Similar Polycyclic Aromatic Hydrocarbons Research Articles

COVID-19 lockdown measures affect polycyclic aromatic hydrocarbons distribution and sources in sediments of Chaohu Lake, China

The COVID-19 pandemic has profoundly impacted human activities and the environment globally. The lockdown measures have led to significant changes in industrial activities, transportation, and human behavior. This study investigates how the lockdown measures influenced the distribution of polycyclic aromatic hydrocarbons (PAHs) in the sediments of Chaohu Lake, a semi-enclosed lake. Surface sediment samples were collected in summer of 2020 (lockdown have just been lifted) and 2022 and analyzed for 16 priority PAHs. The range of ΣPAHs concentrations remained similar between 2020 (158.19–1693.64 ng·g−1) and 2022 (148.86–1396.54 ng·g−1). Among the sampling sites, the west lake exhibited similar PAHs concentrations characteristics over the two years, with higher levels observed in areas near Hefei City. However, the east lake exhibited increased ΣPAHs concentrations in 2022 compared to 2020, especially the area near ship factory. PAHs source analysis using principal component analysis-multiple linear regression (PCA-MLR) revealed an increased proportion of petroleum combustion sources in 2022 compared to 2020. The isotope analysis results showed that organic matter (OM) sources in the western lake remained relatively stable over the two years, with sewage discharge dominating. In contrast, the eastern lake experienced a shift in OM sources from sewage to C3 plants, potentially contributing to the increased PAH levels observed in the eastern lake sediments. Ecological risk assessment revealed low to moderate risk in both 2020 and 2022. Health risk evaluation indicated little difference in incremental lifetime cancer risk (ILCR) values between the two years, with only benzo[a]pyrene (BaP) posing a high risk among the carcinogenic PAHs. Children generally faced higher health risks compared to adults. This study reveals pandemic-induced changes in PAH pollution and sources in lake sediments, offering new insights into the impact of human activities on persistent organic pollutants, with implications for future pollution control strategies.

Characterization of Microplastics and Adsorbed/Dissolved Polycyclic Aromatic Hydrocarbons in the Biggest River System in Saitama and Tokyo, Japan.

This study presents a comprehensive characterization of microplastics (MPs) and adsorbed/dissolved polycyclic aromatic hydrocarbons (PAHs) in the Arakawa River, the largest river system in Saitama and Tokyo, Japan. The MPs were sampled at various points along the river, revealing an average number density of 2.21 ± 1.48 pieces/m3, with a predominant size range of 0.5-1 mm. Polymer analysis indicated that polyethylene (PE) comprised the highest proportion of MPs (55.9%), followed by polypropylene (PP) (22.4%) and polystyrene (PS) (21.7%). Seasonal fluctuations in MPs concentration were observed, with the highest values in winter and the lowest in summer. An analysis of adsorbed PAHs revealed a median partition coefficient (Kd) value of 3.58 × 104 L/kg for MPs, indicating their affinity for PAHs. Further PAHs analysis revealed that the PAHs with the highest mean values were bicyclic naphthalene, pyrene, and fluoranthene. A comparison with coastal MPs showed differences in PAH composition, with higher proportions of high-ring PAHs observed in coastal samples. The study also investigated the distribution of PAHs in the dissolved and suspended states in the river, finding that similar PAHs were distributed in both states, with the PAHs present in MPs being about 1/10,000 of those in the dissolved and suspended states. The study underscores the importance of the continued monitoring and management of MPs and associated pollutants in river ecosystems.

