Date of Award

Spring 2020

Document Type

Open Access Dissertation

Department

Environmental Health Sciences

First Advisor

Jamie R. Lead

Abstract

Oil spills from different sources such as natural seeps, waste waters, runoffs and accidental oil spills can have serious effects on the environment while also resulting in potentially major economic damage. Due to the harmful effects of crude oil components on ecosystems, a rapid response to sequestrate oil is required to minimize any resulting environmental impact. Currently used oil removal methods, in addition to their advantages, also have severe limitations. New techniques have been developed including nanotechnology to address these limitations. A new type of nanoparticle (NP), composed of polyvinylpyrrolidone (PVP) coated iron oxide (magnetite), has been successfully used to remediate oil-contaminated waters. This dissertation reports amelioration of oil toxicity to harpacticoid copepods using these NPs, while at the same time stimulating the growth of oil-degrading bacteria and subsequent oil removal. Finally, a method was developed and validated to quantify internalized Fe from NPs. This method will help to better understand the NP fate in the presence of oil and therefore understand the mechanisms of improved remediation using.

An acute toxicity assay based on the estuarine copepod Amphiascus tenuiremishas been performed to evaluate the toxicity of PVP-coated iron oxide NPs, wateraccommodated fractions (WAF) and both together. The synergistic use of the PVP-coated iron oxide NPs with oil-degrading bacteria for enhancing oil removal at the laboratory scale was performed. To estimate intercellular NP uptake of metal from NPs, the outer cell membrane of Gram-negative bacteria has been removed using ethylenediaminetetraacetic acid (EDTA) at an optimal time and concentration. This was followed by standard digestion and metal measurements. Live/dead staining, transmission electron microscopy (TEM) and metal analysis were used for verification of this method.

Results indicated that the NPs alone had no significant impact on copepod survival up to concentrations of 25 mg L−1 over 4 days of exposure, importantly, while, 18 mg L−1 over a 1 hour time period was the optimal for oil removal by these NPs from the aqueous phase. WAF was highly-toxic to copepods (mortality 95 ± 5%). Mixing the NPs with undiluted WAF and magnetic removal within 1 hour of exposure resulted in a >90% (pvalue < 0.05) reduction in toxicity compared with undiluted WAF alone having no added NPs. Additions of NPs to undiluted WAF for up to 72 hours without magnetic separation also resulted in significantly (p-value < 0.05) reduced toxicity, suggesting that the oil-NP mixture influenced toxicity. The growth of oil-degrading bacteria was significantly (pvalue < 0.05) stimulated in present of NPs and WAF, when compared to WAF alone. This growth enhancement was likely due to the additional available of Carbone and iron source. The combination of PVP-coated iron oxide NPs and oil-degrading bacteria experiments indicated that oil removed essentially 100% of oil within 24 h. For comparison, NPs alone could remove approximately 65% of oil within 1 h, when magnetic separation of NP was used; Oil-degrading bacteria could remove about 80–90%, but it required 48 h. A possible explanation is that the oil-NP complexes became more bioavailable to bacteria as a joint Fe and C source. Furthermore, results showed that the emission of selected volatile organic compounds (VOCs) and semi volatile organic compounds (SVOCs) were reduced after additions of NPs and bacteria separately. When combined, VOC and SVOC emissions

were reduced by up to 80%. These initial data suggest that these NPs could be added rapidly to oil spills in marine system to reduce acute oil toxicity and increase oil degradation. Finally, we developed and validated an extraction method using EDTA, which can estimate internalization of metal NPs into Gram-negative bacteria. Results showed the outer cell membrane was successfully removed from bacterial cells without lysis of the inner plasma membrane of cells, and indicated that the quantitative separation surface-attached NPs from those internalized within the bacterium. This technique offers a promising approach for quantifying NP and metal internalization processes in Gram negative bacteria.

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