Table 4 - uploaded by P.L. Smedley
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Chemical compositions of a range of groundwaters with naturally high fluoride concentrations. The table also gives the modelled dominant species in the waters and fluorite saturation indices, calculated using PHREEQC..
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The element fluorine has long been recognised to have benefits for dental health: low-fluoride intake has been linked to development of dental caries and the use of fluoride toothpastes and mouthwashes is widely advocated in mitigating dental health problems. Fluoridation of water supplies to augment naturally low fluoride concentrations is also un...
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Context 1
... these generally low concentrations, fluoride in surface waters can be much higher in geothermal areas. Many alkaline lakes in the East African Rift Valley for example have concentrations of the order of tens to hundreds of mg L -1 (up to 1980 mg L -1 ; Table 4). ...
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... concentrations are lower in the humid tropics because of high rainfall inputs and their diluting effect on groundwater chemical composition. Table 4 shows the chemical compositions of a range of typical high-fluoride groundwaters from various parts of the world. The data illustrate the dominance of Na over Ca in most, though not all, waters and the high concentrations of HCO 3 that typify high-fluoride waters. ...
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... formation of complexes may have ramifications for human health for example in aluminium-bearing waters, where the total fluorine may be much higher than the measured ionic fluoride. Thus aluminium fluoride may stabilise the fluoride as a complex ion, but if these complexes are broken down during metabolism they could release both F -and potentially toxic Al. Table 4 gives the saturation indices for fluorite for each of the waters. Fluorite solubility is likely to control the upper limits of fluoride concentrations in most natural waters. ...
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Fluoride use as a chemotherapeutic agent for caries prevention has been well researched and documented. The recommendations for the use of fluoride have evolved through the years as a result of many factors. The change in the prevalence of caries and the advent of different fluoride formulations along with the desire to maximize the benefits and mi...
Citations
... High fluoride contamination has been reported worldwide, particularly in countries like India, China, and various regions of Eastern and Southern Africa (Ganyaglo et al., 2019;Hanse et al., 2019;Hossain & Patra, 2020;Karunanidhi et al., 2020;Li et al., 2019;Li et al., 2020;Liu et al., 2020Liu et al., , 2021Zuo et al., 2019). Previous studies have shown that regions with fluoride-contaminated groundwater are mainly influenced by volcanic bedrocks or crystalline basement rocks, aided by arid or semi-arid climatic conditions, Na-HCO3 type groundwater with low calcium levels, long groundwater residence time, and distance from recharge zones (Amini et al., 2008;Apambire et al., 1997;Edmunds & Smedley, 2005;Genxu & Guodong, 2001;Guo et al., 2007;Handa, 1975;Jacks et al., 2005;Nong et al., 2023;Rao, 1997;Saxena & Ahmed, 2001;Shaji et al., 2007;Sreedevi et al., 2006). ...
This study focuses on assessing hydrochemical characteristics and non-carcinogenic health risks associated with fluoride contamination in groundwater within the Palacode and Pennagaram taluks of Dharmapuri district. The presence of fluoride in drinking water is a significant concern due to its potential health impacts on both adults and children. We collected a total of 158 groundwater samples during both the summer (SUM) and monsoon (MON) seasons in 2021 to evaluate the suitability of water for drinking purposes in this region. During the SUM season, groundwater exhibits alkaline characteristics with a pH range of 6.70 to 8.73 and a mean value of 7.43, while the MON season falls within the neutral pH range with values ranging from 6.60 to 7.60 and a mean of 7.00. Hydrogeochemical analysis reveals that fluoride concentrations during the SUM season range from 0.13 to 2.7 mg/L, with a mean of 0.82 mg/L, whereas the MON season exhibits concentrations ranging from 0.08 to 1.6 mg/L, with a mean of 0.5 mg/L. Spatial distribution analysis indicates a gradual increase in fluoride concentrations from the northeast to the central and southern parts of the study area during both seasons. Residents in these areas have been exposed to high fluoride levels for an extended period, leading to health issues related to fluorosis. Our hydrogeochemical analysis attributes fluoride dominance to the Cl⁻-SO4²⁻ water type in both seasons. Furthermore, the relationship between fluoride and pH, HCO3⁻, Ca²⁺, and Na⁺ suggests the influence of geological factors in fluoride dissolution under alkaline conditions, while a reverse cation exchange process and increasing calcium concentration inhibit fluoride concentration. Saturation indices indicate that the unsaturated state of gypsum dissolution contributes to elevated fluoride levels in groundwater. Additionally, Gibbs plots highlight rock-water interactions as a significant factor influencing groundwater chemistry in the study area. Based on our hazard quotient (HQ) investigation, children are at a higher risk during both seasons compared to adults, with the central and northern regions showing alarming HQ values. These findings underscore the urgent need for enhanced groundwater quality monitoring and a comprehensive assessment of health risks, providing valuable insights for groundwater safety management in vulnerable areas of this region.
