The Biokinetics of Plutonium-239 and Americium-241 in the Rat After Subcutaneous Deposition of Contaminated Particles from the Former Nuclear Weapons Site at Maralinga: Implications for Human Exposure

As an input to dose assessments, measurements have been made of the clearance of Pu and Am after subcutaneous implantation in rats for six particulate materials and one dust from the Maralinga test sites. The tissue distribution of Pu and Am were measured in groups of six animals at one month and 6 months after implantation. In addition, in vitro solubility tests were carried out on eight different particulate materials. Histological examination of the subcutaneous implantation site was undertaken after one year for selected materials. Autoradiographs of tissue sections showed that particles were surrounded by fibrotic tissue with macrophage and polymorphonuclear cell infiltration, the normal tissue response to foreign materials. The clearance data have been used to make estimates of the likely range in potential radiation doses in humans. To calculate the dose from dissolved ²³⁹Pu and ²⁴¹Am, four different situations have been considered. For the dust, the results suggest that dissolution essentially ceases after the removal of Pu and Am from the surfaces of dust particles. From the values obtained, the acute release of a fraction of 10^-2 of both nuclides from a dust contaminated wound was assumed. For a number of particles the results suggested continued dissolution and the clearance of 10-3 per year of both nuclides, continuing for a number of years, has therefore been considered. For the least soluble particles, there was no clear evidence of continued clearance and the acute release of 10^-4 has therefore been taken as a lower estimate for dose calculations. To calculate radiation doses to lymphatic tissue the data were taken to suggest that, in general, a fraction of between 10 ^-2 and 10^-4 may be translocated to the lymphatic system each year.