That sunflower in your backyard may be doing a whole lot more than you think.
Many seemingly ordinary plants are showing great promise in removing a wide range of pollutants from the environment through a decontamination process known as phytoremediation. Sunflowers may be the most striking example, but that list also includes such familiar plants as poplars, willows, ragweed, cabbages and even geraniums.
Phytoremediation capitalises on the inherent ability of plants to suck water, minerals, and other substances - including toxic ones - into their tissues from surrounding soil and water. In addition, plant roots exude enzymes which nourish the plethora of microorganisms living in their root zones. Those microorganisms have voracious appetites for any and all energy producing substances and toxins are no exception. This powerful combination of plants and microorganisms breaks down many pollutants and sequesters others, effectively removing them from the environment. The variety of contaminants that can be removed through phytoremediation is nothing short of mind-blowing. It includes pesticides, solvents, petroleum, explosives, leachates, radiation and heavy metals (including copper, zinc, nickel, iron, manganese, uranium and chromium). Sunflowers belong to a unique class of plants known as hyperaccumulators, which are ideal candidates for cleaning up large areas of contamination, particularly heavy metals, because of their ability to absorb up to one percent of their dry weight in heavy minerals. |
 Photo by: Vanessa Farnsworth |
In some cases, these plants are able to degrade the contaminants into less harmful molecules such as hydrogen, oxygen or carbon dioxide and can therefore be left growing in the decontamination zone long after the job is complete or they can be harvested and disposed of like any other plant. In cases where plants store pollutants they cannot break down, as is the case with heavy metals, they are removed and disposed of as hazardous waste. Trees that have absorbed contaminants can be left unharvested for many decades, giving scientists time to explore novel approaches to extracting these metals for future reuse.
Because it’s more cost-effective than traditional remediation methods and easier to implement, interest in phytoremediation has been picking up steam in recent years. It requires relatively little ongoing maintenance and can even beautify the area it's detoxifying, giving you something more interesting to look at than that gash in the landscape where a gas station used to exist.
Still, no one would ever accuse phytoremediation of being either a quick fix or a cure all. It can take anywhere from three to ten growing seasons for plants to clean up an area of light to moderate contamination and it is most effective when the contamination is located at or just below the soil surface where plant roots can easily access the pollutants.
However, results are promising. In 1994, the Sunflower Project was started in a desolate pond in Ukraine, just one kilometer from the disgraced Chernobyl nuclear reactor. Sunflowers grown on rafts in that pond were able to extract 95% of the radioactive strontium 90 from the water at a fraction of the cost it would have taken to remediate that pond by conventional methods. Plants are now being used to remediate the soil in other areas of the 30 kilometer dead zone that surrounds the reactor.
All of this is a long-winded way of saying that sunflower in your backyard may be more than just a pretty face.
If you have any questions or comments, please send them to me at vanessa@gardenmuse.ca.
