Environmental Behaviors and Toxicities of Polycyclic Aromatic Hydrocarbons and Nitropolycyclic Aromatic Hydrocarbons

Levels, enrichment characteristics, and health risks of halogenated and parent polycyclic aromatic hydrocarbons in traditional smoked pork

Chinese traditional smoked pork was contaminated with polycyclic aromatic hydrocarbons (PAHs) and chlorinated and brominated PAHs (ClPAHs and BrPAHs; XPAHs) during the smoking process. Therefore, our study investigated the concentrations, enrichment characteristics, and health risks associated with PAHs, as well as ClPAHs and BrPAHs in Chinese traditional smoked pork. The total concentrations of PAHs, ClPAHs and BrPAHs in traditional smoked pork ranged from 90.0 to 79200 ng/g fat weight (fw), 23.6-2340 pg/g fw and 0.550-200 pg/g fw, respectively, which were significantly higher than their levels found in raw pork. Additionally, the concentrations of PAHs and XPAHs in the surface of smoked pork were higher than those in the inner parts. High-ring PAHs exhibited a greater enrichment compared to low-ring PAHs, and BrPAHs exhibited greater enrichment ability than ClPAHs in smoked pork. Furthermore, the ability of individual congeners to migrate from the surface to the inner parts of the smoked pork were varied. When the smoking fuels were similar, a longer smoking time resulted in higher concentrations of PAHs and XPAHs in smoked pork, while casing effectively reduced their concentrations. The correlation between XPAH and parent PAH concentrations indicated that chlorination of PAHs was one of the primary formation mechanisms of some monochlorinated PAHs. Over half of the smoked pork samples posed a potential carcinogenic risk, particularly the surface samples. It is recommended to remove the surface parts when consuming smoked pork and to improve traditional smoking methods to mitigate the health risks.

Changes in the concentration of polycyclic aromatic hydrocarbons in fecal pellets of Marphysa sp. E and reduced mud in the Yoro tidal flat, Japan

Marphysa sp. E (Annelida, Eunicidae), inhabiting the Yoro tidal flat (inner part of Tokyo Bay, Japan), ingests reduced mud comprising black and high viscosity sediments that contain high levels of polycyclic aromatic hydrocarbons (PAHs); these PAHs are excreted within the fecal pellets. PAH concentration in the fecal pellets rapidly decrease to half its quantity 2 h after its excretion. To investigate their specificity of change, we analyzed the PAHs in fecal pellets and reduced mud using gas chromatography-mass spectrometry. PAH concentration of the fecal pellets was observed to decrease by 46 % in 2 h, whereas that of reduced mud decreased by only 8 % in the same duration. This suggests that the PAH concentration of reduced mud decreases only after passing through the worm's digestive system. These results indicate that Marphysa sp. E contributes to the purification of the tidal flat environment.

Emission characteristic, spatial distribution, and health risk of polycyclic aromatic compounds (PAHs, NPAHs, and OPAHs) from light-duty gasoline and diesel vehicles based on on-road measurements

Vehicle exhaust is the primary source of polycyclic aromatic compounds (PACs). Real road tests using a portable vehicle measurement system on light-duty gasoline vehicles and light-duty diesel trucks were conducted to investigate gas- and particle-phase polycyclic aromatic hydrocarbons (PAHs), nitro-PAHs (NPAHs), and oxy-PAHs (OPAHs) in vehicle exhaust with different emission standards, fuel types, and altitudes. The results showed that with the tightening of emission standards, the overall emission factors (EFs) of PACs decreased. Compared with China V diesel vehicles, the emissions of PAHs, OPAHs, and NPAHs from China VI diesel vehicles were 75.1 %, 84.4 %, and 61.2 % lower, respectively. With a ∼100 m increase in altitude, the EFs of PAHs, OPAHs, and NPAHs of diesel vehicles increased 1.88, 1.92, and 1.59 times due to incomplete combustion. In addition, the EFs of PAHs and OPAHs in gasoline vehicles were lower than those in diesel vehicles. In contrast, the proportion of PAHs with highly toxic components, such as dibenzo[a,h]anthracene (DahA) and benzo[a]pyrene (BaP), and the EFs of gas-phase NPAHs in gasoline vehicles were higher than those in diesel vehicles. Furthermore, the emissions of 1,8-DNP from diesel vehicles cannot be disregarded. 1,8-DNP was the main gas-phase NPAHs emitted by China VI and China V diesel vehicles, accounting for 49.3 % and 26.0 %, respectively. Moreover, gas-phase PACs contributed more to the EFs than particle-phase PACs, whereas particle-phase PACs have greater toxic effects. Although the EFs of PAHs are more than 100 times those of NPAHs, the toxic equivalent concentrations (TEQBaP) of PAHs in diesel and gasoline vehicles were approximately 6.5 times and 35 times those of NPAHs. The spatial distribution characteristics revealed that PACs emissions were mainly concentrated in urban areas and highways, and the differences in the toxicity of PACs emissions between different cities depended on the proportion of diesel vehicles. The average TEQBaP of PAHs and NPAHs in Haidong, Haibei, Huangnan, Hainan, Guoluo, and Yushu was 8.42 μg/m3 and 0.36 μg/m3, respectively, while those of Xining and Haixi were 0.24-0.29 μg/m3 and 0.09-0.108 μg/m3 higher, respectively. This study provides a comprehensive understanding of the emission characteristics, health risks, and spatial distribution of PACs from diesel and gasoline vehicle PACs in urban areas.

A novel procedure for selection of molecular descriptors: QSAR model for mutagenicity of nitroaromatic compounds

Nitroaromatic compounds (NACs) stand out as pervasive organic pollutants, prompting an imperative need to investigate their hazardous effects. Computational chemistry methods play a crucial role in this exploration, offering a safer and more time-efficient approach, mandated by various legislations. In this study, our focus lay on the development of transparent, interpretable, reproducible, and publicly available methodologies aimed at deriving quantitative structure-activity relationship models and testing them by modelling the mutagenicity of NACs against the Salmonella typhimurium TA100 strain. Descriptors were selected from Mordred and RDKit molecular descriptors, along with several quantum chemistry descriptors. For that purpose, the genetic algorithm (GA), as the most widely used method in the literature, and three alternative algorithms (Boruta, Featurewiz, and ForwardSelector) combined with the forward stepwise selection technique were used. The construction of models utilized the multiple linear regression method, with subsequent scrutiny of fitting and predictive performance, reliability, and robustness through various statistical validation criteria. The models were ranked by the Multi-Criteria Decision Making procedure. Findings have revealed that the proposed methodology for descriptor selection outperforms GA, with Featurewiz showing a slight advantage over Boruta and ForwardSelector. These constructed models can serve as valuable tools for the quick and reliable prediction of NACs mutagenicity.

Prioritization of the ecotoxicological hazard of PAHs towards aquatic species spanning three trophic levels using 2D-QSTR, read-across and machine learning-driven modelling approaches

Polycyclic aromatic hydrocarbons (PAHs) represent a common group of environmental pollutants that endanger various aquatic organisms via various pathways. To better prioritize the ecotoxicological hazard of PAHs to aquatic environment, we used 2D descriptors-based quantitative structure-toxicity relationship (QSTR) to assess the toxicity of PAHs toward six aquatic model organisms spanning three trophic levels. According to strict OECD guideline, six easily interpretable, transferable and reproducible 2D-QSTR models were constructed with high robustness and reliability. A mechanistic interpretation unveiled the key structural factors primarily responsible for controlling the aquatic ecotoxicity of PAHs. Furthermore, quantitative read-across and different machine learning approaches were employed to validate and optimize the modelling approach. Importantly, the optimum QSTR models were further applied for predicting the ecotoxicity of hundreds of untested/unknown PAHs gathered from Pesticide Properties Database (PPDB). Especially, we provided a priority list in terms of the toxicity of unknown PAHs to six aquatic species, along with the corresponding mechanistic interpretation. In summary, the models can serve as valuable tools for aquatic risk assessment and prioritization of untested or completely new PAHs chemicals, providing essential guidance for formulating regulatory policies.

Nitro substituent caused negative impact on occurrence and development of atherosclerotic plaque by PM2.5-bound polycyclic aromatic compounds

PM2.5 exposure is a significant risk factor for the occurrence and development of atherosclerosis. Polycyclic aromatic hydrocarbons (PAHs) play prominent roles in PM2.5-related toxicity. However, the nitrated derivatives of PAHs, nitrated polycyclic aromatic hydrocarbons (NPAHs), have strong oxidizing properties due to the nitro substituents. Thus, the in vivo and in vitro experiments exposure to benzo[a]pyrene (BaP) and 6-nitro benzo[a]pyrene (NBaP) were conducted to evaluate the effect of nitro substituent on the atherosclerosis due to (or attributable to) PAHs. The results showed that NBaP exposure induced the inhibition of human umbilical vein endothelial cells (HUVECs) viability and cell morphology damage via more severe oxidative stress than BaP exposure. Furthermore, exposure to PM2.5-bound NBaP caused dyslipidemia in the Apolipoprotein E-deficient (ApoE-/-) mice, including the increment of total cholesterol, triglycerides, low-density lipoprotein cholesterol, and malondialdehyde levels, and the decrement of high-density lipoprotein cholesterol levels, superoxide dismutase and glutathione peroxidase levels in serum and aorta. Furthermore, histology showed atherosclerotic plaque in the aorta of ApoE-/- mice. However, there were no significant differences of the physiological and pathological changes between BaP and control groups. Thus, NPAHs induced endothelial dysfunction and dyslipidemia via severe oxidative stress, and further accelerated the occurrence and development of atherosclerosis compared with the parent PAHs. Our findings provide the first evidence that nitro substituent caused much severer negative health impact of polycyclic aromatic compounds, which highlight the significance of NPAHs in health risk estimation of polycyclic aromatic compounds.

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.

BPDE-DNA adduct formation and alterations of mRNA, protein, and DNA methylation of CYP1A1, GSTP1, and GSTM1 induced by benzo[a]pyrene and the intervention of aspirin in mice

Benzo[a]pyrene (B[a]P), one typical environmental pollutant, the toxicity mechanisms, and potential prevention remain perplexing. Available evidence suggests cytochrome P450 1A1 (CYP1A1) and glutathione S-transferases (GSTs) metabolize B[a]P, resulting in metabolic activation and detoxification of B[a]P. This study aimed to reveal the impact of B[a]P exposure on trans-7,8-diol-anti-9,10-epoxide DNA (BPDE-DNA) adduct formation, level of CYP1A1, glutathione S-transferase pi (GSTP1) and glutathione S-transferase mu1 (GSTM1) mRNA, protein and DNA methylation in mice, and the potential prevention of aspirin (ASP). This study firstly determined the BPDE-DNA adduct formation in an acute toxicity test of a large dose in mice induced by B[a]P, which subsequently detected CYP1A1, GSTP1, and GSTM1 at levels of mRNA, protein, and DNA methylation in the organs of mice in a subacute toxicity test at appropriate doses and the potential prevention of ASP, using the methods of real-time quantitative PCR (QPCR), western blotting, and real-time methylation-specific PCR (MSP), respectively. The results verified that B[a]P induced the formation of BPDE-DNA adduct in all the organs of mice in an acute toxicity test, and the order of concentration of which was lung > kidney > liver > brain. In a subacute toxicity test, following B[a]P treatment, mice showed a dose-dependent slowdown in body weight gain and abnormalities in behavioral and cognitive function and which were alleviated by ASP co-treatment. Compared to the controls, following B[a]P treatment, CYP1A1 was significantly induced in all organs in mice at mRNA level (P < 0.05), was suppressed in the lung and cerebrum of mice at protein level, and inhibited at DNA methylation level in the liver, lung, and cerebrum, whereas GSTP1 and GSTM1 at mRNA, protein, and DNA methylation levels showed organ-specific changes in mice following B[a]P treatment, which was generally alleviated by ASP intervention. In conclusion, B[a]P induced BPDE-DNA adduct formation in all organs in mice and altered the mRNA, protein, and DNA methylation levels in CYP1A1, GSTP1, and GSTM1 in an organ-dependent pattern, which could be related to the organ toxicity and mechanism of B[a]P. ASP intervention may be an effective measure to prevent B[a]P toxicity. The findings provide scientific evidence for further study on the organ toxicity and mechanisms of B[a]P.

New insights into the biology and development of lung cancer in never smokers-implications for early detection and treatment

Lung cancer is the leading cause of cancer deaths worldwide. Despite never smokers comprising between 10 and 25% of all cases, lung cancer in never smokers (LCNS) is relatively under characterized from an etiological and biological perspective. The application of multi-omics techniques on large patient cohorts has significantly advanced the current understanding of LCNS tumor biology. By synthesizing the findings of multi-omics studies on LCNS from a clinical perspective, we can directly translate knowledge regarding tumor biology into implications for patient care. Primarily focused on never smokers with lung adenocarcinoma, this review details the predominance of driver mutations, particularly in East Asian patients, as well as the frequency and importance of germline variants in LCNS. The mutational patterns present in LCNS tumors are thoroughly explored, highlighting the high abundance of the APOBEC signature. Moreover, this review recognizes the spectrum of immune profiles present in LCNS tumors and posits how it can be translated to treatment selection. The recurring and novel insights from multi-omics studies on LCNS tumor biology have a wide range of clinical implications. Risk factors such as exposure to outdoor air pollution, second hand smoke, and potentially diet have a genomic imprint in LCNS at varying degrees, and although they do not encompass all LCNS cases, they can be leveraged to stratify risk. Germline variants similarly contribute to a notable proportion of LCNS, which warrants detailed documentation of family history of lung cancer among never smokers and demonstrates value in developing testing for pathogenic variants in never smokers for early detection in the future. Molecular driver subtypes and specific co-mutations and mutational signatures have prognostic value in LCNS and can guide treatment selection. LCNS tumors with no known driver alterations tend to be stem-like and genes contributing to this state may serve as potential therapeutic targets. Overall, the comprehensive findings of multi-omics studies exert a wide influence on clinical management and future research directions in the realm of LCNS.

Sources of Polycyclic Aromatic Hydrocarbons in Fecal Pellets of a Marphysa Species (Annelida: Eunicidae) in the Yoro Tidal Flat, Japan

The fecal pellets of Marphysa sp. E sensu Abe et al. (2019) (Annelida, Eunicidae) living in the Yoro tidal flat (Ichihara, Chiba, Japan) contain high levels of polycyclic aromatic hydrocarbons (PAHs), and the concentrations rapidly decrease over time. To investigate the origin of the high-concentration PAHs in the fecal pellets and food sources of the worms, the PAH concentrations, carbon and nitrogen stable isotope ratios (δ13C and δ15N), total organic carbon, and total nitrogen for two types of sediment (sands and reduced muds), fecal pellets, and the body of the worms were determined. The PAH concentrations and chemical properties of the fecal pellets were similar to those of the reduced muds (20-30 cm sediment depth). The δ13C, δ15N, and C/N values of reduced muds were the same as the typical values of terrestrial C3 plants, suggesting that reduced muds were derived from terrestrial plants. These data indicated that the worms selectively take up reduced muds containing high levels of PAHs. The δ13C and δ15N values of the worm bodies indicated that the worms did not use the organic carbon derived from terrestrial C3 plants as primary nutrition. Taking into consideration their selective uptake of reduced muds, excretion, and subsequent rapid decrease of PAHs in the fecal pellets, the worms could contribute to the remediation of chemical pollutants in the tidal flat sediments.

Inventory, source and health risk assessment of nitrated and parent PAHs in agricultural soils over a rural river in Southeast China

Nitrated polycyclic aromatic hydrocarbons (NPAHs) have become a concerning topic because of their widespread occurrence and carcinogenicity. However, studies on NPAHs in soils, especially in agricultural soils, are still limited. In this study, a systematic monitoring campaign of 15 NPAHs and 16 polycyclic aromatic hydrocarbons (PAHs) was performed in agricultural soils from the Taige Canal basin in 2018, which is a typical agricultural activity area of the Yangtze River Delta. The total concentration of NPAHs and PAHs ranged from 14.4 to 85.5 ng g^-1 and 118-1108 ng g^-1, respectively. Among the target analytes, 1,8-dinitropyrene and fluoranthene were the most predominant congeners accounting for 35.0% of ∑₁₅NPAHs and 17.2% of ∑₁₆PAHs, respectively. Four-ring NPAHs and PAHs were predominant, followed by three-ring NPAHs and PAHs. NPAHs and PAHs had a similar spatial distribution pattern with high concentrations in the northeastern Taige Canal basin. The soil mass inventory of ∑₁₆PAHs and ∑₁₅NPAHs was evaluated to be 31.7 and 2.55 metric tons, respectively. Total organic carbon had a significant impact on the distribution of PAHs in soils. The correlation between PAH congeners in agricultural soils was higher than that between NPAH congeners. Based on diagnostic ratios and principal component analysis-multiple linear regression model, vehicle exhaust emission, coal combustion, and biomass combustion were the predominant sources of these NPAHs and PAHs. According to the lifetime incremental carcinogenic risk model, the health risk posed by NPAHs and PAHs in agricultural soils of the Taige Canal basin was virtually negligible. The total health risk in soils of the Taige Canal basin to adults was slightly higher than that to children.

