Date of Award:

12-2025

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Committee Chair(s)

Liyuan Hou

Committee

Liyuan Hou

Committee

R. Ryan Dupont

Committee

Joan E. McLean

Committee

Yong Zhou

Abstract

Antibiotic resistance is a growing global concern, and wastewater treatment plants play a critical role in controlling its spread. These facilities process water containing microplastics (small plastic particles), trace elements like copper and zinc, and chemicals from everyday products like pharmaceuticals and personal care products. Together, these pollutants may contribute to the survival and spread of bacteria containing antibiotic resistance genes, but their combined effects are not fully understood. This study investigated how these pollutants behave and interact in wastewater treatment plants using two approaches: direct monitoring of real treatment plants and controlled lab experiments using synthetic wastewater. Results showed that although most pollutants were significantly reduced during wastewater treatment, some antibiotic resistance genes remained in the treated water, about 41.8 million copies per milliliter. Mobile genetic elements that spread resistance between bacteria were still present in large numbers. Microplastic levels dropped sharply from over 8,600 particles per liter to just 24 particles per liter, but were not completely removed. Analysis revealed that microplastics were the strongest direct drivers of antibiotic resistance gene abundance, while pharmaceuticals and personal care products and trace metals exerted indirect effects through their influence on microplastics and microbial communities. Laboratory tests confirmed that microplastics act as platforms for collecting high amounts of resistance genes and mobile genetic elements, with significantly higher levels compared to control surfaces. Plastic type had minimal impact on resistance gene abundance. However, exposure to copper, a common trace element, had mixed effects: it increased some resistance genes while reducing others. In contrast, pharmaceuticals and personal care products at typical environmental levels showed no significant effects during laboratory experiments. Overall, the study demonstrates that microplastics primarily function as physical surfaces that support higher bacterial density and promote antibiotic resistance. These findings highlight the complex ways in which pollutants interact to shape antibiotic resistance patterns in wastewater, emphasizing the need for more research and improved treatment strategies to protect public health.

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