Natural radionuclide activities and their radiological hazard assessment in Taiwanese paddy field soils

This study examined the levels of gamma-emitting natural radionuclides in soils from 11 paddy fields across Taiwan's primary rice-producing regions and assessed the potential radiological risk to farmers. The mean activities of 40K, 232Th, and 226Ra in the 66 soil samples were 591.0 ± 133.8, 45.4 ± 10.2, and 30.9 ± 6.6 Bq/kg, respectively, with variations among sites attributed to geological differences. The average activity ratios of 40K/226Ra (19.3) and 40K/232Th (13.1) were higher than global soil averages, suggesting a soil composition enriched in potassium-rich minerals, such as feldspar and mica. A strong positive correlation observed among 40K, 226Ra, and 232Th activities indicated a common geological origin. The radiological hazard was assessed by calculating the annual effective dose using the United Nations Scientific Committee on the Effects of Atomic Radiation (2010) methodology. The mean effective dose for farmers was estimated to be 46.5 ± 9.9 μSv/y, a value significantly below the public dose limit of 1000 μSv/y.