Ecological Risk Assessment of Crude Oil Impacted Farmland Soils: A Case Study of Ohaji/Egbema in Niger Delta, Nigeria

The study assessed the impact of crude oil on farmland soils in Ohaji Egbema. Farmlands used for this study are farms that were indirectly impacted through overland flow and acid rain. A total of 42 farmland soil samples were used for this study. The farmland soil samples were collected at a depth range of 0 - 10 cm using a hand trowel through random sampling. The samples were air dried for 72 hours before laboratory analysis for arsenic (As), nickel (Ni), chromium (Cr), cadmium (Cd) and lead (Pb). The results obtained show that heavy metals in farmland soils at different locations in Ohaji/Egbema varied in both concentration and trend. The observed trends at different locations are: Cd>As>Ni>Cr>Pb for Mmahu, Abaezi, Abacheke and Awarra while for Assa and Obitti, it is Cd>Ni>As>Cr>Pb. To establish the extent the farmland soils were polluted, contamination factor (CF), degree of contamination (Cd) and geoaccumulation index (Igeo) were applied. Results of the Cf showed that Ni, Cr and Pb had low contamination, As had moderate contamination while Cd had high contamination in the farmland soils with a range of 155.15 - 206.87 and Cd of 1242.72. The Igeo for Cd ranged from 31.13 to 41.52, an indication of extreme contamination. The associated potential ecological risks were assessed using potential contamination index (PCI), ecological risk factor (Eri) and ecological risk index (RI). It was found that Cd had PCI ranging from 155.22 - 198.51, Eri range of 4654.44 - 6206.11 and RI of 37311.56. This indicates that the farmland soils of Ohaji/Egbema are highly contaminated with Cd and exposed to severe ecological risk.