Concentrations of 137Cs, 239240Pu and 210Pb in Sediment Samples ...

PII: S0025-326X(00)00078-3

Marine Pollution Bulletin Vol. 40, No. 10, pp. 830±838, 2000 Ó 2000 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0025-326X/00 $ - see front matter

Concentrations of 137Cs, 239;240Pu and 210 Pb in Sediment Samples from the Pechora Sea and Biological Samples from the Ob, Yenisey Rivers and Kara Sea M. BASKARAN *, SHAUNNA ASBILLà, JON SCHWANTESà, PETER SANTSCHIà, MICHAEL A. CHAMP§, JAMES M. BROOKS§, DAN ADKINSON§ and VYACHESLAV MAKEYEV Department of Geology, Wayne State University, Detroit, MI 48202, USA àDepartment of Oceanography, Texas A&M University at Galveston, Galveston, TX 77551, USA §Geochemical and Environmental Research Group, College Station, TX 77845, USA Research Institute for Nature Conservation of the Arctic and North, St. Petersburg, Russian Federation We have measured the concentrations of 239;240 Pu, 238 Pu, Pb, and 137 Cs in biological samples (5 isopods, 10 bivalves, 2 amphipods, 2 mussell, 1 ®sh fat, 6 ®sh liver and 2 worm tubes) from the Ob and Yenisey Rivers and Kara Sea and sediment samples from the Pechora Sea of the Russian Arctic. Mean concentrations of 137 Cs and 239;240 Pu in bivalves on which measurable concentrations were found are slightly higher than the values reported for the east, west and Gulf coasts of US. The mean concentrations of 137 Cs and 239;240 Pu in 27 sur®cial sediment samples from the Pechora Sea are lower than the corresponding values from the Ob and Yenisey Rivers and Kara Sea. The 238 Pu/ 239;240 Pu activity ratios on 16 of these sediment samples varied between 0.015 and 0.056. The best-®t line between the concentrations of 238 Pu and 239;240 Pu yielded a mean 238 Pu/239;240 Pu activity ratio of 0.035, suggesting that most of this Pu is derived from global fallout and that there is virtually no detectable input of Pu from either the European nuclear euents, close-in fallout from the nuclear test sites or from the dumped nuclear reactors in the Kara Sea or adjoining marine systems. Ó 2000 Elsevier Science Ltd. All rights reserved. 210

Keywords: plutonium; radiocesium; radioactivity; arctic contamination; Pechora Sea; Kara Sea.

Introduction Physical and biological processes primarily control the transfer of nuclear-reactor derived radionuclides such as *Corresponding author.

830

137

Cs, 238 Pu and 239;240 Pu from aquatic environments to man. Biological processes result in the passage of radionuclides through food webs to man. Biological uptake of radionuclides from the water column can result by direct transfer of radionuclides in ionic, colloidal or even in particulate forms. For those nuclides for which the distribution coecients (Kd ) are high (104 ±106 ), the nuclide accumulation in body tissues at higher trophic levels will be dominated by gut absorption rather than by direct uptake from water (Eyman and Trabalka, 1980). The sorption of nuclides on the exterior surface of the biota, gut labeling, and absorption from the gut are the three major pathways for trophic transfer of particle-reactive radionuclides. In addition to these, transfer of nuclides from sediment to organism and to man is another important pathway through which nuclides can reach man. It was shown that benthic marine organisms that were associated with the sediment-water interface contain Pu burdens that are about 100 times higher than those of free-swimming organisms (Pillai and Matthew, 1976). Even though Pu concentrations in some of the biological specimens are much higher than in the waters where the organisms dwell, the concentration decreases by an order of magnitude in each successive link in the food chain leading to man (Marshall et al., 1974). However, exposure to Pu via a single trophic transfer food chain (from sediment to an organism that is consumed by man) will result in the highest Pu concentrations in human food derived from aquatic ecosystems (Eyman and Trabalka, 1980). Most of the particle-reactive radionuclides released into the aqueous phase eventually reach the sediments. The accumulation, retention and transport of particlereactive radionuclides is strongly associated with sedi-

Volume 40/Number 10/October 2000

ment and sedimenting particles. It has been shown from a year long aquatic microcosm experiments that most of the Pu introduced into the aqueous phase reaches the sediments (99.9%) while only trace amounts (0.04%) of the Pu were picked-up by the animal (Eyman and Trabalka, 1980). In a mesocosm experiment where relative mobility of fallout nuclides was investigated, 99.5% of the Pu introduced into the aqueous phase reached the sediment within a month while the remaining 0.5% remained in the aqueous phase (Santschi et al., 1983). The transfer of radionuclides from animal to man can take place by ingestion of animals from nearby contaminated sites and/or by the migration of animals which eventually become food for human consumption. Thus, migration of oceanic nekton from the areas where radioactivity concentrations are high could be a potential pathway of radionuclides to man. The nuclear era in the Former Soviet Union had resulted in the dumping of several nuclear submersibles in the waters of the Kara and Barents seas. In addition, nuclear tests conducted at the Novaya Zemlya Island resulted in extremely high concentrations of 239;240 Pu in southern Novaya Zemlya, where the concentrations exceeded that of the Kara Sea by 2±4 104 times (Smith et al., 2000). Most of the Pu in the Kara Sea sediments was derived from the global fallout; the dumped reactors in the Kara Sea have not yet given rise to any signi®cant amounts of Pu to the sediments of the Kara Sea (Baskaran et al., 1995, 1996). In this paper, the 137 Cs and 239;240 Pu concentrations in biological samples from the Ob and Yenisey Rivers and the Kara Sea are presented. In addition, the concentrations of 137 Cs, 238 Pu, and 239;240 Pu in sur®cial sediments from the Pechora Sea are compared to the concentrations of these nuclides in the Ob, Yenisey Rivers and Kara Sea.

