Metabolic activation of carcinogenic 1-nitropyrene by human cytochrome P450 1B1 in Salmonella typhimurium strain expressing an O-acetyltransferase in SOS/umu assay

Metabolic activation of 1-nitropyrene (1-NP) by human cytochrome P450 (P450) family 1 enzymes co-expressed with NADPH-cytochrome P450 reductase (NPR) in Escherichia coli membranes was investigated. 1-NP induced umu gene expression in Salmonella typhimurium TA1535/pSK1002 in the absence of any P450 system, but the activities were influenced by the levels of bacterial O-acetyltransferase (OAT) and nitroreductase. Metabolic activation of 1-NP by human P450 1B1/NPR membranes was observed and was influenced by the levels of OAT levels in tester strains. Metabolic activation of 1-NP (0.3microM) by P450 1B1 was 750 umu units/min/nmol P450 1B1 in an OAT-overexpressing strain NM2009. The metabolic activation of 1-NP (3-30microM) was similar (approximately 300 umu units/min/nmol P450 1B1) using TA1535/pSK1002 or OAT-deficient strain NM2000. P450 1B1 had the highest catalytic activities among P450 family 1 enzymes for the activation of 1-aminopyrene (1-AP) in the OAT-overexpressing strain NM2009, suggesting nitrenium ion formation via N-hydroxylation/O-acetylation. High-performance liquid chromatography (HPLC) analyses revealed the formation of 1-nitropyrene-6-ol and also 1-nitropyrene-3-ol, 1-nitropyrene-8-ol, and trans-4,5-dihydroxy-4,5-diol-1-nitropyrene from 1-NP (10microM), catalyzed by P450 1B1. These results indicate that 1-NP can be activated by human P450 1B1 to a genotoxic agent by nitroreduction/O-acetylation at low substrate concentrations and probably by epoxidation (independent of OAT) at high concentrations.     

SOS-inducing activity of chemical carcinogens and mutagens in Salmonella typhimurium TA1535/pSK1002: examination with 151 chemicals

The umu test system is a newly developed method to evaluate genotoxic activities of a wide variety of environmental carcinogens and mutagens (Oda et al., 1985). In the present study, we further examined the abilities of 151 chemicals to induce umu gene expression in Salmonella typhimurium TA1535/pSK1002. Among the chemicals examined, 72 compounds induced umu gene expression, which could be defined on a basis of increased beta-galactosidase activity by 2-fold over the background level. The potent genotoxic compounds without metabolic activation were adriamycin, bleomycin, daunorubicin, 1,3-dinitropyrene, 1,6-dinitropyrene, 1,8-dinitropyrene, N-ethyl-N'-nitro-N-nitrosoguanidine, furylfuramide, methyl methanesulfonate, N-methyl-N'-nitro-N-nitrosoguanidine, mitomycin C, 1-nitropyrene and 4-nitroquino-line-1-oxide. In the presence of S9, aflatoxin B1, 2-aminoanthracene, Glu-P-1, IQ, MeIQ, MeIQx, Trp-P-1 and Trp-P-2 also induced umu gene expression markedly. Several chemicals such as 2-acetylaminofluorene, 9-aminoacridine, azobenzene, benzanthracene, benzidine, diethyl nitrosamine, 1-nitronaphthalene, paraquat, potassium dichromate and sodium nitrite were weakly genotoxic and the induction by these compounds could be detected only when the incubation time was prolonged from 2 h to 5 h. Data are also presented that some of the chemicals such as dimethyl sulfoxide, m-dioxan, 5-fluorouracil and paraquat, which have been reported to be non-mutagenic in Ames/Salmonella assay, were found to be active in inducing umu gene expression, while the known mutagenic compounds including acrylonitrile, 4,4'-dinitrobiphenyl, furfural, methylene chloride, 1-naphthylamine, sodium azide, o-tolidine and o-toluidine were non-genotoxic in the present assay system.     

