After the 1986 Chernobyl nuclear disaster, radiation contaminated 3 million acres of farmland. Up to 9,000 died or will die from thyroid cancer after drinking milk laced with radioactive iodine, according to World Health Organization estimates.

The radiation leaks at Fukushima don’t come close to that of Chernobyl. Still, Japanese officials admit their food chain is also contaminated with harmful levels of radiation, in some cases up to 90 miles from the nuclear site.

"You have to make sure that if there's a question about any aspect of the food supply that that part of the food supply doesn't reach consumers. That's the No. 1 objective," says Brian Wright, an agricultural economist at the University of California at Berkeley.

There are two risks: direct contamination from the radioactive fallout, like water supplies; or indirectly, when consumers eat foods from livestock consuming contaminated grasses or feed.

"I would say it's going to be a long time before you'll be able to eat either animals raised in that area or plants," says University of California Berkeley plant biologist Peggy Lemaux.

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Over the weekend, Japan closed 19 dairy farms in the Fukushima prefecture after finding milk with five times the legal limit of radiation. They also halted the spinach harvest in neighboring Ibaraki prefecture after finding radiation seven times higher than safe. The Gunma and Chiba provinces closer to Tokyo also found elevated levels of radiation in kakina and chrysanthemum, both widely consumed local leafy vegetables.

Gamma rays from cesium can break down internal organs, while the intake of radioactive iodine can cause thyroid cancer. Radioactive iodine has a half-life of about 8 days and decays naturally within a matter of weeks. Cesium 137 and strontium can last for decades.

"We won't know until there are measurements taken on terrestrial environments, grasses, plant material and in coastal environments to see how those radioactive materials are working their way into the food chain," says marine biologist David Caron.

Another concern is cattle and fish, especially exports of high grade Kobe beef and sushi. A cash-strapped Japan needs all exports and foreign currency it can get. Yet consumer fears -- legitimate or not -- are expected to damage those exports.

"There will be a demand for certified safe sushi and other fish and that might mean it will increase the cost of those fish for a while," says Wright.

Japan imports most foods but produces 80 percent of their own vegetables and rice. If forced to import more, it will cost consumers more. Experts say the real worry comes in the following days, as more epidemiologists get into the fields to test more crops in more places.

More than 130,000 people lived in the 18-mile 'hot zone' around the plant, but hundreds of thousands more are beginning to move south, away from the reactors.