Appraisal of Fluoride Concentration, Distribution and Geogenic Origin in Ground and Surface Water from Semi-Arid Region, Part of Yobe State North-eastern Nigeria

Abstract

The Fluoride concentration of water sources from part of Yobe State has been investigated, Fluoride levels in Pond water is between 0.71 and 1.36 mg/l, Dugwells concentration is from 0.00 to 1.5mg/l. The sampled water from tube wells and boreholes have concentrations ranges of 0.65-1.5 mg/l and 0.00- 2.2 mg/l respectively with the level of concentration being a function of depth. Health risk assessment have revealed three classes of risk in terms of Fluoride concentration levels in the water with 16 samples representing 14.3% falling within the Risk class of 1.5≤ R≤ 2.5(risk). Individual consuming such water have the tendency of getting dental fluorosis. Origins of Fluoride in the water are from Fluoride bearing minerals like Micas, Amphiboles, Illites, Apatite, Topaz, and Cryolite which occur in the sandy and clayey layers, anthropogenic sources from agricultural and irrigated land and leachate from dumps are the other possible sources of Fluoride in the tube wells and ponds water respectively. The dissolution, distribution and concentration of Fluoride in groundwater in the area are favoured by the high temperature high evapotranspiration rate and low rainfall situation of the semi-arid climate. Geochemical situation that allowed the leaching of Fluoride into the water are; high Alkaline or soda water environment, anion exchange of OH for F of the aquifer material, water residence time in the aquifer and type of climate. Drab and Sierozem Soil types control and facilitate the mobility and leaching of Fluoride in arid and semi-arid area. Generally the result has shown the area to have medium to average concentration of Fluoride in its waters with the highest value slightly above the 1.5 mg/l of WHO (2011) safe limit for drinking water. Periodic monitoring of Fluoride in the water sources is recommended so as to minimize the chances of people taking in water with high undesirable harmful Fluoride concentration.