Environmental Behavior of Silver Nanoparticles: Emissions from Consumer Products and Toxicty in Waste Treatment
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Environmental Behavior of Silver Nanoparticles: Emissions from Consumer Products and Toxicty in Waste Treatment A dissertation submitted to the Division of Research and Advanced Studies of the University of Cincinnati in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Biomedical, Chemical, and Environmental Engineering of the College of Engineering and Applied Science July 2016 By Alireza Gitipour B.Sc. Chemical Engineering Southern Tehran University, Iran Thesis Committee: Stephen W. Thiel, Ph.D., Chair Thabet Tolaymat, Ph.D. Vadim Guliants, Ph.D. George Sorial, Ph.D. Vesselin Shanov, Ph.D. ABSTRACT Nanotechnology has undergone a dramatic increase in popularity in the last decade due to the unique physicochemical characteristics of engineered nanomaterials (ENMs). Currently, approximately a quarter of all nano-enabled consumer products contain silver nanoparticles (AgNPs). AgNPs are incorporated into a wide range of consumer products (e. g., textiles, filters, disinfectants, and washing machines) and have a wide range of medical, industrial and scientific applications. The increased application of AgNPs will inevitably lead to their release into environmental systems. Since the presumed mechanisms governing the fate, transport and toxicity of matter at the bulk scale may not directly apply to nanomaterials, the potential environmental impacts associated with the release of AgNPs must be evaluated. Furthermore, AgNPs are manufactured with a wide range of physicochemical properties that impact their fate, transport and toxicity in the environment. To this end, the impact of silver nanoparticles on the composting of municipal solid waste was evaluated. Neither the presence of AgNPs nor the presence of Ag+ had a statistically significant influence on leachate, gas and solid quality parameters, and therefore, on overall composting performance. However, AgNPs and Ag+ both changed the overall structure of the bacterial communities within the compost. Nevertheless, the functional performance of the composting process was not significantly affected due to the abundance and functional redundancy of the bacterial communities within the compost samples. While surface transformations of AgNPs to AgCl and Ag2S reduce toxicity, complexation with organic matter may also play a role. The results i of this study further suggest that at relatively low concentrations of AgNPs, these organically rich waste management systems can withstand the presence of AgNPs. The microbial toxicity of silver nanoparticles stabilized with different capping agents were evaluated under anaerobic conditions. The AgNPs investigated were similar in size and shape but varied in surface charge. At lower AgNPs concentrations, the anaerobic decomposition process was not affected although the diversity of the microbial community was impacted. Interestingly, at higher concentrations only the cationic AgNPs demonstrated toxicity, while, the neutral and negatively charged AgNPs did not exhibit toxicity. These findings indicate that there are multiple mechanisms for nanoparticles toxicity. In addition to the disposal studies, a study of a commonly-utilized nanosilver solution using a simulated dental unit water delivery system assessed the fate, mode of interaction and physicochemical transformations of AgNPs under a realistic usage scenario. The disinfection process led to the disappearance of the capping agents and consequently transformations of AgNPs. In addition to further understanding the transformations that occur in the process, adsorption of the AgNPs onto the biofilms surface was demonstrated which may assist in further understanding the toxicity mechanisms of AgNPs to biofilms. Finally, a comprehensive review was conducted to identify the key issues and knowledge gaps concerning the environmental impact of AgNPs in consumer products. This review summarizes the existing data related to characterization techniques, routes of environmental exposure and potential ecological risks of AgNPs and provides potential directions for future research. ii Copyright by Alireza Gitipour 2016 iii ACKNOWLEDGEMENTS I would like express my deepest gratitude and undying love to my mother (Parvaneh) who has been my inspiration, and support over the years. My father (Saeid) who relentlessly encouraged me to achieve my dreams. To my confidant and sister (Behnaz) for her friendship, patience and for providing a distraction from the monotony of writing a dissertation. I would also like to thank my grandmother (maman-mali), grandfather (Babajoon) and great uncle (Ghorban amu). Conducting research and developing a Ph.D. dissertation is never an individual effort. There