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Artificial Radionuclides in the East Sea (Sea of Japan) Proper and Peter the Great Bay
PII: S0025-326X(99)00107-1
Marine Pollution Bulletin Vol. 38, No. 10, pp. 933±943, 1999 Ó 1999 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0025-326X/99 $ - see front matter
Arti®cial Radionuclides in the East Sea (Sea of Japan) Proper and Peter the Great Bay GI-HOON HONG *, SUK-HYUN KIM , SANG-HAN LEE , CHANG-SOO CHUNG , ALEXANDER V. TKALINà, EMILIA L. CHAYKOVSKAYà and TERRY F. HAMILTON§ Korea Ocean Research and Development Institute, Marine Biogeochemistry and Isotopes, Ansan P.O. Box 29, Seoul 425-600, South Korea àFar Eastern Regional Hydrometeorological Research Institute, 24 Fontannaya St., Vladivostok 690600, Russian Federation §Lawrence Livermore National Laboratory, P.O. Box 808 L-453, Livermore, CA 94550, USA
Over the past decade there has been growing concern over dumping of radioactive waste in the East Sea (Sea of Japan) proper and adjacent coastal waters. Here we show that the evolution of activity concentrations of 137 Cs and 239240 Pu in the East Sea, and existing levels of radioactive contamination in waters, sediments and biota from Peter the Great Bay (Russia) can be largely attributed to global fallout deposition. The former sequence of data includes results from the AWARES cruise (Active Watch of Arti®cial Radionuclides in the East Sea) conducted between 26 October and 1 November 1993 about ten days after 14 GBq of liquid radioactive waste was dumped into the East Sea. The activity concentration of 137 Cs and 239240 Pu in surface waters ranged between 2.7±3.5 Bq mÿ3 and 3.5± 20.8 mBq mÿ3 , respectively, and were not dierent to levels observed during August 1993 prior to the Russian dumping operation in October. Isotopic ratios also indicate the absence of any signi®cant anthropogenic radioactive contamination in the region other than from global fallout deposition. Ó 1999 Elsevier Science Ltd. All rights reserved. Keywords: arti®cial radionuclides; Peter the Great Bay; East Sea (Sea of Japan).
Introduction The widespread introduction of arti®cial radioactivity into the marine environment arose initially from detonation of nuclear weapons in the atmosphere (Hamilton et al., 1996). Among products of nuclear reactions, ®ssion products, 90 Sr (t1=2 28.82 yr) and 137 Cs *Corresponding author. Tel.: +82-345-400-6180; fax: +82-345-4084493; e-mail: [email protected]
(t1=2 30.17 yr) and neutron induced or unreacted materials of 238 Pu (t1=2 87.7 yr), 239 Pu (t1=2 24 100 yr) and 240 Pu (t1=2 6571 yr) were investigated here. The selection of these radionuclides was based on their wellknown behaviour and signi®cance of radiological concern in the marine environment. Local contributions in the Paci®c Ocean include close-in fallout deposition from US and French Paci®c test programs and dumping of nuclear wastes (Hamilton et al., 1996). Over the past 30 yr about 443 TBq of liquid and 141 TBq of solid wastes were dumped in the East Sea (Sea of Japan), and 0.01 and 113 TBq of liquid and solid wastes, respectively, in the north-west Paci®c Ocean o Kamchatka Peninsula (Yablokov, 1993). Extensive studies of marine radioactivity have been conducted in the Russian Arctic (Hamilton et al., 1994; Livingston, 1995; Morgan and Codispoti, 1995; Baskaran et al., 1996; Povinec et al., 1997) but far less international attention has been given to the Russian Far East. Since the early 1960s the Institute of Experimental Metrology (now SPA Typhoon, Obinsk), the Russian Academy of Sciences, the Russian Navy and the Far Eastern Regional Hydrometeorological Research Institute (FERHRI) have supported on-going national radionuclide monitoring programmes in north-west Paci®c as well as in coastal waters o Primorye, the Sakhalin Island and Kamchatka Peninsula. Also, over the past two decades Japanese scientists have published a large quantity of data on arti®cial radionuclides in waters and sediments from the western Paci®c (Hirose et al., 1993; Nagaya and Nakamura, 1987, 1984, 1981; Miyao et al. 1998; Hirose et al., 1998). More recently Korean researchers have conducted studies on marine radioactivity around the Korean Peninsula by Korea Ocean Research and Development Institute (KORDI) and others (Hong et al., 1996a; Kang et al., 1997; Lee et al. 1998). In this paper we report results from investigations conducted during 1993±96 933
Marine Pollution Bulletin
and compare these data to assess local sources and trends in regional marine radioactivity. Concentration data from these isotopes are also valuable to establish a baseline reference for future studies in dose assessment and bioaccumulation in the marine environment. Study area The East Sea (Sea of Japan) is a typical example of a marginal sea and is located in the north-western Paci®c Ocean. There are three deep basins of 2000±4000 m depth (the Japan, Yamato, and Ulleung Basins) separated by the Korea Plateau and Yamato Ridge that rise to within 500 m below sea level (Fig. 1). The East Sea opens to the East China Sea, Sea of Okhotsk and Northwest Paci®c Ocean only through the four narrow sills shallower than 150 m. The vertical ventilation in the deep basin takes about 100 yr and waters are replaced every 1000 yr (Tsunogai et al., 1993). Recent sediments appear to be primarily derived from a hemipelagic source. While there are no main rivers along the coast of Primorye and the Korean Peninsula, signi®cant amounts of sediments are supplied to the coastal regions by Japanese rivers (Hong et al., 1997). Peter the Great Bay is of special interest because there are many nuclear facilities located in this region. Shore-
based sites for storage of nuclear waste for the Russian Paci®c Fleet are located near Bolshoy Kamen east of Vladivostok (Fig. 2). Also, there are several decommissioned nuclear submarines stored in the region (Handler, 1995). The Russian Paci®c Fleet has a total inventory of 16 000 m3 of solid nuclear waste and 5000 m3 of liquid waste in storage at the present time. About 70±90% of this waste is stored in the Primorsky Territory (Danilyan and Vysotsky, 1995). According to Danilyan and Vysotsky, approximately 2000 m3 of liquid and 5000 m3 of solid waste will be generated annually over the next 10±15 yr taking into account the anticipated ¯eet utilization schedule (3±4 PLA annually). Radioactive waste processing facilities in the region were due to be upgraded and expanded in March 1998 (International Maritime Organization News, 1997). It has also been reported that a nuclear accident occurring on 10 August 1985 contaminated coastal waters in Chazhma, Strelok and Ussuriysky bays with 60 Co (Yablokov, 1993). Long-term observations show that the spatial extent of 60 Co contamination is con®ned to the region due to the dynamic equilibrium between the processes of radionuclide migration and radioactive decay (t1=2 5.27 yr) (Yablokov, 1993; Danilyan and Vysotsky, 1995).
Fig. 1 Map of the sampling stations in the East Sea (Sea of Japan) during October (d) and August 1993 (s, Kang et al., 1997) and radioactive waste dump sites of the former Soviet Union and Russian Federation are shown here (Yablokov et al., 1993). JB, YB and UB stand for Japan, Yamato and Ulleung basins in the sea.
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Fig. 2 Map of sampling stations in Peter the Great Bay.
Materials and Methods Twenty two surface water samples were collected between 26 October and 1 November during the AWARES (Active Watch of Arti®cial Radionuclides in the East Sea) cruise to the East Sea (Sea of Japan) on board the R/V Onnuri (Fig. 1). Water samples were collected using a submersible pump and stored in 20 l polyethylene bottles without ®lteration after acidi®cation with 50 ml of 6 M HCl. In Peter the Great Bay, samples of seawater, sediment and mussel were collected by Russian scientists on board the FERHRI research vessels R/V Akademik Shokalsky during 1994 and the R/V Hydrobiologist during 1996 (Fig. 2). Surface water samples were collected using submersible pump and ®ltered on board. The ®ltered water samples were treated with potassium ferrocynide and sodium carbonate for co-precipitation of Cs and Sr isotopes (Joint Expedition, 1995). 90 Y counting were carried out with low background b counter after secular equilibrium between 90 Sr and 90 Y. 137 Cs were counted using a Russian gamma ray spectrometric system DGDK-80V-3. Bottom sediments were collected using a modi®ed Peterson grab and top 3cm sections were taken for analysis. Gravity cores were also collected from the centre of Amursky and Ussuriysky Bays, and sectioned into 2 cm intervals. All sediment samples were kept frozen until analysis.
KORDI analysed AWARES water samples for 137 Cs and 239240 Pu contents. Plutonium and Cs isotopes were preconcentrated on manganese dioxide and ammonium molybdate phosphate (AMP), respectively, with 242 Pu and stable Cs added as chemical yield tracers (Wong et al., 1994). The plutonium fraction was puri®ed by ionexchange, electroplated onto stainless steel discs and counted by alpha-spectrometry using PIPS detectors coupled to Canberra Series 35 multichannel analyser. The AMP fraction was dissolved and 137 Cs quanti®ed by high resolution gamma-spectrometry using a Canberra Series MCA 90 multichannel analyser. In the laboratory, sediment samples were dried and ground into a ®ne powder. Separate aliquots were used for the determination of plutonium isotopes. Concentrations of 90 Sr and Pu isotopes in the bottom sediments and Pu contents in mussels from Peter the Great Bay were also determined by KORDI. Mussel tissues were dried and Pu isotopes were isolated through successive acid digestion. The analytical procedures of 90 Sr, Pu isotopes were largely taken from Wong et al. (1994).
