Persistence and biodegradation of oil at the ocean floor following Deepwater Horizon.

The 2010 Deepwater Horizon disaster introduced an unprecedented discharge of oil into the deep Gulf of Mexico. Considerable uncertainty has persisted regarding the oil's fate and effects in the deep ocean. In this work we assess the compound-specific rates of biodegradation for 125 aliphatic, aromatic, and biomarker petroleum hydrocarbons that settled to the deep ocean floor following release from the damaged Macondo Well. Based on a dataset comprising measurements of up to 168 distinct hydrocarbon analytes in 2,980 sediment samples collected within 4 y of the spill, we develop a Macondo oil "fingerprint" and conservatively identify a subset of 312 surficial samples consistent with contamination by Macondo oil. Three trends emerge from analysis of the biodegradation rates of 125 individual hydrocarbons in these samples. First, molecular structure served to modulate biodegradation in a predictable fashion, with the simplest structures subject to fastest loss, indicating that biodegradation in the deep ocean progresses similarly to other environments. Second, for many alkanes and polycyclic aromatic hydrocarbons biodegradation occurred in two distinct phases, consistent with rapid loss while oil particles remained suspended followed by slow loss after deposition to the seafloor. Third, the extent of biodegradation for any given sample was influenced by the hydrocarbon content, leading to substantially greater hydrocarbon persistence among the more highly contaminated samples. In addition, under some conditions we find strong evidence for extensive degradation of numerous petroleum biomarkers, notably including the native internal standard 17α(H),21ß(H)-hopane, commonly used to calculate the extent of oil weathering.

Hydrocarbon composition of oils spilt on the Brazilian coast in 2019 and 2022.

The chemical composition of spilt oils from events that took place on the north-eastern coast of Brazil in 2019 and 2022 was investigated to better understand their sources, and post-spill processes. Oils from both events originated from different sources, based on their fingerprints, hydrocarbons composition and specific biomarkers, such as the C23 tricyclic terpane and oleanane. Despite the differences, the source rocks share similarities in paleoenvironments and depositional conditions and both oils suffered little weathering, mainly due to evaporation and dissolution. Our findings for 2019 spilt oil reinforce that it is a mixed product, enriched both in lighter n-alkanes and 25-norhopanes. Differently, the 2022 samples exhibited characteristics of a non-processed crude oil that originated from a paraffinic deposit in storage tanks. The molecular composition and diagnostic ratios reported for samples from these spill events help to establish baselines for ongoing monitoring of oil spills in marine ecosystems.

Levels, source appointment, and ecological risk of petroleum hydrocarbons in tropical coastal ecosystems (northeast Brazil): Baseline for future monitoring programmes of an oil spill area.

We reviewed 20 years of levels, sources, and environmental risks related to the main petroleum hydrocarbons in the northeast region of Brazil. The aim of this study was to conduct a systematic review to serve as a comprehensive baseline for future monitoring programmes related to the oil spill disaster in 2019/2020. Most contamination levels of both PAHs and AHs were classified as low, except those in specific areas influenced by human activities, such as ports, highly urbanised mangroves, or rivers of medium-sized cities with inadequate liquid and solid waste treatment. Most hydrocarbons were linked to natural sources and burning processes, except in regions of extraction activities and petrochemical facilities as well as highly urbanised areas, where degraded petroleum and oil hydrocarbons predominated. Only 2.5% of the samples exceeded threshold effect levels for ∑16-PAHs and no samples exceeded probable effect levels. When regional threshold levels were used, however, the probable effect for the ∑16-PAHs measured was high, ranging from 5.8 to 6.1%. The few studies reporting biological responses showed that hydrocarbons from anthropogenic sources can induce adverse effects on marine organisms even at low to moderate levels. As the region has recently received a considerable quantity of crude oil, studies should be prioritised for a more precise assessment of the impact of this oil spill.

One century of historical deposition and flux of hydrocarbons in a sediment core from a South Atlantic RAMSAR subtropical estuary.

