Fluoride exposure from groundwater as reflected by urinary fluoride and children's dental fluorosis in the Main Ethiopian Rift Valley

TET1 mitigates prenatal fluoride-induced cognition impairment by modulating Bcl2 DNA hydroxymethylation level

Fluoride exposure during pregnancy commonly compromises fetal neurodevelopment and largely results in a broad spectrum of cognitive deficiencies in the adult offspring. However, the precise mechanisms underlying these effects remain to be fully elucidated. Herein, we investigate the impacts of fluoride on neural excitability and apoptosis, synaptic plasticity, and cognitive function, as well as possible underlying mechanisms. Our results indicated that exposure to a high sodium fluoride (100 mg/L) during pregnancy in the mouse can cause the cognitive deficits of their offspring, accompanied by a decrease in the expression of Tet-eleven translocation protein 1 (TET1), an enzyme responsible for DNA hydroxymethylation. Additionally, there is a reduction in the dendritic spine density and the expression of postsynaptic density protein-95 (PSD95) in the hippocampal regions of male offspring. Furthermore, in vitro fluoride treatment significantly exacerbates neuronal apoptosis and reduces the frequency of spikes in spontaneous action potential. More significantly, we also found that TET1 could directly bind to the promotor region of Bcl2, altering its DNA hydroxymethylation and Bcl2 expression. Intriguingly, Tet1 knock-out mice exhibited cognitive deficits similar to those observed in male animals exposed to high levels of fluoride. Furthermore, the down-regulation of TET1 protein, along with the consequent alteration in Bcl2 hydroxymethylation and increased neuronal apoptosis, are likely mechanisms underlying the impact of prenatal fluoride exposure on the neurodevelopment of male offspring. These findings provide novel insights into the molecular mechanisms by which fluoride exposure induces neurodevelopmental impairment of the male offspring.

Fluoride-Mediated Immune Damage Through Cytokine Network Regulation of Tregs

Long-term fluoride exposure can induce inflammatory responses in various tissues of the body, thereby affecting the inflammatory microenvironment. To explore how fluoride induces changes in immune function within this microenvironment, this study collected baseline information and biological samples from participants in areas with the drinking water type of fluorosis, and simultaneously established Wistar rat models with a 12-week and 24-week fluoride exposure, as well as a 12-week fluoride exposure followed by 12-week pure water feeding regimen. Luminex multiplex assays and enzyme-linked immunosorbent assays (ELISAs) were used to measure cytokine expression levels. Subsequently, correlation analysis, multiple linear regression, and mediation analysis were employed to explore the long-term effects induced by the complex cytokine network during fluoride exposure. The population survey results indicated that fluoride suppressed the expression of pro-inflammatory factors such as Interleukin-2 (IL-2), Interleukin-12 (IL-12), Interferon-γ (IFN-γ), Tumor necrosis factor-α (TNF-α), and anti-inflammatory factors such as Interleukin-4 (IL-4), Interleukin-13 (IL-13), and Interleukin-37 (IL-37), while promoting an increase in the proportion of regulatory T cells (Tregs) in peripheral blood. Among these, IL-2 and IFN-γ mediated the fluoride-induced peripheral Tregs expansion. Animal experiments indicate that the proportion of Tregs in peripheral blood and immune organs increases in a time-dependent manner with fluoride exposure. After reducing the fluoride concentration in the drinking water of rats, the number of Tregs remained significantly elevated. The changes in Treg numbers in the 12-week fluoride feeding group, 24-week fluoride feeding group, and 12-week fluoride feeding followed by 12-week water improvement group were related to the cytokine levels. Therefore, the impact of fluoride on the immune homeostasis has cumulative and long-term effects, and may be related to the accumulation and migration of Tregs induced by fluoride in an inflammatory environment, mediated by cytokines.

The potential of urinary miR-200c-3p as a biomarker of fluorosis in rats

Fluorine is a strong oxidizing element and excessive intake can have harmful effects, particularly on the body's calcified tissues. Recent studies have demonstrated a link between miRNA and fluorosis. This study aimed to evaluate the time-dose-effect relationship of miR-200c-3p in plasma, urine and cartilage of rats with drinking water fluorosis, and to explore its potential as a biomarker. Analyses were conducted using Generalised linear models, Restricted cubic spline, Spearman correlation analysis, and Receiver operating characteristic curve (ROC). Results indicated that both fluoride exposure time and dose had significantly affected on urinary and cartilage miR-200c-3p expression in rats, while plasma miR-200c-3p expression was only influenced by fluoride exposure time. Restricted cubic spline plots revealed that urinary miR-200c-3p was non-linearly and positively correlated with serum fluoride, urinary fluoride, dental fluorosis, and Mankin score groups, and also linearly and positively correlated with cartilage fluoride. Regression analysis showed that for each unit increase in urinary miR-200c-3p, the likelihood of dental fluorosis increased by 1.300 times, and in the Mankin score groups, the likelihood increased by 1.251 times. The ROC curves demonstrated that urinary miR-200c-3p had high sensitivity and specificity in diagnosing dental and skeletal fluorosis. Blood and cartilage miR-200c-3p showed weaker diagnostic efficacy. In summary, fluoride has different effects on the expression levels of miRNA-200c in various biological samples of rats, and miRNAs in urine demonstrate potential as biomarkers for fluorosis.

