The distribution of plutonium, Americium and curium isotopes in pond and stream sediments of the Savannah river plant, South Carolina, USA

J. Environ. Radioactivity 3 (1986) 249-271

The Distribution of Plutonium, A m e r i c i u m and Curium Isotopes in Pond and Stream Sediments of the Savannah River Plant, South Carolina, U S A

J. J. Alberts* Savannah River Ecology Laboratory, Aiken, SC 29801, USA

J. E. Halverson Savannah River Laboratory, Aiken, SC 29808. USA

and K. A. Orlandini RER Division, Argonne National Laborato~, Argonne, IL 60439, USA

A BSTRA CT The concentrations of e3Spu, 239"24°Pu,241Am and "-44Cmwere determined in sediment samples from five streams and two ponds on the Savannah River Plant (SRP) and in four sediment samples from the Savannah River above and below the plant site. The following concentration ranges were determined: 238pu, 0.07-386fCi g-l; 239.24Opu' 0.37-1410fCi g-i; 241Am' O'l-4360fCig-t; 244Cm,
J. Environ. Radioactivity 0265-931X/86/$03-50 © Elsevier Applied Science Publishers Ltd, England, 1986. Printed in Great Britain

2.50

J. J. Alberts, J. E. Halverson, K. A. Ortandini the material should be remobili:.ed in oxic environments through organic cornplexation.

INTRODUCTION The Savannah River Plant (SRP), located in Aiken, Allendale and Barnwell Counties of South Carolina, is the principal plutonium and tritium production facility for the US Department of Energy. It has operated since 1953 and its heavy-water-moderated production reactors have produced isotopes of several transuranic elements: plutonium, curium and californium (Moyer, 1968; Holloway & Hayes. 1981). In addition to the product isotopes which are isolated in two chemical separation facilities on site, several waste isotopes are produced which are retained in onsite storage and burial facilities. Prominent among these latter isotopes are ~37Cs and ~'Sr. During the years of plant operations, relatively small quantities of isotopes have been released to the environment in either gaseous or liquid effluents (Ashley & Zeigler, 1976). Reports have appeared in the literature documenting the presence of ~37Cs, :>Pu, 23~'2a'pu and 2~tAm in aquatic systems both on site (Alberts e t a l . , 1979; Alberts & Orlandini, 1981; Holloway & Hayes, 1981) and off site (Hayes et al., 1976; Goldberg et al., 1979; Hayes & Horton, 1981)). While there have been some reports in the literature on the distribution of Pu isotopes in river systems (Hayes & Horton, 1980; Linsalata et al., 1980; Simpson et al., 1980; Beasley et al., 1981), few detailed investigations have appeared comparing the distribution of transuranic elements coming from a plant which produces such a wide array of isotopes. The SRP is a unique study site in that most of its approximately 7-8 × 10 a ha exist as woods or wetlands which receive very' little direct input of radionuclides from plant operations. Many of the ponds and streams are representative of the aquatic environments common to the southeastern U S A and the site is designated as a National Environmental Research Park. Yet, due to plant operations, measurable concentrations of Pu, Am and Cm exist in onsite systems. Thus, the SRP study site allows the comparison of the fate and distribution of these three transuranic elements in components of aquatic systems which are representative of aquatic systems throughout the southeastern USA, and allows investigation of the input to a major river system (Savannah River) of three transuranic elements from a nuclear facility which has operated for 30

Pu, A m and Cm isotopes in Savannah River Plant sediments

251

years. The opportunity to study the behavior of all three of these elements in relatively undisturbed systems is rare. The purpose of this work, therefore, is to detail the distribution of Pu, Am and Cm in the sediments of streams and ponds on the SRP and in the Savannah River, above and below the plant site. We will compare the distribution of these elements in the onsite ponds and streams with data from other geographic regions and discuss the relative elemental distributions in the weathered, subtemperate southeastern USA with those from different climatic regions. In addition, we will deduce the impact of the plant sources of these elements on the Savannah River by examining the elemental and atomic ratios of organic and inorganic phases of sedimentary material.

METHODS AND MATERIALS Sediment samples from the ponds, streams and river were collected with an Ekman dredge. The samples were returned to the laboratory', wetsieved through a 2 mm standard sieve and the <2 mm sediment was freeze-dried. The first series of samples (Fig. 1; STNS 1-9) was collected during August, 1979. After processing, the samples were sent to EAL Corporation, Richmond, CA, for analysis of ~SPu, :3~-'*}Pu, -'~Am and 244Cm by dissolution, chemical separation and alpha-spectromet W. Following alpha-analysis, the planchets containing the electrodeposited Pu were returned to the Savannah River Laboratory (SRL) and the isotopic distribution of 23~Pu, 2>Pu, :~}Pu and TM Pu was determined on the surface-ionization, three-stage mass-spectrometer (Halverson, 1981). A second series of samples (Fig. 1; STNS 6, 8-i4) was collected during December, 198l. In this series, samples were taken at stations 6, 8 and 9 to obtain information on the homogeneity of actinide element distributions within these sediments. In addition, new locations were sampled to extend the survey to include the Lower Three Runs Creek corridor (Fig. 1; STNS 10-14). These samples were sieved, freeze-dried and sent to EAL Corp. as before. A final series of samples was taken in October, 1982, in the Savannah River, above (Fig. 1; STN 15) and below (Fig. 1; STN 16) the portion of the Savannah River Swamp which is contiguous with the plant site. Two samples were collected at each location and, following sieving and freeze-

J. J. Alberts, J. E. Halverson, K. A. Orlandini

~2

g.-

/

,gQ ,'..,,..

o L 0

L

L

~ ~ kilQmltlrl

l~"~-Swamp

Fig. 1. Sediment sample locations: 1 Upper Three Runs Creek at Treadway Bridge; 2 Three Runs Creek at Box Landing; 3 Four Mile Creek at Road A; 4 Pen Branch at Road A; 5 Steel Creek at Road A; 6 Par Pond Midlake; 7 Par Pond Cold Dam; 8 Pond B Inlet; 9 Pond B Dam; 10-14 Lower Three Runs Creek: 10 Denora Station; 11 State Road 1A; 12 State Road S-3-17; 13 State Road S-66; 14 Highway 125---Martin, SC; 15--16 Savannah River: 15 upstream of Jackson Landing; 16 ½mile below Steel Creek Landing. Stations 15 and 16 are outside the SRP boundaries.

