Fluoride: a risk factor for inflammatory bowel disease?

Alleviation of fluoride-induced colitis by tea polysaccharides: Insights into the role of Limosilactobacillus vaginalis and butyric acid

Endemic fluorosis has gained increasing attention as a public health concern, and the escalating risk of colitis resulting from excessive fluoride intake calls for effective mitigation strategies. This study aimed to investigate the potential mechanisms underlying the alleviation of fluoride-induced colitis by Tea polysaccharides (TPS). Under conditions of excessive fluoride intake, significant changes were observed in the gut microbiota of rats, leading to aggravated colitis. However, the intervention of TPS exerted a notable alleviating effect on colitis symptoms. Antibiotic intervention and fecal microbiota transplantation (FMT) experiments provided evidence that TPS-mediated relief of fluoride-induced colitis is mediated through its effects on the gut microbiota. Furthermore, TPS supplementation was found to modulate the structure of gut microbiota, enhance the relative abundance of Limosilactobacillus vaginalis in the gut microbiota, and promote the expression of short-chain fatty acid (SCFAs) receptors in colonic tissue. Notably, L. vaginalis played a significant role in alleviating fluoride-induced colitis and facilitating the absorption of butyric acid in the rat colon. Subsequent butyric acid intervention experiments confirmed its remarkable alleviating effect on fluoride-induced colitis. Overall, these findings provide a potential preventive strategy for fluoride-induced colitis by TPS intervention, which is mediated by L. vaginalis and butyric acid.

Progress in research on the role of fluoride in immune damage

Excessive fluoride intake from residential environments may affect multiple tissues and organs; however, the specific pathogenic mechanisms are unclear. Researchers have recently focused on the damaging effects of fluoride on the immune system. Damage to immune function seriously affects the quality of life of fluoride-exposed populations and increases the incidence of infections and malignant tumors. Probing the mechanism of damage to immune function caused by fluoride helps identify effective drugs and methods to prevent and treat fluorosis and improve people's living standards in fluorosis-affected areas. Here, the recent literature on the effects of fluoride on the immune system is reviewed, and research on fluoride damage to the immune system is summarized in terms of three perspectives: immune organs, immune cells, and immune-active substances. We reviewed that excessive fluoride can damage immune organs, lead to immune cells dysfunction and interfere with the expression of immune-active substances. This review aimed to provide a potential direction for future fluorosis research from the perspective of fluoride-induced immune function impairment. In order to seek the key regulatory indicators of fluoride on immune homeostasis in the future.

Effects of water fluoridation on early embryonic development of zebrafish

Fluoride has strong electronegativity and exposes diversely in nature. Water fluoridation is the most pervasive form of occurrence, representing a significant threat to human health. In this study, we investigate the morphometric and physiological alterations triggered by fluoride stimulation during the embryogenesis of zebrafish and reveal its putative effects of stage- and/or dose-dependent. Fluoride exhibits potent biological activity and can be extensively absorbed by the yolk sac, exerting significant effects on the development of multiple organs. This is primarily manifested as restricted nutrient utilization and elevated levels of lipid peroxidation, further leading to the accumulation of superoxide in the yolk sac, liver, and intestines. Moreover, pericardial edema exerts pressure on the brain and eye development, resulting in spinal curvature and reduced body length. Besides, acute fluoride exposure with varying concentrations has led to diverse teratogenic outcomes. A low dose of water fluoridation tends to induce abnormal development of the embryonic yolk sac, while vascular malformation is widely observed in all fluoride-treated groups. The effect of fluoride exposure on blood circulation is universally present, even in zebrafish larvae that do not exhibit obvious deformities. Their swimming behavior is also affected by water fluoridation, resulting in reduced activity and delayed reactions. In conclusion, this study provides valuable insights into the monitoring of environmental quality related to water fluoridation and disease prevention.

