Natural radioactivity in food

Among the Federal Office for Radiation Protection’s (BfS) tasks are investigations into natural radiation exposure. Besides external radiation exposure caused by cosmic radiation and natural radionuclides in soil and rocks and radiation exposure due to radon and its short-lived decay products, the type of radiation exposure is of interest that is caused by the ingestion of natural radionuclides with food.

Objective of investigations

The knowledge of the natural level of radioactivity in food is necessary, among others, to recognise and be able to evaluate changes resulting from impact of humans. This is e.g. essential for decisions to be taken on the utilisation of surfaces that have been radioactively contaminated by mining.

To get a general idea of the issue, mixed diet samples taken from the daily rations of Community institutions all over the Federal Republic of Germany were examined in 2001/2002. The programme continued until 2004; the results are summarised here.

Investigation results

Food produced in Germany shows in most cases very low concentrations of long-lived radionuclides of the uranium and thorium decay chains. This also applies to food from areas with geologically caused enhanced natural environmental radioactivity.

The Federal Office for Radiation Protection examined the mixed diet, i.e. the solid and liquid components of the mixed diet provided in different Community institutions. The results of these examinations (66 samples of mixed diet for adults, 11 samples of mixed diet for young children aged nine months) are shown in the following table:

The median values are in the same order of magnitude (0.001 to 0.130 becquerels per kilogram fresh mass), only in grain are they in part slightly higher (0.009 to 0.365 becquerels per kilogramme fresh mass). Here, too, the radionuclides lead-210, radium-228 and radium-226 dominate.

The values for thorium-232 and thorium-230 in food were very low, the thorium being strongly bound in the soil and therefore hardly being taken up by plants. On average, the food examined so far had specific activities below 0.003 becquerels per kilogram fresh mass. The activity concentrations were mostly just around the detection limits.

Brazil nuts

Brazil nuts have an exceptional position in food. With specific activities of some 10 becquerels radium-226 or, respectively, radium-228 per kilogram fresh mass, the radium content of Brazil nuts can be about 1,000 times higher than that of the entire food in Germany.

According to data provided by the World Health Organization (WHO), an average amount of 0.1 gram Brazil nuts per person per day is consumed in Germany. Based on this average level of consumption, the annual effective dose of adults resulting from the natural radionuclides listed in the table is about 2 microsieverts and does not pose a risk to health. Scientific publications and various internet forums recommend to eat daily two Brazil nuts (about 8 grams) to improve selenium supply. With the consumption of two Brazil nuts a value of 160 microsieverts can be reached.

A benchmark is the annual effective dose as a result of the intake of natural radionuclides with food. With normal nutritional conditions is amounts to 300 microsieverts. For adults, the consumption of 2 Brazil nuts per day thus arithmetically increases the ingestion dose due to natural radionuclides by roughly one half. With a radiation exposure of this level, nobody needs to fear negative health effects. However, from the radiation protection point of view it needs to be taken into consideration that the selenium status can also be improved by food supplements without additional radiation exposure.

New examinations starting in 2016

In cooperation with the Federal Institute for Risk Assessment (BfR) the BfS will examine food in a typical form prepared in households for its radiation due to natural radionuclides. Within the framework of this BfR-Total Diet Study (MEAL - meals for the exposure assessment and analysis of foods) food is considered which is mostly consumed by the population in Germany, like grain products, vegetables and potatoes, milk products, meat and fish.

Based on the measuring results of the samples, BfS will assess the dose contribution of the population. This study is carried out on behalf of the Federal Ministry of Food and Agriculture (BMEL) and it will last for seven years including the total german food supply. One of the central objectives of the BfR MEAL Study is to generate concentration data that are representative for the German population for different substances in the diet.