Tokyo (CNN) -- Acknowledging what he called a "difficult" situation, Chief Cabinet Secretary Yukio Edano said Friday that the government was helping to facilitate movement from the zone between 20-to-30 kilometers of the Fukushima Daiichi nuclear power plant.

Edano said that authorities will help provide transportation for what he deemed a "voluntary evacuation," in part in response to growing demand among individuals hoping to get further away from the stricken plant. A primary challenge for that region, he said, has had to do with commerce -- namely, the difficulty in getting needed materials in and out of the area.

This is not a mandatory evacuation, the cabinet secretary noted. Still, he said that he couldn't rule such an order out in the future -- if measured radiation in that zone rises to a level deemed unsafe for people.

The governments of other nations, including the United States and England, have urged their citizens to stay 80 kilometers (50 miles) or more outside the embattled power plant due to worries about the past, present and future release of radiation into the air. But Japan has yet to go that far, telling people to leave if they're within 20 kilometers and to try to stay indoors if they are within the 30-kilometer radius.

Still, even those well outside the plant are being affected by the radioactive emissions.

Traces of radioactive iodine tied to the plant have been detected as far away as Sweden and the United States, though in every case authorities have said those levels are far below what's considered harmful to humans.

But in Japan, radioactive materials detected in water, food and elsewhere has already had a major impact -- with the number of banned food items, especially, growing regularly to affect not only consumers but especially those who have made a living farming and selling it.

Tests have showed radioactive materials at levels exceeding legal limits in 12 types of vegetables grown near the nuclear plant, according to Japan's health ministry.

Authorities found high levels of iodine-131 and cesium-134,137 in Mizuna -- a Japanese mustard plant -- shipped to Kyoto from Ibaraki Prefecture on Wednesday.

Ministry officials said the discovery is not at levels that would harm human health, but have instructed distributors and buyers to remove the vegetable from stores. Consuming 20 grams of the vegetable would be the equivalent of 1/400th the radiation of a stomach X-ray, officials said.

Prime Minister Naoto Kan has also asked Ibaraki Prefecture to suspend shipments of raw milk and parsley, according to Chief Cabinet Secretary Yukio Edano.

The government of Fukushima Prefecture also told residents not to eat leafy vegetables, he said.

Radiation levels in the food would not cause health problems right away, Edano said, but if they rise, they may reach levels risky to human health.

The decision to prohibit produce sales is another potentially devastating blow to a part of northeast Japan hit by the earthquake and tsunami.

Fukushima ranks among Japan's top producers of fruits, vegetables and rice. Ibaraki, south of Fukushima, supplies Tokyo with a significant amount of fruits and vegetables and is the third-largest pork producer in the nation.

"This is our livelihood," a Fukushima farmer told Japanese television network TV Asahi. "It's a huge problem that we are unable to ship all our produce. We raised (this produce) with our own hands. It's unbearable that we would have to throw it all away."

On Thursday, Edano indicated that the government was prepared to compensate farmers and others whose income was threatened by the effects of the radiation spikes. He said that it wasn't yet clear how that might happen, whether it was buying up the existing crops or some other form.

That same day, residents of Tokyo got some good news after new tests showed that the levels of radioactive iodine in the city's tap water dropped to levels considered safe for babies.

Tests at the Kanamichi Water Purification Plant, which provides water to 23 wards in Tokyo as well as five other cities, showed 79 becquerels of radioactive iodine per kilogram of water, the city government said in a news release.

A becquerel is a measurement of radioactive intensity by weight.

This is below the 100 becquerel level, the maximum considered safe for infants ages 1 and younger. And it is well below the 210 becquerel reading measured Tuesday night.

As a result, Tokyo Gov. Shintaro Ishihara told reporters Thursday that he was lifting the recommendation that babies not drink tap water -- though bottled water will continue to be distributed to households with youngsters, as was announced hours earlier when the readings were still considered high.

Shintaro said that 240,000 bottles were given out Thursday, with a similar number set to be distributed on Friday.

Test results released Thursday afternoon showed two water treatment plants in the Chiba prefecture still have radioactive iodine levels above the legal limit for infants.

The Chiba Nogiko water treatment plant had a measure of 220 becquerels of radioactive iodine per kilogram of water, while the Kuriyama facility had a reading of 180 becquerels, according to a statement from Chiba's waterworks bureau.

These two plants provide water for the city of Matsudo, about 20 miles northeast of Tokyo.

Companies that package bottled water are being encouraged to increase their production, Edano has said.

And on Thursday, Japan's leading obstetrics and gynecological organization said that pregnant and nursing women should continue to drink tap water -- even if the levels of radioactive iodine rise up to 500 becquerels. Over 280 days, the length of a typical pregnancy, that intake of radioactive iodine would still not be considered overly harmful, according to the group.

The society contends, in a news release, that the harm from not drinking water and dehydrating is far greater for mothers than consuming tap water at their current levels.

Such assessments appeared to have little effect on Tokyo residents, who snapped up bottled water in droves.

Grocery store owner Seiji Sasaki said he had 40 cases of water in his store, but they were gone quickly.