Pu. A m and Crn isotopes in Savannah River Plant sediments

253

drvina, , ~ they were analyzed for -,38Pu, --~-~, .... Pu, :~Am and > C m by acid dissolution, chemical separation and alpha-spectrometry. This series of samples was analyzed by the R E R Division of the Argonne National Laboratory. An E k m a n dredge grab sample was also taken in 1977 at the Cold D a m location of Par Pond (STN 7). Approximately 25 g d u weight of the sample was extracted with 400ml 0. tN N a O H overnight at room temperature. The supernatant was separated by centrifugation at 9000 rpm (approximately 13 000 × g) with a Sorvall SS-3 centrifuge e q u i p p e d with a model G S A rotor. The supernatant was acidified to pH 2 with concentrated HC1 and the mixture allowed to stand overnight at room temperature. The precipitate was separated from the supernatant by centrifugation as before and the supernatant was r e s e ~ e d . The solid material was redissolved in base and the precipitation step repeated. The separation, resolution and reprecipitation steps were repeated a total of three times with all supernatants being combined and analyzed together as the futvic acid fraction. The final solid phase was analyzed as the humic acid fraction. These analvses were conducted at the Argonne National Laboratory's R E R Division as before. After alpha-spectrometry, the Pu-bearing planchets were sent to SRL for Pu isotopic analysis.

SEDIMENT CONCENTRATIONS OF TRANSURANIC ELEMENTS The concentrations of the transuranic isotopes, 23Spu, :>-'*JPu, 24tAmand '~Cm, in the sediments of streams on the SRP and in the Savannah River are shown in Table l. Similar data for the ponds on the SRP are presented in Table 2. Examination of these results reveals that the concentrations of each isotope vary, by approximately three orders of magnitude in the stream and river sediments, with the Savannah River sediment upriver of the plant having the lowest concentrations for all isotopes and the reactor streams (Four Mile Creek, Pen Branch and Steel Creek) all having greatly elevated isotopic concentrations. An interesting observation from the stream data is that the highest concentrations of the isotopes :392U~Pu, :~Am and :~Cm are not found in the three streams with the greatly elevated :3Spu concentrations but rather appear at a station in Lower Three Runs Creek. This station (STN I3) is located in the corridor which is still maintained as a restricted area by the plant. That this elevated

254

J. J. Alberts, J. E. Halverson, K. A. Orlandini

T..~B LE 1 Pu, A m a n d C m Isotope C o n c e n t r a t i o n s ~ in Stream and Ri~er Sediments of the S a v a n n a h River Plant

U p p e r T h r e e Runs TreadwayBridge Box L a n d i n g F o u r Mile C r e e k PenBranch Steel C r e e k L o w e r T h r e e Runs DenoraStation Road tA RoadS-3-17 RoadS-66 Highway-125 S a v a n n a h River Jackson SteelCreek

238Pld

239 2-u)p bt

2; l A m

2a.tCl'n

2-7 _~ 0.4 11.8 +_ 0-7

19.1 +_ 1-5 72.7 +_ 3.6

6-4 = 0.4 t6.8 = 1-2

<0.5 9 . 5 ± t.0

136 +_10 63.6 +- 3-2 386 -- 19

4i-4 = 3.3 34.6 =20.5 146 = 9

14.5 = 0-9 20.5 ± 1.0 49.1 +- 2.9

2.9+_0-2 16.8+-1.0 I7-7 +- 1.6

<0.3 <0-4 4.4 35.9 <1.3 0.07 +(0-17+0.15+(0-42 +_

1-8 4-8 26-4 43l 23-0

2-2 3.6

0.01 0-09-) b 0.01 0.02_)

+- I-0 +_ 0.8 _+ 3.2 ~-'~ +- 3-0

0-37 = (0-67= 1-13+(3.50--

0.05 0.07) 0. t0 0.15)

<0.3 6-1 16-7 105 8.8

++-+-

0-19 +(0.10+0-29+_ (0-77 ±

1.0 3.3 7 2.3

<0.2 ll±0-5 3.5+-0.4 5I-6±5-2 <1.6

0-06 <0-02 0-04) ( < 0 . 0 l ) 0-1l <0.02_ 0.17) (<0.04)

a C o n c e n t r a t i o n s r e p o r t e d as fCi g - t dry weight sediment; reported error = l cr counting error. b Values in p a r e n t h e s e s are isotope concentrations in separate sediment grab samples. TABLE 2 Pu, A m a n d C m Isotope C o n c e n t r a t i o n s a in Pond Sediments of the S a v a n n a h River Plant 238pu

Par P o n d Midlake Cold D a m Pond B Inlet Dam

45.5---2-7 (29-6±2-7) b 34-1--6-7 18.2 +- 1-3 (94-1+_4-7) 100 -4-5 (115 -+6)

239.2""U)p u

659--33 (584+_29) 555--28 2 0 5 ± 10 (1340±67) 1230--62 (1410+-70)

24lAin

367 (219 234

+- 18 = 11) +- 12

85.5-+ 4-3 (4360 +_260) 759 _+ 40 (584 +- 29)

24aCre

0)'8 + - 3-0 (57.3 +- 4.0) 89.2+- 4-5 34.7+- 1.7 (206 +_19) 392 +-31 (216 +_11)

~ C o n c e n t r a t i o n s r e p o r t e d as fCi g - i dry weight sediment; r e p o r t e d error = 1 o- counting error. b V a l u e s in p a r e n t h e s e s are isotope concentrations in separate sediment grab samples.