Intestinal microbiota regulates colonic inflammation in fluorosis mice by TLR/NF-κB pathway through short-chain fatty acids

Intestinal inflammation and microbial dysbiosis are found simultaneously in patients with fluorosis. However, whether the inflammation derived from fluoride exposure only or intestinal microbial disorders has not been clarified. In this study, 100 mg/L NaF exposure for 90 days significantly elevated the expressions of inflammatory factors (TNF-α, IL-1β, IL-6, IFN-γ, TGF-β, and IL-10), and the levels of TLR4, TRAF6, Myd88, IKKβ, and NF-κB P65 in mouse colon, while the above factors were reduced in pseudo germ-free mice with fluorosis, hinting that disordered microbiota might play a more direct role in the development of colonic inflammation than fluoride. Fecal microbiota transplantation (FMT) lowered the levels of inflammatory factors and inactivated the TLR/NF-κB pathway in fluoride-exposed mice. In addition, supplementing short-chain fatty acids (SCFAs) exhibited the identical effects to the model of FMT. In summary, intestinal microbiota may alleviate the colonic inflammatory of mice with fluorosis by regulating TLR/NF-κB pathway through SCFAs.

Does fluoride exposure impact on the human microbiome?

Fluoride is added to drinking water in some countries to prevent tooth decay (caries). There is no conclusive evidence that community water fluoridation (CWF) at WHO recommended concentrations for caries prevention has any harmful effects. However, research is ongoing regarding potential effects of ingested fluoride on human neurodevelopment and endocrine dysfunction. Simultaneously, research has emerged highlighting the significance of the human microbiome in gastrointestinal and immune health. In this review we evaluate the literature examining the effect of fluoride exposure on the human microbiome. Unfortunately, none of the studies retrieved examined the effects of ingested fluoridated water on the human microbiome. Animal studies generally examined acute fluoride toxicity following ingestion of fluoridated food and water and conclude that fluoride exposure can detrimentally perturb the normal microbiome. These data are difficult to extrapolate to physiologically relevant human exposure dose ranges and the significance to humans living in areas with CWF requires further investigation. Conversely, evidence suggests that the use of fluoride containing oral hygiene products may have beneficial effects on the oral microbiome regarding caries prevention. Overall, while fluoride exposure does appear to impact the human and animal microbiome, the long-term consequences of this requires further study.

Integrated 16S rDNA sequencing and metabolomics to explore the intestinal changes in children and rats with dental fluorosis

Dental fluorosis (DF) is a widely prevalent disease caused by excessive fluoride with limited awareness of its underlying pathogenesis. Here, a pilot population study was conducted to explore the pathogenesis of DF from the perspective of intestinal microbiome changes, and verified it in animal experiments combining intestinal microbiome and metabolomics. A total of 23 children were recruited in 2017 in China and divided into DF (n = 9) and control (n = 14) groups (DFG and CG, respectively). The SD rat model was established by drinking water containing sodium fluoride (NaF). Gut microbiome profiles of children and rats were analyzed by16S rDNA V3-V4 sequencing, and the intestinal metabolomics analysis of rats was performed by LC-MS methods. The 16 S rDNA sequencing revealed that the gut microbiome composition was significantly perturbed in children in DFG compared to that in CG. Acidobacteria and Thermi were specifically observed in DFG and CG, respectively. Besides, 15 fecal microbiotas were significantly altered at the genus level in DFG. Furthermore, only the expression of annotated genes for pentose and glucuronate interconversion pathway was significant lower in DFG than that in CG (P = 0.04). Notably, in NaF-treated rats, we also observed the changes of some key components of pentose and glucuronate interconversion pathway at the level of microorganisms and metabolites. Our findings suggested that the occurrence of DF is closely related to the alteration of intestinal microorganisms and metabolites annotated in the pentose and glucuronate interconversion pathway.

Fluoride exposure and blood cell markers of inflammation in children and adolescents in the United States: NHANES, 2013-2016

BACKGROUND

Ingestion of fluoride in drinking water has been shown to result in increased cellular markers of inflammation in rodent models. However, the approximately 5-10 × increase in water fluoride concentrations required in rat and mouse models to obtain plasma fluoride concentrations similar to those found in humans has made relevant comparisons of animal to human studies difficult to assess. As an increased white blood cell count (WBC) is a marker of inflammation in humans, we used available NHANES survey data to assess the associations between plasma fluoride levels in the U.S. and blood cell counts children and adolescents.   METHODS: Multiple linear regressions were done to determine the association of blood cell counts and plasma fluoride in publicly available NHANES survey data from the 2013-2014 and 2015-2016 cycles. Plasma fluoride concentration measurements were available only for children aged 6 to 19, inclusive, and therefore this subpopulation was used for all analyses. Covariate predictors along with plasma fluoride were age, ethnicity, gender, and Body Mass Index (BMI).  RESULTS: Plasma fluoride was significantly positively associated with water fluoride, total WBC count, segmented neutrophils, and monocytes, and negatively associated with red blood cell count when adjusted for age, gender and BMI.

