Hydroponic approach to assess rhizodegradation by sudangrass (Sorghum x drummondii) reveals pH- and plant age-dependent variability in bacterial degradation of polycyclic aromatic hydrocarbons (PAHs)

Patterns of PAH distribution in karst sinkhole soils (Polar Urals)

This work was the first comprehensive study of polycyclic aromatic hydrocarbons (PAHs) accumulation in soils of karst sinkholes and in background soils of the Polar Urals. Principal component analysis and cluster analysis were used to assess the distribution patterns of PAHs. PAH concentrations were measured in 53 soil samples collected from plant communities of two habitat types: dryad-green moss-lichen tundra and herb-grass meadow. We found karst processes influenced contents of PAHs, especially in the deepest sinkholes where the increased PAH contents were mainly due to surface erosion. The shifted peaks of PAH accumulation along the soil profile were found at the slopes of sinkholes. This was possibly due to more active PAH migration and stratification of soil horizons. We also identified the relationship between accumulation of PAHs and species composition of plant communities. PCA analysis showed relationships between soil PAHs, organic carbon and organic nitrogen that were explained mainly by the formation of PAHs from high molecular weight organic substances, humic acids and lignin. Paleocoals also affected the PAH contents in soils. Calculated diagnostic ratios of PAHs indicated their pedogenic origin.

Enhancing emerging pollutant removal mediated by root iron plaques: Integrated abiotic and biotic effects

As a contact interface among plants, microbes, and the liquid phase, root iron plaque (IP) occupies a crucial ecological niche on the root surface in constructed wetlands. However, research on the integrated work mechanisms of the various processes mediated by root IP in removing emerging pollutants is limited. This study analyzed four IP-mediated pathways in plant hydroponic systems, categorizing them into abiotic (adsorption and ·OH oxidation) and biotic (plant uptake and microbial degradation) effects. Employing sulfamethoxazole (SMX) as a target emerging pollutant, the results revealed that root IP improved pollutant removal efficiency by 2.44 times, which could be attributed to the enhanced abiotic effects. Root IP increased the amount of adsorbed SMX from 0.135 to 1.328 µg/g FW. Fe2 + in root IP could activate O2 to generate adsorbed hydroxyl radicals (·OH), which subsequently facilitate the oxidative removal of adsorbed SMX. The contribution of ·OH oxidation to SMX removal reached 27.35 %. However, from the biotic perspective, the stable adsorbed SMX was difficult to transport into plant root tissues, and root IP served as a "barrier" that hindered the plant uptake. In addition, IP weakened biotic effects by altering root-associated microbial community. The total relative abundance of SMX degradation-related genera decreased by 12.4 % with root IP, and the amounts of microbial degradation decreased from 8.33 to 3.49 µg/L.

Lignin-derived compounds assisted with Kocuria marina H-2 and Pseudomonas putida B6-2 co-culture enhanced naphthalene biodegradation

The implementation of environmentally friendly and sustainable remediation strategies positively impacts solid waste management. In this study, the Kocuria marina H-2 and Pseudomonas putida B6-2 co-culture system demonstrated enhanced naphthalene biodegradation efficiency compared to single-strain cultures. Under optimal conditions of 35 °C, 200 rpm/min, and a 1:1 ratio of the co-culture system, the naphthalene biodegradation potential was further increased. Notably, the addition of both ethylenediamine-pretreated lignin and p-hydroxybenzoic acid significantly elevated naphthalene degradation rates to 68.5 %. In addition, the oil-liquid surface tension decreased, while cell surface hydrophobicity and colony-forming units increased with the addition of lignin-derived compounds. The modification of naphthalene bioavailability by ethylenediamine-pretreated lignin would accelerate the uptake and transport of hydrocarbons via ABC transporters and flagellar assembly. Importantly, genes related to bacterial chemotaxis and fatty acid biosynthesis were upregulated during the co-metabolism of naphthalene and p-hydroxybenzoic acid, further enhancing naphthalene bioconversion.

Assessing the ecological impacts of polycyclic aromatic hydrocarbons petroleum pollutants using a network toxicity model

Polycyclic aromatic hydrocarbons (PAHs) are significant petroleum pollutants that have long-term impacts on human health and ecosystems. However, assessing their toxicity presents challenges due to factors such as cost, time, and the need for comprehensive multi-component analysis methods. In this study, we utilized network toxicity models, enrichment analysis, and molecular docking to analyze the toxicity mechanisms of PAHs at different levels: compounds, target genes, pathways, and species. Additionally, we used the maximum acceptable concentration (MAC) value and risk quotient (RQ) as an indicator for the potential ecological risk assessment of PAHs. The results showed that higher molecular weight PAHs had increased lipophilicity and higher toxicity. Benzo[a]pyrene and Fluoranthene were identified as core compounds, which increased the risk of cancer by affecting core target genes such as CCND1 in the human body, thereby influencing signal transduction and the immune system. In terms of biological species, PAHs had a greater toxic impact on aquatic organisms compared to terrestrial organisms. High molecular weight PAHs had lower effective concentrations on biological species, and the ecological risk was higher in the Yellow River Delta region. This research highlights the potential application of network toxicity models in understanding the toxicity mechanisms and species toxicity of PAHs and provides valuable insights for monitoring, prevention, and ecological risk assessment of these pollutants.

