Honey locust (foreground) have been shown to accumulate lead and be tolerant of de-icing salts while grasses such as big bluestem (background) can help degrade petroleum products.

Phytoremediation is a method of using plants and other biological processes in the soil to detoxify a polluted site.  The method is often less costly than conventional methods of treatment that employ chemicals or relocation of contaminated materials.  Treatment of contaminated soil by plants has been evaluated for pollutants including petroleum hydrocarbons, heavy metals, nutrients, radionuclides, explosives, and more.

Non-point source pollutants such as oil, grease, and heavy metals are just a few contaminants that would be of concern near roads and parking lots.  The ability of plants to detoxify a site contaminated by petroleum hydrocarbons can occur through degradation, containment, or volatilization processes.

  • Degradation processes include the breakdown of harmful pollutants into less harmful substances such as alcohol, acids, carbon dioxide, and water (Ndimele 2010; Eweis et al. 1998).  The degradation process occurs through enhanced microbial activity around plant roots due to the improved surface area, oxygen, and nutrients in the rhizosphere.
  • Containment of petroleum hydrocarbons by plants can be through the direct uptake of pollutants into plant tissues or the indirect binding of contaminants to soil organic matter due to enzymes provided by plants.
  • Volatilization is a process in which plants take up toxic compounds through their roots and transpire those toxins through their leaves into the atmosphere.

 The phytoremediation processes for some plants that are commonly found in the Southwest can be seen in a diagram below.

There are multiple methods of addressing stormwater pollutants including extraction, stabilization, degradation, and volatilization.