Pu, A m and Cm isotopes in Savannah River Plant sediments

255

concentration is real and not just a sampling or analytical error is given some credence by the concentration values of these isotopes in the stations immediately above (STN 12) and below (STN 14) on the corridor. The concentrations of the isotopes at STN 14 are only slightly greater than the concentrations of these isotopes seen in STN l, Upper Three Runs Creek at Treadway Bridge, which is located near the northern boundary' of the plant and is believed to be influenced very, little by plant operations. The material in the Lower Three Runs Creek corridor apparently derives from the known rupture of an experimental fuel element in the R reactor disassembly basin, which occurred during the period 1954-64 (Alberts et al., 1979). This discharge originally passed directly into the Lower Three Runs Creek drainage until 1960, when the Par Pond dam was completed. Examination of the concentration data for the Par Pond and Pond B sediments supports the idea that actinide elements were released into this system (Table 2). While there is some variability in these data caused by location, it is apparent that the sediments in the ponds contain higher concentrations of the actinide elements than any of the stream sediments. Hence, actinide elements released into the Par Pond/ Pond B system following completion of the dam were trapped in the particles which settled out of the water column. Further examination of the concentration data in the stream and river sediments shows a small increase in isotope concentrations in Upper Three Runs Creek (STN 1 vs STN 2) and the Savannah River (STN 15 vs STN 16) as a result of their traversing the plant site. While the concentrations appear elevated for all the sediments in this study, it is informative to compare these data with results from other freshwater environments, both those impacted by the operations of nuclear facilities and those influenced only by fallout sources. Few studies have investigated actinide element concentrations in freshwater environments and even fewer have reported on all the isotopes presented in this report. This is understandable for sites which are only receiving fallout material, as atmospheric inputs of 2~tAm and 2aaCm are minute. Furthermore, the quantity of data reported in the literature varies considerably depending on the specific objectives of individual projects. Despite these problems, we have compiled a list of data (Table 3) for use in this comparison. It must be remembered that this list is not complete but is presented only to give the reader an idea of the variability of reported values, with which to compare the results reported here.

256

J. J. Alberts, J. E. H a l v e r s o n , K. A . O r l a n d i n i

TABLE 3 Concentrations of Transuranic Elements ~ in River and Pond Sediments Z3ap u

:_m-"-Op u

"-4tArn

e~ Cr n

Hudson River b 2 . 9 : 3-0(37) 57 :67(42) Savannah River ~ 2.7 23-3 4.4 Miami River (Ohio) d Above plant 0.9= 0.6 (5) 5.2= 2.3 (5) -Below plant 374 =417(2) <6 Nete River (Belgium) ~ Above plant <270 (4) 149 _+20(3) -8-0 x l03 6.2 x 103 -Below plant --15-3×103(30) roll.3 x103(29) 2'8 × 103 1"9 x 103 3"4 x 103 Four Mile Creek fJ 9-0 x l03 Mound Canal (Ohio) J 8.5 x 10a <6 --Lake Michigan g 5.0-+ 2.7 (8) 142 =76(8) 30 +- 18 (8) -U-Pond (Oak Ridge) h 1.7 x 106 1.2 x 10~ 0-34 x [06 -6-3x105 1.9 x 105 3.2x i05 Pond 3513 (Hanford) i 0-6x 105 "Concentrations reported as fCi g-i dry weight sediment; errors stated are --1 standard deviation of the mean with number of samples shown in parentheses. Linsalata et al., 1980; CHayes & Horton, 1980; JWayman et al., 1977; ~Metayer-Piret et al., 1981; fHolloway & Hayes, 1981; *Edgin~on et a t . , 1976; hEmery et al., 1976; iGarten et al., 1981. Data reported are for suspended particles, not surficial sediments.

E x a m i n a t i o n of the data in T a b l e 3 reveals that the c o n c e n t r a t i o n s r e p o r t e d for the s e d i m e n t s o n the S R P generally are a b o v e the values seen in f a l l o u t - d o m i n a t e d systems (e.g. the H u d s o n River, L a k e Michigan a n d T h e G r e a t M i a m i River, a b o v e the M o u n d L a b o r a t o w ) but are c o m p a r a b l e to, or, m o r e o f t e n , several o r d e r s of m a g n i t u d e lower t h a n , values r e p o r t e d for systems directly influenced by nuclear facilities (e.g. U - P o n d , P o n d 3513 at O a k Ridge N a t i o n a l L a b o r a t o r y , the canals b e l o w the M o u n d L a b o r a t o r i e s and the Nete River in Belgium b e l o w the C E N facility). It m u s t be s t a t e d that c o m p a r i s o n s of c o n c e n t r a t i o n d a t a from a large suite o f locales is less satisfactory than c o m p a r i s o n s of total i n v e n t o r i e s in t h o s e l o c a t i o n s , particularly w h e n dealing with i m p a c t e d systems.

Pu, A m and Crn isotopes in Savannah River Plant sedirnems

257

However, given the nature of streams it is quite difficult to determine inventories without having a sediment trap, i.e. reservoir, swamp, settling basin, etc., into which most of the activity,Ttransported bv the stream has been deposited. T h e n only with rigorous sampling by depth can an i n v e n t o u be estimated. The streams examined in these studies do not afford suitable traps for such estimates. Even the Par Pond system is inadequate for such estimates as some material obviously bypassed the impoundment as evidenced by the material in the Lower Three Runs Creek corridor. Finally, even if an invento U could be estimated, its usefulness for comparisons with other geographic locations would be slight given the lack of similar inventories in the literature. Thus, a determination of inventories was not attempted in this study.

ELEMENTAL RATIOS In cases of exceptionally high values, sediment concentrations may be a guide to source terms of impacted sediments. However, as a general rule, high concentrations only indicate sediment deposition points. A more informative method of determining the source term is to employ the isotopic and elemental ratios of the radionuclides of interest. In the present study, the determination of three elements and several isotopes of Pu offers further insight into the source terms for these elements in the sediments. The elemental ratios of P u : A m : C m and the isotopic ratio :>Pu/:>>~Pu for the stream and pond sediments are listed in Tables 4 and 5, respectively. Comparative values from the literature are presented in Table 6. The data for fallout ratios are not completely intercomparable as the 23*pu/:>:'~Pu ratio was calculated from soil data between '40 and 50°N latitude (Hardy et a l . , 1973), while the elemental fallout ratios were calculated from lichen concentrations determined at 62.3°N latitude (Holm & Persson, 1978). However, the isotopic Pu ratios from the latter work are in good agreement with the data from Hardy e t a l . (1973). Since data o n 241Am and :**Cm from fallout sources are generally lacking in the literature, and given the good agreement of ratios already mentioned, we feel that the ratios of Holm and Persson (1978) are reasonable for this comparison. Furthermore, comparison of the "-4tAm/2392~puratios from fallout with those calculated for Lake Michigan (Table 6) again shows acceptable agreement.

