Dissipation Of Polycyclic Aromatic Hydrocarbons Research Articles

Interspecific comparison of polycyclic aromatic hydrocarbons and persistent organochlorines bioaccumulation in bivalves from a Mediterranean coastal lagoon

The bioaccumulation of polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) was characterized in cockle, oyster and noble pen shell from nine areas in the Mar Menor lagoon with different hydrodynamic and pollutant sources. Biota, sediment and water samples were simultaneously collected in the spring and autumn of 2010. Considering all bivalve samples, PAH concentrations ranged from 8.98 to 370μg·kg−1 d.w., those of PCBs from 0.15 to 42.36μg·kg−1 d.w. and those of DDXs from below detection limit to 240.6μg·kg−1 d.w., where p,p′-DDE was the main fraction. The bioaccumulation of PAHs was similar for cockle, oyster and noble pen shell, being higher close to ports and wastewater effluents. However, DDX and PCB bioaccumulations in oyster and noble pen shell were significantly higher than in cockle in spring (p=0.02). The first organic pollutant bioaccumulation data for noble pen shell were obtained in this study, showing a preferential accumulation of pyrene. The increase of PAH bioaccumulation in autumn, as compared to spring, was low, due to high water temperatures during the summer, which favoured PAH dissipation processes. No significant seasonal variations were detected for OCPs and PCBs, except in some specific areas. The PAH, PCB and OCP levels detected in these bivalves were lower than OSPAR/MED POL environmental assessment criteria, except for p,p′-DDE in bivalves sited close to El Albujón watercourse mouth.

Role of arbuscular mycorrhizal fungus Rhizophagus custos in the dissipation of PAHs under root-organ culture conditions

Polycyclic aromatic hydrocarbons (PAHs) are one of the most common contaminants in soil. Arbuscular mycorrhizal (AM) fungi make host plants resistant to pollutants. This study aims to evaluate the impact of anthracene, phenanthrene and dibenzothiophene on the AM fungus Rhizophagus custos, isolated from soil contaminated by heavy metals and PAHs, under monoxenic conditions. We found a high level of tolerance in R. custos to the presence of PAHs, especially in the case of anthracene, in which no negative effect on AM-colonized root dry weight (root yield) was observed, and also a decrease in the formation of anthraquinone was detected. Increased PAH dissipation in the mycorrhizal root culture medium was observed; however, dissipation was affected by the level of concentration and the specific PAH, which lead us to a better understanding of the possible contribution of AM fungi, and in particular R. custos, to pollutant removal.

Inoculation of PAH-degrading strains of Fusarium solani and Arthrobacter oxydans in rhizospheric sand and soil microcosms: microbial interactions and PAH dissipation

Very little is known about the influence of bacterial-fungal ecological interactions on polycyclic aromatic hydrocarbon (PAH) dissipation in soils. Fusarium solani MM1 and Arthrobacter oxydans MsHM11 can dissipate PAHs in vitro. We investigated their interactions and their effect on the dissipation of three PAHs-phenanthrene (PHE), pyrene (PYR) and dibenz(a,h)anthracene (DBA)-in planted microcosms, in sterile sand or non-sterile soil. In sterile sand microcosms planted with alfalfa, the two microbes survived and grew, without any significant effect of co-inoculation. Co-inoculation led to the dissipation of 46% of PHE after 21days. In soil microcosms, whether planted with alfalfa or not, both strains persisted throughout the 46days of the experiment, without any effect of co-inoculation or of alfalfa, as assessed by real-time PCR targeting taxon-level indicators, i.e. Actinobacteria 16S rDNA and the intergenic transcribed spacer specific to the genus Fusarium. The microbial community was analyzed by temporal temperature gradient electrophoresis and real-time PCR targeting bacterial and fungal rDNA and PAH-ring hydroxylating dioxygenase genes. These communities were modified by PAH pollution, which selected PAH-degrading bacteria, by the presence of alfalfa and, concerning the bacterial community, by inoculation. PHE and PYR concentrations significantly decreased (91 and 46%, respectively) whatever the treatment, but DBA concentration significantly decreased (30%) in planted and co-inoculated microcosms only.

