Why take iodide for radiation poisoning?

The picture above is an aerial view of the Fukushima Daiichi power plant. As we all know, it was knocked about in the huge earthquake that hit Japan yesterday morning. At the time of this writing, it seems like there was some radioactive material leakage at the Fukushima Daiichi power plant, but it may have gone down. There’s a lot of confusion about what’s going on, not surprisingly. It does seem like authorities are handing out iodide tablets as a precaution against radiation poisoning, however.

So why would taking extra iodide protect against radiation poisoning? To answer that, we need to take a pretty big step back.

Many nuclear reactors get their energy by smacking uranium-235 with a neutron, called fission. And in a turn of events that is both crazy and amazing, a single act of fission can create more than 200 million times the energy of the neutron that kicked it off in the first place. I’m not going to go into why here, but it has to do with the famous Einstein equation.

So when uranium-235 decays, it gets broken into a lot of smaller fragments. One of these is iodine-131. It’s also radioactive. Out of the most common fission products of uranium, iodine is the only one that’s present naturally in our bodies.

There are actually fourteen major radioactive isotopes of iodine. The majority of them are not considered dangerous, because they have very long half-lives. That’s the time it takes for half the radioactive material in the element to decay.

For example, iodine-129 has a half-life of 15.7 million years. So its decay might be something like this:

Blam!…wait an extremely long time…Blam!…wait an extremely long time…etc.

However, the half-life of iodine-131 is 8 days. So it may look something more like this:

Blamblamblamblamblamblamblamblamblamblamblamblamblamblamblam
blamblamblamblamblamblamblamblamblamblamblamblamblamblamblam!

I’m simplifying here, but you get the general idea: iodine-131 has the potential to do a lot more damage to the body, because it gives off more radiation in a short period of time.

And where it’s going to do that damage is mostly in the thyroid.

That little butterfly-looking thing in your neck is the only part of the body that can absorb iodine. It pulls it out of food and, along with the amino acid tyrosine, converts it into the hormones thyroxine (T₄) and triiodothyronine (T₃).

T₃ and T₄ go off into the blood stream and the rest of the body where they oversee the conversion of oxygen and calories to energy. Every single cell in the body relies on these hormones to regulate their metabolism.

So imagine if the iodine absorbed by the body were radioactive. That would be way, way bad.

Triiodothyronine and thyroxine: hot or not?

Iodine is pretty volatile (in a very purple way). So if a nuclear reactor were to leak, iodine-131 might be in the air. Which people might breathe in. Which could get into their thyroids. Which could cause radiation poisoning in the short term. In the long term, breathing radioactive iodine can cause thyroid cancer, especially in kids.

To minimize the damage, people who may be/have been exposed to radiation from a power plant can take iodide pills. These work by saturating the thyroid with nice, non-radioactive iodide. That way, if any radioactive iodine does come along, the body won’t absorb it–the thyroid can only absorb a finite amount of iodine at a time.

If people can get these pills 48 hours before or eight hours after radiation exposure, it can reduce thyroid uptake of iodine-131 and decrease the risk of radiation-induced thyroid cancer.

[ETA: I do want to point out that this will ONLY protect against internal iodine radiation poisoning. Not radiation from cesium-137 and strontium-90, extremely dangerous fission products of uranium-235.]

These pills contain about 100 milligrams of potassium iodide. You can overdose on iodine, although it takes several grams. But burning of the mouth, throat, and stomach, fever, nausea, vomiting, diarrhea, and/or a weak pulse may be preferable to getting cancer later.

This treatment was used in the the 1986 Chernobyl nuclear reactor accident. There were fewer cases of childhood thyroid cancer in areas that had access to iodine tablets, compared to areas that didn’t, or got them too late (pdf link).

Hopefully, people near the Fukushima Daiichi power plant will have access to iodide pills, and be able to get the hell out of there. Radiation’s not something you want to mess around with, especially if you’re pregnant or a kid.

UPDATE: There are now rumors that one of the reactors has exploded. Follow Reuters for breaking news, and keep your fingers crossed.

Photo credit: Digital-Globe imagery, Wikimedia Commons.