Restoring Balance

I am continually amazed and inspired at the virility of plant material with  its ability to grow in the most uninhabitable places and thrive. Plant life improves our lives on so many levels and has now come to clean up after us in the form of phytoremediation. This process takes advantage of a plants' natural ability to absorb, accumulate, or metabolize contaminants from the soil or other media in which it grows. It has shown it is particularly effective in the clean up of pesticides, metals, crude oil and contaminants that leak from landfill sites.

When the plants have absorbed and accumulated contaminants, they can be harvested and discarded. If organic chemical contaminants are degraded into molecules like water and carbon dioxide, the plants may not require any special method of disposal. Controlled incineration is the most common method used to dispose of plants that have absorbed large amounts of contamination. For plants that have absorbed metals, controlled incineration produces ashes with a high metal content. Researchers are working on methods to recover the original metals from these ashes. Since phytoremediation is a technology still in the early stages of development, many disposal and metal recovery methods are still being explored. These methods include sun-drying and composting.

Common vegetation used for phytoremediation in North America and their targets.

Alnus glutinosa (Black alder) Target = Bitumen and tar
Festuca rubra (Red Fescue) Target = Crude Oil
Panicum virgatum (Switchgrass) Target = Pyrene
Lolium multiflorum (Annual ryegrass) Target = Diesel

Images courtesy of Josh Jackson

In order for a technology to be sustainable, it should be economically viable and environmentally compatible. Phytoremediation uses the existing capabilities of plants and the systems they support to clean up soil and water. It is more cost-effective than traditional remediation methods for contaminated soil, which involve digging up the entire contaminated area and taking it away to another location for chemical treatment, incineration, or burial. With these advantages the process does come without its drawbacks. Depending on the concentration of contaminants in the soil the process can take upwards of 5-15 years to fully remediate a given piece of land. Phytoremediation works best when the contamination is within reach of the plant roots, typically three to six feet underground for herbaceous plants and 10 to 15 feet for trees. The fact is phytoremediation takes less labour and does not disturb the natural surroundings of the contamination site. Although this style of soil remediation takes time, it is a good way to make use of naturally existing resources.