Fluoride contamination in groundwater and associated health risks in Karbi Anglong District, Assam, Northeast India

A review on fluoride contamination in groundwater and human health implications and its remediation: A sustainable approaches

Contamination of drinking water due to fluoride (F-) is a major concern worldwide. Although fluoride is an essential trace element required for humans, it has severe human health implications if levels exceed 1.5 mg. L-1 in groundwater. Several treatment technologies have been adopted to remove fluoride and reduce the exposure risk. The present article highlights the source, geochemistry, spatial distribution, and health implications of high fluoride in groundwater. Also, it discusses the underlying mechanisms and controlling factors of fluoride contamination. The problem of fluoride-contaminated water is more severe in India's arid and semiarid regions than in other Asian countries. Treatment technologies like adsorption, ion exchange, precipitation, electrolysis, electrocoagulation, nanofiltration, coagulation-precipitation, and bioremediation have been summarized along with case studies to look for suitable technology for fluoride exposure reduction. Although present technologies are efficient enough to remove fluoride, they have specific limitations regarding cost, labour intensity, and regeneration requirements.

From fuzzy-TOPSIS to machine learning: A holistic approach to understanding groundwater fluoride contamination

Fluoride (F-) contamination of groundwater is a prevalent environmental issue threatening public health worldwide and in India. This study targets an investigation into spatial distribution and contamination sources of fluoride in Dhanbad, India, to help develop tailored mitigation strategies. A triad of Multi Criteria Decision Making (MCDM) models (Fuzzy-TOPSIS), machine learning algorithms {logistic regression (LR), classification and regression tree (CART), Random Forest (RF)}, and classical methods has been undertaken here. Groundwater samples (n = 283) were collected for the purpose. Based on permissible limit (1.5 ppm) of fluoride in drinking water as set by the World Health Organization, samples were categorized as Unsafe (n = 67) and Safe (n = 216) groups. Mean fluoride concentration in Safe (0.63 ± 0.02 ppm) and Unsafe (3.69 ± 0.3 ppm) groups differed significantly (t-value = -10.04, p < 0.05). Physicochemical parameters (pH, electrical conductivity, total dissolved solids, total hardness, NO3-, HCO3-, SO42-, Cl-, Ca2+, Mg2+, K+, Na+ and F-) were recorded from samples of each group. The samples from 'Unsafe group' showed alkaline pH, the abundance of Na+ and HCO3- ions, prolonged rock water interaction in the aquifer, silicate weathering, carbonate dissolution, lack of Ca2+ and calcite precipitation which together facilitated the F- abundance. Aspatial distribution map of F- contamination was created, pinpointing the "contaminated pockets." Fuzzy- TOPSIS identified that samples from group Safe were closer to the ideal solution. Among these models, the LR proved superior, achieving the highest AUC score of 95.6 % compared to RF (91.3 %) followed by CART (69.4 %). This study successfully identified the primary contributors to F- contamination in groundwater and the developed models can help predicting fluoride contamination in other areas. The combination of different methodologies (Fuzzy-TOPSIS, machine learning algorithms, and classical methods) results in a synergistic effect where the strengths of each approach compensate for the limitations of the other.

Natural and anthropogenic factors regulating fluoride enrichment in groundwater of the Nansi Lake Basin, Northern China

Excess fluoride (F-) in groundwater can be hazardous to human health of local residents who rely upon it. Beside natural sources, anthropogenic input may be an additional source to be considered. Twenty surface water and 396 groundwater samples were collected from the Nansi Lake Basin, with hydrogeochemical and isotope techniques employed to clarify the spatial variability, source, and the natural and anthropogenic factors regulating the occurrence of high F- groundwater. The factors responsible for elevated F- levels in surface water and deep confined aquifers are discussed based on their hydraulic relationship. Also a conceptual model of F- enrichment with different aquifer systems is put forward based on the geomorphic units of the basin. The results show that F- concentration is between 0.1 and 6.9 mg/L in the west of Lake, while ranged from 0.03 to 1.74 mg/L in the east of Lake. The hydrogeological setting and lithology are the primary factor determining the provenance of high-fluoride groundwater in the basin. Fluoride mainly originated from the dissolution of fluorine-bearing minerals, and is affected by the alkaline groundwater environment, cation exchange, adsorption, and evaporation. The landforms on the east side of Nansi Lake are low hills and piedmont sedimentary plains, where the aquifers consist of karst fissure water and overlying porewater. High F- groundwater is not observed in this area due to its rapid flow and Ca2+-enriched hydrochemical characteristics. The anthropogenic input (such as fertilizer application on farms and illegal industrial pollutant discharge), contribute F- to groundwater in varying degrees, especially in the shallow aquifers east of the lake and in some parts west of the lake. This work is a clear example of how natural processes together with human activities can affect the chemical quality of groundwater, which is essential to safeguard the sustainable management of water resources in semi-arid areas.

