Pyrene In Soil Research Articles

Effects of Biostimulation and Bioaugmentation on The Degradation of Pyrene in Soil

Petroleum based products have been widely used as a source of energy for centuries. One of the main petroleum hydrocarbons of concern is Polycyclic Aromatic Hydrocarbon (PAHs) which include pyrene. Pyrene is a four ring PAHs commonly found in soils contaminated with petroleum based products. The effectiveness of the addition of nutrient (biostimulation) and Mycobacterium sp. (bioaugmentation) on biodegradation of pyrene in soil was evaluated. The addition of nutrients (biosimulation) and microorganisms (bioaugmentation) increased the number of viable cells over the control during the bioremediation process. The cell number increased by 40, 70, 59 and 132 fold for the control, biosimulation, bioaugmentation and combined bioaugmentation, respectively. A lag period of 0.5 d and a specific growth rate of 0.896 d-1 were observed with the combined biosimulation-bioaumentation treatment. The temperature results showed that the temperature of the combined biostimulation-bioaugmentation reached 41°C after two days of treatment while the maximum temperature of the control, biostimulation and bioaugmentation were within the range of 28-32°C. The moisture content decreased for all treatments reaching 45-57% but remained within the optimum range of 40-60% for bioremediation process. This was due to the fact that the moisture lost in the exhaust gas was not compensated by the water produced as a by-product of the organic matter degradation. The level of pyrene degradation was indicated by the decline in O2 concentration and the increase in CO2 concentration in the exhaust gas. The control, biostimulation and bioaugmentation treatments showed similar patterns of decreasing O2 and increasing CO2. However, the combined biostimulation-bioaugmentation treatment recorded a declining trend in O2 concentration and increasing trend in CO2 concentration in the exhaust gas at the beginning of experiment (first 7 days) followed by increasing trend in O2 concentration and decreasing trend in CO2concentration in the next 8 days of the experiment. The highest pyrene reduction in percentage (84.29%) was obtained through the combined bioaugmentation-biostimulation process followed by bioaugmentation (57.86%), biostimulation (50%) and control (37%) processes. Different pyrene degradation rates were observed during the various phases of microbial growth (lag, exponential and stationary) of combined bioaugmentation-biostimulation treatment.

Enhanced-electrokinetic remediation of copper–pyrene co-contaminated soil with different oxidants and pH control

Electrokinetic (EK) remediation has potential to simultaneously remove heavy metals and organic compounds from soil, but the removal percent of these pollutants is very low in general if no enhancing treatment is applied. This study developed a new enhanced-EK remediation technology to decontaminate a heavy metal–organic compound co-contaminated soil by applying different oxidants and pH control. A red soil was used as a model clayed soil, and was spiked with pyrene and Cu at about 500mgkg−1 for both to simulate real situation. Bench-scale EK experiments were performed using four oxidants (H2O2, NaClO, KMnO4, and Na2S2O8) and controlling electrolyte pH at 3.5 or 10. After the treatments with 1.0Vcm−1 of voltage gradient for 335h, soil pH, electrical conductivity, and the concentrations and chemical fractionations of soil pyrene and Cu were analyzed. The results showed that there was significant migration of pyrene and Cu from the soil, and the removal percent of soil pyrene and Cu varied in the range of 30–52% and 8–94%, respectively. Low pH favoured the migration of soil Cu, while KMnO4 was the best one for the degradation of pyrene among the tested oxidants, although it unfortunately prevented the migration of soil Cu by forming Cu oxide. Application of Na2S2O8 and to control the catholyte pH at 3.5 were found to be the best operation conditions for decontaminating the Cu-pyrene co-contaminated soil.

