The Determination of Internally Deposited Radioactive Isotopes in the Marshallese People by Excretion Analysis

Page 1

The Determination of Intermilly Deposited Radioactive Isotopes Reed..bmy Institute of Research BEST COPY AVAILABLE States Amy, and in conjunction with the Division of Biology and lledicine,Atomic Energy Commission

Page 2

Following the detonation of a thermonuclear device on 1 March 1954, 239 MarshaJ.lesepeople were exposed to at the Pacific Test Site significant levels of gamma radiation from fallout. Estimated These populations were evacuated to totsl exposures ranged from 175r on Kwajalein for decontxuninationand care. During the two days of fallout exposure before evacuation was completed, the Marshallese also received some radioactive materials internally by ingestion and ‘ inhalation. Estimates of the internal body burden from fallout were obtained from the analysis (1) of urine samples collected soon after exposure. These data indicated that the acute hazard from internally deposited fission fragments was qyite small as conpsred to the whole body gemma radiation exposure. Although the radioactivity levels in the urine were low, the activity was sufficient to obtain reasonable precision and to warrant additional long term studies of the activity levels well isolated population. The people from Alingina.e excretion patterns of this rather large and Utirik were returned to their home islands return to this Radiation intensities on Ron+gelap,however, precluded an early atoll and the Rongelap people lived on Majuro from June 1954 until Basic data on the food crops of the Marshal.leseindicated that after resettlement on the contaminated atollsAintake of strontiumg” would be increased considerably, and that cesium137, zinc’55, and cobalt60 were dietary constituents of island and ocean foodstuffs, and also would be assimilated (2). The expected increases in the trace smounts of radionuclides in the tied supply of a large population would afford an opportunity to investigate the rate of equilibration and the discrimination factors operating between food supply and =. Urinary

Page 3

were measured from March 1954 measured in 1958 ssmples. hwmuius AND METHODS. One hundred and forty one individual urine ssmples collected from 24 March through 7 September 1954 were obtained by the Health md Safety Laboratory, Urine volumes were small (about 350 ml.)and it was nec@sary to pool samples. This was done according to the sge of the subjects and 19 samples of pooled urine were assayed. A 57 liter pooled urine sample from Rongelap was collected and assayed in 1956 (3). Three pooled samples were assayed in 1957. Thirty individual samples and seven individual urine ssmples were ass~ed in In ssmples collected in 1954 and 1957 cesiu#37 was scavangedby nickel ferrocyanide (urine made strongly alkaline) and counted in a cqrsta.1well counter. A twenty channel gamrna-r~ spectrum was detezmd.nedfor each sample and the cesium137 photo spectrum count rate used. The 1958 samples were assayed directly for CS13’7, zn65, and#O in 2.5 liter plastic containers placed on an 8x 4 inch (TH activated) sodium iodide crystal. The act+vity for each radio-isotope was determinedly active standards (+ 5 percent) counted in the same geometry. Strontium9° was precipitated from urine as the carbonate. Yttrium9° was separated and identified by its half-life using thin walled gas flow counters. Urine samples were corrected for radio-active decay to the time”of collection. There is some uncertainty as to the completeness and the duration of time over which semples were collected and therefore twenty-four hour urine volumes indicates an average daily volume of about u.80 ml (+ 56 percent). It was convenient to use one liter as m averege 24 hour urine volume and to express radioassays in micromicrocuries per liter.

Page 4

RESULTS AND DISCUSSION. The urinary excretion levels of cesium137 for the years 1954, 1957, and 1958 are shown in Tables 1 - 4. 0n24 - 25 March, 1954, the mean excretion level of cesiun437 for all ~e groups was 4C5 uuc per liter.

