Inferring the fluoride hydrogeochemistry and effect of consuming fluoride-contaminated drinking water on human health in some endemic areas of Birbhum district, West Bengal

A multi-model study for understanding the contamination mechanisms, toxicity and health risks of hardness, sulfate, and nitrate in natural water resources

Several water quality contaminants have attracted the attention of numerous researchers globally, in recent times. Although the toxicity and health risk assessments of sulfate and water hardness have not received obvious attention, nitrate contamination has gained peculiar research interest globally. In the present paper, multiple data-driven indexical, graphical, and soft computational models were integrated for a detailed assessment and predictive modeling of the contamination mechanisms, toxicity, and human health risks of natural waters in Southeast Nigeria. Majority of the tested physicochemical parameters were within their satisfactory limits for drinking and other purposes. However, total hardness (TH), SO₄, and NO₃ were above stipulated limits in some locations. A nitrate health risk assessment revealed that certain areas present a chronic health risk to children, females, and males due to water intake. However, the dermal absorption route was found to have negligible health risks. SO₄ in some locations was above the 100 mg/L Nigerian limit; thus, heightening the potential health effects due to intake of the contaminated water resources. Most samples had low TH values, which exposes users to health defects. There are mixed contamination mechanisms in the area, according to graphical plots, R-mode hierarchical dendrogram, factor analysis, and stoichiometry. However, geogenic mechanisms predominate over human-related mechanisms. Based on the results, a composite diagrammatic model was developed. Furthermore, predictive radial basis function (RBF) and multiple linear regression (MLR) models accurately predicted the TH, SO₄, and NO₃, with the RBF outperforming the MLR models. Insights from the RBF and MLR models were useful in validating the results of the hierarchical dendrogram, factor, stoichiometric, and graphical analyses.

Association between low fluoride exposure and children's intelligence: a meta-analysis relevant to community water fluoridation

OBJECTIVES

Previous meta-analyses have mainly focused on studies conducted in endemic fluorosis areas with relatively high fluoride concentrations. These are impoverished rural communities in China, India, and Iran, and the findings cannot be generalised to developed countries. Therefore, we investigated the association between fluoride concentrations relevant to community water fluoridation and children's cognition measured with IQ scores by synthesising effect sizes reported in observational studies.

METHODS

A previous meta-analysis and the National Toxicology Program database that included a search of multiple databases and the authors' search of PubMed, Google Scholar, and Mendeley provided the data. Cross-sectional and cohort studies examining the association between fluoride and children's cognition and intelligence scores were selected. Two reviewers abstracted data using standard procedures. We performed three meta-analyses to synthesise the effects using the random effects models.

RESULTS

Eight studies of standardized mean difference in IQ scores from non-endemic fluorosis areas found no statistically significant difference between recommended and lower levels of fluoride (standardized mean difference = 0.07; 95% confidence interval: -0.02, 0.17; I² = 0%), and no significant fluctuation in IQ scores across the differences in fluoride concentrations by non-linear modeling with restricted cubic spline (P = 0.21). Meta-analyses of children's and maternal spot urinary fluoride associated pooled regression coefficients (Beta_children = 0.16; 95% confidence interval: -0.40, 0.73; P = 0.57; I² = 0%, Beta_maternal = -0.92; 95% CI: -3.29, 1.46; P = 0.45; I² = 72%) were not statistically significant. Further regression analysis by standardizing absolute mean IQ scores from lower fluoride areas did not show a relationship between F concentration and IQ scores (Model Likelihood-ratio test: P-value = 0.34.) CONCLUSIONS: These meta-analyses show that fluoride exposure relevant to community water fluoridation is not associated with lower IQ scores in children. However, the reported association observed at higher fluoride levels in endemic areas requires further investigation.

Prenatal exposure to fluoride and neuropsychological development in early childhood: 1-to 4 years old children

BACKGROUND

Cross-sectional and prospective studies have provided evidence of the neurotoxic effect of early exposure to fluoride (F) in pregnancy. It has been negatively associated with cognitive development during childhood, with most research conducted in areas with high F levels in community drinking water (CDW).

METHOD

Data from 316 to 248 mother-child pairs from the Infancia y Medio Ambiente (Childhood and Environment, INMA) birth cohort project with maternal urinary F level adjusted for creatinine (MUFcr) measurements in the first and third trimesters of pregnancy. Children's cognitive domains and intelligence indexes were evaluated using the Bayley Scales (age of 1) and the McCarthy Scales (age of 4). Multiple linear regression analyses were carried out adjusting for a wide range of covariates related to the child, mother, family context and other potential neurotoxicants.