Low cost materials for fluoride removal from groundwater

In several parts of the world, high fluoride concentrations in groundwater have been reported.Fluoride concentrations above the World Health Organization's (WHO) threshold level of 1.5 mg/L in drinkable water pose a health concern for communities and the environment. The distribution of fluoride is mainly related to the geological environment: rocks that contain fluorine, for example basalt, shale, and granite, release their respective minerals containing fluoride to the groundwater by dissolution. Excessive fluoride intake leads to dental and skeletal fluorosis, fragile bones, cancer, infertility, damage to the brain function, Alzheimer syndrome, and thyroid disorder. Cheap, abundant, and locally available fluoride removal techniques are needed to meet the requirement for fluoride-free drinking water in developing countries, especially in rural communities. Different conventional methods, such as membrane technologies, ion exchange, coagulation and precipitation techniques, are employed to remove fluoride from drinking water. However, only a few of these techniques can be applied at large-scale in developing countries due to their high investment costs, high maintenance and operating costs, and the possibility of producing toxic intermediates during the treatment process. Unlike conventional methods, adsorption is a promising technology due to its simple operation in a batch or continuous systems, simple design, low-cost of operation and wide range of locally available adsorbents. Adsorption is widely applied for removing fluoride from groundwater and wastewater, effectively maintaining water quality and taste. Based on the review, adsorption stands out as the best method for fluoride removal, considering surface modification and regeneration to increase the efficiency of adsorbent materials. This makes it an ideal solution for ensuring safe drinking water in resource-limited settings.

Is the Tigray region, Ethiopia also affected by fluoride in drinking water affecting public health?

The purpose of this study was to assess the levels of fluoride in drinking water and its health impact in Semema, Tigray, Ethiopia. Water samples were collected in February, March and April from three potential spring water sources, namely May Atkaru, May Sensela and May Liham. Each sample was analyzed for a variety of physicochemical parameters including fluoride using standard APHA procedures through double beam UV-Visible spectrophotometer, atomic absorption spectrophotometer and titrimetric methods. All the measured physicochemical parameters except hardness (345.78-368.35 mg/L) and alkalinity (231.3-354.6 mg/L) were recorded below the WHO permissible limit set for drinking water. The amount of fluoride in May Atkaru (4.00 mg/L) and May Sensela (3.89 mg/L) was significantly greater than the WHO permissible limit set for drinking water, 1.5 mg/L. Moreover, HQ > 1 from May Atkaru and May Sensela revealed the possibility of dental and skeletal fluorosis over extended exposure to fluoride irrespective of age and sex variations. This confirmed people in the area with mottled teeth are vulnerable to the excessive consumption of fluoride, which poses health risks. Therefore, it needs immediate interventions to minimize the debilitating effect of fluoride in drinking water by creating awareness among the community and policymakers to introduce low-cost defluoridation methods.

Investigation of fluoride concentrations, water quality, and non-carcinogenic health risks of borehole water in bongo district, northern Ghana

Access to potable water is a significant concern due to the increasing global threat posed by fluoride contamination in groundwater sources. This study investigated the concentrations of fluoride (F-), the suitability of groundwater for human consumption, the physicochemical characteristics affecting the water quality, and non-carcinogenic adverse health risks to both children and adults in the Bongo district in Northern Ghana. The findings revealed that the groundwater had a mean pH, salinity, TDS, conductivity, and turbidity below the WHO guideline values with a mean fluoride concentration of 1.76 mg/L above the guideline limit of 1.5 mg/L. The study also found that there was no strong relationship between fluoride and the measured water parameters, which may be attributed to poor control of distribution, transport mechanisms, and sources. The WQI scores ranged from 42.62% to 70.72%, indicating that all borehole water samples were of good and excellent quality. The average chronic daily intake showed that children are often more exposed to the harmful impact of fluoride than adults. The average HQ > 1 indicates the probability of dental and skeletal fluorosis after continuous exposure over time in adults and children. The study recommends taking immediate action to mitigate high groundwater fluoride concentrations, implementing appropriate water management strategies, and raising public awareness of the health risks. These measures can guide future groundwater management practices and help policymakers address contamination and protect local communities.

Unraveling gene expression and genetic instability in dental fluorosis: Investigating the impact of chronic fluoride exposure

Chronic fluoride exposure, even in small quantities, when continuously ingested by the human population, can lead to a significant public health concern known as fluorosis. Our understanding of the effects of fluoride on human health, as well as its potential to impact DNA, is limited. The present study aimed to assess genetic instability in 20 individuals diagnosed with dental fluorosis and 20 individuals without the condition from the state of Rio Grande do Sul, Brazil. The participants' dental fluorosis was evaluated using the Thylstrup-Fejerskov index (TF). To further evaluate genetic instability, several assays were conducted, including the alkaline and modified (+FPG) comet assay (using a visual score, VS), the buccal micronucleus (MN) cytome (BMCyt) assay, the cytokinesis-block MN (CBMN-Cyt) assay, and the measurement of telomere length (TL). In addition, the study utilized tools from Systems Biology to gain insights into the effects of fluoride exposure on humans, which aided in the selection and evaluation of mRNA expression levels of specific genes, namely PPA1 (inorganic pyrophosphatase 1), AQP5 (Aquaporin 5), and MT-ATP6 (Mitochondrially Encoded Adenosine Triphosphate Synthase Membrane Subunit 6). Furthermore, fluoride levels in the blood and urine were assessed using an ion-selective electrode, along with the evaluation of the inflammatory response in serum. The group with dental fluorosis exhibited 2.18 times higher MN frequencies specifically when assessed using the CBMN-Cyt assay, in comparison with individuals without fluorosis. Findings from the enzyme-modified comet assay indicated oxidative damage to purines in DNA. Furthermore, a decrease in TL was observed, along with elevated expression patterns of the PPA1 and AQP5 genes, and significant alterations in cytokine release. Significant correlations were identified between the TF and age, as well as the levels of necrotic cells. Additionally, noteworthy correlations were established between fluoride levels and the levels of MN, VS, and MT-ATP6. Although dental fluorosis results from fluoride exposure, our research highlights the potential influence of this condition on genomic instability and gene expression. Consequently, our findings stress the importance of continuously monitoring populations with a high incidence of dental fluorosis to enhance our comprehension of how genomic instability might correlate with the origins and consequences of health problems in these individuals.

