Search

It has been demonstrated that biostimulation is necessary to investigate the interactions between indigenous bacteria and establish an approach for the bioremediation of soils contaminated with weathered oil. This was achieved by adjusting the carbon (C)/nitrogen (N)/phosphorus (P) ratio to 100/10/1 combined with the application of 0.8 mL/kg Tween-80. In addition, three indigenous bacteria isolated from the same soil were introduced solely or combined concomitantly with stimulation. Removal of n-alkanes and the ratios of n-heptadecane to pristane and n-octadecane to phytane were taken to indicate their biodegradation performance over a period of 16 weeks. One strain of Pseudomonas aeruginosa D7S1 improved the efficiency of the process of stimulation. However, another Pseudomonas aeruginosa, D5D1, inhibited the overall process when combined with other bacteria. One strain of Bacillus licheniformis D1D2 did not affect the process significantly. The Fourier transform infrared analysis of the residual hydrocarbons supported the conclusions pertaining to the biodegradation processes when probing the modifications in densities and stretching. The indigenous bacteria cannot mutually benefit from their metabolisms for bioremediation if augmented artificially. However, the strain Pseudomonas. aeruginosa D7S1 was able to perform better alone than in a consortium of indigenous bacteria.

Oil spills on the ocean surface are a serious threat to the marine ecosystem. Automation of oil spill detection through full/dual polarimetric Synthetic Aperture Radar (SAR) images is considered a good aid for oil spill disaster management. This paper uses the power of log transformation to discern the scattering behavior more effectively from the coherency matrix (T3). The proposed coherency matrix is tested on patches of the clean sea surface and four different classes of oil spills, viz. heavy sedimented oil, thick oil, oil-water emulsion, fresh oil; by analyzing the entropy (H), anisotropy (A), and mean scattering angle alpha (α), following the H/A/ α decomposition. Experimental results show that not only does the proposed T3 matrix differentiate between Bragg scattering of the clean sea surface from a random scattering of thick oil spills but is also able to distinguish between different emulsions of oil spills with water and sediments. Moreover, unlike classical T3, the proposed method distinguishes concrete-like structures and heavy sedimented oil even though both exhibit similar scattering behavior. The proposed algorithm is developed and validated on the data acquired by the UAVSAR full polarimetric L band SAR sensor over the Gulf of Mexico (GOM) region during the Deepwater Horizon (DWH) oil spill accident in June 2010. [ABSTRACT FROM AUTHOR]

Indigenous Qatari bacterial strains were isolated from highly weathered oil-contaminated sites, identified, and differentiated based on their protein profiles using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Their diversity was demonstrated by the principal component analysis (PCA) analysis and establishment of a proteodendogram. Both were based on the protein profile of each strain. Interestingly, this approach also showed diversity within the same subspecies. This high diversity is reflected in the emulsification and solubilization activities of their extracellular biosurfactants. The highest emulsification activity (42.1 ± 2.11 AU/mL) was obtained with a strain of Lysinibacillus fusiformis (SA4) after one week of growth in the minimum salt medium in which diesel (5%) is the sole carbon source, while the highest solubilization activity (9.47% ± 0.47%) was produced by the strain Bacillus subtilis (SA6). The functional diversity of the biosurfactants was demonstrated by PCA analysis which allowed their further clustering based on the Fourier-transform infrared spectroscopy (FTIR) analysis. These findings clearly showed that two types of adaptations occur with hydrocarbons degrading bacteria in the weathered-oily soils, one related to the bacterial cell composition maintaining the biosurfactants composition and one to the biosurfactants, which are the primary tool employed by the cell to interact with the weathered oil. This finding would shed light on the potential and strategies of applications for the bioremediation of highly weathered oil-contaminated soils.

