Dissipation Of Polycyclic Aromatic Hydrocarbons Research Articles

Persistent polycyclic aromatic hydrocarbons removal from sewage sludge-amended soil through phytoremediation combined with solid-state ligninolytic fungal cultures

Polycyclic aromatic hydrocarbons (PAHs) are widely present in the environment, causing increasing concern because of their impact on soil health, food safety and potential health risks. Four bioremediation strategies were examined to assess the dissipation of PAHs in agricultural soil amended with sewage sludge over a period of 120 days: soil-sludge natural attenuation (SS); phytoremediation using maize (Zea mays L.) (PSS); mycoremediation (MR) separately using three white-rot fungi (Pleurotus ostreatus, Phanerochaete chrysosporium and Irpex lacteus); and plant-assisted mycoremediation (PMR) using a combination of maize and fungi. In the time frame of the experiment, mycoremediation using P. chrysosporium (MR-PH) exhibited a significantly higher (P < 0.05) degradation of total PAHs compared to the SS and PSS treatments, achieving a degradation rate of 52 %. Both the SS and PSS treatments demonstrated a lower degradation rate of total PAHs, with removal rates of 18 % and 32 %, respectively. The PMR treatments showed the highest removal rates of total PAHs at the end of the study, with degradation rates of 48–60 %. In the shoots of maize, only low- and medium-molecular-weight PAHs were found in both the PSS and PMR treatments. The calculated translocation and bioconversion factors always showed values < 1. The analysed enzymatic activities were higher in the PMR treatments compared to other treatments, which can be positively related to the higher degradation of PAHs in the soil.

Biosurfactants-based mixed polycyclic aromatic hydrocarbon degradation: From microbial community structure toward non-targeted metabolomic profile determination

Biosurfactants-based bioremediation is considered an efficient technology to eliminate environmental pollutants including polycyclic aromatic hydrocarbons (PAHs). However, the precise role of rhamnolipids or lipopeptide-biosurfactants in mixed PAH dissipation, shaping microbial community structure, and influencing metabolomic profile remained unclear. In this study, results showed that the maximum PAH degradation was achieved in lipopeptide-assisted treatment (SPS), where the pyrene and phenanthrene were substantially degraded up to 74.28 % and 63.05 % respectively, as compared to rhamnolipids (SPR) and un-aided biosurfactants (SP). Furthermore, the high throughput sequencing analysis revealed a significant change in the PAH-degrading microbial community, with Proteobacteria being the predominant phylum (>98 %) followed by Bacteroidota and Firmicutes in all the treatments. Moreover, Pseudomonas and Pannonibacter were found as highly potent bacterial genera for mixed PAH degradation in SPR, SPS, and SP treatments, nevertheless, the abundance of the genus Pseudomonas was significantly enhanced (>97 %) in SPR treatment groups. On the other hand, the non-targeted metabolomic profile through UHPLC-MS/MS exhibited a remarkable change in the metabolites of amino acids, carbohydrates, and lipid metabolisms by the input of rhamnolipids or lipopeptide-biosurfactants whereas, the maximum intensities of metabolites (more than two-fold) were observed in SPR treatment. The findings of this study suggested that the aforementioned biosurfactants can play an indispensable role in mixed PAH degradation as well as seek to offer new insights into shifts in PAH-degrading microbial communities and their metabolic function, which can guide the development of more efficient and targeted strategies for complete removal of organic pollutants such as PAH from the contaminated environment.

Removal of PAHs in paddy fields: How natural periphytic biofilm enhances the removal process and the mechanisms involved

Previous studies on the removal of polycyclic aromatic hydrocarbons (PAHs) from farmland have mostly relied on anthropogenic biotic or abiotic amendments. Here, an indigenous paddy periphytic biofilm (PB) composed of complex symbolic communities was enriched, and its essential role, as well as the potential mechanisms of PAHs dissipation, was investigated. A pot experiment revealed that PB achieved 92.87% and 92.76% removal of the USEPA priority PAHs from the overlying water and soil of a heavily PAHs-contaminated paddy field, respectively. This subsequently decreased ΣPAHs accumulation in rice shoots to 4.12 ± 1.08 ng g-1, under the thresholds based on food safety standards. The physiology of PB in an aquatic culture with PAHs was assessed to understand the toxicity and removal mechanism. Extracellular polymeric substances (EPS) adsorption occurred in the early stage, followed by late biodegradation, which was considered the primary mechanism for removing PAHs. In this process, the PB contributed more to the high molecular weight PAHs compared to the low molecular weight. Furthermore, 16S-rRNA sequencing demonstrated specific functional phyla (Proteobacteria, Ascomycota, and Chloroplastida) with significantly higher relative abundances in periphytic communities with PAHs, which facilitated PAHs degradation. The predicted synergetic metabolic pathway involved 33 PAHs-degrading genes as inferred by PICRUSt. These findings suggest that PB could provide a promising strategy for target PAHs remediation in situ and food safety in contaminated paddy fields.

