Recent Advances in the Study of the Remediation of Polycyclic Aromatic Compound (PAC)-Contaminated Soils: Transformation Products, Toxicity, and Bioavailability Analyses

Identification of Potentially Toxic Transformation Products Produced in Polycyclic Aromatic Hydrocarbon Bioremediation Using Suspect and Non-Target Screening Approaches

Polycyclic aromatic hydrocarbons (PAHs) are a class of ubiquitous environmental contaminants that can be remediated through physical, chemical, or biological means. Treatment strategies can lead to the formation of PAH-transformation products (PAH-TPs) that, despite having the potential for adverse ecological and human health effects, are unregulated and understudied in environmental monitoring and remediation. Unavailability of reference standards for PAH-TPs limits the ability to identify PAH-TPs by targeted methods. This study utilized suspect and nontarget screening approaches to identify PAH-TPs produced by a bacterial culture, Rhodococcus rhodochrous ATCC 21198, using liquid chromatography-high resolution mass spectrometry. Open-source tools were used to predict biotransformation products, predict potential PAH-TP structures from mass spectra, and estimate health hazards of potential PAH-TPs. The workflow developed in this study allowed for the tentative identification of 16 PAH-TPs (confidence levels 2a to 3), seven of which were not previously detected by targeted analysis. Several new potential transformation pathways for our bacterial pure culture were suggested by the PAH-TPs, including carboxylation, sulfonation and up to three hydroxylation reactions. A computational toxicity assessment indicated that the PAH-TPs shared many hazard characteristics with their parent compounds, including genotoxicity and endocrine disruption, highlighting the importance of considering PAH-TPs in future PAH studies.

Transformative knowledge of polar polycyclic aromatic hydrocarbons via high-resolution mass spectrometry

Polycyclic aromatic hydrocarbons (PAHs) are toxic contaminants with a widespread presence in diverse environmental contexts. Transformation processes of PAHs via degradation and biotransformation have parallels in humans, animals, plants, fungi, and bacteria. Mapping the transformation products of PAHs is therefore crucial for assessing their toxicological impact and developing effective monitoring strategies. The present research aimed to explore the PAH detoxification products formed by the marine fish Atlantic haddock (Melanogrammus aeglefinus) after single PAH treatments. Using target and suspect screening analyses on an ion mobility quadrupole time-of-flight mass spectrometer (IM-QTOF MS), deprotonated compounds were identified and archived into a metabolite mass spectral library, which is systematized and presented in this work. The results offer an exclusive overview of the transformation products and their associated mass spectral features. Transformation products include hydroxy compounds, dihydrodiols, polycyclic aromatic acids, glucuronides, sulfates, glutathiones, cysteinylglycines, cysteines, and mercapturic acids. By documenting high-resolution mass spectrometry data, this comprehensive characterization provides a valuable reference point for the development of broad-spectrum analytical methods. It also addresses a critical gap in the field by presenting tentative identifications of PAH transformation products in the absence of analytical standards. Moreover, it encourages further investigation of these compounds as they have important toxicological relevance in both ecotoxicology and human research.

Bioremediation of PAHs-contaminated site in a full-scale biopiling system with immobilized enzymes: Removal efficiency and microbial communities

Bioremediation of PAHs-contaminated soil by immobilized enzymes is a promising technology. Nevertheless, the practical implementation of highly efficient enzymatic remediation remains confined to laboratory settings, with limited experience in full-scale applications. In this study, the extracellular enzymes from white rot fungi are fully applied to treat sites contaminated with PAHs by combining a new hydrogel microenvironment and a biopiling system. The full-scale project was conducted on silty loam soil contaminated with PAHs. In line with China's guidelines for construction land, 7 out of the 12 PAHs identified are considered to be a threat to the soil quality of construction sites, with benzo[a]pyrene levels reaching 1.50 mg kg-1, surpassing the acceptable limit of 0.55 mg kg-1 for the first type of land. After 7 days of remediation, the benzo[a]pyrene level decreased from 1.50 mg kg-1 to 0.51 mg kg-1, reaching the remediation standard of Class I screening values, with a removal rate of 66%. Microbiomes were utilized to assess the microbial biodiversity and structure analyses for PAHs biodegradation. The remediation enhanced the abundance of dominant bacterium (Marinobacter, Pseudomonas, and Truepera) and fugin (Thielavia, Neocosmospora, and Scedosporium). The research offers further insights into the exploration of soil remediation on the full-scale of the immobilized enzyme and biopiling technology.

