Read Piyawan's abstract: Enhancing radiological risk assessment

Enhancing radiological risk assessment: Thailand's first national database on elemental transfer to rice

Radiological risk assessment and emergency preparedness planning require evaluation of radionuclide intake by humans via the soil-crop transfer pathway  (IAEA, 2010; ICRP, 2009). Concentration ratios (CRplant-soil) are commonly used to estimate an element’s concentration (or activity concentration in the case of a radionuclide) in plant from that in soil (IAEA, 2010). Most CRplant-soil data compiled by the International Atomic Energy Agency (IAEA) for food crops come from temperate climatic regions, as evidenced in Technical Report Series No. 472 (TRS 472).  Only four previous studies have contributed Thailand-specific crop data, which are summarised in IAEA TECDOC-1979. Thailand has an increasing need to assess discharges, or perspective discharges, for facilities within the country and also to develop emergency preparedness plans given the increasing focus on nuclear infrastructure development around its borders.  Rice is the staple food crop of Thailand, and the nation was the leading global exporter of rice  globally in 2023 (USDA, 2024), so quantifying transfer to rice is a key component in the assessment of potential human exposures from planned or accidental releases of radioactivity to the environment.  Paired samples of soil (n=295) and rice plant (n=295, subsequently separated into root, stem, and grain) were collected from a total of 59 paddy fields across 17 rice growing provinces. Determining radionuclide activity concentrations in samples from areas that have not been subject to significant radioactive discharges or significant fallout can be challenging, but stable elements can serve as useful proxies due to their similar physical and chemical properties. Therefore, stable elements, including essential nutrients, trace metals and radionuclides analogues, were determined (As, Cd, Co, Cr, Cs, Cu, Li, Ni, Pb, Rb, Se, Sr, Th, Tl, U, Y and Zn). The samples were analysed following the protocols outlined by FAO (2019) and Soil Survey Staff (2014). Results for six of these elements (As, Co, Cr, Cs, Th and U) will be presented here. Soil properties, in particular pH and soil texture, were negative correlated with CR values for rice (Figures 1 and 2). The mean CRroot for As, Co and Cr was consistently higher than CRgrain and CRstem. The CRs for Cs, Th, and U followed the following order: root > stem > grain (Table 1). In general, the results obtained from the present study indicate higher CR values for Thailand than reported within the previous IAEA data compilation (IAEA, 2009; IAEA, 2010).  The new rice transfer database for Thailand presented here provides a valuable resource for future regulatory and emergency preparedness activities and also a significant contribution to the available international knowledgebase on radionuclide transfer to rice.

Table 1 Comparison between concentration ratio of different rice compartments in Thai rice (n = 283 for grain, n = 75 for root and stem each sample). Arithmetic means having same letter are not significantly different (p >0.01) by the Duncan’s Multiple Range Test (DMRT).

FAO. (2019). Standard operating procedure for soil organic carbon Walkley-Black method Titration and colorimetric method: Food and Agriculture Organization of the United Nations.

IAEA. (2010). Handbook of Parameter Values for the Prediction of Radionuclide Transfer in Terrestrial and Freshwater Environments. Technical Reports Series No. 472. Vienna: INTERNATIONAL ATOMIC ENERGY AGENCY.

ICRP. (2009). Environmental Protection: Transfer Parameters for Reference Animals and Plants (Vol. Ann. ICRP 39(6)): International Commission on Radiological Protection.

Soil Survey Staff. (2014). Keys to soil taxonomy (12th ed.): USDA-Natural Resources Conservation Service.

USDA. (2024). Production - Rice. Retrieved from https://fas.usda.gov/data/production/commodity/0422110