9:05 AM - 9:20 AM
[HCG26-01] Risk assessment of radiocesium transfer from soil to plant in decontaminated agricultural land in Tomioka, Fukushima
Keywords:Fukushima, radiocesium, soil, decontamination
After the Fukushima Daiichi nuclear power plant (FDNPP) accident in 2011, decontamination of agricultural land had been taken in highly contaminated areas in Fukushima prefecture except difficult-to-return zone. As a result, the total 137Cs content in the soil surface was basically reduced to less than 5,000 Bq kg-1. However, few studies have elucidated the transfer risk of 137Cs from soil to plant on decontaminated field. Therefore, the objective of this study was to determine total and exchangeable 137Cs content as well as plant-available K content of soil in a wide area of the decontaminated agricultural land because they are reported as important indices to predict the 137Cs transfer risk.
In November 2016, 173 soil samples were collected from the plowed layer (0-15 cm depth) of decontaminated agricultural land in Tomioka town, Fukushima prefecture, Japan (N37°20’, E141°00’) located about 10 km south of the FDNPP. The total 137Cs content in soils was determined by γ-ray spectrometry. Potassium in soils was extracted with 1 M CH3COONH4 and boiling 1 M HNO3 to determine exchangeable K and boiling HNO3 extractable K, respectively. Nonexchangeable K content was obtained by subtracting exchangeable K content from boiling HNO3 extractable K content. For 32 samples which exceeded 2,000 Bq kg-1 in total 137Cs content, exchangeable 137Cs content in soils was also determined by γ-ray spectrometry.
Total 137Cs content in soils was on average 1.2±1.0×103 Bq kg-1 in the decontaminated fields which was much lower than total 137Cs content before decontamination (6,700 Bq kg-1). The exchangeable K content was on average20.7±8.96 mg K2O 100g-1. Those of about 80% of soils were less than the recommended value by Fukushima prefecture (25 mg K2O 100g-1) to reduce 137Cs transfer from soil to plant. Total 137Cs content in soils showed a positive correlation with exchangeable K content (p < 0.01). This correlation indicated that decontamination to reduce total 137Cs content also led to the reduction of exchangeable K content. The exchangeable 137Cs content was on average 230±140 Bq kg-1 (value range: from 40 to 520 Bq kg-1) and showed a negative correlation with nonexchangeable K content (p < 0.05). This negative correlation indicated that 137Cs was strongly adsorbed on the soil in association with nonexchangeable K, since nonexchangeable K was basically related to the specific adsorption site for Cs. In conclusion, in decontaminated agricultural land, 1) the exchangeable K content in soil should be increased for reducing transfer risk of 137Cs and 2) the nonexchangeable K content can be used as a good index to select fields with lower transfer risk of 137Cs.
In November 2016, 173 soil samples were collected from the plowed layer (0-15 cm depth) of decontaminated agricultural land in Tomioka town, Fukushima prefecture, Japan (N37°20’, E141°00’) located about 10 km south of the FDNPP. The total 137Cs content in soils was determined by γ-ray spectrometry. Potassium in soils was extracted with 1 M CH3COONH4 and boiling 1 M HNO3 to determine exchangeable K and boiling HNO3 extractable K, respectively. Nonexchangeable K content was obtained by subtracting exchangeable K content from boiling HNO3 extractable K content. For 32 samples which exceeded 2,000 Bq kg-1 in total 137Cs content, exchangeable 137Cs content in soils was also determined by γ-ray spectrometry.
Total 137Cs content in soils was on average 1.2±1.0×103 Bq kg-1 in the decontaminated fields which was much lower than total 137Cs content before decontamination (6,700 Bq kg-1). The exchangeable K content was on average20.7±8.96 mg K2O 100g-1. Those of about 80% of soils were less than the recommended value by Fukushima prefecture (25 mg K2O 100g-1) to reduce 137Cs transfer from soil to plant. Total 137Cs content in soils showed a positive correlation with exchangeable K content (p < 0.01). This correlation indicated that decontamination to reduce total 137Cs content also led to the reduction of exchangeable K content. The exchangeable 137Cs content was on average 230±140 Bq kg-1 (value range: from 40 to 520 Bq kg-1) and showed a negative correlation with nonexchangeable K content (p < 0.05). This negative correlation indicated that 137Cs was strongly adsorbed on the soil in association with nonexchangeable K, since nonexchangeable K was basically related to the specific adsorption site for Cs. In conclusion, in decontaminated agricultural land, 1) the exchangeable K content in soil should be increased for reducing transfer risk of 137Cs and 2) the nonexchangeable K content can be used as a good index to select fields with lower transfer risk of 137Cs.