Abstract:

Mesocosm experiment was conducted in May 2019 as part of ADDOMex-2 program funded through the Gulf of Mexico Research Initiative (GoMRI). Marine oil snow samples were collected during the mesocosm experiments and analyzed using gas chromatography with flame-ionization detection (GC-FID) and two-dimensional gas chromatography and time-of-flight mass spectrometry (GCXGC-TOFMS). Alkanes and oxidized polycyclic aromatic hydrocarbons (PAH) were quantified and their changes were tracked along with the mesocosm experiments. The results clearly showed rapid degradation of oil by microbes within 3 days of experiments. The bio-degradation trend was further confirmed by a decrease in the ratios of straight-chain to branched-chain hydrocarbons, as the straight-chain hydrocarbons are more labile.

Suggested Citation:

Chen, Hongmei and Patrick Hatcher. 2020. Molecular level characterization of oil and aggregate oxidation products: LTOPOS, a Long Term Oil and Particle Oxidation Study, two-dimensional gas chromatography-mass spectrometry (GCxGC-MS) data. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/6PQ43JR2

Purpose:

To fingerprint and quantify oil degradation in mesocosm simulations of the Deepwater Horizon oil spill event using gas chromatography coupled with mass spectrometry.

Data Parameters and Units:

Dataset contains comprehensive two-dimensional gas chromatography (GCxGC) and gas chromatography–flame ionization detection (GC-FID) analysis of DCM-soluble components of marine oil snow. The dataset contains GC-FID result reports and GC x GC raw data that will be used in manuscripts to be submitted during 2020~2021. For GC-FID results, data file naming convention includes the mesocosm experiment number (M6), treatment (control, dilute chemically enhanced water accommodated fraction of oil = DCEWAF, water accommodated fraction = WAF), time since the start (in days), and replicate filter IDs. Note: GC = Gas chromatography, FID = Flame ionization detector, TOF = Time of fight.

Methods:

Mesocosm 7 bottom Particle samples were taken from the tanks at Days 0.5, 1, 2, 3, 4, 8, and 16, as well as a Control. Marine snow from control samples and marine oil snow (MOS) from diluted chemically enhanced water accommodated fraction of oil (DCEWAF) samples were freeze-dried prior to analysis. Approximately ~50 mg of particulate matter of each sample was soaked in 2mL of dichloromethane (DCM) solvent, and placed on a New Brunswick Scientific Classic Series C24 Incubator Shaker (at 125 rpm) overnight. The DCM-insoluble components were removed by filtering through a 21 mm, 0.7 µm pore Glass Fiber Filter (GF/F). The filtrate was re-concentrated by a factor of 5 to 10 through evaporating out excess DCM under pure nitrogen gas, followed by gas chromatography–flame ionization detection (GC-FID) and two-dimensional gas chromatography-mass spectrometry (GCxGC-MS) analysis. Macondo Surrogate Oil was diluted by using 1 µL to mix with 2 mL Dichloromethane (DCM), and analyzed by GC-FID and GCxGC-MS to obtain reference oil features for comparison. GC-FID analysis was performed with an Agilent Technologies 7890A gas chromatography using a Restek RTX-5: 350°C: 30 m x 250 µm x 0.25 µm column. The parameters were set to start at 35° C and to ramp up 10° C/min to 100°C and then ramp up 20° C/min to 300° C and hold there for 10 minutes. Samples were injected in the splitless mode. Samples were analyzed by GC-MS and GC x GC- MS using an Agilent 6890 2D GC coupled to Leco Pegasus IV Time of Flight Mass Spectrometer (TOFMS). Leco ChromaTOF software was employed to operate the GC x GC – MS system. DCM extracts were analyzed following previously established methods (Reference 1, Hatcher et al., 2018). The seawater used in the Test of Coastal water with coastal microbial concentrate (TeCOAST) mesocosm studies was collected ~0.5 km offshore south of Galveston (Texas) on May 7, 2019, from the Gulf of Mexico. Water was settled in large tanks to remove large particles and debris before collection. A plankton concentrate was collected nearby in Galveston Bay using a mesh size of 63 µm plankton net; 2 L of this “concentrate” was added to all mesocosm treatments, immediately prior to the start of the experiment to make a final volume of 102 L per mesocosm. The control tank was filled with the seawater directly from the storage tank of filtered seawater plus the added plankton concentrate. This seawater was also used to fill recirculating glass flumes (References 2, 3, & 4) to make water accommodated fraction (WAF) and a chemically enhanced water accommodated fraction of oil (CEWAF). A PTFE stopcock 10 cm off the bottom of the tank was used for sampling. The oil used was Macondo “surrogate” oil from the Marlin Platform Dorado and the dispersant used was Corexit. The WAF mixture was prepared by mixing 25 mL oil with ~130 L seawater in a stirring baffled recirculating borosilicate glass tanks of 170 L capacity (43 × 88 × 44 cm) and allowed to equilibrate over 24 hours. After that, only the aqueous phase at the bottom layer (no surface slick: the WAF fraction) was removed and added to the mesocosm tanks. CEWAF was made by adding dispersant to the oil at a ratio of oil‐to‐dispersant of 20:1. The DCEWAF was prepared by diluting the CEWAF with seawater.

Instruments:

Agilent Technologies 7890A gas chromatograph (GC – FID) ; Agilent 6890 2D GC coupled to Leco Pegasus IV Time of Flight Mass Spectrometer (TOFMS).

Provenance and Historical References:

[1] Hatcher, P. G., Obeid, W., Wozniak, A. S., Xu, C., Zhang, S., Santschi, P. H., & Quigg, A. (2018). Identifying oil/marine snow associations in mesocosm simulations of the Deepwater Horizon oil spill event using solid-state 13 C NMR spectroscopy. Marine Pollution Bulletin, 126, 159–165. doi:10.1016/j.marpolbul.2017.11.004 [2] Wozniak, A. S., Prem, P. M., Obeid, W., Waggoner, D. C., Quigg, A., Xu, C., … Hatcher, P. G. (2019). Rapid Degradation of Oil in Mesocosm Simulations of Marine Oil Snow Events. Environmental Science & Technology, 53(7), 3441–3450. doi:10.1021/acs.est.8b06532 [3] Knap, A. H., Burns, K. A., Dawson, R., Ehrhardt, M., & Palmork, K. H. (1986). Dissolved/dispersed hydrocarbons, tarballs and the surface microlayer: Experiences from an IOC/UNEP Workshop in Bermuda, December, 1984. Marine Pollution Bulletin, 17(7), 313–319. doi:10.1016/0025-326x(86)90217-1 [4] Wade, T. L., Morales-McDevitt, M., Bera, G., Shi, D., Sweet, S., Wang, B., Gold-Bouchot, G., Quigg., A. & Knap, A. H. (2017). A method for the production of large volumes of WAF and CEWAF for dosing mesocosms to understand marine oil snow formation. Heliyon, 3(10), e00419. doi:10.1016/j.heliyon.2017.e00419

Individual Files: