Polycyclic aromatic hydrocarbons (PAHs), one of the major environmental pollutants, produced from incomplete combustion of materials like coal, oil, gas, wood, and charbroiled meat, that contaminate the air, soil, and water, necessitating urgent remediation. Understanding the metabolic pathways for PAHs degradation is crucial to preventing environmental damage and health issues. Biological methods are gaining increasing interest due to their cost-effectiveness and environmental friendliness. These methods are particularly suitable for remediating PAHs contamination and mitigating associated risks. The paper also outlines the processes for biodegrading PAHs, emphasizing the function of Pseudomonas spp., a kind of bacterium recognized for its capacity to degrade PAHs. To eliminate PAHs from the environment and reduce threats to human health and the environment, Pseudomonas spp. is essential. Understanding the mechanism of PAH breakdown by means of microbes could lead to effective clean-up strategies. The review highlights the enzymatic capabilities, adaptability, and genetic versatility of the genes like nah and phn of Pseudomonas spp., which are involved in PAHs degradation pathways. Scientific evidence supports using Pseudomonas spp. as biocatalysts for PAHs clean-up, offering cost-effective and eco-friendly solutions.

A strain of Bacillus licheniformis T5 was isolated from soil contaminated with crude oil due to its efficient degradation of polycyclic aromatic hydrocarbons (PAHs). When subjected to stress metabolism using phenanthrene as a carbon source, significant changes were observed in T5 cells. Infrared spectrum analysis revealed the presence of -C=C- and Ph-O-C (aromatic) groups on the bacterial surface, facilitating the adsorption of PAHs on the phospholipid layer and causing damage to the cell membrane. Scanning electron microscope (SEM) analysis showed the changes of cell morphology, including a large number of folds on the lower surface and the folding of cell membrane. Transmission electron microscope (TEM) observation showed that non-stressed bacteria with adequate nutritional conditions accumulated more lipids. However, the stress group contained more protein. It was found that stress metabolism led to the increase of protein content in T5 cells by 16.4% and the activity of oxidoreductase more than doubled. These physiological and biochemical changes enhance the ability of stressed bacteria to degrade PAHs efficiently, thereby reducing the degradation cycle. The findings offer valuable insights for the remediation of PAHs pollution.

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants that pose significant environmental and health risks. These compounds originate from both natural phenomena, such as volcanic activity and wildfires, and anthropogenic sources, including vehicular emissions, industrial processes, and fossil fuel combustion. Their classification as carcinogenic, mutagenic, and teratogenic substances link them to various cancers and health disorders. PAHs are categorized into low-molecular-weight (LMW) and high-molecular-weight (HMW) groups, with HMW PAHs exhibiting greater resistance to degradation and a tendency to accumulate in sediments and biological tissues. Soil serves as a primary reservoir for PAHs, particularly in areas of high emissions, creating substantial risks through ingestion, dermal contact, and inhalation. Coastal and aquatic ecosystems are especially vulnerable due to concentrated human activities, with PAH persistence disrupting microbial communities, inhibiting plant growth, and altering ecosystem functions, potentially leading to biodiversity loss. In plants, PAH contamination manifests as a form of abiotic stress, inducing oxidative stress, cellular damage, and growth inhibition. Plants respond by activating antioxidant defenses and stress-related pathways. A notable aspect of plant defense mechanisms involves plant-derived extracellular vesicles (PDEVs), which are membrane-bound nanoparticles released by plant cells. These PDEVs play a crucial role in enhancing plant resistance to PAHs by facilitating intercellular communication and coordinating defense responses. The interaction between PAHs and PDEVs, while not fully elucidated, suggests a complex interplay of cellular defense mechanisms. PDEVs may contribute to PAH detoxification through pollutant sequestration or by delivering enzymes capable of PAH degradation. Studying PDEVs provides valuable insights into plant stress resilience mechanisms and offers potential new strategies for mitigating PAH-induced stress in plants and ecosystems.

