The worried person’s guide to the effects of radiation

I once knew a student who swallowed radioactive iodine. We (I was a student at the time, too) used radioactive iodine as a tracer for various experiments — it came in a little vial inside a lead container and the student decided to remove some by sucking it into an open pipette. Why she swallowed it is beyond me. The thyroid gland contains a marvelous molecular pump that pulls iodine from the bloodstream into the thyroid, where it is used to make thyroid hormone. So it was no surprise that the Geiger counter we put to her neck was soon screaming. Not a sedate click-click-click but a jet-engine roar. We calculated how much radioactive iodine she had swallowed and realized that she was not going to die. She was given non-radioactive iodine to clog the molecular pump and she excreted the radioactive stuff, with no apparent harm. Whether she got thyroid cancer later in life, I do not know.Why was she not immediately harmed by such a blazing dose of radiation? Some answers lie in the nature of radioactivity, which decays, and in the extraordinary capacity of human cells to repair radiation damage. Almost all elements have radioactive forms, but let’s stick with iodine, currently being released from the Fukushima nuclear power plant. An iodine atom has 53 protons and 74 neutrons in its nucleus and is called I-127 (53+74). It is stable — an atom of I-127 will still be iodine in a million years. In nuclear reactors like Fukushima, among the fission products of uranium-235 are iodine-131 and cesium 137, which accumulate in the reactor until there is a breach. I-131 looks like iodine to the thyroid gland, but with four more neutrons in its nucleus, it is unstable and decays such that half is gone in eight days, forming harmless xenon. Each decaying atom releases a beta particle (the actual radiation) that could have smashed into our student’s DNA and mutated it. Studies in the 25 years since Chernobyl suggest that initial high doses of radioactive iodine caused many cases of thyroid cancer in children, who are more susceptible than adults. Avoiding contaminated produce and, if necessary, taking iodine pills should solve this problem in Japan. The levels of iodine-131 in the United States resulting from Fukushima are detectable but are a tiny fraction of the normal background radiation. Levels would have to increase by 5,000-fold to cause concern. It’s the cesium-137 that is the problem for the unfortunate northern Japanese because it has a half-life of 30 years. Cesium emits a beta particle and a more energetic and dangerous gamma particle during its decay. Most of the cesium and iodine produced by the Fukushima plant has blown out to sea, but some has contaminated the land, which could remain out of use for decades — as at Chernobyl. Contamination may be spotty so that some areas can be reclaimed. Unlike iodine, cesium disperses through the body, but does not linger there, and in serious cases there are drugs to help flush it out. The Fukushima reactors are still in a dangerous state (as of May 12) and it is hard to tell how much iodine and cesium they are still releasing, but that is a critical question.The natural environment emits radiation and we are constantly exposed, whether to ultraviolet light on a sunny day or to cosmic rays. No life would have evolved on earth if cells did not have the capacity to repair the damage to their DNA caused by radiation. My colleague, Lorraine Symington, who studies DNA repair for a living, told me that our iodine-sucking student of long ago surely sustained breaks in the DNA in her thyroid, but these were stitched back together by repair mechanisms. Some of the student’s thyroid cells probably had damage that was too severe to repair and committed suicide by a mechanism called apoptosis. Apoptosis is the body’s way to make sure damaged cells do not become cancer cells. That cancer can result from a failure to repair DNA is known from inherited diseases in which DNA repair genes are mutated.The radiation from Fukushima will not hurt us. Our concerns should be with the Japanese, especially those workers struggling to control these ruined plants, who are at risk. Radiation can be a superb medical tool, but we should worry about the radiation we inflict on ourselves including ultraviolet light (use that sunblock) and the non-essential use of CAT scans (ask if one is really necessary). As to our own aging nuclear power plants, we should calmly apply what has been learned in Japan. Richard Kessin, Ph.D., is professor of pathology and cell biology at Columbia University. He and his wife, Galene, live in Norfolk. He can be reached at rhk2@columbia.edu.