What Was Released? Assessing the Physical Properties and Chemical Composition of Petroleum and Products of Burned Oil

Abstract

The severity of oil spills depends on the quantity of material released and its physical and chemical properties. The total amount of petroleum spilled during the Deepwater Horizon incident and the relative fractions of the chemical compound classes of the Macondo oil were obtained by measurements, observations, and model calculations, with a significant amount of uncertainty. Because petroleum is an extremely complex mixture of many thousands or more of gaseous, liquid, and solid constituents, full elucidation of their compositions at the molecular level is impossible with presently available analytical techniques. This paper reviews published work on widely used analytical techniques and points out that scientists’ varying approaches to research questions and preferences for methods of analysis constitute a source of uncertainty. In addition, the focus is on two technical advancements developed over the last two decades, namely two-dimensional gas chromatography and Fourier transform ion cyclotron resonance mass spectrometry. Both were particularly valuable in the analysis of the spilled Macondo oil and its weathering products. Among the different processes of alteration of the original oil, only in situ oil burning is dealt with in this paper. This review reveals the paucity of data on this mitigation process and shows the need for more systematic coordination of methods in burned oil research studies.

Biogeochemical Processes Affecting the Fate of Discharged Deepwater Horizon Gas and Oil: New Insights and Remaining Gaps in Our Understanding

“…Thus, when tracking the fate of the DWH spilled oil, it has been important to be cognizant of the other sources of hydrocarbon/oil inputs to the same Gulf of Mexico area and to use analytical methods and interpretation of data that can successfully distinguish inputs from the spill, especially over longer periods of time and at low concentrations. It can be helpful to identify the specific chemical composition of the DWH oil and the relative compositions of specific structures of molecules known as petroleum biomarkers (molecular biomarkers to some organic geochemistsdifferent from what are now commonly considered biomarkers in molecular biology; Rullkötter and Farrington, 2021, in this issue, and references therein). The ratios of these petroleum biomarkers to other chemicals in DWH oil, such as the alkylated PAH homologues, become important in distinguishing the presence of DWH oil from other oil sources as well as from other aliphatic hydrocarbons and PAH sources.…”

“…Certain compounds, less susceptible to weathering, accumulated in various ecosystems (e.g., on shorelines, at the seafloor), reaching concentrations above background or detectable levels for varying periods of time. These compounds included some of the chemicals, such as PAHs of concern for known or potentially adverse effects, as discussed in other papers in this issue (Rullkötter and Farrington. 2021;Murawski et al, 2021;Halanych et al, 2021).…”

“…Many, if not most, of these findings would not have been possible without the utilization of new analytical chemistry methods, as discussed in Rullkötter and Farrington (2021, in this issue). In particular, analyses by ultrahigh-resolution FT-ICR-MS (Fourier transform-ion cyclotron resonance-mass spectrometry) have provided extensive data that challenge our ability to identify the myriad reaction pathways and chemical structures of thousands of photo-oxidation-induced reaction products (Rullkötter and Farrington, 2021, in this issue).…”

“…Sediment cores provided a multi-proxy record of MOSSFA events, the intensity of the flux of oil chemicals to the seafloor, and the spatial extent of such deposition and post-depositional events. Bagby et al (2016) examined 125 aliphatic (saturated hydrocarbons), aromatic, and biomarker compounds (Rullkötter and Farrington, 2021, in this issue) in 2,908 sediment samples collected within four years of the spill. The data they interrogated are available from the NRDA website and in the supplementary materials for Bagby et al (2016).…”

“…Fundamental physical chemistry and aquatic chemistry principles and examples for a variety of organic chemicals, including a range of hydrocarbon types and molecular weights found in the DWH gas and oil, are presented and discussed in the comprehensive textbook by Schwartzenbach et al (2017). Rullkötter and Farrington (2021, in this issue) review and briefly describe the complex compositions of petroleum and petroleum products in general and specifically of the DWH oil. Boufadel et al (2021, in this issue) describe the influence of various physical processes within many temporal and spatial scales on the gas and oil discharged at the broken well riser as well as on the resulting surface oil slick.…”