Fungal PAH-metabolites resist mineralization by soil microorganisms

Biotic and Abiotic Transformation Pathways of a Short-Chain Chlorinated Paraffin Congener, 1,2,5,6,9,10-C10H16Cl6, in a Rice Seedling Hydroponic Exposure System

In this work, a typical congener of short-chain chlorinated paraffins (SCCPs) with six chlorine atoms (CP-4, 1,2,5,6,9,10-C₁₀H₁₆Cl₆, 250 ng/mL) was selected to elaborate the comprehensive environmental transformation of SCCPs in rice seedling exposure system. CP-4 was quickly absorbed, translocated, and phytovolatilized by seedlings with a small quality of CP-4 (5.81-36.5 ng) being detected in the gas phase. Only 21.4 ± 1.6% of an initial amount (10,000 ng) of CP-4 remained in the exposure system at the end of exposure. Among the transformed CP-4, some were attributed to the degradation of the rhizosphere microorganism (9.1 ± 5.8%), root exudates (2.2 ± 4.2%), and abiotic transformation (3.0 ± 2.8%) that were proved by several transformation products found in the root exudate exposure groups and unplanted controls, and a majority was phytotransformed by rice seedlings. Here, 61 products were determined through complex transformation pathways, including multihydroxylation, -HCl elimination, dechlorination, acetylation, sulfation, glycosylation, and amide acid conjugation. The acetylated and amide acid conjugates of CPs were first observed. Phase I and Phase II phytometabolic reactions of CPs were found intertwining. These findings demonstrate that multiactive transformation reactions contribute to the overlook of CPs accumulated in plants and are helpful for the environmental and health risk assessments of SCCPs in agricultural plants.

Biodegradation of Naphthalene and Anthracene by Aspergillus glaucus Strain Isolated from Antarctic Soil

Biotechnologies based on microbial species capable of destroying harmful pollutants are a successful way to solve some of the most important problems associated with a clean environment. The subject of investigation is the Antarctic fungal strain Aspergillus glaucus AL1. The culturing of the examined strain was performed with 70 mg of wet mycelium being inoculated in a Czapek Dox liquid medium containing naphthalene, anthracene, or phenanthrene (0.3 g/L) as the sole carbon source. Progressively decreasing naphthalene and anthracene concentrations were monitored in the culture medium until the 15th day of the cultivation of A. glaucus AL1. The degradation was determined through gas chromatography–mass spectrometry. Both decreased by 66% and 44%, respectively, for this period. The GC-MS analyses were applied to identify salicylic acid, catechol, and ketoadipic acid as intermediates in the naphthalene degradation. The intermediates identified in anthracene catabolism are 2-hydroxy-1-naphthoic acid, o-phthalic acid, and protocatechuic acid. The enzyme activities for phenol 2-monooxygenase (1.14.13.7) and catechol 1,2-dioxygenase (1.13.11.1) were established. A gene encoding an enzyme with catechol 1,2-dioxygenase activity was identified and sequenced (GeneBank Ac. No KM360483). The recent study provides original data on the potential of an ascomycete’s fungal strain A. glaucus strain AL 1 to degrade naphthalene and anthracene.

Effects of polycyclic aromatic hydrocarbon structure on PAH mineralization and toxicity to soil microorganisms after oxidative bioremediation by laccase

