22 1000 meters, with the peak in much shallower water. sediments Sr and Ca are barely detectable. Even in shallow water According to Dr. Vaughn Bower, Woods Hole Oceanographic Institution, no one has been able to measure them in deep water sediments. | | Zirconium-95, niobium-95, and corium-141~144 were found in bottom dwelling sca cucumbers at depths of 2800 meters immediately after the 1961-1962 tcsts. It is thought that these nuclides, which are not appreciably _ concentrated in the tissues of orgunisms (if at all), are carried down in the rain of fecal pellets of animals living near the surface of the oceans”, Cerium and promethium isotopes not carried down by biological processes, move downward only very slowly>. Assays of sediments from all oceans show that the major radionuclides present are naturally occurring radionuclides of the uranium-thor ium series and -potassium-40. | Measurements of sea water reveal that practically all of the radioactivity in sea water at the present time is potassium-40, which is universallypresent in the amount of about 331 pCi/liter. Cesium-137 and strontium-90 can be measured only by special techniques in which the radionuclide is concentrated from rather large quantities of sea water prior to radioanalysis. In compariso natural potassium-40 can be measured easily without pre-concentration. Zirconium-95 und the cerium rudioisotopes can be measured in sea water only shortly after forcign atmospheric tests. 2, 3. Osterberg, C., A. Carey, Jr. and fl. Curl, Jr., 1963. 1276-1277. Sugihara, T., and V. Bowen, 1962. and Industry, IAEA, 57. Nature, 200 (4913): Radioisotopes in the Physical Sciences