246 TRON-55 IN RONGELAP PEOPLE, FISH AND SOILS Disintegration rates of °°Fe in the samples were March 1970, and Fig. 1 shows a frequency determined by comparison with 5°Fe electro- distribution of the body burdens of males and deposited from a standard solution obtained females. ‘The Rongelapese which were included from the National Bureau of Standards. in this study consisted entirely of those indiCorrection was made for the self-absorption of viduals who were subjected to external radiation the X-rays in the electrodeposited iron. Stable in 1954. Tron-55 levels in the blood samples iron was determined colorimetrically, using o- were sufficiently high to permit count rate phenanthroline as the color-forming agent.) measurements to +5%at the 95% (20) conBody burdens were estimated by first measur- fidence level. Not all donors were weighed in ing the 5*le in a known volume of blood (4~ 1970, therefore body weights from previous years 26 ml}. ‘Total blood volume was estimated ‘were used to compute total blood volumes. using body weight and average blood volumes However, weights from previous years applied of 82 ml blood per kg body weight for males mostly to younger donors. Since weight generand 74 ml blood per kg body weight for females. ally increases with age, some individual estiThe iron content of blood was assumed to be mates of 55Fe body burdens, and therefore the 65% of the total body iron. This method of averages shown in Table 1, are likely to be calculating total blood volume is that used by conservative. Prersson®*) in his estimate of *°fe body burdens The maximum body burden in the males in Lapps of Northern Sweden. Previous esti- was 0.85 Ci, while 3 females had body burdens mates of body burdens from composite blood greater than this value. The maximum obspecimens":>) were made assuming that the served female body burden was 1.0 Ci, average total blood volume was 51. and that Table 1, Average °Fe body burdens of Rongelapese 60 % of the total iron is in the blood. Using this method with the Rongelap data, the average Date 55Fe 5°Fe body burdens agreed within 15% of those sampled No.of subjects/sex (uCi) * calculated using body weights. RESULTS AND DISCUSSION Table 1 gives the average body burdens of 5>Fe in the group of Rongelapese sampled in March 1970 March 1970 28/M 32/F 0.43 + 0.17 0.40 + 0.27 * Standard error (1c) of the mean. FEMALES No. of samples MALES Q 020 040 O60 0 0.20 O80 =5Fe body burdens (uCi) 0.40 0.60 0.80 >0,90 Fic. 1. Frequency distribution of *°Fe body burdens in Rongelap males and females, Body burdens have been grouped into classes. Example: 3 Rongelap males had °°Fe body burdens between 0.10-0.20 Ci while nine females had ®°Fe body burdens in the sameactivity interval.