Occurrence Of Fluoride In Groundwater Research Articles

Monitoring fluorine levels in tea leaves from major producing areas in China and the relative health risk

The trace element fluoride can exert a preventive function on dental caries at moderate intake levels, but can also lead to skeletal fluorosis and cognitive impairment when consumed in excessive amounts. Tea is a fluoride hyperaccumulator, yet the risks of fluoride intake via tea consumption are yet to be investigated. In this study, we measured fluoride levels in common tea products from major cultivation provinces in China. Fluoride contents ranged from 6 to 808 mg/kg. Of the samples, 15.6% (34/218) demonstrated fluoride contents which exceeded the maximum residue limit of 200 mg/kg. The samples with high fluoride contents mainly represented oolong tea and dark tea. Fluoride contents in tea were significantly varied between producing regions, which is mainly due to different degree of soil acidification and fluoride occurrence in groundwater. Daily fluoride intake via tea consumption among the general population ranged from 0.02-2.20 mg/day, which is lower than the tolerable upper fluoride intake level (UL) of 3.50 mg/day based on Chinese Dietary Reference Intakes, but rather close to the UL of 2.50 mg/day set by the European Food Safety Authority. A risk assessment indicated that the consumption of tea was not associated with any significant health risks (hazard quotient ≤ 0.54). However, we found a potential risk for the simultaneous consumption of tea, drinking water, wheat and seafood based on a simulation assessment. Fluoride intake among the high-risk population should be continuously monitored.

Functional hBN decorated Ni(OH)2 nanosheets synthesized for remarkable adsorption performance for the elimination of fluoride ions.

Occurrence of fluoride in groundwater is a serious concern due to its fatal effects. Functionalized hexagonal boron nitride sheets have been combined with nickel hydroxide nanoparticles by a one step process and a hybrid adsorbent Ni(OH)2@hBN has been developed with an exceptionally high fluoride adsorption capacity of 365 mg g-1, higher than those of Ni(OH)2 and hBN. This maximum adsorption capacity is higher than those of most common adsorbents used for defluoridation including activated alumina, reported nickel oxide and carbon-based 2D material-supported alumina adsorbents. The presence of functionalized boron nitride significantly increased the surface area to 680 m2 g-1 with a pore volume of 0.33687 cm3 g-1 and provided rich hydroxyl group-containing surface sites for the removal of fluoride present in contaminated water. In addition, the adsorption of fluoride onto boron nitride-modified nickel hydroxide followed pseudo-second-order kinetics and the equilibrium data fitted well with the Langmuir adsorption isotherm, suggesting a monolayer adsorption mechanism. Furthermore, the material developed is tested with the water sample collected from a real affected area, from the Dhar district of India, and the material showed promising results in terms of fluoride removal efficacy.

How widespread is fluoride contamination of Ghana’s groundwater?

Spatial modelling using machine-learning methods to predict fluoride occurrence in groundwater has vast potential in data-scarce contexts such as Ghana. Hazard risk maps can help inform health policy targeted towards communities at high risk.

Characterization of Groundwater Chemistry and Fluoride in Groundwater Quality Monitoring Network of Korea

This study presents the data analysis results of groundwater chemistry and the occurrence of fluoride in groundwater obtained from the groundwater quality monitoring network of Korea. The groundwater data were collected from the National Groundwater Information Center and censored for erratic values and charge balance (±10%). From the geochemical graphs and various ionic ratios, it was observed that the Ca-HCO3 type was predominant in Korean groundwater. In addition, water-rock interaction was identified as a key chemical process controlling groundwater chemistry, while precipitation and evaporation were found to be less important. According to a non-parametric trend test, at p=0.05, the concentration of fluoride in groundwater did not increase significantly and only 4.3% of the total groundwater exceeded the Korean drinking water standard of 1.5 mg/L. However, student t-tests revealed that the fluoride concentrations were closely associated with the lithologies of tuff, granite porphyry, and metamorphic rocks showing distinctively high levels. This study enhances our understanding of groundwater chemical composition and major controlling factors of fluoride occurrence and distribution in Korean groundwater.

