ASSESSMENTS OF HEAVY METAL CONCENTRATIONS IN SURFACE WATER AND SEDIMENT OF THE OKHUIAHE RIVER, EDO STATE, NIGERIA

Abstract

The concentrations of seven heavy metals (Fe, Zn, Mn, Cu, Cr, Ni and Pb) were determined in surface water and sediments collected from designated stations on a stretch of Okhuiahe River (latitude 5.450N; 5.510E and longitude 6.150N; 6.220E), Edo State, Nigeria between May to October, 2011 using a Unican 929 Atomic Absorption Spectrophotometer. The ranges of the measured concentrations in the surface water were Fe: 0.09 - 0.54 mg/l; Zn: 0.01-0.22 mg/l; Mn: 0.01-0.05 mg/l; Cu: 0.00-0.03 mg/l; Cr: 0.00-0.05 mg/l; Ni: 0.00-0.01 mg/l and Pb: 0.01-0.04 mg/l. These values which were in the order Fe> Zn>Mn>Pb> Cu> Ni> Cr showed significant difference (p<0.05) among the stations except Cr where no significant difference (p>0.05) was observed.While the average concentrations of Zn, Mn, Cu, Cr and Ni at all stations were within the guidelines of NIS quality for drinking water, the concentrations ofFe at stations 3 and 4 and Pbat all stations did not compare favourably with the NIS quality for drinking water.In the sediment, the heavy metals ranges were Fe: 1.15-3.26 mg/kg; Zn: 0.62-1.86 mg/kg; Mn: 0.13-0.33 mg/kg; Cu: 0.00-0.77 mg/kg; Cr: 0.06-0.10 mg/kg; Ni: 0.01-0.50 mg/kg and Pb: 0.02-0.18 mg/kg. The heavy metals concentrations were in the order Fe> Zn>Mn> Cu> Cr>Pb> Ni. The concentrations of these heavy metals in the sediment were below the values obtained in unpolluted sediment. Assessment of the suitability of the river water for drinking and other domestic purposes using water quality index (WQI) indicated that the status of the water at stations 1 and 2 were good, while that of stations 3 and 4 were not suitable for drinking unless purified.