Materials and Methods Radionuclide analysis of sediments and biological samples Twenty-seven surface sediment samples (upper 3 cm) from the Pechora Sea were collected in July 1994 using the Russian ship `YAKOV SMIRNINSKI' leased from the Hydrobase in Arkhangelsk, Russia. The samples were collected from widely spaced locations using a stainless steel Box corer (Fig. 1). All samples were stored frozen until ready for analysis. The biological samples were collected in the summer of 1993 from the Ob and Yenisey Rivers and Kara Sea (Baskaran et al., 1995). The species of the biological samples were not identi®ed. Most of the bivalves are epifauna. The two wormtubes utilized for this investigation are animal protein-made tubes. The geographical locations and types of samples are given in Table 1. The dried sediment samples were pulverized using an agate mortar and pestle. About 10±20 g of dried samples were leached twice with 30 ml of boiling 6 M HCl and later, the leachate solutions were combined. To this solution, a known amount of 242 Pu spike was added, and

Fig. 1 Sampling sites in Pechora Sea.

the separation and puri®cation of Pu was carried out as described in Krishnaswami and Sarin (1976). The biological samples were not cleaned prior to analysis. For Pu analysis of the biological samples, about 10±30 g of wet biological samples were dried at 100°C for about 12 h and the dry weights were determined. The dried samples were then ashed at 500°C. The ashed samples were digested in a microwave oven after adding 242 Pu spike and were brought into solution. The Pu in the solution was then chemically separated by ion-exchange chromatography. The pure Pu was electroplated onto stainless steel planchets following the method of Kressin (1977). The electroplated Pu source was assayed for 238 Pu and 239;240 Pu by using a Quad alpha spectrometer with surface barrier alpha detectors coupled to a Canberra S-100 multichannel analyser (Baskaran et al., 1995, 1996). The analysis of 137 Cs in sediments and biological samples was carried out after the methods outlined in Baskaran et al. (1991, 1995, 1996). Brie¯y, the dried sediment powder and the ashed biological samples were packed in a 10 ml counting vial and assayed using the 661.6 keV photopeak line in a high purity Ge-well detector (Baskaran et al., 1991). The 226 Ra and 228 Ra concentrations were determined from the 351 and 338 keV photopeaks, respectively (Baskaran et al., 1993a). The excess 210 Pb (total 210 Pb±226 Ra) concentrations were determined using the 46 keV photopeak line, as described in Baskaran et al. (1993b). Typically, the samples were counted for about 12±24 h, depending on the activity of 137 Cs in the sample, since many of the biological samples had relatively low concentrations or were below detection limits. The peak analysis of 137 Cs (I 85.1%, 661.6 keV) was carried out 831

Marine Pollution Bulletin TABLE 1 Sample locations, and concentrationsa of 137 Cs, 239;240 Pu, 226 Ra and 228 Ra in biological samples collected from Ob and Yenisey Rivers and Kara Sea of the Russian Arctic. Station number and location 8 (71°52.050 N±82°50.470 E) 10 (71°41.620 N±83°32.440 E) 13 (72°08.290 N±80°56.280 E) 16 (73°09.730 N±80°21.730 E) 31 (73°13.200 N±78°36.230 E) 14 (72°23.030 N±80°47.600 E) 15 (72°50.560 N±78°31.170 E) 19 (74°45.230 N±74°17.050 E) 20 (74°03.780 N±73°05.180 E) 21 (72°36.570 N±73°19.660 E) 32 (73°22.990 N±79°00.600 E) 35 (74°00.000 N±79°18.080 E) 52 (74°21.770 N±76°40.230 E) 53 (74°14.320 N±75°59.170 E) 54 (74°30.390 N±74°35.440 E) 17 (74°20.160 N±78°45.090 E) 18 (75°17.080 N±77°27.370 E) 20 (74°03.780 N±73°05.180 E) 38 (74°42.800 N±78°11.390 E) 10A (71°41.620 N±83°32.440 E) 5 (70°38.33N±83°28.930 E) 7 (71°21.470 N±83°01.080 E) 9 (71°47.120 N±82°46.030 E) 10 (71°41.620 N±83°32.440 E) 21-30 (72°36.570 N±73°19.660 E) 24 (71°41.620 N±83°32.440 E) 16 (73°09.730 N±80°21.730 E) 21 (72°36.570 N±73°19.660 E) 19 (74°45.230 N±74°17.050 E) a

Sample name Isopods Isopods Isopods Isopods Isopods Bivalves Bivalves Bivalves Bivalves Bivalves Bivalves Bivalves Bivalves Bivalves Bivalves Amphipods Amphipods Mussell Mussell Fat Liver Liver Liver Liver Liver Liver Wormtubes Wormtubes Fe±Mn Nodule

137

Cs (Bq kgÿ1 )

BD BD BD 1.59 0.63 BD 7.0 1.3 BD BD BD BD BD BD BD BD BD 0.50 0.56 BD BD BD BD BD BD BD BD 3.04 0.62 0.55 0.30 10.7 1.6 BD BD

239;240

Pu (Bq kgÿ1 )

0.033 0.023 0.047 0.047 NM 0.080 0.036 0.167 0.035 BD BD BD BD BD 0.076 0.093 0.095 0.055 0.041 0.036 0.179 0.066 0.077 0.026 0.048 0.028 NM NM 0.216 0.102 0.021 0.021 0.010 0.020 0.022 0.010 0.035 0.035 0.047 0.033 0.046 0.046 0.016 0.016 0.307 0.021 0.040 0.008 0.082 0.012

