VI. A Survey of the Metabolism of Caesium in Man

Present knowledge of the metabolism of caesium in man is reviewed; data on stable caesium in autopsy materials, as well as on radioactive caesium both in autopsy material and in vivo are considered. Caesium is distributed widely throughout the body but is mainly in the soft tissues; the concentration in rib appears to be higher than in cortical bone (femur). Uptake of caesium chloride from the gastrointestinal tract is rapid and essentially complete. Excretion is principally via the urine, but there is a continuing loss in the faeces whether the administration was by ingestion or intravenous injection. The urinary/faecal excretion ratio ranges from less than 2 to more than 10 among individuals, but is reasonably constant in any one subject. The wholebody retention of caesium can be expressed by a twocomponent exponential function of time; some 6–15 (mean about 10) per cent of a single oral dose is excreted with a short half-life (1–2 days), but the major part has a half-life between 50 and 150 (mean 110 days) with isolated cases reported of up to 200 days. This variability may account to a large extent for the considerable range of fall-out caesium 137 contents which have been reported.