Fraction Of Polycyclic Aromatic Hydrocarbons Research Articles

A new census of dust and polycyclic aromatic hydrocarbons at z=0.7-2 with JWST MIRI

This paper utilises the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) to extend the observational studies of dust and polycyclic aromatic hydrocarbon (PAH) emission to a new mass and star formation rate (SFR) parameter space beyond our local Universe. The combination of fully sampled spectral energy distributions (SEDs) with multiple mid-infrared (mid-IR) bands and the unprecedented sensitivity of MIRI allows us to investigate dust obscuration and PAH behaviour from $z=0.7$ up to $z=2$ in typical main-sequence galaxies. Our focus is on constraining the evolution of PAH strength and the dust-obscured luminosity fraction before and during cosmic noon, the epoch of peak star formation activity in the Universe. um um um um imaging data, enhancing our understanding of the physical characteristics of dust within these galaxies. We find a strong correlation between the fraction of dust in PAHs (PAH fraction qpah ) with stellar mass. Moreover the sub-sample with robust qpah measurements ($N=216$) shows a similar behaviour between qpah and gas-phase metallicity to that at $z suggesting a universal relation: qpah is constant ($ 3.4$<!PCT!>) above a metallicity of $Z odot $ and decreases to $<1$<!PCT!> at metallicities $ odot $. This indicates that metallicity is a good indicator of the interstellar medium properties that affect the balance between the formation and destruction of PAHs. The lack of a redshift evolution from $z 0-2$ also implies that above $Z odot $ the PAH emission effectively traces obscured luminosity and the previous locally calibrated PAH-SFR calibrations remain applicable in this metallicity regime. We observe a strong correlation between the obscured UV luminosity fraction (ratio of obscured to total luminosity) and stellar mass. Above the stellar mass of $M_*>5 Msun on average, more than half of the emitted luminosity is obscured, while there exists a non-negligible population of lower-mass galaxies with $>50<!PCT!>$ obscured fractions. At a fixed mass, the obscured fraction correlates with SFR surface density. This is a result of higher dust covering fractions in galaxies with more compact star-forming regions. Similarly, galaxies with high IRX (IR to UV luminosity) at a given mass or UV continuum slope (beta ) tend to have higher Ssfr and shallower attenuation curves, owing to their higher effective dust optical depths and more compact star-forming regions.

Polycyclic Aromatic Hydrocarbons (PAHs) in Grilled Marshmallows.

The aim of this study was to assess potential health risks among children and adolescents consuming various grilled marshmallows using a survey and to determine polycyclic aromatic hydrocarbons (PAHs) in these food products. PAH analysis in grilled marshmallows included a dilution stage with deionized water and liquid-liquid extraction with cyclohexane and solid-phase extraction (SPE). PAH fractions were initially analyzed via high-performance thin-layer chromatography, and PAH concentrations were determined via gas chromatography with a tandem mass detector using the selective reaction monitoring (SRM) mode. This study on the consumption of grilled marshmallows was conducted among approximately 300 children and adolescents. The preliminary results indicated that "raw" marshmallows did not contain PAHs. However, the obtained data suggested the exposure of young people to carcinogenic PAHs from grilled marshmallows (63.5% of them consumed marshmallows). Carcinogenic benzo(a)pyrene (BaP) was determined in all samples. The profile of PAH concentrations in the extracts isolated from various grilled types of marshmallows was similar (r2 > 0.8000), regardless of the grilling method. Compared to the white sugar confection, higher concentrations of PAHs were determined in multicolored marshmallows. The lack of social awareness about exposure to carcinogenic substances is alarming.

Chemical and genotoxic characterization of bioaccessible fractions as a comprehensive in vitro tool in assessing the health risk due to dust-bound contaminant ingestion.

