Geochemical Journal, Vol. 46 (No. 4), pp. 287-295, 2012
Takeshi Ohno,1 Yasuyuki Muramatsu,1 Yoshinori Miura,2 Kazumasa Oda,1 Naoya Inagawa,1 Hiromu Ogawa,1 Atsuko Yamazaki,1 Chiaki Toyama1 and Mutsuto Sato3
1Department of Chemistry, Faculty of Science, Gakushuin University, Mejiro 1-5-1, Toshima-ku, Tokyo 171-8588, Japan
2Agriculture, Forestry and Fisheries Department, Fukushima Prefecture, Sugitsumacho, Fukushima, Fukushima 960-8670, Japan
3Fukushima Agricultural Technology Centre, Hiwada, Koriyama, Fukushima 963-0531, Japan
(Received January 27, 2012; Accepted June 4, 2012)
In order to understand the behavior of radionuclides released from the Fukushima Daiichi nuclear power plant, the depth distributions of radiocesium and radioiodine were investigated in a wheat field, a rice paddy, an orchard, and a cedar forest in Koriyama, Fukushima Prefecture. Our results demonstrate that, following the nuclear power plant disaster, more than 90% of the radionuclides were distributed in the upper 6 cm of the soil column in the wheat field and within 4 cm of the surface in the rice paddy, orchard, and cedar forest. According to the measurement of radionuclides in the three adjacent agricultural fields, the variation of deposition densities in the wheat field was smaller than that of the orchard and rice paddy, suggesting that the low permeability of the orchard and paddy soils may cause horizontal migration of radionuclides during the initial deposition. This result indicates that the deposition densities in the wheat field should be appropriate for estimating the amount of fallout in the area. The deposition densities of 134Cs, 137Cs, and 131I in this area were estimated to be 512 ± 76 (SD, n = 5), 522 ± 80 (SD, n = 5), and 608 ± 79 (SD, n = 5) kBq/m2 (decay corrected to April 1, 2011), respectively. A comparison of the deposition density between the wheat field and the cedar forest suggests that more than half of the radionuclides are distributed in the tree canopies of the evergreen forestland.
Key words: Fukushima Daiichi nuclear power plant accident, 134Cs, 137Cs, 131I, agricultural field