Transfer of radiocesium from hydroponic medium to potherb mustard and tomato plants

Abstract

Potherb mustard (Brassica rapa var. nipposinica) and tomato plants (scion, ‘CF Momotaro haruka’; rootstock, ‘Dokutar K’; Solanum lycopersicum) were cultured in hydroponic medium containing cesium-137 (¹³⁷Cs) at three different concentrations (0.03, 0.13 and 1.03 Bq L^?1), and uptake of ¹³⁷C into the plants was determined. When the ¹³⁷Cs radioactivity concentration in the medium was 1.03 Bq L^?1, the ¹³⁷Cs radioactivity concentrations in the edible portions of the plants were 4.80 Bq kg^?1 fresh weight for the potherb mustard plants and 3.60 Bq kg^?1 fresh weight for the tomato plants. In both species, the ¹³⁷Cs radioactivity concentration in the edible portions decreased with decreasing ¹³⁷Cs radioactivity concentration in the culture medium. When the ¹³⁷Cs radioactivity concentration in the medium was 0.03 Bq L^?1, a concentration observed in many streams and in tap water in Fukushima Prefecture after the accident at the Fukushima Daiichi Nuclear Power Plant, the ¹³⁷Cs radioactivity concentrations in the edible portions of the plants were 0.50 and 0.15 Bq kg^?1 fresh weight for potherb mustard and tomato plants, respectively. These values are less than the Japanese allowable limit for radiocesium in food. For both species, the transfer factors for ¹³⁷Cs uptake from the culture media to the edible portions and the average transfer rates over the cultivation period were calculated.