Ozone-assisted low temperature oxidation of indene: An experimental and computational study

Elucidating the oxidation chemistry of polycyclic aromatic hydrocarbons (PAHs) aids in understanding the degradation reaction processes of PAHs, as well as their competitive roles in PAH growth. In this work, ozone-assisted oxidation of indene, the smallest prototype PAH molecule, was investigated in an atmospheric jet stirred reactor at 400–550 K. Ab initio quantum chemistry calculations were conducted to characterize the oxidation kinetics of indene and interpret the experimental observations. Fingerprint oxidation products including 2-(2-oxoethyl) benzoic acid, 2-(formylmethyl) benzaldehyde, 1,2-indanedione and 1-indanone were identified by synchrotron vacuum ultraviolet photoionization mass spectrometry. The initial C9H8O3 adduct resulting from O3-addition to indene exhibits high instability and is primarily detected as 2-(2-oxoethyl)benzoic acid following ozonolysis reactions. Minor amounts of vinylhydroperoxide were also observed as isomeric products of the C9H8O3 adduct. Theoretical calculations indicate that indene ozonolysis is highly structure-dependent, where the conformation of the C9H8O3 adduct determines the configuration of the resulting Criegee intermediates (CI). The distinctive reaction pathways introduced by the bifunctionalized characteristics of indene-derived large CIs are emphasized in this study. syn-Configuration CI features more conversion pathways compared to anti-CI due to the interaction between CI functionality and the neighboring aldehyde group, among which the bicyclic ring-closure reaction yielding secondary ozonide is most favored. The dioxirane intermediates generated from anti-CIs can undergo the Crossed Acid-forming channel to yield the target acid products, which provides an alternative way for dioxirane conversion. Further theoretical analyses demonstrate that ozonolysis is not the exclusive mechanism for indene oxidation under O3-assisted conditions. Instead, it is accompanied by low-temperature reactions initiated by OH/O2, leading to key products such as 2-(formylmethyl) benzaldehyde and 1-indanone. The present work aims to unravel the elusive chemistry involved in the O3-initiated oxidation of indene, providing new insights into the distinctive kinetics introduced by large bifunctionalized CIs in the ozonolysis of structurally similar PAHs.

Polycyclic aromatic hydrocarbon size tracers

ABSTRACT We examine the dependence of polycyclic aromatic hydrocarbon (PAH) band intensity ratios as a function of the average number of carbon atoms and assess their effectiveness as tracers for PAH size, utilizing the data, models, and tools provided by the NASA Ames PAH Infrared Spectroscopic Data base. To achieve this, we used spectra from mixtures of PAHs of different ionization fractions, following a size distribution. Our work, congruent with earlier findings, shows that band ratios that include the 3.3 μm PAH band provide the best PAH size tracers for small-to-intermediate sized PAHs. In addition, we find that band ratios that include the sum of the 15–20 μm PAH features (I$_{\Sigma _{15-20}}$) and the 6.2 or 7.7 μm bands also serve as good tracers for PAH size in the case of small-to-intermediate sized PAHs, for objects under a similar PAH size distribution as with the presented models. For different PAH size distributions, the application of a scaling factor to the I6.2/I$_{\Sigma _{15-20}}$ ratio can provide estimates for the size of the small-to-intermediate PAH population within sources. Employment of the I6.2/I$_{\Sigma _{15-20}}$ and I7.7/I$_{\Sigma _{15-20}}$ ratios can be of particular interest for JWST observations limited only to ∼5–28 μm MIRI(MRS) coverage.

Coupling Environmental Whole Mixture Toxicity Screening with Unbiased RNA-Seq Reveals Site-Specific Biological Responses in Zebrafish.

Passive sampling device (PSD) extracts paired with developmental toxicity assays in Danio Rerio (zebrafish) are excellent sensors for whole mixture toxicity associated with the bioavailable non-polar organics at environmental sites. We expand this concept by incorporating RNA-Seq in 48-h post fertilization zebrafish statically exposed to PSD extracts from two Portland Harbor Superfund Site locations: river mile 6.5W (RM 6.5W) and river mile 7W (RM 7W). RM 6.5W contained higher concentrations of polycyclic aromatic hydrocarbons (PAHs), but the diagnostic ratios of both extracts indicated similar PAH sourcing and composition. Developmental screens determined RM 6.5W to be more toxic with the most sensitive endpoint being a "wavy" notochord malformation. Differential gene expression from exposure to both extracts was largely parallel, although more pronounced for RM 6.5W. When compared to the gene expression associated with individual chemical exposures, PSD extracts produced some gene signatures parallel to PAHs but were more closely matched by oxygenated-PAHs. Additionally, differential expression, reminiscent of the wavy notochord phenotype, was not accounted for by either class of chemical, indicating the potential of other contaminants driving mixture toxicity. These techniques offer a compelling method for non-targeted hazard characterization of whole mixtures in an in vivo vertebrate system without requiring complete chemical characterization.

