Chemical fingerprinting is a key environmental forensics technique used in oil spill investigations to identify the source and type of oil in spill residues. Conventional approaches rely on detecting individual petroleum biomarkers in gas chromatograph-mass spectrometer (GC-MS) chromatograms, examining their distributions, and calculating diagnostic ratios derived from them. The combination of biomarker distribution and diagnostic ratios forms a unique chemical fingerprint for each oil. Source oils and spill residues share similar fingerprints, allowing source identification of the spill's origin. Variations in biomarker distribution cause oils to exhibit distinct chromatographic and mass spectral patterns. This study presents a machine learning (ML) framework for chemical fingerprinting directly from GC-MS data, leveraging pattern recognition to eliminate the need for individual biomarker identification or diagnostic ratio calculations. The framework introduces several methodological innovations to address analytical limitations. It trains ML classifiers exclusively on fresh, unweathered oil data to overcome the scarcity of weathered samples, incorporates synthetic data generation to mitigate small dataset issues, and employs aggregate ensemble models that combine multiple classifiers to improve robustness across sample types. Standardized preprocessing procedures are implemented for data format conversion, ensuring compatibility across GC-MS instruments. The framework was evaluated using GC-MS datasets of fresh unweathered crude oils and spill residues, where aggregate models trained solely on fresh unweathered crude oils achieved the highest accuracy in classifying residues and identifying their source oils. Overall, this study presents a novel ML-based approach for oil spill chemical fingerprinting, offering a practical pathway to advance environmental forensics investigations.

On January 6, 2018, the Sanchi tanker, carrying 111,300 metric tons of natural gas condensate as cargo and 1900 metric tons of heavy fuel oil (HFO) for propulsion, collided with the bulk carrier Changfeng Crystal in the East China Sea. The collision caused a catastrophic explosion, and after burning and drifting for eight days, the Sanchi sank on January 14, 2018. While the incident had the potential to become the world's largest ship-source condensate spill and ninth-largest tanker spill, extensive burning likely reduced the condensate mass significantly. When the wreck sank, any remaining condensate and HFO were released into the ocean. Due to its physiochemical properties, the condensate would have rapidly evaporated or dispersed. By late January 2018, oil spill residues began washing ashore on 26 southern Japanese islands, including Amami-Oshima and Okinawa Main Island. Chemical analysis confirmed that all residues originated from a single source - the oil released from Sanchi. Diagnostic ratios and chromatographic features showed that the residues contained only HFO, with no detectable condensate, and exhibited signs of soot incorporation. This indicates that any condensate accompanying the HFO had completely weathered before reaching the shores, leaving behind only the HFO, which persisted in the environment. Additional analysis suggests that the oil spill residues underwent weathering processes, including evaporation, dissolution, and microbial degradation during ocean transit. These findings provide insight into the fate of spilled condensate and HFO from the Sanchi tanker in the marine environment.

The Deepwater Horizon (DWH) accident spilled over 785 million liters of crude oil into the Gulf of Mexico (GOM). A substantial fraction of the spilled oil impacted the northern GOM shoreline, including Alabama beaches. The beached oil was in the form of brownish-orange, water-in-oil emulsion, commonly known as mousse. Although significant remediation efforts were undertaken to clean the contaminated beaches, oil residues in the form of tarballs continue to contaminate various GOM beaches. This study reviews recent literature related to the DWH tarball contamination problem and its impacts on GOM beaches, primarily focusing on the beaches located in Alabama. Though the DWH oil spill is an unfortunate disaster, for researchers it constitutes a large-scale experiment conducted on a natural system. This anthropogenic experiment has taught scientists numerous useful lessons and has also posed several challenging questions, some of which are discussed in this review.

