Дисертації з теми "Cadmium distribution"

The objective of this work was to investigate the distribution of donor-like centres produced by boron implantation into p-type, Bridgeman grown Hg[0.8]Cd[0.2]Te and fabricate photodiodes from implanted substrates. Low carrier concentration substrates, 4-5x10[16]cm[-3], were implanted at room temperature with dose rates (&phis;) of 4x10[-2] or 6x10[-3]muAcm[-2], to a total dose of 1 x 10[15]B[+] cm[-2] (50,100keV) or 1x10[14]B[+]cm[-2] (150keV), respectively. Encapsulated specimens were annealed at 200°C or 235°C to activate the dopant or redistribute electrically active radiation damage centres to produce p-n junctions. The effects of materials processing on Hg[l-x]Cd[x]Te was investigated by x-ray photoelectron spectroscopy. Concentration profiles of electrically active centres were obtained from differential measurements of the Hall effect and resistivity at 77K. Through a comparison of distributions in as-implanted and annealed samples, the nature of donor-like centres forming the distributions were established. The quality of photodiodes produced from identical samples was assessed through current-voltage, capacitance-voltage and optoelectronic measurements. The nature and distribution of donor-like centres are dependent upon the dose rate of boron ions. An immobile defect is contained within the implanted region. Mercury interstitials (Hg[int]) are complexed within the implanted region for &phis; > 4x10[-2] muAcm[-2]. Irradiation enhanced diffusion of Hg[int] occurs if &phis; < 6x10[-3] muAcm[-2]. Thermal annealing redistributes bound and unbound accompanied by recombination with mercury vacancies and the formation of electrically neutral complexes. Annealing at 235°C for 10 mins completely removes the donor-like activity ascribed to Hg's [int] and reduces the concentration of electrically active immobile defects. P-N junctions are formed between the mercury vacancy distribution and unbound Hg's[int] or the immobile damage centres in annealed substrates. Junction formation is inhibited by the formation of the bound Hg[int] complex. Optimum R[o]A[j] products may be obtained from junctions formed from the immobile defect centre, although degradation of the implanted region occurs after annealing at 235°C. Anodic oxides grow by the differential electromigration of ions, which can produce a passivating layer to further anodization. The native oxide on Hg[0.8] Cd[0.2] Te is an ill-defined chemical mixture of the primary elements (Cd, Hg, Te). Native oxides degrade the R[o]A product of p-n junctions.

The cathode and the anode fall of the DC arcs are measured by fast oscilloscope for Ag-CdO contacts over a range of gap-lengths from 0.05 mm to 1 mm, and currents of 4-10 Amps at atmospheric pressure, with a known electrode closing speed, using the Moving Electrode Method. It was observed that the anode fall can occur in a few places within the arc voltage waveform, and is dependent of the electrodes' surface condition. Both cathode and anode falls increase with gap-length and decrease with current. It was found that when arc length is shorter than electrode separation, discontinuity within the arc voltage waveform during closure is caused, in many cases, by vapourisation of the first point of contact or by a high electric field set up between the two electrodes. These discontinuities are named as Voltage Step Phenomena. These voltage steps are related to the cathode and anode fall voltages, and their regular occurrences are a function of surface roughness. The fluctuations in the arc voltage waveform are thought to originate mainly from the cathode. A technique has been developed to measure the temperature of the electrodes accurately by using a T-type thermocouple, 0.075 mm diameter, in conjunction with a DC amplifier with a gain of 247. The thermocouple is placed as close as possible under the electrode surface (200 µm). This enables the temperature of the contact to be measured, after breaking contact, for an arc-duration even as short as 1ms. The time-constant of the probe (contact containing the thermocouple) is measured to be approximately 18ms. With this technique the temperature of the electrodes are measured for currents and gap-lengths ranging 4-10 Amps and 0.05-1 mm respectively. The effect of contacts being new and change of polarity have been investigated. From these results it is concluded that the co-existence of layers of foreign material on one, or both, surfaces causes the temperature of the electrodes to be high for the first 50-100 operations, before reaching to steady-state conditions. Change of polarity suggests that the moving electrode, either anode or cathode, due to the effect of air movement over its surface, is cooled relative to when fixed. The power transfer to the electrodes is calculated for various currents and gap-length using thermal analogue formulae derived from the transient response of an RC circuit to a d.c. pulse. The results show that below 0.2 mm the sum of the anode and cathode power is approximately equal to the arc power, and hence losses are negligible. At around 0.125 mm, for currents of about 6A and 12A, they both receive an equal amount of power from the arc. This has been related to the thermal energy of the electrons being negligible, at such separation, at the anode end of the plasma column. The power balance equations are solved to calculate the positive ion current to the cathode, and the thermal energy of the electrons in the plasma column, under various test conditions. In the investigation of erosion, the S.E.M. studies show that most of the power dissipated on the surface of the electrodes is used in melting and evaporation. The x-ray analysis shows that the melted metal is composed mostly of Silver. To operate the test rig and collect the generated data automatically, a computerised test system, with a mini data acquisition system, has been designed and constructed here.

