Phytoremediation

Phytoremediation technologies

1. Phytoremediation Maylowen C. Pescador

2. 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

3. Phytoremediation Technologies Phytostabilization Phytodegradation Phytovolatilization Phytoextraction

4. 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

5. Mechanisms of Phytostabilization : Phytochemical complexation in the rhizosphere Natural chelates (ex. Amino acids) of roots can form complex with metals

6. Transport protein inhibition on the root membrane - adsorption Storage in the root cells - absorption

7. Site Contaminants Plants Performance 1 acre test plot Abandoned smelter, Barren land Pb , Zn, Cd (at 20,000 ppm ) Poplars 50% survival after 3 years; site successfully revegetated 1 acre test plot Mine wastes As, Cd Poplars 5% survival; inclement weather, toxicity caused die-off

8. Limitations Phytostabilization is useful at sites with shallow contamination and where contamination is relatively low. Plants that accumulate heavy metals in the roots and in the root zone typically are effective at depths of up to 24 inches. Metals that are readily translocated to leaves in plants may limit the applicability of phytostabilization due to potential affects to the food chain.

9. 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

10. 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

11. 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

12. 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 )

13. Biodegradation of TNT by the enzyme reductase

14. 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

15. 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

16. 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

17. Mechanism of Metal Accumulation

18. Summary Technology Action in Contaminants Main Type of Contaminants Vegetation Phytostabilization Retained in situ Organics and metals Cover maintained Phytodegradation Attenuated in situ Organics Cover maintained Phytovolatilization Removed Organics and metals Cover maintained Phytoextraction Removed Metals Harvested repeatedly

19. 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

20. Aberdeen Proving Ground, Maryland