Association between fluoride exposure in drinking water and cognitive deficits in children: A pilot study

Fluoride (F) exposure in drinking water may lead to reduced cognitive function among children; however, findings largely remain inconclusive. In this pilot study, we examined associations between a range of chronic F exposures (low to high: 0.4 to 15.5 mg/L) in drinking water and cognition in school-aged children (5-14 years, n = 74) in rural Ethiopia. Fluoride exposure was determined from samples of community-based drinking water wells and urine. Cognitive performance was measured using: 1) assessments of ability to draw familiar objects (donkey, house, and person), and 2) a validated Cambridge Neuropsychological Test Automated Battery's (CANTAB) Paired Associate Learning (PAL), which examines memory and new learning and is closely associated with hippocampus function of the brain. Associations between F and cognitive outcomes were evaluated using regression analysis, adjusting for demographic, health status, and other covariates. The median (range) of water and urine F levels was 7.6 (0.4-15.5 mg/L) and 6.3 (0.5-15.7 mg/L), respectively; these measures were strongly correlated (r = 0.74), indicating that water is the primary source of F exposure. Fluoride in drinking water was negatively associated with cognitive function, measured by both drawing and CANTAB test performance. Inverse relationships were also found between F and drawing objects task scores, after adjusting for covariates (p < 0.05). Further analysis using CANTAB PAL tasks in the children confirmed that F level in drinking water was positively associated with the number of errors made by children (p < 0.01), also after adjusting for covariates (p < 0.05). This association between water F and total errors made became markedly stronger as PAL task difficulty increased. Fluoride exposure was also inversely associated with other PAL tasksthe number of patterns reached, first attempt memory score and mean errors to success. These findings provide supportive evidence that high F exposures may be associated with cognitive deficits in children. Additional well-designed studies are critically needed to establish the neurotoxicity of F in children and adults exposed to both low levels known to protect dental caries, as well as excess F levels in drinking water.

A Systematic Review on Water Fluoride Levels Causing Dental Fluorosis

Dental fluorosis is a long-existing public health issue resulting from inequitable access to potable water. Socially disadvantaged rural communities in fluoride-endemic areas, where a conventional irrigation system is absent and groundwater containing natural fluoride is the predominant source of drinking water, face a significant oral public health threat. This study aimed to determine the association between water fluoride levels and dental fluorosis. A systematic review aligned with PRISMA principles was conducted using the SPIDER search methodology and relevant keywords on many search engines, such as Google Scholar, PubMed, Elsevier, Sage, Web of Science, Cochrane, and Scopus. This review sought to ascertain the PICO model’s application as a search strategy tool. The reviewers gathered and assessed 1164 papers from January 2010 to January 2023. In total, 24 research papers from diverse databases were included. Using the Newcastle–Ottawa Scale, grades resulting from several data screens were evaluated. According to a previous systematic review, there may be publication bias in studies examining the association between fluoride in drinking water and dental fluorosis. The findings of this systematic review indicate that subpar fluoride is detrimental to human health. The author outlines legislative tools and technological advancements that might reduce fluoride levels.

Fluoride-Induced Cortical Toxicity in Rats: the Role of Excessive Endoplasmic Reticulum Stress and Its Mediated Defective Autophagy

The cerebral cortex is closely associated with learning and memory, and fluoride is capable of inducing cortical toxicity, but its mechanism is unclear. This study aimed to investigate the role of endoplasmic reticulum stress and autophagy in fluoride-induced cortical toxicity. Rats exposed to sodium fluoride (NaF) were used as an in vivo model. The results showed that NaF exposure impaired the learning and memory capacities and increased urinary fluoride levels in rats. In addition, NaF exposure induced excessive endoplasmic reticulum stress and associated apoptosis, as evidenced by elevated IRE1α, GRP78, cleaved caspase-12, and cleaved caspase-3, as well as defective autophagy, as evidenced by increased expression of Beclin1, LC3-II, and p62 in cortical areas. Importantly, the endoplasmic reticulum stress inhibitor 4-phenylbutyric acid (4-PBA) alleviated endoplasmic reticulum stress as well as defective autophagy, thus confirming the critical role of endoplasmic reticulum stress and autophagy in fluoride-induced cortical toxicity. Taken together, these results suggest that excessive endoplasmic reticulum stress and its mediated defective autophagy lead to fluoride-induced cortical toxicity. This provides new insights into the mechanisms of fluoride-induced neurotoxicity and a new theoretical basis for the prevention and treatment of fluoride-induced neurotoxicity.

Utilization of Community-Level Fluoride-Filtered Water and its Associated Factors in Dugda Woreda of East Shewa Zone, Oromia Region, Ethiopia

BACKGROUND

Long-term consumption of water containing an excessive amount of fluoride causes dental and skeletal fluorosis. De-fluoridation options differ in terms of scale, efficacy, long-term viability, and user acceptance. Therefore, this study aimed to identify the challenges of using fluoride-filtered water and its associated factors among households.

METHODS

A cross-sectional study was conducted from April to May, 2018 among 405 randomly selected households in Dugda Woreda of Ethiopia Rift Valley East Shewa Zone, Oromia Region. A structured interviewer-administered questionnaire was used to collect the data. SPSS version 20 was used to enter and analyze the collected data. Logistic regression analysis was used to identify association between dependent and independent factors and explained by odds ratio with 95%CI.

RESULTS

A total of 228 (56.3%) households were found to utilize fluoride filtered water from community water supply schemes for drinking and cooking purposes. No family history of fluorosis (AOR = 44.4, 95%CI: 18.8, 104.74), monthly income of less than 1000 ETB (AOR = 0.03, 95%CI: 0.004, 0.23), good knowledge of community fluoride filter schemes (AOR = 5.93, 95%CI: 1.30, 26.9), and not afford to pay bill of ⩾0.50 ETB [AOR = 0.4, 95%CI: 0.20, 0.91] were factors significantly associated with utilization of community-level fluoride-filtered water.

CONCLUSION

In this study, more than half of the households used fluoride filtered water. Family monthly income, affordability, presence of family members with the history of fluoride exposure, and knowledge about community fluoride filter schemes were factors significantly associated with utilization of community-level fluoride-filtered water.

