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| Fig. 1: Little boy, the nuclear bomb detonated in Hiroshima. [7] (Courtesy of the DOE) |
The most notable and controversial use of atomic bombing from the twentieth century took place on August 6th, 1945 in Hiroshima, Japan. On this day, the United States dropped a uranium bomb 31,000 feet above the town in an effort to force Japanese surrender and end a catastrophic world war. A nuclear fission reaction began 44 seconds after it was dropped, causing instantaneous and longitudinal devastation to the town and its people. Estimates of the immediate death toll are variable depending on the source, but generally range between 70,000 - 166,000; effects of radiation exposure caused by the bombing are even more difficult to quantify. The bomb, referred to as "Little Boy", weighed 9,700 pounds, 141 of which were the enriched uranium responsible for the explosion (see Fig. 1). [1,2]
The health concerns raised from the bombing broadly fall under cancers and leukemia, birth defects, intellectual disabilities, stroke, circulatory disease, and heart disease. The largest study into the health impacts of this atomic bomb was conducted by the Radiation Effects Research Foundation (RERF), established in 1947 as a US-Japan organization in an effort to investigate the medical effects of radiation. The primary study RERF conducted, called the Life Span Study (LSS), used cohort and case-control studies to quantify the long-term health effects of atomic bomb radiation in a population of 120,000 subjects from Hiroshima and Nagasaki. [2]
Key findings of the LSS thus far include increased risk of cancer mortality throughout life, with a linear increase in solid cancer risk related to radiation dose. The risk increased roughly 20% per decade decrease in age at exposure, indicating the adverse effects of radiation exposure during childhood. Children who were under age 10 at exposure were reported to have 58% more cancer deaths. Risk of cancer mortality was increased significantly in the bladder, breast, colon, esophagus, gallbladder, liver, lung, ovary, and stomach. A significant excess relative risk for solid cancer was 0-0.2 grays. Risk of leukemia increased shortly after the bombing, but then decreased; further analysis revealed a linear-quadratic association between radiation dose and response. [2] This contrasts the linear relationship discovered between radiation dose and cancer response, suggesting a differing pathogenesis between solid cancer and leukemia. Results from the LSS are generally considered the most reliable of other high-dose radiation studies given the sample size and, wide range of precise radiation doses, observation of varying diseases, and long follow-up period. [2-5]
At the time of the publication (2011), 58% of the LSS subjects with estimated DS02 doses (50,620 subjects) had died. Douple et al. observed a 17% increase in cancer deaths among LSS cohort members. [2]
Estimated total number of solid cancer deaths, including esophagus, stomach, colon, rectum, liver, gallbladder, pancreas, other digestive system, lung, breast, uterus, ovary, prostate, bladder, kidney parenchyna, renal pelvis and ureter, and other: 10,929 deaths
Estimated total number of leukemia deaths, including leukemia, malignant lymphoma, and multiple myeloma: 695 deaths
Estimated total solid cancer and leukemia deaths: 11,624 deaths
Percentage of total deaths caused by cancer or leukemia: (11,624 / 50,620) × 100% = 22.96%. The authors report a 22.96% percentage of total deaths caused by cancer or leukemia in patients exposed to atomic radiation. However, this number may bring pause as a comparable percentage of total deaths caused by cancer or leukemia in a general patient population is presently about 18%. [5,6]
© Mia Bennett. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] M. Tomonaga, "The Atomic Bombings of Hiroshima and Nagasaki: A Summary of the Human Consequences, 1945-2018, and Lessons For Homo Sapiens to End the Nuclear Weapon Age," J. Peace Nucl. Disarm. 2, 491 (2019).
[2] E. B. Douple et al., "Long-term Radiation-Related Health Effects in a Unique Human Population: Lessons Learned from the Atomic Bomb Survivors of Hiroshima and Nagasaki," Disaster Med. Public Health Prep. 5, Suppl. 1, S122 (2011).
[3] K. Ozasa, E. J. Grant, and K. Kodama, "Japanese Legacy Cohorts: The Life Span Study Atomic Bomb Survivor Cohort and Survivors Offspring," J. Epidemiol. 28, 162 (2018).
[4] S. Shimizutani and H. Yamada, "Long-Term Consequences of the Atomic Bombing in Hiroshima," J. Jpn. Int. Econ. 59, 101119 (2021).
[5] K. Ozasa et al., "Studies of the Mortality of Atomic Bomb Survivors, Report 14, 1950-2003: An Overview of Cancer and Noncancer Diseases," Radiat. Res. 177, 229 (2011).
[6] "Lifetime Probability of Developing (2017-2019) or Dying (2018-2020) from Cancer," American Cancer Society, 2024.
[7] B. A. Steeves, "The Vault: National Security Then and Now," Los Alamos National Laboratory, LA-UR-21-26246, July 2021.