Effect of low continuous 99Tc intake on its absorption and metabolism in young rats

A continuous daily oral dose of 99TcO4− (5 Bq g−1 day−1) was given to young rats for 56 days. In one group the intake was continued for 98 days, while in the other the intake was stopped to faciliatate the determination of biological half lives in different organs and tissues. The absorbed fraction of 99Tc increased from 0.7 to 0.9 during the experimental period (m=0.85 σ=0.02). The whole body retained fraction (m=0.15 σ=0.05) indicated a storage in the tissues. The liver and kidneys showed increasing concentrations of 99Tc until a plateau was reached after 6 and 9 weeks, then a rapid decline after the intake was stopped (half life of 6 and 5 days respectively). In hair and thyroid tissue, the accumulation of 99Tc increased linearly then declined very slowly after the intake was stopped and did not reach a plateau during the experiment. No significant amounts of 99Tc were detected in the muscular tissues or in the walls of the digestive tract. After the contamination period, urinary and fecal excretions fell off very quickly (1 week), but significant, though low, quantities of urinary and fecal excretions were still observed 6 weeks after stopping intake.