Date of Award
Master of Science
The production and uses of engineered nanoparticles (ENPs) have been increasing with the expansion of science and technology, and their unavoidable disposal into the soil and waterways, eventually ended up in the ocean causes serious concerns about their potential hazards to the environment and human health. The need to comprehend the impacts of ENPs in our aquatic ecosystem has motivated this research to study: 1) effect of TiO2 on Crypthecodinium cohnii; 2) effects of TiO2 and ZnO on an aquatic microbial community simulating a static lake environment; and 3) effects of TiO2, ZnO and Ag on a microbial community simulating those in a river after receiving treated wastewater. The results showed for the first study that TiO2 at different concentrations (50 mg/L, 30 mg/L, 10 mg/L, 2 mg/L, 0.5 mg/L, and 0 mg/L) in a 10-day period of observation did not negatively affect either cell growth, substrate (glucose) utilization, cellular composition or lipid profile of C. cohnii. On the contrary, the size distribution and zeta potential of TiO2 demonstrated that at its highest concentration (50 mg/L), it might present an effect on the microalgae. However, there was not enough evidence to prove toxicity, since all of the other analysis performed confirmed no impact. The second experiment proved that TiO2 and ZnO had different effects on an aquatic microbial community at experimental dosages including river water without ENP addition, TiO2 at a final concentration of 700 µg/L, ZnO at 70 µg/L, and both TiO2 and ZnO at 700 µg/L and 70 µg/L, respectively. TiO2 alone had no effect on the relative abundance of bacterial species, but caused significant decrease and increase of the relative abundances of the Chlorophyte and Streptophyta phyla, respectively, compared with other treatments and controls. ZnO, both alone or together with TiO2, brought increased population within the phylum of Bacteroidetes and decreased population of three species: Mycobacterium riyadhense, Hyphomicrobium spp., and Verrucomicrobium spp. Taken as a whole, the interaction between TiO2 and ZnO was not significant in terms of each ENP’s physicochemical properties and toxicity toward the target microbial community. The third and last study investigated individual and combined effects from three ENPs: TiO2 (700 µg/L – 7,000 µg/L), ZnO (70 µg/L - 700 µg/L) and Ag (200 µg/L – 2,000 µg/L). ENPs at these doses were found to be impactful to the target bacterial community. Similarly, the Eukaryota kingdom was affected by the ENPs at all tested concentrations. Overall, this thesis established that parameters for studying ENPs such as dosage, primary particle size, light effect, exposure time, and species should be taken into considerations to assess their impacts due to their unique physical and chemical properties.
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