137Cs and 239+240Pu levels in the Asia-Pacific regional seas

Journal of Environmental Radioactivity 76 (2004) 139–160 www.elsevier.com/locate/jenvrad

137

Cs and

239þ240

Pu levels in the Asia-Pacific regional seas

E.B. Duran a,, P.P. Povinec b, S.W. Fowler b, P.L. Airey c, G.H. Hong d a

Philippine Nuclear Research Institute, Commonwealth Avenue, Diliman, Quezon City, Philippines b International Atomic Energy Agency, Marine Environment Laboratory, 4, Quai Antoine 1er, MC 98012, Monaco c Australian Nuclear Science and Technology Organization, PMB 1 Menai NSW 2234, Australia d Korea Ocean Research and Development Institute, Ansan P.O. Box 29, 425-600, South Korea Received 21 May 2003; received in revised form 20 October 2003; accepted 24 November 2003

Abstract 137

Cs and 239þ240 Pu data in seawater, sediment and biota from the regional seas of Asiav v v v Pacific extending from 50 N to 60 S latitude and 60 E to 180 E longitude based on the Asia-Pacific Marine Radioactivity Database (ASPAMARD) are presented and discussed. 137 Cs levels in surface seawater have been declining to its present median value of about 3 Bq/m3 due mainly to radioactive decay, transport processes, and the absence of new significant inputs. 239þ240 Pu levels in surface seawater are much lower, with a median of about 6 mBq/m3. 239þ240 Pu appears to be partly scavenged by particles and is therefore more readily transported down the water column. As with seawater, 239þ240 Pu concentrations are lower than 137Cs in surface sediment. The median 137Cs concentration in surface sediment is 1.4 Bq/kg dry, while that of 239þ240 Pu is only 0.2 Bq/kg dry. The vertical profiles of both 137 Cs and 239þ240 Pu in the sediment column of coastal areas are different from deep seas which can be attributed to the higher sedimentation rates and additional contribution of run-offs from terrestrial catchment areas in the coastal zone. Comparable data for biota are far less extensive than those for seawater and sediment. The median 137Cs concentration in fish (0.2 Bq/kg wet) is higher than in crustaceans (0.1 Bq/kg wet) or mollusks (0.1 Bq/kg wet). Benchmark values (as of 2001) for 137Cs and 239þ240 Pu concentrations in seawater, sediment and biota are established to serve as reference values against which the impact of future anthropogenic inputs can be assessed. ASPAMARD represents one of the most com-

 Corresponding author. Present address: Vancouver Coastal Health, VGH-OH&S, 855 West 12th Avenue, Vancouver, B.C., Canada V5Z 1M9. Fax: +63-2-920-1646. E-mail address: [email protected] (E.B. Duran).

0265-931X/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2004.03.023

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E.B. Duran et al. / J. Environ. Radioactivity 76 (2004) 139–160

prehensive compilations of available data on 137Cs and 239þ240 Pu in particular, and other anthropogenic as well as natural radionuclides in seawater, sediment and biota from the Asia-Pacific regional seas. # 2004 Elsevier Ltd. All rights reserved. Keywords: Cesium-137; Plutonium isotopes; Marine radioactivity; Anthropogenic radionuclides; Seawater; Sediment; Biota; Asia-Pacific regional seas

1. Introduction 1.1. Asia-Pacific Marine Radioactivity Database (ASPAMARD) Data on radionuclide levels in the oceans and seas of Asia (including the Indian sub-continent) and to a limited extent, South Pacific region were compiled into a database referred to as the Asia-Pacific Marine Radioactivity Database (ASPAMARD). The development of ASPAMARD was funded jointly by the International Atomic Energy Agency Regional Cooperative Agreement (IAEA/RCA) and the United Nations Development Programme (UNDP) with the following aims: (1) to provide reference or benchmark levels of key anthropogenic radionuclides in the regional seas against which the impact of future man-made contributions can be evaluated; (2) to characterize the distribution and fate of key radioactive contaminants in the regional seas; (3) to better understand transport processes and the fate and behaviour of radionuclides and analogue contaminants in the marine environment; and (4) to assess dose associated with the ingestion pathway for seafood (Duran, 2001). ASPAMARD is a collection of marine radioactivity data contributed by Australia, Bangladesh, China, India, Indonesia, Republic of Korea, Malaysia, Pakistan, Philippines, Sri Lanka, Thailand and Vietnam under the project and from published literature. This paper presents in summary form the ASPAMARD data on key anthropogenic radionuclides, 137Cs and 239þ240 Pu, in seawater, sediment and biota. The v v database covers the regional seas extending from 50 N to 60 S latitude and from v v 60 E to 180 E longitude. The period covered by the database is from 1975 to 2001. 1.2. Significance The marine ecosystem is a valuable resource especially to the Asia-Pacific region as a source of food, livelihood, and economic trade and commerce. Of the total world nominal catch amounting to roughly 93 million tons in 1999, about 43% was contributed by countries belonging to Asia alone (FAO, 2001). More than half of the world’s population live in Asia and consume fish and other seafood regularly as part of their daily diet. The presence of anthropogenic radionuclides in the marine environment can thus lead to radiation exposure through the ingestion of seafood. Monitoring programs and studies such as the recent IAEA’s Marine Radioactivity Dose Assessment (MARDOS) project have aimed at determining the

