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Studies on Radiocesium Transfer in Agricultural Plants in Fukushima Prefecture

Takashi Saito, Yasukazu Suzuki, Shigeto Fujimura, and Hirofumi Tsukada

Abstract After the Fukushima Daiichi Nuclear Power Plant (Tokyo Electric Power Company) accident occurred in March 2011, the concentration of radiocesium in brown rice produced in several areas of Fukushima Prefecture has exceeded a provisional regulation value. Therefore, we attempted research on decreasing the radiocesium concentration in agricultural plants.

To decrease the concentration of radiocesium in brown rice, we investigated the effect of the application of potassium fertilizer in rice paddy fields on the root uptake of radiocesium. The soil-to-brown-rice transfer factor of radiocesium decreased with an increase in exchangeable K2O in the soil, suggesting that the application of potassium fertilizer is an effective countermeasure to reduce the radiocesium concentration in brown rice.

We examine the possibility of decontamination by means of phytoremediation. Four species of plants were sown. The highest removal percentages of 137Cs were obtained in amaranth (0.093 %) and sunflower (0.038 %) in the light-colored Andosol and gray lowland soils, respectively. This result indicates that it is difficult to remove radiocesium from contaminated soil by means of phytoremediation.

Keywords Brown rice • Exchangeable K2O • Phytoremediation • Radiocesium

• Soil • Soil-to-brown-rice transfer factor

Objective

The magnitude 9.0 earthquake and the subsequent large tsunami that occurred on March 11, 2011, caused extensive damage to coastal areas in Tohoku, Japan. In particular, the cooling system of the Fukushima Daiichi Nuclear Power Plant [Tokyo Electric Power Company (TEPCO) FNPP] collapsed from the tsunami in excess of 10 m, which resulted in several explosions in the four reactors of the plant. Large amounts of radioactive materials, mainly noble gas, 131I, 134Cs, and 137Cs, were released into the atmosphere, and consequently agricultural land and forests in Eastern Japan were contaminated. Radiocesium (134Cs + 137Cs) is an important radionuclide that can be used for the assessment of radiation exposure to the public because it has a long half-life (134Cs, 2.06 years; 137Cs, 30.2 years), high transferability, and wide distribution in the environment. Because of their long half-lives, there is concern that radiocesium (134Cs + 137Cs) will remain on the surface of agricultural land and persist for a long time [1, 2]. Therefore, we have started monitoring of radiocesium in soil collected from agricultural land in Fukushima Prefecture from March 2011. Based on these data, Nuclear Emergency Response Headquarters showed planting areas of rice in all regions, except a 20-km exclusion zone and the deliberate evacuation zone (DEZ) in Fukushima Prefecture in 2011. However, the brown rice produced in some areas in northern part of Fukushima prefecture exceeded the provisional regulation value for agricultural crops at the times (>500 Bq kg−1). Consequently, the planting of rice crops for the year 2012 had been restricted in that area. The present studies show investigation of radiocesium transfer in the agricultural plants.

 
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