Results and Discussion The evolution of 137 Cs, 239240 Pu and 90 Sr in the East Sea (sea of Japan) proper Measured 137 Cs activity concentrations in the East Sea during 26 October±1 November 1993 ranged from 2.6 to 935
Marine Pollution Bulletin TABLE 1 Distribution of 137 Cs and 239240 Pu concentrations in the surface waters of the East Sea (Sea of Japan) in the period of 26 October±1 November 1993 (AWARES cruise).a Location
Stn
1 2 3 4 A B C D E F G H I J K L M N O R S T a
Sampling date
Lat. (N)
Long. (E)
41o 00.00 39o 40.00 37o 00.00 38o 00.00 40o 40.00 40o 20.00 40o 00.00 39o 20.00 39o 01.25 38o 41.45 38o 21.45 38o 02.00 37o 40.45 37o 20.45 37o 15.00 37o 30.00 37o 45.00 37o 36.00 37o 12.40 36o 46.30 36o 16.30 35o 39.80
136o 10.00 134o 19.85 131o 00.00 129o 00.00 135o 45.00 135o 16.65 134o 48.15 133o 54.75 133o 30.00 133o 05.00 132o 40.00 132o 15.00 131o 50.00 131o 25.00 130o 30.00 130o 00.00 129o 30.00 129o 17.30 129o 35.00 129o 40.00 129o 42.50 129o 37.80
26 Oct Õ93 28 Oct Õ93 29 Oct Õ93 31 Oct Õ93 27 Oct Õ93 27 Oct Õ93 28 Oct Õ93 28 Oct Õ93 28 Oct Õ93 28 Oct Õ93 28 Oct Õ93 29 Oct Õ93 29 Oct Õ93 29 Oct Õ93 29 Oct Õ93 29 Oct Õ93 30 Oct Õ93 31 Oct Õ93 01 Nov Õ93 01 Nov Õ93 01 Nov Õ93 01 Nov Õ93
137
Cs (Bq mÿ3 )
3.01 0.14 3.11 0.16 3.02 0.26 3.04 0.16 2.86 0.21 2.97 0.21 3.02 0.24 2.83 0.27 3.20 0.18 3.12 0.27 2.60 0.20 3.37 0.15 3.51 0.15 2.96 0.27 3.21 0.27 2.67 0.16 ND 3.36 0.15 3.01 0.15 3.26 0.19 3.51 0.14 2.74 0.16
239240
Pu (mBq mÿ3 )
3.5 0.6 10.2 2.7 8.2 1.1 5.7 0.7 4.9 0.5 3.8 0.6 3.4 0.6 7.8 1.0 7.8 0.7 5.7 0.5 6.1 0.7 10.1 1.0 5.8 0.7 7.5 0.8 18.2 2.7 5.7 0.6 5.3 1.6 7.8 0.8 6.4 1.0 9.9 1.3 20.8 3.41 5.7 0.6
ND: not determined.
3.5 Bq mÿ3 (Table 1). These concentrations in surface waters have been compared with those obtained by Kang et al. (1997) during August 1993 (Fig. 3). These data provide some insight into the impact of the dumping incident of 17 October on the levels and distributions of arti®cial radionuclides in the sea. Some 14.1 GBq of liquid radioactive waste (137 Cs 76%; 90 Sr 21%; 60 Co 1.5%; 134 Cs 1.5%) were dumped into the area 9 in Fig. 1 (later reported by Danilyan and Vysotsky, 1995). If 2.1 ´ 108 Bq of 134 Cs was dumped at a point in the area 9 then 134 Cs will spread out about 27 ´ 109 m2 for 10 days (t) after the dumping, assuming the average eddy diusion coecient (D) of 108 cm2 sÿ1 in the sea, a characteristic distance for dispersal of material diusion can be determined as (Dt)1=2 (Lerman, 1979) and surface mixed layer of 20 m (Hong, unpublished data), then the maximum expected 134 Cs concentration would be 3.9 ´ 10ÿ4 Bq mÿ3 . This size of concentration would not be measurable for the current analytical method. As we observe from analyses of samples collected two months earlier (Fig. 3, Kang et al., 1997), there appears to be no signi®cant change in the temporal distribution of 137 Cs during these two observational periods. Consequently, there appears to have been no measurable impact of Russian dumping operations of 17 October 1993 on the prevailing distribution of 137 Cs in surface waters of the East Sea. Presumably this was related to the rapid dispersion and dilution of the dumped waste. These results were later con®rmed by the Japanese-Russian-Korean Joint Expeditions of 1994 and 1995 (Table 2). Furthermore, there appears to be no direct evidence of elevated levels of 137 Cs (or 90 Sr) in 936
surface waters near the nuclear waste dump sites declared by the Russian Federation in 1992 (Kang et al., 1997; Joint Expedition, 1995, 1997). Measured 239240 Pu concentrations in the East Sea during 26 October±1 November 1993 ranged from 3.4 to 20.8 mBq mÿ3 (Table 1). There appear to be no clear regional trends in these data. 239240 Pu activity concentrations in surface waters collected during August 1993 ranged between 7 and 10 mBq mÿ3 (Kang et al., 1997) and are comparable to results reported by Japanese researchers through 1975±1993 (Hirose et al., 1993; Miyake et al., 1988; Nagaya and Nakamura, 1987). The evolution in the concentration of 239240 Pu in surface waters of the sea proper have been summarized in Table 3 for the period between 1975 and 1995. However, our data (Table 1 and Fig. 4) along with the results from the 1994 and 1995 Japanese-Russian-Korean Joint Expeditions (Table 3 and references therein) show a higher range of values up to 25 mBq mÿ3 . The higher surface water 239240 Pu activity concentrations may result from upwelling of deep Pu-enriched waters leading to the breakdown of the seasonal thermocline during the late autumn and particle removal and remineralization processes (Hirose et al., 1996). Therefore, we believe that the observed changes in the temporal distribution of 239240 Pu can be attributed to oceanographic conditions (Seung and Yoon 1995), and are not necessarily related to impacts of dumping of radioactive waste. Nevertheless, according to long-term data from the Japanese Fisheries Agency and Maritime Safety Agency, 239240 Pu activity concentrations in surface waters around Japan have varied from below detection limit to 120 mBq mÿ3
Volume 38/Number 10/October 1999
Fig. 3 Distribution of 137 Cs (Bq mÿ3 ) in surface waters of the East/ Japan Sea (Sea of Japan) during October (d) and August 1993 (s, Kang et al., 1997).
TABLE 2 Temporal variation in Year
137
Cs (Bq mÿ3 ) in surface water of the East Sea (Sea of Japan).
Concentration
1975±1978 1976±1979 1980±1986 1984 1985 1987 1989 1990 1993 August, 1993 October, 1993 1994 1995
Reference
5.9±8.5 4.9±7.1 3.2±4.2 5.1 4.5±4.8 4.5 3.6±4.2 3.5±3.7 2.7±3.0 2.6±3.4 2.6±3.5 2.8±3.6 2.5±2.9
Miyake et al. (1988) Nagaya and Nakamura (1981) Nagaya and Nakamura (1987) Takeda and Misonou (1991), Japanese Takeda and Misonou (1991), Japanese Takeda and Misonou (1991), Japanese Takeda and Misonou (1991), Japanese Takeda and Misonou (1991), Japanese Hirose et al. (1993) Kang et al. (1997) This study Joint Expedition (1995) Joint Expedition (1997)
coast coast coast coast coast
TABLE 3 Temporal variation in Year 1975±1978 1980±1986 1986±1993 August 1993 October 1993 October 1994 October 1995
239240
Pu (mBq mÿ3 ) in surface water of the East Sea (Sea of Japan).
Concentration
Reference
4.4±14.4 6.7±7.4 1.1±9.7 7±10 3.5±20.8 8±25 3.8±16
Miyake et al. (1988) Nagaya and Nakamura (1987) Hirose et al. (1993) Kang et al. (1997) This study Joint Expedition (1995) Joint Expedition (1997)
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Marine Pollution Bulletin
Fig. 4 Distribution of 239240 Pu (mBq mÿ3 ) in surface waters of the East/Japan Sea (Sea of Japan) during October (d) and August 1993 (s, Kang et al., 1997).
through 1982±1994 (Joint Expedition, 1997), i.e., even higher values were observed (Table 3). Data on the concentration of 90 Sr in surface waters of the East Sea have been summarized in Table 4 for the period from 1964 to 1995. These data show a steady decrease in 90 Sr levels in surface waters consistent with trends observed in atmospheric fallout records following enactment of the atmospheric nuclear test ban treaty of 1963.
60
Co, 90 Sr, 137 Cs and 239240 Pu concentrations in waters and sediments from Peter the Great Bay 90 Sr concentrations in seawater during 1994 varied from 1.7 to 6.6 Bq mÿ3 . 137 Cs concentrations in seawater varied between 1.7 and 5.7 Bq mÿ3 (Table 5). In the bottom surface sediments, 60 Co levels were up to 150 Bq kgÿ1 dry wt. in the western strait of Strelok Bay near the site of the 1995 nuclear accident in Chazhma Bay (Table 5). Cobalt ions adsorbed onto
TABLE 4 Temporal variation in Year 1964 1966a 1966±1968 1970a 1976±1979 1980a 1980±1986 1990a 1991a 1992a 1993a 1994a 1994 1995 a
Number of samples 4 4 4 5 4 4 3 13 9 2
90
Sr (Bq mÿ3 ) in surface water of the East Sea (Sea of Japan). Average concentration
Reference
19.6 11.1 8.1 7.4 4.1±5.1 5.5 2.0±3.5 6.3 3.7 4.8 3.9 2.4 1.6±2.0 2.0
Chumichev (1966) Chumichev (1972) Nagaya and Nakamura (1981) Nagaya and Nakamura (1987)
Joint Expedition (1995) Joint Expedition (1997)
Source: Annual Reports on Environmental Radioactivity (1967±1995), SPA Typhoon, Federal Service of Russia on Hydrometeorology and Environmental Monitoring.
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Volume 38/Number 10/October 1999 TABLE 5 Arti®cial Radionuclides in Peter the Great Bay in the period of 1994±1996.a Region Water Amursky Bay Ussuriysky Bay Bottom sediment Western Strelok Bay (near Chazma Bay) Ussuriysky Bay Amursky Bay Amursky Bay
Ussuriysky Bay
a
60
St.
Sr
137
Cs
239240
Pu
238
Pu
ÿ3
ND ND
2.3±2.6 1.7±6.6
DL-150b
81 85 2 7 14 3 4 8 9 10 13 1 12 11 5 6
DL-21.6b DLb
ND: not determined.DL: detection limit for Data from Tkalin (1995). c Data from Tkalin et al. (1998). b
90
Co
60
Co and
1.60 0.26 1.80 0.39 ND ND ND ND ND ND ND ND ND ND ND ND ND ND 137
(Bq m ) 2.8±3.4 1.7±5.7 (Bq kgÿ1 ) DL-8.5 2.0±14.8b 2.8±19.1b 17.36 0.92 13.43 1.05 4.9c 14.0c 13.3c 13.4c 16.1c 6.3c 13.0c 10.6c 9.1c 1.8c 3.9c 4.7c 1.9c 2.7c
1.15 0.05 1.14 0.04 0.53 0.03 0.60 0.04 0.28 0.02 0.68 0.03 0.92 0.04 0.48 0.02 0.82 0.04 0.77 0.02 1.54 0.08 0.24 0.01 0.63 0.03 1.15 0.09 0.51 0.02 0.28 0.01
0.03 0.00 0.03 0.00 <0.003 <0.003 <0.003 0.009 0.002 0.012 0.002 0.003 0.001 0.010 0.002 0.010 0.001 0.027 0.005 0.004 0.001 0.009 0.001 0.010 0.001 0.006 0.001 0.003 0.001
Cs were 1.1 and 1.7 Bq kg-1 , respectively.