226

Ra (Bq kgÿ1 )

BD 5.0 1.7 BD 2.85 1.13 BD 17.8 1.9 3.7 1.0 4.3 1.1 8.8 1.1 BD BD 47.6 6.7 BD 82.3 8.9 23.2 3.0 2.0 1.1 BD 19.0 4.0 BD BD 1.21 0.68 BD BD 1.19 1.12 1.43 0.64 BD 28.5 2.3 17.8 1.6 281.7 10.9

228

Ra (Bq kgÿ1 )

BD 9.7 3.4 BD BD BD 38.7 4.7 BD BD 10.6 2.1 BD BD 67.1 12.8 BD 57.1 12.9 15.7 6.2 BD BD BD BD BD BD BD BD BD BD BD 225.5 9.6 80.3 5.7 24.9 4.1

BD ± Below detection limit, NM ± Not measured.

using SPECTRAN-AT peak analysis software (CANBERRA Company). There is no peak background in the 137 Cs energy range, 659.1±664.1 keV. The peak/ Compton ratio for 60 Co (1332 keV) was 45.0:1. The gamma counting equipment was calibrated with 137 Cs standards obtained from Lamont Doherty Earth Observatory and was calibrated with respect to a National Institute of Standards and Technology standard. The overall propagated error (1r) in the value of the ®nal concentration arises due to errors from counting statistics and errors associated with detector calibration.

Results Concentrations of 137 Cs, 239;240 Pu, 226 Ra and 228 Ra in biological samples from the Ob, Yenisey Rivers and Kara Sea The 137 Cs, 239;240 Pu, 226 Ra and 228 Ra concentrations in biological samples are given in Table 1. In most of the biological samples, the 137 Cs concentrations were below detection limit. Of the ®ve isopods samples, only one sample contained measurable 137 Cs activity (1.59 0.63 Bq kgÿ1 ). Only one out of 10 bivalve samples contained measurable 137 Cs activity (7.0 1.3 Bq kgÿ1 ). In two mussel samples, the 137 Cs concentrations were below detection limit. Two out of six liver samples contained measurable 137 Cs concentrations. The higher concentrations of 137 Cs in all these biological samples are likely 832

due to varying amounts of detritus present in those samples. The 238 Pu concentrations in all the biological samples were below detection limit. 239;240 Pu concentrations in most of the biological samples were also below detection limit (within 2r of the counting error); however, the 239;240 Pu concentrations are distinctly measurable in two of the isopods samples (0.080 0.036 and 0.167 0.035 Bq kgÿ1 ) and two bivalve samples (0.077 0.026 and 0.179 0.066 Bq kgÿ1 ). 239;240 Pu concentrations in four of the ®ve isopod samples in which measurable 239;240 Pu was detected, ranged between 0.033 and 0.167 Bq kgÿ1 , with a mean of 0.082 Bq kgÿ1 . In ®ve bivalve samples in which measurable 239;240 Pu was detected, the concentrations varied between below detection limit to 0.179 Bq kgÿ1 , with a mean of 0.094 Bq kgÿ1 . In most of the liver and fat samples, the 239;240 Pu concentrations were barely above detection limit. The 226 Ra and 228 Ra concentrations in all the biological samples are reported in Table 1. The 226 Ra and 228 Ra concentrations in bivalves varied between below detection limit to 82.3 Bq kgÿ1 and below detection limit to 67.1 Bq kgÿ1 , respectively. The corresponding values in isopods vary between below detection limit to 5.0 Bq kgÿ1 and below detection limit to 9.7 Bq kgÿ1 , respectively. The 228 Ra concentrations in all the amphipods, mussel, fat and liver samples are below detection limit, while the 226 Ra concentrations vary between below detection limit to 19.0 Bq kgÿ1 .


Concentrations of 238 Pu, 239;240 Pu, 137 Cs and excess 210 Pb in sur®cial sediments from the Pechora Sea The concentrations of 238 Pu, 239;240 Pu, 137 Cs and excess 210 Pb ( total 210 Pb±226 Ra) for 27 sur®cial sediment samples from the Pechora Sea are given in Table 2. The

geographical distributions of 239;240 Pu and 137 Cs are plotted in Figs. 2 and 3, respectively. In sur®cial sediment samples (upper 3 cm) of the Pechora Sea, the 239;240 Pu concentrations varied between 38 and 877 m Bq kgÿ1 , with a mean of 193 m Bq kgÿ1 . The corresponding

TABLE 2 Water depths, locations, and concentrationsa of Station

Location

Water depth (m)

1 2 3 4 5 6 7 8 10 11 12 15 17 18 18 19 19 20 21 22 23 24 25 26 27 29 30

68°39.690 N±48°44.390 E 68°46.230 N±51°43.450 E 69°07.990 N±53°24.560 E 69°02.530 N±55°25.690 E 69°03.980 N±57°20.730 E 69°26.200 N±58°38.670 E 69°32.310 N±56°52.310 E 69°32.170 N±55°50.990 E 69°45.190 N±53°37.570 E 69°55.900 N±51°45.320 E 70°31.860 N±50°13.240 E 69°03.690 N±54°48.860 E 69°21.120 N±55°53.150 E 69°01.640 N±55°43.660 E 69°01.640 N±55°43.660 E 68°58.920 N±56°29.410 E 68°58.920 N±56°29.410 E 69°11.970 N±56°33.990 E 69°25.900 N±57°37.480 E 69°09.800 N±58°23.670 E 68°48.340 N±57°19.860 E 69°39.890 N±55°49.190 E 68°27.620 N±55°00.080 E 68°30.180 N±54°34.510 E 68°33.740 N±55°08.510 E 68°39.870 N±55°49.170 E 68°50.510 N±55°48.990 E

