Fates of petroleum during the deepwater horizon oil spill: A chemistry perspective

Abstract

We describe the initial bulk and compound specific composition of the liquid oil spilled during the Deepwater Horizon (DwH) disaster. The emphasis is on the target hydrocarbon compounds typically found in highest concentrations and on those of concern from a toxicological perspective (i.e., the target normal alkanes and isoprenoids, and PAHs on U.S. Environmental Protection Agency’s (EPA) priority list with their alkyl homolog compounds), and/or those relevant for forensic fingerprinting of spill residues (i.e., sulfur containing PAHs and biomarker compounds). Weathering changed the oil’s composition in various environmental compartments. These compositional changes and potential environmental impacts of the remaining weathered residues are presented in this paper. Biodegradation occurred in both surface and subsurface environments while photooxidation primarily modified and removed hydrocarbons in floating oil slicks. The volatile, soluble and highly labile C1 to C10 hydrocarbons were rapidly degraded in the water column and/or emitted to the atmosphere (evaporation). The semi-volatile hydrocarbons (labile C10 to C25) that remained in the water column and floating oil on the water’s surface were lost from oil residues during weathering. The heavy nonvolatile and insoluble hydrocarbons (recalcitrant C25+) were least affected by initial weathering processes in 2010. The composition of the residual oil fraction in surface floating oil was further altered by the addition of oil soluble oxy hydrocarbons produced from photooxidation. During 2011 and 2012 the resulting highly insoluble recalcitrant C25+ oily residues remained on the shorelines, bottom sediments, or bound to suspended particulates in the water column, with detectable residues mostly returning to near pre-spill levels by 2015 to 2020. Some recalcitrant oil residues can still be found at various locations, including some coastal environments (e.g., marshes), or deep-water sediments, at very low levels, ten years after the spill.

Towards relevant ecological experiments and assessments of coastal oil spill effects: Insights from the 2010 Deepwater Horizon oil spill

“…This included collections of the first baseline inventories in decades, critical documentation that can serve as baseline reference sites for future stressors. Other noteworthy contributions highlighted the enhanced understanding of deep sea population dynamics and community resilience following this disturbance, quantification of nearshore ecosystem properties, and improved understanding of oil chemistry, especially as it relates to physical/meteorological forcings, weathering/degradation, and effects in coastal ecosystems (Hsing et al, 2013;Felder et al, 2014;Prouty et al, 2016;Rabalais and Turner 2016;Murawski et al, 2021;Overton et al, 2022).…”

“…DwH oil (e.g., Sweet Louisiana Crude, MC-252, etc.) was a unique blend of >10,000 chemical compounds, ranging from more toxic, lighter aromatics to less toxic, heavier, and stable compounds (Overton et al, 2022). Lighter compounds (e.g., naphthalenes) precipitate rapidly during the weathering process (via wave action, ultraviolet light degradation, and other chemical processes), while more stable compounds (e.g., asphaltenes) resist weathering.…”

“…Moreover, oil can interact with plastics used in tanks to produce novel toxic chemicals that may impact the survival of experimental organisms (de Soysa et al, 2012). Oil treatments should be reflective of natural conditions, with relevant concentrations, compositions, and weathering to mimic impacted areas (Overton et al, 2022). Trial duration should also be considered, as oil effects in contained systems may overestimate exposure by reducing oil dilution or preventing emigration that occurs in nature.…”