Soil pollution status due to potentially toxic elements in active open dumpsites: insights from different Nigerian geological environments

Potentially toxic elements from heavy metal pollution in soils and water pose significant health risks to humans and ecosystems. This study aims to assess heavy metal pollution in active dumpsite soils in northern Ondo State, Nigeria, and evaluate associated hazards across different Nigerian geological environments using multi-pollution indices and statistical optimization. Twenty-seven soil samples from three major active dumpsites around Owo and Ikare-Akoko were collected from nine profiles at different depths. These samples were analyzed for concentrations of various heavy metals including Na, K, Ca, Mg, Cr, Fe, Pb, Zn, Ni, and Mn. The concentration of earth and heavy metals were considerably low compared to other parts of Nigeria and Africa. Pairwise correlations among heavy metal concentrations in the three dumpsite soils revealed both strong and weak correlations. Only Fe-Zn showed a strong correlation. Interestingly, no common correlation was found among the three geological environments, indicating that the concentrations might not be impacted by the varying geological conditions. In Ondo State's dumpsite soils, contamination factor (CF) ratings indicate moderate to very high contamination, while pollution load index (PLI) values suggest very high pollution. Index of geo-accumulation (I-geo) and ecological risk factor (ERF) values reflect moderately high to very high pollution and low ecological risk, respectively. The mean I-geo values follow this order: Cr < Ni < Mn < Zn < Pb < Fe (Tertiary environments); Cr < Ni < Mn < Pb < Zn < Fe (Cretaceous environments); and Ni < Cr < Zn < Mn < Pb < Fe (Basement environments). For mean ERF values, the order is Cr < Zn < Ni < Mn < Pb < Fe in Tertiary, Cr < Zn < Mn < Ni < Pb < Fe in Cretaceous, and Zn < Cr < Ni < Mn < Pb < Fe in Basement environments. The CF sequence is Cr < Ni < Zn < Mn < Pb < Fe in Tertiary, Cr < Zn < Ni < Mn < Pb < Fe in Cretaceous, and Cr < Ni < Zn < Pb < Mn < Fe in Basement environments. All samples exhibit extremely high contamination, with basement areas dominated by notably high Fe and other heavy metal concentrations, while the Tertiary environments show the lowest concentrations. Based on the research findings, regular monitoring and remediation efforts are essential in other areas to mitigate imminent pollution and risks.