Environ. Sci. Technol. 1997, 31, 1834-1836
36
Cl and 129I in the Yenisei, Kolyma, and Mackenzie Rivers T . M . B E A S L E Y , * ,† L . W . C O O P E R , ‡ J . M . G R E B M E I E R , ‡ L . R . K I L I U S , §,| A N D H.-A. SYNAL⊥ U.S. Department of Energy, 201 Varick Street, New York, New York 10014, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831, IsoTrace Laboratory, University of Toronto, Toronto, M5S 1A7 Canada, and Institute of Intermediate Physics, ETH-Ho¨nggerberg, CH 8093, Zurich, Switzerland
Introduction For the past several years, a number of scientific studies have been conducted in the Arctic Ocean Basin to determine if past radioactive waste management practices of the Former Soviet Union (FSU) have released significant quantities of anthropogenic radioactivity to ecosystems of that region. In a recent summary (1), of the 6.3 × 1019 Bq (1.7 × 109 Ci) of radioactivity released to the environment at the nuclear weapons complexes (excluding former test sites) of both the FSU and the United States, ∼1 × 1015 Bq (3 × 106 Ci) had been released by the United States. The preponderant remainder has been discharged to the environment by the FSU, specifically in Siberia, at the nuclear complexes of Mayak, Tomsk, and Krasnoyarsk-26. Significantly, each of these installations has the potential for releasing radioactivity directly to river systems in their vicinity, most notably the Ob and Yenisei, or to these rivers through smaller tributaries. Of particular interest is that, at both Tomsk (Ob River) and Krasnoyarsk-26 (Yenisei River), approximately 3.7 × 1019 Bq (109 Ci) of high-level nuclear waste has been injected into the subsurface terrain at depths ranging from 200 to 500 m (1). As part of the Department of Defense Arctic Nuclear Waste Assessment Program (ANWAP), managed by the Office of Naval Research, we measured 36Cl (T1/2 ) 3.01 × 105 yr) and 129I (T 7 1/2 ) 1.6 × 10 yr) in selected rivers flowing to the Arctic Ocean. Our interest was in comparing atom concentrations measured there with those measured at and near nuclear fuel reprocessing facilities in the United States Because 36Cl behaves conservatively in the subsurface (2), and 129I nearly so (3), the presence of these radionuclides in groundwaters can be used to provide flow velocity information (2, 4) as well as provenance (2, 3, 5, 6). The technique used in their measurement, accelerator mass spectrometry (AMS), allows quantification at low atom concentrations with good precision and accuracy (7).
Study Area The majority of our measurements were performed on samples collected from the Yenisei River (Figure 1); the general location of the mouths of the three rivers studied is also provided (Figure 1). The major features of each river have been described (8) and will not be repeated here except to point out that our samples were collected during times of low flow and either preceded or followed the large volume flow that occurs in May-July (9). In the case of the Mackenzie River, samples were collected from the freshwater lens in * Corresponding author telephone: 212-620-3636; e-mail address:
[email protected]. † U.S. Department of Energy. ‡ Oak Ridge National Laboratory. § University of Toronto. | Deceased January 1996. ⊥ ETH-Ho ¨ nggerberg.
1834
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 31, NO. 6, 1997
Kugmallit Bay where salinities ranged between 0.2 and 6 ppt. While adequate for 129I measurements, the presence of even trace amounts of stable chloride from any source other than the true, freshwater end member precludes useful measurements for 36Cl; therefore, they were not attempted on the Mackenzie River samples.
Sampling and Analysis Samples were collected by pumping (Mackenzie), by Niskin bottles (Yenisei), or by collecting surface water directly into the plastic bottle used as the container (Kolyma). All samples were then air-freighted to the Department of Energy’s Environmental Measurements Laboratory where the waters destined for 129I analysis were acidified to pH 1 with highpurity HCl to prevent bacterial growth. That portion of the water reserved for 36Cl analyses was transferred to precleaned plastic bottles and stored at room temperature until processed. Stable Cl- was determined by titration with mercuric nitrate using standard methods (10); each sample was run in duplicate. Targets (AgCl) for 36Cl measurements were prepared following the procedures described by Conard et al. (11); those for 129I (AgI) were prepared as described by Mann and Beasley (12). Descriptions of the AMS facilities and their capabilities for measuring 36Cl and 129I have recently been published elsewhere (13, 14).