An approach to uncertainty estimation in determining polycyclic aromatic hydrocarbons in fuel-contaminated soils

An estimation of uncertainty contribution in the entire set of the analytical data of polycyclic aromatic hydrocarbons (PAHs) in soil during a full year is presented. The analyses were performed as part of a project devoted to the assessment of the natural attenuation of selected PAHs in agricultural soil contaminated by a fuel spill. In particular, we investigated the effect of natural attenuation on the PAH dissipation rate in plots of two types of scenarios in agricultural soils. One of them was previously affected by an accidental fuel spill 10 years ago, and the other one was non-affected. The major components for estimating uncertainty contributions have been evaluated based on intermediate precision from different levels of PAH mass fraction, sample locations, and long term data set. An analysis of variance (ANOVA) test was applied to the mass fractions of clean or blank soil sub-samples versus contaminated soil sub-samples for grouping comparable data. Variables of influence in this study were site, month, and lysimeter of sampling (referring to a stainless steel box, with side lengths of 50 cm). Study sites or the spatial arrangement of lysimeter showed a clear effect in sub-sample results with the lowest mass fraction levels for heavier PAH, while monthly sampling was the variable of most significant influence for the more strongly contaminated sub-sample results. Finally, the results of the PAH mass fractions in contaminated soil sub-samples indicated a monthly variation for which lighter, volatile PAHs rapidly decreased while the less volatile did not change.

Enhanced Dissipation of Polycyclic Aromatic Hydrocarbons in the Rhizosphere of the Athel Tamarisk (Tamarix Aphylla L. Karst.) Grown in Saline-Alkaline Soils of the Former Lake Texcoco

Remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated alkaline saline soil with phreatophyte or “water loving plants” was investigated by spiking soil from the former lake Texcoco with 100 mg phenanthrene (Phen) kg−1 soil, 120 mg anthracene (Ant) kg−1 soil and 45 mg benzo(a)pyrene (BaP) kg−1 soil and vegetating it with Athel tamarisk (Tamarix aphylla L. Karst.). The growth of the Athel tamarisk was not affected by the PAHs. In soil cultivated with Athel tamarisk, the leaching of PAHs to the 32–34 cm layer decreased 2-fold compared to the uncultivated soil. The BaP concentration decreased to 39% of the initial concentration at a distance smaller than 3 cm from the roots and to 45% at a distance larger than 3cm, but 59% remained in unvegetated soil after 240 days. Dissipation of Ant and Phen decreased with depth, but not BaP. The biodegradation of PAHs was affected by their chemical properties and increased in the presence of T. aphylla, but decreased with depth.

Biosorption and biodegradation of polycyclic aromatic hydrocarbons by Phanerochaete chrysosporium in aqueous solution

Biosorption and biodegradation of phenanthrene and pyrene by live and heat-killed Phanerochaete chrysosporium are investigated to elucidate the bio-dissipation mechanisms of polycyclic aromatic hydrocarbons (PAHs) in aqueous solution and its regulating factors. The effects of nutrient conditions (carbon source and nitrogen source concentrations), the co-existing Cu2+, and repeated-batch feed of PAHs on the biosorption and biodegradation are systematically studied. The removal of PAHs by dead bodies of P. chrysosporium is attributed to biosorption only, and the respective partition coefficients of phenanthrene and pyrene are 4040 and 17500 L/kg. Both biosorption and biodegradation contribute to the dissipation of PAHs by live P. chrysosporium in water. After a 3-d incubation, the removal percentage via biosorption are 19.71% and 52.21% for phenanthrene and pyrene, respectively. With the increase of the incubation time (3–40 d), biodegradation gradually increases from 20.40% to 60.62% for phenanthrene, and from 15.55% to 49.21% for pyrene. Correspondingly, the stored-PAHs in the fungal bodies decrease. Under the carbon-rich and nitrogen-limit nutrient conditions, the removal efficiency and biodegradation of phenanthrene and pyrene are significantly promoted, i.e. 99.55% and 92.77% for phenanthrene, and 99.47% and 83.97% for pyrene after a 60-d incubation. This phenomenon is ascribed to enhanced-biosorption due to the increase of fungal biomass under carbon-rich condition, and to stimulated-biodegradation under nitrogen-limit condition. For the repeated-batch feed of phenanthrene, the pollutant is continuously removed by live P. chrysosporium, and the contribution of biodegradation is enhanced with the repeated cycles. After 3 cycles, the biodegradation percentage is up to 90% with each cycle of a 6-d incubation.