Cette thèse a été effectuée dans le laboratoire d'écotoxicologie étudiant les phénomènes physico-chimiques et biologiques qui conditionnent la bioaccumulation de micropolluants dans les chaînes alimentaires. Le modèle choisi est un ver estuarien endobenthique (Nereis diversicolor) bien connu pour sa résistance à divers types de pollution et chez lequel la cinétique et les effets du cadmium ont été étudiés par les voies chimique, biochimique, cytochimique, immunologique, radioautographique et de microscopie électronique. Nous avons démontré que le tégument et l'intestin sont à la fois des voies de pénétration et des sites potentiels de piégeage. Le cadmium ayant pu pénétrer dans le ver est complexé, au moins partiellement, à des protéines de la fraction soluble: les métalloprotéines MPI et MPII (masse moléculaire respective >70 kDa et # 13,5 kDa). La MPI correspondrait à l'hémoglobine extracellulaire présente dans les vaisseaux sanguins. La MPII est présente notamment dans des cellules cœlomiques, les granulocytes I, qui la libèrent lors d'un stress. La séquence de cette molécule de 119 acides aminés a été analysée et montre que la molécule appartient à la famille des hémérythrines et myohémérythrines, pigments respiratoires dont la présence est ainsi démontrée dans l'embranchement des Annélides. Les voies de stockage et d'élimination du cadmium (intestin, néphridies) ont également été précisées

Au vu de leur sensibilité importante, les monocristaux de CdTe et de ZnTe photoréfractifs possèdent un avenir certain en tant que supports d'enregistrement holographique en temps réel. Si le premier matériau travaille dans le proche infrarouge (1,06-1,55 mm), le second est mieux adapté aux caméras CCD et aux diodes lasers (850 nm). Dans ce travail, les grandes étapes du développement d'un cristal de CdTe sont abordées : croissance, caractérisations, mise en forme. Le matériau est réalisé par la méthode de Bridgman-Stockbarger verticale et est optimisé en vue d'applications clairement définies. Plusieurs paramètres de croissance sont modifiés. Plus particulièrement, durant celle-ci, l'effet d'un champ magnétique axial à l'ampoule est testé. L'étude des propriétés électriques est effectuée en corrélant des expériences de résonance paramagnétique électronique et de photocourant modulé. La densité d'états est sondée par la première méthode tandis que la seconde attribue une signature structurale aux niveaux énergétiques. L'antisite de tellure ainsi qu'un deuxième centre profond sont mis en évidence. Les procédés de découpe et de polissage ainsi que le problème de claquage électrique à haut champ sont étudiés par polarimétrie. Le développement de la technique expérimentale permet de sonder la biréfringence induite aussi bien par les contraintes que par le champ électrique local. Les travaux concernant le ZnTe se sont concentrés sur sa croissance et son dopage. La cristallogénèse en phase liquide dite THM est optimisée. Deux codopages permettant de rendre le matériau résistif et photoréfractif ont été définis et validés par des caractérisations appropriées.

Thesis (M.S.)--California Polytechnic State University, 2008.
"June 2nd, 2008." "In partial fulfillment of the requirements for the degree [of] Master of Science in Engineering with Specialization in Materials Engineering." "Presented to the faculty of California Polytechnic State University, San Luis Obispo." Major professor: Richard Savage, Ph.D. Includes bibliographical references (leaves 98-100). Also available online and on microfiche (2 sheets).

