Effects of Rapeseed Oil on the Rhizodegradation of Polyaromatic Hydrocarbons in Contaminated Soil

Plants have the ability to promote degradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated soil by supporting PAH degrading microorganisms in the rhizosphere (rhizodegradation). The aim of this study was to evaluate if rapeseed oil increases rhizodegradation because various studies have shown that vegetable oils are able to act as extractants for PAHs in contaminated soils and therefore might increase bioavailability of PAHs for microbial degradation. In this study different leguminous and grass species were tested. The results suggested a significant impact of vegetable oil (1 and 3% w/w) on plant growth (decrease of plant height and biomass). The results of the pot experiment showed a decrease in the PAH content of the soil without amendment of rapeseed oil after six months. In soil amended with 1% and 3% of oil, there was no decrease in PAH content within this period. Although no enhancement of PAH degradation by plants could be measured in the bulk soil of the pot experiments, a rhizobox experiment showed a significant reduction of PAH content in the rhizosphere of alfalfa (Medicago sativa cv. Europe). Our investigations also showed significant differences in the degradation behaviour of the 16 individually analysed PAHs.     

REDUCTION IN SOIL POLYCYCLIC AROMATIC HYDROCARBONS BY ARBUSCULAR MYCORRHIZAL LEEK PLANTS

The effect of arbuscular mycorrhizal fungi (AMF) on the reduction of soil polycyclic aromatic hydrocarbon (PAH), nutrient uptake, and growth of leek (Allium porrum L. cv. Musselburgh) plants was studied under greenhouse conditions. This experiment was a 3 × 2 × 2 × 4 factorial design including three mycorrhizal treatments (non-AMF, Glomus intraradices, and G. versiforme strains), two microorganism statuses (with and without soil bacteria), two PAH chemicals (anthracene and phenanthrene), and four PAH concentrations (three concentrations added and one control). Leek growth was reduced significantly in soils spiked with anthracene or phenanthrene. Inoculation with either Glomus intraradices or G. versiforme not only increased N and P uptake and plant growth, but also enhanced PAH disappearance in soil. After 12 weeks of potcultures, the anthracene and phenanthrene concentrations in soils were decreased as compared to their initial level, 9%–31% versus 43%–88%, respectively. Reductions in concentration were larger for phenanthrene than anthracene. The addition of a soil microorganism (SM) extract in potcultures accelerated the disappearance of PAHs. The decrease of PAHs in soil was mainly attributed to the enhanced nutrient uptake by AMF, leading to improved plant growth, which, in turn, may stimulate soil microbial activity. This study shows the interrelationships between AMF, plants, other SMs, and PAH disappearance in soil. The phytoremediation of soil contaminated with PAHs can be accelerated through inoculation with AMF and other SMs.     

Enhanced Phytoremediation of Crude Oil-Polluted Soil by Four Plant Species: Effect of Inorganic and Organic Bioaugumentation

A field experiment investigating the removal and/or uptake of Polycyclic Aromatic Hydrocarbons (PAHs) and specific metals (As, Cd, Cr) from a crude oil polluted agricultural soil was performed during the 2013 wet season using four plant species: Fimbristylis littoralis, Hevea brasilensis (Rubber plants), Cymbopogom citratus (Lemon grass), and Vigna subterranea (Bambara nuts). Soil functional diversity and soil-enzyme interactions were also investigated. The diagnostic ratios and the correlation analysis identified mixed petrogenic and pyrogenic sources as the main contributors of PAHs at the study site. A total of 16 PAHs were identified, 6 of which were carcinogenic. Up to 42.4 mg kg^?1 total PAHs was recorded prior to the experiments. At 90 d, up to 92% total PAH reduction and 96% As removal were achieved using F. littoralis, the best performing species. The organic soil amendment (poultry dung) rendered most of the studied contaminants unavailable for uptake. However, the organic amendment accounted for over 70% of the increased dehydrogenase, phosphatase, and proteolytic enzymes activities in the study. Overall, the combined use of soil amendments and phytoremediation significantly improved the microbial community activity, thus promoting the restoration of the ecosystem.     

