NRPB-W30: Non-technical summary

Non-technical summary

People receive doses of radiation from a variety of sources. Natural sources are by far the greatest contributor. These include radiation from materials in the earth, from the sun, from the air we breathe and even from the food we eat. Most of the dose we receive comes from natural sources that were formed when the Earth was created and some that are constantly being produced in the upper atmosphere by cosmic rays.

The Food Standards Agency operates a monitoring programme in England and Wales to verify that levels of radioactivity present within foodstuffs are acceptable, and to ensure that the resulting public radiation exposure is within internationally accepted limits. A wide range of foods is sampled in each of the different regions of the UK and then combined, depending on the different amounts of each food normally eaten, to give a Total Diet sample. Only a few items that grow wild, such as blackberries, are included in that programme. What effect that eating such 'free' foods may have on the estimated doses has until now been unknown.

A project was begun in the autumn of 1999 to try to evaluate this effect. The likely variation due to different levels of natural radioactivity across the UK was taken into account by looking at two areas, one with known higher levels, the other with average levels. The two areas were centred around Okehampton in Devon (high) and Chipping Norton in Oxfordshire (average). The work involved collaboration between BMRB International, a market research organisation, and NRPB, and was funded by the Food Standards Agency. The main objectives were to find as many people as possible who regularly collect free foods, and to ask them what and how much they collect.

Samples of the foods collected by most people or in the largest quantity were obtained over the next two growing seasons, and the amounts of naturally-occurring radionuclides in the samples were measured. From these we could estimate how much of each radionuclide people were likely to take in, and therefore calculate the likely dose. The radionuclides we were interested in were polonium-210, lead-210, uranium-234, uranium-235, uranium-238, thorium-230, thorium-232 and radium-226.

Because we were deliberately looking for people who collect free foods, and the Food Standards Agency uses averages of the whole population, the estimated doses cannot strictly be compared. However, the estimated doses to consumers of free foods around Chipping Norton were some three or four times less than the corresponding doses for consumers around Okehampton. The foodstuffs of importance around the two sites differed, however, although different species of mushroom were important at both. People who collect and eat free foods could significantly increase the dose they receive from ingesting naturally-occurring radionuclides, but any increase would be small when compared with the overall variability of dose across the UK.

The numbers of consumers were only a small percentage of the population in the areas studied, although 200 or so were found in each area. Nevertheless, rigorous assessments of dose should still take into account the contribution from free foods.

Last reviewed: 1 September 2009