Table If. Isotope The Naturally Occurring Radioisotopes inSea Water Total activity Per cent Radioactivity in ocean in of total in sea water megacuries 1) activity 97.1 (MP C)y4) d/m/ 12) pefec?) ucice 736 3x1077 * «40 460, 000 Rb 87 8, 400 1.77 13 6x10~2 1073 238 3, 800 . 80 6 8x1079 2x1074 Ra226 1, 100 23 2 1078 1077 5x10710 ci4 270 057 i 235 110 023 1 12 003 1 " .03 8 002 i " 2x1075 HS Th232 Total 473, 700 100.0 758 gx1073 3x1074 3x1077 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 69, 1959) * No value given, hazard negligible