Degradation of phenanthrene and pyrene in spiked soils by single and combined plants cultivation

Phenanthrene metabolism in Panicum miliaceum: anatomical adaptations, degradation pathway, and computational analysis of a dioxygenase enzyme

Polycyclic aromatic compounds (PAHs) are persistent organic pollutants of environmental concern due to their potential impacts on food chain, with plants being particularly vulnerable. While plants can uptake, transport, and transform PAHs, the precise mechanisms underlying their localization and degradation are not fully understood. Here, a cultivation experiment conducted with Panicum miliaceum exposed different concentrations of phenanthrene (PHE). Intermediate PHE degradation compounds were identified via GC-MS analysis, leading to the proposal of a phytodegradation pathway featuring three significant benzene ring cleavage steps. Our results showed that P. miliaceum exhibited the ability to effectively degrade high levels of PHE, resulting in the production of various intermediate products through several chemical changes. Examination of the localization and anatomical characteristics revealed structural alterations linked to PHE stress, with an observed enhancement in PHE accumulation density in both roots and shoots as treatment levels increased. Following a 2-week aging period, a decrease in the amount of PHE accumulation was observed, along with a change in its localization. Bioinformatics analysis of the P. miliaceum 2-oxoglutarate-dependent dioxygenase (2-ODD) DAO-like protein revealed a 299 amino acid structure with two highly conserved domains, namely 2OG-FeII_Oxy and DIOX_N. Molecular docking analysis aligned with experimental results, strongly affirming the potential link and direct action of 2-ODD DAO-like protein with PHE. Our study highlights P. miliaceum capacity for PAHs degradation and elucidates the mechanisms behind enhanced degradation efficiency. By integrating experimental evidence with bioinformatics analysis, we offer valuable insights into the potential applications of plant-based remediation strategies for PAHs-contaminated environments.

Exogenous IAA application affects the specific characteristics of fluoranthene distribution in Arabidopsis

Indole-3-acetic acid (IAA) is a crucial growth regulator involved in the accumulation of polycyclic aromatic hydrocarbons (PAHs). However, the precise physiological and molecular mechanisms underlying IAA-mediated plant growth and PAH accumulation are not yet fully understood. In this study, two distinct IAA-sensitive genotypes of Arabidopsis thaliana (wild type and Axr5 mutant) were chosen to investigate the mechanisms of fluoranthene (Flu) uptake and accumulation in plant tissues (roots and leaves) through physiological and molecular analyses. The results revealed that the Flu concentration in Axr5 leaves was significantly higher than that in wild-type (WT) leaves. In roots, the Flu content decreased significantly with increasing IAA treatment, while no significant changes were observed with lower IAA treatment. Principal component analysis demonstrated that Flu accumulation in Arabidopsis roots was associated with IAA concentrations, whereas Flu accumulation in leaves was dependent on the genotype. Moreover, Flu accumulation showed a positive correlation with the activity of glutathione S-transferase (GST) and root length and a positive correlation with catalase (CAT) and peroxidase (POD) activity in the leaves. Transcriptome analysis confirmed that the expression of the ethylene-related gene ATERF6 and GST-related genes ATGSTF14 and ATGSTU27 in roots, as well as the POD-related genes AtPRX9 and AtPRX25 and CAT-related gene AtCAT3 in leaves, played a role in Flu accumulation. Furthermore, WRKY transcription factors (TFs) in roots and NAC TFs in leaves were identified as important regulators of Flu accumulation. Understanding the mechanisms of Flu uptake and accumulation in A. thaliana provides valuable insights for regulating PAH accumulation in plants.

Revealing the key species for pyrene degradation in Vallisneria natans rhizosphere sediment via triple chamber rhizome-box experiments

To identify key species associated with pyrene degradation in Vallisneria natans (V.natans) rhizosphere sediment, this work investigated the temporal and spatial changes in the rhizosphere microbial community and the relationship between the changes and the pyrene degradation process through a three-compartment rhizome-box experiment under pyrene stress. The degradation kinetics of pyrene showed that the order of degradation rate was rhizosphere > near-rhizosphere > non-rhizosphere. The difference in the pyrene degradation behavior in the sediments corresponded to the change in the proportions of dominant phyla (Firmicutes and Proteobacteria) and genera (g_Massilia f_Comamonadaceae, g_Sphingomonas). The symbiosis networks and hierarchical clustering analysis indicated that the more important phyla related to the pyrene degradation in the rhizosphere was Proteobacteria, while g_Sphigomonas, f_Comamonadaceae, and especially g_Massilia were the core genera. Among them, f_Comamonadaceae was the genus most affected by rhizosphere effects. These findings strengthened our understanding of the PAHs-degradation microorganisms in V.natans rhizosphere and are of great significance for enhancing phytoremediation on PAHs-contaminated sediment.

Biochar application for remediation of organic toxic pollutants in contaminated soils; An update

Bioremediation of organic contaminants has become a major environmental concern in the last few years, due to its bio-resistance and potential to accumulate in the environment. The use of diverse technologies, involving chemical and physical principles, and passive uptake utilizing sorption using ecofriendly substrates have drawn a lot of interest. Biochar has got attention mainly due to its simplicity of manufacturing, treatment, and disposal, as it is a less expensive and more efficient material, and has a lot of potential for the remediation of organic contaminants. This review highlighted the adverse impact of persistent organic pollutants on the environment and soil biota. The utilization of biochar to remediate soil and contaminated compounds i.e., pesticides, polycyclic aromatic hydrocarbons, antibiotics, and organic dyes has also been discussed. The soil application of biochar has a significant impact on the biodegradation, leaching, and sorption/desorption of organic contaminants. The sorption/desorption of organic contaminants is influenced by chemical composition and structure, porosity, surface area, pH, and elemental ratios, and surface functional groups of biochar. All the above biochar characteristics depend on the type of feedstock and pyrolysis conditions. However, the concentration and nature of organic pollutants significantly alters the sorption capability of biochar. Therefore, the physicochemical properties of biochar and soils/wastewater, and the nature of organic contaminants, should be evaluated before biochar application to soil and wastewater. Future initiatives, however, are needed to develop biochars with better adsorption capacity, and long-term sustainability for use in the xenobiotic/organic contaminant remediation strategy.

A review on biosurfactant producing bacteria for remediation of petroleum contaminated soils

The discharge of potentially toxic petroleum hydrocarbons into the environment has been a matter of concern, as these organic pollutants accumulate in many ecosystems due to their hydrophobicity and low bioavailability. Petroleum hydrocarbons are neurotoxic and carcinogenic organic pollutants, extremely harmful to human and environmental health. Traditional treatment methods for removing hydrocarbons from polluted areas, including various mechanical and chemical strategies, are ineffective and costly. However, many indigenous microorganisms in soil and water can utilise hydrocarbon compounds as sources of carbon and energy and hence, can be employed to degrade hydrocarbon contaminants. Therefore, bioremediation using bacteria that degrade petroleum hydrocarbons is commonly viewed as an environmentally acceptable and effective method. The efficacy of bioremediation can be boosted further by using potential biosurfactant-producing microorganisms, as biosurfactants reduce surface tension, promote emulsification and micelle formation, making hydrocarbons bio-available for microbial breakdown. Further, introducing nanoparticles can improve the solubility of hydrophobic hydrocarbons as well as microbial synthesis of biosurfactants, hence establishing a favourable environment for microbial breakdown of these chemicals. The review provides insights into the role of microbes in the bioremediation of soils contaminated with petroleum hydrocarbons and emphasises the significance of biosurfactants and potential biosurfactant-producing bacteria. The review partly focusses on how nanotechnology is being employed in different critical bioremediation processes.

