Aromatic Hydrocarbon Fractions Research Articles

Mutagenicity assessment of aerosols in emissions from domestic combustion processes.

Domestic biofuel combustion is one of the major sources of regional and local air pollution, mainly regarding particulate matter and organic compounds, during winter periods. Mutagenic and carcinogenic activity potentials of the ambient particulate matter have been associated with the fraction of polycyclic aromatic hydrocarbons (PAH) and their oxygenated (OPAH) and nitrogenated (NPAH) derivatives. This study aimed at assessing the mutagenicity potential of the fraction of this polycyclic aromatic compound in particles (PM10) from domestic combustion by using the Ames assays with Salmonella typhimurium TA98 and TA100. Seven biofuels, including four types of pellets and three agro-fuels (olive pit, almond shell and shell of pine nuts), were tested in an automatic pellet stove, and two types of wood (Pinus pinaster, maritime pine, and Eucalyptus globulus, eucalypt) were burned in a traditional wood stove. For this latter appliance, two combustion phases-devolatilisation and flaming/smouldering-were characterised separately. A direct-acting mutagenic effect for the devolatilisation phase of pine combustion and for both phases of eucalypt combustion was found. Almond shell revealed a weak direct-acting mutagenic effect, while one type of pellets, made of recycled wastes, and pine (devolatilisation) presented a cytotoxic effect towards strain TA100. Compared to the manually fired appliance, the automatic pellet stove promoted lower polyaromatic mutagenic emissions. For this device, only two of the studied biofuels presented a weak mutagenic or cytotoxic potential.

Pore structure and acid properties of high-silica zeolites synthesized with different templates and their catalytic performance in conversion of the propane–butane fraction

The effect of the template on the physicochemical properties of zeolitic catalysts and on the yield and selectivity of formation of aromatic hydrocarbons in conversion of the propane–butane fraction was examined. The zeolitic catalyst sample synthesized with an alcohol fraction as template is characterized by the highest values of the acid site concentration, adsorption capacity, micropore volume, and specific surface area. Therefore, this catalyst ensures the highest, compared to the other samples, conversion of the propane–butane fraction and yield of aromatic hydrocarbons.

Estrogenic Activity of Mineral Oil Aromatic Hydrocarbons Used in Printing Inks.

The majority of printing inks are based on mineral oils (MOs) which contain complex mixtures of saturated and aromatic hydrocarbons. Consumer exposure to these oils occurs either through direct skin contacts or, more frequently, as a result of MO migration into the contents of food packaging that was made from recycled newspaper. Despite this ubiquitous and frequent exposure little is known about the potential toxicological effects, particularly with regard to the aromatic MO fractions. From a toxicological point of view the huge amount of alkylated and unsubstituted compounds therein is reason for concern as they can harbor genotoxicants as well as potential endocrine disruptors. The aim of this study was to assess both the genotoxic and estrogenic potential of MOs used in printing inks. Mineral oils with various aromatic hydrocarbon contents were tested using a battery of in vitro assays selected to address various endpoints such as estrogen-dependent cell proliferation, activation of estrogen receptor α or transcriptional induction of estrogenic target genes. In addition, the comet assay has been applied to test for genotoxicity. Out of 15 MOs tested, 10 were found to potentially act as xenoestrogens. For most of the oils the effects were clearly triggered by constituents of the aromatic hydrocarbon fraction. From 5 oils tested in the comet assay, 2 showed slight genotoxicity. Altogether it appears that MOs used in printing inks are potential endocrine disruptors and should thus be assessed carefully to what extent they might contribute to the total estrogenic burden in humans.

