MESQUITA, Ricardy Leonam Pontes. Síntese de nanopartículas de prata através de ultrassom utilizando galactomanana. 2016. 94 f. Dissertação (Mestrado em química)- Universidade Federal do Ceará, Fortaleza-CE, 2016. / Submitted by Elineudson Ribeiro (elineudsonr@gmail.com) on 2016-07-28T17:12:54Z No. of bitstreams: 1 2016_dis_rlpmesquita.pdf: 2439147 bytes, checksum: 18f53a2e3356343fac06a5df49665f6e (MD5) / Approved for entry into archive by José Jairo Viana de Sousa (jairo@ufc.br) on 2016-08-02T14:38:19Z (GMT) No. of bitstreams: 1 2016_dis_rlpmesquita.pdf: 2439147 bytes, checksum: 18f53a2e3356343fac06a5df49665f6e (MD5) / Made available in DSpace on 2016-08-02T14:38:19Z (GMT). No. of bitstreams: 1 2016_dis_rlpmesquita.pdf: 2439147 bytes, checksum: 18f53a2e3356343fac06a5df49665f6e (MD5) Previous issue date: 2016 / Silver nanoparticles (NPAg) have attracted considerable interest in the context of research in recent years due to numerous applications, such as a bactericide, sensors and catalysts. In this paper the use of galactomannan of fava danta (GFD) in obtaining NPAg by ultrasonic method was studied based on the principles of green chemistry without the use of conventional chemical reducing agent. This study aimed to evaluate the ultrasound employment in NPAg synthesis GFD solutions. The NPAg were obtained with the aid of an ultrasonic probe using AgNO3 aqueous solution in concentrations of 10, 40 and 100 mmol / L. The galactomannan in aqueous solution (0,032%, 0,32% and 0,0032% w/ v) was used as stabilizer of NPAg. The synthesis occurred at varying pH (10, 11, 12) and temperature (15, 25 and 35 °C). The characterizations were performed using techniques such as gel permeation chromatography (GPC), nuclear magnetic resonance of hydrogen (NMR1H), spectrophotometry UV-Vis, dynamic light scattering (DLS) and scanning electron microscopy (SEM). UV-Vis analysis for colloids formed during the synthesis at the three concentrations showed the emergence of the plasmon band (around 400 nm) suggesting the formation of NPAg. It was observed faster kinetic profile for concentration systems 10 mmol/ L AgNO3. The pH 11 and 12 provided the best conditions for synthesis of NPAg. The different concentrations of synthetic GFD showed satisfactory results, but the formed colloid concentration 0,0032% w/ v showed no stability. Two of the synthesized colloids were selected FDAg 10/12/25 and FDAg 100/12/25, to submit the study to estimate size during the time of formation of NPAg as were also objects of analysis by electron microscopy scan. DLS was evidenced by the two colloids have decreased the size NPAg during the synthesis time, reaching average sizes near 10 to 4 nm for FDAg 10/12/25 and FDAg 100/12/25 respectively. Monitoring the polysaccharide degradation by GPC analysis was conducted and it was observed the decrease in distribution of the molar masses of the same of 6,65 x 106 to 3,11 x 104 g/ mol during the degradation process. The mannose/ galactose ratio was observed for the GFD, from 1:1,23 to GFD unmodified to 1:2,14 for the GFD degraded in 420 minutes. Thus, this study showed that the ultrasonic path in conjunction with the use of the galactomannan of fava danta in aqueous solution provides a versatile synthetic route for NPAg with good stability. / Nanopartículas de prata (NPAg) têm atraído bastante interesse no âmbito da pesquisa durante os últimos anos devido às inúmeras aplicações, tais como agente bactericida, sensores e catalisadores. Neste trabalho o uso de galactomanana da fava danta (GFD) na obtenção das NPAg por método ultrassônico foi estudado com base nos princípios da química verde sem a utilização de redutores químicos convencionais. Este estudo teve como objetivo, avaliar o emprego do ultrassom na