Polycyclic aromatic hydrocarbon exposure burden: Individual and mixture analyses of associations with chronic obstructive pulmonary disease risk

Accumulating data demonstrate that polycyclic aromatic hydrocarbons (PAH) exposure is linked to compromised respiratory diseases. This study aimed to analyze urinary PAH metabolites and their associations with chronic obstructive pulmonary disease (COPD) in a sample size of 3015 subjects from a total population of 50,588 from the National Health and Nutrition Examination Survey (NHANES) in 2007-2016. Results showed that the most predominant metabolite was 1-Hydroxynaphthalene (1-NAP, 84%) with a geometric mean concentration of 50,265 ng/L, followed by its homologue 2-NAP (10%), both of which arose from sources including road emission, smoking and cooking. Multiple logistic regression showed that seven of the ten major PAH metabolites were correlated with increased COPD risk: including 1-NAP (OR: 1.83, 95%CI: 1.25, 2.69), 2-Hydroxyfluorene (2-FLU, OR: 2.29, 95%CI: 1.42, 3.68) and 1-Hydroxyphenanthrene (1-PHE, OR: 2.79, 95%CI: 1.85, 4.21), when compared to the lowest tertile after adjusted for covariates. Total exposure burden per PAH congener sub-group demonstrated persistent positive correlation with COPD for ∑PHE (OR: 1.80, 95%CI: 1.34, 2.43) and ∑FLU (OR: 2.74, 95%CI: 1.77, 4.23) after adjusted for covariates. To address the contribution of PAH exposure as mixture towards COPD, weighted quantile sum (WQS) regression analyses revealed that 1-NAP, 9-Hydroxyfluorene (9-FLU), 3-Hydroxyfluorene (3-FLU) and 1-PHE were among the top contributors in the associations with COPD. Our results demonstrate the contemporary yet ongoing exposure burden of PAH exposure for over a decade, particularly towards NAPs and FLUs that contribute significantly to COPD risk, calling for more timely environmental regulation.

Sedimentary spatial variation, source identification and ecological risk assessment of parent, nitrated and oxygenated polycyclic aromatic hydrocarbons in a large shallow lake in China

Because polycyclic aromatic compounds (PACs) are persistent, universal, and toxic pollutants, understanding the potential source and ecological risk thereof in lakes is critical to the safety of the aquatic environment. Here, a total of 25 sedimentary samples were collected from Lake Taihu, China, in 2018. The total concentrations of 16 parent polycyclic aromatic hydrocarbons (PAHs), 15 nitrated PAHs (NPAHs), nine oxygenated PAHs (OPAHs), and five hydroxy-PAHs (OH-PAHs) ranged from 294 to 1243, 3.0 to 54.5, 188 to 1897, and 8.3 to 51.7 ng/g dw, with the most abundant compounds being fluoranthene, 1,8-dinitropyrene, 6H-Benzo[cd]pyren-6-one, and 2-phenylphenol, respectively. The spatial distribution of PACs in sediments of Lake Taihu showed elevated concentrations from east to west due to economic development and transportation. The positive correlations between most paired PAHs indicate that these compounds likely originated from similar sources. The total organic carbon and organic matter contents affected the distribution characteristics of PACs in sediments. Diagnostic ratios, principal component analysis-multiple linear regression (PCA-MLR), and positive matrix factorization (PMF) were integrated to identify the sources. PACs had various sources including combustion, petroleum leakage, traffic emissions, hydroxyl metabolism, and other oxidation pathways in sediments of Lake Taihu. The PMF (R² > 0.9824), which showed better optimal performance compared with PCA-MLR (R² > 0.9564) for PAHs and derivatives, is recommended as the preferred model for quantitative source analysis. Ecological risk assessment showed that the risk quotient values of OPAHs in sediments were much higher than those of other PACs and should be given special attention.

Summertime Characteristics of Atmospheric Polycyclic Aromatic Hydrocarbons in a Coastal City of Northern Poland

Parent polycyclic aromatic hydrocarbons (PAHs) in the gas and particle fraction were measured between May and August 2021 at a coastal urban site in Poland, to examine their chemical characteristics, distribution, sources, deposition fluxes and interactions with basic meteorological drivers. The mean concentration of PAHs in the gas phase was significantly higher (26.26 ± 15.83 ng m^-3) than levels measured in the particle phase (1.77 ± 1.26 ng m^-3). The highest concentration in the gas phase was found for phenanthrene (Phe), followed by fluoranthene (Flt), acenaphthene (Ace) and naphthalene (Naph). The contribution from each group of PAHs to the total particulate phase accounted for 50%, 25%, 14% and 12% for 3-, 4-, 5- and 6-ring compounds, respectively. The mean ΣPAH deposition flux was 59 ± 24 ng m^-2 day^-1. During the whole field campaign, the efficient removal of PM-bound PAHs was typically observed after precipitation events. Based on statistical analysis, it was found that 4-ring PAHs were less effectively removed (25%) by daily precipitation as compared to 5- and 6-ring components, whose fluxes decreased by 32% and 53%, respectively. This study revealed local urban sources such as vehicular emissions, coal-fired power plants, shipping activities, docks/ports infrastructure and municipal solid waste recycling units as predominant contributors to PM-bound and gas-phase PAHs.

Occurrence, partition behavior, source and ecological risk assessment of nitro-PAHs in the sediment and water of Taige Canal, China

Nitrated polycyclic aromatic hydrocarbons (NPAHs) are widespread organic pollutants that possess carcinogenic and mutagenic properties, so they may pose a risk to the environment and human health. In this study, the concentrations of 15 NPAHs and 16 polycyclic aromatic hydrocarbons (PAHs) in 30 surface water samples and 26 sediment samples were measured in 2018 from the Taige Canal, one of the main rivers flowing into Taihu Lake, China. The total NPAH concentrations in water and sediment ranged from 14.7 to 235 ng/L and 22.9 to 96.5 ng/g dw, respectively. 9-nitrophenanthrene (nd-76.3 ng/L) was the dominant compound in surface water, while 2+3-nitrofluoranthene (1.73-18.1 ng/g dw) dominated in sediment. Among PAHs, concentration ranging from 1,097 to 2,981 ng/L and 1,089 to 4,489 ng/g dw in surface water and sediment, respectively. There was a strong positive correlation between the log octanol-water partition coefficient (K_ow) and log sediment-water partition coefficient due to hydrophobic interaction. The fugacity fraction value increased with the decrease of log K_ow, and chrysene was transferred from water into sediment. The residual NPAHs in surface water and sediment of the Taige Canal have partial correlation. Diesel engine and coal combustion emissions were probably the principal sources of NPAHs in surface water and sediment. The results of ecological risk assessment showed that some NPAHs in water (e.g, 1-nitropyrene and 6-nitrochrysene) and sediment (e.g., 2-nitrobiphenyl, 5-nitroacenaphthene, 9-nitrophenanthrene and 2+3-nitrofluoranthene) had moderate ecological risks, which should be of concern.

Ecotoxicological QSAR modelling of the acute toxicity of fused and non-fused polycyclic aromatic hydrocarbons (FNFPAHs) against two aquatic organisms: Consensus modelling and comparison with ECOSAR

Fused and non-fused polycyclic aromatic hydrocarbons (FNFPAHs) are a type of organic compounds widely occurring in the environment that pose a potential hazard to ecosystem and public health, and thus receive extensive attention from various regulatory agencies. Here, quantitative structure-activity relationship (QSAR) models were constructed to model the ecotoxicity of FNFPAHs against two aquatic species, Daphnia magna and Oncorhynchus mykiss. According to the stringent OECD guidelines, we used genetic algorithm (GA) plus multiple linear regression (MLR) approach to establish QSAR models of the two aquatic toxicity endpoints: D. magna (48 h LC₅₀) and O. mykiss (96 h LC₅₀). The models were established using simple 2D descriptors with explicit physicochemical significance and evaluated using various internal/external validation metrics. The results clearly show that both models are statistically robust (Q_LOO² = 0.7834 for D. magna and Q_LOO² = 0.8162 for O. mykiss), have good internal fitness (R² = 0.8159 for D. magna and R² = 0.8626 for O. mykiss and external predictive ability (D. magna: R_test² = 0.8259, Q_Fn² = 0.7640∼0.8140, CCC_test = 0.8972; O. mykiss:R_test² = 0.8077, Q_Fn² = 0.7615∼0.7722, CCC_test = 0.8910). To prove the predictive performance of the developed models, an additional comparison with the standard ECOSAR tool obviously shows that our models have lower RMSE values. Subsequently, we utilized the best models to predict the true external set compounds collected from the PPDB database to further fill the toxicity data gap. In addition, consensus models (CMs) that integrate all validated individual models (IMs) were more externally predictive than IMs, of which CM2 has the best prediction performance towards the two aquatic species. Overall, the models presented here could be used to evaluate unknown FNFPAHs inside the domain of applicability (AD), thus being very important for environmental risk assessment under current regulatory frameworks.

