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Friday, Nov. 25, 2011
Nuke accident-linked cancer may be impossible to detect
Experts remain divided over health risks from small doses of radiation
FUKUSHIMA — Even if the world's worst nuclear accident in 25 years results in many people developing cancer, we may never find out.
Looking back on the early days of the Fukushima nuclear disaster, that may sound implausible.
But the ordinary rate of cancer is so high, and our understanding of the effects of radiation exposure so limited, that any increase in cases following the triple meltdowns at the Fukushima No. 1 nuclear plant may go undetected.
Several experts inside and outside Japan said that cancers caused by the massive amounts of radiation the plant emitted may be too few to show up in large population studies, such as the long-term survey of the 2 million residents in Fukushima Prefecture just getting under way.
That could mean thousands of cancers will slip under the radar in a study covering millions of people. Some of the dozen experts interviewed said they believe the radiation doses most people in Japan have been exposed to fall in the "low-dose" range, where the link to cancer remains unclear.
The cancer risk may be absent, or just too small to detect, said Fred Mettler, a radiologist who led an international study into health effects following the 1986 Chernobyl disaster.
That's partly because cancer is one of the top killers in industrialized nations, in which the average lifetime cancer risk is about 40 percent. The odds are high that if people in such countries live long enough, they will die of cancer.
In any case, the radiation doses of the Fukushima Prefecture residents targeted in the new, 30-year survey were probably too small to have a noticeable effect on cancer rates, said Seiji Yasumura of Fukushima Medical University. Yasumura is helping run the project.
"I think he's right," as long as authorities limit children's future exposure to radiation, said Richard Wakeford, a visiting epidemiology professor at the University of Manchester's Dalton Nuclear Institute in England. Wakeford, who's also editor of the Journal of Radiological Protection. He said he's assuming that the encouraging data he's seen on the risk for thyroid cancer are correct.
But the idea that cancers linked to the Fukushima crisis may go undetected gives no comfort to Edwin Lyman, a physicist and senior scientist with the U.S.-based Union of Concerned Scientists, a leading nonprofit group that advocates for nuclear safety. He said that even if cases of cancer don't show 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 the Fukushima accident is not out of line," Lyman said. But he stressed that authorities can do a lot to limit the toll by reducing future exposure to the radiation released into the environment by the plant's wrecked reactors. That could mean conducting expensive decontamination projects, designating large areas of land as permanently off-limits and preventing people from ever returning home, he said. "There's some difficult choices ahead."
The Cabinet this month endorsed a plan to cut contamination levels in half within the next two years. The government also recently announced it plans to study the risk from long-term exposure to the low dose radiation limit it imposed following the nuclear accident. The limit was used as a gauge for evacuating residents in the prefecture.
The Fukushima No. 1 plant was crippled by the 15-meter tsunami generated by the 9.0-magnitude earthquake that struck off the coast of Tohoku on March 11. In some areas the waves swept up to 10 km inland. Authorities estimate the plant's reactors leaked about one-sixth of the radiation released during the Chernobyl accident, and spewed iodine-131, cesium-137 and 29 other radioactive materials that contaminated the water, soil, forests and crops in a large area around the facility. A recent study suggested that emissions of cesium-137 were in fact double the amount estimated by the government.
So far, no radiation-linked deaths or sickness have been reported among either local residents or the workers trying to bring the plant under control.
A preliminary survey over the summer of 3,373 evacuees from the 10 towns closest to the stricken plant showed their estimated internal exposure doses over the next several decades would be far below the levels officials deem harmful.
But while the Fukushima disaster has stopped making headlines around the world, many Japanese remain concerned about the long-term health effects. And many don't trust the reassurances by government scientists such as Fukushima Medical University's Yasumura.
Many consumers worry about the safety of farm produce from Fukushima and surrounding prefectures, although food and fish products found to exceed government-set radiation limits have been barred from the market. For example, mushrooms harvested in and around Fukushima are frequently found to be contaminated and stopped from reaching the market. But the government's choice of a maximum level for internal radiation exposure from food has also caused controversy.
Fukushima Prefecture, meanwhile, has distributed radiation monitors to 280,000 children at its elementary and junior high schools. Many kids are allowed to play outside for only two or three hours a day. Schools have removed topsoil from their grounds to reduce their students' exposure to contamination, and the education ministry has provided radiation handbooks for teachers. Thousands of children have been moved out of the prefecture since the March disasters triggered the nuclear crisis, mainly due to radiation fears.
Many parents and concerned citizens in and around Fukushima, as well as some as far as Tokyo, carry Geiger counters to measure radiation levels in their neighborhoods each day, especially near schools and kindergartens. The devices are probably one of the most popular electronics gadgets in the country since the start of the disaster. People can rent them at DVD shops or drug stores in Fukushima Prefecture, and many Internet rental businesses specializing in Geiger counters also have emerged.
Citizens' groups are also setting up radiation measuring centers where people can submit vegetables, milk or other foods for testing. Some people are turning to the traditional Japanese diet — pickled plum, miso soup and brown rice — based on the belief that it boosts the immune system.
"I try what I believe is the best, because I don't trust the government any more," said Chieko Shiina, a Fukushima Prefecture resident who switched to such a diet. The 65-year-old farmer had to close a small "ryokan" inn because of the nuclear crisis.
She thinks leaving Fukushima would be safer but says she has nowhere else to go.
"I know we continue to be exposed to contamination, even right at this moment. I know it would be best just to leave Fukushima," she said.