síntese de NPAg em soluções de GFD. As NPAg foram obtidas com auxílio de uma sonda ultrassônica, utilizando solução aquosa de AgNO3 nas concentrações 10, 40 e 100 mmol/L. A galactomanana em solução aquosa (0,032%, 0,32% e 0,0032% m/v) foi utilizada como estabilizante das NPAg. As sínteses ocorreram com variação de pH (10, 11 e 12) e de temperatura (15, 25 e 35 °C). As caracterizações foram realizadas através de técnicas como Cromatografia de permeação em gel (GPC), Ressonância magnética nuclear de hidrogênio (RMN 1H), Espectrofotometria UV-Vis, Espalhamento de luz dinâmico (DLS) e Microscopia eletrônica de varredura (MEV). As análises de UV-Vis para os coloides formados durante as sínteses nas três concentrações mostraram o surgimento da banda de plasmon (em torno de 400 nm) evidenciando a formação das NPAg. Observou-se perfil cinético mais rápido para os sistemas de concentração 10 mmol/L de AgNO3. Os valores de pH 11 e 12 proporcionaram as melhores condições de síntese das NPAg. As diferentes concentrações de GFD apresentaram resultados de síntese satisfatórios, porém o coloide formado em concentração 0,0032% m/v não apresentou estabilidade. Dois dos coloides sintetizados foram selecionados, FDAg 10/12/25 e FDAg 100/12/25, a se submeterem a estudo para estimativa de tamanho durante todo o tempo de formação das NPAg, assim como também foram objetos de análise por Microscopia eletrônica de varredura. Por DLS foi evidenciado que os dois coloides tiveram diminuição de tamanho das NPAg no decorrer do tempo de síntese, atingindo tamanhos médios próximos de 10 e 4 nm para FDAg 10/12/25 e FDAg 100/12/25 respectivamente. Foi realizado o acompanhamento da degradação do polissacarídeo através de análise por GPC, tendo sido observado a diminuição da distribuição das massas molares do mesmo de 6,65 x 106 para 3,11 x 104 g/mol durante o processo de degradação. A razão manose/galactose foi verificada para a GFD, passando de 1:1,23 para a GFD não modificada para 1:2,14 para a GFD degradada em 420 minutos. Sendo assim, este estudo mostrou que a via ultrassônica em conjunto com a utilização da galactomanana da fava danta em solução aquosa proporciona uma rota sintética bastante versátil para as NPAg com boa estabilização.

The field of nanoecotoxicology has been pioneered in recent years as concern grows in response to the potential environmental hazards of engineered nanoparticle release. Silver nanoparticle (AgNP) release through induction into commercial products as an antimicrobiont is of particular interest. Plausible routes of AgNPs to reach aquatic systems and their biological impacts have been investigated, but none have addressed the potential remediation of these waters using the heavy metal accumulating fern Azolla caroliniana. This study employed biological staining techniques and fluorescence microscopy to identify oxidative stress, wounding responses of cell wall and membrane, and cell death of A. caroliniana roots to assess the capability of this plant to withstand AgNP exposure. Two concentrations series were applied, 0-1.0ppm and 0-10.0ppm for 1, 3, 5 days after transfer (DAT), 0ppm being a control. Oxidative stress, measured in production of non-specific ROS, increased in a dose-dependent manner with increasing AgNP concentration. Callose (1,3-β-glucan) was deposited in response to potential cell wall damage and was also observed to be elevated in a dose-dependent manner. Cell vitality appeared from a general decline in fluorescence of nucleic content to visual nuclei lysis. Statistically significant and severe responses to AgNPs was observed at 1 DAT but recovery could be seen at 3~5 DAT. In sum, these data suggest a toxicity threshold of 1.0ppm at which A. caroliniana roots can mediate exposure.

