Potential Hydrocarbon Source Research Articles

Meso-Neoproterozoic petroleum systems of the Eastern Siberian sedimentary basins

The elements of the petroleum systems of the Siberian platform have been formed in the course of geological evolution in Meso- and Neoproterozoic time and correspond to the supercontinent stage from assembly of Paleo-Mesoproterozoic Columbia to break-up of Neoproteorzoic Rodinia. Several large sedimentary basins were established within the Siberian craton during the Riphean. A number of passive continental margin basins (the Turukhansk, Cis-Patom basins and others) developed on the southern, western, and, probably, northern craton peripheries. Several other basins, such as the Irkineeva-Vanavara, Kotuy, Anabar-Kureika, and Udzha basins, were entirely intracratonic. The structural patterns of these basins and their petroleum systems were essentially affected by Baikalian orogeny events with intensive dislocations and erosion of Riphean series, especially along the margins of the continent. As a result, hydrocarbon accumulations formed by the source rocks, which have realized their potential in Riphean within the margin basins, were, most likely, completely destroyed. Vendian and Lower Cambrian deposits were the main source for present day oil fields of the central and northern parts of the Nepa-Botuoba Anteclise and the Turukhansk Uplift. The Upper Riphean source rocks of the intracratonic basins, on the contrary, are unlikely to be affected by the significant pre-Vendian erosion and, thus, could be a source for the oil fields of the Yurubchen-Tokhomo Zone and the Katanga Saddle. Such difference in petroleum system evolution for different basins is also supported by results of oil–source rock correlations based on biomarker studies.A new mega-cycle of formation of the sedimentary cover started on the Siberian platform in the Vendian (Ediacaran). The initial fabric of all the main structural elements of the platform was established at this time. The large Vendian depressions (the “prototypes” of Paleozoic Kureika and Cis-Sayan-Yenisei syneclises and Cis-Patom Trough) were areas of mainly marine sedimentation where the high potential hydrocarbon source series could be deposited. Large elevated areas served as a terrigenous provenance in the Early Vendian resulting in a large amount of clastic material deposited along their flanks. The most promising areas for new discoveries of hydrocarbon fields are in the slopes of the Baikit, Nepa-Botuoba and Anabar anticlises faced towards the Kureika Syneclise.

Temporal patterns and potential sources of polycyclic aromatic hydrocarbons in xylem of Pinus kwangtungensis

The temporal patterns and the possible sources of polycyclic aromatic hydrocarbons (PAHs) in the xylem formed from 1883 to 2007 of Kwangtung pine (Pinus kwangtungensis), growing in the Nanling Mountains of Southern China, were detected whether dendrochemistry was sufficient to monitor historical changes in regional airborne PAHs. The total concentrations of 17 PAHs (ΣPAHs) distributed in the xylem of P. kwangtungensis did not progressively increase over time. Temporal patterns of high molecular weight PAHs (HMW–PAHs) coincided to a certain extent with the historical–socioeconomic changes in China. Based on the compositional analysis, PAHs absorbed by and accumulated in the xylem of P. kwangtungensis in the Nanling Mountains might be of pyrogenic origin. Although the possible sources of xylem PAHs were diverse over the studied period, principal component analysis could not convincingly distinguish the main contributors to xylem PAHs. Using only xylem of P. kwangtungensis was not adequate for retrospective monitoring of airborne PAHs in the atmosphere of the Nanling Mountains. Sampling other trees along a gradient and combining other meteorological and socioeconomic index data might provide more reliable information on historical changes in regional airborne PAHs.

Potential source apportionment of polycyclic aromatic hydrocarbons in surface sediments from the middle and lower reaches of the Yellow River, China.

In this work, principal component analysis/multiple linear regression (PCA/MLR), positive matrix factorization (PMF), and UNMIX model were employed to apportion potential sources of polycyclic aromatic hydrocarbons (PAHs) in surface sediments from middle and lower reaches of the Yellow River, based on the measured PAHs concentrations in sediments collected from 22 sites in November 2005. The results suggested that pyrogenic sources were major sources of PAHs. Further analysis indicated that source contributions of PAHs compared well among PCA/MLR, PMF, and UNMIX. Vehicles contributed 25.1-36.7 %, coal 34.0-41.6 %, and biomass burning and coke oven 29.2-33.2 % of the total PAHs, respectively. Coal combustion and traffic-related pollution contributed approximately 70 % of anthropogenic PAHs to sediments, which demonstrated that energy consumption was a predominant factor of PAH pollution in middle and lower reaches of the Yellow River. In addition, the distributions of contribution for each identified source category were studied, which showed similar distributed patterns for each source category among the sampling sites.