Pig manure vermicompost (PMVC) can improve phytoremediation of Cd and PAHs co-contaminated soil by Sedum alfredii

Purpose A major challenge to phytoremediation of co-contaminated soils is developing strategies for efficient and simultaneous removal of multiple pollutants. A pot experiment was conducted to investigate the potential for enhanced phytoextraction of cadmium (Cd) by Sedum alfredii and dissipation of polycyclic aromatic hydrocarbons (PAHs) in co-contaminated soil by application of pig manure vermicompost (PMVC).

PAH biotransformation and sorption by Fusarium solani and Arthrobacter oxydans isolated from a polluted soil in axenic cultures and mixed co-cultures

The polycyclic aromatic hydrocarbon (PAH) dissipation potential of Fusarium solani MM1 and Arthrobacter oxydans MsHM11, isolated from a PAH-polluted soil, was investigated in liquid cultures containing 500, 500, and 50mgl−1 of phenanthrene (PHE), pyrene (PYR), and dibenz(a,h)anthracene (DBA), respectively. The contributions of adsorption, absorption and biotransformation were evaluated separately by extracting and analysing PAHs from the biomass and from the culture medium. In the pure culture, F. solani dissipated approximately 30% of each tested PAH in 28 days when glucose was supplied as the carbon source. PAH adsorption on F. solani hyphae was negligible, whereas absorption was found to account for one-third of the dissipation. Absorbed PAHs, reaching 3% of the fungal dry biomass, could be visualised in autofluorescent intracellular vesicles. In contrast, A. oxydans grew on PAHs as sole carbon source and led to 55% dissipation of PHE in 28 days without any significant absorption. This dissipation potential was inhibited by the presence of glucose, and the PYR and DBA contents were never dissipated in the bacterial pure culture. In the mixed co-culture, the PAH dissipation rates were lower, showing that antagonistic interactions, such as pH changes or competition for carbon source, indirectly inhibited both microbial potentials.

Dissipation of polycyclic aromatic hydrocarbons (PAHs) in soil microcosms amended with mushroom cultivation substrate

The potential of mushroom cultivation substrate (MCS) in bioremediation was examined in polycyclic aromatic hydrocarbon (PAH)-contaminated soil. After a 60-day incubation, 32.9% dissipation of the 15 studied PAHs was observed in MCS-amended microcosms, with anthracene, benzo(a)pyrene and benzo(a)anthracene being the most degradable PAHs. MCS significantly increased the abundance and changed the community compositions of bacteria, fungi and aromatic hydrocarbon degraders. Two species belonging to the Sordariomycetes of the Ascomycota were enriched in all MCS-treated soil samples, and coupled with the unique changes in the PAH profile, this implies the involvement of laccase-like enzymes. Limited improvement was observed after adding Pleurotus ostreatus, possibly because of its poor colonization of the soil. In addition, alfalfa appeared to antagonize the bioremediation effects of MCS. The results of this study suggest that MCS can be a cost-effective and green biostimulation agent, thereby providing support for the development of MCS-based biostimulation of PAH-contaminated soil.

Enhanced dissipation of polycyclic aromatic hydrocarbons in the presence of fresh plant residues and their extracts

The feasibility of using fresh plant residues and their extracts to stimulate the bio-dissipation of polycyclic aromatic hydrocarbons (PAHs) were highlighted. Wood chip, bamboo leave, orange peel and their water-extractable organic matter (WEOM) were chosen as amendment materials. Effect of WEOM on bio-dissipation (bioaccumulation and biodegradation) of phenanthrene and pyrene from water by two bacteria were investigated. Orange peel extract demonstrated the highest efficiency for stimulating PAHs removal by bacterium B1 ( Pseudomonas putida), while bamboo leave extract was the best one to enhance PAHs bio-dissipation by bacterium B2 (unidentified bacterium isolated from PAHs-contaminated soil). Amended the actual contaminated soil with 1% plant residues, PAHs dissipation were increased by 15–20%, 20–39%, 14–24%, 12–23% and 17–26%, respectively, for 2-, 3-, 4-, 5- and 6-ring PAHs via stimulating indigenous microbial degradation activity. Bamboo leave exhibited the most effective one to stimulate dissipation of PAHs in contaminated soil.

