PAH Degradation Research Articles

Assessment of the Deepwater Horizon oil spill impact on Gulf coast microbial communities

One of the major environmental concerns of the Deepwater Horizon oil spill in the Gulf of Mexico was the ecological impact of the oil that reached shorelines of the Gulf Coast. Here we investigated the impact of the oil on the microbial composition in beach samples collected in June 2010 along a heavily impacted shoreline near Grand Isle, Louisiana. Successional changes in the microbial community structure due to the oil contamination were determined by deep sequencing of 16S rRNA genes. Metatranscriptomics was used to determine expression of functional genes involved in hydrocarbon degradation processes. In addition, potential hydrocarbon-degrading Bacteria were obtained in culture. The 16S data revealed that highly contaminated samples had higher abundances of Alpha- and Gammaproteobacteria sequences. Successional changes in these classes were observed over time, during which the oil was partially degraded. The metatranscriptome data revealed that PAH, n-alkane, and toluene degradation genes were expressed in the contaminated samples, with high homology to genes from Alteromonadales, Rhodobacterales, and Pseudomonales. Notably, Marinobacter (Gammaproteobacteria) had the highest representation of expressed genes in the samples. A Marinobacter isolated from this beach was shown to have potential for transformation of hydrocarbons in incubation experiments with oil obtained from the Mississippi Canyon Block 252 (MC252) well; collected during the Deepwater Horizon spill. The combined data revealed a response of the beach microbial community to oil contaminants, including prevalence of Bacteria endowed with the functional capacity to degrade oil.

Isolation of a high molecular weight polycyclic aromatic hydrocarbon-degrading strain and its enhancing the removal of HMW-PAHs from heavily contaminated soil

A high molecular weight polycyclic aromatic hydrocarbons (HMW-PAHs)-degrading strain, designed P10, was isolated from PAHs contaminated soil. Strain P10 was preliminarily identified as Kocuria sp. based on the analysis of 16S rRNA gene sequence. Degradation of individual PAHs was investigated in basal salt medium using PAH as sole carbon and energy source. The results showed that strain P10 could degrade several PAHs including HMW-PAHs, such as fluorene, fluoranthene and indeno[1,2,3-cd]pyrene with degrading percentages of 83.2%, 76.5% and 59.6%, respectively, after incubation for 14 days at 25 °C. Bioremediation experiments of HMW-PAHs heavily contaminated soil were also carried out using strain P10 as inoculum in weathered plots under natural conditions. The results indicated that strain P10 could significantly enhance the removal of HMW-PAHs from the contaminated soil. The removal percentages were increased by about 2-folds for HMW-PAHs in comparison to the non-inoculated one.

Chromium as an inhibitor of PAHs degradation in deposed sewage sludge

The aim of the investigation was to estimate the impact of the presence of chromium ions on decrease in PAHs concentration in sewage sludge stored under aerobic conditions. The studies were carried out using dewatered and biochemically stabilized sludges. The changes in the concentration of PAHs were followed in five series: in sludge samples taken after filter press (biotic samples—control samples), in sludge samples with added sodium azide (abiotic samples), in sludge with the addition of a standard PAH mixture, in sludge with added chromium(III) chloride, and in sludge with the addition of both the standard PAH mixture and Cr. The Cr was added into the sludges samples as a solution of chromium(III) chloride. The sludge samples were incubated for 12 weeks. Determination of PAHs in sludge samples was made at the beginning of the experiment (the initial concentration) and then six times over 2 weeks. The gas chromatography–mass spectrometry was used for qualification and quantification of PAHs. Six PAHs listed by EPA were identified: benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, dibenzo(a,h)anthracene, benzo(g,h,i)perylene, and indeno(1,2,3,c,d)pyrene. In sludges taken from municipal treatment plant, the average PAHs concentration was 289 μg/kg d.m. The inhibition of PAH degradation was found in sludges supplemented with chromium chloride (final average PAH concentration in modified sludges was four times higher than in the control sample).

