Determining the optimal fluoride concentration in drinking water for fluoride endemic regions in South India

Magnetic nanomaterials as an effective absorbent material for removal of fluoride concentration in water: a review

The rapid increases in industrialization and populations are significant sources of water contamination. The speed with which contamination of groundwater and surface water occurs is becoming a serious problem and poses a significant obstacle for water stakeholders. Heavy metals, organic, and inorganic contaminants in the form of suspended and dissolved materials are just a few of the contaminants that can be found in drinking water. One of the most common contaminants in the water is fluoride, which is responsible for numerous toxic diseases. Different traditional techniques, for example, coagulation, ion exchange, absorption, and membrane filtration are being used to dispose of fluoride from water. However, nanomaterials such as magnetic nanoparticles (NPs) are very efficient, reliable, cost-effective, and stable materials to replace traditional water treatment techniques. There has been an increase in interest in the application of nanomaterials to the purification of drinking water over the past few decades. The use of magnetic NPs, such as metal and metal oxide NPs, to remove fluoride ions and organic matter from water is highlighted in this review article. Also, this section also discusses the properties, benefits and drawbacks, and difficulties of utilizing magnetic NPs in the process of purifying drinking water.

Water quality and probabilistic non-carcinogenic health risk of groundwater: a half decadal scenario change in Vadodara

Groundwater is essential to secure the safety of water supply in Vadodara, Gujarat. In this study, groundwater samples were collected from various part of the city which separated in 12 wards. The present study contains analyses of 720 groundwater samples gathered from various tube and open wells and analyzed for fluoride and other physicochemical parameters during 2014 and 2019. The results indicated that fluoride and TDS were high and the overall water quality was poor in the study area. Gastrointestinal and other health-related issues increased due to higher TDS in east, north and northeast regions. Likewise, hierarchical cluster analysis also indicated that TDS and chloride-rich water. Fluoride concentration was observed in the range of 0.66-1.61 mg/l (2014) and 0.86-1.77 mg/l (2019) which indicates that 62% samples are unfit for drinking purpose, which could cause dental and skeletal fluorosis. The water quality index (WQI) indicated lack of excellent water in the studied area in the last half-decade. As per WQI calculation suggest that 82.12% (2014) and 69.00% (2019) of groundwater samples represent poor, very poor and unsuitable categories, whereas remaining 17.85% (2014) and 31.00% (2019) of the samples represent good category for drinking purposes in entire Vadodara, Gujarat. Marginal improvement in the groundwater quality is reported due to good rainfall in 2019. Health risks associated with high fluoride drinking water were assessed for various age groups of inhabitants such as children, infants and adults. The non-carcinogenic hazard quotient estimated by oral intake was 1.38-3.36 (2014) and 1.79-3.70 (2019) for infants; 0.69-1.68 (2014) and 0.90-1.85 (2019) for children, whereas 0.07-0.18 (2014) and 0.10-0.20 (2019) for adults. Therefore, infant and children are relatively at higher health risk due to the intake of fluoride-rich drinking water than adult in the studied region. Both indices were indicated contaminated water or closer to contamination which induced non-carcinogenic health risk on citizens. Thus, the comprehensive results of present study can be used as a baseline data and valuable tool for government authorities for long-term monitoring, health monitoring and sustainable development of Vadodara, Gujarat.

Management of Solid Waste Containing Fluoride-A Review

Technological and economic development have influenced the amount of post-production waste. Post-industrial waste, generated in the most considerable amount, includes, among others, waste related to the mining, metallurgical, and energy industries. Various non-hazardous or hazardous wastes can be used to produce new construction materials after the “solidification/stabilization” processes. They can be used as admixtures or raw materials. However, the production of construction materials from various non-hazardous or hazardous waste materials is still very limited. In our opinion, special attention should be paid to waste containing fluoride, and the reuse of solid waste containing fluoride is a high priority today. Fluoride is one of the few trace elements that has received much attention due to its harmful effects on the environment and human and animal health. In addition to natural sources, industry, which discharges wastewater containing F− ions into surface waters, also increases fluoride concentration in waters and pollutes the environment. Therefore, developing effective and robust technologies to remove fluoride excess from the aquatic environment is becoming extremely important. This review aims to cover a wide variety of procedures that have been used to remove fluoride from drinking water and industrial wastewater. In addition, the ability to absorb fluoride, among others, by industrial by-products, agricultural waste, and biomass materials were reviewed.