A sensitive method for the detection of mutagenic nitroarenes: construction of nitroreductase-overproducing derivatives of Salmonella typhimurium strains TA98 and TA100

'Classical nitroreductase' is an enzyme involved in the intracellular metabolic activation of mutagenic nitroarenes. The nitroreductase gene of Salmonella typhimurium TA1538 was cloned into pBR322 and the plasmids harboring the gene were introduced into TA98 and TA100. The resulting strains (YG1021 and YG1026) had more than 50 times higher nitrofurazone-reductase activity than TA1538 containing pBR322, and were extremely sensitive to the mutagenic action of 2-nitrofluorene, 1-nitropyrene and 2-nitronaphthalene. These results indicate that the new strains permit the efficient detection of mutagenic nitroarenes.     

Salmonella typhimurium mutagenicity tester strains that overexpress oxygen-insensitive nitroreductases nfsA and nfsB

We have designed and constructed a series of plasmids that contain the major and/or minor Escherichia coli nitroreductase genes, nfsA and nfsB, in different combinations with R plasmid mucA/B genes and the Salmonella typhimurium OAT gene. The plasmid encoded gene products are necessary for both the metabolic activation of a range of structurally diverse nitrosubstituted compounds, and for mutagenic translation bypass. Introduction of these plasmids into S. typhimurium TA1538 and TA1535 has created several new tester strains which exhibit an extremely high mutagenic sensitivity and a broad substrate specificity towards a battery of nitrosubstituted test compounds that included 4-nitroquinoline-1-oxide (4-NQO), nitrofurazone (NF), 1-nitropyrene (1-NP), 2-nitronaphthalene (2-NN), 2-nitrofluorene (2-NF), and 1,6-dinitropyrene (1,6-DNP). Our studies show that the nfsA gene encodes a product that is extremely effective in the metabolic activation of a range of structurally diverse nitrosubstituted compounds. Several of the new tester strains are more than two orders of magnitude more sensitive to nitrosubstituted compounds than the Ames tester strains TA100 or TA98. In addition to enhancing mutagenic sensitivity, plasmids encoding both metabolic and mutagenesis functions on a single plasmid provide considerable flexibility for future mechanistic studies or tester strain development, in which it may be necessary to introduce additional plasmids containing different antibiotic resistance markers.     

Evaluation of the new system (umu-test) for the detection of environmental mutagens and carcinogens

The umu operon in Escherichia coli is responsible for chemical and radiation mutagenesis, and the expression of the operon itself is inducible by these DNA-damaging agents. The principle of the umu-test is based on the ability of the DNA-damaging agents, most of which are potential carcinogens, to induce the umu operon. A plasmid (pSK1002) carrying a fused gene umuC'-'lacZ was introduced into Salmonella typhimurium TA1535. The strain TA1535/pSK1002 enabled us to monitor the levels of umu operon expression by measuring the beta-galactosidase activity in the cells produced by the fusion gene. Using this strain, a simple, inexpensive, and sensitive system, the umu-test, for the screening of environmental mutagens and carcinogens was developed. 38 chemicals with different structures and modes of action, including 31 known animal carcinogens, were examined by the test to evaluate the system. The threshold sensitivity of the umu-test was approximately equal to that of the Ames test for chemicals genotoxic in both tests. By the umu-test, using the single tester strain, we detect many types of DNA-damaging agents for which the Ames test requires several tester strains. Furthermore, the umu-test provides a potential practical advantage for the screening of various environmental samples containing amino acids and nutrients such as urine, serum and foods.     

