While the occurrence of heavy metals in groundwater within Nigeria has been well documented, the quantification of human health risks from exposure to these metals via multiple exposure pathways has been critically understudied within rural Nigeria. This study provides the first quantitative Health Risk Assessment of heavy metals such as chromium (Cr), lead (Pb), cadmium (Cd), zinc (Zn), nickel (Ni), vanadium (V), barium (Ba), and copper (Cu) within Sobe (Edo State) and Elegbeka (Ondo State), Nigeria. Heavy metals were collected from hand-dug wells within these communities during the dry and wet seasons. Hazard quotients (HQ) and cancer risk indices (CR) were calculated using the United States Environmental Protection Agency probabilistic risk model for three exposure routes: ingestion, dermal contact, and inhalation. The study found that chromium and cadmium were the most hazardous heavy metals for cancer risk in these communities. The total cancer risk indices were found to be above the acceptable limit of 1x10⁻⁴ for multiple wells in these communities during the dry season. Non-carcinogenic hazard indices were also found for zinc and chromium in these communities, with HI > 1 for multiple wells in Elegbeka, Nigeria. A comparative study of the study areas indicated that the geology of Elegbeka is a basement complex that increases the cancer risk due to the shallow depth of the water table. Additionally, the infiltration of anthropogenic refuse dumpsite leachate into groundwater is more prevalent in Elegbeka. Sobe is under a sedimentary terrain type of the Anambra Basin. While there is a difference in the geology of these study areas, the study found that Sobe is at a comparably higher non-carcinogenic hazard risk.
Osayande et al. (Thu,) studied this question.