Impact evaluation of crude oil spills on surface water, sediment and fish in oil-producing communities of the Niger Delta, Nigeria

Crude oil spills remain frequent in the Niger Delta, yet post-spill studies rarely rate contamination to prioritise clean-up. This study evaluated surface water, sediment and fish at ten spill-affected stations in Delta, Bayelsa and Rivers States, Nigeria, with the Agbarho River as reference. Water was analysed in triplicate for physicochemical parameters, total petroleum hydrocarbons (TPH) by gas chromatography, and Pb, Cu, Cr, Fe and Zn by flame atomic absorption spectrophotometry; TPH was also determined in sediment and in dead African catfish ( Clarias gariepinus ). Contamination was scored on a five-point impact-magnitude scale from the departure of mean TPH from regulatory limits. Surface-water TPH ranged from < 0.001 to 97.6 mg/L and exceeded the 10 mg/L benchmark only at Okerenkoko and Santa Barbara, where crude oil was visible. Sediment TPH reached 21,550 mg/kg at Okerenkoko, over four times the national intervention value of 5,000 mg/kg, and 1,740 mg/kg at Santa Barbara, but was within the 50 mg/kg target elsewhere. Fish from Okerenkoko contained 58,334 mg/kg TPH, against 0.39–0.43 mg/kg at two other stations. Dissolved oxygen (1.40–5.80 mg/L) declined as TPH increased (Spearman ρ = −0.73, p = 0.017). Iron and chromium exceeded their limits at several stations and at the reference river without correlating with TPH, pointing to catchment-wide sources. Impact evaluation rated surface water high at Okerenkoko and medium at Santa Barbara, and sediment severe at both; all other stations were within limits. Both stations need active remediation of water and sediment; all stations need continued monitoring.