of urine activity concentration variability, there was a 60% probability that the male value for K, would be different from the female value by the factor observed. Thus differences in the derived activity ingestion rates and dose equivalents were not significant. fod Figure 14 shows a semi-log plot of the 6575 and 1376. activity ingestion rate histories for adults on Rongelap. A curve was drawn between points, and the appearance of an increasing 1376, ingestion rate during the 1960's indicated the possibility of another contaminating event. The Hardtack Phase I series was conducted just prior to the observed increase in the curve and fallout from the Cactus, Yellow Wood, and Hickory experiments detonated at Bikini and Enewetak would have reached Rongelap. However, several observations fail to support the conclusion that recontamination was significant. increase in 65 137 These are as follows: 1) the Cs ingestion rate was not in conjunction with an increase of Zn; however, since 6575 is an activation product it may have not been produced in the same proportions. 2) The peak 13766 body burden at Utirik occurred nearly three years after the initiating event, Castle BRAVO, while the peak body burden at Rongelap followed six years after the potentially contaminating experiments of the Hardtack series in 1958. 3) The activity ingestion rate at Utirik demonstrated a continuously declining pattern versus the humped pattern observed at Rongelap. This occurred even though there was an equal external exposure rate history following the Hardtack series as measured by the U.S. Public Health Service on both Rongelap and Utirik (Un59). 4) The peak exposure rate on Rongelap following the Hardtack series was 10,000 times less than the peak expo- sure rate following BRAVO. These facts suggest that the Hardtack series was not a major factor influencing the Rongelap body burden patterns. Thus it is postulated that body burden variations were caused by travel away from the atoll 29