Monitoring of Radioactive Cesium in Kawasaki Derived from the Fukushima Daiichi Nuclear Power Plant Accident by a Sequential Leaching Method for Airborne Particulate Matter

The Fukushima daiichi nuclear power plant (FDNPP) was seriously damaged by the huge earthquake and subsequent tsunami on 11 March 2011, and has released large amounts of radioactive materials into the environment. Since the accident, radioactive cesium originating from the FDNPP accident was detected over a wide range of the northeastern half of Honshu, the main island of Japan, including the Kanto region. The long-term monitoring of the activities of FDNPP-derived radioactive cesium in surface air must provide important knowledge concerning the dispersion processes of radioactive cesium and its supply to the atmosphere. In this study, we focused on airborne particulate matters (APM) collected at Kawasaki city, Kanagawa. The aim of this study was to obtain the time series date of radioactive cesium activities and to characterize the chemical properties of radioactive cesium in the APM. Consequently, we obtained the following information. Until the spring of 2014, both of the FDNPP-derived Cs-134 and the Cs-137 activities in the APM, which were still detected, decreased to ca. 10(-5) times those observed just after the FDNPP accident. Specifically, their activities decreased rapidly until September, 2011, and then their decrease rates slowed down. Sequential leaching experiments revealed that the chemical properties of radioactive cesium in the APM differed from those in soil; significant amounts of radioactive cesium in the AMP existed as a water-soluble form, whereas most of the radioactive cesium in soil was insoluble in water.