258

J. J. A l b e r t s , J. E . H a l v e r s o n , K . A . O r l a n d i n i

TABLE 4

Isotopic Ratios of Pu, Am and Cm Isotopes in Stream Sediments of the Savannah River Plant '-38P u

-"~i A m

2"~C m

~-= Crn

239.2VOp/l

239.2,U)p u

239.2.U)p u

2;l A r n

Upper Three Runs Treadway Bridge Box Landing

0.141 0.162

0-335 0.231

<0.02_6 0.13 l

<0-078 0.565

Four Mile Creek Pen Branch Steel Creek

3.29 1.84 2.64

0.350 0-592 0-336

0.070 0.486 0.12l

0.2IN) 0-820 0-362)

<0.167 1.27 0-633 0.244 0.383

<0- i i 1 0.229 0.133 0.120 <0.070

-0.180 0-210 0-491 <0.182

Lower Three Runs Denora Station Road 1A Road S-3-17 Road S-66 Highway-125 Savannah River Jackson Steel Creek

<0.167 <0.083 0.167 0-083 <0.057 0-189 (0-254) ~ 0-133

0.514 (0-149) 0.257

<0-054 (<0-015) <0-018

<0-105 (<0.100) <0-069

(0-120)

(0.220)

(<0.011)

(<0-052)

Values in parentheses are ratios calculated for separate sediment ~ab samples.

T h e i s o t o p i c a n d e l e m e n t a l ratios for the s t r e a m s a n d p o n d s o f the S R P i n d i c a t e i n p u t s o f m a t e r i a l to all s y s t e m s f r o m the plant site. In all cases, the v a l u e s in T a b l e s 4 a n d 5 r e s e m b l e the distributions s e e n in e i t h e r U - P o n d o n the H a n f o r d r e s e r v a t i o n o r P o n d 35 13 on the O a k R i d g e site. S o m e v a l u e s w h i c h are s h o w n as 'less t h a n ' values c a n n o t be said to differ f r o m t h e a t m o s p h e r i c values. C o u n t i n g times in the v a r i o u s studies are o f t e n d e t e r m i n e d by the q u e s t i o n s which are b e i n g a d d r e s s e d r a t h e r t h a n b y an a t t e m p t to q u a n t i ~ a p a r t i c u l a r isotope. T h e latter is p a r t i c u l a r l y t r u e f o r A m a n d C m as m o s t studies are i n t e r e s t e d in the usually m o r e a b u n d a n t Pu i s o t o p e s . H e n c e , 'less t h a n ' values ( m o s t n o t a b l e in the case o f 2 a C m ratios in t h e S a v a n n a h R i v e r , U p p e r T h r e e R u n s C r e e k at T r e a d w a y B r i d g e a n d S T N 14 in the L o w e r T h r e e R u n s C r e e k c o r r i d o r )

Pu, A m and C m isotopes in Savannah River Plant sediments

259

TABLE 5 Isotopic Ratios of Pu. A m and Cm Isotopes in Pond Sediments of the S a v a n n a h River Plant

Par P o n d Midlake Cold D a m Pond B Inlet Dam

"-38Pu 239.24~)Pu

2~1A m 239,240Pu

2~Cm 239.240Pu

2~Cm 24rAm

0.069 (0.051)" 0-061

0.557 (0.375) 0.422

0.092_ (0.098) 0.161

0.166 (0.262) 0-38l

0.089 (0-070) 0-081 (0-082)

0-417 (3-25) 0-617 (0-414)

0.169 (0.154) 0,153 (0,153)

0-406 (0.047) 0-248 (0-370)

Values in p a r e n t h e s e s are ratios calculated for separate sediment grab samples.

TABLE 6 E l e m e n t a l Activity Ratios and Isotopic Ratios of T r a n s u r a n i c E l e m e n t s in Selected Environments

Fallout Lake Michigan c S a v a n n a h River c U-Pond c Pond-3513 C F o u r Mile C r e e k c S R P Soils a Floodplain Upland Lowland H a r d y et al., 1973. b H o l m & Persson, 1978. CCalculated from Table 3. '~Pers. c o m m . , unpublished.

23~Pu

241Am

23c~,24.Op u

239.2.a)p u

239,24.Opu

0-037 ~ 0-035 0-116 1.417 0-095 3-913

0.1675 0-211 0-189 0.283 0-302_ 0.679

< 1.7 x 10-55 ---0-492 1.214

< 1 x 10-45 ---1-68 1-79

0-250 0.021 0-163

15-1 0-006 0-034

58-8 0-265 0.208

96-7 0-311 0-401

244Cm

24aCrrl 241~FyL

260

J. J. Alberta, J. E. Halverson, K. A. Orlandini

may, in fact, not be different from fallout levels but rather may reflect counting protocols unsuitable to differentiation of the values. Since :~Cm appears in elevated concentrations in many of the sediments on the SRP and is rarely found in sediments only impacted by fallout, its source is obvious. This conclusion is supported by the elemental ratios and the fact that :~Cm was produced on the site (Moyer, 1968). However, the source of the >~Am is not as apparent. It would seem that the material must be derived from plant operations. However, the Four Mile Creek Floodplain soils which have received liquid releases from the chemical separations area have :~Am/:>:'~Pu ratios similar to the fallout ratios, while particulate material suspended in Four Mile Creek has a higher ratio more similar to other onsite sediments (Table 6). Similarly, soils receiving atmospheric inputs of isotopes from chemical separation operations have even lower :~Am/:>:~'Pu ratios (Table 6, Upland and Lowland soils). Yet the values of this ratio in most of the onsite sediments resemble the values reported for soils receiving inputs from the Sellafield (Windscale) site in Cumbria, England ( - 0 . 8 within 0-2 km (Cambray & Eakins, 1982)). Apparently the source of the >'~Am is historical and the deposited material has remained in the sediments near the site. Monitoring records do not separately list :~Am so that this hypothesis is difficult to prove. Unidentified alpha concentrations have, however, been monitored and indicate releases which could have contained this material (Ashley & Zeigler, I976). The ratios of 23Spu/Z>2~Pu, :~Cm/:>:~Pu and 2~Cm/:~t,&aI-1clearly separate the stations which have received no liquid inputs from plant operations (i.e. Upper Three Runs Creek at Treadway Bridge and the Savannah River at Jackson) from the other sites. The >1 values of the 23Spu/:>'2a*~Pu ratios in Four Mile Creek, Pen Branch and Steel Creek are characteristic for those streams, as are the elevated 2~Cm/2>:a~Pu and 2aCm/:~Am ratios in Par Pond, Pond B and the Lower Three Runs Creek corridor stations characteristic of those sediments. Thus, sediments with known histories of liquid inputs can be identified by either the 238pu/239'2'a~Pu ratio or the elevated :~Cm concentrations as evidenced in measurable 2~Cm/2>:~Pu and :=Cm/>~Am ratios. Interestingly, the Upper Three Runs Creek station at Box Landing has :~Cm/:>-'~'Pu and 2aCm/2atAm ratios indicative of a past release to that stream below Treadway Bridge. Based on all four ratios, Treadway Bridge and both Savannah River stations (above and below the SRP at Jackson and Steel Creek, respec-