abstract: With the application of reverse osmosis (RO) membranes in the wastewater treatment and seawater desalination, the limitation of flux and fouling problems of RO have gained more attention from researchers. Because of the tunable structure and physicochemical properties of nanomaterials, it is a suitable material that can be used to incorporate with RO to change the membrane performances. Silver is biocidal, which has been used in a variety of consumer products. Recent studies showed that fabricating silver nanoparticles (AgNPs) on membrane surfaces can mitigate the biofouling problem on the membrane. Studies have shown that Ag released from the membrane in the form of either Ag ions or AgNP will accelerate the antimicrobial activity of the membrane. However, the silver release from the membrane will lower the silver loading on the membrane, which will eventually shorten the antimicrobial activity lifetime of the membrane. Therefore, the silver leaching amount is a crucial parameter that needs to be determined for every type of Ag composite membrane. This study is attempting to compare four different silver leaching test methods, to study the silver leaching potential of the silver impregnated membranes, conducting the advantages and disadvantages of the leaching methods. An In-situ reduction Ag loaded RO membrane was examined in this study. A custom waterjet test was established to create a high-velocity water flow to test the silver leaching from the nanocomposite membrane in a relative extreme environment. The batch leaching test was examined as the most common leaching test method for the silver composite membrane. The cross-flow filtration and dead-end test were also examined to compare the silver leaching amounts. The silver coated membrane used in this experiment has an initial silver loading of 2.0± 0.51 ug/cm2. The mass balance was conducted for all of the leaching tests. For the batch test, water jet test, and dead-end filtration, the mass balances are all within 100±25%, which is acceptable in this experiment because of the variance of the initial silver loading on the membranes. A bad silver mass balance was observed at cross-flow filtration. Both of AgNP and Ag ions leached in the solution was examined in this experiment. The concentration of total silver leaching into solutions from the four leaching tests are all below the Secondary Drinking Water Standard for silver which is 100 ppb. The cross-flow test is the most aggressive leaching method, which has more than 80% of silver leached from the membrane after 50 hours of the test. The water jet (54 ± 6.9% of silver remaining) can cause higher silver leaching than batch test (85 ± 1.2% of silver remaining) in one-hour, and it can also cause both AgNP and Ag ions leaching from the membrane, which is closer to the leaching condition in the cross-flow test. / Dissertation/Thesis / Masters Thesis Civil, Environmental and Sustainable Engineering 2017

Universidade Federal do Cearà / Silver nanoparticles (NPAg) have attracted considerable interest in the context of research in recent years due to numerous applications, such as a bactericide, sensors and catalysts. In this paper the use of galactomannan of fava danta (GFD) in obtaining NPAg by ultrasonic method was studied based on the principles of green chemistry without the use of conventional chemical reducing agent. This study aimed to evaluate the ultrasound employment in NPAg synthesis GFD solutions. The NPAg were obtained with the aid of an ultrasonic probe using AgNO3 aqueous solution in concentrations of 10, 40 and 100 mmol / L. The galactomannan in aqueous solution (0,032%, 0,32% and 0,0032% w/ v) was used as stabilizer of NPAg. The synthesis occurred at varying pH (10, 11, 12) and temperature (15, 25 and 35 ÂC). The characterizations were performed using techniques such as gel permeation chromatography (GPC), nuclear magnetic resonance of hydrogen (NMR1H), spectrophotometry UV-Vis, dynamic light scattering (DLS) and scanning electron microscopy (SEM). UV-Vis analysis for colloids formed during the