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[en] We have already reported the migration of ⁹⁰Sr and ¹³⁷Cs in lake sediment (Ogi Dam) and its forestry catchment. The ⁹⁰Sr infiltrates more to 10 cm soil profile in contrast to ¹³⁷Cs, showing a faster vertical migration of ⁹⁰Sr than that of ¹³⁷Cs. Sediment to soil ratio for ⁹⁰Sr showed a higher value than that of ¹³⁷Cs, which depicted more horizontal flowing of ⁹⁰Sr from forest soil to lake sediment than ¹³⁷Cs. The surface sediments became relatively uniform by the disturbance near surface (0∼4 cm) for ¹³⁷Cs. Cesium-137 adsorbed strongly to sediment became uniform, while ⁹⁰Sr weakly adsorbed to sediment re-dissolved to the lake water. The re-dissolved ⁹⁰Sr was adsorbed to the sediment again (0∼1 cm). Therefore, the sediment (0∼1 cm) has significantly higher ⁹⁰Sr concentration compared to the rest. The ⁹⁰Sr concentration of 4∼5 cm lake sediment is higher than that of 1∼4 cm, which might suggest the migration by pore water. In the present study, we discussed the distribution and migration of ⁹⁰Sr and ¹³⁷Cs using solid-liquid distribution coefficient (K_d), The larger K_d for ¹³⁷Cs revealed the slow migration in the soil, while the smaller K_d for ⁹⁰Sr revealed the fast migration in the soil. The first horizontal migration of ⁹⁰Sr from catchment to lake was explained by the elution of ⁹⁰Sr from the soil surface. The distribution in the lake sediment was also explained using K_d. The present discussion is based on the simple model. The more detailed discussion is needed by considering a biological diffusion and more detailed environmental factors. (author)

[en] In the present study, we reported the investigation of radiocesium migration from steep slope surrounding catchment to water body based on the radiocesium distribution and soil to sediment ratio. It was confirmed that the radiocesium was derived from the Fukushima accident by considering the ¹³⁴Cs to ¹³⁷Cs ratio corrected to the released day which is about 1. We found the higher radiocesium inventory in higher elevation area and steep slope forest catchment, revealing the atmospheric dry initial deposition-derived radiocesium and high retention of the forest zone. The radiocesium distribution data revealed that the radiocesium migrated more from the transition zone to the water body than from forest catchment, and accumulated in the deeper layer of sediment. The lower value of ¹³⁷Cs soil to sediment ratio provided an evidence of radiocesium migration from the catchment and its accumulation in the sediment. The physicochemical property of surface soil was revealed as one of the possible factors of radiocesium high retention in forest catchment. (author)

[en] The long-term migration of ¹³⁷Cs in the environment is mainly through the ¹³⁷Cs adsorbed on the dispersed soil particles of various sizes. However, the transfer of ¹³⁷Cs from soil to plant, especially rice plant, remains questionable. The objective of this study is to determine the relation among soil characteristics, ¹³⁷Cs distribution and transfer factor (TF) of ¹³⁷Cs from soil to rice. In this study paddy fields in Kawauchi and Fukushima were chosen. This is because more studies have focused only on one sampling field and there have not been much discussion comparing various fields as envisaged in this study. The results have shown that TF for Kawauchi is 5-fold higher than that of Fukushima. Physicochemical properties of the soils showed that Fukushima soil has less percentage of exchangeable ¹³⁷Cs and high percentage of exchangeable K in contrast to Kawauchi soil. These factors likely disturbed the transfer of ¹³⁷Cs from soil into the rice plant. Powder X-ray diffraction has shown that Fukushima soil is rich in micaceous minerals which also release a lot of K⁺ to distract the ¹³⁷Cs transfer. This study suggests that the presence of micaceous minerals in the soil would be a good amendment for radiocesium-contaminated rice paddy fields in enhancing adsorption of ¹³⁷Cs in the soil. However, there is still a need to investigate adsorption kinetics of ¹³⁷Cs to ascertain higher values of TF in Kawauchi soil. (author)

[en] Strontium-90 (⁹⁰Sr) and cesium-137 (¹³⁷Cs) were released from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011. Strontium-90 concentration in environment was extremely lower than that of ¹³⁷Cs in the soil after the FDNPP accident. However, ⁹⁰Sr may induce higher risk of health effect to human than ¹³⁷Cs by considering longer biological half-life of ⁹⁰Sr than ¹³⁷Cs. Moreover, there is not sufficient data on ⁹⁰Sr horizontal and vertical distribution compared to ¹³⁷Cs, which is important for predicting their long-term migration. In the present study, the distribution of ⁹⁰Sr and ¹³⁷Cs in the soils of Kawauchi and Fukushima paddy rice fields was investigated and the migration of ⁹⁰Sr and ¹³⁷Cs in Lake Ogi sediment and its forestry catchment area was studied. A rough relation between ⁹⁰Sr and ¹³⁷Cs levels in soil is shown and such insufficient correlation might be defined by the low ⁹⁰Sr concentration and because of global fallout. Furthermore, ⁹⁰Sr gave higher coefficient of variation in comparison to ¹³⁷Cs, portraying that the movement of ⁹⁰Sr is more affected by the environmental factors rather than ¹³⁷Cs. The depth dependency of ⁹⁰Sr and ¹³⁷Cs in Lake Ogi forestry catchment area is shown for both radionuclides, and the activity concentration decreases with the increase of depth. However, the ⁹⁰Sr infiltrates more to 10 cm soil profile in contrast to ¹³⁷Cs, showing ⁹⁰Sr faster vertical migration than ¹³⁷Cs. Sediment to soil ratio for ⁹⁰Sr reported a higher value than that of ¹³⁷Cs, which possibly depicts more horizontal flowing of ⁹⁰Sr from forest soil to lake sediment than ¹³⁷Cs. Consequently, the higher mobility of ⁹⁰Sr than ¹³⁷Cs was proposed. (author)

