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    Thallium phytoextraction and its economic significance: a thesis presented in partial fulfilment of the requirements for the degree of Master of Science at Massey University
    (Massey University, 2000) LaCoste, Cher
    Thallium is a volatile toxic metal which has many industrial uses. The sources of thallium include natural geochemical sources and by-products of industrial processes. One of the problems in assessing thallium pollution potential is the lack of an accurate method of quantification of this element. Flame atomic absorption spectrometry (FAAS) is a good method of analysis but only down to the 1.0 mg/kg (ppm) level. For lower concentrations, analytical techniques have been difficult and inaccurate. A newly described method using graphite furnace atomic absorption spectrometry (GFAAS) has been found useful for low T1 concentrations. A method was designed to detect low concentrations of thallium in plant and soil samples. The graphite furnace technique worked well for the data presented in this paper. However, samples of different origin could have more severe matrix effects such as high iron contents. Thallium has been found to be readily available for plant uptake. The extractability of thallium was significantly higher then other metals such as cadmium and zinc. This property is ideal when considering a possible phytoextraction operation. Two plant species were found to accumulate thallium to levels up to 411 mg/kg in Iberis intermedia and 504mg/kg in Biscutella laevigata. These high values indicate potential for phytoremediation and phytomining in areas of sufficient contamination. The properties of which make thallium an ideal candidate for phytoremediation also make the metal a high risk for biota. Experiments were also conducted to determine the partitioning and sequestration of thallium within plant organelles. This work was limited to the two hyperaccumulating species but future work could compare non-tolerant species. Evidence from this research might give a better understanding to the mechanism involved in plant uptake and storage of thallium. Agricultural crops used for human consumption or animal grazing may cause deleterious health effects. Thallium is extremely toxic, effecting the nervous system and impairing heart function at low levels. Higher concentrations will cause death. It is possible that some of the illness symptoms observed in humans may be derived from low levels of thallium in foodstuffs. Aside from a few economic mineral deposits, there is no information of a world-wide distribution of thallium, so health effects can not be accurately assessed. This thesis describes experiments carried out on common vegetable and their uptake of thallium to determine safe levels of this element within the soil. This information will also be useful to farmers growing crops on contaminated soil will advise them on which plants would uptake less thallium. Thallium has not been studied as extensively as many other heavy metals that are more common in the environment. Although the crustal abundance of thallium is low (0.49-0.7 mg/kg average range), the toxicity of this element is very high, and it is readily available for plant uptake. The toxic effects on animals and plants should be monitored closely.
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    Studies on plants that hyperaccumulate copper, cobalt and nickel : their potential for use in phytomining and phytoremediation : a thesis presented in partial fulfillment of the requirements for the degree of Masterate of Science in Soil Science at Massey University
    (Massey University, 1998) Bennett, Frances Anneli
    This thesis reviews three lines of research on hyperaccumulators to examine their potential for phytoremediation and phytomining. The first line of research was to test the affect of nutrient addition on biomass and nickel uptake by two nickel hyperaccumulators, Alyssum bertotonii and Streptanthus polygaloides. Addition of fertiliser increased the biomass although the maximum amount added was found to be suboptimal. Nutrient addition did not affect the rate of nickel uptake. Larger plants contained a more dilute nickel content but still had an overall larger amount than smaller plants. The second line of research was to test the affect of chelates on metal uptake by copper and cobalt flora of the Democratic Republic of Congo (formally Zaïre) and a copper tolerant plant from Spain, Erica andevalensis. EDTA and Citric Acid increased uptake of copper in these plants but had no effect on the uptake of cobalt and nickel. EDTA increased the uptake of lead by Alyssum bertotonii but did not affect the uptake of zinc and cadmium. The third line of research was to examine the reality of hyperaccumulators of copper and cobalt. Copper and cobalt hyperaccumulation does in fact exist but not to the extent reported previously. There is a good possibility that the previously reported values for copper and cobalt hyperaccumulation are in some cases erroneous due to high iron levels indicating contamination of plant samples by soil.
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    Environmental implications of phytoextraction for mercury and gold : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Earth Science
    (Massey University, 2000) Msuya, Fletcher Abduel Msami
    The overall objective of this study was to investigate how plants could be used to harvest gold (phytomining) and at the same time remove mercury (phytoremediation) from auriferous mercury-contaminated soils. This study was undertaken to find appropriate plants that could be used to harvest gold, residual in mine tailings or in uneconomic low-grade ore, and at the same time remove residual mercury, commonly used to extract the gold in artisanal mining areas. Different procedures involving analytical methodology, leaching of acid mine tailings and the growing of plants in both gold and mercury-bearing substrates were undertaken. The analytical methods involved in the analysis of gold in the laboratory using the modern instruments were Flame Atomic Absorption Spectrometry (FAAS) and Graphite Furnace Atomic Absorption Spectrometry (GFAAS). The determination of mercury involved using Flameless Atomic Absorption Spectrometry. To understand the induced solubility of metals in phytoextraction, Tui mine tailings were leached with several chemicals known to solubilise gold: ammonium thiocyanate, ammonium thiosulphate and urea. The pH of the tailings material was varied through amendment with lime to examine the effect of this geochemical parameter on metal solubility and thus the potential for both plant uptake and leaching. The Tui mine tailings were chosen because of their geochemistry; these are highly weathered sulphide-ore tailings that leach heavy metals into adjacent water systems. The induced-phytoextraction potential of root crops was also examined in this thesis. Five root crops were grown in an artificial substrate consisting of 3.8 mg/kg (ppm) of elemental gold dispersed in sand. The possibility of using these root crops for phytomining was determined by separately adding chelating agents ammonium thiocyanate and ammonium thiosulphate to the substrate. In most cases there was a higher gold concentration in the roots than in the shoots. The highest mean gold concentrations were found in carrot roots and in roots of two radish cultivars. It was concluded that there was some potential for the use of carrot to grow an economic crop of gold from mine tailings. Results obtained from experiments where plants were grown in Tui tailings indicated that both chicory and Brassica juncea could be used for the phytoextraction of gold and mercury in the same crop. Under acidic conditions thiocyanate induced the uptake of gold by Brassica juncea and the uptake of mercury by chicory; and thiosulphate induced the uptake of mercury by chicory, but it did not induce the uptake of gold by the same plant. Under alkaline conditions, treatment with ammonium thiosulphate induced the uptake of gold and mercury by Brassica juncea; and treatment with thiosulphate induced the uptake of mercury by chicory but it did not induce the uptake of gold. It was therefore concluded that, Brassica juncea could be used for phytoextraction of gold and mercury when ammonium thiosulphate is applied to the substrate. Results from the root-crop experiment indicate that, carrots could supersede most of the plants used due to the greater apparent metal-uptake potential. Finally, a model is proposed for field trials to examine the potential of phytoextraction for gold and mercury in Tanzania. The aim of this model is to examine how the positive results obtained from research conducted in the laboratory and greenhouse can be put into practice. The use of similar plants as well as traditional tropical species (e.g. wild cassava - a known accumulator of cyanide) is suggested along with suitable chemical amendments.