28 25 22 11 13 15 21 34 72 85 88 13 19 11 11 13 13 14 24 17 8 7 7 7 10 8 20

a

238

Pu,

239;240

239;240

Pu,

137

Cs, and excess

Pu (´10ÿ3 Bq kgÿ1 ) 142.2 16.7 173.3 17.5 51.7 10.5 43.3 8.5 80.5 11.2 72.6 10.4 99.0 10.2 243.9 19.6 877.2 53.0 843.0 96.6 383.5 28.5 54.5 5.7 80.9 8.3 61.3 12.1 613.8 34.4 129.8 15.9 113.3 13.3 49.3 9.5 195.5 20.9 104.8 11.2 57.6 12.4 179.6 21.0 98.6 14.5 106.5 16.7 142.6 14.7 184.6 19.5 113.5 14.1

238

210

Pb in sur®cial sediment samples from the Pechora Sea.

Pu (´10ÿ3 Bq kgÿ1 ) 7.0 5.0 5.0 5.0 BD BD 2.0 4.0 BD 3.0 3.0 6.0 3.0 28.0 6.0 17.0 21.0 15.0 5.0 3.0 3.0 2.0 7.0 BD 24.0 5.0 7.0 4.0 4.0 3.0 BD 5.0 5.0 BD BD 4.0 7.0 BD BD BD BD 2.0 3.0

137

Cs (Bq kgÿ1 )

2.48 0.44 4.02 0.51 0.44 0.38 BD BD 2.26 0.51 BD 2.89 0.56 9.56 0.70 5.01 0.74 1.57 0.47 BD BD BD 9.92 0.65 1.11 0.51 0.90 0.47 BD 2.08 0.47 BD 1.42 0.58 9.38 1.21 10.4 0.75 3.57 0.74 8.54 0.70 7.68 0.66 1.23 0.46

Excess

210

Pb (Bq kgÿ1 )

2.57 2.2 BD 0.690 3.0 BD 17.2 5.0 8.93 2.6 1.27 2.7 11.2 3.4 75.8 4.8 BD 34.1 3.9 BD 3.48 3.2 8.95 2.8 10.2 3.6 18.4 3.2 BD BD 12.0 3.6 5.39 5.2 BD 37.8 6.3 BD 7.11 4.9 13.9 4.4 15.0 3.9 9.79 2.6

BD ± Below detection limit.

Fig. 2 Geographical distribution of 239;240 Pu concentrations in the sediments from the Pechora Sea.

Fig. 3 Geographical distribution of ments from the Pechora Sea.

137

Cs concentrations in the sedi-

833

Marine Pollution Bulletin

values for 137 Cs varied between below detection limit to 10.4 Bq kgÿ1 , with a mean of 3.13 Bq kgÿ1 . In 11 out of 27 sediment samples, the 238 Pu concentrations were below detection limit.

decrease between the mid 1970s and the early 1990s (Valette-Silver and Lauenstein, 1995). The concentrations of radiocesium and Pu in biological samples from the Ob and Yenisey Rivers and Kara Sea likely re¯ect lower levels of radionuclides in the environmental waters, where these organisms lived. The presence of 226 Ra and 228 Ra in biological samples is likely due to the uptake from the water column during the skeletal growth. The 137 Cs, 239;240 Pu, 226 Ra and 228 Ra concentrations in wormtubes are much higher than all other biological samples and are attributed to detritus present in these samples.

Discussion Some of the suggested major mechanisms by which radionuclides are accumulated by bivalves include ingestion of particulate material from seawater, ingestion of radionuclide-laden food organisms, complexation of radionuclide by organic functional groups, adsorption onto membrane surfaces, and incorporation of ions across membranes into important body parts (Eyman and Trabalka, 1980). The 239;240 Pu concentrations in bivalves are higher than the values reported for the US coastlines, 0.016 0.018 Bq kgÿ1 (range: 0.0026±0.088 Bq kgÿ1 , Valette-Silver and Lauenstein, 1995). The dissolved 239;240 Pu concentrations in the Ob and Yenisey Rivers and Kara Sea (0.003 m Bq kgÿ1 ) are lower than in most other ocean basins (Schwantes, unpublished results; Aarkrog, 1988). With our present data, it is not possible to unequivocally de®ne the source(s) of the higher concentration of Pu and radiocesium in some of these biological samples from the Ob and Yenisey Rivers and the Kara Sea. However, these elevated concentrations are likely due to detritus associated with the samples as these biological samples were not cleaned prior to sample analysis for 239;240 Pu. The 137 Cs concentrations in bivalve samples can be compared to values reported for the US coastlines, 0.017±0.4 Bq kgÿ1 (Valette-Silver and Lauenstein, 1995). Here again, the higher concentrations in some of our samples are likely due to detritus present in our samples. It is not clear what other factors could lead to somewhat elevated concentrations of radiocesium and Pu in some of the bivalve samples. It has been shown by earlier works that estuarine organisms, especially bivalve molluscs, can be particularly sensitive indicators of radioactivity in the environment (Schelske et al., 1965). More recently it was reported that 137 Cs concentrations in bivalves along the west coast are higher compared to the east and Gulf coasts of the United States. On the contrary, 239;240 Pu concentrations along the east coast are higher than the west and Gulf coasts (Valette-Silver and Lauenstein, 1995). In addition, the concentrations of 137 Cs and 239;240 Pu in bivalves showed a statistically signi®cant

