Final Report: Resolving the Unresolved Complex Mixture in Petroleum Residues in Environmental Matrices

EPA Grant Number: R830393
Title: Resolving the Unresolved Complex Mixture in Petroleum Residues in Environmental Matrices
Investigators: Reddy, Christopher M.
Institution: Woods Hole Oceanographic Institution
EPA Project Officer: Carleton, James N
Project Period: September 1, 2002 through August 31, 2004
Project Amount: $224,955
RFA: Futures Research in Natural Sciences (2001) RFA Text |  Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Land and Waste Management , Hazardous Waste/Remediation


The objective of this research project was to use comprehensive two-dimensional gas chromatography (GC×GC) to study the unresolved complex mixture (UCM) of petroleum hydrocarbons in environmental samples. The latter is the most abundant, ubiquitous, and understudied class of organic contaminants in aquatic sediments. The term UCM is derived from traditional gas chromatography and refers to a hump of unresolved, and hence unidentified, hydrocarbons in gas chromatograms. Unfortunately, the ability to follow environmental weathering of petroleum in the environment has been hindered with traditional techniques once resolved compounds (such as normal and branched alkanes) are removed or degraded. However, recent advances in chromatography have led to the development of GC×GC. This acronym is used because orthogonal gas chromatographic separations are used in both analytical dimensions by employing stationary phases with different selectivity. GC×GC relies on thermal modulation to transfer analytes from the first-dimension column to the second-dimension column. The thermal modulator uses a stream of cold gas to trap eluent from the first-dimension column and then hot gas to desorb, spatially compress, and inject these portions into the second column. Injection into the second column is very fast and produces a peak width on the order of 80 ms. Narrow peaks allow fast chromatography in the second dimension, where as many as 10 separate peaks have been observed in a 5 s chromatogram. With this increased separation capability, my research group was involved in several laboratory and field-based studies on studying petroleum hydrocarbons in the environment.

Summary/Accomplishments (Outputs/Outcomes):

Numerous petroleum-related projects were studied in this project. Here, we will highlight are results from accidental oil spills from the Bouchard 120, Bouchard 65, and Florida and several laboratory-based biodegradation experiments. We will also present work that investigated the petroleum hydrocarbons seeping from the Santa Barbara oil seeps (Santa Barbara, California). Last, we will discuss work that used GC×GC to provide physical property information on petroleum hydrocarbons.

One manuscript is in press, and another has been submitted on work related to using GC×GC to investigate the Bouchard 120 oil spill. The latter occurred on April 25, 2003, when the barge Bouchard 120 spilled approximately 375,000 liters of No. 6 fuel oil into Buzzards Bay, Massachusetts. To gain a better understanding of the natural processes affecting the fate of the spilled product, we collected and analyzed oil-covered rocks from Nyes Neck beach in North Falmouth, Massachusetts. In one study, which is in press in Environmental Forensics, we presented results from the analysis of samples collected on May 9, 2003, and 6 months later, November 23, 2003. Along with standard GCxGC analysis, we employed unique data visualization techniques such as difference, ratio, and addition chromatograms to highlight how evaporation, water washing, and biodegradation weathered the spilled oil. These approaches provide a new perspective to studying oil spills and aide attempts to remediate them.

In the other manuscript on the Bouchard 120 oil spill, which was recently submitted to Organic Geochemistry, we closely examined changes in the distribution of petroleum hydrocarbons on rocks collected at Nyes Neck in early June 2003. We then compared these data to the radiocarbon content of bacterial phospholipids found on the rocks. This study revealed that bacteria were respiring only n-alkanes and incorporating this petroleum-derived carbon into the bacterial biomass of a predominantly algal microbial community during intrinsic bioremediation. We expect that this coupled GC×GC and radiocarbon approach will be useful in any areas when attempting to gauge biodegradation.

We have also investigated two local sites in Cape Cod where studies on the long-term fate of petroleum hydrocarbons in salt marsh sediments are underway. The barge Florida spilled approximately 700,000 L of diesel fuel on September 16, 1969, and marsh sediments near Wild Harbor were severely impacted. A sediment core collected in 2000 revealed that oil still persists at sediment depths of 8 to 20 cm. On October 9, 1974, the barge Bouchard 65 spilled an undetermined amount of its cargo (also diesel fuel) and contaminated Winsor Cove, which is located about 4 km north of Wild Harbor. GC×GC analysis has revealed that the hydrocarbon composition at these two sites is quite different (even though traditional one-dimensional gas chromatography indicates a very similar fingerprint). Hence GC×GC has provided increased resolution that was previously unattainable and can allow for more refined studies on weathering processes. We believe that the environmental conditions at the two sites have lead to these differences. Significant amounts of naphthalenes and larger aromatics remain at the Wild Harbor site, because the oil resides in buried anoxic sediments and are not fully exposed to environmental weathering (mainly water washing). At the Winsor cove site, aromatics are greatly reduced in concentration because the oil remained in the near-surface sediments where water washing has likely occurred. At both sites, branched and cyclic alkanes comprise the majority of the remaining petroleum hydrocarbons. The n-alkanes at both locations have been biodegraded. We are currently preparing one manuscript and a book chapter on this work.

