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

Increased phenanthrene toxicity to Eisenia fetida upon co-exposure to o-xylene

Polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene, and xylene (BTEX) compounds are often found in contaminated soil and have been shown to be toxic to the ecosystem, but their combined environmental risks and ecological effects remain poorly understood. Herein, Eisenia fetida was exposed to phenanthrene (PHE) and o-xylene (OX) in artificial soil to assess their toxic effects (including mortality, reproduction, antioxidant enzyme activities, and malondialdehyde levels) and bioaccumulation. The 48 h LC50 values for single contaminated PHE and OX were 71.6 and 121 mg kg-1, respectively, while 28 day EC50 values for reproduction were 4.73 and 5.20 mg kg-1, respectively. Co-exposure to PHE and OX intensified toxicity, reducing fecundity by over 15% compared to exposure to PHE alone. The synergistic effect was confirmed via a mathematical model based on probabilities. Furthermore, distinct biomarker responses were found between earthworms exposed to PHE and OX, implying different toxic mechanisms. However, similar biomarker responses were detected in earthworms exposed to PHE and combined treatments, suggesting the predominant role of PHE in the combined toxicity. In the combined treatments, OX exhibited a catalyst-like effect, enhancing the accumulation and toxicity of PHE in earthworms. These findings highlight the importance of accounting for the combined effects of pollutants when assessing the ecological risks of co-contaminated soils.

Enhancing the efficiency of P-SMFCs in degrading phenanthrene by modifying the anode with carbon nanomaterials

In plant-sediment microbial fuel cells (P-SMFCs), the anode serves as the primary site for biochemical reactions. In this study, different carbon nanomaterials (graphenes (GNs), carbon nanotubes (CNT), hydroxylated-carbon nanotubes (CNT-OH), and carboxylated-carbon nanotubes (CNT-COOH)) were used to modify the anode of the P-SMFCs to explore the enhancement of phenanthrene (Phe) degradation. The devices were operated for 131 days, CNT-COOH-modified P-SMFCs (P-CNT-COOH) exhibited a shorter start-up period and higher voltage during the stable operation stage. The voltage of P-CNT-COOH during the stationary phase was approximately 250 mV higher than that of the control device. The voltage and Phe removal of P-CNT-COOH were higher than those of CNT-COOH (without plants in the SMFC), which achieved 67.5% Phe removal, which was 1.25 times higher than the P-CNT, whereas CNT (without plants in the SMFC) showed higher performance than P-CNT. The anode modified with P-CNT-COOH became enriched with small-molecule volatile fatty acids (VFAs) (e.g., acetic acid) and degrading bacteria (e.g., Thiobacillus and Desulfobulbus) attributed to the higher hydrophilicity. The removal of Phe was positively correlated with dehydrogenase activity (DHAA).

Diverse adaptation strategies of generalists and specialists to metal and salinity stress in the coastal sediments

Understanding the distinct roles and responses of bacterial community to environmental stressors is crucial for effective ecosystem management and conservation. Despite this, there is limited research on how environmental gradients specifically impact generalist and specialist subcommunities. This study investigates these subcommunities in the sediments of Jinzhou Bay, highlighting their distinct responses to environmental gradients. Generalists thrive in disturbed environments due to their broad ecological tolerances, while specialists show higher diversity in the stable, less contaminated upstream areas. At the genus level, Porphyrobacter and Subgroup_23 were identified as the dominant taxa of generalists, while Woeseia and Lutibacter were the dominant species of specialists. Physicochemical parameters, especially metals and salinity, significantly influence subcommunity composition. Generalists are adaptable to a wider range of factors, whereas specialists are affected by specific parameters, reflecting their narrower niches. The generalists exhibit a greater abundance of salinity tolerance genes compared to the specialists; however, this trend does not extend to metal resistance genes. Keystone taxa, primarily specialists, play crucial roles in maintaining community stability. Our results underscore the importance of considering both generalists and specialists in ecological assessments, offering insights for the management and conservation of bacterial microbial diversity in coastal ecosystems.