Associations of low level of fluoride exposure with dental fluorosis among U.S. children and adolescents, NHANES 2015-2016

Drinking water fluoridation was a mid-twentieth century innovation based on the medical hypothesis that consuming low doses of fluoride at the teeth forming years provided protection against dental decays. Numerous studies showed that high level exposure to fluoride could cause dental and skeleton fluorosis. However, there was limited study focusing on the fluorosis effect of low levels of exposure to fluoride. Therefore, our study aimed to examine whether the low level of fluoride exposure (measured in blood plasma and household tap water) was associated with the risk of dental fluorosis based on data of the National Health and Nutrition Examination Survey (NHANES) 2015-2016. We analyzed data in 2098 children and adolescents who had Dean's Index scores, and water and plasma fluoride measures. The Dean's Index score was measured by calibrated dental examiners using the modified Dean's fluorosis classification system. Fluoride was measured in plasma and household tap water. In this study, we found that the rate of fluoride concentration in water above the recommended level of 0.7 mg/L was 25%, but the prevalence of dental fluorosis was 70%. Binary logistic regression adjusted for covariates showed that higher water fluoride concentrations (0.31-0.50, 0.51-0.70, > 0.70 compared 0.00-0.30) were associated with higher odds of dental fluorosis (OR = 1.48, 95% CI: 1.13-1.96, p = 0.005; OR = 1.92, 95% CI: 1.44-2.58, p < 0.001, and OR = 2.30, 95% CI: 1.75-3.07, p < 0.001, respectively). The pattern of regression between plasma fluoride and dental fluorosis was similar. Inclusion, our study showed that even low level of water or plasma fluoride exposure was associated with increased the risk of dental fluorosis. The safety of public health approach of drinking water fluoridation for global dental caries reduction are urgently needed further research.

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

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

Urinary Fluoride Levels among Canadians with and without Community Water Fluoridation

Drinking water is a major source of dietary fluoride intake in communities with water fluoridation. We examined the association between urinary fluoride adjusted for specific gravity (UFSG) and tap water fluoride levels, by age and sex, among individuals living in Canada. Participants included 1629 individuals aged 3 to 79 years from Cycle 3 (2012-2013) of the Canadian Health Measures Survey. We used multiple linear regression to estimate unique associations of tap water fluoride levels, age, sex, ethnicity, body mass index (BMI), use of fluoride-containing dental products, smoking in the home, and tea consumption with UFSG. UFSG concentration was significantly higher among participants who received fluoridated drinking water (mean = 1.06 mg/L, standard deviation = 0.83) than among those who did not (M = 0.58 mg/L, SD = 0.47), p < 0.01. UFSG increased over adulthood (ages 19 to 79). Higher UFSG concentration was associated with being female, tea drinking, and smoking in the home. In conclusion, community water fluoridation is a major source of contemporary fluoride exposure for Canadians. Lifestyle factors including tea consumption, as well as demographic variables such as age and sex, also predict urinary fluoride level, and are therefore important factors when interpreting population-based fluoride biomonitoring data.

Associations between Urinary, Dietary, and Water Fluoride Concentrations among Children in Mexico and Canada

Fluoride, which may be toxic to the developing brain, is added to salt in Mexico and drinking water in Canada to prevent dental caries. We compared childhood urinary fluoride (CUF) concentrations in Mexico City and Canada to characterize patterns of fluoride exposure in these two populations. We also examined associations of CUF with dietary and water fluoride levels in Mexico City and Canada respectively. We included 561 children (ages 4–6; mean age 4.8 years) from the Programming Research in Obesity, Growth, Environment, and Social Stress (PROGRESS) cohort in Mexico City, and 645 children (ages 2–6; mean age 3.7 years) from the Maternal–Infant Research on Environmental Chemicals (MIREC) cohort in Canada. We applied Spearman correlations, T-tests, ANOVA or covariate-adjusted linear regression to examine associations of CUF (mg/L; adjusted for specific gravity) with demographics and dietary or water fluoride concentrations. We used Welch equivalence testing to compare means across cohorts. Mean (SD) CUF was equivalent (t = 4.26, p < 0.001) in PROGRESS: 0.74 (0.42) and fluoridated Canadian communities: 0.66 (0.47), but lower in non-fluoridated Canadian communities: 0.42 (0.31) (t = −6.37, p < 0.001). Water fluoride concentrations were significantly associated with CUF after covariate adjustment for age and sex in MIREC (B = 0.44, 95% CI: 0.30, 0.59, p < 0.001). In contrast, daily food and beverage fluoride intake was not associated with CUF in PROGRESS (p = 0.82). We found that CUF levels are comparable among children in Mexico City and fluoridated Canadian communities, despite distinct sources of exposure. Community water fluoridation is a major source of fluoride exposure for Canadian children.

A review on the potential sources and health implications of fluoride in groundwater of Sub-Saharan Africa

Groundwater is a major source of drinking water for millions of people around the world. Over 400 million people in Africa depend solely on it as their main source of water supply. Fluoride is a common contaminant in groundwater. In low concentration (0.5-1.0 mg/L), fluoride is needed by humans for healthy development of bones and teeth, however, a concentration >1.5 mg/L has been linked with several fluorosis and non-fluorosis diseases. Dental and skeletal fluorosis are the major fluorosis diseases commonly reported with the consumption of fluoride-rich water. Although fluoride intake through other pathways such as the drinking of tea and eating of vegetables have been reported, the drinking of fluoride-rich water remains the major pathway of fluoride into humans. Cases of high fluoride levels in groundwater have been reported in almost all the sub-Saharan Africa region but it is more prevalent in East African countries, Sudan and South Africa. Although fluoride is present in surface water mostly in the East African Rift Valley across different countries in East Africa, its significant or high levels are usually associated with groundwater. Geogenic sources such as fluorite, apatite, biotite, amphibole, micas, topaz, cryolite, muscovite and fluorspar have been identified as the major sources of fluoride in groundwater. High fluoride levels have been reported across sub Saharan Africa, with generally higher levels in East Africa resulting from the volcanic activities in the rift system. Dental fluorosis has been reported in many sub-Saharan African countries including South Africa, Tanzania, Uganda, Ethiopia, Kenya, Sudan, Niger, Nigeria, Benin, Ghana and Malawi. Geothermal temperature has been regarded as one of the driving forces for high fluoride levels recorded in groundwater from deep aquifers and geothermal springs. The most affected people with the consumption of fluoride-rich water are the poor with low socioeconomic status who live in rural areas. Some of the proposed alternative sources include rainwater and fog water harvesting and blending of water from various sources. Low-cost and sustainable deflouridation technique remains one of the best ways to treat fluoride contaminated water either at communal level or at the point-of-use.

