High Phenanthrene Research Articles

Oxidation effectiveness and kinetics of potassium permanganate on low-permeability phenanthrene-contaminated soil under fracturing conditions

For low-permeability contaminated sites, existing combined fracturing-oxidation remediation technologies rely on diffusive migration of the oxidant to remediate only a small area near the fracture, resulting in long site-wide remediation times. Therefore, this study proposed a new fracturing-enhanced oxidative remediation method aimed at achieving rapid remediation of low-permeability polycyclic aromatic hydrocarbon-contaminated sites. Specifically, this study investigated the effect of potassium permanganate (KMnO4) oxidation on the remediation time, total oxidant demand, phenanthrene (PHE) removal, oxidation kinetics, and physicochemical properties of low-permeability PHE-contaminated soil under fracturing conditions through one-dimensional rigid-wall hydraulic conductivity tests and a series of laboratory experiments. The results indicate that according to systematic evaluation, the optimal Darcy velocity was ≥ 5.95 × 10-6 m/s, and the optimal KMnO4 concentrations for remediation of contaminated soils with low and medium–high PHE concentrations were 1 g/L and 2 g/L, respectively. The migration of KMnO4 within the soil matrix between two adjacent parallel fractures followed piecewise first-order reaction kinetics. Additionally, KMnO4 oxidation under fracturing conditions had less impact on the physicochemical properties of low-permeability PHE-contaminated soils while significantly reducing their ecotoxicity. Overall, this new remediation method shows promise for the rapid and efficient cleanup of low-permeability contaminated sites. Further research is warranted to evaluate the influence of other factors (e.g., permeability) on the oxidation effectiveness and kinetics of KMnO4 in low-permeability PHE-contaminated soils.

Simultaneous removal of phenanthrene and Pb using novel PPG-CNTs-nZVI beads.

PPG-CNTs-nZVI bead was synthesized by polyvinyl alcohol, pumice, carbon nanotube, and guar gum-nanoscale zero-valent iron to be applied on simultaneously removal of polycyclic aromatic hydrocarbons (PAHs; phenanthrene) and heavy metals (Pb2+) via adsorption. The individual and simultaneous removal efficiency of phenanthrene and Pb2+ using the PPG-CNTs-nZVI beads was evaluated with a range of initial concentrations of these two pollutants. The kinetics and isotherms of phenanthrene and Pb2+ adsorption by the PPG-CNTs-nZVI beads were also determined. The PPG-CNTs-nZVI beads show reasonably high phenanthrene adsorption capacities (up to 0.16 mg/g), and they absorbed 85% of the phenanthrene (initial concentration 0.5 mg/L) in 30 min. High Pb2+ adsorption capabilities were also demonstrated by the PPG-CNTs-nZVI beads (up to 11.6 mg/g). The adsorption fits the Langmuir model better than the Freundlich model. The adsorption still remained stable with various ionic strength circumstances and a wide pH range (2-5). Additionally, the co-adsorption of phenanthrene and Pb2+ by the PPG-CNTs-nZVI beads resulted in synergistic effects. Particularly, phenanthrene-Pb2+ complex formation via π-cation interactions demonstrated a greater affinity than phenanthrene or Pb2+ alone. The present findings suggest that PPG-CNTs-nZVI beads may be effective sorbents for the simultaneous removal of PAHs and heavy metals from contaminated waters.

High phenanthrene degrading efficiency by different microbial compositions construction.

Microbial remediation has become the most promising technical means for the remediation of polycyclic aromatic hydrocarbons (PAHs) non-point source contaminated soil due to its low cost of treatment, complete degradation of pollutants, and in-situ remediation. In this study, in order to demonstrate the phenanthrene degrading microbial diversity, phenanthrene was chosen as the representative of PAHs and strains capable of degrading phenanthrene were isolated and screened from the sedimentation sludge and the bottom sludge of oil tank trucks, and high throughput sequencing was used to check the dominant strains with a good degrading effect on phenanthrene. Results showed even more than 50% of phenanthrene was degraded in all samples, the composition of PAH-degrading bacteria was diverse, and different environments constructed different functional microbial groups, which resulted in the microbial adapting to the diversity of the environment. Finally, a series of bacterial species with phenanthrene-degrading functions such as Achromobacter, Pseudomonas, Pseudochelatococcus, Bosea was enriched after nine transferring process. Overall, our study offers value information for the enrichment of functional degrading microbes of phenanthrene or other pollutants that more concern should be paid in not only the degradation rate, but also the diversity variation of microbial community composition.

