Table 3. Levels in the sea of naturally occurring nuclides of elements also present as radioisotopes in fallout. Also shown are the physical forms of the naturally occurring elements in sea water, per cent solution of fallout radioisotopes in sea water, and percentages of radioisotopes observed in plankton. Gram/ton of Form of in sea water element in stable element (ppm) y Fallout in sea water stable Per cent in solution sea water evidence Indirect (8) Direct evidence _ percentage fallout element sea water plankton samples form of (9) elements in particulate Isotope Average Principal of radio- in five zn©5 O14 mostly 02 -- C0271 58,60 0001 solution** .0007 -- " 24.2 Fe>? .02 particulate** .00007 -- " 23.5 Zr95-NpI5 Cel44_ppl44 ? . 0004 Mn54 solution*** ? ? -.001 1.0 0 .O1 mostly .002 -- C837 .002 mostly --* sr89_90 .13 mostly Rut6_Rp106 2 Stable calcium " potassium 2 solution** solution solution 400. solution 380. solution -- 7.2 o ‘ 25.1 " " 20.2 8.6 " 0.2 " 1.4 70 solution 0.1 87 solution 0 * A value of .05 per cent is given for cesium. The apparent insolubility is caused by a strong adsorption of the cesium ion to colloidal particles of hydrolysate sediments and not to its insolubility in sea water. #* Goldberg 1954 (7). *## Kawabata, personal communication. a4 Dor. Cur, &s