Fluoride In Natural Waters Research Articles

Sukhareva O.Yu., Kushtan S.M., Sukharev S.M. SCREENING OF CONTENT OF BIOAVAILABLE FORMS OF FLUORIDE IN SURFACE AND GROUNDWATER OF THE TISA RIVER BASIN

Fluorine, as a essential trace element, plays an important role in maintaining human health, but an excess of fluorides causes various diseases. The main way fluoride enters the human is drinking water, the source of which is natural surface and underground water. In surface and groundwater, fluorides can exist in bound (compounds with aluminum, iron, calcium and magnesium) and free (bioavailable) forms, therefore, when monitoring natural waters, it is important to distinguish between the total content of fluorides and the content of bioavailable forms. This work presents a screening of the content of bioavailable forms of fluorides in surface (river) and underground (well) waters of the Tisza River basin. The study was carried out in the summer (June-August) period of 2023. The screening results showed that river waters have a lower concentration of bioavailable forms of fluorides (2.9-8.3 μg×L-1) than groundwater (7.5-14.4 μg×L-1). It was established that the content of bioavailable forms of fluorides in natural waters is determined, first of all, by the geology of the territories (the lowest content in mountainous areas, and the highest in lowland areas), and for surface waters also by the morphologys of the river. For river waters, the general pattern of fluoride content distribution is complicated and ambiguous. In general, the content of bioavailable forms of fluorides in the surface and underground waters of the Tisza River basin is small, which causes a risk to the human dental health of the region.
 Keywords: monitoring of natural waters; indirect spectrophotometry; liquid-liquid microextraction; human health risk.

Hotspot mapping and risk prediction of fluoride in natural waters across the Tibetan Plateau

Intake of high fluoride concentrations through water affects up to 1 billion people worldwide, and the Tibetan Plateau (TP) is one of the most severely affected areas. Knowledge regarding the high fluoride risk areas, the driving factors, and at-risk populations on the TP remains fragmented. We collected 1581 natural water samples from the TP to model surface water and groundwater fluoride hazard maps using machine learning. The geomean concentrations of surface water and groundwater were 0.26 mg/L and 0.92 mg/L, respectively. Surface water fluoride hazard hotspots were concentrated in the north-central region; high fluoride risk areas of groundwater were mainly concentrated in the southern TP. Hazard maps showed a maximum estimate of 15% of the total population in the TP (approximately 1.47 million people) at risk, and 500,000 people considered the most reasonable estimate. Critical environment driving factors were identified, in which climate condition was taken for the vital one. Under the moderate climate change scenario (SSP2.45) for 2089–2099, the high fluoride risk change rate differed inside the TP (surface water −24%−55% and groundwater −56%−50%), and the overall risk increased in natural waters throughout the TP, particularly in the southeastern TP.

(Invited) Electrochemically Driven Ion-Exchange Remediation of Water Containing High Fluoride Content

