Environmental Impacts of Nanoplastics and Plastic Additives on Model Bacteria Shewanella oneidensis & Development and Assessment of a Revised General Chemistry Laboratory Course to Introduce Inquiry-Based Learning

Abstract

Pedagogical best practices suggest that creating open-ended, inquiry-based learning experiences will address gaps in students’ science processing and critical thinking skills. This thesis work demonstrates my own application of these research questions into benchwork and redesigning, and subsequent assessment, of a general chemistry laboratory curriculum. Advancements in undergraduate STEM education have resulted in a widespread effort to introduce inquiry-based learning into student experiences, requiring adaptations of traditional teaching methods. Laboratory courses in the Chemistry and Biochemistry Department at the University of Minnesota-Duluth have been taught using traditional, step-by-step protocols. Though this technique has proved to be an efficient and effective way of introducing basic laboratory skills, this type of laboratory curriculum fails to provide student opportunity to learn and develop experimental design skills. A General Chemistry Laboratory course was selected for a curriculum reform to focus on the development of student abilities to design experiments. To evaluate the effectiveness of the curriculum redesign, we created an instrument aimed at assessing gains in experimental design ability. While tools for assessing experimental design have been created, chemistry specific instruments are needed within the field of education research. Our instrument offers a tool for skill assessment focus on chemical concepts. The developed instrument consisted of a multiple-choice, short answer open response, a case study open response and an affective domain section. Together, the results of the instrument provide a comprehensive assessment on student understanding and knowledge of techniques, ability to design a reasoned experiment, and feelings toward chemistry laboratory practices. Performance comparisons between students in the revised laboratory course and students in a traditionally taught General Chemistry Laboratory course were compared. Students completed the assessment tool at the start and end of the academic year, to highlight gains made after a full year of instruction. Analysis of these results integrates item analysis approaches, an adapted EDAT (Experimental Design Ability Test) rubric and the evaluation of affective domain responses based on a Likert scale. While some results indicate that students in the revised course performed at slightly elevated levels was recorded, conclusive statements about gains in experimental design skills made after enrollment in an inquiry-based introductory laboratory course cannot be made. While, conclusive statements about student performance are not supported, differential gains in student confidence to design and performing experiments were measured in the revise course cohort, meaning that student became more comfortable with designing an experiment after a year of the revised inquiry-based lab. The properties of plastic materials, while resulting in beneficial products, has led to a challenging, long-term environmental problem. As advancements have been made in quantifying and identifying plastics in natural systems, there are many gaps in our understanding of the ecological impact of nanoplastics and plastic additives. Within this work I evaluated the impact of nanoplastic materials, and plastic additives on a model bacterial species in aerobic and anaerobic conditions. Specifically, Shewanella oneidensis were exposed to nanoplastic polystyrene(nano-PS) and a variety of plastic additives and monitored for changes in viability using a growth-based viability assay. Assessment of cell function upon exposure to nano-PS was also pursued by following riboflavin secretion, a molecule secreted to serve in the terminal electron transport chain during metal reduction. Upon 4, 8 or 12 hours of exposure to nano-PS, there were minimal changes in viability of the S. oneidensis; yet, the amount of riboflavin secreted varied when exposed to different concentrations of nano-PS. The localization of the nanoplastics within or on the surface of the cells was pursued with inductively coupled plasma mass spectrometry (ICP-MS). ICP-MS results showed the presence of nano-PS in both the supernatant and associated with the bacterial cells. Taken together, it can be concluded that S. oneidensis associates with nano-PS and nano-PS presence elicits functional changes. Toxicity effects of acute and chronic exposure to bisphenols and diester additives was evaluated with viability changes. Bisphenol A (BPA) and bisphenol S (BPS) had minimal effects during acute (4 h) exposures but showed decreased S. oneidensis viability at longer, 48 h exposures. Tetrabromo BPA (TBBPA), however, caused a decrease in viability after only 4 h incubation time. Dibutyl sebacate (DBS) and diisobutyl phthalate (DIBH) caused minimal toxicity upon acute exposure; yet, chronic exposures caused toxicity response where lower concentrations(8.2-32.8µM) decreased viability while higher concentrations(65.8 and 131.5µM) were not toxic as compared to the control. This work highlights that nanoplastics and plastic additives can affect viability and cellular function that could ultimately be an impact to ecosystem health.