... Most leachates showed solubility equilibrium with respect to fluorite in the pH range of 4.0 to 7.0, meaning that this mineral likely acted as an upper limit of Al and F concentration above which precipitation would have occurred. This is in line with the known control of fluorine concentrations in natural waters, which is usually controlled by fluorite solubility (Edmunds and Smedley, 2005;VROM, 2008). These modelling results also suggest that the amount of aluminum and fluoride released to the solutions during the leaching tests could have been underestimated due to this fluorite solubility limit. ...
... The problem of fluorine and aluminum migration and toxicity in volcanic areas is well known and has been subject of extensive research (e.g. Oskarsson, 1980;Wenzel and Blum, 1992;Cronin et al., 2000Cronin et al., , 2003Edmunds and Smedley, 2005;D'Alessandro, 2006;Kockum et al., 2006;Cabré et al., 2016). In short, despite fluoride being an essential nutrient for human and animal growth, excessive doses of this element may lead to serious dental or even skeletal fluorosis (Edmunds and Smedley, 2005;Linhares et al., 2019). ...
... Oskarsson, 1980;Wenzel and Blum, 1992;Cronin et al., 2000Cronin et al., , 2003Edmunds and Smedley, 2005;D'Alessandro, 2006;Kockum et al., 2006;Cabré et al., 2016). In short, despite fluoride being an essential nutrient for human and animal growth, excessive doses of this element may lead to serious dental or even skeletal fluorosis (Edmunds and Smedley, 2005;Linhares et al., 2019). Besides, plants may accumulate high concentrations of F − , so that livestock feeding on these plants (e.g. ...
Leaching tests conducted on fresh ashfall samples taken soon after the onset of the 2021 Tajogaite eruption occurred at the Northwest flank of the Cumbre Vieja Volcanic Ridge in La Palma (Canary Islands) have revealed relevant geochemical trends which have important environmental significance and practical implications. The ashfall deposited on most of the island during the eruptive episode (9/19/2021–12/13/2021) contains, in addition to common constituents in volcanic tephra (e.g. volcanic glass, silicates like olivine, amphibole or pyroxene, magnetite, etc.) a significant amount of very fine-grained (diameter range of 10–500 μm) crystals of highly soluble salts like AlF3, NaCl, KCl or CaSO4. These salts likely crystallized at high temperature by interaction of acid volatile phases (e.g., HF, HCl, SO2) with volcanic glass and silicate minerals during the ascending flow of the eruptive plume, though some adsorption of marine aerosols on ash surfaces during the subsequent descending flow and transport to more distal areas could have also taken place. The dissolution of these salts in the leaching tests (conducted with ultrapure distilled water during 90 min) reveals a fast release of important amounts of F−, Cl− and SO42− as major anions, and Al3+, Na+, K+, Ca2+, Mg2+ and Si4+ as major cations, in addition to minor amounts of trace metals like Mn2+, Zn2+, Ba2+ or Sr2+. The release of F− and Al3+, both potentially toxic and travelling together as aluminum fluoride species (AlF3, AlF2+, AlF4−) is particularly noteworthy and represents a potential threat for the environment (including soils, surface waters or groundwater existing beneath the ashfall layers covering the island) as well as for food safety (e.g. banana plantations) and/or human health (exposure to F- or Al-contaminated water). On the other hand, the tephra does not represent an environmental hazard as regards to other toxic elements traditionally reported for ashfall released in other volcanic eruptions, such as As, Pb, Hg or Se, which were always close to or below the limit of detection. Besides, the Tajogaite 2021 ashfall shows a significant acid-neutralizing capacity as a result of the partial dissolution of volcanic glass in the F-rich solutions. This study presents a discussion of geochemical and mineralogical controls on element mobility during ashfall/water interaction in the environment which may be worth considering in any future restoration or land management plans for the island.
