Scholarly article on topic '210Po in the marine biota of Korean coastal waters and the effective dose from seafood consumption'

210Po in the marine biota of Korean coastal waters and the effective dose from seafood consumption Academic research paper on "Earth and related environmental sciences"

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Abstract of research paper on Earth and related environmental sciences, author of scientific article — S.H. Kim, G.H. Hong, H.M. Lee, B.E. Cho

Abstract The activity concentrations of 210Po were determined in plankton and selected species of macroalgae, crustaceans, molluscs, and fish from Korean coastal waters to understand 210Po distribution in these trophic levels and to assess the effective dose of 210Po from seafood ingested by the average Korean. The activity concentration of 210Po in macroalgae, mixed plankton, anchovy (whole body), abalone muscle, and abalone viscera was 0.97–1.43, 32–137, 59–392, 2.93 ± 0.86, and 1495 ± 484 Bq kg−1 (w.w.), respectively. Polonium-210 concentration in the whole flesh of mussel and oyster were 47.8 ± 5.9 and 45.3 ± 7.1 Bq kg−1 (w.w.), respectively. Polonium-210 concentration in the muscle of the five tested species of fish other than anchovy ranged from 0.51 to 5.56 Bq kg−1 (w.w.), with the lowest amount in a demersal species. In fish, 210Po activity concentration was as much as three orders of magnitude higher in viscera than in muscle. The average annual effective 210Po dose per average Korean adult, who consumes 42.8 kg of seafood a year (excluding anchovy), was estimated to be 94 μSv y−1, with 42–71% of this attributed to shellfish. Further studies are required to assess the dose of 210Po from anchovy owing to its high activity concentration and the manner in which anchovy is consumed.

Academic research paper on topic "210Po in the marine biota of Korean coastal waters and the effective dose from seafood consumption"

Journal of Environmental Radioactivity xxx (2016) 1—8

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Journal of Environmental Radioactivity

journal homepage: www.elsevier.com/locate/jenvrad

210Po in the marine biota of Korean coastal waters and the effective dose from seafood consumption

S.H. Kim a,b, *, G.H. Hong a'b, H.M. Lee a, B.E. Cho a'b

a Korea Institute of Ocean Science & Technology, Ansan, 15627, Republic of Korea

b Graduate School of Ocean Science and Technology, Korea Maritime and Ocean University, Busan, 49112, Republic of Korea

ARTICLE INFO

ABSTRACT

Article history: Received 11 May 2016 Received in revised form 31 October 2016 Accepted 1 November 2016 Available online xxx

Keywords: Dose Ingestion Marine organism 210Po

The activity concentrations of 210Po were determined in plankton and selected species of macroalgae, crustaceans, molluscs, and fish from Korean coastal waters to understand 210Po distribution in these trophic levels and to assess the effective dose of 210Po from seafood ingested by the average Korean. The activity concentration of 210Po in macroalgae, mixed plankton, anchovy (whole body), abalone muscle, and abalone viscera was 0.97-1.43, 32-137, 59-392, 2.93 ± 0.86, and 1495 ± 484 Bq kg"1 (w.w.), respectively. Polonium-210 concentration in the whole flesh of mussel and oyster were 47.8 ± 5.9 and 45.3 ± 7.1 Bq kg" (w .w.), respectively. Polonium-210 concentration in the muscle of the five tested species of fish other than anchovy ranged from 0.51 to 5.56 Bq kg"1 (w.w.), with the lowest amount in a demersal species. In fish, 210Po activity concentration was as much as three orders of magnitude higher in viscera than in muscle. The average annual effective 210Po dose per average Korean adult, who consumes 42.8 kg of seafood a year (excluding anchovy), was estimated to be 94 mSv y"1, with 42-71% of this attributed to shellfish. Further studies are required to assess the dose of 210Po from anchovy owing to its high activity concentration and the manner in which anchovy is consumed.

© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND

license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

Polonium-210 (210Po) is a natural radionuclide in the 238U decay series that accumulates in marine biota (Beasley et al., 1969,1973; Bustamante et al., 2002; Carvalho, 2011; Cherry and Heyraud, 1982; Cherry and Shannon, 1974; Folsom et al., 1972; Folsom and Beasley, 1973; McDonald et al., 1986; Rodriguez y Baena et al., 2007; Ryan et al., 1999; Schell et al., 1973; Shannon, 1973; Skwarzec, 1988; Suh et al., 1995; Waska et al., 2008). Polonium-210 activity concentrations in marine organisms vary widely among taxonomic groups and among different tissues of a given species, with concentration factors varying from 103 to 106 (Fowler, 2011 ). The reference value of 210Po concentration in fish is 2.0 Bq kg-1 (w.w.), but actual amounts vary widely, from 0.08 to 12 Bq kg"1 (w.w.) (UNSCEAR, 2000).