Phytoremediation of polycyclic aromatic hydrocarbons in soil: part I. Dissipation of target contaminants

Phytoremediation has been demonstrated to be a viable cleanup alternative for soils contaminated with petroleum products. This study evaluated the application of phytoremediation to soil from a manufactured gas plant (MGP) site with high concentrations of recalcitrant, polycyclic aromatic hydrocarbons (PAHs). Two greenhouse studies investigated the potential dissipation and plant translocation of PAHs by fescue (Festuca arundinacea) and switchgrass (Panicum virgatum) in the first experiment and zucchini (Curcubita pepo Raven) in the second. The MGP soil was highly hydrophobic and initially inhibited plant growth. Two unplanted controls were established with and without fertilization. In the first experiment, concentrations of PAHs decreased significantly in all treatments after 12 mo. Plant biomass and microbial numbers were statistically equivalent among plant species. PAH concentrations in plant biomass were negligible for fescue and switchgrass. In the second experiment, zucchini enhanced the dissipation of several PAHs after 90 d of treatment when compared to the unvegetated soil. Plant tissue concentrations of PAHs were not elevated in the zucchini roots and shoots, and PAHs were not detectable in the fruit.     

PYRENE EFFECTS ON RHIZOPLANE BACTERIAL COMMUNITIES

Certain plant species promote biodegradation of polycyclic aromatic hydrocarbons (PAHs), but few studies have examined the microbial populations that are associated with the rhizoplane of these plants. In this study, the bacterial composition of the rhizoplane were characterized for four plant species during in soils with different histories of exposure to PAH and in the presence or absence of a pyrene spike at 100 mg kg^?1 pyrene. Three of the plant species including Andropogon gerrardii, Panicum coloratum and Melilotus officinalis were known to stimulate PAH degradation. Wheat (Triticum aestivum) was used as a reference species. Results showed that after 90 days, approximately 45% of the pyrene spike disappeared from soil without plants. In contrast, cultivation of plants resulted in 95% disappearance of pyrene. There were no significant differences in the extent of pyrene disappearance for different plants. In all cases, 16S rRNA gene profiles of the rhizoplane were less complex in the pyrene-spiked soils, suggesting that richness and evenness of the predominant bacteria were reduced. Our results show that pyrene contamination results in significant shifts in the composition of rhizosphere bacterial communities that are still further influenced by the plant species and prior exposure history to PAH contamination.     

Phenanthrene toxicity and dissipation in rhizosphere of grassland plants (Lolium perenne L. and Trifolium pratense L.) in three spiked soils

Rhizodegradation is a technique involving plants that offers interesting potential to enhance biodegradation of persistent organic pollutants such as polycyclic aromatic hydrocarbons (PAHs). Nevertheless, the behaviour of PAHs in plant rhizosphere, including micro-organisms and the physico-chemical soil properties, still needs to be clarified. The present work proposes to study the toxicity and the dissipation of phenanthrene in three artificially contaminated soils (1 g kg^-1 DW). Experiments were carried out after 2 months of soil aging. They consisted in using different systems with two plant species (Ryegrass—Lolium perenne L. var. Prana and red clover—Trifolium pratense L. var. fourragère Caillard), three kinds of soils (a silty-clay-loam soil “La Bouzule”, a coarse sandy-loam soil “Chenevières” and a fine sandy-loam soil “Maconcourt”). Phenanthrene was quantified by HPLC in the beginning (T ₀) and the end of the experiments (30 days). Plant biomass, microbial communities including mycorrhizal fungi, Rhizobium and PAH degraders were also recorded. Generally phenanthrene contamination did not affect plant biomass. Only the red clover biomass was enhanced in Chenevières and La Bouzule polluted soils. A stimulation of Rhizobium red clover colonisation was quantified in spiked soils whereas a drastic negative phenanthrene effect on the mycorrhization of ryegrass and red clover was recorded. The number of PAH degraders was stimulated by the presence of phenanthrene in all tested soils. Both in ryegrass and red clover planted soils, the highest phenanthrene dissipation due to the rhizosphere was measured in La Bouzule soils. On the contrary, in non-planted soils, La Bouzule soils had also the lowest pollutant dissipation. Thus, in rhizospheric and non-rhizospheric soils the phenanthrene dissipation was found to depend on soil clay content.     

