Changes in Antioxidant Enzyme Activities in Allium cepa Roots Cultivated in Crude Oil Contaminated Soil

A study was carried out to evaluate the changes in Superoxide dismutase (SOD) and Glutathione peroxidase activities (GPx) in Allium cepa roots exposed to crude oil. Crude oil used in this study was fractionated in water (ratio 1 to 2) to produce water-soluble fractions (WSF) and water insoluble fractions (WIF). Allium cepa was grown in soil treated with 2%, 5%, 10% or 20% of Whole Crude (WC), WIF or WSF for 14 days, while the control was with distilled water. Antioxidant enzyme activity was evaluated after treatment for 14days using standard protocols. The result showed that there was a significant increase in SOD activity at higher concentrations for WSF and WIF treated plants. However, there was a decrease in SOD activities at 10% concentration and no root sprout was seen at 20% concentrations for WC treated plants. On the other hand, GPx activity increased at significant levels at 20% concentration for WSF while significant changes were observed in plant treatments with WIF and WC at lower concentrations. Results from this study suggest that soils contaminated with varying fractions of crude oil could portend great risk for plants, animals and humans in general.