Improvement of mineral oil saturated and aromatic hydrocarbons determination in edible oil by liquid–liquid–gas chromatography with dual detection

Mineral oils, which are mainly composed of saturated hydrocarbons and aromatic hydrocarbons, are widespread food contaminants. Liquid chromatography coupled to gas chromatography with flame ionization detection represents the method of choice to determine these two families. However, despite the high selectivity of this technique, the presence of olefins (particularly squalene and its isomers) in some samples as in olive oils, does not allow the correct quantification of the mineral oil aromatic hydrocarbons fraction, requiring additional off-line tools to eliminate them. In the present research, a novel on-line liquid chromatography coupled to gas chromatography method is described for the determination of hydrocarbon contamination in edible oils. Two different liquid chromatography columns, namely a silica one (to retain the bulk of the matrix) and a silver-ion one (which better retains the olefins), were coupled in series to obtain the mineral oil aromatic hydrocarbons hump free of interfering peaks. Furthermore, the use of a simultaneous dual detection, flame ionization detector and triple quadrupole mass spectrometer allowed us not only to quantify the mineral oil contamination, but also to evaluate the presence of specific markers (i.e. hopanes) to confirm the petrogenic origin of the contamination.

Habitat and hydrocarbon potential of the Kimmeridgian strata in the central part of the Polish Lowlands

The quantity, genetic type and maturity of organic matter dispersed in the Kimmeridgian strata of the central part of the Polish Lowlands were determined on the basis of results of Rock-Eval, stable carbon isotope composition of bitumen, their fractions and kerogen, biomarker distribution in saturate and aromatic hydrocarbon fraction, elemental composition of kerogen, vitrinite reflectance and maceral composition analyses of 225 rock samples collected from 32 boreholes. The study was conducted separately for Lower and Upper Kimmeridgian rocks in the Szczecin-Miechów and Kościerzyna-Puławy synclinoriums and Mid-Polish Anticlinorium. The best source rocks with TOC up to 6.8 wt.%, were found in the vicinity of Gostynin in the Mid-Polish Anticlinorium. Generally, the Upper Kimmeridgian strata are fair and good potential source-rocks whereas the Lower Kimmeridgian strata have much lower hydrocarbon potential. Gas-prone, terrigenous Type-III kerogen predominates in the Lower Kimmeridgian strata. The contribution of oil-prone, marine Type-II kerogen increases in the Upper Kimmeridgian rocks. In the whole profile, only low-sulphur kerogen was recorded, although the situation, when high-sulphur Type-IIS kerogen was mixed with re-worked, non-generative Type-IV kerogen supplied to the sedimentary basin with rocks from eroded land, cannot be excluded. Sedimentary conditions of organic material were variable, usually anoxic and suboxic with domination of siliclastic material in mineral matrix. The maturity of the dispersed organic matter refers mostly to the final phase of the microbial process, or to the initial phase of the low-temperature thermogenic process ( oil window ). The most mature rocks, corresponding up to 0.75% in the vitrinite reflectance scale, were recognised in the deepest buried parts of the basin (axial part of the Mogilno-Łódź Segment of the Szczecin-Miechów Synclinorium). The most prospecting source rocks were recognised in this area.

Assessment of the bioavailability and phytotoxicity of sediment spiked with polycyclic aromatic hydrocarbons.

Large amounts of sediment are dredged globally every year. This sediment is often contaminated with low concentrations of metals, polycyclic aromatic hydrocarbons, pesticides and other organic pollutants. Some of this sediment is disposed of on land, creating a need for risk assessment of the sediment disposal method, to minimize the degradation of environmental quality and prevent risks to human health. Evaluating the available fractions of certain polycyclic aromatic hydrocarbons is very important, as in the presence of various organisms, they are believed to be easily subject to the processes of bioaccumulation, biosorption and transformation. In order to determine the applicability of applying these methods for the evaluation of pollutant bioavailability in sediments, the desorption kinetics from the sediment of various polycyclic aromatic hydrocarbons in the presence of Tenax and XAD4 were examined over the course of 216 h. Changes in the PAH concentrations in dredged sediments using five different seed plants during a short time of period (10 days) were also followed. Using chemical extraction techniques with Tenax and XAD4, a time of around 24 h is enough to achieve equilibrium for all four PAHs. Results showed good agreement between the seed accumulation and PAH extraction methods with both agents. If we compare the two extraction techniques, XAD4 gave better results for phenanthrene, pyrene and benzo(a)pyrene, and Tenax gave better results for chrysene.