In the last two decades, awareness grew on the matter of the impact of environment on human health. Contaminants sorbed onto soil and settled dust can be ingested and thus represent a hazard, particularly to young children, who play on the ground and bring their hands and objects to their mouth. Metal(loid)s and polycyclic aromatic hydrocarbons (PAHs) are of concern as they are both carcinogenic to humans and ubiquitous in outdoor environments. The present study aims to assess the total and bioaccessible fractions of PAHs and metal(loid)s present in settled dust of four preschools located in industrial, urban, and suburban areas. On the one hand, children's incremental life cancer risks (ILCR) were calculated according to ingestion pathway. On the other hand, the genotoxicities of the bioaccessible dust-bonded contaminants were determined on gastric cells. PAH concentrations ranged from 50.9 to 2267.3 ng/g, and the bioaccessible fraction represented 10.7% of the total in average. Metal(loid) concentration ranged from 12,430 to 38,941 µg/g, and the mean bioaccessibility was of 40.1%. Cancer risk ranged from 2.8.105 to 8.6.105, indicating that there is a potential cancer risk for children linked to the ingestion of settled dust. The inorganic bioaccessible fraction induced little DNA (< 20%TailDNA) and chromosomal damages (30% increase in micronuclei), whereas the organic bioaccessible fraction induced higher DNA (17-63%TailDNA) and chromosomal damages (88% increase in micronuclei). Such experimental approach needs to be deepen, as a tool complementary to cancer risk calculation, since the latter only lays on a set of targeted contaminants with known toxicity values.

Effect of changes in the fuel type of thermal power plants on the spatial distribution and levels of PAH pollution in the Vorkuta agglomeration beyond the Arctic Circle

The paper is a study of the composition of 15 polycyclic aromatic hydrocarbons (PAHs) in the snow cover of Vorkuta (Komi Republic) in the impact zone of the fuel and energy complex in 2017 and 2023. We have identified high aerotechnogenic pollution of the Vorkuta city and adjacent territories with PAHs during heating with fuel oil and coal, with a mean concentration of 301.6 ng/L (meltwater plus particles) and spatial distribution of 85.2 μg/m2. There is a significant decrease in PAH levels when the fuel for thermal power plants has been changed to natural gas, with a mean concentration of 26.1 ng/L (meltwater plus particulates) and spatial distribution of 4.9 μg/m2. The deposition areas of different PAH fractions are identified in the impact zones of Thermal Power Plants 1 and 2, the Central Boiler House and the urbanised areas of the Vorkuta agglomeration. 2-4-ring PAHs dominate in the emissions, accounting for 92–100 % of the sum of PAHs from coal/oil combustion and 66–93 % from natural gas combustion. The indicator ratios of PAHs in the snow cover of Vorkuta in both 2017 and 2023 indicate their predominantly pyrogenic genesis. The environmental risk coefficients of PAHs in the snow cover and their change from 2017 to 2023 are calculated. TEQ changed from 2.1 ng/L (mean) in the 2017 season to 1.7 ng/L (mean) in the 2023 season. The risk quotients have been reduced from moderate risk to low risk. Reconstruction of thermal power plants when replaced by more environmentally friendly fuel (natural gas) reduces the amount of atmospheric emissions of organic pollutants.

Radio Jet Feedback on the Inner Disk of Virgo Spiral Galaxy Messier 58

Spitzer spectral maps reveal a disk of highly luminous, warm (>150 K) H2 in the center of the massive spiral galaxy Messier 58, which hosts a radio-loud active galactic nucleus (AGN). The inner 2.6 kpc of the galaxy appears to be overrun by shocks from the radio jet cocoon. Gemini NIRI imaging of the H2 1–0 S(1) emission line, Atacama Large Millimeter/submillimeter Array CO 2–1, and Hubble Space Telescope multiband imagery indicate that much of the molecular gas is shocked in situ, corresponding to lanes of dusty molecular gas that spiral toward the galactic nucleus. The CO 2–1 and ionized gas kinematics are highly disturbed, with velocity dispersion up to 300 km s−1. Dissipation of the associated kinetic energy and turbulence, likely injected into the interstellar medium by radio-jet-driven outflows, may power the observed molecular and ionized gas emission from the inner disk. The polycyclic aromatic hydrocarbon (PAH) fraction and composition in the inner disk appear to be normal, in spite of the jet and AGN activity. The PAH ratios are consistent with excitation by the interstellar radiation field from old stars in the bulge, with no contribution from star formation. The phenomenon of jet-shocked H2 may substantially reduce star formation and help to regulate the stellar mass of the inner disk and supermassive black hole in this otherwise normal spiral galaxy. Similarly strong H2 emission is found at the centers of several nearby spiral and lenticular galaxies with massive bulges and radio-loud AGNs.

