Carbon Isotope Fractionation During Reductive Dechlorination of TCE and Intermediate Degradation Products PDF Download

Author: Yvonne Elizabeth Bloom
Publisher:
ISBN:
Category :
Languages : en
Pages : 352

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Author: Sarah Kathleen Hirschorn
Publisher:
ISBN:
Category :
Languages : en
Pages : 340

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Stable carbon isotope fractionation during biotransformation of the chlorinated ethanes 1,2-dichloroethane (1,2-DCA), 1,1,1-trichloroethane (1,1,1-TCA) and 1,1-dichloroethane (1,1-DCA) was investigated. Isotopic fractionation during aerobic 1,2-DCA biotransformation in microcosms, enrichment cultures and pure microbial cultures was measured and was found to be pathway dependent. Biodegradation of 1,2-DCA under aerobic conditions produced a consistent bimodal distribution of enrichment factors (s) with one mean c centered on --3.9 +/- 0.6 and the other on --29.2 +/- 1.9. Reevaluation of epsilon in terms of kinetic isotope effects 12k/ 13k, gave values of 12k/13k = 1.01 and 1.06, which are typical of oxidation and hydrolytic dehalogenation (S N2) reactions, respectively. The relationship between degradation pathway and measured carbon isotope fractionation was applied to constrain the degradation pathway of 1,2-DCA in a microbial enrichment culture capable of degrading 1,2-DCA under both O2 and NO3-reducing conditions, but where the degradation pathway was previously uncharacterized. delta 13C values indicated biodegradation in the enrichment culture under both O2 and NO3-reducing conditions likely proceeded via a hydrolytic dehalogenase enzyme. Stable carbon isotope analysis during biotransformation of other chlorinated ethanes was then investigated. Isotopic enrichment factors of -1.9 and -10.4 were measured during reductive dechlorination of 1,1,1-trichloroethane (1,1,1-TCA) and 1,1-dichloroethane (1,1-DCA), respectively. These are the first reported isotopic enrichment factors for microbial biotransformation of these compounds, which can now potentially be applied to investigate and quantify biodegradation of 1,1,1-TCA and 1,1-DCA in the field. Stable carbon isotope analysis was used to provide a conservative estimate of the extent of 1,2-DCA and trichloroethene (TCE) biodegradation in a biostimulation field study. Isotope analysis was able to confirm that 1,2-DCA degradation, rather than degradation of vinyl chloride, was the primary mechanism of ethene production at the site. This thesis not only advances the application of compound specific carbon isotope fractionation to identify and quantify biodegradation of chlorinated ethanes in groundwater, but in particular progresses our understanding of the relationship between the enzymatic mechanisms of contaminant degradation and isotopic fractionation, and the ability to use that knowledge to predict degradation mechanisms for previously unconstrained pathways of contaminant remediation.

Author: Nancy Anne VanStone
Publisher:
ISBN: 9780494157541
Category :
Languages : en
Pages : 426

