POSTED 11 AUGUST 2005
In the bombs' aftermath Amid the astonishing devastation wrought by the two atomic bombs that ended World War II, it quickly became clear that the twin graveyards of Hiroshima and Nagasaki -- where the bombs killed at least 200,000 -- could say a lot about the long-term health effects of ionizing radiation.
Photo: Ca. 1945, NARA
When the Atomic Bomb Casualty Commission started studying Hiroshima and Nagasaki, it focused on searching for genetic abnormalities caused by radiation. By 1975, when the Radiation Effects Research Foundation (RERF) was formed, the focus had shifted to cancer.
We asked Dale Preston, who retired a year ago as chief RERF's department of statistics and is now a radiation-health consultant in Northern California, to sum up the lessons from Japan, and he told us radiation is causing a "lifelong increase in cancer risk, for people who were exposed, that is largely proportional to dose." But the risk is not as large as many people think. For example, between 1950 and 2000, among 48,000 bomb survivors with elevated radiation exposures (at least 5 milliseivert), there were about 5,900 solid (not blood) cancer deaths, of which only 480 cases could be blamed on radiation exposure, Preston said -- hardly a radiation-related cancer epidemic.
Almost half of the 200 deaths from the blood cancer leukemia among survivors with elevated radiation exposures were due to the radiation exposure from the bombs. Most of these radiation-associated leukemia deaths occurred in the decade after the bombings. This early surge in leukemia deaths has largely abated, Preston says.
Preston has also taken part in studies on Mayak, an old Soviet plutonium plant in the Ural Mountains in Central Russia, where large numbers of heavily-exposed workers have elevated rates of cancer. Downstream from the plant, along the radiation-polluted Techa River, 30,000 villagers got "a long-term, chronic exposure, and we are seeing some indication of elevated risk" of cancer, Preston adds.
Although the Hiroshima-Nagasaki studies began by focusing on genetic damage, Preston says, "we haven't really found any compelling evidence of inheritable gene effects in the survivors. This doesn't mean that radiation is not causing mutations in the germ line [reproductive] cells. It may be that the human reproductive and gestational processes do a pretty good job of dealing with the heritable mutations caused by radiation."
It ain't cancer. Does it count?
Our discussion has focused on cancer, and to some extent on birth defects, because these were the first conditions to be compellingly linked to radiation. But could ionizing radiation cause other deaths? Perhaps. For example, the RERF data show what Preston calls a surprising number of "non-cancer risks" like heart disease and stroke, in a pattern suggesting they are associated with radiation. Among people exposed to at least 5 millisieverts of radiation in Hiroshima and Nagasaki, RERF counted about 18,000 non-cancer deaths, and about 250 of those were associated with radiation exposure, Preston told us. (Need help with radiation's confusing measurements?
The idea that radiation is causing non-cancer deaths is controversial. The International Commission on Radiological Protection, in a recent draft report, said, "Risks of non-cancer disease at low doses remain uncertain and no specific judgment is possible."
And the mechanism for such effects remains unknown. "No-one knows, it's an unexpected finding," Preston acknowledges. Two possibilities, he says, include a "chronic, sub-clinical inflammatory response" caused by the exposure, or a persistent immune-system disturbance that is "very subtle but can still be detected 50 to 60 years after the exposure."
If Hiroshima and Nagasaki show the effects of instantaneous radiation exposure, the nuclear power-plant explosion at Chernobyl offers insight into long-term exposure.
Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive