There are few environmental dangers that spook people more than radioactivity. And there is surely no country in the world that comes by that fear more rightly than Japan — which, alone among nations, has felt the pain of a nuclear conflagration first hand. So it’s understandable that the Japanese public is terrified by the danger posed by their crisis-sticken nuclear power plants. But is all the fear justified? Is the risk as great as it seems? Yes — with caveats.
There are four kinds of isotopes that are likeliest to be emitted by the crippled Fukushima Daiichi plant, as well as the other three that have been taken offline: iodine-131, cesium-137, strontium-90 and plutonium-239. Iodine-131 is, in many ways, the most dangerous of the four, because it can lead to cancer — specifically thyroid cancer — in people exposed to it in the shortest time. Epidemiologists estimate that there were 6,000 to 7,000 cases of thyroid cancer that never would have occurred as a result of the 1986 Chernobyl explosion in Russia. Most of the victims were people who were children at the time of their exposure and developed the disease later.
Strontium and cesium are the next up the danger scale. While iodine tends to concentrate its damage to the thyroid, those two are not nearly so selective. “Strontium is chemicaly similar to calcium,” says Dr. Ira Helfand, a board member for Physicians for Social Responsibility. “So it gets incorporated into bones and teeth and can stay there, irradiating the body, for a long time.” Strontium is most commonly linked to leukemia.
Cesium works in other ways, behaving more like potassium when it’s inside the body — which means it circulates everywhere and can contaminate anything. Cesium doesn’t linger as long as strontium does — it gets excreted in urine over the course of months or years — but that’s more than long enough to cause cancer of the liver, kidneys, pancreas and more. “Basically all of the solid tumors,” says Helfand.
More troubling, cesium and strontium linger not just in the body, but in the environment. Strontium has a half-life of 29 years; cesium’s is 30. A radioactive isotope is generally considered dangerous for 10 to 20 times its half life, which in these cases tops out at about 600 years.
Most worrisome of all is plutonium-239 — for a number of reasons. First of all, the vast majority of a fuel rod is made of plutonium, which means there’s just more of it in play. What’s more, says Helfand, “It’s extraordinarily toxic.” Plutonium exposure usually comes from inhalation rather than ingestion, so it’s mostly associated with lung cancer. What’s more, plutonium’s half life is 24,000 years, which means anything released in Fukushima today could be around at dangerous levels for up to half a millon years.
The key question is what, exactly, constitutes a dangerous level — and here is where fear and science part ways a little bit. One of the most talked-about numbers being batted about yesterday was that the radiation levels outside the reactor were eight times normal. But, says Helfand, “eight times is not something you would think of as a great public health hazard. It would take a fair amount of time to get a dangerous whole-body dose.” Still, if some of that exposure was to iodine-131, it might still be enough to cause thyroid cancer.
More alarming still was the radiation level inside the Fukushima control room, which was reported to be 1,000 times above normal. Even that might not be immediately fatal, depending on what normal is, but it wouldn’t do to hang around and find out.
Radiation levels are measured in units called rems — for “Roentgen equivalent man.” The average background exposure that most people absorb simply by living on Earth is 130 to 150 millirems (mrem, or thousandths of a rem) per year. The figure may change depending on location and elevation. Such a low does does not do most people much harm, but it may well account for some of the cases of cancer that appear in the general population that have no other evident causes like smoking.
People exposed to 100 full rems begin to experience nausea, one of the first signs of radiation sickness. At 200 rems and up you suffer loss of hair, suppression of the immune system, vomiting and bleeding. A dose of 300 rems is fatal to about 50% of people exposed. At 600 rems, nobody survives. In some cases, the timing of the dosing matters. It’s much worse, for example, to absorb 300 rems in an hour than over the course of a year.
For the Japanese, the best precaution is the one that the government is already putting into play: evacuation. Wherever it is that a power plant is leaking radiation, you want to be somewhere else — preferably a very distant somewhere else. Doses of nonradioactive iodine can also help prophylactically. There is a limit to how much of any kind of iodine the body can absorb and if you reach your maximum with the safe kind, you shut out the dangerous kind. But it can also be risky to take iodine without knowing the right dose and having it administered by a professional. “There are government guidelines that explain how it must be done,” says Helfand.
It’s a hard truth of the modern age that controlled nuclear power may be essential for an industrial economy that doesn’t have a lot of other energy resources. But, as the Japanese are tragically learning again, when the radioactive genie gets out of the bottle, it can be awfully hard to stuff it back inside.