The Consequences of Ingestion by Man of Real and Simulated Fallout (Vol. 12)

Page 1

THE COXSEQUENCES OF INGESTION BY MAN OF REAL Dcpartmcot, of hlcdicine and Pharmacology, The Univ&ty Crc Chicago, m d the ArgoaDe b c u Ruearch Hospital,: Chicago, Illinoh Abstract-Rcal and rimulattd particulate W o u t and m1utiOnr of W’srCl, and wae fcd to 102 healthy vo1un:ccn. Absorption and retention d ingatad rr did Vi ~wu mevured by whole-body counting using the gamma-my rpectromtta at the h o m e Racarch Hrpid. An avcragc of 3 pcf ccnt d thc do activity dweel-old l dU out wy simulated falout behaved in t h e i m c way, mctabolidy, shcr absorption L( they did when the tracer waj wallowed in a solution or injcctal intravcnourly. The large number dmbjects studi cd providd additional information on the range of variation of intam dty, biological availability of strontium, Caium m d barium following ingation of fillout, and retention of t h e radionudida of thee elanenb. 1961 CON(=ERN about some of the problcms of ,c’ internal deposit of fission products (FP) fo1loyi.q ingestion of local fallout led us to prop o ~studies using real fallout G-om the Nevada Tat Site (NTS); simulated tallo*i* pti cles of “SrCl, and WCI. T h e proposal involved fceding the test mate&& to healthy adult voluntecrs and estimating retention and absorption from measurements of their gamma radiation the Argonne Cancer Ratarch Hospital. The results rtported h a c art wncerrcl with the transit time of particles in the ptrointutinal tract (Section 11); the biological ad ability of radioactivity following ingestion D f real local Wlout (Section 111); and the a tent to which the process of lcaching from simulated Mout An at a ded &on of Lhir rrudy appearai in 3 Oparted by tbe Univau’ty of Ch t lpo fix th m a y mocWy the metabolic bchaviorofrtrontium, cuium and barium (Scction IV). The f’out that we studied and attempted to rimulate is designated variously u ha!,W’ or United Stata at the NTS zuch Eallout consists ob particles mging in rite from Im than I p in diameter to more than 1 mm. The particla am composed of FP, and roil materials and cornponents of the nuclear device in which radb . activity hm ‘been kduced by neutrons. Near the point of dewnation the particlu ut lwgc and silicaccous With radioactivity distributed throughout and condensed on the The ratio of biologidy available 8ctivit-y to toid m a away and downwind from the poiat d detonation the partides become der, rehtively more of the radioactivity is oondeared on their surhcu, and biological aMil.b&ty of the FP is :ncraued. The extent of the dirtributh of fillout d c p & on the size of the nudear aplosion, rnctaxological mnditions, and the m htion of tht fireball to the d a c e of thc earth. average weather conditions local fbllout MI atend to dktanrea arcceding 500 mila, and the radioactivity is reported to be d.