Assessment of bacterial biotransformation of alkylnaphthalene lubricating base oil component 1-butylnaphthalene by LC/ESI-MS(/MS)

Alkylnaphthalene lubricating oils are synthetic Group V base oils that are utilized in wide-ranging industrial applications and which are composed of polyalkyl chain-alkylated naphthalenes. Identification of alkylnaphthalene biotransformation products and determination of their mass spectrometry (MS) fragmentation signatures provides valuable information for predicting their environmental fates and for development of analytical methods to monitor their biodegradation. In this work, laboratory-based environmental petroleomics was applied to investigate the catabolism of the alkylnaphthalene, 1-butylnaphthalene (1-BN), by liquid chromatography electrospray ionization MS data mapping and targeted collision-induced dissociation (CID) analyses. Comparative mapping revealed that numerous catabolites were produced from soil bacterium, Sphingobium barthaii KK22. Targeted CID showed unique patterns of production of even-valued deprotonated fragments that were found to originate from specific classes of bacterial catabolites. Based upon results of CID analyses of catabolites and authentic standards, MS signatures were proposed to occur through formation of distonic radical anions from bacterially-produced alkylphenol biotransformation products. Finally, spectra interpretation was guided by CID results to propose chemical structures for twenty-two 1-BN catabolites resulting in construction of 1-BN biotransformation pathways. Multiple pathways were identified that included aromatic ring-opening, alkyl chain-shortening and production of α,β-unsaturated aldehydes from alkylated phenols. Until now, α,β-unsaturated aldehydes have not been a class of compounds much reported from alkylated polycyclic aromatic hydrocarbon (APAH) and PAH biotransformation. This work provides a new understanding of alkylnaphthalene biotransformation and proposes MS markers applicable to monitoring APAH biotransformation in the form of alkylated phenols, and by extension, α,β-unsaturated aldehydes, and toxic potential during spilled oil biodegradation.

Environmental significance of PAH photoproduct formation: TiO2 nanoparticle influence, altered bioavailability, and potential photochemical mechanisms

Interactions between polycyclic aromatic hydrocarbons (PAHs) and titanium dioxide (TiO2) nanoparticles (NPs) can produce unforeseen photoproducts in the aqueous phase. Both PAHs and TiO2-NPs are well-studied and highly persistent environmental pollutants, but the consequences of PAH-TiO2-NP interactions are rarely explored. We investigated PAH photoproduct formation over time for benzo[a]pyrene (BaP), fluoranthene (FLT), and pyrene (PYR) in the presence of ultraviolet A (UVA) using a combination of analytical and computational methods including, identification of PAH photoproducts, assessment of expression profiles for gene indicators of PAH metabolism, and computational evaluation of the reaction mechanisms through which certain photoproducts might be formed. Chemical analyses identified diverse photoproducts, but all PAHs shared a primary photoproduct, 9,10-phenanthraquinone (9,10-PQ), regardless of TiO2-NP presence. The computed reaction mechanisms revealed the roles photodissociation and singlet oxygen chemistry likely play in PAH mediated photochemical processes that result in the congruent production of 9,10-PQ within this study. Our investigation of PAH photoproduct formation has provided substantial evidence of the many, diverse and congruent, photoproducts formed from physicochemically distinct PAHs and how TiO2-NPs influence bioavailability and time-related formation of PAH photoproducts.