Results and Discussion Atom concentrations of both 36Cl and 129I show that there is a significant enrichment of 129I in Yenisei River waters over those observed for both the Kolyma and Mackenzie Rivers (Table 1). The atom concentrations of 36Cl in the Yenisei show no particular enrichment over those seen in the Kolyma; as discussed below, they are quite comparable to measurements made at lower latitudes. Chlorine-36. The mean 36Cl concentration in Yenisei River water, at the time of collection, was (5.5 ( 0.2) × 107 atoms L-1 where the uncertainties represent the 1σ confidence interval about the mean. The 36Cl atom concentrations were calculated as the product of the measured 36Cl/Cl ratio in the sample and the stable Cl- content of the water; the mean 36Cl/Cl ratio for the Yenisei water samples was (400 ( 61) × 10-15. There is no pronounced difference between samples collected at the surface or near the river bottom at the same location, nor at the same station sampled at different times (stations 3 and 3R, Table 1). The mean 36Cl/Cl ratio in Yenisei water of (400 ( 61) × 10-15 can be compared to 36Cl/Cl ratios measured in soil samples collected from dated moraines in the dry valleys of Antarctica to determine the natural, 36Cl/Cl meteoric ratio; samples from five such moraines gave 36Cl/Cl ratios that ranged between 400 and 600 × 10-15 (15). Such a comparison is useful because of the dependence of meteoric 36Cl deposition with latitude (2); at high latitudes, 36Cl deposition is low and increases to a maximum at 45° N. The drainage basins of the large Alaskan and Siberian rivers extend below 65° N latitude, where meteoric 36Cl deposition rates would be some 4-5 times higher than those in Antarctica. Consequently, because 36Cl/Cl ratios are similar to those observed in Antarctica (for comparable chloride ion concentrations), it is difficult to argue for a significant anthropogenic source of 36Cl to the Yenisei River at the present time. Injection of low-level, radioactive waste into groundwaters at a fuel reprocessing site in Idaho (5) led to 36Cl concentrations near 1011 atoms L-1 at distances of 15 km, some 40 yr following introduction to the subsurface; “background” concentrations of 36Cl in the groundwaters were near 108 atoms L-1. It is reasonable to assume that if high-level radioactive waste,
S0013-936X(96)00936-4 CCC: $14.00
1997 American Chemical Society
FIGURE 1. Location of Arctic Basin rivers sampled. Yenisei River samples were taken between Igarka and 71°02.55′ N, well above tidal influences (bottom salinities ) 0.07‰; see ref 20). The Kolyma River was sampled some 330 km above the river’s mouth and was also un-influenced by saltwater intrusions.
