Phytoremediation Of Polycyclic Aromatic Hydrocarbons Research Articles

Rice husk and its derived biochar assist phytoremediation of heavy metals and PAHs co-contaminated soils but differently affect bacterial community

In order to evaluate the feasibility of rice husk and rice husk biochar on assisting phytoremediation of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) co-contaminated soils, a 150-day pot experiment planted with alfalfa was designed. Rice husk and its derived biochar were applied to remediate a PAHs, Zn, and Cr co-contaminated soil. The effects of rice husk and biochar on the removal and bioavailability of PAHs and HMs, PAH-ring hydroxylating dioxygenase gene abundance and bacterial community structure in rhizosphere soils were investigated. Results suggested that rice husk biochar had better performance on the removal of PAHs and immobilization of HMs than those of rice husk in co-contaminated rhizosphere soil. The abundance of PAH-degraders, which increased with the culture time, was positively correlated with PAHs removal. Rice husk biochar decreased the richness and diversity of bacterial community, enhanced the growth of Steroidobacter, Bacillus, and Sphingomonas in rhizosphere soils. However, Steroidobacter, Dongia and Acidibacter were stimulated in rice husk amended soils. According to the correlation analysis, Steroidobacter and Mycobacterium may play an important role in PAHs removal and HMs absorption. The combination of rice husk biochar and alfalfa would be a promising method to remediate PAHs and HMs co-contaminated soil.

Biochars assisted phytoremediation of polycyclic aromatic hydrocarbons contaminated agricultural soil: Dynamic responses of functional genes and microbial community

A biochar-intensified phytoremediation experiment was designed to investigate the dynamic effects of different biochars on polycyclic aromatic hydrocarbon (PAH) removal in ryegrass rhizosphere contaminated soil. Maize and wheat straw biochar pyrolyzed at 300 °C and 500 °C were amended into PAH-contaminated soil, and then ryegrass (Lolium multiflorum L.) was planted for 90 days. Spearman's correlations among PAH removal, enzyme activity, abundance of PAH-ring hydroxylating dioxygenase (PAH-RHDα), and fungal and bacterial community structure were analyzed to elucidate the microbial degradation mechanisms during the combined remediation process. The results showed that 500 °C wheat straw biochar had higher surface area and more nutrients, and significantly accelerated the phytoremediation of PAHs (62.5 %), especially for high molecular weight PAH in contaminated soil. The activities of urease and dehydrogenase and the abundance of total and PAH-degrading bacteria, which improved with time by biochar and ryegrass, had a positive correlation with the removal rate of PAHs. Biochar enhanced the abundance of gram-negative (GN) PAH-RHDα genes. The GN PAH-degraders, Sphingomonas, bacteriap25, Haliangium, and Dongia may play vital roles in PAH degradation in biochar-amended rhizosphere soils. Principal coordinate analysis indicated that biochar led to significant differences in fungal community structures before 30 days, while the diversity of the bacterial community composition depended on planting ryegrass after 60 days. These findings imply that the structural reshaping of microbial communities results from incubation time and the selection of biochar and ryegrass in PAH-contaminated soils. Applying 500 °C wheat straw biochar could enhance the rhizoremediation of PAH-contaminated soil and benefit the soil microbial ecology.

Distribution, source, risk and phytoremediation of polycyclic aromatic hydrocarbons (PAHs) in typical urban landscape waters recharged by reclaimed water