Biotoxicity Assessment of Pyrene in Soil Using a Battery of Biological Assays

A test battery, composed of a range of biological assays, was applied to evaluate the ecological health of soil aged for 69 days and spiked with a range of pyrene levels (1.04, 8.99, 41.5, 72.6, 136, and 399 μg g(-1) dry soil; Soxhlet-extracted concentrations after 69 days of aging). Chinese cabbage (Brassica rapa), earthworm (Eisenia fetida), and bacteria (Vibrio fischeri) were used as test organisms to represent different trophic levels. Among the acute ecotoxicity bioassays used, the V. fischeri luminescence inhibition assay was the most sensitive indicator of pyrene toxicity. We observed >8 % light inhibition at the lowest concentration (1.04 μg g(-1)) pyrene, and this inhibition increased to 60 % at 72.6 μg g(-1). The sensitivity ranking for toxicity of the pyrene-contaminated soil in the present study was in the following decreasing order: root elongation of Chinese cabbage < earthworm mortality (14 days) < earthworm mortality (28 days) < luminescence inhibition (15 min) < luminescence inhibition (5 min). In addition, genotoxic effects of pyrene were also evaluated by using comet assay in E. fetida. The strong relationship between DNA damage and soil pyrene levels showed that comet assay is suitable for testing the genotoxicity of pyrene-polluted soil. In addition, tail moment was well correlated with soil pyrene levels (r (2) = 0.99). Thus, tail moment may be the most informative DNA-damage parameter representing the results of comet assay. Based on these results, the earthworm DNA damage assay and Microtox test are rapid and sensitive bioassays and can be used to assess the risk of soil with low to high levels of hydrocarbon pollution. Furthermore, an analysis of the toxic effects at several trophic levels is essential for a more comprehensive understanding of the damage caused by highly contaminated soil.

Ethyl lactate-Fenton treatment of soil highly contaminated with polycyclic aromatic hydrocarbons (PAHs)

This study reports on a novel ethyl lactate based Fenton treatment for soils contaminated with polycyclic aromatic hydrocarbons (PAHs). The degradation of four PAHs, i.e. phenanthrene, anthracene, fluoranthene and benzo[a]pyrene in soil using this novel treatment was compared to ethanol-Fenton and conventional Fenton treatments. Ethyl lactate/water system manifested a greater desorption capacity than ethanol/water system. A 6h ethyl lactate/water (fc=0.60) pretreatment followed by a 4h ethyl lactate/water (fc=0.20) based Fenton treatment effectively degraded all tested PAHs (>97% removal). Ethanol/water treatment was highly selective towards the degradation of anthracene and benzo[a]pyrene, with ∼30% of phenanthrene and fluoranthene remaining untreated, while conventional Fenton resulted in 31–57% of untreated PAHs after 24h. The pseudo-first order kinetic reaction rate constants of ethyl lactate/water based Fenton system were 12–42 times higher than conventional Fenton treatment in soil. The efficiency of treatment was mainly caused by enhanced solubility and desorption, and to a less extent, PAH reactivity, hydrogen peroxide stabilisation and enhanced OH radicals generation by the Fe3+/lactate complex formed.

Biosorption and biodegradation of phenanthrene and pyrene in sterilized and unsterilized soil slurry systems stimulated by Phanerochaete chrysosporium

To assess the “bioaccessible” pool of mycelia-bound polycyclic aromatic hydrocarbons (PAHs) and to quantify its biodegradation kinetics in soil, a soil-slurry system containing mycelial pellets of Phanerochaete chrysosporium as a separable biophase was set up. In sterilized and unsterilized soil-slurry, the distribution and dissipation of phenanthrene and pyrene in soil, fungal body of P. chrysosporium and water were independently quantified over the incubation periods. Biosorption and biodegradation contributions to bio-dissipation of dissolved- and sorbed-PAHs were identified. The biodegradation kinetics of PAHs by allochthonous P. chrysosporium and soil wild microorganisms was higher than those predicted by a coupled desorption–biodegradation model, suggesting both allochthonous and wild microorganisms could access sorbed-PAHs. The obvious hysteresis of PAHs in soil reduced their biodegradation, while the biosorbed-PAHs in P. chrysosporium body as an interim pool exhibited reversibly desorption and were almost exhausted via biodegradation. Both biosorption and direct biodegradation of PAHs in soil slurry were stimulated by allochthonous P. chrysosporium. After 90-day incubation, the respective biodegradation percentages for phenanthrene and pyrene were 63.8% and 51.9% in the unsterilized soil without allochthonous microorganisms, and then increased to 94.9% and 90.6% when amended with live P. chrysosporium. These indicate that allochthonous and wild microorganisms may synergistically attack sorbed-PAHs.