synthesis at the three concentrations showed the emergence of the plasmon band (around 400 nm) suggesting the formation of NPAg. It was observed faster kinetic profile for concentration systems 10 mmol/ L AgNO3. The pH 11 and 12 provided the best conditions for synthesis of NPAg. The different concentrations of synthetic GFD showed satisfactory results, but the formed colloid concentration 0,0032% w/ v showed no stability. Two of the synthesized colloids were selected FDAg 10/12/25 and FDAg 100/12/25, to submit the study to estimate size during the time of formation of NPAg as were also objects of analysis by electron microscopy scan. DLS was evidenced by the two colloids have decreased the size NPAg during the synthesis time, reaching average sizes near 10 to 4 nm for FDAg 10/12/25 and FDAg 100/12/25 respectively. Monitoring the polysaccharide degradation by GPC analysis was conducted and it was observed the decrease in distribution of the molar masses of the same of 6,65 x 106 to 3,11 x 104 g/ mol during the degradation process. The mannose/ galactose ratio was observed for the GFD, from 1:1,23 to GFD unmodified to 1:2,14 for the GFD degraded in 420 minutes. Thus, this study showed that the ultrasonic path in conjunction with the use of the galactomannan of fava danta in aqueous solution provides a versatile synthetic route for NPAg with good stability. / NanopartÃculas de prata (NPAg) tÃm atraÃdo bastante interesse no Ãmbito da pesquisa durante os Ãltimos anos devido Ãs inÃmeras aplicaÃÃes, tais como agente bactericida, sensores e catalisadores. Neste trabalho o uso de galactomanana da fava danta (GFD) na obtenÃÃo das NPAg por mÃtodo ultrassÃnico foi estudado com base nos princÃpios da quÃmica verde sem a utilizaÃÃo de redutores quÃmicos convencionais. Este estudo teve como objetivo, avaliar o emprego do ultrassom na sÃntese de NPAg em soluÃÃes de GFD. As NPAg foram obtidas com auxÃlio de uma sonda ultrassÃnica, utilizando soluÃÃo aquosa de AgNO3 nas concentraÃÃes 10, 40 e 100 mmol/L. A galactomanana em soluÃÃo aquosa (0,032%, 0,32% e 0,0032% m/v) foi utilizada como estabilizante das NPAg. As sÃnteses ocorreram com variaÃÃo de pH (10, 11 e 12) e de temperatura (15, 25 e 35 ÂC). As caracterizaÃÃes foram realizadas atravÃs de tÃcnicas como Cromatografia de permeaÃÃo em gel (GPC), RessonÃncia magnÃtica nuclear de hidrogÃnio (RMN 1H), Espectrofotometria UV-Vis, Espalhamento de luz dinÃmico (DLS) e Microscopia eletrÃnica de varredura (MEV). As anÃlises de UV-Vis para os coloides formados durante as sÃnteses nas trÃs concentraÃÃes mostraram o surgimento da banda de plasmon (em torno de 400 nm) evidenciando a formaÃÃo das NPAg. Observou-se perfil cinÃtico mais rÃpido para os sistemas de concentraÃÃo 10 mmol/L de AgNO3. Os valores de pH 11 e 12 proporcionaram as melhores condiÃÃes de sÃntese das NPAg. As diferentes concentraÃÃes de GFD apresentaram resultados de sÃntese satisfatÃrios, porÃm o coloide formado em concentraÃÃo 0,0032% m/v nÃo apresentou estabilidade. Dois dos coloides sintetizados foram selecionados, FDAg 10/12/25 e FDAg 100/12/25, a se submeterem a estudo para estimativa de tamanho durante todo o tempo de formaÃÃo das NPAg, assim como tambÃm foram objetos de anÃlise por Microscopia eletrÃnica de varredura. Por DLS foi evidenciado que os dois coloides tiveram diminuiÃÃo de tamanho das NPAg no decorrer do tempo de sÃntese, atingindo tamanhos mÃdios prÃximos de 10 e 4 nm para FDAg 10/12/25 e FDAg 100/12/25 respectivamente. Foi realizado o acompanhamento da degradaÃÃo do polissacarÃdeo atravÃs de anÃlise por GPC, tendo sido observado a diminuiÃÃo da distribuiÃÃo das massas molares do mesmo de 6,65 x 106 para 3,11 x 104 g/mol durante o processo de degradaÃÃo. A razÃo manose/galactose foi verificada para a GFD, passando de 1:1,23 para a GFD nÃo modificada para 1:2,14 para a GFD degradada em 420 minutos. Sendo assim, este estudo mostrou que a via ultrassÃnica em conjunto com a utilizaÃÃo da galactomanana da fava danta em soluÃÃo aquosa proporciona uma rota sintÃtica bastante versÃtil para as NPAg com boa estabilizaÃÃo.