Sedimentological and geochemical characterization of the Cretaceous strata of Calabar Flank, southeastern Nigeria

An integrated sedimentological and geochemical evaluation has been carried out on the Cretaceous sediments of the Calabar Flank. This study is to characterize the provenance, depositional environments and hydrocarbon potentials.The techniques involved field descriptions, textural parameters, petrographic analysis and biostratigraphic studies using standard sedimentological methods. The geochemical studies involved the determination of major oxides and trace elements using Inductively Coupled Plasma–Mass Spectrometry (ICP–MS); Total Organic Carbon (TOC) and Rock Eval Pyrolysis.Results show that sandstone from Awi Formation have elongation ratio ranging from 0.4b to 0.9, oblate–prolate index and maximum sphericity index range from 9.6 to 9.7 and 0.5 to 0.9 respectively. The sandstone units are arkosic and mineralogically immature (MI=3); ZTR indexes range from 54.6% to 82.5%, with tourmaline, zircon, staurolite, garnet, apatite, augite and rutile grains being angular-sub-angular. This suggests nearness to source, and that Awi Formation was deposited in a fluvial environment. The limestone deposit of Mfamosing Formation is predominantly bioclastic consisting of algal stromatolites, oolitic and pelloidal grainstones/packstones with high carbonate content. The dark grey fissile shales of Nkporo and Ekenkpon Formations indicate deposition in quiet oxic and/or anoxic conditions. Average TOC suggests good source rocks. Predominance of Type III kerogen, Tmax and hydrocarbon source potential of Mfamosing, Ekenkpon, New Netim Marl and Nkporo Formations suggest marginal mature to mature source rocks deposited in shallow continental to open marine setting that some gas may have been generated. The sediments are derived from passive continental margin in plutonic humid palaeoclimatic setting of continental block province.

Pyrolysis of oil sludge with calcium-containing additive

The focus of recent research is the utilization of oil sludge as a potential source of hydrocarbons via pyrolysis with the presence of calcium oxide as an additive. Pyrolysis of oil sludge was studied by thermogravimetry and in a laboratory-scale reactor. Results obtained by both methods are consistent. Formation of char, common for slow pyrolysis was very limited. A possible explanation could be in the reaction of calcium sulfate with char which leads to the consumption of carbon and formation of CaS. Oil sludge produced a large amount of oil rich on aliphatic compounds with a higher calorific value of about 42MJkg−1 and low sulfur content. A large increase in polyaromatic hydrocarbons during the pyrolysis was observed. Precursors of polyaromatic hydrocarbons were identified in the gas phase.

Higher plant biomarker signatures of Early Eocene sediments of North Eastern India

The biomarkers, molecular fossils of paleobiota, have been studied in detail from a coal-bearing sequence of Early Eocene Lakadong sandstone member of Sylhet Formation of Upper Assam Basin, NE India, using gas chromatography–mass spectrometry. Corresponding hydrocarbon source potential of the same unit has been studied using Rock-Eval pyrolysis. The Rock-Eval data suggest dominant terrestrial land plant contribution, i.e., Type III kerogen and the sediments of the section had entered the early stage of catagenesis. The alkane and isoprenoid distributions are characterized by odd over even preference (OEP) (1.1–1.2) of n-alkanes and high pristane/phytane ratio (2.9–7.6) which corroborate the Rock-Eval data. The distribution of aliphatic biomarkers is characterized by dominance of C24 tetracyclics over C23 tricyclics, high concentration of des-E hopane, moderate to high C29/C30 hopane ratio, extremely low oleanane index and low C35 homohopane index. The extremely low oleanane index is correlated with a high degree of aromatization of oleanane skeleton, favoured by acidic swampy depositional environment. The presence of diterpanes at the base of the Early Eocene section indicates contribution from gymnosperms (Coniferales order of land plants) whereas angiospermous biomarkers with oleanoid skeleton are also preserved. This pattern subsequently evolved to angiosperm dominated towards the top of the section with no gymnosperm signature indicating possible climatic variation during the Early Eocene. Towards the top of the section presence of bicadinanes indicates contribution of Dipterocarpaceae family of trees and advent of the evergreen tropical rain forest element in eastern India in Early Eocene, similar to the pattern found in western India, e.g., Cambay and Kutch basins.

