Fluoride Distribution, Health Risk Assessment and Prevalence of Human Fluorosis in Domestic Water Sources of Langtang Region, Nigeria

Abstract Langtang region is a high risk area for human fluorosis due to elevated fluoride levels in domestic water sources. The study objectives was to; analyse fluoride levels in domestic water sources, identify source of fluoride enrichment in water, determine health risk of fluoride and prevalence of human fluorosis, assess public perception of human fluorosis, and patterns of both fluoride levels and human fluorosis. Forty water samples, with 10 each from boreholes, hand dug-wells, dams and streams were collected from 10 communities and analysed. 370 copies of questionnaire administered to selected households provided additional data. Data was analysed using ANOVA, Duncan Multiple Range Test (DMRT) and Health Risk Index (HRI). Results show significant variation in fluoride levels among water sources with higher values above 1.5mg/l recommended limits only in groundwater in areas of metamorphic basements rocks that host fluoride bearing minerals; biotite granites, mignatite, rhyolite and pegmatite within latitudes 090010011 and 090201001N due to weathering and rock-water interactions. Fluoride levels in groundwater show a north-south decreasing pattern with rocks of older ages having higher values. Adults were at risk of fluoride toxicity from eight sites; 11, 12, 13, 14, 21, 22, 23 and 24 with HRIs of 1.450, 4.667, 3.133, 2.683, 3.300, 2.600, 1.550, and1.300, while children from 11 sites; 11, 12, 13, 14, 15, 16, 18, 21, 22, 23, 24, and 25 with HRIs of 2.000, 6.450, 4.333, 3.700, 1.250, 1.017, 1.233, 4.567, 3.583, 2.133, 1.783, and 1.250. Average HRI for adults and children were 1.439 and 1.980 respectively. HRI values were higher in boreholes than hand dug-wells indicating the influence of depth on fluoride levels in groundwater. Therefore, children and households that use boreholes as main water source were at higher risk of fluoride toxicity. The study revealed prevalence rate of 23.5% for dental and 10.3% for skeletal fluorosis endemic in communities underlain by metamorphic basement rocks. The diseases also demonstrate a north-south decreasing pattern similar to fluoride levels in groundwater. Therefore, human fluorosis in Langtang is due to consumption of fluoride above 1.5mg/l in groundwater and not genetic. The provision of alternative drinking water by government, rainwater harvesting and use of defluoridation tablets to reduce the health risk were recommended.