Periodontal and dental conditions of a school population in a volcanic region of Tanzania with highly fluoridated community drinking water

Introduction

Dental fluorosis is endemic in the Rift Valley in Africa, especially around volcanic areas, due to the high fluoride content in daily drinking water.

Objective

This study evaluates the oral health status and types of occlusion in a school population, and to assess the possible association between dental fluorosis and other pathologies such as decay, gingivitis and periodontitis.

Material and methods

An observational study of 581 individuals recruited from a public secondary school in Arusha, Northern Tanzania was undertaken. The indices used were: the Silness & Löe Plaque Index, the Community Periodontal Index and the Decayed/Missing/Filled index. Descriptive statistical analyses were performed and a chi-square test was used to assess the associations between independent variables.

Results

Almost all the school children evaluated (96.73%) presented Angle class I dental occlusion, and 75.22% presented some degree of dental fluorosis. Most of the population (511, 87.95%) showed bleeding on probing. A moderate/high degree of some dental pathology (DMF score) was recorded in 14.46%. The association between dental fluorosis, gingival bleeding and tooth decay indicated a higher concentration of pathology in groups with more severe fluorosis (p<0.05).

Conclusion

In this large population sample, both tooth decay and gingivitis were significantly associated with moderate or severe dental fluorosis.

Fluoride concentration in ground water and prevalence of dental fluorosis in Ethiopian Rift Valley: systematic review and meta-analysis

BACKGROUND

The concentration of fluoride in ground drinking water greater than the world health organization standard value imposes a serious health, social and economic problem in developing countries. In the Ethiopian Rift Valley where deep wells are the major source of drinking water, high fluoride level is expected. Though many epidemiological studies on fluoride concentration and its adverse effects have been conducted in the region, the result is highly scattered and needs systematically summarized for better utilization.

OBJECTIVE

This research is aimed at estimating the pooled level of fluoride concentration in ground drinking water and the prevalence of dental fluorosis among Ethiopian rift valley residences.

METHODS

Cochrane library, MEDLINE/PubMed and Google scholar databases were searched for studies reporting the mean concentration of fluoride in ground water and prevalence of dental fluorosis in Ethiopian Rift valley. Search terms were identified by extracting key terms from reviews and selected relevant papers and review medical subject headings for relevant terms.

RESULTS

The mean fluoride level in ground water and the prevalence of dental fluorosis were pooled from eleven and nine primary studies conducted in Ethiopian Rift Valley respectively. The pooled mean level of fluoride in ground water therefore was 6.03 mg/l (95% CI; 4.72-7.72, p < 0.001) and the pooled prevalence of dental fluorosis among residents in Ethiopian rift valley was 32% (95% CI: 25, 39%, p < 0.001), 29% (95% CI: 22, 36%, p < 0.001) and 24% (95% CI: 17, 32%, p < 0.001 for mild, moderate and sever dental fluorosis respectively. The overall prevalence of dental fluorosis is 28% (95% CI, 24, 32%, p < 0.001).

CONCLUSIONS

Though, the concentration level varies across different part of the rift valley region, still the level of fluoride in ground drinking water is greater than the WHO standard value (1.5 mg/l). Relatively high-level pooled prevalence of dental fluorosis was also seen in Ethiopian rift valley. Therefore, further studies covering the temperature, exposure time and other intake path ways with large sample size is recommended. Interventional projects should be implemented to decrease the concentration of fluoride in the ground drinking water source.

The use of urinary fluoride excretion to facilitate monitoring fluoride intake: A systematic scoping review

BACKGROUND

As a recognised effective and economical agent for dental caries prevention, fluoride has been used in many different fluoridation schemes implemented across the world. Considering the narrow 'dose-gap' between the benefit of caries reduction and the risk of dental fluorosis, it is recommended that fluoride intake is monitored by measuring urinary fluoride excretion. The aim of this scoping review is to map the current literature/evidence on fluoride intake and excretion studies in relation to the study population, settings, type of study design, methodology, and analytical approach.

METHODS

Embase/Ovid, MEDLINE/Ovid, CINAHL/EBSCO, Scopus/Elsevier were searched for relevant articles until April 2018. Studies were included if they reported intake and excretion of fluoride in healthy humans of all age groups. Findings were explored using a narrative synthesis to summarise studies characteristics and outcome measures.

RESULTS

Removal of duplicates from the originally 2295 identified records yielded 1093 studies of which 206 articles were included. Only 21.6% of the studies were conducted in children (<8-year-olds). Most studies (38.8%) used drinking water concentration as a proxy for fluoride intake, whereas only 11.7% measured fluoride intake from all sources. Of the 72 studies that measured dietary fluoride intake, only 10 reported the validity of the employed dietary assessment method. Only 14 studies validated the urine sample collection methods. No information on the validity of the employed analytical method was reported by the majority (64.6%) of studies. Only a small proportion (8.7%) of the included studies investigated the association between fluoride intake and excretion.

CONCLUSION

The findings reveal much variability in terms of conducting the studies and reporting the findings, illustrating a high heterogeneity in data collection across settings and populations. Future studies should provide more detail on sampling technique, measurement protocols (including validation), and on clearly defining the relationship between intake and urinary excretion of fluoride.

