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    Some observations on the ecology and phytochemistry of nickel-accumulating alyssum species from the Iberian peninsula : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University
    (Massey University, 1980) Shaw, Sugirthamani
    Experiments were carried out on the tolerance to, and uptake of nickel by Iberian subspecies of A. serpyllifolium. Two of these subspecies, the serpentinic-endemics s.sp. lusitanicum (from Bragança, Portugal) and s.sp. malacitanum (from Málaga, Spain) were hyperaccumulators (>1,000 μg/g in dried leaves) of nickel. Their precursor, s.sp. serpyllifolium (from Granada, Spain) was a non-accumulator of this element. Seeds of the two serpentine-endemics germinated extensively in nickel concentrations up to 12,000μg/g (1.2%) whereas s.sp. serpyllifoliurn only germinated in nickel concentrations of up to 60 μg/ml. Tolerance tests involving measurement of new root lengths of excised seedlings placed in varying nickel concentrations again showed much greater tolerance of the two serpentinophytes. In both series of experiments, the order of tolerance was: s.sp. lusitanicum > s.sp. malacitanum > s.sp. serpyllifolium. In pot trials involving seedlings of s.sp. malacitanum grown in mixtures containing varying amounts of calcium, magnesium and nickel, the most important findings were that nickel uptake is somewhat stimulated by an excess of calcium in the substrate. This relationship was confirmed by interspecies and intra-species analyses of naturally-occurring plants. Enhanced calcium uptake concomitant with nickel uptake by hyperaccumulators results in a higher (more favourable) Ca/Mg ratio and thereby counteracts one of the unfavourable edaphic effects of serpentine soils. The form of nickel in leaves of the three Iberian subspecies was investigated. Nickel existed mainly as a water-soluble polar complex in the vacuoles. Small concentrations of nickel did however exist in cell fractions particularly in the mitochondria where enzyme systems are located. GLC studies on the purified nickel complexes showed that this element is associated principally with malic and malonic acids which are present in high concentrations in the hyperaccumulators but not in s.sp. serpyllifolium. It is suggested that production of malic acid is a mechanism whereby hyperaccumulators can tolerate unfavourable edaphic factors such as nickel-rich soils. Presence of nickel in the mitochondria blocks the citric acid cycle by deactivating malic dehydrogenase leading to build-up of malic acid in the vacuoles which then absorbs excess nickel by a complexing reaction and leads to its diffusion back into the vacuoles from the mitochondria, hence unblocking the citric acid cycle. Malonic acid also blocks the cycle and leads to a reduced level of malic acid and hence lesser tolerance to nickel. This is shown to be the case for s.sp. malacitanum which contains more malonic acid than s.sp. lusitanicum and is also less tolerant to nickel. It is postulated that the chemical evidence suggests that s.sp. lusitanicum and s.sp. malacitanum are sufficiently different chemically to lend weight to the argument that the latter should be promoted to full specific rank as has already been done for s.sp. lusitanicum.
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    Nickel (II)-citric acid complex formation in aqueous solution : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University
    (Massey University, 1979) Liddle, John Raymond
    Titrimetric analysis of solutions of nickel(II) chloride and citric acid, H 3 L, has led to the characterization of four complexes in the acidic pH range NiL - , NiHL, NiH 2 L + , and Nil 4- 2 . Equilibrium constants for the formation of these complexes are reported. Results from a visible spectrophotometric study are analysed in terms of these four complexes. The stability and possible structures of the complexes are discussed and compared with other nickel-carboxylic acid complexes.
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    Aspects of the accumulation of cobalt, copper and nickel by plants : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry, Massey University
    (Massey University, 1980) Morrison, Richard Stephen
    Hyperaccumulation of heavy metals was studied with the intention of elucidating the mechanisms of tolerance of hyperaccumulator plant species. Two main areas are covered; cobalt and copper accumulation by plants from Shaba Province, Zaïre, and nickel accumulation by species of the genus Alyssum. In surveys of vegetation of metalliferous soils of Shaba, nine or ten new hyperaccumulators of cobalt were discovered along with eight or nine very strong accumulators. For copper, seven hyperaccumulators and five or six very strong accumulators were discovered. Some families contained a higher frequency of hyperaccumulators than others. There is also a difference in superorder classification of cobalt and copper hyperaccumulators on one hand and nickel hyperaccumulators on the other. Surveys of the genera Aeolanthus, Ipomoea and Pandiaka were made but only one new copper hyperaccumulator was found: no new cobalt hyperaccumulators were found. Several species had their abilities to accumulate confirmed. Pot trials on three hyperaccumulators Aeolanthus biformifolius, Haumaniastrum katangense and H. robertii, showed accumulation of cobalt but not the expected accumulation of copper. The uptake curve was of the exclusion-breakdown form. The limit of breakdown, for each metal, was similar from species to species. Cobalt was less readily excluded than copper. The tolerance tests showed that some species have individuals with greatly enhanced abilities to survive higher metal concentrationsthan is normal for that species, while other species have more uniform tolerances. There appears to be no requirement for large metal concentrations at germination and seeds germinate more readily in the absence rather than the presence of the metals. The distribution of cobalt and copper within leaf tissues, of five species, appears to be parallel within each species. For each metal, the distribution is parallel between different species with the exception of Buchnera metallorum. More detailed studies on cobalt in H. robertii showed the distribution to be even over the leaf area but with small anomalous regions of high concentration. The possibility that some of the cobalt was precipitated as oxalate crystals is considered. The water-soluble cobalt fraction ligand could not be identified but was not proteinaceous. It has a mass of 5,200 g per mole of cobalt. A survey of the genus Alyssum revealed thirty-four taxa as hyperaccumulators to add to the fourteen previously known. All the taxa are from section Odontarrhena. The geographical distribution of the hyperaccumulators is discussed as is the possible evolution of hyperaccumulators in subsections Compressa and Samarifera from non-accumulators within them. Studies of nickel accumulation by eleven Alyssum species and the closely related Bornmuellera tymphaea showed similar characteristics for all hyperaccumulators but two non-accumulators differed. A rise-to-saturation uptake form was noted. In the absence of nickel, cobalt could be accumulated with a similar uptake form. Cobalt accumulation in the presence of nickel is unknown. The rate of uptake is relatively rapid. The tolerance of hyperaccumulators to high nickel concentrations was confirmed in two types of tolerance tests; a substrate medium test and a solution test. The results from the two tests are compared. The distribution of nickel between the plant organs is discussed. The analysis of mineral elements in leaf material showed interesting differences between hyperaccumulators and non-accumulators for calcium, magnesium and manganese content but these could not be related to differing nickel concentrations. A similar find was made for glucosinolates. An organic acid survey was restricted by the non-identification of many acids. Separation of the nickel complexes was made. Identification of ligands involved in nickel complexatian was attempted but few positive results were found. Two ligands were common in significant quantities for all species studied. The results of these experiments were used to discuss possible evolution of hyperaccumulator species both in terms of their superorder distribution and their method of metal ion uptake. An equilibrium mechanism of uptake is proposed which involves a multiplicity of complexes for the ion absorbed. The mechanism differs from that which is commonly proposed for micronutrient elemental uptake.
