Chromosome Aberrations in A-Bomb Survivors, Hiroshima and Nagasaki

Abstract

In the course of chromosome study of atomic bomb survivors in Hiroshima and Nagasaki, we have obtained evidence relevant to the biological dose assessment in persons exposed to ionizing radiation (Awa 1974, 1975, 1983, 1984; Awa et al. 1971, 1978). The findings are summarized as follows: 1. Radiation-induced chromosome aberrations of the stable type were found to persist many years after exposure in cultured blood lymphocytes of A-bomb survivors in Hiroshima and Nagasaki. 2. The frequency of cells with chromosome aberrations increased with increasing radiation dose for individual survivors in the two cities, although there was a striking variability (or overdispersion) of the frequency of aberrant cells between survivors within a dose category. 3. The aberration frequency was consistently higher in Hiroshima than in Nagasaki in all dose ranges. The observed intercity difference was almost by a factor of 2. Furthermore, the shape of dose-response curves for chromosome aberrations seemed to be linear in Hiroshima, while it was dose-quadratic in Nagasaki. Therefore, the differences in chromosome aberration frequencies as well as in the shape of the dose-response relationship observed in the two cities were thought to be attributable to the difference in the proportion of a neutron component relative to the total kerma (kerma = kinetic energy released in material). 4. Stable chromosome aberrations, such as reciprocal translocations and inversions, were observed to predominate, and they contributed to a large extent to determining the dose-response relationship. In contrast, dicentrics and rings of the unstable type were found less pronounced in frequency in all dose ranges. This suggested that preferential loss of cells with dicentrics and rings has occurred with lapse of time from the circulating lymphocyte population due to mitotic disturbances