Polonium-210 is highly radioactive as an alpha emitter, and has a characteristic energy of 5.3 MeV. The committed effective dose coefficient for ingestion of 210Po for an adult (1.2 x 10"6 Sv Bq"1) is

* Corresponding author.Korea Institute of Ocean Science & Technology, Ansan, 15627, Republic of Korea

E-mail address: shkim@kiost.ac.kr (S.H. Kim).

much higher than those of artificial radionuclides such as 137Cs (1.3 x 10"8 Sv Bq"1), 90Sr (2.8 x 10"8 Sv Bq"1), and 239+240Pu (2.5 x 10"7 Sv Bq"1), which have been dispersed widely in the environment since nuclear weapon tests began in the 1940s (ICRP, 2012). The median lethal dose (LD50) for acute radiation exposure is generally about 4.5 Sv (Strom, 2003). A fatal dose from ingestion of 210Po corresponds to 3.75 MBq, which is equivalent to about 21 ng of 210Po with a committed effective dose coefficient of 1.2 x 10"6 Sv Bq"1. The death of Russian dissident Alexander Litvinenko in 2006 was due to 210Po poisoning (Maguire et al., 2010).

Given its high concentration in marine biota and high committed effective dose for ingestion, radiation doses of 210Po from seafood consumption have been assessed in various regions (Aoun et al., 2015; Carvalho and Fowler, 1993; IAEA, 1995; Smith and Towler, 1993; Suriyanarayanan et al., 2010; Yamamoto et al., 1994). The radiation exposure of adult populations from ingestion of natural radionuclides is 0.11 mSv y"1, and a large portion of that is contributed by 210Pb/210Po (UNSCEAR, 2000). Marine fish products are consumed around the world, but seafood consumption is relatively high in eastern Asia and northern and western Europe, with an average per capita rate of 30-60 kg yr"1 in these regions (FAO, 2014). In the Republic of Korea, the 15-year average per capita

http://dx.doi.org/10.1016/j.jenvrad.2016.11.001

0265-931X/© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

S.H. Kim et al. / Journal of Environmental Radioactivity xxx (2016) 1—8

consumption of seafood is 47.6 kg yr , or 42.8 kg yr-1 excluding anchovy (KREI, 2012). The objectives of this study were to investigate the concentrations and distribution of 210Po in selected marine organisms that constitute the primary seafood items in Korea, and to estimate consumption.

the effective dose of 210Po from seafood

2. Materials and methods

2.1. Study area

The study area is located between the East China Sea and the southern coast of the Korean peninsula. The East China Sea is one of the largest continental shelves in the world. This area is influenced by the warm Thushima current and is subject to the influence of the Changjiang Diluted Water inflow from the west. Thus, this area has rich grounds for capture fisheries. The species diversity of fishes in the Korea Strait is impressively high. A total of 301 marine fish species are known from off the southern coast of the Korean peninsula, and 612 species are known from the waters off Jeju Island (Kim, 2009). The southern coast of the Korean peninsula has a heavily indented coastline and provides many suitable habitats for aquaculture. More than 90% of aquaculture and 70% of coastal and offshore capture fisheries in the Republic of Korea are located in this area (MOF, 2015).

2.2. Sampling

Fig. 1. Location of the sampling sites off the Korean coast. Samples were collected within the open circles. Numbers in map indicate coastal fishery area codes of Republic of Korea.

Marine biota from selected trophic levels were collected in Korean coastal waters throughout 2013—2015. Sample species included mixed plankton, two species of macroalgae, one crustacean, four molluscs (one gastropod, two bivalves, and one cepha-lopod), one planktivorous fish, and five carnivorous fish. Plankton samples were collected with plankton nets with mesh sizes of 20 mm or 300 mm towed behind a small boat at 1—1.5 m s-1. Plankton were classified according to the size fractions of 20—300 mm and >300 mm. After collection, plankton samples were sieved immediately with a same-sized mesh filter, stored in acid-cleaned plastic petri dishes, and frozen. The two kinds of macro-algae, laver (Porphyra tenera) and sea mustard (Undaria pinnatifida), were collected from a macroalgae farm along the southwestern Korean coast in February, the typical harvest month. Mussels (Mytilus coruscus) and oysters (Crassostrea gigas) were collected from farms on the southern coast. Abalone (Nordotis discus) were collected from the coast of Jeju Island. Samples of other popular Korean fishery products were purchased from a commercial fishery market, and their harvest dates and collection localities were noted. Sampling locations and dates are shown in Fig. 1 and Table 1. Samples were stored in cold storage boxes and transported to the laboratory. Samples (except plankton) were washed with distilled water to remove any material attached to the surface. The edible tissue, skin, and internal organs of individual fish and shellfish were separated as much as possible before being pooled, freeze-dried, and homogenized by species. Samples were weighed twice: wet weight immediately after separation and dry weight after freeze-drying, homogenization, and oven drying. All results were expressed as Bq kg-1 wet weight (w.w) or Bq kg-1 dry weight (d.w.). The wet sample weight for the pooled parts was more than 10 kg. For plankton, dry weight was not determined and the analysis of 210Po concentration was performed with a fresh wet sample.