While bioremediation using soil microorganisms is considered an energy-efficient and eco-friendly approach to treat polycyclic aromatic hydrocarbon (PAH)-contaminated soils, a variety of polar PAH metabolites, particularly oxygenated ones, could increase the toxicity of the soil after biodegradation. In this study, a typical bio-oxidative transformation of PAH into quinones was investigated in soil amended with laccase using three PAHs with different structures (anthracene, benzo[a]anthracene, and benzo[a]pyrene) to assess the toxicity after oxidative bioremediation. The results show that during a 2-month incubation period the oxidation process promoted the formation of non-extractable residues (NERs) of PAHs, and different effects on mineralization were observed among the three PAHs. Oxidation enhanced the mineralization of the high-molecular-weight (HMW) PAHs (benzo[a]anthracene and benzo[a]pyrene) but inhibited the mineralization of the low-molecular-weight (LMW) PAH (anthracene). The inhibition of anthracene suggests increased toxicity after oxidative bioremediation, which coincided with a decrease in soil nitrification activity, bacterial diversity and PAH-ring hydroxylating dioxygenase gene copies. The analysis of PAH metabolites in soil extract indicated that oxidation by laccase was competitive with the natural transformation processes of PAHs and revealed that intermediates other than quinone metabolites increased the toxicity of soil during subsequent degradation. The different metabolic profiles of the three PAHs indicated that the toxicity of soil after PAH oxidation by laccase was strongly affected by the PAH structure. Despite the potential increase in toxicity, the results suggest that oxidative bioremediation is still an eco-friendly method for the treatment of HMW PAHs since the intermediates from HMW PAHs are more easily detoxified via NER formation than LMW PAHs.

A tiered analytical approach for target, non-target and suspect screening analysis of polar transformation products of polycyclic aromatic compounds

Polycyclic aromatic compounds (PACs) possess toxicity towards humans, and their presence in the environment is unwanted. Polar transformation products (TPs) are more mobile, and can be considered emerging contaminants, as they represent a more bioavailable carrier of the same toxic properties. Acidic TPs has been proposed as an important class of polar TPs. This study presents a tiered analytical approach to investigate acidic and polar PAC TPs in environmental conditions. The tiered approach exploits target analysis for quantification of acids; suspect screening for tentative identification based on retention time and spectral matching using databases; and finally non-target analysis based on chromatography and data independent broadband MS to highlight potentially unknown analyte peaks. The approach includes a mixed-mode anion exchange solid phase extraction (MAX-SPE) to fractionate neutral and acidic compounds, and is applied to three cases: I) Photo-oxidation of six PACs generated suspected hydroxylated-, carbonylated- and carboxylated PACs but also proposed the presence of mono- and dicarboxylic acids, which have not been reported elsewhere. For a subset of four acids, conversion rates were determined. II) Recovery of spiked acids from diesel spilled harbor water was 80% by LC-MS, and diesel spill weathering was evaluated from the neutral fraction by GC-MS. III) By non-target analysis sulfonated PACs, presumable derived from photo-oxidation, were detected in run-off basins of an arctic landfarm, alongside hypothesized naturally occuring fatty acids. The tiered approach is a sensitive and versatile tool to extract information on PACs and their polar TPs from polluted environmental sites.

Continuing Impacts of Selective Inhibition on Bacterial and Fungal Communities in an Agricultural Soil

Selective inhibition (SI) has been routinely used to differentiate the contributions of bacteria and fungi to soil ecological processes. SI experiments typically measured rapid responses within hours since the addition of inhibitor, but the long-term effects of selective biocides on microbial community composition and function were largely unknown. In this study, a microcosm experiment was performed with an agricultural soil to explore the effectiveness of two bactericides (bronopol, streptomycin) and two fungicides (cycloheximide, captan), which were applied at two different concentrations (2 and 10 mg g^-1). The microcosms were incubated for 6 weeks. A radiolabeled substrate, [1,2,3,4,4a,9a-¹⁴C] anthracene, was spiked to all microcosms, and the derived CO₂ was monitored during the incubation. The abundance and composition of bacteria and fungi were assessed by qPCR and Miseq sequencing of ribosomal rRNA genes. It was demonstrated that only 2 mg g^-1 bronopol and cycloheximide significantly changed the bacteria to fungi ratio without apparent non-target inhibition on the abundances; however, community shifts were observed in all treatments after 6 weeks incubation. The enrichment of specific taxa implicated a selection of resistant or adapted microbes by these biocides. Mineralization of anthracene was continuingly suppressed in all SI microcosms, which may result in biased estimate of bacterial and fungal contributions to pollutant degradation. These findings highlight the risks of long-term application of selective inhibition, and a preliminary assessment of biocide selection and concentration is highly recommended.