Seasonal characterization, sources, and source-specific risks of PM2.5 bound PAHs at different types of urban sites in central China

Polycyclic aromatic hydrocarbons (PAHs) have been extensively investigated in China. However, most previous studies only focused on specific locations. Here, we conducted field studies simultaneously to explore the seasonal characterization, sources, and source-specific risks of 16 PAHs in four polluted cities in China. Similar seasonal Σ16 PAHs variations are observed in all four sites with relatively high values in winter and low values in summer and the ratios of Σ16 PAHs between winter and summer range from 2.7 to 4.4. From summer to winter, the extent of PAH increase outpaces that of PM2.5 increase resulting in significant increase of ∑16 PAHs/PM2.5 in winter. Five potential sources were resolved by PMF: (1) coal combustion (32–52%); (2) vehicle emissions (19–29%); (3) evaporation (9–26%); (4) coke oven emission (11–15%); and (5) biomass burning (5–13%). The highest fraction of evaporation is found in the Luoyang site due to the presence of many petrochemical plants, the largest oil refinery in Henan and large oil storage tanks. The coking factor contributes the largest proportion in Anyang site because of many out of date inefficient coking facilities. The source-related risks in four sites are all higher than the USEPA guideline value (1.0 × 10−6) except for biomass burning. The largest total risks are observed at Luoyang site, slightly higher than those of other cities. Our results suggest that the PAHs still need to be concerned due to the complexity of sources and source emitted risks in different type of cities, and specific source control strategies should be target in different regions.

Evaluating predictive relationships between wristbands and urine for assessment of personal PAH exposure

During events like the COVID-19 pandemic or a disaster, researchers may need to switch from collecting biological samples to personal exposure samplers that are easy and safe to transport and wear, such as silicone wristbands. Previous studies have demonstrated significant correlations between urine biomarker concentrations and chemical levels in wristbands. We build upon those studies and use a novel combination of descriptive statistics and supervised statistical learning to evaluate the relationship between polycyclic aromatic hydrocarbon (PAH) concentrations in silicone wristbands and hydroxy-PAH (OH-PAH) concentrations in urine. In New York City, 109 participants in a longitudinal birth cohort wore one wristband for 48 h and provided a spot urine sample at the end of the 48-hour period during their third trimester of pregnancy. We compared four PAHs with the corresponding seven OH-PAHs using descriptive statistics, a linear regression model, and a linear discriminant analysis model. Five of the seven PAH and OH-PAH pairs had significant correlations (Pearson’s r = 0.35–0.64, p ≤ 0.003) and significant chi-square tests of independence for exposure categories (p ≤ 0.009). For these five comparisons, the observed PAH or OH-PAH concentration could predict the other concentration within a factor of 1.47 for 50–80% of the measurements (depending on the pair). Prediction accuracies for high exposure categories were at least 1.5 times higher compared to accuracies based on random chance. These results demonstrate that wristbands and urine provide similar PAH exposure assessment information, which is critical for environmental health researchers looking for the flexibility to switch between biological sample and wristband collection.

Effect of charcoal grilling on polycyclic aromatic hydrocarbons (PAHs): content, composition, and health risk in edible fish in Japan.

