Fraction Of Polycyclic Aromatic Hydrocarbons Research Articles

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.   Key words: Agbabu, bitumen, bacteria, biodegradability, hydrocarbons. &nbsp

Developmental toxicity of PAH mixtures in fish early life stages. Part II: adverse effects in Japanese medaka

In aquatic environments, polycyclic aromatic hydrocarbons (PAHs) mostly occur as complex mixtures, for which risk assessment remains problematic. To better understand the effects of PAH mixture toxicity on fish early life stages, this study compared the developmental toxicity of three PAH complex mixtures. These mixtures were extracted from a PAH-contaminated sediment (Seine estuary, France) and two oils (Arabian Light and Erika). For each fraction, artificial sediment was spiked at three different environmental concentrations roughly equivalent to 0.5, 4, and 10 μg total PAH g(-1) dw. Japanese medaka embryos were incubated on these PAH-spiked sediments throughout their development, right up until hatching. Several endpoints were recorded at different developmental stages, including acute endpoints, morphological abnormalities, larvae locomotion, and genotoxicity (comet and micronucleus assays). The three PAH fractions delayed hatching, induced developmental abnormalities, disrupted larvae swimming activity, and damaged DNA at environmental concentrations. Differences in toxicity levels, likely related to differences in PAH proportions, were highlighted between fractions. The Arabian Light and Erika petrogenic fractions, containing a high proportion of alkylated PAHs and low molecular weight PAHs, were more toxic to Japanese medaka early life stages than the pyrolytic fraction. This was not supported by the toxic equivalency approach, which appeared unsuitable for assessing the toxicity of the three PAH fractions to fish early life stages. This study highlights the potential risks posed by environmental mixtures of alkylated and low molecular weight PAHs to early stages of fish development.

OBSERVATIONAL STUDIES ON THE NEAR-INFRARED UNIDENTIFIED EMISSION BANDS IN GALACTIC H II REGIONS

Using a large collection of near-infrared spectra (2.5-5.4 um) of Galactic HII regions and HII region-like objects, we perform a systematic investigation of the astronomical polycyclic aromatic hydrocarbon (PAH) features. 36 objects were observed by the use of the infrared camera onboard the AKARI satellite as a part of a directer's time program. In addition to the well-known 3.3-3.6 um features, most spectra show a relatively-weak emission feature at 5.22 um with sufficient signal-to-noise ratios, which we identify as the PAH 5.25 um band previously reported. By careful analysis, we find good correlations between the 5.25 um band and both the aromatic hydrocarbon feature at 3.3 um and the aliphatic ones at around 3.4-3.6 um. The present results give us convincing evidence that the astronomical 5.25 um band is associated with C-H vibrations as suggested by previous studies and show its potential to probe the PAH size distribution. The analysis also shows that the aliphatic to aromatic ratio of I(3.4-3.6)/I(3.3) decreases against the ratio of the 3.7 um continuum intensity to the 3.3 um band, I(3.7 cont)/I(3.3), which is an indicator of the ionization fraction of PAHs. The mid-infrared color of I(9)/I(18) also declines steeply against the ratio of the hydrogen recombination line Bralpha at 4.05 um to the 3.3 um band, I(Bralpha)/I(3.3). These facts indicate possible dust processing inside or at the boundary of ionized gas.

Spatial and temporal distribution of polycyclic aromatic hydrocarbons (PAHs) in surface water from Liaohe River Basin, northeast China

Liaohe River Basin is an important region in northeast China, which consists of several main rivers including Liao River, Taizi river, Daliao River, and Hun River. As a highly industrialized region, the basin receives dense waste discharges, causing severe environmental problems. In this study, the spatial and temporal distribution of aqueous polycyclic aromatic hydrocarbons (PAHs) in Liaohe River Basin from 50 sampling sites in both dry (May) and level (October) periods in 2012 was investigated. Sixteen USEPA priority PAHs were quantified by gas chromatography/mass selective detector. The total PAH concentration ranged from 111.8 to 2,931.6 ng/L in the dry period and from 94.8 to 2766.0 ng/L in the level period, respectively. As for the spatial distribution, the mean concentration of PAHs followed the order of Taizi River > Daliao River > Hun River > Liao River, showing higher concentrations close to large cities with dense industries. The composition and possible sources of PAHs in the water samples were also determined. The fractions of low molecular weight PAHs ranged from 58.2 to 93.3 %, indicating the influence of low or moderate temperature combustion process. Diagnostic ratios, principal component analysis, and hierarchical cluster analysis were used to study the possible source categories in the study area, and consistent results were obtained from different techniques, that PAHs in water samples mainly originated from complex sources, i.e., both pyrogenic and petrogenic sources. The benzo[a]pyrene equivalents (EBaP) characterizing the ecological risk of PAHs to the aquatic environment suggested that PAHs in Liaohe River Basin had already caused environmental health risks.