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.

Rapid and enhanced adsorptive mitigation of groundwater fluoride by Mg(OH)2 nanoflakes

Fluoride is one of the most abundant anions in groundwater, posing a significant threat to the safe drinking water supply worldwide. Fluoride contamination in drinking water at levels greater than 1.5 mg L^-1 causes a variety of serious health problems. To address this problem, the current study deals with the synthesis of Mg(OH)₂ nanoflakes by a facile and simple hydrothermal method in the absence of any added template. The sizes of these nanoflakes are in the range of 90 to 200 nm. These nanoflakes are pure and crystalline, possessing hexagonal phase structures. The surface areas of Mg(OH)₂ nanoflakes are varying from 75.8 to 108.1 m² g^-1. These Mg(OH)₂ nanoflakes exhibit excellent adsorption performance for fluoride over a pH range of 2.0 to 9.0 with a maximum Langmuir adsorption capacity of 3129 mg g^-1 at pH 7.0 at 313 K which is the highest for such kind of adsorbent reported so far. The adsorption process is spontaneous and endothermic which primarily follows pseudo-second-order kinetics. The adsorbent is effective in the presence of co-existing anions and is reusable up to the fifth cycle with a minimal loss of adsorption performance. The nanoflakes can effectively remove highly concentrated groundwater fluoride to a permissible limit within a short time which increases the versatility of using these nanoflakes for practical applications.

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.

Distribution of Fluoride in Plasma, Brain, and Bones and Associated Oxidative Damage After Induced Chronic Fluorosis in Wistar Rats

The study was aimed to determine fluoride levels in plasma, brain, and bones of Wistar rats following chronic administration of fluoride at different dose levels and the consequent oxidative damage inflicted in these tissues. Brain histomorphology and bone radiographs were also evaluated to assess the extent of damage in these organs. Eighteen rats were randomly divided into three groups with six animals in each group. Group I served as control and groups II and III received 50 and 100 ppm fluoride in tap water, respectively for 180 days. A dose-dependent rise in the levels of fluoride in plasma, brain, and bones was observed in rats. Significant (P < 0.05) alterations in levels of total thiols, glutathione peroxidase, glutathione reductase, acetylcholinesterase, catalase, superoxide dismutase, lipids, as well as protein peroxidation in blood and brain were observed as compared to control in a dose-dependent manner. Radiological examination of bone revealed thinning of bone cortex with haphazard ossification, reduced bone density, and widening of marrow cavity indicating occurrence of flawed bone remodeling upon chronic fluoride exposure. Improper mineralization in bones of intoxicated rats indirectly reflected reduced bone tensile strength. Moreover, alterations in plasma Ca:P ratio and high levels of fluoride in bone ash indicated that chronic fluoride exposure leads to alterations in the bone matrix further corroborating the radio-graphical findings. Additionally, severe microscopic alterations were recorded in the cerebrum and cerebellum of treated rats which included neuronal necrosis, gliosis, spongiosis, perivascular cuffing, congestion, and hemorrhage which correlated well with oxidative changes induced by fluoride intoxication in the brain tissue of rats.

