Human Cell Mutagenicities of PAHs and PACs

Two human cell lines with good sensitivities have proven useful for laboratory and field studies MCL-5 (Crespi et al., 1991), and hlAlv2 (Penman et al., 1994). Durant and co-workers (1996) report specific activities determined with the hlAlv2 assay for standard (reference) samples of 67 PAHs and PACs. Fifty-five have been identified or are suspected to be present in ambient urban aerosols. The human cell potencies (relative to BaP = 1.00) of selected PAHs and PACs, along with their cancer potency equivalence factors (PEFs), are given in Tables 10.13 and 10.14. Dibenzo[a,/]pyrene (XXIX), cyclopenta[cd]pyrene 

Durant and co-workers (1998) analyzed an organic extract of the NIST reference complex mixture SRM 1649 (see Box 10.3) using the same human cell line (hlAlv2) and bioassay-directed fractionation. In the nonpolar fraction, cy c 1 o pe n t a[ cz/ ] py re n e, benzo[a]-pyrene, and benzo[ b ]fl uo ran the ne were responsible for 7, 4, and 2%, respectively, of the total extract mutagenicity. Only one potent O-PAC mutagen was identified in the semipolar fraction, the ketone, 6H-benzo[cd ]pyren-6-one ( 0.5%) (see discussion in Section D.3). 

Dibenzo[a,/]pyrene, a potent mutagen in the MCL-5 assay, was not detected in this analysis of SRM 1649. However, this 6-ring PAH XXIX was identified (but not quantified) by comparison to an authentic standard by Allen and co-workers (1998) in their analysis of size-segregated aerosols in urban Boston ambient air. Furthermore, in their August 1994 study of biologically active, particle-associated PAHs in ambient Riverside, California, Atkinson and Arey (1997) measured concentrations of 18, 20, and 15 pg m-3 of this compound for one daytime and two nighttime sampling events, respectively. These concentrations were 40-50% of the BaP concentrations in the same aerosol samples. 

In a laboratory environmental chamber study of the gas-phase photooxidation of naphthalene and phenan-threne, Sasaki and co-workers (1997b) found two products, 2-nitronaphthalene and 2-nitrodibenzopyranone (XI), that displayed significant genotoxicity in the MCL-5 human cell assay. This finding emphasized the importance of atmospheric reactions in forming mutagens, since the concentrations of such compounds are relatively high in ambient air compared to those expected for nitroarenes directly emitted from primary combustion sources (see Section F). 

Cyc I o pe n t a[ c 7 ] py re n e is also present in ambient aerosols collected in urban airsheds throughout the world at levels approximately equal to those of BaP and in some locations at significantly higher concen- 

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