Kinetics of Polycyclic Aromatic Hydrocarbon (PAH) Degradation in Long-term Polluted Soils during Bioremediation

Bioremediation experiments with ten different soil samples from former industrial sites which were long-term polluted with polycyclic aromatic hydrocarbons (PAHs) were carried out using outdoor pot trials. The degradation of 15 PAHs according to the US EPA was investigated for 168 weeks through repeated soil sampling and determination of the total PAH concentration. On average, degradation was largest for acenaphthene (88%; 63 to 99%) and smallest for anthracene (22%; no significant degradation to 89%). For most of the PAH single substances, degradation kinetics were characterised by a first initial phase of fast degradation. In a subsequent second phase, degradation diminished and residual PAH concentrations were approached within 168 weeks, resulting in a similar PAH pattern in the ten soil samples. Degradation kinetics was calculated through the selection of the appropriate differential rate equation from a set of seven equations. Kinetics of PAH degradation was best fitted by single and two coupled first order exponential equations with median R2 of 0.71 (0.01 to 1.00). Degradation rate constants of the rapid phase (k ₁) ranged from 0.05×10⁻² week⁻¹ for benzo[k]fluoranthene to 18.3 week⁻¹ for naphthalene and for the subsequent slow degradation phase (k ₂) they ranged from 0.01×10⁻² week⁻¹ for benzo[a]anthracene to 2.3×10⁻² week⁻¹ for fluoranthene. Degradation was governed by desorption and diffusion processes of different rates, while microbial activity did not influence the kinetics. Median disappearance times (DT₅₀) ranged from 6.1 weeks for naphthalene to 522 weeks for benzo[k]fluoranthene. With the exception of the 6-ring PAHs dibenzo[ah]anthracene and indeno[1,2,3-cd]pyrene, this sequence followed the PAHs’ degree of condensation. The total initial PAH concentration and the residual concentration were correlated with R2 of 0.69, with larger initial PAH concentrations leading to larger residual concentrations and degradation rates.     

Enhanced degradation of polycyclic aromatic hydrocarbons in soil treated with an advanced oxidative process — Fenton's Reagent

Polycyclic aromatic hydrocarbons (PAHs) are resistant to present bioremediation practices. This study was conducted to determine if pretreatment with an advanced oxidative process (Fenton's reagent; H₂O₂ + FeSO₄) could enhance PAH degradation in soil that had previously been exposed to crude oil. PAHs were more readily degraded after incubation for 56 d when treated with H₂O₂ (2.8 M) plus FeSO₄ (0.1 M) compared with degradation rates without the addition of Fenton's reagent during the same time period. Overall, the use of Fenton's reagent as a pretreatment promoted the mineralization of the nine spiked PAHs by an average of 87%. Degradation of native PAH parent compounds (180 to 840 μg of PAH per kilogram of soil) in the same soil incubated with Fenton's reagent for 7 d was enhanced 44 and 39% for phenanthrene and fluoranthene, respectively, but only 5 and 1% for pyrene and chrysene, respectively, when compared with no addition of Fenton's reagent. Pretreatment of the soil with a surfactant (10 mM sodium dodecylsulfate) before the addition of Fenton's reagent increased the native PAH degradation rate 84, 83, 55, and 32% for the parent compounds phenanthrene, fluoranthene, pyrene, and chrysene, respectively, compared with no addition of Fenton's reagent. Degradation of PAHs was confirmed by HPLC‐UV analyses. The use of Fenton's reagent (OH") appears to have applications in bioremediation practices of the most recalcitrant chemical compounds in nature (PAHs), particularly with the use of surfactants.     

