Also 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.
The company said in a statement that even those large amounts would have "no immediate impact" on the environment but added that it was working to stop the leak as soon as possible.
The readings released Tuesday were taken closer to the plant than before — apparently because new measuring points were added after the crack was discovered — and did not necessarily reflect a worsening of the contamination. Other measurements several hundred yards (meters) away from the plant have declined to levels about 1,000 times the legal limit — down from more than four times that last week.
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 cesium-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 cesium, however, will need to be studied, he said.
"It is extremely important to implement a plan to reduce the outflow of contaminated water as soon as possible," he said.
Although the Fukushima prefecture surrounding the plant is not a major fishing region, fishermen there are growing alarmed. No fishing is allowed in the direct vicinity of the plant, but they fret that demand will collapse for catches elsewhere in the region — whether or not they are contaminated.
"Our prefecture's fisherman have lost their lives, fishing boats, piers and buildings" in the earthquake and tsunami and now must suffer the added effects of radioactive runoff from the plant, local fishermen's federation head Tetsu Nozaki said in a letter faxed to the company.