INTERNAL DEPOSITION OF RADIONUCLIDES detonation were more active than the alveolar tissue. The importance of ingestion as a continuing source of contamination is evidenced by the level of internal contaminationof the pigs from Rongelap. These animals had about ten times the body burden of the human population in the same locality. .As the air-borne activity hadalready dropped to a low value at the time of evacuation of the humans, the contamination of the pigs duringtheir prolonged stay on the island necessarily derived from ingestion of radioactive food and water. Radioanalysis of water and soil samples from Rongelap indicated high levels of contamination from the fallout at early times following detonation. ; It appears that during the first month a limited amountof fission products was available to plants growing on the contaminated soil. Significant amounts of beta activity as well as small amounts of alpha activity were present on the external surface of plants at 42 days post detonation. Only very small amounts of beta activity and no alphaactivity were detected in the edible portions of fruits such as pandanus, papayas and coconuts. However, highlevels of activity were foundin the coconut tree sap, and the isotopic concentration was very similarto that of water. High levels of activity were found in fish taken from Rongelap lagoon. It appears that the ingestion of contaminated water and fish were the principal sources of internal contamination of human beings. Of the individual radionuclides, Sr®, because of its high solubility and relatively long radioactive half-life was probably the isotope of greatest potential hazard in the environment. Internal Radioactive Decontamination Therapy. Since there is no method of counteracting the effects of radiation from internally deposited emitters, treatmentconsists of removing the nuclides from the body as rapidly as possible. The ability of ethylene-diaminetetra-acetic acid (EDTA) to mobilize certain of the fission products from the skeleton and 75 to increase the rate of their excretion has pre- viously been demonstrated (11-13). It is most effective with the rare earth group, but has no effect on strontium (13). These studies have shown that most of the biologically hazardous material remaining in the bodyis firmly fixed in bone within a short time, so that effective systemic decontamination by chemical agents can occur only in a short period following exposure. Nevertheless, an attempt to effect in- ternal decontamination was made 7 weeks post detonation, since it would mobilize and make detection of isotopes easier, even thoughit was realized that the procedure would have limited value at this time. A representative group of seven individuals from Rongelap were selected for this study. During a control period of 5 days, 24-hour urine samples were collected daily for radioanalysis in order to establish a basal excretion rate. During the next 3 days, caleltum EDTA wasadministered orally, 1 gm per 25 lbs of body weight daily instead of the preferable intravenous drip because parenteral therapy was not practical under the circumstances. Twenty-four hour urine samples were collected daily during the treatment period and for 5 days following treatment to determine the effectiveness of EDTA in accelerating the excretion rate of the radioelements. Noside effects from the use of EDTA were observed. Blood counts and blood pressure remained unchanged throughout the treatment. The meanactivity of the urine during the EDTAtreatment period was 2.5 times the pretreatment activity. The probability that the differences observed are due to chanceis less than 0.01. Thus the oral administration of EDTAfor a period of 8 days beginning 52 days post detonation increased the excretion rate of internally deposited fission products, but the over-all effect on decreasing the body burden wasslight, as the excretion rates were very low at this time. Summary. Thefirst instance of internal deposition of mixed fission products in humans occurred as a result of fallout following a ther-