Migration Patterns of Petroleum Hydrocarbons across Soil Horizons in an Oil Spill-Affected Area of Mkpanak, Akwa Ibom State

This study investigated the vertical migration and contamination levels of total petroleum hydrocarbons (TPH) across the soil profile in Mkpanak Community, located in Ibeno Local Government Area of Akwa Ibom State, Nigeria. The objective was to assess the potential risk of groundwater contamination from surface petroleum pollutants, in alignment with baseline Environmental Impact Assessment (EIA) practices. Four sampling boreholes designated SP1, SP2, SP3, and SP4 were randomly established within the area affected by a documented oil spill. Soil samples were collected at 0.5-meter intervals down to a depth of 6.0 meters at each location. The samples were transported to the laboratory in labeled polythene bags, air-dried, ground, and sieved through a 2 mm mesh. Total hydrocarbon concentration was determined by extracting 10g of fresh soil with 20ml of toluene, followed by spectrophotometric analysis of the extract at 420 nm using a Supertonic 21-D spectrophotometer. TPH concentrations were calculated with reference to a standard calibration curve and adjusted for moisture content and dilution. Results revealed significantly high TPH concentrations at SP1, peaking at 40,645.00 mg/kg at 0.5 m depth, with a general trend of decreasing concentration with increasing depth. TPH values at 0.5 m for SP2, SP3, and SP4 were 3.38 mg/kg, 20.00 mg/kg, and 3.38 mg/kg, respectively. Spatial variation in TPH concentrations was notable: SP1 ranged from 3.38 to 40,645.00 mg/kg (mean 3710.65 ± 3083.36), SP2 from 3.38 to 80.00 mg/kg (mean 10.75 ± 5.87), SP3 from 3.38 to 190.00 mg/kg (mean 36.58 ± 16.21), and SP4 from negligible levels up to 105.00 mg/kg (mean 11.64 ± 7.90). The findings confirm that the soils in Mkpanak Community are significantly contaminated with petroleum hydrocarbons. This contamination, primarily a result of crude oil exploration and pipeline vandalism, poses considerable environmental, health, and socio-economic risks. The study highlights the urgent need for public awareness campaigns on the adverse impacts of oil pollution and calls for the implementation of robust mitigation and remediation strategies