Maylowen C. Pescador

Phytoremediation Refers to the use of plants and associated microbes to

reduce the concentrations or toxic effects of contaminants in the environment.

Widely accepted as a cost-effective environmental restoration technology.

Contaminants

Organic: petroleum hydrocarbons, gas condensates, crude oil, chlorinated compounds, pesticides, and explosive s

Inorganic: metals, metalloids, radioactive materials

Phytoremediation Technologies Phytostabilization

Phytodegradation

Phytovolatilization

Phytoextraction

Phytostabilization Aims to immobilize contaminants in the soil and

prevent further dispersal.

Revegetation in mine tailings using metal tolerant grasses such as Festuca rubra, Agrostis tenius

Mechanisms of Phytostabilization:

1. Phytochemical complexation in the rhizosphere

Natural chelates (ex. Amino acids) of roots can form complex with metals

2. Transport protein inhibition on the root membrane -adsorption

3. Storage in the root cells - absorption

Site Contaminants Plants Performance

1 acre test plotAbandoned smelter,Barren land

Pb, Zn, Cd(at 20,000 ppm)

Poplars 50% survival after 3 years; site successfully revegetated

1 acre test plotMine wastes

As, Cd Poplars 5% survival; inclement weather, toxicity caused die-off

Limitations Phytostabilization is useful at sites with shallow

contamination and where contamination is relativelylow. Plants that accumulate heavy metals in the rootsand in the root zone typically are effective at depths ofup to 24 inches. Metals that are readily translocated toleaves in plants may limit the applicability ofphytostabilization due to potential affects to the foodchain.

Phytodegradation Refers to the uptake of

contaminants with the subsequent breakdown, mineralization, or metabolization by the plant itself through various internal enzymatic reactions and metabolic processes.

Remediate some organic contaminants, such as chlorinated solvents, herbicides, and munitions

Plant Enzymes Oxygenases have been identified in plants that are able

to address hydrocarbons such as aliphatic and aromatic compounds.

Nitroreductases are produced in some plants that can reduce and breakdown compounds such as the explosives TNT, RDX and HMX.

Other enzymes include dehalogenase, peroxidase, laccase, and nitrilase

Contaminants Ethylene dibromide (EDB)

Additive to leaded gasoline

Metabolized by Leuceana leucocephala

Benzotriazoles

Used in photographic emulsions, as anti-tarnish

Metabolized by Helianthus annuuss

Trinitrotoluene (TNT)

One of the world’s most dangerous explosives

Metabolized by vetiver grass

Trinitrotoluene (TNT) Entereo cloaca can utilize ester explosive as its source of

nitrogen

It can produce enzymes pentaerythritol tetranitrate(PETN) reductase and nitroreductase

The genes expressing the production of these enzymes are introduced in tobacco plant (Nicotiana tabacum)

Biodegradation of TNT by the enzyme reductase

Phytovolatilization This involves the use of plants to take up contaminants

from the soil, transforming them into volatile forms and transpiring them into the atmosphere

Uptake of organic contaminant such as Trichloroethylene (TCE) by poplar trees

v Tobacco carries the bacterial detoxification genes merB and merA

merB encodes for organomercurial lyase that catalyzes mercury bond (Hg-C bond), removing the organic ligand and releasing Hg(II)

merA encodes for mercuric ion reductase that reduces ionic mercury Hg(II) to Hg(0) using NADPH

Phytoextraction use plants to absorb, translocate and store toxic

contaminants from a soil matrix into their root and shoot tissue.

Involves repeated harvesting of the biomass

Uses metal hyperaccumulating plants or fast growing plants such as T. caerulescens

Mechanism of Metal Accumulation

SummaryTechnology Action in

ContaminantsMain Type of

ContaminantsVegetation

Phytostabilization Retained in situ Organics and metals

Cover maintained

Phytodegradation Attenuated in situ Organics Cover maintained

Phytovolatilization Removed Organics andmetals

Cover maintained

Phytoextraction Removed Metals Harvested repeatedly

Plant Chemicals

Arabidopsis Mercury

Bladder campion Zinc, Cupper

Brassica family (Mustard & Broccoli) Selenium, Sulfur, Lead, Chromium, Nickel, Zinc, Copper, Cesium, Strontium

Compositae family Cesium, Strontium

Euphorbiaceae Nickel

Tomato Lead, Zinc, Copper

Poplar trees Pesticides, Atrazine, Tricholoethylen(TCE), Carbon tetrachloride, Nitrogen compounds, TNT, RDX

Sunflower Cesium, Strontium, Uranium

Aberdeen Proving Ground, Maryland