Biological degradation of selected hydrocarbons in an old PAH/creosote contaminated soil from a gas work site

Identification and biodegradation characterization of high-density polyethylene using marine bacteria isolated from the coastal region of the Arabian Sea, at Gujarat, India

High-Density Polyethylene (HDPE) PE is one of the primary contributors of long-lasting and prolonged pollution in the environment. In this study, more than three hundred marine isolates collected off the Gujarat Sea coast were tested for HDPE plastic utilizing ability. Among fifty-one positive noted isolates, RS124 as a potential strain was identified as Micrococcus flavus (accession is PP858228) based on 16 S rRNA gene sequencing and total cellular fatty acid profiling. Initial bacterial adherence on the film surface was shown in a scanning electron microscopy (SEM) image as a key step to biodegradation. Moreover, atomic force microscopy (AFM) shows that the film surface became more fragile, damaged, and rougher than untreated films. Shifts and alterations in peak transmittance with emergence of two new shouldered peak in degraded HDPE observed by fourier transform infrared spectroscopy (FTIR) was associated to chemical and mechanical alteration. Thermogravimetric analysis (TGA) analysis designated larger difference in percent weight loss provisions thermal instability. In the enzymatic study, the highest activity of peroxidase and dehydrogenase was recorded on the 3rd and 4th weeks of treatment with strain, respectively, during co-incubation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis disclosed the presence of a distinct 19 kDa size protein, uncovering its role in the colonization of bacteria on the hydrophilic HDPE surfaces. About 1.8% weight reduction in HDPE was recorded as a result after 30 days of bio-treatment with M. flavus. Hence, the entire observed results reveal that the M. flavus RS124 could be effectively applied for the degradation of HDPE. This is the first report on M. flavus that it exhibits plastic degrading characteristic ever, which may allow for green scavenging of plastic waste.

A complex mixture of polycyclic aromatic compounds causes embryotoxic, behavioral, and molecular effects in zebrafish larvae (Danio rerio), and in vitro bioassays

Polycyclic aromatic compounds (PACs) are prevalent in the environment, typically found in complex mixtures and high concentrations. Our understanding of the effects of PACs, excluding the 16 priority polycyclic aromatic hydrocarbons (16 PAHs), remains limited. Zebrafish embryos and in vitro bioassays were utilized to investigate the embryotoxic, behavioral, and molecular effects of a soil sample from a former gasworks site in Sweden. Additionally, targeted chemical analysis was conducted to analyze 87 PACs in the soil, fish, water, and plate material. CALUX® assays were used to assess the activation of aryl hydrocarbon and estrogen receptors, as well as the inhibition of the androgen receptor. Larval behavior was measured by analyzing activity during light and darkness and in response to mechanical stimulation. Furthermore, qPCR analyses were performed on a subset of 36 genes associated with specific adverse outcomes, and the total lipid content in the larvae was measured. Exposure to the sample resulted in embryotoxic effects (LC50 = 0.480 mg dry matter soil/mL water). The mixture also induced hyperactivity in darkness and hypoactivity in light and in response to the mechanical stimulus. qPCR analysis revealed differential regulation of 15 genes, including downregulation of opn1sw1 (eye pigmentation) and upregulation of fpgs (heart failure). The sample caused significant responses in three bioassays (ERα-, DR-, and PAH-CALUX), and the exposed larvae exhibited elevated lipid levels. Chemical analysis identified benzo[a]pyrene as the predominant compound in the soil and approximately half of the total PAC concentration was attributed to the 16 PAHs. This study highlights the value of combining in vitro and in vivo methods with chemical analysis to assess toxic mechanisms at specific targets and to elucidate the possible interactions between various pathways in an organism. It also enhances our understanding of the risks associated with environmental mixtures of PACs and their distribution during toxicity testing.

Toxicity evaluation of the metabolites derived from the degradation of phenanthrene by one of a soil ubiquitous PAHs-degrading strain Rhodococcus qingshengii FF

Rhodococcus qingshengii strain FF is a soil ubiquitous strain that has a high polycyclic aromatic hydrocarbons (PAHs) biodegradation capability. In this work, phenanthrene was used as a PAH model compound. The accumulated pattern of the metabolites of phenanthrene by strain FF was investigated, and their toxicity to Vibrio fischeri, effect on microbiota diversity of farmland soil and influence on seed of wheat were evaluated. Total of 29 main intermediates were observed for the phenanthrene degradation process. Pyrogallol was the predominant accumulated metabolite, and 59% of the accumulated metabolites were oxygen-containing PAHs that have only one benzene ring. The acute toxicity assessment showed the accumulated metabolites in later phase were more toxic to Vibrio fischeri. Microbe and wheat seed response to the different stages of phenanthrene metabolites indicated pollution significantly decreased microbial richness and evenness of farmland soil and lower germinal length, root length or root number of wheat seed. These results indicated that not only the elimination of PAHs, but also the easily accumulated metabolites produced during the PAHs degradation process should be paid enough attention. The comprehensive evaluation of toxicity during the degradation process would provide useful information for the use of microbe-orientated strategies in PAHs bioremediation.

Adsorption of phenanthrene and its monohydroxy derivatives on polyvinyl chloride microplastics in aqueous solution: Model fitting and mechanism analysis

The pervasiveness of microplastics, which can absorb pollutants, has a certain impact on pollutant migration in natural waters. Differences in functional groups, such as the hydroxyl group, of pollutants will affect their adsorption on microplastics. In this study, the adsorption of phenanthrene (PHE) or its monohydroxy derivatives, including 1-hydroxyphenanthrene (1-OHP), 2-hydroxyphenanthrene (2-OHP), 4-hydroxyphenanthrene (4-OHP), and 9-hydroxyphenanthrene (9-OHP), on polyvinyl chloride (PVC, measured mean particle size = 134 μm) microplastics was studied. The adsorption efficiency of PHE was shown to be higher than that of either of OHPs. A better fit for pseudo-second-order and Freundlich isotherm models was obtained, indicating different binding sites on the surface of PVC microplastics. The adsorption processes of PHE and OHPs on PVC microplastics were demonstrated to be exothermic and spontaneous. Combined with FT-IR analysis, theoretical calculation, and comparative adsorption experiments, hydrophobic interaction was the dominant mechanism during the adsorption process. In contrast, electrostatic repulsion, CH/π interaction, and halogen bonding played a minor role, to an extent, in the adsorption of PHE/OHPs on PVC microplastics. These findings indicate the influence of the hydroxyl group on adsorption and improve the understanding of interactions between PVC microplastics and PHE/OHPs.

How important is abiotic dissipation in natural attenuation of polycyclic aromatic hydrocarbons in soil?

Natural attenuation capacity, as one of the most important ecosystem functions in soil, plays a vital role in the detoxification of organic pollutants such as polycyclic aromatic hydrocarbons (PAHs). However, despite the role of biodegradation is established, the contribution of abiotic dissipation to natural attenuation has long been overlooked. Herein, the abiotic dissipations of 16 types of PAHs in a past coking site and of anthracene (ANT) in various cultivated soils were studied. Results showed that the contributions of abiotic dissipation to the total attenuation were in a wide range from 11.8 to 99.7% depending on the types of PAHs. Specifically, abiotic dissipation is higher for heavy PAHs (68.3-99.7%) than for light PAHs (11.8-71.5%), with the exception of ANT (80.7%). Similarly, the contribution of abiotic dissipation to ANT attenuation ranged from 30.7 to 68.6% in eight soils. The abiotic dissipation rate of ANT followed the order of lateritic-red earth > gray-desery soil > coastal solonchaks > cumulated-irrigated soil > cinnamon soil > fluvo-aquic soil > purplish soil ~ yellow-brown earth, which was positively correlated with transition metal contents in soils. These findings demonstrated that the abiotic dissipation of PAHs is determined by both molecule properties and soil types. Overall, this work provided valuable insights into clarifying the roles of abiotic dissipation in PAH attenuation in soil.