The condensate spill accident from the Sanchi oil tanker collision in the East China Sea is unique in world history. To date, the spilled and burnt amounts of condensate remain unknown. The present study demonstrates the chemical fingerprints of a surrogate condensate (SC) from the same source, and of the carried heavy fuel oil (HFO) of the Sanchi accident. The evaporative features of the condensate are demonstrated by allowing the SC to naturally volatilize in a dark fume hood. In addition, the combustion emission of the SC is characterized by conducting a laboratory-scale combustion experiment. The evaporation experiment suggests that the volatilization process plays a significant role in the weathering of the condensate. The results show that the SC and HFO can be clearly distinguished based on their chemical fingerprints of C-27-C-35 hopanes and C-9-C-36 n-alkanes, along with priority polycyclic aromatic hydrocarbons (PAHs) and their alkylated derivatives. The compositional data reveal that the lighter component is predominant in the SC, thereby supporting its high volatility and flammability. The greater amounts of heavier components in the HFO indicate its long-term degradation and potential ecological risks to the environment. Further, the trisnorhopane thermal indicator (T-s/T-m) and C-29/C-30 ratio of hopanes are validated for identification of the SC and the HFO. More importantly, the changes in the hopane ratios of the soot particles are analyzed for the first time in this study, and the results demonstrate the validity of using hopane ratios to fingerprint the condensate soot particles. The diagnostic ratios of 2-MP/1-MP, 9/4-MP/1-MP, and InP/(InP+BghiP) also show decent performance on source identification after the condensate evaporation and combustion processes.

Earth and Space Science Open Archive PosterOpen AccessYou are viewing the latest version by default [v1]Long-Term Environmental Consequences and Fate of the Oil Residues Found along Alabama’s Beaches after the Deepwater Horizon Oil Spill on the Gulf of MexicoAuthorsMariehArekhiiDLeighTerryiDGeraldJohnPrabhakarClementSee all authors Marieh ArekhiiDCorresponding Author• Submitting AuthorThe University of AlabamaiDhttps://orcid.org/0000-0002-3512-1262view email addressThe email was not providedcopy email addressLeigh TerryiDUniversity of AlabamaiDhttps://orcid.org/0000-0002-3593-0481view email addressThe email was not providedcopy email addressGerald JohnAuburn Universityview email addressThe email was not providedcopy email addressPrabhakar ClementUniversity of Alabamaview email addressThe email was not providedcopy email address

The long-term fate of three groups of petroleum biomarker compounds (terpanes, steranes, and triaromatic steranes) was investigated in the Deepwater Horizon (DWH) oil spill residues collected from Alabama (USA) beaches over the past 10 years. This is the first study to investigate the long-term fate of these three groups of petroleum biomarkers in DWH oil spill samples over 10 years. We employed the highly recalcitrant C30 αβ-hopane as an internal biomarker to quantify the degradation levels of different biomarker compounds, and also to estimate the overall weathering levels of DWH oil spill residues. The data show that four lower molecular weight tricyclic terpanes (TR21, TR22, TR23, and TR24), three lower molecular weight steranes (S21, S22, and C27), and all triaromatic steranes degraded over the 10-year study period. All other terpanes (including hopanes) and steranes remained recalcitrant. There have been contradicting literature data on the degradation levels of homohopanes, and this field study demonstrates that all the homohopanes remained recalcitrant after 10 years of natural weathering. Our data also show that despite some degradation, the relative diagnostic ratios of the biomarkers remained stable for all three groups of biomarkers over the 10-year period.

Rationale Polycyclic aromatic hydrocarbons (PAHs) present in oil spill samples are analyzed by gas chromatography/mass spectrometry (GC/MS) and gas chromatography/tandem mass spectrometry (GC/MS/MS) using four different methods: (1) full scan (SCAN), (2) selected ion monitoring (SIM), (3) multiple reaction monitoring (MRM), and (4) pseudo multiple reaction monitoring (PMRM). This study quantifies the relative performance of these methods. Methods Novel experiments were designed to measure the signal‐to‐noise (S/N) ratios of all four methods. This was accomplished by spiking the crude oil with five deuterated PAHs (dPAHs) in two distinct ways: (1) varying the background noise by changing crude oil concentrations before spiking the samples with 1 ng/mL of dPAHs, and (2) varying the signal by spiking dPAHs concentrations of 0.5 and 5 ng/mL into a crude oil sample. Results The MRM method is the most selective and sensitive of the four methods. It also provides the lowest limit of detection (LOD) and limit of quantitation (LOQ). MRM is the optimal approach for quantifying PAHs in complex petroleum samples containing high levels of background noise. Also, our data show that the PAHs in complex oil spill samples can be quantified by MRM without using any complicated sample preparation steps. Conclusions Based on our experimental data, the relative performance of the four methods used for quantifying PAHs in crude oil samples can be ranked as MRM > PMRM > SIM > SCAN.

