248 TRON-55 IN RONGELAP PEOPLE, FISH AND SOILS Table 3. Iron-55 content in goatfish (Mulloidichthys, sp.) and soil samplesfrom Rongelap Atoll. Number of jish livers contributing to single, pooled sample analyzed are in parentheses; stable Fe and *°Fe are expressed per kilogram of wet tissue or per kilogram dry sotl Content ope Location Collection date Sample 55Fe (uCi)* Stable Fe Fe (g) (Ci) g 0.98 0.76 1.15 0.37 4.1 0.9 1.2 6.7 Biological samples Rongelapislet Kabelle islet Rongelapislet Kabeile islet Liver Liver Liver Liver (20) (7) (10) (71) September 1959 September 1961 March 1963 August 1963 4.04 0.68 1.40 2.49 Soils Kabelle islet Kabelle islet Rongelapislet Rongelap islet Soil Soil Soil Soil (0--2.5 (0-2.5 (0-2.5 (Q-2.5 cm) cm) cm) cm) August August March August 1959 1963 1959 1963 0.24 0,06 0.05 0.006 * Sample counting times were arranged to determine *°Fe in biological samples to +5% at the 95% confidencelevel (20); soilsamples to +5-20% at the 67% confidencelevel (Ic). Stable Fe determination, +10% at the 67% confidence level (lo), Activities are corrected to collection date. on the levels of Zn, ®7Cs and Sr observed, 55Fe body burdens were probably small.4® The plant detritus could significantly alter the stable iron content but not the 55Fe activity. In this 1957. Whole body counting and urinalysis measurements one year later disclosed increased body burdens ofseveral radionuclides, the most of input or loss than is specific activity. The decrease in **Fe specific activities in Rongelapese returned to the atoll in mid-July notable being "Cs. It is probable that ®*Fe body burdensincreased similarly. The concentrations of **Fe in a selected species of fish and in the calcareous soils are listed in Table 3. Activity in the fish is based on wet weights for comparison with previous work, The amount of sample that was available for analysis was smal] and therefore it was necessary to combine individual samples. This prevents an estimate of the range of 5°Fe concentrations which occur between fish, te. the within sample variation. The number in parenthesis in Table 2 for the biological samples indicates the number of fishes which contributed to the pooled, single sample analyzed. The 55Fe values for soil samples collected in 1963 at both Kabelle Islet and Rongelap Islet are averages of samples collected at depth increments of 0-1.3 and 1.3-2.5em. Specific activities are not given for soils since varying amounts of pre-1954 instance, activity per unit weight of soil is a better index of changes which occur as a result Mulloidichthys, sp. (goatfish) at Rongelap between 1959-1961 corresponds to an ecological half-life of 11 months, identical to that ob- served by Jennincs.“*) Higher specific activities may have occurred at earlier times; however, estimates based only on exponential loss would not take into account possible retention and cycling of **¥e within the lagoon, or the time lag between deposition and maximum specific activity in the aquatic biota. The increase in specific activity of goatfish liver between late 1961 and mid 1963 reflects the increased environmental concentrations of 55Fe resulting from testing nuclear devices in 1961-1962. Introduction of this radionuclide to Rongclap Atoll can occur both by atmospheric fallout and by water transport of radioactivity from oceanic regimes. ‘The westward-moving North Equatorial Current is comprised of waters from northern latitudes where fallout from the