Radiocesium contamination of soybean (Glycine max) produced with no fertilization in 2014: A case study in Minamisoma City, Fukushima Prefecture, Japan

Abstract

Radioactive contamination of farmland and crops is a matter of public concern in Japan after the catastrophe of the Fukushima Daiichi Nuclear Power Plant occurred in March 2011. In this study, three organic (unfertilized) and one conventional soybean fields in Minamisoma City, Fukushima Prefecture, were selected in collaboration with local farmers, and soil and soybean (Glycine max) samples were collected at the harvest in 2014. Radioactive cesium (Cs) concentration of the soybean samples was then measured and the relationship among soil chemical properties and radioactive Cs contamination in the soybean samples were investigated. Soil radioactive Cs concentration (¹³⁴Cs+¹³⁷Cs) was ranged in 510-1,100Bq/kg-dry soil (ds). Radioactive Cs in the bean samples collected in the unfertilized fields showed 12-60Bq/kg-dry weight (dw), while that from the conventional field was 2.8Bq/kg-dw. Transfer factors (TFs) were calculated as the following formula : TFs＝(soybean ¹³⁷Cs [Bq/kg-dw]/soil ¹³⁷Cs [Bq/kg-ds]). The TFs of the bean samples collected from the four fields were 0.007-0.054, which were comparable with the known values. Significant hyperbolic correlation between TFs and soil exchangeable potassium (K) concentrations were found. Soil exchangeable K concentrations in the unfertilized soybean fields were less than the desired values proposed by the Fukushima Prefectural government; therefore, application of appropriate K fertilizers into the fields may be necessary to reduce radioactive Cs uptake in soybean.