Pu, A m and Crn isotopes in Savannah River Plant sediments

261

tively) appear not to have been influenced by liquid inputs. Ho~vever, relative to atmospheric fallout, the :~8pu/'-~-'a~Pu and :~ 'Am/~9-'~>Pu ratios are high. Thus, it would appear that all three of these stations have been affected by atmospheric releases, which have ratios closer to the observed sediment values (see SRP soils, Upland and Lowland, Table 6). The :3SPu/:>:a~Pu and -'atAm/:>ea~Pu ratios of these three stations are very similar to those of sediments in the Savannah River Estua U 60 miles (96 km) downriver of the SRP (Goldberg er al., 1979: Haves & Horton, 1980), which have been proposed to result from aerial inputs rather than liquid releases (Goldberg et al., 1979). An alternative mechanism to produce the lower ratios seen in the Savannah River station sediments could involve selective transport of small particle-size sediments by the streams, with concomitant lower ratios of isotopes in the smaller particles. Little information is available on isotopic and elemental ratios as a function of particle size in sediments. A slight tendency towards decreased ='SPu/:>-'~)Pu ratios in smaller particle-size sediments has been observed in Lake Michigan (Alberts & Muller, 1979) but that data set is small and hardly conclusive. No data exist for :
PLUTONIUM ISOTOPE RATIOS Beasley et al. (1981) effectively used the isotopic ratios of specific Pu isotopes (2>pu, 2U)Pu, 2a'Pu and :42Pu) to quantify the input of this radioelement into the Columbia River from the production reactors on the Hartford Reservation during their operation from 1944 to 1970. We attempted a similar calculation for the inputs of the SRP reactors to the sediments of the ponds and streams on site. Unlike the work of Beasley et al. (1981) the samples used in this study were taken primarily for actinide element analyses rather than for Pu isotopic ratio studies. As such, the samples had :42pu added as a chemical yield monitor, so that the mPu isotope could not be used in subsequent

262

J, J. Alberts, J. E. Halverson, K. A. Orlandini TABLE 7 P e r c e n t C o m p o s i t i o n of Pu Isotopes in S a v a n n a h River Plant Sediment Samples

% Vgpu

% "-a)pu

% ealpu

Upper Three Runs T r e a d w a y Bridge Box L a n d i n g

84.64 = 0.i5 9°_.79 = 0- 18

1.4-85 = 0-17 7.00 --_ 0-15

0-52=0.02, 0.22 ___0-04

F o u r Mile C r e e k Pen B r a n c h Steel C r e e k

9 I,.4 -2-_0-28 82. I, = 0-07 9l-5 ± 2 - I

7.97 __ 0.48 16-00 = 0.07 7-77 ± 0-43

0-65 ± 0-1,6 I,.8-1 ± 0-04 0-74=0-06

Par P o n d Midlake Cold D a m

88"5 = 0 . 7 89. I, = 0.7

ll.0 =I.5 9-8 = 0.4

1-0 = 0 - 1 0.45 ± 0-12

Pond B Inlet Dam

89.0 = l-0 89-3 = 0 . 0 7

9.9 = 0.2 10. i, s 0 . 7

0.77 = 0-04 0.71=0.07

T h e o r e t i c a l low-irradiation Pu"

93.6

5.9

0.4

~Sanders & Boni, 1980.

calculations. However, in the study reported here, this is not a highly significant omission. The atom percent compositions of the isotopes :39pu, :4°Pu and :~LPu for several of the sediment samples already discussed are presented in Table 7, along with the theoretical values for low-irradiaton Pu (Sanders & Boni, 1980). With the exception of samples from Upper Three Runs Creek at Treadway Bridge and Pen Branch, the atom percent values tend towards the theoretical values given for irradiated Pu. Particularly interesting are the relatively high percent >~Pu values observed in Upper Three Runs Creek at Box Landing relative to Treadway Bridge. These values substantiate the hypothesis expressed earlier, based on elemental concentrations, elemental ratios and isotopic ratios, that Upper Three Runs Creek has been impacted by plant operations despite no record of direct aqueous inputs into the stream. In an attempt to quantify, the amount of Pu added to these streams by the reactors, calculations were made using the equation of Krey et al. (1976): (Pu)t

R2 - R --

(Pu),

-

-

R - RI

1 + 3"60Rl X

1 + 3"60R2

Pu, Am and Cm isotopes in Savannah River Plant sediments

263

where: (Pu) t (Pu): R R~ R: 3-60

= = = = = =

plutonium activity in source l, plutonium activity in source 2, :~'Pu/Z>Pu ratio in mixture, -'~)Pu/:>Pu ratio in source t, :'~Pu/:>Pu ratio in source 2, ratio of half-lives of :3~Pu to >U)Pu.

As a first approximation for these calculations, the ratios of -'~)Pu/:3~Pu in low-irradiation Pu reported by Sanders and Boni (1980) were used for the reactor source. Fallout ratios were used as reported by Krev et al. (1976) for the second source term. The calculations (Table 8) show that U p p e r Three Runs Creek at T r e a d w a y Bridge and Pen Branch have little or no input of Pu from the TABLE 8 : a ) P u / : > P u Ratios in Savannah River Plant Sediments ~ and Calculated Pu Contributions from Plant Operations and Atmospheric Fallout

'-~)Pu/"34 Pu

% Pu contributed by. Fallout

Atmospheric fallout ~

0. I76 ± 0.014

Low-irradiation Pu C

Plant operat~orr~

100

0

0.063

0

l(i~)

U p p e r Three Runs Treadway Bridge Box Landing

0. t76 0-075

100 14

0 86

Four Mile Creek Pen Branch Steel Creek

0-087 0-195 0-085

27 [ 12 24

73 - 12 76

Par Pond Midlake Cold Dam

0.124 0- t l 0

61 49

39 5l

Pond B Inlet Dam

0-111 0.113

50 51

50 49

All ratios corrected to January, 1971. Krey et al., 1976. CCaleulated from Table 7.

