Science panel affirms cancer risks from very low radiation levels

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Science panel affirms cancer risks from very low radiation levels

 

By H. JOSEF HEBERT

ASSOCIATED PRESS WRITER

 

WASHINGTON -- 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 prominent scientists concluded Wednesday.

 

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 also 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 where

exposure is not harmful, or possibly even beneficial. They said

current risk modeling may exaggerate the health impact.

 

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

 

" 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's School

of Public Health.

 

 

The committee gave support to the so-called " linear, no threshold "

model that is currently the generally acceptable approach to radiation

risk assessment. This approach assumes that the health risks from

radiation exposure declines as the dose levels decline, but that each

unit of radiation - no matter how small - still is assumed to cause

cancer.

 

" It is unlikely that there is a threshold below which cancer are not

induced, " said the report, although it added that at low doses " the

number of radiation-induced cancers will be small. " And it said

cancers from such low dose exposures may take many years to develop.

 

The panel, formally known as the Committee on Biological Effects of

Ionizing Radiation, or BEIR, generally supported previous cancer risk

estimates - the last one by an earlier BEIR group in 1990.

 

Contrary to assertions that risks from exposure from low-level

radiation may have been overstated, the panel said " the availability

of new and more extensive data have strengthened confidence in these

(earlier) estimates. "

 

The committee examined doses of radiation of up to 100 millisievert, a

measurement of radiation energy deposited in a living tissue. A single

chest X-ray accounts for 0.1 millisievert, average background

radiation 3 millisievert a year and a whole body CT scan delivers 10

millisievert..

 

The committee estimated that 1 out of 100 people would likely develop

solid cancer or leukemia from an exposure of 100 millisievert of

radiation over a lifetime with half of those cases being fatal.

 

The report noted that exposure from a whole body CT scan is much

higher than a normal X-ray, and it raised concerns about the frequency

in which such medical diagnostics should be used.

 

While medical radiation is often done for good reasons, said Monson,

" exposure to unnecessary radiation should be avoided. "

 

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