| Abstract
| - The transfer of radioactivity to the milk and meat of farmanimals is likely be a major exposure pathway of humanpopulations, following an environmental release ofradioactivity. The importance of source-dependent bioavailability in determining absorption from the ruminantgastrointestinal tract of the radiologically significantradionuclides (radiocesium, radiostrontium, radioiodine,and plutonium) is reviewed. The requirements for andsuitability of in vitro methods of determining bioavailabilityfor absorption of these radionuclides is also assessed.Radiocesium absorption varies over a 50-fold range, dependingupon dietary source. Source-dependent bioavailability istherefore an important factor in determining the radiocesiumcontamination of ruminant-derived food products, andreliable in vitro techniques have been developed to rapidlydetermine its bioavailability. In contrast, under conditionsof adequate calcium intake, the absorption of radiostrontiumwill not be greatly influenced by the dietary source. Resultsof in vitro extractions of radiostrontium could be misleading,as they indicate differences in bioavailability that arenot observed in the animal. Absorption of radioiodine iscomplete and independent of source. There is currently alack of data on plutonium absorption in ruminants.However, on the basis of the limited data available, invitro incubations provide a measure of the relativebioavailabilities of plutonium from different sources. Theapplicability of the techniques reviewed to the study of otherradionuclides and heavy metals is discussed.
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