Chapter 2 



Natural Radiation of Selected Organisms 



33 



meters; it carries along its own source of in- 

 ternal radiation, however. 



4. A marine microorganism, having a mean 

 radius of 0.01 mm, receives only about 10 per 

 cent of the surface dose at a depth of 100 

 meters in the sea; most of the dose comes from 

 sea water activity unless exceptionally high in- 

 ternal activities are accumulated. 



5. In a deep fresh water lake those microor- 



ganisms living in deep water (but not right at 

 the bottom) receive from their surroundings 

 what is probably the lowest natural ionizing dose 

 within the biospheres of the earth. It would ap- 

 pear that geneticists should consider seeking 

 evidence of abnormal mutation rates amongst 

 microorganisms which live in deep waters of 

 clear lakes, particularly amongst those which 

 have low affinity for radioactive elements. 



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