Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 24-27). Also available via the Internet.

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 273-277).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. Description based on print version record. Includes bibliographical references.

<p> Conductivity measurements on liquid hydrogen fluoride solutions of some simple bases and fluoroanion salts were carried out, and a set of equivalent ionic conductivities have been determined. The conductivities of electrolytes in hydrogen fluoride have been compared to those of analogous electrolytes in water and strong acid solvents. A method for the investigation of more complex electrolytes was developed.</p> <p> The mode of ionization of adducts of sulfur tetrafluoride, thionyl tetrafluoride and selenium tetrafluoride with fluoride acceptors in hydrogen fluoride has been investigated by conductivity and nmr spectroscopy. The structures of the solid adducts have also been investigated by Raman spectroscopy. The structure and stability of other sulfur-oxide-fluoride adducts have been investigated and found to differ from adducts of thionyl tetrafluoride. </p> / Thesis / Doctor of Philosophy (PhD)

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Groundwater is a major and sometimes lone source of drinking water worldwide. The chemical composition of groundwater is a combined product of the composition of water that enters the aquifer and its reaction with various minerals present in the soil and rock mass, which alter the water composition with time and space. Some important factors influencing groundwater quality are (1) physiochemical characteristics o the rocks through which the water circulates; (2) geology of the location; (3) climate of the area; (4) role of microorganisms, which includes oxidative and reductive biodegradation of organic matter; (5)chemical, physical, and mineralogical characteristics of the overburden soils through which the rainwater percolates; and (6) human intrusion affecting the hydrological cycle and degradation in water quality through utilization of water for agricultural and industrial activities. By far the most serious naturally occurring groundwater-quality problem in India derives from high fluoride, arsenic and iron concentrations which are dissolved from the bedrocks by geochemical processes. Presence of excess fluoride in groundwater is identified as a naturally occurring health hazard by the World Health Organization (WHO). Prolonged ingestion of fluoride beyond certain permissible limit leads to ffluorosis, one of the common water-related diseases recognized by the WHO and the United Nations Children's Fund (UNICEF). Endemic fluorosis is now known to be global in scope, occurring on all continents and affecting many millions of people. According to estimates made in the early 1980s, around 260 million people in 30 countries worldwide were drinking water with more than 1 ppm of fluoride. The ultimate source of fluoride in water, soil or biosphere is associated with its distribution in rocks and its dispersion in groundwater. The three most important minerals of fluoride are fluorite (CaF2), cryolite (Na3AlF6) and fluorapatite (Ca5(PO4)3F); cryolite is a rare mineral where as by far the largest amount of fluorine in the earth's crust is in the form of fluorapatite (about 3.5% by weight of fluorine) which is processed almost exclusively for its phosphate content. Fluoride substitutes readily in hydroxyl positions in late-formed minerals in igneous rocks, and in primary minerals especially micas (such as biotites) and amphiboles (such as hornblende). The most important controlling factors influencing fluoride presence in groundwater include: distribution of easily weathered fluoride-bearing minerals, the accessibility of circulating water to these minerals, pH of the percolating water, calcium content of the leaching water, temperature of the percolating water and the soil, exchangeable ions in the percolating water, extent of fresh water exchange in an aquifer, evaporation and evapotranspiration, complexing of fluoride ions with other ions, presence of CO2 and other chemicals in draining water and residence time of the percolating water in soil. High fluoride levels are observed in the groundwater in 19 states of the country. Fluorite, apatite, rock phosphate, phosphorites, phosphatic nodules and topaz are major fluoride bearing minerals in India with varying levels of fluoride content. There are three major fluoride bearing areas in India :1) Gujarat-Rajasthan in the north-west and 