Characterization of polycyclic aromatic hydrocarbon levels in the vicinity of a petrochemical complex located in a densely populated area of the Rio de Janeiro, Brazil

The Petrochemical Complex of Duque de Caxias, Rio de Janeiro, is situated on a coastal strip between Guanabara Bay and a mountainous region covered with tropical forest. The complex comprises a refinery, a thermal power plant and several petrochemical industries. Higher rates of particulate–matter emissions are found in the region, mainly due to diesel emissions and the industrial activities of this area. In 2009 and 2010, samples were collected in three sites, and the 16 polycyclic aromatic hydrocarbons (PAHs) that are designated as priority pollutants by the US Environmental Protection Agency were determined. The sites are located in the vicinity of the Petrochemical Complex, one of them is on a roadside and the others are urban areas around the industrial complex. Multivariate analyses and diagnostic ratios show that the three studied areas were different, and the emissions seemed to be due to both gasoline and diesel vehicles. The carcinogenic PAHs represented the main fraction of the total PAHs determined in the particulate matter, and because the region is densely populated, these values may represent a health concern. The results indicate that regarding PAHs, the principal impact of the petrochemical complex is the high increase in the traffic of diesel vehicles and related tailpipe emissions.

Emission Characteristics for Polycyclic Aromatic Hydrocarbons from Solid Fuels Burned in Domestic Stoves in Rural China

Emission characterization of polycyclic aromatic hydrocarbons (PAHs) from residential combustion of crop residues, woody material, coal, and biomass pellets in domestic stoves in rural China are compared in term of emission factors (EFs), influencing factors, composition profiles, isomer ratios and phase distributions. The EFs of PAHs vary by 2 orders of magnitude among fuel types suggesting that a detailed fuel categorization is useful in the development of an emission inventory and potential in emission abatement of PAHs by replacing dirty fuels with relatively cleaner ones. The influence of fuel moisture in biomass burning is nonlinear. Biofuels with very low moisture display relatively high emissions as do fuels with very high moisture. Bituminous coals and brushwood yield relatively large fractions of high molecular PAHs. The emission factor of benzo(a)pyrene equivalent quantity for raw bituminous coal is as high as 52 mg/kg, which is 1-2 orders of magnitude higher than the other fuels. For source diagnosis, high molecular weight isomers are more informative than low molecular weight ones and multiple ratios could be used together whenever possible.

Sediment baseline study of levels and sources of polycyclic aromatic hydrocarbons and heavy metals in Lake Nicaragua

Selected metals and polycyclic aromatic hydrocarbons (PAHs) were analyzed in sediment samples from 24 sites in Lake Nicaragua sampled May 2010 to provide a baseline of pollution levels. Cu exceeded the Consensus-Based Sediment Quality Guideline (CBSQG) Threshold Effect Concentrations (TECs) at 21 sites while Ni exceeded the value at one site. Comparison of the sampling sites showed that the south-eastern shore and a central part of the lake contained the highest levels of As, Cd, Cr, and Ni, while the western part of the lake contained the highest levels of Cu, Pb, and Zn. Analysis of PAH levels showed that the CBSQG TECs were exceeded by naphthalene at five sites. The sum concentrations of the 16 US EPA priority PAHs (∑PAH16) ranged from 0.01mgkg−1dw to 0.64mgkg−1dw. The highest ∑PAH16 concentration was found upstream in River Mayales and the PAH composition revealed a heavy PAH fraction (e.g., creosote). The main sources of PAHs in Lake Nicaragua were determined as of diffuse petrogenic and pyrogenic origin as well as diagenetic produced perylene. The relative importance of these PAH sources was determined by interpretation of loading and score plots from a principal component analysis. This study concluded that areas of Lake Nicaragua represent an important pollution baseline for future studies in this lake and other tropical lakes.

