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

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 (Cs-137) at three different concentrations (0.03, 0.13 and 1.03BqL(-1)), and uptake of C-137 into the plants was determined. When the Cs-137 radioactivity concentration in the medium was 1.03BqL(-1), the Cs-137 radioactivity concentrations in the edible portions of the plants were 4.80Bqkg(-1) fresh weight for the potherb mustard plants and 3.60Bqkg(-1) fresh weight for the tomato plants. In both species, the Cs-137 radioactivity concentration in the edible portions decreased with decreasing Cs-137 radioactivity concentration in the culture medium. When the Cs-137 radioactivity concentration in the medium was 0.03BqL(-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 Cs-137 radioactivity concentrations in the edible portions of the plants were 0.50 and 0.15Bqkg(-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 Cs-137 uptake from the culture media to the edible portions and the average transfer rates over the cultivation period were calculated.