The explosion of atom bombs over the cities of Hiroshima and Nagasaki in August 1945 resulted in very high casualties, both immediate and delayed but also left a large number of survivors who had been exposed to radiation, at levels that could be fairly precisely ascertained. Extensive follow-up of a large cohort of survivors (120,000) and of their offspring (77,000) was initiated in 1947 and continues to this day. In essence, survivors having received 1 Gy irradiation (∼1000 mSV) have a significantly elevated rate of cancer (42% increase) but a limited decrease of longevity (∼1 year), while their offspring show no increased frequency of abnormalities and, so far, no detectable elevation of the mutation rate. Current acceptable exposure levels for the general population and for workers in the nuclear industry have largely been derived from these studies, which have been reported in more than 100 publications. Yet the general public, and indeed most scientists, are unaware of these data: it is widely believed that irradiated survivors suffered a very high cancer burden and dramatically shortened life span, and that their progeny were affected by elevated mutation rates and frequent abnormalities. In this article, I summarize the results and discuss possible reasons for this very striking discrepancy between the facts and general beliefs about this situation.
THE first (and only) two A-bombs used in war were detonated over Hiroshima and Nagasaki on August 6 and 9, 1945. Casualties were horrendous, approximately 100,000 in each city including deaths in the following days from severe burns and radiation. Although massive bombing of cities had already taken place with similar death tolls (e.g., Dresden, Hamburg, and Tokyo, the latter with 100,000 casualties on March 9, 1945), the devastation caused by a single bomb was unheard of and remains one of the most horrifying events in the past century. The people who had survived the explosions were soon designated as Hibakusha and were severely discriminated against in Japanese society, as (supposedly) carriers of (contagious?) radiation diseases and potential begetters of malformed offspring. While not reaching such extremes, the dominant present-day image of the aftermath of the Hiroshima/Nagasaki bombings, in line with the general perception of radiation risk (Ropeik 2013; Perko 2014), is that it left the sites heavily contaminated, that the survivors suffered very serious health consequences, notably a very high rate of cancer and other debilitating diseases, and that offspring from these survivors had a highly increased rate of genetic defects. In fact, the survivors have been the object of massive and careful long-term studies whose results to date do not support these conceptions and indicate, instead, measurable but limited detrimental health effects in survivors, and no detectable genetic effects in their offspring. This Perspectives article does not provide any new data; rather, its aim is to summarize the results of the studies undertaken to date, which have been published in more than 100 papers (most of them in international journals), and to discuss why they seem to have had so little impact beyond specialized circles.
