How Persistent and Bioavailable Are Oxygenated Deepwater Horizon Oil Transformation Products?

Abstract

About half of the surface oil floating on the Gulf of Mexico in the aftermath of the 2010 Deepwater Horizon spill was transformed into oxygenated hydrocarbons (OxHC) within days to weeks. These OxHC persist for years in oil/sand aggregates in nearshore and beach environments, and there is concern that these aggregates might represent a long-term source of toxic compounds. However, because this OxHC fraction is a continuum of transformation products that are not well chemically characterized, it is not included in current oil spill fate and effect models. This challenges an accurate environmental risk assessment of weathered oil. Here, we used molecular and bulk analytical techniques to constrain the chemical composition and environmental fate of weathered oil samples collected on the sea surface and beaches of the Gulf of Mexico. We found that approximately 50% of the weathering-related disappearance of saturated and aromatic compounds in these samples was compensated by an increase in OxHC. Furthermore, we identified and quantified a suite of oxygenated aliphatic compounds that are more water-soluble and less hydrophobic than its presumed precursors, but only represent <1% of the oil residues' mass. Lastly, dissolution experiments showed that compounds in the OxHC fraction can leach into the water; however, the mass loss of this process is small. Overall, this study shows that the OxHC fraction is prevalent and persistent in weathered oil/sand aggregates, which can act as a long-term source of dissolved oil-derived compounds.

Bacterial Community Legacy Effects Following the Agia Zoni II Oil-Spill, Greece

“…Once again this could be due to carbon and energy storage, or the persistence of trace amounts of high molecular weight PAHs. Alternatively, hydrocarbons can be undetected through analytical methods such as GC-MS ( McKenna et al, 2013 ) when weathered hydrocarbons from an oil spill undergo transformation into oxygenated hydrocarbons (though currently there is no evidence that Cycloclasticus is able to degrade oxygenated hydrocarbons) ( Kiruri et al, 2013 ), which can persist for years within oil/sand aggregates ( Aeppli et al, 2018 ).…”

“…While OHCB have been demonstrated to degrade other compounds in pure culture (Radwan et al, 2019;Zadjelovic et al, 2020), there is still limited evidence that the OHCB are competitive for non-hydrocarbon substrates in the environment. This is evidenced by the fact OHCB are typically present in extremely low numbers in uncontaminated environments but rapidly increase in abundance following oil-spills (Yakimov et al, 2004a;Atlas and Hazen, 2011;Acosta-González et al, 2015;Nogales and Bosch, 2019). Therefore, while it is evident that OHCB use a few other carbon and energy sources, for clarity we refer to them hereafter as "OHCB" to distinguish between these highly adapted and competitive hydrocarbon degraders and those more metabolically diverse bacteria, which can also degrade hydrocarbons.…”

Oxygen Isotopes (δ18O) Trace Photochemical Hydrocarbon Oxidation at the Sea Surface

“…Second, partially oxidized OC can be traced at a molecular-level using mass spectrometry (e.g., Aeppli et al, 2018;Cao & Tarr, 2017;Cory et al, 2010;Ruddy et al, 2014). The strength of mass spectrometry is two-fold: it is sensitive and provides insights into the diverse array of compounds produced by sunlight.…”

“…The major weaknesses of this approach are difficulties in quantifying molecular abundance and the costs of specialized equipment and personnel. Coupled gas‐ or liquid‐chromatography with quadrupole or time‐of‐flight mass spectrometry techniques have been applied to quantify partial photo‐oxidation products; however, only a small fraction of total products was quantifiable (<1%) even with multiple derivatization steps, and the analysis remains costly and highly specialized (Aeppli et al, ; Cao & Tarr, ).…”

Influence of Climatic Parameters on Changes in the Density and Viscosity of Diluted Bitumen after a Spill

“…The chemical process of photo-oxidation has emerged to be an equally important process to evaporation; a recent lab study has shown that exposure of oil to solar radiation can cause photo-chemical weathering of oil, causing significant changes in the chemical composition of light crude oil within a few days [10]. In addition, based on photo-oxidation of oil under ultraviolet irradiation conducted in the lab, Appeli et al [11] reported that the partial photo-oxidation of oil on the water surface led to 50% of the weathered saturates and aromatics being transformed to oxygenated hydrocarbons within 10 days during the Deepwater Horizon oil spill. The eventual fate (months to years) of the remaining oil is influenced by biological processes involving microorganisms (e.g.…”