@article {hanke_sequential_2023,
	title = {Sequential thermal analysis of complex organic mixtures: Procedural standards and improved CO2 purification capacity},
	journal = {Radiocarbon},
	volume = {65},
	number = {2},
	year = {2023},
	note = {Publisher: Cambridge University Press},
	month = {03/2023},
	pages = {389{\textendash}409},
	abstract = {Sequential thermal analysis allows for deconvoluting the refractory nature and complexity of carbon mixtures embedded in mineral matrices for subsequent offline stable carbon and radiocarbon (14C) isotope analyses. Originally developed to separate Holocene from more ancient sedimentary organic matter to improve dating of marine sediments, the Ramped Pyrolysis and Oxidation (RPO) apparatus, or informally, the {\textquotedblleft}dirt burner{\textquotedblright} is now used to address pressing questions in the broad field of biogeochemistry. The growing interest in the community now necessitates improved handling and procedures for routine analyses of difficult sample types. Here we report on advances in CO2 purification during sample processing, modifications to the instrumentation at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility, and introduce sodium bicarbonate procedural standards with differing natural abundance 14C signatures for blank assessment. Measurements from different environmental samples are used to compare the procedure to the different generations of sequential thermal analyses. With this study, we aim to improve the standardization of the procedures and prepare this instrumentation for innovations in online stable carbon isotopes and direct AMS-interface measurements in the future.},
	keywords = {chemical analysis, dirt burner, full oxidation (FOX) mode, Radiocarbon dating, ramped pyrolysis oxidation},
	issn = {0033-8222, 1945-5755},
	doi = {10.1017/RDC.2023.13},
	url = {https://www.cambridge.org/core/journals/radiocarbon/article/sequential-thermal-analysis-of-complex-organic-mixtures-procedural-standards-and-improved-co2-purification-capacity/E225F01B421614EE176553014E7B38BE},
	author = {Hanke, Ulrich M. and Gagnon, Alan R. and Reddy, Christopher M. and Gaylord, Mary C. Lardie and Cruz, Anne J. and Galy, Valier and Hansman, Roberta L. and Kurz, Mark D.}
}
@article {2946,
	title = {Rapid Degradation of Cellulose Diacetate by Marine MicrobesRapid Degradation of Cellulose Diacetate by Marine Microbes},
	journal = {Environmental Science \& Technology Letters},
	volume = {9},
	year = {2022},
	month = {Nov-01-2022},
	pages = {37 - 41},
	abstract = {The persistence of cellulose diacetate (CDA), a biobased plastic used in textiles and single-use consumer products, in the ocean is currently unknown. Here, we probe the disintegration and degradation of CDA-based materials (25 mu m films, 510 mu m foam, and 97 g/m2 fabric) by marine microbes in a continuous flow seawater mesocosm. Photographic evidence and mass loss measurements demonstrate that CDA-based materials disintegrate in months. Disintegration is marked by the increasing esterase and cellulase activity of the biofilm community, suggesting that marine microbes degrade CDA. The natural abundance stable (13C) and radiocarbon (14C) isotopic signature of carbon dioxide respired during short-term bottle incubations confirms the rapid degradation of both acetyl and cellulosic components of CDA by seawater microbial communities. These findings challenge the paradigm set by governmental agencies and advocacy groups that CDA-based materials persist in the ocean for decades, and represent a positive step toward identifying highutility, biobased plastics with low environmental persistence.},
	keywords = {ACETATE, BIODEGRADATION},
	issn = {2328-8930},
	doi = {10.1021/acs.estlett.1c0084310.1021/acs.estlett.1c00843.s001},
	url = {https://www.webofscience.com/wos/woscc/full-record/WOS:000730351300001?AlertId=ab9062f8-b111-4f95-a2b8-66e7afac0471\&SID=7DMV3hUCqV1Mt8lQGWY},
	author = {Mazzotta, Michael G. and Reddy, Christopher M. and Ward, Collin P.}
