The distribution and significance of dimethyldibenzothiophenes,trimethyldibenzothiophenes and benzo[b]naphthothiophenes in source rock extracts from offshore Niger Delta basin,Nigeria

The distribution of dimethyldibenzothiophenes, trimethyldibenzothiophenes and benzo[b]naphthothiophenes were investigated in rock extracts from Niger Delta, Nigeria, by gas chromatography-mass spectrometry. The dimethyldibenzothiophenes were characterized by the predominance of 4,6-dimethyldibenzothiophene and 3,6-dimethyldibenzothiophene while 2,4,6-trimethyldibenzothiophene was the dominant compound among the trimethyldibenzothiophenes. Among the benzo[b]naphthothiophenes, the abundance of benzo[b]naphtho[2,1-d]thiophene was higher than other isomers. The rock samples were found to have immature to early mature status. The dimethyl- and trimethyldibenzothiophene ratios showed good correlation with 4-/1-methyldibenzothiophen ratio, T_max (°C) and % Ro, indicating their dependency on maturity increase. The distribution and abundance of dimethyldibenzothiophenes and trimethyldibenzothiophenes were found to be effective in determining the thermal maturity of source rock extracts in Niger Delta basin.     

Occurrence and Distribution of Carbazoles and Benzocarbazoles in Tertiary Niger Delta Source Rocks

The distributions of carbazoles and benzocarbazoles in source rocks from the Northern depobelt of the Tertiary Niger Delta, Nigeria, have been investigated by gas chromatography-mass spectrometry (GC-MS). Biomarker compositions of the source rocks indicate that the source rocks were formed from organic matter of mixed origin (terrestrial and marine) and are either immature or at early maturity stage. The carbazoles distributions in the source rocks are dominated by C₀-C₂-carbazoles and strong variation was observed in their distributions with increasing maturity. Among the C₁-carbazoles, 1-methylcarbazole shows a decrease trend at the immature stage and an increase trend at higher maturity levels. 2- and 3-methylcarbazoles display an increasing trend with increasing maturity while 4-methylcarbazole exhibits a decreasing pattern with increasing maturity. Within the C₂-carbazoles isomers, 1,8- and 2,7-dimethylcarbazoles, show an increasing trend with increasing maturity while the partially exposed isomers 1,3- and 1,6-dimethylcarbazoles decrease with increasing maturity. The ratio of benzo[a]carbazole/benzo[a]carbazole +benzo[c]carbazole varies significantly from 0.36 to 0.55 in the entire maturity range, indicating a strong maturity dependence. These results show that maturity will have great effect on the use of carbazoles and benzocarbazoles distributions as oil migration parameter in the Niger Delta.     

Changes in PAHs levels in edible oils during deep-frying process

Changes in the 16 PAHs in rapeseed, soybean, peanut and olive oil during deep-frying were examined to evaluate PAH levels in edible oils and the effects of deep-frying time. Chicken nuggets and potatoes were deep-fried in four types of oil for 15, 30 and 45 min. PAH concentrations were quantified via high-performance liquid chromatography (HPLC). The results show that all four fresh (unused) edible oils contain PAHs (189.9–2754.8 μg/kg) and mainly low-ring (2- to 4-ring) PAHs. PAH concentrations in the edible oils increased with increasing deep-frying time, especially among the high-ring (5-ring and above) PAHs. The mean values of high-ring PAHs (5-ring and above) in the samples deep-fried for 45 min were 1.9-fold higher than the oil samples that were deep-fried for 15 min and 31.5-fold higher than the levels for the fresh oils. The mean concentrations of benzo[a]pyrene in the deep-fried peanut and olive oils were 6.1- and 5.2-fold, respectively, the control value established in China (10 μg/kg). Average levels of ∑4PAH (consisting of benzo[a]anthracene, chrysene, benzo[b]fluoranthene, and benzo[a]pyrene) for the two deep-fried oils also exceeded the maximum permitted limit (10 μg/kg) set by the European Union (9.2- and 6.8-fold higher, respectively). At present, regulations imposed in China limit only concentrations of benzo[a]pyrene. The results of this study show that more standards and regulations on PAHs in edible oils must be established. In addition, the repeated use of edible oils must be avoided.     

Polycyclic aromatic hydrocarbons in vegetable oils from unconventional sources

The levels of 4 compounds from the group of light PAHs listed by the US EPA and 15 PAHs listed by the EU Scientific Committee on Food were determined in selected unconventional oils. PAHs determination was performed by high-pressure liquid chromatography with fluorescent and diode array detectors (HPLC-FLD/DAD). Similar quality profiles of PAHs, with light PAHs being predominant, were stated. Total content of 19 PAHs varied from 23.41 (poppy seed oil) to 234.30 μg/kg (pumpkin seed oil). In most analyzed products, from the group of 15 PAHs benzo[a]anthracene, chrysene, benzo[b]fluoranthene and benzo[k]fluoranthene were detected. Benzo[a]pyrene was detected in amaranth, pumpkin, sesame, blackseed and borage oil, whereas in pumpkin seed oil its concentration was about 8 times higher than the maximum tolerable limit (2 μg/kg) stated in Commission Regulation (EU) No. 835/2011. The sum of benzo[a]pyrene, benzo[a]anthracene, benzo[b]fluoranthene and chrysene, for which the maximum tolerable limit has been set in Commission Regulation (EU) No. 835/2011 at the level of 10 μg/kg, were found in the range from 0.00 (linseed oil) to 35.03 μg/kg (pumpkin seed oil).     

Aromatic sulfur-containing structural units of resins and asphaltenes in heavy hydrocarbon feedstock

The composition of aromatic sulfur compounds of oils formed during the thermolysis (160?C650°C) of resins and asphaltenes from heavy crude of the Permian-Carboniferous deposit in the Usa oilfield (Komi Republic) has been studied. (C₁-C₄)-alkylbenzothiophenes; dibenzothiophene and (C₁-C₃)-alkyl derivatives; and phenanthro[4,5-bcd]-, benzo[b]naphtho-, triphenyleno[1,12-bcd]-, dinaphtho[2,3-b:2??,3??-d]-, perylo[1,12-bcd]-, benzothieno[3,2-b]benzo-, benzo[1,2-b:3,4-b??]bisbenzo-, and phenyldibenzothiophenes have been identified. The tri- and tetracyclic structures with predominance of dibenzothiophene and benzo[b]naphtho[2,1-d]thiophene prevail in the oils obtained by the thermolysis of resins and asphaltenes.     

Oil-source Rock Correlation and Distributions of Pyrrolic Nitrogen Compounds in Oils From the Niger Delta,Nigeria

The occurrence and distributions of carbazole compounds were investigated in crude oils from Niger Delta, Nigeria, by gas chromatography-mass spectrometry-mass spectrometry. Geochemical characterization of the oils and the available source rocks based on saturate and aromatic biomarkers showed that the oils have higher thermal maturity than the source rocks. All the oils are isotopically related and might have originated from the same source rocks. However, subtle maturity differences exist among the oils from the same field. C₂- carbazoles are the dominant components of the crude oils. 4-methylcarbazole is the most abundant of the methylcarbazoles isomers while 1,5-dimethylcarbazole occurs as the most abundant among the dimethylcarbazoles. The abundance of benzocarbazoles are low compared to the alkylcarbazoles. Cross plots of the methylcarbazoles and dimethylcarbazoles against Pr/Ph ratio showed that carbazoles distributions in the oils are not affected by source facies. However, the cross plots of C₁- carbazoles and C₂- carbazoles against the calculated vitrinite reflectance indicated that the carbazoles concentrations increase with increasing maturity.     

