Elevated Fluoride Concentrations Research Articles

Simultaneous removal of fluoride and arsenic from drinking groundwater using limestones from Bajío Guanajuatense, Mexico

Numerous groundwater wells in Mexico exceed the maximum allowable fluoride (F−) and arsenic (As) drinking water concentration requirements, posing an environmental and health risk to the population that relies solely on these wells for drinking water sources. Since encouraging results have been obtained utilizing native limestones to remove some toxic elements from contaminated water, the ability of the limestone rock outcrop to the south of the Sierra de Guanajuato in Mexico to remove As and F− from groundwater was assessed. A sampling campaign was conducted in the study area, focusing on wells exhibiting elevated concentrations of arsenic (As) and fluoride (F−) in compliance with international standards. This water was employed in the treatment experiment involving limestone rocks. The rock sampling process involved a reconnaissance campaign covering the study area and outcrop points of limestone rocks. Representative limestone samples were collected and subsequently subjected to mineralogical and geochemical characterization. Using rock samples, synthetic water, and groundwater from contaminated wells in the region, batch experiments were conducted to evaluate the As and F− removal capacity of limestone. The batch testing consisted of water–rock interactions at various times with different samples of limestone rocks, grain sizes, and water containing distinct concentrations of both elements, artificial and groundwater extracted close to the limestones outcrop. The results indicate that the rock with the highest calcium carbonate (CaCO3) content and the smallest grain size (< 0.05 mm) removes the highest concentrations of both As and F−, with As removal being superior. The removal mechanisms were studied using scanning electron microscopy with energy-dispersive spectroscopy (SEM–EDS) images, saturation index calculations, and Eh–pH diagrams,. Fluoride precipitation was favored when the pH of the solution was slightly acidic, whereas sorption was favored when the pH was higher. The results obtained are encouraging for the removal of high levels of As, and to a lesser extent for F−; consequently, the use of regional limestone rocks could be a viable option for improving the water quality ingested by rural inhabitants in the study area. Calcium carbonate (CaCO3) concentration can be used to identify limestone rocks with the potential to effectively remove As and F− in other locations.

Worldwide Variations in Fluoride Content in Beverages for Infants.

In situations where breastfeeding is impractical, milk formulas have emerged as the primary choice for infant nutrition. Numerous global studies have scrutinized the fluoride content in these formulas, uncovering fluctuations in fluoride levels directly associated with the method of preparation. This variability poses a potential risk of elevated fluoride concentrations and, consequently, an increased susceptibility to dental fluorosis in infants. The primary objective of this review is to intricately delineate the fluoride content in dairy formulas and emphasize the variability of these values concerning their reconstitution process. The review's findings reveal that, among the 17 studies assessing fluoride levels in infant formula, milk-based formulas exhibit a range of 0.01-0.92 ppm, with only two studies exceeding 1.30 ppm. Conversely, soy-based formulas demonstrate values ranging from 0.13-1.11 ppm. In conclusion, the observed variability in fluoride levels in infant formulas is ascribed to the choice of the water source employed in the preparation process. This underscores the paramount importance of meticulously adhering to recommendations and guidelines provided by healthcare professionals concerning the utilization of these formulas and their meticulous reconstitution.

Optimization of fluoride removal using calcined bauxite: Adsorption isotherms and kinetics

Geogenic contamination of groundwater due to elevated fluoride (F−) concentrations is a significant issue worldwide (including in Tanzania). The present study focussed to assess the adsorption capacity of thermally treated (calcined) bauxite to remove the F− from contaminated water. Characterization of bauxite by X-ray fluorescence spectroscopy (XRF) revealed Al2O3, Fe2O3, and SiO2 as the major oxides in both raw and calcined bauxite. The major mineral phase in the raw bauxite was gibbsite, which disappeared after calcination. The optimum calcination temperature, dosage and contact time for F− removal by calcined bauxite were 400 °C, 40 g/L and 8 min, respectively. The experimental data revealed Freundlich isotherm as the best model to fit the F− adsorption process with kF and 1/n being 0.1537 mg/g and 0.8607, respectively. The pseudo-second-order kinetic and intra-particle diffusion models explained well the F− adsorption process with the rate constants of 115.43 g/mg min and 0.0025 mg/g min0.5, respectively. The values of ΔG, ΔH and ΔS indicate the F− adsorption on bauxite surface indicated that the adsorption process was spontaneous, endothermic and structural changes occurred during the adsorption process. The F− adsorption under optimum conditions lowered the pH and F− concentration to WHO and Tanzania Bureau of Standards (TBS) standards.