Concentration profile of selected polycyclic aromatic hydrocarbon (PAH) fractions in some processed meat and meat products

This study investigates the concentration profiles of selected polycyclic aromatic hydrocarbon (PAH) fractions in selected processed meats, in order to evaluate their dietary and health implications. Smoked, grilled and boiled meat products were bought from different locations in Cape Town and Cape Town environs. PAHs were extracted from each meat sample according to standard methods. The concentrations of benzo[k]fluoranthene (BkP), benzo[a]pyrene (BaP), indeno[1, 2, 3-cd]pyrene (IP), and benzo[g, h, i]perylene(BghiP) in the processed meat extracts were determined using a gas chromatograph coupled with flame ionization detector. Total PAH concentrations in smoked, grilled and boiled chicken fillets, pork, and beef stripes were ranged 2.79, 0.99, 2.33 μg/kg; 19.11, 11.17, 15.04 μg/kg; and 14.84, 9.29, 7.20 μg/kg respectively. There were significant differences (p > 0.05) in the concentration levels of PAHs detected in different types, with the highest levels observed in smoked pork meat. The concentration of BkP, BaP, IP and BghiP detected in the various meat samples were below the EU and WHO dietary exposure limit.

Analysis of Polycyclic Aromatic Hydrocarbons in Egyptian Petroleum Condensate Oils

The polycyclic aromatic hydrocarbons (PAH) in Egyptian condensates are analyzed for the first. A solid phase extraction (SPE) followed by gas chromatography-mass selective detection was used for their analysis. The method was calibrated for optimal extraction conditions. Excellent recoveries were found (78–114%) for the PAHs that were identified using a variety of standards and GC-MS spectra. The solid-phase extracted PAH fraction was further separated by HPLC on a Ag(I) mercaptopropanosilica gel to reduce the complexity of the sample by separating the PAHs based on the number of aromatic rings. The analytes were quantified using GC with a flame ionization detector. For this kind of sample SPE is a more convenient separation technique than an open column. PAHs containing two to four rings in the concentration range 0.6–11 μg/L were measured. Some preliminary geochemical hypotheses based on the analyzed PAHs and the previously analyzed S-containing aromatic compounds were formed as to the depositional environment and source rock type.

Influence of the bioaccessible fraction of polycyclic aromatic hydrocarbons on the ecotoxicity of historically contaminated soils

Sequential supercritical fluid extraction together with a two-site desorption model were employed to estimate the bioaccessible fraction of polycyclic aromatic hydrocarbons (PAHs) in four historically contaminated soils. The ecotoxicity of the soils was assayed by four different contact tests. The same soils were exposed to exhaustive extraction and the extracts were returned to the soils to ensure total 100% bioaccessibility of the pollutants. Then the soils were assayed again. Statistical evaluation revealed that the predicted bioaccessible PAHs generally correlated with the ecotoxicity responses of the tests. The estimated bioaccessible fractions varied from 10 to 98%. This value increased for PAHs with higher lipophilicity and showed no correlation with the organic carbon content in the soils. The ecotoxicity tests in the study indicated different sensitivity toward PAHs and the tests employing Heterocypris incongruens and Eisenia fetida were found to be more suitable than Lemna minor and Vibrio fischeri. Mortality and growth inhibition of ostracods correlated with all the types of PAHs and earthworm growth inhibition and mortality were preferentially sensitive to PAHs with only 3–4 aromatic rings. Determination of the biota-soil accumulation factors indicated that the earthworm growth inhibition corresponded to increased accumulation of PAHs in the earthworm tissue.

Geologically distinct crude oils cause a common cardiotoxicity syndrome in developing zebrafish

Crude oils from different geological formations vary in composition, yet most crude oils contain a polycyclic aromatic hydrocarbon (PAH) fraction that would be expected to produce cardiotoxic effects in developing fish. To determine whether different crude oils or PAH compositions produce common or distinct effects, we used zebrafish embryos to directly compare two crude oils at different states of weathering. Iranian heavy crude oil (IHCO) spilled in the Yellow Sea following the 2007 Hebei Spirit accident was compared to the intensively studied Alaska North Slope crude oil (ANSCO) using two different exposure methods, water-accommodated fractions containing dispersed oil microdroplets and oiled gravel effluent. Overall, both crude oils produced a largely overlapping suite of defects, marked by the well-known effects of PAH exposure on cardiac function. Specific cardiotoxicity phenotypes were nearly identical between the two oils, including impacts on ventricular contractility and looping of the cardiac chambers. However, with increased weathering, tissue-specific patterns of aryl hydrocarbon receptor (AHR) activation in the heart changed, with myocardial AHR activation evident when alkyl-PAHs dominated the mixture. Our findings suggest that mechanisms of cardiotoxicity may shift from a predominantly AHR-independent mode during early weathering to a multiple pathway or synergistic mode with prolonged weathering and increased proportions of dissolved alkyl-PAHs. Despite continued need for comparisons of crude oils from different sources, the results here indicate that the body of knowledge already acquired from studies of ANSCO is directly relevant to understanding the impacts of other crude oil spills on the early life history stages of fish.

