w 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 contamination of 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 had already dropped to a low value at the time of evacuation of the humans, the contamination of the pigs during their 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 avail- able 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 alpha activity were detected in the edible portions of fruits such as pandanus, papayas and coconuts. However, high levels of activity were found in the coconut tree sap, and the isotopic concentration was very similar to 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 herapy. Since there is no method of counteracting the effects of radiation from internally deposited emitters, treatment consists 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 previously 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 body is 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 internal decontamination was made 7 weeks post detonation, since it would mobilize and make detection of isotopes eusier, even though it was realized that the procedure would have limited value at this time. A representative group of seven individuals from Rongelup were selected for this study. During a contro] 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, calcium EDTA wasadministered orally, 1 gm per 25 lbs of body weight daily instead of the preferable intravenous drip becnuse 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. No side effects from the use of EDTA were observed. Blood counts and blood pressure remained unchanged throughout the treatment. The mean activity of the urine during the EDTA treatment period was 2.5 times the pretreatment activity. The probability that the differences observed are due to chance is less than 0.01. Thus the oral administration of EDTA for a period of 3 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. NSummery. The first instance of interns] deposition of mixed fission products in humans occurred as a result of fallout following a ther-