Environmental contamination by heterocyclic Polynuclear aromatic hydrocarbons and their microbial degradation

Daphnia magna as an Alternative Model for (Simultaneous) Bioaccumulation and Chronic Toxicity Assessment─Controlled Exposure Study Indicates High Hazard of Heterocyclic PAHs

Testing the bioaccumulation and chronic toxicity of (highly) hydrophobic compounds is extremely challenging, but crucial for hazard assessment. Fish are used as a model organism in these tests, but have many limitations, including a long time to reach steady-state, difficulty in maintaining constant exposure, and ethical concerns. We developed a method for the (simultaneous) assessment of chronic reproductive toxicity and bioaccumulation using Daphnia magna as a model organism. As test chemicals, we selected heterocyclic polyaromatic hydrocarbons (heterocyclic PAHs), which are often persistent and show high acute aquatic toxicity, raising concerns about their long-term effects. In this study, we developed a robust passive dosing method to maintain constant exposure in chronic toxicity and bioaccumulation tests of four heterocyclic PAHs in Daphnia magna. Passive dosing maintained stable exposure concentrations in the ng to μg L-1 range, even after reusing disks up to three times. All chemicals were toxic to Daphnia magna with EC10 values between 0.1 and 15 μg L-1. Bioaccumulation tests showed that steady-state was not reached, and the uptake rate constant (k1) could not be reliably determined due to complex exposure routes (both via water and diet). However, depuration rates in Daphnia magna were about 2 orders of magnitude higher than in fish, which is advantageous in the assessment of highly hydrophobic compounds. We propose to use the depuration rate constant (k2), which is independent of the uptake route, as an indicator of bioaccumulation potential. The k2 thresholds for Daphnia magna were estimated to identify (very) bioaccumulative compounds by correlating k2 values with bioconcentration factors (BCFs) for Daphnia magna and applying fish BCF thresholds. We suggest that a Daphnia magna bioaccumulation test can be used as a screening tool to trigger further bioaccumulation testing in fish, as it offers higher throughput, is more ethical, and reaches steady-state faster. However, further validation with reference test protocols and substances is essential.

Data-Driven Approach for Designing Eco-Friendly Heterocyclic Compounds for the Soil Microbiome

Soil microbiota plays crucial roles in maintaining the health, productivity, and nutrient cycling of terrestrial ecosystems. The persistence and prevalence of heterocyclic compounds in soil pose significant risks to soil health. However, understanding the links between heterocyclic compounds and microbial responses remains challenging due to the complexity of microbial communities and their various chemical structures. This study developed a machine-learning approach that integrates the properties of chemical structures with the diversity of soil bacteria and functions to predict the impact of heterocyclic compounds on the microbial community and improve the design of eco-friendly heterocyclic compounds. We screened the key chemical structures of heterocyclic compounds─particularly those with topological polar surface areas (<74.2 Å2 or 111.3-154.1 Å2), carboxyl groups, and dissociation constant, which maintained high soil bacterial diversity and functions, revealing threshold effects where specific structural parameters dictated microbial responses. These eco-friendly compounds stabilize communities and increase beneficial carbon and nitrogen cycle functions. By applying these design parameters, we quantitatively assessed the eco-friendliness scores of 811 heterocyclic compounds, providing a robust foundation for guiding future applications. Our study disentangles the critical chemical structure-related properties that influence the soil microbial community and establishes a computational framework for designing eco-friendly compounds with ecological benefits from an ecological perspective.

Characterizing the Contaminant-Adhesion of a Dibenzofuran Degrader Rhodococcus sp

The adhesion between dibenzofuran (DF) and degrading bacteria is the first step of DF biodegradation and affects the efficient degradation of DF. However, their efficient adhesion mechanism at the molecular level remains unclear. Therefore, this study first examined the adhesive behaviors and molecular mechanisms of Rhodococcus sp. strain p52 upon exposure to DF. The results showed that the adhesion between strain p52 and DF is mediated by extracellular polymeric substances (EPSs). Compared with sodium acetate as a carbon source, the percentages of glucose and proteins related to electron transfer, toxin-antitoxin, and stress responses were elevated, which were analyzed by polysaccharide composition and proteomics, and the contents of extracellular polysaccharides and proteins were increased. Moreover, biofilm analysis suggested an increase in EPS content, and the change in components increased biofilm yield and promoted loose and porous aggregation between the bacteria; this aggregation caused an increase in the specific surface area in contact with DF. The surface characteristics analysis indicated that the production of EPS reduced the absolute value of the zeta potential and increased the hydrophobicity of strain p52, which was beneficial for the adhesion of strain p52 and DF. These findings help us to enhance the understanding of the adhesion mechanisms and bioremediation of polycyclic aromatic hydrocarbons by degrading bacteria.

Mechanisms of nano zero-valent iron in enhancing dibenzofuran degradation by a Rhodococcus sp.: Trade-offs between ATP production and protection against reactive oxygen species

Nano zero-valent iron (nZVI) can enhance pollutants biodegradation, but it displays toxicity towards microorganisms. Gram-positive (G+) bacteria exhibit greater resistance to nZVI than Gram-negative bacteria. However, mechanisms of nZVI accelerating pollutants degradation by G+ bacteria remain unclear. Herein, we explored effects of nZVI on a G+ bacterium, Rhodococcus sp. strain p52, and mechanisms by which nZVI accelerates biodegradation of dibenzofuran, a typical polycyclic aromatic compound. Electron microscopy and energy dispersive spectroscopy analysis revealed that nZVI could penetrate cell membranes, which caused damage and growth inhibition. nZVI promoted dibenzofuran biodegradation at certain concentrations, while higher concentration functioned later due to the delayed reactive oxygen species (ROS) mitigation. Transcriptomic analysis revealed that cells adopted response mechanisms to handle the elevated ROS induced by nZVI. ATP production was enhanced by accelerated dibenzofuran degradation, providing energy for protein synthesis related to antioxidant stress and damage repair. Meanwhile, electron transport chain (ETC) was adjusted to mitigate ROS accumulation, which involved downregulating expression of ETC complex I-related genes, as well as upregulating expression of the genes for the ROS-scavenging cytochrome bd complex and ETC complex II. These findings revealed the mechanisms underlying nZVI-enhanced biodegradation by G+ bacteria, offering insights into optimizing bioremediation strategies involving nZVI.

