Monitoring and assessment of sediment contamination with toxic heavy metals: case study of industrial effluent dispersion in Alaro River, Nigeria

Abstract The influx of effluents from industrial area into the Alaro River in Ibadan has made the investigation of the sediment quality of the river an important environmental issue for discussion. The objective of this study was to determine the concentrations of toxic heavy metals in surface sediment of the river in order to evaluate the impact of the effluent and spatial distribution of the metals downstream. pH, total organic carbon and grain-sized particles of the sediment samples were determined according to standard methods of analysis, while heavy metal concentrations were determined by AAS. Linear least square regression (LLSR) model was employed to describe the distribution pattern of heavy metals along the river network. Hierarchical cluster analysis was applied to locate the heavy metals contamination source and interpret the association between the metal concentrations upstream and downstream, which were found to be significantly different (p = 0.05) The concentrations of Ni, Zn, Cr, Co, Cu, Cd and Pb in downstream sediments were 7.74 ± 0.97, 19.5 ± 4.6, 5.78 ± 0.47, 9.6 ± 1.6. 7.36 ± 0.61, 0.47 ± 0.03 and 7.76 ± 0.80 mg/kg, respectively. The enrichment factor (EF > 1.5) and pollution load index (PLI > 1.0.) showed that the sediment was contaminated with these heavy metals. The toxicity estimation carried out suggested that the sediment was slightly toxic. Metal distribution as shown by LLSR was such that the concentration decreased with distance downstream with R 2 ranging from 0.8810 to 0.9990. The LLSR models obtained are useful to predict the metal concentrations based on the known distance of the river