Reiko Nakamura, a 37-year-old mother of three children, said she has been checking radiation levels outside her house in Meguro Ward, Tokyo, every day since she bought a dosimeter in May.
Based on her readings, she decides whether to open the windows or leave them shut tight.
Trying to protect her children from radioactive materials spewing from the Fukushima No. 1 nuclear power plant, Nakamura has been buying produce grown in west Japan since mid-March.
“I’m buying produce on the Internet. Also we’ve been drinking water delivered from Yakushima (in Kagoshima Prefecture),” said Nakamura, who was at a gathering organized by Setagaya Kodomo Mamoru Kai (The Group to Protect Children in Setagaya) in late June. Nearly 30 mothers discussed ways to prevent radiation exposure.
“I’m not bothered about us adults. But thinking of my children’s future health, I’ve been taking protective measures based on experts’ opinion that I thought was the most conservative,” Nakamura said.
Living in central Tokyo, more than 200 km southwest of the stricken plant in Fukushima Prefecture, does little to mitigate the anxiety people feel about exposure, as radiation-tainted produce and radioactive hot spots have been found far beyond the boundaries of Fukushima Prefecture.
Experts say it is desirable to reduce unnecessary exposure as much as possible — as Nakamura and many mothers are trying to do for their children — given the uncertainty over whether the radiation could cause cancer years later.
But they also say that given the official figures about radiation-contaminated air, water, vegetables, tea and other food products, the current exposure level in Tokyo is not something residents should get stressed over.
The Tokyo Metropolitan Government recently took air samples at 100 different locations around the capital. The highest hourly reading was detected in Katsushika Ward at 0.2 microsievert, while the level measured in Shinjuku has been steady at around 0.06 microsievert per hour for weeks.
Kunikazu Noguchi, a specialist on radiation protection at Nihon University, said the figures are not problematic.
“Even newborn babies are exposed to natural radiation of about 1.5 millisieverts a year (in Japan).
“Even if the dose doubles, it’s not at a level to be frightened of,” he said.
Since March 17, 23 prefectural governments have tested 6,371 samples of vegetables, fruit, milk, eggs, meat, fish and tea, and as of June 30, 404 of those products were found to be contaminated above the government limit.
But no food items have been found to be contaminated above the government-set safety limit since June 1, apart from those from Fukushima Prefecture and tea produced in Shizuoka, Ibaraki, Tochigi, Kanagawa and Chiba prefectures.
Domestic rules set the limit for radioactive cesium — now the main radioactive threat in food — for a person with average eating habits at up to 5 millisieverts per year. When someone is exposed to a cumulative dose of 100 millisieverts, the risk of dying from cancer goes up by 0.5 percent, according to a widely accepted consensus by scientists. Below that level, radiation risks are too small to distinguish from the effects of other major cancer risks, including smoking, an unbalanced diet or lack of exercise.
Meanwhile, experts are split over whether exposure below 100 millisieverts increases the risk of cancer. Some experts say exposure below that level will not increase the risk, as data from long-term surveys on hibakusha have suggested.
Other experts, however, argue that it should be assumed that proportional cancer risks should exist even below the 100 millisievert level.
For example, Hiroaki Koide, a polemic antinuclear scholar at Kyoto University, claims exposure of 1 millisievert per year increases the risk of dying from cancer by one for every 10,000 people exposed to radiation at that level.
The assumed risk might appear rather small for individuals, given that now about one-third of all Japanese die from cancer. But it could be a big issue for the government and nuclear regulators, and the perception of that hypothetical risk under the 100-millisievert level might differ from person to person.
Ikuro Anzai, professor emeritus at Ritsumeikan University and a specialist in radiation, said it is better not to ingest any unnecessary radioactive materials if possible.
But he said people should make rational judgements and should not overly fear ingesting food with contamination levels below the limits set by the state.
“As long as food you eat is contaminated, you will be exposed to some extent. But the important thing is to what extent the exposure is,” he said.
Tea leaf contamination is another hot topic.
The Shizuoka Prefectural Government earlier this month detected 581 to 981 becquerels per kilogram in seven tea factories, above the central government’s limit of 500 becquerels per kilogram.
But Tadashi Tsukamoto, a prefectural official, said that even if one keeps drinking contaminated green tea currently excluded from the food distribution chain, it will not pose any health risks to consumers.
The 500 becquerel per 1 kg limit, now applied to tea leaves, was originally set by the government for vegetables on the assumption that a consumer eats vegetables regularly.
But when brewing tea, the radioactive material in the leaves is diluted with water by around one-eightyfifth, far below the government’s radiation limit for drinking water of 200 becquerels per kilogram.
Thus, drinking tea made from Shizuoka-grown leaves will not pose a health risk to consumers, Tsukamoto said.
Still, Shizuoka has asked factories to voluntarily recall shipped products and refrain from shipping current stocks in the plants “since we value the prefecture’s standard,” he added.
Shizuoka Prefecture, 300 km from Tokyo Electric Power Co.’s Fukushima facility, has around 2,300 tea factories and accounts for 45 percent of the nation’s overall output.