INTERNAL DEPOSITION OF RADIONUCLIDES 5.3. Internal Contamination in Human Beings Tue INTERNAL ConNTAMINATION study was be- gun 15 days post-detonation with the collection of pooled 24 hour urine samples from the Marshallese and American groups. Maximum activity in the urine occurs during the first few days after internal contamination. By 1 week an approximate equilibrium state is reached in which the contaminants remaining in the body are firmly fixed, chiefly in the skeletal tissues. The activity in the urine then derives from radioelements which have been replaced in the natural process of biological turnover. Thus, the study madeis essentially that of an equilibriumcondition. The urine samples were sent to laboratories in the United States for analysis, since the high backgroundencountered in the field masked the relatively low levels of activity in the aliquot samples used. <A field laboratory is most desirable for a rapid survey, and was shown to be feasible, if adequate facilities are provided for the counting of the samples. The first urine samples, mentioned above, were collected for the Los Alamos Scientific toad Crt ~~! a co Laboratory (LASL). Similar samples collected 44 days post detonation were also sent there. On the 23rd, 24th and 47th days post detonation, 24-hour urine collections from each individual from Rongelap and Ailinginae were sent to the New York Operations Office, Atomic Energy Commission (NYOO-AEC) for analysis. In addition, samples from representative individuals in these groups were collected 21%, 3 and 6 months post detonation and sent to NYOO-AEC. The USNRDLcollected samples from each member of the exposed groups at 43 and 46 days post detonation. Samples from representatives of these groups were also collected at 214, 3 and 6 months by the USNRDL. In addition, samples from a representative group of 6 Amerieans and 20 Marshallese were collected for 6 consecutive days beginning 383 days post detonation. 5.31 69 Methods As a complete radiochemical analysis of all the urine samples was not feasible, samples were analyzed for only Sr**, Ba’°, the rare earth group andfissile material. These analyses are the most useful for evaluating the concentration and identity of all the potentially hazard- ous internally deposited radioactive isotopes. Measurement was also made of the gross beta activity of all the samples. Tofacilitate the processing of the large number of urine samples sent from the field, a scanning method for beta measurement consisting of a basic oxalate precipitation with a lanthanum carrier was employed on an aliquotof the 24-hour urine samples. This method rapidly concentrates the radioactive elements into a small volume and eliminates the normal K* background. A carbonate precipitation of the entire 24-hour sample increased the sensitivity of measurement sufficiently for analysis of samples collected later than 214 months post detonation. Thebeta activity was counted with a thin end window Geiger-Muller counter. The counter was calibrated with a U.O, standard, and an appropriate correction for self-absorption was made using a Sr® standard. 5.32 Findings and Interpretations 1. Beta Activity of the Urine. Internal dep- osition of radioactive elements was evidenced by the presence of significant amounts of beta activity in the urine. This activity decreased rapidly as a function of time, as it was derived chiefly from short-lived radioisotopes. For example, at 3 months post detonation, the mean activity of the urine of adults from Rongelap was 28 percent of the value measured 45 days post detonation, and at 6 months, the activity in the urine wasbarely detectable in most of the individuals. Comparison of the means of the urine samples for the adults from Rongelap and Ailinginae and from Americans from Rongerik indicated that at 45 days post detonation the