Determination of Fluoride and Selected Metals in the Soils of Ethiopian Rift Valley and Irrigation Water in the Surrounding Area
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Date
2011-06
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Addis Ababa Universty
Abstract
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
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Keywords
Fluoride; Metals; Water; Soil; Ethiopian Rift Valley