}
@article {walsh_synergy_2022,
	title = {Synergy between Sunlight, Titanium Dioxide, and Microbes Enhances Cellulose Diacetate Degradation in the Ocean},
	journal = {Environmental Science \& Technology},
	volume = {56},
	number = {19},
	year = {2022},
	note = {Publisher: American Chemical Society},
	month = {09/2022},
	pages = {13810{\textendash}13819},
	abstract = {Sunlight chemically transforms marine plastics into a suite of products, with formulation-the specific mixture of polymers and additives-driving rates and products. However, the effect of light-driven transformations on subsequent microbial lability is poorly understood. Here, we examined the interplay between photochemical and biological degradation of fabrics made from cellulose diacetate (CDA), a biobased polymer used commonly in consumer products. We also examined the influence of \~{}1\% titanium dioxide (TiO2), a common pigment and photocatalyst. We sequentially exposed CDA to simulated sunlight and native marine microbes to understand how photodegradation influences metabolic rates and pathways. Nuclear magnetic resonance spectroscopy revealed that sunlight initiated chain scission reactions, reducing CDA{\textquoteright}s average molecular weight. Natural abundance carbon isotope measurements demonstrated that chain scission ultimately yields CO2, a newly identified abiotic loss term of CDA in the environment. Measurements of fabric mass loss and enzymatic activities in seawater implied that photodegradation enhanced biodegradation by performing steps typically facilitated by cellulase. TiO2 accelerated CDA photodegradation, expediting biodegradation. Collectively, these findings (i) underline the importance of formulation in plastic{\textquoteright}s environmental fate and (ii) suggest that overlooking synergy between photochemical and biological degradation may lead to overestimates of marine plastic persistence.},
	issn = {0013-936X},
	doi = {10.1021/acs.est.2c04348},
	url = {https://doi.org/10.1021/acs.est.2c04348},
	author = {Walsh, Anna N. and Mazzotta, Michael G. and Nelson, Taylor F. and Reddy, Christopher M. and Ward, Collin P.}
}
@article {3003,
	title = {Plastic Formulation is an Emerging Control of Its Photochemical Fate in the Ocean},
	journal = {Environmental Science \& Technology},
	volume = {55},
	year = {2021},
	month = {09/2021},
	pages = {12383 - 12392},
	abstract = {Sunlight exposure is a control of long-term plastic fate in the environment that converts plastic into oxygenated products spanning the polymer, dissolved, and gas phases. However, our understanding of how plastic formulation influences the amount and composition of these photoproducts remains incomplete. Here, we characterized the initial formulations and resulting dissolved photoproducts of four single-use consumer polyethylene (PE) bags from major retailers and one pure PE film. Consumer PE bags contained 15{\textendash}36\% inorganic additives, primarily calcium carbonate (13{\textendash}34\%) and titanium dioxide (TiO2; 1{\textendash}2\%). Sunlight exposure consistently increased production of dissolved organic carbon (DOC) relative to leaching in the dark (3- to 80-fold). All consumer PE bags produced more DOC during sunlight exposure than the pure PE (1.2- to 2.0-fold). The DOC leached after sunlight exposure increasingly reflected the 13C and 14C isotopic composition of the plastic. Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry revealed that sunlight exposure substantially increased the number of DOC formulas detected (1.1- to 50-fold). TiO2-containing bags photochemically degraded into the most compositionally similar DOC, with 68{\textendash}94\% of photoproduced formulas in common with at least one other TiO2-containing bag. Conversely, only 28\% of photoproduced formulas from the pure PE were detected in photoproduced DOC from the consumer PE. Overall, these findings suggest that plastic formulation, especially TiO2, plays a determining role in the amount and composition of DOC generated by sunlight. Consequently, studies on pure, unweathered polymers may not accurately represent the fates and impacts of the plastics entering the ocean.},