Influence of bacterial community composition and soil factors on the fate of phenanthrene and benzo[a]pyrene in three contrasting farmland soils

The fate of polycyclic aromatic hydrocarbons (PAHs) determines their potential risk in soil, which may be directly affected by abiotic conditions and indirectly through the changes in decomposer communities. In comparison, the indirect effects on the fate remain largely elusive. In this study, the fate of phenanthrene and benzo[a]pyrene and the corresponding bacterial changes were investigated in three contaminated farmland soils using a ¹⁴C tracer method and Miseq sequencing. The results showed that most benzo[a]pyrene was consistently extractable with dichloromethane (DCM) after the 60-day incubation (60.4%-78.2%), while phenanthrene was mainly mineralized to CO₂ during the 30-day incubation (40.4%-58.7%). Soils from Guangzhou (GZ) showed a different distribution pattern of ¹⁴C-PAHs exemplified by low mineralization and disparate bound residue formation. The PAH fate in the Shenyang (SY) and Nanjing (NJ) soils were similar to each other than to that in the GZ soil. The fate in the GZ soil seemed to be linked to the distinct edaphic properties, such as organic matter content, however soil microbial community could have influenced the distribution pattern of PAHs. This potential role of microorganisms was reflected by the unique changes in the copy numbers of Gram positive RHD_α gene, and by the distinct shifts in bacterial community composition during the incubation. A quite different shift in bacterial communities was found in the GZ microcosms which may influence PAH mineralization and non-extractable residue (NER) formation.

Oxidation of benzo[a]pyrene by laccase in soil enhances bound residue formation and reduces disturbance to soil bacterial community composition

Laccases are capable of rapidly oxidizing benzo[a]pyrene. It is thought that the metabolites with an increase in water solubility caused by the oxidation of benzo[a]pyrene may stimulate the subsequent mineralization. However, to date, there has been no experimental evidence to support this. In this study, the fate of benzo[a]pyrene in soil affected by laccase amendment and the resulting soil bacterial responses were investigated. Laccase amendment promoted benzo[a]pyrene dissipation (15.6%) from soil, accompanied by trace mineralization (<0.58 ± 0.02%) and substantial bound residue formation (∼80%). An increase of ∼15% in the bound residue fraction was observed by laccase amendment, which mainly resulted from covalent binding of the residues to humin fraction. During the incubation, the abundance of bacterial 16S rRNA and polycyclic aromatic hydrocarbon ring-hydroxylating dioxygenase genes did not change markedly. In contrast, benzo[a]pyrene treated with laccase resulted in a smaller shift in the bacterial community composition, indicating a reduced disturbance to the soil microbial communities. These results here suggest that benzo[a]pyrene contaminated soil can be detoxified by laccase amendment mainly due to the enhanced bound residue formation to soil organic matter via covalent binding.

Tracing the Biotransformation of Polycyclic Aromatic Hydrocarbons in Contaminated Soil Using Stable Isotope-Assisted Metabolomics

Biotransformation of organic pollutants may result in the formation of oxidation products more toxic than the parent contaminants. However, to trace and identify those products, and the metabolic pathways involved in their formation, is still challenging within complex environmental samples. We applied stable isotope-assisted metabolomics (SIAM) to PAH-contaminated soil collected from a wood treatment facility. Soil samples were separately spiked with uniformly ¹³C-labeled fluoranthene, pyrene, or benzo[a]anthracene at a level below that of the native contaminant, and incubated for 1 or 2 weeks under aerobic biostimulated conditions. Combining high-resolution mass spectrometry and automated SIAM workflows, chemical structures of metabolites and metabolic pathways in the soil were proposed. Ring-cleavage products, including previously unreported intermediates such as C₁₁H₁₀O₆ and C₁₅H₁₂O₅, were detected originating from fluoranthene and benzo[a]anthracene, respectively. Sulfate conjugates of dihydroxy compounds were found as major metabolites of pyrene and benzo[a]anthracene, suggesting the potential role of fungi in their biotransformation in soils. A series of unknown N-containing metabolites were identified from pyrene, but their structural elucidation requires further investigation. Our results suggest that SIAM can be successfully applied to understand the fate of organic pollutants in environmental samples, opening lines of evidence for novel mechanisms of microbial transformation within such complex matrices.

