Abstract

Sediments collected from Bomu and Oginigba rivers were treated according to recommended standards and subsequently analyzed for heavy metals and further tested with index models. The results showed that all the metals examined were higher than the recommended upper limits in sediments by China and USEPA except lead in the Oginigba River and cadmium in both rivers. In both rivers, all the metals, copper (Cu), nickel (Ni), chromium (Cr) and zinc (Zn) fell within the category of heavily polluted, lead (Pb) in the sediment from the Oginigba River was moderately polluted and cadmium (Cd) showed no indication of contamination/pollutionin any of the sediments from the rivers. The order of the concentration of the heavy metals in the sediments was Zn> Ni > Cr >Cu>Pb>Cd. Contamination factor (Cf) analysis showed that the sediments from both rivers were free from Cd pollution, slightly polluted with Cu and Cr and moderately polluted with Ni, Zn and Pb. Pollution load index (PI) results showed that Bomu River sediments were moderately polluted while Oginigba river sediments were slightly polluted by the metals. Geo-accumulation index (I-geo) measurements showed that sediments from both rivers are free from pollution by the metals. Ecological risk factor and ecological risk assessment of the sediments from both rivers indicated that both aquatic environments are free from ecological risk. However, the results suggested that there is the possibility of a near future or long run pollution. Therefore, adequate measures should be put in place to monitor thes environments.

Key words: Heavy metals, pollution, index models, Bomu River, Oginigba River, sediments.