Changes of activity inducing chromosomal aberrations and transformations of chlorinated humic acid

The change of the toxicity of chlorinated water after chlorine injection wa s examined. For the measurement of toxicity, chromosomal aberration test an d transforming test were carried out as indexes to initiating activity and to promoting activity in the carcinogenesis process. respectively. Activity inducing chromosomal aberrations of chlorinated humic acid gradually decre ased with time after chlorination. In contrast, activity inducing transform ations measured by the two-stage assay gradually increased. Thus, the toxic ity that decreases or increases is present in chlorinated water. Furthermor e, activity inducing transformations measured by the non-two-stage assay gr adually decreased. This direction of change was reverse to that of activity inducing transformations by the two-stage assay and consistent with that o f activity inducing chromosomal aberrations. It is speculated that the main reason of decreasing activity inducing transformations by the non-two-stag e assay is because initiating activity detected as activity inducing chromo somal aberrations in chlorinated water decreases drastically. Directions of changes of total organic halogen and carbonyl group were qualitatively con sistent with that of activity inducing chromosomal aberrations. Directions of changes of chloroform and dichloroacetic acid were qualitatively consist ent with that of activity inducing transformations by the two-stage assay. Findings of this study suggest that further research is necessary to compar e carcinogenicity of tap water near water purification plant and distant la p water. (C) 2001 Elsevier Science Ltd. All rights reserved.