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    The phytoextraction of heavy metals from metalliferous soils : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University
    (Massey University, 1997) Robinson, Brett Harvey; Robinson, Brett Harvey
    This study concerns the investigation of the potential use of plants to remove heavy metals, in particular nickel, zinc and cadmium, from soils. The study is divided into three sections, bioavailability, phytomining, and phytoremediation. The effect of various extractants on the solubility of heavy metals in some soils was tested. It was found that the solubility of the metal invariably increased as the pH of the extractant decreased, and as the concentration of the extractant increased. These relationships could be predicted mathematically. It concluded that a more concentrated, neutral, non-chelating extractant such as 1M ammonium acetate, is the most suitable for estimating bioavailability. An investigation into the addition of some compounds to soils to increase metal solubility showed that EDTA and citric acid should maximise solubility while keeping soil parameters (pH, osmotic potential, nutrient availability) within the growth range of the plant. These compounds are also relatively inexpensive. The effect of bioavailable elements on a New Zealand serpentine flora was investigated with regard to the soil's potential for phytoextraction. It was found that nickel was the only element that would be suitable for phytoextraction from these soils. The relative infertility of the serpentines was attributed primarily to the toxic effects of magnesium and/or nickel. Removing nickel from the soil by phytoextraction may enable the soil to be used as a magnesium-rich fertiliser. The potential of the hyperaccumulator plants Alyssum bertolonii and Berkheya coddii for nickel phytoextraction was studied. With the addition of fertilisers, the plants could remove respectively in excess of 72 kg and 100 kg of nickel per hectare per annum. Were the metal to be sold, and energy from the plant's incineration utilised, the net profit per hectare would be greater than that of a crop of wheat. Both of these plants re-grew after harvesting without the need to re-sow. In the case of B. coddii, the nickel concentration in the regrowth was more than twice that of the original crop. Phytomining for nickel is a viable proposition provided the operation is carried out over a large area. The nickel concentration in the plants was logarithmically related to the nickel extracted by a 1M ammonium acetate extract. Theoretical nickel yields from various soils could be predicted by performing a 1M ammonium acetate extraction on the soils. About half of the soils tested from various locations around the world contained enough soluble nickel to be economically phytomined. Alyssum bertolonii and B. coddii also have the potential to remove nickel from polluted soils. The addition of EDTA and citric acid to the soil in which the plants grew actually decreased the nickel concentration in the plants despite increasing the nickel solubility in the soil. The economics of phytomining are closely linked to the value of the metal. Cobalt and possibly even the noble metals could be economically phytomined at low concentrations in plants: a fertile area for future research. Sequential extractions were used to model the effect of successive hyperaccumulator crops on the bioavailability of nickel in ultramafic soils from around the world. The nickel concentration in all of the soils tested, decreased in a regular manner and could be predicted mathematically. Assuming an initial nickel crop of 100 kg/ha, the number of nickel crops above 70 kg/ha that could be obtained was calculated for each soil. The number of economic nickel crops varied between 3 and 18 before the soil would have to have been modified to increase nickel bioavailability. The possibility of removing zinc and cadmium using Thlaspi caerulescens showed that the plant has a potential use for removing cadmium from weakly polluted soils. The low bioaccumulation factor for zinc accumulation means that this element will never be removed in a reasonable time span. The concentration of both zinc and cadmium in the plant could be predicted by the extractable fraction in the soil as estimated by using 1M ammonium acetate as extractant. It was concluded that phytomining and phytoremediation are feasible possibilities under certain conditions. (1) Metals necessarily have to be slightly soluble in the soil before they can be phytoextractcd. Metal solubility may be improved by the addition of chemicals such as chelating agents. (2) Due to relatively low yields, phytomining will only be viable for more valuable elements where the concentrations in soils are too low for conventional mining. (3) Phytoremediation will be most effective on weakly polluted soils. (4) The economics of phytoextraction favour its use over large areas. The amount of metal able to be extracted from an area can be predicted by performing an extraction with 1M ammonium acetate.