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Transfers of radionuclides onto the external surface of plants, particularly fruits, to internal compartments

Project Code: R01025

28/02/2003

ADAS Consulting Ltd, Groesfaen
Wilson, D ;
Harwell Scientifics Ltd
Kendall, M

Three species of crops (apple, dwarf French bean and cabbage) were artificially dosed, inter alia, with stable isotopes of caesium (¹³³Cs), strontium (⁸⁴Sr) and lead (²⁰⁶Pb) to simulate wet deposition of radioisotopes from the atmosphere onto the leaves. In addition, different types of co-contaminants likely to be found with the isotopes in natural deposits were applied with the three isotopes; these represented simulated acid rain, acid rain plus basic cations, clay particles, and carbon particles. A control or blank solution was also used, giving five solutions in total. Solutions had concentrations of contaminants comparable to those reported from atmospheric measurements, and were applied to the plants in amounts of 125 μl per plant or 25-50 μl per leaf (depending on its size) using a micropipette. Measurements of natural, background levels of the isotopes established that the amounts applied to the plants would be likely to be detected assuming that uptake took place.

The solutions were applied on two occasions to the leaves of separate plants; about 5-6 weeks, and about 1 week, before harvest. Dosed leaves were marked or tagged for later identification. After application, the dosed plants/leaves either remained exposed to ambient conditions, or were sheltered in order to prevent wash-off by rain. Three replicate plants were used for each treatment.

At harvest, plants were separated into various structures e.g. fruit, stem and leaves (dosed and undosed) and dried and weighed. Isotope analyses for each plant structure were carried out using Induction Coupled Plasma Mass Spectrometry (ICP MS). These nuclide data were used to estimate transfer coefficients, where data would allow, that can be used with the SPADE model (Soil Plant Animal Dynamic Evaluation) for estimating the transfer of radionuclides from the environment to compartments within beans, cabbages and apples, with emphasis on the structure consumed as foodstuff. Of the 3 isotopes studied, it was ¹³³Cs isotope that appeared to be more mobile within the plant with appreciable amounts taken up by bean-pods, and fruit of apples, but there is a large variation and sometimes a significant background level. The experimental technique allowed the quantification of isotope uptake for plant compartments but analysis of the isotope data on bulked samples did not allow a statistical evaluation of the data for the various treatments to be formally undertaken. These data contribute to our understanding of radioactive contamination of apples, beans and cabbages by routine or accidental releases of nuclear material, e.g. Chernobyl.

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