Benzo[a]pyrene Degradation Research Articles

Tolerance, growth and degradation of phenanthrene and benzo[a]pyrene by Rhizobium tropici CIAT 899 in liquid culture medium

Polycyclic aromatic hydrocarbons (PAH) are ubiquitous pollutants that are toxic and recalcitrant to degradation by bacteria. This research evaluated the toxicity of different concentrations [10, 20, 40, 60, 80 and 100μgmL−1] of phenanthrene (PHE) or benzo[a]pyrene (BaP) on the growth of Rhizobium tropici CIAT899 under in vitro conditions as well as the potential degradation of PHE and BaP by this bacterium. At 24h, a 40% decrease in Rhizobium growth was observed when exposed to 40μgmL−1 of either PHE or BaP. Furthermore, bacterial growth was completely inhibited by PHE or BaP applied in 80 and 100μgmL−1. After 96h, the growth of R. tropici at 40μg PHEmL−1 or 60μg BaPmL−1 was similar to those treatments without PAH. To evaluate R. tropici degrading capabilities, supernatants of cultures with 40μg PHEmL−1 or 60μg BaPmL−1 were analyzed by gas chromatography coupled to mass spectrophotometer (GC–MS). R. tropici was able to degrade either PHE or BaP diminishing its concentration in 20% and 25% during the first 24h, degradation obtained at 120h was 50% and 45% for PHE or BaP, respectively. This research shows for the first time that R. tropici CIAT 899 grows in liquid culture medium contaminated with PAH, and moreover is able to growth and to degrade either PHE or BaP.

Exploring micromycetes biodiversity for screening benzo[a]pyrene degrading potential

Twenty-five strains of filamentous fungi, encompassing 14 different species and belonging mainly to Ascomycetes, were tested for their ability to degrade benzo[a]pyrene (BaP) in mineral liquid medium. The most performing isolates for BaP degradation (200 mg l(-1)) in mineral medium were Cladosporium sphaerospermum with 29 % BaP degradation, i.e., 82.8 μg BaP degraded per day (day(-1)), Paecilomyces lilacinus with 20.5 % BaP degradation, i.e., 58.5 μg BaP day(-1), and Verticillium insectorum with 22.3 % BaP degradation, i.e., 64.3 μg BaP day(-1), after only 7 days of incubation. Four variables, e.g., biomass growth on hexadecane and glucose, BaP solubilization, activities of extracellular- and mycelium-associated peroxidase, and polyethylene glycol degradation, were also studied as selective criteria presumed to be involved in BaP degradation. Among these variables, the tests based on polyethylene glycol degradation and on fungal growth on hexadecane and glucose seemed to be the both pertinent criteria for setting apart isolates competent in BaP degradation, suggesting the occurrence of different mechanisms presumed to be involved in pollutant degradation among the studied micromycetes.

Biodegradation of Benzo[a]pyrene by Arthrobacter oxydans B4

A bacterial strain, Arthrobacter oxydans (B4), capable of degrading benzo[a]pyrene (BaP) in water body, was isolated from a polycyclic aromatic hydrocarbons-contaminated site. Effects of different factors, such as reaction time, pH value, temperature and organic nutrients, on BaP biodegradation by the strain B4 were studied. After 5 d treatment, the concentration of BaP in mineral salts medium was reduced to 0.318 mg L−1, compared to the initial concentration of 1.000 mg L−1. There was a process of acid formation during the degradation with pH falling from initial 7.01 to 4.61 at 5 d, so keeping the water body under slightly alkaline condition was propitious to BaP degradation. Strain B4 efficiently degraded BaP at 20 to 37 °C with addition of organic nutrients. The biodegradation and transformation of BaP mainly occurred on cell surfaces, and extracellular secretions played an important role in these processes. Fourier transform infrared spectroscopy and gas chromatograph-mass spectrometer analyses of metabolites showed that ring cleavage occurred in the BaP degradation process and the resulting metabolically utilizable substrates were generated as sole carbon sources for B4 growth. Furthermore, mineralization extent of metabolites was verified by determining the total organic carbon and inorganic carbon in the degradation system.