Vertical distribution and influencing factors of soil PAHs under different ecosystem habitats in the Liaohe River Estuary Wetlands, Northeastern China

The vertical distribution, sources and influencing factors of polycyclic aromatic hydrocarbons (PAHs) in soil across ecosystem habitats were investigated around the Liaohe River Estuary (LRE) Wetland. The concentration of Ʃ16PAHs ranged from 41.0 to 435.4 ng g-1 dw, with a predominance of low molecular weight PAHs. Overall, PAHs and physicochemical properties of soil decreased with depth. Vegetation was found to increase soil PAHs. Additionally, soil physicochemical properties also regulated PAHs concentration, particularly for PAHs with high molecular weight. Among the habitats, total organic carbon was the key influencing factor for Suaeda heteroptera, while specific surface area was crucial for Phragmites australis. Results of characteristic ratio method and principal component analysis revealed that PAHs in LRE primarily originate petroleum, coal and biomass combustion. In summary, vegetation colonization significantly affected the distribution, sources, and controlling factors of PAHs. These findings are meaningful for management of soil PAHs across various ecosystem habitats.

Interaction of heavy metals and polycyclic aromatic hydrocarbons in soil-crop systems: The effects and mechanisms

In natural environments, the removal and degradation of two major pollutants, heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs), are explored through targeted experimental investigations. However, these endeavors reveal that outcomes in situ may significantly diverge from the idealized effects observed in laboratory settings due to the complex interaction between HMs and PAHs, underscoring a pressing need for thorough research into their mutual impacts. This review examines the origins and migratory pathways of compound pollution stemming from HMs and PAHs. Concurrently, it provides an overview of the farmland ecosystem's response to combined HMs-PAHs pollution. This encompassed the assessments of changes in the soil's physical and chemical properties, the intricacies of the migration and transformation processes of the combined pollution within plants, and the consequential impact on the physiological functions of soil microorganisms. The varying concentration ratios of HMs and PAHs can modulate the permeability of plant root cell membranes, thereby influencing the translocation of these substances within the plant via symplastic and apoplastic pathways. Recent research has uncovered the mechanisms underlying cation-π interactions between HMs and PAHs. This review aims to offer a comprehensive overview of the current state of HMs-PAHs co-pollution, offering both qualitative and quantitative insights into their interaction patterns within the farmland ecosystem. The ultimate goal is to establish a robust theoretical foundation to support the in-situ remediation of these pollutants in agricultural practices and to provide a theoretical basis for soil health management in agricultural production.

Enhanced bioremediation of organically combined contaminated soil by white rot fungal agent: physiological characteristics and contaminants degradation

Microbial remediation of organically combined contaminated sites is currently facing technical challenges. White rot fungi possess broad-spectrum degradation capabilities, but most of the studies are conducted on polluted water bodies, and few research focus on the degradation of combined organically contaminated soils. This study aimed to investigate the physiological changes in Trametes versicolor to enhance its simultaneous degradation ability towards benzo(a)pyrene (BaP) and TPH. The results demonstrated that Trametes versicolor, when subjected to liquid fermentation, achieved an 88.08% degradation of individual BaP within 7 days. However, under the combined contamination conditions of BaP and TPH, the BaP degradation rate decreased to 69.25%, while the TPH degradation rate was only 16.95%. Furthermore, the degradation rate of BaP exhibited a significant correlation with the extracellular protein concentration and laccase activities. Conversely, the TPH degradation rate exhibited a significant and positive correlation with the intracellular protein concentration. Solid-state fermentation utilizing fungal agents proved to be the most effective method for removing BaP and TPH, yielding degradation rates of 56.16% and 15.73% respectively within 60 days. Overall, Trametes versicolor demonstrated a commendable capability for degrading combined PAHs-TPH pollutants, thereby providing theoretical insights and technical support for the remediation of organically combined contaminated sites.

Deep eutectic solvent for the extraction of polycyclic aromatic compounds in fuel, food and environmental samples

Polycyclic aromatic compounds (PACs) encompass a wide variety of organic analytes that have mutagenic and carcinogenic potentials for human health and are recalcitrant in the environment. Evaluating PACs levels in fuel (e.g., gasoline and diesel), food (e.g., grilled meat, fish, powdered milk, fruits, honey, and coffee) and environmental (e.g., industrial effluents, water, wastewater and marine organisms) samples are critical to determine the risk that these chemicals pose. Deep eutectic solvents (DES) have garnered significant attention in recent years as a green alternative to traditional organic solvents employed in sample preparation. DES are biodegradable, have low toxicities, ease of synthesis, low cost, and a remarkable ability to extract PACs. However, no comprehensive assessment of the use of DESs for extracting PACs from fuel, food and environmental samples has been performed. This review focused on research involving the utilization of DESs to extract PACs in matrices such as PAHs in environmental samples, NSO-HET in fuels, and bisphenols in foods. Chromatographic methods, such as gas chromatography (GC) and high-performance liquid chromatography (HPLC), were also revised, considering the sensibility to quantify these compound types. In addition, the characteristics of DES and advantages and limitations for PACs in the context of green analytical chemistry principles (GAC) and green profile based on metrics provide perspective and directions for future development.