Electrochemical Degradation of PAHs in Produced Water Using Ti/Sb2O5-SnO2-IrO2 Anode

Electrochemical Degradation of PAHs in Produced Water Using Ti/Sb2O5-SnO2-IrO2 Anode

Biotechnological procedures to select white rot fungi for the degradation of PAHs

White rot fungi are essential in forest ecology and are deeply involved in wood decomposition and the biodegradation of various xenobiotics. The fungal ligninolytic enzymes involved in these processes have recently become the focus of much attention for their possible biotechnological applications. Successful bioremediation requires the selection of species with desirable characteristics. In this study, 150 taxonomically and physiologically diverse white rot fungi, including 55 species, were investigated for their performance in a variety of biotechnological procedures, such as dye decolorization, gallic acid reaction, ligninolytic enzymes, and tolerance to four PAHs, phenanthrene, anthracene, fluoranthene, and pyrene. Among these fungi, six isolates showed the highest (>90%) tolerance to both individual PAH and mixed PAHs. And six isolates oxidized gallic acid with dark brown color and they rapidly decolorized RBBR within ten days. These fungi revealed various profiles when evaluated for their biotechnological performance to compare the capability of degradation of PAHs between two groups selected. As the results demonstrated the six best species selected from gallic acid more greatly degraded four PAHs than the other isolates selected via tolerance test. It provided that gallic acid reaction test can be performed to rank the fungi by their ability to degrade the PAHs. Most of all, Peniophora incarnata KUC8836 and Phlebia brevispora KUC9033 significantly degraded the four PAHs and can be considered prime candidates for the degradation of xenobiotic compounds in environmental settings.

Polycyclic Aromatic Hydrocarbons in Rainwater Collected in a Tropical Polluted Urban Area

Polycyclic aromatic hydrocarbons present in rainwater were studied in two distinct areas in Mexico City Metropolitan Area throughout the rainy season. The results showed no significant difference between the two sites, thus suggesting a more regional phenomenon driving the dissolution of the PAHs in the rain. The PAHs concentration ranged from 1.7–30.2 ngL−1with the predominance of phenanthrene, fluoranthene, and pyrene. The PAH sources were traced predominantly to vehicular emission with signature PAHs, diagnostic ratios, and cluster statistical analyses. On the other hand, the temporal analysis of the PAHs showed that the fluxes of the Total PAH were slightly different for both sites. The urban-industrial site showed fluxes that ranged from 145–3263 ng m−2d−1, while the urban site ranged from 134–3139 ng m−2d−1, with the urban site having a moderate rate at which the total PAHs diminished throughout the rainy season while the urban-industrial showed no change throughout the rainy season. This study also addressed two occurrences when studying PAHs in rain: the degradation of PAHs in the samples with acidic rain and the dilution of the PAH in the samples with continued collection of rain.

Tourmaline combined with Phanerochaete chrysosporium to remediate agricultural soil contaminated with PAHs and OCPs

The potential application on tourmaline was explored. The combination of tourmaline and Phanerochaete chrysosporium was conducted to remediate the field soil from the Dagu Drainage River bank of Tianjin in China. The total PAH and OCP concentrations in the soil were 6.4±0.05 and 145.9±1.9mg/kg, respectively. During the 60 day remediation program, the remediation degradation rates of all the 16 U.S. EPA priority PAHs and OCPs were 53.2±4.7% and 43.5±3.1%, respectively. The PAH and OCP removal rates were 31.9±2.9% and 26.4±1.8%, respectively, in soil with the addition of tourmaline, and the removal rates were 40.5±2.3% and 34.2±3.9%, respectively, in soil with the addition of P. chrysosporium. Thus, the combination of tourmaline and P. chrysosporium promoted the bioremediation rate of PAHs and OCPs in the soil, compared with the rates obtained using tourmaline or P. chrysosporium individually for the remediation of PAH and OCP degradation. In addition, tourmaline can promote the generation of soil hydrogen peroxidase and invertase enzyme, significantly increase the indigenous bacterial community and the number of PAH and OCP-degraders compared to those in the control, and reduce the soil humic acid content. Hence, the present study provides a potential alternative for the remediation of soils contaminated by PAHs and OCPs.