Phytoremediation of a pyrene-contaminated soil by Cannabis sativa L. at different initial pyrene concentrations

This study proposes the phytoremediation of a pyrene (PYR)-contaminated soil by Cannabis sativa L. The experimental campaign was conducted along a 60 days period using three different initial PYR concentrations (i.e., 50, 100 and 150 mg kg TS^-1 of soil) in 300 mL volume pots under greenhouse conditions (18-25 °C and 45-55% humidity). After 60 days of hemp growth and flourishing, the highest PYR removal reached approximately 95% in planted soil, 35% higher than in the unplanted control. PYR accumulation was observed in both roots and aerial parts of the plant, with a higher PYR uptake at increasing initial PYR concentrations in soil. The initial PYR concentration affected the growth and, thus, the phytoremediation potential of C. sativa L., which was the result of different removal mechanisms. Overall, the lowest initial PYR concentration was the one that resulted in the highest PYR removal. The interaction between the plant roots and microorganisms in rhizosphere was likely associated with PYR removal in this study. The highest DHO activity of 66.26 μg INTF g^-1 TS^-1 was observed in the soil spiked with 50 mg PYR·kg TS^-1.

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 150 days, 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.

Biotechnological Combination for Co-contaminated Soil Remediation: Focus on Tripartite "Meta-Enzymatic" Activity

Soil pollution is a pressing problem requiring solutions that can be applied without large-scale side effects directly in the field. Phytoremediation is an effective strategy combining plant and root-associated microbiome to immobilize, degrade, and adsorb pollutants from the soil. To improve phytoremediation, it is necessary to think of plants, fungi, and bacteria not as individual entities, but as a meta-organism that reacts organically, synergistically, and cooperatively to environmental stimuli. Analyzing the tripartite enzymatic activity in the rhizosphere is necessary to understand the mechanisms underlying plant-microorganism communication under abiotic stress (such as soil pollution). In this work, the potential of a microbial consortium along with a plant already known for its phytoremediation capabilities, Schedonorus arundinaceus (Scheb.) Dumort., was validated in a mesocosm experiment with pluricontaminated soil (heavy metals, PAHs, and PCBs). Chemical analyses of the soil at the beginning and end of the experiment confirmed the reduction of the main pollutants. The microscopic observation and chemical analyses confirmed the greater root colonization and pollutant removal following the microbial treatment. To obtain a taxonomic and functional picture, tripartite (plant, fungi, and bacteria) enzyme activity was assessed using a metatranscriptomic approach. Total RNA was extracted from a sample of rhizosphere sampled considering 2 centimeters of root and soil attached. From the total reads obtained, mRNAs were filtered, and analysis focused on reads identified as proteins with enzymatic activity. The differential analysis of transcripts identified as enzymes showed that a general increase in potential enzyme activity was observed in the rhizosphere after our biotechnological treatment. Also from a taxonomic perspective, an increase in the activity of some Phyla, such as Actinobacteria and Basidiomycota, was found in the treated sample compared to the control. An increased abundance of enzymes involved in rhizospheric activities and pollutant removal (such as dehydrogenase, urease, and laccase) was found in the treated sample compared to the control at the end of the experiment. Several enzymes expressed by the plant confirmed the increase in metabolic activity and architectural rearrangement of the root following the enhancement of the rhizospheric biome. The study provides new outcomes useful in rhizosphere engineering advancement.

Effect of soil contamination with polycyclic aromatic hydrocarbons from drilling waste on germination and growth of lawn grasses

In many studies, grasses were used to increase the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in soil because they are the most common plant species on the ground level and are quite resistant to contamination with these compounds. One of the main failures in PAH remediation in soil using plant species was the negative impact on germination and seedling growth. The objective of this study was to evaluate grass seed germination and seedling growth affected by drill cuttings to determine the resistance of selected grass species to the impact of PAH and their suitability for an effective phytoremediation of soils contaminated with waste that contain compounds from this group. In the study four grass species: tall fescue (Festuca arundinacea), red fescue (Festuca rubra), perennial ryegrass (Lolium perenne) and common meadow-grass (Poa pratensis). The germination energy of all species decreased as the amount of drill cuttings increased. Among the species studied, the highest germination energy and capacity were found in Lolium perenne (54.1 and 73.2 respectively), and the lowest - in Poa pratensis (16.7 and 23.3 respectively). With an increasing amount of drill cuttings, the root and seedling height were decreased. Festuca arundinacea seedlings were distinctly the highest and had the longest roots (96.7 and 52.7, respectively), while Poa pratensis seedlings showed the significantly slowest seedling and root elongation rate (30.4 and 12.4, respectively). However, the strongest decrease in seedling height and root length compared to the control was observed in Festuca rubra. Based on IC50, the greatest tolerance to the addition of drilling waste to the substrate was found for Festuca arundinacea and Festuca rubra. The conducted investigation indicates that Festuca arundinacea and Lolium perenne are grass species that are least sensitive to drilling waste in the substrate because no significant differences were found in root length and seedling height between the control soil and the soil where a PAH dose of 5% and 10% was applied.

Nitrogen addition facilitates phytoremediation of PAH-Cd cocontaminated dumpsite soil by altering alfalfa growth and rhizosphere communities

Thousands of unlined landfills and open dumpsites seriously threatened the safety of soil and groundwater due to leachate leakage with a mass of pollutants, particularly heavy metals, organic contaminants and ammonia. Phytoremediation is widely used in the treatment of cocontaminated soils because it is cost-effective and environmentally friendly. However, the extent to which phytoremediation efficiency and plant physiological responses are affected by the high nitrogen (N) content in such cocontaminated soil is still uncertain. Here, pot experiments were conducted to investigate the effects of N addition on the applicability of legume alfalfa remediation for polycyclic aromatic hydrocarbon‑cadmium (PAHCd) co-/contaminated soil and the corresponding microbial regulation mechanism. The results showed that the PAH dissipation rates and Cd removal rates in the high-contamination groups increased with the external N supply, among which the pyrene dissipation rates in the cocontaminated soil was elevated most significantly, from 78.10% to 87.25%. However, the phytoremediation efficiency weakened in low cocontaminated soil, possibly because the excessive N content had inhibitory effects on the rhizobium Ensifer and restrained alfalfa growth. Furthermore, the relative abundance of PAH-degrading bacteria in the rhizosphere dominated PAH dissipation. As reflected by principal coordinate analysis (PCoA) analysis and hierarchical dendrograms, the microbial community composition changed with N addition, and a more pronounced shift was found in the rhizosphere relative to the endosphere or shoots of alfalfa. This study will provide a theoretical basis for legume plant remediation of dumpsites as well as soil contaminated with multiple pollutants.

Soil initial bacterial diversity and nutrient availability determine the rate of xenobiotic biodegradation

Understanding the relative importance of soil microbial diversity, plants and nutrient management is crucial to implement an effective bioremediation approach to xenobiotics-contaminated soils. To date, knowledge on the interactive effects of soil microbiome, plant and nutrient supply on influencing biodegradation potential of soils remains limited. In this study, we evaluated the individual and interactive effects of soil initial bacterial diversity, nutrient amendments (organic and inorganic) and plant presence on the biodegradation rate of pyrene, a polycyclic aromatic hydrocarbon. Initial bacterial diversity had a strong positive impact on soil biodegradation potential, with soil harbouring higher bacterial diversity showing ~ 2 times higher degradation rates than soils with lower bacterial diversity. Both organic and inorganic nutrient amendments consistently improved the degradation rate in lower diversity soils and had negative (inorganic) to neutral (organic) effect in higher diversity soils. Interestingly, plant presence/type did not show any significant effect on the degradation rate in most of the treatments. Structural equation modelling demonstrated that initial bacterial diversity had a prominent role in driving pyrene biodegradation rates. We provide novel evidence that suggests that soil initial microbial diversity, and nutrient amendments should be explicitly considered in the design and employment of bioremediation management strategies for restoring natural habitats disturbed by organic pollutants.

