Table II. Isotope The Naturally Occurring Radioisotopes in Sea Water Total activity Per cent Radioactivity in ocean in of total in sea water megacuries! activity 97.1 (MP C)y,4) d/m/1 uc/ec?? pc/ee 736 3x1077 * K40 460, 000 Rb 87 8, 400 1.77 13 6xi079 1073 238 3, 800 80 6 3xi07°9 2x1074 Ra226 1, 100 23 2 1079 1077 5x107!0 ci4 270 057 1 235 110 023 I 12 003 1 " 03 8 002 i " 2xi075 H3 Th*32 Total 473, 700 100.0 758 gx1073 $x1074 3xi077 1) Revelle (1957) 2) Disintegrations per minute per liter based upon calculated value for K40 3) Microcuries per cubic centimeter 4) Maximum permissible concentration for water consumed by man (Handbook 89, 1959) * No value given, hazard negligible