Pyrene In Soil Research Articles

Relationship Between Soil Concentrations of PAHs and Their Regional Emission Indices

Actual information on the level of accumulation of PAHs in soils, their inputs/outputs and fate is still unsatisfactory. The regional scale of data collection is important from practical point of view, since decisions regarding environment protection often require proper assessment of soil information aggregated on this level. The objective of the study was to define the regional levels of PAHs in soils and to examine the relationship with the parameters related to their inputs (emission factors) and to natural conditions (soil properties, geographical localisation). The territory of Poland, comprising 16 regions, was chosen as a model area representing the Central/East European countries. The concentrations of 16 PAH compounds were determined in 266 soil samples collected from 0 to 30-cm upper soil layer from agricultural lands. The data were supplemented with basic soil properties. The regional concentrations of Σ16PAHs were within the limits of 125–756 μg kg−1 (geometric means) and did not exceed the limit values specified in Polish regulations. They complied also with European soil screening values for intermediate or negligible risk. The key variable affecting the accumulation of PAHs in soils was the regional emission of those contaminants, which described soil concentrations of PAHs in at least 50%; the results suggest time-dependent (delayed) reaction of soil environment to the emission changes. The effect was sensitive to PAH compositions in soils and was most pronounced in the case of higher molecular weight compounds (≥4 rings) transported predominantly with atmospheric particles. The regression models, comprising actual regional emission data, did not indicated on the increasing risk of PAHs accumulation in soils. The evaluations based on the regional content of benzo(a)pyrene in soils implied significant discrepancies between Polish and other internationally accepted criteria in soil contamination. The natural factors (soil characteristics and climate) affected the regional PAH concentrations in very small extent.

Desorption of phenanthrene and pyrene in soils by root exudates

A batch experiment was conducted to evaluate the impact of root exudates on the desorption of phenanthrene and pyrene in soils. Rhizosphere model systems where soils are given artificial root exudates (AREs) have been utilized. ARE addition markedly influenced the desorption of phenanthrene and pyrene in soils, and the effects depended on ARE concentration, aging time, and soil properties. The desorption of phenanthrene and pyrene increased with ARE concentration of 0–1000 mmol/L. Soils with higher soil organic matter content ( f oc) had lower desorption than soils with lower f oc values, at the same ARE concentration. The aging of phenanthrene and pyrene in soils markedly reduced the desorption of both compounds. The increment of phenanthrene and pyrene desorption was always higher with the addition of citric and oxalic acid than with the same concentration of AREs, indicating that the effects of AREs on desorption may be dominantly due to the organic acids.

Enzyme activities during degradation of polycyclic aromatic hydrocarbons by white rot fungus Phanerochaete chrysosporium in soils

The degradation of three polycyclic aromatic hydrocarbons (PAHs), phenanthrene, pyrene and benzo[a]pyrene in soils by Phanerochaete chrysosporium, and the enzyme activities of lignin peroxidase (LiP) and manganese peroxidase (MnP) produced during degradation, were analyzed. The results showed that the 19-d percentage degradation ranged from 72.77 ± 1.39% to 25.50 ± 3.41% for the three compounds, and the maximum LiP and MnP activities ranged from 0.16 ± 0.005 to 0.05 ± 0.002 U g −1 and from 1.92 ± 0.03 to 0.54 ± 0.03 U g −1, respectively. Degradation percentage and enzyme activities both exhibited inverse relationships with the octanol/water partition coefficient ( K ow) of the compounds, indicating that LiP and MnP from P. chrysosporium may be the primary enzymes responsible for PAH degradation in soil. As the soil organic matter (SOM) content increased from 0.3% for Soil 1 to 19% for Soil 4, the 19-d degradation percentage of pyrene decreased from 66.20 ± 2.72% to 32.42 ± 1.05%, and correspondingly, the maximum of LiP and MnP activities increased from 0.05 ± 0.002 to 1.78 ± 0.15 U g −1 and from 0.34 ± 0.03 to 1.78 ± 0.15 U g −1, respectively. Hence, it is plausible to conclude that the P. chrysosporium appeared to degrade not only the PAHs with small molecular size but also the macromolecular SOM. When SOM differences are large, as in this study, SOM has greater influence on enzyme activity than low-level exotic pollutants.