A park that had used reclaimed water as the sole water supply for fourteen years, was selected to analyze the distribution, sources and risks of 16 priority polycyclic aromatic hydrocarbons (PAHs) in waters and sediments. The effects of phytoremediation were investigated in waterbodies classified as phytoremediation, transitional and non-phytoremediation areas. Diagnostic ratio (DR) and principal component analysis (PCA) were used to analyze the sources of PAHs, while risk quotient (RQ) was used as risk assessment tool. Results showed that ∑PAH concentrations in sediments ranged from 29.4 to 1245.6 ng‧g−1, with average of 354.3 ng‧g−1, corresponding to a moderate pollution level. The concentration of PAHs in water ranged from 10.6 to 326.3 ng‧L−1, with average of 147.2 ng‧L−1, corresponding to a low pollution level. The ∑PAHs in sediments showed a downward trend from northwest to southeast along with the water flow direction, with average values of 459.5, 362.9 and 246.1 ng‧L−1 in the upstream, midstream and downstream, respectively. In contrast, PAH concentrations in water were consistent with recreational activities in the urban park area. There were 95% of water samples and 72% of sediment samples obtaining the Ant/(Ant + Phe) > 0.1 and Flu/(Flu + Pyr) > 0.5, indicating that coal combustion was the major source of PAHs in both the water and sediment. The RQ∑PAH(NCs) values in water and sediment were all between 1 and 800, while RQ∑PAH(MPCs) reached equal to 0, suggesting that ∑PAHs presented a low ecological risk. Acenaphthene accounted for 28.4% of RQ(NCs), and became the most risk PAH in water column. Aquatic plants effectively removed high-ring PAHs from water and middle-ring PAHs from sediments, reducing the overall risks posed by PAHs.

Allochthonous arbuscular mycorrhizal fungi promote Salix viminalis L.–mediated phytoremediation of polycyclic aromatic hydrocarbons characterized by increasing the release of organic acids and enzymes in soils

Polycyclic aromatic hydrocarbons (PAHs) are well known persistent organic pollutants that have carcinogenic, teratogenic, and mutagenic effects on humans and animals. Arbuscular mycorrhizal fungi (AMF) that can infest plant hosts and form symbioses may help plants to enhance potential rhizosphere effects, thus contributing to the rhizodegradation of PAH-contaminated soils. The present study aimed to assess the effectiveness of AMF on enhancing Salix viminalis–mediated phytoremediation of PAH-polluted soil and clarify the plant enzymatic and organic acid mechanisms induced by AMF. Natural attenuation (NA), phytoremediation (P, Salix viminalis), S. viminalis-AMF combined remediation using willow inoculated with Funneliformis mosseae (PM), Laroideoglomus etunicatum (PE), and Rhizophagus intraradices (PI) were used as strategies for the remediation of PAH-polluted soils. The results showed that AMF inoculation contributed to the dissipation of the high-molecular-weight PAH benzo (α) pyrene that had concentrations in PM, PE, and PI treatments of 40.1 %, 24.49 %, and 36.28 % of the level in the NA treatment, and 62.32 %, 38.05 %, and 56.38 % of the level in the P treatment after 90 days. The mycorrhizal treatment also improved the removal efficiency of phenanthrene and pyrene, as their concentrations were sharply decreased after 30 days compared to the NA and P treatments. The research further clarified the changes in rhizosphere substances induced by AMF. Organic acids including arachidonic acid, octadecanedioic acid, α-linolenic acid, 10,12,14-octadecarachidonic acid and 5-methoxysalicylic acid that can act as co-metabolic substrates for certain microbial species to metabolize PAHs were significantly increased in AMF-inoculated treatments. AMF inoculation also elevated the levels of polyphenol oxidase, laccase, and dehydrogenase, that played crucial roles in PAHs biodegradation. These findings provide an effective strategy for using AMF-assisted S. viminalis to remediate PAH-polluted soils, and the results have confirmed the key roles of organic acids and soil enzymes in plant-AMF combined remediation of PAHs.

