Evaluations of Weathering of Polar and Nonpolar Petroleum Components in a Simulated Freshwater-Oil Spill by Orbitrap and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry.

The comprehensive chemical characterization of crude oil is important for the evaluation of the transformation and fate of components in the environment. Molecular-level speciation of naphthenic acid fraction compounds (NAFCs) was investigated in a mesoscale spill tank using both negative-ion electrospray ionization (ESI) Orbitrap mass spectrometry (MS) and positive-ion atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry (APPI-FT-ICR-MS). Both ionization techniques are coupled to high-resolution mass spectrometric detectors (ESI: Orbitrap MS; APPI: FT-ICR-MS at 9.4 T), enabling insight into the behavior and fate of petrogenic compounds during a simulated freshwater crude oil spill. Negative-ion ESI Orbitrap-MS reveals that oxygen-containing (Ox) classes are detected early in the spill, whereby species with more oxygen per molecule evolve later in the simulated spill. The O2-containing species gradually decreased in relative abundance, while O3 and O4 species increased in relative abundance throughout the simulated spill, which could correspond to a relative degree of oxygen incorporation. Nonpolar speciation by positive-ion APPI 9.4 T FT-ICR-MS allowed for the identification of water-soluble nonpolar and less polar acidic species. Molecular-level graphical representation of elemental compositions derived from simulated spill water-soluble and oil-soluble species suggest that biological activity is the primary degradation mechanism and that biodegradation was the dominant mechanism based on the negative-ion ESI Orbitrap-MS results.

Low adsorption affinity of athabasca oil sands naphthenic acid fraction compounds to a peat-mineral mixture.

Much of the toxicity in oil sands process-affected water in Athabasca oil sands tailings has been attributed to naphthenic acids (NAs) and associated naphthenic acid fraction compounds (NAFCs). Previous work has characterized the environmental behaviour and fate of these compounds, particularly in the context of constructed treatment wetlands. There is evidence that wetlands can attenuate NAFCs in natural and engineered contexts, but relative contributions of chemical, biotic, and physical adsorption with sequestration require deconvolution. In this work, the objective was to evaluate the extent to which prospective wetland substrate material may adsorb NAFCs using a peat-mineral mix (PMM) sourced from the Athabasca Oil Sands Region (AOSR). The PMM and NAFCs were first mixed and then equilibrated across a range of NAFC concentrations (5-500 mg/L) with moderate ionic strength and hardness (∼200 ppm combined Ca2+ and Mg2+) that approximate wetland water chemistry. Under these experimental conditions, low sorption of NAFCs to PMM was observed, where sorbed concentrations of NAFCs were approximately zero mg/kg at equilibrium. When NAFCs and PMM were mixed and equilibrated together at environmentally relevant concentrations, formula diversity increased more than could be explained by combining constituent spectra. The TOC present in this PMM was largely cellulose-derived, with low levels of thermally recalcitrant carbon (e.g., lignin, black carbon). The apparent enhancement of the concentration and diversity of components in PMM/NAFCs mixtures are likely related to aqueous solubility of some PMM-derived organic materials, as post-hoc combination of dissolved components from PMM and NAFCs cannot replicate enhanced complexity observed when the two components are agitated and equilibrated together.