Biodegrading of pyrene by a newly isolated Pseudomonas putida PL2

Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent organic compounds derived from natural sources and anthropogenic processes, which have been recommended as priority pollutants. Degradation of PAHs in the environment is becoming more necessary and urgent. In the current study, strain PL2, which is capable of growing aerobically on pyrene (PYR) as the sole carbon source, was isolated from hydrocarbons-contaminated soil and then identified as Pseudomonas putida by morphological and physiological characteristics as well as 16S rDNA sequence. The strain PL2 was able to degrade 50.0% of the pyrene at 28°C within 6 days in the presence of 50 mg/L pyrene, while the strain PL2 degraded 50.0% of the pyrene within 2 days when a solution of 50 mg/L pyrene and 50 mg/L phenanthrene was used. In addition, phenanthrene was shown to increase the biodegradation efficiency of pyrene by the strain PL2. The order of degradation by the strain PL2 was pH 6.0 > pH 7.0 > pH 5.0 > pH 8.0. The degradation rate of PYR in the soil by the strain PL2 reached 70.0% at the 10th day. The dynamics of PYR degradation in soil by PL2 was fit to the first order model and the strain PL2 was shown to efficiently degrade PYR in soil. The current study showed that P. putida PL2 was a novel bacterium that could degrade pyrene and holds great promise for use in PAHs bioremediation in soil.

Responses of Scirpus triqueter, soil enzymes and microbial community during phytoremediation of pyrene contaminated soil in simulated wetland

The aim of this study was to determine the enhancement of Scirpus triqueter in the dissipation of pyrene and the interaction of pyrene with plant, soil enzymes and microbial community. The results indicated that the dissipation ratios of pyrene in the rhizospheric and non-rhizospheric soil were 64.65 ± 3.86% and 54.49 ± 2.74%, respectively, and were higher than that in the unplanted soil (42.60 ± 0.71%) at 80d after planting S. triqueter. The pyrene was toxic to S. triqueter, as evidenced by growth inhibition in height, diameter, shoot number and biomass during the planting period. The activities of dehydrogenase decreased significantly at the presence of pyrene in soils, and increased remarkably with the introduction of S. triqueter. It was found that the pyrene addition increased the ratios of fungal/total fatty acids and gram-positive/gram-negative, but the presence of S. triqueter decreased the ratios of gram-positive/gram-negative. A larger stress level was found in the pyrene treated soils without S. triqueter. The ratio of aerobic/anaerobic bacteria decreased with increasing pyrene concentration, but increased when S. triqueter was planted. The principal analysis of phospholipid fatty acid signatures revealed that microbial community structures in the rhizospheric and non-rhizospheric soil were similar, but different from those in the unplanted and control soil.

Enhanced Microbial Removal of Pyrene in Soils in the Presence of Earthworms

Microbial degradation of pyrene was studied in soils in the presence and absence of earthworms (Eisenia foetida) to demonstrate an integrated innovative strategy for bioremediation of sites lightly polluted by polycyclic aromatic hydrocarbons. Desorption of pyrene and soil microbial respiration were measured to elucidate the mechanism of enhanced microbial degradation. The results showed that both soil properties and contact time could influence pyrene biodegradation. The introduction of E. foetida enhanced pyrene removal significantly both in freshly spiked and aged soils. The percentage pyrene removal in the presence of E. foetida was 45.5–91.0% after 14 d of incubation, which were 2.1 to 2.8 times greater than those without the worms. The enhanced pyrene removal is attributed to both enhanced microbial degradation and uptake by the worms. Microbial degradation of pyrene increased by 1.2 to 1.6 times in the presence of the worms. Overall, the introduction of live worms could improve both pyrene bioavailability and microbial activity, which leads to enhanced microbial degradation of pyrene.