Hydrocarbon Source Potential and Depositional Environment of the Surma Group Shales of Bengal Basin, Bangladesh

Abstract: Surma Group is the most important geological unit of Bengal basin, Bangladesh, because petroleum resources occur within this group. It is mainly composed of alternation of shale and sandstone and the shale fraction has long been considered as source rocks and the sandstone fraction as reservoir. These source and reservoir rocks have been studied by different authors by different approach but none of them adopted organic geochemistry and organic petrology as a means of study of source rock and their possible depositional environment. A total of thirty shale core samples have been collected from eight different gas fields to fulfill the short coming. The collected samples have been subjected to Source Rock Analysis (SRA) and/or Rock-Eval (RE) followed by pyrolysis gas chromatography (PyGC), gas chromatography mass spectrometry (GCMS), elemental analysis (EA) and organic petrological study such as vitrinite reflectance measurement and maceral analysis. The analyzed organic matter extracted from the shales of Surma Group consists mainly of Type III along with some Type II kerogen. The studied shales are mostly organically lean (TOC ±1%) and the extracted organic matter is fair to moderate. Based on these results, the analyzed shales have been ranked as poor (mostly) to fair quality source rock. The organic matter of the analyzed shale samples is thermally immature to early mature for hydrocarbon generation considering their Tmax and measured mean vitrinite reflectance values. The hopane 22S/(22S + 22R), moretane/hopane ratio and sterane parameters are also in good agreement with these thermal maturity assessments. The predominance of odd carbons over even carbons (most common) and/or even carbons over odd carbon numbered n-alkanes, moderate Pr/Ph ratio, low to high Tm/Ts ratio, comparative abundance of sterane C29 (i.e., C29 >C27>C28), Pr/nC17 - Ph/nC18 values, C/S ratio and dominance of vitrinite macerals group with the presence of liptinite macerals demonstrate that the organic matter has derived mainly from terrestrial inputs with an insignificant contribution from the marine sources. The condition of deposition alternates from oxic to anoxic.

Depositional Controls On Mudstone Lithofacies In A Basinal Setting: Implications for the Delivery of Sedimentary Organic Matter

Deep-water mudstones from ancient epicontinental settings are significant repositories for organic matter, but the detailed temporal variations of, and controls on, the abundance and type of organic matter (OM) is little studied. Using micro-petrographic and geochemical data from late Mississippian mudstones of the Widmerpool Gulf, UK, the processes that delivered fine-grained sediment to this basin during a glacioeustatic sea-level cycle are interpreted from detailed lithofacies analysis. Seven primary lithofacies are identified from core, which show specific and systematic variations in total organic carbon (TOC) content and bulk carbon isotope composition of organic material (δ13Corg). During sea-level highstands, thin-bedded carbonate-bearing mudstones are the dominant facies deposited, contain up to 6.6% TOC (average 4.6 ± 1.3%), and have mean δ13Corg of −28.5 ± 0.9‰. During phases of lower sea level, thin-bedded silt-bearing clay-rich mudstones with up to 4.1% TOC (average 2.3 ± 0.8%; mean δ13Corg: −28.2 ± 1.0‰) were interbedded with more organic-lean graded silt-bearing mudstones and sand-bearing silt-rich mudstones (average TOC: 1.7 ± 0.6%) derived from turbidity currents. The latter (mean δ13Corg: −26.2 ± 0.7‰) are closely linked to significant proportions of terrestrial plant material, while some rare plant debris- and sand-bearing mudstones produced from debris flows have more than 7.0% TOC and δ13Corg ≥ −26.0‰. The δ13C values of wood fragments ranged from −27.1‰ to −24.0‰ and therefore the δ13Corg is interpreted as a function of the ratio of marine and terrestrial organic matter. More negative values in the carbonate-bearing and the clay-rich mudstones indicate marine planktonic algae whereas the least negative values reflect greater contribution of terrestrial plant material. The data suggest that the marine conditions prevailed and supported marine planktonic algae throughout different sea-level stages. Marine OM was delivered to the sea floor by continuous hemipelagic settling whereas terrestrial OM was delivered by sediment density flows. Variations in bioproductivity and dilution by siliciclastics influenced the burial rate of marine OM. Organic-rich mudstones preserved in these marine basins are potential hydrocarbon source rocks, especially as unconventional (shale gas) reservoirs. Detailed microtextural and compositional analysis coupled with rigorous geochemical parameters as used in this study are important for the understanding of the source-rock potential of basinal mudstones, and of fine-grained organic-rich sediments in general.