... Environmental fluoride is a natural process involving volcanic emissions and movement of soil particles, which can be transported or removed from the atmosphere through wet deposition. 1 Many factors may interfere with fluoride concentrations in public potable water, such as mineral decomposition of rocks, precipitation, and water and air temperature. For example, groundwater has a high concentration of natural fluoride because water in deep wells is warmer than water in Declaration of Interests: The authors certify that they have no commercial or associative interest that represents a conflict of interest in connection with the manuscript. ...
... 1 A high fluoride concentration is also related to groundwater with low Ca/Na ratio since the processes that reduce the dissolved Ca concentration generally promote subsaturation of fluorite and increase the dissolved fluoride concentration. 1 Fluoride in the mineral composition of rocks is released into the water through rock decomposition and may affect its concentration in water for public consumption. 2 Therefore, these conditions may justify the variation in concentration of natural fluoride found in this study. ...
... The presence of fluoride in groundwater is due to the chemical composition of the rocks, alkaline hydrological environment, climatic conditions, residence time in aquifers and geochemical processes (Edmunds & Smedley, 2013). It should be noted that the present study assesses the fluoride doses coming from natural waters, since there is no guidance of fluoridation (fluoride addition) in SAC in Brazil (BRAZIL, 2021). ...
... Fluoride was DPP in the two years evaluated. It is often found in low concentrations in groundwater (Edmunds & Smedley, 2013). However, studies have reported high concentrations of fluoride in aquifers (Ezaki;Aguilar;Hypolito & Shinzato, 2016). ...
Theoretical benchmark: The seasonal and spatial variability of a spring can be monitored by physical, chemical and microbiological parameters, to ensure access to the population of drinking water, managed in a safe manner, since alternative and unsafe sources of water supply, and sometimes without treatment, pose risk to human health. Method: Quantitative, retrospective study of water samples collected monthly by monitoring the quality of water for human consumption in rural and urban areas from collective supply from January 2018 to December 2019. Results and conclusion: Precipitation interfered with all water quality indicators except free residual chlorine; and temperature interfered with turbidity, free residual chlorine, and fluoride. There was a correlation between fluoride and temperature; total coliforms and free residual chlorine, which suggests the possibility of antimicrobial action. Cross-sectoral actions to improve the quality of water supplied in rural areas are therefore proposed, through the adoption of continuous disinfection of all water sources. Research Implications: Presents important indicators on the quality of water consumed by the population, directly influencing the health of consumers. Originality/value: Research carried out in the rural area in Brazil is controversial about the interference of climatic factors in the quality of the distributed water. In view of the need to provide access to the population of drinking water, subject to safe and efficient treatments, without risks to human health, and for this purpose this study assesses the interference of climatic factors in the quality of water.
... High concentrations of Fˉ are observed mainly in the dry areas as a result of high pH and HCO 3ˉ, low concentration of Ca 2+ , and longer residence time of groundwater (Edmunds and Smedley 2013;Vithanage and Bhattacharya 2015;Rashid et al. 2019;Wang et al. 2020a). The results show that only 3 samples collected from Fereydunshahr have a concentration higher than the maximum permissible limit recommended by the WHO for drinking (1.5 mg/L). ...
Nitrate (NO3ˉ) and fluoride (Fˉ) are two major potential contaminants found in the groundwater of Iran. These contaminants are highly dangerous to humans if consumed more than the safe limit prescribed by the WHO. Therefore, in this study, the urban and rural drinking water resources of Isfahan province (central Iran) were investigated to evaluate the quality of groundwater from the perspective of NO3ˉ and Fˉ. The calculated saturation index (SI) shows that the majority of samples are mainly undersaturated or in equilibrium with respect to potential minerals. The most likely interpretation for undersaturation with respect to most minerals is either that the minerals are not present if they are reactive or if they are present, then they are not reactive. This study reveals that the majority of the groundwater samples belong to the Ca-Mg-HCO3 water type. Further, in this study, potential physicochemical variables have been used to calculate entropy weighted water quality index (EWQI). The EWQI reveals that the majority of the groundwater in the area is of good quality. Results show that the water chemistry in the area is largely governed by the water-rock interaction. This study based on large data sets reveals that the majority of drinking water resources are uncontaminated by Fˉ. However, the groundwater is found to be largely contaminated by NO3ˉ. The bivariate plot suggests that the unscientific farming practices and overuse of manures and fertilizers are largely responsible for high content of NO3ˉ. Therefore, emphasis should be given on the cost-effective environmentally friendly fertilizers. The findings from this study will aid the governing authorities and concerned stakeholders to understand the hydrogeochemical evolution of groundwater in this region. The results will help formulate policies in the area for sustainable water supply.