Experimental and modeling study of fuel-rich oxidation of gasoline surrogate components/dimethyl carbonate blends in an atmospheric flow reactor

Fuel-rich oxidation of blending fuels consisting of three typical gasoline surrogate components (n-heptane, iso-octane, and toluene) and dimethyl carbonate (DMC) was investigated in an atmospheric-pressure flow reactor at mean gas temperatures from 1000 to 1350 K, equivalence ratio of 9.0, and residence time of 1.2 s. Blending ratios of DMC were 35 and 70 % on a molar basis. The mole fractions of not only polycyclic aromatic hydrocarbons (PAHs) up to 3 ring structure but also small intermediate species from C1 to C5 contained in sampled gas were experimentally quantified. A kinetic model that includes not only oxidation mechanism of gasoline surrogate components and DMC but also PAH growth reactions was developed to reproduce the experimental data. The experimental and simulated results showed that the blending effect of DMC on PAH production was different according to gasoline surrogate components. By blending DMC with n-heptane and iso-octane, the mole fractions of PAHs were generally reduced with an increase of the DMC blending ratio in the temperature range studied here. On the other hand, when DMC was blended with toluene, PAH production in the blending fuels was larger than that in pure toluene at a temperature below 1150 K, while the mole fractions of PAHs in pure toluene were identical to or larger than those in the blending fuels at a temperature above 1200 K. Because a reactivity of DMC is higher than toluene, toluene conversion was facilitated at a low temperature, leading to the promoted PAH production in the blending fuels compared to pure fuel. However, such a promoting effect of DMC was diminished at an elevated temperature, explaining the identical or large PAH production in neat toluene compared to the blending fuels. On the other hand, n-heptane and isooctane can be easily reacted even at a low temperature, suggesting that the promoting effect of DMC cannot be observed. This study reasonably succeeded in explaining the different DMC blending effects on PAH formation depending on the gasoline surrogate components. Novelty and significance statementExperiments and kinetic modeling for the mixtures consisting of dimethyl carbonate (DMC) and gasoline surrogate components, such as n-heptane, iso-octane, and toluene, were conducted to reveal the blending effect of DMC on polycyclic aromatic hydrocarbon (PAH) formation under the fuel-rich environment. It was found that DMC had a dilution effect in n-heptane/DMC and iso-octane/DMC blends, resulting in a reduction in PAH production with an increase of a DMC blending ratio. On the other hand, while DMC had the dilution effect in the toluene/DMC blend at an elevated temperature similar to other blends, toluene conversion was facilitated in the presence of DMC at a low temperature, resulting in the enhanced PAH production in the toluene/DMC blends compared to pure toluene.

Monk seals (Monachus monachus) in the Mediterranean Sea: The threat of organochlorine contaminants and polycyclic aromatic hydrocarbons

The Mediterranean monk seal (Monachus monachus) is an emblematic species of conservation concern. Anthropogenic pressures have led to severe population declines and significant fragmentation of the remaining populations. Because of their close relationship with coastal areas, Mediterranean monk seals may be potentially exposed to pollution from agricultural sources, as well as from oil tanker spills. Although monitoring of pollution has long been considered a priority for this species, data on monk seal contamination levels are scarce. In this study, 55 blubber samples of all genders and age classes collected during necropsies (1995–2013) from seals of the Eastern Mediterranean subpopulation were analyzed for organochlorine compounds (OCs), i.e., hexachlorobenzene (HCB), polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDTs), and polycyclic aromatic hydrocarbons (PAHs). Overall, PCBs > DDTs ≫ PAHs > HCB in all samples. Results showed a significant downward trend over the 19-year period for DDTs and HCB. No marked pattern was found for PAHs, even though relative abundance of cancerogenic PAH fraction rose in recent years. PCB levels in subadult specimens increased noticeably over time despite worldwide ban. Our findings did not suggest recent releases of DDT or new pesticides (e.g., Dicofol) in the environment, but may indicate an improper disposal of ancient storages of PCBs or a remobilization from reservoirs. OC levels exceeded thresholds that are commonly associated with immunosuppression and reproductive impairment in other pinnipeds. Hence, OCs could be responsible of potential toxicological effects in this subpopulation. This study represents the first report on PAH and one of the few reports on OC bioaccumulation in Mediterranean monk seals. Based on the levels found in the blubber of monk seals from the Eastern Mediterranean, and given the known harmful effects associated to the prolonged exposure to these substances and the reduced long-term expectations of species recovery, regular monitoring is advocated.