Influence of particle size and organic carbon content on distribution and fate of aliphatic and aromatic hydrocarbon fractions in chalks

Abstract Although great efforts had been devoted to investigate the fate and transport of various hydrocarbon sources in major aquifers, there is still a need to better understand and predict their behaviour for robust risk assessment. In this study, the fate and distribution of the aliphatic and polycyclic aromatic hydrocarbons (PAHs) of diesel fuel in chalk aquifer was investigated using a series of leaching column tests and then modelled using the Contaminant Transport module of the Goldsim software. Specifically the influence of chalk particle size on the behaviour and fate of the hydrocarbons was investigated. Distribution coefficient ( K d ) between the water and chalk solid phase according to chalk particle sizes was determined for each hydrocarbon group. The larger sizes of chalk particles have higher K d values. After 60 d of leaching using a water flow of 45 mm d −1 , most of the aliphatic and aromatic hydrocarbon compounds of the diesel were retained within the top 5 cm chalk layer and none of the targeted hydrocarbons were detected in the leachate from the four particles sizes chalk. Further to this, the results showed that the chalk is capable of holding more hydrocarbons than sand and chalk can limit their migration of hydrocarbons. The numerical results and the Monte Carlo analysis showed that the migration of the alkanes and PAHs is greatly retarded by the organic carbon in chalk. It is also observed that the initial mass of the alkanes and PAHs and their respective partition coefficients are important for the decaying of the source at the surface immediately after the spill and the rate-limited dissolution is responsible for entrapping the hydrocarbons in the top layer of the chalk. Overall these results can help to better inform risk assessment and help decision for the remediation strategy.

Geochemistry of Paleozoic marine petroleum from the Tarim Basin, NW China: Part 5. Effect of maturation, TSR and mixing on the occurrence and distribution of alkyldibenzothiophenes

Fifty-four oils and 20 gas condensates from the cratonic region of the Tarim Basin, NW China were quantitatively analyzed by gas chromatography–mass spectrometry to elucidate the influence of thermal maturation, multiple charges and mixing, and thermochemical sulfate reduction (TSR) on the relative distributions of alkyldibenzothiophenes (DBTs) vs alkylphenanthrenes, which are widely used to interpret depositional environment and lithology. Concentrations of DBTs relative to DBTs in the aromatic hydrocarbon fraction and ratios of dibenzothiophene/phenanthrene (DBT/P) exhibit wide variations in the studied samples. Field observations, coupled with a suite of oil sand pyrolysis experimental results, suggest that DBTs are more easily released from kerogen and/or asphaltenes and are more easily destroyed in oil than the alkylphenanthrenes. The DBT/P ratio initially increases during early maturation and then decreases in the post mature stage. Concentrations of DBTs are low in samples from the cratonic region of the Tarim Basin (most samples have DBT/P ratios<1) because of their high maturity. The unusually high concentration of DBTs in some gas condensates from the Tazhong Uplift is possibly the result of back reaction of H2S formed by TSR with hydrocarbons. A typical TSR-altered sample represented by ZS1C has a DBT/P ratio as high as 22.3 with DBTs representing 63.6% of components in the aromatic hydrocarbon fraction. Mixing of a TSR-altered late charge with previously existing oils is responsible for the wide range of variation of DBT concentrations and DBT/P ratios. The influence of TSR on DBT/P ratios is easily distinguishable from thermal maturation because the former increases the ratio while the latter decreases the ratio. Consequently, the DBT/P ratio is not valid as a parameter to interpret source rock lithology and depositional environment in the present case study.

