Sediment Quality of Orashi River at Four Oil Producing Communities of Nigeria

Bed Sediment samples were collected in the Dry Season from Orashi River at three sampling sites each located in Mmahu, Opuoma, Abacheke and Ogwu Aniocha communities. Physicochemical parameters, hydrocarbon and heavy metal (As, Cd, Fe and Pb) concentrations were determined with standard methods. Results showed that total petroleum hydrocarbon (TPH) ranged from 0.11 ±0.03 to 1.91 ±0.25 mg/kg while total hydrocarbon content (THC) and oil and grease had ranges of 0.28 ±0.06-2.98 ±0.19 and 0.69 ±0.09-3.60 ±0.57 mg/kg respectively. The sediment samples were classified as unpolluted in terms of TPH. Mean values for pH had a range of 4.33 ±0.22 - 6.60 ±0.52 while the texture of most samples was sandy. Mean organic carbon contents ranged from 0.58±0.07 to 3.15±0.66 % and mean total nitrogen and total phosphorus had ranges of 0.30±0.00 -2.77±0.46 and 17.34±1.65 - 29.48±1.63 mg/kg respectively. Mean Mg concentrations were significantly higher (P<0.05) than the concentrations of other exchangeable bases and mean As concentration had a range of 1.175±0.086-1.291±0.335 mg/kg. Mean Cd concentrations ranged from 0.948±0.072 to 3.120±0.131 mg/kg while mean Fe and Pb concentrations had ranges of 57.324±10.530-159.707±41.192 and 1.300±0.295-7.462±0.861 mg/kg respectively. As and Pb values were lower than the sediment quality guidelines (SQG) but Cd values were higher than the guidelines in all sites. Contamination factors (CFs) for As and Pb indicated low contamination while CFs for Cd indicated moderate to considerable contamination. Geo-accumulation index (Igeo) values for As and Pb at all sites and that of Cd at one site indicated unpolluted, Igeo values for Cd at all other sites ranged between 0.210 and 1.571 indicating unpolluted to moderately polluted status.