Pattern of Uptake of Americium-241 by the Rat Skeleton and its Subsequent Redistribution and Retention: Implications for Human Dosimetry and Toxicology

Abstract

The distribution and retention of intravenously injected ²⁴¹Am in the skeleton of the female rat has been investigated using autoradiographic and radiochemical techniques. The studies were designed to assess the dosimetric and toxicologic implications of an ²⁴¹Am intake by man. They showed that in the rat approximately one third of the intravenously injected ²⁴¹Am was deposited in the skeleton where it appeared to be retained with a long biological half-time. The studies also showed:

1 ²⁴¹Am is initially deposited onto all types of bone surface including endosteal surfaces, periosteal surfaces and those of the vascular canals within cortical bone, but seems to be preferentially deposited onto those that are resorbing,

2 Bone accretion results in the burial of surface deposits of ²⁴¹Am,

3 Bone resorption causes the removal of 241 Am from surfaces,

4 Resorbed ²⁴¹Am is retained by phagocytic cells (probably macrophages) in the bone marrow,

5 The transfer of ²⁴¹Am from the phagocytic cells in the marrow to adjacent bone surfaces seems to occur, (local recycling).

6 The possibility that some of the ²⁴¹Am removed from the bone surfaces enters the blood and is redeposited in bone, (systemic recycling) cannot be dismissed

These results show that ²⁴¹Am deposition and redistribution in bone shares many characteristics with other 'bone surface-seeking radionuclides' typified by ²³⁹Pu. Consequently, it is suggested that a similar model to that used to calculate annual limits of intake for ²³⁹Pu in man would be suitable for the calculation of corresponding values for the ²⁴¹Am isotopes.