Studies on heavy metals contents of Osun River at the pre-urban settlement and across Osogbo City, Nigeria

Abstract

Heavy metals were analysed in Osun River (Nigeria) between 2017 and 2018. Concentrations of the heavy metals were in the increasing order: Fe > Zn > Cu > Mn > Pb > (Ni, Cr) > (Cd, Co). Iron made up 76% of the total heavy metals measured. Activities at Swanlux Farm (a major oil palm farm) seemed to impart on Osun River as the highest Fe concentration (2.55 mg/L) was measured near the farm. In the urban settlement, average zinc concentration was almost double (0.37 mg/L) of that found in the pre-urban area (0.25 mg/L). The pre-urban settlement had lower concentrations of Pb, Zn and Cd, signifying the effects of anthropogenic activities. Cu and Mn were found in a similar trend in the river; Coker village had their highest concentrations. Use of agrochemicals was conceivably the major source of Cu and Mn at the river sampling point as cocoa farms are predominant in the area. Osun River use for agricultural/irrigational purposes should be with continuous monitoring.

Keywords

• osun river
• heavy metals
• pollution
• anthropogenic activities
• urban settlement