sedimentary particles do not exchange with aqueous Co ions in solution, nor do they compete with Na , K or Mg ions for binding sites (Patel and Patel, 1991). Distribution coecient of 60 Co with coastal sediments is 0.2±1 ´ 106 (IAEA, 1985). Therefore, Co is not readily desorbed from sediments in the oxic marine environment. However, reduction of iron and manganese in the anoxic subsurface of sediment and subsequent upward transportation into the aerobic environment results in reprecipitation and recyling of cobalt (Kremling, 1983). 60 Co contamination appears to be largely con®ned to Chazhma Bay. 137 Cs concentrations in surface sediments varied between <1.7 and 19 Bq kgÿ1 dry wt. and elevated levels of 137 Cs were found near the month of the Razdolnaya River (Amursky Bay). 137 Cs concentration in bottom sediments was lowest in the open part of Peter the Great Bay and those in Amursky Bay were higher than those in Ussuriysky Bay. 239240 Pu activity concentrations in surface sediments collected during 1996 varied from 0.24 to 1.54 Bq kgÿ1 dry wt. 238 Pu activity concentrations in surface sediments varied between <0.003 and 0.03 Bq kgÿ1 dry wt. in Amursky Bay and between 0.003 and 0.01 Bq kgÿ1 dry wt. in Ussuriysky Bay (Table 5). Associated 238 Pu/239240 Pu activity ratios varied between 0.0087 and 0.0139 (with an average of 0.014 0.002) in Amursky Bay and between 0.012 and 0.017 (with an average of 0.014 0.002) in Ussuriysky Bay. Global fallout has an average 238 Pu/ 239240 Pu ratio of 0.0253 (UNSCEAR, 1993). Downcore 239240 Pu activity concentrations in sediments ranged from 0.01 to 1.26 Bq kgÿ1 dry wt. in
Amursky Bay and from 0.001 to 1.52 Bq kgÿ1 dry wt. in Ussuriysky Bay, and generally decreased with increasing depth (Table 6). Associated 238 Pu/239240 Pu activity ratios ranged from 0.02 to 0.08, and from 0.02 to 0.04, respectively (Table 6). Distribution of 239240 Pu concentrations in sediments Pu isotopes are particle reactive and hence to be bound to the bottom sediments. The distribution of Pu concentrations in a coastal and shelf region depends not only on the sources to that particular site but also on the nature of suspended particulate matter and sediments, and on the oxidation states of Pu in that environment (Baskaran et al., 1995). The distribution coecient (Kd ) for plutonium for sediment is very large, 1 ´ 105 (IAEA, 1985). The 239240 Pu inventories in bottom sediments at station CA in Amursky Bay and station CU in Ussuriysky Bay were estimated to be 66.2 and 99.5 Bq mÿ2 , respectively. Hong et al. (1996b) have reported sediment accumulation rates and sediment organic carbon concentration in Peter the Great Bay. According to Hong et al. 210 Pb-derived sediment accumulation rates are 173 and 118 mg cmÿ2 yrÿ1 in Amursky (station CA) and Ussuriysky (station CU) bays, respectively. The surface mixed layer in the core was present in Amursky Bay but not in Ussuriysky Bay. Sediment organic carbon contents in top 0±2 cm below sea ¯oor were 740 and 1953 lmol gÿ1 dry wt. in Amursky (station CA) and Ussuriysky (station CU) bays, respectively. It is also interesting to note that 210 Pb-derived sediment accumulation and mixing rates 939
Marine Pollution Bulletin TABLE 6 Pu isotopes in sediment column in Peter the Great Bay. 239240
Pu (Bq kgÿ1 )
238
Pu (Bq kgÿ1 )
238
Pu/239240 Pu
Region
Sta.
Depth (cm)
Amursky Bay
CA
0±2 2±4 4±6 8±10 12±14 16±18 20±22 22±24 26±28
1.257 0.093 0.760 0.037 0.835 0.044 0.304 0.022 0.022 0.004 0.021 0.003 0.072 0.005 0.068 0.004 0.012 0.002
0.105 0.023 0.014 0.003 0.021 0.004 <0.003 <0.003 <0.003
0.083 0.019 0.019 0.004 0.025 0.005
Ussuriysky Bay
CU
0±2 2±4 4±6 8±10 12±14 16±18 20±22 24±26 26±28
1.516 0.078 1.413 0.070 1.290 0.064 0.544 0.030 0.338 0.021 0.245 0.016 0.011 0.002 0.007 0.002 0.001 0.001
0.105 0.023 0.014 0.003 0.021 0.004 <0.003 <0.003 <0.003
0.019 0.004 0.007 0.002 0.019 0.004
are higher in station CA sediments from Amursky Bay than in Ussuriysky Bay (Hong et al., 1996b). Conversely, the 239240 Pu inventory and surface sediment activity levels are higher in station CU sediments from Ussuriysky Bay. This may be explained by the combined eects of lower sediment accumulation and mixing rates in CU station sediments; transport of plutonium from naval shipyard operations in the Bolshoy Kamen and Chazhma Bay areas; and/or more ecient scavenging and removal of 239240 Pu in the ®negrained and organic rich Ussuriysky Bay sediments. Fine organic rich sediments appear to have a strong anity for particle reactive radionuclides (Baskaran et al., 1996). Baskaran et al. also noted that during early diagenesis of sedimentary organic matter any manganese and iron present may be reduced and released into the interstitial waters. These reduced species can diuse into the overlying water column, re-oxidize and form hydrous oxides that act as eective scavenging agents for particle reactive radionuclides. 239240
Pu/239240 Pu activity ratios in Peter the Great Bay The major sources of plutonium to Peter the Great Bay are derived from the following sources: (1) atmospheric fallout from weapons testing; (2) riverine input from the erosion and leaching of soils; (3) direct discharge of nuclear euents; (4) long range transport from other regions (e.g., leaching of plutonium from decommissioned submarines, storage facilities, ocean dump sites) (Handler, 1995); (5) atmospheric input of resuspension of previously deposited fallout radionuclides on land; (6) the close-in fallout Ôhot particlesÕ from the nuclear accident in Chazhma Bay. The relative contributions from these sources have been assessed below. 238 Pu/239240 Pu activity ratios can be used to distinguish between dierent sources of plutonium in the marine environment. The reported 238 Pu/239240 Pu
940
Activity ratio
activity ratio in dumped reactors in the Kara Sea varies between 0.26 and 0.49 (Baskaran et al., 1996). Assuming the two major sources of plutonium in Peter the Great Bay are global atmospheric fallout and reactor related inputs and each source term can be de®ned by a unique 238 Pu/239240 Pu activity ratio, we can estimate the contribution of plutonium derived from non-global fallout sources as proposed by Baskaran et al. (1996). The measured 238 Pu/239240 Pu activity ratio can be expressed as the fractional sum of these two source terms, i.e., Am Ag 1 ÿ f Ar f ;
1
where Am is the measured 238 Pu/239240 Pu activity ratio, Ag the 238 Pu/239240 Pu activity ratio of global fallout (0.03), Ar the 238 Pu/239240 Pu activity ratio in reactorrelated euent (0.30, taken from Baskaran et al., 1996), f the fraction of plutonium derived from the reactorrelated source term. The fraction of plutonium derived from the reactor-related source term in any sample can therefore be calculated by solving for f, i.e., f Ar ÿ Am = Ar ÿ Ag :
2
The highest 238 Pu/239240 Pu activity ratios were observed in surface sediments collected from Amursky Bay station CA sediments. Taking this value, the upper estimate of the fraction of plutonium in this sample that is derived from reactor-related sources is around 19%. However, the 238 Pu/239240 Pu activity ratios in deeper layers of the sediment are less than 0.03. The dissolution rates of ®ne particles of 238 Pu oxide at neutral pH are about 200 times faster than for 239 Pu because of radiolytic fragmentation eects (Suchanek et al., 1996). The enrichment of 238 Pu in surface sediment could be related to either an increase in the availability of 238 Pu within the region (Suchanek et al., 1996) and subsequent uptake of 238 Pu onto ®ne surface sediment particles, or
Volume 38/Number 10/October 1999
to transport and deposition of contaminated sedimentary particles containing a high 238 Pu/239240 Pu signature, or both. 239240
Pu in mussels collected from Peter the Great Bay The 239240 Pu concentration of mussel samples collected from the central part of Peter the Great Bay (St. 1) was 12.6 mBq kgÿ1 dry wt. This compares with values ranging from 2.5 to 10.9 mBq kgÿ1 dry wt. (with an average of 5.9 mBq kgÿ1 dry wt.) and from <0.5 to 9.3 mBq kgÿ1 dry wt. (with an average of 3.6 mBq kgÿ1 dry wt.) in Amursky Bay and Ussuriysky Bay, respectively (Table 7). The highest value was observed in the middle of the bay. The mean 239240 Pu concentration in mussels from Peter the Great Bay was about 6 4 mBq kgÿ1 dry wt. The plutonium content of mussels in Peter the Great Bay is lower or comparable to other contaminated sites around the world. For examples, 239240 Pu contents in mussels were 12 8 mBq kgÿ1 dry wt. observed in the west coast of United States during 1990 (Valette-Silver and Lauenstein, 1995). These values are lower than the earlier observation during 1976±1978 of the Californian Mussel Watch Program (37 25 mBq kgÿ1 dry wt.) with the exception of the one high value of 130 5 mBq kgÿ1 dry wt. from the Farallon Islands nuclear waste dump site (Suchanek et al., 1996 and references therein). By comparison, mussels collected in 1984 along the coast of the United Kingdom contain 239240 Pu concentrations up to 1193 Bq kgÿ1 dry wt. in basal threads (McDonald et al., 1991, 1993). Similarly, edible species of clam and other invertebrates collected from Bikini Atoll in 1972±1980 contained between 10 and 122 Bq kgÿ1 dry wt. of 239240 Pu (Noshkin et al., 1988) suggesting that the levels of plutonium in Peter the Great Bay are not exceptionally high and are comparable with world-wide fallout values. Mussels are ecient ®lter feeders and may concentrate contaminants from surrounding waters by 200±300 fold. Consequently, mussels are commonly used in worldwide monitoring programs to assess pollutant levels in the natural environment. The average reported concentration factor (CF activity concentration in tissue/activity concentration in seawater) for plutonium in mollusks (except Cephalopods) is 3 ´ 103 (IAEA, 1985). Based on the range of 239240 Pu concentration in TABLE 7 239240
Pu (mBq kgÿ1 dry wt.) in mussels in Peter the Great Bay.
