Twenty-three polycyclic aromatic hydrocarbons (PAH) were determined in atmospheric particulate matter in 4 places of the Paris area at several times of the year. Fractionation was performed by reversed-phase high-pressure liquid chromatography. Determination was done by recording emission or excitation fluorescence spectra via a stopped-flow technique. Triphenylene was also extemporaneously determined by its phosphorescence spectrum at low temperature. Among the PAH determined dibenz(e,ghi)perylene has not been detected before in atmospheric particulate matter. The 10 more abundant PAH ranged from 0.1 to 40 ng/m3 of filtered air. Concentrations in August are from 14 to 250 times less than in January depending on the PAH. The reasons for this difference of behaviour among the PAH were investigated with regard to their photochemical and non-photochemical reactivity.

Dibenzofluoranthene-12,13-dihydrodiol (DBF-12,13-DHD) is six times more mutagenic in Salmonella TA100 than dibenzofluoranthene-3,4-dihydrodiol (DBF-3,4-DHD). However, these two major dibenzo[a,e]fluoranthene (DBF) proximate metabolites, which are immediate precursors of the corresponding diolepoxides, showed on an equimolar basis nearly identical initiation activities on mouse skin; they induced three times more papillomas than the parent hydrocarbon. On the other hand the epithelioma initiation capacities, i.e. the number of papillomas progressing to malignant tumours, of DBF or the two dibenzofluoranthene dihydrodiols were equivalent. Norharman, a putative vicinal diolepoxidation inhibitor in DBF metabolism when administered topically together with the initiation dose (100 nmol), strongly inhibited the induction of tumours by DBF-3,4-DHD and DBF. The relationship between in vitro mutagenic activity in Salmonella and the carcinogenicity of DBF metabolites in mice appears to be qualitative rather than quantitative.

The metabolism of the polycyclic hydrocarbon dibenzo[a,e]fluoranthene (DBF) has been investigated. Two new primary metabolites have been identified by proton n.m.r. as the trans diaxial dihydrodiols of the bay and of the pseudo bay regions of DBF. In addition, twelve new metabolites arising from secondary and tertiary metabolic transformations have been identified. The stereochemistry of eleven of these products has been established by proton n.m.r. spectroscopy. In contrast with other alternant carcinogenic polycyclic hydrocarbons, a vicinal diol epoxidation at the bay region of the trans diequatorial dihydrodiols is a minor reaction relative to attack at distant sites, which leads principally to phenolic derivatives of the dihydrodiols and, with a lower yield, to a bis-dihydrodiol (3,4,12,13-tetrahydro-3,4,12,13-tetrahydroxy-DBF). This offers a possibility of bifunctional metabolic activation in the carcinogenicity of DBF. A catechol of the benzanthracenic moiety of DBF has also be identified, dibenzo[a,e]fluoranthene 3,4-catechol. In summary, all three external rings of DBF can be attacked enzymatically, but apparently ring E does not undergo epoxidation while more usual trans diaxial and diequatorial dihydrodiols, as well as tetraols of rings A and D, were detected.

Dibenzo[a,e]fluoranthene, its 7-hydroxy, 3,4- and 12,13-dihydrodiol metabolic derivatives as well as three synthetic, structurally related hydrocarbons, were tested for mutagenicity towards Salmonella typhimurium TA100 strain in the presence of 3-methylcholanthrene-treated rat and mouse liver post-mitochondrial supernatants. Of these compounds, the 12,13-dihydrodiol showed the highest activity, being 6-10 times more mutagenic than the parent compound. Our data, in conjunction with those of previous studies on the liver microsomal metabolism and DNA binding of dibenzo[a,e]fluoranthene and its dihydrodiols, indicate that activation of dibenzo[a,e]fluoranthene to bacterial mutagens may occur predominantly through a vicinal, non-bay-region 12,13-dihydrodiol epoxide.

The structural identification of nineteen metabolites of dibenzo[a,e]fluoranthene (DBF) obtained by incubation in rat and mouse liver microsomes, allows one to establish a qualitative and semi-quantitative metabolic chart, involving up to three distinct oxidative attacks. The primary steps lead to dihydrodiols on rings A and D and phenols on rings A and E. Secondary vicinal epoxidation of dihydrodiols is a minor route as compared to attack at a second peripheral ring. Even after a third oxidation, one of the peripheral rings A, D and E remains unsubstituted. A model for cytochrome P-450 enzymatic activity which takes into account most of the observations is proposed. It requires that the catalytic site for monooxygenation is 0.6 nm apart from the center of an hydrophobic protein site accommodating one of the unsubstituted peripheral benzenoid rings. both trans diequatorial dihydrodiols of ring A and D corresponding to the 'bay' and 'pseudo bay region'; of DBF appear in the activation pathways for the in vivo carcinogenesis. The ultimate metabolite reacting with DNA is thus, most probably, a vicinal dihydrodiol epoxide of ring A or D. The great complexity of the metabolic chart of DBF as compared to other carcinogenic polycyclic aromatic hydrocarbons leaves also the possibility of sequential reactions at these two distinct sites of the molecule.