E.B. Duran et al. / J. Environ. Radioactivity 76 (2004) 139–160

141

concentrations of 137Cs or 239þ240 Pu in seawater, sediment, or biota and have produced a large amount of data and information on these radionuclides (IAEA, 1995). Based on MARDOS, it was estimated that the Collective Effective Dose Commitment (CEDC) due to 137Cs in marine food was roughly 160 man-Sv for a world population of 5:3  109 in 1990 (IAEA, 1995). The combined FAO areas 57, 61 and 71 which belong to the region of interest contributed about 25% to this CEDC. The region’s oceans (Northwest Pacific and marginal seas plus Bay of Bengal) cover a large area of about 140 million km2 representing roughly 40% of the total surface area of the world’s oceans. Water does not recognize territorial boundaries and hence contaminants, regardless of whether they are radioactive or non-radioactive, can be transported from one area to another by water masses. Sediment, water and biota play an important role in the cycling of contaminants. The sediment accumulates radionuclides as a result of scavenging and settling processes in the water column. Marine biota concentrate radionuclides in their system through direct absorption and/or via ingestion of other organisms and form fecal pellets, which subsequently accelerate sinking of radionuclides. Water acts as the principal medium of transport between biota and sediment. Certain radionuclides are good tracers of water movement, or the transport of substances in the water column and sediment. Hence, information on the distribution and fate of these radionuclides can contribute to the understanding of the transport processes of non-radioactive contaminants that behave similarly. The anthropogenic radionuclides 137Cs and 239þ240 Pu are important indicators of radioactive contamination of the marine environment, and are of primary interest because of existing inventories and possible health effects. 137Cs, which has a halflife of 30.2 years, can also serve as a conservative tracer of the transport and accumulation patterns of contaminants in seawater. 1.3. Sources of

137

Cs and

239þ240

Pu

During the period 1945–1980, a total of 543 atmospheric nuclear weapons tests were conducted, principally in the Northern hemisphere, releasing an estimated fission yield of 189 megatons (UNSCEAR, 2000). 137Cs in the regional seas studied can be attributed mainly to the nuclear weapons tests especially during the periods 1951–1958 and 1961–1962. Other more localized sources of 137Cs in the marine environment include fallout from the Chernobyl accident (UNSCEAR, 2000) and routine nuclear power plant operations (as a constituent of low-level radioactive liquid effluents). 137Cs is also among the beta-gamma emitters which contribute about 98% of the total activity to the wastes dumped into the Atlantic and Pacific Oceans, excluding wastes dumped by Former Soviet Union and Russian Federation (IAEA, 1999). 239 Pu and 240Pu are alpha emitting nuclides with half-lives of 2:4  104 and 6:57 103 years, respectively, and are important indicators of radioactive contamination of the marine environment. Global fallout is the main source of plutonium in the marine environment of the Pacific region with minor close-in fallout from the

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E.B. Duran et al. / J. Environ. Radioactivity 76 (2004) 139–160 v

v

Bikini and Enewetak Atolls of the Marshall Islands (ca. 9 N, 168 E) and v v Mururoa Atolls (ca.15 S, 140 W). Although relatively small quantities of alpha emitters were included in the wastes that were dumped into the seas, about 96% comprised plutonium and americium isotopes (IAEA, 1999).

2. Data and results 2.1. Seawater 2.1.1. 137Cs 137 Cs is one of the best-studied radionuclides in the marine environment, especially in seawater. In ASPAMARD, for example, the database on 137Cs levels in seawater is the largest and is based on 24 published papers or reports which cover the period from 1975 to 2001 (Table 1). Data reported under the UNDP/ IAEA/RCA project pertain mainly to coastal areas, while data obtained from published literature were mostly for samples from deep seas. Fig. 1 shows the frequency distribution of 137Cs data in surface waters (up to 50 m deep). The data were corrected for radioactive decay to March, 2001 to arrive at benchmark values which can still be considered relevant to the present. March, 2001 was used as the reference date since it is the latest sampling date of data included in this review. The data does not follow a normal distribution but is skewed right with moderate skewness (0.6) and kurtosis (1.2). A median of 2.8 Bq/ m3 and a mean of 3  1:2 Bq/m3 (n ¼ 486) were obtained, where 1.2 is the standard deviation (SD) at 1r. About 71% of the values were within the range of 2–4 Bq/m3. The range of all values (0.2–8.2 Bq/m3) is large, mainly because the area covered v v v in ASPAMARD is also large, extending from 50 N to 60 S latitude and from 60 v E to 180 E longitude. Most of the nuclear weapons tests were conducted in the Northern Hemisphere. Deposition rates (directly into the ocean and run-off from terrestrial catchment areas) and residence times of 137Cs from these tests appear to vary with latitude. The highest value for surface concentration was observed off the China coast and may have originated from fallout radionuclides deposited on land and carried subsequently to the coastal zone due to siltation. Data at different lativ tudes (grouped in 5 latitudinal bands) which can serve as benchmark concentration values for 137Cs in surface seawater are presented in Table 2. As can be seen from Table 2, most of the available data are for the areas surrounding the Republic of Korea, Japan and to some extent, China. These are the East Sea/Sea of Japan, Yellow Sea, East China Sea and Northwest Pacific Ocean (Fig. 2). Japan has the highest number of nuclear power plants in Asia (53 in operation) and therefore has one of the most extensive radiological monitoring programs in Asia (IAEA, 2001). Further, the Northwest Pacific Ocean proximal to Japan and the Republic of Korea were the only areas in the Asia-Pacific oceans where radioactive wastes were dumped by Japan, Republic of Korea, and Former Soviet Union and Russian Federation (IAEA, 1999; Danilyan and Vysotsky, 1995;