Producing hydrocarbons by the underground gasification of coal

The composition and yield of the products obtained in the underground gasification of coal at Podzemgaz South Abinsk Station are studied. Data are also presented regarding the rectification and hydrocracking of the products. The underground gasification of coal may be regarded as a potential source of phenolic hydrocarbons, naphthalene, pyridine bases, raw materials for the production of carbon black, and hydroaromatic solvents.

Hydrocarbon source potential of the Jurassic sediments of Salam-3X borehole, Khalda Concession, Northern Western Desert, Egypt

A total of 51 samples, collected from the Jurassic sediments (Ras Qattara, Yakout, Khatatba, Masajid, and Alam El Bueib (member 6) formations) of Salam-3X well, were subjected to organic geochemical analysis. Of the samples, nine have been subjected to palynofacies investigation. Based on the sedimentary organic matter, these sediments show only one palynofacies type, indicating the presence of gas- and oil-prone source rocks and reflecting deposition under marginal dysoxic–anoxic to shelf-to-basin transition conditions. The total organic content of the samples analyzed is characterized by a wide range of content, including fair, good, very good, and excellent. The organic matter quality of these samples is concentrated around types III (gas prone), III–II (gas and oil prone), and II (oil prone), reflecting gas- and oil-prone sediments, with a tendency to generate gas rather than oil; the result matches with the palynological analysis data. The temperature of maximum pyrolytic hydrocarbon generation of analyzed samples are ranging between 440 and 457 °C, reflecting thermally mature organic matter.

Basin seismic stratigraphy and aspects of prospectivity in the NE Baffin Bay, Northwest Greenland

Subsurface mapping in the northeastern part of Baffin Bay, offshore Northwest Greenland indicates the presence of large basement structures and sedimentary basins. We identify eight seismic-stratigraphic units that can be genetically related to the regional geology and tectonic development. The seismic interpretation includes the top of Paleocene to Eocene volcanic rocks, which cover most parts of the southern and western study area. Using this horizon as a time marker, the seismic units are divided into pre-Cenozoic and Palaeogene to Neogene strata based on comparison to equivalent units exposed onshore West Greenland and Canada and sampled by exploration wells farther south in the Disko West/offshore Nuuk region. Our interpretation of the faults and tectonic elements suggest that the main extensional faults and basin formation took place mainly during the Cretaceous and into the Paleocene. Subsequent compressional tectonics and inversion were accompanied by strike-slip faulting and local transtensional faults and flexures. This last phase of deformation corresponds to the well documented Eurekan Orogeny in Ellesmere Island and northern Greenland that developed as a result of northward motion and possible counterclockwise rotation of Greenland relative to the North American plate. We surmise that these tectonic phases exerted a strong control on basin infill by activation of hinterland sediment sources during Cretaceous and Palaeogene times. The deep basins may include Cretaceous and Palaeogene organic-rich sediments with hydrocarbon source potential. We estimate that maturation could have started during the Eocene.