264

J. J. Alberts, J. E. Halverson, K. A. Orlandini

reactors, while up to 86% of the Pu in the other sediments may have been derived from the site. The - 1 2 % contribution of reactor-derived material to Pen Branch is a result of using an average value for the 2~Pu/"3~pu ratio in the fallout end-member and is actually zero within the error estimate around that average. Further examination of the plant contributions to sediments on site reveals that - 5 0 % of the Pu in the pond sediments is derived from plant operations, while - 7 5 % of the Pu activiD' in Four Mile Creek and Steel Creek has an operations source. Perhaps the most interesting observation resulting from these calculations is that the highest percentage addition of Pu is to Upper Three Runs Creek at Box Landing, a stream which has had no known inputs from operations on site. While no direct inputs into the stream are reported, a possible source of the material may have been an atmospheric release from a sand filter breakthrough in the early 1960s (Pinder eral., 1979) with subsequent erosion into the stream. Plutonium in the soil near the site of that event has a 2a~pu/:39pu ratio of -0-030 (Halverson, unpublished data). Using that ratio as the second end-member in the calculation leads to a Pu contribution to the Box Landing site of 60% from plant operations, which is within the range (3%76%) of other additions. This release would also be expected to contain -'~Am and 2~Cm and could easily be the source of those isotopes at the Box Landing site.

D I S T R I B U T I O N OF T R A N S U R A N I C E L E M E N T S IN SEDIMENTARY COMPONENTS While transuranic elements have been added to sediments of streams and ponds on the SRP site, it has been shown that Pu and A m are sequestered in the sediments in a hydrous oxide phase (Wilhite, 1978; Alberts & Orlandini, 1981). There is some controversy in the literature regarding the mobility of these elements under anoxic conditions sometimes e n c o u n t e r e d in the ponds (Alberts & Orlandini, 1981; Sholkovitz et al., 1982; Alberts et al., in press); however, there is little doubt that, under normal oxic conditions encountered in the streams and ponds, the bulk of these materials is associated with the sediments. It has also been demonstrated that small quantities of Pu and Am are associated with organic m a t t e r in soils and sediments (Cleveland & Rees, 1976; Edgington et al., 1976; Alberts & Orlandini, 1981). While the quantities associated with

Pu, A m and Cm isotopes in Savannah River Plant sediments

265

naturally occurring organic matter, usually humic and fulvic acids, are relatively small (< 15%), these elements can be bound strongly to this organic matter, thereby altering patterns of uptake by organisms (Giesy et al., 1977; Giesy & Paine, 1977) and adsorption on sediments (Sibley etal., 1984). Furthermore, the adsorption behavior of the transuranic element Cm on sediments is affected by dissolved organic compounds (Sibley & Alberts, 1984; Sibley etal., 1986). The sediments of the ponds contain all three transuranic elements, Pu, Am and Cm, which have equilibrated for - 2 0 years under environmental conditions. Therefore, it was decided to determine the distribution of these elements in the organic phase of the sediment, as this is the phase most likely to be mobilized from the sediments under oxic conditions. Sediment was collected from Par Pond (STN 7) and extracted with base. The extract was acidified to differentiate the fulvic acid fraction from the humic acid fraction. Each fraction was then analyzed for Pu, Am and Cm. For all the elements studied, less than 13% of the sediment load was extracted in the organic phase (Table 9) and, in all cases, significantly less material was extracted as fulvic acid associated, which agrees with previous observations in Lake Michigan sediments (Edgington et al.. 1976) and soils (Cleveland & Rees, 1976). The latter observation is of interest as the humic acids are usually larger molecules and less mobile than the fulvic acids. In addition, larger molecules tend to inhibit uptake

TABLE 9 Transuranic Element Concentrations and Isotopic Ratios in Humic and Fulvic Adds from Par Pond Sediments Sediment (fCi g - t) 238Pu 239"2a°pu 24lAm e~Cm 238pu/:3~'2a°Pu 2atAm/239'24°pu

24aCm/23924°pu 2~Cm/24~Am

34.1 555 234 89-2 0-061 0"422 O"161 0-381

Fulvic acid (%) 1.3 0.8 1.6 0-9 O. lO 0-829 O"180 0-218

Humic acid (%) 11.2 7.4 8-0 3-3 0-093 0'455 0"655 0-160

266

J. J. Alberta, J. E. Halverson, K. A. Orlandini

of Pu (Giesy et al., t977) and Am (Giesy & Paine. t977) by algae and bacteria in freshwaters. It may be argued that the extraction conditions of the study affect the results to an extent which makes interpretation difficult. However, the base extraction of the sediments only removed 12.5% of the total :-~Pu, 8.2% of the total :>2U~Pu,9.65% of the total :"~Am and 4.2% of the total -'~Cm associated with the sediments. Thus, it is difficult to argue that, under the basic conditions, soluble complexes of the elements were formed and extracted, when such low percentages of the totals were in solution after 18-20 h contact times. This procedure does remove 90% of the humic and fulvic material (Alberts, unpublished). Also, sequential extraction of the sediments with base did not produce significant additional extraction of isotopes, despite up to four such repetitive extractions (Alberts & Orlandini, unpublished). Acidification of the base extracts even to pH 2 caused the majority of all three elements to precipitate with the humic acid fraction despite three dissolution-precipitation sequences. Thus, it would appear that little soluble cationic complexation or organic/elemental bond-breaking was occurring under these conditions. Given the behavior of the elements in strong base and strong acid, we believe that the small amount of Pu, Am and Cm extracted from the sediments was, in fact, associated with an organic moiety. Almost 10% of the '4~Am was extracted in the organic fraction, while only 4.2% of the '*~Cm was associated with that fraction. Given the similar chemistries of these two trivalent actinides, a closer agreement in extractabilities would be expected. The elemental ratios (Table 9) indicate an apparent increase in :~Am relative to :~"-~'Pu in fulvic acids and an increase in 2~Cm relative to 2>:~Pu in humic acids. The 24aCm also appears to be less strongly associated with both organic fractions relative to '-4~Am, as indicated by the :~Cm/2~LAm ratios of the organic fractions and the whole sediment. The Pu isotope ratios of the organic material (Table 10) show that the fulvic acid and humic acid fractions are similar to each other and to the bulk sediment, negating an argument based on fractionation of 2a~Pu among the organic fractions and subsequent "growin" of 2~tAm. The reasons for the differences in the distribution of :~tAm and 2~Cm observed in this study are unknown but may reflect either differences in the complexation chemistries of the two elements relative to naturally occurring humic and fulvic acids or differences in source