Self-recovery study of the adverse effects of fluoride on small intestine: Involvement of pyroptosis induced inflammation

Increasing investigations suggest that fluoride (F) exposure was associated with gastrointestinal diseases, but related literatures were still largely insufficient and the underlying mechanisms have not been fully elucidated. Moreover, previous study in our lab reported F toxicity has the reversible tendency, but it still needs to be further explored. To address this issue, we established a 90 days F exposure and 15 days & 30 days self-recovery mice model, including control and three F groups (25, 50 and 100 mg/L sodium fluoride (NaF)) in each period. The results revealed that after 90 days F exposure, histological structure and ultrastructure of small intestine were markedly disrupted; the value of villus height to crypt depth, and expressions of tight junctions related mRNA and proteins were significantly decreased; intestinal permeability, pro-inflammatory cytokines and pyroptosis related mRNA and proteins were notably increased in duodenum, jejunum and ileum. However, intriguingly, after 30 days recovery period, indices in F groups almost all have recovered towards normalcy. Collectively, this study demonstrated that F exposure could impair the structure and epithelial barrier function of small intestine, leading to the intestinal inflammation, and pyroptosis may contribute to this damage; Furthermore, F toxicity on small intestine is reversible, and could be restored when off the F exposure environment for a certain period of time. Additionally, among the three regions of small intestine, duodenum seems more vulnerable to F exposure than jejunum and ileum.

Groundwater Quality Assessment of a Multi-Layered Aquifer in a Desert Environment: A Case Study in Wadi ad-Dawasir, Saudi Arabia

Sustainable management of groundwater in desert environments dictates better knowledge of the quality status and the controlling processes. To this end, an integrated analysis of hydrochemical and statistical assessment was carried out for 692 groundwater samples collected from the multi-layered aquifer system in Wadi ad-Dawasir area (Saudi Arabia). The four water-bearing formations arranged upwards, namely Lower Wajid, Upper Wajid, Khuff-Kumdah, and Quaternary, were investigated. The prime objective was to delineate the baseline conditions and the dominant process controlling the groundwater evolution that can help make resource management better. We used fifteen indicators, namely the total dissolved solid (TDS), total hardness, Eh, pH, temperature °C, turbidity, Fe2+, dissolved oxygen (DO), NH4, HCO3−, NO3−, F, NO2−, PO42−, and SiO2. Descriptive statistics, violation of the international standards, geostatistical modeling, and factorial analyses (FA) were performed. Geologic, soil, topographic, and climatic factors controlling the quality were investigated. The Quaternary aquifer was the most polluted by TDS, total hardness, NO3−, SiO2, Fe2+, F, and HCO3−. Khuff-Kumdah showed largest means of DO and NH4. Upper Wajid was the largest in NO2−. Lower Wajid proved largest in PO42−. Violation of the international standards clarified largest emergence of the pH for the Lower Wajid; Fe2+ and NO3− for the Upper Wajid; and total hardness, TDS, Fluoride, turbidity, and NH4 for the Quaternary aquifer. Rock interaction and evaporation are the dominant processes that contributed largely to the hydrochemical evolution of the groundwater. FA distinguished six main factors that explained for over 60.8% of the total groundwater quality variation lead byF1 (44.23%) that clarified strong positive loads of TDS (0.98), total hardness (0.95), nitrate NO3− (0.84), turbidity (0.78), NH4 (0.67), moderately loaded by fluoride (0.47), and Fe2+ (0.31).

Spatial variation and health risk assessment of fluoride in drinking water in the Chongqing urban areas, China

Fluoride is an essential trace element for humans, and its deficiency or excess in the environment could lead to disease. To investigate the spatial distribution and health risk assessment of fluoride (F^-) in drinking water, 302 tap water samples from Chongqing urban areas, China, were collected to analyze F^- using an ion chromatograph. The results showed that (1) F^- concentration in drinking water ranged from 0.100 to 0.503 mg/L, with an average of 0.238 ± 0.045 mg/L. (2) The spatial autocorrelation analysis showed that high-low clusters were mostly located in Dadukou District and Beibei District, while low-low clusters were mainly in southern Banan District. (3) The fluoride average daily doses of children, teens and adults were 0.030, 0.029 and 0.031 mg/(kg day). (4) Hazard quotients of excessive fluoride (HQ_e) of children, teens and adults were 0.51 ± 09, 0.49 ± 0.09 and 0.52 ± 0.10, respectively (inferior to 1.00), whereas hazard quotients of inadequate fluoride (HQ_i) of those groups were 1.21 ± 0.26, 1.23 ± 0.26 and 1.15 ± 0.25, respectively (superior to 1.00). Therefore, average daily fluoride intake of residents with drinking water was inadequate. This could pose dental caries and osteoporosis threats for residents from Chongqing urban areas.

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.

