Radioactivity of Invertebrates and Other Organisms at Eniwetok Atoll During 1954-55

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of Government sponsored work. Neither the United States, nor the Commission, nor any person acting on behalf of the Commission: tion, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this report. As used in the above, “per son acting on behalf of the Commission” includes any employee or contractor of the Commission to the extent that sirch employee or contractor prepares, handies or distributes, or provides access to, any information pursuant to his

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Applied llsheries Laboratory tmiveraity of Uashlngton Dperated by the Unlverslty of Washington under Contract MO. A’!‘(W-l)%O with the United States Atomic Energy Corn1sslon

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The wend la born mdloactltlty 8# lwamared vlth ntrmao tlw coumkrm ovep a period of about tvo year8 ir lhoun, ltartlng vith tb 1954 Cartle creries of nuclear detamtiaw, in, mlated to tb8 logarith of the time after the date of period raryln@ vlth the organlrr up to tvo to four wek8 follovfng detonation, 8 mximum level of rrdlcmctirtty b the f leld ample8 collected 18 attilned, folloved by a dccllne mjor portion of the tvo-year period that CM be represented p.8 the negative exponent of the tins after detonation. These organism, reaching a mxlmum of s 3. A fev decay rate8 Of lndlvldual 8aEpl88 Of each Organi8m or umterlal are Included for comparl8on, and these generally vcre equal to, or let8 8teep than, the declines, sugge8tlng In the environment decrease8 more rapidly t&m oan be (LCcounted for solely by phy8lCal decay vhlle for other8 the x-te of decllns can be accounttd for solely by the rate of phy8lCal decay. Dllutlon by natural vater current8 and rain 18 presumed to account for the many ca8es of more rapld decliae tIma

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tomined 8t almost all of the Pacific Prorlng Orouad te8t8, great interval8 of a yerr or The prorent ludy tract8 the trends la the beta redlofrom 8hortly before the Rectar detoaratlon (Iby 14, 1954) for l are included, uaw aomc LniornmtIon given more fully la Palumbo (1957) reported on the radioactivity in algae and laad plants. Held (1957) atudicd the trend8 of radioactivity ln the land hermit crab and discovered the preponderance of radioatrontlrrm In the exoskeleton. Velondcr (1957) de8cMbed Lowman, Palumbo. and South T1957) reported the identity of thu Although the empharis of the present wper is on invertebrates, certain data from laany of the other firew are brought 1s practicable. It should be F,oaalble in this way to obrervo the general pattern of change of radioact:vlt;( In living and non-liv:ly materials. and ta detect divcrgcnccm from Study of the tmnds Ln th’r mer ham waved useful

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vith the raw of p&ymi-1 decry, rbould rctivlty by t& eaiam. tquellty of decry wl declino -Q, in vhlch phyolml decay progrerml bore rap2dly than did the

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ta Atoll rr8 ovahated la two mya* firat by concentrated rbrdJ InroJvLry may oqpalsma collected frequently at one lmland. hllo, aad awmd, by 1080 lnteaalv8 study at mevera lalmd# womd the atoll Zn order to elucidat8 the geographical blatsi1 Belle Imlaad (rig. 1) var t& 4 alto, excopt for mts, for which var. -0 on April 15, 1954 at Belle before the llectar teut, Hectrr collectiona in April and Hay, aad nine to ten port-Rectar collectloam, urwlly expedited by helicopter, at intervals lnat which time 81% lrlandr. Henry, bray, Alice, Olive, Vera, and Bruce vere vialted. The rerrlnverc sampled at approxlmtely Other 8tudier. Ilg. 1. Hap of Enlvetok Survey meter readl?rgs vere taken frequently at Belle, but 01 only about half of the rlslt8 to other Islands. The Juno meter vaa used for high (Tablo 2) level8 of actlvlty and the Uclger usually monitored vlth the Fnstrumnt one inch from the ground aad ulth the 8hlelb both open and cloaod. 3lml lar readings three feet from the ground were taken less frequently and are lor the dlstrlbutlonal study on the various !slwxIs A huu!- ful of island soil from the top Ach, lntcrttdal beach sand 4 lagoon, a milt or tvo centrally from the Islands, served for suplw me4 vater, plenktm, and ~laglc fish by rod and ml. tuo knot8 per hour using two l@mBter net,, fine (g3.32 of 173

