Radioiodine Levels in the U.s. Public Health Service Pasteurized Milk Network from 1963 to 1968 and Their Relationship to Possible Sources

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.Networkfron 1963 to 1968 and their Relationship to Possible Sources Lester Itachtaand Kosta Telegadas Environmental Science Services Administration .Abstract. Llfeteorologicalsaalysis of the paths of nuclear clouds has been used to assign the source of radioiodine in the milk samples collected in the U. S. Public Health Service Pasteurized Milk Network (PLMN). Most of the iastances of elevated values between April 1963 and December 1968 are attributed to six atmospheric nuclear explosions in western China. only . ‘ one of five cratering events at the Nevada Test Site caused elevated values in the PMN milk. Two periods with relatively low concentrations of radioiodiae in miLk possess no apparent explanation. By selecting periods with no atmospheric or cratering events, it is argued that at most small amounts of radioiodine in the P.Ml?can be attributed to accidental releases from underground nuclesr tests in tie United States d~-ing the period of amlysis. Radioiodine from accidental releases, reactor tests, and cratering events lMS been”detected in a local raw silk network surrounding the BEST COPY AVAILABLE

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ve~thgs froa underground nucleer tests, (d) releases frou fuel reprocessing pla~ts and other installations. IQ 1963, Machta (1) attributed the origin of iL31 in milk saaples of the U. S. Fublic Health Service Pasteurized Milk IIIUC) to particular sources duz”irigthe period September 1961 through 1962. The present report updaies the origiml report for the following six-yem Waile radioiodine in mi~ has been measured because of its health implications, the pri-p~ose of this study is to account for the origin the concentration are secondary to tlaeassurance that the milk truly contains p31* At least one PMN ssmple per week was routinely scheduled for analysis in each of about 60 milksheds; the sampling frequency increased to twice weekly when elevated concent.ratio~ were e~ected or found. A single sanple each week my not reflect the highest leva in mi~. ~ The genera13y accepted liait of deteciion for iodine-131 analysis is 10pCi/1. This level is based on the radon detiation in the analysis and count statistics sad is defiaed as that: “level of activity which results in a 10@p error at the 95% confidence However, if there are small quantities of unidezrbified’isotopes present, such as naturally occurring radiuii-226,or unusual background fluctuations which are Dot accounted for in the analysis} a bias can be introduced in the results which will raise the ninimua sensitivity. On this basis, a cut-off value of greater than 30 pCi/1 was chosen as that representi~ a high level of confidence that iodi~e-131 was actually present (2). I examined for support of the F.lilifindi~~s. Beca~se of earlier controversy, sPecid. attCTitiOD is devoted to the possible sources of radioiodi~e from activities at the Nevada Test Site (hJ?S). A local.network Public Eealth Service surmundi~ the test site provided .,

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131... ..-i.a5:10‘G in figuzze1, th=re are tea periods with I concentrations in late 1$X2. Table 1 shows these ten periods in chronological order Uoge-c.”.=~dl’:hthe aost likely source of radioiodine. the eight atmospheric tests co~ducied at Lop Nor in western China (@”N, 9003). Tlie~esix nuclesx tests were reported to have total melds ranging Nuclear expiosioas near the gromd with ~ields in this range inject radioactivity =inly into the tropospkerej the active weather layer of the I at~o~?i.ere(~). The rnovezerksof the leadiug edges of these six nuclear 1 clo~ds eppe= in Fib-es 2 through 7. The behaviar of the clouds from the . y~y ~+~ and My 1966 tests has aheedybeen discussed byllachta (~) in coriectioa k’itllprdfereatial thmderstoru scavenging in the mid-western of ti boab produced radioisotopes from the first negaton test of li’June 196’7 i was vi.rtxill.vnoa-existent.in ground level air or rainwater for months after the eveaz. ‘lkisaay be due to the fact Vlat an e@osion with the yield of ,, about 3 ~mgatoas will inject most of its radioactivity into the stratosphere. Tinesecond aegaton test took place ofi27 December 1968 so that its fallout, !Eni&~eeaatmospheric nuclear tests have been conducted by the Republic of France in the South Pacific near Muraz-oa(22°S, l@’%J), (7, 8). Unddo~-.uately,the sparsity of weather data over”the equatorial oceans preve:.tsthe construction of reliable meteorological-trajectories of the clouds frou these tests. iodine-131 concentrations in excess of 30 pCi/1 1 occ~red duriag period 10 following tests in the South Pacific. One milk 1 saaale, 32 pCi/1, in the.Canal Zone ia the last week of August w58 I probably derived its I from these tests. Other short-lived radioactivity ~ was to-ti~din zir during tk.esame period at stations in South America sad I the tropics, which fits a Pattern expected of a South pactiic ‘*Wce (9)”

