Temporal Variations of Global Fallout-Derived Plutonium and 137Cs in River Water in Japan

Katsumi Hirose,Michio Aoyama

doi: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.

Highlights

Plutonium and 137Cs released into the atmosphere by atmospheric testing of nuclear weapons and nuclear disasters involving nuclear reactor accidents such as the Chernobyl nuclear reactor accident and Fukushima Daiichi Nuclear Power Plant (FDNPP) accident have been deposited on land surfaces by both wet and dry deposition [1,2]
Most anthropogenic radionuclides deposited on land surfaces were initially absorbed onto surface soil particles, adsorption reactions between soil particles and radionuclides differ between radionuclides; typically plutonium reacts with biogenic organic matter including micro organisms [5,6,7], whereas radiocesium adsorbs onto clay minerals [8,9,10,11]
The results suggest that complex processes, such as spatial variability of time-dependent atmospheric deposition fluxes of anthropogenic radionuclides, water–land surface interactions, and chemical conditions of river water, control the radionuclide concentrations in the rivers

Summary

Introduction

Plutonium and 137Cs released into the atmosphere by atmospheric testing of nuclear weapons and nuclear disasters involving nuclear reactor accidents such as the Chernobyl nuclear reactor accident and Fukushima Daiichi Nuclear Power Plant (FDNPP) accident have been deposited on land surfaces by both wet and dry deposition [1,2]. A portion of radionuclides in terrestrial environments was transported into the ocean via river runoff and aeolian processes involving radionuclide-bearing dust particles [12]. After the 1986 Chernobyl and 2011 FDNPP accidents, migration of anthropogenic radionuclides in the terrestrial environment has been major concern to assess radiological effects, in which river runoff of the anthropogenic radionuclides are one of the most important processes [6,11,13,14]

Methods

Results

Conclusion