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I At klle falanb. tte Imcrtebrrtej u ~411~ w-led ven ths i kllbr clam the laad herlsit north or oceaa side, algae on the lagoon and ocenn sides, land plaat8 In the central portion, land hemlt crabs anong the buaher of the north edge, and terns nearby. Rats were obtained mntrrlly an Jaaet 18land. Invertebrates and firh vere collected at lov tldc vhen pow Ible . blolo~lcal specIswn8 were put on Ice In Insulated eontalners and transported ta the labomtwy st Elmer Island for 3011 samples were dried And packaged for shipment. Flveotlllllter samples of sea vater vcce dried on 1 l/P-Inch stainlearn ateel plater and ashed, except that In 1956, lOO-milliliter samples VCM used becnust of the lov level of thr actlvlty. e wre treated vlth sodium carbonate to remove potassium contributes about 0.6 diaIn+--,t%Ions per mLnute per counting. Radlocesium Ia a! *at by treatment with sodium Plankton MS prepared by filtering and removing as much as ?rom occeslonal poor tows the vet samplr .,Lght was as low as PortIons usually sampled from the invertebrates w++re: from clams, mantle, adductor muscle, gill, kidney, visceral mass, and shell; from aplder anaIls, mntle, muscle of foot, terminal portlons of liver and gut, olaceral mass, and shell; from the land hermit crab, gill, dlgestlve gland or llver, gut, carapace, and aubcle of leg; from sea cucumbers, gonari when suf f Ic lently plentlhrl, gut and contents, muscle of the body vail, And body vail or Integument with or vlthout attached nuscls: and from cora: the terminal portlana of samll branches. Shell samples of clams and ~~11s were usually taken froti the thin edge to Lncltldc vas low, larger sampler uerr used. *twecn 59 and ?3J mllllgrats of ash vere usually consldcred dcslmklc, but vcl4hts ranged vldely, fra less tMa 13 to more than 1303 m:liIgrams. Cyhell and gut vlth sandy content verc more 1L~~htlj’ ssm~lmd on a vet

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Uefgtmd saT lea of tl88ue8 In pllofila bags vcre dried otcmuht at 103 C mui sent to the Applied llsherlct &borabout a month after collecting. the samples In pllofllrabagr were applled to the platcs(1 1 $0lmh stalnlcss steel, parlously velghed), dried. The plated ash received A rev drops of lormar dlssolred fn ethylene dlchlortde (up to 1 mq dry equivalent) to affLx the ash to the plate. The plate8 vere then weighed, and counted In methane gas-flaV counters. Except in the case of rats, counts vcrc corrected bac’r to date of collection using the decay rate of island sol1 (plate 7542) collected May 15, 1954 at Belle (Pig. 5, p. 11). For rats the decay correction ~88 beBed upon the lndlvldual decay rate for each plate. Self-absorption correction factors vcre based upon land soil collected June 7, 1954 at Edna, the decay curve of vhlch (plate 9170) appears ln Figure 5, page 11. Ulthln seven months after llectar an Increase ln average energy nccessltated a reduction in the follovlng tabulation lllustrete~ these changes. Self-nbsorptlon correction fflctor for sount Geometry and bAcKscatter for the c mnterr and ;:latcs usd required CI combhod cwrwtlon factor of 1.54. Col.~cldmrc corrected only for colnclbencc. Iq?plyFnq these cormctlon factors grive vrilutb In dtslatsdate of collection. Processing teChnl(iucS me further dlscumaed throughout the calculattons, finally beLng romdcd to two. After plotting d/m/g ccgalnst the the wdlmte vas Ln ¶omt lng 1 uc to equal 2.2 x 1 J r,/tn.

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ltm or rdloactlvlty to logrltbr of tm oi colloctloh 3E Ccmaged lCCOrdiag to ttm data or origin 8818Ct8d, bat it tbo 8aa origb 18 ured for both dercq u&d daclla8, the two my k tkoretlcrl decay of mixed rlov-neutraaover l period froa 1 to 1000 daya a8 a belw 3 and a general rlope varylag A rlmllar pre8entatlon of the tread8 of docllao aml decay a8 becalag more or vhlle on the M plot 8 mixture of or otbr variable8 are lgnord.

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lrltg appoara to prevail, t& tlr spaa lavolved is ltlpulatod ?ar converalm betwen rlcrocurles and dI8lnt8~tlaaa per y-intercept on day number 1, according to the relatIm8hlp: assumed detoaation day, and a 18 the y-Intercept exprersed In unit8 of radioactivity of the rtgrerslon line of slope b on day nuaber 1. lor euaple ) the accond entry In Table 1, survey meter read.‘ngs at Belle, graphed ln Clgure 3, lnrolred obserratloar on 16 day8 over the period S-540 days after nectar. The vith a correlation of 0.971, which Is far beyond the 1s level Along vlth decline data, available decays for as nearly slaultaneous periods as posrlble are presented for ccmparlson. Decays #tart later than deullno because declines vere correated back to date of collection, vhlle decays are for the actual dates of countlag. m ths decay gmphr the ordlmte represents grorr beta plu8 negligible alpha and gamma activity that vould be detected. Decay curve8 even on the aaae graph are not comparable to another a8 to absolute levels, because of vertleal #hiitto obtain compact prerentatlon, but may be compared l 8 to 810~.