Effects and Kinetics of Chlorine Dioxide for Removal of Benzo[a]pyrene in Water

Benzo[a]pyrene (BaP) is one of the persistent organic pollutants (POPs) existing widely in the environment and presenting great threats to ecosystems. Chlorine dioxide (ClO2) has been adopted as an effective alternative to chlorine for disinfection in potable water treatment. In this study, a series of experiments were conducted to investigate the feasibility of using ClO2 as an oxidant for BaP degradation. We examined degradation kinetics and effects of ClO2 dosage, reaction time, and pH on the BaP removal by ClO2. Results demonstrated that ClO2 could remove BaP effectively. ClO2 dosage and reaction time were found to have a significant impact on BaP removal, whereas pH only affected slightly in the range of 3.2–9.7. Under optimal reaction conditions, the removal efficiency could reach an extremely high level of 99.8% within 30 min at a ClO2 dosage of 5 mg/L, temperature of 20°C, and pH 7.2 for the BaP samples with initial concentration of 10 μg/L. The reaction between ClO2 and BaP followed a second-order kinetic, and the corresponding rate constant was determined to be 7.795 L/(mol·s). The predominant end products of BaP degradation by ClO2 were characterized as quinine derivatives. This study not only provides a feasible chemical method to efficiently degrade BaP in water treatment, but also suggests a new strategy to promote the development of technologies for POPs reduction in the environment.

2,3,7,8-Tetrachlorodibenzo-p-dioxin’s Suppression of 1-Nitropyrene-Induced p53 Expression Is Mediated by Cytochrome P450 1A1

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), 1-nitropyrene (1-NP), and benzo[a]pyrene (BaP) are toxic environmental pollutants. TCDD was shown to suppress p53 expression in response to genotoxic stress and hypoxic conditions. However, the mechanism of TCDD's actions is not clearly understood. Our data showed that pretreatment with TCDD abolished 1-NP- but not BaP-induced p53 and mouse double minute 2 (MDM2; HDM2 in humans) expressions. TCDD suppressed 1-NP- but not BaP-induced p53 activity, and in contrast, pifithrin-alpha (PFT-α), a p53 inhibitor, suppressed both 1-NP- and BaP-induced p53 activity. In the presence of nutlin-3, an HDM2 inhibitor, TCDD was still able to suppress 1-NP-induced p53 expression. However, TCDD-activated HDM2 did not distinctly cause the degradation of BaP- or nutlin-3-induced p53 expression. Accordingly, TCDD's suppression of 1-NP-induced p53 expression was compound-specific, and the contribution of HDM2 to the abolition of 1-NP-induced p53 was limited. β-Naphthoflavon (β-NF), an aryl hydrocarbon receptor (AHR) agonist, mimicked TCDD's action and abolished 1-NP-induced p53 expression. In the presence of CH-223191, an AHR antagonist, TCDD was unable to abolish 1-NP-induced p53 expression. Results indicate that activation of the AHR is required for TCDD's suppression of 1-NP's induction of p53. Cytochrome P450 (CYP) 1A1 is an AHR-targeting gene and a xenobiotic-metabolizing enzyme. TCDD was unable to abolish 1-NP's induction of p53 in CYP1A1-deficient cells, the CYP1A1 transcript of which was degraded by small hairpin RNA-CYP1A1. Both TCDD and PFT-α are potent CYP1A1 inducers and decreased 1-NP-induced cell death and mutagenesis. In summary, TCDD induced detoxification of 1-NP's toxicity, which was mediated by the CYP1A1 enzyme.

Removals of some hydrophobic poly aromatic hydrocarbons (PAHs) and Daphnia magna acute toxicity in a petrochemical industry wastewater with ultrasound in Izmir-Turkey

