The Genetic Effects of Radioactive Fallout and Carbon 14 Produced by Nuclear Weapons Tests

One of the consequences of carrying out nuclear reactions on a large scale, first achieved twenty years ago, is that the earth has become contaminated with artificial radioactive materials. It was reported that radioactive fission products from the first atomic bomb, which was detonated on 16 July 1945 at Alamogordo, New Mexico, caused skin damage to cattle grazing 15 miles away. Subsequent tests of nuclear weapons showed that strontium 90, cesium 137, iodine 131, and many other radioactive nuclides are produced in nuclear fission, and that carbon 14 Is produced from atmospheric nitrogen by the neutrons liberated in fission and fusion reactions. The contamination of some areas after a nuclear explosion may be great enough to cause exposure of human beings in the area to hundreds of rem.

Public attention was directed to the fallout problem after the explosion at Bikini on 1 March of the first three-stage bomb, the Bravo bomb, with energy 15 to 20 megatons. The 23 Japanese fishermen aboard the trawler Lucky Dragon and natives and Americans on Rongelap, Rongerik, and other islands were more or less seriously irradiated. The question of world-wide contamination with radioactive materials from nuclear weapons tests was introduced into the 1956 presidential campaign by Adlai Stevenson, and it has continued to be extensively discussed ever since.

Valuable information about radioactive fallout and carbon 14 was made public in a series of scientific papers in the period 1955 to 1956 by Professor W. P. Libby, then a member of the Atomic Energy Commission.

In these papers Libby emphasized that hazards such as automobile accidents might be considered to be more serious than the hazards of nuclear weapons testing; for example, he ended one of his papers with the following sentence: "What we have learned from the studies I have described - which by the way have been conducted under the name Project Sunshine - is that these local precautions should be entirely adequate and the worldwide health hazards from the present rate of testing are insignificant." Other spokesmen for the AEC also made reassuring statements; for example, AEC Chairman Lewis L. Strauss on 17 October 1956 released a telegram by Dr. Shields Warren, former Director of the AEC Division of Biology and Medicine, containing the statement "Bone deposition of strontium-90 due to fallout is a minute fraction of permissible level and well below natural background level of radiation. To cause harmful effects, dose would have to be increased many times."

The difficult problem of attempting to estimate the amount of genetic and somatic damage that might result from the action of radioactive fallout was attacked in a vigorous way by the U. S. NAS-NRC Committee on Biological Effects of Atomic Radiation (which issued its report in June 1956), the corresponding committee of the British Medical Research Council (June 1956), the World Health Organization (Report on Genetic Effects of Radiation, March 1957), the United Nations Scientific Committee on the Effects of Atomic Radiation (1958), and other groups. A tremendous amount of information was made available through the 1957 and 1959 hearings before the Special Subcommittee on Radiation of the Joint Committee on Atomic Energy of the U. S. Congress.

The NAS-NRC report stated "The basic fact is - and no competent persons doubt this - that radiations produce mutations and that mutations are in general harmful... Any radiation dose, no matter how small, can induce some mutations... As geneticists we say: keep the dose as low as you can." The dose of radiation in man that doubles the mutation rate was estimated to lie in the range 30 r to 80 r. Essentially the same estimate was made in the British report. James F. Crow, Professor of Genetics and Zoology in the University of Wisconsin and a member of both the NAS-NRC committee and the UN committee, estimated in his 1957 testimony that in a population of 2 billion exposure of one generation to 0.1 r would produce (assuming no change in population in future generations) an ultimate total of 80,000 children with gross physical or mental defect, 300,000 stillbirths and childhood deaths, and 700,000 embryonic and neonatal deaths, with some overlap between the second and third categories. He said that these are rough guesses, which might be five times too high or low, or more. He described 0.1 r (100 mr) as the amount of irradiation of the gonads that might be expected during a 50-year period from fallout from nuclear weapons tests at the rate at which they were then being carried out.

