Solid cancer mortality risk among a cohort of Hiroshima early entrants after the atomic bombing, 1970–2010: implications regarding health effects of residual radiation

Abstract

There are two types of exposure to atomic bomb (A-bomb) radiation: exposure to initial radiation released at the time of the detonation of the bomb, and exposure to residual radiation, which remains afterwards. Health hazards caused by exposure from residual radiation have not yet been clarified. The purpose of our study was to reveal the relationships between mortality risk from solid cancer and residual radiation based on data from the early entrants to Hiroshima. It is hard to identify the individual residual radiation doses. However, these are assumed to depend on the date of entry and the entrants’ behavior. Individual behavior is thought to be closely related to gender and age at exposure. We investigated a cohort of 45 809 individuals who were living in Hiroshima Prefecture on 1 January 1970 and were registered on the Database of Atomic Bomb Survivors as entrants after the bombing. Poisson regression methods were used to estimate excess relative risks (ERR) with data cross-classified by sex, age at entry, and date of entry. In males in their 20s, 30s, and 40s at entry and in females less than 10 years old and in their 40s at entry, solid cancer mortality risks were significantly higher among persons who entered the city on the day of the bombing than those who entered three or more days later. With adjustments for the age-dependent sensitivities to radiation exposure, it was extrapolated that middle-aged people who entered the city on the day of the bombing were exposed to higher levels of residual radiation than younger people.

Effects of Internal Exposure of Radioactive 56MnO2 Particles on the Lung in C57BL Mice

“…The role of the residual radioactivity produced by the bomb must be explored to better understand the biological impacts of the atomic bombing [ 1 , 2 ]. The neutron-activated radionuclides in the soil of the hypocenter areas at Hiroshima and Nagasaki include 24 Na, 28 Al, 31 Si, 32 P, 56 Mn, and others [ 20 ].…”

“…The neutron-activated radionuclides in the soil of the hypocenter areas at Hiroshima and Nagasaki include 24 Na, 28 Al, 31 Si, 32 P, 56 Mn, and others [ 20 ]. Interestingly, studies of the early entrants showed that ‘risks’ were higher among persons who entered the city on the day of the bombing than those who entered later, which suggested that the corresponding radioisotopes may be short-lived [ 1 , 2 ]. Since 56 Mn (t 1/2 = 2.48 h) is one of the dominant radioactive isotopes during the first day after the atomic bomb explosion, it was chosen as a representative nucleus.…”

“…This is because the people who moved to these cities soon after detonation and were exposed to only residual radiation suffered from acute radiation syndromes [ 1 ]. A recent cohort study concluded that solid cancer mortality risks were significantly high among the early entrants after the Hiroshima atomic bombing, which also suggested the significance of residual radiation [ 2 ]. One of the primary radioisotopes produced in the soil by the neutron beam from the atomic bomb explosion was manganese-56 ( 56 Mn) [ 3 ].…”

Contribution of radioactive particles to the post-explosion exposure of atomic bomb survivors implied from their stable chromosome aberration rates

“…Some independent researches using ABS conducted independently from LSS indicated that solid cancer mortality risk among A-bomb survivors was higher in the west of the hypocenter, i.e., a non-circular symmetry distribution (30)(31)(32). In addition, Otani et al (33) have reported that the risks of solid cancer mortality of the people who entered the area affected by the atomic bombing in Hiroshima City on August 6 and 7, 1945 but received no initial radiation exposures were estimated to exceed by 18 and 7%, respectively, when compared with those who entered the same area few days later (August 9, 1945). Kamada et al (34) have also detected that the risk of leukemia among entrants to the city for the period 1970-1990 was 3.7 times higher for both males and females when the date of entry was August 6, 1945, compared to other Japanese nationals during the same period.…”

Effects of Radioactive 56MnO2 Particle Inhalation on Mouse Lungs: A Comparison between C57BL and BALB/c

“…Although the former enters the atmosphere and "falls out" elsewhere, the effects of the latter have also become a concern because a report has suggested that individuals who moved to these cities soon after the detonation and were exposed to only residual radiation from the ground suffered from acute radiation syndromes [2]. More recently, Otani et al reported that there were significant increases in solid cancer mortality risks in early entrants after the Hiroshima atomic bombing, suggesting the importance of residual radiation created by the neutron beam [3].…”