Pu, A m and Cm isotopes in Savannah River Plant sediments

267

TABLE 10

Atom Percent Concentration~of Pu Isotopes in Humic and Fulvic Acids from Par Pond Sediments

:39Pu

24°pu 2atPu

2"U)Pu/239pu _,a,Pu/:>Pu 2alPu/2a'lPu

Sediment

Fulvic acM

Humic acid

89-1 _-+0-7 9.8 = 0-4 0.45 _+0-12 0"110 0-008 0-077

.86-7 _+0.9 10-2 _+0.3 0-834 _+0" 13 0"118 0-010 0.082

88.4 -+0-3 t0-6 =0-1 0.723 -+0.04 0"120 0-008 0-068

"Values corrected to January, 1971.

material. Further investigation appears warranted to determine whether the apparent fractionation is real and, if so, the nature of the mechanism involved.

SUMMARY The stream and pond sediments on the Savannah River Plant and the sediments of the Savannah River above and below the plant site have measurable concentrations of the transuranic isotopes 23Spu, 239pu. :'S)Pu, 2~pu, >1Am and 2~Cm derived from plant operations. Isotope concentrations in these aquatic systems, which have received aerial/liquid inputs for over 20 years, range over three orders of magnitude and are higher than concentrations of these isotopes in sediments impacted only bv atmospheric fallout. However, the concentrations of these isotopes in these sediments are much less than in the sediments of other nuclear facilities, with the values found offsite, in the Savannah River, nearing fallout levels. Examination of the ratios of the elements, P u : A m : C m , and the isotopes 23Spu/239>°Pu clearly distinguishes sediments of streams and ponds which have had liquid releases from those which have apparently received only aerial inputs, The 23Spu/239>UlPu and -'~Am/~-'~°Pu ratios indicate that aerial inputs, not liquid releases, impact the Savannah River outside the plant boundaries.

268

J. J. Alberts, J. E. Halverson. K. A. Orlandini

Atom ratios of :~Pu/Z39pu reveal that up to 86% of the Pu in some sediments is derived from plant operations. Based on radioactivity release records and elemental ratios, it appears that the "-~lAmand :~Cm arose from historical events and, in the case of :~Cm, the release has remained on the plant site. Less than 13% of any of the isotopes is associated with the organic phases of pond sediments, which represent the most probable complexing ligands that could lead to solution phase mobilization of the actinides in oxic systems. Furthermore, less than 1.6% of any of the elements or isotopes studied here is associated with the fulvic acid fraction of the sedimentary, organic matter. Thus, the small quantity' of material associated with natural organic matter is primarily associated with the larger humic acid fractions. Differences in the distributions of >'~Am and :~Cm between the fulvic and humic acid components of the organic matter suggest either differences in complexation chemistries or differences in source term for these two elements. This study shows that, even after - 3 0 years of operation, the activity concentrations of Pu, Am and Cm in the Savannah River outside the boundaries of the SRP are relatively low and in many cases approximate to concentrations in aquatic systems receiving only fallout inputs. Isotopes released through liquid discharges into onplant aquatic systems have apparently remained on site, while the offsite movement of these isotopes has occurred from aerial releases. The distribution of the three elements within aquatic systems on site appears to be similar to that found in other regions.

ACKNOWLEDGEMENTS We wish to thank S. Lesnek, J. W. Bowling and R. C. Clark III for their assistance in the field and laboratory. This work was funded in part by the US Department of Energy through contracts to the Radiological and Environmental Research Division at Argonne National Laboratory, the Savannah River Laboratory, (Contract DE-AC-09-76SR-00001), a part of E. I. duPont de Nemours and Co., Inc. and the Savannah River Ecology Laboratory (Contract EY-76-C-09-0819), an affiliate of the University' of Georgia's Institute of Ecology. Manuscript preparation was performed at the University of Georgia's Marine Institute at Sapelo Island.

Pu, Am and Cm isotopes in Savannah River Plantsediments

269

REFERENCES Alberts, J. J. & Muller, R. N. (1979). The distribution of -'3<-'-~)Pu,2-'~Puand ' ; C s in various particle size classes of Lake Michigan sediments. J. Environ. Qual., 8, 20-2. Alber*s, J. J. & Orlandini, K. A. (1981). Laboratory, and field studies of the relative mobility of 2>':~°Pu and 'a~Am from lake sediments under oxic and anoxic conditions. Geochim. Cosmochim. Acre, 45, 1931-9. Alberts, 3". J., Tilly, L. J. & Vigerstad, T. J. (1979). Seasonal cycling of cesium-137 in a reservoir. Science, 203,649-51. Alberts, 3. J., Bowling, J. W. & Orlandini, K. A. (in press). The effect of seasonal anoxia on the distribution of the radionuclides 238Pu, 239>°Pu, :atAm, 2~Cm and ~37Cs in pond systems of the southeastern United States. In Environmental research for actinide elements, ed. by J. E. Pinder, III, J. J. Alberts, K. W. McLeod and R. G. Schreckhise, US DOE CONF-841142, Springfield, VA, National Technical Information Service. Ashley, C. A. & Zeigler, C. (1976). Releases of radioactivi~' at the Savannah River plant. 1954 through 1975, US E R D A report DPSPU-75-25-1, E. I. du Pont de Nemours & Co., Springfield, VA, National Technical Information Service. Beasley, T. M., Ball, L. A., Andrews, J. E., III & Halverson, J. E. (1981). Hanford-derived plutonium in Columbia River sediments. Science, 214, 913-5. Cambray, R. S. & Eakins, J. D. (1982). Pu, -'4~Am and t37Cs in soil in West Cumbria and a maritime effect. Nature, 300, 46-8. Cleveland, J. M. & Rees, T. F. (1976). Investigation of solubilization of plutonium and americium in soil by natural humic compounds. Environ. Sci. Technol., 10 (8), 802-6. Edgington, D. N., Alberts, d. J., Wahlgren, M. A., Karttunen, d. O. & Reeve, C. A. (1976). Plutonium and americium in Lake Michigan sediments. In Transuranium nuclides in the environment, 493-516, Vienna, International Atomic Energy Agency. Emery, R. M., Klopper, D. C., Garland, T. R. & Weimer, W. C. (1976). The ecological behavior of plutonium and americium in a freshwater pond. In Radiological and energy resources, ed. by C. E. Cushing, Jr, 74-85, Stroudsburg, PA, Dowden, Hutchinson 8,: Poss, Inc. Garten, C. T., Jr, Trabalka, J. R. & Bogie, M. A. (1981). Comparative food chain behavior and distribution of actinide elements in and around a contaminated fresh-water pond. In Migration in the terrestrial environment of long-lived radionuclides from the nuclear fuel cycle, 299-312, Vienna, International Atomic Energy Agency. Giesy, J. P., Jr & Paine, D. (1977). Effects of naturally occurring aquatic organic fractions on 2a~Am uptake by Scenedesmus obliquus (Chlorophyceae) and Aeromonas hydrophila (Pseudomonadaceae). Appl. Environ. Microbiol., 33(1), 89-96.

