Phytoassessment of an Enhanced Naturally Attenuated Oil-Polluted Soil after Exposure to Various Concentrations of Sodium Bicarbonate Solution

Abstract. The present study investigated the effects of sodium bicarbonate-induced soft water on the intrinsic qualities of a bioremediated petroleum hydrocarbon-polluted soil. this was also subjected to phytoassessment using African yam bean (Sphenostylis stenocarpa). Into already perforated buckets were measured 5kg sun-dried top soil (0-10cm). Waste engine oil (WEO) was added to soil and mixed thoroughly to obtain similar concentrations of 5 % w/w oil in soil. The entire setup was divided into 5 treatment sets, depending on the concentration of NaHCO3 solution used (0, 25, 50, 100 and 200mg/l). Each set was wetted daily with 200ml of different solutions for 3 months. Results showed significant reductions in heavy metal concentrations particularly in the 200mg/l of NaHCO3-wetted soils. Copper reduced to a range of 4.84 - 6.08mg/kg in the NaHCO3-wetted soil, compared to 9.32mg/kg in the control. However, total polyaromatic hydrocarbon (PAH) content of soil was lowest when the soil was wetted with 25mg/l NaHCO3 (96.43mg/kg), indicating a 90.51% efficiency, compared to the control with an efficiency of 79.15%. There were significant reductions in pollution indices (contamination factor, hazard quotient, toxicity equivalency factors, and probable effect concentration) used in the study; an indication that water softness positively impacted on the intrinsic remediation of the waste engine oil-polluted soil. Results of phytoassessment showed the improved plant growth and yield response in the oil-polluted soils upon addition of lower concentrations of NaHCO3 in soil. Grain yield per plant in the oil-polluted soil was 8.33g, compared to 29.29g in the control and 25.87g when oil-polluted soil was wetted with 25mg/l solution.