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Reduced Toxicity of Benzethonium Chloride to Escherichia Coli Through Adsorption Onto Titanium Dioxide Nanoparticles

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Reduced Toxicity of Benzethonium Chloride to Escherichia Coli Through Adsorption Onto Titanium Dioxide Nanoparticles Reduced toxicity of benzethonium chloride to Escherichia coli through adsorption onto titanium dioxide nanoparticles by Raven Waldron A THESIS submitted to Oregon State University Honors College in partial fulfillment of the requirements for the degree of Honors Baccalaureate of Science in BioResource Research - Toxicology (Honors Scholar) Presented May 25, 2018 Commencement June 2018 AN ABSTRACT OF THE THESIS OF Raven Waldron for the degree of Honors Baccalaureate of Science in BioResource Research - Toxicology presented on May 25, 2018. Title: Reduced toxicity of benzethonium chloride to Escherichia coli through adsorption onto titanium dioxide nanoparticles. Abstract Approved: _____________________________________________________ Stacey Harper Antimicrobial agents are being increasingly used in consumer soaps and detergents, despite a lack of data demonstrating their efficacy in such products. This study investigated the nature of the interaction between different crystalline structures of titanium dioxide nanoparticles and benzethonium chloride(BTC), and explored which structure, if any, could be best used to mitigate the toxicity of BTC in various Water systems. The nanoparticles used in the study Were characterized using dynamic light scattering. To examine the toxicity of combinations of BTC and titanium dioxide nanoparticles, the 24-hour IC50 Was determined. UV Vis spectrophotometry Was used to measure cell groWth in LB media containing varying concentrations of titanium dioxide nanoparticles and BTC at the IC50. For all crystalline structures and all concentrations in the supernatant treatment, there Was a significant difference between cell groWth in the treatment media and cell groWth in BTC alone at the IC50. GroWth Was significantly inhibited When cells Were treated With resuspended particles With BTC adsorbed onto the surface, indicating that for combinations of titanium dioxide nanoparticles and BTC found in aquatic ecosystems, special attention must be paid to organisms that spend the most time in sediment or near the bottom of bodies of Water, Where particles Would settle out. There Was no demonstrably significant difference in cell groWth among different crystalline structures of nanoparticles at any concentration. HoWever, P25, anatase, and rutile titanium dioxide nanoparticles were each capable of mitigating the toxicity of benzethonium chloride, and this finding could lead to novel methods for removing these potentially harmful chemicals from different Water sources. KeyWords: nanoparticles, titanium dioxide, benzethonium chloride, antimicrobial, anatase, rutile Corresponding e-mail address: [email protected] ãCopyright by Raven Waldron May 25, 2018 All Rights Reserved Reduced toxicity of benzethonium chloride to Escherichia coli through adsorption onto titanium dioxide nanoparticles by Raven Waldron A THESIS submitted to Oregon State University Honors College in partial fulfillment of the requirements for the degree of Honors Baccalaureate of Science in BioResource Research - Toxicology (Honors Scholar) Presented May 25, 2018 Commencement June 2018 Honors Baccalaureate of Science in BioResource Research project of Raven Waldron presented on May 25, 2018. APPROVED: Stacey Harper, Mentor, representing Oregon State University Department of Environmental and Molecular Toxicology Kate Field, Committee Member, representing Oregon State University BioResource Research Davida BroWn, Committee Member, representing George Fox University Department of Chemistry Toni Doolen, Dean, Oregon State University Honors College I understand that my project Will become part of the permanent collection of Oregon State University Honors College. My signature beloW authorizes release of my project to any reader upon request. Raven Waldron, Author ABSTRACT Antimicrobial agents are being increasingly used in consumer soaps and detergents, despite a lack of data demonstrating their efficacy in such products. This study investigated the nature of the interaction between different crystalline structures of titanium dioxide nanoparticles and BTC, and explore Which structure, if any, could be best used to mitigate the toxicity of BTC in various Water systems. The nanoparticles used in the study Were characterized using dynamic light scattering. To examine the toxicity of combinations of BTC and titanium dioxide nanoparticles, the 24-hour IC50 Was determined and UV Vis spectrophotometry Was used to measure cell groWth in LB media containing varying concentrations of titanium dioxide nanoparticles and BTC at the IC50. For all crystalline structures and all concentrations in the