Effects of soil amendment with different carbon sources and other factors on the bioremediation of an aged PAH-contaminated soil

Carbon supplementation, soil moisture and soil aeration are believed to enhance in situ bioremediation of PAH-contaminated soils by stimulating the growth of indigenous microorganisms. However, the effects of added carbon and nitrogen together with soil moisture and soil aeration on the dissipation of PAHs and on associated microbial counts have yet to be fully assessed. In this study the effects on bioremediation of carbon source, carbon-to-nitrogen ratio, soil moisture and aeration on an aged PAH-contaminated agricultural soil were studied in microcosms over a 90-day period. Additions of starch, glucose and sodium succinate increased soil bacterial and fungal counts and accelerated the dissipation of phenanthrene and benzo(a)pyrene in soil. Decreases in phenanthrene and benzo(a)pyrene concentrations were effective in soil supplemented with glucose and sodium succinate (both 0.2 g C kg(-1) dry soil) and starch (1.0 g C kg(-1) dry soil). The bioremediation effect at a C/N ratio of 10:1 was significantly higher (P < 0.05) than at a C/N of either 25:1 or 40:1. Soil microbial counts and PAH dissipation were lower in the submerged soil but soil aeration increased bacterial and fungal counts, enhanced indigenous microbial metabolic activities, and accelerated the natural degradation of phenanthrene and benzo(a)pyrene. The results suggest that optimizing carbon source, C/N ratio, soil moisture and aeration conditions may be a feasible remediation strategy in certain PAH contaminated soils with large active microbial populations.

Impact of low-molecular-weight organic acids on the availability of phenanthrene and pyrene in soil

The impact of low-molecular-weight organic acids (LMWOAs) on the availability of phenanthrene and pyrene was investigated using laboratory batch assays. Experiments were conducted with two types of soil with different organic contents. The LMWOAs used were citric and oxalic acid. A mild solvent extraction procedure and a sorption–desorption experiment were used to predict the availability of phenanthrene and pyrene. Results showed that the extractable amounts of phenanthrene and pyrene in both soil types increased with increased citric or oxalic acid concentration. Citric acid addition promoted phenanthrene and pyrene extraction to a greater degree than oxalic acid. Compared with freshly spiked soils, the extractable amounts of phenanthrene and pyrene with the addition of LMWOAs decreased significantly after 60 days of cultivation. Soils with higher values of soil organic carbon content ( f oc) showed decreased phenanthrene and pyrene availability after the addition of LMWOAs. The sorption and desorption results also demonstrated the enhanced availability of PAHs with LMWOA addition. Phenanthrene sorption could be described using a linear model, regardless of the addition of LMWOAs. The simulated distribution constants ( K d) for phenanthrene sorption decreased significantly with the addition of LMWOAs. In contrast, phenanthrene desorption clearly increased with the addition of LMWOAs. These results suggest that the availabilities of phenanthrene and pyrene can be increased with the addition of suitable LMWOAs.

Effects of aging and freeze-thawing on extractability of pyrene in soil

The effects of soil freezing and thawing on the extractability by dichloromethane of pyrene from two Chinese soils are investigated. The soils were collected from the Northeast region of China where heavy pollution of soils by Polycyclic Aromatic Hydrocarbons (PAH) is common. Two soils were considered: a burozem obtained from the Shenfu irrigated region in Liaoning province and a phaeozem collected from the Hailun area in Haerbin province. The soils were collected from areas free from PAH pollution. Pyrene was aged in sterilized soil, and autoclaved deionized water was then added to adjust the soil to different moisture levels. The combined dichloromethane extractions of pyrene in soils at various periods showed that the quantity of pyrene extracted with dichloromethane could be divided into two stages: the initially rapid period and a longer, slower period. The frequency of freeze-thawing cycles had different and contradictory effects on pyrene extractability between the two soil types. Soil moisture also was found to have different and opposite effects on pyrene extractability. Freeze-thawing cycles had great influence on pyrene extractability both in aged and unaged soils. The changes in unaged soil were more significant than those in 1-year aged soil and attributed to changes in the soil organic matter. Our research shows that the effect of freezing and thawing on pyrene extraction is complicated due to the differences in physical and chemical properties of soils as well as the aging process.

