2021 Volume 70 Issue 1 Pages 41-54
Systematic measurement of tritium (T) concentration and oxygen, hydrogen stable isotope ratios (δ18O, δD) in precipitation is one of the most effective methods for estimating the environmental behavior. In this manuscript, various studies regarding T, δ18O and δD conducted in Japan in recent years (mainly since 2010) including our research were investigated. Consequently, the following matters have been mainly clarified. (1) The notable seasonal changes of T concentration in precipitation including “spring peak” was generally observed in each sampling area. (2) The tendency that “the higher the latitude of sampling area, the greater the concentration of T (i.e., latitude effect) was also generally observed. (3) It was confirmed that the T concentration in the precipitation temporarily increased due to Fukushima Daiichi Nuclear Power Plant accident in March 2011. However, the concentration of T has returned to the normal level after May of the year concerned. (4) The value of δ18O or δD alone did not show distinct seasonal characteristics, but d-excess (=δD−8×δ18O) calculated from these values was inclined to increase in winter. These results suggest that the precipitation environment in Japan may be strongly influenced by seasonal air masses.