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per kll~ram, the Island 8011 decllaed fairly regularly for a period of tvo years. Ths dip at 130-200 days is reflected Ln the decline curves for land hermit crab but Is not apparent \ In the data for green leave8 of samples of Island soil from Belle (plate 7542) and from Edna (plate 9170), and of intertidal beach sand from Henry --_ eluded for comparison. The Belle Island soil decay curve 4 Is for plate number 7542 which served as !I the b8sls for computation of the decay correction factors for convsrtlng values back to date of collection. The same 1i factors were used for all types of material except rats collected postNectar at Enlwtok Atoll. The dashed, rL, early portion of the curve Is not a straight line because It was orIgInally extrapolated on semi-log paper. For comparison, Figure 6 shovs the decay of the sample of lagoon bottoqr sand dredged November 7, 1952 off Tllda ,northvest of Vera). This decay was used for calculation of decay correction factors W the collectIons follovlng the Mike test In days Its slrllarlty to the theoretical curve of Figure 2 Is striking. It v18 practically uninfluenced by residue8 from previous detonatlons. The more p~o~ce~_ flexures In the curve for Belle Island 8011, f as vell as Its generally more gradual slope 1 are the result

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tim loft a.0 of at Bruce w Elmer, northsrn thur at rarlou8 lrludr owm 8 time rpan of from 0110 or tvo rorrth8 to the 8COpO Of Ob88rVatlO#l8. The period of time covered by the wre Iteoper, and at Vera vhsre decal and decline WM -1.

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18 probably cau8ed by a greater re8ldue of rdloactlvlty from Ttm decay8 for beach sand are given IB Table 4, page 13.

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w roboratelxcopt for t&m lou tallmr of ewu 9f.F. l 8 8t8w l 8 at fsrOJ, in contrast to the decline8 for am of t& 8ea uster declbe data of of ?lgwo 9, Bell. ooean mef. lm for all data other ttan that of Belle, outer. The dat8 far the 8W exelu8Iro of Belle ocean reef give a

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Ttm decay8 for lea vater are givea b Table 5 and Pigum per ltauta per plate VII,uaulnleat to 3 dbhlate, tmamao The data of Table 6 for the Plgure 11. With the exceptlon of grsdusl because of lov early The decay curved

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8 from each tw a pear In Table 7, ud o(1tbs La, wwo 0.73 uu 0.w.

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perwitted compwlson, the data are shovn 8eparately, and other u8ually either Ilo. 6 of 74/inch or No. 20 of 173/inch. TeNe 9 shova for the paired tow the r&lo of the lctlrlty per unit might ln ooarae nrtsh to that in fine (1~0.6/k0.23 on both a vet and ash velght basla. Betveen the northern localltles of Belle Island and the Mike crater and the southern localities of Wide Pa88age and Leroy Island, there vaa a difference using the t test, algnlflcant at the 2% level on the ash -313. The rea8on 18 not apparent for this asaoclatlon of high count8 vlth fine mesh neta at northern, and vith coarse at the 8outhern and tlvity occurred in fLne meah net hauls than in coarse, the present data skov vlde variation. On the vet basis the coarae vhlle on the aah baa18 the figures vcre revemed, the coarae mesh vaa hlgher ln 25 pairs md the fine mesh ln 18 palm. Thus, nelther vet nor sah ~basls ahoved a significant dlfference due to meah size.

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fine lhould be unity. The ratio8 ln Table 9 vem wed to (with perk tovwd tb8 left) frequency dl8tributiaz of the tvo plankton ampler at ‘\* I vet veight basis u8lng the data of tvo value8 for pa lred Except at the the decllnea were . the aah baal8. The 2 gradual decline (-1.0) IO at the Mike crater could tope8, from the crater into the water, thereby malntalnlng the activity 0 q of the plankton. At 1 lij Vera the trend is too to permit comparlaons.

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la Pigurc 13 and Table 13. The mern an4 standard error of tne s~opta of them 18 This average for the decry8 Is leaa steep than the deAt Belle Island, the Deep Entrance, the Wide Pamage, and Leroy Ibland, of decline psiiit3 ia 30 highly uncer taln. At the Mike crater the unumally .due to contributlom from the crater Itself, accounts for one of the rare inHiancea of decay exceeding decline. In general, plankton decllnea vere steeper than decays TSClO 10. bats for pluraton decay cum00 9: Flo. 13.

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8a@ti at the varlou8 18land8. llgure 14 showa that the I absolute love18 of radioactivity vere nearly uniform from i becau8e nearly every potit Is bn average of sever81 samples. At Belle the point8 fall In a curve, nearly level at flr8t, lteepeniag to a rrxlmm st 100 to 200 days, and then again leveling. Thf8 18 the mo8t frequently observed pattern of i deviation iroa linearity noted throughout t.herurvey.

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Plgure 15 and Table 11 give decay8 for 9 (plater 6969-73 from Belle on July 22, 1954) counted $4 and 1106 days post-Nectar gave Thus, at each locality, declines vere appreciably steeper than decaya. Ihllmeda decay curve3 rewmble those of 3ea vater and plankton in being nearly Btralght for a The last three curves, Elmer, Henry, and Leroy, representing the southern ialandq become leas steep at about 600 claya, vhile at islands farther north the rate does not change, suggeMAng a difference In isotopic conatltution in the two

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TM green leaves of land plants st Belle wme 8elected to ahow the trend of activity the decline of irdlvidurl plate valuers aa …