Soil-to-rice transfer parameters for naturally occurring radionuclides and trace elements in Thai paddy fields: A national dataset

The reliability of transfer parameters in radiological assessment is essential for estimating the food chain transfer of radionuclides, which commonly uses the concentration ratio (CR plant-soil ) as a key parameter in evaluating ingestion dose exposure to humans. Rice ( Oryza sativa L. ) is a staple food consumed by half of the world's population, and it plays a particularly significant role in Thailand's diet and economy. The CR rice-soil dataset reported by the International Atomic Energy Agency (IAEA) shows high variability across different environments (temperate and tropical), with a notable scarcity of related parameters such as soil properties within specific study sites. This scarcity is particularly evident in Thailand, where CR rice-soil data have been reported in only a few studies. This study determined CR rice-soil values for natural radionuclides ( 40 K, 226 Ra, 228 Ra, and 228 Th) and trace elements (As, Cd, Co, Cr, Cs, Cu, Li, Ni, Pb, Rb, Se, Sr, Th, Tl, U, Y, and Zn) using 295 paired samples of soil and rice plants (root, stem, and grain) collected from Thailand's principal rice-growing areas. The arithmetic mean CR rice-soil values from this study were generally higher than those reported in international references (IAEA TRS 472 and MODARIA II TECDOC-1979). For most elements, CR values in rice plant parts decreased in the order CR root > CR stem > CR grain . A significant negative correlation between CR rice-soil values and soil physicochemical properties (pH, CEC, and OM) was observed using Spearman's rho. Spatial variation in CR rice-soil was also linked to soil texture. This study provides the first macro-scale quantification of CR rice-soil values in Thai rice and may support radiological assessments in tropical and international contexts.