Polycyclic aromatic hydrocarbons (PAHs): Updated aspects of their determination, kinetics in the human body, and toxicity

Polycyclic aromatic hydrocarbons (PAHs) are legacy pollutants of considerable public health concern. Polycyclic aromatic hydrocarbons arise from natural and anthropogenic sources and are ubiquitously present in the environment. Several PAHs are highly toxic to humans with associated carcinogenic and mutagenic properties. Further, more severe harmful effects on human- and environmental health have been attributed to the presence of high molecular weight (HMW) PAHs, that is PAHs with molecular mass greater than 300 Da. However, more research has been conducted using low molecular weight (LMW) PAHs). In addition, no HMW PAHs are on the priority pollutants list of the United States Environmental Protection Agency (US EPA), which is limited to only 16 PAHs. However, limited analytical methodologies for separating and determining HMW PAHs and their potential isomers and lack of readily available commercial standards make research with these compounds challenging. Since most of the PAH kinetic data originate from animal studies, our understanding of the effects of PAHs on humans is still minimal. In addition, current knowledge of toxic effects after exposure to PAHs may be underrepresented since most investigations focused on exposure to a single PAH. Currently, information on PAH mixtures is limited. Thus, this review aims to critically assess the current knowledge of PAH chemical properties, their kinetic disposition, and toxicity to humans. Further, future research needs to improve and provide the missing information and minimize PAH exposure to humans.

Study on the mechanism of liver toxicity induced by acenaphthene in zebrafish

Acenaphthene is a polycyclic aromatic hydrocarbon (PAH) that is a widely distributed environmental pollutant that accumulates in organisms and leads to health risks in humans. Although acenaphthene is reported to be toxic to aquatic organisms, its effects of acenaphthene on the livers of these organisms have not been evaluated. Here, zebrafish were used as an experimental model. Zebrafish larvae were exposed to 4.5, 5.5, and 6.5 mg/L acenaphthene for 72 h while adult zebrafish were exposed to 1.5, 2, and 2.5 mg/L acenaphthene for 28 days. We investigated the mechanism by which acenaphthene causes liver toxicity in zebrafish. The results showed that acenaphthene affected the early development of zebrafish and led to mitochondrial damage by promoting the production of reactive oxygen species (ROS) resulting in oxidative stress. The expression of genes related to inflammation and apoptosis was analyzed, observing up-regulation of the pro-inflammatory factors IL-8, TNF-α, and IL-6. The pro-apoptotic genes p53, Caspase-3, and Bax and the Bax/Bcl-2 ratio were up-regulated, while the anti-apoptotic gene Bcl-2 was down-regulated. In addition, we investigated the effects of acenaphthene on liver metabolism. When exposed to acenaphthene, the glycogen content of the liver decreased, while lipid accumulation increased together with alterations in related indicators of liver metabolism. In conclusion, acenaphthene induced oxidative stress through ROS production, leading to mitochondrial damage and activation of pathways associated with inflammation and apoptosis, resulting in hepatotoxicity. This affects normal liver metabolism. Our results revealed the mechanism of hepatotoxicity in zebrafish acenaphthene, and provided new evidence for a more comprehensive understanding of the hepatotoxicity of acenaphthene.

Variations in traffic-related polycyclic aromatic hydrocarbons in PM2.5 in Kanazawa, Japan, after the implementation of a new vehicle emission regulation

A three-year sampling campaign was conducted at a roadside air pollution monitoring station in the urban area of Kanazawa, Japan. Due to a new emission regulation, PAHs levels decreased over the sampling campaign, exhibiting values of 706 ± 413 pg/m³ in 2017, 559 ± 384 pg/m³ in 2018, and 473 ± 234 pg/m³ in 2019. In each year, similar seasonal variations in PAHs levels were observed, with higher levels observed in winter and lower levels in summer. Among the PAHs isomer ratios, we observed that the ratio of benzo[b]fluoranthene (BbF) and benzo[k]fluoranthene (BkF), [BbF]/([BbF] + [BkF]), and the ratio of indeno[1,2,3-cd]pyrene (IDP) and benzo[ghi]perylene (BgPe), [IDP]/([BgPe] + [IDP]), showed stability over the sampling campaign and were less affected by the new emission regulation, seasonal variations, and regional characteristics. When using the combined ratio ranges of 0.66 - 0.80 ([BbF]/([BbF] + [BkF]) and 0.26-0.49 ([IDP]/([BgPe] + [IDP]), traffic emissions were clearly distinguished from other PAHs emission sources. Principal component analysis (PCA) and positive matrix factorization (PMF) were also performed to further analyse the characteristics of traffic-related PAHs. Overall, this study affirmed the effectiveness of the new emission regulation in the reduction of PAHs emissions and provided a combined range for identifying PAHs traffic emission sources.

Characteristics and Influencing Factors of Polycyclic Aromatic Hydrocarbons Emitted from Open Burning and Stove Burning of Biomass: A Brief Review

To mitigate global warming and achieve carbon neutrality, biomass has become a widely used carbon-neutral energy source due to its low cost and easy availability. However, the incomplete combustion of biomass can produce polycyclic aromatic hydrocarbons (PAHs), which are harmful to human health. Moreover, increasing numbers of wildfires in many regions caused by global warming have greatly increased the emissions of PAHs from biomass burning. To effectively mitigate PAH pollution and health risks associated with biomass usage, the concentrations, compositions and influencing factors of PAH emissions from biomass burning are summarized in this review. High PAH emissions from open burning and stove burning are found, and two- to four-ring PAHs account for a higher proportion than five- and six-ring PAHs. Based on the mechanism of biomass burning, biomass with higher volatile matter, cellulose, lignin, potassium salts and moisture produces more PAHs. Moreover, burning biomass in stoves at a high temperature or with an insufficient oxygen supply can increase PAH emissions. Therefore, the formation and emission of PAHs can be reduced by pelletizing, briquetting or carbonizing biomass to increase its density and burning efficiency. This review contributes to a comprehensive understanding of PAH pollution from biomass burning, providing prospective insight for preventing air pollution and health hazards associated with carbon neutrality.

Effects of changes in polycyclic aromatic hydrocarbons (PAHs) emissions and degradation on their concentrations in Tokyo from 2007 and 2016

The concentrations of polycyclic aromatic hydrocarbons (PAHs) in aerosol were measured in Shinjuku, which is central Tokyo, Japan, for 10 years from 2007 to 2016. The effects of changes in emission sources and their degradation by reaction with ozone were assessed in this study. There was no significant increasing or decreasing trend of the PAH concentrations during 10 years (P > 0.05). The average selected seven the PAH concentrations (0.88 ng m⁻³) during 10 years was lower than those in New York and Paris. However, the trend of ozone concentrations is increasing in central Tokyo. This inconsistency raises a question. Did the fact that the ozone concentration was higher than the PAH concentrations promote PAH degradation? To apportion the PAH sources, we used PAH concentration profiles and positive matrix factorization analysis. The contribution of vehicle emissions to the PAHs ranged from 40 to 80%. Ozone concentrations increased by 3.70%/year during 10 years. The theoretical degradation rates of PAHs by ozone, which were calculated using a pseudo-first-order rate equation, suggested that the lifetimes of benzo[a]pyrene (BaP) decreased by 1 min from 2007 to 2016. We investigated the aging of BaP using the profile of the isomer ratios. We found that the aging of BaP at the urban and roadside sites were nearly identical indicating aging regardless of the season. Although the decomposition of BaP is promoted by the photochemical oxidation reaction, this result suggests that a certain threshold value exists as the degree of the decomposition. This degradation of PAH can improve chemical loss processes in air quality model.

Systematic QSAR and iQCCR modelling of fused/non-fused aromatic hydrocarbons (FNFAHs) carcinogenicity to rodents: reducing unnecessary chemical synthesis and animal testing

The prediction of new or untested FNFAHs will reduce unnecessary chemical synthesis and animal testing, and contribute to the design of safer chemicals for production activities.

NPAHs and OPAHs in the atmosphere of two central European cities: Seasonality, urban-to-background gradients, cancer risks and gas-to-particle partitioning

Derivatives of polycyclic aromatic hydrocarbons (PAHs) such as nitrated- and oxygenated-PAHs (NPAHs and OPAHs) could be even more toxic and harmful for the environment and humans than PAHs. We assessed the spatial and seasonal variations of NPAHs and OPAHs atmospheric levels, their cancer risks and their gas-to-particle partitioning. To this end, about 250 samples of fine particulate matter (PM2.5) and 50 gaseous samples were collected in 2017 in central Europe in the cities of Brno and Ljubljana (two traffic and two urban background sites) as well as one rural site. The average particulate concentrations were ranging from below limit of quantification to 593 pg m-3 for Σ9NPAHs and from 1.64 to 4330 pg m-3 for Σ11OPAHs, with significantly higher concentrations in winter compared to summer. In winter, the particulate levels of NPAHs and OPAHs were higher at the traffic site compared to the urban background site in Brno while the opposite was found in Ljubljana. NPAHs and OPAHs particulate levels were influenced by the meteorological parameters and co-varied with several air pollutants. The significance of secondary formation on the occurrence of some NPAHs and OPAHs is indicated. In winter, 27-47% of samples collected at all sites were above the acceptable lifetime carcinogenic risk. The gas-particle partitioning of NPAHs and OPAHs was influenced by their physico-chemical properties, the season and the site-specific aerosol composition. Three NPAHs and five OPAHs had higher particulate mass fractions at the traffic site, suggesting they could be primarily emitted as particles from vehicle traffic and subsequently partitioning to the gas phase along air transport. This study underlines the importance of inclusion of the gas phase in addition to the particulate phase when assessing the atmospheric fate of polycyclic aromatic compounds and also when assessing the related health risk.