The content and composition of polycyclic aromatic hydrocarbons (PAHs) induced by charcoal grilling of fish were determined in this study. Using HPLC-DAD, the simultaneously quantitative method for 16 priority PAHs was developed and applied to three common Japanese fish: mackerel, pacific saury, and sardine. Charcoal grilling largely increased the content of both total and representative PAHs. Moreover, all of the three fish showed a similar PAH composition under the effect of charcoal grilling: in raw samples, naphthalene was observed as the dominant PAH, while in charcoal-grilled samples, phenanthrene, fluoranthene, and pyrene served as the major PAHs. Furthermore, a health risk assessment showed that charcoal grilling resulted in high levels of the toxic equivalence quotients, the daily dietary intake exposure to PAHs, and the incremental lifetime cancer risk in three fish, which outclassed the raw samples and exceeded the recommended limitations. The results suggested that charcoal grilling-induced accumulation of PAHs and their potential health risk on human health should be of great concern, which might contribute to the dietary guidance and risk management of food-contained PAHs.

Evaluation of Polycyclic Aromatic Hydrocarbon Content of Selected Fin and Shell Fish from Named Rivers in Ogoniland, Rivers State, Nigeria

Polycyclic aromatic hydrocarbon (PAH) content in selected fin and shell fishes from Bodo and Kaa in Ogoniland were studied. PAH was determined by Gas chromatography, using Texas Natural Resource Conversion Commission, Texas (TNRCC TX) method. There was a total of 16 PAHs detected in the samples from the two sites, test site (Bodo) and control site (Kaa). Similar PAH accumulations were observed in the four species, but the concentrations of the PAH accumulations were different. For samples from Kaa, Mullet showed the highest total mean concentration of PAHs followed by Sompat grunt, Tilapia and the least was Shrimps. However, for samples collected from Bodo, Tilapia showed the highest total mean concentration of PAHs, followed by Sompat grunt, Shrimps, and the least Mullet. These findings were not definitive as to the source of the PAH, seemingly suggesting various or multiple sources of PAHs contamination in the studied sites. These variations may be attributed to their feeding habits. The mean and standard deviations for PAHs from the test site ranged from 0.08±.000b to 23.7±.473b, 0.05±.001b to 7.74±.346b, 0.02±.001b to 9.48±.002b, 0.07±.000b to 11.0±.029b for Tilapia, Mullet, Shrimps and Sompat grunt respectively and 0.18±.006a to 6.56±.064a, 0.08±.000a to 11.8±.555a, 0.05±.002a to 3.11±.036a, 0.05±.002a to 5.12±.059a for samples of Tilapia, Mullet, Shrimp and Sompat grunt respectively from the control site. In conclusion, the calculated potency equivalence concentration (PEC) for all the tested aquatic species collected from Kaa and Bodo were all above the screening value (SV) suggesting that the consumption of these aquatic species from the test and control site at a rate of 68g/day in an adult of about 60kg will expose the individual to a potential risk of cancer.

Competitive Adsorption of Polycyclic Aromatic Hydrocarbons to Carbon Nanotubes and the Impact on Bioavailability to Fathead Minnow (Pimephales promelas)

Recent studies investigating the influence of carbon nanotubes (CNTs) on the bioavailability of organic contaminants have mostly focused on single-solute systems; however, a more likely scenario in the natural environment is a multisolute system where chemical interactions at the surface of the CNT may alter the bioavailability of these chemicals. In the present study bisolute adsorption isotherms of pairs of chemically similar polycyclic aromatic hydrocarbons (PAHs) by multiwalled carbon nanotubes (MWCNTs) were established, in conjunction with quantifying the bioavailability of the 2 competing MWCNT-adsorbed PAHs to Pimephales promelas using bile analysis by high-performance liquid chromatography with fluorescence detection. The results showed that whereas adsorption and bioavailability of chemically similar PAHs (anthracene and phenanthrene, and fluoranthene and pyrene) were the same in a single-solute system, in bisolute systems, PAHs that could better align or flex with the MWCNT surface due to morphological characteristics would outcompete the more rigid or planar PAHs. The bioavailability of individual PAHs in bisolute solutions increased by as much as 50% compared with single-solute solutions. However, the relationship between adsorption (i.e., Kd ) and concentration of PAH in the fish bile was similar in single and bisolute systems. This finding indicates that competitive interactions at the surface of MWCNTs influence bioavailability by way of altering adsorption affinity in a moderately predictable manner. Environ Toxicol Chem 2020;39:1702-1711. © 2020 SETAC.

