Degradation of High Molecular Weight PAHs in Contaminated Soil by a Bacterial Consortium: Effects on Microtox and Mutagenicity Bioassays

Bioaugmentation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil was investigated using a mixed bacterial culture (community five) isolated from an abandoned industrial site. Community five was inoculated into contaminated soil containing a total PAH (two- to five-ring compounds) concentration of approximately 820 mg/kg soil. PAH degradation by the indigenous microbial population was restricted to the lower molecular weight compounds (naphthalene, acenaphthene, fluorene and phenanthrene) even with yeast extract addition: these compounds decreased by 14 to 37%, in soil hydrated to 50% water capacity, following 91 days of incubation at 24°C. Inoculation of community five into this PAH-contaminated soil resulted in significant decreases in the concentration of all PAHs over the incubation period: greater than 86% of naphthalene, acenaphthene, fluorene, and phenanthrene were degraded after 91 days, while anthracene, fluoranthene, and pyrene were degraded to lesser extents (51.7 to 57.6%). A lag period of 48 to 63 days was observed before the onset of benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene removal. However, significant decreases in the concentration of these compounds (32.6, 25.2, and 18.5%, respectively) were observed after 91 days. No significant decrease in the mutagenic potential of organic soil extracts (as measured by the Ames Test) was observed after incubation of the soil with the indigenous microflora; however, the Microtox toxicity of aqueous soil extracts was reduced sevenfold. In contrast, extracts from contaminated soil inoculated with community five underwent a 43% decrease in mutagenic potential and the toxicity was reduced 170-fold after 91 days incubation. These observations suggest that community five could be utilised for the detoxification of PAH-contaminated soil.     

Predicting the Efficacy of Polycyclic Aromatic Hydrocarbon Bioremediation in Creosote-Contaminated Soil Using Bioavailability Assays

Nonexhaustive extraction (propanol, butanol, hydroxypropyl-β-cyclodextrin [HPCD]), persulfate oxidation and biodegradability assays were employed to determine the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in creosote-contaminated soil. After 16 weeks incubation, greater than 89% of three-ring compounds (acenaphthene, anthracene, fluorene, and phenanthrene) and 21% to 79% of four-ring compounds (benz[a]anthracene, chrysene, fluoranthene, and pyrene) were degraded by the indigenous microorganisms under biopile conditions. No significant decrease in five- (benzo[a]pyrene, benzo[b+k]fluoranthene) and six-ring compounds (benz[g,h,i]perylene, indeno[1,2,3-c,d]pyrene) was observed. Desorption of PAHs using propanol or butanol could not predict PAH biodegradability: low-molecular-weight PAH biodegradability was underestimated whereas high-molecular-weight PAH biodegradability was overestimated. Persulfate oxidation and HPCD extraction of creosote-contaminated soil was able to predict three- and four-ring PAH biodegradability; however, the biodegradability of five-ring PAHs was overestimated. These results demonstrate that persulfate oxidation and HPCD extraction are good predictors of PAH biodegradability for compounds with octanol-water partitioning coefficients of < 6.     

Bioavailability of polycyclic aromatic hydrocarbons and formation of humic acid-like residues during bacterial PAH degradation

 The degradation of single polycyclic aromatic hydrocarbons (PAHs: naphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene) and a mixture of all seven PAHs by a bacterial culture enriched from contaminated soil resulted in the formation of a dark-coloured residual fraction of dissolved (DOM) and particulate organic matter (POM). This fraction was highly resistant to bacterial degradation. Analysis of the DOM revealed a molecular-size-distribution similar to that of natural humic acids. A complete degradation of PAHs was apparently prevented by an irreversible incorporation of about 10% of the carbon from single PAHs or 20% of the carbon from the mixture of seven PAHs into the DOM- and POM- fraction. Some metabolites excreted during bacterial PAH-degradation were identified as known precursors for humification. Received: 1 June 1999 / Received revision: 16 July 1999 / Accepted: 1 August 1999     

Bioremediation of Polyaromatic Hydrocarbon-Contaminated Sediments in Aerated Bioslurry Reactors