Bioremediation of Engine Oil-Contaminated Soil using Selected Indigenous Moulds

The polycyclic aromatic hydrocarbons (PAHs) utilizing the potential of moulds from engine oil-polluted soils were assessed. These PAHs are known to be toxic, mutagenic and carcinogenic in the environment. Consequently, the study aims to evaluate the potential of indigenous moulds from engine oil in the remediation of contaminated soil. Samples were collected from engine oil-polluted soils from Samonda, Ibadan, Oyo State Nigeria. The ability of four potential indigenous moulds to degrade the PAH fraction of the engine oil-polluted soil sample was assessed using the gas chromatography technique. Four moulds were identified based on their cultural and microscopic characteristics and were confirmed as Aspergillus flavus, Aspergillus parasiticus, Aspergillus oryzae and Aspergillus nidulans. The highest biodegradation potential was observed in treated soil sample containing Aspergillus flavus (55.15%) followed by Aspergillus parasiticus (55.00%), Aspergillus oryzae (44.51%) and the least biodegradation potential was observed in the sample containing Aspergillus nidulans (24.16%) after 60 days of treatment. This study revealed that indigenous mould has the ability to utilize toxic fractions of petroleum products as their sole carbon sources therefore are the major bio-remediating agents in the sampling area.

Monitoring and Risk Assessment of Polycyclic Aromatic Hydrocarbons in Mainstream Cigarette Smoke

Objectives : Cigarette smoking is an important factor in human exposure to polycyclic aromatic hydrocarbons (PAHs). Machine-smoking methods have been devised to evaluate inhalation exposure to mainstream cigarette smoke. However, there have been only a few studies that have employed these methods for PAH monitoring in Korea.Methods : Total particulate matter samples were collected from the mainstream smoke of five different cigarette types using the ISO 3308 standard smoking method. The samples were analyzed for 16 PAHs using a gas chromatograph/mass spectrometer (GC/MS) following extraction and clean-up procedures.Results and Discussion : The 16 PAH levels of cigarette samples ranged from 87.1 ng/cig to 247.4 ng/cig with an average of 135.4 ng/cig. The average fractions of PAHs classified by the number of rings were as follows: 15% (2 rings), 37% (3 rings), 43% (4 rings), 4% (5 rings), and 1% (6 rings). Diagnostic ratios suggested that the characteristics of PAH pollution in mainstream cigarette smoke were similar to those of biomass burning but different from those of ambient air. The carcinogenic risks of PAHs exceeded the risk threshold of the US EPA (1.0E-06) for the 10%, 30%, and 20% exposure groups of adult males, adult females, and all adults, respectively.Conclusion : This study highlights the significance of mainstream cigarette smoke in examining human inhalation exposure to PAHs and carcinogenic risks, which are primarily influenced by cigarette smoking rather than ambient air. These findings can contribute to a comprehensive assessment of inhalation exposure to PAHs and provide guidance for the development of environmental health policies aimed at reducing such exposure.

