•

~ .. -...

UCRi..-10- 110051

Possible Differences in Biological Availability of Isotopes of

Plutonium: Report of a Workshop

Edited by J.R. Kercher

G.M. Gallegos

Contributions by: LR. Anspaugh, LR. Bauer, E.H. Essington, R.O. Gilbert, T.E. Hakanson, W.C H.mson,

S. lbt~ J.R. Kerchrr, CA. Little and R.G. Schreckhise

Thla paper wu pnpand for Nevada Op~tionJ Office, U.S. Department of EnUJY, La V~u, NV, Workshop 28-29 AUC 1990.

September 1993

Tht. t. an informal ~ l•tndl4 pri .. riJy fer lntfl'UI or llalted e•tft'ftai dittribution. The opinioN au condualoN 1U1ted an th- of the author and

atay or may not be th- of the t..bontory. Work pt'rformed under Lite ••ptC'II of liM U.S. tnpanment of En"'TY by the t...w~nc• linrmo~ Natioul t.abontory undn Contract W-7WS.E.nn-4&.

\ \11\1\ \\U\ 1\U\ 11\\1\\11\ 1\\\\11\ 11525

~ ..

-

. ·tt\'ttv medtan stokes dti'..meter 1 :\~1SD ''! r, l :-:>:T' •.. t:r. .1 .... 'eumt:>trtc standard .l..... ~

Jevtation \GSD) ot 1.3. 6" .. l)t the acu·ttv r .. 1..:1 .1r .. ·\\1SD ,): ; ·:3 mrr. :GSD =:: 7), and

:ne rematntng 0.1': .. passed through .1 L) l·mm tJ!ter

The relattve plant uptake ni ~)QPu ,11 the r,;t~.1tt' ::-eatment ~.1mpies were

,:,"\tiStiC'Illy htsher (:\ = \) 015. n = :,) th,"\n trw ox:dc :r.:.itment rl.H\!5 The mtrate

~reiltment plant uptake values \vert a t.1ctor or ll.' t,) :.>::: greate~ than the oxtde

~reatment plant uptake vaiues tor the three growml; ~easons that the expenment

~:u1 . The plant uptake values tor both chemtcal forms ·.-..ere h1ghest the itrst growmg

~eason and reduced by tactors of ::: :o 50 dunng the ~econd and thtrd harvests.

Brown and Mcfarlane (1978) conducted exper1menrs w1th alialfa. lettuce. and

radtshes that were grown m sod that had been .1mended with monodispersed

:J8Pu02 parttcles (GMD = 0.32 mm) Thetr uptake \','\lues v.:ere stmtlar to those tn

w·hlch more soluble forms of plutomum te g . .:helate-complexed plutomum) had

been cldded to the sot!. These results are contrarv to the Ctne and Schreckhise (1987)

;'.:'SUits tor ::J9puo~ However. the rots .ust'd. II"\ tr.e Brown nnd ~1cFarlane (1978)

~tudv mav have enhanced the upt.ike \','\lues Or. :r .. ~ r:11~ht :nd1cJtP a d1fference 1n

:::-:e phyto~vadnbtlity oi ~~~~PuO:: vs ~~9p~•O:: Adams et ,11 (1975) ,,mended \'Mious tvpt>'> t11 ..,,)tl '' tth l'tlht•r 1(10-mm-dtameter

:.11\Pu02 mtcrosphere!> 0r ,1 2 J~Pu(:'\J01)4 :>ul·Jttun -.;lHnt• ,l: the ~J 4 Pu(N03)4

amended sods were hented to JOO or 'l00°C :o rom"rt tht> plutontum to the oxide

torm Analyses of lettuce. oats. and barlev brown 1n thl? .1mended sotls showed that

the relat1ve plant uptake values were L' nhea ted .· 100"C > 400°C > ~3RPu02

m1crospheres Simply heat1n~ the sot! m.1y not h.we converted the plutontum to

the oxtde form .1nd may have affected the soli \vh1ch mav h.n·e 1n turn affected the

plant uptake values The 100 .. 1-!m microspheres Me much l.uger th;m used tn other

-studtes and mav have also affected the pl.1nt upt.ih '.1ItH'

Revtew of Nevetda TE·st Site Studies

E.H. Essmgton Llrtd R 0 Cll/1crt

Environmental Setting at the Nevada Test Site

Sources of plutoruum on the Nevada Test S1te 1\:TS) mclude both nuclear event

explosiOns and nonnucleu, high-explostve safetv <>hots The expenment that

dtspersed plutomum tn Area-13 of !\.'TS was " s1ngle. non-nuclear exploston of a

nuclear dev1ce. Pluton1um was dispersed over .1 l1mtted .1re,1 w1th lcuger pieces of

tlte dev1ce betn~ depO!>Ited clost> to tht.> ~round Z.l'ro (~~Zi ,1nd :,n·all parttclt!s bemg

depostted Luther .Hv<w lnvestJgatJOn ot the comtruct10n and components of the

devtce tndicated that maten.,ls d1spersed from thP devtet> would likely exhibit a

smgle ~39pu;23Rpu rat1o Generallv. plutomum used 1n safetv tests of nuclear

Jev1ces wi\s ot one 1sotop1c dtstnbut1on <Hid the \'Mious 1sotopes were mtimately

m1xed throughout the matenal It IS i'llso ltkely :h.1t th-.·re was nn 0ther source uf

plutor.1um exhtbttlflg ,, dtfferent tsowptc r:ltto tn ~he .-\re<.-13 d·:'Vtce Based on

11

-

1()/6;93

d1scuss1ons w1th weapon en~u1eers i\r.d LICllo;:r.t..'mt!:>tS ;1: LA0:L .-md LL:--.:L and on

the testing literature. there ~~. no !Cdt.::a~;or. tna: ,:dcittlonal c1mounts ot :: 1 RPu had

been addea to the expenmrnral (<lnrt~ur.lt;o:~ n.scus~:on ot the dl'ta!ls oi the.

nuclear dev1ce used m the t\rea-13 t..''-per:ment :~ -::.1sstttt!d and cannot be related

here. However. as 1nd1Cllted above. therl' ·~ no r1.'.l~Lln w h·lteve th"t the expenment

,:aused anything but <I umtorm dlstnbut;on <11 rluton.um l!:>otOpes presumably In all

parucle s1zes. The _::J9pu I 2JHpu r.1t1o .1ttrtbuteC1 :o the Area-13 matenal was

me.:tsured by the Nevada Applied Ecology (~roup \: .A.EGI tn sod anti \·egetatlon

samples and hild an average value ot .1bout ·lb

If the Area-13 dev1ce contamed plutomLm mlltt:f1,11S 01 d!flenng tsotop1c rauos.

one m1ght expect those ratiOS to be seen m n·.e dtspt:rst:'d matenals on a spat1al bas1s.

Dunng the explos1on. the ~~otoptc r.1t:o \\ ould bt• -.:h;"~n~ed d neutron act1vat1on

occurred. There was no nuclear V1eld tram the :\reA-13 explOSIOn. thus no neutron

act1vat1on of any s1gmflcance oc:urrl'd tt'.a: could aiter :he 1sotop1c d1stnbut10n oi

the dispersed matenals.

There are sources ot piutomum nut .1~so.:t.Hed \'> ith the :\rea- 1:1 explos10n that

may have mfluenced the resultant dtstnbutiL'n ,,r plutonium 15otopes 111 the area of

deposition. World-wtde i.11lout r1as depos1~ed ~m.1ll cut meosurable <~mounts of

pluton1um havmg a well-documented tsot0ptc r.1t10 ut .1bout 4~. wh1ch 1S not very

different from the ratlo of the Arei\-13 m.1ten;'ll ot ,,bout 4b Along w1th fallout from

atmosphenc testmg ts the tmpos1t10n c,f ~'liPu tram the ,\tmosphenc destruction of

the SNAP-9A reactor burnup 111 1964 lf ~uritctent = 1 ~Pu tmm the S!'\JAP were to be

deposited on the Area-13 !:lite. the : 1 '~Pu, : 1 ~Pu r.1t1o would be iowered Finally.

atmosphenc testtng of nuclear devtces · \.,·,1s conducted on NTS proper m Yucca

Ve~lley ildjacent to Arei\-13 Fallout 01 ... q.;nttiC.1nt it!Vf'h ~ .. ·,,s renodlcally depOSited

on Area-13. IsotOpiC r."\tiOS ot the rlutontum !:-om those exploSIOns were very

dtfferent than for the Area-13 pluton1um due to the m.1tenals used tn the dev1ces.

neutron acttvatton reactions creatm~ ::;~Pu . .u•d burnup ot 2:'19Pu.