RESULTS

No association was found between MUFcr levels and Bayley Mental Development Index score. Nevertheless, regarding the McCarthy scales, it was found that per unit (mg/g) of MUFcr across the whole pregnancy, scores in boys were greater for the verbal, performance, numeric and memory domains (β = 13.86, CI 95%: 3.91, 23.82), (β = 5.86, CI 95%: 0.32, 11.39), (β = 6.22, CI 95%: 0.65, 11.79) and (β = 11.63, CI 95%: 2.62, 20.63) respectively and for General Cognitive Index (β = 15.4, CI 95%: 6.32, 24.48). For girls there was not any cognitive score significantly associated with MUFcr, being the sex-F interactions significant (P interaction <0.05). Including other toxicants levels, quality of family context or deprivation index did not substantially change the results.

CONCLUSIONS

In boys, positive associations were observed between MUFcr and scores in cognitive domains at the age of 4. These findings are inconsistent with those from some previous studies and indicate the need for other population-based studies to confirm or overturn these results at low levels of F in CDW.

Prospects for the Role of Ferroptosis in Fluorosis

As a strong oxidant, fluorine can induce oxidative stress resulting in cellular damage. Ferroptosis is an iron-dependent type of cell death caused by unrestricted lipid peroxidation (LPO) and subsequent plasma membrane rupture. This article indicated a relationship between fluorosis and ferroptosis. Evidence of the depletion of glutathione (GSH) and increased oxidized GSH can be found in a variety of organisms in high fluorine environments. Studies have shown that high fluoride levels can reduce the antioxidant capacity of antioxidant enzymes, while increasing the contents of reactive oxygen species (ROS) and malondialdehyde (MDA), resulting in oxidative stress and fluoride-induced oxidative stress, which are related to iron metabolism disorders. Excessive fluorine causes insufficient GSH, glutathione peroxidase (GSH-Px) inhibition, and oxidative stress, resulting in ferroptosis, which may play an important role in the occurrence and development of fluorosis.

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

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

Association between low-to-moderate fluoride exposure and bone mineral density in Chinese adults: Non-negligible role of RUNX2 promoter methylation

Bone mineral density (BMD) changes were reported to be associated with excessive fluoride exposure and abnormal expression of RUNX2. However, whether the alteration of methylation status, a most commonly used marker for the alteration of gene expression in epidemiological investigation, of RUNX2 is associated with low-to-moderate fluoride exposure and BMD changes has not been reported. Our study aims to explore the role of RUNX2 promoter methylation in BMD changes induced by low-to-moderate fluoride exposure. A total of 1124 adults (413 men and 711 women) were recruited from Kaifeng City in 2017. We measured BMD using ultrasound bone densitometer. Concentrations of urinary fluoride (UF) were measured using ion-selective electrode, and the participants were grouped into control group (CG) and excessive fluoride group (EFG) according to the concentration of UF. We extracted DNA from fasting peripheral blood samples and then detected the promoter methylation levels of RUNX2 using quantitative methylation-specific PCR. Relationships between UF concentration, RUNX2 promoter methylation and BMD changes were analyzed using generalized linear model and logistic regression. Results showed in EFG (UF concentration > 1.6 mg/L), BMD was negatively correlated with UF concentration (β: -0.14; 95%CI: -0.26, -0.01) and RUNX2 promoter methylation (β: -0.13; 95%CI: -0.22, -0.03) in women. The methylation rate of RUNX2 promoter increased by 2.16% for each 1 mg/L increment in UF concentration of women in EFG (95%CI: 0.37, 3.96). No any significant associations between UF concentration, RUNX2 promoter methylation, and BMD were observed in the individuals in CG. Mediation analysis showed that RUNX2 promoter methylation mediated 18.2% (95% CI: 4.2%, 53.2%) of the association between UF concentration and BMD of women in EFG. In conclusion, excessive fluoride exposure (>1.6 mg/L) is associated with changes of BMD in women, and this association is mediated by RUNX2 promoter methylation.

Does fluoride cause the mysterious chronic kidney disease of multifactorial origin?

