Transfer factor of 90Sr and 137Cs to lettuce and winter wheat at different growth stage applications

• Higher TFs for both radionuclides were observed for leafy plant in comparison to cereals.
• Despite the growth stages & plants' variety, TFs of 90Sr were always higher than those of 137Cs.
• TFs of 90Sr showed comparable trends in both crops and were higher at earlier growth stages.
• Fluctuation noted in TFs for 137Cs in lettuce with higher TFs at second contamination-stage.
• High TFs for 137Cs when contamination occurred at the latest growth stage of wheat vegetative.

The effect of clay soil contamination time on the transfer factors (Fvs) of 137Cs and 90Sr was investigated in four different growth stages of winter wheat and lettuce crops. The experiment was performed in an open field using lysimeters. The Fvs were the ratio of the activity concentrations of the radionuclides in crops to those in soil, both as dry weight (Bq kg−1). Significant difference of log-Fvs was evaluated using one-way Analysis of Variance (ANOVA). Basically, Fvs of 90Sr were higher than those of 137Cs, despite of the application stage or crop' variety. Higher Fvs for both radionuclides were observed for lettuce in comparison to winter wheat. Fvs of 90Sr showed comparable trends for both crops with enhanced Fvs obtained when contamination occurred in early stages, i.e. 1.20 for lettuce and 0.88 and 0.02 for winter wheat, straw and grains, respectively. Despite the fluctuation noted in the pattern of Fvs for 137Cs, soil contaminated at the second stage gave the highest Fvs for lettuce and grains, with geometric means of 0.21 and 0.01, respectively. However, wheat-straw showed remarkable increase in Fv for the latest contamination (ripening stage), about 0.06. It could be concluded that soil contamination at early growth stages would represent high radiological risk for the scenarios studied with an exception to 137Cs in winter wheat-straw which reflected greater hazard at the latest application.