East Sea/Sea of Japan East Sea (Sea of Japan), Peter the Great Bay East Sea/Sea of Japan Korea Strait, Yellow Sea, East China Sea, Western Pacific Ocean South Sea of Korea (Cheju Strait), East Sea (Sea of Japan), Yellow Sea, Korea Strait, South Sea of Korea (Korea Strait) Korean Seas Northwest Pacific Ocean North Central East Sea, Sea of Japan Central North Pacific Ocean Northeast Pacific Ocean, East Tropical Ocean Pacific Ocean (Northwest, Western Central, Southwest Pacific Ocean) North Pacific Ocean, South Pacific Ocean, Indian Ocean, Southwest Pacific Ocean, Sea of Japan Pacific Ocean (Ibaraki Coast) Northwest Pacific Ocean East China Sea, Yellow Seas East China Sea, Philippine Sea Philippine Sea South China Sea (Western Sulu Sea, Manila Bay, Babuyan channel, Currimao Port, Mindoro Strait) Central Bohai Sea, Liazhou Bay, Bohai Bay, Liaodong Bay, Jinzhou, Yingkou, Dalian, Dandong, Tianjing, Qindao, Lianyungang, East China Sea, Zhejiang coast, Fujian coast, Qinshou, Zapu, Jinshau, Nauhui, Zoushou, Guandong coast

Sampling location

Table 1 Sources of data on seawater in ASPAMARD

Sr Sr

Sr, 210Po

90

90

90

239þ240

Pu,

Am

241

Cs

137

137

Cs Cs, 239þ240 Pu 137 Cs, 239þ240 Pu, 90Sr 210 Po, 210Pb 137 Cs, 210Po, 226Ra, 90Sr 137 Cs, 210Po

137

Cs,

137

239þ240

Pu, 3H Pu 239þ240 Pu, 90Sr 239þ240 Pu, 90Sr 241 239þ240 Pu, Am 239þ240 Pu, 238Pu 137

Cs, Cs, 137 Cs, 137 Cs,

137

239þ240

239þ240

137

Pu,

Pu 239þ240 Pu 239þ240 Pu, 239þ240 Pu,

Cs,

239þ240

Cs, 137 Cs, 137 Cs, 137 Cs,

137

Radionuclides

a

a a a a a a

a

a a a a a a

a

a a a a

Surface

Depth Bottom

a a a

a

a a a

a

a

a

(continued on next page)

Cai et al. (1992)

Yamada and Nagaya (1998) Nagaya and Nakamura (1987a) Nagaya and Nakamura (1992) Nozaki et al. (1990) Duran et al. (2001) Duran et al. (1994)

Miyake et al. (1988)

Kim et al. (1997) Hirose et al. (1992) Hirose et al. (1989) Nagaya and Nakamura (1984) Sakanoue (1987) Nakanishi et al. (1984)

Chung (2000)

Yamada et al. (1996) Hong et al. (1999a) Hong (1996) Hong (1996)

References

E.B. Duran et al. / J. Environ. Radioactivity 76 (2004) 139–160 143

Table 1 (continued )

a, data are provided.

Gulf of Thailand, Andaman Sea Semarang Coast, Muria and Krakal Bay Strait of Malacca Halong Bay Karachi coast, Arabian Sea Bay of Bengal Bay of Bengal

Gulf of Thailand

Sampling location

137

239þ240

241

14

Po, Cs, Pu, Am, C, 40K, 90Sr 239þ240 Pu Gross a, b, 40K, 232Th 239þ240 Pu, 210Pb 137 Cs 137 Cs, 40K, 226Ra, 228Ra 134 Cs, 137Cs, 40K 137 Cs, 134Cs, 40K

210

Radionuclides

a a a a a a a

a

Surface

Depth Bottom

Mahapanyawong et al. (1992) Wood (1999) Wood (1999) Quang et al. (1997) Qureshi et al. (1991) Miah (1999) Alam et al. (1996)

Mahapanyawong et al. (1992)

References

144 E.B. Duran et al. / J. Environ. Radioactivity 76 (2004) 139–160

E.B. Duran et al. / J. Environ. Radioactivity 76 (2004) 139–160

Fig. 1. Frequency distribution of surface water 2001).

145

137

Cs concentration data (decay-corrected to March,

Table 2 137 Cs concentrations (decay-corrected to March, 2001) in surface seawater at different latitudinal bands Coordinates v

45 v 40 v 35 v 30 v 25 v 20 v 15 v 10 v 05 v 00 v 00 v 10 v 15 v 20 v 25 v 30 v 35 v 40 v 45 v 50 v 60

010 –50 v 010 –45 v 010 –40 v 0 01 –35 v 010 –30 v 0 01 –25 v 010 –20 v 0 01 –15 v 010 –10 v 0 00 –05 v 000 –05 v 0 01 –15 v 010 –20 v 0 01 –25 v 010 –30 v 0 01 –35 v 010 –40 v 0 01 –45 v 010 –50 v 0 01 –60 v 010 –65 v

N N N N N N N N N N S S S S S S S S S S S

n

Range (Bq/m3)

Median (Bq/m3)

Mean  SD (Bq/m3)

7 19 125 116 46 33 17 40 21 19 6 4 3 4 3 3 6 4 4 3 2

1.4–3.8 2.2–4.9 0.2–8.4 1.6–6.2 1.9–6.5 0.3–5.2 0.4–6.4 1.9–6.4 1.3–4.3 1.7–4.3 2.0–3.7 2.5–3.9 2.5–3.3 2.3–3.0 2.3–3.3 2.6–3.5 1.0–3.3 1.0–2.0 1.3–1.7 0.4–1.3 0.4–0.7

3.0 2.6 2.6 2.7 4.6 2.9 4.0 3.0 3.3 2.7 3.1 3.0 2.7 2.7 2.5 2.7 1.5 1.5 1.4 0.9 0.5

2:9  0:8 2:8  0:6 2:8  1:0 3:1  1:1 4:3  1:4 2:3  1:8 3:8  1:4 3:2  1:0 3:1  0:8 2:7  0:7 2:9  0:7 3:1  0:6 2:8  0:4 2:7  0:3 2:7  0:5 2:9  0:5 1:9  0:9 1:5  0:4 1:5  0:2 0:9  0:4 0:5  0:2

n ¼ number of sampling locations. SD ¼ standard deviation.