Occurrence and distribution of polycyclic aromatic hydrocarbons (PAHs) in marine organisms from Shenzhen coastal waters and human health risk assessment

This study investigated the levels and composition of 16 priority polycyclic aromatic hydrocarbons (PAHs) in marine organisms from South China Sea and assessed their potential health risks. The results revealed that the pollution levels of total PAHs ranged from 3.56 to 392.21 ng/g dw. Notably, 4-ring PAHs constituted the predominant fraction (58.02 %) of the total PAHs, with pyrene being the most abundant congener across all species. Intriguingly, our findings suggested that consuming these organisms might pose a low non-cancer hazard. Nonetheless, benzo[a]pyrene was detected in most species, with levels ranging from non-detectable to 11.24 ng/g dw. The individual lifetime cancer risk levels associated with seafood consumption in studied regions ranged from 1.10 × 10−5 to 1.52 × 10−5, highlighting a potential cancer risk that warrants special attention. These findings emphasize the need to prioritize carcinogenic compounds over total PAHs and underscore the importance of continuous monitoring of PAH pollution in seafood.

Enhanced biodegradation of phenanthrene and anthracene using a microalgal-bacterial consortium.

Polycyclic aromatic hydrocarbons (PAHs) are chemicals that are released into the environment during activities of the petroleum industry. The bioaccumulation, carcinogenic and mutagenic potential of PAHs necessitates the bioremediation of these contaminants. However, bioremediation of PAHs has a number of limitations including the inability of a single microbe to degrade all of the PAH fraction's environmental constituents. Therefore, a different paradigm, employing microalgal-bacterial consortium (MBC), may be used to effectively remove PAHs contaminants. In this type of interaction, the microalgae and bacteria species in the consortium work together in a way that enhances the overall performance of the MBC. Bacterial species in the consortium provide essential nutrients or growth factors by degrading toxic substances and provide these to microalgae, while the microalgae species provide organic carbon for the bacterial species to grow. For the first time, the ability of Gonium pectorale (G. pectorale) microalgae to break down phenanthrene (PHE) and anthracene (ANT) was investigated. Phenanthrene was shown to be more effectively degraded by G. pectorale (98%) as compared to Bacillus licheniformis (B. licheniformis) 19%. Similarly, G. pectorale has effectively degrade anthracene (98%) as compared with B. licheniformis (45%). The consortia of G. pectorale and B. licheniformis has shown a slight increase in the degradation of PHE (96%) and ANT (99%). Our findings show that B. licheniformis did not inhibit the growth of G. pectorale and in the consortia has effectively eliminated the PAHs from the media. Therefore G. pectorale has a tremendous potential to remove PAHs from the polluted environment. Future research will be conducted to assess Gonium's capacity to eliminate PAHs that exhibit high molar masses than that of PHE and ANT.

Atmospheric occurrences and health risk assessment of polycyclic aromatic hydrocarbons and their derivatives in a typical coking facility and surrounding areas

Coking facilities release large quantities of polycyclic aromatic hydrocarbons (PAHs) and their derivatives into the ambient air. Here we examined the profiles, spatial distributions, and potential sources of atmospheric PAHs and their derivatives in an industrial coking plant and its surrounding environment (gaseous and particulate). The mean concentrations of PAHs, nitrated PAHs (NPAHs), chlorinated PAHs (ClPAHs), and brominated PAHs (BrPAHs) in the air of the coking facility were 923, 23.8, 16.7 and 4.25 ng m−³, respectively, 1–2 orders of magnitude higher than those in the surrounding area and the control area. Linear regressions between contaminant concentrations and distance from the coking facility suggested that the concentrations of PAHs (r2 = 0.82, p < 0.05), NPAHs (r2 = 0.77, p < 0.01), and BrPAHs (r2 = 0.62, p < 0.01) were negatively correlated with distance. Additionally, the particle-bound fractions of PAHs and their derivatives were significantly correlated with their molecular weights (p < 0.01). Based on the calculation of the gas/particle partitioning coefficients (log KP) for PAHs and their derivatives and the corresponding subcooled liquid vapor pressures (log PL), the slope values for PAHs, NPAHs, ClPAHs, and BrPAHs ranged from −1 to −0.6, indicating that deposition of PAHs and their derivatives occurred through both adsorption and absorption. Five emissions sources were identified by positive matrix factorization (PMF), including coking emissions, oil pollution, industrial and combustion sources, secondary formation, and traffic emissions, with coking emissions accounting for more than 50% of total emissions. Furthermore, the results of the health risks assessment suggested that atmospheric PAHs and their derivatives in the coke plant and surrounding area negatively impacted human health.

