Change in the chemical form of 137Cs with age in needles of Japanese cedar

Radiocesium mobility in different parts of the two major tree species in Fukushima

“…We therefore compared our results and our experimental conditions with findings of these other studies (Table S2 ). Hara et al (2020) 31 reported much higher percentages of 137 Cs leached from current-year needles of Japanese cedar (represented as “2015 segment” in Table S2 : 96.8% for water-soluble 137 Cs) than our study found. The exact reason for this difference is unclear: perhaps, in their study, sampling in the flushing stage (June) and from a relatively low height (at 4 m from trees with an average height of 22.7 m), and the difference in pulverizing treatments (to a much finer level than ours) before extraction, might have led to the elution of abundant mobile 137 Cs.…”

“…A possible explanation for this result is that some 137 Cs is physically trapped in the interior matrix of the plant tissue; one contributor to this trapping is the complex nature of the structure of persistent organic matter components such as lignin. This possibility is also suggested by the results of previous decomposition or extraction experiments using actual plant parts and soil organic matter 19 , 30 , 31 , 39 . Some of these results will be compared with our results in the discussion below.…”

“…In both species, we conducted leaching experiments on not only different external parts but also fallen leaves/needles and organic layer samples, to examine the mobility of 137 Cs that had already been taken up and translocated to these parts. Although similar leaching experiments have been conducted on leaves/needles as well as decomposing litters in the context of the chemical forms of 137 Cs or its downstream transport, and the differences in 137 Cs mobility in each sample have been reported [e.g., Hara et al (2020) and Kurihara et al (2020) 31 , 32 ], as far as we know no study has yet focused on 137 Cs mobility and its variations in various external parts of trees. As leaching solutions, we adopt ultrapure water and ammonium acetate to create analogues of 137 Cs mobility on two levels.…”

Meta-analysis of radiocesium contamination data in Japanese cedar and cypress forests over the period 2011–2017

“…The importance of the foliar pathway in the contamination of internal organs, especially stem wood, was already highlighted by several field studies conducted in Japanese forests (e.g. Kuroda et al, 2013;Mahara et al, 2014;Ohashi et al, 2014;Nishikiori et al, 2015;Komatsu et al, 2016;Wang et al, 2016;Hara et al, 2020).…”

Sorption and desorption experiments using stable cesium: considerations for radiocesium retention by fresh plant residues in Fukushima forest soils

“…Biological absorption of radiocesium also should occur. Hara et al [58] suggested the incorporation of 137 Cs into the fine structure of plant tissues and reported the existence of ammonium acetate-insoluble 137 Cs in Japanese cedar needles. By considering the transfer of these leaves/needles onto the forest floor via litterfall, radiocesium in the O horizon should be more immobile compared with our assumption on Cs.…”