Dissipation of polycyclic aromatic hydrocarbons and microbial activity in a field soil planted with perennial ryegrass

Dissipation and plant uptake of polycyclic aromatic hydrocarbons (PAHs) in contaminated agricultural soil planted with perennial ryegrass were investigated in a field experiment. After two seasons of grass cultivation the mean concentration of 12 PAHs in soil decreased by 23.4% compared with the initial soil. The 3-, 4-, 5-, and 6-ring PAHs were dissipated by 30.9%, 25.5%, 21.2%, and 16.3% from the soil, respectively. Ryegrass shoots accumulated about 280 μg·kg−1, shoot dry matter biomass reached 2.48 × 104 kg·ha−1, and plant uptake accounted for about 0.99% of the decrease in PAHs in the soil. Significantly higher soil enzyme activities and microbial community functional diversity were observed in planted soil than that in the unplanted control. The results suggest that planting ryegrass may promote the dissipation of PAHs in long-term contaminated agricultural soil, and plant-promoted microbial degradation may be a main mechanism of phytoremediation.

Study of PAH dissipation and phytoremediation in soils: Comparing freshly spiked with weathered soil from a former coking works

A comparison was made between the dissipation of polycyclic aromatic hydrocarbons (PAHs) in soil freshly spiked with pure PAHs, soil spiked with a coal tar mixture and a contaminated soil from a former coking works where the PAHs had been present for more than a century. The potential of five selected plant species for phytoremediation was investigated. The levels of all 7 PAHs in chemically amended soil, both planted and unplanted, fell significantly (>80% reduction) over the 12 weeks of the growing trial. In the coal tar treated soils all PAHs were significantly reduced. In both the planted and unplanted soils the 2–3 ringed compounds demonstrated much greater loss (>77%) than the 4–6 ringed (16–39%). The 3–4 ringed compounds demonstrated strong evidence of phytoremediation but not the 5–6 ringed. The coking soil showed limited reduction (7–24%) of all 12 PAHs present. There was little difference in dissipation between the PAHs and little evidence of a phytoremediation effect in coking soil. The results demonstrated that the form in which PAHs were added to soil influenced their susceptibility to dissipation. Therefore, predictions of PAH dissipation from laboratory amended soil do not reflect the true situation in the field.

In situ phytoremediation of PAH-contaminated soil by intercropping alfalfa (Medicago sativa L.) with tall fescue (Festuca arundinacea Schreb.) and associated soil microbial activity

A 7-month field experiment was conducted to investigate the polycyclic aromatic hydrocarbon (PAH) remediation potential of two plant species and changes in counts of soil PAH-degrading bacteria and microbial activity. Alfalfa and tall fescue were grown in monoculture and intercropped for 7 months in contaminated field soil. Soil and plant samples were analyzed for PAHs. Plant biomass, densities of PAH-degradation soil bacteria, soil microbial biomass C and N, enzyme activities, and the physiological profile of the soil microbial community were determined. Average removal percentage of total PAHs in intercropping (30.5%) was significantly higher than in monoculture (19.9%) or unplanted soil (−0.6%). About 7.5% of 3-ring, 12.3% of 4-ring, and 17.2% of 5(+6)-ring PAHs were removed from the soil by alfalfa, with corresponding values of 25.1%, 10.4%, and 30.1% for tall fescue. Intercropping significantly enhanced the remediation efficiency. About 18.9% of 3-ring, 30.9% of 4-ring, and 33.4% of 5(+6)-ring PAHs were removed by the intercropping system. Higher counts of soil culturable PAH-degrading bacteria and elevated microbial biomass and enzyme activities were found after intercropping. Soil from intercropping showed significantly higher (p < 0.05) average well-color development obtained by the BIOLOG Ecoplate assay and Shannon–Weaver index compared with monoculture. Cropping promoted the dissipation of soil PAHs. Tall fescue gave greater removal of soil PAHs than alfalfa, and intercropping was more effective than monoculture. Intercropping of alfalfa and tall fescue may be a promising in situ bioremediation strategy for PAH-contaminated soils.