2.3. Determination of the 210Po activity concentration

Analysis of 210Po was done using aliquots of freeze-dried and homogenized samples that had equivalent wet weights (w.w.) of 10

g for fishery samples, and 2 g of fresh samples for plankton. Samples, with the addition of a209Po tracer, were completely digested with concentrated nitric acid and hydrogen peroxide on a hot plate. The resulting solution was gently evaporated to dryness. The residue was repeatedly dissolved in 6 N hydrochloric acid, which was then evaporated off to remove residual nitric acid. The final residue was dissolved with 100 mL 0.5 N hydrochloric acid. Polonium isotopes were spontaneously deposited onto a silver planchet while being stirred continuously at room temperature overnight (Lee et al., 2014). The activity of deposited polonium isotopes was counted using a spectrometry (PIPS detector: Canberra Model 7404 MCA; Canberra Industries, Meriden, CT, USA). Analysis was performed for three aliquots of each sample. Sample preparation and analysis was done within a month of sample collection to reduce the influence of 210Po in-growth from the decay of 210Pb. 210Po activity concentrations were corrected to the time of collection.

To verify the accuracy of 210Po analyses in this study, reference material IAEA-414 (Pham et al., 2004), made from Irish and North Sea fish, was analysed simultaneously (Table 2). The activity concentration of 210Po determined in this study reflected the established value of IAEA-414 (99.5 ± 8.5% accuracy).

3. Results and discussion

Tables 3—5 include the activity concentrations and concentration factors (CFs) of 210Po in the marine organisms investigated in this study. CFs were calculated from the dissolved 210Po concentration of 0.75 ± 0.06 mBq kg-1 in the seawater around Jeju Island (Cho and Kim, 2016).

3.1. Plankton and macroalgae

The activity concentration of210Po was 32—137 Bq kg-1 (w.w.) in the 20—300 mm plankton fraction and 46.8—113 Bq kg-1 (w.w.) in the >300 mm plankton fraction (Table 3). The activity concentrations of 210Po in both plankton fractions were several times higher in winter than in summer. This seasonal variation may be attributed

Table 1

Sampling locations and dates for marine organisms caught in Korean coastal waters.

Name of samples Locationa Date

Plankton 223 Feb-2014; June-2015

Macroalgae

Laver(Porphyra tenera) 213 Feb-2014

Sea mustard (Undaria pinnatifida) 213 Feb-2014

Crustaceans

Red-banded lobster (Metanephrops thomsoni) 230, 231 Feb-2015

Molluscs

Abalone (Nordotis discus) 232 Feb-2014

Far eastern Mussel (Mytilus coruscus) 98 Nov-2013

Giant Pacific Oyster (Crassostrea gigas) 98 Nov-2013

Japanese common Squid (Todarodes pacificus) 222, 232, 242 Feb-2015

Anchovy (Engraulis japonicus) 232; 98 May-14; June-15

Chub mackerel (Scomber japonicus) 222, 232, 242 Feb-15

Largehead hairtail (Trichiurus lepturus) 241 June-15

Japanese Horse mackerel (Trachurus japonicus) 241 June-15

Red tilefish (Branchiostegus japonicus) 241 June-15

Olive flounder (Paralichthys olivaceus) 230, 231 Feb-14

a Numbers are the coastal fishery area codes of Republic of Korea.

Table 2

Determination of 210Pb(210Po)a concentration in Sea Fish Reference Material 1AEA-414.

Information value Confidence interval This study (N = 3)

(unit: Bg kg 1 d.w)

2.1 1.8—2.5 2.21 ± 0.19

a 210Po is in equilibrium with 210Pb at the time of measurement.

to differences in phytoplankton communities. Diatoms dominate in late winter and dinoflagellates in summer along the coast of Jeju Island (Affan and Lee, 2004), where samples were collected. Polonium-210 accumulates more in diatom species than in di-noflagellates (Stewart and Fisher, 2003). The activity concentration of 210Po in the small-sized plankton fraction was somewhat higher than that in the large-sized plankton fraction in winter, but this relationship was reversed in summer. In the 20—300 mm and >300 mm plankton fractions, the 210Po CFs were 4.0—18 x 104 and

Table 3

The 210Po activity concentrations and concentration factors in plankton and macroalgae from Korean coastal waters.

Name of samples Activity (Bq kg 1 w.w) Weight ratio Concentration Factor (x 104)

Mean ± SD dry/wet Mean ± SD

Plankton [20—300 mm] 137 ±51a — 17 ± 9a

32 ± 3b — 4 ± 2b

Plankton [>300 mm] 113 ± 2a — 14 ± 5a

47 ± 9b — 6 ± 2b

Macroalgae

Laver 1.43 ± 0.21 0.099 0.18 ± 0.07

Sea mustard 0.97 ± 0.13 0.080 0.12 ± 0.05

a Sampling in February 2014. b Sampling in June 2015.

