Assessment of Bioavailable Trace Metal Levels in Bed Sediment of River Water System

The study was carried out to assess contamination and seasonal variations in bioavailable forms of trace metal (Cd, Cr, Cu, Fe, Pb, Ni, Zn, Mn) concentrations in bed sediment. Sediment samples were collected from five sampling points during dry and rainy seasons along Mada River, Nasarawa state, Nigeria. The samples were extracted using HCl/HNO3 (3:1v/v) and Ethylenediaminetetraacetic acid (EDTA). Trace metal levels in the extracts were quantified using atomic absorption spectrometer (AAS). Enrichment factors (EF) and Geochemical index (IGeo) were also determined. Acid leachable metal concentrations in bed sediment were higher than the EDTA extractable trace metal levels during the rainy season. Sediments were enriched with Fe and Mn. Igeo index revealed class 0 – uncontaminated for the sediments during both seasons. Acid leachable Cu, Pb and Zn concentrations correlated positively and strongly for both periods of analysis; indicating same source and mechanism. Analysis of variance (ANOVA) indicated significant differences (P<.05) between acid leachable and EDTA trace metal concentrations. Metal concentrations, though higher during the rainy season, were below the Consensus-Based Sediment Quality Guidelines (CBSQG), the threshold and probable effect concentrations. The moderately to strongly contaminated nature of surface sediment could be as a result of anthropogenic source of metals entering the coastal zone through river inputs. Further study on the impact of trace metal contents in bed sediment on the quality of the overlying water column of the river is recommended.