The effects of increasing sonication time (60–150 min), NaCl (1.5–18 g/L), CCl 4 (200–1000 mg/L), pH (2–10) and air as dissolved oxygen (DO = 2–12 mg/L) concentrations on the destruction of four polycyclic aromatic hydrocarbons (PAHs) in a real petrochemical industry wastewater in Izmir (Turkey) were investigated. The yields in more hydrophobic PAHs with high benzene rings [benzo[ a]pyrene (BaP) and benzo[ k]fluoranthene (BkF)] were as high as the less hydrophobic PAHs with lower benzene rings [acenaphthylene (ACL) and carbazole (CRB)] at 60 °C after 150 min sonication. The removals in all PAHs increased significantly as the NaCl concentrations were increased from 1.5 up to 8 g/L, respectively. Continuous sparging of 5 mg/L DO increased the yields to 98% in less hydrophobic PAHs while more hydrophobic ones are removed with low yields. The more hydrophobic BaP, BkF and less hydrophobic ACL and CRB PAHs were sono-degraded under acidic and alkaline conditions, respectively, with high yields. The sono-destruction efficiency of more hydrophobic PAHs (97%) was enhanced by 17% with 600 mg/L CCl 4 after 150 min of sonication while the yields of less hydrophobic PAHs remained around 82%. Sonication alone provided 80% PAH yields. OH was the main process for complete sono-degradation of the ACL and CRB PAHs while pyrolysis was the main process for complete degradation of BaP and BkF PAHs. The Daphnia magna acute toxicity was significantly reduced.

UVB in solar-simulated light causes formation of BaP-photoproducts capable of generating phosphorylated histone H2AX

Polycyclic aromatic hydrocarbons (PAHs), wide-spread mutagenic and carcinogenic environmental pollutants, are consistently exposed to sunlight in the environment. Our previous paper showed that benzo[ a]pyrene (BaP) exposed to solar-simulated light (SSL) induced phosphorylation of histone H2AX (γ-H2AX) [T. Toyooka, G. Ohnuki, Y. Ibuki, Solar-simulated light-exposed benzo[a]pyrene induces phosphorylation of histone H2AX, Mutat. Res. 650 (2008) 132–139], a marker of DNA double strand breaks. In this study, we found the ultraviolet B (UVB) region of SSL to produce photomodified BaP with high cytotoxicity and the ability to generate γ-H2AX. Degradation of BaP by SSL, resulting in an increase in cytotoxicity and the generation of γ-H2AX, was decreased by UVB-masking using a glass plate. Exposure to UVB itself increased the cytotoxicity of BaP and amount of γ-H2AX generated. Other PAHs, 1,2-benzoanthracene and 1,2:5,6-dibenzoanthracene, which absorb UVB, also showed enhanced cytotoxicity and the promoted the generation of γ-H2AX after exposure to SSL, whereas naphthalene and chrysene, which have low absorption in the UVB region, did not. These findings suggested that UVB is important for the degradation of PAHs having absorbance in this region, but that the production of genotoxic intermediates during the degradation process needs to be considered. UVB is a two-edged blade in environments, effectively degrading toxic chemicals but also producing genotoxic compounds as reactive intermediates.

Optimization of an inducible, chromosomally encoded benzo [a] pyrene (BaP) degradation pathway in Bacillus subtilis BMT4i (MTCC 9447)

Benzo [a] pyrene (BaP), a pentacyclic polyaromatic hydrocarbon, is 1 of the 12 target compounds defined in the new US Environmental Protection Agency strategy for controlling persistent, bioaccumulative, and toxic pollutants. We previously isolated a novel strain Bacillus subtilis BMT4i capable of utilizing BaP as sole source of carbon and energy. The present study investigated (1) whether the BaP degradation pathway is inducible, and (2) whether it is plasmid-encoded. Furthermore, physical (temperature, pH, and UV-induced photolysis of BaP) and chemical (BaP concentration, surfactant, and ionic strength) parameters for BaP degradation were determined. Our findings revealed a ten-fold enhanced degradation rate in induced vs non-induced culture in the presence of chloramphenicol, suggesting that the BaP degradation pathway is inducible. Physical methods demonstrated the lack of plasmid in BMT4i—a result further complimented by plasmid curing, which had no effect on BaP degradability thus a chromosomal localization can be inferred. Maximum BaP degradation in BMT4i was observed under the following physical and chemical conditions: 30°C, pH 8.0, UV-induced photolysis of BaP-basal salt mineral medium (BSM), 150 μg/ml BaP, 0.01% Tween-20, and 400–1,800 μM MgSO4. These conditions could be beneficial in the development and standardization of effective bioremediation protocols using B. subtilis BMT4i.

