Comparisons of effective half-lives of radiocesium in Japanese tea plants after two nuclear accidents, Chernobyl and Fukushima

The time-dependence of Cs-137 in new shoots of tea (Camellia sinensis (L.) Kuntze) following a Cs-137-deposition was analyzed and quantified in terms of effective half- lives. The underlying monitoring studies were performed after the accidents in the Chernobyl and the Fukushima Daiichi nuclear power plants for tea plants growing in Japan. The major transfer route for atmospherically deposited radiocaesium to the first new shoots sampled after the accidents were different: for the Fukushima accident, it was mainly translocation of radiocaesium deposited onto old leaves and twigs to the new growth, while direct deposition on the new leaves was the major source after the Chernobyl accident. The effective half-lives in new tea leaves representing the fast and slow components of the decline did not significantly differ between these accidents. Geometric means (ranges) of fast and slow effective half-lives of Cs-137 after the Chernobyl accident were 66 d (25-125 d) and 902 d (342-15900 d), respectively, and those after the Fukushima accident were 50 d (26-105 d) and 416 d (222-1540 d), respectively. From these results, Cs-137 declines in new tea leaves were similar although contamination conditions were different for these two accidents.