2397240Pu and 238Puin Sediments of the Hudson River Estuary Paul Linsalata," McDonald E. Wrenn,? Norman Cohen, and Narayani P. Singht Institute of Environmental Medicine, New York University Medical Center, 550 First Avenue, New York, New York 10016
Plutonium-239,240 and 238Pu were determined in 59 Hudson River sediment dredge samples collected from 1973 to 1977 in the vicinity of the Indian Point Nuclear Power Station. Acid leaching followed by solvent extraction, electrodeposition, and a-spectrometric procedures were used to extract, purify, and quantitate plutonium isotopes present in these samples. Annual median 238Pu/239,240Pu isotopic activity ratios in surficial sediments were 0.032 (1973-74), 0.035 (1975), 0.042 (1976), and 0.040 (1977). Analysis of the sample 238Pu/ 2:39,240Pu activity ratios enabled identification of the source of these nuclides in the estuary (Le., the ratios of these isotopes in weapons test fallout and in reactor fuel may differ by as much as two orders of magnitude). For 59 sample ratios examined, the null hypothesis (Le., that there is no difference between the isotopic plutonium ratio in the sample and that in fallout) was rejected only once at the 1%level of confidence. On the basis of the sampling regimen and the methods used, it is concluded that no input, other than that of fallout, has contributed significantly to the plutonium burden in Hudson sediments.
Introduction With an increase in the production of nuclear generated electricity, there is potential for an increase in the amounts of radioactive contaminants released from reactors to the environment. Although some radionuclides are associated specifically with nuclear weapons testing fallout or nuclear reactors, several can be produced from either or both sources. The origin of a radionuclide contaminant in the environment is an important consideration for a variety of reasons not the least of which is the design of radiological health protection programs. Given two environmentally present radionuclides common to both fallout and reactor production, the fractional source term allocations may be estimated from the known ratios of the nuclides within each source, and from the measured ratio of the two within a particular sample. As an example, environmental traces of 134Csare almost exclusively the result of nuclear reactor releases, while 137Cs is a common product of both reactors and nuclear weapons fallout. With knowledge of the 134Cs/137Csactivity ratio in reactor effluent, and the fact that this ratio is mathematically equal to zero in weapons testing fallout, it is possible to apportion the fractional contributions of 137Csdue to fallout and reactor releases based on measurements of both isotopes. Similarly, considering the isotopic measurements of plutonium in an environmental sample, and utilizing the difference in the 238Pu/239,240Pu activity ratios characteristic of fallout compared to that representative of reactor fuel, it is possible to estimate the origin of plutonium in a specific environment. We acknowledge that definitive "proof" of reactor originating plutonium can only be obtained by a program involving routine collection and analysis of reactor effluent. In the absence of such a program, the best alternative for determining whether reactor releases of plutonium have occurred is to analyze sediment from the vicinity of the outfall and characterize the isotopic ratio. + Present address: Radiobiology Laboratory, University of Utah, College of Medicine, Salt Lake City, U T 84112.
0013-936X/80/0914-1519$01 .OO/O
Plutonium-239,240 and 238Pu concentrations were determined in 59 sediment samples collected between 1973 and 1977 from the Hudson River estuary in the vicinity of the Indian Point nuclear reactors in Buchanan, NY. By utilization of the ratio techniques described above, it was possible to determine the origin of this important radiocontaminant. 