Mutation spectra of chemical fractions of a complex mixture: role of nitroarenes in the mutagenic specificity of municipal waste incinerator emissions

Abstract

Using an ion-exchange procedure coupled to a microsuspension Salmonella assay, we fractionated the dichloromethane-extractable particulate organics emitted by a municipal waste incinerator. Most (80–95%) of the mutagenic activity resided in the neutral/base fraction; however, the polar neutral fraction accounted for 12% of the direct-acting mutagenic activity. The mutagenic potencies of the whole extract and the various fractions were 4–15 times greater in the absence than in the presence of S9. Results with strains deficient in classical nitroreductase (TA98NR) and transacetylase (TA98/1,8-DNP 6) indicated that a majority of the direct-acting mutagenicity was due to nitroarenes. This was confirmed by bioassay-directed subfractionation of the neutral/base faction by a cyanopropyl/HPLC method. The mutations in −3,000 revertants (∼ 400 each induced in TA98 by the whole extract, the neutral/base and polar neutral fractions from the ion-exchange column and 3 of the neutral/base subfractions from the HPLC column; along with 200 revertants each induced by the model nitroarene 1-nitropyrene (1NP) in strains TA98, TA1538 and TA100) were analyzed by probe hybridization and PCR DNA sequence analysis. The results indicated that nitroarenes such as 1NP that eluted in the neutral/base fraction accounted for at least 50% of the direct-acting mutagenicity and induced only a hotspot 2-base deletion in the sequence (CG) 4 in TA98. In contrast, most of the complex frameshifts (a frameshift with a flanking base substitution) induced by the whole extract were induced by nitroarenes other than 1NP that were activated by transacetylation and that eluted in the polar neutral fraction. This study (1) identifies nitroarenes as an important contributor to the mutagenic activity of the emissions from municipal waste incinerators; (2) confirms our previous conclusion that the mutation spectrum of a complex mixture reflects the dominance of particular classes of chemical mutagens within the mixture; and (3) demonstrates the possibility of isolating certain chemical fractions of a complex mixture that induce certain classes of mutations produced by the whole, unfractionated mixture.