Chemometric QSAR modeling of acute oral toxicity of Polycyclic Aromatic Hydrocarbons (PAHs) to rat using simple 2D descriptors and interspecies toxicity modeling with mouse

The information of the acute oral toxicity for most polycyclic aromatic hydrocarbons (PAHs) in mammals are lacking due to limited experimental resources, leading to a need to develop reliable in silico methods to evaluate the toxicity endpoint. In this study, we developed the quantitative structure-activity relationship (QSAR) models by genetic algorithm (GA) and multiple linear regression (MLR) for the rat acute oral toxicity (LD₅₀) of PAHs following the strict validation principles of QSAR modeling recommended by OECD. The best QSAR model comprised eight simple 2D descriptors with definite physicochemical meaning, which showed that maximum atom-type electrotopological state, van der Waals surface area, mean atomic van der Waals volume, and total number of bonds are main influencing factors for the toxicity endpoint. A true external set (554 compounds) without rat acute oral toxicity values, and 22 limit test compounds, were firstly predicted along with reliability assessment. We also compared our proposed model with the OPERA predictions and recently published literature to prove the prediction reliability. Furthermore, the interspecies toxicity (iST) models of PAHs between rat and mouse were also established, validated and employed for filling data gap. Overall, our developed models should be applicable to new or untested or not yet synthesized PAHs falling within the applicability domain (AD) of the models for rapid acute oral toxicity prediction, thus being important for environmental or personal exposure risk assessment under regulatory frameworks.

Calculating source contributions to urban atmospheric polycyclic aromatic hydrocarbons and nitropolycyclic aromatic hydrocarbons using 1-nitropyrene and pyrene: An application to an Asian dust event

A method to calculate source contributions to atmospheric polycyclic aromatic hydrocarbons (PAHs) and their nitrated congeners (NPAHs) is proposed, using pyrene (Pyr) and 1-nitropyrene (1-NP), as respective representatives of PAHs and NPAHs. This is based on the known increases in NPAH to PAH ratios as combustion temperatures increase. The fractions of 1-NP and Pyr from high temperature combustion sources in total 1-NP and Pyr are respectively calculated as a (0 < a <1) and b (0 < b < 1). By using atmospheric concentrations of Pyr and 1-NP obtained at monitoring sites, contributions of high and low temperature combustion sources were calculated. Using this method, the contributions of automobiles and coal combustion facilities/industries to atmospheric Pyr and 1-NP concentrations were calculated for atmospheric samples collected in Kanazawa, Japan during a seasonal Asian dust event. The results show that Pyr was almost entirely emitted from industries in China and transported long-range to Japan. By contrast, 1-NP was emitted primarily from automobiles in Kanazawa and its surrounding areas, with a small amount of 1-NP possibly transported from China. The proposed method can provide greater clarity on source identification compared to the typically used PAH isomer pairs.

Biosorption of LMW PAHs on activated sludge aerobic granules under varying BOD loading rate conditions

Polycyclic aromatic hydrocarbons belong to the main priority substances for the aquatic environment. One of the emission sources of these compounds to environment is wastewater discharged from conventional wastewater treatment systems, which are not designed to cope with this type of pollution. Thus, due to the widely discussed properties of aerobic granular activated sludge in the literature - a conducted study has proven its ability to remove LMW PAHs (naphthalene (Nap), acenaphthylene (Acy), acenaphthene (Ace), fluorene (Flu), phenanthrene (Phe) and anthracene (Ant)) from wastewater by biosorption process at varying loadings of organic compounds expressed as BOD (kg/kg·d) on the activated sludge mass. The maximum biosorption of Nap was 605 µg/kg_d.m., Acy equals to 134 µg/kg_d.m., Ace equals to 355 µg/kg_d.m. Flu equals to 104 µg/kg_d.m. Phe equal to 204 µg/kg_d.m. and Ant equal to 173 µg/kg_d.m. The study showed that the BOD loading rate is one of the factors affecting the biosorption process of LMW PAHs. However, as the amount of adsorbed LMW PAHs increased, the condition of aerobic granular activated sludge deteriorated, which was evidenced by gradual increase in the values of technological parameters of activated sludge (SVI, HRT, SRT) and a smaller increase in activated sludge dry mass.

Polycyclic aromatic compounds (PAHs, oxygenated PAHs, nitrated PAHs, and azaarenes) in air from four climate zones of China: Occurrence, gas/particle partitioning, and health risks

Polycyclic aromatic compounds (PACs) such as polycyclic aromatic hydrocarbons (PAHs) and their derivatives [oxygenated PAHs (OPAHs), nitrated PAHs (NPAHs), and azaarenes (AZAs)] are toxic and ubiquitous air pollutants. In this study, the concentrations of these PACs were determined in air obtained in spring and autumn of 2012 from urban and rural areas of the Tibetan Plateau, temperate, subtropical, and tropical climate zones in China. Average concentrations (gaseous + particulate) of ∑29PAHs, ∑15OPAHs, ∑11NPAHs, and ∑4AZAs were 928 ± 658, 54 ± 45, 5.3 ± 4.4, 14 ± 11 ng m^-3 and 995 ± 635, 67 ± 38, 8.4 ± 6.1, 24 ± 16 ng m^-3 in spring and autumn, respectively. Various C fractions and latitude correlated significantly with the concentrations and ratios of PACs. The slopes of the regression of gas-particle partition coefficients (K_p) of PACs on their sub-cooled liquid vapor pressures (P_L⁰), indicated both adsorption and absorption to total suspended particles (TSP) for PAHs, OPAHs, and NPAHs in the four studied climatic zones. This result was further supported by comparing the fractions of PACs in TSP calculated from field data with those predicted by the Junge-Pankow adsorption and K_OA absorption models. The concentration ratios of most OPAHs or NPAHs to their parent PAHs and of benzo[e]pyrene/benzo[a]pyrene were higher in autumn than in spring and increased with remoteness from point sources. This suggests enhanced secondary formation of PAH derivatives due to the elevated photochemical activity in autumn and longer ageing of air and associated transformation of PACs during their long-distance transport from source regions (urban sites) to rural sites. Lifetime lung cancer risk estimated from PACs ranged from 0.8 ± 0.6 to 3.1 ± 1.0 (×10^-3), exceeding the value (10^-5) recommended by the WHO. Gaseous PACs contributed substantially to the estimated cancer risks and their contributions increased with decreasing latitude in China.

Ultraviolet and Deep-Ultraviolet Excitation Photothermal Heterodyne Interferometer Combined with Semi-Micro HPLC

A detection system consisting of a photothermal heterodyne interferometer (PHI) combined with semi-micro HPLC (high-performance liquid chromatography) has been designed and investigated. An ultraviolet (UV) or deep-UV laser emitting at 375 or 213 nm, respectively, was used for the excitation of nitro-polycyclic aromatic hydrocarbons (NPAHs) and amino acids. A photothermally induced change in the refractive index of the solvent causes an optical phase difference between two arms of the interferometer, one beam passing through the photoexcited region and another used as a reference, which was sensitively detected with the PHI. The separation and detection of NPAHs and amino acids were successfully demonstrated via semi-micro HPLC with the PHI and a UV detector. The detection limits of the UV-excitation PHI for NPAHs were 1.2 - 5.2 times better than that of the commercial UV detector, although the first demonstration of deep-UV excitation suffered from significant baseline fluctuation.

Daytime Restricted Feeding Modifies the Temporal Expression of CYP1A1 and Attenuated Damage Induced by Benzo[a]pyrene in Rat Liver When Administered before CYP1A1 Acrophase

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that heterodimerizes with the AhR nuclear translocator (ARNT) to modulate CYP1A1 expression, a gene involved in the biotransformation of benzo[a]pyrene (BaP). The AhR pathway shows daily variations under the control of the circadian timing system. Daytime restricted feeding (DRF) entrains the expression of genes involved in the processing of nutrients and xenobiotics to food availability. Therefore, we evaluate if temporal AhR, ARNT, and CYP1A1 hepatic expression in rats are due to light/dark cycles or fasting/feeding cycles promoted by DRF. Our results show that AhR oscillates throughout the 24 h period in DRF and ad libitum feeding rats (ALF), showing maximum expression at the same time points. DRF modified the peak of ARNT expression at ZT5; meanwhile, ALF animals showed a peak of maximum expression at ZT17. An increased expression of CYP1A1 was linked to the meal time in both groups of animals. Although a high CYP1A1 expression has been previously associated with BaP genotoxicity, our results show that, compared with the ALF group, DRF attenuated the BaP-CYP1A1 induction potency, the liver DNA-BaP adducts, the liver concentration of unmetabolized BaP, and the blood aspartate aminotransferase and alanine aminotransferase activities when BaP is administered prior to the acrophase of CYP1A1 expression. These results demonstrate that DRF modifies the ARNT and CYP1A1 expression and protects from BaP toxicity.

