Models for radionuclide transfer to fruits and data requirements

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Abstract

This paper presents a review of available models for radionuclide transfer to fruit with particular emphasis on the model types and the purpose for which they were developed. It is clear that the model structures that have been developed range from the simple to the complex and that the underlying data on which they are based is incomplete. The work programme of the BIOMASS Theme 3 Fruits Working Group includes model inter-comparison and model validation studies that will give an indication of the performance of the different model types discussed here. The models included in these comparative studies include several new and as yet unpublished models. In the case of fruit, there is an urgent need for data on changing radionuclide distribution in plant organs with time to increase confidence in current models.

Introduction

Mathematical models for simulating the transport of radionuclides in soils, plants and domestic animals have been developed for agricultural and natural environments. Such models need to take into account the wide variety of different agricultural practices and crops. Edible fruits represent an important component of the diet but relative to other crops little attention has been given to the development of models for this large and diverse group of plant types. In order to have confidence in predictions of the impact of radionuclides deposited onto fruit crops there is a need for models that are based on the processes that influence transfer to fruit and to validate these models against experimental data.

As with all major agricultural and horticultural crop plants, radionuclides reach fruit via three principal routes following a release to atmosphere:The main processes involved in the transfer of radionuclides to fruits are shown in Fig. 1. The relative significance of each pathway is dependent both on the stage of plant development, the crop and the season during which the contamination event occurs. For example, the stage of leaf growth influences the amount that is absorbed and translocated within the plant. In addition, some agricultural and natural occurrences, e.g. pruning and leaf loss, respectively, lead to occasional removal of contaminated plant components and a reduction in the overall burden within the plant. Climate and local weather conditions may affect the level of contamination of fruit.

Several models have been identified that deal specifically with the transfer of radionuclides to fruit as well as others that are used to model fruit but that are adaptations of models for an agricultural crop such as a leafy green vegetables. When models for annual crops are modified there is a need to take into account the biennial or perennial nature of some fruit crops. There are several notable models that are not included in this review: ECOSYS — Institut für Strahlenschutz, Germany (Müller & Pröhl, 1993) and FOODWEB — Magnox Electric, United Kingdom (Nair, Grogan, Minski & Bell, 1983). This is not an oversight but reflects the fact that the models reviewed here have been developed or adapted specifically for fruit and illustrate the approaches taken in other models.

Different approaches have been taken in the development of mathematical models to simulate transfer through food chains to man and those adopted for fruit represent only a small sub-group of those now available. No attempt is made in this paper to categorise the approaches used for fruit in terms of the mathematical solution, equilibrium assumptions, best estimate with or without confidence limits or site specificity. A pragmatic view is taken and existing fruit models are broadly grouped into three categories as follows.Table 1 summarises the main endpoint of the models that are discussed in this paper. In each case the model provides a best estimate for transfer to fruit.

Section snippets

Model descriptions

A detailed discussion of the data that support the above models is not appropriate here but is an integral part of documents produced by the BIOMASS Fruit Working Group and is addressed in accompanying contributions. Illustrative data and or equations are included here for each model.

There are issues that need to be addressed in a Mathematical model for fruit crops. In particular: the potential capacity of some plant parts to accumulate radionuclides and their importance for contamination of

Conclusions and recommendations

The BIOMASS Fruits Working Group has shown that there is considerable interest and active research into the transfer of radionuclides to fruit crops. The data requirements for each of the models described here are very specific. Each model represents the soil–fruit plant system in a different way and parameters have been derived from the literature or from observations that reflect the model structure and the adopted approach. With the exception of Antonopoulos-Domis and co-workers the models

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