TABLE 1. Analysis Data for Water Samples Collected from the Kolyma, Mackenzie, and Yenisei Rivers (1993/1994) date
depth (m)a
location
Cl- (ppm)
36Cl
(10 7 atoms L-1)
129I
(108 atoms L-1)
Kolyma River 68°41′ N, 161°l7′ E
Sfc
1.6
7.1 ( 0.1b
0.27 ( 0.01
April 1994 April 1994 April 1994
69°27.47′ N, 133°04.55′ W 69°27.50′ N, 133°04.46′ W 69°39.71′ N, 133°02.08′ W
Mackenzie Riverc Sfc Sfc Sfc
NAd NA NA
NA NA NA
0.43 ( 0.04 0.38 ( 0.04 0.47 ( 0.03
August 28, 1993 August 4, 1993 August 4, 1993 August 5, 1993 August 5, 1993 August 24, 1993 August 6, 1993 August 7, 1993 August 7, 1993 August 24, 1993 August 26, 1993
67°27.41′ N, 86°33.26′ E 69°29.00′ N, 85°59.42′ E 69°29.00′ N, 85°59.42′ E 69°41.14′ N, 84°04.13′ E 69°41.14′ N, 84°04.13′ E 69°40.65′ N, 84°05.55′ E 70°21.55′ N, 82°58.59′ E 70°38.33′ N, 83°28.94 E 70°38.33′ N, 83°28.94 E 71°02.55′ N, 83°12.76′ E 68°17.42′ N, 86°32.72′ E
Yenisei River Igarka, Sfc station 2, Sfc station 2, (16) station 3, Sfc station 3, (7) station 3R, Sfc station 4, Sfc station 5, Sfc station 5, (15) station 7R, Sfc station 25, Sfc
10.5 8.2 8.2 7.3 7.3 10.8 7.2 6.7 6.7 8.3 9.8
5.8 ( 0.2 5.4 ( 0.2 5.4 ( 0.2 6.2 ( 0.2 5.6 ( 0.2 6.2 ( 0.2 5.7 ( 0.2 4.9 ( 0.1 4.7 ( 0.1 5.5 ( 0.2 5.1 ( 0.2
NA 1.80 ( 0.05 3.54 ( 0.08 3.57 ( 0.07 3.67 ( 0.08 3.08 ( 0.06 4.14 ( 0.09 4.34 ( 0.10 4.45 ( 0.10 3.51 ( 0.07 3.56 ( 0.08
1996
53° N, 108° E
Sfc
0.4
3.8 ( 0.2
April, 1993
Lake Baikal a
Depth corresponds to near river bottom.
b
c
Propagated uncertainties at 1σ. All samples collected in Kugmallit Bay.
introduced into the subsurface at Krasnoyarsk-26, had found its way to the Yenisei River, atom concentrations there would be much higher than those we have measured. This would be particularly true if the integrity of the injection well casings were compromised and wastes were introduced into nearsurface, water-bearing strata which then contribute water to the Yenisei by baseflow. That such well-casing failures can occur has been documented at other fuel reprocessing facilities (12). This is not to imply that 36Cl releases have not occurred at the Krasnoyarsk-26 facility where both reactor operations and fuel reprocessing activities still continue (1). Indeed, it is likely that releases of 36Cl in both process off-gases and wastewaters have occurred as has been observed at U.S. facilities (5, 6). However, the absolute quantities of anthropogenic 36Cl ultimately mobilized to the river by overland
NA d
NA ) not analyzed.
and ground water baseflow or that released directly to the river by regulated wastestreams would reflect input from lowlevel waste discharges rather than from additions of highlevel radioactive waste. Moreover, recent measurements of 36Cl in surface waters of Lake Baikal (Table 1), the source of the Angara River, which provides 20% of the downstream Yenisei River flow (8), have atom concentrations consistent with that conclusion. Finally, our sample from the Kolyma River was collected ∼400 km (river distance) downstream of a small nuclear power station at Bilibino. Small amounts of radioactivity are introduced to the river by discharges to a nearby stream, which then flows to the river. However, because the 36Cl atom concentrations in the Kolyma closely approximate those in the Yenisei and discharges of other radionuclides measured in the stream at the plant site have been shown to be small
VOL. 31, NO. 6, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
1835
(17), we consider the 36Cl concentrations at this site to be principally derived from meteoric sources. Iodine-129. There is a definite enrichment of 129I in Yenisei River water over that observed in both the Kolyma and Mackenzie Rivers (Table 1). In each case, the atom concentrations are ∼8 times higher in the Yenisei than in the other rivers. Even so, 129I in the Yenisei is about an order of magnitude lower than has been measured in the dissolved phase (non-particle bound) of Ob River waters (18). The higher 129I concentrations in the Ob undoubtedly reflect the influence of above-ground discharges from both the Tomsk and Mayak reprocessing facilities as gaseous and liquid releases. It should be mentioned that in