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KIEV, Ukraine—In 1986 the worst nuclear accident in history took place when reactor No. 4 in the power plant at nearby Chernobyl exploded, spewing large amounts of radiation into the atmosphere. Now, almost 25 years later, the lesson that scientists are learning is that radiation might not be the only cause of this disaster's long-term medical effects, and perhaps not even the main one.
The explosion immediately killed two workers, and 28 firemen and nuclear power plant staff died from acute radiation syndrome in the three months afterward. The disaster also released a plume of radioactive fallout that contaminated more than 200,000 square kilometers of Europe, roughly three quarters of which lies in the former Soviet republics of Belarus, Russia and Ukraine. Hints of fallout were also detected elsewhere in the Northern Hemisphere, reaching Japan in six days and the U.S. in 10, but in most cases only negligible amounts were found.
Investigators of the medical consequences of the disaster must contend with both the very real effects of the tragedy and the desire to blame every bad medical outcome on Chernobyl. A major challenge lies in figuring out how much fallout was released during the event. Estimates range from roughly 5 percent of the radioactive material in the reactor, which is what is usually cited, to 95 percent, says civil and environmental engineer Eric Schmieman of Battelle Memorial Institute. It is difficult to make a firmer assessment because the contemporary hazards at the Chernobyl site prevent safe surveys.
Therefore, it remains difficult to know who was exposed to radiation from the event and how large a dose they received, and then to figure out the fallout's real effects. A 2005 report from the Chernobyl Forum, which is made up of the International Atomic Energy Agency (IAEA) and seven United Nations agencies, along with Belarus, Russia and Ukraine, estimated that five million people currently live in contaminated areas of those three countries. In addition, 350,000 workers helped contain and clean the accident, and roughly 240,000 of these "liquidators" worked in key activities at the reactor and in the 30-kilometer "exclusion zone" surrounding the accident. (Later, the number of registered liquidators rose to 600,000, although only a small fraction of these were exposed to high levels of radiation, the report noted.)
There is heated debate about how many deaths should be linked to the tragedy and its fallout. The IAEA's 2005 Chernobyl Forum report estimated that 4,000 such casualties might occur among the 600,000 people they considered . In response, the European Green Party commissioned an alternative study released in 2006, "The Other Report on Chernobyl," or the TORCH report, which estimated 30,000 to 60,000 extra cancer deaths.
"Radiation is the obvious and even exaggerated culprit with Chernobyl," says health physicist Vadim Chumak at the Academy of Medical Sciences of Ukraine's Research Center for Radiation Medicine in Kiev. It's not that simple, he says, adding: "One must consider a whole variety of factors when it comes to Chernobyl."
The problem with studying the effects of this fallout is that the world is bathed with naturally occurring low-level radiation, with sources ranging from long-distance air travel to plasma televisions. There are other confounding factors researchers must cope with as well, such as industrial pollution and differences in lifestyle and health care. In addition, they have to deal with the fact that looking for Chernobyl-linked problems might turn up ones that might have escaped medical attention otherwise but had nothing to do with the disaster. For instance, when it comes to victims of the atomic bombs dropped on Hiroshima and Nagasaki, those who did not die of acute radiation syndrome or the widespread lack of medical care after the attacks lived longer than other members of their generation because they received government-sponsored medical attention for the rest of their lives, Chumak says.