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E.B. Duran et al. / J. Environ. Radioactivity 76 (2004) 139–160

Fig. 2. Sampling locations of surface seawater used for 137Cs concentration measurements.

Sivintsev and Kihnadze, 1998). Very few data (especially recent data) on levels of 137 Cs in the South Pacific waters were available for inclusion in ASPAMARD. Recent publications suggest that 137Cs concentrations in surface seawater have been decreasing over time. Hong et al. (1999a) showed that the 137Cs in surface water in the East Sea/Sea of Japan is decreasing from a range of about 4.9 to 8.5 Bq/m3 in the 70s to 3.2 to 5.1 Bq/m3 in the 80s to 2.5 to 3.7 Bq/m3 in the 90s. Further, recent data obtained by Mahapanyawong et al. (1992) between 1989 and 1991 indicate that 137Cs concentrations in surface water of the Gulf of Thailand appear to have stabilized to 3–4 Bq/m3, at least during the three-year period of observation. Hirose et al. (1992) monitored 137Cs levels in surface seawater between the period of 1979–1987. Their data also suggest a decreasing trend in 137Cs with time. This implies that: (1) physical radioactive decay is a major factor in the changes of 137Cs concentrations over time; and (2) there are no new, significant inputs of 137Cs in the general region of interest except for about 0.1–0.4 PBq over the East Sea/Sea of Japan contributed by the Chernobyl accident in 1986 (Miyao et al., 1998).

E.B. Duran et al. / J. Environ. Radioactivity 76 (2004) 139–160 Table 3 Changes in Period

1975–1979 1980–1984 1985–1989 1990–1994 1995–2001

147

137

Cs concentrations in surface seawater with time n

131 42 38 107 168

Measured 137Cs concentration at the time of sampling (Bq/m3)

Calculated 137Cs concentration decay-corrected to March, 2001 (Bq/m3)

Median

Mean  SD

Median

Mean  SD

5.9 5.8 4.1 3.1 2.8

6:3  2:6 5:9  2:3 4:4  1:6 3:2  0:9 2:7  1:0

3.5 3.7 2.9 2.6 2.6

3:6  1:4 3:9  1:5 3:2  1:1 2:6  0:7 2:5  0:9

n ¼ number of sampling locations. SD ¼ standard deviation.

The effect of physical radioactive decay on 137Cs concentrations and the absence of new, significant inputs can be better appreciated by looking at the data in Table 3. From 1975 to the present, measured 137Cs concentrations in various sampling locations showed a steady decline. 137Cs concentrations in seawater were highest during the period 1975–1979. By 2001, disregarding the effect of other factors such as transport processes and taking into account only radioactive decay, and assuming further that there were no significant new inputs overall, present median levels contributed by existing inventories during 1975–1979 would be about 3.5 Bq/m3 after about one half-life has elapsed. However, the median 137Cs concentration based on more recent data from 1995 to March 2001 (actual measurements) is 2.5 Bq/m3. This is even lower than the expected, decay-corrected value of about 3.5 Bq/m3, leaving the possibility that transport processes may also be significant. Anthropogenic radionuclides are usually transported down the water column mainly by advection, diffusion or particle scavenging processes. Hirose et al. (1992) reported that less than 1% of the total 137Cs in surface waters was in particulate phase. The dissolved 137Cs is transported by the wind-driven and tidal currents, and by dispersion. When the data on 137Cs concentrations (decay-corrected to March, 2001) in the water column of Asia’s regional seas are plotted against depth (Fig. 3), it becomes evident that most of the 137Cs is retained in the surface or near-surface layer and decreases significantly only beginning at great depths of about 1000 m. 2.1.2. 239þ240Pu Data on 239þ240 Pu in seawater that were compiled in ASPAMARD covered only the Northern Hemisphere; there is clear lack of accessible data for the Southern Hemisphere (Table 1). 239þ240 Pu concentrations in surface waters (up to 50 m deep) at various latitudinal bands in the region of interest are shown in Table 4. The concentrations of 239þ240 Pu are at least two orders of magnitude lower than those of 137Cs as expected from the global fallout. However, the plutonium isotopes have physical half-

148

E.B. Duran et al. / J. Environ. Radioactivity 76 (2004) 139–160

Fig. 3. Depth profile of 137Cs concentrations (decay-corrected to March, 2001) in the water column of several regional seas in Asia-Pacific.

lives of thousands of years, and have therefore not decayed appreciably in postnuclear weapons testing times. Whether they are more persistent than 137Cs in the surface layers will depend on the efficiency of vertical dispersion processes. In general, 239þ240 Pu levels appear to be higher at higher latitudes and lower at lower latitudes due to specific deposition from the atmosphere to the oceans (Table 4). The highest concentrations were observed in the East China Sea, confirming the observations of Nagaya and Nakamura (1992) who attribute the higher values observed in the East China Sea to the transport of radionuclides from the Chinese side of the continent to the East China Sea by the Yangtze River. Hirose Table 4 239þ240 Pu concentrations in surface seawater at different latitudinal bands (Northern Hemisphere) Coordinates v

40 v 35 v 30 v 25 v 20 v 15 v 10 v 05 v 00

010 –47 v 010 –40 v 0 01 –35 v 010 –30 v 0 01 –25 v 010 –20 v 0 01 –15 v 010 –10 v 0 00 –05 v

N N N N N N N N N

n

Range (mBq/m3)

Median (mBq/m3)

18 84 55 28 6 18 18 16 18

3.4–34.8 2.2–38.9 2.2–84.3 1.1–31.0 3.5–20.7 3.2–11.0 0.8–7.3 1.6–10.4 2.2–40.0

13.6 7.1 5.9 4.8 6.2 6.5 4.2 2.7 3.5

n ¼ number of sampling locations.

