Chemical Composition and Potential Environmental Impacts of Water-Soluble Polar Crude Oil Components Inferred from ESI FT-ICR MS

Abstract

Polar petroleum components enter marine environments through oil spills and natural seepages each year. Lately, they are receiving increased attention due to their potential toxicity to marine organisms and persistence in the environment. We conducted a laboratory experiment and employed state-of-the-art Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to characterize the polar petroleum components within two operationally-defined seawater fractions: the water-soluble fraction (WSF), which includes only water-soluble molecules, and the water-accommodated fraction (WAF), which includes WSF and microscopic oil droplets. Our results show that compounds with higher heteroatom (N, S, O) to carbon ratios (NSO:C) than the parent oil were selectively partitioned into seawater in both fractions, reflecting the influence of polarity on aqueous solubility. WAF and WSF were compositionally distinct, with unique distributions of compounds across a range of hydrophobicity. These compositional differences will likely result in disparate impacts on environmental health and organismal toxicity, and thus highlight the need to distinguish between these often-interchangeable terminologies in toxicology studies. We use an empirical model to estimate hydrophobicity character for individual molecules within these complex mixtures and provide an estimate of the potential environmental impacts of different crude oil components.

Importance of lateral flux and its percolation depth on organic carbon export in Arctic tundra soil: Implications from a soil leaching experiment

“…Hydrophobicity, molecular weight distribution, and compound classes of samples were used to examine changes in molecular composition. Hydrophobic compounds were defined as NSO:C ≤ 0.1 (molecular mass > 850 amu), and moderately hydrophobic compounds were defined as 0.1 < NSO:C < 0.49 (molecular mass < 850 amu); hydrophilic compounds were defined as NSO:C ≥ 0.49 (molecular mass < 850 amu); where NSO:C is the ratio of number of nitrogen, sulfur, and oxygen atoms over number of carbon atoms in a compound [ Liu and Kujawinski , ]. FT‐ICR‐MS formulas were assigned to the following compound classes: lipids, proteins, carbohydrates, amino sugars, lignin, tannins, and condensed hydrocarbons, based on elemental ratios of H:C and O:C [ Minor et al ., ] (Figure S3a).…”

Evolutionary responses to crude oil from the Deepwater Horizon oil spill by the copepod Eurytemora affinis

“…Within crude oil, components that are particularly toxic due to their bioavailability are contained within the “water‐accommodated fraction” (WAF), consisting of the “water‐soluble fraction” (WSF) and microscopic oil droplets (Liu & Kujawinski, 2015; Melbye et al., 2009; Neff, 2002). The water‐soluble fraction (WSF) is a solution of low molecular mass hydrocarbons naturally released from petroleum hydrocarbon mixtures in contact with water (Liu & Kujawinski, 2015). The toxic constituents of the water‐soluble fraction (WSF) include polar fractions containing many cyclic and aromatic sulfoxide compounds, as well as polycyclic aromatic hydrocarbons (PAHs), such as naphthalene (NAPH) and dimethylnaphthalene (C2‐NAPH) (Melbye et al., 2009).…”

“…Crude oil is a complex mixture containing many unidentified and toxic compounds (Liu & Kujawinski, 2015;Melbye et al, 2009;Robson, Sutton, McCormack, Chilcott, & Rowland, 2017). Within crude oil, components that are particularly toxic due to their bioavailability are contained within the "water-accommodated fraction" (WAF), consisting of the "water-soluble fraction" (WSF) and microscopic oil droplets (Liu & Kujawinski, 2015;Melbye et al, 2009;Neff, 2002). The water-soluble fraction (WSF) is a solution of low molecular mass hydrocarbons naturally released from petroleum hydrocarbon mixtures in contact with water (Liu & Kujawinski, 2015).…”

“…Next, we attempted to induce selection in the laboratory for crude oil tolerance on the population of E. affinis collected before the Deepwater Horizon oil spill. We examined evolutionary responses of the populations to the "water-accommodated fraction" of crude oil, which harbors the PAHs and other toxic compounds (Almeda et al, 2013;Faksness, Brandvik, & Sydnes, 2008;Forth, Mitchelmore, Morris, & Lipton, 2017;Liu & Kujawinski, 2015;Melbye et al, 2009). Copepods, with their exceedingly large numbers and relatively short generation times (~15-20 days in E. affinis) are likely to experience significant evolutionary responses to environmental perturbations.…”

Probing the Chemical Transformation of Seawater-Soluble Crude Oil Components during Microbial Oxidation

“…Ultrahigh-resolution mass spectrometry such as Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) can be widely used in response to the spills and crude oil characterizations, providing insight into crude oil-derived compounds that could not be resolved with GC-based methods. 2,28,29,31,33,34,[40][41][42][43][44] When applied to biological systems, these analytical techniques identify and quantify molecules produced by organisms, thus providing metabolite profiles of microbial cultures or communities under various conditions. 26,28 In this study, we employ untargeted metabolite profiling, guided by biological information (16S rRNA gene and metagenomics), to examine the evolving chemical signature of WSF and the dynamics of polar crude oil compounds within dark aerobic incubations with natural seawater bacterial consortia.…”