CONCLUSION

Our finding that neutrophils and monocytes are associated with higher plasma fluoride in U.S. children and adolescents is consistent with animal data showing fluoride related effects of increased inflammation. These findings suggest the importance of further studies to assess potential mechanisms that are involved in absorption and filtration of ingested fluoride, particularly in tissues and organs such as the small intestine, liver and kidney.

In-depth insights into the disruption of the microbiota-gut-blood barrier of model organism (Bombyx mori) by fluoride

Fluoride is a serious health risk to animals and humans. The microbiota-gut-blood barrier (MGBB) plays an indispensable role in maintaining the systematic homeostasis of host organisms. However, the toxic effects of fluoride on MGBB of organisms have not been extensively investigated. Here, we used the silkworm interspecies model to explore the adverse effects of fluoride on the gut microbiota and intestinal tissue and circulating metabolites of organisms. Results showed that fluoride exposure significantly declined the body weight gain and survival rate of organisms and evidently damaged intestinal epithelial cells. In addition, fluoride altered the composition and abundance of intestinal microbiota, which was accompanied by changing gene expression levels of antimicrobial peptides in intestinal tissue. Shifts in the relative abundance of Enterococcus, Aquabacterium, Aureimonas and Methylobacterium in the gut had significant correlations with the concentrations of certain differential metabolites (e.g., amino acids, nucleotides, and nucleotide derivatives) in the bloodstream. Moreover, most circulating metabolites in related nucleotide metabolism pathways were upregulated, whereas those in the pathways of amino acid metabolism were downregulated. This study deepens our understanding of the disruptive effect of fluoride on the MGBB of host organisms and may provide a new insight into the preventive therapy of fluoride-induced diseases.

Metagenomic Analysis of Intestinal Microbiota in Florated Rats

Changes in gut microbiota have shown that it plays an important role in animal health and metabolic diseases. The intestinal microbiota is a complex structure that functions as an organ system with the presence of trillions of microorganisms. In this study, changes in the intestinal microbiota of Wistar rats with high fluorine were evaluated. Water containing 100 ppm NaF was given to 14 male Wistar albino rats as drinking water for 12 weeks. Fluorine is known to be an inducer of protein oxidation, lipid peroxidation, modulation of intracellular redox homeostasis, and oxidative stress. In this study, it was determined that the level of MDA (molandialdehyde), one of the oxidative stress parameters, increased significantly in the intestinal tissue after fluorine intoxication. The decrease in CAT (catalase) and SOD (superoxide dismutase) enzyme activities was found to be statistically significant. Intestinal tissues were taken under aseptic conditions and microorganisms found in flora were replicated by V3-V4 16S rRNA gene-specific primers. As a result of the sequence analysis, a statistical comparison of the control group and the fluorine applied group was made. The study we have done showed that there was a significant difference in species diversity in the intestinal microbiota of mice treated with fluorine. As a result, the composition of the intestinal microflora, especially Lactobacillus species, was significantly changed in rats with high fluorine.

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.

Toxic effects of fluoride in intestinal epithelial cells and the mitigating effect of methanol extract of coconut haustorium by enhancing de novo glutathione biosynthesis

Fluoride ions are an important environmental contaminant and pollutant found in a wide variety of environmental conditions. The fluoride in drinking water is evident to induce toxic effects including neurodegeneration, skeletal and dental fluorosis as well as organ damage. Nutraceuticals and functional foods are emerging as possible preventive agents against fluoride toxicity. Hence, the possible use of an emerging functional food-the coconut haustorium is being evaluated against sodium fluoride-induced toxicity in intestinal cells (IEC-6). The cells exposed to fluoride showed significant cell death mediated through the increased lipid peroxidation and glutathione depletion. The glutathione biosynthetic enzymes were inhibited by the exposure to fluoride and the apoptotic genes (caspases 3/7 and apaf-1) were upregulated. The CHE pre-treatment improved the activity of enzymes involved in the de novo biosynthesis of glutathione and subsequently improved the intracellular GSH pool. The improved antioxidant defense was also evident from the reduced expression of apoptotic genes (p < 0.05). Overall, the study concludes that fluoride ions induce oxidative stress-mediated apoptosis in intestinal epithelial cells, via inhibiting glutathione biosynthesis. Methanol extract of coconut haustorium increased glutathione biosynthesis and subsequently prevented fluoride toxicity in IEC-6 cells by virtue of its antioxidant potentials.