To investigate how bacteria biodegrade diesel fuel in the marine environment, we compared the weathering patterns that can be generated in laboratory cultures to what we observe in Winsor Cove. By incubating some of the original Bouchard 65 fuel oil with marine microbes, we were able to confirm some preliminary hypotheses regarding the recalcitrance of some compounds that we find in Winsor Cove. We believe that compounds, called C5- and C6-decalins, have very complex structures that protect them from microbial attack. This is a very exciting result, because we can now use these compounds as markers of diesel fuel, even when microbes extensively degrade other components of diesel fuel. A manuscript on this work is also being prepared.

To gain some perspective on the weathering of oil that naturally seeps into coastal waters, we analyzed samples collected in or near the Santa Barbara oil seeps. These oil seeps are considered some of the most active in the world. Currently, widespread seepage of hydrocarbons occurs at offshore faults in the waters of the Santa Barbara basin. Estimates of the amount of hydrocarbons migrating into the environment are approximately 37 tons per day, with the gaseous emissions making up 65 percent of this total (24 tons per day). In one project, we analyzed tar samples by GC×GC found in dated sediments and those recently deposited along the coastline of Santa Barbara. We found that the inventory of petroleum hydrocarbons in both samples was remarkably similar. The latter allowed us to use the amount of tar found in the sediment record as a proxy for emissions of methane from the seeps. A manuscript on this work will be submitted shortly to Nature. In another project, we analyzed samples of oil seeping directly into the ocean, floating on the surface, and on the beach. This study revealed that weathering processes have different kinetics. In particular, evaporation can occur very quickly, whereas water washing is slower. A manuscript on this work will be submitted in the next 3 months.

Another area of success was exploiting the potential wealth of physical property information contained in GC×GC chromatograms. To address this issue, we developed a simple but robust method to estimate GC×GC retention indices for petroleum hydrocarbons. By exploiting n-alkanes as reference solutes in both dimensions, we were able to calculate retention indices that were insensitive to the uncertainty in the enthalpy of gas-stationary phase transfer for a suite of representative components. This work has been recently published in Analytical Chemistry (Arey, et al., 2005). The resulting two-dimensional retention indices can then be used to estimate the liquid vapor pressures, aqueous solubilities, octanol-water partition coefficients, and vaporization enthalpies of a wide range of petroleum hydrocarbons, which, in turn, can be used to investigate phase transfer processes affecting petroleum hydrocarbon mixtures in the environment. One key result of the powerful relationships developed from these retention indices is that the exact compound structure of each hydrocarbon in each complex mixture does not have to be fully identified to model the effects of phase transfer processes on the complete mixture—only the retention times for both dimensions need to be known. This dramatically expands the number of compounds that can be used to model processes like water-washing or gas washing, which are typically limited to less than 20 compounds that are within one or two compound classes in traditional gas chromatography.

The support from this project also allowed me to continue my efforts in understanding the fate of organic compounds in the ocean and to disseminate these results to the general public and government. In the past few years, I have been interviewed by local and national media (print, radio, and television), written several editorials on the need to ban flame retardants in the United States, provided expert testimony on oil spills to the State of Massachusetts and United States Coast Guard, advised the U.S. legislature, and presented numerous lectures to local libraries, historical societies, high school science teachers, and workshops for science journalists.

Journal Articles on this Report : 4 Displayed | Download in RIS Format

Other project views: All 23 publications 4 publications in selected types All 4 journal articles
Type Citation Project Document Sources
Journal Article Arey JS, Nelson RK, Xu L, Reddy CM. Using comprehensive two-dimensional gas chromatography retention indices to estimate environmental partitioning properties for a complete set of diesel fuel hydrocarbons. Analytical Chemistry 2005;77(22):7172-7182. R830393 (Final)
  • Abstract from PubMed
  • Journal Article Nelson RK, Kile BM, Plata DL, Sylva SP, Xu L, Reddy CM, Gaines RB, Frysinger GS, Reichenbach SE. Tracking the weathering of an oil spill with comprehensive two-dimensional gas chromatography. Environmental Forensics 2006;7(1):33-44. R830393 (Final)
  • Abstract: InformaWorld Abstract
  • Other: CSE PDF
  • Journal Article Peacock EE, Nelson RK, Solow AR, Warren JD, Baker JL, Reddy CM. The West Falmouth oil spill: ~100 kg of oil found to persist decades later. Environmental Forensics 2005;6(3):273-281. R830393 (Final)
  • Abstract: InformaWorld Abstract
  • Journal Article Slater GF, Nelson RK, Kile BM, Reddy CM. Intrinsic bacterial biodegradation of petroleum contamination demonstrated in situ using natural abundance, molecular-level 14C analysis. Organic Geochemistry 2006;37(9):981-989. R830393 (Final)
  • Full-text: Science Direct Full Text
  • Abstract: Science Direct Abstract
  • Other: Science Direct PDF
  • Supplemental Keywords:

    petroleum hydrocarbons, comprehensive two-dimensional gas chromatography, weathering, sediment, environmental chemistry, analytical, fate and transport, hazardous chemicals, petroleum waste, hazardous waste, biodegradation,, RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Contaminated Sediments, Environmental Chemistry, chemical mixtures, Fate & Transport, Hazardous Waste, Ecology and Ecosystems, Hazardous, complex mixtures, fate and transport, biogeochemical partitioning, fate, fate and transport , biodegradation, contaminated sediment, hazardous organic substances, chemical contaminants, chemical transport, environmental transport and fate, chemical kinetics, hydrocarbons, hazardous chemicals, unresolved complex mixture, molecular biology, contaminated soils, analytical models

    Relevant Websites: Exit

    Progress and Final Reports:

    Original Abstract
  • 2003 Progress Report