Transfer factor of ¹³⁷Cs and ⁹⁰Sr to various crops in semi-arid environment

This study focuses on evaluating the transfer factor (F_v) of ¹³⁷Cs and ⁹⁰Sr from two basic soil types in the country, i.e. Aridisol and Inceptisol, to 18 common crops belong to six groups, i.e. cereals, leafy, non-leafy vegetables, tubers, leguminous fodder and leguminous vegetables. In addition, the variation of F_vs of ¹³⁷Cs and ⁹⁰Sr with crop components, growth stages of plants and the influence of mineral fertilisation were investigated. The experiments were performed in an open field and the results were expressed as geometric means. The data revealed that F_vs of both radionuclides were higher in Aridisol than Inceptisol for all crops by about 1.03-4.86 fold. F_vs of ⁹⁰Sr were more enhanced than those of ¹³⁷Cs by one or two orders of magnitude despite plant group and soil type, e.g. F_vs ranged 0.12-5.2 for ⁹⁰Sr and 0.0035-0.26 for ¹³⁷Cs in the vegetative portion of the crops. Among the six crop groups investigated, cereals gave the lowest F_vs for both radionuclides, which is compatible with the data reported worldwide. The average F_vs observed in cereal grains reached 0.001 for ¹³⁷Cs and 0.017 for ⁹⁰Sr, in Inceptisol. However, Jew-mallow (one of the major leafy vegetables in the country that is consumed throughout the year) reflected the highest F_vs for ¹³⁷Cs and ⁹⁰Sr, i.e. 0.11 and 2.44 in Inceptisol, respectively. Comparing F_vs of the radionuclides through the growing stages of the plants indicated enhanced values at the mid-season than harvest as a consequence of the decrease of the physiological activity of the plants towards maturation and dilution made by the increase of plant biomass; e.g. F_vs dropped to about 3.0 fold for ¹³⁷Cs and 2.2 for ⁹⁰Sr, in Aridisol. Mineral fertilisation of soil (for four crops, i.e. sorghum, barley, spinach and alfalfa) reduced F_vs for both radionuclides to an extent of 30% probably because of the competing action of their stable nutrient analogues NH₄⁺, K⁺ or Ca²⁺ or because of growth dilution. The data presented herein would form a baseline when decision of land-investment or phytoremediation is the preferable countermeasure for the management of ¹³⁷Cs and ⁹⁰Sr-contaminated soil in semi-arid environment.