Polycyclic aromatic hydrocarbons in surface sediments of Laizhou Bay,Bohai Sea,China

Concentration, distribution, and sources of 16 polycyclic aromatic hydrocarbons (PAHs) were investigated in surface sediments of Laizhou Bay, China. Total PAH concentrations ranged from 97.2 to 204.8 ng/g, with a mean of 148.4 ng/g. High concentrations of PAHs were found in the fine-grained sediments on both sides of the Yellow River estuary (YRE). In contrast, low levels of PAHs were observed in relatively coarse grain sediments, suggesting hydrodynamics influence the accumulation of sedimentary PAHs. The YRE and its adjacent area is the main sink for Yellow River-derived PAHs. Both PAH isomer ratios and principal component analysis (PCA) with multivariate linear regression (MLR) were applied to apportion sources of PAHs. Results indicated that both pyrogenic and petrogenic PAH sources were important. Further PCA/MLR analysis showed that the contributions of coal combustion, petroleum combustion and a combined source of spilled oil and biomass burning were 41, 15 and 44%, respectively. From an ecotoxicological viewpoint, the studied area appears to have low levels of PAH pollution.     

Chemical characteristics and pollution sources of petroleum hydrocarbons and PAHs in sediments from the Beiluohe River,Northern China

To determine the degree of hydrocarbon contamination and the contribution of local petroleum industries to contaminant loadings in sediments from the Beiluohe River, China, 12 surface sediment samples were collected for geochemical analysis in 2005. Sediment samples were extracted by organic solvents, separated by silica gel column chromatography and the profiles of n-alkanes, biomarkers and polycyclic aromatic hydrocarbons (PAHs) in sediments were analyzed by gas chromatography with flame ionization detector and gas chromatography/mass spectroscopy. Concentrations of total hydrocarbons in the sediments varied from 12.1 to 3,761.5 μg g⁻¹ dry wt, indicating that most sediments in Beiluohe River was only slightly to moderately contaminated by hydrocarbons. Concentrations of PAHs for six samples (sum of 16 isomers) varied from 17.7 to 407.7 ng g⁻¹ dry wt and at present low levels of PAHs did not cause adverse biological effects in Beiluohe River sedimentary environment. PAH compositions, n-alkanes and biomarker profiles all suggested that there were different sources of contaminations in studied areas. n-Alkanes reflect two distinct sources: a fossil n-alkane series from crude oil at sites S40, S43, S87 and plantwax n-alkanes at sites S39 and S45. Judged by their PAH ratios, the sediments at site S15 were pyrolytic, sediments at S17 and S43 were petrogenic, and sediments at S39, S40 and S64 had a mixture source of pyrolytic and petrogenic.     

Effects of estuarine organic matter biogeochemistry on the bioaccumulation of PAHs by two epibenthic species

Polycyclic aromatic hydrocarbon (PAH) biota-sediment accumulation factors (BSAF) were quantified in sediments from two sites in southeastern Louisiana in a 14 d microcosm study usingPalaemonetes pugio, andRangia cuneata and two radiolabeled PAHs, phenanthrene and benzo[a]pyrene (b[a]p). For both PAHs studied, mean BSAFs were significantly higher (p<0.0001) in both organisms in sediments from Bayou Trepagnier, (BSAF=0.628 g OC g TLE⁻¹), a brackish swamp, compared to Pass Fourchon (0.065 g OC g TLE⁻¹), a coastal salt marsh. In order to explain observed patterns in BSAFs, organic carbon-normalized PAH distribution coefficients between the sediment and freely dissolved phases (K_OC)_OBS were determined as well as the various geochemical variables of particulate and dissolved organic matter (POM and DOM, respectively). These included analyses of particle surface area, total organic carbon (TOC), carbon to nitrogen ratios (C∶N), and dissolved organic carbon (DOC). Bayou Trepagnier was higher in surface area, TOC, C∶N, as well as DOC suggesting that the difference in BSAFs may be attributed to compositional differences in POM and DOM between sites. We can not exclude the possibility that other factors (such as differences in organism behavior resulting from contrasting sediment characteristics) were responsible for BSAFs varying between the two sites. Phenanthrene BSAFs were typically higher than b[a]p BSAFs, suggesting contaminants were limited in their desorption from sediment particles as a function of PAH molecular weight. Mean BSAFs for both PAHs were higher on Day 7 than on Day 14. The reason for this decrease is unclear, but did not appear to be due to organisms becoming increasingly stressed in the microcosms. Visual observations indicated that animals remained feeding while no decreases in organism total lipid levels were detected. The trends in BSAFs between sites and over the time course of this experiment suggest that contaminant bioaccumulation in estuarine systems should not be considered to be an equilibrium process.     