Dabaoshan Mine Site (DMS) is the biggest polymetallic mine in South China. The Hengshi River receives acid mine drain (AMD) waste leaching from the tailings pond and run-off from the treatment plant which flows into the Wengjiang River, Beijiang River, before discharging into the Pearl River. Discharge from the mine site results in heavy metal contamination  near the mine and lower riparian areas along the river course. The present study focuses on the distribution and mobilization of As, Cd, Pb and Zn along the Hengshi River, groundwater, fluvial sediments and soil, with a special focus on As due to its high toxicity and the fact that mining is one of the main anthropogenic sources of As. Heavy metals, grain-size, XRD, %C and S analysis were done in order to determine the physicochemical characteristics of samples. The results were used for geochemical modeling (PHREEQ) and statistical (PCA) analysis to understand and predict the behavior of heavy metals. Potential ecological risk assessment was conducted by calculating contamination degree of heavy metals in soil and sediment and it’s theoretical toxical risk. Near the tailings pond, heavy metal concentration was 2-100 times higher than chinese surface water standard for agricultural use, which decreases downstream, mianly due to dilution, sorption, precipitation and co-precipitation with minerals. In groundwater, heavy metals concentration remained low. Due to the fact that most wells were abandoned or only for household use, potential risk from groundwater is low. The soils were disturbed by industrial or agricultural activities, and heavy metal concentration varied without showing any specific trend along the river. The potential ecological risk of heavy metals are ranked as: Cd>As>Cu>Pb>Zn in sediments; Cd>Cu>Pb>As>Zn in soil. As(Ⅲ) was the predominant species in surface water, and minerals identified in soil and sediment. Arsenic from most sites exceeded the Chinese soil standard for development land. Although arsenic was assumed to have a moderate ecological risk in sediments and low risk in soils, anthropogenic activities, such as land use change and untreated sewage discharge, might reduce and release arsenic into the environment, which poses potential risk to local residents.

THESIS ORGANISATION This thesis is organised into nine chapters that include seven international and national publications (six accepted and one submitted for publication). The initial overview chapter outlines the justification and direction for this thesis. With the exception of chapter 8 (accepted for publication on the 1st May 2005); all chapters are exact duplicates of published articles in international and national refereed journals (chapters 2 to 7). The initial chapters (2 and 3) presents research findings using a marine fish species, mullet (Mugil cephalus), to measure trace metal bioavailability in Lake Macquarie, NSW Australia. While subsequent chapters (4 to 8) are presenting research under taken to improve the understanding of arsenic cycling in marine and estuarine environments. The final chapter (chapter 9) is a synopsis of the major findings presented in this thesis. Due to the publication nature of this thesis, an unavoidable degree of replication exists within chapters (publications).

Barkley Sound and Alberni Inlet, located on the west coast of Vancouver Island, British Columbia, are home to economically important oyster farms. The headwaters of Alberni Inlet are proximal to the city of Port Alberni, where industrial activities (e.g., paper mills, recycling plants) release significant quantities of heavy metals into Alberni Inlet annually. The distribution of As, Cd, and Pb and Pb isotopic composition of Pb were studied in surface and cored sediments collected downstream from the paper mill using quadrupole and multi collector inductively coupled plasma mass spectroscopy (Q-ICP-MS, MC-ICP-MS). Surface and core sediment concentrations of As, Cd and Pb generally decrease downstream from Port Alberni, with the exception of a Pb spike observed in Barkley Sound. Alberni Inlet and Barkley Sound display ranges of 3.8-24 and 3.5-21.6 ppm for As, from 0.03-0.87 and 0.2-1.1 ppm for Cd, and 4.1-18 and 2.9-24.2 ppm for Pb, respectively. Scavenging of dissolved metals is observed at the distance of 10-25 km downstream from Port Alberni. Based on comparison to Sediment Quality Guidelines, the environmental impact of trace metals in the sediment on bottom dwelling organism is low. Major elements compositions determined using Aluminum as an elemental normalizer indicated that the sediment corresponds to a source predominantly from Vancouver Island bedrock. The isotopic composition for surface sediment ranges from 1.17020 to 1.21602 for ²⁰⁶Pb/²⁰⁷Pb, and 2.0397 to 2.0835 for ²⁰⁸Pb/²⁰⁶Pb. In core samples, the range is from 1.16571 to 1.19109 for ²⁰⁶Pb/²⁰⁷Pb and 2.06883 to 2.08533 for ²⁰⁸Pb/²⁰⁶Pb. Lead isotope fingerprinting indicates that sediments derived from Vancouver Island were contaminated with trace metals by a source displaying the Pb isotopic signature of the Sullivan Ore, the primary anthropogenic Pb source for British Columbia. This is consistent with paper mill effluent from Port Alberni. Sediments from the lower inlet and Barkley Sound also show a contribution from Chinese loess. Other human activities are most likely responsible for the spike in Pb concentrations in Barkley Sound. This study demonstrates that the combination of trace metal analysis and high precision Pb isotopic data are effective tools for monitoring anthropogenic input into the environment.

