Concentrations and biological half-life of radioactive cesium in epigeic earthworms after the Fukushima Dai-ichi Nuclear Power Plant accident. (December 2018)

• Record Type: Journal Article
• Authors: Tanaka, S.; Adati, T.; Takahashi, T.; Fujiwara, K.; Takahashi, S.
• Is Part Of: Journal of environmental radioactivity. Volume 192(2018)
• Page Start: 227
• Page End: 232
• Publication Date: 2018-12
• Subjects: Radioactivity -- Periodicals; Radiation, Background -- Periodicals; Radioecology -- Periodicals; Radioactive pollution -- Periodicals; Environmental Pollutants -- Periodicals; Radioactive Pollutants -- Periodicals; Radioactivity -- Periodicals; Radioécologie -- Périodiques; Pollution radioactive -- Périodiques; Fond de rayonnement -- Périodiques; 539.752
• DOI: 10.1016/j.jenvrad.2018.06.020
• Languages: English
• ISSNs: 0265-931X

Abstract

Abstract: To understand the long-term behavior of radiocesium in the biological processes of a forest ecosystem, its concentration in Japanese epigeic earthworms (Megascolecidae), litter, and soil, and the ambient dose equivalent rates, were investigated after the Fukushima Dai-ichi Nuclear Power Plant accident. The metabolism of radiocesium in the earthworms was also investigated in the laboratory, and its biological half-life (Tb ) was estimated. The concentration of 137 Cs in the habitat soil and litter changed from 2014 to 2016, with levels in the litter going from 44.9 Bq/g dw (in 2014) to 45.3 Bq/g dw (2015) and 10.7 Bq/g dw (2016); in soil, these values were 9.79 Bq/g dw, 7.14 Bq/g dw and 18.0 Bq/g dw, respectively. By contrast, no significant changes were observed in the concentrations in the earthworms, which were 4.87 Bq/g fw, 5.30 Bq/g fw and 4.67 Bq/g fw in 2014, 2015, and 2016, respectively. The ambient dose equivalent rates at the sampling site declined significantly over these three years, going from 2.15 μSv/h to 1.68 μSv/h and 1.35 μSv/h, mostly corresponding to physical decay of radiocesium. The majority (95%) of the 137 Cs in the earthworms, observed via autoradiography, was concentrated primarily in the intestine. The clearance of 137 Cs from the earthworms was described by dual exponential functions: the half-life in the rapid loss due to gut clearance was 0.10 days and a second slower loss due to physiological clearance was 27.4 days. Highlights: The concentrations and biokinetics of radiocesium in earthworms were investigated. No significant changes in radiocesium concentration were observed from 2014 to 2016. The distribution of radiocesium in the earthworms was visualized via autoradiography. About 95% of the radiocesium was located in the intestines. The biological half-life of 137 Cs was estimated for initial and delayed clearance.