E.B. Duran et al. / J. Environ. Radioactivity 76 (2004) 139–160

149

et al. (1992) have shown that the total plutonium concentration in the mid-latitude v v region (ca. 20 to 30 N) in 1987 decreased to roughly one-fifth of its 1979 value. 239þ240 Pu in surface water of the Pacific Ocean is due to global deposition of fallout from nuclear weapons tests. More than 90% of the atmospheric nuclear weapons tests were conducted in the Northern Hemisphere; therefore, the levels in the South Pacific should be much lower. 239þ240 Pu values in surface seawater ranged from 0.8 to 84.3 mBq/m3 with a median of 5.9 mBq/m3 (n ¼ 261). However, about 92% of the data were between the range of 0.8–14 mBq/m3 only, with a frequency distribution that is also skewed right (Fig. 4). For medium-depth waters (51–1000 m deep), 239þ240 Pu levels ranged from 2.2 to 71.5 mBq/m3 with a higher median of 29 mBq/m3 (n ¼ 93). For bottom waters (>1000 m), the median is 15 mBq/m3 (n ¼ 91), with values ranging from 0.8 to 60 mBq/m3. The wide range of values suggests variability in the levels of 239þ240 Pu. The higher values observed for waters deeper than 50 m suggest that the plutonium isotopes are more actively removed from the surface layer. This is also evident in the depth profile of 239þ240 Pu (Fig. 5). 239þ240 Pu does not appear to be retained on the surface layer unlike 137Cs, when comparing Figs. 3 and 5. Physical radioactive decay is not the cause for this decrease in surface concentrations; thus, transport processes both horizontally with the water masses and vertically in the water column are the most probable causes. Unlike 137Cs which remains mainly at the surface mixed layer, 239þ240 Pu appears to reach maximum concentration at sub-surface depths of several hundred meters, decreases, then increases again near or at the bottom of the water column (Nagaya and Nakamura, 1992). Hamilton et al. (1996) have noted that between 30% and 60% of the total 137Cs inventory in the water column is retained in the surface

Fig. 4. Frequency distribution of surface seawater 239þ240 Pu concentration data.

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E.B. Duran et al. / J. Environ. Radioactivity 76 (2004) 139–160

Fig. 5. Depth profile of Pacific.

239þ240

Pu concentrations in the water column of several regional seas in Asia-

mixed layer of the Western North Pacific Ocean while only 1–6% of the total 239þ240 Pu inventory is retained in the surface layer. It appears that vertical transport down the water column significantly affects the levels of 239þ240 Pu in the surface layer. While 137Cs is readily leached by seawater, 239þ240 Pu is comparatively insoluble and usually occurs as oxides associated with particles or colloids which eventually settle to the bottom and become incorporated in the bottom sediment. Indeed, it has been shown that 239þ240 Pu is preferentially scavenged by particles compared with 137Cs (Hirose et al., 1992). Fowler et al. (1983) also demonstrated that zooplankton fecal pellets scavenge transuranic elements as they sink through the water column, since these pellets contain relatively high concentrations of 239þ240 Pu and 241Am. Thus, particle scavenging appears to be an important mode of removal of 239þ240 Pu from surface to sub-surface waters. 2.2. Sediment 2.2.1. 137Cs The sources of data on radionuclide concentrations in bottom sediment in ASPAMARD are shown in Table 5. There were no sediment data for the Southern Hemisphere in ASPAMARD. 137 Cs concentrations (decay-corrected to March, 2001) observed in surface sediment (0–2 cm) collected from areas in the Northern Hemisphere ranged from 0.08 to 23.4 Bq/kg dry, with a median concentration of 1.4 Bq/kg dry (n ¼ 86). These data are presented in Table 6. The highest 137Cs levels in surface sediment were v v observed in the East Sea/Sea of Japan within the 35 N to 40 N band.

E.B. Duran et al. / J. Environ. Radioactivity 76 (2004) 139–160

151

Table 5 Sources of data on sediment in ASPAMARD Sampling location

Radionuclides

Niu Bay Western Northwest Pacific

239þ240

East Sea/Sea of Japan East Sea (Yamato Ridge, Korea Plateau, Ulleung Basin, Japan Basin) East Sea (Korea) Ulleung Basin East China Sea and Yellow Sea Bohai Sea, Liaizhou Bay, Bohai Bay, Liaodong Bay, Jinzhou, Yingkou, Dalian, Daudong, Tianjing, Qiudao, Fijuian, East China Sea, Yellow Sea South China Sea (Lingayen Gulf) Manila Bay, Malampaya Sound St. of Jahor Gulf of Thailand

210

Pu, 237Np Cs, 239þ240 Pu

137

Gulf of Thailand Semarang Muria Peninsula Bay of Bengal Bay of Bengal Bay of Bengal Karachi Coast/Arabian Sea

Pb Cs, 239þ240 Pu, 238Pu, 90Sr, 210 Pb, 241Am 239þ240 Pu, 137Cs, 238Pu, 239þ240 Pu,137Cs, 210Pb 137 Cs 137