Table 4

The 210Po activity concentrations and concentration factors in crustaceans and molluscs from Korean coastal waters.

Name of samples

Activity (Bq kg 1 w.w) Mean ± SD

Weight ratio dry/wet

Concentration Factor (x104) Mean ± SD

Crustaceans Red-banded lobster Muscle Exoskeleton Viscera Molluscs Abalone Muscle Viscera Far eastern mussel

Whole flesh Giant Pacific oyster

Whole flesh Japanese common squid Muscle Skin Viscera

2.84 ± 0.23 46 ± 10 906 ± 226

2.93 ± 0.86 1500 ± 484

47.8 ± 5.9

46.3 ± 7.1

8.61 ± 2.01 948 ± 77 1940 ± 93

0.20 0.36 0.29

0.20 0.20

0.21 0.21 0.30

0.35 ± 0.13 5.7 ± 2.4 112 ± 49

0.36 ± 0.17 185 ± 89

5.9 ± 2.2

5.7 ± 2.2

1.1 ± 0.5 117 ± 43

239 ± 86

S.H. Kim et al. / Journal of Environmental Radioactivity xxx (2016) 1—8

Table 5

The 210Po activity concentrations and concentration factors in fish from Korean coastal waters.

Name of samples

Activity (Bq kg 1 w.w) Mean ± SD

Weight ratio dry/wet

Concentration Factor (x104) Mean ± SD

Anchovy Whole bodya Musclea Viscera3 Heada

Whole bodyb Chub mackerel Muscle Skin

Viscera (except liver) Liver Largehead hairtail Muscle Viscera Japanese horse mackerel Muscle Skin Viscera Red tilefish Muscle Skin Viscera Olive flounder Muscle Skin

Viscera (except liver and gall bladder) Liver

Gall bladder

59 ± 4.59 38.9 ± 11.4 323 ± 85.3 96.3 ± 8.65 392 ± 2.2

0.8 ± 0.03 12.6 ± 3.15 142 ± 10.5 429 ±179

5.56 ± 1.23 157 ± 96.8

5.26 ± 0.13 50.8 ± 8.22 112 ± 20

3.08 ± 0.94 6.45 ± 3.29 49.6 ± 15.5

0.51 ± 0.12 25.1 ± 10.4 2236 ± 242 222 ± 18.4 1017 ± 96.3

0.37 0.46 0.35 0.40

0.28 0.24

0.25 0.40 0.32

0.21 0.34 0.24

0.25 0.34 0.18 0.43 0.13

7.3 ± 2.7 4.8 ± 2.2 41 ± 4 12 ± 18 48 ± 17

0.1 ± 0.04 1.6 ± 0.7

18 ± 6 53 ± 29

0.69 ± 0.29 19 ± 14

0.65 ± 0.23 6.3 ± 2.5 14 ± 6

0.38 ± 0.18 0.8 ± 0.5 6.1 ± 2.9

0.06 ± 0.03 3.1 ± 1.7 276 ±103 27 ± 10 126 ± 46.5

a Sampling in 2015. b Sampling in 2014.

5.8—14 x 104, respectively. These CFs were comparable with the CF for phytoplankton (7 x 104) and several times higher than the CF for zooplankton (3 x 104) reported by IAEA (2004).

Polonium-210 activity concentrations were determined for two species of macroalgae, laver (Porphyra tenera) and sea mustard (Undaria pinnatifida). The 210Po CFs in the macroalgae were 1.3—1.9 x 103, and were comparable to the CF for macroalgae (1.0 x 103) reported by IAEA (2004).

Annual consumption of these two macroalgae is as much as 11 kg per person in the Republic of Korea (KREI, 2012). Samples were collected during the traditional harvest season. Polonium-210 activity concentration in laver (red alga) was higher than in sea mustard (brown macroalga), with average values of 1.43 ± 0.21 and 0.97 ± 0.13 Bq kg-1 (w.w.), respectively (Table 3). These values were two or three times lower than the 2.3—3.1 Bq kg-1 (w.w.) reported for benthic Sargassum in the northern Arabian Gulf (Uddin et al., 2015), several times lower than the 2.8—8.0 Bq kg-1 (w.w.) reported for a brown macroalga (species not identified) along the Japanese shoreline (Baumann et al., 2013). It is known that there are several contributing factors for differences in metal accumulation by different species of macroalgae, including life span, morphology, contact surface area, growth rate, and selective affinity for specific metals by particular species (Chakraborty et al., 2014). Brown algae generally accumulate divalent metal species in considerable amounts due to their high content of binding polysaccharides and polyphenols (Hashim and Chu, 2004). There was a study on the 210Po activity concentrations in several species of macroalgae in the intertidal zone off the coast of Portugal (Carvalho, 2011). Regardless of algae classes, Ploccamium cartilagineum, Gelidium sesquipedale, and Fucus vesiculosus, all with relatively large surface areas, had higher 210Po activity concentrations, at 5.2—9.1 Bq kg-1 (w.w.), than the 1.6—2.7 Bq kg-1 (w.w.) in other species. An experiment on the uptake of americium by three benthic algal species (Ulva rigida,