	isbn = {0013-936X},
	doi = {10.1021/acs.est.1c02272},
	url = {https://doi.org/10.1021/acs.est.1c02272},
	author = {Walsh, Anna N. and Reddy, Christopher M. and Niles, Sydney F. and McKenna, Amy M. and Hansel, Colleen M. and Ward, Collin P.}
}
@article {2757,
	title = {Significance of Perylene for Source Allocation of Terrigenous Organic Matter in Aquatic SedimentsSignificance of Perylene for Source Allocation of Terrigenous Organic Matter in Aquatic Sediments},
	journal = {Environmental Science \& Technology},
	volume = {53},
	year = {2019},
	month = {Apr-07-2020},
	pages = {8244 - 8251},
	abstract = {Perylene is a frequently abundant, and sometimes the only polycyclic aromatic hydrocarbon (PAH) in aquatic sediments, but its origin has been subject of a longstanding debate in geochemical research and pollutant forensics because its historical record differs markedly from typical anthropogenic PAHs. Here we investigate whether perylene serves as a source-specific molecular marker of fungal activity in forest soils. We use a well-characterized sedimentary record (1735-1999) from the anoxic-bottom waters of the Pettaquamscutt River basin, RI to examine mass accumulation rates and isotope records of perylene, and compare them with total organic carbon and the anthropogenic PAH fluoranthene. We support our arguments with radiocarbon (14C) data of higher plant leaf-wax n-alkanoic acids. Isotope-mass balance-calculations of perylene and n-alkanoic acids indicate that \~{}40\% of sedimentary organic matter is of terrestrial origin. Further, both terrestrial markers are pre-aged on millennial time-scales prior to burial in sediments and are insensitive to elevated 14C concentrations following nuclear weapons testing in the mid-20th Century. Instead, changes coincide with enhanced erosional flux during urban sprawl. These findings suggest that perylene is definitely a product of soil-derived fungi, and a powerful chemical tracer to study the spatial and temporal connectivity between terrestrial and aquatic environments. },
	issn = {0013-936X},
	doi = {10.1021/acs.est.9b0234410.1021/acs.est.9b02344.s001},
	url = {https://pubs.acs.org/doi/10.1021/acs.est.9b02344},
	author = {Hanke, Ulrich M. and Lima-Braun, Ana L. and Eglinton, Timothy I. and Donnelly, Jeffrey P. and Galy, Valier and Poussart, Pascale and Hughen, Konrad and McNichol, Ann P. and Xu, Li and Reddy, Christopher M.}
}
@article {2647,
	title = {Sunlight Converts Polystyrene to Carbon Dioxide and Dissolved Organic Carbon},
	journal = {Environmental Science \& Technology Letters},
	year = {2019},
	month = {Oct-10-2019},
	abstract = {Numerous international governmental agencies that steer policy assume that polystyrene persists in the environment for millennia. Here, we show that polystyrene is completely photochemically oxidized to carbon dioxide and partially photochemically oxidized to dissolved organic carbon. Lifetimes of complete and partial photochemical oxidation are estimated to occur on centennial and decadal time scales, respectively. These lifetimes are orders of magnitude faster than biological respiration of polystyrene and thus challenge the prevailing assumption that polystyrene persists in the environment for millennia. Additives disproportionately altered the relative susceptibility to complete and partial photochemical oxidation of polystyrene and accelerated breakdown by shifting light absorbance and reactivity to longer wavelengths. Polystyrene photochemical oxidation increased approximately 25\% with a 10 {\textdegree}C increase in temperature, indicating that temperature is unlikely to be a primary driver of photochemical oxidation rates. Collectively, sunlight exposure appears to be a governing control of the environmental persistence of polystyrene, and thus, photochemical loss terms need to be included in mass balance studies on the environmental fate of polystyrene. The experimental framework presented herein should be applied to a diverse array of polymers and formulations to establish how general these results are for other plastics in the environment.},
