Meanwhile, many scientists say there is no need for people outside Japan to be overly concerned about food contamination.
Among them is Patrick Regan, a professor in the physics department at the University of Surrey in Britain, who pointed out that the world was already covered in radioactive cesium-137 before the power plant accident due to nuclear experiments in the 1950s to 1960s.
Some ordinary people have taken heed.
Stanislav Pak, a 33-year-old chef at a sushi restaurant in Vladivostok, Russia, says he isn't worried.
"More than 90 percent of seafood for sushi comes from Japan, but I'm not concerned as it comes after screening," Pak said. "The number of customers has not changed and I do not see people being terrified about it."
But concern over Japan-made products continues to spread.
Taiwan has started checking the radiation levels of Japanese industrial products such as home appliances, while U.S. authorities have announced the suspension of imports of dairy products, fresh vegetables and fruit produced in Fukushima and nearby Ibaraki, Tochigi and Gunma prefectures.
On Monday, the central government ordered the prefectures to suspend shipments of some vegetables following the detection of radioactive substances at levels beyond recommended limits.
The World Health Organization is conducting its own study on the health effects of food products exposed to radiation leaked into the atmosphere from the damaged nuclear power complex.
The organization said its experts in Geneva are looking at data collected by the Manila-based WHO Western Pacific regional office to offer observations and recommendations to member countries.
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