Metabolic Balances of²¹⁰ Pb and²¹⁰ Po at Natural Levels

Metabolic balances of²¹⁰ Po and²¹⁰ Pb were determined under strictly controlled dietary conditions in adult males. The intakes of the two nuclides were due to the dietary contents of these radioisotopes, inhalation from the atmosphere, and smoking of cigarettes. No additional radioisotope was given. The mean dietary intake of²¹⁰ Pb was 1.25 pCi/day and of²¹⁰ Po, 1.63 pCi/day. The major pathway of excretion of both nuclides is via the gastrointestinal tract and the urinary excretion is much lower. The total excretions of²¹⁰ Pb and²¹⁰ Po were greater than the dietary intake and the overall balances were -0.28 and -0.16 pCi/day for the two nuclides, respectively, during a low calcium intake. The²¹⁰ Pb balances did not change significantly when the calcium intake was increased 7- to 10-fold except for one patient in whom the balance became more negative. The²¹⁰ Po balance was more negative during calcium intakes of 800 and 2200 mg than during a low calcium intake of 200 mg/day. The urinary and fecal excretions of the two radionuclides were not affected by the intake of sodium fluoride, while the diuretic compound Hydrodiuril appeared to decrease the fecal²¹⁰ Pb excretion.