210

Po, 137Cs, 226Ra Cs, 210Po 210 Pb, 232Th, 238U 137 Cs, 234U, 238U, 228Th, 230Th, 232 Th, 210Pb, 239þ240 Pu 90 Sr, 137Cs, 239þ240 Pu, 241Am, 14 C, 40K, 232Th, 234U 40 K, 232Th 226 Ra, 228Ra, 40K, 228Th 137 Cs, 232Th, 238U, 40K, 241Am 241 Am, 238U, 232Th 137 Cs, 40K, 226Ra, 228Ra 137

References Sakanoue (1987) Nagaya and Nakamura (1987a) Hong et al. (1997) Hong et al. (1999b) Lee et al. (1998) Nagaya and Nakamura (1992) Cai et al. (1992)

Duran et al. (1998) Sombrito et al. (2001) Wood et al. (1997) Srisuksawad et al. (1997) Mahapanyawong et al. (1992) Basuki et al. (1998a) Miah (1999) Alam et al. (1997) Islam et al. (1997) Qureshi et al. (1991)

Several authors reported 137Cs concentrations at different depths of the sediment column up to about 30 cm. The median values of the reported concentrations (decay-corrected to March, 2001) for each layer of the sediment core were calculated and plotted to show typical depth profiles for major regional seas (Fig. 6). The concentrations naturally vary from one sampling location to another depending on sources and removal processes, and from coastal areas to deep seas. SiteTable 6 137 Cs concentrations in surface sediment (0–2 cm) at different latitudinal bands (Northern Hemisphere) Coordinates v

40 v 35 v 30 v 25 v 20 v 15 v 10 v 05

010 –45 v 010 –40 v 010 –35 v 0 01 –30 v 010 –25 v 0 01 –20 v 010 –15 v 0 01 –10 v

N N N N N N N N

n

Range (Bq/kg dry)

Median (Bq/kg dry)

6 9 4 4 34 4 15 10

0.6–23.4 0.5–14.9 1.4–4.5 0.2–0.4 0.1–3.9 0.9–1.9 0.6–3.4 0.7–1.4

1.7 9.7 1.8 0.3 1.4 1.2 1.2 1.3

n ¼ number of sampling locations.

152

E.B. Duran et al. / J. Environ. Radioactivity 76 (2004) 139–160

Fig. 6. Vertical profile of ferent layers of cores.

137

Cs in the sediment column of regional seas based on median values for dif-

specific values are also needed when considering the effects of sedimentation rates, but the general trend nonetheless suggests that much of the 137Cs is retained in the surface (0–2 cm) or near-surface layer (2–4 cm) especially for the deep seas (Fig. 6). Nagaya and Nakamura (1987a) observed uniform concentrations of 137Cs in the near-surface layer of the column followed by a decreasing trend with depth in Northwest Pacific Ocean. It is well established that 137Cs appears to be preferentially bound to clay and organic particles and is strongly adsorbed on cation-exchange sites. As such, it is relatively immobile in sediment which is the basis for its use in estimating sedimentation rates. This accounts, at least in part, for the retention of 137Cs in the near-surface layer, particularly in areas where the sedimentation rate is low. In the case of the coastal East China/Yellow Sea where the sedimentation rates are higher than in the deep seas, median 137Cs concentrations are high to up about 8 cm. The transport of radionuclides from the Chinese side of the continent to the East China Sea by the Yangtze River appears to be a major contributor to observed radionuclide levels (Nagaya and Nakamura, 1992). 2.2.2. 239þ240Pu Most of the data in ASPAMARD on 239þ240 Pu concentrations in sediment cover the higher latitudes (Table 5). 239þ240 Pu concentrations in surface sediment (0–2 cm) ranged from 0.02 to 3.7 Bq/kg dry with a median of 0.2 Bq/kg dry (n ¼ 30). The ratios of Pu to Cs in sediment for the available data fall within the typical Pu/ Cs ratio range of 0.02–0.5 which has been observed for the Northern Hemisphere

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153

Table 7 239þ240 Pu concentrations in surface sediment (0–2 cm) at different latitudinal bands (Northern Hemisphere) Coordinates v

40 v 35 v 30 v 25 v 10

0

v

01 –45 v 010 –40 v 0 01 –35 v 010 –30 v 0 01 –15

N N N N N

n

Range (Bq/kg dry)

Median (Bq/kg dry)

7 10 4 4 5

0.1–2.7 0.1–3.7 0.1–0.4 0.02–0.5 0.03–0.1

0.2 2.2 0.2 0.1 0.1

n ¼ number of sampling locations.

in several studies. The median 239þ240 Pu concentration values observed at different v latitudes (grouped into 5 bands) are listed in Table 7. The highest values were v observed in the East Sea and Western Northwest Pacific Ocean between 35 N to v 40 N. Lower concentrations were observed at lower latitudes. The vertical profile for Western Northwest Pacific (deep sea) and East China Sea/Yellow Sea (coastal) based on median values (n ¼ 109) for different layers of the sediment column is shown in Fig. 7. Most of the sediment samples for East China Sea/Yellow Sea were collected at water depths of 40–65 m. In contrast, the samples from the Western Northwest Pacific were collected at water depths of 3000–6000 m. Vertical profiles of coastal areas are different from deep seas

Fig. 7. Vertical profiles of 239þ240 Pu concentrations in the sediment column of the deep Western Northwest Pacific and coastal East China Sea/Yellow Sea.

