TOWSON UNIVERSITY OFFICE OF GRADUATE STUDIES ANAEROBIC ABIOTIC REDUCTION OF DICHLOROACETAMIDE SAFENERS: EFFECTS OF MANGANESE OXIDES AND AGROCHEMICAL CO-FORMULANTS by Allison Ricko A thesis Presented to the faculty of Towson University in partial fulfillment of the requirements for the degree Master of Science Environmental Science Towson University Towson, MD 21252 August 2015 ACKNOWLEDGEMENTS First and foremost, I would like to thank my advisor, Dr. John Sivey, for his support and guidance throughout my graduate career. His input has been instrumental in both the completion of this research and my education. I cannot thank him enough for his willingness to take on a graduate student who didn’t have a chemistry background and for his patience as I learned the fundamentals necessary to successfully complete this research. The input I’ve received throughout this process has been invaluable. I would like to thank the thesis committee, Dr. Joel Moore, Dr. Tim Brunker, and Dr. Ryan Casey, for their input on the experimental design and writing. The entire committee provided useful insight into each of their areas of expertise, contributing to the coherency of the final document. Dr. Tim Brunker performed most of the NMR analyses reported here, and I am grateful for his interpretation of the results. Several undergraduate students provided support and assistance throughout the research process: Mark Burton, Mark Bickley, Dan Victor, Nick Sapienza, and Nick Race. I would also like to thank Dave Szymanik and Sarah Krause, who performed additional NMR analyses. The continued encouragement from my family and friends has been instrumental in the success of my academic career. I will always be grateful for their advice, and their willingness to help proofread and to act as a practice audience has been invaluable. iii ABSTRACT Anaerobic Abiotic Reduction of Dichloroacetamide Safeners: Effects of Manganese Oxides and Agrochemical Co-Formulants Allison Ricko Safeners are added to herbicide formulations to protect crops from toxic effects of active herbicides. Evidence suggests that as dichloroacetamide safeners transform, they can become more biologically active. Dichloroacetamide safeners can transform via reductive dechlorination in anaerobic abiotic systems containing iron oxy-hydroxide minerals. Manganese oxides are important redox-active species that frequently co-occur with iron oxides. This study examines the anaerobic reduction of three dichloroacetamide safeners in the presence of agrochemical co-formulants, in changing pH buffer and ionic strength conditions, and in Fe(II)-amended, abiotic mixed-mineral systems. The safener dichlormid did not transform appreciably over the sampling period (up to 6 hours). Transformation of the safeners benoxacor and furilazole was not appreciably affected by the presence of co-formulants, pH buffer, or changes in ionic strength. The molar ratio of Fe(II)-to-Mn(IV) oxide had an appreciable effect on the transformation rate of benoxacor and furilazole. iv TABLE OF CONTENTS LIST OF TABLES ................................................................................................................ viii LIST OF FIGURES ...................................................................................................................x CHAPTER ONE: Introduction .................................................................................................1 1.1 Safeners in Agrochemical Formulations ............................................................2 1.2 Dichloroacetamide Safeners ..............................................................................6 1.3 Environmental Fate of Herbicides and Safeners ................................................8 1.4 Surfactants in Agrochemical Formulations .....................................................10 1.5 Environmental Fate of Surfactants...................................................................12 1.6 Iron and Manganese Oxides in Soils ...............................................................12 1.7 Influence of Iron and Manganese Oxides on Agrochemicals ..........................16 CHAPTER TWO: Materials and Methods .............................................................................18 2.1 Reagents ...........................................................................................................19 2.2 Experimental Methods .....................................................................................19 2.2.1 Effects of Herbicide and Surfactant Co-Formulants .........................19 2.2.2 Effects of pH Buffer and Ionic Strength ...........................................20 2.2.3 Effects of Mixed-Mineral Systems ...................................................20 2.3 Analytical Methods ..........................................................................................21 2.3.1 Instrumentation .................................................................................21 2.3.2 Rate Constant Determination ............................................................22 2.3.3 Furilazole Product Quantification .....................................................24 v CHAPTER THREE: Effects of Agrochemical Co-Formulants, pH Buffer, and Ionic Strength on the Reductive Dechlorination of Dichloroacetamide Safeners ......................26 3.1 Effects of Agrochemical Co-Formulants .........................................................27 3.1.1 Effects of S-Metolachlor on the Reductive Dechlorination of Benoxacor ..................................................................................................27 3.1.2 Effects of Surfactants on the Reductive Dechlorination of Benoxacor ..................................................................................................29 3.2 Effects of pH Buffer and Ionic Strength ..........................................................31 CHAPTER FOUR: Effects of Iron Oxide and Manganese Oxide Mineral Systems on the Reductive Dechlorination of Dichloroacetamide Safeners ................................................34 4.1 Oxidation of Fe(II) by Mn(IV) Oxide ..............................................................35 4.2 Effects of Mixed-Mineral Systems on Dichloroacetamide Reduction ............37 4.2.1 Effect of Mn(IV) Oxide ....................................................................37 4.2.2 Effect of Addition Order ...................................................................41 4.3 Broader Impacts ...............................................................................................43 APPENDICES ........................................................................................................................45 APPENDIX A: Reagents ...........................................................................................46 APPENDIX B: Preparation and Standardization of Aqueous Fe(II) and Cr(II) .......48 B.1 Preparation and Standardization of Aqueous Fe(II) ............................49 B.2 Reduction and Standardization of Aqueous Cr(II) ..............................49 vi APPENDIX C: Synthesis and Characterization of Monochlorinated Analogue of Benoxacor ..........................................................................................................50 C.1 Synthesis of Monochlorinated Analogue of Benoxacor .....................51 C.2 Characterization of Monochlorinated Analogue of Benoxacor ..........52 APPENDIX D: GC Method Details ..........................................................................55 D.1 Instrument Parameters.........................................................................56 D.2 Calibration ...........................................................................................58 APPENDIX E: Quality Assurance and Quality Control ...........................................63 E.1 Extraction Efficiencies ........................................................................64 E.2 Recoveries Following Centrifugation..................................................65 E.3 Adsorption to Fe and Mn Oxides ........................................................66 APPENDIX F: Summary of Observed Reduction Rate Constants ...........................68 APPENDIX G: Transformation of Dichloroacetamide Safeners in the Presence of Free Chlorine and Free Bromine .......................................................................73 G.1 An HPLC Method for Dichloroacetamide Safeners ...........................74 G.2 Chlorination and Bromination Rates of Dichloroacetamide Safeners ......................................................................................................77 G.3 Phosphate Catalysis of Benoxacor Bromination .................................78 REFERENCES .......................................................................................................................79 CURRICULUM VITA .............................................................................................................87 vii LIST OF TABLES TABLE 1.1. Compound Class, Structure, and Crops Associated with Some Herbicide Safeners ....................................................................................................................3 TABLE 1.2. Structure and Properties of Dichloroacetamide Safeners and Their Associated Herbicides ..............................................................................................7 TABLE 1.3. Structure and Properties of Some Surfactants Used in Herbicide Formulations ..........................................................................................................11