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Cotission Plowshare Progra for the peaceful exclusives took place tietween1963 and 1968. application of nuclear zciivity was detected in the atzos?here fol-lotiw each testy only the Palaaquin event of 14April 1965 resulted in elevated I131 levels in the PXN tilk (Period 2). The meteorological trajectory for this event is shown ia figure 8. Only Eeleaa, Montana, reported detectable levels of I’Q ia zriti. I Rauioiodine must pass from the atmosphere through crops, cows, dairy in milk in the PdS laboratories. These delays involve only a few days one ssnple per week is routinely coilected frou each mil.kshed. ‘Ihus, “ the delays and periodic sampling can result in time differences between ,. nuclear cloud arrival and first xiik cmtzxhation in Table 1 of up to a week =d a haM. The longest tine difference, eleven days, wsssfound in period 2. As discussed in the nex% pazzagraph,the explanation involves :- another factor, the weather. During the colder half of the year in noz’thezmmil.ksheds,herds are fed I stored hay so that the cows have’little op~ortunity to obtain radioiodine even if f~lout were present (10). A specific instsace in w’hichthis was ) observed took place at Helena, Montana, wkich according to ~featherBureau records, was snow-covered on April i~y 1965, the date of’f~out deposition ,, probable del~ in exposure of the cs.ttleto the deposited radioiodine may help to account for the eleven day del~ between deposition and first t There were four other cratering tests at tineNTS between 1963 and 1968, intentionally conducted d~lng the colder half of the yeeu?with wind blowing towards the north to take advantage of the fact that dfi~ cattle were on 131 in milk does not preclude its deposition.dry ~eed; the absence of I ~~e contribution of radioiotilnefrou udergsouzid nuclear tests at the Nevada Test Site (I!WS)in PA~7tilk since Septaiber 1961 has been questioned

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(11 thzo~h 20). Uixler:rouxitests at the XL% must always be viewed as a released ;learthe ground so tkt direct cGntact with the crops and scavenging hy precipitating clGuds is easier tlma fG:r nuclear clouds aloft. Fitiy, since 1131 is gaseous, atmospheric co~tc.ainatioafrou underground tests may be postulated even when partic’ulat.esfail to escape. Questions about the source of radioiodi~e have been raised for the period in 1961 and 1962 when both ~titios~}.(?ric and underground tests were being conducted. Over five =d one half ye=rs have elapsed since the I131. faliout frGa tine196L62 atmospheric nuclear test stopped and there are now intervals with frequent underground b-utno atmospheric nuclear tests. Inspection of Fig. 1 reveals nine such in~enals which are listed in Table 2b, duxxingwhich 5 craiering and 137?contained underground tests were reported to have taken place within the U~ited States. In addition, %L underground tests were reported to ‘navevented. The term “vented” is used to aea that radioactivity was detected off the LTevadaTest Site. Excluding the interval after tine Paknquin cratering event of 14April 1965 and the unexplained Noveaber-Deceaber 1965 episGde in southeastern United States (to be discussed later), no 1131 concentration in aillcof the PXN exceeded Because of the cattle feeding practices during cold weather, a better measui-eof the lack of radioiodine in milk following underground tests in the absence of atmospheric nuclear tests or the Palanquin event may be obtained fron the wara seasons, May though October. ~~atio~ of these wara season ?LMNtil& concentrations also shows that no milk saaple contained over 30 pCi/1 despite 64 reported underground tests of which three were reported to have vented {Table 2c). lhring the periods of I131 fallout froa atmospheric tests in 1963-68 there were also 30 reported underground tests in the Uaited States, i’our of which were reported to have vented. There reaains the possibility that these underground tests contributed i~~i to the PMN milk which may have been msked by atmospheric testing. It is Ud.ikelY, however, that under-