Remediation of water contaminated by anthropogenic activities is required to provide clean water for human consumption and prevent damage to the environment. The scale of the challenge is signaled by its inclusion in the UN 17 Sustainable Development Goals [1]. Major contributors to the problem are industrial activity and agriculture. The former commonly results in the release of metals; analysis and separation of such cationic species have received considerable attention [2]. In the latter instance, run-off of fertilizers used to enhance crop yields can result in unacceptable levels of nitrate or phosphate in natural waters. While monitoring of anionic species is widely undertaken using ion selective electrodes [3], the promise of electrochemical separation technologies [4] in this area is less well developed.For anthropogenic causes, remediation is the last resort following failure to prevent release of toxic materials into the environment. In contrast, there are instances where the “contaminant” is natural: fluoride is a prime example. The beneficial dental health effects of fluoride are widely appreciated, but excessive amounts are harmful to teeth, bones and various organs [5]. The World Health Organization (WHO) identifies the optimum fluoride level in drinking water to be 0.5-1.0 mg/L. In many regions, water is fluoridated to realize the health benefits. However, local geological conditions many countries can result in natural water fluoride levels significantly above the recommended upper limit of 1.5 mg/L.This presentation addresses the challenges associated with remediation of anions, with particular focus on fluoride. At the outset, it is recognized that for potable water the requirement is not full de-ionization but selective removal of contaminants: this is a separation challenge. The attributes, performance and potential for scale-up of a range of (electro)chemical remediation strategies will be discussed in general. We then focus on electrochemically switched ion-exchange (ESIX) [6], for which application to water softening [7] and perchlorate removal [8] has been demonstrated.We explore the facility of aniline-based (co-)polymer films to reversibly extract and eject fluoride ions as the charge (oxidation state) of the films are subject to electrochemical control. Homopolymer and copolymer films based on aniline, o-aminophenol and o-toluidine were deposited potentiodynamically. Film thickness was controlled via the number of potential cycles: the resultant electroactive site population was assayed coulometrically in monomer-free background electrolyte. Film mass was assayed gravimetrically using the EQCM. For relatively thin films, correlation of film mass and charge capacity revealed the solvent content. During deposition of thicker films, acoustic admittance data revealed the progressive evolution of viscoelastic effects. Co-monomer feedstock has a significant influence on film deposition rate, absolute solvent population and redox-driven solvent population change [9].The ion-exchange capacity of the films for redox-driven fluoride uptake was determined upon exposure to aqueous solutions of varying fluoride concentration, both in the absence and presence of chloride as a competing anion. EQCM mass and charge responses, respectively, provide overall “ion+solvent” and “solvent” population changes: correlation permits separation of fluoride and water uptake/release. Copolymer composition significantly influences the ease of fluoride uptake and release and reveals ion trapping. Complementary data on the dynamics of ion and solvent transfers are provided by shorter timescale experiments, involving voltammetry at faster scan rates and chronoamperometry. Correlation of gravimetric and coulometric data permits temporal separation of fluoride and solvent entry and exit.Practical exploitation of these promising fundamental observations will require scale-up and optimization of cycle life, film viscoelasticity and response time as functions of film thickness. We speculate that spatially variant film solvation will be a critical parameter. To this end, we consider the viability of neutron reflectivity measurements with isotopic substitution to determine the spatial distributions of fluoride and solvent in films of graded composition.

Spatial and seasonal variability, control factors and health risk of fluoride in natural water in the Loess Plateau of China

Hundreds of millions of people around the world are currently exposed to excessive amounts of fluoride (F-) in drinking water. Although the factors controlling the spatiotemporal distribution of F- contents have been analyzed, their contributions have rarely been quantified. In this study, 510 water samples were collected in the dry and wet seasons in China’s Loess Plateau to investigate the spatial and seasonal distribution, controlling factors, and potential health risks of F- in natural water. High-F- waters were mainly distributed in valley areas of the Loess Plateau, and more severe fluoride pollution of streamwater and groundwater was found in the wet and dry seasons, respectively. Mineral dissolution, competitive adsorption, adsorption/desorption and cation exchange jointly controlled F- enrichment. Spatiotemporal distribution of high-F- levels was mainly determined by climate and streamwater-groundwater connectivity in the dry season, with contribution rates of 41.7% and 37.6%, and by terrain and anthropogenic activities in the wet season, with contribution rates and 49.9–55.6% and 30.7%, respectively. Fluoride in groundwater through oral intake posed the greatest health risks to infants, followed by children, teenagers and adults in the dry and wet seasons. This study provides a scientific basis for the effective management of high-F- water in arid regions.

PREPARATION OF FLUORIDE ADSORBENT FROM ZIRCON SAND USING MECHANOCHEMICAL TREATMENT, AND ITS APPLICATION FOR FLUORIDE REMOVAL

Removal of low-concentration fluoride in natural water is an important issue all over the world. Japan is a volcanic country with many hot springs, and the removal of low-concentration fluoride from hot spring drainage is desired. In this study, we attempted to prepare a novel adsorbent with high selective removal ability of fluoride from zircon sand using mechanochemical treatment, and applied it for removing fluoride from hot spring water. Mechanochemical treatment of zircon sand was carried out using a planetary ball mill, and fluoride removal of the product was examined using fluoride aqueous solution and hot spring water. The hot spring water is collected from one of the hot spring in Japan, and a typical sulfuric acid hot spring water pH 2 including high contents of SO42-(12000 mg L-1) and Cl- (5000 mg L-1) with 11 - 15 mg L-1 of fluoride ion. Regardless of ball sizes, with increasing the mechanochemical treatment time to 10 min, the removal ability of the product for fluoride increases, and then be almost constant. With decreasing pH of the solution to 2, the adsorption amount increases, and then be almost constant. With increasing the temperature of the solution, the adsorption amount decreases, while the rate of adsorption increases and the amount increases. The adsorption isotherm at pH 2 follows much better Langmuir model than Freundlich model, and the calculated maximum adsorption amount is 0.11 mmol g-1. Fluoride can be adsorbed selectively from hot spring water below Japanese effluent standard for fluoride (8.0 mg L-1).