Insights into the characteristics of changes in dissolved organic matter fluorescence components on the natural attenuation process of toluene

Natural attenuation (NA) is of great significance for the remediation of contaminated groundwater, and how to identify NA patterns of toluene in aquifers more quickly and effectively poses an urgent challenge. In this study, the NA of toluene in two typical soils was conducted by means of soil column experiment. Based on column experiments, dissolved organic matter (DOM) was rapidly identified using fluorescence spectroscopy, and the relationship between DOM and the NA of toluene was established through structural equation modeling analysis. The adsorption rates of toluene in clay and sandy soil were 39 % and 26 %, respectively. The adsorption capacity and total NA capacity of silty clay were large. The occurrence of fluorescence peaks of protein-like components and specific products indicated the occurrence of biodegradation. Arenimonas, Acidovorax and Brevundimonas were the main degrading bacteria identified in Column A, while Pseudomonas, Azotobacter and Mycobacterium were the main ones identified in Column B. The pH, ORP, and Fe(II) were the most important factors affecting the composition of microbial communities, which in turn affected the NA of toluene. These results provide a new way to quickly identify NA of toluene.

Review on biochar as a sustainable green resource for the rehabilitation of petroleum hydrocarbon-contaminated soil

Petroleum pollution is one of the primary threats to the environment and public health. Therefore, it is essential to create new strategies and enhance current ones. The process of biological reclamation, which utilizes a biological agent to eliminate harmful substances from polluted soil, has drawn much interest. Biochars are inexpensive, environmentally beneficial carbon compounds extensively employed to remove petroleum hydrocarbons from the environment. Biochar has demonstrated an excellent capability to remediate soil pollutants because of its abundant supply of the required raw materials, sustainability, affordability, high efficacy, substantial specific surface area, and desired physical-chemical surface characteristics. This paper reviews biochar's methods, effectiveness, and possible toxic effects on the natural environment, amended biochar, and their integration with other remediating materials towards sustainable remediation of petroleum-polluted soil environments. Efforts are being undertaken to enhance the effectiveness of biochar in the hydrocarbon-based rehabilitation approach by altering its characteristics. Additionally, the adsorption, biodegradability, chemical breakdown, and regenerative facets of biochar amendment and combined usage culminated in augmenting the remedial effectiveness. Lastly, several shortcomings of the prevailing methods and prospective directions were provided to overcome the constraints in tailored biochar studies for long-term performance stability and ecological sustainability towards restoring petroleum hydrocarbon adultered soil environments.

Mechanistic and future prospects in rhizospheric engineering for agricultural contaminants removal, soil health restoration, and management of climate change stress

Climate change, food insecurity, and agricultural pollution are all serious challenges in the twenty-first century, impacting plant growth, soil quality, and food security. Innovative techniques are required to mitigate these negative outcomes. Toxic heavy metals (THMs), organic pollutants (OPs), and emerging contaminants (ECs), as well as other biotic and abiotic stressors, can all affect nutrient availability, plant metabolic pathways, agricultural productivity, and soil-fertility. Comprehending the interactions between root exudates, microorganisms, and modified biochar can aid in the fight against environmental problems such as the accumulation of pollutants and the stressful effects of climate change. Microbes can inhibit THMs uptake, degrade organic pollutants, releases biomolecules that regulate crop development under drought, salinity, pathogenic attack and other stresses. However, these microbial abilities are primarily demonstrated in research facilities rather than in contaminated or stressed habitats. Despite not being a perfect solution, biochar can remove THMs, OPs, and ECs from contaminated areas and reduce the impact of climate change on plants. We hypothesized that combining microorganisms with biochar to address the problems of contaminated soil and climate change stress would be effective in the field. Despite the fact that root exudates have the potential to attract selected microorganisms and biochar, there has been little attention paid to these areas, considering that this work addresses a critical knowledge gap of rhizospheric engineering mediated root exudates to foster microbial and biochar adaptation. Reducing the detrimental impacts of THMs, OPs, ECs, as well as abiotic and biotic stress, requires identifying the best root-associated microbes and biochar adaptation mechanisms.

Heat and mass transfer induced by alternating current during desorption of PAHs from soil using electrical resistance heating