Because the Area-13 dat<" suggest t!' .. 1t .1n on'rl.1v rniW be present. charactenstics

vf poss1ble overlay mater1ili .ue d1scussed The mator overlay source IS thought to

be the iltmosphenc nucleilr explos1ons conducted 1n Y~1cca V.1lley Figure 5 is a map

of NTS showmg the locatiOn of Area 13. the large cratermg event SEDAN. and a

corndor of fallout patterns from ,, numbt~r or events known to have depos1ted

fallout on the Area-13 site. Those events or the ~ene~ m wtuch one or more events

sent fallout over Area 13 .ue hsted. Several oi tho~e events caused the h1ghest

concentration of fallout to depos1t d1rectly over the Area-13 Site

The 239pu;238pu rat1os for ,, number of events conducted 111 Yucca valley are

shown m TJble 4. These r;1t1os were determ1ned from !lOti sampl•:>s collected dunng

:he RIDP study m 1986 For compclrtS\.Jn. the LillO tor Area- n (-lo) dati\ determmed

In 1973 is decay corrected to l')fl,h ,jQ) The llr!>t r,-,rt uf the liSt I~ tor nuclear

e~perlments Ylt:>ldtnh r;'ltiO!'- trom :.: : ILl i ) The ~t'(Ond r.lrt 01 tht• ltst I'> f0r ~afety

expt'rlments exh1btt1ng nn nuclL'M ,om~'OIH'nt v•eld'nh r.1t10s of 4:' to 52. An

mtermedli\te sample trom i\re.1 i 5 1 Samplt~ #ll i l \\ rlS collected bv RIDP from

NTS

Buster- Jangle Tumbler- Snapper Upshot - Knothole Rio Arriba Socorro Wrangell Otero Diablo Hood Wilson

~,

J

Area-13

Sample 11 ()

0 Sedan

Figure 5. Map of the Nevada Test Site ~howing Area-13.

Table 4. Selected 2.39PuJ238pu source ratios tor NTS.

Source

Kepler Whitney 01ablo Smoky Sedan Sample #lll

Oberon Plutonium Valley GMX Area 1::.•

Rat1o

3.0 3 1 :' 1

10 55 5 3

s:: 42 51 46150)

:0/6/93

• Dati\ from NAEC dil"' Bil~. () de<iiV cnrre<ted lrnm \'17:- t" l'iKn All11th~r dil"' trorn RIDP

(McArthur ilnd M~.ld liJR'Jl

13

10/tJ/Y3

between the SEDAN t'\ent "no Arl'o ::; ,111 !i.l' .-\rL':l- :~: ,,Je ~)! ,1 :nount.1lfl range

separatmg the two Sltl'S ()ne coulC '-·on.::i~,_:t_' th.l.t ,1 ::ortL)I~ ,:r tne overlav r1t Area 13

mav be from the SEDA~ event known r() nave ;-,ent :,1ilout ;:1 the dHeCtlOn or Area-

13

Analysis ot Physical Data

NAEG Transects. Data collected alan~ ltne trarbl.'Cts -.....-ere evaluated tor poss1ble

rat10 differences with dtstance If smaller particles e'-ntbltl'd a decreased ~JYPut :JBpu

rat10. then samples contatnmg a rugher proport1or. ,11 the :::-maller p;ut1cles would

exhibit a lower ratio. Sml from a long tran.sec. ;vh~ch r.1n south to north from the

more contaminated reg10n to the reg1on or lew levels ot contam1m.tton trom the

Area-13 explos10n was collected m 1972. Sod from ,1 shurt transect JUSt southwest of

CZ was collected m 1988 Mld was dEstgnPd to ev.1lu.11e the spi\tlal Vi\rtabtl.ity ot

pluton1um tn ;1 small MC'i1 ftgurl' n ~~ ,, pot llt thl· pluton1um tsotop1c rat1os

relative to d1stance .1w,1 v r rom thl' A rl'<l-13 CZ The 't'getat1on samples were

(OIIected m October 1978 ,1!"\d .1nalvzed bv r1 Jltlerent l.1boratory than the soil

samples. wh1ch were collected 1n :\iovemtJe · 197~ trom .1 loc:lt!On 1mmediately

adJacent to the vegetatiOn samples Onlv one v·~get.1tH.m ~ample was collected and

analyzed from each locotlOn on the transect. whereas tvvo repllcate "ltquots were

analvzed for the sotls. The south-to-north transect data show a deoded decrease m

the iJ9pu;238Pu rat10 w1th distance

Figure 7 is a plot of the rlutonlum ISOtcptc r.1tiOS relative to distance on the

short (east-to-west) transect. Soil from t?ach ocatlon on the transect was analyzed

twice, i\nd all data Me plotted tn Fig 7 Although .1 ltneM ieast-squ<ue fit of the data

shows a slight decrease 111 ratto w1th d1stC1nce from west to the t•,1st. th1s d1fference 1s

not s1gruficant. There seems to be no mforrr ,1t1on 1n th1s d.1til :,ct suggesung ratio

differences Th.ts observation IS mtu1t1ve bee?. use the samples were collected from a

much smaller area than the south-to-north transect and were \·ery dose to GZ.

where the mfluence of the Area-13 explosiOn ..vas lnrge

Microplot Studies. A small-scale sampitng stud\ was conducted by NAEG in

\1arch 1972 to test sampling methods for surface ~oil. soli depth profiles, and

vegetation. The microplot was ,1 small ilrea L'nclosed 1n a temporary bullding to

prov1de protect;on from the wtnd ;tnd amrr <1l 1ntrus10n .1nd "~lowed investigators

to collect s.1mples of sod .1nd veget<ltton that were not tmpilcted w1th plutonium

..:ont,1m1n.1t1on from the surround1ng Mea Thts ITHcroplot study ~nelded profile

data from which plutomum ISOtoptc ratios were calculated Small particles with a

ratio different from that of larger particles may penetrate the soli profile more easily

than the larger p;utlcles Figure 8 summM1zes the tour profiles collected in the

m1croplot study. The datn represent the me ~ns and stclnd.ud devtatwns (50) of the

data for each depth 1ncrement from the tc ur prattles Tht? top three mcrements

represent four data pmnts each and the deeper mcrements .ue for fewer data points.

The average profile does mdicate a substantial decrease 1n the ratiO w1th depth that

suggests smaller. less fdterable. prtrtlcles h.1ve mq;ratl'd vertically farther than the

.9 -; a:

100! \ i I I

so r-1 I i

..__ __ Soil

:.:::r-----:"1 Vegttlat1on

---1

I

~-----~

2000 4000 Distance (ft)

6000

Figure 6. Ratio ot 239pu to D8pu tor Area-13, S·N tr;w~ect.

I 8000

10/6/93

larger. more tllterable p<1rt1cles. Tho~e 5rnalier p.ut1clc~ presumablY cxh1b1t ,, lower

~:\9pu;2:1Rpu ratio. NAEG Inventory and Distribution Surface and Profile Samples. ln 1973. NAEG

conducted an extens1ve sampling progrc'\m to estilblish the pluton1um 1nventory

and the distributiOn of plutoniUm on the surface c'\nd 1n sod profiles.

Figure 9 shows the mean plutomum rat1os 1n the 1973 profiles wnh the SO. A

linear least-squares fit of the data IS shown for reference only. The data strongly

suggest a decrease in 239pu f238pu rauo w1th depth S1m1lar to that shown for the

microplot study. Not all of the surface samples collected from Areil-13 were analyzed for both

~38pu and 239Pu. and many of the samples were too low m act1v1ty to produce data

for calculation of ratios. However. those samples for which ratws could be

calculated are represented in Fig. 10 plotted ilgamst actiVity level This method of

representation was chosen to ollow the VISUillizatlOn oi changes 1n ratios w1th low

act1v1ty samples. those samples thilt could cont.11n ,, different m1x of particles from

15

10/6/93

100~------------------------

;:) 6() + ~ + .. + .... ... "! + ... + + ± +- + ... + t +

.._ ~ I

"' + -r - ~

.2 + ..... ..,.. -r I iii

+I a: +

\ I I

-1

0 I

0 20 40 &0

Ol~tance I H)

Figure 7. Ratio of 239pu to 238pu for Area-13, W-E transect (1~'89).

multlple sources. If a single source of pCHt:cles was depos1ted on Area-13. the data of

Fig. 10 should show a constant ratio w1th rad1oact1V1ty level.