Oil spills on the ocean surface are a serious threat to the marine ecosystem. Automation of oil spill detection through full/dual polarimetric Synthetic Aperture Radar (SAR) images is considered a good aid for oil spill disaster management. This paper uses the power of log transformation to discern the scattering behavior more effectively from the coherency matrix (T3). The proposed coherency matrix is tested on patches of the clean sea surface and four different classes of oil spills, viz. heavy sedimented oil, thick oil, oil-water emulsion, fresh oil; by analyzing the entropy (H), anisotropy (A), and mean scattering angle alpha (α), following the H/A/α decomposition. Experimental results show that not only does the proposed T3 matrix differentiate between Bragg scattering of the clean sea surface from a random scattering of thick oil spills but is also able to distinguish between different emulsions of oil spills with water and sediments. Moreover, unlike classical T3, the proposed method distinguishes concrete-like structures and heavy sedimented oil even though both exhibit similar scattering behavior. The proposed algorithm is developed and validated on the data acquired by the UAVSAR full polarimetric L band SAR sensor over the Gulf of Mexico (GOM) region during the Deepwater Horizon (DWH) oil spill accident in June 2010.

Understanding the fate of spilled oil in cold environments is essential for oil spill response in Arctic areas. The potential for oils to adhere to sea ice and mechanical skimmers can significantly impact the success of oil spill response and influence the fate of oil in the marine environment. Therefore, the affinity of oil to sea ice and skimmer material was quantified experimentally for three different types of oils at various degrees of weathering. Contact angle measurements of crude oil droplets were performed on the top of and under sea ice and polyethylene-based skimmer material, being submerged in seawater (−2 °C). In addition, "dip- and refloat" tests were performed to quantify the adhesion and study the re-floating process of oil from sea ice at −2 °C (moist ice) and −20 °C (cold dry ice), and from a skimmer material prior to and subsequently to its submersion in seawater (−2 °C). The results indicated limited interaction of oils with sea ice submerged in seawater, but a strong affinity of oils towards polyethylene-based skimmer material. • Limited interaction of oils with sea ice submerged in seawater. • Strong affinity of oils towards polyethylene-based skimmer material. • Contact angle can be used for evaluating the interaction of skimmer materials for different oils and temperature conditions. • The "dip- and refloat" test showed a weak adhesion of oil to moist sea ice at -2 °C. • A stronger adhesion of oil was observed with cold dry ice at -20 °C as the oils rheological flow properties were reduced. [ABSTRACT FROM AUTHOR]

Abstract The Deepwater Horizon (DWH) oil spill was the biggest in US history and released 3.19 million barrels of light crude oil into the Gulf of Mexico. In this study, we compared the toxicity of water accommodated fractions (WAFs) of naturally weathered crude oils, source oil, and source oil with dispersant mixtures and their effects on developing sheepshead minnow and zebrafish. Although a freshwater fish, zebrafish has been used as a model for marine oil spills owing to the molecular and genetic tools available and their amenability to lab care. Our study not only aimed to determine the effect of crude oil on early life stages of these two fish species, but also aimed to determine whether dissolved crude oil constituents were similar in fresh and saltwater, and if freshwater fish might be a suitable model to study marine spills. Weathering and dispersant had similar effects on WAF composition in both fresh and saltwater, except that the saltwater source oil + dispersant WAF had markedly higher PAH levels than the freshwater equivalent. WAF exposure differentially affected survival, as the LC50 values in %WAF for the zebrafish and sheepshead minnow exposures were 44.9% WAF (95% confidence interval (C.I.) 42.1–47.9) and 16.8% WAF (95% C.I. 13.7–20.5); respectively. Exposure increased heart rate of zebrafish embryos, whereas in sheepshead, source oil exposure had the opposite effect. WAF exposure altered mRNA expression of biotransformation makers, vitellogenin and neurodevelopment genes in both species. Muscle deformations were only found in oil-exposed zebrafish. This is one of the most comprehensive studies to date on crude oil toxicity, and highlights the species-specific differences in cardiotoxicity, estrogenic effects, biotransformation enzyme induction and potential neurotoxicity of crude oil exposure. Graphical abstract Unlabelled Image Highlights • The addition of dispersant increased the toxicity of source oil WAFs. • Dispersant + source oil WAF in saltwater had higher PAH levels than the freshwater equivalent. • Free-swimming vs chorion bound exposure time may play a role in determining the toxicity of early life-stage exposures • There are limitations to using freshwater species, like zebrafish, to model marine oil spills. • Interspecies molecular and physiological responses to crude oil can differ significantly. [ABSTRACT FROM AUTHOR]