Unveiling the synergistic mechanism of autochthonous fungal bioaugmentation and ammonium nitrogen biostimulation for enhanced phenanthrene degradation in oil-contaminated soils

Autochthonous bioaugmentation and nutrient biostimulation are promising bioremediation methods for polycyclic aromatic hydrocarbons (PAHs) in contaminated agricultural soils, but little is known about their combined working mechanism. In this study, a microcosm trial was conducted to explore the combined mechanism of autochthonous fungal bioaugmentation and ammonium nitrogen biostimulation, using DNA stable-isotope-probing (DNA-SIP) and microbial network analysis. Both treatments significantly improved phenanthrene (PHE) removal, with their combined application producing the best results. The microbial community composition was notably altered by all bioremediation treatments, particularly the PHE-degrading bacterial and fungal taxa. Fungal bioaugmentation removed PAHs through extracellular enzyme secretion but reduced soil microbial diversity and ecological stability, while nitrogen biostimulation promoted PAH dissipation by stimulating indigenous soil degrading microbes, including fungi and key bacteria in the soil co-occurrence networks, ensuring the ecological diversity of soil microorganisms. The combination of both approaches proved to be the most effective strategy, maintaining a high degradation efficiency and relatively stable soil biodiversity through the secretion of lignin hydrolytic enzymes by fungi, and stimulating the reproduction of soil native degrading microbes, especially the key degraders in the co-occurrence networks. Our findings provide a fresh perspective of the synergy between fungal bioaugmentation and nitrogen biostimulation, highlighting the potential of this combined bioremediation approach for in situ PAH-contaminated soils.

Responses of a polycyclic aromatic hydrocarbon-degrading bacterium, Paraburkholderia fungorum JT-M8, to Cd (II) under P-limited oligotrophic conditions

For the bioremediation of mixed-contamination sites, studies on polycyclic aromatic hydrocarbon (PAH) degradation or Cd (II) tolerance in bacteria are commonly implemented in nutrient-rich media. In contrast, in the field, inocula usually encounter harsh oligotrophic habitats. In this study, the environmental strain Paraburkholderia fungorum JT-M8 was used to explore the overlooked Cd (II) defense mechanism during PAH dissipation under P-limited oligotrophic condition. The results showed that the growth and PAH degradation ability of JT-M8 under Cd (II) stress were correlated with phosphate contents and exhibited self-regulating properties. Phosphates mainly affected the Cd (II) content in solution, while the cellular distribution of Cd (II) depended on Cd (II) levels; Cd (II) was mainly located in the cytoplasm when exposed to less Cd (II), and vice versa. The unique Cd (II) detoxification pathways could be classified into three aspects: (i) Cd (II) ionic equilibrium and dose–response effects regulated by environmental matrices (phosphate contents); (ii) bacterial physiological self-regulation, e.g., cell surface-binding, protein secretion and active transport systems; and (iii) specific adaptive responses (flagellum aggregation). This study emphasizes the importance of considering culture conditions when assessing the metal tolerance and provides new insight into the bacterial detoxification process of complex PAH-Cd (II) pollutants.

Migration of polycyclic aromatic hydrocarbons in the rhizosphere micro-interface of soil-ryegrass (Lolium perenne L.) system

