Abstract

This thesis investigates the environmental degradation of plastic materials, with a focus on polyethylene terephthalate (PET), through a multi-phase study conducted at the Salton Sea, a closed-basin lake in a semi-arid region of California. The research addresses three core objectives: (1) developing a microplastic (MP) extraction method tailored for clay-rich sediments, (2) characterizing surface degradation of various plastic types, including PET, BoPET, HDPE, LDPE, and EPS, using advanced microscopy and spectroscopy, and (3) examining the long-term weathering of PET through samples collected from dated lake strandlines.

The extraction protocol successfully isolates MPs without oxidation, using ZnCl₂ and extended soaking to reduce biogenic interference. Surface analyses revealed progressive cracking, roughness, and morphological changes across weathering levels. ATR-FTIR and Raman spectroscopy identified chemical degradation trends, particularly at 1100, 1245, and 1715 cm⁻¹ (FTIR) and ~1615, ~1730 cm⁻¹ (Raman), associated with ester hydrolysis and oxidation. Notably, newer PET samples with thinner, eco-designed walls degraded faster than older counterparts.

These findings enhance our understanding of plastic persistence in natural environments and offer a scalable framework for assessing plastic degradation across arid and hydrologically closed systems.

LLU Discipline

Geology

Department

Geology

School

School of Medicine

First Advisor

Kevin E. Nick

Second Advisor

Ana María Martínez Ardila

Third Advisor

Christopher Perry

Degree Name

Master of Science (MS)

Degree Level

M.S.

Year Degree Awarded

2025

Date (Title Page)

12-2024

Language

English

Library of Congress/MESH Subject Headings

Microplastics -- Environmental aspects -- California -- Salton Sea; Plastics -- Degradation -- California -- Salton Sea; Polyethylene terephthalate -- Environmental aspects -- California -- Salton Sea; Lake sediments -- California -- Salton Sea -- Analysis; Salton Sea (Calif.) -- Environmental conditions

Type

Thesis

Page Count

xvi, 133 p.

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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