Application of biochar-immobilized Bacillus sp. KSB7 to enhance the phytoremediation of PAHs and heavy metals in a coking plant

The co-existence of heavy metals and polycyclic aromatic hydrocarbons (PAHs) challenges the remediation of polluted soil. This study aimed to investigate whether a combined amendment of biochar-immobilized bacterium (BM) could enhance the phytoremediation of heavy metals and PAHs in co-contaminated soil. The Bacillus sp. KSB7 with the capabilities of plant-growth promotion, metal tolerance, and PAH degradation was immobilized on the peanut shell biochar prepared at 400 °C and 600 °C (PBM4 and PBM6, respectively). After 90 days, PBM4 treatment increased the removal of PAHs by 94.17% and decreased the amounts of diethylenetriamine pentaacetic acid–extractable Zn, Pb, Cr, and Cu by 58.46%, 53.42%, 84.94%, and 83.15%, respectively, compared with Kochia scoparia–alone treatment. Meanwhile, PBM4 was more effective in promoting K. scoparia growth and reducing the uptake of co-contaminants. The abundance of Gram-negative PAH-degrader and 1-aminocyclopropane-1-carboxylic deaminase–producing bacteria within rhizosphere soil was significantly improved after PBM4 treatment. Moreover, the relative abundance of the Bacillus genus increased by 0.66 and 2.05 times under PBM4 treatment compared with biochar alone and KSB7, indicating that KSB7 could colonize in the rhizosphere soil of K. scoparia. However, the removal of PAHs and heavy metals after PBM6 and 600 °C biochar-alone treatments caused no obvious difference. This study suggested that low-temperature BM-amended plant cultivation would be an effective approach to remove PAHs and heavy metals in co-contaminated soil.

Phytoremediation of PAHs in Contaminated Soils: A Review

Polycyclic aromatic hydrocarbons (PAHs), which are also part of persistent organic pollutants (POPs), are considered to be especially toxic to humans (carcinogenic), likewise to plants, microorganisms and other living organisms. PAHs soil contamination occurs by storage leaking, transport loss, the land disposal of petroleum waste, and accidental or intentional spills. Due to their ubiquitous occurrence, recalcitrance, bioaccumulation potential and carcinogenic activity, PAHs are a significant environmental concern. The methods of controlling and repairing PAH-contaminated soils mainly include physical remediation, chemical remediation and phytoremediation. However, there was an increasing focus on phytoremediation technologies as a result of their unique advantages, including low cost, lack of secondary pollution and large-area application. Phytoremediation is therefore one of the soil remediation technologies with the greatest potential.

Non-targeted metabolomics reveal the impact of phenanthrene stress on root exudates of ten urban greening tree species

Different root exudations can modify the bioavailability of persistent organic pollutants (POPs). Among these exudations, the low molecular weight organic acids play an imperative role in this process. The study was conducted to analyze the effect of phenanthrene (PHE) stress on root exudation variations and changes in its chemical composition in ten urban greening tree species, namely Loropetalum chinense, Gardenia ellis, Photinia fraseri, Ligustrum japonicum, Rhododendron simsii, Osmanthus fragrans, Gardenia jasminoides, Buxus sinica, Camellia sasanqua, and Euonymus japonicas. The experiment was carried out in three PHE concentration treatments (0 mg kg−1 (CK), 200 mg kg−1 (PHEL), 2000 mg kg−1 (PHEH)). The root exudates were collected and analyzed by GC-MS method. In total, 673 compounds were identified either with high or low abundance among all species and treatments. Compounds identified in CK, PHEL, and PHEH were 240, 180, and 256, respectively. The results illustrated that carbohydrates, phenols, and esters were the dominant compounds, accounted for more than 92%. Principal component analysis depicted that tree species grown in PHEH showed obvious alteration in compounds of root exudation, whereas little difference was noticed between PHEL and CK. Phenols (80%) were the most abundant, while nitriles contributed a small portion. Moreover, among all species, R. simsii released the maximum number of compounds, and L. japonicum released the least number of compounds accounting for 89 and 46, respectively. The results achieved here to illustrate that plant type, and PHE stress can significantly change the concentrations and species of root exudates. This study provides the scientific reference for understanding the phenanthrene responsive changes in root exudates and phytoremediation of polycyclic aromatic hydrocarbons (PAHs), as well as a screening of urban greening tree species.