The unclear multi-media and multi-interface processes of polycyclic aromatic hydrocarbons (PAHs) in environments have drawn great concern. Here, 16 controlled PAHs were selected to reveal the differences in the bioavailability and migration of congeners in soil-ryegrass exposure system. The presence of ryegrass in the exposure groups (with newly introduced PAHs) resulted in a decrease in PAHs dissipation (31.3 %) from soil compared to the unplanted groups (43.2 %). The presence of ryegrass inhibited the soil-air exchange process, which has not been widely reported. PAH congeners with less benzene rings (molecular weight < B[a]A) had consistent bioavailability before and after long-term aging, the competition between adsorption/absorption to plants and soil was not strong (RCFs < 3.5), and their migration in the rhizosphere rapidly reached equilibrium. PAH congeners with more benzene rings (molecular weight ≥ B[a]A) adsorbed to soil particles and significantly decreased their bioavailability after long-term aging. Their concentrations in the rhizosphere were stable and lower than bulk soil, revealing their slow equilibrium process in soil. In addition, PAHs with larger molecular weight and KOW showed less migration at the rhizosphere micro-interface. The migration behavior of congeners with close KOW depended on their molecular structure. Congeners with non-symmetric K-region or L-region showed greater migration ability in the rhizosphere. These findings revealed the fate of PAHs, especially different PAH congeners, in the rhizosphere interfaces for the first time, and explored the molecular mechanisms that affect their rhizosphere behaviors, improving the understanding and knowledge of PAHs in the microenvironment, providing new data on evaluating and controlling the environmental risks of PAHs.

Exploration of bacterial community-induced polycyclic aromatic hydrocarbons degradation and humus formation during co-composting of cow manure waste combined with contaminated soil

To solve polycyclic aromatic hydrocarbons (PAHs) pollution, composting was chosen as a remediation method. During composting, the dissipation of PAHs was carried out by resource utilization of organic solid waste and its degradation by bacteria. This study was conducted by co-composting with contaminated soil and cow manure. The results showed that the degradation rates of naphthalene (Nap), phenanthrene (Phe), and benzo[α]pyrene (BaP) could reach 82.2%, 79.4%, and 59.6% respectively during composting. Cluster analysis indicated that polyphenol oxidase (PPO), laccase, and protease were important drivers of PAHs transformation. The content of humic substances (HS) was 106.67 g/kg in PAH treatment, which was significantly higher than that in the control group at 65 days. The phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) and network analysis was used to infer the degradation mechanism of PAHs by microorganisms. The degradation of PAHs by PPO was found to have a significant contribution to the formation of HS. It was shown that PAHs and metabolic intermediates were more inclined to be oxidized and decomposed by PPO to form quinone, which in turn condensed with amino acids to form HS. Composting could promote the degradation of PAHs while improving the quality of compost, achieving a win-win situation.

In-situ co-remediation of PAHs contaminated agricultural soil using blood meal and celery: An agricultural greenhouse field study

ABSTRACT Polycyclic aromatic hydrocarbon (PAH) contaminated agricultural soil is widespread globally. To develop a cost-effective remediation technique to effectively degrade PAH contaminated agricultural soil without disturbing crop production, an in-situ co-remediation of PAH contaminated agricultural soil using blood meal and celery was assessed in an agricultural greenhouse. Results showed PAH dissipation rates increased significantly in agricultural soil when co-remediated by blood meal and celery. Planting celery and addition of 5 g•kg−1 blood meal removed 53.13% of PAHs within three months. Residual PAH concentrations in plant tissue were much lower than China Standard food limits. Results indicated the ability of celery to enhance bioavailability of PAHs, and create favorable conditions for microbial, rather than direct plant uptake, played a vital role in degradation of PAHs. Addition of blood meal significantly enhanced soil enzyme activity and PAH degradation, and increased PAH remediation rate with optimal addition of blood meal (5 g•kg−1). Celery enhanced bioavailability of PAHs. Blood meal increased soil enzyme activity and increased PAH degrading bacterial activity, which acted as the main remediation pathway to co-remediate PAHs, where celery was safe to eat. Therefore, a novel in-situ agricultural soil PAH remedial method, which did not disturb normal agricultural production during remediation is presented in this study.

Dissipation of a mix of priority PAHs in soils by using availability enhancers. Effect of aging and pollutant interactions.

