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Date Permissions Signed

5-31-2019

Date of Award

Spring 2019

Document Type

Masters Thesis

Department or Program Affiliation

Environmental Science

Degree Name

Master of Science (MS)

Department

Environmental Sciences

First Advisor

Sofield, Ruth M.

Second Advisor

Bingham, Brian L., 1960-

Third Advisor

Emory, Steven R.

Abstract

Silver nanoparticles (AgNPs) are increasing in presence in commercial and medical products due to their bactericidal properties and can be transported into the environment during the laundering, use, and waste of those products. Strong evidence suggests aqueous silver (Ag+) dissolved from the AgNP surface is the toxic component of AgNPs but there is no consensus on the possibility of additional nanoparticle-specific properties that elicit toxicity. Ag+ toxicity to freshwater organisms has been well studied using the Biotic Ligand Model (BLM), which describes how water quality conditions, such as the concentrations of certain freshwater ions, affect the toxicity of Ag+. Some freshwater ions also cause AgNPs to aggregate, which can reduce the surface area from which Ag+ can dissolve. The sensitivity of AgNPs to water quality conditions has made studying their toxicity challenging in part because the range of acceptable water quality conditions in standardized toxicity testing methods produces different AgNP toxicity results.

This study assessed the impacts of the freshwater ions Ca2+, Na+, Cl-, and SO42- on AgNP toxicity and chemical behavior in ASTM acute Daphnia magna toxicity testing conditions. Toxicity and analytical tests were performed in experimental waters created by adding fixed concentrations of NaCl, CaCl2, and Na2SO4 to ASTM moderately hard water (MHW) in a factorial design. AgNP sedimentation was measured using UV-Vis, and particle size distribution and particle concentration were measured using the single particle ICP-MS technique. LC50s for experimental waters ranged from 53.48 – 383.52 μg/L. NaCl and CaCl2 reduced toxicity in comparison to MHW. The rank order for AgNP LC50s in the experimental waters was the same as the rank order that the BLM predicted for Ag+ toxicity indicating that Ag+ dissolved from the AgNP may have been responsible for some of the AgNP toxicity. However, CaCl2 reduced toxicity more than the BLM predicted should happen based on Ag+ and there was a much larger interaction effect between CaCl2 and NaCl than was predicted. CaCl2 significantly increased particle size and sedimentation rates, which was concluded to be caused by the Ca2+. An interaction effect between CaCl2 and NaCl was also observed for sedimentation, which appeared to be due to the doubled Cl- concentration. AgNP aggregation was likely responsible for the differences between the AgNP toxicity results and the predictions of the BLM supporting that the BLM is not able to completely characterize all of the factors that affect AgNP toxicity.

Type

Text

Keywords

silver nanoparticles, silver nanoparticles--acute toxicity, major freshwater ions, nanoparticle aggregation, single particle ICP-MS

Publisher

Western Washington University

OCLC Number

1103712389

Subject – LCSH

Silver--Toxicology; Fresh water; Ions

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this thesis 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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