Degradation of pyrene in soils by extracellular polymeric substances (EPS) extracted from liquid cultures

The extracellular polymeric substances (EPS) isolated from Zoogloea sp. and Aspergillus niger ( A. niger) were employed in studies of degradation of pyrene in contaminated soils. The results of the present study showed that pyrene could be degraded in the presence of any one EPS, and the reduction of pyrene increased as the initial concentration of EPS increased. The best degradation was obtained in the presence of Zoogloea sp. EPS 5332.34 mg kg −1 + A. niger EPS 6512.17 mg kg −1, and more than 80% of pyrene was degraded after 35 days, meanwhile, the speedy degraded time was greatly reduced to 14 days from the 21 days required for other EPS combination. To understand the underlying principles of EPS depleting pyrene, the potential factors resulted in this phenomenon were discussed in the latter part, which could provide new insight into the function of EPS in bioremediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soils.

Effects of aging and mixed nonaqueous‐phase liquid sources in soil systems on earthworm bioaccumulation, microbial degradation, sequestration, and aqueous desorption of pyrene

The effects of loading and aging pyrene in soils in the presence of four environmentally common nonaqueous-phase liquids (NAPLs) (hexadecane, 2,2,4,4,6,8,8-heptamethylnonane [HMN], toluene, and dimethyl phthalate [DMP]) on its subsequent desorption from those soils, earthworm accumulation, biodegradation, and extractability were tested by using two dissimilar soils. The presence of each of the four NAPLs increased fractions and rates of pyrene desorption, and hexadecane slowed the effects of aging on these same parameters. Loading with hexadecane and HMN caused earthworm accumulation of pyrene to decrease. These results contrast with generally observed faster desorption rates resulting from NAPL addition, suggesting that additional factors (e.g., association of pyrene with NAPL phases and NAPL toxicities to earthworms) may impact bioaccumulation. The presence of HMN and toluene increased pyrene biodegradation, whereas hexadecane and DMP had the opposite effects. These results correlate with changes in the extractability of pyrene from the soils. After aging and biodegradation, hexadecane and DMP substantially increased pyrene residues extractable by methanol and decreased nonextractable fractions, whereas HMN and toluene had the opposite effects.

Microbial Degradation of Soil-Aged 14C-Labeled Pyrene by an Environmental Mycobacterium sp. Strain S65 in Different Soil Environments

