Ayodele Rotimi Ipeaiyeda^1,, Gabriel Monday Obaje²

Sediments of the Onyi river are subjected to pollution from cement industry and tend to accumulate heavy metals as it receives effluent from the industry. This study highlights the concentrations of toxic heavy metals, dissolved organic matter contents and particle size distribution of the sediments. These parameters were measured to determine the sediment quality with reference to some international sediment quality standards. In order to investigate the self-purifying capacity of the river, the upstream and downstream sediments were monitored monthly for a year and the waste assimilation capacity was calculated. The levels of Co, Cd, Cr, Cu, Ni, Pb and Zn in downstream sample were above the levels in upstream samples. Of these metals, Cd concentration exceeded the Australia and New Zealand sediment guidelines for the protection of aquatic life. The pollution load indexes of 1.26 (dry season) and 1.31(wet season) were above one (1.0), confirming that the sediments were deteriorated. The contamination factor (CF>1) for all the metals showed moderate degree of contamination. The Igeo values during the dry and wet season indicated moderately contamination of sediment. The sediments of Onyi river revealed purification capacities of 63.0 %(Co), 7.0 %(Cd), 15.7 %(Cr), 77.4 %(Ni), 5.6 %(Pb) and 18.8 %(Zn).

industrial effluents, heavy metals, Onyi River, pollution load index