Table 4.2-—RADIOACTIVITY OF PLANKTON SAMPLES*t Preshot e Postshot Net . Island AorB Igurin Rigili Bogallua Bogombogo Engebi Rojoa Aaraanbiru Runit 0.79 Net Net D 1.1 13 2.9 0.31 0.34 2.4 0.28 0.10 0.12 0.11 AorB Net D 140 71 1100 34 19 160 100 48 24 67 * Measured in disintegrations per minute per gram (x 1000), wet sample. + Nets A and B: No. 20 silk, 173 meshes/in.; net D: No. 6 silk, 74 meshes/in. For similar areas the postshot samples were 200 to 300 times more radioactive than the pretest samples. The postshot samples from Igurin were higher than those at Rigili, Aaraanbiru, or Runit, which were closer to the shot island. Usually the catch in the fine-mesh net was considerably more radioactive than the catch from a coarser mesh netfor paired hauls from the samestation, especially in the postshot samples. Someradioactivity was also found in the plankton preservative. The activity of the pre- servative from the Bogallua collection which was filtered through No. 42 Whatmanfilter paper was 10,000 d/m/cc as compared to 11,000 d/m/cc for the unfiltered sample. The plankton for the same sample was 100 times greater (1,100,000 d/m/g, wet). The activity of the preservative suggests that some radioactive isotopes associated with the plankton are partly soluble in a 4 per cent formalin solution or that some of the adsorbed particles are washed off the organisms, 4.3. The algae collections included 5 species of blue-green, 14 species of green, 3 species of 4.3.1 Analysis by Area 0 Because of the paucity of samples and the nonrandomness of sampling, the best evaluation of the data can be made by comparing the averages of the radioactivity of all the samples collected at each station In Table 4.3 the average radioactivity of the algae at each collecting : ore shel 4, ALGAE brown, and 7 species of red algae. A check list of species collected for assay is given in Appendix B. ow we yee Pe , net ae we rev PT . Eee , Coe Me re atthe are 4 ie et et ee a Uy : ad TR? eee y . From an inspection of Table 4.2 the following conclusions are made: There were measurable amounts of radioactivity in all the preshot samples, especially those from Bogombogo. - . station is given. In the pretest collection the samples from those islands close to previous atomic tests or upon which previous atomic tests had been conducted were the most radioactive. One sam- ple in particular, collected in a stagnant pool 250 yd east of Lake George on Eberiru Island, had a count of 54,000 d/m/g, wet weight. Three others, collected on the tide flats at the western tip of Runit Island, averaged 31,000 d/m/g. In the postshot series, for stations within 29