Mycobacterium (designated Mycobacterium sp. strain S65 in Genbank), previously isolated and characterized from a jet-fuel contaminated site at the Sept-Iles, Quebec, Canada airport, was found to be competent in mineralizing selected recalcitrant polycyclic aromatic hydrocarbon (PAH) compounds of minimal water solubility and low bioavailability in soils, when grown in yeast extract-tryptone-soluble starch medium. In aerobic liquid microcosms, strain S65 was capable of 61% cumulative mineralization of pyrene over 14 days. Based on 14CO2 evolution, the mineralization capability and capacity of this organism for soil-aged 14C-labeled pyrene was assessed. Gamma-ray sterilized farm soil microcosms were spiked with 1.0 105 dpm 14C-labeled pyrene and allowed to age for up to 360 days. The experimental design consisted of a factorial combination of two types of soil (clay and sandy), two levels of soil organic matter (high and low), and two concentrations of pyrene (1000 and 500 mg L-1) with six replicates per treatment (48 microcosms per inoculation date). One set of 48 aged microcosms was inoculated after each aging period (0, 30, 180, or 360 days) with three replicates per treatment (i.e., 24 microcosms) each receiving 1.0 107 cfu of live Mycobacterium sp. strain S65 (i.e., treatment) and a further three replicates per treatment receiving heat-killed Mycobacterium (i.e., negative control) for an overall total of 192 microcosms. The 14CO2 that evolved over 1, 3, 6, or 9 days and was trapped in a KOH solution was measured by scintillation counter, and cumulative mineralization was calculated as a percent of initial pyrene. As a further basis of comparison, mineralization of un-aged pyrene in culture broth was also measured (i.e., positive control) over the same incubation period. Serial dilution and spread-plate techniques served to assess the possible presence of a viable culturable microorganism population (CFU g-1) in different sterile soils for a total of 4 4 3 = 48 (i.e., soils aging time replicate) microcosm bottles (i.e., sterile control). No microbial colonies were observed on solid media, indicating no culturable competitive microbial strain that might contribute to the mineralization of 14C-labeled pyrene, at any time during the aging process. Un-aged pyrene in soil (day 0) was utilized by Mycobacterium sp. strain S65 without any lag phase, and pyrene mineralization proceeded thereafter. Cumulative mineralization of pyrene added at concentrations of 1000 and 500 mg L-1 reached 19% and 18.5%, respectively, after 24 h and 21% and 20%, respectively, after 96 h in sand-loam, low organic matter soil. At 96 h, cumulative pyrene mineralization in clay-loam, high organic matter soil was only 15.5% and 14.5%, respectively, distinctly less than in the sandy, low organic matter soil. Sampling continued until no further mineralization occurred (i.e., cumulative mineralization reached a plateau). Soil-aged pyrene was metabolized at a moderate rate by Mycobacterium sp. strain S65, whereas un-aged pyrene was mineralized at a greater rate (61% cumulative mineralization) in an aerobic liquid microcosm. For initial additions of 1000 and 500 mg L-1 pyrene, followed by 30 days of aging, Mycobacterium sp. strain S65 showed a maximum cumulative mineralization of 14% and 13.25%, respectively, in sand-loam, low organic matter soil but only 12.5% and 11.5%, respectively, in clay-loam, high organic matter soil. For 180-day and 360-day aged pyrene, cumulative pyrene mineralization was less than 10%, a significant drop from less-aged pyrene-soil microcosms. This suggests that as the aging proceeds in the soil medium, the pyrene becomes less accessible for degradation. Nonetheless, this study supports the idea that Mycobacterium sp. strain S65 has the potential to be useful in bioremediation and biodetoxification of high molecular weight PAH-contaminated sites.

Impact of carbon nanomaterials on the behaviour of 14C-phenanthrene and 14C-benzo-[a] pyrene in soil

The impact of fullerene soot (FS), single-walled (SWCNTs) and multi-walled (MWCNTs) carbon nanotubes on the behaviour of two 14C-PAHs in sterile soil was investigated. Different concentrations of carbon nanomaterials (0, 0.05, 0.1 and 0.5%) were added to soil, and 14C-phenanthrene and 14C-benzo[ a]pyrene extractability assessed over 80 d through dichloromethane (DCM) and hydroxypropyl- β-cyclodextrin (HPCD) shake extractions. Total 14C-PAH activity in soils was determined by combustion, and mineralisation of 14C-phenanthrene was monitored over 14 d, using a catabolically active pseudomonad inoculum. No significant loss of 14C-PAH-associated activity from CNM-amended soils was observed over the ‘aging’ period. CNMs had a significant impact on HPCD-extractability of 14C-PAHS; extractability decreased with increasing CNM concentration. Additionally, 14C-phenanthrene mineralisation was inhibited by the presence of CNMs at concentrations of ≥0.05%. Differences in overall extents of 14C-mineralisation were also apparent between CNM types. It is suggested the addition of CNMs to soil can reduce PAH extractability and bioaccessibility, with PAH sorption to CNMs influenced by CNM type and concentration.

