OCEANOGRAPHY IN THE UNITED STATES 329 



ever, and the progress of their diffusion followed across the Pacific. 



Following the 1954 test series at Bikini-Eniwetok, a vessel from 

 the Coast Guard was sent on this sort of mission. This was about 10 

 months folloAving the end of the 1954 series. At that time the highest 

 levels of radioactivity were found about 3,000 miles to the westward 

 of Bikini-Eniwetok off the coast of the Philippines. The levels of 

 activity here were about one- fourth that of the naturally occurring 

 radioactivity in sea water. 



jMr. Miller. What was the last statement, Doctor ? 



Dr. Seymour. The level of radioactivity off the coast of the Phil- 

 ippines approximately 1 year after the end of the 1954 test series was 

 about one- fourth that of the naturally occurring radioactivity of the 

 water. There are naturally occurring radioisotopes in the ocean. 

 The principal radioisotope is potassium 40, which contributes about 

 97 percent of the naturally occurring radioactivity in the water. This 

 amounts to 720 distmtegrations per minute per liter. A liter is 

 slightly larger than a quart. So, if you had a quart of water, 

 you would find around 720 disintegrations per minute per liter of 

 radioactivity from naturally occurring potassium 40. Off' the coast of 

 the Philippines about a year after the 1954 series, we found some 

 added activity, and this was at a level that was about one- fourth that 

 of the naturally occurring radioisotopes in the water. 



Mr. Miller. That means, if I follow you coiTectly, where you had 

 700 naturally you would have roughly between 900 and 1,000 disinte- 

 grations per minute. 



Dr. Seymour. Total. 



Mr. Miller. Somewhere in that neighborhood as a result of it, 

 which would not be at all dangerous. 



Dr. Seymour. Yes. That is a correct conclusion, sir. However, 

 to make this statement positive, you should know what isotopes are 

 present, because the hazard is dependent upon two things : First, the 

 amount of radioactivity present, and secondly, the radioisotope which 

 is present. The tolerance level, the MPC value, for various isotopes 

 may vary by a factor of a million or more. For instance, the tol- 

 erance for promethium 147 is a million times that for strantium 90. 

 So it is obvious you cannot say that water of certain radioactivity is 

 or is not hazardous without knowing what radioisotopes are present. 



I might further add that this was the area in which we found the 

 highest levels of activity, too, in this 1955 survey. That is, we found 

 some radioactivity practically all the way across the ocean from Bi- 

 kini-Eniwetok, but the highest levels were found near the coast of the 

 Philippines, a distance of about 3,000 or 3,500 miles west of Bikini- 

 Eniwetok. 



Mr, IVIiller. Wliy does it migrate in that direction, do you know ? 



Dr. Seymour. Yes, because the general circulation in the North 

 Pacific is in this way. The waters in the northern hemispliere cir- 

 culate in a clockwise direction. We have the Gulf Stream in the 

 Atlantic circulating in a clockwise direction. Likewise, we have a 

 current in the Pacific circulating in the same manner, in the same 

 general direction. 



In connection with the monitoring of fallout chemicals we expect 

 to learn about oceanography from a number of aspects. Circulation 

 of ocean currents can be measured directly by appraisal of directional 



