This study focuses on the bioremediation of soil contaminated with motor oil. Laboratory investigations were conducted to determine the ability of macro-organism's (i.e., earthworms) survival in soil contaminated with motor oil, and the role of macro-organisms in the contaminated soil (i.e., exposure to high toxicity in the soil). The soil was contaminated with two types of car motor oil, one with used motor oil from cars and the second was the pure car motor oil (i.e. was not used prior) in different concentrations [0% (i.e. control), 1 %, 3 %, 5 % and 10 % by weight contamination]. The soil parameters such as soil moisture %, carbon %, nitrogen %, pH, Eh, organic matter (OM) % and C/N ratio, were measured before and after contamination. Water content was maintained during incubation by making additions as determined from reweighed containers. Four worms (Lumbricus terrestris) were inoculated in each jar of the experiments. The length of the experiments was 30 days. The data of earthworms’ survivability were measured each day. Motor oil content between 1-5 % was not harmful to the survival of earthworms for 30 days but oil concentration of 10 %, increased mortality rate by 75 % in pure motor oil and 45 % in used motor oil. Further, there was a significant difference in survivability of earthworms in used and pure motor oil. Used motor oil can support the survivability of earthworms better than pure (i.e. unused motor oil) motor oil. The properties of the soil at the end of the experiment showed an average reduction of 5 % carbon content, which indicated that the earthworms could consume the organic carbon with the support of micro-organisms in their digestive system. It was concluded that macro-organisms could be used for soil cleanup and restoration but that, Soil contamination of motor oil above 5 % might not allow for a similar process.
Key words: Bioremediation technology, Earthworms, oil spills.