In situ phytoremediation of PAH- and PCB-contaminated marine sediments with eelgrass (Zostera marina)

In view of the fact that there are presently no cost-effective in situ treatment technologies for contaminated sediments, a 60-week-long phytoremediation feasibility study was conducted in seawater-supplied outdoor ponds to determine whether eelgrass (Zostera marina) is capable of removing polynuclear aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) from submerged marine sediments. It was determined that all PAHs and PCBs, independent of the number of aromatic rings and degree of chlorination, respectively, were removed to a much larger extent in planted sediments compared to unplanted controls. After 60 weeks of treatment, the concentration of total PAHs decreased by 73% in planted sediments but only 25% in unplanted controls. Similarly, total PCBs declined by 60% in the presence of plants while none were removed in the unplanted sediment. Overall, the apparent PAH and PCB biodegradation was greatest in the sediment layer that contained most of the eelgrass roots. Abiotic desorption tests conducted at week 32 confirmed that the phytoremediation process was not controlled by mass-transfer or bioavailability limitations since all PAHs and PCBs desorbed rapidly and to a large extent from the sediment. PAHs were detected in both roots and shoots, with root and shoot bioaccumulation factors for total PAHs amounting to approximately 3 and 1, respectively, after 60 weeks of phytoremediation treatment. Similarly, the root bioaccumulation factor for total PCBs was around 4, while no PCBs were detected in the eelgrass leaves at the end of the experiment. The total mass fraction of PAHs and PCBs absorbed and translocated by plant biomass during the 60-week period was insignificant, amounting to less than 0.5% of the total mass of PAHs and PCBs which was initially present in the sediment. Finally, the number of total heterotrophic bacteria and hydrocarbon degraders was slightly but not statistically significantly greater in planted sediments than in unplanted controls. After ruling out contaminant loss to the water column or absorption and transformation within plant cells, it is most likely that the presence of eelgrass stimulated the microbial biodegradation of PAHs and PCBs in the rhizosphere by releasing root exudates, plant enzymes, or even oxygen. Additional research is needed to further elucidate these potential phytoremediation mechanisms.     

Polycyclic Aromatic Hydrocarbon-Induced Structural Shift of Bacterial Communities in Mangrove Sediment

Mangrove sediment is well known for its susceptibility to anthropogenic pollution, including polycyclic aromatic hydrocarbons (PAHs), but knowledge of the sediment microbial community structure with regards to exposure to PAHs is limited. The study aims to assess the effects of PAHs on the bacterial community of mangrove sediment using both 16s rDNA polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and traditional enrichment methods. Both the exposure time and the PAH concentration reduced the microbial diversity, as determined by the DGGE bands. Although PAHs could act as carbon sources for microorganisms, PAHs, at a concentration as low as 20 mg l⁻¹, posed a toxic effect to the microbial community. Sequencing of DGGE bands showed that marine bacteria from the genera of Vibrio, Roseobacter, and Ferrimonas were most abundant after PAH exposure, which suggests that both marine and terrestrial bacteria coexisted in the mangrove sediment, but that the marine microbes were more difficult to isolate using the traditional culture method. DGGE determination further demonstrated that the consistency among triplicates of the enriched consortia was significantly less than that of the sediment slurries. The present study reveals that the mangrove sediment microbial structure is susceptible to PAH contamination, and complex microbial community interactions occur in mangrove sediment.     

