> x3 paper, the ratio of radioactivity in the macro-microplankton to that in the nannoplankton plus particulate matter is insignificant (on the average 0.00025 of the particulate matter), and all the material on the filter paper may be considered to be from nannoplankton and inorganic particulate matter. Also, no macroplankton was retained on any of the filter papers. The radioactivity of the macro-microplankton per unit volume of sea water was calculated by using data on plankton volumes reported by the Pacific Oceanic Fisheries Investigation from surveys made in 1956 and 1957 in the Marshall Island areas. In this study, the volumes of water strained by 2 . . plankton nets were measured and compared with the volumes of plankton obtained. In the open sea approximately one ml of plankton was collected for every 100,000 1 of water filtered. In four different surveys made at the Eniwetok Test Site in 1956 and 1958, the radioactivity in the macro-microplankton was low in comparison to that in the particulate material and to that in the dissolved material (Table IT). ne ” q / ie : ay oe at . te epee ety TABLE II Loo om cm ae . . ets sy . . " yy mer : RATIO OF ACTIVITY IN WATER TO ACTIVITY IN PLANKTON . . Filter paper | plankton | i co; plankton Filter paper + CO, plankton 7,600 10,500 4—23 days after detonation | i ve Te Poo ot ' tes . ‘ a | Walton survey 11—21 June 1956 ' 2,900 | _ Marsh survey 1-21 Sept. 1956 7,800 | | | Collett survey, 8-—14 Aug. 1958 | ' Silverstein survey, Sept. 1958 . Walton—device detonated over - ! water Walton—fired on ground | | 1,500 | 6,100 3,400 . ee May eee ge ee Fe ge, sb, : a . | | 2,900 7,400 36,000 ~90 days after detonation 10,900 at end of series | 105,000 ~ 3 weeksafter | end of test 10,500 . coy + re . oe, a Seee NS ce eali ge RAESE IT he et 9,400 106,000 " , 28,000 | | series 13,900 4 and 6 days post-shot 10,300 23 days postshot The Walton survey was made during the middle two weeks of June 1956 (during the test series) and included 53 sampling stations. Two centres of contamination were included in the survey area and were sampled 4-6 days and 23 days respectively after detonation of the devices producing the fallout. In an average of the Walton samples, the particulate matter greater than 0.45 « contained 2,900 times and the dissolved material 7,600 times as much radioactivity as did the macro-microplankton per litre of water. The samples were also subdivided to include (1) the fallout area resulting from contamination produced by two closely-spaced over-water shots, and (2) a contaminated area with fallout containing large amounts of calcium compounds from a device fired on the ground. No appreciable difference existed between the ratios of particulate activity to macro-microplankton nor the dissolved activity to macro-microplankton in these two areas. Another survey was conducted with the USS Marsh approximately 21/, months after the Walton survey. The filter paper/plankton ratio was 124 1. wee eeee V Ae nV . ;