Recent Advances in the Study of the Remediation of Polycyclic Aromatic Compound (PAC)-Contaminated Soils: Transformation Products, Toxicity, and Bioavailability Analyses

Polycyclic aromatic compounds (PACs) encompass a diverse group of compounds, often found in historically contaminated sites. Different experimental techniques have been used to remediate PACs-contaminated soils. This brief review surveyed over 270 studies concerning remediation of PACs-contaminated soils and found that, while these studies often measured the concentration of 16 parent polycyclic aromatic hydrocarbons (PAHs) pre- and post-remediation, only a fraction of the studies included the measurement of PAC-transformation products (PAC-TPs) and other PACs (n = 33). Only a few studies also incorporated genotoxicity/toxicity/mutagenicity analysis pre- and post-remediation (n = 5). Another aspect that these studies often neglected to include was bioavailability, as none of the studies that included measurement of PAH-TPs and PACs included bioavailability investigation. Based on the literature analysis, future remediation studies need to consider chemical analysis of PAH-TPs and PACs, genotoxicity/toxicity/mutagenicity, and bioavailability analyses pre- and post-remediation. These assessments will help address numerous concerns including, among others, the presence, properties, and toxicity of PACs and PAH-TPs, risk assessment of soil post-remediation, and the bioavailability of PAH-TPs. Other supplementary techniques that help assist these analyses and recommendations for future analyses are also discussed.

Formation of environmentally persistent free radicals during the transformation of anthracene in different soils: Roles of soil characteristics and ambient conditions

Transformation of PAHs, i.e., anthracene, and production of environmentally persistent free radicals (EPFRs) on seven types of representative soils were investigated, focusing on the influences of soil characteristics and ambient conditions on these reactions. The transformation rate of anthracene exhibits the order of red earth > yellow earth > latosol ∼ fluvo-aquic soil > brown earth > chernozem > calcic brown soil, which is positively correlated with Fe content in soils. Afterwards, batch reactions on pure representatives of soil minerals, including Fe₂O₃, Fe₃O₄, FeOOH, and MnO₂, demonstrate that anthracene is prone to mineral-promoted transformation. The presence of higher amount of organic carbon lower the transformation rate of anthracene, whereas the formed EPFRs can be stabilized for a longer time. Subsequent experiments associated with the influences of environmental conditions on mineral-promoted reactions suggest that both anthracene transformation and EPFRs generation readily occur under dry condition. Light irradiation not only promotes the formation of EPFRs, but also greatly accelerates the decay of EPFRs and the 1/e lifetime decreases from 5 to 20 d in dark to approximately 1 d. Meanwhile, the anoxic condition is favorable for the persistence of EPFRs. The obtained results suggested the potential environmental risks association with EPFRs in PAHs-contaminated soils.

Destabilization of polyethylene and polyvinylchloride structure by marine bacterial strain

Plastics are recalcitrant and inert to degrade, and destabilization leads to accumulate in the terrestrial and marine ecosystems; need for the development of strategies for reducing these plastic wastes in a sustainable manner would be revolutionary. We studied the bacterial adherence, degradation and destabilization of polyvinylchloride (PVC), low-density polyethylene (LDPE), and high-density polyethylene (HDPE) by marine bacterial strain AIIW2 by a series of analytical and microscopic observations over 3 months. Based on 16S rRNA gene sequence and the phylogenetic analysis of the strain AIIW2, it showed 97.39% similarity with Bacillus species. Degradation of plastics was determined by the weight loss after 90 days with bacterial strain which detected up to 0.26 ± 0.02, 0.96 ± 0.02, and 1.0 ± 0.01% for PVC, LDPE, and HDPE films, respectively over initial weights. The mineralization of plastic film was found to be maximum in LDPE followed by HDPE and PVC. Bacterial interaction had increased roughness and deteriorated the surface of plastics which is revealed by the scanning electron microscope and atomic force microscope. Bending vibrations of the alkane rock chain (-CH₂ and -CH₃) and carbonyl (-CO) regions in LDPE and HDPE films, while there was slight stretching in the hydroxyl (-OH) regions of carboxylic acid in PVC which is evidenced through Fourier transform infrared spectral studies, suggested the oxidative activities of the bacteria. Though, the bacterial activity was higher on the LDPE and HDPE than PVC film which may be due to the presence of chlorine atom in PVC structure making it more versatile. The results of the present study revealed the ability of marine bacterial strain for instigating their colonization over plastic films and deteriorating the polymeric structure.

Impact of nitrogen-polycyclic aromatic hydrocarbons on phenanthrene and benzo[a]pyrene mineralisation in soil

When aromatic hydrocarbons are present in contaminated soils, they often occur in mixtures. The impact of four different (3-ring) nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs) on ^12/14C-phenanthrene and ^12/14C-benzo[a]pyrene (B[a]P) mineralisation in soil was investigated over a 90 d incubation period. The results revealed that both ^12/14C-phenanthrene and ^12/14C-benzo[a]pyrene showed no significant mineralisation in soils amended with 10mgkg ^-1 and 100mgkg ^-1 N-PAHs (p>0.05). However, increases in lag-phases and decreases in the rates and extents of mineralisation were observed, over time. Among the N-PAHs, benzo[h]quinoline impacted ¹⁴C-phenanthrene mineralisation with extended and diauxic lag phases. Furthermore,^12/14C-B[a]P and ¹⁴C-benzo[a]pyrene-nitrogen-containing polycyclic aromatic hydrocarbons (¹⁴C-B[a]P-N-PAHs) amended soils showed extensive lag phases (> 21 d); with some ¹⁴C-B[a]P-N-PAH mineralisation recording <1% in both concentrations (10mgkg ^-1 and 100mgkg ^-1), over time. This study suggests that the presence of N-PAHs in contaminated soil may impact the microbial degradation of polycyclic aromatic hydrocarbons (PAHs) and the impact was most likely the result of limited success in achieving absolute biodegradation of some PAHs in soil.

Identification of polar transformation products and high molecular weight polycyclic aromatic hydrocarbons (PAHs) in contaminated soil following bioremediation

Bioremediation is a technique commonly used to reduce the toxicity associated with polycyclic aromatic hydrocarbons (PAHs) in contaminated soils. However, the efficacy of bioremedial applications is evaluated based on the removal of a subset of parent (or unsubstituted) PAHs and does not incorporate toxic polar transformation products or the more mutagenic high molecular weight PAHs (MW≥302amu or MW302-PAHs). Previously, an effects-directed analysis approach was used to assess the effect of bioremediation on the toxicity of a coal tar-contaminated soil. Increased genotoxicity and developmental toxicity was measured postbioremedation in the more polar soil extract fractions, as compared to the less polar fractions where the targeted PAHs eluted, and could not be attributed to the 88 target PAHs analyzed for (including selected oxygen-containing PAHs). In this study, comprehensive two-dimensional gas chromatography time-of-flight and liquid chromatography quadrupole time-of-flight mass spectrometry were used to characterize transformation products in the soil extract fractions identified as toxic, previously. Additionally, the degradation of 12MW302-PAHs, picene (MW=278) and coronene (MW=300) were evaluated following bioremediation. Non-targeted analysis resulted in the tentative identification of 10 peaks with increased intensity postbioremediation (based on mass spectral library matching and fragmentation patterns from >5000 candidate peaks in the soil extracts). Several of these compounds contained oxygen, suggesting they would be relatively polar. MW302-PAHs were not significantly degraded during bioremediation, suggesting that the carcinogenic potential associated with these PAHs might remain unchanged. The results of this study suggest that polar transformation products, and MW302-PAHs, should be considered for realistic risk assessment of bioremediated soils.