The uptake of persistent organic pollutants by plants

In a field experiment, the transfer of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) from contaminated soil to maize (Zea mays L.), sunflower (Helianthus annuus), poplar (Populus nigra × P. maximowiczii) and willow (Salix × smithiana) and the distribution of PCB congeners in maize and sunflower was investigated. The former waste incinerator in Hradec Králové (Czech Republic) was chosen for the experiment. Results of plot screening showed heterogenous contamination by PCBs and PAHs. PCB soil contamination was evidently caused by Delor 106 or Aroclor 1260 stocking and PAH contamination by chemicals containing fluoranthene, benzo/b/fluoranthene, phenanthrene and pyrene. Tested plants were planted on a contaminated field site, in soil contaminated with 1530 μg/kg of total PCBs and 0.138 and 3.42 mg/kg of total PAHs. The results show that maize and sunflower roots accumulated the most PCBs from soil. These plants accumulated hexa- and heptachlorobiphenyl congeners more than tri-, tetra-, and pentachlorobiphenyl congeners. Total concentrations of PAHs in tested plants ranged from 0.096 to 1.34 mg/kg. The highest phenanthrene concentration was found in aboveground biomass of sunflower and the highest concentration of pyrene, in maize roots.     

Enhancement of bioconversion of high-molecular mass polycyclic aromatic hydrocarbons in contaminated non-sterile soil by litter-decomposing fungi

With the focus on alternative microbes for soil-bioremediation, 18 species of litter-decomposing basidiomycetous fungi were screened for their ability to grow on different lignocellulosic substrates including straw, flax and pine bark as well as to produce ligninolytic enzymes, namely laccase and manganese peroxidase. Following characteristics have been chosen as criteria for the strain selection: (i) the ability to grow at least on one of the mentioned materials, (ii) production of either of the ligninolytic enzymes and (iii) the ability to invade non-sterile soil. As the result, eight species were selected for a bioremediation experiment with an artificially contaminated soil (total polycyclic aromatic hydrocarbon (PAH) concentration 250 mg/kg soil). Up to 70%, 86% and 84% of benzo(a)anthracene, benzo(a)pyrene, and dibenzo(a,h)anthracene, respectively, were removed in presence of fungi while the indigenous microorganisms converted merely up to 29%, 26% and 43% of these compounds in 30 days. Low molecular-mass PAHs studied were easily degraded by soil microbes and only anthracene degradation was enhanced by the fungi as well. The agaric basidiomycetes Stropharia rugosoannulata and Stropharia coronilla were the most efficient PAH degraders among the litter-decomposing species used.     

Predicting the Efficacy of Polycyclic Aromatic Hydrocarbon Bioremediation in Creosote-Contaminated Soil Using Bioavailability Assays

Nonexhaustive extraction (propanol, butanol, hydroxypropyl-β-cyclodextrin [HPCD]), persulfate oxidation and biodegradability assays were employed to determine the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in creosote-contaminated soil. After 16 weeks incubation, greater than 89% of three-ring compounds (acenaphthene, anthracene, fluorene, and phenanthrene) and 21% to 79% of four-ring compounds (benz[a]anthracene, chrysene, fluoranthene, and pyrene) were degraded by the indigenous microorganisms under biopile conditions. No significant decrease in five- (benzo[a]pyrene, benzo[b+k]fluoranthene) and six-ring compounds (benz[g,h,i]perylene, indeno[1,2,3-c,d]pyrene) was observed. Desorption of PAHs using propanol or butanol could not predict PAH biodegradability: low-molecular-weight PAH biodegradability was underestimated whereas high-molecular-weight PAH biodegradability was overestimated. Persulfate oxidation and HPCD extraction of creosote-contaminated soil was able to predict three- and four-ring PAH biodegradability; however, the biodegradability of five-ring PAHs was overestimated. These results demonstrate that persulfate oxidation and HPCD extraction are good predictors of PAH biodegradability for compounds with octanol-water partitioning coefficients of < 6.     