neither river (Ob and Yenisei) do 129I concentrations reach those measured in the Kara and Barents Seas (∼15 × 109 atoms L-1; 19] where the predominant source of the 129I are discharges from the nuclear fuel reprocessing facilities at Sellafield, U.K., and La Hague, France (19). Indeed, the combined, annual riverine input of 129I to the Arctic Ocean from the Ob and Yenisei Rivers represents something less than 3% of the 129I inventory presently in Arctic Ocean waters (18; this work). The absolute 129I atom concentrations in the Yenisei do not indicate present-day, high-level radioactive waste discharges as the source of the 129I. For example, the fuel reprocessing facility at the Idaho National Engineering Laboratory, over a 35-yr period, injected as much as 44 GBq (1.2 Ci) of 129I into the subsurface as part of its low-level radioactive waste disposal protocol. On average, this represents an annual discharge of ∼9 × 1023 atoms of 129I. If the same number of 129I atoms were added annually to the Yenisei River (annual flow ) 4.4 × 1014 L yr-1; 8) as low-level radioactive waste discharges (and at something of a constant rate), the average annual concentration of 129I in the Yenisei would be ∼2 × 109 atoms L-1, substantially higher than we measured. Unlike 36Cl, 129I does bind to particulate matter in both saline (19) and freshwater (18) systems in the Arctic. For example, 129I atom concentrations in Ob River surficial sediments show an ∼200-fold enrichment over surface waters collected at the same time (18), and similar 129I enrichments undoubtedly occur in Yenisei River sediments. It is possible, therefore, that an additional source of the 129I we measure in Yenisei River waters may come from re-mineralization and release of 129I from the sediments as has been observed elsewhere (21-23). Given that the intermittent addition of 129I to the river from gaseous releases during fuel dissolution at the reprocessing facilities cannot be ignored, the agreement between our measured 129I concentrations and those expected to result from only low-level releases of this radionuclide to the river seem reasonable. We place no particular significance on the fact that the 129I concentrations in the Yenisei are some 6 times higher than the 36Cl concentrations given that the pathways for their production (excluding natural production) are quite different. The amount of 36Cl produced in the fuel cycle depends upon the total amount of stable chloride that is present in reactor fuels and reactor parameters such as thermal neutron flux and irradiation time; the amount of fission-product produced 129I depends, additionally, on the type of fuel irradiated (degree of 235U or 239Pu enrichment). It is believed that the subsurface radioactive wastes will not migrate significant distances due to their depth of injection (200-500 m) and the nature/composition of the geological strata at the injection site (1). Radioactive decay is expected to reduce levels substantially. Our data give no indication that high-level radioactive waste has migrated to the Yenisei during the 30-yr period in which subsurface radioactive waste disposal has been used at Krasnoyarsk-26. That such an eventuality might occur in the future can only be determined by long-term monitoring of selected, long-lived radionuclides downstream of the Krasnoyarsk-26 complex.
1836
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 31, NO. 6, 1997
Acknowledgments During the course of our studies, Dr. Linas R. Kilius passed away unexpectedly. We miss his scholarship, his counsel, and most of all, his friendship. We thank the Geochemical and Environmental Research Group (GERG) of Texas A&M University for water samples from the Yenisei River, Dr. Kelly Falkner of Oregon State University for samples from the Mackenzie River, Dr. R. Schnell of the NOAA Mauna Loa Observatory for the sample collected on the Kolyma River, and Dr. Rolf Kuepfer (EAWAG-Switzerland) for the sample collected from Lake Baikal. We gratefully acknowledge support for this work through Office of Naval Research contracts NOO14-93-0098 (DOE), NOO14-93-0095 (ORNL), and NOO14-94-1-10442 (UT).
