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

Abstract

In the present study, 129I activities and 129I/127I atom ratios were measured in 60 soil samples contaminated by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. The 127I concentrations, 129I activities, and 129I/127I 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 129I activities and 129I/127I 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, 129I concentration; y, 131I concentration; decay-corrected to March 11, 2011) instead of a simple constant may be a better way to express the relationship between 129I and 131I in Japanese soil affected by both global fallout and FDNPP accident fallout. In addition, a moderate correlation was observed between 129I and 135Cs (logy = 0.624logx + 1.01, Pearson's r = 0.627; x, 129I activity; y, 135Cs activity). However, 129I presented larger fractionations with less volatile radionuclides, such as 236U, 239Pu, and 240Pu. These findings indicated 135Cs could be roughly estimated from 129I or 131I; this is advantageous as fewer 135Cs data are available and 135Cs/137Cs is being considered a promising tracer during radiocesium source identification.