Parental trophic exposure to three aromatic fractions of polycyclic aromatic hydrocarbons in the zebrafish: Consequences for the offspring

In recent decades, PAH emissions due to extensive anthropogenic activities have risen sharply causing considerable pollution of aquatic ecosystems. This pollution represents a threat for organisms, among them are fish. Consequently, prenatal stress can have important repercussions, and may impact survival and population recruitment. To investigate this point, eggs were collected from zebrafish exposed during 6months by trophic route to three aromatic fractions from two different origins, pyrolytic (PY) and petrogenic (light (BAL) and heavy (HFO) fractions) sources. Chronic dietary exposure of the parents was performed at environmentally relevant concentrations (0.3×, 1× and 3×; 1× represents an environmental concentration measured in French estuary). In order to explore the consequences of parental exposure for the next first generation, toxic responses were studied in both embryos and larvae using a multiscale approach. Toxic effects were assessed by looking at hatching success, developmental abnormalities, photomotor response and heartbeat. The level of PAH metabolites and EROD activity in fish larvae were measured to assess exposure to PAHs. Egg production of parents was significantly reduced compared to the Control; hence little information was available for BAL and HFO offspring. The size of larvae from PY parents was found to increase despite a reduced yolk sac compared to Control larvae. Furthermore, a high level of behavioral stress was observed in larvae originating from parents exposed to three-fold the environmental concentration. The cardiac activity was reduced in a concentration-dependent manner for the PY exposure group. No effect was however observed on biotransformation markers (cyp1a, EROD), nor on the level of DNA damage for all PY, BAL and HFO offspring. The absence of significant differences in metabolite levels may indicate a potential early depuration of transferred compounds or no PAH-transmission. The disruptions observed at the individual level in the next generation could impact on the longer-term, surviving population.

Insight into unresolved complex mixtures of aromatic hydrocarbons in heavy oil via two-dimensional gas chromatography coupled with time-of-flight mass spectrometry analysis

The aromatic hydrocarbon fractions of five crude oils representing a natural sequence of increasing degree of biodegradation from the Liaohe Basin, NE, China, were analyzed using conventional gas chromatography–mass spectrometry (GC–MS) and comprehensive two-dimensional gas chromatography (GC×GC). Because of the limited peak capability and low resolution, compounds in the aromatic fraction of a heavily biodegraded crude oil that were analyzed by GC–MS appeared as unresolved complex mixtures (UCMs) or GC “humps”. They could be separated based on their polarity by GC×GC. UCMs are composed mainly of aromatic biomarkers and aromatic hydrocarbons with branched alkanes or cycloalkanes substituents. The quantitative results achieved by GC×GC-FID were shown that monoaromatic hydrocarbons account for the largest number and mass of UCMs in the aromatic hydrocarbon fraction of heavily biodegraded crude oil, at 45% by mass. The number and mass of diaromatic hydrocarbons ranks second at 33% by mass, followed by the aromatic biomarker compounds, triaromatic, tetraaromatic, and pentaaromatic hydrocarbons, that account for 10%, 6%, 1.5%, and 0.01% of all aromatic compounds by mass, respectively. In the heavily biodegraded oil, compounds with monocyclic cycloalkane substituents account for the largest proportion of mono- and diaromatic hydrocarbons, respectively. The C4-substituted compounds account for the largest proportion of naphthalenes and the C3-substituted compounds account for the largest proportion of phenanthrenes, which is very different from non-biodegraded, slightly biodegraded, and moderately biodegraded crude oil. It is inferred that compounds of monoaromatic, diaromatic and triaromatic hydrocarbons are affected by biodegradation, that compounds with C1-, C2-substituents are affected by the increase in degree of biodegradation, and that their relative content decreased, whereas compounds with C3-substituents or more were affected slightly or unaffected, and their relative content also increased. The varying regularity of relative content of substituted compounds may be used to reflect the degree of degradation of heavy oil. Moreover, biomarkers for the aromatic hydrocarbons of heavily biodegraded crude oil are mainly aromatic steranes, aromatic secohopanes, aromatic pentacyclotriterpanes, and benzohopanes. According to resultant data, aromatic secohopanes could be used as a specific marker because of their relatively high concentration. This aromatic compound analysis of a series of biodegraded crude oil is useful for future research on the quantitative characterization of the degree of biodegradation of heavy oil, unconventional oil maturity evaluation, oil source correlation, depositional environment, and any other geochemical problems.

