Phytoremediation
Rhizosphere Effects:
Plant roots have a large positive effect on hydrocarbon remediation. The rhizosphere soil (located around the root area) has a greater degradation capability for contaminants than does soil without plant roots. Humification incorporates some of the contaminant, while some is mineralized.
Crested wheatgrass has been used to successfully promote the mineralization and removal of hydrocarbons from the soil:
Nutrient availability and pH optimization may be important to maximize microbial activity in the rhizosphere, but the presence of plant roots does provide further stimulus to microbial populations.
Some plants work in a symbiotic relationship with specific bacteria to metabolize hydrocarbon contamination. For example, Pseudomonas putida F1 (see below) helps degrade toluene in the presence of poplars.
Very nonpolar compounds (most hydrocarbons) are not taken up by plants into the transpiration stream. Unless the compound is metabolized by root-associated enzymes, the plant will have little direct effect on hydrocarbon remediation.
Mycorrhizosphere Effects:
Fungal populations located near the roots of a plant make up the mycorrhizosphere and make a significant contribution to phytoremedial schemes for contaminant degradation. The fungi typically possess enzymes for metabolizing organic contaminants and stimulate the plant production of such enzymes.
Plant Metabolism:
Traces of hydrocarbon contamination can dissolve in aqueous medium and be metabolized by plants. The predominant modification that hydrocarbons undergo during the metabolic process is hydroxylation.
Learn more about phytoremediation as it applies to:
Addition of fertilizers to stimulate phytoremediation:
Nutrient availability governs the success of phytoremediation and can be regulated through the addition of fertilizers. In a study performed by Hutchinson, Banks, and Schwab, total petroleum hydrocarbons declined by an average of 49% within the first six with no significant differences between Bermuda grass, tall fescue and an unvegetated control. After one year, total petroleum hydrocarbons declined by 68% with the Bermuda grass, 62% with the fescue, and 57% for the control.
Bermuda grass:
Tall Fescue:
Degradation of hydrocarbon contamination was lower in the treatments with no fertilizer or in the treatments where just enough fertilizer was added to maintain plant growth. Degradation was much higher in the treatments with higher rates of fertilization. Optimal remediation was obtained with a carbon to nitrogen to phosphorous ratio of 100:2:0.2.
SOURCES: Hutchinson, Wilson