Food Contamination Observed up to 90 miles from Fukushima

March 19, 2011

NYTimes reports:

Yukio Edano, the chief cabinet secretary, said that spinach and milk were the only products found to have abnormally high radiation levels. The level of radioactivity found in the spinach would, if consumed for a year, equal the radiation received in a single CAT scan, he said, while that detected in milk would amount to just a fraction of a CAT scan.

“These levels do not pose an immediate threat to your health,” Mr. Edano said, adding that the Health, Labor and Welfare Ministry would provide additional details. “Please stay calm.”

The milk with the elevated radiation levels was found in Fukushima Prefecture on farms about 19 miles from the nuclear plants. The contaminated spinach was found one prefecture to the south, in Ibaraki Prefecture, on farms 60 to 90 miles south of the plants.

Food safety inspectors said the iodine-131 in the tested milk was up to five times the level the government deems safe, and the spinach had levels more than seven times the safe level. The spinach also contained slightly higher than allowable amounts of cesium-137.

The issue of radiation exposure is more complex than a mere number can express.

Different radionuclides emit different types of radiation, and may be absorbed in different ways by the body.

For instance, Reactor number 3 is fueled by mixed oxide, or “MOX” fuels, which includes plutonium.  Plutonium is an alpha emitter, and alpha waves are relatively easy to shield, even a piece of paper is enough to stop them. However, if inhaled the extremely energetic particles can lodge in the lungs and deliver their radiation directly to sensitive tissue. Radioactive iodine, absorbed from milk products, seeks out the thyroid gland – but it makes a big difference whether one is an adult or a child, children’s thyroids absorb a greater dose per weight, and because they are developing, can sustain more damage.

The most sensitive of all are, of course, developing fetuses.

Boing Boing has an informative post on this issue:

The problem is that this system implies that all radioisotopes are created equal—That there’s no difference between 520 picocuries of Potassium-40 and a similar intake of, say, radioactive iodine. And that simply isn’t true. I contacted Geoff Meggitt—a retired health physicist, and former editor of the Journal of Radiological Protection—to find out more.

Meggitt worked for the United Kingdom Atomic Energy Authority and its later commercial offshoots for 25 years. He says there’s an enormous variation in the risks associated with swallowing the same amount of different radioactive materials—and even some difference between the same dose, of the same material, but in different chemical forms.

It all depends on two factors:
1)The physical characteristics of the radioactivity—i.e, What’s its half-life? Is the radiation emitted alpha, beta or gamma?
2) The way the the radioactivity travels around and is taken up by the body—i.e., How much is absorbed by the blood stream? What tissues does this specific isotope tend to accumulate in?

CBC reports that Japan has banned exports of food from the affected areas.

2 Responses to “Food Contamination Observed up to 90 miles from Fukushima”

  1. […] to remember, talk of “radiation levels” is somewhat meaningless without context – what kind of radiation? what kind of nuclide involved (long lived or short lived, […]

  2. […] Again, comparing radiation “levels” is treacherous. Chernobyl’s fire blasted volumes of material high into the atmophere and spread it globally. Fukushima is unique in that it is directly on the ocean, and prevailing winds have carried the majority of releases “away” – out to sea. The effects on ocean food chains are only now beginning to be examined. […]

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