Synthesis and characterization of micro-sized polyisobutylene and evaluation of its toxicological effects on the development and homeostasis of zebrafish (Danio rerio)

Rampant industrialization has led to widespread reliance on hydrocarbon polymers for various commercial applications. While these synthetic polymers, commonly known as plastics, degrade in slowly in the environments, the toxic effects of their micro-sized particles remain underexplored. In this study, we synthesized polyisobutylene (PIB) microparticles in the lab and evaluated their toxicity and accumulation in a zebrafish model. Pristine and fluorescent PIB-microplastics (MPs), with particle sizes ranging from 2 to 10 μm, were synthesized using the solvent evaporation method. Fourier-transform infrared spectroscopy (FTIR) confirmed the stability of the suspensions. Zebrafish larvae exposed to various concentrations of PIB-MPs exhibited numerous morphological and molecular changes, including delayed hatching, impaired swimming behavior, increased reactive oxygen species levels, altered mRNA levels of genes encoding antioxidant proteins, and reduced survival rates. Dissections revealed PIB-MP accumulation in the guts of larvae and adult fish within 7-21 days, causing damage to the intestinal mucosa. These findings provide insights into how contaminants like PIB can induce pathophysiological defects in aquatic fauna and pose potential health hazards to humans.

Predicting the Occurrence of Substituted and Unsubstituted, Polycyclic Aromatic Compounds in Coking Wastewater Treatment Plant Effluent using Machine Learning Regression

Organic contaminants such as polycyclic aromatic compounds (PACs) occurring in industrial effluents can not only persist in wastewater but transform into more toxic and mobile, substituted heterocyclic products during treatment. Thus, predicting the occurrence of PACs and their heterocyclic derivatives (HPACs) in coking wastewater is of utmost importance to reduce the environmental risks in water bodies that receive industrial effluents. Although HPACs can be monitored through sampling and analysis, the characterisation techniques used in their analyses are costly and time-consuming. In this study, we propose 3 distinct kernel-based machine learning (ML) models for predicting PACs including substituted HPACs and alkylated PACs occurring in coking wastewater. By using routinely measured wastewater quality data as input for our models, we predicted the occurrence of 14 HPACs in the final effluent of a coking wastewater treatment plant. Support Vector Machine based regression model (SVR) used for HPAC prediction showed the highest R2 of 0.83. Performance assessment of SVR model showed a mean absolute logarithmic error (MALE) of 0.46 and root mean square error (RMSE) of 0.073 ng/L. Comparatively, K-Nearest Neighbor and Random Forest models showed lower R2 of 0.75 and 0.76 respectively for HPAC prediction. Feature analysis attributed the superior predictability of SVR model likely to its higher weightage (81%) towards dissolved organic carbon and total ammonia as input variables. Both these variables could capture the underlying secondary PAC transformations likely occurring in the treatment plant. Partial dependence plots predicted that ammonia levels higher than 120 mg/L and DOC levels of 50-60 mg/L were likely linked to higher HPACs occurring in the final effluent. This work highlights the capability of kernel-based ML models in capturing nonlinear wastewater chemistry and offers a tool for monitoring trace organic contaminants released in coking effluents.

Metabolic cross-feeding between the competent degrader Rhodococcus sp. strain p52 and an incompetent partner during catabolism of dibenzofuran: Understanding the leading and supporting roles

Microbial interactions, particularly metabolic cross-feeding, play important roles in removing recalcitrant environmental pollutants; however, the underlying mechanisms involved in this process remain unclear. Thus, this study aimed to elucidate the mechanism by which metabolic cross-feeding occurs during synergistic dibenzofuran degradation between a highly efficient degrader, Rhodococcus sp. strain p52, and a partner incapable of utilizing dibenzofuran. A bottom-up approach combined with pairwise coculturing was used to examine metabolic cross-feeding between strain p52 and Arthrobacter sp. W06 or Achromobacter sp. D10. Pairwise coculture not only promoted bacterial pair growth but also facilitated dibenzofuran degradation. Specifically, strain p52, acting as a donor, released dibenzofuran metabolic intermediates, including salicylic acid and gentisic acid, for utilization and growth, respectively, by the partner strains W06 and D10. Both salicylic acid and gentisic acid exhibited biotoxicity, and their accumulation inhibited dibenzofuran degradation. The transcriptional activity of the genes responsible for the catabolism of dibenzofuran and its metabolic intermediates was coordinately regulated in strain p52 and its cocultivated partners, thus achieving synergistic dibenzofuran degradation. This study provides insights into microbial metabolic cross-feeding during recalcitrant environmental pollutant removal.

High enrichment and measurement of heterocyclic aromatic hydrocarbons from environmental waters with magnetic resorcinol-formaldehyde nanocomposites coupled with high performance liquid chromatography

Heterocyclic aromatic hydrocarbons are concerned pollutants with carcinogenic toxicity, which exist universally in various environmental matrices and have great harm to environmental and human health. In present work, magnetic resorcinol-formaldehyde composites (Fe3O4@SiO2@R-F) were fabricated via aldol condensation reaction under alkaline condition. The prepared magnetic materials were examined and analyzed with Fourier transform infrared spectroscopy and other related instruments. The Fe3O4@SiO2@R-F composites were utilized to develop an efficient magnetic solid phase extraction (MSPE) method for extracting six heteropolyclic aromatic hydrocarbons from environmental water samples including carbazole (CB), 7-methylquinoline (7-MQL), 9-methylcarbazole (9-MCB), dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The analytes were analyzed by high performance liquid chromatography-ultraviolet variable wavelength detector (HPLC-VWD). The main factors affecting MSPE were optimized. With the optimal parameters, 9-MCB and 4-MDBT have good linearity over the concentration range of 0.1-300 μg L-1, and 7-MQL, CB, DBT and 4,6-DMDBT have good linearity over the concentration range of 0.5-300 μg L-1. The limits of detection were over the concentration range of 0.012-0.031 μg L-1. This method was successfully employed to measure real waters, and the spiked recoveries ranged from 89.4% to 99.9%. The results confirmed that the developed method was reliable, robust and could be employed as a usefully alternate way for analyzing such pollutants in waters.

