Targeted Petroleomics: Analytical Investigation of Macondo Well Oil Oxidation Products from Pensacola Beach

Abstract

Of the estimated 5 million barrels of crude oil released into the Gulf of Mexico from the Deepwater Horizon oil spill, a fraction washed ashore onto sandy beaches from Louisiana to the Florida panhandle. Here, we compare the detailed molecular analysis of hydrocarbons in oiled sands from Pensacola Beach to the Macondo wellhead oil (MWO) by electrospray (ESI) and atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to identify major environmental transformation products of polar, high molecular weight (C >25 ) "heavy ends" (high-boiling species) inaccessible by gas chromatography. The petrogenic material isolated from the Pensacola Beach sand displays greater than 2-fold higher molecular complexity than the MWO constituents, most notably in oxygenated species absent in the parent MWO. Surprisingly, the diverse oxygenated hydrocarbons in the Pensacola Beach sediment extracts were dominant in all ionization modes investigated, (±) ESI and (±) APPI. Thus, the molecular-level information highlighted oxygenated species for subsequent "targeted" analyses. First, time-of-flight mass spectrometry analysis of model compounds attributes the unusually large oxygen signal magnitude from positive electrospray to ketone transformation products (O 1 −O 8 classes). Next, negative electrospray mass spectrometry reveals carboxylic acid transformation products. Two-dimensional gas chromatography with mass spectrometry analysis of anion-exchange chromatographic fractions unequivocally verifies the presence of abundant alkyl ketone fragments in sand extracts, and FT-ICR MS analysis reveals the distribution of high-boiling ketone, carboxylic, and higher numbered (3+) oxygen-containing transformation products too polar to be analyzed by gas chromatography. The results expand compositional coverage of oxygen-containing functionalities beyond the classic naphthenic acid type species to complex/mixed ketone, hydroxyl, and carboxylic acid classes of molecules that have been recently identified in produced water, emulsions, and petroleum production deposits.

Responses of Microbial Communities to Hydrocarbon Exposures

“…A time series study conducted at Pensacola Beach, Florida, where total petroleum hydrocarbons reached 11,000 mg kg -1 , revealed a bloom of bacteria during the first four months after oil came ashore, with microbial abundance in oiled sands 10 to 10,000 times that of clean sands (Kostka et al, 2011). Geochemical evidence confirmed the role microorganisms play in the degradation of weathered oil (Ruddy et al, 2014), and the succession of indigenous microbial populations paralleled the chemical evolution of the petroleum hydrocarbons (Rodriguez-R et al, 2015). The most extensive metagenomic time series describing microbial hydrocarbon degradation, which was collected from these Pensacola Beach sands, showed a similar progression of microbial populations linked to hydrocarbon degradation " [O]ur ignorance of the conditions necessary for successful cultivation of many organisms, coupled to a lack of understanding of how ecological factors such as competitive exclusion and niche differentiation influence growth in vitro, mean cultivation-dependent techniques likely underestimate the range of microorganisms that can directly and indirectly access hydrocarbon mixtures for energy and biomass production.…”

Weathering of Oil Spilled in the Marine Environment

“…In addition, its ultrahigh resolving power and mass accuracy allow unambiguous identification of molecular formulas. FT-ICR-MS was combined with GC×GC to investigate weathered products of Macondo well oil found on sand samples from Pensacola Beach, Florida (Ruddy et al, 2014). Numerous oxidized species were detected by FT-ICR-MS (Figure 4), and ketones were observed in the complex GC×GC chromatograms.…”

Impact of Photooxidation and Biodegradation on the Fate of Oil Spilled During the Deepwater Horizon Incident: Advanced Stages of Weathering

“…10,12,14-19 Not surprisingly, the environmental fate of the oil was influenced by many well documented weathering processes. [20][21][22][23][24][25] These processes resulted in the massive transformation of the oil components and a chemical footprint that differed substantively from the crude oil released at the wellhead. Most notably, the transformation of the crude Macondo 252 oil resulted in the formation of a group of partially oxidized organic compounds collectively termed 'oxyhydrocarbons.'…”

“…[1][2][3] This crude oil was transformed by a number of weathering processes and eventually converted into sand patties that are largely composed of partially oxidized organic compounds termed 'oxyhydrocarbons'. 20,21,25,54 The weathered sand patties may remain on the seafloor or be transported to beaches where they can settle in the swash zone. 15,18,55,56 where they are exposed to direct sunlight, continual wave action and the ambient microbial communities.…”