Weathered hydrocarbons, commonly emulsified or in the form of tar balls, wash ashore along beaches due to natural oil seepages or offshore oil spills. They remain buried in the sand until a storm or erosion exposes them; therefore it is important to understand the progression and extent of these hydrocarbons. Elmer’s Island, Louisiana, a site known for having large amounts of oil washed ashore from the 2010 Deepwater Horizon oil spill, was selected for a geophysical survey in order to detect the presence of buried weathered oil. Two survey trips to Elmers Island were carried out using 200 MHz, 400 MHz, and 900 MHz ground penetrating radar (GPR) antennas. The 400 MHz data show two distinct anomalous layers with positive amplitudes and 900 MHz data show anomalous features that also display positive amplitudes. An electromagnetic induction (EMI) tool, used over the same traverses as GPR, provided insight into subsurface conductivity. The conductivity maps from the first survey trip display rows of anomalies and two large anomalous zones. These anomalous zones correspond with the 400 MHz GPR data. During the second survey trip, a three-dimensional GPR survey was conducted over a small grid where similarities between the two instruments were evident. Field observations confirmed the existence of contaminated sand (beach sand that enclosed small aggregates of weathered hydrocarbons) and tar balls buried at the survey site in distinct layers. These contaminated sand layers are most likely associated with the anomalies found on both the GPR and EMI data. Thus, a strong correlation with GPR and EMI anomalies co-locating buried weathered hydrocarbons suggests they can be used in future oil spill clean up efforts to map the extent of these hazardous materials. This integrated technique also has implications for the investigation of other buried features. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the spatial distribution of total petroleum hydrocarbons (TPH) in rhizoplane and non-rhizosphere of Leersia hexandra, known as Japanese grass, the effect of oil on the aerial biomass of L. hexandra, the population of plant growth-regulating bacteria, and microbial respiration in rhizosphere and non-rhizospheric soil. Samples of rhizosphere and soil were collected at 14 points across a surface of 2.3 ha, layer 1 (0-15-cm depth), layer 2 (15-30 cm), and layer 3 (30-70 cm), to measure TPH (mg kg). The spatial distribution of TPH defined four study zones (Z): Z1: 1393, Z2: 3455, Z3: 5574, and Z4: 7544. TPH were higher in underlying layers in the four zones. Zone 2 produced the largest amount of aerial biomass; oil induced hormesis in the grass, but inhibited it at doses ≥5574. For the rhizosphere of L. hexandra, it was cut with a sterilized knife, stimulated the population of N-fixing and phosphorus solubilizing, heterotrophic bacteria, as well as microbial respiration (day 1, 14, 21, 42, and 63 after incubation) in the four zones. The population of the three groups of bacteria was more stimulated by weathered oil in rhizosphere soil, compared to non-rhizosphere soil and with control treatment, suggesting that the rhizosphere system of L. hexandra has the potential to bioestimulate beneficial microbial activity in unpolluted and polluted areas compared to non-rhizosphere soil. We recommend the use of L. hexandra to recover soils degraded by weathered oil in farms located in the Mexican humid tropics. [ABSTRACT FROM AUTHOR]

This study evaluated the toxic effects of total petroleum hydrocarbons (TPH) on growth of the legumes Crotalaria incana L. and Leucaena leucocephala Lam., and on the development of nitrogen-fixing soil microorganisms, using biological toxicity indices and the toxicity potential index (TPI c ), which enable comparison of effects of exposure time and concentration. Growth and biomass accumulation in both plant species decreased with high pollutant concentrations. The EC 50 and the NOEC were not identified for either species. The Phytotoxicity Relative Index showed that root length was most strongly affected by the oil, and the Impact Index on Nitrogen Fixer Microorganisms indicated that, despite damage to the root system, L. leucocephala rhizosphere bacteria doubled at 10,000 mg kg −1 TPH after of 240 days of exposure. Finally, the TPI c revealed that C. incana was more sensitive than L. leucocephala to chronic TPH toxicity and might strongly depend on beneficial soil bacteria. [ABSTRACT FROM AUTHOR]