母源、沉积环境和成熟度对中性含氮化合物分布的影响

南翼山构造油气藏是目前柴西北区发现的最大油气藏。其深层E23是凝析气藏, 浅层N22是正常密度的油藏, 这种分布格局在柴西北区是唯一的, 对它进行成藏解剖对整个柴西北区的油气勘探具有重要的意义。结合原油轻烃、天然气碳同位素和生物标志化合物综合判识油源, 认为南翼山构造的N22与E23储集层原油来源不同, 深层E23油气来自E23烃源岩, 浅层N22的油来自N1 烃源岩; 南翼山构造的油气是就近捕获的产物, 不是从南边长距离运移而来, 深部凝析气藏的形成受有机质类型和成熟度共同控制。     

Thermodynamic stability of petroleum C<Subscript>15</Subscript> polyalkylated bicyclo[4.4.0]decanes at 500 and 600 K

The thermodynamic equilibrium concentrations of petroleum C₁₅ polymethylated bicyclo[4.4.0]decanes (sesquiterpanes) at 500 and 600 K have been experimentally obtained for the first time via the aluminosilicate-mediated equilibrium isomerization of the saturated 200–300°C fraction of crude oils of different genotypes. It has been found that sesquiterpane isomers with an angular carbon atom and methyl and ethyl substituents in the molecule are the least thermodynamically stable in the equilibrium mixture and their relative concentration increases with increasing temperature from 500 to 600 K; the most stable isomer is 2,3,3,7,7-pentamethylbicyclo[4.4.0]decane.     

Oil maturity assessment using maturity indicators based on methylated dibenzothiophenes

Aromatic fractions of 140 oils and condensates that originated from different types of source rocks(marine shale, terrestrial shale and marine carbonate) were analyzed using gas chromatography–mass spectrometry(GC–MS) to investigate the relative distributions of methylated dibenzothiophenes with respect to thermal maturity. The positions of methyl groups of trimethyldibenzothiophene isomers(TMDBTs) including those used in the definition of maturity indicator TMDBT index in previous studies were firmly identified by co-elution of internal standards in GC–MS analysis and by comparing with reported retention indices. A new maturity ratio related to dimethyldibenzothiophenes(DMDBTs) is proposed on the basis of the differences in thermodynamic stability among different DMDBT isomers. Another maturity index(TMDBT-I2) based on TMDBTs is also suggested on the basis of our empirical observations and presumed thermodynamic stability of TMDBT isomers. These two newly proposed(2,6 + 3,6)-/1,4-DMDBT ratio and TMDBT-I2 correlate well with MDR(4-/1-methyldibenzothiophene) and 2,4-/1,4-DMDBT ratios, suggesting their common chemical reaction mechanisms and similar behavior with increasing maturity. Therefore, they can be effectively applied for maturity assessments. Furthermore, the TMDBTs related maturity parameters are more reliable for over-mature oils and condensates due to the relatively higher concentrations of thermodynamically unstable TMDBT isomers, i.e. 1,4,6-, 1,4,8- and 3,4,6-TMDBT in this study than those of 1-methyldibenzothiophene(1-MDBT) or 1,4-DMDBT. In contrast with 4,6-/1,4-DMDBT, the newly proposed(2,6 + 3,6)-/1,4-DMDBT ratios for oils that originated from different types of source rocks have approximately same relationship with the oil maturity(Rc %). This suggests that the lithology and organic facies may have relatively less influence on(2,6 + 3,6)-/1,4-DMDBT ratio compared to 4,6-/1,4-DMDBT. The maturity parameters based on methylated dibenzothiophenes are particularly useful in the maturity assessments of post- and over-mature oils and condensates and can complement maturity indicators based on steranes and terpanes.     