Fluoride levels in deep aquifers of Makurdi, North-central, Nigeria: an appraisal based on multivariate statistics and human health risk analysis

Fluoride enrichment of groundwater has been adjudged to be a global environmental challenge in the past decade as most humans depend on groundwater for their domestic needs. This study was conducted to investigate the ionic and fluoride concentrations in borehole water and its associated health risk potentials to residents of Makurdi town and its environs, Benue state, Nigeria. Multivariate statistical techniques were for the first time used to explain the mechanisms of fluoride occurrence in groundwater in the study area. An aggregate of sixty-three (63) groundwater samples were retrieved from boreholes in twenty-one (21) diverse points within the study area and assessed for its physico-chemical composition with emphasis on fluoride content and health risk potentials following standard field and laboratory procedures. It was observed that fluoride content in the sampled water exceeded the stipulated safe limit of 1.5mg/L in about 33.33% of the total samples and ranged from 0.34 to 2.06mg/L with an average of 1.26 ± 0.41mg/L. Moderate affirmative relationships were observed to exist between F- and TDS, F- and EC, F- and Cl-, and F- and NO3- in the water samples indicative of a common source pollution. Principal component analysis (PCA) revealed that high fluoride content in the water samples was associated with the dissolutions from quartzite and shale into the underlying deep aquifers as well as from contributions from anthropogenic activities including fertilizer and pesticide uses. Fluoride risk assessment indicated that the hazard quotient (HQ) for ingestion of fluoride laden water exceeded the threshold value in 66.7, 71.4, 52.4, and 9.5% of the samples for infants, children, teenagers, and adults respectively. It was found that multivariate statistical procedures such as PCA and correlation analysis (CA) are capable of establishing the relationship among groundwater pollutants, while hierarchical cluster analysis (HCA) was found suitable for explaining the likely sources/processes of pollutant enrichment in the groundwater. It is recommended that the findings of this study would serve as a basis for policy makers and regulatory bodies towards ameliorating the menace of groundwater contamination within the study area.

Bedrock petrology controls on hydrogeochemistry and fluoride concentrations in Precambrian aquifers of central Benin, Western Africa

In central Benin, fluoride concentrations in groundwater generally exceed the national and WHO guideline values (1.5 mg/L) and are locally above 7 mg/L (max. 7.19 mg/L). In this area, aquifers are found in a Precambrian bedrock made of migmatitic gneiss and granites. Recent hydrogeochemical studies have shown that the occurrence of fluoride in groundwater in this area is of geogenic origin. The aims of this investigation are to determine the sources of fluorine in the bedrock and to assess the role of geology on the mineralization and high fluoride concentrations in groundwater.Thirty-five rock samples were collected in different areas that display contrasting concentrations of fluoride in groundwater. We carried out analyses of petrology, mineralogy and geochemistry on the samples. The results show that fluorine concentrations vary between 100 and 2900 ppm. Several fluorine-bearing minerals such as (biotite, muscovite, amphibole), titanite, fluorite, fluor-apatite, fluor-allanite, epidote and chlorite were identified. Groundwaters with elevated concentrations of fluoride are found in geological aquifers units and watershed rocks that contain fluorine bearing minerals. Biotite occurring in the granitic formations has the highest fluorine concentrations and appears as the most important contributor to the total fluorine from the bedrock to the groundwater.

Spatial analysis and GIS mapping of regional hotspots and potential health risk of fluoride concentrations in groundwater of northern Tanzania

Safe drinking water supply systems in naturally contaminated hydrogeological environments require precise geoinformation on contamination hotspots. Spatial statistical methods and GIS were used to study fluoride occurrence in groundwater and identify significant spatial patterns using fluoride concentrations. The global and local Morans I indices were used. While the significant positive global Morans I index indicated spatial structure in fluoride occurrence, the significant spatial clusters were identified using local Morans I index and mapped at p-value of 0.05. The spatial clusters demonstrated patterns of drinking water sources with fluoride concentrations below or above WHO guideline and Tanzania standard for drinking water and were considered as ‘regional fluoride cool spots’ and ‘regional fluoride contamination hotspots’, respectively. Two regional fluoride contamination hotspots were identified and mapped around the Stratovolcano Mountains in the north-east and south-west of the study area; and along the Neogene Quaternary volcanic formations and Palaeo-Neoproterozoic East African Orogen (Mozambique Belt). The two largest regional fluoride cool spots dominated the major and minor rift escarpments in the west and east of the study area respectively while the small ones emerged around the volcanic mountains in the north and south. Furthermore, significant spatial outliers emerged at the boundary of regional fluoride hotspots and cool spots as an indication of the spatial processes controlling the mobilization of fluoride in groundwater. While all water sources in the cool spots had fluoride concentrations below 1.5 mg/L, some had extremely low concentrations below 0.5 mg/L which is not safe for human consumption. For hotspots, 96% of water sources had fluoride concentrations above 1.5 mg/L. The probability of having safe source of drinking water varied from one geological unit to another with sources in the Neogene Quaternary volcanic formations having least probabilities.

