Transfer of Radium-226 from Soil to Rice: A Comparison of Sampling Area Differences

Abstract

Due to limited numbers of radium-226 (²²⁶Ra) soil-to-plant transfer data, it has been difficult to analyze the sampling area differences. In this study, we measured ²²⁶Ra concentrations in brown rice and associated soils collected from 61 locations throughout Japan and obtained soil-to-rice transfer factors (TFs). Concentrations of ²²⁶Ra in the soils collected in southwestern Japan were higher than those in northeastern Japan (t-test, p < 0:001); for example, the geometric mean (GM) of ²²⁶Ra in southwestern Japan was 40.4 Bq/kg-dry (N = 33) and it was 27.8 Bq/kg (N = 28) in northeastern Japan, reflecting geological differences between these areas. Using the measured data, we compared TFs in these two areas and found no difference, i.e., the GM in southwest was 4:6 × 10⁻⁴ and it was 4:9 × 10⁻⁴ in northeast. The observed TFs were about one order of magnitude lower than the previously reported TF values for cereals (maize, wheat, and rice), but in the same range for previously reported data for white rice. Among the alkaline earth metals, TF for Ba was well correlated to TF for Ra, but because Ba and Ra concentrations in brown rice were highly correlated, the TF would also be expected to correlate.

KEYWORDS:

• paddy soil
• rice plant
• brown rice
• transfer factor
• radium-226
• barium
• agricultural field