Effect of excess Fluoride consumption on Urine-Serum Fluorides, Dental state and Thyroid Hormones among children in “Talab Sarai” Punjab Pakistan

190 children aged 7-18 years from an endemic fluorotic village “Talab Sarai (n = 130) and a non-fluorotic, control, village “Ottawa” (n = 60) were selected for comparison. Children were examined for fluoride (F-) concentration in drinking water, urine, and serum as well as Dental fluorosis (DF) and thyroid hormone levels. The mean concentration of water fluoride (WF) in the sample group was 6.23 mg/L, urine fluoride (UF) 3.38 mg/L, and serum fluoride (SF) 0.21 mg/L, while DF was 93.07%. Significant elevations (P = 0.000) in the concentration of all these four variables were observed in sample group children as compared to control. Mean Free Tetra-iodothyronine (FT4), Free Tri-iodothyronine (FT3) and Thyroid Stimulating Hormone (TSH) concentrations in the sample group were 16.64pmol/L, 5.57 pmol /L and 4.41 mlU/L, respectively. No marked difference in FT4 (P = 0.1) was noted, while significant elevations in FT3 and TSH (P = 0.000) were found in the sample relative to the control group. 80% of the children displayed clear thyroid hormonal derangements, with 36.92% having high TSH and 43.07% with FT3 and FT4 disorders. A moderate to strong correlation among WF, UF, SF and DF (r = 0.94, 0.60, 0.60, 0.72) and a very strong correlation between WF and TSH (r = 0.9) were observed. Our results suggest that excess F- level that is four times greater than the “safe limit” is not only increasing fluoride concentration in body fluids but is also affecting thyroid hormones in 4 out of 5 children which could lead to abnormal physical and mental growth in later developmental stages.

Hydrogeochemical characterisation and health hazards of fluoride enriched groundwater in diverse aquifer types

High concentration of fluoride (up to 20.9 mg/L) in groundwater with significant variation (p = 5.9E-128) among samples was reported from Birbhum district, an acknowledged fluoride endemic region in India. The groundwater samples (N = 368) were grouped based on their hydrochemical properties and aquifer geology for hydro-geochemical characterization. Friedman's test showed p < 0.0001 confidence level which indicates that fluoride concentration among geological groups and water groups are independent. Bland-Altman plot was used to study the inter-relationships among the groups through bias value (∂) and limit of agreement (LoA). Among the geological groups, laterites and granite-gneiss groups exhibited statistically significantly difference in fluoride geochemistry; whereas the younger and older alluvium groups displayed similar characteristics. The fluoride concentration was found to be in the order Lateritic > Granite-gneiss > Older alluvium ≥ Younger alluvium. Dissolution of minerals (such as fluorite, biotite) in laterite sheeted basalt, and granite-gneiss is the main source of groundwater fluoride in the region. Fluoride concentration is also influenced by depth of water table. Hydrochemical study indicated that fluoride concentration was higher in Na-HCO₃ than in Ca-SO₄ and Ca-HCO₃ type of groundwater. The fluoride concentration were positively correlated with Na⁺ and pH and negatively correlated with the Ca²⁺ and Mg²⁺ signifying linkage with halite dissolution and calcite, dolomite precipitation. Geostatistical mapping of WQI through empirical bayesian kriging (EBK) with respect to regional optimal guideline value (0.73 mg/L) classified that groundwater in some parts of the district are unfit for drinking purpose. Health survey (N = 1767) based on Dean's criteria for dental fluorosis indicated presence of slight to moderate dental hazard. Besides, providing baseline data for management of groundwater quality in the study area, the study demonstrated the applicability of Bland-Altman analysis and empirical bayesian kriging (EBK) in delineation and interpolation of fluoride contaminated region.

Assessment of the Use of Epicarp and Mesocarp of Green Coconut for Removal of Fluoride Ions in Aqueous Solution

Fruit consumption and processing result in considerable volumes of residual biomass. Transformation of this biomass into biosorbents offers an alternative for its reuse and disposal. As the green coconut shell is a waste often discarded in landfills and dumps, generating gases and leachate, two biosorbents were developed from the epicarp and mesocarp of green coconut to adsorb fluoride ions in aqueous solution. The kinetic experiments showed that sorption of fluoride ions reached equilibrium at 300 min for both epicarp and mesocarp at temperatures of 25°C, 35°C, and 45°C. The removal efficiency of fluoride ions varied from 66.25% (at 25°C) to 77.50% (at 45°C) for the epicarp and from 90% (at 25°C) to 97.50% (at 45°C) for the mesocarp. The thermodynamic parameters of the adsorption process showed that adsorption is a spontaneous, endothermic process for both biosorbents. The adsorption was classified as chemical, with the Langmuir isotherm model best suited to the adsorption isotherms data.

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.

