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Phytoremediation

What Is Phytoremediation?
This is a process using plants to clean up pollution in the environment. It is most effective when the site has low to medium amounts of pollution.

Plants can help clean up many other kinds of pollution including metals, pesticides, explosives, and oil.3 Plants grown for phytoremediation can also help keep harmful chemicals from moving from a polluted site and into other areas by limiting the amount of chemicals that can be carried away by blowing wind, by rain soaking into the soil and by surface water flowing off the site.

How Does it Work?
Some plants can remove harmful chemicals from the ground when their roots take in water and nutrients from groundwater, polluted soils or streams. Once collected inside the plant, the pollutants can be:

  • Stored in the roots, stems, or leaves.
  • Changed into less harmful chemicals within the plant.
  • Changed into gases that are released into the air as the plant transpires (breathes).

Phytoremediation can occur even if the polluting chemicals are not taken up by the plant. For example, these chemicals can stick (sorb) to plant roots or they can be changed into less harmful chemicals by enzymes and organisms that live both near and upon the plant roots (Bioremediation).

Plants can clean up chemicals as deep as their roots can grow. Tree roots grow deeper than smaller plants, so they are used to reach pollution deeper in the ground.

How Do You Dispose of Phytoremediation Plants?
Some plants metabolize contaminants so the material is no longer a biohazard. These plants can continue to grow or be composted.

Plants that do not metabolize the toxic metals they take up (i.e., lead, cadmium, arsenic, ect) can be smelted for recovery and recycling.1 If there are no recycling opportunities, the plants have to be disposed of in a safe manner. They must not be used for animal or human consumption, burned nor use as mulch. They are toxic waste and must be treated as such.

Is Phytoremediation Effective for Lead?
In the natural setting, lead hyper-accumulating plants (those that can absorb toxins to a greater concentration than that in the soil in which it is grown) has not been documented. However, certain plants have been identified with the potential to uptake lead from soil.2 Many of these plants belong to the following families:

  • Brassicaceae
  • Euphorbiaceae
  • Asteraceae
  • Lamiaceae
  • Scrophulariaceae

Brassica juncea, commonly called Indian Mustard, has been found to have a good ability to transport lead from the roots to the shoots, which is an important characteristic for the phytoextraction of lead.2

How Long Does Phytoremediation Take?
The time it takes to clean up a site using phytoremediation depends on several factors:

  • Type and number of plants being used.
  • Type and amounts of harmful chemicals present.
  • Size and depth of the polluted area.
  • Type of soil and conditions present.

These factors vary from site to site and plants may have to be replaced if they are destroyed by bad weather or animals. This adds time to the cleanup. Generally, it takes many years to clean up a site with phytoremediation.

Is Phytoremediation Safe?
Before phytoremediation begins, the EPA studies whether plants grown to clean up pollution can be harmful to people. The EPA tests the plants and the air to make sure plants are not releasing harmful gases into the air.

Some insects and small animals may eat the plants used for phytoremediation. Scientists are studying these animals to see whether the plants can harm them. Scientists are also studying whether these animals pose harm to the larger animals that eat them. In general, as long as phytoremediation plants are not eaten and disposed of properly, they are not harmful to people.

References
  1. Pytoremediation, Center for Public Environmental Oversight, www.cpeo.org, retrieved October 16, 2014
  2. Introduction to Phytoremediation, U.S. Environmental Protection Agency, Office of Research and Development, Cincinnati, OH. Agency (USEPA). 2000, EPA 600/R-99/107.
  3. Phytoremediation of Soils Using Ralstonia Eutropha, Pseudomas Tolaasi, Burkholderia Fungorum, Sofie Thijs