Environmental risk assessment of River ljana, Ekpan, Delta State Nigeria

Abstract

The level and distribution of physiochemical contaminants (cadmium, chromium, copper, iron, nickel, lead, zinc, temperature, pH, suspended solids (SS), dissolved solids (DS), conductivity, oil and grease, dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD) and phenol) were investigated in water samples obtained from River Ijana and the Warri Refinery and Petrochemical Company (WRPC) effluents, using APHA standard methods of wastewater analysis. This research is aimed at quantifying the contribution of the refinery effluent, rural/urban runoff, refinery sludge lagoon to the pollution load of the river, and the magnitude of trace metal flux to Tobi creek. The concentration of pollution indicators varies between 0.01 and 0.13 mg L−1 for Cd, 0.01 and 0.09 mg L−1 for Cr, 0.01 and 0.07 mg L−1 for Cu, 0.04 and 0.25 mg L−1 for Fe, 0.02 and 0.09 mg L−1 for Ni, 0.02 and 0.07 mg L−1 for Pb, 0.08 and 0.13mg L−1 for Zn, 28.93 and 31.93°C for temperature, 6.72 and 8.64 for pH, 42.61 and 48.75 mg L−1 for DS, 21.31 and 25.18mg L−1 for SS, 3.22 and 15.11 mg L−1 for oil and grease, 81.01 and 97.02 μ S cm−1 for conductivity, 5.27 and 6.70 mg L−1 for DO, 13.20 and 22.34 mgL−1 for BOD, 40.88 and 52.64mg L−1 for COD and 0.97 and 1.37 mg L−1 for phenol. Correlation analysis shows that P<0.05, and is significant for conductivity, SS, DS, oil and grease, BOD, COD, Cd, Cu, Fe, Ni, Pb and Zn. When compared with WHO/FEPA permissible limits for aquatic ecosystems, our results are indicative of the contribution of pollutant from the refinery effluent. The refinery sludge lagoon is also suspected to be responsible for the elevated concentrations downstream of the river.