Morinda citrifolia L. (Noni) dietary supplementation ameliorates fluoride toxicity in the freshwater fish, Cyprinus carpio L.

Fluoride is the organic and inorganic compound of the element fluorine, has detrimental effect to all animals including fish at higher concentration. Ground water with elevated concentration of fluoride is a major global problem including India. On the other hand, Morinda citrifolia (also called ‘Noni’ in Polynesia) is a medicinal plant, has antioxidative, anti-inflammatory and immunostimulatory properties. The ameliorating effect of M. citrifolia fruit extract dietary supplementation against fluoride induced toxicity on the growth performance, haematological parameters, and fluoride accumulation in the muscular tissue was investigated in the freshwater fish, Cyprinus carpio L. for 35 days in triplicate. One hundred and twenty acclimated C. carpio fingerlings were randomly allocated into five experimental groups (Groups I, II, III, IV and V) each with 24 fish divided into three replicates (eight fish/replicate). Group I (Control) and II (Toxic control or negative control) were provided with basal/control diet, whereas groups III, IV, and V were provided with 0.25% (2.5 g/kg), 0.50% (5.0 g/kg) and 0.75% (7.5 g/kg) M. citrifolia fruit extract supplemented diet respectively. All groups except for group I were exposed to 10% of the LC50 of fluoride. Selected growth and haematological parameters were estimated. The fluoride content in the muscular tissue of fish was also estimated following SPADNS method. Results revealed that exposure of sublethal concentration of fluoride significantly (P &lt;0.05) reduced the growth performance and haematological parameters in Gr. II (toxic control) compared to the Gr. I (control). However, M. citrifolia dietary supplementation significantly (P &lt;0.05) improved fluoride induced alteration of growth performance and haematological parameters of fish in the groups III, IV and V compared to Gr. II. Morinda citrifolia fruit extract dietary supplementation also significantly (P &lt;0.05) decreased the accumulation fluoride in the muscular tissue of fish in groups III, IV and V compared to the Gr. II (toxic control). In conclusion, M. citrifolia dietary supplementation ameliorates the fluoride toxicity by preventing the accumulation of fluoride in the muscular tissue of the fish. The M. citrifolia dietary supplementation at 0.25% showed the best response, hence it is considered as the optimum dose.

Groundwater chemistry and health hazard risk valuation of fluoride and nitrate enhanced groundwater from a semi-urban region of South India.

