Radiocaesium accumulation capacity of epiphytic lichens and adjacent barks collected at the perimeter boundary site of the Fukushima Dai-ichi Nuclear Power Station.

Terumi Dohi,Yoshihito Ohmura,Kazuya Yoshimura,Kazuki Iijima,Takayuki Sasaki,Seiichi Kanaizuka,Kenso Fujiwara,Shigeo Nakama,Tim A Mousseau

doi:10.1371/journal.pone.0251828

Terumi Dohi, Yoshihito Ohmura + Show 7 more

Open Access

https://doi.org/10.1371/journal.pone.0251828

Copy DOI

Abstract

We investigated the radiocaesium content of nine epiphytic foliose lichens species and the adjacent barks of Zelkova serrata (Ulmaceae, "Japanese elm") and Cerasus sp. (Rosaceae, "Cherry tree") at the boundary of the Fukushima Dai-ichi Nuclear Power Station six years after the accident in 2011. Caesium-137 activities per unit area (the 137Cs-inventory) were determined to compare radiocaesium retentions of lichens (65 specimens) and barks (44 specimens) under the same growth conditions. The 137Cs-inventory of lichens collected from Zelkova serrata and Cerasus sp. were respectively 7.9- and 3.8-times greater than the adjacent barks. Furthermore, we examined the radiocaesium distribution within these samples using autoradiography and on the surfaces with an electron probe micro analyzer (EPMA). Autoradiographic results showed strong local spotting and heterogeneous distributions of radioactivity in both the lichen and bark samples, although the intensities were lower in the barks. The electron microscopy analysis demonstrated that particulates with similar sizes and compositions were distributed on the surfaces of the samples. We therefore concluded that the lichens and barks could capture fine particles, including radiocaesium particles. In addition, radioactivity was distributed more towards the inwards of the lichen samples than the peripheries. This suggests that lichen can retain 137Cs that is chemically immobilised in particulates intracellularly, unlike bark.

Highlights

This study analysed lichens and bark samples taken from trees near to the boundary site of the Fukushima Dai-ichi Nuclear Power Station (FDNPS) to quantify 137Cs inventories and accumulation capacities
Radiocaesium accumulation capacity of biomonitors decay corrected to the sampling date
The isotopic ratios (134Cs/137Cs) decay-corrected to 11 March 2011 ranged from 0.9 to 1.2 which was consistent with the ratio of radiocaesium released from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident (S1 Table) [11, 20, 21]

Summary

Introduction

Lichens are symbiotic organism composed of fungi and algae that are well known to incorporate and store a variety of radionuclides derived from both natural origins, like U-238, Ra-226, Th-232 etc. in mine areas [1, 2], and artificial origins such as atmospheric nuclear weapon tests. These funders did not play a role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The 137Cs inventory is a reasonable proxy for the accumulation capacity of lichens, as radionuclide migration from dry or wet deposition of atmospheric fallout depends on the flux density (i.e. the migration rate per unit area). This study analysed lichens and bark samples taken from trees near to the boundary site of the Fukushima Dai-ichi Nuclear Power Station (FDNPS) to quantify 137Cs inventories and accumulation capacities.

Materials and methods

Results and discussion

Conclusion