A chronic kidney disease of multifactorial origin (CKDmfo), also known as CKD of unknown origin, started to manifest during the past four decades in certain economically poor, peri-equatorial agricultural countries. CKDmfo is an environmentally induced, occupationally-mediated, chronic tubulointerstitial disease. Prolonged exposure to environmental nephrotoxic agents and extenuating conditions are prerequisites for its manifestation. More than 30 causative factors have been postulated, but none one has been properly scientifically tested, to be able to include or exclude. In recent years, fluoride has come to be considered a key contender as a causative agent of CKDmfo. Therefore, this review examines the pros and cons of that theory and the potential plausibility that fluoride causes CKDmfo. It also examines the potential interactions and additive or synergistic effects of certain geogenic factors, especially, the plausibility of CaPO₄^-3 apatite and fluorapatite crystals and nanotube formation in concentrated tubular filtrate and within tubular cells, in renal tubules. The information presented is based on published work and data collected over the past two decades in Sri Lanka. However, the evidence and concepts are applicable to all CKDmfo-affected countries. Thus, the presented content might facilitate scientists to narrowed down causative factors to just a few and government departments to implement effective programs for preventing this disease. The findings suggest that in addition to the geogenic components, disease manifestation requires (A) prolonged exposure to environmental nephrotoxins and factors, (B) interactions among elements (Ca²⁺, PO₄^-3 , F^-, and Mg²⁺), and (C) vulnerability of the person, such as chronic dehydration, and antioxidant and micronutrient deficiencies. In vivo precipitation of nanominerals in renal tubular tissues that arising over several years causes tubulointerstitial disease-CKDmfo. Inherent vulnerabilities and conditions, together with nanomineral precipitation, trigger renal tubular cell oxidative stresses, inflammation, and fibrosis, and eventually causing tubulointerstitial chronic renal failure-CKDmfo.

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

In order to assess the geochemical mechanism liable for fluoride contamination in groundwater and its health effects on the people of the Shanmuganadhi River basin, Tamil Nadu, India, 61 groundwater samples were collected during post- and pre-monsoon seasons from the wells used for drinking purposes. Collected samples were analysed for various physico-chemical parameters. The parameters estimated in the present study are hydrogen ion concentration (pH), total dissolved solids, electrical conductivity, calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), potassium (K⁺), bicarbonate (HCO₃^-), chloride (Cl^-), sulphate (SO₄^2-), nitrate (NO₃^-), phosphate (PO₄^3-) and fluoride (F^-). The fluoride ion concentration in the groundwater samples of this region varied from 0.01 to 2.50 mg/l and 0.01 to 3.30 mg/l during post- and pre-monsoon seasons, respectively. Out of 61 groundwater samples, 14 samples of post-monsoon season and 16 samples of pre-monsoon season represented high, very high and extremely high classes of fluoride, which cause dental fluorosis in this region. The fluoride-bearing minerals in the granitic and gneissic rocks such as apatite, hornblende, muscovite, biotite and amphiboles are the major sources for fluoride contamination in this area. In addition to the geogenic sources, applications of synthetic fertilizers in the agricultural fields also contribute significant amount of fluoride ions to groundwater. The spatial distribution of fluoride in different geological formations clearly indicate that the wells located in charnockite terrain were possessing very low fluoride concentration when compare with the wells located in the hornblende-biotite gneiss formation. Therefore, dental fluorosis risks are mostly associated with rock types in this region. People living over the basement rock comprising of hornblende-biotite gneiss are prone for fluorosis. Fluoride exhibited good positive correlation with bicarbonate in groundwater. As fluoridated endemic regions normally acquire lot of bicarbonate in groundwater samples, Shanmuganadhi basin falls under fluoride endemic category. The present study identified 26 villages in Shanmuganadhi basin as probable fluorosis risk areas where attention should be given to treat the fluoride-rich groundwater before drinking water supply. The groundwater level fluctuation study also designates that rise in water level reduces the concentration of fluoride due to dilution mechanism. Therefore, recharge of groundwater by artificial methods will definitely improve the present scenario.

Toxicity of fluoride: critical evaluation of evidence for human developmental neurotoxicity in epidemiological studies, animal experiments and in vitro analyses