Levels and fluxes of Polycyclic aromatic hydrocarbons (PAHs) and aliphatic hydrocarbons (AHs), including n-alkanes and petroleum biomarkers (PBMs), were measured in a sedimentary core from a nominated RAMSAR (Guaratuba Bay, Brazil) subtropical estuary experiencing relatively low human impacts, to describe the evolution of anthropogenic activities over the last century. TOC contents varied from 0.80 to 1.25%. No significant correlation between hydrocarbons and TOC with grain size (predominantly sand) was observed. Concentration and flux of total AHs ranged from 65.5 to 195 µg g-1 and 27.6 to 82.0 µg cm-2 y-1, respectively, with the highest levels found in 1960-1966, when access routes to Guaratuba city were improved. Diagnostic ratios based on AH components showed an apparent change in the sources over time, with biogenic origins prevailing until 1966-1971, followed by subsequent increases in petroleum sources. Petroleum tricyclic terpanes were detected in the core (0.40 to 3.0 µg g-1), suggesting the use of lubricating oil in the bay area. Hopanes were mainly attributed to biological sources. Concentration and flux of total PAHs ranged from 8.65 to 35.9 ng g-1 and 3.64 to 15.1 ng cm-2 y-1, respectively, with the highest levels found in the top core section, reflecting recently increased human activity, while a peak PAH concentration at approximately 1977-1983 can be assumed to be a delayed signal of increased human occupation as a consequence of the improvement of access roads to the area, which started in the 1960s. Alkylated were the most abundant group of PAHs throughout the core. Despite relatively low concentrations of hydrocarbon deposition over approximately 90 years, this study highlights the influence of human occupation and slight petroleum contamination in this preserved area, mainly in recent core sections.

A mesocosm experiment to determine half-lives of individual hydrocarbons in simulated oil spill scenarios with and without the dispersant, Corexit.

Here, we report results from a 15-day mesocosm experiment examining changes in estimated oil equivalents (EOEs), n-alkanes (n-C10 to n-C35), polycyclic aromatic hydrocarbons (PAHs) and petroleum biomarkers. Water accommodated fractions (WAF) of oil and diluted chemically enhanced WAF (DCEWAF) were prepared and concentrations of oil residues determined on day 0, 3 and 15, respectively. Significant removals of n-alkane and PAHs were observed starting from day 3. The n-C17/pristane and n-C18/phytane ratios suggested that the n-alkane removal was due to biodegradation in the mesocosms. The ratios of C2-dibenzothiophenes/C2-phenanthrenes (D2/P2) and C3-dibenzothiophenes/C3-phenanthrenes (D3/P3) were found to be stable through the experiment. DCEWAF treatment had longer half-lives for most n-alkanes but shorter half-lives for most PAHs than the WAF treatment. Most petroleum biomarkers were stable throughout the experiment. However, depletion of TAS (tricyclic aromatic steroids) was observed on day 15 of DCEWAF treatment.

Quantitative evaluation of n-alkanes, PAHs, and petroleum biomarker accumulation in beach-stranded tar balls and coastal surface sediments in the Bushehr Province, Persian Gulf (Iran).

Coastal areas within the Bushehr Province (BP), Persian Gulf, Iran, face great challenges due to the heavy organic contamination caused by rapid industrialization, and the presence of numerous oil fields. In addition, in 2014, a significant number of tar balls are found along the coasts of BP. A total of 96 samples (48 coastal sediments and 48 tar balls) were taken from eight sampling points at the BP coast during the summer of 2014. These samples were analyzed to identify the sources and characteristics of their organic matter using diagnostic ratios and fingerprint analysis based on the distribution of the source-specific biomarkers of n-alkanes, PAHs,1 hopanes and steranes. Mean concentration of n-alkanes (µg g-1 dw) and PAHs (ng g-1 dw) varied respectively from 405 to 220,626, and 267 to 23,568 in coastal sediments, while ranged respectively from 664 to 145,285 and 390 to 46,426 in tar balls. In addition, mean concentration of hopanes and steranes (ng g-1 dw) were between 18.17 and 3349 and 184.66 to 1578 in coastal sediments, whereas in tar balls were 235-1899 and 520-1504, respectively. Pri/Phy2 ratio was 0.25 to 1.51 (0.65) and 0.36 to 1 (0.63) in coastal sediment and tar ball samples, respectively, and the occurrence of UCM3 in both matrices, reflecting the petrogenic OM4 inputs and chronic oil contamination, respectively. The C30 and C29 homologues followed Gammacerane were detected in both matrices, in particular those collected from intensive industrial activities, suggesting petrogenic sources of OM. The coastal sediment PAHs profiles were significantly dominated by HMW5-PAHs in the Bahregan Beach (BAB) (78% of total PAHs), Bandare-Genaveh (GP) (66%), and Bandare-Bushehr (BUB) (61%) stations, while the Bashi Beach (BSB) (40%), Bandare-Kangan (KP) (57%), and Bandare-Asaluyeh (AP) (51%) stations exhibited higher proportion of LMW6-PAHs. PCA7 indicated that the tar ball and coastal sediment samples deposited along the Southwest of the BP beaches are most likely originated from the Abuzar oil. Based on the intensity of the anthropogenic activities, NPMDS8 analysis revealed that the GP, BAB, NNP, AP, and KP sampling sites had a high concentration of detected organic pollutants. To the best of our knowledge, this is the first study that investigates oil pollution in costal sediments and tar balls in the BP, providing insights in to the fate of oil in the coastal areas of the Persian Gulf, Iran.

