Metal(loid)s, nitrate, polycyclic aromatic hydrocarbons, and radioactive contaminants in Nigerian water resources: state-of-the-art of their ecological and health risk assessments

Water quality issues in Nigeria pose significant environmental and public health challenges. While previous reviews have addressed aspects of water contamination, a comprehensive analysis of ecological and health risk assessment models across surface and groundwater sources was lacking. This review addressed this gap by analyzing 93 studies (2014–2023) on risk assessments in Nigeria. It covered 20 ecological and 73 health risk models, examining metal(loid)s, nitrate, polycyclic aromatic hydrocarbons, and radionuclides. The study analyzed the geographical distribution, methodologies, and results across six geopolitical zones of Nigeria. Findings revealed that about 60% of the studies concentrated in the Southeast and Southwest regions. Pb and Cd were identified as the most frequent priority potentially toxic elements in both ecological and health risk assessments. About 40% of the studies found higher health risk values in groundwater compared to surface water. In these cases, the average hazard index for groundwater was 1.5 to 2 times higher than surface water. The review observed the evolution from conventional US-EPA approaches to sophisticated tools like HHRISK and HERisk codes, enabling age-specific risk evaluations. Limitations include lack of country-specific exposure factors and absence of emerging contaminants like microplastics in assessments. This review provides crucial insights for improving water resource management and public health policies in Nigeria. It emphasizes the need for focused, region-specific interventions and integration of advanced risk assessment methodologies. The findings clarify the complex nature of water contamination risks across Nigeria and provide robust insights for improving contaminant risk assessment strategies both regionally and globally.