Treatment of dredged sediments contaminated by polyaromatic hydrocarbons (PAHs) is a significant problem in the New York/New Jersey (NY/NJ) Harbor. 0.5 m³-scale slurry-phase bioreactors were used to determine whether bioaugmentation with a PAH-degradative bacterial consortium, or with the salt marsh grass S. alterniflora, could enhance the biodegradation of PAHs added to dredged estuarine sediments from the NY/NJ Harbor. The results were compared to biodegradation effected by the indigenous sediment microbial community. Sediments were diluted 1:1 in tap water and spiked to a final concentration of 20 mg/kg dry weight sediment of phenanthrene, anthracene, acenaphthene, fluorene, fluoranthene, and pyrene. The sediment slurry was then continuously sparged with air over 3 months. In all bioreactors a rapid reduction of greater than 95% of the initial phenanthrene, acenaphthene, and fluorene occurred within 14 days. Pyrene and fluoranthene reductions of 70 to 90% were achieved by day 77 of treatment. Anthracene was more recalcitrant and reductions ranged from 30 to 85%. Separate experiments showed that the sediment microbial communities mineralized ¹⁴C-pyrene and ¹⁴C-phenanthrene. PAH degradation, and the number of phenanthrene-degrading bacteria, were not enhanced by microbial or plant bioaugmentation. These data demonstrate that bioaugmentation is not required to effect efficient remediation of PAH-contaminated dredged sediments in slurry-phase bioreactors.     

Distribution patterns of selected PAHs in bulk peat and corresponding humic acids from a Swiss ombrotrophic bog profile

An ombrotrophic peat core was collected in 2005 from Etang de la Gruère, Jura Mountains, Switzerland. The concentrations of nine among the U.S. Environmental Protection Agency priority polycyclic aromatic hydrocarbons (PAHs) (i.e., acenaphthene, phenanthrene, fluorene, pyrene, fluoranthene, benzo[jbk]fluoranthene, benzo[a]pyrene, benzo[ghi]perylene, and indeno[1,2,3-cd]pyrene) were determined in both bulk peat and corresponding humic acids (HA) samples by gas chromatography equipped with a mass spectrometry detector (GC-MS). The maximum PAHs concentrations in peat (around 1,250 μg Σ PAHs kg^?1 dry matter) were found at 28–30 cm of depth, which correspond to ca. 1920–1930, when coal inputs to Switzerland reached their maximum level. Amongst the nine PAHs analyzed in the peat samples, pyrene (Pyr) was the predominant species, accounting for ca. 20–100% of the total PAHs throughout the profile. In the HA fraction, that represents 24.7% (average value) of the bulk peat, only phenanthrene (Phe), and sporadically Pyr and fluoranthene (Fth), were detected. In particular, HA showed Phe concentrations that were ten–150 times higher than corresponding bulk peat samples, thus suggesting its preservation against biodegradation due to the incorporation into HA molecules.     

Phenanthrene stimulates the degradation of pyrene and fluoranthene by <Emphasis Type="Italic">Burkholderia</Emphasis> sp. VUN10013

Pyrene and fluoranthene, when supplied as the sole carbon source, were not degraded by Burkholderia sp. VUN10013. However, when added in a mixture with phenanthrene, both pyrene and fluoranthene were degraded in liquid broth and soil. The amounts of pyrene and fluoranthene in liquid media (initial concentrations of 50 mg l⁻¹ each) decreased to 42.1% and 41.1%, respectively, after 21 days. The amounts of pyrene and fluoranthene in soil (initial concentrations of 75 mg kg⁻¹ dry soil each) decreased to 25.8% and 12.1%, respectively, after 60 days. None of the high molecular weight (HMW) polycylic aromatic hydrocarbons (PAHs) tested adversely affected phenanthrene degradation by this bacterial strain and the amount of phenanthrene decreased rapidly within 3 and 15 days of incubation in liquid broth and soil, respectively. Anthracene also stimulated the degradation of pyrene or fluoranthene by Burkholderia sp. VUN10013, but to a lesser extent than phenanthrene. The extent of anthracene degradation decreased in the presence of these HMW PAHs.     

