathering, whereas Ca2+ and Mg2+ ions are derived due to both silicate and carbonate weathering. Saturation index calculation point towards calcite-dolomite supersaturation and consequent precipitation, along with fluorite dissolution under alkaline condition.