Beaches of Ras Rakan Island, located off the northern tip of Qatar, are extensively contaminated by highly weathered tarmat deposits. The focus of this study is to determine the possible source of the contamination and complete a preliminary assessment of its potential environmental impacts. The field data collected at this site indicated that the tarmat residues contained highly weathered, black, asphalt-like material and the contamination problem was widespread. Based on these field observations, the following two hypotheses were formulated: (1) the tarmats must have formed from the residual oil deposited by a relatively large, regional-scale oil spill event, and (2) the oil spill must be relatively old. As part of this study, we collected tarmat residues from several beaches located along the northern region of Qatar Peninsula. We found the hopane fingerprints of these tarmat samples were identical to the fingerprints of the samples collected from Ras Rakan Island. These results together with our physical field observational data validated our hypothesis that the oil spill should have been a regional-scale event. Furthermore, we compared the measured hopane fingerprints of our field samples with fingerprints of reference crude oils from Qatar, Saudi Arabia, and Basrah (located close to Kuwait border), and with the literature-derived hopane fingerprints of Kuwaiti and Iranian crude oils. This analysis indicated that the hopane fingerprints of the tarmat samples closely matched the Kuwaiti and Basrah crude oil fingerprints. Since there were no known oil spills of Basrah crude in this region, the highly weathered, asphalt-looking tarmats should have most likely formed from the 1991 Gulf War oil spill, an old oil spill. The concentrations of parent and alkylated PAHs in the tarmat samples were also quantified to provide a preliminary assessment of potential environmental risks posed by these tarmats to Qatar's coastal ecosystem.

In-situ burning (ISB) is a common oil spill response technique used for managing marine oil spills. The burnt residues generated from ISB can have several toxic compounds and therefore their impacts on aquatic ecosystem are of major environmental concern. When quantifying the fate of the toxic compounds in ISB residues, C-30-alpha beta hopane is routinely used as a conservative biomarker since it has shown to be resistant to most natural weathering processes. However, a recent laboratory study has shown that C-30-alpha beta and other hopane compounds have the potential to degrade when crude oil was physically burnt under controlled conditions. When crude oil is burnt, the temperature of the oil can raise up to 350-500 degrees C; however, so far, no one has studied the fate of hopanes when crude oil is simply heated to very high temperatures. In this study, we hypothesize that heating crude oil to very high temperatures would result in the degradation of hopane compounds. Results of our study show that C-30-alpha beta hopane in crude oil will start to degrade at around 160 degrees C and the degradation pattern follows first order kinetics. Other types of hopanes and their diagnostic ratios can also change when the oil is exposed to severe heating conditions. We conclude that removal of hopane biomarkers via thermal degradation is a possible depletion pathway during ISB. Therefore, caution should be exercised when using hopanes as conservative biomarker compounds for characterizing ISB residues. (C) 2019 Elsevier B.V. All rights reserved.

Oil impacting the northern Gulf of Mexico shoreline from the 2010 Deepwater Horizon accident was predominantly in the form of water-in-oil emulsions (WOE), a chemically weathered, highly viscous, neutrally buoyant material. Once formed, WOE are extremely difficult to destabilize. Commercially-available oil dispersants are largely ineffective de-emulsifiers as a result of the inability of dispersant surfactants to displace asphaltenes stabilizing the oil-water interface. This study investigated the effectiveness of the commercially-available dispersant Corexit 9500A, modified to enhance its polar fraction, in destabilizing WOE. Results suggest that Corexit modified to include between 20-60% fractional amount of either polar additive (1-octanol or hexylamine) will produce a modest increase in WOE instability, with a Corexit to hexylamine ratio of approximately 80/20 providing the most effective enhanced destabilization. Results support the hypothesis that modifying the fraction of polar constituents in commercial dispersants will increase asphaltene solubility, decrease oil-water interface stability, and enhance WOE instability.

In-situ burning (ISB) is a remediation strategy that is used for managing oil spills. ISB generates heavy residues that can submerge and negatively impact benthic environments. To track the fate of toxic contaminants in ISB residues, a conservative hopane biomarker, such as C30-αβ hopane, is often used. Furthermore, diagnostic ratios of various hopanes are used for source oil identification. Use of these biomarkers assume that during ISB the quantity of C30-αβ hopane will be conserved, and the diagnostic ratios of various hopanes will be stable. The objective of this study is to test the validity of these two assumptions. We conducted laboratory-scale ISB experiments using a model oil prepared from commercial C30-αβ hopane standard, and a reference crude oil. Laboratory data collected under controlled burning conditions show that C30-αβ hopane will not be conserved; however, the diagnostic ratios of hopanes will still remain fairly stable.