Degradation of Benzo [a] Pyrene by a novel strain Bacillus subtilis BMT4i (MTCC 9447)

Benzo [a] Pyrene (BaP) is a highly recalcitrant, polycyclic aromatic hydrocarbon (PAH) with high genotoxicity and carcinogenicity. It is formed and released into the environment due to incomplete combustion of fossil fuel and various anthropogenic activities including cigarette smoke and automobile exhausts. The aim of present study is to isolate bacteria which can degrade BaP as a sole source of carbon and energy. We have isolated a novel strain BMT4i (MTCC 9447) of Bacillus subtilis from automobile contaminated soil using BaP (50 g /ml) as the sole source of carbon and energy in basal salt mineral (BSM) medium. The growth kinetics of BMT4i was studied using CFU method which revealed that BMT4i is able to survive in BaP-BSM medium up to 40 days attaining its peak growth (10(29) fold increase in cell number) on 7 days of incubation. The BaP degradation kinetics of BMT4i was studied using High Performance Liquid Chromatography (HPLC) analysis of BaP biodegradation products. BMT4i started degrading BaP after 24 hours and continued up to 28 days achieving maximum degradation of approximately 84.66 %. The above findings inferred that BMT4i is a very efficient degrader of BaP. To our best of knowledge, this is the first report showing utilization of BaP as a sole source of carbon and energy by bacteria. In addition, BMT4i can degrade a wide range of PAHs including naphthalene, anthracene, and dibenzothiophene therefore, it could serve as a better candidate for bioremediation of PAHs contaminated sites.

Fenton degradation assisted by cyclodextrins of a high molecular weight polycyclic aromatic hydrocarbon benzo[a]pyrene

This paper investigates the effect of native β-cyclodextrin (β-CD) and its CD derivatives, such as hydroxypropyl-β-cyclodextrin (HPBCD) and randomly methylated-β-cyclodextrin (RAMEB), on the solubilization of a high molecular weight polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP) and on its degradation by Fenton's reaction. The results show that BaP apparent solubility was significantly increased in the presence of cyclodextrin (CD) in the following order: β-CD < RAMEB < HPCD. BaP Fenton degradation was strongly dependent on the capacity of cyclodextrin to solubilize BaP. In the presence of a radical scavenger (mannitol), BaP Fenton degradation was inhibited with RAMEB but not in the presence of HPCD. Molecular modelisation was used to visualize the steric complementarity of these host-guest systems. No significant difference of encapsulation between the two modified CDs was observed. Nevertheless, the results suggest a probable existence of a ternary complex HPCD–BaP–iron permitting the generation of hydroxyl radicals in close proximity to BaP. On the basis of these results, it appears that HPCD may be useful for developing targeted BaP degradation system.

Benzo[a]pyrene degradation using simultaneously combined chemical oxidation, biotreatment with Fusarium solani and cyclodextrins

The interest of simultaneously combining chemical (Fenton’s reaction) and biological treatments for the degradation of a high molecular weight polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP) has been studied in laboratory tests. An optimal concentration of 1.5 × 10 −3 M H 2O 2 as Fenton’s reagent was firstly determined as being compatible with the growth of Fusarium solani, the Deuteromycete fungus used in the biodegradation process. For the enhancement of BaP solubilisation, cyclodextrins were also used in the performed tests. The best degradation performance was achieved through the use of 5 × 10 −3 M hydroxypropyl-β-cyclodextrin (HPBCD) in comparison with randomly methylated-β-cyclodextrin (RAMEB). When Fenton’s treatment was combined with biodegradation, a beneficial effect on BaP degradation (25%) was obtained in comparison with biodegradation alone (8%) or with chemical oxidation alone (16%) in the presence of HPBCD for 12 days of incubation.

Degradation of Benzo [a] Pyrene by a novel strain Bacillus subtilis BMT4i (MTCC 9447)