Association between Personal Abiotic Airborne Exposures and Body Composition Changes among Healthy Adults (60-69 Years Old): A Combined Exposome-Wide and Lipidome Mediation Approach from the China BAPE Study

BACKGROUND

Evidence suggested that abiotic airborne exposures may be associated with changes in body composition. However, more evidence is needed to identify key pollutants linked to adverse health effects and their underlying biomolecular mechanisms, particularly in sensitive older adults.

OBJECTIVES

Our research aimed to systematically assess the relationship between abiotic airborne exposures and changes in body composition among healthy older adults, as well as the potential mediating mechanisms through the serum lipidome.

METHODS

From September 2018 to January 2019, we conducted a monthly survey among 76 healthy adults (60-69 years old) in the China Biomarkers of Air Pollutant Exposure (BAPE) study, measuring their personal exposures to 632 abiotic airborne pollutions using MicroPEM and the Fresh Air wristband, 18 body composition indicators from the InBody 770 device, and lipidomics from venous blood samples. We used an exposome-wide association study (ExWAS) and deletion/substitution/addition (DSA) model to unravel complex associations between exposure to contaminant mixtures and body composition, a Bayesian kernel machine regression (BKMR) model to assess the overall effect of key exposures on body composition, and mediation analysis to identify lipid intermediators.

RESULTS

The ExWAS and DSA model identified that 2,4,5-T methyl ester (2,4,5-TME), 9,10-Anthracenedione (ATQ), 4b,8-dimethyl-2-isopropylphenanthrene, and 4b,5,6,7,8,8a,9,10-octahydro-(DMIP) were associated with increased body fat mass (BFM), fat mass indicators (FMI), percent body fat (PBF), and visceral fat area (VFA) in healthy older adults [Bonferroni-Hochberg false discovery rate ( FD R BH ) < 0.05 ]. The BKMR model demonstrated a positive correlation between contaminants (anthracene, ATQ, copaene, di-epi-α -cedrene, and DMIP) with VFA. Mediation analysis revealed that phosphatidylcholine [PC, PC(16:1e/18:1), PC(16:2e/18:0)] and sphingolipid [SM, SM(d18:2/24:1)] mediated a significant portion, ranging from 12.27% to 26.03% (p-value < 0.05 ), of the observed increase in VFA.

DISCUSSION

Based on the evidence from multiple model results, ATQ and DMIP were statistically significantly associated with the increased VFA levels of healthy older adults, potentially regulated through lipid intermediators. These findings may have important implications for identifying potentially harmful environmental chemicals and developing targeted strategies for the control and prevention of chronic diseases in the future, particularly as the global population is rapidly aging. https://doi.org/10.1289/EHP13865.

From Antagonism to Enhancement: Triton X-100 Surfactant Affects Phenanthrene Interfacial Biodegradation by Mycobacteria through a Shift in Uptake Mechanisms

Polycyclic aromatic hydrocarbons (PAHs), as persistent environmental pollutants, often reside in nonaqueous-phase liquids (NAPLs). Mycobacterium sp. WY10, boasting highly hydrophobic surfaces, can adsorb to the oil-water interface, stabilizing the Pickering emulsion and directly accessing PAHs for biodegradation. We investigated the impact of Triton X-100 (TX100) on this interfacial uptake of phenanthrene (PHE) by Mycobacteria, using n-tetradecane (TET) and bis-(2-ethylhexyl) phthalate (DEHP) as NAPLs. Interfacial tension, phase behavior, and emulsion stability studies, alongside confocal laser scanning microscopy and electron microscope observations, unveiled the intricate interplay. In surfactant-free systems, Mycobacteria formed stable W/O Pickering emulsions, directly degrading PHE within the NAPLs because of their intimate contact. Introducing low-dose TX100 disrupted this relationship. Preferentially binding to the cells, the surfactant drastically increased the cell hydrophobicity, triggering desorption from the interface and phase separation. Consequently, PAH degradation plummeted due to hindered NAPL access. Higher TX100 concentrations flipped the script, creating surfactant-stabilized O/W emulsions devoid of interfacial cells. Surprisingly, PAH degradation remained efficient. This paradox can be attributed to NAPL emulsification, driven by the surfactant, which enhanced mass transfer and brought the substrate closer to the cells, despite their absence at the interface. This study sheds light on the complex effect of surfactants on Mycobacteria and PAH uptake, revealing an antagonistic effect at low concentrations that ultimately leads to enhanced degradation through emulsification at higher doses. These findings offer valuable insights into optimizing bioremediation strategies in PAH-contaminated environments.