	issn = {2328-8930},
	doi = {10.1021/acs.estlett.9b00532},
	url = {https://pubs.acs.org/doi/abs/10.1021/acs.estlett.9b00532},
	author = {Ward, Collin P. and Armstrong, Cassia J. and Walsh, Anna N. and Jackson, Julia H. and Reddy, Christopher M.}
}
@article {2805,
	title = {What on Earth Have We Been Burning? Deciphering Sedimentary Records of Pyrogenic CarbonWhat on Earth Have We Been Burning? Deciphering Sedimentary Records of Pyrogenic Carbon},
	journal = {Environmental Science \& Technology},
	volume = {51},
	year = {2017},
	month = {Jul-11-2017},
	pages = {12972 - 12980},
	abstract = {Humans have interacted with fire for thousands of years, yet the utilization of fossil fuels marked the beginning of a new era. Ubiquitous in the environment, pyrogenic carbon (PyC) arises from incomplete combustion of biomass and fossil fuels, forming a continuum of condensed aromatic structures. Here, we develop and evaluate 14C records for two complementary PyC molecular markers, benzene polycarboxylic acids (BPCAs) and polycyclic aromatic hydrocarbons (PAHs), preserved in aquatic sediments from a suburban and a remote catchment in the United States (U.S.) from the mid-1700s to 1998. Results show that the majority of PyC stems from local sources and is transferred to aquatic sedimentary archives on subdecadal to millennial time scales. Whereas a small portion stems from near-contemporaneous production and sedimentation, the majority of PyC (\~{}90\%) experiences delayed transmission due to {\textquotedblleft}preaging{\textquotedblright} on millennial time scales in catchment soils prior to its ultimate deposition. BPCAs (soot) and PAHs (precursors of soot) trace fossil fuel-derived PyC. Both markers parallel historical records of the consumption of fossil fuels in the U.S., yet never account for more than 19\% total PyC. This study demonstrates that isotopic characterization of multiple tracers is necessary to constrain histories and inventories of PyC and that sequestration of PyC can markedly lag its production.},
	issn = {0013-936X},
	doi = {10.1021/acs.est.7b03243},
	url = {https://pubs.acs.org/doi/10.1021/acs.est.7b03243},
	author = {Hanke, Ulrich M. and Reddy, Christopher M. and Braun, Ana L. L. and Coppola, Alysha I. and Haghipour, Negar and McIntyre, Cameron P. and Wacker, Lukas and Xu, Li and McNichol, Ann P. and Abiven, Samuel and Schmidt, Michael W. I. and Eglinton, Timothy I.}
}
@article {135,
	title = {Composition and fate of gas and oil released to the water column during the Deepwater Horizon oil spill},
	journal = {Proceedings of the National Academy of Sciences of the United States of America},
	volume = {109},
	year = {2012},
	note = {id: 2247; PT: J; TC: 10; UT: WOS:000312605600028},
	pages = {20229-20234},
	abstract = {Quantitative information regarding the endmember composition of the gas and oil that flowed from the Macondo well during the Deepwater Horizon oil spill is essential for determining the oil flow rate, total oil volume released, and trajectories and fates of hydrocarbon components in the marine environment. Using isobaric gas-tight samplers, we collected discrete samples directly above the Macondo well on June 21, 2010, and analyzed the gas and oil. We found that the fluids flowing from the Macondo well had a gas-to-oil ratio of 1,600 standard cubic feet per petroleum barrel. Based on the measured endmember gas-to-oil ratio and the Federally estimated net liquid oil release of 4.1 million barrels, the total amount of C-1-C-5 hydrocarbons released to the water column was 1.7 x 10(11) g. The endmember gas and oil compositions then enabled us to study the fractionation of petroleum hydrocarbons