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elevated isolated radioiodine concerkrations in the PIvZN that ‘haveDot bees previously discussed. Froa Xoveioer 30 to Decezber 8, 1965, to Lit+le Rock, Ark.) reported concentrations between 14 and 36 pCi/1. Reanalysis of the ga?ma spectra for the detectable values durringthe iiovecber30 - December 8, 1965 period corifixmedthe presence of radioiodine as originally repotied. The Sc,vamah River and Oak fi”dgeAtomic tiergy Cozzuh3sioninstell.ationslie in this area and mere proximity suggests then as possible sources. However, neither tlneirlocsl monitoring results nor repo~ed 1~31 releases, if any, implicate either plant. The other period, July 1966, followed the South Pacific atmospheric tests. A value :. of 60 pCi/1 was observed at palmer, Alaska, OQ July 19, 1966. But it is . > deemed unlikely that an .41askanmilkshed would be contaminated by a source at 22°S. There is, however, no independent evidence for acce?ting Or rejecting southern hemisphere nucle= tests for the several elevated 1131 In addition to the two unexplained periods in November-Decenber 1965 and July 1966, there are others during which the radioiodine concentrations :. exceeded 10 pCi/1 but failed to reach 30 pCi/1, xnostlying close to the In all of these latter cases the geographical and temporal distribution of miiksheds appears to be almost randoa. These relatively few concentrations above 10 pCi/1 might be expected as statistical.fluctuations because of the routine handling and aaalysis OZ the many thousands of In additioa to the F.MN,about @ states monitor 4 only 11 states reported to the PHs> which publishes their resfits in the Radiological Health Data and Reports (21). By 1968 the number of states repotiing had increased to fifteen. ]@W of tinestate networks collect and analyze miLk ssmples on a monthly basis while some collect more freqxeztly. Neill and Sr.a.vely(22) s~~ized the criteria used by states in their milk sampling Prooc=. ..

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?;’X CM, the state findings also co2fiz22the absence of mdioiodine in silk in tiaeUnited States, with two minor exceptions. on September 12 1966 TL12S2,GkMhozla, reported 45 pCi/1 but four other milksheds in Oklahoma :Owz: . These elevated values in the state networks are not accounted for. T:e ~e~eral. lac:f of 1-4 in tilk semples collected by the states is not a Service (Sh~) operates e,silk sauuling network which surrounds the Nevada mA62stSi-ie. MIJc is routinely sampled each month from dairy f~ and iuEvidual family cows ia Nevada, weste~. Utah and eastern California. In 1I tileevent of’a release of a,irbozzeradioactivity from the testing activities at the AMS sone 155 producing dairies in 11 western states can be alerted by telephone to collect uillkss,rxples.Tae SWRKL conducts a continuous A s~ry of 113~ findings in milk in the SWRR network appears in 4. Table 3 for nucle~ ~ocket tests, Crateriag tests, and unscheduled venting tests in Jackass Flats of’the NTS show a peak value of 2hOpCi/1. Tne I farthest farm f’ronthe test site with a concentration in excess of 30 pCi/1 t (frcu ~ test on February 23, 1967) was located at a distance of 250 tiles. ! There was co detectable 1131 in the SWRHL milk networlcfor about half of I the rezctoz evzats. coacefiiratioasof radioiodine in the SWRZL network. The Sulky cratering event created a zmuzndrather tlnaaa convectional crater and only vexy small. szol.z”.tsor radioactivity weze released to Voe atmospkcre. Tnus, ik is

