ABSTRACT
The effect of refined petroleum products on the activities of selected enzymes (catalase and dehydrogenase) was studied. There was a significant decrease (p < 0.01) in catalase activity. Catalase activity was higher in diesel and engine-oil treated soil after twelve days relative to petrol and kerosene. These observations indicate that the enzyme activity is the order of petrol > kerosene > diesel > engine oil. However, a significant increase (p < 0.01) was observed in dehydrogenase activity after twelve days relative to control values. Although, the refined petroleum products caused a similar pattern in the alteration of soil dehydrogenase activity, as they affected catalase activities, the general results indicate that the toxic effect is in the order of kerosene > diesel > petrol > engine oil. On the whole the results reveal that refined petroleum products alter soil biochemistry.