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F 134 (1.0)

89 (0.7)

159(1.2)

" Adapted irom Einisto et al. (1991).

h Mutagenic activities on strains TA98 and TA100 assigned a value of 1.0. Relative mutagenicities on other strains given in parentheses. ' For mutagenic activities on TA98NR, TA98/l,8-DNPfl, TA100NR, and TA100/1.8-DNP, see Einisto et al. (1991).

" Adapted irom Einisto et al. (1991).

h Mutagenic activities on strains TA98 and TA100 assigned a value of 1.0. Relative mutagenicities on other strains given in parentheses. ' For mutagenic activities on TA98NR, TA98/l,8-DNPfl, TA100NR, and TA100/1.8-DNP, see Einisto et al. (1991).

and Arey, 1993); Table 10.18 reports values for f4 methylnitronaphthalenes assayed with the microsuspension modification (Gupta et al., 1996; Arey, 1998a). Both studies include mutagenicities for f- and 2-nitronaphthalene. The fact that the 2- and 3-nitro-fluorene isomers (Table 10.20) are the most active (with the 2-isomer more active than the 3-isomer) is consistent with an earlier report and theoretical considerations (see Arey et al., 1992, and references therein).

The wide range of mutagenicities of the methylni-tronaphthalene isomers, e.g., from "none detected" for 2-methyl-3-nitronaphthalene to 1700 rev/nmol for 2-methyl-6-nitronaphthalene, and the greater activity of 2-nitro- vs 1-nitronaphthalene (Table 10.18), is consistent with the proposal of Yu and co-workers (1992)

that within a class of isomeric nitro-PAH, the one with the nitro group located at the longest molecular axis should be the most potent direct mutagen in Salmonella typhimurium strain TA98 (Gupta et al., 1996). Other studies dealing with the experimental and theoretical aspects of structure-mutagenicity relationships in nitro-PAHs include, for example, those by El-Bayoumy et al. (1981), Ball et al. (1984), Hirayama et al. (1986), and Jung et al. (1991).

In the early f990s, several nitro-polycyclic aromatic compounds that are powerful direct mutagens were identified in ambient particulate matter, including the nitrophenanthrene lactones 2- and 4-nitro-6//-dibenzo[6,<i]pyran-6-one, whose mutagenicities are given in Table 10.20. The 2-isomer (XI) is not only very

TABLE 10.20 Direct Mutagenicities in Strain TA98 (— S9) for 1- and 2-Nitronaphthalene and Several Nitrofluorenes and Nitrodibenzopyranones in the Salmonella typhimurium Plate Incorporation and Microsuspension Preincubation Assays"

Microsuspension Plate incorporation assay, TA98 assay, TA98

TABLE 10.20 Direct Mutagenicities in Strain TA98 (— S9) for 1- and 2-Nitronaphthalene and Several Nitrofluorenes and Nitrodibenzopyranones in the Salmonella typhimurium Plate Incorporation and Microsuspension Preincubation Assays"

Microsuspension Plate incorporation assay, TA98 assay, TA98

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