Electronic Theses and Dissertations

Date

2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Civil Engineering

Committee Chair

Maryam Salehi

Committee Member

Paul J PP Palazolo

Committee Member

Charles CC Camp

Committee Member

Farhad FJ Jazaei

Abstract

The soaring accumulation of discarded plastics in the environment is a pressing global issue, primarily driven by increased plastic usage and improper waste management. From 2012 to 2019, among various applications of plastic products, the global utilization of plastics in agriculture witnessed a notable rise, surging from 4.4 million tons to 7.4 million tons, creating plastic pollution problems. Plastic pollution within the farmlands threatens food safety and negatively impacts soil health. Therefore, this dissertation focuses on studying the environmental weathering of plastic residuals within the terrestrial environment and investigating their impacts on the plastic particles' fate within the aquatic systems. This dissertation addresses several knowledge gaps regarding the interrelated influence of environmental conditions and plastics' intrinsic characteristics on their photo and biodegradation behavior within the farmlands. Moreover, the photodegradation of microplastics (MPs) within the terrestrial environment was linked to their aggregation in water as they get transported to the aquatic systems. The first chapter provides an overview of the research background, knowledge gaps, and dissertation outline. The second chapter examined the combined influence of MPs characteristics and environmental conditions [e.g., relative humidity and soil deposition conditions] on the photodegradation of low density polyethylene (LDPE) MPs within the agricultural soil system. The results demonstrated that LDPE MPs with a lower molecular weight were subjected to a greater extent of photodegradation than those with a greater molecular weight. Moreover, elevated relative humidity and deposition of soil particles on top of the MPs limited the photooxidation process and consequently reduced the surface chemistry alterations of MPs. The third chapter elucidated the influence of plastic mulches’ photodegradation on their biodegradation behavior. The results of surface morphology variations, crystallinity raises, molecular weight reduction, weight loss, and declining mechanical properties revealed the significant role of photodegradation in accelerating the biodegradation process of biodegradable plastic mulch. In the fourth chapter, a simple in-situ methodology was developed to examine the links between the photodegradation of MPs to their aggregation behavior under various water chemistry conditions. The results showed a significant reduction in MPs’ tendency for aggregation due to the photodegradation and presence of natural organic matter. The fifth chapter concludes the dissertation and suggests future relevant research works.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to ProQuest

Notes

Embargoed until 10/6/2025

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Available for download on Monday, October 06, 2025

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