Potential for Aerobic and Anaerobic Biodegradation of Petroleum Hydrocarbons in Boreal Subsurface

Remediation of petroleum-contaminated site soil by bioaugmentation with immobilized bacterial pellets stimulated by a controlled-release oxygen composite

Bioaugmentation techniques still show drawbacks in the cleanup of total petroleum hydrocarbons (TPHs) from petroleum-contaminated site soil. Herein, this study explored high-performance immobilized bacterial pellets (IBPs) embed Microbacterium oxydans with a high degrading capacity, and developed a controlled-release oxygen composite (CROC) that allows the efficient, long-term release of oxygen. Tests with four different microcosm incubations were performed to assess the effects of IBPs and CROC on the removal of TPHs from petroleum-contaminated site soil. The results showed that the addition of IBPs and/or CROC could significantly promote the remediation of TPHs in soil. A CROC only played a significant role in the degradation of TPHs in deep soil. The combined application of IBPs and CROC had the best effect on the remediation of deep soil, and the removal rate of TPHs reached 70%, which was much higher than that of nature attenuation (13.2%) and IBPs (43.0%) or CROC (31.9%) alone. In particular, the CROC could better promote the degradation of heavy distillate hydrocarbons (HFAs) in deep soil, and the degradation rates of HFAs increased from 6.6% to 33.2%-21.0% and 67.9%, respectively. In addition, the IBPs and CROC significantly enhanced the activity of dehydrogenase, catalase, and lipase in soil. Results of the enzyme activity were the same as that of TPH degradation. The combined application of IBPs and CROC not only increased the microbial abundance and diversity of soil, but also significantly enhanced the enrichment of potential TPH-biodegrading bacteria. M. oxydans was dominant in AP (bioaugmentation with addition of IBPs) and APO (bioaugmentation with the addition of IBPs and CROC) microcosms that added IBPs. Overall, the IBPs and CROC developed in this study provide a novel option for the combination of bioaugmentation and biostimulation for remediating organic pollutants in soil.

Biodegradation half-lives of biodiesel fuels in aquatic and terrestrial systems: A review

Information on biodegradation kinetics of biodiesel fuels is a key aspect in risk and impact assessment practice and in selection of appropriate remediation strategies. Unfortunately, this information is scattered, while factors influencing variability in biodegradation rates are still not fully understood. Therefore, we systematically reviewed 32 scientific literature sources providing 142 biodegradation and 56 mineralization half-lives of diesel and biodiesel fuels in various experimental systems. The analysis focused on the variability in half-lives across fuels and experimental conditions, reporting sets of averaged half-life values and their statistical uncertainty. Across all data points, biodegradation half-lives ranged from 9 to 62 days, and were 2-5.5 times shorter than mineralization half-lives. Across all fuels, biodegradation and mineralization half-lives were 2.5-8.5 times longer in terrestrial systems when compared to aquatic systems. The half-lives were generally shorter for blends with increasing biodiesel content, although differences in number of data points from various experiments masked differences in half-lives between different fuels. This in most cases resulted in lack of statistically significant effects of the type of blends and experimental system on biodegradation half-lives. Our data can be used for improved characterization of risks and impacts of biodiesel fuels in aerobic aquatic and terrestrial environments, while more experiments are required to quantify biodegradation kinetics in anaerobic conditions. Relatively high biodegradability of biodiesel may suggest that passive approaches to degrade and dissipate contaminants in situ, like monitored natural attenuation, may be appropriate remediation strategies for biodiesel fuels.

Impacts of groundwater level fluctuation on soil microbial community, alkane degradation efficiency and alkane-degrading gene diversity in the critical zone: Evidence from an accelerated water table fluctuation simulation

