The flow of highly radioactive water into the Pacific Ocean near Japan's distressed nuclear power plant has stopped, the plant's owners said.
The water was escaping from a concrete pit with a large crack in it, the Tokyo Electric Power Co. said. Officials said the company used a substance called liquid glass to seal the crack and the leak stopped Wednesday morning.
The release of radioactive waste has raised concerns in Japan and elsewhere about the safety of seafood. On Tuesday, Japan's government set its first radiation safety standards for fish after radioactive contamination in nearby seawater was measured at several million times the legal limit.
TEPCO 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.
"Even if the government says the fish is safe, people won't want to buy seafood from Fukushima," said Ichiro Yamagata, a fisherman who used to live within sight of the nuclear plant and has since fled to a shelter in Tokyo.
"We probably can't fish there for several years," he said.
Radiation had been leaking into the Pacific Ocean near the plant, located on the northeastern Japanese coast, since the magnitude 9.0 earthquake on March 11 spawned a massive tsunami that inundated the complex. Over the weekend, workers there discovered a crack in a pit where supply cables are stored. Officials suspected that highly contaminated water was spilling directly into the ocean from that crack.
On Tuesday, TEPCO announced that samples taken on April 2 from seawater near one of the reactors contained 7.5 million times the legal limit for radioactive iodine. When the water was retested two days later, the figure had dropped to 5 million.
The company said in a statement that even those large amounts would have "no immediate impact" on the environment.
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, taken several hundred yards 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 contained 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.
Some government assurances of safety have done little to quell panic. In Tokyo, for instance, there were runs on bottled water after officials said radiation in tap water there was above the level considered safe for infants, though they insisted it was still OK for adults.
On Tuesday, officials decided to apply the maximum allowable radiation limit for vegetables to fish, according to Chief Cabinet Secretary Yukio Edano.
"We will conduct strict monitoring and move forward after we understand the complete situation," 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 exceeded the new legal limit. Cesium was also found just below the limit. The fish were caught Friday, before the safety limit was announced.
Such limits are usually very conservative. After spinach and milk tested at levels far exceeding the safety standard, health experts said someone would have to eat enormous quantities of tainted produce or dairy before getting even the amount of radiation contained in a CT scan.
Radioactivity is pouring into the ocean, in part, because workers at the plant have been forced to use a makeshift method of bringing down temperatures and pressure by pumping water into the reactors and allowing it to bleed out wherever it can. It is a messy process, but it is preventing a full meltdown of the fuel rods that would release even more radioactivity into the environment.
The government on Monday gave the go-ahead to pump more than 3 million gallons of less contaminated water into the sea, in addition to what is leaking, to make room at a plant storage facility to contain more highly radioactive water.
TEPCO's reputation has taken a serious hit in the crisis. On Tuesday, its stock dropped 80 yen — the maximum daily limit, or 18 percent — to just 362 yen ($4.3), falling below its previous all-time closing low of 393 yen from December 1951.
Since the quake, TEPCO's share price has nose-dived a staggering 80 percent.
The stress of announcing all the bad news also appears to be taking a toll. One official teared up and his voice began shaking as he gave details at a news conference near the plant this week.
In what could be an effort to counter the bad publicity, Takashi Fujimoto, TEPCO's vice president, said it was offering 20 million yen ($240,000) to each town or city affected by a mandatory evacuation zone. He called the cash "apology money" and noted that one town had refused it because it disagreed with the approach. He did not give further details.
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