Effects of Lead (Pb) and Benzo [a] Pyrene (B[a]P) and their Combined Exposure on Element Accumulation in Ryegrass (Lolium perenne L.)

It was observed in this work that application of Pb and B[a]P co-exposure significantly (p < 0.05) reduced Pb content in ryegrass leaves and roots. The effect of Pb dominated the change of N, P, K, Cu, and Cr content in leaves and roots of ryegrass under joint stress of Pb and B[a]P. Principal component analysis showed that the foliar spraying of 400 μmol L^-1 Pb and 80 μmol L^-1 B[a]P had the best effect on improving the mineral element absorption under combined pollution. Ryegrass has strong resistance and certain Pb and B[a]P absorptive capacities, and can resist combined contamination by transferring N, P, K, Zn, Cu, and Cr contents between the overground and the root. These results highlight the potential capacity of ryegrass for use in the phytoremediation of soils contaminated by Pb and B[a]P.

The catabolic pathways of in situ rhizosphere PAH degraders and the main factors driving PAH rhizoremediation in oil-contaminated soil

Rhizoremediation is a potential technique for polycyclic aromatic hydrocarbon (PAH) remediation; however, the catabolic pathways of in situ rhizosphere PAH degraders and the main factors driving PAH rhizoremediation remain unclear. To address these issues, stable-isotope-probing coupled with metagenomics and molecular ecological network analyses were first used to investigate the phenanthrene rhizoremediation by three different prairie grasses in this study. All rhizospheres exhibited a significant increase in phenanthrene removal and markedly modified the diversity of phenanthrene degraders by increasing their populations and interactions with other microbes. Of all the active phenanthrene degraders, Marinobacter and Enterobacteriaceae dominated in the bare and switchgrass rhizosphere respectively; Achromobacter was markedly enriched in ryegrass and tall fescue rhizospheres. Metagenomes of ¹³ C-DNA illustrated several complete pathways of phenanthrene degradation for each rhizosphere, which clearly explained their unique rhizoremediation mechanisms. Additionally, propanoate and inositol phosphate of carbohydrates were identified as the dominant factors that drove PAH rhizoremediation by strengthening the ecological networks of soil microbial communities. This was verified by the results of rhizospheric and non-rhizospheric treatments supplemented with these two substances, further confirming their key roles in PAH removal and in situ PAH rhizoremediation. Our study offers novel insights into the mechanisms of in situ rhizoremediation at PAH-contaminated sites.

Phytoremediation of pyrene-contaminated soils: A critical review of the key factors affecting the fate of pyrene

Soil contamination by pyrene has increased over the years due to human-related activities, urgently demanding for remediation approaches to ensure human and environment safety. Within this frame, phytoremediation has been successfully applied over the years due to its green and cost-effectiveness features. The scope of this review includes the main phytoremediation mechanisms correlated with the removal of pyrene from contaminated soils and sediments to highlight the impact of different parameters and the supplement of additives on the efficiency of the treatment. Soil organic matter (SOM), plant species, aging time, environmental parameters (pH, soil oxygenation, and temperature) and bioavailability are among the main parameters affecting pyrene removal through phytoremediation. Phytoextraction only accounts for a small part of the entire phytoremediation process, but the addition of surfactants and chelating agents in planted soils could increase pyrene accumulation in plant tissues by 20% as a consequence of the increased pyrene bioavailability. Rhizodegradation is the main phytoremediation mechanism involved due to the activity of bacteria capable of degrading pyrene in the root area. Inoculated-planted soil treatments have the potential to decrease pyrene accumulation in shoots and roots by approximately 30 and 40%, respectively, further stimulating the proliferation of pyrene-degrading bacteria in the rhizosphere. Plant-fungi symbiotic association results in an enhanced accumulation of pyrene in shoots and roots of plants as well as a higher biodegradation. Finally, pyrene removal from soil can be improved in the presence of amendments, such as natural non-ionic surfactants, biochar, and bacterial mixtures.

Phytotoxicity of petroleum hydrocarbons: Sources, impacts and remediation strategies

Extraction and exploration of petroleum hydrocarbons (PHs) to satisfy the rising world population's fossil fuel demand is playing havoc with human beings and other life forms by contaminating the ecosystem, particularly the soil. In the current review, we highlighted the sources of PHs contamination, factors affecting the PHs accumulation in soil, mechanisms of uptake, translocation and potential toxic effects of PHs on plants. In plants, PHs reduce the seed germination andnutrients translocation, and induce oxidative stress, disturb the plant metabolic activity and inhibit the plant physiology and morphology that ultimately reduce plant yield. Moreover, the defense strategy in plants to mitigate the PHs toxicity and other potential remediation techniques, including the use of organic manure, compost, plant hormones, and biochar, and application of microbe-assisted remediation, and phytoremediation are also discussed in the current review. These remediation strategies not only help to remediate PHs pollutionin the soil rhizosphere but also enhance the morphological and physiological attributes of plant and results to improve crop yield under PHs contaminated soils. This review aims to provide significant information on ecological importance of PHs stress in various interdisciplinary investigations and critical remediation techniques to mitigate the contamination of PHs in agricultural soils.

Isolation and Characterization of Oil-Degrading Enterobacter sp. from Naturally Hydrocarbon-Contaminated Soils and Their Potential Use against the Bioremediation of Crude Oil

The contamination of crude oil in soil matrices is a persistent problem with negative repercussions because of the recalcitrant, hazardous, and mutagenic properties of its constituents. To mitigate the effect of crude oil contamination in soil, the use of microorganisms is a cheap and feasible option. In the current study, bacterial species from numerous polluted oil field surfaces were isolated and examined for their ability to degrade crude oil. Random soil samples polluted with hydrocarbons were collected and various bacterial isolates were isolated. Results revealed that 40% of total isolates had potential use for hydrocarbon biodegradation, the synthesis of exopolysaccharides and the solubilization of phosphorous. Following isolation and characterization to degrade crude oil, a pot trial was conducted using maize inoculated with the four best strains—i.e., S1 (PMEL-63), S2 (PMEL-67), S3 (PMEL-80), and S4 (PMEL-79)—in artificially hydrocarbon-polluted soil with concentrations of crude oil of 0, 1000, and 2000 ppm. Results revealed that S4 (PMEL-79) had significant potential to degrade hydrocarbon in polluted soils. The root length, shoot length, and fresh biomass of maize were increased by 65%, 45%, and 98%, respectively, in pots inoculated with S4 (PMEL-79) Enterobacter cloacae subsp., whereas the lowest root length was observed where no strain was added and the concentration of crude oil was at maximum. Moreover, S4 (PMEL-79) Enterobacter cloacae subsp. was found to be the most effective strain in degrading crude oil and increasing maize growth under polluted soil conditions. It was concluded that the isolation of microorganisms from oil-contaminated sites should be considered in order to identify the most effective microbial consortium for the biodegradation of naturally hydrocarbon-contaminated soils.

Combined remediation of polychlorinated naphthalene-contaminated soil under multiple scenarios: An integrated method of genetic engineering and environmental remediation technology

This study explored the types of polychlorinated naphthalene (PCN)-contaminated soil and determined the practicable scheme of combined remediation using an integrated method of genetic engineering and environmental remediation technology. A multi-scenario comprehensive evaluation system of a plant-microbial combined bioremediation of PCN-contaminated soil was established using the intelligent integration of analytic hierarchy process and formula evaluation methods based on the current situation of PCN contamination in China, which showed the bioremediation of PCN-contaminated soil by the plant-microbial system could be divided into four scenarios. QSAR models were constructed to quantify the remediation mechanism that electronic parameter ∆E was the key factor changing the efficiency of combined bioremediation. Moreover, the macro-control scheme of PCN-contaminated soil was established, which indicated that four new multifunctional proteins promoted the absorption, degradation, and mineralization of PCNs in specific soil pollution types significantly, were obtained through cross gene recombination. The molecular dynamics (MD) simulation results showed the efficiency of the plant-microbial combined bioremediation were increased by 15.45% (Scenario 1, 2, 3) and 20.02% (Scenario 4) under the optimal regulation scheme. The findings will be helpful to realize the regional control of PCN-contaminated soil.