Alkyl Polyglucoside (APG) Amendment for Improving the Phytoremediation of Pb-PAH Contaminated Soil by the AquaticPlant Scirpus triqueter

This study assessed the potential abilities of Scirpus triqueter for phytoremediation of soils contaminated with Pb-PAHs, amended with environment-friendly surfactant alkyl polyglucoside (APG). The effects of APG on the removal of PAHs from soil and the plant uptake and translocation of Pb were tested with plant growth and soil enzymatic activities. Experiments demonstrated that APG has an ability to facilitate PAH degradation and Pb uptake in the plant body at appropriate concentrations (20–40mg L−1). The highest PAH removal rate was observed in 30 mg L−1 APG treatment, and the highest accumulation of Pb was detected as 40 mg L−1 APG. Experiments documented the effects of APG on plant growth, soil enzymatic activity, bioaccumulation and translocation of Pb in Scirpus triqueter. Results indicated that the addition of appropriate APG enhanced PAH removal rate and increased plant uptake and translocation of Pb.

On the effects of the dispersant Corexit 9500© during the degradation process of n-alkanes and PAHs in marine sediments

In many coastal countries, oil spill contingency plans include several alternatives for removal of the spilled oil from the ocean. Frequently, these plans include dispersants. Because this process applies chemical substances that may add toxicity to oil that already contains toxic compounds, it is, at times, a controversial method to fight oil pollution. Additionally, local conditions may result in particular complications. We investigated the possible effects of the dispersant Corexit 9500© under conditions similar to those of subtropical oceans. We used fuel oil #6+ diesel as the test mixture. Under certain conditions, at least part of the dispersed oil may reach the sediment, particularly if the dispersant is applied in coastal waters. Nine experimental units were used in this experiment. Similar conditions of water temperature, salinity, air fluxes into the experimental units, and hydrocarbon concentrations in sediments were used. Two treatments and one control, each one with three replicates, were carried out. We concentrated our investigation on sediment, although measurements of water were also taken. Our results suggest that once the oil has penetrated the sediment, no significant differences exist between oil that contains dispersant and oil without dispersant. Noticeable degradation of aliphatic hydrocarbons occurred mainly in the low molecular weight aliphatic hydrocarbons and not in the others. Apparently, degradation of aromatics was easier than that of alkanes. However, some differences were noticed for the degradation of PAHs in the sediment, suggesting a faster degradation under particular conditions in aerobic environments such as under this experiment.

Bioaccessibility-based predictions for estimating PAH biodegradation efficacy – Comparison of model predictions and measured endpoints

In this study, PAH biodegradation was assessed in historically contaminated soils collected from former manufacturing gas plant (MGP), wood preservation (WPS) and tram yard (TY) sites. Measured enhanced natural attenuation (ENA) endpoints were compared to bioaccessibility-based endpoint predictions (i.e. using non-exhaustive extraction or oxidation methodologies) to determine the suitability of previously published bioaccessibility–biodegradability models for predicting the efficacy of bioremediation. Under ENA conditions, the concentration of total PAHs in MGP, WPS and TY was reduced by 24.7, 22.4 and 41.7% respectively, however, the extent of PAH removal varied for individual compounds with limited degradation of the high molecular weight PAHs. PAH bioaccessibility assessment using butanol, hydroxypropyl-β-cyclodextrin (HP-β-CD) extraction or persulfate oxidation gave varying results with butanol extraction providing the highest estimates of individual PAH bioaccessibility (27.3–97.4%). Similarly, when bioaccessibility data were used as input values into bioaccessibility–biodegradability linear regression models, butanol extraction predicted the greatest extent of PAH biodegradability. When predicted and measured biodegradation endpoints were compared, a high correlation (R2 = 0.62) was observed for predictions using HP-β-CD extraction and the model of Reid et al. (2000), however, discrepancies were highlighted following Bland–Altman analysis. These discrepancies may be overcome by strengthening model correlation and validation by increasing the size of the data set (number of soils) which vary in soil characteristics and contaminant loading.