The possibility that carbon 14 produced by neutron irradiation of nitrogen 14 during nuclear weapons tests could do extensive genetic and somatic damage was first suggested by O. I. Leipunskii in 1957, and was then discussed by me (Science 128, 1183) and by J. R. Tatter, M. R. Zelle, and H. Hollister of the Division of Biology and Medicine, U. S. AEC (Science 123, 1490) in 1958. The estimates in the two last papers were compared in the letter of 8 January 1959 from the General Manager of the AEC to the Executive Director of the Joint Congressional Committee on Atomic Energy, as follows:

Estimated effect of carbon 14 from bomb tests to end of 1958, assuming no increase in world population, and with factor 2 for transmutation effect

Pauling, modified: Gross defects, 120,000; Stillbirths and childhood deaths, 380,000; Embryonic and neonatal deaths, 900,000.

Totter, Zelle and Hollister: Gross defects, 100,000; Stillbirths and childhood deaths, 380,000; Embryonic and neonatal deaths, 900,000.

In 1959 the U. S. Federal Radiation Council was created to advise the President on health problems involving radiation. The chairman of the committee is the Secretary of the Department of Health, Education and Welfare, and the committee also includes the Chairman of the AEC, the Secretary of Defense, the Secretary of Commerce, and the Secretary of Labor. In May 1962 the Council issued a report entitled Health Implications of Fallout from Nuclear Weapons Testing through 1961, in which for the first time an agency of the government presented numerical estimates of the number of human beings predicted to be damaged by radioactive fallout and carbon 14 from nuclear weapons tests. This report, by giving authoritative estimates of values of some quantities, simplifies the problem of estimating the amount or possible genetic damage by radioactive fallout and carbon 14 from nuclear weapons tests. In the following paragraphs I make use of the FRC report in the effort to estimate not only probable values but also probable ranges of values of this genetic damage.

The FRC report gives the following values for estimated radiation doses from fallout and carbon 14 for human beings in the United States: for the reproductive cells, first thirty years, 60 to 130 mr; for bone, first seventy years, 400 to 900 mr; for bone marrow, first seventy years, 150 to 350 mr; for the whole body, first seventy years, 70 to 150 mr. The amount of irradiation by bomb-test carbon 14 after equilibrium between the atmosphere and the ocean has been established is given as 0.025 mr per year; to continue for an effective period of 8070 years, the mean life of the nuclide. The estimated numbers of cases of children born with gross physical or mental defect in future generations in the United States as the result of fallout radioactivity and carbon 14 produced by all tests through 1961, assuming no increase in population, are 1,000 (range 200 to 5,000) for fallout and 2,000 (range 400 to 10,000) for carbon 14.

The factors to convert from the United States to the whole world are given in the report as 10 for fallout and 20 for carbon 14. The factor by which the number of children with gross physical or mental defect should be multiplied to give the number of children with gross physical or mental defect plus the much larger number of embryonic, neonatal, and childhood deaths is about 10. With these factors we obtain as the estimated total amount of genetic damage, on the assumption of no increase in population and certain other assumptions discussed below, the values 100,000 (20,000 to 500,000) from fallout and 400,000 (80,000 to 2,000,000) from carbon 14.

It is, however, unlikely that there will be no change in the population of the earth. Unless there occurs a nuclear catastrophe the population will have doubled by the year 2000. In my 1958 paper on carbon 14 I assumed that the average population of the earth through the lifetime of carbon 14 would be about five times the present population. The Russian scientist A. D. Sakharof in his discussion of carbon 14 (What Russian Scientists Say About Fallout, Collier Books, 1962) assumed a tenfold increase in population. I think that it is reasonable to use the factor 2 to 3 to correct for increase in population during the next dozen generations, when fallout radioactivity will exert its major genetic effect, and 2 to 5 for carbon 14.

