Application of Soil Composition for Inferring Fluoride Variability in Volcanic Areas of Mt. Meru, Tanzania

Abstract

Predicting fluoride levels in water within fluoride endemic areas is an issue of high significance. As a result several methods including mathematical models have been reported to suit the task. However, most of these methods have limited practicality to low income communities. This study presents the potentials of employing soil characteristics to predict the level of fluoride in groundwater. The study is based at the areas around Mount Meru in Northern Tanzania. The volcanic sediments around this mountain had been segregated by geological studies into various lithologies. In this study water and soil samples were collected at springs in volcanic sediments categorized as main cone group, mantling ash, Tengeru lahar, Ongadongishu lahar and Ngarenanyuki lahar. Fluoride levels in water were then correlated to elemental composition of the soil. Water samples showed that fluoride was low in the main cone group, mantling ash and Tengeru lahar whereby the median concentration was 1mg/l but it was high in Ngarenanyuki and Ongadongishu lahars whereby the median concentrations were 4mg/l and 9mg/l respectively. Soil analyses indicated that high levels of aluminium do coincide along with low sodium levels, and vice versa. In addition high levels of sodium in soil are accompanied by high levels of calcium. Correlation studies indicated a strong negative relationship between aluminium in soil and fluoride in spring water with r2 = 0.847. On the other hand, a positive correlation was obtained between calcium in soil and fluoride in water with correlation coefficient, r2= 0.765. Likewise, sodium indicated a positive correlation with fluoride in water (r2= 0.458). So long as high levels of Na and Ca in soil or water normally result to formation of salts on the banks of water sources after prolonged evaporation during dry seasons, the correlation established between fluoride and such elements in soil can enable people within volcanic areas to identify water sources with unacceptable levels of fluoride in their areas hence reducing the risks of fluorosis.