are a number of individuals without whom my research would have been impossible this. I would like to acknowledge my advisors Dr. Thiel, and Dr. Tolaymat for their guidance, time, and ecouragment. Furthermore, I am grateful to other members of my committee Drs. Guliants, Sorial and Shanov. I also would like to thank Dr. Al-Abed. While he was not a member of my committee, he was instrumental in the development of many aspects of my research. Additionally, I would like to further recognize Dr. Guliants for assistance with the admissions to the Ph.D. program at the University of Cincinnati and Mr. David Carson for introducing me to researchers who were pivotal in accomplishing my research goals. I am also grateful to Dr. Arjmand, my undergraduate advisor, for his unconditional support and kindness over the years. A special word of appreciation to the Pegasus Technical Services Inc. staff members: Dr. Venkatapathy, Dr. El-Badawi, Mr. Tegenaw, Mrs. Yang, Dr. Huang and Dr. Arambewela. Finally, I would like to thank the Center Hill Facility staff members: Miss. Goetz, Dr. Luxton, Dr. Scheckel, Dr. Zimmer and Mr. Voit for their contributions. iv Dedicated to my mother v Table of Contents ABSTRACT…………………………………………………………………………………….………… i ACKNOWLEDGEMENTS………………………………………………………………………..…….. iv List of Tables………………………………………………………………………………….................... x List of Figures……………………………………………………………………………………….……. xi List of Abbreviations……………………………….……………………………………………..…...... xiv CHAPTER 1…………………………………………………………………………………..................... 1 Introduction………………………………………………………………………………………………... 1 1.1 Nanotechnology …………………………..…………………………………………......................... 2 1.2 Silver Nanomaterials (AgNPs)………………………………………………………......................... 5 1.3 Disposal of Nanoparticles …………………………………………………………………….……... 9 1.4 Objectives…………………………………………………………………………………………… 11 1.5 Overview……………………………………………………………………………………………. 12 Literature Cited……………………………………………………………………………..…………..... 15 CHAPTER 2……………………………………………………………………………..……………..... 20 The Impact of Silver Nanoparticles on the Composting of Municipal Solid Waste………..…………… 20 Abstract…………………………………………………………………………………………………... 21 2.1 Introduction.…………………………………………........................................................................ 22 2.2 Experimental Section……………………………………………………………...…..…………..... 25 2.2.1 Nanoparticles, Selection, Synthesis, and Purification…………………………………………... 25 2.2.2 The Compost Reactors…………………………….………………………………..................... 26 2.2.3 Composting Sampling and Analysis…………………………………………….….................... 26 2.2.4 DNA Sequencing and Bacterial Composition and Diversity Analyses……...……..................... 27 2.2.5 Species Richness, Diversity, and Statistical Analysis of Microbial Communities……………... 29 2.3 Results and Discussion……………………………………………………………….……………... 29 2.3.1 AgNPs Characterization…………………………………………………………….................... 29 2.3.2 Gas Quantity and Quality…………………………………………………………...................... 30 2.3.3 Leachate Quality………………………………………………………………………………... 31 2.3.4 Solids Quality……………………………………………………………………….................... 32 2.3.5 Bacterial Diversity Analyses……………………………………………………………………. 34 2.4 Environmental Implications…………………………………………………………….................... 36 Literature Cited……………………………………………………………………………....................... 37 APPENDIX A……………….…………………………………………………………………………… 49 vi A1. Purification of AgNPs suspensions……………………………………...…………………………... 50 A2. C: N Ratio Measurement…………………………………………………...………………………... 50 A3. PCR Methodology………………………………………………………….…………....................... 51 A4. XPS Analysis………………………………………………………………….………...................... 51 A5. XAS Analysis………………………………………………………………...…………………….... 51 CHAPTER 3………………………………………………………………………..…………………..... 66 Anaerobic Toxicity of Cationic Silver Nanoparticles………………………………...……...................... 66 Abstract……………………………………………………………………………….……...................... 67 3.1 Introduction………………………………………………………………………..…....................... 68 3.2 Experimental Section………………………………………………………………...……………... 70 3.2.1 Nanoparticles Synthesis, Purification and Characterization………………………..................... 70 3.2.2 Anaerobic Digesters Setup…………………………………………………………...………..... 70 3.2.3 Sampling and Analysis………………………………………………………………...……....... 71 3.2.3.1 Biogas Analysis…………………………………………………………………...……..... 71 3.2.3.2 Taxonomical Analysis……………………………………………………………...……... 71 3.2.3.3 Silver Speciation Analysis by X-ray Absorption Spectroscopy (XAS)…........................... 72 3.2.3.4 Modelling Speciation of Dissolved Ag (MINTEQ)………………………......................... 72 3.2.3.5 Statistical Analysis………………………………………………………........................... 73 3.3 Results and Discussion…………………………………………………………………………........ 73 3.3.1 AgNPs Characterization…………………………………………………………………….......