Journal of Global Ecology and Environment

This study aims to address this gap by using spatiotemporal mapping and monitoring of heavy-metal concentrations and assessing their corresponding pollution levels and ecological risks to evaluate the environmental quality of oil-degraded sites. This study investigates the presence of metals, their pollution levels, and the associated ecological risks at an oil-spill site in Eleme, Nigeria. Twenty-six soil samples were analysed, comprising twenty-two from the spill site and four from reference sites. The concentrations of cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), nickel (Ni), lead (Pb), and zinc (Zn) were determined during two sampling phases at a six-month interval. The geoaccumulation index (Igeo) showed values < 2 after the first sampling phase, indicating moderate contamination, and values < 1 after the second phase, signifying uncontaminated levels. The metal pollution index (MPI) decreased from 1.01 to 0.59, indicating a significant reduction in pollution associated with post-remediation activities such as metal immobilisation and leaching, as well as environmental processes such as rainfall, weathering, and groundwater movement. The contamination factor (CF) primarily indicated low contamination for most heavy metals across the samples, except Cd, which remained persistent, while the potential ecological risk index (PERI) revealed a shift from moderate to low ecological risk. The findings showed progressive contaminant reduction and improved environmental quality, with heavy-metal concentrations spatially concentrated in the southern parts of the site and significant second-phase reductions, particularly for Cr and Pb, which fell within permissible limits of the U.S. Environmental Protection Agency (USEPA). However, Cd, Zn, and Fe remained persistent in certain areas, reflecting ongoing attenuation dynamics that may affect heavy-metal behaviour and mobility and highlighting the need for targeted remedial efforts and public health protection.