Indigenous microbes induced fluoride release from aquifer sediments

Release of fluoride from Quaternary sediments produces F-contaminated groundwater which threatens the health of millions of people worldwide. Despite the mechanisms of fluoride release from sediments are documented by numerous studies, it remains poorly understood that whether indigenous microbes participate in or not for the formation of F-rich groundwater by releasing fluoride from aquifer sediments. A microcosm-based approach, geochemistry and techniques of microbiology and molecular ecology were conducted together to investigate these mechanisms. Results show that microbes are abundant in high [F] groundwater containing at least 1129 operational taxonomic units (OTUs), and indigenous microbes can have an essential role in the mobilization of fluoride in sediments collected from aquifers in a typical fluorosis area in China. It also shows that for the sediments in this study, fluoride release (ca. 2 mg/L) is coupled with elevated concentrations of Ca (△ = 75 mg/L), Mg (△ = 33 mg/L), Al (△ = 0.2 mg/L) and Mn (△ = 1.4 mg/L). This suggests that the fluoride may source from the dissolution of F-bearing carbonate minerals and/or Al-Mn hydroxides in a local acidic environment. The findings provide additional insights into the biogeochemical circulation of fluoride in natural environment, especially in groundwater system and the development of effective strategies for the management of F-contaminated groundwater worldwide.

Age-sex specific disability-adjusted life years (DALYs) attributable to elevated levels of fluoride in drinking water: A national and subnational study in Iran, 2017

National and subnational burden of disease attributable to elevated fluoride levels in drinking water apportioned by sex, age group, province, and community type in Iran, 2017 were quantified based on disability-adjusted life years (DALYs). The attributable burden of disease was estimated using four input data: (1) effect size of elevated drinking water fluoride levels for dental and skeletal fluorosis, (2) population distribution of drinking water fluoride levels, (3) the threshold levels of fluoride in drinking water for contribution in dental and skeletal fluorosis, and (4) age-sex distribution of population. The attributable burden of disease was only related to dental fluorosis, because the fluoride levels were lower than the threshold value for skeletal fluorosis (4.0 mg/L) in all of the cases. The national attributable prevalence (per 100,000 people), DALYs, and DALY rate in 2017 were calculated to be 60 (95% uncertainty interval 48-69), 3443 (1034-6940), and 4.31 (1.29-8.68), respectively. The national attributable burden of disease was not significantly different by sex, but was affected by age and community type in a manner that the highest DALY rate was related to the age group 10-14 y (6.06 [1.82-12.21]) and over 66% of the national attributable DALYs occurred in rural communities. The attributable burden of disease occurred only in 10 out of 31 provinces and about 94% of the attributable DALYs were concentrated in four provinces Fars (1967 [592-3964]), Bushehr (414 [124-836]), West Azarbaijan (400 [120-808]), and Hormozgan (377 [113-761]). Implementation of fluoride-safe drinking water supply schemes in the four leading provinces can prevent most of the national health losses and partly compensate the increasing trend of disease burden from oral conditions at the national level.

Threshold effects of moderately excessive fluoride exposure on children's health: A potential association between dental fluorosis and loss of excellent intelligence

BACKGROUND

Excessive fluoride exposure is associated with adverse health outcomes, but little is known of the effects of moderately chronic fluoride exposure on children's health.

OBJECTIVES

We conducted a cross-sectional study to explore the health impact of moderately excessive fluoride in drinking water.

METHODS

We recruited 2886 resident children, aged 7 to 13 years, randomly from endemic and non-endemic fluorosis areas in Tianjin, China. The fluoride levels in drinking water and urine were measured using the national standardized ion selective electrode method. We examined the dose-response effects of low-to-moderate fluoride exposure on dental fluorosis (DF) and intelligence quotient (IQ), and evaluated the potential relationships between DF grades and intelligence levels using piecewise linear regression and multiple logistic regression, respectively.

RESULTS

The adjusted odds ratios (ORs) of DF were 2.24 (95% confidence interval [CI]: 2.02 to 2.48) for every 0.1 mg/L increment in the water fluoride concentration in the range of 0.80 to 1.50 mg/L, and 2.61 (95% CI: 2.32 to 2.93) for every 0.5 mg/L increment in the urinary fluoride level up to 1.80 mg/L. Every 0.5 mg/L increment in the water fluoride level was associated with a reduction of 4.29 in the IQ score (95% CI: -8.09 to -0.48) in the range of 3.40 to 3.90 mg/L, and a decreased probability of developing excellent intelligence (IQ ≥ 130, OR = 0.60, 95% CI: 0.47 to 0.77) in the range of 0.20-1.40 mg/L, respectively. Every 0.5 mg/L increment in the urinary fluoride level was related to a decrease of 2.67 in the IQ scores (95% CI: -4.67 to -0.68) between 1.60 mg/L to 2.50 mg/L. Excellent intelligence decreased by 51% in children with higher urinary fluoride, and by 30% with each degree increment of DF.

CONCLUSIONS

Our study suggests threshold and saturation effects of moderately excessive fluoride exposure on DF and intelligence loss in children, and a potential association between DF and the loss of excellent intelligence.

Biomarkers of chronic fluoride exposure in groundwater in a highly exposed population

This study examined the relation between fluoride (F-) concentrations in fingernail clippings and urine and the prevalence and severity of enamel fluorosis (EF) among Ethiopian Rift Valley populations exposed to high levels of F- in drinking water. The utility of fingernail clippings as a biomarker for F- exposure and EF was also assessed for the first time in a high-F- region. The study recorded the EF status of 386 individuals (10 to 50years old), who consume naturally contaminated groundwater with widely varying F- concentration (0.6-15mg/L). The mean F- concentrations among residents of communities with primary reliance on groundwater were 5.1mg/kg (range: 0.5-34mg/kg) in fingernails and 8.9mg/L (range: 0.44-34mg/L) in urine. We show strong positive correlations between F- in drinking water and 12-hour urinary excretion (r=0.74, p<0.001, n=287), fingernail F- content (r=0.6, p<0.001, n=258), and mean individual measures of EF severity as measured using the Thylstrup and Fejerskov (TF) Index (r=0.42, p<0.001, n=316). The data indicate that both fingernail and urine measures are good biomarkers for F- exposure and EF outcomes, the latter being slightly more sensitive. Cases of moderate/severe EF were significantly more common among younger subjects (10 to 15years old) than older subjects (mostly >25years old) (p<0.001), consistent with their greater exposure to F- during early childhood, which is the only period of life the enamel is at risk of fluorosis. In this younger population, EF may be useful as a biomarker for identifying individuals with other potential health effects that depend on a specific age window of susceptibility. The finding of exceptionally high F- concentrations in water, fingernail clippings and urine in this region should motivate further investigations of other potential health consequences such as bone disease and abnormalities in the function of the neurological and endocrine systems.

