Two Studies of Acute Internal Exposure to Man Involving Cerium and Tantalum Radioisotopes (Health Physics, 1969, Vol 16, Pages 325 - 332)

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Health Physics Pergamon Press 1969. Vol. 16, pp. 325-332. Printed in Northern Ireland TWO STUDIES OF ACUTE INTERNAL EXPOSURE TO MAN INVOLVING CERIUM AND TANTALUM Health Services Laboratory, U.S. Atomic Energy Commission, Idaho F'alls, Idaho Abstract-Actual exposuresofhumans to internal radioactive contamination provide our most valuable data in determining the behavior of these substancesin man. Two recent urposura at theNationalReactorTdng Stationdunomtratethe markedly different behavior that canrault from inhalation of insoluble particdata. In onc incident, an individual received a body burden burden was eliminatedin only 4 days, all of which was through the gatrointatinal tract with a total dose of about 10.3 rems to the lowu Iarge intestine. In the other incident, an individual received a body burden of 30 pCi of U2Ta and 150 pci of I q a . Approximately 937; of the activity was diminatcd in 7 days, the elimination being entirely in the feca. The remaining activity decreased at a rate not statistically different than the 115-day radiological half life of l*Ta, resulting in a d o x of 13 rems to the lungs. T h e actual biological elimination could be detected only on large samples of feca and amounted to less than O.OS%/day. The major contaminants were not detected in Z4hr urines in 6th- incident. THEHealth Services Laboratory of the Idaho Operations Office provides a routine in vivo whole-body counting progam for the protection of nearly 6000 employees at the National Reactor Testing Station in southeastern Idaho. During the last 7.5 yr, nearly 13,000 in vivo determinations have been made. Foreign activity involving 45 different nuclides has been detected in nearly half of all examinations made. Over 97% of the exposures involved less than 0.1 pCi with only 0.4% being in the range of 1-10 pCi. Yet in many cases, we have been able to determine the mode of excretion from the body, the effective half life of the specific nuclide involved, and other valuable information from such generally minute and physiologically insignificant quantities of radioVirtually all of the esposures have occurred from apparent inhalation of particulate matter of unknown particle-size distribution under uncertain circumstances during routine operations. In fact, the most important conclusions derived from this program to date are that the most likely source of internal contamination to be encountered around operating reactors is from inhalation of insoluble particulates and that their elimination from the body takes place so exclusively by way of the gastrointestina1 (GI) tract that the nuclide cannot be detected in urine even in a 24-hr sample. Consequently, urinalysis has long since been abandoned in this laboratory as a routine monitoring technique. It still finds application in the determination of organ dose from systemically deposited nuclides and in the detection of certain specific soluble nuclides such as iodine, uranium, cesium, etc., that are known to be absorbed by the body and excreted in the urine. The metabolic fate of inhaled insoluble particles in the body is much more dependent on the physical characteristics of the particle with which the activity is associated than with the ionic, periodic-table chemistry of the element itself. Actual exposures of humans to internal radioactive contamination provide our most valuable data in determining the behavior of these substances in man. Such information is much more informative and realistic than other data of this kind which is usually obtained