Fucus vesiculosus, and Gigartina stellata) showed that the uptake by the green alga was 3—5 times greater than that by the brown and red species. This experimental evidence indicated that Am accumulation is a passive process and that adsorption takes place mainly on the thin outer organic coating of seaweed (Carvalho and Fowler, 1985). The reason why Porphyra tenera (red algae) showed higher 210Po activity concentration than Undaria pinnatifida (brown algae) in this study may be associated with the difference in contact surface area. However, there should be more investigation into the reasons for the differences in 210Po activity concentration among species of macroalgae.

3.2. Crustaceans and molluscs

Measurements of 210Po from crustaceans and molluscs were conducted with muscle, skin, and viscera from red-banded lobster (Metanephrops thomsoni) and squid, muscle and viscera from abalone, and all soft tissues for mussel and oyster (Table 4). The exoskeleton of red-banded lobster was considered its skin, and viscera were all internal organs and stomach contents.

The concentration of 210Po in red-banded lobster was 2.84 ± 0.23 Bq kg-1 (w.w.) in muscle, 46 ± 10 Bq kg-1 (w.w.) in the exoskeleton, and 906 ± 226 Bq kg-1 (w.w.) in the viscera. High 210Po concentration in the viscera of red-banded lobster may be attributed to a210Po-rich diet, which includes organic particulates and copepods (Cherry and Heyraud, 1981). The percentages of 210Po in each part relative to the total amount of 210Po in the whole body were 0.6 (muscle), 12.2 (exoskeleton), and 87.2% (viscera). This indicates that in red-banded lobster, 210Po accumulates primarily in the viscera through diet. Polonium-210 concentrations from more than 30 species of marine shrimp, collected from the Mediterranean Sea, Kuwait, South Africa, USA, and Great Britain, spanned two orders of magnitude, from 15.5 to 1670 Bq kg-1 (d.w.) in the whole

S.H. Kim et al. / Journal of Environmental Radioactivity xxx (2016) 1—8

shrimp (Cherry and Heyraud, 1981), depending on the species and the local environment. The concentration of 210Po in the whole body of Metanephrops thomsoni investigated in this study was calculated as 612 ± 134 Bq kg"1 (d.w.), based on the wet weight analysis and the wet: dry ratio. This value was approximately two times higher than the median 210Po concentration of 296 Bq kg"1 (d.w.) of more than 30 species of shrimp and similar to the concentration in penaeid shrimp from the Mediterranean and caridean shrimp from the Natal, which live in pelagic and deep pelagic environments (Cherry and Heyraud, 1981). Metanephrops thomsoni is distributed in the Indo-West Pacific region, including the Korea Strait, Yellow Sea, and East China Sea, and is found at a depth of 50—500 m, on sandy mud bottoms (Bate, 1888).

Polonium-210 concentration in the muscle of abalone (Nordotis discus) was 2.93 ± 0.86 Bq kg"1 (w.w.), two or three times higher than concentrations in the macroalgae that form its diet. Polonium-210 concentrations in abalone viscera were 1495 ± 484 Bq kg"1 (w.w.), approximately three orders of magnitude higher than in the muscle. The dry weight (d.w.) 210Po concentration of 15.0 ± 4.4 Bq kg"1 (d.w) in the muscle of Nordotis discus in this study was several times higher than the 2.3—3.5 Bq kg"1 (d.w.) in the muscle of Haliotis tuberculata, another species of abalone, on the French coast (Connan et al., 2007). The d.w. 210Po concentration of 7660 ± 2480 Bq kg"1 (d.w) in the viscera of Nordotis discus was several to ten times higher than the 134.3—135.2 Bq kg"1 (d.w.) in the viscera of Haliotis tuberculata. Comparison of 210Po concentrations in abalone species is difficult because few have been studied. However, Nordotis discus had higher accumulations of 210Po than did Haliotis tuberculata, especially in the viscera. Polonium-210 CFs in the muscle and viscera of Nordotis discus were 3.9 x 103 and 1.99 x 106, respectively. Even though the 210Po concentration in Nordotis discus muscle was several times higher than in Haliotis tuberculata, the CF was several times lower than the recommended value of 2 x 104 in molluscs reported by 1AEA (2004).

