2016 Volume 27 Issue 3 Pages 207-213
Edible wild mushrooms collected in Nagano Prefecture were immersed in water for 1,440 min. The eluted radioactive cesium (Cs) was detected by an auto radiography method (ARG). The eluted potassium (K) was detected by a total reflection X-ray fluorescence analysis method. The mushrooms were divided into the following 4 groups: MW-g; 500 W microwave for 1 minute, Dry-g; 60 degrees centigrade for 12 hours, Frozen-g, -20 degrees centigrade for 12 hours and Raw-g; no treatment. Each treated mushroom was placed in 50 ml of pure water, immersion fluid was sampled 1.0 ml after 10, 30, 60, 180, 360 and 1,440 minutes of immersion, then filtered through a 0.45 μm pore size filter.
The dried immersion samples were imaged by ARG. It was suggested that radioactive Cs was eluted into the water from each of the treated mushrooms. The photo-stimulated luminescence density (PSL) of the Raw-g was lower than these of the treated groups (MW-g, Dry-g and Frozen-g) at each time point. Also, the K concentration of the Raw-g was lower than those of the treated groups. It was suggested that Cs and K are easily eluted due to destruction of the mycelium cells. The elution curves, which were created as a percentage of each concentration of the PSL and K, were similar. It was postulated that the elution mechanisms of the radioactive Cs and K are similar.
Furthermore, the elution rate of 137Cs was calculated based on its radioactivity, which was measured by a high-purity germanium (HPGe) semiconductor detector before and after the immersion of each mushroom. The elution rate of 137Cs was > 80% for the treated mushrooms. On the other hand, the elution rates of K for the control shiitake and mushrooms which were calculated using the value of the K concentration of the raw shiitake in the 7th revised Japan food composition table were < 20%. It was postulated that the radioactive Cs, which was easily removed, had accumulated in the mushrooms as an ionic species.