Polycyclic aromatic hydrocarbon fingerprints in the Pichavaram mangrove–estuarine sediments,southeastern India

The sources and historical deposition of 16 polycyclic aromatic hydrocarbons (PAHs) were investigated in dated sediment cores from the Pichavaram mangrove–estuarine complex. The ΣPAH flux in mangrove and estuarine sediments was 0.064 ± 0.031 μg/cm²/yr and 0.043 ± 0.020 μg/cm²/yr, respectively. The PAH flux in sediments increased up-core, coinciding with rapid urbanization since the 1970s. The flux showed a decrease in recent years (since 1990), coinciding with less riverine discharge, and perhaps more effective implementation of environmental regulations. The sediments were dominated by low molecular weight PAHs, suggesting anthropogenic input. Ratios of specific PAH isomer pairs suggested a greater input of petrogenic vs. pyrogenic derived PAHs. Notably, the deposition of high molecular weight PAHs increase in mangrove surface sediments was due to lignite and firewood combustion. Because of their overall low concentration in sediments it is unlikely these PAHs pose an immediate ecological hazard.     

Sources and bioavailability of polynuclear aromatic hydrocarbons in Galveston Bay, Texas

Oyster and sediment samples collected from six sites in Galveston Bay from 1986 to 1998 were analyzed for polynuclear aromatic hydrocarbons (PAHs). Total concentrations of parent PAHs in oysters ranged from 20 ng g⁻¹ at one site to 9,242 ng g⁻¹ at another and varied randomly with no clear trend over the 13 year period at any site. Concentrations of alkylated PAHs, which are indications of petroleum contamination, varied from 20 to 80,000 ng g⁻¹ in oysters and were in higher abundance than the parent PAHs, indicating that one source of the PAH contaminants in Galveston Bay was petroleum and petroleum products. Four to six ring parent PAHs, which are indicative of combustion source , were higher than those of 2–3 ring parent PAHs, suggesting incomplete combustion generated PAHs was another source of PAHs into Galveston Bay. Concentrations of parent PAHs in sediments ranged from 57 to 670 ng g⁻¹ and were much lower than those in oysters. Sediments from one site had a high PAH concentration of 5,800 ng g⁻¹. Comparison of the compositions and concentrations of PAHs between sediment and oysters suggests that oysters preferentially bioaccumulate four to six ring PAHs. PAH composition in sediments suggests that the sources of PAH pollution in Galveston Bay were predominantly pyrogenic, while petroleum related PAHs were secondary contributions into the Bay.     

Characterization and source apportionment of polycyclic aromatic hydrocarbons (PAHs) in sediments in the Yellow River Estuary, China

Concentrations and sources of polycyclic aromatic hydrocarbons (PAHs) were investigated in surface sediments of the Yellow River Estuary (YRE). The isobath-parallel tidal and residual currents play important roles in the variation of PAH distribution, such that the contamination level of PAHs in fine-grained sediments is significantly higher than in the relatively coarse grain size sediments. Both diagnostic ratios and principal component analysis (PCA) with multivariate linear regression (MLR) were used to apportion sources of PAHs. The results revealed that pyrogenic sources are important sources of PAHs. Further analysis indicated that the contributions of coal combustion, traffic-related pollution and mixed sources (spills of oil products and vegetation combustion) were 35, 29 and 36 %, respectively, using PCA/MLR. Pyrogenic sources (coal combustion and traffic-related pollution) contribute 64 % of anthropogenic PAHs in sediments, which indicates that energy consumption could be a predominant factor in PAH pollution of YRE. Acenaphthylene and acenaphthene are the two main species of PAHs with more ecotoxicological concern in YRE.     