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Reductive dechlorination reactions occurring on zero-valent metal surfaces for chlorinated ethenes and chlorinated ethanes are investigated using compound specific isotopic analysis (CSIA) to measure carbon isotopic fractionation and carbon kinetic isotope effects (KIE). Reductive dechlorination of chlorinated contaminants on zero-valent iron (Fe0) is used for remediation purposes at over 100 sites worldwide employing permeable reactive barrier (PRB) technology. Degradation can occur via 3 main pathways: (1) alpha-elimination, (2) beta-elimination and (3) hydrogenolysis. Experiments documenting carbon isotopic fractionation observed during degradation of a suite of chlorinated ethenes are described, and it is demonstrated that reproducible carbon isotopic fractionation occurs for perchloroethene (PCE), trichloroethene (TCE), cis-dichloroethene (cis-DCE) and vinyl chloride (VC). The results for Fe0 from two different sources show distinct differences in both rates of reaction and isotopic fractionation factors (epsilon), particularly for the cis-DCE and VC. Using ground water samples from pre- and post-treatment of a Fe0 PRB at F.E. Warren Air Force Base, it is established that carbon isotopic fractionation of chlorinated ethenes follows the same principles under field conditions, and it is shown that CSIA, in combination with traditional compositional analysis, can help to resolve complex performance-related problems for PRBs. Finally, it is demonstrated that reaction pathways and mechanisms can be investigated using CSIA and ranges of epsilon and KIE are established for the investigated reactions on different zero-valent metals. In batch experiments monitoring dichloroethane (DCA) degradation on Zn0, CSIA was used to determine that a common rate limiting step occurs for hydrogenolysis and alpha-elimination reactions of 1,1-DCA. As well, overall epsilon and KIE are greater for beta-elimination of 1,2-DCA than for hydrogenolysis and alpha-elimination of 1,1-DCA. The degradation of a chlorinated ethene, cis-DCE, was investigated on Fe0. Direct measurements of epsilon and KIE for hydrogenolysis and beta-elimination were measured using CSIA. It is established that these reactions do not share a rate limiting step, and unique and reproducible carbon isotopic fractionation is associated with each reaction pathway. CSIA has been shown to be a versatile tool, aiding research as both a reliable diagnostic (i.e. identification of degradation) and as a valuable analytical instrument for mechanistic studies.

Author: Calvin Chi Hung Chan
Publisher:
ISBN: 9780494928615
Category :
Languages : en
Pages :

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Author: Maik A Jochmann
Publisher: Royal Society of Chemistry
ISBN: 1782626107
Category : Science
Languages : en
Pages : 306

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The use of Compound-specific Stable Isotope Analysis (CSIA) is increasing in many areas of science and technology for source allocation, authentication, and characterization of transformation reactions. Until now, there have been no textbooks available for students with an analytical chemical background or basic introductory books emphasising the instrumentation and theory. This book is the first to focus solely on stable isotope analysis of individual compounds in sometimes complex mixtures. It acts as both a lecture companion for students and a consultant for advanced scientists in fields including forensic and environmental science. The book starts with a brief history of the field before going on to explain stable isotopes from scratch. The different ways to express isotope abundances are introduced together with isotope effects and isotopic fractionation. A detailed account of the required technical equipment and general procedures for CSIA is provided. This includes sections on derivatization and the use of microextraction techniques in GC-IRMS. The very important topic of referencing and calibration in CSIA is clearly described. This differs from approaches used in quantitative analysis and is often difficult for the newcomer to comprehend. Examples of successful applications of CSIA in food authenticity, forensics, archaeology, doping control, environmental science, and extraterrestrial materials are included. Applications in isotope data treatment and presentation are also discussed and emphasis is placed on the general conclusions that can be drawn from the uses of CSIA. Further instrumental developments in the field are highlighted and selected experiments are introduced that may act as a basis for a short practical course at graduate level.

Author: Katie Colleen Harding
Publisher:
ISBN:
Category :
Languages : en
Pages : 157

