Radioisotope Concentration by Marine Organisms - Indirect Hazard: 
Many of the fission product elements are present in natural 
sea water in trace quantities,. However, the concentrations present 
are not known for more than a few. Strontium is one which has been 
studied in the natural environment. Most algae and other plants 
concentrate concentrate Sr by a factor of about 8. For those protozoa 
which are known to make skeletons of strontium sulfate, it is possible 
to estimate a concentration factor of about 10" on a wet volume basis. 
Generally, the Sr concentration factor from organism to organism 
ranges from 0 to 10". 
The weighted, mean concentration factor for the organism 
known to concentrate iodine is approximately 500,000, and in many 
instances this goes up to 107, Nitrates are concentrated by dino- 
flagellates by a factor of about 10 ne Each year organisms of 
biological importance are discovered to concentrate various elements 
which no one had previously suspected could be concentrated by such 
organisms. 
Ecological Hazard: From the biologist's point of view, the 
pertinent factor is how high the radioactivity dumped in the sea 
can be allowed to go before it has physiological effects on organisms. 
Organisms will be affected, not by the radioactivity in the volume 
of sea water, but by the radioactivity in the volume of the organism. 
In the past few years the effects on large varieties of organisms 
exposed to continuous radiation over long periods have been studied. 
Some organisms are very insensitive and others very sensitive. The 
sensitivity extends to 10" on each side of the mean for a sample of 
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