PAH bioremediation with Rhodococcus rhodochrous ATCC 21198: Impact of cell immobilization and surfactant use on PAH treatment and post-remediation toxicity

Polycyclic aromatic hydrocarbons (PAHs) are prevalent environmental contaminants that are harmful to ecological and human health. Bioremediation is a promising technique for remediating PAHs in the environment, however bioremediation often results in the accumulation of toxic PAH metabolites. The objectives of this research were to demonstrate the cometabolic treatment of a mixture of PAHs by a pure bacterial culture, Rhodococcus rhodochrous ATCC 21198, and investigate PAH metabolites and toxicity. Additionally, the surfactant Tween ® 80 and cell immobilization techniques were used to enhance bioremediation. Total PAH removal ranged from 70-95% for fluorene, 44-89% for phenanthrene, 86-97% for anthracene, and 6.5-78% for pyrene. Maximum removal was achieved with immobilized cells in the presence of Tween ® 80. Investigation of PAH metabolites produced by 21198 revealed a complex mixture of hydroxylated compounds, quinones, and ring-fission products. Toxicity appeared to increase after bioremediation, manifesting as mortality and developmental effects in embryonic zebrafish. 21198's ability to rapidly transform PAHs of a variety of molecular structures and sizes suggests that 21198 can be a valuable microorganism for catalyzing PAH remediation. However, implementing further treatment processes to address toxic PAH metabolites should be pursued to help lower post-remediation toxicity in future studies.

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.

An Integrated Workflow Assisted by In Silico Predictions To Expand the List of Priority Polycyclic Aromatic Compounds

The limited information in existing mass spectral libraries hinders an accurate understanding of the composition, behavior, and toxicity of organic pollutants. In this study, a total of 350 polycyclic aromatic compounds (PACs) in 9 categories were successfully identified in fine particulate matter by gas chromatography high resolution mass spectrometry. Using mass spectra and retention indexes predicted by in silico tools as complementary information, the scope of chemical identification was efficiently expanded by 27%. In addition, quantitative structure-activity relationship models provided toxicity data for over 70% of PACs, facilitating a comprehensive health risk assessment. On the basis of extensive identification, the cumulative noncarcinogenic risk of PACs warranted attention. Meanwhile, the carcinogenic risk of 53 individual analogues was noteworthy. These findings suggest that there is a pressing need for an updated list of priority PACs for routine monitoring and toxicological research since legacy polycyclic aromatic hydrocarbons (PAHs) contributed modestly to the overall abundance (18%) and carcinogenic risk (8%). A toxicological priority index approach was applied for relative chemical ranking considering the environmental occurrence, fate, toxicity, and analytical availability. A list of 39 priority analogues was compiled, which predominantly consisted of high-molecular-weight PAHs and alkyl derivatives. These priority PACs further enhanced source interpretation, and the highest carcinogenic risk was attributed to coal combustion.

