Polycyclic aromatic hydrocarbons in the diet.

Polycyclic aromatic hydrocarbons (PAHs), of which benzo[a]pyrene is the most commonly studied and measured, are formed by the incomplete combustion of organic matter. They are widely distributed in the environment and human exposure to them is unavoidable. A number of them, such as benzo[a]pyrene, are carcinogenic and mutagenic, and they are widely believed to make a substantial contribution to the overall burden of cancer in humans. Their presence in the environment is reflected in their presence at detectable levels in many types of uncooked food. In addition, cooking processes can generate PAHs in food. PAHs can also be formed during the curing and processing of raw food prior to cooking. Several studies have been carried out to determine the levels of exposure to PAHs from representative human diets, and the proportion of the overall burden of environmental exposure to PAHs that is attributable to the diet. In most cases, it is concluded that diet is the major source of human exposure to PAHs. The major dietary sources of PAHs are cereals and vegetables, rather than meat, except where there is high consumption of meat cooked over an open flame. More recently, biomonitoring procedures have been developed to assess human exposure to PAHs and these have also indicated that diet is a major source of exposure. Exposure to nitro-PAHs through food consumption appears to be very low.     

Effects of co-occurring aromatic hydrocarbons on degradation of individual polycyclic aromatic hydrocarbons in marine sediment slurries.

Rates of polycyclic aromatic hydrocarbon (PAH) degradation and mineralization were influenced by preexposure to alternate PAHs and a monoaromatic hydrocarbon at relatively high (100 ppm) concentrations in organic-rich aerobic marine sediments. Prior exposure to three PAHs and benzene resulted in enhanced [14C]naphthalene mineralization, while [14C]anthracene mineralization was stimulated only by benzene and anthracene preexposure. Preexposure of sediment slurries to phenanthrene stimulated the initial degradation of anthracene. Prior exposure to naphthalene stimulated the initial degradation of phenanthrene but had no effect on either the initial degradation or mineralization of anthracene. For those compounds which stimulated [14C]anthracene or [14C]naphthalene mineralization, longer preexposures (2 weeks) to alternative aromatic hydrocarbons resulted in an even greater stimulation response. Enrichment with individual PAHs followed by subsequent incubation with one or two PAHs showed no alteration in degradation patterns due to the simultaneous presence of PAHs. The evidence suggests that exposure of marine sediments to a particular PAH or benzene results in the enhanced ability of these sediments to subsequently degrade that PAH as well as certain other PAHs. The enhanced degradation of a particular PAH after sediments have been exposed to it may result from the selection and proliferation of specific microbial populations capable of degrading it. The enhanced degradation of other PAHs after exposure to a single PAH suggests that the populations selected have either broad specificity for PAHs, common pathways of PAH degradation, or both.     

Biodegradation of polycyclic aromatic hydrocarbons

The intent of this review is to provide an outline of the microbial degradation of polycyclic aromatic hydrocarbons. A catabolically diverse microbial community, consisting of bacteria, fungi and algae, metabolizes aromatic compounds. Molecular oxygen is essential for the initial hydroxylation of polycyclic aromatic hydrocarbons by microorganisms. In contrast to bacteria, filamentous fungi use hydroxylation as a prelude to detoxification rather than to catabolism and assimilation. The biochemical principles underlying the degradation of polycyclic aromatic hydrocarbons are examined in some detail. The pathways of polycyclic aromatic hydrocarbon catabolism are discussed. Studies are presented on the relationship between the chemical structure of the polycyclic aromatic hydrocarbon and the rate of polycyclic aromatic hydrocarbon biodegradation in aquatic and terrestrial ecosystems.     

Non-enzymic activation of polycyclic aromatic hydrocarbons as mutagens.

