https://doi.org/10.15344/2456-351X/2017/125
Abstract
Temporal variations of global fallout-derived plutonium and 137Cs concentrations in river water in Japan were examined using a composite dataset for 1966–1987 (1966-1987 for 239,240Pu, 1978-1987 for 137Cs). Plutonium and 137Cs concentrations in Japanese river water exhibited exponential decreases during the sampling periods, with the exception of 137Cs concentrations immediately after the Chernobyl nuclear reactor accident in 1986. The apparent half-decrease time of dissolved 137Cs (1.9 ± 0.3 years), which means a time that radionuclide concentrations in river water decrease to a half, was similar to that for dissolved 239,240Pu for the same period, whereas the apparent half-decrease time of particulate 239,240Pu (4.5 ± 2.2years) was longer. Temporal changes in dissolved 239,240Pu and 137Cs in river water can be explained by direct contribution of radionuclides from rainwater and leaching of radionuclides from surface-layer soil particles on land.