Mutation Research 609 (2006) 26–33 The mutation spectra of chlorinated drinking water samples using the base-specific TA7000 strains of Salmonella in the microsuspension assay Gisela de Arag˜ ao Umbuzeiro a , Sarah H. Warren b , Larry D. Claxton b,∗ a CETESB, Cia de Tecnologia de Saneamento Ambiental, Av. Prof. Frederico Hermann Jr, 345, 05459-900 S˜ ao Paulo, Brazil b Environmental Carcinogenesis Division, Mail Drop B143-06, U.S. Environmental Protection Agency, Research Triangle Park, NC 27709, USA Received 31 August 2005; received in revised form 29 March 2006; accepted 7 June 2006 Available online 1 August 2006 Abstract Mutation spectra analysis can provide important information about the types of genotoxic compounds that can be present in environmental samples. In this study, we used the TA7000 base-specific Salmonella typhimurium tester strains to characterize water samples from two drinking water treatment plants (DWTPs) in S˜ ao Paulo, Brazil. Because of the small sample sizes of these environmental samples, the use of the microsuspension protocol was necessary. Acidic extracts of drinking water samples from the two DWTPs gave similar responses in the TA7000 strains and caused primarily CG to AT transversions. It is likely that halogenated disinfection by-products, generated during the chlorination of water, are causing the response seen with the TA7000 strains. Published by Elsevier B.V. Keywords: Microsuspension; Chlorination; Mutation 1. Introduction Previous efforts showed that organic extracts of the nonvolatile fraction of drinking water samples and 3- chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), a representative compound from that fraction, produced mutation spectra with primarily CG → AT transversions [1,2]. These studies [1,2] showed that MX and other compounds of this class account for much of the mutagenic activity of the nonvolatile fraction of drinking water and for much of the mutagenic specificity of the organic fraction. Therefore, one ∗ Corresponding author. Tel.: +1 919 541 2329; fax: +1 919 685 3281. E-mail address: claxton.larry@epa.gov (L.D. Claxton). would expect that drinking water samples, containing halogenated disinfection by-products generated from the chlorination of surface water containing humic and fulvic acids, would produce mainly CG to AT transversions. The methodology used by DeMarini et al. [2] to ana- lyze the mutation spectra of drinking water was molec- ular analysis by means of colony probe hybridization of the revertants obtained in the Salmonella assay. For TA98, a single probe that detects a two-base deletion of a CG or GC within the sequence of the hotspot CGCGCGCG was used [3]. For TA100, six probes were used to detect various base substitutions at the target sequence CC/GG [4]. The revertants that did not hybridize with a probe or gave ambiguous results were subjected to PCR and DNA sequence analysis as described previously for TA98 according to Bell et al. [5] 1383-5718/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.mrgentox.2006.06.024