Assessment of Fluoride Exposure and Non-Carcinogenic Health Risks associated with Groundwater Consumption from Olbanita Boreholes, Nakuru County, Kenya

Abstract

Purpose: The aim of this study is therefore to estimate the level of fluoride exposure from groundwater consumption at Olbanita wellfield boreholes and associated potential non-carcinogenic risks to children and adults. Methodology: Water samples were collected from six productive boreholes (BB2, BB3, BB4, BB5, BB6 and BB7) during dry season of the study area for three months and analyzed for fluoride concentrations using spectrophotometric method. Fluoride exposure levels and potential non carcinogenic health risk were evaluated using the United States Environmental Protection Agency (USEPA) method by calculating Chronic Daily Intake (CDI) and Hazard Quotient (HQ) for adults and children. Findings: From the results, mean fluoride concentration ranged from 1.50 to 11.60 mg/l, with five of the six boreholes exceeding the World Health Organization (WHO) guideline value of 1.5 mg/l for drinking water. The calculated CDI for adults ranged from 0.0429 to 0.3314 mg/kg/day, while higher values of 0.1000 to 0.7733 mg/kg/day were observed in children population, exceeding USEPA safe oral Reference Dose (RfD) for fluoride of 0.06 mg/kg/day. Corresponding HQ values for adults ranged from 0.71 to 5.52, while children had a recording of 1.67 to 12.89, exceeding the safety threshold of one unit. The findings showed elevated groundwater fluoride contamination in Olbanita boreholes where consumption represents a significant fluoride exposure pathway and potential non-carcinogenic health risk problems for both groups with children being highly vulnerable. Unique contribution to theory, practice and policy: The study uniquely advances theoretical understanding of the link between groundwater geogenic fluoride enrichment, specific population group exposure and non-carcinogenic health risk assessment using the USEPA CDI and HQ framework. In practice, it provides a risk-based method that can guide identification of high-fluoride groundwater sources and vulnerable consumers to support targeted interventions to reduce exposure. From a policy perspective, the findings can provide evidence base for risk informed groundwater management and public health protection in the study area and other fluoride-prone areas of Kenya’s Rift Valley.