Accumulation mechanisms of radiocaesium within lichen thallus tissues determined by means of microscale localisation observation

Dohi, Terumi; Iijima, Kazuki; Machida, Masahiko; Suno, Hiroya*; Omura, Yoshihito*; Fujiwara, Kenso; Kimura, Shigeru*; Kanno, Futoshi*

PLOS ONE (Internet), 17(7), p.e0271035_1 - e0271035_21, 2022/07

https://doi.org/10.1371/journal.pone.0271035

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

Dohi, Terumi; Omura, Yoshihito*; Yoshimura, Kazuya; Sasaki, Takayuki*; Fujiwara, Kenso; Kanaizuka, Seiichi*; Nakama, Shigeo; Iijima, Kazuki

PLOS ONE (Internet), 16(5), p.e0251828_1 - e0251828_16, 2021/05

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

Quantum chemical calculation studies toward microscopic understanding of retention mechanism of Cs radioisotopes and other alkali metals in lichens

Suno, Hiroya; Machida, Masahiko; Dohi, Terumi; Omura, Yoshihito*

Scientific Reports (Internet), 11(1), p.8228_1 - 8228_13, 2021/04

https://doi.org/10.1038/s41598-021-87617-w

We evaluate stability of caesium (Cs) and other alkali-metal cation complexes of lichen metabolites in both gas and aqueous phases to discuss why lichens can retain radioactive Cs in the thalli over several years. We focus on oxalic acid, (+)-usnic acid, atranorin, lecanoric acid, and protocetraric acid, which are common metabolite substances in various lichens including, e.g., and retaining Cs in Fukushima, Japan. By performing quantum chemical calculations, their gas-phase complexation energies and aqueous-solution complexation free energies with alkali-metal cations are computed for their neutral and deprotonated cases. Consequently, all the molecules are found to energetically favor cation complexations and the preference order is LiNaKRbCs for all conditions, indicating no specific Cs selectivity but strong binding with all alkali cations. Comparing complexation stabilities among these metabolites, lecanoric and protocetraric acids seen in medullary layer are found to keep higher affinity in their neutral case, while (+)-usnic acid and atranorin in upper cortex exhibit rather strong affinity only in deprotonated cases through forming stable six atoms' ring containing alkali cation chelated by two oxygens. These results suggest that the medullary layer can catch all alkali cations in a wide pH range around the physiological one, while the upper cortex can effectively block penetration of metal ions when the metal stress grows. Such insights highlight a physiological role of metabolites like blocking of metal-cation migrations into intracellular tissues, and explain long-term retention of alkali cations including Cs in lichens containing enough such metabolites to bind them.

Radiocaesium activity concentrations in parmelioid lichens within a 60 km radius of the Fukushima Dai-ichi Nuclear Power Plant

Dohi, Terumi; Omura, Yoshihito*; Kashiwadani, Hiroyuki*; Fujiwara, Kenso; Sakamoto, Yoshiaki; Iijima, Kazuki

Journal of Environmental Radioactivity, 146, p.125 - 133, 2015/08

https://doi.org/10.1016/j.jenvrad.2015.04.013

Radiocaesium activity concentrations (Cs, Cs) were measured in parmelioid lichens collected within the Fukushima Prefecture approximately 2 y after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. A total of 44 samples consisting of nine species were collected at 16 points within a 60 km radius of the FDNPP. The activity concentration of Cs ranged from 4.6 to 1000 kBq kg and for Cs ranged from 7.6 to 1740 kBq kg. A significant positive correlation was found between the Cs activity concentration in lichens and the Cs deposition density on soil, based on the calculated Spearman's rank correlation coefficients as = 0.90 ( 0.01). The two dominant species, Flavoparmelia caperata and Parmotrema clavuliferum, showed strong positive correlations, for which the r values were calculated as 0.92 ( 0.01) and 0.90 ( 0.01) respectively. Therefore, they are suggested as biomonitoring species for levels of radiocaesium fallout within the Fukushima Prefecture.