Benzo [a] Pyrene (BaP) is a highly recalcitrant, polycyclic aromatic hydrocarbon (PAH) with high genotoxicity and carcinogenicity. It is formed and released into the environment due to incomplete combustion of fossil fuel and various anthropogenic activities including cigarette smoke and automobile exhausts. The aim of present study is to isolate bacteria which can degrade BaP as a sole source of carbon and energy. We have isolated a novel strain BMT4i (MTCC 9447) of Bacillus subtilis from automobile contaminated soil using BaP (50 g /ml) as the sole source of carbon and energy in basal salt mineral (BSM) medium. The growth kinetics of BMT4i was studied using CFU method which revealed that BMT4i is able to survive in BaP-BSM medium up to 40 days attaining its peak growth (1029 fold increase in cell number) on 7 days of incubation. The BaP degradation kinetics of BMT4i was studied using High Performance Liquid Chromatography (HPLC) analysis of BaP biodegradation products. BMT4i started degrading BaP after 24 hours and continued up to 28 days achieving maximum degradation of approximately 84.66 %. The above findings inferred that BMT4i is a very efficient degrader of BaP. To our best of knowledge, this is the first report showing utilization of BaP as a sole source of carbon and energy by bacteria. In addition, BMT4i can degrade a wide range of PAHs including naphthalene, anthracene, and dibenzothiophene therefore, it could serve as a better candidate for bioremediation of PAHs contaminated sites.

Biodegradation of Benzo[a]pyrene in Soil by Immobilized Fungus

Mucor sp., a filamentous fungus capable of degrading polycyclic aromatic hydrocarbons (PAHs), was immobilized on maize cob (MC) by physical adsorption and used to degrade benzo[a]pyrene (BaP). The characteristics of BaP degradation by both immobilized and free fungus were then investigated and compared. The degradation rate using the immobilized fungus was higher than that of the freely mobile fungus. When the initial BaP concentration was 50 mg · kg−1, the removal rate was 68% within 42 days using immobilized fungus but only 52% for free fungus in that same time. The optimal amount of inoculated immobilized fungus for BaP degradation was shown to be 2%. The immobilized fungus also showed better removal efficiencies of BaP than free fungus, independent of the moisture content. The increasing concentration of BaP was better tolerated and more quickly degraded by immobilized fungus than by free fungus when the initial BaP concentration was in the range of 10 to 200 mg · kg−1. The scanning electronic microscope (SEM) analysis showed that the immobilized microstructure was suitable for Mucor sp. growth. The results demonstrate the potential for employing Mucor sp., immobilized on MC, for in situ bioremediation of PAH-contaminated soil.

Degradation of metabolites of benzo[a]pyrene by coupling Penicillium chrysogenum with KMnO 4

Several main metabolites of benzo[a]pyrene (BaP) formed by Penicillium chrysogenum, Benzo[a]pyrene-1, 6-quinone (BP 1.6-quinone), trans-7, 8-dihydroxy-7, 8-dihydrobenzo[a]pyrene (BP 7, 8-diol), 3-hydroxybenzo[a]pyrene (3-OHBP), were identified by high-performance liquid chromatography (HPLC). The three metabolites were liable to be accumulated and were hardly further metabolized because of their toxicity to microorganisms. However, their further degradation was essential for the complete degradation of BaP. To enhance their degradation, two methods, degradation by coupling Penicillium chrysogenum with KMnO 4 and degradation only by Penicillium chrysogenum, were compared; Meanwhile, the parameters of degradation in the superior method were optimized. The results showed that (1) the method of coupling Penicillium chrysogenum with KMnO 4 was better and was the first method to be used in the degradation of BaP and its metabolites; (2) the metabolite, BP 1, 6-quinone was the most liable to be accumulated in pure cultures; (3) the effect of degradation was the best when the concentration of KMnO 4 in the cultures was 0.01% (w/v), concentration of the three compounds was 5 mg/L and pH was 6.2. Based on the experimental results, a novel concept with regard to the bioremediation of BaP-contaminated environment was discussed, considering the influence on environmental toxicity of the accumulated metabolites.

Degradation mechanisms of benzo[a]pyrene and its accumulated metabolites by biodegradation combined with chemical oxidation