There 1s a wide vanatwn in plutoruum 1SOtop1c r;~t1os shown m F1g. 10, but the

data do suggest three regtons of interest. The first ~~ the very large ratlos that are.

unexplainable at this time. The second is the regton of ratios located above about

10 pCi/g and that center on a ratio value of about 46, which is the average ratio

value established for Area-13. The horizontal line shown in Fig. 10 represents the

ratio for worl ·1-wide fallout (42) and suggests that Area-13 ratios would probably be

indistinguishable from world-wide fallout ratios. The third region of interest is

below about 10 pCi/ g. ln this region the ratios <lppeM to decrease with radioactiv1ty

level. This observation would be consistent wtth a decH!;"ISlllg mflu~nce of the Area-

13 plutonium source and i\n mcreasing 1nfluence of the overlay exhibiting a lower

239Puf238Pu ratio. In fact, that contention 1s consistent wlth i\11 of the ratio data of

Fig. 10 except for the very large ratios.

Solubility Data. There is some data on solubility of isotopes of plutonium from

nuclear event source~. published by Larson (1966). for particles from balloon and

tower events as shown in Table 5 These events were conducted in 1957 and several

16

100~-----------------------------

• en

! i i I

80 ~

~ !

~ ! 4 201-

~ i

10/6/93

I i i

0~--------------------------~------------------~

4 8 12 Soil depth (em)

16 20

Figure 8. Mean otnd stotndotrd devi;ttions of 23 9 .HOpu to 238pu ratio for Area-13,

microplot profiles.

of each type sent f:1llout over the Area-13 Site ')olubiiitY 1s expressed relattve to

water or dilute acid for piUttcles l;uger or srn;,ller thon 44 mtcrons. Part&cles

origmating from tower events show limited solubilitY In water and substantia.!

solubility m dilute i\Ctd. Partlclt.>s tram the bi\lloon events show cons1derable

solubility in both media. In both cases. the· smaller pMtlcles were more soluble than.

the larger particles. The tmpact of this data 1s that the smaller parttcles are the ones

presumed to have been deposited on the Area-i3 and are the ones predominating

the lower acuvtty samples. In addttiOn. the parttcles dtspersed by the Area-13

explosion are fired oxides. which are typtcallv very msoluble compared to the

balloon and tower f~ilrtiCies th:lt are predornmantly siiiCC\te 111 ni\ture

17

'I

10/6193

80~--------------------------------------------~

~ ~ ... ..

60 f-1

I

~ 40 .. N

.2 -e Gl I g' 20 f-.. Gl > <

OL - 20 0 ~5----,0 15

Soil depth (em)

---1 I

1

-1

\ I

l. I

i

I 20 25

Figure 9. Mean and standard deviations ot 2J9,HOpu to 2J8pu ratios for Area-13,

general.

Analysis of Biological Data

The Nevada Apphed Ecology Group (NAEG) conducted envtronmental

radionuclide studies on the NTS. the Tonopah Tt>st Range (ITR) and the Nellis

Bombmg and Gunnery Range between 1970 and 1986. The ob,ectlves of the NAEG

mcluded determining concentrations of rad1onucl1des tn ecosystem components

{soil. air, native vegetat10n, small mammals, and grazmg cattle), quantifymg the

rates that radionuclides move from soil to the other components and developing

radionudide transport and dose-to-r::lan models. This section briefly summarizes

NAEG data that suggest differential movement of 23flpu, 2J9+240Pu, ond 241 Am from

sod to t1ssues of smoll mammals or grazmg cattle m the NTS env1rons.

Animal Grazing. An ammal grazmg on the sparse vegetat10::1 of Area-13 will

mgest contammated particles 10 several ways As the ammal attempts to eat grass,

some amount of soli is wgested by the a:·umal 1nto both the Gl trac[ and lungs. The

18

L·--·······

10/6/93

300

I 250 ~ --i

I

+ I 200 I

I

:::1 I

l Q. + • ,., N .;;

150 ++ ,., ... . 2 + + + 'ii cr. + l .fi"

100 - + + I + + + +

Figure 10. Ratio dependence on i\Ctivity level.

ilntmal w1ll also mgest soli particles that are tri1pped .;.m the surface of the vegetat1on

due to resuspension of contam1nated soli (Wtucker <1nd Schultz. 1982).

Incorporation ot r>lutomum mto the plant structure after uptake through the

roots is known to be very small compared to the measured amounts of plutonium

on the plant surfaces. Thus. the graz.mg <lmmals wlll obtam little plutonium

through that route even though that pluton1um may be more available biologically.

Kangaroo Rats. Gilbert et al. (1988) reported data suggestmg increased movement of

238pu relative to 239•24\lpu and of 241Am relauve to 239•24llpu m kangaroo rats at

Nuclear Site 201. These data suggested that the b1oavn:lability of radionuclides t•> the carcass of kangaroo rilts was 1n the order 23Rpu > 24 tAm > 2JIJ•240Pu. The data

mdicated a possible three-fold (on the average) enhanced bioavailability of 238pu to

the carcass of kangaroo rats relat1ve to 239•240pu ilnd a two-fold enhanced

bioavailability of 241Am to the carcass relative to 239•240Pu. These conclusions were

based on computed carcetss/GI ratio:~ for these radionuclides for mdividual kangarco

rats that resided al: Nuclear S1te 201 The reported data were (reported <.s

19

10/6!93

Table :i. Solubility of isotopes of plutomum trom nuclear event sources. --Support Particle Solubd1ty (":.) (micron) \Vater (0.1N HCl)

Tower >44 < i ,])

•,44 . -, <.- 1l4to36J

Balloon >44 ':.1 \>901

<44 :4 (>60)

Note: D.1ta from L..uson t't .11. ( 196(.).

radionuclide, geometnc mean. £eometnc sc.mdard error. number ot kangaroo rats):

238Pu, 0.032. 1.2, 52; 241Am. 0.018, 1.~. 56; ilnd 239•240Pu. 0.012, 1.2. 59. There was a

statistically stgnificant difference (p < 0.05) between the geometnc-mean rattos for

238pu and 239+240Pu, but not between thf' geometnc·meiln-riltiOS tor ~~lAm and

239+240Pu. The data used to compute the geometnc means were tor ammals wtth

positive concentration measurements reported by the analvtiCi\l l<\boratory (negative

measurements were reported for some tissue samples) That 1s. ammals with

negative measurements were not used In computmg the geometnc means. This

data analysis procedurE' 1s not expected to result m biased geometnc-mean ratios

unless the ilrumals with neg<'ltlve measurements tend to have a different carcass/Gl

ratio than animals with posttive measurements. The tests were wnducted using

Bonferroru t tests (Miller 1981) on the loganthrns of the ri\tios.

Gilbert et ill. ( 1988, Figure 8) also computed 2 ~9 • 241lp u 1 238pu and

239+240pu;241Am rahos for pelt. Gland carcass tissues of the Si\cnficed kangaroo rats

from Nuclear Site 201, again, usmg onlv positive measurements The data reported

for the 239•240pu;23Rpu ratws were (11ssue. geometnc mean, geometnc standard

error. number of rats): pelt. 38. 1.1. 58; GL 30, 1.1. 57. and carcass. 9.5, 1.2. 54. There·

was a statistically significant difference In the geometnc-meiln riltio for pelt and

carcass and for Gl and Cilrcass, but not for pelt 01nd Cl. The dilta rt!ported for the

239+240Puf241Am ratios were: pelt, 9.3, 1.2. 41; Gl. 6.6. 1.1, 59; and carcass. 4.8, 1.1, 56.