How weathering might intensify the toxicity of spilled crude oil in marine environments.

Crude oils are highly complex mixtures containing many toxic compounds for organisms. While their level of toxicity in a marine environment depends on many parameters, one of the main factors is their composition. After oil spills, their compositions are significantly changed, so it changes the toxicity. In this study, different weathering processes such as evaporation, photooxidation, and biodegradation were applied to crude oil to understand how composition changed over time and how this affects its toxicity on phytoplankton. In laboratory settings, three distinct water-accommodated fraction samples of crude oil were prepared, unweathered, evaporated, and weathered and were exposed to phytoplankton communities at different dilution levels. After 3days, evaporation reduced the crude oil concentration by 47%, and the concentration of the crude oil affected by photooxidation, biodegradation, and evaporation reduced by 81%. This study also showed that even though the weathering reduced the overall amount of crude oil substantially, its toxicity increased significantly. In the microcosm experiments, 7-day EC50 values of the unweathered oil, the evaporated oil and the weathered oil were 49.07, 21.09, and 7.16µg/L, respectively. Different processes altered the crude oil composition, and weathered crude oil ended up with a higher fraction of high molecular weight (HMW) polycyclic aromatic hydrocarbons (PAHs). A promising relation between the increasing toxicity and HMW PAH fraction indicates that increasing the fraction of HMW PAHs might be one of the main reasons for the weathering process to cause higher crude oil toxicity. These results could be used as a diagnostic tool to estimate the extent of weathering and toxicity of crude oil after spills.

On the soot formation characteristics of an ammonia-ethylene counterflow diffusion flame based on the orthogonal decoupling method

Ammonia is regarded to be one of the most competitive fuels for achieving carbon neutral due to its carbon-free properties. In this work, the effects of adding ammonia (NH3) to the fuel stream of an ethylene counterflow diffusion flame on the soot formation characteristics were numerically investigated. The orthogonal decoupling method was used to completely separate the dilution, chemical and thermal effects of the added NH3 by introducing two different virtual NH3. The influence of these effects and their interactions were explored by the range analysis, respectively. The results show that the soot volume fraction (SVF) of the flame decreases under the dilution, chemical and thermal effects of NH3, with the dominated effect being the chemical effect, followed by the dilution effect, and the least is the thermal effect. Besides, the chemical-thermal interaction also has an important impact on the SVF. The increase of SVF is dominated by the HACA surface growth, while the decrease of that is dominated by the OH oxidation. The HACA surface growth reaction is inhibited under the three effects of NH3 addition mainly due to a lower concentrations of C2H2 and H radical. The number density of soot increases under the chemical effect, while decreases under the dilution effect. The mole fractions of polycyclic aromatic hydrocarbons (PAHs) reduces under these three effects, leading to a lower inception rate, which in turn has a significant effect on the number density of soot.

Application of Positive Matrix Factorization for Source Apportionment of Polycyclic Aromatic Hydrocarbons (PAH) in the Adriatic Sea, and the Evaluation of PAH-Related Carcinogenic Risks

Concentrations of polycyclic aromatic hydrocarbons (PAH) were studied in 36 sediment samples collected from 29 sites in the central Adriatic Sea. The total concentration of PAH showed high variability, ranging from 42.85 µg kg−1 in open sea sediments to 28,662 µg kg−1 in the sediments of Šibenik Bay. Unsubstituted, parent PAH were dominant PAH compounds in the entire area of Šibenik Bay and most of the stations in the coastal area. In Kaštela Bay, methyl PAH concentrations were higher than the concentrations of unsubstituted PAH, whereas in the sediments along the mid-Adriatic transect, similar concentrations of both PAH fractions were determined. PAH sources were investigated by applying the Positive Matrix Factorization software developed by the U.S. Environmental Protection Agency (USEPA). The results indicate the presence of four sources, two of which can be considered petrogenic and two pyrogenic. The contribution of the sources to the total concentration PAH at each station indicates the dominance of pyrogenic sources in Šibenik Bay and at most stations in the coastal area. In the sediments along the mid-Adriatic transversal, as well as in Kaštela Bay, PAHs originate mainly from petrogenic sources. The obtained results show that PMF can be a suitable tool for control of PAH pollution and thus, for the management of various activities in the Adriatic region. Seasonal differences between the contributions of sources in the Kaštela and Šibenik bays indicate that the contribution of traffic to the total concentration of PAH was higher during the tourist season. The carcinogenic risk of PAH determined by toxicity equivalent (TEQ) calculations showed an increased carcinogenic risk in the whole area of Šibenik Bay, regardless of the number of PAH compounds considered for the calculations. A low PAH-related carcinogenic risk was found for the rest of the study area.

