Investigation of Titanium Dioxide Engineered Nanomaterials in Microbially Driven Environments
This dissertation characterized two forms of TiO2 engineered nanomaterials (ENMs) to determine the role of solution conditions in mediating differences in the environmental impacts of emerging nanomaterials. In general, ENMs designed for specific product matrices are functionalized to impart distinct characteristics capable of altering the environmental fate and transport (i.e. shape and surface composition). Observations of TiO2 ENM release during product life cycles presents a concern as nanoparticles with unique characteristics begin accumulating in environmental systems. TiO2 nanomaterials were introduced to three consecutive, environmental systems with microbial presence to characterize environmental implications of ENM presence, namely: a model human colon, septic tank, and a quartz sand filtration column.
The following critical findings resulted from this dissertation research. Colonic exposure to food (FG) and industrial (IG) grade TiO2 inhibited a natural shift in microbial composition from Proteobacteria to Firmicutes phyla, with FG TiO2 having the greater impact. Colonic pH levels decreased from IG and FG TiO2 exposure where FG TiO2 (pH 4) again had the greatest impact compared to IG TiO2 (pH 5) and the control (pH 6). Therefore, inherent physical and chemical properties of FG and IG TiO2 can produce different microbial responses in the colonic environment. Next, exposure of the septic system to IG TiO2 particles had minimal effect on the composition of the denitrifying-dominant microbial community, while FG exposures resulted in a mixed functionality community less effective at waste treatment. Nano-FG TiO2 exposure in septic systems may facilitate considerable changes in microbial community activity.
Lastly, FG TiO2 exhibited a high degree of stability in septic conditions and both monovalent electrolyte suspensions. Elution of FG and IG TiO2 was greatest in septic effluent at the higher nanoparticle concentration (100 ppm); however, FG TiO2 was well retained at the low (2 ppm) concentration suggesting low elution from the drainage field.
Valuable insight into the role that inherent physical and chemical properties of emerging ENMs play in environmental systems is gained from this dissertation research. Additionally, the significance of the solution environment at mediating differences observed between uniquely, engineered nanomaterials sheds light on potential mechanisms for minimizing detrimental environmental implications of nanomaterials.