Doutoramento em Biologia
The increasing human activity has been responsible by profound changes and a constinuos degradation of the soil compartment in all the European territory. Some European policies are appearing focusing soil’s protection and the management of contaminated sites, in order to recover land for other uses. To regulate the risk assessment and the management of contaminated soils, many European member states adopted soil guideline values, as for example soil screnning values (SSV).These values are particularly useful for the the first tier of the Ecological Risk Assessment (ERA) processes of contaminated sites,especially for a first screening of sites requiring a more site-specific evaluation. Hence, the approriate definition of regional SSVs will have relevant economic impacts in the management of contaminated sites. Portugal is one of European Member States that still lack these soil guideline values. In this context, this study gaves a remarkable contribution in the generation of ecotoxicological data for soil microbiological parameters, terrestrial plants and invertebrates for the derivation of SSVs for uranium (U), cadmium (Cd) and copper (Cu), using a Portuguese natural soil, representative of a dominant type of soil in the Portuguese territory. SSVs were derived based on two methods proposed by the the Technical Guidance Document for Risk Assessment of the European Commission; namely the assessment factor method (AF) and the species sensitivity distribution (SSD) method (with some adaptations). The outputs of both methods were compared and discussed. Further, this study laid the foundation for a deeper reflection about the cut-off (hazard concentration for a given percentage of species - HCps) to be estimated from the SSDs, and to be selected for the derivation of SSVs, with the adequate level of protection. It was proven that this selection may vary for different contaminants, however a clear justification should be given, in each case. The SSvs proposed in this study were for: U (151.4 mg U kg-1dw), Cd (5.6 mg Cd kg-1dw), and Cu (58.5 mg Cu kg-1dw) These values should now be tested for their descriminating power of soils with different levels of contamination. However, this studies clarifies the approach that should be followed for the derivation of SSVs for other metals and organic contaminants, and for other dominant types of Portuguese natural soils.
O aumento das atividades humanas tem sido responsável por mudanças profundas e por uma degradação contínua do compartimento solo, em todo o território Europeu. Em resposta a este problema, algumas políticas Europeias estão agora a emergir orientadas especificamente para a proteção do solo e para a gestão das áreas contaminadas, a fim de recuperar os solos degradados para outros usos. Para regulamentar a avaliação de risco e a gestão de solos contaminados, muitos Estados-Membros Europeus adoptaram valores de qualidade do solo, como por exemplo os “valores de rastreio ou triagem” (do inglês: soil screening values ou SSVs). Estes valores são particularmente úteis para a primeira etapa dos processos de avaliação de risco ecológico (ARE) de locais contaminados, especialmente para um primeiro rastreio dos locais, destinado a separar aqueles em que os riscos são claramente reduzidos daqueles que exigem uma avaliação mais específica e aprofundada para o local. Assim, a definição de SSVs regionais terá impactos económicos relevantes na gestão dos locais contaminados. Portugal é um dos Estados-Membros Europeus que ainda não definiu SSVs. Neste contexto, este estudo dá uma notável contribuição na geração de dados ecotoxicológicos para parâmetros microbiológicos do solo, plantas terrestres e invertebrados necessários para a obtenção de SSVs para urânio (U), cádmio (Cd) e cobre (Cu), utilizando um solo natural Português, representante de um tipo dominante de solo existente no território nacional. Assim, foram obtidos SSVs para os metais referidos com base em dois métodos propostos pelo Documento de Orientação Técnica para Avaliação de Riscos da Comissão Europeia, nomeadamente o método dos factores de avaliação (do inglês: assessment factors ou AF) e o método probabilístico da distribuição da sensibilidade espécies (do inglês: species sensitivity distributions ou SSDs) (com algumas adaptações). Os resultados dos dois métodos foram comparados e discutidos. Além disso, este estudo lançou as bases para uma reflexão mais profunda sobre o ponto de corte (concentração de risco para uma determinada percentagem de espécies) a ser estimado a partir das distribuições de sensibilidade das espécies (SSDs), e para ser selecionado para a obtenção de SSVs, com o nível adequado de proteção. Neste estudo foi comprovado que esta seleção pode variar para diferentes metais ou outros contaminantes, no entanto, uma justificação clara deve ser dada, em cada caso. Os SSvs propostos neste estudo foram de: U (151,4 mg U kg- 1ms ), Cd (5,6 mg Cd kg- 1ms ) e Cu ( 58,5 mg Cu kg- 1 ms) Estes valores devem agora ser testados quanto à sua capacidade para descriminar solos com diferentes níveis de contaminação. No entanto, este estudo esclarece e sugere a abordagem que deve ser seguida para a derivação de SSVs para outros metais e contaminantes orgânicos, e para outros tipos dominantes de solos naturais portugueses.

