Table 9. Mean concentrations of 59Co in the muscle tissue of reef and pelagic fish collected at different times. Collection year intervals All reef species 60Co (pCi/kg wet wt) Number of samples Mean concentration Range in concentrations 1977-1978 27 2352209 19-897 1980-1981 12 146+110 31-430 1982-1984 12 60+51 7-180 ’ w All pelagic species 1977-1978 4 166+124 1981-1984 6 81+56 43-199 collections to those detected in the same tissues of the species collected from the same locations during 1964 and 1969.!1.13 A least-squares fit of the The effective decay constant is the sum of the physical decay constant (0.1317 y~!) and an environmental loss rate term that reflects the removal rate of 60Co. This removal rate is usually expressed as the ecological half-life (or decay Constant) and has a value for [Co of 7.8 y. The disappearance of ®0Co from Bikini lagoon and its availability to fishes is controlled both by radiological dilution. decay and by processes of remobilization, transport, and If 60¢q continues to decline in the environment at the present rate, the mean concentration of 50Co in the edible muscle tissue of fish from the lagoon should be less than 20 pCi/kg wet weight by the year 1990. BISMUTH-207 IN FISH The presence of 207p; (tj/2 = 33.4 y) was first reported in marine Samples obtained from the Pacific Proving Grounds in 1961.2! It was formed Possibly from a series of nuclear reactions such as 207Pb(p,n) or 206pb(p,y), assuming stable lead was present during testing as shielding material near the Nuclear devices.22 5000511 Other than a recent report describing 297Bi as a component ou ee Se inertia constant of 0.22 + 0.05 y-! (effective half-life of 3.2 y). aos been declining in the tissues of fish from Bikini with an effective decay atin stan at | appropriate present and historical data shows that the mean level of ®[Co has