Abstract

This study looked at the geo-assessment and ecological risk of heavy metals in the bottom sediments of the Okpare Olomu River in Southern Nigeria. An Ekman grab sampler was used to gather bottom sediment samples every three months for a year from four points along the river. We used standard analytical methods and Atomic Absorption Spectroscopy (Solaar 969 Unicam Series Model) to look for certain physicochemical features and heavy metals in the samples. The sediment texture was predominantly sandy, while several physicochemical properties varied significantly across the sampled stations. Mean concentrations of heavy metals and THC in sediment samples were 64.653±40.52 (Fe), 0.699±1.02 (Cr), 0.098±0.13 (Cd), 0.902±0.82 (Cu), 4.179±1.06 (Zn), 2.87±1.68 (Mn), 0.022±0.03 (Pb), and 681.146±967.36 (THC), respectively. The order of heavy metal concentrations was Fe > Zn > Mn > Cu > Cd > Cr > Pb. Geo-assessment indices indicated that the sediments were influenced by varied levels of human contamination. The enrichment factor showed that some metals, especially chromium and copper at the stations that were most severely impacted, were moderately to very highly enriched. The geo-accumulation index showed that chromium levels varied from very polluted to extremely polluted. Cadmium and copper levels were also high at several locations. The pollution load index, contamination factor, and degree of contamination showed that all of the stations that were analysed were polluted. Stations 2 and 4 had the highest levels of pollution. The prospective ecological risk index showed that Station 1 had a low ecological risk, Station 3 had a moderate risk, Station 4 had a high risk, and Station 2 had a very high ecological risk. These findings underscore the importance of remediation and continuous sediment quality monitoring.

Keywords:Geo-assessment, Bottom sediments, Heavy metals, Ecological risk, Okpare Olomu River