Page 2

am co nhn at cd by a single wcapon ma)’ t xcccd thousands of squarr mila. me principal hazzrd from this variety of fallout i!? rxternal cxposurc to ganma radiation, &e in tmi ty of which may o;cccd 1000 Rfi pletcd. T h e risk of internal deposition of FP iS rial but the magnitude of the risk iS ~ Ct rta in. FaUout particla cntcr the body by inhalation and ingation. Ekcausc of h e relatively large size of the partidcs, the majority of those inhaled are promprly trapped in mucw and quickly cleared from the respiratory passaga either to be expectorated or swallowed. Fallout ingated with f d or water (plus that from the respiratory tract) pdfses through the gastrointestinal system where the particles are exposed to a changing chcmicP1 environment in which some fraction of the FP may be dissolved and thus become available for absorption and subsequent dcposition in internal organs and tiSS~a. T h e facton raponsiblc for absorption of FP determine the biological availability of the radionuclides in fallout. Thee facton inclilde: (1) the physical and chemical characteristics of die particla, i.e. the leachability and solubility of the nuclides they contain; - (2) the absorbability of the chcmical compouw’s formed in the intestinal contents; and (3) thl: transit & h e of particla through t h e gastroi;l,utinal tract. Vanow estimates have bccn made of the biological availaba ty in man of local fallout. According to Efecfr of K u h r J4iopordl) 10 per cent of FP in local fallout i* available, but there are no experimental data to support this estimate. MXLLER~*)ha calculated the potential solubility of the principal nuclides as a function of partide size. In the case of u:I the cst iru ie ranga from 0.016 (fraction soluble) for particles deposited dose to the detonation, to 1.0 for the more distant ona. For ‘ OS, theoretical rolubility ranges from 0.16 close in, to 1.0 at the outer bility oflocal fallout collected at STS after tests of various nuclear dcvices ranga from niI to more than 50 per cent. Some writen assume that biological availability parallels the chemical mlubility in dilute solutions of acids. In sonic atimata of the hazard from ingated falout the biological availability b taktn u qual to the abundance of a particular radionuclide. T h e possibility of obtaining suitable aimulantr for fallout occurrcd to us d e r reading a report(’) of spherical shape and belected size whit5 contain and immobilize relatively large quanthia of many usdd isotopes”. I n reply to our inquiry, said that he could make microspheres in which a radionuclide would not be completely immobilized so that some fraction would leach out ia a weak a d d solution. In December 1961 two of us (JHR and GVL)met with a pup of ha - thts interested in fallout a t Atomic Energy Commission headquarters in Germantorn. The ROBERTSON)agreed that it thould be possible to prepare satisfactory simulants with the following properties: the close-in rh ulan t should be glassy or ceramic, and about 10 per cent of the radioactivity should be leachable; the dt tant simulant should resemble a sintered oxide with a solubAty of about 70 per cent; a ruitable particle size would be in the range 20-60 p in diameter. In addition the group a@ that &e proposed studia were fcasible and worth doing, and that the elements of greatest interat were rtrontiuni, cdum and barium. T h e radionuclides of these elements (and iodine) in FP are considered d u d nuclidrJ because metabolic procases lead to concentration in bone, muscle and the thyroid gland. Once concentrdted, each turns over slowly to that the cornbination of selective deposition, ‘ and energetic nuclear radiations can result in 8 significant internal radiation dw.The estimate of internal dose following ingation ir based on auumptioru rcgardir.g the fraction absorbed, the fraction of the aniount absorbed that goes to the target organ, and the rate of removal from the target organ. For most purpoaa the values =igntd to these assumptions are thase given in ICKP Publkation hro.2,O) and listed in Table 1.1. Although these are convenient averages the hct u that absorption, concentration in 8 target organ, and biological turnover m a y be profoundly modified by ruch facton as the motility of the gawointatinal tract, the chemical

Page 3

compounds formed in the intestinal Contents, the route of administration which may regdate the amount that goa to thc target organ, and the nhysiological state of the individual. : e is an extcruivc literature on fallout,+ tion hazard from local fallout; (2) the body burden of critical nuclidcs in anima& collected near atat site; (3) the movement thrnii~hthc biosphere of critical nuclide from Ioai well as world-wide fallout; and (4) the metabolism of iodine, strontium and cerium following oral and partntcral administration of.rolutions, and aware of any report of the feeding of real, local fallout to volunteers. To our knowlcdge thL is also the bnt study where Ftrontiurn. riium or barium were administered in a fashion that simulated the actual ingation of particula te fallout. Since it was debatable if there w a any advantage to the use of simulanu, an important objective of our study w?u to compare the behavior of radionuclides leached from the simut n t with that of airnpIc solutions of strontium The dcsign of the experiments was simple: wholebody counting was wed to masure the amount of y-cmitting activity that remained in the bodiu of the volunteers at intends rfttr ingestion of the test mataiak. The real Wout and the sirnulanb were swallowed in gelatin were swallowed with several ounm ofwater. AlI t a t materials were administered without regard to meals or times of day. The identity and the amount of the radionuclide in each dose wu determined by one of us (CVL)before administration using an Auagamma pray rpectrorneter. Imm&tely before the dost was takcp, for 4060 min in the WBS. At some time during w a made, The net counting rate a t the time of thc h t postdose count wzs taken as 100 PQ cent of dwe for the purpose of calculrting retention at Iattr times. Thereafter, 8t in& that m~cdfrom a few daya to a fkw walu serial the few how following the d w - ad be fa rmainig so that the probable error ofcounw wal rmlll. scrial countt wpt continued until: (1) the net counting rate deed to IUS than 1.0 per cmt of the h t pt-dm c o ~ t .

