Thursday, June 30, 2005


The preponderance of scientific evidence shows that even very low doses of radiation pose a risk of cancer or other health problems and there is no threshold below which exposure can be viewed as harmless, a panel of scientists concluded yesterday.

The finding by the National Academy of Sciences panel is viewed as critical because it addresses radiation amounts commonly used in medical treatment and is likely to influence radiation levels the government will allow at abandoned nuclear sites.

The nuclear industry, as well as some independent scientists, have argued that there is a threshold of very low-level radiation at which exposure is not harmful, or possibly even beneficial. They said current risk modeling may exaggerate the health effects.

The panel, after five years of study, rejected that assertion.

“The scientific research base shows that there is no threshold of exposure below which low levels of ionized radiation can be demonstrated to be harmless or beneficial,” said Richard R. Monson, the panel chairman and a professor of epidemiology at Harvard School of Public Health.

The committee gave support to the “linear, no threshold” model that is the generally acceptable approach to radiation risk assessment. This approach assumes that the health risks from radiation exposure decline as the dose levels decline, but each unit of radiation — no matter how small — still is assumed to cause cancer.

“It is unlikely that there is a threshold below which cancers are not induced,” the report said, although it added that at low doses “the number of radiation-induced cancers will be small.”

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