Polonium-210 concentrations measured in the whole flesh of mussel (Mytilus coruscus) and oyster (Crassostrea gigas) were similar to each other, at 47.8 ± 5.9 and 45.3 ± 7.1 Bq kg"1 (w.w.), respectively. They were collected in the same location on the same date, so their shared physicochemical habitat may have produced similar 210Po concentrations. Polonium-210 concentrations measured in these species along the French coast were similar within locations, but showed great variation across sites (Connan et al., 2007). Mytilus coruscus and Crassostrea gigas, as filter feeders, may show different levels of 210Po based on the type and concentration of suspended food. Crassostrea gigas demonstrated little change with diet quality or concentration (Ward et al., 2003). Mytilus trossulus is known to non-selectively transport particles (Ward et al., 1998). The similar trends in 210Po concentration in Mytilus coruscus and Crassostrea gigas may be attributed to their feeding on similar diets.

Polonium-210 concentrations in the whole flesh of mussels from several other places differed greatly within species by location: in Mytilus galloprovincialis, 210Po ranged from 18.5 ± 0.7 Bq kg"1 (w.w.) along the Portuguese coast (Carvalho, 2011), to 22.1—207 Bq kg"1 (w.w.) on the Croatian Adriatic coast (Rozmaric et al., 2012), and 53—1960 Bq kg"1 (d.w.) on the Turkish coast (Ugur et al., 2011). In Mytilus edulis, 210Po was 156—275 Bq kg"1 (w.w.) along the French coast (Connan et al., 2007), and in Perna perna, 210Po was 78—320 Bq kg"1 (w.w.) on the Kanyakumari coast in South 1ndia (Macklin Rani et al., 2014).

Polonium-210 concentrations in the whole flesh of oysters also showed variation of one order of magnitude according to the location and species: 23.4—126 Bq kg"1 (w .w.) (species not identified) from the coast ofTaiwan (Lee and Wang, 2013), 10—24 Bq kg"1 (w.w.) in Crassostrea gigas from the coast of France (Connan et al.,

2007), and 12.7 Bq kg"1 (w.w.) in Crassostrea madrasensis from the east coast of 1ndia (Satheeshkumar et al., 2016).

The recommended CF of 210Po in the edible part of crustaceans and molluscs is 2 x 104 (IAEA, 2004). In this study, CFs of 210Po were 0.4 x 104 in crustacean muscle and in the muscle of the gastropod and 6 x 104 in the edible soft body of filter-feeding molluscs.

Squid comprises the largest quantity of shellfish seafood in the Republic of Korea (KRE1, 2012). Polonium-210 concentrations measured from the muscle, skin, and viscera of squid (Todarodes pacificus) were 8.61 ± 2.01, 948 ± 77, and 1940 ± 93 Bq kg"1 (w.w.), respectively. 210Po concentrations in the muscle of squid ranged from 0.42 to 5.5 Bq kg"1 (w.w.) in Loligo vulgaris from the Atlantic Ocean (Heyraud and Cherry, 1979), 1.33—2.3 Bq kg"1 (w.w.) in Nototodarus spp. from New Zealand (Pearson et al., 2016), 3.5 ± 0.3 Bq kg"1 (w.w.) in Loligo spp. from Slovenia (Strok and Smodis, 2011), and 12.9 ± 0.69 Bq kg"1 (w.w.) in Loligo duvauceli from India (Satheeshkumar et al., 2016). Polonium-210 concentration in squid muscle was three times higher than that in other crustaceans and molluscs investigated in this study. The 210Po concentration in squid viscera was also the highest, but the ratio of concentration in viscera to that in muscle was 225 in squid, which was somewhat lower than the 319 in red-banded lobster and 512 in abalone.

3.3. Fish

Polonium-210 was determined from six species, including one planktivorous fish (anchovy, Engraulis japonicus), four pelagic carnivorous fish (chub mackerel, Scomber japonicus; largehead hairtail, Trichiurus lepturus; Japanese horse mackerel, Trachurus japonicus; and red tilefish, Branchiostegus japonicus), and one demersal fish (olive flounder, Paralichthys olivaceus). Results are presented by tissue in Table 5.

Anchovy is one of the most commonly consumed fish in the Republic of Korea (KRE1, 2012). Polonium-210 concentration in the whole body of anchovy (Engraulis japonicus) collected in May 2014 was 392 ± 2 Bq kg"1 (w.w.), several times higher than in the plankton that comprise their main diet. This value was the highest among the fish in this study. In 2015, 210Po concentration in anchovy was determined for a sample collected in another location. Polonium-210 concentration in the whole body in June 2015 was 59.0 ± 4.6 Bq kg"1 (w.w.), slightly higher than the values from plankton. The difference in 210Po concentrations in anchovy collected in May 2014 and in June 2015 may be due to habitat differences. In anchovy studied from a single region of the Black Sea, the whole-body 210Po concentration differed by a factor of two within the space of one month (Lazorenko et al., 2002). Assuming fish obtain most or all of their 210Po burden from the plankton they ingest, the higher 210Po concentrations in anchovy, compared to those in plankton, suggest that 210Po is biomagnified up the food web to anchovy. Polonium-210 concentrations measured in the muscle, viscera, head, and whole body of anchovy in June 2015 were 38.9 ± 11.4, 323 ± 85, 96.3 ± 8.7, and 59.0 ± 4.6 Bq kg"1 (w.w.), respectively, demonstrating that 210Po accumulated eight times more in viscera than in muscle. Polonium-210 concentrations in anchovy from other regions had a range of 26.1—638 Bq kg"1 (w.w.) in the whole body, and were the highest among all species of fish investigated in the same regions (Khan and Wesley, 2012; Lazorenko et al., 2002; Strady et al., 2015; Strok and Smodis, 2011). Akozcan and Ugur (2013) reported that the mechanism of uptake of 210Po and 210Pb by fish reflects biological variables such as feeding habits and location, based on their investigation of these radionuclides from some fish species of the Izmir, showing that the measured activities in the species that feed on plankton are much higher than the average values (Akozcan and Ugur, 2013). Strok and SmodiSs stated that the pelagic environment and plankton feeding