Evaluation of groundwater chemistry and its related health hazard risk for humans is a prerequisite remedial measure. The semi-urban region in southern India was selected to measure the groundwater quality to know the human health risk valuation for different age groups of adults and children through oral intake and skin contact with elevated concentrations of fluoride ([Formula: see text]) and nitrate ([Formula: see text]) groundwater. Groundwater samples were collected from the semi-urban region for pre- and post-rainfall periods and resolute its major ion chemistry. The pH values showed the water is alkaline to neutral in nature. Total dissolved solid (TDS) ranged from 201 to 3612mg/l and 154 to 3457mg/l. However, [Formula: see text] concentration ranges from 0.28 to 5.48mg/l and 0.21 to 4.43mg/l; and NO3- ranges from 0.09 to 897.28mg/l and 0.0 to 606.10mg/l elevating the drinking water standards of [Formula: see text] in 32% and 38% samples and for [Formula: see text] about 62% and 38% during pre- and post-rainfall seasons, respectively. The fluoride-bearing minerals are the main sources of elevated concentrations of [Formula: see text] and excessive use of chemical fertilizers as the chief source of NO3- concentration in the aquifer regime. Water quality index (WQI) ranged from 18.3 to 233 and 12.97 to 219.14; 20% and 22% showed poor water quality for pre- and post-rainfall seasons with WQI ≥ 200. Piper plot suggests that 46% and 51% of samples signify carbonate water type ([Formula: see text]), and 32% and 28% of groundwater samples show ([Formula: see text]) type water for pre- and post-rainfall seasons respectively. Gibbs' plot suggests the dominance of water-rock interaction in the aquifer system. Further, the principal component analysis (PCA) revealed three and four components which explain 74.85% and 79.30% of the variance in pre- and post-rainfall seasons with positive loading of EC, TDS, Ca2+, Na+, Mg2+, K+, [Formula: see text], Cl-, and [Formula: see text] due to mineral weathering and water-rock interactions altering the chemistry for an elevated concentration of [Formula: see text] and [Formula: see text] in groundwater. Cluster analyses of chemical variables observed four clusters with a linkage distance of 5 to 25 with a linkage between different variables displaying predominant ion exchange, weathering of silicate and fluoride-rich minerals, salinization of the water, and a high value of [Formula: see text] concentration, resulting from fertilizers. The hazard quotient (HQ) through ingestion (HQing) and dermal (HQder) pathways of F- and NO3- was observed higher than its acceptable limit of 1.0 for different age groups indicating the non-carcinogenic effect on human health. Effective strategic measures like defluoridation, denitrification, safe drinking water supply, sanitary facilities, and rainwater harvesting structures are to be implemented in the area for improvement of human health conditions and also bring awareness to the local community about the health hazard effects of using high concentrated [Formula: see text] and [Formula: see text] water for daily uses.

Predicting and modelling availability of fluoride in soil from sorption properties

AbstractUsage of alkaline and saline groundwater with elevated concentrations of fluoride (F−) for irrigation of pastures requires an assessment of the mobility of F− within the plant‐water‐soil continuum. Factors influencing F− sorption and desorption in 95 Australian soils were examined. Pronounced differences in F− sorption were observed across the soils, but these differences could not be explained by differences in soil pH, electrical conductivity or organic carbon. Rather, sorption was correlated with the content of Fe/Al hydrous oxides and kaolinite in soil. Sorption of F− onto soils increased the solution pH and the ratio of (F− adsorbed) to (OH− desorbed) was consistently below 1, thereby indicating that adsorption of F− results in the release of water and hydroxyl groups from, or co‐adsorption of protons to, the sorbent surface. Maximum sorption occurred at pH values of approximately 5–6, whilst sulphate slightly increased (&lt;5%) F− sorption. Desorption was slightly decreased (~3%–7%) in presence of sulphate anions. Hence, it is unlikely that irrigation of soil with alkaline and saline groundwater, in combination with soil applications of gypsum and sulphur to limit pH fluctuations, would increase mobility of F− in soil. Finally, the irrigation of soil columns with 1200–1500 mm of alkaline and saline groundwater containing 0.18 mM F−, as would commonly occur in irrigation systems using coal seam gas associated water in Australia, resulted in a F− concentration of 0.05 mM at 10 cm depth and the measured values were in excellent agreement with modelled F− movement based on sorption parameters. Thus, sorption parameters can be used to identify soils which minimize movement of F− because of their strong F− sorption. Based on these results, safe limits for irrigation of soil can be established which avoid F− toxicity risks to plants, animals and contamination of water resources.

