Can (129)I track (135)Cs, (236)U, (239)Pu, and (240)Pu apart from (131)I in soil samples from Fukushima Prefecture, Japan?

In the present study, (129)I activities and (129)I/(127)I atom ratios were measured in 60 soil samples contaminated by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. The (127)I concentrations, (129)I activities, and (129)I/(127)I atom ratios in dry-weight were observed to be 0.121–23.6 mg kg(−1), 0.962–275 mBq kg(−1), and (0.215–79.3) × 10(−7), respectively. The maximum values of both (129)I activities and (129)I/(127)I atom ratios in Japanese soil increased about three orders of magnitude due to this accident. The equation logy = 0.877logx + 0.173 (Pearson’s r = 0.936; x, (129)I concentration; y, (131)I concentration; decay-corrected to March 11, 2011) instead of a simple constant may be a better way to express the relationship between (129)I and (131)I in Japanese soil affected by both global fallout and FDNPP accident fallout. In addition, a moderate correlation was observed between (129)I and (135)Cs (logy = 0.624logx + 1.01, Pearson’s r = 0.627; x, (129)I activity; y, (135)Cs activity). However, (129)I presented larger fractionations with less volatile radionuclides, such as (236)U, (239)Pu, and (240)Pu. These findings indicated (135)Cs could be roughly estimated from (129)I or (131)I; this is advantageous as fewer (135)Cs data are available and (135)Cs/(137)Cs is being considered a promising tracer during radiocesium source identification.