Polycyclic aromatic hydrocarbons and their nitro-derivatives in urban road dust across China: Spatial variation, source apportionment, and health risk

As an essential carrier of hazardous substances, fugitive road dust has become a severe issue in China. In this study, 212 road dust samples from 53 cities in China were collected to comprehensively investigate the spatial variations, potential sources, and cancer risk of 16 polycyclic aromatic hydrocarbons (PAHs) and 16 nitro-PAHs. The total PAHs concentrations ranged from 0.07 to 345 μg/g dry weight, which is at a moderate level compared to other regions in the world. The mean concentration of Σ₁₆nitro-PAHs was 111 ± 115 ng/g, which is 2-3 orders of magnitude lower than that of Σ₁₆PAHs. A clear geographical trend of dust PAHs and nitro-PAHs was observed in the northeast, north, and east coastal regions of China at a higher level. Moreover, a significant correlation between latitude and PAHs/nitro-PAHs revealed the influences of outdoor temperature and coal combustion for heating in the different regions on the emission and reaction of PAHs and nitro-PAHs. The secondary formation of most nitro-PAHs increases with a decrease in latitude indicated that solar radiation and temperature are important factors on secondary formation of nitro-PAHs. The average concentration of total PAHs and their derivatives in trunk road samples were statistically higher than those in other road samples (p < 0.05), indicating the influence of traffic load on target compound concentration. Generally, the primary sources of PAHs in the road dust samples were coal combustion (23.9%), vehicles (57.1%), and wood/biomass combustion (19.0%). For nitro-PAHs, the main sources were secondary formation (30.9%), biomass/coal combustion (28.4%), and vehicles (44.9%). Furthermore, a moderate potential carcinogenic risk due to PAHs and nitro-PAHs in the dust samples was found in China.

Modeling the Formation, Degradation, and Spatiotemporal Distribution of 2-Nitrofluoranthene and 2-Nitropyrene in the Global Atmosphere

Polycyclic aromatic hydrocarbons (PAHs) are common atmospheric pollutants and known to cause adverse health effects. Nitrated PAHs (NPAHs) are formed in combustion activities and by nitration of PAHs in the atmosphere and may be equally or more toxic, but their spatial and temporal distribution in the atmosphere is not well characterized. Using the global EMAC model with atmospheric chemistry and surface compartments coupled, we investigate the formation, abundance, and fate of two secondarily formed NPAHs, 2-nitrofluoranthene (2-NFLT) and 2-nitropyrene (2-NPYR). The default reactivity scenario, the model with the simplest interpretation of parameters from the literature, tends to overestimate both absolute concentrations and NPAH/PAH ratios at observational sites. Sensitivity scenarios indicate that NO₂-dependent NPAH formation leads to better agreement between measured and predicted NPAH concentrations and that photodegradation is the most important loss process of 2-NFLT and 2-NPYR. The highest concentrations of 2-NFLT and 2-NPYR are found in regions with strong PAH emissions, but because of continued secondary formation from the PAH precursors, these two NPAHs are predicted to be spread across the globe.

In vivo toxicity of nitroaromatic compounds to rats: QSTR modelling and interspecies toxicity relationship with mouse

Nitroaromatic compounds (NACs) in the environment can cause serious public health and environmental problems due to their potential toxicity. This study established quantitative structure-toxicity relationship (QSTR) models for the acute oral toxicity of NACs towards rats following the stringent OECD principles for QSTR modelling. All models were assessed by various internationally accepted validation metrics and the OECD criteria. The best QSTR model contains seven simple and interpretable 2D descriptors with defined physicochemical meaning. Mechanistic interpretation indicated that van der Waals surface area, presence of C-F at topological distance 6, heteroatom content and frequency of C-N at topological distance 9 are main factors responsible for the toxicity of NACs. This proposed model was successfully applied to a true external set (295 compounds), and prediction reliability was analysed and discussed. Moreover, the rat-mouse and mouse-rat interspecies quantitative toxicity-toxicity relationship (iQTTR) models were also constructed, validated and employed in toxicity prediction for true external sets consisting of 67 and 265 compounds, respectively. These models showed good external predictivity that can be used to rapidly predict the rat oral acute toxicity of new or untested NACs falling within the applicability domain of the models, thus being beneficial in environmental risk assessment and regulatory purposes.

Calculating sources of combustion-derived particulates using 1-nitropyrene and pyrene as markers

Airborne particulate matter (PM) contains numerous hazardous polycyclic aromatic hydrocarbons (PAHs) as well as their functionalized congeners. However, the lack of useful methods to identify the sources of PM has hindered the development of researches in atmospheric and public health fields. This report proposes a new method for estimating the source contribution of combustion-derived particulate (P_c) by using 1-nitropyrene (1-NP) and pyrene (Pyr) as markers. This is premised on the fact that the formation of nitrogen oxides in the flame gas and the subsequent nitration of PAHs are functions of combustion temperature and therefore the concentration ratios of NPAHs to PAHs are highly temperature dependent. This method divides combustion sources into two groups - high and low temperatures - which here are respectively represented by automobile engine and coal combustion in urban areas. Formulae are derived for combustion-derived particulate (P_c), whose fraction in the total particulate is y (0 < y < 1), and particulates from combustion sources with high temperatures (P_h), whose fraction in P_c is x (0 < x < 1), and low temperatures (P_l), whose fraction is (1 －x). When concentrations of 1-NP and Pyr in P_h and P_l are known, values x and y can be calculated from the formulae by determining atmospheric 1-NP and Pyr concentrations at monitoring sites. Then atmospheric concentrations of P_c, P_h and P_l can be calculated. The proposed method has been applied for total suspended particulate matter (TSP) samples collected in Kanazawa and Kitakyushu (Japan) and Beijing (China) having different types of atmospheric pollution to clarify the change of contributions of automobiles and coal combustion.

Understanding the role of Cl and NO3 radicals in initiating atmospheric oxidation of fluorene: A mechanistic and kinetic study

The photooxidation of volatile organic compounds (VOCs) initiated by Cl and NO₃ radicals has been investigated for decades to assess the atmospheric fates of pollutants. Gas-phase fluorene is one of the most abundant polycyclic aromatic hydrocarbons (PAHs) that can be oxidized by activated radicals. In this study, we used quantum chemical calculation to study the atmospheric degradation of fluorene initiated by Cl and NO₃ radicals. The results showed that the Cl radical initiated reaction of fluorene mainly produces 9-fluorene radical that has significant potential to form secondary pollutants with more persistent toxic properties. The NO₃ radical initiated reaction of fluorene leads to the formation of oxygenated PAHs (OPAHs) and nitrated PAHs (NPAHs) including nitrooxyfluorene, nitrooxyfluorenone and 1,4-fluorenequinone. The rate constants and branch ratios of elementary reactions were determined based on Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The atmospheric lifetime of fluorene determined by NO₃ radical is deduced to be 1.52 days according to the calculated overall rate constant, 1.52 × 10^-14 cm³ molecule^-1 s^-1. The derivatives produced from the atmospheric degradation of fluorene initiated by Cl and NO₃ radicals increase the environmental risks of fluroene. Combined with previous experimental and theoretical findings, this work can help to clarify the atmospheric fate and assess the environmental risks of fluorene.

Degradation of PAHs during long range transport based on simultaneous measurements at Tuoji Island, China, and at Fukue Island and Cape Hedo, Japan

We investigated the degradation of polycyclic aromatic hydrocarbons (PAHs) during long-range transport. Aerosols were collected simultaneously at remote sites on Tuoji Island, China; Fukue Island, Japan; and the Cape Hedo Atmosphere and Aerosol Measurement Station (CHAAMS), Okinawa, Japan in April, October, and December from 2012 to 2013. These remote sites were convenient for investigating the degradation of PAHs during long-range transport. PAHs were analyzed via gas chromatography/mass spectrometry. We identified air masses that passed over all sites and combined our measurements with a chemical transport model. We estimated the relative contributions of the PAHs at the three sites by normalizing the PAH concentrations to elemental carbon. Benzo[a]pyrene persisted in 5-16% of samples. The results of this study are consistent with laboratory studies in which secondary organic aerosol (SOA) coatings protected PAHs from degradation by ozone. We detected an inhibition of the degradation PAHs by SOA coatings by collecting PAHs simultaneously at the three sites. To elucidate the major sources of the SOAs, we carried out a positive matrix factorization analysis to identify the major sources of SOA coating, which controls the lifetime of PAHs. In spring and winter, the contribution of vehicle emissions was higher (46%) at Tuoji Island than at CHAAMS (13%). In contrast, the contribution of coal combustion was higher at CHAAMS (59%) than at Tuoji Island (28%). This result implies that during long-range transport, PAHs derived from coal combustion are more slowly degraded than PAHs derived from vehicle emissions. We found that the viscosity of SOA coatings derived from vehicle emissions in China was low, and the corresponding PAHs were rapidly degraded. In contrast, the viscosity of SOA coatings derived from coal combustion was high, and degradation of the corresponding PAHs was relatively slow. These results imply that PAHs derived from coal combustion have long lifetime.

