This dissertation focuses on the effects of lead (Pb) on the expression of thyroid hormone distributor proteins and how that affects the developing brain in Xenopus laevis tadpoles. Previous work has shown that Pb has the ability to dysregulate thyroid hormone (TH)-signaling in vertebrates and that Pb can impair brain development. This dissertation reports results for a series of Pb-treatment experiments conducted in Xenopus laevis tadpoles. The first primary hypothesis of this dissertation is that Pb impairs TH-dependent mechanisms of brain development. The second primary hypothesis of this dissertation is that Pb-induced impairments of brain development happen via dysregulation of thyroid hormone distributor proteins (THDPs) transthyretin (TTR) and β-trace. Analyses of the effects of Pb on overall body growth showed dose-dependent decreases in body length with increasing concentrations. Evaluation of the effect of Pb on tectal size and cell death in the developing brain yielded bimodal changes that depended upon Pb concentration in both features. Furthermore, Pb impaired TH-induced changes in brain development, including neurogenesis and brain volume. Pb abolished the T4-mediated increase in proliferating cell nuclear antigen (PCNA) expression, while having only marginal effects on neuronal regeneration related protein (NREP) and Krueppel-like factor 9 (klf9). Analyses of the effects of Pb on TTR and β-trace expression yielded results demonstrating a significant decrease in expression of both proteins in response to Pb-treatment. Contrary to prior studies in the literature, I demonstrate here that TTR is present in the brains of Xenopus. While electroporation of TTR morpholino did result in fewer TTR puncta, electroporation with morpholinos for TTR and β-trace knock down did not mimic the effects of Pb on neurogenesis. However, overexpression of these proteins in the choroid plexus (CP) of these animals was sufficient to produce an increase in neurogenesis. Finally, overexpression of these proteins was sufficient to ameliorate the effects of Pb-treatment on neurogenesis. The results affirm both the primary and secondary hypotheses, illustrating that Pb does, indeed, impair TH-mediated mechanisms of brain development and that these impairments are mitigated by dysregulation of TTR and β-trace. / Doctor of Philosophy / This dissertation focuses on the effects of lead (Pb) poisoning on thyroid hormone (TH)-mediated mechanisms of brain development in Xenopus laevis tadpoles. The work detailed here seeks to shine a light on the effects of Pb on brain development and one mechanism by which those effects may be mediated. This dissertation details experiments done in Xenopus laevis tadpoles, which are a prime animal model for studying environmental toxicants, especially those that disrupt TH physiology. This dissertation focuses on two primary hypotheses within a two journal manuscript format. The first primary hypothesis of this dissertation is that Pb impairs TH-dependent mechanisms of brain development. The second primary hypothesis of this dissertation is that Pb-induced impairments of brain development happen via dysregulation of thyroid hormone distributor proteins (THDPs) TTR and β-trace. The results found in this dissertation are consistent with the conclusions that Pb impairs TH-mediated mechanisms of brain development and that those impairments are mitigated by dysregulation of THDPs in the brain and body.

M. Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / Lead, nickel and cobalt dithiocarbamates complexes were synthesized using methanol and water as solvents. All complexes were refluxed at 60 °C, cooled at room temperature, washed with methanol to remove the impurities and dried under the fume hood. A combination of Fourier transformer infrared (FTIR), elemental analysis (EA) and thermogravimetric analysis (TGA) were used to characterize these complexes. There was shifting of bands from low to high frequencies of the dithiocarbamates complexes compared to benzimidazole derivatives. The absence of the N-H band and the presence of new C=S bands confirmed that the complexes can be used in the preparation of metal sulphide nanoparticles. Elemental analysis showed that there was a percentage mismatch for the complexes I, III, IV and V. Complexes II and VI calculated percentages were within the limits with the found percentages except for sulphur which was low. The TGA curves decomposed to form a mixture of metal and metal sulphides for complex I, II, III and IV except for complex VI which gave metal sulphide only. All benzimidazole complexes decomposed at higher temperatures and were considered as stable complexes. Lead sulphide (PbS) is an important group IV-VI metal chalcogenide semiconductor. It has a direct narrow band gap of 0.41 eV at 300K and a large excitonic Bohr radius of 18 nm. Lead sulphide absorption band can be tuned to anywhere between near IR to UV (0.4μm) covering the entire visible spectrum, while achieving the quantum confinement region. The synthesis of lead sulphide nanoparticles was conducted by varying the effect of the reaction conditions such as the type of capping agents and temperature. Lead dithiocarbamate complex derived from benzimidazole, [Pb(S2N2C8H5)2] was thermolysed in hexadecylamine (HDA) and trioctylphosphine oxide (TOPO) at different reaction temperatures (140, 160 and 180 °C) to produce HDA and TOPO capped PbS nanoparticles. The nanoparticles were characterized using X-ray diffraction (XRD) for structural analysis, transmission electron microscopy (TEM) for shape and size, Ultraviolet visible (UV/Vis) and Photoluminescence (PL) spectroscopy for optical properties. An increase in temperature gave a decrease in the sizes of the nanoparticles when using the HDA capped lead benzimidazole dithiocarbamate complex. The observed morphology was cubes. TOPO capped lead benzimidazole dithiocarbamate complex gave no specific trend when temperature was varied. A cross-like layer with quasi spherical particles on top was observed at 160 °C. At 180 °C, the cross-like layer decomposed into rods- like materials with quasi spherical particles on top for TOPO capped PbS nanoparticles. For lead 2-methylbenzimidazole [Pb(S2N2C9H7)2] dithiocarbamate complex, TOPO capped PbS produced agglomerated cubic morphology at low temperature but as the temperature was increased agglomerated cylindrical shapes were observed. HDA capped PbS produced polydispersed nanocubes which were increasing in size when the temperature was increased. Nanoparticles displayed a blue shift in band edges with good photoluminescence behaviour which was red shifted from their respective band edges all temperatures and capping agents. XRD confirmed the crystal structure of cubic phase (galena) of PbS at all temperatures except for HDA capped PbS nanoparticles at 140 °C from lead benzimidazole dithiocarbamate complex which confirmed the crystal structure of face-centred cubic phase of PbS nanoparticles. Nickel sulphide has much more complicated phase diagram than cobalt sulfides and iron sulfides. Their chemical composition has many crystalline phases such as α-NiS, β=NiS, NiS2, Ni3S2, Ni3S4, Ni7S6 and Ni9S8. Ni3S2 phase has shown potential as a low-cost counter electrode material in dye sensitised solar cells, while the α-NiS phase has been applied as a cathode Material in lithium-ion batteries. The synthesis of nickel sulphide nanoparticles was done by varying the effect of the reaction conditions such concentration and temperature. Nickel benzimidazole dithiocarbamate [Ni(S2N2C8H5)2] and nickel 2-methylbenzimidazole [Ni (S2N2C9H7)2] dithiocarbamates complexes were thermolysed in hexadecylamine (HDA) at different reaction temperatures (140, 160 and 180 °C) and precursor concentrations (0.30, 0.35 and 0.40 g) to produce HDA capped NiS nanoparticles. It was observed that increasing both temperature and precursor concentration increased the size of the