Cesium-137 and Strontium-90 Retention Following an Acute Ingestion of Rongelap Food (Partial)

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sc\r York. and tBroolih.aven National Laboratory, Upton, New York. Marine and plant foods used by natives living on Rongelap in the Marshall Islands contain higher levels of long-lived fission-product rdionuclicies th?m do diets of people living in the United States due to residual contamination from fallout in 1954. During the 1963 med,ical survey of the ~ongelap population, three food items indigeno~s to the ilonge~ap diet were brought back to the United Stazes and consuz,ed over a seven-day period by a member of the medical team. The inges - Iion of thess foods introduced levels of 90Sr and 137CS which were 20 and 60 umes higher, respectively, than in the normal diet and was therefore considered in terms of an acute intake of two fission-product radiomclides tixt are important from a radiological standpoint. Urinary measurements were made with a whole-body counter. The urine was ‘37CS whereas the feces was thethe principal excretory route for the nam removal means for the ‘OSr. The’ retention of ‘OSr could be , represented by a series of exponentials, whereas the retention of cesium as determined by whole-body counting indicated that a single long-term component with a biological half-life of 74 days describes LIe removal process. Reasonably good agreement was obtained be- :!v?en retention as determined by whole-body counting and by excretion meay~rements. It is estimated that about 2570 of the ‘OSr from the i?mgelap food was retained by the body at the end of 190 days. The

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744 HARDY, RIVERA, AND CONARD average urinary to fecal excretion ratio was 3.5 for ‘J7CS and 0.06 for ‘OSr. These findings are in agreement with other .Wutiies during With Natives of Rongelap in the Marshall Islands consume indigenous plant and sea foods that contain long-lived fission-product radionuchcies from fallout that occurred in 1954 during Operation Castle. The body burdens of these people, particularly with regard to ‘OSr and 13TCS, are higher than those of U. S. inhabitants. Although estimates of total-bociy concentrations of these two radionuclides have been made directly for ls?cs with a portable whole-body counter and indirectly for ‘“Sr from urine analyses, the amount of foods consumed varies at different times ,, of the year, and therefore information on the assimilation xcd excretion of specific nuclides as related to body burden has been difficult to evaluate. It was felt that a controlled intake and excretion study with the use of the 90sr ‘and ~37cs naturally present in Rongelap iood would provide valuable data. Since controlled intake and excretion studies on Rongelap natives was not feasible in the field, it was decided by one of the authors (Robert A. Conard) that useful information in this regard might be obtained from an intake and excretion study Carried out on himself using Rongelap foods brought back to 13rookllaven National Laboratory (BNL), where a whole-body counting facility would be available for the study, and consumed under controlled conditions. Although these foods did not represent a typical native diet, it was fe!t that the relatively high levels of ‘OSr and ‘37CS present in them would make it possible to study quantitatively the excreclon rates of these nuclldes after an acute ingestion. As part of the annual medical examinations of Rongekp ~atives who have been exposed to fallout radiation following the detonation of a high-yield thermonuclear device at Bikini Atoll in Ma:ch 1954, 2k-hr urine specimens are collected. These samples have been analyzed for 90sr at the Health and Safety Laboratory (H.$SL) during the past several years. The purpose of these analyses has been to the long-term chronic exposure of the natives to this radionuclide through ingestion. A portable whole-body counter was csea aunng the 1961 survey, as in previous surveys, to meas~re the 137CS body burdens of the natives directly, but this instrument has not been available for

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subsecldent surveys. Therefore HASL was requested to analyze the urine Specimens collected in 1963 &nd 1964 for ‘37CS as well as for ‘OSr. In 1962, the year Oi :he l~st reported survey,l the mean urinary irom which the body burden was estimztedi,2 to be 12 nc. In comparison ac:uits m & metabohc wa.rc? at Hines Hospital in Ch~cago, Ill., in 1962 In 1961 the average 13:CS bo&J burden of the Rongelapese was 14.7 nc per kilogram of body weigM compared to 0.048 nc per kilogram of body ‘37CS body burdens of Rongelapese in 1961 and 1962 were therefore about 24 znd 300 times higher, respectively, than those oi individuals living in the United States. The average 13qCs body burdsn of Rongelap n%tives in 1961 was as high as or higher than the burdens of L~pps arid Es’knr.os, who have unusually high body burdens. Assurmng th~t 50 ‘kg is the average weight of a Rongelap native, ons can calculate, based on the reported data, an average body burden in 1961 of 735 nc of ‘3TCS. Tilis value may be corqnred 10 the measurem.ents5 made on Finnish Lapps in May 1962 which showeci an zverage body burden of 508 nc of 137CS. Whole-body coumsG, of Alaskans at Anaktuvuk Pass showed an average of 421 nc of 13TCs clurmg the summer of 1962. It is now clear dxit the high Rongelapese body burdens are the result of consuming the vmious typzs of contaminated food which co.m e from the sea or are count data showed that the mean 13Tcs levels of Rongelapese who were exposed to the heavy fallout in 1954 were not significantly cliff erent from the boay burdens of those who were not ex~osed.4 During z single 24-hr period in September 1959, nine Ron@ap total-diet samples were coilected by the University of Washington Laboratory of Radiation Biolo=gy and subsequently analyzed for ‘37CS takes averaged 2.4 and 0.084 nc, respectively. Although individual foods were not analyzed in this study, it was reported that >andanus was one of the highest contryoutors of these radionuclides to total diet. MATERIALS AND METHODS During the 1963 Rong&jlap medical survey, several kilograms each of pzndarms pulp, coconut meat, and coconut milk were collected, frozen, and brought bzck to the United States. Over the seven-ciay period from JuIy 2 to 8, 1963, one of the authors consumed 4.85, 1.75, and 3.20 kg of the pandanus, coconut ,meat, and coconut milk, respec - tlvel~, in addition to a, normal diet. Total fecal and urinary samples were collected for two consecutive three-day periods prior to the

