Table Il. The Naturally Occurring Radioisotopes in Sea Water Isotope K40 Total activity Per cent megacuries 1) activity in ocean in 460, 000 of total 97.1 Radioactivity in sea water (MP C)y*) d/m/12) pefec?) pefcc 736 3x1077 * Rb8? 8, 400 1.77 13 6x10-9 10-3 y238 3, 800 80 6 3x10°9 2x1074 Ra226 1, 100 .23 2 10-9 10-7 cl4 270 057 1 5x10-10 gx10-3 y235 110 023 1 " 3x1074 12 003 1 " 03 8 002 1 " 2x1075 H3 Tn232 Total 473, 700 100.0 758 1) Revelle (1957) 2) Disintegrations per minute per liter based upon calculated value for K49 3) Microcuries per cubic centimeter 4) Maximum permissible concentration for water * consumed by man (Handbook 69, 1959) No value given; hazard negligible 3x1077