Region Open part of Peter the Great Bay Amursky Bay
Ussuriysky Bay
Station 1 7 4 8 9 10 11 5 6
239 240
Pu
12.6 2.3 4.5 1.4 5.7 1.8 5.8 1.7 10.9 2.3 2.5 0.9 1.5 0.9 9.3 2.2 <0.5
seawater (Table 1) and mussels (Table 7), the approximate concentration factor of 239240 Pu is estimated to be 0.3±2 ´ 103 in the region. In general, non-essential particle reactive trace metals such as lead and the actinide elements are mainly accumulated by animals from the dissolved phase while essential elements like copper and zinc are more likely to be accumulated from food. The plutonium assimilation eciency for mussels feeding on diatoms is about 1±8 and much lower than that of zinc (Fisher and Reinfelder, 1995). Data on other radionuclides concentration in mussel are very limited in the sea. Notable ones are reported here. Mussels (Mytilus edulis including shell and soft tissue) collected during 1988 reportedly contained 0.04 0.01 Bq kgÿ1 dry wt. of 137 Cs and 0.09 0.02 Bq kgÿ1 dry wt. of 60 Co in the south-western Korean coast of the East Sea (Lee, 1989). The 137 Cs activity concentration in the soft parts of the invertebrate, Stichopus japonicus, collected along the Japanese coastline during 1986 ranged from 0.03 Bq kgÿ1 wet wt. near Oshoro to 0.08 Bq kgÿ1 wet wt. near Tsuyazaki (Takeda and Misonou, 1991).
Conclusions We have determined arti®cial radionuclides in surface waters of the East Sea (Sea of Japan) proper and bottom sediments of Peter the Great Bay to assess the evolution and spatial distribution of dierent radionuclides. Based on the data presented in this paper, we draw the following observations and conclusions: (1) 137 Cs and 239240 Pu concentrations in the East Sea (Sea of Japan) proper during late October 1993 ranged from 2.6 to 3.7 Bq mÿ3 , and 3.5 to 20.8 mBq mÿ3 , respectively. The mean and range of concentrations observed was similar to those reported in August 1993 prior to the Russian dumping operation of 17 October 1993 and suggest that the 17 October 1993 Russian dumping did not signi®cantly aect the region. (2) The 90 Sr and 137 Cs concentrations in surface waters of Peter the Great Bay are not signi®cantly dierent to those in the East Sea proper. (3) 239240 Pu activity concentrations in surface sediments varied from 0.24 Bq kgÿ1 dry wt. in the open part of Peter the Great Bay to 1.54 Bq kgÿ1 dry wt. in Amursky Bay. 239240 Pu activity ratios ranged from 0.087 to 0.014 with an average of 0.011 0.002 in Amursky Bay, and from 0.012 to 0.018 with an average of 0.014 0.002 in Ussuriysky Bay. There appears to be no signi®cant plutonium contribution from sources other than global fallout. (4) The 239240 Pu inventories in sediments from Amursky Bay and from Ussuriysky Bay were 66.2 and 99.5 Bq mÿ2 , respectively. (5). 239240 Pu concentrations in mussels varied from 2.5 to 12.5 mBq kgÿ1 dry tissue wt. in the region, and the values are comparable to the non-nuclear facility in¯uenced areas and less than those found near nuclear fuel reprocessing plants. A preliminary study of radionuclide contamination in Peter the Great Bay shows low levels of radioactive contamination and isotope activity ratios and radionuclide 941
Marine Pollution Bulletin
inventories do not show evidence of any signi®cant anthropogenic contamination other than from global fallout despite the presence of a large number of nuclear facilities in the region. Along with the work of Russian scientists, this preliminary investigation shows that the present levels of radioactivity in Peter the Great Bay are consistent with those expected from global fallout deposition alone. However, we recommend that further studies should be conducted to help improve our present assessment and provide continuous radionuclide surveillance and monitoring. Sampling in Peter the Great Bay in 1996 was supported by the Center of Field Research, Earth Watch. Dr. J. M. Kim and Mr. D. J. Kang of KORDI assisted with sample collection during the AWARES 9310 cruise. Ms. S. H. Chung provided laboratory technical assistance. The authors thank Drs. M. Baskaran (Texas A&M University, USA), S. W. Fowler (IAEA-MEL) and D. S. Woodhead (MAFF, UK) for their critical comments and supplies of references. Work performed under the auspices of the Ministry of Science and Technology of Korea (BSPN00253) and U.S. Department of Energy at Lawrence National Laboratory under contract W-7405-Eng-48. Baskaran, M., Asbill, S., Santschi, P., Davis, T., Brooks, J., Champ, M., Makeyev, V. and Khlebovich, V. (1995) Distribution of 239;240 Pu and 238 Pu concentrations in sediments from the Ob and Yenisey Rivers and the Kara Sea. Applied Radiation and Isotopes 46, 1109± 1119. Baskaran, M., Asbill, S., Santschi, P., Brooks, J., Champ, M., Adkinson, D., Colmer, M. R. and Makeyev, V. (1996) Pu, 137 Cs and excess 210 Pb in Russian Arctic sediments. Earth and Planetary Science Letters 140, 243±257. Chumichev, V. B. (1966) Strontium-90 content in the waters of the Paci®c Ocean in 1962 and in 1964. Transactions of the Institute of Oceanology, Academy of Sciences of the USSR 82, 20±23 (in Russian). Chumichev, V. B. (1972) Strontium-90 in the north-western parts of the Paci®c Ocean in 1966±1968. Transactions of the Institute of Experimental Meteorology, Hydrometeorological Service of the USSR 1 (32), 45±50 (in Russian). Danilyan, V. A. and Vysotsky, V. A. (1995) Nuclear waste disposal practice in RussiaÕs Paci®c Ocean Region. Arctic Research of the United States 9, 84±87. Fisher, N. S. and Reinfelder, J. R. (1995) The trophic transfer of metals in marine systems. In Metal Speciation and Bioavailability in Aquatic Systems, eds. A. Tessier and D. R. Turner, pp. 363±406. Wiley, New York. Hamilton, T. F., Millies-Lacroix, J. C. and Hong, G. H. (1996) 137 Cs (90 Sr) and Pu isotopes in the Paci®c Ocean: sources and trends. In Radionuclides in the Oceans, Inputs and Inventory, eds. P. Guegueniat, P. Germain and H. Metivier, Les Editions de Physiques, pp. 29±58. Hamilton, T. F., Ballestra, S., Baxter, M. S., Gastaud, J. Osvath, I., Parsi, P., Povinec, P. O. and Scott, E. M. (1994) Radiometric investigations of Kara Sea sediments and preliminary radiological assessment related to dumping of radioactive wastes in the Arctic Seas. Journal of Environmental Radioactivity 25, 113±134. Handler, J. (1995) The radioactive waste crisis in the Paci®c Area. Arctic Research of the United States 9, 105±108. Hirose, K., Aoyama, M., Hatori, M. and Igarashi, Y. (1993) 137 Cs and plutonium in the Japan Sea. Journal of Radiation Research 34, 386. Hirose, K., Hong, G. H. and Miyao, T. (1996). A preliminary study of the temperature structure in the north central Japan Sea. Oceanographical Magazine 45, 1±8. Hirose, K., Amano, H., Baxter, M. S., Chaykovskaya, E., Chumichev, V. B., Hong, G. H., Isogai, K, Kim, C. K., Kim, S. H., Miyao, T., Morimoto, T., Nikitin, A., Oda, K., Pettersson, H. B. L., Povinec, P. P., Seto, Y., Tkalin, A., Togawa, O., Veletova, N. K., (1998) Anthropogenic radionuclides in seawater in the East Sea/Japan Sea: Results of the ®rst stage Japanese-Korean-Russian expedition. Journal of Environmental Radioactivity 43, 1±13.
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Hong, G. H., Lee, S. H. and Lee, W.C. (1996a) 239;240 Pu in Neocalanus cristatus and Thysyaneossaa sp in the Bering Sea. Ocean Research 18, 107±111 (in Korean). Hong, G. H., Park, S. K., Chung, C. S., Kim, S. H., Tkalin, A. V. and Lishavskaya, T. S. (1996b) Biogenic particulate matter accumulation in Peter the Great Bay, East Sea (Japan Sea). Journal of the Korean Society of Oceanography 31, 134±143. Hong, G. H., Kim, S. H., Chung, C. S., Kang, D. J., Shin, D. H., Lee, H. F. and Han, S.J. (1997) 210 Pb-derived sediment accumulation rates in the southwestern East Sea (Sea of Japan). Geo-Marine Letters 17, 126±132. IAEA (1985) Sediment kd s and concentration factors for radionuclides in the marine environment. Technical Report Series No. 247. International Atomic Energy Agency, Vienna, 71 pp. Joint Expedition (1995) Investigation of Environmental Radioactivity in Waste Dumping Areas of the Far Eastern Seas, Results from the First Japanese±Korean±Russian Joint Expedition, 1994, p. 62. Joint Expedition (1997) Investigation of Environment Radioactivity in Waste Dumping Areas in the Northwest Paci®c Ocean. Results from the Second Stage of Japanese±Korean±Russian Joint Expedition, 1995, p. 56. Kang, D. J., Chung, C. S., Kim, S. H., Kim, K. R. and Hong, G. H. (1997) Distribution of 137 Cs and 239;240 Pu in the surface waters of the East Sea (Sea of Japan). Marine Pollution Bulletin 35, 305±312. Kremling, K. (1983) The behavior of Zn, Cd, Cu, Ni, Co, Fe and Mn in anoxic Baltic waters. Marine Chemistry 13, 87±108. Lee, D. S., ed. (1989). A Study on the Coastal Water Pollution And Monitoring, Research and Development Institute, Technical Report BSPG 00083-242-4, pp. 360 (in Korean). Lee, M. H., Lee, C. W., Moon, D. S., Kim, K. H. and Boo, B. H. (1998) Distribution and inventory of fallout Pu and Cs in the sediment of the East Sea of Korea. Journal of Environmental Radioactivity 41, 99±110. Lerman, A. (1979) Geochemical Processes. Wiley, New York, p. 481. Livingston, H. D., ed. (1995) Arctic radioactivity and related transport processes. Deep-Sea Research, Part II. Topical Studies in Oceanography 42, 1337±1555. McDonald, P., Baxter, M. S. and Fowler, S. W. (1993) Distribution of radionuclides in mussels, winkles and prawns. part I. Study of organisms under environmental conditions using conventional radio-analytical techniques. Journal of Environmental Radioactivity 18, 181±202. McDonald, P., Cook, G. T. and Baxter, M. S. (1991) Natural and arti®cial radioactivity in coastal regions of UK. In Radionuclides in the Study of Marine Processes, eds. P. J. Kershaw and D. S. Woodhead, pp. 329±339. Elsevier Applied Science, London. Miyake, Y., Saruhashi, K., Sugimura, Y., Kanazawa, T. and Hirose, K. (1988) Contents of 137 Cs, Plutonium and Americium isotopes in the southern ocean waters. Papers in Meteorology and Geophysics 39, 95±113. Miyao, T., Hirose, K., Aoyama, M. and Igarashi, Y. (1998) Temporal variation of 137 Cs and 239;240 Pu in the Sea of Japan. Journal of Environmental Radioactivity 40, 239±250. Morgan, J. and Codispoti, L. (1995) Department of Defense Arctic Nuclear Waste Assessment Program. FY's 1993±94. Oce of Naval Research Report, ONR 322-95-5. Nagaya, Y. and Nakamura, K. (1981) Arti®cial radionuclides in the western Northwest Paci®c. I. 90 Sr and 137 Cs in the deep waters. Journal of the Oceanographical Society of Japan 37, 135±144. Nagaya, Y. and Nakamura, K. (1984) 239;240 Pu 137 Cs and 90 Sr in the central North Paci®c. Journal of the Oceanographical Society of Japan 40, 345±355. Nagaya, Y. and Nakamura, K. (1987) Arti®cial radionuclides in the western Northwest Paci®c. II. 137 Cs and 239;240 Pu inventories in water and sediment columns observed from 1980 to 1986. Journal of the Oceanographical Society of Japan 43, 345±355. Noshkin, V. E., Wong, K. M., Eagle, R. J., Jokela, T. A., Brunk, J. A. (1988) Radionuclide concentrations in ®sh and invertebrates from Bikini Atoll, Lawrence Livermore National Laboratory, Technical Report, UCRL-53846. Patel, B. and Patel, S. (1991) Radioecology of cobalt-60 under tropical environmental conditions, In Radionuclides in the Study of Marine Processes, eds. P. J. Kershaw and D. S. Woodhead, pp. 276±282. Elsevier Applied Science, London. Povinec, P. P., Osvath, I., Baxter, M. S., Ballestra, S., Carroll, J. Gastaud, J., Harmes, I., Huyn-Ngoc, L., Kwong, L.L.W. and Pettersson, H. (1997) IAEA-MELÕs investigation of Kara Sea