Geochemical imprints of occurrence, vertical distribution and sources of aliphatic hydrocarbons, aliphatic ketones, hopanes and steranes in sediment cores from ten Iranian Coral Islands, Persian Gulf.

The levels, vertical distribution and sources of hydrocarbons and petroleum biomarkers were estimated for the first time in sediment cores (0-40 cm) from ten coral Islands of the Persian Gulf, Iran. Discrepant hydrocarbons, including linear n-alkanes (n-C11 to n-C40) and isoprenoids (AHs), aliphatic ketones (AKs), hopanes and steranes were measured in all core samples, showing mean concentrations ranging from 209 to 5388 µg g-1dw (∑30AH), 2-244 µg g-1-dw (∑13AK), 189-3713 ng g-1dw (∑31hopane) and 42-3864 ng g-1dw (∑15sterane), respectively. All sediment cores were found to be petroleum polluted, with ∑30AH > ∑31hopane > ∑15sterane > ∑13AK, with higher levels recorded at 10-20 cm, mainly at industrial sites. Various diagnostic indices revealed that hydrocarbons derived mainly from anthropogenic inputs, with significant contribution of biogenic origin at sites less polluted. Moreover, total organic carbon (0.24-23.45 mg g-1-dw), terrestrial and marine organic matter had an overwhelming effect on hydrocarbons deposition in sediment cores. Overall, findings provide relevant information for monitoring and preventing petroleum pollution in the sensitive ecosystems of the Persian Gulf.

Compositional Analysis of Heavy Petroleum Distillates by Comprehensive Two-dimensional Gas Chromatography, Field Ionization and High-resolution Mass Spectrometry.

We report recent progresses of combining comprehensive two-dimensional gas chromatography (2DGC or GC × GC) separation, field ionization (FI), and time-of-flight mass spectrometry (TOF MS) for the detailed analysis of vacuum gas oil distillation (VGO) cuts. 2DGC separates petroleum molecules by the combination of boiling point and polarity. FI generates molecule ions-only mass spectra. TOF MS allows accurate mass analysis of hydrocarbon molecules. A new data analysis strategy is implemented for compositional analysis. First, all masses were separated into nominal mass classes. Since petroleum homologues have unique Kendrick mass defects (KMD), KMD plots were generated for easy recognition of homologues series within each nominal mass class. Finally, KMD windows were imposed for complete resolution of petroleum molecules. Using this approach, a total of 16 hydrocarbon types, 14 sulfur types, and their carbon number distributions were determined in the three VGO distillation cuts. Two series of geological biomarkers were also revealed by the analysis.

Spatial distribution and composition of aliphatic hydrocarbons, polycyclic aromatic hydrocarbons and hopanes in superficial sediments of the coral reefs of the Persian Gulf, Iran.