Composition and source identification of polycyclic aromatic hydrocarbons in mangrove sediments of Peninsular Malaysia: indication of anthropogenic input

This is a comprehensive study of the composition, origin and sources of specific polycyclic aromatic hydrocarbons (PAHs) in sediments of mangrove estuary in the western part of Peninsular Malaysia. Mangrove sediments were analyzed for 17 PAHs by gas chromatography–mass spectrometry. Total PAH concentrations in the sediments ranged from 20 to 112 ng/g on a dry-weight basis. High molecular weight PAHs were abundant in the sediments. Parent PAH ratios revealed that pyrogenic input has important contribution to the sedimentary PAHs. Ratios of alkylated PAHs indicate that the sedimentary PAHs were influenced by petrogenic PAHs, which implies that petrogenic input has contribution to the sedimentary PAHs but that it is not a major factor in distribution of PAHs within the estuary. Combustion-derived PAHs show a positive and very strong correlation with total PAHs (R ² = 0.926, p < 0.05). Total methylphenanthrenes show very weak correlation with total PAHs (R ² = 0.0928, p < 0.05). The PAH concentrations were found to increase with distance from the upstream of the estuary to the coastal area of the Straits of Malacca. For the assessment of sediment contamination using biological thresholds, none of the individual studied PAH compounds exceeded the values of the effect range low–effect range median guideline and the threshold effects level–probable effects level guideline. This study demonstrates that the sediments of the mangrove ecosystem facing the Straits of Malacca and Sumatra are influenced by anthropogenic PAH inputs as a result of human activities such as biomass burning, vehicle emissions and boating activities.     

Source apportionment of elevated PAH concentrations in sediments near deep marine outfalls in Esquimalt and Victoria,BC, Canada: Is coal from an 1891 shipwreck the source?

Previous studies have suggested that coal from the 1891 shipwreck of a collier off Victoria, BC, Canada is responsible for elevated parent (unsubstituted) PAH concentrations in sediments near deep marine outfalls from Esquimalt and Victoria in the Strait of Juan de Fuca. To resolve this question, we analysed a comprehensive suite of resolved and unresolved complex mixture (UCM) alkanes, tricyclic terpane, hopane and sterane biomarkers, and parent and alkyl polycyclic aromatic hydrocarbons (PAHs) in samples of coal, wastewater and sediments. Composition patterns, principal components analysis (PCA) models and PAH and biomarker ratios all indicate that coal from the collier does not make a dominant contribution to any sediment sample. Mass balance calculations based on the n-C₂₄ content and 24/4 tetracyclic terpane to 26/3R tricyclic terpane ratio in coal provide a particularly good match between predicted and observed alkyl PAH concentrations for sediments with high alkyl naphthalenes and phenanthrene/anthracenes and low UCM, but the predicted coal contribution substantially underestimates the measured parent PAHs for all sediment samples. Methylbenz[a]anthracene/chrysene profiles for sediments with a dominance of parent PAHs are very close to coal tar, with a marked predominance of methylbenz[a]anthracenes and the possible 10-methylbenz[a]anthracene as a major constituent, while the methylchrysenes predominate in coal. Hence, coal from the collier could account for most alkyl PAHs in the sediments, but dredged sediment containing pyrolised coal waste from a former coal gas plant in Victoria Harbour is a more likely source for the samples with elevated parent PAHs. PAH ratios indicate that these sources are superimposed on combustion PAHs introduced by a combination of atmospheric deposition and delivery via stormwater and the outfalls. Parent PAH distributions also suggest that PAHs in wastewater that originate from oils and soot in liquid fossil fuel combustion are dispersed and degraded, while the larger wood char particles (containing PAHs more protected from degradation) settle closer to the outfalls. Overall, results suggest that PAHs have predominant sources in wood combustion, coal and possibly coke, with a likelihood of much lower bioavailability than would be expected from wastewater dominated by oils and soot from vehicle combustion.     

Black carbon in soils from different land use areas of Shanghai,China: Level,sources and relationship with polycyclic aromatic hydrocarbons

