First Advisor

Elise Granek

Term of Graduation

Spring 2025

Date of Publication

6-4-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.) in Earth, Environment, & Society

Department

Earth, Environment, & Society

Language

English

Subjects

aquatic, ecotoxicology, invertebrates, microplastics, pesticides, stressors

DOI

10.15760/etd.3975

Physical Description

1 online resource (xiii, 231 pages)

Abstract

Pesticides are ubiquitous in aquatic environments, alongside numerous contaminants and other stressors that can result in combined exposure to target and non-target organisms. Nevertheless, traditional toxicity studies quantify the effects of these compounds at an individual level, and to a narrow range of traditional test organisms. Through this dissertation, I explored the presence and effects of commonly detected pesticides of concern in the Pacific Northwest in order to realistically quantify potential effects from combined stressors. In Chapter 2, I demonstrated my background knowledge on these select pesticides (atrazine, bifenthrin, diuron, indaziflam, and imidacloprid), including their chemical and physical properties. Using this information, I discussed their environmental fate in aquatic systems as well as likelihood of exposure to the study organisms of this dissertation (bivalves and echinoderms), as well as the potential for or observed quantification of biomagnification in tissues.

In Chapter 3, I focused on current environmental detections by conducting environmental sampling in Southern Oregon estuaries. Working alongside the Confederated Tribes of the Coos, Lower Umpqua and Siuslaw Indians (CTCLUSI) and the U.S. Geological Survey (USGS), I sampled clams, eelgrass, sediment, and water for pesticide and pharmaceutical analysis at four sites in Coos Bay (Fossil Point, South Slough) and Florence, OR (Florence Marina, North Fork Siuslaw). A total of ten pesticides and eight pharmaceuticals were detected across the four sites, with the most pesticide detections at the Fossil Point and Florence Marina sites, and most pharmaceutical detections at Florence Marina and South Slough. The most commonly detected pesticide was bifenthrin (34.2% of all detections) and the most commonly detected pharmaceutical was metformin (30% of all detections). In this chapter, I identified a co-occurrence of pesticides and pharmaceuticals in sites of ecological and community significance.

In Chapter 4, I conducted a laboratory experiment to investigate the effects of chronic (90 days) exposure by the soft-shell clam, Mya arenaria, to environmentally relevant concentrations of four pesticides registered for use in forestry (atrazine, 5 μg/L; hexazinone, 0.3 μg/L; indaziflam, 5 μg/L; and bifenthrin, 1.5 μg/g organic carbon [OC; 0.51 μg/L whole water]). I tested pesticides individually and in combination, except bifenthrin, which was tested only in combination with the other three. I measured shell growth and condition index every 30 days, as well as feeding rates, mortality, and chemical concentrations in tissue from a subset of clams at the end of the experiment to measure contaminant uptake. Indaziflam caused a high mortality rate (max. 36%), followed by atrazine (max. 27%), both individually as well as in combination with other pesticides. Additionally, indaziflam concentrations in tissue (61.70-152.56 ng/g) were higher than those of atrazine (26.48-48.56 ng/g), despite equal dosing concentrations, indicating higher tissue accumulation. Furthermore, clams exposed to indaziflam and hexazinone experienced reduced condition index and clearance rates individually and in combination with other compounds; however, the two combined did not result in significant mortality. The findings from this study underscore the need for more comprehensive studies combining multiple compounds at relevant concentrations to understand their impacts on aquatic ecosystems.

In Chapter 5, I conducted a chronic exposure (48 days) experiment on the larvae of the endangered sunflower star (Pycnopodia helianthoides), exposing them to the insecticide imidacloprid and polyester microfibers both individually, and in combination. This study focused on quantifying the effects of combined stressors on Pycnopodia to a previously unstudied life stage, specifically examining stressors on early development rather than on adults. Additionally, P. helianthoides is currently experiencing delayed recovery from sea star wasting syndrome, with no existing research on the role of contaminant stressors in that delay. Larvae were exposed to environmentally relevant concentrations of imidacloprid and polyester microfibers (10 ng/L and 25 fibers/L, respectively). Imidacloprid exposure resulted in stomach malformation in 10% of larvae and increased mortality during early development (p< 0.001), and all treatments resulted in increased larval lengths relative to controls (p< 0.001). During settlement, imidacloprid resulted in more rapid settlement responses than in the controls (p< 0.01). This study highlighted the need for further research investigating the effects of contaminant stressors to endangered organisms during reintroduction as well as a more comprehensive understanding of the effects of pesticides to nontarget organisms.

These four chapters serve as an investigation both of the presence of pesticides alongside other contaminants in the aquatic environment, as well as the effects they can exhibit on non-target organisms of differing ecological roles, as well as life stages. Chapter 3 is the first study to quantify the environmental uptake of pesticides in eelgrass tissues, shedding further light on the environmental fate and exposure routes of these chemicals in estuaries. Chapter 4 is the first study to quantify the effects of indaziflam and hexazinone at environmentally relevant concentrations to bivalves. Chapter 5 is the first study to ever quantify the effects of contaminant stressors to Pycnopodia helianthoides and strongly supports the need for toxicological studies in concert with recovery efforts for endangered species. This dissertation contributes to a growing amount of literature that argues for toxicity studies focused on multiple stressors rather than individual ones.

Rights

In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).

Comments

Funding for this dissertation was provided by Oregon Sea Grant Biennial Grant (grant number NB325E-B), Sea Grant Project Development Grant (grant number R/ECO-53- PD), the Charles Lambert Memorial Endowment through the University of Washington, and the Edward D. and Olive C. Bushby Scholarship and Chen Fellowship through Portland State University.

Persistent Identifier

https://archives.pdx.edu/ds/psu/43917

Download

Available for download on Thursday, June 04, 2026

Share

COinS