It has been demonstrated that biostimulation is necessary to investigate the interactions between indigenous bacteria and establish an approach for the bioremediation of soils contaminated with weathered oil. This was achieved by adjusting the carbon (C)/nitrogen (N)/phosphorus (P) ratio to 100/10/1 combined with the application of 0.8 mL/kg Tween-80. In addition, three indigenous bacteria isolated from the same soil were introduced solely or combined concomitantly with stimulation. Removal of n-alkanes and the ratios of n-heptadecane to pristane and n-octadecane to phytane were taken to indicate their biodegradation performance over a period of 16 weeks. One strain of Pseudomonas aeruginosa D7S1 improved the efficiency of the process of stimulation. However, another Pseudomonas aeruginosa, D5D1, inhibited the overall process when combined with other bacteria. One strain of Bacillus licheniformis D1D2 did not affect the process significantly. The Fourier transform infrared analysis of the residual hydrocarbons supported the conclusions pertaining to the biodegradation processes when probing the modifications in densities and stretching. The indigenous bacteria cannot mutually benefit from their metabolisms for bioremediation if augmented artificially. However, the strain Pseudomonas. aeruginosa D7S1 was able to perform better alone than in a consortium of indigenous bacteria., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2022 The Author(s).)

Highlights: [•] MC252 oil:sand aggregates were sampled from tidal zones on a Louisiana shoreline. [•] Salinity and nutrient status varied with position on the beach. [•] Supratidal aggregates had different PAH and alkane profiles indicating weathering. [•] Oxygen consumption within aggregates occurred after 4days of inundation. [•] Aggregate microbial populations varied with zone and included PAH-degrading taxa. [ABSTRACT FROM AUTHOR]

Abstract: Marine oil pollution can result in the persistent presence of weathered oil. Currently, removal of weathered oil is reliant on chemical dispersants and physical removal, causing further disruption. In contrast few studies have examined the potential of an environmentally sustainable method using a hydrocarbon degrading microbial community attached to a carrier. Here, we used a tank mesocosm system (50l) to follow the degradation of weathered oil (10gl−1) using a bacterial consortium mobilised onto different carrier materials (alginate or shell grit). GCMS analysis demonstrated that the extent of hydrocarbon degradation was dependent upon the carrier material. Augmentation of shell grit with nutrients and exogenous hydrocarbon degraders resulted in 75±14% removal of >C32 hydrocarbons after 12weeks compared to 20±14% for the alginate carrier. This study demonstrated the effectiveness of a biostimulated and bioaugmented carrier material to degrade marine weathered oil. [Copyright &y& Elsevier]

Abstract: The aim of this study was to assess medium-term toxicity of weathered oil on European seabass. A mesocosm system reproducing an oil spill at sea was applied. Fish were collected after 48 h, 7, 30 and 60 days. Cyp1a gene transcription, EROD and UDPGT activities, bile PAHs metabolites and micronuclei frequency were investigated. A progressive disappearance of low molecular weight n-alkanes and PAHs in the water of the mesocosm occurred during the experimentation. Fishes exposed to oil displayed a significant increase of cyp1a expression and EROD activity during the entire experiment as well as higher concentrations of PAHs metabolites in bile. Micronulei frequency resulted significantly higher during all experiment in oil exposed sea bass compared to controls. The results highlight the environmental risk associated with the release of oil products at sea and confirm the adopted parameters as useful tools for studying the impact of accidental oil spills on fish. [Copyright &y& Elsevier]

