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Date Permissions Signed


Date of Award

Fall 2021

Document Type

Masters Thesis

Department or Program Affiliation

Environmental Sciences

Degree Name

Master of Science (MS)


Environmental Sciences

First Advisor

Sofield, Ruth M.

Second Advisor

Bingham, Brian L. 1960-

Third Advisor

Spanjer, Andrew R.


Microplastics have become ubiquitous in the environment and have been intensively studied in recent years. Researchers have documented several toxic effects to aquatic organisms, but the role of different microplastic properties in the toxic responses is not well understood. Toxic effects can be altered by the microplastic pieces themselves, by chemicals from the microplastics, and by sorbed environmental organic or metal pollutants, which microplastics concentrate and transport. I decided to focus on the chemical aspect of microplastic toxicity by observing responses of a marine invertebrate when exposed to several types of leachate solutions, created by soaking microplastics in seawater for 48 hours. Juvenile mysids (Americamysis bahia) were exposed to various types of polystyrene (PS), polyethylene terephthalate (PET), polycarbonate (PC), polyester, and polyacrylonitrile microplastic leachates for 4 days and mortality was recorded. Toxicity tests were also performed on environmentally aged versions of each leachate, which were created using microplastics deployed in Bellingham Bay for 70-76 days. I used log-logistic models to model concentration-response relationships and determined the concentration of leachate that results in 50% mortality (the LC50). LC50 values were compared with log-likelihood ratios to determine significant differences between leachate types and aging conditions. Non-aged and aged versions of the PS, PET, and PC leachates caused no significant mortality at concentrations as high as 100 grams per liter. All types of non-aged microplastic fiber leachates caused mysid mortality, with red polyacrylonitrile being the most toxic, followed by green polyester and white polyester. In contrast, all three of the same fiber leachates that were aged caused no mortality at concentrations as high as 50 grams per liter, suggesting that the acute toxicity of microplastic fibers decreases after being subject to environmental processes. Chemical analysis of the fiber leachate types was performed with LC-QTOF-MS, and it shows unique chemical features differentiating the toxic leachates (created from non-aged fibers) and the non-toxic leachates (created from aged fibers). My results have important implications for future microplastic toxicity studies and regulations on plastic debris, suggesting more study of microplastic fibers is warranted, and the role of chemicals in microplastic toxicity needs consideration in addition to physical hazards of microplastic ingestion.




microplastics, environmental aging, microplastic leachate, microplastic fibers, mysid shrimp


Western Washington University

OCLC Number


Subject – LCSH

Microplastics--Toxicity testing; Marine pollution; Mysidae--Effect of pollution on




masters theses




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