Phenanthrene sorption studies on coffee waste– and diatomaceous earth–based adsorbents, and adsorbent regeneration with cold atmospheric plasma

Phenanthrene (PHE) is a polycyclic aromatic hydrocarbon categorized as a high priority organic pollutant being toxic for the ecosystem and human health, and its sorption on natural organic or inorganic substances seems a well-promising method for its removal from water streams. The goals of the present work are (i) to assess the capacity of low-cost adsorbents fabricated by treating coffee wastes and diatomaceous earth to remove PHE from water; (ii) to elucidate the role of the pore structure on PHE sorption dynamics; and (iii) to assess the potential to regenerate adsorbents loaded with PHE, by using the novel technology of cold atmospheric plasma (CAP). Diatomaceous earth (DE) and DE pre-treated with sodium hydroxide (NaOH) or phosphoric acid (H3PO4) were chosen as inorganic adsorbents. Coffee waste (CW) and activated carbons (AC) produced from its pyrolysis at 800 °C (CWAC), either untreated (CWAC-800) or pre-treated with NaOH (CWAC-NaOH-800) and H3PO4 (CWAC-H3PO4-800), were chosen as organic adsorbents. The adsorbents were characterized with nitrogen adsorption–desorption isotherms, attenuated total reflectance-Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and mercury intrusion porosimetry. Based on the PHE sorption capacity and pore structure/surface characteristics, the CWAC-NaOH-800 was chosen as the most efficient adsorbent for further equilibrium and kinetic sorption studies. The multi-compartment model was used to describe the PHE sorption dynamics in CWAC-NaOH-800 by accounting for the pore/surface diffusion and instantaneous sorption. The CWAC-NaOH-800 exhibited remarkable values for (i) the specific surface area (SBET = 676.5 m2/g) and meso- and micro-pore volume determined by nitrogen sorption (VLN2 = 0.415 cm3/g); (ii) the macro- and meso-pore volume determined by mercury intrusion porosimetry (VMIP = 3.134 cm3/g); and (iii) the maximum PHE sorption capacity (qmax = 142 mg/g). The percentage of adsorbent recovery after its regeneration with CAP was found to be ~ 35%. From the simulation of sorption dynamics, it was found that at early times, the sorption kinetics is governed by the film diffusion towards the external surface of grains, but at late times, most of the adsorbed mass is transferred primarily to meso-/macro-pores via diffusion, and secondarily to micro-porosity via surface diffusion. Based on the adsorbent characteristics, effect of pH on sorption efficiency, and numerical analysis of sorption dynamics, it was concluded that probably the dominant adsorption mechanism is the π-π interactions between hydrophobic PHE aromatic rings and CWAC-NaOH-800 graphene layers. The high PHE removal efficiency of CWAC-NaOH-800, the successful interpretation of sorption dynamics with the multi-compartment model, and the potential to regenerate PHE-loaded adsorbents with the green and economic technology of CAP motivate a strategy for testing CWACs towards the adsorption of other PAHs, application of adsorbents to real wastewaters, and scaling-up to pilot units.Graphical

Autochthonous bioaugmentation accelerates phenanthrene degradation in acclimated soil

Bioaugmentation helps to obtain a microbiome capable of remediating polycyclic aromatic hydrocarbons (PAHs). In this study, acclimation of microorganisms to soil supplemented with phenanthrene (PHE) led to enrichment with PAH-degraders, including those in Actinobacteriota and in the genera Streptomyces, Rhodococcus, Nocardioides, Sphingomonas, and Mycobacterium. Aqueous (28 °C, pH 6.5) and soil cultures inoculated with PHE-acclimated soil showed a high PHE (ca. 50 mg L−1) degradation efficiency. The PHE degradation kinetics in aqueous and soil incubations fitted to the Gompertz equation and the first-order kinetic equation, respectively. Indigenous microorganisms adapted to PHE in their environment, and this increased their capacity to degrade PHE. The effect of co-contaminants and pathway intermediates on PHE degradation showed that the degradation of PHE improved in the presence of diesel while being hindered by lubricant oil, catechol, salicylic and phthalic acid. Our findings provide theoretical and practical support for bioremediationof PAHs in the environment.