Crop plants often accumulate heavy metals to concentrations that exceed recommended food standard guidelines. Cadmium (Cd) is particularly problematic because of its high toxicity and its ability to be accumulated and retained in kidney and bones for decades. In most cases, reduction in the concentration of toxic metals in soil is impractical, so plant-based strategies aimed at restricting Cd accumulation in edible plant parts need to be considered. What follows is a study of the factors that affect the uptake and distribution of Cd within a representative cereal, barley (Hordeum vulgare cv. Schooner). Since Cd is a non-essential metal in plants, the transport characteristics were compared with those of an essential micronutrient, Ni in a series of supplementary experiments. The effects of nutrient status and cation competition on Cd uptake were investigated to analyse the main route for Cd entry into the plants. Cd uptake into whole plants (hydroponically grown) was measured by radiotracer studies and elemental analysis. Fe and Zn were found to have large effect on the uptake of Cd both via deficiencies and by the competition for uptake. This strongly suggests that the main route for Cd uptake is via Fe and Zn transporters. The inhibition of Cd influx only by FeII (but not by FeIII) suggests that Cd uptake into the root occurs through divalent cation transporters. At the same external concentration more than twice as much Cd was absorbed as Ni. Ni translocation to the shoot was also much lower than for Cd. The transport studies on protoplasts showed that transporters in the shoot respond to plant nutrient status but differently to that of the root. Comparison of the concentrations of 109Cd in whole protoplasts and vacuoles isolated from shoots demonstrated that the majority of the cellular Cd was located in the vacuole. In vacuolar transport assays, the addition of ATP alone significantly increased Cd uptake into the vacuole, but more so when both ATP and GSH were supplied together. This suggests that Cd may be partly sequestered as Cd2+ ions via divalent cation transporters, but predominantly as Cd-GSH complexes, most likely via ABC-type transporters. Cd distribution within the plant was investigated following 109Cd supplied through the roots or applied to individual leaf surfaces. The preferential movement of Cd to the tip of the youngest leaf was noticed in both cases. Following foliar application, a significant amount of Cd was rapidly distributed to roots instead of shoots. Over 48 h, 12% of this root Cd was effluxed into the external solution. This active excretion may be a detoxification strategy, in addition to sequestration into vacuoles. The bidirectional movement of Cd within the plant indicates that Cd is highly mobile in both xylem and phloem. This study has provided a detailed picture of the movement of Cd in barley at various levels. Prevention of Fe and Zn deficiencies and higher Fe/Zn nutrition levels should reduce Cd accumulation.
Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 2019

