Assessing the Impacts of Size, Structure, and Surface Chemistry on the Toxicity of Two High Production Organic Nanomaterials using the Embryonic Zebrafish Model Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/z029p818z

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  • The low risk and sustainable implementation of nanotechnology requires understanding how nanomaterial physicochemical properties influence their toxicity. Major drivers of toxicity need to be avoided while maximizing product efficacy so nanomaterials can be produced to best serve their applications and be of low risk when intentionally or unintentionally released into the environment. The two papers of this thesis investigate how surface chemistry, structure, and size influence the toxicity of two organic nanomaterials. Chapter one provides information on the state-of-the-science in nanotoxicology as it relates to a series of high production volume organic nanomaterials and the possible toxicological impacts of size, structure, and surface chemistry. Chapter two, specifically investigates the toxicity and uptake of carbon nanotubes (CNTs) that vary in structure and surface functionalization. Four different CNTs were investigated using embryonic zebrafish: pristine and carboxylated single- wall (pSWNTs or cSWNTs) and pristine and carboxylated multiwall (pMWNTs or cMWNTs) nanotubes, each were stabilized with a Pluronic® surfactant. Pluronic® sonolytic degradation products were toxic to zebrafish embryos. When the toxic Pluronic® fragments were removed by dialysis, there was little effect of pMWNTs, cMWNTs, or pSWNTs on embryo viability and development, even at high concentrations. cSWNTs were associated with embryo toxicity at all concentrations tested, even after removal of the sonolytic byproducts. From the data gathered, multiwall or single wall structure or pristine or carboxylated surface chemistry did not independently influence toxicity, although a combination of structure and surface chemistry could impact toxicity, possibly due to byproducts of chemical synthesis methods. cSWNTs were also associated with the lowest uptake in the zebrafish compared to the other materials which could be due to lower bioavailability of the materials or the compromised health of the animals. Chapter three focuses on polymeric capsules that are part of a commercially available pesticide formulation. By separating the capsules according to size, a toxicity evaluation is completed to investigate how capsule diameter influenced the toxicity of the entrapped pesticidal active ingredient (AI). The analysis compared particles of about 200 nm in diameter to particles with diameters of about 2 μm. Toxicity was evaluated 24 hours after exposure to equivalent amounts of AI by the presence and severity of pyrethroid-specific tremors, 14 sublethal developmental impacts and mortality. Fish exposed to greater than 20 μg a.i. L⁻¹ technical λ-Cy or formulated product experienced curvature of the body axis, pericardial edema, craniofacial malformations, and mortality. Exposure to the unfractionated formulation, micro fraction, nano fraction and technical a.i. resulted in no significant differences in the occurrence of sublethal impacts or mortality; however, the technical a.i. exposure resulted in significantly less fish experiencing tremors and shorter tremors compared to any of the formulated product exposures. This suggests that the capsule size alone does not influence the toxic response of the entrapped λ-Cy. Testing across other encapsulated products is needed to determine if size does not have influence on toxicity regardless of encapsulation technology. Lastly, chapter 4 discusses the main conclusions of the thesis body of work. It provides highlights of key findings, interprets the meaning of those findings to the general public and suggested next steps for this line of research.
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