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Mesocosm Studies: Polycyclic Aromatic Hydrocarbons (Pahs)

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Mesocosm Studies: Polycyclic Aromatic Hydrocarbons (Pahs) MESOCOSM STUDIES: POLYCYCLIC AROMATIC HYDROCARBONS (PAHS) EXPOSURE, CONCENTRATIONS AND REMOVAL RATES A Dissertation by DAWEI SHI Submitted to the Office of Graduate and Professional Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Chair of Committee, Terry L. Wade Committee Members, Piers Chapman Gerardo Gold Bouchot Andrew G. Klein Head of Department, Shari Yvon-Lewis August 2019 Major subject: Oceanography Copyright 2019 Dawei Shi ABSTRACT Polycyclic Aromatic Hydrocarbons (PAHs) are toxic constituents found in crude oils, which can be removed from the water column through a combination of processes: evaporation, sedimentation, photo-oxidation and/or biodegradation, collectively termed weathering. Marine snow consists of many particles including bacteria, phytoplankton, mineral particles, fecal pellets and aggregates and plays an important role in the process of removing PAHs from the water column through sedimentation and enhanced biodegradation. The microbial community produces exopolymeric substances (EPS) in response to stresses including exposure to petroleum may lead to excess production of marine snow, therefore affecting the biodegredation and transport and fate of PAHs. This research hypothesizes that the PAH removal from the water column is enhanced by microbial activity in the presence of petroleum and petroleum plus Corexit. In this study, mesocosm experiments were used to investigate PAH half- lives when petroleum and dispersants are present. The first four mesocosm experiments were undertaken with water collected from near shore or off-shore locations in the Gulf of Mexico. As part of these studies, oil and oil plus dispersant mixtures known as WAF (water accommodated oil fraction) and CEWAF (chemically enhanced water accommodated fraction) were generated ii in 130 L baffled recirculation tanks, and ~80 L transferred to the mesocosms. A 1:10 dilution of the CEWAF (DCEWAF) was an additional mesocosm treatment. Control treatments with no oil or dispersant were used for comparison. Concentrated phytoplankton collected from Galveston Bay were added to all mesocosm tanks. In mesocosm 3 (M3) and 4 (M4) f/20 nutrient additions were made. Total scanning fluorescence (TSF) analysis was performed to determine estimate oil equivalents (EOE) concentrations at the start, during and at the end of the experiment. PAH composition and concentration were determined using Gas Chromatography/Mass Spectroscopy (GC/MS). The concentrations of EOE and PAH as well as changes in the PAH composition of the WAF, DCEWAF and CEWAF over time were determined. Biomarker data were measured in selected samples in order to investigate the biodegradation process. The mesocosm experiments were designed to: 1) simulate the conditions of DWH oil spill using WAF, DCEWAF and CEWAF generated from a baffled recirculating system; 2) establish a relationship between EOE measured by TSF that allows for real time oil concentration estimates in mesocosm experiments; 3) compare PAH removal pattern under different biological conditions and 4) examine the impact of Corexit addition in the removal half-lives of PAH, providing additional information for evaluation of future usage of Corexit during marine oil spills. iii ACKNOWLEDGEMENTS Firstly, I would like to express my sincere gratitude to my advisor Dr. Terry L. Wade for the continuous support of my Ph.D. study and related research, for his patience, motivation, and immense knowledge. He guided me consistently through the research and writing of this dissertation. I would also like to thank the rest of my dissertation committee: Drs. Piers Chapman, Gerardo Gold Bouchot and Andrew Klein, for their insightful comments and their constant guidance and support through the course of this research at Texas A&M University. I am also pleased to say thanks to Dr. Antonietta Quigg and all the ADDOMEx members for making this happen. Special thanks to Steve Sweet, Blake Mackay and Ibrahim Al Atwah for their help in the laboratory work. Finally, I am grateful to my parents, for their unconditional love and support. Thanks to my wife, Fei, for being my eternal source of inspiration. iv CONTRIBUTORS AND FUNDING SOURCES Contributors This work was supported by my committee chair, Dr. Terry L. Wade and my committee members, Drs. Piers Chapman, Gerardo Gold Bouchot from Department of Oceanography and Dr. Andrew Klein from Department of Geography. Instrumental Analysis was done with the help of Steve Sweet, Blake Mackay and Ibrahim Al Atwah. All other work conducted for the dissertation was completed by the student independently. Funding Sources This research was made possible by a grant from The Gulf of Mexico Research Initiative