Concentration factors and transfer factors Even though signi®cant uptake of radionuclides by biological organisms may not take place directly from the water but indirectly via nutritious particle pathways, concentration factor provides some information about the uptake mechanism of the radionuclides. The concentration factor (CF, also known as concentration ratio) is de®ned as the ratio of the concentration of a nuclide in the biological sample (Bq kgÿ1 ) to that in the source (here seawater, Bq kgÿ1 ; e.g., Ravera and Riccardi, 1997). It must be pointed out that this de®nition is simplistic since the aquatic organisms commonly accumulate the radionuclides from a variety of sources, including water, suspended or deposited sediments. The recently measured dissolved 239;240 Pu concentration in the Ob, Yenisey Rivers and Kara Sea is 3 ´ 10ÿ3 m Bq kgÿ1 and the corresponding 137 Cs concentration is 0.5 m Bq kgÿ1 (Schwantes, unpublished data). Taking the following concentrations of 137 Cs (Isopod 1.59 Bq kgÿ1 ; Bivalve 7.0 Bq kgÿ1 ) and 239;240 Pu (Isopod 80 m Bq kgÿ1 and Bivalve 179 m Bq kgÿ1 ), the concentration factors for 137 Cs and 239;240 Pu are 3:2 103 and 2:7 104 , respectively, for isopods and 1:4 104 and 6:0 104 , respectively, for bivalves (Table 3). Since the nuclide concentrations of the biological samples used in calculating the above concentration factors are maximum values, the CFs are upper limits as well. In addition, these values are likely upper limits since the biological samples were not cleaned from detritus impurities before analysis. Concentrations of 210 Pb, 137 Cs and 239;240 Pu in sediment samples The reactor-derived radionuclides in the Pechora Sea are derived from the fallout of weapons testing,

TABLE 3 Concentration factorsa (CF) for Sample Isopods Bivalves a

137

Cs (Bq kgÿ1 ) 1.59 7.0

239;240

137

Cs, and

Pu (m Bq kgÿ1 ) 80 179

239;240

Pu in isopods and bivalves. 137

Cs CF (´104 ) 0.3 1.4

239;240

Pu CF (´104 ) 2.7 6.0

CF [concentration of a nuclide in the biological sample, Bq kgÿ1 ]/[concentration in the source, Bq kgÿ1 , here seawater]; the assumed values for Pu and 137 Cs concentration in seawater in this area are: 137 Cs 0.5 m Bq kgÿ1 and 239;240 Pu 3 ´ 10ÿ3 m Bq kgÿ1 (see discussion in the text).

239;240

834

Holm et al. (1986) Baskaran et al. (1995, 1995) This paper

Holm et al. (1986)

Holm et al. (1986)

British Nuclear Fuels (1985) Calmet and Guegueniat (1985) Mount et al. (1993) Aarkrog (1988) Holm et al. (1986)

1980 1993 1994 Numbers in parenthesis denote the range of values reported. a

79.2±82.3°N; 25.3±33.7°E Ob, Yenisey Rivers and Kara Sea Pechora Sea

10 55 27

1980 12

Sur®cial sediments Sur®cial Sediments Sur®cial Sediments

Water samples-particulate phase

Terrestrial samples (Lichen, Moss, Soil)

41

41

1980

0.29 0.02 0.46 0.26±0.49 0.021 (0.030) 0.060 0.010 (0.037 0.0160± 0.077 0.012) 0.052 0.018 (0.019 0.025± 0.083 0.066 0.042 0.007 (0.036 0.005± 0.055 0.005) 0.062 0.006 0.036 0.003 (0.009±0.065) 0.030 (0.015±0.056) 1978±1984 1962±1982 ) 1982 1980 7 7 Estimate

Irish Sea English Channel Kara Sea Northern hemisphere Barents, Greenland, Norwegian and North Seas Barents, Greenland, Norwegian and North Seas Svalbard Isfjord, NE Greenland Euents from Sella®eld Euents from Cap de la Hague Dumped reactors in Kara Sea Global fallout (+SNAP) Water samples-dissolved phase

238 Pu/239;240 Pua Activity ratios in 1994

Year of collection Number of samples Location Nature of sample

TABLE 4

Pu/239;240 Pu activity ratios in nuclear euents, dissolved particulate phases, sur®cial sediments and terrestrial samples in the Arctic Region. 238

including transport from the area receiving close-in fallout in shallow, coastal waters o southern Novaya Zemlya, riverine inputs from the erosion and leaching of continental soils and nuclear waste sites, and transport from areas receiving nuclear euents directly discharged into the sea (such as northeastern Irish Sea from Sella®eld, UK, Murray and Kautsky, 1977; Kershaw and Baxter, 1993). Direct fallout from the Novaya Zemlya nuclear test site and underwater nuclear explosions and dumping of nuclear wastes in the shelf areas could be other potential sources. It has been documented that a total of 132 nuclear explosions were conducted at the nuclear weapons tests site at Novaya Zemlya, out of which 87 were conducted in the atmosphere, 3 underwater in Chernaya Bay on Novaya Zemlya and 43 underground (Israel et al., 1993). Of these 132 explosions, 1 ground and 3 underground explosions in Chernaya Bay have contaminated the local area. A signi®cant portion of radiocesium and a small portion of the dissolved Pu that are released by the Sella®eld reprocessing plant is transported via Scottish waters to the North Sea, Norwegian Sea, Barents Sea, Arctic Ocean and Greenland (Murray et al., 1978, 1979; Livingston et al., 1982, 1984; Aarkrog et al., 1983, 1984; McKay et al., 1986; Holm et al., 1986; Hallstadius et al., 1986; Dahlgaard et al., 1986, 1991). It has been shown that the 137 Cs released from European reprocessing facilities is eectively transported by the Gulf Stream into the Barents and Greenland Seas (Holm et al., 1986). Another potential source of radiocesium and Pu to the Russian Arctic is from the release of radioactive contaminants from the nuclear materials that have been dumped since 1959 in the Kara and Barents Seas (Yablokov et al., 1993 as cited in P®rman et al., 1993). In sur®cial sediment samples (upper 3 cm) of the Pechora Sea, the mean concentration (from 27 samples) of 239;240 Pu, 193 m Bq kgÿ1 , is lower than the average value (107 samples) of 247 m Bq kgÿ1 of sediment samples from the Ob and Yenisey Rivers and Kara Sea. The mean sur®cial sediment concentration of 137 Cs in Pechora Sea, 3.13 Bq kgÿ1 is also lower than the corresponding value in the Ob, Yenisey Rivers and Kara Sea, of 14.9 Bq kgÿ1 . The lower values of the 137 Cs and 239;240 Pu concentrations in sur®cial sediments from the Pechora Sea can be attributed to dierences in grain-size parameters between the two sedimentary regimes, as the Pechora Sea sediments are more sandy than the Ob, Yenisey Rivers and Kara Sea sediments (Bryant, personal communication). Recently, Cooper et al. (1998) reported widely varying concentrations of radiocesium in the sediments entrained in Arctic Ocean sea ice and attributed the variations in 137 Cs concentrations to geographical origin of the sediment, rather than mineral composition, or physical processes that increase the content of ®ne clays in sediments. Recent results also indicate that ®ne grain sediments are transported several

