Fungal spore involvement in the resuspension of radiocaesium in summer

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.

Rain-induced bioecological resuspension of radiocaesium in a polluted forest in Japan

“…The radiocaesium concentration in the atmosphere over the polluted mountainous village area investigated in this study is several times higher in summer than in winter 13,14 . Carbon with a biological origin in filter samples had a good correlation with radiocaesium concentrations, and there were sometimes close to 1 million bioaerosols per m 3 in summer 13 .…”

“…The radiocaesium concentration in the atmosphere over the polluted mountainous village area investigated in this study is several times higher in summer than in winter 13,14 . Carbon with a biological origin in filter samples had a good correlation with radiocaesium concentrations, and there were sometimes close to 1 million bioaerosols per m 3 in summer 13 . In addition, based on a combination of optical and electron microscopy, stateof-the-art DNA analysis, and radiological measurement, it was confirmed that fungal spores, one of the major components of bioaerosols 29,30 , were possibly the major host bioaerosol of radiocaesium (e.g., Ref.…”

“…In addition, based on a combination of optical and electron microscopy, stateof-the-art DNA analysis, and radiological measurement, it was confirmed that fungal spores, one of the major components of bioaerosols 29,30 , were possibly the major host bioaerosol of radiocaesium (e.g., Ref. 31 ) during summer 13 . A 3-D transport model study also revealed the significance of the secondary emission of radiocaesium from the forest during summer 20 .…”

“…We assume no emission/liberation of volatile organic Cs compounds under environmental temperatures (if any salt forms) from biota, as Cs is an alkaline metal. Our previous conclusion is that in cold seasons, a typical major driver of resuspension is the uplift of contaminated soil dust by gusts 16,20 , while in warm seasons, the major factors are bioaerosols, including contaminated fungal spores 13,14 and cedar pollen 24 . Suspension of contaminated pollen was reported 6 years in Germany after the Chernobyl nuclear power plant accident 25 .…”

“…Although the initial primary emission surge from the F1NPP site by the accident decreased circa the fall of 2011 17,18 , radiocaesium has been detected continuously in the atmosphere since 2011. The source of these continuous atmospheric radiocaesium levels is considered to be resuspension (i.e., secondary emissions from polluted surfaces 19 ); notably, the measured radiocaesium concentrations in the range of 10 -1 to 10 -5 Bq m −3 (Supplementary Information Figure S1) have not reached a level with certain health impacts (see Annex in Igarashi et al 13 ). In a typical mountainous village area in Fukushima (see Fig.…”