Effect of Long-term Pumping on Fluoride Concentration Levels in Groundwater: A Case Study from East of Blue Nile Communities of Sudan

Many studies reported that groundwater constituents are not always stable during long-term pumping. This study conducted to investigate fluoride ion (Fˉ) trend in some boreholes in the study area. A total of 26 boreholes were analyzed and compared with the Construction Analyses (CA). The data from CA and Study Analysis (SA) were graphed and trends of Fˉ levels were prepared. The consequent results revealed that, in general, Fˉ levels decreased in almost all of the investigated boreholes. Only one borehole exhibited of Fˉ ion concentration level from 0.7-0.9 mg L-1 (4.3% increasing rate per year) while another borehole showed a negligible decrease of Fˉ concentration level, from 2-1.9 mg L-1 (0.2% decreasing rate per year). In general, decreasing rates of Fˉ concentration levels were almost observed in communities with intensive population in the study area. This study attributed the decreasing rate of Fˉ concentration levels in boreholes of the study area to the continuous withdrawal of groundwater that eventually washing up and depleting Fˉ content in aquifers. Researchers should be advised to develop and use the "fluoride trend method" used in this study to determine Fˉ concentration levels previously registered in well water and to properly pinpoint the exact Fˉ concentration level providing the threshold of dental fluorosis prevalence among schoolchildren.