Source


835

Marine Pollution Bulletin

hundred km from the estuarine regions to the deep Arctic basin through ice-rafting (Krishnamurthy et al., 2000, in review; Cooper et al., 1998; Landa et al., 1998; Nies et al., 1999). The excess 210 Pb concentration varied between below detection limit and 76 Bq kgÿ1 . This variation is also likely due to the dierences in grain sizes. The 238 Pu/239;240 Pu activity ratios The activity and atomic ratios of Pu isotopes have been used to obtain information on the sources and pathways of these nuclides (Koide et al., 1975, 1979; Beasley et al., 1982; Holm et al., 1986; Buesseler and Sholkovitz, 1987). The 238 Pu/239;240 Pu activity ratios of the global fallout for the Northern and Southern hemispheres are distinctly dierent from the close-in fallout and nuclear euents from the reprocessing plants. It has been estimated that the 238 Pu/239;240 Pu activity ratio of the euents from Sella®eld was 0.29 (British Nuclear Fuels, 1985) while the euents from Cap De la Hague between the years 1962±1982 was 0.46 (Calmet and Guegueniat, 1985). The 238 Pu/ 239;240 Pu activity ratio in the dumped reactors in the Kara Sea was estimated to be 0.26±0.49 (Mount et al., 1993). The activity ratios in various samples from the Arctic are summarized in Table 4. The expected 238 Pu/ 239;240 Pu activity ratio resulting from the global fallout (including SNAP) for the year 1994 is 0.030 (Table 3). The mean of the activity ratios for 16 samples, given in Table 1, is 0.030. The concentration of 238 Pu is plotted against 239;240 Pu in Fig. 4. The slope value, 238 Pu/239;240 Pu, 0.030 is comparable to the value expected for the global fallout in the Northern Hemisphere. Thus, it appears that virtually all of the Pu is derived from the global fallout, and the amount of Pu derived from close-in fallout and submerged nuclear reactors in the connected ocean basins is negligible.

Similar conclusions have been arrived by Valette-Silver et al. (1999).

Conclusions We have measured the 137 Cs, 238 Pu and 239;240 Pu concentrations from the sur®cial sediments of the Pechora Sea, as well as biological samples from the Ob and Yenisey Rivers and Kara Sea, to quantitatively evaluate the contribution of Pu from the nuclear reactors dumped in the Kara Sea. From this present investigation, the following conclusions are drawn. 1. The 239;240 Pu concentrations in the sur®cial sediments (upper 3 cm) of the Pechora Sea varied from 38 to 877 m Bq kgÿ1 , with a mean of 193 m Bq kgÿ1 . The 238 Pu concentrations in these sediments varied between below detection limit and 28 m Bq kgÿ1 . The corresponding values for 137 Cs varied between below detection limit and 10.4 Bq kgÿ1 , with a mean of 3.13 Bq kgÿ1 . These mean values of 137 Cs and 239;240 Pu are lower than the average values determined for the sediments from the Ob and Yenisey Rivers and Kara Sea. 2. The 238 Pu/239;240 Pu activity ratios in the sur®cial sediment samples of the Pechora Sea varied between 0.015 and 0.056. The best-®t-line between 238 Pu and 239;240 Pu concentration in these samples yields an activity ratio of 0.035. Comparing this value with the published values on the European nuclear euents discharged into the coastal waters, fallout values of the nuclear weapons tests, and the estimated activity ratios in the dumped reactors in Kara Sea, we conclude that there is virtually no detectable input from either the European nuclear euents or from the dumped nuclear reactors in the Kara and Barents Sea. 3. In those biological samples that contained measurable 137 Cs and 239;240 Pu concentrations from the Ob, Yenisey Rivers and Kara Sea, the mean concentrations of these nuclides are generally higher than those reported for the east, west and Gulf coasts of the US. This elevated concentration is attributed to the detritus impurities in the biological samples. This research was funded by the US Oce of Naval Research (Grant # N00014-93-1-1195).

Fig. 4

836

238

Pu concentrations are plotted against 239;240 Pu concentrations for 16 surface sediment samples (upper 3 cm) collected from the Pechora Sea. The slope value, 0.030, is close to the value expected from the nuclear weapons test fallout (for the year 1993), 0.030, for the Northern hemisphere.