... Cation exchange promoted the enrichment of F − in groundwater through the exchange between Na + adsorbed on the aquifer and Ca 2+ and Mg 2+ in groundwater (Li et al., 2018;Edmunds and Smedley, 2013). The relationship between (K + + Na + − Cl − ) and (Ca 2+ + Mg 2+ − HCO 3 − -SO 4 2− ) is generally used to verify the occurrence of cation exchange in groundwater. ...
A comprehensive understanding of the role of natural and anthropogenic factors in groundwater pollution is essential for sustainable groundwater resource management, especially in alluvial plains with intensive anthropogenic activities. Numerous studies have focused on the contribution of individual factors on groundwater pollution in alluvial aquifers, but distinguishing the effects of natural and anthropogenic factors is limited. In this study, 64 wells were sampled in different seasons from the Yellow River alluvial plain in China for hydrochemical and isotopic analysis to investigate the spatiotemporal distribution, sources and health risks of fluoride and nitrate in alluvial aquifers. Results showed that fluoride contamination was widely distributed without significant seasonal variation, and 78.1 % of the dry season samples and 65.6 % of the wet season samples showed fluoride concentrations above the permissible limit (1.5 mg/L). High-F- groundwater was generally accompanied by Na-HCO3 and Na-HCO3·SO4 water types. Fluoride was from a natural origin mainly associated with mineral dissolution, competitive adsorption, cation exchange, and evaporation. Groundwater nitrate contamination was spatially sporadic and showed significant seasonal differences. Only 13.6 % of the dry season samples and 3.2 % of the wet season samples had NO3- concentrations exceeded the permissible limit of 50 mg/L. The hydrochemical phase evolved from bicarbonate or sulfate type to chloride type with increasing nitrate concentration. Manure and sewage attributed to agricultural activities contributed the most nitrogen to groundwater, followed by soil organic nitrogen and chemical fertilizers, revealing the anthropogenic origin of nitrate. Nitrification was the dominant nitrogen transformation process in the wet season, and denitrification was prevalent in the dry season. Oral ingestion of high fluoride groundwater was a major threat to human health, especially for infants. This study provided a significant reference for water resources management in alluvial aquifers.
... Therefore, it is also said to be a sword with two edges. It was estimated that nearly 200 million people globally are potentially exposed to fluorosis (Edmunds and Smedley 2013), and significant vulnerable population lives jointly in India and China . Predicting affected people from fluorosis is challenging; therefore, the exposed number is infect clearly more than estimated. ...
Groundwater contamination by fluoride (F¯ >1.5 mg/L) is pervasive and typically confined to arid and semi-arid regions. Therefore, several parts of India are contaminated by F¯. However, the genesis, sources, and mobilization of F¯ in groundwater are unclear or evaluated based often on studies conducted at a local scale. To understand the severity of F¯ contamination at the national scale and to devise remedial strategies, we performed a statistical evaluation between F¯ and its influencing factors, including geology, hydro-meteorology, and potential hydro-chemical parameters based on a large dataset (n = ∼2000) published in the last two decades throughout India. Results revealed that (a) alkalinity plays a pivotal role in the mobilization of F¯ into groundwater from the sediments/rocks, (b) high F¯ in groundwater is more pronounced in the arid and semi-arid areas of alluvial plains than hard rock regions, and (c) positive correlation of elevated F¯ with SiO2 and K+ indicates the dominance of geogenic sources linked to the weathering of fluorine bearing silicates. Investigations show that one-third of the Indian drinking water wells are contaminated by F¯, thereby risking the health of over millions of people through the drinking water pathway. Findings from this study have addressed the most possible sources, pathways, and regional prevalence of F¯ contamination in the groundwater of India, and suggested the remediation measures suitable based on prevailing surface and sub-surface conditions. The review will also address challenges and propose future research directions to tackle high fluoride groundwater and ensure safe drinking water supply in India.