Photomutagenicity of 16 polycyclic aromatic hydrocarbons from the US EPA priority pollutant list

The photomutagenicity of 16 polycyclic aromatic hydrocarbons (PAHs), all on the United States Environmental Protection Agency (US EPA) priority pollutant list, was studied. Concomitant exposing the Salmonella typhimurium bacteria strain TA102 to one of the PAHs and light (1.1 J/cm2 UVA+2.1 J/cm2 visible) without the activation enzyme S9, strong photomutagenic response is observed for anthracene, benz[a]anthracene, benzo[ghi]perylene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene, and pyrene. Under the same conditions, acenaphthene, acenaphthylene, benzo[k]fluoranthene, chrysene, and fluorene are weakly photomutagenic. Benzo[b]fluoranthene, fluoranthene, naphthalene, phenanthrene, and dibenz[a,h]anthracene are not photomutagenic. These results indicate that PAHs can be activated by light and become mutagenic in Salmonella TA102 bacteria. At the same time, the mutagenicity for all the 16 PAHs was examined with the standard mutagenicity test with 10% S9 as the activation system. Benzo[b]fluoranthene, benzo[k]fluoranthene, chrysene, acenaphthylene, and fluorene are weakly mutagenic, while the rest of the PAHs are not. In general, the photomutagenicity of PAHs in TA102 does not correlate with their S9-activated mutagenicity in either TA102 or TA98/TA100 since they involve different activation mechanisms.     

Levels,Sources, and Toxic Potential of Polycyclic Aromatic Hydrocarbons in Urban Soil of Delhi,India

This study was done to determine the concentration of PAHs in urban soil of Delhi (India). Surface top soil (up to 10 cm depth) samples were collected from four different sampling sites including industrial, roadside, residential, and agricultural areas of Delhi and 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs) were evaluated. Total PAH concentrations at industrial, roadside, residential, and agricultural sites were 11.46 ± 8.39, 6.96 ± 4.82, 2.12 ± 1.12, and 1.55 ± 1.07 mg/kg (dry weight), respectively, with 3–7 times greater concentrations in industrial and roadside soils than that in residential and agricultural soils. The PAH pattern was dominated by 4- and 5-ring PAHs (contributing >50% to the total PAHs) at industrial and roadside sites with greater concentration of fluoranthene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]anthracene, benzo[ghi]perylene, and pyrene, whereas, residential and agricultural sites showed a predominance of low molecular weight 2- and 3-ring PAHs (fluoranthene, acenaphthene, naphthalene, chrysene, and anthracene). Isomeric pair ratios suggested biomass combustion and fossil fuel emissions as the main sources of PAHs. The toxic equivalency factors (TEFs) showed that carcinogenic potency (benzo[a]pyrene-equivalent concentration (B[a]P_eq) of PAH load in industrial and roadside soils was ～10 and ～6 times greater than the agricultural soil.     

Influence of cadmium and mercury on activities of ligninolytic enzymes and degradation of polycyclic aromatic hydrocarbons by Pleurotus ostreatus in soil

The white-rot fungus Pleurotus ostreatus was able to degrade the polycyclic aromatic hydrocarbons (PAHs) benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene, and benzo[ghi]perylene in nonsterile soil both in the presence and in the absence of cadmium and mercury. During 15 weeks of incubation, recovery of individual compounds was 16 to 69% in soil without additional metal. While soil microflora contributed mostly to degradation of pyrene (82%) and benzo[a]anthracene (41%), the fungus enhanced the disappearance of less-soluble polycyclic aromatic compounds containing five or six aromatic rings. Although the heavy metals in the soil affected the activity of ligninolytic enzymes produced by the fungus (laccase and Mn-dependent peroxidase), no decrease in PAH degradation was found in soil containing Cd or Hg at 10 to 100 ppm. In the presence of cadmium at 500 ppm in soil, degradation of PAHs by soil microflora was not affected whereas the contribution of fungus was negligible, probably due to the absence of Mn-dependent peroxidase activity. In the presence of Hg at 50 to 100 ppm or Cd at 100 to 500 ppm, the extent of soil colonization by the fungus was limited.     