Literature Cited (1) Bradley, D. J.; Frank, C. W.; Mikerin, Y. Phys. Today, 1996, April, 40-45. (2) Bentley, H. W.; Phillips, F. M.; Davis, S. N. In Handbook of Environmental Isotope Geochemistry; Fritz, P., Fontes, J. Ch., Eds.; Elsevier: New York, 1986; Vol. 2, pp 426-480. (3) Fontes, J. Ch.; Andrews, J. N. Proceedings of the Sixth International Conference on Accelerator Mass Spectrometry, Sydney, Australia, 1993; North Holland: The Netherlands, 1994; pp 367-375. (4) Beasley, T. M. U.S. Department of Energy Report EML-567; U.S. Department of Commerce, National Technical Information Service: Springfield, VA, 1995; 51 pp. (5) Beasley, T. M.; Cecil, L. D.; Sharma, P; Kubik, P. W.; Fehn, U.; Mann, L. J.; Gove, H. E. Ground Water 1993, 31, 302-310. (6) Beasley, T. M.; Elmore, D; Kubik, P. W.; Sharma, P. Ground Water 1992, 30, 539-548. (7) Elmore, D.; Phillips, F. M. Science 1987, 236, 543-550. (8) Telang, S. A.; Pocklington, R.; Naidu, A. S.; Romankevich, E. A.; Gitelson, I. I.; Gladyshev, M. I. In Biogeochemistry of Major World Rivers; Degens, E. T., Kempe, S., Richey, J. E., Eds.; Wiley: New York, 1991; pp 75-104. (9) Dai, M.-H.; Martin, J.-M. Earth Planet. Sci. Lett. 1995, 131, 127141. (10) American Public Health Association. In Standard Methods for the Analysis of Water and Wastewater; 11th ed.; APHA: New York, 1960; pp 79-81. (11) Conard, N. J.; Elmore, D.; Kubik, P. W.; Gove, H. E.; Tubbs, L. E.; Chrunyk, B. A.; Wahlen, M. Radiocarbon 1986, 28, 556-560. (12) Mann, L. J.; Beasley, T. M. Open-File Rep.sU.S. Geol.Surv. 1994, No. 94-4053. (13) Kilius, L. R.; Baba, N.; Garwan, M. A.; Litherland, A. E.; Nadeau, M.-J.; Rucklidge, J. C.; Wilson, G. C.; Zhao, X.-L. Nucl. Instrum. Methods Phys. Res. 1990, B52, 357-365. (14) Synal, H.-A.; Beer, J.; Bonani, G.; Lukasczyk, Ch.; Suter, M. Nucl. Instrum. Methods Phys. Res. 1992, B92, 79-84. (15) Carlson, C. A.; Phillips, F. M.; Elmore, D.; Bentley, H. W. Geochim. Cosmochim. Acta 1990, 54, 311-318. (16) Elmore, D.; Tubbs, L. E.; Newman, D.; Ma, X. Z.; Finkel, R.; Nishizumi, K.; Beer, J.; Oeschger, H.; Andree, M. Nature 1983, 300, 735-737. (17) Cooper, L. W.; Larsen, I. I.; Franklin, G. L.; Houser, G. F.; Emelyanova, L. G.; Neretin, L. N. Polar Geogr. 1996, 29, 3-19. (18) Moran, S. B.; Cochran, J. K.; Fisher, N. S.; Kilius, L. R. In Environmental Radioactivity in the Arctic; Strand, P., Cook, A., Eds.; Scientific Committee of the Environmental Radioactivity in the Arctic: Østerås, Norway, 1995; pp 75-78. (19) Kilius, L. R.; Raisbeck, G. M.; Yiou, F.; Zhou, Z. Q.; Smith, J. N.; Dahle, S; Matishov, D. G. In Environmental Radioactivity in the Arctic and Antarctic; Stand, P., Holm, E., Eds.; Scientific Committee of the Environmental Radioactivity in the Arctic: Østerås, Norway, 1993; pp 333-336. (20) Preller, R. H., Edson, R., Eds. Proceedings of the ONR/NRL Workshop on Modeling the Dispersion of Nuclear Contaminants in the Arctic Seas; Naval Research Laboratory Report NRL/MR/ 5322-95-7584; NRL: Washington, DC, 1995; 415 pp. (21) Ullman, W. J.; Aller, R. C. Geochim. Cosmochim. Acta 1980, 44, 1177-1184. (22) Ullman, W. J.; Aller, R. C. Geochim. Cosmochim. Acta 1983, 47, 1423-1432. (23) Ullman, W. J.; Aller, R. C. Geochim. Cosmochim. Acta 1985, 49, 967-978.
Received for review November 5, 1996. Revised manuscript received February 26, 1997. Accepted March 10, 1997. ES9609361