In the last decade, a refinery plant located in Lido Adriano, East Ravenna (Italy) has been subject to mineral oil contamination. The mineral crude oil, extracted from the offshore in Adriatic sea, consisted of 78% aliphatics, cyclic alkanes and saturated polycyclic hydrocarbons, 9% aromatics, polycyclic aromatic hydrocarbons (PAHs) and alkylated derivatives, and 13% of tars/asphaltenes. Analysis of soil after 10 years of natural attenuation revealed a complete depletion of linear (n-C9–C24), light aromatics (C1–C3/benzenes) and PAHs (C2/naphthalene, C1/phenanthrene); besides a substantial degradation of isoprenoids prystane and phytane, branched and cyclic alkanes. The remaining contaminants which withstood to natural degradation was saturated polycyclic hydrocarbons (perhydro-PAH derivatives), unsaturated polycyclic hydrocarbons (tetrahydro, dihydro-PAH derivatives), terpanes, steranes and unidentified compounds. Such residues resulted in 80% reduction of its concentration after two months of laboratory treatment. Samples were extracted by organic solvents, separated by silica/alumina gel column chromatography and analyzed by gas chromatography–mass selective detector (GC–MSD). Identification and quantification of aliphatic, cyclic alkanes, typical PAHs, terpanes and steranes were carried out to chromatograms of M/Z =85, 83, individual M/Zs, M/Z =191 and 217, respectively. The present work shows that, among numerous biomarkers present in the source oil, stigmastane and two isomers of hopane showed invariable concentrations after laboratory experiments that mimic natural biodegradation in the field, so they can be used as conserved internal biomarkers. These are very useful tools to assess alterations in less stable classes of saturated compounds contained in petroleum. Marked degradation of perhydro, tetrahydro, dihydro-PAH derivatives in the laboratory treatment has been evidenced. [Copyright &y& Elsevier]

In 1970, approximately 2000 m3 of Bunker C crude oil impacted 300 km of Nova Scotia’s coastline following the grounding of the tanker Arrow. Only 10% of the contaminated coast was subjected to cleanup, the remainder was left to cleanse naturally. To determine the long-term environmental impact of residual oil from this spill event, samples of sediment and interstitial water were recovered in 1993, 1997 and 2000 from a sheltered lagoon in Black Duck Cove. This heavily oiled site was intentionally left to recover on its own. Visual observations and chemical analysis confirmed that substantial quantities of the weathered cargo oil were still present within the sediments at this site. However, direct observations of benthic invertebrate abundance suggest that natural processes have reduced the impacts of the residual oil. To confirm this hypothesis, sediment and interstitial water samples from Black Duck Cove were assessed with a comprehensive set of biotests and chemical assays.Residual oil in the sediments had limited effect on hepatic CYP1A protein levels and mixed function oxygenase (MFO) induction in winter flounder (Pleuronectes americanus). No toxicity was detected with the Microtox solid phase test (Vibrio fischeri). Significant sediment toxicity was detected by the amphipod survival test (Eohaustorius estuarius) in four out of the eight contaminated sediments. Interstitial water samples were deemed non-toxic by the Microtox 100% test (Vibrio fischeri) and the echinoid fertilization test (Lytechinus pictus). Sediment elutriates were also found to be non-toxic in the grass shrimp embryo-larval toxicity (GSELTOX) test (Palaemonetes pugio).Recovery at this contaminated site is attributed to natural processes that mediated biodegradation and physical removal of oil from the sediments. In support of the latter mechanism, mineralization experiments showed that all test sediments had the capacity for hexadecane, octacosane and naphthalene degradation, while chemical analysis confirmed that the Bunker C oil from the Arrow had undergone substantial biodegradation. [Copyright &y& Elsevier]

Crude oils produced in the North West shelf of Western Australia are highly volatile, a characteristic not shared by most of the Northern Hemisphere crude oils on which internationally accepted toxicity test protocols were developed. Because of this volatility and some other factors, the LC50 and EC50 values obtained from acute toxicity tests will be significantly affected by the changes of toxicant concentration in test solutions during the period of exposure. To address these issues all steps of a standard protocol for crude oil toxicity testing have been revised. A systematic study has been performed on factors which affect petroleum hydrocarbon solubilisation in aqueous systems during test solution preparations. The influence of mixing time, agitation energy and volume/interface ratio on a hydrocarbon concentration in a water-soluble fraction (WSF) was studied for heavy, medium and light crude oils. A study of the sensitivity of marine unicellular algae to WSF of crude oils was conducted with Isochrysis sp., Nannochloropsis-like sp. and Nitzchia closterium. Total concentrations of hydrocarbons dissolved in test solutions were estimated by UV-spectrometry and GC/FID chemical analyses. When the toxicant concentration decreased during the exposure period, the EC50 values derived from initial or final concentrations either underestimate or overestimate toxicity, respectively. Therefore, weighted average concentrations (WAC) calculated for the whole test period were recommended for expressing hydrocarbon concentrations in test solutions of crude oils. Toxicity indices calculated from WAC of total hydrocarbons for different crude oils can be compared regardless of the rates of hydrocarbon loss. [Copyright &y& Elsevier]