Organic molecules based palaeoenvironmental inferences and U mineralization in Palaeoproterozoic Bijawar basins of Central India

Palaeoproterozoic, siliclastic, intracratonic rocks of the Bijawar and Sonrai basins contain anomalous U concentration and abundant Organic Matter (OM), although, earlier studies documented rare data on commonality between high U content and closely associated OM. Moreover, OM contains several biomolecules of complex carbonaceous compounds with macro-molecular structures, but insignificant information is available on the origin and associated palaeoenvironmental conditions. Thus, present study on organo-uranyl-complexes is relevant and carried out to understand palaeoenvironmental reasons accountable for U mineralization. For this purpose, OM (isolated from each bulk sample) was analyzed for Total Organic Carbon (TOC), n-alkanes, n-fatty acids and Polycyclic Aromatic Hydrocarbon compounds (PAHs). Obtained TOC values range between 0.02 and 0.23 wt%. Mostly, calculated [(C/S)/12] and [(C/N)/12] values are low; indicate algal source and anoxic depositional conditions, but, Rohini carbonate, Bandai sandstone and Chloritic shale high values signify sub-oxic conditions. Also, low (<1.25) U/Th and high authigenic U data of mineralized Chloritic shale imply anoxic conditions and post-depositional enrichment of U ions (mostly as organo-uranyl-complexes), respectively.GC-MS data show high concentration of n-alkane, fatty acid methyl ester (FAME) and PAH molecules in the OM associated with the rocks signifying high U values. The predominance of Short Chain (SC) n-alkanes together with the SC n-fatty acids revealed derivation of OM from marine algae and bacteria. The Rohini carbonate and Chloritic shale show low isoprenoids, Pristane (Pr)/Phytane (Ph), CPI, OEP, Pr/n-C-17, Ph/n-C18, but high TC-/(Pr/Ph), TC/(Pr + Ph), MP, MPI, MPR and VR values, suggest biodegraded and thermally matured OM which has undergone hydrothermal alteration under anoxic to sub-anoxic conditions. Considerably, high degree of OM oxidization occurred synchronously with the reduction of U6+ to U4+ by sulfate-reducing bacteria. The consistent loss of diaromatic PAHs is also noticed from older to younger rock-units. Further, scanty appearance of PAHs in the lower Gorakalan shale and their disappearance in the upper Chloritic and black shale units, indicate progressive maturation of sediments. The Low Molecular Weight (LMW)-PAHs predominate over the High Molecular Weight (HMW)-PAHs. Comparatively, high phenanthrene abundance is also noticed in the Rohini carbonate, Chloritic shale and -black shale (with high U content). The high proportion of LMW-PAHs and absence of HMW-PAHs (>6 rings) is pointing towards the presence of hydrothermally derived bitumen. Moreover, partial combustion of OM (pyrogenic) contributed to the formation of PAHs. The Chloritic shale and Rohini carbonate are coeval with the Bijawars of the Sonrai basin, representing almost similar organo-molecular records. Organo-molecular abundance and their structural attributes when plotted across the stratigraphic successions, revealed alternate humid conditions facilitated U4+oxidation and formation of U6+ rich solutions, although arid/semiarid climatic conditions assisted precipitation, sorption and absorption of U4+. Almost, similar clay mineral attributes for both the basins lend support to cyclic humid to arid/semiarid palaeoenvironmental conditions. Moreover, majority of the OM derived from the algal mats has played critical role in U mineralization by trapping and adsorption of tiny uraninite grains as well as U ions onto the OM.

Histology study and transcriptome analysis of the testis of Loach(Misgurnus anguillicaudatus) in response to phenanthrene exposure

Phenanthrene (PHE) is one of the most abundant polycyclic aromatic hydrocarbon compounds (PAHs) in the aquatic environment. The loaches were exposed at concentrations of 0.30、1.00、3.00 mg L−1 for 60 days. The effects of PHE on the testis development were evaluated by calculating the survival rate, observing the structure of testis and analyzing transcriptome. Firstly, PHE markedly decreased the survival rate in a dose-dependent manner. Then, the number and density of spermatogonia, primary spermatocytes, secondary spermatocytes and spermatids were substantially reduced under PHE exposure. The space in the seminiferous tubule obviously increased in the high PHE concentration group. Meanwhile, transcriptome comparative analysis identified 5329 differentially expressed genes (DEGs) including 2928 up-regulated and 2401 down-regulated in the testis of loach exposed PHE for 60 days. Meiotic cell cycle, arganelle fission, ATPase activity and adenylate nucleotide binding were significantly differences by GO (Gene Ontology) enrichment. KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis revealed that TNF (Tumor Necrosis Factor) signaling pathway, CAMs (Cell Adhesion Molecules), cytochrome P450 and lipid metabolism were markedly regulated. In addition, eight DEGs were randomly selected from the testis transcriptomics results for qPCR verification, the results were consistent with RNA-Seq. Finally, related genes (piwil2, dmc1, vasa, ubr2, dnd, rnf17, plcb2, c-fos, gpx4) of testis development were further confirmed and they were differentially regulated after PHE exposure. In summary, a survey of the mechanism of loach testis response to PHE was performed, and a large number of gene expression levels regarding metabolism, spermatogenesis and immunity genes were acquired from RNA-seq. This study provide informations for elucidating the molecular mechanism of PHE affected the testis development of loach.

