Abstract
BackgroundStable cesium (133Cs) naturally exists in the environment whereas recently deposited radionuclides (e.g., 137Cs) are not at equilibrium. Stable cesium has been used to understand the long-term behavior of radionuclides in plants, trees and mushrooms. We are interested in using 133Cs to predict the future transfer factor (TF) of radiocesium from contaminated logs to shiitake mushrooms in Eastern Japan. However, the current methodology to obtain a representative wood sample for 133Cs analysis involves mechanically breaking and milling the entire log (excluding bark) to a powder prior to analysis. In the current study, we investigated if sawdust obtained from cutting a log along its length at eight points is as robust but a faster alternative to provide a representative wood sample to determine the TF of 133Cs between logs and shiitake.MethodsOak logs with ready-to-harvest shiitake fruiting bodies were cut into nine 10-cm discs and each disc was separated into bark, sapwood and heartwood and the concentration of 133Cs was measured in the bark, sapwood, heartwood, sawdust (generated from cutting each disc) and fruiting bodies (collected separately from each disc), and the wood-to-shiitake TF was calculated.ResultsWe found that the sawdust-to-shiitake TF of 133Cs did not differ (P = 0.223) compared to either the sapwood-to-shiitake TF or heartwood-to-shiitake TF, but bark did have a higher concentration of 133Cs (P < 0.05) compared to sapwood and heartwood. Stable cesium concentration in sawdust and fruiting bodies collected along the length of the logs did not differ (P > 0.05).DiscussionSawdust can be used as an alternative to determine the log-to-shiitake TF of 133Cs. To satisfy the goals of different studies and professionals, we have described two sampling methodologies (Methods I and II) in this paper. In Method I, a composite of eight sawdust samples collected from a log can be used to provide a representative whole-log sample (i.e., wood and bark), whereas Method II allows for the simultaneous sampling of two sets of sawdust samples—one set representing the whole log and the other representing wood only. Both methodologies can greatly reduce the time required for sample collection and preparation.
Highlights
Over 25 million logs are used annually for shiitake mushroom (Lentinula edodes) production in Japan (Ministry of Agriculture, Forestry & Fisheries, 2017)
Stable cesium concentration in fruiting bodies collected from odd- (600 μg/kg dry weight (DW)) and even-numbered discs (581 μg/kg DW) did not differ (P > 0.05) (Fig. 3C) and the sawdust-toshiitake transfer factor (TF) from odd- (TF = 22.6) and even-numbered (TF = 23.1) cut positions did not differ (P > 0.05) (Fig. 4A)
One reason the TF of 133Cs is higher than the TF of radiocesium on a fresh weight (FW) basis is because the log-to-shiitake TF of radiocesium was determined within 1 year of the nuclear accident when only the bark was contaminated (Mahara et al, 2014), whereas 133Cs was shown to be distributed through all parts of a log in this study (Table 1), and is likely to be more available for uptake
Summary
Over 25 million logs are used annually for shiitake mushroom (Lentinula edodes) production in Japan (Ministry of Agriculture, Forestry & Fisheries, 2017). We investigated if sawdust obtained from cutting a log along its length at eight points is as robust but a faster alternative to provide a representative wood sample to determine the TF of 133Cs between logs and shiitake. Methods: Oak logs with ready-to-harvest shiitake fruiting bodies were cut into nine 10-cm discs and each disc was separated into bark, sapwood and heartwood and the concentration of 133Cs was measured in the bark, sapwood, heartwood, sawdust (generated from cutting each disc) and fruiting bodies (collected separately from each disc), and the wood-to-shiitake TF was calculated. Discussion: Sawdust can be used as an alternative to determine the log-to-shiitake TF of 133Cs. To satisfy the goals of different studies and professionals, we have described two sampling methodologies (Methods I and II) in this paper. Both methodologies can greatly reduce the time required for sample collection and preparation
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