Recently, epidemiological studies have suggested that fluoride is a human developmental neurotoxicant that reduces measures of intelligence in children, placing it into the same category as toxic metals (lead, methylmercury, arsenic) and polychlorinated biphenyls. If true, this assessment would be highly relevant considering the widespread fluoridation of drinking water and the worldwide use of fluoride in oral hygiene products such as toothpaste. To gain a deeper understanding of these assertions, we reviewed the levels of human exposure, as well as results from animal experiments, particularly focusing on developmental toxicity, and the molecular mechanisms by which fluoride can cause adverse effects. Moreover, in vitro studies investigating fluoride in neuronal cells and precursor/stem cells were analyzed, and 23 epidemiological studies published since 2012 were considered. The results show that the margin of exposure (MoE) between no observed adverse effect levels (NOAELs) in animal studies and the current adequate intake (AI) of fluoride (50 µg/kg b.w./day) in humans ranges between 50 and 210, depending on the specific animal experiment used as reference. Even for unusually high fluoride exposure levels, an MoE of at least ten was obtained. Furthermore, concentrations of fluoride in human plasma are much lower than fluoride concentrations, causing effects in cell cultures. In contrast, 21 of 23 recent epidemiological studies report an association between high fluoride exposure and reduced intelligence. The discrepancy between experimental and epidemiological evidence may be reconciled with deficiencies inherent in most of these epidemiological studies on a putative association between fluoride and intelligence, especially with respect to adequate consideration of potential confounding factors, e.g., socioeconomic status, residence, breast feeding, low birth weight, maternal intelligence, and exposure to other neurotoxic chemicals. In conclusion, based on the totality of currently available scientific evidence, the present review does not support the presumption that fluoride should be assessed as a human developmental neurotoxicant at the current exposure levels in Europe.

Fluorosis and cognitive development among children (6-14 years of age) in the endemic areas of the world: a review and critical analysis

The fluoride contamination in water is still a live discussion among the scientific community, because of its beneficial and injurious health effects inflicted on the human population. The magnitude of groundwater fluoride contamination is aggravated by increasing anthropogenic activities. Groundwater is supposedly the main source through which people are highly exposed to fluoride, compared with other sources of exposure. Among human populations, fluoride-related health issues span from mild effects on teeth and bones to severe kidney problems, neurotoxicity, and even cancer. Nowadays, fluoride toxicity is gaining much attention in the endemic areas due to its adverse impact on the children's cognitive function, since children are more susceptible to fluoride toxicity as compared to adults. The primary mechanism behind the neurotoxicity of fluoride is still not clearly understood. However, knowingly, fluoride disrupts the biochemical mechanism and thus alters the normal functioning of the brain. Several human studies are suggestive of lowering children's IQ who was exposed to fluoride during their childhood. The conclusive findings of past research suggest that the fluoride concentration in potable water tends to grossly affect the children's IQ level. However, the body of proof is limited, because most of the studies are concentrated in few countries, and have their own limitations and data gaps. The grave implications of fluoride toxicity, therefore, demand extensive and properly designed research to bridging the data gap in developing countries. Furthermore, spanning research work across all the endemic areas of the world could generate larger database, helping resolve the issue on a large scale.

Monitoring, mapping and health risk assessment of fluoride in drinking water supplies in rural areas of Maku and Poldasht, Iran

The aim of this study was to investigate and determine fluoride concentrations in drinking water supplies in rural areas of Maku and Poldasht in West Azerbaijan Province, the northwest of Iran. Fluorosis risk assessment and characterization was also investigated. Fluoride concentrations mapping was accomplished by using the GIS system. Totally, 356 water samples, including one sample in each season, were collected from 89 water supplies providing water for 95 and 61 rural areas of Maku and Poldasht, respectively. According to the results, in Maku and Poldasht, 25 and 30 rural areas had contaminated water sources, respectively. Average annual fluoride concentrations ranged from 3.04 to 7.31 mg/l in the contaminated villages of Maku, which is about 2-4.8 times higher than the maximum standard level of the Iranian drinking water standard, and 4.52-8.21 mg/l in the contaminated areas of Poldasht, which is about 3-5.47 times higher than the maximum standard level. The maximum fluoride level was determined 11.12 mg/l and 10.98 mg/l in one of villages of Maku and Poldasht Counties in summer, respectively. Neither in Maku nor in Poldasht, water resources showed dental cavity risk, while dental fluorosis risk and skeletal fluorosis risk were very significant in some villages of both cities. Children were at most risk of fluorosis. New alternative water supplies for the contaminated villages if possible, consumption of bottled water and application of reverse osmosis are recommended as remedial actions in the contaminated areas.