Traditionally, the toxic effects of petroleum have been investigated by conducting studies in the absence of ultraviolet radiation (UV). Photomediated toxicity is often not considered, and the toxic effects of an oil spill can be grossly underestimated. The toxicity of a weathered oil collected from a monitoring well at an abandoned oil field to Ceriodaphnia dubia was examined in the presence of UV. A solar simulator equipped with UVB, UVA, and cool white lamps was used to generate environmentally comparable solar radiation intensities. C. dubia were exposed to six concentrations of water accommodated fractions (WAF) of weathered oil in conjunction with three levels of laboratory simulated UV (Reference = < 0.002 μW/cm2UVB; 3.0 μW/cm2 UVA; Low = 0.30 μW/cm2 UVB; 75.0 μW/cm2 UVA; High = 2.0 μW/cm2 UVB; 340.0 μW/cm2 UVA) and visible light. Seven day static renewal bioassays were used to characterize WAF/UV toxicity. WAF toxicity significantly (p < 0.05) increased when the organisms were exposed to WAF in the presence of UV. The photoenhanced toxicity of the WAF increased with WAF concentration within each UV regime. Relative to the reference light regime, the average number of neonates from adults exposed to 1.6 mg TPH/L decreased significantly by 20% within the low light regime, and by 60% within the high light regime. These results indicate that organisms exposed to dissolved-phase weathered oil in the presence of environmentally realistic solar radiation, exhibit 1.3–2.5 times greater sensitivity, relative to organisms exposed under traditional laboratory fluorescent lighting. [ABSTRACT FROM AUTHOR]

Macondo source oils and artificially weathered oil residues from 150 °C+ to 300 °C+, including artificially photo oxidized oils, were prepared and used for generating low energy water accommodated fractions (LE-WAFs) in order to assess the impact of oil weathering on WAF chemistry composition and toxicity to marine organisms. Two pelagic species representing primary producers (the marine algae Skeletonema pseudocostatum) and invertebrates (the marine copepod Acartia tonsa) were tested. Obtained acute toxicity levels, expressed as EC/LC50 values, were in the same range or above the obtained maximum WAF concentrations for WAFs from most weathering degrees. Based on % WAF dilutions, reduced toxicity was determined as a function of weathering. The chemical compositions of all WAFs were compared to compositions obtained from water samples reported in the GRIIDC database using multivariate analysis, indicating that WAFs of photo oxidized and two field weathered oils resembled the field data the most. • Chemistry and acute toxicity in WAFs from fresh and artificially weathered DWH oils. • Acute toxicity tests using S. costatum (algae) and A. tonsa (copepod) performed. • Solubility and maximum WAF concentration decrease during the weathering process. • All EC50 and LC50s were at or above the maximum total WAF concentration tested. • The EC10 and LC10 values decreased with increased weathering. [ABSTRACT FROM AUTHOR]