Chemical Characteristics of Fine Particles Emitted from Different Chinese Cooking Styles

Cooking process was regarded as one of the most significant contributor to fine particles (PM2.5) in ambient atmosphere and its chemical characteristics would be great different among various cooking styles. In this study, PM2.5 emitted from four different Chinese cooking styles, including Home cooking, Shandong cuisine, Hunan cuisine, and Barbecue, were collected using a dilution sampling system. Then, PM2.5 mass concentrations were weighted, and its chemical composition were analyzed. It was found that Barbecue emitted PM2.5 concentrations with the highest level, followed by Home cooking, Shandong cuisine and Hunan cuisine. PM2.5 emission amounts and emission factors were also estimated according to the measured data. Home cooking notably had the highest levels. The difference between Barbecue and other cuisines of PM2.5 chemical profiles were the largest by using the coefficient of divergence (CD) method. The predominant chemical composition was organic carbon (OC) in PM2.5. The main water-soluble ions were Na+, SO42–, NO3–, Cl–, and Ca2+, and Fe, S, and Ca had made up a big proportion of element. Little difference had been found between the mass fractions of n-alkanes and polycyclic aromatic hydrocarbons (PAHs) from different cooking cuisines. However, Barbecue displayed the highest mass fractions of organic acids in cooking fume.

Measurement and modelling of the ingestion bioaccessibility of polyaromatic hydrocarbons in soils

Total and human ingestion bioaccessible polycyclic aromatic hydrocarbon fractions of individual polycyclic aromatic hydrocarbons were determined (representative of a combination of the saliva, gastric and upper intestine compartments) on 26 soil samples from 3 gasworks sites and from a domestic garden. A Random Forest model using the Infra-red spectra of the soils and the PAH properties successfully predicted the bioaccessibility of PAHs in the soils. The Near Infra-red and Mid Infra-red diffuse reflection spectra of the soils were subjected to a mixture resolution algorithm. Comparison with spectra of known minerals tentatively identified carbonate, silica, clay and iron oxide components in the Mid Infra-red spectra. Multiple linear regression analysis suggested that three Mid Infra-red components were associated with the organic carbon. Principal Component Analysis of polycyclic aromatic hydrocarbon properties identified three components associated with the hydrophobicity, the aliphatic nature and the vapour phase partition coefficient of the polycyclic aromatic hydrocarbons.

Catalytic fast pyrolysis of waste pepper stems over HZSM-5

Catalytic fast pyrolysis over HZSM-5 of red pepper stems, a representative agricultural residue material in the southern area of South Korea, was carried out. The SiO2/Al2O3 ratio of the catalyst were 23 and 280. Pyrolysis-gas chromatography/mass spectrometry was used to pyrolyze the pepper stem samples at 550 °C and directly analyze the product distribution. The main product species of the non-catalytic pyrolysis of pepper stems were phenolics, followed by oxygenates and acids. The production of aliphatic and aromatic hydrocarbons was marginal. On the contrary, catalytic pyrolysis over HZSM-5 reduced the fractions of phenolics and acids significantly, while considerably increasing the fractions of aliphatic and aromatic hydrocarbons. The catalytic activity of the HZSM-5 with a SiO2/Al2O3 ratio of 23 was much higher, owing to its much larger amount of strong Brønsted acid sites, than the one with a SiO2/Al2O3 ratio of 280. Conversion of carbohydrate via furans to aromatics over strong acid sites was observed, which was in good agreement with previous studies. This study suggests that the catalytic pyrolysis of lignin-rich biomass over acidic zeolite catalysts can be a promising method to produce valuable chemicals such as aromatic compounds.

