Measurement of tritium in some environmental samples in Japan

Atmospheric nuclear tests, nuclear power reactors - especially BWR type reactors, nuclear fuel reprocessing plants, nuclear reaction of high energy neutrons in cosmic rays with 14N are the sources of tritium entering the environment. One more source in future will be thermonuclear reactors. The two methods of measurement of low level tritium in natural water are: (1) one based on enrichment of tritium by electrolysis and (2) the other based on reducing background count. These methods are described. Data collected on measurement of tritium in various environmental materials such as ground water, rain water, surface sea water in Japan are reviewed and presented. Studies on biological half-life of tritium are also reviewed and biological effects of tritium are briefly described. The tritium concentrations of surface sea water of Japan (in the Pacific ocean) are found to be of the same order of magnitude as the ones measured in the Mediterranean. The level of tritium in the rain in Japan is about the average of the values observed in different parts of the world. The level of tritium in the deep underground water in Japan is lower than that in surface sea water, but is showing a tendency to increase slightly. (M.G.B.)