This study is the first quantitative report on petroleum biomarkers from the coral reefs systems of the Persian Gulf. 120 reef surface sediment samples from ten fragile coral reef ecosystems were collected and analyzed for grain size, biogenic elements, elemental ratios, and petroleum biomarkers (n-alkanes, PAHs1 and Hopanes) to assess the sources and early diagenesis of sedimentary organic matter. The mean grain size of the reef sediments ranged from 13.56 to 37.11% (Clay), 26.92 to 51.73% (Sand) and 35.97 to 43.85% (Silt). TOC2 (3.35-9.72 mg.g-1) and TON3 (0.4-1.10 mg.g-1) were identified as influencing factors on the accumulation of petroleum hydrocarbons, whilst BC4 (1.08-3.28 mg.g-1) and TIN5 (0.13-0.86) did not exhibit any determining effect. Although BC and TIN demonstrated heterogeneous spatial distribution, TOC and TON indicated homogenous distribution with continually upward trend in concentration from the east to west ward of the Gulf. The mean calculated TOC/TN ratios vacillated according to the stations (p < 0.05) from 2.96 at Shidvar Island to 8.64 at Hengam Island. The high TOC/TN ratios were observed in the Hengam (8.64), Kharg (8.04) and Siri (6.29), respectively, suggesting a predominant marine origin. The mean concentrations of ∑C11-35n-alkanes, ∑30 PAHs and ∑9Hopanes were found in the ranges of 385-937 µg.g-1dw, (overall mean:590 µg.g-1dw), 326-793 ng.g-1dw (499 ng.g-1dw), 88 to 568 ng.g-1 d (258 ng.g-1dw), respectively. Higher concentrations of detected petroleum biomarkers in reef sediments were chiefly distributed near main industrial areas, Kharg, Lavan and Siri, whilst the lower concentrations were in Hormoz and Qeshm. In addition, one-way ANOVA6 analysis demonstrated considerably significant differences (p < 0.05) among concentration of detected total petroleum hydrocarbons between most sampling locations. Some sampling sites especially Kharg, Lavan, Siri and Lark indicated higher concentration of n-alkanes due to the higher maintenance of organic matter by high clay content in the sediments. Furthermore, most sediment samples, except for Hormoz, Qeshm and Hengam showed an even carbon preference for n-alkanes which could be correlated to bacterial input. NPMDS7 analysis also demonstrated that among the congeners of petroleum biomarkers, n-C12,n-C14, n-C16,n-C18 and n-C20 for n-alkanes, Phe8 and Naph9 along with their Alkyl homologues for PAHs (2-3 rings accounted for 60%) and C30αß and C29αß for Hopanes were discriminated from their other congeners in the whole study area. Our results based on the PCA10 analysis and diagnostic indices of AHs11 and PAHs along with ring classification of PAHs, in addition, the ubiquitous presence of UCM,12 and Hopanes revealed that the main sources of the pollution were petroleum and petroleum combustion mainly from offshore oil exploration and extraction, discharge of pollutants from shipping activities.

PAHs, nitro-PAHs, hopanes, and steranes in lake trout from Lake Michigan.

The present study examines concentrations and risks of polycyclic aromatic hydrocarbons (PAHs), nitro-PAHs (NPAHs), steranes, and hopanes in lake trout collected in Lake Michigan. A total of 74 fish were collected in 2 seasons at 3 offshore sites. The total PAH concentration (Σ9 PAH) in whole fish ranged from 223 pg/g to 1704 pg/g wet weight, and PAH concentrations and profiles were similar across season, site, and sex. The total NPAH (Σ9 NPAH) concentrations ranged from 0.2 pg/g to 31 pg/g wet weight, and carcinogenic compounds, including 1-nitropyrene and 6-nitrochrysene, were detected. In the fall, NPAH concentrations were low at the Illinois site (0.2-0.5 pg/g wet wt), and site profiles differed considerably; in the spring, concentrations and profiles were similar across sites, possibly reflecting changes in fish behavior. In the fall, the total sterane (Σ5 Sterane) and total hopane (Σ2 Hopane) levels reached 808 pg/g and 141 pg/g wet weight, respectively, but concentrations in the spring were 10 times lower. Concentrations in eggs (fall only) were on the same order of magnitude as those in whole fish. These results demonstrate the presence of target semivolatile organic compounds in a top predator fish, and are consistent with PAH biodilution observed previously. Using the available toxicity information for PAHs and NPAHs, the expected cancer risk from consumption of lake trout sampled are low. However, NPAHs contributed a significant portion of the toxic equivalencies in some samples. The present study provides the first measurements of NPAHs in freshwater fish, and results suggest that additional assessment is warranted.