Petroleum hydrocarbons are hazardous to ecosystems and human health, commonly containing n-alkanes and polycyclic aromatic hydrocarbons. Previous researches have studied alkane degraders and degrading genes under aerobic or anaerobic conditions, but seldom discussed them in the intermittent saturation zone which is a connective area between the vadose zone and the groundwater aquifer with periodic alteration of oxygen and moisture. The present study investigated the difference in alkane degradation efficiency, bacterial community, and alkane degrading gene diversity in aerobic, anaerobic, and aerobic-anaerobic fluctuated treatments. All biotic treatments achieved over 90% of n-alkane removal after 120 days of incubation. The removal efficiencies of n-alkanes with a carbon chain length from 16 to 25 were much higher in anaerobic scenarios than those in aerobic scenarios, explained by different dominant microbes between aerobic and anaerobic conditions. The highest removal efficiency was found in fluctuation treatments, indicating an accelerated n-alkane biodegradation under aerobic-anaerobic alternation. In addition, the copy numbers of the 16S rRNA gene and two alkB genes (alkB-P and alkB-R) declined dramatically when switched from aerobic to anaerobic scenarios and oppositely from anaerobic to aerobic conditions. This suggested that water level fluctuation could notably change the presence of aerobic alkane degrading genes. Our results suggested that alkane degradation efficiency, soil microbial community, and alkane-degrading genes were all driven by water level fluctuation in the intermittent saturation zone, helping better understand the effects of seasonal water table fluctuation on the biodegradation of petroleum hydrocarbons in the subsurface environment.

Natural Source Zone Depletion (NSZD) Quantification Techniques: Innovations and Future Directions

Natural source zone depletion (NSZD) is an emerging technique for sustainable and cost-effective bioremediation of light non-aqueous phase liquid (LNAPL) in oil spill sites. Depending on regulatory objectives, NSZD has the potential to be used as either the primary or sole LNAPL management technique. To achieve this goal, NSZD rate (i.e., rate of bulk LNAPL mass depletion) should be quantified accurately and precisely. NSZD has certain characteristic features that have been used as surrogates to quantify the NSZD rates. This review highlights the most recent trends in technology development for NSZD data collection and rate estimation, with a focus on the operational and technical advantages and limitations of the associated techniques. So far, four principal techniques are developed, including concentration gradient (CG), dynamic closed chamber (DCC), CO2 trap and thermal monitoring. Discussions revolving around two techniques, “CO2 trap” and “thermal monitoring”, are expanded due to the particular attention to them in the current industry. The gaps of knowledge relevant to the NSZD monitoring techniques are identified and the issues which merit further research are outlined. It is hoped that this review can provide researchers and practitioners with sufficient information to opt the best practice for the research and application of NSZD for the management of LNAPL impacted sites.

Tracking Mangrove Oil Bioremediation Approaches and Bacterial Diversity at Different Depths in an in situ Mesocosms System

In this study, oil spills were simulated in field-based mangrove mesocosms to compare the efficiency of bioremediation strategies and to characterize the presence of the alkB, ndo, assA, and bssA genes and the ecological structures of microbial communities in mangrove sediments at two different depths, (D1) 1–10 cm and (D2) 25–35 cm. The results indicated that the hydrocarbon degradation efficiency was higher in superficial sediment layers, although no differences in the hydrocarbon degradation rates or in the abundances of the alkB and ndo genes were detected among the tested bioremediation strategies at this depth. Samples from the deeper layer exhibited higher abundances of the analyzed genes, except for assA and bssA, which were not detected in our samples. For all of the treatments and depths, the most abundant phyla were Proteobacteria, Firmicutes and Bacteroidetes, with Gammaproteobacteria, Flavobacteriales and Clostridiales being the most common classes. The indicator species analysis (ISA) results showed strong distinctions among microbial taxa in response to different treatments and in the two collection depths. Our results indicated a high efficiency of the monitored natural attenuation (MNA) for oil consumption in the tested mangrove sediments, revealing the potential of this strategy for environmental decontamination and suggesting that environmental and ecological factors may select for specific bacterial populations in distinct niches.

Combining electrokinetic transport and bioremediation for enhanced removal of crude oil from contaminated marine sediments: Results of a long-term, mesocosm-scale experiment

Marine sediments represent an important sink of harmful petroleum hydrocarbons after an accidental oil spill. Electrobioremediation techniques, which combine electrokinetic transport and biodegradation processes, represent an emerging technological platform for a sustainable remediation of contaminated sediments. Here, we describe the results of a long-term mesocosm-scale electrobioremediation experiment for the treatment of marine sediments contaminated by crude oil. A dimensionally stable anode and a stainless-steel mesh cathode were employed to drive seawater electrolysis at a fixed current density of 11 A/m². This approach allowed establishing conditions conducive to contaminants biodegradation, as confirmed by the enrichment of Alcanivorax borkumensis cells harboring the alkB-gene and other aerobic hydrocarbonoclastic bacteria. Oil chemistry analyses indicated that aromatic hydrocarbons were primarily removed from the sediment via electroosmosis and low molecular weight alkanes (nC₆ to nC₁₀) via biodegradation.