nanoparticles. Anisotropic particles were observed for both complexes when varying precursor concentration and temperature. Nickel benzimidazole dithiocarbamate complex produced stable shapes (spheres and cubes) of nickel sulphide nanoparticles. Nickel 2-methylbenzimidazole dithiocarbamate complex produced a mixture of spheres, cubes, triangles and rods nickel sulphide nanoparticles at all concentrations. But when varying temperature, it only produced that mixture at 160 °C. The optical measurements supported the presence of smaller particles at all temperatures and concentrations. XRD showed the presence of C7OS8 and pure nickel as impurities. However, the crystal structure of cubic Ni3S4 was observed at low temperatures and an introduction of monoclinic NixS6 at high temperature (180 °C) when varying temperature for both complexes. When varying concentration using nickel benzimidazole dithiocarbamate complex, XRD showed the presence of NiSO4.6H2O impurities at high temperatures. At 160 °C a mixture of hexagonal NiS and cubic Ni3S4 was observed. At low temperatures only nickel as a metal was found as an impurity and the crystal structure of cubic Ni3S4 was observed. When nickel 2-methylbenzimidazole complex was used, C7OS8 and pure nickel were found as impurities but the crystal structure of cubic Ni3S4 was observed. Cobalt sulphide (CoS) belongs to the family of group II-IV compounds with considerable potential for application in electronic devices. They have a complex phase diagram and their chemical composition have many phases such as Co4S3, Co9S8, CoS, Co1-xS, Co3S4, Co2S3 and CoS2. The synthesis of cobalt sulphide nanoparticles was conducted by varying the effect of temperature on size and shape of the nanoparticles. Nickel benzimidazole dithiocarbamate, [Ni(S2N2C8H5)2] and nickel 2-methylbenzimidazole [Ni(S2N2C9H7)2] complexes were thermolysed in hexadecylamine (HDA) at different reaction temperatures (140, 160 and 180 °C) to produce HDA capped CoS nanoparticles. Cobalt benzimidazole dithiocarbamate complex produced close to spherical shapes nanoparticles at all temperatures. The images showed that as temperature was increased, the size of the particles decreased. All the main reflection peaks were indexed to face-centred cubic Co3S4 and there were some impurities of C7OS8 at all temperatures. The optical measurements supported the presence of smaller particles at all temperatures. Cobalt 2-methylbenzimidazole dithiocarbamate complex produced big and undefined morphology. The optical properties were also featureless and XRD only showed impurities of C7OS8. The impurity is thought to be generated from a side reaction between benzimidazole and carbon disulphide to give this persistent organic moiety.

Superconductivity is a remarkable quantum phenomenon in which a macroscopic number of electrons form a condensate of Cooper pairs that can be described by a single quantum wave function. According to the celebrated Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity, there is a minimum length scale (the coherence length) below which the condensate has a rigid quantum phase. The fate of superconductivity in a system with spatial dimensions smaller than [the coherence length] has been the subject of intense interest for decades and recent studies of superconductivity in ultra-thin epitaxial metal films have revealed some surprising behaviors in light of BCS theory. Notably, it was found that superconductivity remains robust in thin lead films with thicknesses orders of magnitude smaller than the coherence length (i.e. in the extreme two dimensional limit). Such studies raise the critical question: what happens to superconductivity as all dimensions are reduced toward the zero dimensional limit? By controlling the lateral size of ultra thin 2D islands, we systematically address this fundamental question with a detailed scanning tunneling microscopy/spectroscopy study. We show that as the lateral dimension is reduced, the strength of the superconducting order parameter is also reduced, at first slowly for dimensions larger than the bulk coherence length, and then dramatically at a critical length scale of ~ 40nm. We find this length scale corresponds to the lateral decay length of the order parameter in an island containing regions of different heights and different superconducting strength. Overall, our results suggest that fluctuation corrections to the BCS theory are important in our samples and may need to be systematically addressed by theory. / text

