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Abiotic Transformations of Pesticides in Prairie Potholes

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Abiotic Transformations of Pesticides in Prairie Potholes Abiotic Transformations of Pesticides in Prairie Potholes A DISSERTATION SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA BY Teng Zeng IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Adviser: Dr. William A. Arnold August 2012 © Teng Zeng 2012 Acknowledgements I owe my gratitude to many people who have helped me get to this destination. My deepest gratitude goes to my advisor, Dr. William A. Arnold. I have been fortunate to have Bill as an advisor who gave me the freedom to explore on my own, and at the same time the guidance and encouragement to overcome unexpected challenges and crisis situations. In particular, I am thankful to Bill for holding me to a high research standard, for helping me sort out the technical details of my work, and for carefully reading and commenting every piece of my writing. More importantly, Bill taught me to be a versatile environmental chemist. I must thank my dissertation committee members, Dr. Paige J. Novak, Dr. R. Lee Penn, and Dr. Paul D. Capel, for reading previous drafts of this dissertation and providing many valuable comments that improved the presentation and contents of this dissertation. I am especially grateful to Paige for her willingness to serve as my committee chair with relatively short notice. I am also thankful to Dr. Raymond M. Hozalski, who served on my written and oral exam committee and generously allowed me to use large portions of his laboratory space. I am also indebted to our research collaborators Dr. Yu-Ping Chin and Kate L. Ziegelgruber at the Ohio State University as well as Dr. David N. Mushet at the U.S. Geological Survey Northern Prairie Wildlife Research Center. Special thanks are due to Yo for teaching me the art of sediment coring and porewater extraction and for providing thorough review and constructive comments on my manuscripts. I would like to thank Kate for helping me with sediment sample processing and DOC analysis. I also would i like to express my gratitude to Dave for guiding us through sampling sites and for sharing his first-hand experience with prairie potholes. I would like to offer special thanks to Dr. Brandy M. Toner for introducing me to the remarkable XANES technique and for sharing her valuable beamtime and beamline wisdom. Without Brandy’s input, there would not have been Chapter 5 of this dissertation. I also would like to thank Dr. Matthew A. Marcus and Dr. Sirine C. Fakra at the ALS Beamline 10.3.2 for their expert guidance and consistent support during my beamtime. I further wish to thank members of the Toner research group, especially Brandi Cron, Jeffry Sorensen, Jill Coleman Wasik, and Sarah Nicholas, for assisting me with XANES data collection and analysis. I would like to express my appreciation to Dr. Edward L. Cussler for providing focused and constructive commentary on my dissertation practice talk. Ed also guided me through a paint research project and has taught me innumerable lessons and insights on the workings of academic research in general. I am grateful to my fellow graduate students within the Environmental Engineering and Chemistry group, past and present. I would like to thank Amanda Stemig, Andy McCabe, Cale Anger, David Tan, Erin Surdo, Hao Pang, Megan Kelly, Noah Hensley, Jay Roth, Fabrizio Sabba, Greg LeFevre, Mark Krzmarzick, Nate Fleishhacker, Pat McNamara, Andrew Rescorla, Kathryn Wilkinson, Srijan Aggarwal, Alina Grigorescu, and Tucker Burch for their help, talents, and friendship along the way. On the more personal side, I wish to thank Andrew, Fab, Pat, and Srijan for their steadfast encouragement and Megan for always brightening up the office. ii Most importantly, none of this would have been possible without the love and support of my parents and my girlfriend Lydia. Finally, I appreciate the financial support from the Department of Civil Engineering and the National Science Foundation. iii Dedication This dissertation is dedicated to my parents. iv Abstract The prairie pothole region (PPR) is among the most extensively altered ecosystems on Earth. This region covers approximately 780,000 km2 of central North America, and contains numerous glacially formed wetlands embedded in an agricultural landscape. These wetlands, commonly known as prairie pothole lakes (PPLs), provide essential ecosystem services. Over the last 150 years, agricultural drainage has resulted in severe loss of native prairie wetlands. The remaining PPLs continue to be threatened by nonpoint source pesticide pollution from agriculture. Currently, little is known about the fate and persistence of pesticides in PPLs. In this work, the abiotic transformations of commonly used pesticides in PPL sediment porewaters and surface water were explored. Chloroacetanilide and dinitroaniline pesticides were found to react rapidly with naturally abundant reduced sulfur species (i.e., hydrogen sulfide and polysulfides) in sediment porewaters via nucleophilic substitution and reduction reactions, respectively. Dissolved organic matter (DOM) was also found to play a vital role in the reductive transformation. Next, the photodegradation of a suite of pesticides was investigated in PPL surface water under both simulated and natural sunlight. Enhanced pesticide removal rates pointed to the importance of indirect photolysis pathways involving photochemically produced reactive intermediates such as singlet oxygen and triplet excited-state DOM. Finally, the sedimentary sulfur speciation was examined by sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy. Sulfur species in PPL sediments were found to consist of organic (di)sulfides, sulfonate, sulfate, and the mineral pyrite. Notably, the fractional abundances of reduced and oxidized sulfur species fluctuate on a seasonal basis. v Table of Contents Acknowledgements .............................................................................................................. i Dedication .......................................................................................................................... iv Abstract ............................................................................................................................... v Table of Contents ............................................................................................................... vi List of Tables ..................................................................................................................... xi List of Figures ................................................................................................................... xv Chapter 1: Introduction ....................................................................................................... 1 1.1 Pesticides in the Aquatic Environments ....................................................... 2 1.2 Prairie Pothole Region of North America ..................................................... 4 1.3 Aqueous Inorganic Sulfur Chemistry: Bisufide and Polysulfides ................ 9 1.4 Aquatic Photochemistry: Direct and Indirect Photolysis ............................ 13 1.5 X-ray Absorption Near-Edge Structure (XANES) spectroscopy ............... 18 1.6 Scope of Dissertation .................................................................................. 23 1.7 References ................................................................................................... 25 Chapter 2: Abiotic Transformation of Pesticides in Prairie Pothole Porewaters: Nucleophilic Reactions ..................................................................................................... 38 2.1 Introduction ................................................................................................. 39 2.2 Experimental Section .................................................................................. 41 2.2.1 Chemicals, Reagents, and Glassware.......................................................... 41 2.2.2 Field Sampling and Sample Analysis ......................................................... 43 2.2.3 Analysis of Porewater Total Hydrogen Sulfide .......................................... 45 2.2.4 Analysis of Porewater Total Polysulfides ................................................... 46 2.2.5 Batch Kinetic Studies and Product Derivatization...................................... 48 2.2.6 Chloroacetanilide and Product Analysis ..................................................... 49 2.2.7 Data Analysis .............................................................................................. 49 2.3 Results and Discussion ............................................................................... 49 2.3.1 Water Chemistry of PPLs ........................................................................... 49 2.3.2 Transformations of Pesticides in PPL Porewaters ...................................... 51 2.3.3 Roles of Bisulfide and Polysulfides ............................................................ 53 vi 2.3.4 Transformation Products of Chloroacetanilides ......................................... 59 2.4 Summary ..................................................................................................... 61 2.5 References ................................................................................................... 61 Chapter 3: Abiotic Transformation of Pesticides in Prairie Pothole Porewaters: Reduction Reactions ..........................................................................................................................
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