Common contributing factors to COVID-19 and inflammatory bowel disease

The devastating complications of coronavirus disease 2019 (COVID-19) result from an individual's dysfunctional immune response following the initial severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Multiple toxic stressors and behaviors contribute to underlying immune system dysfunction. SARS-CoV-2 exploits the dysfunctional immune system to trigger a chain of events ultimately leading to COVID-19. We have previously identified many contributing factors (CFs) (representing toxic exposure, lifestyle factors and psychosocial stressors) common to myriad chronic diseases. We hypothesized significant overlap between CFs associated with COVID-19 and inflammatory bowel disease (IBD), because of the strong role immune dysfunction plays in each disease. A streamlined dot-product approach was used to identify potential CFs to COVID-19 and IBD. Of the fifty CFs to COVID-19 that were validated for demonstration purposes, approximately half had direct impact on COVID-19 (the CF and COVID-19 were mentioned in the same record; i.e., CF---→COVID-19), and the other half had indirect impact. The nascent character of the COVID-19 core literature (∼ one year old) did not allow sufficient time for the direct impacts of many CFs on COVID-19 to be identified. Therefore, an immune system dysfunction (ID) literature directly related to the COVID-19 core literature was used to augment the COVID-19 core literature and provide the remaining CFs that impacted COVID-19 indirectly (i.e., CF---→immune system dysfunction---→COVID-19). Approximately 13000 potential CFs for myriad diseases (obtained from government and university toxic substance lists) served as the starting point for the dot-product identification process. These phrases were intersected (dot-product) with phrases extracted from a PubMed-derived IBD core literature, a nascent COVID-19 core literature, and the COVID-19-related immune system dysfunction (ID) core literature to identify common ID/COVID-19 and IBD CFs. Approximately 3000 potential CFs common to both ID and IBD, almost 2300 potential CFs common to ID and COVID-19, and over 1900 potential CFs common to IBD and COVID-19 were identified. As proof of concept, we validated fifty of these ∼3000 overlapping ID/IBD candidate CFs with biologic plausibility. We further validated 24 of the fifty as common CFs in the IBD and nascent COVID-19 core literatures. This significant finding demonstrated that the CFs indirectly related to COVID-19 -- identified with use of the immune system dysfunction literature -- are strong candidates to emerge eventually as CFs directly related to COVID-19. As discussed in the main text, many more CFs common to all these core literatures could be identified and validated. ID and IBD share many common risk/contributing factors, including behaviors and toxic exposures that impair immune function. A key component to immune system health is removal of those factors that contribute to immune system dysfunction in the first place. This requires a paradigm shift from traditional Western medicine, which often focuses on treatment, rather than prevention.

Borassus flabellifer Linn haustorium methanol extract mitigates fluoride-induced apoptosis by enhancing Nrf2/Haeme oxygenase 1 -dependent glutathione metabolism in intestinal epithelial cells

Fluoride is the most common cause of drinking water-associated toxicity and is known to induce various metabolic imbalances and dental/skeletal fluorosis. The present study analyzed the protective effect of Borassus flabellifer Linn. haustorium extract (BHE) against fluoride-induced intestinal redox metabolism and apoptosis. The total polyphenols and total flavonoids present in BHE were estimated to be 39.67 ± 5.14 mg gallic acid equivalent/g extract and 8.59 ± 0.74 mg quercetin equivalent. In cultured intestinal epithelial cells (IEC-6), sodium fluoride exposure-induced apoptosis mediated through antioxidant enzyme inhibition and subsequent oxidative damages. Further, there observed an increased expression of caspase-3, caspase-7, and apoptotic protease activating factor-1 (apaf-1) genes, increased cytochrome C release, and caspase 3/7 activity indicating the apoptosis- mediated cell death (p < 0.05). Upon pretreatment with BHE, the cytotoxic effect of fluoride was reduced by decreasing the expression of apoptotic genes and increased the cytochrome release as well as caspase 3/7 activity (p < 0.01). Providing the mechanistic basis, the expression of nuclear factor erythroid 2-related factor-2 (Nrf2)/haeme oxygenase-1 (HO1) gene was increased in the BHE pretreated cells; corroborating to these, there observed increased activity of glutathione biosynthetic enzymes (p < 0.05) and glutathione reductase. Hence, the protective effect of BHE may be mediated through Nrf2-mediated glutathione biosynthesis, the subsequent establishment of redox balance, and inhibition of apoptosis in intestinal epithelial cells.