The transfer of heat and contaminants by alternating current (AC) and the removal mechanism of polycyclic aromatic hydrocarbons (PAHs) in electrical resistance heating (ERH) need further study. The main factors affecting heat transfer and water evaporation in the ERH experiment were studied, and the desorption efficiency, temporal and spatial distribution and kinetic behavior under various conditions were analyzed. The results suggested that moisture content was a necessary condition to ensure effective heating of soil, and soil moisture content above 30% was recommended. Higher voltage intensity and/or ion concentration meant stronger input power, resulting in the rapider heating process and the shorter the boiling time. At a low desorption temperature (about 100°C), the Phe desorption mainly depended on the volatilization of surface Phe and the co-boiling of Phe-water. In ERH, the participation of AC would accelerate the diffusion of pollutants from the internal pores of soil particles and their redistribution with water phase, thus improving the Phe removed by co-boiling. It was noteworthy that AC just greatly promoted solid-liquid mass transfer, but it hardly promoted desorption directly, and the removal still depended on Phe-water co-boiling. The Phe desorption efficiency could be significantly improved from 14.0~18.4% to 59.6~70.8% under the combined action of current strengthening Phe diffusion and co-boiling. Thermogravimetric and product analysis confirmed that no new organic matter was generated, but only Phe entered the gas phase through phase change.

Effects of biochar on soil microbial communities: A meta-analysis

Changes in soil microbial communities may impact soil fertility and stability because microbial communities are key to soil functioning by supporting soil ecological quality and agricultural production. The effects of soil amendment with biochar on soil microbial communities are widely documented but studies highlighted a high degree of variability in their responses following biochar application. The multiple conditions under which they were conducted (experimental designs, application rates, soil types, biochar properties) make it difficult to identify general trends. This supports the need to better determine the conditions of biochar production and application that promote soil microbial communities. In this context, we performed the first ever meta-analysis of the biochar effects on soil microbial biomass and diversity (prokaryotes and fungi) based on high-throughput sequencing data. The majority of the 181 selected publications were conducted in China and evaluated the short-term impact (<3 months) of biochar. We demonstrated that a large panel of variables corresponding to biochar properties, soil characteristics, farming practices or experimental conditions, can affect the effects of biochar on soil microbial characteristics. Using a variance partitioning approach, we showed that responses of soil microbial biomass and prokaryotic diversity were highly dependent on biochar properties. They were influenced by pyrolysis temperature, biochar pH, application rate and feedstock type, as wood-derived biochars have particular physico-chemical properties (high C:N ratio, low nutrient content, large pores size) compared to non-wood-derived biochars. Fungal community data was more heterogenous and scarcer than prokaryote data (30 publications). Fungal diversity indices were rather dependent on soil properties: they were higher in medium-textured soils, with low pH but high soil organic carbon. Altogether, this meta-analysis illustrates the need for long-term field studies in European agricultural context for documenting responses of soil microbial communities to biochar application under diverse conditions combining biochar types, soil properties and conditions of use.

Enhanced trichloroethylene biodegradation: The mechanism and influencing factors of combining microorganism and carbon‑iron materials

Trichloroethylene (TCE) is one of the most prevalent contaminants with long-term persistence and a strong carcinogenic risk. Biological dechlorination has gradually become the mainstream method due to its advantages of low treatment cost and high environmental friendliness. However, microorganisms are easily restricted by environmental factors, such as an insufficient energy supply and a slow biological dechlorination process. This study focused on the coupled degradation of TCE with the combination of microorganisms and assistant materials (biochar, nZVI, nZVI modified biochar, HPO₃ modified biochar), and set up microorganisms (alone) and materials (alone) as separate controls. Biochar provided nutrients, increased contact with pollutants, and promoted electron transfer to improve TCE degradation, although it did not change the pathway of degradation. The coupled treatment with anaerobic microorganisms (Micro) and 1 g/L unmodified biochar (BC) had the strongest degradation capacity. Compared with microorganisms alone, the addition of biochar resulted in the complete removal of TCE within 4 days. The influence of ambient temperature was mainly related to microbial activity, and 35 °C showed better degradation than 20 °C. Under 20 °C, 1 g/L of nZVI significantly promoted microbial dechlorination. As the dosage increased to 2 g/L and 4 g/L, nZVI showed a strong toxic effect. After 16 days, TCE was completely converted to ethylene by Micro-BC with C₃H₅O₃Na, while 4.40 μmol dichloroethane (DCE) and 1.48 μmol vinyl chloride (VC) remained in the treatment with Micro-BC alone. As an electron acceptor, NaNO₃ directly competed with TCE in the reduction process, which decreased the reduction efficiency of TCE. These findings provide a better understanding of the mechanism of the chemical materials coupling microbial dechlorination process and an optimal treatment method for trichloroethylene degradation.

