ASSESSMENT OF TEMPORAL VARIATION OF HEAVY METALS IN SEDIMENTS OF WARRI RIVER, SOUTHWESTERN NIGERIA

Abstract

Contaminated sediment poses a serious environmental problem, therefore knowledge of the concentration of heavy metals in stream sediments is very important because of their significance to aquatic life and human health. The concentration of heavy metals (Cd, Pb, Cr, As, Ni, Zn, Fe and Cu), in stream sediments of some parts of Warri River, Southwestern Nigeria were examined during the rainy and dry seasons using Atomic Absorption Spectrophotometer, in order to assess their contamination levels using the environmental contamination indexes; Geoaccumulation Index, Enrichment Factor (EF), and Contamination Factor (CF). For both the rainy and dry seasons, the results revealed average heavy metal concentrations obtained in all samples in the study area in the order As>Cd>Pb>Ni>Cr>Zn>Cu>Fe. The trend in mean Igeo values was as follows: As (-0.66) > Zn (-4.93) > Cu (-5.8) > Fe (-5.31) > Cd (5.76) > Pb (-6.35) > Ni (11.25), showing that River Warri’s sediments were not polluted by heavy metals. Cu= Zn (0.08), Cd (0.34), Pb (0.02), As (0.01), and Ni (0.00) were the mean CF values across all measured locations, indicating a low contamination factor. The average EFs for the sediments were As (1.09) > Cd (1.10) > Cu (1.46) > Zn (1.61) > Pb (1.09) > Ni (1.09) > Fe (0.83), showing low enrichment (<2). Evaluation of enrichment factor, geo-accumulation index and contamination factor values showed that the stream sediments of the study area were unpolluted. Heavy metals in the sediments were found to be linked to anthropogenic activities in the study region, according to the results of the hierarchical cluster analysis (HCA). The metal concentrations in the sediment were found to be elevated at some sampled points, it is therefore recommended that annual monitoring of the stream sediments of the study area is undertaken. Also, sustainable practices should be employed in order to conserve the resources of the Warri River.