Propylene glycol-mixed steam enhanced extraction for an efficient and sustainable remediation of PAHs-contaminated soil

An innovative thermal desorption method, propylene glycol (PG)-mixed steam enhanced extraction, is proposed for a highly efficient remediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated soil. It is found that injecting PG-mixed steam into soil column could obtain > 99% removal efficiencies of PAHs either for the pyrene-spiked soil, or for the contaminated field soil with high-molecular-weight PAHs. PG is a safe and low-cost dihydric alcohol with a boiling point higher than water. When the PG-mixed steam penetrated the contaminated soil, the PG vapor preferentially condensed to form a hot liquid with concentrated PG (e.g., from 30 wt% PG in gas phase to 90 wt% PG in the liquid phase), which would significantly solubilize the PAHs and enhance their desorption from soils. The results also revealed that the effluents derived from the PG-mixed steam could be purified by removing the desorbed PAHs using a simple coagulation treatment, and the recovered PG solution could be reused. The plant assay using wheat seeds showed that the remediated soil had a good regreening potential. Our results demonstrate that PG-mixed steam injection is a promising thermal desorption method for an efficient and sustainable remediation of PAHs-contaminated soil.

Fluorescent spectroscopy paired with parallel factor analysis for quantitative monitoring of phenanthrene biodegradation and metabolite formation

Polycyclic aromatic hydrocarbons (PAHs) are a class of environmental contaminants released into the environment from both natural and anthropogenic sources that are associated with carcinogenic, mutagenic, and teratogenic health effects. Many remediation strategies for the treatment of PAH contaminated material, including bioremediation, can lead to the formation of toxic transformation products. Analytical techniques for PAHs and PAH transformation products often require extensive sample preparation including solvent extraction and concentration, chromatographic separation, and mass spectrometry to identify and quantify compounds of interest. Excitation-emission matrix (EEM) fluorescent spectroscopy paired with parallel factor analysis (PARAFAC) is an approach for analyzing PAHs that eliminates the need for extensive sample preparation and separation techniques before analysis. However, this technique has rarely been applied to monitoring PAH biotransformation and formation of PAH metabolites. The objectives of this research were to compare an established targeted analytical method to two-dimensional fluorescent spectroscopy and combined EEM-PARAFAC methods to monitor phenanthrene degradation by a bacterial pure culture, Mycobacterium Strain ELW1, identify and quantify phenanthrene transformation products, and derive kinetic constants for phenanthrene degradation and metabolite formation. Both phenanthrene and its primary transformation product, trans-9,10-dihydroxy-9,10-dihydrophenanthrene, were identified and quantified with the EEM-PARAFAC method. The value of the EEM-PARAFAC method was demonstrated in the superiority of sensitivity and accuracy of quantification to two-dimensional fluorescent spectroscopy. Quantification of targets and derivation of kinetic constants using the EEM-PARAFAC method were validated with an established gas chromatography-mass spectrometry (GC-MS) method. To the authors' knowledge, this is the first study to use an EEM-PARAFAC method to monitor, identify, and quantify both PAH biodegradation and PAH metabolite formation by a bacterial pure culture.

Co-contamination by heavy metal and organic pollutant alters impacts of genotypic richness on soil nutrients

Co-contamination by heavy metal and organic pollutant may negatively influence plant performance, and increasing the number of genotypes for a plant population may reduce this negative effect. To test this hypothesis, we constructed experimental populations of Hydrocotyle vulgaris consisting of single, four or eight genotypes in soils contaminated by cadmium, cypermethrin or both. Biomass, leaf area and stem internode length of H. vulgaris were significantly lower in the soil contaminated by cypermethrin and by both cadmium and cypermethrin than in the soil contaminated by cadmium only. A reverse pattern was found for specific internode length and specific leaf area. In general, genotypic richness or its interaction with soil contamination did not influence plant growth or morphology. However, soil nutrients varied in response to soil contamination and genotypic richness. Moreover, plant population growth was positively correlated to soil total nitrogen, but negatively correlated to total potassium and organic matter. We conclude that co-contamination by cadmium and cypermethrin may suppress the growth of H. vulgaris population compared to contamination by cadmium only, but genotypic richness may play little role in regulating these effects.

