The effect of age on the absorption and excretion of lead.

The retention (the proportion of ingested or administered lead found in the carcass at slaughter) of lead in the carcass and tissues of rats given 203Pb intraperitoneally or by mouth was measured over a period of a few days at 3-month intervals for 9 months from weaning. Total carcass retention of 203Pb administered intraperitoneally reached a minimum at 6 months of age, but the retention of 203Pb in blood, liver, and kidney changed little with time. When 203Pb was given by mouth, the fraction of the dose absorbed and the fraction retained in the carcass reached a minimum at 6 months, but the recovery in the tissues continued to decrease up to the end of the experiment. The addition of 20 mg of lead/kg of diet had no consistent effect on the metabolism of 203Pb.