Laboratory Simulations of Abiotic Hydrocarbon Formation in Earth's Deep Subsurface

In recent years, methane and other light hydrocarbons with an apparently abiotic origin have been identified in an increasing number of geologic fluids on Earth. These compounds have been found in a variety of geologic settings, including seafloor hydrothermal systems, fracture networks in crystalline rocks from continental and oceanic crust, volcanic gases, and gas seeps from serpentinized rocks (e.g., Abrajano et al. 1990; Kelley 1996; Sherwood Lollar 2002, 2008; Fiebig et al. 2007, 2009; Proskurowski et al. 2008; Taran et al. 2010b). Understanding the origin of these compounds has significant implications for range of topics that includes the global carbon cycle, the distribution of life in the deep subsurface (Gold 1992), and the origin of life (Martin et al. 2008). There are even claims that abiotic sources are major contributors to global hydrocarbon reservoirs (Gold 1993; Glasby 2006; Kutcherov and Krayushkin 2010; Sephton and Hazen 2013). While most experts are highly skeptical of such broad claims, it seems possible that at least some petroleum and gas reservoirs could contain hydrocarbons with an abiotic origin. Conceptually, there are two potential major sources of abiotic hydrocarbons to fluids in Earth’s crust. First, abiotic hydrocarbons could migrate to the crust from deeper sources within Earth, through processes such as convective transport, grain boundary diffusion, or release of magmatic volatiles. Second, abiotic hydrocarbons could form in situ within the crust through reduction of inorganic carbon sources. Potential substrates for carbon reduction include CO2 and CO in circulating fluids, and carbon-bearing solids such as carbonate minerals and graphite. In either case, the ultimate source of the inorganic carbon may be primordial (i.e., from the mantle) or recycled from Earth’s surface. This paper summarizes some of the recent laboratory experimental studies conducted to investigate potential …

Stable isotopes of organics and inorganics, clay mineralogy and chemical environment of an Aptian lacustrine succession in northeastern Brazil

Abstract The studied Aptian lacustrine succession of the continental Jatobá Rift Basin varies mainly between pure carbonates (predominantly laminated limestones), marls and shales, with some intercalations of presumably deltaic sandstone complexes. In accordance with geochemical data, the occurrence of dolomite indicates intensive microbial activity in a stratified water column with slightly enhanced salinity. Petrographic data prove mild weathering conditions. Aggregates of authigenic smectite observed in sandstones, probably representing transformed volcanogenic glass particles, strongly indicate explosive volcanic activity. Occasionally occurring dolomite seems to have been formed due to intensive microbial activity under moderately increased salinity conditions. Potential hydrocarbon source rocks containing Type I organic matter (OM) were deposited during various phases of the Aptian. Enhanced biological productivity is indicated by bulk organic geochemical data (C org , hydrogen index, extraction yield) and δ 13 C values of carbonates within peletoidal and laminated limestone layers. Carbon-isotope ratios of carbonates argue for OM cycling and remineralization. High δ 18 O values of carbonates are attributed to periods of lower lake levels. A major contribution of aquatic organisms (green algae, microalgae, zooplankton) and minor input from macrophytes and land plants to OM accumulation is indicated by n -alkane distributions, steroid composition and δ 13 C values of individual biomarkers. Microbial communities included heterotrophic bacteria and cyanobacteria, as well as purple and green sulphur bacteria. The sediments were deposited in an alkaline palaeolake. Highly reducing (saline) bottom water conditions and a stratified water column existed during OM accumulation of the Crato Formation. This is indicated by low pristane/phytane, gammacerane index, and the presence of β-carotane and aryl isoprenoids. Differences in OM composition and stable isotope data reflect the evolution of the basin from a stratified saline lake to a freshwater environment with limited potential for OM preservation.

Distribution and Potential Sources of Polycyclic Aromatic Hydrocarbons in Urban Surface Dust and Soil of Shanghai, China

Concentrations and profiles of polycyclic aromatic hydrocarbons (PAHs) were measured in road dust and soil from different functional urban areas in Shanghai. The ΣPAHs concentrations varies from 99.4 to 66900 ng/g dw, where the highest one is found in dust from a chemical industry producing black carbon. The mean concentrations of ΣPAHs for dust increase in the following order of land uses: park and lake area DBahA > BbF > IDP > BkF > BaA > Chr, underlining the importance of BaP as a surrogate compound of a PAHs mixute.