in discrete water samples collected in June 2010 within a southwest trending hydrocarbon-enriched plume of neutrally buoyant water at a water depth of 1,100 m. The most abundant petroleum hydrocarbons larger than C-1-C-5 were benzene, toluene, ethylbenzene, and total xylenes at concentrations up to 78 mu gL(-1). Comparison of the endmember gas and oil composition with the composition of water column samples showed that the plume was preferentially enriched with water-soluble components, indicating that aqueous dissolution played a major role in plume formation, whereas the fates of relatively insoluble petroleum components were initially controlled by other processes.},
	issn = {0027-8424},
	doi = {10.1073/pnas.1101242108},
	author = {Reddy, Christopher M. and Arey, J. Samuel and Seewald, Jeffrey S. and Sylva, Sean P. and Lemkau, Karin L. and Nelson, Robert K. and Carmichael, Catherine A. and McIntyre, Cameron P. and Fenwick, Judith and Ventura, G. Todd and Van Mooy, Benjamin A. S. and Camilli, Richard}
}
@article { ISI:000299864400020,
	title = {Modern and Fossil Contributions to Polycyclic Aromatic Hydrocarbons in PM2.5 from North Birmingham, Alabama in the Southeastern U.S.},
	journal = {ENVIRONMENTAL SCIENCE \& TECHNOLOGY},
	volume = {46},
	number = {{3}},
	year = {2012},
	month = {FEB 7},
	pages = {1422-1429},
	type = {Article},
	abstract = {Analyzing the radiocarbon (C-14) content of polycyclic aromatic hydrocarbons (PAHs) in atmospheric particulate matter can provide estimates on the source contributions from biomass burning versus fossil fuel. The relative importance of these two sources to ambient PAHs varies considerably across regions and even countries, and hence there is a pressing need to apportion these sources. In this study, we advanced the radiocarbon analysis from bulk carbon to compound class specific radiocarbon analysis (CCSRA) to determine Delta C-14 and delta C-13 values of PAHs in PM2.5 samples for investigating biomass burning and fossil fuel source contributions to PAHs from one of the Southeastern Aerosol Research and Characterization (SEARCH) sites in North Birmingham (BHM), Alabama during winter (December 2004-February 2005) and summer (June-August 2005) by accelerator mass spectrometry. To compare our ambient samples to known sources, we collected and analyzed fenceline samples from the vicinity of a coke plant in BHM. As expected, PAHs from the coke plant fenceline samples had very low radiocarbon levels. Its Delta C-14 varied from -990 to -970 parts per thousand, indicating that 97 to 99\% were of fossil source. PAHs in the ambient PM2.5 had Delta C-14 from -968 to -911 parts per thousand, indicating that 92-97\% of PAHs were from fossil fuel combustion. These levels indicated the dominance of fossil sources of ambient PAHs. The radiocarbon level of ambient PAHs was higher in winter than in summer. Winter samples exhibited depleted delta C-13 value and enriched Delta C-14 value because of the increased contribution of PAHs from biomass burning source. However, biomass burning contributed more to heavier PAHs (modern source accounting for 6-8\%) than fighter ones with a modern contribution of 3\%.},
	issn = {0013-936X},
	doi = {10.1021/es2043189},
	author = {Xu, Li and Zheng, Mei and Ding, Xiang and Edgerton, Eric S. and Reddy, Christopher M.}
}
@article {209,
	title = {Contemporary 14C radiocarbon levels of oxygenated polybrominated diphenyl ethers (O-PBDEs) isolated in sponge{\textendash}cyanobacteria associations},
	journal = {Marine pollution bulletin},
	volume = {62},
	year = {2011},
	note = {id: 2192},
	pages = {631-636},
