Want Cleaner Soil? Plant a Tree.

You may know that the leaves of plants act as natural air purifiers, taking in carbon dioxide and emitting oxygen through a process called photosynthesis. You may not know that their roots can provide a similar function within contaminated soil. Through a process called phytoremediation, plants called hyperaccumulators naturally store (through bioaccumulation) or break down contaminants in soil, sediments, groundwater, and surface water. Plants with this ability can soak up metals, pesticides, solvents, explosives, crude oil, and other kinds of toxic wastes in an energy efficient and aesthetically pleasing process. They also prevent wind, rain, and groundwater from carrying the pollution elsewhere.

Phytoremediation has numerous advantages. First of all, it costs much less than traditional cleanup measures like soil replacement and groundwater pumping. Additionally, whereas these methods merely transport the problem to another location, phytoremediation allows the soil to be purified so that it may be used again. Furthermore, by allowing plants to do most of the work, remediation occurs without subjecting workers to the health hazards of toxic waste cleanup. Ultimately, it is much less disruptive to the environment than traditional methods at a much lower price. However, phytoremediation is not without its drawbacks.

The process is dependent on many different factors, such as depth of the roots and the concentration of the contaminant in the soil in relation to the tolerance of the plant absorbing it. Also, if the material is absorbed and held in the plant’s leaves, this could pose a danger to animals or humans who may harvest or eat the plant. It requires close monitoring. The biggest variable, however, may be time. As compared to some traditional measures of remediation, phytoremediation can take a long time. This depends on the type of plants used, number of plants used, the size and depth of the polluted area, and the type of soil among other factors. It often takes many years to clean up a site with phytoremediation.

Nevertheless, the disadvantages should not prevent phytoremediation from being considered a viable cleanup option. It can be a highly useful method, especially if time is not a factor. For instance, if land on which a lead paint factory once sat were targeted to build a park, phytoremediation would be an ideal solution if lead were found in the soil. Sunflowers have proven to be excellent hyperaccumulators, especially for lead. They are so effective that they were successfully used to clean up radioactive soil in Chernobyl after their nuclear disaster. Other potent hyperaccumulators include hydrangeas (aluminum), Blue Tongue (aluminum), water hyssop (lead, mercury, cadmium, and chromium), and willow trees (cadmium, zinc, copper), among many others.

Although phytoremediation, by itself, may not always prove to be the most practicable option, it should at least be considered as a compliment to traditional methods of hazardous waste cleanup. Many remediation projects use plants after soil replacement to eliminate remaining trace contaminants in the soil. All that remains then of the once polluted land are plants and trees. Much in the same way plants purify our atmosphere, they can be equally useful in cleaning up the earth under our feet.

-Kyle Johnson, Legal Intern