Transuranics in Bikini Lagoon *39Pu and 0.6 of ituting these val3.5 years and the 1k. we can com- reservoir supplythe lagoon. The ‘Pu must have st 97 total Curies y 1972, of this lost to the lagoon ansported to the samples from Bi- for *41Am and a total amount of cm of sediment Ci and represents ' the total activity npublished data). 1 ratio in samples omponents from was 0.74+0.17. is constant over ve estimate there Pu inthe surface nt. This source cient to account Pu reservoir pre- > of the reservoir substantially less ‘contained in the - sediment alone, < whether new or asses will act on > future (equivahan constant k,) nceentrations, or 240Pu in the atoll ilable to the wa- sms of the lagoon. -On the basis of the four most re- he average water 1 and Sr given -oncentration faces in Bikini coral % and 11 x 103. ral sections aver- The specific acs 0.072 pCi mg; its specific activity in the Bikini Lagoon water, assuming an average of 8 mg literof strontium in seawater (Goldberg et al. 1971), is 0.071 pCi mg”. The Sr therefore is incorporated by the living coral polyps in direct proportion to its concentration in the water andthere is no discrimination between Sr and stable strontium. The concentration factor for Sr is in good agreement with the average specific activity of 37 +10 pCi g™ strontium in recent coral surface sections from Enewetak reported by Knutson and Buddemeier (1973). If the stable strontium in coral is 8.9 mg g1, the Sr concentration is 0.33 pCi g¢7? coral. Based on our average 1972 concentration of Sr in water (0.33 pCi liter) at Enewetak (Noshkin et al. 1974), the concentration factor in Enewetak coral is 1.0 x 103. Our computed 7%°74°Py concentration factor agrees well with the results of Imai and Sakanoue (1973) who reported a concentration factor of 1 to 2 x 10° for fallout 239 240Py coral collected from Yoran Island (27°04’N, 128°25'E). The similar values in corals from different environments with different levels of contamination indicate that coral species take up ®°Sr and 29°24°Pu in proportion to the concentration in the water; therefore they serve as excellent indicators for environmental levels of these radionuclides. Values of 370 and 9,400 fCi literfor S0Sr and 137Cs were reported from a single filtered midlagoon bottom water sample collected at Bikini in August 1964 (Welander et al. 1967). In our November 1972 filtered midlagoon bottom water sample (Noshkin et al. 1974) we detected 315 and 340 £Ci liter? Sr and 187Cs. The similarity in the ©Sr values after decay correction showslittle change in the lagoon concentration at a specific location over the 8-year period. Our coral record over the same period confirms this observation. Again we must conclude that the mechanisms now releasing °°Sr and, as the coral record indicates, plutonium nuclides and lanthanides as well, are supplying these radionuclides to the lagoon at a rate that will 739 only slowly change the lagoon concentration with time. Specific radionuclides in the coral section—Precise measurements of *°Pu, **°Pu, and *41Pu were madein nearly all sections by mass spectrometry. Small, but nevertheless significant, changes are noted in the 240Py ; 239Py activity ratios (Table 3, Fig. 5) in the coral sections. The average **°Pu: 239Pu activity ratio was 0.77 + 0.07, the range from 0.57 to 0.88. In each post-test series year, 1957 and 1959, the ratio was reduced to an average of 72% of its test year value. In 1960 it increased by 20% over the 1959 ratio and has since changed by no more than +10% of the 1960 value. Assuming that the coral does not discriminate between the same chemical forms of 241Pu and 28°Pu, we found more variation in the activity ratio, as a function of time, than was anticipated. If both isotopes are released to the environment at the samerates, the ratio change in the coral sections should follow a 14.3-year decay curve (Fig. 5). An inspection of Fig. 5 and Table 3 will show that the 241Pu : 7®Pu de- cay-corrected ratios in the test year growths, 1954, 1956, and 1958, are lower than any extrapolated post-test year ratio would predict. These differences in test and post-test year ratio can only be explained if the plutonium isotopes had different ratios, in unique chemicalor physical forms, after production. A smaller amount of soluble 24!Pu relative to 2°°Pu was deposited in the lagoon water during the years of the test series while relatively more *41Py ended up in the atoll reserviors that now supply both ?41Pu and ?#°Pu to the lagoon. Even more significant are the variations with time in the 7°8Pu : 28°Pu values. In 17 Bikini water samples collected during 1973 (Noshkin et al. 1974), the average 758Pu : 239.240Py ratio was 0.018+0.006 (range 0.011-0.026). In the three most recent coral growth sections the average ratio is 0.040 + 0.005. The plutonium concentration factor based on *8°Pu is higher than the computed value using 79924°Pu concen- “ BR, aResTy! ° por *