Contamination and source assessment of metals, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons in urban soils from Addis Ababa, Ethiopia

Urban areas in developing countries are facing vast environmental problems as a result of rapid urbanization and industrialization. Of major concern is the contamination of soils which are increasingly becoming sinks for environmental pollutants. However, to date only little is known about the pollution in the megalopolises of developing countries. The aim of this study was to assess the contamination and potential sources of metals, polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in the urban environment of Addis Ababa, the capital of Ethiopia. The investigation revealed the presence of most of the analyzed pollutants in soil and sediment samples with total concentrations (dry wt) of PAHs ranging from 186 to 3150 µg kg−1, PCBs from 0.4 to 19 µg kg−1, Cu from 14 to 173 mg kg−1, Zn from 36 to 440 mg kg−1, Pb from 9 to 700 mg kg−1, and Ni from 16 to 72 mg kg−1. In addition, polyaromatic sulfur heterocycles, typical for oil and petrol residues, were detected in several soil samples. Source identification approaches revealed that Pb, Zn, and Cu are most likely derived from pyrolytic sources, with elevated values in samples related to waste combustion and traffic emissions. Ni is most probably of geogenic origin. For PCBs it is indicated that they are derived from a single source. However, correlations with technical PCB mixtures were inconsistent. PAHs originate from the combustion of biomass, vehicular exhausts, and petrogenic sources.

The Geochemical Characterization of Sediments from Early Cretaceous Sembar Formation

The soluble organic matter (SOM) and kerogen of sediments contain organic molecules, and can be interpreted in terms of source, generative potential, thermal maturity, and depositional environment of the organic matter. Early Cretaceous sedimentary sequence of Sembar Formation comprising five sediments samples was analyzed. Both SOM and hydrocarbons bound to the kerogen terms as pyrolyzed organic matter (POM) were characterized geochemically. Hydrous pyrolysis was carried out to release hydrocarbons from extracted sediments and fractionated by liquid chromatography. Saturated fractions from both SOM and POM were further analyzed by gas chromatography-flame ionization detector. The study suggested that Cretaceous sequence of Sembar Formation has fair to good hydrocarbon source potential. Thermal maturity parameters indicate onset of oil genesis zone. The presence of even carbon numbered n-alkenes, Pr/Ph and Pr/n-C17 versus Ph/n-C18 plots reveal marine algal source and anoxic depositional environment of organic matter from Sembar Formation.

Biostratigraphic correlation of the Ordovician black shales in Tarim Basin and its peripheral regions

Ordovician black shales are widely distributed in the Tarim Basin and its peripheral regions, and some of them may serve as potential hydrocarbon source rocks. The present study of the Ordovician graptolite fauna from these shales, together with the yielded conodonts and chitinozoans etc., permits a refined correlation of the rocks. Based mainly on a new collecting of the graptolites and a study of the faunas in Kalpin and Kuruktag regions, and the successful identification of the new graptolite material from a few drill cores within the basin, we are able to update our knowledge of the Ordovician in the regions, and draw some conclusions: (1) The most widespread distribution of the black shales in the Tarim Basin and its peripheral regions, which correspond to the Nemagraptus gracilis Zone, may be related to a global sea-level rise during this time interval. (2) Black shales of Ordovician occur most frequently and extensively in the Kuruktag (also spelled as Quruq Tagh) region in eastern Tianshan Mountains, spanning Tremadocian to mid-Katian (D. spiniferus Zone) temporally and extending southeastwards into Manjiaer Depression. The black shales of the D. spiniferus Zone may even extend into the central Tarim Basin. (3) Three different bio- and litho-facies belts (Bachu: carbonate platform and reef belt; Kalpin-Aksu: marginal platform and upper slope belt; Wushi: slope belt) are recognized in the northwestern Tarim Basin. (4) The internationally well-correlated Saergan black shale, which has been considered to possess high potential for hydrocarbon source rock, may possess a restricted distribution in the Kalpin and Aksu areas.

Formation Pressure Evolution in Lynedoch Fields, Northern Bonaparte Basin, Australia

The Lynedoch Fields are located in the flanks of Calder Graben. Wells lynedoch-1, lynedoch-2 and Seismic line N11809 are selected to evaluate the pressure evolution history, investigate the mechanisms of overpressures generation and the timing of oil and gas generation from the potential hydrocarbon source rock. Three areas of pressure evolution were identified namely normal pressure, slight excess pressure and intense excess pressure. The pressure releases are consistent with the tectonic events increasing with depth and dissipating laterally. The peak of excess pressure generation, the peak sedimentation rates in wells Lynedoch-1 and Lynedoch-2 and the peak generation of oil and gas of the same wells were occurred during the Late Cretaceous at 65Ma. High sedimentation rates with rapid subsidence and oil and gas generation are the main favorable conditions for overpressure generation in the study area.