Preparation of Newly Polymer-Coated Microbial Pellets and Their Adsorption and Degradation Properties for Oil-Containing Wastewater

Water is the lifeblood of everything on earth, nourishing and nurturing all forms of life, while also contributing to the development of civilization. However, with the rapid development of economic construction, especially the accelerated process of modern industrialization, the pollution of oily sewage is becoming increasingly serious, affecting the ecological balance and human health. The efficient elimination of pollutants in sewage is, therefore, particularly urgent. In this paper, a core-shell microbial reactor (MPFA@CNF-SA-AM) was fabricated by using nanocellulose and sodium alginate (SA) particles embedded with microorganisms as the core and lipophilic and hydrophobic fly ash as the outer shell layer. Compared with that of free microorganisms and cellulose and SA aerogel pellets loading with microorganisms (CNF-SA-AM), which has a degradation efficiency of 60.69 and 82.89%, respectively, the MPFA@CNF-SA-AM possesses a highest degradation efficiency of 90.60% within 240 h. So that this self-floating microbial reactor has selective adsorption properties to achieve oil-water separation in oily wastewater and high effective degradation of organic pollutants with low cost. The adsorption curves of MPFA@CNF-SA-AM for diesel and n-hexadecane were studied. The results showed that the adsorption follows the Freundlich model and is a multimolecular layer of physical adsorption. In addition, the degradation mechanism of diesel oil was studied by gas chromatography-mass spectrometry. The results showed that diesel oil was selectively adsorbed to the interior of MPFA@CNF-SA-AM, and it was degraded by enzymes in microorganisms into n-hexadecanol, n-hexadecaldehyde, and n-hexadecanoic acid in turn, and finally converted to water and carbon dioxide. Compared with existing oily wastewater treatment methods, this green and pollution-free dual-functional core-shell microbial reactor has the characteristics of easy preparation, high efficiency, flexibility, and large-scale degradation. It provides a new, effective green choice for oily wastewater purification and on-site oil spill accidents.

Toxicity assessment of dioxins and their transformation by-products from inferred degradation pathways

Due to the significant POPs characteristics, dioxins caused concern in public health and environmental protection. Evaluating the toxicity risk of dioxin degradation pathways is critical. OCDD, 1,2,3,4,6,7,8-HpCDD, and 1,2,3,4,6,7,8-HpCDF, which are highly abundant in the environment and have strong biodegradation capabilities, were selected as precursor molecules in this study. Firstly, their transformation pathways were deduced during the metabolism of biometabolism, microbial aerobic, microbial anaerobic, and photodegradation pathways, and density function theory (DFT) was used to calculate the Gibbs free energy to infer the possibility of the occurrence of the transformation pathway. Secondly, the carcinogenic potential of the precursors and their degradation products was evaluated using the TOPKAT modeling method. With the help of the positive indicator (0-1) normalization method and heat map analysis, a significant increase in the toxic effect of some of the transformation products was found, and it was inferred that it was related to the structure of the transformation products. Meanwhile, the strength of the endocrine disrupting effect of dioxin transformation products was quantitatively assessed using molecular docking and subjective assignment methods, and it was found that dioxin transformation products with a higher content of chlorine atoms and molecules similar to those of thyroid hormones exhibited a higher risk of endocrine disruption. Finally, the environmental health risks caused by each degradation pathway were comprehensively assessed with the help of the negative indicator (1-2) standardization method, which provides a theoretical basis for avoiding the toxicity risks caused by dioxin degradation transformation. In addition, the 3D-QSAR model was used to verify the necessity and rationality of this study. This paper provides theoretical support and reference significance for the toxicity assessment of dioxin degradation by-products from inferred degradation pathways.

Polymer-Supported Heterogeneous Fenton Catalysts for the Environmental Remediation of Wastewater

Materials based on polymer hydrogels have demonstrated potential as innovative Fenton catalysts for treating water. However, developing these polymer-supported catalysts with robust stability presents a significant challenge. This paper explores the development and application of polymer-supported heterogeneous Fenton catalysts for the environmental remediation of wastewater, emphasizing the enhancement of metal incorporation into catalysts for improved efficiency. The study begins with an introduction to the heterogeneous Fenton process and its relevance to wastewater treatment. It further delves into the specifics of polymer-supported heterogeneous Fenton catalysts, focusing on iron oxide, copper complexes/nanoparticles, and ruthenium as key components. The synthesis methods employed to prepare these catalysts are discussed, highlighting the innovative approaches to achieve substantial metal incorporation. Operational parameters such as catalyst dosage, pollutant concentration, and the effect of pH on the process efficiency are thoroughly examined. The catalytic performance is evaluated, providing insights into the effectiveness of these catalysts in degrading pollutants. Recent developments in the field are reviewed, showcasing advancements in catalyst design and application. The study also addresses the stability and reusability of polymer-supported heterogeneous Fenton catalysts, critical factors for their practical application in environmental remediation. Environmental applications are explored, demonstrating the potential of these catalysts in addressing various pollutants. The Conclusions offers future perspectives, underlining the ongoing challenges and opportunities in the field, and the importance of further research to enhance the efficacy and sustainability of polymer-supported heterogeneous Fenton catalysts for wastewater treatment.

