The main object of this study has been to provide quantitative information on the distribution and retention of a2P, 45Ca, 85Sr and ' q a in the mouse skeleton as a function of age at the time of injection.At 24 hr after intraperitoneal (i.p.) injection into 8-week old mice the distribution of the four radionuclides throughout the skeleton was essentially identical. I n the case of 86Sr, however, the skeleton accumulated about 90% of the total body activity at this time, whereas for szP the amount was only about 40%. The levels of accumulation of activity by the bones depended upon the age of the animals at the time of injection. Thus at 24 hr after i.p. injection of8% into 3 and 26-week old animals the concentration of%r in the bones varied by factors of less than 1.5 and 5 respectively. These differences were attributed mainly to the degree of vascularisation and the surface area available for absorption in individual bones. The relative concentrations of activity in the bones changed considerably with time after injection due mainly to varying rates of loss of activity from different bones. In older animals the levels of activity in the various bones became more uniform with time but in the youngest mice injected (3 weeks old) concentrations in individual bones varied by about a factor of 9 by 128 days after injection.It was also shown that in the mouse there is no significant release of 9 formed from gOSr deposited in bone.

The metabolic behavior of 239Pu and 241Am present in three industrial dusts has been studied after their inhalation by the rat. A comparative experiment has also been carried out with a mixture of these actinides, inhaled as their nitrates. The aim of this work was to provide an experimental basis for assessing limits on intake and to establish whether the 239Pu content in the lungs could be interpolated from measurements of 241Am. The results (1) demonstrate the wide differences in the lung retention kinetics of the actinides and in the absolute and relative amounts which translocate to the blood that can occur for industrially produced materials; (2) show that the annual limits on intake (ALI) for the different materials vary between those postulated for class W and Y compounds by the International Commission on Radiological Protection; (3) indicate that, depending on the nature of the dust, acute intakes of 239Pu equivalent to the ALI can be estimated from 241Am chest-monitoring data at times from a few days up to about 3 y after exposure.

The International Commission on Radiological Protection has recently issued Publication 88, giving dose coefficients for the embryo, fetus and newborn child from intakes of selected radionuclides of 31 elements by the mother, either before or during pregnancy. The biokinetic models used for calculating these doses were based upon the available human data and the results of animal experiments. This paper summarises the approach used for the development of biokinetic and dosimetric models. It also compares the estimates of dose received by the offspring with those received by the reference adult. The main findings are that, in general, doses to the offspring are similar to or lower than those to the reference adult. For a few radionuclides, however, the dose to the offspring can exceed that to the adult. The reasons for these variations in comparative doses are examined.

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