A remediation strategy using three non-toxic availability enhancers (two cyclodextrins and a rhamnolipid biosurfactant) was applied to various soils artificially contaminated with a mix of Polycyclic Aromatic Hydrocarbons (PAHs) considered priority pollutants at two levels of contamination: only with 7 low molecular weight PAHs (LMW PAHs, 5 with 3-ring and 2 with 4-ring - fluoranthene and pyrene) or with 14 PAHs (from 3 to 6 rings). Natural attenuation of PAHs in all soils showed degradation capacity for the LMW PAHs, with a final content of LMW PAHs <5% of their initial concentration. Conversely, the rest of PAHs (high molecular weight PAHs, HMW) remained in the soils (61% - 83.5%), indicating abiotic dissipation of HMW PAHs due to formation of non-extractable residues in soils. The influence of the presence of HMW PAHs on the degradation of the 7 LMW PAHs was also tested, showing a general decrease in the time to obtain 50% dissipation (DT50), statistically significant for acenaphthene, acenaphthylene and fluorene. Availability enhancers showed different effects on PAHs dissipation. 2-hydroxypropyl-β-cyclodextrin (HP) decreased DT50 of some of the lighter PAHs, whereas the rhamnolipid (RL) caused a slight DT50 increase due to its initial toxicity on native soil microorganisms, but showing later high degradation rate for LMW PAHs. On the contrary, randomly methylated-β-cyclodextrin (RAMEB) slowed down PAHs degradation due to its high adsorption onto soil surface, blocking the desorption of PAHs from the soils. The high number of experimental factors not studied simultaneously before (soil type, co-contamination, availability enhancers and incubation time) allowed to conduct a statistical analysis which supported the conclusions reached. Principal Component Analysis separated the studied PAHs in 3 groups, in relation with their molecular weight and Kow. The first principal component was related with LMW PAHs, and separate the inefficient RAMEB from the other availability enhancers.

Effects of Comamonas testosteroni on dissipation of polycyclic aromatic hydrocarbons and the response of endogenous bacteria for soil bioremediation.

Bioremediation is a promising method of treating polycyclic aromatic hydrocarbons (PAHs) in contaminated soil; however, the understanding of the efficiency and the way of microbial inoculants work in complex soil environments is limited. Comamonas testosteroni (Ct) strains could efficiently degrade PAHs, especially naphthalene (Nap) and phenanthrene (Phe). This study aimed to explore the functional role of Ct in soil indigenous microorganisms and analyze the effect of Ct addition on PAHs concentration in PAH-contaminated soil. The results showed that inoculation with Ct degraded naphthalene (Nap), phenanthrene (Phe), and benzo [α] pyrene (BaP) significantly; the degradation rates were 63.38%, 81.18%, and 37.98% on day 25, respectively, suggesting that the low molecular weights of Nap and Phe were more easily degraded by microorganisms than those of BaP. We speculated that BaP and Phe might be converted into Nap for further degradation, which is the main reason for the low degradation rate of Nap detected after 10-25days. Network analysis showed that inoculation with Ct significantly increased bacteria community abundance closely related to PAHs. Structural equation models confirmed that Steroidobacter, as functional bacteria, could affect the degradation of Nap and BaP. Inoculated Ct effectively enhanced the synergy among indigenous bacteria to degrade PAHs. This finding will help understand the function of inoculated Ct strains in PAH-contaminated soil at the laboratory level.

Biochar application strategies for polycyclic aromatic hydrocarbons removal from soils

Polycyclic aromatic hydrocarbons (PAHs) are known as a hazardous group of pollutants in the soil which causes many challenges to the environment. In this study, the potential of biochar (BC), as a carbonaceous material, is evaluated for the immobilization of PAHs in soils. For this purpose, various bonding mechanisms of BC and PAHs, and the strength of bonds are firstly described. Also, the effect of impressive criteria including BC physicochemical properties (such as surface area, porosity, particle size, polarity, aromaticity, functional group, etc., which are mostly the function of pyrolysis temperature), number of rings in PAHs, incubation time, and soil properties, on the extent and rate of PAHs immobilization by BC are explained. Then, the utilization of BC in collaboration with biological tools which simplifies further dissipation of PAHs in the soil is described considering detailed interactions among BC, microbes, and plants in the soil matrix. The co-effect of BC and biological remediation has been authenticated by previous studies. Moreover, recent technologies and challenges related to the application of BC in soil remediation are explained. The implementation of a combined BC-biological remediation method would provide excellent prospects for PAHs-contaminated soils.

