Phytoremediation of Organic Compounds -

Description

Phytoremediation of organic compounds consists of three mechanisms: rhizosphere biodegradation, phytovolatilization, and phytodegradation.

Plant roots produce natural substances (sugars, amino acids, organic acids,plant growth promoters, etc.) that promote microbial growth, and stimulate the biodegradation of organic compounds in the rhizosphere, the area immediately surrounding the root. Root growth creates channels and preferential paths that facilitate soil aeration in the root zone.

By the process of phytovolatilization certain hydrophylic organic contaminants can be taken up by plant roots and subsequently released into the atmosphere through the plant leaves. During this process of transpiration, these contaminants can be released in their original state after having undergone a transformation.

Phytodegradation consists of the uptake and transformation or metabolization of organic compounds within plant tissues (ie. roots, leaves, shoots). Plant compounds secreted by the roots can also play a role in phytodegradation.

Internet links:



Recommended Analyses for Detailed Characterization

Chemical Analysis

  • Contaminant concentrations   Footnotes1
  • pH 
  • Organic matter content  
  • Nutrient concentrations   Footnotes2
  • Metals concentrations  

Physical Analysis

  • Soil water content  
  • Soil granulometry  
  • Evaluation of biological conditions and ecological factors  

Recommended Trials for Detailed Characterization

Biological Trials

  • Seed germination toxicity test  
  • Root elongation toxicity test  
  • Greenhouse trials  

Other Information Recommended for Detailed Characterization

Phase II

  • Contaminant delineation (area and depth)  
  • Presence of environmental receptors   Footnotes3

Phase III

  • Soil stratigraphy  
  • Characterization of the hydrogeological system   Footnotes4
  • Conceptual site model with hydrogeological and geochemical inputs  

Applications

  • Allows for the treatment of residual organic contamination in the unsaturated zone, but can also be applied to the saturated zone
  • Applies to organic contamination
  • Contamination must be located near soil surface (< 1.0 m), or within the growth zone of the plant root system
  • Can be used over large areas

Treatment Type

  • Applies In situ
  • Does not apply Ex situ
  • Applies Biological
  • Applies Chemical
  • Does not apply Control
  • Applies Dissolved contamination
  • Does not apply Free Phase
  • Applies Physical
  • Applies Residual contamination
  • Applies Resorption
  • Does not apply Thermal

State of Technology

  • Does not applyTesting
  • AppliesCommercialization

Target Contaminants

With restrictions Aliphatic chlorinated hydrocarbons

With restrictions Chlorobenzenes

Applies Explosives

Does not apply Metals

Applies Monocyclic aromatic hydrocarbons

         Does not apply Non metalic inorganic compounds

Applies PCBs

Applies Pesticides

Applies Petroleum hydrocarbons

Applies Phenolic compounds

Applies Policyclic aromatic hydrocarbons

Applies   Applies    With restrictions   With restrictions    Does not apply   Does not apply

Notes:

This technique does not apply to aliphatic chlorinated hydrocarbons that contain 4 to 5 chlorine atoms. It is easier for plants to absorb and transfer organic compounds when the log of the octanol-water partition coefficient (log Kow) is between 0.5 and 0.3.




Treatment Time

  • Does not apply< 1 year
  • Does not apply1 to 3 years
  • Does not apply3 to 5 years
  • Applies> 5 years


Secondary By-products and/or Metabolites

Generally, phytoremediation of organic compounds does not generate deleterious secondary by-products or metabolites. However, some contaminants may be transformed by microorganism in the rhizosphere and may generate metabolites which are more toxic than the initial compound. For example, the bacterial transformation of dichloroethene may produce vinyl chloride.



Limitations of the Technology

  • The depth of contamination must be very limited (less than 1 meter depth for soil and less than 3 m depth for groundwater)
  • Treatment time extends over several years (more than 5 years)
  • High contaminant concentrations can have a toxic effect on the plants
  • The geographic situation (climate/season)
  • Presence of buildings or underground structures
  • Contamination can be transferred from one medium to another (ex: from soil to air)
  • This technology can only be applied at sites with a low potential risk to human and environmental health, eg. extended remediation times are permissible and the bioconcentration of toxic contaminants in plants is not an important risk factor


Complementary Technologies that Improve Treatment Effectiveness

Fertilizers rich in nitrogen stimulate plant growth as well as microbial activity and the rate of degradation.



Required Secondary Treatments

A management program for plant residues must be implemented.



Application Examples

The phytoremediation of organic compounds is a technique that has demonstrated its effectiveness on several sites.

Application examples are available at these addresses:



Performance

The time required for completion of phytoremediation treatment varies according to the type of contaminants, the selected plants, the rhizosphere population and activity (for rhizodegradation only) and the physical and chemical conditions of the contaminated site.



References


Composed by:

Magalie Turgeon
National Research Council


External Verifier:

Michel Labrecque, Phd.
Institut de recherche en biologie végétale


Latest update provided by:

Jennifer Holdner, M.Sc.
Public Works Government Services Canada


Updated Date:

3/1/2015



Footnotes

Return to footnote1 Contaminant concentrations: Identification and concentration of all contaminants (sorbed, dissolved, and free phase).

Return to footnote2 Nutrient concentrations includes: ammonia nitrogen, total Kjeldahl nitrogen, nitrates and nitrites.

Return to footnote3 Presence of potential environmental receptors, above and below ground infrastructure, and the risk of off-site migration.

Return to footnote4 Complete characterization of the hydrogeological system includes: the depth and thickness of the aquifer, the direction and speed of the groundwater flow, etc.