Characterization of aerosol associated non-polar organic compounds using TD-GC-MS: A four year study from Delhi, India

Aerosol associated Non-Polar Organic Compounds (NPOCs) – 25 n-alkanes, 17 Polycyclic Aromatic Hydrocarbons (PAHs), and 3 Isoprenoid hydrocarbons – have been identified and quantified in PM10 samples collected over four years in time sequence (2006–2009), using Thermal Desorption Gas Chromatography Mass Spectrometry, in Delhi region. Established organic markers, associated diagnostic parameters, and molecular diagnostic ratios were used to assess and discern the contributing biogenic, petrogenic and pyrogenic sources to NPOCs. Analysis show that anthropogenic contributions to NPOCs exhibit increase from 2006 to 2009. Distribution profiles of NPOCs were significantly affected by change in season. Lower concentrations of NPOCs during summer months, and higher during winter, once scaled to Planetary Boundary Layer height, suggests that contributing sources were most active during summer months. During monsoon season high mass fractions of Total n-alkanes (ppm), Total PAHs (ppm), and Black carbon (BC) % alludes at the role of differential washout process involving hydrophilic and hydrophobic fractions of ambient aerosols. Significantly high, four year average concentrations of TPAH and BC signify the dominance of pyrogenic source contributions to PM10. High correlation between monthly mean concentrations of TPAH and BC (R2=0.75) suggests that besides common emission source, they are also contributed, individually, by exclusive independent sources.

Assessing Limitations for PAH Biodegradation in Long-Term Contaminated Soils Using Bioaccessibility Assays

Polycyclic aromatic hydrocarbons (PAHs) are generated by a range of industrial processes including petroleum and gas production and are often found in high concentrations at industrial sites. Once PAHs enter the environment, the predominant mechanisms for removal are biological via microbial activity. However, PAHs have the potential to partition onto soil organic matter thereby decreasing their bioavailability to microorganisms and limiting their degradation. This explanation was felt to be the reason for a lack of evidence of PAH biodegradation in a study of long-term contaminated soils. To test the hypothesis that bioavailability was a limiting factor for biodegradation in theses soils, PAH bioavailability was determined using nonexhaustive extraction (propanol, butanol, hydrooxypropyl-β-cyclodextrin) and oxidation (persulfate) methodologies designed to determine the fraction of contaminants within soil which are available for biological uptake. The assays gave varying results for each soil, and no specific trends across all soils were observed. PAH bioaccessibility, derived from the HP-β-CD assay which has been the most extensively tested in the literature, was estimated to be between 0 and 10 % for most soils, with the exception of pyrene, indicating that a large fraction of the soil-borne PAHs at the site are not available to microorganisms and that bioavailability limitations may be a primary cause for the lack of observed biodegradation at this site. These results highlight the importance of bioavailability to PAH degradation as well as the relevance of utilizing an assay that has been evaluated across many soil conditions and parameters.

Characteristics of the Nanoparticles in a Road Tunnel

In a one-way road tunnel with a sidewalk for pedestrians (total length: 667 m, 2 lanes: 7 m width, sidewalk: 3.5 m width), size-fractionated particles that were suspended in the air were sampled and tested for the potential health risks to pedestrians. These particles were predominantly emitted from motorized traffic. Particles down to the nano-size range were collected using a PM0.07 sampler based on the “inertial filter” technology, which can be applied for the separation of nano-size particles. PM10 and fine particles less than 1 μm were simultaneously monitored online by a tapered element microbalance (TEOM), a condensation particle counter (CPC) and scanning mobility particle sizer (SMPS), and a video camera was used to monitor the amount of traffic and the wind velocity inside the tunnel. Concentrations of mass and polycyclic aromatic hydrocarbons (PAHs) in each size range of particles were discussed relative to the total traffic amount, the types of motorized vehicles, and the sampling duration, and then compared with other data that had been either simultaneously or separately obtained at different sampling locations outside the tunnel. The correlation was clear between PM0.1 and heavy traffic involving large diesel vehicles, such as buses and trucks. The mass concentrations and fractions of PAHs in the road tunnel became larger than at the mouth of the tunnel and the rural sampling site. PM emissions could be classified into fine particles smaller than 0.5 μm and coarse particles larger than 2.5 μm, which referred to exhaust and road dust, respectively. PM0.07 particles from vehicle exhaust might have contained a higher component of PAHs.