Enhanced remediation of oil-contaminated intertidal sediment by bacterial consortium of petroleum degraders and biosurfactant producers

Oil pollution in intertidal zones is an important environmental issue that has serious adverse effects on coastal ecosystems. This study investigated the efficacy of a bacterial consortium constructed from petroleum degraders and biosurfactant producers in the bioremediation of oil-polluted sediment. Inoculation of the constructed consortium significantly enhanced the removal of C₈-C₄₀n-alkanes (80.2 ± 2.8% removal efficiency) and aromatic compounds (34.4 ± 10.8% removal efficiency) within 10 weeks. The consortium played dual functions of petroleum degradation and biosurfactant production, greatly improving microbial growth and metabolic activities. Real-time quantitative polymerase chain reaction (PCR) showed that the consortium markedly increased the proportions of indigenous alkane-degrading populations (up to 3.88-times higher than that of the control treatment). Microbial community analysis demonstrated that the exogenous consortium activated the degradation functions of indigenous microflora and promoted synergistic cooperation among microorganisms. Our findings indicated that supplementation of a bacterial consortium of petroleum degraders and biosurfactant producers is a promising bioremediation strategy for oil-polluted sediments.

Root microbiome diversity and structure of the Sonoran desert buffelgrass (Pennisetum ciliare L.)

Buffelgrass (Pennisetum ciliare) is an invasive plant introduced into Mexico's Sonoran desert for cattle grazing and has converted large areas of native thorn scrub. One of the invasion mechanisms buffelgrass uses to invade is allelopathy, which consists of the production and secretion of allelochemicals that exert adverse effects on other plants' growth. The plant microbiome also plays a vital role in establishing invasive plants and host growth and development. However, little is known about the buffelgrass root-associated bacteria and the effects of allelochemicals on the microbiome. We used 16S rRNA gene amplicon sequencing to obtain the microbiome of buffelgrass and compare it between samples treated with root exacknudates and aqueous leachates as allelochemical exposure and samples without allelopathic exposure in two different periods. The Shannon diversity values were between H' = 5.1811-5.5709, with 2,164 reported bacterial Amplicon Sequence Variants (ASVs). A total of 24 phyla were found in the buffelgrass microbiome, predominantly Actinobacteria, Proteobacteria, and Acidobacteria. At the genus level, 30 different genera comprised the buffelgrass core microbiome. Our results show that buffelgrass recruits microorganisms capable of thriving under allelochemical conditions and may be able to metabolize them (e.g., Planctomicrobium, Aurantimonas, and Tellurimicrobium). We also found that the community composition of the microbiome changes depending on the developmental state of buffelgrass (p = 0.0366; ANOSIM). These findings provide new insights into the role of the microbiome in the establishment of invasive plant species and offer potential targets for developing strategies to control buffelgrass invasion.

The co-application of biochar with bioremediation for the removal of petroleum hydrocarbons from contaminated soil

Soil pollution from petroleum hydrocarbon is a global environmental problem that could contribute to the non-actualisation of the United Nations Sustainable Development Goals. Several techniques have been used to remediate petroleum hydrocarbon-contaminated soils; however, there are technical and economical limitations to existing methods. As such, the development of new approaches and the improvement of existing techniques are imperative. Biochar, a low-cost carbonaceous product of the thermal decomposition of waste biomass has gained relevance in soil remediation. Biochar has been applied to remediate hydrocarbon-contaminated soils, with positive and negative results reported. Consequently, attempts have been made to improve the performance of biochar in the hydrocarbon-based remediation process through the co-application of biochar with other bioremediation techniques as well as modifying biochar properties before use. Despite the progress made in this domain, there is a lack of a detailed single review consolidating the critical findings, new developments, and challenges in biochar-based remediation of petroleum hydrocarbon-contaminated soil. This review assessed the potential of biochar co-application with other well-known bioremediation techniques such as bioaugmentation, phytoremediation, and biostimulation. Additionally, the benefits of modification in enhancing biochar suitability for bioremediation were examined. It was concluded that biochar co-application generally resulted in higher hydrocarbon removal than sole biochar treatment, with up to a 4-fold higher removal observed in some cases. However, most of the biochar co-applied treatments did not result in hydrocarbon removal that was greater than the additive effects of individual treatment. Overall, compared to their complementary treatments, biochar co-application with bioaugmentation was more beneficial in hydrocarbon removal than biochar co-application with either phytoremediation or biostimulation. Future studies should integrate the ecotoxicological and cost implications of biochar co-application for a viable remediation process. Lastly, improving the synergistic interactions of co-treatment on hydrocarbon removal is critical to capturing the full potential of biochar-based remediation.