Chemotaxis-mediated degradation of PAHs and heterocyclic PAHs under low-temperature stress by Pseudomonas fluorescens S01: Insights into the mechanisms of biodegradation and cold adaptation

As wellknown persistent contaminants, polycyclic aromatic hydrocarbons (PAHs) and heterocyclic polyaromatic hydrocarbons (Heterocyclic PAHs)'s fates in cryogenic environments are remains uncertain. Herein, strain S01 was identified as Pseudomonas fluorescens, a novel bacterium tolerant to low temperature and capable of degrading PAHs and heterocyclic PAHs. Strain S01 exhibited growth at 5-40 ℃ and degradation rate of mixed PAHs and heterocyclic PAHs reached 52% under low-temperature. Through comprehensive metabolomic, genomic, and transcriptomic analyses, we reconstructed the biodegradation pathway for PAHs and heterocyclic PAHs in S01 while investigating its response to low temperature. Further experiments involving deletion and replacement of methyl-accepting chemotaxis protein (MCP) confirmed its crucial role in enabling strain S01's adaptation to dual stress of low temperature and pollutants. Additionally, our analysis revealed that MCP was upregulated under cold stress which enhanced strain S01's motility capabilities leading to increased biofilm formation. The establishment of biofilm promoted preservation of distinct cellular membrane stability, thereby enhancing energy metabolism. Consequently, this led to heightened efficiency in pollutant degradation and improved cold resistance capabilities. Our findings provide a comprehensive understanding of the environmental fate of both PAHs and heterocyclic PAHs under low-temperature conditions while also shedding light on cold adaptation mechanism employed by strain S01.

Spatial distribution of polycyclic aromatic hydrocarbons in water and sediment in the Ganga River: source diagnostics and health risk assessment on dietary exposure through a common carp fish Labeo rohita

We evaluated spatial distribution and source apportionment of polycyclic aromatic hydrocarbons (PAHs) in water and sediments at four selected sites of the Ganga River. Also, we measured PAHs in muscle tissues of Rohu (Labeo rohita), the most common edible carp fish of the Ganga River and potential human health risk was addressed. Total concentration of PAHs (∑PAHs) in water was highest at Manika Site (1470.5 ng/L) followed by Knuj (630.0 ng/L) and lowest at Adpr (219.0 ng/L). A similar trend was observed for sediments with highest concentration of ∑PAHs at Manika (461.8 ng/g) and lowest at Adpr Site (94.59 ng/g). Among PAHs, phenanthrene (Phe) showed highest concentration in both water and sediment. Of the eight major carcinogenic contributors (∑PAH8C), Indeno (1,2,3-C,D) pyrene (InP) did appear the most dominant component accounting for 42% to this group at Manika Site. Isomer ratios indicated vehicular emission and biomass combustion as major sources of PAHs. The ∑PAHs concentrations in fish tissue ranged from 117.8 to 758.0 ng/g (fresh weight basis) where low molecular weight PAHs assumed predominance (above 80%). The risk level in fish tissues appeared highest at Manika Site and site-wise differences were statistically significant (p < 0.05). The ILCR (> 10-4) indicated carcinogenic risk in adults and children associated with BaP and DBahA at Manika Site and with BaP at Knuj Site. Overall, the concentrations exceeding permissible limit, carcinogenic potential and BaP equivalent all indicated carcinogenic risks associated with some individual PAHs. This merits attention because the Ganga River is a reservoir of fisheries.

Phenanthrene metabolism in Panicum miliaceum: anatomical adaptations, degradation pathway, and computational analysis of a dioxygenase enzyme

Polycyclic aromatic compounds (PAHs) are persistent organic pollutants of environmental concern due to their potential impacts on food chain, with plants being particularly vulnerable. While plants can uptake, transport, and transform PAHs, the precise mechanisms underlying their localization and degradation are not fully understood. Here, a cultivation experiment conducted with Panicum miliaceum exposed different concentrations of phenanthrene (PHE). Intermediate PHE degradation compounds were identified via GC-MS analysis, leading to the proposal of a phytodegradation pathway featuring three significant benzene ring cleavage steps. Our results showed that P. miliaceum exhibited the ability to effectively degrade high levels of PHE, resulting in the production of various intermediate products through several chemical changes. Examination of the localization and anatomical characteristics revealed structural alterations linked to PHE stress, with an observed enhancement in PHE accumulation density in both roots and shoots as treatment levels increased. Following a 2-week aging period, a decrease in the amount of PHE accumulation was observed, along with a change in its localization. Bioinformatics analysis of the P. miliaceum 2-oxoglutarate-dependent dioxygenase (2-ODD) DAO-like protein revealed a 299 amino acid structure with two highly conserved domains, namely 2OG-FeII_Oxy and DIOX_N. Molecular docking analysis aligned with experimental results, strongly affirming the potential link and direct action of 2-ODD DAO-like protein with PHE. Our study highlights P. miliaceum capacity for PAHs degradation and elucidates the mechanisms behind enhanced degradation efficiency. By integrating experimental evidence with bioinformatics analysis, we offer valuable insights into the potential applications of plant-based remediation strategies for PAHs-contaminated environments.