The distribution of integral indicators of the soil-plant system components contamination with polycyclic aromatic hydrocarbons in the urban area has been considered. An anthropogenically modified natural complex of the RUDN University campus and the adjacent South-Western Forest Park (Moscow) was the object of study. Soils (Albic Retisols (Ochric)) and common plant species were studied. Traffic load was the main pollution source. Emissions from five sections of roads, around and across the territory, formed a specific pattern of pollutants, which was demonstrated by the example of marker compounds, namely, polycyclic aromatic hydrocarbons. Background concentrations of individual polyarenes in the environment, determined by the method of dynamic phase portraits, have been calculated as an approximate safe level of contamination of soils and vegetation. A local redistribution of contamination zones was revealed owing to the migration of polyarenes from snow into soils, and then into root systems, and the above-ground parts of plants distribution. The proposed methodological approach, based on the use of integral indicators, allows us to assess the degree of damage to ecosystems caused by a complex of priority pollutants.

Nanobubbles (NBs), given their unique properties, could theoretically be paired with rhamnolipids (RL) to tackle polycyclic aromatic hydrocarbon contamination in groundwater. This approach may overcome the limitations of traditional surfactants, such as high toxicity and low efficiency. In this study, the remediation efficiency of RL, with or without NBs, was assessed through soil column experiments (soil contaminated with phenanthrene). Through the analysis of the two-site non-equilibrium diffusion model, there was a synergistic effect between NBs and RL. The introduction of NBs led to a reduction of up to 24.3 % in the total removal time of phenanthrene. The direct reason for this was that with NBs, the retardation factor of RL was reduced by 1.9 % to 15.4 %, which accelerated the solute replacement of RL. The reasons for this synergy were multifaceted. Detailed analysis reveals that NBs improve RL's colloidal stability, increase its absolute zeta potential, and reduce its soil adsorption capacity by 13.3 %-19.9 %. Furthermore, NBs and their interaction with RL substantially diminish the surface tension, contact angle, and dynamic viscosity of the leaching solution. These changes in surface thermodynamic and rheological properties significantly enhance the migration efficiency of the eluent. The research outcomes facilitate a thorough comprehension of NBs' attributes and their relevant applications, and propose an eco-friendly method to improve the efficiency of surfactant remediation.

Thermal desorption (TD) is known as an effective technique to remediate PAHs-contaminated sites. However, effectively removing PAHs using TD while saving time, and energy, and minimizing soil damage remains a challenge. In this study, we examined the combined effects of various factors on the removal efficiency of pyrene (PYR) by TD and developed an optimal numerical model based on conducting a series of soil experiments. The results showed that temperature (T) and time (t) promoted the desorption of PYR, while water (Sw) and organic matter (fom) were just the opposite. Besides, water and organic matter had a synergistic effect proportionally. It was found that adjusting the soil-water ratio (which can be controlled by organic matter) maximized the desorption rate of PYR. An ideal Sw/fom 1.56 and a minimized recommended temperature (173 degrees C) were pro-posed based on the model. Finally, the efficacy of the optimized scheme was validated in real-world site soil. These findings not only mechanistically revealed the desorption behavior of PYR under the influence of various factors, but also provided an optimized scheme for efficiently removing PAHs using TD, thereby accelerating the remediation process and reducing energy consumption. The modeling ideas and conclusions obtained may be applicable to other PAHs, guiding the effective remediation of PAHs-polluted sites.

Much attention is drawn to polycyclic aromatic hydrocarbons (PAHs) as an air pollutant due to their toxic, mutagenic and carcinogenic properties. Therefore, to understand the levels, seasonality, sources and potential health risk of PAHs in two distinct geographical locations at Karachi and Mardan in Pakistan, total suspended particle (TSP) samples were collected for over one year period. The average total PAH concentrations were 31.5 +/- 24.4 and 199 +/- 229 ng/m(3) in Karachi and Mardan, respectively. The significantly lower concentration in Karachi was attributed to diffusion and dilution of the PAHs by the influence of clean air mass from the Arabian sea and high temperature, enhancing the volatilization of the particle phase PAHs to the gas phase. Conversely, the higher concentration (6 times) in Mardan was due to large influence from local and regional emission sources. A clear seasonality was observed at both the sites, with the higher values in winter and post-monsoon due to higher emissions and less scavenging, and lower values during monsoon season due to the dilution effect. Diagnostic ratios and principal component analysis indicated that PAHs in both sites originated from traffic and mixed combustion sources (fossil fuels and biomass). The average total BaP equivalent concentrations (BaPeq) in Karachi and Mardan were 3.26 and 34 ng/m(3) , respectively, which were much higher than the WHO guideline of 1 ng/m(3) . The average estimates of incremental lifetime cancer risk from exposure to airborne BaPeq via inhalation indicated a risk to human health from atmospheric PAHs at both sites. (C) 2021 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

