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Date Permissions Signed

8-15-2022

Date of Award

Summer 2022

Document Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Environmental Sciences

First Advisor

Sofield, Ruth M.

Second Advisor

Hecker, Marcus (College teacher)

Third Advisor

Bunn, Rebecca

Fourth Advisor

Kodner, Robin

Abstract

Tire-wear particles (TWPs) are considered among the largest contributors of microplastics to the environment. They are subject to break-down due to environmental weathering, which allows for potentially toxic chemicals to be released from and sorbed onto the particles. In this study, leachate generated from “weathered” and “un-weathered” TWPs were used for sublethal toxicity tests with Americamysis bahia. Organisms were exposed for 2, 4, and 6 days and the effects endpoints included changes in respiration rate and molecular responses (i.e., changes in the abundance of transcripts after 4 days of exposure). A threshold for stimulated respiration rate was detected for weathered leachate on day 2 only between 0.133 and 0.67 g/L TWP leachate. For the un-weathered leachate, the threshold was on days 4 and 6 and was between 0.54 and 1.08 g/L TWP leachate. There were dysregulated contig sequences, in all tested concentrations for weathered (0.67, 1.34, and 2.68 g/L) and un-weathered (0.27, 0.54, and 1.08 g/L) TWP leachates; the contigs had sequences orthologous to specific gene descriptions in arthropods and were considered significantly dysregulated at an FDR ≤ 0.05 and |log2FC| ≥ 1. There were 80 dysregulated contigs across all tested weathered leachate concentrations and 139 dysregulated contigs across all tested un-weathered concentrations. Upregulated contigs at 2.68 g/L for weathered and 1.08 g/L for un-weathered leachates showed enrichment compared to the de novo reference transcriptome; this coincided with a significant respiration stimulation observed at 1.08 g/L in the un-weathered leachate. There were five enriched pathways in the weathered group and 10 enriched pathways in the un-weathered group; serine hydrolase, serine-type peptidase, and peptidase activity were enriched in both groups. Many contig sequences mapped to gene descriptions that regulated physical body structure, inflammatory response, and mediated protein-protein interactions, signifying that TWP leachate exposure disrupts many internal molecular processes in A. bahia.

Type

Text

Keywords

Tire particle leachate, respiration, transcriptomics, differential expression

Publisher

Western Washington University

OCLC Number

1341361281

Subject – LCSH

Tires--Erosion; Microplastics--Environmental testing; Leachate--Toxicology; Mysidae--Effect of pollution on; Nucleotide sequence

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

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