Remediation of polycyclic aromatic hydrocarbon (PAH) contaminated soil through composting with fresh organic wastes

Composting may enhance bioremediation of PAH-contaminated soils by providing organic substrates that stimulate the growth of potential microbial degraders. However, the influence of added organic matter (OM) together with the microbial activities on the dissipation of PAHs has not yet been fully assessed. An in-vessel composting-bioremediation experiment of a contaminated soil amended with fresh wastes was carried out. Four different experimental conditions were tested in triplicate during 60 days using laboratory-scale reactors: treatment S (100% soil), W (100% wastes), SW (soil/waste mixture), and SWB (soil/waste mixture with inoculation of degrading microorganisms). A dry mass loss of 35 ± 5% was observed in treatments with organic wastes during composting in all the treatments except treatment S. The dissipation of the 16 USEPA-listed PAHs was largely enhanced from no significant change to 50.5 ± 14.8% (for SW)/63.7 ± 10.0% (for SWB). More obvious dissipation was observed when fresh wastes were added at the beginning of composting to the contaminated soil, without significant difference between the inoculated and non-inoculated treatments. Phospholipid fatty acid (PLFA) profiling showed that fungi and G-bacteria dominated at the beginning of experiment and were probably involved in PAH dissipation. Subsequently, greater relative abundances of G + bacteria were observed as PAH dissipation slowed down. The results suggest that improving the composting process with optimal organic compositions may be a feasible remediation strategy in PAH-contaminated soils through stimulation of active microbial populations.

Effects of Autoclaving and Mercuric Chloride Sterilization on PAHs Dissipation in a Two-Liquid-Phase Soil Slurry

A two-liquid-phase (TLP) soil slurry system was employed to quantify the efficiencies of autoclaving and mercuric chloride sterilization in the dissipation of polycyclic aromatic hydrocarbons (PAHs). The fates of 11 PAHs (naphthalene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo( a)anthracene, benzo( a)pyrene, benzo( b)fluoranthene, benzo( k)fluoranthene, dibenzo( a, h)anth-racene) were recorded over 113 days of incubation. No microorganisms were detected in the HgCl 2-sterilized soil slurries during the whole incubation period, indicating very effective sterilization. However, about 2%–36% losses of PAHs were observed in the HgCl 2-sterilized slurry. In contrast to the HgCl 2-sterilized soil slurry, some microorganisms survived in the autoclaved soil slurries. Moreover, significant biodegradation of 6 PAHs (naphthalene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene) was observed in the autoclaved soil slurries. This indicated that biodegradation results of PAHs in the soil slurries, calculated on basis of the autoclaved control, would be underestimated. It could be concluded that the sterilization efficiency and effectiveness of HgCl 2 on soil slurry was much higher than those of autoclaving at 121 °C for 45 min.

Enhanced dissipation of PAHs from soil using mycorrhizal ryegrass and PAH-degrading bacteria

The major aim of this experiment was to test the effects of a multi-component bioremediation system consisting of ryegrass (Lolium multiflorum), polycyclic aromatic hydrocarbons (PAHs)-degrading bacteria (Acinetobacter sp.), and arbuscular mycorrhizal fungi (Glomus mosseae) for cleaning up PAHs contaminated soil. Higher dissipation rates were observed in combination treatments: i.e., bacteria+ryegrass (BR), mycorrhizae+ryegrass (MR), and bacteria+mycorrhizae+ryegrass (BMR); than bacteria (B) and ryegrass (R) alone. The growth of ryegrass significantly (p<0.05) increased soil peroxidase activities, leading to enhanced dissipation of phenanthrene (PHE) and pyrene (PYR) from soil. Interactions between ryegrass with the two microbes further enhanced the dissipation of PHE and PYR. Mycorrhizal ryegrass (MR) significantly enhanced the dissipation of PYR from soil, PYR accumulation by ryegrass roots and soil peroxidase activities under lower PHE and PYR levels (0 and 50+50mgkg−1). The present results highlighted the contribution of mycorrhiza and PAH-degrading bacteria in phytoremediation of PAH contaminated soil, however more detailed studies are needed.