Iron-oxide nanoparticles by the green synthesis method using Moringa oleifera leaf extract for fluoride removal

In this work, we synthesized iron-oxide nanoparticles (NPsFeO) via a green synthesis method, using Moringa oleifera leaf extract, and evaluated its fluoride ion adsorption potential, comparing its efficiency with a commercially available adsorbent (activated carbon of bone [BGAC]). The adsorbent materials were characterized using X-ray diffraction, transmission, and scanning electronic microscopy, X-ray dispersive energy spectrometry, and N2 adsorption/desorption. The results showed that the maximum adsorption occurred in pH 7 for NPsFeO and pH 5 for the BGAC. Adsorption kinetic tests showed that the equilibrium was reached in 40 min for the NPsFeO, and 90 min for BGAC, with adsorption potential of 1.40 and 1.20 mg g^-1, respectively. The model that best described the kinetic data was pseudo-first-order for NPsFeO and pseudo-second-order for BGAC. The Langmuir isotherm had a better fit for both adsorbents. The thermodynamic parameters indicated spontaneous and endothermic adsorption at 30°C, 40°C, and 50°C for BGAC, and at 30°C for NPsFeO. The regeneration process showed that it is possible to reuse NPsFeO three times in the fluoride ion adsorption process. As a result of its adsorption capabilities and the shortest contact time to achieve equilibrium, the NPsFeO is a highly promising material for fluoride ion removal.

Fluoride prevalence in groundwater around a fluorite mining area in the flood plain of the River Swat, Pakistan

This study investigated the fluoride (F^-) concentrations and physicochemical parameters of the groundwater in a fluorite mining area of the flood plain region of the River Swat, with particular emphasis on the fate and distribution of F^- and the hydrogeochemistry. To better understand the groundwater hydrochemical profile and F^- enrichment, groundwater samples (n=53) were collected from shallow (24-40m), mid-depth (48-65m) and deep (85-120m) aquifers, and then analysed using an ion-selective electrode. The lowest F^- concentration (0.7mg/L) was recorded in the deep-aquifer groundwater, while the highest (6.4mg/L) was recorded in shallow groundwater. Most groundwater samples (62.2%) exceeded the guideline (1.5mg/L) set by the World Health Organization (WHO); while for individual sources, 73% of shallow-groundwater samples (F^- concentration up to 6.4mg/L), 42% of mid-depth-groundwater samples, and 17% of deep-groundwater samples had F^- concentrations that exceeded this permissible limit. Assessment of the overall quality of the groundwater revealed influences of the weathering of granite and gneisses rocks, along with silicate minerals and ion exchange processes. Hydrogeochemical analysis of the groundwater showed that Na⁺ is the dominant cation and HCO₃^- the major anion. The anionic and cationic concentrations across the entire study area increased in the following order: HCO₃>SO₄>Cl>NO₃>F>PO₄ and Na>Ca>Mg>K, respectively. Relatively higher F^- toxicity levels were associated with the NaHCO₃ water type, and the chemical facies were found to change from the CaHCO₃ to (NaHCO₃) type in calcium-poor aquifers. Thermodynamic considerations of saturation indices indicated that fluorite minerals play a vital role in the prevalence of fluorosis, while under-saturation revealed that - besides fluorite minerals - other F^- minerals that are also present in the region further increase the F^- concentrations in the groundwater. Finally, a health risk assessment via Dean's classification method identified that the groundwater with relatively higher F^- concentrations is unfit for drinking purposes.

Fluoride contamination in groundwater sources in Southwestern Nigeria: Assessment using multivariate statistical approach and human health risk

The present study investigated the ionic and fluoride concentrations in tap water and its associated health risk to local dwellers of Ogun State (Abeokuta south), Nigeria. 63 samples were collected from twenty-one different locations. Results obtained revealed the mean concentration of fluoride (F^-) as 1.23 mg/L. Other water quality parameters such as total dissolved solids (TDS), electrical conductivity (EC), F^-, Fe^2+, and SO₄^2- surpassed the WHO guidance for drinking water. Strong positive correlation was observed between F^- and TDS; F^- and pH; TDS and EC; TDS and Mg²⁺; TDS and SO₄^2-; TDS and HCO₃^-; EC and HCO₃^-; EC and SO₄^2-; Na⁺ and Cl^-; SO₄^2- and Cl^-. In addition, Empirical Bayesian Kriging (EBK) model was employed to spatially distribute the concentration of the analyzed elements within the study region. The chronic daily dose (CDD) and hazard quotient (HQ) were also used to evaluate the health risk associated with F^-, considering dermal and ingestion as pathways. The results revealed that the associated HQ for infants between the age range of 6-12months within about 91% of the study region surpassed the accepted HQ limit. However, the HQ for age categories 11-16years; >65years; 18-21years; 21years; 16-18years within 95.2%, 90.5%, 80.95% and 100% of the study location were less than 1. Conclusively, the HQ values obtained in this study should serve as a baseline information for water management authorities, policymakers and the society at large towards addressing these pollution issues.

