Form of cesium in fungi substrates and transfer to mushrooms

High ability to accumulate cesium in mushrooms has been widely reported after the Chernobyl accident. In the case of the Fukushima-Daiichi Nuclear Power Plant accident, radioactive cesium contamination of fungi has rather affected cultivated mushroom industries. In order to reveal a chemical behavior of the cesium in substrates for cultivated mushrooms, we analyzed mushrooms and substrates and washed the substrates. We determined concentration of radioactive cesium in extracts with a high purity Ge semiconductor detector. We also determined concentration of stable cesium in those samples by an ICP-MS. We found different behavior between stable and radioactive cesium in the substrates and transfer factor. The results suggested that the chemical form of radioactive cesium in the substrate should be different from that of stable cesium. Since the substrate was cut just after the accident, radioactive cesium from the surface of the wood has not been sufficiently diffused in the substance. And, to investigate cesium distribution in wood, we separated wood disk into four parts; bark, outer sapwood, inner sapwood, and heartwood. Radioactive cesium concentration differed clearly between sapwood and heartwood. The results suggested that the chemical form of cesium in the sapwood should be different from that in the heartwood. Additionally, to closely investigate radioactive cesium form in the extracts, we separated the corrosive material. From the results, we suspected that there is most of radioactive cesium in fulvic acid. Radioactive cesium was existed in the solution after acid treatment, suggesting that the radioactive cesium was soluble in acid and adhered to fulvic acid having small molecular weight. (author)