Yuka Saito, a mother of four who lives in a neighborhood near the reactors where the government recently lifted its evacuation order, said she and her three youngest children spent the summer in Hokkaido to get away from the radiation. She tells her children, aged 6 to 15, to wear medical masks, long-sleeved shirts and a hat whenever they go out, and not to play outside.
She still avoids drinking tap water and monitors radiation levels daily around her house and the kindergarten and schools her children attend. She keeps a daily log of the readings.
"We in Fukushima are exposed to radiation more than anyone else outside the prefecture, but we just have to do our best to cope," she said. "We cannot stay inside our homes forever."
Officials say that mental health problems caused by excessive fear of radiation are prevalent among Fukushima residents and are more of a problem than the actual risk of developing cancer from the radiation.
But what kind of cancer risks do people really face?
Information on actual radiation exposure for individuals is scarce, and some experts say they can't draw any conclusions yet about the risk to the general population.
But Michiaki Kai, professor of environmental health at Oita University of Nursing and Health Sciences, said that based on tests he has seen on people and their exposure levels, nobody in Fukushima Prefecture — except for some workers at the nuclear plant — has been exposed to harmful levels of radiation.
Radiation generally raises the risk of cancer in proportion to the exposure. Many experts and regulators still believe this holds true for low dosages. But other experts say direct evidence to prove this theory is lacking, and that it remains unclear whether such small levels raise the cancer risk.
"Nobody knows the answer to that question," said Mettler, who led the Chernobyl study, and is also a professor emeritus of radiology at the University of New Mexico and the U.S. representative to the U.N. Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). If such low doses do produce cancers, they'd be too few to be detected against the backdrop of normal cancer rates, he said.
To an individual the question may have little meaning, since it deals with the difference between no risk and small risk. For example, the general population was told to evacuate from areas where they would be exposed to more than 20 millisieverts of radiation a year. A dosage of 20 millisieverts is about seven times the average dose of background radiation Americans are exposed to in a year. A child exposed to 20 millisieverts for a year would face a calculated risk of about 1 in 400 of getting cancer someday as a result, said David Brenner of Columbia University. So that would only increase the typical lifetime cancer risk of about 40 percent by 0.25 percent, he said.
The average radiation dose among the 14,385 workers who worked at the nuclear plant through July was 8 millisieverts, according to the central government. The average lifetime risk of cancer to an individual from such a dose alone would be calculated at about 0.05 percent, or 1 in 2,000, Brenner said.
But he also stressed that such calculations are uncertain because scientists know so little about the effects of such small doses of radiation.
In assessing the Fukushima disaster's effect on the population, low radiation doses pose another question: If many people are each exposed to a low dose, can you multiply their individual calculated risks to forecast the number of cancer cases in the population?
Brenner thinks this is possible, which is why he believes some instances of cancer related to the Fukushima crisis might even appear in Tokyo, although each resident's risk is "pretty minuscule."
But Wolfgang Weiss, who chairs the UNSCEAR radiation committee, said the U.N. body considers it inappropriate to predict a certain number of cancer cases due to low doses of radiation because the risks of low levels of exposure remain unproven.
Nuclear accidents can cause cancer of the thyroid gland, but the disease is highly treatable and rarely fatal. The thyroid absorbs radioactive iodine.
After the Chernobyl disaster, some 6,000 children exposed to radioactive fallout subsequently developed thyroid cancer. Experts blame contaminated milk.
But the thyroid threat was apparently reduced in Japan as authorities closely monitored the radiation levels of dairy products and Japanese children do not traditionally consume a lot of milk, although their dairy intake has been rising in recent years.
Still, the new Fukushima survey will check the thyroids of about 360,000 people under age 18, with followups planned every five years throughout their lifetimes. It will also track women who were pregnant in the early stages of the crisis, conduct checkups focused on mental health and lifestyle-related illnesses for evacuees and others living near the no-go zone around the plant, and ask residents to fill out a 12-page questionnaire to assess their radiation exposure during the first weeks of the reactor meltdowns.
But the survey organizers are having trouble getting responses, partly because many locals are living at new addresses. As of mid-October, fewer than half the residents had responded to the health questionnaire.
Some residents are also skeptical about the survey's objectivity because of their general mistrust of the government, which repeatedly delayed disclosing key data and revised evacuation zones and safety standards after the accident. In addition, the government's nuclear safety commission recommended the use of iodine tablets, but none of the residents received them either before or during the evacuations, when the medicine would have been most effective at protecting thyroid glands.
Some even wonder whether the study is using them as human guinea pigs to examine the impact of radiation on humans.
Eisuke Matsui, a lung cancer specialist and a former associate professor at Gifu University School of Medicine, criticized the project, saying it appears to largely ignore potential radiation-related health risks such as diabetes, cataracts and heart problems that some studies of the Chernobyl crisis have hinted at.
"If thyroid cancer is virtually the only abnormality on which they are focusing, I must say there is a big question mark over the reliability of this survey," he said.
He also suggested sampling hair, clipped nails and shed baby teeth to test for radioactive isotopes such as strontium that are undetectable under the survey's current approach.
"We should check as many potential problems as possible," Matsui said.
Fukushima Medical University's Yasumura acknowledges the main purpose of the study is "to relieve radiation fears."
Matsui, however, said that "a health survey should be a start, not a goal."
Tatsuhiko Kodama, head of the Radioisotope Center at the University of Tokyo, urged quick action to determine cancer risks.
He said large population surveys and analyses will take so long that it would make more sense to run a careful simulation of radiation exposure and do everything possible to reduce the risks.
"Our responsibility is to tell the people now what the possible risks to their health could be," he said.