MUTATION SPECTRA IN SALMONELLA OF CHLORINATED, CHLORAMINATED, OR OZONATED DRINKING-WATER EXTRACTS - COMPARISON TO MX

Drinking water samples were prepared in a pilot scale treatment plant by chlorination (Cl-2), chloramination (NH2Cl), ozonation (O-3), or O- 3 followed by Cl-2 or NH2Cl; and the nonvolatile acidic organics of th e raw and treated waters were extracted by XAD/ethyl acetate and evalu ated for mutagenicity in Salmonella (-S9). The extracts were 2-8 times more mutagenic in TA100 than in TA98, and the mutagenic potencies of the water extracts ranked similarly in both strains: Cl-2 > O-3 + Cl-2 > NH2Cl > O-3 + NH2Cl > O-3) raw. Chloro-4-(dichloromethyl)-5-hydroxy -2(5H)-furanone (MX), which was estimated to account for similar to 20 % of the mutagenic activity of the extracts, was shown to be the most potent compound tested thus far in a prophage-induction assay in Esche richia coil and a forward-mutation assay in Salmonella TM677. The muta tions in similar to 2,000 revertants of TA98 and TA100 induced by MX a nd the water extracts were analyzed by colony probe hybridization and polymerase chain reaction/DNA sequence analysis. The water extracts an d MX produced similar mutation spectra, which consisted in TA100 of pr edominantly of GC --> TA transversions in the second position of the C CC (Or GGG) target of the hisG46 allele. This spectrum resembles that produced by large aromotic compounds and is distinct from that produce d by alkylating agents and the semivolatile drinking water mutagen dic hloroacetic acid. In TA98, MX and those water extracts resulting from the introduction of the chlorine atom produced 50-70% hotspot 2-base d eletions and 30-50% complex frameshifts (frameshifts with an adjacent base substitution - mostly GC --> TA transversions as found in TA 100) . No other compound or mixture is known to induce such high frequencie s of complex Frameshifts. These results suggest that MX and ''MX-like' ' compounds (possibly halogenated aromatics, such as halogenated polyc yclic aromatic hydrocarbons) account for much of the mutagenic activit y and specificity of the nonvolatile organics in drinking water and th at these halogenated organics ore especially capable of promoting misi ncorporation by the DNA replication complex. This study provides furth er evidence that the mutation spectrum of a complex mixture reflects t he dominance of one or a few classes of chemical mutagens within the m ixture. (C) 1995 Wiley-Liss, Inc.