Determination of Fluoride and Selected Metals in the Soils of Ethiopian Rift Valley and Irrigation Water in the Surrounding Area

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Addis Ababa Universty


The occurrence of dental and skeletal fluorosis among the population in the Ethiopian Rift Valley provided the motivation to investigate occurrence of fluoride in soil and water. The objective of this study was to determine the levels of fluoride in Ethiopian Rift Valley soils and the nearby irrigation water sources and the correlation of fluoride with metals. Nine soil samples from the surface horizon (0-20 cm) depth and water samples were collected from high fluoride zone of Ethiopian Rift Valley and one controlling group collected from the College of Natural Sciences (Arat Killo Campus), Addis Ababa University. The sample was collected by random sampling technique. The soil samples were air dried, grinded, sieved and weighed, then measured for both fluoride and metals content. The pH, conductivity, salinity and total dissolved solid in water and soil sample were also measured. Fluoride determination was made by fluoride ion selective electrode and metal determination by flame atomic absorption spectrophotometer. The validation of optimized procedure was evaluated using standard addition (spiking) method and an acceptable percentage recovery was obtained. The fluoride concentration in water sample was found in the range of 0.143-8.03 mg/L which are below the WHO limits of fluoride concentration for irrigation (less than 10 mg/L). The water soluble and total fluorides in soil were 2.32-16.2 μg/g and 209-1210 μg/g, respectively. The mean metal concentration (μg/g dry weight basis) range in soil samples and mg/L in water samples respectively were: Na (684-6703, 8.64-67.3), Mg (1608-11229, 22.7-66.7), K (1776-4394, 1.11-20.3), Ca (7547-22998, 16.7-267), Cr (9.79-79.3, 0.071-0.169), Mn (143-700, 0.048-37.2), Co (50.3-112, 0.354-1.48), Ni (446-1288, 0.274-40.9), Fe (12180-32681, 6.04-47.7), Cu (8.85-45.4, 0.088-0.251) and Zn (30.5-89.2, 0.144-0.562). Fluoride was found to have significant correlation with major metals (Fe, Cu and Cr), but the correlation with other trace metals were not significant. KEYWORDS: Fluoride, Metals, Water, Soil, Ethiopian Rift Valley



Fluoride; Metals; Water; Soil; Ethiopian Rift Valley