Evaluation of potentially toxic element pollution in the benthic sediments of the water bodies of the city of Addis Ababa, Ethiopia

The concentrations of toxic and potentially toxic elements (As, V, Cr, Fe, Co, Ni, Cu, B, Ba, Sr, Zn, Mn, Pb and Cd) collected from benthic sediments in the water bodies of the city of Addis Ababa were investigated to evaluate their distribution and pollution levels. The average concentration of Cr, Mn, Pb, Ni, Fe, Cu, Zn and Cd exceeded the threshold effect level of the sediment quality guidelines. Many of the concentrations were higher than previously reported. The sediments were moderately to heavily polluted with Cr, non-polluted to severe with Cu, Zn and Pb elements, moderate to heavily polluted with Ni and non-polluted by As and Cd. The sediments were enriched with these elements in the increasing order As < Ba < V < Ni < Cu < Cd < Co < Zn < Mn < Pb < Cr. The geo-accumulation index values for Pb, Cu, Cr and Mn indicate that at some sites unpolluted to strongly polluted. The first three principal components represented about 79% of the total variance in the sediment data sets. The significant positive correlation between elements indicates their common anthropogenic origin most likely from industrial effluents, municipal wastes and domestic wastewater inputs to the river. Since the polluted environment significantly impacts the beneficial uses of the water body and has health implication, remedial actions (e.g. capping or removal of the sediments) need to be considered. A comprehensive environmental management strategy should be formulated to address the pollution of the sediments. In parallel, there should be a strict prohibition of discharges of contaminated wastewater into the river.