Improved Formation of Biomethane by Enriched Microorganisms from Different Rank Coal Seams

The influence of enrichment of culturable microorganisms in in situ coal seams on biomethane production potential of other coal seams has been rarely studied. In this study, we enriched culturable microorganisms from three in situ coal seams with three coal ranks and conducted indoor anaerobic biomethane production experiments. Microbial community composition, gene functions, and metabolites in different culture units by 16S rRNA high-throughput sequencing combined with liquid chromatography-mass spectrometry-time-of-flight (LC-MS-TOF). The results showed that biomethane production in the bituminous coal group (BC)cc resulted in the highest methane yield of 243.3 μmol/g, which was 12.3 times higher than that in the control group (CK). Meanwhile, Methanosarcina was the dominant archaeal genus in the three experimental groups (37.42 ± 11.16-52.62 ± 2.10%), while its share in the CK was only 2.91 ± 0.48%. Based on the functional annotation, the relative abundance of functional genes in the three experimental groups was mainly related to the metabolism of nitrogen-containing heterocyclic compounds such as purines and pyrimidines. Metabolite analysis showed that enriched microorganisms promoted the degradation of a total of 778 organic substances in bituminous coal, including 55 significantly different metabolites (e.g., purines and pyrimidines). Based on genomic and metabolomic analyses, this paper reconstructed the heterocyclic compounds degradation coupled methane metabolism pathway and thereby preliminarily elucidated that enriched culturable bacteria from different coal-rank seams could promote the degradation of bituminous coal and intensify biogenic methane yields.

Deciphering the photocatalytic degradation of polyaromatic hydrocarbons (PAHs) using hausmannite (Mn3O4) nanoparticles and their efficacy against bacterial biofilm

Polyaromatic hydrocarbons (PAHs) are life-threatening organic pollutants that severely threaten ecosystems worldwide due to their poisonous qualities, cancer-causing properties, and mutation-causing qualities. Water and soil together form a critical component of the ecosystem that supports all life. Due to the pollutants that are being disposed of in them, their characteristics have changed, and their toxicity has increased. The goal of this study was to investigate the ability of hausmannite nanoparticles to degrade fluorene from soil and water. Using the chemical method, hausmannite nanoparticles were synthesized and further characterization was performed using UV-Vis, FTIR, DLS, XRD, and SEM-EDAX. Hausmannite significantly degraded fluorene using the batch adsorption method. The degradation was also confirmed by performing reactive kinetics using Freundlich's isotherm model and Langmuir's pseudo-second-order model of soil and water. In addition to the degradation efficacy, hausmannite was also proved to inhibit biofilm formation by Pseudomonas aeruginosa. The findings of the experiments confirmed the presence of hausmannite nanoparticles, as well as their physical properties, chemical properties, degradation properties, and parameters of the kinetic study. As a result, synthesized nanoparticles have been extensively utilized as a low-cost option for removing pollutants and microbial biofilm.

Highly efficient activation of periodate by a manganese-modified biochar to rapidly degrade methylene blue

In this study, the manganese oxide/biochar composites (Mn@BC) were synthesized from Phytolacca acinosa Roxb. The Mn@BC was analyzed via techniques of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction analysis (XRD). The results show that MnOx is successfully loaded on the surface of BC, and the load of MnOx can increase the number of surface functional groups of BC. X-ray photoelectron spectroscopy (XPS) shows that MnOx loaded on BC mainly exists in three valence forms: Mn(Ⅱ), Mn(Ⅲ), and Mn(Ⅳ). The ability of Mn@BC to activate periodate (PI) was studied by simulating the degradation of methylene blue (MB) dye. The degradation experiment results showed that the MB removal rate by the Mn@BC/PI system reached 97.4% within 30 min. The quenching experiment and electron paramagnetic resonance (EPR) analysis confirmed that Mn@BC can activate PI to produce iodate (IO3•), singlet oxygen (1O2), and hydroxyl radical (•OH), which can degrade MB during the reaction. Response surface methodology (RSM) based on Box-Behnken Design (BBD) was used to determine the interaction between pH, Mn@BC and PI concentration in the Mn@BC/PI system, and the optimum technological parameters were determined. When pH = 5.4, Mn@BC concentration 0.56 mg/L, PI concentration 1.1 mmol/L, MB removal rate can reach 98.05%. The cyclic experiments show that Mn@BC can be reused. After four consecutive runs, the removal rate of MB by the Mn@BC/PI system is still 82%, and the Mn@BC/PI system also shows high performance in treating MB in actual water bodies and degrading other pollutants. This study provides a practical method for degrading dyes in natural sewage.

Designing Inorganic-Organic Dual-Acid Deep Eutectic Solvents for Synergistically Enhanced Extractive and Oxidative Desulfurization

Acidic deep eutectic solvents (DESs) have been considered desirable extractants and catalysts for desulfurization. However, their hydrogen bond donors (HBDs) are usually sole organic acids, which are not conducive to efficient green catalysis. Herein, a novel inorganic-organic dual-acid DES (DADES) was reported for efficient extractive and oxidative desulfurization. Benefiting from the physical interaction among the three components in a DADES, a transparent homogeneous liquid can be obtained even though inorganic acid (boric acid, BA) and organic acid (acetic acid, AA) can be immiscible. Furthermore, the dual-acid HBD can increase the acidity of the DADES and reduce its viscosity, accelerating its mass transfer efficiency and enhancing its catalytic activity. With 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) as the hydrogen bond acceptor, [Bmim]Cl/BA/0.3AA effectively activated hydrogen peroxide and achieved sulfur removal of 96.6% at 40 °C. Furthermore, the universality of the synergistic effect in various DADESs was confirmed by the modulation of the types of organic acids. This study not only motivates the construction of more intriguing novel DESs based on the DADES concept but also highlights their potential in clean fuel production.

