Translocation of 125I, 75Se and 36Cl to Wheat edible parts following wet foliar contamination under field conditions

Apart from radiocaesium and radiostrontium, there have been few studies on the foliar transfer of radionuclides in plants. Consequently, specific translocation factor (ftr) values for 129I, 79Se and 36Cl are still missing from the IAEA reference databases. The translocation of short – lived isotopes, 125I and 75Se, and of 36Cl to wheat grain were measured under field conditions following acute and chronic wet foliar contamination at various plant growth stages in the absence of leaching caused by rain. The translocation factors ranged from 0.02% to 1.1% for 125I (a value similar to Sr), from 0.1% to 16.5% for 75Se, and from 1% to 14.9% for 36Cl. Both 36Cl and 75Se were as mobile as Cs. The phenomenological analysis showed that each element displayed a specific behavior. Iodide showed the lowest apparent mobility because of its preferential fixation in or on the leaves and a significant amount probably volatilized. Selenite internal transfer was significant and possibly utilized the sulphur metabolic pathway. However bio - methylation of selenite may have led to increased volatilization. Chloride was very mobile and quickly diffused throughout the plant. In addition, the analysis underlined the importance of plant growth responses to annual variations in weather conditions that can affect open field experiments because plant growth stage played a major role in ftr values dispersion. The chronic contamination results suggested that a series of acute contamination events had an additive effect on translocated elements. The highest translocation value obtained for an acute contamination event was shown to be a good conservative assessment of chronic contamination if data on chronic contamination translocation are lacking. The absence of rain leaching during the experiment meant that this investigation avoided potential radionuclide transfer by the roots, which also meant that radionuclide retention on or in the leaves was maximized. This study was therefore able to obtain accurate translocation factors, which are probably among the highest that could be recorded.

► Specific values of translocation factors (ftr) for iodide, selenite and chloride.
► Medium mobility of iodide, high mobility of selenite and chloride.
►  Plant growth response to climate variations is a source of ftr values dispersion.
► Very early stages of plant growth are sensitive to foliar uptake.