Stratigraphy and Fluoride Levels Variation in Borehole Water: A Case of River Njoro Catchment

Boreholes are main sources of water for human use in the Rift Valley. However these boreholes have fluoride levels higher than the World Health Organization (WHO) recommended levels of 1.5 mg/l and consequently have raised serious health issues. This study sought to determine the relationship between borehole stratigraphy and fluoride levels in ground water in river Njoro catchment. This study adopted purposive longitudinal survey. The study adopted descriptive analysis of the borehole stratigraphy characteristics and fluoride levels recorded. The sources of data included; field surveys which were used to collect data on the borehole fluoride levels data and qualitative analysis of the stratigraphy data. From the results of the study, it was observed that the fluoride levels in boreholes in river Njoro catchment were dependent on the stratigraphy matrix of the boreholes. Therefore lithological formations have an influence on fluoride level River Njoro catchment. This study will form a pool of knowledge to other researchers who have an interest in the study of fluoride occurrence in ground water in the Rift Valley. Further the study will help in assisting the drillers in decision making after geological surveys of where to locate the boreholes.

Fluoride abundance and their release mechanisms in groundwater along with associated human health risks in a geologically heterogeneous semi-arid region of east India

The present study investigated the source, release mechanisms, mobility and controlling factors of fluoride in groundwater. It has been conducted in the semi-arid rural tract of Birbhum district, located in the eastern part of peninsular India which comprises of the granite genesis aquifers, soft to medium hard rocks with laterite and lateritic soils and alluvial aquifers. The groundwater fluoride level of the study area varied from 0.3 to 9.36 mg/L with an average value of 1.7 mg/L. In the granite region, weathering of granitic rocks, dissolution and iron-exchange processes are responsible for fluoride occurrence in groundwater and its concentration is controlled by the concentration of carbonate and bicarbonate ions. In clay, laterite soil and sedimentary aquifer regions, pH of the circulating water and clay/soil, surface charge characteristics of clay/soils, soil permeability and residence time control the groundwater fluoride through adsorption/desorption of fluoride by the clay and laterite soil. High evaporation rate of the study area also plays an important role to increase the groundwater fluoride concentration. The study also evaluated the health risks to the residents based on the dose-response characterization and USEPA human health risk assessment model through ingestion and dermal contact exposure pathways. The population of infants and children within the study area is more susceptible to the non-carcinogenic health hazards of fluoride than adults. This takes place mainly through direct ingestion route where the dominance order of the population is infants > children > men > women.

Assessment of fluoride hazard in groundwater of Palghat District, Kerala: a GIS approach

Fluoride contamination of groundwater is an emerging problem all over the world. Occurrence of fluoride in groundwater has drawn worldwide care due to its significant influence on human physiology. Fluoride is a vital element, which is good for the teeth enamel and helps to avoid dental and skeletal caries. In excessive doses, it leads to fluorosis. In India most of the people in rural areas are dependent on groundwater for drinking purposes and have a possible chance of developing fluorosis. In the present study, assessment of fluoride hazard of groundwater quality was carried out in Palghat District from January and December 2012. Assessed 64 groundwater sample locations were interpolated using inverse distance weighted (IDW) method in ArcGIS 9.3. The results shows that fluoride contamination in groundwater is high in month of January (>0.87 mg/l) compared to December (>0.69 mg/l). Among the 12 blocks of Palghat District, Kollengode block is highly affected by fluoride contamination in the month of January and Chittur block in December. Groundwater quality of Kollengode and Chittur blocks is highly affected and it is unhealthy for drinking with prior treatment.