Plant-microorganism combined remediation of polychlorinated naphthalenes contaminated soils based on molecular directed transformation and Taguchi experimental design-assisted dynamics simulation

The molecular directed transformation procedure was adopted by combining molecular docking and homology modeling to reconstruct the proteins, which are involved in the absorption, degradation, and mineralization of polychlorinated naphthalenes (PCNs). A comprehensive evaluation system for developing new proteins that are responsible for the absorption (aquaporin: 1Z98), degradation (peroxidase: 1ATJ), and mineralization (lignin peroxidase: 1B85) of PCNs was established using the Rank Sum Ratio (RSR) and weighted average methods. The Taguchi experimental design-assisted dynamics simulation was used to determine the optimal external stimulus conditions of plant-microorganism combined remediation system to absorb, degrade, and mineralize PCNs. Results showed that a total of 60 amino acid sequences were designed, and 19 new proteins (increasing amplitude: 66.67%-500.00%) were significantly higher than those of target proteins through the screening of comprehensive evaluation system. Additionally, 10 new proteins improved the efficiency of absorption, degradation, and mineralization of PCNs in a real environment which were simulated under the optimal external stimulus conditions. Moreover, remediation efficiency was significantly enhanced when the template proteins was replaced with a combination of 1Z98-9, 1ATJ-7, and 1B85-20 in plant-microorganism systems, and the van der Waals force and polar solvation were the main factors affecting the absorption, degradation, and mineralization of PCNs.

Phytoremediation for co-contaminated soils of cadmium and pyrene using Phragmites australis (common reed)

Soil contamination is currently the most severe problem as it poses a toxicological impact on human health and ecosystems. A greenhouse experiment was carried out to investigate the effect of 20 and 40 mg kg^-1 of cadmium (Cd) or 50 and 100 mg kg^-1 of pyrene (PYR) and the combined effect of Cd-PYR on the growth of Phragmites australis together with the uptake and accumulation of Cd as well as removal of PYR. Results demonstrated that the single or co- contaminants of Cd and PYR did not affect plant growth relative to control treatments, except low Cd and high PYR treatment, which showed a significant increase in 91% biomass compared to the control. However, under the joint effect of Cd-PYR, P. australis was unwilling to uptake and translocate Cd, and bioconcentration factor (BCF) and translocation factor (TrF) values were less than one. The removal rate of PYR in the soils and soil enzymes was negatively impacted at the elevated Cd level in the soil. Our study shows that P. australis may have the potential for phytostabilization but cannot be useful for phytoextraction.

Effects of surfactants on the fractionation, vermiaccumulation, and removal of fluoranthene by earthworms in soil

Vermiremediation, which uses earthworms to remediate polluted soils, is an expanding technology in recently years. Surfactants have been widely used in bioremediation and other remediation technologies. However, the roles of surfactants in vermiremediation have been rarely studied. In this paper, an investigation of the effects of Tween-80 and rhamnolipid surfactant on the fluoranthene fraction distribution, vermiaccumulation, and removal during vermiremediation was conducted. Both Tween-80 and rhamnolipid improved the proportion of the desorbed fraction, bound residual fluoranthene, and correspondingly, proportions of the non-desorbed fraction were reduced. The vermiaccumulation of fluoranthene was significantly elevated by 35-64.1% and 34.5-44.2% by the Tween-80 and rhamnolipid, respectively. The vermiaccumulation of fluoranthene is positively correlated with the proportion of desorbed fraction of fluoranthene. Moreover, Tween-80 and rhamnolipid enhanced the removal of fluoranthene from contaminated soil during vermiremediation by 43.6-189.2% and 14.7-45.6%, respectively. The enhanced removal of fluoranthene was attributed to stimulated microbial degradation and increased vermiaccumulation resulting from the desorption ability of surfactants and earthworm activity. However, the total amount of fluoranthene that accumulated in earthworms was approximately 4-10% of the initial amount in the treatments, which suggested that microbial degradation rather than direct uptake contributed to the fluoranthene removal. The study suggests that the use of surfactants to enhance the efficiency of vermiremediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soils might be feasible, and that surfactants-enhanced vermiremediation is an alternative strategies for treat PAHs contaminated soils.

The effect of different levels of leachate on phytoremediation of pyrene-contaminated soil and simultaneous extraction of lead and cadmium

Pyrene is one of the 16 group combinations of polyaromatic hydrocarbons, which are known as primary pollutants in the U.S. Environmental Protection Agency (USEPA) list. This study aimed to investigate the cross effect of different levels of landfill leachate on phytoremediation of pyrene-contaminated soil using the sorghum bicolor plant. The study parameters included the presence or absence of the plant, different concentrations of pyrene (150, 300, 500, 750, and 1000 mg kg^-1), time (30, 60, and 90 days), and different levels of irrigation with leachate (0, 30, 50, 70, and 100%). Soil pyrene was measured every 30 days, and heavy metals (lead and cadmium) added to the soil by irrigation with leachate were measured in the soil and the plant at the end of 90 days. According to the results, pyrene removal efficiency after 90 days was 96% in irrigation treatments with 30% leachate in the presence of the plant and 67% in irrigation treatments with tap water in the presence of the plant. In addition, 95% of lead and 49% of cadmium added to the soil by irrigation with 30% leachate were extracted from the soil by the sorghum bicolor. According to the results, by increasing nutrients and number of soil bacteria during the cross treatment, landfill leachate increased the pyrene removal efficiency significantly during phytoremediation (p < 0.006) and the sorghum bicolor plant extracted the lead and cadmium of the leachate. In non-planting treatments, although adding high levels of leachate to the soil significantly improved the pyrene removal, it caused the levels of heavy metals, such as lead and cadmium, to exceed the allowable limit (p < 0.001).

Enhanced phytoremediation of PAHs-contaminated soil from an industrial relocation site by Ochrobactrum sp

Nowadays, the remediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated soil has received wide attention. In this work, Ochrobactrum sp. (PW) was isolated through selective enrichment from PAHs-contaminated soil in coking plant of Beijing, and the effects of PW on phytoremediation of that soil by alfalfa (Medicago sativa L.) and ryegrass (Lolium multiflorum Lam.) were investigated through pot experiments. Plant biomass, peroxidase (POD) activity, malondialdehyde (MDA) contents, soil enzyme activity (polyphenol oxidase and dehydrogenase activity), and residual concentration of PAHs in soils were determined to illustrate the ability of PW for enhancing the degradation of PAHs by plants. The results showed that the fresh weight of ryegrass and alfalfa inoculated with PW was significantly (p < 0.05) increased while the activity of POD and MDA contents were notably (p < 0.05) reduced than that without inoculation. Additionally, PW enhanced the activity of polyphenol oxidase and dehydrogenase in soil significantly (p < 0.05), and further enhanced the degradability of the system to PAHs. Different treatment methods could be ranked by the following order according to the degradability: SP (alfalfa + PW) > RP (ryegrass + PW) > PW (PW) > S (alfalfa) > R (ryegrass). The combined action of PW and alfalfa/ryegrass could accelerate the degradability of PAHs from soil contaminated by coking plants. PW could be used as potential bacteria to promote phytoremediation of the soil contaminated by PAHs.

