248 



CHAPTER 28 



It should be noted that the period of time 

 over which mutations are produced is dif- 

 ferent for these different radioactive chemi- 

 cals. For relatively short-lived radioactive 

 substances like strontium and cesium, the 

 induction of new mutations would be re- 

 stricted almost entirely to a few generations 

 following the explosions that produced them. 

 This may be compared with the distribution 

 in time of the mutations produced by car- 

 bon-14. Carbon-14 has a half-life of 6,000 

 years. So, if the exposure were unchanged, 

 even 200 generations from now there would 

 be about half as many mutations produced, 

 as there will be in the generation most mu- 

 tated by the bombs already exploded. Ac- 

 cordingly, because of its abundance and long 

 half-life, carbon-14, before it decays to nitro- 

 gen, has been calculated to deliver to the 

 gonads 4 to 17 times as much radiation as 

 cesium and strontium combined. This will 

 produce proportionally more point muta- 

 tions. 



In the United States National Academy of 

 Sciences — National Research Council report 

 of 1956 (see References), the gonadal dose 

 expected from fallout, if weapons of the same 

 type continued to be tested at the same rate, 

 was given as about 0.1 rad in the next 30 

 years. On the basis of the United Nations 

 report, this would cause approximately 10 

 to 400 mutations per million people. How 

 much modification does this figure now need 

 to bring it up to date? Several considera- 

 tions need to be taken into account. One is 

 carbon-14, whose long half-life was not taken 

 into account in that report. Another is 

 the changed rate of testing, which was such 

 that, according to the United States Atomic 

 Energy Commission, the amount of fallout- 

 producing radioactive material in the strato- 

 sphere was doubled by the numerous test 

 explosions of nuclear weapons conducted by 

 the U.S. and the U.S.S.R. in 1958 alone. 

 Third, the unequal distribution of fallout in 

 different parts of the world needs to be con- 



sidered. Fourth, since fallout is descending 

 faster than expected, less decay has taken 

 place in the stratosphere. Finally, changes 

 in the quality of bombs tested and the sites 

 of the tests must also be taken into account 

 before accurate estimates of germ-line muta- 

 tional damage due to fallout may be obtained. 



Each month brings more of the data re- 

 quired to estimate the fallout risk to the germ 

 cells. Apparently, the possible damage has 

 been underestimated. For, whereas the 

 International Commission on Radiological 

 Protection recommended a maximum per- 

 missible concentration of strontium-90 in 

 food of 80 units in 1953, which was then 

 adopted by various U.S. government agen- 

 cies, in 1958 the Commission recommended 

 this be lowered to 33 units, and the new value 

 was recently employed as a guideline by the 

 United States government. 



There are several genetic problems, in ad- 

 dition to those already mentioned on page 

 246, which need to be solved, in order to esti- 

 mate the effects of radiation upon future gen- 

 erations. It is necessary to determine the 

 relative mutability, for various types of mu- 

 tation, of a dose given in a concentrated, as 

 opposed to a protracted, manner. It is also 

 necessary to learn as accurately as possible, 

 the doubling dose for spermatogonia (about 

 40 r in the mouse) and oocytes (probably less 

 than 40 r in mouse and man), for it is in these 

 stages that the human germ cells used to pro- 

 duce the next generation remain for the long- 

 est period of time. It may be suggested that 

 the largest number of germ-line mutations 

 may occur in the oocytes. Spermatogonia 

 are constantly dividing, during which time 

 mutants producing a detrimental effect may 

 be selected against so that a considerable 

 portion are lost prior to gamete formation. 

 However, there is no parallel situation in the 

 germ line of the human female. The human 

 female is born with all, or almost all, her 

 future gametes already in the oocyte stage. 

 No further mitotic cell multiplication takes 