Abilities and genes for PAH biodegradation of bacteria isolated from mangrove sediments from the central of Thailand

PAH-degrading bacteria, including Novosphingobium sp. PCY, Microbacterium sp. BPW, Ralstonia sp. BPH, Alcaligenes sp. SSK1B, and Achromobacter sp. SSK4, were isolated from mangrove sediments. These isolates degraded 50–76% of 100mg/l phenanthrene within 2weeks. Strains PCY and BPW also degraded pyrene at 98% and 71%, respectively. Furthermore, all of them probably produced biosurfactants in the presence of hydrocarbons. Interestingly, PCY has a versatility to degrade various PAHs. Molecular techniques and plasmid curing remarkably revealed the presence of the alpha subunit of pyrene dioxygenase gene (nidA), involving in its pyrene/phenanthrene degrading ability, located on megaplasmid of PCY which has never before been reported in sphingomonads. Moreover, genes encoding ferredoxin, reductase, extradiol dioxygenase (bphA3A4C) and exopolysaccharide biosynthetase, which may be involved in PAH degradation and biosurfactant production, were also found in PCY. Therefore, we conclude that these isolates, especially PCY, can be the candidates for use as inoculums in the bioremediation.

Formation of nitro-PAHs from the heterogeneous reaction of ambient particle-bound PAHs with N2O5/NO3/NO2.

Reactions of ambient particles collected from four sites within the Los Angeles, CA air basin and Beijing, China with a mixture of N2O5, NO2, and NO3 radicals were studied in an environmental chamber at ambient pressure and temperature. Exposures in the chamber system resulted in the degradation of particle-bound PAHs and formation of molecular weight (mw) 247 nitropyrenes (NPYs) and nitrofluoranthenes (NFLs), mw 273 nitrotriphenylenes (NTPs), nitrobenz[a]anthracenes (NBaAs), nitrochrysene (NCHR), and mw 297 nitrobenzo[a]pyrene (NBaP). The distinct isomer distributions resulting from exposure of filter-adsorbed deuterated fluoranthene to N2O5/NO3/NO2 and that collected from the chamber gas-phase suggest that formation of NFLs in ambient particles did not occur by NO3 radical-initiated reaction but from reaction of N2O5, presumably subsequent to its surface adsorption. Accordingly, isomers known to result from gas-phase radical-initiated reactions of parent PAHs, such as 2-NFL and 2- and 4-NPY, were not enhanced from the exposure of ambient particulate matter to N2O5/NO3/NO2. The reactivity of ambient particles toward nitration by N2O5/NO3/NO2, defined by relative 1-NPY formation, varied significantly, with the relative amounts of freshly emitted particles versus aged particles (particles that had undergone atmospheric chemical processing) affecting the reactivity of particle-bound PAHs toward heterogeneous nitration. Analyses of unexposed ambient samples suggested that, in nighttime samples where NO3 radical-initiated chemistry had occurred, heterogeneous formation of 1-NPY on ambient particles may have contributed to the ambient 1-NPY concentrations at downwind receptor sites. These results, together with observations that 2-NFL is consistently the dominant particle-bound nitro-PAH measured in ambient atmospheres, suggest that for PAHs that exist in both the gas- and particle-phase, the heterogeneous formation of particle-bound nitro-PAHs is a minor formation route compared to gas-phase formation.

