Thesis (MSc.(Pharmacology)--Faculty of Health Sciences)-University of Pretoria, 2008.

Thesis (Ph.D.) - Carleton University, 2005. / Includes bibliographical references (p. 292-309). Also available in electronic format on the Internet.

Orientador: André Henrique Rosa / Banca: Paulo Sérgio Tonello / Banca: Marcia Cristina Bisinoti / Banca: Maria Olimpia de Oliveira Resende / Banca: Wander Gustavo Botero / Resumo: Os estudos de especiação em águas naturais são a chave para a compreensão do comportamento e destino dos íons metálicos no ambiente, uma vez que estes elementos podem ser encontrados em diversas formas químicas (livres ou complexados). A mobilidade, biodisponibilidade e transporte desses íons podem ser influenciados pela presença da matéria orgânica natural (MON) e as substâncias húmicas aquáticas (SHA), principais ligantes presente no ambiente aquático. Nesse contexto, o objetivo desse trabalho foi desenvolver métodos eletroanalíticos utilizando a cronopotenciometria de redissolução anódica (SCP) e a técnica de redissolução nernstiana na ausência de gradientes (AGNES) capazes de determinar a concentração de cádmio total (CdT) e livre (CdL), respectivamente, diretamente em amostras de águas dos rios Itapanhaú (RI) e Sorocabinha (RS) localizados no estado de São Paulo, que possibilitem uma futura aplicação on-site. E avaliar a influência da MON e SHA extraídas desses rios nas interações com o Cd(II) e/ou Pb(II). Para investigar o efeito da sazonalidade foram coletadas amostras de água no março e novembro de 2014, as quais foram caracterizadas através de parâmetros de qualidade da água, carbono orgânico dissolvido (COD), espectroscopia UV/Vis e concentrações de metal total, dissolvido e "livre" (ultrafiltrado em 1kDa com fluxo tangencial - UFT). As SHA e suas frações (ácido húmico (AH) e fúlvico (AF) foram caracterizadas por meio da análise elementar, RMN 13C e fracionadas atra... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The study of speciation in natural waters are crucial to understand the behaviour and fate of metal ions in the environment, since these elements can be found in different chemical forms (complexed or free). The mobility, bioavailability and transport of these ions can be influenced by natural organic matter (NOM) and aquatic humic substances (AHS), which are the main ligands in aquatic environments. The objective of this thesis was to develop electroanalytical methods using the techniques stripping chronopotenciometry (SCP) and absence of gradients and nernstian stripping (AGNES), which are able to determine the concentration of total (TCd) and free (FCd) cadmium directly in water samples from the rivers Itapanhaú (RI) and Sorocabinha (RS), located in the state of São Paulo. It would make possible a future on-site measurement applications. This study also aimed to evaluate the influence of NOM and AHS extracted from these rivers in the interactions with Cd(II) and Pb(II). Water samples were taken in march and november/2014 in order to investigate the effect of seasonality. These samples were characterised using water quality parameters, dissolved organic carbon (DOC), UV/VIS spectroscopy and concentrations of total, dissolved and free metal (ultrafiltered through 1 kDa membrane with tangential flow- TUF). AHS and their fractions (humic, HA, and fluvic acid, FA) were characterised by elemental analysis, NMR 13C. They were fractionated through TUF through membranes 100, 30, 10, 3 and 1 kDa. The methods developed of SCP (TCd determination) and AGNES (CdL determination) applied in the in natura and ultrafiltered (1 kDa) samples were validated using graphite furnace atomic absorption spectrometry (GFAAS). The results showed that the main differences between the waters from RI and RS are related probably to the influence of seawater and seasonality. The structural composition of AHS and FA presented hig... / Doutor