Occurrence of 3-nitrobenzanthrone and other powerful mutagenic polycyclic aromatic compounds in living organisms: polychaetes

In this work we report the occurrence of powerful mutagenic 3-nitrobenzanthrone (3-NBA), in addition to 18 polycyclic aromatic hydrocarbons (PAHs), 6 oxygenated PAHs and 27 nitrated PAHs in polychaete worms. Benzanthrone (BA), another important mutagenic polycyclic aromatic compound (PAC) also was detected in the samples. Polychaete annelids have great ecological relevance, being widely distributed in different environmental conditions, from intertidal zones up to seven thousand feet deep areas. They are abundantly found in both contaminated and uncontaminated areas and, therefore, used as indicators of the pollution status of a given area. As we know, so far, most of these PACs has not been previously reported in living organisms before. The 3-NBA concentrations determined in this study were within 0.11-5.18 µg g^-1. Other relevant PACs such as PAHs, quinones and nitro-PAHs were found in maximum concentrations at 0.013 µg g^-1 (coronene) to 11.1 µg g^-1 (benzo[k]fluoranthene), 0.823 µg g^-1 (9,10-phenenthrenequinone) to 12.1 µg g^-1 (1,4-benzoquinone) and 0.434 (1-nitronaphthalene) µg g^-1 to 19.2 µg g^-1 (6-nitrobenzo[a]pyrene), respectively. Principal component analysis (PCA), ternary correlations and diagnostic ratios were employed in order to propose probable sources for PACs. Although statistical analysis preliminarily has indicated both pyrogenic and petrogenic contributions, petrogenic sources were predominant reflecting the impacts of petroleum exploration and intensive traffic of boats in the study area.

Characteristics of PM2.5-Bound Polycyclic Aromatic Hydrocarbons and Nitro-Polycyclic Aromatic Hydrocarbons at A Roadside Air Pollution Monitoring Station in Kanazawa, Japan

Polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs (NPAHs) in PM_2.5 samples were collected at a roadside monitoring station in Kanazawa, Japan, in every season from 2017 to 2018. Nine PAHs and five NPAHs were determined using high-performance liquid chromatography with fluorescence detection and chemiluminescence detection, respectively. The mean concentrations of PAHs and NPAHs were highest in winter and lowest in summer. Fluoranthene and pyrene were the dominant PAHs and 1-nitropyrene was the dominant NPAH in all seasons, and these compounds were mainly emitted by diesel vehicles. The concentration ratio of benzo(a)pyrene (BaP) to benzo(ghi)perylene (BgPe) ((BaP)/(BgPe)) and of indeno(1,2,3-cd)pyrene (IDP) to the sum of IDP and benzo(ghi)perylene (BgPe) ((IDP)/((IDP)+(BgPe0) might still be useful indicators for identifying traffic emission sources today. Moreover, our results showed that the carcinogenic risk in all seasons was below the acceptable limit set by the WHO.

Changes in black carbon and PM2.5 in Tokyo in 2003-2017

Black carbon (BC) particles cause adverse health effects and contribute to the heating of the atmosphere by absorbing visible solar radiation. Efforts have been made to reduce BC emissions, especially in urban areas; however, long-term measurements of BC mass concentration (M_BC) are very limited in Japan. We report M_BC measurements conducted in Tokyo from 2003 to 2017, showing that M_BC decreased by a factor of 3 from 2003 to 2010 and was stable from 2010 to 2017. Fine particulate concentrations (PM_2.5) decreased by a much smaller factor during 2003-2010. The diurnal variations of BC size distributions suggest that the BC in Tokyo originates mainly from local sources, even after 2010. Our three-dimensional model calculations show that BC from the Asian continent contributes a small portion (about 20%) of the annual average M_BC in the Kanto region of Japan, which includes Tokyo. This indicates that continued reduction of BC emissions inside Japan should be effective in further decreasing M_BC.

Prediction on the mutagenicity of nitroaromatic compounds using quantum chemistry descriptors based QSAR and machine learning derived classification methods

Nitroaromatic compounds (NACs) are an important type of environmental organic pollutants. However, it is lack of sufficient information relating to their potential adverse effects on human health and the environment due to the limited resources. Thus, using in silico technologies to assess their potential hazardous effects is urgent and promising. In this study, quantitative structure activity relationship (QSAR) and classification models were constructed using a set of NACs based on their mutagenicity against Salmonella typhimurium TA100 strain. For QSAR studies, DRAGON descriptors together with quantum chemistry descriptors were calculated for characterizing the detailed molecular information. Based on genetic algorithm (GA) and multiple linear regression (MLR) analyses, we screened descriptors and developed QSAR models. For classification studies, seven machine learning methods along with six molecular fingerprints were applied to develop qualitative classification models. The goodness of fitting, reliability, robustness and predictive performance of all developed models were measured by rigorous statistical validation criteria, then the best QSAR and classification models were chosen. Moreover, the QSAR models with quantum chemistry descriptors were compared to that without quantum chemistry descriptors and previously reported models. Notably, we also obtained some specific molecular properties or privileged substructures responsible for the high mutagenicity of NACs. Overall, the developed QSAR and classification models can be utilized as potential tools for rapidly predicting the mutagenicity of new or untested NACs for environmental hazard assessment and regulatory purposes, and may provide insights into the in vivo toxicity mechanisms of NACs and related compounds.

Ultraviolet-Excitation Photothermal Heterodyne Interferometer as a Micro-HPLC Detector

The first demonstration of a photothermal heterodyne interferometer (PHI) combined with micro-HPLC (high-performance liquid chromatography) is reported. A semiconductor laser (375 nm) was used for excitation, and the temperature change caused by heat released from photoexcited species was detected with a He-Ne laser (632.8 nm). The temperature-dependent refractive index change of the solvent modified the optical path of the probe beam. The phase difference between two arms of the interferometer, one passing through the heated sample and another as a reference, was sensitively detected with the PHI. The nitro-polycyclic aromatic hydrocarbon and vitamin mixture separated via micro-HPLC was successfully detected with the PHI as well as a UV detector. The detection limit of the PHI for riboflavin in the absorbance units was 77 times better than that of the commercial UV detector. The detection limit of the PHI with a small flow cell (6 nL) was the same as that with a large flow cell (18 nL) for 1-nitropyrene.

Seasonal and annual changes in PAH concentrations in a remote site in the Pacific Ocean

This paper reports the long term observation of particle-associated polycyclic aromatic hydrocarbons (PAHs) at Cape Hedo Atmosphere and Aerosol Monitoring Station, a remote site in the Western Pacific Ocean, from 2008 to 2015. This is the first long-term study that evaluated the contribution of long-range transport of PAHs in East Asia. No obvious trend (P > 0.05) was found in a particular season over the years. However, there are seasonal variations of PAH concentrations with higher in spring and winter. The higher PAH are attributed to air masses from the area including part of China. Source apportionment using three different approaches, i.e., PAH compositional pattern analysis, PAH diagnostic ratio analysis and positive matrix factorization modeling, showed the combined high contribution of biomass burning (18%, 14%) and coal combustion (33%, 24%) in spring and winter. In addition, the contribution of ship emissions (35%) was relatively high in spring, whereas that of vehicle emissions (36%) was relatively high in winter. The contribution of coal combustion to PAH has decreased throughout the years, likely due to changes in energy structure in China. The contribution of biomass burning to PAH has showed no trend, being stable, and that of vehicular emissions has increased.

The Characteristics of Polycyclic Aromatic Hydrocarbons in Different Emission Source Areas in Shenyang, China

Particulate matter (PM) was collected in three different areas, SY-1, SY-2, and SY-3, in Shenyang, China, during the warm and cold seasons from 2012 to 2014. SY-1 was located beside a thermal power plant, far from the central area. SY-2 was near a coal heating boiler on the main road, close to the central area. SY-3 was on the main road, without fixed emission sources. Nine PM-bound polycyclic aromatic hydrocarbons (PAHs) were analyzed. The results showed that the mean concentration of total PAHs was higher in the cold season (92.6-316 ng m-3) than in the warm season (18.4-32.2 ng m-3). Five- and six-ring PAHs occupied a large percentage at all sites in the warm season, and four-ring PAHs were the dominant components in the cold season. Several diagnostic PAH ratios indicated that the main sources of PAHs in Shenyang in the warm and cold seasons were not only coal burning but also vehicle emission. In this study, we suggest that a benzo[a]pyrene/benzo[ghi]perylene ratio ([BaP]/[BgPe]) of 0.6 was a useful indicator to speculate the relative significance of coal burning and vehicle exhaust. Although the Shenyang government has undertaken actions to address air pollution, the PM and PAH concentrations did not decrease significantly compared to those in our previous studies. The cancer risk calculated from the BaP equivalent total concentration at all three sites in the warm and cold seasons exceeded the acceptable limit established by the US EPA.