Application of organic wastes on a benzo( a)pyrene polluted soil. Response of soil biochemical properties and role of Eisenia fetida

In this paper we studied the bioremediation effects of a soil artificially contaminated by benzo( a)pyrene with and without two organic wastes (organic municipal solid waste, MSW, and poultry manure, PM) and with and without worms ( Eisenia fetida) over 90 days. For the organic treatments, soil samples were mixed with MSW at a rate of 10% or PM at a rate of 7.6%, in order to apply the same amount of organic matter to the soil. An unamended and non-polluted soil was used as control. Cellulase and glutathione-S-transferase activities in worms and the earthworms’ weight were measured at four different incubation times (3, 15, 60 and 90 days). Cocoon numbers, average weight per cocoon and number of juveniles per cocoon were measured 30 days after the benzo( a)pyrene exposure. Extractable benzo( a)pyrene in soils and E. fetida was determined during the incubation period. To observe the effects of bioremediation of the contaminated soil, ATP, urease and phosphatase activities were measured. At the end of the incubation period and when compared with the polluted soil without worms and organic matter, the extractable benzo( a)pyrene decreased by 41.2% for the unamended polluted soil and without worms, by 45.8% for the organic-PM polluted soil and without worms, 48.3% for the organic-MSW polluted soil and without worms, 55.4% for the organic-PM polluted soil and with worms, and 66.3% for the organic-MSW polluted soil and with worms. This meant that worm hydrocarbon absorption was lowest in the contaminated soil amended with MSW and with worms, causing an increase in catabolic activity of the soil. These results suggested that the co-application of organic wastes and E. fetida for the bioremediation of benzo(a)pyrene polluted soil is potentially advantageous.

Effect of short-chain organic acids and pH on the behaviors of pyrene in soil–water system

The effects of five short-chain organic acids (SCOAs) on the behaviors of pyrene in soil–water system were investigated. The influences of the quantity and species of organic acids, pH, and soil dissolved organic matter were considered. The results showed the presence of SCOAs inhibited the adsorption and promoted the desorption of pyrene in the following order: citric acid > oxalic acid > tartaric acid > lactic acid > acetic acid. The decreased extents of pyrene adsorption performance enhanced with increasing SCOA concentrations, while the decreasing rate became less pronounced at high SCOA concentrations. In the presence of organic acids, the adsorption ability of pyrene decreased with increasing pH. However, there was a slight increase of pyrene adsorption with the addition of oxalic acid, tartaric acid and citric acid above pH 8. The capacity for pyrene retention differentiated significantly between the soils with and without dissolved organic matter. The presence of SCOAs was also favorable for the decrease of pyrene adsorption on soil without dissolved organic matter. The results of this study have important implications for the remediation of persistent organic pollutants in soil and groundwater.

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.

Development and application of a skin cancer slope factor for exposures to benzo[a]pyrene in Soil

Humans may be dermally exposed to the carcinogenic substance benzo[a]pyrene (B[a]P) via contact with soil at contaminated sites. The potential for risk is typically assessed using the proportion of dose estimated to penetrate through exposed skin for comparison with an oral route slope factor. An alternate dermal slope factor of 25 (mg/kgday)−1 was previously developed (Knafla et al., 2006) based on skin carcinogenicity, since skin painting studies with mice suggest the formation of epidermal tumors may be a more sensitive endpoint than systemic tumors following dermal exposure. An extension of this work resulted in a skin cancer slope factor derived on a per unit skin surface area basis of 3.5 (μg/cm2day)−1 that can be used to estimate risk as a function of exposed surface area. Various factors were examined for interspecies extrapolation of risks from mice to humans and for estimating skin exposures to B[a]P in soil. Using a nominal soil concentration of 1.0mg/kg, a range of cancer risk values of 29–220 in 100,000 was calculated. Soil concentrations associated with a one in 100,000 risk ranged from 0.0046 to 0.035μg/g, which are lower than those derived using an oral slope factor. These results suggest that B[a]P-related skin cancer (point of contact) risks should be considered at contaminated sites.