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746 HARDY, RIVERA, AND CON.4RD consumption of the Rongelap food, for three- and four-{izy per:mls whiie the food was beixig consumed, and for two consecutive t!mee-d>y per:ods after the last day on which the Rongelap food was consumec.. Thereafzer, for tine next 184 days, 24-hr excreta samples wer? collected Cn Fi-id~y of each week. Whole-body counts were dons at regular X.erV21S. Food aliquois anti excreta specimens were se~t to H.ASL ior ‘OSr and ‘sTCs malyses. The food was dry-ashed in a muffle ?mmace at a~~roximately 450° C and solubilized by fusing with sodium carbonate and dissolving the pulverized melt in hot water and finally minersl acxi. Cesium- 137 was separated by the hot-watsr leach and th?n exzracted from solution with ammonium phosphornolybdzte. The cesium was purified by sorption on the selective elution from a cQLooexchange resin and then precipitated as the tetrapheny~~orzte Zor ccrmting. A complete description of this procedure is give: m the HASL procedural manual.g The mineral-acid portion of the dlssolv ed melt was evaporated to dryness in dilute acid. The dehyd:-atsci silica was filtered, and a carbonate-collection precipitation was carried out on the solution. After filtration the carbonate precipitate was tiisscdved in nitric acid, and the solution was’ evaporated to drycsss. Successive fuming nitric acid separations were used to separate stroritimn from calcmm and other interfering ions. Radium and lead were rernoveci by scavemgicg with barium precipitated as the chromate. Traces of other SOY was ~rec:pitated as the90Sr With its daughter)bration of the hydroxide and converted to the oxalate for counting. This procedure is also described in the HASL manual .8 All counting was done w~i~ 10Wlevel beta scintillation counters designed at HASL. 9 The urinary a.zd the fecal samples were wet-ashed with nitric acid, and the resxices were fused to effect complete dissolution. From this point, iciemic~! procedures to those previously described were usec? to sepzrzt? Cesium- 137 body burdens were measured with the BNL wkole - bociy counter. Measurements were taken at conveniem xtervals durizg and after the consumption of the Rongelap food. These 137CS values were corrected for. contributions of 137cs present in the norm,al diet. l’hIs correction was made with the assumption that the subject’s norz,zl diet during the experimental period was similar to that of non– miikdririking BNL personnel during the same, period. The nornm! bo@ burden was assumed to have increased linearlyl” from 6.35 EC m July to 10.8 nc at the end of December 1963. the seven-day period is shown in Table 1. Panckmus contributed the

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137cs AXD ‘OSr RETENTION FRONI RONGELAP FOODS 747 ROXGELAP FOOD, JULY 2 TO 8, 1963 Picocuries of ‘OSr per ,major porrion of the activity of Intake for seven-day period Ulc. ‘21.Cs retake per day from these Rongelap foods was xbout 20 md 60 trees Ahigher, respectively, than from a normal New York City area diet during this time. II initially, the activity from the Rongelap food essei:iizlly masked the contribution from the normal diet, but later in mcrsasingly important. In retrospect, it was unfortunate thzt the normal diet of the subject was not measured because the ‘OSr axial l~yCs levels m foods were increasing during tins period, caii?c~:ans me given in Table 2 and are plotted as a function of time m Figs. 1 and 2. Calcium measurements were made on the food and excreta szrnples, but, since the calcium intake from the normal diet Wzs riot lmown, the urinary and fecal calcium excretion dma are dif - ficuit :0 interpret quantitatively. The average urinary calcium wzs 170 ~ -Xl mgiday, and the average fecal calcium was 360 ~ 150 mg/day. Ties e values do not indicate a metabolic abnormality, although the low ieczi caicium reflects a very high absorption. In Fig. 1 the 137CS excretion via the urine and the feces is plotted. The smoo~hed curves through the data points were drawn by eye. .Is has been observed in other studies,12-17 the main means oi 13TCS excre:ion is urine. Fecal excretion fell off very rapidly, indicating thm ~37c~ invested was not absorbzd.osly G relatively small amount of the Se~iher the urinary nor the fecal excretion r~te fell 10 preexperimem levels zc Zhe end of 190 days. This was probably due to the increase in zhe normal dier 13Tcs which took place during this ?eriod. 9osr as shown in Fig.‘I’he excr e~ion pattern of 2 contrasts markedy Wi:h .:hd of l~~cs. The fact that tie majority of the ingested 90Sr was ~~i absor”~ed ‘by the boay is evidenced by the high fecal excretion levels z}.at were observed almost immediately following the consumpt Ion of

