An investigation into the use of Australian native plants and designer metal-binding particles for remediation of metal-contaminated landscapes

Abstract

Contamination of soils with arsenic (As), lead (Pb), copper (Cu), manganese (Mn), zinc (Zn), cadmium (Cd) and aluminium (Al) as a result of mining and other industrial activities is a pervasive problem worldwide. High concentrations of these metal/loids and other contaminants in surface soil layers may prevent the growth of vegetation, leading to wind and water erosion of the soil and dispersion of the contaminants to adjacent areas. As a result, ecosystem and human health are put at risk via exposure through the food chain, drinking water and air. Phytoremediation uses metal-tolerant plants (i.e. metallophytes) to extract or stabilize metals in the soils of contaminated sites. Plant establishment for phytoremediation may be limited and delayed when soil contamination is severe. Reduction of contaminant concentrations in the surface soil is a common but not always effective means of enhancing plant establishment on polluted sites. The understanding of plant responses to various concentrations of metals in soils and their metal accumulation characteristics is crucial to selection of the metallophyte plants most appropriate for specific phytoremediation purposes. The design and use of micron-size hydrogel particles that have the capacity to bind toxic soluble metals and supply water offers an effective means to enhance plant establishment. A literature review identified new key parameters for the characterization of plant responses to metals in soil. Based on metal transporter kinetic parameters, a conceptual framework of plant metal uptake in relation to plant available metal concentration in soil was developed, and a new associated terminology for metallophytes is proposed, i.e. metal tolerators. The framework applies to all plant parts and plant available metal concentrations in soils, and was validated using independent datasets from field surveys of Queensland native plant species and the literature. This new framework may be a useful tool for selecting suitable metal tolerators for specific phytoremediation purposes, and may be also applied to non-metal elements or ions. The thesis also examined four Australian native plant species, Astrebla lappacea, Themeda australis, Austrostipa scabra and Acacia harpophylla for their tolerances to different concentrations of arsenic (As(V), 13.34-667.36 µM), copper (Cu 2+ , 0.5-200 µM), zinc (Zn 2+ , 9-500 µM), manganese (Mn 2+ , 8-10240 µM) and lead (Pb 2+ , 240-9600 µM) in single solutions during germination in controlled laboratory conditions. Metal/loid tolerance indicators used were maximum germination percentage (G max), mean germination time (MGT), radicle and shoot tolerance indexes (RTI & STI). Radicle tolerance index was the most sensitive indicator of metal I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis and have sought permission from co-authors for any jointly authored ...