[en] To study the level of radioactivity concentrations from a coal-based power plant (Barapukuria, Bangladesh) and to estimate the associated radiological hazards, coal and associated combustion residuals from the power plant were analyzed by gamma-ray spectrometry with high-purity germanium (HPGe) detector. The results reveal that the mean radioactivity (Bq kg⁻¹) concentrations in feed coal samples are 66.5 ± 24.2, 41.7 ± 18.2, 62.5 ± 26.3, and 232.4 ± 227.2 for U-238, Ra-226, Th-232, and K-40, respectively, while in coal combustion residuals (CCRs), they are 206.3 ± 72.4, 140.5 ± 28.4, 201.7 ± 44.7, and 232.5 ± 43.8, respectively. With the exception of K-40, all the determined natural radionuclides are considerably higher in the investigated feed coal and associated combustion residues as compared with the world soil and world coal mean activities. On the average, CCRs contains 3.10–3.37 times more natural radionuclides than the feed coal, except for K-40. The radioactivity of fly ash and bottom ash is fractionated, and ratio ranges from 1.40 to 1.57. The mean values of the radiological hazard indices in the coal and their associated residuals are 153.1 and 446.8 Bq kg⁻¹ for radium equivalent activity, 0.41 and 1.21 for the external hazard index, 70 and 200.1 nGy h⁻¹ for the absorbed gamma dose rate, 0.09 and 0.25 mSv year⁻¹ for the annual effective dose rate, and 3.0 × 10⁻⁴ and 8.6 × 10⁻⁴ Sv⁻¹ for the excess lifetime cancer risk, respectively, most of which exceed the UNSCEAR-recommended respective threshold limits. The outcome of this study suggests a potential radiological threat to the environment as well as to the health of occupational workers and nearby inhabitants from the examined samples.

[en] The original version of this article unfortunately contained an error in eq. 1. The denominator Ɛ of Eq. (1) was missing.

[en] Coal-fly-ash is one of the major byproducts of coal-based power plant in which naturally occurring radioactive materials (NORMs) are drastically enriched compared to those of feed coals. Thus, improper management of fly-ash may introduce additional radioactivity to the surrounding environment and cause radiological risk. So, in order to study the distribution of radionuclides in soil around a coal-based power plant and to evaluate their radiological risk, soil, coal and fly-ash samples were analyzed by using a HPGe detector for U-238, Ra-226, Th-232 and K-40 radioactivity concentrations. Furthermore, soil minerals were also studied by X-ray diffractometer to assess the mineralogical provenance of the radionuclides. Mean radioactivity concentrations (in Bq $\cdot <!--\; ???\; -->$ kg${}^{\text{â<!-- ?? -->}\text{ˆ<!-- ?? -->}\text{’<!-- ??? -->}1}$) of U-238, Ra-226, Th-232 and K-40 in soil samples are 102.9$\pm <!--\; ??\; -->$41.4, 63.6$\pm <!--\; ??\; -->$7.4, 103.4$\pm <!--\; ??\; -->$13.9 and 494.2$\pm <!--\; ??\; -->$107.5, respectively which are comparatively higher than the typical world mean value. Elevated levels of radioactivity are likely due to the presence of illite, kaolinite, monazite, rutile and zircon minerals in the soil samples rather than technogenic contributions from the power plant. Furthermore, mean soil contamination factor (CF) are close to unity and mean pollution load index (PLI) is below unity while the average radium equivalent activity (Ra${}_{eq}$ in Bq $\cdot <!--\; ???\; -->$ kg${}^{\text{â<!-- ?? -->}\text{ˆ<!-- ?? -->}\text{’<!-- ??? -->}1}$), external hazard index (H${}_{ex}$), absorbed $\mathrm{\gamma <!--\; ??\; -->}$ dose rate (D in nGyh${}^{\text{â<!-- ?? -->}\text{ˆ<!-- ?? -->}\text{’<!-- ??? -->}1}$), annual effective dose rate (E in mSv $\cdot <!--\; ???\; -->$ y${}^{\text{â<!-- ?? -->}\text{ˆ<!-- ?? -->}\text{’<!-- ??? -->}1}$) and excess lifetime cancer risk (ELCR in Sv${}^{\text{â<!-- ?? -->}\text{ˆ<!-- ?? -->}\text{’<!-- ??? -->}1}$) are 249.5$\pm <!--\; ??\; -->$21.7, 0.67$\pm <!--\; ??\; -->$0.06, 114.2$\pm <!--\; ??\; -->$9.4, 0.20$\pm <!--\; ??\; -->$0.02, 4.9$\times <!--\; ??\; -->$10${}^{\text{â<!-- ?? -->}\text{ˆ<!-- ?? -->}\text{’<!-- ??? -->}4}$$\pm <!--\; ??\; -->$0.4$\times <!--\; ??\; -->$10${}^{\text{â<!-- ?? -->}\text{ˆ<!-- ?? -->}\text{’<!-- ??? -->}4}$, respectively, which are within the permissible limit. Thus, in terms of radioactivity concentrations and associated environmental and radiological indices, the effect of the power plant is insignificant.