Sorption of benzene and naphthalene on (semi)-arid coastal soil as a function of salinity and temperature

Considerable activities from the oil and natural gas sector have risen some concerns about the pollution of soil and groundwater by petroleum hydrocarbons (PHCs) in (semi)-arid coastal regions. The understanding of the fate and transport of PHCs in these regions is therefore necessary to develop strategies for remediation. To quantify the sorption rates of PHCs in (semi)-arid coastal soil environments, we conducted a series of controlled-laboratory batch experiments under variable temperature and salinity conditions. The soil samples were collected from the eastern coast of Qatar which is near the two largest off-shore oil and natural gas fields of the country (North Gas and Al-Shaheen Oil Fields), and the volatile benzene and naphthalene were used as PHCs. The characterization of soil samples showed sand classification with the texture class of sabkha and saline beach sandy soils with calcite as potential dominant mineral. The concentrations of dissolved chloride and sodium were found to be high (> 400 mg L^-1) with a chloride-to‑sodium ratio of about 1.7. The results of sorption experiments showed that the rates of naphthalene sorption were more than for benzene, where the initial aqueous concentrations of benzene and naphthalene were reduced at equilibrium due to sorption by about 14-25% and 65-79%, respectively. This difference was attributed mainly to the organic carbon-water partitioning coefficient which is higher for naphthalene. The sorption rate experiments showed that sorption was stronger for benzene under higher salinity and lower temperature conditions. The sorption of naphthalene was not affected by the change in salinity but increased by 18% when the temperature decreased from 35 to 5 °C. A sorption kinetic model was also applied to define the sorption behavior of benzene and naphthalene for the coastal soil collected in Qatar and the best fits were achieved with the Langmuir sorption isotherm.

BTEX exposure assessment and quantitative risk assessment among petroleum product distributors

The aim of this study was to evaluate benzene, toluene, ethylbenzene, and xylene (BTEX) exposure among workers at four stations of a major oil distribution company. Personal BTEX exposure samples were collected over working shift (8h) for 50 workers at four stations of a major oil distribution company in Iran. Measured mean values for workers across four sites were benzene (2437, 992, 584, and 2788μg/m³ respectively), toluene (4415, 2830, 1289, and 9407μg/m³), ethylbenzene (781, 522, 187, and 533μg/m³), and xylene (1134, 678, 322, and 525μg/m³). The maximum mean concentration measured across sites for benzene was 2788μg/m³ (Station 4), toluene was 9407μg/m³ (Station 4), ethylbenzene was 781μg/m³ (Station 1) and xylene was 1134μg/m³ (Station 1). The 8h averaged personal exposure benzene concentration exceeded the recommended value of 1600μg/m³ established by the Iranian Committee for Review and Collection of Occupational Exposure Limit and American Conference of Governmental Industrial Hygienists. Mean values for excess lifetime cancer risk for exposure to benzene were then calculated across workers at each site. Estimates of excess risk ranged from 1.74 ± 4.05 (Station 4) to 8.31 ± 25.81 (Station 3). Risk was assessed by calculation of hazard quotients and hazard indexes, which indicated that xylene and particularly benzene were the strongest contributors. Tanker loading was the highest risk occupation at these facilties. Risk management approaches to reducing exposures to BTEX compounds, especially benzene, will be important to the health of workers in Iran.

Remediation of Petroleum-contaminated Soil Using Bulrush Straw Powder, Biochar and Nutrients

The aim of this study was to determine the remediation efficiency of petroleum-contaminated soil from an oilfield using different types of remediation treatments under laboratory conditions. Compared with unamended soil as the control treatment (T1), soil samples were amended with bulrush straw powder (T2), with biochar alone (T3) and in combination with nutrients (nitrogen and phosphorus) (T4). The remediation experiment was carried out for 8 weeks. The extent of hydrocarbon degradation was monitored gravimetrically, and the residual oil fractions were analyzed by gas chromatography. The characteristics of the polluted soil (water-holding capacity and nutrients) were improved significantly by biochar addition (p < 0.05). The total microbial count increased significantly in the treatment containing biochar and added nutrients (t = 23.429, p = 0.002). The degradation of total petroleum hydrocarbons (TPH) and the main hydrocarbon fractions was higher in T3 and T4, especially in T4, than in T1 and T2. The intensities of the n-alkane fraction, C27-C29 steranes and C33-C35 homohopanes were efficiently decreased in T4 compared to the other treatments. According to the results, petroleum-contaminated soil can be remediated efficiently by adding biochar and nutrients simultaneously, and this combination of remediation was superior to that observed with added bulrush straw powder.

