The bombs dropped on Hiroshima and Nagasaki were the only nuclear weapons ever to have been used in war.
In August 1945, during the final throes of World War II, America, backed by the Allies, dropped two atom bombs on Japan.
The immediate effects of the attacks were devastating.
First to be dropped was a uranium-based weapon dubbed Little Boy; it hit the city of Hiroshima, killing 90,000-146,000 people in the first few days.
Three days later, a plutonium-based bomb, called Fat Man, was dropped on Nagasaki. Within the first few days of the explosion, an estimated 39,000-80,000 people were dead.
The majority of the immediate deaths were due to the explosion blast itself, acute radiation poisoning, and the ensuing firestorm.
Hiroshima and Nagasaki's gigantic detonations were the first and only time that nuclear weapons have been used during warfare.
Documenting the fallout
These events, unique in their destruction and horror, sparked a thorough scientific investigation into the long-term effects of surviving such weapons. From 1947 onward, the Japanese government set out to measure and understand the ongoing health implications of nuclear war.
A group, called the Radiation Effects Research Foundation (RERF), collates this information; they are funded by the Japanese and American governments. RERF followed roughly 100,000 survivors, 77,000 of their offspring, and, as a control, 20,000 people who were not exposed to radiation.
Data provided by these studies have been invaluable in quantifying the risks of radiation poisoning. Because each survivor knew where they were when the detonation occurred, it has been possible to measure each person's radiation exposure precisely. The findings of RERF have helped set safety standards for people who work in the nuclear industry and the public.
This week in the journal Genetics, Bertrand Jordan, a molecular geneticist, published his findings from an analysis of the data collected by RERF. Rather than providing new data, he aimed to "summarize the results of the studies undertaken to date, which have been published in more than 100 papers."
Using over 60 years worth of information, Jordan looked at the effects of Hiroshima and Nagasaki on survivors and their children. He found a large discrepancy between people's general understanding of the atom bomb's effects and the reality.
It is commonly believed that the survivors of Hiroshima and Nagasaki have a high cancer burden, a significantly shortened lifespan, and children with high rates of mutations and abnormalities. After a careful examination of the data, the author found this to be an incorrect assumption.
Jordan summarizes his findings: "There's an enormous gap between that belief and what has actually been found by researchers."
Hiroshima and Nagasaki cancer rates
Cancer rates were indeed found to be higher in individuals who had survived the bombs, when compared with residents who had been out of town at the time of the explosions. Risk of cancer increased depending on proximity to the site, age (younger people had a larger lifetime risk), and gender (women had a greater risk).
However, the majority of survivors did not develop cancer. Because most people only had a modest exposure to radiation, the overall risk of developing solid cancers between 1958 and 1998 increased by 10 percent. This represents 848 additional cancer cases among 44,635 survivors.
But the picture was much worse for those who received higher doses. Individuals who received 1 Gray fared less well. A Gray is a unit of measurement defined as the absorption of one joule of radiation energy per kilogram of matter, equivalent to 1,000 times the normal safety limit for the public. These individuals had a 42 percent increase in cancer risk.
Even in those who received the highest doses of radiation, although cancer risk was greater, their lifespan was reduced by just 1.3 years.
Effects on the children of survivors
RERF also follow the health of the children of survivors. So far, no negative health effects or mutations have been found in the offspring. Jordan believes that in the future, as genetic tools become ever finer, subtle differences might be seen in their genomes. But what is clear, is that if there are negative health consequences for the children of survivors, they are very small.
In his paper, Jordan discusses the reasons for the mismatch between public perception and the the facts.
"People are always more afraid of new dangers than familiar ones. For example, people tend to disregard the dangers of coal, both to people who mine it and to the public exposed to atmospheric pollution.
Radiation is also much easier to detect than many chemical hazards. With a hand-held Geiger counter, you can sensitively detect tiny amounts of radiation that pose no health risk at all."
Jordan is careful to ensure that he is not seen as a pro-nuclear lobbyist. That is not his stance at all. For instance, he says, "I used to support nuclear power until Fukushima happened." He realized that even in a country as technologically advanced and well-regulated as Japan, disasters with the potential to spill out across the world were still possible.
The thrust of Jordan's argument is that any debate should be carried out in a rational way. He says, "I would prefer that people look at the scientific data, rather than gross exaggerations of the danger."