Distribution and sources of polycyclic aromatic hydrocarbons in the water column of Kongsfjorden, Arctic

Kongsfjorden is known for its characteristic multi-layer water mass formed by the convergence of freshwaters from nearby glaciers and rivers and saline water from the Atlantic and Arctic. The distribution of polycyclic aromatic hydrocarbons (PAHs) in the water column of Kongsfjorden was investigated and their potential sources were analyzed. The total concentrations of 16 PAHs in the surface seawater and river water were in the range of 33.4−79.8 ng/L (mean 48.5 ng/L) and 2.3−201.4 ng/L (mean 126.1 ng/L), respectively. Horizontally, PAHs were mainly concentrated around river estuaries and the glacier front in the dissolved phase. Vertically, the PAHs in the particulate phase followed surface-enrichment and depth-depletion patterns in most stations, with the maximum concentration found at 50 m depth in the central area of Kongsfjorden. The compositions of PAHs in seawater and rivers were similar, with two-ring and tricyclic PAHs comprising the majority of the dissolved and particulate phases. PAHs found in Kongsfjorden waters appeared to be derived from multiple sources such as petroleum and coal combustion. PAHs in the bay mouth of Kongsfjorden were mainly introduced by the West Spitsbergen Current and the Arctic waters, while in the inner bay, atmospheric deposition and local sources were the major contributors. The distribution of PAHs was mainly attributed to the suspended particulate distribution.

Polycyclic aromatic hydrocarbons in processed yard trash.

This work examines polycyclic aromatic hydrocarbon (PAH) concentrations in yard trash at various stages of the yard trash management cycle of collection, stockpiling, grinding and screening into mulch, and composting. Total extractable PAH concentrations were measured in yard trash at various management stages from 10 locations in Florida. The concentrations of 16 PAH compounds in processed yard trash ranged from 0.38 to 14 mg kg-1. PAH concentrations were detected in vegetative material harvested from a residential neighborhood, but were below the United States Environmental Protection Agency residential regional screening levels (RSLs). PAH concentrations near or above the RSLs were common in both unprocessed and processed yard trash collected at waste management facilities. PAH concentrations were amongst the highest in newly ground yard trash samples and were amongst the lowest in composted yard trash samples. These findings are important because land application of some waste materials, such as construction and demolition debris fines and street sweepings, are sometimes limited due to PAH. If processed yard trash, which is commonly land applied in residential settings, possesses similar PAH concentrations, evaluation of current risk assessment practices for land-applied wastes may require further examination.

Polycyclic aromatic hydrocarbons and heavy metals in urban environments: Concentrations and joint risks in surface soils with diverse land uses

AbstractAlthough polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) are abundant around cities, few researchers have studied the complex concentrations and joint risks of these pollutants in urban surface soils containing diverse land uses. We collected 69 urban surface soil samples from roadside districts, green belts, public green space, commercial districts, and residential district in urban areas of Nanjing, China to determine the concentrations, distributions, deposition patterns, and joint risks of PAH and HM contaminants. No significant differences were found among the five studied land uses, but a wide range of PAH levels were found in these land uses, as these diverse land uses have similar PAH pollution sources. As these areas persistently generate high PAH levels by gasoline/diesel engine or coal combustion, the PAH distribution characteristics indicated that commercial centers or city centers are the most heavily contaminated sites. The distributions of black carbon and HMs, except for Pb, were found to be significantly correlated. Except for Cd and As, HM levels among diverse land uses also showed no significant differences, possibly stemming from the non‐point source pollution of these metals in the study areas. Factor analysis showed that 46.2% of the elevated pollutant concentrations resulted from combustion processes, 24.3% were caused by natural background fluctuations, and 11.9% resulted from non‐combustion processes. The studied PAHs and As presented low carcinogenic risks. Cd, Cu, Pb, and Zn depicted acceptable total non‐carcinogenic risks in all land uses; however, the risks associated with these HMs possessed detailed differences.