Samples of 22 polycyclic aromatic hydrocarbons and related derivatives were subjected to ⁶⁰Co gamma radiation in air, and the irradiated samples were tested for mutagenicity with the Salmonella typhimurium strains TA 98, TA 1535, TA 1537, and TA 1538. Testing was conducted with the bacterial strains alone, thus not fortified with liver-microsomal enzymes or other metabolizing systems. Marked mutagen responses were obtained for several irradiated samples with the TA 98, TA 1537, and TA 1538 strains but not with the TA 1535 strain. Irradiated samples of benzo[a]anthracene, benzanthrone, benozo[g,h,i]perylene, benzo[a]pyrene, chrysene, fluorene, 9-methylanthracene, 1-methylphenanthrene, 2-methylphenanthrene, and pyrene gave positive mutagenic tests and dose-responses, whereas unirradiated control samples of these were inactive. Acenaphthene, phenanthrene, and phenanthrenequinone exhibited toxicity which interfered with interpretation of mutagenicity testing. Samples of 2-methylanthracene and tetracene were mutagenic with or without irradiation. Alizarin, anthracene, anthraquinone, anthrone, dobenzo[a,h]anthracene, picene, and triphenylene negative results. Samples of benzo[a]pyrene adsorbed on silica gel irradiated in air by ⁶⁰Co gamma radiation or by 254 nm ultraviolet light and samples adsorbed on filter paper irradiated by visible light yielded preparations mutagenic towards the TA 98, TA 1537, and TA 1538 strains. These results suggest that parent polycyclic aromatic hydrocarbons not themselves mutagenic towards S. typhimurium may be oxidized in air by radiation-induced processes to products whose mutagenicity resembles that of liver-microsomal metabolites of the parent polycyclic aromatic hydrocarbon.     

Microsomal target proteins of metabolically activated aromatic hydrocarbons.

The specificity of binding to microsomal proteins of metabolically activated hydrocarbons has been studied. Radioactively labelled benzene, phenol, chlorobenzene, BP and MC were incubated with liver microsomes from control, phenobarbital- and MC-treated rats in the presence of an NADPH-generating system. The patterns of metabolite binding to microsomal proteins were examined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis and fluorography. Benzene, phenol and chlorobenzene metabolites showed one type of binding pattern dominated by a band at 72 000 Mr. This band was strong both in control and induced microsomes. Additional radioactive bands were seen in the 50 000--60 000 Mr region particularly in MC-induced microsomes. BP and MC metabolites showed a different type of binding pattern with incorporation of radioactivity into several fractions in the 50 000--60 000 Mr region of MC-induced microsomes. Two other strongly labelled fractions occurred at 68 000 and 72 000 Mr. The incorporation was low into control and phenobarbital-induced microsomes. Two labelled bands (Mr 56 000 and 72 000) were common for all hydrocarbons in MC-induced microsomes. The 56 000 Mr band had the same mobility in the gel as an MC-induced protein likely to be cytochrome P-448. The NADPH-generating system was essential for metabolite binding and GSH and UDPGA greatly reduced binding. We suggest that differences in metabolite binding patterns reflect differences in the routes of metabolite formation and that activated hydrocarbons are likely to bind to proteins close to their site of formation.     

污染土壤中多环芳烃生物降解的调控研究

选用温度、湿度、表面活性剂ＴＷ８０和ＣＮＰ比４个因素为调控因子,采用正交法进行周期为１５０天的实验研究．结果表明,３０天后,土壤中ＰＡＨｓ的降解率可达４４．５～７４．６％,６０天后,达７０．４～９３．７％,降解率的不同与调控条件显著相关．在此期间,降解最佳条件为４０℃,湿度２５％,ＣＮＰ比为１２０１０１,ＴＷ８０分别为２００～５００ｍｇ·ｋｇ－１．实验结束时,土壤中ＰＡＨｓ的降解率达９１．２～９９．８％．降解的最佳条件是４０℃,湿度１５％．经Ｒ值判别表明,不同时期各因子对ＰＡＨｓ降解影响有所不同．温度对ＰＡＨｓ降解影响较大,表面活性剂对土壤中ＰＡＨｓ的生物降解有调控作用．     