Geochemical sources, hydrogeochemical behavior, and health risk assessment of fluoride in an endemic fluorosis area, central Iran

The present study is the first attempt to put forward the possible source(s) and health risk assessment of fluoride in Bahabad, central Iran. Fluoride concentrations ranged from 0.22 to 2.35 mg/L and 292-355 mg/kg in the groundwater and soil samples, respectively. Geochemical provenance techniques using major and rare earth elements in soils revealed that local shale is the most probable source rock of fluoride in the area. A two-step chemical fractionation method applied on soil samples demonstrated that residual and water-soluble fractions were the most probable modes of fluoride in soil, whereas exchangeable fraction had a minor role. The coefficient of aqueous migration showed that fluoride in the studied soils behaved as a mobile element. Moreover, the relative mobility indicated that soils played a more important role than rocks in releasing fluoride into groundwater. In groundwater medium, chemical weathering, evaporation, and ion exchange acted as the main geochemical controlling factors of fluoride enrichment. Findings of this study signify that the role of NaCl and NaSO₄-type waters should be considered more to recognize susceptible areas to fluoride contamination in groundwater. People in the study area are exposed to high levels of fluoride intake through drinking water, thus making dental fluorosis a major public health concern in the area. Scanning electron microscopy of the dentin's enamel showed morphological modifications (e.g., cracks and fissures) in residents' enamel structures. The results of this study may lead to suitable management strategies to mitigate the endemic fluorosis problem.

Novel DGT method with tri-metal oxide adsorbent for in situ spatiotemporal flux measurement of fluoride in waters and sediments

Natural mineral-water interface reactions drive ecosystem/global fluoride (F(-)) cycling. These small-scale processes prove challenging to monitoring due to mobilization being highly localized and variable; influenced by changing climate, hydrology, dissolution chemistries and pedogenosis. These release events could be captured in situ by the passive sampling technique, diffusive gradients in thin-films (DGT), providing a cost-effective and time-integrated measurement of F(-) mobilization. However, attempts to develop the method for F(-) have been unsuccessful due to the very restrictive operational ranges that most F(-)-absorbents function within. A new hybrid-DGT technique for F(-) quantification containing a three-phase fine particle composite (FeAlCe, FAC) adsorbent was developed and evaluated. Sampler response was validated in laboratory and field deployments, passing solution chemistry QC within ionic strength and pH ranges of 0-200 mmol L(-1) and 4.3-9.1, respectively, and exhibiting high sorption capacities (98 ± 8 μg cm(-2)). FAC-DGT measurements adequately predicted up to weeklong averaged in situ F(-) fluvial fluxes in a freshwater river and F(-) concentrations in a wastewater treatment flume determined by high frequency active sampling. While, millimetre-scale diffusive fluxes across the sediment-water interface were modeled for three contrasting lake bed sediments from a F(-)-enriched lake using the new FAC-DGT platform.

Spatial distribution mapping of drinking water fluoride levels in Karnataka, India: fluoride-related health effects

Objectives:

(1) To estimate the concentrations of fluoride in drinking water throughout different zones and districts of the state of Karnataka. (2) To investigate the variation of fluoride concentration in drinking water from different sources, and its relationships to daily temperature and rainfall status in the regional districts. (3) To develop an updated fluoride concentration intensity map of the state of Karnataka, and to evaluate these data in the context of fluoride-related health effects such as fluorosis and their prevalence.

Materials and Methods:

Aqueous standard solutions of 10, 100 and 1,000 ppm fluoride (F−) were prepared with analytical grade Na+/F− and a buffer; TISAB II was incorporated in both calibration standard and analysis solutions in order to remove the potentially interfering effects of trace metal ions. This analysis was performed using an ion-selective electrode (ISE), and mean determination readings for n = 5 samples collected at each Karnataka water source were recorded.

Results:

The F− concentration in drinking water in Karnataka state was found to vary substantially, with the highest mean values recorded being in the north-eastern zone (1.61 ppm), and the lowest in the south-western one (only 0.41 ppm). Analysis of variance (ANOVA) demonstrated that there were very highly significant ‘between-zone’ and ‘between-districts-within-zones’ sources of variation ( p < 10−5–10−9), results consistent with a substantial spatial variance of water source F− levels within this state.

Conclusions:

The southern part of Karnataka has low levels of F− in its drinking water, and may require fluoridation treatment in order to mitigate for dental caries and further ailments related to fluoride deficiency. However, districts within the north-eastern region have contrastingly high levels of fluoride, an observation which has been linked to dental and skeletal fluorosis. This highlights a major requirement for interventional actions in order to ensure maintenance of the recommended range of fluoride concentrations (0.8–1.5 ppm) in Karnataka’s drinking water sources.