Biosorption is a phenomenon involving the mechanisms that basically mediate heavy metal tolerance of microorganisms as well as sequestration of heavy metals from environment. Different classes of microorganisms have different biosorption capacities, as a result of the differences in composition and types of functional groups found on cell surfaces. The present study was undertaken to identify the molecular mechanisms for lead [Pb(II)] biosorption in the white-rot fungus, Phanerochaete chrysosporium. The methodology involved selective blocking of the functional groups known to participate in heavy metal biosorption and allowed us to determine their relative roles in Pb (II) biosorption in this organism. The relative concentrations of the Pb (II) sorbed from the aqueous environment and Mg2+ and Ca2+ ions released to the aqueous environment were measured and compared with both native and chemically-modified biomasses by using atomic absorption spectroscopy. Fourier-Transform Infrared (FTIR) spectroscopy technique was used to monitor and analyze the molecular-level changes in both native and chemically modified cell surfaces upon Pb (II) exposure. Interactions of Pb (II) with the biomass surface was determined by observing the changes in wavenumber and absorbance of NH stretching and Amide I bands arising from the amine groups and C=O stretching band arising from the carboxyl groups. The roles of phosphate groups and lipids were also investigated. Carboxyl groups seemed to be the most important functional groups for Pb (II) biosorption in P. chrysosporium, since the biosorption capacity dramatically decreased (by 92.8 %) in carboxyl groups-blocked biomass. Amine groups were found to play a secondary and minor role in Pb (II) biosorption, only a slight decrease (6 %) in Pb (II) biosorption was detected with amine groups-blocked biomass. Blocking of phosphate groups provided a small increase in biosorptive capacity and did not appear to have much significant role in biosorption. Upon chemical treatment with acetone to extract lipids of the cell surfaces, an increase of 20.3 % in the Pb (II) biosorptive capacity was determined. It was concluded that carbonyl and carboxyl groups of chitin and glucan are the major sites and ion exchange via these groups is the main mechanism for Pb (II) biosorption in P. chrysosporium.

The recent expansion in chemical and manufacturing and innovation has led to a large influx of chemicals to the market, and subsequent release into the environment. Many of these new chemicals, as well as legacy chemicals are untested for their potential developmental toxicity, especially in early embryonic stages. This creates a need for a timely and cost-effective method for screening these chemicals. Furthermore, advances in in vitro methods and human pluripotent cell culturing techniques have revealed some weaknesses in our current animal model-based paradigms. Here we tested an in vitro model for developmental toxicity screening using human embryonic stem cells (hESCs) for environmental chemicals. In this study, hESCs were exposed to three known developmental toxicants that are prevalent in the environment, bisphenol A (BPA), perfluorooctane sulfonate (PFOS), or lead chloride (PbCl₂), at environmentally relevant concentrations of 0-2500 µg/L, 0-2275 µg/L, and 0-6200 µg/L respectively, for 6-days. hESCs were evaluated for dose responses on proliferation level by assaying cell viability, mitochondrial dehydrogenase activity (MDHA), cell confluency, and cell cycle distribution. Differentiation capability was assayed by induction of differentiation into ectoderm, mesoderm, and endoderm; hESCs and differentiated cells were then sequenced for their full transcriptome. Gene expression effects were analyzed by a single cell transcriptome sequencing and analysis of global DNA methylation. Proliferation and methylation effects were tested for all 3 chemicals, while differentiation and single cell sequencing was only tested on PbCl₂. Our results show hESCs were able to identify known and novel proliferation effects of BPA, PFOS, and PbCl₂, reflect differentiation level effects of PbCl₂, and elucidate molecular level drivers of these toxic effects. We also showed that hESCs responded to developmental toxicants at lower doses than in vivo models. In conclusion, our hESC-based model could act as an effective developmental toxicity screening tool for pre- peri- and post-implantation stages of embryo development.

No description available.