Removal of Pyrene from Contaminated Soils by White Clover

Abstract Phytoremediation has been used as an emerging technology for remediation of soil contamination with polycyclic aromatic hydrocarbons (PAHs), ubiquitous persistent environmental pollutants derived from natural and anthropogenic processes, in the last decade. In this study, a pot experiment was conducted to investigate the potential of phytoremediation of pyrene from spiked soils planted with white clover ( Trifolium repens) in the greenhouse with a series of pyrene concentrations ranging from 4.22 to 365.38 mg kg −1. The results showed that growth of white clover on pyrenecontaminated soils was not affected. The removal of pyrene from the spiked soils planted with white clover was obviously higher than that from the unplanted soils. At the end of the experiment (60 d), the average removal ratio of pyrene in the spiked soils with white clover was 77%, which was 31% and 57% higher than those of the controls with or without micobes, respectively. Both roots and shoots of white clover took up pyrene from the spiked soils and pyrene uptake increased with the soil pyrene concentration. However, the plant-enhanced dissipation of soil pyrene may be the result of plant-promoted microbial degradation and direct uptake and accumulation of pyrene by white clover were only a small part of the pyrene dissipation. Bioconcentration factors of pyrene (BCFs, ratio of pyrene, on a dry weight basis, in the plant to that in the soil) tended to decrease with increase in the residual soil pyrene concentration. Therefore, removal of pyrene in the contaminated soils was feasible using white clove.

Biodegradation of pyrene and catabolic genes in contaminated soils cultivated with Lolium multiflorum L

Background, aim, and scopeIn the soil environment, polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) are of great environmental and human health concerns due to their widespread occurrence, persistence, and carcinogenic properties. Bioremediation of contaminated soil is a cost-effective, environmentally friendly, and publicly acceptable approach to address the removal of environmental contaminants. However, bioremediation of contaminants depends on plant–microbe interactions in the rhizosphere. The microorganisms that can mineralize various PAHs have PAH dioxygenase genes like nahAc, phnAc, and pdo1. To understand the fate of pyrene in rhizospheric and non-rhizospheric soils in the presence or absence of Pb, pyrene biodegradation, bacterial community structure, and dioxygenase genes were investigated in a pot experiment.MethodsSoil was amended with Pb (a representative heavy metal), pyrene, and a Pb/pyrene mixture. After 8 weeks of aging, one set of pot microcosms was cultivated with rye grass (Lolium multiflorum L) seedlings, while another set was not cultivated for the purpose of comparing rhizosphere and non-rhizosphere pyrene degradation. Pyrene was extracted from freeze-dried soil and plant samples using a Soxhlet extraction method and the extracts were dried to 1 mL under gentle nitrogen flow and analyzed using gas chromatograph mass spectrometry (Agilent 6890, USA). Soil DNA was extracted from triplicate samples and the DGGE was performed using a Bio-Rad Dcode™ Universal Mutation Detection System (Bio-Rad, USA). PAH dioxygenase genes, including nahAc, phnAc, and pdo1, were detected using PCR amplification. Similarly, pyrene degraders were also investigated using plate counting technique.ResultsBiodegradation rates recorded over an 18-week period showed that rye grass promoted significant (P < 0.05) pyrene degradation. Pyrene removal efficiency from rhizospheric soils was 59.1 ± 2.1% and 68.7 ± 2.3% in pyrene- and Pb/pyrene-amended soils, respectively. The results indicate that pyrene dissipation was significantly (P < 0.05) higher in Pb/pyrene-amended soils than only-pyrene-amended soils. The plant growth promoted the degradation of pyrene and accounted for 12.1% to 17.0% of dissipation enhancement in the rhizospheric soils. In this study, the DGGE profiles revealed a shift in soil bacterial community structure in all amended soils, with a higher number and greater complexity of banding patterns in Pb/pyrene-amended samples than in either Pb- or pyrene-amended samples. In the control and Pb-amended soil, pdo1 and nahAc genes were not detected throughout the incubation period but were detected in the pyrene- and Pb/pyrene-amended soils. However, phnAc genes were not detected in either amended or non-amended soils throughout the incubation period. The addition of pyrene had a dramatic effect on the number of pyrene degraders.DiscussionPlants contribute to the degradation of PAHs by increasing the size of microbial population, promoting microbial activity, and modifying microbial community diversity in the rhizosphere. In this study, the presence of plants significantly promoted the degradation of pyrene in the soil due to enhanced bacterial community size and increased the number of pyrene degraders. Similarly, the results of this study have also clearly shown that pyrene remaining in soils only accounted for about 1/3 of the total pyrene addition, suggesting that most of the pyrene added could be removed by plant and/or microbial degradation. HMs and PAHs interaction towards degradation of PAHs can be both negative and positive depending on type and concentration of both HMs and PAHs. In both rhizospheric and non-rhizospheric soils, the pyrene degradation was in line with the changes of bacterial structure, increasing number of pyrene degraders, and the prevalence of dioxygenase genes (nahAc and pdo1). This work represents the first report that Pb can affect the dissipation of pyrene and functional genes were detected in both rhizospheric and non-rhizospheric soils amended with pyrene and Pb/pyrene.ConclusionsPyrene removal efficiency for rhizospheric soils was higher than for non-rhizospheric soils and pyrene dissipation was accelerated in the presence of Pb in both rhizospheric and non-rhizospheric soils. The bacterial community structure was changed and the addition of pyrene indicated dramatic effects on the number of pyrene degraders. The catabolic genes, including nahAc and pdo1, which are responsible for HMW-PAH degradation, were confirmed in both rhizosphere and non-rhizosphere soils amended with pyrene or Pb/pyrene.Recommendations and perspectivesOur findings suggest that the interaction between bacterial community and plant roots could influence the PAH degradation both in the presence and absence of HMs in the contaminated soils.

