For residents of Fukushima Prefecture, anxiety over their exposure to low levels of radiation has been palpable since the March 11 twin disasters crippled the Fukushima No. 1 power plant.
Residents both in and near the prefecture have been living with these fears as experts seem unable to give clear-cut answers about the possible health impact.
The differing opinions of three radiation experts at the recent Hoshasen to Mukiau (Facing Radiation) symposium reflects how scientists have yet to reach a consensus on how small doses of radiation affect the human body.
Despite this, the experts did agree on one thing: They all urged the public to study and deepen their understanding of radiation risks and make their own judgments in deciding what to avoid.
People need to “measure with their own yardsticks,” National Institute of Radiological Science Executive Director Makoto Akashi told the crowd of some 600 at the Oct. 30 symposium at Yurakucho Asahi Hall in Tokyo. “While our role (as scientists) is to give out accurate data, we want everyone to have their own criteria (for measuring exposure risk) by being knowledgeable.”
Akashi, who heads the Chiba-based NIRS, which currently is monitoring the health of Fukushima residents with Fukushima Medical University, said none of the 4,460 Fukushima residents examined between the end of June and the end of September had been found to have internal exposure levels exceeding 1 millisievert a year, the legal limit for the general public. Based on these examination results, Akashi said it was difficult to believe the health risk of Fukushima residents would increase.
A cumulative dose of 100 millisieverts could increase one’s cancer mortality rate by 0.5 percent and the rate rises with an increase in amount of exposure, according to the International Commission on Radiological Protection, an organization of scientists that created radiation protection guidelines used worldwide.
A level below 100 millisieverts, however, is beyond the reach of today’s science to prove statistically significant in boosting the risk of cancer, Akashi said, as the risk is too small to detect and is buried among many other risk factors, including smoking and obesity.
But any increased risk would certainly be smaller than that above 100 millisieverts, Akashi added.
“We are not saying that exposure below 100 millisieverts is safe,” Akashi said. “What we are saying is that the risk (from radiation exposure) exists among many other risk factors, so that it probably can’t be detected.”
Gen Suzuki, medical director of the International University of Health and Welfare Clinic in Tochigi Prefecture, said it was too early to speak about the exposure levels of Fukushima residents because complete health examinations have yet to be completed. But Suzuki agreed that the current exposure levels are very small.
Animal experiments have shown that health effects from prolonged exposure to low-level radiation are fewer than that of a one-time high-level exposure, Suzuki said.
Based on this experiment, it was possible to assume that the cancer mortality rate of long-term radiation exposure could be lower than that of atomic bomb survivors in Hiroshima and Nagasaki, where victims were exposed to high doses of radiation in a quick burst, he said.
“Whether (the current radiation level) is something that you or your children really have to avoid depends on each person’s philosophy. But when making judgments, it is important to grasp the basic level of risk,” Suzuki said.
Pointing out other factors that put people at a much higher risk level for cancer — including obesity — Suzuki said that being obsessed with avoiding low-level radiation exposure may contribute to these other riskier factors.
He also noted that all food contains the radioactive material potassium-40, which has a half-life of 1.28 billion years. Therefore, he said, if one wants to eliminate every little radioactive isotope from one’s diet, there would be no food left to eat.
Contrary to Akashi and Suzuki, who noted internal exposure levels as being minor, Saburo Murata, a physician and vice chairman of Hannan Chuo Hospital in Osaka Prefecture who has been helping nuclear plant workers with compensation issues, argued there is no safe dose of radiation exposure.
Murata, who has also given health checks to residents in the village of Tokai, Ibaraki Prefecture, site of a fatal 1999 nuclear accident at the JCO nuclear fuel-processing plant, questioned the way government-appointed institutions — including NIRS — have carried out health examinations of Fukushima residents.
He called the measurable limits of whole body counter examinations used for checking the internal exposure of Fukushima residents too high.
“The purpose of health examinations should not be to eliminate people’s fears over the health effects of radiation exposure,” Murata said.
For those who have been or will be exposed to more than 1 millisievert a year, the government must provide thorough health examinations and lifetime medical support, including mental health care, Murata said.
From his experiences with atomic bomb survivors and nuclear plant workers, Murata also stressed the importance of having a record of one’s behavior and health.
“At the moment, it’s difficult to estimate how much you’ve been exposed to, because even if you are examined (the level) could be below the measurable limits,” he said. “When you don’t know (the accurate figure of exposure), you have to have records of where you lived and what actions you took at the time (of exposure).
“If you develop some illness, (such records) could be used to determine the link” between the health effects and the past exposure, Murata said.