Assessment of heavy metal pollution in marine sediments receiving produced water, Delta State, Nigeria

Every aspect of oil and gas operations poses significant negative impacts on the environment in varying levels, these environmental impacts have economic and public health consequences on the indigenes of the operation locality. Produced water discharge is one of such aspects of the upstream oil and gas operation whose potential for environmental degradation has necessitated both local and international regulations for its governance. This research focuses on the environmental assessment of heavy metal pollution on marine sediments receiving treated produced water in Delta state, Nigeria. Sediment samples were obtained from produced water discharge area at various distances from the disposal point. Heavy metals (Cadmium, Zinc, Iron, Lead, Chromium, Vanadium, Barium, Nickel and Manganese) concentrations in the sediment were analyzed using Atomic Absorption Spectrophotometry method. In the sediment, manganese, nickel, chromium, lead, cadmium and zinc were detected in all the locations and showed no significant difference across the various locations. Barium and vanadium were detected in some location although no statistical difference was established across the locations. Iron concentration showed significant difference across the various locations. The results of heavy metals contamination factor in marine sediments ranged from low contamination to very high contamination (CF<1; 3 ≤ CF ≥ 6). High contamination values were recorded for vanadium (Location SD16, 21 and 22) and barium locations (SD8 and 21). The enrichment factor of heavy metals ranged from minimal to moderate, significant and very high enrichment. Barium, Nickel and Manganese showed the highest variation in enrichment factor. Other than cadmium and barium that showed moderate risk (40 ≤ Er <80) and very high risk (Er ≥ 320) at some locations respectively, the Ecological Risk Index of heavy metals based on the criteria for risk assessment showed low risk (Er<40) for most of the locations.   Key words: Assessment, environmental impact, produced water, pollution, heavy metal, contamination, sediments.