Evaluation of soil pH and moisture content on in-situ ozonation of pyrene in soils

In this study, pyrene spiked soil (300 ppm) was ozonated at pH levels of 2, 6, and 8 and three moisture contents. It was found that soil pH and moisture content impacted the effectiveness of PAH oxidation in unsaturated soils. In air-dried soils, as pH increased, removal increased, such that pyrene removal efficiencies at pH 6 and pH 8 reached 95–97% at a dose of 2.22 mg O 3/mg pyrene. Ozonation at 16.2 ± 0.45 mg O 3/ppm pyrene in soil resulted in 81–98% removal of pyrene at all pH levels tested. Saturated soils were tested at dry, 5% or 10% moisture conditions. The removal of pyrene was slower in moisturized soils, with the efficiency decreasing as the moisture content increased. Increasing the pH of the soil having a moisture content of 5% resulted in improved pyrene removals. On the contrary, in the soil having a moisture content of 10%, as the pH increased, pyrene removal decreased. Contaminated PAH soils were stored for 6 months to compare the efficiency of PAH removal in freshly contaminated soil and aged soils. PAH adsorption to soil was found to increase with longer exposure times; thus requiring much higher doses of ozone to effectively oxidize pyrene.

The Removal and Remediation of Phenanthrene and Pyrene in Soil by Mixed Cropping of Alfalfa and Rape

