Concentrations of heavy metals in effluent discharges downstream of Ikpoba river in Benin City, Nigeria

Abstract

Various effluent samples were collected from their sources of discharge to the Ikpoba river in Benin City, Edo State between September and October, 2008. Six heavy metals (cadmium, chromium, copper, nickel, lead and zinc) in the effluents and receiving water were analyzed by atomic absorption spectrophotometric technique (AAS) in separate experiments. The concentrations of heavy metals in the effluents were compared with corresponding heavy metal values in the water. The results show that
metal concentrations were higher in the effluents than in the water. Total mean metal concentrations (mg/l) recorded in the effluents were as follows: Cd = 0.072; Cr = 0.079; Cu = 0.194; Ni = 0.122; Pb = 0.125 and Zn = 0.174 while corresponding mean values recorded in the water were Cd = 0.043; Cr = 0.072; Cu = 0.152; Ni = 0.091; Pb = 0.110 and Zn = 0.128. Significant differences (P < 0.05) were recorded between heavy metal levels in urban run-off effluents and rubber/brewery effluents. No significant differences (P > 0.05) were recorded between the concentrations of cadmium in the water procured from the four sampled stations. Significant correlations (P < 0.05) were recorded between metals in effluents and water. The concentrations of Cu, Pb and Zn in urban run-off effluents exceeded the limit recommended in effluent discharges to surface waters by the Federal Ministry of Environment (FMENV).