Date of Award

Summer 8-19-2022

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Onur Apul

Second Committee Member

Jean MacRae

Third Committee Member

Francois Perreault

Abstract

Microplastics in the aquatic system are among the many inevitable consequences of plastic pollution, which has cascading environmental and public health impacts. The implications lead to the production of leachate comprised of dissolved organic matter (DOM) and increasing adsorption potential of organic compounds (OCs) onto the microplastic surfaces. In this study, the adsorption potential of organic pollutants and the formation of microplastic leachate from ultraviolet (UV) light were explored. The adsorption potential was created through a summarization and critical review of the literature on the adsorption of synthetic OCs by microplastics in aqueous environments since their emergence in 2008. A database of 92 articles, reporting 178 OCs, was created to provide a reference for our work. Our findings indicated that phenanthrene was the most commonly investigated OC, appearing in 13 of these studies. The adsorption of OCs were compared between the four most prevalent polymer types: polyethylene (PE), polystyrene (PS), polypropylene (PP), and polyvinyl chloride (PVC) using the linear isotherm parameter, KD, to determine adsorption variability and understand the controlling factors for adsorption. ii Surface interactions and leachate production of six microplastics under UV irradiation were determined. Leachate production was analyzed for the dissolved organic content (DOC), UV absorbance (i.e., UV254), and fluorescence through excitation emission (EEM) to determine the amount of leachate produced and the mechanisms involved in leachate production via UV irradiation. The aged microplastic samples were analyzed for Fourier-transform infrared spectroscopy (FT-IR), Raman, and X-ray photoelectron spectroscopy (XPS), to determine the surface changes in combination with leachate formation. The differences in leachate formation for different polymers were attributed to their chemical makeup and their potency to interact with UV. Findings indicated that all microplastics showed evidence of surface oxidation, affirming that the leachate formation is an interfacial interaction and could be a significant source of organic compound influx to natural waters due to the abundance of microplastics and their large surface area. In terms of adsorption of organic compounds by microplastics, it was found that the octanolwater partitioning coefficient, Kow, is an appropriate predictor for adsorption capacity with simply structured polymer types, particularly PE. As hydrophobicity increases, PE adsorbs the most, followed by PVC, and then PP. Comparing the KD to the dipole moments for several different compounds on PE and PS showed that microplastics probably do not have induced electronic interactions, and supported the conclusion that adsorption is most likely driven by a compound’s repulsion from water rather than its affinity for microplastics.

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