Groundwater fluoride contamination, probable release, and containment mechanisms: a review on Indian context

Fluoride contamination in the groundwater has got great attention in last few decades due to their toxicity, persistent capacity and accumulation in human bodies. There are several sources of fluoride in the environment and different pathways to enter in the drinking water resources, which is responsible for potential effect on human health. Presence of high concentration of fluoride ion in groundwater is a major issue and it makes the water unsuitable for drinking purpose. Availability of fluoride in groundwater indicates various geochemical processes and subsurface contamination of a particular area. Fluoride-bearing aquifers, geological factors, rate of weathering, ion-exchange reaction, residence time and leaching of subsurface contaminants are major responsible factors for availability of fluoride in groundwater. In India, several studies have reported that the groundwater of several states are contaminated with high fluoride. The undesirable level of fluoride in groundwater is one of the most natural groundwater quality problem, which affects large portion of arid and semiarid regions of India. Rajasthan, Andhra Pradesh, Telangana, Tamil Nadu, Gujarat, and West Bengal are the relatively high-fluoride-contaminated states in India. Chronic ingestion of high doses of fluoride-rich water leads to fluorosis on human and animal. Over 66 million Indian populations are at risk due to excess fluoride-contaminated water. Therefore, groundwater contamination subject to undesirable level of fluoride needs urgent attention to understand the role of geochemistry, hydrogeology and climatic factors along with anthropogenic inputs in fluoride pollution.

Association between water fluoride and the level of children's intelligence: a dose-response meta-analysis

OBJECTIVES

Higher fluoride concentrations in water have inconsistently been associated with the levels of intelligence in children. The following study summarizes the available evidence regarding the strength of association between fluoridated water and children's intelligence.

STUDY DESIGN

Meta-analysis.

METHODS

PubMed, Embase, and Cochrane Library databases were systematically analyzed from November 2016. Observational studies that have reported on intelligence levels in relation to high and low water fluoride contents, with 95% confidence intervals (CIs) were included. Further, the results were pooled using inverse variance methods. The correlation between water fluoride concentration and intelligence level was assessed by a dose-response meta-analysis.

RESULTS

Twenty-six studies reporting data on 7258 children were included. The summary results indicated that high water fluoride exposure was associated with lower intelligence levels (standardized mean difference : -0.52; 95% CI: -0.62 to -0.42; P < 0.001). The findings from subgroup analyses were consistent with those from overall analysis. The dose-response meta-analysis suggested a significant association between water fluoride dosage and intelligence (P < 0.001), while increased water fluoride exposure was associated with reduced intelligence levels.

CONCLUSIONS

Greater exposure to high levels of fluoride in water was significantly associated with reduced levels of intelligence in children. Therefore, water quality and exposure to fluoride in water should be controlled in areas with high fluoride levels in water.

Fluoride enrichment in an alluvial aquifer with its subsequent effect on human health in Birbhum district, West Bengal, India

This research work primarily deals with the geochemistry and genesis of fluoride (F^-) in an alluvial aquifer with an emphasis on prevalence of dental and skeletal fluorosis among the endemic population. Hydrogeochemical outcomes reveal that chemical weathering and ion-exchange phenomena are the two dominant processes that make study area groundwater into NaHCO₃ water type. Presence of intercalated zeolite rich sediments (F_Total 412-446 mg/kg) having higher ion-exchange capacity (120-125 meq/100 g) within the aquifer is the source and mobilizing factors of F^- in groundwater respectively. Laboratory experiment further justifies higher desorption potential of aquifer sediments at the groundwater pH of 6.5-7.5. Health survey reveals that out of 235 studied population 60% suffer from dental fluorosis while females >30 years of age became exposed early to osteoporosis disease.

Effect of fluoridated water on intelligence in 10-12-year-old school children

Aim:

The aim of the present study was to evaluate the relationship of drinking water fluoride levels with children's intelligence quotient (IQ).

Materials and Methods:

Water was collected from initially identified endemic fluoride regions according to the geological research of Government of India. Fluoride concentration of the water was assessed by utilizing fluoride ion selective electrode, Orion 9609BN, and categorized on the basis of fluoride concentration into low, medium, and high-fluoride regions, i.e., Virajpet (low fluoride level < 1.2 ppm), Banavara (Medium fluoride level 1.2–2 ppm), and Mastihalli (High fluoride levels > 3 ppm). Government school from all three villages were selected randomly and IQ levels were assessed by using Raven's Standard Progressive Matrices. This test was conducted on each child in the study sample.

Results:

A significant inverse relationship was found between the fluoride concentration in drinking water and IQ (r value = −0.204; P < 0.000). It was observed that IQ level was negatively correlated with fluoride concentration in drinking water.

Conclusion:

It is concluded that IQ level was negatively correlated with fluoride level in drinking water. Factors that might affect children's IQ need to be considered, and it is necessary to devise solutions for preventing the harmful effects of excessive intake of fluoride ion to the body.