Enhanced phytoremediation of PAHs and cadmium contaminated soils by a Mycobacterium

This study investigated Fire Phoenix (Festuca L.) and Echinacea purpurea (L.) Moench inoculated with a Mycobacterium strain N12 in remediation of soils contaminated with both polycyclic aromatic hydrocarbons (PAHs) and cadmium (Cd). Plant growth and PAH and Cd removal were monitored in 60, 120, and 150 days after transplanting. Results showed that Fire Phoenix plants grown in soil containing 200 mg/kg PAHs and 15 mg/kg Cd inoculated with N12 were able to remove 76.3% PAHs compared to removal of 68.3% of PAHs by the plants without N12 inoculation. On day 150, the underground biomass of Fire Phoenix plants grown in soil inoculated with N12 increased 59.40% compared to that without N12 inoculation. The enhanced removal of PAH by Fire Phoenix and N12 was related to the improved rhizosphere microbial activities. However, inoculation of N12 to E. purpurea grown soil did not significantly improve the removal of PAHs and Cd. Our results showed that phytoremediation of PAHs and Cd can be enhanced by a Mycobacterium strain N12, especially when PLFA concentrations of bacteria and fungi exceeded 60% of the initial concentrations, but the enhancement is plant species dependent.

Nano-SiO2 combined with a surfactant enhanced phenanthrene phytoremediation by Erigeron annuus (L.) Pers.

The objective of this experiment was to evaluate the effects of Triton X-100 (1000mgkg-1) and nano-SiO2 (500mgkg-1) on Erigeron annuus (L.) Pers. grown in phenanthrene spiked soil (150mgkg-1) for 60days. Results show that untreated groups, groups treated with both Triton X-100 and nano-SiO2, exhibited better phenanthrene degradation rates and improved root biomasses, chlorophyll contents, and soil enzyme activities. This study demonstrates that Triton X-100 combined with nano-SiO2 protects plants, alleviating the stress of polycyclic aromatic hydrocarbons (PAHs), and can provide a means for improving phytoremediation of PAH contaminated soils.

Iron Plaque Prevents Partitioning of Polycyclic Aromatic Hydrocarbons on Rice (Oryza sativa) Root Surface.

Adsorption of polycyclic aromatic hydrocarbons (PAHs) on root surfaces has essential impacts on PAH phytoremediation. An Fe plaque is commonly formed on the root surface of aquatic plants. Therefore, it is worth investigating the impact of the Fe plaque on PAH adsorption on rice root surfaces. Using Bayesian linear water-methanol cosolvent models, we estimated accurate water-biosorbent partition coefficient values for phenanthrene, pyrene, and benzo[a]pyrene between water and rice root biosorbent fractions, including rice root materials with Fe plaque, removed Fe plaque, and removed Fe plaque and lipids. Our results showed that Fe plaque inhibited the adsorption of PAHs on rice root surface; the inhibition impacts increased with hydrophobicity of PAHs. This result highlights the need for considering the impact of Fe plaque on PAH adsorption during phytoremediation. Integr Environ Assess Manag 2020;16:392-399. © 2020 SETAC.

The relief effects of organic acids on Scirpus triqueter L. under pyrene-lead stress.

During phytoremediation of polycyclic aromatic hydrocarbons (PAHs) and heavy metals, the phytoremediation plants are often stressed by pollutants, which would reduce the efficiency of phytoremediation. The addition of organic acids from root exudates could alleviate the stress. In this study, three organic acids (citric acid, succinic acid, glutaric acid) were added to investigate the effects of organic acids on the stress response of Scirpus triqueter L. at two pyrene-lead concentrations. The activities of reactive oxygen species, malondialdehyde, plasma membrane H+-ATPase, and vacuolar H+-ATPase and PPase activity, as well as the activities of antioxidant enzymes (SOD, POD, and CAT) in Scirpus triqueter L. were determined. The addition of organic acids could effectively reduce the activities of reactive oxygen species, malondialdehyde, plasma membrane H+-ATPase, and vacuolar H+-ATPase and PPase activities. Under higher pollution, the damage of plant plasma membrane is more serious, but the addition of citric acid can alleviate this situation and even more effective than the relief under low pollution. The effect of citric acid was more significant than that of succinic acid and glutaric acid. These results demonstrated that organic acids could attenuate the stress of pyrene and lead to Scirpus triqueter L.