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.

Removal pathway quantification and co-metabolic mechanism evaluation of alkylphenols from synthetic wastewater by phenolic root exudates in the rhizosphere of Phragmites australis

Phenolic root exudates (PREs) released from wetland plants are potentially effective for accelerating the biodegradation of alkylphenols, yet the inherent behavior is still unclear. In this study, two representative root exudates (REs), namely p-coumaric acid (PREs) and oxalic acid (non-PREs) were exogenously added as specific and non-specific co-metabolic substrates, respectively, to elucidate the quantification of each removal pathway and degradation mechanism of co-metabolism for alkylphenols (i.e. p-tert-butylphenol (PTBP)) from synthetic wastewater. The results showed that soil adsorption (31-37%), microbial degradation (27-37%), and plant uptake (16-41%) are the main removal pathways of PTBP by PREs in the Phragmites australis rhizosphere. Both REs enriched anaerobic functional community (anaerobic ammonium oxidation bacteria and denitrifying bacteria) and promoted the usage of PTBP as carbon source and/or electron donor. The activity of non-specific enzyme (polyphenol oxidase) was enhanced by RE which owning a significant positive correlation with bacterial abundance, whereas only PREs strengthened the activity of specific enzyme (monophenol oxidase) catalyzing the phenolic ring hydroxylation of PTBP followed by a dehydrogenation route. Moreover, exogenous PREs significantly improved the growth of degrading-related bacteria (Sphingomonas and Gemmatimonas), especially in unplanted soils with high activity of dioxygenase catalyzing the cleavage pathway of PTBP, instead of plant presence.

Impacts of bio-stimulants on pyrene degradation, prokaryotic community compositions, and functions

Bio-stimulation of the indigenous microbial community is considered as an effective strategy for the bioremediation of polluted environments. This examination explored the near effects of various bio-stimulants on pyrene degradation, prokaryotic community compositions, and functions using 16S rRNA amplicon sequencing and qPCR. At first, the results displayed significant differences (p < 0.05) between the prokaryotic community structures of the control group, PYR (contains pyrene only), and bio-stimulants amended groups. Among the bio-stimulants, biochar, oxalic acid, salicylate, NPK, and ammonium sulfate augmented the pyrene degradation potential of microbial communities. Moreover, the higher abundance of genera, such as Flavobacterium, Hydrogenophaga, Mycobacterium, Rhodococcus, Flavihumibacter, Pseudomonas, Novosphingobium, etc., across the treatments indicated that these genera play a vital role in pyrene metabolism. Based on the higher abundance of GP-RHD and nidA genes, we speculated that Gram-positive prokaryotic communities are more competent in pyrene dissipation than Gram-negative. Furthermore, the marked abundance of nifH, and pqqC genes in the NPK and SA treatments, respectively, suggested that different bio-stimulants might enrich certain bacterial assemblages. Besides, the significant distinctions (p < 0.05) between the bacterial consortia of HA (humic acid) and SA (sodium acetate) groups from NPK, OX (oxalic acid), UR (urea), NH4, and SC (salicylate) groups also suggested that different bio-stimulants might induce distinct ecological impacts influencing the succession of prokaryotic communities in distinct directions. This work provides new insight into the bacterial degradation of pyrene using the bio-stimulation technique. It suggests that it is equally important to investigate the community structure and functions along with studying their impacts on degradation when devising a bio-stimulation technology.

Enhanced trichloroethylene biodegradation: Roles of biochar-microbial collaboration beyond adsorption

Trichloroethylene (TCE) is a pollutant widely found in groundwater, especially in the heavily contaminated industrial sites. Biological dechlorination method is environmentally friendly and low-cost. However, microorganisms grow slowly and their activity is susceptible to environmental fluctuations. This study used biochar as an additive to promote anaerobic biodegradation of TCE with mixed culture. Results showed that biochar with dose of 0.1-0.4% (w/v) brought a rapid initial decrease of TCE concentration by 39.4-88.8% in 24 h via adsorption mechanism. Biochar produced at 500 °C pyrolysis temperature (BC500) achieved the highest TCE adsorption in comparison to BC300 and BC700. Subsequently, a significantly shortened microbial stagnation phase (from 85 h to 37 h) was observed in the system with the presence of biochar. During the exponential growth phase, BC700 outperformed BC300 and BC500 in terms of TCE degradation efficiency. Electrochemical analysis demonstrated that BC700 possessed the greatest electron transfer capability. Finally, biochar shortened the time for achieving 100% removal of TCE by 54.5-69.7% (from approximate 330 h to 100-150 h). Even at high concentration of TCE (20-30 mg·L^-1) that could lead to serious microbial growth inhibition, the TCE degradation efficiency could be recovered in the presence of BC500. The high-throughput sequencing data revealed that biochar promoted the relative abundance of co-metabolizing dechlorinating microorganisms (Pseudomonas, Burkholderia) in the aqueous solution, and simultaneously led to the selective colonization of reductive dechlorinating microorganisms (Enterobacteriaceae, Clostridium) attached on biochar surface. On the other hand, biochar addition decreased the relative abundance of hydrogen-competing microorganisms, thereby forming an efficient co-metabolism-reductive dechlorination system. These findings allow a better understanding of the promotion mechanism of biochar for microbial dechlorination technology supporting the biochar-assisted bioremediation in practice.