Bioaugmentation of soil contaminated with high-level crude oil through inoculation with mixed cultures including Acremonium sp

Heavy contamination of soil with crude oil has caused significant negative environmental impacts and presents substantial hazards to human health. To explore a highly efficient bioaugmentation strategy for these contaminations, experiments were conducted over 180 days in soil heavily contaminated with crude oil (50,000 mg kg(-1)), with four treatments comprised of Bacillus subtilis inoculation with no further inoculation (I), or reinoculation after 100 days with either B. subtilis (II), Acremonium sp.(III), or a mixture of both organisms (IV). The removal values of total petroleum hydrocarbons were 60.1 ± 2.0, 60.05 ± 3.0, 71.3 ± 5.2 and 74.2 ± 2.7 % for treatment (I-IV), respectively. Treatments (III-IV) significantly enhanced the soil bioremediation compared with treatments (I-II) (p < 0.05). Furthermore, significantly (p < 0.05) greater rates of degradation for petroleum hydrocarbon fractions were observed in treatments (III-IV) compared to treatments (I-II), and this was especially the case with the degradative rates for polycyclic aromatic hydrocarbons and crude oil heavy fractions. Dehydrogenase activity in treatment (III-IV) containing Acremonium sp. showed a constant increase until the end of experiments. Therefore reinoculation with pure fungus or fungal-bacterial consortium should be considered as an effective strategy in bioaugmentation for soil heavily contaminated with crude oil.

Potential of Sagittaria trifolia for Phytoremediation of Diesel

The phytoremediation potential and responses of Sagittaria trifolia to diesel were investigated. In order to elucidate the biochemical and physiological responses of S. trifolia to diesel, the chlorophyll content, root vitality, soluble protein content and antioxidant enzymes activity (peroxidase (POD), catalase (CAT) and antioxidant enzymes superoxide dismutase (SOD)) were determined in the plant tissues after 50 d of diesel treatment. The results showed the presence of S. trifolia significantly improved the removal ratios of diesel, from 21∼36% in the control soils to 54∼85% in the planted soils. The chlorophyll content, root vitality and soluble protein content all increased at low diesel concentration, then decreased at high diesel concentration. The activities of CAT and POD exhibited peak values at 5 g·kg(-1) diesel treatment and declined at higher diesel concentrations. However, the activity of SOD kept stable at lower diesel concentration (1 and 5 g·kg(-1)), and also declined at higher diesel concentration. Collectively, S. trifolia had the ability to tolerate certain amount of diesel, but when the concentration was up to 10 g·kg(-1), the growth of S. trifolia would be restrained. The results also showed that variation of antioxidant enzyme activity was an important response in plants to diesel pollution.

Ethanol-based in situ bioremediation of acidified, nitrate-contaminated groundwater

A novel approach for the in situ bioremediation of acidified, nitrate-contaminated groundwater was developed. Ethanol was introduced into the groundwater to enhance the activity of intrinsic denitrifying micro-organisms. Infiltration of the carbon source was made via an infiltration gallery constructed in the unsaturated zone to avoid clogging problems and to allow wider distribution of ethanol in the groundwater. The changes in the groundwater geochemistry and soil gas composition were monitored at the site to evaluate the efficiencies of the infiltration system and nitrate removal. Moreover, the impact of pH and ethanol addition on the denitrification rate was studied in laboratory. A reduction of 95% was achieved in the groundwater nitrate concentrations during the study. Neither clogging problems nor inefficient introduction of ethanol into the saturated zone were observed. Most crucial to the denitrifying communities was pH, values above 6 were required for efficient denitrification.

