ECOLOGICAL RISK ASSESSMENT

The quality of aquatic environments is an important contributor to good environmental health. This study assessed the ecological risk assessment of heavy metals in sediments from Ossiomo River, Edo State in order to ascertain the status and degree of contamination. Nine sediment samples were collected using an Eckman Grab from Ossiomo River from November 2021 to January 2022. Samples collected were air-dried, crushed and sieved through a 2mm sieve, pre-treated using standard methods before determining the heavy metal concentrations in Atomic Absorption Spectrophotometer according to the method of the Association of Analytical Chemists. The average mean concentration of heavy metals in sediments from Ossiomo river were1137±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 respectively while total hydrocarbon content had an average mean value of 826.80±457.27 mg/kg. The result showed that the concentration of heavy metal were in the following decreasing order: Fe>Zn>Mn>Cu> Pb> Cr>Cd. The composition of
computed Enrichment factor (EF) 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. Geo accumulation index (Igeo)
showed that sediments from Ossiomo River indicates Cu and Mn were practically unpolluted, Cr and Cd were moderately to heavily polluted, Pb was heavily polluted and extremely polluted. The contamination factor showed a moderate contamination exist for Cu and Mn across the sampled stations from Ossiomo River, a very high contamination exist for Cr, Cd, and Pb across the three sample stations. The contamination degree (CD) showed that a very high degree of contamination(CD ≥ 24) exists across all the three sample stations. Pollution load Index (PLI) showed that Ossiomo river is polluted (PLI>1) by metals. Potential ecological risk index (PERI) showed slight pollution degree of Cu, Zn, and Mn, a medium pollution degree of Cr, a strong pollution degree and a very strong pollution degree of Pb while Cd exhibited an extremely strong pollution degree. The risk level or risk degree for Ossiomo River indicated an extremely strong risk degree or level Dacross the sediments across the stretch of Ossiomo River. The potential ecological risk showed that station1and 3 indicates considerable ecological risk (300<RI≤600), while station 2 indicates a very high ecological risk (RI>600). The heavy metals content exhibited a positive and significant correlation. Therefore the pollution by heavy metals in sediments from Ossiomo River should not be ignored.