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 R2 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.
Highlights
The incidence of surface water contamination with toxic and persistent heavy metals is increasing worldwide because of the ever increasing industrialization in most countries (Ahmed and Ahmaruzzaman 2016; Tripathee et al 2016; Wu et al 2016; Zhang et al 2017)
The few attempts made on Nigerian rivers were to determine only the heavy metal concentrations in major river water, leaving out dearth of information on small river sediment the dispersion of heavy metals in river system that is of importance to the country
This implies that the hydromorphic distribution patterns of contaminants are supported in the fine sandy fraction of the river sediment (El Azhari et al 2016)
Summary
The incidence of surface water contamination with toxic and persistent heavy metals is increasing worldwide because of the ever increasing industrialization in most countries (Ahmed and Ahmaruzzaman 2016; Tripathee et al 2016; Wu et al 2016; Zhang et al 2017). The main receptacles in surface waters for contaminants from industrial discharges are river sediment (He. 1 3 Vol.:(0123456789) 161 Page 2 of 10. As important as the river is, it still receives effluent discharges from industries, which result in pollutants deposition in the sediment. Studies have shown that these industries contribute to increased concentration of heavy metals in river sediment. Kumarkhali textile in Kushtia industrial area of Bangladesh contaminated Goral River sediment with toxic heavy metals (Islam et al 2015). The presence of heavy metals in Guadiamar River in Spain was adduced to wastewater from pharmaceutical and textile industries (Garrido et al 2016)
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