Distribution of 131I, 134Cs, 137Cs and 239,240Pu concentrations in Korean rainwater after the Fukushima nuclear power plant accident

Radionuclides such as 131I, 134Cs, 137Cs, and 239,240Pu in Korean rainwater have been analyzed by Korea Research Institute of Standards and Science (KRISS) since the Fukushima nuclear power plant accident in March 2011 to investigate the activity level, distribution pattern, and temporal variation and to assess the radiation dose the public is exposed to. The concentration of 131I in the Korean rainwater samples varied between 0.033 (minimum detectable activity; MDA) and 1.30 Bq kg−1 and the concentrations tended to decrease exponentially with time. The concentrations of 134Cs and 137Cs in rainwater ranged from 0.01 to 334 ± 74 and 0.29 ± 0.01 to 276 ± 1 mBq kg−1, respectively. The mean activity ratio of 137Cs/134Cs in the rainwater samples collected from April 18 to May 12 was estimated to be 0.44 ± 0.21, and this value is lower than that (ca. 1) observed in Fukushima, Japan, when there was an escape from the nuclear reactors. When an attempt was made to analyze Pu isotopes in rainwater samples, no Pu isotopes were detected above the MDA in any of the rainwater samples. Although the locations investigated were different from Asia to Europe, the concentrations of 131I, 134Cs and 137Cs in the rainwater are comparable, which suggests a global contamination of 131I, 134Cs, and 137Cs occurred because of the Fukushima nuclear power plant accident.