Dental fluorosis and urinary fluoride concentration as a reflection of fluoride exposure and its impact on IQ level and BMI of children of Laxmisagar, Simlapal Block of Bankura District, W.B., India

There has been growing public concern about intellectual performance of children at high levels of fluoride exposure. A cross-sectional study was conducted in Simlapal Block of Bankura District, West Bengal, to find out the relationship between fluoride (F) exposure as exposure dose (ED) with dental fluorosis (DF), urinary fluoride concentration (UF), intelligence quotient (IQ) and body mass index (BMI). Fifty groundwater samples were collected from the target area. One hundred forty-nine children belonging to age group 6 to 18 years were considered for this study. Experimental results reveal that mean F(-) concentration of that area is 2.11 mg/L (±SD 1.64). On the basis of F concentration in groundwater and water consumption pattern, ED was calculated to explore the impact of F(-) on DF, UF, IQ, and BMI. Paired t test results suggest that exposure rate of F does not show any significant differences (<0.05) among the children of 12 different places. As a result of F exposure, DF cases are mostly found in the order of moderate > severe > mild > very mild > questionable > normal conditions. The highest UF concentration was recorded as 17 mg/L, but the status of DF in the affected children was recorded as moderate. The results also reveal that ED has a positive correlation with DF (r = 0.299, P < 0.01) and UF (r = 0.513, P < 0.01) and a negative correlation with IQ (r = -0.343, P < 0.01) along with BMI (r = 0.083, non-significant). Therefore, from this study, it may be concluded that UF and DF concentration could act as a biomarker of fluoride toxicity.

Fluoride: A naturally-occurring health hazard in drinking-water resources of Northern Thailand

In Northern Thailand, incidences of fluorosis resulting from the consumption of high-fluoride drinking-water have been documented. In this study, we mapped the high-fluoride endemic areas and described the relevant transport processes of fluoride in enriched waters in the provinces of Chiang Mai and Lamphun. Over one thousand surface and sub-surface water samples including a total of 995 collected from shallow (depth: ≤ 30 m) and deep (> 30 m) wells were analysed from two unconnected high-fluoride endemic areas. At the Chiang Mai site, 31% of the shallow wells contained hazardous levels (≥ 1.5 mg/L) of fluoride, compared with the 18% observed in the deep wells. However, at the Lamphun site, more deep wells (35%) contained water with at least 1.5mg/L fluoride compared with the shallow wells (7%). At the Chiang Mai site, the high-fluoride waters originate from a nearby geothermal field. Fluoride-rich geothermal waters are distributed across the area following natural hydrological pathways of surface and sub-surface water flow. At the Lamphun site, a well-defined, curvilinear high-fluoride anomalous zone, resembling that of the nearby conspicuous Mae Tha Fault, was identified. This similarity provides evidence of the existence of an unmapped, blind fault as well as its likely association to a geogenic source (biotite-granite) of fluoride related to the faulted zone. Excessive abstraction of ground water resources may also have affected the distribution and concentration of fluoride at both sites. The distribution of these high-fluoride waters is influenced by a myriad of complex natural and anthropogenic processes which thus created a challenge for the management of water resources for safe consumption in affected areas. The notion of clean and safe drinking water can be found in deeper aquifers is not necessarily true. Groundwater at any depth should always be tested before the construction of wells.

Recommendations for fluoride limits in drinking water based on estimated daily fluoride intake in the Upper East Region, Ghana

Both dental and skeletal fluorosis caused by high fluoride intake are serious public health concerns around the world. Fluorosis is particularly pronounced in developing countries where elevated concentrations of naturally occurring fluoride are present in the drinking water, which is the primary route of exposure. The World Health Organization recommended limit of fluoride in drinking water is 1.5 mg F(-) L(-1), which is also the upper limit for fluoride in drinking water for several other countries such as Canada, China, India, Australia, and the European Union. In the United States the enforceable limit is much higher at 4 mg F(-) L(-1), which is intended to prevent severe skeletal fluorosis but does not protect against dental fluorosis. Many countries, including the United States, also have notably lower unenforced recommended limits to protect against dental fluorosis. One consideration in determining the optimum fluoride concentration in drinking water is daily water intake, which can be high in hot climates such as in northern Ghana. The results of this study show that average water intake is about two times higher in Ghana than in more temperate climates and, as a result, the fluoride intake is higher. The results also indicate that to protect the Ghanaian population against dental fluorosis, the maximum concentration of fluoride in drinking water for children under 6-8 years should be 0.6 mg F(-) L(-1) (and lower in the first two years of life), and the limit for older children and adults should be 1.0 mg F(-) L(-1). However, when considering that water treatment is not cost-free, the most widely recommended limit of 1.5 mg F(-) L(-1) - which is currently the limit in Ghana--may be appropriate for older children and adults since they are not vulnerable to dental fluorosis once the tooth enamel is formed.