Origin and migration of fluoride in the area of the Aluto Volcanic Complex (Main Ethiopian Rift)

Fluoride-enriched ground and surface waters represent a major health risk for the local population in many areas along the East African Rift. The present study investigates the origin of fluoride and the reason for its accumulation in the rift waters, following two hypotheses: (i) fluid-rock-interactions release fluoride from minerals into the water and (ii) magmatic-derived fluoride-containing liquids and gases migrate along permeable fault zones until they dissolve in ground- and surface water or be released to the atmosphere.Rock-, gas, water-, soil-, and plant samples were collected from the area within and close by the Aluto Volcanic Complex, which is part of the Main Ethiopian Rift. Most analyzed waters showed fluoride concentrations above the drinking water limit (>1.5 mg/L) with the highest values in hot springs (up to 70 mg/L) and the geothermal well (76 mg/L). In the solid phase, a high fluoride content was found in acid volcanic rocks (ignimbrite: 4391 ppm; rhyolite: 3248 ppm) as well as in pumice (up to 1955 ppm). The fluoride content of soil samples collected within the volcanic complex varied between 82 and 1036 ppm, whereas former lake sediments from outside the Aluto Volcanic Complex showed higher fluoride contents ranging from 674 to 8171 ppm.Identified fluoride-rich minerals are various amphiboles (about 3 wt.-% F−), fluor-apatite (about 3 wt % F−), minerals of the fluor-caphite group (about 5 wt.-% F−), parisite (up to 9 wt.-% F−), and fluorite (CaF2). Elevated fluoride concentrations were also measured in some gas samples from fumaroles (up to 50 ppm) and in plant samples collected next to the fumaroles (up to 65 ppm). Leaching experiments of solid samples with deionized water demonstrated that fluoride can easily be mobilized from pumice and sediments but hardly from consolidated rocks. This fluoride release increased with temperature (up to 150 °C) and correlated roughly with dissolved silica indicating the binding of some fluoride to the amorphous or weakly crystalline silica fraction.Based on these results it was concluded that fluoride migrates via different pathways through the environment: At the depth of the magma chamber during magmatic differentiation fluoride enriches initially in the magmatic melt and accumulates in some late-crystallizing minerals of igneous rocks such as fluorite or mica. Upon volcanic eruption fluoride is predominantly incorporated in the glass (ignimbrite) and ash phase (pumice). On the surface, these rocks are exposed to weathering and fluoride leaches partly out into the aqueous phase. Soft and porous rocks such as pumice release fluoride first whereas hard extrusive/igneous rocks are less prone to weathering and retain the fluoride. Pumice and (lake) sediments might act both, as source and as sink for fluoride in the area. Although some fluoride might drain from the surface into the deeper subsoil, we conclude that magmatic fluids (liquid and gas) contribute more substantially to the overall fluoride ground water content because (i) of the much higher fluoride content in deep geothermal waters and hot springs as compared to surface-near waters; (ii) active geothermal surface manifestations located along fault zones indicate that fluids migrate from deep magmatic intrusions (as gas and liquid) towards the surface, where fluoride dissolves in groundwater; (iii) and the good correlation between bicarbonate (deriving from dissolution of magmatic CO2) and fluoride content in all analyzed water samples.

Enhanced defluoridation in household filter using binary metal hydrochar composite

Elevated fluoride concentration in water can trigger several health-related problems. In this study, the influence of post pyrolysis hydrothermal activation on defluoridation has been investigated to check their interacting effect using response surface methodology. Amongst the various optimizing factors which were investigated, temperature and time emerged as the most significant factors (p-value < 0.05). The Fe–Zn (2:1) binary metal hydrochar composite synthesized from optimized hydrochar demonstrated an optimum dose, contact time, initial concentration and solution pH of 0.8 g/L, 120 min, 5 mg/L and 7 respectively. The isotherm and kinetic results indicated that experimental data best fitted to Langmuir and pseudo-second order, with a determination coefficient approaching one (R2 = 0.99). Maximum monolayer adsorption capacity for this composite was found to be 28.41 mg/g. Thermodynamic parameters corroborate that defluoridation was chemisorption in nature (ΔH⁰ >10 kJ/mol) and was favoured at lower temperature (30 °C). An extensive characterization was employed to explain the adsorption mechanism, and confirmed occurrence of Lewis acid-base interactions, ion-exchange processes and electrostatic interactions. The performance of a fixed bed column was assessed based on breakthrough curve analysis. This novel composite could therefore serve as an efficient fluoride adsorbent because of enhanced sorption at neutral pH and reusability, thereby ensuring a sustainable and practical solution for low-cost defluoridation of drinking water.