Microcosm evaluation of autochthonous bioaugmentation to combat marine oil spills

Oil spills can be disastrous to any ecosystem. Bioremediation through bioaugmentation (addition of oil-degrading bacteria) and biostimulation (addition of nutrients N&P) options can be a promising strategy for combating oil spills following first response actions. However, bioaugmentation is one of the most controversial issues of bioremediation since nutrient addition alone has a greater effect on oil biodegradation than the addition of microbial products that are highly dependent on environmental conditions. There is increasing evidence that the best way to overcome the above barriers is to use microorganisms from the polluted area, an approach proposed as autochthonous bioaugmentation (ABA) and defined as the bioaugmentation technology that uses exclusively microorganisms indigenous to the sites (soil, sand, and water) to be decontaminated. In this study, we examined the effectiveness of an ABA strategy for the successful remediation of polluted marine environments. A consortium was enriched from seawater samples taken from Elefsina Gulf near the Hellenic Petroleum Refinery, a site exposed to chronic crude oil pollution. Pre-adapted consortium was tested alone or in combination with inorganic nutrients in the presence (or not) of biosurfactants (rhamnolipids) in 30-day experiments. Treatment with fertilizers in the presence of biosurfactants exhibited the highest alkane and PAH degradation and showed highest growth over a period of almost 15 days. Considering the above, the use of biostimulation additives in combination with naturally pre-adapted hydrocarbon degrading consortia has proved to be a very effective treatment and it is a promising strategy in the future especially when combined with lipophilic fertilizers instead of inorganic nutrients. Such an approach becomes more pertinent when the oil spill approaches near the shoreline and immediate hydrocarbon degradation is needed.

Avoidance Test for the Assessment of Microbial Degradation of PAHs

Removed due to plagiarism. The original was published as follows: Lors, C., Martínez Aldaya, M., Salmon, S., Ponge, J.F., 2006. Use of anavoidance test for the assessment of microbial degradation of PAHs. SoilBiology and Biochemistry 38:2199-2204www.elsevier.com/locate/soilbio

Dominant petroleum hydrocarbon-degrading bacteria in the Archipelago Sea in South-West Finland (Baltic Sea) belong to different taxonomic groups than hydrocarbon degraders in the oceans

The natural petroleum hydrocarbon degrading capacity of the Archipelago Sea water in S-W Finland was studied in a microcosm experiment. Pristine and previously oil exposed sites were examined. Bacterial community fingerprinting was performed using terminal restriction fragment length polymorphism (T-RFLP) and samples from selected microcosms were sequenced. The abundance of PAH degradation genes was measured by quantitative PCR. Bacterial communities in diesel exposed microcosms diverged from control microcosms during the experiment. Gram positive PAH degradation genes dominated at both sites in situ, whereas gram negative PAH degrading genes became enriched in diesel microcosms. The dominant bacterial groups after a 14 days of diesel exposure were different depending on the sampling site, belonging to the class Actinobacteria (32%) at a pristine site and Betaproteobacteria (52%) at a previously oil exposed site. The hydrocarbon degrading bacteria in the Baltic Sea differ from those in the oceans, where most hydrocarbon degraders belong to Gammaproteobacteria.

Biodegradation of benzo(a)pyrene mediated by catabolic enzymes of bacteria

An investigation was carried out to compare the ability of two bacteria Pseudomonas aeruginosa PSA5 and Rhodococcus sp. NJ2 isolated from petroleum sludge for degradation of benzo(a)pyrene [B(a)P], a HMW PAH compound in MSM. During 25 days of incubation, 50 ppm B(a)P was degraded by 88 and 47 % by P. aeruginosa PSA5 and Rhodococcus sp. NJ2, respectively. Besides, involvement of different catabolic enzymes, that is, salicylate hydroxylase, 2-carboxybenzaldehyde dehydrogenase, catechol 1,2-dioxygenase and catechol 2,3-dioxygenase, was also examined to identify their differential role in B(a)P degradation. Among these enzymes, the highest induction of 2-carboxybenzaldehyde dehydrogenase (773.5 nmol mg−1 protein) was recorded in P. aeruginosa PSA5, while salicylate hydroxylase was highly expressed (839.6 nmol mg−1 protein) in Rhodococcus sp. NJ2. Both the bacteria were found biosurfactant (glycolipid) producing, and role of biosurfactant in PAH degradation was also ascertained by reduced surface tension, higher emulsification index and increased cell surface hydrophobicity.