Comparative direct-acting mutagenicity of 1- and 2-nitropyrene: Evidence for 2-nitropyrene mutagenesis by both guanine and adenine adducts

The mutations and DNA adducts produced by the environmental pollutant 2-nitropyrene were examined in Salmonella typhimurium tester strains. 2-Nitropyrene was a stronger mutagen than its extensively studied structural isomer 1-nitropyrene in strains TA96, TA97, TA98, TA100, TA102, TA104 and TA1538. Both 1- and 2-nitropyrene were essentially inactive in TA1535. The mutagenicity of 1- and 2-nitropyrene in TA98 was much higher than in TA98NR and the activity of these compounds in TA100 was much higher than in TA100NR. While 1-nitropyrene exhibited similar mutagenicity in strains TA98 and TA98/1,8-DNP₆, the mutagenicity of 2-nitropyrene in TA98/1,8-DNP₆ was much lower than in TA98. Analysis of DNA from TA96 and TA104 incubated with 2-nitropyrene indicated the presence of two adducts, N-(deoxyguanosin-8-yl)-2-aminopyrene and N-deoxyadenosin-8-yl)-2-aminopyrene. The results suggest that 2-nitropyrene is metabolized by bacterial nitroreductase(s) to N-hydroxy-2-aminopyrene, and possibly by activation to a highly mutagenic O-acetoxy ester. DNA adduct formation with deoxyguanosine and deoxyadenosine correlates with the mutagenicity of 2-nitropyrene in tester strains possessing both G:C and A:T mutational targets.     

Development of a new genotoxicity test system with Salmonella typhimurium OY1001/1A2 expressing human CYP1A2 and NADPH-P450 reductase.

In order to develop a new tester strain detecting environmental promutagens and procarcinogens, we introduced two plasmids into Salmonella typhimurium TA1535; one contains the cDNAs of human cytochrome P450 (P450 or CYP) 1A2 and NADPH-P450 reductase and the other (pOA101) a umuC"lacZ fusion gene. The newly developed tester strain, S. typhimurium OY1001/1A2, was found to express P450 at a level of 0.15 nmol/ml in whole cell culture. Membrane fractions, when isolated from this tester strain, contained 0.04 P450 nmol/mg protein and a reductase activity of 170 nmol cytochrome c reduced/min/mg protein and were active in catalyzing CYP1A2-dependent 7-ethoxyresorufin O-deethylation and metabolic activation of heterocyclic aromatic amines to DNA-damaging products in a conventional tester S. typhimurium NM2009 strain, only when NADPH was added as a reducing equivalent. In the OA1002/1A2 strain, heterocyclic aromatic amines (e.g., IQ, MeIQ, and MeIQx) were found to be activated to reactive metabolites that cause induction of umuC gene expression in a dose-dependent manner, without addition of external NADPH. These results indicate that the newly established strain can be of use to detect mutagenic and carcinogenic potencies of environmental chemicals without addition of metabolic activation system.     

Metabolism of 1,8-dinitropyrene by Salmonella typhimurium

Earlier work has shown that many nitroaromatic and nitroheterocyclic compounds are directly 'activated' to their ultimate mutagenic forms through the action of bacterial nitroreductase enzymes. However, in the case of 1,8-dinitropyrene (DNP) and certain other nitroarenes the pathway of activation is more complex and neither the identity of the ultimate mutagens nor the nature of the DNA adducts formed are known. We now show that Salmonella typhimurium strains TA98 and TA1538, which are sensitive to DNP and have wild type nitroreductase complements, do metabolize DNP to 1-amino-8-nitropyrene (ANP) and 1,8- diaminopyrene (DAP) but that these compounds are much weaker mutagens than DNP. These two strains (TA98 and TA1538) contain two separable components of nitroreductase activity as determined using nitrofurazone as the substrate. The major component, at least, is capable of reducing both 1-nitropyrene (NP) and DNP although the rates are much lower than with nitrofurazone. TA98NR , a mutant of TA98 that is resistant to nitrofurazone and NP but not to DNP, lacked the major nitroreductase but retained two minor components. In contrast, a mutant ( DNP6 ) which is resistant to DNP (but not to NP) contained a full complement of nitroreductases. When the metabolism of [3H]DNP by crude extracts of TA98 was re-examined, previously undetected metabolites were found. These were more polar than DAP and ANP and were also seen when TA98NR was used as the source of enzyme. These metabolites were not formed when enzymes from TA98DNP6 or TA98NR / DNP6 were used. This work supports the notion that some enzymic activity other than (or in addition to) nitroreductase is required for the activation of DNP and that the new polar metabolites may be related to this process.     