Selenium enhances Conyza canadensis phytoremediation of polycyclic aromatic hydrocarbons in soil

To determine whether supplemental selenium (Se) enhances the tolerance of Conyza canadensis (C. canadensis) to polycyclic aromatic hydrocarbons (PAHs) and thereby accelerates PAH dissipation in soils. We examined the dissipation of different concentrations of two PAHs, phenanthrene (PHE) and pyrene (PYR), from contaminated soils after 60 days of growth of C. canadensis supplemented with or without a low level of Se (0.5 mg kg−1) in a pot culture experiment. PAH concentrations were 0, 50, 200, and 800 mg kg−1. Response variables included plant biomass, PAH accumulation in plants, soil microbial biomass carbon (MBC), root morphogenesis, antioxidant enzyme activity, and PHE/PYR dissipation. Plant biomass and root morphogenesis decreased with increasing PAH concentration, whereas malondialdehyde concentration, an indicator of oxidative stress, increased. Catalase activity, total superoxide dismutase activity, MBC, and the PAH dissipation ratio all increased with increasing PAH concentration until 800 mg kg−1. Se supplementation of soil increased the tolerance of C. canadensis to PAHs and significantly increased PAH phytoremediation after 60 days of plant growth. The PHE dissipation ratios with and without Se supplementation were 57 ± 3% and 28 ± 8%, respectively, and PYR dissipation ratios were 30 ± 7% and 24 ± 8%. The increase in the PAH dissipation ratio with Se supplementation was largest in PHE-contaminated soils at 800 mg kg−1. A low concentration of supplemental Se in soil enhances the dissipation of PHE and PYR by C. canadensis. This enhancement is due to an increased plant tolerance toward PAHs, which results in increased C. canadensis biomass, soil MBC, and decreased plant uptake of PAHs. This study suggests that Se supplementation can contribute to ongoing efforts to develop effective phytoremediation systems for soils contaminated with PAHs.

