Bioremediation of petroleum-hydrocarbon contaminated soils using an ecosystem-based approach in the Yukon
by Kawina Robichaud
This 2-year bioremediation project started in May 2013. It aims to study the effectiveness of an ecosystem-based approach to cleanup hydrocarbon-contaminated soils using fungi, willow and compost. The project will also look at the degradation of chlorinated compounds and the bioaccumulation of heavy metals. The project is taking place at two locations in the Whitehorse, Yukon area. The contaminants are strictly diesel at one site. At the other, very high concentrations of a variety of petroleum hydrocarbons are present. Heavy metals and chlorinated compounds also happen to be present at this second site.
The goal is to create a system that has multiple biological elements working together in synergy, tackling different angles of the problem; like a small ecosystem. The organisms chosen are local native plant and fungi species. The ultimate goal is to develop a system that can be implemented and left in place, with the confidence that all it’s components working together will degrade the hydrocarbons in the soil and lead the path to the re-vegetation of the area.
Different combinations is be used at each site. At the first: oyster mushrooms (Pleurotus ostreatus) and Salix plantifolia (a willow species). At the second: turkey tail mushroom (Trametes versicolor) and Salix alaxensis (a willow species). Municipal compost is also used at both sites.
The main role of the fungi is to degrade the hydrocarbons. Fungi digest their food by secreting enzymes outside themselves and then they absorb the nutrients released. They are primarily interested in eating lignin (added to this project in the form of woodchips) but they will also digest hydrocarbon molecules as a secondary metabolic process. It’s a concept that makes sense when you consider that petroleum comes from plant matter that has been buried and pressurized underground for hundreds of thousands of years! The turkey tail mushroom has also been shown to degrade chlorinated compounds with its strong enzymes. Fungi will also increase soil integrity and attract beneficial insects. Compost improves texture, composition and nutrients in the soil as well as contributing beneficial microorganisms. Willows provide shade to help retain moisture and they bioaccumulate or immobilize some contaminants (like metals). They also prevent erosion, aid in the transportation of water, and host beneficial microorganisms in their roots that can help break down contaminants in the soil.
The benefit to using this system is that it doesn’t require any additional chemicals or fertilizers to break down pollutants. Conventional soil remediation usually requires petroleum-based fertilizers and fossil fuel burning machines to till and aerate the soil. It really doesn’t make a lot of sense if you look at the big picture of the total carbon cost and environmental footprint of such methods. Our growing season is also shorter in the North, and bioremediation techniques developed in the south may not be so easily transferable here. It’s important to develop our own techniques and solutions, using local native species, which are in harmony with our environment, climate and people.