Page 5

rate of CS137 should have resulted in an equilibrated CS137 burden, with an 137. Unfortunately no systematicestimated daily intake of about 1560 uuc of Cs sumey of foodstuffs grown on these atolls has been reported. Data available, however show that coconut grown on Rongelap contained about 9 uuc Cs137 per 137 per gram. The dailygram, and arrowroot (Utirik) contained about 8 uuc Cs intake of several hundred grams of either staple would be sufficient to account for the 1957 excretion level in the Utirik groq. The Rongelap groups had been resettled for about nine months at the time of the Nk-ch 1958 medicsl survey, and urinazy excretion levels of Cs137 ~d increased about one hundred fold over 1957 levels. Mean body burden for the two groups at this the was 0.9 uc (k 27 percent) and 1.2 uc (* 47 percent) 137 body burden may have equilibratedby late 1958 and(Tables 3 and 4). Cesium predicted burdens were about 1.3 and 1.6 uc respectively Urinary excretion levels of strontiumgo are presented in Tables1, 2, ~d 3“ *e Strontimgo excretion level in 1956 was 0.5 uuc/liter as detemined in a pooled sample of 57 liters Figure 2 shows the excretion of S#O for the three years following fsllout exposure. Although there is considerable variation in the data for the various age groups at early times, mean values for all groups plotted suggest that the excretion pattern can be expressed conveniently as the sum of two exponential terms. The larger portion of S2° was excreted with a half time of about 40 days, and a small fraction, 2G percent, was excreted fi~ hdf time of about 500 dpys. This is similar to Cowan’s (7) urinary excretion study of an accident case involving As was noted in the March 1958 were also increased to 3.5-4.0/0.2, CS137 levels, the excretion levels of S#O or about 20 fold. Since CS137 levels increased 4300 - 5300/34, or about 140 fold, the > With the increases in urinary S#O ratio is about seven in favor of excretion levels in 1958, it was

Page 6

pertinent to estimate body burden, burden expected at eqy.llibrium,and daily intake of Sr9° from these excretion levels. T& metabolic behavior of strontium as outlined In Supplement #6 of the British JoumM. of Radiology was used to estimate body burden, etc. from urinary excretion levels of strontium9° (Appendix). The fraction of strontium absorbed from the gastro-intestinal tract is 0.6 and the biological excretion rate from cent is deposited that the absorbed fractlon is excreted entirely in urine, the mean body burden of the exposed Rongelap group in March 1958 was 2 muc (t 52 percent). !FMs i.s about nine percent of the expected equilibrium value of 23 muc. The estimated burden of strontiumgo for March 1958 is probably too low and compares with levels measured in stillborn children in the U. S. several.years ago (8). The daily intake of strontiumgo is estimated to be about 15 micromicrocuries or 15 Sunshine Units (assuming a daily calcium intake of one gram). Dunning (2) reported that the average concentration of strontium9° in the Marshallese food supply could be about 360 Sunshine Units, but this would reduce to well under 100 Sunshine Units if the consumption of high S??O content foods were eliminated. With the elimination of pandanus d land crabs the diet used 90 wouldbe 17 Sunshine Unitsby Dunning indicated that the intake of strontium “per day. This compares favorably with the estimated intake of about 15 micromicrocuries from excretion analysis. Zinc65 Excretion Levels and Body Burden In early 1957 Miller (9) detected Zn65 in selected residents of Rongela~ and Utirlk by whole body gamma-rw spectrometry. Body burden rangedfr~ 29.5 to 73.0 muc for the Rongelap residents, and 482 and 229 muc was detected in two subjects from Utirik. The Rongelap subjects were residing on Majuro at this tine.