Polycyclic Aromatic Hydrocarbons (PAHs) in Road Dust Collected from Myanmar, Japan, Taiwan, and Vietnam.

In this study, we determined the concentrations of polycyclic aromatic hydrocarbons (PAHs) in road dust from Myanmar, Japan, Taiwan, and Vietnam. PAHs were detected in urban and rural areas of Myanmar at mean concentrations of 630ng/g dry weight and 200ng/g dry weight, respectively. PAHs were also detected in road dust from Vietnam (mean 1700ng/g) and Taiwan (2400ng/g). PAH diagnostic ratios suggested that fossil fuel vehicular exhaust and biomass combustion are major sources of PAHs in road dust in Myanmar. Road dust samples from Japan, Taiwan, and Vietnam had similar PAH diagnostic ratios, implying that PAH sources are similar. We assessed the human health risks posed by PAHs in road dust using carcinogenic equivalents (CEQs) and incremental lifetime cancer risk (ILCR). Mean CEQs were decreased in the order Taiwan (173ng/g) > Vietnam (162ng/g for Hanoi) > Myanmar (42 and 31ng/g for Yangon and Pathein, respectively) > Japan (30ng/g for Kumamoto). Benz[a]pyrene, fluoranthene, and benzo[b]fluoranthene, the predominant PAHs, contributed > 70% of total CEQs. High ILCR values were found for Taiwan (5.9 × 10-4 and 9.9 × 10-4 for children and adults, respectively) and Vietnam (6.5 × 10-4 and 9.2 × 10-4 for children and adults, respectively, in Hanoi), indicating that PAHs in road dust pose cancer risks to the inhabitants of Taiwan and Hanoi. To our knowledge, this is the first report to identify PAH pollution in the environment and to evaluate the human health risks of these PAHs in Myanmar.

Polycyclic aromatic hydrocarbons in atmospheric particulate depositions and urban soils of Moscow, Russia

The study was conducted to quantify the polycyclic aromatic hydrocarbons (PAHs) accumulation in urban soils from different functional areas via atmospheric inputs with particulate matter. PAH concentration and pattern were measured in the particulate matter of snow depositions, in the upper layers of artificial soils from densely built-up areas and in the undisturbed natural soils (Umbric Retisols) from green park area. Samples were collected in 2011–2013 at 58 sites with different traffic activities located at the territory of the Eastern Administrative Okrug of Moscow. The soil samples and filters with particulate matter were extracted by pressurized liquid extraction using Dionex ASE200. Clean-up analyses were performed on SPE cartridges filled with silica gel. Concentrations of PAHs were determined by high-performance liquid chromatography using an Agilent 1100 System equipped with fluorescent detector. Mean values of PAH input with snow particles were 45–57 μg/m2 for recreational and residential zones, and 140–264 μg/m2 for traffic zones. The samples of depositions from different functional areas showed a similar PAH pattern and consisted primarily of 3–4-ring PAHs. Total PAH concentrations in upper layers of artificial soils showed similar mean values of 1.43–2.21 μg/g for all functional zones. The PAH content in soils from the park area was twofold lower than that from the built-up area (0.34–0.63 μg/g), despite equal levels of atmosphere contamination on these territories. The upper layers of natural soils from recreational and traffic zones showed slight differences in PAH content, though PAH input with snow was fivefold higher in the traffic zone. Compared with airborne depositions, soils contained significant amounts of 5–6-ring PAHs. A high level of soil PAH contamination in urban areas of Moscow, several orders of magnitude higher than the current PAH input to them from the atmosphere, indicates a lack of direct connection of the PAH pool in soils with this source. The high PAH content in the upper layer of constructed soils can be the result of repeated use of materials subjected to a constant technogenic impact for the production of artificial soils.

