A promising alternative to this conventional clean-up method is rhizofiltration, a phytoremediative technique designed for the removal of metals in aquatic environments. The process involves raising plants hydroponically and transplanting them into metal-polluted waters where plants absorb and concentrate the metals in their roots and shoots. Root exudates and changes in rhizosphere pH also may cause metals to precipitate onto root surfaces. As they become saturated with the metal contaminants, roots or whole plants are harvested for disposal. Dushenkov and Kapulnik, (2000) describe the characteristics of the ideal plant for rhizofiltration. Plants should be able to accumulate and tolerate significant amounts of the target metals in conjunction with easy handling, low maintenance cost, and a minimum of secondary waste requiring disposal. It is also desirable plants to produce significant amounts of root biomass or root surface area. Several aquatic species have the ability to remove heavy metals from water, including water hyacinth (Eichhornia crassipes (Mart.) Solms; , pennywort , and duckweed.
Terrestrial plants are thought to be more suitable for rhizofiltration because they produce longer, more substantial, often fibrous root systems with large surface areas for metal sorption. Sunflower (Helianthus annuus L.) and Indian mustard (Brassica juncea Czern.) are the most promising terrestrial candidates for metal removal in water. The roots of Indian mustard are effective in the removal of Cd, Cr, Cu, Ni, Pb, and Zn, and sunflower removes Pb, U, 137Cs, and 90Sr from hydroponic solutions.
DUSHENKOV, S. and KAPULNIK, Y. Phytofilitration of metals. In: RASKIN, I.and Ensley, B.D. eds. Phytoremediation of toxic metals - using plants to clean-up the environment. New York, John Wiley & Sons, Inc., 2000, p. 89-106.
The plants that grow normally in polluted river area are considered as resistant plant. For heavy metals premeditation, you need to collect plant samples. Clean it with acid water, oven dry, crush and make acid digestion with HNO3. then determine the heavy metals in the digestion. The high concentration of heavy metals in the leaves indicate the ability of the plant for phytoremidiation.
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