Too Much Radiation?

Of the sources of the radioactivity that batters man, fallout from nuclear weapons testing is the least. At current levels, it is less than 5% of radiation from natural sources. But this is small comfort: the total of all radiation, largely from rocks, body chemicals, cosmic rays and X rays, may already be at a dangerous level. So warned a 15-country United Nations scientific committee last week, after studying world radiation for 2 1/2 years. Shunning politics, the experts voted against urging a ban on nuclear tests. As top scientists, they voiced a sobering opinion: "Even the smallest amounts of radiation are likely to cause deleterious genetic and perhaps somatic effects."

A unit that science uses to measure radiation exposure is the rem. It expresses a fixed amount of absorbed energy, corrected for the biological effects of different kinds of radiation. Radiation's vital targets: gonads and bone marrow. From natural sources, the average man is exposed to about one-tenth rem annually. In developed countries, he may also get almost as much extra each year from medical and dental X rays.

These figures are averages. They do not reveal what the extremes of exposure may be for individuals in many parts of the world. But by any gauge, most scientists agree that man is already exposed to too much radiation. Last week, at the first International Co'ngress of Radiation Research in Burlington, Vt., Brookhaven National Laboratory's Dr. Howard J. Curtis reported evidence that a single modern fluoroscopic examination of a pregnant woman's pelvis will shorten her child's life by two weeks.

Body Damage. The U.N. scientists pinpointed the added significance of nuclear fallout. They found least long-range danger from that which swirls through the troposphere (the part of the atmosphere that goes seven to eleven miles up) for several months before falling. At most, its short-lived isotopes raise annual external marrow and gonad dosage by .0005 rem. But the higher stratosphere (beyond eleven miles) is a reservoir of long-lived isotopes that fall for many years. Chief dangers:

P: Caesium 137, which is a genetic peril because it spreads throughout the body. P: Strontium 90, which affects the bones, especially of young children, because it is absorbed like calcium. P: Carbon 14, which has a half-life of 5,700 years and has probably risen in all living matter -3%-.6% since the beginning of nuclear weapons tests.

As a result of bomb tests to date, caesium 137 dosage in Japan and the U.S. will rise by one hundredth of a rem per capita over the next 30 years. The strontium 90 rise in the next 70 years will vary in each country. For milk-drinking Americans, it will average an estimated .16 rem (or roughly the present dosage from X rays). For rice-eating Japanese, whose crops draw in more strontium because their soil lacks calcium, the per capita increase will be nearly one rem.

What will be the effects? In terms of direct physical effects, the answer bristles with unknowns. Assuming that the world population is 3 billion, U.N. scientists said they believe that current nuclear-bomb fallout accounts for between 400 and 2,000 leukemia cases a year (total: 150,000), as compared to 15,000 from natural radiation. Science is not yet sure how much radiation is needed to produce leukemia. The U.S. National Academy of Sciences estimates the threshold as 40 rem. If this is true, and if all bomb tests stop this year, said the U.N. report, then the ultimate total of fallout leukemia cases would be between 25,000 and 150.-000. (But should the threshold be as much as 400 rem. probably no leukemia cases could be caused by fallout whether the tests were stopped or not.)

Poorer Progeny. Much less uncertain are genetic effects. Said the report: "Exposure of gonads to even the smallest doses of ionizing radiations can give rise to mutant genes which accumulate, are transmissible to the progeny, and are considered to be, in general, harmful to the human race." Doubling the present human mutation rate would probably not lead to the race's extinction. But the scientists felt little doubt that any increase at all will lower the average of human intelligence and life expectancy.

For this fallout reading, the committee was praised as "thoroughgoing" by the AEC, which maintains that bomb tests are not critically dangerous. Praise flowed also from such AEC critics as New Mexico's Senator Clinton P. Anderson, vice chairman of the Joint Committee on Atomic Energy, who took the same report to mean that the AEC has "no place to go, no place to hide." The U.N. committee's own summation of the significance: "The knowledge that man's actions can impair his genetic inheritance . . . clearly emphasizes the responsibilities of the present generation."

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