The effect of age on the absorption and intestinal retention of ingested radionuclides

The available data from animal experiments and limited human studies indicate that increased absorption of ingested radionuclides in the newborn is a general phenemenon. The greatest absorption is observed immediately after birth, followed generally by a progressive reduction over the suckling period. For the actinides and other elements studied, adult values are reached by about the time of weaning on to solid foods. However, for essential elements such as iron and calcium, and related elements such as cobalt, strontium and lead, increased absorption may also occur at later stages in response to changes in physiological demand. The Nuclear Energy Agency has recommended fractional absorption (f₁) values for the first year of life using a general approach of assuming a factor of ten increase for elements with adult values of 0.001 or less and a factor of two increase for values up to 0.5. A Task Group of ICRP Committee 2, currently considering age-dependent doses from ingested radionuclides, has endorsed this general approach. However, changes during childhood have been taken into account for lead, strontium, barium and radium.