Evaluation of Colloidal Stability and Ecotoxicity of Metal-based Nanoparticles in the Aquatic and Terrestrial Systems

<p>Intrinsic to the many nano-enabled products are atomic-size multifunctional engineered nanomaterials, which upon release contaminate the environments, raising considerable health and safety concerns. This Ph.D. dissertation is designed to investigate (i) whether metals or oxide nanoparticles are more toxic than ions, and if MetPLATE^TM bioassay is applicable as a rapid nanotoxicity screening tool; (ii) how variable water chemistry (dissolved organic carbon (DOC), pH, and hardness) and organic compounds (cysteine, humic acid, and trolox) modulate colloidal stability, ion release, and aquatic toxicity of silver nanoparticles (AgNP); and (iii) the developmental responses of crop plants exposed to Ag- or ZnO- (zinc oxide) nanoparticles.</p> <p>Results suggest that the MetPLATEcan be considered a high-throughput screening tool for rapid nanotoxicity evaluation. Detectable changes in the colloidal diameter, surface charge, and plasmonic resonance revealed modulating effects of variable water chemistry and organic ligands on the particle stability, dissolution, and toxicity of AgNPs against <em>Escherichia coli </em>or<em> Daphnia magna</em>. Silver dissolution increased as a function of DOC concentrations but decreased with increasing hardness, pH, cysteine, or trolox levels. Notably, the dissociated Ag⁺ was inadequate to explain AgNP toxicity, and that the combined effect of AgNPs and dissolved Ag⁺ under each ligand treatment was lower than of AgNO₃. Significant attenuation by trolox signifies an oxidative stress-mediated AgNP toxicity; its inability to attenuate AgNO₃ toxicity, however, negates oxidative stress as Ag⁺toxicity mechanism, and that cysteine could effectively quench free Ag⁺ to alleviate AgNO₃toxicity in <em>D. magna</em>. Surprisingly, DOC-AgNPs complex that apparently formed at higher DOC levels might have led daphnids filter-feed on aggregates, potentially elevating internal dose, and thus higher mortality. Maize root anatomy showed differential alterations upon exposure to AgNPs, ZnONPs, or their ions.</p> <p>Overall, various metal-based nanoparticles revealed lower toxicity than their ions against multiple organisms. This study showed that particle size, surface properties, and ion release kinetics of AgNPs modify following release into aquatic environment, suggesting potential implications to ecosystem health and functions, and that caution be applied when extending one species toxicity results to another because obvious differences in organism biology—supporting species sensitivity paradigm—can significantly alter nanoparticle or ionic toxicity.</p>

Name thesis:degree_name

PhD (Doctor of Philosophy)

Level thesis:degree_level

Dissertation - unrestricted

Discipline thesis:degree_discipline

Environmental Health

Year dc:date.issued

2013

Author dc:creator

• Pokhrel, Lok R

• aggregation
• dissolution
• ecotoxicity
• hazard
• metal nanoparticles
• stability
• Environmental Health

Statement dc:rights

• Copyright by the authors.

Repository record dc:identifier

https://dc.etsu.edu/etd/1132

OAI identifier oai:identifier

oai:dc.etsu.edu:etd-2282