Interaction of Cobalt Atoms, Dimers, and Co4 Clusters with Circumcoronene: A Theoretical Study

We study the interaction of circumcoronene molecule C54H18 with cobalt in the form of atoms, dimers, and clusters of four atoms. We find that the cobalt atom prefers to be on a hollow site in the edge zone. The cobalt dimer is bonded perpendicularly to another different hollow site in the edge zone. The Co4 cluster adopts a tetrahedral shape with a face parallel to circumcoronene, placing each of the three atoms over contiguous hollow sites, starting from the edge. Cobalt remains bonded to circumcoronene as Co2 molecules or Co4 clusters, rather than spread as isolated atoms, because the cobalt–cobalt interaction is stronger than the cobalt–carbon bond. The interaction with cobalt clusters induces a small magnetic moment on circumcoronene. The magnetic moment of cobalt is reduced when bonding to circumcoronene. There is charge transfer between those systems and its direction depends on the relative position of the cluster with respect to circumcoronene. We then propose that the presence of cobalt over circumcoronene or similar polycyclic-aromatic hydrocarbons can be detected in experiments, looking at the carbon isomer shift which arises due to the contact charge densities at the nuclei.

An optical spectrum of a large isolated gas-phase PAH cation: C78H[formula omitted

A gas-phase optical spectrum of a large polycyclic aromatic hydrocarbon (PAH) cation - C78H26+− in the 410−610 nm range is presented. This large all-benzenoid PAH should be large enough to be stable with respect to photodissociation in the harsh conditions prevailing in the interstellar medium (ISM). The spectrum is obtained via multi-photon dissociation (MPD) spectroscopy of cationic C78H26 stored in the Fourier Transform Ion Cyclotron Resonance (FT-ICR) cell of the PIRENEA setup using the radiation from a mid-band optical parametric oscillator (OPO) laser.The experimental spectrum shows two main absorption peaks at 431 nm and 516 nm, in good agreement with a theoretical spectrum computed via time-dependent density functional theory (TD-DFT). DFT calculations indicate that the equilibrium geometry, with the absolute minimum energy, is of lowered, nonplanar C2 symmetry instead of the more symmetric planar D2h symmetry that is usually the minimum for similar PAHs of smaller size. This kind of slightly broken symmetry could produce some of the fine structure observed in some diffuse interstellar bands (DIBs). It can also favor the folding of C78H26+ fragments and ultimately the formation of fullerenes.This study opens up the possibility to identify the most promising candidates for DIBs amongst large cationic PAHs.

PAH EMISSION AT THE BRIGHT LOCATIONS OF PDRs: THE grandPAH HYPOTHESIS

The polycyclic aromatic hydrocarbon (PAH) emission observed in the Spitzer Infrared Spectrograph spectra of bright mid-IR locations of NGC 7023, NGC 2023, and NGC 1333 was analyzed. These objects show large variations in PAH band ratios when studied through spectral mapping. Nevertheless, the mid-IR spectra at these bright spots show a remarkably similar PAH emission. We used the NASA Ames PAH IR Spectroscopic Database to fit the observations and analyze the derived PAH populations. Our results show that PAH emission in the 5–15 μm range appears to be rather insensitive to variations of the radiation field. Similar PAH populations of neutral small to medium-sized PAHs (∼50%), with ionized species contributing in slightly less than 50%, provide very good fits. Analyzing the degeneracy of the results shows that subtle (but intrinsic) variations in the emission properties of individual PAHs lead to observable differences in the resulting spectra. On top of this, we found that variations of <30% in the PAH abundances would lead to noticeable spectral differences between the three photodissociation regions (PDRs). Therefore, PAH populations must be remarkably similar at these different lines of sight. To account for this, we suggest the concept of grandPAHs as a unique mixture of the most stable PAHs emitting at these spots. Using NGC 7023 as an example, the grandPAHs refer to the robust PAH population that results from the intense processing of PAHs at the border limit between the PDR and the molecular cloud, where, due to the UV radiation that destroys the PAH population, the abundance of PAHs starts decreasing as we move toward the star.