Polycyclic aromatic hydrocarbons (PAHs) in yerba maté (Ilex paraguariensis St. Hil) traditional infusions (mate and tereré)

This study describes the occurrence of polycyclic aromatic hydrocarbons (PAHs) in traditional yerba maté hot and cold infusions (mate and tereré), by monitoring the content of benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[ah]anthracene, benzo[ghi]perylene and indeno[1,2,3-cd]pyrene (PAH8), that have been chosen as indicators for the occurrence and toxicity of PAHs in food by the European Food Safety Agency. PAH8 content in mate and tereré was determined by high performance liquid chromatography using fluorescence detection (HPLC-FLD).PAH8 contents in hot and cold maté infusions ranged from 371.2 to 2438.8 ng/L and from 19.2 to 937.3 ng/L, respectively. Benzo[a]pyrene contents varied between 37.0 and 373.9 ng/L in hot yerba maté infusions and between 7.0 and 92.1 ng/L in cold yerba maté infusions. None of the samples analyzed exceeded the World Health Organization criteria for drinking water, since the maximum level allowed for benzo[a]pyrene is 700 ng/L.     

利用咔唑类化合物研究油气的运移——以塔里木盆地环阿瓦提凹陷志留系古油藏为例

咔唑类化合物是原油中极性较大的化合物,是研究油气运移的有效指标.在油气运移过程中,咔唑类与围岩发生作用而被吸附;苯并咔唑比苯并咔唑运移速度快;C₃-咔唑的极性相对于C₂-咔唑的较小而运移较快.因此,随运移距离增大,原油中的咔唑类化合物的含量将不断减少,苯并咔唑/苯并咔唑比值增大,C₂-咔唑/C₃-咔唑比值变小.塔里木盆地的第二期油气成藏发生在海西晚期,阿瓦提凹陷在海西期不断沉降,为塔里木盆地主要的生油凹陷,寒武系—下奥陶统源岩此时处于大量排烃期,根据上述几项含氮化合物指标的研究可知,排出的油气从生烃中心向四周呈辐射状运移,在构造高部位聚集成藏,晚海西期运动时被抬升至地表形成现今广泛分布的干沥青.      

Geochemical characterization of aromatic hydrocarbons in crude oils from the Tarim,Qaidam and Turpan Basins, NW China

Based on the systematic study of aromatic hydrocarbons in over 100 crude oil samples collected from the Tabei and Tazhong uplifts in the Tarim Basin, the western depression area in the Qaidam Basin and the Tabei depression in the Turpan Basin, the geochemical characteristics of the marine (Tarim Basin), saline lacustrine (Qaidam Basin), and swamp (Turpan Basin) oils were investigated. The marine oils from the Tarim basin are characterized by relatively low abundance of diaromatic hydrocarbons such as biphenyl and naphthalene, and relatively high abundance of triaromatic hydrocarbons including phenanthrene, dibenzothiophene and fluorene. In contrast, the swamp oils from the Turpan Basin are dominated by the highest relative abundance of diaromatic hydrocarbons and the lowest relative abundance of triaromatic hydrocarbons in all the oil samples in this study. The relative abundance of diaromatic and triaromatic hydrocarbons in the saline lacustrine oils from Qaidam Basin is between that in Tarim oils and Turpan oils. Aromatic parameters based on the isomer distributions of dimethylnaphthalenes (DMN), trimethylnaphthalenes (TMN), tetramethylnaphthalenes (TeMN) and methylphenanthrenes (MP), i.e., 1,2,5-trimethylnaphthalene(TMN)/1,3,6-TMN ratio, 1,2,7-TMN/1,3,7- TMN ratio, (2,6- +2,7-)-dimethylnaphthalenes (DMN)/1,6-DMN ratio, 1,3,7-TMN/(1,2,5- +1,3,7-)-TMN, 1,3,6,7-TeMN/(1,3,6,7- +1,2,5,6- +1,2,3,5-)-TeMN ratio and MP index, may reflect the diversity of organic source input, thermal maturity and depositional environments. In addition, the dibenzothiophenes (DBTs)/fluorenes(Fs) and dibenzofurans (DBFs)/Fs ratios were found to the very useful and effective in determining genetic types of crude oils for the marine, saline lacustrine, and swamp depositional environments, and for oil-oil correlations.     