Diverse mechanisms drive fluoride enrichment in groundwater in two neighboring sites in northern China

Excessive amounts of fluoride in drinking groundwater are harmful to human health, but the mechanisms responsible for fluoride enrichment in groundwater are not fully understood. Samples from two neighboring areas with endemic fluorosis were collected to test the hypothesis that there are distinctly different mechanisms responsible for the enrichment of fluoride in these groundwater. Hydrochemistry, stable isotopes and geochemical simulation were conducted together to investigate the fluoride spatial distribution and the diversity of responsible mechanisms. Our results showed that the spatial distributions of fluoride are different: I) high [F] in fresh shallow groundwater (SGQJ) and II) medium [F] in fresh to brackish deep groundwater (DGQJ) in the Qiji area; and III) medium [F] in brackish shallow groundwater (SGYH) and IV) low [F] in fresh deep groundwater (DGYH) in the Yanhu area. We also found that the fluoride concentration in groundwater is primarily controlled by the dissolution equilibrium of fluorite, as suggested by the correlation between [F] and [Ca]. However, there are other significant mechanisms: 1) for SGQJ, fluoride-bearing minerals (such as fluorite) dissolution, along with moderate evaporation, cation exchange and the more alkaline conditions are the driving factors; 2) for SGYH, the contributing factors are strong evaporation, the salt effect, dissolution of evaporites, gypsum and dolomite, bicarbonate-fluoride competition and anthropogenic activity; 3) for DGQJ, cation exchange, alkaline conditions and competitive adsorption are major factors; and 4) dolomite dissolution promotes the [F] increase in DGYH. Our findings suggest that the hydrogeochemical conditions play key roles in the enrichment of fluoride and that caution should be taken in the future when evaluating fluoride occurrence in groundwater, even in nearby areas.

The Hydrogeochemical Occurrence of Fluoride in Groundwater and Its Effect on Human Health: A Case Study from Sanliurfa, Turkey

Fluoride ions in drinking water higher than the permissible level lead to negative effects on the human health. More than 200 million people in the world were adversely affected from the high fluorine water. Endemic fluorosis originating from the consumption of high fluorine water was observed also in some parts of Anatolia, Turkey. Volcanic formations are found in areas with high fluoride concentrations in ground waters. In this study, fluoride concentration in ground water was researched in two villages in Sanliurfa where comprised generally sedimental formations thereupon the identified fluorosis cases on the primary school students.

Statistical Analysis of High Fluoride Groundwater Hydrochemistry in Southern India: Quality Assessment and Implications for Source of Fluoride

The present investigation studied fluorosis among the population in the Jaggayyapalem area of Southern India resulting from the occurrence of fluoride in groundwater. Thirty water samples were collected and analyzed for major cations: Na+, Ca2+, K+, Mg2+, and anions: Cl−, CO32−, HCO3−, SO42−, and F−. Analyzed data were utilized to characterize the hydrochemical process dominant in this area. Gibb's diagrams suggested that the water rock interaction was the major driving force controlling water chemistry. Possible sources of fluoride were chemical weathering and leaching of fluorine-bearing minerals present in hard rocks and alluvial formations under the alkaline environment in arid to semiarid conditions. Multivariate analysis in terms of principle component analysis and cluster analysis furnished information about the sources of various parameters in groundwater samples. The correlation study revealed that Ca-K-HCO3-CO3, Mg-HCO3, and K-CO3-Cl are significantly correlated. Furthermore, from this study, it is clear that the source of F was related to Na-Mg silicate minerals and also due to dissolution of carbonate and chloride.

Geochemistry and multivariate statistical analysis for fluoride occurrence in groundwater in the Kuhbanan basin, Central Iran

The groundwater is the only major source of drinking water in central part of Iran. The study was carried out to locate and decipher hydrogeochemical reactions responsible for elevated concentration of fluoride. In the Kuhbanan basin groundwater samples were collected at 24 sites and analyzed. The concentration of fluoride ranged from 0.05 to 10.8 mg/l in groundwater of study area. Statistical analyses were applied to a subgroup of the dataset to evaluate their usefulness to classify the groundwater samples, and to identify geochemical processes controlling groundwater geochemistry. Groundwater in the study area is mainly saline (Na–Cl type water), and statistical analyses show that weathering of the fluorapatite and silicate minerals is the common source for F− in study area.