Photolysis of polycyclic aromatic hydrocarbons (PAHs) on Fe3+-montmorillonite surface under visible light: Degradation kinetics, mechanism, and toxicity assessments

Photochemical behavior of various polycyclic aromatic hydrocarbons (PAHs) on Fe³⁺-modified montmorillonite was explored to determine their potential kinetics, pathways, and mechanism under visible light. Depending on the type of PAH molecules, the transformation rate follows the order of benzo[a]pyrene ≈ anthracene > benzo[a]anthracene > phenanthrene. Quantum simulation results confirm the crucial role of "cation-π" interaction between Fe³⁺ and PAHs on their transformation kinetics. Primary intermediates, including quinones, ring-opening products and benzene derivatives, were identified by gas chromatography-mass spectrometer (GC-MS), and the possible photodegradation pathway of benzo[a]pyrene was proposed. Meanwhile, radical intermediates, such as reactive oxygen species (ROS) and free organic radicals, were detected by electron paramagnetic resonance (EPR) technique. The photolysis of selected PAHs, such as anthracene and benzo[a]pyrene, on clay surface firstly occurs by electron transfer from PAHs to Fe³⁺-montmorillonite, followed by degradation involving photo-induced ROS such as ·OH and ·O₂^-. To investigate the acute toxicity of photolysis products, the Microtox^® toxicity test was performed during the photodegradation processes of various PAHs. As a result, the photo-irradiation initially induces increased toxicity by generating reactive intermediates, such as free organic radicals, and then the toxicity gradually decreases with increasing of reaction time. Overall, the present study provides useful information to understand the fate and photo-transformation of PAHs in contaminated soils.

Comprehensive database of Manufactured Gas Plant tars. Part C. Heterocyclic and hydroxylated polycyclic aromatic hydrocarbons

RATIONALE

Coal tars are a mixture of organic and inorganic compounds that were by-products from the manufactured gas and coke making industries. The tar compositions varied depending on many factors such as the temperature of production and the type of retort used. For this reason a comprehensive database of the compounds found in different tar types is of value to understand both how their compositions differ and what potential chemical hazards are present. This study focuses on the heterocyclic and hydroxylated compounds present in a database produced from 16 different tars from five different production processes.

METHODS

Samples of coal tar were extracted using accelerated solvent extraction (ASE) and derivatized post-extraction using N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) with 1% trimethylchlorosilane (TMCS). The derivatized samples were analysed using two-dimensional gas chromatography combined with time-of-flight mass spectrometry (GCxGC/TOFMS).

RESULTS

A total of 865 heterocyclic compounds and 359 hydroxylated polycyclic aromatic hydrocarbons (PAHs) were detected in 16 tar samples produced by five different processes. The contents of both heterocyclic and hydroxylated PAHs varied greatly with the production process used, with the heterocyclic compounds giving information about the feedstock used. Of the 359 hydroxylated PAHs detected the majority would not have been be detected without the use of derivatization.

CONCLUSIONS

Coal tars produced using different production processes and feedstocks yielded tars with significantly different heterocyclic and hydroxylated contents. The concentrations of the individual heterocyclic compounds varied greatly even within the different production processes and provided information about the feedstock used to produce the tars. The hydroxylated PAH content of the samples provided important analytical information that would otherwise not have been obtained without the use of derivatization and GCxGC/TOFMS.

Comprehensive composition of Creosote using comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GCxGC-TOFMS)

Creosote is a distillation product of coal tar and is widely used as wood preservative for railway sleepers, utility poles and for other applications. Creosote can have potentially negative effects on the environment and many of the components are toxic. This study presents the analysis of a Creosote sample from a former wood impregnation plant located in the UK. The sample was analysed using two dimensional gas chromatography time-of-flight mass spectrometry (GCxGC-TOFMS) and a database of compounds that could be detected was produced. The GCxGG-TOFMS was capable of detecting 1505 individual compounds, which is far more than previous estimates for the number of compounds present within Creosote. Post extraction derivatization using BTSFA with 1% TMCS was employed to increase the potential number of compounds detected with 255 derivatized compounds detected, 231 of which would not have been detected without prior derivatization. Selected derivatized compounds were quantified with limits of detection ranging from 0.6 mg/kg to 1.6 mg/kg from a concentrated dense non-aqueous phase liquid (DNAPL). This work presents the first published full analysis of a Creosote using GCxGC-TOFMS combined with derivatization.

Bioremediation of PAH-contamined soils: Consequences on formation and degradation of polar-polycyclic aromatic compounds and microbial community abundance

A bioslurry batch experiment was carried out over five months on three polycyclic aromatic compound (PAC) contaminated soils to study the PAC (PAH and polar-PAC) behavior during soil incubation and to evaluate the impact of PAC contamination on the abundance of microbial communities and functional PAH-degrading populations. Organic matter characteristics and reactivity, assessed through solvent extractable organic matter and PAC contents, and soil organic matter mineralization were monitored during 5 months. Total bacteria and fungi, and PAH-ring hydroxylating dioxygenase genes were quantified. Results showed that PAHs and polar-PACs were degraded with different degradation dynamics. Differences in degradation rates were observed among the three soils depending on PAH distribution and availability. Overall, low molecular weight compounds were preferentially degraded. Degradation selectivity between isomers and structurally similar compounds was observed which could be used to check the efficiency of bioremediation processes. Bacterial communities were dominant over fungi and were most likely responsible for PAC degradation. Abundance of PAH-degrading bacteria increased during incubations, but their proportion in the bacterial communities tended to decrease. The accumulation of some oxygenated-PACs during the bioslurry experiment underlines the necessity to monitor these compounds during application of remediation treatment on PAH contaminated soils.

Development of a novel kinetic model for the analysis of PAH biodegradation in the presence of lead and cadmium co-contaminants

We report on the results of a 40 week study in which the biodegradation of 16 US EPA polycyclic aromatic hydrocarbons (PAHs) was followed in microcosms containing soil of high organic carbon content (11%) in the presence and absence of lead and cadmium co-contaminants. The total spiked PAH concentration was 2166mg/kg. Mercury amendment was also made to give an abiotic control. A novel kinetic model has been developed to explain the observed biphasic nature of PAH degradation. The model assumes that PAHs are distributed across soil phases of varying degrees of bioaccessibility. The results of the analysis suggest that overall percentage PAH loss is dependent on the respective rates at which the PAHs (a) are biodegraded by soil microorganisms in pore water and bioaccessible soil phases and (b) migrate from bioaccessible to non-bioaccessible soil phases. In addition, migration of PAHs to non-bioaccessible and non-Soxhlet-extractable soil phases associated with the humin pores gives rise to an apparent removal process. The presence of metal co-contaminants shows a concentration dependent inhibition of the biological degradation processes that results in a reduction in overall degradation. Lead appears to have a marginally greater inhibitory effect than cadmium.

Characterizing the parent and oxygenated polycyclic aromatic hydrocarbons in mangrove sediments of Hong Kong

Parent and oxygenated polycyclic aromatic hydrocarbons (PAHs) were investigated in mangrove sediments of Hong Kong. Most of the analytes were detected, and the dominant carbonylic and hydroxylated PAHs in mangrove sediments were 9-fluorenone and 2-hydroxy fluorene, respectively. The concentration of 9-fluorenone and 9,10-anthraquinone was higher than their parent PAHs. Moreover, the concentration of total organic matter (TOM) related with those of the parent PAHs and carbonylic PAHs, except for hydroxylated PAHs, which indicated that TOM was not the only factor regulating the distribution of oxygenated PAHs. Nevertheless, the parent PAHs in mangrove sediments was correlated positively with carbonylic PAHs which demostrated not only the similar source but also the fate of these two compound class. However, hydroxylated PAHs had different source by comparing with parent PAHs and carbonylic PAHs, they were probably originated from biodegradation and accumulated in mangrove sediments.