Enhanced phytoremediation of soils contaminated with PAHs by arbuscular mycorrhiza and rhizobium

Greenhouse experiment was conducted to evaluate the potential effectiveness of a legume (Sesbania cannabina), arbuscular mycorrhizal fungi (AMF) (Glomus mosseae), and rhizobia (Ensifer sp.) symbiosis for remediation of Polycyclic aromatic hydrocarbons (PAHs) in spiked soil. AMF and rhizobia had a beneficial impact on each other in the triple symbiosis. AMF and/or rhizobia significantly increased plant biomass and PAHs accumulation in plants. The highest PAHs dissipation was observed in plant + AMF + rhizobia treated soil, in which >97 and 85–87% of phenanthrene and pyrene, respectively, had been degraded, whereas 81–85 and 72–75% had been degraded in plant-treated soil. During the experiment, a relatively large amount of water-soluble phenolic compounds was detected in soils of AMF and/or rhizobia treatment. It matches well with the high microbial activity and soil enzymes activity. These results suggest that the mutual interactions in the triple symbiosis enhanced PAHs degradation via stimulating both microbial development and soil enzyme activity. The mutual interactions between rhizobia and AMF help to improve phytoremediation efficiency of PAHs by S. cannabina.     

Controls for rhizosphere microorganisms to study effects of vesicular-arbuscular mycorrhizae on Artemisia tridentata

Seven treatments were set up to test the effects of vesicular-arbuscular (VA) mycorrhizal fungi and other rhizosphere microorganisms on the growth of Artemisia tridentata ssp. tridentata. Soil sievings had no significant effect on root or shoot mass. Spores and surface-sterile spores were a poor inoculum source, but roots and fresh soil caused 45–75% mycorrhizal infection. Whereas root-inoculated plants still had low growth responses by the end of the experiment, fresh soil inoculum caused the greatest response, and partial fresh inoculum caused a lesser response. These results suggest that fresh soil is an appropriate inoculum for this plant-fungal-soil system, and that the major effect on plant growth of the fresh soil inoculum is from the mycorrhizal fungi and not from the other microorganisms, because the sievings had no effect on plant growth. In addition, soil dilution plating of saprophytic fungi showed 85% species similarity between sterile and fresh soil inoculum by the end of the experiment. Since the effects of non-VA microorganisms are complex and varied, we suggest that researchers work out the type of mycorrhizal controls that best suit their system.     

The Water-Soluble Pool in Biochar Dominates Maize Plant Growth Promotion Under Biochar Amendment

Although amending biochar into agricultural soils has been regarded as an effective measure to improve crop productivity, it remains unclear why biochar increases crop yield. The objective of this study was to compare the relative contribution of different biochar components in crop growth promotion. Three biochar components were separated: (i) water-soluble biochar extract (BE), (ii) mineral nutrients from biochar ash (BA), and (iii) washed biochar residue (WB). Two soils (Anthrosol and Primosol) with distinctly different organic carbon content, soil texture and land use were amended with the three biochar components and their effects on maize (Zea mays L.) growth were tested in a pot experiment. We hypothesized that (1) plant grown in the Anthrosol benefitted more from the water-soluble compounds of biochar than from its mineral nutrients or washed residue, since the soil is already fertile and has a good structure; (2) plant grown in the Primosol benefitted more from the mineral nutrients of biochar and its washed residual, since the soil is nutrient-poor and has a poor structure. The addition of biochar and its three components increased maize aboveground biomass for both soils. In the Anthrosol, BE, BA, and WB increased the aboveground biomass by 41.6%, 32.7%, and 27.1%; in the Primosol, they increased the aboveground biomass by 41.3%, 24.4%, and 18.2%, respectively. BE had the highest plant growth-promoting effect compared to the other two biochar components, which was regardless of soil condition. In addition, the biomass, total volume, surface area, and number of maize root tips under BE amendment were significantly enhanced, particularly the fine roots (< 0.2 mm in diameter). And a strong positive correlation was observed between maize aboveground biomass and the total length of the fine roots. The results demonstrated that the water-soluble compounds present in biochar, in addition to the mineral nutrients and the washed biochar residue, dominate the plant growth promotion under both soil conditions.