Geochemical processes regulating F-, as and NO3- content in the groundwater of a sector of the Pampean Region, Argentina

The presence of F(-) and As in groundwater is common in volcanic aquifers. Excessive concentrations of these ions affect the quality of drinking water and can be harmful to health. When there is an anthropogenic source in phreatic aquifers, NO3(-) is incorporated to the groundwater components, deteriorating its quality. The objective of this work is to assess the geochemical processes that regulate the contents of F(-), As and NO3(-) of the groundwater in a sector of the Pampean Region in Argentina. This area is supplied with water by exploiting a multilayer aquifer, composed of a phreatic aquifer occurring in loess sediments and a fluvial semi-confined aquifer, separated by an aquitard. The results obtained show that the phreatic aquifer has a higher concentration of F(-), As and NO3(-) than the semi-confined aquifer. Fluoride derives from the dissolution of volcanic glass at a slightly alkaline pH and from anion exchange; however, it may also be absorbed by the reprecipitating carbonates. The As is released by desorption, with the main source being the glass and lithic fragments of the loess. The NO3(-) originates from the decomposition of organic matter, mainly in the septic tanks of the peri-urban areas. Meanwhile, the As and F(-) content in the semi-confined aquifer is lower and its origin is the result of water inflow by vertical downward infiltration from the phreatic aquifer through the aquitard. The Pampean Region is one of the areas with the largest volume of agricultural exports in the world and at present it is undergoing a strong social and economic growth. Understanding the geochemical processes that regulate the quality of drinking water is of vital importance to generate water management guidelines aiming at minimizing the deterioration of drinking water sources.

A Review on Adsorption of Fluoride from Aqueous Solution

Fluoride is one of the anionic contaminants which is found in excess in surface or groundwater because of geochemical reactions or anthropogenic activities such as the disposal of industrial wastewaters. Among various methods used for defluoridation of water such as coagulation, precipitation, membrane processes, electrolytic treatment, ion-exchange, the adsorption process is widely used. It offers satisfactory results and seems to be a more attractive method for the removal of fluoride in terms of cost, simplicity of design and operation. Various conventional and non-conventional adsorbents have been assessed for the removal of fluoride from water. In this review, a list of various adsorbents (oxides and hydroxides, biosorbents, geomaterials, carbonaceous materials and industrial products and by-products) and its modifications from literature are surveyed and their adsorption capacities under various conditions are compared. The effect of other impurities on fluoride removal has also been discussed. This survey showed that various adsorbents, especially binary and trimetal oxides and hydroxides, have good potential for the fluoride removal from aquatic environments.

Performance of an optimized Zr-based nanoparticle-embedded PSF blend hollow fiber membrane in treatment of fluoride contaminated water

Consumption of water that has excessive fluoride can cause adverse health impacts on human beings. A Zr-based nanoparticle-embedded PSF blend hollow fiber membrane was successfully prepared and optimized for removal of fluoride from the aqueous solution. Both static and dynamic adsorption of fluoride on the membrane was investigated. It was showed that the membrane could effectively remove fluoride within a wide pH ranging from 3 to 10. At neutral pH, the adsorption equilibrium was reached within 24 h. The maximum adsorption capacity of the optimized membrane was 60.65 mg/g, much higher than many commercial adsorbents. The presence of NO3(-), SiO3(2-) or HA has insignificant effects on the fluoride removal. However, the removal was retarded as the concentration of HCO3(-) or PO4(3-) was increased. Furthermore, the membrane could remove fluoride efficiently through the continuous filtration, even in presence of natural organic matters. The spent membrane could be regenerated and then reused for the removal of fluoride with great efficiency. The adsorption history could be well described by an intraparticle diffusion model. The XPS analysis showed that the adsorption of fluoride was mainly associated with the ion-exchange between SO4(2-) and F(-) ions. Finally, the toxicity analysis revealed that the treated water was safe for human consumption.

Fluoride content of soft drinks, nectars, juices, juice drinks, concentrates, teas and infusions marketed in Portugal

A potentiometric method using a fluoride combination ion-selective electrode was validated and used to analyse 183 samples, including soft drinks, juices, nectars, juice drinks, concentrates, teas and infusions marketed in Portugal. The fluoride levels were higher in extract-based soft drinks, juice drinks and juice, with fluoride values of 0.86 ± 0.35, 0.40 ± 0.24 and 0.37 ± 0.11 mg l⁻¹, respectively. The lowest fluoride concentration was found in infusion samples (0.12 ± 0.01 mg l⁻¹), followed by teas and carbonated soft drinks with fluoride concentrations of 0.16 ± 0.12 and 0.18 ± 0.07 mg l⁻¹, respectively. Nectars, concentrates and juice-based drinks had similar fluoride concentrations of 0.33 ± 0.16, 0.29 ± 0.12 and 0.25 ± 0.14 mg l⁻¹, respectively. The fluoride concentrations in all these samples would only contribute intakes below the acceptable daily intake (ADI = 0.05 mg kg⁻¹ body weight day⁻¹), indicating that, individually, these beverages cannot induce fluoride toxicity in the population group of children.

