38 BIOLOGICAL EFFECTS OF ATOMIC RADIATION 



2. We believe that the atmospheric content of radioactive particles from fallout origi- 

 nating from all previous nuclear tests presents a considerably smaller radiation exposure to the 

 lung than does the average natural radon concentration in the air. 



3. Under certain circumstances involving either acute or chronic inhalation exposures 

 to long-lived fission products and/or alpha particle-emitting fissionable materials, their 

 pulmonary retention could give large and potentially carcinogenic focal exposures to the 

 respiratory organs while subjecting the individuals to minimal external beta-gamma radiation 

 exposures. 



4. The evidence for induction of cancer by inhaled radioactive materials in experimental 

 animals is convincing. There is no reason to think this cannot occur in man despite the lack 

 of definitive evidence at present. Therefore, continued study of inhalation hazards is urgent, 

 and the continuation of stringent envircmmental control measures is justified pending the com- 

 pletion of adequate studies. 



E. Research Needs 



1. Inhalation studies with specific radionuclides should be continued in several species 

 of animals in order to better define deposition, retention, clearance, turnover, and biological 

 effects. 



2. The influence of pre-existing pathological processes on deposition, clearance, and 

 retention of particles in both upper and lower respiratory tract should be determined. 



3. Information is needed on the relative biological effectiveness of various radiations in 

 causing late injury such as cancer. 



4. Possible synergism between radiation and chemicals should be studied. 



5. Better instrumentation is needed for measurements of solubility, and of particle size 

 and distribution of radioactivity on particles in the 0.05- to 50-micron size range, in order to 

 correlate physical properties with observed biological effects. The instruments should be 

 usable in the field as well as in the laboratory. 



6. More information should be obtained on the physical and chemical properties of 

 small particles. 



7. Better methods are required to estimate lung burdens in humans. 



8. Programs should be considered for measuring concentrations of radionuclides in 

 human tissue where there is reason to believe there was significant exposure to radioactive 

 particles. 



9. The least effectively controlled inhalation hazards from radioactive materials appear 

 to be those associated with radon and daughter products in mining operations. Efforts to 

 control this hazard should be intensified. 



10. Since knowledge of the effects of inhaled materials is rapidly expanding, reconsider- 

 ation of these recommendations should be made from time to time as new information is 

 acquired. 



Harry A. Kornberg, Chairman Francis R. Holden 



W. J. Bair James K. Scott 



Stanton H. Cohn J. Newell Stannard 



C. C. Gamertsfelder George V. Taplin 

 J. W. Healey 