Zirconium gallocyanin MS complex as a highly selective reagent for the spectophotometric determination of fluoride

A new photometric procedure for the determination of fluoride ion based on its destruction of zirconium-gallocyanin MS complex is described.The method exhibits great selectivity towards fluoride compared to alkaline-earth, non-ferrous and rare-earth metals, iron, sulfate, nitrate, and phosphate ions and allows to carry out the determination of fluoride in complex objects complex without a preliminary separation of matrix components. The linear range of the quantitative determination of F− was determined to be 0.03 to 2 mg/L with a detection limit of 0.02 mg/L and a correlation coefficient of 0.9989. This method has been successfully applied to the determination of fluorides in natural waters, metallurgic wastewaters, cryolite and condensates of volcanic gases and has good convergence with the results of potentiometric analysis.

Open-Source Portable Device for the Determination of Fluoride in Drinking Water.

The prolonged exposure to fluorides results in the development of several diseases, from dental fluorosis to crippling deformities of the spine and major joints. The population exposed to high fluoride concentration is located in developing countries where the assurance of water quality is difficult to perform. Addressing this challenge, an open-source system for the determination of fluoride in natural water was developed using the equilibrium between the red Fe-SCN complex and the colorless Fe-F. The reaction develops in cotton substrates to reduce the manipulation of liquid reagents and reduce the errors by nontrained operators. The system was optimized by image analysis and implemented in an open-source Arduino-based device and data was acquired through the serial port of a cell phone, which is also used as a power source, avoiding the use of a battery and reducing production costs. The device showed a detection limit of 0.7 mg L-1 and a linear range of up to 8 mg L-1. This extended detection limit makes the device useful for the application in regions where the fluoride concentration in drinking water is far higher than the United Nations limit (1.5 mg L-1), e.g., the United Republic of Tanzania, where the upper limit of F- was extended to 4 mg L-1 or in USA, where the Environmental Protection Agency established the Maximum Contaminant Level of F- in drinking water at 4 mg L-1. The method was tested with natural waters from the Arusha region in the northeast of Tanzania and validated against the results from ion chromatography showing a good correlation. The developed device exhibits chemical stability of 5 days, allowing it to be manufactured and distributed in local areas and, also, modified according to the requirements of the water composition due to Industry 4.0 concepts used in the design.

Masking Ability of Various Metal Complexing Ligands at 1.0 mM Concentrations on the Potentiometric Determination of Fluoride in Aqueous Samples.

Fluoride is a common anion present in natural waters. Among many analytical methods used for the quantification of fluoride in natural waters, potentiometric analysis is one of the most widely used methods because of minimum interferences from other ions commonly present in natural waters. The potentiometric analysis requires the use of ionic strength adjusting buffer abbreviated as TISAB to obtain accurate and reproducible data. In most of the reported literature, higher concentrations of strong metal chelating ligands are used as masking agents generally in the concentration range of 1.0 to 0.01 M. In the present study, effectiveness of the masking agents, phosphate, citrate, CDTA ((1,2-cyclohexylenedinitrilo)tetraacetic acid), EDTA (ethylenediaminetetraacetic acid) HE-EDTA ((hydroxyethyl)ethylenediaminetriacetic acid)), triethanolamine, and tartaric acid at 1.0 mM in TISAB solutions was investigated. The experimental data were compared with a commercially available WTW 140100 TISAB solution as the reference buffer. According to the experimental data, the reference buffer always produced the highest fluoride concentrations and the measured fluoride concentrations were in the range of 0.611 to 1.956 mg/L. Out of all the masking agents investigated, only CDTA performed marginally well and approximately a quarter of the samples produced statistically comparable data to the reference buffer. All the other masking agents produced significantly low concentrations compared to the reference buffer. The most probable reasons for the underestimation of fluoride concentrations could be shorter decomplexing time and lower masking agent concentrations.