Outline of Investigation for radiocaesium concentrations in lichens after Fukushima Dai-ichi Nuclear Power Plant accident

Dohi, Terumi; Omura, Yoshihito*; Kashiwadani, Hiroyuki*; Fujiwara, Kenso; Sakamoto, Yoshiaki; Iijima, Kazuki

Raiken, 18(1), p.11 - 13, 2014/12

no abstracts in English

Long-term monitoring of radiocaesium in lichens

Dohi, Terumi; Iijima, Kazuki; Yoshimura, Kazuya; Omura, Yoshihito*; Fujiwara, Kenso; Kanaizuka, Seiichi*

no journal, , 

no abstracts in English

Application of lichens to evaluate distribution of radionuclides nearby the Fukushima Dai-ichi Nuclear Power Station

Dohi, Terumi; Iijima, Kazuki; Omura, Yoshihito*; Fujiwara, Kenso; Kikuchi, Naoyuki*

no journal, , 

The local radioactive contaminations (i.e. radioactive plume's trace) around the FDNPS were caused by the releasing radionuclides from each reactor, weather conditions, etc. Japan Atomic Energy Agency is carrying out the project to evaluate off-site distribution of radionuclides and to determine the origin of plume's traces at each point, since we develop the model to estimate on-site distribution. As lichens are known to be effective tools to monitor environmental radionuclides in both time and space because of their ability to retain radionuclides for a long period, lichen samples are expected to be used to examine initial fallout distribution. The purpose of this study is to measure radionuclides concentrations in lichens and analyse elemental composition in particles captured on lichen thalli, in order to evaluate initial distribution of radionuclides and clarify the contamination characteristics of the plume's traces nearby the FDNPS.

Cs in lichens after the Fukushima Nuclear Accident

Dohi, Terumi; Omura, Yoshihito*; Fujiwara, Kenso; Iijima, Kazuki

no journal, , 

Large quantity of radionuclides, including Cs and Cs, were released into the atmosphere caused by the Fukushima Dai-chi Nuclear Power Plant (FDNPP) accident on March 11, 2011. As lichens are known to be effective tools to monitor environmental radioelements in both time and space, lichen samples are expected to be used to examine and monitor radiocaesium fallout from FDNPP in Japan. The purpose of this study is to discuss the estimation of radiocaesium fallout in the ecosystem based on the following examinations using lichens. Fifty-eight samples including foliose and fruticose lichens were collected from northern to central Japan especially focusing on Fukushima Prefecture during 2012 and 2013. After correction for radioactive decay (on each sampling date), the detected radiocaesium concentrations ranged from 16.1 Bq kg (d.w.) to 510,000 Bq kg for Cs and from 33.8 to 880,000 Bq kg for Cs in lichens. Cs concentration in the lichen samples generally increased with increase in the amount of fallout estimated by the Cs deposition in soil. The positive correlation was supported between Cs in lichens collected from Fukushima Prefecture and Cs inventories on soil calculated by Inverse Distance Weighted with Spearman's rank correlation coefficient (0.90, p 0.01). The activity ratios of Cs and Cs for the lichen samples ( = 44) collected within Fukushima Prefecture (decay corrected to March 11, 2011) were between 0.950.04 and 1.080.41. The ratios are consistent with those for radiocaesium derived from the FDNPP accident (reported as 0.89 to 1.2). The ratios obtained from lichen samples collected in outside of Fukushima Prefecture were 0.750.23 to 1.480.48. They were consistent with those from Fukushima. But one sample showing significantly small value, 0.480.16, might be influenced by different origin from Fukushima.

Computational molecular study of predominant organic molecules in forest ecosystems concerning cesium accumulation and transport

Suno, Hiroya; Machida, Masahiko; Dohi, Terumi; Omura, Yoshihito*; Sasaki, Yoshito

no journal, , 

Complexation of biomolecules with radiocesium is known to play an important role in the accumulation and migration of radioactivity on the organic matter in forests. In this work, we identify typical molecules forming a metal complex in the forest organic matter and carry out atomistic analyses by performing quantum mechanical calculations in order to understand the alkali metal cation complexation selectivity of these organic molecules. Among these molecules, of particular interest are norbadione A (CHO), a primary pigment molecule present in mushrooms, oxalic acid (CHO), atranorin (CHO), lecanoric acid (CHO), and usnic acid (CHO), main secondary metabolites in lichens.

Concentration of radiocesium in lichens after Fukushima NPP accident

Dohi, Terumi; Omura, Yoshihito*; Kashiwadani, Hiroyuki; Sakamoto, Yoshiaki

no journal, , 

Most lichens grow on rocks and barks, and they are found in terrestrial ecosystems. We will present the radiocesium concentration in lichens sampled in Ibaraki and Fukushima Prefecture, etc. after the accident at Fukushima Daiichi Nuclear Power Station.