Ex situ evaluation of the effects of biochars on environmental and toxicological availabilities of metals and polycyclic aromatic hydrocarbons

The present study experimented five biochars, one made from wood (400 °C, 12 h) and four made from miscanthus cultivated on contaminated soils (temperature 400/600 °C, duration 45/90 min). They were used as amendments at a 2% application rate on soil, cultivated or not cultivated with ryegrass, contaminated with (i) metals (Cd, Pb, and Zn), (ii) eight polycyclic aromatic hydrocarbons (PAHs), and (iii) a mix of metals and PAHs. The objectives were (i) to compare the effectiveness of the five biochars on soil parameters and pollutant availability and (ii) to determine the influence of soil multicontamination and ryegrass cultivation on biochar effectiveness. The results showed that biochar application did not necessarily lead to lower pollutant extractability and metal bioaccessibility. However, differences were highlighted between the biochars. The miscanthus biochars produced at 600 °C (BM600) showed higher effectiveness at decreasing metal extractability than the miscanthus biochars produced at 400 °C (BM400) due to its better sorption characteristics. In addition, ryegrass cultivation did not impact pollutant availability but modified metal bioaccessibility, especially for the soil amended with the BM600 and the woody biochar. Moreover, the presence of PAHs also negatively impacted the metal bioaccessibility in the soil amended with the BM600, and, on the contrary, positively impacted it in the soil amended with the BM400. Complementary studies are therefore necessary to understand the mechanisms involved, particularly in a context where soils requiring remediation operations are often multicontaminated and vegetated.

Soil phenanthrene phytoremediation capacity in bacteria-assisted Spartina densiflora

Polycyclic aromatic hydrocarbons (PAH) have become a threat for the conservation of wetlands worldwide. The halophyte Spartina densiflora has shown to be potentially useful for soil phenanthrene phytoremediation, but no studies on bacteria-assisted hydrocarbon phytoremediation have been carried out with this halophyte. In this work, three phenanthrene-degrading endophytic bacteria were isolated from S. densiflora tissues and used for plant inoculation. Bacterial bioaugmentation treatments slightly improved S. densiflora growth, photosynthetic and fluorescence parameters. But endophyte-inoculated S. densiflora showed lower soil phenanthrene dissipation rates than non-inoculated S. densiflora (30% below) or even bulk soil (23% less). Our work demonstrates that endophytic inoculation on S. densiflora under greenhouse conditions with the selected PAH-degrading strains did not significantly increase inherent phenanthrene soil dissipation capacity of the halophyte. It would therefore be advisable to provide effective follow-up of bacterial colonization, survival and metabolic activity during phenanthrene soil phytoremediation.

Effect of salicylic acid and mycorrhizal symbiosis on improvement of fluoranthene phytoremediation using tall fescue (Festuca arundinacea Schreb)

Polycyclic aromatic hydrocarbons are an important group of pollutants that are widely distributed in the environment. The present study aimed to investigate the effect of salicylic acid (a phenolic phytohormone) and mycorrhizal fungi on the growth and phytoremediation ability of tall fescue in the soil contaminated by fluoranthene. The initial concentrations of fluoranthene in this study were 100, 200, and 300 mg kg^-1. The experimental treatments were included: T0 uncultivated soil; T1 cultivated soil with tall fescue; T2 cultivated soil with tall fescue + salicylic acid application; T3 cultivated soil with tall fescue + application of mycorrhizal fungi; T4 cultivated soil with tall fescue + salicylic acid and mycorrhizal fungi application; and P planting tall fescue in uncontaminated soil. The removal of fluoranthene was measured after 90 days. Furthermore, at the end of the experiment, the amount of shoot and root biomass, soil bacteria, and dehydrogenase activity were measured. According to the results, in all levels of contamination, removal of fluoranthene in cultivated treatments significantly was higher than uncultivated treatments. Increasing the concentration of fluoranthene had a negative effect on the shoot and root biomass in different treatments. Salicylic acid and mycorrhizal fungi significantly increased the shoot and root biomass and also the number of soil bacteria, dehydrogenase activity, and fluoranthene removal in T2, T3, and T4 treatments compared to T1. At the highest concentration of fluoranthene, as a result of simultaneous application of salicylic acid and mycorrhizal fungi (T4), the fluoranthene removal increased by 63, 21, 13, and 16% in comparison with T0, T1, T2, and T3, respectively. Based on the results, salicylic acid and mycorrhizal fungi, either alone or in combination, have a significant effect on the improvement of phytoremediation potential in tall fescue.

The responding and ecological contribution of biofilm-leaves of submerged macrophytes on phenanthrene dissipation in sediments

The bacterial communities and ecological contribution of biofilm-leaves of the Vallisneria natans (VN), Hydrilla verticillata (HV) and artificial plant (AP) settled in sediments with different polluted levels of phenanthrene were investigated by high-throughput sequencing in different growth periods. There was no significant difference among the detected Alpha diversity indices based on three classification, attached surface, spiking concentration and incubation time. While Beta diversity analysis assessed by PCoA on operational taxonomic units (OTU) indicated that bacterial community structures were significantly influenced in order of attached surface > incubation time > spiking concentration of phenanthrene in sediment. Moreover, the results of hierarchical dendrograms and heat maps at genus level were consistent with PCoA analysis. We speculated that the weak influence of phenanthrene spiking concentration in sediment might be related to lower concentration and smaller concentration gradient of phenanthrene in leaves. Meanwhile, difference analysis suggested that attached surface was inclined to influence the rare genera up to significant level than incubation time. In general, the results proved that phenanthrene concentrations, submerged macrophytes categories and incubation time did influence the bacterial community of biofilm-leaves. In turn, results also showed a non-negligible ecological contribution of biofilm-leaves in dissipating the phenanthrene in sediments (>13.2%-17.1%) in contrast with rhizosphere remediation (2.5%-3.2% for HV and 9.9%-10.6% for VN).

Pilot-scale demonstration of phytoremediation of PAH-contaminated sediments by Hydrilla verticillata and Vallisneria spiralis

The results of phytoremediation of sediments contaminated with polycyclic aromatic hydrocarbons (PAHs) by two submerged aquatic plants (Vallisneria spiralis and Hydrilla verticillata) at pilot scale were reported for the first time in this study. During a 108-day period, the plants grew well, and more PAHs were dissipated in planted sediments than in unplanted sediments. At the end, dissipation ratios of phenanthrene and pyrene were 85.9% and 79.1% in sediments planted with V. spiralis, 76.3% and 64.6% in sediments planted with H. verticillata, but only 64.8% and 55.8% in unplanted sediments. V. spiralis exhibited higher phytoremediation ability, which was significantly related to its root oxygenation as indicated by the redox potential in sediments. The remediation results at pilot scale were also compared with those previously obtained in our laboratory. The ratio of root weight to sediment weight showed a similar trend to PAH dissipation enhancement. Bioconcentration factors of PAHs in the two plants were larger in the pilot experiment than in the laboratory tests as a result of quicker increase of plant weight in the pilot experiment.

Effect of plant growth promoting bacterium; Pseudomonas putida UW4 inoculation on phytoremediation efficacy of monoculture and mixed culture of selected plant species for PAH and lead spiked soils

Plant growth promoting bacteria (PGPB) enhanced phytoremediation (PEP) is an attractive remedial strategy for the remediation of polycyclic aromatic hydrocarbon (PAH) and heavy metal (HM) contaminated sites. The effect of PGPB; Pseudomonas putida UW4 inoculation on the phytoremediation efficiency of Medicago sativa, Festuca arundinacea, Lolium perenne, and mixed plants (L. perenne and F. arundinacea) was assessed. This involved two contaminant treatments; "PAH" (phenanthrene; 300 mg·kg^-1, fluoranthene; 200 mg·kg^-1, and benzo[a]pyrene; 5 mg·kg^-1) and "PAH + HM" ('PAH' treatments +100 mg of Pb/kg). PGPB inoculation significantly enhanced root biomass yield of F. arundinacea in PAH treatment, and the mixed plant shoot biomass and L. perenne root biomass yields of the PAH + HM treatment. PGPB significantly enhanced dissipation of phenanthrene and fluoranthene for M. sativa-PAH + PGPB treatment and fluoranthene for F. arundinacea-PAH + HM + PGPB treatment. In others, PGPB inoculation either had no impact or inhibited PAH dissipation. PAH dissipation for the single and mixed plant treatments with PGPB inoculation were not different. The efficiency of PEP is dependent on different factors such as PGPB inoculum biomass, plant species, plant-microbe specificity and type of contaminants. Exploiting PEP technology would require proper understanding of plant tolerance and growth promoting mechanisms, and rhizosphere activities.

