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Researchers are using plants to tackle urban pollution

The City of Montreal has partnered with university researchers in a major project to decontaminate an old industrial site through vegetation.


Plants in their many different forms have yet to reveal all their secrets. For several years now, Michel Labrecque, a botanist and adjunct professor at Université de Montréal – also a member of the university’s plant biology research institute (known by its French acronym IRBV) – has been studying the ability of vegetation to filter contaminants. Over the past two years, under his leadership, a multidisciplinary team of researchers has been working on a major phytoremediation project funded by the City of Montreal. This technique makes use of a combination of plants and soil microorganisms to clean up contaminated soil or water. Plants remove pollutants from the soil or water, then absorb them into their tissues where they are stored or broken down.

A purification garden

Although this decontamination technique has been around for years, it’s the first time that the City of Montreal has actively invested in it. “This project is the most extensive and the most promising; the site is also the largest in Canada,” says Dr. Labrecque. The grant from the city has been used to create a purification garden that will cover four hectares by the project’s end in 2019. On this industrial site in Montreal’s East End, the multidisciplinary research team is trying various plant groupings to identify and analyze which combinations are the most effective in decontaminating the soil.

“We are also assessing various combined approaches, like seedlings or cuttings, which increase microorganism activity in the soil,” notes the researcher.

A collaborative effort

A team of researchers from McGill University and Université de Montréal recently published the results of a genetic analysis of interactions between fungi, bacteria and fast-growing tree roots (such as willow roots) in the Microbiome journal. “We were trying to figure out how to make plants and microorganisms more efficient in rejuvenating soils contaminated by oil,” explains Dr. Labrecque, who co-authored the article.

Decontamination through phytoremediation takes much longer (five to 10 years) than the standard dig-and-dump approach, where the soil from contaminated land, or brownfields, is excavated and sent to a landfill elsewhere. “But it costs a lot less to use plants,” he maintains, pointing out how they improve urban quality of life through the greening of often abandoned industrial areas.

Better protection of trees

Planting strategies may be more desirable for cleaning up contaminated soil, but it is also important for the city to protect its existing tree stock. The latest book by researcher Jeanne Millet, Arbres sous tension, advocates for a change in the way that trees growing near or under power lines are pruned. “Trees play a very important role in purifying city air. To be effective, their canopies must be very tall,” explains Ms. Millet, who conducted her research over a span of 20 years at IRBV.

Dr. Millet noted that in recent years the maintenance of trees has been left to Hydro-Québec. “My research on tree architecture has shown that the currently recommended practices for trimming trees can have a reverse effect to what was intended.” Trees that are kept short around power lines become weak, break easily and end up causing problems.

Pierre Bourque, ex-mayor and former director of the Montreal Botanical Garden, in a preface to Dr. Millet’s book, underscores the importance of trees in urban environments and the need to better understand their growth. “Jeanne Millet’s work is very important. We are all doing our part to help improve urban living conditions.”

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