Unusual occurrence of alkylphenanthrenes in upper Eocene to Oligocene sediments from the western margin of Tasmania, Australia

The occurrence and distribution of alkylphenanthrenes in upper Eocene–Oligocene sediments from Ocean Drilling Program Leg 189 (Sites 1168, 1170, 1171 and 1172) that were drilled off the coast of Tasmania have been examined by gas chromatography–mass spectrometry. Samples are thermally immature and contain predominantly terrigenous organic matter. Peculiar alkylphenanthrene distributions occur in four samples from Site 1168 at depths from 748 m to 762 m, with methylphenanthrene (MP) isomers showing complicated and irregular distributions. A dominance of 3-MP, 9-MP and 1-MP occurs in different samples, while 2-MP is systematically low in all the samples. Concentrations of alkylphenanthrenes and various other aromatic hydrocarbons generally increase with burial depth at Site 1168, likely indicating diagenetic formation. Commonly used source input and thermal maturity parameters derive inconsistent and confusing interpretations for all four sites. Maturity does not appear to be a decisive factor that influences the distributions of methylphenanthrene and dimethylphenanthrene (DMP) isomers and the degree of alkylation. The direct decomposition of retene to form an abnormal enrichment of 1-MP in one sample from Site 1168 is also difficult to envisage. The low 1,7-DMP/1,3- + 3,9- + 2,10- + 3,10-DMPs and ∑alkylphenanthrenes/∑alkylnaphthalenes ratios, coupled with the predominance of hopanoids over steroids, point to microbial input of 3-MP and 1-MP as a plausible interpretation in certain samples, while the dominance of 9-MP throughout the sedimentary column reflects local biomass input formed in the marine environment. Input of combustion-derived alkylphenanthrenes is unlikely to be the sole reason to cause unusually high phenanthrene/∑methylphenanthrenes ratios in the samples from the four sites. Oxidation during deposition and the immaturity of the sediments at an early diagenesis stage are likely to be an alternative interpretation.

Resilience of the wheat root-associated microbiome to the disturbance of phenanthrene

The microbial communities are of high importance to the restoration of ecological function and plant health, while little information about the influence of exogenous pollutants on the resilience and temporal dynamics of root microbial communities is available. In this study, a greenhouse experiment was conducted to investigate the effects of exogenous phenanthrene in terms of time and pollution disturbance on the wheat root-associated microbial communities. It was found that a high phenanthrene degradation rate of 86 % was achieved in the rhizosphere of wheat after the first-week planting. Compared to phenanthrene pollution, temporal changes had more significant impacts on the wheat root microbial communities. Obvious change of microbes influenced by PHE had been revealed at the initial three-week planting even most of PHE has been degraded, and the enriched microbes in the rhizosphere were affiliated to Altererythrobacter, Massilia, Mycobacterium, Ramlibacter, Sphingobium, Novosphingobium and Romboutsia. However, at the later stage after four-week incubation, the wheat root-associated microbial communities gradually recovered to the state without pollution. The results of this study were helpful to deepen the understanding of the response of root-associated microbial resilience to the exogenous phenanthrene pollution, and would benefit the stability and balance of agricultural ecology facing exogenous organic pollutants.