Biocomponent Containing Jet Fuel Production with Using Coconut Oil

Recent demands for low aromatic content jet fuels have shown significant increase in the last 20 years. This was generated by the growing of aviation. Furthermore, the quality requirements have become more aggravated for jet fuels. This was generated by the more severe environmental regulations and the increasing demand for performance requirements. Nowadays reduced aromatic hydrocarbon fractions are necessary for the production of jet fuels with good burning properties, which contribute to less harmful material emission. The aim of our experimental work was to study the catalytic transformability to jet fuel of coconut oil at different process parameters (temperature, pressure, liquid hourly space velocity, H2/feedstock volume ratio). We carried out the experiments on a metal/support catalyst (T = 280 - 360 °C, LHSV = 1.0 - 3.0 h -1 , P= 30 bar, H2/feedstock volume ratio = 600 Nm 3 /m 3 ). Based on the experimental results in case of the studied feedstock the yield and the properties of the products were favourable at the following process parameter combinations: temperature 360°C, pressure 30 bar, LHSV 1.0 h -1 , volume ratio H2/feedstock volume ratio 600 Nm 3 /m 3 . Based on the quality properties of the product mixtures we determined that we successfully produced products with a high yield (approaching theoretical yield >90 %), that have a reduced aromatic content, their performance properties are excellent. These are excellent jet fuel blending components, what are compatible with current fuel systems and jet fuel blending components, they damage the environment less.

Sooting limits and PAH formation of n-hexadecane and 2,2,4,4,6,8,8-heptamethylnonane in a micro flow reactor with a controlled temperature profile

Sooting limits of n-hexadecane (n-cetane)/air and 2,2,4,4,6,8,8-heptamethylnonane (iso-cetane)/air mixtures were investigated using a micro flow reactor with a controlled temperature profile at equivalence ratios, ϕ, of 1.5–4.5, inlet mean flow velocities, U0, of 10–100cm/s and atmospheric pressure. Result for n-cetane showed wider ϕ and U0 region of the soot formation than that for iso-cetane. Temperature dependence of mole fractions of polycyclic aromatic hydrocarbons (PAHs) were investigated for n-cetane/air and iso-cetane/air mixtures at ϕ=4.0, U0=2.0cm/s and atmospheric pressure by gas sampling and analysis. At all temperature conditions studied, n-cetane showed higher mole fractions of PAHs than iso-cetane. However, iso-cetane showed higher mole fractions of small alkylbenzenes (toluene, xylene isomers, and ethylbenzene) than n-cetane. Numerical simulation showed the opposite tendency, namely, iso-cetane showed higher/lower mole fraction of benzene/toluene than n-cetane. The species measurement showed branched-chain unsaturated species, 2,4,4-trimethyl-1-pentene (TMP1), was observed in the iso-cetane case at low temperature in which the significant formation of PAHs were not observed, but TMP1 was not observed in the n-cetane case. Considering the molecular structures of the two fuels, branched-chain unsaturated radicals would be formed in the iso-cetane case while those would not be formed in the n-cetane case. The branched-chain unsaturated radicals would play an important role for the formation of the small alkylbenzenes. The capabilities of the micro flow reactor to examine the difference in sooting limits and the PAH formation between rich n-cetane/air and iso-cetane/air mixtures were successfully demonstrated.