Effects of organic carbon/elemental carbon and particle size on inhalation bioaccessibility of particle-bound PAHs

Bioaccessible fractions of particle-bound hydrophobic organic compounds (HOCs) are critical to evaluating human inhalation exposure risk. However, the key factors for controlling the release of HOCs into the lung fluid are not adequately examined. To address this issue, eight particle size fractions (0.056–18 μm) from different particle emission sources (barbecue and smoking) were collected and incubated with an in vitro method for determining inhalation bioaccessibilities of polycyclic aromatic hydrocarbons (PAHs). The bioaccessible fractions of particle-bound PAHs were 35–65% for smoke-type charcoal, 24–62% for smokeless-type charcoal, and 44–96% for cigarette. The size distributions of bioaccessible fractions of 3–4 ring PAHs were symmetric with the patterns of their masses, characterized as a unimodal distribution with both the trough and peak at 0.56–1.0 μm. Analysis from machine learning showed that chemical hydrophobicity appeared to be the most significant factor affecting inhalation bioaccessibility of PAHs, followed by organic carbon and elemental carbon contents. Particle size seemed to have little effect on the bioaccessibility of PAHs. A compositional analysis of human inhalation exposure risk from total concentration, deposition concentration, and bioaccessible deposition concentration in alveolar region showed a shift in the key particle size from 0.56−1.0 μm to 1.0–1.8 μm and an increasing in the contributions of 2–3 ring PAHs to risk for cigarette due to the high bioaccessible fractions. These results suggested the significance of particle deposition efficiency and bioaccessible fractions of HOCs in risk assessment.

Microorganisms and their metabolites affect the content of polycyclic aromatic hydrocarbons and their derivatives in pyrolyzed material

Toxic polycyclic aromatic hydrocarbons (PAHs) and more toxic N- and O-containing derivatives can be determined in biochar. However, their fate in the environment and bioavailability depends on many parameters and was not studied yet. In the presented studies a set of biochars obtained from various feedstock at the same pyrolysis temperature (600 °C) subjected to environmental pressure e.g. soil microorganisms and enzymes was described. Presented study aimed to determine the effect of biological agents on the physicochemical characteristic and the content of PAHs and their derivatives in biochars after long-term treatment (6 months). The results indicated that enzymatic aging usually lowered (up to 94 %) the content of PAHs and their derivatives in biochar. Simultaneously, biological aging reduced the bioavailability of tested compounds. Considering the total fraction of PAHs and their derivatives, biochars treated with nutrients and microbial inoculum were characterized by the lowest content of analytes (even in comparison to biochars treated with nutrients alone). To complement the obtained results, the content of C, H, N, O, and ash as well as specific surface area, aromaticity, polarity, and hydrophilicity in biochar before and after modifications were determined. In general, enzymatic aging increased, and biological aging decreased the content of C% and H% in biochar. Both aging processes lowered the H/C ratio which indicated the decrease of the aromatization degree for artificially altered biochar.

Assessment of entrainment of key PAHs emanating from major combustion sources into the ambient air

