Host: The Japanese Society of Toxicology
Under the Japanese Water Supply Act, the water quality standard has been established for the safe and secure of drinking water. Water Authorities are required to inspect the 51 standard items, and water supplying must fulfill the required conditions pursuant to the provision of “Drinking Water Quality Standards”. Twenty-six substances not yet fully assessed for their risks are listed in “Complementary Items”, not-legally binding with target values. In addition, 47 substances are regarded as “Items for Further Study” that require further study and a grip of detection level. For instance, the typical disinfection by-product, total trihalomethane is included in the 51 standard items, whereas BDCAA, a halogenated acetic acid among the disinfection by-products, is listed in “Items for Further Study”, because the risk assessment had been only provisional, and its target value had never been established at the last revision of the Act. Therefore, we conducted the hazard assessment to derive its health-based guidance value. Carcinogenetic potential of BDCAA was reported in rat and mouse 2-year drinking water studies as reliable information. The benchmark dose analysis was adopted for incidences of all neoplastic endpoints in rats and mice. The most appropriate BMDL10 of 2.83 mg/kg/day was obtained for male rat malignant mesothelioma in all organs.
Because BDCAA is considered to be a genotoxic carcinogen, the Virtually Safe Dose at 10−5 risk level was calculated as 2.83 × 10−4 mg/kg. This will be useful to establish the safety standard of BDCAA in drinking water.