English

The recovery of an environment polluted by petroleum and allied hydrocarbons through bioremediation is being embraced globally as the best technology of removing hydrocarbon pollutants from environment. Infrared spectral changes and gravimetric analysis from the preliminary biodegradability study carried out on Agbabu Natural Bitumen showed the vulnerability of the bitumen to some bacteria: Pseudomonas putrefaciens, Pseudomonas nigrificans, Bacillus licheniformis, Pseudomonas fragi and Achromobacter aerogenes. This study investigates the ability of P. putrefaciens, P. nigrificans, B. licheniformis, P. fragi and A. aerogenes to degrade the aliphatic and polycyclic aromatic hydrocarbon fractions of Agbabu natural bitumen. Samples of the bitumen were separately inoculated with each of the bacteria for 14 days and the hydrocarbon profiles before and after inoculation were quantified using gas chromatography technique. The total aliphatic hydrocarbon compounds (C11 - C29) in the bitumen degraded by P. putrefaciens and P. nigrificans was slightly higher than that in the undegraded bitumen, while the concentration of compounds (C11 - C29) found in samples of the bitumen degraded by B. licheniformis, P. fragi and A. aerogenes was less than what was contained in the undegraded bitumen. Also the even-odd carbon-ratios of the degraded bitumen were higher than unity while these were less than unity in the undegraded bitumen. The polycyclic aromatic hydrocarbons (PAHs) profile in the bitumen degraded samples also differed from that of undegraded bitumen. A substantial reduction in the concentration of some PAHs was found in the bitumen samples following their degradation by the bacteria strains, typically from 55.98 to 30.79%, thus suggesting the possibility of using the bacteria strains for bioremediation process. &nbsp; Key words: Agbabu, bitumen, bacteria, biodegradability, hydrocarbons. &nbsp

Molecular characterization of sulfur compounds in some specieal sulfur-rich Chinese crude oils by FT-ICR MS

Routine GC/MS analysis may apply to the volatilized Low-Molecular-Weight compounds in saturate and aromatic hydrocarbon fractions; thus, relative studies using this technique inevitably bring about some limitations on distribution of miscellaneous sulfur atom. In this article, Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) with high resolution is employed to investigate the distribution of organic sulfur compounds (OSCs) in the crude oil typically derived from the Eogene carbonate-evaporite sediments with further chemical compositional characterization in molecular level by miscellaneous atomic type, carbon number, and double bond equivalent (DBE). A variety of miscellaneous atomic types with S1, S2, S3, OS, OS2, O2S, O2S2, NS, and NOS etc. (S1 means those OSCs with one sulfur atom in a molecule) were identified in OSCs in these oil samples. High levels of alkyl thioether series compounds with one ring structure were presented mainly in the crude oil in the Jianghan Basin whereas high amounts of benzothiophene, dibenzothiophene etc. compounds with higher values in DBE and carbon number range occurred in the sulfur-rich heavy oil in the Jinxian Sag. Although carbonate-evaporite sediments deposited in the saline lacustrine facies in the Eogene basin both occurred in the Jinxian Sag and Jianghan Basin, obviously, they possess different chemical diagenetic pathway of sulfur under various microbial reactions, leading to diverse distributional characteristics on biomarkers, OSCs, and even different hydrocarbon generation mechanism of immature crude oil.

The petroleum geochemistry of the Termit Basin, Eastern Niger

Sixty crude oils from the Termit Basin (Eastern Niger) were analysed using biomarker distributions and bulk stable carbon isotopic compositions. Comprehensive oil-to-oil correlation indicates that there are two distinct families in the Termit Basin. The majority of the oils are geochemically similar and characterized by low Pr/Ph (pristane to phytane ratios) and high gammacerane/C30 hopane ratios, small amounts of C24 tetracyclic terpanes but abundant C23 tricyclic terpane, and lower δ13C values for saturated and aromatic hydrocarbon fractions. All of these geochemical characteristics indicate possible marine sources with saline and reducing depositional environments. In contrast, oils from well DD-1 have different geochemical features. They are characterized by relatively higher Pr/Ph and lower gammacerane/C30 hopane ratios, higher amounts of C24 tetracyclic terpane but a low content of C23 tricyclic terpane, and relatively higher δ13C values for saturated and aromatic hydrocarbon fractions. These geochemical signatures indicate possible lacustrine sources deposited under freshwater, suboxic-oxic conditions. This oil family also has a unique biomarker signature in that there are large amounts of C30 4α-methylsteranes indicating a freshwater lacustrine depositional environment.The maturity of the Termit oils is assessed using a number of maturity indicators based on biomarkers, alkyl naphthalenes, alkyl phenanthrenes and alkyl dibenzothiophenes. All parameters indicate that all of the oils are generated by source rocks within the main phase of the oil generation stage with equivalent vitrinite reflectance of 0.58%–0.87%.

