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

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 c ocoa farms are predominant in the area. Osun River use for agricultural/irrigational purpose s hould be with continuous monitoring.