Surveying the mutagenicity of tap water to elicit the effects of purification processes on Japanese tap water

The mutagenicity levels of tap water in Japan were surveyed using the Ames test. Tap water samples (179) were collected at 17 sampling sites located from the northern tip (Hokkaido) to the southern tip (Kagoshima Prefecture). The mutagenicity values ranged from under the detection limit to 3600 net rev. L−1. The average mutagenicity was 1100 net rev. L−1 and the levels were significantly higher in the wintertime than in the summertime. The average mutagenicity of each site ranged from under the detection limit to 2000 net rev. L−1. There was no significant correlation of the mutagenicity with TOC, A260 or THMs. The highest positive ratios of the Ames test and the umu test were 92% under the condition TA100 − S9 and 9% under the condition NM2009 − S9, respectively, which indicated that the Ames test has higher sensitivity for the test of tap water than the umu test. This survey incorporated the 1992–1993 survey. The comparison of these survey-results in a further study will reveal the improvement of Japanese tap water quality from the perspective of mutagenicity.