Health Risk Assessment of Nitrate and Fluoride in Groundwater Across 10 Nigerian States

Nitrate and Fluoride are both useful and deadly at varying concentrations, hence the need for continuous monitoring. This study assessed the human health risks associated with groundwater usage by adults, teenagers, children, and infants across Lagos, Ogun, Oyo, Osun, Ekiti, Ondo, Imo, Ebonyi, Delta, and Abuja. A total of 623 groundwater samples (537 wells and 86 boreholes) were analyzed for nitrate and fluoride using standard procedures. Fluoride concentrations ranged from 1.25 ± 0.07 to 8.47 ± 3.19 mg/L, with most samples exceeding the WHO, SON, and NESREA guideline of 1.5 mg/L. Elevated levels were particularly evident in Abuja, Osun, Ondo, and Oyo, reflecting widespread geogenic enrichment. Nitrate levels were generally within safe limits (2.50–13.37 mg/L), except in Delta State communities (Kurutie, Kunukunuma, Okerenkoko), where values exceeded 50 mg/L, suggesting contamination from oil activities, industrial discharges, and poor sanitation practices. Risk assessment showed oral ingestion as the primary exposure pathway. The Hazard Quotient for fluoride via ingestion (HQ > 1) indicated significant non-cancer risks for all age groups, especially infants and teenagers. Dermal risk was negligible in all cases. The Hazard Quotient for nitrate via ingestion (HQ < 1) was also negligible in all communities except for Kurutie, Kunukunuma and Okerenkoko. The Mean Cancer Risk (MCR) values for nitrate exceeded the USEPA threshold (1 × 10⁻⁶) across all age groups, with Delta State hotspots reaching 10⁻³. Findings demonstrate that groundwater in the region poses both non-cancer and cancer risks, underscoring the urgent need for intervention strategies such as defluoridation, denitrification, and provision of safe alternatives.