2) Chandidongri-Raipur in central India 3) Tamil Nadu-Andhra Pradesh in the south; besides other areas in Karnataka, Bihar, Punjab and in the North-west Himalayas. The total mineral reserves of fluorite, rock phosphate and apatite in the country are estimated at 11.6, 71 and 2.82 million tonnes respectively. The distribution of areas with excess fluoride in groundwater concurs with that of fluorine-bearing minerals. Further high fluoride concentrations are observed from arid and semi arid regions of the country and the areas with advanced stage of groundwater development. An estimated 62 million people, including 6 million children suffer from fluorosis in India because of consuming fluoride-contaminated water. Endemic fluorosis is found to practically exist only in the villages due to lack of piped water supply. The Indian Drinking Water Standard specifies the desirable and permissible limits for fluoride in drinking water as 1.0 and 1.5ppm respectively. De-fluoridation of groundwater is the only alternative to prevent fluorosis in the absence of alternate water source especially for immediate and/or interim relief. De-fluoridation of drinking water in India is usually achieved by the Nalgonda technique or activated alumina process. The Nalgonda method involves addition of aluminum salts (aluminium sulphate and/or aluminium chloride), lime and bleaching powder to water, followed by rapid mixing, flocculation, sedimentation, filtration and disinfection. Only aluminum salt is responsible for removal of fluoride from water .Fluoride removal is achieved in a combination of complexation with polyhydroxy aluminium species and adsorption on polymeric alumino hydroxides (floc). Activated alumina(Al2O3) was proposed for de-fluoridation of water for domestic use in 1930’s and since then it has become one of the most advocated de-fluoridation methods. Activated alumina is a semi crystalline porous inorganic adsorbent and an excellent medium for fluoride removal. When the source water passes through the packed column of activated alumina, fluoride (and other components in the water) is removed via exchange reaction with surface hydroxides on alumina; this mechanism is generally called adsorption although ligand exchange is a more appropriate term for the highly specific surface reactions involved. The fluoride removal capacity of alumina is highly sensitive to pH, the optimum being about pH5.5-6. Significant reduction in fluoride removal by activated alumina is also observed in presence of sulfate and silicate ions. The column needs periodic regeneration once break point(where the effluent concentration is, for example, 2ppm at normal saturation) is reached. For regeneration, the medium is backwashed for 5-10 min and then subjected to two step regeneration with base (NaOH) followed by acid(H2SO4). A major cause for concern with the Nalgonda method is the possibility of formation of residual aluminum and soluble aluminum fluoride complexes in the treated water and a potential breach of the 0.2ppm Indian drinking water standard for aluminium. Concerns with the activated alumina filter method are that the process is pH dependent, with an optimum (pH) working range of 5-6. Further, the activated alumina column requires periodic recharge using caustic soda and acid solutions to rejuvenate the fluoride retention capacity of the column. After 3-4 regenerations the medium has to be replaced. If the pH is not readjusted to normal following the regeneration process, there is a possibility that the aluminum concentration in the treated water may exceed the 0.2ppm standard. Due to the aforementioned drawbacks of the currentde-fluoridation technologies in India that chiefly rely on aluminum based compounds, magnesia(magnesium oxide, MgO) is selected to develop an alternate sustainable de-fluoridation method. The potential of MgO for de-fluoridation has been examined owing to its very limited solubility(6.2mg/L), non-toxicity and excellent fluoride retention capacity. A review of the previous studies on fluoride removal using MgO reveals that the relevant information is essentially scattered. Though studies demonstrated the fluoride removing ability of MgO and brought into focus certain aspects of the fluoride removal mechanism and change in water quality upon MgO addition, vital issues necessary for efficient design and successful field implementation of the de-fluoridation processusing MgO were not addressed. The significant limitations in the earlier works include: influence of process variables(such as MgO dosage, initial fluoride concentration, contact