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milk Concentxctions of any NTS event and, as noted earlier, its I exA~e:lsives~-.plin~concentrated in seven states. The ftihest distance of 1 in milk >30 pCi/1 was found at Xiles City, ltiontana,approximately 900 miles from the test site. Tne date of this sample preceded that found ground tests at the i?U7Sproduced no detectable I in the local NTS milk samples. The Pin Stripe event on.April 25, 1966, resulted in a milk concentration of 4,8oo pCi/1 at a distance of 60 miles. Concentrations decreased to 70 pCi/1 i~ a sample obtained at 550 tiles. Aside from Fin Stripe, the highest concentration of I131 in the SWRHL milk network fron an unscheduled release of radioactivity frcm an underground test (130 pCi/1) occurred from the June 16, 1965 event. Actually, at this time, fallout from a Lop Nor nuclear test deposited radioactivity over the United States and the ass@ment of the origin of cotidsion on the Why did the the radioiodine inmilJc is ambiguous (23). Tinesame source of ra&ioiodine in milk existed a yesx later for PMN not reflect the presence of radioiodine when it was seen in the local SWRIL network? The probable explanations are both meteorological and non-meteorological. In the latter category one notes that the PLMNcomposites milk from farzLsdispersed over hundreds to thousands of square miles. Milk frou Farms with detectable concentrations of I can be diluted by milk from other farms in the milkshed with no radioiodine, - the composite A being too small.to detect. l?lniscontrasts with the SllllELnetwork where, for the most part, individual.fsrrsor dairies are sanpled. The clouds from soae of the at~ospheric releases in Table 3 moved northwewd in the cold half of the year whea cows were not on pasture. But probably Bore impo.tiantare the several meteorological reasons. A cloud of radioiodine dilutes as it moves dowmwiad of its souzzcedue to both horizontal and vertical turbulent mixing and to removal processes. The dilution caused by atmospheric diffusion, on the average, decreases the peak concentration in the cloud at Vne rate O: uo~g;hiythe square of-t-.—!lhe peak concentration at 5 hd~-s would thcyefore be reduced by a factor of 1= by the soil and25 one day later. Tne rate of loss ke to uptake of I

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rcdioiodiae have passed through t’ne Such a passage is possible but is ~W2yuilkshed that the debris will J-.....eX23, depending on direction Gi’ clod travel. ~ne answer to the question heading this par-a~raphtherefore is that the concentration of radioiodine in aost czses is 2r0?)S~iytoo low to cause an elevated milk conce~tration by the time the raiioiodine cloud reaches the PAW. Six atmospheric tests conducted in Western Cnina provided the source of radioiodine for the majority of cases of elevated concentrations of I131 in PMN nil-kin the United States froa April 1963 to December 1968. Atmospheric tests in the South Pacific probably accounted for only oae elevated value, in the Canal Zone. underground and 5 cre.teringtesis were reported in the U. the liiS. In addition, $mderwowd iests were reported to have vented. —“ pCi/1 except for the period following the F’alanquincratering event and the unexplained episode in the southeastern U. S. ~.e evidence since 1963 strongly suggests that mcleazz c:-ateringevents coaducted in the cold season with wiad blowing toward the ~orth did not contribute significantly to elevated radioiodine in the PXN mill:. The limited data fron sta’cenetworks ~easuriag radioiodine in milk However, a ldcal PulllicHealth Service iletworksurroumiing the NT’Sshowed and z- of Si&beea uaschedulei verxtingsfrom underground tests. in silk. It is su~gested …