Date of Award

Fall 2021

Document Type

Open Access Dissertation

Department

Environmental Health Sciences

First Advisor

Mohammed Baalousha

Abstract

Engineered nanomaterials (ENMs) with unique nanoscale properties, including novel optical behavior and superparamagnetic, are continually being developed for biomedical and industrial applications. In specific biomedical applications, ENMs are surface-functionalized using polymers, proteins, and other stabilizing agents to facilitate their resistance to salt-induced aggregation. Since their colloidal stability in high ionic-strength matrices, functionalized ENMs are anticipated to be persistent aquatic contaminants. Despite their potential environmental significance, the persistence of surface-functionalized ENMs as individually stabilized nanoparticles in marine environments is largely unknown. Further, few studies have investigated the fundamental factors that influence ENMs uptake and fate/transport processes in ecologically susceptible aquatic biota, such as filter-feeding bivalves, which ingest and accumulate a broad range of dissolved- and particulate-phase contaminants.

This study was aimed to explain a comprehensive approach to prepare and rigorously characterize ENM test suspensions to facilitate fundamental examinations of nanoparticle toxicity and fate/behavior processes in marine bivalves. We have investigated the synthesis and characterization of AgNPs through chemical and biological approaches. The chemical approach (cit-AgNPs) is based on the reduction of ionic silver using sodium borohydride (NaBH4) as a reducing agent and trisodium citrate (Na3C6H5O7) as a reducing agent. The biological synthesis approach (bio-AgNPs ) is based on the reduction of ionic silver using biomolecules extracted from the fungi Aspergillus parasiticus strain AFS10. The biomolecules also act as a capping agent. The physicochemical properties of the synthesized AgNPs were determined using UV-vis Spectrophotometer, dynamic light scattering (DLS), laser Doppler electrophoresis, inductively coupled plasma-atomic mass spectroscopy (ICP-MS), transmission electron microscopy (TEM), asymmetric flow-field flow fractionation (AF4-ICP-MS), and single-particle (SP-ICP-MS). Both synthesis approaches generated spherical AgNPs. The core and hydrodynamic diameters (9.72± 0.1 nm and 21.5 ± 0.1nm) of the chemically synthesized AgNPs were slightly smaller than those (15.85 ± 0.8 nm and 38.6 ± 0.1 nm) of the biologically synthesized AgNPs. The chemical synthesis approach produced AgNPs with narrower size distributions (more monodispersed) than those generated through the biological synthesis approach. The magnitude of the zeta potential of the chemically synthesized AgNPs was higher than those of the biologically synthesized AgNPs.

The environmental behavior (i.e., aggregation and dissolution) and toxicity (i.e., mortality) of commercially powder AgNPs (Ag-n-powder), cit-AgNPs, bioAgNPs, and dissolved silver (AgNO3) to Juvenile Mercenaria mercenaria (0.820 – 1.2 mm) at 24-h exposure. The hydrodynamic diameter of cit-AgNPs, bio-AgNPs, Ag-n-powder in stock suspensions, determined by dynamic light scattering, were 21.5 ± 0.1, 38.6 ± 0.1, and 132 ± 2.0 nm, respectively. All AgNPs formed aggregates in natural seawater. The dissolution of AgNPs in natural seawater (the toxicological test media) was measured by an inductively coupled plasma-mass spectrometer following ultrafiltration (3kDa). The dissolved Ag concentration increased with the increases in AgNP concentration over a range of environmentally relevant concentrations: 0.2, 0.35, 0.6, 1.0, 1.5, and 2.6 mg-Ag L −1 . Mortality (%) of juvenile clams decreased following the order AgNO3 (24-h mean LC50 value of 0.24 mg L-1 , 95% confidence intervals: 0.22–0.27 mg L-1 ) > cit- AgNPs (24-h LC50 of 0.7 mg L-1 , 95% confidence intervals: 0.645–0.87) > and bio-AgNPs (24-h LC50 of 1.05 mg L-1 , 95% confidence intervals: 0.90–1.36 mg L-1 ) > powder-AgNPs (24-h LC50 of 2.44 mg L-1 , 95% confidence intervals: 1.81–2.43 mg L -1 ). Dissolved Ag could not explain the toxicity of AgNPs, indicating that the toxicity of AgNPs can be attributed to a combined effect of dissolved ions and the AgNPs.

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