Nature’s way of cleaning contaminated soils

The next time you think of pulling that mushroom out of your lawn or garden, consider that it might actually be doing your garden a favour. There's growing evidence that mushrooms can break down contaminants, like petroleum products, in soil.

The next time you think of pulling that mushroom out of your lawn or garden, consider that it might actually be doing your garden a favour. There’s growing evidence that mushrooms can break down contaminants, like petroleum products, in soil.

A Yukon researcher is currently testing this theory to see how well fungi can remediate tainted soil, particularly in the North. The Cold Climate Innovation at the Yukon Research Centre recently received funding from the Natural Sciences and Engineering Research Council of Canada to study natural methods of soil remediation.

Researcher Kawina Robichaud has set up two test sites in the Whitehorse area, one of which is contaminated by diesel and another contaminated by a mixture of petroleum hydrocarbons, heavy metals and chlorinated compounds. In addition to planting mushrooms, the graduate student is also testing the efficacy of willow and compost at both of these sites.

Robichaud says the idea for the experiment came from a desire to use an ecosystem-based approach to remediate land. “Nature has had four billion years to find a way to breakdown contaminants like petroleum hydrocarbons and other problematic molecules. I believe solutions are out there and we just need to observe them,” she says.

The University of Montreal student has long been intrigued by what fungi can do. “Mushrooms are a very interesting form of life. They’re more closely related to animal than they are to plants; they breathe in oxygen and release carbon dioxide just like us,” she says. Fungi digest hydrocarbon molecules outside their bodies and then use the broken molecule’s atoms as food. The resulting compounds become part of the mushroom’s tissue and are no longer toxic. The mushroom is theoretically safe to eat at this point, says Robichaud – although she says she won’t be eating any of her test mushrooms because they need to stay there as part of the experiment and they have been exposed to potentially contaminated dust from the area.

Robichaud adds wood chips to the soil in order for this metabolic process to take place. Mushrooms break down hydrocarbons as a secondary metabolic process. Fungi are primarily interested in “eating” wood but will also digest hydrocarbon molecules in the process because it resembles wood molecules, says Robichaud. 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.

Willows and compost have their own particular benefits, says Robichaud. Compost improves texture, composition and nutrients in the soil while willows prevent erosion, aid in the transportation of water and host beneficial bacteria and fungi in their roots that can help break down contaminants in the soil. There is evidence that the tip of the rhizosphere – the region of soil in the vicinity of the roots – can even break down DDT, a particularly harmful insecticide, which accumulates in the environment and is difficult to get rid of. Together the fungi, compost and willow tackle different angles of the problem, which starts to resemble how a small ecosystem would function, says Robichaud.

Although not commonly used in Canada, these so-called natural soil remediation or bioremediation methods are starting to gain traction around the world. The benefit to using mushrooms, willow and compost is that they don’t require any additional chemicals to break down pollutants, says Robichaud. Conventional soil remediation usually requires petroleum-based fertilizers and fossil-fuel burning machines to till and aerate the soil often. “It’s a process that doesn’t make a whole lot of sense if you look at the big picture and total carbon cost,” she says.

Robichaud has created several different scenarios to test the efficacy of each of these decontaminates. She’s set up 42 separate bins of diesel-contaminated soil at Arctic Backhoe’s land treatment facility. Arctic Backhoe donated the soil and land for the experiment.

The researcher wants to know how well willow, mushroom and compost can break down contaminants on their own as well as when they’re mixed together in different combinations. For this test site, Robichaud has chosen to use oyster mushrooms, which are edible and native to the Yukon. She’s also adding conventional fertilizer to some of the bins as well as leaving a number of the bins untouched to compare the data to.

Her second test site, which is behind the city of Whitehorse landfill, was originally a waste oil pit from the ‘70s, dumped on the waste rock of an old copper mine. It’s a cocktail of contaminants that includes oil, lubricants, dry-cleaning chemicals and heavy metals. “The city has tried different remediation tactics on the land but so far the results have been inconclusive. And trying to haul out that enormous volume of contaminated material would be way too expensive, and just displacing the problem,” says Robichaud, who is working with the city and Boreal Composting Enterprises on this site.

As at her other site, Robichaud is using different combinations of willow, compost and mushrooms to break down mixed contaminants. Instead of the oyster mushroom, however, the researcher is using another native, medicinal species: the turkeytail mushroom. “The turkeytail mushroom has shown success in degrading chlorinated compounds. It’s a very aggressive mushroom and I’m hoping it works well on this slew of mixed contaminants,” she says.

Over the next year, Robichaud will visit, take samples and monitor plant health from both of her test sites to see how effective these bioremediation techniques are. As far as Robichaud is aware, it’s the first time that willow, mushrooms and compost have been used in combination to tackle contaminated sites.

It’s an experiment that is particularly interesting to the North, says Robichaud. “Our growing season is shorter in the North. It’s important to develop our own solutions, using local species, to apply to our environment and climate.”

In addition, if the results of the experiment are a success, it might just mean that a northern idea may spread to the rest of Canada. “If we can prove this method up here, then there’s a greater likelihood scientists will apply this technique down south as opposed to the other way around,” she says.

This column is co-ordinated by the Yukon Research Centre at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at www.yukoncollege.yk.ca/research/publications/newsletters_articles.

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