Application of microextraction techniques for indirect spectrophotometric determination of fluorides in river waters

The present study is dedicated to development of improved method for determination of trace amounts of fluorides in natural waters which is based on the interaction of fluorides with ion associate (IA) of Al(III), salicylic aldehyde acylhydrazones (benzhydrazone (SABH) and 4-picolinhydrazone (SAPH)) and polymethine dye Astra Phloxine FF (AP). Comparison of analytical forms [Al(SABH)2]⋅AP and [Al(SAPH)2]⋅AP showed that the analytical system Al(III)-SAPH-AP is more effective, namely, a higher level of preconcentration of the analytical form is ensured by and extraction equilibrium is achieved faster. Based on the study, we propose a new, fast, simple, reliable, sensitive, and accurate method of the indirect UV–Vis-spectrophotometric determination of fluorides grounded on the interaction of fluorides with IA of Al(III), SAPH and AP with the utilization of vortex-assisted liquid-liquid microextraction (VALLME). The method is based on the discoloration of the microextract of IA of Al(III), SAPH and AP (Al-SAPH-AP) in presence of fluoride ions due to the formation of fluoride complexes of aluminum with higher stability. The effect of various factors has been studied. The optimal conditions of the UV–Vis-spectrophotometric determination of fluorides were defined as: pH 7.0–10.0, 1.0⋅10−6 mol⋅L−1 Al(III); 4.0⋅10−5 mol⋅L−1 SAPH; 1.0⋅10−6 mol⋅L−1 AP; λ = 560 nm. VALLME have been carried out in 250 μL of CCl4 at 20:1 vol ratios of aqueous and organic phases, with vortexing at 3000 rpm for 15 s followed by centrifugation at 2000 rpm for 2 min. The determination of fluorides is feasible in the presence of various interferences. The calibration curve shows the linear dependence in the range of 0.3–114 μg⋅L−1 of the fluorides concentration (R2 = 0.993) with the limit of detection of 0.086 μg⋅L−1 and the limit of determination of 0.284 μg⋅L−1. The accuracy of the proposed protocol of fluorides determination was verified towards a reference method on the samples of natural rivers waters (RSD 2.6–3.1%, recovery 98.3–101.4%).

Implementing a geographical information system to assess endemic fluoride areas in Lamphun, Thailand.

IntroductionMany studies have shown that fluoride can cross the placenta and that exposure to high fluoride during pregnancy may result in premature birth and/or a low birth weight. Lamphun is one of six provinces in Thailand where natural water fluoride (WF) concentrations >10.0 mg/L were found, and it was also found that >50% of households used water with high fluoride levels. Nevertheless, geographical information system (GIS) and maps of endemic fluoride areas are lacking. We aimed to measure the fluoride level of village water supplies to assess endemic fluoride areas and present GIS with maps in Google Maps.MethodsA cross-sectional survey was conducted from July 2016 to January 2017. Purpose sampling was used to identify villages of districts with WF >10.0 mg/L in the Mueang Lamphun, Pasang, and Ban Thi districts. Water samples were collected with the geolocation measured by Smart System Info. Fluoride was analyzed with an ion-selective electrode instrument using a total ionic strength adjustment buffer. WF >0.70 mg/L was used to identify unsafe drinking water and areas with high endemic fluoride levels. Descriptive statistics were used to describe the findings, and MS Excel was used to create the GIS database. Maps were created in Google Earth and presented in Google Maps.ResultsWe found that WF concentrations ranged between 0.10–13.60 mg/L. Forty-four percent (n=439) of samples were at unsafe levels (>0.70 mg/L), and. 54% (n=303) of villages and 46% (n=79,807) of households used the unsafe drinking water. Fifty percent (n=26) of subdistricts were classified as being endemic fluoride areas. Five subdistricts were endemic fluoride areas, and in those, there were two subdistricts in which every household used unsafe drinking water.ConclusionThese findings show the distribution of endemic fluoride areas and unsafe drinking water in Lamphun. This is useful for health policy authorities, local governments, and villagers and enables collaboration to resolve these issues. The GIS data are available at https://drive.google.com/open?id=1mi4Pvomf5xHZ1MQjK44pdp2xXFw&usp=sharing.

