Dose effect for Japanese due to 232Th and 238U in imported drinking water

The consumption rate of bottled mineral water in Japan has increased due to changes in eating habits and contamination of water sources. Radioactivity levels of 238U and 232Th in imported mineral water were checked from the viewpoint of internal radiation for Japanese subjects. Concentration ranges of 238U and 232Th in imported bottled mineral water, domestic bottled mineral water, domestic tap water, and domestic soft drinks were as follows: for U, N.D to 7.48 x 10(3), 1.07 to 344, 0.66 to 104, and 3.04 to 46.2 ng dm (ppt); for Th, 0.60 to 5.12, 0.65 to 22.4, 0.64 to 22.1, and 11.0 to 48.5 ng dm, respectively. In some brands of imported bottled mineral water, U concentration was sometimes much higher than domestic bottled mineral water and domestic tap water. The annual effective dose (1.5 x 10(-3) mSv y(-1) estimated from intake of 238U was approximately 7 times higher than that through dietary intake in Japanese. However, the internal dose added by drinking the imported portable water is negligible compared with total annual internal dose. Concentrations of non-radioactive elements were also compared between imported and domestic bottled water. Geometric means of cobalt, arsenic, strontium, cesium, phosphorous, and calcium in imported bottled water were higher compared with those of domestic bottled mineral water and domestic tap water. Maximum values of 11 elements (arsenic, rubidium, strontium, cesium, barium, sodium, magnesium, potassium, calcium, and manganese) were also found in imported bottled water.