There was a statistically s1gnificant difference between the geometnc-mean ratio for

pelt and carcass. but not between the geometnc-mean riltio for pelt and GI or Gl and

carcass (Sonferroni t tests on the loganthms of the ratios) Grazing Cattle. ln Area 13 on the Nellis Bombmg and Gunnery Range

adjacent to the NTS, a nuclear device was explos1vely destroyed Clt ground level in

1957. This test contammated the surrounding soil and vegetat10n with plutonium

and amencium. Between 1973 and 1976. " reproducmg herd of beef cattle were

grazed within two fenced enclosures m Area 13 for up to 1064 days under natural

conditions (no supplemental feed. unlimtted water) (Barth 1979). The cattle were

killed and their tissues were analyzed for radionuclides. including 239+240Pu, 238Pu.

and 241Am. The data for 17 of the 20 cattle were SUltable for esumatmg fractional

20

l0/6/93

1000 1000

Flatulated BHI

StMt'a Canle

Rlmen contents

+ + 100

:l Q. .. ... 3

+ t I + . - +

* +

I :t * l • t t - + - t t t • - -+ + + • - + - • + - • - -- -

100

Q. 0 10 .. N . ...

• + - t -t ' ., 10

... "' + - t -

+ • t • - -

Maximum + + • 75th ~'-lie -Meal.., 25th "Y.IIe + Minimum

t f

0.1 (31)" t'3 '} (56) (58) !'9/ (14/ I 73/ :91 I l4J I !J) 9> '61 ~' I I , 5) 7) !51 7} 0.1

SoU V!Hl VlliJ Flu Sed Ru- Ru- Ret- Hide LunoTBLN Uver Vert Kid Muse 81· Fem

V89 Flu Sed Ser

Sample type

Figure 11. Ratios of 239+240Pu to 238pu for isotopes measured in soil. vegetation, and

tissues of cattle grazing Area 13 (number of observation• n parentheses).

transfers. (One cow died wsth no Silmples collected. ont> cow d1ed from exposure to

the elements one day i'lfter b1rth; one cow was i\ br<1chc.1philic dwarf) Figure 11

shows the measured isotop1c ratios tor the i'lmmills grazmg m the Area·13

contaminated region. Bone, lung, lymph nodes. muscle, gonads and rumen

contents (both vegetation nnd liquid contents) are shown w1th the respective

numbers of animals analyzed. The figure shows the range of rauos with the mean

ratio. For reference, the ratio of the soli and vegetatiOn upon whsch the animals

w~re grazmg IS i\lso shown. In illmost illl c;,ses. tht• tLS!>lll'S l'xhsbsted ri\tiOS that are

lower than those of the sotl ilnd vegetnt10n Only thl' rumen contents were not

sLgmficantly different from the sod or vegetatton r<Hto

Gilbert et al. (1989) used the cattle t1ssue rndionucltde data tn conJunction with

data on concentrations of plutonium and amencLUm 1n soli i\nd vegetatlon, as well

.1s other 1nformatton from the literature, to esttmnte for each cow the frilctlonal

transfer of 239+240Pu, 2JRPu, ilnd 241 Am to cattle t1ssuE·s usmg a s1mple single

compilrtment model (constant snput C\nd output) Gilbert et al. (1989) reported that

10/6/9~

statistical tests (sign tests) lndlcatecl Slgruflcantly \;) < u.OS) ldrger Gl-tO-tiSSUe

transfers (1) of 238pu as compared to 239 • 24 1Pu for all t :ssue exammed (blood serum.

muscle, ilver. femur, vertebra. and kidney'.(~) or DRpu as compared to 241Am for

muscle, liver, femur. and vertebra. and i3) ot ~41 Am .1~. compared to 239•24Dpu tor

blood serum, femur. and kidney StatiStical s1gn tests -::ould not be conducted to

compare 238pu w1th 241Am tor biood serum and k1dnev because only::: or 3 cows had

data for both tts:;ues. The s1gn test comparmg : ~ 1 Am anj 239 • 240pu were

nonsignificant for muscle (p = ll09), liver 1 p = l) 15). nne vertebra IP = d 7)

The GI-to-blood fractional transfer of 2JRpu (u OOCil \ was about 20 times larger

than the estimated transfer of 239•240pu (1).000005). \vhde the est1mated transfer of

241Am (0.00001) was about 2 times larger than that or :Jq .. Hnpu. ~1ed1an geometric

mean 238PuJ239+240Pu ratios were (ttssue, Meometnc meiln. number of cattle (rattos)):

blood serum, 28. 5; femur, 16, 7, muscle, 10, 7. kldnev, 5. 5; vertebra, 3, 11; and liver,

2, 16. The med1an geometnc mean 241 Am 1239+240p~ ratios were blood ·'rum, 4, 5;

femur, 2, 12; muscle. 3, 9; kidney. 4, 8; vertebri'l. 1. 15; and hver. 1. 15).

The estimated fractiOnal transfers depend for then valaditv on assuming the

selected model and model parameter values <He appropnate The etfect ot mode·l

parameter uncertamty on the uncer':ilmtv ot the estimated fract1onal transfers IS

currently being assessed us1ng uncertamtv i\nalyses (Monte Carlo stmuliltJOns). The·

possibility that a mon' complex and realistic model m1ght have gtven different

conclusions cannot be d1sm1ssed lightly The model that we used considered only gut absorptton. A more realistiC model would wclude tnhillatlOn ilnd absorption of

Pu in the lungs of the cattle. Rumen contents of fistulated steers (<Hld a non-hstulated steer sampled at the

ume of slaughter) grazing Areil-13 were collected dunng the year and analyzed for

plutonium isotopes. Table 6 is a summary of the 1sotop1c ratios of the contents of

four components of the bovme GI tract for severill grazing penods. The designation

"shrub," "g!'ass," and "mtx'' m Table o 1s a verv crude 1nterpretilt10n of the general

nature of the vegetation grazed, .md IS shown onlv .1s ."'n Indtcatlon of what the

animals mtght have been grazmg. The dat<l show that dunng the wmter months,

when the animals browse shrub materials, the plutomum ratios are closer to that

determined for the soil materials. Dunng the spnng nnd early summer months, the

ratios are lower, perhaps associated w1th grazmg on the grasses. One can postulate

two plant·spedes-dependent effects that may influence ~he ingE?Stion and ultimate

i\Ssimilation of plutomum: ( 1) the nature of the leaf surfilce relative to its ability to

trap and .hold particles; and (2) the part1ally dtgestE:·d plant mi\tenal in the GI tract of

the grazing animal may create a diffc~ent chem1cal cond1t10n thnt can alter the

solubility of the plutoruum contammg i. ·tcles. Based on the data m Tilb.le 6, 1t is f~~o..l')Sible that the brazing cattle have mgested

particles of considerably lower .sotop1c ratios at l~ast dunng a portion of their stay m

Area 13. The Yucca Y.lllev source ratto or : t•J It) and the rat1o of the ilssimilated matenal of 2 to 24 are consistent wtth the observed :~nm1al tissue rat1os of 2 to 25.

10/6193

Table 6. Ratios of 239Puf23Bpu in ~oluble fraction ot rumen contents (j. Barth 1975,

p. 141)

Nov hb \1av jul Aug

Organ pH ::.hrub shruo hrass grass ffilX

Abomasum 3 33. ~8 q -l 3.

Duodenum 4.5 36 :-t ... .., 35. -

Jejunum b. 40 19 1l b 38.

Lower lntestme 7.5 42 38 ~.; 42.

These data are consistent w1th the hvpotnes1~ that the observed rat10 d1fferences

between the sod and the ammal ttssues Me due to d1fferences m rat1os assoe1ated

w1th particles of diffenng ong1ns and solub1llt1es

Also, cons1der the range of r<1t1o values reported tor the ilmmal t1ssues shown m

Ftg. 10. Some ilmmals dtd not show the ratto differences. those r.1t1os were s1milar

to those oi the Area-13 soli matena1s Poss1blv. those an1mals were sacnhced after

graz.mg the wmter months bee Table b 1 Those ;m1mals exh1b1tmg the reduced

ratios possibly grazed dunng the ~prmg ,1nd summer months when they were

mgestmg matenals of i\ lower ratto.

Savannah River Studies L. R Bauer

Extensive studies of plutomum concentratiOns tn a vanety of environmental

compartments have been ~.1erformed ,11 the S<1v.1nnah Hiver Site (SRS). The

,malyses descnbed in th1s sect1on were conducted by the S;wanni\h R1ver Laboratory

,1nd Savannah Rlver Ecology Laboratorv dunng the penod 1976 through 1989.