Because of the high production of oil and gas in Qatar, the likelihood of oil spill occurrence is most probably susceptible to happen. Contaminated soil treatment is very expensive. Cost effective mechanisms are investigated to treat this threatening issue. For that reason, bioremediation and biotechnology tools are introduced to help accelerate and remove the pollution caused by the contamination process. This paper demonstrated the importance of optimising the treatment conditions to the indigenous bacterial strain to obtain the highest biodegradation efficiency rates. The usage of biopile system technology was used with biostimulation and bioaugmentation processes. The indigenous Bacillus sonorensis (B. sonorensis) D1 bacterium played a crucial role in the biodegradation process when introduced to optimized conditions; carbon/nitrogen/phosphorus (C/N/P) (100/10/1), temperature (37 °C), surfactant tween 80 (0.12% (v/w)), and moisture (10%). Gas chromatography (mass spectrometry/flame ionization detector) (GC- (MS/FID)), Fourier transform infrared (FTIR), and colony-forming unit (CFU) analyses were performed. The diesel range organics (DRO) and polycyclic aromatic hydrocarbons (PAH) removal (%) of the weathered oil contaminated soil reached, after 160 days, 39.2% and 32.4% simultaneously when ammonium nitrate was used as a nitrogen source. Whereas urea inhibited the oil degradation process and caused the pH to rise to 9.55. Image 1040 • Urea inhibited oil degradation process and caused pH to rise to 9.55 • Adding the surfactant tween 80 to urea enhanced bacterial growth with urea. • The bioavailability of the hydrocarbons is not always related to bacterial growth. • B. sonorensis D1 was able to biodegrade weathered oil at optimized conditions. • Using ammonium nitrate as a nitrogen source improved the biodegradation process. [ABSTRACT FROM AUTHOR]

Methanogenic degradation of crude oil in subsurface sediments occurs slowly, but without the need for exogenous electron acceptors, is sustained for long periods and has enormous economic and environmental consequences. Here we show that volatile hydrocarbons are inhibitory to methanogenic oil biodegradation by comparing degradation of an artificially weathered crude oil with volatile hydrocarbons removed, with the same oil that was not weathered. Volatile hydrocarbons (nC5-nC10, methylcyclohexane, benzene, toluene, and xylenes) were quantified in the headspace of microcosms. Aliphatic (n-alkanes nC12-nC34) and aromatic hydrocarbons (4-methylbiphenyl, 3-methylbiphenyl, 2-methylnaphthalene, 1-methylnaphthalene) were quantified in the total hydrocarbon fraction extracted from the microcosms. 16S rRNA genes from key microorganisms known to play an important role in methanogenic alkane degradation (Smithella and Methanomicrobiales) were quantified by quantitative PCR. Methane production from degradation of weathered oil in microcosms was rapid (1.1 ± 0.1 μmol CH4/g sediment/day) with stoichiometric yields consistent with degradation of heavier n-alkanes (nC12-nC34). For non-weathered oil, degradation rates in microcosms were significantly lower (0.4 ± 0.3 μmol CH4/g sediment/day). This indicated that volatile hydrocarbons present in the non-weathered oil inhibit, but do not completely halt, methanogenic alkane biodegradation. These findings are significant with respect to rates of biodegradation of crude oils with abundant volatile hydrocarbons in anoxic, sulphate-depleted subsurface environments, such as contaminated marine sediments which have been entrained below the sulfate-reduction zone, as well as crude oil biodegradation in petroleum reservoirs and contaminated aquifers.

Artificially weathered crude oil was degraded by four diverse cultures of mixed marine bacteria under optimized conditions for 7 and 14 days. Loss in total weight of starting oil (30 g) ranged from 6.8-17.3% in biologically active incubations compared with only 0.9-1.1% in sterile and nutrient-limited controls. In all incubations, both neutral and acidic water-soluble fractions (WSF) were accumulated. In biologically active systems, 50.9-249.0 mg neutral and 63.3-406.8 mg acidic WSF were accumulated whereas only 6.5-11.1 mg neutral and 1.7-2.2 mg acidic WSF were accumulated in control incubations. Analysis by gaschromatography demonstrated that accumulated WSF in biologically active systems contained compounds different from those washed from the starting crude oil. Exposure of grass shrimp (Palaemonetes pugio) embryos to neutral WSF from each of the biologically active cultures resulted in high embryo mortalities relative to sterile and nutrient-limited controls which exhibited >90% hatching success and larval survival. Toxicity of neutral WSF was also demonstrated on larvae of mysids(Mysidopsis bahia). In both cases, toxicity occurred only on exposure to neutral material accumulated by active, oil-degrading cultures and not with material washed from the weathered crude oil. These results imply that unique compounds were accumulated during degradation that may have been responsible for increased toxicity. [ABSTRACT FROM AUTHOR]