Multi-Omic Profiling of a Newly Isolated Oxy-PAH Degrading Specialist from PAH-Contaminated Soil Reveals Bacterial Mechanisms to Mitigate the Risk Posed by Polar Transformation Products

Polar biotransformation products have been identified as causative agents for the eventual increase in genotoxicity observed after the bioremediation of PAH-contaminated soils. Their further biodegradation has been described under certain biostimulation conditions; however, the underlying microorganisms and mechanisms remain to be elucidated. 9,10-Anthraquinone (ANTQ), a transformation product from anthracene (ANT), is the most commonly detected oxygenated PAH (oxy-PAH) in contaminated soils. Sand-in-liquid microcosms inoculated with creosote-contaminated soil revealed the existence of a specialized ANTQ degrading community, and Sphingobium sp. AntQ-1 was isolated for its ability to grow on this oxy-PAH. Combining the metabolomic, genomic, and transcriptomic analyses of strain AntQ-1, we comprehensively reconstructed the ANTQ biodegradation pathway. Novel mechanisms for polyaromatic compound degradation were revealed, involving the cleavage of the central ring catalyzed by Baeyer-Villiger monooxygenases (BVMO). Abundance of strain AntQ-1 16S rRNA and its BVMO genes in the sand-in-liquid microcosms correlated with maximum ANTQ biodegradation rates, supporting the environmental relevance of this mechanism. Our results demonstrate the existence of highly specialized microbial communities in contaminated soils responsible for processing oxy-PAHs accumulated by primary degraders. Also, they underscore the key role that BVMO may play as a detoxification mechanism to mitigate the risk posed by oxy-PAH formation during bioremediation of PAH-contaminated soils.

Efficient bioremediation of laboratory wastewater co-contaminated with PAHs and dimethylformamide by a methylotrophic enrichment culture

A methylotrophic enrichment culture, MM34X, has been assessed for its exceptional ability in biodegradation of dimethylformamide (DMF) and bioremediation of laboratory wastewater (LWW) co-contaminated with polycyclic aromatic hydrocarbons (PAHs). The culture MM34X tolerated high concentrations of DMF and efficiently degraded 98% of 20,000 mg L^-1 DMF within 120 h. LWW bioremediation was performed in stirred bottle laboratory-scale bioreactor. After 35 days of incubation, 2760.8 ± 21.1 mg L^-1 DMF, 131.8 ± 9.7 mg L^-1 phenanthrene, 177.3 ± 7.5 mg L^-1 pyrene and 39.5 ± 2.7 mg L^-1 BaP in LWW were removed. Analysis of post-bioremediation residues indicated the absence of any known toxic intermediates. The efficacy of bioremediation was further evaluated through cyto-genotoxicity assays using Allium cepa. The roots of A. cepa exposed to bioremediated LWW showed improved mitotic index, whereas original LWW completely arrested cell growth. Similarly, the alkaline comet assay indicated alleviation of genotoxicity in bioremediated LWW, as evidenced by significantly lower DNA damage in terms of tail DNA and Olive tail moment. In addition, oxidative stress assays, performed using fluorescent probes 2',7'-dichlorodihydrofluorescein diacetate, C11-BODIPY and dihydrorhodamine 123, revealed significant mitigation of oxidative stress potential in bioremediated LWW. Our findings suggest that the enrichment MM34X may prime the development of inexpensive and efficient large-scale bioremediation of LWW co-contaminated with PAHs and DMF.

Extensive chemical and bioassay analysis of polycyclic aromatic compounds in a creosote-contaminated superfund soil following steam enhanced extraction

