Electronic Theses and Dissertations

Date

2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Civil Engineering

Committee Chair

Farhad Jazaei

Committee Member

Brian Waldron

Committee Member

Maryam Salehi

Committee Member

Peyman Babakhani

Abstract

Global plastic production has increased tremendously since the mid-twentieth century due to its widespread applications. Microplastics (MPs), that are less than 5 mm in size, are produced through urban and farming activities, and degradation due to UV-sunlight. Many researchers have identified that farmlands and stormwater ponds are among the terrestrial environments most heavily contaminated by MPs. Yet, our understanding of the abundance and transport mechanisms of MPs within soil systems remains limited in the current literature. Therefore, this dissertation focuses on understanding these mechanisms using an integrated field, laboratory, and modeling approach to answer questions; (1) How are MPs distributed within the stormwater detention ponds of different physical characteristics? (2) How do MPs infiltrate from surface to subsurface soil, and is their transport affected by soil clay content, presence of natural organic matter and UV-photodegradation. Field and laboratory investigations show that larger MPs retain more in surface soil near the inlet of the ponds. MPs vertical distribution is uniform in the pond with considerable vegetation cover. Fragments are the most abundant MP shape. Moreover, we also investigate the transport of low-density polyethylene MPs of 10±2 µm with buoyant (non-colloidal) characteristics through two types of natural farmland soils. Results demonstrate that buoyant MPs generally show similar transport behaviors to extensively studied colloidal MPs. MP interactions with clay particles in silt loam soil can induce retention and thus reduce transport. We also found that transport is greater in presence of humic acid for UV-photodegraded MPs compared to pristine MPs because of increased electrostatic repulsion and thus less attachment of MPs to soil. Mathematical modeling of MPs transport highlights the importance of processes such as attachment, detachment, blocking, and straining, typically associated with colloidal particles, and demonstrates that these processes also effectively occur for 10±2 µm buoyant MPs.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to ProQuest.

Notes

Embargoed until 11-22-2026

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Available for download on Sunday, November 22, 2026

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