~ 14 - pe 185 100 [25 a7 le |. 90 80. A - Silverstein plankton B - Collett plankton 7O 60 Activity 50 4O 30 20 10 MEV Fig. 4. Gamma spectrum curves of combined plankton samples of the Collett and of the Silverstein survey which was conducted three weeks Tater. Wto5 was present at a high level in the plankton from the Collett survey but was absent in the plankton from the Silverstein survey. The Collett samples contained higher levels of radioactivity than did the Silverstein samples and the gamma curves are not indicative of the relative gamma activity in the two samples.