Fungal spore involvement in the resuspension of radiocaesium in summer

Yasuhito Igarashi,Tsuyoshi Thomas Sekiyama,Kazuhiko Ninomiya,Chisato Takenaka,Kouji Adachi,Kazuyuki Kita,Atsuyuki Sorimachi,Takeshi Kinase,Masahide Ishizuka,Mizuo Kajino,Kentaro Hosaka,Hiroshi Okochi,Teruya Maki,Naho Hayashi,Yuji Zaizen

doi:10.1038/s41598-018-37698-x

Abstract

We observed the atmospheric resuspension of radiocaesium, derived from the Fukushima Dai-ichi Nuclear Power Plant accident, at Namie, a heavily contaminated area of Fukushima, since 2012. During the survey periods from 2012 to 2015, the activity concentrations of radiocaesium in air ranged from approximately 10−5 to 10−2 Bq per m3 and were higher in the warm season than in the cold season. Electron microscopy showed that the particles collected on filters in summer were predominantly of biological origin (bioaerosols), with which the observed radiocaesium activity concentration varied. We conducted an additional aerosol analysis based on fluorescent optical microscopic observation and high-throughput DNA sequencing technique to identify bioaerosols at Namie in 2015 summer. The concentrations of bioaerosols fluctuated the order of 106 particles per m3, and the phyla Basidiomycota and Ascomycota (true Fungi) accounted for approximately two-thirds of the bioaerosols. Moreover, the fungal spore concentration in air was positively correlated with the radiocaesium concentration at Namie in summer 2016. The bioaerosol emissions from Japanese mixed forests in the temperate zone predominately included fungal cells, which are known to accumulate radiocaesium, and should be considered an important scientific issue that must be addressed.

Highlights

We observed the atmospheric resuspension of radiocaesium, derived from the Fukushima Dai-ichi Nuclear Power Plant accident, at Namie, a heavily contaminated area of Fukushima, since 2012
The bioaerosol concentrations and the 137Cs activity concentration determined by the filter samples from Kawamata and Namie were both high in the warm season and low in the cold season, and these results suggested that bioaerosols may play an important role in radiocaesium resuspension during the warm season[8]
We examined the bioecological resuspension of radiocaesium and the composition of the bioaerosols that serve as host particles at Namie in August and September 2015

Summary

Introduction

We observed the atmospheric resuspension of radiocaesium, derived from the Fukushima Dai-ichi Nuclear Power Plant accident, at Namie, a heavily contaminated area of Fukushima, since 2012. We measured radiocaesium resuspension[6] in the atmosphere at Kawamata and Namie, Fukushima Prefecture, after the accident[7,8] In this area, which is 30 to 35 km northwest of the FDNPP and surrounded by heavily contaminated forest, as defined above, the effects of the primary emission of radiocaesium from the FDNPP likely ceased in fall 20119,10; from 2012–2015, the radiocaesium activity concentration in the air slowly decreased, seasonal fluctuations were observed, with increases during the warm season and decreases during the cold season (Supplementary Fig. S2). At Namie, the average summer concentration (June–August 2013–2014) was approximately 6 times the average winter concentration (December–February 2013–2014) This seasonal pattern is the opposite that observed in urban areas[8,9,10,11], but emission inventory calculations with an aerosol transport model have shown that direct/delayed primary emissions from the FDNPP cannot explain the seasonal fluctuations in 20134. The study attributed the seasonal trends to changes in the prevailing local wind direction and the distribution of surface contamination

Methods

Results

Conclusion