L'exploitation, puis l'abandon, des sites miniers, dans l'oriental marocain, a entraîné une importante pollution des zones avoisinantes, générée par la dispersion de déchets riches en Pb. Pour résoudre ce problème, des programmes de phytomanagement sont à développer. Cependant, la réalisation de ces projets se heurte à deux contraintes : une faible diversité des plantes métallophytes et une méconnaissance des mécanismes de la tolérance au Pb.Dans ce contexte, l'objectif de mon travail de thèse a été de sélectionner une ou des plantes susceptibles d'entrer dans un programme de phytoremédiation et d'identifier des gènes impliqués dans la tolérance au Pb. Dans un premier temps, l'analyse des sols et des résidus miniers a révélé une importante contamination polymétallique du site d'étude. Des prospections floristiques ont ensuite permis d'identifier une plante de la famille des brassicacées, Hirschfeldia incana, prédominante sur les sites miniers pollués et qui accumule le Pb. L'accumulation du Pb chez H. incana a été confirmée en conditions contrôlées et une stratégie « gène candidat » a montré l'implication dans la tolérance au Pb de deux gènes, l'un codant pour une métallothionéine MT2a et l'autre pour un transporteur membranaire HMA4. Enfin, la comparaison des transcriptomes d'H. incana et d'A. thaliana a abouti à l'édification d'une liste de gènes candidats susceptibles d'être impliqués dans la tolérance au Pb. L'analyse fonctionnelle de quatre de ces gènes, codant pour une ferritine, une métallothionéine, une protéine fixatrice du cuivre et une défensine, a précisé leur rôle dans la tolérance au Pb. / Exploited, and then abandoned, mining sites, in the oriental Morocco, have polluted the neighboring regions, by dispersion of mining wastes containing Pb. Facing this problem, it is necessary to develop phytomanagement programs. Nevertheless, these project realisations encountered two major constraints: weak metallophyte plant diversity and misunderstanding of Pb tolerance mechanisms. In this context, the objectif of my work was to select plants compatible with a phytoremediation program and to identify genes implicated in lead tolerance. Firstly, soil and mining waste analysis has revealed an important polymetallic pollution of the studied region. Then, floristic explorations had permitted to identify a plant of the brassicaceae family, Hirschfeldia incana, which is predominant on the polluted mining regions and accumulated Pb. Pb accumulation in H. incana was confirmed in controlled conditions and a candidate gene approach has shown the lead tolerance implication of two genes, one coding for a metallothionein (MT2A) and the other a membrane transporter (HMA4). Finally, the transcriptome comparison from H. incana and A. thaliana has generated a list of candidate genes putatively implicated in Pb tolerance. Functional analysis of four genes, coding a ferretin, a metallothionein, a copper binding protein and a defensin, has permitted to clarify their role in Pb tolerance.

Thesis (M. Sc. Agriculture (Animal Production)) -- University of Limpopo, 2021 / The study was carried out to determine the concentration levels of mercury (Hg), lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni) and zinc (Zn) in water, soil, witbuffels grass and meat of goats reared along the river banks of Middle Olifants (Mogalatsana village) and Mogalakwena (Papegaai village) rivers. The samples were collected from the river water, soils along the river banks, grass grown along the river banks and male Pedi goats reared in Mogalatsana and Papegaai villages. The samples were analysed for the selected heavy metals with an inductively coupled plasma mass spectroscopy (ICP-MS). Data was analysed as in a complete randomised design. The results of selected heavy metals in water of both rivers ranged from 0.00 mg/litre of water (Ni and Cr) to 0.04 mg/litre of water (Hg). The concentration levels of selected heavy metals in water were similar (P>0.05) for Middle Olifants and Mogalakwena rivers. The concentration levels of selected heavy metals in the soils along the banks of Middle Olifants and Mogalakwena rivers ranged from 0.00 mg/kg DM soil (Hg and Cd) to 63.70 mg/kg DM soil (Cr). There were similar (P>0.05) concentration levels of selected heavy metals in the soils along the banks of Middle Olifants and Mogalakwena rivers. Heavy metal concentration levels in the witbuffels grass grown along the banks of Middle Olifants and Mogalakwena rivers ranged from 0.00 mg/kg DM of grass (Hg and Cd) to 5.05 mg/kg DM of grass (Zn). Similar (P>0.05) concentrations of selected heavy metals were observed in witbuffels grass grown along the banks of Middle Olifants and Mogalakwena rivers. However, the