... Fluoride rich minerals gradually weathers and releases fluoride ions into ground and surface water (Rafique et al., 2015). Fluoride is beneficial for human health as it promotes the growth of healthy bones and teeth (Edmunds & Smedley, 2013;Prasad et al., 2018). Various dietary components help absorption of fluorides from the gastrointestinal tract and the absorbed fluoride is distributed throughout the body. ...
... Various dietary components help absorption of fluorides from the gastrointestinal tract and the absorbed fluoride is distributed throughout the body. According to World Health Organization (WHO), fluoride is beneficial only in the narrow concentration range of 0.5 to 1.5 mg L -1 in drinking water (Amini et al., 2008;Edmunds & Smedley, 2013;García & Borgnino, 2015). Higher concentrations of fluoride cause serious health effects such as dental and skeletal fluorosis, brain damage and chronic kidney diseases (Edmunds & Smedley, 2013;Kanduti et al., 2016). ...
... According to World Health Organization (WHO), fluoride is beneficial only in the narrow concentration range of 0.5 to 1.5 mg L -1 in drinking water (Amini et al., 2008;Edmunds & Smedley, 2013;García & Borgnino, 2015). Higher concentrations of fluoride cause serious health effects such as dental and skeletal fluorosis, brain damage and chronic kidney diseases (Edmunds & Smedley, 2013;Kanduti et al., 2016). The hypo-mineralization of teeth commonly known as dental fluorosis develops at fluoride concentrations above 1.5 mg L -1 (O Mullane et al., 2016;Akuno et al., 2019). ...
Fluoride is beneficial for human health only in a narrow concentration range. Over the years, many analytical techniques have been developed to quantify fluoride in a variety of sample matrices. In this research, fluoride concentrations of twenty (20) natural water samples determined by SPADNS (SPA) and Eriochrome Cyanine R (ECR) colorimetric methods were evaluated to ascertain whether these methods can produce comparable fluoride concentrations. According to the paired t test for comparing individual differences, the two datasets are different at 95% confidence level suggesting that the two analytical methods produce statistically different fluoride concentrations for the analysed water samples. The potential interferences of Al3+, Ca2+, and Mg2+ on the fluoride analysis was evaluated using 0.85 mg L-1 fluoride standard solutions spiked with various amount of the above-mentioned metal ions. The highest interference was observed with Al3+ ions, which underestimated the fluoride concentration by 26% and 23% for ECR and SPA methods respectively at 20.0 mg L-1 Al3+ concentrations. The minimum interference was observed for Ca2+ ions which underestimated the fluoride concentration by 8% and 7% for ECR and SPA methods respectively at 100.0 mg L-1 Ca2+ concentrations. Acid distillation resulted in the samples spiked with Ca2+ and Mg2+ ions in the range of 0.50 to 100.0 mg L-1 reaching the theoretical concentration of 0.85 mg L-1. Acid distillation also worked well for the Al3+- fortified samples, except for Al3+ concentration at 20 mgL-1. The efficiency of the acid distillation method was also tested with three (03) natural water samples. The fluoride concentration increased significantly after the acid distillation; however, even after the acid distillation, statistically comparable fluoride concentrations were not observed.
... Drinking water is one of the primary sources of F for the human body, supplying approximately 2/3-4/5 of the daily F requirement [17,18]. The F content in streams and lakes typically ranges between 0.1 and 0.3 mg/L, in atmospheric precipitation between 0.1 and 0.2 mg/L, in groundwater between 0.1 and 10 mg/L, and in oceans and seawater between 1.2 and 1.4 mg/L [19]. ...
Fluoride (F) ions actively participate in the dental enamel remineralisation process and inhibit the activity of cariogenic bacteria of the oral biofilm. However, increased systemic intake of F during critical periods of amelogenesis can lead to dental fluorosis (DF). The necessity of our study stemmed from the growing consumption of bottled water, as water is one of the primary sources of F in humans, and labelling F concentration is optional. Our aim was to evaluate the F concentration in bottled natural mineral or spring still waters available on the market in Iasi, Romania. We purchased forty different brands of still bottled water from the major grocery stores and tested them using an ion-selective electrode method. The reliability of the data was assessed by the intraclass correlation coefficient (ICC), while the differences between the obtained and labelled F values were examined using a paired samples t-test. The tested F levels ranged between 0.0338 and 4.6262 milligrams per litter (mg/L). The majority of the samples, around 85% recorded F values ranging from 0.232 to 0.0338 mg/L, offering slight or no benefit in caries prevention. Another 10% of the samples had F values ranging between 0.3 and 0.4 mg/L and could provide a dental health benefit. A percentage of 5% of the tested samples recorded F levels above the optimal level of 0.7 mg/L, as set by the American Dental Association (ADA) and the United States Department of Health and Human Services (U.S. HHS). This elevated F concentration poses a potential risk for DF in infants and toddlers, indicating that regular consumption of these samples may be unsafe.
