The occurrence of high fluoride in groundwater and its health implications in Nakuru County in the Kenyan Rift Valley

M.Sc. (Geology)Abstract: Most semi-urban and rural communities in developing countries rely on groundwater for their daily domestic supply. Unfortunately, contamination from the local geology can render the often only source of water unhealthy for consumption. Such case is in Nakuru County in the Central Kenyan Rift Valley where high fluoride in groundwater causes dental and skeletal fluorosis. Public water supply by the government in the area has been faced with many challenges such as insufficient water for the increasing population, deterioration of infrastructure, and poor maintenance and only 36% of the households are reported to have access to piped water. As a result, most of the local population relies on private and community owned boreholes. Despite the known high fluoride in groundwater, its concentrations in the local aquifers is not yet known. The aim of this study was to identify fluoride concentrations and distributions in the Nakuru aquifers and its correlation to the status of dental fluorosis affecting the local population. Waterquality data from 32 boreholes acquired from the Catholic Diocese of Nakuru-Water program (CDN), a water service organization in Nakuru, were used to determine fluoride’s correlation and association with the physico-chemical parameters in groundwater and how they influence its concentrations and spatial distribution in the local aquifers. The prevalence and severity of dental fluorosis in the local population was investigated in 170 patients from two dental clinics in the area and correlated to fluoride distribution. All the data were statistically and spatially analyzed. The results show a sodium-bicarbonate and slightly sodium-bicarbonate-chloride groundwater type in the area dominated by sodium, fluoride, chloride, sulphate, bicarbonate, TDS, pH, borehole depth, water hardness, and calcium, which where the principal parameters. More than 86% of the boreholes had fluoride levels higher than the WHO recommended value of 1.5 mg/l for safe drinking water. Fluoride levels ranged from 0.5 to 72 mg/l with a mean of 11.08 mg/l and had a strong positive correlation with most of the principal parameters except calcium, borehole depth, and water hardness, which had a weak negative correlation. The strong positive correlations between fluoride and the dominant parameters suggest that mineral dissolution and evaporative..