Halophilic Martelella sp. AD-3 enhanced phenanthrene degradation in a bioaugmented activated sludge system through syntrophic interaction

Polycyclic aromatic hydrocarbons (PAHs) are a group of common recalcitrant pollutant in industrial saline wastewater that raised significant concerns, whereas traditional activated sludge (AS) has limited tolerance to high salinity and PAHs toxicity, restricting its capacity to degrade PAHs. It is therefore urgent to develop a bioaugmented sludge (BS) system to aid in the effective degradation of these types of compounds under saline condition. In this study, a novel bioaugmentation strategy was developed by using halophilic Martelella sp. AD-3 for effectively augmented phenanthrene (PHE) degradation under 3% salinity. It was found that a 0.5∼1.5% (w/w) ratio of strain AD-3 to activated sludge was optimal for achieving high PHE degradation activity of the BS system with degradation rates reaching 2.2 mg⋅gVSS−1⋅h−1, nearly 25 times that of the AS system. Although 1-hydroxy-2-naphthoic acid (1H2N) was accumulated obviously, the mineralization of PHE was more complete in the BS system. Reads-based metagenomic coupled metatranscriptomic analysis revealed that the expression values of ndoB, encoding a dioxygenase associated with PHE ring-cleavage, was 5600-fold higher in the BS system than in the AS system. Metagenome assembly showed the members of the Corynebacterium and Alcaligenes genera were abundant in the strain AD-3 bioaugmented BS system with expression of 10.3±1.8% and 1.9±0.26%, respectively. Moreover, phdI and nahG accused for metabolism of 1H2N have been annotated in both above two genera. Degradation assays of intermediates of PHE confirmed that the activated sludge actually possessed considerable degradation capacity for downstream intermediates of PHE including 1H2N. The degradation capacity ratio of 1H2N to PHE was 87% in BS system, while it was 26% in strain AD-3. These results indicated that strain AD-3 contributed mainly in transforming PHE to 1H2N in BS system, while species in activated sludge utilized 1H2N as substrate to grow, thus establishing a syntrophic interaction with strain AD-3 and achieving the complete mineralization of PHE. Long-term continuous experiment confirmed a stable PHE removal efficiency of 93% and few 1H2N accumulation in BS SBR system. This study demonstrated an effective bioaugmented strategy for the bioremediation of saline wastewater containing PAHs.

Stimulatory and inhibitory effects of phenanthrene on physiological performance of Chlorella vulgaris and Skeletonema costatum

The effects of polycyclic aromatic hydrocarbons on phytoplankton have been extensively documented, but there is limited knowledge about the physiological responses of marine primary producers to phenanthrene at environmentally relevant levels. Here, we investigated the toxicity of phenanthrene (0, 1, and 5 or 10 μg L−1) to the physiological performance of two cosmopolitan phytoplankton species: the green alga Chlorella vulgaris and bloom-forming diatom Skeletonema costatum. The specific growth rates of both species were remarkably inhibited at both low (1 μg L−1) and high phenanthrene concentrations (5 or 10 μg L−1), while their tolerance to phenanthrene differed. At the highest phenanthrene concentration (10 μg L−1), the growth of C. vulgaris was inhibited by 69%, and no growth was observed for S. costatum cells. The superoxide dismutase activity of both species was enhanced at high phenanthrene concentration, and increased activity of catalase was only observed at high phenanthrene concentration in C. vulgaris. Interestingly, the low phenanthrene concentration stimulated the photosynthetic and relative electron transport rates of S. costatum, whereas hormetic effects were not found for growth. Based on our results, phenanthrene could be detrimental to these two species at a environmentally relevant level, while different tolerance levels were detected.

Indigenous bacterial community and function in phenanthrene-polluted coastal wetlands: Potential for phenanthrene degradation and relation with soil properties

The Yellow River Delta, adjacent to Shengli Oilfield, has a potential risk of petroleum pollution. In this study, soil samples were collected from phenanthrene (PHE)-polluted (adjacent to abandoned oil well, Zone D) and non-polluted (far away from abandoned oil well, Zone E) coastal wetlands. The influence of PHE pollution on indigenous bacterial community and function, and their relationship with soil characteristics were investigated. The levels of PHE, salinity and NH4+-N were higher in Zone D than in Zone E. PHE-degrading bacteria Achromobacter and Acinetobacter were mainly distributed in Zone E, whereas Halomonas, Marinobacter, and Roseovarius were highly abundant in Zone D. Halomonas and Marinobacter had the potential for denitrification and could achieve PHE degradation through mutual cooperation. PHE pollution could increase the abundance of functional bacteria but reduce the diversity of microbial community. PHE and salinity played key roles in shaping microbial community structure and function. High PHE level inhibited microbial metabolism but stimulated self-protection potential. PHE aerobic degradation associated with the catechol and phthalic acid pathways was found in Zone D, whereas the catechol pathway dominated in Zone E. Interestingly, PHE anaerobic degradation with nitrate reduction also dominated in Zone D, whereas the process coupled with multiple electron acceptors co-existed in Zone E, which was associated with tidal seawater carrying nutrients. This study illustrated the importance of comprehensive consideration of microbial community structure and function under PHE pollution, suggesting indigenous microorganisms as potential microbial consortium for bioremediation in coastal wetlands.