Global analysis and prediction of fluoride in groundwater

The health of millions of people worldwide is negatively impacted by chronic exposure to elevated concentrations of geogenic fluoride in groundwater. Due to health effects including dental mottling and skeletal fluorosis, the World Health Organization maintains a maximum guideline of 1.5 mg/L in drinking water. As groundwater quality is not regularly tested in many areas, it is often unknown if the water in a given well or spring contains harmful levels of fluoride. Here we present a state-of-the-art global fluoride hazard map based on machine learning and over 400,000 fluoride measurements (10% of which >1.5 mg/L), which is then used to estimate the human population at risk. Hotspots indicated by the groundwater fluoride hazard map include parts of central Australia, western North America, eastern Brazil and many areas of Africa and Asia. Of the approximately 180 million people potentially affected worldwide, most reside in Asia (51–59% of total) and Africa (37–46% of total), with the latter representing 6.5% of the continent’s population. Africa also contains 14 of the top 20 affected countries in terms of population at risk. We also illuminate and discuss the key globally relevant hydrochemical and environmental factors related to fluoride accumulation.

Assessment of human health risk arising due to fluoride and nitrate in groundwater: a case study of Bhokardan tehsil of Maharashtra

Change in drinking water quality causes significant impacts on human health. Current research aims to identify the risk arising for infants, children, and adults due to the elevated concentration of nitrate and fluoride in groundwater. Groundwater samples from dug wells (100 samples) and bore wells (90 samples) were collected across the Bhokardan tehsil in December 2018. The physicochemical parameters like pH, EC, salinity, TDS, Nitrate, and Fluoride were analyzed. In most Bhokardan tehsil, NO3 concentration (45 mg/l) in bore well samples falls within the desirable limit. Still, in the case of dug wells, average nitrate is beyond the BIS permissible limits. 77% and 15.6% samples from dug and bore wells exceed the allowable limit (1.5 mg/l) of fluoride in drinking water. It is observed that in bore well samples, nitrate and fluoride depicts the highest risk to children (Avg. 1.44 and 1.88) as the average value is above critical value, i.e., 1 followed by infants (Avg. 1.06 and 1.64) and adults (Avg. 0.94 and 1.22) for the nitrate health risk. The highest THQ value for nitrate (4.81) and fluoride (2.42) was recorded for children. This analysis will help policymakers and practitioners develop policies at the administrative (tehsil) level to evaluate and monitor human health implications.

High levels of fluoride in groundwater from Northern parts of Indo-Gangetic plains reveals detrimental fluorosis health risks

Fluoride contamination in groundwater is a worldwide phenomenon. Excess fluoride in drinking water causes serious health risks, and as a result, fluoride contamination of water resources is a global concern. In this study, an attempt has been made to provide the distribution of fluoride and related non-carcinogenic health hazards to local individual groups (males, females, and children separately) in the fluoride endemic region of Patiala, Punjab located in the Northern Indo-Gangetic Plain (IGP). The study shows that the dissolved groundwater fluoride concentration ranged between 1.5 and 9.2 mg/L with ∼98% of the sampling locations having fluoride levels higher than the permissible limit. Samples collected from deeper aquifers (>284 m bgl) showed ∼27% more fluoride contamination compared to those collected from <284 m bgl. Maximum incidence of elevated fluoride concentrations was observed in the eastern part of the study area in-sync with groundwater movement. The hazard quotient of fluoride (HQFluoride) calculated to assess the non-carcinogenic health risk was higher than the unitary value in all individual groups suggesting a prevalence of distressful fluorosis and chronic health risk. Results show that the children are the most vulnerable to fluoride toxicity followed by males and females. Our results are consistent with the recent trends in an increase in dental, skeletal fluorosis, and liver functional damage problems reported in children and adults of the studied region. The study area, therefore, needs the urgent attention of policymakers and government agencies to implement proper water management and cost-effective fluoride remedial measures to reduce the current and future chronic health risks associated with high fluoride intake.

