Dependency of radioiodine root uptake by crops on soil characteristics

The aim of this study was to quantify the parameters of root uptake of radioiodine by agricultural crops under steady state conditions depending on the main soil characteristics. For this purpose, a long-term (483-days) pot experiment was conducted under natural conditions in the Chornobyl Exclusion Zone to grow radish in soils of four different types with added isotope ¹²⁵I. The experiment demonstrated an increase in root uptake of radioiodine by radish roots in the following sequence of soil types: clay soil < loam soil ≪ sandy soil (Chernozem ≈ Phaeozem < Greyzem ≪ Podzoluvisol). The obtained results have been analyzed in conjunction with the results of our previous studies to identify the factors determining the parameters of root uptake of radioiodine by the studied crop species. The ¹²⁵I concentration ratios (CRs) in edible parts of crop species (radish roots: from 0.003 for Chernozem to 0.02 for Podzoluvisol; lettuce leaves: 0.004-0.04; bean pods: 0.0003-0.004; wheat straw: 0.01-0.1; and wheat seeds: 0.0001-0.001) anticorrelated with the characteristics of the soils studied: the distribution coefficients Kd of ¹²⁵I (from 112 L kg^-1 for clay soils to 19 L kg^-1 for sandy soil, R² = 0.56-0.97) and Kd' of stable iodine (93-19 L kg^-1, R² = 0.43-0.74), stable iodine concentration in soil (6.2-0.5 mg kg^-1, R² = 0.71-0.88), and humus content (4.0-0.8%, R² = 0.44-0.78). The obtained steady-state CR values and their dependence on the soil characteristics can be used to model the root uptake of ¹²⁹I, a long-lived radiological contaminant, and to predict its accumulation in human food and animal feed.