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mainly because: (1) coastal areas receive additional inputs of radionuclides from land-based sources due to run-offs from catchment areas, and (2) sedimentation rates are approximately three orders of magnitude lower in deep seas compared to coastal areas. Thus, in general, 239þ240 Pu concentrations in sediment from the East China Sea /Yellow Sea are higher than from the Western Northwest Pacific. For East China Sea/Yellow Sea, the same median value of 0.2 Bq/kg dry was obtained for each 2-cm layer up to 12 cm with a decrease evident at about 14 cm. For the Western Northwest Pacific, 239þ240 Pu median concentration was 0.1 Bq/kg dry up to 4 cm, then decreased to 0.02 Bq/kg dry at a sediment depth of 6 cm only. These differences underscore the need to distinguish between deep seas and coastal areas for sediment data when developing databases covering large areas. 2.3. Marine biota 2.3.1. 137Cs Radionuclide concentrations in biota have not been as well-monitored or measured as in seawater or even sediment. Unlike seawater or sediment, characterizing radionuclide concentrations in biota is more difficult since distributions can vary from one species to another and within different tissues in the same species. Organisms can concentrate different radionuclides to varying degrees. The concentration factor, which is obtained by comparing the concentration of a specific radionuclide in the organism to that in the medium (water), gives a measure of how well organisms can concentrate a given radionuclide. From the viewpoint of dose assessment, the concentrations in edible tissues are important information in estimating risks due to ingestion of seafood. The sources of data on biota in ASPAMARD are listed in Table 8. Based on the limited data available (n ¼ 72) in ASPAMARD, 137Cs concentration in fish muscle and whole fish were observed to range from 0.02 to 2 Bq/kg wet weight with a median of 0.2 Bq/kg wet weight (decay-corrected to March, 2001). Nagaya and Nakamura (1987b) observed that the 137Cs concentration was highest in the muscle, followed in decreasing order by viscera, gills, digestive tract and skin of fish. According to Yamada and Nagaya (1998), 137Cs levels in marine biota have been decreasing almost exponentially with time. Again, this may be a result, at least in part, of decreasing concentrations of 137Cs in the regional seas due to radioactive decay. Changes in 137Cs activity concentration in marine biota were also monitored over a 10-year period in the Yellow Sea and Bohai Sea of China and a decreasing trend with time was also observed (Cai et al., 1992). Nagaya and Nakamura (1987b) further observed that 137Cs concentration in fish did not differ significantly if the fish were from shallow waters or deep bottom waters. The average values obtained suggest a concentration factor of 100 for 137Cs in fish. However, since the 137Cs activity concentrations are lower in deep bottom waters (Fig. 3), it is conceivable that the concentration factor for bottom-water fish may be higher than for shallow-water fish.

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155

Table 8 Sources of data on marine biota in ASPAMARD Sampling location

Radionuclides

References

Ibaraki, Hokkaido Seas, Central Japan, NW Pacific, Northern Japan, Southern Ocean, North Pacific Pacific Ocean Pacific Ocean Bohai Sea, Yellow Sea, Tianjing, Qindao, Lianyungang, East China Sea, Zoushou, Fujian, Dalian, Jinshau, Zapu, Andong, Fenchen, Shejiamen, Daishau, Chensi, Liaodong Bay Western Central Pacific, South China Sea Coast, Pacific Ocean Coast Western Central Pacific, South China Sea Coast, Pacific Ocean Coast Lingayen Gulf, Manila Bay Gulf of Thailand

137

Nagaya and Nakamura (1987b)

137

Cs, 239þ240 Pu Cs 137 Cs

Yamada (1997) Yamada and Nagaya (1998) Cai et al. (1992)

210

Duran et al. (1994)

137

Duran et al. (1996)

137

Cs, 210Po Cs, 239þ240 Pu, 210Po, 40 K, 14C, 241Am 137 Cs, 210Po, 40K 210 Po, 210Pb 137 Cs, 232Th, 226Ra, 40K 40 K, 232Th 137 Cs, 238U, 232Th 40 K, 90Sr 137 Cs, 40K, 238U, 232Th 137 Cs, 210Po, 40K, 210Pb, 226 Ra 239þ240 Pu, 210Po, 228Ac, 60 134 Co, Cs, 90Sr, 226Ra, 232 Th, 40K 40 K, 7Be, 131I

Duran et al. (1998) Mahapanyawong et al. (1992)

210

Jeffree et al. (1997)

Andaman Sea Gulf of Thailand, Andaman Sea Gulf of Thailand, Andaman Sea Semarang and Muria Peninsula Nhatrang Karachi coast, Arabian Sea Bay of Bengal Australian coastal waters Gulf of Carpentaria, Northern Australia Potter Point Ocean Outfall, Sydney Coast South Pacific

Cs, 239þ240 Pu

137

Po Cs

137

Po

Mahapanyawong et al. (1992) Panyatipsakul and Chaysang (1996) Ithipoonthanakorn et al. (2000) Basuki et al. (1998b) Quang and Binh (1999) Parveen et al. (1985) Alam et al. (1995) Jeffree (1999) Poletico and Jeffree (1994)

Jeffree (1999)

Table 9 shows 137Cs concentrations on a wet weight basis (decay-corrected to March, 2001) in marine biota. In general, concentrations in fish are higher than in mollusks, crustaceans or algae. Jeffree et al. (1997) observed very low 137Cs concentrations (<3.5 Bq/kg dry or below detection limits) in zooplankton. Table 9 137 Cs concentrations in marine biota (decay-corrected to March, 2001)

Fish (whole or muscle) Crustaceans Mollusks Algae n ¼ number of sampling locations.

n

Range (Bq/kg wet)

Median (Bq/kg wet)

72 34 37 15

0.02–2 0.02–0.7 0.02–1.3 0.02–0.7

0.2 0.1 0.1 0.1

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Table 10 239þ240 Pu concentrations in marine biota

Fish (whole or muscle) Crustaceans Mollusks

n

Range (mBq/kg wet)

Median (mBq/kg wet)

13 6 6

0.1–5.4 0.1–18.7 0.2–7.4

1.5 6 0.8

n ¼ number of sampling locations.