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326 . TM'O STUDIES OF ACUTE INTERXAL EXPOSURE TO h43.?? by extrapolation from animal data. Two recent exposures at this site demonstrate the markedly different behavior that can result from one case to another and confirm the need to document each incident as fully as possible. These exposures are of particular interest because they illustrate the difficulties of evaluation and dose projections a t an early time when therapeutic decisions are required. Particularly, the need for instrumentation and techniques for rapid determination of the distribution of radioactivity in the body for early decision making is demonstrated. The in vivo measurement of body radioactivity was made using the conventional 50-cm arc . technique with an 8 in. x 4 in. NaI(Tl)crystd in a cubical steel room, 9 ft on each side. However, because empirical calibrations had not been made for the particular nuclides involved in either case, the activity w a determined by direct calculation from the gamma tive results to be obtained within hours after the initial whole body mw u rune nb were made rather than the days or weeks that would have been required if it had been necessary to obtain the isotopes and calibrate the counter in the usual empirical way. Of particular importance, the dismbution of the activity in the body was determined by the technique of rotascanning'3.4) which involves scanning the subject from his nose,to his knees with a collimated NaI(T1) detector while the body is being rotated continuously. This technique permits an early estimate of whether the activity is in the lungs or the GI tract and thereby facilitates immediate and proper remedial medical action being instituted at the earliest possible time. Urinary and fecal elimination were followed by counting appropriate samples in a NaI(T1) well crystal. When necessary, specific determinations were made for 90Sr, ques. THE CERIUM INCIDENT At about 2200 hr, four workmen became contaminated with mixed fission producb during an assignment to perform non-routine maintenance on a crane which was normally located in a highly contaminated room. The crane had been placed on the roof of a large hot-cell room for decontamination and repair. The work area was surrounded with a plastic tion into the hot-cdl room below with air-flow velocities of about 50 ftlmin. The particular assignment of the four employees was to return the repaired and decontaminated crane to the hot-cell location. They were dressed in protective clothing, including shoe covers and rubber gloves, but no respiratory protection was used because of the ventilation present. After they had finished their work, readings of 60 to 120 &/hr were obtained from their clothing. A lifting device used to lower the crane back into the hot cell was found to be h e a d y contaminated. Three of the individuals were decontaminated without difficulty, but one had a level in excess of the 20 d j h r full-scale readings of the meter when placed in contact with his nostrils. Further ' decontamination performed by the pIant health physics technicians consisted of brush scrubbing, nasal swabbing, and induced sneezing. On a t least one occasion, matter cxpclled from the nose or throat had surface readings of 10-20 mR/hr. This individual had been in very dose proximity to the contaminated lifting beam, shaking and pushing it vigorously to make it fit the crane to be Iifted. m fact, he kicked it once so hard that he lost a shoe cover. By the time the radiation readings in the nasal area had been reduced to less than 0.5mR/hr at contact, it was approximately 0200 hr the following morning and he was permitted to go home. Unfortunatdy, he did not return to the laboratory for a whole-body count until 1600 hr that afternoon or about 18 hr after the exposure. His initial whole-body measurement showed major nuclides present. However, because of the relative insensitivity of the 2.18-MeV photopeak of 14Pr and the interference of the peak obtained with a SaI(T1) detector, the relative activity of the more radiologically hazardous ' W e was determined indirectly. Initially, cerium was separated chemically from a sample of material taken from the same area as that in which the exposure had occurred

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and the ratio of ' W e to determined from the 0.696-3ieV photopeak of the 'MPr daughter was found to be 1.5. However, whole-body spectra of the other three individuals who had presumably inhaled the same material showed markedly dissimilar ratios between the photopeaks of the cerium nuclides and those of the P5Zr-95Nb. Since this evidence suggested strongly that either the source was extremely heterogeneous or that more than one source was involved, the ratio of the cerium isotopes was redetermined on material actually known to have been present in the individual involved. O n 6 different samples of feces, values ranging from 0.6 to 0.8 were obtained. A value of 0.75 was used in the dose calculations. Gamma spectra of the Same fecal samples showed distinct differences in the cerium-zirconium ratios as well. Both results conk the heterogeneity of the material involved, . counts, a rotational whole-body scan was made to determine the source position or distribution in the body. At 18.5 h r after exposure, the maximum activity was already wdl down the trunk, corresponding to the upper GI tract or lowcr lung area. At 23 hr after exposure, the activity had moved further and now appeared to be located in the lower large intestine with little if any detectable involvement of the lungs. Since most of the activity could logically be expected to be eliminated in the following day or so, and on the assumption that most of the activity was due to with a relatively low effective energy of about 0.2 MeV, it was felt that the dose sustained would not be large and did not call for emergency measures that night. Consequently, the medical department was not notified until the following morning, about 36 h r after the exposure, when additional body measurements would be available. Even though the ratio of ' W e to lalCe was not yet available, the early dose estimates were sufficiently large, particularly if most of the cerium activity should turn out to be from IUCe, that remedial medical treatment seemed indicated and prudent without further delays while waiting for additional analytical information. Consequently, the subject was given an enema, 3 teaspoonfuls of magnesium sulfate orally in a half glass of water and 1 g of the calcium salt of diethylenetriaminepentacetic acid saline solution. The same DTPA dosage was repeated on each of the next 2 days in the hopes of solubilizing any material deposited in the lungs to hasten its excretion. A shown in Fig. 1, elimination of the activity was surprisingly rapid and complete although this result cannot be attributed to the remedial action taken. Despite the rapidity of the elimination and the small number of experimental observations made, the difference in the slopes of the two c w e s with effective half lives of 8 and 10 hr might be real in view of the fractionation known to have taken place. The dashed portion of the two cuwes reflects the time of passage through the GI tract before elimination began. Using the value of 0.75 for the ratio of "Ce to "Ce finally obtained, the initial whole-body measurement indicated and 13.5 pCi of 95Zr-gSNb for a total body burden of about 77 pCi of activity. Almost exactly 4 days later, the to& body burden was composed essentially of 0.1 pCi of 141CC'44Ce 99.7 % of the total body burden was eliminated All feces and urine eliminated during the 5 days required for virtually all of the body radioactivity to disappear was analyzed, concurrently with the in viva measurements. The excretion pattern was the same as that observed in this laboratory for years when insoluble particles are involved: elimination of both cerium isotopes and the zirconium-niobium took place exclusively through the GI tract with no trace of these nuclides being detectable in any 24-hr sample of urine, even though several microcuries were known to have been eliminated per day in the feces. However, the activity known to have been eliminated from the body by direct in viva measurement could not be accounted for in the excreta. Of the 77 pCi known to have been present initially, the total elimination in feces was only 19 p c i . For example, 26.4 pCi of total activity disappeared between the first two whole-body measurements shown in Fig. 1 ; yet, a single small sample of feces voided in this same period contained less than 400 dislmin including any

