Neato of drained wet weight, concentrated the artificial radioisotopes 175 times above that found in the same amount of sea water they inhabited. A bundredfold variation of radioactivity was detected among different genera with the concentration over that of sea water ranging from zero to a thousandfold. i Table 1.4 gives the gammaactivity of seventeen bulk zooplankton samples, as well as the activity of selected organisms separated from the gross samples. Station positions are shown in Figure 2.1. The highest activity was detected in the mucus and filter-feeding pteropods and filter-feeding copepods both of which feed upon microscopic organisms and suspended detritus. , The lowest activity was found in the filter-feeding salps and the rapacious, plankton-feeding Sagitta, both of which have a high water content. A radiochemical and gamma spectrographic analysis of the combined zooplankton samples from seventeen stations showed the presence of Ce“, Mn™, Zn®®, Co*” and Co® in the amounts given in Table 1.4. Cs’ was not detected and no analysis was made for radiostrontium. As shown in Table 1.3, the levels of activity of the water were quite low throughout the entire area studied. However, it is significant that the greatest activity was found TABLE 1.5 j RADIGACTIVITY OF LAGOON WATERS Station Bikini Atoll, Site Nan Bikini Atoll, Site Charlie Bikini Atoll, Site Charlie Bikini Atoll, mid Jagoon Ailinginse Eniwetok Atoll, Site Elmer . Depth (y/min)/iter* Probable Error | pet j 575 27 5 Near shore 1,065 1 meter deep 15 . ’ Surface Surface 810 Surface Surface Surface 645 535 200 20 23 30 42 * The values of (7/min)/liter (0.075 to 1.5 Mev) have been corrected to account for a 22 percent efficiency and a 41 percent geometry of the scin- tillation counter when standardized with Co” and Zn®*. The average background due to instrument noise and cosmic rays has been subtracted from the reported values. The natura) K* background of 74 (y/min)/liter of sea water has not been subtracted and is included in the above figures. within the influence of the eddy system around Bikini, Ailinginae and Rongelap Atolls (Figures 2.5 to 2.9}. It is probable that within this area the supply of radioactivity in the ocean was being constantly renewed by tidal flow from Bikini and neighboringatolls to the east. Swept into the eddy where it does not escape for an extended period of time, crop after crop of the short-lived plankton becomes contaminated. Organisms from three samples of the deep-sea fauna, obtained by trawling at depths from surface to 730 to 2,560 meters, showed activity levels similar to those of the zooplankton from the upper water levels. Selected fish and planktonic organisms sorted from one trawl are listed in Table 1.6. As in the case of near surface zooplankton, the pteropods contained the greatest amount of radioactive material per gram of tissue on & wet weight basis. The activity is listed in Table 1.6 as total] gammas, compared to & zn®standard, emitted per minute per gram of wet tissue. 33 !