The effect of supplementation of calcium, vitamin D, boron, and increased fluoride intake on bone mechanical properties and metabolic hormones in rat

Evidence indicates that optimal nutrition plays a role in bone formation and maintenance. Besides major components of mineralization such as calcium, phosphorus, and vitamin D, other nutrients like boron and fluoride have beneficial role, too. In this study, 34 male Wistar rats were divided into five groups: control diet, fluoride, fluoride + boron, fluoride + calcium + vitamin D, and flouride + boron + calcium + vitamin D. Boron equal to 1.23 mg, calcium and vitamin D equal to 210 mg + 55 IU and fluoride equal to 0.7 mg/rat/day was added to their drinking water for 8 weeks. Plasma blood samples and bones were collected. Findings are evidence that fluoride + boron intake revealed significant positive effects on bone mechanical properties and bone metabolic hormones. These findings suggest that combined intake of these two elements has beneficial effects on bone stiffness and breaking strength comparing to even calcium + vitamin D supplementation. This evidence dealing with health problems related to bone and skeletal system in humans should justify further investigation of the role of boron and fluoride with other elements in relation to bone.

Performance of granular zirconium-iron oxide in the removal of fluoride from drinking water

In this study, a granular zirconium-iron oxide (GZI) was successfully prepared using the extrusion method, and its defluoridation performance was systematically evaluated. The GZI was composed of amorphous and nano-scale oxide particles. The Zr and Fe were evenly distributed on its surface, with a Zr/Fe molar ratio of ∼2.3. The granular adsorbent was porous with high permeability potential. Moreover, it had excellent mechanical stability and high crushing strength, which ensured less material breakage and mass loss in practical use. In batch tests, the GZI showed a high adsorption capacity of 9.80 mg/g under an equilibrium concentration of 10 mg/L at pH 7.0, which outperformed many other reported granular adsorbents. The GZI performed well over a wide pH range, of 3.5-8.0, and especially well at pH 6.0-8.0, which was the preferred range for actual application. Fluoride adsorption on GZI followed pseudo-second-order kinetics and could be well described by the Freundlich equilibrium model. With the exception of HCO(3)(-), other co-existing anions and HA did not evidently inhibit fluoride removal by GZI when considering their real concentrations in natural groundwater, which showed that GZI had a high selectivity for fluoride. In column tests using real groundwater as influent, about 370, 239 and 128 bed volumes (BVs) of groundwater were treated before breakthrough was reached under space velocities (SVs) of 0.5, 1 and 3 h(-1), respectively. Additionally, the toxicity characteristic leaching procedure (TCLP) results suggested that the spent GZI was inert and could be safely disposed of in landfill. In conclusion, this granular adsorbent showed high potential for fluoride removal from real groundwater, due to its high performance and physical-chemical properties.

Assessment of water contribution on total fluoride intake of various age groups of people in fluoride endemic and non-endemic areas of Dindigul District, Tamil Nadu, South India

The prevalence of fluorosis is mainly due to the intake of large quantities of fluoride through water. It is necessary to determine the contribution of water used for drinking and food processing and other diet sources on daily fluoride intake for finding the ways to reduce the excess fluoride intake than the minimum safe level intake of 0.05 mg/kg/day. The main objectives of this study are to determine the quantitative impact of water through drinking and cooking of food and beverages on total fluoride intake as well as to estimate the contribution of commonly consumed diet sources on total fluoride intake. Contribution of water on daily fluoride intake and estimation of total fluoride intake through the diet sources were accomplished through analysis of fluoride in drinking water, solid and liquid food items, Infant formulae, tea and coffee infusions using fluoride ion selective electrode. Determination of incidence of fluorosis in different fluoride endemic areas in Dindigul District of Tamil Nadu, South India is achieved through clinical survey. The percentage of daily fluoride intake through water is significantly higher for infants than children, adults and old age groups of people. The percentile scores of fluoride intake through water from drinking and cooking increases with increase of water fluoride level. The rate of prevalence of fluorosis is higher in adolescent girls and females than adolescent boys and males residing in high fluoride endemic areas. More than 60% of the total fluoride intake per day derived from water used for drinking and food processing. Hence the people residing in the fluoride endemic areas in Dindigul District of Tamil Nadu, South India are advised to take serious concern about the fluoride level of water used for drinking and cooking to avoid further fluorosis risks.