     

Biodegradation of Pyrene in Marine Beach Sediments

The potential of chitosan (0.1% dry weight equivalent) as a bioremediation additive for removal of the recalcitrant polycyclic aromatic hydrocarbon (PAH) pyrene in marine beach sediments was investigated using an open irrigation system over a 63-day period. Osmocote, a slow release fertilizer, was used as the key nutrient supplement at a concentration of 1% in sediment (dry weight equivalent). Osmocote significantly (p < .05) enhanced nutrient levels, and the metabolic activity of the indigenous microbial biomass. Both additives were comparable in stimulating pyrene biodegradation rates; with chitosan (0.062 day^?1) being slightly more effective as an amendment than Osmocote (0.051 day^?1). Loss of pyrene in a control sediment (i.e., pyrene, without additives) was 66.6% over a 63-day period. The concurrent application of additives yielded the greatest biodegradation rates (0.072day^?1), resulting in a 98.2% loss of pyrene over 63 days. The treatment of oil contaminated beach sediments with both osmocote (1%) and chitosan (0.1%) is therefore recommended as an effective treatment for the intrinsic biodegradation of recalcitrant PAHs in oil-contaminated beach sediments.     

Nutrient-limited biodegradation of PAH in various soil strata at a creosote contaminated site

The effects of nutrient addition on the in situ biodegradation of polycyclic aromatic hydrocarbons in creosote contaminated soil were studied in soil columns taken from various soil strata at a wood preserving plant in Norway. Three samples were used: one from the topsoil (0–0.5 m), one from an organic rich layer (2–2.5 m) and one from the sandy aquifer (4.5–5 m). The addition of inorganic nitrogen and phosphorous stimulated the degradation of polycyclic aromatic hydrocarbons (PAHs) in the top soil and the aquifer sand. These two soils, which differed strongly in contamination levels, responded similarly to nutrient addition with the corresponding degradation of 4-ring PAHs. The ratio between available nitrogen (N) and phosphorous (P) might explain the degree of degradation observed for the 4-ring PAHs. However, the degree of degradation of 3-ring PAHs did not significantly increase after nutrient addition. An increase in the respiration rate, after nutrient addition, could only be observed in the topsoil. In the aquifer sand, 4-ring PAH degradation was not accompanied by an increase in the respiration rate or the number of heterotrophic micro-organisms. PAH degradation in the organic layer did not respond to nutrient addition. This was probably due to the low availability of the contaminants for micro-organisms, as a result of sorption to the soil organic matter. Our data illustrate the need for a better understanding of the role of nutrients in the degradation of high molecular weight hydrocarbons for the successful application of bioremediation at PAH contaminated sites.     

4种绿化树种盆栽土壤微生物对柴油污染响应及对PAHs的修复

采用室内盆栽实验,利用柴油按不同比例混合土壤0 g/kg(CK),2 g/kg(L1),10 g/kg(L2)和50 g/kg(L3)制备了含不同浓度PAHs的污染土样,选择1年生樟树(Cinnamomum camphora)、广玉兰(Magnolia grandiflora)、栾树(Koelreuteria bipinnata)、马褂木(Liriodendron chinense)幼苗为供试植物,进行了土壤微生物对柴油的响应及对PAHs的修复研究。结果表明:(1)4个树种土壤微生物区系组成以细菌占优势,放线菌次之,真菌最少。(2)在各测定时间树种间土壤微生物总数对污染处理响应差异较大。栾树各污染处理组土壤微生物总数均高于对照组;樟树各污染处理土壤微生物在实验前期低于对照;广玉兰为污染处理组在4月份显著低于对照,而在其他月份多高于对照;马褂木在4月份均低于对照,其他月份为L1处理低于对照,L2、L3处理高于对照(1月L2除外)。(3)4个树种对照土壤中微生物总数随时间的变化都是从10月逐渐增加至翌年4月,然后不断减少至10月;污染处理土壤微生物总数呈现峰值提前或滞后现象,主要出现在1月或7月。真菌是控制PAHs降解的重要因素。(4)经过1a实验,各树种L1、L2处理土壤中的PAHs浓度已与对照土壤相当;L3处理各树种土壤中PAHs含量为马褂木>栾树>广玉兰>樟树。