Humic substances, such as the closely related humic and fulvic acids are ubiquitous, naturally occurring organic macromolecules of complex but undefined structure. These compounds are known complexing agents due to their supramolecular like structures and are capable of binding a wide variety of compounds. Numerous studies have confirmed that humic and fulvic acids exhibit diverse medicinal and therapeutic properties. For this reason, alternative or “natural” medicinal preparations rich in these substances are being self-administered, often concomitantly with conventional drugs. The possibility exists that these humic substances, found in the alternative medicinal products, may result in drug-drug interactions and bind to simultaneously ingested drugs. Complex formation may affect absorption and alter overall bioavailability. Changes in these parameters may lead to reduced therapeutic effect or toxic side effects of prescribed drugs in patients. Similarly, these humic substances may bind to and alter the uptake of ingested nutrients, such as vitamins and minerals, obtained from food sources as well as dietary supplements. Changes in absorption may result in a loss of proper physiological functioning in the body or in unwanted effects of overdose. This study investigated the effect of fulvic and humic acids on the absorption of commonly administered classes of drugs, vitamins and minerals using the everted mouse gut model that was successfully used to assess the membrane transport of the test compounds. This model made use of everted segments of excised intestinal tissue placed in Krebs Ringer Buffer (pH7.4), where physiological functioning of the tissue is maintained for up to two hours after excision. The amount of test compound which crossed through the intestinal membrane without and in the presence of each humic substance was quantified using LC-MS/MS methods developed for each of the drugs and vitamins, and ICP-MS, in the case of the minerals. The amount of test compound absorbed alone was compared to the amount absorbed when in the presence of each humic substance. Changes in the uptake, for each test compound was noted, the extent of the absorption increase or decrease was compound specific. The changes in absorption observed could be attributed to changes in compound solubility and mechanism of transport across the intestinal membrane once in complex. Drugs and vitamins were seen to be more prone to decreases in absorption in the presence of the humic substances, whereas the majority of the minerals showed significantly increased absorption. Binding of the minerals to the humic substances through chelation, and not complex formation, could have a greater effect on compound solubility. Health care professionals, as well as individuals ingesting these and other substances concurrently, should be aware of the potential effects on absorption that may occur due to drug-drug interactions in order to avoid a loss of therapeutic/physiological activity or negative toxic symptoms. / Dissertation (MSc)--University of Pretoria, 2015. / tm2015 / Pharmacology / MSc / Unrestricted

The diploma thesis is focused on the determination of tetracyclines, sulfonamides and fluoroquinolones from soil. Antibiotics such as tetracycline, chlortetracycline, oxytetracycline. ciprofloxacin, trimethoprim, sulfamethaxazole and sulfadiazin were selected due to frequent use in veterinary medicine. Due to the fact that the soil is a complex matrix and contains many components that can interfere with the detection signal of analytes, it was necessary to use the MAX column in the SPE method, which removes fulvic aned humic acid from analytes and the HLB column Final analysis of the analytes was performed by liquid chromatography with mass detesction (LC-MS). The method was also used for real soil samples, which were delivered from ÚKZUS.

This diploma thesis is focused on the study of dissociation behaviour of natural biocolloids, namely humic acids and fulvic acids. Humic and fulvic acids are natural, heterogeneous, high molecular weight substances which behave as weakly acidic polyelectrolytes and they have complex not exactly described structure. They are formed by biochemical transformations of organic residues (mainly plants). They are part of the soil, water, peat, sediments and coal. Solubility of humic acids is affected by pH value. The higher the pH value is the higher the solubility is. Fulvic acids are soluble in whole range of pH values. The aim of this diploma thesis is to determine the dissociation constant for the five kinds of humic acids and four kinds of fulvic acids, which have been isolated from various natural sources. These samples were purchased from IHSS. Dissociation constants were determined by the conductometric method and a combination of measurment pH and the content of acidic functional groups in Na2SO4. UV-VIS spectrophotometry method was used to characterize the quality of humic acids and fulvic acids.

No description available.

A cation exchange method (Chelex 100) that distinguishes weakly bound and strongly bound copper was investigated for its ability to measure bioavailable copper in estuarine waters. Copper bound to the Chelex 100 resin was operationally defined as bioavailable copper. Varying initial copper concentration from 195 to 495 ug/L at a constant 12.5 mg/L natural organic matter (NOM) did not affect percent bioavailability. There were also no noticeable effects when varying total Cu concentration in the presence of 0, 12, and 24 mg/L NOM. An increase in pH from 4 to 8.5 and NOM from 0 mg/L to 12.5 mg/L reduced percent bioavailability. Using the Chelex 100 resin to measure bioavailable copper, about 20 to 40% of the total copper was bioavailable in the absence of NOM, while about 15 to 20% was bioavailable when either 12 or 24 mg/L NOM was present. Acute toxicity bioassays were performed with mysid shrimp (Americamysis bahia) to evaluate the toxic effects of copper in the presence of Suwannee River Fulvic Acid, which served as a source of NOM. Static or static renewal tests, based on EPA method OPPTS 850.1035 with a minimum of 10 mysid shrimp per test condition, were used to determine the LC50 and EC50 of copper and the effects of NOM. Test solutions consisted of artificial synthetic seawater at 20 parts per thousand containing concentrations of 0, 100, 200, 400, 800 ug/L copper with either 0, 12, 24 mg/L NOM. Forty-eight hour acute toxicity tests were performed on larval (2 to 3 day) mysid shrimp that were fed Artemia (brine shrimp); mortality and immobilization were the endpoints. The 48 hour LC50 was 200 ug/L dissolved Cu and 94 ug/L bioavailable Cu without NOM, 340 ug/L dissolved Cu and 98 ug/L bioavailable Cu when 12 mg/L NOM was present, and 495 ug/L dissolved Cu and 105 ug/L bioavailable Cu at 24 mg/L NOM. The consistency of the LC50 measurement using bioavailable Cu suggest that the Chelex 100 resin is a useful technique for toxicity analysis in saline water. / Master of Science