Effects of pharmaceuticals on microbial communities and activity of soil enzymes in mesocosm-scale constructed wetlands

Cyperus alternifolius based mesocosm-scale constructed wetland was employed to remove pharmaceuticals. We investigated the microbial community composition using phosphor lipid fatty acids (PFLAs) analysis and substrate enzyme activity during long-term exposure to pharmaceuticals in mesocosm-scale constructed wetlands. The results showed that there was no visible inhibition effect of pharmaceuticals on CW substrate enzymes activities in the experimental range (0-500 μg/L). Microbial communities, as revealed by PFLAs, were enhanced by the presence of plants, while the PFLAs content was highest when the pharmaceutical concentration was 10 μg/L or 30 μg/L at CWs. Except for anaerobic bacteria and Saturated fatty acids, the maximum PLFAs levels were reached when the pharmaceuticals were 10 μg/L or 30 μg/L, while Bacteria, G (-), fungal bacteria, Aerobic bacteria and Monounsaturated fatty acids were remarkably affected by high pharmaceuticals (100-500 μg/L). However, the main microbial florae were not changed among the treatments. In this study, the removal efficiencies of the studied pharmaceuticals in Planted (30) was greatest, which could be attributed to the higher microbial biomass. These results indicate that C. alternifolius can phytoremediate pharmaceutical-contaminated waters in CWs. Individual fatty acid cannot be used to represent specific species; therefore, more approaches to species identification such as rRNA-based methods must be included in future studies to better understand the metabolic mechanisms of microorganisms involved in the removal of studied pharmaceuticals and improve the performance of CWs.

Different responses to soil petroleum contamination in monocultured and mixed plant systems

The role of plant composition should be considered during ecological risk assessment of soil petroleum contamination. To evaluate the influences of plant composition on phytotoxicity, petroleum degraders, and petroleum degradation, four treatments were arranged in the present study: unplanted, bristle grass only, alfalfa only, and bristle grass and alfalfa mixed planted in uncontaminated soil or petroleum contaminated soil (w/w, 1.0%). Petroleum contamination inhibited the growth of bristle grass and alfalfa significantly, and alfalfa growth inhibition was significantly alleviated when mixed planted with bristle grass (p < 0.05). MPN analysis indicated that the mixed plant treatment can gather the benefits of two species, and facilitate the development of alkane, total hydrocarbon and PAH degraders in contaminated soil, but not occur in uncontaminated soil. Compared with alfalfa only treatment, the degradation rates for total petroleum hydrocarbons (TPH) and aliphatic fraction were significantly increased in the mixed plant treatment (p < 0.05). However, the degradation of aromatic petroleum fraction was not received substantial improvement in the mixed plant treatment, despite containing an abundant PAH degraders. Overall, mixed plant cultivation had the significant influences on plant growth, microbial community and petroleum degradation in contaminated soils. The study provides valuable insights for vegetation restoration and remediation systems in petroleum contaminated sites of study area.

Treatment technologies for PAH-contaminated sites: a critical review

To reduce environmental and human health risks of contaminated sites, having a comprehensive knowledge about the polycyclic aromatic hydrocarbon (PAH) removal processes is crucial. PAHs are contaminants which are highly recognized to pose threats to humans, animals, and plants. PAHs are hydrophobic and own two or more benzene rings, and hence are resistant to structural degradation. There are various techniques which have been developed to treat PAH-contaminated soil. Four distinct processes to remove PAHs in the contaminated soil, thought to be more effective techniques, are presented in this review: soil washing, chemical oxidation, electrokinetic, phytoremediation. In a surfactant-aided washing process, a removal rate of 90% was reported. Compost-amended phytoremediation treatment presented 58-99% removal of pyrene from the soil in 90 days. Chemical oxidation method was able to reach complete conversion for some PAHs. In electrokinetic treatment, researchers have achieved reliable results in removal of some specific PAHs. Researchers' innovations in novel studies and advantages/disadvantages of the techniques are also investigated throughout the paper. Finally, it should be noted that an exclusive method or a combination of methods by themselves are not the key to be employed for remediation of every contaminated site but the field characteristics are also essential in selection of the most appropriate decontamination technique(s). The remedy for selection criteria is based on PAH concentrations, site characteristics, costs, shortcomings, and advantages.

Intercropping of Gramineous Pasture Ryegrass (Lolium perenne L.) and Leguminous Forage Alfalfa (Medicago sativa L.) Increases the Resistance of Plants to Heavy Metals

Intercropping can increase the biomass of plants and reduce the accumulation of heavy metals in plants. However, the mechanisms of intercropping increasing plant biomass and resistance to heavy metals are still unclear. Therefore, the pot experiment had been conducted to investigate the effect of intercropping treatment on the growth of gramineous pasture ryegrass (Lolium perenne L.) and leguminous forage alfalfa (Medicago sativa L.) in metal-contaminated soil. Our results showed that intercropping alleviated inhibition of heavy metals to plant growth and increased nitrogen and chlorophyll contents in the shoots and roots. Moreover, the Pb concentrations in the shoots and roots of ryegrass and alfalfa in the intercropping were significantly lower than those in the monoculture. And, the contents of saccharase and alkaline phosphatase were significantly increased in the intercropping treatment. Additionally, the intercropping treatment could reduce the oxidative damage and increase enzymatic antioxidant activities to improve the resistance of plants in contaminated soil. The intercropping treatment can increase the resistance of plants to heavy metals through reduction of plant oxidative damage and increase of antioxidant activity. It could provide us with a strategy that intercropping of ryegrass and alfalfa can increase biomass and reduce the absorption of Pb on forage plants.

Effect of single and mixed polycyclic aromatic hydrocarbon contamination on plant biomass yield and PAH dissipation during phytoremediation

Polycyclic aromatic hydrocarbon (PAH)-contaminated sites have a mixture of PAH of varying concentration which may affect PAH dissipation differently to contamination with a single PAH. In this study, pot experiments investigated the impact of PAH contamination on Medicago sativa, Lolium perenne, and Festuca arundinacea biomass and PAH dissipation from soils spiked with phenanthrene (Phe), fluoranthene (Flu), and benzo[a]pyrene (B[a]P) in single and mixed treatments. Stimulatory or inhibitory effects of PAH contamination on plant biomass yields were not different for the single and mixed PAH treatments. Results showed significant effect of PAH treatments on plant growth with an increased root biomass yield for F. arundinacea in the Phe (175%) and Flu (86%) treatments and a root biomass decrease in the mixed treatment (4%). The mean residual PAHs in the planted treatments and unplanted control for the single treatments were not significantly different. B[a]P dissipation was enhanced for single and mixed treatments (71-72%) with F. arundinacea compared to the unplanted control (24-50%). On the other hand, B[a]P dissipation was inhibited with L. perenne (6%) in the single treatment and M. sativa (11%) and L. perenne (29%) in the mixed treatment. Abiotic processes had greater contribution to PAH dissipation compared to rhizodegradation in both treatments. In most cases, a stimulatory effect of PAH contamination on plant biomass yield without an enhancement of PAH dissipation was observed. Plant species among other factors affect the relative contribution of PAH dissipation mechanisms during phytoremediation. These factors determine the effectiveness and suitability of phytoremediation as a remedial strategy for PAH-contaminated sites. Further studies on impact of PAH contamination, plant selection, and rhizosphere activities on soil microbial community structure and remediation outcome are required.