238Pu/239,240Pu Isotopic Ratio in Fallout. Most of the globally distributed 239,240Puand -35% of the 238Pu now present in the environment originated from nuclear weapons testing conducted during the 1950s and early 1960s. The remainder or -65% of the 238Pu now present in the environment was released in 1964 from the reentry burnup of a 238Puauxiliary powered navigational satellite (SNAP-SA).Estimates of the worldwide inventories of 239,240Pu and 238Pu,based on latitude-dependent soil measurements, have been reported ( I ) and are summarized in Table I. Based on these levels, the isotopic ratios (238Pu/239,240Pu) before and after the SNAP-SA incident have been calculated for the northern hemisphere as 0.024 f 0.004 and 0.036 f 0.006, respectively ( I ) . Since it is known that fallout deposition is latitude dependent ( Z ) , the isotopic plutonium ratio in the area of interest, Le., within the latitudinal boundaries of the Hudson drainage basin (40' 40' N to 44' 10' N), was carefully defined. The best estimate of the isotopic plutonium ratio in this sector can be made by utilizing the data reported for soil in the 40-50' N latitude band ( I ) . The mean 239,240Pu and 238Pusoil deposition estimates of 2.2 f 0.5 ( f l SD) and 0.079 f 0.016 mCi/km2, respectively, represent the mean values from nine individual sites in the 40-50' N latitude band. The 238Pu/239,240Pu ratio of the means, 0.036 f 0.011, is in excellent agreement with a New York City soil measurement ratio of 0.037 f 0.004 and with the mean northern hemisphere value of 0.036 f 0.006 ( I ) . Since the 238Puvalues to be reported have been decay-corrected to the time of collection, the fallout ratio has likewise been decay-corrected to the middle of the sampling period (mid-1975), yielding a ratio of 0.035 f 0.011. This ratio assumes that the majority of 238Pu has been delivered to the drainage basin in times prior to 1971 (time of sample collection noted in ref I ) and that the plutonium quantities in fallout delivered since 1971 have not differed greatly in isotopic abundance. 23sPu/239~240Pu Isotopic Ratio Characteristic of Reactor Production. Reactor-grade plutonium consists of a mixture of 238,239,240Pu and 241Pu.The exact composition depends on the particular reactor type, the fuel cycle chosen, the location in the core, and most importantly, the stage of fuel burnup (Le., the age of the core) (3).It is extremely difficult, therefore, to estimate the 238Pu/239,240Pu ratio contained in the core a t any particular time. The isotopic composition of a typical light water reactor (LWR) is presented in Table 11. The plutonium isotopic composition has been described for the uranium fuel cycle following the first discharge (newer fuel), and the equilibrium discharge (older fuel). On the basis of Table 11, the activity ratio of 238Pu/239,240Pu varies between 1and 3 for newer and older fuel, respectively. Since the probability of plutonium escaping the fuel rod assembly is highest for the aged portion of the core, an estimated plutonium activity ratio closer to 3 may be considered typical for that in reactor fuel and effluent. Clearly, there is as much as a 100-fold difference between the 238Puto 239,240Pu activity ratio found in fallout (0.035 f 0.011) and that considered typical of reactor effluent (=3).
@ 1980 American Chemical Society
Volume 14, Number 12, December 1980
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Hudson River Sarnplina Locations
Materials Sampling Regime. All sediment samples analyzed were collected from a minimum depth of 5 f t of water by using an Emory dredge. This instrument typically collects the upper 2-4 in. of surface sediment. Wet sediments were homogenized before the removal of a 50-100-g sample aliquot and stored in polyethylene containers. Sampling sites were concentrated around the Indian Point nuclear reactor vicinity as shown in Figure 1.A control site, located -20 mi north (up river) of the reactors provided background data useful for evaluating the source of plutonium in sediments measured in the Indian Point vicinity. Past observations of radionuclides in water, sediment, and biota have shown that this northern location (Newburgh Bay) is relatively unaffected by liquid effluent discharged a t the reactor site ( 4 ) . Chemical Methodology ( 5 ) .Sediment samples were dried, weighed (as 10-20-g aliquots), spiked with from 1to 5 dpm of 242Putracer, and heated overnight in a muffle furnace at 400 "C. Plutonium was leached from the sediment with a 400-mL mixture of concentrated nitric and hydrochloric acids (3:l). After the sample had been filtered through Whatman no. 42 paper, the sediment portion was again leached, the leachates were combined, and the remaining sediment residue and filter paper were discarded. Plutonium was next coprecipitated with
'
f!
Table 1. Fallout Inventory of 2399240Pu and 238Pua kCI deposlted 239,240~~ weapons
Northern Hemisphere Southern Hemisphere global a
256 f 33 69 f 14 325 f 36
Hide Pork
i
Newburgh- Beacon Bridge
Figure 1. Hudson River sampling locations.
flu 238Pu
weapons
SNAP-9A
6.1f 0.8 1.6f 0.3 7.7f 0.9
3.1 f 0.8 10.8f 2.1 13.9 f 2.2
Reference 7.
