Studying survivors of America’s atomic attacks on Japan have helped scientists better understand radiation—and how we fear it.

Eric Roston
August 11, 2016 — 10:00 AM EDT

The horror of the U.S. atomic attacks on Hiroshima and Nagasaki immediately and forever molded public thinking about nuclear energy. Some 200,000 people were killed, and thousands upon thousands more were sentenced to shorter lifespans.

Among the sane, nuclear weapons are unthinkably dangerous without hesitation or ambiguity. That message of cataclysm is so straightforward that it also shaped how people think about their key byproduct—radiation.

Since the bombings, which occurred 71 years ago this week, many survivors and their children participated in studies that helped scientists understand the long-term effects of radiation exposure. About 120,000 survivors of the 1945 attacks, and 77,000 of their children, have taken part in the ongoing work since the 1940s. The research was conducted by the U.S. from 1947 to 1975, when Japan set up the Radiation Effects Research Foundation, in partnership with the U.S. This work helped inform the empirical basis for modern radiation exposure standards.

A new review released Thursday, which analyzes more than 100 studies, concludes that the long-term effects of radiation don't support the level of dread we have come to take for granted. "There is a general tendency to overestimate radiation risks and to underestimate other risks," said Bertrand Jordan, a molecular biologist who also trained in nuclear physics and the author of the new paper in the journal Genetics.

Radiation can kill you, and it can do it in horrific fashion. No one disputes that. Misunderstanding radiation, however, complicates already complicated problems, such as how to store nuclear waste, where to site new reactors, and how to dismantle old ones. The ubiquity of natural radiation, its invisibility to humans, the connection to nuclear war and to reactor meltdowns all contribute to public confusion and anxiety. "The extent of the overestimation even in the scientific community is quite striking," Jordan said.

People exposed to a large amount of bomb radiation—a level more than 2,000 times today's safe level for an entire year—developed cancer much more frequently than otherwise would have been expected, 61 percent more. Including the groups exposed less, scientists can attribute 10.7 percent of cancers to excess radiation. But in a finding that pushes back against a common public fear, if radiation affected survivors' genetic makeup, such mutations have yet to be detected in their children.

"An enormous effort has been devoted to the scientific study of the A-bomb survivors, which is why the data are so valuable," said Richard Wakeford, an epidemiology professor at the University of Manchester. "Even so, public perception of the risks of radiation exposure is at variance with the scientific evidence, possibly because of fear surrounding nuclear weapons."

David Ropeik, who writes and consults about risk, traces the origin of anti-nuclear activism to the 195os, predating the environmental movement. Ropeik said a general fear of radiation throws off people's sense of what's dangerous. Generating electricity from coal—which kicks out particulate matter (soot) and noxious gases—is worse than making power from nuclear reactors, he said. "Particulates kill people," Ropeik said. "Radiation kills fewer people. Those particulates are in the air in part because we're afraid of turning on nukes."

Joachim Schuz is head of the environment and radiation section of the International Agency for Research on Cancer at the World Health Organization. As he put it, "for Europe, taking all sources of ionizing radiation together, it is estimated that about 1 percent to 2 percent of all cancers would be attributable to radiation, compared to about 20 percent to tobacco smoking."

It doesn't help that radiation is measured in multiple units, none of them intuitive. One sievert (Sv) of radiation carries about a 5 percent risk for eventually developing cancer. The standard U.S. safety measure for a year's exposure is a thousandth of that, 1 millisievert (1 mSv). Dental x-rays give off as much as 10 microsieverts, or millionths. A fatal dose might take about 6 Sv. (The U.S. Centers for Disease Control and Prevention publishes information about radiation and emergencies here. )

Average life expectancy fell by 1.3 years among survivors who were exposed to about 1 Sv and by declining amounts among those who faced lesser exposure. "As a comparison," Jordan writes, "note that in Russia, life expectancy decreased by 5 years between 1990 and 1994, essentially because of social disruption impacting on living conditions and health care."

http://www.bloomberg.com/news/articles/2016-08-11/radiation-can-kill-but-not-as-easily-you-think

Survivors of the 1945 atomic bomb attacks developed solid cancers at higher rates than normal. The elevated levels (white bars) are smaller than public opinion might anticipate. The x-axis represents the number of cases.