Silver nanoparticles (AgNPs) are a promising nanomaterial with numerous applications and high level of commercialization. Biomass-mediated AgNP synthesis has emerged as a novel approach for producing AgNPs and microalgal biomasses have been found particularly advantageous. However, few studies have so far focused on microalgae-mediated biosynthesis and the mechanism of AgNP biosynthesis is still elusive. The purpose of this study was twofold: 1) to investigate effects of different parameters on the biosynthesis of AgNPs; 2) to investigate the mechanisms involved in such a bioprocess. It was found that the cell extract of Neochloris oleoabundans prepared by whole cell aqueous extraction (WCAE) in boiling water bath was able to reduce Ag+ to AgNPs. It was further discovered that sonication of algal cells before extraction could enhance the efficiency of cell extraction and enable AgNP biosynthesis using cell extract obtained by disrupted cell aqueous extraction (DCAE) at room temperature. Light was required for AgNP biosynthesis and rainbow tests showed that purple and blue lights were particularly necessary. Based on experimental results, we hypothesize the mechanism of microalgae-mediated AgNP synthesis to be a chlorophyll-mediated reaction, in which chlorophylls are excited upon absorbing photons in the purple and blue spectra and donate electrons to reduce Ag+, the lost electrons are replenished by water-splitting reaction.

>Magister Scientiae - MSc / The global lack of clean water for human sanitation and other purposes has become an emerging dilemma for human beings. The presence of organic pollutants in wastewater produced by textile industries, leather manufacturing and chemical industries is an alarming matter for a safe environment and human health. For the last decades, conventional methods have been applied for the purification of water but due to industrialization these methods fall short. Advanced oxidation processes and their reliable application in degradation of many contaminants have been reported as a potential method to reduce and/or alleviate this problem. Lately, it has been assumed that incorporation of some metal nanoparticles such as magnetite nanoparticles as photocatalyst for Fenton reaction could improve the degradation efficiency of contaminants. Core/shell nanoparticles, are extensively studied because of their wide applications in the biomedical, drug delivery, electronics fields and water treatment. The current study is centred on the synthesis of silver-doped Fe₃O₄/SiO₂/TiO₂ photocatalyst. Magnetically separable Fe₃O₄/SiO₂/TiO₂ composite with core–shell structure were synthesized by the deposition of uniform anatase TiO₂ NPs on Fe₃O₄/SiO₂ by using titanium butoxide (TBOT) as titanium source. Then, the silver is doped on TiO₂ layer by hydrothermal method. Integration of magnetic nanoparticles was suggested to avoid the post separation difficulties associated with the powder form of the TiO₂ catalyst, increase of the surface area and adsorption properties. Lastly and most importantly magnetic nanoparticles upsurge the production of hydroxyl groups or reduced charge recombination. The a synthesized catalysts were characterized using Transmission Electron Microscopy, X-ray Diffraction; Infra-red Spectroscopy, Scanning Electron Microscope and Energy Dispersive Spectroscopy. Other characterization techniques includeVibrating Sample Magnetometry, Brunauer Emmett Teller analysis and Thermogravimetric analysis. The average size of the particles size is 72 nm. Furthermore the photocatalytic performances of the magnetic catalysts were assessed in comparison with that commercial titanium dioxide for the degradation of methylene blue using photochemical reactor under ultra violet light. The results showed that the photocatalytic activity was enhanced using Fe₃O₄/SiO₂/TiO₂ and Ag-Fe₃O₄/SiO₂/TiO₂ compared with that for Fe₃O₄, commercial titanium dioxide powder.

>Magister Scientiae - MSc / Water is essential for life, yet access to safe drinking water is still a major concern worldwide due to waterborne diseases. The current study proposes silver nanoparticles (AgNPs) as an antibacterial agent. Silver nanoparticles were synthesised using different reductants and stabilisers, and the resulting structures were characterised with Ultra-violet visible (UV-vis) spectroscopy, transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) analysis. The antibacterial properties of the AgNPs were tested against a panel of 5 indicator organisms: Cupriavidus metallidurans, Staphylococcus epidermidis, Mycobacterium smegmatis, Bacillus cereus and a multi-drug resistant Escherichia coli 1699. Spherical AgNPs that absorbed at around 400 nm, with diameters ranging between 18.8-26.4 nm or 5.4-13.1 nm were prepared by ascorbic acid or sodium borohydride respectively. The optimum processing conditions that produced 6±1.8 nm spherical nanoparticles included maintaining the temperature at 0 ⁰C, the pH at 9.78 and the NaBH4/Ag/PVP ratio at 16:1:10. Exposing AgNPs to light for 6 hours did not alter the particle size rather it changed the particles shape from spherical to icosahedral. Stirring caused particles to agglomerate, however, no agitation resulted in the formation of irregular structures of different sizes. Sensitivity to the AgNPs ranged between 25 % and 100 % reduced bacterial growth depending on the strains used and the concentration of the AgNPs. The Gram negative bacteria were more sensitive to AgNPs than Gram positive bacteria. However silver ions were more toxic than AgNPs for all but one of the strains tested, B. cereus was completely resistant to both Ag+ and AgNPs. C. metallidurans and E.coli (1699) showed a dose dependent sensitivity to AgNPs and the minimum inhibitory concentrations were established at 50 and 20 mg/L AgNPs respectively. C. metallidurans and E.coli (1699) were also eradicated by 10 mg/L Ag+. The E. coli TEM images showed accumulation of AgNPs within the cells, cell shrinking and leakage of cellular components. This suggests that AgNPs have a similar toxicity effect on bacterial cells as Ag+.