Enrichment, isolation, and biodegradation potential of long-branched chain alkylphenol degrading non-ligninolytic fungi from wastewater

4-t-Octylphenol (4-t-OP) has become a serious environmental concern due to the endocrine disruption in animals and humans. The biodegradation of 4-t-OP by pure cultures has been extensively investigated only in bacteria and wood-decaying fungi. In this study we isolated and identified 14 filamentous fungal strains from wastewater samples in Taiwan using 4-t-OP as a sole carbon and energy source. The isolates were identified based on sequences from different DNA regions. Of 14 fungal isolates, 10 strains grew effectively on solid medium with a wide variety of endocrine disrupting chemicals as the sole carbon and energy source. As revealed by high-performance liquid chromatography analysis, the most effective 4-t-OP degradation (>70%) in liquid medium was observed in Fusarium falciforme after 15days. To our knowledge, this is the first report on the degradation of 4-t-OP as a sole carbon and energy source by non-ligninolytic fungi.

Exploring the potential of fungi isolated from PAH-polluted soil as a source of xenobiotics-degrading fungi

The aim of this study was to find polycyclic aromatic hydrocarbon (PAH)-degrading fungi adapted to polluted environments for further application in bioremediation processes. In this study, a total of 23 fungal species were isolated from a historically pyrogenic PAH-polluted soil in Spain and taxonomically identified. The dominant groups in these samples were the ones associated with fungi belonging to the Ascomycota phylum and two isolates belonging to the Mucoromycotina subphylum and Basiodiomycota phylum. We tested their ability to convert the three-ring PAH anthracene in a 42-day time course and analysed their ability to secrete extracellular oxidoreductase enzymes. Among the 23 fungal species screened, 12 were able to oxidize anthracene, leading to the formation of 9,10-anthraquinone as the main metabolite, a less toxic one than the parent compound. The complete removal of anthracene was achieved by three fungal species. In the case of Scopulariopsis brevicaulis, extracellular enzyme independent degradation of the initial 100 μM anthracene occurred, whilst in the case of the ligninolytic fungus Fomes (Basidiomycota), the same result was obtained with extracellular enzyme-dependent transformation. The yield of accumulated 9,10-anthraquinone was 80 and 91 %, respectively, and Fomes sp. could slowly deplete it from the growth medium when offered alone. These results are indicative for the effectiveness of these fungi for pollutant removal. Graphical abstract ᅟ.

Limited recovery of soil microbial activity after transient exposure to gasoline vapors

During gasoline spills complex mixtures of toxic volatile organic compounds (VOCs) are released to terrestrial environments. Gasoline VOCs exert baseline toxicity (narcosis) and may thus broadly affect soil biota. We assessed the functional resilience (i.e. resistance and recovery of microbial functions) in soil microbial communities transiently exposed to gasoline vapors by passive dosing via headspace for 40 days followed by a recovery phase of 84 days. Chemical exposure was characterized with GC-MS, whereas microbial activity was monitored as soil respiration (CO2 release) and soil bacterial growth ([(3)H]leucine incorporation). Microbial activity was strongly stimulated and inhibited at low and high exposure levels, respectively. Microbial growth efficiency decreased with increasing exposure, but rebounded during the recovery phase for low-dose treatments. Although benzene, toluene, ethylbenzene and xylene (BTEX) concentrations decreased by 83-97% during the recovery phase, microbial activity in high-dose treatments did not recover and numbers of viable bacteria were 3-4 orders of magnitude lower than in control soil. Re-inoculation with active soil microorganisms failed to restore microbial activity indicating residual soil toxicity, which could not be attributed to BTEX, but rather to mixture toxicity of more persistent gasoline constituents or degradation products. Our results indicate a limited potential for functional recovery of soil microbial communities after transient exposure to high, but environmentally relevant, levels of gasoline VOCs which therefore may compromise ecosystem services provided by microorganisms even after extensive soil VOC dissipation.