The biogeochemical cycling of oceanic dissolved cadmium (dCd) has been an active area of research for the past ~40 years, due in part to the close correlation with phosphate (PO4). The global Cd:PO4 relationship has led to the use of microfossil Cd/Ca as a paleoproxy for ocean circulation and nutrient utilization; however considerable spatial and temporal variability in the relationship - particularly in surface waters - limits the utility of the proxy. Understanding the global biogeochemical cycling of Cd is an active area of research; however the Arctic Ocean is largely omitted from global models due to lack of data. This work presents depth profiles of dCd and Cd/PO4 ratios from 18 individual stations in the Canadian Arctic, collected during the Canadian GEOTRACES cruises GN02 and GN03, which connect the Arctic Ocean to the North Atlantic through the Canadian Arctic Archipelago (CAA). Salinity-driven water mass stratification exerts a primary control on the spatial distribution of Cd in the region, with elevated dCd and high Cd/PO4 ratios (~0.37 pM/μM) associated with waters of Pacific-origin. The elevated dCd and Cd/PO4 ratios are used as a tracer of Pacific-origin waters, identifying the presence of Pacific-origin water through the CAA and into Baffin Bay. High surface Cd/PO4 ratios were observed across the transect, consistent with a general global increase in surface water Cd/PO4 with increasing latitude. The analysis of Cd and other bioactive trace metals (Mn, Fe, Ni, Cu, Zn and Pb) still presents considerable analytical challenges due to the high-risks of contamination, low concentrations and complex matrices. I present a novel multi-element analytical method, which combines the commercially-available seaFAST pico preconcentration system with ICP-MS/MS analysis. In this work, we demonstrate that ICP-MS/MS, which combines two mass-selecting quadrupoles separated by an octopole collision/reaction cell, effectively removes common interferences (ArO+ on 56Fe and MoO+ on Cd) when pressurized with O2 gas. Accurate and precise measurements of iv the consensus references standards SAFe S and SAFe D and the certified reference material NASS-6 are presented as validation of the method. This thesis presents a novel method for the analysis of trace
Graduate

碩士
國立臺灣大學
農業工程學研究所
87
The miscible displacement is a traditional theory to describe transport of ion in the soil. Concentration curves always consider as a S type break through with pore volume. However cadmium ions which have strong tending to retain in soil are not fit in this traditional theory. The purpose of this study is applying concept of thermodynamics to devise a new model. The new model show as follow-model .Several experiment results are counted to verify this model, and show reasonable agreements. The criteria of soil pollution are the legal lattice standard for government to execute the soil pollution prevention. In 1993, Environment Protection Agency tried to establish the standard of heavy metal quantity of the soils in Taiwan. However, above standard doesn''t include cadmium distribution in soil by natural process or pollutant effect. This study use finite mixture distribution theory to classify cadmium concentration in and establish standard. The result counted at last can group the cadmium quantity of soils in Taiwan into a one level which is 0~0.368mg/kg in background and five levels in the polluted soil, including 0.368~1.123mg/kg, 0.123~2.515mg/kg, 2.515~4.283mg/kg, 4.283~5.170mg/kg and over 5.170mg/kg. The boundary between the cadmium quantity within the normal soils and the one within the polluted soils is 0.368 mg/kg. Moreover, we suggest pollution value can be stipulated as 1 mg/kg.

An understanding of the cadmium levels in the Australian wheat crop and areas of elevated levels that may be of concern to health has great potential for both the export market and the domestic consumer in Australia. This understanding is most effective if the sources of the cadmium in the wheat, the fate of the cadmium during the milling process and how this affects the levels in bread products is also known. The objectives of this study were to investigate cadmium levels in wheat from Australian silo sites, determine if a correlation existed between cadmium level and soil type, pH and fertiliser usage and determine the reasons for any correlation. In addition, to determine if the cadmium was partitioned during the normal commercial milling process into the milling fractions and how this affected cadmium levels in bread.

碩士
國立臺灣大學
植物學系
85
Cadmium toxicity was reflected on morphological and biological change . The major morphological abnormalities of cadmium-treated plants were the retardation of plant growth, chlorosis of leaves (especially young leaves), and earlier senescence of old leaves. The time for toxicity expression was reversed to cadmium concentration in solution. Cadmium affected plants showed that chloroplast abnormalities in mesophyll of leaf, such as the swelling and looseness of thylakoid membrane ,and reduction of stack disc of thylakoid in grana. But the effects of cadmium on chloroplasts in vascular bundles of stems were not so prominent. Transfer cells were not only found in phloem tissues and minor veins of vascular bundles, they were also found in xylem tissues nearly vessels in stems of cadmium-treated plants. However, they were not found in roots and leaves of cadmium-treated plants. The distribution of cadmium was mainly in root. The accumulation of cadmium in stems was higher than that in leaves. Cadmium accumulation ability of young leaves was much higher than that of older leaves. The isozyme patterns of superoxide dismutase, peroxidase and acid phosphatase were also altered by the duration of cadmium treatment.

