The impact of bitumen exploration on the physical and chemical quality of the Benin river, Nigeria

Abstract

The impact of bitumen exploration on the physicochemical parameters of the Benin River in Delta State was assessed between May and November 2010. There was no statistically significant difference (P>0.05) in the physico-chemical parameters of the study stations, except for total suspended solids (TSS), zinc and chromium which differed significantly (P<0.05) across the stations. A posteriori Duncan Multiple Range (DMR) test showed that these significant parameters were higher around the bitumen processing plant than at the other stations. The mean ranking distribution pattern of the heavy metals in surface water was Fe>Mn>Ni=V>Zn>Cu>Pb>Cr>Cd. The water quality parameters were within the Federal Ministry of Environment (FMEnv) and World Health Organization (WHO) minimum criteria for drinking waters, except TSS, TDS, iron, manganese, lead, nickel and vanadium which were not compliant. The sediment had higher concentrations of all the heavy metals and the rank profile of the metals was Fe>Zn>Mn>Ni>Cu>V>Cr>Cd>Pb. The distribution coefficient K_d, which is an indication of the adsorbing capacity of the substrate, varies within a wide range, from 11.097 (Pb) to 202.122 kg/l (Fe). Desorption of metals from the solid phase is thus small, indicating that the sediment matrix is significantly affecting the mobility of metals by modifying the bonding of pollutants to the sediment system. The dissolved oxygen, TSS and the levels of heavy metals indicate degradation of the Benin River. Apart from bitumen exploitation, the river and its adjoining creeks are exposed to intense anthropogenic activities which include industrial, boat transportation, agricultural and domestic sewage disposal. The need to regulate and closely monitor all such activities in the river and its catchment area becomes imperative for natural attenuation and restoration of the aquatic ecosystem.

Keywords: bitumen, exploitation, impacts, water, sediment, quality, Kd