iron by the addition of concentrated ammonium hydroxide to pH 9. After dissolving the hydroxide in a minimum amount of concentrated nitric acid, the valence state of plutonium was adjusted to 4+ by boiling with a few milligrams of sodium nitrite. The solution was cooled and the normality adjusted to 7 N before solvent extraction using 25% trilaurylamine in xylene. The organic phase was purified by repeated washings
Table II. Isotopic Composition of Plutonium Assumed for a Uranium Fuel Cycle After First and Equilibrium Dischargesa first dlscharge
isotope
'38Pu 239Pu '4OPu 24'Pu
(6-,
T1/29 Yr
86.4 24 400 6 580 15
specific actlvlty. Cllg
wt,
17 0.062 0.23 115
'42Pu 379000 0.004 sum of a emitters activity ratio = 238Pu/239*240Pu a
Yo
actlvlty In 1 g Of Pu, CI
0.6 69 20
0.102 0.043 0.046
8 2
9.2 8X 0.1911 1.15
YO of
total
a actlvlty
53.4 32.5 24.1
wt,
Yo
1.6 56 26
0.042
11 5
equlllbrlum discharge actlvlty In 1 g Of Pu, CI
0.272 0.035 0.06
% of total a actlvlty
74.1 9.5 16.3
12.65 2 x 10-4 0.3672 2.86
0.054
Modified from ref 3.
Table 111. Plutonium Concentrations in Hudson River Sediments Collected during 1973 and 1974 sample no.
sampllng statlon
1 2 3 4 5 6 7
Esopus (Hyde Park) Newburgh Bay Lent's Cove Indian Point Mid Green's Cove Newburgh Bay Twin Towers
2399240PU
date of collectlon
monthly composite, May-Sept monthly composite, May-Sept monthly composite, May-Sept monthly composite, May-Sept monthly composite, May-Sept monthly composite, May-Sept
10/26/73
1974 1974 1974 1974 1974 1973
15f2 23 f 2 15f 1 18 f 2 27 f 3 44 f 3 13 f 2
plutonlum concn, pCl/kg dry f l u 238PU 238pu,23S,24OPu
10.4a 1.3 f 0.4 0.8f 0.2 10.4a 10.4a 1.47f 1.47 0.51 f 0.62
b
0.047f 0.018 0.053 f 0.014 b b
0.032 f 0.032 0.038f 0.046
a This value represents the lower limit of detection (LLD) (9) expressed at the 95 % confidence level. Estimates of the ratio for these sites are not given since the 238Puestimate was less than the LLD. In Table VII, where mean and median ratios are listed, the actual measured 238Puvalue was incorporated In the calculation.
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Environmental Science & Technology
Table IV. Plutonium Concentrations in Hudson River Sediments Collected during 1975 sample no.
sampllng statlon
1 2 3 4 5
Newburgh Lent's Cove Indian Point Mid Verplanck Beach Buoy 14 East
a
date of collection
06/18/75 07/21/75 07/21/75 07/21/75 07/21/75
239,240~~
38 f 3 20 f 2 51f5 13f4 26 f 4
plutonlum concn, pCi/kg dry 238Pu
f le 238pu/239,240pu
0.035 f 0.014 0.029 f 0.017 0.043 f 0.02
1.32 f 0.53 0.58 f 0.34 2.21 f 0.99 10.4a
b
1.43 f 0.98
0.055
f 0.039
See footnote a, Table 111. 'See footnote b, Table Ill.
Table V. Plutonium Concentrations in Hudson River Sediments Collected during 1976 sample no.
