Levels of naturally occurring radionuclides in foods from the first German total diet study

Although natural radionuclides are always present in foods, information about the levels is scarce. The diet-related exposure to radiation is, however, dependent on the radionuclide content of respective food items. In this study, the levels of the naturally occurring radionuclides lead-210 (Pb-210), uranium-234 (U-234), uranium-238 (U-238), radium-226 (Ra-226) and radium-228 (Ra-228) were investigated in over 200 foods as part of the first German total diet study. Radioanalytical techniques and measurements were applied for determination. The natural radionuclide activity concentrations obtained were generally low compared to international data compilations. Together, Ra-228 and Ra-226 mostly dominated the levels of activity concentrations. Of all Ra-226, Ra-228 and Pb-210 results, between 1 % and 19 % exceeded the International Atomic Energy Agency (IAEA) guidance level for food products of 0.1 Bq/kg or 1 Bq/kg. The received activity levels for both U-234 and U-238 were found to be below the suggested IAEA guidance level of 10 Bq/kg. The radionuclide activity ratios of Ra-226/Ra-228, U-234/U-238 and Pb-210/Ra-226 of the foods were examined as well. In particular, it was found that the average Ra-226/Ra-228 ratio in all main food groups was substantially lower than the average Ra-226/Ra-228 ratio in soils. An isotope dependent transfer of Ra-226 and Ra-228 from soil to plants and foods is suggested to explain the difference. The obtained data set will be a valuable contribution to international data collections and thus help to a better understanding of the public exposure to natural radionuclides from the food consumption in the future.