Fluorosis and Dental Caries in Mexican Schoolchildren Residing in Areas with Different Water Fluoride Concentrations and Receiving Fluoridated Salt

Objective: To explore the association between fluoride in drinking water and the prevalence and severity of fluorosis and dental caries in children living in communities receiving fluoridated salt. Material and Methods: Participants were schoolchildren (n = 457) living in two rural areas of the State of Morelos, Mexico, where the water fluoride concentration was 0.70 or 1.50 ppm. Dental caries status was assessed using Pitts’ criteria. Lesions that were classified as D₃ (decayed) were identified to determine the decayed, missing, and filled teeth index (D₃MFT). Fluorosis was assessed using the Thylstrup-Fejerskov Index (TFI). Information regarding drinking water source and oral hygiene practices (tooth brushing frequency, dentifrice use, and oral hygiene index) was obtained. Results: The prevalence of fluorosis (TFI ≥1) in communities with 0.70 and 1.50 ppm water fluoride was 39.4 and 60.5% (p = 0.014), respectively, while the prevalence of more severe forms (TFI ≥4) was 7.9 and 25.5% (p < 0.001), respectively. The mean D₃MFT was 0.49 (±1.01) in the 0.70 ppm community and 0.61 (±1.47) in the 1.50 ppm community (p = 0.349). A logistic regression model for caries (D₃ >1) showed that higher fluorosis categories (TFI 5–6 OR = 6.81, p = 0.001) were associated with higher caries experience, adjusted by age, number of teeth present, tooth brushing frequency, bottled water use, and natural water fluoride concentration. Conclusions: The prevalence of fluorosis was associated with the water fluoride concentration. Fluorosis at moderate and severe levels was associated with a higher prevalence of dental caries, compared with lesser degrees of fluorosis. The impact of dental fluorosis should be considered in dental public health programs.

Proposed flow system for spectrophotometric determination of fluoride in natural waters

An environmentally-friendly flow system was developed for the determination of fluoride in natural waters, based on its reaction with zirconium ions and 2-(parasulfophenylazo)-1,8-dihydroxy-3,6-naphthalene-disulfonate (SPADNS). The flow system was designed with solenoid valves in order to increase the versatility and improve the analytical performance, since each device handles the solution independently leading to a more efficient use of reagents. The minimization of reagent consumption and waste generation favors the development of a noteworthy system. Under optimized conditions, a linear response was observed within the range of 0.1–2.2mgL−1, with the detection limit, coefficient of variation and sampling rate estimated as 0.02mgL−1, 4.1% and 60 determinations per hour, respectively. In order to analyze samples containing high fluoride content a wider linear range (0.3–6.6mgL−1) can be obtained by using a low sample flow rate and low sample volume. In comparison with other methods, the proposed system offers advantages such as wider analytical range (1.7–2.2 times), higher sample throughput (1.5–4.0 times) and lower quantification limit (by a factor of 5–68). Along with the consumption of reagents being 20–55 times lower, the generation of wastes is 1.2–3.0 times lower, which contributes to the development of a ‘greener’ system. This method is fast, amenable to automation, environmentally-friendly and of low-cost. In addition, it could be successfully applied to the determination of fluoride in water samples, the results obtained being in agreement with those of the ISE method.

Fluorine contamination in groundwater: a major challenge

Fluoride in high concentration in groundwater has been reported from many parts of India. However, a systematic study is required to understand the behavior of fluoride in natural water in terms of local hydrogeological setting, climatic conditions, and agricultural practices. The present study is an attempt to assess hydrogeochemistry of groundwater in parts of Palar river basin pertaining to Kancheepuram district Tamil Nadu to understand the fluoride abundance in groundwater and to deduce the chemical parameters responsible for the dissolution activity of fluoride. The study area is geologically occupied by partly sedimentary and partly crystalline formations. A total of 50 dug cum borewell-water samples, representing an area of 2,628.92 km2. The results of the chemical analyses in September 2009 show fluoride abundance in the range of 1 to 3.24 mg/l with 86% of the samples in excess of the permissible limit of 1.5 mg/l. Presence of fluoride-bearing minerals in the host rock, chemical properties like decomposition, dissociation, and dissolution, and their interaction with water are considered to be the main causes for fluoride in groundwater. Chemical weathering with relatively high alkalinity favors high concentration of fluoride in groundwater. Villagers who consume nonpotable high fluoride water may suffer from yellow, cracked teeth; joint pains; and crippled limbs and also age rapidly.