sampllng statlon
date of collection
1 2 3a 3b 3c 4a 4b 4c 4d 4e 5 6a 6b 6c 7 8 9a 9b 1Oa 1Ob 1oc 1Od 1Oe 1Of 11 12a 12b 13a 13b 13c 14a 14b 15a 15b 16 17a 17b
Newburgh Bay Newburgh Bay Newburgh Bay Newburgh Bay Newburgh Bay Con Hook Con Hook Con Hook Con Hook Con Hook lona Island Bear Mt Bridge Bear Mt Bridge Bear Mt Bridge Peekskill Bay Lents Cove Tomkins Cove Tomkins Cove Indian Point Mid Indian Point Mid Indian Point Mid Indian Point Mid Indian Point Mid Indian Point Mid Indian Point Mid Indian Point Mid Indian Point Mid Verplanck Beach Verplanck Beach Verplanck Beach Green's Cove Green's Cove Stony Pt. South Stony Pt. South Buoy 14, East Buoy 14, East Buoy 14, East
07/08/76 08/04/76 11/19/76 11/19/76 11119176 11119176 11/19/76 11/19/76 11/19/76 11119176 11/19/76 10/15/76 10/15/76 10/15/76 11/19/76 11/19/76 11/19/76 11/19/76 08/04/76 08/04/76 08/04/76 08/04/76 08/04/76 08/04/76 10115/76 11119176 11/19/76 10/15/76 10/15/76 10115/76 11119/76 11/19/76 11/19/76 11/19/76 08/04/76 11/19/76 11/19/76
239,240~~
47 f 3 39 f 6 71 f 6 64 f 8 125 f 20 48 f 9 49 f 8 51f5 49 f 8 32 f 7 27 f 5 13f4 16 f 2 11 f 6 22f 1 19 f 4 29 f 6 29 f 3 221 f 1 214 f 18 195 f 11 178 f 12 236 f 16 208 f 9
l o f t 6 f 2 9 f 3 28 f 7 18f5 18f4 32 f 3 22 f 4 26 f 4 27 f 4 14f2 14f3 23 f 7
a Multiple analyses are from aliquots of the same dredge sample. 'See footnote a, Table 111.
(3X) with 7
M nitric acid to remove uranium and then with
10 M hydrochloric acid (3X) to remove thorium. Plutonium
was backextracted into the aqueous phase with 2 M sulfuric acid (2X). The backextractant was evaporated and wet ashed by using nitric and sulfuric acids before the electrodeposition of plutonium onto platinum planchets. Isotopic plutonium concentrations were determined by a spectrometry using a 300-mm silicon surface barrier detector coupled to a computer-based multichannel analyzer. Because the a particle
piutonlum concn, pCi/kg dry 238Pu
4.2 f 1.0 1.0 f 1.0 2.9 f 1.2 1.0 f 1.0 4.8 f 6.0 1.6 f 1.6 2.8 f 2.0 4.0 f 1.0 3.0 f 2.0 50.4 -0.01 f 1.5 1.0 f 1.0 1.0 f 0.5 6.6 f 5.4 0.44 f 0.14 0.2 f 0.2 1.4 f 1.0 1.3 f 0.7 7.7 f 2.2 14.5 f 6.0 3.1 f 1.4 6.1 f 2.2 8.9 f 3.1 3.9 f 1.0 0.3 f 0.2 2.0 f 1.0 1.0 f 1.0 7.0 f 3.0 97%) of plutonium present in Hudson estuary sediments is derived from weapons testing fallout with minimal detectable contributions arising from other sources. L i t e r a t u r e Cited (1) Hardy, E. P.; Krey, P. W.; Volchok, H. L. Nature (London) 1973, 241, 444-5. (2) Eisenbud. M. “Environmental Radioactivitv”: Academic Press: New York, 1973; p p 81-118. (3) Liikala, R. C. Plutonium l n f . Meet. Ad Hoc Subcomm. Aduis. Comm. React. Safeguards, [Proc.]1974,8-15. (4) New York University Medical Center, Institute of Environmental Medicine. Annual Reoorts to the Consolidated Edison ComDanv of New York, Inc., “Radioecological Studies of the Hudson Rive; (1970- 19781.’’ (5) Singh, N. P.; Linsalata, P.; Gentry, R.; Wrenn, M. E. Anal Chim. Acta 1979,111,265-74. (6) Simpson, H. J.; Williams, S. C. In “Annual Technical Progress Report to the Energy Research and Development Administration”, Report No. COO-2529-1, 1975, pp 1-14. (7) Noshkin, V. E. Health Phys. 1971,22,537-49. (8) Seymour, A. H.; Nevissi, A,; Schell, W.; Sanchez, A. “Distribution Coefficients for Radionuclides in Aquatic Environments”,Annual Report, Aug 1976-July 1977, College of Fisheries, University of Washington, NUREGKR-0801 (Oct 1979). (9) Harley, J. H., Ed. “HASL Procedures Manual” (HASL-300);U.S. Energy Research and Development Administration, Health and Safety Laboratory: New York, NY; pp D-08-02-D-08-06, 1972. “
I
Received for review May 2,1980.Accepted August 5,1980. This study was funded by the Consolidated Edison Company of New York, lnc. and is part of center programs supported by Grant ES-00260 from t h e National Institute of Environmental Health Sciences and by Grant CA-13343 from the National Cancer Institute Volume 14, Number 12, December 1980
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