Potentially toxic metals record high contamination indices in three small African rivers

Abstract

Heavy metal pollution is one of the threats to aquatic ecosystems globally and it portends a great danger to the sustenance of aquatic biodiversity in Afro-tropics, in particular. Bottom sediment samples were collected from three small African rivers, namely: Obudu river, Opa river, and Esinmirin river from Sep 2004 to July 2005. The samples were air-dried in the laboratory, digested and subsequently extracted for Ni, Fe, Zn, Cu, Pb, Cr, As, Co, Mn, and Cd using the atomic absorption spectrophotometry. Most of these metals recorded their highest values in the Esinmirin river and the lowest values in the Obudu river. However, the Kruskal–Wallis test revealed that only two metals (i.e., Cu and Pb) showed a significant difference (p < 0.05) in the variations. Geo-accumulation index, contamination factor, and enrichment factor all indicated that the bottom sediments of the rivers were highly impacted with Cd, followed by Cu and Pb. The three contamination indices suggest that the benthic fauna and the entire biota of each river system could be predisposed to pollution stress on account of these metals. Good waste management practice of Afro-tropical river basins by the local communities could contribute greatly to preserving pristine/near-pristine rivers and restoring the degraded ones.