Volume 38/Number 10/October 1999 radioactivity and radiological assessment. Marine Pollution Bulletin 35, 235±241. Seung, Y. H. and Yoon, J. H. (1995) Some features of winter convection in the Japan Sea. Journal of Oceanography 21, 61±73. Suchanek, T. H., Lagunas Solar, M. G., Raabe, O. G, Helm, R. C., Gielow, E., Peek, N. and Carvacho, O. (1996) Radionuclides in ®shes and mussels from the Farallon Islands nuclear waste dump site, California. Health Physics 71, 167±178. Takeda, Y. and Misonou, J. (1991) The ecological half-life of Cs-137 in Japanese coastal marine biota. In Radionuclides in the Study of Marine Processes, eds. P. J., Kershaw and D. S. Woodhead, pp. 340±349. Elsevier Applied Science, London. Tkalin, A. V., Lishavskaya, T. S. and Sulkin, V. M. (1998) Radionuclides and trace metals in mussels and bottom sediments around Vladivostok, Russia. Marine Pollution Bulletin 36, 551±554. Tkalin, A. V. (1995) Investigation of marine environmental radioactivity in the dumping areas and coastal zone of Sea of Japan. Arctic Research of the United States 9, 88±89. Tsunogai, S., Watanabe, Y., Harada, K., Watanabe, S., Saito, S. and Nakajima, M. (1993) Dynamics of the Japan Sea deep water studied
with chemical and radiochemical tracers. In Elsevier Oceanography Series, ed. T. Teramoto, vol. 59, pp. 105±119. Deep Ocean Circulation, Physical and Chemical Aspects. UNSCEAR (1993) Source and eects of ionization radiation, United Nations Scienti®c Committee on the Eects of Atomic Radiation, UNSCEAR, 1993 report to the General Assembly, with scienti®c annexes. Valette-Silver, N. and Lauenstein, G. G. (1995) Radionuclide concentrations in bivalves collected along the coastal United States. Marine Pollution Bulletin 30, 320±331. Wong, K. M., Jokela, T. A. and Noshkin, V. E. (1994) Radiochemical procedures for analysis of Pu, Am. Cs, and Sr in water, soil, sediments and biota samples. Report UCRL-ID-116497. Lawrence Livermore National Laboratory, USA. Yablokov, A. V., ed. (1993). Facts and Problems Related to Radioactive Waste Disposal in Seas Adjacent to the Territory of the Russian Federation, Oce of the President of the Russian Federation, Moscow, Russia, p. 72.
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Marine Pollution Bulletin Vol. 38, No. 10, pp. 933±943, 1999 Ó 1999 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0025-326X/99 $ - see front matter
Arti®cial Radionuclides in the East Sea (Sea of Japan) Proper and Peter the Great Bay GI-HOON HONG *, SUK-HYUN KIM , SANG-HAN LEE , CHANG-SOO CHUNG , ALEXANDER V. TKALINà, EMILIA L. CHAYKOVSKAYà and TERRY F. HAMILTON§ Korea Ocean Research and Development Institute, Marine Biogeochemistry and Isotopes, Ansan P.O. Box 29, Seoul 425-600, South Korea àFar Eastern Regional Hydrometeorological Research Institute, 24 Fontannaya St., Vladivostok 690600, Russian Federation §Lawrence Livermore National Laboratory, P.O. Box 808 L-453, Livermore, CA 94550, USA
Over the past decade there has been growing concern over dumping of radioactive waste in the East Sea (Sea of Japan) proper and adjacent coastal waters. Here we show that the evolution of activity concentrations of 137 Cs and 239240 Pu in the East Sea, and existing levels of radioactive contamination in waters, sediments and biota from Peter the Great Bay (Russia) can be largely attributed to global fallout deposition. The former sequence of data includes results from the AWARES cruise (Active Watch of Arti®cial Radionuclides in the East Sea) conducted between 26 October and 1 November 1993 about ten days after 14 GBq of liquid radioactive waste was dumped into the East Sea. The activity concentration of 137 Cs and 239240 Pu in surface waters ranged between 2.7±3.5 Bq mÿ3 and 3.5± 20.8 mBq mÿ3 , respectively, and were not dierent to levels observed during August 1993 prior to the Russian dumping operation in October. Isotopic ratios also indicate the absence of any signi®cant anthropogenic radioactive contamination in the region other than from global fallout deposition. Ó 1999 Elsevier Science Ltd. All rights reserved. Keywords: arti®cial radionuclides; Peter the Great Bay; East Sea (Sea of Japan).
Introduction The widespread introduction of arti®cial radioactivity into the marine environment arose initially from detonation of nuclear weapons in the atmosphere (Hamilton et al., 1996). Among products of nuclear reactions, ®ssion products, 90 Sr (t1=2 28.82 yr) and 137 Cs *Corresponding author. Tel.: +82-345-400-6180; fax: +82-345-4084493; e-mail: [email protected]
(t1=2 30.17 yr) and neutron induced or unreacted materials of 238 Pu (t1=2 87.7 yr), 239 Pu (t1=2 24 100 yr) and 240 Pu (t1=2 6571 yr) were investigated here. The selection of these radionuclides was based on their wellknown behaviour and signi®cance of radiological concern in the marine environment. Local contributions in the Paci®c Ocean include close-in fallout deposition from US and French Paci®c test programs and dumping of nuclear wastes (Hamilton et al., 1996). Over the past 30 yr about 443 TBq of liquid and 141 TBq of solid wastes were dumped in the East Sea (Sea of Japan), and 0.01 and 113 TBq of liquid and solid wastes, respectively, in the north-west Paci®c Ocean o Kamchatka Peninsula (Yablokov, 1993). Extensive studies of marine radioactivity have been conducted in the Russian Arctic (Hamilton et al., 1994; Livingston, 1995; Morgan and Codispoti, 1995; Baskaran et al., 1996; Povinec et al., 1997) but far less international attention has been given to the Russian Far East. Since the early 1960s the Institute of Experimental Metrology (now SPA Typhoon, Obinsk), the Russian Academy of Sciences, the Russian Navy and the Far Eastern Regional Hydrometeorological Research Institute (FERHRI) have supported on-going national radionuclide monitoring programmes in north-west Paci®c as well as in coastal waters o Primorye, the Sakhalin Island and Kamchatka Peninsula. Also, over the past two decades Japanese scientists have published a large quantity of data on arti®cial radionuclides in waters and sediments from the western Paci®c (Hirose et al., 1993; Nagaya and Nakamura, 1987, 1984, 1981; Miyao et al. 1998; Hirose et al., 1998). More recently Korean researchers have conducted studies on marine radioactivity around the Korean Peninsula by Korea Ocean Research and Development Institute (KORDI) and others (Hong et al., 1996a; Kang et al., 1997; Lee et al. 1998). In this paper we report results from investigations conducted during 1993±96 933
Marine Pollution Bulletin
and compare these data to assess local sources and trends in regional marine radioactivity. Concentration data from these isotopes are also valuable to establish a baseline reference for future studies in dose assessment and bioaccumulation in the marine environment. Study area The East Sea (Sea of Japan) is a typical example of a marginal sea and is located in the north-western Paci®c Ocean. There are three deep basins of 2000±4000 m depth (the Japan, Yamato, and Ulleung Basins) separated by the Korea Plateau and Yamato Ridge that rise to within 500 m below sea level (Fig. 1). The East Sea opens to the East China Sea, Sea of Okhotsk and Northwest Paci®c Ocean only through the four narrow sills shallower than 150 m. The vertical ventilation in the deep basin takes about 100 yr and waters are replaced every 1000 yr (Tsunogai et al., 1993). Recent sediments appear to be primarily derived from a hemipelagic source. While there are no main rivers along the coast of Primorye and the Korean Peninsula, signi®cant amounts of sediments are supplied to the coastal regions by Japanese rivers (Hong et al., 1997). Peter the Great Bay is of special interest because there are many nuclear facilities located in this region. Shore-
based sites for storage of nuclear waste for the Russian Paci®c Fleet are located near Bolshoy Kamen east of Vladivostok (Fig. 2). Also, there are several decommissioned nuclear submarines stored in the region (Handler, 1995). The Russian Paci®c Fleet has a total inventory of 16 000 m3 of solid nuclear waste and 5000 m3 of liquid waste in storage at the present time. About 70±90% of this waste is stored in the Primorsky Territory (Danilyan and Vysotsky, 1995). According to Danilyan and Vysotsky, approximately 2000 m3 of liquid and 5000 m3 of solid waste will be generated annually over the next 10±15 yr taking into account the anticipated ¯eet utilization schedule (3±4 PLA annually). Radioactive waste processing facilities in the region were due to be upgraded and expanded in March 1998 (International Maritime Organization News, 1997). It has also been reported that a nuclear accident occurring on 10 August 1985 contaminated coastal waters in Chazhma, Strelok and Ussuriysky bays with 60 Co (Yablokov, 1993). Long-term observations show that the spatial extent of 60 Co contamination is con®ned to the region due to the dynamic equilibrium between the processes of radionuclide migration and radioactive decay (t1=2 5.27 yr) (Yablokov, 1993; Danilyan and Vysotsky, 1995).
Fig. 1 Map of the sampling stations in the East Sea (Sea of Japan) during October (d) and August 1993 (s, Kang et al., 1997) and radioactive waste dump sites of the former Soviet Union and Russian Federation are shown here (Yablokov et al., 1993). JB, YB and UB stand for Japan, Yamato and Ulleung basins in the sea.
