Chemical Evaluation of Petroleum Sludge Impacted Soils from Itsekiri Communities around Warri Refinery, Delta State, Nigeria

Effluents from petrochemical operations are generally considered to be harmful to the environment particularly due to their accumulated levels of petroleum hydrocarbons which distort the properties of the habitat immediate to such facilities. This study was undertaken to compare and appraise the petroleum hydrocarbon constituents from oily sludge discharge as well as changes in the physicochemical composition of soils within an 8.5 km radius from Warri refinery in Delta State, Nigeria. Data obtained revealed an almost identical acidic soil environment (5.31 – 5.54) to that of the contaminating sludge (5.25) unlike that of the control (7.81). The overall levels of sulphate (412.73 – 465.13 mg/l), electrical conductivity (0.44 – 0.57 µs/cm), organic carbon (10.02 – 18.22%), oil and grease (96077 – 587642 mg/kg) were observed to be higher across all tested soil samples in comparison to that of the control sample; 56.73 mg/l, 0.26 µs/cm, 4.25%, 1032 mg/kg in that order while that of the total nitrogen (0.08 – 0.44%) and phosphorus (8.72 – 12.40% ) were low compared to the control (0.87, 15.62)% respectively. The total petroleum hydrocarbon (TPH) content ranged from 48063 – 293846 (mg/kg) across the 5 tested sampling sites with the sludge sample having 686615.6 mg/kg whilst that of the control was found to be averaging 651 mg/kg as detected via GC-FID. The Polycyclic aromatic hydrocarbon (PAH) values ranged from 189.93 – 4255.87 (mg/kg) across the 5 tested sites with that of the sludge being 13648.33 mg/kg while the control site exhibited a 68.06 mg/kg PAH concentration as detected via GC-MS. Dibenzothiophene was also detected with values ranging from 3167.31 – 19001.84 mg/kg which was very high compared to other hydrocarbons. The risk assessment of the soil quality conducted indicated that all the studied sites were seriously contaminated but the level of contamination was a function of proximity of each site to the refinery. The presence of oily sludge due to the operational activities at the refinery resulted in change of known physicochemical properties of the soil which undoubtedly distorted the natural fauna and flora in the affected sites.