Environmental impact of heavy metals distribution in water and sediments of Ogunpa River, Ibadan area, southwestern Nigeria

Geochemical evaluation of distribution of heavy metals in water and sediments of Ogunpa River within Ibadan metropolis in Southwestern Nigeria is presented in respect of anthropogenic contamination from the surrounding urbanized catchment area. The results revealed low contamination or enrichment of the heavy metals (Pb, Zn, Cu, Cd, and As) in the water phase. Also, the sediment phase (<63μm) of the drainage system is anthropogenically enriched in Ph, Zn, Cu, Cd, As and t-Hg with all recording an estimated anthropogenic factor (AF) value above 1. The estimated index of geoaccumulation (I_gco) with a value of approximately 2 for Pb, Zn and t-Hg indicates moderate or middle level contamination in the sediments while I_gco of <1 recorded for Cu, Cd, and As indicate very low or no contamination. This trend is however, reversed in the water column with Cu and Cd having I_gco value of 1.2 and 3.2 respectively, pointing to relative partitioning of the metals between the two media. Quantification of degree of pollution revealed high anthropogenic contribution for Pb (75%), Zn (75%) and t-Hg (60%), indicating enrichment by a factor of at least 5 in the sediment phase, while anthropogenic in-put also accounts for 70% (Cu) and 90% (Cd) in the water column. Furthermore, correlation of electrical conductivity (EC) peaks with the high values of Pb, Zn and t-Hg indicated that the inputs are related to anthropogenic sources along the stretches of the Ogunpa channel. The sources of contamination are attributed to urbanised anthropogenic sources, mostly vehicular emissions and related repair products, domestic sewage and effluents, varied household garbages and refuse dumps including incineration bye-products. Based on the overall evaluation, recommendations in respect of sanitization and contamination control/monitoring strategies in the study area are also presented.