Transuranics in Bikini Lagoon data to conform a most important complicates the vior of plutonium ronment. It does hese data, to prehavior of all pluironment from an stope of the elesearch is still reogeochemistry of he coral sections with Eu (Fig. 55Bu : 239Pu ratio ises in value with ears which is the 3 of 5Eu. Simi- appear to govern ‘ this lanthanide 1, and the way in > correlates with sessment of each that the 244Am in originates from soral and also dient. If the envim is from 24!Pu loes not discrimitransuranics, the tio in the coral le growth curve . 7 are the ratios 1Pu in each coral ilculated growth (t) = 1954). Al- : we find that the irs, with the ex- le, are changing nsistent with the r, all the values 1954 curve and 1 from a growth 3 or 1958. The »wth section falls wowing there was ly produced dur- £ we assumethis 1 1958 test series, e been preferen- tially enriching ?4‘Am over *41Pu, or the concentration factor of *#Am must be greater than plutonium for this marine organism. Concentrations of several radionuclides in the sediment from station B-3 are shown in Table 1. The ratios of *#1Am, ®Co, and 207Bi to 15Eu in the surface 5 cm of the fine and coarse (>0.5 mm) fractions are compared to the ratios in the most recent coral section in Table 7. Both the *1Am : 155Eu and the Co : 7°7Bi ratios in the coral are similar to those in the sedimentary phases. However, the Co: 155Eu and *07Bi : 15EFu values are greater in the recent coral than in the sedimentary environment. If the sediments are a_ principal source now supplying radionuclides to the lagoon, by dissolution or exchange or other processes, then wefind that relative to the sediment the coral does not discriminate between Eu and *#1Am, but ®Co and 707Bi are greatly enriched relative to 1Eu. This implies that processes governing the fate of 1°5Eu in the lagoon are similar to those for ?41Am. From the above comparisons, and the concentration factor arguments, we may discountthe possibility that the source of the radionuclides in this particular coral that we analyzed is in trapped, previously resuspended, sedimentary material. The coral is functioning rather as an indicator of the aquatic environment. In an attempt to see whether a naturally occurring radionuclide could be used to confirm the age of the coral sections, we separated from the coral and measured the 210Po, the daughter of 2!°Pb (#12 = 22 yr). Provided that the environmental levels of 210Ph are constant, the amounts taken up by the coral reflect the age of any section relative to the youngest section, because the concentration within the coral changes due to radioactive decay. When the activity levels are corrected to the date of coral growth (as shown in Table 5), the concentration-time relationship should be invariant. The data from 1966 to 1971 fit this model very well. The decay corrected 210P9 (71°Pb) concentrations during these years averaged 0.20 + 0.03 pCi g". In the TAl sections identified with the test years, however, there are small but definite increases in ?!°P9 (?!°Ph) concentrations, which cor- relate in time with the increases noted for the artificial radionuclides. Several investigators (cited in Beasley 1969) have discounted the possibility that 7!°Pb was produced from weaponstesting, but the elevated levels recorded in the coral during nuclear test series are at least circumstan- tial evidence that elevated levels of *1°Po (?°Pb) were present in the Bikini environment during those periods. It appears, from the later years’ growth, that *1°Po (7°Pb) levels in coral from remote environments may be used as another means to date modern coral growth, confirming the work by Dodge and Thomson (1974) and Moore and Krishnaswami (1972). References Beastry, T. M. 1969. Lead-210 production by nuclear devices: 1946-1958. Nature (Lond.) 224: 573. 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