Radiocesium uptake through leaf surfaces of tea plants (Camellia sinensis L.)

To clarify the source of radiocesium detected in newly emerged tea leaves contaminated just before the time of bud opening by fallout of radionuclides from Fukushima Dai-ichi Nuclear Power Plant, 137CsCl solution (0.185 M Bq mL−1) was applied to the front or the backside surfaces of mature leaves of tea plant (Camellia sinensis L. cv. Yabukita) at the time of bud opening. A 21 days after foliar application, the buds had grown and developed to the three- or four-leaf stage. In the front treatment, almost all (95%) of the applied 137Cs was present in the mature leaves (hot mother leaves). In the backside treatment, 68% of applied 137Cs also remained in hot mother leaves, but 22% and 10% was found in the new shoots attached to hot mother leaves and the other parts (non-applied mature leaves, stems and roots), respectively. The images of a hot leaf and its attached new shoots by imaging plate analysis revealed that the results coincided with those of the 137Cs distribution above. These suggested that radiocesium was primarily absorbed from the backside surface of tea leaves through the stoma, and then the greater part was transported to newly emerged tea organs during the new shoot growth period.