Biochar enhanced polycyclic aromatic hydrocarbons degradation in soil planted with ryegrass: Bacterial community and degradation gene expression mechanisms

Biochar and ryegrass have been used in the remediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated soils; however, the effects of different biochar application levels on the dissipation of PAHs, bacterial communities, and PAH-ring hydroxylating dioxygenase (PAH-RHDα) genes in rhizosphere soil remain unclear. In this study, enzyme activity tests, real-time quantitative polymerase chain reaction (PCR), and high-throughput sequencing were performed to investigate the effects of different proportions of rape straw biochar (1%, 2%, and 4% (w/w)) on the degradation of PAHs, as well as the associated changes in the soil bacterial community and PAH-RHDα gene expression. The results revealed that biochar enhanced the rhizoremediation of PAH-contaminated soil and that 2% biochar-treated rhizosphere soil was the most effective in removing PAHs. Furthermore, urease activity, abundance and activity of total bacteria, and PAH-degrading bacteria were enhanced in soil that was amended with biochar and ryegrass. Additionally, the activity of 16S rDNA and PAH-RHDα gram-negative (GN) genes increased with increasing biochar dosage and had a positive correlation with the removal of PAHs. Biochar changed the rhizosphere soil bacterial composition and α-diversity, and promoted the growth of Pseudomonas and Zeaxanthinibacter. In addition, the relative abundance of Pseudomonas was positively correlated with PAH removal. These findings imply that rape straw biochar can enhance the rhizoremediation of PAH-contaminated soil by changing soil bacterial communities and stimulating the expression of PAH-RHDα GN genes. The 2% of rape straw biochar combined with ryegrass would be an effective method to remediate the PAH-contaminated soil.

Nitrogen addition enhanced the polycyclic aromatic hydrocarbons dissipation through increasing the abundance of related degrading genes in the soils

High concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) in the soils cause significant threats to human health. Since nitrogen plays a crucial role in controlling microbial composition and functions in terrestrial ecosystems, bio-stimulation based on nitrogen has been used in PAHs contaminated environments remediation. Recent studies show that microbial community composition and organic pollutants dissipation correlate with nitrogen addition. Here, we investigated the effect of nitrogen addition on the abundance of microbial community, degrading genes, and their relationship to PAHs dissipation. After a 32-day experiment, PAHs residues in nitrogen treatment soil were reduced by 23.23%−34.21%. The application of 80 mg·kg−1 nitrate and ammonium nitrogen resulted in higher PAHs removal efficiency, and the dissipation rate of PAHs was 59.61% and 62.09%, respectively. Nitrogen application could improve the abundance and the diversity of soil microbial community. Degrading genes involved in PAH detoxification were enhanced after nitrogen addition, particularly those encoding ring-hydroxylating and catechol dioxygenases such as nahAc and nidA, thus, accelerating PAH dissipation in the soil. The results will facilitate the development of beneficial microbiome-based remediation strategies and improve agricultural production safety in PAHs-contaminated soils.

Efficiency of Penicillium canescens in Dissipating PAH in Industrial Aged Contaminated Soil Microcosms and Its Impact on Soil Organic Matter and Ecotoxicity

The filamentous fungus Penicillium canescens, isolated from oil-polluted soil, was evaluated for its ability to dissipate high-molecular-weight polycyclic aromatic hydrocarbons (PAH). The study was conducted in a microcosm containing 180 g of historical PAH-contaminated soil under non-sterile conditions with two incubation temperatures (14 °C and 18 °C) on a 12-h cycle. The experiment was conducted over 8 months, with four experimental conditions created by varying the volumes of the bulking agent and vegetable oil (olive oil) and the time of addition of these compounds. The PAH dissipation performance of the fungal augmentation treatment was compared with that achieved with a biostimulated soil (bulking agent and vegetable oil) and with the untreated soil as control. The greatest PAH dissipation was obtained with P. canescens bioaugmentation (35.71% ± 1.73), with 13 of the 16 US EPA PAH significantly dissipated, at rates above 18%, and particularly high-molecular-weight PAH, composed of more than three fused aromatic rings. Nematode toxicity tests indicated a significant decrease in the toxicity of soil bioaugmented by this fungus. Fulvic and humic contents were significantly increased by this treatment. All these results suggest that bioaugmentation with P. canescens can be used to restore soils with long-term PAH contamination.

Plant contribution to the remediation of PAH-contaminated soil of Dagang Oilfield by Fire Phoenix.