Field Studies

A field study area was established near a nuclear·tuel reprocessmg facility located

at the SRS. The charactensucs of the study area, ,1nd Its locatiOn relat1ve to the

pnmnry process stack assoCiated w1th the separi\tlons ti\Cihty, are shown m Figure 12.

The s1te for the study .uea was selected based on known patterns of low·level

plutomum contammnt1on near the filCihty

Of the two study plots shown 1n the figure. Field 2 has been used more

extensively. This approach was ti\ken bec,,use Field ~ hi\S a more natural soli profile;

the top-soil and sub-soli layers of F1eld 1 h;we been disturbed by construction

activities m the area.

The plutoruum concentrations of broadleat crops ~rown on Field 2 havl~ been.

exi\mtned by McLeod et ill. (1984o. 1984b) The ~esulrs were reported .1s isotope­

specific concentratiOns of pluton1um per gram of <;Oil. and ns rat1os of plutonium

l __ ........ ----------................ ~~

l0/6/93

30 ·300

t ;1~ 240pu

i 1\ t I I

25 i-· I \ 1250 I I \

J~ I I I \

\ \

I \ l200

\

i I

I I

I ~

i·~ ~

~ 0 0 \ I \ en en ' \ I

CD

"t \ :::..

CD ~ ~ \ I \ ~ \ I \ :I a. :I

\ \ 0 a. I ~ .. ..

~ \ I "" ...

- I ~ .,; "' \ ...

' ...

10 f. ' I ·- ... j ... +oo 1

""'- 1 1

s - so 2l8pu

0 ~--------------------------------------------------~0 67 69 71 73 75 n 79

Year

Figure 14. Annual variation in 2J8 Pu and 239 •240pu concentrations in Alaska lichen samples during the period 1967 to 1979.

Possibility of Experimental Artifacts in Existing Data

Sample Collection, Preparation, and Analysis Problems that May Cause Variation in 239puf238pu Ratios E..H. £ss~n~tor1 11nd S l/1rulum

There .ue severill poss1ble reasons v-.·hv the -:;tlcul.1ted ~:lllpu / 2JHpu ratiO for a

g1ven sample may not accurately represent the true rat1o for th~ svstem sampled.

31

:'\lon-representat1ve rat10~ rnav c._J..:..:~r .1~ ,1 resu:t ut :n~FCrt~prtetJe~ ur errors 1n (1) the·

des1gn ot sampl~ coliect!Or1. \~i :'-,!mple :'rl?r'M~ItlO:l_ '.' :'J,'lrnpie d:SSOIUt!On/chemtCal

punficatlOn. (4) alpha spectrometr1.:: -:,;.u~:::~~.; ~ ~-~zy, ·otng tor cnemtcai ytelc

determmatwns. and (6) quail tv control These ~·omrs Me d1scussed betow ";th il'~.l!'C :,, rr.e methodoiLJ~Y Lsed 1n

.::ollectwn. prep<Hatlon. ,1nd ,1natvS1S ot c,.1mptes :c•r LJ.:termmat1on ut piutoruum

.::oncentratlons 1n so1ls. plants. :md an:rnal Lssues \'.'e .ue iooklng tor b1ases that

mav cause the :JRpu results to be h1gher thar expectec resultmg n low 2.39pu 1 238pu

rilt;os. In these d1scusstons <239 Pu" .::. used to r.1ean : 1 "·2·Wp~ because the two

1sotopes can not be d1stm~u1shed bv ·,pt•.::trometrv ~.s;n~ ·-urt.\ce L•.uner dett.>ctors.

Sample Collection

Sample collectiOn 1s ~eneralh Jes1.,;:ned to c._Jt::>t.Hn r. .. 'lterJ.ll representative of the

..:ontamtnant dtstnbut1on m tne ft>.Hurl' t1 e1n~ ~.,,fT'.~':eJ .. l' . ~oil. \ e~etatwn. rumen

..:ontents. ,H an1mal tl-,sul'l :\~ ;,1,-h ,;:. :r<l' ~ :~ton1um 1:->lHopes .ue eveniv

d1stnbuted among the 'oH1ous -,.,mpleJ (Umponent~ '' t' • :1ot tractwnated), one

would not expect the .let ot sampl!n~ to :nduct' .1 "t'!JoH.ltlOn of the 1sotopes. The

sampling procedures used .It :\rea- i 3 tor ~urtace -,od .1nd profile tncrements

mcluded the use of a template ,,nd collectiOn l)t the toti\l sample wtthin that

template w1th no furtr.er mantpulatton oi t:.e :,.,mple CollectiOn of \·egetation

samples was accomplished b:-r· cllpptng exposed br,'lnches or gri\ss blades hm1tmg the

choice of matenals to the current ~ears growth .\g<Hn. there vvas no further

mampulat10n of the vegetatton sc1mples Ruml'n ,ontents \,·en' L)bt;Hned so that

nearly all of the veget<ltlOn. ~od solids. ,1nd l•quta 'ontents nt the rumen were

collected e1tr.er from flstulated steers or upon .,,,cr1f1ce l)f the ,,ntmal. Tissue

',amples were collected c15 entire l!nllS ,'\\'Oidm~:; ,·~n~s-,·ont;)mln;'ltiOn Usmg these

teChniqUeS, 1! IS bl:'llt'\'t'd !h,"\t the '-,1mpl1ng r'fOCl'dUrf:''> were '>OUnd .H\d no

unexpected mampulat10n dunnh the .,,,mp::n~ ~'f\1\t'uures nccurred th;lt could have

caused 1Sotop1c fractlO!liltlon.

However. If the dtstobut!On ot the Fluton:~,.;m 1sotopes h.1d vaned among

dtfferent system components or ."'t d1fferent locatiOns 1e g, washes or d1fferent plant

speCies), appltcatJOn ot M\ 1mproper s.1mpl1ng i-'rocedure rni\y produce samples of

dtfferent 1sotop1c rat1o~ An ex;m1ple m1ght be the .,,,mplmg ot soil for purposes of

determmmg mventory but usmg the same datil to determme 1SOtop1c ratiOS among

umque 'eatures. such a:;, 1n dramage channels. Larger or more dense put1cles can be

separated from smaller or less dense piHttcles bv smttn~ ,1nd redeposttton dunng

eros10n ep1sodes gtv1n1; r1se to Isotopic rat1os dltferent th<m those of the source

mf\terlc'll.

Another example rmght mv~)l\l' :~e :-n.1ruwr :n \vh1ch vegetatiOn ,,.._-cumulates

-:ontamtnf\ted putJcles \'egetat1on :n th.> Mtd :'<TS 1.:nv1ronment can ,,.:cumulate

pluton1um :n two \\,1\S !l) rl1l)! l•t't.li-.1.' '.1t dJ::.'.ul,t>d f'lutoni;Jm .. \nd (2) d!fect

.................................... __________________________ ._ __

., >i. t/ <J]

depm1t10n and capture nt resuspenaed ;·.~rtJC.t'~ ,·_,r,t.>Inin~ f-~lutomum lt 1s believed that the ISOtopt>~ nr pi~tO~I~JrT. \\ :ii :·.-:t : ~.\.~L<'n.>te tlnce d1ssoi .-~·d and dunng the uptake process Ho>vt'\t'r r:.•.:t.,,i~.;:Iun ,.~n tlCCur ;: the ~,1urce ot plutoruum parttdes 1mpact1n~ the ~~I.HH \ .H:e~ 11~ '~''tt1~':.: ~;\tto w1th siz.c dens1tv. or solub!litv

Another exampie mvolves the po~.s1t:ie ~t>paratJOn t)l part:cles 111 the oovme rumen. Larger or more d.mse part1cles ot one 1sotop1c rJtlo may settle and not be t!asilv dtssolved whereas smaller or less dense p.ut:c!es -. ... ·1th a dtfferent 1sotop1c rano wtll be more eastly m1xed w1th the rumen l!qutds ·~amplmg ot rumen contents that does not accommodate those several components could Introduce b1ases tn

ratios. Sampling of ammal tissues at var.ous t1mes dunng the life of the animal may introduce d1fferences 1n Isotoptc ratJ,)S li the depos1t1on of the plutomum In vanous tissues zs dependent on tzme or ~tage t'f tt~sue ~rowth .1nd the .1mmal 1s exposed to source maten.1ls ut dtffertn~ ~.•t:os .1: d1fiert.':1t t1mes

Sample Preparation

Certam steps 111 ~"1mpit.> prep.u.1twn :; .. )'. -.:.1u~t' :r.~t:tiOn<Hton ot m~tenals of differing !SOtoptc ratto ln the case ot soil prep.uat1on. hr1ndmg ana s1evmg are two steps that alter the prtrttcle SIZe clnd distribUtiOn tn the Frepored sample If small particles are ennched 1n nne plutontum t~otope .HHl :hP l.uger puttcles .ue erutched in another plutomum tsotope, the resulti'lnt ":>tevt>d <..1mple could rdlect .1 bias relative to the tsotoptc d1stnbut10n tn the totcli ":>l)tl ~.1mple

VegetatiOn samples usually .1re not mantpulatt:>d bv phvstcal means except for direct ashing before dtssolut!On There .1ppeus to be no meam. oi tsotoptc separation dunng the preparatiOn ot vegetation samples for .1nalys1s.