time, temperature, initial solution pH, presence of co-ions and ionic strength) on fluoride retention characteristics (such as removal rate, equilibrium time, capacity) of MgO were not systematically determined, optimum operating parameters/conditions (such as MgO dosage, stirring and settling time) for effective de-fluoridation process applicable to a wide range of groundwater chemical composition and fluoride concentrations were not defined, mechanism of fluoride retention by MgO was not fully understood, issue of lowering the pH of MgO treated water within potable water limits was not comprehensively addressed, safe disposal methods of fluoride bearing sludge were not explored. Failure to address the above issues has impeded the adoption of the MgO treatment method for fluoride removal from water. Scope of the study Present study aims to develop a new sustainable de-fluoridation method, applicable to a wide range of groundwater chemical compositions and fluoride concentrations, based on co-precipitation/precipitation-sedimentation-filtration processes using light MgO. Efforts are made to implement the method at domestic level in a rural area with incidence of high fluoride concentration in groundwater and to understand the status and geochemistry of fluoride contamination in the area. The main objectives of the study include: To determine the fluoride retention characteristics of MgO viz.,rate, equilibrium time and capacity of fluoride retention. To examine the influence of process variables on fluoride retention characteristics of MgO and to determine the optimum operating parameters for effective de-fluoridation process. To understand the mechanism and rate limiting step of MgO de-fluoridation process. To propose methods and specifications to lower the pH of MgO treated water within permissible limits to ensure its potability. To design a simple to use, single-stage domestic de-fluoridation unit. To propose procedures for implementation of the new de-fluoridation method in field. To evaluate the efficiency of the new de-fluoridation method as a useful remedial measure in the fluoride affected areas. To understand the geochemical factors governing the quality of the fluoride rich groundwater and to ascertain the status and geochemistry of fluoride contamination in the area where felid implementation of de-fluoridation method is planned. To characterize the fluoride bearing sludge and propose methods for safe disposal and reuse of fluoride bearing sludge. Organization of the thesis Chapter1 presents an overview of the various aspects of excess fluoride presence in groundwater, remedial measures, and emphasizes the need for a new sustainable de-fluoridation method and defines the scope of present study. Chapter 2 performs a detailed investigation to determine the fluoride retention characteristics of MgO under the influence of various process variables at transient and equilibrium conditions using batch studies. The process variables that have been considered are, contact time, initial fluoride concentration, dosage of MgO, temperature, initial pH, presence of co-ions and ionic strength. Studies to determine the optimum operating parameters for efficient de-fluoridation and to understand some basics of reaction mechanisms involved are also part of this chapter. Chapter 3 examines the true nature of the reaction mechanism between fluoride ions and MgO in aqueous media and the rate-limiting step of the de-fluoridation process by investigating the hydration process of MgO and its influence/relation on fluoride removal. Chapter 4 addresses issues that will assist applying the MgO treatment method for fluoride removal in field such as 1)methods and specifications for lowering the pH of the MgO treated water within permissible limits, 2)design of a simple to use, single-stage de-fluoridation unit, and 3)characterization of the resultant fluoride bearing sludge. Chapter 5 performs a detailed investigation to evaluate the efficiency of the new de-fluoridation method in laboratory and field, and to understand the origin and the geochemicall mechanisms driving the groundwater fluorine enrichment in the area where field implementation of the de-fluoridation unit was planned. Chapter 6 explores an environmentally safe route for the disposal and re-use of fluoride bearing sludge in soil based building materials such as, stabilized soil blocks (produced by cement stabilization of densely compacted soil mass) which are alternative to burnt bricks. Chapter 7 summarizes the major results, observations and contributions from the study.

