Michael Penn / Juneau Empire / AP
Gus van Vliet of the Air Quality Division of the Alaska Department of Environmental Conservation works on a radiation detection monitor that is on the roof of the Floyd Dryden Middle School in Juneau, Alaska.
Last updated 9:30 p.m. ET:
Americans are being exposed to almost twice as much radiation as they used to get — but not because of fallout from nuclear accidents in Japan or elsewhere. Medical tests, not nuclear accidents, account for the dramatic rise in our radiation exposure. Based on today's readings, the radiation coming from the troubled Fukushima Dai-ichi nuclear complex rates barely a blip.
The Environmental Protection Agency said the readings from its nationwide network of atmospheric air-sniffing sensors showed "typical fluctuations in background radiation levels" that were "far below levels of concern." (You can check the updates on this Web page.) The initial U.N. radiation counts from California were "about a billion times beneath levels that would be health-threatening," one diplomat told The Associated Press.
In a later statement, the EPA and the U.S. Department of Energy said none of their detectors picked up "any radiation levels of concern."
The agencies also provided more details on the U.N. count, which was detected by a radiation-sniffing station in Sacramento and fed into the Comprehensive Nuclear Test Ban Treaty Organization's monitoring network. For the geeks out there, the level was 0.0002 disintegrations per second per cubic meter of air, with radioactive isotopes of iodine, tellurium and cesium represented in the mix.
A similar reading was reported by the Department of Energy in Washington state: 0.1 disintegrations per second per cubic meter of air, attributed to xenon-133.
"The doses received by people per day from natural sources of radiation — such as rocks, bricks, the sun and other background sources — are 100,000 times the dose rates from the particles and gas detected in California or Washington state," the agencies said in their joint statement.
That would imply that the fallout packed a punch on the order of 0.00003 millisieverts a year. In comparison, a dental X-ray amounts to 0.01 millisieverts, and a full-body CT scan can deliver 10 millisieverts. It used to be that our average exposure was 3 millisieverts a year from natural sources and 0.6 millisieverts from extra sources (such as X-rays). Today, the average is more like 3 plus 3 or more.
Researchers have found that increased cancer risk is associated with extra radiation exposures ranging from 10 to 100 millisieverts, depending on how spread out the doses are and who's conducting the study. When you're exposed to a 1,000-millisievert dose over a short period of time, you're likely to experience the symptoms of radiation sickness. And 10,000 millisieverts is lethal.
At one point this week, the readings at Fukushima rose to 400 millisieverts per hour. Two and a half hours of that would make you sick. A day would kill you.
All this makes 0.00003 millisieverts sound pretty puny. It's true that these are merely the first U.S. readings to be announced, and if significantly more radiation is released in Japan, those numbers might go up. But they won't go up by a factor of a million or a billion — which is why even those who have sounded grave warnings about the radiation threat say that U.S. residents needn't fear the winds coming from the west.
"I don't think the people in California need to be overly concerned with it, other than the fact that the people in Japan are facing disaster," said David Lochbaum, director of the Nuclear Safety Program at the Union of Concerned Scientists, a watchdog group.
For the Japanese, the situation could get more dire. Here are some of the factoids from the UCS briefing, as well as from my talks with other experts:
- If the nuclear fuel rods stored at the Fukushima complex were to break down and catch fire, it would take just hours for a cloud containing radioactive fallout to rise from the site, Lochbaum said. "Cesium would be the worst, but there's an awful lot of other radioisotopes that would follow along. You have krypton. There's just a whole litany of things that are in that spent fuel that are posing the risk," he said.
- Aerial readings suggest that the worst hazardous contamination has not spread beyond the 19-mile-radius (30-kilometer-radius) zone established by the Japanese government. A fuel-rod fire would spread significant fallout farther, but not all the way to America, said Edwin Lyman, a senior staff scientist at UCS. "It's still my judgment that most of the fallout would be within several hundred miles of the site," he said. "There would be hot spots, you know, potentially further away, like we did see in Chernobyl, but still, the dilution over the course of thousands of miles would be significant."
- Even with today's upgrade in Fukushima's danger level, Chernobyl still ranks as the world's worst nuclear accident. But in terms of its fallout effect for the United States, the nuclear weapons tests from a half-century ago loom even larger. "What most people don't realize is that only 6 percent of the cesium floating around out there is from Chernobyl," said Fred Mettler, a professor emeritus of radiology at the University of New Mexico who has studied the effects of the 1986 disaster. More than 90 percent of the cesium contamination has been traced to weapons testing, he said.
Update for 8:10 p.m. ET: Researchers from the University of Maryland are drawing up computerized projections showing how radiation from the Fukushima nuclear site should be transported through the atmosphere. Check out this Web page for the latest projections, and this news release for an explanation of the projections.
Update for 9:30 p.m. ET: The figures from the EPA and the Department of Energy have been updated to reflect the latest radiation readings.
More on the disaster in Japan:
- Robot scouts en route to Japan
- Radiation risk can be hard to assess
- Is it time for the Chernobyl option?
- U.S. military detects more radiation
- What is Japan doing to fix reactors?
- If there's a meltdown, then what?
- Q&A: Clearing up nuclear questions
- Cosmic Log archive on the Japan crisis
- Special report on the disaster in Japan
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