Chapter 2: Germination and Growth of Radish (Raphanus sativus) and Lettuce (Lactuca sativus) Exposed to Arsenite and Arsenate in Hydroponic Growth Solution Little information is available on the survival, uptake, and dry mass production of vegetable seedlings and maturing plants in arsenic enriched environments. Such information is however very important to many vegetable growers in areas of subsistent agricultural like Bangladesh or home-gardeners in closer proximity of As sources such as metal smelters. Accordingly we conducted research investigating (i) the germination and radical formation of radish and lettuce seeds at varying As (V) and As (III) concentrations and (ii) radish and lettuce plants in solution culture. Seed germination studies demonstrated that 0.1mM and 0.025mM are toxic threshold levels of As (III and V) for radishes and lettuce, respectively, while As (V) is more toxic to radish seeds than As (III). Arsenic (III and V) impacted both germination and radical development in radish seeds. For lettuce we observed that As had no impact on germination but reduced radical length significantly (p < 0.01). At most equimolar concentrations, As (III) was more toxic than As (V) in lettuce seeds (0.025 - 0.10mM As), a result contrary to those obtained in radish seeds (0.05 - 0.5mM As). The hydroponic growth studies showed that losses and increases in dry weight are a function of absorbed As and are dependent on the source of As: As (V) or As (III). Moreover, the effect of absorbed As (V) or As (III) on dry weight reductions and increases differed between root and shoot portions of the plants and are crop dependent. Tissue-As (originally solution As (V)) was more toxic at the radish root level and tissue-As (originally solution As (III)) was more toxic at the radish shoot level. Conversely for lettuce, As (III) caused reductions in dry weight, while As (V) had a stimulating effect on biomass production. Lower As (V) concentrations in plant tissue throughout the lettuce study and at low As (V) concentrations (0.02mM) in the radish study may be explained by the molar ratio of P:As of approximately 5. From a food nutrition safety standpoint, studies need to concentrate on sub-lethal levels in order to ensure the proper formation of the harvestable portion of the plant. Chapter 3: Adsorption of Arsenate (V) and Arsenite (III) on Goethite in the Presence and Absence of Soluble Organic Carbon The environmental fate of arsenic is of utmost importance as the U.S. EPA has recently proposed to tighten the arsenic drinking water standard from 50 ppb to 5 ppb. In natural systems the presence of dissolved organic carbon (DOC) may compete with As for adsorption to mineral surfaces, hence increasing its potential bioavailability. Accordingly, the adsorption of arsenate As (V) and As (III) on goethite (α-FeOOH) was investigated in the presence of either a peat humic acid (Hap), a Suwannee River Fulvic Acid (FA) (IHSS) or citric acid (CA). Adsorption edges and kinetic experiments were used to examine the effects of equimolar concentrations of organic adsorbates on arsenic adsorption. Adsorption envelopes were conducted over a pH range of 11 to 3, while the kinetic studies were conducted at pH 6.5 for As (V) and pH 5.0 for As (III). Arsenate adsorption was inhibited in the order of Hap > FA > CA while arsenite adsorption was inhibited in the order of CA > FA > Hap. Humic acid reduces As V adsorption starting at pH 9, with a maximum reduction at pH 6.5. Fulvic acid slightly inhibited As (V) adsorption starting at pH 5, and this inhibition increased with a decrease in pH. No effect was observed in the presence of CA. Arsenite adsorption is inhibited by HA starting a pH 7 and increases with a decrease in pH, while FA and CA reduce As (III) adsorption beginning at pH 8, with a continuous reduction as the pH decreases. The differential extent of As V adsorption in the presence of the organic acids suggests that the distribution and the respective densities of the abundant functional groups (phenol/ catechol OH or COO⁻) are significant in the adsorption of As (V). Furthermore, larger organic acids may hydrophobically partition to surfaces via a more favorable entropy driven reaction mechanism which may influence As (V) diffusion and its subsequent adsorption to surfaces. The decrease in As (III) adsorption is caused by its reduced affinity for the surface at pH values lower than 9, and the simultaneous increase in surface activity by the organic substances' via their COO⁻ functional groups. The results of these experiments suggests that dissolved organic carbon substances are capable of increasing the bioavailability of As in soil and water systems in which the dominant solid phase is a crystalline iron oxide. Chapter 4: Adsorption of Arsenate and Arsenite on Ferrihydrite in the Presence and Absence of Dissolved Organic Carbon (DOC) The adsorption of As (V) and As (III) on synthetic 2-line ferrihydrite in the presence and absence of a peat humic acid (Hap), Suwannee River Fulvic Acid (FA) or citric acid (CA) was investigated. Previous work with goethite has demonstrated the ability of DOC materials to reduce As (V) and As (III) adsorption. In this study, a batch technique was used to examine the adsorption of arsenic (III and V) and DOCs on ferrihydrite in the pH range from 3 to 11. The results obtained demonstrated that As (V) adsorption on ferrihydrite was reduced only in the presence of CA. Arsenate reduced the adsorption of all organic acids except Hap. Both FA and CA reduced As (III) adsorption on ferrihydrite, while Hap had no effect. Fulvic and citric acid adsorption on ferrihydrite was reduced in the presence of As (III), however, adsorption increases of FA and CA were observed at lower pH, which is consistent with a decrease in As(III) adsorption. The peat humic acid had no effect on As (III) adsorption, and we believe that the adsorption process of Hap and As (III and V) on ferrihydrite are independent of each other. The observed differences between this study and the study on goethite are believed to be an intricate function of ferrihydrite's surface characteristics, which affects the mechanisms of surface adsorption and hence the affinity of organic acids such as Hap, FA, and CA for the ferrihydrite surface. As such, the adsorption of DOCs to ferrihydrite are assumed to be energetically less favorable and to occur with a fewer number of ligands, resulting in lower surface coverage of weaker bond strength. Additional factors for the observed differences are discussed. This work demonstrates the importance of the solid phase in adsorption processes and functional group composition, as noticeable differences are observed in comparison to a crystalline Fe-oxide solid phase. / Master of Science

