In 2001/2002, samples of food from community institutions all over Germany were analysed

In order to gain an overview of the level of natural radionuclides in food, a study carried out by the BfS between 2001 and 2004 initially analysed samples of the total diet obtained from daily rations at community institutions throughout Germany.

Test results

Food produced in Germany usually contains very low levels of long-lived radionuclides from the decay series of uranium and thorium. This also applies to food from areas with greater natural environmental radioactivity due to geological circumstances.

The BfS analysed the total diet, i.e. the solid and liquid components in the mixed diet, from different community institutions. The results of these analyses (66 samples from total diet for adults, 11 samples from total diet for babies aged nine months) are shown in the following table:

The specific activities of the radionuclides lead-210, radium-226 and radium-228 dominate both in baby food and in the total diet of adults.

The values for thorium-232 and thorium-230 in foodstuffs were extremely low, as thorium is strongly bound in the soil and is therefore hardly absorbed by plants. The foods analysed so far had an average specific activity of less than 0.003 becquerels per kilogram of fresh mass. The specific activities were mostly in the region of the metrological detection limits.

Samples of foods typically prepared in households have been analysed since 2016 Source: Татьяна Волкова/Stock.adobe.com

In collaboration with the Federal Institute for Risk Assessment (BfR), the BfS has analysed the natural radionuclide content of foods typically prepared in households. The BfR MEAL study (MEAL stands for "meals for exposure assessment and analysis of food" in German) took account of foods that are most commonly consumed by the population in Germany. These include foods made from cereal products, vegetables and potatoes, fruit, dairy products, meat and fish, nuts and pulses as well as processed foods and baby food. Based on the measurements of the samples, the BfS will determine the effective dose for the population resulting from food intake.

The study, which was commissioned by the Federal Ministry of Food and Agriculture (BMEL), was carried out over a period of seven years and covered a large part of the German food supply. The aim of the BfR MEAL study was to obtain comprehensive information on the levels of various substances in a representative selection of foods for the first time in Germany.

An initial scientific publication about the study provides information on methods developed as part of the study for the purpose of determining the level of the natural radionuclides lead-210, uranium-234, uranium-238, radium-228 and radium-226 in a large number of food samples.

A second scientific publication sets out the levels of the natural radionuclides lead-210, uranium-234, uranium-238, radium-228 and radium-226 in the analysed foodstuffs. The measurement results are available in a public use file from the Federal Institute for Risk Assessment.

Our potassium requirement is completely covered by our diet and is kept constant by the body within narrow limits. Source: monticellllo/Stock.adobe.com

One exception is potassium, which naturally contains radioactive potassium-40. Potassium is vital for all organisms and is therefore usually present in them in considerable quantities

Potassium is also essential for the human body: in order for our metabolism to function, our body constantly needs a largely consistent amount of potassium. This potassium requirement is completely covered by our diet and is kept constant by the body within narrow limits: if our body absorbs more potassium than it needs, it immediately excretes it again.

In this way, the human body also indirectly keeps its potassium-40 content constant: the element potassium naturally contains 0.0117% potassium-40 with an activity of 31.6 becquerels per gram of potassium. As this proportion is always the same, the potassium-40 activity can be calculated from the potassium content:

• Depending on age, gender and other factors, the potassium-40 activity of the human body is between 40 and 60 becquerels per kg of body weight.
• On average, the effective dose from potassium-40 is around 0.17 millisieverts per year for adults and around 0.19 millisieverts per year for children.

Based on the BfS's analysis results in relation to total diet, the following table shows the dietary radiation exposure for different age groups of the German population:

Depending on age, the contributions from the uranium decay series and the thorium decay series to the effective dose can differ significantly – from 0.04 to 0.27 millisieverts per year.

According to the customary international guidelines on the average age distribution of population groups (adults: 65%, children: 30%, infants: 5%) indicated in the Report of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) 2000, this can be used to calculate an age-weighted average value of 0.10 millisieverts per year.

When potassium-40, which provides an age-weighted contribution of about 0.17 millisieverts per year, is included, the natural radiation dose of the population from food intake is about 0.27 millisieverts per year – assuming average dietary habits.

This data shows good agreement with the data in the UNSCEAR Report 2008, in which the authors estimate:

• the dietary contribution from potassium-40 at 0.17 millisieverts per year and
• the contribution from the uranium decay series and the thorium decay series at 0.12 millisieverts per year.

This results in a total value of 0.29 millisieverts per year.