Women apparently face almost twice the risk that men do of developing cancer after exposure to low-level radiation, according to a long-awaited study by a committee of the National Academy of Sciences.
In a report released yesterday, the 22-member Committee on Biological Effects of Ionizing Radiation (the socalled BEIR II committee) reaffirmed, for the most part, findings of a similar 1972 panel that the overall risk of cancer or genetic malformation from exposure to low-level radiation is very small.
Also endorsed by yesterday's report was the 1972 panel's controversial conclusion that there is no minimum level, or threshold, of exposure below which an individual is safe from adverse health effects.
Yesterday's report said that "solid tumors" found in "the breast in women, the lungs, the thyroid and the digestive system" are the major types of cancers associated with low-level radiation.
The 1972 report cited leukemia - a killing cancer of the blood - as the major adverse result of low-level exposure.
The new finding, according to yesterday's repost, means that a long latent period of 30 years or more may pass before a cancer caused by low-level radiation appears.
It also means, the report shows, that there is less of a risk of dying from low-level-radiation-induced cancers than was believed seven years ago. That is because thyroid, and to some degree breast cancer, can be successfully treated.
Another new finding of the BEIR II report is that age "is a major factor in cancer risk related to radiation exposure."
The 1972 report said some cancer risks were greater than average for children and for fetuses exposed while being carried in the mother.
The new report found that "other age groups may also have risks above those of the general population." With breast cancer, the report said, "women exposed during the second decade of life" are at greater risk than others.
The BEIR committee chairman, Dr.Edward P. Radford, of the University of Pittsburgh Graduate School of Public Health, said yesterday that, based on the new risk estimates of the BEIR II report, the low doses of radiation measured after the Three Mile Island nuclear accident are likely to result in only one excess cancer case. It would be "totally undetectable," he said, among the 2,500 cancer cases normally expected to develop from the exposed population.
There is no scientific means of proving that a cancer was caused by low-level radiation exposure that took place at some time in the past. Thus scientists study those exposed to such radiation and attempt to determine by statistical means how many cancers should develop within that group normally and how many excess to that number turn up within the exposed population.
There is controversy within the scientific community as to how accurate such findings may be.
The new BEIR II REPORT CAME DOWN IN THE MIDDLE BETWEEN TWO SCIENTIFIC GROUPS CURRENTLY FIGHTING OVER JUST WHAT HEALTH EFFECTS DEVELOP AT THE LOWEST RADIATION LEVELS.
IT ADOPTED THE 1972 "LINEAR HYPOTHESIS," WHICH SAYS THAT THE RATES OF CANCERS FOUND AT HIGH DOSES CAN BE PROJECTED DOWN TO THE VERY LOW DOSES.
AT LEAST FIVE MEMBERS OF THIS YEAR'S PANEL DISSENTED FROM THAT VIEW, SAYING THAT, BY GIVING SUPPORT TO THE PROSPECT THAT THERE ARE SOME EXCESS CANCERS DEVELOPED AT VERY LOW DOSES, THE REPORT "WILL CONTRIBUTE TO EXCESSIVE AND POTENTIALLY DETRIMENTAL APPREHENSION OVER RADIATION HAZARDS."
ON THE OTHER SIDE THE REPORT DISMISSED RECENTLY PUBLICIZED FINDINGS THAT VERY LOW DOSES CAUSE EVEN MORE CANCERS THAN THE PROJECTED LINEAR LEVEL.
THE NEW BEIR report's position, however, showed how far scientists have come in redefining just what is a low dose of radiation.
When the BEIR I committee discussed low levels, it used 50,000 millirems as dose against which some scientific data existed on cancer incidence.
For the new report, data have developed in the 10,000 millirem to 50,000 millirem range.
From those data, however, the new report said it could not prove that doses as low as 100 millirems "are detrimental to exposed people."
The report noted that natural radiation from the cosmic rays of the sun and other matter annually give 82 millirems to an individual.
Man-made radiation from medical and dental X-rays add another 20.4 millirems to the average person's annual dose.
Another 20 millirems come from assorted sources, with nuclear power facilities adding 1.15 millirems.
Special groups however, have additional low-level radiation burdens, according to the BEIR II report.
Tops among them are some 30,000 persons in the nuclear power industry who average 600 to 800 millirems each year.
Radford yesterday repeated his statement of more than a year ago that the present permissible occupational standard of 5,000 millirems per year ought to be cut for individuals under 35 years old.
He also suggested that there should be separate standards for men and women.