Abstract
The estimated domestic usage of DD (a typical nematocide) has been the greatest among all the agricultural chemicals in Japan. DD is involved in a document which is used to establish tap water quality standard in Japan. The document indicates that DD is potentially detectable in raw water for tap waters. DD in raw water will be treated with chlorine at waterworks, which raises concerns about formation of mutagenic chlorination by-products through the treatment. The objective of this work was to identify a mutagenic chlorination by-product by using high resolution mass spectrometers and multivariate analyses. Mutagenicity of the chlorination by-product was evaluated with the Ames Salmonella mutagenicity assay. (E)-1,3-Dichloropropene (DCP) was used as a model compound of DD. The mutagenicity of chlorine treated model aqueous solutions of DD increased with increasing chlorine dosages up to 3.00 mol-Cl2/mol-DCP. From the chlorine treated aqueous solutions of DD, 1,3-dichloroacetone (DCA) was identified as a major mutagen by a cochromatography with an authentic standard, precursor ion analyses and first-generation product ion analyses with the high resolution mass spectrometers. The mutagenicity of DCA against TA100 strain without microsomal activation was 160,000 net revertant colony/μmol (the toxicity equivalent factor was 0.14). Based on the mutagenicity of the chlorine treated DCP sample, the specific mutagenicity of DCA, and the DCA concentration in the sample, the mutagenic contribution of DCA to the chlorine treated DCP sample was calculated. High contribution (98%) clearly shows that DCA is a major mutagen in the chlorine treated DCP sample. Because the exploration of DCA was performed by using the unrealistic high concentration samples of DCP and chlorine, formation of DCA in the practical concentration samples (0-200 μg-DCP/L, 0.10 or 1.27 mg-Cl2/L) was examined. It was proven that DCA formation reaction takes place in the practical concentrations of DCA and chlorine.
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