Fluoride-Induced Alteration in the Diversity and Composition of Bacterial Microbiota in Mice Colon

Fluoride, as an environmental toxin, causes damage to intestinal mucosa. It may promote pathogen infection by increasing the intestinal mucosa permeability. In this study, the colonic fecal samples from the control group (C group, 0 mg/L NaF for 60 days) and the fluoride group (F group, 100 mg/L NaF for 60 days) were subjected to high-throughput 16S rRNA sequencing to verify the effects of fluoride on the colonic flora of animals. Results revealed a total of 253 operative taxonomical units (OTUs) in two groups, and 22 unique OTUs occurred in the F group. Fluoride increased the microbiota diversity and species richness of the colon. Concretely, the abundance of the Tenericutes was increased at the level of the phyla in the F group. In addition, in the F group, significant differences at the genus level were observed in Faecalibaculum, Alloprevotella, [Eubacterium]_xylanophilum_group, Prevotellaceae_UCG-001, and Ruminiclostridium_9, compared to the C group. Among them, except for the reduction in Faecalibaculum, the other four bacteria were increased in the F group. In summary, the intestinal microbial composition of mice was reconstituted by the presence of fluoride, and the significantly changing bacteria may partly account for the pathogenesis of fluoride-induced intestinal dysfunction.

History of Inflammatory Bowel Disease and Self-Reported Oral Health: Women's Health Initiative Observational Study

Background and Objective: Both periodontal disease and inflammatory bowel disease (IBD), are chronic inflammatory conditions, which are mediated by a complex interplay among a dysbiotic microbiota, dysregulated host immune-inflammatory responses, and lifestyle factors. Despite substantial differences in physical and chemical environments, rather strong correlations have been detected between microbial compositions of the oral cavity and stool. In this study, we tested the hypothesis that oral health conditions are affected by the presence of IBD. Materials and Methods: We analyzed the data from 73,621 women who were enrolled in the Women's Health Initiative observational cohort study and completed a follow-up questionnaire that surveyed oral health status specifically at year 5. Among these, 880 reported IBD at the baseline, including 47% who were symptomatic cases and 27% who were on immunosuppressive treatment. We estimated odds ratios (ORs) and 95% confidence intervals (CIs) for the association of IBD and medication status for self-reported oral health outcomes, using logistic regression models, adjusted for selected covariates. Results: IBD was not associated with periodontal disease history itself in a multivariable model; however, poorer self-rated oral health was modestly associated with the presence of IBD (OR = 1.15, 95% CI: 1.01-1.30). Likewise, more frequent eating limitations due to teeth were associated with the presence of IBD history (OR = 1.22, 95% CI: 1.07-1.39). When IBD cases were limited to those who were symptomatic, the associations with these two self-rated oral health outcomes were more pronounced with ORs of 1.28 (95% CI: 1.07-1.54) and 1.36 (95% CI: 1.07-1.54), respectively. Immunosuppressive treatment had little effect on these risk estimates. Conclusions: Among this nation-wide cohort of women 50-79 years of age, history of IBD was associated with poorer perceived oral health status.