Geochemical characterization of aromatic hydrocarbons in crude oils from the Tarim,Qaidam and Turpan Basins,NW China

Based on the systematic study of aromatic hydrocarbons in over 100 crude oil samples collected from the Tabei and Tazhong uplifts in the Tarim Basin, the western depression area in the Qaidam Basin and the Tabei depression in the Turpan Basin, the geochemical characteristics of the marine (Tarim Basin), saline lacustrine (Qaidam Basin), and swamp (Turpan Basin) oils were investigated. The marine oils from the Tarim basin are characterized by relatively low abundance of diaromatic hydrocarbons such as biphenyl and naphthalene, and relatively high abundance of triaromatic hydrocarbons including phenanthrene, dibenzothiophene and fluorene. In contrast, the swamp oils from the Turpan Basin are dominated by the highest relative abundance of diaromatic hydrocarbons and the lowest relative abundance of triaromatic hydrocarbons in all the oil samples in this study. The relative abundance of diaromatic and triaromatic hydrocarbons in the saline lacustrine oils from Qaidam Basin is between that in Tarim oils and Turpan oils. Aromatic parameters based on the isomer distributions of dimethylnaphthalenes (DMN), trimethylnaphthalenes (TMN), tetramethylnaphthalenes (TeMN) and methylphenanthrenes (MP), i.e., 1,2,5-trimethylnaphthalene(TMN)/1,3,6-TMN ratio, 1,2,7-TMN/1,3,7-TMN ratio, (2,6-+2,7-)-dimethylnaphthalenes (DMN)/1,6-DMN ratio, 1,3,7-TMN/(1,2,5- +1,3,7-)-TMN, 1,3,6,7-TeMN/(1,3,6,7- +1,2,5,6- +1,2,3,5-)-TeMN ratio and MP index, may reflect the diversity of organic source input, thermal maturity and depositional environments. In addition, the dibenzothiophenes (DBTs)/fluorenes(Fs) and dibenzofurans (DBFs)/Fs ratios were found to the very useful and effective in determining genetic types of crude oils for the marine, saline lacustrine, and swamp depositional environments, and for oil-oil correlations.     

Distribution and geochemical significance of phenylphenanthrenes and their isomers in selected oils and rock extracts from the Tarim Basin,NW China

Twenty-two oil samples and eight source rock samples collected from the Tarim Basin,NW China were geochemically analyzed to investigate the occurrence and distribution of phenylphenanthrene(PhP),phenylanthracene(PhA),and binaphthyl(BiN) isomers and methylphenanthrene(MP) isomers in oils and rock extracts with different depositional environments.Phenylphenanthrenes are present in significant abundance in Mesozoic lacustrine mudstones and related oils.The relative concentrations of PhPs are quite low or below detection limit by routine gas chromatography-mass spectrometry(GC-MS) in Ordovician oils derived from marine carbonates.The ratio of 3-PhP/3-MP was used in this study to describe the relative abundance of phenylphenanthrenes to their alkylated counterparts-methylphenanthrenes.The Ordovician oils in the Tabei Uplifthave quite low 3-PhP/3-MP ratios(0.10),indicating their marine carbonate origin,associating with low Pr/Ph ratios(pristane/phytane),high ADBT/ADBF values(relative abundance of alkylated dibenzothiophenes to alkylated dibenzofurans),low C_(30) diahopane/C_(30)hopane ratios,and low Ts/(Ts+Tm)(18α-22,29,30-trisnorneohopane/(18α-22,29,30-trisnorneohopane+17α-22,29,30-trisnorhopane)) values.In contrast,the oils from Mesozoic and Paleogene sandstone reservoirs and related Mesozoic lacustrine mudstones have relatively higher 3-PhP/3-MP ratios(0.10),associating with high Pr/Pli,low ADBT/ADBF.high Ts/(Ts + Tm).and C_(30) diahopane/C_(30) hopane ratios.Therefore,the occuirence of significant amounts of phenylphenanthreiies in oils typically indicates that the organic matter of the source rocks was deposited in a suboxic environment with mudstone deposition.The phenylphenanthreiies may be effective molecular markers,indicating depositional environment and lithology of source rocks.     