Interaction effects of polycyclic aromatic hydrocarbons and heavy metals on a soil microalga, Chlorococcum sp. MM11

Environmental risk assessment of sites contaminated with chemicals needs to also consider mixtures of chemicals as these toxicants act more differently in a mixture than when they occur alone. In this study, we describe, for the first time, the use of a full factorial design experiment to evaluate the toxicity of a quaternary mixture comprising two polycyclic aromatic hydrocarbons (PAHs; benzo[a]pyrene (BaP) and phenanthrene (Phe)) and two heavy metals (cadmium (Cd) and lead (Pb)) toward a soil microalga, Chlorococcum sp. MM11. Biomass, in terms of cell number, and proline accumulation were used to evaluate toxicity responses. Factorial analysis of the data revealed statistically significant interaction effects between the mixtures of toxicants on 96-h biomass endpoint, while no significant interaction effects were observed on proline accumulation in the microalga. A comparison of the data on the toxicity of individual chemicals and those of the factorial main effect analysis clearly showed that Cd is more toxic to the alga, followed by BaP, Pb, and Phe. There was a substantial heavy metal accumulation and PAH degradation by the strain MM11 at EC10 and EC50 of the chemical mixtures.

Experimental increase in availability of a PAH complex organic contamination from an aged contaminated soil: Consequences on biodegradation

Although high PAH content and detection of PAH-degraders, the PAH biodegradation is limited in aged-contaminated soils due to low PAH availability (i.e., 1%). Here, we tried to experimentally increase the soil PAH availability by keeping both soil properties and contamination composition. Organic extract was first removed and then re-incorporated in the raw soil as fresh contaminants. Though drastic, this procedure only allowed a 6-time increase in the PAH availability suggesting that the organic constituents more than ageing were responsible for low availability. In the re-contaminated soil, the mineralization rate was twice more important, the proportion of 5–6 cycles PAH was higher indicating a preferential degradation of lower molecular weight PAH. The extraction treatment induced bacterial and fungal community structures modifications, Pseudomonas and Fusarium solani species were favoured, and the relative quantity of fungi increased. In re-contaminated soil the percentage of PAH-dioxygenase gene increased, with 10 times more Gram negative representatives.

The Effect of pH Value on the Polycyclic Aromatic Hydrocarbons Degradation in Sludge during Biological Aerobic Fermentation Process

The degradation of polycyclic aromatic hydrocarbons in sludge in aerobic fermentation process is affected by many factors, and the pile body pH value is one of the important factors. Through the test of mixing lime pile body regulating pH value (7.7, 8.2, 9), the polycyclic aromatic hydrocarbon degradation effect was researched under the different pH conditions and the same of the other aerobic fermentation conditions. The results showed that, pH=7.7 test device (not mixing lime ) on PAHs degradation effect was best, worst was the pH=8.2 test device, the sludge degradation of the polycyclic aromatic hydrocarbons effect is negative effect.

Assessing microbial carbon sources and potential PAH degradation using natural abundance 14C analysis

Natural abundance 14C analysis was applied to PLFAs collected from an industrial site in southern Ontario in order to assess microbial carbon sources and potential PAH biodegradation in soils. Δ14C of microbial phospholipid fatty acids (PLFA) at the site ranged from +54‰ to −697‰. Comparison of these values to surrounding carbon sources found that microbial carbon sources were derived primarily from vegetation and/or natural organic matter present in the soils rather than PAHs. This study highlights that microbes are able to utilize almost all available pools of organic matter including older pools which are thought to contain recalcitrant compounds. Furthermore, it shows that even with the presence of an active microbial community, there may be little biodegradation of PAHs. This study illustrates challenges in assessing microbial activity in the environment and the advantage of using natural abundance 14C analysis as a tool to elucidate microbial carbon sources.