Spatial variability of the sources and distribution of fluoride in groundwater of the Sanya alluvial plain aquifers in northern Tanzania

Groundwater contamination from geogenic sources poses challenges to many countries, especially in the developing world. In Tanzania, the elevated fluoride (F−) concentration and related chronic fluorosis associated with drinking F− rich water are common in the East African Rift Valley regions. In these regions, F− concentration is space dependence which poses much uncertainty when targeting safe source for drinking water. To account for the spatial effects, integrated exploratory spatial data analysis, regression analysis, and geographical information systems tools were used to associate the distribution of F− in groundwater with spatial variability in terrain slopes, volcanic deposits, recharge water/vadose materials contact time, groundwater resource development for irrigated agriculture in the Sanya alluvial plain (SAP) of northern Tanzania. The F− concentration increased with distance from steep slopes where the high scale of variation was recorded in the gentle sloping and flat grounds within the SAP. The areas covered with debris avalanche deposits in the gentle sloping and flat grounds correlated with the high spatial variability in F− concentration. Furthermore, the high spatial variability in F− correlated positively with depth to groundwater in the Sanya flood plain. In contrast, a negative correlation between F− and borehole depth was observed. The current irrigation practices in the Sanya alluvial plain contribute to the high spatial variability in F− concentration, particularly within the perched shallow aquifers in the volcanic river valleys. The findings of this study are important to the overall chain of safe water supply process in historically fluorotic regions. They provide new insights into the well-known F− contamination through the use of modern geospatial methods and technologies. In Tanzania's context, the findings can improve the current process of drilling permits issuance by the authority and guide the local borehole drillers to be precise in siting safe source for drinking water.

Naturally occurring potentially toxic elements in groundwater from the volcanic landscape around Mount Meru, Arusha, Tanzania and their potential health hazard

The population of the semi-arid areas of the countries in the East African Rift Valley (EARV) is faced with serious problems associated with the availability and the quality of the drinking water. In these areas, the drinking water supply largely relies on groundwater characterised by elevated fluoride concentration (> 1.5 mg/L), resulting from interactions with the surrounding alkaline volcanic rocks. This geochemical anomaly is often associated with the presence of other naturally occurring potentially toxic elements (PTEs), such as As, Mo, U, V, which are known to cause adverse effects on human health. This study reports on the occurrence of such PTEs in the groundwater on the populated flanks of Mt. Meru, an active volcano situated in the EARV.Our results show that the majority of analysed PTEs (Al, As, Ba, Cd, Cr, Cu, Fe, Mn, Ni, Se, Sr, Pb, and Zn) are within the acceptable limits for drinking purpose in samples collected from wells, springs and tap systems, suggesting that there is no immediate health risk associated with these PTEs. However, some of the samples were found to exceed the WHO tolerance limit for U (> 30 μg/L) and Mo (> 70 μg/L). The sample analysis also revealed that in some of the collected samples, the concentrations of total dissolved solids, Na+ and K+ exceed the permissible limits. The concerning levels of major parameters and PTEs were found to be associated with areas covered with debris avalanche deposits on the northeast flank, and volcanic ash and alluvial deposits on the southwest flanks of the volcano. The study highlights the need to extend the range of elements monitored in the regional groundwater and make a more routine measurement of PTEs to ensure drinking water safety and effective water management measures.

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.

