Table 4.1 RADIOACTIVITY OF WATER SAMPLES* Pretest Island Posttest Sample depth, Fe(OH); Ca-Sr_ Sample depth, Whole Fe(OH), 7 Ca-Sr ft scavenge oxalate ft sample scavenge oxalate 4 25 Background 0.09 0.17 Japtan: Surface Bottom - 0.48 Background Igurin: Surface Bottom 40 Background 0.01 60 16 Background 0.32 0.72 0.30 0.14 62 0.07 0.04 55 19 Background 2.3 1,8 0.83 0.66 Rigili: Surface Bottom Bogombogo: Surface Bogallua: Bottom 0.35 0.05 350 96 18 45 1.11 0.26 23 330 92 16 55 0.02 0.04 25 46 70 20 22 84 0.01 0.02 25 Background Background 5.0 7.0 1,0 1.0 20 0.13 0.25 20 40 Background 0.84 0.04 0.35 0.22 Engebi: Surface Bottom 2.7 3.1 Aomonand Rojoa: Surface Bottom Runit: Surface Bottom OR. * Measured in disintegrations per minute per milliliter. A gross examination of the types of organisms present in the catches was made to de- termineif the difference in counts between net hauls and between stations could be accounted for by the type of organism in the cateb. Although the catches varied considerably, both quantitatively and qualitatively, there was strong evidence that the activity of the samples was not associated with the presence of any one group of organisms. Autoradiographs of a dried 9, plankton sample showed that the activity was usually associated with inanimate objects, but, even when the organisms were active, the association was not with any one particular group (see Sec. 4.9.1). Further evidence was obtained from the paired hauls, in which the activity of the samples often varied, but the composition of the catch was similar. For example, the catch in net B and net D at Bogallua appeared similar in composition (foraminifers, principally, and some snails, copepods, and a few miscellaneous eggs and arrowworms), but the sample from net B was seven times more active than the sample from net D (1,160,000 d/m/g as compared to 155,000 d/m/g). Since net B was of finer mesh than net D (173 and 74 meshes/ in., respectively), it might be thought that some small radioactive organism was escaping the D net and was being caught in B, but microscopic examination of the catches did not demonstrate this to be true. It is believed that the fine-mesh net was more efficient in capturing suspended inanimate radioactive particles. The radioactivity in plankton samples is recorded in Table 4.2. 28 NCLASSIFIFN