The spatial distribution and hydrogeological controls of fluoride in the confined and unconfined groundwater of Tuoketuo County, Hohhot, Inner Mongolia, China

Insufficient or excessive intake of fluoride can create health problems for humans. The objective of this study was to understand the occurrence of fluoride in groundwater as well as its spatiotemporal variation and sources in Tuoketuo County, Hohhot, Inner Mongolia, China. Sixty-seven water samples, from 34 phreatic and 33 confined sources, were collected from hand pumps, dug wells and tube wells. All samples were analyzed for pH, electric conductivity (EC), total dissolved solids (TDS), total hardness (TH), as well as content of Na+, K+, Ca2+, Mg2+, HCO3 −, SO4 2−, Cl− and F−. The fluoride concentration in water samples varied from 0.40 to 7.20 (2.33 ± 1.79) and 0.06 to 12.70 (1.65 ± 2.38) mg/L in phreatic and confined water, respectively. An analysis of the hydrogeochemical characteristic of samples indicated that the high fluoride content of groundwater was caused by the alkaline environment with high levels of HCO3 −, Na+, TDS, EC and with a Ca2+ deficiency. The highest concentration of fluoride (>5 mg/L) in phreatic water was located in the groundwater discharge area because this water was affected by the groundwater flow field. In confined aquifers, the concentration of fluoride was mainly controlled by lithology; a high fluoride content (>1.5 mg/L) was only observed in lacustrine platform zone in confined aquifers.

GIS based Inverse Distance Weighting Spatial Interpolation Technique for Fluoride Occurrence in Ground Water

This study was conducted to evaluate fluoride contamination in ground water of the central part of Nagaur district where ground water is the main source of drinking as well as irrigation. Samples from hand pumps and tube wells of forty four stations were analyzed during the summer session with the help of standard methods of APHA. The analytical results show that eleven ground water samples are unfit for drinking purpose. A map has been prepared using an inverse distance weighting method which shows the fluoride concentration in the study area. The maximum concentration was recorded in the Sirsi village while the minimum was found in Sabalpura.

Geochemistry of Fluoride Rich Groundwater in a Weathered Granitic Rock Region, Southern India

Groundwater used for drinking should contain all ions within the prescribed limits for drinking purpose proposed by various health organisations. Keeping this in mind, this study was carried out with an objective to understand the present status of fluoride occurrence in groundwater, its spatiotemporal variation and sources in a part of Nalgonda district, Andhra Pradesh, India. Groundwater samples were collected and monitored for fluoride concentration in forty-five wells from March 2008 to January 2010. The concentration of fluoride in groundwater varied from 0.07 to 8.8 mg/l. The spatial variation in groundwater level and fluoride concentration indicated that fluoride concentration increases along the flow direction. The vertical variation in fluoride concentration indicated that the fluoride concentration was relatively higher in wells having a depth ranging from 5.1 to 10 m, i.e. wells penetrating up to the weathered part of the formation had more concentration of fluoride. Granitic rocks rich in fluoride and application of fertilisers containing fluoride were the main causes for fluoride contaminated groundwater in this area. This two-year study carried out by regular collection of samples once every two months showed that only 55 km2 of the total 724 km2 considered for the study had groundwater suitable for drinking and domestic purpose with respect to fluoride. It is very important to adopt groundwater management measures at the earliest to improve the groundwater quality in this area as the local people depend on groundwater for their everyday needs.

