During the Deepwater Horizon oil spill, weathering of crude oil resulted in the formation of oxygenated hydrocarbons whose precursors and formation mechanisms are currently unknown.1 Some combination of photooxidation and biodegradation are suspected to produce these compounds, but the relative significance of each process has not been established. As part of a broader study to examine this question, we investigated the compositional changes caused by irradiation of Dorado well crude oil, a surrogate for Macondo Well oil from the Deepwater Horizon spill. Approximately 1 mm thick slicks were placed on glass and exposed for 88 hours to radiation from a class-1A solar simulator. Using a combination of p-nitroanisole/pyridine actinometry and spectrometry, we estimate that the total solar radiation delivered was equivalent to approximately 102 hours of solar energy from 350 to 400 nm, and 55 hours of solar energy from 300 to 350 nm. Chromatographic and spectroscopic analyses, including two-dimensional gas chromatography (GC x GC), thin-layer chromatography-flame ionization detection (TLC-FID) and fluorescence spectroscopy were employed to characterize the changes in composition. Spectroscopic data were corrected for evaporative enrichment of chromo- and fluorophores by monitoring mass changes during experimentation. Integrated total fluorescence intensities from 290-450 nm (excitation) and 305-545 nm (emission) showed a 60% decrease while UV-Vis absorbance intensities showed no significant loss. Although no significant spectral shifts were observed, total fluorescence loss did not follow fixed-order kinetics; this was likely due to the formation of a crust that slowed the rate of photodegradation with time. TLC-FID analysis indicated some loss of the aromatic fraction relative to dark controls, while a small increase in the oxygenated fraction was also observed. Ongoing research is directed at examining the extent to which fluorescence spectroscopy can serve as a proxy measurement of the photodegradation of selected polycyclic aromatic hydrocarbons (PAHs). Results from these analyses and from irradiation experiments of crude oil on glass and on water with a full suite of analyses augmented by quantitative GCMS will be presented. 1. Aeppli, C., et al., Oil weathering after the Deepwater Horizon disaster led to the formation of oxygenated residues. Environ Sci Technol, 2012. 46(16): p. 8799-807.

Effect of photochemical weathering on the composition and spectroscopic properties of crude oil

249th National Meeting (2015)

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