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Volume 38/Number 10/October 1999
Fig. 2 Map of sampling stations in Peter the Great Bay.
Materials and Methods Twenty two surface water samples were collected between 26 October and 1 November during the AWARES (Active Watch of Arti®cial Radionuclides in the East Sea) cruise to the East Sea (Sea of Japan) on board the R/V Onnuri (Fig. 1). Water samples were collected using a submersible pump and stored in 20 l polyethylene bottles without ®lteration after acidi®cation with 50 ml of 6 M HCl. In Peter the Great Bay, samples of seawater, sediment and mussel were collected by Russian scientists on board the FERHRI research vessels R/V Akademik Shokalsky during 1994 and the R/V Hydrobiologist during 1996 (Fig. 2). Surface water samples were collected using submersible pump and ®ltered on board. The ®ltered water samples were treated with potassium ferrocynide and sodium carbonate for co-precipitation of Cs and Sr isotopes (Joint Expedition, 1995). 90 Y counting were carried out with low background b counter after secular equilibrium between 90 Sr and 90 Y. 137 Cs were counted using a Russian gamma ray spectrometric system DGDK-80V-3. Bottom sediments were collected using a modi®ed Peterson grab and top 3cm sections were taken for analysis. Gravity cores were also collected from the centre of Amursky and Ussuriysky Bays, and sectioned into 2 cm intervals. All sediment samples were kept frozen until analysis.
KORDI analysed AWARES water samples for 137 Cs and 239240 Pu contents. Plutonium and Cs isotopes were preconcentrated on manganese dioxide and ammonium molybdate phosphate (AMP), respectively, with 242 Pu and stable Cs added as chemical yield tracers (Wong et al., 1994). The plutonium fraction was puri®ed by ionexchange, electroplated onto stainless steel discs and counted by alpha-spectrometry using PIPS detectors coupled to Canberra Series 35 multichannel analyser. The AMP fraction was dissolved and 137 Cs quanti®ed by high resolution gamma-spectrometry using a Canberra Series MCA 90 multichannel analyser. In the laboratory, sediment samples were dried and ground into a ®ne powder. Separate aliquots were used for the determination of plutonium isotopes. Concentrations of 90 Sr and Pu isotopes in the bottom sediments and Pu contents in mussels from Peter the Great Bay were also determined by KORDI. Mussel tissues were dried and Pu isotopes were isolated through successive acid digestion. The analytical procedures of 90 Sr, Pu isotopes were largely taken from Wong et al. (1994).
Results and Discussion The evolution of 137 Cs, 239240 Pu and 90 Sr in the East Sea (sea of Japan) proper Measured 137 Cs activity concentrations in the East Sea during 26 October±1 November 1993 ranged from 2.6 to 935
Marine Pollution Bulletin TABLE 1 Distribution of 137 Cs and 239240 Pu concentrations in the surface waters of the East Sea (Sea of Japan) in the period of 26 October±1 November 1993 (AWARES cruise).a Location
Stn
1 2 3 4 A B C D E F G H I J K L M N O R S T a
Sampling date
Lat. (N)
Long. (E)
41o 00.00 39o 40.00 37o 00.00 38o 00.00 40o 40.00 40o 20.00 40o 00.00 39o 20.00 39o 01.25 38o 41.45 38o 21.45 38o 02.00 37o 40.45 37o 20.45 37o 15.00 37o 30.00 37o 45.00 37o 36.00 37o 12.40 36o 46.30 36o 16.30 35o 39.80
136o 10.00 134o 19.85 131o 00.00 129o 00.00 135o 45.00 135o 16.65 134o 48.15 133o 54.75 133o 30.00 133o 05.00 132o 40.00 132o 15.00 131o 50.00 131o 25.00 130o 30.00 130o 00.00 129o 30.00 129o 17.30 129o 35.00 129o 40.00 129o 42.50 129o 37.80
26 Oct Õ93 28 Oct Õ93 29 Oct Õ93 31 Oct Õ93 27 Oct Õ93 27 Oct Õ93 28 Oct Õ93 28 Oct Õ93 28 Oct Õ93 28 Oct Õ93 28 Oct Õ93 29 Oct Õ93 29 Oct Õ93 29 Oct Õ93 29 Oct Õ93 29 Oct Õ93 30 Oct Õ93 31 Oct Õ93 01 Nov Õ93 01 Nov Õ93 01 Nov Õ93 01 Nov Õ93
137
Cs (Bq mÿ3 )
3.01 0.14 3.11 0.16 3.02 0.26 3.04 0.16 2.86 0.21 2.97 0.21 3.02 0.24 2.83 0.27 3.20 0.18 3.12 0.27 2.60 0.20 3.37 0.15 3.51 0.15 2.96 0.27 3.21 0.27 2.67 0.16 ND 3.36 0.15 3.01 0.15 3.26 0.19 3.51 0.14 2.74 0.16
239240
Pu (mBq mÿ3 )
3.5 0.6 10.2 2.7 8.2 1.1 5.7 0.7 4.9 0.5 3.8 0.6 3.4 0.6 7.8 1.0 7.8 0.7 5.7 0.5 6.1 0.7 10.1 1.0 5.8 0.7 7.5 0.8 18.2 2.7 5.7 0.6 5.3 1.6 7.8 0.8 6.4 1.0 9.9 1.3 20.8 3.41 5.7 0.6
ND: not determined.
3.5 Bq mÿ3 (Table 1). These concentrations in surface waters have been compared with those obtained by Kang et al. (1997) during August 1993 (Fig. 3). These data provide some insight into the impact of the dumping incident of 17 October on the levels and distributions of arti®cial radionuclides in the sea. Some 14.1 GBq of liquid radioactive waste (137 Cs 76%; 90 Sr 21%; 60 Co 1.5%; 134 Cs 1.5%) were dumped into the area 9 in Fig. 1 (later reported by Danilyan and Vysotsky, 1995). If 2.1 ´ 108 Bq of 134 Cs was dumped at a point in the area 9 then 134 Cs will spread out about 27 ´ 109 m2 for 10 days (t) after the dumping, assuming the average eddy diusion coecient (D) of 108 cm2 sÿ1 in the sea, a characteristic distance for dispersal of material diusion can be determined as (Dt)1=2 (Lerman, 1979) and surface mixed layer of 20 m (Hong, unpublished data), then the maximum expected 134 Cs concentration would be 3.9 ´ 10ÿ4 Bq mÿ3 . This size of concentration would not be measurable for the current analytical method. As we observe from analyses of samples collected two months earlier (Fig. 3, Kang et al., 1997), there appears to be no signi®cant change in the temporal distribution of 137 Cs during these two observational periods. Consequently, there appears to have been no measurable impact of Russian dumping operations of 17 October 1993 on the prevailing distribution of 137 Cs in surface waters of the East Sea. Presumably this was related to the rapid dispersion and dilution of the dumped waste. These results were later con®rmed by the Japanese-Russian-Korean Joint Expeditions of 1994 and 1995 (Table 2). Furthermore, there appears to be no direct evidence of elevated levels of 137 Cs (or 90 Sr) in 936
surface waters near the nuclear waste dump sites declared by the Russian Federation in 1992 (Kang et al., 1997; Joint Expedition, 1995, 1997). Measured 239240 Pu concentrations in the East Sea during 26 October±1 November 1993 ranged from 3.4 to 20.8 mBq mÿ3 (Table 1). There appear to be no clear regional trends in these data. 239240 Pu activity concentrations in surface waters collected during August 1993 ranged between 7 and 10 mBq mÿ3 (Kang et al., 1997) and are comparable to results reported by Japanese researchers through 1975±1993 (Hirose et al., 1993; Miyake et al., 1988; Nagaya and Nakamura, 1987). The evolution in the concentration of 239240 Pu in surface waters of the sea proper have been summarized in Table 3 for the period between 1975 and 1995. However, our data (Table 1 and Fig. 4) along with the results from the 1994 and 1995 Japanese-Russian-Korean Joint Expeditions (Table 3 and references therein) show a higher range of values up to 25 mBq mÿ3 . The higher surface water 239240 Pu activity concentrations may result from upwelling of deep Pu-enriched waters leading to the breakdown of the seasonal thermocline during the late autumn and particle removal and remineralization processes (Hirose et al., 1996). Therefore, we believe that the observed changes in the temporal distribution of 239240 Pu can be attributed to oceanographic conditions (Seung and Yoon 1995), and are not necessarily related to impacts of dumping of radioactive waste. Nevertheless, according to long-term data from the Japanese Fisheries Agency and Maritime Safety Agency, 239240 Pu activity concentrations in surface waters around Japan have varied from below detection limit to 120 mBq mÿ3
Volume 38/Number 10/October 1999
Fig. 3 Distribution of 137 Cs (Bq mÿ3 ) in surface waters of the East/ Japan Sea (Sea of Japan) during October (d) and August 1993 (s, Kang et al., 1997).
TABLE 2 Temporal variation in Year
137
Cs (Bq mÿ3 ) in surface water of the East Sea (Sea of Japan).
Concentration
1975±1978 1976±1979 1980±1986 1984 1985 1987 1989 1990 1993 August, 1993 October, 1993 1994 1995
Reference
5.9±8.5 4.9±7.1 3.2±4.2 5.1 4.5±4.8 4.5 3.6±4.2 3.5±3.7 2.7±3.0 2.6±3.4 2.6±3.5 2.8±3.6 2.5±2.9
Miyake et al. (1988) Nagaya and Nakamura (1981) Nagaya and Nakamura (1987) Takeda and Misonou (1991), Japanese Takeda and Misonou (1991), Japanese Takeda and Misonou (1991), Japanese Takeda and Misonou (1991), Japanese Takeda and Misonou (1991), Japanese Hirose et al. (1993) Kang et al. (1997) This study Joint Expedition (1995) Joint Expedition (1997)
coast coast coast coast coast
TABLE 3 Temporal variation in Year 1975±1978 1980±1986 1986±1993 August 1993 October 1993 October 1994 October 1995
239240
Pu (mBq mÿ3 ) in surface water of the East Sea (Sea of Japan).
Concentration
Reference
4.4±14.4 6.7±7.4 1.1±9.7 7±10 3.5±20.8 8±25 3.8±16
Miyake et al. (1988) Nagaya and Nakamura (1987) Hirose et al. (1993) Kang et al. (1997) This study Joint Expedition (1995) Joint Expedition (1997)
937
Marine Pollution Bulletin
Fig. 4 Distribution of 239240 Pu (mBq mÿ3 ) in surface waters of the East/Japan Sea (Sea of Japan) during October (d) and August 1993 (s, Kang et al., 1997).
through 1982±1994 (Joint Expedition, 1997), i.e., even higher values were observed (Table 3). Data on the concentration of 90 Sr in surface waters of the East Sea have been summarized in Table 4 for the period from 1964 to 1995. These data show a steady decrease in 90 Sr levels in surface waters consistent with trends observed in atmospheric fallout records following enactment of the atmospheric nuclear test ban treaty of 1963.