Inoculation of Triticum Aestivum L. (Poaceae) with Plant-Growth-Promoting Fungi Alleviates Plant Oxidative Stress and Enhances Phenanthrene Dissipation in Soil

Polycyclic aromatic hydrocarbons (PAHs) are strong toxic compounds mainly released to the environment during combustion of fossil fuels, and have strong toxic effects on living organisms, with soil being one of their main reservoirs. High PAH levels in soils can interfere with plant growth and biomass production, causing several losses of diversity. In this study, we evaluated the effects of the co-inoculation of Trichoderma viride and Funneliformis mosseae on PAH dissipation and alleviation of oxidative stress in Triticum aestivum L. (wheat) plants growing in a phenanthrene-spiked soil. We determined the effect of single and dual fungal inoculation on phenanthrene dissipation rates, soil enzyme activities, dry biomass, antioxidant enzymes, lipid peroxidation, and organic acid exudation of plants growing in a soil spiked with phenanthrene at 500 and 1000 mg kg−1 soil. The co-inoculation with T. viride and F. mosseae resulted in a high phenanthrene dissipation from the soil. Also, dry biomass, soil enzymes, antioxidant response, organic acid exudation and phenanthrene content in roots were increased by the dual inoculation treatments, whereas lipid peroxidation and phenanthrene content in shoots were reduced. Our results show that the co-inoculation with these two soil fungi significantly promotes phenanthrene dissipation from soil and contributes to alleviating oxidative damage in wheat plants exposed to high levels of phenanthrene.

Formation and distribution of phenanthrene and its metabolites (monohydroxy-phenanthrenes) in Korean rockfish (Sebastes schlegelii)

This study investigated the tissue distribution of phenanthrene (PHE) and the formation of monohydroxy-phenanthrene (OH-PHE) metabolites in Korean rockfish (Sebastes schlegelii). PHE was intragastrically administered to two groups of rockfish. The first group was exposed to PHE at a low dose (10 mg/kg body weight) and the second group was exposed at a high dose (30 mg/kg body weight). The rockfish were analyzed and the levels of PHE were higher in the liver, followed by muscle, and then bile. PHE concentrations in the liver, muscle, and bile were 1.4–26, 0.10–2.01, and not detected (ND)–0.13 μg/g wet weight, respectively. All five monohydroxylated PHE metabolites (1-OH-PHE, 2-OH-PHE, 3-OH-PHE, 4-OH-PHE, and 9-OH-PHE) were detected only in bile. Among these OH-PHE metabolites, 3-OH-PHE was found at the highest concentration from all fish bile samples in both PHE exposure groups, indicating that regioselective OH-PHE formation occurs in rockfish and 3-OH PHE could be a good biomarker of exposure of Korean rockfish to PHE. Suspect screening analysis of the rockfish bile was performed by LC-QTOF/MS, and the formation of two OH-PHE-DNA adducts (thymine–OH–PHE and cytosine–OH–PHE) were identified in the bile sample collected 6 h after rockfish were exposed to the high PHE dose, indicating that OH-PHE metabolites may be toxic to fish. This is the first report on the formation characteristics of OH-PHE metabolites in rockfish and their use as biomarkers of exposure of rockfish to parent PHE.

Can biochar and oxalic acid alleviate the toxicity stress caused by polycyclic aromatic hydrocarbons in soil microbial communities?

It remains unclear whether biochar amendment can mediate changes in soil microbial communities caused by organic contaminants in the rhizosphere. In this study, phenanthrene-contaminated soil was amended with biochar and oxalic acid (OA) alone or in combination and incubated for 21 days. Phospholipid fatty acids (PLFAs) and high-throughput sequencing were used to evaluate shifts in bacterial and fungal community structure. Phenanthrene stress led to significant shifts in both soil bacterial and fungal community structure, in particularly, 82% of microbial phyla decreased in abundance. Biochar and/or OA improved the phenanthrene-polluted soil by positively mediating shifts in soil microbial communities stressed by phenanthrene. Specifically, biochar and/or OA led to the survival of certain microbial taxa that were inhibited by phenanthrene stress. In addition, many functional microbial individuals and genes participating in polycyclic aromatic hydrocarbon (PAH) degradation were positively stimulated by high phenanthrene stress and further stimulated by the simultaneous application of biochar and OA. Based on these findings, tandem biochar and rhizoremediation may be a feasible strategy for relieving PAH toxicity to soil microbial communities.

