Minuscule amounts of radioactive iodine also were found in tap water Friday in Tokyo and elsewhere in Japan -- although experts said none of those tests showed any health risks. The Health Ministry also said that radioactive iodine slightly above government safety limits was found in drinking water at one point Thursday in a sampling from Fukushima prefecture, the site of the nuclear plant, but later tests showed the level had fallen again.
Six workers trying to bring the Fukushima Dai-ichi plant back under control were exposed to more than 100 millisieverts of radiation -- Japan's normal limit for those involved in emergency operations, according to Tokyo Electric Power Co., which operates the complex. The government raised that limit to 250 millisieverts on Tuesday as the crisis escalated.
Officials said the crisis at the plant appeared to be stabilizing, with near-constant dousing of dangerously overheated reactors and uranium fuel, but the situation was still far from resolved.
"We more or less do not expect to see anything worse than what we are seeing now," said Hidehiko Nishiyama of the Nuclear and Industrial Safety Agency.
Japan has been grappling with a cascade of disasters unleashed by the 9.0-magnitude earthquake on March 11. The quake spawned a tsunami that ravaged Japan's northeastern coast, killing more than 7,600 people and knocking out cooling systems at the Fukushima Dai-ichi nuclear plant, causing the complex to leak radiation.
More than 11,000 people are still missing, and more than 452,000 are living in shelters.
Chief Cabinet Secretary Yukio Edano, meanwhile, insisted the contaminated foods "pose no immediate health risk."
An expert in the United States also said the risk appeared limited and urged calm.
"The most troubling thing to me is the fear that's out of proportion to the risk," said Dr. Henry Duval Royal, a radiologist at Washington University Medical School.
The tainted milk was found 20 miles (30 kilometers) from the plant, a local official said. The spinach was collected from six farms between 60 miles (100 kilometers) and 75 miles (120 kilometers) to the south of the reactors.
Those areas are rich farm country known for melons, rice and peaches, so the contamination could affect food supplies for large parts of Japan.
More tests was being done on other foods, Edano said, and if they show further contamination, then food shipments from the area would be halted.
Officials said it was too early to know if the nuclear crisis caused the contamination, but Edano said air sampling done near the dairy showed higher-than-normal radiation levels.
Iodine levels in the spinach exceeded safety limits by three to seven times, a food safety official said. Tests on the milk done Wednesday detected small amounts of iodine-131 and cesium-137, the latter being a longer-lasting element that can cause more types of cancer. But only iodine was detected Thursday and Friday, a Health Ministry official said.
After the announcements, Japanese officials immediately tried to calm an already-jittery public, saying the amounts detected were so small that people would have to consume unimaginable amounts to endanger their health.
"Can you imagine eating one kilogram of spinach every day for one year?" said State Secretary of Health Minister Yoko Komiyama. One kilogram is a little over two pounds.
Edano said someone drinking the tainted milk for one year would consume as much radiation as in a CT scan; for the spinach, it would be one-fifth of a CT scan. A CT scan is a compressed series of X-rays used for medical tests.
The Health Ministry said iodine levels slightly above the safety limit were discovered Thursday in drinking water samples from Fukushima prefecture. On Friday, levels were about half that benchmark; by Saturday, they had fallen further.
Drinking one liter of water with the iodine at Thursday's levels is the equivalent of receiving one-eighty-eighth of the radiation from a chest X-ray, said Kazuma Yokota, a spokesman for the prefecture's disaster response headquarters.
The trace amounts of iodine were found in Tokyo's water on Friday, the first day since the government ordered nationwide daily sampling due to the nuclear crisis, the Ministry of Education, Culture, Sports, Science and Technology said. A ministry statement said the amounts found did not exceed government safety limits. But tests on water, which for decades were only done once a year, usually show no iodine.
At the Fukushima plant, emergency workers have been struggling to cool the reactors and the pools used to store used nuclear fuel, as well as to put the facility back on the electricity grid.
A replacement power line reached the complex Friday, but workers needed to methodically work through badly damaged and deeply complex electrical systems to make the final linkups without setting off a spark and potentially an explosion. Company officials hoped to be able to switch on the cooling systems Sunday.
Once the power is reconnected, it is not clear if the cooling systems will still work.
A fire truck with a high-pressure cannon pumped water directly from the ocean into one of the most troubled areas of the complex -- the cooling pool for used fuel rods at the plant's Unit 3. Because of high radiation levels, firefighters only went to the truck every three hours to refuel it.
Holes were also punched in the roofs of units 5 and 6 to vent buildups of hydrogen gas, and the temperature in Unit 5's fuel storage pool dropped after new water was pumped in, according to officials with Tokyo Electric Power Co., which owns the complex.
More workers were thrown into the effort -- bringing the total at the complex to 500 -- and the safety threshold for their radiation exposure was raised 2 1/2 times so they could keep working.
Officials insisted that would cause no health damage.
Edano said conditions at the reactors in Units 1, 2 and 3 -- all of which have been rocked by explosions in the past eight days -- had "stabilized."
The reactors and the storage pools both need constant sources of cooling water. Even when they are taken from reactors, uranium rods remain very hot and must be cooled for months, possibly longer, to prevent them from heating up again and emitting radioactivity.
Low levels of radiation have been detected well beyond Tokyo, which is 140 miles (220 kilometers) south of the plant, but hazardous levels have been limited to the plant itself.
People evacuated from around the plant, along with some emergency workers, have tested positive for radiation exposure. Three firefighters needed to be decontaminated with showers, while among the 18 plant workers who tested positive, one absorbed about one-tenth of the amount that could induce radiation poisoning.
Outside the bustling disaster response center in the city of Fukushima, 40 miles (60 kilometers) northwest of the plant, government nuclear specialist Kazuya Konno was able to take only a three-minute break for his first meeting since the quake with his wife, Junko, and their children.
"It's very nerve-racking. We really don't know what is going to become of our city," said Junko Konno, 35. "Like most other people, we have been staying indoors unless we have to go out."
She brought her husband a small backpack with a change of clothes and snacks. The girls -- aged 4 and 6 and wearing pink surgical masks decorated with Mickey Mouse -- gave their father hugs.
The government conceded Friday that it was slow to respond to the crisis and welcomed ever-growing help from the U.S. in hopes of preventing a complete meltdown.
Nishiyama, of the nuclear safety agency, also said backup power systems at the plant had been improperly protected, leaving them vulnerable to the tsunami.
The failure of Fukushima's backup power systems, which were supposed to keep cooling systems going in the aftermath of the earthquake, let uranium fuel overheat and were a "main cause" of the crisis, Nishiyama said.
"I cannot say whether it was a human error, but we should examine the case closely," he told reporters.
A spokesman for Tokyo Electric said that while the generators were not directly exposed to the waves, some electrical support equipment was outside. The complex was protected against tsunamis of up to 5 meters (16 feet), he said. Media reports say the tsunami was at least 6 meters (20 feet) high when it struck Fukushima.
Spokesman Motoyasu Tamaki also acknowledged that the complex was old, and might not have been as well-equipped as newer facilities.
The crisis has led to power shortages and factory closures, and triggered a plunge in Japanese stock prices.
On Saturday evening, Japan was rattled by 6.1-magnitude aftershock, with an epicenter just south of the troubled nuclear plants. The temblor, centered 150 kilometers (90 miles) northeast of Tokyo, shook buildings in the capital.