Toxic mechanism on phenanthrene-induced cytotoxicity, oxidative stress and activity changes of superoxide dismutase and catalase in earthworm (Eisenia foetida): A combined molecular and cellular study

Phenanthrene (PHE) is an important organic compound, which is widespread in the soil environment and exhibits potential threats to soil organisms. Toxic effects of PHE to earthworms have been extensively studied, but toxic mechanisms on PHE-induced cytotoxicity and oxidative stress at the molecular and cellular levels have not been reported yet. Therefore, we explored the cytotoxicity and oxidative stress caused by PHE in earthworm coelomocytes and the interaction mechanism between PHE and the major antioxidant enzymes SOD/CAT. It was shown that high-dose PHE exposure induced the intracellular reactive oxygen species (ROS) generation, mediated lipid peroxidation, reduced total antioxidant capacity (T-AOC) in coelomocytes, and triggered oxidative stress, thus resulted in a strong cytotoxicity at higher concentrations (0.6-1.0 mg/L). The intracellular SOD/CAT activity in cells after PHE exposure were congruent with that in molecular levels, which the activity of SOD enhanced and CAT inhibited. Spectroscopic studies showed the SOD/CAT protein skeleton and secondary structure, as well as the micro-environment of aromatic amino acids were changed after PHE binding. Molecular docking indicated PHE preferentially docked to the surface of SOD. However, the key residues Tyr 357, His 74, and Asn 147 for activity were in the binding pocket, indicating PHE more likely to dock to the active center of CAT. In addition, H-bonding and hydrophobic force were the primary driving force in the binding interaction between PHE and SOD/CAT. This study indicates that PHE can induce cytotoxicity and oxidative damage to coelomocytes and unearthes the potential effects of PHE on earthworms.

Can biochar be an effective and reliable biostimulating agent for the remediation of hydrocarbon-contaminated soils?

Petroleum hydrocarbons represent one of the most common soil contaminants, whose presence poses a significant risk to soil biota and human health; for example, in Europe, hydrocarbon contamination accounts for more than 30% of contaminated sites. The use of biochar as a proposed alternative to the conventional remediation of soil contaminated with petroleum hydrocarbons has gained credence in recent times because of its cost-effectiveness and environmentally friendly nature. Biochar is a carbonaceous material produced by heating biomass in an oxygen-limited environment at high temperature. This review provides an overview of the application of biochar to remediate petroleum hydrocarbon-contaminated soils, with emphasis on the possibility of biochar functioning as a biostimulation agent. The properties of biochar were also examined. Furthermore, the mechanism, ecotoxicological impact and possible factors affecting biochar-based remediation are discussed. The review concludes by examining the drawbacks of biochar use in the remediation of hydrocarbon-contaminated soils and how to mitigate them. Biochar impacts soil microbes, which may result in the promotion of the degradation of petroleum hydrocarbons in the soil. Linear regression between bacterial population and degradation efficiency showed that R² was higher (0.50) and significant in treatment amended with biochar or both biochar and nutrient/fertiliser (p < 0.01), compared to treatment with nutrient/fertiliser only or no amendment (R² = 0.11). This suggest that one of the key impacts of biochar is enhancing microbial biomass and thus the biodegradation of petroleum hydrocarbons. Biochar represents a promising biostimulation agent for the remediation of hydrocarbon-contaminated soil. However, there remains key questions to be answered.

