Michiaki Kai, professor of environmental health at Oita University of Nursing and Health Sciences, said that based on tests he’s seen on people and their exposure levels, nobody in Fukushima except for some plant workers has been exposed to harmful levels of radiation.
Radiation generally raises cancer risk in proportion to its amount. At low-dose exposures, many experts and ‘regulators embrace the idea that this still holds true. But other experts say direct evidence for that is lacking, and that it’s not clear whether such small doses raise cancer risk at all.
If such low doses do produce cancers, they’d be too few to be detected against the backdrop of normal cancer rates, he said. The general population was told to evacuate areas that would expose them to more than 20 millisieverts a year. A millisievert measures radiation dose and 20 mSv is about seven times the average dose of background radiation Americans get in a year. A child exposed to 20 mSv for a year would face a calculated risk (if low dose no threshhold is correct) of about 1 in 400 of getting cancer someday as a result, says David Brenner of Columbia University. So that would add 0.25 percent onto the typical lifetime cancer risk of about 40 percent, he said. [or 0% of there are lower threshholds that are safe.
Wolfgang Weiss, who chairs the UNSCEAR radiation committee, said the committee considers it inappropriate to predict a certain number of cancer cases from a low-dose exposure, because low-dose risk isn’t proven.
Nuclear accidents can cause cancer of the thyroid gland, which can absorb radioactive iodine and become cancerous. That disease is highly treatable and rarely fatal.
After the Chernobyl disaster, some 6,000 children exposed to radioactive fallout later developed thyroid cancer. Experts blame contaminated milk. But the thyroid threat was apparently reduced in Japan, where authorities closely monitored dairy radiation levels, and children are not big milk drinkers anyway.
Still, the new Fukushima survey will check the thyroids of some 360,000 young people under age 18, with follow-ups planned every five years throughout their lifetimes.
Japan’s Cabinet this month endorsed a plan to cut contamination levels in half within the next two years