Radiation dose rate to Japanese cedar and plants collected from Okuma, Fukushima Prefecture

After the 2011 Fukushima Dai-ichi Nuclear Power Station (FDNPS) accident, wild populations of animals and plants living in the evacuation zone received additional ionizing radiation of both internal and external radiation doses. Morphological abnormalities of pine and fir trees near the FDNPS were reported. In order to evaluate dose effect relationships, it is necessary to quantify the radiation doses to trees and plants. In this study, the internal and external dose rates to Japanese cedar and plants collected at three sites in Okuma, approximately 4 km southwest of FDNPS were estimated applying the ERICA Assessment Tool. The activity concentrations of Cs-134 and Cs-137 in soils, cedar trunks, and plants were determined. The total dose rates to cedar ranged from 2.2 +/- 1.2 to 6.1 +/- 2.2 mu Gy h(-1). These rates were within the derived consideration reference levels (DCRLs) reported by ICRP 108 as 4-40 mu Gy h(-1) for pine trees. The highest estimate for plants was 7.1 +/- 2.7 mu Gy h(-1), much smaller than the DCRLs reported for grasses and herbs (40-400 mu Gy h(-1)). On average, the internal radiation dose rates to cedars at the two sites accounted for 5% and 29% of the external dose rates, respectively, while the value in another site was only 0.4% for cedar. This was attributed to differences in the crown area between the three sites. The trunk diameter of cedars shows a positive correlation with the ratio of internal to external radiation dose rates. It indicates that the total dose rate to cedars is easily estimated with the soil radiocaesium inventory and trunk diameter. The internal radiation dose rate to the plant varied depending on the plant species. This variation was considerably large in plants due to the presence of two species, including Solidago altissima and Artemisia indica var. maximowiczii. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study estimated the internal and external radiation doses to trees and plants near the Fukushima Dai-ichi Nuclear Power Station, finding that the total dose rates to cedars were within the reference levels, while the rates for plants were much lower compared to grasses and herbs. The research also revealed varying internal radiation dose rates among plant species, with considerable differences observed due to the presence of specific species.