Water stress is the most critical environmental factor limiting crop production in the US Piedmont. The presence of humic substances in composted organic amendments may increase crop tolerance to water stress through their hormone-like effects on plant metabolism. The objectives of this study were to calculate N mineralization rates of composted and non-composted organic materials used in this long-term field study, and to determine differences in soil physiochemical properties, corn and soybean leaf physical and biochemical properties yield and seed quality between organically amended and inorganically fertilized treatments. Nitrogen mineralization rates were greatest in the poultry litter (21%) and Panorama yard waste compost (4.5%) amended plots. Nitrogen uptake (120 mg/pot, 133 mg/pot, respectively) in these treatments were greater than that in the control (0N) (91.3 mg/pot) treatment. Wolf Creek biosolids compost and Huck's Hen Blend yard waste compost induced N immobilization (-5.0% and 0.18%, respectively), and had N uptake values similar to the control (92.6 mg/pot and 95.7 mg/pot). Rivanna biosolids compost immobilized N (-14.8%) but N uptake (136 mg/pot) was greater than that in the control due to the relatively high inorganic N content in the amendment. The total N concentration and C:N values were less reliable variables in predicting N mineralization when a significant portion of the total N was in the inorganic form. The annual application of poultry litter, Rivanna biosolids compost, and Panorama yard waste compost at 100% agronomic nitrogen and 30 % agronomic nitrogen rates in the field study improved soil fertility and increased total organic and humified carbon contents relative to the inorganically fertilized and control treatments. The amended treatments had slightly greater plant available water contents (average 10.0 cm/15 cm) than the control (8.38 cm/15 cm). Leaf water potential measurements revealed that neither crop experienced water stress during the sampling season. Treatment differences in leaf antioxidant activity were only observed in corn. All corn plants that were fertilized with amendments supplying the crop's nitrogen needs, regardless of the source, had greater leaf nitrogen (+29%), chlorophyll (+33%), and protein contents (+37%), lower superoxide dismutase (-29%) and ascorbate peroxidase (-17%) activities, and lower malondialdehyde (-33%) contents relative to the control and low nitrogen treatments. There were no observed differences in catalase activity, which was likely due to the evolutionary advantage of C4 metabolism. Yield was strongly related to midseason leaf nitrogen contents (R2=0.87, p<0.0001) and not soil humified carbon (R2=0.02, p=0.0543). There were no observed treatment differences in soybean leaf physiology and metabolism. Differences, however, were observed over time. As the leaves senesced, leaf chlorophyll, protein, superoxide dismutase and catalase activities decreased, and the malondialdehyde content increased. Ascorbate peroxidase activity slightly increased with time. Catalase activity in soybean was primarily driven by the oxidation of glycolate, a product of photorespiration, and not the formation of reactive oxygen species in the chloroplasts. The organically amended treatments had higher yields (9-21% increase), greater protein contents (4-9% increase), and seed weights (5-14% increase) relative to the fertilizer and control treatments. It was concluded that differences in soybean yield and seed quality were due to non-nutritive benefits of the organic amendments and not available water or plant nutrition. / Master of Science