Variability of naturally occurring fluoride in diverse community drinking-water sources, Tanna Island, Vanuatu

Abstract Large variations in fluoride concentrations exist in natural waters, many of which are the source of community drinking-water supplies. Determining fluoride concentrations in community drinking waters can be challenging in developing Pacific countries such as Vanuatu that have limited laboratory capacity. Knowledge of naturally elevated fluoride concentrations that cause irreversible, adverse health outcomes may allow communities the opportunity to treat and manage their drinking-water supplies. Community drinking-water samples (n = 69), sourced from groundwaters, roof catchment rainwaters, surface waters and springs, were sampled on Tanna Island, Vanuatu between 2017 and 2020. In an 18 km2 area of Western Tanna, a set of 30 groundwater-based drinking-water samples had a median fluoride concentration of 3.3 mg/L, with 20 samples &amp;gt;1.5 mg/L and seven samples &amp;gt;4.0 mg/L. These concentrations increase the risk of dental and skeletal fluorosis, respectively. Repeat resampling at five sites showed little variation over the sampling period. Rainwater-fed drinking-water supplies were lower overall and highly variable in fluoride concentrations (&amp;lt;0.05–4.0 mg/L, median of 0.53 mg/L), with variable inputs from volcanic emissions from Yasur volcano. We recommend a comprehensive oral health and bone health study for the whole island to determine adverse health effects of excess fluoride in this vulnerable population.

Influence of torrefaction and pyrolysis on engineered biochar and its applicability in defluoridation: Insight into adsorption mechanism, batch adsorber design and artificial neural network modelling

Natural and anthropogenic activities lead to massive contamination of groundwater with various organic and inorganic pollutants. Of these, fluoride is a major contaminant and elevated concentration of fluoride results in many health-related issues such as dental and skeletal fluorosis. This study aims to exploit an agricultural waste (rice husk) as a feedstock for synthesis of a value-added product (biochar), for effective defluoridation of drinking water. To that effect, thermal (torrefaction/pyrolysis) and chemical (iron/zinc) activation of rice husk-derived biochar were tested. Activation of biochar via pyrolysis followed by iron modification was capable of maximum fluoride removal (95.4 %). Optimized conditions for fluoride adsorption were time (120 min), biochar dose (4 g/L), solution pH (4) and initial F− concentration (5 mg/L). Additionally, a predictive modelling was carried out using an artificial neural network (ANN) model with four input variables and one output variable. Accuracy of the model was tested using error functions such as mean absolute error (0.002), root mean squared error (0.32) and coefficient of determination (0.99) for training, 3.78, 13.54 and 0.62 for validation and 5.10, 6.66 and 0.98 for testing respectively. Langmuir isotherm was best suited model among the isotherms tested with adsorption capacity of 4.45 mg/g. Rice husk derived biochar was found to be an economically viable alternative to commercially available adsorbents, which could also be employed for the remediation of other groundwater pollutants.

Groundwater contamination in sub-Saharan Africa: Implications for groundwater protection in developing countries

Rural and peri-urban communities in the developing world typically rely on boreholes and wells for drinking water, since freshwater resources on the land surface are heavily polluted and groundwater is perceived to be safe. Nonetheless, in these areas wastewater is managed onsite, often close to the groundwater abstractions points. Unbeknownst to most members of these local communities, this poses an unprecedented threat to their health, since chemicals and pathogens are leaking from onsite systems to groundwater. Polluted groundwater could also act as an environmental reservoir for bacteria and viruses, including new and emerging infectious diseases. In this study, groundwater from rural and peri-urban South Africa was assessed in terms of drinking water quality. Indicators of faecal pollution were identified across the examined boreholes, with E. coli and nitrates concentrations as high as 195 ​cfu 100 ​mL −1 and 104 ​mg ​L −1 , respectively, being identified. This suggests that onsite wastewater systems have grossly impacted groundwater quality. Elevated concentrations of fluoride and chloride (as high as 8.6 and 392 ​mg ​L −1 , respectively) were also identified, hence suggesting that the local geological setting also affects groundwater quality. Overall, groundwater was found in need of treatment before consumption, which is currently not the case. To inform local communities and the water industry about the problem, a simple classification model was developed. This could help to assess water quality, identify the nature of pollution, suggest the type of treatment required, and prioritise the need for water and wastewater infrastructure investment in the developing world. It can also inform local communities about the impact of their current wastewater management practices on water resources and the pressing need to upgrade them. • The water quality of a large number of boreholes was examined in South Africa. • Groundwater was heavily polluted and was in need of treatment before consumption. • Result suggested that wastewater from onsite systems leak to the groundwater. • Groundwater can be an environmental reservoir, for bacteria and virions transmission.

