Contamination Levels and Ecological Risk Assessment of Potentially Toxic Metals in Sediments of Eleyele Lake and Odo-Iyaalaro River, Nigeria

Abstract

Increasing anthropogenic activities due to rising global human population and urbanization have resulted into contamination of many urban lakes and rivers with potentially toxic metals (PTMs). This study investigates the contamination levels and ecological risk assessment of selected PTMs (Fe, Cu, Zn, Cr, Pb and Cd) in sediments of Eleyele Lake in Ibadan and Odo-Iyaalaro River in Lagos, Nigeria using appropriate standard methods after nitric acid/perchloric acid digestion and analyzing with atomic absorption spectrophotometer (Buck 210 Model). Results show that the highest concentrations, among the analyzed PTMs, were measured for Fe in the ranges of 51-143.7 mg kg^-1 and 177.4 – 344.2 mg kg^-1 for Odo-Iyaalaro River and Eleyele Lake sediments, respectively. Only Cd concentrations exceeded the toxicity reference value and sediment quality guidelines, showing that the sediments may be contaminated with Cd. Contamination factor and geo-accumulation index show that all studied PTMs had low contamination in the sediments except Cd which had a moderate pollution in sediments of Odo-Iyaalaro River and considerable pollution in Eleyele Lake sediments. Extreme enrichment was observed for Pb and Cd in Odo-Iyaalaro River sediments and for Cd in Eleyele Lake sediments, indicating anthropogenic influences. Cd also presented moderate and considerable ecological risks in sediments of Odo-Iyaalaro River and Eleyele Lake, respectively while other studied PTMs showed low ecological risks in sediments of both water bodies. Periodic monitoring of Odo-Iyaalaro River and Eleyele Lake sediments for PTMs (particularly Cd) is, therefore, advocated to protect the aquatic and benthic/pelagic organisms.