supernatant treatment, there Was a significant difference between cell groWth in the treatment media and cell groWth in BTC alone at the IC50. GroWth Was significantly inhibited When cells were treated With resuspended particles With BTC adsorbed onto the surface, indicating that for combinations of titanium dioxide nanoparticles and BTC found in aquatic ecosystems, special attention must be paid to organisms that spend the most time in sediment or near the bottom of bodies of Water, Where particles Would settle out. There Was no demonstrably significant difference in cell groWth among different crystalline structures of nanoparticles at any concentration. HoWever, P25, anatase, and rutile titanium dioxide nanoparticles are each capable of mitigating the toxicity of benzethonium chloride, and this finding could lead to novel methods for removing these potentially harmful chemicals from different Water sources. 1 INTRODUCTION Antimicrobial agents are being increasingly used in consumer soaps and detergents, despite a lack of data demonstrating the efficacy or necessity of antimicrobial agents in such products (Tan et al., 2002). As certain antimicrobial materials have been found to be harmful to organisms or to the environment, they have been taken off the market and replaced With neW chemicals designed for the same purpose, rather than removed altogether. Triclosan, one such commonly used antimicrobial additive in many consumer products such as liquid soaps, detergents and hand sanitizers, Was banned and removed from commercial use in rinse-off antiseptic Wash products by the U.S. Food and Drug Administration in 2016 (FDA 2016). Studies citing ineffectiveness of antibacterial Washes, environmental impacts, and the development of bacterial resistance contributed to the decision to remove these products from the market (Tan et al., 2002; Jones et al., 1999). HoWever, in response to comments by industry representatives during the investigation, the FDA proposed three alternatives to triclosan: benzalkonium chloride, benzethonium chloride, and chloroxylenol, and recommended more data be collected on these materials in the coming years. This study examined one of these alternatives, benzethonium chloride (BTC). Titanium dioxide nanoparticles have also been Widely used in products such as sunscreens, toothpastes, and White pigments in paints and coatings, and are frequently Washed doWn drains and off skin into Water sources (Suttiponpamit et al., 2011; Chen et al., 2007). Due to their variety of practical uses, they are increasingly produced and 2 therefore increasingly present in the environment and WasteWater (Guzman et al., 2006; Mueller and NoWack, 2008; Jomini et al., 2015). Due to their Wide use, titanium dioxide nanoparticles are likely to be introduced as a co-contaminant With BTC in WasteWater, drinking Water, and aquatic ecosystems. Because of concerns surrounding the impact of antimicrobial agents in household products on naturally occurring microbes in aquatic ecosystems, it is important to understand hoW titanium dioxide nanoparticles present in the same Water could affect the toxicity and behavior of BTC in the environment. Titanium dioxide nanoparticles have also been explored as a means of remediating, removing or breaking doWn contaminants and pollutants in Water systems, including antimicrobial alternatives to triclosan (Savage et al. 2005; Adesina 2004; Chitose et al. 2003). Nanotechnology is increasingly investigated as a method of remediation due to the unique properties of materials at the nanoscale (Kung and Kung, 2004). Previous studies have confirmed that triclosan can be photocatalytically oxidized and remediated by titanium dioxide nanoparticles (Yu et al., 2006). Adsorption also plays a role in the complete neutralization of triclosan, specifically targeting the intermediates produced by photocatalysis (Yu et al., 2006). The two main mechanisms by Which titanium dioxide nanoparticles could interact With antimicrobial agents are hypothesized to be: (1) photocatalysis in the presence of UV light and (2) physical adsorption onto the surface of the particles. The latter is the focus of this study. BTC can adsorb onto the surface of titanium dioxide particles With a primary particle size of 0.29 ± 0.04 µm (Yaremeko & Petryshyn 2013). HoWever, the specific interaction between BTC and titanium dioxide nanoparticles has yet to be investigated. 3 The increased relative surface area of nanoparticles compared to their bulk counterparts could correlate to an increased ability to adsorb materials onto their surface. In addition, special attention must be paid to the media in Which particles are incubated, as different solutions can potentially affect the agglomeration and therefore total surface area of the particles in solution (Jiang et al., 2009). Crystalline structure of titanium dioxide nanoparticles can also contribute to differences
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