Pot experiments were conducted to evaluate plant contribution during remediation of the polycyclic aromatic hydrocarbons (PAH)-contaminated soil of Dagang Oilfield by Fire Phoenix (a mixture of Festuca L.). The results showed that Fire Phoenix could grow in soil contaminated by high and low concentrations of PAHs. After being planted for 150days, the total removal rate of six PAHs in the high and low PAH concentrations was 80.36% and 79.79%, significantly higher than the 58.79% and 53.29% of the unplanted control group, respectively. Thus, Fire Phoenix can effectively repair the soil contaminated by different concentrations of PAHs. In high concentrations of PAHs, the results indicated a positive linear relationship between PAH absorption in tissues of Fire Phoenix and the growth time in the early stage. In contrast, the contents of PAHs were just slightly increased in the late period of plant growth. The main factor for the dissipation of PAHs was plant-promoted biodegradation (99.04%-99.93%), suggesting a low contribution of PAH uptake and transformation (0.07%-0.96%). The results revealed that Fire Phoenix did not remove the PAHs in the soil by accumulation but promoted PAH dissipation in the soil by stimulating the microbial metabolism in the rhizosphere.

Microbial diversity drives pyrene dissipation in soil

Soil microbial diversity is an essential driver of multiple ecosystem functions and services. However, the role and mechanisms of microbial diversity in the dissipation of persistent organic pollutants in soil are largely unexplored. Here, a gradient of soil microbial diversity was constructed artificially by a dilution-to-extinction approach to assess the role of soil microbial diversity in the dissipation of pyrene, a high molecular weight polycyclic aromatic hydrocarbon (PAH), in a 42-day microcosm experiment. The results showed that pyrene dissipation (98.1%) and the abundances of pyrene degradation genes (the pyrene dioxygenase gene nidA and the gram-positive PAH-ring hydroxylating dioxygenase gene PAH-RHDα GP) were highest in soils with high microbial diversity. Random-forest machine learning was combined with linear regression analysis to identify a range of keystone taxa (order level) associated with pyrene dissipation, including Sphingobacteriales, Vampirovibrionales, Blastocatellales, Myxococcales, Micrococcales and Rhodobacterales. The diversity of these keystone taxa was significantly and positively correlated with the abundance of pyrene degradation genes and the removal rate of pyrene. According to (partial) Mantel tests, keystone taxa diversity was the dominant factor determining pyrene dissipation compared with total microbial diversity. Moreover, co-occurrence network analysis revealed that diverse keystone taxa may drive pyrene dissipation via more positive interactions between keystone species and with other species in soil. Taken together, these findings provide new insights on the regulation of keystone taxa diversity to promote the dissipation of PAH in soil.

Amendments and bioaugmentation enhanced phytoremediation and micro-ecology for PAHs and heavy metals co-contaminated soils

Co-existence of polycyclic aromatic hydrocarbons (PAHs) and multi-metals challenges the decontamination of large-scale contaminated sites. This study aims to comprehensively evaluate the remediation potential of intensified phytoremediation in coping with complex co-contaminated soils. Results showed that the removal of PAHs and heavy metals is time-dependent, pollution-relevant, and plant-specific. Removal of sixteen PAHs by Medicago sativa L. (37.3%) was significantly higher than that of Solanum nigrum L. (20.7%) after 30 days. S. nigrum L. removed higher amounts of Cd than Zn and Pb, while M. sativa L. uptake more Zn. Nevertheless, amendments and microbial agents significantly increased the phytoremediation efficiency of pollutants and shortened the gap between plants. Cd removal and PAHs dissipation reached up to 80% and 90% after 90 days for both plants. Heavy metal stability in soil was promoted after the intensified phytoremediation. Plant lipid peroxidation was alleviated, regulated by changed antioxidant defense systems (superoxide dismutase, peroxidase, catalase). Soil enzyme activities including dehydrogenase, urease, and catalase increased up to 5-fold. Soil bacterial diversity and structure were changed, being largely composed of Proteobacteria, Actinobacteria, Patescibacteria, Bacteroidetes, and Firmicutes. These findings provide a green and sustainable approach to decontaminating complex-polluted environments with comprehensive improvement of soil health.

Bioremediation of polycyclic aromatic hydrocarbons from an aged contaminated agricultural soil using degrading bacteria and soil amendments