Polycyclic aromatic compounds (PACs) are organic compounds commonly found in contaminated soil. Previous studies have shown the removal of polycyclic aromatic hydrocarbons (PAHs) in creosote-contaminated soils during steam enhanced extraction (SEE). However, less is known about the removal of alkyl-PAHs and heterocyclic compounds, such as azaarenes, and oxygen- and sulfur-heterocyclic PACs (OPACs and PASHs, respectively). Further, the impact of SEE on the freely dissolved concentration of PACs in soil as well as the soil bioactivity pre- and post-SEE have yet to be addressed. To fulfil these research gaps, chemical and bioanalytical analysis of a creosote-contaminated soil, collected from a U.S. Superfund site, pre- and post-SEE were performed. The decrease of 64 PACs (5-100%) and increase in the concentrations of nine oxygenated-PAHs (OPAHs) (150%) during SEE, some of which are known to be toxic and can potentially contaminate ground water, were observed. The freely dissolved concentrations of PACs in soil were assessed using polyoxymethylene (POM) strips and the concentrations of 66 PACs decreased post-SEE (1-100%). Three in vitro reporter gene bioassays (DR-CALUX®, ERα-CALUX® and anti-AR CALUX®) were used to measure soil bioactivities pre- and post-SEE and all reporter gene bioassays measured soil bioactivity decreases post-SEE. Mass defect suspect screening tentatively identified 27 unique isomers of azaarenes and OPAC in the soil. As a remediation technique, SEE was found to remove alkyl-PAHs and heterocyclic PACs, reduce the concentrations of freely dissolved PACs, and decrease soil bioactivities.

Adsorption of Naphthalene on Clay Minerals: A Molecular Dynamics Simulation Study

Naphthalene, as one of the representative polycyclic aromatic hydrocarbons, widely exists in contaminated sites and is a potential threat to human health due to its high mobility in soil. The interaction between naphthalene and clay minerals is of great significance to the environmental behavior of naphthalene and the design of remediation technology. In this study, montmorillonite and kaolinite were selected as representative clay minerals. Naphthalene adsorption behavior on mineral surfaces and water-wet kaolinite surfaces was investigated using molecular dynamics (MD) simulation. The interaction energy was calculated to represent the interaction between naphthalene and soil fractions, and the relative concentration and density distribution of naphthalene was analyzed to describe the distribution of naphthalene on the clay surfaces. The self-diffusion coefficient of naphthalene was obtained to represent its mobility under different water content. The electron density calculation was performed to reveal the different adsorption behavior of naphthalene on different surfaces of kaolinite. The simulation results show that montmorillonite had a stronger interaction with naphthalene due to larger electrostatic interaction energy compared to kaolinite, and naphthalene distributed more intensively on the montmorillonite surface. With regards to kaolinite, naphthalene tended to be absorbed on the alumina octahedral surface rather than the silicon tetrahedral surface due to the weak hydron bond interaction. The results indicate that water impeded the adsorption of naphthalene, and the optimal initial thickness of water film, which was 10 Å, was put forward for the application of thermal remediation technology. Furthermore, the average interaction energies between water and mineral surfaces largely depended on the water content, and the competitive adsorption between water and naphthalene only occurred under absorbed and bound water conditions. Overall, the knowledge of naphthalene–soil fractions interaction gained in this study is critical to the understanding of the environmental behavior of naphthalene and the reference for remediation technology.

Characterization of polycyclic aromatic compounds in historically contaminated soil by targeted and non-targeted chemical analysis combined with in vitro bioassay

Soil samples from a contaminated site in Sweden were analyzed to identify the presence of 78 polycyclic aromatic compounds (PACs) using gas chromatography coupled with mass spectrometry (GC-MS). The target analysis revealed large contributions not only from polycyclic aromatic hydrocarbons (PAHs), but also from alkylated- and oxygenated-PAHs (alkyl- and oxy-PAHs, respectively), and N-heterocyclics (NPACs). PAC profiles indicated primarily pyrogenic sources, although contribution of petrogenic sources was also observed in one sample as indicated by a high ratio of alkylated naphthalene compared to naphthalene. The aryl hydrocarbon receptor (AhR)-activity of the soil extracts was assessed using the H4IIe-pGudluc 1.1 cells bioassay. When compared with the calculated total AhR-activity of the PACs in the target list, 35-97% of the observed bioassay activity could be explained by 62 PACs with relative potency factors (REPs). The samples were further screened using GC coupled with Orbitrap™ high resolution MS (GC-HRMS) to investigate the presence of other PACs that could potentially contribute to the AhR-activity of the extracts. 114 unique candidate compounds were tentatively identified and divided into four groups based on their AhR-activity and environmental occurrence. Twelve substances satisfied all the criteria, and these compounds are suggested to be included in regular screening in future studies, although their identities were not confirmed by standards in this study. High unexplained bio-TEQ fractions in three of the samples may be explained by tentatively identified compounds (n = 35) with high potential of being toxic. This study demonstrates the benefit of combining targeted and non-targeted chemical analysis with bioassay analysis to assess the diversity and effects of PACs at contaminated sites. The applied prioritization strategy revealed a number of tentatively identified compounds, which likely contributed to the overall bioactivity of the soil extracts.