Bioconcentration, biotransformation and elimination of pyrene in the arctic crustacean Gammarus setosus (Amphipoda) at two temperatures

The influence of temperature on the bioaccumulation, toxicokinetics, biotransformation and depuration of pyrene was studied in the arctic marine amphipod Gammarus setosus. A two-compartment model was used to fit experimental values of total body burden, total metabolites and parent pyrene concentrations and to calculate toxicokinetic variables derived for two experimental treatments (2 and 8 °C). No statistically significant differences were observed with temperature for these toxicokinetic variables or bioconcentration factors. Contrarily, the Q10 values suggested that the toxicokinetic variables ke and km were temperature-dependent. This may be explained by the high standard deviation of the Q10 values. Q10 is the variation in the rate of a metabolic reaction with a 10 °C increase in temperature. Depuration rate constants were calculated from linear best fit equations applied to measured pyrene concentrations over time during the depuration phase of the experiment. During depuration, the parent pyrene was eliminated in two stages with faster elimination observed at 8 °C compared to 2 °C. This finding was also indicated by the Q10. No changes in total body burdens of metabolite concentrations were observed during the monitoring of depuration over a period of 96 h. The biotransformation pathway of pyrene in G. setosus was also investigated in this study with two main phase II biotransformation products discovered by liquid chromatography. These products are conditionally identified as the sulphate and glucose conjugates of 1-hydroxy-pyrene. Overall, the study contributes new knowledge to the understanding of the fate of PAHs in arctic biota. In particular, the study provides valuable insight into the bioaccumulation and biotransformation of an important PAH and its metabolites in a species that serves as both a predator and prey in the arctic ecosystem.

Polycyclic Aromatic Acids Are Primary Metabolites of Alkyl-PAHs-A Case Study with Nereis diversicolor

Although concentrations of alkylated polycyclic aromatic hydrocarbons (alkyl-PAHs) in oil-contaminated sediments are higher than those of unsubstituted PAHs, only little attention has been given to metabolism and ecotoxicity of alkyl-PAHs. In this study we demonstrated that metabolism of alkyl-PAHs primarily forms polycyclic aromatic acids (PAAs). We generalize this to other alkyl-PAHs, based on literature and the present study of the metabolism of 1-methylphenanthrene, 3,6-dimethylphenanthrene, and 1-, 2-, 3-, and 6-methylchrysene related to their unsubstituted parent PAHs. Also, we observed that body burdens and production of PAAs was related to the position of the methyl group, showing the same isomer specific preferences as for microbial degradation of alkyl-PAHs. We detected a high production of PAAs, and larger metabolism of alkyl-PAHs than their unsubstituted parent PAHs. We therefore propose that carboxylic acid metabolites of alkyl-PAHs have the potential of constituting a new class of contaminants in marine waters that needs attention in relation to ecological risk assessments.

Polar metabolites of polycyclic aromatic compounds from fungi are potential soil and groundwater contaminants

This study investigated the sorption to soil of water-soluble metabolites from polycyclic aromatic compounds (PACs). The soil fungus Cunninghamella elegans was used to produce PAC metabolites from two un-substituted PACs (phenanthrene, pyrene), three alkyl-substituted PACs (2-methylnaphthalene, 1-methylphenanthrene, 1-methylpyrene), and one sulfur-containing heterocyclic PAC (dibenzothiophene). Fifty-eight metabolites were tentatively identified; metabolites from the un-substituted PACs were hydroxylated and sulfate conjugated, whereas metabolites from alkyl-substituted PACs were sulfate conjugated and either hydroxylated or oxidized to carboxylic acids at the methyl group. The metabolism of the sulfur-containing heterocyclic PAC resulted in sulfate conjugates. The sorption of the PAC metabolites to three soils was determined using a batch equilibrium method, and partition coefficients (Kd's) were calculated for fourteen representative metabolites. Sulfate conjugated metabolites displayed Kd's below 70 whereas the metabolites with both a sulfate and a carboxylic acid group had Kd's below 2.8. The low Kd's of water-soluble PAC metabolites indicate high mobility in soil and a potential for leaching to surface- and groundwaters.