Assessment of ecological risks at former landfill site using TRIAD procedure and multicriteria analysis

Old industrial landfills are important sources of environmental contamination in Europe, including Finland. In this study, we demonstrated the combination of TRIAD procedure, multicriteria decision analysis (MCDA), and statistical Monte Carlo analysis for assessing the risks to terrestrial biota in a former landfill site contaminated by petroleum hydrocarbons (PHCs) and metals. First, we generated hazard quotients by dividing the concentrations of metals and PHCs in soil by the corresponding risk-based ecological benchmarks. Then we conducted ecotoxicity tests using five plant species, earthworms, and potworms, and determined the abundance and diversity of soil invertebrates from additional samples. We aggregated the results in accordance to the methods used in the TRIAD procedure, conducted rating of the assessment methods based on their performance in terms of specific criteria, and weighted the criteria using two alternative weighting techniques to produce performance scores for each method. We faced problems in using the TRIAD procedure, for example, the results from the animal counts had to be excluded from the calculation of integrated risk estimates (IREs) because our reference soil sample showed the lowest biodiversity and abundance of soil animals. In addition, hormesis hampered the use of the results from the ecotoxicity tests. The final probabilistic IREs imply significant risks at all sampling locations. Although linking MCDA with TRIAD provided a useful means to study and consider the performance of the alternative methods in predicting ecological risks, some uncertainties involved still remained outside the quantitative analysis.

Modeling of vapor intrusion from hydrocarbon-contaminated sources accounting for aerobic and anaerobic biodegradation

A one-dimensional steady state vapor intrusion model including both anaerobic and oxygen-limited aerobic biodegradation was developed. The aerobic and anaerobic layer thickness are calculated by stoichiometrically coupling the reactive transport of vapors with oxygen transport and consumption. The model accounts for the different oxygen demand in the subsurface required to sustain the aerobic biodegradation of the compound(s) of concern and for the baseline soil oxygen respiration. In the case of anaerobic reaction under methanogenic conditions, the model accounts for the generation of methane which leads to a further oxygen demand, due to methane oxidation, in the aerobic zone. The model was solved analytically and applied, using representative parameter ranges and values, to identify under which site conditions the attenuation of hydrocarbons migrating into indoor environments is likely to be significant. Simulations were performed assuming a soil contaminated by toluene only, by a BTEX mixture, by Fresh Gasoline and by Weathered Gasoline. The obtained results have shown that for several site conditions oxygen concentration below the building is sufficient to sustain aerobic biodegradation. For these scenarios the aerobic biodegradation is the primary mechanism of attenuation, i.e. anaerobic contribution is negligible and a model accounting just for aerobic biodegradation can be used. On the contrary, in all cases where oxygen is not sufficient to sustain aerobic biodegradation alone (e.g. highly contaminated sources), anaerobic biodegradation can significantly contribute to the overall attenuation depending on the site specific conditions.

Monitored natural attenuation

Monitored natural attenuation (MNA) is an in situ remediation technology that relies on naturally occurring and demonstrable processes in soil and groundwater which reduce the mass and concentration of the contaminants. Natural attenuation (NA) involves both aerobic and anaerobic degradation of the contaminants due to the fact that oxygen is used up near the core of the contaminant plume. The aerobic and anaerobic microbial processes can be assessed by microbial activity measurements and molecular biology methods in combination with chemical analyses. The sampling and knowledge on the site conditions are of major importance for the linkage of the results obtained to the conditions in situ. Rates obtained from activity measurements can, with certain limitations, be used in modeling of the fate of contaminants whereas most molecular methods mainly give qualitative information on the microbial community and gene abundances. However, molecular biology methods are fast and describe the in situ communities and avoid the biases inherent to activity assays requiring laboratory incubations.

[Not Available]

Relatively little is known about the microbial communities adapted to soil environments contaminated with aged complex hydrocarbon mixtures, especially in the subsurface soil layers. In this work we studied the microbial communities in two different soil profiles down to the depth of 7 m which originated from a 30-year-old site contaminated with petroleum hydrocarbons (PHCs) and from a clean site next to the contaminated site. The concentration of oxygen in the contaminated soil profile was strongly reduced in soil layers below 1 m depth but not in the clean soil profile. Total microbial biomass and community composition was analyzed by phospholipid fatty acid (PLFA) measurements. The diversity of fungi and actinobacteria was investigated more in detail by construction of rDNA-based clone libraries. The results revealed that there was a significant and diverse microbial community in subsoils at depth below 2 m, also in conditions where oxygen was limiting. The diversity of actinobacteria was different in the two soil profiles; the contaminated soil profile was dominated by Mycobacterium -related sequences whereas sequences from the clean soil samples were related to other, generally uncultured organisms, some of which may represent two new subclasses of actinobacteria. One dominating fungal sequence which matched with the ascomycotes Acremonium sp. and Paecilomyces sp. was identified both in clean and in contaminated soil profiles. Thus, although the relative amounts of fungi and actinobacteria in these microbial communities were highest in the upper soil layers, many representatives from these groups were found in hydrocarbon contaminated subsoils even under oxygen limited conditions.

