Quantitative Evaluation of the Genotoxic Activity of Japanese Tap Water Using the Umu Test

The genotoxicity of Japanese tap water was investigated using the umu test in order to clarify the relative and absolute genotoxic levels. Samples were collected at 25 sites in Japan and the umu test was carried out with concentrated solutions. The values of genotoxic activity (GA) varied significantly from less than 72 to 670 ng 4NQO/L depending on the site location and/or sampling period. Typical GA value among the tested tap water samples was around 200 ng 4NQO/L. According to a roughly estimated safety level, it was shown that the genotoxicity level of the tested tap water was not negligible. A comparison of the results of the present study with those of a previous investigation using Ames mutagenicity test indicates that the genotoxic level of Japanese tap water did not decrease significantly between the two investigations. In addition, it was shown that there was a weak positive correlation between the genotoxicity of the tap water and the value of the total organic carbon content.