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NRPB-W46: Non-technical summary

Non-technical summary

The Food Standards Agency in the UK needs to be able to predict what the concentrations of radioactivity in food might be following the deposition of radioactive material onto the ground for both accidental and routine discharges of radioactivity to the atmosphere.

This study looks at how fruit grown in the UK can become contaminated by actinide elements (see Jargon Watch), with the aim of developing a mathematical model (see Jargon Watch) for predicting concentrations of radioactivity in fruit after a radioactive release into the atmosphere. Information on the contamination of fruit is relatively sparse in the scientific literature and, although some mathematical models already exist for predicting radioactivity levels in crops, these are not necessarily appropriate for actinide element transfer into fruit. A review of the available scientific literature and existing models has been undertaken and a mathematical model developed based on the findings of this review.

There are many different routes by which radioactive material can contaminate the edible part of a fruit crop. Each of these routes is governed by a series of transfer processes (see Jargon Watch). For example, the route through the soil into the internal part of the crop is governed by the processes of deposition of radioactive material onto the soil and by absorption through the roots of the plant into the edible part of the crop. Each of the identified processes has been considered and a method for calculating the effect of each process on the overall concentration of radioactivity in the fruit crop has been developed.

The different transfer processes interact with one another. For example, the amount of radioactive material deposited onto the fruit surface has a direct impact on the amount that is weathered off the surface onto the soil by rain and wind, which, in turn, affects the amount of radioactive material that is available for uptake through the roots. A compartment model (see Jargon Watch) is used to allow for all of these interactions to be dealt with simultaneously.

All of the details required to use the compartment model are included in the report, along with some example results for different applications of the model.

The model results indicate that if deposition occurs when the fruit crop is in the field, then any deposition that lands directly on the fruit surface will dominate the activity concentrations in the fruit at harvest. However, if deposition occurs outside of this period, the fruit will become contaminated, mainly due to absorption of radionuclides through the roots and contamination of the fruit surface by soil particles. In this case, the overall contamination of the fruit crop will be much lower.

Often, green vegetable models have been used to estimate activity concentrations in fruit in the absence of an appropriate fruit model. This study has shown that activity concentrations in fruit are likely to be significantly lower than those in green vegetables and that a specific model for fruit (such as the model described here) should be used in preference to one for green vegetables.

Jargon Watch

  • Actinide: One of a series of elements in the periodic table. The most important ones for this report are plutonium and americium.
  • Mathematical model: A mathematical description of the real world, which can be used for making predictions. Mathematical models rarely give a completely accurate description of the real world, but provide a practical means of making reliable predictions.
  • Transfer process: A mechanism by which radionuclides move around the environment.
  • Compartment model: A particular type of mathematical model. A compartment model consists of compartments and transfers. The compartments represent the various parts of the system that the radionuclides can get to, for example, the soil, or the external part of the fruit. The transfers define the rate at which the radionuclides move from one part of the system to another, for example, the 'weathering' transfer gives the proportion of the contamination on the surface of the fruit is transferred to the soil each day.

Last reviewed: 1 September 2009