Functional gene abundances (nahAc, alkB, xylE) in the assessment of the efficacy of bioremediation

In this study, we compared the mineralization rates of three selected (14)C-labeled hydrocarbon compounds, octacosane, toluene, and naphthalene, with the presence of the corresponding functional genes (alkB, xylE, nahAc) in a large number of soil samples representing different types of soil and petroleum hydrocarbon contamination. Functional genes were enumerated by the replicate limited dilution (RLD) polymerase chain reaction (PCR) technique. RLD-PCR was further compared to real-time PCR measurements for nahAc and xylE for some samples. At a heating oil-contaminated site, octacosane mineralization rates were higher (on average 0.0015 day(-1)) when compared to aerobic naphthalene and toluene mineralization (on average 0.00003 and 0.0007 day(-1)). The corresponding gene abundances measured by RLD-PCR were on average 0.95, 0.3, and 0.13 x 10(3) gene copies g(-1) soil for alkB, nahAc, and xylE, respectively. At a site contaminated with gasoline, the situation was the opposite: Toluene mineralization was the highest (on average 0.0031 day(-1)), and only xylE genes could be detected (on average 0.13 x 10(3) gene copies g(-1) soil by RLD-PCR). XylE and nahAc gene abundances were correlated with the (14)C-toluene and naphthalene mineralization activities, respectively, in samples from aerobic layers. AlkB gene abundances were not correlated with the octacosane mineralization. Real-time PCR was a more sensitive method than RLD-PCR by a factor of 1,200 for nahAc and 300 for xylE. In conclusion, functional gene abundances seemed to reflect the type of the contamination. With optimized assays, the gene abundances can be used to assess bioremediation efficacy.

Degradation rates of aged petroleum hydrocarbons are likely to be mass transfer dependent in the field

Evidence for on site biodegradation may be difficult to provide at heterogeneous sites without additional experiments in controlled laboratory conditions. In this study, microbial activities measured as CO2 and CH4 production were compared in situ, in intact soil cores and in bottle microcosms containing sieved soils. In addition, biodegradation rates were determined by measuring the decrease in petroleum hydrocarbon concentrations at 7 degrees C in aerobic and anaerobic conditions. Elevated concentrations of CO2 and CH4 in the soil gas phase indicated that both the aerobic and anaerobic microbial activity potentials were high at the contaminated site. Aerobic and anaerobic microbial degradation rates in laboratory experiments of petroleum hydrocarbons were highest in soils from the most contaminated point and degradation in the aerobic and anaerobic microcosms was linear throughout the incubation, indicating mass-transfer-dependent degradation. Different results for microbial activity measurements were obtained in laboratory studies depending on pretreatment and size of the sample, even when the environmental conditions were mimicked. These differences may be related to differences in the gas exchange rates as well as in changes in the bioavailability of the contaminant in different analyses. When predicting by modeling the behavior of an aged contaminant it is relevant to adapt the models in use to correspond to conditions relevant at the contaminated sites. The variables used in the models should be based on data from the site and on experiments performed using the original aged contaminant without any additions.

Novel upper meta-pathway extradiol dioxygenase gene diversity in polluted soil

For the determination of the catabolic community diversity that is related to biodegradation potential, we developed a protocol for the assessment of catabolic marker genes in polluted soils. Primers specific to upper pathway extradiol dioxygenase genes were designed which amplified a 469-bp product from Sphingomonas sp. HV3. The constructed primers were used in PCR amplification of upper pathway ring cleavage genes from DNA directly isolated from a mineral oil polluted landfill site, a mineral oil landfarming site and a birch rhizosphere-associated soil that was either artificially polluted with a PAH mixture or not polluted. Amplicons were cloned and subjected to restriction fragment length polymorphism analysis dividing the HhaI-digested products into operational taxonomic units. Altogether 26 different operational taxonomic units were detected with the sequence similarity to known catabolic genes of Alpha-, Beta-, and Gammaproteobacteria. Phylogenetic analysis divided the operational taxonomic units from the polluted soils into seven clusters. Two contained exclusively sequences with no close homologues in the database, therefore representing novel catabolic genes. This large proportion of novel extradiol sequences shows that there is an extensive unknown catabolic diversity in polluted environments.

