T. M. BEASLEY, E. E. HELD and R. M. CONARD 1961-1962 tests were maximal."8 Speeds of surface currents in both the California and North Equatorial Currents are sufficiently large to account for transport of waters from 30 to 40°N latitude to Rongelap Atoll”) in the time period 1961-1963; similarly, maximum surface de- position of §5Fe occurred in 1963," and thus the data ofTable 2 probablyreflect contributions from both sources. The higherspecific activity noted in goatfish liver in August 1963 may reflect more nearly the specific activity of waters at Rongelap Atoll than does the sample of March 1963. Livers from immature goatfish were used in the August specimen, while the March sample was obtained from mature fish. Recent measurements of the specific activity of immature and mature goatfish liver collected at Johnston Atoll in 1968 showed that immature fish livers contained less stable iron and more 55Fe per unit wet weight than did livers from mature fish. We assume that the immature fish are in the process of forming their iron stores and therefore more nearly reflect the 'o 5% at .a). Stable » collection environmental specific activities than do the mature fish whose iron stores are already formed. In the latter case, exchange rates may + alter the stable be slow. Our measurements of 55Fe in soils collected from the samesites between 1959-1963 do not clarify either of the input sources mentioned above; the changes in concentrations are greater activity. In this che of soil is a rccur as a result .ctivity, ine activities in than can be accounted for by physical decay. : Rongelap be2 an ecological Natural processes which remove 59Fe from the upper 2.54 cm of soil may preclude its use as a val to that obsmecific activities umes; however, precise collector, and therefore the results are useful only to indicate order ofmagnitude values of ®5Fe soil concentrations present at the collection time. Unfortunately it is not possible to offer a clear argument in explanation of the 55Fe body burdens of the Rongelapese presented here, at this time. Samples from 1963 through 1969 would have shed light on the problem, but cnual loss would ~ retention and “mn, or the time axumum specific . iear devices in 4% radionuclide . by atmospheric of radioactivity -Uward-moving “cised of waters ..tout from the none are available for analysis. In a speculative nee eee hee ae teen ‘wity of goatfish :d 1963 reflects ‘neentrations of vein, several explanations can be advanced. First, the possibility of Rongelap lagoon acting as a nutrient and trace-element ‘“‘trap”’ similar to estuaries'!8) is intriguing. Removal and retention within the lagoon of both stable iron and §5Fe from the North Equatorial Current could lead to high specific activities of **Fe in 3 249 species important in the Rongelapese diet. The fact that livers from mature goatfish contain between 2-3 times as muchstable iron per unit wet weight as do livers of mature salmon!) is consistent with this argument. Second, Jennincs7) and more recently Preston@*) have suggested that large amounts of 55Fe were introduced into the northern hemisphere as tropospheric fallout during the 1961~1962 test series and that deposition may have occurred in rather narrow latitudinal bands (maximum input at 60°-70°N (Preston). JostrH ef al.@% suggest that subsequent stratospheric deposition of 5*Fe from these tests was similar to that observed for 90Sr, i.e. maximum deposition at 45°N. Transport of 55Fe from these high latitudes by major ocean current systems feeding the North Equatorial Current (in addition to biological and physico-chemical factors) will deplete northern waters of this radionuclide. As dis- cussed earlier, transit time for these waters from high latitudes to Rongelap Atoll ismeasured in year, and it is therefore possible that the higher 55Fe body burdens in the Rongelapesereflects a “‘lag”’ time between the *5Fe specific activities of Northern Pacific and Southern Pacific Ocean biota due to this transport. Finally it is possible that the high 55Fe Rongelapese body burdens relative to the Japanese donors results from a combination of dietary intake and uptake and retention differences for iron between the two groups sampled. Unfortunately precise dietary information for both groups is lacking andlittle is known about the 5*Fe specific activities of the foods eaten by both groups. The Rongelapese do not suffer from iron deficiency anemia, so enhanced uptake of iron from the diet is probably inconsequential. Itis clear that further measurementsof the specific activities of 55Fe in the diets of the Rongelapese and other maritime cultures and the effective half-life they display for this radionuclide will be needed to clarify the questions raised here. Acknowledgement—We thank Mr. T. A. Joxera for technical assistance and Dr. M. Fuarra for kindly arranging for the blood specimens from Tokai-mura, Japan. Dr. A. H. Seymour and Mr. H. E. PatMer provided helpful discussions during preparation of the manuscript. Supported by AEC under Contract No. AT(45-1)-2225-14 and AT(26-1)-269.