60
Co, 90 Sr, 137 Cs and 239240 Pu concentrations in waters and sediments from Peter the Great Bay 90 Sr concentrations in seawater during 1994 varied from 1.7 to 6.6 Bq mÿ3 . 137 Cs concentrations in seawater varied between 1.7 and 5.7 Bq mÿ3 (Table 5). In the bottom surface sediments, 60 Co levels were up to 150 Bq kgÿ1 dry wt. in the western strait of Strelok Bay near the site of the 1995 nuclear accident in Chazhma Bay (Table 5). Cobalt ions adsorbed onto
TABLE 4 Temporal variation in Year 1964 1966a 1966±1968 1970a 1976±1979 1980a 1980±1986 1990a 1991a 1992a 1993a 1994a 1994 1995 a
Number of samples 4 4 4 5 4 4 3 13 9 2
90
Sr (Bq mÿ3 ) in surface water of the East Sea (Sea of Japan). Average concentration
Reference
19.6 11.1 8.1 7.4 4.1±5.1 5.5 2.0±3.5 6.3 3.7 4.8 3.9 2.4 1.6±2.0 2.0
Chumichev (1966) Chumichev (1972) Nagaya and Nakamura (1981) Nagaya and Nakamura (1987)
Joint Expedition (1995) Joint Expedition (1997)
Source: Annual Reports on Environmental Radioactivity (1967±1995), SPA Typhoon, Federal Service of Russia on Hydrometeorology and Environmental Monitoring.
938
Volume 38/Number 10/October 1999 TABLE 5 Arti®cial Radionuclides in Peter the Great Bay in the period of 1994±1996.a Region Water Amursky Bay Ussuriysky Bay Bottom sediment Western Strelok Bay (near Chazma Bay) Ussuriysky Bay Amursky Bay Amursky Bay
Ussuriysky Bay
a
60
St.
Sr
137
Cs
239240
Pu
238
Pu
ÿ3
ND ND
2.3±2.6 1.7±6.6
DL-150b
81 85 2 7 14 3 4 8 9 10 13 1 12 11 5 6
DL-21.6b DLb
ND: not determined.DL: detection limit for Data from Tkalin (1995). c Data from Tkalin et al. (1998). b
90
Co
60
Co and
1.60 0.26 1.80 0.39 ND ND ND ND ND ND ND ND ND ND ND ND ND ND 137
(Bq m ) 2.8±3.4 1.7±5.7 (Bq kgÿ1 ) DL-8.5 2.0±14.8b 2.8±19.1b 17.36 0.92 13.43 1.05 4.9c 14.0c 13.3c 13.4c 16.1c 6.3c 13.0c 10.6c 9.1c 1.8c 3.9c 4.7c 1.9c 2.7c
1.15 0.05 1.14 0.04 0.53 0.03 0.60 0.04 0.28 0.02 0.68 0.03 0.92 0.04 0.48 0.02 0.82 0.04 0.77 0.02 1.54 0.08 0.24 0.01 0.63 0.03 1.15 0.09 0.51 0.02 0.28 0.01
0.03 0.00 0.03 0.00 <0.003 <0.003 <0.003 0.009 0.002 0.012 0.002 0.003 0.001 0.010 0.002 0.010 0.001 0.027 0.005 0.004 0.001 0.009 0.001 0.010 0.001 0.006 0.001 0.003 0.001
Cs were 1.1 and 1.7 Bq kg-1 , respectively.
sedimentary particles do not exchange with aqueous Co ions in solution, nor do they compete with Na , K or Mg ions for binding sites (Patel and Patel, 1991). Distribution coecient of 60 Co with coastal sediments is 0.2±1 ´ 106 (IAEA, 1985). Therefore, Co is not readily desorbed from sediments in the oxic marine environment. However, reduction of iron and manganese in the anoxic subsurface of sediment and subsequent upward transportation into the aerobic environment results in reprecipitation and recyling of cobalt (Kremling, 1983). 60 Co contamination appears to be largely con®ned to Chazhma Bay. 137 Cs concentrations in surface sediments varied between <1.7 and 19 Bq kgÿ1 dry wt. and elevated levels of 137 Cs were found near the month of the Razdolnaya River (Amursky Bay). 137 Cs concentration in bottom sediments was lowest in the open part of Peter the Great Bay and those in Amursky Bay were higher than those in Ussuriysky Bay. 239240 Pu activity concentrations in surface sediments collected during 1996 varied from 0.24 to 1.54 Bq kgÿ1 dry wt. 238 Pu activity concentrations in surface sediments varied between <0.003 and 0.03 Bq kgÿ1 dry wt. in Amursky Bay and between 0.003 and 0.01 Bq kgÿ1 dry wt. in Ussuriysky Bay (Table 5). Associated 238 Pu/239240 Pu activity ratios varied between 0.0087 and 0.0139 (with an average of 0.014 0.002) in Amursky Bay and between 0.012 and 0.017 (with an average of 0.014 0.002) in Ussuriysky Bay. Global fallout has an average 238 Pu/ 239240 Pu ratio of 0.0253 (UNSCEAR, 1993). Downcore 239240 Pu activity concentrations in sediments ranged from 0.01 to 1.26 Bq kgÿ1 dry wt. in
Amursky Bay and from 0.001 to 1.52 Bq kgÿ1 dry wt. in Ussuriysky Bay, and generally decreased with increasing depth (Table 6). Associated 238 Pu/239240 Pu activity ratios ranged from 0.02 to 0.08, and from 0.02 to 0.04, respectively (Table 6). Distribution of 239240 Pu concentrations in sediments Pu isotopes are particle reactive and hence to be bound to the bottom sediments. The distribution of Pu concentrations in a coastal and shelf region depends not only on the sources to that particular site but also on the nature of suspended particulate matter and sediments, and on the oxidation states of Pu in that environment (Baskaran et al., 1995). The distribution coecient (Kd ) for plutonium for sediment is very large, 1 ´ 105 (IAEA, 1985). The 239240 Pu inventories in bottom sediments at station CA in Amursky Bay and station CU in Ussuriysky Bay were estimated to be 66.2 and 99.5 Bq mÿ2 , respectively. Hong et al. (1996b) have reported sediment accumulation rates and sediment organic carbon concentration in Peter the Great Bay. According to Hong et al. 210 Pb-derived sediment accumulation rates are 173 and 118 mg cmÿ2 yrÿ1 in Amursky (station CA) and Ussuriysky (station CU) bays, respectively. The surface mixed layer in the core was present in Amursky Bay but not in Ussuriysky Bay. Sediment organic carbon contents in top 0±2 cm below sea ¯oor were 740 and 1953 lmol gÿ1 dry wt. in Amursky (station CA) and Ussuriysky (station CU) bays, respectively. It is also interesting to note that 210 Pb-derived sediment accumulation and mixing rates 939
Marine Pollution Bulletin TABLE 6 Pu isotopes in sediment column in Peter the Great Bay. 239240
Pu (Bq kgÿ1 )
238
Pu (Bq kgÿ1 )
238
Pu/239240 Pu
Region
Sta.
Depth (cm)
Amursky Bay
CA
0±2 2±4 4±6 8±10 12±14 16±18 20±22 22±24 26±28
1.257 0.093 0.760 0.037 0.835 0.044 0.304 0.022 0.022 0.004 0.021 0.003 0.072 0.005 0.068 0.004 0.012 0.002
0.105 0.023 0.014 0.003 0.021 0.004 <0.003 <0.003 <0.003
0.083 0.019 0.019 0.004 0.025 0.005
Ussuriysky Bay
CU
0±2 2±4 4±6 8±10 12±14 16±18 20±22 24±26 26±28
1.516 0.078 1.413 0.070 1.290 0.064 0.544 0.030 0.338 0.021 0.245 0.016 0.011 0.002 0.007 0.002 0.001 0.001
0.105 0.023 0.014 0.003 0.021 0.004 <0.003 <0.003 <0.003
0.019 0.004 0.007 0.002 0.019 0.004
are higher in station CA sediments from Amursky Bay than in Ussuriysky Bay (Hong et al., 1996b). Conversely, the 239240 Pu inventory and surface sediment activity levels are higher in station CU sediments from Ussuriysky Bay. This may be explained by the combined eects of lower sediment accumulation and mixing rates in CU station sediments; transport of plutonium from naval shipyard operations in the Bolshoy Kamen and Chazhma Bay areas; and/or more ecient scavenging and removal of 239240 Pu in the ®negrained and organic rich Ussuriysky Bay sediments. Fine organic rich sediments appear to have a strong anity for particle reactive radionuclides (Baskaran et al., 1996). Baskaran et al. also noted that during early diagenesis of sedimentary organic matter any manganese and iron present may be reduced and released into the interstitial waters. These reduced species can diuse into the overlying water column, re-oxidize and form hydrous oxides that act as eective scavenging agents for particle reactive radionuclides. 239240
Pu/239240 Pu activity ratios in Peter the Great Bay The major sources of plutonium to Peter the Great Bay are derived from the following sources: (1) atmospheric fallout from weapons testing; (2) riverine input from the erosion and leaching of soils; (3) direct discharge of nuclear euents; (4) long range transport from other regions (e.g., leaching of plutonium from decommissioned submarines, storage facilities, ocean dump sites) (Handler, 1995); (5) atmospheric input of resuspension of previously deposited fallout radionuclides on land; (6) the close-in fallout Ôhot particlesÕ from the nuclear accident in Chazhma Bay. The relative contributions from these sources have been assessed below. 238 Pu/239240 Pu activity ratios can be used to distinguish between dierent sources of plutonium in the marine environment. The reported 238 Pu/239240 Pu
940
Activity ratio
activity ratio in dumped reactors in the Kara Sea varies between 0.26 and 0.49 (Baskaran et al., 1996). Assuming the two major sources of plutonium in Peter the Great Bay are global atmospheric fallout and reactor related inputs and each source term can be de®ned by a unique 238 Pu/239240 Pu activity ratio, we can estimate the contribution of plutonium derived from non-global fallout sources as proposed by Baskaran et al. (1996). The measured 238 Pu/239240 Pu activity ratio can be expressed as the fractional sum of these two source terms, i.e., Am Ag 1 ÿ f Ar f ;
1
where Am is the measured 238 Pu/239240 Pu activity ratio, Ag the 238 Pu/239240 Pu activity ratio of global fallout (0.03), Ar the 238 Pu/239240 Pu activity ratio in reactorrelated euent (0.30, taken from Baskaran et al., 1996), f the fraction of plutonium derived from the reactorrelated source term. The fraction of plutonium derived from the reactor-related source term in any sample can therefore be calculated by solving for f, i.e., f Ar ÿ Am = Ar ÿ Ag :
2
The highest 238 Pu/239240 Pu activity ratios were observed in surface sediments collected from Amursky Bay station CA sediments. Taking this value, the upper estimate of the fraction of plutonium in this sample that is derived from reactor-related sources is around 19%. However, the 238 Pu/239240 Pu activity ratios in deeper layers of the sediment are less than 0.03. The dissolution rates of ®ne particles of 238 Pu oxide at neutral pH are about 200 times faster than for 239 Pu because of radiolytic fragmentation eects (Suchanek et al., 1996). The enrichment of 238 Pu in surface sediment could be related to either an increase in the availability of 238 Pu within the region (Suchanek et al., 1996) and subsequent uptake of 238 Pu onto ®ne surface sediment particles, or
Volume 38/Number 10/October 1999
to transport and deposition of contaminated sedimentary particles containing a high 238 Pu/239240 Pu signature, or both. 239240
Pu in mussels collected from Peter the Great Bay The 239240 Pu concentration of mussel samples collected from the central part of Peter the Great Bay (St. 1) was 12.6 mBq kgÿ1 dry wt. This compares with values ranging from 2.5 to 10.9 mBq kgÿ1 dry wt. (with an average of 5.9 mBq kgÿ1 dry wt.) and from <0.5 to 9.3 mBq kgÿ1 dry wt. (with an average of 3.6 mBq kgÿ1 dry wt.) in Amursky Bay and Ussuriysky Bay, respectively (Table 7). The highest value was observed in the middle of the bay. The mean 239240 Pu concentration in mussels from Peter the Great Bay was about 6 4 mBq kgÿ1 dry wt. The plutonium content of mussels in Peter the Great Bay is lower or comparable to other contaminated sites around the world. For examples, 239240 Pu contents in mussels were 12 8 mBq kgÿ1 dry wt. observed in the west coast of United States during 1990 (Valette-Silver and Lauenstein, 1995). These values are lower than the earlier observation during 1976±1978 of the Californian Mussel Watch Program (37 25 mBq kgÿ1 dry wt.) with the exception of the one high value of 130 5 mBq kgÿ1 dry wt. from the Farallon Islands nuclear waste dump site (Suchanek et al., 1996 and references therein). By comparison, mussels collected in 1984 along the coast of the United Kingdom contain 239240 Pu concentrations up to 1193 Bq kgÿ1 dry wt. in basal threads (McDonald et al., 1991, 1993). Similarly, edible species of clam and other invertebrates collected from Bikini Atoll in 1972±1980 contained between 10 and 122 Bq kgÿ1 dry wt. of 239240 Pu (Noshkin et al., 1988) suggesting that the levels of plutonium in Peter the Great Bay are not exceptionally high and are comparable with world-wide fallout values. Mussels are ecient ®lter feeders and may concentrate contaminants from surrounding waters by 200±300 fold. Consequently, mussels are commonly used in worldwide monitoring programs to assess pollutant levels in the natural environment. The average reported concentration factor (CF activity concentration in tissue/activity concentration in seawater) for plutonium in mollusks (except Cephalopods) is 3 ´ 103 (IAEA, 1985). Based on the range of 239240 Pu concentration in TABLE 7 239240
Pu (mBq kgÿ1 dry wt.) in mussels in Peter the Great Bay.