A characterization of groundwater fluoride, influencing factors and risk to human health in the southwest plain of Shandong Province, North China

This study investigated 324 groundwater samples collected from the southwest plain of Shandong Province during the dry and wet seasons. Groundwater fluoride in the study area and the influencing factors were characterized and discussed using statistical analysis, ion ratios, Piper diagrams, the saturation index (SI) and ArcGIS software. In addition, the risk posed by groundwater fluoride to human health was assessed. The results showed that groundwater in the study area had elevated fluoride concentrations, with average dry and wet season concentrations of 1.15 mg·L−1 and 1.08 mg·L−1, respectively. Groundwater fluoride showed consistent spatial variations during the dry and wet seasons, with a significant regionalization pattern of low concentrations in the east and high concentrations in the west. Groundwater F− was significantly negatively correlated with Ca2+ and positively correlated with pH, HCO3− and Na+. Important factors identified as having an effect on groundwater F− in the study area included the balance of dissolution of fluorite and calcite, the weakly alkaline environment and cation exchange. In addition, hydrochemical types of high-fluoride groundwater in the study area were identified as mainly HCO3-Na and SO4·Cl-Na. The assessment of the risk of high groundwater fluoride to human health showed that children are more at risk compared to adults, with the risk during the dry season exceeding that over the wet season. It is recommended that water quality management in the study area prioritize the formulation of measures to mitigate high concentrations of fluoride in groundwater .

Equine dental and skeletal fluorosis induced by well water consumption.

Two horses that consumed well water with high fluoride content exhibited clinical signs of chronic dental and skeletal fluoride toxicosis and were later euthanized and autopsied. Both horses had degenerative disease of multiple joints and multiple dental defects. Elevated fluoride concentrations were found in bone and tooth samples of both horses, well water, and feed. Microscopically, abnormalities were noted in bone and tooth samples, and consisted mostly of foci of cement necrosis and hypercementosis. Horses exhibiting bilateral, highly symmetrical dental and/or skeletal lesions, with chronic lameness, should be evaluated for the possible presence of fluoride toxicosis.

Origin, diversity and geothermal potentiality of thermal and mineral waters in Vrnjačka Banja, Serbia

Based on the results of 15 years of research on the physical and chemical parameters of 11 occurrences of thermal and mineral water in the extended area of the spa town of Vrnjacka Banja, diverse hydrochemical types of water have been identified, originating from different lithological formations (serpentinite, schist, marble, etc.). Currently, the total amount of abstracted thermo-mineral water is close to 70 L/s, with water temperatures up to 33.8 °C. However, interpretation of collected data indicates that the chemical composition of the mineral water is not exclusively related to the mineralogical composition of the host rock, i.e., aquifer material. To better understand the genesis of these waters, multivariate statistical analysis was undertaken in combination with hydrochemical interpretation of different ionic ratios. This approach revealed the existence of three distinct clusters of thermal and mineral waters: (1) low temperature, low mineral content and mild alkaline; (2) slightly acidic, with a moderate mineral content and elevated iron and fluoride concentrations; and (3) thermal, rich in CO2, with elevated mineral content and iron, manganese and fluoride concentrations. Two primary hydrogeochemical processes, which influence the composition of the thermo-mineral waters, were also identified: dissolution of serpentinite rocks and dissolution of schists, both enhanced by the presence of CO2 gas, circulating through fault zones. Estimates of available geothermal energy suggest a significant potential for expanding current uses of thermal waters of this most popular spa center in Serbia.