Deposttlon of Ingested plutontum In c1ntmal !iSSues tn the broad sense IS

umform. Dtfferenttal depos1tton 111 org.1ns. :,uch "~ bone. does occur on a m1cro scale. Sampling of ."'mm<\1 t1ssues lor .1n.1lvs1~ gener.1llv uses large port1ons of the t1ssue so that spattal depos1t10n ot d1iferent ISotopes henerally would not be detected.

Chemical Purification

Proper analysts for pluton1urn 111 en\ lrtHHnei\t.ll "·'mple:, requtres (Ornplete dissolutiOn of the ~.,mple rnatrtx ,,nd :urwers1on ui the plutontum to an appropnate ox1dat10n state. For soils .1nd geolobtc :natenals, the sample 1s dtssolved 1n hydrofluonc-nttrtc·hydrochlonc <ICtds For veget,>ttOn, the same procedure follows a prelimm.uy .1sh1ng step lf d1ssolut1on ::-. tncomplete. so that mor~ refractory parttcles ennched m one ~~otope Me not completelv d1ssolved. the resultmg ,,nalyttcal results wtll retlect more ot the less retractorv matenal (more soluble) and thus b1.1s the resultant ~~otoptc ~.1t1o tor the qmple

Dissolved plutontum 1::. sc.1n:onged on :ron hH1rox.de. converted to Pu• 4 , and separated from the matrtx ,1nd ,·nntamln,H'.b h <iliOn t.>xchange nr solvent extr.<ctton lncomplt?te :-,ep.or;tlton or diSSOi\ ~·u m •-,)ltd nLHrtx m.uen.<ls produces .1

i0/6/93

thiCk ·!iectrodepOSlt. whiCh CJn degr;1l1t' nw .upna ~pt'Ctrum \uiSCUSSed below)

Incomplete separatiOn c.:~n .1lso allow tne retent1on m the sample ot rad10nuclides.

wtth alpha energ1es SlmticU to those or tne i-'lutomum botopes anc thus mtertere in

the quantlficat10n ot those pluwntum .sotopes .1lso \.ltscussed below).

Rad10nuclldes that c<1n tntertere .He hsted :n T.)ble • ; <lnd tnc!L.de natura~ly

occurnng ISotopes as well as r.1d1onucildes added a~ '-teid tracers :\menClurn-243

and 232U may be added to the .:mgmal sam?le as tracer~ tor 2~1Am tand cunum) and

the uramum ISOtopes, respecuvelv. tn a sequentlai separat;on of plutomum .

. 1menc1um lcunum), and urar.1um

·weapons plutomum contams stgnlficant levels oi :4\Pu. Th1s plutomum

decays w1th a 13.2-y h;~lf-life mto :4\Am. If the amertctum 1s not quantitat1vely

removed dunng the chem1cal ckanup. : 4 : Am (an contnbute alpha counts to the

:38pu peak reg10n. If the punfled plutoruum ')ep<Hated irom the sample lS not alpha

.:ounted w1th1n a week or twu. measurJb•e ,,mounts ot ~4\Am wdl grow mto the

sample, adding counts to the ~JRpu peak re~1on The amount ot both ~41pu and

~3Rpu were determmed .1nd the .1mount ot ::'-ll Am tr.~rowth w<\S c.1lculated as a

fraction (Relative A(tlVltv) or the :JHpu r·resent tn the ~.1mple For Area-13

plutomum, the eifect l)t 241Am tnpowth on ~~HPu ~~,,bout 1'\, 1n JO days and

reaches ;1 maximum m .1bout 70 ve.us Ingrowth ot ~ 4 1 Am ;'PP('i\rS to be " negllg1ble

problem tn most labor<~:ones

Alpha Spectrum Analysis .tnd l.1boratory Procedure~

Plutomum measurements bv .1lph;1 <.pectrometrv us1ng surface barner

detectors mvolve several problems :v1ost .1lphll em1tter5 ()!ten encountered in

environmental samples Me tn the r<1nge of 4 to o MeV. as md1c<1ted in Table 11.

Thus, 1n the extraction oi plutomum It 1s 1mport<1nt to remove other interfering

r<ldionuclldes. Figure 15 shows ,, typ1cal. clean ,1lpha spectrum that the analyst

.utempts to obtam. Th1s type of spectrum 1s obta1ned 1f the chem1cal purification

steps ue conducted properlv .1nd rt?mov.:tl t)f tnterf('rtng rildtonuchdes IS effective.

However. -:ontamm.1t1on from ~41 Am would not De detected 1n th1s type of

spectrum Poloruum-210 can be m1smterpreted ,1s DRpu d the i\nalyst does not properly

l'Valuate the alpha spectrum A clean spectrum 1ncludmg 210po 1s shown 1n Fig. 16.

The mtederence due to 210Po 1s most llkely to occur w1th a less clean spectrum with

lew 238pu counts; m such cases. the pos1t10n of both the ~ l!lpo <'lnd 2:\Rpu alpha peaks

.ue not ,1 wavs well defined \-1tslnterprPtl1tlon mav .11so occur tf peilk sei\rching

routmes ,,re used to extr<~ct .1lpha spectrum J,1tl1. :1nd the .1nl1lvsts h.we difficulty

rE~cogmzmg the 2:\Rpu energy reg1on w1th Il)w numbers of counts Polomum-210, 1f

present. can mterfere w1th :!J'/•2-lllpu energy bv t.11llng Polontum contammat10n

mav <HlSe from tncomplete ·hemtc.11 .,epariltlcn .1nd/or from detector

cont.lmtnatlon bUildup over t!ldenC:Pd u-.e :ncomptete sepruat1on ut 2lllPo can occur

lU/6/':13

Table 11. Alpha energies of import.uH radionuclides in plutonium measurements.

2·Wru z:wru ~ 3"ru

Isotope

~~2Pu CTra.:t:r) ~36Pu

2~1Am (also as mgrowth from 2~1Pu 243Am (Trilcer) 234U

23C'r'fh 22BTh 2lllp0 ::2~Ra

~~2Cm (,llso decavs to 2lRpu 1

::~2L:

2500

2~J Ill

c :I 1500 -0 u

1000 r-

242pu

:1 energy MeV

n11. <•Opu

~

c,J7.'l]~

'~ lh. 511 S5u.54tJ

-- ,... ~., ') I I. ':J.I-

5 49. 544 5.28. 5.23 4.77. -1.72 4 68. 4.b2

5 43, 5.34 5 31 568.545 t") 1::. () 07 - ~.,

) .J ...

