FUKUSHIMA, Japan — Even if the worst nuclear accident in 25 years leads to many people developing cancer, the public may never find out. The ordinary rate of cancer is so high, and medical understanding of the effects of radiation exposure so limited, that any increase in cases from the Fukushima nuclear plant disaster may be undetectable.
Several experts inside and outside Japan told the Associated Press that cancers caused by the radiation may be too few to show up in large population studies, like the long-term survey just getting under way in Fukushima.
That could mean thousands of cancers undetected in a study of millions of people.
Some of the dozen experts the AP interviewed said they believe radiation exposure most Japanese people have gotten fall in a “low-dose” range, where the effect on cancer remains unclear.
The cancer risk may be absent, or just too small to detect, said Dr. Fred Mettler, a radiologist who led an international study of health effects from the 1986 Chernobyl disaster.
That is partly because cancer is one of the top killers of people in industrialized nations, where the average lifetime cancer risk is about 40 percent.
In any case, the 2 million residents of Fukushima province, targeted in the new, 30-year survey, probably got too little radiation to have a noticeable effect on cancer rates, said Seiji Yasumura of the state-run Fukushima Medical University. Mr. Yasumura is helping run the project.
“I think he’s right,” as long as authorities limit children’s future exposure to the radiation, said Richard Wakeford, a visiting epidemiology professor at the Dalton Nuclear Institute at the University of Manchester in England.
Mr. Wakeford, who is also editor of the Journal of Radiological Protection, said he’s assuming that the encouraging data he’s seen on the risk for thyroid cancer is correct.
The idea that Fukushima-related cancers may go undetected gives no comfort to Edwin Lyman, a physicist and senior scientist with the Union of Concerned Scientists, a group that advocates for nuclear safety.
He said that even if cancers don’t turn up in population studies, that “doesn’t mean the cancers aren’t there, and it doesn’t mean it doesn’t matter.”
“I think that a prediction of thousands of cancer deaths as a result of the radiation from Fukushima is not out of line,” Mr. Lyman said.
But he stressed that authorities can do a lot to limit the toll by reducing future exposure to the radiation. That could mean expensive decontamination projects, large areas of condemned land and people never returning home, he said. “There’s some difficult choices ahead.”
Japan’s Cabinet this month endorsed a plan to cut contamination levels in half within the next two years. The government recently announced it plans to study the risk from long-term exposure to the low-dose radiation level used as a trigger for evacuations.
The plant was damaged March 11 by a tsunami triggered by a magnitude-9 earthquake. Japanese authorities estimate it leaked about one-sixth as much radiation as the Chernobyl accident.