Human Health Risk Assessment of Heavy Metals in Groundwater of Nasarawa West Senatorial Zone, Nasarawa State, Nigeria: Seasonal Dynamics, Exposure for Adults and Children, and Risk Mitigation Strategies

Abstract

This study evaluates human health risks posed by heavy metals in groundwater sources of Nasarawa West Senatorial District, Nigeria, focusing on eight priority metals: cadmium (Cd), chromium (Cr), lead (Pb), nickel (Ni), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu). Groundwater samples from 25 boreholes and 25 hand-dug wells across five LGAs (Karu, Keffi, Kokona, Nasarawa, Toto) were analyzed for metal concentrations in both dry and wet seasons. The results show widespread heavy metal contamination: for example, dry season lead levels averaged 0.36–0.56 mg/L in boreholes and 0.38–0.60 mg/L in wells (WHO limit 0.01 mg/L), and cadmium exceeded the 0.003 mg/L guideline in all samples (up to 0.055 mg/L in some wells). Seasonal trends indicate significantly lower metal concentrations in the wet season for boreholes (due to dilution and increased aquifer recharge), whereas shallow wells showed little to no improvement, hence heavy metal levels remained comparably high year-round. Health risk assessment was performed using USEPA methods for both carcinogenic and non-carcinogenic effects via ingestion. Hazard Quotients (HQ) and Hazard Index (HI) for non-cancer risk were calculated for adults and children; Cancer Risk (CR) was estimated for lifetime exposure to Cd, Cr(VI), Ni, and Pb. The findings reveal extremely elevated risk levels: adult HIs in dry season wells ranged up to ~43 (Nasarawa), and child HIs exceeded 200 in the worst-case scenario (Nasarawa dry wells), far above the safe limit of 1. Dominant contributors to HI were Ni and Cr, followed by Pb, while Cd, though present above guidelines, contributed comparatively less to HI. Carcinogenic risks were similarly high, for example, Cr(VI) in Keffi’s dry-season well water led to an estimated CR of ~2×10^-2 for children (20 times the 1×10^-4 acceptable risk level). All sampled water sources showed cumulative cancer risks well above safe thresholds for both adults and children. This paper discusses the health implications of these findings, noting potential outcomes like neurological damage from chronic lead exposure and cancer risks from Cr and Ni. It also proposes mitigation strategies including source remediation (e.g., sealing off contaminated wells, treating mining effluents), household water treatment (advanced filtration for metals), and public health interventions to reduce exposure among vulnerable groups (especially children). The severity of heavy metal pollution in Nasarawa West’s groundwater calls for urgent action to protect community health and highlights the need for integrating water quality management into local mining and agricultural practices.