Drumbeat of Nuclear Fallout Fear Doesn’t Resound With Experts

The fear is unwarranted, experts say. People in Japan near the Fukushima Daiichi nuclear power plant may have reason to worry about the consequences of radiation leaks, scientists say, and some reactor workers, in particular, may suffer illness. But outside of Japan, the increase is tiny, compared with numerous other sources of radiation, past and present.

Experts say that humans are bombarded by so much radiation from so many other sources, including many natural ones, that the uptick from Japan disappears as a cause of concern the big picture is considered.

That perspective suggests a human population and a global environment in which exposure to radiation is constant and significant. For example, people around the globe were exposed to radioactive fallout from hundreds of nuclear bomb test explosions in the atmosphere during the cold war. Today, medical patients choose to be exposed to regular doses of radiation from millions of X-rays and CT scans.

In the world’s oceans, thousands of decomposing drums of radioactive waste pose bigger dangers than the relatively small amounts of radioactive water released from the Fukushima Daiichi plant. And natural radiation from rocks, cosmic rays and other aspects of the environment, experts say, represents the biggest factor of all — far bigger than all the man-made emissions, including the current increase from the crippled Japanese reactors.

“It disappears as a contributor to population radiation doses,” said Frank N. von Hippel, a nuclear physicist who advised the Clinton administration and now teaches at Princeton University. But the fear of radiation is different. “Somehow,” Dr. von Hippel added, “nuclear things get stigmatized relative to their statistical risks.”

After the Japanese disaster began on March 11, blogs warned of government conspiracies to cover up radiation dangers, and public-interest groups sounded alarms.

Dr. Dale Dewar, executive director of Physicians for Global Survival, a group that advocates the abolition of nuclear arms, said the accident meant future generations would live in a world with higher levels of background radiation.

“Your hair won’t fall out,” she told an interviewer at the Vancouver Sun. “But ‘No immediate danger’ is an easy way for the nuclear industry to duck the long-term effects.”

Even Washington got the jitters. On March 15, four days after the disaster’s start, the surgeon general, Regina M. Benjamin, said it was no overreaction for Americans to stock up on iodine pills. “It’s a precaution,” Dr. Benjamin told a television interviewer.

Her office backpedaled two days later, after President Obama said Americans needed to take no protective measures.

“Most people don’t have a good handle on the risks,” Dr. Fred A. Mettler Jr., professor of radiology at the University of New Mexico and the American representative to a United Nations panel on radiation assessment, said in an interview. “They don’t know the magnitude of the sources, so they don’t know how to put the risks in perspective.”

The jargon doesn’t help. Radiation is measured in obscure units that change significantly depending on the strength of the radiation and whether the units characterize radioactivity itself, or the interaction of the radiation with the human body. Radioactive sources are said to emit curies or becquerels of radiation, but the effect on living things is measured in sieverts or rem (for “roentgen equivalent man” — it’s true).

Given what may appear to be chaotic or incomplete information, people may base their perceptions of atomic risk on a volatile mix of sensational reports and instincts.

“Risk resides mostly as a feeling,” said Paul Slovic, a pioneer of nuclear psychology at the University of Oregon. “It’s a quick gut reaction often triggered by an image,” especially ones in the movies and on television.

Dr. Mettler said, “Children in the United States are inundated with all kinds of nonsense on television from the time they are 6 months old.” Cartoon characters like the Incredible Hulk, Spider-Man and Homer Simpson, he said, all of whom experience scientifically impossible but highly entertaining effects of radiation, tend to provide most of the nation’s “radiation biology lessons.”

Dr. Slovic cited medical radiation as an example of variability in risk perception. Many experts see the public as getting a potentially risky overdose. But the public tends to think otherwise, he said. “We’re very tolerant of exposure,” Dr. Slovic said in an interview. “We want it or need it, so we feel it’s a strongly beneficial technology. And so the sense of risk is depressed.”