Foliar and soil uptake of 134Cs and 85Sr by grape vines

The foliar and soil uptake of 134Cs and 85Sr by grape vines and their subsequent translocation to fruits and to the other plant compartments is described. Grape vine plants growing in pots and kept in an open field were contaminated with 134Cs and 85Sr in ionic form by sprinkling on the aerial part, or by addition to the soil. Sprinkling was effected at the stage of ripening of the grapes. Interception, determined by analysing all the leaves picked from three plants after the sprinkling, was approx. 50% of the sprayed activity. Soil contamination was effected after the fruit setting, 1 month earlier than sprinkling. At ripening, the whole plant was picked. Berries, leaves, shoots, stems, roots and soil were analysed by gamma spectrometry. Activities of the different parts of the plant were expressed as: (a) translocation factors of intercepted activity for foliar treatment; (b) transfer factors of activity applied to the soil for soil treatment. Both factors were calculated per unit of fresh weight, or referred to the total biomass of the plant compartment. Leaf-to-fruit translocation factors per unit of weight are of the order of magnitude of 10−1 for 134Cs and of 10−2 for 85Sr. One/two order of magnitude lower are soil-to-fruit transfer factors: 10−3 both for 134Cs and for 85Sr. Radiocesium behaves quite differently from radiostrontium, but the behaviour of both radionuclides within the grape vine is independent of the path of absorption, by leaves or by roots. 134Cs is absorbed more easily than 85Sr by plant foliage, but is absorbed with more difficulty than 85Sr by roots. After absorption by either route, radiocesium concentrates mainly in the fruit compartment of the plant, whereas radiostrontium concentrates in the foliar compartment. Loss from the aerial part of the plant is higher for 85Sr than for 134Cs. 85Sr remains more available in soil than 134Cs, is more absorbed by roots and is more leached downward. After foliar contamination, the dominant pathway of radionuclides to reach the soil is by dislodging of non-absorbed radionuclides or senescent cells from the aerial part of the plant by action of wind and rain.