Crude oil that is inadvertently spilled in the marine environment can interact with suspended sediment to form oil-mineral aggregates (OMA). Researchers have identified OMA formation as a natural method of oil dispersion, and have sought ways to enhance this process for oil spill remediation. Currently there is a lack of understanding of how the weathering of oil will affect the formation of OMA due to a lack of published data on this relationship. Based on literature, we identified two conflicting hypotheses: OMA formation 1) increases with weathering as a result of increased asphaltene and polar compound content; or 2) decreases with weathering as a result of increased viscosity. While it is indeed true that the viscosity and the relative amount of polar compounds will increase with weathering, their net effects on OMA formation is unclear. Controlled laboratory experiments were carried out to systematically test these two conflicting hypotheses. Experimental results using light, intermediate, and heavy crude oils, each at five weathering stages, show a decrease in OMA formation as oil weathers.

The explosion of the Deepwater Horizon (DWH) oil drilling rig resulted in widespread contamination of Alabama's white sandy beaches. These beaches continue to be impacted by the various forms of oil spill residues that were formed from the DWH oil. We review published literature and several federal cleanup response reports to develop a set of hypotheses that are broadly used to describe the DWH oil spill–related contamination problems and their impacts on Alabama's beaches. We later test the validity of these hypotheses based on field-scale observations and several recently published datasets. Based on the results of this study, we make the following conclusions: (1) the current background oil–contamination levels are much higher than the relatively low (in some cases, negligible) background levels that existed prior to the DWH oil spill; (2) virtually all of the visible oil spill residues currently deposited along the Alabama shoreline, in the form of fragile, brownish, sticky tar balls and tar patties, originated from the DWH oil spill; and (3) several higher molecular weight PAHs, such as chrysene and its alkylated homologs, trapped in DWH oil spill residues are degrading at a much slower rate than they were prior to the oil being submerged near the shoreline; and it is highly likely that these contaminants will remain in the nearshore environment for an extended period of time. These conclusions were based on our analysis of the data collected from Alabama beaches and more field studies are needed to test their validity to other Gulf of Mexico beaches. Long-term monitoring data are not available to evaluate the changes in background oil levels occurring along the Alabama shoreline, and therefore future research efforts should conduct well-organized long-term surveys to capture both temporal and spatial variations in oil deposition levels. Future studies should also focus on developing rational metrics that can help quantify background oil levels and track its seasonal variabilities. Finally, the biological and ecological implications of the increases in background oil levels that resulted from the DWH oil spill are presently unknown; more biological studies are needed to better understand these implications.

The Deepwater Horizon (DWH) oil spill event released a large amount of sweet crude oil into the Gulf of Mexico (GOM). An unknown portion of this oil that arrived along the Alabama shoreline interacted with nearshore sediments and sank forming submerged oil mats (SOMs). A considerable amount of hydrocarbons, including polycyclic aromatic hydrocarbons (PAHs), were trapped within these buried SOMs. Recent studies completed using the oil spill residues collected along the Alabama shoreline have shown that several PAHs, especially higher molecular weight PAHs (four or more aromatic rings), are slowly weathering compared to the weathering levels experienced by the oil when it was floating over the GOM. In this study we have hypothesized that the weathering rates of PAHs in SOMs have slowed down because the buried oil was isolated from direct exposure to sunlight, thus hindering the photodegradation pathway. We further hypothesized that re-exposing SOMs to sunlight can reactivate various weathering reactions. Also, SOMs contain 75–95% sand (by weight) and the entrapped sand could either block direct sunlight or form large oil agglomerates with very little exposed surface area; these processes could possibly interfere with weathering reactions. To test these hypotheses, we completed controlled experiments to study the weathering patterns of PAHs in a field recovered SOM sample after re-exposing it to sunlight. Our experimental results show that the weathering levels of several higher molecular weight PAHs have slowed down primarily due to the absence of sunlight-induced photodegradation reactions. The data also show that sand particles in SOM material could potentially interfere with photodegradation reactions.