Aarkrog, A. (1988) Worldwide data on ¯uxes of 239;240 Pu and 238 Pu to the oceans. In Inventories of selected radionuclides in the ocean, IAEA-TECDOC-481, 103±138. Aarkrog, A.,Dahlgaard, H., Hallstadius, L., Hansen, H. and Holm, E. (1983) Radiocesium from Sella®eld euents in Greenland waters. Nature 303, 49±51. Aarkrog, A., Dahlgaard, H. and Nilsson, K. (1984) Further studies of plutonium and americium at Thule, Greenland. Health Physics 46, 29±44. Baskaran, M., Kelley, J. M., Naidu, A. S. and Holleman, D. F. (1991) Environmental radiocesium in subarctic and Arctic following Chernobyl. Arctic 44 (4), 346±350. Baskaran, M., Murphy, D. J., Santschi, P. H., Orr, J. C. and Schink, D. R. (1993a) A method for rapid in situ extraction and laboratory determination of Th, Pb, and Ra isotopes from large volumes of seawater. Deep-Sea Research 40, 849±865.

Volume 40/Number 10/October 2000 Baskaran, M., Coleman, C. H. and Santschi, P. H. (1993b) Atmospheric depositional ¯uxes of 7 Be and 210 Pb at Galveston and College Station, Texas. Journal of Geophysical Research 98, 20,555± 20,571. Baskaran, M., Asbill, S., Santschi, P. H., Davis, T., Brooks, J. M., Champ, M. A., Makeyev, V. and Khlebovich, V. (1995) Distribution of 239;240 Pu concentrations in sediments from the Ob, Yenissey Rivers and the Kara Sea. Applications of Radiation Isotope 11, 1109±1119. Baskaran, M., Asbill, S., Santschi, P. H., Davis, T., Brooks, J. M., Champ, M. A., Adkinson, D., Colmer, M. R. and Makeyev, V. (1996) Pu, 137 Cs and 210 Pbexcess in Russian arctic sediments. Earth and Planetary Science Letters 140, 243±257. Beasley, T. M., Carpenter, R. and Jennings, C. D. (1982) Plutonium, 241 Am and 137 Cs ratios, inventories and pro®les in Washington and Oregon continental shelf sediments. Geochimica et Cosmochimica Acta 46, 1931±1946. British Nuclear Fuels. (1985) Annual report on radioactive discharges and monitoring of the environment 1984 (and earlier years reports) Risley, Warrington, Cheshire, UK. Buesseler, K. O. and Sholkovitz, E. R. (1987) The geochemistry of fallout plutonium in the North Atlantic: 240 Pu/239 Pu ratios and their signi®cance. Geochimica et Cosmochimica Acta 51, 2623±2637. Calmet, D. and Guegueniat, P. (1985) Les Rejets d'Euents liquides radioactifs du Centre de Traitement des Combustibles irradies da la Hague (France) et l'Evolution radiologique du Domaine marin. Annex 2 in Behaviour of Radionuclides redu Domaine marin. Annex 2 in Behaviour of Radionuclides released to Coastal Waters. IAEA-TECDOC-329, Vienna, pp. 111±144. Cooper, L. W., Larsen, I. L., Beasley, T. M., Dolvin, S. S., Grebmeier, J. M., Kelley, J. M., Scott, M. and Johnson-Pyrtle, A. (1998) The distribution of radiocesium and plutonium in sea ice-entrained sediments in relation to potential sources and sinks. Journal of Environmental Radioactivity 39, 279±303. Dahlgaard, H., Aarkrog, A., Hallstadius, L., Holm, E. and Rioseco, J. (1986) Radiocesium transport from the Irish Sea via the North Sea and the Norwegian Coastal Current to East Greenland. Rapports et Proces-Verbaux des Reunions, Conseil International pour l' Exploration de la Mer 186, 70±79. Dahlgaard, H., Chen, Q. J. and Neilsen, S. P. (1991) Radioactive tracers in the Greenland Sea. In Radionuclides in the Study of Marine Processes, eds. P. J. Kershaw and D. S. Woodhead, pp. 12± 22. Elsevier, Amsterdam. Eyman, L. D. and Trabalka, J. R. (1980) Patterns of transuranic uptake by aquatic organisms: consequences and implications. In Transuranic Elements in the Environment, ed. W. C. Hanson, pp. 612±624. Technical Information Center, US Department of Energy. Hallstadius, L., Aarkrog, A., Dahlgaard, H., Holm, E., Boelskifte, S., Duniec, S. and Persson, B. (1986) Plutonium and americium in Arctic waters, the North Sea and Scottish and Irish coastal zones. Journal of Environmental Radioactivity 4, 11±30. Holm, E., Aarkrog, A., Ballestra, S., and Dahlgaard, H. (1986) Origin and isotopic ratios of plutonium in the Barents and Greenland Seas. Earth and Planetary Science Letters 79, 27±32. Israel, Y. A., Tsiban, A. V. and Vakulovsky, S. M. (1993) Radioactivity and environmental problems for the Seas and Ocean. In Proceedings of the Radioactivity and Environmental Security in the New Research and Policy Priorities in the Arctic and North Atlantic, pp. 65±78. Woods Hole Oceanographic Institution, Massachusetts, USA. Kershaw, P. J. and Baxter, A. (1993) Sella®eld as a source of radioactivity to the Barents Sea. In Proceedings of the Radioactivity and Environmental Security in the New Research and Policy Priorities in the Arctic and North Atlantic, pp. 91±103. Woods Hole Oceanographic Institution, Massachusetts, USA. Koide, M., Grin, J. J. and Goldberg, E. D. (1975) Records of plutonium in marine and terrestrial samples. Journal of Geophysical Research 80, 4153±4162. Koide, M., Michel, R. Goldberg, E. D., Herron, M. M. and Langway, C. C. (1979) Depositional history of arti®cial radionuclides in the Ross Ice Shelf, Antarctica. Earth and Planetary Science Letters 44, 205±223. Kressin, I. K. (1977) Electrodeposition of plutonium and americium for high resolution spectrometry. Analytical Chemistry 49, 842± 846.