Environmental persistence assessment of heterocyclic polyaromatic hydrocarbons - Ultimate and primary biodegradability using adapted and non-adapted microbial communities

Heterocyclic polyaromatic hydrocarbons (heterocyclic PAHs) are of increasing concern and their environmental and human health impacts should be assessed due to their widespread presence and potential persistence in the environment. This study investigated the ultimate and primary biodegradability of ten heterocyclic PAHs, nine of which were found to be non-readily biodegradable. To generate a microbial community capable of degrading such compounds, a bacterial inoculum isolated from the effluent of a wastewater treatment plant (WWTP) was adapted to a mixture of heterocyclic PAHs for one year. Throughout the adaptation process, bacterial samples were collected at different stages to conduct primary biodegradation, ultimate biodegradation, and inoculum toxicity tests. Interestingly, after one year of adaptation, the community developed the ability to mineralize carbazole, but in the same time showed an increasing sensitivity to the toxic effects of benzo[c]carbazole. In two consecutive primary biodegradation experiments, degradation of four heterocycles was observed, while no biodegradation was detected for five compounds in any of the tests. Furthermore, the findings of this work were compared with predictions from in silico models regarding biodegradation timeframe and sorption, and it was found that the models were partially successful in describing these processes. The results of study provide valuable insights into the persistence of a representative group of heterocyclic PAHs in aquatic environments, which contributes to the hazard assessment of this particular class of substances.

Multivariate optimization of a green procedure for determination of emerging polycyclic aromatic nitrogen heterocycles in PM2.5 from sites with different characteristics

Emerging polycyclic aromatic nitrogen heterocycles (PANHs) contributes significantly to the health risk associated with inhaling polluted air. However, there is a lack of analytical methods with the needed performance to their determination. This study presents the optimization and validation for the first time of a green microscale extraction procedure for the determination of twenty-one PANHs, including carbazole, indole, and quinolone classes, in particulate matter (PM2.5) samples by gas chromatography-mass spectrometry. A simplex-centroid mixture design and full factorial design (23) were employed to optimize the following extraction parameters: type and volume of solvent, sample size, extraction time, and necessity of a cleanup step. Low limits of detection and quantification (LOD < 0.97 pg m-3 and LOQ < 3.24 pg m-3, respectively) were obtained in terms of matrix-matched calibration. The accuracy and precision of the method were adequate, with recoveries in three levels between 73 to 120% and intraday and interday relative standard deviations from 2.0 to 12.9% and 7.3 to 18.9%, respectively. The green character of the method was evaluated using the Analytical Greenness (AGREE) tool, where a score of 0.69 was obtained, indicating a great green procedure. The method was applied to PM2.5 samples collected from sites with different characteristics; the concentrations ranged from 69.3 pg m-3 (2-methylcarbazole) to 11,874 pg m-3 (carbazole) for individual PANHs and from 2306 to 24,530 pg m-3 for ∑21PANHs. Principal component analysis (PCA) and hierarchical clustering enabled discrimination of the sampling sites according to the PANHs concentrations. The score plots formed two distinct groups, one with samples containing higher concentrations of PANHs, corresponding to sites with a major influence from diesel emissions, and another group with minor PANH contents, corresponding to sites impacted by emissions from urban traffic and industrial activities.

Toxicity evolution and control for the UV/H2O2 degradation of nitrogen-containing heterocyclic compounds: SDZ and PMM

This study aimed to achieve toxicity control of sulfadiazine (SDZ) and pirimiphos-methyl (PMM) via the UV/H2O2 process by optimizing the reaction parameters. The results show that both drugs had a good degradation effect under the following parameters: a H2O2 molar ratio of 1:200, and neutral conditions. SDZ and PMM could be degraded by more than 99% within 3 min, respectively. In the Daphnia magna acute toxicity assay and Vibrio fischeri inhibition assay, both SDZ and PMM exhibited a phenomenon of increasing toxicity. Additionally, through the use of density functional theory (DFT) calculation and HPLC-QTOF-MS, 21 transformation products (TPs) were identified, and the principal degradation pathways were proposed. The toxicity of the TPs was determined by comparing the QSAR prediction results with toxicity test data. As a result, under the higher UV light intensity (2300 μW/cm2) and neutral conditions, SDZ showed highest toxicity, whereas PMM showed lowest toxicity under the lowest UV light intensity (450 μW/cm2) and neutral conditions. Four main toxic TPs were identified, and their yields could be reduced by adjusting the reaction parameters. Therefore, the selection of appropriate reaction parameters could reduce the production of toxic TPs and ensure the safety of water environment.

Comparison of the rate of certain trace metals accumulation in indoor plants for smoking and non-smoking areas

Tobacco smoke causes to release severe toxic metals into the environment. It is recognized as the most significant issue in indoor air quality. Pollution and toxic substances in smoke quickly spread and penetrate the indoor environment. Environmental tobacco smoke is responsible for lowering indoor air quality. There is much evidence that poor air quality occurs with inadequate ventilation conditions in indoor environments. The plants have been observed to absorb the smoke in the environment into their own body like a sponge. The plant species in this study can be used easily in almost every office, home, or other indoor areas. Using indoor plants is very beneficial in biomonitoring and absorbing these trace metals. Some indoor plants have shown successful performance as biomonitors for health-damaging pollutants. The study aims to determine the concentration of three trace metals (Cu, Co, and Ni) using five indoor ornamentals frequently used in smoking areas, namely D. amoena, D. marginata, F. elastica, S. wallisii, and Y. massengena. The Ni uptake and its accumulation in S. wallisii, and Y. massengena increased in correlation with smoke areas. However, the rate of accumulation of Co and Cu was found to be independent due to consideration of the environmental emissions. Consequently, our results suggest that F. elastica is more resistant to smoking, whereas S. wallisii would be a better choice as a biomonitoring plant of tobacco smoke.

