Seiki Kawagoe, an environmental science professor at Tohoku University, said the radioactive substances were unlikely to affect drinking water, noting that radiation tends to dissipate quickly in the ground, as it does in the ocean.

But there are two ways the iodine could eventually affect drinking water if concentrations were high enough. One is if it were to seep into wells in the area. For now, a 12-mile (20-kilometer) radius around the plant has been cleared, though residents of the area are growing increasingly frustrated with evacuation orders and have been sneaking back to check on their homes.

The other concern is that contaminated water from the plant could seep into underground waterways and eventually into rivers used for drinking water. Tomohiro Mogamiya, an official with the Ministry of Health, Labor and Welfare’s water supply division, said that was “extremely unlikely” since groundwater would flow toward the ocean, and the plant is right on the coast.

Radioactive cesium can build up in the body and high levels are thought to be a risk for various cancers. It is still found in wild boar in Germany 25 years after the Chernobyl nuclear disaster, making the pigs off-limits for eating in many cases.

Contamination has also affected work at the plant itself, where radioactive water has been pooling, often thwarting the vital work of powering up the complex’s cooling systems.

Despite the leaks, TEPCO hasn’t had enough dosimeters to provide one for each employee since many were destroyed in the earthquake. Under normal circumstances, the gauges, which measure radiation, would be worn at all times.

Officials said Friday that more meters had arrived and there are now enough for everyone.

“We must ensure safety and health of the workers, but we also face a pressing need to get the work done as quickly as possible,” said nuclear safety agency spokesman Hidehiko Nishiyama. Until now, sharing meters “has been an unavoidable choice.”

TEPCO has repeatedly relaxed safety standards during the crisis in order to prevent frequent violations. That is not uncommon during emergencies.

Though the company has acknowledged that it was initially slow to ask for help in dealing with the nuclear crisis, experts from around the world are now flooding in. French nuclear giant Areva, which supplied fuel to the plant, is helping figure out how to dispose of contaminated water, and American nuclear experts are joining Japanese on a panel to address the disaster.

Japan has also ordered two giant pumps, typically used for spraying concrete, from the U.S. They are being retrofitted to spray water first, according to Kelly Blickle, a spokeswoman at Putzmeister America Inc. in Wisconsin. At least one similar pump is already in operation at the plant.

U.S. troops also are involved in the search for the dead. Japan’s defense ministry said that, starting Friday, the two militaries will create joint teams to look for bodies from the air. So far 11,500 people have been confirmed dead. Another 16,400 are missing, and many may never be found.

Hundreds of thousands more people are living in evacuation centers, most because they lost their homes in the tsunami. But others have been forced to leave their houses near the plant because of radiation concerns.

Some residents are growing angry and frustrated with the government and are increasingly violating the bans to return to their homes to gather whatever they can find.