Phytoremediation of Toxic Organics

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• Phytoremediation of Toxic Organics
• Direct
• Plant may release enzyme to the environment that
  break down the organic contaminants which result
  in detoxification
• Indirect
• Plant provide a favorable environment in the
  rhizosphere for microbial growth that result in
  break down of soil contaminants.
• Plant release organic acids or chelating agents
  that increase solubility of the contaminant,
  which result in increased degradation by soil
  microorganisms.

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Plant derived degradative enzyme Five plant
derived enzymes have been identified that can
degrade soil contaminants, including nitrate and
nitrite reductase, laccase, nitrilase, and
dehalogenase. (Note over 50 soil enzymes have
been detected. Presumably, they are mostly
microbial origin.)
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• Nitrate reductase involved in reducing nitrate
  to nitrite
• Nitrite reductase involved in reducing nitrite
  to ammonium
• Nitrilase also named nitrile aminohydrolase.
  Acts on a wide range of aromatic nitriles and
  some aliphatic nitriles. (C?N)
• Laccase A group of multi-copper proteins of low
  specificity acting on both o- and p-quinols, and
  often acting on aminophenols and phenylenediamine
  and produce semiquinone.
• Dehalogenase degrades hexachloroethane
  (Cl3C-CCl3) and TCE (ClHCCCl2).

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Example Filed trials of phytoremediation of
petroleum-contaminated soils by researchers at
Kansas State Univ. Objectives 1. To evaluate
effect of plant species 2. To determine the
effect of management techniques 3. To develop
protocols for quantification of contaminants in
large numbers of soils.
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Three field trials were chosen 1. CRO. Crude
oil site locate near the Gulf of Mexico 2. CAR.
California refinery site 3. VAD. Virginia diesel
contaminated site
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Schwab and Banks, 1999
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Schwab and Banks, 1999
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Schwab and Banks, 1999
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Schwab and Banks, 1999
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• CRO site has been returned to its original
  agricultural use and the others are still being
  treated.
• At least two growing season is required to return
  the site for agricultural use.

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• Potential and limitations of phytoremediation
• Not competitive if a quick remediation is needed.
• Not appropriate if immediate risk of groundwater
  contamination exist due to imperfect containment
  of pollutants against leaching
• Limited by conditions that inherently limit plant
  growth.
• Suitable for remediation of large surface
  contaminated areas. Contaminated soil could be
  used to produce energy and fiber crops.

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Phytoremediation of TCE in Groundwater using
Populus Hybrid poplar (Populus charkowiiensis x
incrassata, NE 308) at Edward Sears Property
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Air Force Plant 4 Phytoremediation Site Layout,
Carswell Air Force Base - Ft. Worth, TX