>Magister Scientiae - MSc / Unavailability and contamination of available water resources are major factors contributing to adverse health conditions worldwide. AgNPs present a potential strategy for water purification; however, their ability to accumulate in organs such as the kidneys, lungs and spleen is a possible source of toxicity. This study investigates the toxicity of AgNPs to Saccharomyces cerevisiae (S. cerevisiae). S. cerevisiae is an excellent model organism for assessing toxic compounds that affect eukaryotic organisms due to their ease of cultivation. AgNPs were prepared by photo-reduction of silver nitrate with OSRAM Vitalux lamp (300 W and 230 V) in the presence of stabilizing agents such as polyvinylpyrrolidone and citric acid, yielding AgNPs. The effects of varying the concentration of the stabilizing agent, time of exposure to the light source, and pH were investigated. The formation of AgNPs was analysed by ultra-violet spectroscopy (UV-Vis) and transmission electron microscope techniques. The results showed that the AgNPs absorbed ultra-violet radiation between 400 and 500 nm and TEM images showed the particles to be both spherical and needle-like in shape. The shapes of the AgNPs were largely dependent on the synthesis method applied. The toxicity of AgNPs was assessed using metabolic activity of yeast cells as biomarker andmonitored with of the chromogenic assay, XTT. S. cerevisiae was introduced into different concentrations of AgNPs and incubated at 37oC for 72 h. After the incubation, XTT assay was performed to assess the cell viability. The XTT results showed that high concentration of AgNPs (100 µg/mL) inhibited the growth of S. cerevisiae. The synthesis of AgNPs and theassessment of their toxicity on S. cerevisiae was thus undertaken and established in this work.

Philosophiae Doctor - PhD / There has been extensive growth in nanoscale technology in the last few decades to such a degree that nanomaterials (NMs) have become a constituent in a wide range of manufactured commercial and domestic products. This surge has resulted in uncertainties regarding their environmental impact, due to the significant increases in the amount of NMs released into the environment (Dowling et al., 2004) through intentional and unintentional releases. Like many other toxins, the aquatic environment is particularly vulnerable as it acts as a sink for nanoparticles (NPs) (Scown et al., 2010). The escalating growth of NMs has not advanced without efforts to understand its properties. Despite the dramatic advances in both the production and application of NMs, very little is known regarding their interaction with and effects on environmental and human health. Given the lack in scientific knowledge, particularly under various environmental conditions, it is often difficult to accurately assess the potential exposure pathways to ecological receptors of all NMs, silver nanoparticles (AgNPs) are the most widely used NPs, present in several consumer products mainly because of their anti-bacterial properties. It is estimated that the annual production exceeds 1000 tons/year (Piccinno et al., 2012). The increase uses of AgNPs in consumer products (e.g. textiles, cosmetics and personal hygiene), household appliances (e.g. washing machines and vacuum cleaners) and medical equipment have led to their increase release into the environment, thereby posing an environmental risk and human health concern. Silver NPs are known to induce the production of Reactive Oxygen Species (ROS) (Ahamed et al., 2010; Levard et al., 2012; Piao et al., 2011). Also since AgNPs are oxidized to ionic Ag (Ag+), it is still unclear whether the effects of ROS can be attributed to Ag+ release or to the AgNP itself (Fabrega et al., 2009; Miao et al., 2009). The behaviour of AgNPs is collectively influenced by inherent (nanoparticle size, shape, surface area, surface charge, crystal structure, coating, solubility/dissolution) and environmental factors (temperature, pH, ionic strength, salinity, organic matter). Climate change predictions indicate that the frequency, intensity and duration of extreme natural events (such as temperature elevations) will increase in the future (IPCC, 2001; IPCC, 2007). Global warming and climate change could increase atmospheric temperatures by 2.4 – 6.4 °C (IPCC, 2001; IPCC, 2007). The main feature associated with global climate change is the anticipation of wetter winters (i.e. increased flood events) and drier, warmer summers (i.e.extreme temperatures). These changes are likely to affect the inputs of contaminants into the environment as well as affect their behaviour, fate and transport, and toxicity in aquatic environments. It is known that the current temperature predictions in climate change scenarios could directly affect aquatic ecosystem communities (Carpenter et al., 1992), since temperature is also regarded as an important abiotic factor influencing growth and production of primary producers (i.e. algae, macrophytes etc.), and may also affect species distribution. For example, Liu et al. (2010) reported higher dissolution rates of AgNPs with increased temperature. Similarly, sudden hydrographic activity like high flood conditions may cause resuspension and redistribution of sediments. Few studies have linked the foreseeable climate change with contaminant release and ecosystem impacts. Similarly, few studies have analyzed the behaviour of NMs in the environment considering these predicted changes in mean temperatures. This thesis focuses on the effects of AgNPs on oxidative stress responses in the Cape River crab Potamonautes perlatus. The present work was undertaken to interpret the biological effects of AgNPs (< 100 nm) on P. perlatus, as well as to assess its effects under different environmental conditions. To understand the uptake, accumulation and biological effects of AgNPs, freshwater microcosms were produced to mimic a typical aquatic environment and temperature manipulated microcosms to which a commercially-available AgNP powder was added. Nanoparticles were characterized in the dry state and in suspension under different environmental conditions. Dissolution of total Ag was measured by inductively coupled plasma mass spectrometry (ICP-OES). Nanoparticle toxicity was assessed by measuring mortality and biomarkers of oxidative stress (CYP450, SOD, CAT, GST) evaluated in crab tissues. The overall results demonstrated that: (1) AgNPs may be transformed in both size and state under variable environmental conditions. The formation of smaller aggregates at higher temperatures suggests higher toxicity, (2) the release of free metal ions from NPs and NPs aggregates contribute to a higher toxicity towards aquatic organisms, (3) oxidative stress is a significant mechanism of AgNP toxicity and consequently enzymatic activation/inhibition with increasing AgNP concentration and temperatures, (4) oxidative stress responses to AgNPs particles were significantly modulated by temperature stress in P. perlatus, (5) mortality was observed from day 2 with maximum mortality achieved at day 7, (6) enzymes involved in detoxification, i.e. CYP450, has functional significance in the haemocytes, (7) P. perlatus has proved to be a significant target for AgNP exposure and, furthermore, has proved to be a suitable species to assess the ecotoxicity of AgNP in the aquatic environment, (8) antioxidant enzymes activities (are valuable tools to assess the oxidative status of crab tissues co-exposed to AgNPs and temperature. Furthermore, the results obtained in this study contributed to the understanding of the behaviour, bioavailability, uptake and toxicity of AgNPs under variable temperatures. / National Research Foundation (NRF) Thuthuka Fund and CSIR

>Magister Scientiae - MSc / Nanoscience is the study of phenomena and objects at the nanoscale (around 1-100 nm), socalled nanomaterials. These nanomaterials exhibit novel properties that are often very different to those of the bulk materials used for their synthesis. Hence, nanoparticles are widely commercialised, especially silver nanoparticles (AgNPs) due to their antimicrobial properties and some other useful phenomena. This commercialisation leads to inevitable exposure to the environment and humans, which leads to inhalation, ingestion or dermal uptake of AgNPs by the human body culminating in distribution to several major organs, including the liver. Both chronic and acute exposure to AgNPs have been linked to detrimental effects in both in vitro and in vivo studies. These include oxidative stress, induction of inflammation, DNA damage, cell death and many others.