Feleke Zewge

Water defluoridation by aluminium oxide–manganese oxide composite material

In this study, aluminium oxide–manganese oxide (AOMO) composite material was synthesized, characterized, and tested for fluoride removal in batch experiments. AOMO was prepared from manganese(II) chloride and aluminium hydroxide. The surface area of AOMO was found to be 30.7 m2/g and its specific density was determined as 2.78 g/cm3. Detailed investigation of the adsorbent by inductively coupled plasma-optical emission spectrometry, inductively coupled plasma-mass spectrometry, and ion chromatography (for sulphate only) showed that it is composed of Al, Mn, SO4, and Na as major components and Fe, Si, Ca, and Mg as minor components. Thermogravimetric analysis was used to study the thermal behaviour of AOMO. X-ray diffraction analysis showed that the adsorbent is poorly crystalline. The point of zero charge was determined as 9.54. Batch experiments (by varying the proportion of MnO, adsorbent dose, contact time, initial F− concentration, and raw water pH) showed that fluoride removal efficiency of AOMO varied significantly with percentage of MnO with an optimum value of about 11% of manganese oxide in the adsorbent. The optimum dose of the adsorbent was 4 g/L which corresponds to the equilibrium adsorption capacity of 4.8 mg F−/g. Both the removal efficiency and adsorption capacity showed an increasing trend with an increase in initial fluoride concentration of the water. The pH for optimum fluoride removal was found to be in the range between 5 and 7. The adsorption data were analysed using the Freundlich, Langmuir, and Dubinin–Radushkevich models. The minimum adsorption capacity obtained from the non-linear Freundlich isotherm model was 4.94 mg F−/g and the maximum capacity from the Langmuir isotherm method was 19.2 mg F−/g. The experimental data of fluoride adsorption on AOMO fitted well to the Freundlich isotherm model. Kinetic studies showed that the adsorption is well described by a non-linear pseudo-second-order reaction model with an average rate constant of 3.1×10−2 g/min mg. It is concluded that AOMO is a highly promising adsorbent for the removal of excess fluoride from drinking water.

A high-capacity aluminum hydroxide-based adsorbent for water defluoridation

AbstractIn this study, the properties and fluoride-uptake capacity of aluminum hydroxide-based (AO) adsorbent has been investigated. AO was synthesized, characterized, and tested in batch and column experiments. The surface area of the AO was found to be 37.7 m2 g−1. The composition was determined to be 90% Al(OH)2.8(SO4)0.1 (or 78.3% Al(OH)3 plus 10.7% Al2(SO4)3) with 10% Na2SO4 (as an impurity). The material is X-ray amorphous and scanning electron microscopic (SEM) studies show AO to be a network of fibers with a size range of 200–300 nm. Fluoride uptake was found to be unaffected by sodium salts of chloride and sulfate in concentrations up to 500 mg/L. A reduction of fluoride uptake with increasing concentrations of hydroxide and bicarbonate was ascribed to the pH dependence of fluoride sorption, while phosphate appeared to compete with fluoride for sorption sites. The surface site concentration determined by acid–base titrations is 0.5 meq/g (equivalent to a surface site concentration of 8 sites/nm2)...

Daily dietary fluoride intake in rural villages of the Ethiopian Rift Valley

Dental and skeletal fluorosis is widespread in the Ethiopian Rift Valley region. Drinking water has been considered the main reason for the development of fluorosis, but dietary intake may also be a contributor in areas with high concentration of fluoride in water, soil, and biota. The purpose of this study is to assess the total daily dietary fluoride intake by adults in a rural part of the Ethiopian Rift Valley. The food, beverage, and water samples were collected from selected households of three neighboring villages with similar dietary pattern, but with different fluoride content in their water sources. Village A uses water with 1.0 mg L−1 fluoride, village B uses water with 3.0 mg L−1 fluoride, and village C uses water with 11.5 mg L−1 fluoride both for food preparation and for drinking. The level of fluoride was determined in all food ingredients, in the prepared food, beverages, and in the water used for food preparation and drinking. Recipe and food frequency questionnaires were used to gather household food preparation and consumption patterns. An alkali fusion method was used for digestion of food samples and for subsequent determination of fluoride with ion-selective electrode. The daily fluoride intake varied depending on its concentration in the water used for cooking and drinking. In households using water with 1 mg L−1, 3 mg L−1, and 11.5 mg L−1 fluoride, the total personal intake was found to be 10.5, 16.6, and 35.3 mg d−1, respectively. Contribution of the water to the daily fluoride intake was 33%, 58%, and 86%, respectively. Even in households using water containing fluoride at a concentration of 1 mg L−1, the daily intake was higher than the recommended safe intake of 1.5–4.0 mg d−1 for adults, which indicates that the fluoride intake through food may cause health risks. Minimizing the fluoride concentration in water to the lowest possible level will greatly reduce the daily intake. The form of fluorine (organic or inorganic) in the food items and the associated health risk factors need further investigation.