Complexity of bacterial communities within the rhizospheres of legumes drives phenanthrene degradation

Determining the mechanisms underlying complex plant-microbe interactions and feedbacks is crucial for effective rhizoremediation of contaminated soils. Here, rhizosphere bacterial communities of 10 common legumes planted in arable and aged oil-contaminated soils for 90 days were used to degrade phenanthrene (PHE). Bacterial community structures were analyzed to reveal the mechanisms underlying the varying PHE degradation capacities. We found that bacterial β-diversity within the rhizospheres played a major role in predicting PHE degradation rates, and more complex bacterial communities exhibited higher PHE degradation capacities. The highest PHE degradation rates were obtained with bacterial communities of Coronilla varia and Vigna unguiculata planted in oil-contaminated soils (almost 80%). There were significant differences in bacterial community composition between arable and contaminated soils, and among different legumes rhizospheres and the unplanted soils, although minimal differences were observed in bacterial α-diversity. The potential degradation-related taxa were more abundant in bacterial communities from contaminated soils, indicating more effective PHE degradation than in arable soils. Network analysis revealed the vital ecological roles of the potential degradation-related taxa in the maintenance of complex associations among bacterial taxa. Oil contamination reduced the differences in bacterial community composition between rhizosphere soils with high and low PHE degradation rates. These results suggest that the formulation of effective rhizoremediation strategies ought to focus on more diverse and complex interactions between rhizosphere-inhabiting organisms from aged oil-contaminated soils through the selection of optimal plant-microbiota association.

Isolation and Characterization of Phenanthrene Degrading Bacteria from Diesel Fuel-Contaminated Antarctic Soils.

Antarctica is an attractive target for human exploration and scientific investigation, however the negative effects of human activity on this continent are long lasting and can have serious consequences on the native ecosystem. Various areas of Antarctica have been contaminated with diesel fuel, which contains harmful compounds such as heavy metals and polycyclic aromatic hydrocarbons (PAH). Bioremediation of PAHs by the activity of microorganisms is an ecological, economical, and safe decontamination approach. Since the introduction of foreign organisms into the Antarctica is prohibited, it is key to discover native bacteria that can be used for diesel bioremediation. By following the degradation of the PAH phenanthrene, we isolated 53 PAH metabolizing bacteria from diesel contaminated Antarctic soil samples, with three of these isolates exhibiting a high phenanthrene degrading capacity. In particular, the Sphingobium xenophagum D43FB isolate showed the highest phenanthrene degradation ability, generating up to 95% degradation of initial phenanthrene. D43FB can also degrade phenanthrene in the presence of its usual co-pollutant, the heavy metal cadmium, and showed the ability to grow using diesel-fuel as a sole carbon source. Microtiter plate assays and SEM analysis revealed that S. xenophagum D43FB exhibits the ability to form biofilms and can directly adhere to phenanthrene crystals. Genome sequencing analysis also revealed the presence of several genes involved in PAH degradation and heavy metal resistance in the D43FB genome. Altogether, these results demonstrate that S. xenophagum D43FB shows promising potential for its application in the bioremediation of diesel fuel contaminated-Antarctic ecosystems.

Marine Bacterial Biofilms in Bioremediation of Polycyclic Aromatic Hydrocarbons (PAHs) Under Terrestrial Condition in a Soil Microcosm

Polycyclic aromatic hydrocarbons (PAHs) in soil retain for a quite long period due to their hydrophobicity and aggregation properties. Biofilm-forming marine bacterial consortium (named as NCPR), composed of Stenotrophomonas acidaminiphila NCW702, Alcaligenes faecalis NCW402, Pseudomonas mendocina NR802, Pseudomonas aeruginosa N6P6, and Pseudomonas pseudoalcaligenes NP103, was used for the bioremediation of PAHs in a soil microcosm. Phenanthrene and pyrene were used as reference PAHs. Parameters that can affect PAH degradation, such as chemotaxis, solubility of PAHs in extracellular polymeric substances (EPS), and catechol 2,3-dioxygenase (C23O) activity, were evaluated. P. aeruginosa N6P6 and P. pseudoalcaligenes NP103 showed chemotactic movement towards both the reference PAHs. The solubility of both the PAHs was increased with an increase in EPS concentration (extracted from all the 5 selected isolates). Significantly (P < 0.001) high phenanthrene (70.29%) and pyrene (55.54%) degradation was observed in the bioaugmented soil microcosm. The C23O enzyme activity was significantly (P < 0.05) higher in the bioaugmented soil microcosm with phenanthrene added at 173.26 ± 2.06 nmol min−1 mg−1 protein than with pyrene added at 61.80 ± 2.20 nmol min−1 mg−1 protein. The C23O activity and gas chromatography-mass spectrometer analyses indicated catechol pathway of phenanthrene metabolism. However, the metabolites obtained from the soil microcosm added with pyrene revealed both the catechol and phthalate pathways for pyrene degradation.