低分子有机酸对土壤中菲降解及细菌群落结构的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 低分子有机酸对土壤中菲降解及细菌群落结构的影响 DOI: 10.5846/stxb201806281420 作者: 作者单位: 中南林业科技大学生命科学与技术学院,中南林业科技大学生命科学与技术学院,中南林业科技大学生命科学与技术学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家科技支撑计划子项目（2015BAD07B0503）；林业科学技术推广项目（[2017]12号）；城市森林生态湖南省重点实验室资助；湖南省科技计划项目（2015SK2002） Effects of low-molecular-weight organic acids on the degradation of phenanthrene and bacterial community structure in soil Author: Affiliation: Central South University of Forestry and Technology,ForestrySCollege,Changsha,Central South University of Forestry and Technology,ForestrySCollege,Changsha,Central South University of Forestry and Technology,ForestrySCollege,Changsha Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:多环芳烃是一类普遍存在于环境中的持久性有机污染物，其通过食物链进入生态系统，直接危害人类健康和整个生态系统的安全。为探讨低分子有机酸对土壤中菲降解及细菌群落结构的影响，通过室内培养的方式研究了在添加不同种类有机酸处理下第0-180天土壤中菲含量的变化状况，并采用高通量Illumina Miseq技术分析了土壤细菌群落种类和数量的变化特征。结果表明，低分子有机酸对于土壤中菲的降解有明显的促进作用，由一级动力学方程得出乙酸对菲降解的促进作用最明显。从细菌群落结构来看，土壤细菌的数量及其多样性或许不是导致土壤菲降解的主要因素，反而特定的菲降解菌的丰度对菲降解有重要影响。添加低分子有机酸减少了细菌OTU数及细菌菌群多样性，但增加了PAHs降解菌的丰度。随着时间推移细菌总OTU数呈现下降趋势，独有种类数均呈现出先增长后下降的趋势。检测到了6种典型的菲降解菌，分别为：Bacillus、鞘氨醇单胞菌属、Massilia、Azospirillum、Burkholderia-paraburkholderia、红球菌。研究结果可为多环芳烃污染土壤的植物修复提供基础数据和科学参考。 Abstract:Polycyclic aromatic hydrocarbons (PAHs) are common persistent organic environmental pollutants, which enter the ecosystem through the food chain and directly endanger human health and the safety of the entire ecosystem. To investigate effects of low-molecular-weight organic acids on degradation of phenanthrene and bacterial community structure in soil, changes in soil phenanthrene content during 0-180 d after addition of different organic acids were assessed via variations in indoor culture characteristics of soil bacterial community types and quantities via high-throughput Illumina Miseq. Consequently, addition of low-molecular-weight organic acids significantly promoted phenanthrene degradation in soil, and the first-order reaction kinetids revealed that acetic acid had the most significant effect on phenanthrene degradation. Considering the bacterial community structure, addition of low-molecular-weight organic acids reduced the number of operational taxonomic units (OTUs) and the diversity of bacterial flora but increased the abundance of PAH-degrading bacteria. The total number of bacterial OTUs displayed a decreasing trend with time, and the number of unique species initially displayed an increasing trend, followed by a decreasing trend. Six typical phenanthrene-degrading bacteria were detected:Bacillus, Sphingomonas, Massilia, Azospirillum, Paraburkholderia, and Rhodococcus. These results provide a basis and a scientific reference for phytoremediation of PAHs contaminating soil. 参考文献 相似文献 引证文献

Mechanistic understanding and future prospect of microbe-enhanced phytoremediation of polycyclic aromatic hydrocarbons in soil

Abstract Restoring polluted land is a time-consuming endeavor due to the difficulty inherent in the process. The quality of soil considerably worsens with the addition of toxic persistent organic pollutants (POPs) of industrial origin. Industrialization results in millions of tonnes of POPs worldwide, which pose a threat to surrounding ecosystems. In India alone, oil refineries generate approximately 28,000 tonnes of oily sludge (toxic organic compounds) per annum containing POPs—polycyclic aromatic hydrocarbons (PAHs). These PAHs have existed in environments throughout the globe for the last several decades due to long half-lives. The fate of PAHs and their residues pose a threat to all forms of life. High levels of the 16 PAHs (US EPA) were found in soil in Asia’s oldest oil and gas drilling site, with a range spanning from a minimum of 13.48 to a maximum of 86.3 mgkg − 1 due to exploration of crude oil. The management of such a paradoxical situation is a challenge. The mitigation of PAHs by employing plant–microbe systems from soil is a low-cost prospective biotechnological approach. This technology engineers the rhizosphere and helps restoration of degraded land. Recent findings demonstrated how adding biochar (carbon rich phytoproduct) to the soil resulted in positive effects on plant–microbe assisted PAH removal. This review focuses on the mechanistic understanding of plant–microbe assisted remediation. We consider the future prospect to optimize the phytoremediation process through genomics and metabolomics data. The genetic manipulation of plants and microbes seems to have improved the phytoremediation process by utilizing the signaling network of plant–microbe interactions

Mixed-surfactant-enhanced phytoremediation of PAHs in soil: Bioavailability of PAHs and responses of microbial community structure