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750 HARDY, RIVERA, AND CONARD ths ~igh- aczivity food. Only a small increase in urinary 90Sr excretion was observed, and both fecal and urinary elimination rates fell ofi sharply within 10 days after the acute- ingesticm period. By 180 days Throiigh integration of the smoothed excretion-rate curves, tke over the entire I?-day period. With the assumption that the increase m the ‘37CS excretion rate of the subject was proportion~i to the llicrease in the normal body burdens of laboratory personnel, z background correction was determined and applied to each 10-d~J exerelevels toward the end of the study, it was assumed that any increase i~ the excretion rate due to an increase in the normal ‘OSr d~e~ ievel was not measurable. Therefore only the preexperiment ‘“sr level was percent of intalke are plotted against time in Figs. 3 and 4. Fifty percerx of the ‘37CS ingested via the Rongelap food hzd been excreted in urine after 85 days, whereas only 14?0 had been excreizd in ieces dxmg the same time. In contrast, almost 50~o of the ‘“Sr dose hac been excreted in feces at 10 days, whereas only 2.5?0 had been eliminated ia urine. DAYS AFTER INGESTION l

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DAYS AFTER INGESTION Since the integration limits were relatively large initially compxred to the ram of change of excretion level, the cumulative curves were no; emzapolated beyond the point at 10 days after termination of the hi2h- ~veraged 3.5, ranging between 2.8 and 3.8, and the ‘OSr excretion ratio averzged 0.96, ranging between 0.05 and 0.07. The cumulative excretion data were subtracted from the total inmke zo obtain the amount of each radionuclide retained. T!mse re - Table 3. When the two sets of 13Tcs data are compared, they aPPear ~o be m reasofia.’oly good agreement with each other. The fact that thz whole-body measurements are the more accurate, however, is seen from the semilog plot in Fig. 5. The expected single exponential fit 137cs from Rongelap food behaves in a Sim.iiardemonstrates that the metabolic manner to that observed under other intake conditions.12-i T The deviations from a single exponential function of the retention data as derived from excretion measurements may be attribu~ed to inac- :ur~cies in the estimation of the contributions from the normal dietary retake and the accunmlation of errors inherent in the procedm-e. The biological haif-life as measured by the whole-body counter is 74 days, ‘::~ereas che apparent half-life as measured on the initial straight-line portion ot the excretion-data curve is 64 days. When it is considered rkt the excr etlon dzta znderestimat e the retention slightly in th~ e~rlY st~ges’of measurement, the agreement is not unreasonable. It should be

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752 HARDY, RIVERA, AND CONARD bees alxserved by other investigators 14’io’iT wzs not measured in lhis study si~ce ths acute-ingestion period was longer than the espected The 9~sr retention curve as determined from excretion ‘~ta (F;g. 6) does not describe a single exponential function as is the cas a sect ed by a sum of exponential 18’1g or a power function.l 9“’0 In this

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~rj~ HARDY, RIVERA, AND CONARD study the retention curve is best described as a Series Gf exponential tht level off after 140 days and approach a value of 25%. This E a somewh~t iwgher retention value than that reported m cxher studies.li tion for a single administration of ‘3TCS can be expressed by a zwowhere R ~ is the fractional retention at t days, a is a consta.?i, and l’, and T2 are biological half-lives in days. The short-term component nent has a half-life, Tz, that varies from study to study, ranging from W to 150 days (Refs. 12 to 16 and 22 to 25). The comparison of biological hdf - lives ufider conditions of both acute and chronic exposures is not cdcula~ed in this study since the acute ingestion took place over a seven-day period znd the initial excretion collection periods were over three-day intervals. The long-term component as deterxnineci by both whole-body countiag and excretion data (74 and 64 days, respectively) was within the range of biological half -1.if e values fount by ozher investigators. Rundo’4 has pointed out that a …