Release of dissolved organic matter from wetland plants and its interaction with polycyclic aromatic hydrocarbons

Dissolved organic matter (DOM) derived from wetland plants played a critical role in CWs pollutant migration. This study investigated the character and release pattern of DOM derived from two wetland plants, Phragmites australis and Cladophora sp., and the interaction between DOM with phenanthrene (PHE), benzo(a)pyrene (Bap), and benzo [k]fluoranthene (BkF) under different physical conditions were also studied using spectroscopic techniques. DOM release was related to plant species and withering stage. Humic acid (HA)-like fractions (C3 and C5) were dominated in P. australis (52%) and completely withered Cladophora sp. groups (55%), while protein-like fractions (C1 and C2) dominated in early withered Cladophora sp. groups (52%). Due to the cell and tissue structure difference among plants and their withering stage, DOM derived from early withered P. australis revealed a two-stage slow-fast phase, while other groups were linearly released (R2 0.87207-0.97091). A strong correlation existed between HA-like fractions and water quality index, reflecting the critical influence of plant decay in CWs operation performance. The analysis with Stern-Volmer equation indicated that plant-based DOM interacted with PAHs to form ground state complexes with possible involvement of π-π interaction, hydrogen bonding and cation bridging effect. Aromatic, molecular weight, and hydrophilicity of both DOM and PAHs affected their binding with the interaction capability in the order of BKF > Bap > PHE and C3 > C5 > C2 > C1 > C4. Besides, alkaline environment and high DO condition was highly unsuitable for the combination. Scientific management and appropriate operating condition were important in optimizing operation performance and controlling pollutant migration in CWs.

Mangroves leaves phyllosphere bacteria community and its ability to survive under pyrene stress during the acclimation process

Plants in general and mangroves in particular can harbor hyper-diverse microorganisms in their different compartments including the phyllosphere area. This study used the leaves of three mangrove species; black mangrove (Avicenia germinans), red mangrove (Rhizophora mangle) and mangrove apple (Sonneratia alba) in order to evaluate the phyllosphere epiphytic bacterial community on their leaves surface and assess the ability of some epiphytic bacteria to tolerate and survive under pyrene stress. Through the 16S rRNA genes sequencing, 380203, 405203 and 344863 OTUs were identified respectively in the leaves of mangroves apple, black and red mangroves. The identified OTUs was positively correlated with leaves-wax (p < 0.05, r² = 0.904), nitrogen (r² = 0.72), phosphorus content (r² = 0.62) and the water factor (r² = 0.93). It was however highly and negatively correlated with the canopy cover (r² = 0.93). The pyrene degradation rate in the mineral salt medium (MSM) containing pyrene as external stress was different in each mangrove species and varied depending on various factors. Therefore, through the succession culture in MSM, several bacteria strain belonging to Rhizobiales and Enterobacteres were found to be abundant in red mangroves. Bacteria belonging to Bacilliales and Sphingobacteriales were more abundant in mangroves apples and bacteria from Xanthomonadales and Sphingomonadales were more presents in back mangroves. The important finding was to reveal that the black mangrove at the non-submerged substrate, recorded the highest number of OTU, coinciding with its highest leaf's nitrogen and phosphorus content and most importantly, its highest rate of pyrene degradation. The general result of this study join previous research results and get place in the mangrove agenda, as part of a better understanding insight into the role of plant identity in driving the phyllosphere epiphytic microbial community structures in mangrove ecosystems.

A comprehensive review of recent research concerning the role of low molecular weight organic acids on the fate of organic pollutants in soil

Plants exude through the roots different compounds, including, among others, low-molecular weight organic acids (LMWOAs), with a relevant effect on multiple metabolic activities. Numerous studies have revealed their role in improving soil mineral acquisition and tolerance against inorganic pollutants. However, less information is available on how they may alter the fate of organic pollutants in soil, which may cause environmental problems, compromise soil quality and have a detrimental effect on animal and human health. This review intends to cover recent studies (from 2015 onwards) and provide up-to-date information on how LMWOAs influence environmental key processes of organic pollutants in soil, like adsorption/desorption, degradation and transport, without forgetting plant uptake, with obvious environmental and health repercussions. Critical knowledge gaps and future research needs are also discussed, because understanding these processes will help searching effective strategies for pollutant reduction and control in soil.