Se enhanced phytoremediation of diesel in soil by Trifolium repens

A pot-culture experiment was conducted to assess the effects of selenium (Se) (0.5 mg kg^-1) on Trifolium repens exposed to various levels of diesel (0, 15, 20, 25 g kg^-1) for 30 days and 60 days. Exposure to diesel for 60 day led to concentration-dependent decreases in root morphogenesis, chlorophyll content and CAT activity, and to dose-dependent increases in MDA content and SOD activity. The residual diesel concentration in soil increased and the removal efficiency decreased with soil diesel concentration. The chlorophyll content and residual diesel concentration after were slightly higher at 30 days than at 60days. Application of Se to soil increased Trifolium repens tolerance to diesel and significantly increased the phytoremediation effect at 60 days, with a removal rate of 36 ± 8%, compared to 28 ± 7% in the control. These results contribute to the ongoing effort to develop an effective phytoremediation system for soils highly contaminated by diesel.

Carotenoid and superoxide dismutase are the most effective antioxidants participating in ROS scavenging in phenanthrene accumulated wheat leaf

Polycyclic aromatic hydrocarbons (PAHs) are a kind of pollutants which could stimulate stress reaction in plant cells. In this study, we systematically verify that PAHs could induce an oxidative stress in plants, and describe their damages on wheat leaf subcellular structure and organelle, together with the contributions of antioxidants working against reactive oxygen species. The observation of transmission electron microscope exhibits that cell structures become plasmolyzed and distorted, and organelles disappear under phenanthrene (a model PAH) treatments. Osmiophilic granules arise with increasing phenanthrene concentrations, displaying the evidence for oxidative stress. As more H₂O₂ produce, and the accumulation of H₂O₂ is a fatal reason for cell death under PAH treatments. Through cluster analysis, Pearson correlation coefficient, principal component analysis and redundancy analysis, carotenoid and superoxide dismutase are the two most effective antioxidants to scavenge superoxide radicals among nine major antioxidants (ascorbate, glutathione, polyamines, α-tocopherol, carotenoid, catalases, ascorbate peroxidase, superoxide dismutase and glutathione-S-transferase), glutathione-S-transferase is a potential antioxidant, and Asa-GSH cycle would turn active under higher phenanthrene treatments. Ascorbate peroxidase and α-tocopherol would cause leaf moisture increase. Thus, this work provides better comprehension on the antioxidant performances and their potential application to improving plants' resistance under PAH pollution in the environment.

Impact of plant photosystems in the remediation of benzo[a]pyrene and pyrene spiked soils

The phytoremediation potential of 14 different plant species belonging to C3 and C4 carbon fixation pathway for soils spiked with polycyclic aromatic hydrocarbons (PAHs) such as benzo[a]pyrene (B[a]P) and pyrene (PYR) was investigated. A glasshouse experiment was conducted to measure the changes in morphological, physiological, biochemical parameters and the bioaccumulation and biodegradation ability of the plants in soils spiked with 48 and 194 mg kg^-1 of B[a]P and PYR, respectively. The per cent removal efficacy of B[a]P and PYR by the tested plant species over a period of 50 days was from 6 to 26% and 14 to 40% respectively. The maximum removal of both B[a]P and PYR was observed in Sudan grass (C4), vetiver (C4), maize (C4), and sunflower (C3). In terms of accumulation in root and shoot, the concentration of PYR was higher in both C3 and C4 plant species when compared to B[a]P. Overall the results indicated that C4 plants were more efficient than their C3 counterparts in terms of morphological, physiological, biochemical and degradation ability of PAHs.

Comparison of the effects of poultry manure and its biochar on barley growth in petroleum-contaminated soils

This study was conducted to evaluate and compare the effectiveness of two organic amendments [poultry manure (PM) and poultry manure biochar (PMB)] for the degradation of petroleum hydrocarbons in contaminated soils by barley plant at three levels of total petroleum hydrocarbons (TPHs) during 5 months under greenhouse conditions. TPHs removal efficiency and microbial respiration were shown to be higher at soil-cultivated plant than at uncultivated soil and in lowest level of contamination rather than other levels of contamination and at organic amendment treatment than unamended soil. Soil microbial respiration and TPHs degradation in the rhizosphere of barley increased by 15.64 and 12.74% for PM-amended treatment and 28.07 and 26.83% for PMB-amended treatment, respectively, in the 4% TPHs level compared with unamended treatment. Comparison of two amendments showed that in PMB treatment soil, highest dry weight, microbial respiration, and TPHs degradation potential were observed.

Effect of wetland plants and bacterial inoculation on dissipation of phenanthrene

This study attempts to evaluate the capacity of wetland plants' ability to dissipate phenanthrene (PHE) under waterlogged conditions. The results indicate that Typha latifolia and Vetiveria zizanioides may efficiently degrade PHE, and were much more effective when under combined plant cultivation with the inoculation of Pseudomonas frederiksbergensis (ATCC BAA-257) . Concentrations of PHE declined from 200 to less than 52 mg kg^-1 in all treatments with plant cultivation. At the end of the experimental period, PHE was undetectable in combined plant cultivation in the presence of bacteria inoculation. Microbial biomass C(carbon), N(nitrogen), and P(phosphate) were significantly different (p < 0.05) in the presence and absence of bacteria inoculation with bacteria inoculation significantly (p < 0.05) increased microbial biomass P. The presence of bacteria inoculation and different plant species significantly (p < 0.05) decreased the PHE concentrations in the microcosms. The inoculation of bacteria and release of exudates from plant roots further enhanced the dissipation of PHE in sand. Concentrations of citric and malic acids were decreased up to 69% in bacteria-inoculated treatments, showing large citric and malic acids serving as a food source and growth substrate for bacteria.

Phytoremediation potential of Acorus calamus in soils co-contaminated with cadmium and polycyclic aromatic hydrocarbons

Phytoremediation is a promising technology for the remediation of sites co-contaminated with inorganic (heavy metal) and organic pollutants. A greenhouse experiment was conducted to investigate the independent and interactive effects of cadmium (Cd) and polycyclic aromatic hydrocarbons (PAHs) on the growth of the wetland plant Acorus calamus and its ability to uptake, accumulate, and remove pollutants from soils. Our results showed that growth and biomass of A. calamus were significantly influenced by the interaction of Cd and PAHs after 60 days of growth. The combined treatment of low Cd and low PAHs increased plant biomass and Cd accumulation in plant tissues, thus enhancing Cd removal. Dissipation of PAHs from soils was not significantly influenced by Cd addition or by the presence of plants. Correlation analysis also indicated a positive relationship between residual concentrations of phenantherene and pyrene (PAHs), whereas enzyme activities (dehydrogenase and polyphenol oxidase) were negatively correlated with each other. Cluster analysis was used to evaluate the similarity between different treatments during phytoremediation of Cd and PAHs. Our results suggest that A. calamus might be useful for phytoremediation of co-contaminated soil.