Degradation of PAHs in soil by Lasiodiplodia theobromae and enhanced benzo[a]pyrene degradation by the addition of Tween-80

Benzo[a]pyrene (BaP), a five-ring polycyclic aromatic hydrocarbon (PAH), which has carcinogenic potency, is highly recalcitrant and resistant to microbial degradation. A novel fungus, Lasiodiplodia theobromae (L. theobromae), which can degrade BaP as a sole carbon source in liquid, was isolated in our laboratory. To prompt the further application of L. theobromae in remediation of sites polluted by BaP and other PAHs, the present study was targeted toward the removal of BaP and PAHs from soil by L. theobromae. The degradation of BaP by L. theobromae was studied using a soil spiked with 50 mg/kg BaP. L. theobromae could remove 32.1 % of the BaP after 35 days of cultivation. Phenanthrene (PHE) inhibited BaP degradation as a competitive substrate. The tested surfactants enhanced BaP degradation in soil by different extents, and a removal rate of 92.1 % was achieved at a Tween-80 (TW-80) concentration of 5 g/kg. It was revealed that TW-80 could not only enhance BaP bioavailability by increasing its aqueous solubility and decreasing the size of its colloid particles but also increase enzyme secretion from L. theobromae and the population of L. theobromae. Moreover, ergosterol content together with the biomass C indicated the increase in L. theobromae biomass during the BaP biodegradation process in soils. Finally, a soil from a historically PAH-contaminated field at Beijing Coking Plant in China was tested to assess the feasibility of applying L. theobromae in the remediation of polluted sites. The total removal rate of PAHs by L. theobromae was 53.3 %, which is 13.1 % higher than that by Phanerochaete chrysosporium (P. chrysosporium), an effective PAH degrader. The addition of TW-80 to the field soil further enhanced PAH degradation to 73.2 %. Hence, L. theobromae is a promising novel strain to be implemented in the remediation of soil polluted by PAHs.

Emerging chemicals and the evolution of biodegradation capacities and pathways in bacteria

The number of new chemicals produced is increasing daily by the thousands, and it is inevitable that many of these chemicals will reach the environment. Current research provides an understanding of how the evolution of promiscuous enzymes and the recruitment of enzymes available from the metagenome allows for the assembly of these pathways. Nevertheless, physicochemical constraints including bioavailability, bioaccessibility, and the structural variations of similar chemicals limit the evolution of biodegradation pathways. Similarly, physiological constraints related to kinetics and substrate utilization at low concentrations likewise limit chemical-enzyme interactions and consequently evolution. Considering these new data, the biodegradation decalogue still proves valid while at the same time the underlying mechanisms are better understood.

Effects of Nereis diversicolor on the transformation of 1-methylpyrene and pyrene: transformation efficiency and identification of phase I and II products

Transformation of nonsubstituted and alkyl-substituted polycyclic aromatic hydrocarbons (PAHs) by the benthic invertebrate Nereis diversicolor was compared in this study. Pyrene and 1-methylpyrene were used as model compounds for nonsubstituted and alkyl-substituted PAHs, respectively. Qualitative and quantitative analyses of metabolites and parent compounds in worm tissue, water, and sediment were performed. Transformation of 1-methylpyrene generated the benzylic hydroxylated phase I product, 1-pyrenecarboxylic acid that comprised 90% of the total metabolites of 1-methylpyrene, and was mainly found in water extracts. We tentatively identified 1-methylpyrene glucuronides and 1-carbonylpyrene glycine as phase II metabolites not previously reported in literature. Pyrene was biotransformed to 1-hydroxypyrene, pyrene-1-sulfate, pyrene-1-glucuronide, and pyrene glucoside sulfate, with pyrene-1-glucuronide as the most prominent metabolite. Transformation of 1-methylpyrene (21% transformed) was more than 3 times as efficient as pyrene transformation (5.6% transformed). Because crude oils contain larger amounts of C₁-C₄-substituted PAHs than nonsubstituted PAHs, the rapid and efficient transformation of sediment-associated 1-methylpyrene may result in a high exposure of water-living organisms to metabolites of alkyl-substituted PAHs, whose toxicities are unknown. This study demonstrates the need to consider fate and effects of substituted PAHs and their metabolites in risk assessments.