Insights into the Binding Interaction of Catechol 1,2-Dioxygenase with Catechol in Achromobacter xylosoxidans DN002

Microbial remediation has become one of the promising ways to eliminate polycyclic aromatic hydrocarbons (PAHs) pollution due to its efficient enzyme metabolism system. Catechol 1,2-dioxygenase (C12O) is a crucial rate-limiting enzyme in the degradation pathway of PAHs in Achromobacter xylosoxidans DN002 that opens the benzene ring through the ortho-cleavage pathway. However, little attention has been given to explore the interaction mechanism of relevant enzyme-substrate. This study aims to investigate the binding interaction between C12O of strain DN002 and catechol by means of a molecular biological approach combined with homology modeling, molecular docking, and multiple spectroscopies. The removal rate of catechol in the mutant strain of cat A deletion was only 12.03%, compared to the wild-type strain (54.21%). A Ramachandran plot of active site regions of the primary amino acid sequences in the native enzyme showed that 93.5% sequences were in the most favored regions on account of the results of homology modeling, while an additional 6.2% amino acid sequences were found in conditionally allowed regions, and 0.4% in generously allowed regions. The binding pocket of C12O with catechol was analyzed to obtain that the catalytic trimeric group of Tyr164-His224-His226 was proven to be great vital for the ring-opening reaction of catechol by molecular docking. In the native enzyme, binding complexes were spontaneously formed by hydrophobic interactions. Binding constants and thermodynamic potentials from fluorescence spectra indicated that catechol effectively quenched the intrinsic fluorescence of C12O in the C12O/catechol complex via conventional static and dynamic quenching mechanisms of C12O. The results of ultraviolet and visible (UV) spectra, synchronous fluorescence, and circular dichroism (CD) spectra revealed conspicuous changes in the local conformation, and site-directed mutagenesis confirmed the role of predicted key residues during catalysis, wherein His₂₂₆ had a significant effect on catechol utilization by C12O. This is the first report to reveal interactions of C12O with substrate from the molecular docking results, providing the mechanistic understanding of representative dioxygenases involved in aromatic compound degradation, and a solid foundation for further site modifications as well as strategies for the directed evolution of this enzyme.

Biosynthesis and chemical composition of nanomaterials in agricultural soil bioremediation: a review

Nanomaterials (NMs) are currently being used in agricultural soils as part of a new bioremediation (BR) process. In this study, we reviewed the biosynthesis of NMs, as well as their chemical composition and prospective strategies for helpful and sustainable agricultural soil bioremediation (BR). Different types of NMs, such as nanoparticles, nanocomposites, nanocrystals, nano-powders, and nanotubes, are used in agricultural soil reclamation, and they reflect the toxicity of NMs to microorganisms. Plants (Sargassum muticum, Dodonaea viscose, Aloe Vera, Rosemarinus officinalis, Azadirachta indica, Green tea, and so on) and microorganisms (Escherichia coli, Shewanella oneidensis, Pleurotus sp., Klebsiella oxytoca, Aspergillus clavatus, and so on) are the primary sources for the biosynthesis of NMs. By using the BR process, microorganisms, such as bacteria and plants, can immobilize metals and change both inorganic and organic contaminants in the soil. Combining NMs with bioremediation techniques for agricultural soil remediation will be a valuable long-term solution.

Construction and Degradation Performance Study of Polycyclic Aromatic Hydrocarbons (PAHs) Degrading Bacterium Consortium

PAHs are widely distributed in the environment and pose a serious threat to ecological security and human health. The P&A (Pseudomonas aeruginosa and Alcaligenes faecalis) bacterium consortium obtained in this study comes from oily sludge and is reused for the degradation of PAHs mixture in oily sludge. Few articles pay attention to the PAHs mixture in oily sludge and reuse the bacterium consortium for its degradation. The PAHs solution degradation efficient of P&A bacterial consortium under different environmental conditions, bioaugmentations, and exogenous stimulations were studied by ultraviolet visible spectrophotometer and gas chromatography–mass spectrometry. The result shows that, after 8 days of degradation under 35 °C, pH 7, with 5% (volume percent) of the inoculation amount, the degradation rate of NAP, PHE, and PYR solution could higher than 90%, 80%, and 70%, respectively. The additional crude oil could further improve the NAP, PHE, and PYR degradation efficiency. The minimum inhibitory concentration of Cu2+, Zn2+, and Pb2+ to bacterium were 2.002, 17.388, and 9.435 mM, respectively. The addition of surfactants had negative or limited positive effect on the PAHs degradation rate. Furthermore, the average degradation rates of NAP, PHE, and PYR, in oily sludge of local petroleum polluted area by P&A bacterial consortium, could all reach above 80%. Based on gas chromatography–mass spectrometry test results before and after incubation, P&A bacterial consortium also provides more opportunities for other organic compounds’ degradation.

Manganese oxide-modified biochar: production, characterization and applications for the removal of pollutants from aqueous environments - a review

The development of manganese (Mn) oxides (MnOx) modified biochar (MnOBC) for the removal of pollutants from water has received significant attention. However, a comprehensive review focusing on the use of MnOBC for the removal of organic and inorganic pollutants from water is missing. Therefore, the preparation and characterization of MnOBC, and its capacity for the removal of inorganic (e.g., toxic elements) and organic (e.g., antibiotics and dyes) from water have been discussed in relation to feedstock properties, pyrolysis temperature, modification ratio, and environmental conditions here. The removal mechanisms of pollutants by MnOBC and the fate of the sorbed pollutants onto MnOBC have been reviewed. The impregnation of biochar with MnOx improved its surface morphology, functional group modification, and elemental composition, and thus increased its sorption capacity. This review establishes a comprehensive understanding of synthesizing and using MnOBC as an effective biosorbent for remediation of contaminated aqueous environments.