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msnbc.com contributor
updated 3/28/2011 6:40:22 PM ET 2011-03-28T22:40:22

Each day it seems there’s more scary news from the stricken Japanese reactor. Monday brought the dreaded "p"-word: measurements from the reactor site turned up signs of plutonium leakage.  

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Whenever there’s a discussion about the dangers of nuclear power, people always bring up plutonium because it sticks around for a long time — hundreds of years, in fact. That sounds a lot scarier than the 30-year half life of cesium and the 8-day half life of radioactive iodine.

But experts say that plutonium isn’t the most dangerous of the isotopes seeping out of the reactor. Over the short term, radioactive iodine may be the most worrisome, they say.

“In reactor accidents iodine-131 comprises the vast majority of radioactive material,” said Yuri Nikiforov, a professor of pathology at the University of Pittsburgh Medical Center. “It’s easy to inhale and it can get into the soil and it can contaminate vegetables and milk.”

Radioactive iodine can blow the farthest
Because it’s the lightest of the radioactive elements spewing out of a damaged reactor, it can blow the farthest and therefore affect the most people, Nikiforov adds. It tends to accumulate in the thyroid, which is why radioactive iodine exposure can increase the risk of thyroid cancer.

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Still, Nikiforov says, radioactive iodine is the shortest lived of the radioisotopes seeping from a reactor, so if you can avoid eating contaminated food for a few weeks, you’ll be fine.

Plutonium sticks around for a lot longer, but it’s very heavy so it’s not going to blow far from the reactor site. You could possibly develop lung cancer from inhaling large quantities of plutonium, says Andrew Maidment, an associate professor of radiology and chief of physics and radiology at the University of Pennsylvania.

“Plutonium acts upon the lungs the same way as radon. At low exposures, plutonium is considered safe, just like radon," Maidment says. “It is only at continuous high doses that concern arises.”

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There is some evidence that plutonium can raise the risk of lung cancer, says Nikiforov. “It’s been shown that miners who have been exposed to plutonium, have a slightly higher risk of lung cancer compared to the average person,” he explains.

As for cesium-137, a third radioisotope that’s been identified in fallout from the Japanese reactor, it’s effects are pretty much in-between. It’s heavier than iodine-131, but lighter than the plutonium isotopes, Nikiforov says.

“There was considerable contamination around Chernobyl by cesium,” Nikiforov says. “But not as far from the site of the accident as with the iodine — less than 100 miles."

Cesium tends to build up in the muscles, but so far nobody has documented a heightened cancer risk in these tissues, Nikiforov says.

Although there are other radioisotopes that can result from a nuclear reactor accident, such as strontium, these haven’t been reported in Japan. Strontium was found near Chernobyl, but that may be because the type of fuel used in that reactor was different Nikiforov says.

Ultimately, people should be reassured that the levels of plutonium and cesium found around the reactor site are low, Maidment says.

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