Environmental effects of soil contamination by shale fuel oils

Estonia is currently one of the leading producers of shale oils in the world. Increased production, transportation and use of shale oils entail risks of environmental contamination. This paper studies the behaviour of two shale fuel oils (SFOs)--'VKG D' and 'VKG sweet'--in different soil matrices under natural climatic conditions. Dynamics of SFOs' hydrocarbons (C10-C40), 16 PAHs, and a number of soil heterotrophic bacteria in oil-spiked soils was investigated during the long-term (1 year) outdoor experiment. In parallel, toxicity of aqueous leachates of oil-spiked soils to aquatic organisms (crustaceans Daphnia magna and Thamnocephalus platyurus and marine bacteria Vibrio fischeri) and terrestrial plants (Sinapis alba and Hordeum vulgare) was evaluated. Our data showed that in temperate climate conditions, the degradation of SFOs in the oil-contaminated soils was very slow: after 1 year of treatment, the decrease of total hydrocarbons' content in the soil did not exceed 25 %. In spite of the comparable chemical composition of the two studied SFOs, the VKG sweet posed higher hazard to the environment than the heavier fraction (VKG D) due to its higher mobility in the soil as well as higher toxicity to aquatic and terrestrial species. Our study demonstrated that the correlation between chemical parameters (such as total hydrocarbons or total PAHs) widely used for the evaluation of the soil pollution levels and corresponding toxicity to aquatic and terrestrial organisms was weak.

Investigation of the impacts of ethyl lactate based Fenton treatment on soil quality for polycyclic aromatic hydrocarbons (PAHs)-contaminated soils

This study aims to investigate the impacts of ethyl lactate (EL) based Fenton treatment on soil quality for polycyclic aromatic hydrocarbons (PAHs)-contaminated soils. Accumulation of oxygenated-polycyclic aromatic hydrocarbons (oxy-PAHs) was observed, but quantitative measurement on the most abundant compound 9,10-anthraquinone (ATQ) showed lower accumulation of the compound than that reported for ethanol (ET) based Fenton treatment. In general, as compared to conventional water (CW) based Fenton treatment, the EL based Fenton treatment exerted either a lower or higher negative impact on soil physicochemical properties depending on the property type and shared the main disadvantage of reduced soil pH. For revegetation, EL based Fenton treatment was most appropriately adopted for soil with native pH >/~ 6.2 in order to obtain a final soil pH >/~ 4.9 subject to the soil buffering capacity.

Is it possible to increase bioavailability but not environmental risk of PAHs in bioremediation?

The current poor predictability of end points associated with the bioremediation of polycyclic aromatic hydrocarbons (PAHs) is a large limitation when evaluating its viability for treating contaminated soils and sediments. However, we have seen a wide range of innovations in recent years, such as an the improved use of surfactants, the chemotactic mobilization of bacterial inoculants, the selective biostimulation at pollutant interfaces, rhizoremediation and electrobioremediation, which increase the bioavailability of PAHs but do not necessarily increase the risk to the environment. The integration of these strategies into practical remediation protocols would be beneficial to the bioremediation industry, as well as improve the quality of the environment.

How suitable are peat cores to study historical deposition of PAHs?

Ombrotrophic peat bogs are natural archives of atmospheric pollution, their depth profiles can be used to study the deposition chronology of harmful contaminants. Prerequisites for deriving historical deposition rates from the peat archive are that contaminants are persistent and immobile in the peat and that the applied dating technique is accurate. To examine these requirements and the accuracy of peat archives for polycyclic aromatic hydrocarbons (PAHs) 12 peat profiles were sampled in 4 bogs in Ontario, Canada, as well as surface peat in one bog. Additionally we carried out laboratory incubations; no degradation occurred over a 3-year period in these experiments. The standard deviations of PAH concentrations in surface samples and of PAH inventories in whole cores was approximately 30%, and concentrations in surface peat were on average 50% higher in hollows than in hummocks. No indications for mobility of PAHs were observed in peat. Temporal deposition trends inferred from peat cores were generally in agreement with trends derived from a sediment core sampled close by but deposition rates to the sediment were substantially higher. A major source of uncertainty was the rather coarse vertical sampling resolution of 5 cm which introduced substantial uncertainty in the dating of the individual segments. This caused variations of the deposition rates up to 70% per PAH between three replicate cores, and it also impedes the identification of deposition peaks. Overall, we conclude that peat cores are suitable archives for inferring atmospheric deposition trends, but due to their relatively low temporal resolution short-term events may not be identified and the development of sampling methods that allow a higher vertical resolution would greatly improve the performance of the method. The analysis of more than one core per site is suggested to provide a realistic estimate of the historic deposition and total inventories.

Long-term simulation of in situ biostimulation of polycyclic aromatic hydrocarbon-contaminated soil

A continuous-flow column study was conducted to evaluate the long-term effects of in situ biostimulation on the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in soil from a manufactured gas plant site. Simulated groundwater amended with oxygen and inorganic nutrients was introduced into one column, while a second column receiving unamended groundwater served as a control. PAH and dissolved oxygen (DO) concentrations, as well as microbial community profiles, were monitored along the column length immediately before and at selected intervals up to 534 days after biostimulation commenced. Biostimulation resulted in significantly greater PAH removal than in the control condition (73% of total measured PAHs vs. 34%, respectively), with dissolution accounting for a minor amount of the total mass loss (~6%) in both columns. Dissolution was most significant for naphthalene, acenaphthene, and fluorene, accounting for >20% of the total mass removed for each. A known group of PAH-degrading bacteria, 'Pyrene Group 2' (PG2), was identified as a dominant member of the microbial community and responded favorably to biostimulation. Spatial and temporal variations in soil PAH concentration and PG2 abundance were strongly correlated to DO advancement, although there appeared to be transport of PG2 organisms ahead of the oxygen front. At an estimated oxygen demand of 6.2 mg O(2)/g dry soil and a porewater velocity of 0.8 m/day, it took between 374 and 466 days for oxygen breakthrough from the 1-m soil bed in the biostimulated column. This study demonstrated that the presence of oxygen was the limiting factor in PAH removal, as opposed to the abundance and/or activity of PAH-degrading bacteria once oxygen reached a previously anoxic zone.

The potential of Chromolaena odorata (L) to decontaminate used engine oil impacted soil under greenhouse conditions

This study reports on the use of Chromolaena odorata (L) R.M. King and H. Robinson, an Asteraceae (compositae) and an invasive alien weed in Africa for the remediation of soil contaminated with used engine oil. Used engine oilfrom a motor service garage was used to artificially contaminate soil taken from a garden to give total petroleum hydrocarbon (TPH) of between 1 and 40 g kg(-1). Chromolaena odorata (L), propagated by stem cuttings were transplanted into the contaminated soil and watered just enough to keep the soil at about 70% water holding capacity for 90 day. A set of control experiments containing 40 g kg(-1) used engine oil but without plants was set up. All experiments were set up in triplicates. Although the plants in the experiments containing higher than 30 g kg(-1) used engine oil showed relatively slower growth (fewer branches and leaves, and shorter in height) compared to those containing lower concentrations, the plants in all the experiments continued to grow until the end of the 90 day period. Residual TPH after 90 days showed that between 21 and 100% of oil was lost from the planted soil while only 11.5% was lost in the control, which did not contain plants during the same period. Analysis of plant tissues showed that both shoot and root tissues contained detectable levels of TPH and selected PAHs were also detectable. Biomass accumulation by Chromolaena odorata was affected adversely by concentrations of oil higher than 20 g kg(-1). Results of germination rates and germination energy measurements showed that Chromolaena odorata was able to reduce the toxicity of the contaminated soil after 90 days as compared to soils containing freshly contaminated soiL

Modeling sorption and biodegradation of phenanthrene in mangrove sediment slurry

A mathematical model, combining both sorption and biodegradation process, was developed to predict the biodegradation of phenanthrene by Sphingomonas sp. in different sediment slurries. The model includes two sorption parameters, α (the partition coefficient) and 1/K (the diffusion resistance); a kinetic parameter k (the first order rate constant); and a sediment parameter, A(V) (the specific sediment surface area in unit volume of slurry). These parameters were evaluated and verified in three types of sediment slurry systems (namely sandy clay loam Ho Chung sediment with fastest degradation, sandy Kei Ling Ha sediment with medium degradation, and clay Mai Po sediment with slowest degradation) at different initial phenanthrene concentrations. High R(2) values, ranging from 0.935 to 0.969, were obtained. Based on this integrated sorption-biodegradation model, the phenanthrene biodegradation in any sediment slurry could be predicted as long as the parameters of the specific sediment surface area in unit volume of slurry, total organic carbon and clay content were measured.

