Gastrointestinal Absorption of Ingested Cerium

A summary of information on gastrointestinal absorption of radiocerium in laboratory studies with animals is given in Table 10. In adult animals, absorption was between 0.0001 and 0.001 of the administered radioactivity when given in relatively soluble chemical forms. This range of absorption values applies to adult and young adult swine, sheep, dogs, mice, and rats over 14 days of age. Radiocerium administered to mice or rats between birth and 14 days of age was absorbed 

The uptake of radiocerium by intestinal lining cells is not unique but may be expected to occur in similar chemical compounds that form colloids or large complexes within the intestine (Sullivan, 1966). Macromolecules are known to be easily absorbed by the intestinal cells of newborn animals through the process of pinocytosis (Clark, 1959). Polyvinylpyrrolidone (PVP) has been shown to be taken into the intestinal cells of rats less than 18 days old (Clarke and Hardy, 1969). 

The PVP accumulated in large supranuclear vacuoles and, like immune globulins, remained there until the cells were sloughed. This pattern bears a marked similarity to radiocerium uptake in the intestinal cells of suckling rats. 

In studies with normal adult animals, orally administered radiocerium moves rapidly through the gastrointestinal tract. About 0.96 of a cerium nitrate solution administered orally to rats was excreted within 24 hours (Sagan and Lengemann, 1973). However, external irradiation of the gastrointestinal tract with a 137Cs source (800 R) delayed excretion of the radiocerium. Only about 0.85 of the administered cerium was excreted by 3 days but 0.992 was excreted by 4 days. In swine, 0.98 of an oral dose of radiocerium was excreted by 3 days (Miller et al., 1969) while in cattle, radiocerium placed in the rumen required 3.7 days for 0.9 of the dose to be excreted. Fecal excretion of the cerium still occurred after 4 days. When radiocerium was placed in the abomasum of cattle, it was almost entirely voided in 1.2 days. 

Irradiation of the gastrointestinal tract itself due to passage of radiocerium will not be considered in detail in this report. Possibilities 

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