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

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

Plant Growth-Promoting Bacteria (PGPB) integrated phytotechnology: A sustainable approach for remediation of marginal lands

Land that has little to no utility for agriculture or industry is considered marginal land. This kind of terrain is frequently found on the edge of deserts or other arid regions. The amount of land that can be used for agriculture continues to be constrained by increasing desertification, which is being caused by climate change and the deterioration of agriculturally marginal areas. Plants and associated microorganisms are used to remediate and enhance the soil quality of marginal land. They represent a low-cost and usually long-term solution for restoring soil fertility. Among various phytoremediation processes (viz., phytodegradation, phytoextraction, phytostabilization, phytovolatilization, phytofiltration, phytostimulation, and phytodesalination), the employment of a specific mechanism is determined by the state of the soil, the presence and concentration of contaminants, and the plant species involved. This review focuses on the key economically important plants used for phytoremediation, as well as the challenges to plant growth and phytoremediation capability with emphasis on the advantages and limits of plant growth in marginal land soil. Plant growth-promoting bacteria (PGPB) boost plant development and promote soil bioremediation by secreting a variety of metabolites and hormones, through nitrogen fixation, and by increasing other nutrients' bioavailability through mineral solubilization. This review also emphasizes the role of PGPB under different abiotic stresses, including heavy-metal-contaminated land, high salinity environments, and organic contaminants. In our opinion, the improved soil fertility of marginal lands using PGPB with economically significant plants (e.g., Miscanthus) in dual precession technology will result in the reclamation of general agriculture as well as the restoration of native vegetation.

Marine Snow Aggregates are Enriched in Polycyclic Aromatic Hydrocarbons (PAHs) in Oil Contaminated Waters: Insights from a Mesocosm Study

Marine snow was implicated in the transport of oil to the seafloor during the Deepwater Horizon oil spill, but the exact processes remain controversial. In this study, we investigated the concentrations and distributions of the 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs) in marine snow aggregates collected during a mesocosm experiment. Seawater only, oil in a water accommodated fraction (WAF), and Corexit-enhanced WAF (DCEWAF) were incubated for 16 d. Both WAF and DCEWAF aggregates were enriched in heavy molecular weight PAHs but depleted in naphthalene. DCEWAF aggregates had 2.6 times more total 16 PAHs than the WAF (20.5 vs. 7.8 µg/g). Aggregates in the WAF and DCEWAF incorporated 4.4% and 19.3%, respectively of the total PAHs in the mesocosm tanks. Our results revealed that marine snow sorbed and scavenged heavy molecular weight PAHs in the water column and the application of Corexit enhanced the incorporation of PAHs into the sinking aggregates.

Potential of Biosurfactants’ Production on Degrading Heavy Oil by Bacterial Consortia Obtained from Tsunami-Induced Oil-Spilled Beach Areas in Miyagi, Japan

Bioremediation is one of the promising environment-friendly approaches to eliminate oil contamination. However, heavy oil is known to degrade slowly due to its hydrophobicity. Therefore, microorganisms capable of producing biosurfactants are gaining substantial interest because of their potential to alter hydrocarbon properties and thereby speed up the degradation process. In this study, six bacterial consortia were obtained from the oil-spilled beach areas in Miyagi, Japan, and all of which exhibited high potential in degrading heavy oil measured by gas chromatography with flame ionization detector (GC-FID). The polymerase chain reaction—denaturing gradient gel electrophoresis (PCR-DGGE) and next-generation sequencing (NGS) revealed that the diverse microbial community in each consortium changed with subculture and became stable with a few effective microorganisms after 15 generations. The total petroleum hydrocarbons (TPH) degradation ability of the consortia obtained from a former gas station (C1: 81%) and oil refinery company (C6: 79%) was higher than that of the consortia obtained from wastewater treatment plant (WWTP) (C3: 67%, and C5: 73%), indicating that bacteria present in C1 and C6 were historically exposed to petroleum hydrocarbons. Moreover, it was intriguing that the consortium C4, also obtained from WWTP, exhibited high TPH degradation ability (77%). The NGS results revealed that two bacteria, Achromobacter sp. and Ochrobactrum sp., occupied more than 99% of the consortium C4, while no Pseudomonas sp. was found in C4, though this bacterium was observed in other consortia and is also known to be a potential candidate for TPH degradation as reported by previous studies. In addition, the consortium C4 showed high biosurfactant-producing ability among the studied consortia. To date, no study has reported the TPH degradation by the combination of Achromobacter sp. and Ochrobactrum sp.; therefore, the consortium C4 provided an excellent opportunity to study the interaction of and biosurfactant production by these two bacteria during TPH degradation.