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Fxc. I. Decrease in b d y radioactivity observed POST- EXPOSURE TIME, hours natural activity present. In contrast, between the sixth and seventh body measurements made between the third and fourth days after exposure, 6.8 ,uCi was found to have disappeared by in uiuo measurement and 6.6 pCi was present in two normal samples of feces. Apparently, much of the initial contamination was external which, despite the vigorous deiiberate efforts to decontaminate, was removed quite rapidly and compIeteIy by normal washing, perspiration, abrasion of clothing and bedding, etc., during the subsequent few days. In view of the txtensive nasal contamination observed during the initial efforts at decontamination, another such elimination, perhaps discarded unconsciously, could easily have accounted for the difference. Even if only 19 pCi was actually present internally, elimination was still about 99% in 4 days. It appears that even a good mented by adequate analyses of excreta to prevent overestimation of the internal hazard resulting from external contamination. Also, because of the physical Gactionation of components that can and does occur in the body from heterogeneous :ouces, fecal samples should undoubtedly be analyzed spectralIy both for determination of the quantity present and for proper determination of the 'contsbution of each component to the dose received. 131r were detected in the urine samples but in such minute quantities that the resulting dose to the muscle, bone, and thyroid, respectively, were completely negligible. The same is true of the dose to either lung or bone from either plutonium or enriched uranium that might have been present. The total dose to the GI tract was calculated to be 10.3 rems, taking the lower large intestine to be the critical portion. The dose \vas calculated by a step-wise integration of the activity present in the body over the time interval that it

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was known to have remained before excretion. After each elimination, each successive segment was similarly calculated from the new activity level obtained from whole body counting over the time period until the next elimination. Duwsion of Case I The management of Case I indicates the need for prompt recognition by the plant health physicist that internal contamination might be significant. Irrigation of the nose and nasopharynx should be considered an important part of the initial medical management. Plant nursing personnel should be trained to perform such irrigations. This action will frequently reduce the quantity of radioactive material which passes through the GI tract and thus be a major factor in reducing the dose to'the GI system. Vigorous decontamination procedures, particularly brush scrubbing, should not be continued to a point of injury to the patient. T h e present individual had brush burns on the upper lip and around the nose due to the initial decontamination efforts which formed a superficial eschar that required about 1 week to heal. Positive readings on a survey instrument can and do occur with high-level internal contamination and promote continued and %-advised efforts to decontaminate the surface. The frequency of superficial contaminations in plant operations make the health physicist or technician vulnerable to assuming contamination to be on the skin …