S.H. Kim et al. / Journal of Environmental Radioactivity xxx (2016) 1—8

contribute significantly to 210Po accumulation. They also reported that the larger the animal, the lower the 210Po activity concentration. This is due to the slower metabolism of the larger, older, and heavier animals (Strok and Smodis, 2011). Laboratory experiments involving foods containing various natural concentrations of 210Po showed that the 210Po content of a marine organism reflects the 210Po concentration in the food it eats and the process of incorporation of 210Po from the food into the fish is faster for the anchovy than for other species, proceeding on a time-scale of 2—4 days (Cherry et al., 1989).

Polonium-210 concentrations in fish muscle (except anchovy) ranged from 0.8 to 5.26 Bq kg-1 (w.w.) in the four species of pelagic fish and 0.51 ± 0.12 Bq kg-1 (w.w.) in the demersal fish. Polonium-210 concentration was highest in the viscera, which included internal organs and stomach contents. Polonium-210 concentrations in the viscera and skin of fish were 49.6—2236 and 6.45—50.8 Bq kg-1 (w.w.), respectively. Olive flounder, the demersal fish species, had the highest 210Po concentration in the internal organs, excluding the liver and gall bladder. Polonium-210 concentration in the viscera of olive flounder was 2236 ± 242 Bq kg-1 (w .w.) and was ten times and three orders of magnitude higher than that in liver and that in muscle, respectively. This high 210Po concentration in the viscera of olive flounder may come from their diet, which includes crustaceans, polychaetes, and other taxa that contain high 210Po concentrations.

The 210Po CFs in fish muscle varied widely from 0.7 to 52 x 103. The CFs in pelagic fish (except anchovy) were 1.1—7.4 x 103, comparable with the recommended value of 2 x 103 in the fraction of fish intended for human consumption (IAEA, 2004).

3.4. Dose estimation from seafood consumption

The annual effective dose of 210Po from seafood consumption by an adult was estimated from the 210Po concentrations measured in edible parts of macroalgae, crustaceans, molluscs, and fish in this study. The average daily supply of seafood per capita includes one hundred species and is 64.8 ± 8.5, 35.4 ± 6.8, and 30.0 ± 10.5 g day-1 for fish, shellfish including crustaceans and molluscs, and macroalgae, respectively, in the Republic of Korea (KREI, 2012). Although few species of fish, shellfish, and macroalgae were investigated in this study, they account for 37, 64, and 72% of the total annual per capita supply of these groups. The minimum, maximum, and average 210Po concentrations in the edible portions were used to assess the effect of natural variations on the effective dose. Anchovy was considered separately because it is consumed primarily in a broth made from dried salted fish. To calculate dose, the ingestion dose coefficient of 1.2 mSv Bq-1 for an adult was used (UNSCEAR, 2000). A delay factor of 0.6 (Aarkrog et al., 1997) was applied to account for time elapsed between catch and consumption, owing to the 138 d half-life of 210Po.

The annual effective dose for an individual from seafood consumption was calculated as follows:

AED = MF x e(T) x A x h ) (1)

where AED is the annual committed effective dose (mSv y-1), MF is a weighted factor to account for the delay between catch and consumption, e(T) is an effective dose coefficient (1.2 mSv Bq-1), Ai is the activity concentration of 210Po in the edible tissues of seafood products (Bq kg-1 (w.w)), and hi is the annual intake rate of mac-roalgae, shellfish, and fish per individual in the Republic of Korea (kg y-1). Intake rate was calculated from per capita consumption and the rate of edible parts in each category (Yamamoto et al., 1994).