In the calculation reported by the FRC a factor 1/6 was introduced because of results obtained by experiments with mice carried out by W. L. Russell and his coworkers in the Oak Ridge National Laboratory during recent years (Science 128, 1546 (1958), and later papers), which have indicated that the amount of genetic damage per mr may be only 1/6 as great if the irradiation of the gonads is chronic (low dose rate) as if it is acute (high dose rate). I feel that it might be justified to give some weight to the new experiments, but that there is as much justification now to use the factor unity as to use the factor 1/6. I have asked six leading American geneticists who were members of the NAS-NRC Committee on Genetic Effects of Atomic Radiation to express an opinion on this matter. One answered that he saw no reason to change from the earlier estimate of 30 r to 80 r for the doubling dose. One accepted the factor 1/6. One preferred not to make a statement. The other three said that they continued to use the original estimate, but that it might turn out that a factor such as 1/6 should be used. In order to take this uncertainty into consideration I shall use the correction factor 1 to 6, the value 1 corresponding to use of the Russell factor and 6 to retention of the earlier estimate of the doubling dose in man.

In the FRC calculation use was made of the value 0.025 mr per year as the equilibrium irradiation of human beings by carbon 14 produced by nuclear weapons tests. Information given by Libby in 1956 (Science 123, 657) and 1958 (Proc. NAS 42, 945) about the amount of carbon 14 produced per megaton in the explosion of nuclear weapons corresponds to a yield of 1.05 kg per megaton of fission and 13.8 kg per megaton of fusion. These numbers lead to 2670 kg of carbon 14 for the 115 megatons of fission and 185 megatons of fusion of the tests to the end of 1961, and, with Libby's estimate that irradiation of the human body by natural carbon 14 occurs at the rate of 1.5 mr per year and with the value 49000 kg used by the FRC for the amount of natural carbon 14, to 0.082 mr per year for the equilibrium rate of irradiation by bomb-test carbon 14. This value is 3.3 times the value used by the FRC. The FRC estimate of bomb-test carbon 14 was in part based on the measured increase in carbon 14 in the atmosphere. Libby had pointed out that for ground tests a considerable fraction, estimated by me in 1958 as two-thirds, of the carbon 14 is trapped in condensing vaporized material and falls into the ocean. This fraction would not contribute to the observed increase in carbon 14 in the atmosphere during the first few years; I believe, however, that in the course of a century or two the small particles would dissolve and the carbon 14 would all become available to the biosphere. Accordingly I believe that the carbon-14 upper limit should be increased by 3.3, as given by the above calculation. With the FRC value as the lower limit, this carbon-14 correction factor is 1 to 3.3.

A special mutagenic effect, the transmutation effect, of carbon 14 is the result of the decomposition of a carbon-14 atom that is a part of the DNA molecule that itself constitutes a gene. My 1958 estimate of the extent of this effect was that it would amount to 10 percent of the ionization effect by the carbon-14 beta rays, without the Russell factor (60 percent with this factor). Totter, Zelle, and Hollister estimated that it would be equal to 100 percent of the ionization effect (600 percent with the Russell factor). In his letter to the Joint Congressional Committee on Atomic Energy the General Manager of the AEC corrected my carbon-14 estimates by the factor 2, to obtain the 'Pauling, modified' values, apparently on the assumption that the estimate of the AEC scientists should be accepted. The Federal Radiation Council chose to accept neither my estimate nor the estimate of the AEC scientists, but to ignore the transmutation effect as "too speculative"; if the estimate of the AEC scientists had been accepted, the FRC numbers for genetic effects of carbon 14 would have had to be multiplied by 7. I shall take zero as the lower limit for the transmutation effect, and the AEC estimate as the upper limit; the factor for the transmutation correction is thus 1 to 2.

The products of the smaller values and those of the larger values of the several correction factors just discussed are 2 and 18 for fallout and 2 and 200 for carbon 14. The independence of the several factors indicates that the geometric means of the extreme values, 6 for fallout and 20 for carbon 14, should be used as the probable values.