Evaluation of exposure to fluoride in child population of North Argentina

Fluoride is an important element for humans. It inhibits initiation and progression of dental caries and stimulates bone formation. However, excessive intake may lead to the appearance of dental and/or skeletal fluorosis and a decrease in intellectual coefficient in child populations. This study evaluates exposure to fluoride in the child population of Chaco province (Argentina) by analysis of drinking water, food and its bioaccessible fraction (quantity of fluoride solubilised by gastrointestinal digestion and available for intestinal absorption) and urine as a biomarker of internal dose. The concentration of fluoride in drinking water varied between 0.050 and 4.6 mg L^-1, and 80% of the samples exceeded the WHO drinking-water guideline value (1.5 mg L^-1). Fluoride concentrations in food ranged between 0.80 and 3.0 mg kg^-1 fresh weight (fw), being lower in bioaccessible fraction (0.43-1.9 mg kg^-1, fw). On the basis of the consumption data declared for the young child population, fluoride intake varies between 4.1 and 6.5 mg day^-1, greater than the level recommended for this age group. Moreover, in some cases, concentrations of fluoride found in urine (0.62-8.9 mg L^-1) exceeded those reported in areas with declared fluorosis. All data obtained show the worrying situation of child population in this area of Argentina.

Preliminary human health risk assessment of arsenic and fluoride in tap water from Zacatecas, México

Zacatecas state is located in the central area of Mexico, where the underground water contains elevated quantities of natural arsenic and fluoride. In order to estimate health risk associated with human exposure to these pollutants, tap water samples from the southern-central region of the state were analyzed. Ninety percent of the samples exceeded the levels of arsenic established by the World Health Organization (WHO) of 0.01 mg/L and 43 % exceeded the limit established by the NOM-127-SSA1(1) of 0.025 mg/L. Forty-three percent of the samples had fluoride levels above the Mexican regulation limit of 1.5 mg/L (NOM-127-SSA1). We used WHO and EPA's health risk assessment method, we estimated 80 % of the inhabitants of sites studied could be exposed to arsenic levels higher than those recommended by EPA and the WHO, 22 % could be exposed to fluoride levels higher than those recommended by EPA, and 16 % of the local population may be in risk of suffering dental fluorosis.

"Borderline" fluorotic region in Serbia: correlations among fluoride in drinking water, biomarkers of exposure and dental fluorosis in schoolchildren

This study explores relation between dental fluorosis occurrence in schoolchildren, residents of Ritopek, a small local community near Belgrade, and fluoride exposure via drinking water. Additionally, fluoride levels were determined in children's urine and hair samples, and efforts were made to correlate them with dental fluorosis. Dental fluorosis and caries prevalence were examined in a total of 52 schoolchildren aged 7-15 years (29 boys and 23 girls). Fluoride levels in three types of samples were analyzed using composite fluoride ion-selective electrode. Results showed high prevalence of dental fluorosis (34.6 %) and low prevalence of dental caries (23.1 %, mean DMFT 0.96) among children exposed to wide range of water fluoride levels (0.11-4.14 mg/L, n = 27). About 11 % of water samples exceeded 1.5 mg/L, a drinking-water quality guideline value for fluoride given by the World Health Organization (2006). Fluoride levels in urine and hair samples ranged between 0.07-2.59 (n = 48) and 1.07-19.83 mg/L (n = 33), respectively. Severity of dental fluorosis was positively and linearly correlated with fluoride levels in drinking water (r = 0.79). Fluoride levels in urine and hair were strongly and positively correlated with levels in drinking water (r = 0.92 and 0.94, respectively). Fluoride levels in hair samples appeared to be a potentially promising biomarker of fluoride intake via drinking water on one hand, and severity of dental fluorosis on the other hand. Based on community fluorosis index value of 0.58, dental fluorosis revealed in Ritopek can be considered as "borderline" public health issue.

Occurrence and hydrogeochemical characteristics of high-fluoride groundwater in Xiji County, southern part of Ningxia Province, China

High-F(-) groundwater is widely distributed in Xiji County, which endangers the safety of drinking water. In order to evaluate the key factors controlling the origin and geochemical mechanisms of F(-) enrichment in groundwater at Xiji County, one hundred and five groundwater samples and sixty-two sediment samples were collected. Fluoride concentration in the groundwater samples ranged from 0.2 to 3.01 mg/L (mean 1.13 mg/L), with 17 % exceeding the WHO drinking water guideline value of 1.5 mg/L and 48 % exceeding the Chinese drinking water guideline value of 1.0 mg/L. High-F(-) groundwaters were characterized by hydrochemical types of Na-HCO3 and Na-SO4·Cl, which were found in Quaternary sediment aquifer and in Tertiary clastic aquifer, respectively. Conditions favorable for F(-) enrichment in groundwater included weakly alkaline pH (7.2-8.9), low concentration of Ca(2+), and high concentrations of HCO3 (-) and Na(+). Calcite and fluorite were the main minerals controlling F(-) concentration in groundwaters. The hydrolysis of F-bearing minerals in aquifer sediments was the more important process for F(-) release in Tertiary clastic aquifer, which was facilitated by long residence time of groundwater, in comparison with Quaternary sediment aquifer. Cation exchange would also play important roles, which removed Ca(2+) and Mg(2+) and led to more free mobility of F(-) in groundwater and permitted dissolution of fluorite, especially in Tertiary clastic aquifer. However, evapotranspiration and competing adsorption of B and HCO3 (-) were the more important processes for F(-) enrichment in Quaternary groundwater. Groundwater in Lower Cretaceous aquifer had relatively low F(-) concentration, which was considered to be the potential drinking water resource.