Re-use of remediated soils for the bioremediation of waste oil sludge

We investigated the possibility of re-using remediated soils for new bioremediation projects by spiking these soils with waste oil sludge in laboratory based microcosms. The level of Total Petroleum Hydrocarbon (TPH) reduction was high (>80%) in naturally attenuated microcosms and was not significantly improved by biostimulation, bioaugmentation and the combined treatment of bioaugmentation and biostimulation by week 12. This indicated that the observed TPH reduction might have been related to the soil's inherent hydrocarbon-degrading potential. Microbial community analysis (16S rDNA and ITS-based Denaturing Gradient Gel Electrophoresis fingerprints) confirmed the dominance of hydrocarbon degrading genera such as Alcanivorax and Scedosporium. Cluster and Shannon diversity analysis revealed similar but stable bacterial and fungal communities in naturally attenuated and amended microcosms indicating that rapid reduction in TPH may not always be accompanied by changes in soil microbial communities. This study has therefore shown that soils previously used for bioremediation can have an improved hydrocarbon degrading potential which was successfully re-harnessed for new projects. This ability to re-harness this potential is attractive because it substantially reduces operational costs as no additional bioremediation treatments are needed. It can also extend a landfill's lifespan as soils can be re-used again before landfill disposal.

Oxygen-containing polycyclic aromatic hydrocarbons (OPAHs) in urban soils of Bratislava, Slovakia: patterns, relation to PAHs and vertical distribution

We determined concentrations, sources, and vertical distribution of OPAHs and PAHs in soils of Bratislava. The ∑14 OPAHs concentrations in surface soil horizons ranged 88-2692 ng g(-1) and those of ∑34 PAHs 842-244,870 ng g(-1). The concentrations of the ∑9 carbonyl-OPAHs (r=0.92, p=0.0001) and the ∑5 hydroxyl-OPAHs (r=0.73, p=0.01) correlated significantly with ∑34 PAHs concentrations indicating the close association of OPAHs with parent-PAHs. OPAHs were quantitatively dominated by 9-fluorenone, 9,10-anthraquinone, 1-indanone and benzo[a]anthracene-7,12-dione. At several sites, individual carbonyl-OPAHs had higher concentrations than parent PAHs. The concentration ratios of several OPAHs to their parent-PAHs and contribution of the more soluble OPAHs (1-indanone and 9-fluorenone) to ∑14 OPAHs concentrations increased with soil depth suggesting that OPAHs were faster vertically transported in the study soils by leaching than PAHs which was supported by the correlation of subsoil:surface soil ratios of OPAH concentrations at several sites with K(OW).

Effect of electrokinetics on the bioaccessibility of polycyclic aromatic hydrocarbons in polluted soils

Bioaccessibility is one of the most relevant aspects to be considered in the restoration of soils using biological technologies. Polycyclic aromatic hydrocarbons (PAH) usually have residual fractions that are resistant to biodegradation at the end of the biological treatment. In some situations, these residual concentrations could still be above legal standards. Here, we propose that the available knowledge about electroremediation technologies could be applied to enhance bioremediation of soils polluted with PAH. The main objective of this study was to show that a previous electrokinetic treatment could reduce the PAH residual fractions when the soil is subsequently treated by means of a bioremediation process. The approach involved the electrokinetic treatment of PAH-polluted soils at a potential drop of 0.9 to 1.1 V/cm and the subsequent estimations of bioaccessibility of residual PAHs after slurry-phase biodegradation. Bioaccessibility of PAH in two creosote-polluted soils (clay and loamy sand, total PAH content averaging 300 mg/kg) previously treated with an electric field in the presence of nonionic surfactant Brij 35 was often higher than in untreated controls. For example, total PAH content remaining in clay soil after bioremediation was only 62.65 +/- 4.26 mg/kg, whereas a 7-d electrokinetic pretreatment had, under the same conditions, a residual concentration of 29.24 +/- 1.88 mg/kg after bioremediation. Control treatments without surfactant indicated that the electrokinetic treatment increased bioaccessibility of PAHs. A different manner of electric field implementation (continuous current vs. current reversals) did not induce changes in PAH bioaccessibility. We suggest that this hybrid technology may be useful in certain bioremediation scenarios, such as soils rich in clay and black carbon, which show limited success due to bioavailability restrictions, as well as in highly heterogeneous soils.

Ketone and quinone-substituted polycyclic aromatic hydrocarbons in mussel tissue, sediment, urban dust, and diesel particulate matrices

Polycyclic aromatic hydrocarbons (PAHs) substituted with a ketone or quinone functionality (OPAHs) may be important environmental contaminants. The OPAHs from environmental samples have demonstrated toxicity and may be more harmful than PAHs. Knowledge gaps concerning the occurrence of OPAHs in the total environment arise from analytical difficulties, as well as limited standards and methodologies. An optimized method was developed to quantify five ketone and four quinone OPAHs from matrices ranging from biological tissue to diesel particulates. Five National Institute of Standards and Technology Standard Reference Materials (SRMs) were analyzed. This is the first report of OPAH quantitation in SRM 2977 (mussel tissue), SRM 1944 (New York/New Jersey, USA waterway sediment), SRM 1975 (diesel extract), and SRM 1650b (diesel particulate matter) and among the few to report concentrations from SRM 1649 (urban dust). Furthermore, this is one of the first reports of OPAHs in biological tissue. Σ₉OPAHs were 374 ± 59 mg/kg (mussel tissue), 5.4 ± 0.5 mg/kg (sediment), 16.9 ± 1.6 mg/kg (urban dust), 33.4 ± 0.4 mg/kg (diesel extract), and 150 ± 43 mg/kg (diesel particulate matter). In all SRMs, the levels of OPAHs were similar to or exceeded levels of PAHs. Of the OPAHs tested, the most frequently occurring in the environmental matrices were 9-fluorenone, 9,10-anthraquinone, benzofluorenone, and 7,12-benz[a]anthracenequinone.

Spatial uncoupling of biodegradation, soil respiration, and PAH concentration in a creosote contaminated soil

Hotspots and coldspots of concentration and biodegradation of polycyclic aromatic hydrocarbons (PAHs) marginally overlapped at the 0.5-100 m scale in a creosote contaminated soil in southern Sweden, suggesting that concentration and biodegradation had little spatial co-variation. Biodegradation was substantial and its spatial variability considerable and highly irregular, but it had no spatial autocorrelation. The soil concentration of PAHs explained only 20-30% of the variance of their biodegradation. Soil respiration was spatially autocorrelated. The spatial uncoupling between biodegradation and soil respiration seemed to be governed by the aging of PAHs in the soil, since biodegradation of added 13C phenanthrene covaried with both soil respiration and microbial biomass. The latter two were also correlated with high concentrations of phospholipid fatty acids (PLFAs) that are common in gram-negative bacteria. However, several of the hotspots of biodegradation coincided with hotspots for the distribution of a PLFA indicative of fungal biomass.

