The effects of microplastics and nanoplastics upon history, policies, and Drosophila melanogaster

Microplastics (MPs) and nanoplastics (NPs) are major contaminants in the environment in unprecedented amounts both in mass and volume. As it can take plastic hundreds of years to degrade, the amount of plastic in the environment continues to increase yearly, and it will reside for long periods environmentally. As a result, organisms are exposed to MPs and NPs through inhalation, dermal, and dietary routes of exposure. Of special concern are the potential effects of dietary exposure of MPs and NPs to humans and other organisms. This dissertation provides a review of MPs and NPs in terms of their research history and regulation, as well as the results of experiments designed to assess their effects on the fruit fly-Drosophila melanogaster. The research focused on four major areas. First, a bibliometric analysis was performed from 1900-2019 to summarize the history of MPs' and NPs' research as well as highlight influential papers and key areas of investigation (Chapter 2). Second, current legislation addressing the regulation of plastics in the United States at the city, state/territory, and federal levels was reviewed, and potential future legislation that could address plastic and MPs regulations was proposed (Chapter 3). Third, fruit flies were exposed orally to polystyrene MPs and NPs to model potential effects of human dietary exposure. Here, studies focused on quantification of MPs exposure to fruit flies and their potential effects on fecundity, metabolism, and heart function and parameters (Chapter 4) Finally, effects of MPs and NPs on wing size and shape of fruit flies was investigated (Chapter 5). Previous studies have shown contradicting results for metabolism, and no study has evaluated fecundity past 20 days, metabolic rate via respirometry, and heart function and parameters. No study has evaluated plastic on the wing phenotype. The overarching hypothesis applied to the empirical research with fruit flies is that oral exposure to polystyrene MPs and NPs will negatively alter fecundity, metabolic rate, heart function and parameters, and wing shape and size. The results of this dissertation are 1) the amount of literature regarding MPs and NPs has increased by 2,000% from 2009 to 2019; 2) MPs and NPs are largely unregulated in the United States; however in the future, it is possible that current legislation could be used to regulate MPs if they are classified as toxic or contaminants; 3) exposure to MPs and NPs decrease fecundity and alter heart rate and function while exposure to MPs specifically decreases metabolic rate of fruit flies; 4) exposure to MPs shortened the L2 vein in female flies, caused elongated wings in MPs and NPs female flies, elongated wings in MPs male flies, and decreased wing size of NPs male flies. As flies are used as toxicity models for humans, these results indicate potential areas of concern after oral exposure to MPs/NPs—especially in regard to the heart, metabolism, and reproductive systems. Future efforts should continue to evaluate MPs and NPs research, track changes in MPs regulations, and expand understanding of MPs and NPs dietary toxicity in Drosophila through experiments with plastics that have different sizes, shapes, and polymer types. Findings from such studies would enhance the means of designing mechanistic research and extrapolating effects to humans and terrestrial insects.