Concentration of Polycyclic Aromatic Hydrocarbon (PAHs) in the Sediments and Milkfish (<i>Chanos chanos</i>, Forsk) at Marunda and Blanakan Ponds, Indonesia

The polycyclic aromatic hydrocarbons (PAHs) are pollutants of concern due to their persistence in the marine ecosystem. The aim of the research was to analyse concentration of Polycyclic Aromatic Hydrocarbons (PAHs) in the sediments and milkfish ( Chanos chanos , Forsk) at Marunda and Blanakan ponds.The PAHs fraction were analysed using GC-MS model Shimadzu QP5000.The results revealed that PAH detected in the surface sediments of Marunda and Blanakan Ponds, were Naphthalene, Benzo (b) fluoranthene, Benzo (k) fluoranthene, Benzo (a) pyrene and Indeno (1,2,3-cd) pyrenewith the range concentrations were 27.1~63.0 ng/g and 24.0~64.9 ng/g. Total PAH concentration observed in the meat and gills of Chanos chanos at Marunda ponds were 13.3 ng/g and 0.4 ng/g, respectively, while in Blanakan ponds, PAH were not detected.PAHs were detected in Marunda and Blanakan indicates input source petrogenic and pyrogenic both sediment, meat, and gills Chanos chanos , Forskal.

넙치(Paralichthys olivaceus) 치어조직의 나프탈렌(Naphthalene) 생물농축

Polycyclic aromatic hydrocarbons (PAHs) such as naphthalene, are released into the aquatic environment and have been identified as endocrine effects on marine organisms. Naphthalene makes up the highest fraction of PAHs in oil and shows the strong toxicity to aquatic organisms. I analyzed 24h-median lethal concentration (24h-) for juvenile olive flounder Paralichthys olivaceus to study the acute toxicity of naphthalene. Bioconcentrations in the gill, liver, kidney and muscle of olive flounder were analyzed after to 6 naphthalene concentrations of 0, 1000, 1800, 3200, 5600 and 10000 . Olive flounder has 24h- value of 2410.76 in Large group, and 2230.67 in Samll group. Naphthalene concentration was varied with tissues. The concentrations of naphthalene were much higher in liver and kidney than in gill and muscle.

Long-term volatility measurements of submicron atmospheric aerosol in Hyytiälä, Finland

Abstract. The volatility of submicron atmospheric aerosol particles was investigated at a boreal forest site in Hyytiälä, Finland from January 2008 to May 2010. These long-term observations allowed for studying the seasonal behavior of aerosol evaporation with a special focus on compounds that remained in the aerosol phase at 280 °C. The temperature-response of evaporation was also studied by heating the aerosol sample step-wise to six temperatures ranging from 80 °C to 280 °C. The mass fraction remaining after heating (MFR) was determined from the measured particle number size distributions before and after heating assuming a constant particle density (1.6 g cm−3). On average 19% of the total aerosol mass remained in the particulate phase at 280 °C. The particles evaporated less at low ambient temperatures during winter as compared with the warmer months. Black carbon (BC) fraction of aerosol mass correlated positively with the MFR at 280 °C, but could not explain it completely: most of the time a notable fraction of this non-volatile residual was something other than BC. Using additional information on ambient meteorological conditions and results from an Aerodyne aerosol mass spectrometer (AMS), the chemical composition of MFR at 280 °C and its seasonal behavior was further examined. Correlation analysis with ambient temperature and mass fractions of polycyclic aromatic hydrocarbons (PAHs) indicated that MFR at 280 °C is probably affected by anthropogenic emissions. On the other hand, results from the AMS analysis suggested that there may be very low-volatile organics, possibly organonitrates, in the non-volatile (at 280 °C) fraction of aerosol mass.

