Male Wistar rats were administered 253EsC1, by intratracheal instillation and the biological effects were followed for the animals lifespan or 880 days. Three dose levels were employed; 47.2, 10.7 and 0.214 pCi/kg along with controls given pH 2 HCl by instillation. The estimated radiation dose to lung was 9800, 1900 and 38 rads, respectively. The dose to bone wa3 about + the lung dose. The earliest biological effects were dose related, e.g. impaired weight gain and death due to radiation pneumonitis. The late effects included bone and/or lung tumors in all experimental groups. The tumor site and incidence are discussed and related to similar data for plutonium compounds.EINSTEINIUM-253 (TI,, = 20.5 days; 6.6 MeV alpha) is a transuranic element formed by multiple neutron capture in the heavier actinide elements. The chemical characteristics of Es, as indicated by the behavior on ion exchange columns, are expected to be typically those of other tripositive actinides (KATZ et al., 1957). Because of the short half-life and low efficiency of production 253Es is not a radioisotope of particular biological hazard concern. It has, however, been of interest to radiation biologists because of the energetic alpha emission and the relatively short physical half-life compared to the more well known transuranic elements. Thus the unique physical properties of 253Es may be exploited in comparative biological effects studies with 239Pu (TI,, N 24,000 yr, 5.2 MeV alpha) in order to explore the effect of radiation dose rate and radiation dose distribution on the induction of latent effects such as lung and bone tumors. Studies reported here present results of preliminary investigations to determine the carcinogenicity of intratracheally instilled 263EsC1,. The intratracheal mode of administration was employed rather than the more natural inhalation route in order to facilitate the administration of accurately known amounts of radionuclide. More recent investigations which will be reported elsewhere have employed exposure by inhalation using --~ * This paper is based on research performed under United States Atomic Energy Commission Contract AT(45-1)-1830. 263Es(N0,) , aerosols and standard inhalation exposure techniques.
METHODS AND MATERIALSAnimals used in this study were SPF rats of the Wistar strain obtained from Hilltop Laboratory Inc., Scottdale, Pennsylvania. Male and female animals were used, both 66 days of age, weighing 270 and 230 g, respectively. The rats were maintained in wire bottom cages with six rats in each cage initially. Food (Wayne Lab-Blox) and tap water were supplied ad libitum. Cages were changed at weekly or biweekly intervals. The animal quarters were maintained on a day-night cycle which changed at 6 a.m. and 6 p.m. Temperature and humidity were controlled at 72 f 4'F and 40-60 %, respectively.The radionuclide was administered by intratracheal instillation employing a previously described method (MORROW, 1971). A volume of 0.5 ml containing 263EsC1, in 0.01 N HCI was instilled. Control animals received th...