Application of solid phase extraction and two-dimensional gas chromatography coupled with time-of-flight mass spectrometry for fast analysis of polycyclic aromatic hydrocarbons in vegetable oils

A fast and simple solid-phase extraction (SPE) method followed by comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC–TOFMS) has been developed for analysis of 15 + 1 carcinogenic polycyclic aromatic hydrocarbons (PAHs) in vegetable oils. Of three critically assessed sample preparation approaches – (i) gel permeation chromatography (GPC), (ii) GPC followed by silica based SPE, and (iii) SPE employing PAHs-dedicated molecularly imprinted polymers (MIPs), the latter one was selected as the best option. Recoveries of the overall analytical procedure ranged from 70 to 99%, with repeatabilities in the range of 2–11%. Limits of quantitation (LOQs) ranging for individual PAHs from 0.1 to 0.3 μg kg⁻¹, were fairly below the maximum level 2 μg kg⁻¹ established for the PAHs representative, benzo[a]pyrene (BaP), by EU Legislation for this commodity. Within the mini-survey in which the new method was employed for examination of 35 samples of various kinds of vegetable oils collected at the Czech market, the highest PAH4 levels, i.e. the sum of BaP, benz[a]anthracene (BaA), benzo[b]fluoranthene (BbFA) and chrysene (CHR) were found in sea buckthorn (708 μg kg⁻¹) followed by rapeseed oil (99.8 μg kg⁻¹). Altogether 8 samples from 35 examined vegetable oils exceeded the maximum limit 2 μg kg⁻¹ for BaP and 10 samples exceeded 10 μg kg⁻¹ set for PAH4 which is fixed by Commission Regulation (EU) no 835/2011 for oils.     

Oil charging history and pathways of the Ordovician carbonate reservoir in the Tuoputai region, Tarim Basin, NW China

Geochemical analysis of 64 oils sampled from an Ordovician carbonate reservoir in the Tuoputai region was undertaken to study the composition of molecular markers. All the oils have similar geochemical characteristics and belong to a single oil family. They are presumed to derive from the same source kitchen and have similar oil charging history. A histogram of homogenization temperatures(Th) of aqueous inclusions in reservoir rocks shows a bimodal distribution pattern, indicating that the Ordovician reservoir has been charged twice. Coupling the measured Th(°C) with the burial and geothermal histories reconstructed using 1D basin modeling, we relate the homogenization temperature to the relevant geological ages: i.e.,425–412 and 9–4 Ma, corresponding to the Middle to Late Silurian and the Miocene to Pliocene, respectively. The oil filling orientation and pathways are traced using molecular indicators related to alkyldibenzothiophenes and benzo[b]naphthothiophenes. The oil charging orientation is from south to north generally. It can be predicted that the Ordovician reservoirs were sourced from a kitchen located to the south of the Tuoputai region, most probably between the Awati and Manjiaer Depressions. Traps located in the southern side of the Tuoputai region, along the oil charging pathways, should therefore be preferred oil exploration targets.     

