Phytoremediation techniques for a lead contaminated site focusing on hyperaccumulating plants | |
| Author | Benjaporn Boonyapookana |
| Call Number | AIT Diss. no.EV-04-05 |
| Subject(s) | Phytoremediation Hyperaccumulator plants |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science, Asian Institute of Technology; Inter-University Program on Environmental Toxicology, Technology and Management, Chulabhorn Research Institute and Mahidol University |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. EV-04-05 |
| Abstract | Phytoremediation has shown great potential as an alternative treatment for the remediation of heavy metal contaminated soil and groundwater. However, the lack of a clear understanding pertaining to metal uptake/translocation mechanisms, enhancement amendments, and external effect on phytoremediation has hindered its full-scale application. The objective of this research was to investigate the capability of three local plant species namely; Helianthus annuus, Nicotiana tabacum, and Vetiveria zizanioides for Pb uptake and deposition within the plant from nutrient solution base and contaminated soil. The role and function of synthetic chelators for enhancing the phytoremediation of Pb removal was also determined. In addition, this study was designed to follow up the major route of Pb transport and localization within the cells and tissues of different plant parts using scanning electron microscopy equipped with energy dispersive X-ray spectrometers (SEM-EDS) and transmission electron microscopy (TEM). For hydroponic experiment, the test plants growing in Nutrient Film Technique (NFT) were exposed to Pb(N03)2 at two concentrations (0.25 and 2.5 mM) in the presence and absence of chelating agents (EDTA or DTP A) at the ratio of 1: 1 to stimulate metal mobility. The treated plants were separately harvested after the 15 \ 2"d, 3rd, and 4th weeks of exposition. A control treatment without Pb and chelate was included to compare the effects on plant performance. Adding chelators led to plant growth and biomass reduction across the Pb treatments. Results indicated that addition of both chelators significantly enhanced shoot concentration of Pb in all treated plants. The shoot Pb content of H. annuus and N. tabacum were increased up to 23-fold and 17-fold for V. zizanioides in the higher Pb treatment (2.5 mM Pb-EDTA) during the 4th week. Overall, Pb accumulation potential of H. annuus is higher than that of N tabacum and V. zizanioides as indicating by the value of individual BCF (171, 70, and 88, respectively). The highest accumulated concentration of H. annuus were at 2668, 843, and 3611 μgig DW in roots, stems, and leaves, respectively from the 2.5 mM Pb-EDTA treatment. When compared between plant parts, leaves accounted for the majority of the Pb uptake and accumulation. Further this finding had suggested that all three plant species tested have shown good potential for clean up hazardous waste site since more Pb was localized in the harvesting portions (leaf and stem in combination). The application of chelators produced plants with more than 50% Pb found in the leaves as compared with only 11-18% Pb in the leaves of those plants without chelators. For pot experiments, the results showed that the concentration of Pb in the shoots of H. annuus significantly increased (P<0.05) after chelators were applied. The highest accumulated concentration of H. annuus were at 378, 89, and 528 μgig DW in roots, stems, and leaves, respectively from the Pb-EDT A treatment. The percentages of Pb removal from contaminated soil were 65% and 54% in the Pb-EDTA and Pb-DTPA treatments, respectively during the 4th week. Additional chelator was thus essential to facilitate translocation of Pb from either roots or stem to further deposit into the leaves of the plant. With the electron microscopy technique, tissue and cellular observation were carried out on H. annuus sections derived from 2.5 mM Pb-EDTA treated tissues. The novel findings from this study revealed the pattern and site of Pb deposition in tissue and cell of H. annuus as well as the main mechanism in Pb detoxification. The scanning electron micrograph and X-ray map of root section showed the spots of Pb, forming patterns of concentric circles inside the stele, more precisely in the xylem vessel, phloem, and sclerenchyma cells. These spots were also visible on the surface of root epidermis, in the parenchyma cells and outside the endodermis. Lead deposits were also observed in stem and leaf regions of H. annuus. In stem tissue, the result revealed that Pb deposits in the region of vascular bundles and tended to be accumulated in collenchyma and fiber cells. In the leaf section, the spot of Pb were also observed in the xylem vessels, phloem, and sclerenchyma fibers. EDS X-ray microanalysis confomed the presence of Pb in these compartments. Ultrastructural study using TEM demonstrated the localization of large Pb grains in the intercellular space, cell wall, cytoplasm, and vacuole in the root sections. In the case of stem, Pb deposits were found along the plasma membrane and cytoplasm. In sections of leaf tissue, the fine Pb particles depositions have occurred continuously along the outer layer of the cell wall regions. In addition, Pb appeared to deposit in minute amount in the vacuole of the cell and also finely dispersed particles within the some chloroplasts. This study clearly demonstrated that H. annuus could detoxify Pb by transported them into the vacuole of the leaf cell or captured them by cell wall. These novel findings can help to develop new genetic modification techniques for Pb phytoremediation using H. annuus such as vacuolar engineering or overproducing some endogenous substances for Pb binding on the cell wall. Over all, this investigation indicated that H. annuus has met the prerequisites to become a hyperaccumulator, and thus might be useful, particularly, in the restoration of abandoned mines and factories contaminated with low to medium Pb contents. Providing that soil amendments such as chelator and basal nutrients as required by the plant should be included in couple with adequate water supply to start up the phytoremediation process. |
| Year | 2004 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. EV-04-05 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Preeda Parkpian; |
| Examination Committee(s) | Chongrak Polprasert; Skorn Mongkolsuk;Hwan, Lee Seung; Sombun Techapinyawat;Fujikawa, Yoko; |
| Scholarship Donor(s) | CRI;Mahidol University;AIT Fellowship Program on Post-Graduate Education, Training and Research Program in Environmental Science, Technology and Management; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2004 |