... To explore controls on fluoride concentrations in groundwater in the RGMB, we examine log-log scale correlations between concentrations of F −1 and both pH and HCO 3 −1 (Edmunds and Smedley 2013;Su et al. 2019). The concentration of F −1 increases with a rise in concentrations of HCO 3 −1 and pH (Fig. 5e, f, Table S1), suggesting that higher alkalinity and more alkaline conditions favor the release of F −1 into groundwater. ...
... High fluoride concentrations in groundwater observed in the RGMB have been noted in many parts of the world (Ali et al. 2016;Wang et al. 2020;Nordstrom and Smedley 2022;Podgorski and Berg 2022) and associated with both geological settings and human activity. The geogenic origin of fluoride include the dissolution of fluoride-bearing minerals found in sedimentary, metamorphic, and igneous rocks (Edmunds and Smedley 2013;Olaka et al. 2016;Haji et al. 2018). Human activities that contribute to fluoride contamination of groundwater include the intensification of agriculture that includes use of pesticides and phosphate fertilizers (Kundu and Mandal 2009;Xu et al. 2022). ...
... In drylands, the occurrence of fluoride in groundwater systems is thought primarily to be controlled by cation exchange, rock/soil weathering, and evaporation (Edmunds and Smedley 2013;Su et al. 2019;Wang et al. 2020;Nordstrom and Smedley 2022;Podgorski and Berg 2022). Groundwater sampled from a range of weathered crystalline rock aquifer systems including metamorphic rocks, intrusive granite, and volcanic rocks has been associated with high fluoride concentrations in Sudan (up to 3.6 mg/L), northeastern Ghana (up to 20 mg/L), and the East African Rift System in Kenya (up to 10.5 mg/L), Uganda (up to 3.0 mg/L), Tanzania (up to 8.8 mg/L), and Ethiopia (up to 12.0 mg/L) (Kut et al. 2016;Olaka et al. 2016;Haji et al. 2018;Ijumulana et al. 2020;Onipe et al. 2020). ...
In the River Goulbi Maradi Basin (RGMB), groundwater is a vital source of drinking water and plays a central role in the region’s socio-economic development. The quality and suitability of groundwater for irrigation and drinking-water remain inadequately understood. We examine hydrochemical analyses of 35 groundwater samples from the shallow alluvial (17) and underlying Continental Hamadien (CH) sandstone (18) aquifers and evaluate these against standard measures of their suitability for drinking water (World Health Organization (WHO) guideline values) and irrigation (i.e., sodium adsorption ratio, sodium percentage, and the residual sodium carbonate). Hydrochemical facies are principally of Na–HCO3 and Na–Cl types. Bivariate plots combined with saturation indices and electrical conductivity monitoring suggest that the main hydrogeochemical processes influencing groundwater quality are cation exchange in the CH aquifer and solute leaching from soils during focused recharge in the alluvial aquifer. 76% (13/17) of groundwater samples from the alluvial aquifer were suitable for irrigation compared to 38% (6/16) of the samples from the CH. The identification of high fluoride concentrations exceeding the WHO drinking-water guideline value (> 1.5 mg/L) in 33% (6/18) of samples from the CH aquifer and 18% (3/17) in the alluvial aquifer, and their respective attribution to the release of fluoride of geogenic origin through cation exchange and local use of fluorapatite fertilisers, provide valuable insight into efforts to address the on-going challenge of fluorosis in the Maradi region of Niger and more widely across African drylands. The health consequences of the widespread observation of Mn in concentrations exceeding the new WHO guideline value (0.08 mg/L) in the alluvial aquifer (6/9 samples), often alongside elevated Fe concentrations, are unclear.
