Environmental Impact of Oil Spills on Coastal Sediments in Ondo State

Repeated oil spill incidents along the Ondo State coastline in the South West geopolitical zone of Nigeria have adversely altered the physical and geochemical character of coastal sediments, affecting aquatic biodiversity and the livelihoods of fishing communities. This study investigates the environmental impact of oil spills on coastal sediments in Ilaje Local Government Area of Ondo State, where offshore oil infrastructure and artisanal refining activities have historically released significant hydrocarbon volumes. Sediment samples were collected from three contaminated transects and one reference site at low tide, with samples retrieved at two depth intervals to capture both surface and subsurface contamination. Total petroleum hydrocarbons and polycyclic aromatic hydrocarbon concentrations were determined by gas chromatography-mass spectrometry. Grain size analysis provided evidence of physical alteration in contaminated zones, while redox potential and acid volatile sulphide measurements were used to assess changes in sediment geochemistry. A contamination index based on individual polycyclic aromatic hydrocarbon ratios was applied to distinguish petrogenic from pyrogenic hydrocarbon sources. The study finds persistent polycyclic aromatic hydrocarbon contamination to a depth of twenty centimetres in the most heavily impacted sites, indicating limited natural attenuation since the last documented spill event. Findings are forwarded to the Ondo State Environmental Protection Agency and the National Oil Spill Detection and Response Agency. Keywords: oil spill, coastal sediments, polycyclic aromatic hydrocarbons, Ondo State, environmental contamination.