Trophic transfer of pyrene metabolites and nonextractable fraction from Oligochaete (Lumbriculus variegatus) to juvenile brown trout (Salmo trutta)

The trophic transfer of pyrene metabolites was evaluated by a 2-month exposure of the freshwater annelid Lumbriculus variegatus (Oligochaeta) to pyrene, followed by feeding to juvenile brown trout (Salmo trutta). The results obtained by scintillation counting (SC) proved that the pyrene metabolites produced by L. variegatus were transferred to juvenile S. trutta through diet. More detailed analyses by LC-FLD (liquid chromatography with fluorescence detection) showed that an unknown pyrene metabolite originating from L. variegatus was present in fish liver. This metabolite, although yet not properly identified, may be the glucose conjugate of 1-hydroxy-pyrene. This metabolite was not present in chromatograms of fish that were fed pyrene-spiked food pellets. In addition, the strongly bound tissue residue of L. variegatus, which was nonextractable neither by organic solvents nor by the proteolytic enzyme Proteinase K, was most likely not available for the fish through diet. Altogether, the present study shows that the metabolites of pyrene produced at low levels of the food chain may be potentially available for upper levels through diet, raising a concern about their potential toxicity to predators and supporting their inclusion in the risk assessment of PAHs.

Changes in hydrocarbon groups, soil ecotoxicity and microbiology along horizontal and vertical contamination gradients in an old landfarming field for oil refinery waste

Horizontal and vertical contaminant gradients in an old landfarming field for oil refinery waste were characterised with the aim to assess parallel changes in hydrocarbon groups and general, microbiological and ecotoxicological soil characteristics. In the surface soil polar compounds were the most prevalent fraction of heptane-extractable hydrocarbons, superseding GC-FID-resolvable and high-molar-mass aliphatics and aromatics, but there was no indication of their relatively higher mobility or toxicity. The size of the polar fraction correlated poorly with soil physical, chemical and microbiological properties, which were better explained by the total heptane-extractable and total petroleum hydrocarbons (TPH). Deleterious effects on soil microbiology in situ were observed at surprisingly low TPH concentrations (0.3%). Due to the accumulation of polar and complexed degradation products, TPH seems an insufficient measure to assess the quality and monitor the remediation of soil with weathered hydrocarbon contamination.

Adsorption of polycyclic aromatic hydrocarbons (PAHs) on Rhizopus oryzae cell walls: application of cosolvent models for validating the cell wall-water partition coefficient

The cell wall-cosolvent partition coefficients (Km) of polycyclic aromatic hydrocarbons (PAHs) were determined for Rhizopus oryzae cell walls by controlling the volume fraction of methanol (f) ranging from 0.1 to 0.5. Five cosolvent models were employed for extrapolating the cell wall-water partition coefficients (Kw) in pure water. The extrapolated Kw values of four PAHs on R. oryzae cell walls were ranged from 2.9 to 5.1. Comparison of various Kw values of pyrene generated from extrapolation and the QSPR model, together with predicted different (PD), mean percentage deviations (MPD), and root mean square errors (RSE), revealed that the performance of the LL and Bayesian models were the best among all five tested cosolvent models. This study suggests that R. oryzae cell walls play an important role in the partitioning of PAHs during bioremediation because of the high Kw of fungal cell walls.

Quantification of centimeter-scale spatial variation in PAH, glucose and benzoic acid mineralization and soil organic matter in road-side soil

The aim of the study was to determine centimeter-scale spatial variation in mineralization potential in diffusely polluted soil. To this end we employed a 96-well microplate method to measure the mineralization of 14C-labeled organic compounds in deep-well microplates and thereby compile mineralization curves for 348 soil samples of 0.2-cm3. Centimeter-scale spatial variation in organic matter and the mineralization of glucose, benzoic acid, and PAHs (phenanthrene and pyrene) was determined for urban road-side soil sampled as arrays (7×11cm) of 96 subsamples. The spatial variation in mineralization was visualized by means of 2-D contour maps and quantified by means of semivariograms. The geostatistical analysis showed that the easily degradable compounds (glucose and benzoic acid) exhibited little spatial variation in mineralization potential, whereas the mineralization was highly heterogeneous for the PAH compounds that require specialized degraders. The spatial heterogeneity should be taken into account when estimating natural attenuation rates.