Determination of the water and sediment quality of the Ellah river, Edo state, Nigeria

Abstract

The physicochemical characteristics and heavy metal levels in water samples and sediments from the Ellah River in Esan South East Local Government Area of Edo State, Nigeria were investigated to assess the quality status of the river. Four sampling stations were chosen from upstream (station 1), the bridge (station 2) and downstream stations 3 and 4. The values of all measured parameters were within the WHO safe limits for drinking water, and sediment concentrations of heavy metals were also low. Analysis of Variance (ANOVA) revealed significant spatial difference (P<0.05) in the mean values of Ca, PO₄, Fe and Cr in surface water, with the highest values in station 4. The sediment concentrations of all heavy metals except Ni and V were highly significantly different (P<0.001) amongst stations, with the highest values in station 3. The concentrations of heavy metals in sediment were generally higher than in the surface water. The distribution coefficient Kd varied from 0.00 in Vanadium to 2010 kg/l in Nickel indicating that the sediment matrix is significantly affecting the bonding of pollutants to the sediment system. The order of affinity of metals to sediment (hydrophobicity) was: Ni>Zn>Cd >Mn >Pb>Cu>Cr>Fe>V. The higher metal concentration in sediment necessitates the need to continuously monitor the water body to minimize adverse health impacts of heavy metal poisoning.

Key words: Ellah, water quality, sediment, heavy metals, distribution coefficient