Interactive effect of dissolved organic matter and phenanthrene on soil enzymatic activities

The investigation of dissolved organic matter (DOM) on urease, catalase and polyphenol oxidase activity in a phenanthrene (Phe)-contaminated soil was conducted under laboratory incubation conditions. Values of soil enzymatic activity depended mainly on incubation time. In the initial 16 days, urease activity increased, and was followed by a decrease. In the initial 8 days, catalase activity decreased and then increased. Variation of polyphenol oxidase activity was just the reverse of catalase activity. After 30 days of incubation, no pronounced difference among treatments with Phe, Phe and DOM, and control were detected in urease, catalase and polyphenol oxidase activity. Phe might inhibit urease and catalase, and stimulate polyphenol oxidase. DOM could improve inhibition of Phe in soil urease and catalase activity during the initial period of applying DOM. Nevertheless, DOM had no significant effect on polyphenol oxidase activity in the Phe contaminated soil. There was a negative correlation between catalase and polyphenol oxidase (r = -0.761***), and catalase and urease (r = -0.554**). Additionally, a positive correlation between polyphenol oxidase and urease was also detected (r = 0.701***). It is implied that the formed DOM after application of organic wastes into soils may counteract the inhibition of polycyclic aromatic hydrocarbons in soil enzyme activities.

Mutagenicity of an aged gasworks soil during bioslurry treatment

This study investigated changes in the mutagenic activity of organic fractions from soil contaminated with polycyclic aromatic hydrocarbons (PAHs) during pilot-scale bioslurry remediation. Slurry samples were previously analyzed for changes in PAH and polycyclic aromatic compound content, and this study examined the correspondence between the chemical and toxicological metrics. Nonpolar neutral and semipolar aromatic fractions of samples obtained on days 0, 3, 7, 24, and 29 of treatment were assayed for mutagenicity using the Salmonella mutation assay. Most samples elicited a significant positive response on Salmonella strains TA98, YG1041, and YG1042 with and without S9 metabolic activation; however, TA100 failed to detect mutagenicity in any sample. Changes in the mutagenic activity of the fractions across treatment time and metabolic activation conditions suggests a pattern of formation and transformation of mutagenic compounds that may include a wide range of PAH derivatives such as aromatic amines, oxygenated PAHs, and S-heterocyclic compounds. The prior chemical analyses documented the formation of oxygenated PAHs during the treatment (e.g., 4-oxapyrene-5-one), and the mutagenicity analyses showed high corresponding activity in the semipolar fraction with and without metabolic activation. However, it could not be verified that these specific compounds were the underlying cause of the observed changes in mutagenic activity. The results highlight the need for concurrent chemical and toxicological profiling of contaminated sites undergoing remediation to ensure elimination of priority contaminants as well as a reduction in toxicological hazard. Moreover, the results imply that remediation efficacy and utility be evaluated using both chemical and toxicological metrics.

Fungal bioremediation of the creosote-contaminated soil: influence of Pleurotus ostreatus and Irpex lacteus on polycyclic aromatic hydrocarbons removal and soil microbial community composition in the laboratory-scale study

The aim of this study was to determine the efficacy of selected basidiomycetes in the removing of polycyclic aromatic hydrocarbons (PAH) from the creosote-contaminated soil. Fungi Pleurotus ostreatus and Irpex lacteus were supplemented with creosote-contaminated (50-200 mg kg(-1) PAH) soil originating from a wood-preserving plant and incubated at 15 °C for 120 d. Either fungus degraded PAH with 4-6 aromatic rings more efficiently than the microbial community present initially in the soil. PAH removal was higher in P. ostreatus treatments (55-67%) than in I. lacteus treatments (27-36%) in general. P. ostreatus (respectively, I. lacteus) removed 86-96% (47-59%) of 2-rings PAH, 63-72% (33-45%) of 3-rings PAH, 32-49% (9-14%) of 4-rings PAH and 31-38% (11-13%) of 5-6-rings PAH. MIS (Microbial Identification System) Sherlock analysis of the bacterial community determined the presence of dominant Gram-negative bacteria (G-) Pseudomonas in the inoculated soil before the application of fungi. Complex soil microbial community was characterized by phospholipid fatty acids analysis followed by GC-MS/MS. Either fungus induced the decrease of bacterial biomass (G- bacteria in particular), but the soil microbial community was influenced by P. ostreatus in a different way than by I. lacteus. The bacterial community was stressed more by the presence of I. lacteus than P. ostreatus (as proved by the ratio of the fungal/bacterial markers and by the ratio of trans/cis mono-unsaturated fatty acids). Moreover, P. ostreatus stimulated the growth of Gram-positive bacteria (G+), especially actinobacteria and these results indicate the potential of the positive synergistic interaction of this fungus and actinobacteria in creosote biodegradation.

Sources, fate, and toxic hazards of oxygenated polycyclic aromatic hydrocarbons (PAHs) at PAH-contaminated sites

In this paper we show that oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) are important cocontaminants that should be taken into account during risk assessment and remediation of sites with high levels of PAHs. The presented data, which have been collected both from our own research and the published literature, demonstrate that oxy-PAHs are abundant but neglected contaminants at these sites. The oxy-PAHs show relatively high persistency and because they are formed through transformation of PAHs, their concentrations in the environment may even increase as the sites are remediated by methods that promote PAH degradation. Furthermore, we show that oxy-PAHs are toxic to both humans and the environment, although the toxicity seems to be manifested through other effects than those known to be important for polycyclic aromatic compounds in general, that is, mutagenicity and carcinogenicity. Finally, we present data that support the hypothesis that oxy-PAHs are more mobile in the environment than PAHs, due to their polarity, and thus have a higher tendency to spread from contaminated sites via surface water and groundwater. We believe that oxy-PAHs should be included in monitoring programs at PAH-contaminated sites, even if a number of other toxicologically relevant compounds that may also be present, such as nitro-PAHs and azaarenes, are not monitored. This is because oxy-PAH levels are difficult to predict from the PAH levels, because their environmental behavior differs substantially from that of PAHs, and oxy-PAHs may be formed as PAHs are degraded.

Integrating biodegradation and electroosmosis for the enhanced removal of polycyclic aromatic hydrocarbons from creosote-polluted soils

This paper presents a hybrid technology of soil remediation based on the integration of biodegradation and electroosmosis. We employed soils with different texture (clay soil and loamy sand) containing a mixture of polycyclic aromatic hydrocarbons (PAH) present in creosote, and inoculation with a representative soil bacterium able to degrade fluorene, phenanthrene, fluoranthene, pyrene, anthracene, and benzo[a]pyrene. Two different modes of treatment were prospected: (i) inducing in soil the simultaneous occurrence of biodegradation and electroosmosis in the presence of a biodegradable surfactant, and (ii) treating the soils sequentially with electrokinetics and bioremediation. Losses of PAH due to simultaneous biodegradation and electroosmosis (induced by a continuous electric field) were significantly higher than in control cells that contained the surfactant but no biological activity or no current. The method was especially successful with loamy sand. For example, benzo[a]pyrene decreased its concentration by 50% after 7 d, whereas 22 and 17% of the compound had disappeared as a result of electrokinetic flushing and bioremediation alone, respectively. The use of periodical changes in polarity and current pulses increased by 16% in the removal of total PAH and in up to 30% of specific compounds, including benzo[a]pyrene. With the aim of reaching lower residual levels through bioremediation, an electrokinetic pretreatment was also evaluated as a way to mobilize the less bioaccessible fraction of PAH. Residual concentrations of total biodegradable PAH, remaining after bioremediation in soil slurries, were twofold lower in electrokinetically pretreated soils than in untreated soils. The results indicate that biodegradation and electroosmosis can be successfully integrated to promote the removal of PAH from soil.