Efficiency and mechanism of the phytoremediation of decabromodiphenyl ether-contaminated sediments by aquatic macrophyte Scirpus validus

Phytoremediation is an economic and promising technique for removing toxic pollutants from the environment. Freshwater sediments are regarded as the ultimate sink of the widely used PBDE congener decabromodiphenyl ether (BDE-209) in the environment. In the study, the aquatic macrophyte Scirpus validus was selected to remove BDE-209 from three types of sediments (silt, clay, and sand) at an environmentally relevant concentration. After 18 months of phytoremediation experiment, S. validus significantly enhanced the dissipation rates of BDE-209 in all the sediments compared to the controls. Average removal rates of BDE-209 in the three treatments of silt, clay, and sandy sediments with S. validus were respectively 92.84, 84.04, and 72.22%, which were 148, 197, and 233% higher than that in the control sediments without S. validus. In the phytoremediation process, the macrophyte-rhizosphere microbe combined degradation was the main pathway of BDE-209 removal. Sixteen lower brominated PBDE congeners (di- to nona-) were detected in the sediments and plant tissues, confirming metabolic debromination of BDE-209 in S. validus. A relatively higher proportion of penta- and di-BDE congeners among the metabolites in plant tissues than that in the sediments indicated further debromination of PBDEs within plants. The populations and activities of microorganisms in the sediments were greatly promoted by S. validus. Bacterial community structure in BDE-209-contaminated rhizosphere sediments was different from that in the control rhizosphere sediment, as indicated by the dominant proportions of β-proteobacteria, δ-proteobacteria, α-proteobacteria, Acidobacteria, and Chloroflexi in the microbial flora. All these results suggested that S. validus was effective in phytoremediation of BDE-209 by the macrophyte-rhizosphere microbe combined degradation in aquatic sediments.

Dissipation and phytoremediation of polycyclic aromatic hydrocarbons in freshly spiked and long-term field-contaminated soils

Pot experiments were used to compare the dissipation and phytoremediation effect of alfalfa (Medicago sativa L.) for polycyclic aromatic hydrocarbons (PAHs) in a freshly spiked soil and two field-contaminated soils with different soil organic carbon (SOC) contents (Anthrosols, 1.41% SOC; Phaeozems, 8.51% SOC). In spiked soils, the dissipation rates of phenanthrene and pyrene were greater than 99.5 and 94.3%, respectively, in planted treatments and 95.0 and 84.5%, respectively, in unplanted treatments. In field-contaminated Anthrosols, there were limited but significant reductions of 10.2 and 15.4% of total PAHs in unplanted and planted treatments, respectively. In field-contaminated Phaeozems, there were no significant reductions of total PAHs in either unplanted or planted treatments. A phytoremediation effect was observed for the spiked soils and the Anthrosols, but not for the Phaeozems. The results indicated that laboratory tests with spiked soils cannot reflect the real state of field-contaminated soils. Phytoremediation efficiency of PAHs in field-contaminated soils was mainly determined by the content of SOC. Phytoremediation alone has no effect on the removal of PAHs in field-contaminated soils with high SOC content.

Mineralization of pyrene induced by interaction between Ochrobactrum sp. PW and ryegrass in spiked soil

This study was conducted to investigate the capability of pyrene-degrading bacterium Ochrobactrum sp. PW and ryegrass (Lolium multiflorum) grown alone and in combination on the degradation of pyrene in soil. After 60 days of ryegrass growth, plant biomass, pyrene-degrading microbial mass, soil enzyme activity (catalase activity and polyphenol oxidase activity) and residual concentration of pyrene in soils were determined. Higher dissipation rates were observed in PW inoculation treatments: ryegrass+PW rhizosphere soil (RP-r) and ryegrass+PW non-rhizosphere soil (RP-nr), than planting of ryegrass alone, rhizosphere (R-r) or non-rhizosphere (R-nr). The inoculation with PW significantly (p<0.05) increased the dry weight of ryegrass root and shoot, nearly 2.8 and 3.3 times higher than ryegrass treatment. The pyrene-degrading microbial mass indicated that a much larger mass of bacteria, actinobacteria were present in RP treatment. The catalase activity in all different treatments were significantly (p<0.05) higher than in with treatment R-nr, and the polyphenol oxidase activity was also significantly (p<0.05) increased by inoculation with PW, leading to enhanced mineralization of pyrene from soil. Our results suggest that adding of PAHs-degrading bacteria to soil can enhance remediation of PAHs contaminated soil, while improving plant growth.

Unraveling the early molecular and physiological mechanisms involved in response to phenanthrene exposure

BACKGROUND

Higher plants have to cope with increasing concentrations of pollutants of both natural and anthropogenic origin. Given their capacity to concentrate and metabolize various compounds including pollutants, plants can be used to treat environmental problems - a process called phytoremediation. However, the molecular mechanisms underlying the stabilization, the extraction, the accumulation and partial or complete degradation of pollutants by plants remain poorly understood.

RESULTS

Here, we determined the molecular events involved in the early plant response to phenanthrene, used as a model of polycyclic aromatic hydrocarbons. A transcriptomic and a metabolic analysis strongly suggest that energy availability is the crucial limiting factor leading to high and rapid transcriptional reprogramming that can ultimately lead to death. We show that the accumulation of phenanthrene in leaves inhibits electron transfer and photosynthesis within a few minutes, probably disrupting energy transformation.

CONCLUSION

This kinetic analysis improved the resolution of the transcriptome in the initial plant response to phenanthrene, identifying genes that are involved in primary processes set up to sense and detoxify this pollutant but also in molecular mechanisms used by the plant to cope with such harmful stress. The identification of first events involved in plant response to phenanthrene is a key step in the selection of candidates for further functional characterization, with the prospect of engineering efficient ecological detoxification systems for polycyclic aromatic hydrocarbons.

Combined remediation of pyrene-contaminated soil with a coupled system of persulfate oxidation and phytoremediation with ryegrass

The in situ chemical oxidation technology (ISCO) and phytoremediation for PAHs have been studied respectively, but few focus on the feasibility of combining persulfate with ryegrass. This literature revealed the effect of persulfate oxidation on the growth of ryegrass and the removal ratios of pyrene in the couple system of persulfate oxidation and phytoremediation. The results demonstrated that half of pyrene in test soil was oxidized by persulfate in 7 days and then the residual pyrene concentration was decreased to a lower level by ryegrass in the following 2 months in oxidation treatment and drip washing and plants (OWP) and oxidation treatment and drip washing and plants and fertilization (OWFP) treatment. Ryegrass could grow well after persulfate oxidation with the oxidized soil washed by water. Ryegrass in OWP and OWFP treatments had higher ratios of overground and underground biomass. However, the seeds of ryegrass cannot germinate when drip washing was omitted. Pyrene together with residual persulfate changed soil enzyme activities. Drip washing and the growth of ryegrass made soil enzyme activities tend to returned to normal levels. Persulfate oxidation and phytoremediation were compatible to make contributions to the dissipation of pyrene. Persulfate oxidation activated by heat had higher removal efficiency of PAHs and phytoremediation could further decrease the pyrene concentration in spiked soil.

The effects of simultaneous application of plant growth regulators and bioaugmentation on improvement of phytoremediation of pyrene contaminated soils

Polycyclic aromatic hydrocarbons (PAHs) refer to a wide group of soil contaminants whose presence in the environment is a cause of concern. The present study aimed to evaluate the effects of Indole Acetic Acid (IAA) and Pseudomonas aeruginosa on the phytoremediation activities of sorghum bicolor and increase in pyrene removal efficiency in the soil. The initial concentration of pyrene was 150 and 300 mg kg(-1) in this experiment. The treatments included unplanted soil (T0), planted soil with sorghum (T1), planted soil with application of IAA (T2), planted soil with application of Pseudomonas sp. (T3), and planted soil with simultaneous application of IAA and Pseudomonas sp. (T4). The pyrene removal rate in the soil was measured every 30 days. Moreover, plant biomass and soil bacteria were measured after 90 days. The results showed that pyrene removal rate significantly increased in the planted treatments compared to the unplanted ones. After 90 days, at the initial concentration of 150-300 mg kg(-1), pyrene removal efficiency was 52-92% in T1-T4 and 35-47% in the unplanted treatment (T0). Application of IAA and Pseudomonas sp. significantly increased plant biomass, soil bacteria, and pyrene removal rate in T2, T3, and T4 compared to T1. Therefore, application of IAA in the planted treatments with sorghum could have a significant effect on increasing the removal efficiency of pyrene.