The present study was conducted to explore the mechanisms of surfactant-enhanced phytoremediation of soils contaminated with polycyclic aromatic hydrocarbons (PAHs), focusing on the bioavailability of PAHs and microbial diversity. We investigated the remediation efficiencies of phenanthrene and pyrene after the addition of mixed surfactants (sodium dodecyl benzene sulfonate (SDBS) and Tween 80) of different ratios (1:1, 1:2, and 2:1) at the concentration of 100 mg/kg to soils cultured with ryegrass (Lolium multiflorum L.). The fractions of phenanthrene and pyrene were determined using a sequential extraction method, and the microbial diversity was evaluated using 16S rRNA gene high-throughput sequencing. The results showed that mixed surfactants could enhance the remediation efficiencies of PAHs, and mainly occurred in the initial 21 days. Mixed surfactants at the ratio of 1:1 (HM1) showed the best remediation efficiency in enhancing the dissipation of pyrene in 21 days. Mixed surfactants showed little effects on the removal of phenanthrene. In general, HM1 significantly decreased the bioavailable, bound and residual fractions of pyrene; additionally, higher abundances of PAH-degradation bacteria and degradation-related genes were observed. Pearson correlation analysis among PAH degraders, degradation-related genes and bioavailable fraction of PAHs was performed. Our results indicated that mixed surfactants could promote the transformation of pyrene from the bound and residual fractions to bioavailable fractions and enhance the abundances of PAH degradation bacteria and PAH degradation-related genes, thereby enhancing the degradation of pyrene.

Isolation of Endophytic Bacteria and Phytoremediation of Soil Contaminated with Polycyclic Aromatic Hydrocarbons Using Cajanus cajan and Lablab purpereus

Polycyclic aromatic hydrocarbons (PAHs) are among the major compounds posing environmental and health problems worldwide. In the present study, phytoremediation of PAHs using Cajanus cajan and Lablab purpereus in addition to isolation of endophytic bacteria associated with the plant tissues was undertaken. Soil samples contaminated with PAHs were collected from a mechanic workshop in Sokoto metropolis and analysed using standard laboratory procedures. Seeds of the two plants species were sown in the contaminated soil and irrigated for eight weeks to determine the plants’ ability to remediate PAHs. Bacterial count revealed that the plants’ tissues contained 2.3×104 cfu/g and 2.7×104 cfu/g of endophytes. The endophytes were identified to be the members of Pseudomonas, Micrococcus, Bacillus, Rhodococcus and Flavobacterium. GC-MS analysis revealed that the soil samples contained 19.21 ppm PAHs, which were reduced to 2.34 ppm (12.18%) and 4.88 ppm (25.40%) in soils treated with C. cajan and L. purpureus, respectively. Naphthalene was completely degraded in both cases, whereas pyrene, flourene and flouranthene were either completely degraded or significantly reduced. Only indeno (1,2,3 cd) pyrene was least degraded with more than 50% residual concentration. Therefore, the plant species was considered as an important tool in the remediation of PAHs contaminated soil and the role of their endophytes in degradation was thoroughly investigated.

Microbial mechanisms controlling the rhizosphere effect of ryegrass on degradation of polycyclic aromatic hydrocarbons in an aged-contaminated agricultural soil

The phytoremediation of polycyclic aromatic hydrocarbons (PAHs) depends on plant-microbe interactions in the rhizosphere, but the extent and mechanisms of these effects are still unclear. The aim of this study was to investigate the effects of plants on PAHs degradation and on associated changes in transcriptionally active bacterial community structures, degrading bacteria, and especially functional gene expression in a PAH-contaminated agricultural soil. We conducted a rhizo-box experiment planted with ryegrass for 60 days under glasshouse conditions. The degradation of 12PAHs in rhizosphere and non-rhizosphere soils during the experiment was quantified using HPLC analysis. The dynamics of active bacterial community structure in soil were assessed using the molecular tool of cDNA-based denaturing gradient gel electrophoresis (DGGE). Functional PAH-ring hydroxylating dioxygenase (PAH-RHDα) genes were cloned using the Gram-positive (GP) and Gram-negative (GN) primers. The abundance and activity of total bacteria and GP/GN PAH-degraders were monitored by real-time PCR. Results demonstrate that the agricultural soil contained known PAH degraders and RHDα genes, such as nidA3, pdoA, nahAc and phnAc. The presence of ryegrass promoted the dissipation of PAHs and changed the structures of active bacterial communities in soil. In general, the abundance of total bacteria and GP PAH-degrader increased during the inoculation time. The ryegrass root enhanced the functional bacterial diversity in the early stages (0–10 days). However, the effect of ryegrass roots may stimulate the expression of GP and GN PAH-RHDα genes after 40 days. Our results indicate that ryegrass increased the degradation of PAHs by promoting bacteria diversity, increasing the abundance of total bacteria and PAH degraders, and stimulating RHDα gene expression.