Hydrochemical status of groundwater in district Ajmer (NW India) with reference to fluoride distribution

High fluoride in groundwater has been reported from many parts of India. However, a systematic study is required to understand the behaviour of fluoride in natural water in terms of local hydrogeological setting, climatic conditions and agricultural practices. Present study is an attempt to assess hydrogeochemistry of groundwater in Ajmer district in Rajasthan to understand the fluoride abundance in groundwater and to deduce the chemical parameters responsible for the dissolution activity of fluoride. Ajmer district falls in the semi-arid tract of central Rajasthan and is geologically occupied by Precambrian rocks (granites, pegmatites, gneisses, schists etc) where groundwater occurs under unconfined condition. A total of 153 well-water samples, representing an area of 8481 km2 (further subdivided into eight blocks), were collected and chemically analyzed. The results of chemical analyses (pre-monsoon 2004) show fluoride abundance in the range of 0.12 to 16.9 mg/l with 66% of the samples in excess of permissible limit of 1.5 mg/l.

Solvent extraction and fluorometric determination of fluoride ion at ppb level in the presence of large excess of aluminum(III) and iron(III) by using an expanded porphyrin, sapphyrin

Solvent extraction of fluoride as low as 10 −6 M into chloroform using [2,23-diethyl-8,17-bis(2-ethoxycarbonylethyl)-3,7,12,13,18,22-hexamethylsapphyrin (H 3sap), sapphyrin] have been studied in the presence of 0.1 M sodium nitrate by spectrophotometric and fluorometric methods at pH 3–13 and 25°C. Sapphyrin is protonated at pH<8 and exists as the ion-pair complexes with nitrate ion, such as H 4sap +·NO 3 − and H 5sap 2+·2NO 3 − in chloroform. The equilibrium constants, K 1 for [H 4sap +·NO 3 −] org[H 3sap] org −1[H +] aq −1[NO 3 −] aq −1 and K 2 for [H 5sap 2+·2NO 3 −] org[H 4sap +·NO 3 −] org −1[H +] aq −1[NO 3 −] aq −1 were found to be 9.90±0.08 and 7.20±0.07 in the logarithmic form, where the subscripts of org and aq denote the chemical species in organic and aqueous phases, respectively. Fluoride ion was extracted from chloroform with the positively charged sapphyrin that gave a new absorption maximum wavelength at 448 nm. The extraction constant, log ( K FP), for the reaction of (F −) aq+(H 5sap 2+·2NO 3 −) org⇌(H 5sap 2+·F −·NO 3 −) org+(NO 3 −) aq was 3.66±0.01. These results were applied to the determination of fluoride in natural waters containing Al(III) and Fe(III) by the measurement of fluorescence intensity at 684 nm under excitation at 448 nm. Al(III) of 10 −4 M and Fe(III) of 10 −3 M were quantitatively masked by DCTA ( trans-1,2-aminocyclohexane- N, N, N′, N′-tetraacetic acid).

Decision-making for national programs of community fluoride use.

Every community, region or country with a high or rising prevalence of dental caries should implement a caries-preventive program that automatically brings the benefits of systemic and topically applied fluoride to the entire population. The fluoridation of community water supplies or salt fulfills the requirements of providing safe, effective protection from dental caries at reasonable cost. The use of dietary fluoride supplements or fluoridated milk does not meet the requirements of a comprehensive national or community program because compliance is poor or only selected age groups are targeted. Water fluoridation is ideal for countries, regions or communities with many central water supplies or where salt production or distribution is not centralized or easy to control. Water fluoridation also has advantages where many areas exist with natural water fluoride concentrations at optimal or greater than optimal concentrations. Salt fluoridation is ideal for countries or regions with few, potable central water supplies in which salt production and distribution are centralized and easily controlled. Concentrations of fluoride for water fluoridation range from 0.5 to 1.2 parts per million (ppm) parts of water depending on climate and dietary practices. The concentration for fluoridation of salt is approximately 200 to 250 mg fluoride per kg of salt, also depending on dietary practices. Properly fluoridated salt should produce levels of urinary fluoride excretion similar to those found in communities with fluoridated water. Benefits of the two methods are similar. Salt fluoridation may be done more cheaply.

