To investigate the formation of mobile organic plutonium, we analyzed the plutonium contents of the fulvic (FA) and humic
(HA) acids from the soil samples obtained at Nishiyama, Nagasaki, Japan. The percentages of the plutonium bound strongly to
HA and to FA vs. the total plutonium in the soil were 5–10% and 1%, respectively, at the depth of 0–0.1 m, much higher values
than those of137Cs and uranium. After being weathered for 51 years under a temperate climate, the initial highfired oxides of fallout plutonium
have become as chemically reactive plutonium from nuclear fuel reprocessing plants.