Effects of diet composition on mutagenic activity in urine

The effects of dietary habits on mutagenic activity in urine were investigated using the umu test based on the use of the genetically engineered bacteria Salmonella typhimurium TA 1535 pSK1002. Genotoxic effects in sample urine were detected by measuring the activation of the SOS response in the bacteria and recording the beta- galactosidase activity. Human subjects consisted of smokers and non-smokers. Urine from subjects who consumed fish showed the highest mutagenic activity, followed by the urine samples from subjects who ate pork or beef. Chicken induced a low level of mutagenic activity. When the subjects ate fried or roasted animal foods, the urine samples gave higher mutagenicity than the urine samples from the subject who consumed non-fried or non-roasted animal foods. When the subject ate vegetables along with a diet rich in animal foods, the activity in urine decreased. Herbs and spices gave the same tendency toward decline as vegetables. Non-smoker urine shower mutagenic activity than samples from smokers.     

Study of promutagen biotransformation in the Ames test. III. The role of conjugation with glucuronic acid and sulfate in the modification of mutagenic effect of nitrosomorpholine, diethylnitrosamine and cyclophosphamide

The role of reactions of conjugation with uridine diphosphoglucuronic acid (UDPGA) and with 3-phosphoadenosine-5-phosphosulfate (PAPS) in modification of the mutagenic effect of diethyl nitrosamine (DENA), nitrosomorpholine (NM) and cyclophosphane (CP) was studied by the Ames test. It was shown that adding UDPGA to the activating mixture significantly decreased the level of the mutagenic effect of DENA, NM and CP on bacteria Salmonella typhimurium TA 1950, when S9 and microsomal fractions of rat liver homogenate were used. Adding PAPS to the activating mixture when S9 and cytosole fractions were used, did not affect mutagenic action of DENA on S. typhimurium TA 1950 and TA 1535, enhancing the mutagenic effect of CP on TA 1535, with no such influence on TA 1950. Introduction of PAPS into the activating mixture elevated the mutagenic effect of NM on both bacterial strains using S9 fraction but not cytosole fraction.     

A comparative analysis of mutagenic and SOS-induced activity in three classes of chemical compounds

Mutagenic and SOS-inducing potential of 23 derivatives of fluorenone, phenanthrenequinone and biphenyl have been studied in tester strains of Salmonella typhimurium and in Escherichia coli strain PQ 37. 14 of these compounds revert the mutation hisD3052 (much less than -1 much greater than type), but none of them induce mutations in the strain TA 1535. Maximal mutagenic activity has been shown in strain TA 1538 for amide of 2,7-dinitrofluorenone-4-carbonic acid (580 revertants per nmol), 2,7-dinitrophenanthrenequinone (308 revertants per nmol), 2,4,7-trinitrophenanthrenequinone (306 revertants per nmol) and 2',4,4'-trinitrobiphenyl-2-carbonic acid (251 revertants per nmol). In plasmid-containing strain TA 98 the mutagenic potential of the compounds tested is lower than in the TA 1538 strain. It has been suggested that mutagenic activity of these compounds can be attributed to their acceptor properties, namely, the ability to form charge transfer complexes with DNA. SOS-inducing activity has been shown for 5 compounds, also positive in mutation induction. Mutagenic and SOS-inducing activities positively correlate in fluorenone derivatives. Among phenanthrenequinone derivatives, compounds with high mutagenic activity only can induce SOS response. None of the biphenyls tested induce SOS functions. The compounds giving the positive result in the SOS-chromotest have rigid co-planar structure.     