The mechanisms and efficiencies of the removal and remediation of polycyclic aromatic hydrocarbons (PAHs) in soils by different planting patterns with rape ( Brassica campestris) and alfalfa ( Medicago sativa) were studied by pot experiments in a greenhouse. Results showed that the remediation efficiencies under mixed cropping of alfalfa and rape significantly exceeded those under single cropping when the initial concentrations of phenanthrene and pyrene were at 20.05-322.06 mg kg −1 and 20.24-321.42 mg kg −1, respectively. After 70 days plantation of crops, the contents of extractable PAHs in soils under mixed cropping were much lower than those under single cropping. About 65.17-83.52% of phenanthrene and 60.09%-75.34% of pyrene was removed from the soils under mixed cropping, respectively, which were averagely 43.26 and 40.38% for phenanthrene, and 11.03 and 16.29% for pyren higher than those under single cropping. Alfalfa or rape did absorb and accumulate PAHs from the soils apparently; the PAHs concentrations in plants monotonically increased with the increase of initial PAHs concentrations in soil; the accumulations of PAHs in plants showed following sequence as roots > above parts, phenanthrene > pyrene and single cropping > mixed cropping at same contamination level. Despite the presence of vegetation significantly enhanced the remediation of PAHs in soils, contributions of abiotic loss, plant uptake, accumulation and microbial degradation was much lower than those of plant-microbial interactions in the process of phytoremediation. Thus plant-microbial interactions are the main mechanisms for the remediation enhancement of soil PAHs pollution under mixed cropping models. Results suggested a feasibility of the establishment of multi-species phytoremediation for the improvement of remediation efficiencies of PAHs, which may decrease accumulations of PAHs in crops and thus reduce their risks.

Biodegradation of Benzo[a]pyrene in Soil by Immobilized Fungus

Mucor sp., a filamentous fungus capable of degrading polycyclic aromatic hydrocarbons (PAHs), was immobilized on maize cob (MC) by physical adsorption and used to degrade benzo[a]pyrene (BaP). The characteristics of BaP degradation by both immobilized and free fungus were then investigated and compared. The degradation rate using the immobilized fungus was higher than that of the freely mobile fungus. When the initial BaP concentration was 50 mg · kg−1, the removal rate was 68% within 42 days using immobilized fungus but only 52% for free fungus in that same time. The optimal amount of inoculated immobilized fungus for BaP degradation was shown to be 2%. The immobilized fungus also showed better removal efficiencies of BaP than free fungus, independent of the moisture content. The increasing concentration of BaP was better tolerated and more quickly degraded by immobilized fungus than by free fungus when the initial BaP concentration was in the range of 10 to 200 mg · kg−1. The scanning electronic microscope (SEM) analysis showed that the immobilized microstructure was suitable for Mucor sp. growth. The results demonstrate the potential for employing Mucor sp., immobilized on MC, for in situ bioremediation of PAH-contaminated soil.

Application of Phytoremediation on Soil Contaminated by Pyrene

The purpose of this study was to treat soils contaminated by pyrene through phytoremediation. The plant species selected were Phragmites communis Trin., Typha orientalis Presl, Vetiveria zizanioides, Rohdea japonica (Thunb.) Roth et Kunth, Cyperus malaccensis. Lam. subsp. monophyllus (Vahl) T. Koyama, Bolboschoenus planiculmis (F. Schmidt) T. Koyama, and Bidens pilosa. The degradation of pyrene in soils was analyzed. The experimental results of this study indicated that the degradation efficiencies of pyrene from soils by V. zizanioides, R. japonica, and T. orientalis were 86, 84, and 77%, respectively, after 14 weeks. These values of degradation percentages were higher than those measured in the unplanted control experiment, which was found equal to 66%. In addition, the pyrene degradation efficiencies in summer were found to be higher than those in winter. The degradation percentages of pyrene sterilized soil with and without T. orientalis were found to be 59 and 55%, respectively. These values were fou...

Fate of 14C–Pyrene in soil–plant system amended with pig manure compost and Tween 80: A growth chamber study

