The government set its first radiation safety standards for fish Tuesday after Japan's tsunami-ravaged nuclear plant reported radioactive contamination in nearby seawater measuring at several million times the legal limit.
The plant operator insisted that the radiation will rapidly disperse and that it poses no immediate danger, but an expert said exposure to the highly concentrated levels near the Fukushima Dai-ichi plant could cause immediate injury and that the leaks could result in residual contamination of the sea in the area.
The new levels coupled with reports that radiation was building up in fish led the government to create an acceptable radiation standard for fish for the first time. Some fish caught Friday off Japan's coastal waters would have exceeded the new provisional limit.
Tuesday, TEPCO announced that samples taken from seawater near one of the reactors contained 7.5 million times the legal limit for radioactive iodine on April 2. Two days later, that figure dropped to 5 million.
Experts agree that radiation dissipates quickly in the vast Pacific, but direct exposure to the most contaminated water measured would lead to “immediate injury,” said Yoichi Enokida, a professor of materials science at Nagoya University's graduate school of engineering.
He added that seawater may be diluting the iodine, which decays quickly, but the leak also contains long-lasting caesium-137. Both can build up in fish, though iodine's short half-life means it does not stay there for very long. The long-term effects of caesium, however, will need to be studied, he said.
The move came after the health ministry reported that fish caught off Ibaraki prefecture, which is about halfway between the plant and Tokyo, contained levels of radioactive iodine that would have exceeded the new provisional limit.
Caesium also was found, at just below the limit. The fish were caught Friday, before the new provisional safety limits were announced.
Such limits are usually very conservative. After spinach and milk tested at levels far exceeding the safety standard, health experts said you would have to eat enormous quantities of tainted produce or dairy before getting even the amount of radiation contained in a CT scan.