Increasing health problems owing to air pollution is the major cause of concern in the present time, especially in regions with exceptionally high particulate matter (PM) namely Indo-Gangetic Plains (IGP). In the ambient PM, polycyclic aromatic hydrocarbons (PAHs) have been reported to be carcinogenic in nature and its dominant sources are diesel emissions, coal combustion, agricultural waste burning, wood, and cow-dung cake burning. The chemical characteristics of particulate-bound PAHs from all the mentioned sources, their intercomparison, and entrainment into the atmosphere have been assessed in this study. High-molecular weight (HMW) PAHs fraction is highest in emissions from coal combustion (∼95%), followed by agricultural waste burning (83%), wood burning (83%) and cow-dung cake (77%) combustion. Among all the PAH compounds, benzo (b,j) fluoranthene (B[bj]F) was found to be predominant (highest in wood combustion ∼20.3%) in all source samples except exhaust from diesel and bio-diesel engine installed with diesel oxidation catalyst (DOC). Dominant PAH compounds contributing to the carcinogenic potential (CP) are benzo (a) pyrene (B[a]P), dibenzo (a,h) anthracene (D[ah]A), benzo (b,j) fluoranthene (B[bj]F), benzo (a) anthracene (B[a]A) and indeno (1,2,3-c,d) pyrene (IP). Wood combustion (CP = 1.4 ± 0.8) emission is observed to be the most carcinogenic followed by coal combustion (0.8 ± 0.2), diesel exhaust emission (0.4 ± 0.3), cow-dung cake burning (0.2), and agricultural waste burning (0.2 ± 0.1). Further, the range of various diagnostic ratios for each of the source samples has been reported that can be utilized in future studies for more comprehensive source apportionment.

Effects of different carbon substrates on PAHs fractions and microbial community changes in PAHs-contaminated soils

Different types of carbon substrates were widely used in soil remediation. However, differences of their impacts and related mechanisms on degradation of polycyclic aromatic hydrocarbons (PAHs) and microbial community structures in contaminated soil still remain unclear. Here, we investigated the effects of corn straw (S), glucose (G), straw combined with glucose (SG), and sodium azide (N, as an abiotic control) on PAHs fractions and bacterial communities in soil. After 70 days’ microcosm experiments, total PAHs concentrations were significantly reduced by 30.9%, 19.5% and 44.6% under S, G and SG treatments. Water soluble, acid soluble and residual PAHs under all treatments were significantly decreased after 70 days of incubation, while organically bound PAHs were increased by 11.4%, 22.7% and 36.1% under G, S and SG treatments. Additionally, straw and glucose application increased relative abundance related PAHs-degrading bacteria and the copy numbers of gram-negative (PAHs-RHDα GN) and gram-positive genes (PAHs-RHDα GP) in the contaminated soil. Redundancy analysis (RDA) and Random Forest (RF) indicated that PAHs fractions are crucial factors for biodegradation of PAHs in PAHs-contaminated soils amended with carbon substrates. These suggested that carbon substrates contributed to PAHs conversion from residual PAHs (nonlabile fractions) to organically bound PAHs and thus increased the potential for PAHs conversion to water-soluble and organic acid-soluble PAHs, which were more easy to be utilized by soil microorganisms. This study revealed the new insights of different carbon substrates on degradation and dynamic changes of PAHs fractions and the better potential of combined application of straw and glucose in enhancing degradation of PAHs in PAHs-contaminated soils.

PHANGS–JWST First Results: Variations in PAH Fraction as a Function of ISM Phase and Metallicity

We present maps tracing the fraction of dust in the form of polycyclic aromatic hydrocarbons (PAHs) in IC 5332, NGC 628, NGC 1365, and NGC 7496 from JWST/MIRI observations. We trace the PAH fraction by combining the F770W (7.7 μm) and F1130W (11.3 μm) filters to track ionized and neutral PAH emission, respectively, and comparing the PAH emission to F2100W, which traces small, hot dust grains. We find the average R PAH = (F770W + F1130W)/F2100W values of 3.3, 4.7, 5.1, and 3.6 in IC 5332, NGC 628, NGC 1365, and NGC 7496, respectively. We find that H ii regions traced by MUSE Hα show a systematically low PAH fraction. The PAH fraction remains relatively constant across other galactic environments, with slight variations. We use CO+Hi +Hα to trace the interstellar gas phase and find that the PAH fraction decreases above a value of in all four galaxies. Radial profiles also show a decreasing PAH fraction with increasing radius, correlated with lower metallicity, in line with previous results showing a strong metallicity dependence to the PAH fraction. Our results suggest that the process of PAH destruction in ionized gas operates similarly across the four targets.