|Title:||Phytoremediation of heavy metal-contaminated soils using high biomass plants|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Heavy metals -- Environmental aspects
Soils -- Heavy metal content
|Department:||Department of Civil and Structural Engineering|
|Pages:||xxi, 293 leaves : ill. ; 30 cm. + 1 computer optical disc|
|Abstract:||The contamination of soils with metals is a major environmental problem throughout the world. The emerging phytoremediation techniques, with their lower cost and environmental friendly nature, have received increasing attention in the last decades. The main aim of this research project is to study the phytoextraction of heavy metals from soils with the application of chelates. Screening high-biomass plant species more sensitive to the application of chelates and optimizing chelate application methods were investigated for a better combination of plants and chelate applications to increase the metal phytoextraction efficiency and reduce potential metal leaching to the surrounding environment. Results from plant screening experiment showed that, of all of the plants that were tested, garland chrysanthemum (Chrysanthemum coronarium L.) was the species most sensitive to the application of EDTA (ethylenediaminetetraacetic acid), and had the highest enhancement of Cu and Pb concentrations in its shoots. For Cu and Pb, 9.5- and 69-fold increases in metal concentrations were achieved 7 d after the application of 3 mmol kg-1 of EDTA, respectively. The plant of garland chrysanthemum may be as a good candidate plant species in the area of chelate-enhanced phytoextraction. Regarding chelate application, results showed that EDDS was more effective than EDTA at increasing the concentrations of Cu and Zn in corn (Zea mays L.) and beans (Phaseolus vulgaris L.). For Pb and Cd, EDDS was less effective than EDTA.|
Understanding the mechanisms involved in enhancing metal accumulations in plants through chelate application will be helpful for optimizing chelate-induced phytoremediation. Results showed pretreatments on the roots of Indian mustard with MC, HC1, and hot water increased the concentration of Pb in shoots by 14-, 7-, and 15-fold, respectively, compared with the shoots that had not been pretreated. Using a pot experiment, the biodegradable chelating agent of EDDS was added in a hot solution at 90℃ to the soil in which garland chrysanthemum and beans were growing. Results showed when 1 mmol kg-1 of EDDS as a hot solution was applied to soil, the concentrations of Cu, Pb, Zn and Cd and the total phytoextraction by the shoots of the two plant species exceeded or approximated those in the shoots of plants treated with 5 mmol kg-1 of normal EDTA solution. The concentrations of metals in the shoots of beans were significantly correlated with the relative electrolyte leakage rate of root cells, indicating that the root damage resulting from the hot solution might play an important role in the process of chelate-enhanced metal uptake. Metal leaching study due to chelate application to soil was also carried out immediately after harvesting of the plants in pot experiments. Results showed on an average, the leached metal amounts of Cu, Pb, Zn and Cd on the application of EDDS at the rate of 1 mmol kg-1 were reduced by 46%, 21%, 57% and 35% compared with that leached from the 5 mmol kg-1 of EDDS application, respectively. For the treatment of 1 mmol of EDDS, the leached metals decreased to the control group 14 days after the application of EDDS. Therefore, the application of biodegradable EDDS in hot solutions to soil can be a good alternative in chelate-enhanced phytoextraction. The naturally enhanced phytoextraction using plant root exudates to induce metal uptake was also studied in the current project. Results showed when the plant of pea (Pisum sativum L.) were mixing-cultured with barley (Hordeum vulgare L.), the concentrations of Cu, Pb, Zn, Cd and Fe in the shoots of pea reached 1.5-, 1.8-1.4-, 1.4- and 1.3-fold of those grown in sole. Adding root exudates of barley to the pea plants grown in the pots resulted in significant increases of metal accumulation in the shoots of pea, which indicated that root exudates in the mixed culture system played an important role in solubilizing metals in soil and facilitating the metal uptake by plants. The results may provide a new potential direction on more economical and much safer phytoremediation methods.
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