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HPLC Fraction number Increasing polarity —>

FIGURE 10.26 Mutagrams of direct mutagenicity on different HPLC fractions for composite 12-h daytime and nighttime vapor-phase samples collected on PUF plugs in Redlands, California, in October 1994. Mutagen densities (rev m~3) on TA98, — S9, microsuspension modification (adapted from Gupta et al., 1996).

Redlands, California, a receptor site ~ 110 km downwind from central Los Angeles.

Bioassay-directed fractionations of the daytime and nighttime samples produced the mutagrams shown in Fig. fO.26. The ambient nitronaphthalenes and methylnitronaphthalenes in fraction 4 contribute ~18% of the total daytime mutagenic activity of 23 rev m"3; they are formed by OH radical attack on the parent PAHs (see Sasaki et al., 1995, and Section F). The total nighttime activity is higher than the daytime activity, 3f rev m~3, and was attributed to more efficient formation of the nitronaphthalenes and methylnitronaphthalenes in NO, radical initiated reactions (Atkinson and Arey, 1994).'

In summary, Gupta and co-workers (1996) reported that ambient concentrations of the vapor-phase nitronaphthalenes and methylnitronaphthalenes are generally greater than those of other particle-phase nitro-PAHs present simultaneously (Arey et al., 1987; Wilson et al., 1995). This is particularly important in that, as noted earlier (Pitts et al., 1985c; Pitts, 1987), 2-nitronaphthalene has been reported on intraperitoneal injection to be converted to 2-hydroxyaminonaphtha-lene, the same metabolite that 2-aminonaphthalene (Johnson and Cornish, 1978), an animal and human

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