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Trichloroethene (TCE) is one of the most commonly detected groundwater contaminants in the United States and has been characterized by the U.S. Environmental Protection Agency as carcinogenic to humans. Past TCE storage and disposal procedures following use in dry-cleaning operations and metal degreasing has resulted in numerous contaminated sites where TCE and chlorinated transformation products, such as dichloroethene (DCE) and vinyl chloride (VC), are detected in soil, groundwater, and air. Poly- and perfluoroalkyl substances (PFASs) are key constituents of aqueous film-forming foams (AFFFs) and are responsible for the surface tension reduction properties that facilitate rapid foam spreading over ignited liquid fuels. Various PFASs have been detected in the soil and groundwater of AFFF-impacted sites, while certain PFASs, such as the eight-carbon homologs perfluorooctanoic acid (PFOA) and perfluorosulfonic acid (PFOS), have been linked to adverse human health effects. The use of AFFF to extinguish chlorinated solvent-fueled fires has led to the co-contamination of TCE and PFASs at sites where foam wastewater and fuel were allowed to infiltrate the subsurface. Historically, groundwater and soil remediation at these sites was optimized for achieving TCE reductive dechlorination to ethene. However, due to recent increases in activities for measuring and characterizing PFAS contamination, particularly in groundwater and soils beneath firefighter training sites, greater attention is being paid to the fate and transformation of PFASs, as well as their effects on TCE-dechlorinating microbial communities. The in situ biotransformation of AFFF-derived PFAS compounds and the effects of AFFF and PFAS transformation products on TCE bioremediation must be understood. The biotransformation of a principle PFAS compound used in multiple AFFF formulations, fluorotelomer thioether amido sulfonate (FtTAoS), was investigated under aerobic conditions in soil microcosms amended with AFFF. The aerobic biotransformation pathways for 4:2, 6:2, and 8:2 FtTAoS were determined by direct LC-MS/MS quantification of intermediate and end products and through the characterization of previously unidentified intermediate products with high resolution MS measurements. FtTAoS was biotransformed under aerobic conditions to a fluorotelomer sulfonate, two fluorotelomer carboxylic acids, and a suite of perfluorinated carboxylic acids. The detection of two intermediate compounds, corresponding to singly- and doubly-oxygenated species of FtTAoS, suggest that the first two reactions in the biotransformation pathways are sequential oxygen additions to the thioether group. This is likely followed by a third oxygenation and cleavage between the resulting sulfonate and the amidosulfonate group to form a fluorotelomer sulfonate. The perfluorinated carboxylic acids appear to be the end products of FtTAoS biotransformation and were persistent in live microcosms. An oxidative assay employing PFAS oxidation by hydroxyl radical was applied to microcosm samples to indirectly quantify the total concentration of polyfluorinated compounds present during FtTAoS biotransformation for closure of the mass balance. The assay produced a full mass recovery of PFAS oxidation products before and after complete FtTAoS biotransformation even though only 10% (mol/mol) of the initial amended FtTAoS was accounted for by directly-measured PFASs. The effects of AFFF and various PFASs on anaerobic TCE dechlorination were investigated in a Dehalococcoides (Dhc)-containing microbial community that dechlorinated TCE to ethene. When AFFF formulations from three different manufacturers: 3M, National Foam, and Ansul were amended to the cuture's growth medium as the sole carbon and energy source, varying yet sufficient quantities of hydrogen and acetate were produced to support dechlorination during all three foam-amendments. However, TCE dechlorination only occurred under 3M AFFF amendment, while no dechlorination was observed under National Foam and Ansul AFFF amendments. All PFAS compounds were persistent in the anaerobic communities and did not transform biologically or abiotically. The degradation of diethylene glycol butyl ether (DGBE), the primary glycol ether solvent in most AFFFs, produced less hydrogen and acetate when amended alone than in AFFF-amended microcosms, suggesting that smaller quantities of other organic carbon substances in the foams, such as hydrocarbon surfactants, may be more easily fermentable. Amendment of 16 mg/L 6:2 fluorotelomer sulfonamido betaine (6:2 FtSaB) slowed TCE dechlorination while 32 mg/L FtSaB completely inhibited dechlorination, suggesting dechlorination did not occur in the National Foam AFFF-amended experiment due to the presence of its most abundant PFAS. In cultures amended with perfluroalkyl acids, 110 mg/L total perfluorosulfonic acids did not inhibit TCE dechlorination, while 110 mg/L total perfluorocarboxylic and perfluorosulfonic acids did, suggesting that inhibition is dependent on PFAS structure as well as concentration. Carbon stable isotope analysis is a frequently employed tool used to confirm and quantify in situ bioremediation of PCE and TCE to ethene. The impact of growth condition on the carbon isotope fractionation of TCE by Dhc was investigated by quantifying fractionation while Dhc was grown in pure and co-cultures as well as in mixed communities. Enrichment factors were not significantly affected by changes in any of the tested growth conditions for the pure cultures, co-cultures or the mixed communities, indicating that despite a variety of temperature, nutrient, and co-factor-limiting conditions, carbon isotope fractionations remain consistent for given Dhc cultures. However, the fractionation factors for the pure and co-cultures were outside the range of those quantified for the mixed communities, indicating that the fractionation may be strain-dependant.

