Phytoremediation is a form of bioremediation
and applies to all chemical or physical processes that involve plants for degrading or immobilizing contaminants in soil and ground water. While the technology is not new, current trends suggest its popularity is growing. The following is a list of six different types of phytoremediation with explanations describing how they work.
Also called phytostabilization
. Many different processes fall under this category which can involve absorption by roots, adsorption to the surface of roots or the production of biochemicals by the plant that are released into the soil or ground water in the immediate vicinity of the roots, and can sequester
, precipitate, or otherwise immobilize nearby contaminants.
2. RhizodegradationThis takes place in the soil or ground water immediately surrounding the plant roots. Exudates from plants stimulate rhizosphere bacteria to enhance biodegradation of soil contaminants.
3. PhytohydraulicsUse of deep-rooted plants (usually trees) to contain, sequester or degrade ground water contaminants that come into contact with their roots. In one example of this, poplar trees were used to contain a ground water plume of methyl-tert-butyl-ether (MTBE) (Hong et al. 2001. Environmental Science and Technology 35(6):1231-1239).
Also known as phytoaccumulation. Plants take up or hyperaccumulate contaminants through their roots and store them in the tissues of the stem or leaves. The contaminants are not necessarily degraded but are removed from the environment when the plants are harvested. This is particularly useful for removing metals from soil and, in some cases, the metals can be recovered for reuse, by incinerating the plants, in a process called phytomining
5. PhytovolatilizationPlants take up volatile compounds through their roots, and transpire the same compounds, or their metabolites, through the leaves, thereby releasing them into the atmosphere.
6. PhytodegradationContaminants are taken up into the plant tissues where they are metabolized, or biotransformed. Where the transformation takes place depends on the type of plant, and can occur in roots, stem or leaves.