Region Open part of Peter the Great Bay Amursky Bay
Ussuriysky Bay
Station 1 7 4 8 9 10 11 5 6
239 240
Pu
12.6 2.3 4.5 1.4 5.7 1.8 5.8 1.7 10.9 2.3 2.5 0.9 1.5 0.9 9.3 2.2 <0.5
seawater (Table 1) and mussels (Table 7), the approximate concentration factor of 239240 Pu is estimated to be 0.3±2 ´ 103 in the region. In general, non-essential particle reactive trace metals such as lead and the actinide elements are mainly accumulated by animals from the dissolved phase while essential elements like copper and zinc are more likely to be accumulated from food. The plutonium assimilation eciency for mussels feeding on diatoms is about 1±8 and much lower than that of zinc (Fisher and Reinfelder, 1995). Data on other radionuclides concentration in mussel are very limited in the sea. Notable ones are reported here. Mussels (Mytilus edulis including shell and soft tissue) collected during 1988 reportedly contained 0.04 0.01 Bq kgÿ1 dry wt. of 137 Cs and 0.09 0.02 Bq kgÿ1 dry wt. of 60 Co in the south-western Korean coast of the East Sea (Lee, 1989). The 137 Cs activity concentration in the soft parts of the invertebrate, Stichopus japonicus, collected along the Japanese coastline during 1986 ranged from 0.03 Bq kgÿ1 wet wt. near Oshoro to 0.08 Bq kgÿ1 wet wt. near Tsuyazaki (Takeda and Misonou, 1991).
Conclusions We have determined arti®cial radionuclides in surface waters of the East Sea (Sea of Japan) proper and bottom sediments of Peter the Great Bay to assess the evolution and spatial distribution of dierent radionuclides. Based on the data presented in this paper, we draw the following observations and conclusions: (1) 137 Cs and 239240 Pu concentrations in the East Sea (Sea of Japan) proper during late October 1993 ranged from 2.6 to 3.7 Bq mÿ3 , and 3.5 to 20.8 mBq mÿ3 , respectively. The mean and range of concentrations observed was similar to those reported in August 1993 prior to the Russian dumping operation of 17 October 1993 and suggest that the 17 October 1993 Russian dumping did not signi®cantly aect the region. (2) The 90 Sr and 137 Cs concentrations in surface waters of Peter the Great Bay are not signi®cantly dierent to those in the East Sea proper. (3) 239240 Pu activity concentrations in surface sediments varied from 0.24 Bq kgÿ1 dry wt. in the open part of Peter the Great Bay to 1.54 Bq kgÿ1 dry wt. in Amursky Bay. 239240 Pu activity ratios ranged from 0.087 to 0.014 with an average of 0.011 0.002 in Amursky Bay, and from 0.012 to 0.018 with an average of 0.014 0.002 in Ussuriysky Bay. There appears to be no signi®cant plutonium contribution from sources other than global fallout. (4) The 239240 Pu inventories in sediments from Amursky Bay and from Ussuriysky Bay were 66.2 and 99.5 Bq mÿ2 , respectively. (5). 239240 Pu concentrations in mussels varied from 2.5 to 12.5 mBq kgÿ1 dry tissue wt. in the region, and the values are comparable to the non-nuclear facility in¯uenced areas and less than those found near nuclear fuel reprocessing plants. A preliminary study of radionuclide contamination in Peter the Great Bay shows low levels of radioactive contamination and isotope activity ratios and radionuclide 941
Marine Pollution Bulletin
inventories do not show evidence of any signi®cant anthropogenic contamination other than from global fallout despite the presence of a large number of nuclear facilities in the region. Along with the work of Russian scientists, this preliminary investigation shows that the present levels of radioactivity in Peter the Great Bay are consistent with those expected from global fallout deposition alone. However, we recommend that further studies should be conducted to help improve our present assessment and provide continuous radionuclide surveillance and monitoring. Sampling in Peter the Great Bay in 1996 was supported by the Center of Field Research, Earth Watch. Dr. J. M. Kim and Mr. D. J. Kang of KORDI assisted with sample collection during the AWARES 9310 cruise. Ms. S. H. Chung provided laboratory technical assistance. The authors thank Drs. M. Baskaran (Texas A&M University, USA), S. W. Fowler (IAEA-MEL) and D. S. Woodhead (MAFF, UK) for their critical comments and supplies of references. Work performed under the auspices of the Ministry of Science and Technology of Korea (BSPN00253) and U.S. Department of Energy at Lawrence National Laboratory under contract W-7405-Eng-48. Baskaran, M., Asbill, S., Santschi, P., Davis, T., Brooks, J., Champ, M., Makeyev, V. and Khlebovich, V. (1995) Distribution of 239;240 Pu and 238 Pu concentrations in sediments from the Ob and Yenisey Rivers and the Kara Sea. Applied Radiation and Isotopes 46, 1109± 1119. Baskaran, M., Asbill, S., Santschi, P., Brooks, J., Champ, M., Adkinson, D., Colmer, M. R. and Makeyev, V. (1996) Pu, 137 Cs and excess 210 Pb in Russian Arctic sediments. Earth and Planetary Science Letters 140, 243±257. Chumichev, V. B. (1966) Strontium-90 content in the waters of the Paci®c Ocean in 1962 and in 1964. Transactions of the Institute of Oceanology, Academy of Sciences of the USSR 82, 20±23 (in Russian). Chumichev, V. B. (1972) Strontium-90 in the north-western parts of the Paci®c Ocean in 1966±1968. Transactions of the Institute of Experimental Meteorology, Hydrometeorological Service of the USSR 1 (32), 45±50 (in Russian). Danilyan, V. A. and Vysotsky, V. A. (1995) Nuclear waste disposal practice in RussiaÕs Paci®c Ocean Region. Arctic Research of the United States 9, 84±87. Fisher, N. S. and Reinfelder, J. R. (1995) The trophic transfer of metals in marine systems. In Metal Speciation and Bioavailability in Aquatic Systems, eds. A. Tessier and D. R. Turner, pp. 363±406. Wiley, New York. Hamilton, T. F., Millies-Lacroix, J. C. and Hong, G. H. (1996) 137 Cs (90 Sr) and Pu isotopes in the Paci®c Ocean: sources and trends. In Radionuclides in the Oceans, Inputs and Inventory, eds. P. Guegueniat, P. Germain and H. Metivier, Les Editions de Physiques, pp. 29±58. Hamilton, T. F., Ballestra, S., Baxter, M. S., Gastaud, J. Osvath, I., Parsi, P., Povinec, P. O. and Scott, E. M. (1994) Radiometric investigations of Kara Sea sediments and preliminary radiological assessment related to dumping of radioactive wastes in the Arctic Seas. Journal of Environmental Radioactivity 25, 113±134. Handler, J. (1995) The radioactive waste crisis in the Paci®c Area. Arctic Research of the United States 9, 105±108. Hirose, K., Aoyama, M., Hatori, M. and Igarashi, Y. (1993) 137 Cs and plutonium in the Japan Sea. Journal of Radiation Research 34, 386. Hirose, K., Hong, G. H. and Miyao, T. (1996). A preliminary study of the temperature structure in the north central Japan Sea. Oceanographical Magazine 45, 1±8. Hirose, K., Amano, H., Baxter, M. S., Chaykovskaya, E., Chumichev, V. B., Hong, G. H., Isogai, K, Kim, C. K., Kim, S. H., Miyao, T., Morimoto, T., Nikitin, A., Oda, K., Pettersson, H. B. L., Povinec, P. P., Seto, Y., Tkalin, A., Togawa, O., Veletova, N. K., (1998) Anthropogenic radionuclides in seawater in the East Sea/Japan Sea: Results of the ®rst stage Japanese-Korean-Russian expedition. Journal of Environmental Radioactivity 43, 1±13.
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