The occurrence and geochemistry of fluoride in some natural waters of Kenya

In recent years the acquisition of considerable additional data on the hydrogeochemical behaviour of fluoride in natural waters of Kenya has been made possible by extensive surface-water and groundwater sampling campaigns as well as by improvements in analytical techniques. Ultimately, the principal source of fluoride relates to emissions from volcanic activity associated with the East African Rift System. Through various intermediate steps, but also directly, fluoride passes into the natural water system and components of the food chain. Ingestion by man is mainly through drinking water and other beverages. River waters in Kenya generally have a fluoride concentration lower than the recommended level (1.3 ppm) for potable water, thus promoting susceptibility to dental caries. Groundwaters and lake waters show considerably higher fluoride contents, resulting in the widespread incidence of fluorosis in areas where groundwater is the major source of drinking water, and lake fish is a regular component of the diet. This paper presents a synthesis of the data so far obtained on the sources and distribution of fluoride in the hydrological system of Kenya, examines the extent of fluorine toxicity and puts forward recommendations to combat or minimise the problem.

The occurrence and geochemistry of fluorides in natural waters in Finland and East Africa with reference to their geomedical implications

Coarse-grained K-rich granites in Finland, particularly rapakivi granites, have a higher concentration of fluorine (0.2–0.4%) than other plutonic or metamorphic rocks. The main accessory minerals containing appreciable amounts of F are fluorite and fluorapatite, although OH-bearing minerals such as micas and amphiboles may also contain abundant F (0.2–1.1%). High F concentrations in rocks are reflected as regional F anomalies in soils, natural surface waters and shallow groundwaters. In streams and shallow groundwater draining areas composed of rapakivi granites. F concentrations are more than an order of magnitude higher (1–2 mg/l) than elsewhere (below 0.1 mg/l). This level of F concentrations in drinking water has proved to diminish the incidence of dental caries in Finland and elsewhere. In some parts of the world, granites (India, China) and particularly some recent or Neogene volcanics (East Africa) may release abundant F into waters to be further concentrated by strong evapotranspiration (up to 10–20 mg/l in potable water). As a consequence, F intake may reach harmful levels causing dental or skeletal fluorosis.

Mutans streptococci in saliva and dental caries in children living in a high and a low fluoride area

The aim of this study was to obtain information about the quantitative distribution of salivary mutans streptococci and the relation to dental caries in children with contrasting levels of natural water fluoride. A total of 698 schoolchildren aged 12 yr were selected from areas with high (1.2 ppm) or low (0.1 ppm) fluoride concentration in the drinking water. They were all examined for the presence and number of mutans streptococci in saliva by a specially prepared plastic strip, the "Strip mutans" method, cultivated in a selective broth. Data on the caries experience were obtained from the dental records and from bite-wing radiographs. Mutans streptococci were identified in 82% of all children with no difference between the two areas. The number of mutans streptococci was however significantly (p less than 0.05) lower among the children from the high fluoride area than those from the low fluoride area. Children with no detectable or low levels (0-10 CFU) of mutans streptococci had less caries experience than children with moderate or high levels (11- greater than 500 CFU) in both areas investigated.

Adult Root Caries Survey of two Similar Communities with Contrasting Natural Water Fluoride Levels

For a comparative study of root caries, 502 adult lifelong residents of a naturally fluoridated community (1.6 ppm F) and 465 such residents of a nearby, comparable nonfluoridated community (0.2 ppm F) were examined. Substantially fewer carious lesions were found among adults in the fluoridated community relative to the nonfluoridated community. This was observed in virtually all age- and gender-specific groups. Given a cross-sectional design and considering only exposed root surfaces, root caries was related to age. In addition, the data from this study show that the number of root caries lesions is underestimated but that root caries prevalence is overestimated by the standard Root Caries Index (RCI). A less restrictive form of the RCI may lead to more valid estimation of root caries prevalence.