Page 4

w a ~no longer avrilable. In a few cases sampla few weeks after simdants were fed, and these wen measwed in apm ~ I ycalibrated larq ~ volume well counter. The information from the effort expended and molltction~of excreta were dhcontinued early in the study. The voluntcm wert healthy addts - Univa - sity rtudenb and munben of our staff-who for Civil Defenx. None reported any gasintestina: symptoms following ingestion of any of the test materials. The experiments were approvcd by the Committee for the Human Use of Radioisotopes of the Univcnity of Chicago Hospitals and Clinics. T h e total number of All mCaSurCments of radioactivity retained in the subjects were made with the whole-body Cancer R d Hospital. This instrument, vhich has been described in dctd elsewhere") coruists of four 5 x 5-in.thallium-activated NaI crystals coupled to photomultirlier tuba arranged above a couch in an iron-shielded roon. The output ofeach crpal detect?; 5 transferred through a mixing circuit to a rnulti-channel puLe height analyzer adjustable for rcadouts of 3, 6 or 12keV per channel. The readout is stored on punched paper tape. MIcn the volunteen were counted the four crystals were placed ap pro htc ly equidistant frQm each other along the midline of the subject and 18.5 in. above the couch. For OIX : dfthe counting time the subject w a supine: for the other half prone. Preliminary triaL demonstrated that there was only a fcw per ccnt difference in the effiaency with which the WBS measured a point source (such as a capsule) inside a subject's b o d y and the same amount of activity distributed throughout the Mya an at ended )ou~c~.T h e practice of counting in the prone und the rupine position adequately compensated fot any inquality in the anterior-poutenor d i e - tribution of mdjoactivity in the course of m wert pmperly informed of the nature of the The hg on ne Carce- Ruearch Hospital instrument is very stable: twenty-two W y taining a total of 0 . 5 7 ~ ~ )gave a mean of 12,398 f 190 net cpm. Variations of t h e background of the iron-shielded room were equally s d , and when contamination occurrtd it was clcaned up promptly. T h e dead time of our WBS is corrected for automatically by a proportional increase in the live time of the duty cycle. At counting rata less than about 500,900 cpm the response of the ht nunc nt is a Linear fhction of the amount of radioactivity praent. Since few of our comb T h e background counting rate of the ironshielded mom w2u measured cach day by a 40- or 6O-min count, and the performance of the detccton was checked using a scaled calibrated rium with its daughten. The efficiency of the WBS for the various t a t materials and for the energy ranges used to count them is shown in T h ef ration of dose refainrd at any time, f , day whcrc to is the time of the first count after the from serial whck b o d y counu made during the sccond through the sixth week after the dose was given. We assumed that 99+ per cent of ingated insoluble material was eliminated from the intestinal tract bcfo-e t h e end of the seventh serial values for net cpm corrected for decay were plotted on a semi-log chart and they-intercept for day 1 (the day after the dose w a given) was obtained by atrapolatin& a line fitted by eye for the period 1-7 weeks. For USr and mBa serial counts were plotted on I n the case of Supplied by h e National Bureau of S t ~ ~ darb. do not duplicate my of t h e rymbob w d in ICRP

Page 5

read off the eye-fitted line. T h e fraction of dose f* = extrapolated net cprn at d a y 1 Although it is the convention to assume that biological elimination of most elemcnts follom a simple exponential function, it is well known that many data 8Uppofl t h e view & A t the fraction of the M y burden aa-ctcd p c ~day may vary invcnely with time and may bc bcst represented by a power function. Following a single bjeo. m those of strontium and barium-the body burden can bt expressed m injection; A = normalized fraction of injected d m ntained at the end of unit time; and n = a We have chosen not to employ t h h apreuion for individual subjects b u x there is romc indication that a pow- function d m not reprercnt pdy the true situation, since the a p ncnt n hm been foound to v a q with time. In addition to this, its metabolic significance remaim uncxphincd. For the sake of simplicity wc apr& long term retention of strontium, barium and cesium t h e per cent of the amount absorbed (IA)runaining in the body at tima longcr than 50 dap. In the clue of cesium where elimination appean to follow a rimpk exponential function indefinitely, the rate of climbtion is reported as the half-time in &ys. It is common knowledge that the time requid for some rccognizabk utida of the diet (corn, for example) to appear in the fectr varies from a matter of how to sevd dap. In fsct, the variation in intestinal motility of healthy peoplc L SO great that few cliniduu will agree on an average time for …