This paper evaluated the effects of a pig manure compost (PMC) and a nonionic surfactant Tween 80 on the fate of 14C–Pyrene (Pyr) in a soil –plant system ( Agropyron elongatum). Soils spiked with 14C–4, 5, 9, 10-Pyr were amended with 7.5% (w/w) PMC together with or without 100 mg kg −1 of Tween 80. Unplanted soil without amendments was set as the control. Gas phases of the systems were monitored for 14CO 2 over a 60 days period. The impact of PMC and Tween 80 on the apparent loss of the PAH and the distribution of 14C-activity in the systems was studied. 14C-activity associated with different soil fractions was further examined by using methyl-isobutyl-ketone (MIBK) fractionation method. The results showed that the addition of PMC could increase the dissipation of Pyr in vegetated soil from 12.1% to 58.7%, while the co-addition of Tween 80 and PMC could further enhance the dissipation to 90.3%. Pyr dissipation in soil was correlated with the mineralization of 14C–Pyr, indicating that Pyr dissipation was mainly due to mineralization. A higher formation of water-extractable metabolites was observed in soil amended with PMC and Tween 80, and this was correlated with a higher biomass accumulation of 14C-activity and higher bound residue formation in the soil. Overall, this study suggested that the co-application of PMC and Tween 80 could improve phytoremediation of Pyr-contaminated soil.

Development of Engineered Natural Organic Sorbents for Environmental Applications. 4. Effects on Biodegradation and Distribution of Pyrene in Soils

The effects of engineered natural organic amendments on the biodegradation and distribution of pyrene in soils were assessed. Pyrene was aged for 105 days in soils amended with either raw or superheated water (SHW)-processed MI peat or soybean stalks, and then subjected to biodegradation with specifically selected microorganisms for 130 days. Initial rates of pyrene mineralization in the soils were increased by addition of raw MI peat, but markedly decreased by additions of SHW-processed MI peat and both processed and raw soybean stalks. Pyrene sorbed by the processed organic sorbents was, however, slowly but steadily degraded by microorganisms over a greater than 4-month test period. Pyrene distributions in the soils were examined by sequential extractions of samples before and after biodegradation. Fractions of pyrene extracted readilywith water or water/methanol mixtures were decreased substantially in both soils bythe addition of processed amendments, while the nonextractable fractions associated with humic and fulvic acids and humin were increased markedly. The results demonstrate that SHW-processed amendments effectively reduce the ecological and human availability and aqueous phase extractability of organic contaminants while facilitating their steady microbial degradation and eventually complete remediation.

Solid-Phase Microextraction (SPME) as a Tool to Predict the Bioavailability and Toxicity of Pyrene to the Springtail, Folsomia candida, under Various Soil Conditions

The porewater concentrations of pyrene were estimated by a negligible depletive solid-phase microextraction (SPME) method. The effects of organic matter (OM) and soil aging on the bioavailability of pyrene in soil were investigated by generation of reproductive effect concentrations (EC50) for the euedaphic springtail, Folsomia candida, under various test conditions. The soil used was a sandy loam soil with natural OM content of 2.6% (Askov soil). It was enriched with increasing organic matter concentrations of 5%, 10%, and 20% and was aged for 0, 56, and 112 days. The EC50 values of the springtails increased with increasing OM and aging of the soil. The increase of the OM content in the soil reduced the extractability of pyrene by SPME, as well as the toxicity of pyrene. An aging effect was demonstrated in Askov soil, EC50 values increased with increased contact time. The amounts of pyrene extracted by SPME were significantly affected by the soil concentration. Porewater concentrations determined by SPME decreased with increasing OM and aging. However, the pyrene EC50 porewater concentration remained largely constant at approximately 23 microg L(-1). The results demonstrated that the SPME method is a useful indicator for bioavailability to soil microarthropods.

Polycyclic aromatic hydrocarbons in soils of Moscow

The contents of polycyclic aromatic hydrocarbons (PAHs) in the upper horizons of Moscow soils range up to 1400 mg/kg for individual compounds and up to 10000 mg/kg for their sum. The concentration coefficients of PAHs in the soil vary from 0.7 to 200 depending on individual polyarene properties and land use. The heavy polynuclear structures of technogenic origin have the highest concentration coefficients. The highest accumulation of PAHs is observed for the soils of dumping sites, residential-transport areas, and industrial zones. According to the state sanitary norms set in the Russian Federation for the content of benzo[a]pyrene in soils, more than one-third of the urban soils studied are classified as pure, and about half soils are classified as acceptable.