Occurrence and rates of terminal electron-accepting processes and recharge processes in petroleum hydrocarbon-contaminated subsurface

The occurrence and rates of terminal electron acceptor processes, and recharge processes in the unsaturated zone of a boreal site contaminated with petroleum hydrocarbons in the range C(10) to C(40) were examined. Soil microcosms were used to determine the rates of denitrification, iron (Fe) reduction, sulfate (SO(4)) reduction, and methanogenesis in two vertical soil profiles contaminated with oil, and in a noncontaminated reference sample. Furthermore, the abundances of the 16S rRNA genes belonging to Geobacteracaea in the samples were determined by real-time quantitative polymerase chain reaction (PCR). Analyses of ground water chemistry and soil gas composition were also performed together with continuous in situ monitoring of soil water and ground water chemistry. Several lines of evidence were obtained to demonstrate that both Fe reduction and methanogenesis played significant roles in the vertical profiles: Fe reduction rates up to 3.7 nmol h(-1) g(-1) were recorded and they correlated with the abundances of the Geobacteracaea 16S rRNA genes (range: 2.3 x 10(5) to 4.9 x 10(7) copies g(-1)). In the ground water, ferrous iron (Fe(2+)) concentration up to 55 mg L(-1) was measured. Methane production rates up to 2.5 nmol h(-1) g(-1) were obtained together with methane content up to 15% (vol/vol) in the soil gas. The continuous monitoring of soil water and ground water chemistry, microcosm experiments, and soil gas monitoring together demonstrated that the high microbial activity in the unsaturated zone resulted in rapid removal of oxygen from the infiltrating recharge thus leaving the anaerobic microbial processes dominant below 1.5 m depth both in the unsaturated and the saturated zones of the subsurface.

Biodegradation of short-chain n-alkanes in oil sands tailings under methanogenic conditions

The biodegradation of a mixture of low molecular weight n-alkanes (C6, C7, C8, and C10) was assessed under methanogenic conditions using mature fine tailings (MFT) produced by the oil sands industry in Alberta, Canada. Microorganisms present in the MFT mineralized the added n-alkane mixture, producing 16.2 (+/- 0.3) or 20.5 (+/- 0.1) mmol of methane in the headspace of microcosms spiked with 0.2% or 0.5% w/v n-alkanes, respectively, during 29 weeks of incubation. The spiked n-alkanes biodegraded in the sequence C10 > C8 > C7 > C6. Degradation of 100% C10, 97% C8, 74% C7, and 44% C6 occurred in a mixture of n-alkanes in the MFT spiked at 0.2% after 25 weeks of incubation. The same pattern of biodegradation was also observed in the MFT spiked with 0.5% n-alkanes. Stoichiometric calculations confirmed the mineralization of the degraded n-alkanes to methane. This study showed that the short-chain n-alkanes, which comprise a significant portion of the unrecovered naphtha used in bitumen extraction and released into the settling basins, can be biodegraded into methane. These findings may influence decisions regarding extraction processes and long-term management of MFT, and they suggest that intrinsic, methanogenic metabolism of these n-alkanes may occur in other anoxic environments.

The abundance of nahAc genes correlates with the 14C-naphthalene mineralization potential in petroleum hydrocarbon-contaminated oxic soil layers

