Migration characteristics of ²²⁶Ra radionuclide in topsoil: a case study for water spinach soil

Studying the migration of natural radionuclides is important for agricultural development strategies in regions with high background radiation and contamination. In this research, an experiment was conducted to assess the migration of ²²⁶Ra in the soil of water spinach. Water spinach (Ipomoea aquatica) was grown in 7 soils collected from different locations in southern Vietnam. The migration rate was determined by R_p (the uptake rate of ²²⁶Ra by water spinach) and R_ℓ (the leaching rate of ²²⁶Ra to the subsoil). The results show that the R_p values range from 0.448 to 4.50 mBq kg_{dry soil}^-1 d^-1. The R_ℓ values range from 3.253 to 16.52 mBq kg_{dry soil}^-1 d^-1. Both R_p and R_ℓ are important and contribute a major fraction to the total migration rate of ²²⁶Ra in topsoil in comparison with the decay process. The fractions for R_p, R_ℓ, and R_d to the total rate are 26.98%, 71.96% and 1.06%, respectively. The effective half-life of ²²⁶Ra (T_1/2^eff) was estimated from 21.64 to 90.06 y. This research also provides additional data on the transfer factor (TF) and partition coefficient (K_d) of ²²⁶Ra in some soil types. The correlations found between TF and K_d with soil properties are valuable for further studies, which aim to mitigate the effects of this radionuclide in the agricultural soil.