Study of pyrene biodegradation capacity in two types of solid media

Removal of pyrene, a representative PAH, was studied using laboratory tests in two different types of solid media: an organic matter collected on the surface of a vertical flow constructed wetland (VFCW) and a formulated clay silicate sand (inorganic matter). The aim of this study was to evaluate the capacity of pyrene biodegradation in these media in order to use them for treating run-off water. The sorption process, the kinetics of pyrene biodegradation and the influence of selected bacteria were also investigated. The sorption process was evaluated by adsorption isotherms and desorption kinetics using a batch equilibration method. The adsorption coefficient values of 28.8 and 2.1 for the organic and the inorganic matter respectively, confirmed the relationship of adsorption with organic carbon content. A small proportion of the sorbed pyrene was available for desorption (8% and 15% for the organic and the inorganic matter, respectively), indicating that sorption was partially irreversible, with the presence of hysteresis. For the formulated clay silicate sand inoculated with a specific bacteria (Mycobacterium sp.6PY1), selected for its ability to degrade PAHs, pyrene removal was complete in 32 days. With the organic matter, these values ranged from 40% to 95% for the different experiments, following a lag time of 3 weeks before observation of a significant degradation. Indigenous bacterial species in the organic medium had the metabolic capacity to degrade pyrene, and microbial populations pre-exposed to the PAH degraded pyrene faster than similar unexposed populations. Three metabolites of pyrene degradation by Mycobacterium were found. They accumulated in both organic and inorganic matter, indicating that the enzymes catalyzing them have slow kinetics.

Microbial community changes during the bioremediation of creosote-contaminated soil

AIMS

To investigate the effects of aeration on the ex situ biodegradation of polycyclic aromatic hydrocarbons (PAHs) in creosote-contaminated soil and its effect on the microbial community present.

METHODS AND RESULTS

Aerated and nonaerated microcosms of soil excavated from a former timber treatment yard were maintained and sampled for PAH concentration and microbial community changes by terminal restriction fragment length polymorphism (TRFLP) analysis. After an experimental period of just 13 days, degradation was observed with all the PAHs monitored. Abiotic controls showed no loss of PAH. Results unexpectedly showed greater loss of the higher molecular weight PAHs in the nonaerated control. This may have been due to the soil excavation causing initial decompaction and aeration and the resulting changes caused in the microbial community composition, indicated by TRFLP analysis showing several ribotypes greatly increasing in relative abundance. Similar changes in both microcosms were observed but with several possible key differences. The species of micro-organisms putatively identified included Bacilli, pseudomonad, aeromonad, Vibrio and Clostridia species.

CONCLUSIONS

Excavation of the contaminated soil leads to decompaction, aeration and increased nutrient availability, which in turn allow microbial biodegradation of the PAHs and a change in the microbial community structure.

SIGNIFICANCE AND IMPACT OF THE STUDY

Understanding the changes occurring in the microbial community during biodegradation of all PAHs is essential for the development of improved site remediation protocols. TRFLP allows useful monitoring of the total microbial community.

Comparison of techniques for estimating PAH bioavailability: uptake in Eisenia fetida, passive samplers and leaching using various solvents and additives

The aim of this study was to evaluate different techniques for assessing the availability of polycyclic aromatic hydrocarbons (PAHs) in soil. This was done by comparing the amounts (total and relative) taken up by the earthworm Eisenia fetida with the amounts extracted by solid-phase microextraction (SPME), semi-permeable membrane devices (SPMDs), leaching with various solvent mixtures, leaching using additives, and sequential leaching. Bioconcentration factors of PAHs in the earthworms based on equilibrium partitioning theory resulted in poor correlations to observed values. This was most notable for PAHs with high concentrations in the studied soil. Evaluation by principal component analysis (PCA) showed distinct differences between the evaluated techniques and, generally, there were larger proportions of carcinogenic PAHs (4-6 fused rings) in the earthworms. These results suggest that it may be difficult to develop a chemical method that is capable of mimicking biological uptake, and thus estimating the bioavailability of PAHs.

Electrokinetic enhancement of phenanthrene biodegradation in creosote-polluted clay soil

Given the difficulties caused by low-permeable soils in bioremediation, a new electrokinetic technology is proposed, based on laboratory results with phenanthrene, to afford bioremediation of polycyclic aromatic hydrocarbons (PAH) in clay soils. Microbial activity in a clay soil historically polluted with creosote was promoted using a specially designed electrokinetic cell with a permanent anode-to-cathode flow and controlled pH. The rates of phenanthrene losses during treatment were tenfold higher in soil treated with an electric field than in the control cells without current or microbial activity. Results from experiments with Tenax-assisted desorption and mineralization of 14C-labeled phenanthrene indicated that phenanthrene biodegradation was limited by mass-transfer of the chemical. We suggest that the enhancement effect of the applied electric field on phenanthrene biodegradation resulted from mobilization of the PAH and nutrients dissolved in the soil fluids.

Bioavailability assessment and environmental fate of polycyclic aromatic hydrocarbons in biostimulated creosote-contaminated soil

When hydrocarbon-contaminated soil is subjected to bioremediation technology, hydrocarbon depletion is typically marked by an initially rapid reduction rate. This rate decreases over time and frequently a residual concentration remains in the soil. This kinetic has been attributed primarily to the enrichment of more recalcitrant fractions, as well as to the lack of resting hydrocarbon bioavailability. Thus, at the end of the bioremediation process, a part of the residual hydrocarbon soil concentration represents the non-bioavailable fraction, which is difficult to degrade by microbial populations and which poses a minor hazard. Therefore, determination of the bioavailable fraction in a bioremediation project represents both an estimation of the maximum level of achievable biodegradation, as well as an additional indication of the environmental health hazard. In the present study, aged creosote-contaminated soil was subjected to biostimulation processes, and the bioavailable fraction for several target polycyclic aromatic hydrocarbons (PAHs) was calculated using a mild extraction with cyclodextrines. The amount of PAH extracted corresponded to the desorbing fraction and can be regarded as the bioavailable fraction. The non-desorbing fraction data obtained from this procedure were compared to the remaining PAH concentrations following bioremediation treatment of soil microcosms. These results permitted the establishment of a theoretical biodegradation limit based on the desorbing fraction. In addition, neither accumulation of intermediate metabolites, nor the formation of bound-residues or reduced acute toxicity was observed.

Bacterial community dynamics and polycyclic aromatic hydrocarbon degradation during bioremediation of heavily creosote-contaminated soil

Bacterial community dynamics and biodegradation processes were examined in a highly creosote-contaminated soil undergoing a range of laboratory-based bioremediation treatments. The dynamics of the eubacterial community, the number of heterotrophs and polycyclic aromatic hydrocarbon (PAH) degraders, and the total petroleum hydrocarbon (TPH) and PAH concentrations were monitored during the bioremediation process. TPH and PAHs were significantly degraded in all treatments (72 to 79% and 83 to 87%, respectively), and the biodegradation values were higher when nutrients were not added, especially for benzo(a)anthracene and chrysene. The moisture content and aeration were determined to be the key factors associated with PAH bioremediation. Neither biosurfactant addition, bioaugmentation, nor ferric octate addition led to differences in PAH or TPH biodegradation compared to biodegradation with nutrient treatment. All treatments resulted in a high first-order degradation rate during the first 45 days, which was markedly reduced after 90 days. A sharp increase in the size of the heterotrophic and PAH-degrading microbial populations was observed, which coincided with the highest rates of TPH and PAH biodegradation. At the end of the incubation period, PAH degraders were more prevalent in samples to which nutrients had not been added. Denaturing gradient gel electrophoresis analysis and principal-component analysis confirmed that there was a remarkable shift in the composition of the bacterial community due to both the biodegradation process and the addition of nutrients. At early stages of biodegradation, the alpha-Proteobacteria group (genera Sphingomonas and Azospirillum) was the dominant group in all treatments. At later stages, the gamma-Proteobacteria group (genus Xanthomonas), the alpha-Proteobacteria group (genus Sphingomonas), and the Cytophaga-Flexibacter-Bacteroides group (Bacteroidetes) were the dominant groups in the nonnutrient treatment, while the gamma-Proteobacteria group (genus Xathomonas), the beta-Proteobacteria group (genera Alcaligenes and Achromobacter), and the alpha-Proteobacteria group (genus Sphingomonas) were the dominant groups in the nutrient treatment. This study shows that specific bacterial phylotypes are associated both with different phases of PAH degradation and with nutrient addition in a preadapted PAH-contaminated soil. Our findings also suggest that there are complex interactions between bacterial species and medium conditions that influence the biodegradation capacity of the microbial communities involved in bioremediation processes.