The impact of MC252 oil on northern Gulf of Mexico (GOM) beaches from the 2010 Deepwater Horizon (DWH) catastrophe was extensive along Alabama's beaches. While considerable amount of cleanup has occurred along these beaches, as of August 2014, DWH oil spill residues continue to be found as surface residual balls (SRBs), and also occasionally as submerged oil mats (SOMs). Four years of field observations informing the fate and transport of DWH SRBs in Alabama's beach system are presented here, along with a conceptual framework for describing their physical evolution processes. The observation data show that SRBs containing MC252 residues currently remain in Alabama's beach system, although their relationship to SOMs is not fully known. Based on our field observations we conclude that small DWH SRBs are likely to persist for several years along the Alabama shoreline.

The 2010 Deepwater Horizon (DWH) catastrophe had considerable impact on the ∼50km long sandy beach system located along the Alabama shoreline. We present a four-year dataset to characterize the temporal evolution of various polycyclic aromatic hydrocarbons (PAHs) and their alkylated homologs trapped in the residual oil buried along the shoreline. Field samples analyzed include the first arrival oil collected from Perdido Bay, Alabama in June 2010, and multiple oil spill samples collected until August 2014. Our field data show that, as of August 2014, DWH oil is still trapped along Alabama's beaches as submerged oil, predominately in the form of surface residual oil balls (SRBs). Chemical characterization data show that various PAHs present in the spilled oil (MC252 crude) weathered by about 45% to 100% when the oil was floating over the open ocean system in the Gulf of Mexico. Light PAHs, such as naphthalenes, were fully depleted, whereas heavy PAHs, such as chrysenes, were only partially depleted by about 45%. However, the rate of PAH weathering appears to have decreased significantly once the oil was buried within the partially-closed SRB environment. Concentration levels of several heavy PAHs have almost remained constant over the past 4years. Our data also show that evaporation was most likely the primary weathering mechanism for PAH removal when the oil was floating over the ocean, although photo-degradation and other physico-chemical processes could have contributed to some additional weathering. Chemical data presented in this study indicate that submerged oil containing various heavy PAHs (for example, parent and alkylated chrysenes) is likely to remain in the beach system for several years. It is also likely that the organisms living in these beach environments would have an increased risk of exposure to heavy PAHs trapped in the non-recoverable form of buried DWH oil spill residues.

RATIONALE:Recent advances in analytical techniques have led to the development of gas chromatography/triple quadrupole mass spectrometry methods that allow the identification of target analytes in complex environmental samples. We have employed this technology to develop a method for characterizing alkylated chrysenes, which are environmental toxins that are resistant to weathering.METHODS:An Agilent 7890 gas chromatograph coupled to an Agilent 7000B triple quadrupole mass spectrometer was used. The mass spectral fragmentation of seven commercially available alkylated chrysene standards was studied under full-scan and product-ion scan conditions. The calibration curves used were in the linear range with r(2) values greater than 0.99. The recovery and limit of detection of target analytes in the samples were in the range of 80-120% and 0.11-1.09 ng/mL, respectively.RESULTS:The information inferred from full-scan and product-ion scan data was combined with literature data to develop a GC/MS/MS method for the identification and quantification of C1 -, C2 -, C3 -, and C4 -chrysene homologues. The method was employed to characterize MC252 crude oil which was released during the 2010 Deepwater Horizon accident. The results showed that the chrysene concentrations estimated by the proposed method were well within the range of previously reported values.CONCLUSIONS:The proposed method is useful for analyzing chrysene and its alkylated homologues in crude oil samples.

We compare the chromatographic signatures of petroleum biomarkers in Deepwater Horizon (DH) source oil, three other reference crude oils, DH emulsified mousse that arrived on Alabama’s shoreline in June 2010, and seven tar balls collected from Alabama beaches from 2011 to 2012. Characteristic hopane and sterane fingerprints show that all the tar ball samples originated from DH oil. In addition, the diagnostic ratios of various hopanes indicate an excellent match. Quantitation data for C30αβ-hopane concentration levels show that most of the weathering observed in DH-related tar balls found on Alabama’s beaches is likely the result of natural evaporation and dissolution that occurred during transport across the Gulf of Mexico prior to beach deposition. Based on the physical and biomarker characterization data presented in this study we conclude that virtually all fragile, sticky, brownish tar balls currently found on Alabama shoreline originated from the DH oil spill.