Mitigation of petroleum-hydrocarbon-contaminated hazardous soils using organic amendments: A review

The term "Total petroleum hydrocarbons" (TPH) is used to describe a complex mixture of petroleum-based hydrocarbons primarily derived from crude oil. Those compounds are considered as persistent organic pollutants in the terrestrial environment. A wide array of organic amendments is increasingly used for the remediation of TPH-contaminated soils. Organic amendments not only supply a source of carbon and nutrients but also add exogenous beneficial microorganisms to enhance the TPH degradation rate, thereby improving the soil health. Two fundamental approaches can be contemplated within the context of remediation of TPH-contaminated soils using organic amendments: (i) enhanced TPH sorption to the exogenous organic matter (immobilization) as it reduces the bioavailability of the contaminants, and (ii) increasing the solubility of the contaminants by supplying desorbing agents (mobilization) for enhancing the subsequent biodegradation. Net immobilization and mobilization of TPH have both been observed following the application of organic amendments to contaminated soils. This review examines the mechanisms for the enhanced remediation of TPH-contaminated soils by organic amendments and discusses the influencing factors in relation to sequestration, bioavailability, and subsequent biodegradation of TPH in soils. The uncertainty of mechanisms for various organic amendments in TPH remediation processes remains a critical area of future research.

Root exuded low-molecular-weight organic acids affected the phenanthrene degrader differently: A multi-omics study

As a class of highly toxic and persistent organic pollutants, polycyclic aromatic hydrocarbons (PAHs) are an increasingly urgent environmental problem. Low-molecular-weight organic acids (LMWOAs) are important factors that regulate the degradation of PAHs by plant rhizosphere microorganisms, which affect the absorption of PAHs by plant roots. However, the comprehensive mechanisms by which LMWOAs influence the biodegradation of PAHs at cellular and omics levels are still unknown. Here, we systematically analyzed the roles of citric, glutaric and oxalic acid in the PAH-degradation process, and investigated the mechanisms through which these three LMWOAs enhance phenanthrene (PHE) biodegradation by B. subtilis ZL09-26. The results showed that LMWOAs can improve the solubility and biodegradation of PHE, enhance cell growth and activity, and relieve membrane and oxidative stress. Citric acid enhanced PHE biodegradation mainly by improving the strain's cell proliferation and activity, while glutaric and oxalic acid accelerated PHE biodegradation mainly by improving the expression of enzymes and providing energy for the cells of B. subtilis ZL09-26. This study provides new insights into rhizospheric bioremediation mechanisms, which may enable the development of new biostimulation techniques to improve the bioremediation of PAHs.

Effects of Fire Phoenix (a genotype mixture of Fesctuca arundinecea L.) and Mycobacterium sp. on the degradation of PAHs and bacterial community in soil

Phytomicrobial remediation technology of PAH-contaminated soils has drawn great attention due to its low-cost, eco-friendly, and effective characteristics, but the mechanism underlying the removal of PAHs by rhizosphere in wastewater-irrigated soil is so far not clear. To evaluate the dissipation of PAHs and the shifts of bacterial community structure under plant-microorganism symbiotic system in an agricultural soil, a rhizo-box experiment with Fire Phoenix (a genotype mixture of Fesctuca arundinecea L.) or/and inoculated Mycobacterium sp. was conducted for 60 days. The changes of bacterial community structure and the contents of PAHs were analyzed by denaturing gradient gel electrophoresis (DGGE) and high-performance liquid chromatography (HPLC), respectively. The results showed that the removal rate of PAHs in phytomicrobial combined treatment was 53.7% after 60 days. The PAH-degraders were dominated by Microbacterium sp., Sphingomonas sp., Mycobacterium sp., and Flavobacterium sp. The plant of Fire Phoenix induced the appearance of Pseudomonas sp. and TM7 phylum sp. oral clone. The highest of bacterial diversity index was observed in unrhizosphere soils (MR-), rather than that in rhizosphere soils (MR+). In combination, phytomicrobial combined treatment of Fire Phoenix and Mycobacterium strain enhanced the removal rate of PAHs and changed the structure of bacterial community and bacterial diversity. Bacterial community has great effect on PAH degradation in PAH-contaminated soil from the wastewater-irrigated site. Our study can provide support information for PAH degradation enhancement by the synergetic effect of Fire Phoenix and Mycobacterium sp.

