The diet-milk transfer coefficient, Fm (Bq L-1 output in milk divided by Bq d-1 intake to the animal) was studied for eight radionuclides that previously had been given little attention. The Fm values for cows and goats, respectively, were: 2.3 X 10(-5) and 1.5 X 10(-4) for 99mTc, 1.4 X 10(-4) and 8.5 X 10(-4) for 95mTc, 1.1 X 10(-2) for 99Tc (goats only); 1.7 X 10(-3) and 9 X 10(-3) for 99Mo; 4.8 X 10(-4) and 4.4 X 10(-3) for 123mTe; 4.8 X 10(-4) and 4.6 X 10(-3) for 133Ba; 5.5 X 10(-7) and 5.5 X 10(-6) for 95Zr; and 4.1 X 10(-7) and 6.4 X 10(-6) for 95Nb. The goat/cow transfer coefficient ratios for milk were approximately 10, but the goat/cow ratios for meat varied by three orders of magnitude.

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Transfer coefficients to eggs and meat were determined after acute oral doses of 95mTc, 99Mo, 123mTe, 133Ba, 131I, 95Zr and 95Nb to laying hens. The mean values (in units of d kg-1) to eggs and hen meat were, respectively, 3.0 and 0.03 for Tc, 0.87 and 0.18 for Mo, 5.1 and 0.60 for Te, 0.87 and 9.2 X 10(-3) for Ba, 3.2 and 0.01 for I, 2 X 10(-4) and 6 X 10(-5) for Zr, and 1 X 10(-3) and 3 X 10(-4) for Nb. For the same radionuclides administered in the same chemical form, transfer coefficients for eggs are about one to two orders of magnitude higher than for cow's milk, while the transfer coefficients for hen meat are several orders of magnitude higher than for beef.

A study of transfer to milk of three isotopes of Tc indicated different results for 99mTcO4-, 95mTcO4-, and 99TcO4-. When the three isotopes were given orally to lactating goats in separate experiments, the milk transfer coefficients increased with decreasing specific activity. Gut absorption of Tc administered as pertechnetate (TcO4-) was decreased by reduction of TcO4- in the rumen. The rate of reduction of TcO4- in the rumen was greater for higher specific activity doses of Tc. These results suggest that the specific activity of a radioisotope may significantly influence the estimated dose to humans from contaminated milk and, probably, other food products.

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