Table 2. Specific activities of nickel-63 in clam kidneys. Location Nickel-63 (disintegrations per minute) Eniwetok Atoll Bikini Atoll Christmas Island Penrhyn Atoil 3052 3 1050 + 11 7x O04 3+ O07 Sample Tridacna Tridacna Tridacna Tridacna sp. gigas gigas crocea ml of 6N CH,COOH, 2 ml of BioSolv (Beckman Instruments), and 15 ml of a solution containing 5 g of 2,5- diphenyloxazole (PPO) and 0.5 g of 1,4-bis-[2-(4-methyl-5-phenyloxazolyl)]benzene (POPOP) perliter of toluene. Specific activity of nickel-63 (disintegrations per minute per milligram) Stable nickel (mg) 12.4 3.8 8.7 4.0 24 276 0.8 0.8 +02 +3 + 0.05 + 0.17 United States to a high of 163 disinte- grations per minute per gram of dry weight for a clam kidney taken on the western rim of Bikini Atoll. Nicholls et al. (7) reported high concentrations of stable nickel in chaetognaths, which expected to be much lower than this. In addition, there are large dilutions in the Columbia River and ocean waters; thus the river is an unimportant source of “Ni for the marine environment. Folsom and Young supplied us with the squid specimen (Stenoteuthis bart- rami) for which they reported values for the concentrations of ®Co and ldmAg of 4100 and 1500 pc per kilo- gram of wet weight, respectively (9). Using a ratio of wet weight to dry weight of 4 for this specimen, we calcu- lated that the “Ni concentration is approximately two orders of magnitude lower than the reported Co concentration present at the time of catch, 1965. The average concentration of prompted us to analyze this organism for “Ni. The concentrations were very low, approaching the limit of detection. lower by only a factor of 2 than the 69Co concentrations of lichens reported Fe, ®3Ni in surface waters in this area and indicates the absence of appreciable amounts of “Ni in Columbia River Pass, Alaska; however, the comparison of results from insular species in the Aleutians to those of similar continental 125§b, 144Ce, %Zr-Nb, 120mAg, 226Ra coolant for the nuclear reactors at the We measured the yield by wet-ashing the liquid scintillation solution with HNO, and HCI1O,, reprecipitating the nickel as the heptoxime complex, and weighing the dried product. Decontamination factors of > 104 were observed tor the ICs, radioisotopes 207Bi, 6Ry-Rh, %Sr-Y, 147Pm, 6Co, plus daughters, and ®Zn. The clean separations obtained suggest that the activity in the low-activity samples is indeed “Ni. Figure I shows the relative activity plotted against lower level settings derived from the liquid scintillation count- ing of a Ni standard and a *®Nispike, along with the spectrum obtained from the analysis of a clam kidney that was collected at Bikini Atoll. Clearly, the activity separated from this tissue was 63Ni. The concentrations of ®Ni in This suggests a low concentration of water, which is used upstream as a Hanford complex. This observation is consistent with Kirby’s (8) radiochemical procedure forthe isolation of “Ni from Columbia River water (8 to 12 liters) collected near the reactors. This procedure makes possible the measurement of a concentration of 10—8 «ue of S5Ni per milliliter. Because of its low specific activity, the activity of “Ni is detection was 1.4 + 1.0 disintegrations per minute per sample at the 95 percent confidence level (6). The values species ranged from a low of approxi- mately 0.02 disintegration per minute per gram of dry weight for shellfish taken on the eastern seaboard of the tween similar organisms. Table 2 shows the results of the measurements of ®Ni specific activity in clam kidneys collected at test sites and from islands some distance away. The high specific activity in the clam to the fact that this specimen was taken edge of the atoll. Wind-driven surface currents movethe lagoon waters toward the southwest and, as a consequence, Bokororyuru Islet receives waterborne radionuclides in addition to local fallout at the time of testing. The presence of ®Ni in association with short-lived 57Co (171) in the specimens taken from Christmas Island and Penrhyn Atoll in April 1962, prior to the United States tests of that year, suggests that the source of “Ni in these specimens was the Soviet tests of 1961. The evidence is not conclusive, however, since the age of the clams was not determined and it is probable that they were accumulating “Ni over a period of time. listed in Table 1 are adjusted to unit dry weight and therefore are numerically smaller than the detection limit. However, sample sizes exceeded 10 g, except for the chaetognaths, and the values for all samples were above the calculated detection limit. The Ni concentrations in marine species may be invalid. Some specimens contained sufficient stable nickel to permit comparison of the specific activities of “*Ni, an indication of the variations that occur be- at Bokororyuru Islet on the western Relative counts per minute counting rate and at an average overall efficiency of 59 percent for ™Ni by Hanson et af. (10) for Anaktuvak kidney from Bikini Atoll is due, in part, these samples are listed in Table 1. Generally, the liquid scintillation counter was set to record 10,000 sample counts or to count for 500 minutes. Background was counted for 500 minutes. and the average rate for the ™Ni settings was 15.8 + 0.4 count min~!, The detection limit at this background ®INi for lichens from the Aleutians is 20 0 al. 50 L - 4 100 150 200 Lower level discriminator settings 3 256 Fig. 1. Relative activity and discriminator settings for "Ni (A) and “Ni (©) spike solutions, plus the activity isolated from Tridacna gigas clam kidney collected from Bikini Atoll ((). Instrument settings were 20 percent gain and 4 percent window. Bikini and Eniwetok atolls lie in the path of the North Equatorial Current which moves water toward the Asian continent. Yon Arx (72) has described the circulation and refreshment times of both Bikini and Rongelap atolis and has found that the exchange of lagoon water with seawater resulted in winter jee daha von