Microbial degradation of polycyclic aromatic hydrocarbons in soils affected by the organic matrix of compost

This paper describes the degradation of naphthalene, phenanthrene, anthracene, fluoranthene, and pyrene in soil and soil/compost mixtures. Compost addition facilitated the degradation of 500 mg naphthalene/kg soil and 100 mg/kg each of other polycyclic aromatic hydrocarbons (PAH) within 25 days in soil systems with water contents below the water-holding capacity. By means of a humic acid extraction, it was demonstrated that the decrease of PAH concentrations after compost addition was not caused by a sorption to organic matter preventing PAH analysis. The enhanced PAH degradation was examined in a series of batch experiments with contaminated soil to evaluate whether the effect of compost addition is caused by the microorganisms of the compost itself, by the properties of the organic matrix of the compost material, or by water-soluble fertilising substances. The experiments revealed that the release of fertilising substances from the compost and the shift of soil pH brought about by the compost did not cause the stimulatory effect. The microorganisms inherent to the compost were also not necessary for the enhanced degradation. Sterilised compost was recolonised by soil microorganisms after a lagphase yielding a degradation activity similar to that of the non-sterilised compost. The presence of the solid organic matrix of the compost seemed to be essential for the enhanced degradation. The soil/compost microflora, which was separated from the organic matrix in liquid cultures, exhibited a much lower degrading activity than in the presence of the solid organic material.     

Degradation of polycyclic aromatic hydrocarbons and long chain alkanes at 6070 °C by Thermus and Bacillus spp

Although polycyclic aromatic hydrocarbons (PAH) and alkanesare biodegradable at ambient temperature, in some cases low bioavailabilities are thereason for slow biodegradation. Considerably higher mass transfer rates and PAH solubilities and hence bioavailabilities can be obtained at higher temperatures. Mixed and pure cultures of aerobic, extreme thermophilic microorganisms (Bacillus spp., Thermus sp.) were used to degrade PAH compounds and PAH/alkane mixtures at 65 °C. The microorganismsused grew on hydrocarbons as sole carbon and energy source. Optimal growthtemperatures were in the range of 60–70 °C at pH values of 6–7. The conversion of PAH with 3–5 rings (acenaphthene, fluoranthene, pyrene, benzo[e]pyrene) was demonstrated. Efficient PAH biodegradation required a second, degradable liquid phase. Thermus brockii Hamburg metabolized up to 40 mg (l h)^-1 pyrene and 1000 mg(1 h)^-1 hexadecane at 70 °C. Specific growth rates of 0.43 h^-1 were measured for this strain with hexadecane/pyrene mixtures as the sole carbon and energy source in a 2-liter stirred bioreactor. About 0.7 g cell dry weight were formed from 1 g hydrocarbon. The experiments demonstrate the feasibility and efficiency of extreme thermophilic PAH and alkane biodegradation.     

Biodegradation of a PAH Mixture by Native Subsurface Microbiota

Laboratory microcosm studies were conducted to estimate biodegradation rates for a mixture of five polycyclic aromatic hydrocarbon compounds (PAHs). Static microcosms were assembled using soil samples from two locations collected at a No. 2 fuel oil-contaminated site in the Atlantic Coastal Plain of Virginia. In microcosms from one location, five PAHs (acenaphthene, fluorene, phenanthrene, pyrene, and benzo(b)fluoranthene) biodegraded at net first-order rates of 1.08, 1.45, 1.13, 1.11, and 1.12 yr^?1, respectively. No observable lag period was noted and degradation in live microcosms ceased with the depletion of oxygen and sulfate after 125 days. In microcosms from a second location, net first-order biodegradation rates after an approximately 2-month lag period were 2.41, 3.28, and 2.98 yr^?1 for fluorene, phenanthrene, and pyrene, respectively. Acenaphthene and benzo(b)fluoranthene mass loss rates in the live microcosms were not statistically different from mass loss rates in control microcosms. Stoichiometric mass balance calculations indicate that the dominant PAH mass loss mechanism was aerobic biodegradation, while abiotic losses (attributed to micropore diffusion and oxidative coupling) ranged from 15 to 33% and biotic losses from sulfate-reduction accounted for 7 to 10% of PAH mass loss. Stoichiometric equations that include biomass yield are presented for PAH oxidation under aerobic and sulfate-reducing conditions.     