concentration levels of Zn, Pb and Cd in water from both sites were above internationally maximum permissible levels, indicating that the water from these rivers was not safe for drinking by humans and animals. The concentration levels of Ni and Pb in soils from both sites were above internationally recommended maximum permissible limits. Similarly, chromium concentration levels in witbuffels grass from both sites were above the recommended maximum permissible limits for livestock, indicating that the grass was not safe for consumption by livestock. It is recommended that further studies be conducted to ascertain these findings. Blood, liver, kidney and meat samples of yearling male Pedi goats grazing along the banks of Middle Olifants river (Mogalatsana village) had similar (P>0.05) Cr, Cd, Hg, Ni and Pb concentration levels, respectively. However, goat liver samples had higher (P<0.05) Zn concentrations than meat, kidney and blood samples. Samples of goat v meat contained higher (P<0.05) Zn concentrations than those of kidneys and blood. Similarly, goat kidney samples contained more (P<0.05) Zn than blood samples. Blood, liver, kidney and meat samples of Pedi goats grazing along the banks of Mogalakwena river (Papegaai village) contained similar (P>0.05) concentration levels of Cr, Cd, Hg, Ni and Pb, respectively. However, goat meat samples contained higher (P<0.05) Zn concentrations than liver, kidney and blood samples. Samples of goat liver contained higher (P<0.05) Zn concentration levels than kidney and blood samples. Similarly, goat kidney samples contained more (P<0.05) Zn than blood samples. Meat, blood, liver and kidney samples of male Pedi goats raised in Mogalatsana and Papegaai villages had similar (P>0.05) chromium, cadmium, mercury, nickel and lead concentrations, respectively. However, liver and kidney samples of goats from Mogalatsana village had higher (P<0.05) zinc levels than those from Papegaai village. Blood and meat samples of goats from Papegaai village had higher (P<0.05) zinc levels than those from Mogalatsana village. The concentration levels of Zn, Ni, Pb, Cr and Cd in the blood, liver, kidney and meat samples of male Pedi goats reared along the banks of Middle Olifants and Mogalakwena rivers were within the maximum permissible levels for human consumption. Mercury concentration levels in liver, kidney and meat samples of the goats were within the maximum permissible levels for human consumption. However, mercury concentration levels in the blood of goats grazing along the banks of Middle Olifants and Mogalakwena rivers were above the maximum permissible limit of 0.2 mg/litre of blood. It was concluded that meat, livers and kidneys of the goats were fit for human consumption. However, blood from these goats was not fit for human consumption.

Världen står inför ett stort vattenförsörjningsproblem som måste lösas – så många som 884 miljoner människor använder idag potentiellt förorenade vattenkällor till sitt dricksvatten. Denna rapport fokuserar på ett av de drabbade länderna som är Uganda. Syftet med projektet är att undersöka vilket/vilka av de fem olika ugandiska växterna; Erythrina abyssinica, Musa spp, Cyperus papyrus, Imperata cylindrica och Coffea canephora som är mest lämplig för rening av kadmium- och blykontaminerat grundvatten. Katjonbyteskapaciteten bestäms genom laboration. Analyser kring växtmaterialen görs med hjälp av litteraturstudier och intervjuer med en doktorand från Uganda. M. spp visar sig ha klart högst katjonbyteskapacitet och finns även i form av mycket avfall, därför anses denna vara det mest lämpliga materialet för rening. Lösningen skulle kunna implementeras i samhället med ett filter gjort av växtmaterial, om vidare forskning görs. / The world is facing a major water supply problem to solve, as many as 884 million people currently use potentially polluted water sources for their drinking water. This report focuses on one of the affected countries, which is Uganda. The project aims to examine which of the five different Ugandan plants; Erythrina abyssinica, Musa spp, Cyperus papyrus, Imperata cylindrica and Coffea canephora that is the most suitable for purification of cadmium- and lead contaminated groundwater. The cation exchange capacity is determined by laboratory experiment. Literature studies and interviews with a Ugandan postgraduate student are used for the analysis of the plant materials. M. spp has the highest cation exchange capacity and contributes with a lot of waste material; therefore it is considered the most suitable material for purification. The solution could be implemented in the community with a filter made of plant material, if further research is done.

No description available.