270

J. J. Albert.x, J. E. Halverson, K. A. Orlandini

Giesy, J. P., Jr, Paine, D. & Hersloff, L. W. (1977). Effect of naturally occurring organics on plutonium-237 uptake by algae and bacteria, in Transuranics in natural environments, ed. by M. G. White & P. B. Dunaway, 531-43. US ERDA report NVO-I,78, Springfield, VA, National Technical Information Service. Goldberg, E. D., Griffin, J. J., Hodge, V., Koide, M. & Windom, H. (1979). Pollution history of the Savannah River estuary. Environ. Sci. Technol., 13(5), 588-94. Halverson, J. E. (1981). A three-stage mass spectrometer Cbr isotopic analysis of radionuclides in environmental samples, US DOE report DP-16II, E. I. du Pont de Nemours & Co., Springfield, VA, National Technical Information Service. Hard?', E. P., Krey, P. W. & Volchok. H. L. (1973). Global inventory and distribution of fallout plutonium. Nature, 7,41, 11,1 5. Hayes, D. W. & Horton, J. H. (1980). Plutonium and americium behavior in the Savannah River marine environment. In Transuranic elements in the environment, ed. by W. C. Hanson, 602-11, DOE/TIC-22800, Springfield, VA, National Technical Information Service. Hayes, D. W., LeRoy, J. H. & Cross, F. A. (1976). Plutonium in atlantic coastal estuaries in the southeastern United States of America. In Transuranium nuclides in the environment, 79--88, STI/PUB/410, Vienna, International Atomic Energy Agency. Holloway, R. W. & Hayes, D. W. (1981). Transuranics in a stream near a nuclear fuel chemical separations plant. US DOE report DP-1592, E. I. du Pont de Nemours & Co., Springfield, VA, National Technical Information Service. Holm, E. & Persson, B. R. R. (1978). Global fallout of curium. Nature, 273, 289-90. Krey, P. W., Hardy, E. P., Pachucki, C,, Rourke, F., Coluzza, J, & Benson, W. K. (1976). Mass isotopic composition of global fall-out plutonium in soil. In Transuranium nuclides in the environment, 671-8, Vienna, International Atomic Energy Agency. Linsalata, P., Wrenn, M. E., Cohen, N. & Singh, N. P. (1980). 23u'-"UlPuand :3*pu in sediments of the Hudson River estuary. Environ. Sci. Technol., 14{12), 1519-23. Metayer-Piret, M., Gerber, G. B., Konings, J., Foulquier, J., Colard, J. & Koch, G. (1981). Behaviour of long-lived radionuclides released into a small river by a nuclear installation at Mol, Belgium. In Migration in the terrestrial environment o f long-lived radionuclides from the nuclear fuel cycle, 517-24, Vienna, International Atomic Energy Agency. Moyer, R. A. (1968). Savannah River experience with transplutonium elements. Health Phys., 15, 133-8. Pinder, J. E., III, Smith, M. H., Boni, A. L., Corey, J. C. & Horton, J. H. (1979). Plutonium inventories in two old-field ecosystems in the vicinity of a nuclear-fuel reprocessing facility. Ecology, 611, 1141-50.

Pu, Am and Cm isotopes in Savannah River Plant sediments

271

Sanders, S. M., Jr & Boni, A. L. (1980). The detection and study of plutoniumbearing particles following the reprocessing of reactor fuel. In Transuranic elements in the environment, ed. by W. C. Hanson, 107-44, DOE/TIC-22800. Springfield, VA, National Technical Information Service. Sholkovitz, E. R., Carey, A. E. & Cochran, J. K. (I982). Aquatic chemistry of plutonium in seasonally anoxic lake waters. Nature, 300, 159--61. Sibley, T. H. & Alberts, J. J. (1984). Adsorption of :~Cm: effects of dissolved organics and sediment extractions. J. Environ. Qual., 13,553-6. Sibley, T. H., Clayton, J. R., Jr, Wurtz, E. A., Sanchez, A. L. & Alberts, J. J. (1984). Effect of dissolved organic compounds on the adsorption of transuranic elements. In Complexation of trace metals in natural waters, ed. by C. J. M. Kramer & J. C. Duinker, The Hague, Martinus Nijhoff/Dr W. Junk publishers. Siblev,, T. H., Wurtz, E. A. & Alberts, J. J. (1986). Partition coefficients for :ZaCm on freshwater and estuarine sediments. J. Environ. Radioactivi~, 3 (1986) 203-217. Simpson, H. J., Trier, R. M. & Olsen, C. R. (1980). Transport of plutonium by rivers. In Transuranic elements in the environment, ed. by W. C. Hanson, 684--90, DOE/TIC-22800, Springfield, VA, National Technical Information Service. Wavman, C, W., Bartelt, G. E. & Alberts, J. J. (1977). Distribution of '-SSPuand ~f~ 2ao - ' Pu in aquatic macrophytes from a midwestern watershed. In Transuranics in natural environments, ed. by M. G. White & P. B. Dunaway, 505-15, US ERDA report NVO-178, Springfield, VA, National Technical Information Service. Wilhite, E. L. (1978). Chemical speciation of plutonium in the radioactive waste burial ground at the Savannah River Plant, 1-16, US DOE report DP-1511, Springfield, VA, National Technical Information Service.