I

\

I

I I

I 1

~~~----------------~/~-~~'---~---~L2J-I~~~u-----------~ 4.0 4.5 5.0

Energy (MeV) 5.5

Figure 15. Ideal spectrum of plutomum including 2Upu yield tracer.

::15

6.0

10/6/93

3000 I

i I

' I '

I I

I 2500 1- -1

i ' I I l \

239pu I

2J&pu !

2~l _.

I

Ul \ c: I

1500 I

::J l 0 u i

i

1000 f- I I -1

I ::Japu i I I

500 f- I 210p0 1 I I

) I

' l) I 0 4.0 4.5 5.0 5.5 6.0

Energy (MeV)

Figure 16. Spectrum of plutonium and 210Po with l36pu tracer.

m the sample or 210po can occur as iln 1mpursty 1n reagents (e g., phosphoric acid

used to polish the electrodepos1t1on plates) The removal of 210po contamination is

possible by self-plating on mckel or copper from dilute HCl pnor to plutonium

electroplating. When 242Pu tracer 1s used for v1eld determination. sample

decontamination from natural uramum should be complete due to the possible

mterference of 234lJ into 242pu energy regton ( .1lthough this m.ay not affect the

239•240Pu/ 238pu ratio, 1t will result m an over estlmote chem1ci\l yteld). Sample

decontamm<~tion from nllturlll thonum should be also complete because some

232Th progeny may mterfere w1th the plutomum peaks. If 23llpu tracer is used for

chemtcal yield determinatton, peak tatltng of 23opu 1nto the DRpu regiOn must be

considered. Americium-241, if present m h1gh concentrilttons and not completely

elimtnated from the pluton1um tract1un. wtll uHcrft:'rt' w1th ::!:'\Xpu

It is also Important for .1lpha spectroscopy to produce very th111 plutomum

depostts pnor to counting to prov1de mcll(lmum resolutiOn. With the mcrease cf

36

\

'

i I I

I i

I

depo51t th1ckness. the energv t.1111111:, '' :i\ J:.Cfl'J!'>t' ;'t.'•"'-· f'OSitlon :-.h11ts to lower

energy, .u1d peak he1ght decrease~. T!-,e ~,~t'~t·nu•:-. ,,: :.•ntn;1n1Jes. :ron. "ugar:1c

Jepo~.tts ,u1d sdtc.1. :or eompie. \\ d! Je~r.1.Jt· ~:.t• .l:~'na ~~~·ect~;~. makmg peak

resolutiOn more d1iflc.J:t \'hth t!".:ck. .Jq.;os1ts. ~-t~<tt. ::'.ten .1 • ..,dect1on becomes

more sub1ect1VC i'lnd the ,·;ilcui;HI(':I ,,t iliph:; ;1c~1\ :t\ L'•.'CtJme::, it·ss relli'lble As t:1e:

thlckness or the depos1ts JncrL'ases. the 23:-ipu peal>- .:.1n l;;:-,,!Fpeor c:ue Ill the tntluence

or the degraded 236pu alpha Slgn.'ll ( d U!>t?d .15 an i'Lltupc tracer 1 Degrildea alp!1a

reaks for the plutomum I!>OtOpeS ilfl' shmvn In fl.: ; -:-(_)the r t.l c tors ll t 1 m port" n c e ' :< p 1 u ton 1 " m ; ne ,, :-. u r e 11\ en t s . 1 r e rea gent

contammat1on w1th r<ldtOaCtiVIt\'. ter:'lper.1ture r:·...~ctu.ltlOns 111 the .:ount1ng area 1wh1ch cause peak shdtmg) .. 1nd the a.pha .:hamoer \'ilCuum. \\ h1ch will dfect peak

energy resolution. The prtmarv problem encountered 1n .1tpn:~ :0unt1ng 1s the 1nsufficu:-nt

accumulatton of counts for proper que~nLflc,ltlOn l1t .m energy peak area. Often se~mples are counted sc that the mator pt'<tk .~ rropert\· quant1t1ed but coilectmg suffioent counts 1n mn10r pertks milv oe 1 mpr.<C:IC.11 J ~e :o :he lung count t1mes

reqUlred. In samples from Area-!l. the alphil count r.1te ot ~.1<:1pu runs 40 to 50 times

that of 23HPu. and often the ~.1mp1es .He 10w 1n piuton1um content C.1lculat1ng a ratio where one component IS wpak :n 1ntorm.1t1on wdl mtroduce constderable Vi'lnabillty and poss1bly hidden b1ases

There are other posstble sources ot error m countmg, .1lthough most ,1nalysts are awcue of them and t;~ke precautiOns to .wmd the1r etiect Contammat10n of the. detector irom '' prev1uus sample cont;:11nmg ,, dtffPrent 1:,otop1c rC\tlo ciln cause 1mproper data to be generi\ted r\s mentiOned .1bove. collectmg msuffiClent numbers ot counts could 111tluence the lnlorm."'tlon tur une ~~otope more than the other. resultmg poss1blv 1n ;1n erroneous r<HIO Other more mundane problems are known to uccur occ.151UIIc1llv. ::.uch .!!> lmprtlper .dentttiC.Itlon ot the ::.ample. errors 1 n .;: .11 c u L1 11 o n s . f.11 I 1 11 ;.:: d l't e c to r s , ) r l'l~.· ct r o n ,,. " • ,- • · '>~; l t 1 n ~: 1 n loss o t d .1 t a o r nonllneantv 111 t:.>lfiCit'IKv Llver the .11ph.1 l'lwr~::_v ;.ln(l' \lt 111ll'fl'St) .. 11\d peak !>hlfhng

Yield Determin<ltion

lsotop1c tracers used to determ1ne the . nem1c.11 v1e1d ot the ~1lutomum analys1s .~re 2:H'Pu and 242pu A problem 1n tht• .~:,e ,11 :'''Pu .1s ,, tr.1cer occurs when

s1gmf1cant talling IS present. If tiHilng occurs , dtscu!>!>t'd .1bovt> ), the :3HPu peak cont.11ns some response from the ~:lt;pu .11ph.1 ~.:ontrtbutwn. bl<ISII\h the ~:wru;23Rpu rat1o upw.ud (see Fig. 17)

The 2·i2Pu trilcer ... mless spec1Jlly (-'unfled. cont."'lns both ~J~Pu and 239pu as

shown 10 Fig 18. Generally .• 1 correctiOn 1s made to the 2JRp.J and :!39pu alpha

spectrum rest,.~lts tor such ~.:ontnb.;t:ons. the d.Hrl'Ctton t:sed b\ nne L1boratory for 23Rpu and also tor ~~'lPu 1::. .1bout 2":. lH the .1ddea :.;:ru Tht> corr•'Ctlon h<~s a

3~~----------------

I I

2500 I­! I

\ I

2000 t­!

Ill j c L :s 1500 I

8 I

1000

Summation

spectrum~

4.5

',

2311pu

5.0 Energy (MeV)

5.5

Figure 17. Spectrum of plutonium from "thick" ~lectrodepof>it.

10/6;93

i I .....

! -1

\ I

_j \ i !

l 6.0

proportionately greater miluence tor the =•l'\ru <llph;~ penk than for 239pu alpha peak;

for samples wtth low 23!\pu, th.ls correctiOn may be a very I<Hge proportion of the

.1lpha counts thus masktn£ the DXpu peilk 1nform.1t1on

Quality Assurance/Control

Lack of appropriate quality control may <lllow 1ncorrect results to be generated.

Blanks, spikes, ;md replicates are usual'y mcluded 1n the s.1mple stream. Rev1ews of

the results from blanks, spikes. and replicates illong w1th logtci\1 ,,ssessments of the

sample results Me used to assure thilt gross errors e1ther 1n the whole data set or in

38

10/6/93

3000

\

i ;:42pu

I i 2500 f- I

I ! I

I : i

2000 ~ I

-1 I

i

Ill I

c 1500 ~

:I 0 I u

1000 ~ ~ !

\ ~ SOOL 239. ~40pu 2J&pu I

6 ./1\.._ l 0 6.0 4.0 4.5 5.0 5.5

Energy (MeV)

Figure 18. Spectrum of H2pu showing DCJpu and l38pu contamination.

mdividual analyses c"tre mm1m1zed In the case of plutomum analys1s. often the

~38pu act1v1ty levels ore low compared to ::J9pu oS noted obove. and the tendency lS

to concentrate on 239pu analysts for qu.11ltv control. th1s may leave 238pu data at risk­

.1nd thus b1ases m the calculated tsotoptc r.lttos

Counting Statistics and Censored Data Sets

R.O. Gilbert

The use of ratlos of concentratiOns or actlVttleS of radionuclides is an 1mportant

top1c in environmental studies of radioactivity Statistical considerations in the

generation and use of such ratios have been reviewed (Doctor et al. 1980). Apparent

differences tn bioavaililbility of 23Mpu and 239pu cC\n be C\n ;utifact of different