Fluoride sensitivity in freshwater snail, Bellamya bengalensis (Lamarck, 1882): An integrative biomarker response assessment of behavioral indices, oxygen consumption, haemocyte and tissue protein levels under environmentally relevant exposure concentrations

There is limited information on fluoride toxicity and risk overview on ecotoxicological risks to aquatic invertebrate populations particularly molluscan taxa. This necessitated the assessment of toxicity responses in the freshwater snail, Bellamya bengalensis exposed to environmentally relevant concentrations of sodium fluoride. Under lethal exposures (150, 200, 250, 300, 400 and 450 mg/l), the median lethal concentrations (LC₅₀) were determined to be 422.36, 347.10, 333.33 and 273.24 mg/l for B. bengalensis at 24, 48, 72 and 96 h respectively. The rate of mortality of the snails was increased significantly with elevated concentrations of the toxicant. The magnitude of toxicity i.e., toxicity factor at different time scale was also higher with increased exposure duration. Altered behavioural changes i.e., crawling movement, tentacle movement, clumping tendency, touch reflex and mucous secretion in exposed snail with elevated concentrations and exposure duration. Similarly, oxygen consumption rate of the treated snail also lowered significantly during 72 and 96 h of exposure. Under 30-day chronic exposures (Control-0.00 mg/L; T1-27.324 mg/L; T2-54.648 mg/L), protein concentrations in gonad and hepatopancreas of exposure groups was significantly lowered. Chronic exposures also revealed lowered haemocytes counts in exposure groups. The potential for loss of coordination, respiratory distress and physiological disruption in organisms exposed to environmentally relevant concentrations of fluoride was demonstrated by this study. The estimation and magnitude of toxicity responses are necessary for a more accurate estimation of ecological risks to molluscan taxa and invertebrate populations under acute and chronic fluoride exposures in the wild.

Bioaccumulation of Fluoride in Plants and Its Microbially Assisted Remediation: A Review of Biological Processes and Technological Performance

Fluoride is widely found in soil–water systems due to anthropogenic and geogenic activities that affect millions worldwide. Fluoride ingestion results in chronic and acute toxicity, including skeletal and dental fluorosis, neurological damage, and bone softening in humans. Therefore, this review paper summarizes biological processes for fluoride remediation, i.e., bioaccumulation in plants and microbially assisted systems. Bioremediation approaches for fluoride removal have recently gained prominence in removing fluoride ions. Plants are vulnerable to fluoride accumulation in soil, and their growth and development can be negatively affected, even with low fluoride content in the soil. The microbial bioremediation processes involve bioaccumulation, biotransformation, and biosorption. Bacterial, fungal, and algal biomass are ecologically efficient bioremediators. Most bioremediation techniques are laboratory-scale based on contaminated solutions; however, treatment of fluoride-contaminated wastewater at an industrial scale is yet to be investigated. Therefore, this review recommends the practical applicability and sustainability of microbial bioremediation of fluoride in different environments.

A characterization of groundwater fluoride, influencing factors and risk to human health in the southwest plain of Shandong Province, North China

This study investigated 324 groundwater samples collected from the southwest plain of Shandong Province during the dry and wet seasons. Groundwater fluoride in the study area and the influencing factors were characterized and discussed using statistical analysis, ion ratios, Piper diagrams, the saturation index (SI) and ArcGIS software. In addition, the risk posed by groundwater fluoride to human health was assessed. The results showed that groundwater in the study area had elevated fluoride concentrations, with average dry and wet season concentrations of 1.15 mg·L^-1 and 1.08 mg·L^-1, respectively. Groundwater fluoride showed consistent spatial variations during the dry and wet seasons, with a significant regionalization pattern of low concentrations in the east and high concentrations in the west. Groundwater F^- was significantly negatively correlated with Ca²⁺ and positively correlated with pH, HCO₃^- and Na⁺. Important factors identified as having an effect on groundwater F^- in the study area included the balance of dissolution of fluorite and calcite, the weakly alkaline environment and cation exchange. In addition, hydrochemical types of high-fluoride groundwater in the study area were identified as mainly HCO₃-Na and SO₄·Cl-Na. The assessment of the risk of high groundwater fluoride to human health showed that children are more at risk compared to adults, with the risk during the dry season exceeding that over the wet season. It is recommended that water quality management in the study area prioritize the formulation of measures to mitigate high concentrations of fluoride in groundwater .