Fluoride content of Ethiopian khat (Catha edulis Forsk) chewing leaves

The levels of water soluble and total fluoride concentration in 11 different varieties of Ethiopian khat (Catha edulis Forsk, an evergreen stimulant plant) commonly consumed in the country and exported to the neighboring countries were determined by fluoride ion-selective electrode. Known amounts of fresh khat samples were suspended in deionized water, stirred, and the supernatants exposed to a chelator that decomplexes fluoride were assayed. The total fluoride concentration in the leaves was also analyzed after the leaves were dried, charred, and ashed. Water soluble and total fluoride concentration in khat varieties varied, ranging from 0.19 to 0.43 µg g−1 fresh weight and 3.4 to 7.1 µg g−1 dry weight, respectively. The fluoride concentration in matured leaves (12 µg g−1) was higher than that in young leaves (6.5 µg g−1) dry weight. Assuming that daily khat leaves chewing for an adult is 100 g, fluoride intake from chewing leaves of the analyzed khat varieties is far below the daily fluoride tolerable upper limit. The safe intake of fluoride is recommended to be 1.5–4.0 mg day−1 for adults and less for children. However, chewing khat leaves may contribute a significant amount of fluoride for the total daily intake of an individual and should not be overlooked while estimating the total dietary intake of fluoride for individuals chewing khat leaves regularly.

Fluoride levels in tef [Eragrostis tef (Zucc.) Trotter] and enjera and its health implications

The main objective of this study was to estimate the fluoride levels in tef grain and in enjera , its fermentation product in different regions of Ethiopia, especially in the regions where tef is dominantly cultivated. The effect of water used to bake the enjera was assessed by preparing fluoride-containing water in the laboratory. The daily dietary fluoride intake through enjera was assessed in Wonji Shoa by recipe questionnaires and field observations in ten households. The fluoride contents of both tef grain and enjera were higher in the Rift-Valley region of Ethiopia than in the highlands. Of the different varieties of tef, the mixed tef grain was higher (8.74 mg/kg) in its fluoride content and the brown tef grain was the least (1.89 mg/kg). Enjera from mixed tef grain baked using 10 mg/l fluoride water was found to have high (26.82 mg/kg) fluoride contents and the least (2.63 mg/kg) was for enjera processed from brown tef grain baked using tap water. Daily dietary fluoride intake was different with different fluoride concentration of the water used. In this study, the fluoride content of enjera ranges from 2.63–26.82 mg/kg and the daily-recommended human intake of fluoride ranges from 4.8-14.6 mg/kg/day. The fluoride contents of the different tef varieties vary depending on the soil type, soil ph and the type of minerals in the soil. The value of fluoride in enjera baked using tap water is safe for human consumption while enjera baked using 5 and 10 mg/l fluoride containing water may cause dental as well as skeletal fluorosis.

Levels of Fluoride in the Ethiopian and Imported Black Tea (Camellia sinensis) Infusions Prepared in Tap and Fluoride-Rich Natural Waters

Abstract In this study, the possible effect of original fluoride (F) concentration in six natural waters on the fluoride release from nine brands of tea leaves (whose origin was from Ethiopia, Sri Lanka, and China) during the infusion has been investigated. The capacity of tea leaves (commercially available tea) to absorb F from high-fluoride ground waters which were collected from the Ethiopia Rift Valley has also been investigated in this study. Infused F content of black (either powder or bag form) and green (bag form) teas and water from different sources were assayed. The fluoride content of waters used in this study ranged from 0.254 to 30.2 mg/L, while the fluoride in tea infusion of nine brands of tea ranged from 0.51 to 20.57 mg/L. The F content in moderately F-rich water was reduced from 12.5 to <5 mg/L in tea infusion while F content in highly F-rich water was reduced from 30.2 to <10 mg/L in tea infusion of most of the tea brands even with 3 min infusion time. Thus one can reduce the daily intake of F level by drinking tea rather than F-rich water itself.