Dm. Demarini et al., MUTATION SPECTRA IN SALMONELLA OF CHLORINATED, CHLORAMINATED, OR OZONATED DRINKING-WATER EXTRACTS - COMPARISON TO MX, Environmental and molecular mutagenesis, 26(4), 1995, pp. 270-285
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.