Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
Institute for Agro-Environmental Sciences, NARO, 3-1-3 Kannondai, Tsukuba, Ibaraki, 305-0864, Japan.
Sci Rep. 2019 Mar 5;9(1):3520. doi: 10.1038/s41598-019-40423-x.
Radiocaesium-bearing microparticles (CsMPs) composed of silicate glass were released by the Fukushima Daiichi Nuclear Power Plant accident in March 2011. Since CsMPs contain a high concentration of radiocaesium, their dynamics and fate in the environment are urgent issues to be investigated. Here, we show that CsMPs are dissolved by weathering in the environment and that their radioactivity is more rapidly decreased by dissolution than the physical decay of radiocaesium. We conducted dissolution experiments with CsMPs in pure water that absorbed CO from the atmosphere and in artificial seawater at several temperatures. The dissolution progress was monitored by the decrease in the Cs radioactivity in CsMPs, and the dissolution rate was estimated. The activation energy for the dissolution of CsMPs was estimated to be 65 and 88 kJ/mol and the dissolution rate at 13 °C (approximate annual mean temperature in Fukushima City) was 0.014 and 0.140 μm/y for pure water and seawater, respectively, assuming that radiocaesium is uniformly distributed in spherical CsMPs. The shapes of the CsMPs dissolved in pure water were considerably altered, suggesting that the dissolution proceeded without maintaining the geometry. Tin oxide and iron oxide nanoparticulates formed on the surfaces. Such features were similar to those observed in CsMPs recently collected in Fukushima Prefecture, indicating that weathering dissolution of CsMPs is also occurring in the environment. For the CsMPs dissolved in seawater, a crust of secondary Mg- and Fe-rich minerals was formed, and the glass matrix inside the crust decreased, creating space between the crust and the glass matrix.
2011 年 3 月福岛第一核电站事故释放出了含有硅酸钠玻璃的放射性铯微粒（CsMPs）。由于 CsMPs 含有高浓度的放射性铯，因此它们在环境中的动力学和归宿是亟待研究的问题。在这里，我们表明 CsMPs 在环境风化作用下会溶解，其放射性比放射性铯的物理衰变更快地降低。我们在纯水中进行了 CsMPs 的溶解实验，该纯水吸收了大气中的 CO，并在几个温度下进行了人工海水实验。通过 CsMPs 中 Cs 放射性的降低来监测溶解过程，并估算溶解速率。估算出 CsMPs 溶解的活化能为 65 和 88 kJ/mol，在 13°C（福岛市的年平均温度）下，在纯水中和海水中的溶解速率分别为 0.014 和 0.140 μm/y，假设放射性铯在球形 CsMPs 中均匀分布。在纯水中溶解的 CsMPs 的形状发生了很大的变化，表明溶解过程没有保持几何形状。在表面形成了氧化锡和氧化铁纳米颗粒。这些特征与最近在福岛县收集的 CsMPs 中观察到的特征相似，表明 CsMPs 的风化溶解也在环境中发生。对于在海水中溶解的 CsMPs，形成了富含镁和铁的次生矿物壳，壳内的玻璃基质减少，在壳和玻璃基质之间形成了空间。
