Oil weathering after the Deepwater Horizon disaster led to the formation of oxygenated residues.
Following the Deepwater Horizon disaster, the effect of weathering on surface slicks, oil-soaked sands, and oil-covered rocks and boulders was studied for 18 months. With time, oxygen content increased in the hydrocarbon residues. Furthermore, a weathering-dependent increase of an operationally defined oxygenated fraction relative to the saturated and aromatic fractions was observed. This oxygenated fraction made up >50% of the mass of weathered samples, had an average carbon oxidation state of -1.0, and an average molecular formula of (C(5)H(7)O)(n). These oxygenated hydrocarbon residues were devoid of natural radiocarbon, confirming a fossil source and excluding contributions from recent photosynthate. The incorporation of oxygen into the oil's hydrocarbons, which we refer to as oxyhydrocarbons, was confirmed from the detection of hydroxyl and carbonyl functional groups and the identification of long chain (C(10)-C(32)) carboxylic acids as well as alcohols. On the basis of the diagnostic ratios of alkanes and polycyclic aromatic hydrocarbons, and the context within which these samples were collected, we hypothesize that biodegradation and photooxidation share responsibility for the accumulation of oxygen in the oil residues. These results reveal that molecular-level transformations of petroleum hydrocarbons lead to increasing amounts of, apparently recalcitrant, oxyhydrocarbons that dominate the solvent-extractable material from oiled samples.
Department of Marine Chemistry & Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, United States. caeppli@whoi.edu
Christoph
C
Aeppli
Catherine A
CA
Carmichael
Robert K
RK
Nelson
Karin L
KL
Lemkau
William M
WM
Graham
Molly C
MC
Redmond
David L
DL
Valentine
Christopher M
CM
Reddy
D002849:Chromatography, Gas; D010100:Oxygen / Q000737:chemistry*; D010578:Petroleum; D059392:Petroleum Pollution; D017550:Spectroscopy, Fourier Transform Infrared
D010578:Petroleum; D010100:Oxygen