Cheng Chung-yin. / Thesis submitted in: December 2004. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 185-195). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgements --- p.vi / Table of contents --- p.viii / List of tables --- p.xi / List of figures --- p.xii / List of plates --- p.xiv / Plant species used in the experiments --- p.xv / Chapter 1 Introduction / Chapter 1.1 --- Soil wastes as an environmental challenge --- p.1 / Chapter 1.2 --- Landfilling --- p.1 / Chapter 1.2.1 --- Waste degradation --- p.4 / Chapter 1.2.2 --- Control of degradation by-products --- p.6 / Chapter 1.3 --- Landfill leach ate --- p.8 / Chapter 1.3.1 --- Generation and control of landfill leachate --- p.8 / Chapter 1.3.2 --- Leachate characterization --- p.10 / Chapter 1.3.3 --- Leachate from local landfills --- p.15 / Chapter 1.3.4 --- Leachate treatment --- p.15 / Chapter 1.4 --- Leachate irrigation --- p.16 / Chapter 1.4.1 --- Common practices of wastewater irrigation --- p.17 / Chapter 1.4.1.1 --- Spray irrigation / Chapter 1.4.1.2 --- Rapid infiltration / Chapter 1.4.1.3 --- Overland flow / Chapter 1.4.2 --- Effects of leachate irrigation --- p.19 / Chapter 1.4.2.1 --- Effect of leachate irrigation on soil percolate / Chapter 1.4.2.2 --- Effect of leachate irrigation on soil / Chapter 1.4.2.3 --- Effect of leachate irrigation on plants / Chapter 1.5 --- Landfilling in Hong Kong --- p.24 / Chapter 1.5.1 --- Climate --- p.24 / Chapter 1.5.2 --- Geography and economy --- p.25 / Chapter 1.5.3 --- Waste composition --- p.25 / Chapter 1.5.4 --- Leachate sampling sites --- p.27 / Chapter 1.6 --- Objectives of this study --- p.30 / Chapter 1.6.1 --- Knowledge gaps --- p.30 / Chapter 1.6.2 --- Project outline --- p.33 / Chapter Chapter 2 --- Phytotoxicity evaluation of landfill leachate using seed germination tests / Chapter 2.1 --- Introduction --- p.34 / Chapter 2.1.1 --- Tests involving the use of germinating seeds --- p.34 / Chapter 2.1.2 --- Importance of germination to plants --- p.34 / Chapter 2.1.3 --- Advantages of germination tests --- p.35 / Chapter 2.1.4 --- Limitations of using germination as an endpoint --- p.35 / Chapter 2.1.5 --- Methods of germination test --- p.36 / Chapter 2.1.5.1 --- Test design / Chapter 2.1.5.2 --- Plant species / Chapter 2.1.5.3 --- Measurement endpoints / Chapter 2.1.5.4 --- Statistical analysis and test endpoints / Chapter 2.2 --- Objectives of study --- p.41 / Chapter 2.3 --- Materials and methods --- p.42 / Chapter 2.3.1 --- Sample collection --- p.42 / Chapter 2.3.2 --- Chemical analysis --- p.42 / Chapter 2.3.3 --- Statistical analysis --- p.43 / Chapter 2.3.4 --- Phytotoxicity assay --- p.43 / Chapter 2.4 --- Results and discussion --- p.44 / Chapter 2.4.1 --- Leachate characterization --- p.44 / Chapter 2.4.1.1 --- Comparison among landfill sites / Chapter 2.4.2 --- Phytotoxicity assay --- p.51 / Chapter 2.4.2.1 --- Dose response relationships / Chapter 2.4.2.2 --- Implication of hormetic-like response on the selection of statistical model / Chapter 2.4.2.3 --- Phytotoxicity of leachate samples / Chapter 2.4.2.4 --- Comparison between species / Chapter 2.5 --- Conclusions --- p.65 / Chapter Chapter 3 --- Leachate irrigation: Effects on plant performance and soil properties / Chapter 3.1 --- Introduction --- p.67 / Chapter 3.2 --- Materials and methods --- p.70 / Chapter 3.2.1 --- Leachate sampling and analysis --- p.70 / Chapter 3.2.2 --- Leachate irrigation experiment --- p.71 / Chapter 3.2.3 --- Soil and plant analysis --- p.73 / Chapter 3.2.3.1 --- Soil sampling and preparation / Chapter 3.2.3.2 --- Soil texture / Chapter 3.2.3.3 --- pH and electrical conductivity / Chapter 3.2.3.4 --- Organic carbon / Chapter 3.2.3.5 --- Nitrogen / Chapter 3.2.3.6 --- Phosphorus / Chapter 3.2.3.7 --- Chloride / Chapter 3.2.3.8 --- Metals / Chapter 3.2.3.9 --- Foliage analysis / Chapter 3.3 --- Results and discussion --- p.75 / Chapter 3.3.1 --- Leachate --- p.75 / Chapter 3.3.1.1 --- Chemical properties / Chapter 3.3.1.2 --- Phytotoxicity / Chapter 3.3.2 --- Plant responses --- p.79 / Chapter 3.3.2.1 --- Growth / Chapter 3.3.2.2 --- Plant survival and health / Chapter 3.3.2.3 --- Tissue contents / Chapter 3.3.2.4 --- Incorporating the results of germination tests in leachate irrigation practice / Chapter 3.3.3 --- Soil --- p.101 / Chapter 3.3.3.1 --- Initial properties / Chapter 3.3.3.2 --- Soil reaction (pH) / Chapter 3.3.3.3 --- Nitrogen / Chapter 3.3.3.4 --- Phosphorus / Chapter 3.3.3.5 --- Conductivity / Chapter 3.3.3.6 --- Chloride / Chapter 3.3.3.7 --- Metals / Chapter 3.4 --- Conclusions --- p.119 / Chapter Chapter 4 --- Fate and distribution of N after soil application of landfill leachate / Chapter 4.1 --- Introduction --- p.121 / Chapter 4.1.1 --- The needs of external N supply in ecological restoration --- p.121 / Chapter 4.1.2 --- Objectives of study --- p.122 / Chapter 4.2 --- Materials and methods --- p.123 / Chapter 4.2.1 --- Leachate --- p.124 / Chapter 4.2.2 --- Soil column --- p.124 / Chapter 4.2.3 --- Plant selection and establishment --- p.127 / Chapter 4.2.3 --- Leachate application --- p.129 / Chapter 4.2.4 --- Post irrigation harvesting and analysis --- p.130 / Chapter 4.3 --- Results and discussion --- p.130 / Chapter 4.3.1 --- Leachate --- p.130 / Chapter 4.3.2 --- Plants --- p.132 / Chapter 4.3.2.1 --- Growth / Chapter 4.3.2.2 --- Tissue N contents / Chapter 4.3.3 --- Soil and soil percolate --- p.139 / Chapter 4.3.3.1 --- Percolate volume and soil moisture / Chapter 4.3.3.2 --- pH / Chapter 4.3.3.3 --- Electrical conductivity / Chapter 4.3.3.4 --- Nitrate / Chapter 4.3.3.5 --- Ammonium / Chapter 4.3.4 --- N balance of the soil-plant system --- p.160 / Chapter 4.3.4.1 --- Change in the N capital after leachate irrigation / Chapter 4.3.4.2 --- Leaching loss / Chapter 4.3.4.3 --- Unaccountable N loss / Chapter 4.4 --- Conclusions --- p.174 / Chapter Chapter 5 --- General conclusion / Chapter 5.1 --- Summary of findings --- p.176 / Chapter 5.2 --- Ecological consequence of increased and excess N deposition --- p.179 / Chapter 5.3 --- Research prospects --- p.182 / References --- p.185

This research explored fate of organic contaminants in aquatic plant systems through (i) experimental development of relationships to describe sorption, uptake and enzymatic processing of contaminants by plants and inhibition of aquatic plants by contaminants and (ii) incorporation of experimental relationships into a conceptual model which describes contaminant fate in aquatic plant systems. This study focused on interactions of aquatic plants L. minor and M. aquaticum with halogenated phenols. 2,4,5-trichlorophenol (2,4,5-TCP) and 2,4-dichlorophenol (2,4-DCP) are precursors for the highly toxic and heavily applied herbicides 2,4,5-T and 2,4-D and were examined in detail. Chlorophenols are generally resistant to microbial degradation, a property which may limit microbial remediation options as effective alternatives for clean up of contaminated sites. Relationships for fundamental interactions between plants and contaminants that dictate uptake, enzymatic processing and sequestration of contaminants by aquatic plants were established. An assay which quantified production of oxygen by plants was developed to quantify plant metabolic activity and inhibition. Uptake of chlorinated phenols depended on plant activity and aqueous phase concentration of contaminant in the protonated form. Therefore, plant activity, contaminant pKa and media pH were established as critical parameters controlling rate of contaminant uptake. A conceptual model was developed which incorporated plant activity and inhibition into a mathematical description of uptake of organic contaminants by aquatic plants. The conceptual model was parameterized using experimental data delineating effect of plant activity, inhibition and speciation on contaminant uptake and the model was verified using independently gathered data. Experimentation with radio-labeled chlorinated phenols established that contaminants were sequestered internal to plants by plant enzymatic processing. 19F NMR was established as a technique to quantify transformation and conjugation products internal to plants and contaminant assimilation by plants and demonstrated that multiple metabolites containing the parent compound were present and quantifiable internal to plants. Finally, fate of plant-sequestered contaminants in an anaerobic bioassay was examined using Desulfitobacterium sp. strain Viet1. The results of this study address the role of aquatic plants in sequestration of contaminants in surface waters that indicate the potential and limitations of use of aquatic plants in natural and engineered treatment systems.