Scott A. Stout

Molecular aspects of the peatification and early coalification of angiosperm and gymnosperm woods

Selected genera represented by recent and peatified woods common to the southeastern US and their lignitic equivalents from Vermont and North Dakota have been characterized by Curie-point pyrolysis-mass spectrometry and Curie-point pyrolysis-gas chromatography, mass spectrometry. Pyrolysis data have shown that similar chemical trends are exhibited during the peatification and early coalification of both hardwood and softwood cell wall components. These trends are: 1. (1) the relatively rapid removal of pentosans i.e., hemicelluloses), 2. (2) the initial enrichment followed by the gradual removal of cellulose (and other hexose sugars), and 3. (3) the gradual modification of lignin to a less functionalized aromatic polymer. These observations imply that cell wall-derived huminitic macerals in coals consist predominantly of demethoxylated, demethylated, and more highly condensed lignin derived macromolecules.

Weathering of field-collected floating and stranded Macondo oils during and shortly after the Deepwater Horizon oil spill

Chemical analysis of large populations of floating (n=62) and stranded (n=1174) Macondo oils collected from the northern Gulf of Mexico sea surface and shorelines during or within seven weeks of the end of the Deepwater Horizon oil spill demonstrates the range, rates, and processes affecting surface oil weathering. Oil collected immediately upon reaching the sea surface had already lost most mass below n-C8 from dissolution of soluble aliphatics, monoaromatics, and naphthalenes during the oils ascent with further reductions extending up to n-C13 due to the onset of evaporation. With additional time, weathering of the floating and stranded oils advanced with total PAH (TPAH50) depletions averaging 69±23% for floating oils and 94±3% for stranded oils caused by the combined effects of evaporation, dissolution, and photo-oxidation, the latter of which also reduced triaromatic steroid biomarkers. Biodegradation was not evident among the coalesced floating oils studied, but had commenced in some stranded oils.

Curie-point pyrolysis mass spectrometry, Curie-point pyrolysis-gas chromatography-mass spectrometry and fluorescence microscopy as analytical tools for the characterization of two uncommon lignites

Abstract A case study is presented of two uncommon lignite samples, PSOC-975 and PSOC-427, which were studied by microscopic and analytical pyrolysis methods. Pyrolysis-mass spectrometric (Py-MS), pyrolysis-gas chromatographic (Py-GC) and Py-GC-MS data demonstrate that lignite PSOC-975 contains a high abundance of resinous material of some sort, whereas PSOC-427 is characterized by two major unknown pyrolysis products, prist-1-ene and alkylphenols. The chemical data contradict the microscopic observations, which point to a maceral composition of woody and cortical tissues, although a considerable part is unrecognizable. Apparent discrepancies between low-voltage Py-MS and 80-eV Py-GC-MS results were evaluated by a study of standards. It was shown that the aliphatic hydrocarbons are highly underestimated in low-voltage Py-MS. The nature of the disagreement observed between maceral composition and the pyrolysis data needs further study.

Structural characterization of the organic polymers comprising a lignite's matrix and megafossils

Abstract The geochemical and petrographic character of the matrix of the Oligocene, angiospermous Brandon lignite, Vermont, is examined and compared to samples of a common fossilized angiosperm wood and fruit endocarp contained within the lignite. The lignite matrix is composed primarily of humodetrinite and liptodetrinite while the megafossils are overwhelmingly humotelinitic (textinite and ulminite). Curie-point Py-MS, in-source Py-EI-MS, in-source Py-CI-MS, and CPMAS 13C NMR reveal that the polymers comprising the matrix include a highly aliphatic polymer(s) and polymer(s) derived from the significantly modified remains of angiosperm lignin(s). Very few polysaccharides are preserved in the matrix. The polymer(s) in each megafossil contain(s) significant proportions of polysaccharides and lignins which are, however, significantly altered from their Recent equivalents. The results suggest that anatomical preservation and physical integrity of discrete megafossils within peats and lignites are directly related to the degree to which the original ligno-cellulosic framework is preserved. This implies that the humotelinitic macerals comprising the megafossils contain ligno-cellulose-derived polymers that are less modified than those comprising the humodetrinite within the matrix. The liptodetrinite within the matrix is probably comprised of highly aliphatic polymers derived from cutans and/or alginans. Upon further coalification the vitrinite within the vitrain bands derived from the megafossils and vitrinite within the clarain bands derived from the matrix would be distinct.