	abstract = {Considerable debate surrounds the sources of oxygenated polybrominated diphenyl ethers (O-PBDEs) in wildlife as to whether they are naturally produced or result from anthropogenic industrial activities. Natural radiocarbon (14C) abundance has proven to be a powerful tool to address this problem as recently biosynthesized compounds contain contemporary (i.e. modern) amounts of atmospheric radiocarbon; whereas industrial chemicals, mostly produced from fossil fuels, contain no detectable 14C. However, few compounds isolated from organisms have been analyzed for their radiocarbon content. To provide a baseline, we analyzed the 14C content of four O-PBDEs. These compounds, 6-OH-BDE47, 2'-OH-BDE68, 2',6-diOH-BDE159, and a recently identified compound, 2'-MeO-6-OH-BDE120, were isolated from the tropical marine sponges Dysidea granulosa and Lendenfeldia dendyi. The modern radiocarbon content of their chemical structures (i.e. diphenyl ethers, C12H22O) indicates that they are naturally produced. This adds to a growing baseline on, at least, the sources of these unusual compounds.},
	issn = {0025-326X},
	doi = {10.1016/j.marpolbul.2010.12.022},
	url = {http://www.sciencedirect.com/science/article/pii/S0025326X11000075},
	author = {Guitart, Carlos and Slattery, Marc and Ankisetty, Sridevi and Radwan, Mohamed and Ross, Samir J. and Letcher, Robert J. and Reddy, Christopher M.}
}
@article {2442,
	title = {Relationships between carbon isotopic composition and mode of binding of natural organic matter in selected marine sediments},
	volume = {38},
	year = {2007},
	month = {2007/11//},
	pages = {1824 - 1837},
	abstract = {We have investigated the relationships between radiocarbon (14C) and stable carbon (13C) isotopic composition and the different modes of binding of organic matter (OM) in surficial sediments selected from near-shore and continental margin sites that vary in terms of input and depositional conditions. To improve our understanding of the entire OM pool, isotopic analysis of sedimentary sub-fractions, as opposed to individual compounds, was performed. This was achieved by sequentially treating sediments via solvent extraction to examine unbound compounds, followed by saponification to cleave ester linked moieties. Isotopic analysis was performed on the bulk sediment and resulting residues. The molecular composition of the extracts was examined using gas chromatography/mass spectrometry (GC/MS) and the relative contributions of terrestrial and marine biomarkers were assessed. Radiocarbon abundances (Δ14C) of the bulk sediment reflect a mixture of modern, pre-aged and fossil carbon. Offsets in Δ14C between the bulk sediment and sediment residues demonstrate varying associations of these carbon pools. For the majority of sites, a negative offset between extracted (EX-RES) and saponified (SA-RES) sediment residues results from the removal of relatively 14C-rich material during saponification. Saponification extracts (SAEs) are mainly composed of short chain (n-C12 to n-C24) alkanoic acids with an even/odd dominance, indicating a predominantly marine algal or microbial source. This provides evidence for the protection of labile marine carbon by chemical binding. This study bridges the gap between molecular level and bulk OM analysis of marine sediments.},
	isbn = {0146-6380},
	doi = {10.1016/j.orggeochem.2007.07.008},
	url = {http://www.sciencedirect.com/science/article/pii/S0146638007001751},
	author = {White, Helen K. and Reddy, Christopher M. and Eglinton, Timothy I.}
}
@article {1921,
	title = {14C methane and DIC in the deep terrestrial subsurface: implications for microbial methanogenesis},
	journal = {Geomicrobiology Journal},
	volume = {23},
	year = {2006},
	note = {id: 1100},
	month = {2006},
	pages = {453-462},
	author = {Slater, Greg F. and Lippmann-Pipke, Johanna and Moser, Duane P. and Reddy, Christopher M. and Onstott, T. C. and Lacrampe-Couloume, Georges and Lollar, Barbara Sherwood}
}
@article {1919,
	title = {Intrinsic bacterial biodegradation of petroleum contamination demonstrated in situ using natural abundance, molecular-level 14C analysis},
	journal = {Organic Geochemistry},
	volume = {37},
	year = {2006},
	note = {id: 594},
	month = {2006},
	pages = {981-989},
	author = {Slater, Gregory F. and Nelson, Robert K. and Kile, Brian M. and Reddy, Christopher M.}
}