The annual effective dose of 210Po per adult individual from the ingestion of seafood (except anchovy) was estimated to be 94 (average), 19 (minimum), and 189 mSv y-1 (maximum) (Table 6). The dose from shellfish accounted for 42—71% of the average total dose owing to the relatively high 210Po activity concentration in shellfish, even though they accounted for only 14% of the total seafood consumption. The dose for 210Po from the ingestion of seafood estimated in this study may be compared with results from other studies: 19 mSv y-1 in Ireland (Pollard et al., 1998), 45.6 mSv y-1 in Slovenia (Strok and Smodis, 2011), 129 mSv y-1 from the ingestion of molluscs and fish in France (Connan et al., 2007), 700 mSv y-1 in countries around the Baltic Sea (Nielsen et al., 1999), and 50—200 mSv y-1 in Venice (Jia et al., 2003).

Assuming that anchovy is consumed in the same manner as other seafood, the dose from the ingestion of anchovy would be 307 (average), 80 (minimum), and 534 mSv y-1 (maximum). These values are two or three times greater than the total dose from seafood excluding anchovy, even though anchovies represent just 10% of the total seafood supply. Anchovy's high dose may reflect the fact that its 210Po concentration is several times higher than that of shellfish, which have the highest concentration among seafood excluding anchovy. Polonium-210 from anchovy consumption may depend on when the fish are caught and the preparation and storage methods before ingestion. Polonium-210 has a short halflife, so it may be minimally present in anchovy broth as typically prepared in Korean cuisine. The dose of 210Po from anchovy needs to be more precisely assessed.

4. Conclusions

210Po concentrations in plankton from Korean coastal waters ranged from 32 to 137 Bq kg-1 (w.w.) and were higher in winter than summer. 210Po concentration in a small plankton size fraction (20—300 mm) was somewhat higher than that in a large plankton size fraction (>300 mm) in winter when diatom species were

Table 6

Annual Effective dose for the adult consumer in Republic of Korea by the ingestion of 210Po from seafood.

Category Supply (kg p-1 y-1) Rate of edible part Activity concentration (Bq kg-1 (w.w)) Min. Avg. Max. Annual effective dose (mSv y Min. Avg. 1) Max.

Macroalgae 11.0 0.9 0.97 1.20 1.43 7 9 10

Shellfish 12.9 0.3 2.84 21.7 47.8 8 61 133

Fisha 18.9 0.6 0.51 3.04 5.56 4 25 45

Anchovy' 4.S 0.6 3S.9 Í49 25S S0 307 534

Total seafoodc 42.8 19 94 189

a Fish except anchovy.

b Assumed the case anchovy is consumed by same ways with other seafood. c Total seafood except anchovy.

dominant, but the opposite was observed in summer when di-noflagellates were dominant. 210Po concentration in the whole body of anchovy varied from 59 to 392 Bq kg-1 (w.w.), which was higher than that in plankton. 210Po concentrations in two species of macroalgae, laver and sea mustard, were 1.43 ± 0.21 and 0.97 ± 0.13 Bq kg-1 (w.w.), respectively. 210Po concentration in the muscle and viscera of abalone was 2.93 ± 0.86 and 1495 ± 484 Bq kg-1 (w.w.), respectively, and was higher in both than in macroalgae, which is the primary food source for abalone. 210Po concentration in red-banded lobster was 2.84 ± 0.23 Bq kg-1 (w.w.) in muscle, 46 ± 10 Bq kg-1 (w.w.) in the exoskeleton, and 906 ± 226 Bq kg-1 (w.w.) in the viscera, respectively. The percentages of 210Po in each part relative to the total amount of 210Po in the whole body were 0.6, 12.2, and 87.2% in muscle, exoskeleton, and viscera, respectively. Most of the 210Po burden in the body of red-banded lobster was contributed through diet to the viscera. 210Po concentrations in the whole flesh of mussel and oyster collected in same location on the same date were similar to each other, 47.8 ± 5.9 and 45.3 ± 7.1 Bq kg-1 (w.w.), respectively. 210Po concentration in the muscle of five species of fish (not including anchovy) ranged from 0.51 to 5.56 Bq kg-1 (w.w.) and was the lowest in a demersal species. 210Po concentrations in the viscera and skin of fish were 49.6—2236 and 6.45—50.8 Bq kg-1 (w.w.), respectively. 210Po in fish was enriched from one to three orders of magnitude higher in viscera than in muscle. A biomagnification of 210Po between trophic levels from plankton to anchovy and from macroalgae to abalone is strongly suggested.

The annual effective dose of 210Po per adult individual from the ingestion of seafood excluding anchovy in the Republic of Korea was estimated to be 94,19, and 189 mSv y-1 for the average, minimum, and maximum. Forty-two to seventy-one percent of the total dose was contributed through shellfish consumption. The dose effect from anchovy had to be considered separately owing to its consumption as a broth prepared from dried fish. Although it had a high 210Po concentration, the dose from anchovy needs to be assessed more precisely.

Acknowledgments

An earlier version of this manuscript was greatly improved by incorporating two anonymous reviewers' comments and suggestions. This work was funded by grants from the Korea Institute of Ocean Science & Technology (PE99403) and the Korean Ministry of Food and Drug Safety (PG48320).

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