Impacts of microbial redox conditions on the phase distribution of pyrene in soil–water systems

Variations in the soil/sediment organic matter (SOM)-hydrophobic organic contaminant (HOC) bindings upon microbially mediated redox conditions were examined. While the extractability of pyrene associated with soil declined after its biodegradation began during aerobic incubation, its variations were almost constant (±3.0–4.4%) during anoxic/anaerobic incubations. The dissolved organic matter released from the soil incubated under highly reduced conditions became more humified and aromatic, had a higher average molecular weight, and was more polydispersed compared to that obtained from oxic incubation, similar to the SOM alterations in the early stage of diagenesis (humification). The concentrations of pyrene in the aqueous phase increased significantly during the soil incubations under highly reduced conditions due to its favorable interaction with the altered DOM. Our results suggest that the microbially mediated redox conditions have significant impacts on SOM and should be considered for the transport, fate, bioavailability, and exposure risk of HOCs in the geo-environments.

Microbial consortium bioaugmentation of a polycyclic aromatic hydrocarbons contaminated soil

In this study we evaluated the capacity of a defined microbial consortium (five bacteria: Mycobacterium fortuitum, Bacillus cereus, Microbacterium sp., Gordonia polyisoprenivorans, Microbacteriaceae bacterium, Naphthalene-utilizing bacterium; and a fungus identified as Fusarium oxysporum) isolated from a PAHs contaminated landfarm site to degrade and mineralize different concentrations (0, 250, 500 and 1000 mg kg −1) of anthracene, phenanthrene and pyrene in soil. PAHs degradation and mineralization was evaluated by gas chromatography and respirometry, respectively. The microbial consortium degraded on average, 99%, 99% and 96% of the different concentrations of anthracene, phenanthrene and pyrene in the soil, in 70 days, respectively. This consortium mineralized 78%, on average, of the different concentrations of the 3 PAHs in soil after 70 days. Contrarily, the autochthonous soil microbial population showed no substantial mineralization of the PAHs. Bacterial and fungal isolates from the consortium, when inoculated separately to the soil, were less effective in anthracene mineralization compared to the consortium. This signifies synergistic promotion of PAHs mineralization by mixtures of the monoculture isolates (the microbial consortium).

Biostimulation of PAH Degradation with Plants Containing High Concentrations of Linoleic Acid

Many plant species enhance the biodegradation of polycyclic aromatic hydrocarbons (PAHs), but there is little understanding of the mechanisms by which this occurs. This research identified phytochemicals that stimulate pyrene degradation using crushed roottissues from 43 plants that were screened in soil spiked with 100 ppm pyrene. Among the plants tested, root tissues from Apium graveolens (celery), Raphanus sativus (radish), Solanum tuberosum (potato), and Daucus carota (carrot) were most effective for promoting disappearance of pyrene within 40 days. Experiments with A. graveolens showed that plant culture in soil contaminated with pyrene or benzo[a]pyrene was as effective as addition of crushed root tissues. Comparison of the chemical compositions of the effective plants suggested that linoleic acid was the major substance that stimulated PAH degradation. This hypothesis was supported in experiments examining degradation of pyrene and benzo[a]pyrene in soil amended with linoleate, whereas linolenic and palmitic acids did not stimulate degradation within a 20 day period. Antibiotic inhibitor studies implicated gram positive bacteria as a predominant group responding to linoleic acid. These findings provide insight into the mechanisms by which plants enhance degradation of PAHs, and have practical application for remediation of PAH contaminated soils.

Degradation of Pyrene in Soils by Free and Immobilized Yeasts, Candida tropicals

The aim of this research was to ascertain the efficacy of immobilized yeasts for the degradation of pyrene in soil. Pyrene degradation by individual yeasts and their mixtures was clearly enhanced when the yeasts were immobilized with chemical and physical entrapments, and cross-shaped beads from physical entrapment were more promising than spherical beads from chemical entrapment. Immobilized yeast mixture Candida tropicals Y 219 + Y 220 showed the best degradation of pyrene, exhibiting collaboration in pyrene removal. Scanning electron micrographs demonstrated good macroporous structure for mass transfer of substrates and immobilized cell growth.