Page 7

Miller obtained an effective half-time of 110 days for the Assuming the excretion to be entirely exponential and 10 percent of the body burden of Zn65 excreted in urine, the March 1958 urinary excretion levels of 174 and 342 micromicrocuries indicate body burden, eqtiibrium body burdenl and daily intake as follows: Equilibrated Body Burden: 330 Exposed Group Control Group (Unexposed 1954) Percent Equilibration: 85.0 percent 83.0 percent mean body burden estimated correlates with the return from 1958 excretion analysis for all Rongelap over the 1957 whol’ebody meamrements. This of the~e people to Rongelap atoll from Also the 1958 Rongelap Zn65 burdens are comparable with the Utirik in 1957, and the Utirik subjects would have been in equilibrium in 1957 (half time of 110 days for the elimination of zinc65)0 The estimated intake of zinc65 (2000 to 4000 uuc per day) can not be accounted for by Zn6~ activity levels reported in foodstuffs. Although this radio-nuclide reportedly accounts for a large fraction of the total activity in fish, this amounts to only about six uuc per pound of muscle up to 75 uuc per pound of whole fish (2) or at most four percent of the estimated intake. Since resettlement of the the urinary excretion level of Marshallese people on Ron&lap atoll in JulY 1957, ce5im137 has increased about 140 fold and about #Assumi.ng 100 percent absorption from the GI Tract

Page 8

20 fold for strontium . Zinc65 was readily detected in samples from the March 137‘I!&estimated mean body burden at equilibrium for cesium is about 1.5 microcuries or about 1/6 of the tolerance recommended by the International Commission for Radiological Protection for non-industrial populations. For 00 the mean body burden of the exposed Rongelap ~roup in March 1958 wasstrontium~ estimated to be two millimicrocuries. This is about nine percent of the expected equilibrium value of 23 millimicrocuries. 90 burdenThe equilibrated strontium is about 1/5 of tolerance. The estimated mean body burden of zinc for of O.& microcuries and the equilibration value is 1/70 of tolerance.

Page 9

Some Effects of Ioniuing Radiation on Human Beings, Atomic Ener~ Commission, Radioactive Cent.tination of Certain Areas in the Pacific Ocean from Nuclear Tests, Atomic Energy Commission, August (1957) Medical Survey of Marshallese Two Years Post Exposure to Fallout Radiation, Brookhaven national Laboratory, BNL-412 (T-80), September (1956) Measurements of Retention and ticretion of Radioisotopes of the Alkali Metals by Mice and Rats, Using an Annular Liquid Scintillation Counter, Proc. Health Phys. Sot. 79 (195~) People and Foods, Science, 125:1273 (1957) Am. J. Roentgenol., Rad. Ther., and Nut. lled,67:805 (1952) Current Research Fi@in.gs on Radioactive Fallout. I%oc. Nat. Acad. Sci. Measurements on Gome Residents of the Marshall Islsnd, J&gonne National Laboratory, Report No. ANL 5752, PLP56 (1957)

Page 11

EXCRETION LEVELS OF URINARY CES~37 AND STRONl?IUM9° IN W MARSHALLESE DURING MARCH 1957 MEAN SAMPLE ACTIVITY (uuc/liter)

Page 15

Fi~e 1. lhcretion kvels of Urinary Cesiun#~ at Various Times After RYPOSUK ,~\\l&

Page 17

90 at Various Tines After Exposm.Figure 2. Excretion Levels of Urinary Strontium

Page 18

I. In the case of strontium elhnination, the following assumptions were made: a. The population was returned to with a zero strontium body burden. b. me population absorbs a daily to be a constant independent of time. the contaminated atoll at time t = o, increment of x UC, snd x is considered c. The amount of strontium excreted in the urine each day is given by . a constant independent of time. d. The body is considered total excreted by all routes each day, and k is to be a two compartment system, A and B, where for each compartment are a and b -s -1 respectively. The portion of E(t) excreted from each compartment to the burden remaining in that compartment. For cesium and zinc similar assumptions are made, except that only one compartment is S(t) is total strontium Considering each compartment body burden at time t In uc portions in each comp~ent separately and adding the results,

Page 19

No. 6 of the foilowing values for strontium metabolism were obtained from Supplement

Page 20

II. In the case of cesium and zinc: x is the daily accretion in uc/d~, and So is the body burden in uc at t = o. #%he urinary/fecal ratio of racliocesiumfor human subjects is about 5/1, so that estimates of body burden are too low by about 20 percent.