Abstract

The distribution of trace metals (Zn, Cu, Ni, Mn, Fe, Co, V, Pb and Cd) in surface water and sediments from Imo River estuary in relation with the physicochemical variables were studied for both dry and wet seasons. The results obtained revealed that trace metal levels displayed marked spatial and seasonal variations in surface water and sediments, which is attributed to both anthropogenic natural processes in the environment. Trace metal levels were generally higher in the sediments than overlying water column. Seasonal variability in trace metal distribution was mostly observed in sediments than in the water phase of the relatively anoxic estuarine ecosystem. The highest average concentration of trace metal in the sediments was recorded for Fe (1101.18 mg/kg) during the dry season while the lowest was recorded for Cd (0.08 mg/kg) during the wet season. For the surface water, highest average concentration was recorded for Zn (0.04 mg/L) for the dry season and the lowest level was recorded for Cd (0.002 mg/L) for both seasons. The levels of trace metals in the water were within the permissible limits of some regulatory bodies. Pearson correlation analysis revealed that some of the physicochemical variables were associated with patterns of trace metals distribution. Based on trace metal concentrations, the health risk assessment based on the chronic daily intake (CDI) and hazard quotients (HQ) were calculated. Zinc and cadmium contributed most to the total intake through drinking water. As HQ for all trace metals were less than unity, it is suggested that there is little or no significant health risk to the exposed population.

Key words: Trace metals, surface water, sediments, seasons, Imo River estuary, Nigeria.