Fact Sheet - Los Alamos Involvement in the Human Studies of Plutonium

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Human Studies Project Team Fact Sheet Los Alamos Involvement in the Human Studies of Plutonium Basis of Tolerance Animal Studies of As Los Alamos scientists used increasingly larger amounts of plutonium in the Manhattan Project work of 1944 and 1945, they r e c o p e d that strict precautions were necessary to protect workers from h s hazardous substance. However, no definitive information was avadable that could be used to establish plutonium tolerance limits for humans or to measure occupational exposures. (Tolerance limit or dose was the terminology used at that tune.) In 1945, the Manhattan Engineering Distnct authorized human studies for the collection of these important data. In January 1944. milligram quantities of plutonium were first delivered to Los Alamos for its work in the Manhattan Project. At that time, Project scientists had proposed a tentative safe tolerance limit of 5 micrograms of internally deposited plutonium as a standard for Project sites. This tolerance limit for plutonium was based on limits adopted for use in the radium dial-painting industries. By comparing the equivalent radiation depositions of plutonium and radium. the Manhattan Project's Medical Division speculated that plutonium was one-fiftieth as toxic ;1s radium. hence the 5-nucropram limit. Because of the lack of knowledge about plutonium's toxicin., animal metabolic studies were initiated in 1944 at three Manhattan Project laboratories: the Cni\,ers:t! of California Radiation Laboratory at Berkeley, the Metallurgical Laboratory ar the University of Chicago, and the University of Rochester School of Medicine and These studies showed that plutonium depositions in the body (body burdens) could be determined by measuring the concentrations of plutonium in urine samples. The excretion model based on animal data would be a means to monitor workers for evidence of plutonium exposure. In June 1944. data from the Chicago animal srudirs that the excretion rates for plutonium among the various types of laboralor). animals could v a q by as much as a factor of 5 , and that humans probabljp would daily excrete 0.01 '% of the plutonium retained in their bodies. An animal study at Los Alamos. authorized by L o s Alamos Laboratory Director J . Robert Oppenheimer in August 1944, was initiated because Los Alamos personnel wanted a method to detect plutonium burdens less than 5 micrograms. These studies showed that the percentage of plutonium excreted by rats was independent of the total amount administered: regardless of the size of the dose, the percentage of plutonium excrered remained the same Los .4lamos Health Group personnel saw this information as critical for evaluating occupational exposures to plutonium based on the analysis of urine samples

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Human Studies Project Team Fact Sheet By February 1945, the arumal-derived 0 01 X excretion model had been used at Los Alamos to estimate plutonium burdens for personnel who were workmg with large amounts of plutonium Unne analysis results obtuned m February and March 1945 suggested that some of the workers mght have approached or exceeded a burden of 1 mcrogram The concern was that doses to workers would exceed the 5-rmcrogram lebel as larger quantities of plutoruum were processed In a letter dated March 29, 1945. addressed to Colonel Stafford Warren, Director of the Manhattan District Medical Division at Oak Ridge, Oppenheimer pointed out that the hazards of workmg with plutonium at Los Alamos were probably much more serious than were those at orher Project sites. The risk associated with 5-microgram depositions and the uncertainty associated with the animal-derived excretion rate were reasons for Oppenheimer to endorse a series of animal and human srudies aimed at protection for plutonium workers. The subsequent human plutonium injection studies authorized by the Manhattan Engineering District involved 18 hospitalized patients in four locations: one patient at Oak Ridge. three patients at the Universip of Chicago. three patients at the University of California, Berkeley. and eleven patients at the University of Rochester School of Medicine and The purpose of these studies was to decrease the uncenanr). of extrapolating animal experimental data to provide data on the deposition and excretion of plutonium by humans, and provide a quantitative basis for de tem ning plutonium exposures to worhers and establish cnteria for remox ing personnel from further exposure Oak Ridge study. In April 1945, the Manhattan Project's Medical Division, headquartered at Oak Ridge, Tennessee, arranged for a hospitalized patient at Oak Ridge to be injected with a plutonium solution (this solution was not provided by Los Alamosi. A sample of this solution, as well as urine, fecal, and other biological samples. was collected and shipped to Los Alamos for analysis. The first series of urine samples were analyzed for their plutonium activity on April 24, 1945. None of these biological samples remam at Los Alamos. Chicago and University of California, Berkeley, studies. Los Alamos did not participate in these studies. From October 1945 to July 1946, eleven patients at the University of Rochester School of Medicme and Dentistn each received one injection of a plutonium solution supplied by Los Alamos Unne. fecal. and other biological samples LALP-94-25 Los Alamos Involvement in the Human Studies of Plutonium Page 2

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Human Studies Project Team Fact Sheet were sent to Los Alamos for radiochemical analysis. None of these samples remain at Los Alamos. The results of these studies were valuable to scientists in their efforts to find ways to ensure protection for plutonium workers. Below are some of the findings: The injection of a single dose of up to 100 micrograms of plutonium had no acute subjective or objective clinical effects on the patients. As with laboratory animals, the skeletal system was the major site of An equation (the Langham equation) was derived that describes the excretion rate of plutonium as a function of time after exposure. The biological half-life (the time it takes the body to excrete half of its original plutonium deposition) was estimated to be about 118 years. The results of these studies continue to play a major role in nuclear heaith-monitoring activities. Today health physicists still rely on these findings to estimate plutonium exposures and to ensure radiation protection for workers. The principal findings of these studies have been confirmed by evaluations of A classified report (LA-1151) on the Rochester studies was prepared in 1950 b! Wright Langham. who was principal investigator for this research at Los Alamos. The information was declassified in May 1971 and republished in the 25th anniversap special issue of Healrh Physics, June 1980. The results of the Rochester study have been cited in several open literature publications beginning in the late During recent reviews of the Rochester records, tabulation errors were noted in several sets of data. These errors did not significantly change the conclusions of the studies or the health protection methods derived from them. LALP-94-25 Los Alamos Involvement in the Human Studies of Plutonium Page 3