Contamination status and source identification of heavy metals in the riverbank soils and sediments of Ona River, Ibadan, southwest Nigeria

Abstract

The present study investigated the pollution levels, sources, and contamination status of trace metals (Pb, Cd, Fe, Zn, Cu and Mn) in riverbank soils and sediments at three different sections of Ona River bordering residential area. The relationship of studied metals with selected soil chemical properties was also examined. The average concentration of each of the studied metals in soils and sediments at each sampling site was less than 1 mg/kg having a decreasing trend of Zn > Cu > Fe > Cd > Pb > Mn and Zn > Cd > Fe > Cu > Pb > Mn, respectively in soils and sediments. Results of enrichment factors (EF) were generally less than 1.5 for all assessed metals; index of geoaccumulation (Igeo) in soils and sediments of the investigated sites were less than 1 while contamination factor (CF) of assessed metals were in the range: 1< CF < 3. The results of integrated pollution indicators support lithogenic sources and a low-to-restrained pollution of the considered soils/sediments by metals. The environmental risks indices of sampling sites that could be ascribed to the metals revealed low mean ecological risks potential in soils and sediments. The values of co-efficient of variation (CV) of analyzed metals were less than 50%, indicating absence of strong anthropogenic inputs, while Fe-Zn, Fe-Pb, and Pb-Zn pairs in soils and sediments exhibited strong positive correlations, an indication of common sources due to lithogenic processes. Inverse relation between analyzed metals and organic matter further confirmed little impact of anthropogenic inputs as sources of metals in soil/sediment. This study elucidated that the area was not heavily polluted by metals and revealed that the investigated riverbank areas were mildly contaminated by assessed metals, thus posing a low ecological risk.