The combined effects of degrading bacteria (Paracoccus sp. LXC), humic acid (HA), and soil amendments, including chicken manure, biochar, and wormcast, were investigated through 84 d of incubation in order to improve the remediation of polycyclic aromatic hydrocarbon (PAH) in aged contaminated agricultural soil. PAH concentrations and dissipation kinetics were analyzed, and the biomass and communities of microorganisms and soil enzyme activities were examined to clarify the possible mechanism. The highest removal efficiency of PAHs was 42.1% when treated with Paracoccus sp. LXC combined with biochar and HA. PAH dissipation was consistent with the first-order kinetics model and the half-life of PAHs decreased from 2323.3 d in the natural attenuation to 103–277 d in the amended microcosms. Soil amendments and HA promoted the development of PAH-degrading bacteria and diversity of bacterial communities in soil but not that of fungi. The removal efficiency of PAHs was positively correlated with the density of PAH-degrading bacteria and soil urease (Ure), dehydrogenase (Deh), and manganese-dependent peroxidase (Mnp) activities (r = 0.824–0.941, p < .01). The Paracoccus sp. LXC apparently removed 2–4-ring PAHs, and biochar and wormcast were effective in removing 2–4-ring and 5–6-ring PAHs, respectively. The combined bioremediation strategy using degrading bacteria with soil amendments and HA has high potential for PAH removal in aged contaminated agricultural soil and the possible mechanism was the combination of bioaugmentation with Paracoccus sp. LXC and biostimulation with HA and soil amendments.

Soil bacterial diversity and functionality are driven by plant species for enhancing polycyclic aromatic hydrocarbons dissipation in soils

Plant-microorganisms symbiosis has been widely used in developing strategies for the rhizoremediation of polycyclic aromatic hydrocarbon (PAHs) contaminated agricultural soils. However, understanding the potential mechanisms for using complex plant-microbe interactions to enhance rhizoremediation in contaminated soils is still limited. In this study, rhizosphere microbiomes were established by cultivating four types of cover crops for 15 months in a PAHs-contaminated field. The results showed that the PAHs removal rates were significantly higher in rhizosphere soils (55.2–82.3%) than the bare soils (20.5%). Of the four cover crops, the rhizosphere soils associated with the alfalfa and clover had higher removal rates for high molecular weight (HMW) PAHs (78.5–87.1%) than the grasses (39.0–46.2%). High-throughput sequencing analysis showed that bacterial community structure between the planted and bare soils, and among four cover crops rhizosphere soils were significantly different. The rhizosphere soils associated with the alfalfa and clover had more abundant degradation-related taxa. Correlation network analysis showed that bacterial communities with high removal rates have stronger interactions. Metagenome analysis indicated that the relative abundance of the key functional genes involved in PAHs degradation and nutrient metabolisms were significantly higher in rhizosphere soils, especially for alfalfa and clover. Overall, this study provides new insights for us to understand the mechanisms by different plants enhancing PAHs dissipation from the viewpoint of microbiology.

Assessment of degradation potential of Pseudomonas species in bioremediating soils contaminated with petroleum hydrocarbons

AbstractBACKGROUNDThe bioremediation versatility of soil indigenous microbial community for the degradation of oil contaminated soils has been evidenced previously. In this study, three dominant bacterial strains, Pseudomonas putida (P. putida) and two Pseudomonas aeruginosa (P. aeruginosa) (accession numbers ATCC‐27853, BAA‐427, and ATCC‐49128), were isolated from three different oil‐contaminated sites to evaluate their bioremediation potential. Degradation potential was determined against two compounds, naphthalene and pyrene, from polycyclic aromatic hydrocarbons (PAHs) in batch experiment.RESULTSThe bacterial strains were effective in degrading naphthalene and pyrene. Further, the degradation potential of these compounds was correlated with total organic carbon (TOC). Among the bacterial strains, P. putida (accession number ATCC‐27853) effectively degraded naphthalene and pyrene by 92% and 83%, respectively. The other bacterial strain, P. aeruginosa (ATCC‐27853), equally degraded the naphthalene (83.6%) but differed considerably for pyrene, with the lowest removal efficiency of 24.2% at 3 ppm. Growth profiles of the proposed bacterial strains, P. putida (accession number ATCC‐27853), P. aeruginosa (accession number BAA‐427), and P. aeruginosa, ATCC‐49128), revalidated through colony‐forming unit (CFU·mL−1). P. putida showed the highest cell count 5.06 × 108 (CFU·mL−1) for naphthalene.CONCLUSIONThis study highlights that isolated Pseudomonas strains showed the highest degrading activity for naphthalene and pyrene‐degrading without the addition of any chemical or co‐substrate within a short interval. Overall, findings indicate that inoculation of the bacterial strains belonging to Pseudomonas species can stimulate low and high weight PAH compounds degradation and maintain the bacterial biomass, thus accelerating the dissipation of soil PAHs. It further provides evidence for perspectives on the potential of bacterial community assembly of PAH‐contaminated soils. © 2021 Society of Chemical Industry (SCI).