Arbuscular mycorrhizal phytoremediation of soils contaminated with phenanthrene and pyrene

An available remediation technique — arbuscular mycorrhizal phytoremediation (AMPR) — is further proposed for soils contaminated with phenanthrene and pyrene as representative polycyclic aromatic hydrocarbons (PAHs) utilizing a greenhouse pot experiment. The initial concentrations of phenanthrene and/or pyrene in soils were 103 mg kg −1 and 74 mg kg −1, respectively. The host plant was alfalfa ( Medicago sativa L.), and the experimental arbuscular mycorrhizal fungi (AMF) were Glomus mosseae and G. etunicatum. More than 98.6% and 88.1% of phenanthrene and pyrene were degraded after 70 days in soils with AMPR. Use of multiple mycorrhizal species significantly promoted degradation of PAHs in soils. The co-contaminant (pyrene) present clearly inhibited the degradation of a single PAH (phenanthrene) in soil. Mycorrhizal colonization caused increased accumulation of PAHs in plant roots but a decrease in shoot. However, plant uptake contributed negligibly to PAH dissipation in AMPR, and plant accumulated PAHs amounted to less than 3.24% of total PAH degradation in mycorrhizal soils. In contrast, the optimized microbiota in mycorrhizal association was responsible for PAH degradation in AMPR. The high rate of PAH dissipation in mycorrhizal soils, the evident promotion of PAH degradation by AM colonization, and the healthy plant growth suggest encouraging opportunities for AMPR of PAH-contaminated soils.

Microbial communities to mitigate contamination of PAHs in soil—possibilities and challenges: a review

Although highly diverse and specialized prokaryotic and eukaryotic microbial communities in soil degrade polycyclic aromatic hydrocarbons (PAHs), most of these are removed slowly. This review will discuss the biotechnological possibilities to increase the microbial dissipation of PAHs from soil as well as the main biological and biotechnological challenges. Microorganism provides effective and economically feasible solutions for soil cleanup and restoration. However, when the PAHs contamination is greater than the microbial ability to dissipate them, then applying genetically modified microorganisms might help to remove the contaminant. Nevertheless, it is necessary to have a more holistic review of the different individual reactions that are simultaneously taking place in a microbial cell and of the interactions microorganism-microorganism, microorganism-plant, microorganism-soil, and microorganisms-PAHs. Elucidating the function of genes from the PAHs-polluted soil and the study in pure cultures of isolated PAHs-degrading organisms as well as the generation of microorganisms in the laboratory that will accelerate the dissipation of PAHs and their safe application in situ have not been studied extensively. There is a latent environmental risk when genetically engineered microorganisms are used to remedy PAHs-contaminated soil.

Quantitative structure–activity relationship (QSAR) models for polycyclic aromatic hydrocarbons (PAHs) dissipation in rhizosphere based on molecular structure and effect size

Rhizoremediation is a significant form of bioremediation for polycyclic aromatic hydrocarbons (PAHs). This study examined the role of molecular structure in determining the rhizosphere effect on PAHs dissipation. Effect size in meta-analysis was employed as activity dataset for building quantitative structure–activity relationship (QSAR) models and accumulative effect sizes of 16 PAHs were used for validation of these models. Based on the genetic algorithm combined with partial least square regression, models for comprehensive dataset, Poaceae dataset, and Fabaceae dataset were built. The results showed that information indices, calculated as information content of molecules based on the calculation of equivalence classes from the molecular graph, were the most important molecular structural indices for QSAR models of rhizosphere effect on PAHs dissipation. The QSAR model, based on the molecular structure indices and effect size, has potential to be used in studying and predicting the rhizosphere effect of PAHs dissipation.

Roles of abiotic losses, microbes, plant roots, and root exudates on phytoremediation of PAHs in a barren soil

Phytoremediation is an emerging technology for the remediation of polycyclic aromatic hydrocarbons (PAHs). In this study, pot experiments were conducted to evaluate the efficacy of phytoremediation of phenanthrene and pyrene in a typical low organic matter soil (3.75 g kg −1), and the contribution proportions of abiotic losses, microbes, plant roots, and root exudates were ascertained during the PAHs dissipation. The results indicated that contribution of abiotic losses from this soil was high both for phenanthrene (83.4%) and pyrene (57.2%). The contributions of root-exudates-enhanced biodegradation of phenanthrene (15.5%) and pyrene (21.3%) were higher than those of indigenous microbial degradation. The role of root exudates on dissipation of phenanthrene and pyrene was evident in this experiment. By the way, with the increasing of ring numbers in PAHs structures, the root-exudates-enhanced degradation became more and more important. BIOLOG-ECO plate analysis indicated that microbial community structure of the soil receiving root exudates had changed. The removal efficiency and substrate utilization rate in the treatment with plant roots were lower than the treatment only with root exudates, which suggested that possible competition between roots and microbes for nutrients had occurred in a low organic matter soil.