Distribution and potential sources of polycyclic aromatic hydrocarbons in soils around coal-fired power plants in South Africa

The distribution and potential sources of 15 polycyclic aromatic hydrocarbons (PAHs) in soils in the vicinity of three South African coal-fired power plants were determined by gas chromatography-mass spectrometry. PAH compound ratios such as phenanthrene/phenanthrene + anthracene (Phen/Phen + Anth) were used to provide reliable estimation of emission sources. The total PAH concentration in the soils around three power plants ranged from 9.73 to 61.24μgg(-1), a range above the Agency for Toxic Substances and Disease Registry levels of 1.0μgg(-1) for significantly contaminated site. Calculated values of Phen/Phen + Anth ratio were 0.48 ± 0.08, 0.44 ± 0.05, and 0.38 + 0.04 for Matla, Lethabo, and Rooiwal, respectively. Flouranthene/fluoranthene + pyrene (Flan/Flan + Pyr) were found to be 0.49 ± 0.03 for Matla, 0.44 ± 0.05 for Lethabo, and 0.53 ± 0.08 for Rooiwal. Such values indicate a pyrolytic source of PAHs. Higher molecular weight PAHs (five to six rings) were predominant, suggesting coal combustion sources. A good correlation existed between most of the PAHs implying that these compounds were emitted from similar sources. The carcinogenic potency B[a]P equivalent concentration (B[a] Peq) at the three power plants ranged from 3.61 to 25.25 indicating a high carcinogenic burden. The highest (B[a] Peq) was found in samples collected around Matla power station. It can therefore be concluded that the soils were contaminated with PAHs originating from coal-fired power stations.

Source apportionment of sediment-associated aliphatic hydrocarbon in a eutrophicated shallow lake, China

Chaohu Lake, one of the most eutrophicated lakes in China, has been suffering from long-term outside pollution, urban sewage, river outflows, and agricultural runoff which expectedly have been the main contributors of hydrocarbons. However, the contributions from these various sources have not been specified. The present study is aimed at identifying the potential sources of hydrocarbons in surface sediment around the whole lake and assessing the relative contributions using principal components analysis-multiple linear regression (PCA-MLR). Sixty-one surface sediments covering the whole Chaohu Lake and three main estuaries of inflowing rivers were collected, dried, extracted, and analyzed for 27 normal alkanes (n-alkanes, from C(12) to C(38), defined Σ(27)AH) and unresolved complex mixture (UCM) by GC/MS. Diagnostic ratios and PCA-MLR were utilized to apportion their sources. The concentrations of Σ(27)AH and UCM ranged from 434 to 3,870ng/g and 11.9 to 325μg/g dry weight, respectively, for all samples. The concentrations of Σ(27)AH in western region and estuary of Nanfei River were slightly higher but without statistical significance than those from eastern region and estuaries of Yuxi River and Hangbu River. The concentration of UCM from western region was significantly higher than that obtained from eastern region. These results reflect the importance of input of urban runoff by Nanfei River and serious eutrophication in western region. Aliphatic hydrocarbons in Chaohu Lake were mainly derived from high plant wax with mixed sources of phytoplankton and petroleum. Weak microbial decomposition of n-alkanes would be expected to occur from the low ratios of isoprenoid hydrocarbons pristine (pri) and phytane (phy) to n-C(17) and n-C(18), respectively. Higher plant, fossil combustion, petroleum residue, and phytoplankton were proposed as the main origines of aliphatic hydrocarbons by PCA while the contributions of individual n-alkane homologues, pri and phy from the identified sources (31% from higher plant, 30% from fossil combustion, 26% from petroleum, and 19% from phytoplankton) were well predicted using MLR. The distribution profile and corresponding diagnostic ratios of normal alkanes show the promising potential as a useful proxy for estimating the source and loading of pollutants in Chaohu Lake.