Author: Sarah M. Kissell
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Trichloroethylene (TCE) is a chlorinated solvent most commonly used as an industrial degreaser for cleaning mechanical equipment. Historic improper management and disposal of TCE has resulted in contaminated soil and groundwater across the United States, including Hill Air Force Base in Utah. The abundance of TCE in the environment presents a public health risk because it is categorized as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC). The purpose of this study was to improve the bioremediation techniques of biostimulation and bioaugmentation. A continuous flow-through column study was performed where columns packed with aquifer material received a continuous flow of groundwater collected from Hill AFB. The groundwater contained TCE and a carbon source, lactate or whey, a waste product of the cheese industry to stimulate the aquifer microbial community, create anaerobic conditions, and facilitate the use of TCE as a terminal electron acceptor during respiration. Both carbon treatments reduced TCE to the final product of ethene gas, but unlike the lactate treatment, whey provided the energy required to fully reduce TCE, without accumulating the harmful degradation byproduct, vinyl chloride. The substrate, whey, provides an effective carbon and energy source for the bioremediation of TCE, and is also more economical than highly refined chemicals, such as lactate.

Author: Nicholas P. Cheremisinoff
Publisher: John Wiley & Sons
ISBN: 1119407737
Category : Science
Languages : en
Pages : 329

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Written by one of the world's foremost authorities on the subject, this is the most comprehensive and in-depth treatment available to environmental engineers and scientists for the remediation of groundwater, one of the earth's most precious resources. Groundwater is one of the Earth's most precious resources. We use it for drinking, bathing, and many other purposes. Without clean water, humans would cease to exist. Unfortunately, because of ignorance or lack of caring, groundwater is often contaminated through industrialization, construction or any number of other ways. It is the job of the environmental engineer to remediate the contaminated groundwater and make what has been tainted safe again.Selecting the proper remediation strategy and process is the key to moving forward, and, once this process has been selected, it must be executed properly, taking into consideration the costs, the type of contaminants that are involved, time frames, and many other factors. This volume provides a broad overview of the current and most widely applied remedial strategies. Instead of discussing these strategies in a generic way, the volume is organized by focusing on major contaminants that are of prime focus to industry and municipal water suppliers. The specific technologies that are applicable to the chemical contaminants discussed in different chapters are presented, but then cross-referenced to other chemical classes or contaminants that are also candidates for the technologies. The reader will also find extensive cost guidance in this volume to assist in developing preliminary cost estimates for capital equipment and operations & maintenance costs, which should be useful in screening strategies. The eight chapters cover all of the major various types of contaminants and their industrial applications, providing a valuable context to each scenario of contamination. This is the most thorough and up-to-date volume available on this important subject, and it is a must-have for any environmental engineer or scientist working in groundwater remediation.

Author: Bernard H. Kueper
Publisher: Springer Science & Business
ISBN: 1461469228
Category : Technology & Engineering
Languages : en
Pages : 759

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The purpose of this book is to help engineers and scientists better understand dense nonaqueous phase liquid (DNAPL) contamination of groundwater and the methods and technology used for characterization and remediation. Remediation of DNAPL source zones is very difficult and controversial and must be based on state-of-the-art knowledge of the behavior (transport and fate) of nonaqueous phase liquids in the subsurface and site specific geology, chemistry and hydrology. This volume is focused on the characterization and remediation of nonaqueous phase chlorinated solvents and it is hoped that mid-level engineers and scientists will find this book helpful in understanding the current state-of-practice of DNAPL source zone management and remediation.

Author: Stefan Cretnik
Publisher:
ISBN:
Category : Carbon
Languages : en
Pages :

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