A high degradation extent of benzo[a]pyrene (BaP) should not be considered as the sole desirable criterion for the bioremediation of BaP-contaminated soils because some of its accumulated metabolites still have severe health risks to human. Two main metabolites of BaP, benzo[a]pyrene-1,6-quinone (BP1,6-quinone) and 3-hydroxybenzo[a]pyrene (3-OHBP) were identified by high performance liquid chromatography (HPLC) with standards. This study was the first time that degradation of both BaP and the two metabolites was carried out by chemical oxidation and biodegradation. Three main phases during the whole degradation process were proposed. Hydrogen peroxide-zinc (H(2)O(2)-Zn), the fungus - Aspergillus niger and the bacteria - Zoogloea sp. played an important role in the different phases. The degradation parameters of the system were also optimized, and the results showed that the effect of degradation was the best when fungus-bacteria combined with H(2)O(2)-Zn, the concentration range of BaP in the cultures was 30-120mg/l, the initial pH of the cultures was 6.0. However, as co-metabolites, phenanthrene significant inhibited the degradation of BaP. This combined degradation system compared with the conventional method of degradation by domestic fungus only, enhanced the degradation extent of BaP by more than 20% on the 12d. The highest accumulation of BP1,6-quinone and 3-OHBP were reduced by nearly 10% in the degradation experiments, which further proved that the combined degradation system was more effective as far as joint toxicity of BaP and its metabolites are concerned.

Biodegradation of benzo[a]pyrene in soil by Mucor sp. SF06 and Bacillus sp. SB02 co-immobilized on vermiculite

Two indigenous microorganisms, Bacillus sp. SB02 and Mucor sp. SF06, capable of degrading polycyclic aromatic hydrocarbons (PAHs) were co-immobilized on vermiculite by physical adsorption and used to degrade benzo[a] pyrene (BaP). The characteristics of BaP degradation by both free and co-immobilized microorganism were then investigated and compared. The removal rate using the immobilized bacterial-fungal mixed consortium was higher than that of the freely mobile mixed consortium. 95.3% of BaP was degraded using the co-immobilized system within 42 d, which was remarkably higher than the removal rate of that by the free strains. The optimal amount of inoculated co-immobilized system for BaP degradation was 2%. The immobilized bacterial-fungal mixed consortium also showed better water stability than the free strains. Kinetics of BaP biodegradation by co-immobilized SF06 and SB02 were also studied. The results demonstrated that BaP degradation could be well described by a zero-order reaction rate equation when the initial BaP concentration was in the range of 10—200 mg/kg. The scanning electronic microscope (SEM) analysis showed that the co-immobilized microstructure was suitable for the growth of SF06 and SB02. The mass transmission process of co-immobilized system in soil is discussed. The results demonstrate the potential for employing the bacterial-fungal mixed consortium, co-immobilized on vermiculite, for in situ bioremediation of BaP.

Bioremediation of polycyclic aromatic hydrocarbon-contaminated saline–alkaline soils of the former Lake Texcoco

Polycyclic aromatic hydrocarbons (PAHs) such as phenanthrene, anthracene and Benzo[ a]pyrene (BaP) are toxic for the environment. Removing these components from soil is difficult as they are resistant to degradation and more so in soils with high pH and large salt concentrations as in soil of the former lake Texcoco, but stimulating soil micro-organisms growth by adding nutrients might accelerate soil restoration. Soil of Texcoco and an agricultural Acolman soil, which served as a control, were spiked with phenanthrene, anthracene and BaP, added with or without biosolid or inorganic fertilizer (N, P), and dynamics of PAHs, N and P were monitored in a 112-day incubation. Concentrations of phenanthrene did not change significantly in sterilized Acolman soil, but decreased 2-times in unsterilized soil and >25-times in soil amended with biosolid and NP. The concentration of phenanthrene in unsterilized soil of Texcoco was 1.3-times lower compared to the sterilized soil, 1.7-times in soil amended with NP and 2.9-times in soil amended with biosolid. In unsterilized Acolman soil, degradation of BaP was faster in soil amended with biosolid than in unamended soil and soil amended with NP. In unsterilized soil of Texcoco, degradation of BaP was similar in soil amended with biosolid and NP but faster than in the unamended soil. It was found that application of biosolid and NP increased degradation of phenanthrene, anthracene and BaP, but to a different degree in alkaline–saline soil of Texcoco compared to an agricultural Acolman soil.

Formation and decomposition of hazardous chemical components contained in atmospheric aerosol particles.

