Abstract

Post flooded forest soil profile samples obtained near Afam power station, contiguous to Imo River were analysed for quantitative determination of polycyclic aromatic hydrocarbons (PAHs). Relatively moderate bulk density (1.17 g/cm³), permeability (1.79 cm³/s) and macro-porosity (60%) values indicate that fluid flow through the soil profile would be unimpeded. PAHs content for the top soil horizon appeared similar to that of one of the point-source samples suggesting possible transport via flooding event on 25^th April, 2008. Variation in PAHs content for the lower soil horizons may reflect a record of past PAHs deposition as a consequence of differences in Imo river current trajectory. The decreasing trends in the distribution of ∑thiophenes, ∑alkylPAHs and total PAHs (excluding perylene levels) may be associated with the sorptive character of soil organic matter (SOM) which limits transfer of PAHs deep into the soil. However, the relatively high level of perylene at the bottom soil horizon increases the likelihood of the compound to reach the shallow aquifer and contaminate the ground water. Utilization of six selected molecular ratios such as Fla/(Fla + Pyr) (0.20-0.70), Ant/(Ant + Phe) (0.22-0.41), BaA/(BaA + Chrys) (0.54-0.70), LMW/HMW (0.30-1.47), MPhe/Phe (0.72-1.59) and 1,7/(1,7 + 2,6-DMP) (0.57-0.90) enabled PAH source apportionment to be made. The results indicate a mixed source scenario with predominance of petroleum hydrocarbons input found for the top soil while the lower soil horizons were predominated by PAHs of combustion origin.

Key words: Molecular ratios, natural gas, petroleum condensate, soil, Imo River.