What is it?

A contaminated site must often be restored before reuse. This presents a major challenge as conventional methods of decontamination are costly and sites are generally neglected for years.

What if nature had the solution?Research has given rise to a number of phytoremediation methods, which involve the use of plants and associated microorganisms to eliminate, contain or reduce the toxicity of environmental contaminants.

What is it used for?

In Quebec, over 6,000 contaminated sites have been identified! They include former landfill, industrial and mining sites, snow dumps, military lands, sewage sludge spreading operations and more. Phytoremediation can be a big part of the response to this environmental, economic and social problem:

  • It is roughly ten times cheaper than conventional decontamination methods based solely on engineering principles.  It does not require any transportation of contaminants because the plants do their work on-site.
  • It can generate biomass, which can then be used to produce compost, mulch and wood for a variety of purposes.
  • It can also produce value-added products like ethanol, a second-generation biofuel, and other bioproducts.

However, phytoremediation requires time and can only be used to remediate moderately polluted sites where plants are still able to grow.

How is it made?

The plants introduced to these contaminated sites act on several fronts:

  • They remove certain contaminants from the soil and accumulate them in their aerial tissues, which can then be collected.
  • They immobilize soil contaminants and prevent them from dispersing into surface and ground water.
  • They break down the pollutants locked in their tissues or release them into the atmosphere.

Phytoremediation can be effective on both organic contaminants (like hydrocarbons) and inorganic contaminants (like heavy metals and fertilizer residue).

In Quebec

A number of phytoremediation projects have been launched in recent years. One of them was successfully carried out in Varennes, in southern Quebec, by the petrochemical company Pétromont. Willow plantations helped reduce the level of certain pollutants on this contaminated site. What’s more, the harvested shrubs are used as fuel for the CRH Canada cement plant in Joliette. This is a wonderful example of “circular economy.” Unlike a linear economy, which generates waste in the process’ final stage, a circular economy recovers waste and reuses it as raw material. As a result, it is a “zero-waste” or even carbonneutral economy: one that captures as much greenhouse gas as it gives off.

Photo : Michel Labrecque

In the world

One example comes from Brazil, where abandoned gold mines are leaking mercury and other heavy metals into the soil and water. Mercury is one of the most toxic of heavy metals, and once in the soil it is soaked up by grass, which is eaten by cows, which are eaten by … humans. Farmers are now growing maize and canola plants in the area, which soak up heavy metals quite nicely – gold as well as mercury. One scientist overseeing the project estimated farmers could get a kilogram of gold per hectare from doing this, which would help pay for the clean-up.

Mustard greens were used to remove 45% of the excess lead from a yard in Boston to ensure the safety of children who play there. Pumpkin vines were used to clean up an old Magic Marker factory site in Trenton, New Jersey, while Alpine pennycress helped clean up abandoned mines in Britain.1 As for sunflowers, they are used to absorb radioactive metals in the Fukushima region of Japan2

A New Zealand researcher proved that the cost of using plants to decontaminate a mine in Amazonia was the same as the cost of using the conventional method of dig and dump to decontaminate a mine in Australia.3

Photo : Christopher Anderson

Phytotechnology cost to decontaminate the Agarape Bahia mine in Amazonia: $7K US per hectare in 2004.