This thesis is the first report linking differential distribution of cadmium (Cd) among tissues of hydroponically-grown soybean with Cd amendments – lower seed Cd-accumulating OAC Champion and higher seed Cd-accumulating OAC Bayfield – and the mechanisms responsible for these differences. OAC Champion retains 94% (64% for OAC Bayfield) of accumulated Cd in the root stock and Cd in its xylem sap is eleven-fold less concentrated than OAC Bayfield by seed fill. Though the movement of Cd to shoots is more restricted in OAC Champion, the concentration in some seed still approximates or exceeds 0.1 mg Cd • kg-1, indicating that in soils with elevated available Cd, there is potential for many cultivars of soybean to exceed the new suggested maximum for soybean, under an amendment to regulation (EC) No 1881/2006. Phytic acid was also assayed in seed tissue and OAC Bayfield was found to contain the highest concentrations.

碩士
國立臺灣大學
農業化學研究所
104
When a soil is under submerging condition, the water layer above the soil cuts off the oxygen supplying from the air. As a consequence, anaerobic respiration of soil microbial drives the occurrence of a series of reduction reactions. The excretion of oxygen from rice roots result in the oxidized condition in the rice rhizosphere, which may result in a redox gradient from rice rhizosphere to bulk soil. Therefore, it is hypothesized that this redox gradient may lead to the spatial distribution of iron and cadmium between rice rhizosphere and bulk soils, and subsequently affect their uptakes by rice roots. Soil incubation and rhizobox experiments were applied to the study the concentration of iron and cadmium in soil solution as a function of time, and the spatial distributions of iron and cadmium in soil solution, respectively. The results of soil incubation experiment showed that the concentration of ferrous ion in soil solution increased with the time of submergence, while the concentration of cadmium decreased gradually. The difference between the redox conditions in the rhizosphere and bulk soils induced the accumulation of iron in the rhizosphere of rice. The linear combination fitting (LCF) results of Fe k-edge XANES spectra of the soil samples shows that the formation of lepidocrocite in the rhizosphere (63.1 %) was higher than that in the corresponding bulk soil (45.7 %). Accordingly, ferrous ions were oxidized in the rice rhizosphere, leading to precipitation of Fe in the rice rhizosphere, On the other hand, the decrease of Cd concentration in soil solutions from the bulk to rhizosphere soils indicated the absorption of cadmium by ferric hydroxides. In addition, the concentration of sulfate in the rice rhizosphere was higher than the counterpart in the bulk. This indicates that the oxidation of reduced S species (e.g., CdS) in rice rhizosphere may be responsible for the release of Cd, which was then absorbed by rice roots.

Cd levels were measured in three different body compartments of the echinoid Stomopneustes variolaris after exposure to concentrations of 5 ug 1l, 20 ug 1l and 50 ug 1l Cd for a period of two weeks. The body compartments investigated included the intestine, gonads and skeleton. The gonads did not exhibit dose-dependent bioaccumulation. The levels of cadmium in the intestine and skeleton were significantly different between the treatments, suggesting that dose dependent bioaccumulation had occurred in these compartments (except in the skeleton where higher levels -were recorded for those exposed to 20 ug 1l than those exposed to 50 ug 1l) The levels recorded in the intestine were higher than those recorded in the gonads and skeleton at the higher Cd exposures of 20 and 50 ug 1i. The levels accumulated in the gonads and skeleton were not significantly different from each other. A separate group, exposed to 20 ug 1`1Cd over a period of two weeks, was placed in uncontaminated seawater to determine if the echinoids were capable of bioremediation. Bioremediation was found to lower the Cd levels in the gonads, but not in the intestine and skeleton. Cadmium levels for the three body compartments were also recorded from specimens collected from the field, indicating the presence of this element in the environment. In addition to using atomic absorption spectroscopy (AAS), energy dispersive X-ray analysis (EDX) was used as a comparative technique to detect the presence of Cd in the skeleton of the urchin. Cadmium was detected in the skeleton with AAS, but not with EDX. S. variolaris proved to be a capable biomonitor of Cd contamination.
Thesis (M.Sc.Eng.)-University of Durban-Westville, 2002.