Porphinatoiron-mediated oxidation of polycyclic aromatic hydrocarbons

Although porphinatoiron complexes have been used extensively as biomimetic catalysts for oxidation of aliphatic and olefinic hydrocarbons, few oxidations of polycyclic aromatic hydrocarbons (PAH) have been reported. In all cases, heterogeneous iodosobenzene/tetraphenylporphinatoiron(III) systems were employed, oxidations were inefficient and control experiments demonstrating the requirement for catalyst were not described. The current study investigates the oxidation of pyrene, benzo[a]pyrene and benzanthracene in a homogeneous m-chloroperoxybenzoic acid/bifacially hindered porphinatoiron system in which the peroxyacid was shown to be unreactive in the absence of catalyst. Pyrene and benzo[a]pyrene were oxidized efficiently, with pyrene yielding mixtures of 1.6- and 1.8-quinones and benzo[a]pyrene yielding mixtures of phenols and quinones. Benzanthracene was oxidized less efficiently, primarily at the meso positions, to give 7.12-quinone. Initial oxidation of meso carbons of benzo[a]pyrene (confirmed by the presence of the 6-hydroxy derivative as a product) and benzanthracene indicates that PAH-to-catalyst charge transfer may be an important oxidation pathway. Oxidation of pyrene was performed by addition of pyrene to observable oxo iron(V) species as well as in a catalytic reaction where excess peroxyacid was added to a solution of pyrene and catalyst and oxo iron(V) is not generated as an observable intermediate. Yields (based on oxidant consumed), were identical under both conditions, strongly supporting oxo iron(V) as a common intermediate.     

Interaction of polynucleotides with aromatic hydrocarbons

DNA in its native and denatured form and yeast RNA complex individual aromatic hydrocarbon molecules but single-stranded poly A does not. The degree of complexing appears to depend on molecular dimensions; it is appreciable for phenanthrene, pyrene, and benzpyrene but very small or undetectible for coronene, tetracene, pentacene, and 20-methylcholanthrene.     

Effects of co-occurring aromatic hydrocarbons on degradation of individual polycyclic aromatic hydrocarbons in marine sediment slurries

Rates of polycyclic aromatic hydrocarbon (PAH) degradation and mineralization were influenced by preexposure to alternate PAHs and a monoaromatic hydrocarbon at relatively high (100 ppm) concentrations in organic-rich aerobic marine sediments. Prior exposure to three PAHs and benzene resulted in enhanced [14C]naphthalene mineralization, while [14C]anthracene mineralization was stimulated only by benzene and anthracene preexposure. Preexposure of sediment slurries to phenanthrene stimulated the initial degradation of anthracene. Prior exposure to naphthalene stimulated the initial degradation of phenanthrene but had no effect on either the initial degradation or mineralization of anthracene. For those compounds which stimulated [14C]anthracene or [14C]naphthalene mineralization, longer preexposures (2 weeks) to alternative aromatic hydrocarbons resulted in an even greater stimulation response. Enrichment with individual PAHs followed by subsequent incubation with one or two PAHs showed no alteration in degradation patterns due to the simultaneous presence of PAHs. The evidence suggests that exposure of marine sediments to a particular PAH or benzene results in the enhanced ability of these sediments to subsequently degrade that PAH as well as certain other PAHs. The enhanced degradation of a particular PAH after sediments have been exposed to it may result from the selection and proliferation of specific microbial populations capable of degrading it. The enhanced degradation of other PAHs after exposure to a single PAH suggests that the populations selected have either broad specificity for PAHs, common pathways of PAH degradation, or both.     

Metabolism of aromatic hydrocarbons by yeasts

Six yeasts were examined for their ability to metabolize naphthalene, biphenyl and benzo(a)pyrene. All of the organisms tested oxidized these aromatic hydrocarbons. Candida lipolytica oxidized naphthalene to 1-naphthol, 2-naphthol, 4-hydroxy-1-tetralone and trans-1,2-dihydroxy-1,2-dihydronaphthalene. The major metabolite was 1-naphthol. C. lipolytica oxidized biphenyl to produce 2-, 3-, and 4-hydroxybiphenyl, 4,4′-dihydroxybiphenyl and 3-methoxy-4-hydroxybiphenyl. 4-Hydroxybiphenyl was the predominant metabolite formed. C. lipolytica oxidized benzo(a)pyrene to 3-hydroxybenzo(a)pyrene and 9-hydroxybenzo(a)pyrene. Metabolites were isolated and identified by absorption spectrophotometry, mass spectrometry and thin-layer, gasliquid and high-pressure liquid chromatography. Where possible the structures of these metabolites were confirmed by comparison with authenic compounds.     

Anaerobic degradation of non-substituted aromatic hydrocarbons

Aromatic hydrocarbons are among the most prevalent organic pollutants in the environment. Their removal from contaminated systems is of great concern because of the high toxicity effect on living organisms including humans. Aerobic degradation of aromatic hydrocarbons has been intensively studied and is well understood. However, many aromatics end up in habitats devoid of molecular oxygen. Nevertheless, anaerobic degradation using alternative electron acceptors is much less investigated. Here, we review the recent literature and very early progress in the elucidation of anaerobic degradation of non-substituted monocyclic (i.e. benzene) and polycyclic aromatic hydrocarbons (PAH such as naphthalene and phenanthrene). A focus will be on benzene and naphthalene as model compounds. This review concerns the microbes involved, the biochemistry of the initial activation and subsequent enzyme reactions involved in the pathway.     

