e 80 ever, organisms discriminate somewhat against strontium and hence, in the presence of the calcium in sea water, radiostrontium behaves as if it were even more highly diluted insofar as organisms are concerned; that is, Cs'*’ and Sr’ in the sea water act as if they were diluted more than a millionfold by natural, similar, or identical chemi- cal elements. Even if the biological requirements of an organism were high for these elements, the abundanceof the natural elements in sea water and the extreme dilution of the radioactive isotopes act adversely towards the concentration of the radioelement of ble by an organism. Nevertheless it is observed that trace elements in sea water may be highly concentrated in certain organisms over the amount in the water. This can be understood from the following numerical examples. Zinc concentration in sea water is about 5 x 1073 mg/liter, cobalt about § x 107‘ mg/liter, and cerium about 4x 1074 mg/liter. The addition of 1 pe of Zn® (0.12 x 1078 mg) per liter would increase the zinc concentration by 0.002 percent and 1 ye of Co® (0.86 x 107° mg) per liter would increase the concen- IN tration of cobalt by 0.17 percent. Although the ratio of the radioisotope to the stable isotope is still low, the total isotopic abundance in the sea is so low that an organism requiring this element for growth must absorb a relatively large proportion of the total amount in the water to supply its body needs. |“ Most of the elements shown in Table 1.1 appear to exist in sea water as insoluble oxides and hydroxides. These insoluble species would probably be strongly adsorbed on particulate matter such as colloidal ferric hydroxide. The natural radioactivity of sea water is due chiefly to K*", Rb®’, and the members of the uranium and thorium series. c%, H’, and some of the rare earths contribute a smal] amount. ’ A separation of the daughters of uranium occurs in the oceans, resulting in a concentration of radium in recent sedimentary deposits. Both radium and potassium are highly concentrated by some species of marine algae. In order to comparefission product contamination with the activity of the natural background, the properties and concentrations of some of the natural radioactive isotopes in the oceans are given in Table 1.2 (References 7 and 8). In order to determine the natural radioactivity of several uncontaminated phospho~ rite and manganese nodules, an approximate analysis was made on samples obtained off the coast of California and from the northern Pacific. These analyses showed the presence of K*, radium, and thorium with their decay products, as follows: Phosphorite rock California Coast | . Manganese Nodule Horizon, North Pacific 90 total (y/min)/gm 7.2 total (y/min)/gm 34 total (y/min)/gm K* present but obscured by radium 0.3 pet K® 3.3 ppc K@/gm 1.2 pet K® 10 pyc K"/gm 34 pyc Ra?**/gm 2.5 pyc Ra™6/gm © 2.7 pyc Ra?*/gm 2.6 wpe Th®*/gm 0.3 ype Th?/gm 16 po Th? /gm (0.1 to 2.2 Mev) S=- Manganese Nodule Ranger Bank, California Coast (0.1 to 2.2 Mev) (0.1 to 2.2 Mev) Only the K® concentration of 74 (y/min)/liter of sea water or 640 (8/min)/liter should be encountered during field measurements of the uncontaminated surface waters. The dissolved uranium and radium concentrations are below the levels of detectability as outlined in Section 1.5. The radium and thorium concentration, on the other hand, maybe sufficient to interfere with gross fission product analysis of the sediments. 15