Fluoride in Groundwater: Toxicological Exposure and Remedies

Fluoride is a chemical element that is found most frequently in groundwater and has become one of the most important toxicological environmental hazards globally. The occurrence of fluoride in groundwater is due to weathering and leaching of fluoride-bearing minerals from rocks and sediments. Fluoride when ingested in small quantities (<0.5 mg/L) is beneficial in promoting dental health by reducing dental caries, whereas higher concentrations (>1.5 mg/L) may cause fluorosis. It is estimated that about 200 million people, from among 25 nations the world over, may suffer from fluorosis and the causes have been ascribed to fluoride contamination in groundwater including India. High fluoride occurrence in groundwaters is expected from sodium bicarbonate-type water, which is calcium deficient. The alkalinity of water also helps in mobilizing fluoride from fluorite (CaF2). Fluoride exposure in humans is related to (1) fluoride concentration in drinking water, (2) duration of consumption, and (3) climate of the area. In hotter climates where water consumption is greater, exposure doses of fluoride need to be modified based on mean fluoride intake. Various cost-effective and simple procedures for water defluoridation techniques are already known, but the benefits of such techniques have not reached the rural affected population due to limitations. Therefore, there is a need to develop workable strategies to provide fluoride-safe drinking water to rural communities. The study investigated the geochemistry and occurrence of fluoride and its contamination in groundwater, human exposure, various adverse health effects, and possible remedial measures from fluoride toxicity effects.

Fluoride Removal from Water Using Combined Moringa oleifera/Ultrafiltration Process

The occurrence of fluoride in groundwater has been reported in many countries, mainly because the excess fluoride in drinking water can lead to dental or skeletal fluorosis. Fluoride removal by coagulation with Moringa oleifera seeds, followed by separation with membranes, was investigated in this work. Artificially fluoridated water, at a starting fluoride concentration of 10 mg L−1, was submitted to a coagulation process with aqueous extracts of M. oleifera seeds. The coagulation process was followed by ultrafiltration with membranes at different pressures. The coagulation process with 2.5 g L−1 of M. oleifera promoted a reduction of 90.90 % in the fluoride content of the treated water, making it possible for poor communities to consume this water. It is noteworthy that the combined coagulation/filtration process using raw coagulant showed the highest values of colour and turbidity, which, however, were still below the limits set for drinking water by Brazilian legislation. The advantage of proposing a sequential process using membrane separation is that it removes colour and turbidity, caused by the use of M. oleifera as a coagulant, resulting in water that meets potability standards.

Multivariate statistical analysis for fluoride occurrence in groundwater in the Northern region of Ghana

The presence of excess fluoride in groundwater in the Northern region of Ghana has resulted in the closure of many boreholes for drinking water supply to avoid the incidence of fluorosis and other related health effects. The fluoride concentration in 357 groundwater samples from the area ranged between 0.0 and 11.6mg/L, with a mean value of 1.13mg/L. Piper graphical classification, correlation coefficients, principal component analysis (PCA) and thermodynamic calculations were used as an approach to gain insight into the groundwater chemical composition and to help understand the dominant mechanisms influencing the occurrence of high fluoride waters. Spatial join procedure was used to examine the relationship between the underlying geology of the study area and fluoride distribution. Six groundwater types were identified for the area: Ca–Mg–HCO3, Ca–Mg–SO4, Na–Cl, Na–SO4, Na–HCO3 and mixed water type. PCA performed on the groundwater chemical data resulted in 4 principal components (PCs) explaining 72% of the data variance. The PCs represented the predominant processes controlling the groundwater chemistry in the study area which include; mineral dissolution reactions, ion exchange processes and evapotranspiration processes. PHREEQC calculations for saturation indices for the groundwater samples indicated they were largely saturated with respect to calcite and under-saturated with respect to fluorite, suggesting that dissolution of fluorite may be occurring in the areas where it is present. A review of the PCA results and an evaluation of the equilibrium state of the groundwater based on the saturation indices, suggest that some of the processes controlling the overall groundwater chemistry in the study area also influenced the fluoride enrichment. These predominant processes include the dissolution of the mineral fluorite, anion exchange processes (F−/OH−) involving clay minerals and evapotranspiration processes. Elevated fluoride levels in the study area were found to occur predominantly in the Saboba and Cheriponi districts and also in the Yendi, Nanumba North and South districts. These areas are underlain by the Middle Voltain formation (Obossom and Oti beds), comprising mainly of sandstone, limestone, conglomerate, shale, arkose and mudstone. Results of the hydrochemical analysis show that aside from the boreholes with elevated concentrations of fluoride (beyond 1.5mg/L), groundwater in the study area based on the parameters analyzed is generally chemically acceptable and suitable for domestic use.