Existence, removal and transformation of parent and nitrated polycyclic aromatic hydrocarbons in two biological wastewater treatment processes

Polycyclic aromatic hydrocarbons (PAHs) and nitrated polycyclic aromatic hydrocarbons (NPAHs) are pollutants commonly present in the environment. Some NPAHs are considered to have more severe toxic effects than their parent PAHs. The existence of 16 PAHs (678.5-3817.8 ng/L in wastewater, 499.9 ng/g-1239.6 ng/g in sludge) and 5 NPAHs (175.8-1392.4 ng/L in wastewater, 483.5 ng/g-2763.1 ng/g in sludge) was determined in a biological wastewater treatment plant (WWTP) in Qingdao, China. Anthracene and naphthalene were the predominant PAHs, and 2-nitrofluorene and 9-nitroanthracene were the predominant NPAHs. Petroleum, liquid fossil fuel combustion and exhaust emissions were the main sources of PAHs and NPAHs in this study. In both the sequencing batch reactor/moving-bed biofilm (SBR/MBBR) and the anaerobic-anoxic-aerobic (A²O) process, low-molecular-weight PAHs were mainly removed through volatilization and biodegradation/biotransformation. Meanwhile, the removal of high-molecular-weight PAHs and NPAHs depended on adsorption and sedimentation. The transformation from PAHs to NPAHs mainly occurred in the aqueous-phase, especially in summer and that was confirmed by mass flow and ratios variation. Overall, the removal capacity of the A²O process for PAHs and NPAHs was better than that of the SBR/MBBR process. Tertiary treatment processes had little effect or even a negative effect on the removal of PAHs and NPAHs.

Chemical and Biological Components of Urban Aerosols in Africa: Current Status and Knowledge Gaps

Aerosolized particulate matter (PM) is a complex mixture that has been recognized as the greatest cause of premature human mortality in low- and middle-income countries. Its toxicity arises largely from its chemical and biological components. These include polycyclic aromatic hydrocarbons (PAHs) and their nitro-derivatives (NPAHs) as well as microorganisms. In Africa, fossil fuel combustion and biomass burning in urban settings are the major sources of human exposure to PM, yet data on the role of aerosols in disease association in Africa remains scarce. This review is the first to examine studies conducted in Africa on both PAHs/NPAHs and airborne microorganisms associated with PM. These studies demonstrate that PM exposure in Africa exceeds World Health Organization (WHO) safety limits and carcinogenic PAHs/NPAHs and pathogenic microorganisms are the major components of PM aerosols. The health impacts of PAHs/NPAHs and airborne microbial loadings in PM are reviewed. This will be important for future epidemiological evaluations and may contribute to the development of effective management strategies to improve ambient air quality in the African continent.

Sources and Characteristics of Polycyclic Aromatic Hydrocarbons in Ambient Total Suspended Particles in Ulaanbaatar City, Mongolia

The purpose of this study was to identify pollution sources by characterizing polycyclic aromatic hydrocarbons from total suspended particles in Ulaanbaatar City. Fifteen polycyclic aromatic hydrocarbons were measured in total suspended particle samples collected from different sites, such as the urban center, industrial district and ger (Mongolian traditional house) areas, and residential areas both in heating (January, March), and non-heating (September) periods in 2017. Polycyclic aromatic hydrocarbon concentration ranged between 131 and 773 ng·m-3 in winter, 22.2 and 530.6 ng·m-3 in spring, and between 1.4 and 54.6 ng·m-3 in autumn. Concentrations of specific polycyclic aromatic hydrocarbons such as phenanthrene were higher in the ger area in winter and spring seasons, and the pyrene concentration was dominant in late summer in the residential area. Polycyclic aromatic hydrocarbons concentrations in the ger area were particularly higher than the other sites, especially in winter. Polycyclic aromatic hydrocarbon ratios indicated that vehicle emissions were likely the main source at the city center in the winter time. Mixed contributions from biomass, coal, and petroleum combustion were responsible for the particulate polycyclic aromatic hydrocarbon pollution at other sampling sites during the whole observation period. The lifetime inhalation cancer risk values in the ger area due to winter pollution were estimated to be 1.2 × 10-5 and 2.1 × 10-5 for child and adult exposures, respectively, which significantly exceed Environmental Protection Agency guidelines.

A Case Study Describing a Community-Engaged Approach for Evaluating Polycyclic Aromatic Hydrocarbon Exposure in a Native American Community

In 2015, the Swinomish Indian Tribal Community (SITC) was impacted by an air toxic release from one of two nearby oil refineries. This experience motivated SITC members to learn more about their exposure to air toxics. On the invitation of SITC, this community-based study measured personal exposure to polycyclic aromatic hydrocarbons (PAHs) and conducted interviews with the volunteers to evaluate perceptions of the data and experience of participating. Non-smoking SITC members were recruited in March 2016 (N = 10) and January 2017 (N = 22) with seven volunteers participating both times. Volunteers wore a wristband passive sampler for 7 days and completed daily activity diaries. Wristbands were analyzed for 62 PAHs using gas chromatography mass spectrometry. Wilcoxon exact tests determined if the sum total PAHs (ΣPAH) differed by activity, proximity to the refineries, and time. Aggregated results were shared during community meetings, and volunteers received individual reports. Volunteers (N = 9) participated in individual interviews. All volunteers were exposed to different amounts and types of PAHs. Burning candles or using a wood stove and/or propane heating were associated with higher ΣPAH exposures. While ΣPAH was similar in both sampling periods, the composition of PAHs differed. More priority listed PAHs were detected in January (N = 17) versus March (N = 10). Among volunteers who participated in both sampling events, exposure to four PAHs significantly differed between seasons. Overall, volunteers reported that the study made them more aware of air pollution sources in their community. They also commented that the chemical nomenclature was difficult to understand, but appreciated the individual reports that allowed them to visually compare their data to the distribution of data collected in their community. For volunteers with lower exposures, these comparisons gave them relief. However, volunteers with higher exposures reported concern and several changed their behaviors to reduce their exposure to known PAH sources. This study provided an opportunity for SITC members to learn about their personal exposure to a class of air toxics within the context of their community. While the limitations of the study hindered the ability to identify sources of air toxics in the community, this activity appeared to raise awareness about ambient and indoor air pollution among the volunteers.

Occurrence of the potent mutagens 2- nitrobenzanthrone and 3-nitrobenzanthrone in fine airborne particles

Polycyclic aromatic compounds (PACs) are known due to their mutagenic activity. Among them, 2-nitrobenzanthrone (2-NBA) and 3-nitrobenzanthrone (3-NBA) are considered as two of the most potent mutagens found in atmospheric particles. In the present study 2-NBA, 3-NBA and selected PAHs and Nitro-PAHs were determined in fine particle samples (PM 2.5) collected in a bus station and an outdoor site. The fuel used by buses was a diesel-biodiesel (96:4) blend and light-duty vehicles run with any ethanol-to-gasoline proportion. The concentrations of 2-NBA and 3-NBA were, on average, under 14.8 µg g⁻¹ and 4.39 µg g⁻¹, respectively. In order to access the main sources and formation routes of these compounds, we performed ternary correlations and multivariate statistical analyses. The main sources for the studied compounds in the bus station were diesel/biodiesel exhaust followed by floor resuspension. In the coastal site, vehicular emission, photochemical formation and wood combustion were the main sources for 2-NBA and 3-NBA as well as the other PACs. Incremental lifetime cancer risk (ILCR) were calculated for both places, which presented low values, showing low cancer risk incidence although the ILCR values for the bus station were around 2.5 times higher than the ILCR from the coastal site.

Cyclodextrin-Promoted Fluorescence Detection of Aromatic Toxicants and Toxicant Metabolites in Commercial Milk Products

The detection of polycyclic aromatic hydrocarbons (PAHs) and their metabolites in food and in agricultural sources is an important research objective due to the PAHs' known persistence, carcinogenicity, and toxicity. PAHs have been found in the milk of lactating cows, and in the leaves and stems of plants grown in PAH-contaminated areas, thereby making their way into both cow milk and plant milk alternatives. Reported herein is the rapid, sensitive, and selective detection of 10 PAHs and PAH metabolites in a variety of cow milks and plant milk alternatives using fluorescence energy transfer from the PAH to a high quantum yield fluorophore, combined with subsequent array-based statistical analyses of the fluorescence emission signals. This system operates with high sensitivity (low micromolar detection limits), selectivity (100% differentiation even between structurally similar analytes), and general applicability (for both unmodified lipophilic PAHs and highly polar oxidized PAH metabolites, as well as for different cow and plant milk samples). These promising results show significant potential to be translated into solid-state devices for the rapid, sensitive, and selective detection of PAHs and their metabolites in complex, commercial food products.