In this study, we evaluated whether the abundance of the functional gene nahAc reflects aerobic naphthalene degradation potential in subsurface and surface samples taken from three petroleum hydrocarbon contaminated sites in southern Finland. The type of the contamination at the sites varied from lightweight diesel oil to high molecular weight residuals of crude oil. Samples were collected from both oxic and anoxic soil layers. The naphthalene dioxygenase gene nahAc was quantified using a replicate limiting dilution-polymerase chain reaction (RLD-PCR) method with a degenerate primer pair. In the non-contaminated samples nahAc genes were not detected. In the petroleum hydrocarbon-contaminated oxic soil samples nahAc gene abundance [range 3 x 10(1)-9 x 10(4) copies (g dry wt soil)(-1)] was correlated (Kendall non-parametric correlation r2=0.459, p<0.01) with the aerobic 14C-naphthalene mineralization potential (range 1 x 10(-5)-0.1 d(-1)) measured in microcosms at in situ temperatures (8 degrees C for subsurface and 20 degrees C for surface soil samples). In these samples nahAc gene abundance was also correlated with total microbial cell counts (r2=0.471, p<0.01), respiration rate (r2=0.401, p<0.01) and organic matter content (r2=0.341, p<0.05). NahAc genes were amplified from anoxic soil layers indicating that, although involved in aerobic biodegradation of naphthalene, these genes or related sequences were also present in the anoxic subsurface. In the samples taken from the anoxic layers, the aerobic 14C-naphthalene mineralization rates were not correlated with nahAc gene abundance. In conclusion, current sequence information provides the basis for a robust tool to estimate the naphthalene degradation potential at oxic zones of different petroleum hydrocarbon-contaminated sites undergoing in situ bioremediation.

Use of potassium formate in road winter deicing can reduce groundwater deterioration

We present here an aquifer scale study on the fate of potassium formate, an alternative, weakly corrosive deicing agent in soil and subsurfaces. Potassium formate was used to deice a stretch of a highway in Finland. The fate of the formate was examined by monitoring the groundwater chemistry in the underlying aquifer of which a conceptual model was constructed. In addition, we determined aerobic and anaerobic biodegradation rates of formate at low temperatures (-2 to +6 degrees C) in soil microcosms. Our results show that the formate did not enter the saturated zone through the thin vadose zone; thus, no undesirable changes in the groundwater chemistry were observed. Furthermore, the conceptual model explained the distribution of chloride in the aquifer used in deicing for the past 30 years. We recorded mineralization potential up to 97% and up to 17% within 24 h under aerobic and anaerobic conditions, respectively, in the soil and subsurface samples obtained from the site. This demonstrates that biodegradation in the topsoil layers was responsible for the removal of the formate. We conclude that the use of potassium formate can potentially help diminish the negative impacts of road winter deicing on groundwater without jeopardizing traffic safety.

Biodegradation of xenobiotics by anaerobic bacteria

Xenobiotic biodegradation under anaerobic conditions such as in groundwater, sediment, landfill, sludge digesters and bioreactors has gained increasing attention over the last two decades. This review gives a broad overview of our current understanding of and recent advances in anaerobic biodegradation of five selected groups of xenobiotic compounds (petroleum hydrocarbons and fuel additives, nitroaromatic compounds and explosives, chlorinated aliphatic and aromatic compounds, pesticides, and surfactants). Significant advances have been made toward the isolation of bacterial cultures, elucidation of biochemical mechanisms, and laboratory and field scale applications for xenobiotic removal. For certain highly chlorinated hydrocarbons (e.g., tetrachlorethylene), anaerobic processes cannot be easily substituted with current aerobic processes. For petroleum hydrocarbons, although aerobic processes are generally used, anaerobic biodegradation is significant under certain circumstances (e.g., O(2)-depleted aquifers, oil spilled in marshes). For persistent compounds including polychlorinated biphenyls, dioxins, and DDT, anaerobic processes are slow for remedial application, but can be a significant long-term avenue for natural attenuation. In some cases, a sequential anaerobic-aerobic strategy is needed for total destruction of xenobiotic compounds. Several points for future research are also presented in this review.

Biodegradabilities of some chain oils in groundwater as determined by the respirometric BOD OxiTop method

The respirometric BOD OxiTop method was used to monitor the biodegradation of different chain oils (mineral, rapeseed and tall oils) over 28 days in groundwater, as well as in standard conditions described by OECD 301 F. The aim of the study was to gather more information about the biodegradability of forestry oils in groundwater, as well as about the suitability of the automatic OxiTop method for biodegradation measurements. The BOD OxiTop method proved to be a precise and reliable technique for determining the biodegradations of different oils. Some comparative studies were also made using a traditional IR method in order to clarify the total oil concentrations. The results show that if biodegradation only is to be monitored, the OxiTop method is preferable. This is due to the influence of other reactions aside from biodegradation on total hydrocarbon concentrations when using the IR method.