Air particulate matter contains a wide range of substances, some of which pose a threat to human health. Chemical reactions occurring on aerosol particles in the atmosphere can transform hazardous components and increase or decrease their potential for adverse health effects. Especially organic compounds react readily with atmospheric oxidants, and since fine aerosol particles have a high surface-to-volume ratio, their chemical composition can be efficiently changed by interaction with trace gases such as ozone and nitrogen oxides. In this paper the concepts required to understand and describe the formation and decomposition of hazardous chemical components contained in atmospheric aerosol particles are outlined. The processes at work on a molecular level in the chemical transformation of atmospheric particle components are illustrated for soot and polycyclic aromatic compounds (PACs), in particular for benzo[a]pyrene (BaP) which is one of the most prominent hazardous pollutants in the class of polycyclic aromatic hydrocarbons (PAHs). Recent results on the reaction kinetics and mechanisms of BaP degradation by ozone and nitrogen dioxide are presented. These results indicate faster degradation by atmospheric oxidants than previously estimated, which implies a higher potential for sampling artifacts and underestimation of the actual atmospheric abundance of BaP and other PAHs. Thus human exposure close to the sources of these compounds such as busy roadways may be significantly higher than previously assumed.

The effect of polycyclic aromatic hydrocarbons on the degradation of benzo[a]pyrene by Mycobacterium sp. strain RJGII‐135

Mycobacterium sp. strain RJGII-135 is capable of degrading a wide range of polycyclic aromatic hydrocarbons (PAHs), including benzo[a]pyrene (BaP). In this study, critical aspects of degradation were investigated, including compound uptake, relative rates of PAH degradation, and the effects of co-occurring PAH substrates on BaP degradation and mineralization to CO2. Mycobacterium sp. strain RJGII-135 was capable of degrading phenanthrene, anthracene, and pyrene at a 10- to 20-fold greater rate than benz[a]anthracene (BaA) and BaP. A significant amount of phenanthrene and pyrene, 30% and 10%, respectively, was completely mineralized, whereas less than 4% of anthracene, BaA, and BaP was mineralized. The PAH uptake assays demonstrated that high amounts of BaP and BaA, 81% and 75% of added compound, respectively, could be recovered from bacterial cell fractions after a 4-h incubation compared with pyrene (61%), anthracene (53%), and phenanthrene (47%). The half-saturation constant (Km) for pyrene was threefold lower for pyrene over BaP, suggesting that the degradation system in Mycobacterium sp. strain RJGII-135 has a higher affinity for pyrene, reaching maximal degradative activity at lower concentrations. No hybridization to dioxygenase gene probes nahAc, bphA1, or tolC1C2 was detected. Studies to investigate competition between different PAH substrates demonstrated that the rate of BaP metabolism was influenced by the presence of a second PAH substrate. The BaP metabolism was inhibited when coincubated with BaA, pyrene, and anthracene. Phenanthrene did not inhibit but enhanced BaP metabolism sixfold. These data suggest that induction effects of components of complex mixtures may be as important as competitive metabolism when assessing the ability of bacteria to effectively degrade high-molecular-weight PAHs in the environment.

UTILIZATION OF ELECTROCHEMICALLY GENERATED OZONE IN THE DEGRADATION AND DETOXICATION OF BENZO[a]PYRENE

The ability of electrochemically generated ozone (O3) to degrade and detoxify the polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (BaP) was assessed utilizing the chick embryotoxicity screening test (CHEST) and Hydra attenuata bioassays. Aqueous solutions containing 10 mug/ ml BaP and 0.5% (v/v) acetonitrile were subjected to ozonolysis for 0 to 30 min. Rapid degradation of BaP was evident by both gas chromatography/mass spectroscopy (GC/MS) and high-performance liquid chromatography (HPLC) analysis. HPLC fluorescence detection revealed no BaP shortly after 5 min of ozonolysis, while HPLC with PDA detection demonstrated continued reactions with ozone over the 30-min time course. As little as 2 min of O3 treatment afforded protection from BaP-induced mortality and toxicity (embryolethality and liver discoloration) in the chicken embryos. In the hydra bioassay, no toxicity was observed in the adult hydra until the ozonolysis products were reconstituted 100-fold from their initial post-ozonolysis concentrations. The results obtained from this study clearly demonstrate the potential application of electrochemically generated O3 for the detoxication and prevention of toxicity of BaP. Both CHEST and hydra assays predict that the ozonolysis products of BaP are less toxic than the parent compound.