ORIGIN OF CRUDE OILS IN OMAN

The petroleum geochemistry of Oman provides a picture of considerable variey, since crude oils and their source rocks are found both throughout the country and throughout the stratigraphic column from the Infra-Cambrian to the Tertiary. This paper reviews the geological history history of the area and places the petroleum geochemistry within the geological context. The oils can be geochemically classified into five groups. Three groups can be related to god oil source rocks found in the pre-Cambrian Huqf Group, the Silurian Safiq and the Cretaceous Natin Formation. Another group of oils probably originates from the Upper Jurassic Diyab Formations, while the fifth group of crudes (named ‘Q’) cannot be correlated to a known source rock, but is inferred to have originated from an unsampled Huqf level. The “Huqf oils” are those that have been correlated to known Infra-Cambrian Huaf source rocks, and are characterized by a strong C₂₉ sterane predonominance and very light carbon isotope values of around-36.0%. In contrast, the ‘Q’ crudes, drived from the unknown source are characterized by a C₂₇ strerane predominance and carbon istope ratios of around -30.5%. Both the Huaf and ‘Q’ crudes also contain a series of characteristic compounds referred to as the ‘X’ compounds (all isomers of methyle and dimethyl alkanes). Oils reasoned to originate from Silurian Safiq source rocks have a week C₂₉ sterane precominance, a significant content of rearranged steranes and carbon isotope ratios of -30.5%. The oils thought to originate from the Jurassic Diyab Formation have a similar sterane distribution but heavier carbon isotope values of around -26.5%. Finally, the crude oils from the mid-Cretaceous Naith Formation source rocks are characteirzed by steranes with an equivalent distribution of C₂₇, C₂₈ and C₂₉ isomers, and carbon isotope values of around -26.9%. These variations in biomarker distributions and carbon isotope values are sufficiently distinct to ensure a high degree of certainty in the grouping of the crude oils.     

Applications of Polycyclic Aromatic Hydrocarbons to Assess the Source and Thermal Maturity of the Crude Oils from the Lower Indus Basin,Pakistan

Abstract

A suite of six crude oils from Lower Indus Basin, Pakistan, were analyzed for geochemical characterization of source organic matter (OM) and thermal maturity. Distribution of polycyclic aromatic hydrocarbons (PAHs), alkylnaphthalenes, alkylphenanthrenes, alkyldibenzothiophenes, and aromatic biomarkers were reported from aromatic fractions of the crude oils. The aromatic hydrocarbons parameters revealed a higher thermal maturity of OM of source rock-generated Lower Indus Basin oils. Calculated vitrinite reflectance values from the methylphenanthrenes index 1 (MPI-1) and methyldibenzothiophene ratio (MDR) indicate that most of the oils reached a late oil generation window of thermal maturity. PAH distributions revealed the oils of two different origins are present in the Lower Indus Basin; two oil samples indicate aquatic source of OM and the aromatic biomarker distributions of retene, 1-MP, and 1,7-DMP indicate a significant contribution of land plant OM in the other four oils. This is the first study to report the distribution of aromatic hydrocarbons from Lower Indus Basin crude oils.     

Polycyclic aromatic hydrocarbons in canola,sunflower and corn oils and estimated daily intake

Polycyclic aromatic hydrocarbons (PAHs) are compounds formed during incomplete combustion of organic matter; some are considered to be potentially carcinogenic. The drying step of the seeds or grains is considered the main source of contamination of vegetable oils. Presence of 13 PAHs was evaluated in canola, sunflower and corn oils from the Brazilian market by HPLC-FLD. PAHs were present in 69 of the 70 samples. Levels of summed 13 PAHs varied from not detected to 31.70 μg/kg for canola oil, 0.65 to 17.88 μg/kg for sunflower and 2.61 to 38.23 for corn. There were statistical differences between different types of oil, brands batches. Levels of benzo[a]pyrene and PAH4 were not in accordance with maximum limit established by European regulation in 36 and 33 samples, respectively. Estimated daily intakes were from 7 ng/kg bw/day for to 15.1 ng/kg bw/day. Any action to reduce and/or control their presence in this type of products should be encouraged.     

Sulfur compounds in crude oils of the Jurassic-Paleozoic play in Western Siberia

The composition and structure of sulfur compounds in low-, medium-, and high-sulfur crude oils from the Jurassic-Paleozoic play of Western Siberia have been studied. It has been shown that the distribution of organic sulfur compounds in the oils is determined by the depositional environment of source organic matter. Highly alkylated dibenzothiophenes (up to 15 carbon atoms in the aliphatic chain), naphthobenzothiophene isomers and their C₁ and C₂ homologues, and the α-n-alkylthiolane and α-n-alkylthiane homologous series have been identified for the first time among sulfur compounds of Western Siberia crude oils.