Variations of 129I in the atmospheric fallout of Tokyo, Japan: 1963-2003

► The atmospheric fallout samples collected monthly from Tokyo during 1963-1977 were determined for 129I/127I ratios. ► The 129I/127I ratios in the atmosphere of the 1960s were increased mainly by atmospheric nuclear weapons tests. ► The 129I depositions started to increase markedly at the latter half of the 1970s. ► The secular variation of the 129I deposition in Tokyo showed influences of the discharge of 129I from the Tokai Reprocessing plant.