Similar PAH fate in anaerobic digesters inoculated with three microbial communities accumulating either volatile fatty acids or methane.

Urban sludge produced on wastewater treatment plants are often contaminated by organic pollutants such as polycyclic aromatic hydrocarbons (PAH). Their removal under methanogenic conditions was already reported, but the factors influencing this removal remain unclear. Here, we determined the influence of microbial communities on PAH removal under controlled physico-chemical conditions. Twelve mesophilic anaerobic digesters were inoculated with three microbial communities extracted from ecosystems with contrasting pollution histories: a PAH contaminated soil, a PCB contaminated sediment and a low contaminated anaerobic sludge. These anaerobic digesters were operated during 100 days in continuous mode. A sterilised activated sludge, spiked with 13 PAH at concentrations usually encountered in full-scale wastewater treatment plants, was used as substrate. The dry matter and volatile solid degradation, the biogas production rate and composition, the volatile fatty acids (VFA) production and the PAH removals were monitored. Bacterial and archaeal communities were compared in abundance (qPCR), in community structure (SSCP fingerprinting) and in dominant microbial species (454-pyrosequencing). The bioreactors inoculated with the community extracted from low contaminated anaerobic sludge showed the greater methane production. The PAH removals ranged from 10 % to 30 %, respectively, for high and low molecular weight PAH, whatever the inoculums tested, and were highly correlated with the dry matter and volatile solid removals. The microbial community structure and diversity differed with the inoculum source; this difference was maintained after the 100 days of digestion. However, the PAH removal was not correlated to these diverse structures and diversities. We hence obtained three functional stable consortia with two contrasted metabolic activities, and three different pictures of microbial diversity, but similar PAH and matter removals. These results confirm that PAH removal depends on the molecule type and on the solid matter removal. But, as PAH elimination is similar whether the solid substrate is degraded into VFA or into methane, it seems that the fermentative communities are responsible for their elimination.

Temperature dependence of Henry's law constants and KOA for simple and heteroatom-substituted PAHs by COSMO-RS

Henry's Law constants (H) and octanol–air partition coefficients (KOA) for polycyclic aromatic hydrocarbons (PAHs) and selected nitrogen-, oxygen- and sulfur-containing derivatives have been computed using the COSMO-RS method between −5 and 40 °C in 5 °C intervals. The accuracy of the estimation was assessed by comparison of COSMOtherm values with published experimental temperature-dependence data for these and similar PAHs. COSMOtherm log H estimates with temperature-variation for parent PAHs are shown to have a root-mean-square (RMS) error of 0.38 (PAH), based on available validation data. Estimates of O-, N- and S-substituted derivative log H values are found to have RMS errors of 0.30 at 25 °C. Log KOA estimates with temperature variation from COSMOtherm are shown to be strongly correlated with experimental values for a small set of unsubstituted PAHs, but with a systematic underestimation and associated RMS error of 1.11. Similar RMS error of 1.64 was found for COSMO-RS estimates of a group of critically-evaluated log KOA values at room temperature. Validation demonstrates that COSMOtherm estimates of H and KOA are of sufficient accuracy to be used for property screening and preliminary environmental risk assessment, and perform very well for modeling the influence of temperature on partitioning behavior in the temperature range −5 to 40 °C. Temperature-dependent shifts of up to 2 log units in log H and one log unit for log KOA are predicted for PAH species over the range −5 and 40 °C. Within the family of PAH molecules, COSMO-RS is sufficiently accurate to make it useful as a source of estimates for modeling purposes, following corrections for systematic underestimation of KOA. Average changes in the values for log H and log KOA upon substitution are given for various PAH substituent categories, with the most significant shifts being associated with the ionizing nitro functionality and keto groups.