Abstract

This study assessed the pollution characteristics and geochemical study of core sediments from the Ossiomo River. Sediment samples were air-dried, crushed and sieved through a 2mm sieve and analysed for physicochemical and heavy metals using standard methods. The average mean concentration of physicochemical properties in sediments were 5.43±0.37 pH, 186.28±59.15 (uS/cm) EC, 1.41±0.94 % TOC, 89.25±1.20 % sand, 5.03±1.81 % silt and 4.95±0.65 % clay. Mean concentration of heavy metals in bottom sediments were 1137±760.55 for Fe, 6.83±1.24 for Cu, 28.94±11.93 for Zn, 0.14±0.06 for Cd, 5.80±5.27 for Pb, 9.02±3.80 for Mn, 4.30±1.04 mg/kg for Cr. Total hydrocarbon content (THC) had an average mean value of 826.80±457.27 mg/kg. Heavy metal concentration was in the order: Fe>Zn>Mn>Cu>Pb>Cr>Cd. The computed Enrichment factor indicated that there is a moderate enrichment for Fe and Zn, a significant enrichment for Fe, Cr, Cd and a very high enrichment for Pb. Geoaccumulation index showed that Cu and Mn were practically unpolluted, Cr and Cd were moderately to heavily polluted, Pb was extremely polluted. Contamination factor showed a very high contamination exists for Cr, Cd, and Pb across the sample stations. Pollution load Index was greater than 1 (PLI>1) indicating pollution. Potential ecological risk index showed a very strong pollution degree of Pb while Cd exhibited an extremely strong pollution degree. The risk degree indicated an extremely strong risk degree across the stations. The potential ecological risk showed that station 1 and 3 had considerable ecological risk (300<RI≤600) while station 2 have a very high ecological risk (RI>600). Heavy metals content exhibited a positive and significant correlation and therefore, it is important to take heavy metal contamination in Ossiomo River sediments seriously.

Key Words:Heavy metals, Ecological risk, Enrichment factor, Contamination factor, Pollution load index, Geo-accumulation index