Black carbon (BC) in soils plays a key role of carrying hydrophobic pollutants like polycyclic aromatic hydrocarbons (PAHs). However, little is known about the spatial distribution, sources of BC and its relationship with PAHs in urban soils. We studied BC, total organic carbon (TOC) and PAHs concurrently in 77 soils collected from downtown area, suburban and rural area and industrial area of Shanghai, China. BC was determined by both chemical oxidation (dichromate oxidation, BC_Cr) and chemo-thermal oxidation (CTO-375, BC_CTO). BC sources were identified qualitatively by BC/TOC concentration ratios and BC-cogenerated high molecular weight (HMW) PAH isomer ratios and quantitatively by principal component analysis followed by multiple linear regression (PCA-MLR). Results showed that BC_Cr concentration (4.65 g/kg on average) was significantly higher than BC_CTO (1.91 g/kg on average) in Shanghai soils. BC_Cr concentrations in industrial area were significantly higher than those in other two. Stronger correlation was found between PAHs and TOC, BC_Cr than that between PAHs and BC_CTO, which indicates the possibility of PAHs being carried by charcoal and other organic matters thus negating its exclusive dependence on soot. Charcoal was therefore suggested to be taken into account in studies of BC and its sorption of PAHs. BC/TOC ratios showed a mixed source of biomass burning and fossil fuel combustion. PCA scores of BC-cogenerated HMW PAHs isomer ratios in potential sources and soil samples clearly demonstrated that sources of BC in urban soils may fall into two categories: coal and biomass combustion, and traffic (oil combustion and tire wear). PCA-MLR of HMW PAHs concentrations in soil samples indicated that coal and oil combustion had the largest contribution to BC in urban soils while tire wear and biomass combustion were important in downtown and rural area, respectively, which indicated they were main sources of HMW PAHs and presumably of BC.     

Role of prior exposure on anaerobic degradation of naphthalene and phenanthrene in marine harbor sediments

The anaerobic degradation of the polycyclic aromatic hydrocarbons (PAHs) naphthalene and phenanthrene was investigated in several marine harbor sediments. In sediments from Boston Harbor that were heavily contaminated with petroleum, [¹⁴C]-naphthalene and [¹⁴C]-phenanthrene were oxidized to ¹⁴CO₂ without a lag, suggesting that the microbial community was adapted for anaerobic PAH oxidation in situ. The addition of molybdate, a specific inhibitor of sulfate-reducing microorganisms, inhibited PAH mineralization which suggested that sulfate reducers were involved in the anaerobic oxidation of the PAHs. PAHs were also anaerobically oxidized at another site in Boston Harbor that was less heavily contaminated, but at a slower rate than in the most heavily contaminated sediments. Sediments not contaminated with petroleum did not significantly oxidize the PAHs. A similar correspondence between rates of anaerobic PAH oxidation and the degree of PAH contamination was observed in sediments from Tampa Bay and San Diego Bay. When relatively pristine sediments from San Diego Bay that did not have a significant capacity for anaerobic PAH oxidation were exposed to high concentrations of naphthalene, they developed a potential for naphthalene degradation that was comparable to that in sediments that had a history of PAH contamination. The increase in potential for naphthalene degradation in the sediments exposed to naphthalene was associated with an increase in naphthalene-degrading microorganisms. These results suggest that many marine harbor sediments contain microorganisms capable of anaerobically oxidizing PAHs under sulfate-reducing conditions and that these microorganisms will respond with an increase in their activity when PAHs are introduced into the sediments. Thus, if PAH inputs into harbor sediments from petroleum can be reduced there may be a widespread potential for microorganisms to remove this PAH contamination from the sediments, despite anaerobic conditions.     

Polycyclic aromatic hydrocarbons in sediments from the Pearl river and estuary,China: spatial and temporal distribution and sources

Polycyclic aromatic hydrocarbons (PAHs) were measured in surface sediments and dated core sediments from the Pearl river and estuary, China, to investigate the spatial and temporal variability of anthropogenic pollutants. The sediments from the sampling stations at the Guangzhou channel have the highest concentrations of PAHs, owing to contributions from the large amount of urban/industrial discharges from the city of Guangzhou. The significant decrease of PAHs concentrations in sediments from the Shiziyang channel is mainly attributed to the increasing degradation and desorption of low molecular weight PAHs and alkyl PAHs, and the dilution by less contaminated water and particles from the East river. The PAH contaminants were concentrated on the western side in the Lingding bay of the Pearl river estuary because of the hydrodynamic and sedimentation conditions. Based on the characteristics of the parent compound distributions (PCDs) and the alkyl homologue distributions (AHDs) of PAHs, the potential source of PAHs in sediments from each sampling station was identified. Results indicated that the pyrogenic (combustion) source, characterized by the abundance of parent PAHs, were predominant in the heavily contaminated station (ZB01) near the aging industrial area, and the petrogenic (petroleum- derived) PAHs were more abundant in the stations (ZB02, ZB03) adjacent to the petrochemical plant and shipping harbor. Sediments from Lingding bay show variable distributions of PAH composition and variety in the proportion of combustion and petrogenic sources for the PAHs in different stations. Perylene, a naturally derived PAH, was found to be highly abundant in less contaminated stations. Analysis of the dated sediments (²¹⁰Pb) indicates that higher PAH concentrations occurred in the sediments deposited after 1980, and higher fluxes of PAHs discharged to the Pearl river are found after 1990.     