to support consortium research entitled ADDOMEx (Aggregation and Degradation of Dispersants and Oil by Microbial Exopolymers) Consortium. Data is publicly available through the Gulf of Mexico Research Initiative Information and Data Cooperative (GRIIDC) at http://data.gulfresearchinitiative.org (doi:10.7266/N7XG9P60, doi: 10.7266/N71G0JX8, doi: 10.7266/n7-hs2n-xf29). v NOMENCLATURE ADDOMEx Aggregation and Degradation of Dispersants and Oil by Microbial Exopolymers AF Amplification Factor BRT Baffled Recirculation Tanks CEWAF Chemically Enhanced Water Accommodated oil Fraction CROSERF Chemical Response to Oil Spills Ecological Effects Research Forum DBTs Dibenzothiophenes DCEWAF Diluted Chemically Enhanced Water Accommodated oil Fraction DCM Dichloromethane DWH Deepwater Horizon EOE Estimated Oil Equivalent EPS Exopolymeric Substances GC/FID Gas Chromatography/Flame Ionization Detector GC-MS Gas Chromatography coupled with Mass Spectrometry GERG Geochemical and Environmental Research Group HMW High Molecular Weight hydrocarbons LMW Low Molecular Weight hydrocarbons M1 Mesocosm 1 M2 Mesocosm 2 vi M3 Mesocosm 3 M4 Mesocosm 4 M5 Mesocosm 5 MOS Marine Oil Snow NOAA National Oceanic and Atmospheric Administration PAH Polycyclic Aromatic Hydrocarbons PHENs Phenanthrenes ppm parts per million rpm revolutions per minute UCM Unresolved Complex Mixtures WAF Water Accommodated oil Fraction TPH total petroleum hydrocarbons TR total resolved peaks vii TABLE OF CONTENTS Page ABSTRACT ................................................................................................................ ii ACKNOWLEDGEMENTS .......................................................................................... iv CONTRIBUTORS AND FUNDING SOURCES ........................................................... v NOMENCLATURE .................................................................................................... vi TABLE OF CONTENTS .......................................................................................... viii LIST OF FIGURES ..................................................................................................... x LIST OF TABLES ...................................................................................................... xi INTRODUCTION ........................................................................................................ 1 LITERATURE REVIEW .............................................................................................. 5 PAHs ............................................................................................................ 5 Marine snow ................................................................................................. 9 Dispersants ................................................................................................. 12 QUESTIONS AND ASSOCIATED HYPOTHESIS .................................................... 16 METHODS ............................................................................................................... 18 Baffled recirculation system ........................................................................ 19 WAF and CEWAF generation ..................................................................... 20 Mesocosm experiments – M1 & M2 ............................................................ 22 Mesocosm experiments – M3 & M4 ............................................................ 25 Mesocosm experiments – M5 ..................................................................... 27 Estimated oil equivalents (EOE) ................................................................. 27 Hydrocarbons analysis ............................................................................... 28 RESULTS AND DISCUSSION ....................................................................... 34 Estimated oil equivalents (EOE) ................................................................. 34 Aliphatic hydrocarbons ............................................................................... 38 viii PAHs .......................................................................................................... 42 Initial PAH concentrations ....................................................................... 45 Removal of PAHs in WAF, DCEWAF and CEWAF treatments ............... 50 Rates of removal ..................................................................................... 59 Ratio of C2-DBTs to C2-PHENs and C3-DBTs to C3-PHENs ................. 70 Biomarkers ................................................................................................. 72 CONCLUSIONS ............................................................................................. 80 REFERENCES .............................................................................................
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