ESTIMATION OF RADIATION EXPOSURE FROM NATURALLY OCCURRING RADIONUCLIDES IN FOOD AND FOODSTUFF

Sammanfattning: Purpose: The main purpose of this study was to provide an estimation of the committed effective dose received by the Swedish population from naturally occurring radionuclides (NORM) in the diet. This study was also aiming to investigate the impact on the committed effective dose due to the new developments in the biokinetic model for Po 210 . In addition to dose estimation, this project was also aiming to investigate how to make interpolation maps using the software ArcGIS. Background & theory: In previous studies of radioactivity in food, the focus has been on anthropogenic radionuclides. Even though NORM in food is contributing to a larger committed effective dose than anthropogenic radionuclides, no detailed assessment of the committed effective dose from NORM to the Swedish population has been done. For Po 210 , which is an important radionuclide for the committed effective dose from the diet, new developments have been done in the systemic model. One of the new developments include an additional excretion pathway, via hair and sweat. Method: Activity concentrations of Po 210 , U 234 and U 238 in various food and foodstuff were collected from the ongoing research projects Radiological Implications of Swedish Food Consumption and Natural radioactivity in the Nordic diet. Committed effective doses were calculated for adults and children of three age groups. Comparisons were made of committed effective doses received by Swedish men vs. women and also lacto-ovo vegetarians vs. people including animal protein in their diet. The investigation of the impact on the committed effective dose from Po 210 due to new developments in the biokinetics was done using the softwares IMBA, SAAM II and Ecolego. In IMBA, the impact on the committed effective dose was simulated by varying the GI uptake fraction, the tissue weighting factors and the transfer rate between stomach and small intestine. In SAAM II and Ecolego, the biokinetics of Po 210 was simulated using the Human Alimentary Tract Model and the updated systemic model. By using the methodology in ICRP 133, the committed effective dose coefficient was calculated and compared with the coefficient from ICRP 119. The interpolation of dose rate data was carried out in the software ArcGIS 10.6, using the Empirical Bayesian Kriging method. Results & conclusion: The committed effective doses received by adults and children were 77 ± 2 µSv/y and 94 ± 9 µSv/y, respectively. The Swedish men receive a 20% higher committed effective dose than the Swedish women. Diet including animal protein results in a 4.5 higher committed effective dose from Po 210 than lacto-ovo vegetarian diet. The overall effect of cooking of food is a reduction of the levels of Po 210 . By varying the GI uptake fraction, the estimate of the committed effective dose from Po 210 differed by ± 9% from the dose calculated using the GI uptake fraction defined by ICRP. When using the tissue weighting factors from ICRP 133, the estimate of the committed effective dose from Po 210 was 23% higher than the dose calculated using the weighting factors from ICRP 68. When using the sex dependent transfer rates, a higher committed equivalent dose to stomach was estimated for women than men. The simulation of biokinetics of Po 210 suggested that the new developments in the biokinetic models is leading to a 5-18% higher estimation of the committed effective dose from NORM in food received by Swedish adults. Measured values were compared with predicted values in the interpolated dose rate map. Good agreement was found, suggesting that the Empirical Bayesian Kriging method works well for this purpose.