Degradation of pyrene by Mycobacterium flavescens

 A strain of Mycobacterium flavescens was isolated from polluted sediments. It was capable of utilizing pyrene as a sole source of carbon and energy. When pyrene was supplied as a suspension at 50 μg/ml, the generation time was 9.6 h and the rate of pyrene utilization was 0.56 μg ml^-1 day^-1. In addition to pyrene, the strain could mineralize phenanthrene (17.7%) and fluoranthene (17.9%), but failed to mineralize naphthalene, chrysene, anthracene, fluorene, acenaphthene and benzo[a]pyrene, as determined by recovery of radiolabeled CO₂ in incubations conducted for 2 weeks under growth conditions. Metabolites produced during growth on pyrene were detected and characterized by HPLC and GC-MS. The product of initial ring oxidation, 4,5-dihydroxy-4,5-dihydropyrene was identified, as well as ring-fission products including 4-phenanthroic acid, phthalic acid, and 4,5-phenanthrenedioic acid. Received: 3 October 1995/Received last revision: 1 April 1996/Accepted: 15 April 1996     

The uptake of persistent organic pollutants by plants

In a field experiment, the transfer of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) from contaminated soil to maize (Zea mays L.), sunflower (Helianthus annuus), poplar (Populus nigra × P. maximowiczii) and willow (Salix × smithiana) and the distribution of PCB congeners in maize and sunflower was investigated. The former waste incinerator in Hradec Králové (Czech Republic) was chosen for the experiment. Results of plot screening showed heterogenous contamination by PCBs and PAHs. PCB soil contamination was evidently caused by Delor 106 or Aroclor 1260 stocking and PAH contamination by chemicals containing fluoranthene, benzo/b/fluoranthene, phenanthrene and pyrene. Tested plants were planted on a contaminated field site, in soil contaminated with 1530 μg/kg of total PCBs and 0.138 and 3.42 mg/kg of total PAHs. The results show that maize and sunflower roots accumulated the most PCBs from soil. These plants accumulated hexa- and heptachlorobiphenyl congeners more than tri-, tetra-, and pentachlorobiphenyl congeners. Total concentrations of PAHs in tested plants ranged from 0.096 to 1.34 mg/kg. The highest phenanthrene concentration was found in aboveground biomass of sunflower and the highest concentration of pyrene, in maize roots.     

Polynuclear Aromatic Hydrocarbons (PAHs) in fish from the Red Sea Coast of Yemen

A detailed analytical study using combined normal phase high pressure liquid chromatography (HPLC), gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) of Polynuclear Aromatic Hydrocarbons (PAHs) in fish from the Red Sea was undertaken. This investigation involves a preliminary assessment of the sixteen parent compounds issued by the U.S. Environmental Protection Agency(EPA). The study revealed measurable levels of Σ PAHs (the sum of three to five or six ring parent compounds) (49.2 ng g⁻¹ dry weight) and total PAHs (all PAH detected) (422.1 ng g⁻¹ dry weight) in edible muscle of fishes collected from the Red Sea. These concentrations are within the range of values reported for other comparable regions of the world. Mean concentrations for individual parent PAH in fish muscles were; naphthalene 19.5, biphenyl 4.6, acenaphthylene 1.0, acenaphthene 1.2, fluorene 5.5, phenanthrene 14.0, anthracene 0.8, fluoranthene 1.5, pyrene 1.8, benz(a)anthracene 0.4, chrysene 1.9, benzo(b)fluoranthene 0.5, benzo(k)fluoranthene 0.5, benzo(e)pyrene 0.9, benzo(a)pyrene 0.5, perylene 0.2, and indeno(1,2,3-cd)pyrene 0.1 ng g⁻¹ dry weight respectively. The Red Sea fish extracts exhibit the low molecular weight aromatics as well as the discernible alkyl-substituted species of naphthalene, fluorene, phenanthrene and dibenzothiophene. Thus, it was suggested that the most probable source of PAHs is oil contamination originating from spillages and/or heavy ship traffic. It was concluded that the presence of PAHs in the fish muscles is not responsible for the reported fish kill phenomenon. However, the high concentrations of carcinogenic chrysene encountered in these fishes should be considered seriously as it is hazardous to human health. Based on fish consumption by Yemeni‘s population it was calculated that the daily intake of total carcinogens were 0.15 μg/person/day. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mycoremediation of PAH-contaminated soil

