| Phytoremediation, the use of green plants to extract, sequester and detoxifyorganic or inorganic pollutants as a cheap and eco-friendly alternate technology hasevoked a lot of interest in the last few years. Heavy metals have been and continue tobe used for industrial, agricultural, and domestic purposes. For example, mining,smelting, electroplating, energy and fuel production, power transmission, intensiveagriculture, sludge dumping and military operations have all used metals such as Cd,Cu, Pb and Zn. Furthermore, some heavy metals, e.g. Mn,Fe,Cu,Zn,Mo,and Ni,areessential or beneficial micronutrients for micro organisms, plants and animals,whereas others such as Cd, Pb, and Hg have no known biological or physiologicalfunction. At high concentrations, heavy metals can have strong toxic effects and be athreat to the environment. Elevated soil metal concentrations can not only negativelyimpact plant growth, but also deteriorate human and animal health through ingestionof water, soil and food produced on contaminated soils. Cadmium (Cd), whichnaturally occurs at low levels in the environment, tends to accumulate to toxicconcentrations as a consequence of mining, smelting as well as excessive use ofphosphate fertilizers and sewage sludge in agriculture. Cd is a potentially hazardoustrace metal which causes environmental and human health problems due to its highmobility in the soil–plant system. Soil Cd is generally highly available which partlyexplains why, although it is neither an essential nor beneficial element for vascularplants (except presumably for hyperaccumulating species), their organs generallyexhibit measurable concentrations of the metal when it is present in the s oil.Excessive Cd can be readily taken up by roots and often accumulates to a largenumber in plant system. Cd can be taken up into plant root system through some othernutrient metabolic pathways such as zinc, iron and calcium and then it reaches rootcell membrane via the apoplast, including cell wall continuum and intercellular space.Cd induces complex changes in plants at genetical, biochemical and physiologicallevels, leading to phytotoxicity, the most obvious symptoms of which are reduction oftissue and growth, leaf roll and chlorosis, and leaf root necroses. Integrated on, Cdphytoaccumulation is an important research topic as food and particularly vegetablesconstitute a major source of human exposure to Cd and also because plants are,through phytoextraction, a potentially efficient means of remediating soilscontaminated with this trace metal. The ideal plant species for phytoremediation of contaminated soil is a plantspecies that has high yields and both tolerates and accumulates the targetedcontaminants. Vetiver grass (Vetiveria zizanioides (L.) Nash) has been widely knownfor its effectiveness in erosion and sediment control. It has a strong root system whichcan reach up to3m depth. In addition, vetiver is fast growing, and can survive inharsh environments including sites with high metal levels. Some researchers havereported that vetiveria zizanioides. is an optimal plant for phytoremediation attributedto its high tolerance to heavy metals, high biomass, and low fertilizer requirement.So,we set Vtiveria Zizanioides as our object of study.In present work, with the goals of removing Cd, we studied the effect of EDTA+oxaltate on Cd accumulation bothe in solution and soil. Moreover, we also studied theoptimal transplanted root length of Vetiveria zizanioides in Cd polluted soil. Detailsare given as follows:(1) We do the research on the application of combined two chelates (EDTA+oxalate). Although phytoremediation is an attractive, economic alternative to soilremoval and burial methods to remediate contaminated soil. However, it is also a slowprocess. Chelate-enhanced phytoremediation has been proposed as an effective toolfor the extraction of heavy metals from soils by plants. Most recent researches havefocused on single chelate, such as the application of EDTA, to increase thebioavailability of heavy metals in soils. A combination of EDTA and OA is rarelyinvestigated to explore their effect on Cd absorption and toxicity relief. Therefore, theeffect of EDTA+oxalate in enhancing Cd phytoextraction from contaminated soilswas studied (both hydroponic experiment and pot experiment) using transplantedVetiveria zizanioides. Meanwhile, the hydroponic experiment was also conducted tostudy the effects of EDTA+OA on chlorophyll, activities of antioxidant enzymes(POD and SOD), glutathione (GSH) of vetiveria zizanioides. In the pot experiment,the uptake and transport of Cd by different root length vetivers from Cd contaminatedsoils under chelates application was investigated. The results showed that0.5mmol L-1EDTA+1mmol L-1Oxalate work cooperatively only in shoots Cdabsorption in hydroponic experiment. In addition, it is more efficient for EDTA+Oxalate other than single EDTA or Oxalate to alleviate Cd toxicity when plantsadapted to0.5mmol L-1Cd treated solution. In pot experiment, two combined chelates(EDTA+Oxalate) work cooperatively both in roots Cd and shoots Cd absorption ofeach root length (apart from3cm) vetiver under10~40mg kg-1Cd stress. We conclude that EDTA+Oxalate addition to vetiver grass can be an effective way toenhance phytoremediation of Cd both in Cd contaminated water and soil.(2) We do the research on the relatively optimal root length for vetiveriazizanioides when transplanted in Cd contaminated soil. In order to facilitatetransportation and accelerate growth, roots of Vetiveria zizanioides must be prunedbefore transplanting. In my knowledge, few reporters have showed which root lengthis the best for vetiver cultivated in Cd polluted soil. Pots experiment was carried outto study the effect of root length on Cd accumulation, root elongation, indole-3-aceticacid of vetivers. The results indicated that6cm root length plants is the best choice inCd contaminated soils for its stronger tolerance to high-dosed Cd (40mg kg-1) andbetter growth promoting activities. |
PDF Full Text Request