TOKYO—On the 4th anniversary of the earthquake and tsunami that triggered meltdowns at the Fukushima Daiichi Nuclear Power Station, there is one bit of reassuring news: A new study concludes that contaminated food was likely kept out of the market.

"In my honest opinion, the Japanese government did a terrific job to keep their people safe" from contaminated food, says Georg Steinhauser, an environmental radiochemist at Colorado State University,  Fort Collins, who led the study.

The meltdowns at three reactors and subsequent explosions released massive radioactive plumes. To limit exposure, authorities evacuated more than 150,000 residents. (And many more left the area in fear of the radiation.) Mindful that drinking contaminated milk led to most of the cancers that resulted from the Chernobyl nuclear accident in 1986, the Japanese government also launched a massive effort to check foods for contamination and ban any items exceeding set limits. The limit for most food was initially set at 500 becquerels per kilogram (Bq/kg), and then lowered to 100 Bq/kg a year later. For comparison, the European Union's limit is 1250 Bq/kg.

In 4 years, the government has examined roughly a million samples, posting all the data online. Steinhauser and colleagues at the Vienna University of Technology and the University of Tokyo mined the data, looking for trends and lessons. They report that radioactivity in tap water in the Tohoku region, which includes the Fukushima plant, had dropped below the specified limit for liquids within a month of the accident. Contamination in fruits and vegetables peaked immediately after sampling started, which was within 10 days or so of the accident. But by early summer, only some mushroom and dried produce samples exceeded the limit. The team says mushrooms are known accumulators of radionuclides and serve as sentinel products when watching for contamination.

Sampling of meat and eggs was slower to ramp up. But the number of contaminated samples and level of contamination peaked by July 2011 and then decreased. The exception was wild boar meat, which peaked somewhat later as the boars were apparently eating contaminated wild mushrooms.  

"It seems very unlikely that more than very few members of the public in Japan exceeded the maximum permissible internal exposure of 1 mSv [millisievert]/year," the team writes in the 3 March issue of Environmental Science & Technology. One millisievert per year is the recommended maximum radiation dose for the general public set by the International Commission on Radiological Protection.

Nongovernmental watchdog groups have reported finding items on grocery store shelves that exceed the limit. Steinhauser is not surprised, noting that the government's random sampling program was aimed at ensuring the overall safety of the food supply. "The consumption of one singular above-limit food item does not automatically pose a radiological risk to consumers," he says.

The paper does not address what Keith Baverstock, a radiation health expert formerly at the World Health Organization and now at the University of Eastern Finland in Joensuu, considers the most important public health question: What were the external and internal doses in the days and months after the release of the radiation? "A significant quantity" of the vegetable foodstuffs initially exceeded the government's limits, he notes, while acknowledging that those limits are much stricter than those in force in Europe. "How these data can be interpreted in terms of doses is not at all clear," he says.

Steinhauser and others think that the government's food-screening program effectively limited the amount of contaminated food reaching the public. "I believe the conclusions about exposure are generally solidly based; they are believable and reassuring, as well," says Steven Simon, a radiation epidemiologist at the U.S. National Cancer Institute of the National Institutes of Health in Bethesda, Maryland.

One gap in his study, Steinhauser concedes, is that it doesn't cover seafood, a major component of the Japanese diet. "The reason for not looking at seafood was simply the huge amount of data," Steinhauser says. A preliminary assessment suggests there were fewer cases of seafood exceeding allowable limits, he says. But follow-up studies are expected to also cover seafood.