Beyond 16 Priority Pollutant PAHs: A Review of PACs used in Environmental Forensic Chemistry

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in soils and sediments, particularly in urbanized environments in which the concentrations of 16 (or so) PAHs are regulated. Distinguishing among the numerous PAH sources is of practical and legal concern and thereby is often an objective of environmental forensic chemistry studies. Studies of prospective sources and impacted soils and sediments that rely upon the 16 U.S. EPA Priority Pollutant PAHs are disadvantaged, as these few compounds generally lack the specificity to distinguish among different PAH sources in the environment. Advances in analytical and interpretive methods over several decades have shown that different PAH sources can be more defensibly distinguished using modified EPA Method 8270 that, among other improvements, measure many other polycyclic aromatic compounds (PACs) that co-occur with the Priority Pollutant PAHs in different sources and in the environment. The PACs include variously-alkylated PAHs and polycyclic aromatic sulfur heterocyclics (PASHs) homologs and individual isomers, which are herein reviewed. Collectively, these PACs provide a higher degree of specificity among PAC sources and can be used to understand the effects of weathering on PAH assemblages. Despite their diagnostic capacity, PACs should not be relied upon at the exclusion of other compound groups (e.g., petroleum biomarkers) in most environmental forensic chemistry studies. In light of these advances, source characterization studies that rely only upon the 16 (or so) Priority Pollutant PAHs warrant considerable caution.

Chemical heterogeneity in modern marine residual fuel oils

Because of their preponderant use as fuel in marine vessels, marine residual fuels are often the focus of maritime oil spill investigations. Residual fuels, often referred to generically as heavy fuel oil or HFO, pose a variety of challenges to oil spill investigators. Variability in the composition of modern heavy marine fuels provides unique opportunities for chemical “fingerprinting” of HFOs in the environment. This chapter focuses on the forensic chemistry of HFO—the most widely used of the commercial marine fuel oils—and chemical features of these fuels pertinent to oil spill investigations. Two most popular groups of heavy fuel oils, IFO 180 and IFO 380, differ largely in their blending formulas. From a forensic chemistry standpoint, it is the combination of the refining and blending processes that impose unique chemical “fingerprints” on IFO 380 HFOs, which oil spill investigators can use to identify and track spilled fuel in the environment. Gas chromatographic analysis of petroleum fuels reveals the distinctive boiling point distribution of the chromatographable hydrocarbons that compose the fuels.

Laser pyrolysis—gas chromatography / mass spectrometry of two synthetic organic polymers

Abstract The utility of near-IR laser radiation in thermal degradation studies of two synthetic organic polymers is investigated. Continuous wave, near-IR laser radiation (1064 nm) is used to thermally degrade poly- para - tert -butylstyrene: graphite (1:1) and linear polyethylene: graphite (1:1) mixtures in quartz tubes. Pyrolysates are cryogenically trapped and subsequently analysed by GC/MS. The thermal degradation of these polymers during laser pyrolysis (LPy) proceeds via the mechanisms of depolymerization and random scission which are comparable to conventional filament pyrolysis. The emissive graphite serves to increase the heat transfer to the polymers. Sample temperatures during these LPy experiments are estimated to approach 600°C. While many unknowns remain surrounding the interaction of laser radiation with organic solids, this preliminary work provides a satisfactory basis for future LPy studies aimed at better understanding complex, natural organic polymers such as occur in geological and biological materials.

