Innovative Use of Earthworms for the Remediation of Soil Contaminated with Crude Oil

Abstract

Crude oil soil contamination is widespread, and due to the complex chemical nature of crude oil, remediation can be expensive and challenging. Crude oil that remains in soil for long periods of time can become sequestered in the soil matrix and become difficult to biodegrade. Heavier, more complex hydrocarbons are persistent in the environment due to resistance to biodegradation, which makes remediation problematic. Earthworms ingest soil, exposing it to intense physical and chemical processes and can increase soil microbial activity and therefore are promising candidates for enhancement of crude oil bioremediation. I examined if different earthworm species could tolerate and degrade crude oil. Toxicity tests established that Eisenia fetida and Apporectodea caliginosa were crude oil tolerant and suitable for use in crude oil degradation experiments. Two primary degradation experiments were performed. In the first, laboratory made soil was mixed with crude oil at concentrations of approximately 30,000 mg/kg, with and without the addition of a microbial inoculum consisting of contaminated, native soil from an active remediation site. Petroleum degradation was examined in the presence and absence of E fetida. This experiment measured the importance of a hydrocarbon adapted microbial community to crude oil degradation rates. In the second, petroleum degradation in the contaminated, native soil from the remediation site was examined in the presence and absence of the E. fetida and A. caliginosa. The second experiment measured the effectiveness of earthworms on real-world soils that had weathered in the field for several decades. In the first degradation experiment, petroleum concentrations declined significantly (p<0.01) in the presence of E. fetida compared to controls. After 342 days, concentrations declined by 56% without the microbial inoculum and 63% with the microbial inoculum. Heavier and more complex hydrocarbons were more resistant to degradation. In the second experiment, petroleum concentrations declined by approximately 93% in the native soil in the presence of each of the worm species, significantly more than the declines observed in the controls. The results of these experiments show that earthworms accelerate degradation of crude oil and are a promising candidate for the enhancement of crude oil bioremediation (vermiremediation).