Caesium fallout in Tokyo on 15th March, 2011 is dominated by highly radioactive, caesium-rich microparticles

TL;DR

This study analyzes highly radioactive caesium-rich microparticles from the 2011 Fukushima fallout in Tokyo, revealing their composition, structure, and potential health impacts due to their low solubility and high radioactivity.

Contribution

It provides the first atomic-scale characterization of CsMPs from Tokyo, comparing them with Fukushima particles, and assesses their environmental and health implications.

Findings

CsMPs constituted 80-89% of Cs radioactivity during initial fallout

CsMPs from Tokyo and Fukushima share nanoscale texture and composition

CsMPs have extremely high radioactivity per unit mass, posing health risks

Abstract

In order to understand the chemical properties and environmental impacts of low-solubility Cs-rich microparticles (CsMPs) derived from the FDNPP, the CsMPs collected from Tokyo were investigated at the atomic scale using high-resolution transmission electron microscopy (HRTEM) and dissolution experiments were performed on the air filters. Remarkably, CsMPs 0.58-2.0 micrometer in size constituted 80%-89% of the total Cs radioactivity during the initial fallout events on 15th March, 2011. The CsMPs from Tokyo and Fukushima exhibit the same texture at the nanoscale: aggregates of Zn-Fe-oxide nanoparticles embedded in amorphous SiO2 glass. The Cs is associated with Zn-Fe-oxide nanoparticles or in the form of nanoscale inclusions of intrinsic Cs species,rather than dissolved in the SiO2 matrix. The Cs concentration in CsMPs from Tokyo (0.55-10.9 wt%) is generally less than that in particles from Fukushima (8.5-12.9 wt%).The radioactivity per unit mass of CsMPs from Tokyo is still as high as 1E11 Bq/g, which is extremely high for particles originating from nuclear accidents. Thus, inhalation of the low-solubility CsMPs would result in a high localized energy deposition by beta (0.51-12)*1E-3 Gy/h within the 100-micrometer-thick water layer on the CsMP surface) and may have longer-term effects compared with those predicted for soluble Cs-species.