Specificity and sensitivity of Salmonella typhimurium YG1041 and YG1042 strains possesing elevated levels of both nitroreductase and acetyltransferase activity

Acetyltransferase and nitroreductase are enzymes involved in the intracellular metabolic activation of nitroarenes and/or aromatic amines in Salmonella typhimurium. The plasmid carrying both the acetyltransferase and nitroreductase genes was introduced into S. typhimurium TA98 and TA100. The resulting strains, YG1041 and YG1042, respectively, showed high levels of both enzyme activities and were more sensitive to the mutagenic action of some nitro-aromatic compounds such as 2-nitrofluorene, 1-nitropyrene and p-nitrophenetole than did the sensitive strains previously established in this laboratory or the conventional strains. These results indicate that the new strains permit the very efficient detection of the mutagenicity of nitroarenes in the environment.     

Mutagenicity of the phenolic microsomal metabolites of 3-nitrofluoranthene and 1-nitropyrene in strains of Salmonella typhimurium

The environmental pollutant 3-nitrofluoranthene is metabolized in vitro and in vivo to several products including the phenolic metabolites 3-nitrofluoranthen-6-ol (3NF-6-ol), 3-nitrofluoranthen-8-ol (3NF-8-ol), and 3-nitrofluoranthen-9-ol (3NF-9-ol). Similarly, 1-nitropyrene is metabolized to the phenolic metabolites 1-nitropyren-3-ol (1NP-3-ol), 1-nitropyren-6-ol (1NP-6-ol), and 1-nitropyren-8-ol (1NP-8-ol). The mutagenicity of these compounds was investigated using strains of Salmonella typhimurium deficient in either certain nitroreductase or the aryl hydroxylamine O-esterificase. In TA98, 3-nitrofluoranthene and 3NF-8-ol were equally mutagenic at approximately 10³ revertants/nmole while 3NF-6-ol and 3NF-9-ol were 10-fold less mutagenic. 1-Nitropyrene and 1NP-3-ol likewise were equally mutagenic at approximately 700 revertants/nmole and 1NP-6-ol and 1NP-8-ol were 100-fold less mutagenic. The mutagenicity of 1-nitropyrene was dependent on the ‘classical nitroreductase’ which is absent in TA98NR, and that of 3-nitrofluoranthene, 3NF-8-ol, and 1NP-3-ol was less dependent on this nitroreductase. Using TA98/1,8DNP₆, it was determined that the mutagenicity of 3-nitrofluoranthene, 3NF-8-ol, and 1NP-3-ol but not 1-nitropyrene was dependent on the presence of the O-esterificase. 3-Nitrofluoranthene and 3NF-8-ol were mutagenic in TA100, while 3NF-6-ol and 3NF-9-ol were considerably less mutagenic. 3-Nitrofluoranthene was not mutagenic in TA100NR nor in TA100-Tn5-1,8-DNP1012. None of the phenolic metabolites of 3-nitrofluoranthene were mutagenic in TA100-Tn5-1,8DNP1012 indicating a strong dependence for mutagenicity of the O-esterificase of the 1,8-dinitropyrene nitroreductase which is absent in this strain. These results are discussed in view of possible mechanisms for the differences in the mutagenicity of the phenolic metabolites of these two nitrated arenes.     

Nitroarenes in Suimon River sediment

Mutagenic activity was observed in sediments of the Suimon River bed with and without S9 mix. The direct-acting mutagens in the sediment were investigated. The sediment was extracted with methanol and fractionated on a Silica gel column. The benzene fraction from the Silica gel column exhibited mutagenic activity without S9 mix in strain TA98, while it failed to show mutagenic activity in nitroreductase-deficient strain TA98NR. This observation led to the suspicion that nitro compounds were the direct-acting mutagens of these samples. The benzene fraction was treated by heptafluorobutyric anhydride (HFBA) and investigated with gas chromatography equipped with an electron capture detector (GC-ECD). 2-Nitrofluorene, 4,4'-dinitrobiphenyl, 2,7-dinitrofluorene and 1-nitropyrene were detected and measured quantitatively. The mutagenic activity of a mixture of these compounds was compared with that of the original fraction and the direct-acting mutagenicity of Suimon River sediment can be explained by these nitroarenes, especially 1-nitropyrene.     