Association of Polycyclic Aromatic Hydrocarbons (PAHs) with Different Sizes of Atmospheric Particulate in Hisar City and its Health Aspects

The concentration of polycyclic aromatic hydrocarbons (PAHs) associated with different particulate sizes of suspended particulate matter (SPM) was studied in Hisar city with the help of a MOUDI-NR 10-stage (18 μm to 0.056 μm) cascade impactor. The vehicular-cum-commercial, vehicular, commercial, and institutional/residential locations had the average concentration (ng/g) of 11.39, 10.39/10.22 (NH 10/Bus Terminus), 8.89, and 8.93, respectively. Vehicular emission was the chief source and diesel-vehicle dominated areas represented higher concentration of PAHs associated with coarse fraction. An increase in PAH associated with fine fraction was observed with an increase in vehicular density. Maximum average concentration (11.26 ng/g) was found to be associated in particle range of <0.56–0.32 μm. It was followed by particle range (μm) of <18–10, <1.8–1, <0.18–0.1, <1–0.56, <5.6–3.2, <0.32–0.18, <3.2–1.8 <0.1–0.056, and <10–5.6 with average values (ng/g) of 10.75, 10.35, 10.22, 10.16, 10.06, 9.50, 9.18, 9.18, and 9.00, respectively. Among the PAHs studied, maximum levels were observed for pyrene, followed by Benzo(b)fluoranthene, Benzo(e)pyrene, benzo(k)fluoranthene, fluoranthene, phenanthrene, benzo(ghi)perylene, anthracene, and naphthalene. With respect to the percent fraction of PAHs studied, the vehicular-cum-commercial area represented maximum fraction (22%) followed by vehicular area (21% each for NH-10 and Bus Terminus), institutional/residential area (18%), and commercial area (18%). The isomeric ratios revealed that most of the PAHs originate from combustion of diesel, gasoline, used engine oil, and coal/wood. The association of PAHs with fine fraction of health concern since it can penetrate and get accumulated in deep respiratory regions.

INVESTIGATION OF PAHs IN GALACTIC PLANETARY NEBULAE WITH THE AKARI/IRC AND THE SPITZER/IRS

Polycyclic aromatic hydrocarbons (PAHs) in Galactic planetary nebulae (PNe) are investigated by means of the unidentified infrared (UIR) bands. Continuous near- to mid-infrared spectra of PNe are obtained with the AKARI/IRC and the Spitzer/IRS. All 19 PNe in the present study show prominent dust emissions and we investigate the variation in the intensity ratios among the UIR bands. The ionization fraction and the size distribution of PAHs in PNe are derived using the UIR band ratios. We find that the ionization fraction of PAHs in PNe is around 0.0-0.6 and that small PAHs are scarce. The present result indicates a systematic trend of the <TEX>$3.4{\mu}m$</TEX> aliphatic feature to become weak as the PAH ionization fraction increases.

Evidence for in situ methanogenic oil degradation in the Dagang oil field

In situ biotransformation of oil to methane was investigated in a reservoir in Dagang, China using chemical fingerprinting, isotopic analyzes and molecular and biological methods. The reservoir is highly methanogenic despite chemical indications of advanced oil degradation, such as depletion of n-alkanes, alkylbenzenes and light polycyclic aromatic hydrocarbon (PAH) fractions or changes in the distribution of several alkylated polycyclic aromatic hydrocarbons. The degree of degradation strongly varied between different parts of the reservoir, ranging from severely degraded to nearly undegraded oil compositions. Geochemical data from oil, water and gas samples taken from the reservoir are consistent with in situ biogenic methane production linked to aliphatic and aromatic hydrocarbon degradation. Microcosms were inoculated with production and injection waters in order to characterize these processes in vitro. Subsequent degradation experiments revealed that autochthonous microbiota are capable of producing methane from 13C labelled n-hexadecane or 2-methylnaphthalene and suggest that further methanogenesis may occur from the aromatic and polyaromatic fractions of Dagang reservoir fluids. The microbial communities from produced oil–water samples were composed of high numbers of microorganisms (on the order to 107), including methane producing Archaea within the same order of magnitude. In summary, the investigated sections of the Dagang reservoir may have significant potential for testing the viability of in situ conversion of oil to methane as an enhanced recovery method and biodegradation of the aromatic fractions of the oil may be an important methane source.