Genotoxicity of polycyclic aromatic hydrocarbons in Escherichia coli PQ37.

In the present investigation, 32 polycyclic aromatic hydrocarbons (PAHs) were tested for genotoxicity in E. coli PQ37 using the standard tube assay of the SOS chromotest. PAHs such as benzo[ghi]fluoranthene, benzo[j]fluoranthene, benzo[a]pyrene, chrysene, dibenzo[a,l]pyrene, fluoranthene and triphenylene exhibited high genotoxicity when incubated in the presence of an exogenous metabolic activation mixture. The results were compared to those obtained with the Salmonella/microsome test.     

Bacterial oxidation of the polycyclic aromatic hydrocarbons acenaphthene and acenaphthylene.

A Beijerinckia sp. and a mutant strain, Beijerinckia sp. strain B8/36, were shown to cooxidize the polycyclic aromatic hydrocarbons acenaphthene and acenaphthylene. Both organisms oxidized acenaphthene to the same spectrum of metabolites, which included 1-acenaphthenol, 1-acenaphthenone, 1,2-acenaphthenediol, acenaphthenequinone, and a compound that was tentatively identified as 1,2-dihydroxyacenaphthylene. In contrast, acenaphthylene was oxidized to acenaphthenequinone and the compound tentatively identified as 1,2-dihydroxyacenaphthylene by the wild-type strain of Beijerinckia. Both of these products were also formed when the organism was incubated with synthetic cis-1,2-acenaphthenediol. A metabolite identified as cis-1,2-acenaphthenediol was formed from acenaphthylene by the mutant Beijerinckia sp. strain B8/36. Cell extracts prepared from the wild-type Beijerinckia strain contain a constitutive pyridine nucleotide-dependent dehydrogenase which can oxidize 1-acenaphthenol and 9-fluorenol. The results indicate that although acenaphthene and acenaphthylene are both oxidized to acenaphthenequinone, the pathways leading to the formation of this end product are different.     

Detoxification of polycyclic aromatic hydrocarbons by fungi

Summary The polycyclic aromatic hydrocarbons (PAHs) are a group of hazardous environmental pollutants, many of which are acutely toxic, mutagenic, or carcinogenic. A diverse group of fungi, includingAspergillus ochraceus, Cunninghamella elegans, Phanerochaete chrysosporium, Saccharomyces cerevisiae, andSyncephalastrum racemosum, have the ability to oxidize PAHs. The PAHs anthracene, benz[a]anthracene, benzo[a]pyrene, fluoranthene, fluorene, naphthalene, phenanthrene, and pyrene, as well as several methyl-, nitro-, and fluoro-substituted PAHs, are metabolized by one or more of these fungi. Unsubstituted PAHs are oxidized initially to arene oxides,trans-dihydrodiols, phenols, quinones, and tetralones. Phenols andtrans-dihydrodiols may be further metabolized, and thus detoxified, by conjugation with sulfate, glucuronic acid, glucose, or xylose. Although dihydrodiol epoxides and other mutagenic and carcinogenic compounds have been detected as minor fungal metabolites of a few PAHs, most transformations performed by fungi reduce the mutagenicity and thus detoxify the PAHs.     

Anaerobic oxidation of aromatic compounds and hydrocarbons

Aromatic compounds and hydrocarbons have in common a great stability due to resonance energy and inertness of CbondH and CbondC bonds. It has been taken for granted that the metabolism of these compounds obligatorily depends on molecular oxygen. Oxygen is required first to introduce hydroxyl groups into the substrate and then to cleave the aromatic ring. However, newly discovered bacterial enzymes and reactions involved in oxidation of aromatic and hydrocarbon compounds to CO(2) in the complete absence of molecular oxygen have been discovered. Of special interest are two reactions: the reduction of the aromatic ring of benzoyl-coenzyme A and the addition of fumarate to hydrocarbons. These reactions transform aromatic rings and hydrocarbons into products that can be oxidized via more conventional beta-oxidation pathways.