Zinc (Zn) and cadmium (Cd) have nutrient-type vertical distributions reflecting control driven by biological uptake in surface waters and remineralization of sinking biogenic particles at depth. Both metals show strong correlations with major algal nutrients (Cd with phosphate (PO43-) and Zn with silicic acid (Si)) in the world ocean. Through their roles as micronutrients and toxins to marine phytoplankton, Zn and Cd can influence surface biological community composition. Preserved Zn and Cd records have been employed as proxies to gain insight into nutrient distributions, circulation, and organic carbon export in the paleocean. A thorough and mechanistic understanding of the biogeochemical cycling of Zn and Cd is necessary for accurate paleoceanographic reconstructions as well as predicting alterations in metal supply to the modern surface ocean and its impacts on primary productivity due to oceanic changes. My dissertation aims to further this understanding through an investigation of Zn and Cd distributions in the subarctic northeast Pacific through samples collected along the Line P transect. A major focus of this dissertation was identifying and characterizing depletions of metals in O2-depleted waters relative to global and basin scale metal:macronutrient correlations. Dissolved Cd profiles from the subarctic northeast Pacific and the eastern North Atlantic show a deficit of Cd relative to regional Cd:PO43- relationships. Particulate Cd and Cd stable isotopes (ε112/110Cd) from low-O2 North Atlantic waters and published sedimentary data from the subarctic northeast Pacific point to a previously undocumented water-column metal removal process acting in O2-depleted waters. Metal sulphide formation, likely in association with particulate microenvironments, can explain the observed deficits. Other metals with similar sulphide coordination chemistry should also form metal sulphides if this process is occurring. Dissolved Zn from Line P showed distributions and Zn:Si relationships that are consistent with the removal of metal in O2-depleted waters through sulphide formation. A first order approximation of the Cd deficit suggests that sulphide formation may be an important sink term in the global Cd cycle. Surface and upper nutricline Zn:Si and Cd:PO43- relationships in the chronically iron (Fe)-limited subarctic northeast Pacific showed distinct trends, which differ from those seen in Fe-replete regions. Distributions suggest the formation of surface biogenic particles with high Cd:PO43- and Zn:Si, leaving surface waters depleted in metals relative to macronutrients and resulting in high metal:macronutrient ratios in the nutricline as these particles sink and are remineralized. This is consistent with understandings of phytoplankton physiology and uptake of divalent metals under Fe-limitation, and corresponds well with global data for dissolved Cd:PO43- patterns in Fe-limited regions. Subsurface high Cd:PO43- and Zn:Si may also be influenced by the advection of water enriched in trace metals. The distinct shallow remineralization horizon observed for Zn compared to Si in the subarctic northeast Pacific by this and previous work presents a fundamentally different distribution than observed in global Zn:Si compilations. Directed sampling in the subarctic northeast Pacific should help elucidate the mechanism behind the oceanographically distinct distributions in this basin. Dissolved ε112/110Cd from Line P demonstrates a remarkably uniform subarctic northeast Pacific deepwater reflecting an advected source signal. Particulate ε112/110Cd samples show an active Cd cycle, which is not imprinted upon the dissolved phase. Particulate ε112/110Cd from 200-600 m depth is among the lightest ε112/110Cd ever reported for natural telluric samples. This may be an important sink for light Cd in the global ocean, which at present is heavy with respect to known sources. Line P surface waters with very low Cd concentrations are not accurately represented by a closed-system Rayleigh model, which can describe ε112/110Cd in the Southern Ocean. This suggests spatially and/or temporally variable surface ε112/110Cd fractionation. A large difference is observed in reported dissolved ε112/110Cd at very low Cd concentrations between different instrumentations. An intercalibration is necessary to determine if this is an analytical artefact or reflects real oceanic variability.
Graduate