This study aims to determine the concentrations of fluoride in UK tea products and their infusions. This is related to the uptake and distribution of fluoride within tea plants Camellia sinensis (L.). Human oral bioaccessibility of fluoride from the consumption of tea infusions was estimated, using an in vitro approach. The possible health significance from fluoride exposure is discussed. Fluoride in tea products and the distribution within the tea plant was determined using a method, involving alkali fused digestion with ion chromatography and a conductivity detector for the instrumentation. For the aqueous infusions and the supernatants in the bioaccessibility experiments, ion selective electrode with a voltmeter was adopted. Mean fluoride concentrations in tea products and their infusions varied significantly (p<0.001; n=3) and were related to the type of tea product and the retail cost. The higher priced teas, such as Darjeeling, Assam and Oolong, had lower fluoride concentrations. The lower priced supermarket Economy ranged teas were significantly higher (p<0.05) in fluoride and exhibited concentrations similar to Chinese Brick tea, which is prepared using mature tea leaves. The higher quality products are prepared by selecting the finest tips of tea (buds), whereas an Economy products use coarser harvesting techniques to include mature leaves in the product. Fluoride affinity and tolerance of C. sinensis was assessed by a series of fluoride dosing experiments, ranging from 0 to 200 mg. Following fluoride dosing, a rapid uptake and accumulation occurred throughout the tea plants, resulting in partial necrosis of random leaves. Despite the necrosis, the plants tolerated the fluoride and continued to increase in height, although at a significantly slower rate (p<0.05) compared to the control plants. Accumulation of fluoride was observed to be mostly in the mature leaves followed by younger buds, then the roots. This relates to the part of the plant used to produce the tea types, with mature leaves for Economy products and the buds for the finer teas. The in vitro bioaccessibility assessment of fluoride estimated that over 91.4% of fluoride from a tea infusion is available in the human gastric compartment, with 92.1% in the gastro-intestinal compartment. The addition of milk reduced fluoride absorption in the gastric and gastro-intestinal compartments to 73.8 and 83.1%, respectively, possibly reacting to form calcium fluoride. Despite the percentage bioaccessibility, the concentration of fluoride available for absorption in the human gut was dependent upon choice of tea product. Based on an adult male, the findings suggest that consuming a litre of Economy tea can fulfil or exceed (75 to 120%) the recommended dietary reference intake (DRI) of fluoride at 4 mg a day, but only partially fulfil (25 to 40%) when consuming a more expensive Pure blend such as Assam. With regards to health, tea consumption is a source of fluoride in the diet and is highly available for absorption in the human gut. Tea alone can fulfil an adult fluoride DRI, but is dependent upon choice of tea product. Excess fluoride in the diet can lead to detrimental health effects such as fluorosis of the teeth and skeletal fluorosis and consuming economy branded tea can lead to a higher exposure.

Objective: The purpose of this study was to determine the fluoride recharging capability of Opal Seal, a fluoride releasing orthodontic primer, as compared to Transbond XT, the control. Material and Methods: 1mm x 5mm disks of Opal Seal and Transbond were prepared according to the respective manufacturer’s instructions. Initially, the samples were stored in deionized water (DI) for 8 weeks. The samples were then randomly divided into one of two groups: Over-the-counter (OTC) fluoride mouthwash and prescription strength (PS) fluoride mouthwash. The OTC group samples were immersed in 5mL of 0.0219% sodium fluoride containing mouthwash for one minute every day for seven days. The PS group samples were immersed in 5mL of 0.2% sodium fluoride containing mouthwash for one minute. All of the samples were suspended in 5mL fresh DI water and fluoride release measurements were taken at baseline (the end of initial 8 weeks of storage), 24 hours, 3 days, 5 days, 7 days, and 14 days. Results: Opal Seal samples treated with the OTC fluoride mouthwash exhibited significant fluctuation in fluoride ion release across time (p=0.0058). However, there were no statistically significant differences in fluoride ion release between the individual timepoints and baseline. Similarly, Opal Seal samples treated with the PS fluoride mouthwash exhibited significant variation in the fluoride ion concentration across time (p< 0.001), and a statistically significant increase over baseline was seen at 24 hours only (p= 0.0006). The control group samples treated either with the OTC or PS mouthwash did not exhibit any significant difference in fluoride ion release between any individual timepoint and baseline. Conclusion: For Opal Seal and Transbond XT, there were no statistically significant differences of fluoride concentration at any timepoint compared to baseline measurements when using OTC mouthwash. When using PS mouthwash, there was a small, statistically significant increase of fluoride concentration of the Opal Seal samples after 24 hours but no differences were seen at any other timepoints. Opal Seal did not demonstrate a substantial amount of fluoride recharge when fluoride mouthwash is used as a fluoride delivery vehicle. Future well-designed randomized controlled trials are needed to evaluate the efficacy of Opal Seal primer when coupled with the use of fluoride mouthwashes.