Co-composting of PAH-contaminated soil with poultry manure

AIMS

To investigate the effects of co-composting poultry manure with soil contaminated with different concentrations of polycyclic aromatic hydrocarbons (PAHs), on the degradation of selected PAHs in a static-pile compost system.

METHODS

Mispah form (Food & Agricultural Organisation, FAO : lithosol) soil contaminated with PAHs was co-composted with poultry manure for 19 months. The soil was mixed with wood chips in a ratio of 1:1 to improve aeration and then mixed with poultry manure in a ratio of 4:1. A data logger measured temperature monthly. Residual concentrations of selected PAHs in the compost were determined monthly by gas chromatography/flame ionisation detection (GC/FID). Moisture, pH, ash content and C:N ratios were also monitored monthly. Microbial activity was measured by measuring CO(2) evolution.

CONCLUSIONS

The results obtained in this experiment have shown that co-composting poultry manure with PAH-contaminated soil is capable of removing large concentrations of high molecular weight PAH from contaminated soil to levels below 1 mg kg(-1) in 19 months.

SIGNIFICANCE AND IMPACT OF THE STUDY

The paper adds to the body of knowledge necessary for the development of a cost effective technology for the remediation of soil contaminated with high molecular weight PAHs by providing information on the behaviour of selected PAHs and factors such as nutrient ratio, temperature and pH during composting.

Bioremediation of creosote-contaminated soil in South Africa by landfarming

AIMS

To determine the combined effects of biostimulation and bioaugmentation in the landfarming of a mispah form (lithosol; food and Agriculture Organisation (FAO)) soil contaminated with >310000 mg kg-1 creosote with a view to developing a bioremediation technology for soils heavily contaminated with creosote.

METHODS AND RESULTS

The excavated soil was mixed with 2500 kg ha-1 dolomitic lime and 2000 kg ha-1 mono-ammonium phosphate (MAP) before spreading over a treatment bed of shale reinforced with clay. Sewage sludge (500 kg) was ploughed into 450 m3 of contaminated soil in the second and sixth months of treatment. A further 1000 kg ha-1 MAP was added to the soil at the end of the fifth month. Moisture was maintained at 70% field capacity. Total creosote was determined by the US Environmental Protection Agency (EPA) method 418.1 and concentrations of selected creosote components were determined by gas chromatography/flame ionisation detection (GC/FID). Total creosote was reduced by more than 90% by the 10th month of landfarming. The rate of reduction in creosote concentration was highest after the addition of sewage sludge. The three-ring PAHs were more slowly removed than naphthalene and the phenolic compounds. The four- and five-ring PAHs, although persist until the end of treatment, were reduced by 76-87% at the end of the experiment.

CONCLUSIONS

A combination of biostimulation and bioaugmentation during landfarming could enhance the bioremediation of soils heavily contaminated with creosote.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study provides information on the management of a combination of biostimulation and bioaugmentation during landfarming, and contributes to the knowledge and database necessary for the development of a technology for bioremediating creosote-contaminated land.

Degradation and formation of polycyclic aromatic compounds during bioslurry treatment of an aged gasworks soil

The goals of this study were to investigate the relative degradation rates of polycyclic aromatic compounds (PACs) in contaminated soil, and to assess whether persistent oxidation products are formed during their degradation. Samples were taken on five occasions during a pilot-scale bioslurry treatment of soil from a former gasworks site. More than 100 PACs were identified in the soil, including unsubstituted polycyclic aromatic hydrocarbons (PAHs), alkylated PAHs (alkyl-PAHs), heterocyclic PACs, and oxygenated PAHs (oxy-PAHs), such as ketones, quinones, and coumarins. During the treatment, the low molecular weight PAHs and heterocyclics were degraded faster than the high molecular weight compounds. The unsubstituted PAHs also appear to have degraded more quickly than the corresponding alkyl-PAHs and nitrogen-containing heterocyclics. No new oxidation products that were not present in the untreated soil were identified after the soil treatment. However, oxy-PAHs that were present in the untreated soil were generally degraded more slowly than the parent compounds, suggesting that they were formed during the treatment or that they are more persistent. Two oxidation products, 1-acenaphthenone and 4-oxapyrene-5-one, were found at significantly higher concentrations at the end of the study. Because oxy-PAHs can be acutely toxic, mutagenic, or carcinogenic, we suggest that this group of compounds should also be monitored during the treatment of PAH-contaminated soil.

Biodegradation of the synthetic pyrethroid cypermethrin in used sheep dip

AIMS

To investigate the breakdown of cypermethrin synthetic pyrethroid (SP) insecticide-based used sheep dip (USD), with its indigenous microbial community and two previously isolated SP-degrading microorganisms.

METHODS AND RESULTS

Cultures of USD (50 ml) containing 250 ml l(-1) cypermethrin were inoculated with the SP-degrading organisms and incubated at 25 degrees C with agitation at 80 rev min(-1) for 14 days. The viable cell counts and concentration of cypermethrin were monitored. A non-stimulated control was also carried out. The previously isolated bacteria were the most effective at degrading cypermethrin, leaving approximately two-thirds the concentration of SP as was found in the control. The non-stimulated cultures showed negligible breakdown of SP over the experimental period.

CONCLUSIONS

The previously isolated SP-degrading bacteria could have a use in the treatment of SP USD.

SIGNIFICANCE AND IMPACT OF STUDY

In situ treatment of SP-based USDs to detoxify the active ingredient before disposal could be very useful in helping to deal with agricultural pesticide waste. Such an approach, or by ex situ treatment would be more preferable to current methods, such as those of incineration and disposal to land.

Degradation of polycyclic aromatic hydrocarbons at low temperature under aerobic and nitrate-reducing conditions in enrichment cultures from northern soils

The potential for biodegradation of polycyclic aromatic hydrocarbons (PAHs)at low temperature and under anaerobic conditions is not well understood, but such biodegradation would be very useful for remediation of polluted sites. Biodegradation of a mixture of 11 different PAHs with two to five aromatic rings, each at a concentration of 10 micro g/ml, was studied in enrichment cultures inoculated with samples of four northern soils. Under aerobic conditions, low temperature severely limited PAH biodegradation. After 90 days, aerobic cultures at 20 degrees C removed 52 to 88% of the PAHs. The most extensive PAH degradation under aerobic conditions at 7 degrees C,53% removal, occurred in a culture from creosote-contaminated soil. Low temperature did not substantially limit PAH biodegradation under nitrate-reducing conditions. Under nitrate-reducing conditions,naphthalene, 2-methylnaphthalene, fluorene, and phenanthrene were degraded. The most extensive PAH degradation under nitrate-reducing conditions at 7 degrees C, 39% removal, occurred in a culture from fuel-contaminated Arctic soil. In separate transfer cultures from the above Arctic soil, incubated anaerobically at 7 degrees C, removal of 2-methylnaphthalene and fluorene was stoichiometrically coupled to nitrate removal. Ribosomal intergenic spacer analysis suggested that enrichment resulted in a few predominant bacterial populations,including members of the genera Acidovorax,Bordetella, Pseudomonas, Sphingomonas, and Variovorax. Predominant populations from different soils often included phylotypes with nearly identical partial 16S rRNA gene sequences (i.e., same genus) but never included phylotypes with identical ribosomal intergenic spacers (i.e., different species or subspecies). The composition of the enriched communities appeared to be more affected by presence of oxygen, than by temperature or source of the inoculum.