Transfer of (85)Sr and (134)Cs from diet to reindeer foetuses and milk

Sr-85 and (134)Cs in aqueous solution of the chlorides were administered daily to four pregnant reindeer during the last part of gestation. Radionuclide concentrations were determined in calves sacrificed at birth, and secretion of the nuclides was measured in milk. Although the gastrointestinal absorption of (85)Sr was low, an apparently higher transfer of the absorbed fraction of (85)Sr than (134)Cs from the mother to the foetus led to similar accumulation of (85)Sr and (134)Cs in foetuses. At birth 1.4-1.6 and 1.5-2.5% of the total administered activities of (85)Sr and (134)Cs, respectively, were present in the calves' bodies. Transfer coefficients (F (m)) for (85)Sr and (134)Cs from feed to milk were estimated at 0.0218+/-0.0026 and 0.185+/-0.025 day kg(-1), respectively, and the observed ratio (OR(milk-diet)) for (85)Sr was 0.124+/-0.037. Transfer of radiostrontium to reindeer milk was in agreement with previously reported relationships between Ca intake and radiostrontium transfer in ruminants. These relationships suggest that the transfer of radiostrontium to foetuses and milk of free-ranging reindeer can be 3-4 times higher than observed in this experiment (due to lower Ca intake with natural forage), but the transfer to milk will not be as high as that of ionic (134)Cs. The concentrations of (85)Sr in milk suggested that the does mobilized skeletal stores of Ca and (85)Sr for milk production, although the diet appeared to satisfy the Ca requirements. In reindeer with radiostrontium intake during the whole year, radiostrontium concentrations in milk will therefore be higher than indicated by the F (m) value observed in our study. No differences in half-times for (85)Sr and (134)Cs secretion in milk were detected. Both nuclides were secreted with short- and long-term half-times of 1-2 and 12-19 days, respectively. For (85)Sr, 80-90% of the activity was excreted with the short half-time, whereas the corresponding value for (134)Cs was 30-50%.