Out of a number of white-rot fungal cultures, strains ofIrpex lacteus andPleurotus ostreatus were selected for degradation of 7 three- and four-ring unsubstituted aromatic hydrocarbons (PAH) in two contaminated industrial soils. Respective data for removal of PAH in the two industrial soils byI. lacteus were: fluorene (41 and 67%), phenanthrene (20 and 56%), anthracene (29 and 49%), fluoranthene (29 and 57%), pyrene (24 and 42%), chrysene (16 and 32%) and benzo[a]anthracene (13 and 20%). In the same two industrial soilsP. ostreatus degraded the PAH with respective removal figures of fluorene (26 and 35%), phenanthrene (0 and 20%), anthracene (19 and 53%), fluoranthene (29 and 31%), pyrene (22 and 42%), chrysene (0 and 42%) and benzo[a]anthracene (0 and 13%). The degradation of PAH was determined against concentration of PAH in non-treated contaminated soils after 14 weeks of incubation. The fungal degradation of PAH in soil was studied simultaneously with ecotoxicity evaluation of fungal treated and non-treated contaminated soils. Compared to non-treated contaminated soil, fungus-treated soil samples indicated decrease in inhibition of bioluminescence in luminescent bacteria (Vibrio fischerii) and increase in germinated mustard (Brassica alba) seeds. An erratum to this article is available at .     

Mutagenicity of C24H14 PAH in human cells expressing CYP1A1

Relatively little is known about the mutagenicity of C24H14 PAH, a diverse group of five- and six-ring PAH, some of which are present at trace levels in the environment. To better understand the mutagenicity of this class of compounds, 11 C24H14 PAH, including benzo[a]perylene, benzo[b]perylene, dibenzo[a,e]fluoranthene, dibenzo[a,f]fluoranthene, dibenzo[j,l]fluoranthene, dibenzo[a,h]pyrene, dibenzo[a,i]pyrene, dibenzo[e,l]pyrene, naphtho[1,2-b]fluoranthene, naphtho[2,3-a]pyrene, and naphtho[2,3-e]pyrene, were tested in a mutagenicity assay based on human h1A1v2 cells. h1A1v2 cells are a line of human B-lymphoblastoid cells that have been engineered to express cytochrome P4501A1 (CYP1A1), an enzyme capable of metabolizing promutagenic PAH. Mutagenicity was measured at the thymidine kinase (tk) locus following a 72-h exposure period. Our results show that nine of the compounds were mutagenic. Benzo[a]perylene, dibenzo[a,e]fluoranthene, dibenzo[a,i]pyrene, and naphtho[2,3-a]pyrene were the most potent mutagens, having minimum mutagenic concentrations (MMC) (i.e., the dose at which the induced response was twice that of the negative controls) in the 1-5 ng/ml range. Benzo[b]perylene, dibenzo[a,h]pyrene, dibenzo[a,f]fluoranthene, and naphtho[2,3-e]pyrene were somewhat less potent mutagens, having MMC in the 10-30 ng/ml range. Dibenzo[e,l]pyrene, which had an MMC of 280 ng/ml, was the least potent mutagen. Dibenzo[j,l]fluoranthene and naphtho[1,2-b]fluoranthene were not mutagenic at the doses tested (1-3000 ng/ml). The most mutagenic compounds were also quite toxic. At the highest doses tested, benzo[a]perylene, dibenzo[a,e]fluoranthene, dibenzo[a,i]pyrene, dibenzo[a,h]pyrene, and dibenzo[a,f]fluoranthene induced > 60% killing, and naphtho[2,3-a]pyrene and naphtho[2,3-e]pyrene induced > 50% killing. Benzo[b]perylene, dibenzo[e,l]pyrene, dibenzo[j,l]fluoranthene, and naphtho[1,2-b]fluoranthene induced < 50% killing at the highest doses tested. Comparing these results to a previous study in which nine other C24H14 PAH were tested for mutagenicity in this same assay, it was found that dibenzo[a]pyrene isomers were generally more mutagenic than the other groups of C24H14 PAH tested. These observations are discussed with emphasis given to identifying C24H14 PAH that may be important environmental mutagens.     