Nutritional status and dental fluorosis among schoolchildren in communities with different drinking water fluoride concentrations in a central region in Mexico

Poor water quality and under nutrition are important factors affecting the health of many communities in developing countries. The aims of this study were: i) to describe the fluoride water concentration and the hydrogeological conditions in a region of a state located in the central in Mexico ii) to measure the association between undernutrition and dental fluorosis in children living in communities with different drinking water fluoride concentrations in a state located in the central region of Mexico.

METHODS

Field work was performed in the region to identify the prevailing groundwater flow characteristics and water wells were sampled to analyze water fluoride concentration. Children were selected from three communities that had different drinking water fluoride concentrations (i.e., 0.56, 0.70 and 1.60 mg/l). Fluoridated salt was available in these communities. The Thylstrup-Fejerskov Index (TFI) was used to assess dental fluorosis. Categories four or higher of this index involve changes in the entire tooth surface (ITF ≥ 4). The weight and height of the children were measured. The assessment of undernutrition was based on the World Health Organization criteria: children were classified as being at risk of low-height (Height-for-Age Z score < − 1.0 SD) and having low-height (Height-for-Age Z score < − 2.0 SD) for age and sex, the same cutoff points of the Z score were used to classify "risk of low-weight" and" low-weight children".

RESULTS

In the region the mineralization of the water captured by the wells is the result of a reaction with volcanic materials. The water fluoride concentration in the region ranged from 0.2 to 1.6 mg/l. A total of 734 schoolchildren participated in the study. The percentage of children in fluorosis categories (ITF ≥ 4) was 15.9%, 21.1% of the children were at risk of low height-for-age, and 8.0% had low height-for-age. The percentage of children with fluorosis (ITF ≥ 4) was 6.3%, 9.1% and 31.9% (p ˂ 0.001) and low high-for-age was 2.9%, 2.5% and 8.4% (p ˂ 0.001), for the communities with F concentrations of 0.56 mg/l, 0.70 mg/l and 1.6 mg/l, respectively. The logistic regression model showed an association between dental fluorosis (TFI ≥ 4) and low height-for-age (OR 2.09, p = 0.022) after adjusting for sex, number of teeth erupted, source of drinking water, use of fluoridated toothpaste and tap water fluoride concentration in the community.

CONCLUSION

Children with low height-for-age were more likely to have dental fluorosis in the TFI categories that affect the entire tooth surface. The results suggest that subpopulations with chronic undernutrition are more susceptible to dental fluorosis.

Restoration of Fluorosis Stained Teeth: A Case Study

Dental fluorosis manifests by too much ingestion of fluoride resulting in disturbances in enamel mineralization. The result is intrinsic discolorations in the maxillary and mandibular teeth with a poor esthetic appearance. In challenging cases, an esthetic result may be achieved only by a combination of techniques. This case report demonstrates a combination of modalities used to treat a patient presenting with atypical staining as a result of high-level exposure to ingested fluoride present in the drinking water as a child. Conservative treatment consisted of a combination of in-office bleaching to reduce the discoloration and porcelain veneers to create an esthetic result.

Nephrotoxic contaminants in drinking water and urine, and chronic kidney disease in rural Sri Lanka

Chronic kidney disease of unknown ("u") cause (CKDu) is a growing public health concern in Sri Lanka. Prior research has hypothesized a link with drinking water quality, but rigorous studies are lacking. This study assesses the relationship between nephrotoxic elements (namely arsenic (As), cadmium (Cd), lead (Pb), and uranium (U)) in drinking water, and urine samples collected from individuals with and/or without CKDu in endemic areas, and from individuals without CKDu in nonendemic areas. All water samples - from a variety of source types (i.e. shallow and deep wells, springs, piped and surface water) - contained extremely low concentrations of nephrotoxic elements, and all were well below drinking water guideline values. Concentrations in individual urine samples were higher than, and uncorrelated with, those measured in drinking water, suggesting potential exposure from other sources. Mean urinary concentrations of these elements for individuals with clinically diagnosed CKDu were consistently lower than individuals without CKDu both in endemic and nonendemic areas. This likely stems from the inability of the kidney to excrete these toxic elements via urine in CKDu patients. Urinary concentrations of individuals were also found to be within the range of reference values measured in urine of healthy unexposed individuals from international biomonitoring studies, though these reference levels may not be safe for the Sri Lankan population. The results suggest that CKDu cannot be clearly linked with the presence of these contaminants in drinking water. There remains a need to investigate potential interactions of low doses of these elements (particularly Cd and As) with other risk factors that appear linked to CKDu, prior to developing public health strategies to address this illness.

Activation of the AGE/RAGE system in the brains of rats and in SH-SY5Y cells exposed to high level of fluoride might connect to oxidative stress

To explore the mechanisms by which chronic fluorosis damages the brain, we determined the levels of the advanced glycation end-products (AGEs), the receptor for AGE (RAGE), NADPH oxidase-2 (NOX2), reactive oxygen species (ROS) and malondialdehyde (MDA) in the brains of rats and/or SH-SY5Y cells exposed to different levels of sodium fluoride (5 or 50 ppm in the drinking water for 3 or 6 months and in the incubation medium for as long as 48 h, respectively). The levels of AGEs, RAGE and NOX2 protein and mRNA were measured by an Elisa assay, Western blotting and real-time PCR, respectively. The ROS content was assessed by fluorescein staining and MDA by thiobarbituric acid-reactive substance assay. In comparison to the unexposed controls, the protein and mRNA levels of AGEs, RAGE and NOX2 in the brains of rats after 6 months of exposure and in SH-SY5Y cells following high-dose exposure to fluoride were elevated. In contrast, no significant changes in these parameters were detected in the rats exposed for 3 months. In addition, the levels of ROS and MDA in the SH-SY5Y cells exposed to high-dose of fluoride were elevated in a manner that correlated positively with the levels of AGE/RAGE. In conclusion, our present results indicate that excessive fluoride can activate the AGE/RAGE pathway, which might in turn enhance oxidative stress.