On the Biological Half-Life of Caesium in Pregnant Women and in Infants

In the 1960s, changes were observed in the levels of 137Cs in women who were pregnant or who had recently given birth. These were not associated with changes in the rate of fall-out, and they were interpreted as the consequences of changes in the biological half-life. It was deduced that the biological half-life of caesium just before parturition averaged 59% of the value (87 ± 33 days) after the birth of the baby; the assumption was made that there was a step change at parturition. The behaviour of the levels during pregnancy suggested that there was a gradual decrease in the biological half-life. During the same period, similar measurements were made in very young children. The concentration of the radionuclide in a breast fed baby was usually a little less than that in the mother, indicating some discrimination in the transfer from plasma to milk, whereas the concentration in a bottle-fed baby increased substantially and rapidly from the level at or shortly after birth. Data for three babies were sufficiently extensive to permit determination of the biological half-life in each. Values of 8.7±0.6 days, 15.4±1.1 days, and 14.9±3.6 days were derived.