Chapter IX 



CURRENT AND RECOMMENDED RESEARCH 



Since the previous report of this Subcommittee^, substantial progress has been 

 made in overcoming certain of the deficiencies discussed above. The accumulation 

 of fallout Sr90 and Cs^^T ^^ man has provided an opportunity to check on a global 

 scale the accuracy of predictions based on limited laboratory and clinical experience. 

 Of particular interest has been the demonstration of a relatively small degree of in- 

 dividual variation in the accumulation of these fallout radionuclides— a finding which 

 could not have been confidently deduced from laboratory or clinical data . The pro- 

 portionally higher levels of Sr90 accumulated by children, while not unexpected, has 

 emphasized the need for a consideration of age in the evaluation of internal emitter 

 hazards. 



In the past few years there has been an intensification of efforts to locate and 

 study more of those persons exposed 30 or more years ago to radium and, more 

 recently, to thorium. The continued study of these persons offers an opportunity 

 for obtaining data on both metabolism and toxicity which will probably not again be 

 available. Epidemiological studies of populations living in areas where the background 

 radioactivity of food and water are above average constitute an important supplementary 

 area of investigation in this field. 



The construction during the past several years of a considerable number and 

 variety of sensitive total-body counting facilities should greatly improve the prospects 

 for obtaining data from planned tracer experiments in man. Such instruments are 

 now so sensitive that the metabolism of gamma-emitting isotopes can be followed 

 for several weeks after administration of only 0. 1 to 1 percent of a daily maximum 

 permissible dose of the radionuclide. Studies of the gross retention of several ele- 

 ments, notably the alkali metals, in a variety of animals, including man, have been 

 reported '7'^, and much additional data of this sort may be anticipated in the future. 



Perhaps most significant among the recent animal studies are the experiments 

 with larger animals which were initiated a number of years ago and which are only 

 now beginning to produce critical data. Such studies with radium and other bone- seeking 

 radionuclides in dogs have furnished detailed confirmation of retention and excretion 

 patterns predicted from very limited data on man. The superiority of the power 

 function in describing the retention of bone-seeking radionuclides seems clearly 

 established by these results^^. Such long-term studies in large animals require 

 extensive facilities and many years of effort before results are obtained. Recent 

 expansion of efforts along these lines is therefore particularly encouraging. 



Current experiments with smaller mammals, mice in particular, are focused 

 upon the relationship between the distribution of the absorbed dose, with respect to 

 both time and space, and the pathologic sequelae. Particular attention is being 

 given to the quantitative differences between the effects of exposure by way of a single 

 intravenous injection and exposure by way of continuous ingestion. Emphasis is also 



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