Indications for pedogenic formation of perylene in a terrestrial soil profile: Depth distribution and first results from stable carbon isotope ratios

Concentrations and isotope compositions of polycyclic aromatic hydrocarbons (PAHs) were determined in natural soils of Southern Germany. In selected profiles perylene concentrations increased with soil depth when compared to the other PAH compounds present. However, its low solubility made vertical transport by seepage water unlikely. Therefore two mechanisms are discussed that could have caused the unusual distribution of perylene in these soils:

(a) Atmospheric deposition of combustion-derived (i.e. pyrogenic) perylene in the top-soil and

(b) in situ generation in the sub-soil of these specific terrestrial environments. This could have been caused by microbial activities or other catalytic processes yet unknown.

In order to distinguish between pyrogenic and natural generation compound-specific ¹³C/¹²C ratios (δ¹³C) were compared between perylene and other PAHs in samples from the top-soil and sub-soil. Despite successful clean-up of the extracts, low perylene concentrations and peak overlaps with benzo(e)pyrene and benzo(a)pyrene prevented determination of a unique δ¹³C value for perylene in the upper horizon. However, the δ¹³C value of perylene in the sub-soil was 5.7 permille more negative than other equal-mass PAHs (with m/z of 252) in the top-soil, which rather supports in situ generation of perylene in the sub-soil.     

Polycyclic aromatic hydrocarbon concentrations in urban soils representing different land use categories in Shanghai

An extensive soil survey was carried out in Shanghai to investigate the spatial distribution and possible sources of polycyclic aromatic hydrocarbons (PAHs) in urban soils. Soil samples were collected from highways, iron-smelting plants, steel-smelting plants, shipbuilding yards, coking plants, power plants, chemical plants, urban parks, university campuses and residential areas and were analyzed for 16 PAHs by gas chromatography with mass detection. High PAH concentrations were found in all locations investigated, with mean values of soil total PAH concentrations in the range 3,279–38,868 μg/kg DM, and the PAH concentrations were significantly influenced by soil organic matter content. Soil PAH profiles in all districts were dominated by PAHs with 4–6 rings. Principal components analysis and diagnostic ratios of PAHs indicate that they were mainly derived from coal combustion and petroleum but in soils from highways the PAHs were derived largely from vehicle exhaust emissions. The high concentrations of PAHs found indicate that many urban soils in Shanghai represent a potential hazard to public health.     

Using GC-MS/Combustion/IRMS to determine the C/C ratios of individual hydrocarbons produced from the combustion of biomass materials--application to biomass burning

Simultaneous mass spectral detection and stable carbon isotope analysis was performed on individual indigenous n-alkanes isolated from single C₄ and C³ plant species and on a series of aliphatic and polycyclic aromatic hydrocarbons (PAH) produced from the combustion of these same biomass materials. The analysis technique used a combined gas chromatograph-mass spectrometer/combustion/isotope ratio mass spectrometer (GC-MS/C/IRMS). Precision (2σ) for replicate measurements of individual compounds in standard solutions using this novel configuration ranged between 0.2 and 0.5‰ for n-alkanes and 0.3 and 0.8‰ for PAH. Accuracy of the n-alkane measurements ranged between 0.1 and 0.4‰ and that of the PAH measurements ranged between 0.2 and 0.9‰. Replicate GC-MS/C/IRMS measurements on the combustion-derived n-alkene/alkane pairs were performed to within a precision of between 0.1 and 1.1‰ and the precision for the combustion PAH was similar to the standard PAH solution. No notable isotopic effects were observed when altering the temperature of the combustion process from 900 to 700°C, or as a result of the individual n-alkenes/alkanes partitioning between the gaseous and condensate fractions. Combustion-derived n-alkenes/alkanes ranged from C₁₁ to C₃₁, and the C₄-derived n-alkenes/alkanes were approx. 8‰ more enriched in ¹³C than the C₃-derived compounds. Both the C₄ and C₃-derived n-alkenes/alkanes (C₂₀-C₃₀) were isotopically similar to the indigenous n-alkanes and were 2-3‰ more depleted in ¹³C than the lower mol. wt (C₁₁₁₁-C₁₉) n-alkenes/alkanes, suggesting an independent origin for the lower mol. wt compounds. Combustion-generated C₄ and C₃-derived 2-, 3-, and 4-ring PAH were also isotopically distinct (Δδ = 10‰). Unlike the n-alkenes/alkanes, no compound-to-compound variations were observed between the low and high mol. wt PAH. This study demonstrates that the isotopic composition of original plant biomass material is mainly preserved in the aliphatic hydrocarbons and PAH generated by its combustion. Consequently, analyses of these compounds in sediments impacted by fire occurrences may provide useful information about paleo-fire activity that may help elucidate the impact biomass burning may have had and could have on climate-biosphere interactions.     