amounts of CE!nsoring of data sets fer these two tsotopes A data set IS sa1d to be

"censored" if a known proportion of the data set 1s mtss1ng. For many data sets, a

measurement below the detectton llm1t 1s reported ;-1s "not detected" (NO). "below

39

tne aetectton hm1t."' ~H 'less than· iLT: t:1c uL'tt•c:wn :::n1: Tren tr.l' datil 5et 15

"censored on the !eit" because vaild r7H~asurements .1re not .1vt11lable tor :1 known

proporttor, of the samples Data ~t>ts or 21 ~Pu trequt>t'.t>' :--..>ve a :'.reater degree oi

ceruonng than those oi 23<Jpu because en\·tronmer.tal -:oncentr<'tto 1s ot 23!lpu tend

to be lower thi\n those ior : 39 Pu Th;s ,•rrect -:.-:n lL'.hJ t() ~pu.xous (onclusLons

r~gi\fdtng dtfferentlul biOi\\'illiabdlt~ .

The effect of a differenual amount of censorxni; nn estxmated biOov<ulabtilty

depends on how the data are statlsttcall•· analvzed. One method of analysts ts to

d1vide the mean 2JRpu concentratiOn bv the mean ::.9pu concPntrat!On. For

example. suppose for a gtven medta. sav soil. \'lie\ 1) compute the mean of the 23Bpu

data that are above the 238pu detecuon hmtt. t2) compute the mean of the 2J9pu data

that are above the 239pu detection hmtt. and 13) dtvtde the :3Hpu mean bv the 239pu

mean. ~ow, tf the 23Rpu data set 1s more heav:iv censored than the a :39pu data set.

1 e .. a greater proportion ot the smallest :JRpu ..::oncentri\ttons ;ue mtssm~. then the

computed ratiO of means will be l<Hger than d no censonn~ h,"'d occurred. If 238pu

data sets become progresstvelv more cen~.ored on the 1eft .1~ we go up the rood cham

te.g. m the order sod. vegetat1on .. uthropods. -;mall r:1ilmm<~ls l. then the rauo of

means also becomes progresstvelv more b1.1sed h1~h Hence. thts type of analysts

td1v1dmg the lJRpu n,ean by the ~39Pu mean\ could result 111 ,, spunous conclus1on

that the true (unknown) 23Rpu over 2:'19pt: riltlO mcrc•<~ses wtth mcreasmg trophic

level. i.e .. that differential movement of DRpu and D 11 Pu has occurred. Of course. tf

the1r true ratio does mdeed 1ncrease w1th trophtc !evel. th1s statiStical estlmatlon

b1as wlil exaggerate the true tncrease. Some :.tattsttcal methods for obtammg valid

est1mates of means from censored data sets Me d1scu~~ed 1n Helsel (1990) and GLlbert

(19~7) If some measureml'nts bl>low the dctect1on l1mxt .~re reported ils zero. these

zeros should not be used as real measurements L'smg these zeros as tf they are

vahd data will result m means that .ue b1ased low T~erefore. spunous conclustons

regarding differential movement could occur 11 ~he number nf 111d1cator zero

measurements ts larger tor the htgher trophtc levets

Often. both 238Pu ;md 23'JPu measurements .ue made on each t~nvtronmental

sample of sod. "veget<Hton. etc In th1s case. lor e;\o.:h sample. we can divtde the 238Pu

measurement by the ~J'lpu measuremet'< ro obt;Hn ,, r.1110 tor the 1ndtv1dual sample.

Then we can compute the mean or the geomt:>tr1c rr.e,,n ,11 the 1nd1vtdual ratiOS for

each enVIronmental medi,1 Of COUr~e. the mei\n filtlO IS COmputed USing

measurements only for those medta samplts \ ... here both :lHpu and 231Jp u

measurements .ire above thetr detect1on hm1ts Hence. the value of the computed

mean ratto will be dtfferent from the nxe;ln r<'ltto th;'lt v.-ould have been computed 1f

:neasurements for all samples are above the delect1on l:mtt If the 238pu data sets

become progressively more censored on the left as we ;o up the food chain, the

mean ratio may or may not tend to 1ncre<~se .1r decr('ose Certamly. a spurious

1ncrease •Jr decrease could occur d mdt\'ld'Jal ~amples wtth ~~RPu or 239p u

measurements below the detectHm llm1t h.w( .1 concentr.1t1on ratto that 1s different

40

'I

:rom sa:npieS tor WhiCh both lSOtOpt:~ :· .. nt' ~~:t_>,~~urements clbO\'(' the deteCtlOn

:neasurement ,1nd countmg t'rrors· .lr.lon~ ~.~rn~'.t':, ...:.>l'~ ::.Jt

t:1.1n rro::n rZ~ndom

-:,t't'm ~~laus1ble. the

-:omputat10n or mean r.HIOS St't?ms pereraote t<' -:DrnFu::ng r.ltlOS l11 means as

.::ilscussed Ill the lrnmedlatelv preceding r.~rapapn :\n :r..port(lnt ;·.spect of the etfect

oi censonng 1s the correlation ben .. :een .::onccnrrJt:ons or ~3llpu Jnd ~38Pu. If

perrectly correlated (r = 1.0). w1th some cunstant rat1o. then censonr.g or the data sets

'.vlll have no erfect on the mean of the r."'tiOS or the r .1110 ,n the meiins However. at

~ess than perfect correlatiOn. the effect or censor1ng w:ll be as descnbed above. In the

Section "Expenmental Tests" below. '' cornputer :-:lmUii\tlon studv IS suggested for

exam1mng the magn1tude of b1as for the two estimators the ratio oi means and the

mean ratio. The effect of censored dJta sets on the \'.'llldlt\' of the data summanes

discussed m the sectiOn 'Utl'r(lture Rent>\'\'· :s .1ddre~~ed bv each author of that

sect1on.

Hypotheses

E H [sszn~ron

The observc1t10n th<H organ.~ or .m1m."~ nrut':tl'() .1 lllV"l'r :·wru; ::~HPu r.1t10 than

that of the sod or plants upon wh1ch thev brazed h.1s r.11::.ed the que::,tlOn of possible

differences 1n 1sotoplc preference 1n btOiog1cal mcorpori\t1on It 1s poss1ble that the

aruma! can absorb the 1sotopes dlfferent1allv, LH that llnce .1bsorbed the 1sotopes can

bf' depos1ted 1n organs m rJtlOS d1fferent trom the ~ource m.1tenal Other possible

~ources for the observed rat1o d1fference rn;n- be the n.1ture of the source material

;md subsequent .jlfferentl.'ltlOn due to t•nvlrcnml'nt.1l L1ctors. mechamsrns of

1ngest1on. and mechantsrns of .1SSlffill.ltlon For t•xi\mple. 1ngest1on mto the

gastromtestmal (Gl) tract bv grazmg and 1ngest10n 1nto the lungs by inhalation are

two d1fferent pathways for mgest1on Poss1ble d1fference~ can also be mterpreted

from errors 1n analys1s llr problems 1n ISOtope qu.1nt1flc.1•1on cons1denng the lower

concentrations of DRpu .md greater d1ff1cultv :n quantification compored to that of

::l9P;;. The tollowmg d1scuss1on pesents hvpotrH.>St>s lll1 poss1hle iZ~ctors that relate

to the marufestatlon 1n organs oi ;>;rumals or '2~ 9 Pu: ~,HpJ I:':.Otoplc r:1t1os appearing to

be lower than those of the source m.1tPnal

D1fferences m biolog1c,,l uptake h.1ve been obsened v.:hen !>mgle 1sotope sources

were stud1ed For ell.<lmple. b1010g1c.1l asSilnd.ltlon l)t ~'"Pu trom ·' ~olut1on of 238Pu

hils been shown to d1ffer from th.lt ot .1 s1mllar solut1on oi :2~ 4 Pu. In one case. the

two ISotopes 111 the ::,,1me ,:hem1c.1l ..:.__,n~t.>r.tr;~t:on \'1. ill h.1ve n•rv different alpha

,1Ctl\.'ltles. ~JIIpu (ilalt-l:te = ~b 4 v; 1mp.1:ts ,, l11rger ,,mount ot .1lphil energy to the.

:-\stem. pos::.1blv (JUSlng the ~\~tl'm t.l ~'l' 1;anrl' r··.1Ct.>t> thc1n th(lt of the 239pu

41

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