Alterations in cecal microbiota and intestinal barrier function of laying hens fed on fluoride supplemented diets

The objective of this study was to investigate the effects of fluorine at levels of 31, 431, 1237 mg/kg feed on cecum microbe, short-chain fatty acids (SCFAs) and intestinal barrier function of laying hens. The results showed that the intestinal morphology and ultrastructure were damaged by dietary high F intake. The mRNA expression levels of zonula occludens-1, zonula occludens-2, claudin-1, and claudin-4 were decreased in jejunum and ileum. However, the concentrations of serum diamine oxidase, and D-lactic acid and intestinal contents of interleukin 1 beta, interleukin 6, and Tumor necrosis factor-alpha were increased. Consistent with this, dietary high F intake altered the cecum microbiota, with increasing the concentration of pathogens, such as Proteobacteria and Escherichia-Shigella, as well as, decreasing the contents of beneficial bacteria, such as Lactobacillus, and expectedly, reduced the SCFAs concentrations. In conclusion, the actual results confirmed that (1) high dietary F intake could damage the intestinal structure and function, with impaired intestinal barrier and intestinal inflammation, and (2) destroy the cecum microbial homeostasis, and decrease the concentrations of SCFAs, which aggravate the incidence of intestinal inflammation in laying hens.

Principles of fluoride toxicity and the cellular response: a review

Fluoride is ubiquitously present throughout the world. It is released from minerals, magmatic gas, and industrial processing, and travels in the atmosphere and water. Exposure to low concentrations of fluoride increases overall oral health. Consequently, many countries add fluoride to their public water supply at 0.7-1.5 ppm. Exposure to high concentrations of fluoride, such as in a laboratory setting often exceeding 100 ppm, results in a wide array of toxicity phenotypes. This includes oxidative stress, organelle damage, and apoptosis in single cells, and skeletal and soft tissue damage in multicellular organisms. The mechanism of fluoride toxicity can be broadly attributed to four mechanisms: inhibition of proteins, organelle disruption, altered pH, and electrolyte imbalance. Recently, there has been renewed concern in the public sector as to whether fluoride is safe at the current exposure levels. In this review, we will focus on the impact of fluoride at the chemical, cellular, and multisystem level, as well as how organisms defend against fluoride. We also address public concerns about fluoride toxicity, including whether fluoride has a significant effect on neurodegeneration, diabetes, and the endocrine system.

Intestinal fungal dysbiosis in mice induced by fluoride

To explore the effects of fluoride on intestinal fungi in mice, the internal transcriptional spacer (ITS) region in colon feces of mice exposed to 100 mg sodium fluoride (NaF)/L of distilled water for 60 days were sequenced. Results showed that, there were 305 operational taxonomic units (OTUs) unique to the control group, 154 OTUs to the fluoride group, and 295 OTUs were detected in both groups. There was no significant difference in relative species abundance between the two groups at phylum levels. Compared with control group, Ustilaginomycetes class, showed a significant change in fluoride group. At the genus level, Epicoccum, Penicillium, Microdochium, Plectosphaerella and Pluteus were significantly affected by fluoride exposure. Among them, there was a strong positive correlation between Penicillium and Pluteus (+0.43). Therefore, it showed that fluoride can influence the relative species abundance of intestinal fungi in mice, mainly at the genus levels. It can provide some new ideas about the harmful effects of fluorosis on intestinal fungal homeostasis.

Exploring a multi-exposure-pathway approach to assess human health risk associated with groundwater fluoride exposure in the semi-arid region of east India

Human health risks associated with groundwater fluoride have been assessed using USEPA method in few parts of India, but those assessments were conducted based on a single value for each parameter, which may lead to certain inaccuracy and uncertainties in results. In this study, a higher degree of accuracy in health risk assessment was achieved through Monte Carlo simulations, sensitivity analysis and uncertainty analysis. As fluoride hazards to human health are chronic, a total of 4560 water samples (N = 4560) were collected during consecutive four seasons (2 pre-monsoon and 2 post-monsoon seasons; 1140 samples/season) from the entire Birbhum district, covering all the blocks and geological settings to obtain the spatiotemporal variation of fluoride level. The Empirical Bayesian Kriging geostatistical model was employed to determine fluoride endemic areas. Amongst all blocks, Nalhati-1 had exhibited the highest fluoride level (18.25 mg/L). The study revealed that most of the blocks are vulnerable to groundwater fluoride due to its occurrences in excess level. The average and 95th percentile values of total hazard index indicate that the infants and children populations of the district are more susceptible than the adults and teens. The sensitivity analysis revealed that water ingestion rate and fluoride concentration are the most influential parameters for higher risk of fluoride-related health hazards. Health risks were evaluated through ingestion and dermal exposure routes for infants, children, teens, and adult residents. The exposure was much higher through ingestion than dermal contacts. Ingestion of defluoridated water will reduce the health risks associated with groundwater fluoride exposure.