Transfer of Cs and Sr from soil-to-potato: Interpretation of the association from global fallout in Aomori to accidental release in Fukushima and Chornobyl.

Ceasium-137 and Sr are major artificial radionuclides that have been released into the environment. Soil-to-plant transfer of radionuclides is an important route to food contamination. The radionuclide activity concentrations in crops must be quantitatively predicted for estimating the internal radiation doses from food ingestion. In this study, soil and potato samples were collected from three study sites contaminated with different sources of Cs and Sr: Aomori Prefecture (global fallout) and two accidental release areas (Fukushima Prefecture and the Chornobyl exclusion zone). The Cs activity concentrations in the soil and potato samples widely ranged from 1.0 to 250,000 and from 0.048 to 200,000 Bq kg dry weight, respectively. The soil-to-potato transfer factor of Cs also ranged widely (0.0015-1.1) and decreased with increasing concentration of exchangeable K. Meanwhile, the activity concentrations of Sr in the soil and potato samples were 0.50-64,000 and 0.027-18,000 Bq kg dry weight respectively, and the soil-to-potato transfer factor of Sr was 0.023-0.74, decreasing with increasing concentration of exchangeable Ca. The specific activity ratios of Cs/Cs and Sr/Sr in the exchangeable fraction were similar to those in potatoes, with a factor of 3 in the ±95 % confidence intervals over six orders of magnitude and a factor of 2 in the ±95 % confidence intervals over five orders of magnitude, respectively. According to the data, the accuracy of predicting the activity concentrations of Cs and Sr in potatoes can be improved by applying the specific activity ratios of Cs/Cs and Sr/Sr in the exchangeable fraction. This approach accounts for variable factors such as the effects of K and Ca fertilization and soil characteristics. It also emphasizes the benefit of determining the stable Cs and Sr concentrations in potatoes and other crops prior to possible future contamination.