Field-Scale Phytoremediation of Mixed Contaminants in Upland Area of Big Marsh Site, Chicago, USA

The suitability of nine native restoration plant species has been evaluated for phytoremediation of polycyclic aromatic hydrocarbons (PAHs) and heavy metals in upland area of Big Marsh site (Chicago, IL, USA). From the initial nine species planted in the experimental area, only the prairie grass Little Bluestem (Andropogon scoparius) survived the three growing seasons. Replicate test plots were prepared by tilling and homogenizing the surface soil and underlying fill materials to approximate depth of 0.3 m. The survival and growth of the plant species were monitored for the first two growing seasons. Soil samples from each plot were collected before and after preparing the test plots and after the second and third growing seasons. Plant root and shoot samples were also collected at the end of the second and third growing seasons. PAHs and heavy metals were analyzed in the soil and plant samples. In addition, sequential extraction procedure was followed to determine the fractionation of the heavy metals in soils before and after planting. Analysis of benzo-a-pyrene (typical PAH) concentrations in roots showed an uptake and accumulation of this contaminant in the below-ground part of the plant, while the presence of the organic contaminants in stems and leaves of the surviving plant were non-detectable. No significant decrease of heavy metals was found in the soil at the end of the experiment. Furthermore, the presence of plants did not affect the heavy metal mobility or speciation in the soil. However, the presence of chromium (Cr), lead (Pb), manganese (Mn) and zinc (Zn) in the roots of Little Bluestem indicated the uptake and accumulation of these metals in the plant. The presence of Cr and Pb in stems and leaves was below detection limits, while concentrations of Mn and Zn were found to increase in the aerial part of the plant towards the end of the experiment. The survival of Little Bluestem and its high tolerance to the site conditions, makes it a suitable species for the phytoremediation of conditions representative of the upland areas of the field site.

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.

Phenanthrene and Pyrene Modify the Composition and Structure of the Cultivable Endophytic Bacterial Community in Ryegrass (Lolium multiflorum Lam).

This study provides new insights into the dynamics of bacterial community structure during phytoremediation. The communities of cultivable autochthonous endophytic bacteria in ryegrass exposed to polycyclic aromatic hydrocarbons (PAHs) were investigated with regard to their potential to biodegrade PAHs. Bacterial counts and 16S rRNA gene sequence were used in the microbiological evaluation. A total of 33 endophytic bacterial strains were isolated from ryegrass plants, which represented 15 different genera and eight different classes, respectively. Moreover, PAH contamination modified the composition and structure of the endophytic bacterial community in the plants. Bacillus sp., Pantoea sp., Pseudomonas sp., Arthrobacter sp., Pedobacter sp. and Delftia sp. were only isolated from the seedlings exposed to PAHs. Furthermore, the dominant genera in roots shifted from Enterobacter sp. to Serratia sp., Bacillus sp., Pantoea sp., and Stenotrophomonas sp., which could highly biodegrade phenanthrene (PHE). However, the diversity of endophytic bacterial community was decreased by exposure to the mixture of PAHs, and increased by respective exposure to PHE and pyrene (PYR), while the abundance was increased by PAH exposure. The results clearly indicated that the exposure of plants to PAHs would be beneficial for improving the effectiveness of phytoremediation of PAHs.