In this way we obtain as the total estimated genetic effects of radioactive fallout from all nuclear weapons tests to the end of 1961 (115 megatons of fission and 185 megatons of fusion) the following values (total number of viable children with gross physical or mental defect and of embryonic, neonatal, and childhood deaths over all future generations): from radioactive fallout, 600,000 (range 40,000 to 9,000,000), and from carbon 14, 8,000,000 (range 160,000 to 400,000,000). About 10 percent of the fallout cases and 0.1 to 0.5 percent of the carbon-14 cases may be expected to occur in the first generation.

The lower and upper limits of the ranges are related to the probable values by the number 15 as divisor and factor for the fallout effect and 50 for the carbon-14 effect. These numbers are somewhat larger than those customarily used to express the uncertainty in such estimates. Thus the Federal Radiation Council used the number 5 as divisor and factor, and stated that the limits "represent the range within which the true value may reasonably be expected to lie." I have in the past used the number 5 or 10; discussing the genetic effect of the fission products alone, I wrote in 1958 (No More War!, p.73) that the testing of one bomb with 10 megatons of fission involves the sacrifice of 15,000 children, with this estimate possibly 10 times too large or 10 times too small - perhaps only 1,500, perhaps 150,000 children. My present estimate is 52,000 (range 3,500 to 780,000) for the fission products from 10 megatons of fission, and 430,000 (range 8,500 to 21,500,000) for the carbon 14 from 10 megatons each of fission and fusion.

The effects expressed by the numbers given above correspond to gross genetic damage, such as to cause death or serious physical or mental defect. When a grossly defective child is born he and his parents suffer, but the suffering ceases with his death without progeny, and his defective genes are removed from the pool of human germ plasm by his death. There are, however, many mutated genes that correspond to so-called minor defects, such as asthma, arthritis, cleft palate, club foot, excessive or deficient number of fingers or toes or other minor anatomic abnormalities, minor psychiatric disorders, and many other causes of human suffering. These minor defects do not in general prevent procreation, and the defective genes are accordingly passed on to the progeny. In this way a single gene mutation may cause an increased amount of human suffering in human beings for generation after generation, until finally the defective gene is removed from the pool of human germ plasm by the death without progeny of one person in the sequence.

Accordingly the amount of human suffering that is caused by the genetic damage done by radioactive fallout and carbon 14 from the bomb tests to the end of 1961 may well be much greater than that suggested by the numbers that have been estimated in the preceding paragraphs.

During the year 1962 the U.S.S.R. and the U. S. have tested about 300 megatons of nuclear weapons, equal to the total for all preceding years (on 12 October 1962 the Uppsala University Seismological Station released its estimate of 230 megatons for the fifteen U.S.S.R. 1962 tests before that date). The total estimated genetic effects (numbers of viable children with gross physical or mental defect and of embryonic, neonatal, and childhood deaths over all future generations) of all nuclear weapons (600 megatons) tested to December 1962 thus is the following; from radioactive fallout, 1,200,000 (range 80,000 to 18,000,000), and from carbon 14, 16,000,000 (range 320,000 to 800,000,000), with about 150,000 (range 10,000 to 2,000,000) expected to occur in the first generation.

These estimates of genetic damage, despite the uncertainties associated with them and despite the long period of time over which they will occur, constitute a powerful argument for bringing all tests of nuclear weapons to an end, through an effective international agreement. The recognition that nuclear weapons testing leads to genetic damage was a powerful argument for the cessation of nuclear tests in 1958 and for the initiation of the Geneva Conference to negotiate a bomb-test agreement. During 1962 alone the U.S.S.R. and the U. S. have doubled the total amount of bomb-test radioactive pollution of the earth. There is no doubt that these actions by the two great powers will cause a tremendous amount of human suffering. It is imperative that the testing of nuclear weapons be stopped.