Determination of Total Petroleum Hydrocarbon Levels in Surface Soils Near Petroleum Filling Stations in Warri, Delta State

Petroleum filling stations are established point sources of hydrocarbon contamination in urban environments, with spills and leaks frequently contaminating adjacent soils through direct contact and subsurface infiltration. This study determined total petroleum hydrocarbon levels in surface soils collected from the vicinity of petroleum filling stations in Warri metropolis, Delta State, South South Nigeria. Soil samples were collected at distances of 0, 5, 10, and 20 metres from the pump islands of twelve selected filling stations, yielding a total of forty-eight sampling points. Extraction of total petroleum hydrocarbons was performed using n-hexane in a Soxhlet extractor, and quantification was carried out gravimetrically. Soil texture, pH, organic matter content, and total organic carbon were also determined. Total petroleum hydrocarbon concentrations at 0 m distance ranged from 4,840 to 18,730 mg/kg, all substantially exceeding the Nigerian Department of Petroleum Resources intervention threshold of 5,000 mg/kg for residential soils. Concentrations decreased significantly with increasing distance from pump islands. Older filling stations with fuel spillage histories showed higher contamination levels. Total organic carbon was positively correlated with total petroleum hydrocarbon concentrations, reflecting hydrocarbon contributions to the soil organic fraction. Sandy textured soils exhibited deeper hydrocarbon penetration profiles. The study underscores the need for mandatory containment measures at filling stations in Nigeria and recommends bioremediation as a practical intervention strategy for impacted soils in Warri.

Keywords: total petroleum hydrocarbons, soil contamination, filling stations, Warri, Delta State