With the recent rapid development of urbanization, atmospheric pollutants such as polycyclic aromatic hydrocarbons (PAHs) have attracted wide attention, particularly in remote regions. The Tibetan Plateau (TP), known as the third pole is adjacent to areas with heavy atmospheric pollution, such as South and East Asia. However, the spatial distribution and sources of PAHs on the TP remain unclear. Thus, we investigated the sources and spatio-temporal distributions of PAHs on the TP by combining aerosol sample data from six sites, including Ngari (NG), Laohugou (LHG), Beiluhe (BLH), Nam Co (NMC), Everest (EV), and Yulong (YL), in 2014 and 2016. The average concentrations of 15 PAHs at the six sites ranged from 3.4 to 15.2 ng m(-3), with a decreasing trend from the marginal to inner areas of the plateau. The highest concentration was that in YL in the southeastern part of the TP, with an average of 15.2 ng m(-3). The PAH concentrations in NG, NMC, and YL were higher in autumn and winter and lower in summer. High molecular weight PAHs usually exists in the particulate phase whereas tricyclic PAHs can change from particulate to gaseous phase, therefore it can indicate long-range transport. Tricyclic PAHs were the dominant PAHs on the TP (44%-58%), indicating long-range atmospheric transport as the major source of PAHs. Principal component analysis (PCA) and diagnostic ratio analysis showed that biomass and coal combustion were the major sources of PAHs in inland areas of the TP; however, marginal plateau areas were affected by fossil fuel emissions. Compared with levels in Beijing and other urban sites, the toxic equivalent quantity (TEQ) was low (0.36-1.06 ng m(-3)), suggesting a low risk to human and ecosystem health. (C) 2020 Elsevier Ltd. All rights reserved.

Brown carbon (BrC), an organic aerosol, plays an important role in radiative forcing. Polycyclic aromatic hydrocarbons (PAHs) and their derivatives such as oxygenated and nitrated polycyclic aromatic hydrocarbons (OPAHs & NPAHs) are the major constituents of BrC and are persistent environmental pollutants. Our strategy here is to utilize time dependent-density functional theory (TD-DFT) to model the absorption spectra of PAHs and their derivatives in two Chinese industrial sites: Qingcheng district (site A) and Longtang town of Qingyuan (site B). These data are corrected for Real-world experimental concentrations of PAHs over these cities. For the first time, nocturnal/diurnal and seasonal variations of PAHs are being simultaneously studied under a theoretical framework. These findings show that the absorptions at site A and B take place mainly due to PAHs while OPAHs and NPAHs have negligible contribution. The site A is highly affected by climate forcing caused by these PAHs. The absorption in winter is higher as compared to that of in summer. Our theoretical modeling approach remarkably identifies the most relevant PAHs for climate forcing in both Chinese regions.

Polycyclic aromatic hydrocarbons (PAHs) and their oxygenated (OPAHs) and nitrated (NPAHs) derivatives are main chromophores of the carbonaceous aerosol brown carbon (BrC), which is linked with radiative forcing. Here, we investigated the atmospheric absorption spectra of 64 PAHs, OPAHs, and NPAHs directly over the Chinese megacity of Xi'an, by employing a time-dependent density functional theory (TD-DFT) computational approach and correcting the results for the experimentally determined atmospheric concentration of the studied molecules. The obtained data showed that these molecules contribute more to radiative forcing by absorbing light in the UVA and (sub)visible region of the spectrum. Investigating daily absorption spectra revealed major seasonal variation in the intensity of light absorption, but little changes in the shape of the absorption spectra. The observed light absorption can be explained mainly by contributions from PAHs and to a lesser extent by carbonyl-OPAHs, with relatively low contributions of the other OPAHs and NPAHs. Among them, benzo[b+j+k] fluoranthenes, benzo[e]pyrene, benzo[a]pyrene, benzo[ghi]perylene, indeno[1,2,3-cd]pyrene, 6H-benzo[cd] pyren-6-one, 7H-benz[de]anthracen-7-one, and benz[a]anthracene-7,12-dione are highlighted as potentially problematic contributors for radiative forcing over Xi'an.