Assessing the footprint and volume of oil deposited in deep-sea sediments following the Deepwater Horizon oil spill.

The lateral and vertical extents of Macondo oil in deep-sea sediments resulting from the 2010 Deepwater Horizon oil spill were determined using chemical forensics and geostatistical kriging of data from 2397 sediment samples from 875 cores collected in 2010/2011 and 2014. The total mass of Macondo-derived hopane on the seafloor in 2010/2011 was conservatively estimated between 2.00 and 2.26metric tons, derived from 219,000 to 247,000barrels of oil; or 6.9 to 7.7% of the 3.19millionbarrels spilled. Macondo-derived hopane was deposited over 1030 to 1910km2 of the seafloor, mostly (>97%) in surface (0-1cm) and near-surface (1-3cm) sediments, which is consistent with short-term oil deposition. Although Macondo oil was still present in surface sediments in 2014, the total mass of Macondo-derived hopane was significantly lower (~80 to 90%) than in 2010/2011, affirming an acute impact from the spill and not long-term deposition from natural seeps.

Hydrocarbon Fingerprinting Methods

Abstract Virtually all environmental forensics investigations focus on addressing questions pertaining to the nature, source, age, and ownership of site-related contamination. Contamination, particularly at complex historic sites, is usually a multifarious mixture of both organic and inorganic chemicals. Thus, the forensic investigator is typically faced with “unravelling” a complicated mixture of chemicals into component parts in order to better link the chemicals to their historic origins and differentiate them from often similar types and sources of contaminants. This chapter describes advanced methods of chemical analyses that have evolved, and continue to be refined by environmental chemists to address the specific needs of the forensic investigator and focuses on arguably some of the most important organic contaminants commonly encountered in terrestrial and sediment investigations: petroleum hydrocarbons and polycyclic aromatic hydrocarbons (PAH). The details of advanced methods for the measurement of these chemicals in multiple media (water, soils, sediment, air, and biological tissues) are presented. Laboratory techniques, including sample preparation, instrumental analysis, and quality control and quality assurance procedures are presented so that the reader can readily adapt forensic measurement techniques to suit his or her specific site investigation activities. Case studies are presented throughout the text that demonstrate the application of advanced methods of chemical analysis to varying kinds of complicated, real world forensic instigations.

Semivolatile Hydrocarbon Residues of Coal and Coal Tar

This chapter presents the current analytical methods used for the characterization of the semivolatile hydrocarbon source signatures of coal and coal-derived by-products. A particular focus is given to the thermally derived by-products of coal formed from its thermal decomposition by industrial carbonization (coking), which mirror the by-products formed during natural coal fires. Semivolatile hydrocarbons are solvent-extractable compounds found in coals and coal-derived by-products that include a broad range of compounds. Functionally they can be defined as solvent-extractable compounds that elute between about n-nonane (n-C9) and n-tetratetracontane (n-C44)ona gas chromatograph (GC) equipped with a nonpolar silicone capillary column. The semivolatile hydrocarbons include normal alkanes, acyclic isoprenoids, aromatics, sesqui-, di-, and triterpanes, regular and rearranged steranes, mono- and triaromatic steranes, and many other compound groups. Numbering in the thousands of individual compounds, the relative abundances or absolute concentrations of diagnostic semivolatile hydrocarbons can differentiate fossil fuels and various derived products. Sophisticated analytical methods exist for the chemical characterization of the extractable, semivolatile hydrocarbons that occur in the nonvolatile by-products produced in the course of coal fires, namely, carbonized coal residues and coal tars. Both coal fires and industrial coal carbonization plants produce by-products with hydrocarbon signatures imbued with information about the native (unburned) parent coal, the conditions of carbonization, and the weathering of the by-products in the environment (particularly volatilization). This information can prove useful in environmental investigations that involve coal carbonization by-products.