The Deepwater Horizon spill provides a unique opportunity to advance the understanding of oil degradation and environmental resilience at one specific sampling location nearly a decade after the initial spill. Here, we couple advanced analytical methodologies such as selective fractionation, isolation and fragmentation, with Fourier transform ion cyclotron resonance mass spectrometry to catalogue and assess the resilience of coastal salt marsh vegetation that remain contaminated with oil since 2010. Chemical transformation products are more water-soluble than the pre-spill oil thus pose a long term threat to the environment. These transformation products are compositionally complex, highly polar compounds that contain sulfur, nitrogen and up to ten oxygen’s per molecule. FT-ICR MS achieves resolving power sufficient for elemental formula assignment without volatility limitations of GC-based techniques. A small fraction of these highly polar compounds formed through multiple weathering processes behave like surfactants (soap-like) and form an interfacial layer. Isolation of these interfacially-active compounds from sediments collected since 2010 reveals a wide range of Ox compounds that dictate the transition from oil-soluble to water-soluble species. However, preferential ionization of low molecular weight carboxylic acids mask the detection of higher molecular weight acidic species. Thus, the fractionation of interfacially-active compounds isolated from coastal sediments based on hydrophobicity (carbon number) followed by FT-ICR MS characterization reveals a wide range of acidic species that reach molecular weights as high as 1.4 kDa, much higher than the direct (unfractionated) analysis. Through multidimensional fractionation, we isolate the interfacially-active species from field samples, further separate these species based on hydrophobicity, and characterize these naturally-occurring petroleum surfactants by FT-ICR MS. These compounds challenge the effectiveness of chemical dispersant as the oil weathers through photodegradation, and are critical factors in the development of effective remediation strategies.[6] Microcosm studies indicate that these interfacially-active compounds are generated primarily through photodegradation, as their molecular-level composition correlates to field samples.

Multidimensional fractionation and molecular characterization of lingering oil compounds in coastal sediments: A nine year evolution

2019 Fall National Meeting

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