Degradation of polycyclic aromatic hydrocarbons by the copper(II)-hydrogen peroxide system

A non-enzymic system containing CuSO₄ (10 mmol/L) and hydrogen peroxide (100 mmol/L) was used for the degradation of three polycyclic aromatic hydrocarbons: phenanthrene, fluoranthene, and pyrene (all at 10 mmol/L). The system degraded the compounds rapidly and efficiently. After 1 d at room temperature, more than 80 % of pyrene, phenan-threne, and fluoranthene disappeared. Several products are formed during the reaction including a black precipitate.     

嗜麦芽寡养单胞菌PX1的降解芘特性及定殖效能

为丰富多环芳烃降解菌菌种库、降低农作物的污染风险,本研究对一株可高效降解多环芳烃(PAHs)的植物内生菌进行筛选鉴定,并初步探究其降解途径以及定殖效能。结果表明: 菌株PX1为嗜麦芽寡养单胞菌。该菌株对多环芳烃的降解具有广谱性,7 d几乎可彻底降解PAH无机盐培养基中的萘,在分别含有50.0 mg·L^-1菲、20.0 mg·L^-1芘、20.0 mg·L^-1荧蒽和10.0 mg·L^-1苯并[a]芘的培养体系中,对菲、芘、荧蒽、苯并[a]芘的降解率分别为72.6%、50.7%、31.9%和12.9%。选取芘作为PAHs模型研究菌株PX1的降解特性。酶活性试验表明,芘可诱导菌株PX1体内邻苯二甲酸双加氧酶、邻苯二酚-1,2-双加氧酶和邻苯二酚-2,3-双加氧酶的活性。在芘降解过程中检测到4,5-环氧化芘、4,5-二羟基芘、龙胆酸/原茶儿酸、水杨酸、顺-己二烯二酸/2-羟粘糠酸半醛、顺-2′-羧基苯丙酮酸、1-羟基-2-萘甲酸、水杨醛等中间产物。浸种定殖试验表明,菌株PX1可高效定殖到空心菜和小麦体内,显著促进空心菜和小麦生长,并能够将空心菜、小麦体内及其生长基质中的芘浓度分别降低29.8%～50.7%、52.4%～67.1%和8.0%～15.3%。表明菌株PX1主要通过“水杨酸途径”和“邻苯二甲酸途径”降解芘,且可以定殖到植物体内,促进植物生长。     

Conversion of polycyclic aromatic hydrocarbons by <Emphasis Type="Italic">Sphingomonas</Emphasis> sp. VKM B-2434

A versatile bacterial strain able to convert polycyclic aromatic hydrocarbons (PAHs) was isolated, and a conversion by the isolate of both individual substances and PAH mixtures was investigated. The strain belonged to the Sphingomonas genus as determined on the basis of 16S rRNA analysis and was designated as VKM B-2434. The strain used naphthalene, acenaphthene, phenanthrene, anthracene and fluoranthene as a sole source of carbon and energy, and cometabolically oxidized fluorene, pyrene, benz[a]anthracene, chrysene and benzo[a]pyrene. Acenaphthene and fluoranthene were degraded by the strain via naphthalene-1,8-dicarboxylic acid and 3-hydroxyphthalic acid. Conversion of most other PAHs was confined to the cleavage of only one aromatic ring. The major oxidation products of naphthalene, phenanthrene, anthracene, chrysene, and benzo[a]pyrene were identified as salicylic acid, 1-hydroxy-2-naphthoic acid, 3-hydroxy-2-naphthoic acid, o-hydroxyphenanthroic acid and o-hydroxypyrenoic acid, respectively. Fluorene and pyrene were oxidized mainly to hydroxyfluorenone and dihydroxydihydropyrene, respectively. Oxidation of phenanthrene and anthracene to the corresponding hydroxynaphthoic acids occurred quantitatively. The strain converted phenanthrene, anthracene, fluoranthene and carbazole of coal-tar-pitch extract.