Distribution of polycyclic aromatic hydrocarbons in recent sediments of Sundarban mangrove wetland of India and Bangladesh: a comparative approach

The present work is the first attempt to compare the data of a comprehensive study of the origin and distribution of 16 priority pollutant polycyclic aromatic hydrocarbons (PAHs) in surface sediments (<63 μm) from 18 sampling stations, 9 from Sundarban of Bangladesh and 9 from Indian counterpart. Σ19PAHs concentration in sediments showed wide variations from 208.3 to 12,993.1 ng g^?1 dry weight in Indian Sundarban, whereas 208.4 to 4,687.9 ng g^?1 in the case of Bangladesh. Fluoranthene, pyrene, benzo(b)fluoranthene, benzo(a)pyrene and dibenzo(a,h)anthracene were predominant species for both the countries. The PAH diagnostic ratios indicated that the PAHs in sediments from both the countries were of mixed source of hydrocarbons of both petrogenic and pyrolytic origin. According to the numerical effect-based sediment quality guidelines, the levels of PAHs in the Sundarban wetland of Bangladesh and India should not exert adverse biological effects. The TEQ values calculated for samples from the Bangladesh and Indian Sundarban varied from 13.68 to 1,014.75 and 1.31 to 2,451 ng g^?1 d.w. with an average of 221.02 and 358.63 ng g^?1, respectively. The overall contamination status of PAH was higher in India than Bangladesh.     

Vertical distribution and source identification of polycyclic aromatic hydrocarbons in anoxic sediment cores of Chini Lake, Malaysia: Perylene as indicator of land plant-derived hydrocarbons

Four anoxic sediment cores were collected from Chini Lake, Malaysia in order to investigate the variability of polycyclic aromatic hydrocarbon (PAH) and perylene concentrations. The study also determined significant differences of perylene concentrations in different sediment layers. Total PAH concentrations ranged from 248 to 8098 ng g⁻¹ in the samples. Diagnostic PAH ratios such as methylphenanthrenes/phenanthrene (MP/P), phenanthrene/anthracene (P/A) and fluoranthene/(fluoranthene + pyrene) (Fl/(Fl + Py) revealed a dominance of pyrogenic influences and partial petrogenic inputs to the top sediment layers. Perylene concentrations were high in the top layers (<12 cm) and increased with increasing depth. There is a significant positive correlation (r = 0.705, p = 0.01) between perylene concentrations and TOC. Analysis of variance (ANOVA) and LSD revealed significant differences (p < 0.05) in TOC-normalized perylene concentrations between the upper (<12 cm) and bottom layers (>12 cm). The average perylene concentrations accounted for 26–50% (0–12 cm) and 50–77% (12–36 cm) of pentacyclic-aromatic hydrocarbon isomers (PAI) present whereas it made up 10–34% (0–12 cm) and 46–66% (12–36 cm) of the total PAH. The average pyrene concentrations decreased with increasing depth and accounted for 62% (0–3 cm), 20–23% (3–12 cm) and 3–1.4% (12–36 cm) of perylene present. The results of hierarchical cluster analysis based on these ratios suggested different input sources for the top and bottom layers. It is concluded that the activity of termites on woody plants produced perylene which is supplied to the lake by run-off from the heavy and frequent rains in this Asian tropical climate. In addition, there was also in situ formation of perylene in the bottom layers due to diagenetic processes.     