2.3.2. 239þ240Pu Available data for 239þ240 Pu in marine biota are even less extensive than for 137 Cs. A median concentration of 1.5 mBq/kg wet weight was obtained, with values ranging from 0.1 to 5.4 mBq/kg wet weight (Table 10). 239þ240 Pu levels in fish, like in seawater, are considerably lower than 137Cs levels. In the different tissues or organs of fish, 239þ240 Pu tends to be highest in the gills, followed by viscera, digestive tract and skin (Nagaya and Nakamura, 1987b). The lowest 239þ240 Pu activity concentration was found in muscle (Nagaya and Nakamura, 1987b) which for the most part is the edible portion. From the viewpoint of dose assessment, this distribution pattern of 239þ240 Pu in fish tissues and organs will result in lower doses to the public consuming fish that are not eaten whole. Table 10 also shows the data obtained for other biota. The higher values obtained for crustaceans were mostly for non-edible parts. 239þ240 Pu concentrations in mixed zooplankton collected from the Northwest Pacific Ocean and Southern Ocean between 1993 and 1996 appear to be higher at higher latitudes, ranging from 15 to 390 mBq/kg dry, with a median of 127 mBq/kg dry (Hong et al., 2002).

3. Conclusions The marine environment is a dynamic system. The data on key anthropogenic radionuclides such as 137Cs show that physical radioactive decay contributes to changes in radionuclide concentrations over time at a given sampling station. Transport processes, in turn, account for observed spatial changes. For long-lived radionuclides such as 239þ240 Pu, observed changes are mainly due to transport processes in the absence of new, significant inputs. 137 Cs levels in surface water in the regional seas of Asia-Pacific extending from v v v v 50 N to 60 S latitude and 60 E to 180 E longitude have been declining to its 3 present median value of 2.8 Bq/m mainly due to radioactive decay, transport processes and the absence of new significant inputs. 239þ240 Pu levels in surface seawater are much lower, with a median of 5.9 mBq/m3. 239þ240 Pu appears to be preferentially scavenged by particles and is therefore more readily transported down the water column. In surface sediment, the median 137Cs concentration is 1.4 Bq/kg dry which is higher than the 239þ240 Pu median of 0.2 Bq/kg dry. The highest concentrations of

E.B. Duran et al. / J. Environ. Radioactivity 76 (2004) 139–160 137

157

Cs and 239þ240 Pu in surface sediment were observed between 35 N and 40 N and in particular, the East Sea. Coastal areas with higher sedimentation rates and with higher radionuclide concentrations, due to the additional contribution of runoffs from terrestrial catchment areas, show a different vertical profile of the sediment column than the deep, open seas. The median 137Cs concentration in fish (0.2 Bq/kg wet) is higher than in crustaceans (0.1 Bq/kg wet) and mollusks (0.1 Bq/kg wet). Like in seawater, observed 137 Cs concentrations in fish are considerably higher than 239þ240 Pu levels. The median concentration of 239þ240 Pu in crustaceans (6 mBq/kg wet) is higher than in fish (1.5 mBq/kg wet) or mollusks (0.8 mBq/kg wet), but this is largely due to higher concentrations in non-edible parts. Radionuclide concentrations in marine biota, although important from the viewpoint of dose assessment, are more difficult to characterize than those in seawater and sediment, given the limited data available and the intrinsic variations between species. Considering that ingestion is the main pathway of radiation exposure, that more than half of the world’s population lives in Asia, and that seafood is a major dietary item in the region, more concentration data for biota will be useful for future dose assessments. While certain areas such as the Northwest Pacific Ocean and in particular, East Sea/Sea of Japan and Yellow Sea have been well studied and monitored for marine radioactivity, there appears to be limited data for other areas, notably in the South Pacific and Indian Ocean regions. v

v

Acknowledgements This work was funded by the International Atomic Energy Agency (IAEA) Regional Cooperative Agreement (RCA) and United Nations Development Programme (UNDP) under the IAEA/RCA/UNDP project, ‘‘Management of Marine Coastal Environmental Pollution’’. The data used in this review were obtained from published literature or from reports provided by 12 countries that participated in developing the Asia-Pacific Marine Radioactivity Database (ASPAMARD). Many data were contributed by the country focal points Ross Jefree (Australia), Fazie Karim Miah and Muhammad N. Alam (Bangladesh), Fulong Cai (China), N. Sadasivan (India), Kris Tri Basuki and A. Prayitno (Indonesia), Ab Khalik Wood (Malaysia), Riffat Qureshi (Pakistan), Seyed Azmy (Sri Lanka), Kanitha Srisuksawad (Thailand), Nguyen Hao Quang and Nguyen Thanh Binh (Vietnam). Assistance by Elisa Enriquez, Cecilia de Vera, Alejandro Q. Nato, Jr., Carol Coloma, Teresa Y. Nazarea and Ma. Lucia Cobar in the preparation of ASPAMARD and by Elvira Z. Sombrito, Ryan Olivares and Efren Sta. Maria (all of the Philippine Nuclear Research Institute, PNRI) in the preparation of this paper are gratefully acknowledged. Special thanks go to Mohd. Nordin Razley and Carlito Aleta of IAEA and to Alumanda de la Rosa (PNRI) for their assistance throughout the project.

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The IAEA Marine Environment Laboratory operates under an agreement between the International Atomic Energy Agency and the Government of the Principality of Monaco.

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