Phytoremediation works with the natural capabilities of plants to repair and regenerate toxic soils, groundwater and surface water. Plants can help bind, extract, transform and clean up many kinds of pollution including metals, pesticides, chlorinated solvents, polychlorinated biphenyls (PCBs), explosives, radionuclides and petroleum hydrocarbons. Plants clean up these forms of pollution as far down as their roots can grow. Plants also help prevent wind and rain from carrying pollution away from the site to other areas.
There are 6 different ways that plants help heal the land and deal with contamination:
Phytoextraction: Plants pull up contaminants – mostly metals and radionuclides – with their roots and accumulate them within their stems and leaves. Plants that are particularly good at doing this are called hyperaccumulators. It is important to note that if a plant is able to phytoextract contaminants such as metals and radionuclides, the plant waste itself may become toxic and needs to be disposed of appropriately.
Phytodegradation: Plants pull up and break down chemicals through the release of enzymes and through metabolic processes.
Phytovolatization: Plants take up volatile chemicals and release into them into the atmosphere through transpiration. The contaminant is either transformed within the plant into a less toxic state and then released into the air or it is released as is and then degraded by the sun.
Rhizodegradation: The root zones of certain plants create an environment that facilitates microbial remediation by providing the ideal habitat and food for some bacteria and fungi, which are able to bind and break down different contaminants.
Rhizofiltration: Some plant roots can filter contaminated water by adsorbing contaminants into their root and plant tissue. Similar to phytoextraction, plant matter may become toxic and must be tested and disposed of accordingly.
Phytostabilization: Plants can bind or immobilize contaminants by absorbing them into their roots and releasing a chemical that converts the contaminant into a less toxic state. This method limits the movement of contaminants through erosion, leaching, wind or soil dispersal. It is often referred to as a “green cap.”
Phytoremediation works best at sites with low to medium amounts of pollution. It is a low-cost, community alternative to many conventional and corporate land remediation practices. Instead of using excavators and dump trucks to remove tons of toxic soil and fill a site with new clean soil mined from elsewhere, on-site plants remove contaminants from the soil and store it within their plant tissues or bind them and/or break them down at their roots. In some cases, the plants themselves are then removed as toxic waste, while in other cases plants break down the chemicals and transform them altogether.