337
20.4 Conclusions and Future Research Directions
In this chapter we discuss initial observations related to the analysis of oil residues
found in coastal sGoM environments known to be impacted by the historic Ixtoc 1
spill, using an approach which combines targeted fingerprinting of GC-amenable
biomarkers (GC-MS/MS-MRM) with non-targeted exploratory screening of heavy
molecular weight, heteroatom-containing compound classes, using ultrahighresolution FTICR-MS. Biomarker ratios in the oil residues from the prop roots of
mangrove trees of the western Yucatan Peninsula show a reasonably good match to
the source Ixtoc 1 oil, given the time elapsed since the spill, with apparent decadal
recalcitrance of C27–C32 homohopanes, triaromatic steroids, and high molecular
weight PAHs, a trend which is somewhat similar to the observations made in the
coastal residues of the DWH spill. Further, the samples also show the presence of
oxygen-bearing compound classes, as indicated by FTICR-MS, likely indicating
the preservation of partially weathered oil in these low-energy environments, a
good analog for the prediction of DWH residues’ fate in the similar, marshy areas
of the nGoM.
On the contrary, heavily weathered samples from the exposed supratidal rocky
shorelines show enrichment of sulfur-bearing compound classes, including polysulfurized species. Possible contributors to these residues may include the modern
exploration of oil in the area and/or natural seeps. Regardless of the origin, the
composition of these samples might reveal pathways of sulfur compound preservation during prolonged and extreme weathering. Relatively high sulfur content found
in these oil residues is an interesting feature, which should be explored further using
complementary techniques such as comprehensive two-dimensional gas chromatography or sulfur isotope analysis to improve and strengthen the conventional
source apportionment using biomarker fingerprinting ratios.
Finally, an exact molecular characterization of the range of oil transformation
products found in the samples, using tools such as LC-MS or NMR, coupled to
environmental and toxicological modelling and biological transect studies in the
affected areas, is warranted for better understanding of long-term risks of oil spill
impacts in coastal areas.
Acknowledgments †Dr. John “Wes” Tunnell passed away during the preparation of this chapter.
Dr. Tunnell was a marine ecology and biology professor at Texas A&M University-Corpus Christi
and an early orchestrator of the Harte Research Institute (HRI) for Gulf of Mexico studies. Within
C-IMAGE, Dr. Tunnell provided a foundation to expand our oil spill studies to include the entire
Gulf of Mexico studying the decade-long impacts of the 1979 Ixtoc 1 oil spill to compare with the
recent Deepwater Horizon oil spill.
This research was made possible in part by a grant from the Gulf of Mexico Research Initiative,
C-IMAGE, and in part thanks to support from CFI, NSERC, the University of Calgary, and the
Canada Research Chairs. Data are publicly available through the Gulf of Mexico Research
Initiative Information and Data Cooperative (GRIIDC) at https://data.gulfresearchinitiative.org/
data/R6.x805.000:0064 [doi:10.7266/n7-zeda-tw26].
20 40 Years of Weathering of Coastal Oil Residues in the Southern Gulf of Mexico
20.4 Conclusions and Future Research Directions
In this chapter we discuss initial observations related to the analysis of oil residues
found in coastal sGoM environments known to be impacted by the historic Ixtoc 1
spill, using an approach which combines targeted fingerprinting of GC-amenable
biomarkers (GC-MS/MS-MRM) with non-targeted exploratory screening of heavy
molecular weight, heteroatom-containing compound classes, using ultrahighresolution FTICR-MS. Biomarker ratios in the oil residues from the prop roots of
mangrove trees of the western Yucatan Peninsula show a reasonably good match to
the source Ixtoc 1 oil, given the time elapsed since the spill, with apparent decadal
recalcitrance of C27–C32 homohopanes, triaromatic steroids, and high molecular
weight PAHs, a trend which is somewhat similar to the observations made in the
coastal residues of the DWH spill. Further, the samples also show the presence of
oxygen-bearing compound classes, as indicated by FTICR-MS, likely indicating
the preservation of partially weathered oil in these low-energy environments, a
good analog for the prediction of DWH residues’ fate in the similar, marshy areas
of the nGoM.
On the contrary, heavily weathered samples from the exposed supratidal rocky
shorelines show enrichment of sulfur-bearing compound classes, including polysulfurized species. Possible contributors to these residues may include the modern
exploration of oil in the area and/or natural seeps. Regardless of the origin, the
composition of these samples might reveal pathways of sulfur compound preservation during prolonged and extreme weathering. Relatively high sulfur content found
in these oil residues is an interesting feature, which should be explored further using
complementary techniques such as comprehensive two-dimensional gas chromatography or sulfur isotope analysis to improve and strengthen the conventional
source apportionment using biomarker fingerprinting ratios.
Finally, an exact molecular characterization of the range of oil transformation
products found in the samples, using tools such as LC-MS or NMR, coupled to
environmental and toxicological modelling and biological transect studies in the
affected areas, is warranted for better understanding of long-term risks of oil spill
impacts in coastal areas.
Acknowledgments †Dr. John “Wes” Tunnell passed away during the preparation of this chapter.
Dr. Tunnell was a marine ecology and biology professor at Texas A&M University-Corpus Christi
and an early orchestrator of the Harte Research Institute (HRI) for Gulf of Mexico studies. Within
C-IMAGE, Dr. Tunnell provided a foundation to expand our oil spill studies to include the entire
Gulf of Mexico studying the decade-long impacts of the 1979 Ixtoc 1 oil spill to compare with the
recent Deepwater Horizon oil spill.
This research was made possible in part by a grant from the Gulf of Mexico Research Initiative,
C-IMAGE, and in part thanks to support from CFI, NSERC, the University of Calgary, and the
Canada Research Chairs. Data are publicly available through the Gulf of Mexico Research
Initiative Information and Data Cooperative (GRIIDC) at https://data.gulfresearchinitiative.org/
data/R6.x805.000:0064 [doi:10.7266/n7-zeda-tw26].
20 40 Years of Weathering of Coastal Oil Residues in the Southern Gulf of Mexico