Krishnaswami, S. and Sarin, M. M. (1976) Procedure for the simultaneous determination of Th, Pu, Ra isotopes, 210 Pb, 55 Fe, 32 Si and 14 C in marine suspended phases. Analytica Chimica Acta 83, 143±156. Landa, E. R., Reimnitz, E., Beals, D. M., Pochkowski, J. M., Winn, W. G. and Rigor, I. (1998) Transport of Cs-137 and Pu-239,240 with ice-rafted debris in the Arctic Ocean. Arctic 51, 27±39. Livingston, H. D., Bowen, V. T. and Kuperman, S. L. (1982) Radionuclides from Windscale discharges, I. Non-equilibrium tracer experiment in high latitude oceanography. Journal of Marine Research 40, 253±272. Livingston, H. D., Kupferman, S. L., Bowen, V. T. and Moore, R. M. (1984) Vertical pro®le of arti®cial radionuclide concentrations in the Central Arctic Ocean. Geochimica et Cosmochimica Acta 48, 2195± 2203. Marshall, J. S., Waller, B. J. and Yaguchi, E. M. (1974) Plutonium in the Laurentian Great Lakes: Food Chain Relationships, In Proceedings of the XIX Congress Association of Limnology. Winnipeg, Manitoba, Canada, 23±28 August 1974. McKay, W. A., Baxter, M. S., Ellett, D. J. and Meldrum, D. T. (1986) Radiocesium and circulation patterns west of Scotland. Journal of Environmental Radioactivity 4, 205±232. Mount, M. E., Layton, D. W., Schwertz, N. L., Anspaugh, L. R. and Robison, W. L. (1993) Estimated inventory of radionuclides in former Soviet Union Naval Reactors dumped in the Kara Sea and their associated health risk. In Proceedings of the Radioactivity and Environmental Security in the New Research and Policy Priorities in the Arctic and North Atlantic, pp. 91±103. Woods Hole Oceanographic Institution, Massachusetts, USA. Murray, C. N. and Kautsky, H. (1977) Plutonium and americium activities in the North Sea and German coastal regions. Estuarine and Coastal Marine Science 5, 319±328. Murray, C. N., Kautsky H., Hoppenheit, M. and Domain, M. (1978) Actinide activities in water entering the northern North Sea. Nature 276, 225±230. Murray, C. N., Kautsky, H. and Eicke, H. F. (1979) Transfer of actinides from the English Channel into the Southern North Sea. Nature 276, 225±230. Nies, H., Harms, I. H., Karcher, M. J., Dethle, D. and Bahe, C. (1999) Anthropogenic radioactivity in the Arctic Ocean ± review of the results from the joint German project. Science of the Total Environment 238, 181±191. P®rman, S. L., Eicken, H. and Grabitz, D. (1993) Potential transport of radionuclides and other pollutants by arctic sea ice. In Proceedings of the Radioactivity and Environmental Security in the New Research and Policy Priorities in the Arctic and North Atlantic, pp. 267±277. Woods Hole Oceanographic Institution, Massachusetts, USA. Pillai, K. C. and Mathew, E. (1976) Plutonium in the aquatic environment: its behavior, distribution and signi®cance. In Transuranium Nuclides in the Environment, Symposium Proceedings, pp. 25±45. San Francisco, STI/PUB/410, International Atomic Energy Agency, Vienna. Ravera, O. and Riccardi, N. (1997) Biological monitoring with organisms accumulator of pollutants. Marine Chemistry 58, 313± 318. Santschi, P. H., Li, Y.-H., Adler, D. M., Amdurer, M., Bell, J. and Nyeler, U. P. (1983) The relative mobility of natural (Th, Pb and Po) and fallout (Pu, Am, Cs) radionuclides in the coastal marine environment: results from model ecosystems (MERL) and Narragansett Bay. Geochimica et Cosmochimica Acta 47, 201±210. Schelske, C. L., Smith, W. D. C. and Lewis, J. (1965) In Radioassay, ed. T. R. Rice, pp. 12±14. Annual Report of the Bureau of Commercial Fisheries Radiobiological Laboratory, Beaufort, N.C. For the ®scal year ending 30 June 1965. US Fish and Wildlife Service, Circ. 244. Smith, J. N., Ellis, K. M., Polyak, L. Ivanov, G. Forman, S. L. and Moran, S. B. (2000) 239;240 Pu transport into the Arctic Ocean from underwater nuclear tests in Chernaya Bay, Novaya Zemlya. Continental Shelf Research 20, 255±279. Valette-Silver, N. J. and Lauenstein, G. G. (1995) Radionuclide concentrations in bivalves collected along the coastal United States. Marine Pollution Bulletin 30, 320±331. Valette-Silver, N. J., Hameedi, M. J. Efurd, D. W. and Robertson, A. (1999) Status of the contamination in sediments and biota from the western Beaufort Sea (Alaska). Marine Pollution Bulletin 38, 702± 722.

837

Marine Pollution Bulletin Yablokov, A. V., Karasev, V. K., Rumyantsev, V. M., Kokeyev, M. Ye., Petrov, O. I., Lytsov, V. N., Yemelyanenkov, A. F. and Rubtsov, P. M. (1993) Facts and Problems Related to Radioactive

838

Waste Disposal in the Seas Adjacent to the Territory of the Russian Federation. Oce of the President of the Russian Federation, Moscow, p. 72.