Cytogenetic effects of protracted exposures to alpha-particles from plutonium-239 and to gamma-rays from cobalt-60 compared in male mice.

Adult C3H X 101 hybrid male mice were injected intravenously with 4 muCi of 239Pu citrate per kg body weight and examined for evidence of cytogenetic damage to the testis after exposures of 21, 28 and 34 weeks, with average doses from alpha-particles estimated as 13, 18 and 18 rad respectively (mean dose rate 0.00006 rad/min). Results were compared with those obtained when equivalent males were exposed continuously and concurrently to 1128 rad 60Co gamma-irradiation over 28 weeks (0.004 rad/min). The following estimates of the relative effectiveness of the alpha- and gamma-radiation were made: 24 for reciprocal translocations and for chromosome fragments, 22 for dominant lethal mutations acting after implantation. These values (with mean of 23) are based on average testis doses, with no correction for probable non-homogeneity of alpha dose distribution. In the mice exposed to gamma-irradiation there were significant reductions in testis mass and epididymal sperm-count. Although corresponding differences from control were not significant in the alpha series, consideration of results from a previous experiment by the same authors [2] allowed the relative effectiveness of the alpha- and gamma-irradiation for testis mass reduction to be estimated as roughly 10-15. Existing data on translocation induction in mouse spermatogonia by low dose-rates of gamma-rays (down to 0.003 rad/min) were analysed. They suggested that minimum rates of induction at very low intensities were not less than 1 X 10(-5) translocations per rad. A comparison of the frequencies of induction of fragments and of sperm-head abnormalities obtained after chronic gamma-ray exposures in the present experiment with those found by other workers after acute X-ray exposures suggested that there were no marked dose-rate effects with these types of mutational effect. Finally, the special problems associated with cytogenetic studies on alpha-emitters are discussed.