Enhancement of pyrene removed from contaminated soils by Bidens maximowicziana

The research utilized Bidens maximowicziana along with pyrene-degrading bacteria to evaluate their potential in cleaning up pyrene contamination. The removal of pyrene from the planted soil was obviously higher than that from the unplanted soils. After 50 d of B. maximowicziana growth, the average removal ratio of pyrene in planted soil was 79%, which was 28% higher than that of pyrene in unplanted soil. In contrast to other plants, both roots and shoots of B. maximowicziana could accumulate a large amount of pyrene from the soil and pyrene uptake increased with the soil pyrene concentration. Through analysis of pathways of pyrene removal, this enhanced removal of pyrene by plant–microbial association might be mainly the result of B. maximowicziana-promoted microbial degradation. Both the catalase and polyphenol oxidase activities in soil were higher in planted soil than those in unplanted soil. And the bacteria populations in soil, especially in rhizosphere, were also inspired by the growth of B. maximowicziana. These could be explained by the rhizosphere effect. Therefore, bio-removal of pyrene in the contaminated soils was feasible using B. maximowicziana.

Ageing behavior of phenanthrene and pyrene in soils: A study using sodium dodecylbenzenesulfonate extraction

The surfactant SDBS has potential to be used as an extractant in advanced extraction methods. It was investigated if SDBS in concentrations of 10,000 mg L −1 can be used to study the ageing behaviors of phenanthrene and pyrene in two soils. Compared to dichloromethane extraction, extraction with 10,000 mg L −1 SDBS can improve the precision of the determination due to the low volatility of surfactant solution. In all cases tested, the amount of sorbed phenanthrene and pyrene in soils increased with contact time from 1 to 120 days, and can be applied well to both the three-domain model and the dual mode model. Redundancy analysis showed that time, organic carbon content and log K ow are major factors affecting the fitted Freundlich parameters and the sorption kinetics of phenanthrene and pyrene. The amount of sorbed phenanthrene and pyrene in low-concentrations samples varied more with time than the one in high concentrations, indicating that the sorption on soils is concentration-dependent. Also, the isotherms were operationally separated into a “fast” fraction and a “slow” fraction. The results imply that the adsorption sites are internal to the SOM matrix and unevenly distributed.

Dynamic changes in functional gene copy numbers and microbial communities during degradation of pyrene in soils

This study investigates the dynamics of pyrene degradation rates, microbial communities, and functional gene copy numbers during the incubation of pyrene-spiked soils. Spiking pyrene to the soil was found to have negligible effects on the bacterial community present. Our results demonstrated that there was a significant difference in nidA gene copy numbers between sampling dates in QZ soil. Mycobacterium 16S rDNA clone libraries showed that more than 90% mycobacteria detected were closely related to fast-growing PAH-degrading Mycobacterium in pyrene-spiked soil, while other sequences related to slow-growing Mycobacterium were only detected in the control soil. It is suggested that nidA gene copy number and fast-growing PAH-degrading Mycobacterium could be used as indicators to predict pyrene contamination and its degradation activity in soils.

Assessment of Pyrene Bioavailability in Soil by Mild Hydroxypropyl-β-Cyclodextrin Extraction

Bioavailability of organic pollutants in soil is currently a much-debated issue in risk assessment of contaminated sites. Ecorisk of an organic pollutant in soil is strongly influenced by the properties of the soil and its contamination history. To evaluate the effect of aging on the availability of pyrene, earthworm (Eisenia fetida) accumulation and chemical extraction by exhaustive and nonexhaustive techniques in soil spiked with a range of pyrene levels (1.07, 9.72, 88.4, 152, and 429 μg g⁻¹ dry soil) were measured in this study using both unaged (i.e., 0 days) and aged (i.e., 69, 150, and 222 days) soil samples. The results showed that the amount of pyrene accumulated by earthworms did not change greatly with aging time under different high-dose contamination levels, but changed significantly at lower concentrations. Moreover, aging (after 222 days) significantly decreased biological and chemical availability of pyrene. Furthermore, the relationship between earthworm bioaccumulation, hydroxypropyl-β-cyclodextrin (HPCD), and organic solvent extraction was investigated in order to find a suitable and rapid method to predict pyrene bioavailability. Results showed that, at different levels of pyrene, the mean values of earthworm uptake and HPCD extractability were 10-40% and 10-65%, respectively. Correlation (r² = 0.985) and extraction results for pyrene suggested that mild HPCD extraction was a better method to predict bioavailability of pyrene in soil compared with organic solvent extraction.