Phytodegradation

• Definition: Breakdown of organic contaminants using plant-secreted enzymes like dehalogenase and oxygenase.
• Independence: This process functions without the aid of rhizospheric microorganisms.
• Function of Plants: Plants absorb and detoxify organic pollutants via metabolic processes, functioning as the "Green Liver" of the biosphere.
• Limitations: Effective solely on biodegradable organic contaminants such as synthetic insecticides and herbicides.

Rhizodegradation

• Definition: Joint remediation of pollutants in the rhizosphere by microorganisms and plants.
• Rhizosphere: The zone extending approximately 1 mm around plant roots.
• Enhancement of Degradation: Increased microbial density and activity enhance biodegradation.
• Plant Exudates: Root exudates (carbohydrates, amino acids, flavonoids) can increase microbial activity by 10-100 times.

Phytoextraction

• Definition: Uptake of contaminants from contaminated media (soil, water) by plant roots, which are then translocated and accumulated in aboveground biomass.
• Application: Primarily used for polluted soil remediation.
• Types:
  • Continuous Phytoextraction: Employs hyperaccumulator plants via established agricultural practices.
  • Chelate-induced Phytoextraction: Uses chelating agents to enhance the uptake of pollutants by non-hyperaccumulators.

Continuous Phytoextraction

• Process: Involves planting pollutant-accumulating species at contaminated sites, leading to root absorption and aerial accumulation of pollutants.
• Hyperaccumulator Traits: Can absorb 100 times more metals than typical plants. Key characteristics include rapid growth, deep roots, and high biomass.
• Metal Candidates: Zinc, copper, and nickel are ideal for phytoextraction by hyperaccumulators.

Chelate-induced Phytoextraction

• Definition: Applied when contaminants in soil are in a non-bioavailable form, enhancing pollutant uptake by adding chelates to the soil.
• Common Chelators:
  • EDTA (Ethylenediaminetetraacetic acid)
  • Nitrilo triacetic acid
  • EDDS (Ethylene diamine disuccinate)
  • Low-molecular-weight organic acids (LMWOA)
• Advantages of EDTA: Widely recognized and studied chelating agent for improving pollutant bioavailability.

Blastofiltration

• Definition: An advanced water remediation method utilizing young plant seedlings for metal removal from water.
• Efficiency: More effective than rhizofiltration due to increased surface-to-volume ratio during germination.
• Innovation: Represents a second-generation plant-based remediation technology, enhancing absorption capabilities of seedlings.

Phytostabilization (Phytoimmobilization)

• Definition: Reduces the mobility or bioavailability of contaminants in soil via specific plant species.
• Applications: Used for remediating contaminated soil, sludge, or sediment, stabilizing pollutants to prevent groundwater and food chain contamination.
• Mechanisms: Involves sorption by roots, precipitation, complexation, and reduction of metal valences in the rhizosphere.

Plants Used in Phytoremediation

• Examples of Plant and Pollutant Relationships:
  • Alyssum markgrafii - Ni
  • Eleocharis acicularis - Cu
  • Solanum photeinocarpum - Cd
  • Gossypium hirsutum - Hg
  • Cytisus striatus - HCC
  • Brassica nigra - Pb, Co, Cr
  • Helianthus annuus - Pb, Co, Cr
  • Hydrangeas - Al
  • Jatropha curcas - Hg
  • Miscanthus spp. - Heavy metals

Summary of Different Strategies of Phytoremediation