TABLE 1 Average values of radioisotopes in plankton from two surveys made during 1958 and one in 1956 (Marsh). The six samples collected during the period less than 48 hours post-shot were from one detonation. The four samples collected at greater than one week had been contaminated by fallout from several nuclear devices. The five samples taken approximately six weeks after contamination had been subjected to radioactive fallout from several detonations. A Rehoboth half-life Mo**—Tc##m | Cel41__Ppr!41 Cel#4._Ppri44 Rul%83__Rhp!03 | Ruls_Rh195 Ruts.R106 f Ba!49__Ta148 12.8 d 77h 65d Sr§9—_Syroa 50d, 28 y C5187 26.6 ¥ Np? U3? Co4? 2.3d 6.8d 270d Coss Cot? Zn% Fess Fe! Mn*4 33d 285d 40d 4.5h, 36.3h ly Tel32__J132 Zr®5_Np* | 66h 71d B.2y 245d 2.6y | 45d 291d Surve < 48 hours | 12 2 <1 | ; 1 Collett 23 0 0 0 0 0 0 | 0 2 0 0 0 0 1 0 5 69 3 0 | 0 3 8 1 | Marsh Survey Surve >l1 weok | 0 0 1.4 | | | | 33 3 3 15 1 0 | | 5 0 6 2 2 7 6 weeks 0 0 20 | | 0 0 0 0 9 140 l | 25 | 24 ! 0 <1 one week after contamination, these radioelements comprised 62% of the total radioactivity, and at the end of six weeks accounted for 74°, of the contamination associated with the plankton. The two anions accumulated by plankton (Zr?°—Nb*®* and Ru1®*—Rh!°) probably follow the metabolic path of some chemically similar anion or anions normally present in the marine environment. Evidence that radioactive anions are not retained per se is found in observations on the uptake by plankton of a radioactive anion with no known metabolic function. In an oceanic survey made in 1958, Lowman ef al (19) found a neutron- induced radioisotope of tungsten, W185, for the first time. The isotope was found in high amount in water and plankton (~50° of the total activity) in an area of high total radioactivity about 180 miles in diameter. About one-half of the W148> in the plankton was associated with silica, probably from the skeletons of marine diatoms. Almost all the radioactivity in the water samples was contributed by Zr*5— Nb*> and W185, A major part of the material containing the latter radioelement in the water samples passed througha filter with a pore size of 0.45 p. A second survey was conducted three weeks later. During the time between the two surveys the centre of contamination moved 150 miles to the WSW, a net advance of 7.3 miles per day. In plankton samples collected during the second survey no W?!* was found, although almost all the radioactivity 122