Study of the biodegradation levels of oils from the Orinoco Oil Belt (Junin area) using different biodegradation scales

This work presents a study of the molecular composition of the saturated and aromatic hydrocarbon fractions of crude oils from the Orinoco Oil Belt (Junín area) in the Eastern Venezuelan Basin, with the purpose of classifying these samples following two distinct biodegradation assessment schemes: the PM scale [Peters, K.E., Moldowan, J.M., 1993. The Biomarker Guide: Interpreting Molecular Fossils in Petroleum and Ancient Sediments. Prentice Hall, Englewood Cliffs, New Jersey, p. 363] and the Manco scale [Larter, S., Huang, H., Adams, J., Bennett, B., Snowdon, L.R., 2012. A practical biodegradation scale for use in reservoir geochemical studies of biodegraded oils. Organic Geochemistry 45, 66–76]. Both scales agree on the presence of different levels of biodegradation for the analyzed oils, although they are based on different groups of compounds. The PM scale uses mainly compounds from the saturated hydrocarbon fractions (e.g., n-alkanes, acyclic isoprenoids, terpanes and steranes) as well as aromatic steroids. On the other hand, the Manco scale considers other compounds (e.g., alkyltoluenes, naphthalene, methylnaphthalene, phenanthrene, alkylphenanthrenes and methyldibenzothiophenes) not included in the PM biodegradation scale. Thus, the combined use of these two scales allows the determination of the level of biodegradation of both saturated and aromatic compound classes. Dibenzothiophene (DBT), which was not included for the Manco score determination, also shows variations in peak intensity when compared to C4-alkylnaphthalenes, presumably associated with the process of biological alteration. The differences in the biodegradation levels observed in the present study may be attributed to variations in parameters that control biodegradation rates laterally across the study area or the existence of varying communities of microorganisms, among other possible factors.

Succession of Hydrocarbon-Degrading Bacteria in the Aftermath of the Deepwater Horizon Oil Spill in the Gulf of Mexico

The Deepwater Horizon oil spill produced large subsurface plumes of dispersed oil and gas in the Gulf of Mexico that stimulated growth of psychrophilic, hydrocarbon degrading bacteria. We tracked succession of plume bacteria before, during and after the 83-day spill to determine the microbial response and biodegradation potential throughout the incident. Dominant bacteria shifted substantially over time and were dependent on relative quantities of different hydrocarbon fractions. Unmitigated flow from the wellhead early in the spill resulted in the highest proportions of n-alkanes and cycloalkanes at depth and corresponded with dominance by Oceanospirillaceae and Pseudomonas. Once partial capture of oil and gas began 43 days into the spill, petroleum hydrocarbons decreased, the fraction of aromatic hydrocarbons increased, and Colwellia, Cycloclasticus, and Pseudoalteromonas increased in dominance. Enrichment of Methylomonas coincided with positive shifts in the δ(13)C values of methane in the plume and indicated significant methane oxidation occurred earlier than previously reported. Anomalous oxygen depressions persisted at plume depths for over six weeks after well shut-in and were likely caused by common marine heterotrophs associated with degradation of high-molecular-weight organic matter, including Methylophaga. Multiple hydrocarbon-degrading bacteria operated simultaneously throughout the spill, but their relative importance was controlled by changes in hydrocarbon supply.