Sensitive method for the detection of mutagenic nitroarenes and aromatic amines: new derivatives of Salmonella typhimurium tester strains possessing elevated O-acetyltransferase levels

Acetyl-CoA: N-hydroxyarylamine O-acetyltransferase is an enzyme involved in the intracellular metabolic activation of arylhydroxylamines derived from mutagenic nitroarenes and aromatic amines. The acetyltransferase gene of Salmonella typhimurium TA1538 was cloned into pBR322 and the plasmids harboring the gene were introduced into TA98 and TA100. The resulting strains (YG1024 and YG1029) had about 100 times higher 2-hydroxyamino-6-methyldipyrido[1,2-a:3',2'-d]-imidazole (N-hydroxy-Glu-P-1) O-acetyltransferase activity than TA1538 containing pBR322, and were extremely sensitive to the mutagenic actions of 2-nitrofluorene, 1-nitropyrene, 1,8-dinitropyrene, 2-amino-6-methyldipyrido[1,2-a:3',2-d)-imidazole (Glu-P-1), 2-aminofluorene and 2-aminoanthracene. These results indicate that the new strains permit the efficient detection of the mutagenicity of environmental nitroarenes and aromatic amines.     

Genotoxic activation of 2-phenylbenzotriazole-type compounds by human cytochrome P4501A1 and N-acetyltransferase expressed in Salmonella typhimurium umu strains

Four 2-phenylbenzotriazole (PBTA)-type compounds (PBTA-4, PBTA-6, PBTA-7, and PBTA-8) were identified as major mutagens in blue cotton/rayon-adsorbed substances collected at sites below textile dyeing factories or municipal water treatment plants treating domestic waste and effluents from textile dyeing factories in several rivers in Japan. The main purpose of this study is to understand the basis of the roles of human cytochrome P450 (CYP) and N-acetyltransferases (NATs) in genotoxic activation of PBTA derivatives. We compared the induction of umuC gene expression as a measure of genotoxicity using Salmonella typhimurium TA1535/pSK1002 (parental strain), NM2009 (bacterial O-acetyltransferase-overexpressing strain) established in our laboratories. PBTA-4, PBTA-6, PBTA-7, and PBTA-8 induced the umuC gene expression more strongly in the bacterial O-acetyltransferase-overproducing strain than in the parental strain in the presence of rat S9 mix. We determined the activation of PBTA derivatives by cDNA-based recombinant (Trichoplusia ni) systems expressing human or rat cytochrome P450 enzymes (P450 or CYP) and NADPH-P450 reductase using S. typhimurium NM2009. The results showed that human recombinant CYP1A1 enzyme was much more active than CYP1A2 and CYP3A4 in the genotoxic activation of PBTA-4, PBTA-6, PBTA-7, and PBTA-8. Similarly, rat recombinant CYP1A1 enzyme catalyzed the activation of these chemicals at high rates. alpha-Naphthoflavone, a known inhibitor of CYP1A1, was found to inhibit genotoxic activation caused by PBTA derivatives. We further determined the activation of PBTA derivatives using S. typhimurium NM6001 (human NAT1-expressing strain), S. typhimurium NM6002 (human NAT2-expressing strain), and S. typhimurium NM6000 (O-AT-deficient parent strain) in the presence of S9 mix. PBTA-4 showed almost similar sensitivity in the NAT1-expressing strain and the NAT2-expressing strain, although NAT2-expressing strain exhibited relatively higher sensitivity to PBTA-6, PBTA-7, and PBTA-8 than NAT1-expressing strain. The results support the view that O-acetylation by human NAT1 and NAT2 enzymes is involved in the genotoxic activation of PBTA compounds. These results demonstrate for the first time that human P4501A1 and NATs (NAT1 and NAT2) contribute significantly to the activation of PBTA-type compounds to genotoxic metabolites that induce umuC gene expression in S. typhimurium tester strains.     

