32 



Atomic Radiation and Oceanography and Fisheries 



at 100 meters depth. Furthermore, should an 

 individual plankter accidentally concentrate an 

 excessive amount of radioactive material in its 

 tissue there is little probability that this indi- 

 vidual would ever pass along any effect of it; 

 there would be very little chance of a disinte- 

 gration occuring before division. Purely physi- 

 cal reasoning therefore indicates that mutations 

 leading to a capability for accumulating rela- 

 tively large amounts of activity might be car- 



ried to offspring for ten or more generations 

 before any nuclear energy would be released in 

 any cell whatever. 



Because of the "patchiness" of the radiation, 

 the use of a unit like the millirad per year for 

 feeble doses of strongly ionizing radiation un- 

 fortunately cannot convey the complete picture 

 of the interesting bombardments which must be 

 experienced by the very small organism. 



TABLE 3 Radiations in Eleven Radiological Domains 



Man over granite 



1. At 10,000' elevation 



Cosmic rays 100 -f granite 90 + internal 17 



2. At sea surface 



Cosmic rays 35 + granite 90 + internal 17 



Man over sedimentary rock 



3. At sea level 



Cosmic rays 35 + rock 23 + internal 17 



Man over sea 



4. Cosmic rays 35 -\- sea 0.5 ^ + internal 17 



Large fish in sea 



5. Near surface 



Cosmic rays 35 + sea 0.9 ^ -finternal 28 



6. 100 meters deep 



Cosmic rays ^ -f- sea 0.9 ^ + internal 28 



Total mrads/year 

 = 207 

 = 142 



= 75 

 = 52 



= 64 



= 30 



Micro-organism (mean radius 0.01 mm or less) in water 



7. Near sea surface 



Cosmic rays 35 + sea 3.6 ^ -j- internal ^ =39 



8. 100 meters deep in sea or more 



Cosmic rays 0.5 -f sea 3.6 ^ -|- internal 3 =: < 5 



9. Buried in deep sea sediments 



Cosmic rays 0.000 -f clay 40-620 + internal * = 40-620 



10. Near fresh water surface 



Cosmic rays 35 + water activity - -|- internal - ^35 



11. 100 meters deep in a fresh lake 



Cosmic rays < 0.5 -|- water activity - + internal - = < 0.5 



1 For every radiopotassium disintegration there are 10 betas having average energy 0.5 mev and also one 

 gamma ray having 1.5 mev. The man receives half the gammas from activity in the sea; the large fish, 

 substantially all the gammas; while the micro-organism receives gammas and betas together. 



2 In fresh water natural activity is extremely low and little of this energy stays in the cell. For example 

 (Robeck et al., 1954) in the Columbia River the beta background of the water is at or below 1 X 10"* micro- 

 curie per ml (2 X 10"* d/m/g) while the activity of aquatic organisms is at or below 1 X 10"* microcuries 

 per gram (2 X 10"^ d/m/g). For comparison, the beta activity in normal sea water is 0.66 d/m/g. 



3 The marine microplankton probably carries more internal activity than does the lake plankton, never- 

 theless effect can be neglected unless activity is concentrated more than 100 fold. 



* All deep-water organisms have not escaped radiations. Micro-organisms buried in true deep-sea sedi- 

 ments have exceptionally high exposure to radium (Love, 1951); they receive 40-620 mrads/year de- 

 pending upon the type of sediment. 



CONCLUSIONS 



1. Some humans actually live under exposure 

 levels surprisingly near the magnitude, 10 roent- 

 gen during 40 years, which has been suggested 

 as a genetic tolerance level, i.e., see Figure 2 

 and Table 2 (domain 1, high elevation over 

 granite) . 



2. A man may experience 207 mrad/year on 

 high mountains, or 142 on a sandy shore; he 

 may reduce this further by half, say, by staying 

 aboard a ship. 



3. A large fish experiences a 50 per cent reduc- 

 tion in dose when going to a depth of 100 



