Phytoremediation

Eco-friendly management of wastes

1. Phytoremediation Adnan shakeel M.Sc botany ( Env . biology) En. No. GH1717

2. Introduction Phytoremediation ( phyto - plant, remedium – restoring balance ) is the name given to a set of technologies that clean contaminated sites using plants. Phytoremediation relies on plant’s ability to act as a solar –driven pumping and filtering system. Heavy metal pollution is a serious environmental problem. Since heavy metals are non-biodegradable ,they accumulate in the food chain. Some important disasters caused by heavy metals are ; Minamata disater , Sandoz chemical spill, Spanish waste water spill and itai itai disease

3. Brief historical view About 300 years ago, plants were used in waste water treatment. Thlaspi caerulescens and Viola - calaminaria were the first plant species documented to accumulate high levels of metals in leaves . Utsunamiya and chaney first made a field trial on Zn and Cd phytoextraction in 1991. 1935 , Byers reported that plants of the genus Astragalus were capable of accumulating up to 0.6 selenium in dry shoot biomass.

4. Process of phytoremediation

5. Phytostimulation Degradation of the contaminant by plant rhizosphere microorganisms . Media : Mainly soil, sediment and sludge but also surface and ground water Examples : Grasses, hybrid poplar, red mulberry, alfalfa, cattails

6. Phytodegradation Degradation of the contaminant through plant matabolism or through the release of enzymes by the plant. Media : Soil, sediment, sludge, ground and surface water. Examples : Algae,, stonewarts , hybrid poplar, rice, cattails .

7. Phytoextraction Plants accumulate metals and radio-nuclides and translocate them to their harvestable parts. Media : Soil, sediment and sludge. Examples : Indian mustard, alpine pennycress, sun flower, poplars.

8. Rhizofilteration Plants absorb or precipitate metals and radionuclides from aqueous solutions around the roots, therefore immobilizing the contaminants. Media : Surface or ground water Examples : Sunflower, Indian mustard, water hyacinth.

9. Phytovolatization Uptake and possible transformation of a compound by the plant and subsequent release into the atmosphere Media: Ground water, soil, sediment, and sludge Examples : Poplar, alfalfa, Indian mustard

10. Phytostabilisation Stabilisation of the metal-contaminated soil by plant roots, reducing the movement off-site. Media : soil Examples : Indian mustard, grasses, hybrid poplars .

11. Plants used in phytoremediation Alfalfa is living in symbiosis with hydrocarbon-degrading bacteria . Arabidopsis can transform Hg into gaseous state. Bamboo family can accumulate silica in its stalk. Bladder campion can accumulate Zn and Cu. Indian mustard can accumulate Se, Pb , Cr, Cd , Ni, Zn and Cu. Buxaceae and Euphorbiaceae can accumulate Ni. Tomato and alpine pennycress can accumulate Pb , Zn and Cd . Poplar is used for the absorption of the atrazine .

12. Cadmium, using Salix viminali s , cadmium and zinc using alpine pennycress ( Thlaspi caerulescens ). Lead, using Indian mustard ( Brassica juncea ), Ambroisa artemisifolia and poplar trees. Arsenic, using the sunflower ( Helianthus annus ), or Chinese Break fern ( Pteris vittata ). Caesium-137 and stromium-90 were recovered from a pond using sunflowers. Mercury, selenium, and organic pollutants like polychlorinated biphenyls have been removed by using transgenic plants containing genes for bacterial enzymes.

13. Role of biotechnology and genetics in phytoremediation Selenium (Se) : Transgenic plants have been produced through methylation of amino acids at specific sites which have the ability to volatize Se. Mercury (Hg) : Transgenic tobacco has been produced due to the integration of certain bacterial genes like merA and merB due to which it shows resistance to Hg Arsenic ( Ar ) : Certain bacterial genes present in E.coli , such as ArsC is responsible for reduction of arsenic and formation of a complex in presence of glutathione (GSH). An increased amount of GSH can be produced by expression of glutamyl cysteine synthetase enzyme .

14. Advantages and disadvantages Advantages Disadvantages 1 . Natural method. 1. long clean-up process. 2. Suitable for broad 2. Uncertain performance. range of contaminants. 3. Cost effective for large 3. Not applicable for every land areas where other site (deep wastes, ana - technologies are not feasible. erobic soils, etc.) 4. Sensible, appropriate and 4. Regulatory hurdles sustainable technology.

15. Field Scale A pplications Recovery of heavy metals from soil : Brassica juncea and its modified strains have been shown to accumulate up to 40% of their biomass as heavy metals such as lead and chromium . Researchers in the state of New jersey in U.S.A carried out field trials in 1994 and demonstrated that the plants could be safely grown in chromuim contaminated soil at a site adjacent to Liberty State Park, N.J.A. Small amount of chromium was taken by the plants and removed from the soil. T he plants were then harvested and metal was recovered. Currently Indian mustard is under work at various research centers of U.S.A, to optimise metal uptake by such modified brassica strains.

16. Treatment of muncipal wastewater and industrial wastes : Roots and rhizomes of some plants provide an ideal habitat for the growth of various kinds of microorganisms. These microbes are very effective in remediation of contaminated wastewater and industrial wastes. In U.S.A , Albermarle’s two bromine plants in magnolia , has been artificially designed by suitable plant species to study the potential of plants in wastewater treatment. The plant species used are ; Scirpus lacustris , maiden cane and Typha latifolia .