Transfer of 137Cs and stable Cs from soil to potato in agricultural fields.

The concentrations of 137Cs, stable Cs and K were measured in soils and potatoes collected from 26 agricultural fields in Aomori, Japan and soil-to-potato transfer factors of 137Cs and stable Cs were determined. The concentrations of 137Cs derived from fallout deposition and stable Cs in soils were 1-37 Bq kg-1 and 1-11 mg kg-1, respectively. The isotopes, 137Cs and stable Cs, were homogeneously mixed in the rooting zone in the upper 20 cm of soil in agricultural fields. The concentrations of 137Cs and stable Cs in potatoes were 50-2000 mBq kg-1 dry wt. and 0.004-0.13 mg kg-1 dry wt., respectively. The soil-to-potato transfer factor of 137Cs was in the range of 0.0037-0.16, which was higher than that of stable Cs of 0.00052-0.080. The transfer factors of 137Cs and stable Cs were correlated and the geometric mean of 137Cs was 0.030, which was four times higher than that of stable Cs at 0.0075. This implied that artificially added 137Cs is more mobile and more easily absorbed by plants than stable Cs in the soil. The concentration of K in potatoes showed a relatively constant value, independent of that in the soil. The transfer factors of both 137Cs and stable Cs decreased with increasing K concentration in the soil, which was mainly supplied as fertilizers to the fields. This suggests that the transfer of both 137Cs and stable Cs from soil to potato was affected by the presence of K in the soil. However, the transfer factors of 137Cs and stable Cs were independent of the amount of organic materials in soils.