On the induction of umu gene expression in Salmonella typhimurium strain TA1535/pSK1002 by some nitrofurans.

Several nitrofurans were found to induce umu gene expression in Salmonella typhimurium TA1535/pSK1002 as defined on the basis of at least a 2-fold increase of beta-galactosidase activity over the background level. beta-Galactosidase activity increased with increasing concentrations of the chemical, attained a maximum at a concentration which was different for different nitrofurans used, and then gradually decreased with a further increase of the nitrofuran concentration. The umu gene expression test revealed that the genotoxic activity was highest for furazolidone and lowest for 5-nitro-2-furaldehyde.     

Methyl methanesulphonate (MMS) is clearly mutagenic in S. typhimurium strain TA1535; a comparison with strain TA100

No mutagenicity or an uncertain mutagenic response has been reported in the literature for methyl methanesulphonate (MMS) in S. typhimurium strain TA1535 when using the plate assay. In our studies we found a reproducible mutagenic activity of 62 revertants/mumole and plate for MMS in strain TA1535 when using the preincubation assay. A dose-dependent increase in revertants was, however, observed only at fairly high doses (exceeding 4 mumole). Two different slopes were observed in the dose-response curve when testing MMS with strain TA100. Slope A is dependent on the error-prone response, possible only in strain TA100 due to the pKm101 plasmid (R factor) but not possible in strain TA1535 due to its umuDC deficiency. Slope B observed at higher doses (as in strain TA1535) could be explained through a GC----AT transition initiated by the O6-methylation of guanine. Our findings demonstrate that MMS induces back mutation in S. typhimurium strains carrying the hisG46 missense mutation due to the formation of O6-methylguanine. In the case of strain TA100 the pKm101 plasmid-mediated error-prone mechanism is, however, the predominant process in MMS mutagenesis which leads to a higher mutagenic response at much lower doses than the GT----AT transition in strain TA1535.     

Photochemical instability of 1-nitropyrene, 3-nitrofluoranthene, 1,8-dinitropyrene and their parent polycyclic aromatic hydrocarbons

The environmental contaminants pyrene, 1-nitropyrene, 1,8-dinitropyrene, fluoranthene, and 3-nitrofluoranthene were exposed to light (greater than or equal to 310 nm) either in DMSO, or following coating onto silica. Under all conditions tested the pyrenyl were less stable than the fluoranthenyl compounds. During irradiation in DMSO or on silica, 1-nitropyrene had half-lives of 1.2 and 6 days, while those of 3-nitrofluoranthene were 12.5 and greater than 20 days, respectively. The photodecomposition of 1,8-dinitropyrene resembled that of 1-nitropyrene with half-lives of 0.7 and 5.7 days. A principle photodecomposition product of 1,8-dinitropyrene was identified as 1-nitropyren-8-ol. It was also found that when the nitroarenes were exposed to light, the loss of compound was associated with a concomitant loss of mutagenicity in Salmonella typhimurium strain TA98. The mechanism of nitrated polycyclic aromatic hydrocarbon decomposition and 1-nitropyren-8-ol formation, and the relevance to the atmospheric disposition of these compounds are discussed.     

Airplane emissions: a source of mutagenic nitrated polycyclic aromatic hydrocarbons

Organic solvent extracts from airplane emission particulates are mutagenic for Salmonella typhimurium strain TA98. Using Salmonella tester strains deficient in enzymes required for the bioactivation of various nitroarenes, the mutagenicity present in these emissions was ascribed to the presence of nitrated polycyclic aromatic hydrocarbons. Based on the known aircraft particulate emission rates at U.S. airports, and using 1-nitropyrene (1-NP) and 1,8-dinitropyrene (1,8-DNP) as surrogates, it is calculated that at a minimum 7 kg 1-NP and 20 g, 1,8-DNP are emitted daily at a typical U.S. airport.