The effect of biodegradation on polycyclic aromatic hydrocarbons in reservoired oils from the Liaohe basin, NE China

The occurrence and distribution of polycyclic aromatic hydrocarbons (PAHs) has been studied in oil columns from the Liaohe basin, NE China, characterized by varied degrees of biodegradation. The Es3 oil column has undergone light to moderate biodegradation – ranging from levels 2 to 5 on the [Peters, K.E., Moldowan, J.M., 1993. The Biomarker Guide: Interpreting Molecular Fossils in Petroleum and Ancient Sediments. Prentice Hall, Englewood Cliffs, NJ, p. 363] scale (abbreviated as ‘PM level’) – while the shallower Es1 column has undergone more severe biodegradation, ranging from PM level 5 to 8. Both columns show excellent vertical biodegradation gradients, with degree of biodegradation increasing with increasing depth toward the oil–water contact (OWC). The compositional gradients in the oil columns imply mass transport control on degradation rates, with degradation occurring primarily at the OWC. The diffusion of hydrocarbons to the OWC zone will be the ultimate control on the maximum degradation rate. The chemical composition and physical properties of the reservoired oils, and the ‘degradation sequence’ of chemical components are determined by mixing of fresh oil with biodegraded oil.The PAH concentrations and molecular distributions in the reservoired oils from these biodegraded columns show systematic changes with increasing degree of biodegradation. The C₃₊-alkylbenzenes are the first compounds to be depleted in the aromatic fraction. Concentrations of the C_0–5-alkylnaphthalenes and the C_0–3-alkylphenanthrenes decrease markedly during PM levels 3–5, while significant isomer variations occur at more advanced stages of biodegradation (>PM level 4).The degree of alkylation is a critical factor controlling the rate of biodegradation; in most cases the rate decreases with increasing number of alkyl substituents. However, we have observed that C₃-naphthalenes concentrations decrease faster than those of C₂-naphthalenes, and methylphenanthrenes concentrations decrease faster than that of phenanthrene. Demethylation of a substituted compound is inferred as a possible reaction in the biodegradation process.Differential degradation of specific alkylated isomers was observed in our sample set. The relative susceptibility of the individual dimethylnaphthalene, trimethylnaphthalene, tetramethylnaphthalene, pentamethylnaphthalene, methylphenanthrene, dimethylphenanthrene and trimethylphenanthrene isomers to biodegradation was determined. The C₂₀ and C₂₁ short side-chained triaromatic steroid hydrocarbons are degraded more readily than their C_26–28 long side-chained counterparts. The C_21–22-monoaromatic steroid hydrocarbons (MAS) appear to be more resistant to biodegradation than the C_27–29-MAS.Interestingly, the most thermally stable PAH isomers are more susceptible to biodegradation than less thermally stable isomers, suggesting that selectivity during biodegradation is not solely controlled by thermodynamic stability and that susceptibility to biodegradation may be related to stereochemical structure. Many commonly used aromatic hydrocarbon maturity parameters are no longer valid after biodegradation to PM level 4 although some ratios change later than others. The distribution of PAHs coupled with knowledge of their biodegradation characteristics constitutes a useful probe for the study of biodegradation processes and can provide insight into the mechanisms of biodegradation of reservoired oil.     

Polycyclic aromatic hydrocarbons (PAHs) in particle-size fractions of urban topsoils

Polycyclic aromatic hydrocarbons’ (PAHs) concentrations in bulk samples are commonly used to assess contamination but PAHs are unevenly distributed among particle-size fractions. Seventeen urban surface soil samples from the city of Xuzhou, China, were collected and then fractionated into five size fractions (2,000–300, 300–150, 150–75, 75–28, and <28 μm). The concentrations of 12 US EPA PAHs were measured using gas chromatograph/mass spectrometry in various fractions, and the bulk soil samples and distribution patterns of PAHs in different particle-size fractions were investigated. The mean concentration of total PAHs in bulk soil samples was 1,879 ng/g. The median concentrations for all individual PAH were higher for the 75–2,000 μm fraction than for the <75 μm fraction. The distribution factors for various PAHs in <28 μm soil fraction were closely correlated (r = ?0.661, p < 0.019) to bulk soil fugacity capacity. The values of PAH isomer indicated that traffic emissions might be the major origin of PAHs in Xuzhou surface soils. Spearman correlation analysis was performed and the result suggested that soil organic carbon might be a factor controlling the concentrations of PAHs in soils.