Effects of polycyclic aromatic hydrocarbon structure on PAH mineralization and toxicity to soil microorganisms after oxidative bioremediation by laccase

While bioremediation using soil microorganisms is considered an energy-efficient and eco-friendly approach to treat polycyclic aromatic hydrocarbon (PAH)-contaminated soils, a variety of polar PAH metabolites, particularly oxygenated ones, could increase the toxicity of the soil after biodegradation. In this study, a typical bio-oxidative transformation of PAH into quinones was investigated in soil amended with laccase using three PAHs with different structures (anthracene, benzo[a]anthracene, and benzo[a]pyrene) to assess the toxicity after oxidative bioremediation. The results show that during a 2-month incubation period the oxidation process promoted the formation of non-extractable residues (NERs) of PAHs, and different effects on mineralization were observed among the three PAHs. Oxidation enhanced the mineralization of the high-molecular-weight (HMW) PAHs (benzo[a]anthracene and benzo[a]pyrene) but inhibited the mineralization of the low-molecular-weight (LMW) PAH (anthracene). The inhibition of anthracene suggests increased toxicity after oxidative bioremediation, which coincided with a decrease in soil nitrification activity, bacterial diversity and PAH-ring hydroxylating dioxygenase gene copies. The analysis of PAH metabolites in soil extract indicated that oxidation by laccase was competitive with the natural transformation processes of PAHs and revealed that intermediates other than quinone metabolites increased the toxicity of soil during subsequent degradation. The different metabolic profiles of the three PAHs indicated that the toxicity of soil after PAH oxidation by laccase was strongly affected by the PAH structure. Despite the potential increase in toxicity, the results suggest that oxidative bioremediation is still an eco-friendly method for the treatment of HMW PAHs since the intermediates from HMW PAHs are more easily detoxified via NER formation than LMW PAHs.

Correlation between Polycyclic Aromatic Hydrocarbons in Wharf Roach (Ligia spp.) and Environmental Components of the Intertidal and Supralittoral Zone along the Japanese Coast

Polycyclic aromatic hydrocarbon (PAH) concentrations in wharf roach (Ligia spp.), as an environmental indicator, and in environmental components of the intertidal and supralittoral zones were determined, and the PAH exposure pathways in wharf roach were estimated. Wharf roaches, mussels, and environmental media (water, soil and sand, and drifting seaweed) were collected from 12 sites in Japan along coastal areas of the Sea of Japan. PAH concentrations in wharf roaches were higher than those in mussels (median total of 15 PAHs: 48.5 and 39.9 ng/g-dry weight (dw), respectively) except for samples from Ishikawa (wharf roach: 47.9 ng/g-dw; mussel: 132 ng/g-dw). The highest total PAH concentration in wharf roach was from Akita (96.0 ng/g-dw), followed by a sample from Niigata (85.2 ng/g-dw). Diagnostic ratio analysis showed that nearly all PAHs in soil and sand were of petrogenic origin. Based on a correlation analysis of PAH concentrations between wharf roach and the environmental components, wharf roach exposure to three- and four-ring PAHs was likely from food (drifting seaweed) and from soil and sand, whereas exposure to four- and five-ring PAHs was from several environmental components. These findings suggest that the wharf roach can be used to monitor PAH pollution in the supralittoral zone and in the intertidal zone.