Impact of phenanthrene exposure on activities of nitrate reductase, phosphoenolpyruvate carboxylase, vacuolar H+-pyrophosphatase and plasma membrane H+-ATPase in roots of soybean, wheat and carrot

Crops differ in uptake of polycyclic aromatic hydrocarbons (PAHs). However, the physiological mechanism underlying the differences in PAH uptake among crop species is unclear. As PAH transport by H+-coupled symporters may affect cytosolic pH, and intracellular pH is precisely regulated for metabolism, four enzymes linked with cytosolic pH regulation in root cells were determined at different concentrations of phenanthrene (PHE) and pHs. Activity of nitrate reductase (NRase) is stimulated by PHE and follows the order: wheat>carrot>soybean. The optimum pH of NRase is 7.5 in wheat and carrot, while 6.5 in soybean. The activity of phosphoenolpyruvate carboxylase (PEPCase) is generally decreased by PHE and always lower in soybean than in wheat and carrot. PEPCase peaks its maximum activity at pH 7.0 and wheat shows the highest value with high PHE (1.2mgL−1) at pHs of 7.0 and 8.0 in comparison with carrot and soybean. Vacuolar H+-pyrophosphatase (V-H+-PPase) is promoted by PHE in wheat and carrot, while it does not change significantly in soybean (P>0.05). V-H+-PPase reaches its maximum value at pH 7.5 and follows the order of wheat>carrot>soybean at alkaline medium with high PHE. Plasma membrane (PM) H+-ATPase is enhanced by K+ and follows the order: wheat>soybean>carrot. The orders of activity of these enzymes are not consistent with that of PHE uptake, indicating their various functions. However, in soybean, PM H+-ATPase activity under high PHE and the uptake of PHE are always higher than those in wheat and carrot, suggesting that PM H+-ATPase plays an essential role in PHE uptake. Therefore, the changes of PM H+-ATPase activity seem to be a direct consequence responding to PHE stress and those of NRase, PEPCase and V-H+-PPase might be the downstream accidents regulated by cytosoilc pH. Our study provides insight into the roles of these enzymes in non-photosynthetic tissues and supports their importance in the physiological responses to PHE stress among different crops.

Pseudo-basal levels of and distribution of anti-oxidant enzyme biomarkers in Eisenia fetida and effect of exposure to phenanthrene

In the paper, the pseudo-basal levels of anti-oxidant system in different earthworm life stages (juvenile and adult) and the pseudo-basal distribution in different regions of adult earthworms (pre-clitellum, clitellum and post-clitellum) were studied using filter contact tests. The effects of phenanthrene (PHE) at different exposure levels on anti-oxidant enzymes along the earthworm body were also investigated after 24 and 48h of exposure.The pseudo-basal levels of the anti-oxidant enzymes varied during the different growth phase, and results indicated that earthworm has a low oxidative risk and SOD plays important roles during the development whereas CAT and POD are more important in maintain the low ROS level in adult earthworm.The pseudo-basal distribution of the anti-oxidant enzymes along the earthworms was heterogeneous and MDA mainly located in clitellum. POD in pre-clitellum, SOD in clitellum and CAT in post-clitellum were important to eliminate excess total ROS. Time of exposure impacted the anti-oxidant enzyme activities and their distribution patterns along earthworms, from the viewpoint of which supported that exposure time was an environment stress factors.In a short exposure time (24h), CAT and SOD in the three regions, POD in pre-clitellum and clitellum might be good indicator to a low PHE stress level (0.0629μgcm−2 treatments). In a long exposure time (48h), only SOD in clitellum is a good indicator to both low and high PHE stress (0.629μgcm−2 treatments). Earthworm biomembrane system inflicted no oxidative damage until the stress magnitude reached or exceeds the level of exposure in low PHE concentration condition for 48h.