Altered fungal communities in contaminated soils from French industrial brownfields

Polycyclic aromatic hydrocarbons (PAHs) and metals are contaminants of industrial brownfield soils. Pollutants can have harmful effects on fungi, which are major actors of soil functioning. Our objective was to highlight fungal selection following long-term contamination of soils. Fungal diversity was assessed on 30 top-soil samples from ten sites gathered in three groups with different contamination levels and physico-chemical characteristics: 1) uncontaminated controls, 2) slag heaps displaying high PAH and moderate metal contaminations, and 3) settling ponds displaying high metal and intermediate PAH contaminations. Although fungal abundance and richness were similar among the soil groups, the diversity and evenness indices were lower for the slag heap group. Fungal diversity differed among soil groups at the phylum and OTU levels, and indicator species were identified. The relative abundance of Agaricomycetes, Saccharomycetes, Leotiomycetes and Chytridiomycota was higher in the control soils than in the two groups of contaminated soils. Cryptomycota LKM11 representatives were favoured in the slag heap and settling pond groups, and their relative abundance was correlated to the zinc and lead contamination levels. Dothideomycetes - positively linked to PAH contamination - and Eurotiomycetes were specific to the slag heap group. Pucciniomycetes and especially Gymnosporangium members were favoured in the settling pond soils.

Assessment of Ecological Condition of Haplic Chernozem Calcic Contaminated with Petroleum Hydrocarbons during Application of Bioremediation Agents of Various Natures

Petroleum hydrocarbon contamination disrupts ecological and agricultural soil functions. For their restoration, bioremediation agents of various natures are used (nonorganic or organic fertilizers, bacterial preparations, adsorbing agents) featuring different remediation mechanisms (adsorption or biostimulation of petroleum hydrocarbon decomposition). The objective of this research is the assessment of the ecological condition of petroleum hydrocarbon-contaminated Haplic Chernozem Calcic after the application of bioremediation agents of various natures. The influence of glauconite, nitroammophos, sodium humate, the bacterial preparation “Baikal EM-1”, and biochar on the intensity of petroleum hydrocarbon decomposition and the ecological condition of Haplic Chernozem Calcic was analyzed. The ecological condition of Haplic Chernozem Calcic was assessed based on the residual content of petroleum hydrocarbons in soil and the following biological parameters: changes in the number of soil bacteria, activity of catalase and dehydrogenases, soil respiration (CO2 emission), germinating ability, lengths of roots and shoots, and integrated index of the biological state. The minimum concentrations of residual petroleum hydrocarbons in soil were observed after the use of biochar (44% from initial content) and glauconite (49%). The biological properties of soils were affected in different ways. Soil respiration was stimulated by 3-6-fold after adding nitroammophos. Indices for the intensity of the early growth and germination of radish in soil with glauconite, sodium humate, and biochar were increased by 37–125% (p < 0.01) compared with the reference value. After the application of biochar, sodium humate, and “Baikal EM-1”, the number of soil bacteria was 66–289% higher (p < 0.01) than the reference value. At the same time, the activities of catalase and dehydrogenases were inhibited by up to 35% in variants with bioremediation agents and petroleum hydrocarbons relative to the reference values. The maximum stimulation of the biological activity (as the integrated index of the biological state (IISB)) of Haplic Chernozem Calcic was observed after applying sodium humate and biochar, with 70 and 66% (p < 0.01) increases from the reference value, respectively. Considering the net cost of bioremediation agents, the maximum cost efficiency is achieved with “Baikal EM-1”, sodium humate, and biochar: 110, 527, and 847 USD·103/ha, respectively. After using Baikal EM-1”, sodium humate, and biochar, the ecological state of Haplic Chernozem Calcic was restored.

Structure-Bioactivity Relationship Study of Xanthene Derivatives: A Brief Review

Over the last decades, several heterocyclic derivatives compounds have been synthesized or extracted from natural resources and have been tested for their pharmaceutical activities. Xanthene is one of these heterocyclic derivatives. These compounds consist of an oxygen-containing central heterocyclic structure with two more cyclic structures fused to the central cyclic compound. It has been shown that xanthane derivatives are bioactive compounds with diverse activities such as anti-bacterial, anti-fungal, anti-cancer, and anti-inflammatory as well as therapeutic effects on diabetes and Alzheimer. The anti-cancer activity of such compounds has been one of the main research fields in pharmaceutical chemistry. Due to this diverse biological activity, xanthene core derivatives are still an attractive research field for both academia and industry. This review addresses the current finding on the biological activities of xanthene derivatives and discussed in detail some aspects of their structure-activity relationship (SAR).